The Pigmentary System: Physiology and Pathophysiology
The Pigmentary System: Physiology and Pathophysiology Edited by...
56 downloads
1635 Views
28MB Size
Report
This content was uploaded by our users and we assume good faith they have the permission to share this book. If you own the copyright to this book and it is wrongfully on our website, we offer a simple DMCA procedure to remove your content from our site. Start by pressing the button below!
Report copyright / DMCA form
The Pigmentary System: Physiology and Pathophysiology
The Pigmentary System: Physiology and Pathophysiology Edited by
James J. Nordlund Dermatologist and Professor Emeritus, Group Health Associates, Cincinnati, OH, USA
Raymond E. Boissy Professor of Dermatology and Cell Biology, University of Cincinnati College of Medicine, Cincinnati, OH, USA
Vincent J. Hearing Chief, Pigment Cell Biology Section, Laboratory of Cell Biology, National Institutes of Health, Bethesda, MD, USA
Richard A. King Director, Genetics Division, Department of Medicine, Institute of Human Genetics, University of Minnesota, Minneapolis, MN, USA
William S. Oetting Associate Professor, Genetics Division, Department of Medicine Institute of Human Genetics, University of Minnesota, Minneapolis, MN, USA
Jean-Paul Ortonne Professor of Dermatology and Chairman, Department of Dermatology, University of Nice-Sophia Antipolis, Nice, France
SECOND EDITION
© 2006 Blackwell Publishing Ltd Blackwell Publishing, Inc., 350 Main Street, Malden, Massachusetts 02148-5020, USA Blackwell Publishing Ltd, 9600 Garsington Road, Oxford OX4 2DQ, UK Blackwell Publishing Asia Pty Ltd, 550 Swanston Street, Carlton, Victoria 3053, Australia The right of the Author to be identified as the Author of this Work has been asserted in accordance with the Copyright, Designs and Patents Act 1988. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by the UK Copyright, Designs and Patents Act 1988, without the prior permission of the publisher. First published 1998 by Oxford University Press Second edition 2006 1 2006 Library of Congress Cataloging-in-Publication Data The pigmentary system : physiology and pathophysiology / edited by James J. Nordlund . . . [et al.]. — 2nd ed. p. ; cm. Includes bibliographical references and index. 1. Pigmentation disorders. 2. Melanocytes. I. Nordlund, James J. [DNLM: 1. Pigmentation Disorders–physiopathology. 2. Melanocytes. 3. Pigmentation–physiology. WR 265 P6309 2006] RL790.P53 2006 616.5¢5–dc22 2005030369 A catalogue record for this title is available from the British Library Set in 9/12 pt Sabon by SNP Best-set Typesetter Ltd., Hong Kong Printed and bound in India by Replika Press PVT Ltd ISBN-13: 978-1-4051-2034-0 ISBN-10: 1-4051-2034-7 Commissioning Editor: Stuart Taylor Editorial Assistant: Saskia Van der Linden Development Editor: Rob Blundell Production Controller: Kate Charman For further information on Blackwell Publishing, visit our website: http://www.blackwellpublishing.com The publisher’s policy is to use permanent paper from mills that operate a sustainable forestry policy, and which has been manufactured from pulp processed using acid-free and elementary chlorine-free practices. Furthermore, the publisher ensures that the text paper and cover board used have met acceptable environmental accreditation standards. Blackwell Publishing makes no representation, express or implied, that the drug dosages in this book are correct. Readers must therefore always check that any product mentioned in this publication is used in accordance with the prescribing information prepared by the manufacturers. The author and the publishers do not accept responsibility or legal liability for any errors in the text or for the misuse or misapplication of material in this book.
Contents
Contributors, x Foreword, xv Preface, xvii Acknowledgements, xviii Frontispiece can be found between pages ii and iii Part I: The Physiology of the Pigmentary System Section 1: Historical and Comparative Perspectives of the Pigmentary System, 3 1 A History of the Science of Pigmentation, 5 Sidney N. Klaus 2 Comparative Anatomy and Physiology of Pigment Cells in Nonmammalian Tissues, 11 Joseph T. Bagnara & Jiro Matsumoto Section 2: The Science of Pigmentation, 61 3 General Biology of Mammalian Pigmentation, 63 Walter C. Quevedo Jr. & Thomas J. Holstein 4 Extracutaneous Melanocytes, 91 Raymond E. Boissy & Thomas J. Hornyak 5 Regulation of Melanoblast Migration and Differentiation, 108 David M. Parichy, Mark V. Reedy, & Carol A. Erickson 6 Melanoblast Development and Associated Disorders, 140 Richard A. Spritz 7 Biogenesis of Melanosomes, 155 Raymond E. Boissy, Marjan Huizing, & William A. Gahl 8 Melanosome Trafficking and Transfer, 171 Glynis A. Scott 9 Melanosome Processing in Keratinocytes, 181 H. Randolph Byers 10 The Regulation of Melanin Formation, 191 Vincent J. Hearing 11 The Tyrosinase Gene Family, 213 William S. Oetting & Vijayasaradhi Setaluri 12 Molecular Regulation of Melanin Formation: Melanosome Transporter Proteins, 230 Murray H. Brilliant 13 Transcriptional Regulation of Melanocyte Function, 242 Kazuhisa Takeda & Shigeki Shibahara 14 Enzymology of Melanin Formation, 261 Francisco Solano & José C. García-Borrón
15 Chemistry of Melanins, 282 Shosuke Ito & Kazumasa Wakamatsu 16 The Physical Properties of Melanins, 311 Tadeusz Sarna & Harold A. Swartz 17 Photobiology of Melanins, 342 Antony R. Young 18 Toxicological Aspects of Melanin and Melanogenesis, 354 Edward J. Land, Christopher A. Ramsden, & Patrick A. Riley 19 Regulation of Pigment Type Switching by Agouti, Melanocortin Signaling, Attractin, and Mahoganoid, 395 Gregory S. Barsh 20 Human Pigmentation: Its Regulation by Ultraviolet Light and by Endocrine, Paracrine, and Autocrine Factors, 410 Zalfa Abdel-Malek & Ana Luisa Kadekaro 21 Paracrine Interactions of Melanocytes in Pigmentary Disorders, 421 Genji Imokawa 22 Growth Factor Receptors and Signal Transduction Regulating the Proliferation and Differentiation of Melanocytes, 445 Ruth Halaban & Gisela Moellmann 23 Aging and Senescence of Melanocytes, 464 Debdutta Bandyopadhyay & Estela E. Medrano 24 The Genetics of Melanoma, 472 Vanessa C. Gray-Schopfer & Dorothy C. Bennett 25 The Transformed Phenotype of Melanocytes, 489 Dong Fang & Meenhard Herlyn Part II: The Pathophysiology of Pigmentary Disorders Section 3: An Overview of Human Skin Color and its Disorders, 497 26 A More Precise Lexicon for Pigmentation, Pigmentary Disorders, and “Chromatic” Abnormalities, 499 James J. Nordlund, Tania Cestari, Pearl Grimes, Henry Chan, & Jean-Paul Ortonne 27 The Normal Color of Human Skin, 504 James J. Nordlund & Jean-Paul Ortonne 28 Mechanisms that Cause Abnormal Skin Color, 521 Jean-Paul Ortonne & James J. Nordlund v
CONTENTS
29
30
31
32
33
vi
Section 4: Disorders of Hypopigmentation, Depigmentation and Hypochromia, 539 Genetic Hypomelanoses: Disorders Characterized by Congenital White Spotting — Piebaldism, Waardenburg Syndrome, and Related Genetic Disorders of Melanocyte Development — Clinical Aspects, 541 Richard A. Spritz Genetic Hypomelanoses: Acquired Depigmentation, 551 Rozycki Syndrome, 551 Jean L. Bolognia Vitiligo Vulgaris, 551 James J. Nordlund, Jean-Paul Ortonne, & I. Caroline Le Poole Genetic Hypomelanoses: Generalized Hypopigmentation, 599 Oculocutaneous Albinism, 599 Richard A. King & William S. Oetting Albinoid Disorders, 613 Philippe Bahadoran & Jean-Paul Ortonne Ataxia Telangiectasia, 621 Anne-Sophie Gadenne Hallerman–Streiff Syndrome, 623 James J. Nordlund Histidinemia, 623 Marnie D. Titsch Homocystinuria, 625 Allan D. Mineroff Oculocerebral Syndrome with Hypopigmentation, 626 Jean L. Bolognia Tietz Syndrome, 630 Jean-Paul Ortonne Kappa-Chain Deficiency, 631 Jean-Paul Ortonne Menkes’ Kinky Hair Syndrome, 631 Tanusin Ploysangam Phenylketonuria, 634 Allan D. Mineroff Genetic Hypomelanoses: Localized Hypopigmentation, 636 “Hypomelanosis of Ito” and Mosaicism, 636 Wolfgang Küster & Rudolf Happle Focal Dermal Hypoplasia, 645 James J. Nordlund Hypomelanosis with Punctate Keratosis of the Palms and Soles, 646 Jean L. Bolognia Darier–White Disease (Keratosis Follicularis; 124200), 647 Jean L. Bolognia Nevus Depigmentosus, 649 Stella D. Calobrisi Tuberous Sclerosis Complex, 652 Pranav B. Sheth Genetic Hypomelanoses: Disorders Characterized by Hypopigmentation of Hair, 657
34
35
36 37 38
39
Bird-Headed Dwarfism (Seckel Syndrome), 657 Stan P. Hill Down Syndrome, 658 Rosemary Geary Fisch Syndrome, 659 Stan P. Hill Premature Canities, 659 James J. Nordlund Mandibulofacial Dysostosis (Treacher Collins Syndrome), 660 Rosemary Geary Myotonic Dystrophy, 660 Peggy Tong PHC Syndrome (Böök Syndrome), 661 Stan P. Hill Pierre Robin Syndrome, 661 James J. Nordlund Prolidase Deficiency, 662 Pranav B. Sheth Metabolic, Nutritional, and Endocrine Disorders, 664 Metabolic and Nutritional Hypomelanoses, 664 Peter S. Friedmann Hypomelanosis Associated with Endocrine Disorders, 667 Peter S. Friedmann Chemical, Pharmacologic, and Physical Agents Causing Hypomelanoses, 669 Chemical and Pharmacologic Agents Causing Hypomelanoses, 669 Stefania Briganti, Monica Ottaviani, & Mauro Picardo Physical Agents Causing Hypomelanoses, 683 Jean-Philippe Lacour Infectious Hypomelanoses, 686 Jean-Philippe Lacour Inflammatory Hypomelanoses, 699 Jean-Philippe Lacour Hypomelanoses Associated with Melanocytic Neoplasia, 705 Lieve Brochez, Barbara Boone, & Jean-Marie Naeyaert Miscellaneous Hypomelanoses: Depigmentation, 725 Alezzandrini Syndrome, 725 Wiete Westerhof, David Njoo, & Henk E. Menke Idiopathic Guttate Hypomelanosis, 726 Wiete Westerhof, David Njoo, & Henk E. Menke Leukoderma Punctata, 729 Wiete Westerhof, David Njoo, & Henk E. Menke Lichen Sclerosus et Atrophicus, 731 Philippe Bahadoran Vagabond Leukomelanoderma, 732 Wiete Westerhof, David Njoo, & Henk E. Menke Vogt–Koyanagi–Harada Syndrome, 734 Wiete Westerhof, David Njoo, & Henk E. Menke Westerhof Syndrome, 741 Wiete Westerhof, David Njoo, & Henk E. Menke
CONTENTS
40 Miscellaneous Hypomelanoses: Hypopigmentation, 745 Disseminated Hypopigmented Keratoses, 745 Wiete Westerhof, David Njoo, & Henk E. Menke Hypermelanocytic Punctata et Guttata Hypomelanosis, 746 Wiete Westerhof, David Njoo, & Henk E. Menke Progressive Macular Hypomelanosis, 748 Henk E. Menke, Germaine Relyveld, David Njoo, & Wiete Westerhof Sarcoidosis, 751 Wiete Westerhof, David Njoo, & Henk E. Menke 41 Miscellaneous Hypomelanoses: Extracutaneous Loss of Pigmentation, 754 Alopecia Areata, 754 Wiete Westerhof Heterochromia Irides, 756 Wiete Westerhof, David Njoo, & Henk E. Menke Senile Canities, 760 Wiete Westerhof, David Njoo, & Henk E. Menke Sudden Whitening of Hair, 764 Wiete Westerhof, David Njoo, & Henk E. Menke 42 Hypochromia without Hypomelanosis, 767 Jean-Philippe Lacour Section 5: Disorders of Hyperpigmentation and Hyperchromia, 769 43 Genetic Epidermal Syndromes: Disorders Characterized by Generalized Hyperpigmentation, 771 Adrenoleukodystrophy, 771 Sheila S. Galbraith & Nancy Burton Esterly Familial Progressive Hyperpigmentation, 774 Nancy Burton Esterly, Eulalia Baselga, Beth A. Drolet, Susan Bayliss Mallory, & Sharon A. Foley Fanconi Anemia, 776 Sheila S. Galbraith & Nancy Burton Esterly Gaucher Disease, 778 Sheila S. Galbraith & Nancy Burton Esterly 44 Genetic Epidermal Syndromes: Disorders Characterized by Reticulated Hyperpigmentation, 780 Berlin Syndrome, 780 Eulalia Baselga & Nancy Burton Esterly Cantu Syndrome, 781 Eulalia Baselga & Nancy Burton Esterly Kindler Syndrome, 781 Eulalia Baselga & Nancy Burton Esterly Dermatopathia Pigmentosa Reticularis, 784 Eulalia Baselga & Nancy Burton Esterly Dyschromatosis Universalis Hereditaria, 786 Eulalia Baselga & Nancy Burton Esterly Epidermolysis Bullosa with Mottled Pigmentation, 788 Eulalia Baselga & Nancy Burton Esterly Familial Mandibuloacral Dysplasia, 790 Eulalia Baselga & Nancy Burton Esterly Hereditary Acrokeratotic Poikiloderma, 792 Eulalia Baselga & Nancy Burton Esterly
Hereditary Sclerosing Poikiloderma, 795 Eulalia Baselga & Nancy Burton Esterly Mendes Da Costa Disease, 796 Eulalia Baselga & Nancy Burton Esterly Naegeli–Franceschetti–Jadassohn Syndrome, 798 Eulalia Baselga & Nancy Burton Esterly Reticulated Acropigmentation of Dohi (Dyschromatosis Symmetrica Hereditaria), 799 Eulalia Baselga & Nancy Burton Esterly Reticulate Acropigmentation of Kitamura, 802 Eulalia Baselga & Nancy Burton Esterly Rothmund–Thomson Syndrome, 804 Eulalia Baselga & Nancy Burton Esterly 45 Genetic Epidermal Syndromes with Café-au-lait Macules, 809 Familial Multiple Café-au-lait Spots, 809 Nancy Burton Esterly Neurofibromatosis, 809 Nancy Burton Esterly, Eulalia Baselga, & Sheila S. Galbraith Neurofibromatosis 1 with Noonan Syndrome, 816 Nancy Burton Esterly McCune–Albright Syndrome, 817 Sheila S. Galbraith & Nancy Burton Esterly Segmental Neurofibromatosis, 819 Nancy Burton Esterly & Eulalia Baselga Silver–Russell Syndrome, 820 Nancy Burton Esterly, Eulalia Baselga, & Sheila S. Galbraith Watson Syndrome, 823 Nancy Burton Esterly 46 Genetic Epidermal Pigmentation with Lentigines, 824 Lentigo Simplex, 824 Mary K. Cullen Lentigo Senilis et Actinicus, 829 Mary K. Cullen Centrofacial Lentiginosis, 837 Mary K. Cullen LEOPARD Syndrome, 842 Mary K. Cullen Carney Complex, 851 Mary K. Cullen Other Lentiginoses, 863 Mary K. Cullen 47 Genetic Epidermal Syndromes: Localized Hyperpigmentation, 873 Anonychia with Flexural Pigmentation, 873 Nancy Burton Esterly, Eulalia Baselga, & Beth A. Drolet Incontinentia Pigmenti, 873 Sheila S. Galbraith & Nancy Burton Esterly Periorbital Hyperpigmentation, 879 Nancy Burton Esterly, Eulalia Baselga, & Beth A. Drolet vii
CONTENTS
Pigmentary Demarcation Lines, 880 Sheila S. Galbraith & Nancy Burton Esterly Dowling–Degos Disease, 882 Sheila S. Galbraith & Nancy Burton Esterly 48 Genetic Epidermal Syndromes: Disorders of Aging, 884 Acrogeria, 884 Nancy Burton Esterly, Eulalia Baselga, Peter M. H. Chan, & Beth A. Drolet Metageria, 886 Nancy Burton Esterly, Eulalia Baselga, Peter M. H. Chan, & Beth A. Drolet Progeria, 886 Nancy Burton Esterly, Eulalia Baselga, Peter M. H. Chan, & Beth A. Drolet Xeroderma Pigmentosum, 889 Anita P. Sheth, Nancy Burton Esterly, Eulalia Baselga, Peter M. H. Chan, & Beth A. Drolet Werner Syndrome, 894 Nancy Burton Esterly, Eulalia Baselga, Peter M. H. Chan, Beth A. Drolet, & Cindy L. Lamerson 49 Congenital Epidermal Hypermelanoses, 898 Dyskeratosis Congenita, 898 Susan Bayliss Mallory, Peggy L. Chern, & Sharon A. Foley Ectodermal Dysplasias, 901 Susan Bayliss Mallory, Peggy L. Chern, & Sharon A. Foley Transient Neonatal Pustular Melanosis, 905 Susan Bayliss Mallory, Peggy L. Chern, & Sharon A. Foley Universal Acquired Melanosis, 906 Susan Bayliss Mallory, Peggy L. Chern, & Sharon A. Foley 50 Acquired Epidermal Hypermelanoses, 907 Acanthosis Nigricans, 907 Norman Levine & Cynthia Burk Acromelanosis Progressiva, 914 Norman Levine & Cynthia Burk Becker Nevus, 915 Norman Levine & Cynthia Burk Café-au-lait Spots, 917 Norman Levine & Cynthia Burk Carcinoid Syndrome, 919 Norman Levine & Cynthia Burk Confluent and Reticulated Papillomatosis, 922 Norman Levine & Cynthia Burk Cutaneous Amyloidosis, 924 Norman Levine & Cynthia Burk Dermatosis Papulosa Nigra, 928 Norman Levine & Cynthia Burk Ephelides (Freckles), 929 Norman Levine & Cynthia Burk Erythema ab Igne, 931 Norman Levine & Cynthia Burk viii
Erythema Dyschromicum Perstans, 933 Norman Levine & Cynthia Burk Erythromelanosis Follicularis Faciei et Colli, 935 Norman Levine & Cynthia Burk Erythrose Péribuccale Pigmentaire of Brocq, 937 Norman Levine & Cynthia Burk Extracutaneous Neuroendocrine Melanoderma, 938 Norman Levine & Cynthia Burk Felty Syndrome and Rheumatoid Arthritis, 939 Norman Levine & Cynthia Burk Hyperpigmentation Associated with Human Immunodeficiency Virus (HIV) Infection, 941 Philippe Bahadoran Melanoacanthoma, 946 Norman Levine & Cynthia Burk Phytophotodermatitis, 948 Norman Levine & Cynthia Burk Polyneuropathy, Organomegaly, Endocrinopathy, M Protein, and Skin Changes: POEMS Syndrome, 951 James J. Nordlund Urticaria Pigmentosum and Mastocytosis, 954 James J. Nordlund Poikiloderma of Civatte, 959 Vlada Groysman & Norman Levine Riehl’s Melanosis, 961 Scott Bangert & Norman Levine Atrophoderma of Pasini et Pierini, 963 James J. Nordlund, Norman Levine, Charles S. Fulk, & Randi Rubenzik Hyperpigmentation Associated with Scleromyxedema and Gammopathy, 965 Kazunori Urabe, Juichiro Nakayama, & Yoshiaki Hori Ichthyosis Nigricans, Keratoses, and Epidermal Hyperplasia, 965 James J. Nordlund Morphea and Scleroderma, 967 James J. Nordlund Pigmentary Changes Associated with Addison Disease, 969 Cindy L. Lamerson & James J. Nordlund Pigmentary Changes Associated with Cutaneous Lymphomas, 972 Debra L. Breneman 51 Hypermelanosis Associated with Gastrointestinal Disorders, 979 Porphyria Cutanea Tarda, 979 Eun Ji Kwon & Victoria P. Werth Cronkhite–Canada Syndrome, 983 Eun Ji Kwon, James J. Nordlund, & Victoria P. Werth Hemochromatosis and Hemosiderosis, 986 Joerg Albrecht & Victoria P. Werth Primary Biliary Cirrhosis, 992 Joerg Albrecht & Victoria P. Werth Inflammatory Bowel Disease and Pigmentation, 995 Joerg Albrecht & Victoria P. Werth
CONTENTS
Pellagra, 995 Eun Ji Kwon & Victoria P. Werth Peutz–Jeghers Syndrome, 999 Nancy Burton Esterly, Eulalia Baselga, & Beth A. Drolet 52 Acquired and Congenital Dermal Hypermelanosis, 1003 Sacral Spot of Infancy, 1003 Sang Ju Lee, Seung Kyung-Hann, & Sungbin Im Nevus of Ota, 1006 Sang Ju Lee, Seung Kyung-Hann, & Sungbin Im Nevus of Ito, 1012 Sang Ju Lee, Seung Kyung-Hann, & Sungbin Im Phakomatosis Pigmentovascularis, 1013 Sang Ju Lee, Seung Kyung-Hann, & Sungbin Im Other Congenital Dermal Melanocytosis, 1015 Sang Ju Lee, Seung Kyung-Hann, & Sungbin Im Acquired Dermal Melanocytosis, 1016 Sang Ju Lee, Seung Kyung-Hann, & Sungbin Im Carleton–Biggs Syndrome, 1017 Sang Ju Lee, Seung Kyung-Hann, & Sungbin Im Acquired Bilateral Nevus of Ota-like Macules (ABNOM), 1017 Sang Ju Lee, Seung Kyung-Hann, & Sungbin Im Blue Macules Associated with Progressive Systemic Sclerosis, 1018 Sang Ju Lee, Seung Kyung-Hann, & Sungbin Im 53 Mixed Epidermal and Dermal Hypermelanoses and Hyperchromias, 1020 Melasma, 1020 Sang Ju Lee, Seung Kyung-Hann, & Sungbin Im Melanosis from Melanoma, 1023 Sang Ju Lee, Seung Kyung-Hann, & Sungbin Im 54 Drug-induced or -related Pigmentation, 1026 Peter A. Lio & Arthur J. Sober Section 6: Disorders of Pigmentation of the Nails and Mucous Membranes, 1055 55 The Melanocyte System of the Nail and its Disorders, 1057 Robert Baran, Christophe Perrin, Luc Thomas, & Ralph Braun
56 Pigmentary Abnormalities and Discolorations of the Mucous Membranes, 1069 John C. Maize, Jr. & John C. Maize, Sr. Section 7: Benign Neoplasms of Melanocytes, 1091 57 Common Benign Neoplasms of Melanocytes, 1093 Pigmented Spindle Cell Nevi, 1093 Julie V. Schaffer & Jean L. Bolognia Speckled Lentiginous Nevus (Nevus Spilus), 1098 Julie V. Schaffer & Jean L. Bolognia Melanocytic (Nevocellular) Nevi and Their Biology, 1112 Julie V. Schaffer & Jean L. Bolognia 58 Rare Benign Neoplasms of Melanocytes, 1148 Nevus Aversion Phenomenon, 1148 James J. Nordlund Melanotic Neuroectodermal Tumor of Infancy, 1148 Julie V. Schaffer & Jean L. Bolognia Pilar Neurocristic Hamartoma, 1157 Julie V. Schaffer & Jean L. Bolognia Section 8: Treatment of Pigmentary Disorders, 1163 59 Topical Treatment of Pigmentary Disorders, 1165 Rebat M. Halder & James J. Nordlund 60 Chemophototherapy of Pigmentary Disorders, 1175 Rebat M. Halder & James J. Nordlund 61 UVB Therapy for Pigmentary Disorders, 1183 Thierry Passeron & Jean-Paul Ortonne 62 Sunscreens and Cosmetics, 1188 James J. Nordlund & Rebat M. Halder 63 Surgical Treatments of Pigmentary Disorders, 1191 Rebat M. Halder & James J. Nordlund 64 Laser Treatment of Pigmentary Disorders, 1198 Rebat M. Halder, Lori M. Hobbs, & James J. Nordlund Index, 1205 Color Plates, 1230
ix
Contributors
Zalfa Abdel-Malek
PhD Research Professor of Dermatology, Department of Dermatology, University of Cincinnati College of Medicine, Cincinnati, OH, USA
Joerg Albrecht MD Department of Dermatology, University of Pennsylvania, Philadelphia, PA, USA Mayra Alvarez-Franco
(deceased) Formerly of the Departments of Dermatology and Pathology, Yale University School of Medicine, New Haven, CT, USA
Joseph T. Bagnara PhD Professor Emeritus, Department Cell Biology and Anatomy, University of Arizona College of Medicine, Tucson, AZ, USA Philippe Bahadoran
MD PhD Assistant Professor of Medicine, Service de Dermatologie, Hôpital l’Archet, Nice, France
Debdutta Bandyopadhyay
PhD Instructor of Dermatology, Huffington Center on Aging, Baylor College of Medicine, Houston, TX, USA
Raymond E. Boissy PhD Professor of Dermatology and Cell Biology, Department of Dermatology, University of Cincinnati College of Medicine, Cincinnati, OH, USA Jean L. Bolognia MD Professor of Dermatology, Department of Dermatology, Yale University School of Medicine, New Haven, CT, USA Barbara Boone MD Resident in Dermatology, Universitair Ziekenhuis Ghent, Ghent, Belgium Ralph P. Braun
MD Assistant Professor, Pigmented Skin Lesion Unit, Department of Dermatology, University Hospital, Geneva, Switzerland
Debra L. Breneman
MD Associate Professor of Dermatology, University of Cincinnati, Cincinnati, OH, USA
Stefania Briganti
PhD San Gallicano Dermatological Institute, Rome, Italy
Scott D. Bangert
MD Banner Good Samaritan Hospital, Department of Medical Education, Phoenix, AZ, USA
Murray H. Brilliant PhD Lindholm Professor of Genetics, Department of Pediatrics, University of Arizona College of Medicine, Tucson, AZ, USA
Robert Baran MD Head of Nail Disease Center, Cannes, France
Lieve Brochez
Gregory S. Barsh MD PhD Professor of Genetics and Pediatrics, Beckman Center for Molecular and Genetic Medicine, Stanford University School of Medicine, Stanford, CA, USA
Cynthia J. Burk
Eulalia Baselga
Stella D. Calobrisi
MD Consultant in Pediatric Dermatology, Hospital de la Santa Creu I Sant Pau, Barcelona, Spain
Dorothy C. Bennett
MA PhD Professor of Cell Biology, St George’s Hospital, University of London, London, UK
x
MD PhD Professor of Dermatology, Department of Dermatology, University Hospital of Ghent, Ghent, Belgium
MD Section of Dermatology, University of Arizona Health Sciences Center, Tucson, AZ, USA MD Medical Director, The Dermatology Clinic, Boca Raton, FL, USA
Tania Cestari
MD PhD Associate Professor of Dermatology, Department of Dermatology, University of Rio Grande do Sul, Hospital de Clínicas de Porto Alegre, Brazil
CONTRIBUTORS
Henry H. L. Chan MBBS MSc (Clin Derm) MD FRCP FRCP(Ed) FRCP(Glasg) FHKCP FHKAM (Med) Specialist in Dermatology and Honorary Clinical Associate Professor, University of Hong Kong and Chinese University of Hong Kong, Hong Kong Peter Man Hon Chan MD Clinical Research Fellow, University of Minnesota, Eagan, MN, USA Peggy L. Chern MD Department of Dermatology, University of Iowa Hospitals and Clinics, Iowa City, IA, USA Mary K. Cullen
MD Department of Cell Biology and Physiology, Clinical Instructor, Washington University School of Medicine, St Louis, MO, USA
José C. García-Borrón PhD Professor of Biochemistry and Molecular Biology, School of Medicine, University of Murcia, Murcia, Spain Rosemary J. Geary MD President, East Valley Dermatology Center, Chandler, AZ, USA Vanessa C. Gray-Schopfer PhD Signal Transduction Team, Cellular and Molecular Biology Section, Institute of Cancer Research, London, UK Pearl E. Grimes MD Vitiligo and Pigmentation Institute of Southern California, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, CA, USA Vlada Groysman
Beth A. Drolet
MD Section of Dermatology, University of Arizona Health Sciences Center, Tucson, AZ, USA
Carol A. Erickson
Ruth Halaban PhD Senior Research Scientist, Department of Dermatology, Yale University School of Medicine, New Haven, CT, USA
MD Department of Dermatology, The Medical College of Wisconsin, Milwaukee, WI, USA PhD Professor of Molecular Cellular Biology, University of California at Davis, Davis, CA, USA
Nancy B. Esterly MD Professor of Dermatology and Pediatrics, Department of Dermatology, The Medical College of Wisconsin, Milwaukee, WI, USA Dong Fang MD PhD Staff Scientist, The Wistar Institute, Philadelphia, PA, USA Sharon A. Foley MD Department of Dermatology, Washington University School of Medicine, St Louis, MO, USA Peter S. Friedmann MD FRCP FMedSci Professor of Dermatology and Head of Division, Dermatopharmacology Unit, Southampton General Hospital, Southampton, UK Charles S. Fulk
MD FACP Department of Pathology, Vanderbilt University, Nashville, TN, USA
Rebat M. Halder
MD Professor and Chairman, Department of Dermatology, Howard University, Washington, DC, USA
Seung-Kyung Hann MD PhD Director, Korea Institute of Vitiligo Research, Yongsan-Gu, Seoul, Korea Rudolf Happle MD Professor of Dermatology, Department of Dermatology, Philipp’s University of Marburg, Marburg, Germany Vincent J. Hearing
PhD Chief, Pigment Cell Biology Section, Laboratory of Cell Biology, National Institutes of Health, Bethesda, MD, USA
Meenhard Herlyn DVM, DSc Professor and Chair of Program of Molecular and Cellular Oncogenesis, The Wistar Institute, Philadelphia, PA, USA Stan P. Hill
MD Denver, CO, USA
Anne-Sophie J. Gadenne MD Department of Dermatology, University of Cincinnati College of Medicine, Cincinnati, OH, USA
Lori M. Hobbs MD
William A. Gahl MD PhD Clinical Director, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD, USA
Thomas J. Holstein
Sheila S. Galbraith MD Assistant Professor of Dermatology, Dermatology Department, Medical College of Wisconsin, Milwaukee, WI, USA
Assistant Professor, Department of Dermatology, Howard University, Washington, DC, USA PhD Professor Emeritus, Roger Williams University, Bristol, RI, USA
Yoshiaki Hori
MD PhD (deceased) Formerly Honorary Professor, Department of Dermatology, Kyushu University, Fukuoka, Japan
xi
CONTRIBUTORS
Thomas J. Hornyak MD PhD Dermatology Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA
I. Caroline Le Poole
Marjan Huizing
Norman Levine MD Professor of Medicine, Section of Dermatology, University of Arizona College of Medicine, Tucson, AZ, USA
PhD Head, Cell Biology of Metabolic Disorders Unit, Medical Genetics Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD, USA
PhD Loyola University Medical Center Department of Pathology, Cancer Center, Maywood, IL, USA
Peter A. Lio Sungbin Im MD PhD Director, Kangnam Wootaeha Skin and Esthetic Clinic, Yeoksam-Dong, Kangnam-Gu, Seoul, Korea Genji Imokawa
PhD Director, Skin-Bio Assess Institute, Utsunomiya, Tochigi, Japan
Shosuke Ito
PhD Professor of Chemistry, Department of Chemistry, Fujita Health University School of Health Sciences, Toyoake, Aichi, Japan
Ana Luisa Kadekaro
PhD Research Instructor of Dermatology, University of Cincinnati College of Medicine, Cincinnati, OH, USA
Richard A. King MD PhD Director, Genetics Division, Department of Medicine and Associate Director, Institute of Human Genetics, University of Minnesota, Minneapolis, MN, USA Sidney N. Klaus
MD Professor of Dermatology, Dartmouth-Hitchcock Medical Center, Lebanon, NH, USA
Wolfgang Küster MD Professor and Chief of Dermatology, TOMESA Clinic, Department of Dermatology, Bad Salzschlirf, Germany Eun Ji Kwon
BSc Department of Dermatology, University of Pennsylvania, Philadelphia, PA, USA
Jean-Philippe Lacour
MD Service de Dermatologie, Hôpital Archet 2, Nice, France
Cindy L. Lamerson MD Clinical Assistant Professor, University of Nevada, Reno, NV, USA
MD Instructor in Dermatology, Beth Israel Deaconess Medical Center, Boston, MA, USA
John C. Maize Sr MD Medical Director, DermPath Diagnostics, Maize Center for Dermatopathology, Mt Pleasant, SC, USA John C. Maize Jr
MD DermPath Diagnostics, Maize Center for Dermatopathology, Mt Pleasant, Clinical Assistant Professor of Dermatology, Medical University of South Carolina, SC, USA
Susan Bayliss Mallory MD FAAD FAAP Professor of Internal Medicine (Dermatology) and Pediatrics, Division of Dermatology, Washington University School of Medicine, St Louis, MO, USA Jiro Matsumoto
PhD Emeritus Professor, Department of Biology, Keio University, Kohoku-ku, Yokohama, Japan
Estela E. Medrano PhD Professor of Molecular and Cellular Biology and Dermatology, Huffington Center on Aging, Baylor College of Medicine, Houston, TX, USA Henk E. Menke MD PhD Dermatologist, Department of Dermatology, Sint Franciscus Gasthuis, Rotterdam, The Netherlands Allan D. Mineroff MD Lansdale, PA, USA
Gisela E. Moellmann
PhD Professor Emeritus, Yale University School of Medicine, New Haven, CT, USA
Jean-Marie Naeyaert
MD PhD Professor of Dermatology and Head, Department of Dermatology, University Hospital of Ghent, Ghent, Belgium
Edward J. Land
BSc PhD Honorary Professor, Lennard-Jones Laboratories, School of Geographical and Physical Sciences, Keele University, Keele, UK
Juichiro Nakayama
Sang Ju Lee MD PhD Director, Yonsei Star Skin and Laser Clinic, Chancheon-Dong, Seodaemun-Gu, Seoul, Korea
Marcelius Davy Njoo
xii
MD PhD Department of Dermatology, School of Medicine, Fukuoka University, Fukuoka, Japan
MD PhD Streekzierenhuis Middentwente, Hengelo, The Netherlands
CONTRIBUTORS
James J. Nordlund MD Dermatologist and Professor Emeritus, Group Health Associates, Cincinnati, OH, USA
Patrick A. Riley
William S. Oetting PhD Associate Professor, Genetics Division, Department of Medicine, Institute of Human Genetics, University of Minnesota, Minneapolis, MN, USA
Randi E. Rubenzik
Jean-Paul Ortonne
MD Professor of Dermatology and Chairman, Department of Dermatology, University of Nice-Sophia Antipolis, Nice, France
Monica Ottaviani PhD San Gallicano Dermatological Institute, Rome, Italy
MBBS PhD DSc FRCPath CBiol FIBiol FLS Professor Emeritus of Cell Biology and Director, Totteridge Institute for Advanced Studies, London, UK MD FAAD
Sun City West, AZ, USA
Tadeusz Sarna
PhD DSc Professor of Biophysics, Department of Biophysics, Faculty of Biotechnology, Jagiellonian University, Krakow, Poland
Julie V. Schaffer MD Assistant Professor of Dermatology and Pediatrics, New York University School of Medicine, New York, NY Glynis A. Scott
David M. Parichy
MD Associate Professor of Dermatology and Pathology, Department of Dermatology, University of Rochester School of Medicine, Rochester, NY, USA
Thierry Passeron
MD Clinical Assistant in Medicine, Nice, France
Vijayasaradhi Setaluri PhD Associate Professor of Dermatology, University of Wisconsin School of Medicine and Public Health, Madison, WI, USA
Christophe Perrin
MD Laboratoire d’Anatomie Pathologique, Hôpital L. Pasteur, Nice, France
Anita P. Sheth
Mauro Picardo
Pranav B. Sheth MD Assistant Professor, Department of Dermatology, University of Cincinnati, Cincinnati, OH, USA
PhD Assistant Professor, Department of Biology, University of Washington, Seattle, WA, USA
MD San Gallicano Dermatological Institute, Rome, Italy
Tanusin Ploysangam
MD PhD Director, Institute of Beauty and Health Science, and Director, Belage Skin Care and Cosmetic Center, Nunthawan Prachacheun, Bangtalad, Nonthaburi, Thailand
Walter C. Quevedo Jr PhD Emeritus Professor of Biology, Department of Molecular and Cell Biology and Biochemistry, Brown University, Providence, RI, USA Christopher A. Ramsden BSc PhD DSc Cchem FRSC Professor of Organic Chemistry, Lennard-Jones Laboratories, School of Geographical and Physical Sciences, Keele University, Keele, UK
H. Randolph Byers MD PhD Professor of Dermatology, Boston University School of Medicine, Boston, MA, USA Mark V. Reedy
PhD Assistant Professor of Biology, Creighton University, Omaha, NE, USA
Germaine N. Relyveld
MD Department of Dermatology, Academic Medical Center, Amsterdam, The Netherlands
MD Department of Dermatology, University of Cincinnati College of Medicine, Cincinnati, OH, USA
Shigeki Shibahara MD PhD Professor, Department of Molecular Biology and Applied Physiology, Tohoku University School of Medicine, Aoba-ku, Sendai, Miyagi, Japan Arthur J. Sober MD Professor of Dermatology, Harvard Medical School, Massachusetts General Hospital, Boston, MA, USA Francisco Solano PhD Professor of Biochemistry and Molecular Biology, School of Medicine, University of Murcia, Spain Richard A. Spritz, MD Professor and Director, Human Medical Genetics Program, University of Colorado Health Sciences Center at Fitzsimons, Aurora, CO, USA Harold M. Swartz MD PhD Professor of Radiology, Dartmouth Medical School, Hanover, NH, USA Kazuhisa Takeda
MD PhD Assistant Professor of Molecular Biology, Department of Molecular Biology and Applied Physiology, Tohoku University School of Medicine, Aoba-ku, Sendai, Miyagi, Japan
xiii
CONTRIBUTORS
Luc Thomas MD PhD Professor and Chairman, Department of Dermatology, Lyon 1 University, Hotel Dieu, Lyon, France
Victoria P. Werth MD Professor of Dermatology and Chief, VA Dermatology, Department of Dermatology, University of Pennsylvania, Philadelphia, PA, USA
Marnie D. Titsch MD Dermatology Specialist, Oyster Point Dermatology Inc., Newport News, VA, USA
Wiete Westerhof
Peggy Tong MD Dermatology Associates, Milwaukee, WI, USA Kazunori Urabe
MD PhD Associate Professor, Department of Dermatology, Graduate School of Medical Science, Kyushu University, Fukuoka, Japan
Kazumasa Wakamatsu
PhD Professor, Fujita Health University School of Health Sciences, Toyoake, Aichi, Japan
xiv
MD PhD Assistant Professor of Dermatology, Netherlands Institute for Pigment Disorders and Department of Dermatology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
Antony R. Young PhD Professor of Experimental Photobiology, King’s College London and St John’s Institute of Dermatology, St Thomas’ Hospital, London, UK
Foreword
In this second edition of The Pigmentary System: Physiology and Pathophysiology, the editors have expanded upon the dynamic field of pigment cell biology to reflect not only the rapidly moving pace of developments in this broad field but also the explosive growth of research and development across the basic life sciences. We have all benefited enormously from the recent growth in the research budgets of agencies such as the National Institutes of Health (NIH), and these benefits transcend beyond grant recipients to citizens who benefit from better treatments or management protocols for diseases that in the past were nearly always seriously debilitating. Never before have advances come so rapidly or with so much promise for improving the human condition. These improvements come as a result of better understanding of all aspects of the composition and function of living cells. From the molecules that direct activity to those that confer shape and phenotype, we know more today about the basic building blocks of living matter than at any time previously in our history. Perhaps even more astounding is the pace at which discoveries in the life sciences continue to be made. In recent years we have experienced near-exponential growth in the quantity and quality of information available across all sectors of the life sciences. There is little doubt that as we move toward the end of the first decade of the twenty-first century we will have answers to many questions, some of which we never imagined being able to ask. The pigmentary system, as a model system for studying basic questions about differentiating stem cells, has provided ample opportunities for study across a broad range of inter-
ests and expertise. Animal pigment has long been known to function protectively in some animals as well as decoratively in others. Pigment can provide camouflage for some and flamboyant advertisement for others. The embryonic origin of skin pigment cells, the neural crest, suggests that pigment cells share common traits with a wide variety of nerve cells. And yet, like all stem cells, neural crest cells can differentiate along a multitude of pathways, perhaps to become a sensory neuron or to become a melanocyte. These highly motile embryonic cells, even after settling down and differentiating, still retain a remarkable capacity for further motion and differentiation or reversion. Witness the havoc that can ensue if melanocytes become cancerous and migrate to all parts of the body to form tumors. The first edition of The Pigmentary System was unquestionably the definitive text of its time. The editors, who are themselves pre-eminent in this field, have worked with the authors to provide significant revisions to nearly every chapter, and a new chapter on melanocytes as malignant cells has been added. Virtually any topic related to pigmentary systems can be found in this single source, from animal chromatophores to human pigmentary disorders, from basic cell biology to clinical studies and results. Congratulations to the editors and to those researchers who are actively engaged in helping us better understand the complexities of this fascinating system! Sally Frost Mason PhD Purdue University West Lafayette, IN, USA
xv
Preface
This second edition of The Pigmentary System: Physiology and Pathophysiology presents the latest information about the biology of melanocytes and their disorders. The first section is dedicated to the science of pigmentation and has been completely rewritten, not just updated. The chapters have been reorganized to provide the most current and comprehensive review of the science of pigmentation. New chapters have been added and some old chapters in the first edition have been deleted. All of these were chapters on methodology that were rapidly outdated after publication. Some information and data remain constant and are unchanged in this edition. Other topics are entirely new or significantly enlarged since publication of the previous edition. Part II on the pathophysiology of pigmentary disorders is mostly updated. New chapters have been included. A lexicon on proper terminology for description of skin color has been included as the first chapter in this section. Unless the scientific and clinical communities use the same terminology to describe and identify scientific or clinical topics, there will be confusion about the nature and treatment of pigmentary or dyschromic disorders. We hope that this lexicon becomes standard in the dermatological and scientific communities. The comments that we made in the preface to the first edition are still very relevant. A few are worth repeating. This book is intended to be a reference book for both the scientific and the clinical communities. The fact that there is so much
ongoing scientific work related to pigmentation is an indicator of the importance of melanocytes. It also is a clue that melanocytes, melanotropins and related cells and factors are not just a mechanism for sun protection. It is obvious and certain that melanocytes and melanin are protective against sunlight. But the role of melanin in the eyes and ears is more than just sun protection. Melanocytes are involved in many processes within the epidermis. Melanotropins have effects on virtually every organ system in the body and control inflammation, appetite, some functions within the nervous system, and other critical functions. The pigmentary system, including melanin, melanocytes and melanotropins, is best described as a modulator that helps the body adapt to the environmental changes related to seasonal fluctuations in sunlight, temperature, and humidity. We hope that scientists, clinicians, students, and residents find this book useful in their studies on skin color, melanocytes, and melanin, and that it expands their perspective and view about the pigmentary system as a modulator, not just a method of sun protection. James J. Nordlund Raymond E. Boissy Vincent J. Hearing Richard A. King William S. Oetting Jean-Paul Ortonne
xvii
Acknowledgments
The editors wish to acknowledge the very gracious and generous support of the following companies. Without their support, this project would not have been possible. Galderma International, Paris, France Proctor and Gamble, Cincinnati, OH, USA Combe Inc., White Plains, NY, USA
xviii
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
I
The Physiology of the Pigmentary System
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
1
Historical and Comparative Perspectives of the Pigmentary System
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
1
A History of the Science of Pigmentation Sidney N. Klaus
Introduction In Europe, prior to the seventeenth century, notions about the origin of human skin color were based largely on myths and fanciful stories passed down from the ancient world. The stories focused on providing explanations for the blackness of Africans. Europeans with an ethnocentric perspective thought that it was necessary to justify the darkness of outsiders rather than to explain their own paleness. In Europe, two theories about the origin of Africans’ color predominated. The first proposed that the black hue of African skin was a consequence of the intense sunlight and heat to which Africans were exposed. The second idea proposed that African color was a result of divine intervention, a concept that stemmed from the well-known passage in Genesis describing Noah’s curse on Ham and his progeny. Such traditional views of skin color were questioned during the Age of Discovery. Explorers were returning home from remote regions of the globe and bringing with them descriptions of black-, yellow-, or red-hued peoples. The array of colors fascinated scientists and excited them to investigate how these skin colors originated. During the sixteenth century, the scientific community prepared for this task. Scientists learned new techniques of human dissection and new methods of chemical analysis. More importantly, they adopted a new philosophical approach for the study of natural phenomena. Rather than analysis of phenomenon based on a priori assumptions, they based their analyses on firsthand observations and experimentation. By the seventeenth century, anatomists and physicians had begun to collect objective data about skin color. For the next two centuries, so many important observations had been collected about the seat of skin color and the causes of its diversity that, as one researcher boasted, “a good sized volume was scarcely large enough to contain them.” The furious pace of forward progress was slowed somewhat in the early part of the nineteenth century when skin color scientists in both Europe and America were drawn into acrimonious debates over social issues, especially slavery and the place of “peoples of color” in the family of man. By the end of the century, the slavery issue had been settled, and the discovery of the cell and improved methods for the microscopic examination of the skin had stimulated the discipline to set off in new directions.
In retrospect, it is clear that the science of skin color had completed its early phase of development by the 1840s. With the discovery of the cellular nature of the epidermis, the “modern” phase of skin color science had begun (Meirowsky, 1940). This chapter briefly summarizes the first 250 years of the earlier phases of pigment research, from its birth in the 1600s to its “coming of age” in the 1840s. A history of the modern era, from the 1840s to the present, may be found in reviews by Becker (1959) and Nordlund et al. (1989).
Early Anatomic Discoveries To the ancient Greeks and Romans who were acquainted with the peoples of Ethiopia, the black color of the Africans was regarded as their most characteristic and most curious feature. Greek and Roman scientists were not equipped to investigate the causes of dark complexions in a meaningful way. They understood little about dissection of individual tissues and were unable to sort out the anatomic details related to the skin. They regarded the skin as an amorphous membrane made from the congealing of “moist exhalations” driven to the surface of the body by internal heat. They believed that the color of skin was imposed either from outside by the sun or by some inner humor. These notions about skin color persisted through the Middle Ages and into the Renaissance. In 1543, Vesalius succeeded in splitting the skin into two layers by applying a burning candle to the abdomen of a living subject. He did not examine the skin layers for their content of color. It was not until 75 years later that the first “scientific” study of skin color was performed. In 1618, Jean Riolan the younger, a Parisian anatomist, was the first person to make a detailed analysis of skin color. He used a technique similar to that of Vesalius to separate the skin of a black subject into two layers. But he used a vesicant rather than a flame to produce a blister and carefully examined the two layers for their color and texture. He found that, while the top of the blister (the cuticle) was pigmented, the base (the cutis) remained white. “Color . . .” he announced “. . . lay in the outer layer, and did not go so deep as the true skin” (Riolan, 1618). To Riolan, this finding reinforced the idea that heat and sunlight were the ultimate causes of blackness. Riolan reasoned that, if the sun caused skin darkening, it was expected that the outer cuticle would be darker than the inner cutis. 5
CHAPTER 1
A few years later, Alexander Read, an anatomist working in London, repeated Riolan’s experiments and found the same results. However, Read offered a different interpretation. The skin pigment, he concluded, was not caused by singeing the body’s surface. He concluded rather that skin color was derived from the body’s inner humors. As they escaped through the skin, some of the elements became attached to the surface and dried, thus producing the pigment. Negroes, he argued, had darker skin because they had larger pores than whites, a morphologic variation allowing greater volumes of their humors to escape leaving behind larger amounts of black “remnants” of the humors (Read, 1642). Perhaps the most detailed analysis of skin color in the seventeenth century was carried out by the distinguished writer and physician, Sir Thomas Browne. Browne had listened carefully to the accounts of explorers who had found variously colored races, and he concluded from these accounts that color did not arise from the influence of climate. “If the fervor of the Sun were the cause of the Negroes’ complexion, . . .” he wrote, “. . . it is reasonable to assume that inhabitants of the same latitude, subjected unto the same vicinity of the Sun, partake of the same hue and complexion, which they do not.” In addition, he noted that Africans who had been transplanted into “. . . cold and phlegmatic habitations . . .” had not turned white, but “. . . continued their hue, both in themselves and their generations.” He rejected the idea that skin blackness was acquired from a “. . . power of imagination . . .” or from “. . . anointing with bacon and fat substances.” Instead, he thought that the tincture of the skin was based on an inborn trait, a trait that was passed from father to son by the sperm. Browne was not an armchair scientist. His diary records the outline of numerous experiments he carried out to determine for himself the seat of color. For example, he set out to make a “. . . blistering plaster in a negroes skinne and trie if the next skin will bee white . . .” and to see whether a “. . . vesication will do anything upon a dead cold body.” He even urged his son Edward, a medical student, to carry out additional studies. He wrote to him asking that he “. . . separate the skin of a black person with boiling water and take notice of the cuticula and cutis and observe how the scarres become whiter or less blacke than any other parts.” He also urged him to “. . . touche the skin with aqua fortis and see how it will alter the colour.” Unfortunately, Browne did not record the results of these experiments (Keynes, 1964). Another seventeenth century polymath, Robert Boyle, devoted a chapter of his book Experiments and Considerations Touching Colours to what he called “the Cause of the Blackness of those many nations which by one common Name we are wont to call Negroes.” He examined the various causes proposed at that time and denied that either Noah’s curse on Ham or “heat alone” could produce a true blackness. Instead, he focused on principles of inheritance, concluding that the “Principal Cause of the Blackness of Negroes is some Peculiar and Seminal Impression.” As evidence, he reported that “the off-spring of Negroes, trans6
planted out of Africa, retain still the complexion of their Progenitors” (Boyle, 1664).
Malpighi’s Innovation: the Rete Mucosum Riolan’s contention that the cuticle was the seat of color had been in place for less than a century when it was superseded by an entirely different notion proposed by the Italian anatomist, Marcello Malpighi. In 1667, Malpighi stated that the seat of color was not the cuticle. Rather, he proclaimed that color was located in a separate layer of the skin sandwiched between the cuticle and the cutis. He named this layer the rete mucosum. The discovery of rete came about in the following way. In 1665, Malpighi had been searching for the structures that mediated the sensation of taste, and he succeeded in finding large papillae just below the surface of the tongue. Turning to the skin to see if he could find similar structures that mediated touch, he found that he was unable to separate the skin’s layers properly by boiling, the method that he had used previously. He was forced to use putrefaction, an old dissection technique in which the separation of parts is enhanced by allowing a small piece of tissue to decompose partially. Using this method, he prepared skin from cadavers and found that he could easily lift the cuticle from the cutis. By this method, he was able to identify the dermal papillae. However, he also found a mucoid material draped over the papillae, which he regarded as a protective covering. The material had a netlike appearance when seen from above, so he called it the rete mucosum. Malpighi’s experiments were not directed at discovering the proximate cause of skin color. However, in one experiment in which he used skin from an Ethiopian cadaver, he noted that the mucoid material was tinged black. On the basis of this finding, he later wrote “It is certain that the cutis (of the Ethiopian) is white, as is the cuticula too; hence all their blackness arises from the underlying mucous and netlike body” (Malpighi, 1665). Malpighi did not follow up on his discovery of the “seat of color” but the putrefaction technique he used allowed the layers of the skin to be separated gently. The method produced reliable results, and other investigators soon expanded on Malpighi’s finding. In 1677, three years after Malpighi published his findings, Johann Pechlin, a Dutch anatomist, used Malpighi’s method of dissection to make a thorough study of Ethiopian skin. In one experiment, after he lifted off the cuticle, he scraped away the black mucous and reapplied the scarf to the cutis. He reported that “. . . a whiteness came forth immediately of the sort seen often enough in Europe. In truth the surface of the skin was scarcely unattractive.” Pechlin was concerned that his results obtained using cadaver skin might not be the same had he studied living skin. To his dismay, he was unable to convince living subjects to cooperate in his experiments “. . . because of I don’t know what sort of evil on the part of the Negroes” (Pechlin, 1677).
A HISTORY OF THE SCIENCE OF PIGMENTATION
A few years later, the Dutch microscopist Antoni van Leeuwenhoek, in a letter to the Royal Society of London, reported on his observations made using his microscope of the skin of a black Moorish girl. “I took from several parts of the arms the outer skin with a fine little instrument and found that it consisted of little scales. Putting these scales before my microscope I found them to be not as transparent as those of my skin.” Van Leeuwenhoek concluded that the black color of the skin was the result of the black scales, and that “the little vessels which form the scales of the Moors” may possibly develop a slightly darker color (Collected Letters of Antoni van Leeuwenhoek, 1683–1684; see Schierbeek, 1952). If one follows Malpighi’s directions for uncovering the rete, as the cuticle is lifted off one observes tiny mucoid threads bridging the angle between the two layers. William Hunter described them as “. . . an infinite number of filaments, as fine as the most delicate threads of a spider’s web, that pass between the cutis and the more external integuments” (Hunter, 1764). According to some anatomists, the threads were tiny vessels. This idea led some of the more inventive investigators to propose that the coloring matter in Africans’ skin was not the mucous material itself but was a black fluid contained within the web of small vessels. One contemporary observer wrote “. . . between the outward and inner skin of the corpse can be found a kind of vascular plexus, spread over the whole body like a web or net, which was fill’d with a Juice as black as Ink” (Marana, 1801). It became something of a challenge to prove unequivocally that these filaments were in fact “vessels.” In anatomic laboratories, the identification of small vessels in anatomic preparations relied on their visualization after they had been injected with colored glue or isinglass. Only a few investigators were skilled enough to inject these “. . . most delicate threads.” One anatomist who was given credit for the first demonstration of this vascular network was William Baynham, an American who had moved to London in 1769. Although Baynham never published his findings, he placed his specimens on exhibition in John Hunter’s anatomic museum. Not all Baynham’s colleagues were convinced by his discovery. William Cruickshank made a careful study of Baynham’s preparations and later wrote that he was “. . . not perfectly satisfied” with them. He concluded that Baynham had not injected the vessels of the rete, but rather a series of vessels that lay between the rete and the cutis (Cruickshank, 1795). In the eighteenth century, the attention of researchers began to move from the anatomy of the rete to the “nature” of the coloring matter itself. Early attempts to collect and analyze material from the rete were not productive. Alexis Littre, a French surgeon, soaked pieces of skin from a Negro cadaver for a week either in warm water or in spirits of wine but was unable to extract any of the coloring matter (Littre, 1720). A few years later, another French scientist, Pierre Barrere, in an essay submitted to the Academy of Bordeaux in 1741, denied Malpighi’s claim that the pigment of Africans’ skin arose from the “corps reticulaire.” It is evident, he wrote, the coloring matter in the skin of Africans was bile. He reported
that he had examined cadavers of Africans and observed that “the bile is black, and the blackness of the skin is in proportion to the blackness of the bile.” Later in the century, another investigator attempted to prove that the pigment of Africans was derived from bile. Samuel Stanhope Smith, a professor of moral theology at the College of New Jersey, had learned from an American colleague that bile exposed to the sun and air changed its color to black. Smith hypothesized that, in southern climates, the secretion of bile was augmented and, when the bile reached the skin, it became “. . . more languid and almost fixed.” In the skin, the aqueous parts of the bile easily escape through the pores of the skin by perspiration, while the more dense portion remained in a glutinous state within the rete. There, it received the repeated radiation from the sun and atmosphere and turned black. Smith believed that a cold environment would reverse the process of darkening and render the complexion “. . . clear and florid.” According to Smith, if Africans moved to temperate climates from Africa “. . . they would soon lose their imposed color and become the color of Europeans” (Smith, 1788). Johann Friedrich Blumenbach, the German ethnologist, also proposed that bile was the coloring agent of the skin. He had learned that bile was made of a mixture of carbon and hydrogen. He suggested that, as the bile reached the skin, the hydrogen it contained became more volatile than the carbon and combined with atmospheric oxygen. This reaction left behind a black carbon residue that became embedded in the Malpighian mucous and caused the skin to darken (Blumenbach, 1865). Another “chemical” theory was advanced by the young Humphrey Davy in 1799. Davy thought that light had a great affinity for oxygen and could extract it from other compounds. Davy had evidence that the mucous material of the rete was made of a colorless mixture of carbon, nitrogen, and oxygen. He proposed that sunlight extracted the oxygen from this mixture and left behind a black material made of carbon and nitrogen. To Davy, this explained differences in skin hues found throughout the world. “In northern latitudes, where the inhabitants are less exposed to light, the rete continues to contain its full proportion of oxygen, and the inhabitants are lighter in color. In the torrid zone, on the other hand, where the sun was especially intense, larger quantities of oxygen would be removed, and the blackness peculiar to the negroes will be found.” Davy had no direct proof that light could subtract oxygen from the skin, but he did cite other chemical experiments to support his claim. He reported that, when a compound that binds oxygen, such as sulfur of potash, is applied to the skin of a white person, the skin blackens. When a compound that gives off oxygen, such as muriatic acid, is applied to the skin of a Negro, it lightens (Davy, 1799). An even more imaginative notion about the nature of skin color was suggested by Immanuel Kant. Kant based his theory on the well-known capacity of phlogiston to turn blood a black color. Phlogiston was an imaginary element considered to be the essential principle of combustion. It was said to be 7
CHAPTER 1
released from the body through the lungs as part of the metabolic process. Kant believed that, in regions of the globe where the atmosphere was heavily phlogisticated, such as the coast of Africa, it would be impossible to eliminate all the body’s phlogiston by breathing. Kant proposed that the excess phlogiston would travel through the circulation and, on reaching the skin, it would precipitate in the ends of the small cutaneous vessels and turn the skin black (Lovejoy, 1959). Claude Le Cat, a French physician, claimed that the source of Africans’ blackness was neither bile nor blood. He said that the black mucous, which he called ethiops, was found only in Africans and that it was secreted directly into the skin through the tips of the cutaneous nerves (Le Cat, 1765). Although most early scientists believed that skin pigment was derived from some “internal” source such as bile or blood, a few investigators decided that the coloring matter was produced by glands within the skin itself. The earliest version of this hypothesis was offered by an English anatomist, Edward Tyson. He proposed that the black colour in Negroes’ skins came from glands that were full of a “black liquor.” He suggested that the climate might alter the glands so that “. . . they might separate from the mass of blood a differing humor from White, and by this means give a different hue to the inhabitants” (Montagu, 1943). Two French researchers, G. H. Breschet and Roussel de Vauzeme, reported that they had found a “. . . chromatogenous apparatus . . .” in the cutis which secreted the black mucous. They said that the mucous was deposited on the surface of the dermal papillae through short, excretory ducts emanating from glandular parenchyma located in the cutis (Plumbe, 1837). Another French investigator, M. Gaultier, also argued that the coloring matter was secreted within the skin but not from glands. The pigment of the skin, he said, was produced instead from hair bulbs. Gaultier’s claim was based on the results of an experiment he carried out on a living subject. He burned the skin of a Negro and then closely observed the pattern of repigmentation during the healing process. According to Gaultier, the pigment appeared first around the “pores” through which the hairs exited and only later did it radiate out to cover the entire area of the burn (Prichard, 1813).
Differences Between Blacks and Whites As a more complete picture of skin color began to emerge by the end of the eighteenth century, political and social forces required the disciplines of anatomy and biology to take on a social dimension. Advocates of black slavery argued that Africans were not the “brothers” of Europeans but rather were the product of a separate creation. Skin color, the most obvious marker of racial identity, was forced to the center of the debate over the unity of mankind. The polygenists began looking for “significant” anatomic differences between blacks and whites to prove they were separate species. Monogenists began looking for evidence of similarities. 8
Bolstering the polygenist cause was the English anatomist, John Gordon. Gordon claimed that whites, unlike blacks, had no rete mucosum. “I have satisfied myself by many dissection that in the Negro there is a Black membrane interposed between the epidermis and true skin upon which their dark color entirely depends . . . But after the strictest examination I have not been able to find any light colored rete mucosum in the inhabitants of Great Britain, nor in those of other nations resembling them in color” (Gordon, 1815). Several anatomists disagreed. Richard Harlan, a young lecturer in anatomy from Philadelphia, wrote that “. . . the existence of the rete mucosum in the white race, so frequently denied, has been demonstrated occasionally in the European by skilful anatomists and if not deceived I myself have discovered it several times in a living European subject, by raising the epidermis with a blister, especially upon the back of the hands and the neck” (Harlan, 1835). Charles Caldwell, who had moved from Philadelphia to become a professor in a medical college in Lexington, Kentucky, reported that he too found the rete in both races, although the structures were not identical in appearance. “The rete mucosum in blacks is comparatively thick, while in the Caucasian, the rete is present but it is much thinner.” In spite of this similarity, however, Caldwell concluded that Negroes and Caucasians were sufficiently distinct to be called separate biological species (Caldwell, 1830).
Experiments of Nature In addition to the work carried out by anatomists and chemists in dissecting rooms and laboratories, many physicians made important contributions to the fund of information about skin color through reporting and analyzing patients with clinical problems. John Josselyn, a physician from England who was visiting the Massachusetts Bay Colony in 1675, was one of the first physicians to advance the science of skin color by using observations based on a clinical case. While in Boston, Josselyn had been called upon to lance a “corruption” in the palm of a “Moor.” Later, he described his findings. “After I lanced it, I perceived that the Moor had one skin more than Englishmen, deeper in colour than our European veins, and upon it rests the epidermis” (Josselyn, 1675). Samuel Marcy, a physician from rural New Jersey, reported the case of an albino girl. After providing a full account of her family history, including the fact that she had two albino sisters, he went on to consider the cause of the disorder. “The mother accounts for the appearance of the child by attributing it to a severe fright she receive by the falling down of an old white mare she was driving,” wrote Marcy. “Although I was unwilling to admit at first that the Great Creator ever left his work in so loose a manner, that the imagination of the mother should alter or determine form or color of her children, the birth of two other albino children go further to strengthen the doctrine that the mind of the mother may affect the fetus in utero” (Marcy, 1839).
A HISTORY OF THE SCIENCE OF PIGMENTATION
John Morgan, from Philadelphia, reported the case of Adelaide, a pied Negro girl from the West Indies. Like Marcy, Morgan considered the possibility that maternal impression might cause the disorder. Morgan related that, while pregnant, the mother of the girl “. . . delighted in laying out all night in the open air, and contemplating the stars and planets. Whether the strong impression made upon the mother of Adelaide by the nightly view of the stars and planetary system may be the cause of the very extraordinary appearances in this girl, everyone will have to determine for themselves” (Morgan, 1784). During the seventeenth and eighteenth centuries, the pigment disorder that attracted most attention among the medical community, as well as the general public, was vitiligo vulgaris. In 1697, a remarkable case was presented to the Royal Society by William Byrd, a Virginian who had recently returned to London after a visit home. Under the title “An Account of a Negro-Boy that is dappeld in several Places of his Body with White Spots,” Byrd reported that the boy was born in Virginia of black parents, who was “well till 3 years old, and now was speckled of his breast and back and that no fancy had taken his Mother.” The spots he wrote are “wonderfully White, at least equal to the skin of the fairest Lady. His Spots grow continually larger and larger, and ’tis probable, if he lives, he may in time become all over white.” Thomas Jefferson described an African slave whom he encountered on his own plantation. He described the man as “A Negro man within my knowledge, born black and of black parents, developed when a boy, a white spot on his chin. This continued till he became a man, by which time it had extended over his chin, lips, and the neck on that side. He is robust and healthy and the change of color is not accompanied with any sensible disease, either general or topical” (Jefferson, 1904). Charles Peale, the painter and natural historian, also described a case under the title “An Account of a person born a Negro who afterwards became white” (Peale, 1791). The case of vitiligo that attracted most attention during this period from both lay and medical communities was Mr Henry Moss. At the age of 38 years, Moss first noted a change in the color of his skin. The change began on his fingers and hands and extended over his arms, legs, and face. Six years later, in the summer of 1796, Moss traveled from his home in Maryland to exhibit himself for money at the Black Horse Tavern in Philadelphia. He became a popular attraction and, according to one account, was so well known to the local citizens “. . . that his name was almost as familiar as John Adams, Thomas Jefferson, or James Madison” (Caldwell, 1855). Several prominent physicians from Philadelphia visited Mr Moss. Benjamin Barton, a professor at the medical school, was impressed with the distribution of the white spots. Noting that Moss’ color had disappeared completely from his armpits, Barton suggested initially that it was likely that the pigment had been washed away by perspiration. Charles Caldwell also examined Moss and was skeptical of Barton’s interpretation.
He decided to study Moss in detail. “Anxious to know as much of his case as possible, I took him in some measure under my care, . . . and . . . for a slight reward made on him such experiments as suited my purpose. While thousands visited and gazed at Moss as an object of curiosity and wonder, I alone endeavored to make him a source of scientific information.” Caldwell asked Moss “. . . to excite by exercise a copious perspiration to ascertain whether the fluid perspired by the colored portions of the skin was itself colored. And I found that it was not.” Caldwell examined Moss’ skin and found that the rete mucosum had disappeared from the depigmented areas. He concluded that the rete had been removed “. . . by means of absorption.” Moss’ sensitivity to low temperatures he thought supported his theory that Moss was losing his rete. He concluded that Moss’ true skin was now “protected” from a cold atmosphere by nothing but the cuticle (Caldwell, 1855). Samuel Stanhope Smith, who had earlier pioneered the idea that African blackness was caused by environmental factors, was another visitor. He was accompanied by two other gentlemen “. . . of whom none are more capable of observing a fact of this nature with a sound and accurate judgment.” Smith paid great attention to the pattern of Moss’ pigment loss and concluded that this provided elegant proof of his hypothesis. “Although there was evidently a strong and general tendency in the constitution of this negro to a change of color, yet this tendency was much longer resisted in those parts of the body which were most exposed to the immediate action of the sun’s rays. As he was a laboring man, wherever there were rents in the thin clothes which covered him there were generally seen the largest spots of black.” From this pattern, Smith inferred that “. . . where any dark color has been contracted by the human skin, the solar influence alone, and the free contact of the external air, will be sufficient to continue it a long time even in those climates which are most favorable to the fair complexion” (Smith, 1810). Benjamin Rush suggested perhaps the most unusual hypothesis to explain Moss’ pigment loss. In a paper published in 1799, Rush argued that it was the blackness of Moss, and not his white spots, that represented his disease. I shall prove, he wrote, that “. . . the color and figure of our fellow creatures who are known by the epithet of negroes are derived from a modification of that disease which is known by the name of Leprosy.” Rush went on to explain that the black color of the negroes, their thick lips, and their insensitivity to pain were all common signs of leprosy. He suggested that it was likely that leprosy was an infectious disorder “. . . since a white woman in North Carolina living with a black husband has not only acquired a dark color but also several features of a negro.” Rush proposed that Moss was not suffering from a disease but was actually undergoing a spontaneous cure of one. “If the color of negroes is a disease . . .” he added, “. . . let science and humanity combine their efforts and endeavor to discover a remedy for it.” From his experience with other ailments, Rush suggested that bleeding or purging be tried to lessen the black color (Rush, 1799). 9
CHAPTER 1
The Beginnings of Modern Pigment Research The “early” phase of pigment research ended in the 1840s when the cell theory ended the rete’s reign as a separate amorphous layer of the skin and assigned the seat of skin color to the lower portion of a cell-rich epidermis. Microscopic anatomists had also discovered that the pigment was not in the form of a liquid or mucoid material but was rather composed of tiny intracellular granules. With the discovery that a population of dendritic cells derived from the neural crest served as the source of the coloring matter for the skin and hair, the “modern” phase of pigment research moved into high gear. For the past 150 years, researchers have relied on a melanocyte-centered paradigm to lead them along new paths of discovery. To see how far their investigations have proceeded and how wide-ranging their interests and disciplines, one needs only to look through the remaining chapters in this volume.
References Becker, S. W. Historical background of research on pigmentary diseases of the skin. J. Invest. Dermatol. 32: 185–196, 1959. Blumenbach, J. F. The Anthropological Treatises of Johann Friedrich Blumenbach. London: Longman Green, 1865. Boyle, R. Experiments and Considerations Touching Colours. London: Henry Herringman, 1664, pp. 151–167. Caldwell, C. Thoughts on the Original Unity of the Human Race. New York: E. Bliss, 1830. Caldwell, C. Autobiography of Charles Caldwell, MD. Philadelphia: Lippincott, Grambo and Co., 1855. Cruickshank, W. Experiments on the Insensible Perspiration of the Human Body. London: George Nicol, 1795. Davy, H. Essays on heat and light. In: Contributions to Physical and Medical Knowledge Principally From the West of England, T. Beddoes (ed.). Bristol: Biggs and Cottle, 1799, pp. 193–198. Gordon, J. A System of Human Anatomy. Edinburgh: William Blackwood, 1815. Harlan, R. Medical and Physical Researches. Philadelphia: Lydia Bailey, 1835. Hunter, W. Remarks on the cellular membrane and some of its diseases. Med. Observ. Inquiries 2: 26–55, 1764. Jefferson, T. Notes on Virginia, in the Writings of Thomas Jefferson. Washington, DC: Thomas Jefferson Memorial Association, 1904.
10
Josselyn, J. An Account of Two Voyages to New-England. London: G. Widdowes, 1675. Keynes, G. The Works of Sir Thomas Browne. Chicago: University of Chicago Press, 1964. Le Cat, C. N. Traite de la Couleur de la Peau Humaine en General, de celle des Negres en Particulier, et de la Metamorphose d’une de ces Coleurs en l’autre, soit de Naissance, soit Accidentellement. Amsterdam, 1765. Littre, A. La Peau in Histoire de l’Academie Royale des Sciences. Paris: Hochereau, 1720, pp. 30–32. Lovejoy, A. O. Kant and Evolution in Forerunners of Darwin. Baltimore: Johns Hopkins, 1959, pp. 173–206. Malpighi, M. De Externo Tactus Organo Anatomica Observatio. Naples: Apud Agidium Longu, 1665. Marana, G. P. Letters Written by a Turkish Spy, vol. 8. London: Vernor and Hood, 1801. Marcy, S. S. On the albino. Am. J. Med. Sci. 24: 517–518, 1839. Meirowsky, E. A critical review of pigment research in the last hundred years. Br. J. Dermatol. 52: 205–217, 1940. Montagu, M. F. A. Edward Tyson, MD, FRS, and the Rise of Human and Comparative Anatomy in England. Philadelphia: The American Philosophical Society, 1943, pp. 212–213. Morgan, J. Some account of a motley coloured, or pye, negro girl and mulatto boy. Trans. Am. Phil. Soc. 2: 392–395, 1784. Nordlund, J. J., Z. A. Abdel-Malek, R. E. Boissy, and L. A. Rheins. Pigment cell biology: An historical review. J. Invest. Dermatol. 92(Suppl.): 53s–60s, 1989. Peale, C. W. Account of a person born a negro, or a very dark mullato, who afterwards became white. Univ. Asylum Columbia Mag. 2: 409–410, 1791. Pechlin, J. N. Du Habitu & Colore Aethiopum Qui Vulgo Nigritae. Koln: Joach Reumani, 1677. Plumbe, S. A Practical Treatise on the Diseases of the Skin. London: Sherwood, Gilbert & Piper, 1837, pp. 9–16. Prichard, J. C. Researches into the Physical History of Man. London: John and Arthur Arch, 1813, pp. 163–164. Read, A. The Manual of the Anatomy or Dissection of the Body of Man. London: Francis Constable, 1642. Riolan, J. Anthropographia. Paris: Hadrianum Perier, 1618. Rush, B. Observations intended to favour a supposition that the black color (as it is called) of the negroes is derived from leprosy. Am. Philos. Soc. Trans. 4: 289–297, 1799. Schierbeek, A. (ed.). Collected Letters of Antoni van Leeuwenhoek, Vol. IV, 1683–1684, Amsterdam: Swets & Zeitlinger, 1952, pp. 245–251. Smith, S. S. An Essay on the Causes of the Variety of Complexion and Figure in the Human Species. Edinburgh: C. Elliot, 1788. Smith, S. S. An Essay on the Causes of the Variety of Complexion and Figure in the Human Species. New Brunswick: J. Simpson and Co., 1810.
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
2
Comparative Anatomy and Physiology of Pigment Cells in Nonmammalian Tissues Joseph T. Bagnara and Jiro Matsumoto
Summary 1 The terms “chromatophore” and “pigment cell” are equivalent, although the former is usually applied to lower vertebrates and the latter to homeotherms (birds and mammals). 2 Epidermal melanophores (-cytes) are ubiquitous pigment cells present in all vertebrate classes. They are primarily elements of morphologic color change (the increase or decrease in skin pigments) and are thus responsible for the amounts of melanins found in the epidermis, feathers, and hair. 3 Dermal melanophores predominate in the dermis of lower vertebrates and are elements of both morphologic color change and physiologic color change (the rapid changes from pallor to darkening and vice versa). Other dermal chromatophores include iridophores (and leukophores) and xanthophores and erythrophores, which are also elements involved in both morphologic and physiologic color changes. The pigment composition of the three basic dermal chromatophore types is different from one another, and each contains unrelated pigments. Similarly, their cytoplasmic pigmentary organelles differ from one another in appearance, although they all seem to have a common origin from the endoplasmic reticulum. Dermal chromatophores function in background adaptation (cryptic coloration), thermal regulation, warning coloration, reproduction, and possibly in protection against solar radiation. 4 Morphologic and physiologic color changes are primarily mediated by hormones, especially melanocyte-stimulating hormone (MSH). Melatonin, melanophore-contracting hormone (MCH), catecholamines, and sex hormones play more particular roles. MSH release from the pituitary is controlled by the hypothalamus in response to background color and intensity. Melatonin is produced and released by the pineal gland (epiphysis cerebri) under conditions of darkness. While MSH causes dispersion of dermal and epidermal melanophores and aggregation of iridophores, melatonin causes aggregation of only dermal melanophores whereas epidermal melanophores and iridophores are unaffected by melatonin. Some chromatophores are directly affected by light and disperse or aggregate in response to the presence or absence of specific wavelengths of light. 5 All pigment cell types originate from the neural crest and are determined (in the embryonic sense) either in situ or by
extrinsic factors encountered during migration or after their final destination is reached. These factors may include elements of the extracellular matrix and local factors present in the integument, including a melanization-inhibiting factor (MIF) and a melanization-stimulating factor (MSF). The last two factors may be major elements in controlling the expression of pigmentation patterns. In the zebrafish model, a hostile relationship of xanthophores toward adult-type melanophores plays a key role in color pattern independent of dorsal/ventral regions. The organellogenesis of all pigmentary types seems to involve a primordial vesicle derived from the endoplasmic reticulum. 6 Such hormones as MSH, thyroid hormones, and sex hormones influence pigment cell development, but do not seem to determine pigmentation patterns. 7 The pigment cells of all vertebrate classes are homologous in that they have in common embryonic origin, pigment composition, morphology, and hormonal control. Chromatophores, usually thought to be restricted to lower vertebrates, are also present in homeotherms. Proteins or peptides that regulate pattern expression, such as MIF from amphibians and agouti protein from mammals, may be chemically and physiologically related. 8 Numerous anomalies and pathologies of lower vertebrate pigment cells exist including neoplasms such as erythrophoroma. These are not unlike malignant melanomas of higher forms. 9 As the burgeoning knowledge and technology derived from work on mammalian systems is applied to those of lower vertebrates, much can be learned about the fundamental cell biology and physiology of lower vertebrate pigmentation. In turn, because of the relative accessibility of lower vertebrates for experimentation, new knowledge about the normal and abnormal biology of mammalian pigmentation, including that of humans, will be accrued from continuing studies on these lower forms.
Historical Background For many years, knowledge, understanding, and experimentation on lower vertebrate pigmentation went on separately from that of higher vertebrates, including humans. Not until the middle of the twentieth century was it realized that the 11
CHAPTER 2
bright and often rapidly changing pigmentation of fishes, frogs, and lizards (poikilotherms) is fundamentally related to the more static and more uniform pigmentation of birds and mammals (homeotherms). This divergence in understanding was significantly registered in pigment cell terminology and nomenclature. For a detailed discussion, see Bagnara and Hadley (1973). No real confusion existed with respect to birds and mammals, in which melanin-bearing pigment cells seemed to be the only ones present and were called melanocytes without question. Among lower animals, the first term to be applied was chromoforo (Sangiovanni, 1819; according to Parker, 1948) and, thus, with translation from the Italian, the term chromatophore has precedence. This was a term of prevalence for both lower vertebrates and invertebrates, notwithstanding the use of the suffix -zyte as a substitute for -phore in much of the German literature. Thus, with respect to melanin-bearing pigment cells, the reference was to melanophores (or melanozyten). It was early realized that melanophores were present primarily in the dermis, where a variety of other brightly colored nonmelanin-bearing pigment cells were also often found, and their nomenclature provided a new source of confusion because of the discovery of specific nonmelanin pigments in or in association with these dermal pigment cells (Fox, 1953; Fox and Vevers, 1960). Thus, guanine-bearing chromatophores were often designated as guanophores based upon the pigment they contained; however, these same pigment cell types were designated by others as xantholeukophores, based upon what colors they manifested. By the end of the 1970s, much new information about structure, function, and composition of all pigment cell types had accumulated, and it was thus possible to establish a reasonable and unifying pigment cell terminology for both lower and higher vertebrates (Bagnara, 1966a). The unifying element in pigment cell terminology considered that pigment cells should be designated primarily by their appearance rather than their composition, and details of its application were presented earlier (Bagnara and Hadley, 1973). It was concluded that, among poikilotherms, there exist epidermal and dermal melanophores. The latter, together with iridophores (silvery to white) and xanthophores (yellow) and/or erythrophores (red), are also dermal. The pigmentary organelles of melanophores were referred to as melanosomes, those of iridophores as reflecting platelets, and those of erythrophores/xanthophores as pterinosomes and carotenoid vesicles. The embryonic origin of the various chromatophore types was addressed in early experiments performed mostly on amphibians, and on salamanders in particular. All poikilothermic chromatophores are derived from the neural crest, as was shown by the early elegant extirpation and transplantation experiments of DuShane (1935). From this site on the neural tube, chromatoblasts migrate to all regions of the integument and to other areas of the body to give rise to the particular and striking patterns of lower vertebrates. Among the early questions considered by investigators were: when were the specific chromatophores determined (in the embryonic sense); and how were the various circumscribed patterns 12
accomplished? These questions are discussed at length in an extraordinary book, Of Scientists and Salamanders, by Professor Victor T. Twitty (1966). Two of Professor Twitty’s students investigated these problems in detail. M. C. Niu (Twitty and Niu, 1954) considered the mutual inhibitory effects of individual chromatoblasts as they encountered one another during migration, while H. E. Lehman [see Lehman and Youngs (1959)] concluded that both extrinsic and intrinsic factors influenced chromatoblast expression and thus were responsible for pigmentation patterns. Later, Volpe (1964) concluded that pigmentation patterns of frogs were an autonomous function of neural crest cells, but this was disproved by Bagnara (1982) who had earlier proposed that the diverse pigment cell types of vertebrates had a common origin from a neural crest stem cell and were specified later (Bagnara et al., 1979). This concept has stood the test of time. The capacity for rapid color change (physiologic color change) among lower vertebrates has long attracted attention, and an enormous literature accumulated by the start of World War II [see Parker (1948)]. With the understanding that individual chromatophores brought about color change due to their capacity to “expand or contract,” the search was on for factors controlling these cells that allowed them to respond in an integrated fashion. Among the first candidates for chromatophore control was the nervous system and direct innervation of chromatophores. As early as 1876, Pouchet provided information that, in teleost fishes, the sectioning of peripheral nerves or the electrical stimulation of spinal nerves led, respectively, to darkening or pallor in appropriate areas. Even earlier, Brücke (1852) presented data to support the idea that color change in chameleons is under nervous control. A history of work demonstrating the control of fish chromatophores by direct innervation is well provided in Parker (1948) and Fujii (1993a). Chromatophore control by direct innervation is not a general phenomenon in lizards (Bagnara and Hadley, 1973), but such is surely the case for African chameleons (Whimster, 1971). While chromatophore control through direct innervation was shown not to be a general phenomenon among vertebrates, indirect control of chromatophores by neurotransmitter agents and hormones was shown to be significant in most lower vertebrates (see Bagnara and Hadley, 1973; Fujii, 1993a; Parker, 1948). Of particular importance are the catecholamines, epinephrine and norepinephrine, which affect melanophores directly by causing melanophore contraction, thus leading to the phenomenon of excitement pallor seen among many fishes, amphibians, and reptiles. Because these catecholamines are released by the adrenal medulla, excitement pallor can be viewed as a color change controlled by hormones. While this is the case, the role of catecholamines is minor compared with that of the hypophysial hormone, MSH. That the pituitary contains an important factor that influences pigment cells was first realized from the simultaneous early work of P. E. Smith (1916) and B. M. Allen (1916). Early on, this factor was designated “intermedin” (Zondek and Krohn, 1932) and later it received its current designation of
COMPARATIVE ANATOMY AND PHYSIOLOGY OF PIGMENT CELLS IN NONMAMMALIAN TISSUES
MSH (Shizume et al., 1954). The older literature on this subject has been extensively summarized by Waring (1963) and by Bagnara and Hadley (1973). More recently, the role of MSH on poikilotherm chromatophores has been reviewed by Fujii (1993a) for fishes and by Fernandez and Bagnara (1991, 1993) for amphibians. Almost 30 years ago, it became clear that MSH is the principal agent bringing about melanosome dispersion in lower vertebrates and that it does so through cyclic adenosine monophosphate (AMP) as a second messenger (Bagnara and Hadley, 1969; Goldman and Hadley, 1969). This hormone was also shown to bring about iridophore aggregation and xanthophore or erythrophore dispersion in amphibians (Bagnara, 1958, 1969). The same is now known to be true for fishes (Fujii, 1993a). Before the characterization of MSH, the pituitary was sometimes viewed as possessing two opposing chromatophorotropic hormones that controlled color changes of lower vertebrates. This “bihumoral” theory of hormonal control was originally championed by Sir Lancelot Hogben in the 1940s and was refined by his scholarly descendants, notably H. Waring in his monograph Color Change Mechanisms of Cold-Blooded Vertebrates (Waring, 1963). It considers that the pituitary stimulates melanophore dispersion through the elaboration of a “melanophore-dispersing hormone” (essentially MSH according to Bradshaw and Waring, 1969) and melanophore aggregation through the action of a melanophore-aggregating hormone, which had not yet been identified at that time. While the bihumoral theory failed to reach acceptance, it lurked in the background largely because of the discovery by Enami (1955) of a MCH in the pituitary of a catfish. Because of his untimely death, this putative hormone received little attention until its cause was revived by Professor Bridget Baker in the 1980s. Its nature and biological significance were reviewed by her (Baker, 1993). Among other hormones found to be of importance in the regulation of chromatophores is melatonin, a hormone produced and released by the pineal gland during darkness to bring about aggregation of dermal melanophores and thus lead to the body blanching reaction of amphibian embryos and larvae (Bagnara, 1960, 1963, 1966b). It was known from the early study of McCord and Allen (1917) that the mammalian pineal contained an agent that aggregated dermal melanophores, but it was not until the work of Lerner et al. (1958) that the agent was purified, characterized as an indole, and designated melatonin. Shortly thereafter, Bagnara (1960) announced that melatonin was elaborated from the pineal during darkness and was actually a hormone released to bring about a body blanching reaction that occurs in amphibian larvae at night in a circadian rhythm (Bagnara, 1960, 1963). Subsequently, this hormonal role for melatonin was extended to many other vertebrates including fishes (see Fujii, 1993a). It is significant that melatonin’s direct action in bringing about melanophore aggregation is restricted to dermal melanophores; thus, epidermal melanophores and dermal iridophores do not respond directly to the hormone (Bagnara, 1964a).
It has long been known that the integument of animals is directly sensitive to light in a little-understood phenomenon known as the “dermal light sense.” An excellent review of this subject has been presented by Steven (1963), who included numerous references to the possibility that pigment cells themselves are directly responsive to changes in illumination. This topic is addressed further in the later section on adaptation to darkness. Among the important concepts of pigment cell biology that have long commanded interest is that of the intracellular movements of pigment granules and, in particular, the melanosomes. Even to this day, this area of research continues to be most active and even controversial. One of the earliest theories of melanosomal movements was that of Marsland (1944), who considered that melanosomal movements were related to the solation and gelation of the chromatophore cytoplasm. Later, because it was known that colchicine causes melanosome dispersion (Wright, 1955) and reflecting platelet aggregation (Bagnara, 1969) in amphibians, Malawista’s (1965) conclusion that this result suggested solation of chromatophore cytoplasm seemed reasonable. Attention then shifted to piscine melanophores when Bikle et al. (1966) suggested that microtubules were important for the dispersion and aggregation of melanophores. Later, Malawista (1971) suggested a role for microfilaments in these processes, and thus the involvement of the cytoskeleton in melanosomal movement was established. From this period to today, most work on the translocation of pigmentary organelles has focused on fish chromatophores and especially on melanophores and erythrophores/xanthophores, and the issue has become exceedingly complicated by the many variables involved. There seem to be species differences, and there is a profound variation in the velocity of organellar movements, some occurring in seconds and others over minutes. Organellar movements involve different organellar types within the same cell, such as pterinosomes and carotenoid vesicles. In some cases, individual organellar types migrate differentially within the cell and thus preclude the possibility of passive movements during aggregation and dispersion. The actin–myosin system has been invoked in explanations of many types of organellar motility, but not all. Tubulin–dynein interactions have been considered to provide the forces that drive pigmentary organelles along the length of microtubules (Oshima and Fujii, 1987), but organellar motility can occur even in the absence of microtubules. Other force-generating proteins such as kinesin and dynamin have gained attention as possible movers of pigmentary organelles as they slide along microtubules in both aggregation and dispersion. To add to the complexity of the situation, the endoplasmic reticulum has now been invoked as a major player in organellar motility. The continuing history of this phenomenon is complicated, but discussions are available in numerous reviews that have emerged (Kimler and Taylor, 1995; Obika, 1986; Schliwa, 1984; Taylor, 1992) and in the subsequent section on molecular mechanisms for intracellular transport of pigment granules. 13
CHAPTER 2 Table 2.1. Chromatophore terminology and characterization. Chromatophore
Organelle
Pigment
Color
Source
Epidermal melanophore (-cyte) Melanophore
Melanosome Melanosome Pterino-melanosome
Eumelanin Eumelanin Pterorhodin–eumelanin
Black, brown Black, brown Black, red
Iridophore
Reflecting platelet (iridosome)
Structural colors and iridescence
Leukophore
Leukosome (refractosome) Pterinosome (xanthosome) Carotenoid vesicles Pterinosome (erythrosome) Carotenoid vesicles Cyanosome
Purines, especially guanine; some pteridine crystals Uric acid (?), other purines (?) Pteridines
Fishes, amphibians, reptiles Fishes, amphibians, reptiles Phyllomedusine frogs, rhacophorid frogs (?) Fishes, amphibians, reptiles
Structural white
Fishes
Yellow to orange
Fishes, amphibians, reptiles
Carotenoids Pteridines
Orange to red
Fishes, amphibians, reptiles
Carotenoids ?
Blue
Mandarin fish
Xanthophore
Erythrophore
Cyanophore
Epidermal melanin unit: an association of an epidermal melanophore (-cyte) with adjacent keratinocytes that serve to receive cytocrine melanin. Dermal chromatophore unit: an association of the dermal chromatophores (xanthophores or erythrophores, iridophores, and melanophores) to bring about integrated color changes. These are especially important in the expression of green colors in amphibians and reptiles.
Current Concepts It is impossible in one chapter alone to consider all the salient aspects of lower vertebrate pigment cells that should be of interest and importance to scholars of pigmentation. Thus, in this section, an attempt is made to focus on those topics that may be most valuable to current workers in the field. These topics are considered to be perhaps most relevant to the ongoing research of today. At the same time, it should be understood that much of the knowledge presented in the previous section on history remains current. Much of it will not be discussed further because, unfortunately, current relevance dictates the direction of current research support, even at the expense of allowing important concepts to lie fallow. In recent years, most pigmentary research on poikilotherms has centered on fishes and amphibians (Bagnara, 1976). The cytophysiology of fish chromatophores has been the subject of detailed review (Fujii, 1993a, b). Accordingly, amphibian examples will be stressed here.
Chromatophore Characterization Because of new knowledge gained during the past few years, it is time to re-examine chromatophore terminology and perhaps establish a nomenclature that can be used universally. Table 2.1 presents a suggested terminology to be used for the near future. It does not differ markedly from that which we presented earlier (Bagnara, 1966a; Bagnara and Hadley, 1973); however, other terms that have emerged more recently are included as are some lesser known synonyms that are indicated in parentheses. Figures 2.1–2.3 demonstrate some of the brightly colored pigment cells. 14
Fig. 2.1. Living red-backed salamander, Plethodon cinereus, showing the distribution of erythrophores and melanophores over capillaries between the skin glands of the dorsal surface. A few silvery iridophores are also visible (see also Plate 2.1, pp. 494–495). [From Bagnara, J. T. Color change. In: Physiology of the Amphibia, vol. 3, B. Lofts (ed.). New York: Academic Press, 1976, pp. 1–52 with permission.]
COMPARATIVE ANATOMY AND PHYSIOLOGY OF PIGMENT CELLS IN NONMAMMALIAN TISSUES
Fig. 2.2. A living scale from the red-colored variant of swordtail fish, Xiphophorus helleri. Note the presence of numerous erythro(xantho)phores with red pterinosomes in the periphery and yellow carotenoids in the center under a dispersed state (see also Plate 2.2, pp. 494–495). [From Bagnara, J. T., and M. E. Hadley. Chromatophores and Color Change: The Comparative Physiology of Animal Pigmentation. Englewood Cliffs, NJ: Prentice-Hall, 1973, with permission.]
Melanophores and Melanocytes Whether these cells should be designated -phores or -cytes is a question that has often been addressed, and there seems to be no answer other than to let use by the scientific community be the ultimate judge. In an earlier attempt to reconcile the problem, Fitzpatrick et al. (1966) suggested that “melanophore” be the term of preference for lower vertebrates because this pigment cell was important in rapid color change phenomena (physiologic color change) and involved the rather rapid and profound intracellular movements of melanosomes, the melanin-containing organelles. It was suggested that the term “melanocyte” be used for higher vertebrates primarily because their epidermal pigment cells were of a form different from that of dermal melanophores and presumably were not involved in physiologic color change. Actually, some of the rationale for their premise no longer holds, but their conclusion that melanocyte be used for birds and mammals seems justified because this term has come to be used almost exclusively for melanin-bearing pigment cells by current workers. Accordingly, although this chapter is devoted to the pigment cells of lower vertebrates, the mutuality of nomenclature for melanin-bearing pigment cells will be acknowledged by liberal use of the suffix -cyte, as in melanophore (-cyte). Epidermal Melanophores (-cytes) While the epidermal melanocytes of birds and mammals had long been recognized and reasonably characterized, it was not until the work of Hadley and Quevedo (1967) that it was generally realized that this very same pigment cell type exists in the epidermis of lower vertebrates where it functions as it does in homeotherms. Indeed, it has been observed to be a prominent pigment cell of most lower vertebrates, from primitive fishes to reptiles, where it exhibits its typical spindle shape (Fig. 2.4) and
Fig. 2.3. Melanophore and xanthophores from the teleost, Fundulus heteroclitus. Note that the xanthophores appear as aggregated oil droplets (see also Plate 2.3, pp. 494–495). [From Bagnara, J. T., and M. E. Hadley. Chromatophores and Color Change: The Comparative Physiology of Animal Pigmentation. Englewood Cliffs, NJ: Prentice-Hall, 1973, with permission.]
Fig. 2.4. Epidermal melanophores of adult Rana pipiens, dispersed at left and aggregated at right. Note cytocrine melanin in adjacent epidermal cells. Each epidermal melanocyte with its surrounding epidermal cells comprises an epidermal melanin unit (courtesy of Professor M. E. Hadley).
15
CHAPTER 2
V pre
mel
V mel pre
Fig. 2.6. Dispersed (left) and aggregated (right) dermal melanophores in the tail fin of Xenopus larvae.
Fig. 2.5. Dermal melanophores from larvae of Pachymedusa dacnicolor. Left, melanosomes (mel) and fibrillar premelanosomes (pre) are typical of early stages. Right, at metamorphic climax, melanosomes begin to develop into the adult form and, at this stage, are characterized by elevation of the limiting membrane and the rough appearance of the eumelanin mass; prominent Golgi (G) and numerous vesicles (V) are found within the cytoplasm together with premelanosomes (pre) (from Bagnara et al., 1978b).
serves to deposit considerable quantities of cytocrine melanin into adjacent epidermal cells (Bagnara and Hadley, 1973). Each epidermal melanophore (-cyte), together with the epidermal cells that it serves, comprise a true “epidermal melanin unit” as first described by Fitzpatrick and Breathnach (1963). Much of what is known about organellogenesis of lower vertebrate epidermal melanophores is extrapolated from studies on mammals (see Chapter 7); however, there are probably few differences among all vertebrate groups with respect to melanosome formation. The melanin-containing organelles of poikilotherms are similar in shape and size to those of mammals and include fibrillar premelanosome stages (Fig. 2.5). The similarity between epidermal melanophores among the various taxonomic groups is also registered in their responses to hormones. Epidermal melanophores of lower vertebrates respond to MSH by dispersing their melanosomes just as do mammalian epidermal melanocytes in the presence of the hormone (Snell, 1967). This response to MSH is rather interesting in view of the fact that their thin spindle shape precludes much of a role in physiologic color change. In contrast, epidermal melanophores of lower vertebrates play an important role in morphologic color change, as is manifested by the significant amounts of melanin that they deposit in the epidermis (see Figs 2.4 and 2.8). Obviously, there is an increase in melanogenesis in these cells in response to MSH stimulation, but it is not known how this occurs. Presumably, MSH affects melanogenesis as it does in mammals (see Chapter 19). In contrast to dermal melanophores, epidermal melanophores are not sensitive to melatonin. They do not aggregate in response to melatonin in any vertebrate studied so far (Bagnara and Hadley, 1970a). 16
Fig. 2.7. Dispersed dermal melanophores from the dorsal surface of a Xenopus larva demonstrating the broad flattened form of this dermal pigment cell.
Dermal Melanophores These prominent black or brown chromatophores of lower vertebrates are profoundly important not only because they provide most of the dark pigmentation of fishes, amphibians, and reptiles, but because they are exceedingly active in physiologic color change in these animal groups (Fig. 2.6). They are large cells with broad dendrites; they usually reside in the upper portion of the dermis, just below the basal lamina. Often, they are flat and thus occupy a broad area of the dermal surface (Fig. 2.7). This is especially true of organisms in larval or embryonic stages. Flat melanophores seem more prevalent when the dermis is relatively thin. In some adults, especially those of amphibians and reptiles, which possess a thicker dermis, the form of dermal melanophores is more threedimensional. Such forms often possess “dermal chromatophore units,” to be discussed subsequently, composed of an upper layer of xanthophores (yellow pigment cells) lying
COMPARATIVE ANATOMY AND PHYSIOLOGY OF PIGMENT CELLS IN NONMAMMALIAN TISSUES
EM X I
M
Fig. 2.8. Transverse section of the dorsal skin from an MSH-treated adult R. pipiens showing basket-shaped dermal melanophore (M). Iridophores are in a punctate state (I), and the clear xanthophore layer (X) is also visible. An epidermal melanin unit is seen in the epidermis with an epidermal melanophore (EM) and surrounding epidermal cells containing cytocrine melanin (from Bagnara and Hadley, 1969).
just below the basal lamina and above a layer of iridophores, and a basal layer of melanophores. These dermal melanophores extend processes upward to terminate between the xanthophores and iridophores (reflecting cells) in amphibians (Bagnara et al., 1968) or above the xanthophores in lizards (Taylor and Hadley, 1970). In both cases, the form of the melanophore becomes basket-like (Fig. 2.8). Melanophores of the dermal type are not restricted to the dermis, but are often present on and in internal organs such as the liver, kidney, heart, thymus, and gonads, on blood vessels, in the peritoneum, and on the meninges (see Figs 2.25, 2.26, and 2.30). That these are of the dermal type is inferred from their sensitivity to hormones such as MSH or melatonin. For example, in hypophysectomized larvae of Xenopus, these deep melanophores are aggregated (see Fig. 2.26), in contrast to those of intact larvae, which are dispersed. Similarly, such deep melanophores aggregate in the presence of melatonin (see Fig. 2.34). Melanosomes of dermal melanophores are not unlike those of epidermal melanophores except for the fact that they are often larger than those of the latter. Generally, they are more spherical in form and about 0.5 mm in diameter. Most poikilotherm dermal melanosomes, especially those of amphibians, possess typical fibrillar premelanosomes (Fig. 2.5) and form in the usual way from the Golgi–endoplasmic reticulum (GERL). In contrast, piscine melanosomes, such as those of the goldfish, form in a different manner (Turner et al., 1975). Here, a multivesicular body of endoplasmic reticular origin forms the premelanosome and no fibrillar substructure is observed. Whereas melanosomes of all vertebrates seem consistently similar, there are remarkably unusual types found in some taxonomic groups. The most notable of these are the melanosomes of the phyllomedusine frogs (leaf frogs) of the New World (Bagnara et al., 1973; Bagnara, 2003). Dermal
Fig. 2.9. Wholemount of portion of brown dorsal skin of P. dacnicolor that had been masked and photographed with epiillumination. The sharp transition between the masked (above) and unmasked (below) skin is evident. The preparation involved passage through solvents, thus the iridophore surfaces are exposed because of the loss of yellow pigments and blue coloration is expressed. Note the red color of the melanophore pigment (see also Plate 2.4, pp. 494–495).
melanophores of adults of these species are a red color (Fig. 2.9) and, as shown in Figure 2.10, they may contain large fibrillar melanosomes (Taylor and Bagnara, 1969). They may or may not contain eumelanin, but their predominant pigment is pterorhodin, a pteridine dimer (Misuraca et al., 1977). They are unquestionably melanophores on the basis of their form, position, and function (Figs 2.9 and 2.11); moreover, in at least the Mexican leaf frog, Pachymedusa dacnicolor, adult melanosomes are derived from typical melanin-containing melanosomes (Bagnara et al., 1978a). Although these unusual organelles have never been named formally, we have designated them as pterino-melanosomes in Table 2.1. At metamorphic climax, the typical larval melanosomes undergo a “redifferentiation” such that pterorhodin fibers begin to deposit upon the eumelanin core of the melanosome to form a compound organelle containing a central kernel of eumelanin surrounded by a concentric mass of pterorhodin (Bagnara and Ferris, 1974). It is likely that such unusual organelles are not restricted to the phyllomedusine frogs (Bagnara and Ferris, 1975), but may be present in taxonomically unrelated frogs such as the rhacophorids (J. T. Bagnara, personal observations; P. Schwalm, personal communication). Iridophores and Leukophores Pigment cells that function primarily through the reflection of light from the surface of orderly distributed organelles, or reflecting platelets, are called iridophores (Fig. 2.12) (Bagnara, 1966a; Taylor, 1969). Although not true pigments, the purines guanine, uric acid, hypoxanthine, and adenine have long been considered to be deposited in crystalline form in the reflecting platelets, which are usually arranged in oriented stacks. More recently, studies of pure iridophores from frog larvae grown 17
CHAPTER 2
A
0.1 µ
B
0.1 µ
Fig. 2.10. Unusual large melanosomes in dermal melanophores of two phyllomedusine species, P. dacnicolor (A) and Agalychnis callidryas (B). The melanosomes of the two species are each larger than the typical vertebrate melanosome and contain the pigment pterorhodin. Each melanosome is composed of a fibrous mass enclosed by a limiting membrane, but that of A. callidryas lacks the electron-dense eumelanin kernel typical of the P. dacnicolor melanosome (from Bagnara et al., 1973).
Fig. 2.11. An adult Pachymedusa dacnicolor in a “semi-natural” outdoor cage in full illumination on a light background. The black plastic letter masks, UA (University of Arizona), to the left and right of this brown-adapted frog were removed after having been in place on the frog’s back for 1 hour. Note the green color that developed under the mask (see also Plate 2.5, pp. 494–495). [From Iga, T., and J. T. Bagnara. An analysis of color change phenomena in the leaf frog, Agalychnis dacnicolor. J. Exp. Zool. 192:331–342, 1975.]
in cell culture have revealed that guanine was the sole purine present; moreover, it was discovered that some pteridine pigments were also present in these cells (Bagnara et al., 1988). It seems that reflecting platelets may contain both crystalline purines and pteridines. The orientation of these stacks of platelets determines the nature of the pigmentary function of the iridophore. Normally, when viewed with reflected light, iridophores appear to contribute a metallic gold or silver luster (see Figs 2.1 and 2.47–2.49). When viewed with transmitted light, iridophores exhibit blues, greens, and reds. These are structural colors probably arising from thin-layer interference and the scatter or the diffraction of light from the stacks of reflecting platelets. Some iridophores examined with reflected light appear to be blue, while others appear to be brown or tan in color. These colors probably relate to the size, shape, orientation, and conformation of reflecting platelets. A pene18
trating analysis of the optics of iridophores in fishes has been presented by Fujii (1993a), and a more specific study of the structural colors of spiny lizards has been made by Morrison (1995). The latter study emphasizes the role of thin-layer interference in establishing the various iridescent colors in these lizards. A complete analysis and understanding of the structural colors of any individual iridophore or group of iridophores is very difficult for numerous reasons, not least of which is the size and shape of reflecting platelets. Among the more common types found in amphibians and fishes are those represented by long, thin profiles (Fig. 2.12). Among the leaf frogs, small bead-like or cubic reflecting platelets prevail (Fig. 2.13) as they often do in some lizards (Fig. 2.14). Distances between reflecting platelets are very important, and only slight changes in spacing can markedly alter the
COMPARATIVE ANATOMY AND PHYSIOLOGY OF PIGMENT CELLS IN NONMAMMALIAN TISSUES
ians and reptiles (see Bagnara and Hadley, 1973; Bagnara et al., 1978b). An elementary scheme of how these colors are brought about is shown in Figure 2.17.
Fig. 2.12. An iridophore from the dorsum of an adult R. pipiens showing stacks of reflecting platelets (actually spaces previously occupied by purine crystals that shattered and dissolved during sectioning and staining). An individual reflecting platelet is trapped between two lobes of the nucleus. Scale = 1 mm (from Bagnara, 1976).
apparent color, as was shown for the tree frog Hyla arborea by Nielsen (1978). Another chromatophore active in structural coloration has been recognized in fishes (see Fujii, 1993a). This chromatophore, the leukophore, seems to be somewhat different from the iridophore; however, it functions much as iridophores and probably utilizes purines as pigments in its pigmentary organelles, as do the reflecting platelets of iridophores. The introduction of another chromatophore designation may add to nomenclatural confusion; however, out of deference to recent investigators of piscine chromatophores who have described these cells, the leukophore is acknowledged as a distinctive chromatophore (Menter et al., 1979). Very likely, it is a particular type of iridophore found primarily in fishes or in anomalous situations in other vertebrates, for example, as in the periodic albino mutant of Xenopus (Fukuzawa, 2004). With the acceptance of the existence of both iridophores and leukophores, new names for their inclusions (Table 2.1) must be recognized; these include “leukosome” or “refractosome.” Despite the existing differences between iridophores and leukophores, their similarities are such that it warrants their being grouped together as a basic pigment cell type. Iridophores play an important role in imparting blue coloration as a structural color (Figs 2.15 and 2.16). Blue coloration is relatively uncommon among most poikilotherms and blue pigments are rare; however, blue as a structural color is important because it plays a major role in the elaboration of green coloration, which is very common among amphib-
Xanthophores and Erythrophores Dermal chromatophores that range in color from pale yellow to bright red are designated xanthophores (yellow) or erythrophores (red) depending upon how yellow or red they appear (Figs 2.1–2.3). Despite their differences in color, xanthophores and erythrophores should be considered as the same basic pigment cell type (Table 2.1). At the beginning of the twentieth century, they were called lipophores because many of these cells contain fat-soluble yellow, orange, or red carotenoid pigments that are localized in fatty vesicles (Bagnara, 1966a; Bagnara and Hadley, 1973). It was not until much later (Bagnara, 1961; Bagnara and Obika, 1965; Obika, 1963; Obika and Bagnara, 1964) that another group of pigments, pteridine in nature, was found to be even more important pigments of xanthophores and erythrophores. Soon afterwards, it was discovered by Matsumoto (1965a) that pteridine pigments are localized in organelles called pterinosomes and that both carotenoid vesicles and pterinosomes are often found within the same cell, be it a xanthophore or an erythrophore (Figs 2.2, 2.13, and 2.18). The specific color manifested by the cell often depends upon the pattern of carotenoids and pteridines it contains. In addition, it is possible that there exist other pigments so far undiscovered. All these facts were important considerations in the decision to designate chromatophores in accordance with their color rather than their chemical composition (Bagnara, 1966a). Although the association of carotenoid pigments with xanthophores or erythrophores has a long history, there have been relatively few definitive studies on their specific carotenoid content. Moreover, it has been only recently that attempts have been made to correlate carotenoid composition with xanthophore or erythrophore ultrastructure. Matsui et al. (2002) have observed that the bright red ventral integument of the Japanese newt, Cynops pyrrogaster, contains beta-carotene and at least five other carotenoids including canthaxanthin and lutein. They suggest that these pigments are contained in either thin-walled vesicles or thicker-walled “ring-type” vesicles. The precise localization of carotenoids in these vesicles remains unclear. In a general sense, perhaps the most important of the xanthophore and erythrophore pigments is the pteridine group. Pteridines are a group of yellow, orange, or red compounds having the structure of pyrimido[4,5-b]pyradine and are known to be synthesized from guanosine triphosphate (GTP) by GTP-cyclohydrolase I (GTP-CHI) that has a variety of isoforms (Thony et al., 2000). The vast majority of naturally occurring pteridines have the structure of 2-amino-4oxopteridine and are called unconjugated pteridines collectively. This terminology is convenient to discriminate them from folic acid or its related compounds, which have a long side-chain at position 6 of the pteridine ring. Thus far in medical research, much attention has been focused on 19
PT
CV
RP
MS
5 Fig. 2.13. Transverse section through the dorsal dermis of P. dacnicolor. Xanthophores are filled with pterinosomes (PT) and carotenoid vesicles (CV). Iridophores contain reflecting platelets with round or oval profiles, which seem to be strung together in a bead-like fashion. Melanosomes (MS) are typical for this species. The organelle indicated by an arrow may be a pterinosome. Magnification ¥ 6000 (from Taylor and Bagnara, 1972).
Fig. 2.14. Iridophores of the lizard, Urosaurus ornatus, at low magnification at left (¥ 2000) and high magnification at right (¥ 75 000). Note the rectangular profiles of reflecting platelets and their orderly arrangement. The image on the left includes views of melanophores (bottom) and xanthophores (top) (courtesy of Dr Randall Morrison).
20
COMPARATIVE ANATOMY AND PHYSIOLOGY OF PIGMENT CELLS IN NONMAMMALIAN TISSUES
Fig. 2.15. Melanophores (aggregated) and iridophores (dispersed) in a wholemount dorsal skin preparation of Rana pipiens photographed with transmitted light. Note the varied structural colors evident in the iridophores (see also Plate 2.6, pp. 494–495). [From Bagnara, J. T., and M. E. Hadley. Chromatophores and Color Change: The Comparative Physiology of Animal Pigmentation. Englewood Cliffs, NJ: Prentice-Hall, 1973, with permission.]
biopterin, particularly its tetrahydro form, because of its role as a cofactor for hydroxylation of phenylalanine and tryptophan (Nicol et al., 1985). In lower vertebrates, large amounts of unconjugated pteridines accumulate specifically in xanthophores and erythrophores. Some, such as sepiapterin, serve as yellow pigments by themselves, whereas others, such as biopterin, 2-amino-4-oxopterin, 7-oxobiopterin (ichthyopterin), and isoxanthopterin, are colorless in nature. The roles of these colorless pteridines are unknown, but it is possible that they function in the absorption of ultraviolet light as their spectrophotometric characteristics include strong absorption in the 340–360 nm region (Mori et al., 1960; Tschesche and Glaser, 1958). It is also known that some unconjugated colorless pteridines, such as drosopterins, form dimers that act as chromophores (Pfleiderer, 2001). Biosynthetic pathways of pteridines common to lower vertebrates are well established, as summarized in Figure 2.19
Fig. 2.16. Wholemount of portion of brown dorsal skin of P. dacnicolor that had been masked and photographed with epiillumination. The sharp transition between the masked (above) and unmasked (below) skin is evident. The preparation involved passage through solvents, thus the iridophore surfaces are exposed because of the loss of yellow pigments and blue coloration is expressed. Note the red color of the melanophore pigment (see also Plate 2.7, pp. 494–495).
(Masada et al., 1990; Ziegler et al., 2000). As seen in this scheme, it is apparent that pteridine metabolism is regulated by three key enzymes including GTP-CHI, 6-pyruvoyl-tetrahydropterin synthase (PTPS), and sepiapterin reductase (SPR) (Masuda et al., 1990; Ziegler et al., 2000). Therefore, mutations in genes associated with these enzymes, particularly GTP-CHI, would inevitably affect development and differentiation of xanthophores and thus yield pigmentary mutants. This seems to be the case in zebrafish where there exists a variety of mutants, three of which are associated with xanthophore pigmentation and pteridine composition, including one that displays an alteration in pteridine metabolism similar to a mutation in Drosophila (Odenthal et al., 1996). The autonomy of xanthophores and erythrophores for pteridine biosynthesis was shown by elegant techniques of classic embryology. Obika (1963) demonstrated by in vitro 21
CHAPTER 2
Fig. 2.17. Diagrammatic interpretation for the basis of green coloration in amphibians and other vertebrates. As light strikes the surface of an animal such as a frog, short wavelengths of light (blue–violet) are largely absorbed by the filtering xanthophore or yellow pigment layer; the rest are scattered by the iridophore or scattering layer. Long wavelengths (red–orange) largely pass through the filtering and scattering layers of the skin and are absorbed by the melanophore or melanin layer. Intermediate wavelengths (yellow–green) pass through the filtering layer and are scattered from the surface of the iridophore layer (Tyndall scattering) and pass back through the filtering layer. Thus, the light reflected from the surface contains a high proportion of yellow–green wavelengths and the animal appears green (from Bagnara and Hadley, 1973).
Fig. 2.18. Schematic interpretation of the dermal chromatophore unit based upon observations from several anurans. Adaptation to a dark background is represented. Processes from basally located melanophores, between overlying xanthophores and iridophores, become filled with melanosomes and thus obscure light reflection from the iridophore surface (from Bagnara et al., 1968).
hanging drop culture of urodele (Triturus and Hynobius) neural crest that yellow pigmentation of larval xanthophores occurs simultaneously with formation of pteridines in simple physiological salt (Holtfreter) solution. Richards and Bagnara (1967) further demonstrated autonomous formation of species-specific pteridines, such as 6-hydroxymethylpteridine, by larval urodele xanthophores through the use of xenoplastic transplantation of neural crest between Axolotl and Pleurodeles. These experiments also revealed the autonomous expression of “Pleurodeles blue,” a pteridine relative and a presumed yellow pigment in larval xanthophores. This novel 22
pyridone N-glycoside (Yoshida et al., 1988) seems to be newt specific (J. T. Bagnara, unpublished). Combined cytochemistry and chemical analytical studies on skin preparations provided proof that pteridines function as pigments in these brightly colored pigment cells. Their intracellular localization in particular cytoorganelles, as in the aforementioned pterinosomes, was ascertained by ultracentrifugal fractionation of subcellular components of xanthophores and erythrophores in sucrose density gradients (Matsumoto, 1965a; Matsumoto and Obika, 1968; Obika and Matsumoto, 1968). Skin samples laden solely with these pigment cells were collected from fishes or frogs by careful dissection of homogeneously colored spots or stripes. Combined pteridine assay and electron microscopy on separated fractions disclosed that the vast majority of pteridines were detected in a fraction composed of large cytoplasmic granules, the pterinosomes, although certain amounts were present in fractions composed of membranous elements, mostly those of smooth endoplasmic reticula or Golgi complexes. Carotenoids, when present, were detectable in fractions composed of small vesicles or membrane fragments, indicating an apparent disparate distribution of pteridines and carotenoids within the cells. The morphology of pterinosomes is characterized by a spherical shape, slightly larger than melanosomes, and a distinct boundary of unit membrane enclosing an internal structure consisting of thin concentric lamellae or deposits of thin fibrils (Matsumoto, 1965a; Matsumoto and Obika, 1968; Obika and Matsumoto, 1968). Little is known about the relationship between the internal structure of pterinosomes and the composition of pteridines deposited. In developing xanthophores or erythrophores, multivesicular bodies are present
GTP GTP-CHI O
OH OH N
HN H2N
N
PHO
N H
H
O
C
C CH2O
P O
H
H
OH
3
H
Dihydroneopterin-3-phosphate PTPS
O HN H2N
N
O
OH OH N
C
C CH2OH
H
H
HN H2N
N
N
H N
HO O C C CH3 H N H H
H2N
N
H HH O N C C CH3 OH H N H H
HN H 2N
6-Lactoyltetrahydropterin
N
N H
H
Dihydropterin
SPR O
H HO H N C C CH3 H OH N H H
H H
H2N
XOR
AR O
N HN
6-Pyruvoyltetrahydropterin
Neopterin
HN
O
N
6-(1’-Hydroxy, 2’-oxopropyl) tetrahydropterin
O
O
H N
HN
O
H
N
HN
H H2N
N H
N
H
H2N
Dihydroxanthopterin
N
N
Pterin
SPR
XOR SPR
N
HN H2N
N
O
O H
O
N H
C C CH3 OH H H
H2N
N
O
O
O HN
H2N
N
N
H2N
Xanthopterin
N
N
H
N H
O
Isoxanthopterin
H H H C C CH3 OH OH H N H H N
HN HN
O
H N
HN
Tetrahydrobiopterin
Sepiapterin
SPR
H H H H N C C CH3 OHOH N HH H
HN
N
Quinoiddihydrobiopterin
O N
HN H2N
N
N H
H H C C CH3 OH OH H H
Dihydrobiopterin
O N
HN
COOH
O N
HN
H H C C CH3
O N
HN
OHOH H2N
N
N
Pterin-6-carboxylic acid
H 2N
N
N
Biopterin
H 2N
N
N H
H H C C CH3 OHOH O
Ichthyopterin
Fig. 2.19. Biosynthetic pathways of unconjugated pteridines common to xanthophores and their related pigment cells of lower vertebrates. Abbreviations of enzymes: AR, aldose reductase; GTP-CHI, GTP-cyclohydrolase I; PHO, phosphatase; PTPS, 6-pyruvoyl-tetrahydropterin synthase; SPR, sepiapterin reductase; XOR, xanthine oxidoreductase (adapted from Katoh and Akino, 1986; Masada et al., 1990; Takigawa and Nakagoshi, 1994; Ziegler et al., 2000).
23
CHAPTER 2
in the vicinity of Golgi complexes or GERL (J. Matsumoto et al., unpublished data). The similarity of these multivesicular bodies to Stage I melanosomes suggests that pterinosome genesis shares an origin common to that of melanosomes. These observations are consistent with the concept of the common origin of pigment cells (Bagnara et al., 1979). Cyanophores A most remarkable discovery was made a decade ago by Goda and Fujii (1995) who found blue dermal chromatophores that they designated cyanophores. These chromatophores contain a true blue pigment of unknown chemical nature. The blue pigment is found in fibrous organelles that they termed cyanosomes. Whereas cyanophores have been found, so far, in only two species of callionymid fish, it may be premature to afford them legitimate status. However, they are real and unique and must be recognized. Accordingly, they are included in Table 2.1.
Fig. 2.20. Green eggs (yolk plug stage) of P. dacnicolor. Eggs normally vary in color from blue-green to yellow-green (see also Plate 2.8, pp. 494–495).
Other Unknown Chromatophores Among some of the less studied groups of amphibians, there exist unusual pigmentary organelles in chromatophores that may be xanthophores or erythrophores. Schwalm and McNulty (1980) described some unusual chromatophores that seem to contain large vesicles with pigments that have not been elucidated. The dendrobatid (poison arrow) frogs also contain brightly colored chromatophores with vesicular organelles, the compositions of which are also unresolved (J. T. Bagnara, personal observations).
The Amphibian Egg as a Pigment Cell One would hardly think that there could be any relationship between the pigmentation of the integument and that of the eggs. On the contrary, the pigmentation of the eggs of frogs and skin have much in common both by homology and by analogy (Bagnara, 1985). The frog integumental pigmentary pattern of a dark dorsum and light ventrum is paralleled in the animal and vegetal poles, respectively, of frog eggs. Moreover, melanin is the dark pigment in both cases, and the pigment in each is contained in melanosomes. It appears that this pattern of pigmentation serves protective functions in both cases. In addition to dark pigmentation, the bright colors of the integument have much in common with the comparable colors that are found in the eggs of some species. In particular, the eggs of leaf frogs, the Pyllomedusinae, which are usually laid on green vegetation above the surface of pools of water, are often bright green (Fig. 2.20). A fundamental difference in egg pigmentation is that the green color is arrived at in a manner different from that of the skin. In both cases, the green color derives from a combination of blue and yellow; however, the blue element of the skin is a structural color whereas that of eggs is provided by the blue pigment, biliverdin IXa. This can be seen in Fig. 2.21, in which a blue area from a portion of P. dacnicolor skin is manifested when the overlying yellow pigment is leached from normally green skin. In contrast, as shown in Fig. 2.21, a blue pigment 24
Fig. 2.21. Pigments extracted from P. dacnicolor eggs. Left, biliverdin IXa; right, lutein (see also Plate 2.9, pp. 494–495).
(biliverdin) and a yellow pigment (lutein) provide the green color of P. dacnicolor eggs (Marinetti and Bagnara, 1982, 1983). In the absence of yellow pigments from xanthophores in the integument, frogs become blue. In Fig. 2.22, a blue individual of P. dacnicolor is shown. This frog was apparently deficient in xanthine dehydrogenase, a key enzyme in pteridine biosynthesis, and thus failed to produce pteridine pigments (Frost, 1978; Frost and Bagnara, 1978). In cases of carotenoid deficiency, the skin of this species also becomes bluish. This is a consequence of the absence of yellow carotenoid pigments from the xanthophores. In Fig. 2.23, sibling juveniles of P. dacnicolor are shown, one green and the other blue. The latter was raised on carotenoid-deficient crickets (potato-fed) and the former on carrot-fed crickets (J. T. Bagnara and G. V. Marinetti, unpublished). Analysis of the crickets revealed a preponderance of carotenes in the carrot-fed individuals and very low levels of any carotenoid in crickets fed potatoes. Of special interest here is the fact that the integumental
COMPARATIVE ANATOMY AND PHYSIOLOGY OF PIGMENT CELLS IN NONMAMMALIAN TISSUES
Fig. 2.22. “Blue Boy,” a young male P. dacnicolor, which lacked xanthophore pigments from his metamorphosis until sexual maturity when he gradually began to turn green. Presumably, he was xanthine dehydrogenase-deficient, but eventually produced enough pteridine pigments to restore normal green coloration (see also Plate 2.10, pp. 494–495).
Fig. 2.23. Sibling froglets of P. dacnicolor. The green frog was raised on crickets fed carrots exclusively, while the blue frog was fed potato-raised crickets that were carotenoid-deficient (see also Plate 2.11, pp. 494–495).
carotenoids of P. dacnicolor appear to be exclusively acidic xanthophylls. Thus, it appears that the frog liver must undertake major metabolic steps to convert carotenes to xanthophylls. How this occurs in frogs is unknown. Moreover, the transport of the xanthophylls from the liver to the skin is a mystery. Probably, this transport to the integument is similar to that of lutein, an acidic xanthophyll, to the egg wherein vitellogenin seems to serve as a transport protein for both biliverdin and lutein (Bagnara, 1985). Such transport in insects, that of biliverdin and lutein, involves specific transport proteins (see Kanost et al., 1990; Kawooya et al., 1985) and thus, by analogy, it seems reasonable to consider that the same may hold for amphibians.
Chromatophore Function A major function of integumental chromatophores is in background adaptation (cryptic coloration). Most lower vertebrates exhibit rapid body color changes for use in camouflage or background matching, as is well exemplified by the tropical flounder (Ramachandran et al., 1996). The simplest type, adaptation to black or white backgrounds, mainly involves the participation of both melanophores and iridophores. Thus, on black surfaces, melanosomes within melanophores become widely dispersed within the dendritic processes of the cell. At the same time, iridophores are minimally visible as their reflecting platelets aggregate to the center of the cell. In other words, black coloration is maximized and white is minimized. 25
CHAPTER 2
Fig. 2.24. In vitro response of R. pipiens skin photographed with reflected light. Left, in Ringer solution, iridophores, which appear silvery, are expanded; dermal melanophores are punctate. Right, in the presence of caffeine, intracellular levels of cyclic AMP become elevated; thus, iridophores are contracted to the punctate state while melanophores are well expanded (from Bagnara, 1976).
On white surfaces, these two pigment cells respond in an opposite manner. Adaptation to more particular backgrounds, such as to specific colors or shades or even mottled surfaces, may entail the participation of all three basic pigment cell types. Aside from their role in cryptic coloration, chromatophores function in a variety of other roles. Thermal regulation, protection from solar radiation, nuptial coloration, and warning coloration represent a few of the other more prominent roles of lower vertebrate chromatophores. Because of their roles in so many adaptive activities, the physiology of lower vertebrate chromatophores is by necessity exceedingly complex and is an important component of the integrative biology of poikilotherms. A fundamental feature is the fact that color change results from the translocation of pigmentary organelles within the cell (Figs 2.4 and 2.6). In early times, chromatophores were referred to as being “expanded or contracted” with the implication that the cell boundaries were actually motile. We now know that pigment cells are firmly attached to the extracellular matrix and that contractile motility actually refers to movements of the pigmentcontaining organelles within the chromatophore. Nevertheless, unfettered chromatophores, as in cell culture, do have the capacity to expand and contract, but it is not known whether this is a passive result of intracellular organellar motility or the result of some other contractile event. In any case, we now 26
consider color change to result from the aggregation or dispersion of pigmentary organelles within the cell (Fig. 2.24). This type of chromatophore motility has been the subject of continued scrutiny in recent years, especially as new knowledge about the cytoskeletal system of pigment cells has accumulated. The responses of pigment cells during color change are integrated, and mechanisms for this integration reside in several signaling mechanisms. As color change often results from the visual perception of background change, the nervous system has long been considered to be a key element in chromatophore signaling, and direct innervation of chromatophores was an early focus of investigation. Over the years, we have learned that chromatophore control through direct innervation occurs in some poikilotherms, but is by no means a general phenomenon. While best evidence for such innervation comes from studies of piscine chromatophores (see Bagnara and Hadley, 1973; Fujii, 1993a), not all orders of the class Osteichthyes possess innervated chromatophores. Early reports of possible innervation of amphibian chromatophores have been discounted (Iga and Bagnara, 1975); however, the early reports of the late 1880s describing innervation of reptilian chromatophores (chameleons) certainly remain valid (Whimster, 1971). In other lizards, such as Anolis, direct nervous control of chromatophores does not
COMPARATIVE ANATOMY AND PHYSIOLOGY OF PIGMENT CELLS IN NONMAMMALIAN TISSUES
exist (see Bagnara and Hadley, 1973); thus, we are left with the unanswered question of how pervasive direct innervation of chromatophores exists among reptiles.
Responses of Pigment Cells Physiologic Color Change Physiologic color changes are defined as those rapid changes in color caused by an intracellular movement of pigmentbearing organelles (Parker, 1948). As has been indicated, the response can be elicited by a variety of stimuli such as light or hormone action. The response is rapid, requiring a few minutes or a few hours to occur, and is transitory, i.e. the animal either regains its original coloration or assumes an intermediate state depending on stimulatory cues. Perhaps the most common manifestation of physiologic color change occurs in background adaptation. On a darkcolored background, amphibians that can adapt contain melanophores with dispersed melanosomes, while those on light-colored backgrounds are pale because their melanosomes have aggregated to a perinuclear position within the cell (Figs 2.4, 2.6 and 2.24). Iridophores respond in an opposite manner, being dispersed on light-colored backgrounds and aggregated on dark backgrounds. Apparently, the lateral eyes play a fundamental role in governing these background responses of both melanophores and iridophores. In most amphibian larvae, there is a distinct point in development at which they become able to adapt to background. Before this time, when they are not able to adapt to background, they remain dark colored whether on a light or a dark background, and they are said to be in a primary phase or stage. Older larvae that can adapt to background are said to be in a secondary stage. The secondary stage describes what essentially constitutes adaptation to background based upon the reception of light through the eyes and the control of MSH release from the pituitary. Melanosome aggregation can occur in primary-stage larvae in darkness, but this does not result from alterations in MSH release, but relates to other physiological systems that operate in darkness as mentioned earlier and to be described more fully later. It should be noted that onset of the secondary phase varies with species: whereas melanophores of Xenopus larvae respond to background changes from very young stages onward, larvae of Rana and Hyla do not display the secondary response until they are several weeks old, and some Bufo larvae never seem to acquire the secondary phase. These observations of the ontogeny of physiologic color change have been made primarily on amphibians and, although much is known about the physiology of chromatophores of fishes, the majority of the work has been on adults or at least on post-embryonic stages. Morphologic Color Change Color changes that are evoked slowly and result from alterations in the amount of pigment contained in the integument have long been called morphologic color change (Parker, 1948). Morphologic color change is a relatively slow process that includes the synthesis or destruction of relatively large
amounts of pigment in response to a persistent stimulus. Background adaptation is a common cause of morphologic color change: animals maintained on dark backgrounds develop more melanin whereas those on light backgrounds lose their melanin (Dawes, 1941). The opposite is true of iridophores with respect to their purine pigments (Bagnara and Neidleman, 1958; Fernandez, 1988; Fernandez and Collins, 1988; Taylor, 1969). The total increase or decrease in the amount of pigment can result from several causes, one of which relates to the number of chromatophores present. For example, Xenopus larvae that have been deprived of their pituitary gland (and hence have no melanophore stimulation) contain many fewer dermal melanophores than they do normally (Bagnara, 1957). That the hypophysis exerts its influence on morphologic color change by causing a profound proliferation of dermal melanophores has been elegantly shown (Fig. 2.25) by Pehlemann (1967a, b, 1972). Probably, the increase in chromatophore number following persistent stimulation also results from the synthesis of pigments in hitherto undifferentiated melanoblasts. This phenomenon seems to be a general one and provides a valid interpretation of the fact that iridophores appear in the tail fin of Xenopus larvae that have been deprived of their hypophysis (Fig. 2.26), although such chromatophores are not observed in intact normal larvae (Bagnara, 1957). Amphibian iridophores are markedly inhibited by MSH, both physiologically and morphologically (Bagnara, 1958). In his PhD dissertation, Hadley (1966) described how, in juvenile Xenopus maintained on dark backgrounds for 10 weeks, there is a fivefold increase in the number of web melanophores present in comparison with controls maintained on white backgrounds. The spacing of these new melanophores seems to exclude the presence of doublets as would be expected in cases of rapid increase in melanophore numbers due to proliferation; thus, it is presumed that these new melanophores were derived from latent melanoblasts that underwent melanization in response to the elevated blood levels of MSH present in those animals on black backgrounds. Similar results were obtained by Fernandez and Bagnara (1991, 1993), who studied morphologic color change in leopard frogs (Figs 2.27 and 2.28). They showed that the intense melanization corresponded directly to elevated blood levels of MSH as measured by radioimmunoassay (RIA) (Fig. 2.29). Definitive proof that latent undifferentiated melanoblasts are the source of new melanophores comes from an unpublished study described by Bagnara and Fernandez (1993) in which the pars intermedia of juvenile Xenopus were implanted into the lower unpigmented jaw of larvae (Fig. 2.30). Melanophores differentiated in an area concentric to the implant, implying that they were derived from latent melanoblasts. Manifestations of morphologic color change occur at the organellar level and in some cases can be seen with the electron microscope. For example, after administration of large dosages of MSH to adult frogs, a condensation of the reflecting platelets can be seen in iridophores (Bagnara et al., 1968, 1969; Taylor, 1969). Through action on the adjacent epidermal cells, epidermal 27
CHAPTER 2
Fig. 2.25. Details of the upper right side of the head of a Xenopus larva, (A) 1, (B) 5, (C) 7 days after transection of the hypophysial stalk leading to greatly increased levels of circulating MSH and melanophore proliferation. A single melanophore (arrow) can be traced through two mitotic divisions in (B) and (C) (courtesy of Dr F. W. Pehlemann; from Pehlemann, 1967b).
melanophores also play an important role in morphologic color change (Hadley and Quevedo, 1967). During profound melanophore stimulation, such as prolonged exposure to a dark background, pronounced cytocrine activity of the dendrites of epidermal melanophores causes melanin to be deposited in adjacent epidermal cells (Figs 2.4 and 2.8). This process in frogs has not been studied with the electron microscope, and the mechanism of melanin deposition is not understood; however, studies made at lower magnification indicate that considerable amounts of melanin are deposited in the epidermis in this manner. In adult frogs, cytocrine deposition of melanin is the primary means of morphologic color change (Hadley and Quevedo, 1967). The importance of epidermal melanophores (-cytes) in homeotherms is well known, and it has been suggested that epidermal melanocytes of all vertebrates are homologous in that they seem to be identical in every way (Bagnara and Ferris, 1971).
The Control of Color Change The Pituitary and the Role of MSH Fig. 2.26. A Xenopus larva hypophysectomized as a tailbud embryo. Note the presence of iridophores and the great reduction in melanophores of the integument, brain case, and other deep areas (from Bagnara, 1957).
28
The ability of lower vertebrates to carry out morphologic and physiologic color change in response to appropriate environmental cues is based upon the existence of precise control mechanisms involving the pars intermedia of the pituitary and the release of MSH. Whereas the existence of this hormone was inferred from experiments on poikilotherms, characteri-
COMPARATIVE ANATOMY AND PHYSIOLOGY OF PIGMENT CELLS IN NONMAMMALIAN TISSUES
α–MSH (pg/ml)
200 175 150 125 100 75 50 25 0
α–MSH (pg/ml)
Fig. 2.27. Dorsal (top) and ventral (bottom) views of adult R. chiricahuensis adapted to dark backgrounds (left individuals) or white backgrounds (right individuals). Note the profound darkening of the dark background-adapted individuals and especially the ventral surface (from Bagnara and Fernandez, 1993).
1800 1600 1400 1200 1000 800 600 400 200 0
Rana pipiens
White
Gray
Fig. 2.28. Dorsal (top) and ventral (bottom) views of adult R. pipiens adapted to dark backgrounds (left individuals) or white background (right individuals). Note the darkening of the dorsal surface of the dark background-adapted individuals and the lack of darkening of the ventral surface of the dark background-adapted individuals (from Bagnara and Fernandez, 1993).
Black
Rana chiricahuensis
Gray Black White Background color
Fig. 2.29. Plasma a-MSH of R. pipiens and R. chiricahuensis on white, gray, and black backgrounds. Each bar represents the mean (±SE) of 1–4 frogs. Plasma a-MSH of frogs on a black background is greater than those on white or gray (P < 005). Note the particularly profound increase in plasma a-MSH of R. chiricahuensis (modified from Fernandez and Bagnara, 1991).
zation of MSH was achieved from mammalian sources. A personal account of the biochemical characterization of the MSHs in the mid-1950s has been graciously written by Professor Aaron B. Lerner (1993). It was not until some 30 years later that poikilothermic MSHs were isolated, purified, and characterized from fishes and amphibians. Thus, some idea of
Fig. 2.30. Lower jaw of a larva of Xenopus laevis that had been implanted subcutaneously with the pars intermedia of a froglet. A spherical blood clot marks the site of the transplant, which releases MSH chronically. Note that the nearby dermis is populated with melanophores distributed over the graft. No melanophores were observed in the dermis of the jaw before the transplantation (from Bagnara and Fernandez, 1993).
the phylogeny of MSH was obtained (Dores et al., 1993). It has been shown that, although the tridecapeptide a-MSH is a ubiquitously secreted peptide derived from the ancestral molecule, proopiomelanocortin, N-acetylation of the hormone is 29
CHAPTER 2
a key element in the phylogeny of the molecule. Like that of mammals, ranid a-MSH is N-acetylated, a scheme inherited from an ancient tetrapod. During evolution, the scheme was retained except among some of the squamate reptiles, which have lost this capacity. Among the latter is the fence lizard Anolis, which secretes a non-N-acetylated a-MSH that is nevertheless a functional melanotropin.
Melanophore Stimulation The most well-known activity of MSH is to stimulate the dispersion of melanosomes within melanophores of poikilotherms. In the absence of MSH, melanophores assume a punctate (contracted) configuration in which melanosomes are concentrated in the central (perinuclear) portion of the melanophore (Figs 2.4, 2.6 and 2.24). Both dermal and epidermal melanophores respond to stimulation by MSH by demonstrating physiologic color change, whereas prolonged exposure to the hormone, especially at high concentration, is conducive to morphologic color change. It has been thought that morphologic color change is an indirect function of MSH activity that actually results from persistent physiologic color change; however, Pehlemann’s (1972) demonstration of increased melanization resulting from enhanced mitotic activity in melanophores under MSH stimulation indicates that some expressions of morphologic color change are independent of physiologic color change. It is concluded that MSH affects both dermal and epidermal melanophores and is capable of eliciting morphologic color change in both chromatophores. The possible role of MSH on pigment pattern formation through its effects on morphologic color change will be considered later. Iridophore Effects Earlier work on color change centered around melanophore responses. During later years, however, attention was given to the effect of MSH on iridophores, the reflecting pigment cells commonly found in poikilotherms (Figs 2.8, 2.31, and 2.32). In normal larvae and in intact adult frogs as well as in fishes, iridophores are in a punctate state due to a concentration of reflecting platelets toward the center of the cell (see Bagnara and Hadley, 1973; Fujii, 1993a). In the absence of the pituitary, reflecting platelets are dispersed and the iridophore exists in an expanded state. The “silvery” appearance of hypophysectomized ranid larvae observed by Smith (1916) and Allen (1916) results from the “expansion” of iridophores and the “contraction” of melanophores; in intact larvae, the reverse is true. Smith (1920) recognized that the hypophysis exerted an influence on iridophores, which he referred to as xantholeukophores; however, except for Hogben and Winton (1924) and Stoppani et al. (1954), most other workers emphasized melanophore effects, and gradually the prominent role of iridophores in amphibian color change was overlooked and almost forgotten. Interest in amphibian iridophores was renewed when it was discovered that these cells are controlled by MSH just as are melanophores (Bagnara, 1958). Substantial proof for this 30
Fig. 2.31. A mixed primary cell culture of chromatophores, containing mostly iridophores, isolated from R. pipiens tadpoles. Left, attached iridophores in their normal semi-aggregated (expanded) state. Right, a similar culture after 1 h of exposure to [Nle4,D-Phe7]a-MSH (10-5 M). Both photographs were taken under epi-illumination. Note the aggregated (contracted) state of the treated iridophores, which have actually detached from the surface of the culture dish.
Fig. 2.32. Cells similar to those in Fig. 2.31, viewed in thin sections. Upper left, a rounded iridophore before attachment. Bottom, a dispersed iridophore attached to the culture dish. Upper right, detached and rounded iridophores following MSH treatment.
concept was obtained when highly purified a- and b-MSH first became available and were shown to cause iridophore aggregation in both hypophysectomized larvae (Bagnara, 1964b) and in isolated skins of adult frogs (Hadley, 1966; Hadley and Bagnara, 1969). That iridophores are not only sensitive to MSH, but also react by aggregating rather than dispersing under its influence led to the question of whether both melanophore expansion and iridophore contraction require the same sites on the MSH molecule (Fig. 2.24). That this is indeed the case was demonstrated through the utilization of the fact that, in adult frog skins, the entire MSH molecule is not essential for melanophore-expanding activity (Lee et al., 1963) and that some melanophore response can be induced
COMPARATIVE ANATOMY AND PHYSIOLOGY OF PIGMENT CELLS IN NONMAMMALIAN TISSUES
by the centrally located polypeptide sequence, His-Phe-ArgTrp-Gly. When pentapeptide and larger synthetic MSH peptides were injected into hypophysectomized larvae, definite iridophore aggregation was observed, and the iridophore response was always paralleled by melanophore dispersion (Bagnara, 1964b). A similar parallelism of iridophore and melanophore responses was obtained with a thermal polymer of arginine, glutamic acid, histidine, phenylalanine, and tryptophan (Bagnara and Hadley, 1970b). This early work that utilized short amino acid sequences of the MSH molecule to study iridophore responses made little impact because it was very much obscured by the rapid accumulation of new knowledge about MSH chemistry that was mounting up. This work centered on the frog skin bioassay, which was generally considered to involve melanophore responses, although Hadley and Bagnara (1969) clearly described the integrated responses of both melanophores and iridophores in this assay. Early on, Bagnara (1958) had demonstrated that the alkali-enhanced activity of MSH peptides was evidenced in both melanophore and iridophore responses. In later years during the development of superpotent a-MSH analogs (Sawyer et al., 1980), their effects on iridophores were not observed. Recently, such a study has been carried out (J. T. Bagnara et al., unpublished) on tadpole iridophores in culture and, as can be seen in Figure 2.31, iridophores exposed to the superpotent analog [Nle4,D-Phe7]a-MSH indeed become aggregated. This is of special interest not only because it demonstrates iridophore sensitivity to the hormone, but because the response displays both aggregation of reflecting platelets and actual contraction of the iridophore, causing it to round up and detach from its substrate (Fig. 2.32). Early work on the role of MSH in iridophore control was done on amphibians, and only in recent years was it shown that piscine iridophores respond to the hormone in the same way (see Fujii, 1993a). Leukophores, however, may provide a bit of a paradox in that leukophores of the medaka may disperse in the presence of MSH (Negishi and Obika, 1980). Iridophores play a role in both physiologic and morphologic color changes. When high doses of MSH are administered or when hormone treatment is prolonged, larvae of some species such as Rana sylvatica display a morphological response so great that the many iridophores of hypophysectomized larvae may completely lose their pigment (Bagnara, 1958; Bagnara and Neidleman, 1958). This morphological effect of MSH on iridophores has been studied by Taylor (1969), who points out that reflecting platelets in iridophores become thinner in frogs receiving MSH injections. The diminution in reflecting platelet thickness is a morphological manifestation of a quantitative loss of measured purines. Xanthophore Effects Relatively little is known about the physiological responses of amphibian xanthophores or erythrophores to MSH because these chromatophores are difficult to see. They are often pale, especially at their margins, and the presence of large numbers of iridophores and melanophores serves to mask the xan-
thophores. Nevertheless, there are at least some clear cases in which xanthophores are influenced by MSH. In adults of Hyla arenicolor, xanthophores of skins kept in Ringer solution are aggregated; however, upon administration of MSH, these cells expand (Bagnara, 1969; Bagnara et al., 1968). In more recent times, there have been numerous studies on the xanthophores and erythrophores of fish, and it is now well documented that both these chromatophores generally disperse under the influence of MSH (see Fujii, 1993a). The morphological effect of MSH on xanthophores of amphibians is more prominent and is best demonstrated by quantitative changes in pteridine pigments. In the skin of hypophysectomized larvae, the content of pteridines is considerably lower than that of intact larvae, but it returns to normal when such larvae are injected with MSH (Bagnara, 1961, 1969; Bagnara and Neidleman, 1958). Xanthophores in normal larvae of the salamander Pleurodeles waltlii are expanded such that their broad arms form a continuous yellow sheet over the surface. Xanthophores of hypophysectomized larvae are also dispersed; however, individual processes are thin and delicate and individual chromatophores stand out clearly. Thus, the morphological effect of MSH on xanthophores is manifested by the amount of pteridine pigments contained and is reflected in the general appearance of the chromatophore. In Pleurodeles, there is also a marked difference in the total carotenoid content between normal and hypophysectomized larvae (Bagnara, 1969). It is not known, however, whether the diminution of carotenoids from the skin of hypophysectomized larvae is a result of the absence of MSH or an indirect manifestation of the lack of a hypophysis. Despite the profound effect of MSH on the pteridine content of xanthophores, there has been no observation of an MSH effect on the pterinosome. No differences have been noted between the pterinosomes of skins from normal frogs and those from frogs receiving MSH injections. Cyanophore Effects With their discovery of cyanophores in both the mandarin fish, Synchiropus splendidus, and the psychedelic fish, S. picturatus, Goda and Fujii (1995) showed that these chromatophores responded to various stimulatory cues. Whereas their exposure to norepinephrine resulted in slow aggregation, a-MSH induced pigment dispersion.
Melanin-Concentrating Hormone (MCH) MCH is a cyclic heptadecapeptide secreted from the posterior lobe of the pituitary that has the capacity to bring about melanin aggregation in piscine melanophores (Kawauchi et al., 1983). It seems to be present primarily in teleost fishes (Sherbrooke et al., 1988). This neuropeptide has been found in the brain of other lower vertebrates where its neuronal cell bodies seem to be localized in the hypothalamus (Baker, 1993). In most species, only a few of its axons project to the posterior pituitary; however, in teleosts, the neurohypophysial lobe receives many MCH fibers, and thus the neuropeptide has 31
CHAPTER 2
achieved legitimate hormonal status in this group. It seems to function in the regulation of skin color through its ability to bring about pigment aggregation within melanophores and apparently in xanthophores and erythrophores as well (Baker, 1993). It is possible that the use of MCH in the control of color change in this group of fishes is an evolutionary novelty that arose near the end of the Paleozoic or during the early Mesozoic, just before or in the evolution of the Holostei, a group ancestral to modern teleosts (Sherbrooke and Hadley, 1988). Baker (1993) has summarized the evidence that MCH is used in color change in teleosts. Among the points that she raises is the fact that MCH can induce melanin concentration in isolated fish skin melanophores. The differential effects observed following the use of MCH fragments on different species suggests variation in the MCH receptor. MCH has the capacity to antagonize the melanin-dispersing action of aMSH directly at the melanophore level. MCH may also play a role in pigmentary control by depressing release of MSH from the pituitary. Among the fruits of continuing investigation in this field is the revelation by Oshima and Wannitikul (1996) that cyclic AMP is probably the messenger for MCH action.
The Effects of Other Hormones on Pigment Cells In addition to MSH, other hormones are known to affect chromatophores. Two of these, melatonin and epinephrine, will be discussed in the following sections because they are associated with specific responses. The thyroid has long been implicated in pigmentary changes that occur during amphibian metamorphosis. Woronzowa (1932) reported that thyroid extracts affected the spotting pattern in metamorphosing ambystomids, and Kollros and Kaltenbach (1952) observed pigmentary changes in the vicinity of thyroid implants in Rana pipiens larvae. A profound increase in chromatophore number occurs at metamorphic climax in such larvae (Bagnara and Hadley, 1973). Similarly, specific pteridine changes were induced in localized areas of the skin of Pleurodeles larvae following the implantation of thyroxine cholesterol pellets (Bagnara, 1964c). Among pteridine-associated changes is the abrupt disappearance of “Pleurodeles blue,” long thought to be a pteridine, but now known to be a novel pyridine derivative (Yoshida et al., 1988). The mode of action of thyroxine on the metabolism of this compound is a question that begs an answer. Effects of thyroxine on physiologic color change have been observed. Chang (1957) indicated that the blanching of frogs following administration of thyroxine may be attributable to an inhibition of MSH release from the pars intermedia. The same may hold for salmonids (Bagnara and Hadley, 1973). The direct action of this hormone on pigment cells was found in the in vitro study by Wright and Lerner (1960). Triiodothyronine is more potent than thyroxine or any other known hormonal agent, except for melatonin, in reversing the action of MSH on isolated frog skins (Bagnara and Hadley, 1970a; Hadley and Bagnara, 1969). 32
Studies on other vertebrates have long indicated that steroid hormones influence pigmentation, and such an effect on amphibian pigmentation was reported by Himes and Hadley (1971), who observed that progesterone exerts an MSH-like response on frog skins in vitro. A strong case for a role for sex hormones in in vivo color changes was presented by Richards (1982), who demonstrated a profound alteration of chromatophore expression by sex hormones in the Kenyan reed frog Hyperolius. Adaptive Mechanisms Background Adaptations MSH has long been considered the major hormone involved in background adaptation, and this peptide has provided the basis for the unihumoral theory of chromatophore control (see Parker, 1948). This theory considers that, during adaptation to white backgrounds, little or no MSH is released from the pars intermedia, resulting in low circulating levels of this hormone and a consequent lack of stimulation of chromatophores. Thus, melanophore pigments are aggregated and iridophore pigments are dispersed. During black background adaptation, MSH is released leading to a dispersion of melanophore pigments and an aggregation of reflecting platelets within iridophores; consequently, the animal darkens. This concept is supported by observations of cytological changes in the pars intermedia of frogs in correlation with background adaptation (Cohen, 1967; Imai, 1971; Perryman, 1974; Saland, 1967). The appearance of pars intermedia cells in frogs adapted to black backgrounds is consistent with a state of hormone synthesis and release. This was also the conclusion of Burgers et al. (1963) made on the basis of actual MSH assays. In background adaptation, it is implicit that the animal can perceive differences in background. It seems that the lateral eyes are involved as blinded animals equilibrate to an intermediate state of pigmentation and do not alter coloration in response to changes in background (see Parker, 1948; Bagnara and Hadley, 1973). Moreover, direct electrophysiological studies by Dawson and Ralph (1971) have shown that changes in illumination of the lateral eyes of adult R. pipiens are clearly recorded in the pars intermedia. The mechanism by which the retina discriminates background difference is not understood, although it has long been thought (Butcher, 1938) that dorsal and ventral regions of the retina have different sensitivities to incident and reflected light and thus allow appropriate perception of albedo (the amount of light reflected from the substrate, as explained in Fig. 2.33). Ultimately, background adaptation is regulated by the control of MSH release through the involvement of the hypothalamus. The control is mediated through the inhibition of MSH release, as was suggested by Etkin (1941, 1962a, b) who along with others obtained extremely dark tadpoles after isolating the pituitary by hypophysial transplantation or by hypophysial stalk section (Fig. 2.25). During the past 30 years, an immense literature has accumulated in this area, and the current state of knowledge has been summarized by René et al. (1993) and Roubos et al. (1993). The evidence is over-
COMPARATIVE ANATOMY AND PHYSIOLOGY OF PIGMENT CELLS IN NONMAMMALIAN TISSUES
Light source
Reflecting substrate High albedo
Absorbing substrate Low albedo A
Light source
High albedo environment
Light source
Low albedo environment
Fig. 2.33. Perception of light by Arizona tiger salamanders differs between white and black substrates. Light is reflected from a white substrate and provides a high albedo, whereas a black substrate absorbs light and the albedo is low. Larvae in a turbid pond (lower left) experience a high albedo because of light reflected from suspended particles, while those in a clear pond are subjected to a low albedo because light is absorbed by plants and the dark-colored pond bottom (courtesy of P. Fernandez; from Fernandez and Collins, 1988).
whelming that hypothalamic inhibition of MSH secretion is controlled by catecholamines, notably dopamine. Presumably, the pars intermedia chronically releases MSH, and this release is controlled through neurosecretory fibers that reach the pars intermedia from the hypothalamus. Perception of a light background (high albedo) results in inhibition of MSH release and consequent paling of the animal. On a dark background (low albedo), hypothalamic neurosecretory neuron release of dopamine is reduced and resulting high levels of MSH lead to darkening (Figs 2.27–2.29). Adaptation to Darkness Unlike adults, larval stages of most amphibians display a
B
Fig. 2.34. Xenopus larvae, stage 42. (A) Larva under normal room illumination on a white background; larva does not background adapt because it is in a primary stage. (B) Similar larva in darkness for 1 h; note prominent melanophore contraction in response to melatonin release from the pineal (from Bagnara, 1976).
remarkable ability to blanch when they are maintained in darkness (see Bagnara, 1965, 1966b; Bagnara and Hadley, 1970a). This blanching reaction was first observed long ago (Babak, 1910); however, it was only much later that a basic mechanism controlling this response was described (Bagnara, 1960, 1961). The proposed mechanism describes a role for the pineal in a normal physiological function. It is essentially hypothetical, but it remains unchallenged and is widely accepted (Bagnara and Hadley, 1970a; Bogenschütz, 1965). The hypothesis suggests that, under conditions of darkness, the pineal is stimulated to release melatonin, presumably a pineal hormone, into the general circulation. Melatonin exerts a profound contracting effect on dermal melanophores leading to a rapid blanching (Fig. 2.34). As first described by Bagnara (1960), the involvement of the pineal relates to two aspects of its physiology: light reception and endocrine function. The former has been a role attributed to the pineal since before the classic work of von Frisch (1911) on fishes and has since found substantial support from both ultrastructural and electrophysiological studies (see Eakin, 1973). The role of the pineal as an endocrine organ is more obscure and requires a fuller explanation. The first evidence that the pineal contains a humoral agent is attributable to the studies of McCord and Allen (1917), who discovered that feeding mammalian pineals to tadpoles evoked a profound blanching. Later, Lerner et al. (1958) isolated a potent melanophore-contracting agent from beef pineal glands, which they identified as melatonin (Nacetyl-5-methoxytryptamine). A detailed analysis of the data supporting the concept that the body-blanching reaction is mediated by the pineal has been presented elsewhere (Bagnara, 1965; Bagnara and Hadley, 1970a; Eakin, 1973); however, a few important points need to be made here. First of all, it should be mentioned that 33
CHAPTER 2
blinded larvae become pale when they are placed in darkness (Bagnara, 1960; Laurens, 1915, 1917). Moreover, the blanching reaction is abolished by “pinealectomy” (Bagnara, 1960, 1963; Charlton, 1966). Temporal events in the onset and recovery from the blanching reaction are consistent with the view of an endocrine mediation of the response. Of many indoles tested, only melatonin is a potent melanophorecontracting agent (Quay, 1968; Quay and Bagnara, 1964), and the pigmentary changes induced by the action of melatonin duplicate the responses that occur in darkness. Young tadpoles, not yet able to respond to dark backgrounds by inhibiting MSH release from the pars intermedia, are in the primary stage and thus have dispersed melanophores. Such larvae blanch when placed in darkness due to the direct effects of melatonin on dermal melanophores causing them to aggregate. In larvae that possess epidermal melanophores or iridophores, these chromatophores do not change in darkness because they do not respond directly to melatonin. While these data support the hypothesis that the bodyblanching reaction of amphibian larvae is controlled by the pineal, it must be emphasized that this mechanism is restricted to larvae and does not appear to be generally functional in adults. It is well known that adult amphibians do not blanch in darkness (see Parker, 1948). Moreover, both epidermal and dermal melanophores in skins of adult frogs are generally unresponsive to the administration of melatonin, as has been demonstrated both in vitro (Bagnara and Hadley, 1970a; Hadley and Bagnara, 1969) and in vivo. Whether they lack the melatonin receptor originally deduced by Heward and Hadley (1975) on the basis of structure–function studies and characterized recently by expression cloning from Xenopus (Ebisawa et al., 1994) is not known. Among the various color changes displayed by vertebrates, those resulting from the direct action of light are among the most striking. Perhaps the most remarkable of these is the tail-darkening reaction observed when hypophysectomized Xenopus larvae were placed in the dark (Bagnara, 1957) and subsequently shown to occur in isolated tails maintained in darkness (Fig. 2.35) (Bagnara, 1957, 1966b; Burgers and van Oordt, 1962; van der Lek et al., 1958). Under usual conditions of illumination, dermal melanophores of the fin are punctate, or nearly so, and the tail is essentially transparent. When isolated tails or whole tadpoles are placed in darkness for half an hour or more, a profound dispersion of melanosomes occurs in these melanophores so that the tail becomes black. Upon resumption of illumination, these melanophores quickly revert to the original punctate state and the tail becomes pale. Illumination of given regions of the tail (Bagnara, 1957) or of individual melanophore processes (van der Lek, 1967) can cause aggregation of melanosomes, suggesting that the response is mediated by a photochemical system operating at the level of the chromatophores themselves. The tail-darkening reaction was first considered to be a rather peculiar specialization of Xenopus larvae, but we now know that it occurs in larvae of a Mexican leaf frog, P. dacnicolor (Bagnara, 1974), and in many other hylid tadpoles. 34
Fig. 2.35. In vitro tail-darkening response of isolated tails from Xenopus larvae under normal conditions of illumination (top) and in darkness (bottom). The tail-darkening response was prevented in a central area which was left illuminated (center) (from Bagnara, 1957).
The dynamic light-sensitive tail fin melanophores have been used to address another infrequently considered phenomenon of chromatophore physiology, that of the energy requirements for the aggregation–dispersion phenomenon. Some investigators have considered that pigment aggregation is the principal energy-requiring step (Horowitz, 1958), whereas others have concluded that dispersion is the principal energy-demanding process. Iga and Bagnara (1975) have demonstrated that both aggregation and dispersion of melanosomes are energy requiring and will not occur in the absence of oxygen (Fig. 2.36). Furthermore, they showed that, although darkness-induced darkening of Xenopus tail fin melanophores does not occur in oxygen-free media, restoration of oxygen to such tails even after they have been returned to lighted conditions leads to a dispersion aftereffect. This indicates that the phenomena of light reception and melanosome dispersion are two separate components of the tail-darkening reaction. In addition to the tail-darkening reaction, the direct effect of light on melanophores cultivated in vitro has been reported. Kuhlemann (1960) indicated that embryonic melanophores of Xenopus grown in tissue culture respond to illumination by becoming punctate (confirmed more recently by Daniolos et al., 1990), just as do embryonic melanophores of neural crest explants of several anurans (Fig. 2.37) (Bagnara and Obika, 1967). The significance of these direct effects of light on melanophores grown in culture is not known.
COMPARATIVE ANATOMY AND PHYSIOLOGY OF PIGMENT CELLS IN NONMAMMALIAN TISSUES A
Fig. 2.37. Neural crest explant of Xenopus. Under normal room illumination, melanophores remain in an aggregated state (left) but, following a 45-min period in darkness, these melanophores become punctate (right) (modified from Bagnara and Obika, 1967). B
C
Fig. 2.36. (A) Response of tail fin melanophores of a Xenopus tadpole to darkness (D) and to light (L) in Ringer solution; the dark period is indicated on the abscissa by a solid black bar. Melanosome dispersion takes place gradually in darkness, and aggregation occurs quickly in light. (B) Inhibition of melanosome dispersion in the tail fin melanophores of a Xenopus tadpole in oxygen-free Ringer solution and the dispersion “aftereffect,” which occurs in oxygen-containing Ringer solution. The dark period is indicated on the abscissa by a solid black bar. (C) A typical example of retardation of melanosome aggregation in the tail fin melanophores of a Xenopus tadpole in oxygen-free Ringer solution; the dark period is indicated on the abscissa by the solid black bar (D). Pigment dispersion of the melanophores was induced by dark treatment of the tails for 45 min in Ringer solution, and then the tails were transferred into oxygen-free Ringer solution in a dark room (from Iga and Bagnara, 1976).
In addition to amphibian melanophores, examples of direct light sensitivity of fish chromatophores are well documented. Iga and Takabatake (1986) have demonstrated that teleost melanophores may respond to local light stimulation by aggregating in darkness and dispersing in the light. Of special interest among fishes is the demonstration of light-sensitive iridophores in the neon tetra (Lythgoe et al., 1984; Nagaishi and Oshima, 1989), such that the distance between reflecting platelets within these cells is changed through the action of the light. In a search for the basis of this photosensitivity of iridophores, Lythgoe et al. (1984) demonstrated the presence of an opsin-based visual pigment in these iridophores, either or both rhodopsin or/and porphyropsin. The presence of visual pigments in a photosensitive chromatophore is both fascinating and significant and asks the question whether similar visual pigments are present in other chromatophores such as the light-sensitive melanophores discussed previously. It seems likely that, as more species are studied with respect to lightinduced color changes, more unusual phenomena will be revealed. Such seems to be the case with P. dacnicolor, in which the skin of brown individuals displays a direct photosensitivity (Iga and Bagnara, 1975). When masks are placed on the brown surface, the skin beneath becomes green in exact conformation with the mask (Fig. 2.11).
Mechanisms of Hormone Action on Pigment Cells The Cyclic AMP as a Second Messenger of MSH Action In accordance with the first messenger–second messenger scheme (Sutherland et al., 1965), MSH acts as a first messenger and brings about its effects by promoting an intracellular increase in a second messenger, 3¢,5¢-cyclic adenosine monophosphate (cyclic AMP), which is in turn responsible for the particular response of the effector cell (Sutherland et al., 1968), in this case pigment cells. Thus, cyclic AMP mimics the action of MSH by darkening frog skin in vitro (Bagnara and Hadley, 1969; Bitensky and Burstein, 1965; Novales and Davis, 1967). The response is not as effective as that of MSH itself or as that of the dibutyryl derivative of cyclic AMP (Goldman and Hadley, 1969); however, the response to either of these cyclic nucleotides is truly MSH-like, for cytological 35
CHAPTER 2
examination of darkened skin reveals that both melanophores and iridophores react. Probably, both iridophores and melanophores contain similar or identical MSH receptor sites, and the different events in the two cells following MSH stimulation could then be attributable to the interaction of the second messenger and the specific distal functional elements of the particular chromatophore. Further support for the involvement of the first messenger–second messenger concept in the regulation of chromatophore control is derived from the fact that methylxanthines, such as caffeine or theophylline, can bring about both iridophore and melanophore responses (Fig. 2.24). Methylxanthines are known to increase cellular levels of cyclic AMP by inhibition of cyclic nucleotide phosphodiesterase (Butcher and Sutherland, 1962; Sutherland and Rall, 1958). Furthermore, it has been reported that MSH stimulates cyclic AMP formation in frog skin in correlation with the degree of darkening (Abe et al., 1969). The parallelism between iridophore and melanophore responses to the various MSH peptides, be they unnatural synthetic partial sequences or entire molecules such as a-MSH or b-MSH (Bagnara, 1958, 1964b), is to be expected from the point of function. The most efficient darkening response involves both melanosome dispersion and reflecting platelet aggregation. Accordingly, it seems logical to conclude that, despite the differing intracellular responses of these two divergent chromatophores, they must each possess similar MSH receptors. In modern times, the quest for characterization of the MSH receptor has led to the discovery of several different MSH receptors that function in accordance with specific roles for MSH (Cone et al., 1993). At present, at least five receptors are known from mammals for the melanocortin [MSH/adrenocorticotropic hormone (ACTH)] peptides. These melanocortins are labeled numerically in order of their discovery, with melanocortin-1 (MCR-1) assigned to the surface of melanocytes. It is known through the use of various specific a-MSH antagonists that frog melanophores possess at least one MCR, but which of the five is not known (Hruby et al., 1995). An interesting question concerns the possible similarities or differences between the mammalian MCR-1 and that of amphibians. An answer to this question may be forthcoming when the amphibian MCR-1 gene is cloned. In the meantime, we assume that the amphibian MCR-1 is present on the iridophore cell surface, but the distribution of this receptor on the surfaces of these differing pigment cells is unknown, and the question of whether these two chromatophores share identical profiles is unanswered. It is known through the use of various specific a-MSH antagonists that frog melanophores possess multiple MSH receptors, but such studies are in their infancy (Hruby et al., 1995). As such studies proceed, problems of species variation will be of concern. For example, an interesting study by Quillan et al. (1995) has revealed that D-Trp-Arg-Leu-NH2 is a potent a-MSH antagonist in Xenopus and that it is capable of causing pallor in adults when injected systemically. Moreover, it has the capacity to cause local lightening when applied top36
ically to such frogs. Xenopus is a rather particular amphibian; thus, the question arises of whether this MSH antagonist is generally active among amphibian species or is uniquely active in Xenopus.
The Role of Adrenergic Receptors While MSH seems to be the major factor regulating amphibian chromatophores, other hormones may also play a role in color change. Among these are catecholamines, such as epinephrine and norepinephrine, that apparently control the rapid color changes associated with “excitement pallor” (see Parker, 1948). Catecholamines are known to mediate certain effects through two types of receptors, a and b (Ahlquist, 1948), each of which controls responses that are antagonistic to the other. Accordingly, the response of a system to catecholamine stimulation depends on the presence or absence of a and b receptors, and it has been shown that both receptors may be present on amphibian chromatophores. With the aid of the receptor concept, it becomes possible to elucidate some previously unexplained paradoxical effects. For example, while both epinephrine and norepinephrine lighten the skins of R. pipiens by overriding the MSH effects (Wright and Lerner, 1960), catecholamines darken the skin of both Xenopus (Burgers et al., 1963) and Scaphiopus (Goldman and Hadley, 1969). Apparently, a receptors are present in R. pipiens (Lerner et al., 1954; Novales and Novales, 1965), accounting for the paling reaction, whereas in Xenopus (Graham, 1961; Novales and Davis, 1969) and Scaphiopus (Goldman and Hadley, 1969), b receptors predominate allowing darkening to occur in the presence of catecholamines. Although later advances in the pharmacology of a and b receptors have elaborated subclasses of these receptors, little has been done with respect to their definition in amphibians and reptiles. In contrast, the adrenoreceptors of fishes have been better characterized in this regard (Fujii, 1993a). The color changes that occur in response to receptor stimulation in R. pipiens are attributable to changes in both iridophores and melanophores (Hadley and Bagnara, 1969). Moreover, the presence or absence of a and b receptors on iridophores and melanophores seems to complement one another. This is shown in the variation of response to catecholamine stimulation by different sibling species of R. pipiens (Hadley and Goldman, 1970). Norepinephrine lightens the MSH-darkened skins of R. pipiens of northern origin, but further darkens the skins of frogs of Mexican origin, probably Rana forreri. Lightening of the northern species is based not only on the presence of a receptors on the melanophores leading to an aggregation of pigment in these cells, but it appears that a receptors on the iridophore lead to dispersion of the reflecting platelets. In skins from southern frogs (R. forreri), b receptors predominate on both melanophores and iridophores so that catecholamine stimulation of skins in which MSH has already stimulated melanophores and iridophores leads to further melanosome dispersion in melanophores and greater reflecting platelet aggregation in iridophores. The simultaneous activation of the same receptor
COMPARATIVE ANATOMY AND PHYSIOLOGY OF PIGMENT CELLS IN NONMAMMALIAN TISSUES
type on both melanophores and iridophores does not always occur. For example, the catecholamine darkening of Scaphiopus skins mentioned above entails the activation of b receptors on only melanophores; although melanosome dispersion takes place in melanophores, iridophores remain unchanged (Goldman and Hadley, 1969). It seems reasonable that, as more studies are made relative to the application of the adrenergic receptor concept to pigment cell biology, it will be revealed that these receptors comprise an important part of the chromatophore system that can be used by a variety of agents known to affect chromatophores. An obvious question in this respect concerns the relationship between adrenergic receptors and cyclic AMP; does stimulation of adrenergic receptors lead to an alteration in the level of cyclic AMP within the chromatophore? It is tempting to speculate on this point in view of the report by Turtle and Kipnis (1967) that stimulation of b adrenergic receptors in tissues leads to an increase in tissue levels of cyclic AMP, whereas a adrenergic stimulation leads to a decrease in this substance. For a review of this topic, especially with respect to amphibians and reptiles, consult Bagnara and Hadley (1973) and Hadley and Bagnara (1975). An even richer literature has accumulated with respect to fishes and has been cogently discussed by Fujii (1993a).
Molecular Mechanisms for Intracellular Translocation of Pigment Granules A variety of techniques and procedures have been utilized in order to comprehend the mechanism for intracellular transport of pigmentary organelles. In pharmaceutical studies of such motile responses, small pieces of skin or scales containing chromatophores were often used after removal of the epidermis by treatment with collagenase and/or chelating agents. For cell manipulation and microinjection of drugs and antibodies, in vitro cultured chromatophores were obtained as emigrants from skin explants or from tissues dissociated with collagenase and trypsin with subsequent centrifugal purification in Percoll or Ficoll and immortalized as cell lines (Akiyama and Matsumoto, 1983; Akiyama et al., 1981, 1987; Aspengren et al., 2003; Daniolos et al., 1990; Fujii 1993a, b; Matsumoto et al., 1978, 1984; Negishi and Obika, 1980; Rogers et al., 1997, 1998). Electron microscopy discloses that fish and amphibian chromatophores contain an abundance of microtubules and actin filaments in a definite arrangement, together with relatively few intermediate filaments, the density and pattern of which are variable among species. When these cells are exposed to microtubule-disassembling agents such as colchicine, lumicolchicine, vinblastine, hexylene glycol, and nocodazole, as utilized in earlier studies, pigment aggregation is totally blocked or severely disrupted, mostly irreversibly and concomitantly with a disarrangement of their cytoplasmic framework (Obika, 1986; Obika and Negishi, 1985; Porter, 1973; Schliwa, 1984). When these cells are treated with drugs affecting actin filaments, viz. cytochalasins, DNase I, phalloidin, the results
are mostly confusing: in Xenopus and Rana melanophores treated with cytochalasin, dispersion is inhibited (Malawista, 1971; McGuire and Moellmann, 1972), whereas in fish melanophores exposed to cytochalasin B, pigment migration is not affected (Visconti and Castrucci, 1985). In goldfish xanthophores, cytochalasin B inhibited heavy meromysin (HMM)-binding dispersion of carotenoid droplets (Lo et al., 1980; Obika et al., 1978). In swordtail erythrophores, microinjection of the anti-actin antibody clearly interferes with both aggregation and dispersion (Fig. 2.38) (Akiyama and Matsumoto, 1983). From these findings, it becomes clear that these two cytoskeletons are implicated in pigment translocation, more decisively for microtubules and with some diversification for actin filaments. A unique aspect of this motility is bidirectionality with repeated centripetal or centrifugal migrations of the organelles occurring synchronously in whole dendrites of the cells. The question arises as to how these directed movements and their reversal occur. Inasmuch as microtubules have a polarity with minus and plus ends in their structure (Euteneuer and McIntosh, 1981; McNiven and Porter, 1986; McNiven et al., 1984), and inasmuch as they exist under a parallel alignment along the migratory tracks, as was indicated from pioneering studies (Bikle et al., 1966; Porter, 1973), these cytoskeletons are considered to be key instruments in this motility. As to motors driving pigment granules along microtubules, it was shown that cytoplasmic dyneins are inseparably implicated in aggregation as a minus end-directed motion whereas kinesins, mechanochemical ATPases, are involved in a plus end-directed dispersion (Asai and Lee, 1995; Haimo, 1996; Horikawa, 1998; Horikawa et al., 1998; Karki and Hozbaur, 1999; Rodionov et al., 1991; Thaler and Haino, 1996). The involvement of these motor proteins is primarily suggested by the requirement of this motility for a nucleotide triphosphatelike adenosine triphosphate (ATP) or guanosine triphosphate (GTP). This seems to be the case because the application of vanadate, which inhibits ATPase activity of dyneins, disrupts pigment aggregation in fish pigment cells (Beckerle and Porter, 1982; Clark and Rosenbaum, 1982; Luby and Porter, 1980; Negishi et al., 1985; Rozdzial and Haimo, 1986). Later, it was shown that cytoplasmic dyneins are colocalized with melanosomes along microtubules in both fish and amphibian melanophores (Nilsson et al., 1996; Rogers et al., 1997). Further decisive evidence supporting cytoplasmic dynein as the motor resides in the fact that purified melanosomes of Xenopus are capable of moving along microtubules towards the minus end in vitro (Rogers et al., 1997), and that microinjection of an anti-dynein antibody blocks pigment aggregation in fish melanophores (Nilsson and Wallin, 1997). In addition to these findings, it was also shown that microinjection of an antibody raised against kinesins (domain) into frog melanophores blocks pigment dispersion without affecting aggregation (Rogers et al., 1998). This suggests the possible participation of different motors in two phases of dispersion and aggregation. Biochemical analyses of purified 37
CHAPTER 2
A
D
B
E
C
F
melanosomes from Xenopus melanophores disclosed that kinesins are tightly associated with these organelles, moving them in vitro in the absence of cytosolic factors (Rogers et al., 1997, 1998). As kinesin II is a heterotrimer composed of two motor subunits of 85 and 95 kDa and a nonmotor of 115 kDa, mutations in these subunits should disrupt movement along microtubules. When a dominant-negative mutant of the 95 kDa motor subunit, which lacks the ATP-binding region of the motor domain, is produced, this headless kinesin II is unable to move organelles along microtubules (Tuma et al., 1998). In actin-based motility, myosin is considered to be the most reasonable candidate motor protein. As early as 1973, it was shown with mammalian melanocytes that myosin V, a nonmuscle myosin, is involved in melanosome transport from the cell center to the cell periphery where these melanosomes are transferred to keratinocytes (Wolff, 1973). In the dilute mutant of mice bearing defects in hair pigmentation, it is known that melanosomes are distributed in the perinuclear region of the melanocytes. Inasmuch as the dilute gene encodes myosin V, it is considered that melanosome transport along actin filaments toward the cell periphery is disordered by these mutated motor proteins, disrupting melanosome transfer from melanocytes to hair keratinocytes (Wu et al., 1997, 1998). 38
Fig. 2.38. The blockade of pigment displacement in cultured swordtail erythrophores by microinjection of an antiactin antibody. (A) Before microinjection. Cells are in a dispersed state in standard culture medium. (B) The same as (A) after administration of 5 ¥ 10-4 M epinephrine. All pigment (pterinosomes) is aggregated to the cell center. (C) The same as (B) after a brief rinsing in phosphate-buffered saline and subsequent administration of 10-3 M theophylline. Pigment is redispersed. (D) The same as (C) immediately after microinjection of the anti-actin antibody into a cell present in the center of the field of view. A liquid paraffin droplet injected following the antibody solution is seen inside the cell body (arrow). (E) The same as (D) after exposure to epinephrine after injection. Note that pigment aggregation is blocked only in the injected cell, whereas uninjected cells nearby display complete pigment aggregation. (F) The same as (E) after exposure to theophylline. Note that no change is seen in the state of pigment dispersion in an injected cell, whereas pigment in the others is redispersed. Scale bar = 50 mm (from Akiyama and Matsumoto, 1983).
In Xenopus, it was shown with the use of isolated melanosomes that myosin V, although coexisting with kinesin II and cytoplasmic dynein, is tightly associated with these organelles, and that such isolated melanosomes are able to move along actin filaments in vitro (Rogers and Gelfand, 1998; Rogers et al., 1997). The localization of myosin V on melanosomes was also revealed in fish (cod) melanophores by immunoelectron microscopy combined with on-grid labeling using an antibody raised against 200 kDa mouse myosin Va heavy chain (Skold et al., 2002). The results of these studies strongly support the view that myosin V is implicated in pigment migration along actin filaments. Judging from the distribution pattern of actin filaments, which are rich at the cell periphery, it appears that motility based on their presence is of short-range nature. Physiological color change is mostly fast in fish and slow in amphibians, although fairly variable among species. In melanophores of the fish Oryzias latipes, the migratory speed of melanosomes is estimated as 0.06~0.3 mm/s as mass movement and 1~2 mm/s at 22∞C in an ideal linear track without a marked difference in the rate between aggregation and dispersion (Obika, 1986). In swordtail erythrophores (Fig. 2.39), pterinosomes migrate on average at 1 mm/s in aggregation and 0.01 mm/s in dispersion at room temperature, over about
COMPARATIVE ANATOMY AND PHYSIOLOGY OF PIGMENT CELLS IN NONMAMMALIAN TISSUES A
50 µm
Aggregation(%)
B 100
50
Voltage 0.01mV
0 0
20 0 20 40 Time (min)
60
Fig. 2.39. Pigmentary responses of a swordtail erythrophore in an isolated scale. (A) Tracing of one cycle of pigment aggregation (left row) and dispersion (right row). The red pterinosomes are aggregated by administration of 5 ¥ 10-4 M epinephrine and dispersed by 10-3 M theophylline after washing in physiologic salt solution. The frame indicates the dimension of a recording photo cell. Note that there is little change in cell shape after one cycle of pigment responses. (B) Photoelectric recording of pterinosome displacement made on a single cell using a Rose chamber at room temperature (about 25∞C). The effects of yellow carotenoid vesicles are blocked by the use of a filter with a peak at 470 nm (see Matsumoto et al., 1984 for further details on instrumentation).
a 15~35 mm track in the dendrites (Matsumoto et al., 1984). In myosin-based motion, the velocity is estimated as about 0.04 mm/s, which would be appropriate for melanosome migration in amphibian melanophores (Tuma and Gelfand, 1999). The time needed for the completion of aggregation or dispersion would be affected by the proportion of processes using microtubule- or actin filament-based motors as well as the efficiency of their linkage. A proposal for the relationship of these two motility systems is depicted in Figure 2.40. It suggests that a microtubule-based motor works in long-range movement, utilizing cytoplasmic dynein for aggregation and kinesins for dispersion, while an actin filament-based motor, myosin V, acts in short range (Radionov et al., 1998; Wu et al., 1998). In the latter, pigment granules at aggregation are trapped at the cell periphery to be brought to microtubules for transport by cytoplasmic dynein, whereas at dispersion, pigment granules are dispersed evenly throughout the cytoplasm after transport from the cell center through microtubule-based motors (Tuma and Gelfand, 1999). This model is referred to as the “dual filament model of transport” by Langford (1995). Because fish chromatophores, when their actin filaments are drug disrupted, exhibit hyperdispersion possibly through a strong, centrifugal driving force of unaffected microtubule-based motors, and as frog melanophores under similar treatment show uneven distribution of melanosomes, possibly due to the lack of a local, short-range drive by a myosin motor (Radionov et al., 1998), it appears that this model is suitable for the interpretation of available findings. In signaling pathways for this motility, as mentioned earlier, the control of intracellular levels of cAMP plays a crucial role. This naturally suggests the involvement of protein phosphatases and protein kinases such as cAMP-dependent protein kinase A (PKA) or calcium-dependent protein kinase C (PKC) in this cascade (Nery and Castrucci, 1997). It is known that phosphatase 2A, but not 1 and 2B, is required for pigment aggregation of Xenopus melanophores, whereas phosphatase 2B, calcineurin, is necessary in fish (Reilein et al., 1998; Thaler and Haimo, 1990). In melatonin-induced aggregation of Xenopus melanophores, it was shown that mitogen-activated protein kinase (MAPK) is activated to supplement movement operated by the cAMP/PKA pathway (Andersson et al., 2003). On the other hand, it was shown that both PKA and PKC are implicated in pigment dispersion of Xenopus melanophores, despite the manner of their action being different and the role of PKC being supplemental. Activation of these two protein kinases is essential for dispersion of fish melanophores (Daniolos et al., 1990; Graminski et al., 1993; Reilein et al., 1998; Sammak et al., 1992; Sugden and Rowe, 1992). From these findings, it is apparent that phosphorylation and dephosphorylation of a target subunit of motor proteins is associated with regulation of bidirectional pigment transport (Rozdzial and Haimo, 1986). Current studies on this subject are focused on identification of target subunits or phosphorylation sites of the motor proteins associated with the direction of migration. Knowledge of the role of calcium 39
CHAPTER 2 Aggregation
Dispersion Cytoplasmic dynein Kinesin II Myosin V
Melanosome Microtubule Actin filament
in this signaling cascade is still fairly controversial, depending upon the species used.
Cellular Associations in Color Change Alterations in the state of dispersion or aggregation of any single chromatophore type can often lead to profound color changes in an animal. However, color change often results from the integrated responses of the various pigment cells that exist together in well-organized associations. The association of one chromatophore type with another does not necessarily mean that either cell must undergo a physiological color change. Often, the association of two pigment cells is passive and serves to emphasize a permanent color pattern. As an example, the red spots on the adult dorsal surface of the newt, Notophthalmus viridescens, are based upon a precise superimposition of an erythrophore layer upon an iridophore layer (J. T. Bagnara, unpublished; Forbes et al., 1973). The red coloration of the spots is enhanced by reflection of light from the iridophores beneath. A similar situation applies to the bright spots of other species such as the spotted salamander, Ambystoma maculatum. Here, the yellow spots are based upon the exact superimposition of xanthophores upon iridophores in an otherwise homogeneous background of dermal melanophores (J. T. Bagnara, unpublished). There are many similar examples of chromatophore associations; however, the most important are the dermal chromatophore unit (Bagnara et al., 1968) and the epidermal melanin unit (Fitzpatrick and Breathnach, 1963). Neither of these units represents a precise structure in the anatomical and functional sense, but rather are concepts based upon the location of various chromatophores in the dermis and epidermis.
The Dermal Chromatophore Unit The primary function of dermal chromatophores is the pro40
Fig. 2.40. A model illustrating the implication of three motor proteins in melanosome translocation of fish and amphibian melanophores (adapted from Gross et al., 2002; Tuma and Gelfand, 1999; Wu et al., 1998).
duction of physiological color changes through the rapid intracellular mobilization of pigment-containing organelles. Among the adults of many amphibians, color changes are brought about by coordinated responses of the three basic chromatophore types, which are so situated that they comprise an integral, functional unit that has been designated the dermal chromatophore unit (Bagnara et al., 1968) (Figs 2.13, 2.18, and 2.41). More recently, a comparable unit has been described for fishes (Fujii et al., 1989). Uppermost in the unit, just below the basement membrane, is a layer of xanthophores and immediately beneath this layer of yellow pigment is found a layer of iridophores. In frogs, the iridophore layer that forms the reflecting component of the unit is composed of a layer of melanophores that have dendrites extending upward. In frogs, these dendrites terminate in fingerlike processes on the surface of the iridophore, just beneath the xanthophore layer. During adaptation to dark-colored backgrounds, melanosomes fill these processes, thus obscuring the reflecting surface of the iridophore and leading to consequent darkening of the animal (Fig. 2.9). When the animal lightens, melanosomes move from the terminal processes and occupy a perinuclear position. As a result, their dermal melanophores are almost completely obscured by overlying xanthophore and iridophore layers and the animal appears light in color. The pigmentary role of the xanthophore layer relates to the establishment of the green color of many forms (Figs 2.23 and 2.42). In such animals, light waves leaving the iridophore surface appear blue because of Tyndall scattering and, as the light waves pass through overlying yellow pigment cells, the shortest wavelengths are absorbed so that finally the animal appears green (Fig. 2.17). The importance of the xanthophore pigments in imparting green coloration is shown not only by the blue coloration of green frogs from which yellow pigments have been leached (Fig. 2.9), but by the existence of blue mutants of frogs or
COMPARATIVE ANATOMY AND PHYSIOLOGY OF PIGMENT CELLS IN NONMAMMALIAN TISSUES
BL
X
PT
CV F
I RP
Fig. 2.42. Wholemount in Karo syrup of dorsal skin of a green tree frog, Hyla cinerea, photographed with epiillumination. Because of the presence of xanthophore pigments, green color is manifested. When yellow pigments are leached away, the preparation appears blue as in Fig. 2.9. The numerous black spots are openings of skin glands (see also Plate 2.12, pp. 494–495).
as larvae but not as adults when they have acquired the ability to change color rapidly. The loss of epidermal melanophores as metamorphosis approaches is paralleled by the differentiation of dermal chromatophore units.
M C MS
Fig. 2.41. Transverse section of Hyla cinerea skin from the dorsal surface showing dermal chromatophore unit in white backgroundadapted state. M, melanophore; I, iridophore; X, xanthophore. Melanosomes (MS) are uniformly distributed in processes extending around the sides of the iridophore, but fingerlike endings (F) over iridophores are empty. BL, basal lamella; RP, reflecting platelets; CV, carotenoid vesicles; C, collagenous masses; PT, pterinosomes. Magnification ¥ 9700 (from Bagnara et al., 1968).
snakes (Fig. 2.22). In such mutants, the pigment content of the overlying xanthophores or erythrophores is almost completely depleted (Bagnara et al., 1978b). The effectiveness of dermal chromatophores and the dermal chromatophore unit as elements of physiological color change is very much affected by the presence of epidermal melanophores and epidermal melanin units. Because the latter lead to the deposition of melanin in overlying epidermal cells, physiologic color changes in the dermis beneath are obscured, and thus an inverse correlation exists between the degree of development of the two systems. In tree frogs, which undergo rapid and profound color changes, a well-developed system of dermal chromatophore units is present and epidermal melanin units are lacking. These frogs have epidermal melanophores
Subcellular Associations Over the past 25 years, it has been suggested on several occasions that the various kinds of pigment-containing organelles of dermal chromatophores are closely related to one another from the point of view of origin (for full details, see Bagnara, 1972; Bagnara and Ferris, 1971; Bagnara et al., 1979; Taylor and Bagnara, 1972). Essentially, it is believed that specific pigment-containing organelles, melanosomes, reflecting platelets, and pterinosomes may be derived from a common equipotential primordial organelle that may form, depending on specific developmental cues, any of the definitive organellar types. The strongest evidence in support of this conclusion is based upon the existence of chromatophores of one type that contain pigmentary organelles of another type (Fig. 2.43). So many examples of this phenomenon exist among amphibians that new observations are often not reported. It was first noted that dermal melanophores of the canyon tree frog, H. arenicolor, sometimes contain a few reflecting platelets intermingled between melanosomes (Bagnara, 1972; Bagnara and Ferris, 1971; Taylor, 1971). Another example is represented in the skin from the dorsal surface of the red-backed salamander, Plethodon cinereus (Bagnara and Taylor, 1970). Erythrophores of the red form of this species contain pterinosomes for the most part but, in addition, a few melanosomes are found. Similarly, in melanophores of the dark form of this species, all three of these organelles are found. Also observed in erythrophores of this species are electron-dense organelles that may be mosaic intergrades between the melanosome and the pterinosome. The first example of a 41
CHAPTER 2
C
P
RP
Fig. 2.43. A mosaic dermal chromatophore of the leaf frog (P. dacnicolor). Melanosomes, reflecting platelets (RP), pterinosomes (P), and carotenoid vesicles (C) are all present in the same cell (from Bagnara, 1983).
definitive normal pigmentary organelle containing at least two different unrelated pigments within the same limiting membrane is the earlier mentioned melanosome of adult P. dacnicolor, which contains both eumelanin and a pteridine pigment (Fig. 2.10). This species has also been shown to produce mosaic pigment cells and mosaic organelles of several types (Bagnara et al., 1979). Mosaic pigment cells and mosaic organelles are not limited to amphibians but have also been observed in reptiles and fishes (Matsumoto et al., 1980). The general phenomenon of chromatophore mosaicism speaks to the obvious close developmental relationships among these neural crest-derived cells that are so obviously different in phenotype. It may also provide an explanation for the remarkable existence of chromatophore transdifferentiation, whereby a fully differentiated chromatophore of one type may change its phenotype and convert to a chromatophore of another type (see Ide, 1986). It appears likely that, as chromatophores of more species are examined, more examples of such chromatophore polymorphism will be observed, which may contribute to a fuller understanding of the mechanisms of chromatophore differentiation.
Pigmentation Patterns The striking and varied pigmentation patterns of poikilotherms have long attracted interest, and an understanding of their biological and physical bases has been sought after for 42
Fig. 2.44. Ventral surface of the same froglet which had received a neural fold graft at the neurula stage. Note the clearly circumscribed area of the graft and its pattern of atypical small spots. The original graft included prospective dorsal skin which had been already determined at the time of transplantation (see also Plate 2.13, pp. 494–495).
many years. Despite these efforts, substantial definitive knowledge about the development and maintenance of pigmentation patterns is lacking, although it is obvious that the ultimate expression of specific patterns depends upon the distribution of specific pigment cells. Pigmentation patterns may be general, such as the frequently encountered one in which the dorsum is darkly pigmented while the ventrum is light colored (Fig. 2.44 and see Fig. 2.49). The cellular basis for this pattern usually involves a greater presence of melanophores in the dorsum than in the ventrum and, conversely, a maximal presence of iridophores or leukophores in the ventrum and a minimal expression of these cells in the dorsum. More specific patterns result from the localized expression or lack of expression of selected chromatophores in circumscribed areas that are shaped as spots, stripes, mottlings, etc. These points are illustrated in Fig. 2.44 and see also Figures 2.47–2.49.
The Role of Endogenous Factors of the Integument The concept that patterns of chromatoblast differentiation are
COMPARATIVE ANATOMY AND PHYSIOLOGY OF PIGMENT CELLS IN NONMAMMALIAN TISSUES
Fig. 2.45. Dorsal surface of a newly transformed froglet of Rana pipiens showing the typical large spot pattern (see also Plate 2.14, pp. 494–495).
established early, even at the level of the neural crest before migration starts, has been considered for many years (see Bagnara, 1987); however, much recent experimentation has supported the alternative view that the pattern resides in the embryonic skin and that uncommitted chromatoblasts are influenced by specific local factors that influence the differentiation of these chromatoblasts (Bagnara et al., 1979). The first concerted effort to discover factors of local integumental origin that might regulate chromatoblast differentiation was made by Fukuzawa and Ide (1988), who discovered a putative inhibitor of melanoblast differentiation in ventral but not dorsal skin of young Xenopus froglets. They considered that this agent present in ventral skin inhibited melanization of melanoblasts and thus designated it a melanization-inhibiting factor (MIF). They considered the differential activity of MIF in dorsal and ventral skin to be responsible for dorsal/ventral patterns. Later, Fukuzawa and Bagnara (1989) demonstrated that MIF (ventral conditioned medium) could override the stimulatory effects of trophic factors such as MSH that would normally be present in the living organism. They further showed (Bagnara and Fukuzawa, 1990) that putative MIF had
Fig. 2.46. The dorsal surface of a half-grown adult which had a portion of dorsal skin rotated 180° at a mid-larval stage. Note the exactness of fit between the separated areas, indicating that the spot pattern was determined precisely at the time of rotation, when no indication of the pattern was yet evident (see also Plate 2.15, pp. 494–495).
a stimulatory effect on iridophores, as would be expected if MIF were indeed responsible for dorsal/ventral pattern formation (see Figs 2.47–2.49). The MIF molecule has been partially characterized, and a monoclonal antibody against MIF has been obtained (Samaraweera et al., 1994). Use of this antibody as an immunohistochemical probe has revealed that MIF is specifically localized in ventral skin of leopard frogs (Fukuzawa et al., 1995). The disclosure of an MIF from lower vertebrates coincides with the discovery that the agouti locus of mammals codes for a specific protein that similarly inhibits melanization of both mammalian melanocytes and melanophores of Xenopus and may be responsible for the dorsal and ventral pigmentation pattern of mice (Miller et al., 1993; Vrieling et al., 1994). The possibility that the agouti protein is related to MIF is a distinct one in view of the fact that agouti protein is an antagonist of the MSH receptor (Lu et al., 1994) and MIF blocks the melanogenic effect of MSH on Xenopus neural crest cells (Fukuzawa and Bagnara, 1989). 43
CHAPTER 2
Fig. 2.47. Iridophores of Pachymedusa dacnicolor in primary culture in control medium. Each iridophore has few processes and little or no branching of attached cells (see also Plate 2.16, pp. 494–495).
There is evidence that MIF has a similar effect on the mammalian system as it has been found that MIF extracted from the ventral skin of the leopard frog, Rana forreri, has an inhibitory effect on the activity levels of tyrosinase and dopachrome tautomerase in B16/F10 and Cloudman S-91 melanoma cell lines (Lopez-Contreras et al., 1996). Moreover, MIF seems to block the stimulatory effects of a-MSH on these enzymes. As MIF does not block the melanogenic effects of theophylline on these melanoma cells, it appears that it acts proximal to the MSH receptor. A similar search for a melanization-stimulating factor (MSF) has revealed the presence of such a putative factor in fishes (Zuasti et al., 1992, 1993), and this factor has been partially characterized from catfish skin (Johnson et al., 1992). What may be a similar factor has been demonstrated in the dorsal skin of the leopard frog where it appears to be particularly manifested in the dark spots (Mangano et al., 1992). Consistent with the view that the integument itself is responsible for the establishment of specific patterns is the demonstration by Bagnara (1982) that, in the leopard frog, dorsal ectoderm at the open neural plate stage has already been deter44
Fig. 2.48. A similar culture of iridophores in a medium conditioned by exposure to ventral skin of a leopard frog and presumably containing MIF. Note the large size of the iridophore mass containing confluent cells and possessing many branching processes. MIF is presumed to stimulate iridophore differentiation (see also Plate 2.17, pp. 494–495).
mined as dorsal and can program immigrating chromatoblasts to differentiate in accordance with a dorsal spot pattern of a general type. He also showed that, at some point in early larval life, a highly specified final spot pattern is put in place, long before it is expressed during metamorphic climax. Very likely, this specification (or determination) takes place at the onset of the feeding stage (Naughten, 1971). It is attractive to consider the possibility that, at this early stage, factors such as MIF and MSF are expressed at a sufficient level to affect chromatophore differentiation and thus to dictate the highly specified pigmentation pattern (see Figs 2.44–2.49 for details). The putative MIF and MSF molecules are presumably produced by cellular elements of the environment in which the pigment cells are found or pass through. In contrast, it is possible that patterns of migration and expression are influenced by molecules produced by the pigment cells themselves. In a study to investigate this possibility, Fukuzawa and Obika
COMPARATIVE ANATOMY AND PHYSIOLOGY OF PIGMENT CELLS IN NONMAMMALIAN TISSUES
(1995) considered that cell adhesion molecules (CAMs) expressed by specific pigment cell types might be important in poikilotherms. They discovered that, in both the medaka (Oryzias latipes) and Xenopus, N-CAM and N-cadherin are expressed specifically in xanthophores, but not in melanophores and iridophores. At present, it is too early to assess the meaning of these findings in the total expression of pigmentation patterns, but continuing studies hold promise of augmenting our knowledge in this area. It would be helpful if numerous pigmentary mutations were available in order to add a genetic component to our understanding of amphibian pigmentation patterns; however, only a few are adequately described, and even these are difficult to utilize as development to sexual maturity in amphibians is relatively slow, and breeding colonies are restricted to only a few species, most notably the Mexican axolotl, Ambystoma mexicanum. Three pigmentary genes in this species, wild type (D), white (d), and albino (a), have been utilized in conjunction with microsurgical manipulations (chimera formation, reciprocal neural crest grafts, and grafts of gonadal primordia) to provide insights into an understanding of pigment pattern formation (Fig. 2.50). Houillon and Bagnara (1996) noted that “in chimeras between white and albino embryos, melanoblasts from the white half crossed the graft interface to differentiate in albino skin. Neural crest grafts from white embryos to albinos provided melanophores of white origin that were capable of differentiation in albino skin. Grafts of gonadal primordia from albino to white embryos provided albino germ cells that formed unpigmented ovocytes together with dark ovocytes: white ovocytes from the albino grafted ovary, and dark ovocytes from the host ovary. The donor albino white ectoderm included in the graft was able to support the differentiation of melanophores, iridophores, and xanthophores that invaded the graft ectoderm from the neural crest of the white host. It was concluded that manifestation of the white or wild phenotypes may be related to the possible presence or absence of inhibiting or stimulating pigmentary factors in the skin.” It seems possible that these respective inhibiting or stimulating factors are the circumscribed agents MIF and MSF that have been discussed.
Color Pattern Formation in Zebrafish Integumental color patterns of fish are amazingly diverse even among mutants or variants of a single species (Kirschbaum, 1975; Yamamoto, 1975). It is no wonder then that biologists and fish fanciers alike are attracted to them: the former to elucidate the mechanisms responsible for the expression of particular patterns and the latter to produce new and interesting color forms or patterns. With the advent of the present age of molecular genetics, the zebrafish, Danio rerio, and related species of this genus have become widely utilized as model organisms in studies on pattern formation. These species offer a wide choice of pigmentary mutants that are readily detectable through visible characteristics that are advantageous for the screening of mutations (Haffter et al., 1996). Integumental pigmentary patterns of adult zebrafish are
Fig. 2.49. The margin of a graft of ventral larval skin of R. pipiens to the dorsal surface. Note that, after metamorphosis, the typical adult skin was expressed and thus a precise margin is manifested between the heavily iridophore-laden ventral skin and the dorsal surface. The former is considered to contain a melanization-inhibiting factor (MIF) that inhibits melanization and stimulates iridophore expression (see also Plate 2.18, pp. 494–495).
characterized primarily by melanophores that form either narrow, horizontal stripes on the body, as seen in the wild type, or dispersed discrete spots as in the panther or leopard mutants (McClure, 1999; Quigley and Parichy, 2002; Rawls et al., 2001) (Fig. 2.51). In other related species of this genus, such as Danio malabaricus, melanophores are also involved in the development of complicated reticulations over the flank (McClure, 1999). All these color patterns of adults are formed after metamorphosis when the basic body structure switches from the larval to the adult form. In contrast to the diverse pigmentation patterns of wild-type or mutant adults of this genus, larvae display an essentially similar pigmentation pattern (McClure, 1999). Pigmentation of the larvae begins with the expression of melanophores in a few loose lines and is followed, with some delay, by the appearance of xanthophores distributed randomly. Based upon the onset of their appearance and cell size and density, 45
CHAPTER 2
A
B
A
B (a)
(b)
(c) C
(d)
(e)
Fig. 2.50. A. Two-year-old adult albino white chimeras. On the left chimera, note the clear line of demarcation separating the white (d/d) anterior half from the albino (a/a) posterior half. Some melanoblasts from the white half have migrated a short distance across the junction to differentiate and provide the black patches seen in the albino half. The same explanation applies to the chimera on the right except that, in this individual, white is posterior and albino anterior. Female on left, male on right (from Houillon and Bagnara, 1996). B. Two aD/aD albinos 2 years after having received neural crest grafts. Note the presence of melanophore patches distributed randomly in the dorsal area corresponding with the level of the neural crest graft. Female on left, male on right (from Houillon and Bagnara, 1996). C. A young adult female white Ad/Ad host 9 months after having received a gonadal primordium graft from an albino aD/aD donor. Note that the grafted albino integument is clearly delineated from that of the white host by its heavy pigmentation identical to that seen in wild-type individuals; both melanophores and iridophores are clearly visible. This female oviposited a majority of pigmented eggs corresponding with her dd genotype and a significant number of white eggs derived from albino (a/a) germ cells contained in the graft (from Houillon and Bagnara, 1996) (see also Plate 2.19, pp. 494–495).
it is considered that there are two types of melanophores in these fish, larval and adult types. The occurrence of larval- and adult-type melanophores during ontogeny is well known for other teleost species (Matsumoto et al., 1960; Matsumoto, 1965b). In wild-type zebrafish, adults are marked by several horizontal and regularly spaced melanophore stripes over the 46
(f)
(g)
Fig. 2.51. Schematic drawings of pigment (melanophore) patterns of zebrafish, Danio rerio, and its related species. (A) A larva of the wild-type zebrafish. (B) Adults: a, wild-type zebrafish; b, panther (fms) mutant; c, sparse (kit) mutant; d, rose (endothelin) mutant; e, nacre (mitf) mutant; f, D. kerri; g, D. malabaricus (adapted from McClure, 1999; Quigley and Parichy, 2002; Rawls et al., 2001).
flank. This pattern is known to form on the basis of two events: (1) intensive proliferation of adult-type melanophores at or after metamorphosis; and (2) expulsion of these melanophores by pre-existing xanthophores (Johnson et al., 1995; McClure, 1999). On the basis of the careful tracing of pigment cell development, McClure indicates clearly that adult-type melanophores appearing after metamorphosis are forced to coalesce, through contact with xanthophores, into lines along loosely aligned larval melanophore stripes, and that two populations of melanophores and xanthophores are gradually seg-
COMPARATIVE ANATOMY AND PHYSIOLOGY OF PIGMENT CELLS IN NONMAMMALIAN TISSUES
regated into two regions, narrow melanophore stripes with distinct margins and interspaces of xanthophores that are free of melanophores. The capacity of xanthophores to expel melanophores is clearly substantiated from observations of pigment pattern formation in the panther (fms), which lacks xanthophores in larval forms and in which stripes fail to form at metamorphosis. Instead, numerous tiny melanophorecontaining spots form over the adult body (Haffter et al., 1996; Johnson et al., 1995; McClure, 1999). It was also shown that the width of the black stripes, when xanthophores are present, depends upon the growth rate of adult-type melanophores appearing after metamorphosis and leading to the formation of wide stripes or large reticulations as a marked increase in their numbers occurs (Johnson et al., 1995; McClure, 1999; Quigley and Parichy, 2002). All these findings indicate that interactions between different pigment cell types, melanophores and xanthophores, and a genetically defined proliferation rate of xanthophores play crucial roles in pigment pattern formation in these fish. In some related species such as Danio albolineatus and Danio sp. cf. aequipinnatus, erythrophores have been shown to play a role in pattern formation similar to that of xanthophores. An apparent “hostile” relationship between adult-type melanophores and xanthophores is considered to function in maintaining stripes in a definitive pattern (McClure, 1999). When melanophore migration along the dorso-ventral axis is disrupted locally in the course of stripe formation, the regularity of stripe alignment is lost, resulting in irregular-shaped reticulations or patches as seen in Danio kerri or D. malabaricus (McClure, 1999). Additional factors leading to such distorted stripes may include the development of neuromasts in the migratory pathways of melanophores and an uneven distribution of extracellular matrix. As to the apparent hostile relationship between adult-type melanophores and xanthophores, the possibility is suggested that it derives from their differing dependency on fms and kit in the course of development from common precursors, as the former requires either kit or fms, depending upon lineage, while the latter definitely requires fms (Mellgren and Johnson, 2002; Parichy and Turner, 2003; Rawls and Johnson, 2000). With respect to cell adhesion molecules of chromatophores, it was shown in the fish medaka (Oryzias latipes) and the amphibian, Xenopus laevis, that N-CAM and N-cadherin are specifically expressed in xanthophores, but not in melanophores and iridophores (Fukuzawa and Obika, 1995). If the same holds true for zebrafish or its closely related species, such differences between melanophores and xanthophores may relate to a hostile relationship in their respective behaviors. It is interesting that this concept of chromatophore hostility, so well documented for zebrafish in modern studies, is a reaffirmation of the views of Twitty and Niu (1954), voiced more than 50 years ago from work on newts. Recent studies on zebrafish mutants with the use of the techniques of molecular genetics have disclosed that a variety of genes, most of which are orthologs of those in mammals, func-
tion in pigment cell development of this species and ultimately determine their pigmentation patterns (Haffter et al., 1996; Rawls et al., 2001). With respect to genes associated with melanophore development, the following mutations are known to be well-established examples (Fig. 2.51). In homozygous nacre (mitf ) mutants, no melanophores develop during embryonic, larval, and adult stages, indicating an absence of larval- and adult-type melanophores. In homozygous panther (fms) and rose (ednrb1) mutants, the proliferation of adulttype melanophores associated with body stripe formation is reduced, as mentioned previously, although fms and enrb1 are ortholog genes encoding, respectively, a type III receptor tyrosine kinase and a G-protein-coupled endothelin receptor B in mammals. In homozygous sparse (kit) mutants, the development of adult-type melanophores to be incorporated into body stripes and dorsal scales is disrupted. In double sparse (kit) and rose (ednrb1) mutants, two types of larval- and adulttype melanophores fail to develop, while a certain number of melanophores appear in the caudal and anal fins. In view of the development of caudal and anal fin melanophores in sparse and rose double mutants, even in the absence of larvaland adult-type melanophores in the flank, and in light of the development of melanophores having different requirements for kit in regenerating fins, it seems that four different classes or lineages exist in zebrafish (Rawls et al., 2001). Some of these genes associated with the fate of melanophores of this species are also implicated in the development of other types of chromatophores as exemplified by fms for adult-type xanthophores and ednrb1 for adult-type iridophores (Rawls et al., 2001). In addition, a group of genes such as pfeffer (pfe) and salz (sal) causes reduction in xanthophore populations, whereas another group including rose (rse), shady (shd), and transparent (tra) does the same for iridophores (Haffter et al., 1996; Rawls et al., 2001). With respect to mutations affecting melanogenesis itself in adults, a number of genes including albino (alb), mustard (mrd), and sandy (sdy) are reported to be incapable of supporting the production of melanin, and a group of brass (brs), fading vision (fdv), and golden (gol) express a phenotype of reduced melanin (Haffter et al., 1996). As studies of the molecular genetics of zebrafish pigmentation are largely facilitated by those on mammals, available information on pigment genes of this species is rather restricted to melanophores. The information so far derived indicates that the functions of pigmentation-associated genes in zebrafish are in essence comparable to those in mammals, except for the occurrence of a variety of melanophore lineages in this species. In view of the fact that Wnt-1 and Sox 10, essential for the development of mammalian neural crest, are expressed in developing melanophores of zebrafish (Rawls et al., 2001), it is evident that a common basis is shared in the development of pigment cells of both groups. Knowledge about pigment cells of lower vertebrates certainly provides a useful key for understanding the mechanisms of pigment pattern formation and its related phenomena in the vertebrate kingdom. 47
CHAPTER 2
Hormonal Influences on the Development of Pigmentation Patterns Because of its importance in morphological color change, MSH would seem to be a likely candidate as a major role player in pigment pattern formation. As was pointed out earlier, MSH exerts a powerful proliferative effect on melanophores (Pehlemann, 1967a, b, 1972) and, as shown in Figure 2.30, apparently stimulates the differentiation of latent melanoblasts (Bagnara and Fernandez, 1993). Its stimulatory effects can be so potent on some frogs that the normally pale ventrum is darkened (Figs 2.27 and 2.28) (Fernandez and Bagnara, 1991, 1993). The morphological effect stemming from the lack of MSH must also be considered when evaluating the expression of pigmentation patterns. In this case, iridophores are maximally expressed in the absence of MSH. As was pointed out earlier, Xenopus larvae deprived of MSH from the earliest larval stages develop iridophores in the tail fin (Fig. 2.26) where they normally never appear (Bagnara, 1957). One of the best examples of the influence of MSH on the expression of normal pigmentation patterns is that in wild isogenic populations of tiger salamanders, in which the environment markedly affects the amount of MSH secreted and thus the pigmentation pattern that is manifested (Fig. 2.33) (Fernandez and Collins, 1988). High-albedo environments result in low MSH levels and the high expression of iridophores that mask melanophore influences on pigmentation patterns. Low-albedo individuals secrete high levels of MSH and thus a pattern dominated by melanophores is expressed. As potent as these effects of MSH are on morphological color change, they nevertheless must not be construed as an indication that MSH is a primary determinant of pattern formation (Bagnara and Fernandez, 1993). In fact, a clearly formed pigmentation pattern of dorsal spots is manifested in leopard frogs hypophysectomized as embryos, but induced to metamorphose (Fig. 2.52). The role of MSH is not a causative one in the development of primary pigmentation patterns; rather, it is a modifier through its actions on the differentiation of latent chromatoblasts or on proliferation. Similarly, thyroxine plays a permissive role in pigment pattern formation through its general action on the skin, and thus on pigment pattern expression, at metamorphic climax (Bagnara, 1982).
Pigmentation Anomalies Obviously, in nature many undiscovered pigmentary abnormalities exist. These range from albinism and other color mutations to serious pathological conditions such as pigment cell malignancies. With the tremendous growth in the popularity of fishes, amphibians, and reptiles as pets, a large industry has grown up in the breeding of these poikilotherms, and color variants have been selected for. Unfortunately, the professional research community has not taken advantage of these variants for research, in large measure because of the lack of financial support for such seemingly esoteric studies. In contrast, pigment cell malignancies have been the focus of inves48
Fig. 2.52. A R. pipiens tadpole in metamorphic stasis due to an anomalous development of the hypophysis such that MSH is lacking and TSH is insufficient to induce metamorphic climax. Note the obvious onset of the formation of a typical spot pattern even in the absence of MSH.
tigation for many years and, in fact, the establishment of pigment cell biology as a recognized discipline (Bagnara, 1991) stems from the discovery of the Xiphophorine GordonKosswig Melanoma System. This subject has been reviewed frequently in recent years by Professor Fritz Anders, and thus the reader is referred to one of his important works (Anders, 1991). A lesser known malignancy is erythrophoroma from goldfish, an erythrophore neoplasm first described by Prince Masahito and his collaborators (Ishikawa et al., 1978), who ultimately established several lines of neoplastic erythrophores (Matsumoto et al., 1980) (Fig. 2.53). Later, uncloned cell lines of iridophores and melanophores were derived from an iridophore–melanophore tumor found on a marine teleost, the nibe croaker (Matsumoto et al., 1981). This neoplasm (iridomelanophoroma) metastasized on both dorsal and ventral regions of the fish with the melanophore component more prevalent in the dorsum and the iridophore phenotype more prevalent in the ventrum. It is tempting to speculate that the two phenotypes appear where they do as a result of the actions of MSF and MIF respectively. A similar neoplasm has been described from the pine snake (Fig. 2.54) (Jacobson et al., 1989). It was referred to as an iridosarcoma, but it appears very much like the irido-melanophoroma and has the capacity to transform from a largely iridophore type to one that is more phenotypically melanophore-like. Although the malignancy is primarily dermal, neoplastic cells seem to traverse the basement membrane with ease to invade the epidermis (Fig. 2.55). Lower vertebrate pigment cell neoplasms (chromatophoromas) have much to offer in basic research; however, little is being done with them at present. Very likely, there are numerous such malignancies that appear both in nature and in the colonies of fish, frog, and reptile breeders.
COMPARATIVE ANATOMY AND PHYSIOLOGY OF PIGMENT CELLS IN NONMAMMALIAN TISSUES
Fig. 2.53. Morphological properties of spontaneous cutaneous erythrophoromas and irido-melanophoromas occurring in teleost fish. Left column, erythrophoroma formed on the dorsal surface of an adult goldfish. Note that the tumor contains several growing nodules (middle). Component cells of the tumor, even in the central portion, are pigmented red to orange as are normal erythrophores present in the skin. Right column, the profiles of cells from the GEM 81 cell line of goldfish erythrophoromas (top), and nibe croaker irido-melanophoroma (middle and bottom) exhibiting either melano(phoro)ma-like pigmentation (middle) or iridophoroma-like cells (bottom) depending upon the site of the lesion. Scale bars = 100 mm (see also Plate 2.20, pp. 494–495).
Unfortunately, these usually escape the attention of pigment cell investigators; however, the case of the aforementioned goldfish erythrophoroma is an exception, for its discovery followed by appropriate investigation has led to valuable contributions to our knowledge of pigment cells. Interesting aspects of goldfish erythrophoroma cells are
their instability or multiplicity of phenotypic expression. The vast majority of erythrophoromas in situ are recognized by their yellow or orange pigmentation as a tumor of erythrophores, although some may contain a few black lumps composed of numerous melanophore-like cells (Ishikawa et al. 1978; Matsumoto et al., 1980). When these erythrophoroma 49
CHAPTER 2
cells are cultured in a standard culture medium in vitro as a permanent cell line derived from a sporadic tumor of orangecolored goldfish, they remain essentially unpigmented, although they may become pigmented following the addition of fish serum to the culture medium (Matsumoto et al., 1980; 1983). When these cells are subjected to factors that induce differentiation, viz. the use of carp serum in combination with
Fig. 2.54. An adult northern pine snake (Piterophia) with irregularly thickened and pitted black and white ventral scales. A large subcutaneous iridosarcoma nodule bulges to overlying skin (arrow) (from Jacobson et al., 1989).
dimethyl sulfoxide (DMSO) or others, they begin to form, mostly on a clonal basis, a variety of products such as melanin, reflecting substance, teeth- or bone-like structures, and lenslike bodies (Matsumoto et al., 1981, 1983, 1989) (Fig. 2.56). Cells expressing an abundance of melanin are essentially similar to melanophores with respect to both their dendritic appearance and their immense deposition of melanosomes and, upon clonal subcultivation, develop a responsiveness to aggregating or dispersing agents such as epinephrine or cAMP respectively (Matsumoto et al., 1982, 1989). Cells that contain a reflecting substance appear similar in profile to iridophores, as evidenced by the presence of bizarre-shaped platelets (Matsumoto et al., 1981, 1989). Within cell mounds that develop in long-sustained cultures of these cells are lentoid bodies that form occasionally and in which crystallins are detectable by immunochemical assay (Akiyama et al., 1986). In other cases, teeth-like structures are recognized within such cell mounds, suggesting their differentiation toward odontoblasts or the like (Matsumoto et al., 1983). In some cultures, neuron-like cells appear, extending thin, long dendrites that lack pigment deposition (Matsumoto et al., 1983). As most of the cell characteristics that are thus expressed are of neural crest origin (Weston, 1970), it is considered that immortalized erythrophoroma cells are neural crest stem cells in nature. It seems likely that previously described differentiations such as schwannomas or neurofibromas, etc. deriving from goldfish tumors (Duncan and Harkin, 1969) are manifestations of the multiplicity of possible phenotypic expression that these tumor cells are capable of. The capacity for multiple differentiation exhibited by both goldfish erythrophoroma cells and nibe iridomelanophoroma cells offers a wide potential for their use in studies of pigment cell differentiation.
Fig. 2.55. Dermal epidermal junction from an abnormal black scale from the affected region shown in the previous figure. Note the many abnormal iridophores (left) and a single iridophore in the corresponding epidermis just above the basement membrane (arrows). Magnification ¥ 3700 (modified from Jacobson et al., 1989).
50
COMPARATIVE ANATOMY AND PHYSIOLOGY OF PIGMENT CELLS IN NONMAMMALIAN TISSUES
Fig. 2.56. Multiple differentiation of goldfish erythrophoroma cells in vitro. Top, clone of melanophore-like cells that are capable of exhibiting pigmentary responses such as melanosome displacement from a dispersed state (left) to an aggregated state (right). Aggregation is induced by the addition of epinephrine at 5 ¥ 10-4 M. Arrows indicate corresponding sites of the clone. Middle, clone of iridophore-like cells that exhibit brownish profiles under a transmitted light (left) and reflectance under reflecting illumination (right). Bottom, formation of tooth-like (left) structures (arrows) and bone-like (right) structures (arrows) within a cell mound. Differentiation is induced by the administration of dimethyl sulfoxide (DMSO) and fish serum (see Matsumoto et al., 1989 for details). Bars indicate 50 mm for top/middle and 25 mm for bottom (see also Plate 2.21, pp. 494–495).
Perspectives Much of the knowledge discussed herein has accumulated during the last 50 years and, given the low number of scien-
tists engaged in the area of pigment cell research on lower vertebrates, there is a wealth of untapped knowledge to be gained. In order properly to take advantage of the opportunities offered by these lower vertebrates, investigators engaged in research on mammalian pigmentary problems must realize 51
CHAPTER 2
that the pigmentary phenomena studied in lower vertebrates are not necessarily unique to these lower forms. Lower vertebrate pigmentary problems should not be studied merely because, by analogy, they offer model systems for relatively distant mammalian or human phenomena. It must be realized that, frequently, homologies exist among the pigmentary phenomena displayed by lower and higher vertebrates alike. After all, the pigment cells of all vertebrates are of neural crest origin, and they migrate in a similar manner to distal sites where they respond to similar factors present in either the immediate area they occupy or in the organism as a whole. An exceedingly important problem about vertebrate pigment cells that needs study is that of chromatophore organellogenesis. The few studies available have indicated that melanosomes, reflecting platelets, and pterinosomes are of endoplasmic reticular origin (Bagnara et al., 1979), but little is known about details. Unlike the situation with respect to melanosome formation, which has been much studied for mammals and can thus be extrapolated to lower vertebrates, there is no such possibility for iridophores and xanthophores. Perhaps the reverse will be true one day when it becomes appreciated that vestiges of xanthophores and iridophores are present in the iris of homeotherms, which may serve as a refuge for these chromatophores that have long been considered to be unique to poikilotherms (Oliphant et al., 1992). A related problem and one ultimately related to the question of chromatophore characterization and identification concerns the mysterious pigmentary organelles that have been found in chromatophores of little-studied species such as the Centrollenid and Dendrobatid frogs mentioned earlier. A better understanding of these organelles can only be derived from studies on species of less recognized taxa. Probably, the existence of some of the unusual pigmentary organelles is related to specific ecological needs of the various taxa. Certainly, background color matching is an important antipredator behavior; however, it is possible that some of the unusual organelles contain pigments that help in other means of protection from predators. For example, Schwalm et al. (1977) have shown that some leaf-sitting frogs reflect infrared, and they suggest that this ability may confer advantages to the frogs with respect to both thermoregulation and infrared cryptic coloration. In this regard, some of the unusual organelles of poison arrow frogs, the Dendrobatids, may contain pigments that provide the bright warning colors typical of this group. Because of the rather favored status of ecological studies during present times, it is not unlikely that the role of chromatophores and their pigmentary organelles in topics such as thermoregulation, osmoregulation, predator avoidance, and reproduction stand a good chance for study. This is in contrast to the possibilities of studying chromatophores, merely for the sake of knowledge, for such investigations are too esoteric for these modern times. One of the intriguing aspects of chromatophore physiology that certainly needs investigation is that of photoreception. The suggestion that we made, almost 50 years ago, that
52
amphibian chromatophores may possess visual pigments (Bagnara, 1957), seems to have been vindicated by the demonstration that piscine chromatophores do, indeed, seem to possess visual pigments (Lythgoe and Thompson, 1984). However, this discovery seems to have escaped the attention of investigators of higher vertebrate pigmentation and of photobiology. Sooner or later, this knowledge will strike home, especially because of possible implications in the photobiology of tanning or in oncology. It would be fascinating, indeed, if it were found that some chromatophores of all types contain visual pigments, either those already characterized from the retina or entirely new types. Moreover, given the absence of the usual photoreceptive membranes typical of photoreceptors, it would be interesting to know whether the limiting membranes of the pigmentary organelles, themselves, serve as the surface repository for such pigments. Of possible relatedness to the question of direct light reception by chromatophores is the extracutaneous distribution of such cells. In one species or another, chromatophores occur in practically every internal organ, on blood vessels, body cavity linings, meninges, etc. It has been suggested that the presence of pigment cells and melanin in internal organs is related to the impact of solar radiation. It was beyond the scope of this chapter to delve into this subject, especially as much of the work is older and speculative; however, in this regard, two possible functions for these internal pigment cells stand out, thermoregulation and protection. As an example of the former, in a fascinating study by Guillete et al. (1983), it was discovered that one testis in several related species of spiny lizards is heavily melanized and is thus warmer. As a consequence, its spermatogenesis is accelerated over that of its partner. From the standpoint of protection, the presence of melanin in the kidney (Zuasti et al., 1989) and the liver (Sichel, 1988) has been viewed as being part of antioxidant systems based upon the reducing action of melanin. There is so little work being done in this area on lower vertebrates that it stands out as an important target for future investigation. Probably the area of research that holds the most promise for investigators of lower vertebrate pigmentation is that of pattern expression. In particular, the extrapolation of results stemming from mammalian molecular genetics to these lower forms has the most to offer. Earlier, it was commented upon that the putative MIF from amphibians is analogous to the agouti protein derived from the cloning of the gene from the mouse agouti locus. As can be seen from later chapters in this volume, several mammalian genes dealing with pigmentation have been characterized, and an array of mutations affecting mouse coat color have been described (see Jackson, 1994). Among the affected genes are those that affect melanocyte development and migration, melanocyte morphology, melanosomal structure and function, the enzymes of melanogenesis, and the MSH receptor. These characters are elements of pigment cell biology common to all vertebrates. Thus, it remains for the lower vertebrate counterparts of these mammalian genes to be found. Analyses of piscine and amphibian
COMPARATIVE ANATOMY AND PHYSIOLOGY OF PIGMENT CELLS IN NONMAMMALIAN TISSUES
tyrosinase genes and their products are well under way (Miura et al., 1995; Morrison et al., 1994; Peng et al., 1994; Takase et al., 1992; Yamamoto et al., 1992); however, genes dealing with pattern-specific products have not been extended to lower vertebrates. As mentioned earlier, attention to the nature of MSH receptors of lower vertebrates is just commencing. Such studies need to move forward with urgency given the important and varied roles of MSH in lower and higher vertebrates alike. The recent discovery by Valverde et al. (1995) that alterations in the MSH receptor markedly affect the pigmentary phenotype of man should provide special impetus to studies of MSH receptors and the genes that govern them in lower vertebrates. It is important to remember that the pigmentary systems of higher vertebrates are homologous to those of lower forms; thus, investigators involved in research at each of these levels should keep open minds and be able to apply knowledge obtained at one level to pigmentary problems of vertebrates at another level.
References Abe, K., W. Butcher, W. E. Nicholson, C. E. Bairde, R. A. Liddle, and G. W. Liddle. Adenosine 3,5-monophosphate (cyclic AMP) as the mediator of the actions of melanocyte stimulating hormone (MSH) and norepinephrine on the frog skin. Endocrinology 84:362–368, 1969. Ahlquist, R. P. A study of the adrenotropic receptors. Am. J. Physiol. 153:586–600, 1948. Akiyama, T., and J. Matsumoto. Implication of actin filaments in pigment aggregation of swordtail erythrophores. Pigment Cell 1981; Phenotypic Expression in Pigment Cells (Proceedings of the XIth International Pigment Cell Conference, Sendai, Japan, 1980), Tokyo University Press, pp. 417–426, 1981. Akiyama, T., and J. Matsumoto. The blockade of pigment displacement in swordtail erythrophores by microinjection of antiactin antibody. J. Exp. Zool. 227:405–411, 1983. Akiyama, T., J. Matsumoto, T. Ishikawa, and G. Eguchi. Production of crystallins and lens-like structures in differentiation-induced neoplastic pigment cells (goldfish erythrophoroma cells) in vitro. Differentiation 33:34–44, 1986. Akiyama, T., J. Matsumoto, and T. T. Tchen. An association of actin isoforms with the expression of motile response in pigmentation variants induced from goldfish erythrophoroma cells. Cell Differentiation, 20:271–277, 1987. Allen, B. M. Extirpation of the hypophysis and thyroid glands of Rana pipiens. Science 44:755–757, 1916. Anders, F. Contributions of the Gordon-Kosswig melanoma system to the present concept of neoplasia. Pigment Cell Res. 3:7–29, 1991. Andersson, T. P. M., S. P. S. Svensson, and A. M. Karlsson. Regulation of melanosome movement by MAP kinase. Pigment Cell Res. 15:215–221, 2003. Asai, D. J., and S. W. Lee. The structure and function of dynein heavy chains. Mol. Cells 5:299–305, 1995. Aspengren, S., H. N. Skold, G. Quiroga, L. Martensson, and M. Wallin. Noradrenalin- and melatonin-mediated regulation of pigment aggregation in fish melanophores. Pigment Cell Res. 16:59–64, 2003. Babak, E. Zur chromatischen Hautfunktion der Amphibien. Pflugers Arch. Gesamte Physiol. Menschen Tiere 131:87–118, 1910. Bagnara, J. T. Hypophysectomy and the tail-darkening reaction in Xenopus. Proc. Soc. Exp. Biol. Med. 94:572–575, 1957.
Bagnara, J. T. Hypophyseal control of guanophores in anuran larvae. J. Exp. Zool. 137:265–284, 1958. Bagnara, J. T. Pineal regulation of body lightening reaction in amphibian larvae. Science 132:1481–1483, 1960. Bagnara, J. T. Chromatotropic hormone, pteridines and amphibian pigmentation. Gen. Comp. Endocrinol. 1:124–133, 1961. Bagnara, J. T. The pineal and the body lightening reaction of larval amphibians. Gen. Comp. Endocrinol. 3:86–100, 1963. Bagnara, J. T. Independent actions of pineal and hypophysis in the regulation of chromatophores of anuran larvae. Gen. Comp. Endocrinol. 4:290–294, 1964a. Bagnara, J. T. Stimulation of melanophores and guanophores by MSH peptides. Gen. Comp. Endocrinol. 4:290–294, 1964b. Bagnara, J. T. Analyse des transformations des ptéridines de la peau au cours de la vie larvaire et à la métamorphose chez le Triton Pleurodeles waltlii Michah; Changements induits par l’action localisée d’implants de thyroxine-cholestérol. C. R. Acad. Sci. Paris 258: 5969–5971, 1964c. Bagnara, J. T. Pineal regulation of body blanching in amphibians. Prog. Brain Res. 10:299–303, 1965. Bagnara, J. T. Cytology and cytophysiology of non-melanophore pigment cells. Int. Rev. Cytol. 20:173–205, 1966a. Bagnara, J. T. Control of melanophores in amphibians. In: Symposium on Structure and Control of the Melanocyte, G. Dell Porta, and O. Muhlbock (eds). Heidelberg: Springer Verlag, 1966b, pp. 16– 28. Bagnara, J. T. Responses of pigment cells of amphibians to intermedin. In: La Specificité Zoologique des Hormones Hypophysaires et de Leurs Activities. Paris: Centre National de la Recherche Scientifique, 1969, pp. 153–159. Bagnara, J. T. Interrelationships of melanophores, iridophores, and xanthophores. In: Pigmentation: Its Genesis and Biological Control, V. Riley (ed.). New York: Appleton Century Crofts, 1972, pp. 171–180. Bagnara, J. T. The tail-darkening reaction of phyllomedusine tadpoles. J. Exp. Zool. 187:149–154, 1974. Bagnara, J. T. Color change. In: Physiology of the Amphibia, vol. 3, B. Lofts (ed.). New York: Academic Press, 1976, pp. 1–52. Bagnara, J. T. Development of the spot pattern in the leopard frog. J. Exp. Zool. 224:283–287, 1982. Bagnara, J. T. Developmental aspects of vertebrate chromatophores. Am. Zool. 23:465–478, 1983. Bagnara, J. T. The amphibian egg as a pigment cell. Pigment Cell 6:277–281, 1985. Bagnara, J. T. The neural crest as a source of stem cells. In: Developmental and Evolutionary Aspects of the Neural Crest, P. F. A. Maderson (ed.). New York: J. Wiley & Sons, 1987, pp. 57–87. Bagnara, J. T. An historical perspective on pigment cell biology from the editor. Pigment Cell Res. 4:2–6, 1991. Bagnara, J. T. Enigmas of pterorhodin, a red melanosomal pigment of tree frogs. Pigment Cell Res. 16:510–516, 2003. Bagnara, J. T., and P. J. Fernandez. Hormonal influences on the development of amphibian pigmentation patterns. Zool. Sci. 10:733– 748, 1993. Bagnara, J. T., and W. Ferris. Interrelationship of chromatophores. In: Biology of Normal and Abnormal Melanocytes, T. Kawamura, T. B. Fitzpatrick, and M. Seiji (eds). Tokyo: University of Tokyo Press, 1971, pp. 57–76. Bagnara, J. T., and W. Ferris. Localization of rhodomelanochrome in melanosomes of leaf frogs. J. Exp. Zool. 190:367–372, 1974. Bagnara, J. T., and W. Ferris. The presence of phyllomedusine melanosomes and pigments in Australian hylids. Copeia 3:592–595, 1975. Bagnara, J. T., and T. Fukuzawa. Stimulation of cultured iridophores by amphibian ventral conditioned medium. Pigment Cell Res. 3: 243–250, 1990.
53
CHAPTER 2 Bagnara, J. T., and M. E. Hadley. Control of bright colored pigment cells of fishes and amphibians. Am. Zool. 9:465–478, 1969. Bagnara, J. T., and M. E. Hadley. Endocrinology of the amphibian pineal. Am. Zool. 10:201–216, 1970a. Bagnara, J. T., and M. E. Hadley. Intermedin-like effect of a thermal polymer on vertebrate chromatophores. Experientia 26:167–169, 1970b. Bagnara, J. T., and M. E. Hadley. Chromatophores and Color Change: The Comparative Physiology of Animal Pigmentation. Englewood Cliffs, NJ: Prentice-Hall, 1973. Bagnara, J. T., and S. Neidleman. Effect of chromatotropic hormones on pigments of anuran skin. Proc. Soc. Exp. Biol. Med. 97: 671–673, 1958. Bagnara, J. T., and M. Obika. Comparative aspects of integumental pteridine distribution among amphibians. Comp. Biochem. Physiol. 15:33–49, 1965. Bagnara, J. T., and M. Obika. Light sensitivity of melanophores in neural crest transplants. Experientia 23:155–157, 1967. Bagnara, J. T., and J. D. Taylor. Differences in pigment-containing organelles between color forms of the red-backed salamander, Plethodon cinereus. Z. Zellforsch. Mikroskop. Anat. 106:412–417, 1970. Bagnara, J. T., J. D. Taylor, and M. E. Hadley. The dermal chromatophore unit. J. Cell Biol. 38:67–69, 1968. Bagnara, J. T., M. E. Hadley, and J. D. Taylor. Regulation of bright colored pigmentation of amphibians. Gen. Comp. Endocrinol. Suppl. 2:425–438, 1969. Bagnara, J. T., J. D. Taylor, and G. Prota. Color changes, unusual melanosomes, and a new pigment from leaf frogs. Science 182: 1034–1035, 1973. Bagnara, J. T., W. Ferris, W. A. Turner, and J. D. Taylor. Melanophore differentiation in leaf frogs and the deposition of a new pigment. Dev. Biol. 65:149–163, 1978a. Bagnara, J. T., S. K. Frost, and J. Matsumoto. On the development of pigment patterns in amphibians. Am. Zool. 18:301–312, 1978b. Bagnara, J. T., J. Matsumoto, W. Ferris, S. K. Frost, W. A. Turner Jr., T. T. Tchen, and J. D. Taylor. On the common origin of pigment cells. Science 203:410–415, 1979. Bagnara, J. T., K. L. Kreutzfeld, P. J. Fernandez, and A. C. Cohen. The presence of pteridine pigments in iridophore reflecting platelets. Pigment Cell Res. 1:361–365, 1988. Baker, B. I. The role of melanin concentrating hormone in color change. Ann. N. Y. Acad. Sci. 680:279–289, 1993. Beckerle, M. C., and K. R. Porter. Inhibitors of dynein activity block intracellular transport in erythrophores. Nature 295:701–703, 1982. Bikle, C., L. G. Tilney, and K. R. Porter. Microtubules and pigment migration in melanophores of Fundulus heteroclitus. Protoplasma 61:322–365, 1966. Bitensky, M. W., and S. R. Burstein. Effects of cyclic adenosine monophosphate and melanocyte-stimulating hormone on frog skin in vitro. Nature 208:1282–1284, 1965. Bogenschütz, H. Extraokulare Steuerung des Farbwechsels bei Qualquappen. Experientia 21:541–543, 1965. Bradshaw, S. D., and H. Waring. Comparative studies on the biological activity of melanin-dispersing hormone (MDH). In: La Specificité Zoologique des Hormones Hypophysaires et de leurs Activities. Paris: Centre National de la Recherche Scientifique, 1969, pp. 135–152. Brücke, E. Untersuchungen über den Farbwechsel des afrikanischen Chamaleons. Denkschr. Akad. Wiss. Wien 4:179–210, 1852. Burgers, A. C. J., and G. J. van Oordt. Regulation of pigment migration in the amphibian melanophore. Gen. Comp. Endocrinol. Suppl. 1:99–109, 1962. Burgers, A. C. J., ThA. C. Boschman, and J. C. van de Kamer. Excitement darkening and the effect of adrenaline on the melanophores of Xenopus laevis. Acta Endocrinol. 14:72–82, 1953.
54
Butcher, E. O. The structure of the retina of Fundulus heteroclitus and the regions of the retina associated with the different chromatophoric responses. J. Exp. Zool. 79:275–297, 1938. Butcher, R. W., and E. W. Sutherland. Adenosine 3¢,5¢-phosphate in biological materials: Purification and properties of cyclic 3¢,5¢nucleotide phosphodiesterase and use of this enzyme to characterize adenosine 3¢,5¢-phosphate in human urine. J. Biol. Chem. 237:1244–1250, 1962. Chang, C. Y. Thyroxine effect on melanophore contraction in Xenopus laevis. Science 126:121–122, 1957. Charlton, H. M. The pineal gland and colour change in Xenopus laevis Daudin. Gen. Comp. Endocrinol. 7:384–397, 1966. Clark, T. G., and J. L. Rosenbaum. Pigment particle translocation in detergent-permeabilized melanophores of Fundulus heteroclitus. Proc. Natl. Acad. Sci. USA 79:4655–4659, 1982. Cohen, A. G. Observations on the pars intermedia of Xenopus laevis. Nature 215:55–56, 1967. Cone, R. D., K. G. Mountjoy, L. S. Robbins, J. H. Nadeau, K. R. Johnson, L. Roselli-Rehfuss, and M. T. Mortrud. Cloning and functional characterization of a family of receptors for the melanotropic peptides. Ann. N. Y. Acad. Sci. 680:342–363, 1993. Daniolos, A., A. B. Lerner, and M. R. Lerner. Action of light on frog pigment cells in culture. Pigment Cell Res. 3:38–43, 1990. Dawes, B. The melanin content of the skin of Rana temporaria under normal conditions and after prolonged light and dark adaptation. A photometric study. J. Exp. Biol. 18:26–49, 1941. Dawson, D. C., and C. L. Ralph. Neural control of the amphibian pars intermedia: Electrical responses evoked by illumination of the lateral eyes. Gen. Comp. Endocrinol. 16:611–614, 1971. Dores, R. M., T. C. Steveson, and M. L. Price. A view of Nacetylation of a-melanocyte stimulating hormone and b-endorphin from a phylogenetic perspective. Ann. N. Y. Acad. Sci. 680:161– 174, 1993. Duncan, T. E., and J. C. Harkin. Electron microscopic studies of goldfish tumors previously termed neurofibroma and schwannomas. Am. J. Pathol. 55:191–202, 1969. DuShane, G. P. An experimental study of the origin of pigment cells in Amphibia. J. Exp. Zool. 72:1–31, 1935. Eakin, R. M. The Third Eye. Berkeley: University of California Press, 1973. Ebisawa, T., S. Karne, M. R. Lerner, and S. M. Reppert. Expression cloning of a high-affinity melatonin receptor from Xenopus dermal melanophores. Proc. Natl. Acad. Sci. USA 91:6133–6137, 1994. Enami, M. Melanophore-concentrating hormone (MCH) of possible hypothalamic origin in the catfish Parasilurus. Science 121:36–37, 1955. Etkin, W. On the control of growth and activity of the pars intermedia of the pituitary by the hypothalamus in the tadpole. J. Exp. Zool. 86:113–139, 1941. Etkin, W. Hypothalamic inhibition of the pars intermedia activity in the frog. Gen. Comp. Endocrinol. Suppl. 1:70–79, 1962a. Etkin, W. Neurosecretory control of the pars intermedia. Gen. Comp. Endocrinol. 2:161–169, 1962b. Euteneuer, U., and J. R. McIntosh. Polarity of some motility-related microtubules. Proc. Natl. Acad. Sci. USA 78:372–376, 1981. Fernandez, P. J. Purine and pteridine pigments of light- and dark-colored Arizona tiger salamanders. J. Exp. Zool. 245:121–129, 1988. Fernandez, P. J., and J. T. Bagnara. Effect of background color and low temperature on skin color and circulating a-MSH in two species of leopard frog. Gen. Comp. Endocrinol. 83:132–141, 1991. Fernandez, P. J., and J. T. Bagnara. Observations on the development of leopard frog ventral skin pigmentation. J. Morphol. 216:9–15, 1993. Fernandez, P. J., Jr., and J. P. Collins. Effect of environment and ontogeny in color pattern variation in Arizona tiger salamanders
COMPARATIVE ANATOMY AND PHYSIOLOGY OF PIGMENT CELLS IN NONMAMMALIAN TISSUES (Ambystoma tigrinum nebulosum hallowell). Copeia 4:928–938, 1988. Fitzpatrick, T. B., and A. S. Breathnach. Das epidermale melamimeinheit System. Dermatol. Wochenschr. 147:481–489, 1963. Fitzpatrick, T. B., W. C. Quevedo Jr., A. L. Levene, V. J. McGovern, Y. Mishima, and A. G. Oettle. Terminology of vertebrate melanincontaining cells: 1965. Science 152:88–89, 1966. Forbes, M. S., R. A. Zaccaria, and J. N. Dent. Developmental cytology of chromatophores in the red-spotted newt. Am. J. Anat. 137:37–72, 1973. Fox, D. L. Animal Biochromes and Structural Colours. London: Cambridge University Press, 1953. Fox, H. M., and G. Vevers. The Nature of Animal Colour. New York: Macmillan, 1960. Frost, S. K. 1978. Developmental aspects of pigmentation in the Mexican leaf frog, Pachymedusa dacnicolor. PhD Dissertation. University of Arizona, Tucson. Frost, S. K., and J. T. Bagnara. Allopurinol-induced melanism in the tiger salamander (Ambystoma tigrinum nebulosum). J. Exp. Zool. 209:455–465, 1978. Fujii, R. Coloration and chromatophores. In: The Physiology of Fishes, D. H. Evans (ed.). Boca Raton: CRC Press, 1993a, pp. 535–562. Fujii, R. Cytophysiology of fish chromatophores. Int. Rev. Cytol. 143:191–265, 1993b. Fujii, R., H. Kasukawa, K. Miyaji, and H. Oshima. Mechanism of skin coloration and its changes in blue-green damselfish, Chromis viridis. Zool. Sci. 6:477–486, 1989. Fukuzawa, T. Unusual leucophore-like cells specifically appear in the lineage of melanophores in the periodic albino mutant of Xenopus laevis. Pigment Cell Res. 17:252–261, 2004. Fukuzawa, T., and J. T. Bagnara. Control of melanoblast differentiation in amphibia by a-melanocyte stimulating hormone, a serum melanization factor and a melanization inhibiting factor. Pigment Cell Res. 2:171–181, 1989. Fukuzawa, T., and H. Ide. A ventrally localized inhibitor of melanization in Xenopus laevis skin. Dev. Biol. 129:25–36, 1988. Fukuzawa, T., and M. Obika. N-CAM and N-Cadherin are specifically expressed in xanthophores, but not in the other types of pigment cells, melanophores, and iridophores. Pigment Cell Res. 8:1–9, 1995. Fukuzawa, T., P. Samaraweera, F. T. Mangano, J. H. Law, and J. T. Bagnara. Evidence that MIF plays a role in the development of pigmentation patterns in the frog. Dev. Biol. 167:148–158, 1995. Goda, M., and R. Fujii. Blue chromatophores in two species of Callionymid fish. Zool. Sci. 12:811–813, 1995. Goldman, J. M., and M. E. Hadley. The beta adrenergic receptor and cyclic 3¢,5¢-adenosine monophosphate: Possible roles in the regulation of melanophore responses of the spadefoot toad, Scaphiopus couchi. Gen. Comp. Endocrinol. 13:151–163, 1969. Graham, J. D. P. The response to catecholamines of the melanophores of Xenopus laevis. J. Physiol. 158:5p–6p, 1961. Graminski, G. F., C. K. Jayawickreme, M. N. Potenza, and M. R. Lerner. Pigment dispersion in frog melanophores can be induced by a phorbol ester or stimulation of a recombinant receptor that activates phospholipase C. J. Biol. Chem. 268:5957–5964, 1993. Gross, S. P., M. C. Tuma, S. W. Deacon, A. S. Serpinskaya, A. R. Reilein, and V. I. Gelfand. Interactions and regulation of molecular motors in Xenopus melanophores. J. Cell Biol. 156:855–856, 2002. Guillette, L. J. Jr., J. Weigel, and G. Flater. Unilateral testicular pigmentation in the Mexican lizard Sceloporus varabilis. Copeia 1983:155–161, 1983. Hadley, M. E. 1966. Cytophysiological studies on the chromatophores of Rana pipiens. PhD Thesis. Brown University, Providence, Rhode Island.
Hadley, M. E., and J. T. Bagnara. Integrated nature of chromatophore responses in the in vitro frog skin bioassay. Endocrinology 84:69–82, 1969. Hadley, M. E., and J. T. Bagnara. Regulation of release and mechanism of action of MSH. Am. Zool. 14 (Suppl. 1):81–84, 1975. Hadley, M. E., and J. M. Goldman. Adrenergic receptors and geographical variation in Rana pipiens chromatophore responses. Am. J. Physiol. 219:72–77, 1970. Hadley, M. E., and W. C. Quevedo Jr. The role of epidermal melanocytes in adaptive color changes in amphibians. Adv. Biol. Skin 8:337–359, 1967. Haffter, P., J. Odenthal, M. C. Mullins, S. Lin, M. J. Farrell, E. Vogelsang, F. Haas, M. Brand, F. J. M. van Eeden, M. FurutaniSeiki, M. Granato, M. Hammerschmidt, C. Heisenberg, Y. Jiang, D. A. Kane, R. N. Kelsh, N. Hopkins, and C. Nusslein-Volhard. Mutations affecting pigmentation and shape of the adult zebrafish. Dev. Genes Evol. 206:260–276, 1996. Haimo, L. T., and C. D. Thaler. Regulation of organelle transport: lessons from color change in fish. Bioassays 16:727–733, 1994. Heward, C. B., and M. E. Hadley. Structure–activity relationship of melatonin and related indoleamines. Life Sci. 17:1167–1178, 1975. Himes, P. J., and M. E. Hadley. In vitro effects of steroid hormones on frog melanophores. J. Invest. Dermatol. 57:337–343, 1971. Hogben, L. T., and F. R. Winton. The pigmentary effector system. III. Colour response in the hypophysectomized frog. Proc. R. Soc. Lond. B Biol. Sci. B95:15–31, 1924. Horikawa, N. Kinesin and dynein superfamily proteins and the mechanism of organelle transport. Science 279:519–526, 1998. Horikawa, N., Y. Noda, and Y. Okada. Kinesin and dynein superfamily proteins in organelle transport and cell division. Curr. Opin. Cell Biol. 10:60–73, 1998. Horowitz, S. B. The energy requirements of melanin granule aggregation and dispersion in the melanophores of Anolis carolinensis. J. Cell. Comp. Physiol. 51:341–357, 1958. Houillon, C., and J. T. Bagnara. Insights into pigmentary phenomena provided by grafting and chimera formation in the axolotl. Pigment Cell Res. 9:281–288, 1996. Hruby, V. J., D. Lu, S. D. Sharma, A. de L Castrucci, R. A. Kesterson, F. A. Al-Obeidi, M. E. Hadley, and R. D. Cone. Cyclic lactam a-melanotropin analogues of Ac-Nle4-c[Asp5,D-Phe7,Lys10]a-MSH(4–10)-NH2 with bulky aromatic amino acids at position 7 show high antagonist potency and selectivity at specific melanocortin receptors. J. Med. Chem. 38:3454–3461, 1995. Ide, H. Transdifferentiation of amphibian chromatophores. In: Current Topics in Developmental Biology, vol. 20, T. S. Okada (ed.). New York: Academic Press, 1986, pp. 79–87. Iga, T., and J. T. Bagnara. An analysis of color change phenomena in the leaf frog, Agalychnis dacnicolor. J. Exp. Zool. 192:331–342, 1975. Iga, T., and J. T. Bagnara. Inhibition of melanosome migration in tailfin melanophores of Xenopus tadpoles in oxygen-free media. J. Exp. Zool. 198:273–279, 1976. Iga, T., and I. Takabatake. Local light stimulation of melanophores of a teleost, Zacco temmincki. J. Exp. Zool. 238:385–391, 1986. Imai, K. Color change and pituitary function of Xenopus laevis. In: Biology of Normal and Abnormal Melanocytes, T. Kawamura, T. B. Fitzpatrick, and M. Seiji (eds). Tokyo: University of Tokyo Press, 1971, pp. 17–29. Ishikawa, T., P. Masahito, J. Matsumoto, and S. Takayama. Morphologic and biological characterization of erythrophoromas in goldfish (Carassius auratus). J. Natl. Cancer Inst. 61:1461–1470, 1978. Jackson, I. J. Molecular and developmental genetics of mouse coat color. Annu. Rev. Genet. 28:189–217, 1994. Jacobson, E. R., W. Ferris, J. T. Bagnara, and W. O. Iverson. Chromatophoromas in a pine snake. Pigment Cell Res. 2:26–33, 1989.
55
CHAPTER 2 Johnson, S. L., D. Africa, C. Walker, and J. A. Weston. Genetic control of adult pigment stripe development in zebrafish. Dev. Biol. 167: 27–33, 1995. Johnson, W. C., P. Samaraweera, A. Zuasti, J. H. Law, and J. T. Bagnara. Preliminary biological characterization of a melanization stimulating factor (MSF) from the dorsal skin of the channel catfish, Ictalurus punctatus. Life Sci. 51:1229–1236, 1992. Kanost, M. R., J. K. Kawooya, J. H. Law, R. O. Ryan, M. C. Van Heusden, and R. Ziegler. Insect haemolymph proteins. Adv. Insect Physiol. 22:299–396, 1990. Karki, S., and E. L. Holzbaur. Cytoplasmic dynein and dynactin in cell division and intracellular transport. Curr. Opin. Cell Biol. 11:45–53, 1999. Katoh, S., and M. Akino. Biosynthesis of tetrahydrobiopterin in animals. Zool. Sci. 3:745–757, 1986. Kawauchi, H., I. Kawazoe, M. Tsubokawa, M. Kishida, and B. I. Baker. Characterization of melanin-concentrating hormone in chum salmon pituitaries. Nature 305:321–333, 1983. Kawooya, J. K., P. S. Keim, J. H. Law, C. T. Riley, R. O. Riley, and J. P. Shapiro. Why are green caterpillars green? ACS Symp. Series 276:511–521, 1985. Kimler, V. A., and J. D. Taylor. Ultrastructural immunogold localization of some organelle-transport relevant proteins in wholemounted permeabilized nonextracted goldfish xanthophores. Pigment Cell Res. 8:75–82, 1995. Kirschbaum, F. Untersuchungen uber das Farbmuster der Zebrabarbe Brachydanio rerio (Cyprinidae, Teleostei). Roux’s Arch. Dev. Biol. 177:129–152, 1975. Kollros, J., and J. C. Kaltenbach. Local metamorphosis of larval skin of Rana pipiens. Physiol. Zool. 25:163–170, 1952. Kuhlemann, H. Untersuchungen der Pigmentbewegungen in embryonalen Melanophores von Xenopus laevis in Gewebekulturen. Zool. Jahrb. 69:169–197, 1960. Langford, G. M. Actin- and microtubule-dependent organelle motors: Interrelationships between the two motility systems. Curr. Opin. Cell Biol. 7:82–88, 1995. Laurens, H. The reactions of the melanophores of Amblystoma larvae. J. Exp. Zool. 18:577–638, 1915. Laurens, H. The reactions of the melanophores of Amblystoma tigrinum larvae to light and darkness. J. Exp. Zool. 23:195–205, 1917. Lee, T. H., A. B. Lerner, and V. Buettner-Janusch. Species differences and structural requirements for melanocyte-stimulating hormones. Ann. N. Y. Acad. Sci. 100:658–668, 1963. Lehman, H. E., and L. M. Youngs. Extrinsic and intrinsic factors influencing amphibian pattern formation. In: Pigment Cell Biology, M. Gordon (ed.). New York: Academic Press, 1959, pp. 1–48. Lerner, A. B. The discovery of the melanotropins. A history of pituitary endocrinology. Ann. N. Y. Acad. Sci. 680:1–12, 1993. Lerner, A. B., K. Shizume, and I. Bunding. The mechanism of endocrine control of melanin pigmentation. J. Clin. Endocrinol. Metab. 14:1463–1469, 1954. Lerner, A. B., J. D. Case, Y. Takahashi, T. H. Lee, and W. Mori. Isolation of melatonin, the pineal factor that lightens melanocytes. J. Am. Chem. Soc. 80:2587–2593, 1958. Lo, S. J., T. T. Tchen, and J. D. Taylor. Hormone-induced filopodium formation and movement of pigment, carotenoid droplets, into newly formed filopodia. Cell Tissue Res. 210:371–382, 1980. Lopez-Contreras, A., J. H. Martinez-Liarte, F. Solano, P. Samaraweera, J. M. Newton, and J. T. Bagnara. The amphibian melanizing inhibiting factor (MIF) blocks the a-MSH effect on mouse malignant melanocytes. Pigment Cell Res. 9:311–316, 1996. Lu, D., D. Willard, I. R. Patel, S. Kadwell, L. Overton, T. Kost, M. Luther, W. Chen, R. P. Woychik, W. O. Wilkison, and R. D. Cone. Agouti protein is an antagonist of the melanocyte-stimulatinghormone receptor. Nature 371:799–802, 1994.
56
Luby, K. J., and K. R. Porter. The control of pigment migration in isolated erythrophores of Holocentrus ascensionis (Osbeck). I. Energy requirement. Cell 21:13–23, 1980. Lythgoe, J. N., and M. Thompson. A porphyropsin-like action spectrum from Xenopus melanophores. Photochem. Photobiol. 40:411–412, 1984. Lythgoe, J. N., J. Shand, and R. G. Foster. Visual pigment in fish iridocytes. Nature 308:83–98, 1984. Malawista, S. E. On the action of colchicine. J. Exp. Med. 122: 361–384, 1965. Malawista, S. E. The melanocyte model: colchicine like effects of other antimitotic agents. J. Cell Biol. 49:848–855, 1971. Mangano, F., T. Fukuzawa, W. C. Johnson, and J. T. Bagnara. Intrinsic pigment cell stimulating activity in the skin of the leopard frog, Rana pipiens. J. Exp. Zool. 263:112–118, 1992. Marinetti, G. V., and J. T. Bagnara. Yolk pigments of the Mexican leaf frog. Science 203:410–415, 1982. Marinetti, G. V., and J. T. Bagnara. Characterization of blue and yellow pigments in eggs of the Mexican leaf frog. Biochemistry 22:5651–5655, 1983. Marsland, D. A. Mechanism of pigment displacement in unicellular chromatophores. Biol. Bull. Acad. Sci. USSR 87:252–261, 1944. Masada, M., J. Matsumoto, and M. Akino. Biosynthetic pathways of pteridines and their association with phenotypic expression in vitro in normal and neoplastic pigment cells from goldfish. Pigment Cell Res. 3:61–70, 1990. Matsui, K., J. Marunouchi, and M. Nakamura. An ultrastructural and carotenoid analysis of the red ventrum of the Japanese newt, Cynops pyrrhogaster. Pigment Cell Res. 15:265–272, 2002. Matsumoto, J. Studies on fine structure and cytochemical properties of erythrophores in swordtail, Xiphophorus helleri, with special reference to their pigment granules. J. Cell Biol. 27:493–504, 1965a. Matsumoto, J. Role of pteridines in the pigmentation of chromatophores in cyprinid fish. Jap. J. Zool. 14:45–94, 1965b. Matsumoto, J., and M. Obika. Morphological and biochemical characterization of goldfish erythrophores and their pterinosomes. J. Cell Biol. 39:233–250, 1968. Matsumoto, J., T. Kajishima, and T. Hama. Relation between the pigmentation and pterin derivatives of chromatophores during development in the normal black and transparent scaled types of goldfish (Carassius auratus). Genetics 45:1177–1189, 1960. Matsumoto, J., Y. Watanabe, M. Obika, and M. E. Hadley. Mechanisms controlling pigment movements within swordtail (Xiphophorus helleri) erythrophores in primary cell culture. Comp. Biochem. Physiol. Part A 61:509–517, 1978. Matsumoto, J., T. Ishikawa, P. Masahito, and S. Takayama. Permanent cell lines from erythrophoromas in goldfish (Carassius auratus). J. Natl. Cancer Inst. 66:879–890, 1980. Matsumoto, J., T. Ishikawa, P. Masahito, A. Oikawa, and S. Takayama. Multiplicity in phenotypic expression of fish erythrophoroma and iridomelano-phoroma cells in vitro. In: Phyletic Approaches to Cancer, C. J. Dawe, J. C. Harshbarger, S. Kondo, T. Sigimura, and S. Takayama (eds). Tokyo: Japan Scientific Society Press, 1981, pp. 253–266. Matsumoto, J., T. J. Lynch, S. M. Grabowski, J. D. Taylor, and T. T. Tchen. Induction of melanized cells from a goldfish erythrophoroma: isolation of pigment translocation variants. Science 217: 1149–1151, 1982. Matsumoto, J., T. J. Lynch, S. Grabowski, C. M. Richards, S. L. Lo, C. Clark, D. Kern, J. D. Taylor, T. T. Tchen, T. Ishikawa, Prince Masahito, and S. Takayama. Fish tumor pigment cells: differentiation and comparison to their normal counterparts. Amer. Zool., 23:569–580, 1983. Matsumoto, J., T. Akiyama, and M. Nakabari. Surface morphology of fish pigment cells: Its roles in analyses of their motility and func-
COMPARATIVE ANATOMY AND PHYSIOLOGY OF PIGMENT CELLS IN NONMAMMALIAN TISSUES tional differentiation. Scanning Electron Microsc III:1279–1288, 1984. Matsumoto, J., K. Wada, and T. Akiyama. Neural crest cell differentiation and carcinogenesis: capability of goldfish erythrophoroma cells for multiple differentiation and clonal polymorphism in their melanogenic variants. J. Invest. Dermatol. 92 (Suppl.):255–260, 1989. McClure, M. Development and evolution of melanophore patterns in fishes of the genus Danio (Teleostei: Cyprinidae). J. Morphol. 241:83–105, 1999. McCord, C. P., and F. P. Allen. Evidences associating pineal gland function with alterations in pigmentation. J. Exp. Zool. 23: 207–224, 1917. McGuire, J., and G. Moellmann. Cytochalasin B: effects on microfilaments and movement of melanin granules within melanocytes. Science 175:642–644, 1972. McNiven, M. A., and K. R. Porter. Microtubule polarity confers direction to pigment transport in chromatophores. J. Cell Biol. 103: 1547–1555, 1986. McNiven, M. A., M. A. M. Wang, and K. R. Porter. Microtubule polarity and the direction of pigment transport reverse simultaneously in surgical severed melanophore arms. Cell 37:753–756, 1984. Mellgren, E. M., and S. L. Johnson. The evolution of morphological complexity in zebrafish stripes. Trends Genet. 18:128–134, 2002. Menter, D. G., M. Obika, T. T. Tchen, and J. D. Taylor. Leucophores and iridophores of Fundulus heteroclitus: Biophysical and ultrastructural properties. J. Morphol. 160:103–120, 1979. Miller, M. W., D. M. J. Duhl, H. Vrieling, S. P. Cordes, M. M. Ollmann, B. M. Winkes, and G. S. Barsh. Cloning of the mouse agouti gene predicts a secreted protein ubiquitously expressed in mice carrying the lethal yellow mutation. Genes Dev. 7:454–467, 1993. Misuraca, G., G. Prota, S. K. Frost, and J. T. Bagnara. Identification of the leaf-frog melanophore pigment, rhodomelanochrome, as pterorhodin. Comp. Biochem. Physiol. [A] Physiol. 57B:41–43, 1977. Miura, I., H. Okumoto, K. Makino, A. Nakata, and M. Nishioka. Analysis of the tyrosinase gene of the Japanese pond frog, Rana nigromaculata: Cloning and nucleotide sequence of the genomic DNA containing the tyrosinase gene and its flanking regions. Jpn. J. Genet. 70:79–92, 1995. Mori, Y., J. Matsumoto, and T. Hama. On the properties of Cyrinopourpre A2, a pterin isolated from the skin of Cypriinidae, and its relation to Ichthyopterin or 7-hydroxybiopterin. Zeitschr. Vergl. Physiol. 43:531–543, 1960. Morrison, R. L. A transmission electron microscopic (TEM) method for determining structural colors reflected by lizard iridophores. Pigment Cell Res. 8:28–36, 1995. Morrison, R., K. Mason, and S. Frost-Mason. A cladistic analysis of the evolutionary relationships of the members of the tyrosinase gene family using sequence data. Pigment Cell Res. 7:388–393, 1994. Nagaishi, H., and N. Oshima. Neural control of motile activity of light-sensitive iridophores in the neon tetra. Pigment Cell Res. 2:485–492, 1989. Naughten, J. C. 1971. Tissue interaction and the development of the dermal plicae of Rana pipiens. PhD Thesis. University of Iowa. Negishi, S., and M. Obika. The effects of melanophore-stimulating hormone and cyclic nucleotides on teleost fish chromatophores. Gen. Comp. Endocrinol. 42:471–476, 1980. Negishi, S., H. R. Fernandez, and M. Obika. The effects of dynein ATPase inhibitors on melanosome translocation within melanophores of the medaka, Oryzias latipes. Zool. Sci. 2:469–475, 1985. Nery, L. E., and A. M. Castrucci. Pigment cell signalling for physiological color change. Comp. Biochem. Physiol. 118A(4):1135–1144, 1997.
Nicol, C. A., G. K. Smith, and D. S. Duck. Biosynthesis and metabolism of tetrahydrobiopterin and molybdopterin. Annu. Rev. Biochem. 54:729–764, 1985. Nielsen, H. I. Ultrastructural changes in the dermal chromatophore unit of Hyla arborea during color change. Cell Tissue Res. 194: 405–418, 1978. Nilsson, H., M. Rutberg, and M. Wallin. Localization of kinesin and cytoplasmic dynein in cultured melanophores from Atlantic cod, Gadus morhua. Cell Motil. Cytoskel. 33(3):183–196, 1996. Nilsson, H., and M. Wallin. Evidence for several roles of dynein in melanosome transport in melanophores. Cell Motil. Cytoskel. 38:397–409, 1997. Novales, R. R., and W. J. Davis. Melanin-dispersing effect of adenosine 3¢,5¢-monophosphate on amphibian melanophores. Endocrinology 81:283–290, 1967. Novales, R. R., and W. J. Davis. Cellular aspects of the control of physiological color changes in amphibians. Am. Zool. 9:479–488, 1969. Novales, R. R., and B. J. Novales. The effects of osmotic pressure and calcium deficiency on the response of tissue-cultured melanophores to melanocyte-stimulating hormone. Gen. Comp. Endocrinol. 5: 568–576, 1965. Obika, M. Association of pteridines with amphibian larval pigmentation and their biosynthesis in developing chromatophores. Dev. Biol. 6:99–112, 1963. Obika, M. Intracellular transport of pigment granules in fish chromatophores. Zool. Sci. 3:1–11, 1986. Obika, M., and J. T. Bagnara. Pteridines as pigments in amphibians. Science 143:485–487, 1964. Obika, M., and J. Matsumoto. Morphological and biochemical studies on amphibian bright-colored pigment cells and their pterinosomes. Exp. Cell Res. 52:646–659, 1968. Obika, M., and S. Negishi. Effects of hexylene glycol and nocodazole on microtubules and melanosomes translocation in melanophores of the medaka Oryzias latipes. J. Exp. Zool. 235:55–63, 1985. Obika, M., S. J. Lo, T. T. Tchen, and J. D. Taylor. Ultrastructural demonstration of hormone-induced movement of carotenoid droplets and endoplasmic reticulum in xanthophores of the goldfish, Carassius auratus L. Cell Tissue Res. 190:409–416, 1978. Odenthal, J., K. Rossnagel, P. Haffter, R. N. Kelsh, E. Vogelsang, M. Brand, F. J. M. van Eeden, M. Furutani-Seki, M. Granato, M. Hammerschmidt, C. Heisenberg, Y. Jiang, D. A. Kane, M. C. Mullins, and C. Nusslein-Volhard. Mutations affecting xanthophore pigmentation in the zebrafish, Danio rerio. Development 123:391–398, 1996. Oliphant, L. W., J. Hudon, and J. T. Bagnara. Pigment cell refugia in homeotherms – the unique evolutionary position of the iris. Pigment Cell Res. 5:367–371, 1992. Oshima, H., and R. Fujii. Motile mechanism of blue damselfish (Chrysiptera cyanea) iridophores. Cell Motil. Cytoskel. 8:85–90, 1987. Oshima, N., and P. Wannitikul. Signal transduction of MCH in melanophores of the tilapia, Oreochromis niloticus. Zool. Sci. 13:351–356, 1996. Parichy, D. M., and J. M. Turner. Temporal and cellular requirements for Fms signaling during zebrafish adult pigment pattern development. Development 130:817–833, 2003. Parker, G. H. Animal Colour Changes and their Neurohumours. London: Cambridge University Press, 1948. Pehlemann, F. W. Experimentelle Beeinflussung der Melanophorenverteilung von Xenopus laevis-larven. Zool. Anz. Suppl. 29:571– 580, 1967a. Pehlemann, F. W. Der morphologische Farbwechsel von Xenopus laevis-larven. Z. Zellforsch. Mikroskop. Anat. 78:484–510, 1967b. Pehlemann, F. W. Regulation of differentiation and cell division of melanophores in Xenopus laevis larvae. In: Pigmentation: Its
57
CHAPTER 2 Genesis and Biological Control, V. Riley (ed.). New York: Appleton Century Crofts, 1972, pp. 295–306. Peng, G., J. D. Taylor, and T. T. Tchen. Goldfish tyrosinase related protein 1 (TRP-1): deduced amino acid sequence from cDNA and comments on structural features. Pigment Cell Res. 7:9–16, 1994. Perryman, E. K. Fine structure of the secretory activity of the pars intermedia of Rana pipiens. Gen. Comp. Endocrinol. 23:94–110, 1974. Pfleiderer, W. Structure elucidations of dimeric pteridines. In: Chemistry and Biology of Pteridines and Folates. S. Milstien, G. Kapatos, R. A. Levine, and B. Shane (eds). Boston: Kluwer Academic Publishers, 2001, pp. 9–16. Porter, K. R. Microtubules in intracellular locomotion. Ciba Found. Symp. 14:149–166, 1973. Pouchet, G. Des changements de coloration sous l’influence des nerfs. J. Anat. Physiol. 12:1–90, 1876. Quay, W. B. Specificity and structure–activity relationships in the Xenopus larval melanophore assay for melatonin. Gen. Comp. Endocrinol. 11:253–254, 1968. Quay, W. B., and J. T. Bagnara. Relative potencies of indolic and related compounds in the body lightening reaction of larval Xenopus. Arch. Int. Pharmacodyn. Ther. 150:137–143, 1964. Quigley, I. K., and D. M. Parichy. Pigment pattern formation in zebrafish: A model for developmental genetics and the evolution of form. Microsc. Res. Tech. 58:442–455, 2002. Quillan, J. M., C. K. Jayawickreme, and M. R. Lerner. Combinatorial diffusion assay used to identify topically active melanocytestimulating hormone antagonists. Proc. Natl. Acad. Sci. USA 92:2894–2898, 1995. Radionov, V. J., A. J. Hope, T. M. Svitkina, and G. G. Borisy. Functional coordination of microtubule-based and actin-based motility in melanophores. Curr. Biol. 8:165–168, 1998. Rodionov, V. I., F. K. Gyoeva, and V. I. Gelf. Kinesin is responsible for centrifugal movement of pigment granules in melanophores. Proc. Natl. Acad. Sci. USA 88:4956–4960, 1991. Ramachandran, V. S., C. W. Tyler, R. L. Gregory, D. RogersRamachandran, S. Duensing, C. Pillsbury, and C. Ramachandran. Rapid adaptive camouflage in tropical flounders. Nature 379:815– 818, 1996. Rawls, J. F., and S. L. Johnson. Zebrafish kit mutation reveals primary and secondary regulation of melanocyte development during fin stripe regeneration. Development 127:3715–3724, 2000. Rawls, J. F., E. M. Mellgren, and S. L. Johnson. How the zebrafish gets its stripes. Dev. Biol. 240:301–314, 2001. Reilein, A. R., I. S. Tint, N. I. Peunova, G. N. Enikolopov, and V. I. Gelfand. Regulation of organelle movement in melanophores by protein kinase A (PKA), protein kinase C (PKC) and protein phosphatase 2A (PP2A). J. Cell Biol. 142:803–813, 1998. René, F., C. Hindelang, P. Vuillez, M. Plante, M. J. Klein, J. M. Felix, and M. E. Stoeckel. Morphofunctional aspects of melanotrophic cells developing in situ and in vivo. Ann. N. Y. Acad. Sci. 680:89–110, 1993. Richards, C. M. The alteration of chromatophore expression by sex hormones in the Kenyan reed frog, Hyperolius viridiflavus. Gen. Comp. Endocrinol. 46:58–67, 1982. Richards, C. M., and J. T. Bagnara. Expression of specific pteridines in neural crest transplants between Pleurodeles and Axolotl. Dev. Biol. 15:334–347, 1967. Rogers, S. L., and V. I. Gelfand. Myosin cooperates with microtubule motors during organelle transport in melanophores. Curr. Biol. 8:161–164, 1998. Rogers, S. L., I. S. Tint, P. C. Fanapour, and V. I. Gelfand. Regulated bidirectional motility of melanophore pigment granules along microtubules in vitro. Proc. Natl. Acad. Sci. USA 94:3720–3725, 1997. Rogers, S. L., I. S. Tint, and V. I. Gelfand. In vitro motility assay for
58
melanophore pigment organelles. Methods Enzymol. 298:361–372, 1998. Roubos, G. J., M. Martens, and B. C. Jenks. Control of melanotrope cell activity in Xenopus laevis. Ann. N. Y. Acad. Sci. 680:130–134, 1993. Saland, L. C. Ultrastructural differences in cells of pars intermedia of light and dark adapted frogs. Anat. Rec. 157:314–315, 1967. Samaraweera, P., T. Fukuzawa, F. T. Mangano, J. M. Newton, J. H. Law, and J. T. Bagnara. Purification of a melanization inhibiting factor from R. forreri ventral skin. Pigment Cell Res. Suppl. 3:30–31, 1994. Sammak, P. J., S. R. Adams, A. T. Harootunian, M. Schliwa, and R. T. Tsien. Intracellular cAMP, not calcium, determines the direction of vesicle movement in melanophores: direct measurement by fluorescence ratio imaging. J. Cell Biol. 117:57–72, 1992. Sangiovanni, G. Descrizione d’un particolare systema di organi cromoforo-espansivo-dermide e dei fenomeni ch’esso produce, scoperto nei molluschi cefalopodi. Giornale Enciclopedico di Napoli anno 13, no. 9, 1819. Sawyer, T. K., P. J. Sanfilippo, V. J. Hruby, M. H. Engel, C. B. Heward, J. B. Burnett, and M. E. Hadley. 4-Norleucine, 7-D-phenylalaninea-melanocyte-stimulating hormone: A highly potent a-melanotropin with ultralong biological activity. Proc. Natl. Acad. Sci. USA 77:5754–5758, 1980. Schliwa, M. Mechanisms of intracellular organelle transport. In: Cell and Muscle Motility, vol. 5, J. W. Shay (ed.). New York: Plenum Press, 1984, pp. 1–82. Schwalm, P. A., and J. M. McNulty. The morphology of dermal chromatophores in the infra-red reflecting glassfrog, Centrolenella fleischmanni. J. Morphol. 163:37–44, 1980. Schwalm, P. A., P. H. Starrett, and R. W. McDiarmid. Infrared reflectance in leaf-sitting neotropical frogs. Science 199:1225–1227, 1977. Sherbrooke, W. C., and M. E. Hadley. Exploring the evolutionary history of melanin-concentrating and melanin-stimulating hormone receptors on melanophores: Neopterigian (Holostean) and chondrostean fishes. Pigment Cell Res. 1:344–349, 1988. Sherbrooke, W. C., M. E. Hadley, and A. M. L. Castrucci. Melanotropic peptides and receptors: an evolutionary perspective in vertebrate physiologic color change. In: Melanotropic Peptides, vol. II, M. E. Hadley (ed.). Washington: CRC Press, 1988, pp. 175– 190. Shizume, K., A. B. Lerner, and T. B. Fitzpatrick. In vitro bioassay for the melanocyte-stimulating hormone. Endocrinology 54:553–560, 1954. Sichel, G. Biosynthesis and function of melanins in hepatic pigmentary system. Pigment Cell Res. 1:250–258, 1988. Skold, H. N., E. Norstrom, and M. Wallin. Regulatory control of both microtubule- and actin-dependent fish melanosome movement. Pigment Cell Res. 15:357–366, 2002. Smith, P. E. Experimental ablation of the hypophysis in the frog embryo. Science 44:280–282, 1916. Smith, P. E. The pigmentary growth and endocrine disturbances induced in the anuran tadpole by the early ablation of the pars buccalis of the hypophysis. Am. Anat. Mem. No. 11, 1920. Snell, R. S. Hormonal control of pigmentation in man and other animals. In: Advances in Biology of the Skin, vol. VIII, The Pigmentary System, W. Montagna, and F. Hu (eds). Oxford: Pergamon Press, 1967, pp. 447–466. Steven, D. M. The dermal light sense. Biol. Rev. 38:204–240, 1963. Stoppani, A. O. M., P. F. Pieroni, and A. J. Murray. The role of peripheral nervous system in colour changes of Bufo arenarum Hensel. J. Exp. Zool. 31:631–638, 1954. Sugden, D., and S. J. Rowe. Protein kinase C activation antagonizes melatonin-induced pigment aggregation in Xenopus laevis melanophores. J. Cell Biol. 119:1515–1521, 1992.
COMPARATIVE ANATOMY AND PHYSIOLOGY OF PIGMENT CELLS IN NONMAMMALIAN TISSUES Sutherland, E. W., and T. W. Rall. Fractionation and characterization of a cyclic adenine ribonucleotide formed by tissue particles. J. Biol. Chem. 232:1077–1091, 1958. Sutherland, E. W., I. Ye, and R. W. Butcher. The action of epinephrine and the role of the adenyl cyclase system in hormone action. Rec. Prog. Hormone Res. 21:623–642, 1965. Sutherland, E. W., G. A. Robison, and R. W. Butcher. Some aspects of the biological role of adenosine 3¢,5¢-monophosphate (cyclic AMP). Circulation 37:279–306, 1968. Takase, M., I. Miura, A. Nakata, T. Takeuchi, and M. Nishioka. Cloning and sequencing of the cDNA encoding tyrosinase of the Japanese pond frog, Rana nigromaculata. Gene 121:359–363, 1992. Takikawa, S., and M. Nakagoshi. Developmental changes in pteridine biosynthesis in the toad, Bufo vulgaris. Zool. Sci. 11:413–421, 1994. Taylor, J. D. The effects of intermedin on the ultrastructure of amphibian iridophores. Gen. Comp. Endocrinol. 12:405–416, 1969. Taylor, J. D. The presence of reflecting platelets in integumental melanophores of the frog, Hyla arenicolor. J. Ultrastruct. Res. 35:532–540, 1971. Taylor, J. D. Does the introduction of a new player, the endoplasmic reticulum, create more or less confusion in understanding the mechanism(s) of pigmentary organelle translocations? Pigment Cell Res. 5:49–57, 1992. Taylor, J. D., and J. T. Bagnara. Melanosomes of the Mexican tree frog, Agalychis dachnicolor. J. Ultrastruct. Res. 29:323–333, 1969. Taylor, J. D., and J. T. Bagnara. Dermal chromatophores. Am. Zool. 12:43–62, 1972. Taylor, J. D., and M. E. Hadley. Chromatophores and color change in the lizard Anolis carolinensis. Z. Zellforsch. Mikroskop. Anat. 104:282–294, 1970. Thaler, C. D., and L. T. Haimo. Regulation of organelle transport in melanophores by calcineurin. J. Cell Biol. 111:1939–1948, 1990. Thaler, C.D. and L.T. Haimo. Microtubules and microtubule motors: mechanisms of regulation. Int. Rev. Cytol. 164:269–372, 1996. Thony, B., G. Auerback, and N. Blau. Tetrahydrobiopterin biosynthesis, regeneration and functions. Biochem. J. 347:1–16, 2000. Tschesche, R., and A. Glaser. Synthesen des 7-Hydroxy-biopterins und uber seine Beziehungen zum Ichthyopterin. Chem. Ber. 91:2081– 2089, 1958. Tuma, M. C., and V. I. Gelfand. Molecular mechanisms of pigment transport in melanophores. Pigment Cell Res. 12:283–294, 1999. Tuma, M. C., A. Zill, N. LeBot, I. Vernos, and V. I. Gelfand. Heterotrimeric kinesin II is the microtubule motor protein responsible for pigment dispersion in Xenopus melanophores. J. Cell Biol. 143:1547–1558, 1998. Turner, W. A. J., J. D. Taylor, and T. T. Tchen. Melanosomes formation in the goldfish: the role of multivesicular bodies. J. Ultrastruct. Res. 51:16–31, 1975. Turtle, J. R., and D. M. Kipnis. An adrenergic receptor mechanism for the control of cyclic 3¢,5¢ adenosine monophosphate synthesis in tissues. Biochem. Biophys. Res. Commun. 28:797–802, 1967. Twitty, V. C. Of Scientists and Salamanders. San Francisco: WH Freeman and Co., 1966. Twitty, V. C., and M. C. Niu. The motivation of cell migration, studied by isolation of embryonic pigment cells singly and in small groups in vitro. J. Exp. Zool. 125:541–579, 1954. Valverde, P., E. Healy, I. Jackson, J. L. Rees, and A. J. Thody. Variants of the melanocyte-stimulating hormone receptor gene are associated with red hair and fair skin in humans. Nature Genet. 11:328–330, 1995.
van der Lek, G. 1967. Photosensitive melanophores. PhD Thesis. University of Utrecht, Utrecht, Netherlands. van der Lek, G., J. de Heer, A. C. J. Burgers, and G. van Oordt. The direct reaction of the tailfin melanophores of Xenopus tadpoles to light. Acta Physiol. Pharmacol. Neer. 7:409–419, 1958. Volpe, E. P. Fate of neural crest homotransplants in pattern mutants of the leopard frog. J. Exp. Zool. 157:179–196, 1964. Visconti, M. A., and A. M. Castrucci. Microtubule- and microfilament-disrupting drugs and melanosome migration in melanophores of Papilliochromis ramirezi (Cichlidae, Teleostei). An. Acad. Bras. Cienc. 57:233–237, 1985. von Frisch, K. Beiträge zur Physiologie der Pigmentzellen in der Fischhaut. Pflugers Arch. Gesamte Physiol. Menschen Tiere 138: 319–387, 1911. Vrieling, H., D. M. J. Duhl, S. E. Millar, K. A. Miller, and G. S. Barsh. Differences in dorsal and ventral pigmentation result from regional expression of the mouse agouti gene. Proc. Natl. Acad. Sci. USA 91:5667–5671, 1994. Waring, H. Color Change Mechanisms of Cold-Blooded Vertebrates. New York: Academic Press, 1963. Weston, J. A. The migration and differentiation of neural crest cells. Adv. Morphog. 8:41–114, 1970. Whimster, I. W. The group behavior of pigment cells. Trans. St Johns Hosp. Dermatol. Soc. 57:57–86, 1971. Wolff, K. Melanocyte-keratinocyte interactions in vivo: the fate of melanosomes. Yale J. Biol. Med. 46:384–396, 1973. Woronzowa, M. A. Analyse der weissen Fleckung bei Ablystomen. Biol. Zentralbl. 52:676–684, 1932. Wright, M. R., and A. B. Lerner. On the movement of pigment granules in frog melanocytes. Endocrinology 66:599–609, 1960. Wright, P. A. Physiological responses of frog melanophores in vitro. Physiol. Zool. 28:204–218, 1955. Wu, X., B. Bowers, Q. Wei, B. Kocher, and J. A. Hammer III. Myosin V associates with melanosomes in mouse melanocytes: evidence that myosin V is an organelle motor. J. Cell Sci. 110:847–859, 1997. Wu, X., B. Bowers, K. Rao, Q. Wei, and J. A. Hammer III. Visualization of melanosome dynamics within wild-type and dilute melanocytes suggests a paradigm for myosin V function in vivo. J. Cell Biol. 28:1899–1918, 1998. Yamamoto, H. T. Medaka (Killifish). Biology and Strains. Tokyo: Keigkau Publishing Co., 1975. Yamamoto, H., T. Kudo, N. Masuko, H. Miura, S. Sato, M. Tanaka, S. Tanaka, S. Takeuchi, S. Shibahara, and T. Takeuchi. Phylogeny of regulatory regions of vertebrate tyrosinase genes. Pigment Cell Res. 5:284–294, 1992. Yoshida, T., Y. Iwanami, and J. T. Bagnara. Isolation and structure of a novel pyridine derivative from the Algerian newt, Pleurodeles valtii. Eur. J. Biochem. 175:41–44, 1988. Ziegler, I., T. McDonaldo, C. Hesslinger, I. Pelletier, and P. Boyle. Development of the pteridine pathway in the zebrafish, Danio rerio. J. Biol. Chem. 275:18926–18932, 2000. Zondek, B., and H. Krohn. Hormon des Zwischenlappens der Hypophyse (Intermedin). I. Die Rotfarbung der Elritze als Testobjekt. Klin. Wochenschr. 11:405–408, 1932. Zuasti, A., J. R. Jara, C. Ferrer, and F. Solano. Occurrence of melanin granules and melanosynthesis in the kidney of Sparus auratus. Pigment Cell Res. 2:93–99, 1989. Zuasti, A., W. C. Johnson, P. Samaraweera, and J. T. Bagnara. Intrinsic pigment-cell stimulating activity in the catfish integument. Pigment Cell Res. 5:253–262, 1992. Zuasti, A., J. H. Martinez-Liarte, C. Ferrer, M. Canizares, J. Newton, and J. T. Bagnara. Melanization stimulating activity in the skin of the gilthead porgy, Spartus auratus. Pigment Cell Res. 6:359–364, 1993.
59
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
2
The Science of Pigmentation
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
3
General Biology of Mammalian Pigmentation Walter C. Quevedo Jr. and Thomas J. Holstein
Part I: The Melanin Pigmentary System of Postnatal Mammals from Basic Design to Evolutionary Origins Part II: The Development of the Melanin Pigmentary System and the Molecular Genetic Systems that Regulate It
Summary 1 This chapter examines the structure and function of the mammalian pigmentary system in the light of its diversity, evolutionary origin, and contributions to the adaptiveness of mammals to natural environments. 2 A major focus is on the variation in skin color based on the interactions between melanocytes and keratinocytes in the pigmenting of the epidermis. 3 The inborn constitutive melanin pigmentation of human skin is contrasted with facultative melanin pigmentation or tanning in response to solar radiation. 4 As in the epidermis, melanocytes of hair follicles synthesize melanin and transfer it to keratinocytes (epidermal cells) that form the hair proper. 5 With respect to hair growth, follicular melanocytes that pigment each generation of hair appear to die at the end of each cycle and are replaced in the next one by melanocytes recruited from a stem cell population situated in the upper hair follicle. 6 Dermal melanocytes of humans are most frequently found at sites where hair is thin. “Mongolian spots” serve as a general model for the colors generated by dermal melanin. 7 The presence of dermal melanin is highly variable in mammals, suggesting that dermal melanocytes may have functions in addition to providing photoprotection. 8 Although mammals lack the capacity for rapid color changes by shifting pigment within melanocytes, the color interactions between static deposits of dermal melanin and surrounding blood vessels colored red by hemoglobin produce rapid flashes of bright blue color in such primates as the mandrill (Mandrillus sphinx). 9 At least seven adaptive functions have been proposed for melanin in protecting humans from environmental hazards and for promoting effective metabolic functions of skin exposed to solar radiation. 10 The effectiveness of melanin in photoprotection is being debated. The big picture suggests that melanin is photoprotective to the extent that it is in harmony with its other functions.
11 The evolution of very light-skinned humans created the paradox of cutaneous melanin potentiating solar damage rather than providing photoprotection. 12 As an interface, the hair coat provides many signals to observers when used as communication or none at all when used as camouflage. The pigmentation of the hair coat is carefully crafted for these purposes. 13 Among mammals, youth is a time to play and learn. It is a time for protection from aggression from the adults that surround them. Coat colors signal to adults the privileged status of their conspecific juveniles. The coat colors of juveniles also elicit protection by their adults when predators threaten. In some cases, the coat colors of juveniles, rather than calling attention to them, facilitate concealment. 14 Radicalism and conservatism are evident in the human pigmentary system evolved from that of reptiles. Human skin retained certain features of the spatial organization in which melanocyte function is integrated into the functions of skin as a whole. Examples of this integration are melanin’s role in thermoregulation, the paracrine activity of melanocytes in the inflammatory response, and melanin’s neutralization of certain cytotoxic agents. 15 Many of the most basic features of the mammalian pigmentary system have been carried over from reptiles (melanocytes, melanosomes, tyrosinase, melanin, etc.). The major evolutionary change was the evolution of new regulatory mechanisms for orchestrating both genetically and epigenetically the patterns of pigment distribution in the skin and hair to facilitate the survival of mammals in an acutely visionoriented world. The details of the embryonic and postnatal settings in which the melanin pigmentary system is formed and integrated with local surrounding cells and distant glands that regulate it indicate the great importance of melanocytes in the rise of mammals to dominance in the natural world.
Historical Background The evolution of mammals from reptilian ancestors was characterized by the invention of a new system of protection, a 63
CHAPTER 3
coat of hair. This innovation required a revision of strategy for displaying skin color. Unlike their reptilian, amphibian, and fish ancestors, mammals could no longer profit by using dermal chromatophores (xanthophores, melanophores, and iridophores) to produce stable or rapidly changing patterns of skin pigmentation, for their skin was no longer completely visible. In fact, the ability of chromatophores rapidly to disperse or concentrate pigments within their cytoplasm became a liability in mammals. In their case, the strategy for protective coloration had to be shifted from patterning of the skin with a variety of pigments to one of programming the pigmentation of hairs that grew from hair follicles. The pigment used for this purpose was melanin deposited within melanosomes, specialized organelles synthesized by melanocytes. Each hair had to be pigmented precisely from top to bottom to make its appropriate contribution to the pattern expressed by the dead hair coat that invested the skin. There was no place in mammals for disruptive reversals in the movement of melanosomes within melanocytes in response to endocrine or neural stimuli. Although such physiologic color changes were of great importance in lower vertebrates, they were nonadaptive in the hair follicles of mammals. In this location, unscheduled reversible shifts in the distribution of melanosomes within melanocytes would have interrupted the programmed synthesis and transfer of melanosomes from melanocytes into cells (keratinocytes) being incorporated into the developing hair. Any disruption in the program for pigmentation of small populations of individual hairs could produce a serious flaw in the visual impact of the overall coat color pattern. Although melanocytes lost their capacity rapidly to disperse and concentrate their melanosomes in response to hormones, hormones did retain the ability to regulate pigmentation, hence hair color, by influencing the amount and type of melanin [eumelanin (black/brown) vs. pheomelanin (yellow/red)] synthesized by follicular melanocytes. Physiology deals with the functions of living organisms with particular attention to the mechanisms that regulate them at all levels of biological organization, from subcells to social groups and external environmental influences. In many ways, the mammalian pigmentary system is an ideal example for affirming this interpretation of nature. Accordingly, this chapter emphasizes two approaches to exploring the melanin pigmentary system of mammals. Part I, starting from the top down, from complexity to “simplicity,” describes the big picture of the gross and microscopic organization of the melanin pigmentary system, its universal and variable features among mammals, its adaptive significance, evolutionary origin, and the constraints placed on it by its inheritance from reptilian ancestors. Part II begins from the bottom up, from “simplicity” to complexity, in describing the shaping of the melanin pigmentary system during embryonic development. It stresses the roles played by events at the molecular level that regulate development, including the genes and their products, enzymes, hormones, and growth factors that fine-tune the life, differentiation, and death of melanocytes. The interplay (inductions) of the epidermis and dermis prior to the devel64
opment of hair follicles unleashes the appropriate genetic mechanisms that specify and regulate the path that growth will take. Some features of the melanin pigmentary system are important in both mammalian evolution and the molecular biology of development. This chapter examines the links between them. In doing so, it crosses the boundary between physiological genetics and molecular genetics of the mammalian pigmentary system. In general, molecular genetics has focused on the central dogma of DNAÆmRNAÆprotein, whereas physiological genetics has emphasized the path from the gene product, a protein, the initial phenotype, to the derived phenotype, in this case the melanin pigmentary system that emerges during embryonic and postnatal development (Quevedo and Holstein, 1992). In an attempt to give an integrated picture of events at the micro level, some repetition of information about the macro level has been included to expand what was stated earlier in another context. At the end of the chapter, there is a list of other chapters in this book that expand on the topics covered here.
Part I: The Melanin Pigmentary System of Postnatal Mammals from Basic Design to Evolutionary Origins To begin with, the human melanocyte system will be used to illustrate the general principles of mammalian pigmentation. More is known about the melanin pigmentation of humans than for any other mammal, except for the laboratory mouse (Mus musculus). In general structure and function, the human pigmentary system shows little difference from that of other mammals. However, unlike other mammals, the marked reduction of hair that characterized human evolution once again placed the epidermis and not the hair coat as the primary interface between the organism and its environment. In addition, while hemoglobin imparts significant color to human skin, its impact is not as great as in certain other mammals. Therefore, to complete the generalized picture of mammalian pigmentation based on Homo sapiens, (1) mice will be recruited for an analysis of the pigmentary system in skin sprouting dense hair and (2) the mandrill, a baboon-like primate, will be examined for it epitomizes the ability of the circulatory and pigmentary systems to cooperate in producing bright patches of red and blue in glabrous skin.
Current Concepts Human Skin Color In humans, skin color derives mainly from the interplay of two pigments, hemoglobin and melanin. Eumelanin in the epidermis typically imparts a brown to black hue, whereas eumelanin in the dermis may appear blue. However, the epidermis of orange–red-haired, fair-skinned, freckled individuals may
GENERAL BIOLOGY OF MAMMALIAN PIGMENTATION
appear slightly orange–yellow, possibly owing to the presence of pheomelanin in higher proportions than eumelanin than is characteristic of individuals lacking red hair and freckles (Thody et al., 1991). However, recent findings by Hunt et al. (1995) cast doubt on this interpretation. Oxygenated hemoglobin in the superficial dermal arterioles and capillaries appears pink/red and deoxygenated hemoglobin in the venules blue. Dietary carotenoids may contribute a slight yellow tint to the epidermis (Jimbow et al., 1999). For most humans alive today, melanin is the major source of skin color. Although melanocytes are found in hair follicles and occasionally in the dermis, worldwide ethnic variation in heritable (“constitutive”) skin color results mainly from differences in the amount of melanin within the epidermis. Constitutive skin color (CSC) is defined as the level of melanization generated within the epidermis of an individual through the operation of cellular genetic programs in the absence of influences from ultraviolet light. In practical terms, it is taken to be the level of pigmentation in those parts of the human body that are rarely exposed to sunlight. Humans vary in CSC from dark black/brown to almost alabaster white in skin color. CSC can be enhanced by exposure to ultraviolet light (UVR). Facultative skin color (FSC) designates increases in melanin pigmentation of the skin above CSC and is induced by UVR and/or hormones. FSC is reversible in that the hyperpigmentation tends to decline toward CSC when solar and/or endocrine stimulation is discontinued (Quevedo et al., 1974).
The Histological Basis for CSC and FSC: Epidermal Melanocytes Human epidermis is conventionally described as a stratified squamous epithelium consisting of keratinocytes that are modified as they ascend from their origin in the basal layer and ultimately cornify and die as they near the outer surface where they are shed (Bloom and Fawcett, 1962) (Fig. 3.1A). However, the epidermis is a considerably more complex community of cells than this definition implies (Montagna and Parakkal, 1974; Odland, 1991). Although keratinocytes are the principal cells of the epidermis, there are also several types of nonkeratinocytes. Particularly prominent are the melanocytes found in the basal layer of the epidermis (Fig. 3.1A and B). Epidermal melanocytes typically synthesize melanosomes that become ellipsoidal in shape and more or less uniformly pigmented by melanin deposited on an internal matrix of aligned filaments (cf. Chapter 7). The melanin produced by epidermal melanocytes is most often described as eumelanin based on its tendency to appear brown/black in color. The mature melanosomes are moved from the cell body (perikaryon) of the melanocyte to its dendrites that are in contact with neighboring keratinocytes of the Malpighian layer (cf. Chapter 8). The melanosomes move from the dendrites into the keratinocytes. There are three major theories about how melanosomes are acquired by keratinocytes: (1) keratinocytes phagocytize bits of the melanosome-containing dendrites; (2) melanosomes are discharged by the dendrites into the intercellular space and subsequently phagocytized by
SC SS SG
D
A K
MC
MN
G G K
RER B
*
D
Fig. 3.1. Vertical section of skin from the buttocks of a heavily pigmented adult African American male. (A) Note the heavily pigmented keratinocytes of the epidermal basal layer. In some keratinocytes, the arrangement of melanosomes in the form of supranuclear caps is evident (arrowheads). A “clear cell” (arrow), presumably a melanocyte, is present in the basal layer of the epidermis (SC, stratum corneum; SG, stratum granulosum; SS, stratum spinosum; D, dermis). (B) Ultrastructure of a basal melanocyte flanked by two keratinocytes. Melanosomes at various stages of development (arrows) are distributed throughout the cytoplasm of the melanocyte. Arrowheads indicate melanosomes that have been transferred to the cytoplasm of keratinocytes (MN, melanocyte nucleus; MC, melanocyte cytoplasm; K, keratinocytes; G, Golgi apparatus; RER, rough endoplasmic reticulum; *basement membrane at the dermal–epidermal junction; D, dermis) (electron micrograph courtesy of Raymond Boissy).
keratinocytes; (3) the dendrite and keratinocyte plasma membranes fuse, opening a cytoplasmic channel through which the melanosomes pass directly from the melanocyte into the keratinocyte (Jimbow et al., 1999; Marks and Seabra, 2001; Yamamoto and Bhawan, 1994). On incorporation into keratinocytes, melanosomes, which are themselves considered to be specialized lysosomes (Orlow, 1995), interact with lysosomes of the keratinocyte and are sequestered within them forming secondary lysosomes (cf. Chapter 7). As a general rule, melanosomes larger than approximately 1 mm in greatest 65
CHAPTER 3
diameter are packaged singly in secondary lysosomes, whereas those smaller than 1 mm are sequestered in groups of varying size within a secondary lysosome (Jimbow et al., 1999; Quevedo et al., 1986). Lysosomal hydrolases degrade melanosomes as the keratinocytes move to the epidermal surface. The smaller melanosomes packaged in groups appear to be the most susceptible to lysosomal degradation. The degradation of melanosomes appears to reduce the melanin into finer particles, which may increase its effectiveness in shielding the epidermis from penetration and damage by ultraviolet light (Jimbow et al., 1999). The close relationship that exists between a melanocyte and a small population of keratinocytes with which it maintains contact by its dendrites is formalized in the concept of the epidermal melanin unit (EMU) (Fitzpatrick and Breathnach, 1963). An EMU consists of a melanocyte and the population of keratinocytes that acquires, transports, metabolizes, and disposes of the melanin/melanosomes synthesized within the melanocytes (Quevedo et al., 1974) (Fig. 3.1A and B). It is estimated that an EMU contains approximately 36 viable keratinocytes (Quevedo et al., 1974). Although the uninterrupted horizontal distribution of melanin in the outer cornified layer suggests a functional overlap between EMUs, epidermal pigmentation is largely a mosaic of the individual contributions of millions of EMUs. Just as the unaided human eye fails to resolve the large number of individual dots that constitute a newspaper photograph, the same unaided eye fails to detect that individual EMUs vary in their melanin/melanosome content. Consequently, the brain concludes that skin color is essentially homogeneous. However, under the light microscope, it is evident that melanocytes on the ridges of epidermis that press into the dermis are more melanogenically active than those of interridge areas of epidermis that form a flat interface with the dermis. Not only is more melanin found in the basal melanocytes and keratinocytes of the ridges, the stratum corneum above them often appears to be more heavily pigmented than the interridge cornified layer (Quevedo et al., 1989). This condition is partially evident in Becker’s nevus where there is enlargement of the epidermal ridges and an increase in melanocyte numbers (Quevedo et al., 1989). The freckled epidermis of sun-exposed, fair-skinned, red-haired humans is a classic extreme manifestation of the mosaic nature of EMU structure and function (Fig. 3.2A and B). The clusters of EMUs in freckles produce and harbor abundant melanosomes, resulting in islands of dark epidermis surrounded by a sea of light epidermis composed of EMUs containing weakly melanogenic melanocytes (Quevedo et al., 1986). Melanosomes tend to be largest in African Americans, black Africans, and Australian aborigines and are generally arranged singly within secondary lysosomes of keratinocytes (>1 mm). Melanosomes are smaller (700 kDa (Hearing et al., 1982; Orlow et al., 1993b, 1994; Zhou et al., 1993). This complex is responsible for the conversion of tyrosine to eumelanin but does not appear to be involved in pheomelanin biosynthesis. Copurification of these proteins with antityrosinase antibodies suggests a stable interaction between these proteins in which the EGF motif may be important in the formation and stabilization of this complex (Jackson et al., 1992). Recent studies have shown that tyrosinase activity is stabilized in the presence of TRP-1 and TRP-2, providing further evidence of a functional melanogenic complex (Pawelek, 1991; Winder et al., 1994a). Cotransfection of fibroblast with both tyrosinase and TRP-1 showed an increase in both the stability and the activity of tyrosinase with time. This complex can interact with other factors as well, including melanogenic inhibitors (Kameyama et al., 1989) and products of other pigment loci that determine the quantity and quality of melanin pigment synthesized, including the silver (si), pink-eye (p), and MART-1 proteins (Kameyama et al., 1993). Analysis of mice with mutations at different pigment loci can provide information on the effects of protein interaction in vivo. By assaying melanin production in mouse skin, it was shown that mutations at the pink-eye loci will reduce tyrosinase activity (Coleman, 1962) as well as reduce the levels of tyrosinase transcript in mouse melanocytes compared with normal controls (Tamate et al., 1989). More recently, it has been shown that the pink-eye unstable (Pun) mutation, a mutation that contains an integral duplication inside the P gene resulting in altered P-gene transcription, actually disrupts the tyrosinase enzyme complex (Chiu et al., 1993). In the ocular melanocytes of mice that contained the Pun mutation, the highmolecular-weight enzyme complex could not be detected, and protein levels of tyrosinase, TRP1, and TRP2 were drastically reduced. Another example of the disruptive effect of a mutation in one of the members of this complex is found in the platinum (cp) mouse (Orlow et al., 1993a). This mutation of the mouse tyrosinase gene results in a truncated protein and a coat almost completely devoid of pigment. Enzymatic activity of platinum tyrosinase is higher than that of other tyrosinase mutations that result in a darker coat color, but the tyrosinase enzymatic complex cannot be detected, suggesting 222
that the absence of the complex causes a more severe form of albinism than would be expected by the tyrosinase gene mutation alone. More importantly, alteration of one of these protein products by means of mutations can have a drastic effect on other proteins involved in this complex. It is possible that mutations that result in hypopigmentation (or hyperpigmentation) may not act by specifically altering the function of the protein (i.e. reduced catalytic activity), but by disruption of the protein complex, producing a reduction in pigment biosynthesis. In addition to the potential interactions among family members that affect pigmentation, individual tyrosinase family proteins, specifically their cytoplasmic domains, also interact with components of the intracellular protein sorting machinery (reviewed by Setaluri, 2000). Although all tyrosinase family proteins follow a similar biosynthetic route to melanosomes and are expected to share interactions with the same components of trafficking machinery, it is of interest to note that differences exist in their binding specificities. For example, whereas interaction of tyrosinase with the adaptor protein AP-3 is required for its trafficking, interaction with AP-3 is not necessary for TRP-1 trafficking (Huizing et al., 2001). Similarly, TRP-1, but not tyrosinase, interacts specifically with a multifunctional PDZ-domain protein, GIPC, during its transport through the Golgi (Liu et al., 2001).
Human Pigmentation Disorders Oculocutaneous albinism (OCA) is the most common human genetic disease associated with mutations of pigment genes that act at the subcellular level of the melanocyte. OCA is a clinically heterogeneous genetic disease. Mutations in numerous genes including tyrosinase (OCA1), P (OCA2), TRP-1 (OCA3), membrane-associated transporter protein (MATP; OCA4), Chediak–Higashi syndrome (CHS), and Hermansky–Pudlak syndrome (HPS1–7) are thought to be responsible for different forms of OCA in humans. Although, in certain strains of mice, mutations in TRP-1 have also been found to be responsible for a form of pigmentary glaucoma involving iris stromal dystrophy, no TRP-1 mutations were found to be associated with this disease in humans (Anderson et al., 2002; Lynch et al., 2002). Based on the observation that administration of L-DOPA to cytochrome P450 and TYR null mice alleviates developmental ocular abnormalities found in this model for human primary congenital glaucoma (PCG), it is proposed that the tyrosinase/L-DOPA pathway modifies human PCG (Libby et al., 2003). Because of the effect of ocular albinism gene 1 (OA1) on cutaneous melanosome development, this locus may also be considered to be associated with a type of OCA. Besides their role in melanin pigmentation and pigmentary disorders, tyrosinase family proteins are also involved in the biology of melanoma. For example, levels of expression of TRP-2 in melanoma cells appear to correlate positively with their resistance to certain cancer chemotherapeutic drugs (Chu et al., 2000). The exact mechanism by which TRP-2 confers drug resistance is not known. Paradoxically, elevated
THE TYROSINASE GENE FAMILY
expression of TRP-2, and also tyrosinase, in advanced-stage metastatic melanoma lesions appears to correlate with improved overall survival of patients (Takeuchi et al., 2003). One possible reason for this may be the fact that, in patients with metastatic melanoma, all three proteins are recognized by the immune system (Brichard et al., 1993; Vijayasaradhi et al., 1990; Wang et al., 1995, 1996). Accordingly, a number of strategies are being evaluated, in clinical trials, to elicit immune response to these antigens for immunotherapy of melanoma (Rosenberg, 2001). Much of our understanding about human albinism has come from the work done on mutations of the tyrosinase gene and their relationship to tyrosinase-related OCA (OCA1). This relationship has been shown by both formal linkage of the tyrosinase gene to OCA1 and the finding of mutations in the tyrosinase gene that eliminate tyrosinase enzymatic activity (Giebel et al., 1990). Using a combination of PCR amplification of individual exons and single-strand conformational polymorphism (PCR-SSCP) analysis, a number of mutations have been found (Oetting et al., 1994; Oetting and King, 1999). Mutations that produce a tyrosinase protein completely devoid of enzymatic activity are associated with the severest form of albinism, OCA1A. The missense mutations, on the other hand, result in a spectrum of phenotypes ranging from a complete absence of pigment production to near normal amounts of pigment. These latter mutations have residual amounts of enzymatic activity that allow a small amount of pigment to be produced. The missense mutations of tyrosinase have provided a tool to help us understand the biology of the enzyme and pigment production. At present, the three-dimensional structure of tyrosinase family proteins is unknown, and the effects of different mutations cannot be analyzed at the level of protein structure. However, analysis of mutations and their effect on enzymatic activity have provided some insight into the structure of tyrosinase. Mapping of the missense mutations associated with OCA1 reveals several clusters within the tyrosinase polypeptide. This clustering is thought to define functional domains of the enzyme (King et al., 1991; Oetting and King, 1992a, b; Tripathi et al., 1992b). Two of these domains are within the putative copper(A) and copper(B) binding sites respectively. A third cluster is at the 5¢ end (amino-terminal end of the polypeptide) of the coding region. This latter domain may define a putative substrate and/or cofactor binding site, or may be involved in enzyme stability. Missense mutations within the signal peptide of tyrosinase have allowed us to analyze the importance of this region in the enzymatic activity (Breimer et al., 1994; Fukai et al., 1995). Tyrosinase molecules that lack the signal peptide were found to be translated on free ribosomes instead of membranebound ribosomes. This resulted in a peptide that is incorrectly folded and quickly eliminated by the cell (Oetting et al., 1995). Frameshift mutations in the carboxy-terminal end of the protein also result in an enzyme without enzymatic activity. This region contains the transmembrane region and the cytoplasmic tail, which is important for proper sorting and
melanosomal targeting of these proteins (Vijayasaradhi et al., 1995a). The copper binding site of hemocyanin has many similarities to that of tyrosinase (Beltramini et al., 1990). Determining how different mutations affect tyrosinase activity can be aided using the structure of the copper-containing protein hemocyanin in which the three-dimensional structure has been determined (Gaykema et al., 1984, 1986). Based on amino acid sequence alignment between the copper-containing protein hemocyanin and tyrosinase, and extensive spectroscopic studies of tyrosinase, it is evident that the ligation of the copper atoms involves histidine side-chains from the protein. Site-directed mutagenesis of Streptomyces glaucescens tyrosinase has shown that the predicted histidine ligands are indeed involved in copper binding (Lerch, 1988). The presence and placement of these histidine ligands is likely to be critical for the binding of the copper atoms, which is necessary for both the formation of the reactive peroxide species and the complex with the substrate. Thus, changes in the amino acids that form the copper ligands or that change their position in the protein structure are likely to alter the rate and/or specificity of tyrosine hydroxylation. By using hemocyanin as a model for the copper binding sites of tyrosinase, we can begin to determine possible mechanisms of how some of these tyrosinase mutations cause inactivation of or a reduction in enzymatic activity (Oetting and King, 1994). The predicted secondary structure at both the copper binding sites of tyrosinase indicates that the histidine ligands responsible for copper binding are within two a-helices connected by a loop region (Oetting and King, 1992b). This same type of structure exists in the copper binding sites of hemocyanin (Gaykema et al., 1984, 1986). The amino acid sequences of the copper(B) binding region for hemocyanin and tyrosinase are very similar, but the copper(A) binding regions for both proteins are not, and the locations of the copper(A) tyrosinase mutations should be considered less precise. Two tyrosinase mutations in the copper(A) binding site of human tyrosinase are within conserved amino acid motifs found in most tyrosinases and hemocyanin copper binding sites (Müller et al., 1988). The mutation A206T is found in the motif Pro-X-Phe-X-X-X-His, between the proline and the phenylalanine, causing a change from an alanine to a threonine, and the mutation F176I is within the motif Phe-X-X-XHis, changing the highly conserved phenylalanine to an isoleucine. Both these motifs are thought to be involved in the correct placement of the histidine ligands responsible for copper binding. The other mutations are found to be either within the a-helix or at the junction of the a-helix and the connecting loop structure. Our current hypothesis is that these mutations disrupt correct copper atom orientation by displacing the a-helices relative to each other (Oetting and King, 1992b). Spritz et al. (1997) reported that some missense mutations disrupted copper binding, resulting in an inactive protein. There were two missense mutations, P406L and R402Q, that did exhibit copper binding but still had no detectable enzymatic activity. The action of these mutations 223
CHAPTER 11
may either prevent one of the copper atoms from binding or displace the copper atoms by altering the copper to copper distance. Either case would prevent the formation of oxytyrosinase and render the enzyme inactive. The limited number of mutations identified to date in TRP-1 and TRP-2 preclude a similar prediction of structure–function relationship for these proteins. There is also evidence that tyrosinase mutations result in retention of the enzyme in the endoplasmic reticulum and subsequent degradation, leading to speculation that albinism is, in part, an ER retention disease (Halaban et al., 1997, 2000; Toyofuku et al., 2001a, b).
Perspectives The tyrosinase gene family provides an excellent model for understanding a number of biological phenomena. These include gene evolution, the biology of a complex biochemical pathway, protein sorting, and protein–protein interaction. Two of these genes, TYR and TRP1, are involved in albinism. Analysis of tyrosinase mutations associated with oculocutaneous albinism type I has provided insight into the spectrum of phenotypes associated with a single gene disorder.
Acknowledgments V. S. acknowledges the support of NIH grant R01 AR048913.
References Abbott, C., I. J. Jackson, B. Carritt, and S. Povey. The human homolog of the mouse brown gene maps to the short arm of chromosome 9 and extends the known region of homology with mouse chromosome 4. Genomics 11:471–473, 1991. Anderson, M. G., R. S. Smith, N. L. Hawes, A. Zabaleta, B. Chang, J. L. Wiggs, and S. W. John. Mutations in genes encoding melanosomal proteins in pigmentary glaucoma in DBA/2J mice. Nature Genet. 30:81–85, 2002. Aroca, P., J. C. García-Borrón, F. Solano, and J. A. Lozano. Regulation of distal mammalian melanogenesis. I. Partial purification and characterization of a DOPAchrome converting factor: DOPAchrome tautomerase. Biochim. Biochys. Acta 1035:266–275, 1990. Barber, J. I., D. Townsend, D. P. Olds, and R. A. King. DOPAchrome oxidoreductase: a new enzyme in the pigment pathway. J. Invest. Dermatol. 83:145–149, 1984. Barnicot, N. A., M. S. C. Birbeck, and F. W. Cuckow. The electron microscopy of human hair pigments. Ann. Hum. Genet. 19:231–248, 1955. Barton, D. E., B. S. Kwon, and U. Francke. Human tyrosinase gene, mapped to chromosome 11 (q14–>q21), defines second region of homology with mouse chromosome 7. Genomics 3:17–24, 1988. Becker S. W., Jr., T. B. Fitzpatrick, and H. Montgomery. Human melanogenesis: Cytology and histology of pigment cells (melanodendrocytes). Arch. Derm. Syphil. 65:511–523, 1952. Beermann, F., S. Ruppert, E. Hummler, F. X. Bosch, G. Müller, U. Ruther, and G. Schütz. Rescue of the albino phenotype by intro-
224
duction of a functional tyrosinase gene into mice. EMBO J. 9:2819–2826, 1990. Beermann, F., E. Schmid, and G. Schütz. Expression of the mouse tyrosinase gene during embryonic development: Recapitulation of the temporal regulation in transgenic mice. Proc. Natl. Acad. Sci. USA 89:2809–2813, 1992. Beermann, F., S. J. Orlow, R. E. Boissy, A. Schmidt, Y. L. Boissy, and L. Lamoreux. Misrouting of tyrosinase with a truncated cytoplasmic tail as a result of the murine platinum (cp) mutation. Exp. Eye Res. 61:599–607, 1995. Bell, J. A., E. M. Rinchik, S. Raymond, R. Suffolk, and I. J. Jackson. A high-resolution map of the brown (b, Tryp1) deletion complex of mouse chromosome 4. Mamm. Genome 6:389–395, 1995. Beltramini, M., B. Salvato, M. Santamaría, and K. Lerch. The reaction of CN– with the binuclear copper site of Neurospora tyrosinase: its relevance for a comparison between tyrosinase and hemocyanin active sites. Biochim. Biophys. Acta 3:365–372, 1990. Bennett, D. C, and M. L. Lamoreux. The color loci of mice — a genetic century. Pigment Cell Res. 16:333–344, 2003. Bentley, N. J., T. Eisen, and C. R. Goding. Melanocyte-specific expression of the human tyrosinase promoter: activation by the microphthalmia gene product and role of the initiator. Mol. Cell. Biol. 14:7996–8006, 1994. Bernan, V., D. Filpula, W. Herber, M. Bibb, and E. Katz. The nucleotide sequence of the tyrosinase gene from Streptomyces antibioticus and characterization of the gene products. Gene 37:101–110, 1985. Blagoveshchenskaya, A. D., E. W. Hewitt, and D. F. Cutler. Di-leucine signals mediate targeting of tyrosinase and synaptotabmin to synaptic-like microvesicles within PC12 cells. Mol. Biol. Cell 10:3979–3990, 1999. Bloch, B. Chemische untersuchungen uber das specifische pigmentbildende ferment der haut, die dopaoxydase. Hoppe-Seylers Z. Physiol. Chem. 98:226–254, 1917. Boissy, R. E., H. Zhao, W. S. Oetting, L. M. Austin, S. C. Wildenberg, Y. L. Boissy, Y. Zhao, R. A. Sturm, V. J. Hearing, R. A. King, and J. J. Nordlund. Mutation in and lack of expression of tyrosinase-related protein-1 (TRP-1) in melanocytes from an individual with brown oculocutaneous albinism: A new subtype of albinism classified as “OCA3”. Am. J. Hum. Genet. 58:1145–1156, 1996. Boissy, R. E., C. Sakai, H. Q. Zhao, T. Kobayashi, and V. J. Hearing. Human tyrosinase related protein-1 (TRP-1) does not function as a DHICA oxidase activity in contrast to murine TRP-1. Exp. Dermatol. 7:198–204, 1998. Bouchard, B., B. B. Fuller, S. Vijayasaradhi, and A. N. Houghton. Induction of pigmentation in mouse fibroblasts by expression of human tyrosinase cDNA. J. Exp. Med. 169:2029–2042, 1989. Bouchard, B., V. del Marmol, I. J. Jackson, D. Cherif, and L. Dubertret. Molecular characterization of a human tyrosinaserelated-protein-2 cDNA: patterns of expression in melanocytic cells. Eur. J. Biochem. 219:127–134, 1994. Bourquelot, E., and G. Bertrand. Le bleuissement et le noircissement des champignons. C. R. Soc. Biol. 47:582–584, 1895. Branza-Nichita, N., A. J. Petrescu, R. A. Dwek, M. R. Wormald, F. M. Platt, and S. M. Petrescu. Tyrosinase holding and copper loading in vivo: A crucial role for calnexin and a-glucosidasae II. Biochem. Biophys. Res. Commun. 261:720–725, 1999. Breimer, L. H., A. F. Winder, B. Jay, and M. Jay. Initiation codon mutation of the tyrosinase gene as a cause of human albinism. Clin. Chim. Acta 227:17–22, 1994. Brichard, V., A. Van Pel, T. Wolfel, C. Wolfel, E. De Plaen, B. Lethe, P. Coulie, and T. Boon.The tyrosinase gene codes for an antigen recognized by autologous cytolytic T lymphocytes on HLA-A2 melanomas. J. Exp. Med. 178:489–495, 1993. Budd, P., and I. J. Jackson. Structure of the mouse tyrosinase-related protein-2/Dopachrome tautomerase (Tyrp2/Dct) gene and sequence of two novel slaty alleles. Genomics 29:35–43, 1995.
THE TYROSINASE GENE FAMILY Camacho-Hubner, A., C. Richard, and F. Beermann. Genomic structure and evolutionary conservation of the tyrosinase gene family from Fugu. Gene 285:59–68, 2002. Cassady, J. L., and R. A. Sturm. Sequence of the human dopachrome tautomerase-encoding TRP-2 cDNA. Gene 143:295–298, 1994. Chakraborty, A. K., S. J. Orlow, and J. M. Pawelek. Evidence that DOPAchrome tautomerase is a ferrous iron-binding glycoprotein. FEBS Lett. 302:126–128, 1992. Chintamaneni, C. D., R. Halaban, Y. Kobayashi, C. J. Witkop, and B. S. Kwon. A single base insertion in the putative transmembrane domain of the tyrosinase gene as a cause for tyrosinase-negative oculocutaneous albinism. Proc. Natl. Acad. Sci. USA 88:5272–5276, 1991a. Chintamaneni, C. D., M. Ramsay, M. A. Colman, M. F. Fox, R. T. Pickard, and B. S. Kwon. Mapping the human CAS2 gene, the homologue of the mouse brown (b) locus, to human chromosome 9p22-pter. Biochem. Biophys. Res. Commun. 178:227–235, 1991b. Chiu, E., M. L. Lamoreux, and S. J. Orlow. Postnatal ocular expression of tyrosinase and related proteins: disruption of the Pink-eye unstable (pun) mutation. Exp. Eye Res. 57:301–305, 1993. Chu, W., B. J. Pak, M. R. Bani, M. Kapoor, S. J. Lu, A. Tamir, R. S. Kerbel, and Y. Ben-David. Tyrosinase-related protein 2 as a mediator of melanoma specific resistance to cis-diamminedichloroplatinum(II): therapeutic implications. Oncogene 19:395–402, 2000. Cohen, T., R. M. Muller, Y. Tomita, and S. Shibahara. Nucleotide sequence of the cDNA encoding human tyrosinase-related protein. Nucleic Acids Res. 18:2807–2808, 1990. Coleman, D. L. Effect of genic substitution on the incorporation of tyrosine into the melanin of mouse skin. Arch. Biochem. Biophys. 69:562–568, 1962. Cooksey, C. J., P. J. Garratt, E. J. Land, S. Pavel, C. A. Ramsden, P. A. Riley, and N. P. Smit. Evidence of the indirect formation of the catecholic intermediate substrate responsible for the autoactivation kinetics of tyrosinase. J. Biol. Chem. 272:26226–26235, 1997. del Marmol, V., S. Ito, I. Jackson, J. Vachtenheim, P. Berr, G. Ghanem, R. Morandini, K. Wakamatsu, and G. Huez. TRP-1 expression correlates with eumelanogenesis in human pigment cells in culture. FEDS Lett. 327:307–310, 1993. Durham, F. M. On the presence of tyrosinase in the skins of some pigmented veterbrates — Preliminary note. Proc. R. Soc. London 74:310–313, 1904. Fang, D., Y. Tsuji, and V. Setaluri. Selective down-regulation of tyrosinase family gene TYRP1 by inhibition of the activity of melanocyte transcription factor, MITF. Nucleic Acids Res. 30:3096–3106, 2002. Fitzpatrick, T. B., P. Brunet, and A. Kukita. The nature of hair pigment. In: The Biology of Hair Growth, W. Montagna, and R. A. Ellis (eds). New York: Academic Press, 1958, pp. 255– 303. Francis, E., N. Wang, H. Parag, R. Halaban, and D. N. Hebert. Tyrosinase maturation and oligomerization in the endoplasmic reticulum require a melanocyte-specific factor. J. Biol. Chem. 278:25607– 25617, 2003. Fryer, J. P., W. S. Oetting, M. J. Brott, and R. A. King. Alternative splicing of the tyrosinase gene transcript in normal human melanocytes and lymphocytes. J. Invest. Dermatol. 117:1261– 1265, 2001. Fryer, J. P., W. S. Oetting, and R.A. King. Identification and characterization of a DNase hypersensitive region of the human tyrosinase gene. Pigment Cell Res. 16:679–684, 2003. Fukai, K., S. A. Holmes, N. J. Lucchese, V. M. Siu, R. G. Welber, R. E. Schnur, and R. A. Spritz. Autosomal recessive ocular albinism associated with a functionally significant tyrosinase gene polymorphism. Nature Genet. 9:92–95, 1995. Furumura, M., F. Solano, N. Matsunaga, C. Sakai, R. A. Spritz, and V. J. Hearing. Metal ligand-binding specificities of the tyrosinase-related proteins. Biochem. Biophys Res. Commun. 242:579–585, 1998. Ganss, R., L. Montoliu, A. P. Managhan, and G. Schütz. A cell-spe-
cific enhancer far upstream of the mouse tyrosinase gene confers high level and copy number-related expression in transgenic mice. EMBO J. 13:3083–3093, 1994. Garrod, A. E. Croonian lectures on inborn errors of metabolism. Lecture 1. Lancet 2:1–7, 1908. Gaykema, W. P. J., W. G. J. Hol, J. M. Vereijken, N. M. Soeter, H. J. Bak, and J. J. Beintema. 3.2 Å structure of the copper-containing oxygen-carrying protein Panulirus interruptus haemocyanin. Nature 309:23–29, 1984. Gaykema, W. P., A. Volbeda, and W. G. Hol. Structure determination of Panulirus interruptus haemocyanin at 3.2 A resolution. Successful phase extension by sixfold density averaging. J. Mol. Biol. 187:255–275, 1986. Gessard, C. Sur la formation du pigment mélanique dans les tumeurs du cheval. C. R. Acad. 136:1086–1088, 1903. Giebel, L. B., K. M. Strunk, R. A. King, J. M. Hanifin, and R. A. Spritz. A frequent tyrosinase gene mutation in classic, tyrosinasenegative (Type IA) oculocutaneous albinism. Proc. Natl. Acad. Sci. USA 87:3255–3258, 1990. Giebel, L. B., R. K. Tripathi, K. M. Strunk, J. M. Hanifin, C. E. Jackson, R. A. King, and R. A. Spritz. Tyrosinase gene mutations associated with type IB (“yellow”) oculocutaneous albinism. Am. J. Hum. Genet. 48:1159–1167, 1991a. Giebel, L. B., K. M. Strunk, and R. A. Spritz. Organization and nucleotide sequences of the human tyrosinase gene and a truncated tyrosinase-related segment. Genomics 9:435–445, 1991b. Green, M. C. Slaty (slt). Mouse News Lett. 47:36, 1972. Guyonneau, L., F. Murisier, A. Rossier, A. Moulin, and F. Beermann. Melanocytes and pigmentation are affected in dopachrome tautomerase knockout mice. Mol. Cell Biol. 24:3396–3403, 2004. Halaban, R., and G. Moellmann. Murine and human b locus pigmentation genes encode a glycoprotein (gp75) with catalase activity. Proc. Natl. Acad. Sci. USA 87:4809–4813, 1990. Halaban, R., E. Cheng, Y. Zhang, G. Moellmann, D. Hanlon, M. Michalak, V. Setaluri, and D. N. Herbert. Aberrant retention of tyrosinase in the endoplasmic reticulum mediates accelerated degradation of the enzyme and contributes to the dedifferentiated phenotype of amelanotic melanoma cells. Proc. Natl. Acad. Sci. USA 94:6210–6215, 1997. Halaban, R., S. Svedine, E. Cheng, Y. Smicun, R. Aron, and D. N. Herbert. Endoplasmic reticulum retention is a common defect associated with tyrosinase-negative albinism. Proc. Natl. Acad. Sci. USA 97:5889–5894, 2000. Hearing, V. J., A. M. Korner, and J. M. Pawelek. New regulators of melanogenesis are associated with purified tyrosinase isozymes. J. Invest. Dermatol. 79:16–18, 1982. Hemesath, T. J., E. Steingrímsson, G. McGill, M. J. Hansen, J. Vaught, C. A. Hodgkinson, H. Arnheiter, N. G. Copeland, N. A. Jenkins, and D. E. Fisher. microphthalmia, a critical factor in melanocyte development, defines a discrete transcription factor family. Genes Dev. 8:2770–2780, 1994. Hodgkinson, C. A., K. J. Moore, A. Nakayama, E. Steingrímsson, N. G. Copeland, N. A. Jenkins, and H. Arnheiter. Mutations at the mouse microphthalmia locus are associated with defects in a gene encoding a novel basic-helix-loop-helix-zipper protein. Cell 74:395–404, 1993. Hogeboom, G. H., and M. H. Adams. Mammalian tyrosinase and dopa oxidase. J. Biol. Chem. 145:273–279, 1942. Höning, S., I. V. Sandocal, and K. von Figura. A di-leucine-based motif in the cytoplasmic tail of LIMP-II and tyrosinase mediates selective binding of AP-3. EMBO J. 17:1304–1314, 1998. Huber, M., and K. Lerch. Identification of two histidines as copper ligands in Streptomyces glaucescens tyrosinase. Biochemistry 27:5610–5615, 1988. Huber, M., G. Hintermann, and K. Lerch. Primary structure of tyrosinase from Streptomyces glaucescens. Biochemistry 24:6038–6044, 1985.
225
CHAPTER 11 Huizing, M., Y. Anikster, and W. A. Gahl. Hermansky–Pudlak syndrome and Chediak–Higashi syndrome: disorders of vesicle formation and trafficking. Thromb. Haemost. 86:233–245, 2001. Jackman, M. P., A. Hajnal, and K. Lerch. Albino mutants of Streptomyces glaucescens tyrosinase. Biochem. J. 274:707–713, 1991. Jackman, M. P., M. Huber, A. Hajnal, and K. Lerch. Stabilization of the oxy form of tyrosinase by a single conservative amino acid substitution. Biochem. J. 282:915–918, 1992. Jackson, I. J. A cDNA encoding tyrosinase-related protein maps to the brown locus in mice. Proc. Natl. Acad. Sci. USA 85:4392–4396, 1988. Jackson, I. J. Molecular and developmental genetics of mouse coat color. Annu. Rev. Genet. 28:189–217, 1994. Jackson, I. J. Workshop report: Evolution and expression of tyrosinase-related proteins. Pigment Cell Res. 7:241–243, 1995a. Jackson, I. J. Molecular and developmental genetics of mouse coat color. Annu. Rev. Genet. 28:189–217, 1995b. Jackson, I. J., and D. C. Bennett. Molecular characterization of the mouse albino mutation of tyrosinase and an in vitro revertant. Proc. Natl. Acad. Sci. USA 87:7010–7014, 1990. Jackson, I. J., D. M. Chambers, E. M. Rinchik, and D. C. Bennett. Characterization of TRP-1 mRNA levels in dominant and recessive mutations at the mouse brown (b) locus. Genetics 126:451–460, 1990. Jackson, I. J., D. M. Chambers, P. S. Budd, and R. Johnson. The tyrosinase-related protein-1 gene has a structure and promoter sequence very different from tyrosinase. Nucleic Acids Res. 19:3799–3804, 1991. Jackson, I. J., D. M. Chambers, K. Tsukamoto, N. G. Copeland, D. J. Gilbert, N. A. Jenkins, and V. J. Hearing. A second tyrosinaserelated protein, TRP2, maps to and is mutated at the mouse slaty locus. EMBO J. 11:527–535, 1992. Jackson, I. J., P. Budd, J. M. Horn, R. Johnson, S. Raymond, and K. Steel. Genetics and molecular biology of mouse pigmentation. Pigment Cell Res. 7:73–80, 1994. Jiao, Z., R. Mollaaghababa, W. J. Pavan, A. Antonellis, E. D. Green, and T. J. Hornyak. Direct interaction of Sox10 with the promoter of murine dopachrome tautomerase (Dct) and synergistic activation of Dct expression with Mitf. Pigment Cell Res. 17:352–362, 2004. Jimbow, K., H. Hara, T. Vinayagamoorthy, D. Luo, J. Dakour, K. Yamada, W. Dixon, and H. Chen. Molecular control of melanogenesis in malignant melanoma: Functional assessment of tyrosinase and lamp gene families by UV exposure and gene co-transfection, and cloning of a cDNA encoding calnexin, a possible melanogenesis “chaperone”. J. Dermatol. 21:894–906, 1994. Jimbow, K., D. Luo, H. Chen, H. Hara, and M. H. Lee. Coordinated mRNA and protein expression of human LAMP-1 in induction of melanogenesis after UV-B exposure and co-transfection of human tyrosinase and TRP-1 cDNAs. Pigment Cell Res. 7:311–320, 1995. Jiménez, M., K. Tsukamoto, and V. J. Hearing. Tyrosinases from two different loci are expressed by normal and by transformed melanocytes. J. Biol. Chem. 266:1147–1156, 1991. Jiménez-Cervantes, C., F. Solano, T. Kobayashi, K. Urabe, V. J. Hearing, J. A. Lozano, and J. C. García-Borrón. A new enzymatic function in the melanogenic pathway: The 5.6-dihydroxyindole-2carboxylic acid oxidase activity of tyrosinase-related protein-1 (TRP-1). J. Biol. Chem. 269:17993–18001, 1994. Johnson, R., and I. J. Jackson. Light is a dominant mouse mutation resulting in premature cell death. Nature Genet. 1:226–229, 1992. Kameyama, K., M. Jiménez, J. Muller, Y. Ishida, and V. J. Hearing. Regulation of mammalian melanogenesis by tyrosinase inhibition. Differentiation 42:28–36, 1989. Kameyama, K., T. Takemura, Y. Hamada, C. Sakai, S. Kondoh, S. Nishiyama, K. Urabe, and V. J. Hearing. Pigment production in murine melanoma cells is regulated by tyrosinase, tyrosinase-related protein 1 (TRP1), DOPAchrome tautomerase (TRP2) and a
226
melanogenic inhibitor. J. Invest. Dermatol. 100:126–131, 1993. Kameyama, K., C. Sakai, S. Kuge, S. Nishiyama, Y. Tomita, S. Ito, K. Wakamatsu, and V. J. Hearing. The expression of tyrosinase, tyrosinase-related proteins 1 and 2 (TRP1 and TRP2), the silver protein, and a melanogenic inhibitor in human melanoma cells of differing melanogenic activities. Pigment Cell Res. 8: 97–104, 1995. Katz, E., C. J. Thompson, and D. A. Hopwood. Cloning and expression of the tyrosinase gene from Streptomyces antibioticus in Streptomyces lividans. J. Gen. Microbiol. 129:2703–2714, 1983. Kikuchi, H., H. Miura, H. Yamamoto, T. Takeuchi, T. Dei, and M. Watanabe. Characteristic sequences in the upstream region of the human tyrosinase gene. Biochim. Biophys. Acta 1009:283–286, 1989. King, R. A., and W. S. Oetting. Molecular basis of type IA (tyrosinase negative) oculocutaneous albinism. Pigment Cell Res. (Suppl. 2): 19–23, 1992. King, R. A., M. M. Mentink, and W. S. Oetting. Non-random distribution of missense mutations within the human tyrosinase gene in Type 1 (tyrosinase-related) oculocutaneous albinism. Mol. Biol. Med. 8:19–29, 1991. King, R. A., V. J. Hearing, D. Creel, and W. S. Oetting. Albinism. In: The Metabolic and Molecular Basis of Inherited Disease, 8th edn, C. R. Scriver, A. L. Beaudet, W. S. Sly, and D. Valle (eds). New York: McGraw-Hill, 2000, pp. 5587–5627. Kluppel, M., F. Beermann, S. Ruppert, E. Schmid, E. Hummler, and G. Schütz. The mouse tyrosinase promoter is sufficient for expression in melanocytes and in the pigmented epithelium of the retina. Proc. Natl. Acad. Sci. USA 88:3777–3781, 1991. Körner, A. M., and J. M. Pawelek. DOPAchrome conversion: a possible control point in melanin biosynthesis. J. Invest. Dermatol. 75:192–195, 1980. Kromberg, J. G., D. J. Castle, E. M. Zwane, J. Bothwell, S. Kidson, P. Bartel, J. I. Phillips, and T. Jenkins. Red or rufous albinism in southern Africa. Ophthal. Paediatr. Genet. 11:229–235, 1990. Kroumpouzos, G., K. Urabe, T. Kobayashi, C. Sakai, and V. J. Hearing. Functional analysis of the slaty gene product (TRP2) as dopachrome tautomerase and the effect of a point mutation on its catalytic function. Biochem. Biophys. Res. Commun. 202:1060– 1068, 1994. Kumasaka, M., S. Sato, I. Yajima, and H. Yamamoto. Isolation and developmental expression of tyrosinase family genes in Xenopus laevis. Pigment Cell Res. 16:455–462, 2003. Kuzumaki, T., A. Matsuda, K. Wakamatsu, S. Ito, and K. Ishikawa. Eumelanin biosynthesis is regulated by coordinated expression of tyrosinase and tyrosinase-related protein-1 genes. Exp. Cell Res. 207:33–40, 1993. Kwon, B. S., A. K. Haq, S. H. Pomerantz, and R. Halaban. Isolation and sequence of a cDNA locus for human tyrosinase that maps at the mouse c-albino locus. Proc. Natl. Acad. Sci. USA 84:7473– 7477, 1987. Kwon, B. S., R. Halaban, and C. D. Chintamaneni. Molecular basis of the mouse Himalayan mutation. Biochem. Biophys. Res. Commun. 161:252–260, 1989. Le Borgne, R., A. Alconada, U. Bauer, and B. Hoflack. The mammalian AP-3 adaptor-like complex mediates the intracellular transport of lysosomal membrane glycoproteins. J. Biol. Chem. 273: 29451–29461, 1998. Leonard, L. J., D. Townsend, and R. A. King. Function of dopachrome oxidoreductase and metal ions in dopachrome conversion in the eumelanin pathway. Biochemistry 16:6156–6159, 1988. Lerch, K. Protein and active-site structure of tyrosinase. In: Advances in Pigment Cell Research, J. T. Bagnara (ed.). New York: Alan R. Liss, 1988, pp. 85–98. Lerner, A. B., and T. B. Fitzpatrick. Biochemistry of melanin formation. Physiol. Rev. 30:91–126, 1950.
THE TYROSINASE GENE FAMILY Lerner, A. B., T. B. Fitzpatrick, E. Calkins, and W. H. Summerson. Mammalian tyrosinase: preparation and properties. J. Biol. Chem. 178:185–195, 1949. Libby, R. T., R. S. Smith, O. V. Savinova, A. Zabaleta, J. E. Martin, F. J. Gonzalez, and S. W. John. Modification of ocular defects in mouse developmental glaucoma models by tyrosinase. Science 299:1578–1581, 2003. Liu, T. F., G. Kandala, and V. Setaluri. PDZ domain protein GIPC interacts with the cytoplasmic tail of melanosomal membrane protein gp75 (tyrosinase-related protein-1). J. Biol. Chem. 276: 35768–35777, 2001. Logan, A., and B. Weatherhead. Pelage color cycles and hair follicle tyrosinase activity in the Siberian hamster. J. Invest. Dermatol. 71:295–298, 1978. Lowings, P., U. Yavuzer, and C. R. Goding. Positive and negative elements regulate a melanocyte-specific promoter. Mol. Cell Biol. 12:3653–3662, 1992. Lynch, S., G. Yanagi, E. DelBono, and J. L. Wiggs. DNA sequence variants in the tyrosinase-related protein 1 (TYRP1) gene are not associated with human pigmentary glaucoma. Mol. Vis. 8:127–129, 2002. Manga, P., J. G. Kromberg, N. F. Box, R. A. Sturm, T. Jenkins, and M. Ramsay. Rufous oculocutaneous albinism in southern African Blacks is caused by mutations in the TYRP1 gene. Am. J. Hum. Genet. 5:1095–1101, 1997. Martínez-Liarte, J. H., F. Solano, J. C. García-Borrón, J. R. Jara, and J. A. Lozano. a-MSH and other melanogenic activators mediate opposite effects on tyrosinase and DOPAchrome tautomerase in B16/F10 mouse melanoma cells. J. Invest. Dermatol. 99:435–439, 1992. Mason, K. A., and S. K. Mason. The identification and partial cloning by PCR of the gene for tyrosinase-related protein-1 in the Mexican axolotl. Pigment Cell Res. 8:46–52, 1995. Mason, H. S., W. L. Fowlks, and E. Peterson. Oxygen transfer and electron transport by the phenolase complex. J. Am. Chem. Soc. 107:4015–4027, 1955. Miura, I., H. Okumoto, K. Makino, A. Nakata, and M. Nishioka. Analysis of the tyrosinase gene of the Japanese pond frog, Rana nigromaculata: Cloning and nucleotide sequence of the genomic DNA containing the tyrosinase gene and its flanking regions. Jpn. J. Genet. 70:79–92, 1995. Morris, S. W., W. Muir, and D. St Clair. Dinucleotide repeat polymorphism at the human tyrosinase gene. Nucleic Acids Res. 19:68–69, 1991. Murty, V. V. V. S., B. Bouchard, S. Mathew, S. Vijayasaradhi, and A. N. Houghton. Assignment of the Human TYRP (brown) locus to chromosome region 9p23 by nonradioactive in situ hybridization. Genomics 13:227–229, 1992. Müller, G., S. Ruppert, E. Schmid, and G. Schütz. Functional analysis of alternatively spliced tyrosinase gene transcripts. EMBO J. 7:2723–2730, 1988. Oetting, W. S., and R. A. King. Molecular analysis of Type I-A (tyrosinase-negative) oculocutaneous albinism. Hum. Genet. 90:258–262, 1992a. Oetting, W. S., and R. A. King. Analysis of mutations in the copper B binding region associated with Type I (tyrosinase-related) oculocutaneous albinism. Pigment Cell Res. 5:274–278, 1992b. Oetting, W. S., and R. A. King. Analysis of tyrosinase mutations associated with tyrosinase-related oculocutaneous albinism (OCA1). Pigment Cell Res. 7:285–290, 1994. Oetting, W. S., and R. A. King. Molecular basis of albinism: mutations and polymorphisms of pigmentation genes associated with albinism. Hum. Mutat. 13:99–115, 1999. Oetting, W. S., O. C. Stine, D. Townsend, and R. A. King. Evolution of the tyrosinase related gene (TYRL) in primates. Pigment Cell Res. 6:171–177, 1993a.
Oetting, W. S., C. J. Witkop, S. A. Brown, R. Colomer, J. P. Fryer, K. E. Bloom, and R. A. King. A frequent mutation in the tyrosinase gene associated with type I-A (tyrosinase-negative) oculocutaneous albinism in Puerto Rico. Am. J. Hum. Genet. 52:17–23, 1993b. Oetting, W. S., J. P. Fryer, Y. Oofuji, L. R. Middendorf, J. A. Brumbaugh, C. G. Summers, and R. A. King. Analysis of tyrosinase gene mutations using direct automated infrared fluorescence DNA sequencing of amplified exons. Electrophoresis 15:159–164, 1994. Oetting, W. S., W. Skach, J. P. Fryer, and R. A. King. Unusual tyrosinase mutations associated with OCA1. Am. J. Hum. Genet. 53:935, 1995. Orlow, S. J. Melanosomes are specialized members of the lysosomal lineage of organelles. J. Invest. Dermatol. 105:3–7, 1995. Orlow, S. J., M. L. Lamoreux, S. Pifko-Hirst, and B. K. Zhou. Pathogenesis of the platinum (cp) mutation, a model for oculocutaneous albinism. J. Invest. Dermatol. 101:137–140, 1993a. Orlow, S. J., R. E. Boissy, D. J. Moran, and S. Pifko-Hirst. Subcellular distribution of tyrosinase and tyrosinase-related protein-1: implications for melanosomal biogenesis. J. Invest. Dermatol. 100:55–64, 1993b. Orlow, S. J., B.-K. Zhou, A. K. Chakraborty, M. Drucker, S. PifkoHirst, and J. M. Pawelek. High-molecular-weight forms of tyrosinase and the tyrosinase-related proteins: evidence for a melanogenic complex. J. Invest. Dermatol. 103:196–201, 1994. Pawelek, J. M. After DOPAchrome? Pigment Cell Res. 4:53–62, 1991. Pawelek, J. M., A. M. Körner, A. Bergstrom, and J. Bolognia. New regulators of melanin biosynthesis and the autodestruction of melanoma cells. Nature 286:617–619, 1980. Peng, G., J. D. Taylor, and T. T. Tchen. Goldfish tyrosinase related protein I (TRP-1): Deduced amino acid sequence from cDNA and comments on structural features. Pigment Cell Res. 7:9–16, 1995. Ponnazhagan, S., L. Hou, and B. S. Kwon. Structural organization of the human tyrosinase gene and sequence analysis and characterization of its promoter region. J. Invest. Dermatol. 102:744–748, 1994. Porter, S. D., and C. J. Meyer. A distal tyrosinase upstream element stimulates gene expression in neural-crest-derived melanocytes of transgenic mice: position-independent and mosaic expression. Development 120:2103–2111, 1994. Porter, S., L. Larue, and B. Mintz. Mosaicism of tyrosinase-locus transcription and chromatin structure in dark vs light melanocyte clones of homozygous chinchilla-mottled mice. Dev. Genet. 12:393–402, 1991. Pruitt, K. D., and D. R. Maglott. RefSeq and LocusLink: NCBI genecentered resources. Nucleic Acids Res. 29:137–140, 2001. Regales, L., P. Giraldo, A. Garcia-Diaz, A. Lavado, and L. Montoliu. Identification and functional validation of a 5¢ upstream regulatory sequence in the human tyrosinase gene homologous to the locus control region of the mouse tyrosinase gene. Pigment Cell Res. 16:685–693, 2003. Rosenberg, S. A. Progress in human tumor immunology and immunotherapy. Nature 411:380–384, 2001. Sato, S., H. Miura, H. Yamamoto, and T. Takeuchi. Identification of nuclear factors that bind to the mouse tyrosinase gene regulatory region. Pigment Cell Res. 7:279–284, 1994. Schedl, A., L. Montollu, G. Kelsey, and G. Schütz. A yeast artificial chromosome covering the tyrosinase gene confers copy numberdependent expression in transgenic mice. Nature 362:258–261, 1993. Schmidt, A., and F. Beermann. Molecular basis of dark-eyed albinism in the mouse. Proc. Natl. Acad. Sci. USA 91:4756–4760, 1994. Setaluri, V. Sorting and targeting of melanosomal membrane proteins: signals, pathways and mechanisms. Pigment Cell Res. 113:128– 134, 2000.
227
CHAPTER 11 Shibahara, S., Y. Tomita, T. Sakakura, C. Nager, B. Chaudhuri, and R. Muller. Cloning and expression of cDNA encoding mouse tyrosinase. Nucleic Acids Res. 14:2413–2427, 1986. Shibahara, S., S. Okinaga, Y. Tomita, A. Takeda, H. Yamamoto, M. Sato, and T. Takeuchi. A point mutation in the tyrosinase gene of BALB/c albino mouse causing the cysteine to serine substitution at position 85. Eur. J. Biochem. 189:455–461, 1990. Shibahara, S., H. Taguchi, R. M. Muller, K. Shibata, T. Cohen, Y. Tomita, and H. Tagami. Structural organization of the pigment cellspecific gene located at the brown locus in mouse. Its promoter activity and alternatively spliced transcript. J. Biol. Chem. 266: 15895–15901, 1991. Shibata, K., Y. Muraosa, Y. Tomita, H. Tagami, and S. Shibahara. Identification of a cis-acting element that enhances the pigment cellspecific expression of the human tyrosinase gene. J. Biol. Chem. 267:20584–20588, 1992a. Shibata, K., K. Takeda, Y. Tomita, H. Tagami, and S. Shibahara. Downstream region of the human tyrosinase-related protein gene enhances its promoter activity. Biochem. Biophys. Res. Commun. 184:568–575, 1992b. Silvers, W. K. The Coat Colors of Mice. A Model for Mammalian Gene Action and Interaction. New York: Springer-Verlag, 1979. Simmen, T., A. Schmidt, W. Hunzilker, and F. Beermann. The tyrosinase tail mediates sorting to the lysosomal compartment in MDCK cells via a di-leucine and a tyrosine-based signal. J. Cell Sci. 112:45–53, 1999. Solano, F., J. H. Martinez-Liarte, C. Jimenez-Cervantes, J. C. GarciaBorron, and J. A. Lozano. Dopachrome tautomerase is a zinccontaining enzyme. Biochem. Biophys. Res. Commun. 204:1243– 1250, 1994. Spritz, R. A., L. Ho, M. Furumura, and V. J. Hearing. Mutational analysis of copper binding by human tyrosinase. J. Invest. Dermatol. 109:207–212, 1997. Steel, K. P., D. R. Davidson, and I. J. Jackson. TRP2/DT, a new early melanoblast marker, shows that steel growth factor (c-kit ligand) is a survival factor. Development 115:1111–1119, 1992. Sturm, R. A., B. J. O’Sullivan, J. A. F. Thomson, N. Jamshidi, J. Pedley, and P. Parsons. Expression studies of pigmentation and POUdomain genes in human melanoma cells. Pigment Cell Res. 7:235–240, 1994a. Sturm, R. A., E. Baker, and G. R. Sutherland. Assignment of the tyrosinase-related protein-2 gene (TYRP2) to human chromosome 13q31–q32 by fluorescence in situ hybridization: extended synteny with mouse chromosome 14. Genomics 21:293–296, 1994b. Sturm, R. A., B. J. O’Sullivan, N. F. Box, A. G. Smith, S. E. Smit, E. R. J. Puttick, P. G. Parsons, and I. S. Dunn. Chromosomal structure of the human TYRP1 and TYRP2 loci and comparison of the tyrosinase-related protein gene family. Genomics 29:24–34, 1995. Takeda, A., J. Matsunaga, Y. Tomita, H. Tagami, and S. Shibahara. Molecular analysis of the DNA segments cross-hybridizable to the tyrosinase gene in patients afflicted with oculocutaneous albinism. Tohoku J. Exp. Med. 159:333–340, 1989a. Takeda, A., Y. Tomita, S. Okinaga, H. Tagami, and S. Shibahara. Functional analysis of the cDNA encoding human tyrosinase precursor. Biochem. Biophys. Res. Commun. 162:984–990, 1989b. Takeda, A., J. Matsunaga, Y. Tomita, H. Tagami, and S. Shibahara. Nucleotide sequence of the putative human tyrosinase pseudogene. Tohoku J. Exp. Med. 163:295–297, 1991. Takeuchi, H., C. Kuo, D. L. Morton, H. J. Wang, and D. S. Hoon. Expression of differentiation melanoma-associated antigen genes is associated with favorable disease outcome in advanced-stage melanomas. Cancer Res. 63:441–448, 2003. Tamate, H. B., T. Hirobe, K. Wakamatsu, S. Ito, S. Shibahara, and K. Ishikawa. Levels of tyrosinase and its mRNA in coat-color mutants of C57BL/10J congenic mice: effects of genic substitution at the agouti, brown, albino, dilute and pink-eyed dilution loci. J. Exp. Zool. 250:304–311, 1989.
228
Taniguchi, M., T. Iwamoto, I. Nakashima, A. Nakayama, O. Masaharu, M. Matsuyama, and M. Takahashi. Establishment and characterization of a malignant melanocytic tumor cell line expressing the ret oncogene. Oncogene 7:1491–1496, 1992. Tassabehji, M., V. E. Newton, and A. P. Read. Waardenburg syndrome type 2 caused by mutations in the human microphthalmia (MITF) gene. Nature Genet. 8:251–255, 1994. Tomita, Y., A. Takeda, S. Okinaga, H. Tagami, and S. Shibahara. Human oculocutaneous albinism caused by a single base insertion in the tyrosinase gene. Biochem. Biophys. Res. Commun. 164:990– 996, 1989. Toyofuku, K., I. Wada, J. C. Valencia, T. Kushimoto, V. J. Ferrans, and V. J. Hearing. Oculocutaneous albinism type 1 and 3 are ER retention diseases: mutation of tyrosinase or Tyrp1 can affect the processing of both mutant and wildtype proteins. FASEB J. 15:2149–2161, 2001a. Toyofuku, K., I. Wada, R. A. Spritz, and V. J. Hearing. The molecular basis of oculocutaneous albinism type 1 (OCA1): sorting failure and degradation of mutant tyrosinases results in a lack of pigmentation. Biochem. J. 355:259–269, 2001b. Tripathi, R. K., V. J. Hearing, K. Urabe, P. Aroca, and R. A. Spritz. Mutational mapping of the catalytic activities of human tyrosinase. J. Biol. Chem. 267:23707–23712, 1992a. Tripathi, R. K., K. M. Strunk, L. B. Giebel, R. G. Weleber, and R. A. Spritz. Tyrosinase gene mutations in Type I (tyrosinase-deficient) oculocutaneous albinism define two clusters of missense substitutions. Am. J. Med. Genet. 43:865–871, 1992b. Tsukamoto, K., I. J. Jackson, K. Urabe, P. M. Montague, and V. J. Hearing. A second tyrosinase-related protein, TRP2, is a melanogenic enzyme termed DOPAchrome tautomerase. EMBO J. 11:519–526, 1992a. Tsukamoto, K., M. Jiménez, and V. J. Hearing. The nature of tyrosinase isozymes. In: The Pigment Cell: From the Molecular to the Clinical Level, Y. Mishima (ed.). Copenhagen: Munksgaard Press, 1992b, pp. 84–89. Urquhart, A. Human tyrosinase-like protein (TYRL) carboxy terminus: closer homology with the mouse protein than previously reported. Nucleic Acids Res. 19:5803, 1993. Vijayasaradhi,S., B. Bouchard, and A. N. Houghton. The melanoma antigen gp75 is the human homologue of the mouse b (brown) locus gene product. J. Exp. Med. 171:1375–1380, 1990. Vijayasaradhi, S., Y. X. Brigitte, B. Bouchard, and A. N. Houghton. Intracellular sorting and targeting of melanosomal membrane proteins: Identification of signals for sorting of the human brown locus protein, GP75. J. Cell Biol. 130:807–820,1995a. Vijayasaradhi, S., P. M. Doskoch, J. Wolchok, and A. N. Houghton. Melanocyte differentiation marker gp75, the brown locus protein, can be regulated independently of tyrosinase and pigmentation. J. Invest. Dermatol. 105:113–119, 1995b. Wang, R. F., P. F. Robbins, Y. Kawakami, X. Q. Kang, and S. A. Rosenberg. Identification of a gene encoding a melanoma tumor antigen recognized by HLA-A31-restricted tumor-infiltrating lymphocytes. J. Exp. Med. 181:799–804, 1995. Wang, R. F., E. Appella, Y. Kawakami, X. Kang, and S. A. Rosenberg. Identification of TRP-2 as a human tumor antigen recognized by cytotoxic T lymphocytes. J. Exp. Med. 184:2207–2216, 1996. Wilcox, D. E., A. G. Porras, Y. T. Hwang, K. Lerch, M. E. Winkler, and E. I. Solomon. Substrate analogue binding to the coupled binuclear copper active site in tyrosinase. J. Am. Chem. Soc. 107:4015–4027, 1995. Winder, A. J., T. Kobayashi, K. Tsukamoto, K. Urabe, P. Aroca, K. Kameyama, and V. J. Hearing. The tyrosinase gene family: Interactions of melanogenic proteins to regulate melanogenesis. Cell. Mol. Biol. Res. 40:613–626, 1994a. Winder, A. J., A. Wittbjer, G. Odh, E. Rosengren, and H. Rorsman. The mouse brown (b) locus protein functions as a dopachrome tautomerase. Pigment Cell Res. 7:305–310, 1994b.
THE TYROSINASE GENE FAMILY Wittbjer, A., B. Dahlback, G. Odh, A. M. Rosengren, E. Rosengren, and H. Rorsman. Isolation of human tyrosinase from cultured melanoma cells. Acta Derm. Venereol. Suppl. 69:125–131, 1989. Yamamoto, H., S. Takeuchi, T. Kudo, K. Makino, A. Nakata, T. Shinoda, and T. Takeuchi. Cloning and sequencing of mouse tyrosinase cDNA. Jpn. J. Genet. 62:271–274, 1987. Yamamoto, H., T. Kudo, N. Masuko, H. Miura, S. Sato, M. Tanaka, S. Tanaka, S. Takeuchi, S. Shibahara, and T. Takeuchi. Phylogeny of regulatory regions of vertebrate tyrosinase genes. Pigment Cell Res. 5:284–294, 1992. Yasumoto, K.-I., K. Yokoyama, K. Shibata, Y. Tomita, and S. Shibahara. Microphthalmia-associated transcription factor as a regulator for melanocyte-specific transcription of the human tyrosinase gene. Mol. Cell. Biol. 14:8058–8070, 1994. Yasumoto, K.-I., H. Mahalingam, H. Suzuki, M. Yoshizawa, K. Yokoyama, and S. Shibahara. Transcriptional activation of the melanocyte-specific genes by the human homolog of
the mouse microphthalmia protein. J. Biochem. 118:874–881, 1995. Yokoyama, T., D. W. Silversides, K. G. Waymire, B. S. Kwon, T. Takeuchi, and P. A. Overbeek. Conserved cysteine to serine mutation in tyrosinase is responsible for the classical albino mutation in laboratory mice. Nucleic Acids Res. 18:7293–7298, 1990. Yokoyama, K., H. Suzuki, K.-I. Yasumoto, Y. Tomita, and S. Shibahara. Molecular cloning and functional analysis of a cDNA coding for human DOPAchrome tautomerase/tyrosinase-related protein-2. Biochim. Biophys. Acta 1217:317–321, 1994. Zdarsky, E., J. Favor, and I. J. Jackson. The molecular basis of brown, an old mouse mutation, and of an induced revertant to wild-type. Genetics 126:443–449, 1990. Zhou, B. K., R. E. Boissy, S. Pifko-Hirst, D. J. Moran, and S. J. Orlow. Lysosome-associated membrane protein-1 (LAMP-1) is the melanocyte vesicular membrane glycoprotein band II. J. Invest. Dermatol. 100:110–114, 1993.
229
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
12
Molecular Regulation of Melanin Formation: Melanosome Transporter Proteins Murray H. Brilliant
Summary 1 To make melanin, tyrosinase must be correctly targeted to the melanosome, its substrate, tyrosine, must be transported into the melanosome, and conditions that favor the enzymatic activity of tyrosinase must exist inside the melanosome. All these processes are affected by pH and ionic conditions. Therefore, ion transport across the melanosome membrane is critical for the biosynthesis of melanin. Two proteins, the P protein [encoded by the mouse pink-eyed dilution (p) locus and the human P locus] and MATP (membrane-associated transport protein, previously known as AIM-1, encoded by the formerly named mouse underwhite locus) are critical for normal pigmentation and are likely to be involved in ion flux across the melanosomal membrane. 2 The mouse pink-eyed dilution locus, p, and its human homolog, P, encode a protein of 110 kDa with 12 membranespanning domains that is localized to the melanosome membrane, although a significant fraction is thought to be associated with the endoplasmic reticulum. The p protein is required for normal melanin (primarily eumelanin) biosynthesis. Although the exact function of the p protein is currently unknown, it has a predicted structure in common with anion transporters and Na+/H+ antiporters. Melanocytes lacking a functional p protein have immature melanosomes with aberrant pH that only accumulate minute amounts of primarily eumelanin. In these p mutant melanocytes, tyrosinase is incorrectly processed and targeted. 3 Mutations of the human P gene on chromosome 15q11.2–q12 lead to tyrosinase-positive oculocutaneous albinism, defined as OCA2, a recessive genetic disorder present in the general population at 1:38 000. OCA2 is more common among individuals of African origin, where a predominant haplotype is associated with a 2.7-kb deletion that includes exon 7 of the P gene. In some African populations, this deletion allele comprises up to 80% of the P gene mutations. A larger deletion of different origin is commonly associated with OCA2 among the Navajo people, an independent population that exhibits a high frequency of albinism. 4 The only known function of the P gene is in pigmentation. However, deletions of the human chromosomal interval 15q11q13 that contains the P gene lead to distinct phenotypes known as Prader–Willi syndrome or Angelman syndrome, 230
depending on whether the deletion is paternal or maternal in origin respectively. Although the critical regions and/or genes associated with these imprinting syndromes are distinct from each other and from the P gene, one homolog of the P gene is often deleted in PWS and AS patients. Those AS and PWS patients who are hemizygous for the P gene (in the context of a large deletion of 15q) often exhibit hypopigmentation relative to other family members, a puzzling outcome as carriers of null alleles of the P gene (in the context of a normal chromosome 15) are normally pigmented. Many radiation-induced alleles of the mouse p locus on chromosome 7 are associated with nonpigmentation phenotypes. All these other phenotypes are associated with deletions extending into neighboring genes. 5 The Matp (membrane-associated transporter protein) gene encodes a protein of ~58 kDa with 12 membrane-spanning domains that is very likely associated with the melanosome membrane. The encoded protein, Matp, likely functions as a transporter. One of its closest orthologs encodes a plant sucrose/proton transporter, and the Matp protein may play a role in pH and/or osmotic regulation of the melanosome. In Matp mutant melanocytes (as in p mutant melanocytes), tyrosinase is incorrectly processed and targeted. Matp previously shared the name of AIM-1 with at least two other distinct and unrelated proteins. The mouse locus encoding Matp was formerly called the underwhite (uw) locus. 6 Various mouse mutant alleles of Matp (underwhite) lead to a spectrum of hypopigmented phenotypes, most of which are recessive, but one (MatpUw-dbr) is semi-dominant. 7 Mutations in the human MATP gene are associated with a form of oculocutaneous albinism, defined as OCA4. While rare in the worldwide population, OCA4 is more common in the Japanese population, and cases have been described in the Turkish and German populations. 8 Variations in both the MATP and the P genes are associated with normal variations in human pigmentation.
Historical Background Mouse coat color genes have played an important role in understanding basic aspects of mammalian genetics. For example, the original p mutation and a mutation of the tyrosinase gene (c locus) were used to define the first genetic linkage
MOLECULAR REGULATION OF MELANIN FORMATION: MELANOSOME TRANSPORTER PROTEINS
group in the mouse (Haldane et al., 1915), now assigned to mouse chromosome 7 (Brilliant et al., 1996). The p locus was also used as a marker in transplantation studies to define histocompatability antigens (Snell and Stevens, 1961). The original Matp mutant allele, Matpuw, was used as a coat color marker in many gene linkage and mapping studies (Davisson et al., 1990). The existence of genes that are associated with tyrosinasepositive albinism was hypothesized long ago (Witkop et al., 1970). The P and MATP genes are now known to be the most common genes mutated in tyrosinase-positive albinism, causing OCA2 (Gardner et al., 1992; Rinchik et al., 1993) and OCA4 (Newton et al., 2001) respectively.
Current Concepts Overview Melanin biosynthesis occurs in melanosomes, thought to be derived from the fusion of at least two vesicle compartments, including endosome-derived vesicles that share some features with lysosomes (Dell’Angelica et al., 2000; Orlow, 1995). The initial and rate-limiting step in melanin biosynthesis is catalyzed by tyrosinase, converting tyrosine to DOPAquinone (Cooksey et al., 1997; Hearing and Tsukamoto, 1991). Mature (highly pigmented) “Stage IV” melanosomes derive from earlier stages. The first recognizable stage is the premelanosome, which is distinguished by a disorganized luminal matrix and no melanin. Stage I melanosomes also lack melanin, but are defined by a parallel array of the luminal matrix. Stages II and III are characterized by increased melanin deposition, and Stage IV melanosomes contain the most melanin. Although mouse skin melanosomes are acidic (Bhatnagar et al., 1993; Devi et al., 1987; Ramaiah, 1996), the luminal pH is probably not static as melanosomes develop, and differences in melanosome pH in human melanocytes have been reported between those of Caucasian and black origin (Fuller et al., 2001; Smith et al., 2004). To make melanin: (1) tyrosinase must be correctly processed; (2) tyrosine must be targeted to the melanosome; and (3) conditions that favor the enzymatic activity of tyrosinase must exist inside the melanosome. All these processes are affected by pH (Ancans and Thody, 2000; Ancans et al., 2001; Halaban et al., 2002; Manga and Orlow, 2001; Potterf et al., 1998; Ramaiah, 1996; Watabe et al., 2004). The product of the p (pink-eyed dilution) gene is likely an ion transporter (Gardner et al., 1992; Rinchik et al., 1993) that plays a critical role in melanin biosynthesis through the regulation of melanosome pH (Puri et al., 2000). Matp (membraneassociated transport protein, encoded by the mouse locus previously known as underwhite, uw) also plays a key role in melanin biosynthesis (Lehman et al., 2000; Sweet et al., 1998). Matp likely mediates the transport of an unknown, but critical substance across the melanosome membrane and has high homology at the amino acid level to plant proton/ sucrose transporters (Newton et al., 2001).
The Mouse Pink-eyed Dilution (p) Gene and Its Alleles The original mutant p allele probably arose in Manchuria or Japan in Mus molosinus (Brilliant et al., 1994a) and was incorporated into several common laboratory strains of mice (e.g. SJL/J, 129/J, P/J, and FS/Ei) during the early twentieth century. The first mutant allele of the p locus to be characterized molecularly was the pun (pink-eyed unstable) allele, which exhibits high-frequency (somatic) reversion to wild type (Melvold, 1971). Using the technique of genome scanning, the pun allele was found to result from a duplication of 75 kb of genomic DNA (Brilliant et al., 1991; Gondo et al., 1993) that includes exons 6–18 (Oakey et al., 1996) of the 24-exon p gene. A fragment of genomic DNA that cross-hybridized to various mammalian species (now know to include exon 19) was used to screen a melanoma cDNA library to obtain the p gene cDNA and its human homolog (Gardner et al., 1992). Parallel studies using a candidate gene approach found that a previously unknown human cDNA fragment (DN10) identified an alternative exon of the human P gene (Lee et al., 1995; Rinchik et al., 1993). Many mouse mutant p alleles have been characterized at the molecular level (Culiat et al., 1993, 1994; Gardner et al., 1992; Johnson et al., 1995; Nakatsu et al., 1993; Oakey et al., 1996; Rinchik et al., 1993). The discovery of the human P cDNA has led to an understanding of the molecular basis for tyrosinase-positive oculocutaneous albinism (OCA2). More than 100 p alleles have been identified, some of which were de novo in origin and some of which were induced by X-rays or chemical mutagens (Lyon et al., 1992; Russell et al., 1995; M. F. Lyon, personal communication). In the homozygous state, each mutant p allele causes hypopigmentation ranging from a minor reduction in coat color to a dramatic reduction in both coat and eye color characteristic of the original p mutation. In addition to affecting pigmentation, several mutant alleles are associated with other abnormalities, including decreased neonatal viability, neurologic disorders, cleft palate, male sterility, female semi-fertility, viability, and prenatal lethality (Brilliant, 1992; Culiat et al., 1993, 1994; Hagiwara et al., 2000; Lyon et al., 1992; Nakatsu et al., 1993; Russell et al., 1995). All the mutations with these additional phenotypes were induced by radiation, and all affect surrounding genes (Johnson et al., 1995; Lyon et al., 1992; Russell et al., 1995) or are the result of a chromosomal inversion (Hagiwara et al., 2000). Mutations of the p gene alone cause effects on pigmentation only (Gardner et al., 1992; Johnson et al., 1995; Lyon et al., 1992; Russell et al., 1995). The p mutations result in a dramatic reduction in melanin (primarily eumelanin). In the hair, p pigment granules have been described as shred-like (Russell, 1949). The same description has been applied to the small irregular shaped melanosomes in the harderian gland of p mice (Markert and Silvers, 1956). In p mice, premelanosomes from embryonic choroid and retina are fibrillar in appearance, as are those 231
CHAPTER 12
CHOROID
RPE
CHOROID
RPE
Fig. 12.1. Electron micrograph of wild-type and p/p mutant eyes. A wild-type eye is shown on the left; a p/p mutant eye is shown on the right. Note the aberrant sizes and minimal pigment content of the melanosomes (arrows) in the choroid and retinal epithelium (RPE) of the p/p eye, a feature shared with other forms of albinism.
from the adult choroid. However, most melanosomes from the adult retina are more particulate in appearance. Most p melanosomes show some pigment, indicated as an increase in electron density and diameter of melanofilaments, but none is fully melanized (Hearing et al., 1973). The melanosomes within p/p melanocytes appear as Stage 1 and Stage 2 melanosomes, as described in the above references (Fig. 12.1). Transplantation studies in the mouse have demonstrated that the p defect is intrinsic to melanocytes (Stephenson and Hornby, 1985).
The p Gene Protein and Its Function Molecular analysis of the p transcript and protein have corroborated much of the past phenotypic data and have extended our knowledge about the p protein’s role in pigmentation, even if its precise function remains unknown at this time. Northern blot analyses have confirmed that melanocytes are the predominant p gene-expressing cell type, with lowlevel expression of the p gene in brain, testes, and ovaries (Gardner et al., 1992; Rinchik et al., 1993). The expression of the p gene in testes and ovaries is also conserved in medaka fish (Fukamachi et al., 2004). However, the significance of p gene expression in nonpigmented tissues is unknown as animals and humans lacking P gene expression are normally fertile, and any neurologic problems are limited to the visual system, the same problems as those commonly associated with other forms of albinism. The size of the mouse p gene transcript is 3.3 kb, encoding a predicted protein of 833 amino acids (Gardner et al., 1992; Rinchik et al., 1993). The mouse p gene product, like its 232
human homolog P, encodes a protein with 12 membranespanning domains. Using antisera against a synthetic peptide from the first luminal loop (amino acids 285–298), Rosemblat et al. (1994) were able to characterize the p protein as an integral, melanosomal membrane protein of 110 kDa that does not appear to be glycosylated (tunicamycin treatment does not alter its gel mobility). Subsequent studies (Chen et al., 2002) suggested that a significant fraction of the p protein is associated with the endoplasmic reticulum (ER). Whether this fraction of the p protein functions in the ER or is in transit is unknown. The p protein may be specifically targeted to the melanosome or one of its precursors. In normal pigmented melanocytes, a fraction of the p protein is present in an intracellular compartment distinct from that containing tyrosinase and Trp-1. It has also been noted that melanosomes lacking p protein are lacking a high-molecular-weight complex of the p protein, tyrosinase, and Trp-1, and possess characteristics of immature premelanosomes (Rosemblat et al., 1994). Thus, in addition to a potential transport function, the p protein may also play a critical role in the biogenesis of normal melanosomes, perhaps by providing conditions (e.g. pH) favorable for their proper structure and maturation. The melanosome, as a specialized endosome, may derive its protein components by means of signals and sorting mechanisms that distinguish it from a lysosome. In fact, a specific protein sequence motif, capable of targeting Trp-1 to the melanosomal membrane, exists within its carboxyl-terminus (Vijayasaradhi et al., 1995). When this Trp-1 amino acid sequence was incorporated in chimeric proteins, they were correctly targeted. The sequence capable of targeting Trp-1 is conserved across species, and a related sequence is found in several other melanosome proteins, perhaps including the p protein. However, it remains to be shown whether the sequence in the p protein related to the Trp-1 sorting sequence actually functions in the same way. If so, it would confound the observation that a subset of the p protein is in a different intracellular compartment from tyrosinase and Trp-1 (Chen et al., 2002; Rosemblat et al., 1994). The p protein may interact with melanin. The p protein (along with the silver protein) is far less extractable from melanized melanosomes (in melanocytes or in a cell-free assay system) than it is from poorly melanized melanosomes (Donatien and Orlow, 1995). It may be that some of the loops of the p protein that protrude inside the melanosome are somehow trapped within the melanin polymer. If this close association with melanin impedes p gene function, then perhaps this is one way to limit the melanin content of the developing melanosome. An interesting observation is that the p transcript is expressed in the black dorsal skin, but not the yellow ventral skin in agouti at/at mice (Rinchik et al., 1993), corroborating earlier notions that the p mutations affect eumelanin but not pheomelanin biosynthesis. Eumelanin biosynthesis is favored when the melanocortin 1 receptor (Mc1r) is stimulated by aMSH and upregulates cAMP; pheomelanin is favored when
MOLECULAR REGULATION OF MELANIN FORMATION: MELANOSOME TRANSPORTER PROTEINS
this signaling is antagonized by the agouti protein. Expression of the p gene is upregulated by a-MSH and db-cAMP (a synthetic analog of cAMP), implying that the p protein plays a major role in the eumelanin/pheomelanin switch (Ancans et al., 2003). From its predicted protein structure, the p protein is likely to be a transporter critical to melanocyte function (Gardner et al., 1992; Rinchik et al., 1993). The p protein was proposed to be a tyrosine transporter (Rinchik et al., 1993), based on sequence homology that has subsequently been shown not to be significant (Lee et al., 1995; Rosemblat et al., 1994). Supporting the hypothesis, however, are the observations that both mouse and human melanocytes can be induced to pigment in vitro with high tyrosine (Sidman and Pearlstein, 1965; Witkop et al., 1973). This observation was also confirmed using cultured mouse skin melanocytes (Potterf et al., 1998; Rosemblat et al., 1998). It is possible that the increase in pigmentation detected in mutant p cells when exposed to very high concentrations of tyrosine results from driving the reaction by substantially increasing the substrate. Moreover, the melanin produced in these cells does not appear to be synthesized in melanosomes, and may result from the activity of mislocalized tyrosinase (Manga and Orlow, 1999; Potterf et al., 1998). Most importantly, direct biochemical assays show no difference in tyrosine transport between normal and p melanocytes at the level of the melanocyte or the melanosome. Plasma membrane tyrosine transport was found to be normal in p (pcp/pcp) melanocytes (Km 89 mM; Vmax 302 pmol/min/mg cell protein), and the melanosome-rich granular fractions of normal (melan-a) and p melanocytes (pcp/pcp) were essentially the same, taking up 10 mM [3H] tyrosine at about 21 pmol/min/mg protein (Gahl et al., 1995). Thus, although the p protein may be a transporter, it does not contribute significantly to tyrosine transport. The most homologous bacterial proteins to p include the Staphylococcus aureus and Escherichia coli ArsB proteins (the anion-conducting pathway of a group of proteins that together confer resistance to arsenic), the E. coli Na+/H+ antiporter, and protein 38L from Mycobacterium leprae (Lee et al., 1995; Rosemblat et al., 1994). It may be that the p protein is similarly involved in ion transport, potentially modulating the pH of the melanosome. Indeed, it was found that the mouse p gene can function in yeast and affect cellular sensitivity to arsenic and other metalloids and modulate intracellular glutathione metabolism (Staleva et al., 2002). Although distinct, melanosomes and lysosomes share at least partial endosomal origins, and both types of organelles are characterized by an acidic lumen (Dell’Angelica et al., 2000; Orlow, 1995). Mouse melanosomes have been reported to be very acidic, i.e. pH 3.5 (Bhatnagar et al., 1993; Devi et al., 1987; Moellmann et al., 1988; Tripathi et al., 1988) and, as such, may more closely resemble skin melanosomes from human Caucasians, whereas melanosomes from more darkly pigmented individuals (i.e. black Africans) may be more neutral in pH (Fuller et al., 2001; Smith et al., 2004). Additionally, the pH of melanosomes may be dynamic, with
early stage melanosomes more acidic and later stage melanosomes more neutral in pH allowing for higher tyrosinase activity. In general, acidification of various intracellular compartments is important for a number of processes including receptor-mediated endocytosis, receptor recycling, and membrane trafficking within the cell (Dautry-Varsat et al., 1983). Acidification appears to be required for normal melanosome biogenesis and protein trafficking (reviewed by Brilliant, 2001; Raposo and Marks, 2002), whereas a more neutral pH results in higher tyrosinase activity (Ancans and Thody, 2000; Ancans et al., 2001; Fuller et al., 2001; Manga and Orlow, 2001; Smith et al., 2004). The identity of all the molecular components mediating the pH of endosome-derived organelles is not known. However, it is thought that an anion channel is essential for the acidification of vacuole compartments by ATP-driven proton pumps present in endosomes, Golgi-derived vesicles, and lysosomes (Al-Awqati, 1995). Anion (Cl–, SO4=, or HCO3–) conductance provides the compensating charge balance to electrogenic proton transport. It remains to be determined whether or not there is a melanosome-specific, ATP-driven proton pump. Nevertheless, the melanosome has a unique membrane protein, p, that may be an anion transporter or a Na+/H+ antiporter that may play a role in the pH regulation of melanosomes (Puri et al., 2000). The regulation of pH in melanosomes is likely to be complex and to involve additional proteins, such as Matp (discussed below). Alternative hypotheses for the function of the p protein have been proposed. The p protein may function to transport sulfhydryl compounds out of the melanosome to permit the formation of eumelanin (Lamoreux et al., 1995). The p protein has also been hypothesized to affect the rate of an existing melanin-synthesizing enzyme system to achieve normal pigmentation (Coleman, 1962; Sidman and Pearlstein, 1965). Other observations suggest that the p, tyrosinase, and Trp-1 (tyrosinase-related protein-1) proteins exist in a highmolecular-weight complex that is not formed in p mutant melanocytes (Chiu et al., 1993; Lamoreux et al., 1995). More recently, it has been shown in several studies that, in the absence of a normal p protein, tyrosinase is mistargeted and accumulates in the ER (Manga and Orlow, 1999; Potterf et al., 1998). Other studies imply that a significant portion of the p protein is found in the ER, and their authors have put forward the hypothesis that the P protein is involved in tyrosinase maturation and folding in the ER (Chen et al., 2002; Toyofuku et al., 2002), which may also involve glutathione (Staleva et al., 2002). Melanocytes have a specific factor that is critical for tyrosinase maturation; however, as p-null melanocytes also appear to have this factor, the p protein itself appears to be this factor (Francis et al., 2003). Moreover, the absence of the Matp protein has a similar phenotype (Costin et al., 2003), suggesting that both these proteins may play an indirect role in the folding and targeting of tyrosinase, perhaps by modulating pH (Halaban et al., 2002; Watabe et al., 2004). In any case, the p (and Matp) protein plays a critical coordinating role in melanogenesis. 233
CHAPTER 12
OCA2 and the Human P Gene The human ortholog (P) of the pink-eyed dilution gene has been identified and characterized. Mutations of the human P gene are responsible for type II oculocutaneous albinism (OCA2). In addition, polymorphic variation in the human P gene is responsible, in part, for variations in human pigmentation. Oculocutaneous albinism (OCA) is characterized by abnormally low amounts of melanin in the eyes and skin (see Chapter 31). Abnormally low amounts of melanin in the developing eye lead to abnormal routing of optic nerve fibers, resulting in strabismus and loss of binocular vision. Other ocular effects of albinism include photophobia, nystagmus, and foveal hypoplasia with reduced visual acuity. The reduction in skin pigmentation in individuals with OCA is associated with an increased sensitivity to ultraviolet radiation and a predisposition to skin cancer. Before molecular diagnostics, only two major types of OCA were recognized, tyrosinaserelated OCA and tyrosinase-positive OCA. Mutations of the human tyrosinase gene on chromosome 11 lead to tyrosinaserelated albinism, defined as OCA1 (Tomita et al., 1989; reviewed by King et al., 2003a), whereas tyrosinase-positive albinism is genetically complex (see Chapter 31). In most populations, the major cause of tyrosinase-positive albinism is mutation of the P gene (reviewed by Oetting et al., 1998; see Chapter 31), although mutations of the Matp gene cause a similar phenotype (Newton et al., 2001). The human P gene is on chromosome 15q in a region demonstrated to be linked to OCA2 in native South Africans (Kedda et al., 1994; Ramsay et al., 1992). Mutations in the human P gene lead to tyrosinase-positive OCA, defined as OCA2 (Durham-Pierre et al., 1994; Lee et al., 1994a, b; Rinchik et al., 1993). The phenotype of OCA2 is broad, ranging from minimal to moderate pigmentation of the hair, skin, and iris. The skin pigment tends to be localized in freckles, lentigines, or nevi rather than generalized, and the ability to tan is not well defined (Oetting and King, 1999; see Chapter 31). In contrast to OCA1, individuals with OCA2 usually have pigmented hair at birth that tends to darken somewhat with age. A subtype of albinism known as brown oculocutaneous albinism (BOCA), described in African populations, has been shown to be associated with heterozygosity of a partially functioning allele and a null allele (Kerr et al., 2000; Manga et al., 2001). Additionally, at least one case of autosomal recessive ocular albinism (AROA) is the result of P gene mutations (Lee et al., 1994a). Thus, the phenotypic range of P gene mutations is broad. Moreover, normal MC1R (melanocortin receptor 1) variants dramatically influence the OCA2 phenotype (King et al., 2003b). In the general population of the United States, tyrosinasepositive OCA occurs in 1:30 000 Caucasians and in 1:17 000 blacks (Witkop, 1985). P gene mutations (OCA2) have been detected in these and other racial groups. There are several
234
genetic isolates with a very high frequency of tyrosinasepositive OCA, e.g. the Brandywine, Maryland isolate (1:85) and several native North American Pueblo Indian groups: the Zuni, Hopi, and Jemez people (approximately 1:240; Witkop, 1985; Witkop et al., 1972; Woolf and Dukepoo, 1969), as well as the Navajo people (approximately 1:2000; Yi et al., 2003) and several native South American Indian groups (reviewed by Jeambrun and Sergent, 1991). Presumably, because these represent small restricted populations, individuals within these populations are homozygous for the same recessive mutation of a gene required for normal pigmentation. The P gene is a likely candidate for the OCA seen in all these groups. Indeed, individuals with tyrosinase-positive OCA from the Brandywine, Maryland isolate are homozygous for a deletion allele of the P gene (a 2.7-kb deletion that includes exon 7; DurhamPierre et al., 1994), and Navajos with OCA are typically homozygous for an even larger deletion (122.5 kb) of the P gene. However, it is formally possible that mutations in another gene (e.g. MATP) lead to a similar phenotype of tyrosinase-positive OCA in individuals and groups for which no molecular data are yet available. The tyrosinase-positive OCA phenotype in Africans and African-Americans is characterized by yellow hair, white skin (sometimes with localized pigmented ephelides; Stevens et al., 1995), and irises that are partially or completely pigmented (Oetting and King, 1999; see Chapter 31). This is the most common albinism phenotype because of the high frequency in these populations (ranging from 1:2000 to 1:5000 in large parts of subSaharan Africa). The most common mutation in this group (so far found exclusively in Africans and individuals of African ancestry) is a 2.7-kb deletion that removes exon 7 along with flanking intron sequences, first identified in the Brandywine, Maryland isolate (Durham-Pierre et al., 1994). It is estimated that this single mutation is associated with 25–50% of all mutant P alleles in African-Americans (Durham-Pierre et al., 1994, 1996), although other diverse mutant alleles have been described in this population (Lee et al., 1994b). The 2.7-kb deletion allele accounts for close to 80% of mutant P alleles in South Africa, Zimbabwe, Tanzania, and other parts of subSaharan Africa (Durham-Pierre et al., 1994; Lund et al., 1997; Puri et al., 1997; Spritz et al., 1995; Stevens et al., 1995, 1997). The phenotypic range of OCA2 is now being defined through the molecular characterization of the gene in different individuals with albinism, and it is expected that P gene mutations in OCA2 will be diverse. The missense mutations described to date do not seem to cluster in any specific region of the peptide, as observed for tyrosinase, but most mutations described so far are in the carboxy half of the polypeptide that contains the majority of the 12 membrane-spanning domains (Oetting et al., 1998). A significant portion of the P missense mutations is found at amino acids conserved between the mouse and human P genes and a group of bacterial transport proteins with 12 membrane-spanning domains (Lee et al., 1995). The size of the human P gene transcript is 3.4 kb, encoding
MOLECULAR REGULATION OF MELANIN FORMATION: MELANOSOME TRANSPORTER PROTEINS
a predicted protein of 838 amino acids (Rinchik et al., 1993). Both the human and the mouse proteins encode a 12 membrane-spanning domain protein of unknown function, but related to a group of transport proteins (Gardner et al., 1992; Lee et al., 1995; Rinchik et al., 1993; Rosemblat et al., 1994). The P gene is encoded by 24 exons (plus one alternate exon that contains an in-frame stop codon, corresponding to IR10-1, an anonymous genomic clone) that spans approximately 250 to 650 kb of genomic DNA (Lee et al., 1995). The human proximal promoter region contains sequences that might be binding sites for transcription factors including the following 12 motifs: one AP4, four discrete and one complex AP2, one CF1, one GCF, three SP1, and one TFIID. No TATA or CCAAT motifs or melanocyte-specific motifs (i.e. M-box) have been described (Lee et al., 1995).
In addition to observing hypopigmentation in PWS and AS patients, several cases of PWS and AS are associated with OCA2 (Creel et al., 1986; Fridman et al., 2003; Fryburg et al., 1991; Wallis and Beighton, 1989), with deletion of one homolog of the P gene in the context of PWS or AS and inheritance of a mutation on the other homolog (Brilliant et al., 1994b; Rinchik et al., 1993). Another pigmentation disorder, hypomelanosis of Ito (HI), is genetically complex, with a subset of patients being mosaic for 15q anomalies (reviewed by Pellegrino et al., 1995). These HI patients have hypopigmented whorls, streaks, or patches in addition to some phenotypic similarities to PWS or AS. Just as in PWS and AS, the P gene is likely to underlie at least part of the hypopigmentation phenotype in those HI patients with 15q anomalies.
The P Gene in Prader–Willi Syndrome, Angelman Syndrome, Hypomelanosis of Ito, and Hypopigmentation.
Evolution and the p Gene
Prader–Willi syndrome (PWS) and Angelman syndrome (AS) are genetic diseases associated with chromosome 15q aberrations. PWS and AS both localize to the same chromosomal region, 15q11q13, although the critical regions for the two syndromes are distinct (reviewed by Knoll et al., 1993; Nicholls, 1993). Two common types of deletions are seen in PWS and AS patients (Christian et al., 1995), and both types disrupt the marker D15S12 (IR10) within the human P gene. PWS involves the loss of a paternal component of 15q11q13, with or without maternal disomy for 15q. The opposite inheritance pattern is seen in AS, as it is associated with a deletion of the maternal component of 15q11q13, with or without paternal disomy for 15q. Among the common clinical features of PWS are neonatal hypotonia and failure to thrive, hyperphagia leading to obesity (starting at 1–2 years), mental retardation, behavior problems, craniofacial abnormalities, and hypogonadism (especially in males) leading to infertility (Bray et al., 1983). The clinical features of AS include severe mental retardation, microcephaly, seizures, hypotonia, ataxia, and craniofacial abnormalities (Clayton-Smith, 1993; Magenis et al., 1990). Both syndromes are also associated with hypopigmentation, as many of these patients have much lighter skin, eye, and hair color than other family members (Butler, 1989; ClaytonSmith, 1993; Hittner et al., 1982; King et al., 1993; Saitoh et al., 1994; Weisner et al., 1987). The hypopigmentation is observed in most PWS and AS patients with deletions of 15q11q13, and more specifically among those with a disruption of D15S12, identified by the IR10 probe (Hamabe et al., 1991; Spritz et al., 1997). Thus, patients who are hemizygous for the P gene in the context of a large deletion of 15q are hypopigmented. This observation is difficult to resolve with the recessive nature of both human P and mouse p mutations. Perhaps other genetic determinants of pigmentation are in the 15q11q13 interval. In contrast, people with extra copies of the P gene are hyperpigmented (Akahoshi et al., 2001, 2004).
There is substantial evidence for conservation of the pink-eyed dilution and uw genes in different classes of mammals including ungulates, lagomorphs, canines, marsupials, and primates (see below). For pink-eyed dilution, mice, deermice, rats, rabbits, and cats all have an equivalent locus, defined by a tyrosinase-positive, OCA2-like phenotype, which is part of a conserved linkage group in these species (Heim et al., 1988; reviewed by Little, 1958). The porcine ortholog has been identified (Fernandez et al., 2002). In many mammalian species, the conserved linkage group includes the b-globin gene cluster. However, in humans, the b-globin locus (on human chromosome 11) is not linked to OCA2 (Heim et al., 1988), now known to be associated with mutations of the P gene on chromosome 15 (Durham-Pierre et al., 1994; Lee et al., 1994a, b; Rinchik et al., 1993). Like the mouse p gene, the chicken locus “pinkeye,” pk, causes a severe reduction in retinal pigmentation, produces gray feathers in strains in which wild-type birds produce black feathers, and shows histologic similarities to the melanocytes of p/p mice (Brumbaugh and Lee, 1975). The Medaka fish has a p gene ortholog (Fukamachi et al., 2004), and the p gene shares significant homology with genes from Drosophila, yeast, and bacteria (Gardner et al., 1992; Rinchik et al., 1993).
The Mouse Matp Gene and Its Mutant Alleles Another gene likely to function in transport across the melanosome membrane is Matp (membrane-associated transport protein), previously known as AIM-1 (antigen in melanoma 1), a gene expressed exclusively in melanocytes and melanoma (Harada and Robbins, 1999; Harada et al., 2001; GenBank #AF172849). Note there are two other distinct genes called AIM-1 in the literature (Katayama et al., 1998; Teichmann et al., 1998). Among the mouse mutations that lead to severe hypopigmentation, without other phenotypes
235
CHAPTER 12
+
Amino acid transporter
+
Na H exchanger
Tyr (OCA1) Tyrp1 (OCA3)
H+
Na+ Tyrosine Melanin H+ H+ OR Anions Osmolyte Na+ Na+
H+/ATPase Fig. 12.2. Electron micrograph of choroid melanosomes of an adult mouse eye. Left: C57BL/6 (wild type) showing typically well-pigmented and round melanosomes. Right: mutant Matpuw-d/ Matpuw-d showing irregularly shaped melanosomes with uneven distribution of melanin. (Adult Matpuw-d/Matpuw-d mice have dark eyes.) Similar changes are seen in the RPE. Figures of eye melanocytes from these and other mutant Matp alleles are presented in Sweet et al. (1998).
(i.e. effects restricted to melanocytes), mutations in the Matp gene are distinguished by an unusual series of alleles (underwhite) with a spectrum of pigmentation phenotypes. Mutant Matp alleles are associated with small, crenated melanosomes with a range of pigment (Sweet et al., 1998). The original Matpuw allele arose spontaneously in the C57BL/6 strain and is recessive. The outer fur of Matpuw/Matpuw mice is a light beige with very white underfur, and the eyes are pink at birth, but darken with age (Dickie, 1964). Two other recessive alleles, Matpuw-i and Matpuw-d, have also been described (Sweet et al., 1998); homozygous Matpuw-i are slightly more pigmented than homozygous Matpuw; homozygous Matpuw-d are even more pigmented (brown/slate; Sweet et al., 1998). A fourth allele, MatpUw-dbr (dominant brown) is semi-dominant over the wild-type allele, and heterozygous MatpUw-dbr mice have a dark brown coat, while homozygous MatpUw-dbr mice are only slightly darker than uw/uw (Sweet et al., 1998). The phenotype of the eyes of uw allelic series was reported by Sweet et al. (1998), who noted normal numbers of melanocytes or melanosomes in the choroid or retinal pigmented epithelia in mice homozygous for mutant uw alleles. However, the melanosomes of both layers are generally smaller, irregularly shaped (raisin-like or crenated), and contain less pigment than those in wild-type eyes (Fig. 12.2). The action of the Matp gene is autonomous to melanocytes, as shown by transplantation assays (Lehman et al., 2000); its expression is an early marker of pigment cell precursors (Baxter and Pavan, 2002). Because Matp mutations lead to alterations in melanosome shape and pigmentation, it is likely that Matp is associated with the melanosome. The most severe mutant mouse allele, Matpuw/Matpuw is associated with a 7-bp deletion in the coding sequence of exon 3 (Du and Fisher, 2002) leading to a frameshift and resulting in an unstable transcript. Matp transcripts are expressed from the two other alleles that have intermediate pigmentation, but each mutant allele has a unique point mutation that leads to a nonconservative amino acid substitution (Matpuw-d: serine to proline at amino acid 435; MatpUw-dbr: aspartic acid to asparagine at amino acid 153), consistent with their partial function (Du and Fisher, 2002, Newton et al., 2001). 236
OR
P transporter (OCA2)
H+
Matp/uw transporter (OCA4)
Fig. 12.3. A simplified melanosome with key proteins. The melanosome organelle is the site of melanin biosynthesis and storage. The vacuolar H+/ATPase brings in protons (Dell’Angelica et al., 2000; Orlow, 1995; Smith et al., 2004). Two possible functions of the P transporter protein are presented [based on the function of homologous proteins: the P protein may facilitate anion transport needed to maintain electrogenic neutrality or it may function as an Na+/H+ antiporter (exchanger) (Puri et al., 2000)]. One or both Na+/H+ exchangers (NHE3 and/or NHE7) may also modulate the cations present in the melanosome (Smith et al., 2004). Consistent with its high homology to proton- and sodiumsugar symporters, the MATP protein may bring in a sugar (osmolyte) coupled with a proton or sodium (Newton et al., 2001). The model is consistent with changes in tyrosinase activity in melanosomes seen after treatment with agents that disrupt the pH gradient (Ancans et al., 2001; Halaban et al., 2002; Watabe et al., 2004), and differential timing of expression in melanogenesis allows for a dynamic change in the luminal pH. Thus, the P and Matp proteins play a major role in the normal regulation of melanosome biogenesis and melanin content. NB. The melanosome membrane location for Matp is based solely on the phenotype of mutant uw melanocytes. We also note that P protein has been reported in the ER and that both the P and the Matp proteins may primarily function in the vesicles that give rise to melanosomes, if not in the mature organelle.
The Matp Protein and Its Function Matp is transcriptionally modulated by MITF, the melanocytespecific transcription factor essential for pigmentation and a clinical diagnostic marker in human melanoma (Du and Fisher, 2002). Matp shares homology with known transporters, especially with plant H+/sucrose symporters (Newton et al., 2001). Indeed, the five amino acids that are conserved among all known plant H+/sucrose symporters are exactly conserved in mouse and human Matp. Plant H+/sucrose symporters couple the transport of a sucrose molecule with a proton along a proton gradient and often mediate changes in osmolarity (Stadler et al., 1999). Although there are no known mammalian sucrose transporters, it is possible that Matp transports a different sugar (or other related molecule) coupled with proton movement. Along with a reduction in pigment content,
MOLECULAR REGULATION OF MELANIN FORMATION: MELANOSOME TRANSPORTER PROTEINS
melanosomes from Matp mutant mice are small and irregularly shaped (raisin-like, crenated structures; Sweet et al., 1998; Fig. 12.2), consistent with a disruption in osmotic regulation. Moreover, drug- and sugar-mediated disruptions of the osmotic balance of endosomes and lysosomes have effects on protein turnover and luminal pH (Isaac et al., 2000; Schreiber and Haussinger, 1995; Schreiber et al. 1996), and the transport of amino acids across membranes is affected by osmotic imbalance (Gomez-Angelats et al., 1997) and pH (Potterf et al., 1996). Therefore, the Matp transporter is potentially an osmotic and/or pH regulator.
OCA4 and the Human Matp Gene Based on the mouse phenotype, MATP was evaluated as a candidate gene for a form of OCA with a phenotype similar to OCA2 (P gene albinism). The MATP gene was sequenced in several OCA individuals who had minimal pigment, a few of whom had previously been screened for mutations on the P gene. One Turkish OCA individual (with distantly related parents) was found to be homozygous for a splice site mutation of the MATP gene (G to A in the splice acceptor sequence of exon 2) and did not have a P gene mutation. This patient defined a new form of OCA, OCA4 (Newton et al., 2001). Subsequently, MATP mutations leading to OCA4 have been described in additional Turkish individuals (264delC; Ikinciogullari et al., 2004) and several German individuals (L361P, P58A, Y401X, F221del, T329fsX68, Y317C, A477T, W202C, F525fsX15; IVS3+46C4T, IVS3+59+61dup; Rundshagen et al., 2004). In addition, OCA4 is one of the most common forms of albinism in the Japanese population, where 24% of OCA is OCA4, associated with seven mutant alleles [four missense mutations (P58S, D157N, G188V, and V507L) and three frameshift mutations (S90CGGCCAÆGC, V144insAAGT, and V469delG); Inagaki et al., 2004].
Evolution of the Matp Gene The cream color in horses has been associated with the same mutation as the MatpUw-dbr mouse (D153N; Mariat et al., 2003). Mutations of the Medaka ortholog (the B gene) have been identified in the Medaka fish (Fukamachi et al., 2001). The Matp gene shares significant homology with genes from Drosophila and, as mentioned earlier, genes as distant as plant proton/sucrose symporters.
Other Proteins Involved in Transport Across the Melanosome Membrane In addition to the p protein and Matp, other proteins may also play a role in ion transport across melanosome membranes. Recently, two Na+/H+ exchangers, NHE3 and NHE7, have been found associated with melanosomes, and the expression of these Na+/H+ exchangers may vary between Caucasian and black melanocytes (Smith et al., 2004), suggesting that other proteins in addition to p and Matp may regulate ion flux and/or pH, playing a role in the regulation of melanin synthesis in melanosomes. These researchers also confirmed that the melanosome has an ATP-driven proton pump.
Combining what we know about the phenotypes of mutant p and uw melanocytes, the functions of proteins sharing structural similarity with the p and Matp proteins, and the function of other transport proteins known to reside on the melanosome membrane, a model of melanosome transport is presented (Fig. 12.3).
Normal Human Pigmentation Variation and the P and MATP Genes Humans vary considerably in the range of normal pigmentation of the hair, eyes, and skin. It is reasonable to believe that at least part of this variation results from sequence variation in key pigmentation genes, such as the P and MATP genes that underlie forms of albinism. This notion is supported by the range in pigmentation phenotypes seen among mutations of the mouse and human orthologs. Mouse phenotypes vary among different p alleles (Lyon et al., 1992; Russell et al., 1995), and a wide range in OCA2 phenotypes has been noted for various P alleles (Oetting and King, 1999; see Chapter 31). There is also a wide range of phenotypes among mice with various mutant Matpuw alleles (Sweet et al., 1998), and among the limited number OCA4 patients examined to date (Inagaki et al., 2004; Newton et al., 2001; Rundshagen et al., 2004). A gene associated with brown eyes (total brown iris pigment) and a gene associated with brown hair map to 15q, with the P gene as the prime candidate (Eiberg and Mohr, 1996). Population studies looking at the association of specific polymorphisms of the P and MATP genes demonstrate that (together with polymorphisms of the MC1R gene) they play a major role in determining the normal range of pigmentation of the hair (Eiberg and Mohr, 1996, Sturm et al., 2001), skin (Akey et al., 2001; Duffy et al. 2004; Nakayama et al., 2002; Shriver et al., 2003), and eyes (Frudakis et al., 2003; Rebbeck et al., 2002; Sturm and Frudakis, 2004; Zhu et al., 2004). Indeed, a polymorphism of MATP (L374F) may be a useful marker of population origin (Yuasa et al., 2004).
References Akahoshi, K., K. Fukai, A. Kato, S. Kimiya, T. Kubota, and R. A. Spritz. Duplication of 15q11.2–q14, including the P gene, in a woman with generalized skin hyperpigmentation. Am. J. Med. Genet. 104:299–302, 2001. Akahoshi, K., R. A. Spritz, K. Fukai, N. Mitsui, K. Matsushima, and H. Ohashi. Mosaic supernumerary inv dup(15) chromosome with four copies of the P gene in a boy with pigmentary dysplasia. Am. J. Med. Genet. 126A:290–292, 2004. Akey, J. M., H. Wang, M. Xiong, H. Wu, W. Liu, M.D. Shriver, and L. Jin. Interaction between the melanocortin-1 receptor and P genes contributes to inter-individual variation in skin pigmentation phenotypes in a Tibetan population. Hum. Genet. 108:516–520, 2001. Al-Awqati, Q. Chloride channels of intracellular organelles. Curr. Opin. Cell Biol. 7:504–508, 1995. Ancans, J., and A. J. Thody. Activation of melanogenesis by vacuolar type H(+)-ATPase inhibitors in amelanotic, tyrosinase positive human and mouse melanoma cells. FEBS Lett. 478:57–60, 2000. Ancans, J., D. J. Tobin, M. J. Hoogduijn, N. P. Smit, K. Wakamatsu, and A. J. Thody. Melanosomal pH controls rate of melanogenesis,
237
CHAPTER 12 eumelanin/phaeomelanin ratio and melanosome maturation in melanocytes and melanoma cells. Exp. Cell Res. 268:26–35, 2001. Ancans, J., N. Flanagan, M. J. Hoogduijn, and A. J. Thody. P-locus is a target for the melanogenic effects of MC-1R signaling: a possible control point for facultative pigmentation. Ann. N. Y. Acad. Sci. 994:373–377, 2003. Baxter, L. L., and W. J. Pavan. The oculocutaneous albinism type IV gene Matp is a new marker of pigment cell precursors during mouse embryonic development. Mech. Dev. 116:209–212, 2002. Bhatnagar, V., S. Anjaiah, A. Puri, N. Puri, B. N. A. Darshanam, and A. Ramaiah. pH of melanosomes of B16 murine melanoma is acidic: Its physiological importance in the regulation of melanin biosynthesis. Arch. Biochem. Biophys. 307:183–192, 1993. Bray, G. A., W. T. Dahms, R. S. Swerdloff, R. H. Fiser, R. L. Atkinson, and R. E. Carrel. The Prader–Willi syndrome: a study of 40 patients and a review of the literature. Medicine 62:59–80, 1983. Brilliant, M. H. The mouse pink-eyed dilution locus: a model for aspects of Prader–Willi syndrome, Angelman syndrome, and a form of hypomelanosis of Ito. Mamm. Genome 3:187–191, 1992. Brilliant, M. H. The mouse p (pink-eyed dilution) and human P genes, oculocutaneous albinism type 2 (OCA2), and melanosomal pH. Pigment Cell Res. 14:86–93, 2001. Brilliant, M. H., Y. Gondo, and E. M. Eicher. Direct molecular identification of the mouse pink-eyed unstable mutation by genome scanning. Science 252:566–569, 1991. Brilliant, M. H., A. Ching, Y. Nakatsu, and E. M. Eicher. The original pink-eyed dilution mutation (p) arose in Asiatic mice: implications for the H4 minor histocompatibility antigen, Myod1 regulation and the origin of inbred strains. Genetics 138:203–211, 1994a. Brilliant, M. H., R. A. King, U. Francke, S. Schuffenhauer, T. Meitinger, J. M. Gardner, D. Durham-Pierre, and Y. Nakatsu. The mouse pink-eyed dilution gene: association with hypopigmentation in Prader–Willi and Angelman syndromes and with human OCA2. Pigment Cell Res. 7:398–402, 1994b. Brilliant, M. H., R. W. Williams, B. C. Holdener, and J. M. Angel. Mouse chromosome 7. Mamm. Genome 6:S135–S150, 1996. Brumbaugh, J. A., and K. W. Lee. The gene action and function of two dopa oxidase positive melanocyte mutants of the fowl. Genetics 81:333–347, 1975. Butler, M. G. Hypopigmentation, a common feature of Prader–Willi syndrome. Am. J. Hum. Genet. 45:140–146, 1989. Chen, K., P. Manga, and S. J. Orlow. Pink-eyed dilution protein controls the processing of tyrosinase. Mol. Biol. Cell 13:1953–1964, 2002. Chiu, E., M. L. Lamoreux, and S. J. Orlow. Postnatal ocular expression of tyrosinase and related proteins: disruption by the pink-eyed unstable (pun) mutation. Exp. Eye Res. 57:301–305, 1993. Christian, S. L., W. P. Robinson, B. Huang, A. Mutirangura, M. R. Line, M. Nakao, U. Surti, A. Chakravarti, and D. H Ledbetter. Molecular characterization of two proximal deletion breakpoint regions in both Prader–Willi and Angelman syndrome patients. Am. J. Hum. Genet. 57:40–48, 1995. Clayton-Smith, J. Clinical research on Angelman syndrome in the United Kingdom: observations on 82 affected individuals. Am. J. Med. Genet. 46:12–15, 1993. Coleman, D. L. Effect of genic substitution on the incorporation of tyrosine into the melanin of mouse skin. Arch. Biochem. Biophys. 96:562–568, 1962. Cooksey, C. J., P. J. Garratt, E. J. Land, S. Pavel, C. A. Ramsden, P. A. Riley, and N. P. Smit. Evidence of the indirect formation of the catecholic intermediate substrate responsible for the autoactivation kinetics of tyrosinase. J. Biol. Chem. 272:26226–26235, 1997. Costin, G. E., J. C. Valencia, W. D. Vieira, M. L. Lamoreux, and V. J. Hearing. Tyrosinase processing and intracellular trafficking is
238
disrupted in mouse primary melanocytes carrying the underwhite (uw) mutation. A model for oculocutaneous albinism (OCA) type 4. J. Cell Sci. 116:3203–3212, 2003. Creel, D. J., C. M. Bendel, G. L. Weisner, J. D. Wirtschafter, D. C. Arthur, and R. A. King. Abnormalities of the central visual pathways in Prader–Willi syndrome associated with hypopigmentation. N. Engl. J. Med. 314:1606–1609, 1986. Culiat, C. T., L. Stubbs, R. D. Nicholls, C. S. Montgomery, L. B. Russell, D. K. Johnson, and E. M. Rinchik. Concordance between isolated cleft palate in mice and alterations within a region including the gene encoding the beta 3 subunit of the type A gamma-aminobutyric acid receptor. Proc. Natl. Acad. Sci. USA 90:5105–5109, 1993. Culiat, C. T., L. J. Stubbs, C. S. Montgomery, L. B. Russell, and E. M. Rinchik. Phenotypic consequences of deletion of the gamma 3, alpha 5, or beta 3 subunit of the type A gamma-aminobutyric acid receptor in mice. Proc. Natl. Acad. Sci. USA 91:2815–2818, 1994. Dautry-Varsat, A., A. Ciechanover, and H. F. Lodish. pH and the recycling of transferrin during receptor-mediated endocytosis. Proc. Natl. Acad. Sci. USA 80:2258–2262, 1983. Davisson M. T., T. H. Roderick, E. C. Akeson, N. L. Hawes, and H. O. Sweet. The hairy ears (Eh) mutation is closely associated with a chromosomal rearrangement in mouse chromosome 15. Genet. Res. 56:167–178, 1990. Dickie, M. M. Report. Mouse Newslett. 30:30, 1964. Dell’Angelica, E. C., C. Mullins, S. Caplan, and J. S. Bonifacino. Lysosome-related organelles. FASEB J. 14:1265–1278, 2000. Devi, C. C., R. K. Tripathi, and A. Ramaiah. pH-dependent interconvertible allosteric forms of murine melanoma tyrosinase. Physiological implications. Eur. J. Biochem. 166:705–711, 1987. Donatien, P. D., and S. J. Orlow. Interaction of melanosomal proteins with melanin. Eur. J. Biochem. 232:159–164, 1995. Du, J., and D. E. Fisher. Identification of Aim-1 as the underwhite mouse mutant and its transcriptional regulation by MITF. J. Biol. Chem. 277:402–406, 2002. Duffy, D. L., N. F. Box, W. Chen, J. S. Palmer, G. W. Montgomery, M. R. James, N. K. Hayward, N. G. Martin, and R. A. Sturm. Interactive effects of MC1R and OCA2 on melanoma risk phenotypes. Hum. Mol. Genet. 13:447–461, 2004. Durham-Pierre, D., J. M. Gardner, Y. Nakatsu, R. A. King, U. Francke, A. Ching, R. Aquaron, V. del Marmol, and M. H. Brilliant. African origin of an intragenic deletion of the human P gene in tyrosinase positive oculocutaneous albinism. Nature Genet. 7:176–179, 1994. Durham-Pierre, D., R. A. King, and M. H. Brilliant. Estimation of carrier frequency of a 2.7 kb deletion allele of the P gene associated with OCA2 in African-Americans. Hum. Mutat. 7:370–373, 1996. Eiberg, H., and J. Mohr. Assignment of genes coding for brown eye colour (BEY2) and brown hair colour (HCL3) on chromosome 15q. Eur. J. Hum. Genet. 4:237–241, 1996. Fernandez, A., C. Castellanos, C. Rodriguez, J. L. Noguera, A. Sanchez, and C. Ovilo. Physical and linkage mapping of the porcine pink-eye dilution gene (OCA2). Anim. Genet. 33:392–394, 2002. Francis E., N. Wang, H. Parag, R. Halaban, and D. N. Hebert. Tyrosinase maturation and oligomerization in the endoplasmic reticulum require a melanocyte-specific factor. J. Biol. Chem. 278:25607– 25617, 2003. Fridman, C., N. Hosomi, M. C. Varela, A. H. Souza, K. Fukai, and C. P. Koiffmann. Angelman syndrome associated with oculocutaneous albinism due to an intragenic deletion of the P gene. Am. J. Med. Genet. 119A:180–183, 2003. Frudakis, T., M. Thomas, Z. Gaskin, K. Venkateswarlu, K. S. Chandra, S. Ginjupalli, S. Gunturi, S. Natrajan, V. K. Ponnuswamy, and K. N. Ponnuswamy. Sequences associated with human iris pigmentation. Genetics 165:2071–2083, 2003. Fryburg, J. S., W. R. Breg, and V. Lindgren. Diagnosis of Angelman syndrome in infants. Am. J. Med. Genet. 38:58–64, 1991.
MOLECULAR REGULATION OF MELANIN FORMATION: MELANOSOME TRANSPORTER PROTEINS Fukamachi, S., A. Shimada, and A. Shima. Mutations in the gene encoding B, a novel transporter protein, reduce melanin content in medaka. Nature Genet. 28:381–385, 2001. Fukamachi, S., S. Asakawa, Y. Wakamatsu, N. Shimizu, H. Mitani, and A. Shima. Conserved function of medaka pink-eyed dilution in melanin synthesis and its divergent transcriptional regulation in gonads among vertebrates. Genetics 168:1519–1527, 2004. Fuller, B. B., D. T. Spaulding, and D. R. Smith. Regulation of the catalytic activity of preexisting tyrosinase in black and Caucasian human melanocyte cell cultures. Exp. Cell Res. 262:197–208, 2001. Gahl, W. A., B. Potterf, D. Durham-Pierre, M. H. Brilliant, and V. J. Hearing. Melanosomal tyrosine transport in normal and pink-eyed dilution murine melanocytes. Pigment Cell Res. 8:229–233, 1995. Gardner, J. M., Y. Nakatsu, Y. Gondo, S. Lee, M. F. Lyon, R. A. King, and M. H. Brilliant. The mouse pink-eyed dilution gene: association with human Prader–Willi and Angelman syndromes. Science 257:1121–1124, 1992. Gomez-Angelats, M., M. Lopez-Fontanals, A. Felipe, F. J. Casado, and M. Pastor-Anglada. Cytoskeletal-dependent activation of system A for neutral amino acid transport in osmotically stressed mammalian cells: a role for system A in the intracellular accumulation of osmolytes. J. Cell Physiol. 173:343–350, 1997. Gondo, Y., J. M. Gardner, Y. Nakatsu, D. Durham-Pierre, S. A. Deveau, C. Kuper, and M. H. Brilliant. High-frequency genetic reversion mediated by a DNA duplication: the mouse pink-eyed unstable mutation. Proc. Natl. Acad. Sci. USA 90:297–301, 1993. Hagiwara, N., S. E. Klewer, R. A. Samson, D. T. Erickson, M. F. Lyon, and M. H. Brilliant. Sox6 is a candidate gene for p100H myopathy, heart block, and sudden neonatal death. Proc. Natl. Acad. Sci. USA 97:4180–4185, 2000. Halaban, R., R. S. Patton, E. Cheng, S. Svedine, E. S. Trombetta, M. L. Wahl, S. Ariyan, and D. N. Hebert. Abnormal acidification of melanoma cells induces tyrosinase retention in the early secretory pathway. J. Biol. Chem. 277:14821–14828, 2002. Haldane, J. B. S., A. D. Sprunt, and N. M. Haldane. Reduplication in mice. J. Genet. 5:133–135, 1915. Hamabe, J.-I., Y. Fukushima, N. Harada, K. Abe, N. Matsuo, T. Nagai, A. Yoshioka, H. Tonoki, R. Tsukino, and N. Niikawa. Molecular study of the Prader–Willi syndrome: deletion, RFLP, and phenotype analysis of 50 patients. Am. J. Med. Genet. 41:54–63, 1991. Harada, M., and P. F. Robbins. AF172849 GenBank Direct Submission, 27 July 1999. Harada, M., Y. F. Li, M. El-Gamil, S. A. Rosenberg, and P. F. Robbins. Use of an in vitro immunoselected tumor line to identify shared melanoma antigens recognized by HLA-A*0201-restricted T cells. Cancer Res. 61:1089–1094, 2001. Hearing, V. J., and K. Tsukamoto. Enzymatic control of pigmentation in mammals. FASEB J. 5:2902–2909, 1991. Hearing, V. J., P. Phillips, and M. A. Lutzner. The fine structure of melanogenesis in coat-color mutants of the mouse. J. Ultrastruct. Res. 43:88–106, 1973. Heim, R. A., D. S. Dunn, S. E. Candy, E. Zwane, J. G. Kromberg, and T. Jenkins. The tyrosinase-positive oculocutaneous albinism locus is not linked to the beta-globin locus in man. Hum. Genet. 79:89, 1988. Hittner, H. M., R. A. King, V. M. Riccardi, D. H. Ledbetter, R. P. Borda, R. E. Ferrell, and F. L. Kretzer. Ocolocutaneous albinoidism as a manifestation of reduced neural crest derivatives in the Prader–Willi syndrome. Am. J. Ophthalmol. 94:328–337, 1982. Ikinciogullari, A., M. Tekin, F. Dogu, I. Reisli, G. Tanir, Z. Yi, N. Garrison, M. H. Brilliant, and E. Babacan. Meningococccal meningitis and complement component 6 deficiency associated with oculocutaneous albinism. Eur. J. Pediatr. 164:177–179, 2005. Inagaki, K., T. Suzuki, H. Shimizu, N. Ishii, Y. Umezawa, J. Tada, N. Kikuchi, M. Takata, K. Takamori, M. Kishibe, M. Tanaka, Y. Miyamura, S. Ito, and Y. Tomita. Oculocutaneous albinism type 4
is one of the most common types of albinism in Japan. Am. J. Hum. Genet. 74:466–471, 2004. Isaac, E. L., L. E. Karageorgos, D. A. Brooks, J. J. Hopwood, and P. J. Meikle. Regulation of the lysosome-associated membrane protein in a sucrose model of lysosomal storage. Exp. Cell Res. 254:204–209, 2000. Jeambrun, J., and B. Sergent. Les Enfants de la Lune. Paris: INSERMORSTOM, 1991. Johnson, D. K., L. J. Stubbs, C. T. Culiat, C. S. Montgomery, L. B. Russell, and E. M. Rinchik. Molecular analysis of 36 mutations at the mouse pink-eyed dilution (p) locus. Genetics 141:1563–1571, 1995. Katayama, H., T. Ota, K. Morita, Y. Terada, F. Suzuki, O. Katoh, and M. Tatsuka. Human AIM-1: cDNA cloning and reduced expression during endomitosis in megakaryocyte-lineage cells. Gene 224:1–7, 1998. Kedda, M. A., G. Stevens, P. Manga, C. Viljoen, T. Jenkins, and M. Ramsay. The tyrosinase-positive oculocutaneous albinism gene shows locus homogeneity on chromosome 15q11–q13 and evidence of multiple mutations in southern African negroids. Am. J. Hum. Genet. 54:1078–1084, 1994. Kerr, R., G. Stevens, P. Manga, S. Salm, P. John, T. Haw, and M. Ramsay. Identification of P gene mutations in individuals with oculocutaneous albinism in sub-Saharan Africa. Hum. Mutat. 15:166–172, 2000. King, R. A., G. L. Wiesner, D. Townsend, and J. G. White. Hypopigmentation in Angelman syndrome. Am. J. Med. Genet. 46:40–44, 1993. King, R. A., J. Pietsch, J. P. Fryer, S. Savage, M. J. Brott, I. RussellEggitt, C. G. Summers, and W. S. Oetting. Tyrosinase gene mutations in oculocutaneous albinism 1 (OCA1): definition of the phenotype. Hum. Genet. 113:502–513, 2003a. King, R. A., R. K. Willaert, R. M. Schmidt, J. Pietsch, S. Savage, M. J. Brott, J. P. Fryer, C. G. Summers, and W. S. Oetting. MC1R mutations modify the classic phenotype of oculocutaneous albinism type 2 (OCA2). Am. J. Hum. Genet. 73:638–645, 2003b. Knoll, J. H., J. Wagstaff, and M. Lalande. Cytogenetic and molecular studies in the Prader–Willi and Angelman syndromes: an overview. Am. J. Med. Genet. 46:2–6, 1993. Lamoreux, M. L., B. K. Zhou, S. Rosemblat, and S. J. Orlow. The pinkeyed-dilution protein and the eumelanin/pheomelanin switch: in support of a unifying hypothesis. Pigment Cell Res. 8:263–270, 1995. Lee, S.-T., R. D. Nicholls, S. Bundey, R. Laxova, M. Musarella, and R. A. Spritz. Mutations of the P gene in oculocutaneous albinism, ocular albinism, and Prader–Willi syndrome plus albinism. N. Engl. J. Med. 330:529–534, 1994a. Lee, S. T., R. D. Nicholls, R. E. Schnur, L. C. Guida, J. Lu-Kuo, N. B. Spinner, E. H. Zackai, and R. A. Spritz. Diverse mutations of the P gene among African-Americans with type II (tyrosinase-positive) oculocutaneous albinism (OCA2). Hum. Mol. Genet. 3:2047–2051, 1994b. Lee, S. T., R. D. Nicholls, M. T. Jong, K. Fukai, and R. A. Spritz. Organization and sequence of the human P gene and identification of a new family of transport proteins. Genomics 26:354–363, 1995. Lehman, A. L., W. K. Silvers, N. Puri, K. Wakamatsu, S. Ito, and M. H. Brilliant. The underwhite (uw) locus acts autonomously and reduces the production of melanin via a unique pathway. J. Invest. Dermatol. 115:601–606, 2000. Little, C. C. Coat-color genes in rodents and carnivores. Q. Rev. Biol. 33:103–137, 1958. Lund, P. M., N. Puri, D. Durham-Pierre, R. A. King, and M. H. Brilliant. Oculocutaneous albinism in an isolated Tonga community in Zimbabwe. J. Med. Genet. 34:733–735, 1997. Lyon, M. F., T. R. King, Y. Gondo, J. M. Gardner, Y. Nakatsu, E. M. Eicher, and M. H. Brilliant. Genetic and molecular analysis of
239
CHAPTER 12 recessive alleles at the pink-eyed dilution (p) locus of the mouse. Proc. Natl. Acad. Sci. USA 89:6968–6972, 1992. Magenis, R. E., S. Toth-Fejel, L. J. Allen, M. Black, M. G. Brown, S. Budden, R. Cohen, J. M. Friedman, D. Kalousek, and J. Zonana. Comparison of the 15q deletions in Prader–Willi and Angelman syndromes: specific regions, extent of deletions, parental origin, and clinical consequences. Am. J. Med. Genet. 35:333–349, 1990. Manga, P., and S. J. Orlow. The pink-eyed dilution gene and the molecular pathogenesis of tyrosinase-positive albinism (OCA2). J. Dermatol. 26:738–747, 1999. Manga P., and S. J. Orlow. Inverse correlation between pink-eyed dilution protein expression and induction of melanogenesis by bafilomycin A1. Pigment Cell Res. 14:362–367, 2001. Manga, P., J. Kromberg, A. Turner, T. Jenkins, and M. Ramsay. In Southern Africa, brown oculocutaneous albinism (BOCA) maps to the OCA2 locus on chromosome 15q: P-gene mutations identified. Am. J. Hum. Genet. 68:782–787, 2001. Mariat, D., S. Taourit, and G. Guerin. A mutation in the MATP gene causes the cream coat colour in the horse. Genet. Sel. Evol. 35:119–133, 2003. Markert, C. L., and W. K. Silvers. The effects of genotype and cell environment on melanoblast differentiation in the house mouse. Genetics 41:429–450, 1956. Melvold, R. W. Spontaneous somatic reversion in mice. Effects of parental genotype on stability at the p-locus. Mutat. Res. 12:171– 174, 1971. Moellmann, G., A. Slominski, E. Kuklinska, and A. B. Lerner. Regulation of melanogenesis in melanocytes. Pigment Cell Res. 1:79–87, 1988. Nakatsu, Y., R. F. Tyndale, T. M. DeLorey, D. Durham-Pierre, J. M. Gardner, H. J. McDanel, Q. Nguyen, J. Wagstaff, M. Lalande, J. M. Sikela, R. W. Olsen, A. J. Tobin, and M. H. Brilliant. A cluster of three GABAA receptor subunit genes is deleted in a neurological mutant of the mouse p locus. Nature 364:448–450, 1993. Nakayama, K., S. Fukamachi, H. Kimura, Y. Koda, A. Soemantri, and T. Ishida. Distinctive distribution of AIM1 polymorphism among major human populations with different skin color. J. Hum. Genet. 47:92–94, 2002. Newton, J. M., O. Cohen-Barak, N. Hagiwara, J. M. Gardner, M. T. Davisson, R. A. King, and M. H. Brilliant. Mutations in the human orthologue of the mouse underwhite gene (uw) underlie a new form of oculocutaneous albinism, OCA4. Am. J. Hum. Genet. 69:981– 988, 2001. Nicholls, R. D. Genomic imprinting and uniparental disomy in Angelman and Prader–Willi syndromes: a review. Am. J. Med. Genet. 46:16–25, 1993. Oakey, R. J., N. M. Keiper, A. S. Ching, and M. H. Brilliant. Molecular analysis of the cDNAs encoded by the pun and pJ alleles of the pink-eyed dilution locus. Mamm. Genome 7:315–316, 1996. Oetting, W. S., and R. A. King. Molecular basis of albinism: mutations and polymorphisms of pigmentation genes associated with albinism. Hum. Mutat. 13:99–115, 1999. Oetting, W. S., J. M., Gardner, J. P. Fryer, A. Ching, D. Durham-Pierre, R. A. King, and M. H. Brilliant. Mutations of the human P gene associated with Type II oculocutaneous albinism (OCA2). Mutations in brief no. 205. Online Hum. Mutat. 12:434, 1998. Orlow, S. J. Melanosomes are specialized members of the lysosomal lineage of organelles. J. Invest. Dermatol. 105:3–7, 1995. Pellegrino, J. E., R. E. Schnur, R. Kline, E. H. Zackai, and N. B. Spinner. Mosaic loss of 15q11q13 in a patient with hypomelanosis of Ito: is there a role for the P gene? Hum. Genet. 96:485–489, 1995. Potterf, S. B., J. Muller, I. Bernardini, F. Tietze, T. Kobayashi, V. J. Hearing, and W. A. Gahl. Characterization of a melanosomal transport system in murine melanocytes mediating entry of the melanogenic substrate tyrosine. J. Biol. Chem. 271:4002–4008, 1996.
240
Potterf, S. B., M. Furumura, E. V. Sviderskaya, C. Santis, D. C. Bennett, and V. J. Hearing. Normal tyrosine transport and abnormal tyrosinase routing in pink-eyed dilution melanocytes. Exp. Cell Res. 244:319–326, 1998. Puri, N., D. Durbam-Pierre, R. Aquaron, P. M. Lund, R. A. King, and M. H. Brilliant. Type 2 oculocutaneous albinism (OCA2) in Zimbabwe and Cameroon: distribution of the 2.7-kb deletion allele of the P gene. Hum. Genet. 100:651–656, 1997. Puri N., J. M. Gardner, and M. H. Brilliant. Aberrant pH of melanosomes in pink-eyed dilution (p) mutant melanocytes. J. Invest. Dermatol. 115:607–613, 2000. Ramaiah, A. Lag kinetics of tyrosinase: its physiological implications. Ind. J. Biochem. Biophys. 33:349–356, 1996. Ramsay, M., M.-A. Colman, G. Stevens, E. Zwane, J. Kromberg, M. Farrall, and T. Jenkins. The tyrosinase-positive oculocutaneous albinism locus maps to chromosome 15q11.2–q12. Am. J. Hum. Genet. 51:879–884, 1992. Raposo, G., and M. S. Marks. The dark side of lysosome-related organelles: specialization of the endocytic pathway for melanosome biogenesis. Traffic 3:237–248, 2002. Rebbeck, T. R., P. A. Kanetsky, A. H. Walker, R. Holmes, A. C. Halpern, L. M. Schuchter, D. E. Elder, and D. Guerry. P gene as an inherited biomarker of human eye color. Cancer Epidemiol. Biomarkers Prev. 11:782–784, 2002. Rinchik, E. M., S. J. Bultman, B. Horsthemke, S.-T. Lee, K. M. Strunk, R. A. Spritz, K. M. Avidano, M. T. C. Jong, R. D. Nicholls. A gene for the mouse pink-eyed dilution locus and for human type II oculocutaneous albinism. Nature 361:72–76, 1993. Rosemblat, S., D. Durham-Pierre, J. M. Gardner, Y. Nakatsu, M. H. Brilliant, and S. J. Orlow. Identification of a melanosomal membrane protein encoded by the pink-eyed dilution (type II oculocutaneous albinism) gene. Proc. Natl. Acad. Sci. USA 91:12071–12075, 1994. Rosemblat, S., E. V. Sviderskaya, D. J. Easty, A. Wilson, B. S. Kwon, D. C. Bennett, and S. J. Orlow. Melanosomal defects in melanocytes from mice lacking expression of the pink-eyed dilution gene: correction by culture in the presence of excess tyrosine. Exp. Cell Res. 239:344–352, 1998. Rundshagen, U., C. Zuhlke, S. Opitz, E. Schwinger, and B. KasmannKellner. Mutations in the MATP gene in five German patients affected by oculocutaneous albinism type 4. Hum. Mutat. 23:106–110, 2004. Russell, E. S. A quantitative histological study of the pigment found in the coat-color mutants of the house mouse. III. Interdependence among the variable granule attributes. Genetics 34:133–145, 1949. Russell, L. B., C. S. Montgomery, N. L. Cacheiro, and D. K. Johnson. Complementation analyses for 45 mutations encompassing the pink-eyed dilution (p) locus of the mouse. Genetics 141:1547–1562, 1995. Saitoh, S., N. Harada, Y. Jinno, K. Hashimoto, K. Imaizumi, Y. Kuroki, Y. Fukushima, T. Sugimoto, M. Renedo, and J. Wagstaff. Molecular and clinical study of 61 Angelman syndrome patients. Am. J. Med. Genet. 52:158–163, 1994. Schreiber, R., and D. Haussinger. Characterization of the swellinginduced alkalinization of endocytotic vesicles in fluorescein isothiocyanate-dextran-loaded rat hepatocytes. Biochem. J. 309: 19–24, 1995. Schreiber, R., F. Zhang, and D. Haussinger. Regulation of vesicular pH in liver macrophages and parenchymal cells by ammonia and anisotonicity as assessed by fluorescein isothiocyanate-dextran fluorescence. Biochem. J. 315:385–392, 1996. Shriver, M. D., E. J. Parra, S. Dios, C. Bonilla, H. Norton, C. Jovel, C. Pfaff, C. Jones, A. Massac, N. Cameron, A. Baron, T. Jackson, G. Argyropoulos, L. Jin, C. J. Hoggart, P. M. McKeigue, and R. A. Kittles. Skin pigmentation, biogeographical ancestry and admixture mapping. Hum. Genet. 112:387–399, 2003.
MOLECULAR REGULATION OF MELANIN FORMATION: MELANOSOME TRANSPORTER PROTEINS Sidman, R. L., and R. Pearlstein. Pink-eyed dilution (p) gene in rodents, increased pigmentation in tissue culture. Dev. Biol. 12:93–116, 1965. Smith, D. R., D. T. Spaulding, H. M. Glenn, and B. B. Fuller. The relationship between Na(+)/H(+) exchanger expression and tyrosinase activity in human melanocytes. Exp. Cell Res. 298:521–534, 2004. Snell, G. D., and L. C. Stevens. Histocompatibility genes of mice, III. H-1 and H4, two histocompatibility loci in the first linkage group. Immunology 4:366–379, 1961. Spritz, R. A., K. Fukai, S. A. Holmes, and J. Luande. Frequent intragenic deletion of the P gene in Tanzanian patients with type II oculocutaneous albinism (OCA2). Am. J. Hum. Genet. 5675: 1320–1323, 1995. Spritz, R. A., T. Bailin, R. D. Nicholls, S. T. Lee, S. K. Park, M. J. Mascari, and M. G. Butler. Hypopigmentation in the Prader– Willi syndrome correlates with P gene deletion but not with haplotype of the hemizygous P allele. Am. J. Med. Genet. 71:57–62, 1997. Stadler, R., E. Truernit, M. Gahrtz, and N. Sauer. The AtSUC1 sucrose carrier may represent the osmotic driving force for anther dehiscence and pollen tube growth in Arabidopsis. Plant J. 19:269–278, 1999. Staleva, L., P. Manga, and S. J. Orlow. Pink-eyed dilution protein modulates arsenic sensitivity and intracellular glutathione metabolism. Mol. Biol Cell. 13:4206–4220, 2002. Stephenson, D. A., and J. E. Hornby. Gene expression at the pinkeyed dilution (p) locus in the mouse is confirmed to be pigment cell autonomous using recombinant embryonic skin grafts. J. Embryol. Exp. Morphol. 87:65–73, 1985. Stevens, G., J. van Beukering, T. Jenkins, and M. Ramsay. An intragenic deletion of the P gene is the common mutation causing tyrosinase-positive oculocutaneous albinism in southern African Negroids. Am. J. Hum. Genet. 56:586–591, 1995. Stevens, G., M. Ramsay, and T. Jenkins. Oculocutaneous albinism (OCA2) in sub-Saharan Africa: distribution of the common 2.7-kb P gene deletion mutation. Hum. Genet. 99:523– 527, 1997. Sturm, R. A., and T. N. Frudakis. Eye colour: portals into pigmentation genes and ancestry. Trends Genet. 20:327–332, 2004. Sturm, R. A., R. D. Teasdale, and N. F. Box. Human pigmentation genes: identification, structure and consequences of polymorphic variation. Gene 277: 49–62, 2001. Sweet, H. O., M. H. Brilliant, S. A. Cook, K. R. Johnson, and M. T. Davisson. A new allelic series for the underwhite gene on mouse chromosome 15. J. Hered. 89:546–51, 1998. Teichmann, U., M. E. Ray, J. Ellison, C. Graham, G. Wistow, P. S. Meltzer, J. M. Trent, and W. J. Pavan. Cloning and tissue expression of the mouse ortholog of AIM1, a betagamma-crystallin superfamily member. Mamm. Genome 9:715–720, 1998. Tomita, Y., A. Takeda, S. Okinaga, H. Tagami, and S. Shibahara. Human oculocutaneous albinism caused by single base insertion in the tyrosinase gene. Biochem. Biophys. Res. Commun. 164:990– 996, 1989.
Toyofuku, K., J. C. Valencia, T. Kushimoto, G. E. Costin, V. M. Virador, W. D. Vieira, V. J. Ferrans, and V. J. Hearing. The etiology of oculocutaneous albinism (OCA) type II: the pink protein modulates the processing and transport of tyrosinase. Pigment Cell Res. 15:217–224, 2002. Tripathi, R. K., C. Chaya-Devi, and A. Ramaiah. pH-dependent interconversion of two forms of tyrosinase in human skin. Biochem. J. 252:481–487, 1988. Vijayasaradhi, S., Y. Xu, B. Bouchard, and A. N. Houghton. Intracellular sorting and targeting of melanosomal membrane proteins: identification of signals for sorting of the human brown locus protein, gp75. J. Cell Biol. 130:807–820, 1995. Wallis, C. E., and P. H. Beighton. Synchrony of oculocutaneous albinism, the Prader–Willi syndrome, and a normal karyotope. J. Med. Genet. 26:337–339, 1989. Watabe, H., J. C. Valencia, K. Yasumoto, T. Kushimoto, H. Ando, J. Muller, W. D. Vieira, M. Mizoguchi, E. Appella, and V. J. Hearing. Regulation of tyrosinase processing and trafficking by organellar pH and by proteasome activity. J. Biol. Chem. 279:7971–7981, 2004. Weisner, G. L., C. M. Bendel, D. P. Olds, J. G. White, D. C. Arthur, D. W. Ball, and R. A. King. Hypopigmentation in the Prader–Willi syndrome. Am. J. Hum. Genet. 40:431–442, 1987. Witkop, C. J., Jr. Inherited disorders of pigmentation. Clin. Dermatol. 3:70–134, 1985. Witkop, C. J., Jr., W. E. Nance, R. F. Rawls, and J. G. White. Autosomal recessive oculocutaneous albinism in man. Evidence for genetic heterogeneity. Am. J. Hum. Genet. 22:55–74, 1970. Witkop, C. J., Jr., J. D. Niswander, D. R. Bergsma, P. L. Workman, and J. G. White. Tyrosinase positive oculocutaneous albinism among the Zuni and the Brandywine triracial isolate: biochemical and clinical characteristics and fertility. Am. J. Phys. Anthropol. 36:397–406, 1972. Witkop, C. J., Jr., C. W. Hill, S. Desnick, J. K. Thies, H. L. Thorn, M. Jenkins, and J. G. White. Ophthalmologic, biochemical, platelet, and ultrastructural defects in the various types of oculocutaneous albinism. J. Invest. Dermatol. 60:443–456, 1973. Woolf, C. M., and F. C. Dukepoo. Hopi indians, inbreeding, and albinism. Science 164:30–37, 1969. Yi, Z., N. Garrison, O. Cohen-Barak, T. M. Karafet, R. A. King, R. P. Erickson, M. F. Hammer, and M. H. Brilliant. A 122.5kilobase deletion of the P gene underlies the high prevalence of oculocutaneous albinism type 2 in the Navajo population. Am. J. Hum. Genet. 72:62–72, 2003. Yuasa, I., K. Umetsu, G. Watanabe, H. Nakamura, M. Endoh, and Y. Irizawa. MATP polymorphisms in Germans and Japanese: the L374F mutation as a population marker for Caucasoids. Int. J. Legal Med. 118:364–366, 2004. Zhu, G., D. M. Evans, D. L. Duffy, G. W. Montgomery, S. E. Medland, N. A. Gillespie, K. R. Ewen, M. Jewell, Y. W. Liew, N. K. Hayward, R. A. Sturm, J. M. Trent, and N. G. Martin. A genome scan for eye color in 502 twin families: most variation is due to a QTL on chromosome 15q. Twin Res. 7:197–210, 2004.
241
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
13
Transcriptional Regulation of Melanocyte Function Kazuhisa Takeda and Shigeki Shibahara
Summary 1 Microphthalmia-associated transcription factor (Mitf) encoded at the mouse microphthalmia locus or its human homolog MITF is a cell type-specific regulator that is required for development and/or survival of pigment cells. Heterozygous mutations in the MITF gene cause auditory–pigmentary syndromes, known as Waardenburg syndrome type 2. 2 MITF consists of at least seven isoforms, such as MITF-A, MITF-B, MITF-C, MITF-H, and MITF-M, differing at their N-termini and in their expression profiles. MITF-M is a founder member of multiple MITF isoforms and represents a melanocyte-specific isoform. Each N-terminal region is encoded by a separate exon 1 of the MITF gene. 3 The melanocyte-specific (M) promoter of the MITF gene is upregulated by several transcription factors, PAX3, SOX10, LEF-1, and CREB. The activity and degradation of MITF-M are also regulated by extracellular signals via protein phosphorylation, such as c-Kit signaling. Together, multiple signals appear to converge on the M promoter as well as on the MITF-M protein. 4 The tyrosinase family consists of tyrosinase, tyrosinaserelated protein 1 (TRP-1), and TRP-2/DOPAchrome tautomerase. We have summarized the short history of identification and characterization of these proteins, which are specifically or preferentially expressed in pigment cells. The cis-regulatory elements of the tyrosinase family genes have been identified in the 5¢ flanking region of each gene. Many of these regulatory elements contain the CATGTG motif, a consensus sequence recognized by a large family of transcription factors with a basic helix–loop–helix structure, such as Mitf. 5 Retinal pigment epithelium (RPE) is derived from the optic cup of embryonic brain and shares the capacity of melanin production with melanocytes. RPE forms a single layer of cells interposed between the neural retina and the vascular-rich choroids, thereby constituting the blood–retinal barrier. RPE is responsible for correct development of the eye and for survival of photoreceptors in adult retinas.
Historical Background Pigmentation is one of the most demonstrable phenotypes in the animal kingdom, and melanin is a principal pigment found 242
in all living organisms, including fungi and plants. In the mouse, at least 90 different loci have been known to affect coat color. Thus, mice coat color mutations provide an excellent model for studying gene action and its regulation. Melanin production is specifically seen in the differentiated melanocytes that originate from the neural crest and in the RPE derived from the optic cup of the brain. Like other cell lineages of neural crest origin, melanoblasts, a precursor to melanocytes, migrate throughout the dermis during development. The RPE, however, does not need to migrate such a long distance during development. The RPE is a monolayer epithelium interposed between the vascular-rich choroid and the neural retina, and such an anatomical organization of RPE is entirely different from that of melanocytes. In spite of these differences, both cell types share the unique capacity of melanin production. Tyrosinase (EC 1.14.18.1) is a rate-limiting enzyme in melanin biosynthesis and has been a symbolic enzyme in pigment cell research. Thus, using various approaches, many investigators have attempted to purify and characterize tyrosinase. The first pigment cell-specific cDNA was isolated by differential hybridization from B16 mouse melanoma cells and was initially suggested to encode tyrosinase (Shibahara et al., 1986). This report definitely facilitated the research related to pigment cells, although the cDNA has been shown not to encode tyrosinase but what is now known as tyrosinaserelated protein 1 (TRP-1) (Jackson, 1988). Since then, many genes related to pigmentation, including tyrosinase, have been cloned. In particular, the second enzyme structurally related to tyrosinase was discovered and termed tyrosinase-related protein 2 (TRP-2) (Jackson et al., 1992; Tsukamoto et al., 1992). There is about 40% amino acid identity among tyrosinase, TRP-1, and TRP-2, all of which constitute the tyrosinase family and are specifically expressed in melaninproducing cells. TRP-2 possesses the activity of DOPAchrome tautomerase (EC 5.3.2.3), catalyzing the conversion of DOPAchrome to 5,6-dihydroxyindole-2-carboxylic acid (DHICA) (Kroumpouzos et al., 1994; Yokoyama et al., 1994a). TRP-2 is now known as DOPAchrome tautomerase (DCT). TRP-1 was shown to catalyze the conversion of DHICA to indole–quinone–carboxylic acid (JiménezCervantes et al., 1994; Kobayashi et al., 1994). Thus, both TRP-1 and DCT/TRP-2 are the enzymes that determine the quality of melanin. The tyrosinase gene family has been characterized as a model to study the regulation of pigment cellspecific and developmental stage-specific gene transcription.
TRANSCRIPTIONAL REGULATION OF MELANOCYTE FUNCTION ∆R217 A→C in splice acceptor (Tietz) R259Stop G→A in splice donor R214Stop N278D S250P S298P
AE
MITF
mirw
miws
bHLH
misp Miwh
LZ
mi Mior
mivit
Internal Cytosine I212N ∆R216 R216K D222N Deregulation and novel exon 1 deletion insertion miew Mib ∆exons 2–4 in splice acceptor 2 Internal G244E deletion ∆exon 6
mice R263Stop
Fig. 13.1. Schematic illustration of Mitf/MITF and the characterized mutations. A melanocyte-specific isoform, Mitf-M/MITF-M, is shown. The nine exons are indicated by alternate open and closed boxes over the protein structure. The mutations found in individuals affected by WS2 syndrome (Nobukuni et al., 1996; Tassabehji et al., 1994, 1995) are shown above the functional domains. The delR217 is responsible for Tietz syndrome (Amiel et al., 1998). Asterisks and triangles indicate the splicing mutations and the nonsense mutations respectively. The mutations at the 10 Mitf alleles are indicated below (Hodgkinson et al., 1993; Steingrímsson et al., 1994, 1996), and the mutant alleles shown within boxes are unable to bind to DNA in vitro (Hemesath et al., 1994). Region AE indicates the activating exon (exon 4).
Here, we summarize recent advances concerning mechanisms for pigment cell-specific transcription of the tyrosinase family genes. Elucidation of the mechanisms regulating transcription of the tyrosinase family genes is an essential requirement for understanding the molecular events underlying differentiation of pigment cells. A comprehensive text (Silvers, 1979) and good reviews on mouse coat color mutations have been published (Jackson, 1994; Jackson et al., 1994; Urabe et al., 1993).
Genes Regulating the Development of Pigment Cells The genes described in this section are required for development and migration of melanoblasts and melanocytes, and the mutations of each gene cause white spotting or entirely white coat color, characterized by the lack of melanocytes. Most of these mutations do not affect the development of RPE, except for the microphthalmia-associated transcription factor (Mitf); Mitf is required for normal development of neural crestderived melanocytes and RPE.
Microphthalmia-Associated Transcription Factor Overview Mice with mutations at the microphthalmia (mi) locus, now termed Microphthalmia-associated transcription factor (Mitf), have some or all of the following defects: loss of pigmentation, reduced eye size, failure of secondary bone resorption, reduced numbers of mast cells, and early onset of deafness (Silvers, 1979). The most severe manifestations of Mitf alleles, the original Mitf mi and Mitf or (microphthalmia Oak Ridge), are inherited semi-dominantly and include microphthalmia, white coat, deafness (due to lack of inner ear melanocytes),
and osteopetrosis. Less severe alleles tend to be recessive. These phenotypic variabilities have been shown to represent allelic differences. All Mitf alleles are characterized by defects in neural crest-derived melanocytes, leading to coat color dilution, white spotting or complete loss of pigmentation, and deafness. It is clear that the Mitf protein encoded at the Mitf locus plays an essential role in development and/or survival of several cell lineages, including RPE, mast cells, and osteoclasts. Mitf protein has been shown to play a role in promoting the transition of precursor cells to melanoblasts and melanoblast survival (Opdecamp et al., 1997). Mitf as a Member of a Subfamily of Transcription Factors with a bHLH-LZ Independent transgenic insertions disrupted the Mitf locus on mouse chromosome 6 (Krakowsky et al., 1993; Tachibana et al., 1992), which allowed two groups to clone a novel factor encoded at the Mitf locus (Hodgkinson et al., 1993; Hughes et al., 1993). Mitf consists of 419 amino acid residues and is predicted to contain a basic helix–loop–helix and a leucine-zipper (bHLH-LZ) structure (Fig. 13.1). This type of Mitf is now known as Mitf-M representing a melanocyte-specific isoform (Amae et al., 1998). The bHLH-LZ structure is required for DNA binding and dimerization (reviewed by Kadesch, 1993). The predicted Mitf protein shows the highest degree of amino acid similarity to TFE3 and TFEB, both of which are ubiquitously expressed and bind the palindromic sequence (CACGTG), either as homodimers or as TFE3–TFEB heterodimers (Fisher et al., 1991). TFE3 was originally identified as a human protein that binds the E3 box of the m chain immunoglobulin enhancer (Beckmann et al., 1990), and TFEB as the human protein that binds to the adenovirus major late transcription factor (Carr and Sharp, 1990). Hemesath et al. (1994) have shown that Mitf binds in vitro to DNA 243
CHAPTER 13
containing the CACGTG motif derived from adenovirus major late promoter as a homo- or heterodimer with TFEB, TFE3, or TFEC. TFEC was originally identified as a bHLH-LZ protein, forms heterodimers with TFE3, and inhibits TFE3dependent transcription activation (Zhao et al., 1993). TFEC also shows a high degree of amino acid sequence similarity to MITF (Yasumoto and Shibahara, 1997). In contrast, no heterodimers were observed upon mixing Mitf with Max, Myc, or USF. Mitf also bound the CATGTG motif, a core element of the M-box, and was shown to trans-activate the Mbox-driven reporter gene in fibroblasts (Hemesath et al., 1994). Nakayama et al. (1998) reported that expression of TFEB or TFE3 is undetectable in the neural crest at stages when the Mitf mutant phenotype becomes manifest. Furthermore, the phenotypes of Mitf mutant mice in melanocytes and RPE were not affected in double and triple mutant mice lacking Mitf, TFE3, and/or TFEC (Steingrímsson et al., 2002). These results suggest that Mitf may function as a homodimer during the development of melanocytes and RPE. The human homolog of the mouse Mitf gene, MITF, was cloned and mapped to chromosome 3p12.3–p14.1 (Tachibana et al., 1994). MITF-M, a melanocyte-specific isoform, is predicted to consist of 419 amino acid residues and share 94.4% identity with mouse Mitf-M. The predominant species of MITF mRNA is of about 5.5 kb in human melanoma cells (Tachibana et al., 1994). Ectopic expression of MITF-M converts fibroblasts to cells with melanocyte characteristics (Tachibana et al., 1996). Multiple Isoforms of Mitf with Distinct Amino-Termini The MITF gene is expressed as multiple isoforms in humans and mice, termed MITF-M, MITF-A, MITF-B, MITF-C, MITF-D, MITF-E, MITF-H, and MITF-mc (Amae et al., 1998; Fuse et al., 1999; Oboki et al., 2002; Steingrímsson et al., 1994; Takeda et al., 2002; Takemoto et al., 2002; Yasumoto et al., 1994; for a review, see Shibahara et al., 2001). These isoforms share common bHLH-LZ and transcription activation domains, but differ in the amino-terminal regions (Fig. 13.2). MITF-M is a founder member of multiple MITF isoforms, and its amino-terminus, domain M, consists of 11 amino acid residues and is encoded by the exon 1M. All other isoforms with the extended amino-termini share the entire carboxyl portion with MITF-M. The unique aminoterminus of MITF-A, MITF-B, MITF-C, MITF-MC, or MITFH shares the common region of 83 amino acid residues (domain B1b), which is significantly similar to the equivalent portion of TFEB (Amae et al., 1998) and TFE3 (Rehli et al., 1999; Yasumoto et al., 1998). The initiating methionine of MITF-D or MITF-E is located in the B1b domain, as each exon 1 is a noncoding exon. The MITF gene consists of many promoters, their consecutive first exons, such as exon 1A, 1H, 1D, 1B, and 1M (Fig. 13.2), and eight downstream exons that are common to all isoforms (Hallson et al., 2000; Udono et al., 2000). The unique amino-termini of the MITF isoforms are encoded by separate first exons, except for exon 1D, which codes for the 244
Deletion in Mitf mi-rw 1A
1H
Insertion in Mitf mi-bw 1M 2 3 4
1D 1B
5
6
7
8
9
MDE
B1b 3
A 4
5
bHLH LZ 6 7 8
Thr 9
Ser
2
2
3
A 4
5
bHLH LZ 6 7 8
Thr 9
Ser
B1b
2
3
A 4
5
bHLH LZ 6 7 8
Thr 9
Ser
1H B1b
3
A 4
5
bHLH LZ 6 7 8
Thr 9
Ser
2
MITF-M 1M MITF-A MITF-H MITF-D
1A
B1b
Fig. 13.2. Structural organization of the MITF gene encoding multiple isoforms. The protein-coding regions are indicated by closed boxes, and the 5¢- and 3¢-untranslated regions are indicated by open boxes. Each arrow indicates the transcription start site of separate exon 1. MDE represents the MITF-M distal enhancer. The Mitf mi-rw gene lacks the DNA segment containing exon 1H and MDE (Hallsson et al., 2000; Watanabe et al., 2002). The Mitf mi-bw gene contains the L1 element insertion in intron 3 (Yajima et al., 1999). The bottom panel shows the representative MITF isoforms, MITF-M, MITF-A, MITF-H, and MITF-D. Region A indicates the transcription activation domain. Regions Thr and Ser represent the threonine-rich domain and the serine-rich domain respectively.
5¢ untranslated region of the mRNA. Among the first exons, exon 1B is unique because it is also used as a second exon (B1b exon), when the primary transcripts, initiated from exon 1A, exon 1H, or exon 1D, are subjected to splicing (Udono et al., 2000). Exon 1B therefore encodes the 5¢ untranslated region of MITF-B mRNA, the amino-terminal domain of MITF-B (domain B1a), and domain B1b (Fig. 13.2). Dysfunction of Mitf impairs the differentiation and/or survival of neural crest-derived melanocytes in skin and ear, and optic cup-derived RPE in the eye (Hodgkinson et al., 1993). Among the MITF isoforms, MITF-M is exclusively expressed in melanocytes and pigmented melanoma cells, but is not detectable in any other cell types, including human RPE cell lines (Amae et al., 1998; Fuse et al., 1999). In contrast to MITF-M, other MITF isoforms are widely expressed in many cell types including human RPE cell lines (Amae et al., 1998; Fuse et al., 1999; Takeda et al., 2002; Udono et al., 2000). The Mitf gene is also expressed in heart (Steingrímsson et al., 1994) and male germ cells (Saito et al., 2003a), but no abnormalities in these tissues have been described in Mitf mutants. Informative Mitf Alleles The Mitf gene is altered in two independent Mitf alleles, Mitf mi and Mitf ws (Hodgkinson et al., 1993). Both alleles are semidominant, but the original Mitf m allele shows a more severe phenotype. The Mitf mi allele contains a three-base deletion, resulting in loss of an arginine residue from a series of four consecutive conserved arginines (residues 214–217), located at the carboxyl end of the DNA-binding basic region, whereas the Mitf ws mutation results from an intragenic deletion
TRANSCRIPTIONAL REGULATION OF MELANOCYTE FUNCTION
(Fig. 13.1). Subsequently, it was shown that a protein encoded at the Mitf mi allele is unable to bind in vitro to the CACGTG motif (Hemesath et al., 1994) and to the CATGTG motif (Hemesath et al., 1994; Morii et al., 1994). The deletion of the Mtfi gene was also found in genomic DNA of two Mitf alleles, Mitf ws and Mitf rw (Hughes et al., 1993). Molecular defects associated with eight murine Mitf mutations were characterized (Steingrímsson et al., 1994), and the DNA-binding abilities of mutant proteins were examined in vitro (Hemesath et al., 1994), clearly indicating that the phenotypic variation associated with various Mitf alleles can be explained in large part by the underlying nature of the mutation. For example, a mutation associated with a semi-dominant allele, Mitf or, is an Arg216Lys substitution in the basic region (Steingrímsson et al., 1994), where a deletion of one arginine residue of the four consecutive arginine residues (214–217) is present in the Mitf mi mutation (Hodgkinson et al., 1993) (Fig. 13.1). Indeed, both Mitf mi and Mitf or produce nearly identical phenotypes, including osteopetrosis, which represents the defect of bone resorption and is caused by the osteoclast dysfunction. It was then confirmed that the mutation associated with Mitf mi or Mitf or alleles completely abolishes DNA-binding ability as homodimers or heterodimers with TFE3 in vitro (Hemesath et al., 1994). In addition, the presence of either Mitf mi or Mitf or protein ablated TFE3 homodimeric DNA-binding activity. Thus, the semi-dominant Mitf mutations may represent dominant-negative mutations, as each mutation is predicted to inhibit Mitf function. It has also been reported that the nuclear translocation potential of Mitf mi and Mitf ew proteins is impaired and thus, unlike the nuclear-located Mitf protein, both mutant proteins are predominantly located in the cytoplasm (Takebayashi et al., 1996). Essential requirement of Mitf-M for melanocyte development was verified by the molecular lesion of black-eyed white Mitf mi-bw mice (Yajima et al., 1999), which are characterized by the complete white coat color, deafness, and normally pigmented RPE without any ocular abnormalities. In Mitf mi-bw mice, the insertion of an L1 retrotransposable element in the intron 3 between exon 3 and exon 4 leads to complete repression of Mitf-M mRNA expression and to reduction in Mitf-A and Mitf-H mRNAs expression (Yajima et al., 1999). In this context, the M promoter represents the most downstream promoter of the MITF/Mitf gene (Fuse et al., 1996; Hallsson et al., 2000; Tassabehji et al., 1994; Udono et al., 2000), and may be most susceptible to the transcriptional repression caused by the insertion of the L1 element (Fig. 13.2). These results indicate that MITF-M/Mitf-M is a key regulator of melanocyte development but is dispensable for RPE development. The homozygous red-eyed white Mitf mi-rw mice exhibit small red eyes and white coat with some pigmented spots around the head and/or tail (Steingrímsson et al., 1994), and its molecular defect is a deletion of the genomic DNA segment containing exon 1H and exon 1B (Hallsson et al., 2000) (Fig. 13.2). It is therefore conceivable that the phenotype of Mitf mi-rw mice represents the loss of function of all Mitf isoforms with extended amino-termini. Moreover, these mutant
mice are deficient in melanocytes, probably due to the loss of Mitf-M expression, except for melanocytes located in the head and tail regions, suggesting that the deleted genomic DNA segment may contain the enhancer for the M promoter. In fact, an upstream enhancer has been identified, termed MDE (Fig. 13.2) (Watanabe et al., 2002). Mutations in the MITF Gene, Causing Auditory–Pigmentary Syndrome Waardenburg syndrome type 2 (WS2) is an autosomal dominant disorder of sensorineural hearing loss and pigmentary disturbances, and its responsible gene has been mapped to chromosome 3p12.3–p14.1, close to the position of the MITF gene (Hughes et al., 1994). Subsequently, mutations affecting splice sites in the MITF gene were identified in two families with WS2 (Tassabehji et al., 1994). MITF gene dosage may be more critical in the developing human than in the mouse. A mutation responsible for Tietz syndrome (albinism– deafness syndrome) has been identified as an in-frame deletion of the MITF gene, removing one of four consecutive Arg residues (delR217) in the basic region of MITF-M (Amiel et al., 1998) (Fig. 13.1). Tietz syndrome is characterized by profound deafness, generalized albinism with blue eyes, and hypoplasia of the eyebrows. Unlike WS2, Tietz syndrome shows dominant inheritance with complete penetrance and does not involve the eyes. Thus, the delR217 mutation causes more severe dysfunction of melanocytes than do other MITF mutations. Notably, the delR217 mutation found in Tietz syndrome is equivalent to the mouse semi-dominant Mitf mi mutation (Hodgkinson et al., 1993). The functional consequence of the delR217 mutation was shown to be a loss of DNA-binding activity and to function as a dominant-negative form of MITF-M (Hemesath et al., 1994). In contrast to the haploinsufficiency of MITF in WS2 (Saito et al., 2002), a dominant-negative function of the delR217 MITF-M may be responsible for Tietz syndrome. Regulation of the MITF-M Promoter by Multiple Transcription Factors MITF-M expression is upregulated by Wnt signaling (Dorsky et al., 2000; Takeda et al., 2000a). Wnt proteins, secreted cysteine-rich glycoproteins, have been established as developmentally important signaling molecules (reviewed by Cadigan and Nusse, 1997). Wnt signaling induces intracellular accumulation of b-catenin, which functions as a coactivator for LEF-1/TCF transcription factors (reviewed by Cadigan and Nusse, 1997; Clevers and van de Wetering, 1997; Eastman and Grosschedl, 1999). A double knockout mouse of Wnt-1 and Wnt-3a genes exhibits deficiency of neural crest derivatives, including melanocytes (Ikeya et al., 1997). Wnt signaling promotes pigment cell formation from neural crest in zebrafish (Dorsky et al., 1998). Moreover, the onset of Wnt3a expression is detected at 7.5 embryonic days (Takada et. al., 1994), which precedes the onset of Mitf expression in neural crest cells (9.5–10.5 embryonic days) (Nakayama et al., 1998). Thus, MITF-M is a good candidate for the target genes of Wnt signaling. Indeed, the MITF-M promoter is bound by 245
CHAPTER 13
LEF-1 and is activated by Wnt-3a (Takeda et al., 2000a). Wnt3a protein induces endogenous Mitf-M mRNA in cultured melanocytes (Takeda et al., 2000a). Interestingly, the MITFM by itself interacts with LEF-1, which efficiently activates its own transcription (Saito et al., 2002; for a review, see Saito et al., 2003b). Recruitment of MITF-M on the M promoter is an essential step for the self-activation of MITF-M expression and depends on the binding of LEF-1 to the three adjacent binding sites (Saito et al., 2002). It is therefore likely that transcription from the M promoter is relatively sensitive to the concentrations of LEF-1 and MITF-M. Importantly, MITF-M is able to transactivate the M promoter by interacting with LEF-1 but without binding to the M promoter, because the M promoter does not contain the CATGTG motif and is not bound by MITF-M in vitro. In addition, the mutant MITF-M protein lacking the DNA-binding activity also enhances the LEF-1mediated transactivation of the M promoter (Saito et al., 2002). We used the Gly244Glu substitution found in the semidominant Mitf brownish (Mitf b) mouse (Steingrímsson et al., 1996). Likewise, Mitf-M has been shown to interact with c-jun to transactivate the mouse mast cell protease 7 gene promoter that lacks a typical MITF-binding element (Ogihara et al., 2001). It is therefore conceivable that MITF-M functions as a nonDNA-binding cofactor for LEF-1 on the M promoter. This notion is of physiological significance in understanding the phenotypic consequences of various MITF and Mitf mutations that alter the DNA-binding activity. MITF-M expression is also upregulated by a-melanocytestimulating hormone (a-MSH), which stimulates cAMP signaling and activates the transcription factor CREB by phosphorylation. CREB binds the cAMP-responsive element in the MITF-M promoter, resulting in transcriptional activation of the MITF-M gene (Price et al., 1998). The cAMP signalingmediated activation of the MITF-M gene is melanocyte specific (Price et al., 1998). This activation requires SOX10, a transcription factor containing a high-mobility-group domain (Huber et al., 2003). The Function of MITF-M Protein is Regulated by Phosphorylation The Steel/c-kit signaling triggers phosphorylation of MITF-M via the MAP kinase ERK2 at Ser-73, and upregulates the function of MITF-M (Hemesath et al., 1998). The function of MITF-M protein is regulated by many signals, which induce phosphorylation of MITF-M (see Fig. 13.4). Consequently, MITF-M could interact with CBP/p300 transcriptional coactivator efficiently (Price et al., 1998; Sato et al., 1997). Moreover, c-kit signaling results in phosphorylation of MITF-M at Ser-409 via p90 Rsk, a member of the serine/threonine kinases, and causes short-lived activation and destruction of MITF-M (Wu et al., 2000). In this context, the ubiquitin-conjugating enzyme hUBC9 was identified as a potential interacting partner for MITF-M (Xu et al., 2000). It was shown that phosphorylation of MITF-M at Ser-73 is a prerequisite for the hUBC9-mediated degradation of MITF-M. 246
Glycogen synthase kinase 3b (GSK3b) phosphorylates MITF-M at Ser-298, enhancing the DNA-binding ability of MITF-M (Takeda et al., 2000b). In fact, a Ser298Pro substitution was found in the individuals affected by WS2 (Tassabehji et al., 1995). It has been reported that GSK3b is activated by cAMP, which stimulates melanogenesis (Khaled et al., 2002). Mitf Regulates the Genes Involved in Melanin Formation and Melanocyte Survival Mitf protein transactivated the mouse tyrosinase (Ganss et al., 1994a) and TRP-1 promoters probably by binding to the Mbox (Yavuzer et al., 1995). It was also shown that Mitf protein activates the human tyrosinase promoter mainly through the initiator E-box (Bentley et al., 1994). Likewise, MITF noticeably increased the expression of a reporter gene under the control of the human tyrosinase promoter, mainly through the CATGTG motif of the tyrosinase distal element, TDE (positions –1861 to –1842) (Yasumoto et al., 1994). Subsequently, MITF was shown to bind in vitro to TDE and was also shown to transactivate the mouse tyrosinase and TRP-1 promoters, probably by binding to the M-box (Yasumoto et al., 1995). The M-box was originally identified as a positive regulatory element in the mouse TRP-1 promoter (Lowings et al., 1992) and is well conserved in the tyrosinase family genes. In contrast, although DOPAchrome tautomerase (DCT) promoter contains the M-box, its promoter is not activated by MITFM alone (Yasumoto et al., 1997). Subsequently, it has been reported that the DCT promoter is activated by cooperation of MITF with LEF-1 (Yasumoto et al., 2002). These results indicate that MITF is a factor required for pigment cellspecific transcription of the tyrosinase family genes. It is noteworthy that MITF may form a dimer with a cell-specific or ubiquitous DNA-binding protein, which in turn functions to direct the pigment cell-specific transcription of the tyrosinase family genes. Other pigment cell-specific target genes of MITF are Tbx2, a member of the T-box family (Carreira et al., 2000), melanosomal proteins Pmel17 (silver/gp100) and MART1/ MELANA (Du et al., 2003), and MELASTATIN (MLSN1/ TRPM1), an ion channel of the transient receptor potential (TRP) superfamily (Miller et al., 2004). MITF is also responsible for melanocyte survival by regulating the antiapoptotic gene Bcl2 (McGill et al., 2002), disruption of which causes depigmentation in second hair follicle change (Yamamura et al., 1996). Moreover, it has been shown that MITF interacts with the retinoblastoma product in vitro (Yavuzer et al., 1995). Thus, MITF may regulate the cell cycle, but it is unknown whether MITF transactivates the cell cycle-related genes.
Pax-3 or Splotch Homozygous splotch (Sp) mice usually die at 13 days of gestation with multiple abnormalities, including neural tube defects and dysgenesis of neural crest-derived cells (Auerbach, 1954; Silvers, 1979), whereas heterozygous splotch mice display white spotting on the belly and occasionally on the back, feet,
TRANSCRIPTIONAL REGULATION OF MELANOCYTE FUNCTION
and tail. It has been shown that the splotch mutation disrupts the development of functioning melanocytes but does not affect RPE (Auerbach, 1954; Pavan and Tilghman, 1994). The splotch locus encodes the Pax-3 protein, a member of a family of putative transcription factors related to the paired box family of Drosophila segmentation genes (Epstein et al., 1991). In the mouse, the Pax gene family encodes a group of eight related proteins, which share a domain homologous to that encoded by the Drosophila paired box (reviewed by Chalepakis et al., 1993). One mutant splotch allele, Sp2H, contains a deletion of 32 bp in the exon sequence coding for the paired homeodomain of Pax-3 protein (Epstein et al., 1991). Human PAX3 gene encodes a paired domain transcription factor located at chromosome 2q35, and its mutations are associated with Waardenburg syndrome type 1 (WS1) and type 3 (WS3) (Baldwin et al., 1992; Tassabehji et al., 1992, 1993, 1995). WS1 and WS3 are dominantly inherited syndromes of hearing loss, pigmentary disturbances, and heterochromia iridis. Unlike WS2, WS1 and WS3 are characterized by dystopia canthorum and limb abnormality, respectively. Watanabe et al. (1998) has shown that the MITF-M promoter is a direct target gene for PAX3, which accounts for the fact that mutations of either transcription factor PAX3 or MITF could cause Waardenburg syndrome. TRP-1 gene is also activated by PAX3 (Galibert et al., 1999).
SOX10 SOX10 is a transcription factor containing a high-mobilitygroup box as a DNA-binding motif, and is responsible for Waardenburg–Hirschsprung syndrome, also known as WS4 (Pingault et al., 1998), which is characterized by aganglionic colon, sensorineural deafness, and pigmentation abnormalities. In the spontaneous mouse mutant Dominant megacolon (Dom), Sox10Dom is functionally inactive due to a frameshift mutation (Herbarth et al., 1998; Southard-Smith et al., 1998). The Dom mice suffer from several neural crest defects including the enteric nervous system and melanoblasts. At E11.5, mouse embryos homozygous for the Sox10Dom mutation entirely lack neural crest-derived cells expressing the lineage marker DOPAchrome tautomerase (DCT) or Mitf. Moreover, neural crest cell cultures derived from homozygous embryos do not give rise to pigmented cells (Potterf et al., 2001). Thus, Sox10 may regulate transcription of the DCT and MITF genes. In the heterozygous Dom mice, c-kit-expressing melanoblasts are observed at E11.5, but lack Dct expression, suggesting that Sox10 may serve as a transcriptional activator of Dct. Indeed, Sox10 and Dct colocalized in early melanoblasts, and Sox10 is capable of transactivating the Dct promoter in a transient expression assay (Potterf et al., 2001). Moreover, Ludwig et al. (2004) have shown the synergistic activation of the Dct gene by Sox10 and Mitf. By in situ hybridization analysis, we have shown the coexpression of Sox10 and Mitf (most likely Mitf-M) mRNAs in migrating melanoblasts at E11.5 (Watanabe et al., 2000). By E13.5, Sox10 mRNA expression became undetectable in
migrating melanoblasts, whereas Mitf expression continues to be detectable. In postnatal day 8 and adult cochleas, Sox10 expression was detected only in the supporting cells of the organ of Corti (Watanabe et al., 2000). Taken together, these results support the notion that Sox10 is required for transcription from the M promoter of the MITF/Mitf gene during the early stage of melanoblast development. MITF-M gene is also activated by SOX10 via at least three SOX10 binding sites of the proximal promoter (Bondurand et al., 2000; Lee et al., 2000; Potterf et al., 2000; Verastegui et al., 2000). SOX10 synergistically activates the MITF-M promoter by cooperating with PAX3 (Bondurand et al., 2000; Potterf et al., 2000). SOX10 also binds the MITF-M distal enhancer (MDE) located at about the –15-kb region upstream of exon 1M (Watanabe et al., 2002). SOX10 was shown to function as an architectural transcription factor by bending the DNA (Peirano and Wegner, 2000). It is therefore conceivable that the DNA bending, induced by SOX10 bound to MDE, may facilitate the interaction with the transcription factors on the proximal MITF-M promoter region (Fig. 13.3). These data support a model in which deafness and hypopigmentation common to all types of WS are caused by a functional disruption of a key transcription factor, MITF-M.
CITED1 CITED1 was identified as a melanocyte-specific gene 1 (msg1), which is a nuclear protein expressed in pigmented melanocytes and melanoma cells, but not in amelanotic melanoma cells (Shioda et al., 1996). The normal tissue distribution of CITED1 in adult mice was confined to melanocytes and testis. Murine Cited1 and human CITED1 genes encode a predicted protein of 27 kDa with 75% overall Wnt 5’ (MDE) –15 kb SOX10
Frizzled
α-MSH MC1R
GSK3β β-Catenin
cAMP Cascade
MITF-M promoter β-Catenin SOX10 PAX3 (WS4) (WS1 and 3)
LEF1 MITF-M
CREB Exon 1M
3’
+1
Fig. 13.3. Transcriptional regulation of the MITF-M promoter. The proximal MITF-M promoter is bound by PAX3, which is responsible for WS1 and WS3, and by SOX10, which is responsible for WS4. SOX10 also binds the MITF-M distal enhancer (MDE) to activate the MITF-M gene. Wnt signaling induces intracellular accumulation of b-catenin, which functions as a coactivator for LEF-1, leading to activation of the MITF-M gene. MITF-M also interacts with LEF-1 and activates its own transcription. a-Melanocyte-stimulating hormone (a-MSH) stimulates cAMP signaling and activates the transcription factor CREB by phosphorylation. CREB induces MITF-M mRNA expression via a cAMP-responsive element in the MITF-M promoter (Price et al., 1998).
247
CHAPTER 13
also detected in a mouse melanoblast cell line (Eisen et al., 1995; Thomson et al., 1993). Expression of BRN2, in melanoma cells in cotransfection assays, repressed the activity of the melanocyte-specific tyrosinase promoter (Eisen et al., 1995). Additionally, BRN2 ablated melanoma cells revert to a less mature cell type lacking many markers of differentiated melanocytes such as MITF (Thomson et al., 1995). These results suggest that BRN2 maintains the undifferentiated melanocytic phenotype.
Upstream Stimulatory Factor 1 (USF1)
Fig. 13.4. Post-translational regulation of MITF-M by multiple signals. Steel/c-kit signaling triggers phosphorylation of MITF-M via the MAP kinase ERK2 at Ser-73, and increases interaction of MITFM with CBP/p300 transcriptional coactivators. The c-kit signaling phosphorylates MITF-M at Ser-409 via a serine/threonine kinase p90 Rsk, and causes short-lived activation and destruction of MITF-M. For the degradation of MITF-M, the ubiquitinconjugating enzyme hUBC9 interacts with MITF-M. Endothelin 3, which is responsible for WS4, stimulates MAP kinase, and probably phosphorylates MITF-M. Glycogen synthase kinase 3b (GSK3b) is activated by cAMP signaling, and phosphorylates MITF-M at Ser-298, enhancing the DNA-binding ability of MITF-M. MITF-M activates transcription of the target genes, which are related to differentiation of melanocytes, such as tyrosinase family genes, and cell survival, such as Bcl2.
amino acid identity and 96% identity within the C-terminal acidic domain of 54 amino acids. CITED1 is a nonDNAbinding coactivator, and its C-terminal domain can function as a transcription activation domain through interacting with p300/CBP transcriptional coactivators (Fig. 13.4) (Yahata et al., 2000). CITED1 is a member of the CBP/p300-interacting transactivator with an ED-rich tail (CITED). CITED1 also interacts with Smad4 (Shioda et al., 1998) or estrogen receptors a and b (Yahata et al., 2001). Cited1 null mutant mice show growth restriction at 18.5 days post coitum, and most of them die shortly after birth, which suggest that Cited1 is required in trophoblasts for normal placental development and subsequently for embryo viability (Rodriguez et al., 2004). It has been shown that overexpression of CITED1 increases melanin in B16 melanoma (Nair et al., 2001).
BRN2 BRN2 (also called N-Oct3 or POU3F2) is a POU domaincontaining transcription factor, implicated in the development of the brain (reviewed by Nakai et al., 1995; Treacy and Rosenfeld, 1992). BRN2 mRNA was expressed in a range of human melanoma cell lines and was elevated compared with normal human melanocytes, whereas mRNA for Brn-2 was 248
A CANNTG motif is the consensus sequence of the binding site for a large family of transcription factors with a bHLH structure (Murre et al., 1989a, b). The bHLH structure is required for DNA binding and dimerization of transcription factors. A ubiquitous transcription factor, USF1, is one of such factors, containing a bHLH and a leucine zipper (LZ) structure (Gregor et al., 1990; Pognonec and Roeder, 1991). USF1 was initially identified as a nuclear protein that binds to the upstream element of the adenovirus major late promoter (Sawadogo and Roeder, 1985), and was then shown to be involved in the expression of various cellular genes (Carthew et al., 1987; Chodosh et al., 1987; Sato et al., 1990). USF1 was shown to bind in vitro to the mouse TRP-1 gene promoter (Yavuzer and Goding, 1994) and to TDE and TPE of the human tyrosinase gene (Yasumoto et al., 1994) using the antiserum against USF1. The binding of USF1 to TDE was also confirmed using the USF1 produced by in vitro translation. In addition, many properties of the TDE-binding proteins are consistent with those of USF1, such as the elution profile on ion-exchange chromatography and the binding patterns in the gel mobility shift assay (Yasumoto et al., 1994). Furthermore, coexpression of a USF1 cDNA remarkably increased the reporter gene expression under the control of the human tyrosinase promoter. USF1 has been identified as a target of the stress-responsive p38 kinase and could mediate UVinduced tyrosinase expression (Galibert et al., 2001). These results suggest that USF may be involved in efficient transcription of the human tyrosinase gene. However, it should be noted that MITF protein does not form heterodimers with USF in vitro (Hemesath et al., 1994).
Tyrosinase Family Genes The tyrosinase family is directly involved in melanin pigment production and is specifically or preferentially expressed in pigment cells. Each family member has been extensively reviewed in other chapters; this chapter will focus on the transcriptional regulation of these genes. The tyrosinase family genes provide a good system to study the mechanisms of cell type-specific gene transcription. Such understanding is invaluable in studying how pigment cell differentiation is regulated. It is clear that multiple factors, including ubiquitous and cellspecific factors, must cooperate to direct pigment cell-specific transcription of the tyrosinase family genes. Here, we sum-
TRANSCRIPTIONAL REGULATION OF MELANOCYTE FUNCTION
marize some of the transacting factors acting on the tyrosinase family genes.
Tyrosinase or Albino (c) Locus Protein Tyrosinase (EC 1.14.18.1) is a rate-limiting enzyme in melanin biosynthesis that catalyzes the conversion of tyrosine to 3,4dihydroxyphenylalanine (DOPA), DOPA to DOPAquinone, and 5,6-dihydroxyindole to indole-5,6-quinone (Tripathi et al., 1992). The amino acid sequences of tyrosinase were deduced from chicken (Mochii et al., 1992), Japanese pond frog (Takase et al., 1992), Japanese quail, and snapping turtle (Yamamoto et al., 1992). They share significant homology with mammalian tyrosinase. The 5¢ flanking regions of the quail and turtle tyrosinase genes were cloned and compared with mammalian tyrosinase genes (Yamamoto et al., 1992). Through retrovirally mediated gene transfer, it was demonstrated that the quail and mouse promoters of about 500 bp are sufficient to direct efficient expression of a reporter mouse tyrosinase gene in cultured albino chick melanocytes but not in fibroblasts and hepatocytes (Akiyama et al., 1994). This indicates that the quail promoter region used contains the cisacting element responsible for melanocyte-specific expression and that the mouse promoter is also functional in avian melanocytes. The quail promoter contains two copies of the element, containing the CANNTG motif, similar to the proximal melanocyte-specific element (p-MSE) of the mouse tyrosinase and TRP-1 genes (Yamamoto et al., 1992). These results suggest that a molecular mechanism for pigment cell-specific transcription of the tyrosinase gene is well conserved between birds and mammals. Mouse cDNA clones for tyrosinase have been isolated by several groups (Kwon et al., 1988; Müller et al., 1988; Terao et al., 1989; Yamamoto et al., 1987, 1989). The mouse tyrosinase gene, encoded at the albino (c) locus, was characterized and organized into five exons (Müller et al., 1988; Ruppert et al., 1988; Shibahara et al., 1990). The molecular basis of the BALB/c albinism was found as a point mutation, causing a Cys-to-Ser substitution at position 85 (codon 103) (Jackson et al., 1990; Shibahara et al., 1990; Yokoyama et al., 1990). Introduction of functional tyrosinase minigene constructs containing the 5¢ flanking region into the albino mouse can rescue the albino phenotype (Beermann et al., 1990; Tanaka et al., 1992; Yokoyama et al., 1990). The promoter function of the mouse tyrosinase gene was analyzed in transgenic mice, showing that its 5¢ flanking region of only 270 bp is sufficient to provide cell type specificity (Klüppel et al., 1991) and developmental regulation in skin melanocytes and retinal pigment epithelium (Beermann et al., 1992). Within this 270-bp region, there are two copies of a CATGTG motif (positions –104 to –99 and –12 to –7). A high level of position-independent expression of a tyrosinase transgene has been achieved using a yeast artificial chromosome containing the 80-kb mouse tyrosinase gene and the 155-kb 5¢ flanking region (Schedl et al., 1993), indicating that all cis-acting elements required for tyrosinase gene control are located in these DNA segments.
A DNase I hypersensitive site was identified about 15 kb upstream from the first exon of the mouse tyrosinase gene (Porter et al., 1991). This hypersensitive site, located 12 kb upstream, was detected in mouse melanoma cells but not in mouse fibroblasts (Ganss et al., 1994b). Functional analysis of the sequences corresponding to the DNase I hypersensitive site showed the property of a strong cell-specific enhancer in transgenic mice as well as in cultured cells (Ganss et al., 1994b). It was also shown that full enhancer activity in transient expression assays is detected with a minimal sequence of 200 bp located at –12.1 kb. Two protein-binding regions, hs1 and hs2, were identified within the 200-bp enhancer region by DNase I footprinting analysis. Interestingly, either the hs1 or the hs2 region contains a copy of the CANNTG motif. However, by gel retardation assays, the protein-binding activity was detected only with hs1 oligonucleotide, but not with hs2 oligonucleotide, suggesting that protein binding to hs1 is a prerequisite for the binding factors to hs2 (Ganss et al., 1994b). A palindromic sequence 5¢-TGACTTTGTCA-3¢ is present in the hs1 region and is similar to the binding motif of CREB (cAMP-responsive element binding) transcription factor and an AP1 (activator protein 1) binding site, which is recognized by members of the fos/jun family of transcription factors. The enhancer function of the DNase I hypersensitive site of the mouse tyrosinase gene was also confirmed in transgenic mice by other investigators (Porter and Meyer, 1994). They also suggested that the distinct regulatory elements are required for the expression of tyrosinase gene in neural crestderived melanocytes and RPE. The 270-bp upstream region of the mouse tyrosinase gene was analyzed in detail (Ganss et al., 1994a), because this region is sufficient to confer cell-specific and developmentally regulated expression of the tyrosinase gene in the transgenic mice (Beermann et al., 1992). Within this 270-bp region, two positive regulatory elements (positions –245 to –230 and –104 to –93) and one negative regulatory element (position –195 to –125) were identified by transient expression assays (Ganss et al., 1994a). The positive regulatory element, located between –104 and –93, coincides with the M-box, the 11-bp cis-acting element containing the CATGTG motif of the mouse TRP-1 gene (Lowings et al., 1992). It was also shown that MITF activates the mouse tyrosinase gene promoter (Yasumoto et al., 1995). However, the functional analysis of the two positive elements in transgenic mice indicates that these two elements do not determine pigment production in vivo but rather modulate transcription of the mouse tyrosinase gene (Ganss et al., 1994c). Kwon et al. (1987a) isolated a portion of human tyrosinase cDNA by screening a melanocyte expression cDNA library with antityrosinase polyclonal antibodies. Subsequently, the entire structure of human tyrosinase was deduced from the full-length cDNAs (Bouchard et al., 1989; Shibahara et al., 1988; Takeda et al., 1989). The catalytic function of a cloned tyrosinase cDNA was assessed by transient transfection assays, revealing that tyrosinase possesses the two catalytic activities: tyrosine hydroxylase and dopa oxidase (Takeda 249
CHAPTER 13
et al., 1989). The human tyrosinase gene was mapped to chromosome 11q14–q21, and a second “tyrosinase-related” sequence mapped to 11p11.2–cen (Barton et al., 1988). Tomita et al. (1989) clarified the molecular basis of oculocutaneous albinism (type I) by finding a single base insertion in the exon sequence of the patient’s tyrosinase gene. This insertion causes a frameshift and introduces a premature termination codon. The patient has the mutant gene at both alleles, and the truncated protein encoded by the mutant gene is not functional. The human tyrosinase gene is organized into five exons (Tomita et al., 1989), and its size is greater than 70 kb (Takeda et al., 1990). The nucleotide sequence of the 5¢ flanking region of the human tyrosinase gene was also reported (Kikuchi et al., 1989). The promoter function of the mutant gene is confirmed by in vitro transcription using melanoma whole cell extracts (Takeda et al., 1990). The structural organization and the nucleotide sequence of the 5¢ flanking region of the human tyrosinase gene were also reported (Giebel et al., 1991; Ponnazhagan et al., 1994). It was found that the second site, mapped to chromosome 11p11.2–cen by Barton et al. (1988), represents the truncated human tyrosinase pseudogene, which consists of the nucleotide sequence almost identical to that of exons 4 and 5 (Giebel et al., 1991; Takeda et al., 1991). Shibata et al. (1992a) identified the 39-bp enhancer element of the human tyrosinase gene about 1.8 kb upstream from the transcription initiation site, which is responsible for pigment cell-specific expression of a reporter gene. The enhancer element was narrowed to the 20-bp sequence, termed tyrosinase distal element (TDE) (positions –1861 to –1842) (Yasumoto et al., 1994). TDE, containing a CATGTG motif in its center, was specifically bound by MITF-M (Yasumoto et al., 1994, 1997). There are two additional copies of the CATGTG motif in the human tyrosinase promoter region (positions –104 to –99 and –12 to –7) (Yasumoto et al., 1994). The 20-bp region (positions –112 to –93), containing the CATGTG motif (positions –104 to –99), was identified as a weak pigment cell-specific promoter, termed tyrosinase proximal element (TPE) (Yasumoto et al., 1994). It is noteworthy that the 1.0-kb 5¢ flanking region of the human tyrosinase gene containing TPE but lacking TDE was sufficient to confer cellspecific expression of the tyrosinase gene in transgenic mice (Tanaka et al., 1992). However, no pigmented melanocytes were detected in the epidermis of these mice. It is therefore conceivable that TDE is required for efficient and correct expression of the human tyrosinase gene in a pigment cellspecific manner. Suzuki et al. (1994) have reported that overexpression of neurofibromin cDNA in MeWo melanoma cells, which are deficient in neurofibromin, enhanced the expression of a reporter gene under the control of the tyrosinase promoter. Neurofibromin is responsible for neurofibromatosis type 1 (NF1) or von Recklinghausen’s disease, which is a common autosomal dominant disorder characterized by the presence of neurofibromas, café-au-lait spots, Lisch nodules (hamartomas in the iris), bone deformity, and an increased frequency of 250
malignancies (Cawthon et al., 1990; Viskochil et al., 1990; Wallace et al., 1990). Neurofibromin has a domain related to mammalian ras GTPase-activating protein (GAP) (Xu et al., 1990). Notably, the GAP-related domain of neurofibromin is mainly responsible for the activation of the tyrosinase promoter (Suzuki et al., 1994). Likewise, neurofibromin has been shown to activate the promoter activity of the human DCT gene, as judged by transient cotransfection assays (Suzuki et al., 1998). Neurofibromin may modulate intracellular signaling, which in turn stimulates the activity of a factor required for melanocyte-specific transcription of the tyrosinase and DCT genes.
Tyrosinase-related Protein 1 A pigment cell-specific cDNA, pMT4, was cloned from a B16 mouse melanoma cDNA library by differential hybridization (Shibahara et al., 1986). The expression of pMT4 mRNA is restricted to the skin and pigmented melanoma cells. The deduced structure of the pMT4-encoded protein shares significant homology with Neurospora tyrosinase and contains the several domains thought to be characteristic of tyrosinase, such as a signal sequence, two potential Cu-binding regions, a transmembrane domain, and potential glycosylation sites. Furthermore, transient expression of pMT4 revealed that its protein product is reactive with monoclonal antibodies TMH1 and TMH-2, which have been reported as antityrosinase monoclonal antibodies (Tomita et al., 1985). The pMT4 protein was therefore reported as tyrosinase (Shibahara et al., 1986). However, when its gene was mapped to the brown (b) locus on mouse chromosome 4, which determines the type of melanin produced, it was shown to be different from tyrosinase (Jackson, 1988). The pMT4 protein is now known as TRP-1, and monoclonal antibodies TMH-1 and TMH-2 have been established as anti-TRP-1 antibodies (Tomita et al., 1991). The function of TRP-1 was identified as DHICAoxidase, catalyzing the conversion of DHICA to indole– quinone–carboxylic acid (Jiménez-Cervantes et al., 1994; Kobayashi et al., 1994). Thus, TRP-1 is the first gene of the tyrosinase gene family to be cloned, but its exact function was established last. TRP-1 or brown (b) locus protein is composed of 537 amino acids, including a signal peptide with a molecular mass of 58 kDa (Shibahara et al., 1986). Sequence analysis of the BALB/c mouse TRP1 gene revealed five base differences in the exon regions compared with the sequence of the C57BL/6 gene (Shibahara et al., 1991). One is a deletion of three nucleotides in the 5¢-untranslated region, and the other four are point mutations within the protein coding region: two missense mutations and two silent mutations (Zdarsky et al., 1990). These two missense mutations are also found in another b-mutant mouse DBA/2 (Shibahara et al., 1992). The original b mutation has been identified as a Cys-to-Tyr substitution at position 86 (codon 110) (Jackson et al., 1990; Zdarsky et al., 1990). The mutant TRP-1 containing Tyr-110 is not reactive with an anti-TRP-1 monoclonal antibody TMH-1 (Shibahara et al., 1992).
TRANSCRIPTIONAL REGULATION OF MELANOCYTE FUNCTION
The mouse TRP1 gene is about 15~18 kb long and organized into eight exons (Jackson et al., 1991; Shibahara et al., 1991). Jackson et al. (1991) assigned several potential transcriptional initiation sites, and one of them is the same as that assigned by Shibahara et al. (1991). In this review, we have used the numbering that starts with the upstream initiation site (position 1) (Jackson et al., 1991); thus, the initiation site assigned by Shibahara et al. (1991) is the nucleotide at position 5. The promoter function of the mouse TRP1 gene was analyzed using an in vitro transcription system, suggesting that the DNA segment (position –34 to +158) is sufficient to direct pigment cell-specific transcription in melanoma whole cell extracts but not in HeLa whole cell extracts (Shibahara et al., 1991). On the other hand, through transient transfection assays, Lowings et al. (1992) have identified the regulatory region consisting of both positive and negative elements, which confers efficient expression on a reporter gene in pigmented melanoma cells but not in nonmelanoma cells. The positive element contains the nonconsensus octamer motif, 5¢ATTTGAAT-3¢, and has been shown to be bound in vitro by the ubiquitous OCT-1 transcription factor. In addition, a minimal promoter extending between –44 and +107 is sufficient for cell type-specific expression, and it contains the 11bp cis-acting element, termed the M-box. The M-box contains the CATGTG motif and is required for a basal level of expression of a reporter gene in B16 mouse melanoma cells (Lowings et al., 1992). Yasumoto et al. (1995) have found through transient expression analysis that MITF transactivates the mouse TRP-1 promoter, mainly via the M-box. The structure of human TRP-1 has been deduced from its cDNA sequence (Chintamaneni et al., 1991; Cohen et al., 1990), sharing about 93% amino acid identity with a mouse counterpart. Human TRP-1 is composed of 527 amino acids and is shorter than mouse TRP-1 by 10 amino acids at the carboxyl-terminus (Cohen et al., 1990). Human TRP-1 is also known as a melanoma antigen gp75, which is potentially autoimmunogenic, because immunoglobulin G (IgG) antibodies against gp75 are detected in a patient with metastatic melanoma (Vijayasaradhi et al., 1990). Subsequently, an informative single base change was found in the full-length human TRP-1 cDNA, pHT2a, that was isolated from a MeWo human melanoma cDNA library (Takimoto et al., 1995); namely, the HindIII site (AAGCTT) present in the reported sequence (Cohen et al., 1990) is disrupted in pHT2a because of the Cto-T transition at position 750. The human TRP-1 gene contains the C residue at position 750, favoring the sequence previously reported, which was derived from a different human melanoma cell line (Cohen et al., 1990). This base change is not associated with an amino acid substitution and may represent polymorphism. The human TRP1 gene has been mapped to chromosome 9p22–pter (Chintamaneni et al., 1991), and the 5¢ flanking region and exon 1 of the TRP1 gene have been characterized and the promoter function assessed by transient expression assays (Shibata et al., 1992b). The structural organization of
the human TRP1 gene has been characterized (Sturm et al., 1995). Unlike the mouse TRP1 gene (Yasumoto et al., 1995), the pigment cell-specific promoter function of the human TRP1 gene was not detected by transient expression assays in cultured cells with the 5¢ flanking region of up to 3.5 kb (Shibata et al., 1992b; Yasumoto et al., 1997; Yokoyama et al., 1994b).
DOPAchrome Tautomerase/Tyrosinase-related Protein 2 The phenotype of homozygous slaty mice includes the dilution of coat color and premature hair loss. It was proposed that DCT functions to prevent the accumulation of dihydroxyindole, a more toxic product of DOPAchrome generated spontaneously (Jackson et al., 1992). The DCT gene was mapped to the slaty locus on mouse chromosome 14 and is mutated at the slaty locus, which is an arginine to glutamine change at the first copper binding site (Jackson et al., 1992). It was then confirmed by transient expression assays of cDNA that mouse TRP-2 possesses the catalytic activity of DOPAchrome tautomerase and the slaty mutation dramatically decreases the catalytic function (Kroumpouzos et al., 1994). The mouse DCT gene is expressed in migratory melanoblasts shortly after they left the neural crest (Steel et al., 1992); expression of the DCT gene precedes that of the tyrosinase and TRP1 genes. Likewise, DCT expression is detected in the developing telencephalon and the endolymphatic duct, in which expression of the tyrosinase and TRP1 genes was undetectable (Steel et al., 1992). Furthermore, DCT mRNA is expressed in a glioblastoma (Suzuki et al., 1998) and the retinoblastoma (Udono et al., 2001). Thus, the regulation of DCT gene expression is different from that of tyrosinase and TRP1. The structure of the mouse DCT gene has been reported (Budd and Jackson, 1995), and its promoter region contains the M-box. Human DCT shares about 40% amino acid identity with human tyrosinase or TRP-1 (Bouchard et al., 1994; Cassady and Sturm, 1994; Yokoyama et al., 1994a). It has also been confirmed that DCT possesses the catalytic activity of DOPAchrome tautomerase by transient expression assays of a human cDNA (Yokoyama et al., 1994a). The human DCT gene has been mapped to chromosome 13q32 (Bouchard et al., 1994). The 5¢ flanking region and the portion of the human DCT gene have been cloned and characterized (Sturm et al., 1995; Yokoyama et al., 1994b). Comparison of the nucleotide sequence with that of the other tyrosinase gene family members reveals two putative cis-acting elements (–138/–128 and –34/–21), which are similar to those of the M-box (Lowings et al., 1992) and a pigment cell-specific promoter (Shibahara et al., 1991) respectively. The M-box of the human DCT gene (–138 to –128) is identical to the equivalent element of the mouse DCT gene. Transient expression assays revealed that the 5¢ flanking region of the human DCT gene upstream from a luciferase 251
CHAPTER 13
reporter gene is more efficiently expressed in MeWo melanoma cells than in HeLa cells (Yokoyama et al., 1994b), indicating the presence of the pigment cell-specific regulatory element(s). It was then found that the 32-bp regulatory element responsible for pigment cell-specific expression is located between –447 and –415, which was termed the DCT distal enhancer (Amae et al., 2000) (Fig. 13.3), although this enhancer alone is not sufficient to confer cell type-specific expression. An additional element, located between –268 and –56, is required for basal transcription, but again this element by itself is not sufficient to confer pigment cell-specific expression. The latter DNA segment (–268/–56) was tentatively termed the proximal region. Notably, it has been shown that the 71-bp region (–415/–345), immediately downstream from the DCT distal enhancer, is required for activation of the DCT promoter by neurofibromin (Suzuki et al., 1998). Thus, multiple regulatory elements are required for the pigment cell-specific transcription of the DCT gene. Yasumoto et al. (1997) have reported that MITF is unable to trans-activate the DCT promoter in transient transfection assays, despite the fact that MITF binds in vitro to the DCT M-box. Subsequently, it has been confirmed that the M-box of the DCT promoter is bound by MITF-M in vivo (Takeda et al., 2003). Furthermore, an experimentally truncated MITF protein lacking the carboxyl-terminal 125 amino acids activated the tyrosinase promoter less efficiently than did MITF but, surprisingly, the truncated MITF activated the DCT promoter (Yasumoto et al., 1997). These results suggest that the carboxyl-terminus of MITF contains a transcriptional activation domain that is also involved in defining the binding sites for MITF. The synergism between LEF-1 and MITF-M is responsible for the transcriptional regulation of the DCT gene but through a different mechanism from that of the M promoter (Saito et al., 2002; Yasumoto et al., 2002). DCT may be important for the survival of melanocytes. The finding that the vit mutation impairs the synergism with LEF-1 on the DCT promoter but not on the M promoter is of particular interest in view of the phenotype of homozygous Mitf vitiligo (Mitf vit) mice that appear normal as young with uniformly lighter color but show aging-dependent melanocyte loss (Lerner et al., 1986). The Asp222Asn substitution in the helix 1 of Mitf-M represents a molecular lesion of the recessive Mitf vit (Steingrímsson et al., 1994), and the Mitf-Mvit protein is able to bind in vitro to DNA (Hemesath et al., 1994). Thus, the Mitf vit mutation does not profoundly alter the fetal development of melanocytes but impairs the postnatal maintenance of follicular melanocytes, which could be explained by the differential effects of the Mitf vit mutation on the synergism with LEF-1 on the M promoter and the DCT promoter (Saito et al., 2002).
Pmel-17 Protein or Silver Locus Protein A portion of cDNA coding for Pmel-17 protein was initially cloned by screening a human melanocyte cDNA expression library with antityrosinase polyclonal antibodies (Kwon et al., 1987b). A full-length Pmel-17 cDNA was subsequently iso252
lated, and Pmel-17 protein is composed of 645 amino acids with a molecular mass of 68.6 kDa (Kwon et al., 1991). Pmel17 protein contains a putative leader sequence, a potential membrane anchor segment, and relatively high numbers of serine and threonine residues. There are five restricted regions of amino acid similarity among tyrosinase, TRP-1, and Pmel17. The Pmel-17 gene has been mapped to human chromosome 12pter–q21, and its mouse homolog has been mapped to the distal region of mouse chromosome 10, a region known to carry the coat color locus silver (si) (Kwon et al., 1991). The recessive silver mutation causes progressive graying of hair due to the loss of functional follicular melanocytes. The silver gene, a mouse homolog of Pmel-17, is thought to act at the subcellular level and is preferentially expressed in melanocytes (Kwon et al., 1987b). Kwon et al. (1995) found that the mouse silver mutation is caused by a single base insertion in the putative cytoplasmic domain of the mouse homolog of Pmel-17 protein. Pmel-17 is expressed in RPE, because the two cDNA clones derived from chicken and bovine RPE turned out to be a homolog of Pmel-17. The former cDNA encodes a melanosomal matrix protein MMP115 of chicken RPE (Mochii et al., 1991), and the latter encodes the bovine retinal pigment epithelial protein RPE-1 (Kim and Wistow, 1992). In particular, MMP115 was shown to be a useful marker for studying the molecular mechanisms for the differentiation of RPE, because the MMP115 gene was transcriptionally inactivated during the process of dedifferentiation of RPE to a bipotent cell, which can be committed to either the lens cell or RPE (Mochii et al., 1988). Furthermore, expression of Pmel-17 mRNA was remarkably increased following the treatment of murine or human melanoma cells with b-MSH or 3-isobutyl1-methylxanthine (Kwon et al., 1987b), and thus the regulation of its gene expression is of interest.
Transcription Factors Acting at Retinal Pigment Epithelium Correct specification and differentiation of RPE underlie eye morphogenesis, and the impairment of RPE development could lead to severe malformation of the eye, such as anophthalmia (Hero et al., 1990). RPE is derived from the optic cup of embryonic brain and differentiates into a single layer of cells interposed between the neural retina and the vascular-rich choroids, thereby constituting the blood–retinal barrier. At the apical side of RPE, many villi interdigitate with the outer segments of photoreceptors, by which RPE is responsible for phagocytosis of outer segments of photoreceptors (Bok, 1988) and for uptake, processing, and transport of retinoids that are essential for visual function (Bok, 1993). RPE therefore plays important roles in the survival and function of photoreceptors in the adult eye. The mutant homozygous mice for Mitf exhibit depigmentation and hyperproliferation of the RPE and the formation of an ectopic neuroretina at the expense of the dorsal RPE, resulting in microphthalmia (Silver, 1979). In the homozygous Mitf VGA-9 mice, where Mitf is not expressed, expression of
TRANSCRIPTIONAL REGULATION OF MELANOCYTE FUNCTION
tyrosinase and TRP1 genes is reduced in RPE, suggesting that MITF is required for efficient transcription of the tyrosinase and TRP1 genes in RPE as well as in melanocytes (Nakayama et al., 1998). But Mitf is dispensable for Dct expression, as expression of Dct is not affected in Mitf VGA-9 mice (Nakayama et al., 1998). MITF-A is preferentially expressed in a human RPE line of fetal origin and is also expressed in many cell types (Amae et al., 1998; Fuse et al., 1999; Udono et al., 2000). Domain A of MITF-A shares significant amino acid identity with the N-terminus of TFE3 (Rehli et al., 1999; Yasumoto et al., 1998). In addition, three consecutive portions, covering the entire domain A, are aligned to the equivalent portions of cytoplasmic retinoic acid-binding protein (CRABP) (Shibahara et al., 2001). Such similarity is of interest, in view of the phenotype of a recessive Mitf mutant, Mitf vit (Lerner et al., 1986; Steingrímsson et al., 1994), which shows late-onset retinal degeneration and abnormalities in retinoid metabolism (Smith et al., 1994). It is therefore conceivable that the Asp-to-Asn substitution in the helix 1 of MITF-A or other MITF isoforms may impair the interaction with a hitherto unidentified protein in RPE. Transcription of the DCT gene is activated by OTX2 (Takeda et al., 2003). OTX2 is a homolog of the Drosophila homeobox-containing gene orthodenticle (otd), a member of a highly conserved family of homeodomain-containing transcription factors, and is expressed not only at the earliest stage of eye morphogenesis including prospective RPE (MartinezMorales et al., 2001; Simeone et al., 1992, 1993), but also in RPE of the postnatal and adult mouse eye (Baas et al., 2000). In addition, Otx2 null homozygous mice exhibit the absence of the forebrain and embryonic lethality (Acampora et al., 1995), whereas the heterozygotes survive until birth but exhibit anomalies in RPE and retinal development (Matsuo et al., 1995). OTX2 interacts with MITF and synergistically activates tyrosinase and TRP1 genes in RPE (MartinezMorales et al., 2003). It has also been reported that MITF interacts with PAX6 in RPE (Planque et al., 2001). PAX6 is a member of the pairedhomeodomain family of transcription factors (Walther and Gruss, 1991), mutations in which cause the aniridia syndrome in humans (Glaser et al., 1992) and the small eye phenotype in mice (Hill et al., 1991). The interaction with PAX6 and MITF abolishes the DNA binding of MITF, leading to a reduction in MITF-mediated activation in RPE (Planque et al., 2001). Several RPE-specific proteins were identified, including tyrosinase family genes, and cDNAs coding for some of them were cloned. A typical example of such proteins is Pmel-17, also known as MMP115 or RPE-1, which was initially cloned as an RPE-specific gene (Kim and Wistow, 1992; Mochii et al., 1991). Another example is RPE65, which was cloned as a novel RPE-specific microsomal protein with a tissue-specific monoclonal antibody RPE9 (Hamel et al., 1993). Bovine RPE65 consists of 533 amino acid residues with no predicted transmembrane domains. RPE65 mRNA was detected in RPE
but not in other ocular tissues, suggesting that RPE65 is an RPE-specific protein. The human RPE65 gene has been mapped to chromosome 1p31 (Hamel et al., 1994). The gene for ocular albinism type 1 (OA1), located at chromosome Xp22.3–22.2, was identified by positional cloning (Bassi et al., 1995). OA1 is an X-linked disorder characterized by severe impairment of visual acuity, retinal hypopigmentation, and the presence of macromelanosomes. The OA1 gene encodes a protein of 424 amino acids with several putative transmembrane domains and is preferentially expressed in retina as well as in melanoma. Five intragenic deletions and a CG dinucleotide insertion causing a premature stop codon were identified in unrelated OA1 patients. It is of interest to study the pathogenesis of OA1, because the OA1 gene is not RPE specific and is also expressed in melanoma, like many other pigment-related genes. The tyrosinase family genes therefore provide a good system to study the mechanism responsible for RPE-specific gene expression, which in turn allows us to compare regulation in melanocytes.
Perspectives The MITF gene consists of widely spaced multiple promoters, which generate not only the diversity in the transcriptional regulation of these promoters but also the structurally different isoforms. The MITF gene provides a good model for studying the mechanism of promoter selectivity during development or under certain metabolic conditions. The isoform multiplicity of MITF also provides functional diversity and redundancy. Future analysis of MITF isoforms in vivo is required to assess the role of each MITF isoform in differentiation and development of the pigment cell and other cell types. It is also important to identify the interacting partners with the unique N-terminal domains as well as the bHLH-LZ domain that modulate the function of MITF isoforms. Such studies will increase our understanding of the regulation of development and differentiation of the pigment cell. Development of gene therapy and chemotherapy toward melanoma are definitely major goals of pigment cell research. Retinal degeneration of diverse etiologies, either acquired or inherited, accounts for a major cause of aging-dependent visual impairment and blindness in the developed world. It is therefore of significance to understand the mechanism by which various transcription factors maintain the survival or function of RPE in the adult retina. Furthermore, the elucidation of the difference in transcriptional regulation of the tyrosinase family genes between RPE and melanocytes is of particular significance. It is also challenging to explore the possibility of cell therapy targeted for RPE in order to deliver a healthy RPE into an impaired retina.
Acknowledgments We thank Dr Hiroaki Yamamoto (Tohoku University) for 253
CHAPTER 13
helpful discussions. We also thank Ken-ichi Yasumoto, Kazuhiro Takahashi, and other colleagues who contributed to the work on pigment cells.
References Acampora, D., S. Mazan, Y. Lallemand, V. Avantaggiato, M. Maury, A. Simeone, and P. Brulet. Forebrain and midbrain regions are deleted in Otx2–/– mutants due to a defective anterior neuroectoderm specification during gastrulation. Development 121:3279– 3290, 1995. Akiyama, T., B. Whitaker, M. Federspiel, S. H. Hughes, H. Yamamoto, T. Takeuchi, and J. Brumbaugh. Tissue-specific expression of mouse tyrosinase gene in cultured chicken cells. Exp. Cell Res. 214:154–162, 1994. Amae, S., N. Fuse, K. Yasumoto, S. Sato, I. Yajima, H. Yamamoto, T. Udono, Y. K. Durlu, M. Tamai, K. Takahashi, and S. Shibahara. Identification of a novel isoform of microphthalmia-associated transcription factor that is enriched in retinal pigment epithelium. Biochem. Biophys. Res. Commun. 247:710–715, 1998. Amae, S., K. Yasumoto, K. Takeda, T. Udono, K. Takahashi, and S. Shibahara. Identification of a composite enhancer of the human tyrosinase-related protein 2/DOPAchrome tautomerase gene. Biochim. Biophys. Acta 1492:505–508, 2000. Amiel, J., P. M. Watkin, M. Tassabehji, A. P. Read, and R. M. Winter. Mutation of the MITF gene in albinism–deafness syndrome (Tietz syndrome). Clin. Dysmorphol. 7:17–20, 1998. Auerbach, R. Analysis of the developmental effects of a lethal mutation in the house mouse. J. Exp. Zool. 127:305–329, 1954. Baas, C., K. M. Bumsted, J. A. Martinez, F. M. Vaccarino, K. C. Wikler, and C. J. Barnstable. The subcellular localization of Otx2 is cell-type specific and developmentally regulated in the mouse retina. Brain Res. Mol. Brain Res. 78:26–37, 2000. Baldwin, C. T., C. F. Hoth, J. A. Amos, E. O. da-Silva, and A. Milunsky. An exonic mutation in the HuP2 paired domain gene causes Waardenburg’s syndrome. Nature 355:637–638, 1992. Barton, D. E., B. S. Kwon, and U. Francke. Human tyrosinase gene, mapped to chromosome 11 (q14Æq21), defines second region of homology with mouse chromosome 7. Genomics 3:17–24, 1988. Bassi, M. T., M. V. Schiaffino, A. Renieri, F. D. Nigris, L. Galli, M. Bruttini, M. Gebbia, A. A. B. Bergen, R. A. Lewis, and A. Ballabio. Cloning of the gene for ocular albinism type 1 from the distal short arm of the X chromosome. Nature Genet. 10:13–9, 1995. Beckmann, H., L.-K. Su, and T. Kadesch. TFE3: A helix–loop–helix protein that activates transcription through the immunoglobulin enhancer mE3 motif. Genes Dev. 4:167–179, 1990. Beermann, F., S. Ruppert, E. Hummler, F. X. Bosch, G. Müller, U. Rüther, and G. Schütz. Rescue of the albino phenotype by introduction of a functional tyrosinase gene into mice. EMBO J. 9:2819–2826, 1990. Beermann, F., E. Schmid, and G. Schütz. Expression of the mouse tyrosinase gene during embryonic development: Recapitulation of the temporal regulation in transgenic mice. Proc. Natl. Acad. Sci. USA 89:2809–2813, 1992. Bentley, N. J., T. Eisen, and C. R. Goding. Melanocyte-specific expression of the human tyrosinase promoter: activation by the microphthalmia gene product and role of the initiator. Mol. Cell. Biol. 14:7996–8006, 1994. Bok, D. Retinal photoreceptor disc shedding and pigment epithelium phagocytosis. In: Retinal Diseases: Medical and Surgical Management, S. J. Rayan, T. E. Ogden, and A. P. Schachat (eds). St Louis: C. V. Mosby Co., 1988, pp. 69–81. Bok, D. The retinal pigment epithelium: a versatile partner in vision, J. Cell Sci. Suppl. 17:189–195, 1993. Bouchard, B., B. B. Fuller, S. Vijayasaradhi, and A. N. Houghton. Induction of pigmentation in mouse fibroblasts by expression of human tyrosinase cDNA. J. Exp. Med. 169:2029–2042, 1989.
254
Bouchard, B., V. Del Marmol, I. J. Jackson, D. Cherif, and L. Dubertret. Molecular characterization of a human tyrosinaserelated-protein-2 cDNA patterns of expression in melanocytic cells. Eur. J. Biochem. 219:127–134, 1994. Bondurand, N., V. Pingault, D. E. Goerich, N. Lemort, E. Sock, C. L. Caignec, M. Wegner, and M. Goossens. Interaction among SOX10, PAX3 and MITF, three genes altered in Waardenburg syndrome. Hum. Mol. Genet. 9:1907–1917, 2000. Budd. P. S., and I. J. Jackson. Structure of the mouse tyrosinase-related protein-2/dopachrome tautomerase (Tyrp2/Dct) gene and sequence of two novel slaty alleles. Genomics 29:35–43, 1995. Cadigan, K. M., and R. Nusse. Wnt signaling: a common theme in animal development. Genes Dev 11:3286–3305, 1997. Carr, C. S., and P. A. Sharp. A helix–loop–helix protein related to the immunoglobulin E box-binding proteins. Mol. Cell. Biol. 10:4384–4388, 1990. Carreira, S., B. Liu, and C. R. Goding. The gene encoding the T-box factor Tbx2 is a target for the microphthalmia-associated transcription factor in melanocytes. J. Biol. Chem. 275:21920–21927, 2000. Carthew, R. W., L. A. Chodosh, and P. A. Sharp. The major late transcription factor binds to and activates the mouse metallothionein I promoter. Genes Dev. 1:973–980, 1987. Cassady, J. L., and R. A. Sturm. Sequence of the human dopachrome tautomerase-encoding TRP-2 cDNA. Gene 143:295–298, 1994. Cawthon, R. M., R. Weiss, G. F. Xu, D. Viskochil, M. Culver, J. Stevens, M. Robertson, D. Dunn, R. Gesteland, P. O’Connell, and R. White. A major segment of the neurofibromatosis type 1 gene: cDNA sequence, genomic structure, and point mutations. Cell 62:193–201, 1990. Chalepakis, G., A. Stoykova, J. Wijnholds, P. Tremblay, and P. Gruss. Pax: Gene regulators in the developing nervous system. J. Neurobiol. 24:1367–1384, 1993. Chintamaneni, C. D., M. Ramsay, M.-A. Colman, M. F. Fox, R. T. Pickard, and B. S. Kwon. Mapping the human cas2 gene, the homologue of the mouse brown (b) locus, to human chromosome 9p22pter. Biochem. Biophys. Res. Commun. 178:227–235, 1991. Chodosh, L. A., R. W. Carthew, G. J. Morgan, G. R. Crabtree, and P. A. Sharp. The adenovirus major late transcription factor activates the rat g-fibrinogen promoter. Science 238:684–688, 1987. Clevers, H., and M. van de Wetering. TCF/LEF factor earn their wings. Trends. Genet. 13:485–489, 1997. Cohen, T., R. M. Müller, Y. Tomita, and S. Shibahara. Nucleotide sequence of the cDNA encoding human tyrosinase-related protein. Nucleic Acids Res. 18:2807–2808, 1990. Dorsky, R. I., R. T. Moon, and D. W. Raible. Direct regulation of nacre, a zebrafish MITF homolog required for pigment cell formation, by the Wnt pathway. Nature 396:370–373, 1998. Dorsky, R. I., D. W. Raible, and R. T. Moon. Direct regulation of nacre, a zebrafish MITF homolog required for pigment cell formation, by the Wnt pathway. Genes Dev. 14:158–162, 2000. Du, J., A. J. Miller, H. R. Widlund, M. A. Horstmann, S. Ramaswamy, and D. E. Fisher. MLANA/MART1 and SILV/PMEL17/GP100 are transcriptionally regulated by MITF in melanocytes and melanoma. Am. J. Pathol. 163:333–343, 2003. Eastman, Q., and R. Grosschedl. Regulation of LEF-1/TCF transcription factors by Wnt and other signals. Curr. Opin. Cell Biol. 11:233–240, 1999. Eisen, T., D. J. Easty, D. C. Bennett, and C. R. Goding. The POU domain transcription factor Brn-2: elevated expression in malignant melanoma and regulation of melanocyte-specific gene expression. Oncogene 11:2157–2164, 1995. Epstein, D. J., M. Vekemans, and P. Gros. splotch (Sp2H), a mutation affecting development of the mouse neural tube, shows a deletion within the paired homeodomain of Pax-3. Cell 67:767–774, 1991. Fisher, D. E., C. S. Carr, L. A. Parent, and P. A. Sharp. TFEB has DNA-binding and oligomerization properties of a unique
TRANSCRIPTIONAL REGULATION OF MELANOCYTE FUNCTION helix–loop–helix/leucine zipper family. Genes Dev. 5:2342–2352, 1991. Fuse, N., K. Yasumoto, H. Suzuki, K. Takahashi, and S. Shibahara. Identification of a melanocyte-type promoter of the microphthalmia-associated transcription factor gene. Biophys. Biochem. Res. Commun. 219:702–707, 1996. Fuse, N., K. Yasumoto, K. Takeda, S. Amae, M. Yoshizawa, T. Udono, K. Takahashi, M. Tamai, Y. Tomita, M. Tachibana, and S. Shibahara. Molecular cloning of cDNA encoding a novel microphthalmia-associated transcription factor isoform with a distinct amino-terminus. J. Biochem. (Tokyo) 126:1043–1051, 1999. Galibert, M. D., U. Yavuzer, T. J. Dexter, and C. R. Goding. Pax3 and regulation of the melanocyte-specific tyrosinase-related protein-1 promoter. J. Biol. Chem. 274:26894–26900, 1999. Galibert, M. D., S. Carreira, and C. R. Goding. The Usf-1 transcription factor is a novel target for the stress-responsive p38 kinase and mediates UV-induced tyrosinase expression. EMBO J. 20:5022– 5031, 2001. Ganss, R., G. Schütz, and F. Beermann. The mouse tyrosinase gene. Promoter modulation by positive and negative regulatory elements. J. Biol. Chem. 269:29808–29816, 1994a. Ganss, R., L. Montoliu, A. P. Monaghan, and G. Schütz. A cellspecific enhancer far upstream of the mouse tyrosinase gene confers high level and copy number-related expression in transgenic mice. EMBO J. 13:3083–3093, 1994b. Ganss, R., A. Schmidt, G. Schütz, and F. Beermann. Analysis of the mouse tyrosinase promoter in vitro and in vivo. Pigment Cell Res. 7: 275–278, 1994c. Giebel, L. B., K. M. Strunk, and R. A. Spritz. Organization and nucleotide sequences of the human tyrosinase gene and a truncated tyrosinase-related segment. Genomics 9:435–445, 1991. Gregor, P. D., M. Sawadogo, and R. G. Roeder. The adenovirus major late transcription factor USF is a member of the helix–loop–helix group of regulatory proteins and binds to DNA as a dimer. Genes Dev. 4:1730–1740, 1990. Glaser, T., D. S. Walton, and R. L. Maas. Genomic structure, evolutionary conservation and aniridia mutations in the human PAX6 gene. Nature Genet. 2:232–239, 1992. Hallsson, J. H., J. Favor, C. Hodgkinson, T. Glaser, M. L. Lamoreux, R. Magnúsdóttir, G. J. Gunnarsson, H. O. Sweet, N. G. Copeland, N. A. Jenkins, and E. Steingrímsson. Genomic, transcriptional and mutational analysis of the mouse microphthalmia locus. Genetics 155:291–300, 2000. Hamel, C. P., E. Tsilou, B. A. Pfeffer, J. J. Hooks, B. Detrick, and T. M. Redmond. Molecular cloning and expression of RPE65, a novel retinal pigment epithelium-specific microsomal protein that is post-transcriptionally regulated in vitro. J. Biol. Chem. 268:15751–15757, 1993. Hamel, C. P., N. A. Jenkins, D. J. Gilbert, N. G. Copeland, and T. M. Redmond. The gene for the retinal pigment epithelium-specific protein RPE65 is localized to human 1p31 and mouse 3. Genomics 20:509–512, 1994. Hemesath, T. J., E. Steingrímsson, G. McGill, M. J. Hansen, J. Vaught, C. A. Hodgkinson, H. Arnheiter, N. G. Copeland, N. A. Jenkins, and D. E. Fisher. microphthalmia, a critical factor in melanocyte development, defines a discrete transcription factor family. Genes Dev. 8:2770–2780, 1994. Hemesath, T. J., E. R. Price, C. Takemoto, T. Badalian, and D. E. Fisher. MAP kinase links the transcription factor Microphthalmia to c-Kit signalling in melanocytes. Nature 391:298–301, 1998. Herbarth, B., V. Pingault, N. Bondurand, K. Kuhlbrodt, I. HermansBorgmeyer, A. Puliti, N. Lemort, M. Goossens, and M. Wegner. Mutation of the Sry-related Sox10 gene in Dominant megacolon, a mouse model for human Hirschsprung disease. Proc. Natl. Acad. Sci. USA 95:5161–5165, 1998.
Hero, I. Optic fissure closure in the normal cinnamon mouse. An ultrastructural study. Invest. Ophthalmol. Vis. Sci. 31:197–216, 1990. Hill, R. E., J. Favor, B. L. M. Hogan, C. C. T. Ton, G. F. Saunders, I. M. Hanson, J. Prosser, T. Jordan, N. D. Hastie, and V. van Heyningen. Mouse Small eye results from mutations in a pairedlike homeobox-containing gene. Nature 354:522–525, 1991. Hodgkinson, C. A., K. J. Moore, A. Nakayama, E. Steingrimsson, N. G. Copeland, N. A. Jenkins, and H. Arnheiter. Mutations at the mouse microphthalmia locus are associated with defects in a gene encoding a novel basic-helix–loop–helix-zipper protein. Cell 74:395–404, 1993. Huber, W. E., E. R. Price, H. R. Widlund, J. Du, I. J. Davis, M. Wegner, and D. E. Fisher. A tissue-restricted cAMP transcriptional response: SOX10 modulates alpha-melanocyte-stimulating hormone-triggered expression of microphthalmia-associated transcription factor in melanocytes. J. Biol. Chem. 278:45224–45230, 2003. Hughes, M. J., J. B. Lingrel, J. M. Krakowsky, and K. P. Anderson. A helix–loop–helix transcription factor-like gene is located at the mi locus. J. Biol. Chem. 268:20687–20690, 1993. Hughes, A. E., V. E. Newton, X. Z. Liu, and A. P. Read. A gene for Waardenburg syndrome type 2 maps close to the human homologue of the microphthalmia gene at chromosome 3p12–p14.1. Nature Genet. 7:509–512, 1994. Ikeya, M., S. M. Lee, J. E. Johnson, A. P. McMahon, and S. Takada. Wnt signalling required for expansion of neural crest and CNS progenitors. Nature 389:966–970, 1997. Jackson, I. J. A cDNA encoding tyrosinase-related protein maps to the brown locus in mouse. Proc. Natl. Acad. Sci. USA 85: 4392–4396, 1988. Jackson, I. J. Molecular and developmental genetics of mouse coat color. Annu. Rev. Genet. 28:189–217, 1994. Jackson, I. J., and S. Raymond. Manifestations of microphthalmia. Nature Genet. 8:209–210, 1994. Jackson, I. J., D. Chambers, E. M. Rinchik, and D. C. Bennett. Characterization of TRP-1 mRNA levels in dominant and recessive mutations at the mouse brown (b) locus. Genetics 126:451–459, 1990. Jackson, I. J., D. M. Chambers, P. S. Budd, and R. Johnson. The tyrosinase-related protein-1 gene has a structure and promoter sequence very different from tyrosinase. Nucleic Acids Res. 19:3799–3804, 1991. Jackson, I. J., D. M. Chambers, K. Tsukamoto, N. G. Copeland, D. J. Gilbert, N. A. Jenkins, and V. J. Hearing. A second tyrosinaserelated protein, TRP-2, maps to and is mutated at the mouse slaty locus. EMBO J. 11:527–535, 1992. Jackson, I. J., P. Budd, J. M. Horn, R. Johnson, S. Raymond, and K. Steel. Genetics and molecular biology of mouse pigmentation. Pigment Cell Res. 7:73–80, 1994. Jiménez-Cervantes, C., F. Solano, T. Kobayashi, K. Urabe, V. J. Hearing, J. A. Lozano, and J. C. García-Borrón. A new enzymatic function in the melanogenic pathway. J. Biol. Chem. 269:17993– 18001, 1994. Kadesch, T. Consequences of heteromeric interactions among helixloop-helix proteins. Cell Growth Differ. 4:49–55, 1993. Khaled, M., L. Larribere, K. Bille, E. Aberdam, J. P. Ortonne, R. Ballotti, and C. Bertolotto. Glycogen synthase kinase 3beta is activated by cAMP and plays an active role in the regulation of melanogenesis. J. Biol. Chem. 277:33690–33697, 2002. Kikuchi, H., H. Miura, H. Yamamoto, T. Takeuchi, T. Dei, and M. Watanabe. Characteristic sequences in the upstream region of the human tyrosinase gene. Biochim. Biophys. Acta 1009:283–286, 1989. Kim, R. Y., and G. J. Wistow. The cDNA RPE1 and monoclonal antibody HMB-50 define gene products preferentially expressed in retinal pigment epithelium. Exp. Eye Res. 55:657–662, 1992.
255
CHAPTER 13 Klüppel, M., F. Beermann, S. Ruppert, E. Schmid, E. Hummler, and G. Schütz. The mouse tyrosinase promoter is sufficient for expression in melanocytes and in the pigmented epithelium of the retina. Proc. Natl. Acad. Sci. USA 88:3777–3781, 1991. Kobayashi, T., K. Urabe, A. Winder, C. Jiménez-Cervantes, G. Imokawa, T. Brewington, F. Solano, J. C. García-Borrón, and V. J. Hearing. Tyrosinase related protein 1 (TRP1) functions as a DHICA oxidase in melanin biosynthesis. EMBO J. 13:5818–5825, 1994. Krakowsky, J. M., R. E. Boissy, J. C. Neumann, and J. B. Lingrel. A DNA insertional mutation results in microphthalmia in transgenic mice. Transgenic Res. 2:14–20, 1993. Kroumpouzos, G., K. Urabe, T. Kobayashi, C. Sakai, and V. J. Hearing. Functional analysis of the slaty gene product (TRP2) as dopachrome tautomerase and the effect of a point mutation on its catalytic function. Biochem. Biophys. Res. Commun. 202:1060– 1068, 1994. Kwon, B. S., A. K. Haq, S. H. Pomerantz, and R. Halaban. Isolation and sequence of a cDNA clone for human tyrosinase that maps at the mouse c-albino locus. Proc. Natl. Acad. Sci. USA 84:7473– 7477, 1987a. Kwon, B. S., R. Halaban, G. S. Kim, L. Usack, S. Pomerantz, and A. K. Haq. A melanocyte-specific complementary DNA clone whose expression is inducible by melanotropin and isobutylmethyl xanthine. Mol. Biol. Med. 4:339–355, 1987b. Kwon, B. S., M. Wakulchik, A. K. Haq, R. Halaban, and D. Kestler. Sequence analysis of mouse tyrosinase cDNA and the effect of melanotropin on its gene expression. Biochem. Biophys. Res. Commun. 153:1301–1309, 1988. Kwon, B. S., C. Chintamaneni, C. A. Kozak, N. G. Copeland, D. J. Gilbert, N. Jenkins, D. Barton, U. Francke, Y. Kobayashi, and K. K. Kim. A melanocyte-specific gene, Pmel 17, maps near the silver coat color locus on mouse chromosome 10 and is in a syntenic region on human chromosome 12. Proc. Natl. Acad. Sci. USA 88:9228–9232, 1991. Kwon, B. S., R. Halaban, S. Ponnazhagan, K. Kim, C. Chintamaneni, D. Bennett, and R. T. Pickard. Mouse silver mutation is caused by a single base insertion in the putative cytoplasmic domain of Pmel 17. Nucleic Acids Res. 23:154–158, 1995. Lee, M., J. Goodall, C. Verastegui, R. Ballotti, and C. R. Goding. Direct regulation of the Microphthalmia promoter by Sox10 links Waardenburg-Shah syndrome (WS4)-associated hypopigmentation and deafness to WS2. J. Biol. Chem. 275:37978–37983, 2000. Lerner, A. B., T. Shiohara, R. E. Boissy, K. A. Jacobson, M. L. Lamoreux, and G. E. Moellmann. A mouse model for vitiligo. J. Invest. Dermatol. 87:299–304, 1986. Lowings, P., U. Yavuzer, and C. R. Goding. Positive and negative elements regulate a melanocyte-specific promoter. Mol. Cell. Biol. 12:3653–3662, 1992. Ludwig, A., S. Rehberg, and M. Wegner. Melanocyte-specific expression of dopachrome tautomerase is dependent on synergistic gene activation by the Sox10 and Mitf transcription factors. FEBS Lett. 556:236–244, 2004. McGill, G. G., M. Horstmann, H. R. Widlund, J. Du, G. Motyckova, E. K. Nishimura, Y. L. Lin, S. Ramaswamy, W. Avery, H. F. Ding, S. A. Jordan, I. J. Jackson, S. J. Korsmeyer, T. R. Golub, and D. E. Fisher. Bcl2 regulation by the melanocyte master regulator Mitf modulates lineage survival and melanoma cell viability. Cell 109:707–718, 2002. Martinez-Morales, J. R., M. Signore, D. Acampora, A. Simeone, and P. Bovolenta. Otx genes are required for tissue specification in the developing eye. Development 128:2019–2030, 2001. Martinez-Morales, J. R., V. Dolez, I. Rodrigo, R. Zaccarini, L. Leconte, P. Bovolenta, and S. Saule. OTX2 activates the molecular network underlying retina pigment epithelium differentiation. J. Biol. Chem. 278:21721–21731, 2003. Matsuo, I., S. Kuratani, C. Kimura, N. Takeda, and S. Aizawa. Mouse
256
Otx2 functions in the formation and patterning of rostral head. Genes Dev. 9:2646–2658, 1995. Miller, A. J., J. Du, S. Rowan, C. L. Hershey, H. R. Widlund, and D. E. Fisher. Transcriptional regulation of the melanoma prognostic marker melastatin (TRPM1) by MITF in melanocytes and melanoma. Cancer Res. 64:509–516, 2004. Mochii, M., K. Agata, H. Kobayashi, T. S. Yamamoto, and G. Eguchi. Expression of gene coding for a melanosomal matrix protein transcriptionally regulated in the transdifferentiation of chick embryo pigmented epithelial cells. Cell Differ. 24:67–74, 1988. Mochii, M., K. Agata, and G. Eguchi. Complete sequence and expression of a cDNA encoding a chicken 115-kDa melanosomal matrix protein. Pigment Cell Res. 4:41–47, 1991. Mochii, M., A. Iio, H. Yamamoto, T. Takeuchi, and G. Eguchi. Isolation and characterization of a chicken tyrosinase cDNA. Pigment Cell Res. 5:162–167, 1992. Morii, E., K. Takebayashi, H. Motohashi, M. Yamamoto, S, Nomura, and Y. Kitamura. Loss of DNA binding ability of the transcription factor encoded by the mutant mi locus. Biochem. Biophys. Res. Commun. 205:1299–1304, 1994. Müller, G., S. Ruppert, E. Schmid, and G. Schütz. Functional analysis of alternatively spliced tyrosinase gene transcripts. EMBO J. 7:2723–2730, 1988. Murre, C., P. S. McCaw, and D. Baltimore. A new DNA binding and dimerization motif in immunoglobulin enhancer binding, daughterless, MyoD, and myc proteins. Cell 56:777–783, 1989a. Murre, C., P. S. McCaw, H. Vaessin, M. Caudy, L. Y. Jan, Y. N. Jan, C. V. Cabrera, J. N. Buskin, S. D. Hauschka, A. B. Lassar, H. Weintraub, and D. Baltimore. Interactions between heterologous helix-loop-helix proteins generate complexes that bind specifically to a common DNA sequence. Cell 58:537–44, 1989b. Nair, S. S., V.A. Chaubal, T. Shioda, K. R. Coser, and M. Mojamdar. Over-expression of MSG1 transcriptional co-activator increases melanin in B16 melanoma cells: a possible role for MSG1 in melanogenesis. Pigment Cell Res. 14:206–209, 2001. Nakai, S., H. Kawano, T. Yudate, M. Nishi, J. Kuno, A. Nagata, K. Jishage, H. Hamada, H. Fujii, K. Kawamura, K. Shiba, and T. Noda. The POU domain transcription factor Brn-2 is required for the determination of specific neuronal lineages in the hypothalamus of the mouse. Genes Dev. 9:3109–3121, 1995. Nakayama, A., M. T. Nguyen, C. C. Chen, K. Opdecamp, C. A. Hodgkinson, and H. Arnheiter. Mutations in microphthalmia, the mouse homolog of the human deafness gene MITF, affect neuroepithelial and neural crest-derived melanocytes differently. Mech. Dev. 70:155–166, 1998. Nobukuni, Y., A. Watanabe, K. Takeda, H. Skarka, and M. Tachibana. Analyses of loss-of-function mutations of the MITF gene suggest that haploinsufficiency is a cause of Waardenburg syndrome type 2A. Am. J. Hum. Genet. 59:76–83, 1996. Oboki, K., E. Morii, T. R. Kataoka, T. Jippo, and Y. Kitamura. Isoforms of mi transcription factor preferentially expressed in cultured mast cells of mice. Biochem. Biophys. Res. Commun. 290:1250–1254, 2002. Ogihara, H., E. Morii, D. K. Kim, K. Oboki, and Y. Kitamura. Inhibitory effect of the transcription factor encoded by the mutant mi microphthalmia allele on transactivation of mouse mast cell protease 7 gene. Blood 97:645–651, 2001. Opdecamp, K., A. Nakayama, M.-T. T. Nguyen, C. A. Hodgkinson, W. J. Pavan, and H. Arnheiter. Melanocyte development in vivo and in neural crest cultures: crucial dependence on the Mitf basichelix–loop–helix-zipper transcription factor. Development 124: 2377–2386, 1997. Pavan, W. J., and S. M. Tilghman. Piebald lethal (sl) acts early to disrupt the development of neural crest-derived melanocytes. Proc. Natl. Acad. Sci. USA 91:7159–7163, 1994. Peirano, R. I., and M. Wegner. The glial transcription factor Sox10
TRANSCRIPTIONAL REGULATION OF MELANOCYTE FUNCTION binds to DNA both as monomer and dimer with different functional consequences. Nucleic Acids Res. 28:3047–3055, 2000. Pingault, V., N. Bondurand, K. Kuhlbrodt, D. E. Goerich, M. O. Prehu, A. Puliti, B. Herbarth, I. Hermans-Borgmeyer, E. Legius, G. Matthijs, J. Amiel, S. Lyonnet, I. Ceccherini, G. Romeo, J. C. Smith, A. P. Read, M. Wegner, and M. Goossens. SOX10 mutations in patients with Waardenburg–Hirschsprung disease. Nature Genet. 18:171–173, 1998. Planque, N., L. Leconte, F. M. Coquelle, P. Martin, and S. Saule. Specific Pax-6/microphthalmia transcription factor interactions involve their DNA-binding domains and inhibit transcriptional properties of both proteins. J. Biol. Chem. 276:29330–29337, 2001. Pognonec, P., and R. G. Roeder. Recombinant 43-kDa USF bind to DNA and activates transcriptional in a manner indistinguishable from that of natural 43/44-kDa USF. Mol. Cell. Biol. 11:5125– 5136, 1991. Ponnazhagan, S., L. Hou, and B. S. Kwon. Structural organization of the human tyrosinase gene and sequence analysis and characterization of its promoter region. J. Invest. Dermatol. 102:744–748, 1994. Porter, S. D., and C. J. Meyer. A distal tyrosinase upstream element stimulates gene expression in neural-crest-derived melanocytes of transgenic mice: position-independent and mosaic expression. Development 120:2103–11, 1994. Porter, S. D., L. Larue, and B. Mintz. Mosaicism of tyrosinase-locus transcription and chromatin structure in dark vs. light melanocyte clones of homozygous chinchilla-mottled mice. Dev. Genet. 12:393–402, 1991. Potterf, S. B., M. Furumura, K. J. Dunn, H. Arnheiter, and W. J. Pavan. Transcription factor hierarchy in Waardenburg syndrome: regulation of MITF expression by SOX10 and PAX3. Hum. Genet. 107:1–6, 2000. Potterf, S. B., R. Mollaaghababa, L. Hou, E. M. Southard-Smith, T. J. Hornyak, H. Arnheiter, and W. J. Pavan. Analysis of SOX10 function in neural crest-derived melanocyte development: SOX10dependent transcriptional control of dopachrome tautomerase. Dev. Biol. 237:245–257, 2001. Price, E. R., H.-F. Ding, T. Badalian, S. Bhattacharya, C. Takemoto, T. P. Yao, T. J. Hemesath, and D. E. Fisher. Lineage-specific signaling in melanocytes. J. Biol. Chem. 273:17983–17986, 1998. Rehli, M., N. D. Elzen, A. I. Cassady, M. C. Ostrowski, and D. A. Hume. Cloning and characterization of the murine genes for bHLHZIP transcription factors TFEC and TFEB reveal a common gene organization for all MiT subfamily members. Genomics 56:111– 120, 1999. Rodriguez, T. A., D. B. Sparrow, A. N. Scott, S. L. Withington, J. I. Preis, J. Michalicek, M. Clements, T. E. Tsang, T. Shioda, R. S. Beddington, and S. L. Dunwoodie. Cited1 is required in trophoblasts for placental development and for embryo growth and survival. Mol. Cell. Biol. 24:228–244, 2004. Ruppert, S., G. Müller, B. Kwon, and G. Schütz. Multiple transcripts of the mouse tyrosinase gene are generated by alternative splicing. EMBO J. 7:2715–2722, 1988. Saito, H., K. Yasumoto, K. Takeda, K. Takahashi, A. Fukuzaki, S. Orisaka, and S. Shibahara. Melanocyte-specific microphthalmiaassociated transcription factor isoform activates its own promoter through physical interaction with lymphoid-enhancing factor 1. J. Biol. Chem. 277:28787–28794, 2002. Saito, H., K. Takeda, K. Yasumoto, H. Ohtani, K. Watanabe, K. Takahashi, A. Fukuzaki, Y. Arai, H. Yamamoto, and S. Shibahara. Germ cell-specific expression of microphthalmia-associated transcription factor mRNA in mouse testis. J. Biochem. (Tokyo) 134:143–150, 2003a. Saito, H., K. Yasumoto, K. Takeda, K. Takahashi, H. Yamamoto, and S. Shibahara. Microphthalmia-associated transcription factor in the Wnt signaling pathway. Pigment Cell Res. 16:261–265, 2003b.
Sato, M., S. Ishizawa, T. Yoshida, and S. Shibahara. Interaction of upstream stimulatory factor with the human heme oxygenase gene promoter. Eur. J. Biochem. 188:231–237, 1990. Sato, S., K. Roberts, G. Gambino, A. Cook, T. Kouzarides, and C. R. Goding. CBP/p300 as a co-factor for the microphthalmia transcription factor. Oncogene 14:3083–3092, 1997. Sawadogo, M., and R. G. Roeder. Interaction of a gene-specific transcription factor with the adenovirus major late promoter upstream of the TATA box region. Cell 43:165–175, 1985. Schedl, A., L. Montoliu, G. Kelsey, and G. Schütz. A yeast artificial chromosome covering the tyrosinase gene confers copy numberdependent expression in transgenic mice. Nature 362:258–261, 1993. Shibahara, S., Y. Tomita, T. Sakakura, C. Nager, B. Chaudhuri, and R. M. Müller. Cloning and expression of cDNA encoding mouse tyrosinase. Nucleic Acids Res. 14:2413–2427, 1986. Shibahara, S., Y. Tomita, H. Tagami, R. M. Müller, and T. Cohen. Molecular basis for the heterogeneity of human tyrosinase. Tohoku J. Exp. Med. 156:403–414, 1988. Shibahara, S., S. Okinaga, Y. Tomita, A. Takeda, H. Yamamoto, M. Sato, and T. Takeuchi. A point mutation in the tyrosinase gene of BALB/c albino mouse causing the cysteine-serine substitution at position 85. Eur. J. Biochem. 189:455–461, 1990. Shibahara, S., H. Taguchi, R. M. Müller, K. Shibata, T. Cohen, Y. Tomita, and H. Tagami. Structural organization of the pigment cellspecific gene located at the brown locus in mouse. J. Biol. Chem. 266:15895–15901, 1991. Shibahara, S., Y. Tomita, M. Yoshizawa, K. Shibata, and H. Tagami. Identification of mutations in the pigment cell-specific gene located at the brown locus in mouse. Pigment Cell Res. Suppl. 2:90–95, 1992. Shibahara, S., K. Takeda, K. Yasumoto, T. Udono, K. Watanabe, H. Saito, and K. Takahashi. Microphthalmia-associated transcription factor (MITF): Multiplicity in structure, function and regulation. J. Invest. Dermatol. Symp. Proc. 6:99–104, 2001. Shibata, K., Y. Muraosa, Y. Tomita, H. Tagami, and S. Shibahara. Identification of a cis-acting element that enhances the pigment cellspecific expression of the human tyrosinase gene. J. Biol. Chem. 267:20584–20588, 1992a. Shibata, K., K. Takeda, Y. Tomita, H. Tagami, and S. Shibahara. Downstream region of the human tyrosinase-related protein gene enhances its promoter activity. Biochem. Biophys. Res. Commun. 184:568–575, 1992b. Shioda, T., M. H. Fenner, and K. J. Isselbacher. msg1, a novel melanocyte-specific gene, encodes a nuclear protein and is associated with pigmentation. Proc. Natl. Acad. Sci. USA 93:12298– 12303, 1996. Shioda, T., R. J. Lechleider, S. L. Dunwoodie, H. Li, T. Yahata, M. P. de Caestecker, M. H. Fenner, A. B. Roberts, and K. J. Isselbacher. Transcriptional activating activity of Smad4: roles of SMAD heterooligomerization and enhancement by an associating transactivator. Proc. Natl. Acad. Sci. USA 95:9785–9790, 1998. Silvers, W. K. The Coat Colors of Mice: A Model for Mammalian Gene Action and Interaction. New York: Springer-Verlag, 1979. Simeone, A., D. Acampora, M. Gulisano, A. Stornaiuolo, and E. Boncinelli. Nested expression domains of four homeobox genes in developing rostral brain. Nature 358:687–690, 1992. Simeone, A., D. Acampora, A. Mallamaci, A. Stornaiuolo, M. R. D’Apice, V. Nigro, and E. A. Boncinelli. Vertebrate gene related to orthodenticle contains a homeodomain of the bicoid class and demarcates anterior neuroectoderm in the gastrulating mouse embryo. EMBO J. 12:2735–2747, 1993. Smith, S. B., T. Duncan, G. Kutty, R. K. Kutty, and B. Wiggert. Increase in retinyl palmitate concentration in eyes and livers and the concentration of interphotoreceptor retinoid-binding protein in eyes of vitiligo mutant mice. Biochem. J. 300:63–68, 1994.
257
CHAPTER 13 Southard-Smith, E. M., L. Kos, and W. J. Pavan. Sox10 mutation disrupts neural crest development in Dom Hirschsprung mouse model. Nature Genet. 18:60–64, 1998. Steel, K. P., D. R. Davidson, and I. J. Jackson. TRP-2/DT, a new early melanoblast marker, shows that steel growth factor (c-kit ligand) is a survival factor. Development 115:1111–1119, 1992. Steingrímsson, E., K. J. Moore, M. L. Lamoreux, A. R. FerréD’Amaré, S. K. Burley, D. C. S. Zimring, L. C. Skow, C. A. Hodgkinson, H. Arnheiter, N. G. Copeland, and N. A. Jenkins. Molecular basis of mouse microphthalmia (mi) mutations helps explain their developmental and phenotypic consequences. Nature Genet. 8:256–263, 1994. Steingrímsson, E., A. Nii, D. E. Fisher, A. R. Ferré-D’Amaré, R. J. McCormick, L. B. Russell, S. K. Burley, J. M. Ward, N. A. Jenkins, and N. G. Copeland. The semidominant Mib mutation identifies a role for the HLH domain in DNA binding in addition to its role in protein dimerization. EMBO J. 15:6280–6289, 1996. Steingrímsson, E., L. Tessarollo, B. Pathak, L. Hou, H. Arnheiter, N. G. Copeland, and N. A. Jenkins. Mitf and Tfe3, two members of the Mitf-Tfe family of bHLH-Zip transcription factors, have important but functionally redundant roles in osteoclast development. Proc. Natl. Acad. Sci. USA 99:4477–4482, 2002. Sturm, R. A., B. J. O’Sullivan, N. F. Box, A. G. Smith, S. E. Smit, E. R. J. Puttick, P. G. Parsons, and I. S. Dunn. Chromosomal structure of the human TYRP1 and TYRP2 loci and comparison of the tyrosinase-related protein gene family. Genomics 29:24–34, 1995. Suzuki, H., K. Takahashi, K. Yasumoto, and S. Shibahara. Activation of the tyrosinase gene promoter by neurofibromin. Biophys. Biochem. Res. Commun. 205:1984–1991, 1994. Suzuki, H., K. Takahashi, K. Yasumoto, S. Amae, M. Yoshizawa, N. Fuse, and S. Shibahara. Role of neurofibromin in modulation of the expression of the tyrosinase-related protein 2 gene. J. Biochem. (Tokyo) 124:992–998, 1998. Tachibana, M., Y. Hara, D. Vyas, C. Hodgkinson, J. Fex, K. Grundfast, and H. Arnheiter. Cochlear disorder associated with melanocyte anomaly in mice with a transgenic insertional mutation. Mol. Cell. Neurosci. 3:433–445, 1992. Tachibana, M., L. A. Perez-Jurado, A. Nakayama, C. A. Hodgkinson, X. Li, M. Schneider, T. Miki, J. Fex, U. Francke, and H. Arnheiter. Cloning of MITF, the human homolog of the mouse microphthalmia gene and assignment to chromosome 3p14.1–p12.3. Hum. Mol. Genet. 3:553–557, 1994. Tachibana, M., K. Takeda, Y. Nobukuni, K. Urabe, J. E. Long, K. A. Meyers, S. A. Aaronson, and T. Miki. Ectopic expression of MITF, a gene for Waardenburg syndrome type 2, converts fibroblasts to cells with melanocyte characteristics. Nature Genet. 14:50–54, 1996. Takada, S., K. L. Stark, M. J. Shea, G. Vassileva, J. A. McMahon, and A. P. McMahon. Wnt-3a regulates somite and tailbud formation in the mouse embryo. Genes Dev. 8:174–189, 1994. Takase, M., I. Miura, A. Nakata, T. Takeuchi, and M. Nishioka. Cloning and sequencing of the cDNA encoding tyrosinase of the Japanese pond frog, Rana nigromaculata. Gene 121:359–363, 1992. Takebayashi, K., K. Chida, I. Tsukamoto, E. Morii, H. Munakata, H. Arnheiter, T. Kuroki, Y. Kitamura, and S. Nomura. The recessive phenotype displayed by a dominant negative microphthalmiaassociated transcription factor mutant is a result of impaired nuclear localization potential. Mol. Cell. Biol. 16:1203–1211, 1996. Takeda, A., Y. Tomita, S. Okinaga, H. Tagami, and S. Shibahara. Functional analysis of the cDNA encoding human tyrosinase precursor. Biochem. Biophys. Res. Commun. 162:984–990, 1989. Takeda, A., Y. Tomita, J. Matsunaga, H. Tagami, and S. Shibahara. Molecular basis of tyrosinase-negative oculocutaneous albinism. J. Biol. Chem. 265:17792–17797, 1990. Takeda, A., J. Matsunaga, Y. Tomita, H. Tagami, and S. Shibahara.
258
Nucleotide sequence of the putative human tyrosinase pseudogene. Tohoku J. Exp. Med. 163:295–297, 1991. Takeda, K., K. Yasumoto, R. Takada, S. Takada, K. Watanabe, T. Udono, H. Saito, K. Takahashi, and S. Shibahara. Induction of melanocyte-specific microphthalmia-associated transcription factor by Wnt-3a. J. Biol. Chem. 275:14013–14016, 2000a. Takeda, K., C. Takemoto, I. Kobayashi, A. Watanabe, Y. Nobukuni, D. E. Fisher, and M. Tachibana. Ser298 of MITF, a mutation site in Waardenburg syndrome type 2, is a phosphorylation site with functional significance. Hum. Mol. Genet. 9:125–132, 2000b. Takeda, K., K. Yasumoto, N. Kawaguchi, T. Udono, K. Watanabe, H. Saito, K. Takahashi, M. Noda, and S. Shibahara. Mitf-D, a newly identified isoform, expressed in the retinal pigment epithelium and monocyte-lineage cells affected by Mitf mutations. Biochim. Biophys. Acta 1574:15–23, 2002. Takeda, K., S. Yokoyama, K. Yasumoto, Saito, H., T. Udono, K. Takahashi, and S. Shibahara. OTX2 regulates expression of DOPAchrome tautomerase in human retinal pigment epithelium. Biochem. Biophys. Res. Commun. 300:908–914, 2003. Takemoto, C. M., Y. J. Yoon, and D. E. Fisher. The identification and functional characterization of a novel mast cell isoform of the microphthalmia-associated transcription factor. J. Biol. Chem. 277:30244–30252, 2002. Takimoto, H., S. Suzuki, S. Masui, K. Shibata, Y. Tomita, S. Shibahara, and H. Nakano. MAT-1, a monoclonal antibody that specifically recognizes human tyrosinase. J. Invest. Dermatol. 105:764–768, 1995. Tanaka, M., S. Tanaka, H. Miura, H. Yamamoto, H. Kikuchi, and T. Takeuchi. Conserved regulatory mechanisms of tyrosinase genes in mice and humans. Pigment Cell Res. 5:304–311, 1992. Tassabehji, M., A. P. Read, V. E. Newton, R. Harris, R. Balling, P. Gruss, and T. Strachan. Waardenburg’s syndrome patients have mutations in the human homologue of the Pax-3 paired box gene. Nature 355:635–636, 1992. Tassabehji, M., A. P. Read, V. E. Newton, M. Patton, P. Gruss, R. Harris, and T. Strachan. Mutations in the PAX3 gene causing Waardenburg syndrome type 1 and type 2. Nature Genet. 3:26–30, 1993. Tassabehji, M., V. E. Newton, and A. P. Read. Waardenburg syndrome type 2 caused by mutations in the human microphthalmia (MITF) gene. Nature Genet. 8:251–255, 1994. Tassabehji, M., V. E. Newton, X.-Z. Liu, A. Brady, D. Donnai, M. Krajewska-Walasek, V. Murday, A. Norman, E. Obersztyn, W. Reardon, J. C. Rice, R. Trembath, P. Wieacker, M. Whiteford, R. Winter, and A. P. Read. The mutational spectrum in Waardenburg syndrome. Hum. Mol. Genet. 4:2131–2137, 1995. Terao, M., L. Tabe, E. Garattini, D. Sartori, M. Studer, and B. Mintz. Isolation and characterization of variant cDNAs encoding mouse tyrosinase. Biochem. Biophys. Res. Commun. 159:848–853, 1989. Thomson, J. A., P. G. Parsons, and R. A. Sturm. In vivo and in vitro expression of octamer binding proteins in human melanoma metastases, brain tissue, and fibroblasts. Pigment Cell Res. 6:13–22, 1993. Thomson, J. A., K. Murphy, E. Baker, G. R. Sutherland, P. G. Parsons, R. A. Sturm, and F. Thomson. The brn-2 gene regulates the melanocytic phenotype and tumorigenic potential of human melanoma cells. Oncogene 11:691–700, 1995. Tomita, Y., P. M. Montague, and V. J. Hearing. Anti-T4-tyrosinase monoclonal antibodies — specific markers for pigmented melanocytes. J. Invest. Dermatol. 85:426–430, 1985. Tomita, Y., A. Takeda, S. Okinaga, H. Tagami, and S. Shibahara. Human oculocutaneous albinism caused by single base insertion in the tyrosinase gene. Biochem. Biophys. Res. Commun. 164:990– 996, 1989. Tomita, Y., S. Shibahara, A. Takeda, S. Okinaga, J. Matsunaga, and H. Tagami. The monoclonal antobodies TMH-1 and TMH-2
TRANSCRIPTIONAL REGULATION OF MELANOCYTE FUNCTION specifically bind to a protein encoded at the murine b-locus. J. Invest. Dermatol. 96:500–504, 1991. Treacy, M. N., and M. G. Rosenfeld. Expression of a family of POUdomain protein regulatory genes during development of the central nervous system. Annu. Rev. Neurosci. 15:139–165, 1992. Tripathi, R. K., V. J. Hearing, K. Urabe, P. Aroca, and R. A. Spritz. Mutational mapping of the catalytic activities of human tyrosinase. J. Biol. Chem. 267:23707–23712, 1992. Tsukamoto, K., I. J. Jackson, K. Urabe, P. M. Montague, and V. J. Hearing. A second tyrosinase-related protein, TRP-2, is a melanogenic enzyme termed DOPAchrome tautomerase. EMBO J. 11:519–526, 1992. Udono, T., K. Yasumoto, K. Takeda, S. Amae, K. Watanabe, H. Saito, M. Tachibana, K. Takahashi, M. Tamai, and S. Shibahara. Structural organization of the human Microphthalmia-associated transcription factor gene containing multiple promoters. Biochim. Biophys. Acta 1491:205–219, 2000. Udono, T., K. Takahashi, K. Yasumoto, K. Takeda, M. Yoshizawa, T. Abe, M. Tamai, and S. Shibahara. Expression of tyrosinase-related protein 2/DOPAchrome tautomerase in the retinoblastoma. Exp. Eye Res. 72:225–234, 2001. Urabe, K., P. Aroca, and V. J. Hearing. From gene to protein: determination of melanin synthesis. Pigment Cell Res. 6:186–192, 1993. Verastegui, C., K. Bille, J. P. Ortonne, and R. Ballotti. Regulation of the microphthalmia-associated transcription factor gene by the Waardenburg syndrome type 4 gene, SOX10. J. Biol. Chem. 275:30757–30760, 2000. Vijayasaradhi, S., B. Bouchard, and A. N. Houghton. The melanoma antigen gp75 is the human homologue of the mouse b (brown) locus gene product. J. Exp. Med. 171:1375–1380, 1990. Viskochil, D., A. M. Buchberg, G. Xu, R. M. Cawthon, J. Stevens, R. K. Wolff, M. Culver, J. C. Carey, N. G. Copeland, N. A. Jenkins, R. White, and P. O’Connell. Deletions and a translocation interrupt a cloned gene at the neurofibromatosis type 1 locus. Cell 62:187–192, 1990. Wallace, M. R., D. A. Marchuk, L. B. Andersen, R. Letcher, H. M. Odeh, A. M. Saulino, J. W. Fountain, A. Brereton, J. Nicholson, A. L. Mitchell, B. H. Brownstein, and F. S. Collins. Type 1 neurofibromatosis gene: Identification of a large transcript disrupted in three NF1 patients. Science 249:181–186, 1990. Walther, C., and P. Gruss. Pax-6, a murine paired box gene, is expressed in the developing CNS. Development 113:1435–1449, 1991. Watanabe, A., K. Takeda, B. Ploplis, and M. Tachibana. Epistatic relationship between Waardenburg syndrome gene MITF and PAX3. Nature Genet. 18:283–286, 1998. Watanabe, K., K. Takeda, Y. Katori, K. Ikeda, T. Oshima, K. Yasumoto, H. Saito, T. Takasaka, and S. Shibahara. Expression of the Sox10 gene during mouse inner ear development. Mol. Brain Res. 84:141–145, 2000. Watanabe, K., K. Takeda, K. Yasumoto, T. Udono, H. Saito, K. Ikeda, T. Takasaka, K. Takahashi, T. Kobayashi, M. Tachibana, and S. Shibahara. Identification of a distal enhancer for the melanocytespecific promoter of the MITF gene. Pigment Cell Res. 15:201–211, 2002. Wu, M., T. J. Hemesath, C. M. Takemoto, M. A. Horstmann, A. G. Wells, E. R. Price, D. Z. Fisher, and D. E. Fisher. c-Kit triggers dual phosphorylations, which couple activation and degradation of the essential melanocyte factor Mi. Genes Dev. 14:301–312, 2000. Xu, G., P. O’Connell, D. Viskochil, R. Cawthon, M. Robertson, M. Culver, D. Dunn, J. Stevens, R. Gesteland, R. White, and R. Weiss. The neurofibromatosis type 1 gene encodes a protein related to GAP. Cell 62:599–608, 1990. Xu, W., L. Gong, M. M. Haddad, O. Bischof, J. Campisi, E. T. Yeh, and E. E. Medrano. Regulation of microphthalmia-associated transcription factor MITF protein levels by association with the
ubiquitin-conjugating enzyme hUBC9. Exp. Cell Res. 255:135– 143, 2000. Yahata, T., M. P. de Caestecker, R. J. Lechleider, S. Andriole, A. B. Roberts, K. J. Isselbacher, and T. Shioda. The MSG1 non-DNAbinding transactivator binds to the p300/CBP coactivators, enhancing their functional link to the Smad transcription factors. J. Biol. Chem. 275:8825–8834, 2000. Yahata, T., W. Shao, H. Endoh, J. Hur, K. R. Coser, H. Sun, Y. Ueda, S. Kato, K. J. Isselbacher, M. Brown, and T. Shioda. Selective coactivation of estrogen-dependent transcription by CITED1 CBP/p300binding protein. Genes Dev. 15:2598–2612, 2001. Yajima, I., S. Sato, T., Kimura, K. Yasumoto, S. Shibahara, C. R. Goding, and H. Yamamoto. An L1 element intronic insertion in the black-eyed white (Mitfmi-bw) gene: the loss of a single Mitf isoform responsible for the pigmentary defect and inner ear deafness. Hum. Mol. Genet. 8:1431–1441, 1999. Yamamoto, H., S. Takeuchi, T. Kudo, K. Makino, A. Nakata, T. Shinoda, and T. Takeuchi. Cloning and sequencing of mouse tyrosinase cDNA. Jpn. J. Genet. 62:271–274, 1987. Yamamoto, H., S. Takeuchi, T. Kudo, C. Sato, and T. Takeuchi. Melanin production in cultured albino melanocytes transfected with mouse tyrosinase cDNA. Jpn. J. Genet. 64:121–135, 1989. Yamamoto, H., T. Kudo, N. Masuko, H. Miura, S. Sato, M. Tanaka, S. Tanaka, S. Takeuchi, S. Shibahara, and T. Takeuchi. Phylogeny of regulatory regions of vertebrate tyrosinase genes. Pigment Cell Res. 5:284–294, 1992. Yamamura, K., S. Kamada, S. Ito, K. Nakagawa, M. Ichihashi, and Y. Tsujimoto. Accelerated disappearance of melanocytes in Bcl2deficient mice. Cancer Res. 56:3546–3550, 1996. Yasumoto, K., and S. Shibahara. Molecular cloning of a cDNA encoding a human TFEC isoform, a newly identified transcriptional regulator. Biochim. Biophys. Acta 1353:23–31, 1997. Yasumoto, K., K. Yokoyama, K. Shibata, Y. Tomita, and S. Shibahara. Microphthalmia-associated transcription factor as a regulator for melanocyte-specific transcription of the human tyrosinase gene. Mol. Cell. Biol. 14:8058–8070, 1994. Yasumoto, K., H. Mahalingam, M. Yoshizawa, H. Suzuki, K. Yokoyama, and S. Shibahara. Transcriptional activation of the melanocyte-specific genes by the human homolog of the mouse microphthalmia protein. J. Biochem. (Tokyo) 118:874–881, 1995. Yasumoto, K., K. Yokoyama, K. Takahashi, Y. Tomita, and S. Shibahara. Functional analysis of microphthalmia-associated transcription factor in pigment cell-specific transcription of the human tyrosinase family genes. J. Biol. Chem. 272:503–509, 1997. Yasumoto, K., S. Amae, T. Udono, N. Fuse, K. Takeda, and S. Shibahara. A big gene linked to small eyes encodes multiple Mitf isoforms: Many promoters make light work. Pigment Cell Res. 11:329–336, 1998. Yasumoto, K., K. Takeda, H. Saito, K. Watanabe, K. Takahashi, and S. Shibahara. Microphthalmia-associated transcription factor interacts with LEF-1, a mediator of Wnt signaling. EMBO J. 21:2703– 2714, 2002. Yavuzer, U., and C. R. Goding. Melanocyte-specific gene expression: Role of repression and identification of a melanocyte-specific factor, MSF. Mol. Cell. Biol. 14:3494–3503, 1994. Yavuzer, U., E. Keenan, P. Lowings, J. Vachtenheim, G. Currie, and C. R. Goding. The Microphthalmia gene product interacts with the retinoblastoma protein in vitro and is a target for deregulation of melanocyte-specific transcription. Oncogene 10:123–134, 1995. Yokoyama, T., D. W. Silversides, K. G. Waymire, B. S. Kwon, T. Takeuchi, and P. A. Overbeek. Conserved cysteine to serine mutation in tyrosinase is responsible for the classical albino mutation in laboratory mice. Nucleic Acids Res. 18:7293–7298, 1990. Yokoyama, K., H. Suzuki, K. Yasumoto, Y. Tomita, and S. Shibahara. Molecular cloning and functional analysis of a cDNA coding for
259
CHAPTER 13 human DOPAchrome tautomerase/tyrosinase-related protein-2. Biochem. Biophys. Acta 1217:317–321, 1994a. Yokoyama, K., K. Yasumoto, H. Suzuki, and S. Shibahara. Cloning of the human DOPAchrome tautomerase/tyrosinase-related protein 2 gene and identification of two regulatory regions required for its pigment cell-specific expression. J. Biol. Chem. 269:27080–27087, 1994b.
260
Zdarsky, E., J. Favor, and I. J. Jackson. The molecular basis of brown, an old mouse mutation, and of an induced revertant to wild type. Genetics 126:443–449, 1990. Zhao, G.-Q., Q. Zhao, X. Zhou, M.-G. Mattei, and B. de Crombrugghe. TFEC, a basic helix–loop–helix protein, forms heterodimers with TFE3 and inhibits TFE3-dependent transcription activation. Mol. Cell. Biol. 13:4505–4512, 1993.
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
14
Enzymology of Melanin Formation Francisco Solano and José C. García-Borrón
Summary 1 Pigmentation is a widely occurring phenomenon. In microorganisms, plants, and lower animals, carotenoids, anthocyanins, tetrapyrroles, and betalains are pigments designed to afford several features, but other pigments are needed for chemo- and photoprotection. These pigments are generically called melanins, and most of them are formed from phenols. In higher animals and mankind, these pigments are found in the integument regions, retina, and inner ear. 2 The key enzyme of the melanogenic pathway is tyrosinase. This enzyme catalyzes the first rate-limiting steps of melanogenesis, the hydroxylation of l-tyrosine, and the subsequent oxidation of the intermediate l-dopa to yield l-dopaquinone. 3 Tyrosinase contains a bicupric active site. The two copper atoms bind to two regions called CuA and CuB, which contain three highly conserved histidines responsible for metal binding. Copper atoms can undergo redox reactions, and tyrosinase catalysis can be explained by the redox cycling of copper between the Cu(II) and Cu(I) states, with the participation of molecular oxygen. 4 The two types of reactions catalyzed by tyrosinases, namely hydroxylation of monophenols and oxidation of diphenols, display different kinetic properties and likely involve a differential interaction of the substrates with the active site. l-Dopa bound directly to tyrosinase is not equivalent to l-dopa as an intermediate of the tyrosine hydroxylation. 5 Tyrosinases from different sources may display different substrate specificities. In particular, mouse tyrosinase does not recognize 5,6-dihydroxyindole-2-carboxylic acid (DHICA) as a substrate, but the human enzyme shows DHICA oxidase activity. 6 In higher animals, there are two other melanosomal proteins displaying extensive sequence similarity to tyrosinase. They are called tyrosinase-related proteins (Tyrps) 1 and 2. 7 Although a number of enzymatic functions have been proposed for Tyrp1, the mouse protein is most likely a low specific activity pseudotyrosinase recognizing DHICA as substrate. However, as human tyrosinase has a similar DHICA oxidase activity, the actual role of TYRP1 remains uncertain. 8 Tyrp2/Dct is a Zn-containing protein. It catalyzes the nondecarboxylative tautomerization of dopachrome to DHICA. As the product of the spontaneous evolution of dopachrome is 5,6-dihydroxyindole (DHI), Tyrp2/Dct is essential for the incorporation of carboxylated indolic units to the melanin. 9 Within melanosomes, tyrosinase and Tyrps may interact in
a melanogenic complex. The functional consequences of their interactions within this metabolon are not well understood, although Tyrp1 and probably also Tyrp2/Dct seem to stabilize tyrosinase, thus increasing its in vivo half-life. 10 Other proteins, such as silver/Pmel-17, P, and the MATP/AIM-1/underwhite protein, are involved in melanogenesis, although their role is probably not enzymatic and may be either structural or related to the regulation of melanosomal pH and transport. 11 Radiometric methods are best suited for the determination of the rate-limiting tyrosine hydroxylase activity (using l-[3,53 H]-tyrosine as substrate) and of the overall melanogenic potential (using l-[U14C]-tyrosine as substrate). 12 Fluorometric assays for tyrosine hydroxylase activity, designed as sensitive alternatives to the radiometric methods, have not been used as frequently. 13 Spectrophotometric assays, especially those based on the trapping of o-quinones by 3-methyl-2-benzothiazolinone hydrazone (MBTH), are sensitive and simple, and therefore the methods of choice for the determination of the oxidation rate of diphenols and dihydroxyindoles. However, at least in mouse melanocyte extracts, the dopa oxidase activity is associated with tyrosinase and Tyrp1, and the relative contribution of each enzyme cannot be directly determined by spectrophotometric assays. This can be only performed by nonreducing gel electrophoresis, followed by activity stains with radioactive substrates or l-dopa plus MBTH. 14 DHICA oxidase, dopachrome tautomerase, and related activities are best determined by high-performance liquid chromatography (HPLC) assays, allowing for a simultaneous determination of substrate consumption and product formation. 15 In spite of the limitations of the currently available methods for the determination of melanogenic enzymatic activities, it is clear that the type, amount, size, and functional properties of melanins are determined not only by tyrosinase, but also by the Tyrps and probably by other above-mentioned proteins with enzymatic activity that is still doubtful. Moreover, the existence of other uncharacterized melanogenic enzymes and/or effectors cannot be ruled out, particularly in the pheomelanogenic pathway.
Introduction to Pigments, Melanin, and Phenol Oxidases: a Historical Background Pigmentation is a widely occurring phenomenon, which has aroused the attention of mankind since the beginning of 261
CHAPTER 14
history because of the importance of appearance for all living organisms. There are a great variety of natural pigments with different composition and structure. In microorganisms, plants, and lower animals, carotenoids, anthocyanins, tetrapyrroles, and betalains are responsible for most of the colors that we observe (Delgado-Vargas et al., 2000). Most of them are pigments designed to afford environmental advantages, such as camouflage or thermal regulation. Color ornaments are undoubtedly important for sexual processes (from flowers/insects to tropical birds or even mammals). Other pigments are especially designed for chemo- and photoprotection. These pigments are generically called melanins. Their range of colors is not as wide, but melanins are the most abundant and ubiquitous natural pigments throughout the phylogenetic scale. In lower organisms, several types of precursors lead to different types of chemically distinct melanins, but most of them are phenols. Only fungi can form a melanin from acetyl groups through the pentaketide pathway to yield dihydroxynaphthalene-melanin (Tsai et al., 1999). In vertebrates, melanins are formed from the amino acid l-tyrosine by the Raper–Mason pathway. These pigments are found in the integument regions, retina, and inner ear. Although the amount of pigment is genetically determined, in the epidermis, this parameter is also affected by environmental factors, such as exposure to sunlight, as well as by hormonal levels. Tyrosinase, the key enzyme in melanogenesis, is a remarkable protein able to catalyze two types of reactions, hydroxylation of monophenols and oxidations of diphenols. This “ferment” was one of the first enzymes to be reported at the end of the nineteenth century (Bourquelot and Bertrand, 1895). Bourquelot studied up to 281 species of phanerogams for a classification based on pigmentation. He found a large number of pigments, most of them glycosides (some of them still important in pharmacology). Looking for the agent responsible for the massive formation of dark pigments, and using mushrooms as a convenient model, he described one of the first oxidizing ferments in the early age of enzymology, and his report was the first one on the enzyme generically called phenol oxidase and, more specifically, tyrosinase. During the first quarter of the twentieth century, tyrosinase activity was demonstrated in the animal kingdom, and it was also found in cutaneous melanoma from several mammals (horse, hamster, mouse, and others; for a comprehensive review of the state of knowledge at that stage, see Lerner and Fitzpatrick, 1950). The existence of dopa oxidase activity in human skin was first reported by Bloch (1927) by histochemical staining of pigmented human skin specimens immersed in dopa solutions. Because of a very special feature of the tyrosine hydroxylase activity of tyrosinase (a lag period of highly variable length before reaching maximal catalytic rate), this activity was initially very difficult to detect. For a long time, this led to some controversy concerning the double catalytic activity of tyrosinase (tyrosine hydroxylase and dopa oxidase) and the putative existence of two different enzymes to account for those activities. The hypothesis of the occurrence of two inde-
262
pendent enzymes subsisted for many years (Patel et al., 1971; Shapiro et al., 1979). However, Mason (1948), Lerner et al. (1949), and others showed that mammalian tyrosinase was a bifunctional enzyme and proved that tyrosine hydroxylase and dopa oxidase activities reside on the same protein. Even in those years, the same conclusion could be drawn from genetic data. Tyrosinase is encoded by the albino c-locus (chromosome 7 in mouse and 11 in human), and it was perfectly demonstrated that albino mice were negative not only for tyrosine hydroxylation but also for dopa oxidation (Russell and Russell, 1948). Nowadays, the single-enzyme theory for tyrosine hydroxylation and dopa oxidation is totally accepted. Owing to the highly reactive nature of l-dopaquinone, the product of tyrosinase action on l-tyrosine, melanins are formed in vitro from l-tyrosine in the presence of tyrosinase alone. This led to the simplistic view that the melanogenic pathway involved only one enzymatic protein, a model that applies to melanogenesis in bacteria and lower organisms. However, the situation is far more complex in higher organisms and particularly in mammals, where several other proteins residing in a specialized melanin-synthesizing organelle, the melanosome, are involved. Therefore, the melanogenic pathway can be considered at the same time simple and complex. It is simpler in lower organisms and more sophisticated in higher organisms where the regulation of melanosynthesis (in terms of amount, type, and location) is an important point. Thus, the study of melanogenesis is a journey from the simplicity of a pathway involving just tyrosinase as the only melanogenic enzyme (in prokaryotes) to the complexity of a multienzymatic complex confined in a specific subcellular compartment where melanogenesis is subject to tight regulation of its rate and of the type of melanin formed (in mammalian melanocytes). The present chapter will describe different aspects of the enzymes involved in the formation of melanin through the modified Raper–Mason pathway, including those “distal” factors whose action takes place after the reactions catalyzed by tyrosinase. We also refer to Chapters 3, 7, 10, 11, 12, and 15 of the present edition for details on the ultrastructure of the melanocyte, the melanosome, the tyrosinase family, and the chemical structure of the melanin pigment. All this information will offer an integrated view of mammalian melanogenesis.
A Global View of the Mammalian Melanogenesis Pathway The key enzyme of the melanogenic pathway is tyrosinase. This enzyme catalyzes the first two rate-limiting steps of melanogenesis, the hydroxylation of l-tyrosine and the subsequent oxidation of the intermediate o-diphenol (l-dopa) to yield l-dopaquinone (Fig. 14.1). The mechanism of these reactions has been controversial and will be discussed below. l-
ENZYMOLOGY OF MELANIN FORMATION
dopaquinone is the first branch point of melanogenesis leading to the two main types of melanin in animals: light (from red to yellow) pheomelanin or dark (from brown to black) eumelanin (Hearing and Tsukamoto, 1991). In the presence of compounds with free thiol groups, such as reduced glutathione or the amino acid l-cysteine, there is a rapid conjugation between l-dopaquinone and the thiol group to yield a family of sulfur-containing compounds related to pheomelanin (Jara et al., 1988a; Rorsman et al., 1973; Prota, 1988). Whenever free thiol compounds are present in sufficient concentration, this pheomelanogenic route is favored over eumelanogenesis. The pheomelanogenic intermediates and the factors that control thiol availability within melanosomes are still poorly known. The preferred position for the addition of the thiol group to l-dopaquinone is 5 (Prota, 1992), but other free positions in the L-dopaquinone ring such as 2 and 6 are also reactive, so that a complex mixture of isomers is in fact obtained. These reactions occur spontaneously. Huge efforts have been made to isolate from melanocytes an enzyme able to catalyze these reactions in a more regulated and ordered way. In this sense, g-glutamyl transpeptidase and some glutathione transferases were proposed (Mojamdar et al., 1983), but so far their role in pheomelanogenesis is, at best, unclear. Recently, it has been proposed that g-glutamyl transpeptidase does not contribute
significantly to pheomelanosynthesis, but it may stimulate the production of hydrogen peroxide and regulate the expression or activity of some transcription factors, ultimately leading to decreased tyrosinase activity (Chaubal et al., 2002). To give a simplified model of pheomelanogenesis (Fig. 14.1, right), it is usually presumed that l-cysteine reacts with l-dopaquinone to yield mainly 5-cysteinyldopa. This compound may undergo some structural rearrangements and dehydration to form alanyl-hydroxy-benzothiazine, the proposed subunit for pheomelanin. It is nevertheless possible that pheomelanin biosynthesis actually proceeds through a more complex pathway. For instance, it is known that glutathione is much more abundant inside cells than l-cysteine, so that 5-glutathionyldopa is likely the first thiol-conjugated species formed. The release of 5-cysteinyldopa would then be catalyzed by a dipeptidase (Agrup et al., 1975; route not shown in Fig. 14.1 to avoid further complexity). This view of the melanogenic pathway including a glutathione-dependent branch may still be an oversimplification of the in vivo situation, because the involvement of still uncharacterized enzymatic activities is likely. Returning to the branch point after l-dopaquinone formation, this compound can undergo a cyclation reaction by Michael addition of the amino group on position 6 of the ring to form l-cyclodopa (also named leukodopachrome), and
Fig. 14.1. The mammalian melanogenic pathway. This updated version of the pathway was originally proposed by Raper (1928) and Mason (1948) taking into account only tyrosinase, but several enzymatic activities in addition to tyrosinase are involved. Concerning the evolution of l-dopachrome in the distal phase, note that, at neutral pH, it undergoes a decarboxylative reaction to dihydroxyindole. This is a spontaneous reaction, but it can be catalyzed by “dopachrome isomerase” (an enzyme related to dopachrome tautomerase from insects and cuttlefish). In mammalian melanocytes, l-dopachrome can undergo a nondecarboxylative rearrangement catalyzed by authentic Tyrp2/Dct. The pathways for pheomelanin synthesis are less well understood than those for eumelanin synthesis, mostly through the contribution of Prota (1988, 1992).
263
CHAPTER 14
finally dark eumelanins. This reaction is favored as the pH is increased, because the amino group should be nonprotonated for the nucleophilic attack on position 6. Therefore, at the acidic intramelanosomal pH, cyclation may be rather slow, and other side-reactions such as formation of topaquinone are also possible (Rodríguez-López et al., 1992; not shown in Fig. 14.1). It should be clearly stated that l-dopaquinone cyclation is slower than its conjugation with thiols and other reactive groups. Therefore, l-cyclodopa is only formed in the absence of other chemical alternatives for l-dopaquinone, but this is probably the situation inside the eumelanosome. Accordingly, eumelanin is the main pigment formed in many organisms. l-Cyclodopa is a rather unstable reducing species that reacts rapidly with its precursor l-dopaquinone to yield ldopachrome plus l-dopa (Garcia-Cánovas et al., 1982; Lerner and Fitzpatrick, 1950). Note that half the l-dopa oxidized by tyrosinase to l-dopaquinone is reduced back to l-dopa (Fig. 14.1). This is very important as l-dopa is not just a tyrosinase substrate but also a fine regulator of the tyrosine hydroxylase activity of the enzyme (see below). The chemical generation of l-dopa in this redox reaction can account for the in vivo activation of l-tyrosine hydroxylation. Both ldopaquinone cyclation to l-cyclodopa and the redox reaction to l-dopachrome seem to be very fast reactions proceeding without enzymatic control. l-Dopachrome can be considered the second branch point in melanogenesis leading to different eumelanins. This branch is regulated by the tyrosinase-related proteins (Tyrps, discussed below), and it controls the final content of carboxyl groups in the melanin polymer, which is very important for the size, chelating, and absorption properties of the eumelanin formed. Within a pH range from 3 to 9, including the physiological pH values in melanosomes, l-dopachrome undergoes a spontaneous decarboxylation to form 5,6-dihydroxyindole (DHI). However, Tyrp2/dopachrome tautomerase (Dct) catalyzes the nondecarboxylative rearrangement of ldopachrome to 5,6-dihydroxyindole-2-carboxylic acid (DHICA). It is worth noting that traces of metal ions can yield mixtures of DHI and DHICA but, inside the eumelanosome, the level of Dct activity controls the DHICA/DHI ratio (Aroca et al., 1992). This ratio increases at higher Dct and lower tyrosinase activities, but it should be stated that, within melanosomes, there is always a mixture of both indolic species, owing to the spontaneous nature of l-dopachrome decarboxylative rearrangement to DHI at physiological pH. The next step after the formation of 5,6-dihydroxyindoles is their oxidation to 5,6-indolequinones. Oxidation of DHI in aerobic conditions occurs spontaneously at a significant rate, although DHI is a substrate of tyrosinase, so that this enzyme accelerates the reaction. The oxidation of DHICA is more complex. First, spontaneous oxidation is much slower for DHICA than for DHI because of the effect of the carboxyl group at position 2, so that DHICA oxidation in vivo is most likely an enzymatic reaction. Second, this group has 264
important effects on the affinity of the melanogenic enzymes from different mammalian species for the carboxylated indole. Mouse Tyrp1 shows DHICA oxidase activity, but mouse tyrosinase does not (Jiménez-Cervantes et al., 1994; Kobayashi et al., 1994). However, human tyrosinase shows DHICA oxidase activity (Olivares et al., 2001). Therefore, it is possible that the oxidation of DHICA in vivo is carried out by different enzymatic proteins, Tyrp1 or Tyr, depending on the particular mammalian species considered. This opens the question of the physiological role of Tyrp1 in some species, especially in human melanocytes (see section dedicated to this protein), which has been and still is a controversial point. The next steps in eumelanogenesis are poorly characterized. 5,6-Indolequinones (decarboxylated or not) can react with dihydroxyindoles to form semiquinones. These species can spontaneously polymerize in an unordered and intermixed way to form eumelanin. The involvement of the silver protein as an accelerating factor in these last steps was proposed (Chakraborty et al., 1996; Lee et al., 1996), but a catalytic activity has never been definitively proven for this protein. Although this point will be also discussed later, it is clear that the silver protein undergoes a proteolytic process within the eumelanosome that provokes its aggregation and contributes to the formation of the lamellar network of the organelle. These lamellae may trigger melanin deposition (Solano et al., 2000). However, the mechanisms that regulate these processes, from silver protein aggregation to the promotion and binding of indolic units to presumably form a final melanoprotein product containing the silver protein and chains of the melanin polymer, are so far unknown. The size and order of these chains should depend on the initial DHI/DHICA ratio (Aroca et al., 1992; Pawelek, 1991). There is no doubt that l-tyrosine is the main amino acid precursor of melanin in higher organisms, but small amounts of l-tryptophan can also be incorporated into the pigment under special conditions such as an oxidative environment (Blagoeva, 1984; Chakraborty et al., 1986) or in specialized tissues in goldfish or butterflies (Chen and Chavin, 1965; Ubemachi, 1985), yielding pseudomelanin pigments such as papiliochrome and others. This role of l-Trp as a melanin precursor should be considered a highly specialized and rare aspect of melanogenesis, even less frequent than other unusual melanogenic pathways such as, for instance, the fungal pentaketide pathway leading to the dihydroxynaphthalene melanins mentioned above (Tsai et al., 1999). The study of these minor melanins and the enzymes involved in the corresponding pathways are beyond the scope of the present chapter.
The Enzymes Involved in Mammalian Melanogenesis According to Figure 14.1, to date, there are only three enzymes with well-established involvement in mammalian melanogenesis. Tyrosinase is undoubtedly the most important one.
ENZYMOLOGY OF MELANIN FORMATION
Sequence comparison of Tyr, Tyrp1 and Tyrp2/Dct reveals that the three proteins share many key structural features, due to their common origin from a single ancestral gene (Jackson, 1994). They are integral membrane proteins displaying one single membrane-spanning fragment near their C-terminus that anchors them to the melanosomal membrane. More importantly, they share two very similar metal ion binding sites essential for their catalytic action, although the nature of the metal cofactor is not the same. They undergo similar but not identical post-translational processing, including several glycosylation steps in the endoplasmic reticulum (ER) and trimming of the carbohydrate chains in the Golgi network. Glycosylation appears to be crucial for acquisition of full enzymatic activity (Halaban et al., 2000). However, in spite of their extensive sequence similarity, Tyr, Tyrp1, and Dct show remarkable differences in their catalytic abilities. For this reason, the Tyr family has been the subject of intense investigation, not only per se as the mammalian melanogenic machinery but also as an excellent model to study structure–function relationships as well as the molecular basis of divergent functional evolution. Next, we summarize the main properties of the three enzymes and their role(s) in melanogenesis.
Tyrosinase Tyrosinase (monophenol l-dopa: oxygen oxidoreductase, EC 1.14.18.1) is the key enzyme in melanogenesis. It is a glycocopperprotein that catalyzes the first two steps of the pathway, hydroxylation of l-tyrosine (cresolase activity) and oxidation of the o-diphenolic intermediate l-dopa to l-dopaquinone (catecholase activity). Tyr contains a pair of antiferromagnetically coupled copper ions at the active site (Lerch, 1983; Lerner et al., 1949). This coupling is the reason why tyrosinase is not a blue copper electron paramagnetic resonance (EPR)-silent protein in comparison with other copper enzymes such as laccases. So far, mammalian tyrosinase has not been crystallized, probably because it is a microheterogeneous transmembrane glycosylated protein. However, a variety of data based on the damage of H residues after photoinactivation of fungal tyrosinases, the sequence similarity among tyrosinases and hemocyanins (Himmelwright et al., 1980; Huber and Lerch, 1988), and the available crystallographic data on a plant catechol oxidase (Klabunde, 1998) indicate that two copper ions are bound to the protein in a hydrophobic pocket formed by two H-rich peptidic stretches named CuA and CuB. Both CuA and CuB sites contain three conserved H residues that are adjacent and form the binuclear enzyme’s active site due to the folding of the protein (GarcíaBorrón and Solano, 2002). Moreover, this site is very similar in Tyr and Tyrps, although the amino acidic conservation is higher in the CuB peptidic motif. However, it is also in CuB where the most important difference between the Tyr and Tyrps metal binding sites is found. This is related to the third H ligand of the metal ion, with tyrosinases from all sources always displaying two consecutive HH, whereas Tyrps have an LH sequence and, therefore, a single putative ligand at this
position (Martínez-Esparza et al., 1997; Olivares et al., 2002). It is usually accepted that the copper ions are bound only by three H, although some other alternatives with four ligands (one Cys and three His) are still proposed occasionally (Nakamura et al., 2000). It has long been debated whether the hydroxylase and oxidase activities of Tyr share a common catalytic site. The related issue of whether tyrosine hydroxylation and dopa oxidation are obligatorily coupled, or whether they are two independent steps, has also been discussed recently. A direct transformation of l-tyrosine into l-dopaquinone in the catalytic cycle has been proposed (Cooksey et al., 1997), whereas others claim that l-dopa is an intermediate in the oxidation of l-tyrosine that can be released from the tyrosinase active site (Fenoll et al., 2000). Whatever the case, it is clear that ldopa is formed in the pathway and is an alternative substrate for the enzyme, which is oxidized by tyrosinase to yield ldopaquinone. Therefore, the reactions underlying tyrosine hydroxylation and dopa oxidation should differ even if they share the same active site. Some differences between both reactions suggested different requirements at the reaction site (summarized by Lerch, 1983). For instance, the hydroxylase activity, but not the oxidase activity, shows a characteristic lag period before the reaction reaches maximal rate. This lag phase increases with the concentration of the substrate, l-tyrosine, and can be shortened or abrogated by catalytic amounts of l-dopa (Pomerantz, 1966). Therefore, l-dopa is the product of tyrosine hydroxylation, a cofactor for this reaction, and a substrate for the dopa oxidase reaction. In addition, the affinity of mammalian Tyr for l-dopa acting as cofactor for tyrosine hydroxylase is about two orders of magnitude higher than for the same compound acting as substrate for dopa oxidase activity (Pomerantz and Warner, 1967). Lerch (1983) proposed a mechanism to reconcile a common active site for l-tyrosine and l-dopa with the above-mentioned differential features of catalysis. This mechanism has been refined recently by Olivares et al. (2001) using mutant forms of mouse tyrosinase obtained by site-directed mutagenesis of selected active site residues. The main new contributions are related to the role of the HH pair located at the end of the CuB region and the inequivalence of both coppers. It was proposed that l-tyrosine and l-dopa dock to the tyrosinase active site in different orientations (Fig. 14.2). But the key point of the mechanism is the existence of at least three different forms of tyrosinase, called met, oxy, and deoxy, according to the absence/presence of oxygen and the oxidation state of the copper ions (Cu+2/Cu+1) in the active site. Intracellular tyrosinase exists in either the met or the oxy states, with the majority form in the absence of substrates being met-tyrosinase. Only oxy-tyrosinase is able to catalyze tyrosine hydroxylation and dopa oxidation. Met-tyrosinase readily oxidizes l-dopa, but it is inactive for l-tyrosine hydroxylation because a deadend complex is formed (Fig. 14.2). This would account for the low initial tyrosine hydroxylase activity of crude enzymatic extracts in the absence of added cofactors, characteristic of the 265
CHAPTER 14
Fig. 14.2. Mechanism of action for tyrosinase. Starting in the oxy form of tyrosinase, two catalytic cycles are depicted, dopa oxidase (DO) at the top and tyrosine hydroxylase (TH) at the bottom. Note that met-tyrosinase is involved in the DO cycle but not in the TH cycle. When ltyrosine binds to met-tyrosinase, a dead-end complex is formed, accounting for the lag period of the TH activity and the inhibition by excess of this substrate. Dopa acts as cofactor when bound to the above-mentioned met-tyrosinase. The His-389 residue is essential for l-dopa recognition and orientation to CuB (for more details, see Olivares et al., 2002). Im, imidazole.
lag phase of this activity. A progressive accumulation of ldopa would occur, mainly due to the chemical generation of this compound in the redox reaction between l-dopaquinone and l-cyclodopa during the melanogenic pathway (see Fig. 14.1). This accumulation is responsible for the acceleration of tyrosine hydroxylation. Indeed, the increase in the l-dopa/l-tyrosine ratio as the reaction proceeds leads to a concomitant decrease in the fraction of tyrosinase captured in the dead-end complex and raises the proportion of met-tyrosinase molecules recruited to the productive catalytic cycle and, therefore, the hydroxylase reaction rate. In this hydroxylation cycle, l-tyrosine bound to CuA labilizes the oxygen molecule bound in the catalytic center of oxy-tyrosinase in a side-on manner (Solomon and Lowery, 1993). The resulting polarized molecule ortho-hydroxylates the monophenolic ring of ltyrosine, and the subsequent oxidation of the o-diphenolic product to o-quinone would leave the active site in a reduced bicuprous state (deoxy-tyrosinase), allowing the entrance of a new oxygen molecule and further turnover. In the dopa oxidase cycle, l-dopa bound to CuB of oxytyrosinase would also weaken the oxygen molecule, resulting in oxidation of the organic substrate and release of l266
dopaquinone and water. The enzyme is left in a bicupric state, met-tyrosinase, that can next bind l-tyrosine or l-dopa with higher affinity than the oxy-form as the active center is not occupied by oxygen. l-Dopa may dock to the two copper ions in this form through both hydroxyl groups, so that its affinity would be higher than the affinity for oxy-tyrosinase when the binding proceeds only through CuB. This higher affinity would account for the old observation that the Ka measured for l-dopa as cofactor is in the mmolar range (Pomerantz and Warner, 1967). Thus, oxy-tyrosinase would display a higher affinity for l-tyrosine than for l-dopa, whereas the opposite should hold for met-tyrosinase. This different affinity ratio of the met- and oxy-enzymatic forms also accounts for the fact that d-dopa is a relatively efficient cofactor but a poor substrate (Olivares et al., 2001; Winder and Harris, 1991). The disposition of both hydroxyl groups bound to the copper ions would allow for an easy transfer of two electrons from the odiphenol to the binuclear site, leading to the oxidized quinone and the reduced deoxy-tyrosinase form that is again oxidized upon oxygen binding. Other interesting aspects of tyrosinase aside from the abovedescribed mechanism of catalysis, such as hormonal regula-
ENZYMOLOGY OF MELANIN FORMATION
tion, post-translational modifications including glycosylation, processing of the protein, and correlations between activity and mutations in different parts of the polypeptidic chain, are treated in other chapters in this book, so they are omitted here to avoid overlapping. This omission of crucial aspects of protein maturation and processing also applies to Tyrps, the existence and enzymatic roles of which in mammalian melanogenesis are presented next.
Tyrosinase-related Proteins Two melanosomal proteins displaying extensive sequence similarity to tyrosinase have been found in animals from fishes to mammals. They are called tyrosinase-related proteins 1 and 2 (Hearing and Tsukamoto, 1991). Together with tyrosinase, they constitute the tyrosinase family. This family likely evolved from a single ancestral gene and, in spite of a common general origin, structural similarity is higher between Tyrp1 and Tyrp2 than between these and tyrosinase.
Tyrp1 Tyrp1 was in fact the first member of the Tyr family to be cloned (Shibahara et al., 1986), in an attempt to clone the tyrosinase gene. Soon thereafter, the Tyrp1 gene was mapped to the brown locus known to affect pigmentation in mice. After the cloning of the c-locus tyrosinase gene, the homology of both genes was demonstrated, with an identity score higher than 40%, which increases substantially in the metal ion binding sites. This homology strongly suggests that Tyrp1 may be a metalloenzyme, although the nature of the metal cofactor remains unknown (Furumura et al., 1998). Tyrp1 is important for normal melanogenesis, according to a wealth of converging evidence. For instance, mice homozygous for the brown mutation in Tyrp1 display a lighter coat color than wild-type mice. Mutations in the TYRP1 gene are responsible for a subtype of human albinism, brown OCA3 (Boissy et al., 1996; Sarangarajan et al., 2000) and, in cultured human melanocytes and melanoma cells, expression of TYRP1 positively correlates with eumelanogenesis (Del Marmol et al., 1993). However, in spite of its early cloning, the specific function of Tyrp1 in the Raper–Mason pathway underlying these phenotypic effects has been very elusive and, in fact, it is still controversial. The possible enzymatic activity of mammalian Tyrp1 has been extensively investigated by several independent laboratories. Initially, mouse Tyrp1 was considered to be a second tyrosinase encoded by a different locus and showing a poor dopa oxidase activity compared with the c-locus tyrosinase (Jiménez et al., 1991). The same conclusions were obtained by our group, which for some time used the terminology HEMT and LEMT (for higher or lower electrophoretic mobility tyrosinases) to designate two proteins that could be resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) under nonreducing conditions and were positive for an in-gel dopa oxidase activity stain (Jiménez-Cervantes et al., 1993a). Thereafter, specific antibodies developed by V. Hearing allowed the identification of HEMT as tyrosinase and
LEMT as Tyrp1. After purification of Tyrp1 from B16 mouse melanoma, a new enzymatic activity, DHICA oxidase, was demonstrated (Jiménez-Cervantes et al., 1994). This was confirmed by transient expression of the gene in nonmelanocytic cells, as well as by the study of mutant mice (Kobayashi et al., 1994). However, the DHICA oxidase activity of Tyrp1 is quite small, and a similar activity has also been attributed to another melanosomal protein, Pmel-17 (see below). Moreover, in a recent study of DHICA oxidation by extracts from human melanoma cells and by transiently expressed human tyrosinase, it was clearly shown that this enzyme displays a DHICA oxidase activity comparable to mouse Tyrp1 (Olivares et al., 2001). Differences between human and murine Tyrp1 were also observed by Boissy et al. (1998a). This suggests the intriguing possibility that DHICA metabolism could follow different enzymatic pathways in mouse and human melanocytes and raises the question of the actual role of Tyrp1 in human melanocytes. To complicate the situation further, it was reported that transfection of the Tyrp1 gene into fibroblasts conferred dopachrome tautomerase activity to these cells (Winder et al., 1993a). Moreover, other possible catalytic activities were proposed, including a catalase (Halaban and Moellmann, 1990) or even a tyrosine hydroxylase activity devoid of dopa oxidase and responsible for the first l-dopa formed in vivo, and needed to abrogate the lag period in authentic tyrosinase (Zhao et al., 1994). Finally, and in contrast to these different enzymatic activities, it has also been suggested that Tyrp1 could be mostly devoid of enzymatic activity but show a strong stabilizing effect on tyrosinase (Kobayashi et al., 1998). In keeping with the occurrence of a stabilizing effect on tyrosinase, a direct interaction of the two proteins has been clearly demonstrated in vitro (Jiménez-Cervantes et al., 1998). In any case, a stabilizing role is not incompatible with an enzymatic activity for Tyrp1. Indeed, the key to these apparent discrepancies in the role of Tyrp1 could be related to subtle differences among species and its possible double role, on the one hand a catalytic function and on the other hand a stabilizing effect on tyrosinase. In summary, the elusive role of Tyrp1 remains unclear. However, the fact that melanogenesis proceeds in lower organisms in the absence of Tyrp1, and the phenotype associated with the brown mutation in mice and with type 3 human OCA, strongly suggests that this role should be ancillary and related to the determination of the type of pigment formed, rather than to its presence or absence.
Tyrp2 As opposed to Tyrp1, the catalytic activity of Tyrp2 is well established and clearly different from tyrosinase. The protein catalyzes the nondecarboxylative rearrangement of ldopachrome to DHICA and is therefore called dopachrome tautomerase (Dct). Before the cloning of this gene and the characterization of the enzymatic activity of the transiently 267
CHAPTER 14
Fig. 14.3. Mechanism of action for Dct/Tyrp2. The metal cofactor of this enzyme is zinc. This metal has no redox properties, excluding the participation of oxygen in the catalytic cycle. l-Dopachrome binds to the enzyme through the semiquinonic part of the molecule, and an electronic rearrangement with subsequent hydrogen migration from position 3 to position 2 leads to the tautomerization to DHICA, the product of the reaction.
expressed protein, some enzymatic activity acting on ldopachrome was detected by several laboratories. This activity was called dopachrome conversion factor (Aroca et al., 1990a; Pawelek et al., 1980), dopachrome oxidoreductase (Barber et al., 1984), and dopachrome isomerase (Jackson et al., 1992; Pawelek, 1991). Once the product of the enzyme’s action on l-dopachrome was firmly established as DHICA instead of DHI (Fig. 14.1), the more precise name tautomerase was first proposed (Aroca et al., 1990b) and soon after widely accepted. The definitive assigned EC number is 5.3.3.12, as the reaction catalyzed by Dct is a specific type of isomerization (Fig. 14.3) resulting from hydrogen migration in an intramolecular keto-enol tautomerization (International Union of Biochemistry, 1999). Initially, the actual role of Dct in melanogenesis was questioned based on the observation that metal ions are also competent in catalyzing dopachrome conversion. However, metal ions always lead to mixtures of DHI and DHICA, whereas the latter is the exclusive product of the enzymatic reaction (Palumbo et al., 1991). Moreover, metal ion-catalyzed dopachrome rearrangement is not dependent on the substrate stereospecificity, whereas Dct shows a good specificity, acting only on the natural l-dopachrome. Neither the d-stereoisomer nor the decarboxylated dopaminochrome is a substrate for mouse Dct (Aroca et al., 1991). This indicates that the carboxyl group, in an appropriate spatial orientation, should be an essential requirement for the docking of the substrate at the enzyme active site, probably through its interaction with an unidentified electrophilic residue. In this regard, it is interesting to mention that other mammalian (Matsunaga et al., 1999; Odh et al., 1993) and nonmammalian Dct-related enzymes (Palumbo et al., 1994; Sugumaran and Semensi, 1991) are able to act on d-dopachrome or dopaminechrome, and their product is DHI instead of DHICA. These enzymes should not be considered tautomerases as they catalyze a decarboxylation. Obviously, the mechanism of action should 268
be different, and this difference emphasizes the importance of the carboxyl group in the formation and final structure of the mammalian eumelanin polymer. As for Tyrp1, Tyrp2/Dct shows remarkable homology to tyrosinase. It displays several glycosylation sequons, whose occupancy is important for enzyme function, as treatment of cultured melanoma cells with tunicamycin decreases Dct activity. Moreover, treatment of the enzyme with glycosidases increases the specific activity of the enzyme but decreases its stability (Aroca et al., 1992). Dct is also associated with the melanosomal membrane by a single membrane-spanning helix, but the sorting and trafficking signals in its short cytoplasmic C-terminal extension are different from those in tyrosinase, suggesting a differential intracellular processing (Raposo et al., 2001). The sequences of the metal ion binding sites in Dct share with tyrosinase the position and number of the histidine residues likely to be involved in chelation of the metal cofactor. Yet, the nature of the metal cofactor is different. Purified Dct contains two Zn atoms per protein molecule, as measured by atomic absorption spectroscopy, and enzyme activity can be reconstituted from apoenzymatic preparations by addition of Zn ions, but not Cu or Fe ions (Solano et al., 1994, 1996). Therefore, although direct binding of Zn to Dct could not be demonstrated in melanocytic cells cultured in the presence of a radioactive isotope (Furumura et al., 1998), and in spite of reports suggesting the presence of Fe at the active site (Chakraborty et al., 1992), it is widely accepted that Dct is a Zn protein. In keeping with this, and from the chemical point of view, Zn2+ is preferable to other cations to catalyze a tautomerization, because it has no redox properties and is unable to catalyze oxidative reactions. In Dct, each Zn2+ is probably bound to the polypeptidic chain by three histidine residues in a distorted tetrahedron, and the fourth position is occupied by a water molecule (Fig. 14.3). This water molecule would be displaced by the substrate, l-dopachrome, and a rearrange-
ENZYMOLOGY OF MELANIN FORMATION
ment in the distribution of p-electrons on the indolic ring would follow, thus achieving the tautomerization to DHICA (Solano et al., 1996). The physiological consequences of Dct activity on the type and amount of pigment formed are only partially understood. Tyrp2/Dct may contribute to the formation of DHICAenriched melanins with a higher proportion of carboxylated vs. noncarboxylated indolic monomers. These melanins are lighter in color than DHI-rich melanins (Aroca et al., 1992; Orlow et al., 1992). Moreover, the presence of Dct has been shown to decrease the binding of melanin monomers to proteins and to protect enzymatic activities (Salinas et al., 1994). Therefore, Dct may protect the melanocytes from the inherent cytotoxicity of melanogenesis by promoting a less cytotoxic branch of the pathway. In keeping with this possibility, DHICA has been shown to be less cytotoxic than DHI (Pawelek and Lerner, 1978; Urabe et al., 1994). In any case, several mutant alleles of mouse Dct are associated with pigment dilution, but the phenotype is mild. Concerning human melanocytes, no mutations in the human gene have been described, and the levels of Dct activity appear to be lower than in mouse (Bernd et al., 1994).
The Tyrosinase Family and the Melanogenic Complex A number of studies from different laboratories have raised the possibility of the occurrence of a multimeric complex comprising several melanosomal proteins, and particularly tyrosinase and the Tyrps. Orlow et al. (1993a, b) first reported the identification by sucrose density gradient centrifugation of a high-molecular-weight complex including tyrosinase and likely other melanosomal proteins, which was not detected in extracts from platinum mice. Later on, it was shown that, in extracts from Cloudman mouse melanoma cells, antibodies directed to Tyrp1 and Tyrp2 could immunoprecipitate tyrosinase and that the three proteins comigrated in sucrose density gradients under appropriate conditions (Orlow et al., 1994). This suggested a stable interaction among these proteins, at least in detergent-solubilized extracts. In a study performed with purified tyrosinase and Tyrp1, a strong and close interaction between these proteins, with formation of heterodimers, could be demonstrated (Jiménez-Cervantes et al., 1998). This suggested a physical interaction between these proteins in a “melanogenic complex” that may involve other melanosomal components (Winder et al., 1994). The functional consequences of such a complex remain obscure. At least Tyrp1 (Kobayashi et al., 1998, Manga et al., 2000), and also likely Tyrp2 (Manga et al., 2000), stabilize tyrosinase in melanocytes and in transfected heterologous cells. This is best explained in terms of a physical interaction between the proteins within the melanosome. Concerning the enzymatic activities, interaction with Tyrp1 was reported to decrease tyrosinase activity (Manga et al., 2000), but other studies failed to demonstrate a similar effect (Jiménez-Cervantes et al., 1998). Further evidence for complex formation by the melanogenic enzymes comes from studies with enzymes from
fungi and insects (Sugumaran and Semensi, 1991; Sugumaran et al., 1995). It could be shown by a number of techniques that dopachrome “isomerase” and tyrosinase interacted with each other and mutually inhibited their enzymatic activity. It should be noted that complexes of sequential metabolic enzymes, such as the melanogenic complex, are referred to as “metabolons.” A number of evolutionary advantages for such structures have been proposed (Cascante et al., 1994; Srere, 1987). Whatever the case, the advantages of a melanogenic complex seem obvious in terms of optimization of the flow of substrates and products, and also probably as a means to minimize leakage of reactive and potentially cytotoxic intermediates from the melanosome.
Silver/Pmel-17 and Other Melanosomal Proteins Involved in the Regulation of Melanogenesis In addition to the tyrosinase family, there are other melanosomal-specific proteins with clear involvement in the regulation of melanogenesis, in spite of uncertainties as to their enzymatic role or mechanism of action. Donatien and Orlow (1995) found that certain melanosomal proteins interact more closely with melanin than tyrosinase, Tyrp1, and Tyrp2/Dct. Three of these proteins displaying a tighter interaction with the melanin polymer were identified by immunochemical techniques as the silver/gp100/gp87/Pmel-17, P (pink-eyed dilution), and MATP/AIM-1/underwhite proteins. Mutations in these three proteins lead to strong inhibition of melanin formation. Concerning Pmel-17, its mutation causes the silver phenotype in mice (Martinez-Esparza et al., 1999). It is a glycoprotein of molecular mass around 100 kDa in humans (Kobayashi et al., 1994; Kwon et al., 1991, 1994) and 87 kDa in mice (Martínez-Esparza et al., 2000) before its proteolytic cleavage within the melanosome. Chakraborty et al. (1996) proposed a potential enzymatic activity for the Pmel-17/silver protein. They reported that wheat germ agglutinin-purified extracts of both mouse and human melanoma cells contain an enzymatic activity that catalyzes the polymerization of DHICA to melanin in vitro. Similar results were described by Lee et al. (1996), who described a DHICA-converting activity in human Pmel-17. However, this enzymatic activity of Silver/Pmel-17 acting on DHICA polymerization overlaps the activity described for murine Tyrp1 and human tyrosinase (Olivares et al., 2001) and, as a matter of fact, it has never been unequivocally associated with Pmel-17. From the chemical point of view, DHICA is an o-diphenol so that its converting activity is more likely to reside in proteins such as Tyrp1 or tyrosinase, which are metalloenzymes with diphenol oxidase activity, than in Silver/Pmel-17. Furthermore, an opposite activity has also been proposed for this protein that, under certain conditions, could act as “stablin” by stabilizing DHICA and preventing its auto-oxidation and incorporation into melanin (Pawelek, 1991). This raised the possibility that the stablin and DHICA polymerase activities may reside in alternative transcripts of the Pmel-17/silver gene, but so far this has not been confirmed. What is clear is that cells overexpressing Pmel-17 display 269
CHAPTER 14
structures resembling premelanosomal striations. Therefore, Pmel-17 seems to be sufficient to drive the formation of striations within multivesicular bodies and is directly involved in the biogenesis of premelanosomes (Berson et al., 2001). Furthermore, it is also known that melanogenesis does not begin in melanosomes until this protein is processed from its membrane-bound original state to its soluble form and is integrated into the fibrillar matrix characteristic of stage II melanosomes (Kushimoto et al., 2001). Thus, the proteolytic product of Pmel-17 devoid of its C-terminal region seems to be essential for eumelanosome architecture and for initiation of melanosynthesis (Yasumoto et al., 2004). Intriguingly, Pmel-17 has a proline/serine/threonine-rich region in the central portion abundant in O-glycosylation signals similar to typical proteoglycans. One attractive hypothesis is that this saccharide moiety would contribute to the formation of the fibrillar matrix of Stage II premelanosomes and/or catalyze melanin deposition onto this matrix by binding dihydroxyindole-derived units (Solano et al., 2000), but experimental evidence in favor of this possibility is not yet available. In summary, it is clear that Pmel17 is an essential factor for the distal steps of melanogenesis under “in vivo” conditions (Fig. 14.1) but, up to now, there is no clear enzymatic activity associated with this protein. The other two melanosomal proteins mentioned above, p and underwhite, may have a key function in melanogenesis as their mutations also lead to oculocutaneous albinism, OCA2 and OCA4 respectively. However, these proteins do not show enzymatic activity. The P protein is probably an anionic transporter localized to the melanosomal membrane, and partially responsible for the control of the pH within the melanosome (Brilliant, 2001; Puri et al., 2000). Anionic transport should be coupled to vATPases and VDAC, two proton transporters also found in the melanosomal membrane (Basrur et al., 2003), in order to maintain charge neutrality. Early reports suggested that melanogenesis could be triggered by low pH (Bhatnagar et al., 1993). This was related to the observation that acidic pH favors an allosteric interconversion of tyrosinase (Devi et al., 1987; Tripathi et al., 1987). However, melanin synthesis in human pigment cell lysates is maximal at neutral pH, and is suppressed in Caucasian melanocytes when the melanosomal pH is low (Ancans et al., 2001). Moreover, inhibition of the v-type ATPases increases tyrosinase activity and melanin production in human and mouse melanoma cells (Ancans and Thody, 2000) and in melanocytes cultured from Caucasian, but not black, donors (Fuller et al., 2001). Therefore, the melanosomal pH could be critical for the control of tyrosinase activity and melanogenesis. In this scenario, the P protein could provide a key control point for skin pigmentation through its ability to mediate neutralization of the melanosomal pH (Ancans et al., 2001). On the other hand, other effects different from tyrosinase activation by an increase in pH would also be possible as mutations in the p gene cause mislocalization of melanosomal proteins (Boissy et al., 1998b; Manga et al., 2001). Concerning OCA4, related to the murine underwhite gene, 270
the encoded protein is MATP, a membrane-associated transporter protein also named AIM-1 (Newton et al., 2001). As in the case of the P protein, this protein is predicted to span the membrane 12 times, a usual topology in transport proteins. So far, no enzymatic activity has been assigned to MAPT/AIM-1/underwhite and, moreover, its actual substrate for transport is still unclear (Rundshagen et al., 2004). Similar to OCA2, in OCA4 melanocytes, tyrosinase processing and intracellular trafficking to the melanosome is disrupted, and tyrosinase is abnormally secreted from the cells in immature melanosomes (Costin et al., 2003). Therefore, Pmel-17, P, and underwhite proteins, present in mammalian melanocytes, are needed for normal melanogenesis but they lack well-defined enzymatic activity. An opposite situation holds for another protein proposed to play a role in melanogenesis, namely peroxidase, the enzymatic activity of which is well established but whose role in melanogenesis is doubtful. Okun et al. (1970) proposed that tyrosine might be oxidized to melanin by a peroxidase activity in mammalian melanocytes. Additional studies on the oxidation of tyrosine by horseradish peroxidase led these authors to propose that the initiating step in melanogenesis, tyrosine hydroxylation, might be catalyzed by a peroxidase. Today, it is clearly proven that mammalian tyrosinase catalyzes the conversion of ltyrosine to l-dopa, but the possibility still remains that a peroxidase activity might also be involved in the distal phases of melanogenesis. In this regard, the ability of horseradish peroxidase to oxidize DHI is well documented (d’Ischia et al., 1991), although this enzyme is much less efficient with DHICA. In fact, peroxidase seems to be important in melanogenesis in some nonmammalian systems, such as the melanin in the ink of cuttlefish, but its role in mammals should be confirmed after the identification of a protein with peroxidase activity within melanosomes. So far, proteomic analysis of this organelle (Basrur et al., 2003) has failed to achieve this identification. In addition, another critical point would be the origin of hydrogen peroxide needed for this enzyme. In this respect, we have observed that oxidative stress due to the addition of this peroxidase substrate to melanoma cell cultures led to an inhibition, rather than a stimulation, of mammalian melanogenesis (Jiménez-Cervantes et al., 2001). Although the mechanism is likely due to other factors different from enzymatic activities, this fact suggests that peroxidase is not an important factor in mammalian melanogenesis.
Methods for Determination of Melanogenic Enzymatic Activities The measurement of the melanogenic activities is not a trivial matter, as it is complicated by several factors, particularly when the biological sample under study contains more than one of the melanogenic enzymes. On the one hand, the product of one particular reaction can be the substrate of a subsequent and coupled enzymatic step. For instance, the tyrosinase-catalyzed oxidation of l-dopa to l-dopaquinone is
ENZYMOLOGY OF MELANIN FORMATION
rapidly followed by the formation of l-dopachrome, which is a substrate for Tyrp2/Dct, so that the presence of this enzyme in the reaction mixture can modify the rate of dopachrome accumulation. The situation is even more complex for the hydroxylation of l-tyrosine, where l-dopa acts as a necessary cofactor and, simultaneously, as a competing alternative substrate. On the other hand, the reaction specificities of the melanogenic enzymes are in some cases overlapping. The best example is provided by mouse Tyrp1, which is considered to be a pseudotyrosinase of low specific activity (JiménezCervantes et al., 1993a). Moreover, the substrate specificities of the melanogenic enzymes seem to be variable between species, and are sometimes still debated. For instance, mouse tyrosinase does not catalyze DHICA oxidation, whereas the human enzyme appears to be able to do so (Olivares et al., 2001). Finally, the substrates employed in many of the relevant assays are unstable in the presence of molecular oxygen, undergo metal ion-catalyzed transformations, or are not available commercially. Therefore, the interpretation of enzyme activity measurements is complex, and calls for an adequate knowledge of the chemistry of the reaction considered and the possible interferences in the sample under study. Not surprisingly, the first assays for melanogenic activity aimed at determining the rates of the tyrosinase-catalyzed reactions and took advantage of either the requirement for oxygen or the formation of reactive oxidized species, such as o-quinones. These methods consisted of the conventional Warburg technique (Dawson and Magee, 1955), the Clarktype electrode to measure oxygen consumption (Nelson and Mason, 1970), or the chronometric (Dawson and Magee, 1955) and spectrophotometric (El-Bayoumi and Frieden, 1957) assays employing ascorbate to reduce the quinones formed by tyrosinase back to catechols. These assays showed low sensitivity and low specificity. They were applied to samples with high tyrosinase activity from plants, insects, and amphibians, but were not sensitive and/or specific enough to measure tyrosinase activity accurately in mammalian samples where, in addition to a lower tyrosinase activity, the presence of the Tyrps must be taken into account. Thus, new methods of enzymatic analysis of the melanogenic pathway have been designed, aiming at: 1 increasing not only the sensitivity but also the specificity of the tyrosinase assays; 2 measuring the enzymatic activities of Tyrps; 3 minimizing the mutual interferences among these activities in crude extracts (Valverde et al., 1993), as they may catalyze consecutive reactions in the pathway; 4 distinguishing the relative contributions of different proteins to a single enzymatic activity. According to the type of reaction considered, the enzymatic activities of the melanogenic pathway can be classified into three groups: hydroxylation of monophenolic substrates; oxidation of diphenols or dihydroxyindoles; and tautomerizations. The more frequent and useful activity assays are presented below, according to this general classification. Experimental details are generally omitted, as they can be
found in the corresponding references. Table 14.1 summarizes these assay methods, with brief comments on their relative value. However, it should be taken into account that, owing to the presence of enzymes catalyzing coupled reactions in crude extracts, and to the overlapping catalytic potentials of tyrosinase and Tyrp1, there is not an easy and absolutely accurate method for the determination of these melanogenic activities.
Methods for the Measurement of Tyrosine Hydroxylase Activity Tyrosine hydroxylase activity measurements are often considered to be the methods of choice for the assay of tyrosinase. Compared with dopa oxidase activity measurements, they are more specific, but also more technically demanding because of the lower turnover number and the lag period of the tyrosine hydroxylase activity. A further complication derives from the impossibility of isolating tyrosine hydroxylation from dopa oxidation (see the catalytic cycle described in Fig. 14.2). By far, radiometric methods are the most frequently used, sensitive, and specific assays for the tyrosine hydroxylase activity of mammalian tyrosinase. The most versatile of these assays uses l-[3,5-3H]-Tyr as substrate to measure tritium release as water, according to the reaction depicted in Figure 14.4. It was first described by Pomerantz (1964, 1966) as a modification of other assays developed for different hydroxylases. l-Dopa is normally added to the reaction mixture as cofactor of the reaction (Lerner et al., 1949), and tritiated water is separated from the excess of l-tyrosine and other radiolabeled products by absorption on a charcoal–celite mixture. Modifications to standardize, speed up, and optimize the assay have been published (Hearing, 1987; Hearing and Ekel, 1976; Jara et al., 1988b; Townsend et al., 1984). The method can be extended to samples such as human hair bulbs (King and Witkop, 1976). The major limitation is the high background due to tritium exchange between the substrate and water, so that radiolabeled tyrosine should sometimes be repurified. On the other hand, only half the radioactivity present in the substrate is released upon hydroxylation. Accordingly, long incubation times should be avoided as the second tritium retained in the l-dopaquinone molecule could be released in subsequent polymerization reactions, without the direct involvement of tyrosinase. The presence of Dct in crude samples has no significant influence on this. The assay has been modified to allow for its in vivo application to melanocytes in culture. Essentially, this involves the addition of radiolabeled tyrosine to the culture media and the measurement of tritiated water after long incubation periods, usually at least 24 h (Auböck et al., 1983; Oikawa et al., 1972). This assay is used quite frequently, but some caution should be exercised because the results may be influenced by factors other than tyrosinase activity, such as l-tyrosine transport inside the cells. A spectrophotometric assay using the increase in A280 accompanying the oxidation of l-tyrosine has been used as an indicator of this activity in mushroom (Duckworth and 271
272
Dopa oxidase
Oxidation of l-dopa formed to yield fluorescent indoles
Separation and quantitation of l-dopa
Fluorometric
HPLC
Radiometric
HPLC
Spectrophotometric
Sensitive Use d-dopa as cofactor
Release of 14CO2 after oxidation of the reaction mixture
Radiometric
Sensitive
Sensitive
Sensitive and stereospecific
Rapid, simple, and continuous More sensitivity than above Dct interference avoided Sensitive and stereospecific
Detection of an adduct DQ-MBTH at 500 nm Separation and quantitation of l-dopachrome Formation of cysteinyldopa and electrometric detection Incorporation of 3-[14C]-dopa into acid-insoluble melanin Release of 3H from position 6 in 2,5,6-[3H]-Dopa
Rapid, simple, and continuous
Detection of dopachrome formation at 475 nm
Good resolution of substrate and product
Sensitive and nonradiometric
Sensitive and rather specific Can be used in situ for melanocytes in culture
Release of 3H2O from l-[3,5]-3H-Tyr
Radiometric
Tyrosine hydroxylase
Major advantages
Rationale
Technique
Activity
Table 14.1. Summary of methods for the determination of enzymes involved in melanogenesis.
Limited solubility of MBTH A proportion of DQ might evolve DC Technically more complex than spectrophotometric. Discontinuous Technically more complex than spectrophotometric. Discontinuous Dct and other factors influence the rate of polymerization of products High background due to the instability of the radioactive tracer
Thiols and Dct affect results
Interference at long incubation times due to polymerization High background due to 3H exchange Some carboxyl group is retained Evolved CO2 is difficult to trap completely High background but low specificity Affected by the DHI/DHICA ratio formed It needs l-dopa accumulation Less sensitive than radiometric methods
Major drawbacks
Pomerantz (1976)
Aroca et al. (1992)
Tsukamoto et al. (1992a, b) Agrup et al. (1983)
Mason (1948); Horowitz et al. (1970) Winder and Harris (1991)
Jergil et al. (1983)
Adachi and Halprin, (1967); Husain et al. (1982)
Winder and Harris (1991)
Pomerantz (1964)
References
273
Melanin formation
DHICA oxidase
DHI oxidase
Dopachrome tautomerase (Dct)
Radiometric
HPLC
Formation of acid-insoluble melanin from l-[14C]-Tyr
Detection of an IQCA-MBTH adduct at 490 nm Separation and quantitation of residual DHICA by UV
Separation and quantitation of residual DHI by UV
HPLC
Spectrophotometric
Detection of melanochrome at 540 nm
Separation of dopachrome and DHICA quantitation by UV absorption
HPLC
Spectrophotometric
Continuous interferences due to spontaneous DHI formation avoided
Increase in A308 due to DHICA formation
Spectrophotometric
Low background Good sensitivity It measures the global melanogenic activity
Specific for Tyrp1 in mouse samples
Rapid, simple and continuous
Interference of melanin is avoided
Rapid, simple, and continuous
More specific than spectrophotometric methods
Simple and continuous
Decoloration of l-dopachrome at 475 nm
Spectrophotometric
Results do not directly correlate with tyrosinase activity Tyrps and other factors (thiols, metal, detergents) affect results
Limited solubility of MBTH Limited sensitivity Long incubation times are required Substrate disappearance, rather than product formation, is determined
High background due to the DHI instability and rapid melanin formation High background Substrate disappearance, rather than product formation, is determined
Low specificity and sensitivity Time of recording limited by the formation of colored melanin-like products High initial absorbance Interference by UV-absorbing material Limited sensitivity Discontinuous
Chen and Chavin (1965); Jara et al. (1988b)
Jiménez-Cervantes et al. (1994) Kobayashi et al. (1994); Jiménez-Cervantes et al. (1994)
Tsukamoto et al. (1992a, b)
Miranda et al. (1985)
Palumbo et al. (1987)
Aroca et al. (1990b)
Pawelek et al. (1980)
CHAPTER 14 Dehydroascorbate
HO +
COO–
HN
HO
3
1 Ascorbate
O +
O
Fig. 14.4. Tyrosine hydroxylation: reaction measured in the Pomerantz assay by estimation of the tritium released as water when the hydroxylation at position ortho takes place.
COO–
HN 3
2
+Cys
4 3
HO
274
+
HN 3
N H
COO–
Cys-Dopa
lmax= 293 nm
+ MBTH +
HN 3
COO–
HO N+ H
HO
CH3
COO–
+
Reduction back to L-dopa Addition of Thiols
N MBTH-Dopa
N
C S
lmax= 500 nm
l
2
N
HO
L-Dopachrome = 305 & 475 nm max
1
COO–
S
–OOC HO
O
Coleman, 1970) as well as in human melanoma (Wood and Schallreuter, 1991). According to the UV absorption of the possible subsequent products, dopa, thiol-dopa adducts, and dopachrome, and the high interference due to the UV absorption of proteins, this assay is rarely used, and the choice of 280 nm as the wavelength employed to follow the reaction progress does not seem appropriate. If thiol adduct formation is expected, 295 nm (maximal absorption of cysteinyl-dopa and related chemicals) is better suited. If dopachrome formation is anticipated, 305 or 475 nm should be chosen. The fluorescence properties of indoles have been exploited as an alternative for measuring the tyrosine hydroxylase activity of tyrosinase. These methods are based on the accumulation of l-dopa when l-tyrosine is oxidized by tyrosinase in the presence of ascorbate (Fig. 14.5). Subsequent chemical oxidation of l-dopa with ferricyanide in the presence of traces of Zn(II), followed by the rapid stop of this reaction with ascorbate in concentrated NaOH yields a mixture of dihydroxyindoles that can be quantitated on the basis of their fluorescent emission at 490 nm upon excitation at 360 nm. Fluorescence intensity is proportional to the tyrosinase activity. The method was first described by Adachi and Halprin (1967) and later optimized by Husain et al. (1982). A complete description can be found in more recent literature (Hearing, 1987; Tripathi et al., 1992). The assay shows variability depending on the DHI/DHICA ratio formed, as the fluorescence of DHICA is higher than that of DHI. Other drawbacks are the high background due to the amount of l-dopa cofactor initially present in the assay and the putative chemical hydroxylation of ltyrosine catalyzed by ascorbate. Inclusion of metal chelators in the assay medium minimizes this reaction (Husain et al., 1982). HPLC assays have been developed to gain sensitivity and specificity. HPLC makes it possible to separate, identify, and quantitate the substrate remaining in the assay media as well as the products of the reaction. Most of the methods use reverse phase C18 columns for the separation. For tyrosine hydroxylase activity, HPLC was first used in 1983 (Jergil et al., 1983). The method is based on the determination of ldopa generation from l-tyrosine. Ascorbate should be added to allow for l-dopa accumulation (Fig. 14.5). Finally, another radiometric assay for tyrosine hydroxylase activity was reported using l-[HOO14C]-Tyr as substrate (Winder and Harris, 1991). It is based on the fact that, after tyrosinase action, l-[HOO14C]-dopa is formed. Oxidation
HO HO + NH3
3 4
Addition of Besthorn Hydrazone Internal cyclation
Fig. 14.5. Some reactions of l-dopaquinone involved in the different assays for the l-dopa oxidase activity of tyrosinase.
with ferricyanide promotes decarboxylation of dopa, but not tyrosine. Thus, one molecule of 14CO2 is released from the products of tyrosinase action for every molecule of tyrosine hydroxylated to dopa. The main drawback of this method could be the retention of some carboxyl groups in post-dopa products due to the presence of Dct or the incomplete oxidation of dopa.
Methods for the Measurement of Diphenol and Dihydroxyindole Oxidase Activities The dopa oxidase activity is easily measured by spectrophotometric recording of l-dopachrome formation at 475 nm. This rapid and easy to perform assay was introduced by Mason (1948), and it has been used for tyrosinases from all sources, from Neurospora crassa (Horowitz et al., 1970) to mammalian melanoma (Pomerantz and Li, 1970). A comparison with radiometric assays was published (Jara et al., 1988b). The sensitivity is limited by the absorption coefficient of l-dopachrome (e = 3700/M/cm), but it should be considered that the turnover number of tyrosinase as hydroxylase is around one order of magnitude lower than that as oxidase. The main limitations of the assay are: 1 The presence of thiols in the assay media prevents dopachrome formation (Jara et al., 1988a), as l-dopaquinone is trapped to yield thiol–dopa conjugates (Fig. 14.2). 2 Only half the l-dopa molecules oxidized by tyrosinase are transformed into l-dopachrome (Fig. 14.2). The other half is reverted back to l-dopa (García-Cánovas et al., 1982; Lerner and Fitzpatrick, 1950). 3 The assay should be performed in phosphate buffer at neutral pH and low ionic strength, because l-dopachrome stability is lower in other conditions. 4 Dct prevents the accumulation of l-dopachrome, leading to an underestimation of the dopa oxidase activity (Valverde et al., 1993).
ENZYMOLOGY OF MELANIN FORMATION
A modification of this assay (Winder and Harris, 1991) with improved sensitivity is based on the trapping of l-dopaquinone with the Besthorn’s hydrazone (MBTH, 3-methyl-2-benzothiazolinone hydrazone) (Pifferi and Baldassari, 1973) to form a dark pink pigment with maximal absorption at 500 nm (Fig. 14.5). The most important problem of this assay is the low solubility of MBTH and the relative efficiency of this hydrazone to capture l-dopaquinone, compared with other possible reactions such as the formation of thiol conjugates. Two HPLC procedures have also been used for dopa oxidase activity measurements. The first is based on the determination of l-dopa consumption and the appearance of dopachrome and other indoles at 280 nm (Tsukamoto et al., 1992a). The second is based on the trapping of dopaquinone by l-cysteine with the identification of formed cysteinyldopas by electrometric detection with an Ag/AgCl electrode (Agrup et al., 1983; Wittbjer et al., 1989). This last procedure was used to estimate the tyrosinase activity in human hair bulbs (Townsend et al., 1986) and in the serum of patients with malignant melanoma (Sonesson et al., 1995). Finally, the dopa oxidase activity of tyrosinase was assayed by a radiometric method using 2,5,6-[3H]-dopa as substrate (Pomerantz, 1976), and measuring tritium release from position 6 after dopaquinone cyclization (Fig. 14.5). This assay was rarely used, and we believe that the substrate is no longer available. Alternatively, the dopa oxidase activity can also be determined by the production of acid-insoluble products from l-[3-14C]-dopa (Aroca et al., 1992, 1993), although in this case, the likely effect of the Tyrps on the rate of product formation should be considered. Concerning DHICA oxidase activity, a spectrophotometric assay related to the MBTH method for dopa oxidase activity has been designed (Jiménez-Cervantes et al., 1994; Kobayashi et al., 1994). DHICA is used as substrate, and its oxidation product, IQCA, is trapped by MBTH, leading to a conjugate with maximal absorption around 490 nm. In mouse melanocyte extracts, the activity measured can be assigned to Tyrp1, as interference from tyrosinase is unlikely, because murine tyrosinase does not use DHICA as substrate (Olivares et al., 2001). The interpretation of the results may be more complex for human melanocytes because DHICA oxidase activity has been demonstrated for human tyrosinase, but not yet for TYRP1. A spectrophotometric method is also available for the DHI oxidase activity of tyrosinase (Körner and Pawelek, 1982), based on the measurement of melanochrome appearance from DHI at 540 nm (Miranda et al., 1985). Here, spontaneous DHI oxidation causes a high background. In any case, DHI/DHICA oxidase is better determined by HPLC methods. These methods have been designed to follow substrate disappearance after appropriate incubation times. For DHI, 1 h at 37∞C, pH 6.8 is appropriate (Kobayashi et al., 1994; Tsukamoto, 1992a). For DHICA, incubation times can be prolonged up to 24 h because of the greater stability of this indole. Control reaction mixtures should always be performed to subtract the rate of spontaneous auto-oxidation.
Methods for the Measurement of Dopachrome Tautomerase Activity The easiest method for monitoring the dopachrome tautomerase activity of Tyrp2/Dct is the spectrophotometric recording of l-dopachrome decoloration at 475 nm (Aroca et al., 1990a, b; Barber et al., 1984; Körner and Pawelek, 1980; Pawelek, 1990; Pawelek et al., 1980). Two important points should be considered concerning this assay: 1 Preparation of the substrate. l-dopachrome is not stable, and it should be prepared in situ. This is performed by rapid chemical oxidation of l-dopa. Three different agents have been used for this purpose: potassium ferricyanide (Wakamatsu and Ito, 1988), silver oxide (Barber et al., 1984; Körner and Pawelek, 1980; Leonard et al., 1988; Palumbo et al., 1987, 1991; Pawelek et al., 1980), and sodium periodate (Aroca et al., 1990a, b; Graham and Jeffs, 1977; Wilczek and Mishima, 1993). By far, sodium periodate is preferred because of the rapid and stoichiometric oxidation of l-dopa (molar ratio l-dopa:periodate 1:2). Thus, l-dopachrome solutions devoid of l-dopa can be easily obtained. In the other cases, l-dopa is not completely oxidized, and a significant proportion remains that can interfere with the Dct assay in crude extracts. 2 Spontaneous l-dopachrome decoloration. l-Dopachrome undergoes a slow but significant decarboxylation leading to DHI (Fig. 14.1). This reaction causes a background that should be subtracted from enzymatic measurements. The rate of this spontaneous reaction is highly dependent on the pH, ionic strength, and the presence of traces of metal ions (Palumbo et al., 1987). Recommended conditions include 10 mM phosphate buffer, pH 6.0 and 0.1 mM EDTA (Aroca et al., 1990b). As an alternative to the A475 decrease, another spectrophotometric assay for Dct was described (Aroca et al., 1990b). It takes advantage of the different absorption of dopachrome, DHI, and DHICA in the UVA region. Around 310 nm, the order of molar absorption coefficients is DHICA > dopachrome > DHI. Thus, at this wavelength, dopachrome decarboxylation leads to absorbance decreases, whereas Dct-catalyzed transformation of l-dopachrome into DHICA leads to absorbance increases. As for the oxidase activities, HPLC assays are more sensitive and specific for the determination of Dct activity. HPLC permits the simultaneous determination of l-dopachrome disappearance and DHI and DHICA appearance, although only the DHICA formed is proportional to the enzymatic activity. The original chromatographic conditions were reported by Palumbo et al. (1987, 1991), and involved an isocratic separation with 0.2 M sodium borate buffer, pH 2.5, containing 25% methanol. Slight modifications were introduced to improve the resolution of indole separation (Aroca et al., 1993; Leonard et al., 1988; Pawelek, 1990; Solano et al., 1994; Tsukamoto et al., 1992a; Wilczek and Mishima, 1993; Winder et al., 1993a, b). As described for the spectrophotometric Dct assay, periodate is preferred to silver oxide to prepare the l-dopachrome substrate by stoichiometric oxida275
CHAPTER 14
tion of l-dopa, but extra caution should be taken in this case as the iodate subproduct of the oxidation is still oxidant at very acidic pHs, and the indoles formed could be destroyed. Thus, periodate oxidation should be accompanied by mobile phases with pHs higher than 4 (Solano et al., 1994; Wilczek and Mishima, 1993).
Global Melanogenic Activity Measurements The overall melanogenic activity can be estimated by methods measuring melanin formation from l-tyrosine. Although the assay was first introduced (and is still often considered) as a tyrosinase assay, it should be borne in mind that it actually reflects the activity of the total pathway, including the contribution of the Tyrps, because the final product is determined. The assay was introduced by Lerner (1955) and then improved by Chen and Chavin (1965) and Hearing and Ekel (1976). Modifications to facilitate the assay in small samples were described by Hearing (1987) and Jara et al. (1988b). The assay is based on the incorporation of uniformly labeled tyrosine, l[U14C]-Tyr, into acid-insoluble melanin, which is absorbed onto a filter paper, washed, and counted. Owing to the low spontaneous oxidation of l-tyrosine and the insolubility of melanin, the background is low. In addition to the complexity in the interpretation of the results due to the contribution of more than one enzyme activity, another drawback of the method is related to the fate of the 14C-carboxyl group of radiolabeled tyrosine. The release of this group as 14CO2 is a potential hazard, and its rate and extent is dependent on the Dct activity present in the sample. This enzyme can accelerate or decrease the incorporation of indole units into melanin, depending on the incubation time (Aroca et al., 1990a, 1992). Attempts to improve the sensitivity of the method (Jara et al., 1988c) and to extend it to pheomelanin formation (Aroca et al., 1989) have been published.
Activity Stains in Electrophoresis Gels Taking advantage of the high resistance of tyrosinase to denaturing agents such as urea or SDS, and of the specificity of the enzyme, SDS-PAGE followed by activity stain can be used to visualize and compare tyrosinase activity in complex mixtures such as crude melanocyte extracts. The discontinuous system of Laemmli (1970) yields adequate separations. Bearing in mind that an active conformation of the melanogenic proteins must be preserved throughout the procedure, care should be taken to avoid denaturing conditions. SDS can be added to the sample to final concentrations as high as 3%, but b-mercaptoethanol even at low concentrations, or heating, should be avoided. Basically, those conditions were used in the characterization of tyrosinase isoforms (Burnett, 1971; Hearing et al., 1981; Miyazaki and Ohtaki, 1975; Quevedo et al., 1975), as well as in the establishment of the catalytic potentials of the enzyme and its distinction from peroxidase (White and Hu, 1977). This technique has been exploited to show that, in mouse melanoma cells, Tyrp1 behaves as a tyrosinase isoenzyme with lower specific activity for l-tyrosine, l-dopa, and DHI but higher activity for DHICA 276
(Jiménez-Cervantes et al., 1993a, 1994; Kobayashi et al., 1994). After the proteins in the sample under study are resolved by electrophoresis, the gels can be stained by several procedures exploiting the tyrosine hydroxylase or dopa oxidase activities of tyrosinase. Staining for tyrosine hydroxylase activity is difficult because of the low turnover of tyrosinase on l-tyrosine. However, the use of l-[U-14C]-tyrosine as substrate and the fluorographic detection of the radioactive melanin formed is sensitive enough to stain tyrosinase activity in extracts from mouse melanoma cells (Jiménez et al., 1991; Tsukamoto et al., 1992b). Nevertheless, the more frequent activity stain procedures involve incubation of the gels with l-dopa. As the pH of the resolving gels is basic, care should be taken to equilibrate the gels at pH around 6.5 before addition of l-dopa to avoid its rapid oxidation. The stain is reminiscent of the histochemical procedure developed by Bloch (1927) to detect tyrosinase in human skin specimens. Direct staining with ldopa usually requires long incubation times and displays limited sensitivity. Therefore, attempts were made to design specific methods with higher sensitivity and reduced incubation times. Fluorographic stain involving 14C-labeled l-dopa has been used successfully (Jiménez et al., 1991; JiménezCervantes et al., 1993b; Tsukamoto et al., 1992b). A colorimetric procedure based on the formation of colored adducts between dopaquinone and MBTH has also been reported (Jiménez-Cervantes et al., 1993b; Nellaiappan and Vinayagam, 1986). A reddish band is rapidly formed, with sensitivity comparable to the fluorographic procedures. As opposed to tyrosinase and Tyrp1, Dct is very sensitive to SDS (Aroca et al., 1990a). This problem has prevented the general use of SDS-PAGE for the study of mammalian Dct, although the technique has been used to identify isoenzymic forms of a related protein from insect hemolymph (Nellaiappan et al., 1994a, b; Sugumaran and Semensi, 1991). In our hands, the assay cannot be employed to stain authentic mammalian Dct on account of the lower activity and stability and the difference in the product formed.
Perspectives In spite of the cloning and characterization of tyrosinase and the Tyrps, a number of important questions concerning the enzymology of melanogenesis are still unanswered. The pheomelanogenic pathway probably involves still unknown enzymatic reactions. In its present form, it may not be complete in a situation reminiscent of the eumelanogenesis a decade ago. On the other hand, pheomelanin synthesis seems to be the default melanogenic pathway, occurring when tyrosinase activity is low and free thiol compounds are available within the melanosome. The regulatory factors responsible for the switch from pheo- to eumelanogenesis and controlling the size of the thiol pool are also poorly known. Concerning eumelanogenesis, the involvement of the Tyrps is now firmly established, but the actual basis for the relationship between
ENZYMOLOGY OF MELANIN FORMATION
Tyrps expression and eumelanin synthesis remains obscure. This is mainly due to uncertainties as to the actual role of Tyrp1, which may be more complex than the catalysis of DHICA oxidation. As a corollary, and as stated by J. Pawelek and A. K. Chakraborty in the previous edition of this book, we are still not able to explain properly, at the molecular level, the pigmentation phenotype associated with the slaty and brown mutations. Moreover, most of our knowledge of the enzymatic action of tyrosinase and the Tyrps comes from studies performed with purified preparations or under conditions in which noncovalent protein–protein interactions may be weakened. As there is good evidence that a melanogenic complex is formed in vivo, the question of subtle changes in the catalytic properties of individual proteins within the complex is still open. On the other hand, the renewed interest in the role of pH as a dynamic regulatory factor in melanogenesis should lead to a better understanding of its effects, not only on the rate of the enzymatic steps, but also as related to the polymerization of melanogenic intermediates. Another aspect that should yield new information is the role of structural melanosomal proteins such as silver in melanin deposition and polymerization of monomers. New developments in the role of the p and underwhite transporters are also anticipated. The proteomic analysis of the melanosome in its different maturation, and hence metabolic, stages is still just beginning (Basrur et al., 2003). We can expect that this powerful methodology will identify new melanogenic activities and/or effectors of already characterized enzymes. Concerning developments in the enzymatic analysis of melanogenesis, the progress since the first edition has been modest, which leaves room for further refinement of the currently employed methods to increase their sensitivity and specificity. This may need the design of specific substrates or inhibitors for Tyrp1 and tyrosinase that might allow for the specific determination of both enzymes in crude extracts. Progress in the development of sensitive and reliable assays for the last steps of the melanogenic pathway, allowing for an accurate estimation of the rate of polymerization of indolic intermediates, is needed in order to approach the identification of factors controlling the distal steps of melanogenesis. This is true for eumelanogenesis and, more importantly, for pheomelanogenesis. Here, the design of those assays seems to be a necessary prerequisite for the discovery of new pheomelanogenic enzymes.
Acknowledgments This chapter is an update of Chapters 28 and 33 in the first edition of this book, published some years ago. We are therefore indebted to the authors of the former Chapter 28, J. Pawelek and A. K. Chakraborty, especially to J. Pawelek, who was a pioneer in so many aspects of the enzymatic regulation of melanogenesis. The authors are also grateful to all graduate students who performed research on the role of tyrosinase and its related proteins in melanogenesis during approxi-
mately the last 20 years. We thank Dr Santiago Delgado for helpful suggestions concerning the mechanism of dopachrome tautomerization and for drawing Figures 14.2 and 14.3. We are also grateful for the continuous financial support of the Spanish government. Work in the authors’ laboratories is currently supported by grants BIO2001-140 and SAF2004-3411.
References Adachi, K., and K. M. Halprin. A sensitive fluorometric assay method for mammalian tyrosinase. Biochem. Biophys. Res. Commun. 26:241–246, 1967. Ancans J., and A. J. Thody. Activation of melanogenesis by vacuolar type(H+)-ATPase inhibitors in amelanotic, tyrosinase positive human and mouse melanoma cells. FEBS Lett., 478:57–60, 2000. Ancans J., D. J. Tobin, M. J. Hoogduijn, N. P. Smit, K. Wakamatsu, and A. J. Thody. Melanosomal pH controls rate of melanogenesis, eumelanin/phaeomelanin ratio and melanosome maturation in melanocytes and melanoma cells. Exp. Cell Res. 268:26–35, 2001. Agrup, G., B. Falck, B. M. Kennedy, A. M. Rosengren, and E. Rosengren. Formation of cysteinyldopa from glutathionyldopa in melanoma. Acta Derm. Venereol. (Stockh.) 55:1–3, 1975. Agrup, G., L. E. Edholm, H. Rorsman, and E. Rosengren. Diastereomers of 5-S-cysteinyldopa. Acta Derm. Venereol. (Stockh.) 63:59–61, 1983. Aroca, P., J. R. Jara, A. Blazquez, J. C. García-Borrón, and F. Solano. A reexamination of the melanin formation assay of tyrosinase and an extension to estimate phaeomelanin formation. J. Biochem. Biophys. Methods 19:327–338, 1989. Aroca, P., J. C. García-Borrón, F. Solano, and J. A. Lozano. Regulation of mammalian melanogenesis I: Partial purification and characterization of a dopachrome converting factor, dopachrome tautomerase. Biochim. Biophys. Acta 1035:266–275, 1990a. Aroca, P., F. Solano, J. C. García-Borrón, and J. A. Lozano. A new spectrophotometric assay for dopachrome tautomerase. J. Biochem. Biophys. Methods 21:35–46, 1990b. Aroca, P., F. Solano, J. C. García-Borrón, and J. A. Lozano. Specificity of dopachrome tautomerase and inhibition by carboxylated indoles. Considerations of the enzyme active site. Biochem. J. 227:393–397, 1991. Aroca, P., F. Solano, C. Salinas, J. C. García-Borrón, and J. A. Lozano. Regulation of the final phase of mammalian melanogenesis. The role of dopachrome tautomerase and the ratio between 5,6dihydroxyindole-2-carboxylic acid/5,6-dihydroxyindole. Eur. J. Biochem. 208:155–163, 1992. Aroca, P., K. Urabe, T. Kobayashi, K. Tsukamoto, and V. J. Hearing. Melanin biosynthesis patterns following hormonal stimulation. J. Biol. Chem. 268:25650–25655, 1993. Auböck, J., D. Köfler, M. Sifter, and P. Fritsch. Application of the tyrosinase assay to normal melanocytes in culture. Br. J. Dermatol. 109:413–419, 1983. Barber, J.I., D. Townsend, D. P. Olds, and R. A. King. Dopachrome oxidoreductase: A new enzyme in the pigment pathway. J. Invest. Dermatol. 83:145–149, 1984. Basrur, V., F. Yang, T. Kushimoto, Y. Higashimoto, K. Yasumoto, J. Valencia, J. Muller, W. D. Vieira, H. Satane, J. Shabanowitz, V. J. Hearing, and E. Appella. Proteomic analysis of early melanosomes: Identification of novel melanosomal proteins. J. Proteome Res. 2:69–79, 2003. Bernd, A., A. Ramirez-Bosca, S. Kippenberger, J. H. Martinez-Liarte, H. Holzmann, and F. Solano. On the level of dopachrome tautomerase activity in human melanocytes cultured in vitro. Melanoma Res. 4:287–291,1994. Berson, J. F., D. C. Harper, D. Tenza, G. Raposo, and M. S. Marks. Pmel17 initiates premelanosome morphogenesis within multivesicular bodies. Mol. Biol. Cell 12:3451–3464, 2001.
277
CHAPTER 14 Bhatnagar, V., S. Anjaiah, A. Puri, N. Puri, B. N. A. Darshanam, and A. Ramaiah. pH of melanosomes is acidic: Its physiological importance in the regulation of melanin biosynthesis. Arch. Biochem. Biophys. 307:183–192, 1993. Blagoeva, P. M. Aminoacids — precursors of melanin synthesis in hamster melanoma. J. Cancer Res. Clin. Oncol. 108:366–368, 1984. Bloch, B. Handbuch der Haut und Geschlechtdkrankeiten, J. Jadassohn (ed.). Berlin: Julius Springer, 1, 1927, pp. 434–451. Boissy, R. E., H. Zhao, W. S. Oetting, L. M. Austin, S. C. Wildenberg, Y. L. Boissy, Y. Zhao, R. A. Sturm,, V. J. Hearing, R. A. King, and J. J. Nordlund. Mutation in and lack of expression of tyrosinase related protein 1 (TRP1) in melanocytes from an individual with brown oculocutaneous albinism: a new subtype of albinism classified as OCA3. Am. J. Hum. Genet. 58:1145–1156, 1996. Boissy, R. E., C. Sakai, H. Zhao, T. Kobayashi, and V. J. Hearing. Human tyrosinase related protein-1 (TRP-1) does not function as a DHICA oxidase activity in contrast to murine TRP-1. Exp. Dermatol. 7:198–204, 1998a. Boissy, R. E., Y. Zhao, and W. A. Gahl. Altered protein localization in melanocytes from Hermansky–Pudlak syndrome: Support for the role of the HPS gene product in intracellular trafficking. Lab. Invest. 78:1037–1048, 1998b. Bourquelot, E., and G. Bertrand. Le bleuissement et le noircissement des champignons. C.R. Soc. Biol. 47:852–862, 1895. Brilliant, M. H. The mouse p (pink-eyed dilution) and human P genes, oculocutaneous albinism type 2 (OCA2), and melanosomal pH. Pigment Cell Res. 14:86–93, 2001. Burnett, J. B. The tyrosinases of mouse melanoma. Isolation and molecular properties. J. Biol. Chem. 246:3079–3091, 1971. Cascante, M., A. Sorribas, and E. I. Canela. Enzyme-enzyme interactions and metabolite channelling: alternative mechanisms and their evolutionary significance. Biochem. J. 298:313–320, 1994. Chakraborty, C., M. Ichihashi, M. Ueda, M. Mishima, and D. P. Chakraborty. Effects of tryptophan on melanogenesis in B16-F10 melanoma cells in culture. IRCS J. Med. Sci. 14:463–464, 1986. Chakraborty, A. K., S. J. Orlow, and J. M. Pawelek. Evidence that DOPAchrome tautomerase is a ferrous iron-binding glycoprotein. FEBS Lett. 302:126–128, 1992. Chakraborty A. K, J. T. Platt, K. K. Kim, B. S. Kwon, D. C. Bennett, and J. M. Pawelek. Polymerization of 5,6-dihydroxyindole-2carboxylic acid to melanin by the pmel 17/silver locus protein. Eur. J. Biochem. 236:180–188, 1996. Chaubal, V. A., S. S. Nair, S. Ito, K. Wakamatsu, and M. V. Mojamdar. g-Glutamyl transpeptidase and its role in melanogenesis: redox reactions and regulation of tyrosinase. Pigment Cell Res. 15:420–425, 2002. Chen, Y. M., and W. Chavin. Radiometric assay of tyrosinase and theoretical considerations of melanin formation. Anal. Biochem. 13:234–258, 1965. Cooksey, C. J., P. J. Garratt, E. J. Land, S. Pavel, C. A. Ramsden, P. A. Riley, and N. P. M. Smit. Evidence of the indirect formation of the catecholic intermediate substrate responsible for the autoactivation kinetics of tyrosinase. J. Biol. Chem. 272:26226–26235, 1997. Costin, G. E., J. C. Valencia, W. D. Vieira, M. L. Lamoreaux, and V. J. Hearing. Tyrosinase processing and intracellular trafficking is disrupted in mouse primary melanocytes carrying the uw mutation: a model for oculocutaneous albinism (OCA) type 4. J. Cell Sci. 116:3203–3212, 2003. Dawson, C. R., and R. J. Magee. Plant tyrosinase (polyphenol oxidase). In: Methods in Enzymology 2. New York: Academic Press, 1955, pp. 817–827. Delgado-Vargas, F., A. R. Jiménez, and O. Paredes-López. Natural pigments: carotenoids, anthocianins and betalains: characteristics,
278
biosynthesis, processing and stability. Crit. Rev. Food Sci. Nutr. 2000:40, 173–289. Del-Marmol, V., S. Ito, I. J. Jackson, J. Vachtenheim, P. Berr, G. Ghanem, R. Morandini, K. Wakamatsu, and G. Huez. TRP-1 expression correlates with eumelanogenesis in human pigment cells in culture. FEBS Lett. 327:307–310, 1993. Devi, C. C., C. Tripathi, and A. Ramaiah. pH-dependent interconvertible allosteric forms of murine melanoma tyrosinase: physiological implications. Eur. J. Biochem. 166:705–711, 1987. D’Ischia, M., A. Napolitano, and G. Prota. Peroxidase as an alternative to tyrosinase in the oxidative polymerization of 5,6dihydroxyindoles to melanin(s). Biochim. Biophys. Acta 1073:423–430, 1991. Donatien, P. D., and S. J. Orlow. Interaction of melanosomal proteins with melanin. Eur. J. Biochem. 232:159–164, 1995. Duckworth, H. W., and J. E. Coleman. Physicochemical and kinetic properties of mushroom tyrosinase. J. Biol. Chem. 245:1613–1619, 1970. El-Bayoumi, M. A., and E. Frieden. A spectrophotometric method for the determination of the catecholase activity of tyrosinase and some of its applications. J. Am. Chem. Soc. 79:4854–4858, 1957. Fenoll, L. G, J. N. Rodriguez-Lopez, F. García-Sevilla, J. Tudela, P. A. García-Ruiz, R.Varon, and F. García-Cánovas. Oxidation by mushroom tyrosinase of monophenols generating slighly unstable oquinones. Eur. J. Biochem. 267:5865–5878, 2000. Fuller, B. B., D. T. Spaulding, and D. R. Smith. Regulation of the catalytic activity of preexisting tyrosinase in black and Caucasian human melanocyte cell cultures. Exp. Cell Res. 262:197–208, 2001. Furumura, M., F. Solano, N. Matsunaga, C. Sakai, R. A. Spritz, and V. J. Hearing. Metal ligand binding specificities of the tyrosinase related proteins. Biochem. Biophys. Res. Commun. 242:579–585, 1998. García-Borrón, J. C., and F. Solano. Molecular anatomy of tyrosinase and its related proteins: beyond the histidine-bound metal catalytic center. Pigment Cell Res. 15:162–173, 2002. García-Cánovas, F., F. García-Carmona, J. Vera, J. L. Iborra, and J. A. Lozano. The role of pH in the melanin biosynthesis pathway. J. Biol. Chem. 257:8738–8744, 1982. Graham, D. G., and P. W. Jeffs. The role of 2,4,5-trihydroxyphenylalanine in melanin biosynthesis. J. Biol. Chem. 252:5729–5734, 1977. Halaban R., and G. E. Moellmann. Murine and human b locus pigmentation genes encode a glycoprotein (gp75) with catalase activity. Proc. Natl. Acad. Sci. USA 87:4809–4813, 1990. Halaban, R., S. Svedine, E. Cheng, Y. Smicun, R. Aron, and D. Hebert. Endoplasmic reticulum retention is a common defect associated with tyrosinase-negative albinism. Proc. Natl. Acad. Sci. USA 97:5889–5894, 2000. Hearing, V. J. Mammalian monophenol monooxygenase (Tyrosinase): purification, properties and reactions catalyzed. Methods in Enzymology 142. Academic Press, NY. 1987, pp. 154–169. Hearing, V. J., and T. M. Ekel. Mammalian tyrosinase. A comparison of tyrosine hydroxylation and melanin formation. Biochem. J. 157:549–557, 1976. Hearing, V. J., and K. Tsukamoto. Enzymatic control of pigmentation in mammals. FASEB J. 5:2902–2909, 1991. Hearing, V. J., T. M. Ekel, and P. M. Montague. Mammalian tyrosinase: isozymic forms of the enzyme. Int. J. Biochem. 13:99–103, 1981. Himmelwright, R. S., N. C. Eickman, C. D. Lubien, K. Lerch, and E. I. Solomon. Chemical and spectroscopic studies of the binuclear copper active site of Neurospora tyrosinase: comparison to hemocyanins. J. Am. Chem. Soc. 102:7339–7344, 1980. Horowitz, N. H., M. Fling, and G. Horn. Tyrosinase (Neurospora crassa). In: Methods in Enzymology, 17A. New York: Academic Press, 1970, pp. 615–621.
ENZYMOLOGY OF MELANIN FORMATION Huber, M., and K. Lerch. Identification of two histidines as copper ligands in Streptomyces glaucescens tyrosinase. Biochemistry 27: 5610–5615, 1988. Husain, I., E. Vijayan, A. Ramaiah, J. S. Pasricha, and N. C. Madan. Demonstration of tyrosinase in the vitiligo skin of human beings by a sensitive fluorometric method as well as by 14C(U)-L-tyrosine incorporation into melanin. J. Invest. Dermatol. 78:243–252, 1982. International Union of Chemistry. Enzyme Nomenclature Supplement. Recommendations of the Nomenclature Committee of the International Union of Biochemistry. Florida: Academic Press, 1999, p. 505. Jackson, I. J. Evolution and expression of tyrosinase-related proteins. Pigment Cell Res. 7:241–242, 1994. Jackson, I. J., D. M. Chambers, K. Tsukamoto, N. G. Copeland, D. J. Gilbert, N. A. Jenkins, and V. J. Hearing. A second tyrosinaserelated protein, TRP-2, maps to and is mutated at the mouse slaty locus. EMBO J. 11:527–535, 1992. Jara, J. R., P. Aroca, F. Solano, J. H. Martínez, and J. A. Lozano. The role of sulfhydryl compounds in mammalian melanogenesis: the effect of cysteine and glutathione upon tyrosinase and the intermediates of the pathway. Biochim. Biophys. Acta 967:296–303, 1988a. Jara, J. R., F. Solano, and J. A. Lozano. Assays for mammalian tyrosinase: A comparative study. Pigment Cell Res. 1:332–339, 1988b. Jara, J. R., F. Solano, and J. A. Lozano. Improving the melanin formation assay for mammalian tyrosinase. ESPCR Pigment Cell Bull. 4:6–7, 1988c. Jergil, B., Ch. Lindbladh, H. Rorsman, and E. Rosengren. Dopa oxidation and tyrosine oxygenation by human melanoma tyrosinase. Acta Derm. Venereol. (Stockh.) 63:468–475, 1983. Jiménez, M., K. Tsukamoto, and V. J. Hearing. Tyrosinases from two different loci are expressed by normal and transformed melanocytes. J. Biol. Chem. 266:1147–1156, 1991. Jiménez-Cervantes, C., J. C. García-Borrón, P. Valverde, F. Solano, and J. A. Lozano. Tyrosinase isoenzymes in mammalian melanocytes. 1. Biochemical characterization of two melanosomal tyrosinases from B16 mouse melanoma. Eur. J. Biochem. 217:549–556, 1993a. Jiménez-Cervantes, C., P. Valverde, J. C. García-Borrón, F. Solano, and J. A. Lozano. Improved tyrosinase activity stains in polyacrylamide electrophoresis gels. Pigment Cell Res. 6:394–399, 1993b. Jiménez-Cervantes, C., F. Solano, T. Kobayashi, K. Urabe, V. J. Hearing, J. A. Lozano, and J. C. García-Borrón. A new enzymatic function in the melanogenic pathway. J. Biol. Chem. 269: 17993–18001, 1994. Jiménez-Cervantes, C., M. Martinez-Esparza, F. Solano, J. A. Lozano, and J. C. García-Borrón. Molecular interactions within the melanogenic complex: formation of heterodimers of tyrosinase and TRP1 from B16 mouse melanoma. Biochem. Biophys. Res. Commun. 253:761–767, 1998. Jiménez-Cervantes, C., M. Martínez-Esparza, C. Pérez, N. Daum, F. Solano, and J. C. García-Borrón. Inhibition of melanogenesis in response to oxidative stress. Transient downregulation of melanocyte differentiation markers and possible involvement of microphthalmia transcription factor. J. Cell Sci. 114:2335–2341, 2001. King, R. A., and C. J. Witkop. Hairbulb tyrosinase activity in oculocutaneous albinism. Nature 263:69–71, 1976. Klabunde, T., C. Eicken, J. C. Sacchettini, and B. Krebs. Crystal structure of a plant catechol oxidase containing a dicopper center. Nature Struct. Biol. 5:1084–1090, 1998. Kobayashi, T., K. Urabe, A. Winder, C. Jiménez-Cervantes, G. Imokawa, T. Brewington, F. Solano, J. C. García-Borrón, and V. J. Hearing. Tyrosinase related protein 1 (TRP1) functions as a DHICA oxidase in melanin biosynthesis. EMBO J. 13:5818–5825, 1994. Kobayashi, T., G. Imokawa, D. C. Bennett, and V. J. Hearing. Tyrosi-
nase stabilization by Tyrp1 (the brown locus protein). J. Biol. Chem. 273:31801–31805, 1998. Körner, A. M., and J. Pawelek. Dopachrome conversion: A possible control point in melanin biosynthesis. J. Invest. Dermatol. 75:192–195, 1980. Körner, A. M., and J. M. Pawelek. Mammalian tyrosinase catalyzes three reactions in the biosynthesis of melanin. Science 217:1163–1165, 1982. Kushimoto, T., V. Basrur, J. Valencia, J. Matsunaga, W. Vieira, V. J. Ferrans, J. Muller, E. Appella, and V. J. Hearing. A model for melanosome biogenesis based on the purification and analysis of early melanosomes. Proc. Natl. Acad. Sci. USA 98:10698–10703, 2001. Kwon, B. S., C. D. Chintamaneni, C. A. Kozak, N. G. Copeland, D. J. Gilbert, N. A. Jenkins, D. E. Barton, U. Francke, Y. Kobayashi, and K. K. Kim. A melanocyte-specific gene, Pmel 17, maps near the silver coat color locus on mouse chromosome 10 and is a syntenic region on human chromosome 12. Proc. Natl. Acad. Sci. USA 88:9228–9232, 1991. Kwon, B. S., K. K. Kim, R. Halaban, and R. T. Pickard. Characterization of mouse pmel 17 gene and silver locus. Pigment Cell Res. 7:394–397, 1994. Laemmli, U. K. Cleavage of structural proteins during the assembly of the head of bacteriophage T4. Nature 277:680–682, 1970. Lee, Z., L. Hou, G. Moellmann, E. Kublinska, K. Antol, M. Fraser, R. Halaban, and B. S. Kwon. Characterization and subcellular loalization of human Pmel17/silver, a 100 kDa (pre)melanosomal membrane protein associated with 5,6-DHICA converting activity. J. Invest. Dermatol. 106:605–610, 1996. Leonard, L. J., D. Townsend, and R. A. King. Function of dopachrome oxidoreductase and metal ions in dopachrome conversion in the eumelanin pathway. Biochemistry 27:6156–6159, 1988. Lerch, K. Neurospora tyrosinase: structural, spectroscopic and catalytic properties. Mol. Cell Biochem. 52:125–138, 1983. Lerner, A. B. Mammalian tyrosinase. In: Methods in Enzymology 2. New York: Academic Press, 1955, pp. 827–831. Lerner, A. B., and T. B. Fitzpatrick. Biochemistry of melanin formation. Physiol. Rev. 30:91–126, 1950. Lerner, A. B., T. B. Fitzpatrick, E. Calkins, and W. H. Summerson. Mammalian tyrosinase: preparation and properties. J. Biol. Chem. 178:185–195, 1949. Manga, P., K. Sato, L. Ye, F. Beermann, M. L. Lamoreux, and S. J. Orlow. Mutational analysis of the modulation of tyrosinase by tyrosinase-related proteins 1 and 2 in vitro. Pigment Cell Res. 13:364–374, 2000. Manga, P., R. E. Boissy, S. Pifko-Hirst, B. K. Zhou, and S. J. Orlow. Mislocalization of melanosomal proteins in melanocytes from mice with oculocutaneous albinism type 2. Exp. Eye Res. 72:695–710, 2001. Martínez-Esparza, M., C. Jiménez-Cervantes, J. C. García-Borrón, J. A. Lozano, V. del Marmol, G. Ghanem, and F. Solano. Comparisons of TRPs from murine and human malignant melanocytes. Pigment Cell Res. 10:229–235, 1997. Martínez-Esparza, M., C. Jiménez-Cervantes, D. C. Bennett, J. A. Lozano, F. Solano, and J. C. García-Borrón. The murine silver locus: coding and expression of a single transcript truncated by the silver mutation. Mamm. Genome 10:1168–1171, 1999. Martínez-Esparza, M., C. Jiménez-Cervantes, F. Solano, J. A. Lozano, and J. C. García-Borrón. Regulation of the murine silver locus product (gp87) by the hypopigmenting cytokines TGF-bı and TNFa. Pigment Cell Res. 13:120–126, 2000. Mason, H. S. The chemistry of melanin. III. Mechanism of the oxidation of dihydroxyphenylalanine by tyrosinase. J. Biol. Chem. 172:83–99, 1948. Matsunaga, J., D. Sinha, L. Pannell, C. Santis, F. Solano, G. Wistow, and V. J. Hearing. Enzyme activity of macrophage migration inhibitory factor (MIF) towards oxidized catecholamines. J. Biol. Chem. 274:3268–3271, 1999.
279
CHAPTER 14 Miranda, M., D. Botti, A. Bonfigli, and A. Arcadi. 5,6-dihydroxyindole oxidation by mammalian, mushroom and amphibian tyrosinase preparations. Biochim. Biophys. Acta 841:159–165, 1985. Miyazaki, K., and N. Ohtaki. Tyrosinase as glycoprotein. Arch. Derm. Forsch. 252:211–216, 1975. Mojamdar, M., M. Ichihashi, and Y. Mishima. g-glutamyltranspeptidase, tyrosinase and 5-S-cysteinyldopa production in melanoma cells. J. Invest. Dermatol. 81:119–121, 1983. Nakamura, M., T. Nakayima, Y. Ohba, S. Yamauchi, B. R. Lee, and S. Ichishima. Identification of copper ligands in Aspergillus oryzae tyrosinase by site-directed mutagenesis. Biochem. J. 350:537–545, 2000. Nellaiappan, K., and A. Vinayagam. A rapid method for the detection of tyrosinase activity in electrophoresis. Stain Technol. 61: 269–272, 1986. Nellaiappan, K., G. Nicklas, and M. Sugumaran. The ontogeny of dopachrome isomerase patterns in the tobacco hornworm Manduca sexta. Biochem. Biophys. Res. Commun. 200:1072–1078:1994a. Nellaiappan, K., G. Nicklas, and M. Sugumaran. Detection of dopachrome isomerase activity on gels. Anal. Biochem. 220:122–128, 1994b. Nelson, R. M., and H. S. Mason. Tyrosinase (mushroom). In: Methods in Enzymology 17A. New York: Academic Press, 1970, pp. 626–632. Newton, J. M., O. Cohen-Barak, N. Hagiwara, G. M. Gardner, M. T. Davidson, R. A. King, and M. H. Brilliant. Mutations in the human orthologue of the mouse underwhite gene (uw) underlie a new form of oculocutaneous albinism (OCA) type 4. J. Cell Sci. 116:3203–3212, 2003. Odh, G., A. Hindemith, A. M. Rosengren, E. Rosengren, and H. Rorsman. Isolation of a new tautomerase monitored by the conversion of d-dopachrome to 5,6-dihydroxyindole. Biochem. Biophys. Res. Commun. 197:619–624, 1993. Okun, M. R., L. M. Edelstein, N. Or, G. Hamada, and B. Donnellan. The role of peroxidase vs. the role of tyrosinase in enzymatic conversion of tyrosine to melanin in melanocytes, mast cells and eosinophils. J. Invest. Dermatol. 55:1–12, 1970. Oikawa, A., M. Nakayasu, M. Nohara, and T. T. Tchen. Fate of l-[3,5-3H]Tyrosine in cell-free extracts and tissue cultures of melanoma cells: a new assay method for tyrosinase in living cells. Arch. Biochem. Biophys. 148:548–557, 1972. Olivares, C., C. Jiménez-Cervantes, J. A. Lozano, F. Solano, and J. C. García-Borrón. The 5,6-dihydroxyindole-2-carboxylic acid (DHICA) oxidase activity of human tyrosinase. Biochem. J. 354:131–139, 2001. Olivares, C., J. C. García-Borrón, and F. Solano. Identification of active site residues involved in metal cofactor binding and stereospecific substrate recognition in mammalian tyrosinase. Implications to the catalytic cycle. Biochemistry 41: 679–686, 2002. Olivares, C., F. Solano, and J. C. García-Borrón. Conformationdependent post-translational glycosylation of tyrosinase. Requirement of a specific interaction involving the CuB metal binding site. J. Biol. Chem. 278:15735–15743, 2003. Orlow, S. J., P. O. Osber, and J. M. Pawelek. Synthesis and characterization of melanins from dihydroxyindole-2-carboxylic acid and dihydroxyindole. Pigment Cell Res. 5:113–121, 1992. Orlow, S. J., R. E. Boissy, D. J. Moran, and S. Pifko-Hirst. Subcellular distribution of tyrosinase and tyrosinase-related protein-1: Implications for melanosomal biogenesis. J. Invest. Dermatol. 100:55–64, 1993a. Orlow, S. J., M. L. Lamoreux, S. Pifko-Hirst, and B. K. Zhou. Pathogenesis of the platinum (cp) mutation, a model for oculocutaneous albinism. J. Invest. Dermatol. 101:137–140, 1993b. Orlow, S. J., B. K. Zhou, A. K. Chakraborty, M. Drucker, S. PifkoHirst, and J. M. Pawelek. High-molecular-weight forms of tyrosinase and the tyrosinase-related proteins: Evidence for a melanogenic complex. J. Invest. Dermatol. 103:196–201, 1994.
280
Palumbo, A., M. d’Ischia, G. Misuraca, and G. Prota. Effect of metal ions on the rearrangement of dopachrome. Biochim. Biophys. Acta 925:203–209, 1987. Palumbo, A., F. Solano, G. Misuraca, P. Aroca, J. C. García-Borrón, J. A. Lozano, and G. Prota. Comparative action of dopachrome tautomerase and metal ions on the rearrangement of dopachrome. Biochim. Biophys. Acta 1115:1–5, 1991. Palumbo, A., M. d’Ischia, G. Misuraca, L. de Martino, and G. Prota. A new dopachrome-rearranging enzyme from the ejected ink of the cuttlefish Sepia officialis. Biochem. J. 299:839–844, 1994. Patel, R., M. Okun, L. Eldelstein, and D. Epstein. Biochemical studies of peroxidase-mediated oxidation of tyrosine to melanin: demonstration of hydroxylation of tyrosine by plant and human peroxidase. Biochem. J. 124:439–441, 1971. Pawelek, J. M. Dopachrome conversion factor functions as an isomerase. Biochem. Biophys. Res. Commun. 166:1328–1333, 1990. Pawelek, J. M. After dopachrome? Pigment Cell Res. 4:53–62, 1991. Pawelek, J. M., and A. B. Lerner. 5,6-dihydroxyindole is a melanin precursor showing potent cytotoxicity. Nature 276:627–628, 1978. Pawelek, J., A. Körner, A. Bergstrom, and J. Bologna. New regulators of melanin biosynthesis and the autodestruction of melanoma cells. Nature 286:617–619, 1980. Pifferi, P. G., and L. Baldassari. A spectrophotometric method for the determination of the catecholase activity of tyrosinase by Besthorn’s hydrazone. Anal. Biochem. 52:325–335, 1973. Pomerantz, S. Tyrosine hydroxylation catalyzed by mammalian tyrosinase: an improved method of assay. Biochem. Biophys. Res. Commun. 16:188–194, 1964. Pomerantz, S. The tyrosine hydroxylase activity of mammalian tyrosinase. J. Biol. Chem. 241:161–168, 1966. Pomerantz, S. A sensitive new assay for the oxidation of 3,4dihydroxyphenylalanine by tyrosinase. Anal. Biochem. 75:86–90, 1976. Pomerantz, S., and J. P. Li. Tyrosinases (hamster melanoma). In: Methods in Enzymology, 17A. New York: Academic Press, 1970, pp. 621–626. Pomerantz, S. H., and M. C. Warner. 3,4-dihydroxy-l-phenylalanine as the tyrosinase cofactor. J. Biol. Chem. 242:5308–5314, 1967. Prota, G. Progress in the chemistry of melanins and related metabolites. Med. Res. Reviews 4:525–556, 1988. Prota, G. Pheomelanins and trichochromes. In: Melanins and Melanogenesis. San Diego: Academic Press. 1992, pp. 134–512. Puri, N., J. M. Gardner, and M. H. Brilliant. Aberrant pH of melanosomes in pink-eyed dilution (p) mutant melanocytes. J. Invest. Dermatol. 115:607–613, 2000. Quevedo, W. C., T. J. Holstein, and T. C. Bienieki. Action of trypsin and detergents on tyrosinase of normal and malignant melanocytes (39116). Proc. Soc. Exp. Biol. Med. 150:735–740, 1975. Raper, H. S. The aerobic oxidases. Physiol. Rev. 8:245–282, 1928. Raposo, G., D. Tenza, D. M. Murphy, J. F. Berson, and M. S. Marks. Distinct protein sorting and localization to premelanosomes, melanosomes and lysosomes in pigmented melanocytic cells. J. Cell Biol. 152:809–824, 2001. Rodríguez-López, J. N., M. Bañon, F. Martínez-Ortíz, J. Tudela, M. Acosta, R. Varón, and F. García-Cánovas. Catalytic oxidation of 2,4,5-trihydroxyphenylalanine by tyrosinase: identification and evolution of intermediates. Biochim. Biophys. Acta 1160:221–228, 1992. Rorsman, H., A. M. Rosengren, and E. Rosengren. Determination of 5-S-cysteinyldopa in melanoma by a fluorimetric method. Yale J. Biol. Med. 46:516–519, 1983. Rundshagen, U., C. Zuhlke, S. Opitz, E. Schwinger, and B. KasmannKellner. Mutations in the MATP gene in five German patients affected by oculocutaneous albinism type 4. Hum. Mutat. 23:106–110, 2004. Russell, L. B., and W. L. Russell. A study of the physiological genet-
ENZYMOLOGY OF MELANIN FORMATION ics of coat color in the mouse by means of the dopa reaction in frozen sections of skin. Genetics 33:237–262, 1948. Salinas, C., J. C. Garcia-Borron, F. Solano, and J. A. Lozano. DOPAchrome tautomerase decreases the binding of indolic melanogenesis intermediates to proteins. Biochim. Biophys. Acta 1204:53–60, 1994. Sarangarajan, R., Y. Zhao, G. Babcock, J. Cornelius, M. L. Lamoreaux, and R. E. Boissy. Mutant alleles at the brown locus encoding tyrosinase-related-protein-1 (TRP-1) affect proliferation of mouse melanocytes in culture. Pigment Cell Res. 13:337–344, 2000. Shapiro, H. C., L. M. Edelstein, R. P. Patel, M. R. Okun, M. Blackburn, M. Snyder, T. Brennan, and G. Wilgram. Inability to demonstrate hydroxylation of tyrosinase by murine melanoma tyrosinase (L-DOPA oxidase), using the tritiated water assay technique. J. Invest. Dermatol. 72:191–193, 1979. Shibahara, S., Y. Tomita, T. Sakakura, C. Nager, B. Chaudhuri, and R. Muller. Cloning and expression of cDNA encoding mouse tyrosinase. Nucleic Acids Res. 14:2413–2427, 1986. Solano, F., J. H. Martínez-Liarte, C. Jiménez-Cervantes, J. C. GarcíaBorrón, and J. A. Lozano. Dopachrome tautomerase is a zinccontaining enzyme. Biochem. Biophys. Res. Commun. 204:1243– 1250, 1994. Solano, F., J. H. Martínez-Liarte, C. Jiménez-Cervantes, J. C. GarcíaBorrón, J. R. Jara and J. A. Lozano. Molecular mechanism for the catalysis by a new zinc-enzyme: dopachrome tautomerase. Biochem. J. 313: 447–453, 1996. Solano, F., M. Martínez-Esparza, C. Jiménez-Cervantes, S. P. Hill, J. A. Lozano, and J. C. García-Borrón. New insights on the structure of the murine silver locus and on the function of the silver protein. Pigment Cell Res. Suppl. 17th IPCC:118–124, 2000. Solomon, E. I., and M. D. Lowery. Electronic structure contributions to function in bioinorganic chemistry. Science 259:1575–1581, 1993. Sonesson, B., S. Eide, U. Ringborg, H. Rorsman, and E. Rosengren. Tyrosinase activity in the serum of patients with malignant melanoma. Melanoma Res. 5:113–116, 1995. Srere, P. A. Complexes of sequential metabolic enzymes. Annu. Rev. Biochem. 56:89–124, 1987. Sugumaran, M., and V. Semensi. Quinone methide as a new intermediate in eumelanin biosynthesis. J. Biol. Chem. 266:6073–6078, 1991. Sugumaran, M., K. Nellaiappan, T. Scott, and C. Amaratunga. Complex formation between mushroom tyrosinase and Manduca dopachrome isomerase. Pigment Cell Res. 8:180–186, 1995. Townsend, D., P. Guillery, and R. A. King. Optimized assay for mammalian tyrosinase (polyhydroxyl phenyloxidase). Anal. Biochem. 139:345–352, 1984. Townsend, D., D. P. Olds, and R. A. King. Dopa oxidase activity in human hairbulbs measured by high-performance liquid chromatography. J. Invest. Dermatol. 86:570–572, 1986. Tripathi, R. K., C. C. Devi, and A. Ramaiah. pH-dependent interconversion of two forms of tyrosinase in human skin. Biochem. J. 252:481–487, 1987. Tripathi, R. K., V. J. Hearing, K. Urabe, P. Aroca, and A. Spritz. Mutational mapping of the catalytic activities of human tyrosinase. J. Biol. Chem. 267:23707–23712, 1992. Tsai, H. F., M. H. Wheeler, Y. C. Chang, and K. J. Kwon-Chung. A
developmental regulated gene cluster involved in conidial pigment biosynthesis in Aspergillus fumigatus. J. Bacteriol. 181:6469–6477, 1999. Tsukamoto, K., I. A. Jackson, K. Urabe, P. M. Montague, and V. J. Hearing. A second tyrosinase-related protein, TRP-2, is a melanogenic enzyme termed DOPAchrome tautomerase. EMBO J. 11:519–526, 1992a. Tsukamoto, K., M. Jiménez, and V. J. Hearing. The nature of tyrosinase isoenzymes. Pigment Cell Res. Suppl. 2:84–89, 1992b. Ubemachi, Y. Papiliochrome, a new pigment group of butterfly. Zool. Sci. 2:163–174, 1985. Urabe, K., P. Aroca, K. Tsukamoto, D. Mascagna, A. Palumbo, G. Prota, and V. J. Hearing. The inherent cytotoxicity of melanin precursosr: a revision. Biochim. Biophys. Acta 1221:272–287, 1994. Valverde, P., C. Jiménez-Cervantes, C. Salinas, J. C. García-Borrón, F. Solano, and J. A. Lozano. Preparation of purified tyrosinase devoid of dopachrome tautomerase from mammalian melanocytes. Pigment Cell Res. 6:158–164, 1993. Wakamatsu, K., and S. Ito. Preparation of eumelanin-related metabolites 5,6-dihydroxyindole, 5,6-dihydroxyindole-2-carboxylic acid, and their O-methyl derivatives. Anal. Biochem. 170:335–340, 1988. White, R., and F. Hu. Characteristics of tyrosinase in B16 melanoma. J. Invest. Dermatol. 68:272–276, 1977. Wilczek, A., and Y. Mishima. Regulatory factors for polymerization of melanin monomers within coated vesicles and premelanosomes in melanoma cells. Melanoma Res. 3:255–262, 1993. Winder, A., and H. Harris. New assays for the tyrosine hydroxylase and dopa oxidase activities of tyrosinase. Eur. J. Biochem. 198:317–326, 1991. Winder, A. J., A. Wittbjer, E. Rosengren, and H. Rorsman. The mouse brown (b) locus protein has dopachrome tautomerase activity and is located in lysosomes in transfected fibroblasts. J. Cell Sci. 106:153–166, 1993a. Winder, A. J., A. Wittbjer, E. Rosengren, and H. Rorsman. Fibroblasts expressing mouse c locus tyrosinase produce an authentic enzyme and synthesise phaeomelanin. J. Cell Sci. 104:467–475, 1993b. Winder, A., T. Kobayashi, K. Tsukamoto, K. Urabe, P. Aroca, K. Kamayama, and V. J. Hearing. The tyrosinase gene family: interactions of melanogenic proteins to regulate melanogenesis. Cell. Mol. Biol. Res. 40:613–626, 1994. Wittbjer, A., B. Dahlbäck, G. Odh, A. M. Rosengren, E. Rosengren, and H. Rorsman. Isolation of human tyrosinase from cultured melanoma cells. Acta Derm. Venereol. (Stockh.) 69:125–131, 1989. Wood, J. M., and K. U. Schallreuter. Studies on the reactions between human tyrosinase, superoxide anion, hydrogen peroxide and thiols. Biochim. Biophys. Acta 1074:378–385, 1991. Yasumoto, K., H. Watanabe, J. C. Valencia, T. Kushimoto, T. Kobayashi, E. Appella, and V. J. Hearing. Epitope mapping of the melanosomal matrix protein gp100 (PMEL17). J. Biol. Chem. 279:28330–28338, 2004. Zhao, H., Y. Zhao, J. J. Nordlund, and R. E. Boissy. Human TRP-1 has tyrosine hydroxylase but no DOPA oxidase activity. Pigment Cell Res. 7:131–140, 1994. Zhou, B. K., T. Kobayashi, P. D. Donatien, D. C. Bennett, V. J. Hearing, and S. J. Orlow. Identification of a melanosomal matrix protein encoded by the murine (si) silver locus using “organelle scanning”. Proc. Natl. Acad. Sci. USA 91:7076–7080, 1994.
281
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
15
Chemistry of Melanins Shosuke Ito and Kazumasa Wakamatsu
Summary 1 Melanin pigments can be classified into two major groups: the brown to black insoluble eumelanins and the alkali-soluble yellow to reddish-brown pheomelanins. Both pigments derive from the common precursor dopaquinone formed via the oxidation of l-tyrosine by tyrosinase. Trichochromes are a variety of pheomelanic pigments with structures that are fully elucidated. 2 Dopaquinone, a highly reactive ortho-quinone, plays pivotal roles in chemically controlling melanogenesis. When sulfhydryl compounds are absent, it undergoes intramolecular cyclization to form cyclodopa, which is rapidly oxidized by redox reaction with dopaquinone to give dopachrome (and dopa). Dopachrome then gradually rearranges to give mostly 5,6-dihydroxyindole (DHI) and a trace of 5,6-dihydroxyindole-2-carboxylic acid (DHICA). Oxidation of these dihydroxyindoles leads to the production of eumelanins. However, intervention of cysteine with this process gives rise preferentially to the production of cysteinyldopa isomers. Cysteinyldopas are then oxidized through redox reaction with dopaquinone to cysteinyldopaquinones that eventually give rise to pheomelanins. 3 Kinetic data, provided by pulse radiolysis studies of the early stages of melanogenesis involving dopaquinone (and cysteine), indicate that the process of mixed melanogenesis proceeds in three distinctive steps: the production of cysteinyldopas, the oxidation of cysteinyldopas to give pheomelanins, followed finally by the production of eumelanins. The switching from pheomelanogenesis to eumelanogenesis is chemically controlled by the cysteine concentration. 4 Isolation and properties of natural and synthetic melanin pigments are discussed. Artificial modification of pigment structure should be cautioned when acid or base is employed in the isolation procedures. 5 Recent advances in the study of melanogenesis are summarized. In eumelanogenesis, dopachrome rearrangement to DHICA is catalyzed by dopachrome tautomerase (Dct) or by metal ions. DHI and DHICA can copolymerize on the way to eumelanic pigments. In pheomelanogenesis, cysteinyldopaquinone cyclizes to form the ortho-quinonimine intermediate, the rearrangement of which gives the benzothiazine derivative(s). Oxidative polymerization of the latter leads to the production of pheomelanins including the trichochrome pigments. 6 The biological significance of melanin-related metabolites, such as 5,6-dihydroxyindoles and cysteinyldopas, is addressed, with special emphasis given to their use as 282
melanoma markers, the mechanism of their cytotoxicity, and their possible role in photoprotection. 7 Melanins are difficult to characterize because of their intractable chemical properties, the heterogeneity in their structural features, and the lack of methods to split melanin polymers into monomer units. 8 Degradation studies carried out in the 1960s provided a number of useful degradation products, such as pyrrole-2,3,5tricarboxylic acid (PTCA) and 4-amino-3-hydroxyphenylalanine (4-AHP), arising from eumelanins by permanganate or peroxide oxidation and from pheomelanins by hydriodic acid hydrolysis. A rapid and sensitive method for quantitatively analyzing eumelanins and pheomelanins in tissue samples has been developed on the basis of the formation of PTCA and 4-AHP followed by their high-performance liquid chromatography (HPLC) determination. 9 The total amount of melanin (total melanin) in hair samples can be spectrophotometrically assayed by dissolving them in hot Soluene-350 plus water. The PTCA/total melanin and 4-AHP/total melanin ratios are useful in characterizing eumelanins and pheomelanins respectively. The former ratio reflects the DHICA/DHI ratio in various eumelanins. 10 In addition to PTCA and 4-AHP, the significance of which in pigment research has been established, several other degradation products are also useful in characterizing various types of melanin pigments. These products include thiazole-2,4,5tricarboxylic acid (TTCA) and pyrrole-2,3-dicarboxylic acid (PDCA) as markers of pheomelanic pigments and dopaminederived melanins respectively. This methodology has been used to analyze natural dopamine melanins, such as neuromelanin. Finally, 6-b-alanyl-2-carboxy-4-hydroxybenzothiazole (BTCA), a product of alkaline peroxide oxidation, may also be a good marker of pheomelanic pigments.
Historical Background Melanin and melanogenesis have been fascinating subjects for chemists not only because of the widespread presence of pigments in nature but also because of the complexity of their structures and functions. Landmark events in our understanding of the chemistry of melanogenesis are briefly summarized (revised from Prota, 1992; Prota et al., 1998a). 1885 Borquelot and Bertrand discovered the enzyme tyrosinase in fungi and, in 1886, Bertrand identified the amino acid tyrosine as the melanogenic substrate. 1926–27 Raper elucidated the early stages of the oxidation of tyrosine to melanin catalyzed by tyrosinase. He identified the red intermediate as dopachrome and isolated
CHEMISTRY OF MELANINS
dopa, 5,6-dihydroxyindole (DHI), and 5,6-dihydroxyindole2-carboxylic acid (DHICA). 1948 Beer and coworkers first synthesized DHI and DHICA and showed that DHI is more susceptible to oxidation than DHICA. 1948 Mason extended Raper’s studies to the later stages of melanogenesis and identified dopachrome by spectroscopy. 1952 Panizzi and Nicolaus identified pyrrole-2,3,5tricarboxylic acid (PTCA) as the most significant fragment from the degradation of Sepia melanin (PTCA is now used as a specific degradation product of DHICA-derived units in eumelanins). 1955 Leonhardi first recognized that a group of Thormählen-positive urinary melanogens are derivatives of DHI. 1962–66 Based on extensive analytical and degradative studies, Nicolaus, Piatelli, and their associates suggested that Sepia melanin is a heteropolymer derived from copolymerization of various intermediates in the Raper scheme. 1967 Duchón identified the Thormählen-negative melanogens in melanoma urine as metabolites of DHICA. 1967–68 Prota and Nicolaus isolated pheomelanins from red feathers and showed that they contain sulfur, arising by addition of cysteine to dopaquinone. They also isolated trichochromes and showed them to be related to pheomelanins. 1967–70 Fattorusso, Minale, and their associates carried out extensive degradative studies on pheomelanins and suggested that they are complex mixtures of polymers containing benzothiazine, benzothiazole, and isoquinoline units. 1968 Prota and associates synthesized 5-S-cysteinyldopa and showed that it is a precursor of pheomelanins and of trichochromes. 1968 Fattorusso, Minale, and their associates identified a number of characteristic degradation fragments of pheomelanins, including aminohydroxyphenylalanines (AHP) (which are now used as specific markers of pheomelanins). 1970–76 Swan and coworkers provided analytical and biosynthetic evidence in support of Nicolaus’ heteropolymer model of eumelanins. 1972 Rorsman and Rosengren discovered 5-S-cysteinyldopa in the urine of melanoma patients. 5-S-Cysteinyldopa is now widely used as a biochemical marker of melanoma progression. 1980 Pawelek and his associates discovered a new factor, now known as dopachrome tautomerase (Dct), which promotes tautomerization of dopachrome to give DHICA. 1985 Ito established microanalytical methods to quantitate eumelanins and pheomelanins, based on HPLC determination of the specific degradation products, PTCA and AHP. The original methods have been improved and are now commonly used as standard methods. 1985 Land, Chedekel, and colleagues introduced a pulse radiolysis method to study the fates of highly reactive orthoquinone intermediates (leading to the determination of kinetic constants for reactions in the early stages of melanogenesis in 2003 by Land and associates).
1986– Prota, d’Ischia, Palumbo, Napolitano, and their coworkers in Naples have carried out a long series of studies on the biogenesis and structure of eumelanins and pheomelanins. Metal ions were shown to modify the course of melanogenesis. The color of hair, skin, and eyes in animals mainly depends on the quantity, quality, and distribution of the pigment, melanin. Melanocytes are responsible for the synthesis of melanins within membrane-bound organelles, melanosomes, and the transport of melanosomes to surrounding epidermal cells, keratinocytes. Melanocytes in mammals and birds produce two chemically distinct types of melanin pigments, the black to brown eumelanins and the yellow to reddish pheomelanins (Ito, 1998; Ito et al., 2000; Prota, 1992; Prota et al., 1998a). Among the biopolymers, melanins are unique in many respects. The other essential biopolymers, i.e. proteins, nucleic acids, and carbohydrates, are chemically well characterized; their precursors (monomer units) and modes of connection between the monomer units are known, and sequences of their connection can be determined with well-established methodology (Table 15.1). On the other hand, we still do not have, for example, a method to determine accurately the ratio of various units present in melanins. This is due largely to the chemical properties of melanins, such as their insolubility over a broad range of pH, to heterogeneity in their structural features, and to the lack of methods to split melanin polymers into monomer units (all other biopolymers can be hydrolyzed to the corresponding monomer units). In this chapter, we review advances in the chemistry of melanins and melanogenesis and pay equal attention to the chemical analysis of melanins, with special emphasis on methodology to determine the quantity and quality of melanins present in pigmented tissues and cells (Wakamatsu and Ito, 2002). Characterization of synthetic and natural dopamine melanin is also described briefly. An excellent book (Prota, 1992) is available that deals extensively with the chemistry of melanins and melanogenesis, and more condensed information can also be found in several recent reviews (Ito, 1993a; Prota, 1988, 1993; Prota et al., 1998a).
Table 15.1. Comparison of melanins with other biopolymers. Biopolymer
Monomers
Covalent bond
Protein Polysaccharide Nucleic acid Melanin
Amino acids Glucose Nucleotide Dihydroxyindoles Benzothiazines
Peptide bond (C–N) Glucoside bond (C–O) Phosphate diester bond (P–O) Carbon–carbon bond (C–C)
283
CHAPTER 15 Tyrosinase
O
COOH
COOH NH2
O
NH2
HO
O2
Tyrosine
Dopaquinone (DQ)
Tyrosinase O2
COOH N H
HO
NH2
HO
Cyclodopa
Dopa O –O
N+ H
COOH
Dopachrome Dopachrome tautomerase (Tyrp2)
NH2
HO H 2N
HO
O
HO
HO
N H
O2
N H
O2
O
NH2
S N
+
S
O
NH2 COOH
(HOOC)
COOH
HO
COOH NH2
1,4-Benzothiazine Intermediates (O)
Pheomelanin
Current Concepts Melanogenesis and Melanins The Raper–Mason–Prota Pathway of Melanogenesis It is now well recognized that animal melanins can be classified into two major groups: the brown to black eumelanins that are insoluble in all solvents and the yellow to reddishbrown pheomelanins that are soluble in alkali. Nevertheless, most studies on melanins have so far been conducted on eumelanins. One of the reasons for the scantiness of research on pheomelanins is because it was formerly believed that pheomelanins are produced only in follicular and feather melanocytes. However, it has been shown recently that pheomelanins are also produced in melanomas (Prota et al., 1976; Rorsman et al., 1979) and in normal epidermis (Thody et al., 1991). Both eumelanins and pheomelanins derive from the common precursor dopaquinone, which is formed by tyrosinase oxidation of the common amino acid l-tyrosine (Fig. 15.1). Until recently, it was generally believed that dopa is first formed on the way to dopaquinone. However, using N,N-dimethyldopamine as a tyrosinase substrate, Cooksey et al. (1997) showed that ortho-quinones such as dopaquinone are formed directly during the initial stage of melanogenesis. Dopaquinone is a highly reactive intermediate and, in the absence of sulfhydryl compounds (thiols), it undergoes the intramolecular addition of the amino group giving cyclodopa (often called leukodopachrome). The redox exchange between cyclodopa and dopaquinone then gives rise to dopachrome, the red intermediate (Mason, 1948; Raper, 1927), and dopa. This latter is considered as a source of dopa formed during melanogenesis (Fig. 15.1). Dopachrome then gradually 284
+
NH2
N
Eumelanin
COOH S
CD-quinones
Tyrp1 (DHICA oxidase)
Tyrosinase
NH2
S
HO
(HOOC)
HO
COOH NH2
HOOC
5,6-Dihydroxyindole -2-carboxylic acid (DHICA)
HO
NH2 COOH
2-S-Cysteinyldopa (2-S-CD)
5-S-Cysteinyldopa (5-S-CD) DQ Dopa
COOH
5,6-Dihydroxyindole (DHI)
+
HOOC
O HO
S
S
H2N
CO2
COOH
COOH
HO
HO
COOH
HO
+Cysteine
-Cysteine
Fig. 15.1. The biosynthetic pathways to eumelanins and pheomelanins. Note that the activities of tyrosinase, Tyrp1, and Tyrp2 are involved in the production of eumelanins, whereas only tyrosinase (and the amino acid cysteine) is necessary for the production of pheomelanins.
rearranges to give mostly DHI and, to a lesser extent, DHICA (Palumbo et al., 1987a; Raper, 1927). Finally, these dihydroxyindoles are oxidized and polymerized to give eumelanins. On the other hand, intervention of sulfhydryl compounds (such as cysteine) with this process gives rise exclusively to thiol adducts of dopa, cysteinyldopas, among which 5-Scysteinyldopa (5-S-CD) is the major isomer (Ito and Prota, 1977). Further oxidation of the thiol adducts leads to pheomelanin formation via benzothiazine intermediates. In fact, most melanin pigments present in pigmented tissues appear to be mixtures or copolymers of eumelanins and pheomelanins (Prota, 1980; Ito, 1993b). In addition to tyrosinase, two tyrosinase-related proteins have recently been shown to regulate and promote eumelanogenesis (Hearing, 1993). Dopachrome tautomerase (Dct), the presence of which had been suggested for some years (Pawelek et al., 1980), catalyzes the tautomerization of dopachrome to DHICA (Tsukamoto et al., 1992a). Recently, this enzyme was shown to be identical to tyrosinase-related protein 2 (Tyrp2) (Jackson et al., 1992). Certain metal ions are also known to promote the tautomerization (i.e. the isomerization with a shift of hydrogen atom) of dopachrome to DHICA (Palumbo et al., 1987a, 1991). Oxidative polymerization of DHI is known to be catalyzed by mammalian tyrosinase (Tripathi et al., 1991). Another tyrosinase-related protein, Tyrp1, isolated from mouse melanoma (the brown locus protein) has recently been shown to oxidize DHICA (Jiménez-Cervantes et al., 1994; Kobayashi et al., 1994), although human Tyrp1 is unable to catalyze the same reaction (Boissy et al., 1998). Instead, human tyrosinase is able to oxidize DHICA, as well as tyrosine, dopa, and DHI. It now becomes clear that the activities of these tyrosinase-related proteins greatly affect the
CHEMISTRY OF MELANINS
quantity and quality (the ratio of DHI to DHICA and the degree of polymerization) of the eumelanins produced.
reactions are competitive. The reaction with amine compounds does not proceed so fast. However, only when the amino group is present within the same molecule may the amino group fairly rapidly undergo either an addition reaction to give aminochromes (such as dopachrome) or a condensation reaction to give ortho-quinonimines. An example of the latter type of reaction is found in the cyclization of cysteinyldopaquinones (see Fig. 15.1). It should be stressed that all these reactions are controlled by the intrinsic chemical reactivity of ortho-quinones.
The Intrinsic Reactivity of Ortho-quinones Dopaquinone belongs to the category of ortho-quinones, and it is essential to summarize the chemistry of ortho-quinones for a better understanding of melanogenesis. Figure 15.2 summarizes some of the most important reactions of orthoquinones, which are extremely reactive compounds. In 1976, Tse et al. showed that the addition of sulfhydryl compounds proceeds extremely fast to give thiol adducts. In a pulse radiolysis study on the reactivities of 4-substituted ortho-quinones with cysteine and glutathione, Cooksey et al. (1996) showed that the rate constants of thiol addition are over the range 4 ¥ 105 to 3 ¥ 107/M/s (in the case of cysteine at pH ~7) depending on the nature of the substituents. The reduction to parent catechols through redox exchange proceeds as fast as the thiol addition (Tse et al., 1976) and, therefore, these two
HO
R
HO
fast
R’-SH
R
O
Redox exchange
In 2003, Land et al. reported rate constants (r1–r4) for all of the four important steps in the early phase of melanogenesis, based on pulse radiolysis studies (Fig. 15.3; Land and Riley, 2000; Land et al., 2001, 2003). The pulse radiolysis method is a powerful tool to study the fates of highly reactive melanin precursors. The technique depends on the production of bromine radicals Br2•– by pulse radiolysis of an N2O-saturated aqueous buffer containing KBr. The bromine radical thus formed oxidizes dopa to dopasemiquinone, which then disproportionates to give dopaquinone (and dopa). This entire process proceeds within 2–3 ms so that the fate of dopaquinone can be followed by spectrophotometry in the presence (or absence) of a targeted molecule. The first step (r1 = 3.8/s) in eumelanogenesis is the intramolecular addition of the amino group giving cyclodopa, a fairly slow step. However, as soon as cyclodopa is formed, it is rapidly oxidized to dopachrome through a redox exchange (r2 = 5.3 ¥ 106/M/s). On the other hand, the first step in pheomelanogenesis (r3 = 3 ¥ 107/M/s), the addition of cysteine, proceeds very quickly. The second step, the redox exchange giving cysteinyldopaquinone, proceeds at a slower rate (r4 = 8.8 ¥ 105/M/s) (Land and Riley, 2000). From these kinetic data, several important conclusions can be drawn.
R
HO HO
fast
O
Catechols
Pivotal Roles of Dopaquinone in Controlling Melanogenesis
S-R’
ortho - Quinones
Thiol adducts R’-NH2
slow R
O HO
R
HO
NH-R’
or
Amine adducts (Aminochromes)
(+ H2O)
R’-N
ortho - Quinonimines
Fig. 15.2. Intrinsic chemical reactivities of ortho-quinones. Note that, unless the amino group is present in the same molecule, the addition of an amine does not proceed at biologically relevant rates.
COOH NH2
HO
Tyrosine O2
Tyrosinase HO
COOH N H
HO
Fig. 15.3. Schematic outline of the branching point of production of eumelanins and pheomelanins (Ito, 2003; Land et al., 2003). Note that the rate constants r1–r4 are all controlled by the intrinsic chemical reactivity of dopaquinone. No enzymes other than tyrosinase are necessary to promote these reactions. The intramolecular cyclization of dopaquinone to cyclodopa requires deprotonization of the amino group (actually present in the form of –NH3+).
COOH
Cysteine
HO O
r1 3.8
sec–1
Cyclodopa
O
O
3×
O2
r2
Tyrosinase
M–1sec–1
NH2
HO H2N
S
HOOC
r4
5-S -Cysteinyldopa (5-S -CD) 8.8 × 105 M–1sec–1 O
HO + N H
r3 107
Dopaquinone (DQ)
5.3 × 106 M–1sec–1
–O
COOH NH2
COOH
COOH
COOH
Dopachrome
Dopa
NH2
O
NH2
HO
H2N
S
HOOC
5-S -Cysteinyldopaquinone
Eumelanin
Pheomelanin 285
CHAPTER 15 COOH
HO
COOH
COOH
O
+
S
NH2
H 2N
NH2
O
6
HO
HS NH2
HOOC
Dopaquinone (DQ)
6-S-Cysteinyldopa (1%)
COOH S HO
COOH
COOH
H2N
5
NH2 COOH
S
NH2 HO
2
HO
+
HO
2
NH2
COOH
NH2
+
HO
S NH2
H2N
5 S
HO HOOC
5-S-Cysteinyldopa (74%)
HOOC
2-S-Cysteinyldopa (14%)
1 Comparison of the rate constant for the addition of cysteine to dopaquinone (r3) with the rate constant for the intramolecular cyclization (r1) shows that cysteinyldopa formation is preferred over cyclodopa formation as long as the cysteine concentration is higher than 0.13 mM. 2 The redox exchange giving cysteinyldopaquinone (r4) proceeds 30 times more slowly than the addition of cysteine (r3). Cysteinyldopas thus accumulate in the early phase of pheomelanogenesis. 3 Comparison of the rate constant for redox exchange giving dopachrome from dopaquinone (r2) with the rate constant for intramolecular cyclization (r1) shows that dopachrome production becomes faster than cyclodopa production when the cyclodopa concentration is higher than 0.7 mM. Cyclodopa thus does not accumulate in the early phase of eumelanogenesis. 4 Comparison of the rate constant for redox exchange giving cysteinyldopaquinone (r4) with the rate constant for dopachrome formation (2 ¥ r1; Land et al., 2003) shows that pheomelanogenesis is preferred over eumelanogenesis as long as the cysteinyldopa concentration is higher than 9 mM. 5 It is now possible to derive an “index of divergence” between eumelanogenesis and pheomelanogenesis. By taking dopachrome and cysteinyldopaquinone as representatives of the divergent pathways, Land et al. (2003) proposed an index of divergence (D): D = r3 ¥ r4 ¥ [cysteine]/r1 ¥ r2 This leads to a “crossover value” (i.e. for D = 1) for switching between eumelanogenesis and pheomelanogenesis when the cysteine concentration at the site of melanogenesis is 0.8 mM. The above kinetic data are useful in interpreting the early phase of pheomelanogenesis. Thus, tyrosinase oxidation of dopa in the presence of excess cysteine gives a high yield of 5S-cysteinyldopa (74%) and 2-S-cysteinyldopa (14%) in a ratio of about 5:1, together with a minor 6-S-isomer (1%) and a 286
2,5-S,S’-Dicysteinyldopa (5%)
Fig. 15.4. Formation of isomeric cysteinyldopas and 2,5-S,S¢-dicysteinyldopa by the addition of cysteine to enzymically produced dopaquinone (Ito and Prota, 1977).
diadduct, 2,5-S,S¢-dicysteinyldopa (5%) (Fig. 15.4; Ito and Prota, 1977). This result confirms the interpretation that cysteinyldopa formation is preferred as long as cysteine is present. It may also be pointed out that the ratio of these cysteinyldopa isomers is determined by the intrinsic chemical reactivity of dopaquinone. The ratio of r3 to r4 is ~30, indicating that only after the cysteine concentration decreases to 30 times lower than the 5-S-cysteinyldopa concentration does the formation of 5-Scysteinyldopaquinone become predominant. This interpretation is supported by the facts that cysteinyldopa monomers accumulate in the early phase of pheomelanogenesis and that the formation of the diadduct 2,5-S,S¢-dicysteinyldopa is only a minor pathway. This is why high levels of 5-S-cysteinyldopa are produced in melanoma tissues and secreted into the blood of melanoma patients, which makes 5-S-cysteinyldopa a useful biochemical marker of melanoma progression (Wakamatsu et al., 2002a). The proposed pathway of pheomelanogenesis was substantiated by the identification of 5-S-cysteinyldopa (Bjorklund et al., 1972) and other isomers, along with the diadduct, in melanoma urine (Prota et al., 1977) by Rorsman and his associates. The ratios between various cysteinyldopa isomers found in melanoma urine and tissues (Morishima et al., 1983) are close to that obtained in vitro by incubation of dopa with tyrosinase in the presence of cysteine (Ito and Prota, 1977). This indicates that cysteinyldopas originate in vivo by a similar route, involving the addition of cysteine to dopaquinone. As this process is the earliest event in the course of pigment metabolism, it is thus likely that a certain portion of cysteinyldopas formed are secreted into body fluid, regardless of the type of melanin eventually formed. An alternative route has been proposed for the biosynthesis of cysteinyldopas involving the addition of dopaquinone with glutathione (Ito et al., 1985), followed by the hydrolysis of the resultant glutathionyldopas. The latter step requires the action of two enzymes, g-glutamyltranspeptidase and peptidase, which
CHEMISTRY OF MELANINS
Fig. 15.5. Proposed pathway for mixed melanogenesis. Note that the course of melanogenesis proceeds in three distinct steps: cysteinyldopa genesis, pheomelanogenesis, followed by eumelanogenesis (Ito, 2003; Ito et al., 2000).
Melanogenesis
High tyrosine / low cysteine levels
Low tyrosine / high cysteine levels
EM genesis
EM genesis
PM genesis
PM genesis CD genesis (no melanin)
are present in melanoma cells (Agrup et al., 1975; Mojamdar et al., 1983). Which of the two pathways for cysteinyldopa formation is actually operative in vivo has been addressed. Inhibition of glutathione synthesis by the inhibitor l-buthionine sulfoximine led to a strong reduction in glutathione levels with some increase in cysteine levels in both melanoma cells (Benathan, 1996) and normal melanocytes (Benathan and Labidi, 1996). This modification of thiol levels results in a moderate increase in the cellular level of 5-S-cysteinyldopa. Thus, it is now generally believed that glutathione is not directly involved in the production of cysteinyldopas (Potterf et al., 1999).
The Proposed Pathway for Mixed Melanogenesis From the above interpretation of kinetic data, a pathway for mixed melanogenesis can be proposed as shown in Figure 15.5 (Ito, 2003; Ito et al., 2000). The amount of melanin produced is proportional to dopaquinone production, which is in turn proportional to tyrosinase activity. Melanogenesis proceeds in three distinctive steps. The initial step is the production of cysteinyldopas, which continues as long as cysteine is present (0.1 mM). The second step is the oxidation of cysteinyldopas to give pheomelanins, which continues as long as cysteinyldopas are present (9 mM). The last step is the production of eumelanins, which begins only after most of the cysteinyldopas (and cysteine) are depleted. Therefore, it appears that eumelanins deposit on the preformed pheomelanin (Agrup et al., 1982) and that the ratio of eumelanins to pheomelanins is determined by the tyrosinase activity and the cysteine concentration. This proposal has been supported by several studies. Ozeki et al. (1997a) examined the tyrosinase oxidation of tyrosine in the presence of cysteine and showed that the three steps proceed in sequence. By decreasing the extracellular concentration of cysteine in cultured human melanoma cells, del Marmol et al. (1996) showed a shift to more eumelanic cells as a result of a dramatic decrease in intracellular cysteine concentration. By changing concentrations of tyrosine and cysteine in cultured human melanocytes, Smit et al. (1997) found a twofold increase in melanin production with a decreased ratio of pheomelanin to total melanin when cultured at a higher concentration of tyrosine.
CD genesis (no melanin)
Tyrosinase activity (Dopaquinone production)
The proposal that tyrosinase activity plays a major role in controlling melanogenesis is also supported by several studies. It has been shown that tyrosinase activity is lower when pheomelanogenesis proceeds in viable yellow mice compared with eumelanogenesis (Burchill et al., 1986, 1993; Movaghar, 1989). Moreover, the switching to pheomelanogenesis is accompanied by a marked decrease in the melanin content of hair (Burchill et al., 1986; Granholm et al., 1990). However, the change in tyrosinase activity itself is not enough for the switching of melanogenesis as seen in chinchilla mice where tyrosinase activity is decreased to one-third from the wild type (Coleman, 1962; Lamoreux et al., 2001). The eumelanin content is reduced to one-half in black chinchilla without any increase in pheomelanin content compared with black mice, whereas the pheomelanin content is reduced nine-fold in lethal yellow chinchilla compared with lethal yellow mice (Lamoreux et al., 2001). Conversely, the proposal summarized in Figure 15.5 fits well with the above results that pheomelanogenesis is more strongly affected by the decrease in tyrosinase activity than eumelanogenesis. Barsh (1996) has put forth a similar proposal.
Classification and Structure of Eumelanins and Pheomelanins Table 15.2 summarizes criteria for classifying melanins (Prota et al., 1998a). Extensive studies carried out by Nicolaus’ group in Naples (Nicolaus, 1968) and Swan’s group in Newcastle (Swan, 1974; Swan and Waggott, 1970) led to the conclusion that eumelanins are highly heterogeneous polymers consisting of different oxidative states of DHI and DHICA units, and pyrrole units derived from their peroxidative cleavage (structure 1 in Fig. 15.6). Interestingly, a recent study indicates a high proportion of pyrrole units in Sepia melanin (Pezzella et al., 1997). However, how much those pyrrole units contribute to the structure of natural eumelanins in mammalian pigmentation remains to be studied. Most of the present knowledge on pheomelanin chemistry results from work in the late 1960s conducted by Prota, Nicolaus, and collaborators (Prota, 1972; Thomson, 1974). These, combined with some new findings, led us to formulate the representative structure 2 in Figure 15.6 for pheomelanins 287
CHAPTER 15
that consist mostly of benzothiazine units with minor contributions from benzothiazole and isoquinoline units. Some portions of the monomer units may be connected through ether bonds (Di Donato and Napolitano, 2003; Napolitano et al., 1996a). However, the contribution of ether bond formation should be minimal, because monomer units connected through ether bonds should be colorless, which is incompatible with the brownish color of natural pheomelanins. The isoquinoline units may be produced by post-polymerization modifications of freshly formed pheomelanin, because isoquinoline units are not found in the earlier stages of pheomelanogenesis (Fig. 15.3). The modification of alanyl side-chain to the aromatic character is consistent with biosynthetic studies using radioisotopes and 13C-NMR spectroscopy (Chedekel et al., 1987; Deibel and Chedekel, 1984). Trichochromes are the only melanin-like pigments with fully characterized structures (3–6; Fig. 15.6). The close similarity in structural features between trichochromes and pheomelanins and their coexistence in pigmented tissues suggest that they are formed oxidatively from the same monomer units,
Table 15.2. Main types of epidermal melanin pigments (from Prota et al., 1998a). Melanin
Criteria
Eumelanins
Black or brown nitrogenous pigments, insoluble in all solvents, which arise by oxidative polymerization of 5,6-dihydroxyindoles derived biogenetically from tyrosine via dopaquinone Alkali-soluble, yellow to reddish brown pigments, containing sulfur in addition to nitrogen and arising by oxidative polymerization of cysteinyldopas via 1,4-benzothiazine intermediates A variety of sulfur-containing pheomelanins, of low molecular weight, characterized by a pH-dependent bi(1,4-benzothiazine) chromophore
Pheomelanins
Trichochromes
OH H N
O
O OH
(COOH)
N
N H
O
(COOH)
S
HO S
(COOH)
HOOC
N H
HO
NH2 N
HOOC
OH
N
O S
(COOH)
HOOC N H
OH COOH
O
NH2
H2N
COOH
N
S
S
S
N H
HOOC
OH Trichochrome F (4)
NH2
OH N
COOH
N
COOH
S
O
NH2
OH
S
S N H
HOOC
COOH S N
NH2 OH
OH Trichochrome B (5)
288
COOH
N
NH2
Trichochrome C (3)
NH2
H2N
S
OH
HOOC
NH2
OH N
HOOC
HOOC Pheomelanins (2)
Eumelanins (1)
Trichochrome E (6)
Fig. 15.6. Structures of eumelanins (1), pheomelanins (2), and trichochromes (3–6). Structures of eumelanins and pheomelanins are the only representative ones formulated on the basis of biosynthetic and degradative studies. The positions with (–COOH) are connected either to –H or –COOH; these positions may also be available for attachment to other units. The arrows indicate sites for attachment to other units. The isoquinoline units in pheomelanin structure (2) may be produced by the postpolymerization modification of freshly formed pheomelanin, because those units are not produced in the early stages of pheomelanogenesis.
CHEMISTRY OF MELANINS
differing only in the mode of polymerization. Therefore, trichochromes may be regarded as a variety of pheomelanic pigment (Table 15.2). Prota’s group conducted a series of biosynthetic studies to clarify the stages beyond DHI and DHICA in eumelanogenesis and those of cysteinyldopas in pheomelanogenesis. Although considerable advances have been made in these respects (Di Donato and Napolitano, 2003; Napolitano et al., 1996a; Prota et al., 1998a), it appears at present unnecessary to change our basic views on the structures of eumelanins and pheomelanins, as depicted in Figure 15.6 (see Degradative Studies below for further discussion).
Isolation and Preparation of Melanins Natural Eumelanins One of the major problems in studying melanin is the lack of adequate methods to isolate pure melanin pigments. The most frequently used sources of natural eumelanins are ink sacs of cuttlefish Sepia officinalis (Sepia melanin) (Nicolaus, 1968), the uveal tract and the retinal pigment epithelium of bovine eyes (Dryja et al., 1979), and melanoma tumors. Eumelanins are considered to be firmly bound to proteinaceous components, through covalent or ionic bonds (Zeise, 1995). To remove proteins, treatment with hydrochloric acid is used, but complete removal requires a prolonged treatment in concentrated HCl at room temperature or 24 h of boiling in 6 M HCl (Nicolaus, 1968). As early as 1907, von Fürth and Jerusalem isolated “melanin” as an insoluble, black pigment by heating melanoma tissues in concentrated HCl. One should be aware that such harsh treatment causes irreversible structural alterations. For example, carbon dioxide and ammonia molecules are liberated under these conditions from various synthetic eumelanins (Ito, 1986). Also, the indole moiety is known to be labile in strong acid; tryptophan is decomposed during 6 M HCl hydrolysis of proteins. To circumvent these difficulties, treatment with proteinases such as pronase or collagenase may be preferable; but again, treatment with cold acid is often used to remove accompanying residual proteins (Novellino et al., 1981; Prota et al., 1976). Another approach is to solubilize melanins (melanoproteins) with alkali. Fortner (1910) was the first to report a systemic study to isolate melanin pigment by alkali solubilization. It involves extraction of melanins with NaOH followed by repeated precipitation of the melanins with HCl and redissolution in NaOH (Bolt, 1967). However, proteins cannot be removed by this method; approximately 50% of proteins were found to remain in the melanin preparations from human black hair and from red hair (Menon et al., 1983). In addition, treatment of melanins with alkaline solutions causes irreversible uptake of oxygen (Felix et al., 1978), suggesting that further modification in the melanin structure takes place. To overcome these difficulties, the use of intact Sepia melanin is preferable. However, some precautions should be taken when one wishes to use it as a representative of natural eumelanins. The intact Sepia melanin consumes little oxygen and displays poor redox properties, suggesting a high degree
of breakdown in the indolic moiety (Pezzella et al., 1997). Further, the intact, freshly prepared Sepia melanin differs in surface area depending on the isolation procedure employed (Liu and Simon, 2003). The different degree of aggregation may alter the photochemical properties of melanin granules. If one needs to isolate eumelanins of mammalian origin, preparation of melanosomes from bovine eyes seems to be the choice. Duchón et al. (1973) determined the contents of melanin and protein in melanosome preparations from 10 different biological sources and found the melanin contents to be fairly high, ranging between 20% and 70%. If one wishes to remove proteins from the eumelanin preparations, melanosome fractions should be used as starting materials, rather than whole tissues, to reduce the possibility of unnecessary reactions that might occur between melanins and tissue components. An example of such reactions is sulfur incorporation into eumelanins when heated in 6 M HCl in the presence of cysteine or cystine (Ito, 1986). Recently, Novellino et al. (2000) developed a new enzymatic procedure for isolation of eumelanin from black human hair involving digestion with protease, proteinase K, and papain in the presence of dithiothreitol. In an extension of this study, Liu et al. (2003) compared two different acid/base extractions and an enzymatic extraction to isolate eumelanin from black human hair. The data indicate that pigments obtained by the acid/base extractions contain significant protein (52% and 40%), destroy the melanosomes, and possess an altered molecular structure. The enzymatically extracted hair melanin (14% protein content), on the contrary, retains the morphology of intact melanosomes and is an excellent source of human eumelanin.
Natural Pheomelanins As a source of natural pheomelanins, red feathers of New Hampshire chickens have been commonly used (Minale et al., 1967; Prota, 1972; Thomson, 1974). The isolation procedure involves extraction in 0.1 M NaOH, acidification, and dialysis followed by gel chromatography on Sephadex G-50. Although the procedure is much less destructive than those employed for eumelanins, it is still harsh enough to affect the structural features. Trichochromes (3–6), dimeric pheomelanic pigments, have been isolated from red feathers (Prota and Nicolaus, 1967). Interestingly, trichochrome C (and its isomer trichochrome B) was also found in the urine of patients with melanoma metastases (Agrup et al., 1978; Rorsman et al., 1979). It should be noted that trichochrome F (and its isomer E) may be artificially formed from 5-S-cysteinyldopa (and a mixture of 5-S and 2-S isomers) during the extraction and work-up procedures (Prota, 1992; Rorsman et al., 1979).
Synthetic Melanins Synthetic eumelanins can be prepared by the oxidation of ltyrosine or l-dopa at neutral pH in the presence of tyrosinase, usually commercially available mushroom tyrosinase (Ito, 1986). Biosynthetic dopa melanin has long been considered as 289
CHAPTER 15
a good model of eumelanins. However, recent progress in eumelanin chemistry has proved that dopa melanin prepared by tyrosinase oxidation is quite different from natural eumelanins with respect to the carboxyl group content, reflecting a difference in the ratio of DHI to DHICA (Ito, 1986). A synthetic dopa melanin sample finely suspended in neutral buffer and exposed to oxygen showed a marked increase in the carboxyl content over time (Crescenzi et al., 1993). Similar changes may occur during the process of melanin preparation. Dopa melanin prepared by the auto-oxidation of dopa at alkaline pH appears to be degraded to a significant extent by oxidative cleavage of the ortho-quinone moiety, and the use of these preparations should be discouraged (Ito, 1986). Natural eumelanins are now believed to arise from copolymerization of DHI and DHICA in various ratios. Therefore, it is recommended that synthetic eumelanins prepared from DHI, DHICA, and various ratios of their mixture be used as eumelanin standards, at least for structural studies (Ozeki et al., 1997b). A one-step synthesis of DHI and DHICA for such studies is available (Wakamatsu and Ito, 1988). Synthetic pheomelanins can be prepared by tyrosinase oxidation either of a mixture of l-dopa and l-cysteine or of 5-S-cysteinyldopa in the presence of a catalytic amount of ldopa (Ito, 1989). Degradative experiments suggest that these biosynthetic pheomelanins resemble natural pheomelanins present in the yellow hair of rodents (Ito, 1989). Pheomelanins prepared from 5-S- or 2-S-cysteinyldopa are shown by isoelectric focusing to be more homogeneous than those prepared from dopa and cysteine (Deibel and Chedekel, 1984). In contrast to the availability of eumelanin standards, one faces difficulty in obtaining a valid pheomelanin standard, either natural or synthetic. We therefore refined the conditions for preparing pheomelanin by tyrosinase oxidation of l-dopa in the presence of an excess of l-cysteine (Ito, 1989). The method makes it unnecessary to synthesize pure 5-Scysteinyldopa as the starting material for pheomelanin preparation. When one needs to prepare pheomelanins from 5-S-cysteinyldopa or other isomers, both enzymic and chemical methods are available for the synthesis of cysteinyldopa isomers (Chioccara and Novellino, 1986; Ito, 1983; Ito and Prota, 1977). Copolymers of eumelanin and pheomelanin can be prepared by tyrosinase oxidation of l-dopa in the presence of varying ratios of l-cysteine (Ito and Fujita, 1985). When precise analytical data on melanins are required, differences in the water content of melanins prepared can no longer be neglected. It is thus recommended to use melanin standards that are kept in a desiccator of a constant moisture content (Napolitano et al., 1995).
Molecular Weight The unusual insolubility of eumelanins and their blackness suggest that eumelanins consist of several hundreds of monomeric units. However, there is no direct evidence to support this belief. Because of their insolubility, the direct measurement of molecular weight has been difficult. With soluble DHICA melanins, an estimate of molecular weight 290
using HPLC/molecular sieve analyses gave values in the range of 20 000 to 200 000 (Orlow et al., 1992), although the validity of that is questionable because of a possible interaction of melanins and the chromatographic matrix during the molecular weight determinations (Prota et al., 1998a). Recent application of matrix-assisted laser desorption ionization (MALDI) mass spectrometry shows that both DHI and DHICA melanins have a large proportion of oligomeric fractions of lower molecular weight, not exceeding 1.5 kDa (Napolitano et al., 1996b, c; Seraglia et al., 1993). However, whether polymeric melanins exceeding 1.5 kDa are not present in the samples or are not detectable by this method remains to be clarified. In contrast to eumelanins, the measurement of the molecular weights of pheomelanins is more feasible. A molecular weight of less than 2.0 kDa has been obtained for proteinfree gallopheomelanin 1, isolated from red chicken feathers (Fattorusso et al., 1968). However, that estimate is also subject to question because of the heterogeneity of the pigment and the irreversible binding of part of the material to the chromatographic gel (Deibel and Chedekel, 1982).
Recent Advances in the Study of Melanogenesis Late Stages of Eumelanogenesis Dopachrome accumulates in the early stages of eumelanogenesis, and stages beyond the formation of dopachrome are discussed here. The red pigment dopachrome is a fairly stable molecule with a half-life of about 30 min (first-order rate constant of 4.0 ¥ 10–4/s), and it spontaneously decomposes to give mostly DHI by decarboxylation at neutral pHs in the absence of Dct (or metal ions). The ratio of DHI to DHICA under these conditions is 70:1 (Palumbo et al., 1987a). On the other hand, in the presence of Dct (Tyrp2), dopachrome is catalyzed to undergo tautomerization preferentially to produce DHICA (Palumbo et al., 1991). The ratio of DHICA to DHI production is thus determined by the activity of Dct. The presence of metal ions, especially Cu2+, accelerates the rate of dopachrome rearrangement and also affects the DHICA/DHI ratio, but Dct seems to be more effective in catalyzing the tautomerization (Palumbo et al., 1987a, 1991). Until 1980, eumelanins had been believed to be DHI rich, because the decarboxylation of dopachrome is the major pathway taken in the absence of any extrinsic factor. Then, in 1980, Pawelek’s group discovered dopachrome conversion factor, now known as dopachrome tautomerase or Dct (Pawelek, 1991; Pawelek et al., 1980). Therefore, we analyzed the contents of DHICA-derived units in various types of eumelanins (Ito, 1986). Two analytical methods were used: acidcatalyzed decarboxylation and permanganate oxidation to give PTCA. The results showed that synthetic dopa melanin contained only trace amounts of DHICA-derived units, while melanins from Sepia, B16 melanoma, and mouse black hair consisted of about equal amounts of DHI- and DHICAderived units. This study thus confirmed the significance of DHICA-derived units in the structure of natural eumelanins. The same methodology was employed by Palumbo et al.
CHEMISTRY OF MELANINS H N
4 2
OH
HO
OH
HO
NH
NH
HO
HO
24 N H
HO
24 HO
HO
OH
N H
HO
7
8
COOH
HO
HO
COOH
4 4
NH COOH
HO
OH
H N
HO
HO
N H
7 2
HO
N H
7 4
HO
N H
COOH N H
HO
HO
OH
10
9
Fig. 15.7. Structures of representative oligomers formed in the early stages of enzymic conversion of DHI and DHICA to eumelanins. The homotrimers 7 and 8 are products of oxidation of DHI whereas the homotrimer 9 is from DHICA (Prota et al., 1998a). The heterodimer 10 is among products obtained by oxidation of a mixture of DHI and DHICA.
(1988) to show that dopa melanin prepared in the presence of metal ions, especially Cu2+, are more akin to natural eumelanins than those prepared in the absence of metal ions. The fact that DHICA is equally significant compared with DHI as a eumelanin precursor prompted Prota and his associates to carry out extensive, biomimetic studies on the mode of polymerization of these 5,6-dihydroxyindoles (for reviews, see d’Ischia et al., 1996; Prota et al., 1998a). Upon enzymic or chemical oxidation, DHI affords in the early stages a number of dimers and trimers (d’Ischia et al., 1990). Some representative structures, such as the DHI trimers 7 and 8, are shown in Figure 15.7. Judged from the structures of oligomers isolated, the most reactive position is the 2-position, followed by the 4- and 7-positions. Oxidation of DHICA, catalyzed by tyrosinase/O2 or by peroxidase/H2O2, produces mixtures of dimers and trimers in which the indole units are mostly linked through the 4- and 7-positions (Palumbo et al., 1987b; Pezzella et al., 1996). The 4-position appears to be more reactive than the 7-position, as exemplified by the isolation of the trimer 9. Interestingly, the mode of polymerization is influenced by the oxidant employed; Cu2+ ion-catalyzed oxidation of DHICA affords minor 3,4¢- and 3,7¢-coupled dimers arising from participation of the 3-position, in addition to the major 4,4¢-, 4,7¢-, and 7,7¢-dimers (Pezzella et al., 1996). Cooxidation of DHI and DHICA with peroxidase/H2O2 affords, in addition to homo-oligomers, some heterodimers including the dimer 10 (Napolitano et al., 1993a).
As shown above, the pulse radiolysis technique is very useful in following the fate of short-lived ortho-quinone intermediates. Using this technique, Lambert et al. (1989) were able to suggest the possibility that 5,6-indolequinone tautomerizes to its quinone-imine and quinone-methide tautomers, which then undergo nucleophilic addition of water, thus giving trihydroxyindole species. The role of Dct in melanogenesis has been examined using follicular melanocytes of congenic mice (Lamoreux et al., 2001; Ozeki et al., 1995). The slaty mutation in the mouse is known to decrease the activity of Dct. The effects of tyrosinase, Dct, and Tyrp1 on eumelanogenesis were compared (Ito, 2003). Chinchilla and slaty mouse hairs had total melanin values about 50% that of black hair, while brown hair had about 30% (Lamoreux et al., 2001). Black, chinchilla, and brown mouse hairs give similar PTCA to total melanin ratios. Comparison with synthetic eumelanins indicated that the DHI to DHICA ratios in these three mutants were close to 1:3. On the other hand, slaty hair gave a PTCA to total melanin ratio similar to that of synthetic eumelanin having a 3:1 ratio. Thus, Dct accelerates dopachrome tautomerization, increasing the ratio of DHICA in eumelanins and accelerating the production of eumelanins. Human hair (Ozeki et al., 1996a) and skin (Alaluf et al., 2001) appears to produce DHI-rich eumelanins, similar to mouse slaty hair. Then, what is the role of Tyrp1? There is some controversy regarding the role of Tyrp1 (Hearing, 2000), although it is known that mouse Tyrp1 is able to catalyze the oxidation of DHICA (Jiménez-Cervantes et al., 1994). DHICA has a higher oxidation potential than DHI. This means that DHICAquinone may be able to undergo a redox exchange with DHI yielding DHICA and DHI-quinone (Fig. 15.8). This proposal, however, does not exclude the possibility that DHI adds directly to DHICA-quinone to form heterodimers (Napolitano et al., 1993a). Copolymerization of these four intermediates should yield a series of heteropolymers of DHI and DHICA. Thus, the role of Tyrp1 appears to accelerate eumelanogenesis by oxidizing not only DHICA but also DHI indirectly. Our chemical analysis showed that follicular melanocytes of brown mice produce a eumelanin with a smaller molecular size compared with black mice (Ozeki et al., 1997b). As evidence to show that this type of copolymerization takes place, Prota’s group isolated a heterodimer of DHI and DHICA as the acetyl derivative from an oxidation mixture of DHI and DHICA (Napolitano et al., 1993a).
Late Stages of Pheomelanogenesis The early stages of pheomelanogenesis until the formation of cysteinyldopaquinones are well elucidated, as discussed above. In the later stages of pheomelanogenesis, 5-Scysteinyldopaquinone, once formed, then rapidly cyclizes via attack of the cysteinyl side-chain amino group on the carbonyl group to give a cyclic ortho-quinonimine intermediate (Fig. 15.9; Napolitano et al., 1994). The rate (r5) of quinonimine formation was determined by pulse radiolysis to be 5.5/s (Thompson et al., 1985). It should be stressed that the rate of 291
CHAPTER 15 O
HO
Polymerization of 4 intermediates
N H
O N H
HO
DHI-quinone
DHI
O
Eumelanin
HO COOH
O
N H
COOH Tyrp1
DHICA-quinone
DHICA
O
OH
O O H2N COOH
N
COOH
S NH2
N
COOH
r6
r5
HOOC
Fig. 15.8. Proposed role of Tyrp1. Copolymerization of DHI and DHICA is suggested (Ito, 2003).
N H
HO
S
5.5 sec–1 HOOC
NH2
HOOC
ortho-Quinonimine
5-S-Cysteinyldopaquinone (CDQ)
S
0.5 sec–1 NH2
1,4-Benzothiazines
CD
OH H N
COOH
S HOOC
NH2 Dihydrobenzothiazine 11
5-S-cysteinyldopaquinone formation is controlled by the rate of dopaquinone formation, because 5-S-cysteinyldopa itself is a much poorer substrate for tyrosinase than dopa (Agrup et al., 1982). An alternative pathway is possible for the metabolism of 5S-cysteinyldopaquinone; this ortho-quinone also undergoes the addition of cysteine with a rate constant of 1 ¥ 104/M/s to give the diadduct 2,5-S,S¢-dicysteinyldopa (Thompson et al., 1985). It is thus delineated that, unless the cysteine concentration is higher than 5 mM (an unlikely situation in vivo), the quinonimine formation predominates. The ortho-quinonimine then undergoes rearrangement to benzothiazine intermediate(s) with (85%) and without (15%) decarboxylation (Napolitano et al., 1994). The rate (r6) of decay (k = 0.5/s) of the cyclic ortho-quinonimine to the benzothiazines was recently determined by pulse radiolysis (Napolitano et al., 1999). As shown in Figure 15.9, an alternative pathway for ortho-quinonimine is also possible by redox exchange with 5-S-cysteinyldopa, leading to the production of a reduced form of the quinonimine (a 3,4dihydro-1,4-benzothiazine derivative 11) and 5-Scysteinyldopaquinone (Napolitano et al., 2000a). Whether the redox exchange or the rearrangement prevails is strongly influenced by many factors, including the nature of the oxidant and the concentration of the precursor 5-S-cysteinyldopa. It 292
Fig. 15.9. Kinetics in the late stages of the formation of pheomelanins from 5-Scysteinyldopaquinone. Note that the dihydrobenzothiazine 11 is produced via redox exchange whereas benzothiazine intermediates are by rearrangement (with/without decarboxylation).
therefore remains to be seen whether this redox change is a significant pathway in vivo. Reactions beyond the benzothiazines, which lead to pheomelanins, are rather complex, but nevertheless these have also been extensively studied by Prota and associates (reviewed by Di Donato and Napolitano, 2003). It is interesting to note that the presence of metal ions strongly affects the course of later stages; trichochrome-type dimers (reduced form of trichochrome pigments) are produced in the zinccatalyzed oxidation of 5-S-cysteinyldopa (Napolitano et al., 2001), while two monomeric amino acids, the benzothiazinone 12 and the benzothiazole 13 (R = H), are produced by chemical oxidants in the presence of Fe3+ or Cu2+ at neutral pH (Fig. 15.10; Di Donato et al., 2002). Notably, the formation of benzothiazole (13) suggests that the ring contraction of benzothiazines to benzothiazoles is a feasible process under physiological conditions. In this connection, high levels of zinc, iron, and copper ions are detected in melanosomes isolated from human hair (Liu et al., 2003) and in intact melanosomes from the eye (Samuelson et al., 1993). Interestingly, upon irradiation with UVA, the dihydroxybenzothiazine 11 undergoes ring contraction to give 2-methylbenzothiazole 13 (R = CH3) (Costantini et al., 1994a). The presence of benzothiazole and isoquinoline units in pheomelanins has been questioned by Prota (Prota et al.,
CHEMISTRY OF MELANINS OH
OH N
(COOH)
OH H N
O
N
Fe3+ or Cu2+
R
S
Fig. 15.10. Products of metal-catalyzed oxidation of 5-S-cysteinyldopa via the 1,4benzothiazine amino acid.
HOOC
NH2 1,4-Benzothiazines
1998a) based on the fact that the products derived from benzothiazole and isoquinoline units are obtained only when pheomelanins are subjected to drastic degradative reactions. However, as shown above, the ring contraction of benzothiazines giving benzothiazoles proceeds under very mild conditions that mimic in vivo situations. The same argument may hold true for the presence of the isoquinoline units (the unit located at the center of the structure 2). The isoquinoline structure would be readily formed through the Pictet–Spengler reaction (Manini et al., 2001) when an alanyl side-chain on a benzene ring and a carbonyl group are close to each other.
Chemical Properties of Melanins A major role of melanins in vivo is generally believed to be photoprotection of underlying tissues. However, this concept has been challenged from time to time (Hill, 1992; Wood et al., 1999), and this topic is dealt with extensively in Chapter 17 (Photobiology of melanins). However, it should be pointed out here that the measurement of eumelanin and pheomelanin contents is indispensable in these studies (De Leeuw et al., 2001; Tadokoro et al., 2003). Another important property of melanins is the ability to bind to various chemicals and metal ions. This property is discussed in Chapter 18 (Toxicological aspects of melanin and melanogenesis). Chapter 16 also addresses the physical properties of melanins, including free radical properties, redox state, and photo-oxidation.
Melanin-related Metabolites Melanin-related Metabolites as Markers of Melanoma (and Melanin Production) In addition to eumelanins and pheomelanins, normal and malignant melanocytes produce and excrete their precursors, 5,6-dihydroxyindoles and cysteinyldopas. These precursors and their metabolites are found in epidermal and melanoma tissues and in body fluids at variable levels. Therefore, those melanin-related metabolites have been extensively studied as markers of melanoma progression, to detect metastases, evaluate therapeutic effects, and to predict prognosis (for reviews, see Duchón, 1987; Hartleb and Arndt, 2002; Ito, 1992; Rorsman and Pavel, 1990; Rorsman et al., 1983). As for the 5,6-dihydroxyindoles, DHI, DHICA, and their metabolites in urine were once explored as possible markers for screening of metastasizing melanoma (Duchón et al., 1981). The indolic urinary melanogens were classified into two main groups based on the response to the Thormählen reaction (sodium nitroferricyanide). Thormählen-positive
S HOOC
NH2 Benzothiazinone 12
+
S
HOOC
NH2 Benzothiazole 13
melanogens were first recognized by Leonhardi (1955) as DHI derivatives. Through extensive studies by Duchón and his associates in Prague, this group of melanogens was shown to be glucuronides and sulfates of 5-hydroxy-6-methoxyindole and 6-hydroxy-5-methoxyindole (Matous et al., 1981; Pavel et al., 1981). The Thormählen-negative melanogens were shown to consist mainly of 5-hydroxy-6-methoxyindole-2carboxylic acid and 6-hydroxy-5-methoxy-indole-2-carboxylic acid (Duchón and Matous, 1967). These indolic melanogens are formed in melanocytes by O-methylation (Smit et al. 1990), followed by subsequent conjugation with glucuronic acid or sulfuric acid in the liver or kidney. The O-methylation appears to be a mechanism of detoxification of these cytotoxic 5,6-dihydroxyindoles. The potential usefulness of these indole melanogens as markers of melanoma progression (and of melanin production in normal subjects) has attracted the interest of clinicians. 5-Hydroxy-6-methoxyindole-2-carboxylic acid was found to be the best marker of melanin pigmentation in the urine (Westerhof et al., 1987). The level of 6-hydroxy-5-methoxyindole-2-carboxylic acid in plasma was proposed to be more sensitive and reliable than 5-S-cysteinyldopa (Hara et al., 1994), whereas other studies have reached the opposite conclusion (Horikoshi et al., 1994). In contrast to 5-S-cysteinyldopa, which is still drawing attention (Hartleb and Arndt 2001; Wakamatsu et al., 2002a), it appears likely that clinicians have lost interest in those indolic melanogens as melanoma markers. The growing interest in DHI and DHICA as equally important precursors of eumelanins and as markers of melanocyte activities has prompted us to establish more efficient methods to prepare these rather labile compounds, because previously reported methods of DHI and DHICA preparation require tedious, multistep procedures (Benigni and Minnis, 1965). Therefore, by taking advantage of the chemical reactivity of dopachrome, we developed biomimetic procedures to prepare DHI and DHICA in subgram quantities (Wakamatsu and Ito, 1988). Dopachrome generated in situ by ferricyanide oxidation of dopa at neutral pH undergoes spontaneous decarboxylation to give DHI, while treatment with alkali at pH 13 affords mostly DHICA. After recrystallization, DHI and DHICA are obtained in modest yields. As for the cysteinyldopas, the major isomer of cysteinyldopas, 5-S-cysteinyldopa, was first detected in melanoma tissues and in urine (Bjorklund et al., 1972). Subsequently, other minor isomers, i.e. 2-S- and 6-S-cysteinyldopas, along with the diadduct 2,5-S,S¢-dicysteinyldopa, have also been 293
CHAPTER 15
detected in the urine of melanoma patients (Morishima et al., 1983; Prota et al., 1977). Tyrosinase appears to be primarily responsible for the production of 5-S-cysteinyldopa. 5-S-Cysteinyldopa has thus been detected not only in melanoma tissues, in the serum, and in the urine of melanoma patients, but also in skin, hair, serum, and urine of normal subjects (Ito, 1992; Rorsman and Pavel, 1990; Rorsman et al., 1983). However, the detection of small amounts of 5-S-cysteinyldopa in plasma and urine from human and mouse albinos indicates that tyrosinaseindependent routes may also be present (Acquaron et al., 1981; Nimmo et al., 1985). In this connection, it should be noted that some biologically relevant oxidizing systems, in addition to tyrosinase, can mediate the formation of cysteinyldopas from dopa and cysteine, i.e. peroxidase/H2O2, ferrous ion, superoxide, and hydroxyl radicals (Ito, 1983; Ito and Fujita, 1981, 1982). In contrast to 5,6-dihydroxyindoles, 5-S-cysteinyldopa is not metabolized to any major extent; decarboxylation does not take place, and O-methylation (Agrup et al., 1977) and conjugation with glucuronic and sulfuric acids appear to be only minor pathways. These properties, coupled with the high renal clearance, make 5-S-cysteinyldopa a useful marker of pigmentation in normal and malignant melanocytes. Determination of plasma levels of 5-S-cysteinyldopa seems to be useful in predicting distant metastases in melanoma patients, and elevated levels are associated with a poor prognosis (Wakamatsu et al., 2002a). However, one of the drawbacks of 5-Scysteinyldopa as a melanoma marker is that the levels often rise two to several-fold in summer, occasionally to pathological levels, due to sun exposure (Rorsman et al., 1976; Wakamatsu and Ito, 1995), although this property may be used as a measure to assess the degree of sun exposure in normal subjects. The growing demand for 5-S-cysteinyldopa, not only for the study of pheomelanogenesis but also for clinical studies, has prompted us to develop convenient laboratory syntheses. For subgram scale preparation, the reaction of cysteine with dopaquinone produced by tyrosinase oxidation of dopa serves the purpose (Ito and Prota, 1977). For gram scale preparation, oxidation of dopa with ceric ammonium nitrate in sulfuric acid in the presence of cysteine seems a better choice (Chioccara and Novellino, 1986).
Cytotoxicity and Related Properties of Melanin Precursors The concept is generally accepted that melanin precursors are cytotoxic to the cells where melanin pigments are produced, i.e. melanocytes (Hochstein and Cohen, 1963). This concept leads to another concept: that the compartmentalization of melanogenesis in melanosomes represents a strategy by melanocytes to prevent the inherent cytotoxicity of melanin precursors (Prota et al., 1998a). Wick et al. (1977) were the first to explore the possibility of using the cytotoxicity of melanin precursors to develop chemotherapeutic agents against melanoma. They examined the cytotoxic effects of dopa and other related melanin pre294
cursors. These studies were followed by studies on the cytotoxicity of melanin precursors, DHI and 5-S-cysteinyldopa, to cultured melanoma cells (Fujita et al., 1980; Pawelek and Lerner, 1978). However, the mechanism of cytotoxicity of 5-S-cysteinyldopa to melanoma cells soon proved to involve the production of reactive oxygen species, such as H2O2, formed by auto-oxidation in culture media (Ito et al., 1983). The inherent cytotoxicity of DHI and DHICA was also reexamined (Urabe et al., 1994). The observed cytotoxic effects were found to be mainly due to the generation of reactive oxygen species outside the cells. It thus appears that DHI and DHICA may be less cytotoxic than one would imagine as long as they are produced and oxidized within melanosomes. Nevertheless, it is well known that stimulation of melanogenesis leads to the suppression of proliferation and eventually to cell death in cultured normal melanocytes (Hirobe et al., 2003). Further, ectopic expression of tyrosinase in the absence of Tyrp1 or Dct may cause severe cytotoxicity to nonmelanocytic cells in which no melanosomal compartmentalization is present (Singh and Jimbow, 1998). Then, what are the more toxic intermediates than DHI and DHICA that are produced in melanocytes? In the process of melanogenesis, a number of highly reactive ortho-quinones are produced including dopaquinone, dopachrome, DHI-quinone, and DHICA-quinone (Figs 15.2 and 15.8). Among these quinones, dopaquinone, DHI-quinone, and DHICA-quinone appear to be too reactive and would be polymerized within the melanosomes. Dopachrome is, however, quite stable in the absence of Dct or metal ions (Palumbo et al., 1987a). In fact, a recent study indicates that aminochromes such as dopachrome and dopaminechrome are much more toxic to cultured melanoma and neuroblastoma cells than l-dopa, DHI, and DHICA (Matsunaga et al., 2002). Dopachrome reacts with sulfhydryl compounds at the 4-position (d’Ischia et al., 1987). It now appears that dopachrome, although not extremely reactive, is able to react with sulfhydryl enzymes essential for melanocyte survival and to inactivate them, eventually leading to cell death. Supporting this view, Dct is a melanocyte-specific enzyme considered to be a “rescue” enzyme essential for melanocyte survival (Tsukamoto et al., 1992a). Mutations in Dct that decrease catalytic function affect DHICA production and are generally quite cytotoxic to melanocytes. Melanocytes typically express Dct before any of the other melanogenic enzymes, presumably to minimize such toxicity (Steel et al., 1992). Matsunaga et al. (1999) have recently shown that a related enzyme, called macrophage migration inhibitory factor (MIF), is able to catalyze the conversion of dopaminechrome to DHI. MIF is expressed in neuronal tissues and is believed to participate in a detoxification pathway for catecholamine oxidation products. The cytotoxicity of ortho-quinones could potentially lead to chemotherapeutic approaches to treat melanoma using phenolic melanin precursors (Prota et al., 1994; Riley et al., 1997). Phenolic compounds are expected to be less cytotoxic themselves than the corresponding catecholic compounds, yet they can be metabolized in melanocytes to highly reactive
CHEMISTRY OF MELANINS
those of ascorbic acid and glutathione. 5-S-Cysteinyldopa has also been shown to be a potent inhibitor of hydroxylation/ oxidation reactions mediated by H2O2 and the Fe2+/EDTA complex (Fenton reaction) (Napolitano et al., 1996d). Furthermore, DHI is highly efficient in inhibiting the generation of peroxidation products in in vitro models of UVinduced lipid peroxidation compared with 5-S-cysteinyldopa as well as eumelanin and pheomelanin samples (Schmitz et al., 1995). A recent kinetic study using laser flash photolysis also shows that the antioxidant properties of 5,6-dihydroxyindoles, in particular DHI, are as good as those of a-tocopherol (Zhang et al., 2000). The photoprotective role of melanin-related metabolites is also an interesting consideration. Photobiological and photochemical data indicate that DHI and DHICA have protective roles. Upon photoexcitation, these 5,6-dihydroxyindoles undergo photolysis with the generation of semiquinone radicals. DHI semiquinone can react with oxygen and related species, giving rise to hydroxylated oligomer species that can polymerize to eumelanic pigments (d’Ischia and Prota, 1987; Lambert et al., 1989). Thus, DHI and DHICA can contribute significantly to protect the skin from damaging UV radiation by quenching oxygen species and providing an additional amount of photoprotective pigment (Prota et al., 1998a). In contrast to 5,6-dihydroxyindoles, irradiation of 5-Scysteinyldopa with UVB results in the formation of dopa, arising by photolytic cleavage of the S–CH2 bond followed by desulfuration (Costantini et al., 1994b; Land et al., 1986). Thus, UV photolysis of 5-S-cysteinyldopa affords potentially toxic free radicals, capable of affecting important biological targets such as DNA (Chedekel and Zeize, 1988; Koch and Chedekel, 1986) or membrane lipids (Schmitz et al., 1995). However, how much these photoprotective and phototoxic events are functionally important in vivo remains to be studied. The significance of these events should depend on the concentrations of these melanin precursors in epidermal tissues, information that is scarce at present.
R
HO HO GSH R
Tyrosinase
S-G Catechol - GSH adducts
R
O O
HO Phenols OH radical
ortho-Quinones H2O2
(H)
Enz-SH
HO
O2
S-Enz
R
HO
R
HO
Catechol - Protein adducts HO Catechols
Fig. 15.11. Mechanism of melanocytotoxicity of phenolic and catecholic melanin precursors (Ito, 2003).
ortho-quinones by the action of tyrosinase (Fig. 15.11). The ortho-quinones thus formed may be detoxified by glutathione in the cytosol, but those that escape from this detoxification mechanism may enter the nucleus and inactivate sulfhydryl enzymes such as thymidylate synthase, thereby leading to cell death (Prezioso et al., 1992). Among the phenolic compounds so far examined, 4-S-cysteaminylphenol and its derivatives appear to be the most promising antimelanoma agents (Alena et al., 1990; Yukitake et al., 2003). The ultimate toxic metabolite of 4-S-cysteaminylphenol has been shown to be dihydro-1,4-benzothiazine-6,7-quinone, a sulfur homolog of dopaminechrome (Hasegawa et al., 1997; Mascagna et al., 1994). Catechols, such as dopa and DHI, are cytotoxic through two possible routes: one through the generation of ortho-quinones and the other through auto-oxidation producing H2O2 and hydroxyl radicals (Graham et al., 1978). To evaluate the binding of ortho-quinones to proteins through cysteine residues, we developed a method to measure the catechol–protein adducts. The method is based on the HPLC analysis of cysteinyl–catechols formed on HCl hydrolysis of the modified proteins (Ito et al., 1988a). Melanin precursors themselves may have protective roles in melanocytes (Prota et al., 1998a). DHI and, to a lesser extent, DHICA and 5-S-cysteinyldopa are capable of inhibiting lipid peroxidation in several in vitro model systems (Memoli et al., 1997; Napolitano et al., 1993b). These melanin precursors have been shown to have inhibitory effects much greater than
Degradative Studies on Melanins Eumelanins Biosynthetic and degradative studies indicate that natural eumelanins are highly heterogeneous polymers consisting of various monomer units, including DHI unit A, DHICA unit B, and the pyrrole units C and D derived from peroxidative cleavage of units A and B (Fig. 15.12; Prota, 1992).
HO
HO
COOH
N H
HO
A
N H
HO
B
O
O
O
HOOC
COOH
N H
N H
C
D
Fig. 15.12. Monomer units present in the eumelanin polymer. The carbon to nitrogen ratios are 8, 9, 6, and 7 for DHI unit (A), DHICA unit (B), pyrrole unit (C), and pyrrole-carboxylic acid unit (D) respectively. DHI and DHICA units may also be present in the oxidized, orthoquinone form.
295
CHAPTER 15 HOOC
HOOC COOH
HOOC N H
14 (PTCA)
COOH
HOOC N H
COOH
15
Extensive degradative studies provided a number of chemical degradative methods (Nicolaus, 1968; Swan and Waggott, 1970). Among them, oxidative degradation by permanganate or H2O2 appears to be most informative (Panizzi and Nicolaus, 1952; Piattelli and Nicolaus, 1961). Nicolaus (1968) repeated the oxidation of Sepia melanin with H2O2 at pH 7 followed by alkaline hydrolysis, which afforded a 6.5% yield of pyrrole2,3,5-tricarboxylic acid (PTCA; 14 in Fig. 15.13). In another preparative experiment in which 10 g of Sepia melanin was oxidized by H2O2 in acetic acid, 200 mg of PTCA and 61 mg of pyrrole-2,3,4,5-tetracarboxylic acid (15) were isolated (Nicolaus, 1968; Piattelli et al., 1962). In our studies, permanganate oxidation of natural eumelanins gave about a 2% yield of PTCA (Ito and Fujita, 1985). We also noticed that permanganate oxidation gave a considerable amount of the tetracarboxylic acid 15 only when the oxidation was conducted under alkaline conditions (Ito and Fujita, 1985). This suggests that, during oxidative degradation carried out in an alkaline medium, the 3-position of DHICA unit B is connected to another monomer unit, thus giving rise to the artificial formation of the tetracarboxylic acid 15. This represents an example of possible artifact formation during degradative reactions and calls for more attention to such possibilities. The origin of PTCA was interpreted in terms of oxidative breakdown of the DHICA-derived structures (units B and D) in the eumelanin polymer. Another pyrrolic acid, pyrrole-2,3dicarboxylic acid (PDCA, 16), can be expected to arise from DHI-derived structures (units A and C). In fact, small amounts of this pyrrolic acid were detected among oxidation products of Sepia melanin, dopa melanin, and DHI melanin (Piattelli et al., 1962). The significance of its formation has recently been re-examined (Napolitano et al., 1995). Other degradative reactions appeared to be much less informative. Alkaline fusion of Sepia melanin afforded both DHI and DHICA, but the yields were too low to make this reaction significant (Piattelli et al., 1963). Mild treatment of Sepia melanin with sodium borohydride in 0.1 M NaOH also afforded DHICA (d’Ischia et al., 1985). Again, the yield was very low. Some PTCA was also obtained by boiling Sepia melanin in 4% NaOH (Piattelli et al., 1962).
Carboxyl Content in Eumelanins The carboxyl group attached to the indole or pyrrole ring (in units B or D) is labile and may easily be split off as CO2 by heating melanin powder at a high temperature or by heating a melanin suspension in Vaseline (Piattelli et al., 1962) or in 6 M HCl (Ito, 1986). Our experience indicates that the acid decarboxylation is more reproducible and releases CO2 quan296
HOOC HOOC N H 16 (PDCA)
Fig. 15.13. Products of oxidation of eumelanins with acidic potassium permanganate or alkaline H2O2.
titatively (Ito, 1986). This methodology has been applied successfully to estimate the content of carboxyl groups in natural and synthetic eumelanins (Ito, 1986; Novellino et al., 2000; Palumbo et al., 1988; Pezzella et al., 1997). Using decarboxylation, substantial amounts of carboxyl groups were found in all the natural eumelanins examined, suggesting the common presence of DHICA-derived units (Prota, 1992; Prota et al., 1998a). Permanganate oxidation of eumelanins gives PTCA that arises from DHICA-derived structures (units B and D). Comparison of the yields of PTCA from a number of natural and synthetic eumelanins, coupled with results of the acid decarboxylation, indicates that units derived from DHICA comprise only 10% of synthetic dopa melanins, but as much as one-half of intact, natural eumelanins (Ito, 1986). The first unambiguous demonstration of the involvement of DHICA in eumelanogenesis came from a study in which 1-14C-dopa was injected into melanoma-bearing mice (Tsukamoto et al., 1992b). The pigment from the tumor was then isolated, purified, and chemically decarboxylated. Determination of the labeled CO2 evolved showed that at least 20% of the precursor incorporated into the melanin retains the labile isotope in the form of DHICA-linked carboxyl groups. In another approach to determine the carboxyl contents in melanins, Zeise and Chedekel (1992) used a titrimetric analysis to quantify the bioavailable carboxyl groups present on the surface of melanin particles. They found that the ratio of moderately acidic (–COOH) to weakly acidic (phenolic OH) groups was 0.86 in Sepia melanin. This method (Zeise and Chedekel, 1992) would be useful in comparing the functional groups present on the surface of various melanin pigments.
Pheomelanins Biosynthetic and degradative studies carried out on pheomelanic pigments including trichochromes indicate that pheomelanins are also highly heterogeneous polymers arising from the oxidative polymerization of 1,4-benzothiazines derived from cysteinyldopas (Prota, 1992; Prota et al., 1998a). Structural studies on pheomelanic pigments were greatly facilitated by reductive hydrolysis with hydriodic acid that yielded a number of informative degradation products. Although the conditions employed for the degradation were harsh, suggesting the possibility of artifact formation, the relatively high yield of degradation products makes the method indispensable in structural studies of pheomelanic pigments (Patil and Chedekel, 1984; Prota, 1992). When heated in hydriodic acid, the decarboxy derivative of trichochrome C (3) gives as major products 4-amino-3-
CHEMISTRY OF MELANINS
OH
R
NH2
N
NH2
Fig. 15.14. Products of hydriodic acid hydrolysis of trichochromes and pheomelanins. R = H or CH3.
HOOC
OH
HOOC
NH2
NH2
S
HOOC
18 (3-AHP)
17 (4-AHP)
OH OH
NH2
R
N
HOOC
NH2
20
19
OH COOH COOH
N HOOC
HOOC
N
N
COOH S
COOH
Fig. 15.15. Products of oxidation of pheomelanins with acidic potassium permanganate or alkaline H2O2.
HOOC
N
COOH
21
hydroxyphenylalanine (4-AHP; 17) and the benzothiazinone amino acid 12, along with the benzothiazole amino acid 13 (R = CH3) (Fig. 15.14; Nicolaus et al., 1969). Trichochrome F (4), which occurs concomitantly at a much lower concentration than trichochrome C, gives 4-AHP along with a much smaller amount of the benzothiazole 13 (R = H) on hydriodic acid treatment (Prota et al., 1969). On the other hand, degradation of trichochrome E (6) with hydriodic acid gives a mixture of two isomers, 4-AHP (17) and 3-AHP (18). The benzothiazole amino acids 12 (R = H and CH3) can arise readily from trichochromes by ring contraction under acidic or alkaline conditions; heating the benzothiazinone 12 in hydrochloric acid affords the benzothiazole 13 (R = H) (Fattorusso et al., 1968). Gallopheomelanin-1, the major, protein-free, pheomelanic pigment, was isolated from red chicken feathers by alkaline extraction and chromatography on Sephadex (Minale et al., 1967; Prota and Nicolaus, 1967). A most notable feature of gallopheomelanin-1 was its high sulfur content; it contained 9.0% nitrogen and 9.9% sulfur, the molar ratio of nitrogen to sulfur being 2.1:1 (Minale et al., 1967). On hydriodic acid hydrolysis, gallopheomelanin-1 affords the benzothiazole amino acids 13 and 19 (R = H and CH3) along with a comparable amount of AHP isomers, 4-AHP (17) and 3-AHP (18), with benzothiazole (19) and 3-AHP (18) being minor isomers (Fattorusso et al., 1968; Minale et al., 1967). These characteristic products were obtained in similar yields (total yields of about 20%) from synthetic pheomelanins prepared either from a mixture of dopa and cysteine or from 5-S-cysteinyldopa (Fattorusso et al., 1969a). Difficulties in interpreting these results arise from the fact that these natural and synthetic pheomelanin preparations were subjected to strongly alkaline pH during the isolation procedure or chromatographic separation. This would suggest that a major part of the benzothiazole units in pheomelanins arise artificially from the benzothiazine units. In support of this view, our recent study has shown that the benzothiazoles
HOOC
S 22 (TTCA)
HOOC
S
23 (TDCA)
HOOC
NH2 24 (BTCA)
13 and 19 (R = H) were obtained in yields approximately 1/10th those of AHP isomers on hydriodic hydrolysis of both natural and biosynthetic pheomelanins that were not subjected to alkaline conditions (Ito, 1989). The production of AHP isomers occurs specifically at the expense of benzothiazine units, but not benzothiazole units (Fattorusso et al., 1968; Ito, 1989). The reaction involves reductive fission of the aromatic C–S bond induced by the iodide anion. Other interesting products of reductive degradation with hydriodic acid are the isoquinolines 20 (R = H and CH3) (Fattorusso et al., 1970). Also, permanganate oxidation of pheomelanins gives a product arising from the isoquinoline unit, pyridine-2,3,4,6-tetracarboxylic acid (21), in addition to thiazole-2,4,5-tricarboxylic acid (TTCA; 22) and thiazole-4,5tricarboxylic acid (TDCA; 23), which arise from the benzothiazole units (Fig. 15.15; Fattorusso et al., 1969b). Red hair was recently found to be closely associated with loss-of-function mutations of the melanocortin-1 receptor (MC1R) (Valverde et al., 1995). After that discovery, there has been a growing interest in red hair as a risk factor for melanoma and for nonmelanoma skin cancers (Rees, 2000). Napolitano et al. (2000b) recently described another marker of pheomelanins, i.e. 6-b-alanyl-2-carboxy-4-hydroxybenzothiazole (BTCA; 24) in addition to TTCA (22), both of which are produced by alkaline H2O2 treatment of various hair samples. It is suggested that BTCA represents a new biogenetic marker for predicting individuals at high risk for skin cancer and melanoma. Based on these data, a representative structure (2) can be proposed for pheomelanins (Ito, 1993a, 1998). The benzothiazine unit should constitute at least 40% of the monomer units, as hydriodic acid hydrolysis of trichochrome F gives AHP in about a 50% yield, whereas the yields are about 20% from pheomelanins (Ito, 1989; Ito and Fujita, 1985). The other monomer units, such as the isoquinoline and benzothiazole units, may represent only minor constituents. Some of the alanyl and cysteinyl side-chains may be degraded during 297
CHAPTER 15 Table 15.3. Comparison of chemical and physical properties of eumelanins and pheomelanins. Property
Eumelanins
Pheomelanins
Specificity
Color of tissue Solubility Elemental composition IR spectrum UV-vis spectrum NMR spectrum EPR spectrum Chemical degradation
Dark brown to black Insoluble in all solvents C, H, O, N (6–9%), S (0–1%) No characteristic bands General absorption Potentially useful Single peak PTCA
Yellow to reddish brown Soluble in alkali C, H, O, N (8–11%), S (9–12%) No characteristic bands General absorption No data Two peaks AHP†
Low Low Low Low Low* ? High High
*Difference between eumelanins and pheomelanins can be used to differentiate them. †Recently, 4-AHP has been introduced as a more specific marker for pheomelanins (Wakamatsu et al., 2002b).
polymerization (Chedekel et al., 1987; Deibel and Chedekel, 1984).
Chemical Analysis of Melanins Spectrophotometric Analysis of Melanins: Historical Background Regulation of melanogenesis has been the subject of extensive studies. In most such studies, quantitation of melanins in pigmented tissues such as hair and skin and in cultured melanocytes is essential. Effects of the genetic background on hair pigmentation in mammals can also be assessed by analysis of the quantity and quality of the melanins produced. Despite these needs, no simple laboratory methods to quantify melanins have been developed. Most laboratory tests to quantify biomolecules such as proteins, carbohydrates, lipids, and nucleic acids utilize specific reagents that develop a characteristic color with a given biomolecule in solution. On the contrary, a major problem in quantifying melanins appears to be how to solubilize the melanin pigment. Once solubilized, melanin can easily be assayed by absorbance in the visible absorption spectra. Quantitation of melanins present in pigmented tissues is a challenge. By taking advantage of the insolubility of melanins in hydrochloric acid, Oikawa and Nakayasu (1973) reported a spectrophotometric assay of melanins based on solubilizing the deproteinized melanin in Soluene-100 (a 0.5 M solution of dimethyl-n-dodecyl-n-undecylammonium hydroxide in toluene). Eumelanins can be completely dispersed in Soluene100 giving a solution that shows no light scattering (Oikawa and Nakayasu, 1975). If the melanin content is sufficiently high, the dry weight of black pigment remaining after HCl hydrolysis also serves the purpose of quantitation (Borovansky, 1978). On the other hand, melanins present in cultured melanocytes can be solubilized in hot KOH or NaOH of about 1 M concentration, and the resulting solution is analyzed for absorbance between 400 to 500 nm (Whittaker, 1963). Treatments prior to the solubilization include precipitation of melanin (and protein) with perchloric acid or washing with a buffer followed by extraction of lipids with organic solvents. 298
Such pretreatments can be omitted when Soluene-350 is used as a solvent to dissolve all the constituents of cells, including the melanin pigment (Kable and Parsons, 1989). Soluene-350, a tissue solubilizer widely used in liquid scintillation counting, has a higher capacity to dissolve tissue constituents and to retain water than Soluene-100. Melanins can be oxidatively solubilized by heating in an alkaline, dilute H2O2 solution. The resulting solution has a characteristic fluorescence that can be used for quantitation of melanins (Rosenthal et al., 1973). Although the authors claimed that the assay could be applied directly to tissues or cell cultures, it still required a lengthy pretreatment. In another interesting method, sodium borohydride, a mild reducing agent, was used to solubilize melanins (Das et al., 1976), and this method was used to characterize neuromelanin isolated from the substantia nigra (Das et al., 1978).
Comparison of Chemical and Physical Properties of Eumelanins and Pheomelanins Because of the lack of adequate methods to isolate melanins from biochemical sources, their insolubility at neutral pH, and their structural heterogeneity, full characterization of melanins faces great obstacles. Table 15.3 compares various methods as to whether they can differentially characterize eumelanins and pheomelanins. As the physical analysis of melanins is dealt with in the following chapter, it is discussed here only briefly. The color of tissue containing eumelanins is considered to be dark brown to black, whereas that containing pheomelanins is yellow to reddish brown. However, one cannot differentiate between dark brown and reddish brown with certainty. In fact, HPLC analysis of hair samples indicates that the visual differentiation is not reliable (Jimbow et al., 1983). Differences in solubility are also not very specific (Prota et al., 1976), as eumelanins appear to be slightly soluble in alkaline solutions, the property serving as a basis for the spectrophotometric assay of melanins (Watt et al., 1981). Elemental analysis of melanins is often considered unreliable, as repeated analyses of a given preparation of melanin give variable results. However, we have found that this is due to the presence of loosely bound water in the melanin samples;
CHEMISTRY OF MELANINS
melanins are hygroscopic, containing from 10% to 20% water (Ito, 1986; Zeise et al., 1992). In addition, duplicate analyses of melanins from various sources showed satisfactory reproducibility (Dryja et al., 1979). Differences in the elemental composition, especially in sulfur content, serve to distinguish pheomelanins from eumelanins. Theoretically, eumelanins contain no sulfur while pheomelanins possess a sulfur to nitrogen molar ratio of 1:2. Novellino et al. (1981) attributed the high content of sulfur in some melanins isolated from hair, feathers, and melanomas to copolymerization of the two types of melanin pigments (Prota, 1988). However, the possibility that at least some of the sulfur may arise as an artifact was suggested by the finding that as much as 1–2% of the sulfur was incorporated into melanins during isolation procedures under commonly used acidic conditions (Ito et al., 1988b). Elemental analysis is also of considerable value in characterizing eumelanins; the carbon to nitrogen molar ratio may be indicative of the extent of retention of the carboxyl group originally present in dopa and of the extent of oxidative cleavage of 5,6-indolequinone units (Ito, 1986) (Fig. 15.12). Chedekel et al. (1992) prepared Sepia melanin and tyrosine melanin in the form of K+ salts under mild conditions. The elemental analyses of these preparations, corrected for amino acid contents, were C7.67H5.33NO3.68K0.18 for Sepia melanin and C7.88H4.53NO3.78K0.12 for tyrosine melanin. These analytical data indicate that at least 18% and 12%, respectively, of the monomer units contain carboxyl groups (in the form of –COOK), and considerable degrees of peroxidative cleavage of the ortho-quinone moiety have taken place. Infrared absorption spectroscopy appears to be of little value in characterizing melanins (Wilczok et al., 1984). Ultraviolet-visible absorption spectra of both types of melanins exhibit general absorption showing no distinctive absorption maxima. However, it should be pointed out that a solution of black hair melanin dissolved in Soluene-100 showed much higher absorbances at longer wavelengths than those of red hair melanin (Menon et al., 1983). This would suggest a possible use of the absorption spectra to differentiate eumelanins from pheomelanins (see below). Recently, solid-phase nuclear magnetic resonance (NMR) spectroscopy has been introduced to assess structural features surrounding carbon and nitrogen atoms using natural 13C and 15 N as probes (Duff et al., 1988; Hervé et al., 1994). The methodology has thus far been applied to the analysis of synthetic and natural eumelanins; no application has been reported so far for the characterization of pheomelanins. Interestingly, Sepia melanin, partially dissolved in D2O at pH 10, gives a surprisingly simple and well-resolved 1H-NMR spectrum (Katritzky et al., 2002). Thus, NMR would potentially be useful in characterizing both synthetic and natural eumelanins as well as pheomelanins. Among the spectroscopic methods, electron paramagnetic resonance (EPR) spectroscopy has proved most successful in distinguishing between eumelanins and pheomelanins. Both melanins contain radical centers in their polymer matrices; eumelanins are characterized by the O-centered ortho-
semiquinone radical (single peak in the EPR spectrum) and pheomelanins by the N-centered ortho-semiquinone-imine radical (two peaks). One can estimate the content of pheomelanin in mixtures or copolymers of eumelanins and pheomelanins (Sealy et al., 1982a, b; Vsevolodov et al., 1991). Extensive studies carried out in Naples resulted in the detection of many degradation products, some of which are specific to one type of melanin. Notably, permanganate oxidation of eumelanins gave pyrrole-2,3,5-tricarboxylic acid (PTCA, 13) (Nicolaus, 1968; Piattelli et al., 1963), while hydriodic acid hydrolysis of pheomelanins yielded aminohydroxyphenylalanine isomers, 4-AHP (16) and 3-AHP (17) (Minale et al., 1967; Prota, 1972; Thomson, 1974). We have developed a microanalytical method to quantitate eumelanins and pheomelanins in biological materials, based on HPLC analysis of these specific degradation products (Fig. 15.16; Ito and Fujita, 1985; Ito and Jimbow, 1983). The method is relatively simple and rapid and does not require the isolation of melanins from tissue samples. The details of this HPLC method are discussed below.
Quantitative Analysis of Eumelanins and Pheomelanins by Chemical Degradation Previous methods for the quantitation of melanins in pigmented tissues required the isolation of melanins. Moreover, none of those methods was suitable for distinguishing between eumelanins and pheomelanins. In 1983, we introduced a rapid method for quantitatively analyzing eumelanins and pheomelanins in tissue samples, which makes the isolation of melanin pigments unnecessary (Ito and Jimbow, 1983). The method is based on the formation of PTCA (14) by permanganate oxidation of eumelanins and of AHP isomers (17, 18) by hydriodic acid hydrolysis of pheomelanins respectively (Fig. 15.16). These specific degradation products are determined by HPLC; PTCA is quantified with UV detection while a mixture of AHP isomers is determined as a single peak with electrochemical detection. These degradation products were chosen because not only are they the major products from eumelanins and pheomelanins but they are also easily detected with high sensitivity. A similar approach using paper chromatography had been reported previously by Hackman and Goldberg (1971) and Novellino et al. (1981). The original method was later improved to increase the sensitivity and to reduce the time for pre-HPLC work-up (Ito and Fujita, 1985). It should be noted that the alkaline 1 M K2CO3 medium for permanganate oxidation was replaced with acidic 1 M H2SO4. With this modification, the artificial formation of pyrrole-2,3,4,5-tetracarboxylic acid (15) could be avoided. The improved method requires only 5 mg or less of tissue samples or 106 cultured cells for each analysis. Recently, the conditions for permanganate oxidation were refined so that the PTCA values become more linearly correlated to the melanin contents (Ito and Wakamatsu, 1994). The yields of PTCA and AHP (4-AHP and 3-AHP combined) are approximately 2% from natural eumelanins and 20% from synthetic pheomelanins (Fig. 15.16), and the tissue contents of 299
CHAPTER 15
HOOC
HO COOH
KMnO4/H+ HOOC
COOH
N H
2.8% yield
N H
HO
HO
KMnO4/H+
PTCA
DHICA-derived eumelanin
N H
HO
0.03% yield
DHI-derived eumelanin
(COOH) OH
N N
(COOH)
S
OH
+ S NH2
HOOC
HOOC
5-S-CD-derived pheomelanin
11% yield
NH2
2-S-CD-derived pheomelanin
HI
HI
OH
HOOC
NH2 4-AHP
NO2
NH2 NH2
OH
HOOC
NH2 3-AHP
eumelanins and pheomelanins can therefore be estimated by multiplying the PTCA and AHP contents by factors of 50 and 5 respectively (Ito and Fujita, 1985). Thus, a PTCA/AHP ratio of 0.1 indicates a mixed melanin consisting of equal amounts of eumelanins and pheomelanin. Our HPLC method is relatively simple, fairly rapid, and highly sensitive. It has been applied for quantitatively analyzing eumelanins and pheomelanins not only in synthetic melanins, isolated melanosomes, hair, feathers, skin, nevi, and melanomas, but also in human epidermis and in cultured melanocytes (Ito, 1993b, 1998; Ito and Wakamatsu, 2003; Wakamatsu and Ito, 2002). A typical application of the method was to demonstrate that a synthetic analog of a-MSH, Nle4DPhe7aMSH, induces significant increases in the eumelanin content of cultured human melanocytes (Hunt et al., 1995). Several other laboratories have employed the same method in studies on melanin and melanogenesis (reviewed by Ito and Wakamatsu, 2003). As an example of one study using a similar method, pigments present in iris pigment epithelium of human eyes were found to be eumelanic (Prota et al., 1998b). The EPR and HPLC methods have been compared in estimating the contents of eumelanins and pheomelanins in hair samples from newborn sheep. The results showed that the EPR method correlates well with the HPLC method, although the former lacks the sensitivity of the latter with respect to the analysis of pheomelanins (Vsevolodov et al., 1991). 300
OH
HI
HOOC
NH2 3-Nitrotyrosine
Fig. 15.16. Chemical degradation of eumelanins to form PTCA and of pheomelanins to form 4-AHP and 3-AHP. Note that the yield of PTCA from DHIderived eumelanins is extremely low, compared with that from DHICA-derived eumelanin. PTCA is thus a specific degradation product of DHICA-derived eumelanin. Reductive hydrolysis of pheomelanins with hydriodic acid gives two isomers, 4-AHP and 3-AHP, arising from 5S- and 2-S-cysteinyldopa-derived pheomelanins respectively. 3-AHP also arises from 3-nitrotyrosine-containing proteins (Wakamatsu and Ito, 2002).
The formation of PTCA has been interpreted in terms of the oxidative breakdown of indole units, either linked through the 2-position or bearing a carboxyl group at the same position (Napolitano et al., 1995). Permanganate oxidation of DHI melanin and DHICA melanin in acidic medium afforded PTCA in 0.03% and 2.8% yields respectively (Fig. 15.16; Ozeki et al., 1995; Ito, 1998). A similar result was also reported by Prota’s group (Napolitano et al., 1995; Novellino et al., 2000). These results have confirmed our proposal that PTCA is a specific product arising from DHICA-derived structures (units B and D).
4-Amino-3-hydroxyphenylalanine (4-AHP) as a Specific Marker for Pheomelanins In previous reports from our laboratory, the HPLC conditions used were such that 4-AHP (16) and 3-AHP (17) eluted in a single peak. This was based on the assumption that any natural pheomelanin pigment consists of a fixed ratio of 5-Scysteinyldopa and 2-S-cysteinyldopa because the ratio of these cysteinyldopa isomers in biological materials is chemically controlled to be approximately 5:1 (Ito and Prota, 1977; Morishima et al., 1983). In fact, the estimation of pheomelanin as the combined amount of 4-AHP and 3-AHP (“total AHP”) did not impose any serious problem in most cases. However, small amounts of background values of total AHP were found even in hairs from tyrosinase-negative, albino mice (Lamoreux et al., 2001; Ozeki et al., 1995).
CHEMISTRY OF MELANINS
However, one problem with using total AHP as a marker was that background levels of AHP seemed to originate from precursors other than pheomelanin. Considerable and variable amounts of background 3-AHP are produced from other sources, most likely nitrotyrosine residues in proteins. The nitration of tyrosine appears to be a common biological phenomenon originating from nitric oxide. Kolb et al. (1997) and Borges et al. (2001) described the separation of 4-AHP and 3-AHP in hydriodic hydrolysates of various tissue samples. However, their reported methods require ion-exchange chromatography prior to the HPLC separation, which is not only time-consuming but also very costly (because of using commercial, disposable ion-exchange columns). In order to overcome this problem, we developed HPLC conditions that enable the direct injection of the hydriodic acid hydrolysis products into the HPLC system allowing separation of 4-AHP and 3-AHP (Fig. 15.16). As the yield of 4-AHP from synthetic pheomelanin is 11%, the content of pheomelanin can be obtained by multiplying the content of 4AHP by a factor of 9 (Wakamatsu et al., 2002b). We are now using 4-AHP as a more specific marker of pheomelanins in subsequent studies (Naysmith et al., 2004; Tadokoro et al., 2003). For clinical studies, it is often preferable to use serum or urine specimens to monitor the degree of pigmentation. We recently applied the specific pheomelanin assay method to analyze pheomelanin in the serum and urine from melanoma patients. Wakamatsu et al. (2003a) reported that serum levels of 4-AHP in metastatic melanoma patients were sevenfold higher than in control subjects, and they correlated well with serum levels of 5-S-cysteinyldopa. Similarly, Takasaki et al. (2003) showed significant correlations of 4-AHP and 3-AHP in melanoma urine with the urinary levels of 5-S-cysteinyldopa. These results suggest that the levels of 4-AHP in serum and urine could be used to monitor the production of pheomelanin in human skin.
Dopamine Melanin, Cysteinyldopamine Melanin, and Nonmelanocytic Melanins Dark brown pigments, similar to eumelanins and pheomelanins, are also produced in cells other than melanocytes. For example, humans and primates produce neuromelanin in dopaminergic nigrostriatal neurons (Zecca et al., 2001). Recently, Napolitano et al. (1995) showed that peroxide oxidation of DHI melanin in 1 M K2CO3 produces PDCA (16) in a yield (~0.5%) that is much higher than that produced by acidic permanganate oxidation. To characterize the diverse types of melanins, especially to identify dopamine-derived melanins, we have improved the alkaline H2O2 oxidation method of Napolitano et al. (1995) in terms of speed and sample size required (Ito and Wakamatsu, 1998). The results with peroxide oxidation show that: (1) PDCA, a specific marker of DHI units in eumelanins, is produced in yields 10 times higher than by acidic permanganate oxidation; (2) PTCA is produced in higher yields as well, but is also artificially produced from pheomelanins; and (3) the PDCA/PTCA
NH2
OH
OH
NH2
NH2 25 (4-AHPEA)
NH2 26 (3-AHPEA)
Fig. 15.17. Products of hydriodic acid hydrolysis of cysteinyldopamine-derived melanins.
ratio may be useful in characterizing eumelanins with various ratios of the monomers DHI and DHICA. Analogous to pheomelanins, hydriodic acid hydrolysis of cysteinyldopamine melanin produces a high (12%) yield of a 5:1 mixture of 4-amino-3-hydroxyphenylethylamine (4AHPEA; 25) and 3-amino-4-hydroxyphenylethylamine (3AHPEA; 26) (Fig. 15.17). 4-AHPEA may thus serve as a specific indicator of cysteinyldopamine-derived melanin (Wakamatsu et al., 1991, 2003a). It is generally accepted that neuromelanin is produced from dopamine (Zecca et al., 2001). Cysteine may be incorporated into neuromelanin in a mechanism similar to pheomelanin production. However, our group and Rorsman’s group reached opposite conclusions as to whether cysteine (via cysteinyldopamine) is actually incorporated (Carstam et al., 1991; Odh et al., 1994a). To solve this discrepancy, a more accurate method was developed to characterize neuromelanin chemically (Wakamatsu et al., 2003b). We prepared synthetic models of neuromelanin by tyrosinase oxidation of dopamine and cysteine in various ratios (Wakamatsu et al., 1991). Alkaline peroxide oxidation of these model neuromelanins produces thiazole carboxylic acids, TTCA (21) and TDCA (22), in addition to PDCA (13) and PTCA (14). We found that the yield of PDCA is relatively constant in synthetic melanins with various dopamine and cysteine ratios, whereas the yield of TTCA is higher than that of TDCA and is proportional to the sulfur to nitrogen ratio. It is concluded that the TTCA/PDCA ratio is a useful indicator of cysteinyldopamine-derived units in neuromelanin, and that neuromelanin consists mainly of dopamine melanin with some contribution from cysteinyldopamine melanin (Wakamatsu et al., 2003b). Similarly, Odh et al. (1994a, b) used the TDCA/PTCA ratio as an indicator of the benzothiazine units in isolated neuromelanin and in pigment in cultured melanoma cells. These results also suggest that the same methodology should be useful for analyzing eumelanins and pheomelanins in various tissues. Melanin pigments may be characterized by contents of PTCA, PDCA, TTCA, TDCA, and the ratios among them. In particular, TTCA may serve as a specific marker of pheomelanins (Napolitano et al., 2000b). The dark pigment in butterfly wings is another example of a natural melanin whose chemical nature was mostly 301
CHAPTER 15
unknown. We applied peroxide oxidation and hydriodic acid hydrolysis to follow the developmental increase in melanin in wings from Precis coenia and found that cysteinyldopamine melanin was formed first, followed by more eumelanic, dopamine melanin (Wakamatsu et al., 1998). Certain bacteria and fungi also produce insoluble, dark brown, melanin-like pigments. Cryptococcus neoformans is an opportunistic fungal pathogen that causes life-threatening infections in brains of about 10% of AIDS patients. We have applied the alkaline peroxide oxidation to analyze melanin pigments produced in C. neoformans (Williamson et al., 1998). C. neoformans produces dark pigments on its cell wall when grown in media containing a diphenolic substrate, such as dopa or dopamine. We performed peroxide oxidation of C. neoformans cells grown on dopamine or dopa agar. Cells grown on dopamine agar gave a high ratio of PDCA/PTCA whereas cells grown on dopa agar gave a high ratio of PTCA/PDCA. These data provide direct chemical evidence for the formation of eumelanic pigments by oxidation of catecholic precursors by C. neoformans laccase.
indicator of DHI-derived units in eumelanin, and the PDCA/PTCA ratio is useful in characterizing various types of eumelanin, a ratio greater than 1 indicating dopamine melanin; (2) the calibration curves for PDCA and PTCA are linear; and (3) it is easier to perform than the permanganate oxidation. However, the alkaline peroxide oxidation method also has a certain disadvantage: yields of PTCA and PDCA from 5-S-cysteinyldopa melanin are abnormally high compared with those with permanganate oxidation. This indicates that indole units are formed artificially during the oxidation, because the postulated structure of 5-S-cysteinyldopa melanin does not contain an indole unit (Prota, 1992). Prota et al. (1995) and our group (Ito and Wakamatsu, 1998) also found abnormally high yields of PTCA and PDCA when lethal yellow and recessive yellow mouse hairs were subjected to alkaline peroxide oxidation. We therefore recommend that special care be taken when alkaline peroxide oxidation is used to analyze pigmented tissues containing pheomelanin.
Comparison of Permanganate Oxidation and Peroxide Oxidation
Although the melanin assay based on chemical degradation and HPLC determination is relatively simple, it still requires an HPLC system with UV and electrochemical detectors. In addition, PTCA arises from DHICA-derived units but not from DHI-derived units. Therefore, we have developed a spectrophotometric method that is specific to eumelanins but does not discriminate between the DHI- and DHICA-derived units (Ito et al., 1993). In this method, hair and melanoma samples are hydrolyzed in hot hydriodic acid to remove pheomelanic components, and the insoluble eumelanic pigments are subsequently solubilized in hot NaOH in the presence of H2O2 and analyzed for absorbance at 350 nm. Although much less sensitive, this spectrophotometric method can substitute for the PTCA method to measure eumelanin content when substantial amounts of samples are available. Total amounts of melanin pigment in tissue samples can be calculated by the use of conversion factors of 50 and 9 for PTCA and 4-AHP respectively. However, the accuracy of this estimation rests on the assumptions that the DHICA/DHI ratios in different eumelanins from various sources are constant and that the 11% yield of 4-AHP from synthetic pheomelanins holds for different natural pheomelanins. The DHICA/DHI ratio appears to vary from one species to another. These situations made it necessary to introduce a simple, reference method to estimate the total amounts of melanins, even if the method might not give accurate values. We have found that hot Soluene-350 (in the presence of 10–20% water) is able completely to dissolve mouse and human hairs and sheep wool. The resulting brown solutions are analyzed for absorbances at 500 nm (Ito et al., 1996; Ozeki et al., 1995, 1996a, b). Hair samples from different coat color phenotypes of mice and human hairs of various colors were analyzed with this spectrophotometric method. Excellent correlations were found between the absorbance at 500 nm (A500) and the melanin con-
Our HPLC methods for assaying eumelanin and pheomelanin are highly sensitive and specific and possess many advantages, but also have certain disadvantages. The acidic permanganate oxidation method that we have been using for quantitative analysis of eumelanin has a number of advantages (Table 15.4): (1) PTCA is formed primarily from DHICA-derived units in eumelanin, thus making PTCA a specific marker of DHICA content (Wakamatsu and Ito, 2002); and (2) PTCA is not artificially formed from pheomelanin. However, this method also has some disadvantages: (1) the yield of PDCA is too low to be used as a marker of DHI-derived units; and (2) the amount of PTCA formed gives a slightly concave calibration curve against the amount of melanin oxidized despite recent improvements (Ito and Wakamatsu, 1994). The alkaline peroxide oxidation method has several advantages (Ito and Wakamatsu, 1998): (1) PDCA is an excellent
Table 15.4. Advantages and disadvantages of the two oxidation methods. Comparison
Acidic KMnO4 oxidation
Alkaline H2O2 oxidation
PTCA
Specific for DHICA units
PDCA
Little produced
TTCA, TDCA
Produced, but hard to be extracted
Method
Requires some skills
Not specific for eumelanins Indicator of DHI units, but not specific for eumelanins Specific for CD-derived and Cys-DA-derived units Easier to perform
302
Combined Use of Spectrophotometric and Degradative Analyses
CHEMISTRY OF MELANINS
tents calculated from PTCA and AHP levels (Ozeki et al., 1996b). This indicates that the A500 value can serve as an indicator of the total amount of eumelanin and pheomelanin combined, regardless of the type of melanin. Using A500 values, we obtained a conversion factor of 160 for calculating eumelanin content from the PTCA value in human hair (Ozeki et al., 1996b; Wakamatsu and Ito, 2002). This high conversion factor suggests a low activity of Tyrp2 in humans compared with other species. Alaluf et al. (2001) recently reported that the HPLC method underestimates the melanin content in human epidermis by a factor of 3 compared with the spectrophotometric method. This discrepancy can be solved, however, using a conversion factor of 160 instead of 50. The PTCA/total melanin (A500) ratio appears to be a good indicator of the content of DHICA-derived units in eumelanins. The ratios were at similar levels in mouse black, brown, dilute black, and pink-eyed black hairs, whereas they were very low in pheomelanic hairs (Ozeki et al., 1995). In contrast, the opposite holds for the AHP/total melanin ratios. The PTCA/total melanin ratio in slaty hair was only one-fifth that of the black counterpart, the result paralleling the decreased activity of Tyrp2 in the slaty mutation (Krompouzos et al., 1994). It is interesting to note that black to brown hair eumelanins in humans contain low ratios of DHICA-derived units, comparable to the slaty mutation in mouse (Lamoreux et al., 2001; Ozeki et al., 1996a, b). Orlow et al. (1992) suggested that DHICA melanins are responsible for brown colors in the animal kingdom. However, our study using coat color mutants of mice indicates that the brown-type eumelanins differ from the black-type eumelanins in the degree of polymerization but not in the ratio of DHICA/DHI (Ozeki et al., 1995, 1997b). Pheomelanins are soluble in strong alkali solutions. By taking advantage of this property, we were able to solubilize pheomelanin in 8 M urea/1 M NaOH, although not completely, from the yellow hair of pheomelanic mice (Ozeki et al., 1995). Under the same alkaline conditions, brown eumelanins from brown, pink-eyed, black, and silver mutants were slightly soluble. On the basis of the ratios of absorbance at 400 nm of the alkaline solution to total melanin (A500), one can differentiate between pheomelanins, brown-type eumelanins, and black-type eumelanins, with the brown-type eumelanins being characterized by their partial solubility in strong alkali. Using a similar approach to characterizing melanins in human epidermis, Alaluf et al. (2002) showed that European skin contains as much as 40% alkali-soluble melanin compared with about 15% in African skin. When classification of melanin pigments into eumelanins and pheomelanins is not a major concern, the solubilization of melanins in Soluene-350 (or NaOH or KOH, if soluble) appears to be the choice for the quantitation. Absorbance at 500 nm of the Soluene-350 solution (total melanin) can be used to quantify melanin contents in hair samples (Ito et al., 1996; Ozeki et al., 1995, 1996a, b) and in cultured melanocytes (Kable and Parsons, 1989) without any pretreatment. However, before it is applied to tissue samples such as
melanomas, some refinements in pretreatment are required to remove hemoglobin and other interfering tissue components. Eumelanins and pheomelanins in hair show significantly different ratios of absorbances at 650 nm to 500 nm when solubilized in Soluene-350. This difference has been used to develop a simple and rapid spectrophotometric method to distinguish eumelanins from pheomelanins, at least for qualitative purposes (Ito et al., 1996; Ozeki et al., 1996b).
Perspectives The first part of this chapter described the chemistry of melanin pigments and related metabolites. Two types of melanin production, eumelanogenesis and pheomelanogenesis, have been extensively studied. Most of the pathway at the monomer level has been clarified, using biosynthetic and pulse radiolysis approaches. Both approaches have produced valuable information and have been complementary to each other. The former approach has the strength of isolating various monomeric and oligomeric melanin intermediates, while the latter approach is able to follow rapid reactions involving dopaquinone that could not be studied otherwise. Some unsolved problems in the chemistry of melanogenesis include: (1) the nature of post-polymerization modifications of eumelanins and pheomelanins; and (2) the nature of copolymerization of eumelanins and pheomelanins. Problem 1 has been addressed only sporadically (Crescenzi et al., 1993; Deibel and Chedekel, 1984), and is also relevant in clarifying the biodegradation of melanins and melanosomes (Borovansky and Elleder, 2003). No study has examined in depth the mode of copolymerization of the two types of melanin pigments (problem 2). The biological functions of melanin pigments are closely related to their structural features. Therefore, after the great progress in melanin chemistry over the past decade, more intimate cross-talk among specialists from chemistry, biochemistry, biophysics, cell biology, genetics, and dermatology is highly desirable in order to enjoy the fruits of growing chemical knowledge. One example of an unsolved problem in these multidisciplined areas is the mechanism of switching from eumelanogenesis to pheomelanogenesis (Fig. 15.3, 5), which appears to depend on the availability (rate and regulation of uptake) of cysteine in melanosomes. The latter part of this chapter dealt with the methodology to determine the quantity and quality of melanins present in pigmented tissues, an area that has also enjoyed fruitful collaborative studies (Ito et al., 2000; Ito and Wakamatsu, 2003). Extensive degradative studies have provided a number of useful (or potentially useful) markers. These include the contents of PTCA and AHP, the PTCA/AHP ratio, the PTCA/total melanin ratio, the AHP/total melanin ratio, the PTCA/TDCA ratio, the PTCA/PDCA ratio, and the TTCA/PDCA ratio. The significance of PTCA, AHP, and their ratio in the study of melanogenesis has been well established (Ito, 1993b; Ito et al., 303
CHAPTER 15
2000). Recently, AHP (“total AHP”) measurement has been replaced by a more specific 4-AHP measurement (Ito and Wakamatsu, 2003; Wakamatsu et al., 2002b). One problem in using PTCA and 4-AHP as markers of eumelanins and pheomelanins is that two different types of degradation are required for analyzing one sample. When alkaline peroxide oxidation is applied, TTCA and TDCA are formed specifically from pheomelanins, while PTCA and PDCA are derived from both types of melanin pigments (Ito and Wakamatsu, 1998; Wakamatsu and Ito, 2002). It is therefore expected that ratios such as the TTCA/PTCA ratio may be as useful as the 4-AHP/PTCA ratio in characterizing copolymers (or mixtures) of eumelanins and pheomelanins. For the characterization of neuromelanin, the PTCA/TDCA ratio has been used by Odh et al. (1994a, b) whereas the TTCA/PTCA ratio was used by Wakamatsu et al. (2003b). One problem in applying this approach is that TTCA and TDCA are difficult to extract in organic solvents and should thus be analyzed without purification and concentration (Wakamatsu et al., 2003b). This would lead to a lower sensitivity and specificity, unless melanin pigments are purified prior to the oxidation. Alkaline peroxide oxidation also produces BTCA (24) as a specific marker of pheomelanins (Napolitano et al., 2000). How much this marker is useful in pigment research remains to be explored. In the study of eumelanogenesis, the PTCA/PDCA ratio, analyzed by alkaline peroxide oxidation, may become a useful substitute for the PTCA/total melanin ratio as a marker to estimate the DHICA/DHI ratio in eumelanins. At present, only PDCA is available as an indicator specific for the DHI-derived units in eumelanins. A major problem with the alkaline peroxide oxidation is the artificially high yield of PTCA from pheomelanins present in the hair of genetically pheomelanic mice (Ito and Wakamatsu, 1998; Prota et al., 1995). The EPR method appears to be highly sensitive and specific in detecting melanin pigments (Enochs et al., 1993). It may also be able to differentiate between eumelanins and pheomelanins (Sealy et al., 1982a, b). Which of the two methods, the EPR method or the HPLC method, is more sensitive and specific has not been fully determined (Vsevolodov et al., 1991), although some groups claim that the HPLC method is not sufficiently sensitive or specific (Sarna et al., 2003). However, it should be stressed that the HPLC method to detect 4-AHP as the measure of pheomelanins is highly specific and sensitive.
Acknowledgments The authors wish to acknowledge the late Professor Giuseppe Prota and his associates for their inspiring chapter in the first edition of this book (Chapter 24, The chemistry of melanins and related metabolites) (Prota et al., 1998a).
References Acquaron, R. P., F. Rouge, and C. Aubert. Pheomelanin in albino negroes: urinary excretion in Cameroonian subjects. In: Pigment
304
Cell 1981: Phenotypic Expression in Pigment Cells, M. Seiji (ed.). Tokyo: University of Tokyo Press, 1981, pp. 97–103. Agrup, G., B. Falck, B.-M. Kennedy, H. Rorsman, A.-M. Rosengren, and E. Rosengren. Formation of cysteinyldopa from glutathionedopa in melanoma. Acta Derm. Venereol. (Stockh.) 55:1–3, 1975. Agrup, G., B. Falck, C. Hansson, H. Rorsman, A.-M. Rosengren, and E. Rosengren. Metabolism of 5-S-cysteinyldopa by O-methylation. Acta Derm. Venereol. (Stockh.) 57:309–312, 1977. Agrup, G., C. Lindbladh, G. Prota, H. Rorsman, A.-M. Rosengren, and E. Rosengren. Trichochromes in the urine of melanoma patients. J. Invest. Dermatol. 70:90–91, 1978. Agrup. G., C. Hansson, H. Rorsman, and E. Rosengren. The effect of cysteine on oxidation of tyrosine, dopa, and cysteinyldopas. Arch. Dermatol. Res. 272:103–115; 1982. Alaluf, S., A. Heath, N. Carter, D. Atkins, H. Mahalingam, K. Barrett, R. Kolb, and N. Smit. Variation in melanin content and composition in type V and VI photoexposed and photoprotected human skin: the dominant role of DHI. Pigment Cell Res. 14:337–347, 2001. Alaluf, S., D. Atkins, K. Barrett, M. Blount, N. Carter, and A. Heath. Ethnic variation in melanin content and composition in photoexposed and photoprotected human skin. Pigment Cell Res. 15:112–118, 2002. Alena, F., K. Jimbow, and S. Ito. Melanocytotoxicity and antimelanoma effects of phenolic amine compounds in mice in vivo. Cancer Res. 50:3743–3747, 1990. Barsh, G. S. The genetics of pigmentation: from fancy genes to complex traits. Trends Genet. 12:299–305, 1996. Benathan, M. Modulation of 5-S-cysteinyldopa formation by tyrosinase activity and intracellular thiols in human melanoma cells. Melanoma Res. 6:183–189, 1996. Benathan, M., and F. Labidi. Cysteine-dependent 5-S-cysteinyldopa formation and its regulation by glutathione in normal epidermal melanocytes. Arch. Dermatol. Res. 288:697–702, 1996. Benigni, J. D., and R. L. Minnis. The synthesis of 5,6-dihydroxyindole and some of its derivatives. J. Heterocyclic Chem. 2:387–392, 1965. Bjorklund, A., B. Falck, S. Jacobsson, H. Rorsman, A.-M. Rosengren, and E. Rosengren. Cysteinyldopa in human malignant melanoma. Acta Derm. Venereol. (Stockh.) 52:357–360, 1972. Boissy, R. E., C. Sakai, H. Zhao, T. Kobayashi, and V. J. Hearing. Human tyrosinase-related protein-1 (TRP-1) does not function as a DHICA oxidase in contrast to murine TRP-1. Exp. Dermatol. 7:198–204, 1998. Bolt, A. G. Interactions between human melanoprotein and chlorpromazine derivatives. I. Isolation and purification of human melanoprotein from hair and melanoma tissue. Life Sci. 6:1277–1283, 1967. Borges, C. R., J. C. Roberts, D. G. Wilkins, and D. E. Rollins. Relationship of melanin degradation products to actual melanin content: application to human hair. Anal. Biochem. 290:116–125, 2001. Borovansky, J. Quantitative determination of melanin. Mikrochim. Acta 2:423–429, 1978. Borovansky, J., and M. Elleder. Melanosome degradation: fact or fiction. Pigment Cell Res. 16:280–286, 2003. Burchill, S. A., A. J. Thody, and S. Ito. Melanocyte-stimulating hormone, tyrosinase activity and the regulation of eumelanogenesis and pheomelanogenesis in the hair follicular melanocytes of the mouse. J. Endocrinol. 109:15–21, 1986. Burchill, S. A., S. Ito, and A. J. Thody. Effects of melanocytestimulating hormone on tyrosinase expression and melanin synthesis in hair follicular melanocytes of the mouse. J. Endocrinol. 137:189–195, 1993. Carstam, R., C. Brinck, A. Hindemith-Augustsson, H. Rorsman, and E. Rosengren. The neuromelanin of the human substantia nigra. Biochim. Biophys. Acta 1097:152–160, 1991.
CHEMISTRY OF MELANINS Chedekel, M. R., and L. Zeise. Sunlight, melanogenesis and radicals in the skin. Lipids 23:587–591, 1988. Chedekel, M. R., K. V. Subbarao, P. Bhan, and T. M. Schultz. Biosynthetic and structural studies on pheomelanin. Biochim. Biophys. Acta 912:239–243, 1987. Chedekel, M. R., B. L. Murr, and L. Zeise. Melanin standard method: Empirical formula. Pigment Cell Res. 5:143–147, 1992. Chioccara, F., and E. Novellino. A convenient one-step synthesis of 5-cystein-S-yldopa using ceric ammonium nitrate. Synth. Commun. 16:967–971, 1986. Coleman, D. L. Effect of genic substitution on the incorporation of tyrosine into the melanin in mouse skin. Arch. Biochem. Biophys. 96:562–568, 1962. Cooksey, C. J., E. J. Land, F. A. P. Rushton, C. A. Ramsden, and P. A. Riley. Tyrosinase-mediated cytotoxicity of 4-substituted phenols: use of QSAR to forecast reactivities of thiols towards the derived ortho-quinones. Quant. Struct.–Act. Relat. 15:498–503; 1996. Cooksey, C. J., P. J. Garrratt, E. J. Land, S. Pavel, C. A. Ramsden, P. A. Riley, and N. P. M. Smit. Evidence of the indirect formation of the catecholic intermediate substrate responsible for the autoactivation kinetics of tyrosinase. J. Biol. Chem. 272:26226–26235, 1997. Costantini, C., G. Testa, O. Crescenzi, and M. d’Ischia. Photochemical ring contraction of dihydro-1,4-benzothiazines. Tetrahedron Lett. 35:3365–3366, 1994a. Costantini, C., M. d’Ischia, A. Palumbo, and G. Prota. Photochemistry of 5-S-cysteinyldopa. Photochem. Photobiol. 60:33–37, 1994b. Crescenzi, O., M. d’Ischia, A. Napolitano, and G. Prota. The alleged stability of dopa-melanin revisited. Gazz. Chim. Ital. 123:241–242, 1993. Das, K. C., M. B. Abramson, and R. Katzman. A new chemical method for quantifying melanin. J. Neurochem. 26:695–699, 1976. Das, K. C., M. B. Abramson, and R. Katzman. Neuronal pigments: Spectroscopic characterization of human brain melanin. J. Neurochem. 30:601–606, 1978. Deibel, R. M. B., and M. R. Chedekel. Biosynthetic and structural studies on pheomelanin. J. Am. Chem. Soc. 104:7306–7309, 1982. Deibel, R. M. B., and M. R. Chedekel. Biosynthetic and structural studies on pheomelanin 2. J. Am. Chem. Soc. 106:5884–5888, 1984. De Leeuw, S. M., N. P. M. Smit, M. Van Veldhoven, E. M. Pennings, S. Pavel, J. W. I. M. Simons, and A. A. Schothorst. Melanin content of cultured melanocytes and UV-induced cytotoxicity. J. Photochem. Photobiol. B Biol. 61:106–113, 2001. del Marmol, V., S. Ito, B. Bouchard, A. Libert, K. Wakamatsu, G. Ghanem, and F. Solano. Cysteine deprivation promotes eumelanogenesis in human melanoma cells. J. Invest. Dermatol. 107:698–702, 1996. Di Donato, P., and A. Napolitano. 1,4-Benzothiazines as key intermediates in the biosynthesis of red hair pigment pheomelanins. Pigment Cell Res. 16:532–539, 2003. Di Donato, P., A. Napolitano, and G. Prota. Metal ions as potential regulatory factors in the biosynthesis of red hair pigments: a new benzothiazole intermediate in the iron or copper assisted oxidation of 5-S-cysteinyldopa. Biochim. Biophys. Acta 1571:157–166, 2002. d’Ischia, M., and G. Prota. Photooxidation of 5,6-dihydroxy-1methylindole. Tetrahedron 43:431–434, 1987. d’Ischia, M., A. Palumbo, and G. Prota. 5,6-Dihydroxyindole-2carboxylic acid by treatment of sepiomelanin with sodium borohydride. Tetrahedron Lett. 23:2801–2804, 1985. d’Ischia, M., A. Napolitano, and G. Prota. Sulfhydryl compounds in melanogenesis. Part II. Reactions of cysteine and glutathione with dopachrome. Tetrahedron 43:5357–5362, 1987. d’Ischia, M., A. Napolitano, K. Tsiakas, and G. Prota. New intermediates in the oxidative polymerization of 5,6-dihydroxyindoles to
melanin promoted by the peroxidase/H2O2 system. Tetrahedron 46:5789–5796, 1990. d’Ischia, M., A. Napolitano, and G. Prota. Oxidative polymerization of 5,6-dihydroxyindoles. Tracking the biosynthetic pathway to melanin pigments. Gazz. Chim. Ital. 126:783–789, 1996. Dryja, T. P., M. O’Neil-Dryya, and D. M. Albert. Elemental analysis of melanins from bovine hair, iris, choroid, and retinal pigment epithelium. Invest. Ophthalmol. Vis. Sci. 18:231–236, 1979. Duchón, J. Urinary melanogens as a mirror of melanogenesis in vivo. In: Cutaneous Melanoma, U. Veronesi, N. Cascinelli, and M. Santinami (eds). New York: Academic Press, 1987, pp. 225–231. Duchón, J., and B. Matous. Identification of two new metabolites in melanoma urine: 5-hydroxy-6-methoxyindole-2-carboxylic and 5-methoxy-6-hydroxyindole-2-carboxylic acids. Clin. Chim. Acta 16:397–402, 1967. Duchón, J., J. Borovansky, and P. Hach. Chemical composition of ten kinds of various melanosomes. In: Mechanisms in Pigmentation. Proceedings of the 8th International Pigment Cell Conference, Sydney, 1972: Pigment Cell, vol. 1, V. J. McGovern and P. Russell (eds). Basel: Karger, 1973, pp. 165–170. Duchón, J., B. Matous, and S. Pavel. Melanogenuria. In: Pigment Cell 1981: Phenotypic Expression in Pigment Cells, M. Seiji (ed). Tokyo: University of Tokyo Press, 1981, pp. 609–615. Duff, G. A., J. E. Roberts, and N. Foster. Analysis of the structure of synthetic and natural melanins by solid-phase NMR. Biochemistry 27:7112–7116, 1988. Enochs, W. S., M. J. Nilges, and H. M. Swartz. A standardized test for the identification and characterization of melanins using electron paramagnetic resonance (EPR) spectroscopy. Pigment Cell Res. 6:91–99, 1993. Fattorusso, E., L. Minale, S. De Stefano, G. Cimino, and R. A. Nicolaus. Struttura e biogenesi delle feomelanine. Nota V. Sulla struttura della gallofeomelanina-1. Gazz. Chim. Ital. 98:1443–1463, 1968. Fattorusso, E., L. Minale, S. De Stefano, G. Cimino, and R. A. Nicolaus. Struttura e biogenesi delle feomelanine. Nota IX. Feomelanine biosintetiche. Gazz. Chim. Ital. 99:969–992, 1969a. Fattorusso, E., L. Minale, G. Cimino, S. De Stefano, and R. A. Nicolaus. Struttura e biogenesi delle feomelanine. Nota VI. Sulla struttura della gallofeomelanina-1. Gazz. Chim. Ital. 99:29–45, 1969b. Fattorusso, E., L. Minale, S. De Stefano, and R. A. Nicolaus. Struttura e biogenesi delle feomelanine. Nota XIII. Sulla struttura della gallofeomelanina. Gazz. Chim. Ital. 100:880–887, 1970. Felix, C. C., J. S. Hyde, T. Sarna, and R. C. Sealy. Melanin photoreaction in aerated media: Electron spin resonance evidence of production of superoxide and hydrogen peroxide. Biochem. Biophys. Res. Commun. 84:335–341, 1978. Fortner, R. A. Studies on melanin. I. Methods of isolation. The effect of alkali on melanin. J. Biol. Chem. 8:341–363, 1910. Fujita, K., S. Ito, S. Inoue, Y. Yamamoto, J. Takeuchi, M. Shamoto, and T. Nagatsu. Selective toxicity of 5-S-cysteinyldopa, a melanin precursor, to tumor cells in vitro and in vivo. Cancer Res. 40:2543–2546, 1980. Graham, D. G., S. M. Tiffany, W. R. Bell, and W. F. Gutknecht. Autoxidation versus covalent binding of quinones as the mechanism of toxicity of dopamine, 6-hydroxydopamine, and related compounds toward C1300 neuroblastoma cells in vitro. Mol. Pharmacol. 14:644–653, 1978. Granholm, N. H., A. J. Opbroek, G. A. Harvison, and K. E. Kappenman. Tyrosinase activity (TH, DO, PAGE-defined isozomes) and melanin production in regenerating hairbulb melanocytes of lethal yellow (Ay/a), black (a/a), agout (AwJ/AwJ) and albino (a/a/c2J/c2J) mice (C57BL/6J). Pigment Cell Res. 3:233–242, 1990. Hackman, R. H., and M. Goldberg. Microchemical detection of melanins. Anal. Biochem. 41:279–285, 1971. Hara, H., N. Walsh, K. Yamada, and K. Jimbow. High plasma levels of a eumelanin precursor, 6-hydroxy-5-methoxyindole-2-carboxylic
305
CHAPTER 15 acid as a prognostic marker for malignant melanoma. J. Invest. Dermatol. 102:501–505, 1994. Hartleb, J., and R. Arndt. Review. Cysteine and indole derivatives as markers for malignant melanoma. J. Chromatogr. B 764:409–443, 2001. Hasegawa, K., S. Ito, S. Inoue, K. Wakamatsu, H. Ozeki, and I. Ishiguro. Dihydro-1,4-benzothiazine-6,7-dione, the ultimate toxic metabolite of 4-S-cysteaminylphenol and 4-S-cysteaminylcatechol. Biochem. Pharmacol. 53:1435–1444, 1997. Hearing, V. J. Invited editorial: Unraveling the melanocyte. Am. J. Hum. Genet. 52:1–7, 1993. Hearing, V. The melanosome: the perfect model for cellular responses to the environment. Pigment Cell Res. 13 (Suppl. 8):23–34, 2000. Hervé, M., J. Hirschinger, P. Granger, P. Gilard, A. Deflandre, and N. Goetz. A 13C solid-state NMR study of the structure and autooxidation process of natural and synthetic melanins. Biochim. Biophys. Acta 1204:19–27, 1994. Hill, H. Z. The function of melanin or six blind people examine an elephant. Bioessays 14:49–56, 1992. Hirobe T., K. Wakamatsu, and S. Ito. Changes in the proliferation and differentiation of neonatal mouse pink-eyed dilution melanocytes in the presence of excess tyrosine. Pigment Cell Res. 16:619–628, 2003. Hochstein, P., and G. Cohen. The cytotoxicity of melanin precursors. Ann. N. Y. Acad. Sci. 100:876–881, 1963. Horikoshi, T., S., Ito, K. Wakamatsu, H. Onodera, and H. Eguchi. Evaluation of melanin-related metabolites as markers of melanoma progression. Cancer 73:7629–636, 1994. Hunt, G., S. Kyne, K. Wakamatsu, S. Ito, and A. J. Thody. Nle4DPhe7a-melanocyte-stimulating hormone increases the eumelanin:phaeomelanin ratio in cultured melanocytes. J. Invest. Dermatol. 104:83–85, 1995. Ito, S. One-step synthesis of (2-amino-2-carboxyethylthio)dopas (cysdopas) from dopa and cysteine by H2O2 in the presence of ironEDTA complex. Bull. Chem. Soc. Jpn. 56:365–366, 1983. Ito, S. Reexamination of the structure of eumelanin. Biochim. Biophys. Acta 883:155–161, 1986. Ito, S. Optimization of conditions for preparing synthetic pheomelanin. Pigment Cell Res. 2:53–56, 1989. Ito, S. Melanin-related metabolites as markers of melanoma: a review. J. Dermatol. 19:802–805, 1992. Ito, S. Biochemistry and physiology of melanin. In: Pigmentation and Pigmentary Disorders, N. Levine (ed.). Boca Raton: CRC Press, 1993a, pp. 33–59. Ito, S. High-performance liquid chromatography (HPLC) analysis of eu- and pheomelanin in melanogenesis control. J. Invest. Dermatol. 100:166S–171S, 1993b. Ito, S. Advances in chemical analysis of melanins. In: The Pigmentary System: Physiology and Pathophysiology, J. J. Nordlund, R. E. Boissy, V. J. Hearing, R. A. King, and J. P. Ortonne (eds). New York: Oxford University Press, 1998, pp. 439–450. Ito, S. IFPCS presidential lecture. A chemist’s view of melanogenesis. Pigment Cell Res. 16:230–236, 2003. Ito, S., and K. Fujita. Formation of cysteine conjugates from dihydroxyphenylalanine and its S-cysteinyl derivatives by peroxidasecatalyzed oxidation. Biochim. Biophys. Acta 672:151–157, 1981. Ito, S., and K. Fujita. Conjugation of dopa and 5-S-cysteinyldopa with cysteine mediated by superoxide radical. Biochem. Pharmacol. 31:2887–2889, 1982. Ito, S., and K. Fujita. Microanalysis of eumelanin and pheomelanin in hair and melanomas by chemical degradation and liquid chromatography. Anal. Biochem. 144:527–536, 1985. Ito, S., and K. Jimbow. Quantitative analysis of eumelanin and pheomelanin in hair and melanomas. J. Invest. Dermatol. 80:268–272, 1983. Ito, S., and G. Prota. A facile one-step synthesis of cysteinyldopas using mushroom tyrosinase. Experientia 33:1118–1119, 1977.
306
Ito, S., and K. Wakamatsu. An improved modification of permanganate oxidation of eumelanin that gives a constant yield of pyrrole2,3,5-tricarboxylic acid. Pigment Cell Res. 7:141–144, 1994. Ito, S., and K. Wakamatsu. Chemical characterization of melanins: application to identification of dopamine-melanin. Pigment Cell Res. 11:120–126, 1998. Ito, S., and K. Wakamatsu. Quantitative analysis of eumelanin and pheomelanin in humans, mice, and other animals: a comparative review. Pigment Cell Res. 16:523–531, 2003. Ito, S., S. Inoue, and K. Fujita. The mechanism of toxicity of 5-Scysteinyldopa to tumour cells. Hydrogen peroxide as a mediator of cytotoxicity. Biochem. Pharmacol. 32:2079–2081, 1983. Ito, S., A. Palumbo, and G. Prota. Tyrosinase-catalyzed conjugation of dopa with glutathione. Experientia 41:960–961, 1985. Ito, S., T. Kato, and K. Fujita. Covalent binding of catechols to proteins through the sulphydryl group. Biochem. Pharmacol. 37:1707–1710, 1988a. Ito, S. Y, Imai, K. Jimbow, and K. Fujita. Incorporation of sulfhydryl compounds into melanins in vitro. Biochim. Biophys. Acta 964:1–7, 1988b. Ito, S., K. Wakamatsu, and H. Ozeki. Spectrophotometric assay of eumelanin in tissue samples. Anal. Biochem. 215:273–277, 1993. Ito, S., H. Ozeki, and K. Wakamatsu. Spectrophotometric and HPLC characterization of hair melanins. In: Melanogenesis and Malignant Melanoma: Biochemistry, Cell Biology, Molecular Biology, Pathophysiology, Diagnosis and Treatments, Y. Hori, V. J. Hearing, and Y. Nakayama (eds). Amsterdam: Elsevier Science, 1996, pp. 63–72. Ito, S., K. Wakamatsu, and H. Ozeki. Chemical analysis of melanins and its application to the study of the regulation of melanogenesis. Pigment Cell Res. 13 (Suppl. 8):103–109, 2000. Jackson, I. J., D. M. Chambers, K. Tsukamoto, N. G. Copeland, D. J. Gilbert, N. A. Jenkins, and V. J. Hearing. A second tyrosinaserelated protein, TRP-2, maps to and is mutated at the mouse slaty locus. EMBO J. 11:527–535, 1992. Jimbow, K., O. Ishida, S. Ito, Y. Hori, C. J. Witkop, Jr., and R. A. King. Combined chemical and electron microscopic studies of pheomelanosomes in human red hair. J. Invest. Dermatol. 81:506–511, 1983. Jiménez-Cervantes, C., F. Solano, T. Kobayashi, K. Urabe, V. J. Hearing, J. A. Lozano, and J. C. García-Borrón. A new enzymatic function in the melanogenic pathway. The 5,6-dihydroxyindole-2carboxylic acid oxidase activity of tyrosinase-related protein-1 (TRP1). J. Biol. Chem. 269:17993–18001, 1994. Kable, E. P. W., and P. G. Parsons. Melanin synthesis and the action of L-dopa and 3,4-dihydroxybenzylamine in human melanoma cells. Cancer Chemother. Pharmacol. 23:1–7, 1989. Katritzky, A. R., N. G. Akhmedov, S. N. Denisenko, and O. V. Denisko. 1H NMR spectroscopic characterization of solutions of sepia melanin, sepia melanin free acid and human hair melanin. Pigment Cell Res. 15:93–97, 2002. Kobayashi, T., K. Urabe, A. J. Winder, C. Jiménez-Cervantes, G. Imokawa, T. Brewington, F. Solano, J. C. García-Borrón, and V. J. Hearing. Tyrosinase related protein 1 (TRP1) functions as a DHICA oxidase in melanin biosynthesis. EMBO J. 13:5818–5825, 1994. Koch, W. H., and M. R. Chedekel. Photoinitiated DNA damage by melanogenic intermediates in vitro. Photochem. Photobiol. 44:703–710, 1986. Kolb, A. M., E. G. W. M. Lentjes, N. P. M. Smit, A. Schothorst, B. J. Vermeer, and S. Pavel. Determination of pheomelanin by measurement of aminohydroxyphenylalanine isomers by high-performance liquid chromatography. Anal. Biochem. 252:293–298, 1997. Krompouzos, G., K. Urabe, T. Kobayashi, C. Sakai, and V. J. Hearing. Functional analysis of the slaty gene product (TRP2) as DOPAchrome tautomerase, and the effect of a point mutation on its catalytic function. Biochem. Biophys. Res. Commun. 202:1060–1068, 1994.
CHEMISTRY OF MELANINS Lambert, C., J. N. Chacon, M. R. Chedekel, E. J. Land, P. A. Riley, A. Thompson, and T. G. Truscott. A pulse radiolysis investigation of the oxidation of indolic melanin precursors: evidence for indolequinones and subsequent intermediates. Biochim. Biophys. Acta 993:12–20, 1989. Lamoreux, M. L., K. Wakamatsu, and S. Ito. Interaction of major coat color gene functions in mice as studied by chemical analysis of eumelanin and pheomelanin. Pigment Cell Res. 14:23–31, 2001. Land, E. J., and P. A. Riley. Spontaneous redox reactions of dopaquinone and the balance between the eumelanic and phaeomelanic pathways. Pigment Cell Res. 13:273–277, 2000. Land, E. J., A. Thompson, T. G. Truscott, K. V. Subbarao, and M. R. Chedekel. Photochemistry of melanin precursors: dopa, 5-Scysteinyldopa, and 2,5-S,S¢-dicysteinyldopa. Photochem. Photobiol. 44:697–702, 1986. Land, E. J., C. A. Ramsden, and P. A. Riley. Pulse radiolysis studies of ortho-quinone chemistry relevant to melanogenesis. J. Photochem. Photobiol. B Biol. 64:123–135, 2001. Land, E. J, S. Ito, K. Wakamatsu, and P. A. Riley. Rate constants for the first two chemical steps of eumelanogenesis. Pigment Cell Res. 16:487–493, 2003. Leonhardi, G. Uber Struktur und Lichtabsorption der Hahrmelanogene. Naturwissenschaften 42:17–18, 1955. Liu, Y., and J. D. Simon. The effect of preparation procedures on the morphology of melanin from the ink sac of Sepia officinalis. Pigment Cell Res. 16:72–80, 2003. Liu, Y., V. R. Kempf, J. B. Nofsinger, E. E. Weinert, M. Rudnicki, K. Wakamatsu, S. Ito, and J. D. Simon. Comparison of the structural and physical properties of human hair eumelanin following enzymatic or acid/base extraction. Pigment Cell Res. 16:355–365, 2003. Manini, P., M. d’Ischia, and G. Prota. Pictet–Spengler condensation of the antiparkinsonian drug l-DOPA with d-glutaraldehyde. Opposite kinetic effects of Fe3+ and Cu2+ ions and possible implications for the origin of therapeutic side effects. Bioorg. Med. Chem. 9:923–929, 2001. Mascagna, D., C. Costantini, M. d’Ischia, and G. Prota. Biomimetic oxidation of the antimelanoma agent 4-S-cysteaminylphenol and related catechol thioethers: isolation and reaction behaviour of novel dihydrobenzothiazinequinones. Tetrahedron 50:8757–8764, 1994. Mason, H. S. The chemistry of melanin. III. Mechanism of the oxidation of dihydroxyphenylalanine by tyrosinase. J. Biol. Chem. 172:83–99, 1948. Matous, B., A. Budesinska, M. Budesinsky, J. Duchón, and S. Pavel. The identification of Thormälen positive melanogen “A” from the urine of melanoma patients as 6-methoxy-5-indolylglucosiduronate. Neoplasma 28:271–274, 1981. Matsunaga, J., D. Sinha, L. Pannell, C. Santis, F. Solano, G. J. Wistow, and V. J. Hearing. Enzyme activity of macrophage migration inhibitory factor toward oxidized catecholamines. J. Biol. Chem. 274:3268–3271, 1999. Matsunaga, J., P. A. Riley, F. Solano, and V. J. Hearing. Biosynthesis of neuromelanin and melanin: the potential involvement of macrophage inhibitory factor and dopachrome tautomerase as rescue enzymes. In: Catecholamine Research. From Molecular Insights to Clinical Medicine, T. Nagatsu, T. Nabeshima, R. McCarty, and D. S. Goldstein (eds). New York: Kluwer Academic/Plenum Publishers, 2002, pp. 273–276. Memoli, S., A. Napolitano, M. d’Ischia, G. Misuraca, A. Palumbo, and G. Prota. Diffusible melanin-related metabolites are potent inhibitors of lipid peroxidation. Biochim. Biophys. Acta 1346:61–68, 1997. Menon, I. A., S. Persad, H. F. Haberman, and C. J. Kurian. A comparative study of the physical and chemical properties of melanins isolated from human black and red hair. J. Invest. Dermatol. 80:202–206, 1983.
Minale, L., E. Fattorusso, G. Cimino, S. De Stefano, and R. A. Nicolaus. Struttura e biogenesi delle feomelanine. Nota III. Prodotti di degradazione. Gazz. Chim. Ital. 97:1636–1663, 1967. Mojamdar, M. V., M. Ichihashi, and Y. Mishima. Gamma-glutamyl transpeptidase, tyrosinase, and 5-S-cysteinyldopa production in melanoma cells. J. Invest. Dermatol. 81:119–121, 1983. Morishima, T., F. Tatsumi, E. Fukada, M. Saito, M. Fujita, N. Nagashima, and S. Hanawa. Cysteinyldopa isomers and dopa in lesions and urine of Japanese patients with malignant melanoma. Arch. Dermatol. Res. 275:76–80, 1983. Movaghar, M. Tyrosinase activity in the first coat of agouti and black mice. Pigment Cell Res. 2:401–407, 1989. Napolitano, A., O. Crescenzi, and G. Prota. Copolymerization of 5,6dihydroxyindole and 5,6-dihydroxyindole-2-carboxylic acid in melanogenesis: isolation of a cross-coupling product. Tetrahedron Lett. 34:885–888, 1993a. Napolitano, A., A. Palumbo, G. Misuraca, and G. Prota. Inhibitory effect of melanin precursors on arachidonic acid peroxidation. Biochim. Biophys. Acta 1168:175–180, 1993b. Napolitano, A., C. Costantini, O. Crescenzi, and G. Prota. Characterisation of 1,4-benzothiazine intermediates in the oxidative conversion of 5-S-cysteinyldopa to pheomelanins. Tetrahedron Lett. 35:6365–6368, 1994. Napolitano, A., A. Perzzella, M. R. Vincensi, and G. Prota. Oxidative degradation of melanins to pyrrole acids: a model study. Tetrahedron 51:5913–5920, 1995. Napolitano, A., S. Memoli, Crescenzi, O., and Prota, G. Oxidative polymerization of the pheomelanin precursor 5-hydroxy-1,4benzothiazylalanine: a new hint to the pigment structure. J. Org. Chem. 61:598–604, 1996a. Napolitano, A., A. Pezzella, G. Prota, R. Seraglia, and P. Traldi. A reassessment of the structure of 5,6-dihydroxyindole-2-carboxylic acid melanins by matrix-assisted laser desorption/ionization mass spectrometry. Rapid Commun. Mass Spectrom. 10:204–208, 1996b. Napolitano, A., A. Pezzella, G. Prota, R. Seraglia, and P. Traldi. Structural analysis of synthetic melanins from 5,6-dihydroxyindole by matrix-assisted laser desorption/ionization mass spectrometry. Rapid Commun. Mass Spectrom. 10:468–472, 1996c. Napolitano, A., S. Memoli, A. J. Nappi, M. d’Ischia, and G. Prota. 5-S-Cysteinyldopa, a diffusible product of melanocyte activity, is an efficient inhibitor of hydroxylation/oxidation reactions induced by the Fenton reaction. Biochim. Biophys. Acta 1291:75–82, 1996d. Napolitano, A., P. Di Donato, G. Prota, and E. J. Land. Transient quinonimines and 1,4-benzothiazines of pheomelanogenesis: new pulse radiolytic and spectrophotometric evidence. Free Rad. Biol. Med. 27:521–528, 1999. Napolitano, A., P. Di Donato, and G. Prota. New regulatory mechanisms in the biosynthesis of pheomelanins: rearrangement vs. redox exchange reaction routes of a transient 2H-1,4-benzothiazine-oquinonimine intermediate. Biochim. Biophys. Acta 1475:47–54, 2000a. Napolitano, A., M. R. Vincensi, P. D. Dinato, G. Monfrecola, and G. Prota. Microanalysis of melanins in mammalian hair by alkaline hydrogen peroxide degradation: identification of a new structural marker of pheomelanins. J. Invest. Dermatol. 114:1141–1147, 2000b. Napolitano, A., P. Di Donato, and G. Prota. Zinc-catalyzed oxidation of 5-S-cysteinyldopa to 2,2¢-bi(2H-1,4-benzothiazine): tracking the biosynthetic pathway of trichochromes, the characteristic pigments of red hair. J. Org. Chem. 66:6958–6966, 2001. Naysmith, L., K. Waterton, T. Ha, N. Flanagan, Y. Bisset, A. Ray, K. Wakamatsu, S. Ito, and J. L. Rees. Quantitative measures of the effect of the melanocortin 1 receptor on human pigmentary status. J. Invest. Dermatol. 122:423–428, 2004. Nicolaus, R. A. Melanins. Paris: Hermann Press, 1968.
307
CHAPTER 15 Nicolaus, R. A., G. Prota, C. Santacrose, G. Scherillo, and D. Sica. Struttura e biogenesi delle feomelanine. Nota VII. Sulla struturra delle tricosiderine. Gazz. Chim. Ital. 99:323–350, 1969. Nimmo, J. E., J. A. Hunter, I. W. Percy-Robb, B. Jay, C. I. Phillips, and W. O. Taylor. Plasma 5-S-cysteinylDOPA concentrations in oculocutaneous albinism. Acta Derm. Venereol. Suppl. (Stockh.) 65:169–171, 1985. Novellino, E., J. P. Ortonne, C. Voulot, F. Chioccara, G. Misuraca, and G. Prota. Identification of cysteinyldopa-derived units in eumelanins from mammalian eyes. FEBS Lett. 125:101–103, 1981. Novellino, L., A. Napolitano, and G. Prota. Isolation and characterization of mammalian eumelanins from hair and irides. Biochim. Biophys. Acta 2475:295–306, 2000. Odh, G., R. Carstam, J. Paulson, A. Wittbjer, E. Rosengren, and H. Rorsman. Neuromelanin of the human substantia nigra: A mixedtype melanin. J. Neurochem. 62:2030–2036, 1994a. Odh, G., A. Hindemith, R. Carstam, J. Paulson, E. Rosengren, and H. Rorsman. Melanins in IGR1 melanoma cells. Pigment Cell Res. 7:419–427, 1994b. Oikawa, A., and M. Nakayasu. Quantitative measurement of melanin as tyrosine equivalents and as weight of purified melanin. Yale J. Biol. Med. 46:500–507, 1973. Oikawa, A., and M. Nakayasu. Solution of eumelanin showing no light scattering. Anal. Biochem. 63:634–637, 1975. Orlow, S. J., M. P. Osber, and J. M. Pawelek. Synthesis and characterization of melanins from dihydroxyindole-2-carboxylic acid and dihydroxyindole. Pigment Cell Res. 5:113–121, 1992. Ozeki, H., S. Ito, K. Wakamatsu, and T. Hirobe. Chemical characterization of hair melanins in various coat-color mutants of mice. J. Invest. Dermatol. 105:361–366, 1995. Ozeki, H., S. Ito, and K. Wakamatsu. Chemical characterization of melanins in sheep wool and human hair. Pigment Cell Res. 9:51–57, 1996a. Ozeki, H., S. Ito, K. Wakamatsu, and A. J. Thody. Spectrophotometric characterization of eumelanin and pheomelanin in hair and wool. Pigment Cell Res. 9:265–270, 1996b. Ozeki, H., S. Ito, K. Wakamatsu, and I. Ishiguro. Chemical characterization of pheomelanogenesis starting from dihydroxyphenylalanine or tyrosine and cysteine. Effects of tyrosinase and cysteine concentrations and reaction time. Biochim. Biophys. Acta 1336:539–548, 1997a. Ozeki, H., K. Wakamatsu, S. Ito, and I. Ishiguro. Chemical characterization of eumelanins with special emphasis on 5,6dihydroxyindole-2-carboxylic acid content and molecular size. Anal. Biochem. 248:149–157, 1997b. Palumbo, A., M. d’Ischia, G. Misuraca, and G. Prota. Effect of metal ions on the rearrangement of dopachrome. Biochim. Biophys. Acta 925:203–209, 1987a. Palumbo, A., M. d’Ischia, and G. Prota. Tyrosinase-promoted oxidation of 5,6-dihydroxyindole-2-carboxylic acid to melanin. Isolation and characterization of oligomer intermediates. Tetrahedron 18:4203–4206, 1987b. Palumbo, A., M. d’Ischia, G. Misuraca, G. Prota, and T. Schultz. Structural modifications in biosynthetic melanins induced by metal ions. Biochim. Biophys. Acta 964:193–199, 1988. Palumbo, A., F. Solano, G. Misuraca, P. Aroca, J. C. Garcia Borron, J. A. Lozano, and G. Prota. Comparative action of dopachrome tautomerase and metal ions on the rearrangement of dopachrome. Biochim. Biophys. Acta 1115:1–5, 1991. Panizzi, L., and R. A. Nicolaus. Ricerca sulle melanine. Nota I. Sulla melanina di seppia. Gazz. Chim. Ital. 2:435–460, 1952. Patil, D. G., and M. R. Chedekel. Synthesis and analysis of pheomelanin degradation products. J. Org. Chem. 49:997–1000, 1984. Pavel, S., F. A. J. Muskiet, G. T. Nagel, Z. Schwippelova, and J. Duchón. Identification of two Thormälen-positive compounds from melanocytic urine by gas chromatography-mass spectrometry. J. Chromatogr. 222:329–336, 1981.
308
Pawelek, J. M. After dopachrome? Pigment Cell Res. 42:53–62, 1991. Pawelek, J. M., and A. B. Lerner. 5,6-Dihydroxyindole is a melanin precursor showing potent cytotoxicity. Nature 276:627–628, 1978. Pawelek, J. M., A. M. Körner, A. Bergstrom, and J. Bolognia. New regulators of melanin biosynthesis and the autodestruction of melanoma cells. Nature 286:617–619, 1980. Pezzella, A., A. Napolitano, M. d’Ischia, and G. Prota. Oxidative polymerisation of 5,6-dihydroxyindole-2-carboxylic acid to melanin: a new insight. Tetrahedron 52:7913–7920, 1996. Pezzella, A., M. d’Ischia, A. Napolitano, A. Palumbo, and G. Prota. An integrated approach to the structure of Sepia melanin. Evidence for a high proportion of degraded 5,6-dihydroxyindole-2carboxylic acid units in the pigment backbone. Tetrahedron 53:8281–8286, 1997. Piattelli, M., and R. A. Nicolaus. The structure of melanins and melanogenesis. Nota I. The structure of melanin in Sepia. Tetrahedron 15:66–75, 1961. Piattelli, M., E. Fattorusso, S. Magno, and R. A. Nicolaus. The structure of melanins and melanogenesis. II. Sepiomelanin and synthetic pigments. Tetrahedron 18:941–949, 1962. Piattelli, M., E. Fattorusso, S. Magno, and R. A. Nicolaus. The structure of melanins and melanogenesis. III. The structure of sepiomelanin. Tetrahedron 19:2061–2072, 1963. Potterf, S. B., V. Virador, K. Wakamatsu, M. Furumura, C. Santis, S. Ito, and V. J. Hearing. Cysteine transport in melanosomes from murine melanocytes. Pigment Cell Res. 12:4–12, 1999. Prezioso, J. A., N. Wang, and W. D. Bloomer. Thymidylate synthase as a target enzyme for the melanocyte-specific toxicity of 4-Scysteaminylphenol and N-acetyl-4-S-cysteaminylphenol. Cancer Chemother. Pharmacol. 30:394–400, 1992. Prota, G. Structure and biogenesis of pheomelanins. In: Pigmentation: Its Genesis and Biologic Control, V. Riley (ed.). New York: Appleton Century Crofts, 1972, pp. 615–630. Prota, G. Recent advances in the chemistry of melanogenesis in mammals. J. Invest. Dermatol. 75:122–127, 1980. Prota, G. Progress in the chemistry of melanins and related metabolites. Med. Res. Rev. 8:525–556, 1988. Prota, G. Melanins and Melanogenesis. San Diego: Academic Press, 1992. Prota, G. Regulatory mechanisms of melanogenesis: beyond the tyrosinase concept. J. Invest. Dermatol. 100:156S–161S, 1993. Prota, G., and R. A. Nicolaus. Struttura e biogenesi delle feomelanine. Nota I. Isolamento e proprietà dei pigmenti delle piume. Gazz. Chim. Ital. 97:666–684, 1967. Prota, G., G. Scherillo, O. Petrillo, and R. A. Nicolaus. Struttura e biogenesi delle feomelanine. Nota X. Sulla struttura delle tricosiderine. Gazz. Chim. Ital. 99:1193–1207, 1969. Prota, G., H. Rorsman, A.-M. Rosengren, and E. Rosengren. Phaeomelanic pigments from a human melanoma. Experientia 32:970–971, 1976. Prota, G., H. Rorsman, A.-M. Rosengren, and E. Rosengren. Isolation of 2-S-cysteinyldopa and 2,5-S,S-dicysteinyldopa from the urine of patients with melanoma. Experientia 33:720–721, 1977. Prota, G., M. d’Ischia, and D. Mascagna. Melanogenesis as a targeting strategy against metastatic melanoma: a reassessment. Melanoma Res. 4:351–358, 1994. Prota, G., M. L. Lamoreux, J. Muller, T. Kobayashi, A. Napolitano, M. R. Vincensi, C. Sakai, and V. J. Hearing. Comparative analysis of melanins and melanosomes produced by various coat color mutants. Pigment Cell Res. 8:153–163, 1995. Prota, G., M. d’Ischia, and A. Napolitano. The chemistry of melanins and related metabolites. In: The Pigmentary System: Physiology and Pathophysiology, J. J. Nordlund, R. E. Boissy, V. J. Hearing, R. A. King, and J. P. Ortonne (eds). New York: Oxford University Press, 1998a, pp. 307–332.
CHEMISTRY OF MELANINS Prota, G., D.-N. Hu, M. R. Vincensi, S. A. McCormick, and A. Napolitano. Characterization of melanins in human irides and cultured melanocytes from eyes of different colors. Exp. Eye Res. 67:293–299, 1998b. Raper, H. S., XIV. The tyrosinase-tyrosine reaction. VI. Production from tyrosine of 5,6-dihydroxyindole and 5,6-dihydroxyindole-2carboxylic acid — the precursors of melanin. Biochem. J. 21:89–96, 1927. Rees, J. L. The melanocortin 1 receptor (MC1R): more than just red color. Pigment Cell Res. 13:135–140, 2000. Riley, P. A., C. J. Cooksey, C. I. Johnson, E. J. Land, A. M. Latter, and C. A. Ramsden. Melanogenesis-targeted anti-melanoma prodrug development: effect of side-chain variations on cytotoxicity of tyrosinase-generated ortho-quinones in a model screening system. Eur. J. Cancer 33:135–143, 1997. Rorsman, H., and S. Pavel. Metabolic markers and melanoma. In: Cutaneous Melanoma: Biology and Management, N. Cascinelli, M. Santinami, and U. Veronesi (eds). Milan: Masson Press, 1990, pp. 79–82. Rorsman, H., G. Agrup, B. Falck, A.-M. Rosengren, and E. Rosengren. Exposure to sunlight and urinary excretion of 5-Scysteinyldopa. In: Pigment Cell, vol. 2, V. Riley (ed.). Basel: Karger, 1976, pp. 284–289. Rorsman, H., G. Agrup, C. Hansson, A.-M. Rosengren, and E. Rosengren. Detection of phaeomelanins. In: Pigment Cell: Biologic Basis of Pigmentation, vol. 4, S. Kraus (ed.). Basel: Karger, 1979, pp. 244–252. Rorsman, H., G. Agrup, C. Hansson, and E. Rosengren. Biochemical recorders of malignant melanoma. In: Pigment Cell, vol. 6, R. M. MacKie (ed.). Basel: Karger, 1983, pp. 93–115. Rosenthal, M. H., J. W. Kreider, and R. Shiman. Quantitative assay of melanin in melanoma cells in culture and in tumors. Anal. Biochem. 56:91–99, 1973. Samuelson, D. A., P. Smith, R. J. Ulshafer, D. G. Hendricks, D. Whitley, H. Hendricks, and N. C. Leone. X-ray microanalysis of ocular melanin in pigs maintained on normal and low zinc diets. Exp. Eye Res. 56:63–70, 1993. Sarna, T., J. M. Burke, W. Korytowski, M. Rózanowska, C. M. B. Skumatz, A. Zareba, and M. Zareba. Loss of melanin from human RPE with aging: possible role of melanin photooxidation. Exp. Eye Res. 76:89–98, 2003. Schmitz, S., D. T. Panakkezhum, T. M. Allen, M. J. Poznansky, and K. Jimbow. Dual role of melanins and melanin precursors as photoprotective and phototoxic agents: inhibition of ultraviolet radiation-induced lipid peroxidation. Photochem. Photobiol. 61:650–655, 1995. Sealy, R. C., J. S. Hyde, C. C. Felix, I. A. Menon, and G. Prota. Eumelanins and pheomelanins: Characterization by electron spin resonance spectroscopy. Science 217:545–547, 1982a. Sealy, R. C., J. S. Hyde, C. C. Felix, I. A. Menon, G. Prota, H. M. Swartz, S. Persad, and H. F. Haberman. Novel free radical in synthetic and natural pheomelanins: Distinction between dopa melanins and cysteinyldopa melanins by ESR spectroscopy. Proc. Natl. Acad. Sci. USA 79:2885–2889, 1982b. Seraglia, R., P. Traldi, G. Elli, A. Bertazzo, C. Costa, and G. Allergri. Laser desorption ionization mass spectrometry in the study of natural and synthetic melanins. I. Tyrosine melanins. Biomed. Mass Spectrom. 22:687–697, 1993. Singh, M. V., and K. Jimbow. Tyrosinase transfection produces melanin synthesis and growth retardation in glioma cells. Melanoma Res. 8:493–498, 1998. Smit, N. P., S. Pavel, A. Kammeyer, and W. Westerhof. Determination of catechol O-methyltransferase activity in relation to melanin metabolism using high-performance liquid chromatography with fluorimetric detection. Anal. Biochem. 190:286–291, 1990. Smit, N. P., H. Van der Meulen, H. K. Koerten, R. M. Kolb, A. M. Mommaas, E. G. Lentjes, and S. Pavel. Melanogenesis in cultured
melanocytes can be substantially influenced by l-tyrosine and lcysteine. J. Invest. Dermatol. 109:796–800, 1997. Steel, K. P., D. R. Davidson, and I. J. Jackson. TRP-2/DT, a new early melanoblast marker, shows that steel growth factor (c-kit legand) is a survival factor. Development 115:1111–1119, 1992. Swan, G. A. Structure, chemistry, and biosynthesis of the melanins. Fortsch. Chem. Organ. Naturst. 31:521–582, 1974. Swan, G. A., and A. Waggott. Studies related to chemistry of melanins. Part X. Quantitative assessment of different types of units present in DOPA-melanin. Chem. Soc. J. Perkin I 10:1409–1418, 1970. Tadokoro, T., N. Kobayashi, B. Z. Zmudzka, S. Ito, K. Wakamatsu, Y. Yamaguchi, K. S. Korossy, S. A. Miller, Z. Z. Beer, and V. J. Hearing. UV-induced DNA damage and melanin content in human skin differing in racial/ethnic origin. FASEB J. 17:1177–1179, 2003. Takasaki, A., D. Nezirevic, K. Årstrand, K. Wakamatsu, S. Ito, and B. Kågedal. HPLC analysis of pheomelanin degradation products in human urine. Pigment Cell Res. 16:480–486, 2003. Thody, A. J., E. M. Higgins, K. Wakamatsu, S. Ito, S. A. Burchill, and J. M. Marks. Pheomelanin as well as eumelanin is present in human epidermis. J. Invest. Dermatol. 97:340–344, 1991. Thompson, A., E. J. Land, M. R. Chedekel, K. V. Subbarao, and T. G. Truscott. A pulse radiolysis investigation of the oxidation of the melanin precursors 3,4-dihydroxyphenylalanine (dopa) and the cysteinyldopas. Biochim. Biophys. Acta 843:49–57, 1985. Thomson, R. H. The pigments of reddish hair and feathers. Angew. Chem. Int. Ed. Engl. 13:305–312, 1974. Tripathi, R. K., V. J. Hearing, K. Urabe, P. Aroca, and R. A. Spritz. Mutational mapping of the catalytic activities of human tyrosinase. J. Biol. Chem. 267:23707–12, 1991. Tse, D. C. S., R. L. McCreery, and R. N. Adams. Potential oxidative pathways of brain catecholamines. J Med. Chem. 19:37–40, 1976. Tsukamoto, K., I. J. Jackson, K. Urabe, P. M. Montague, and V. J. Hearing. A second tyrosinase-related protein, TRP-2, is a melanogenic enzyme termed DOPAchrome tautomerase. EMBO J. 11:519–526, 1992a. Tsukamoto, K., A. Palumbo, M. d’Ischia, V. J. Hearing, and G. Prota. 5,6-Dihydroxyindole-2-carboxylic acid is incorporated in mammalian melanin. Biochem. J. 286:491–495, 1992b. Urabe, K., P. Aroca, K. Tsukamoto, D. Macagna, A. Palumbo, G. Prota, and V. J. Hearing. The inherent cytotoxicity of melanin precursors: a revision. Biochim. Biophys. Acta 1221:272–278, 1994. Valverde, P., E. Healy, I. Jackson, J. L. Rees, and A. J. Thody. Variants of the melanocyte-stimulating hormone receptor gene are associated with red hair and fair skin. Nature Genet. 11:328–330, 1995. von Fürth O., and E. Jerusalem. Zur Kenntnis der melanotischen Pigmente und der fermentativen Melaninbildung. Beitr. Chem. Physiol. Pathol. 10:131–171, 1907. Vsevolodov, E. B., S. Ito, K. Wakamatsu, I. I. Kuchina, and I. F. Latypov. Comparative analysis of hair melanins by chemical and electron spin resonance methods. Pigment Cell Res. 3:30–34, 1991. Wakamatsu, K., and S. Ito. Preparation of eumelanin-related metabolites, 5,6-dihydroxyindole, 5,6-dihydroxyindole-2-carboxylic acid, and their O-methyl derivatives. Anal. Biochem. 170:335–340, 1988. Wakamatsu, K., and S. Ito. Seasonal variation in serum concentration of 5-S-cysteinyldopa and 6-hydroxy-5-methoxyindole-2-carboxylic acid in healthy Japanese. Pigment Cell Res. 8:132–134, 1995. Wakamatsu, K., and S. Ito. Review: Innovative technology. Advanced chemical methods in melanin determination. Pigment Cell Res. 15:174–183, 2002. Wakamatsu, K., S. Ito, and T. Nagatsu. Cysteinyldopamine is not incorporated into neuromelanin. Neurosci. Lett. 131:57–60, 1991. Wakamatsu, K., S. Ito, and K. B. Koch. Chemical characterization of dopamine-melanin: application to identification of melanins in butterfly wing. Pigment Cell Res. 11:259, 1998.
309
CHAPTER 15 Wakamatsu, K., T. Kageshita, M. Furue, N. Hatta, Y. Kiyohara, J. Nakayama, T. Ono, T. Saida, M. Takata, T. Tsuchida, H. Uhara, A. Yamamoto, N. Yamazaki, A. Naito, and S. Ito. Evaluation of 5-S-cysteinyldopa as a marker of melanoma progression: 10 years’ experience. Melanoma Res. 12:245–253, 2002a. Wakamatsu, K., S. Ito, and J. L. Rees. The usefulness of 4-amino-3hydroxyphenylalanine as a specific marker of pheomelanin. Pigment Cell Res. 15:225–232, 2002b. Wakamatsu, K., M. Yokochi, A. Naito, T. Kageshita, and S. Ito. Comparison of phaeomelanin and its precursor 5-S-cysteinyldopa in the serum of melanoma patients. Melanoma Res. 13:357–363, 2003a. Wakamatsu, K., K. Fujikawa, F. Zucca, L. Zecca, and S. Ito. The structure of neuromelanin as studied by chemical degradative methods. J. Neurochem. 86:1015–1023, 2003b. Watt, K. P., R. G. Fairchild, D. N. Slatkin, D. Greenberg, S. Packer, H. L. Atkins, and S. J. Hannon. Melanin content of hamster tissues, human tissues, and various melanomas. Cancer Res. 41:467–472, 1981. Westerhof, W., S. Pavel, A. Kammeyer, F. D. Beusenberg, and R. Cormane. Melanin-related metabolites as markers of the skin pigmentary system. J. Invest. Dermatol. 89:78–81, 1987. Whittaker, J. R. Changes in melanogenesis during dedifferentiation of chick retinal pigment cells in cell culture. Dev. Biol. 8:99–127, 1963. Wick, M. M., L. Byers, and E. Frei. L-DOPA: selective toxicity for melanoma cells in vitro. Science 197:468–469, 1977. Wilczok, T., B. Bilinska, E. Buszman, and M. Kopera. Spectroscopic studies of chemically modified synthetic melanins. Arch. Biochem. Biophys. 231:257–262, 1984.
310
Williamson, P. R., K. Wakamatsu, and S. Ito. Melanin biosynthesis in Cryptococcus neoformans. J. Bacteriol. 180:1570–1572, 1998. Wood, J. M., K. Jimbow, R. E. Boissy, A. Slominski, P. M. Plonka, J. Slawinski, J. Wortsman, and J. Tosk. What’s the use of generating melanin? Exp. Dermatol. 8:153–164, 1999. Yukitake, J., H. Otake, S. Inoue, K. Wakamatsu, C. Olivares, F. Solano, K. Hasegawa, and S. Ito. Synthesis and selective in vitro anti-melanoma effect of enantiomeric a-methyl- and a-ethy-4-Scysteaminylphenol. Melanoma Res. 13:603–609, 2003. Zecca, L., F. A. Zucca, P. Costi, D. Tampellini, A. Gatti, M. Gerlach, P. Riederer, R. G. Fariello, S. Ito, M. Gallorini, and D. Sulzer. The neuromelanin of human substantia nigra: structure, synthesis and molecular behaviour. J. Neural Transm. (Suppl.) 65:145–155, 2003. Zeise, L. Analytical methods for characterization and identification of eumelanins. In: Melanin: Its Role in Human Photoprotection, L. Zeise, M. R. Chedekel, and T. B. Fitzpatrick (eds). Overland Park, KS: Valdenmar Publishing, 1995, pp. 65–79. Zeise, L., and M. R. Chedekel. Melanin standard method: Titrimetric analysis. Pigment Cell Res. 5:230–239, 1992. Zeise, L., R. B. Addison, and M. R. Chedekel. Bio-analytical studies of eumelanins. I. Characterization of melanin the particle. In: The Pigment Cell: From the Molecular to the Clinical Level. Proceedings from the XIVth International Pigment Cell Conference. Pigment Cell Research Supplement 2, Y. Mishima (ed.). Copenhagen: Munksgaard, 1992, pp. 48–53. Zhang, X., C. Erb, J. Flammer, and W. M. Nau. Absolute rate constants for the quenching of reactive excited states by melanin and related 5,6-dihydroxyindole metabolites: implications for their antioxidant activity. Photochem. Photobiol. 71:524–533, 2000.
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
16
The Physical Properties of Melanins Tadeusz Sarna and Harold A. Swartz
Summary 1 The complexities of melanins make it difficult to reach very specific conclusions as to the properties and structure of these intractable pigments. 2 Different melanins can have different physicochemical properties, with the most important variables being the nature of the monomeric units. 3 Consequently, there are at least three different types of naturally occurring melanins: eumelanin, pheomelanin, and neuromelanin. 4 Although melanins have been viewed as large heterogeneous polymers and amorphous substances, there appears to be a short-range order within the melanin nanostructure, consisting of several layers of stacking 0.34 nm apart. A growing body of experimental evidence indicates that the assembly of melanin oligomers into nanoparticles, and their aggregation into larger particles, is a key process that determines basic physicochemical properties of melanin pigments. 5 The most important functional groups of the melanin oligomeric units are: aryl and a-amino acid carboxylic groups, fully oxidized, semi-reduced, and fully reduced o-quinone groups in eumelanins, and the corresponding o-quinonimine, o-semiquinonimine, and o-aminophenols in pheomelanins. 6 The observable optical properties of natural melanins are a complex function of different melanin monomers and oligomers to absorb light, and ability of melanin particles to scatter and reflect light at different wavelengths. 7 Melanins are poor fluorophores; however, the intensity of fluorescence increases upon their oxidative degradation. 8 Although several band models for melanin have been proposed to explain its optical absorption and electrical properties, there is at present no fully satisfactory theory for melanin to have amorphous semiconductor and related properties. 9 Melanins are the only known biopolymers that both in vivo and in vitro contain a significant amount of persistent free radical centers that are easily detectable by electron paramagnetic resonance (EPR) spectroscopy. 10 Many of the EPR characteristics and the associated free radical and redox reactions of melanin can be explained on the basis of a comproportionation equilibrium involving key redox groups of the melanin oligomers. 11 The ability of melanin to form complexes with multivalent metal ions is one of its basic physicochemical properties that affects the biological effects of this pigment. 12 Binding of transition metal ions by melanin may result in two opposite effects on its free radical EPR signal: while para-
magnetic ions induce magnetic quenching of the intensity of the observable EPR signal of the melanin, diamagnetic ions, such as zinc(II), enhance the EPR signal intensity by shifting the comproportionation equilibrium of the melanin subunits. 13 Melanin polymers are complex redox systems, the resultant properties of which are modified by pH, temperature, illumination with ultraviolet and visible light, and storage conditions. 14 Prolonged illumination of melanin with intense light, in the presence of oxygen, leads to irreversible bleaching of the pigment and its oxidative degradation. 15 Antioxidant properties of melanin, shown in model systems, can be explained by melanin’s ability to sequester redox-active metal ions, scavenge oxidizing free radicals, and quench electronically excited states of molecular oxygen and photosensitizing dye molecules. 16 Much is known about melanin as a result of the use of sophisticated physical and chemical approaches, and it is likely that continued progress will be made.
Historical Background Melanins are a complex group of pigments of different origins, the composition and structure of which depends very much on local conditions, including the type of synthesis (e.g. within specific organelles such as melanosomes vs. polymerization of naturally occurring high concentrations of monomers as in some regions of the brain), the monomeric units that are polymerized (e.g. whether or not cysteine derivatives are involved), the presence of other types of molecules at the time of formation (e.g. tyrosinase, other proteins, lipids, metal ions), and the subsequent history of the usually long-lived polymers (e.g. oxidation, complexing of metal ions). The resulting melanins are usually heterogeneous with very intractable physical properties, which resist attempts to characterize them by simple physical–chemical approaches. Consequently, attempts to characterize melanins have involved the use of a large number of different and often complex techniques. These have led to large amounts of data, but the nature of the data obtained from many different techniques, combined with the heterogeneity of the melanins that have been studied, has resulted in incomplete and sometimes apparently contradictory conclusions on the composition and structure of melanins. Since publication of the first edition of The Pigmentary System, significant advances in biophysical studies of melanin have been made. Particularly impressive are the results of recent studies, in which the ultrastructure of melanin 311
CHAPTER 16
was examined by powerful imaging techniques such as scanning tunneling and atomic force microscopies, and the photodynamics of melanin, after excitation with light, were analyzed by ultrafast emission and absorption spectroscopies. The aim of this chapter is to summarize representative data on the biophysics of melanin that have been published recently and to provide an overview of the existing data on melanins and, where possible, to indicate generally accepted conclusions on their significance. The reader will find, however, that the current state of knowledge, in spite of the recent advances, often does not lead to such conclusions and, therefore, only a summary of experimental findings is provided without fitting them into a comfortably unified picture of melanin. This chapter represents an updated progress report and a source of information that may facilitate understanding and experimental progress on this intriguing and important natural polymer.
Current Concepts Structure and Composition of Melanin The usual melanin pigments are amorphous substances with a distinct particulate character. In biological material, melanin is usually present in the form of discernible units such as pigment granules. The size and shape of the mature melanin granules are, to a significant degree, determined by the process that forms them. In most cells, melanin is synthesized in a specific organelle, the melanosome, the phenotype of which determines the geometry of the melanin particles (Seiji, 1981) (see Chapter 15). For example, melanosomes in human retinal pigment epithelium are typically elongated and relatively large (2–3 mm long and 1 mm wide; Feeney-Burns, 1980), while melanin granules in Harding–Passey melanoma cells are almost spherical in shape and much smaller in size (0.40 mm diameter) (Hach et al., 1977). In normal skin, the ultrastructure of melanosomes usually relates to the type of melanin they produce (Hearing et al., 1973; Jimbow et al., 1979). Typical eumelanosomes have an ellipsoidal–lamellar structure with melanin being deposited in a uniform pattern. Pheomelanosomes, on the other hand, are round and granular with uneven deposition of pigment within the melanosome. It should be noted, however, that another spherical melanosome with a distinct granular ultrastructure, which occurs in the Harding–Passey mouse melanoma, does not produce pheomelanin but mostly eumelanin, as determined by complex physicochemical analysis (Ito and Jimbow, 1983; Jimbow et al., 1984). In human epidermis, melanin granules are transferred to keratinocytes where they appear as single, nonaggregated pigment granules or as aggregates, often termed complex melanosomes (see Chapters 7 and 9). The size and distribution of melanosomes in epidermal keratinocytes depends predominantly on the type of human skin (Toda et al., 1973). Eventually, after fusion with lysosomes, the epidermal melanosomes are degraded and broken up into “melanin 312
dust” (Wolf, 1973). It remains to be determined to what extent the physicochemical properties of the melanin are modified by such a disassembly of the melanin granules. Very significant changes in melanin can occur with age; it has been shown by electron microscopy that, in human retinal pigment epithelium from donors over 90 years old, virtually all the melanin granules are enclosed in other material, thereby creating “melanolipofuscin” or “melanolysosomes” (FeeneyBurns et al., 1990). Neuromelanin has a distinctively different type of pigment granule. Neuromelanin is found in certain dopaminergic neurons of the substantia nigra and locus coeruleus of primate brains (Bazelon and Fenichel, 1967; Marsden, 1969; Van Woert and Ambani, 1974). These neuromelanin granules are irregular in shape and vary in size and, unlike melanin arising from melanosomes, they do not have distinct well-organized limiting membranes. Neuromelanin in situ is a material granule consisting of three different components — an electrondense melanin core, electron-translucent lipid vacuolae, and lipofuscin (Barden and Brizzee, 1987). It has been reported that neuromelanin accumulates with age in the substantia nigra of human brains until it reaches a maximum level at the age of 50–60 years, and then it gradually decreases (Mann and Yates, 1974). Based on scanning electron microscopy studies, it was proposed that the “primary particles” of natural melanin are spherical, nonporous particles with a diameter in the order of 30 nm, with an inherent specific surface area in the order of 160 m2/g (Kollias et al., 1991; Zeise et al., 1992). According to this view, a “melanin aggregate” is composed of strongly associated primary melanin particles placed together in such a fashion that the measured surface area is significantly less than the sum of the specific surface areas of the primary particles of which it is composed. Such aggregates may be similar to, if not identical with, melanin granules derived directly from Sepia officinalis melanosomes, which are spherical in shape, have an average diameter about 160 nm, and a specific surface area 29.31 m2/g (Kollias et al., 1991). Sepia melanin granules are uniformly electron dense and, under electron microscopy, exhibit no detectable ultrastructure. In this respect, it is an open question whether typical elongated eumelanosomes and round pheomelanosomes with distinct ultrastructure should be classified, according to this scheme, as “agglomerates,” i.e. loosely associated clusters of melanin aggregates. More recent scanning electron microscopy (SEM) study of Sepia melanin indicated the existence of much smaller particles with lateral dimensions of about 15 nm that adhered to larger melanin subunits (Nofsinger et al., 2000). This study also suggested significant structural differences between Sepia melanin and a synthetic melanin obtained by enzymatic oxidation of dopa. The presence of such small particles in purified melanin, isolated from the ink of cuttlefish, has been confirmed by another imaging technique. Taking advantage of the three-dimensional spatial resolution of atomic force microscopy (AFM) and the ability of the technique to cut the
THE PHYSICAL PROPERTIES OF MELANINS
imaged object or perform with it other mechanical manipulations, the Simon group demonstrated that, although the spherical particles 100–200 nm in diameter were stable structures, they were composed of tiny particles with lateral dimensions of 15–25 nm (Clancy et al., 2000). In a recent study, images of melanosomes from bovine retinal pigment epithelium and from human hair clearly indicate that these pigment granules are also aggregated assemblies of substructures about 20 nm in diameter (Liu and Simon, 2003a). In a related study, the authors demonstrated the importance of the isolation and purification procedure on the structure and chemical composition of a natural melanin (Liu and Simon, 2003b). Thus, while two different acid/base procedures, used for the isolation of melanin from human hair, yielded amorphous material without any apparent structure, only the enzymatic extraction preserved the normal morphology of the melanosomes. Even though synthetic melanins, from different substrates, often exist in aggregated forms, it has been concluded that neither chemically nor enzymatically prepared tyrosinemelanin is composed of discrete particles (Zeise et al., 1992). Indeed, in a comparative study, Nofsinger et al. (2000), using SEM, showed that, unlike Sepia melanin, a synthetic melanin, obtained by enzymatic oxidation of DOPA, was an amorphous material without any distinct substructure. On the other hand, light scattering experiments on colloidal aqueous suspensions of synthetic auto-oxidized dopa-melanin revealed a particulate character of this melanin preparation, with a particle size of less than 10 nm (Huang et al., 1989). Characterization of the structural units (nodules) of synthetic dopamelanin was also carried out by the X-ray small-angle scattering technique (XSAS) (Miyake and Izumi, 1984; Miyake et al., 1985, 1987). The radius of gyration of melanin in its aqueous solution, calculated from an initial slope of the Guinier’s plot, suggests that the elemental molecular unit of this synthetic melanin may be rod-like in shape, 4.8–8.5 nm long, and 0.6–0.8 nm in diameter. Qualitatively similar conclusions about the submolecular structure of melanin have been reached on the basis of ultrasonic measurements of synthetic diethylamine melanin and natural melanin from Sepia (Aconthosepian), and B16 and Harding–Passey melanomas (Kono, 1984; Kono and Jimbow, 1985; Kono and Yoshizaki, 1987). A pronounced particle wave resonance observed for all studied melanins at 220 MHz was related to a stiff-chain unit that could be approximated by a rod-like rigid molecule. Perhaps the most detailed structure of the synthetic tyrosine-melanin “protomolecule” has been proposed by Zajac et al. (1994). Based on wide-angle X-ray diffraction analysis of dried melanin and scanning tunneling microscopy measurements of monomolecular layers of the melanin deposited on highly oriented pyrolytic graphite, the authors constructed a model of the fundamental unit of synthetic melanin consisting of three stacked sheets with five to eight 5,6-indolequinone residues in each sheet. The spacing between stacks was assumed to be 0.34 nm in order to account for the
prominent features observed by X-ray diffraction and scanning tunneling microscopy. Therefore, the overall dimensions of the melanin protomolecule were calculated to be roughly 2.0 nm in lateral extent and 0.76 nm in height. The X-ray and STM results were verified by structure minimization and molecular orbital techniques. Systematic modeling of the data from X-ray diffraction studies of melanin performed by Cheng et al. (1994a, b) can be summarized as follows. The derived structure factor, S(q), typically shows six diffused peaks within the q-range 0.3/Å to 16/Å in reciprocal space (Fig. 16.1). Although some differences are apparent in the magnitude of S(q) oscillations for DOPA-melanin, tyrosine-melanin, and Sepia melanin, all these melanins are rather similar in the arrangements of their neighbors. The first peak in S(q) (at q = 1.74/Å) reflects mainly the number and spacing of the melanin monomer layers, suggesting that, in real space, the interlayer spacing is 3.4 Å. The plane-polymerized monomeric units produce the second peak at q = 3.0/Å, while the third peak at q = 5.6/Å refers to the number (four or five) of connected monomers in a layer. The last three peaks in the higher q-region are mainly produced by the single monomer structure, the average band length of which determines their locations. A 1.42-Å distance obtained in real space can be attributed to the average bond length of C–C, C–O, and C–N. The four-layer stacking of four to eight 5,6-dihydroxyindole (or 5,6-indolequinone) units gives a dimension of the fundamental melanin unit of 15 Å. Interestingly, a prepeak at q = 0.45/Å (which corresponds to the length 13–20 Å in real space) has also been observed in some melanin samples (Bridelli et al., 1990; Cheng et al., 1994b; Thathachari and Blois, 1969). The X-ray diffraction data revealed that melanin has a relatively low X-ray absorption coefficient (1 < m £ 2/cm), which is consistent with its elemental composition (Cheng et al., 1994b). The collective results of SEM and AFM studies of Sepia melanin, carried out by the Simon group, and of independent structural studies of synthetic melanins, in which the researchers used STM and AFM (Gallas et al., 2000), smallangle neutron scattering (Gallas et al., 1999), or synchrotron small-angle X-ray scattering (Littrell et al., 2003), as well as the results of matrix-assisted desorption ionization (MALDI) mass spectroscopy measurements, are consistent with the proposed model of ultrastructural organization of eumelanins, in which the major building block of eumelanin pigments is a small planar oligomer, probably highly cross-linked, with maximum dimensions 0.4 ¥ 1.0 nm, that is preferentially aggregated into fundamental aggregates of 3–4 p-stocked oligomers (Cheng et al., 1994a, b; Clancy and Simon, 2001; Gallas et al., 2000; Zajac et al., 1994). The macroscopic morphology of eumelanin pigment granules is a result of hierarchical self-assembly, in which the building blocks of eumelanin assemble into hundred-nanometer structures, which then aggregate to form the final pigment granules (Clancy et al., 2000). This model is a radical deviation from the existing model, in which melanin was pictured as a huge heteropolymer, consisting of a large number of different monomers 313
CHAPTER 16
1.6
S(q)
L-dopa 1.4
tyrosine
1.2
Sepia
1 0.8 0.6 0.4
0
4
2
6
8
10
12
14
16
q (Å–1)
28 24
tyrosine melanin
20
L-dopa melanin Sepia melanin
RDF(r)
16 12 8 4 0 -4 1
2
3
4
5
6
r (Å) Fig. 16.1. Structure factors S(q) (A) and the radial distribution functions (RDF) (B) of two synthetic melanins and Sepia melanin. Reproduced from Cheng et al. (1994b), with permission.
linked covalently by a variety of bonds (Nicolaus, 1968). According to the new model, melanin is built of very small building blocks — planar oligomers — consisting of as few as five to eight monomers, which assemble into nanoaggregates that form characteristic stocks. Such nanoaggregates assemble into larger structures, which then aggregate to macroscopic pigment granules. Although the exact nature of the forces that are involved in the assembly of nanoaggregates and of hundred-nanometer structures, as well as in their aggregation, remains unknown, it can be speculated that Van der Waals’, p–p, and hydrophobic interactions play a key role. Unfortunately, until now, no comparable structural studies of pheomelanin have been carried out. Much of our current knowledge about the chemical structure of melanins comes from chromatographic identification 314
and quantitation of the characteristic products arising from chemical degradation of the pigments (Ito, 1986, 1998; Ito and Fujita, 1985; Ito and Jimbow, 1983; Jimbow et al., 1984; Ozeki et al., 1995; Prota et al., 1998a, b). This approach has been applied to human neuromelanin to try to unravel its chemical structure (Carstam et al., 1991; Odh et al., 1994; Wakamatsu et al., 1991). Unfortunately, the conclusions reached by the authors have significant areas of apparent disagreement. The Swedish researchers found large quantities of 4-amino-3-hydroxyphenyl-ethylamine (AHPEA) in neuromelanin samples hydrolyzed with hydriodic acid, whereas the Japanese researchers were unable to detect any significant amount of AHPEA after they analyzed neuromelanins by degradation by hydriodic acid (HI). This discrepancy leaves open whether cysteinyldopamine is incorporated into neuromelanin. While detectable levels of pheomelanin are found in human skin, regardless of race, color, and skin type, eumelanin is always the major constituent of epidermal melanin (Ito and Wakamatsu, 2003). It appears that high levels of pheomelanin are found only in yellow and red hair of mammals and in red feathers of birds (Ito and Wakamatsu, 2003). It is believed that the key intermediates in the biosynthetic pathway for eumelanin are 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA), as well as their fully oxidized forms that determine the nature of the fully formed melanin polymer (reviewed by Hearing, 1993; Hearing and Tsukamoto, 1991; Prota, 1992). In the biosynthetic pathway for pheomelanins, a similar role may be played by 1,4-benzothiazynylalanine, derived from cysteinyldopas (Deibel and Chedekel, 1984; Ito and Wakamatsu, 1989; Prota, 1988; Rorsman et al., 1979). The distributions of the functional groups (CHx, C–O, C=O, O–C=O, –NH2, and R2NH) of synthetic and natural eumelanins have been studied in solid-state samples by electron spectroscopy for chemical analysis (ESCA or X-ray photoelectron spectroscopy) (Clark et al., 1990). Qualitative and quantitative analysis, calibrated with model compounds (various precursors of eumelanin), revealed interesting differences between the synthetic polymers obtained from DOPA and DHI and Sepia melanin. Thus, although none of the synthetic melanins had elemental compositions identical to Sepia melanin, DOPA melanins (both auto-oxidized and enzymatically oxidized) were roughly comparable with the Sepia eumelanin in elemental composition and distribution of functional groups. The high content of nitrogen observed in Sepia melanin was attributed to proteinaceous material still associated with the natural eumelanin. Enzymatically produced DOPA melanin had a higher percentage of carbonyl-type functionalities than auto-oxidized DOPA melanin. As judged by their functional group distribution, the enzymatic DOPA melanin was a better model of natural eumelanin than autooxidized DOPA melanin. Infrared (IR) spectroscopy also has been used in the chemical analysis of melanin (Blois et al., 1964; Bridelli et al., 1980; Garcia-Borrón et al., 1985; Jimbow et al., 1984; Wilczok
THE PHYSICAL PROPERTIES OF MELANINS
et al., 1984; Zecca et al., 1992). Using solid pellets of melanin dispersed in KBr, broad absorption bands with varying intensities were observed at 3400/cm, 3200/cm, 3000– 2800/cm, 2700–2500/cm, 1700–1650/cm, 1600–1400/cm, and 1045/cm. The bands could arise from symmetric and asymmetric stretching and bending of bonds in a variety of functional groups such as amine, imine, carboxylic, carboxylate, phenolic, aliphatic CH3, CH2, C–H, aromatic C–H, etc.; however, precise assignment of these bands is still difficult. Quantum mechanical calculations of the vibrational structure of the key melanin monomers, carried out by Powell et al. (2004), showed that the three main redox forms of 5,6-dihydroxyindole had significantly different infrared and Raman signatures, suggesting that these spectra could be used in situ to identify nondestructively the monomeric content of various melanins. Melanin–protein complexes have been investigated by IR using absorption bands of amide groups. Based on detection of the distinct amide I and amide II bands in natural melanins and in synthetic melanin obtained by auto-oxidation of DOPA in the presence of bovine serum albumin, it was concluded that melanins in vivo exist as true melano-protein complexes with the protein moiety covalently bound to melanin (Bilinska et al., 1987; Garcia-Borrón et al., 1985). It should be noted, however, that no independent unequivocal evidence for covalent binding between melanin and protein has been obtained. IR also has been used to study the effect of potential degradative treatments on melanin. Characteristic changes in the IR spectra of DOPA melanin were observed upon treatment with HCl. The appearance of sharp methyl and methylene bands at 3000/cm and 2800/cm upon acid hydrolysis of this synthetic melanin was attributed to acid-induced decomposition of some indolic monomers, yielding noncyclic units with aliphatic side-chains (Garcia-Borrón et al., 1985). This is consistent with evidence from analysis by degradative chemistry. Ito (1986) found that acid-treated melanins gave much lower yields of pyrrol-2,3,5-tricarboxylic acid (after oxidation of melanin with permanganate) than the corresponding native melanins. The number of accessible aryl carboxylic acid and a-amino acid carboxylic groups in synthetic tyrosine melanins and natural Sepia melanin was estimated by titrimetric analysis using nonaqueous media — 2-propanol and acetic acid (Zeise and Chedekel, 1992). Titratable acidic groups were measured to be 180 mEq/q for Sepia melanin, 490 mEq/q for melanin prepared by oxidation of tyrosine with persulfate, and only 68 mEq/q for enzymatic tyrosine-melanin. It was concluded that, of the two synthetic melanins, only the enzymatic tyrosine-melanin was an adequate functional group model for the surface structure of eumelanin. Elemental analysis and quantitative amino acid analysis were employed for estimation of the elemental composition of the melanin backbone in Sepia melanin and two synthetic melanins (Chedekel et al., 1992a, b). Assuming only one nitro-
gen atom per monomeric unit of eumelanin, the authors were able to determine the average monomeric backbone chromophore of Sepia melanin. The elemental composition of the melanin chromophore backbone is: C, 45.91%; H, 2.66%; N, 6.98%; and O, 29.32%. Accordingly, the C/N and empirical formula for the Sepia melanin were 7.67 and C7.67H5.33NO3.68 respectively. Of course, the derived formula of any natural melanin will critically depend on accurate estimates of the contribution of any amino acids associated with the melanin, which can obscure the determination of the actual elemental composition of the melanin. Taking advantage of the enhanced spectral resolution offered by the NMR techniques of cross-polarization, magic angle-spinning (CP/MAS), and high-power proton decoupling, high-resolution 13C and 15N solid-state NMR have been used for the assignment of functional groups of various eumelanins (Aime and Crippa, 1988; Aime et al., 1991; Duff et al., 1988; Peter and Förster, 1989). Briefly, at a 13C Larmor frequency of 75.7 MHz, the main features of the 13C CPMAS spectrum of Sepia melanin consisted of an intense carboxylate resonance centered at 173 ppm as well as broad and strong absorptions in the aromatic and olephenic region (90–120 ppm). In natural melanins, but not in synthetic melanins, a number of variously substituted aliphatic regions (15–75 ppm) was observed, consistent with the presence of unreacted DOPA and a proteinaceous component (Fig. 16.2) (Herve et al., 1994). Although solid-state CP/MAS and 15N NMR were used recently for characterization of Sepia melanin and human melanin (Adhyaru et al., 2003), and high-resolution 1H NMR was employed for quantification of the aromatic protons of the polymer chain in Sepia melanin and human hair melanin (Katritzky et al., 2002), the application of these advanced analytical methods has not yet yielded any truly unique information about the chemical structure of melanin. Much of the information on the structure and composition of melanin derived by chemical and structural analysis needs to be considered critically and considered tentative because of the experimental complexities involved in such determinations. This is because of the heterogeneous nature of melanins and their difficult physical–chemical properties, and the possible presence of nonintrinsic proteinaceous material. The procedures required to make it feasible to analyze melanins can readily lead to artifacts. The analyses of its chemical composition often depend on the derivatization of relatively small parts of the macromolecule and so, even if the derivatization procedures are entirely valid from a chemical point of view, the portions of the molecule from which they are obtained may not be fully representative of the entire molecule; for example, they may be derived primarily from parts that are on the surface. Analogous considerations apply to many of the structural studies, especially when these require that the melanin be dried or otherwise altered. This can lead to very distinct changes in its physical properties [e.g. as monitored by electron paramagnetic resonance (EPR) or, equivalently, ESR], which may not reflect the fully hydrated state, etc. (Sealy et al., 1980). 315
CHAPTER 16
Fig. 16.2. 13C solid-state NMR spectra of Sepia melanin (A) and a synthetic melanin obtained by auto-oxidation of 5,6dihydroxyindole (C), and their Lorentzian peak fitting spectra (B) and (D) respectively; spectra obtained by conventional crosspolarization/magic-angle spinning (CP/MAS) technique are shown by solid lines, while those obtained by short-contact-time CP/MAS (protonated carbons) are shown by dotted lines and those obtained by dipolar dephasing (quaternary carbons) by broken lines. Reprinted from Hervé et al. (1994), with kind permission of Elsevier ScienceNL.
Optical Properties The absorption of light is one of the most obvious and important properties of melanins. This has proven to be an immensely complex topic, in terms of both understanding the mechanisms and consequences of optical absorption by melanin and exploiting these properties to enhance an understanding of melanins. In this section, we attempt to provide representative highlights of what appears to be a productive and growing area of study. The absorption spectrum of human skin melanin in vivo is a linear function of the wavelength in the range of 500–750 nm (Kollias and Baqer, 1985). Based on diffused reflectance spectra obtained from patients with vitiligo and normal volunteers, it has been proposed that human melanin absorbs visible radiation through two distinct mechanisms: one that is in effect over the entire visible range and is linear in wavelength, and a second one that is evident at wavelengths in the range 400–500 nm and is exponential in frequency (Kollias and Baqer, 1987; Kollias et al., 1991). As natural melanin in situ is in particulate form (Barden and Brizzee, 1987; Feeney-Burns, 1980; Kollias et al., 1991), its observable optical properties are a complex function of melanin’s ability to absorb, scatter, and reflect light at different wavelengths. 316
Therefore, it has been very useful to carry out optical studies on synthetic and isolated natural melanins as well as in situ. The optical density of soluble synthetic melanin, such as auto-oxidized DOPA melanin, increases almost monotonically with decreasing wavelength (Crippa et al., 1978; Sarna and Sealy, 1984a). The apparent absorption coefficient of DOPA melanin increases from about 4/mg/cm2 at 600 nm to over 30/mg/cm2 at 200 nm (Fig. 16.3). It is important to stress that these are only representative values because the detectable absorption spectra of melanin depend, among other factors, on the conditions used for its synthesis, the redox state of the polymer, the pH and the ionic strength of the aqueous media, temperature, and the handling of the sample (Sarna, 1992). Although the molecular origin of melanin determines many of its physicochemical properties, optical absorption of the polymers synthesized from dopa and cysteinyldopas is quite similar (Fig. 16.3). The smooth absorption curve of a solution of synthetic auto-oxidized DOPA melanin, with almost monotonic increase in the absorbance with decreasing wavelength, viewed as a characteristic feature of melanin, has been an enigma for years and is still not fully understood. Although different models have been considered to explain the unusual optical
THE PHYSICAL PROPERTIES OF MELANINS 50 A
Extinction Coefficient ((mg/ml)-1 cm-1)
40
30
20
10
0 200
400
600
800
Wavelength (nm)
0.1
B
Extinction Derivative
0.0
-0.1
-0.2
-0.3
-0.4 200
400
600
800
Wavelength (nm) Fig. 16.3. Apparent absorption coefficients (A) and first derivatives of extinction (B) for auto-oxidized dopa melanin (solid lines) and cysteinyldopa melanin (dotted lines). Experimental conditions: melanins dissolved in 50 mM phosphate buffer, pH 7.4, run in 0.1 cm quartz cells.
properties of melanin, including the solid-state model, in which melanin is treated as an amorphous semiconductor with distinct energy bands (Crippa et al., 1978; Galvao and Caldas, 1988; Jastrzebska et al., 1990; Longnet-Higgins, 1960; McGinness et al., 1974), none of the models proved to be satisfactory. One of the most interesting results of the theoretical studies by Galvao and Caldas (1990a, b) was the finding that key physicochemical properties of melanin start to emerge in systems consisting of a small number of monomeric units. Indeed, a remarkably smooth absorption spectrum in the region 300–800 nm for a random composition of basic
monomer units such as 5,6-dihydroxyindole, indole-5,6quinone, and their semiquinone form has been obtained by Bochenek and Gudowska-Nowak (2003a, b), using the intermediate neglect of differential overlap (INDO) and other semi-empirical methods. A similar trend, with significant absorption in the visible spectral region, has also been observed by Stark et al. (2003), who carried out much more advanced density functional theory (DFT) calculations for simple melanin oligomers. The relative stability of nine tautomers of 5,6-dihydroxyindole and 5,6-indolequinone and their excitation energies in both gas phase and solution were examined by Il’ichev and Simon (2003), who used DFT, timedependent DFT, and self-consistent reaction field calculations. The results of their calculations indicated that the indolequinone units could be responsible for a relatively strong absorption in near infrared. Finally, a first principle density functional theory calculation of the electronic and vibrational structure of key melanin monomers has been reported by Powell et al. (2004). The authors postulated that the difference in energies of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the different monomers could lead to a large range of HOMO–LUMO gaps in eumelanin molecules and thus be related to the observed broadband optical absorption of melanin. In other words, it is the monomer diversity and chemical disorder that are responsible for the optical properties of melanin. Although the existing theoretical studies of melanin have not yet resulted in a satisfactory description of its optical properties, there is little doubt that advanced quantum mechanical calculations of various melanin oligomers should yield important new results and, ultimately, will lead to better understanding of its structure and physical properties. The degree of aggregation of the melanin is an especially important factor that will significantly modify the ability of melanin to transmit light at different wavelengths (Huang et al., 1989; Pilas and Sarna, 1985). This effect can also be exploited to study the aggregation of melanins. Using static and dynamic light scattering emitted by a NeHe laser, the dynamics of aggregation of a synthetic DOPA melanin in acidic aqueous solution was studied (Huang et al., 1989). It was found that, depending on the final pH of the solutions, slow and fast regimes of the kinetics of aggregation could be identified. The precipitates formed in these two regimes could be characterized by fractal structures. It was estimated that, in the fast, diffusion-limited aggregation regime, the aggregate was a fractal with dimension of 1.8, whereas the dimension of the fractal was 2.23 in the slow, reaction-limited aggregation regime. The fractal nature of melanin aggregates has been established over scales ranging from about 0.08 to 2.0 mm (Eisner, 1992). The slow regime of melanin aggregation, with the fractal dimension 2.2, was also observed in the presence of critical amounts of transition metal ions such as copper, nickel, and zinc. That aggregation of melanin affects its optical properties has also been found for very small melanin particles. Thus, Nofsinger et al. (1999) reported distinct differences 317
CHAPTER 16
in the optical absorption of Sepia melanin obtained by ultrafiltration of the bulk melanin using a series of different ultrafiltration disk membranes. The results of this study, perhaps predictably, showed a substantial reduction in melanin absorbance in the visible and near-UV spectral region when very low-molecular fractions of this eumelanin were examined. In a related study, the authors demonstrated that differences in the absorption bands were due to varying levels of melanin aggregation (Nofsinger and Simon, 2001). The optical absorption and scattering properties, and thermal diffusivity of melanin particles from Sepia officinalis were recently determined at 580 nm and 633 nm, using photometric and photothermal techniques (Vitkin et al., 1994). The absorption coefficient (ma) and the transport scattering coefficient (ms1) of Sepia melanin were determined from data of diffuse reflectance and transmittance. The scattering anisotropy was obtained from an additional measurement of the total attenuation coefficient and, independently, by goniometry. Pulsed photothermal radiometry was used to deduce the absorption and transport scattering coefficients by a model based on optical diffusion theory, and to provide the thermal diffusivity of solid melanin. At 633 nm, ma was found to be 127–157/cm/% and 162–176/cm/% at 580 nm. The corresponding transport scattering coefficient values were 24–28 and 28–30/cm/% at 633 nm and 580 nm respectively. The photometrically measured optical absorption and scattering properties of Sepia melanin were consistent with the Mie theory predictions, which indicated strong dependence on the size of melanin particles. The larger the size of melanin particles (melanosomes), the higher their albedo (and more forwardpeaked scattering phase functions). These effects are likely to be important for epidermal melanosomes and for retinal pigment epithelial granules, the size of which is significantly larger than that of Sepia melanin. Data from both optical and photothermal studies suggest that Sepia melanin is not a perfect black body absorber; the melanin significantly scatters light in the yellow–red region. The internal absorption coefficient of melanosomes in situ in human skin was determined, based on measurements of the threshold radiant exposure from a pulsed ruby laser that was necessary to achieve explosive vaporization of the melanosomes (Jacques and McAuliffe, 1991). This phenomenon is observed when the rate of radiant energy deposition within the melanin granule is substantially higher than the thermal relaxation rate of the pigment granule. As the thermal relaxation of melanosomes is estimated to be between 0.5 and 1 ms, threshold radiant exposures for melanosomal injury could easily be obtained using nanosecond Q-switched Nd:YAG or ruby lasers when the energy density exceeds 1 J/cm2 (Anderson et al., 1989; Watanabe et al., 1991). Based on their own data and the literature they provided, a summary of the absorption coefficient (ma) of the melanosome interior vs. wavelength was presented. The ma parameter was found to vary significantly with the wavelength; thus, the average ma values were around 80/cm at 1064 nm, 200/cm at 694 nm, 350/cm at 630 nm,
318
700/cm at 532 nm, and 1500–2000/cm at 355 nm. Dry melanosomes required lower threshold radiant exposure to achieve their explosive vaporization than wet melanosomes, indicating that the effective ma for dry melanosomes is higher (202/cm) than that for wet melanosomes (120/cm). The data have been interpreted in terms of swelling, with wet melanosomes having a 70% larger volume than dry melanosomes. The absorption spectrum for human epidermis in vivo, measured by an optical fiber spectrometer, matched quite well the relative changes with wavelength of the absorption coefficient of the interior of the melanosome. The solid-state appearance of typical melanin and its very efficient nonradiative de-excitation, following the absorption of ultraviolet or visible photons, would suggest photo-acoustic spectroscopy to be a method of choice for studying the optical properties of natural melanins. This spectroscopic technique has been applied, with great success, to many biological systems (Balasubramanian and Mohan Raa, 1986; Braslavsky, 1986; Fork and Herbert, 1993; Moore, 1983) but, surprisingly, has been used sparsely to study melanins. The only photo-acoustic spectrum of melanin reported to date that the authors are aware of is a spectrum of a synthetic DOPA melanin obtained in a limited spectral range (Wróbel et al., 1997). The PAS spectrum of DOPA melanin is similar to typical optical absorption spectra of solubilized eumelanins. Photo-acoustic techniques were used to determine the thermal properties of melanin and to study nonradiative relaxation of excited states in melanin (Crippa and Viappiani, 1990; Gallas et al., 1988). It was found that the acoustic signal induced in synthetic DOPA melanin by chopped light from a krypton laser was dependent on the chopping frequency (~w–1), as predicted by the Rosencwaig–Gersho theory for optically dense samples with a length of thermal diffusion that is greater than the optical extinction length (Rosencwaig and Gersho, 1976). The data suggested, rather unexpectedly, that the optical absorption coefficient in acid- or acetone-precipitated melanin was about 30 times smaller than that of “standard melanin.” Photo-acoustic measurements of dense aqueous melanin suspension made at various chopping frequencies with an argonion laser as the excitation source revealed strong dependence on pH and the redox state of melanin (Crippa and Viappiani, 1990). Control experiments, performed on natural and synthetic melanins in the form of powders or pastes, confirmed the results of Gallas et al. (1988) only to some extent; the photo-acoustic signal intensity varied with the chopping frequency as w–0.9–w–1.1. A very efficient electron–photon coupling, consistent with efficient energy transfer toward the internal degrees of freedom of the melanin macromolecule, was inferred from the effects of phonon amplification observed in a synthetic melanin upon the application of a pulsed electric field with increasing gradient (Crippa et al., 1991). This explains why melanin is a very poor fluorescence emitter. The first unambiguous report of melanin-specific fluorescence was reported only in 1984, using natural melanins, both intact and solubi-
THE PHYSICAL PROPERTIES OF MELANINS
Fig. 16.4. Fluorescence spectra of auto-oxidized dopa melanin (A) and of intact melanin granules from human RPEs of different age groups (B). (A) Fluorescence of melanin was observed as a function of its excitation wavelength: 340 nm (dotted line extending to the shortest wavelengths) and 400 nm (solid line in the longest wavelength region), with fluorescence induced by excitation at 360 nm and 380 nm being characterized by dotted lines in between. (B) Left curves (I) are excitation spectra with emission monitored at 570 nm, and right curves (II) are emission spectra with excitation at 364 nm. (a) Fetal, (b) 5–29 years, (c) 30–40 years, (d) > 50 years and (e) 1 year bovine melanin. Reprinted from Gallas and Eisner (1987), with kind permission; and from Boulton et al. (1990), with kind permission from Elsevier Science.
lized, after drying, in solid-state KBr (Kozikowski et al., 1984). The authors observed a weak broad luminescence, centered at about 540 nm, when natural melanins from human hair and Sepia ink were excited by an argon-ion laser emitting at 488 nm. A dramatic increase in the fluorescence emission intensity was brought about by the solubilization of the melanin, achieved by treatment with H2O2 at high pH. [Similar increases in the detectable fluorescence of synthetic DOPA melanin and melanoproteins, after early oxidative degradation of the melanin by treatment with H2O2, were also reported by Soviet workers (Korzhova et al., 1989).] An induction of a distinct fluorescence of melanin in situ in tissue sections was observed upon irradiation of the sections with UV
light (Elleder and Borovansky, 2001). The phenomenon was explained as being due to an oxidative breakdown of melanin induced by simultaneous action of UV and hydrogen peroxide (Elleder and Borovansky, 2001). Fluorescence of synthetic DOPA melanin was studied by Gallas and Eisner (1987) as a function of excitation wavelength and melanin concentration. Fluorescence of melanin, excited at 340 nm, corrected for attenuation of excitation and emission beams and removal of background Raman and impurity fluorescence signals, exhibited a broad signal. Upon deconvolution, the data indicated the presence of two emission bands, one with a maximum at about 430 nm and the other with a maximum at 510 nm (Fig. 16.4). When melanin
319
CHAPTER 16
was excited at longer wavelengths, such as 400 nm, one emission band (at 500 nm) was observed predominantly. Assuming two interacting species (quinone and hydroquinone moieties of melanin) that can form a complex, quinhydrone, the fluorescence data of melanin were interpreted by a simple model, in which excitation occurs mainly through the broad absorption band of the complex. The complex can then dissociate, leaving the quinone or hydroquinone groups in the excited state, or can decay by radiative processes after a series of vibronic transitions. The latter would lead to one band of fluorescence emission, while the radiative decay of the excited quinone (or hydroquinone) units would constitute another band of fluorescence emission. However, the validity of the conclusions discussed above has been questioned by Nofsinger and Simon (2001), who in a more recent study analyzed spectral and kinetic parameters of radiative relaxation of a natural eumelanin. Using different molecular-weight fractions of melanin, extracted from the ink sacs of Sepia officinalis, these authors measured excitation and emission spectra of the melanins. They found no structure for the corrected emission spectra in the wavelength range 400–550 nm for excitation wavelengths above 325 nm. On the other hand, the authors demonstrated that emission properties of Sepia melanin varied with the aggregation state of the melanin. Although different melanins were examined in these two studies, it seems unlikely that melanin origin was responsible for the observed differences in melanin fluorescence. Indeed, in a recent independent study, Meredith and Riesz (2004) reported on radiative relaxation quantum yields for a synthetic dopa-melanin. Using a strict renormalization procedure to correct for pump beam attenuation and heavy reabsorption of the emission, the authors found no evidence of a double-peaked feature in the emission spectrum of the melanin that was reported by Gallas and Eisner (1987). Meredith and Riesz (2004) observed that the position, width, and intensity of the emission maxima, as well as the quantum yield, varied as a function of the excitation wavelength. The emission quantum yield was calculated to be in the range 0.0005–0.0007, almost an order of magnitude lower than that determined by Nofsinger and Simon (2001) for Sepia melanin. The data may indicate that fluorescence emission in a synthetic eumelanin is derived from ensembles of small chemically distinct oligomeric units that can be selectively pumped. A detailed analysis of the photodynamics of melanin was carried out by the Simon group, using a number of complementary time-resolved techniques, such as femtosecond transient absorption spectroscopy, picosecond fluorescence spectroscopy, and nanosecond photo-acoustic calorimetry (Forrest et al., 2000; Nofsinger and Simon, 2001; Nofsinger et al., 1999, 2001; Ye and Simon, 2002, 2003). The main results could be summarized as follows. The emission dynamics of melanin are nonexponential and require a sum of exponentials to generate functional forms that provide a fit for experimental data. Thus, for Sepia melanin, four exponentials are required with the following lifetimes (and amplitudes): 56 ps (0.54), 0.51 ns (0.22), 2.9 ns (0.16), and 7.0 ns (0.08). 320
Emission decay of a synthetic pheomelanin is also nonexponential and can be fitted by three exponentials: 46 ps (0.66), 1.2 ns (0.166), and 6.2 ns (0.18). When different molecularweight fractions of Sepia melanin were examined, the authors found that, although large size fractions were the source of short emission decay (lifetimes less than 1 ns), small melanin fractions were responsible for long-lived emission dynamics (lifetimes greater than 1 ns). Nonexponential character of transient absorption decay dynamics has also been observed for eumelanin and pheomelanin following photoexcitation with an ultrashort laser pulse at 303 nm. Global fitting parameters, obtained from transient absorption data for Sepia melanin, give the following characteristic lifetimes: 0.56 ps, 3.2 ps, and 31 ps. Corresponding parameters for a synthetic pheomelanin are 0.46 ps, 2.9 ps, and 27 ps. The data clearly show that melanin is a system in which a very efficient thermal relaxation occurs. This is to say that energy absorbed by melanin photons is rapidly converted into heat via very fast internal conversion. Excitation and emission spectra of intact melanin granules of the retinal pigment epithelium (RPE) from human donors of different age groups were studied by continuous wave (CW) and time-resolved spectrofluorometry (Boulton et al., 1990; Docchio et al., 1991). Fluorescence spectra of RPE melanin exhibited distinct age-related changes; the excitation maximum shifted from 350 to 450 nm and became broader with increasing age of the RPE, and the emission spectrum developed a second peak (in addition to the main intensity at 440 nm) at about 560 nm, which grew in intensity with age. The overall fluorescence intensity of RPE melanin increased with increasing age of the donor. Using timeresolved fluorescence spectroscopy, four decay components in the fluorescence spectrum of RPE melanin have been identified (0.14–0.19 ns, 0.43–0.58 ns, 1.98–2.30 ns, and 5.49–7.90 ns). The resultant time-integrated and time-gated fluorescence spectra of RPE melanin also exhibited marked variations with age. Although the results of these impressive investigations are not completely understood, some of the observed age-related changes could be explained by partial oxidative degradation of the melanin and formation of complex pigment granules such as melanolipofuscin (Rózanowska et al., 1995).
Melanin as an Amorphous Semiconductor The remarkable ability of melanin to absorb near infrared, visible, and ultraviolet radiation almost indiscriminately has not been explained satisfactorily. Even though it cannot be ruled out that the observable optical properties of melanin result from the presence of many chromophores, the absorption bands of which overlap to the extent that an absorption continuum is formed in the entire UV-vis range, no evidence has been provided to prove this view. In fact, the existing relevant data are rather ambiguous in this respect. Thus, irreversible bleaching of melanin, induced by oxidative degradation, is at first accompanied by a gradual decrease in the absorbance by melanin in both the visible and the ultra-
THE PHYSICAL PROPERTIES OF MELANINS
violet regions (Korytowski and Sarna, 1990; Wolfram and Albrecht, 1987). This could be explained by assuming that all the chromophores in melanin are equally susceptible to oxidative degradation induced by light plus oxygen or by hydrogen peroxide. Synthetic melanin, which is extensively bleached, has a severely modified absorption spectrum compared with that of native melanin; the absorption in the visible region, particularly the red, is significantly reduced, whereas it increases in the UV. The absorption changes in bleached melanin seem to be correlated with changes in an important intrinsic molecular probe of melanin — its free radical centers (Sarna et al., 2003). In an attempt to explain the unusual optical behavior of melanin (as well as its electrical properties), a band model, viewing the melanin as an amorphous semiconductor, has been proposed (Crippa et al., 1978; Kurtz et al., 1987; McGinness and Proctor, 1973; Strzelecka, 1982a, b). An optical band gap value of 3.4 eV, reported for synthetic DOPA melanin, was based on optical absorption and photoconductivity measurements (Crippa et al., 1978). On the other hand, significantly lower values for the optical gap (1.4–1.73 eV) of several natural melanins and synthetic DOPA melanin were determined by Strzelecka (1982a, b). Band gaps in the range of 1.0–1.4 eV were also found by Kurtz et al. (1987) for various melanins. Finally, an optical gap value of 1.45 eV could be estimated from the photoconductivity edge of about 850 nm reported by Trukhan et al. (1973). The reason for significant discrepancies in the reported band gap values is not clear. It can be speculated that some of the differences may arise from variations in the types of melanin and/or the preparation of the samples that were used. A mechanism for band gaps in melanins, based on mobility gaps, typical for amorphous semiconductors, has been proposed by McGinness (1972), and unusual current–voltage (I–V) characteristics for a wet melanin were explained by amorphous semiconductor switching in the melanin (McGinness et al., 1974). This explanation was later questioned (Chio, 1977), but the hypothesis about melanin being an amorphous semiconductor has led to additional speculations and experiments. Measurements of electrical photoconductivity of melanin were reported in 1968 (Potts and Au, 1968), and photoconductivity of natural melanin from frog RPE was studied by the microwave dispersion technique (Trukhan et al., 1970, 1973). In the latter works, the current carrier was found to be of hole character, and its mobility was estimated to be 15 cm2/Vs. Measuring dark, DC, steady-state conductivity as a function of the applied voltage, and plotting the specific conductivity vs. inverse absolute temperature and optical absorption of melanin vs. the photon energy, basic semiconductor characteristics of synthetic DOPA melanin and several natural melanins were obtained (Strzelecka, 1982a, b, c). Specific conductivity of the natural melanins was in the range 10–11–10–10/W/cm, whereas it was almost 10–7/W/cm for the synthetic melanin. Thermal activation energies for natural melanins were found to be 0.93–1.04 eV at 298–333 K. Interestingly, the synthetic melanin appeared to have two values of
activation energies: below 311 K it was 0.1 eV and above 313 K it increased to 0.78 eV. The energy of 0.1 eV was taken as evidence for a band of states (0.2 eV wide) of the Fermi level. Unfortunately, it does not appear that these results, obtained with DOPA melanin, have been reproduced by an independent study. Dark and photoinduced, DC, steady-state conductivity measurements were also carried out on synthetic melanins prepared from dopamine, epinephrine (adrenaline), adrenochrome, and adrenolutin (Jastrzebska et al., 1990). Specific conductivities of the melanins were in the range 1.3 ¥ 10–12–1.5 ¥ 10–10/W/cm, which is significantly lower than that reported for DOPA melanin (Strzelecka, 1982a, b). Thermal activation energies determined for the catecholamine melanins, on the other hand, were rather similar to that of DOPA melanin: 0.62–0.73 eV. Except for adrenolutin melanin, no photocurrent was observed for other melanins that were tested. The importance of absorbed water on melanin conductivity has been demonstrated in a more recent study (Jastrzebska et al., 1995). The authors reported that thermal activation energy of dark conductivity varied in the range 47–73 kJ/mol, depending on the hydration state of melanin. Indeed, in a more recent study, Meredith et al. (2004) showed that the electrical conductivity of a synthetic eumelanin varied by five orders of magnitude if the melanin was exposed to relative humidity in the range 10–80%. The authors of the latter study concluded that the electronic contribution to the conductivity of melanin was very small and eumelanin should essentially be considered as an insulator. A polaron and hopping model for melanin conductivity, based on the results of dielectric spectroscopy and photoconductivity studies of synthetic DOPA melanin, has been proposed by Jastrzebska et al. (2002a, b). Charge transport in synthetic catechol melanin was studied by analyzing current–voltage characteristics and temperature dependence of DC steady-state conductivity (Osak et al., 1989a), and polarization and depolarization currents at different electric fields and temperatures (Osak et al., 1989b). The data indicated a deviation from Ohm’s law for voltages higher than several hundred volts. The temperature dependence of DC steady-state conductivity at an applied voltage of 85 V (for which Ohm’s law was obeyed in the entire temperature range studied) suggested two thermal activation energies: below 3∞C, the activation energy was 0.76 eV and, at higher temperatures, it was 1.58 eV. Long-lasting polarizing currents, detected in the melanin, were described in terms of the movement of charges trapped in deep states of the polymer. Polarization of the melanin samples had an activation character, with the thermal activation energy of 0.67 eV. According to the authors, the current carrier in the catechol melanin was predominantly of electron character. The authors further concluded that transport of charges involved both charges generated in the sample and charges injected from electrodes. The results of the studies on semiconductor properties of melanin, briefly reviewed in this section, are difficult to interpret. The observable DC dark and photoconduction of melanin are very low and depend critically on the water 321
CHAPTER 16
content in the tested samples. This is a serious consideration in strongly hygroscopic samples such as melanin. Thus, unless all experimental parameters are strictly controlled, including the preparation of melanin and its physicochemical state, DC conductivity measurements on melanin samples may lead to random results and erroneous conclusions. It therefore appears that, at this time, the semiconducting properties of melanin have not been rigorously determined. Even if melanin is an amorphous semiconductor, it remains to be established whether this description of melanin offers any new insight into our understanding of the structure and properties of melanin, and its biological functions. A band model for melanin that could explain some of its optical absorption, electron exchange, and paramagnetic properties has been suggested following theoretical calculations of the electronic structure of the melanin monomer and dimer units (Longnet-Higgins, 1960; Pullman and Pullman, 1961). Extrapolating the bonding character of the lowest unoccupied orbital (LUMO) of one particular dimer of 5,6-indolequinone to the lowest conduction band of the infinite polymer, the authors pointed out the tendency of such a melanin model to be an electron acceptor and that this would explain the trapping of free radicals. The semiconducting polymer model, however, was found to be inconsistent with EPR data that apparently ruled out the occurrence of any extensive p-electron delocalization in melanin (Blois et al., 1964). More recent theoretical investigations of model polymers for eumelanins have been carried out by Galvao and Caldas (1990a). Using the Hückel p-electron approximation, and the same parametrization used by Pullman and Pullman (1963), the authors studied the electronic structure of a family of ideal ordered polymers arising from 5,6-indolequinone in different redox states. The authors found that structural effects, such as direction of polymerization, began to emerge as the length of the polymer increased. The redox state of the melanin units seemingly played an important role in its band structure, e.g. a polymer built from 5,6-dihydroxyindole units consistently showed larger gaps and narrower bands, whereas finite chains of semiquinone units exhibited bonding character of their lowest unoccupied molecular orbital. An important conclusion, reached by the authors, was the inevitable occurrence of end-type defects in any finite melanin polymer. The existence of defects with deep gaps is consistent with the hypothetical electron acceptor properties of melanin. According to the authors, an electron injected at the surface of the pigment (by a donor molecule) could be trapped at an end-type defect state producing the observable electron paramagnetic resonance (EPR) signal. Furthermore, they argued that capture of a second electron at the same defect would not be favored because of electron–electron repulsion effects and, as a result, such an electron would be easily transferable to another empty defect center. In this model, unpaired electrons are likely to have rather uniform distribution among defects, and the spin concentration is expected to be roughly independent of temperature. The authors speculated that, for samples in solution,
322
the chains of the polymer would behave more like isolated molecules so that double occupation of defects was more probable and, therefore, an enhanced temperature dependence of the spin concentration was predicted for samples in solution. In an extension of their theoretical study of model polymers for eumelanins, Galvao and Caldas (1990b) investigated the effects of different kind of defects, such as the aggregation of carboxyl radicals into one skeleton monomer, aggregation of a host monomer in a lateral misplaced position, and faults in the polymerizing sequencing. The data indicated that, although the end-type defect is not deactivated by the introduction of other defects, new capture centers might be formed, which could enhance the electron-accepting properties of the melanin.
Free Radicals in Melanin Melanin is the only known biopolymer that both in vivo and in vitro contains relatively high concentrations of persistent free radical centers that can easily be detected by EPR spectroscopy (Blois et al., 1964; Enochs et al., 1993a; Mason et al., 1960; Sarna and Lukiewicz, 1971; Sarna and Swartz, 1978; Sealy et al., 1980). These free radicals have turned out to be very important experimental parameters both to explain the properties of melanin and to serve as analytical probes for investigating the structure and properties of melanins. The EPR signals of melanin are specific for the two main types of melanin pigments (Fig. 16.5). At X-band (~9.5 GHz), eumelanins have a single slightly asymmetric line 4–6 G wide with a g-factor close to 2.004. The EPR spectrum of pheomelanin typically consists of three spectral features with an overall width of about 30 G, and g = 2.005. It is important to stress that, even though the EPR signal of melanin is very persistent, and no physicochemical procedures are known to quench it irreversibly without decomposition of the material, the free radicals in melanin are by no means “stable.” In fact, it has been demonstrated that the concentration of free radicals can be changed reversibly by almost two orders of magnitude (Sarna et al., 1981). Several physicochemical agents have been shown to modify the amount and/or type of free radicals in melanin: ultraviolet and visible radiation (Cope et al., 1963; Felix et al., 1979; Ostrovsky and Kayushin, 1963; Sarna and Sealy, 1984b; Sarna et al., 1985a, b), pH (Chio et al., 1982; Grady and Borg, 1968), temperature (Arnaud et al., 1983; Chio et al., 1980), complexing of diamagnetic multivalent metal ions (Felix et al., 1978a), redox reactions of the melanin polymer (Dunford et al., 1995; Korytowski et al., 1986; Reszka and Chignell, 1993; Sarna and Swartz, 1993), and the degree of hydration of the melanin (Sealy et al., 1980). As discussed in a later section, it is believed that most of the changes in the free radicals induced by these agents are due to changes in the so-called comproportionation equilibrium, i.e. the equilibrium between fully reduced and oxidized subunits, and the intermediate semi-reduced (semi-oxidized) states that
THE PHYSICAL PROPERTIES OF MELANINS
Red chicken feather pheomelanin
Red hair pheomelanin
Eye melanoma eumelanin
Brown eye eumelanin
Black hair eumelanin 10 G
Fig. 16.5. EPR spectra from frozen suspensions of natural melanins (1 mg/ml) containing 3 mM Zn2+ (pH 4.5) at –196∞C. Spectra were recorded at X-band. Reproduced from Sealy et al. (1982b), with permission.
are free radicals (Felix et al., 1978a; Sealy, 1984). The equilibrium is significantly shifted toward the diamagnetic form of the melanin subunits, and the free radical content of synthetic DOPA melanin is around 2 ¥ 1018 spins/g (referred to mass of the dried melanin) under typical experimental conditions: pH 7, ambient temperature, no irradiation with ultraviolet or visible light, no metal ions, and fully hydrated samples. This corresponds to about one free radical per 1500 polymer units (assuming a molecular weight of 200 for the melanin subunit). The free radical content of purified melanin from the choroid
of bovine eyes was reported to be about half that of DOPA melanin (Chio et al., 1982). Although the number of melanin free radicals detected under typical experimental conditions is rather low because of the equilibria, the total number of participating units is likely to be substantially higher, similar to the maximum spin concentration obtained under any experimental conditions (Sarna et al., 1981; Sealy et al., 1980). It therefore appears that the comproportionation equilibrium, monitored by EPR in melanin, reflects a significant percentage of total monomer units (Chio et al., 1980). In addition to changes in the intensity of the EPR signal of melanin detected, there can be small, but distinct, changes in other spectral characteristics. For example, the g-factor of DOPA melanin is 2.0034 at pH 1, 2.0036 at pH 7, and 2.0042 at pH 12 (Chio et al., 1982). The corresponding changes in the spin concentration are 2 ¥ 1018–1.2 ¥ 1019 spins/g. The EPR signal of eumelanins (particularly synthetic DOPA melanin) at high pH becomes narrower and more asymmetric than at low pH. Dramatically different EPR spectra have been observed for pheomelanins (Sealy et al., 1982a). The spectra, showing distinct changes with varying pH, were interpreted as being due to the presence of a different type of melanin free radical. It has been proposed that, unlike eumelanin, pheomelanin contains ortho-semiquinonimine radicals, in which the unpaired electron is delocalized on both oxygen and nitrogen atoms. As a result, an immobilized, nitroxide-like EPR spectrum is observed with the parallel component of the hyperfine coupling (2 A||) being about 30 G. The ortho-semiquinonimine radical is in equilibrium with the pheomelanin subunits — fully reduced o-aminophenols and oxidized o-quinonimines. The free radical can predominantly be observed at low pH or, in the presence of complexing zinc(II) ions, at neutral and slightly acid pH. The effect of complexing of diamagnetic multivalent metal ions on the melanin EPR signal is an important diagnostic test that can be used to determine the molecular nature of the subunits. Changes in the EPR spectra are consistent with complex formation between the metal ion and chelating polymer radicals (Felix et al., 1978a). The structure of the chelating radicals can be inferred from line width changes that reflect hyperfine splittings associated with the metal ions. The magnitude of the hyperfine splitting from association with a particular metal ion is sensitive to the detailed structure of the free radicals in the melanin (Felix and Sealy, 1981), e.g. radicals complexed with the 113Cd(II) isotope in melanins derived from DOPA, catechol, and cysteinyldopa have splittings of about 3.5 G, 7 G, and 15 G respectively (Sealy, 1984). The established relationship between the amount of inhomogeneous broadening of the EPR signal of melanin induced by complexation of 113Cd(II) with melanin and the origin of the melanin also has an important practical implication because it can be used for unambiguous differentiation of natural melanins (Jimbow et al., 1984; Sealy et al., 1982a; Vsevolodov et al., 1991). Thus, EPR spectroscopy is a unique
323
CHAPTER 16
A
B
Fig. 16.6. The chemical structure of the monomer units of the melanin oligomers.
physical method that enables nondestructive analysis and characterization of melanins with high sensitivity and accuracy. The molecular nature of inducible melanin radicals (extrinsic free radical centers) appears to be well understood. It is most likely determined by the chemical structure of the monomer units of the melanin oligomers that can engage in redox equilibria (Fig. 16.6A): k1 Æ Q + QH2 ¨ 2SQ + 2H+ k–1 These monomers are o-quinones, o-hydroquinones, and osemiquinones in the case of eumelanin. Corresponding units for pheomelanin are o-quinonimines, o-aminophenols, and osemiquinonimines respectively. Any agent that can influence the equilibrium constant, kc/kd, may modify the detectable concentration of free radicals in melanin. A key aspect of the comproportionation equilibrium is stabilization of the radicals (Fig. 16.6B). Thus, diamagnetic metal ions that are able to form chelate complexes with the free radicals in the melanin shift the equilibrium toward the semiquinone free radicals. A similar phenomenon is observed 324
at high pH: the induced deprotonization of the radicals results in their enhanced stabilization. This, in turn, increases the observable concentration of free radicals. A careful analysis of the results of numerous EPR studies of melanin free radicals leads to the conclusion that the above may not be the only free radical centers present in the melanin polymer (Sarna, 1992; Sealy et al., 1980). In the authors’ experience, regardless of the experimental conditions under which melanin is examined, its free radical content does not decrease below a certain level (providing the melanin is not decomposed). This seems to indicate the existence of two independent pools of melanin free radicals: extrinsic and intrinsic radical centers. The extrinsic radicals can be viewed as a convenient molecular probe, reporting on the molecular nature of the melanin monomer units and the redox state of its functional groups. The intrinsic radicals, on the other hand, are somewhat less understood. They are probably paramagnetic centers that were generated during the formation of the melanin and trapped within the growing oligomers and aggregates of basic subunits. Because of severely restricted accessibility to any reactive extraneous agents and low chemical reactivity, these radicals are essentially “stable.” The intrinsic radicals being associated with the melanin core can be viewed as a unique endogenous spin label reporting on the molecular state of the melanin and its integrity. For example, it has been demonstrated that the magnitude of the low-pH EPR signal of DOPA melanin (which is a measure of the intrinsic free radicals in melanin), subjected to oxidative degradation, corresponds to the degree of bleaching of the melanin in a reproducible and consistent way (Sarna et al., 2003). Thus, the EPR spectrum of melanin, examined under nonextreme experimental conditions, is usually a superposition of two or more EPR signals arising from the corresponding free radical centers. Detailed analysis of EPR spectra of melanins of various origins, recorded at 35 GHz (Q-band) to increase spectral resolution, over a range of pH, led to a conclusion that the EPR spectrum of melanin at intermediate pH was a composite of two spectra arising from anionic and neutral radicals with different g-factors (Grady and Borg, 1968). Such an analysis has later been refined by recording second derivative Q-band EPR spectra of DOPA melanin at various pH and the use of more advanced computer simulations of the EPR spectra (Pasenkiewicz-Gierula and Sealy, 1986). The authors interpreted the EPR spectra of frozen aqueous dopa-melanin in terms of four different spectral species related to anion osemiquinone radicals with relatively localized unpaired electrons and cation radicals with extended delocalization of their unpaired spins. Recent advances in EPR spectroscopy made possible the examination and analysis of EPR spectra of various melanins at very high frequency (W-band, 95 GHz; Nilges, 1998). It is expected that such high-resolution EPR measurements and sophisticated computer simulations will make possible unambiguous identification of the molecular nature of all radicals in melanin, and determination of their role in the physicochemical activity of melanin.
THE PHYSICAL PROPERTIES OF MELANINS
As noted previously, dramatic changes in the intensity of the EPR spectrum of melanin free radicals can be induced by paramagnetic metal ions (Blois et al., 1964; Sarna et al., 1976). Even though the quenching effect of copper(II) ions on melanin EPR signal was originally interpreted as a chemical reaction between copper and free radicals (Blois et al., 1964), it has later been shown that the effect is purely magnetic in nature (Sarna et al., 1976). Using lanthanide ions, which have similar chemical properties but quite different magnetic properties, it was possible to observe consistent changes in the amplitude and microwave power saturation of the EPR signal of the radicals in melanin as a function of the type and concentration of the added metal ion. Lanthanides with a very short spin-lattice relaxation time had a strong effect on microwave power saturability of the melanin EPR signal, but only weakly quenched the signal amplitude. The effect can be understood by viewing the interacting melanin radical with neighboring metal ions as magnetic dipoles fixed in space. As a result of such an interaction, dipolar broadening of the narrow EPR signal of melanin occurs. As the magnitude of the broadening depends inversely on the cube of the distance between the melanin free radical and the metal ions, quenching of the melanin EPR signal is a distinct function of the concentration of paramagnetic metal ions in the melanin environment. This static dipolar interaction is modulated by spin-lattice relaxation of the metal ion, which efficiently decreases the amount of the dipolar broadening of the EPR signal of melanin. The faster the rate of relaxation of the metal ion, the weaker the dipolar broadening observed as the metal ion-induced quenching of the melanin EPR signal. The theory of such an unusual dipolar broadening has been described by Leigh (1970). For very rapidly relaxing paramagnetic metals, the fluctuating magnetic dipole field sensed by the melanin free radicals provides a powerful spin-lattice relaxation mechanism. Maximum relaxing efficiency of metal ions occurs when the rate of their spin-lattice relaxation approximates the microwave frequency. The quenching of the EPR signal of melanin is much more pronounced when relatively slowly relaxing metal ions are used, such as copper(II), iron(III), manganese(II) and, among lanthanides, gadolinium(III). It is important to emphasize that, in melanins, the dipolar broadening effect decreases the melanin EPR signal intensity without any apparent broadening of its line width. Thus, the effect can easily be misinterpreted by an inexperienced researcher as a real reduction in the free radical content of the examined melanin. This becomes a serious consideration when analyzing natural melanins, which can, both in vivo and in vitro, accumulate substantial amounts of transition metal ions, including paramagnetic metal ions (Enochs et al., 1993b; Zecca and Swartz, 1993; Zecca et al., 1994). One way to deal with such a problem is carefully to determine the microwave power saturability of the melanin samples and their signal amplitude before and after subjecting the samples to procedures that may stimulate the release of the metal ions that are bound to the melanin. In the authors’ experience, washing the melanin samples in an aqueous solution of
high concentrations of powerful metal ion chelators such as EDTA or DTPA and desferal for several hours is usually quite effective in this respect. Incubating melanin samples in solutions of hydrochloric or sulfuric acid (0.1–1.0 M) is also effective; however, the latter procedure may be unacceptable because of possible modifications of the melanin chemical structure induced by acids (Liu et al., 2003; Prota, 1988).
Ion Exchange Properties The ability of melanin to bind metal ions is one of its basic physicochemical properties that affects the biological effects of this pigment (reviewed by Enochs et al., 1994; Sarna, 1992; Sarna and Rozanowska, 1994; Swartz et al., 1992). As is the situation for other properties of melanins, the study of ion exchange properties of melanin has been valuable both to understand the biological effects of these interactions and as a tool to investigate the structure and properties of melanins. It is well known that melanin, both in vivo and in vitro, can accumulate substantial amounts of multivalent metal ions (Bruenger et al., 1967; Cotzias et al., 1964; Larsson and Tjälve, 1978; Lydén et al., 1984; Okazaki et al., 1985; Simonovic and Pirie, 1963; Valkovic et al., 1973; Zecca and Swartz, 1993). It has been estimated that the number of metal ion binding sites in eumelanins is about 20% of the number of monomeric units in the polymer (Potts and Au, 1976). Similar estimates were made after titrating the EPR signal of melanin with paramagnetic metal ions; plots of microwave power saturability vs. concentration of metal ions were sigmoidal and yielded a value of 6 ¥ 1020 total metal binding sites per gram of dried melanin (Sarna et al., 1976). Binding of multivalent metal ions by melanin is a pHdependent phenomenon; the amount of metal ions bound to melanin usually increases with pH in the pH range 1–7. This indicates that melanin behaves as a weak acid ion exchange resin. This is expected because the melanin polymer contains a number of functional groups (Larsson, 1998) that can serve as potential ligands for the interacting metal ion. Thorough analysis of complexing of metal ions with melanin requires precise control of the sample pH. This is because the pH of the sample (which is likely to change after adding substantial amounts of metal ions to an aqueous suspension of melanin) may determine not only the amount of metal ions that bind to melanin, but also the type of complexes that are formed. The radioactive isotope 54Mn(II) was used to determine binding parameters for interactions with bovine eye melanin (melanoprotein), human hair melanin, and synthetic dopamine melanin, and the binding was analyzed by the method of Scatchard (Lydén et al., 1984). Four classes of binding sites were found in bovine eye melanin, with the corresponding number of sites (in mmol/mg melanin) and the apparent association constants: n1 = 0.072, K1 = 5.2 ¥ 107; n2 = 0.195, K2 = 1.8 ¥ 106; n3 = 0.661, K3 = 2.0 ¥ 104; n4 = 0.398, K4 = 1.1 ¥ 103. The total binding capacity was 1.33 mmol/mg melanin, which is equivalent to about 20% of the number of all melanin units, assuming 200 as the molecular weight for an average melanin monomer unit. The 325
CHAPTER 16
Fig. 16.7. EPR spectra of copper (63Cu2+) bound to melanin from bovine eye choroid at: (A) pH 1.6, (B) pH 1.9, (C) pH 2.9, (D) pH 4.3, (E) pH 5.8, (F) pH 8.7, (G) pH 11, (H) pH 12.6. Spectra were recorded at –196∞C using an X-band EPR spectrometer equipped with second derivative capabilities. The abscissa indicates magnetic field strength in kilograms. The ratio of melanin isonomers to copper ions was 100:1 (assuming a monomeric molecular weight of 200). Reproduced from Sarna et al. (1980a), with permission.
authors indicated, however, that the binding capacity of the bovine eye melanin was rather high, as the total binding capacity was 0.23 mmol/mg melanin for human hair melanin and 0.15 mmol/mg melanin for dopamine melanin. Using X-band EPR spectroscopy and the isotope 63Cu(II) as a molecular probe, the molecular nature of the main binding sites in synthetic DOPA and catechol melanins, and natural melanin from bovine eye choroid have been studied (Froncisz et al., 1980; Sarna et al., 1980a). The results can be summarized as follows. Depending on the pH of the system, copper(II) can form a number of complexes with melanin that involve different functional groups of the polymer and exhibit different stabilities (Fig. 16.7). Nearly all complexes involve just one or two ligands from melanin; the others are presumably H2O or OH– groups. At pH < 7, binding is predominantly to monodentate carboxyl complexes and, in eumelanin, also to bidentate nitrogen–carboxyl complexes. The corresponding EPR spectral parameters are within the range: g|| = 2.26–2.34, A|| = 460–560 MHz, and g^ = 2.066–2.076. The complexing of copper ions by melanin can be observed at low pH (below pH 3) in the EPR spectra of frozen suspensions of melanin in solutions of copper(II) with a ratio of melanin monomers to copper ions of 100:1 (assuming a monomeric molecular 326
weight of 200). At pH 7 and above, binding is to phenolic hydroxyl groups, but the number of such sites is much less in natural melanin than in synthetic DOPA melanin. The corresponding magnetic parameters are: g|| = 2.24–2.26, A|| = 560–579 MHz, g^ = 2.054–2.064. At very high pH (above pH 11), the EPR signal of natural melanin with Cu(II) is unlike any found in synthetic melanins. Its spectroscopic parameters are: g|| = 2.18, A|| = 610–620 MHz, g^ = 2.050. The assignment of complexes of Cu(II) to functional groups of melanin has been further supported by EPR and elemental analysis of chemically modified synthetic DOPA melanin (Sarna et al., 1981). Blocking the melanin phenolic hydroxyl and carboxylic groups by methylation, ethylation, or acetylation was accompanied by consistent changes in the EPR spectra of melanin–Cu(II) complexes and reduction in the amount of Cu(II) that was bound to melanin. Using a potentiometric method, in combination with mathematical fitting and correlative spectroscopies, Szpoganicz et al. (2002) quantitated the binding sites of a colloidal suspension of synthetic melanin, and compared the metal-binding affinities of the melanin functionalities. One of the most interesting conclusions reached by the authors was the apparent role of a quinonimine functionality in metal binding by DHImelanins. On the other hand, recent quantum mechanical calculations of selected melanin monomer units indicate that the quinonimine tautomer of 5,6-indolequinone should not be present in melanin to any appreciable extent (Il’ichev and Simon, 2003). As virtually identical EPR spectra of melanin–copper(II) complexes have been observed for choroidal melanoprotein and for protein-free melanin (obtained from the melanoprotein by hydrolysis with cold hydrochloric acid), it has been concluded that the protein component does not play a significant role in metal ion binding. This conclusion was supported by results of the titration of the free radical signal of melanin with Cu(II) in melanoprotein and purified melanin; the corresponding titration curves were identical. Binding of copper ions to melanin is a time-dependent process. At moderately acidic pH, after addition to suspensions of melanin, cupric ions rapidly form an initial complex, which rearranges within hours to a more stable monodentate or bidentate complex. At pH 3.0, the complex is predominantly the monodentate complex with the carboxyl groups of melanin. Similar intramolecular rearrangements of iron(III) have been observed recently for synthetic neuromelanins (Shima et al., 1997). The binding of metal ions to melanin was also studied by the utilization of ferric ions as molecular probes (Sarna et al., 1981). The EPR spectra of Fe(III)–melanin complexes at neutral and weakly acidic pH (pH 3–7) were found to be almost indistinguishable (apart from signal intensity). The most prominent feature of the spectra was a single asymmetric line at g = 4.3. Similar EPR spectra of iron were detected in natural melanin from bovine eye choroid (Sarna et al., 1980a), in melanosomes from human and bovine retinal pigment epithelium (Zareba et al., 2005), and in neuro-
THE PHYSICAL PROPERTIES OF MELANINS
melanin (Enochs et al., 1993a; Zecca and Swartz, 1993). The EPR data of iron–melanin complexes can be compared with results obtained by another powerful spectroscopic technique — Mössbauer spectroscopy (Bardani et al., 1982; Gerlach et al., 1995; Kochanska-Dziurowicz et al., 1985; Sarna et al., 1981). For fully hydrated DOPA melanin samples incubated with the 57Fe(III) isotope at pH 3 and pH 7, the Mössbauer spectra at 77 K were essentially identical, with quadrupole splitting 0.33 ± 0.005 mm/s and isotopic shift 0.17 ± 0.04 mm/s (Sarna et al., 1981). The data from EPR and Mössbauer studies suggest that ferric ions bind to melanin predominantly via phenolic hydroxyl groups and form high-spin complexes with distorted octahedral or rhombic symmetry, with a coordination number of 4–6. It can be speculated that the functional groups of melanin provide the four planar ligands for Fe(III) complexes with melanin, while the two remaining ligation sites are occupied by OH– or H2O. A significant modification of melanin–iron complexes due to drying may be inferred from the fact that substantially different Mössbauer parameters were observed when examining fully hydrated (Sarna et al., 1981) and dried melanin samples (Bardani et al., 1982; Kochanska-Dziurowicz et al., 1985). Drying of neuromelanin, isolated from human substantia nigra seems to modify the state of iron ions bound to melanin, as their Mössbauer parameters become similar to those of human hemosiderin or ferritin (Galazka-Friedman et al., 1996; Gerlach et al., 1995). In a recent study of ion exchange properties of Sepia melanin, Liu et al. (2004) compared the ability of EDTA to remove Mg(II), Ca(II), Sr(II), and Cu(II) bound to the melanin granules. The authors found that the binding constants of Sepia melanin at pH 5.8 for all these ions were higher than that of EDTA. The binding of Fe(III) was concluded to involve coordination to o-dihydroxyl groups. The authors also found evidence that Ca(II) and Mg(II) were bound to melanin via coordination to carboxylic groups. It is worthwhile emphasizing that ionic binding to melanin is by no means restricted to multivalent metal ions. Strong complexes of melanin with organic cations, both in vivo and in vitro, have been observed (Bielec et al., 1986; D’Amato et al., 1986; Larsson and Tjalve, 1979; Larsson et al., 1977; Lindquist, 1973; Lindquist and Ullberg, 1974; Lindquist et al., 1988; Link et al., 1989; Lydén et al., 1983; Stepien and Wilczok, 1982). Among the molecules that exhibit very high binding affinity with melanin are cationic forms of porphyrin derivatives, phenothiazine derivatives, chloroquine and its derivatives, and quaternary bipyrridyllium salts (paraquat and diquat). Even though different types of interaction can be involved, electrostatic attraction is the dominant force that determines complexing of these organic cations with melanin. Accumulation of drug molecules by melanin was reviewed in depth by Larsson (1998).
Melanin as a Redox System The redox properties of melanin have been recognized for a long time (Figge, 1939). In fact, one of the principal histolog-
ical tests used to detect melanin in situ is based on its reducing power; the presence of melanin in biological samples is deduced from the ability of the specimen to reduce Ag+ to metallic silver (Lillie and Fullmer, 1976). The redox properties of melanin have been investigated extensively because of their potential biological roles, especially with regard to oxidative damage. The redox properties have also served as very valuable probes to elucidate the properties and structure of melanins. The redox properties of melanin are, to a large extent, determined by the redox properties of its monomer units (reviewed by Sarna and Swartz, 1993). The relevant functional groups in eumelanin are most likely 5,6-dihydroxyindole, 5,6-dihydroxyindole-2-carboxylic acid, and their fully oxidized (quinone) and semi-oxidized (semiquinone) forms. In pheomelanins, the relevant monomer units are probably o-aminophenols, such as 1,4-benzothiazine and the corresponding fully oxidized o-quinonimine and semi-oxidized o-semiquinonimine. Although the basic redox features of melanin can be described in terms of the chemical properties of its monomers, significant differences exist between the properties of the free monomers and when they are subunits in melanin. One of the most apparent differences is their chemical reactivity; while free o-quinones such as dopaquinone, cysteinyldopaquinone, 5,6-indolequinone, and dopaminequinone are very reactive and extremely unstable (Graham, 1978; Monks et al., 1992; Thompson et al., 1985), the related subunits are quite stable in melanin. The relative stability and moderate reactivity of melanin subunits are probably due to modifications of their redox potential, electron affinity, and restricted accessibility of these functional groups within the pigment granule as a result of intramolecular interactions and steric hindrance. Using bipyridinium quaternary salts as a redox probe, the one-electron reduction potential E01 (corresponding to the fully oxidized/semi-reduced couples of the melanin subunits) of synthetic DOPA and cysteinyldopa melanins was studied by the pulse radiolysis method (Rozanowska et al., 1999). It was found that a synthetic model of pheomelanin could be reduced by a milder reducing free radical than was required for the synthetic model of eumelanin. Even though quantitative determination of the one-electron reduction potential for the melanins studied was not possible (the melanins interacted with all redox probes without establishing an apparent equilibrium), a very approximate estimation of E01 suggested that the one-electron reduction potential of cysteinyldopa melanin was more positive than –350 mV, while the E01 for the major reactive sites of DOPA melanin was between –450 and –550 mV. Owing to the intrinsic heterogeneity of melanins, a moderate dispersion of the redox properties of the melanin functional group is to be expected and is probably more realistic than a single value. These preliminary data need to be verified by the use of other methods suitable for the determination of redox properties of other aggregated polymeric materials. It remains to be determined what is the second one-electron reduction 327
CHAPTER 16
potential (E01) of the semi-reduced/fully reduced couple of the melanin moieties, and it is necessary to show that data obtained with synthetic melanins can be extrapolated to natural melanins. An interesting attempt to study redox properties of several natural and synthetic melanins by the use of simultaneous electrochemical and EPR measurements has been described by Lukiewicz et al. (1980). Distinct changes in the EPR signal of melanin radicals, observed during electrochemical treatment of the sample induced by the applied voltage, were explained by direct interactions of the melanin polymer with the electrodes. The data were interpreted in terms of the melanin being electroreduced and electro-oxidized via discrete oneelectron steps. Unfortunately, no quantitative data were provided that could be used for estimation of the melanin redox potential or electron exchange capacity, and these very promising investigations have not been followed up by any systematic studies that could provide much needed reference data on the redox properties of various melanins. One-electron reduction (and oxidation) reactions, induced by synthetic DOPA melanins, have been unambiguously shown by EPR spectroscopy using several different nitroxide radicals as redox probes (Sarna et al., 1985a). The interaction between melanin and nitroxide probes was found to be strongly pH dependent, with the rate of reduction of nitroxides at pH 10 being about 20 times faster than that at pH 5 (Sarna et al., 1985a). The data indicate that hydroquinone groups of melanin may be involved in the reduction of the nitroxides. The reduction of the nitroxide radicals was reversible, indicating that a redox equilibrium was established. From equilibrium concentrations of nitroxides and the product of the one-electron reduction of nitroxides, hydroxylamines, the equilibrium constant can be estimated for the reaction between nitroxide and melanin, assuming reasonable values for the concentrations of oxidizing and reducing groups on the polymer. The values that were obtained were in good agreement for a range of nitroxide concentrations, suggesting that the assumptions inherent in the calculations were broadly correct. Thus, for DOPA melanin formed by auto-oxidation, the number of electron-donating groups was found to be 20–30 times higher than that of the electron-accepting groups (the total number of active redox sites on the polymer was assumed to be about 25% of all monomer units). The results are rather surprising; however, if verified, they would suggest that synthetic DOPA melanin occurs predominantly in the reduced state. On the other hand, an estimate, based on available data in the literature, suggested that the reducing and oxidizing capacities of dopa-melanin were about 5 and 3 mEq/g respectively (Sealy et al., 1980). Of course, the storage conditions of the sample, including age and exposure to light, high pH, and oxygen, could significantly modify the resultant redox state of melanins. Molecular oxygen is one of the most common, biologically important, electron acceptors. Although thermodynamically, this species is very reactive with many electron-donating molecules, as a result of spin restriction (its ground state is a 328
triplet), molecular oxygen is kinetically quite unreactive with typical diamagnetic molecules (Koppenol and Butler, 1985). Melanin is no exception in this respect, although its reactivity with O2 may vary significantly, depending on the experimental conditions. The effect of pH, temperature, and chemical modification of synthetic DOPA melanin on melanin-induced oxygen consumption has been studied using EPR oximetry (Sarna et al., 1980b). EPR oximetry is an indirect, physical method that has proved to be a very convenient tool for measuring the concentration of oxygen and its changes, in a variety of biological samples (reviewed by Hyde and Subczynski, 1989; Swartz et al., 1994). The investigation clearly demonstrated that pH is the most effective experimental parameter for enhancing the rate of melanin-induced oxygen consumption: at pH 5.5, the auto-oxidation rate was slow — 10–6 g of O2 per minute, per 1 g of DOPA melanin dissolved in 1 l; the rate increased several thousand times at pH 11. The rapid increase in the rate of consumption of oxygen, particularly evident between pH 9 and 10.5, was attributed to ionization of the phenolic hydroxyl groups of the polymer. The process was found to be thermally activated, with the thermal activation energy of the order 10 Kcal/mol. The inhibitory effect of catalase on the consumption of oxygen suggests the formation of hydrogen peroxide as a product of the interaction of melanin with molecular oxygen. This conclusion has been supported by the results of studies in which the formation of H2O2 during auto-oxidation of melanin pigment was shown, using an oxidase electrode (Hintz and Kalyanaraman, 1986; Korytowski et al., 1985). The amount of hydrogen peroxide produced upon autooxidation of melanin was found to be dependent on the type of melanin, with the melanin obtained by auto-oxidation of DOPA being five times more efficient than DOPA melanin synthesized in the presence of tyrosinase, and 10 times more efficient than purified melanin from bovine eye choroid. Superoxide dismutase accelerated the rate of production of H2O2, indicating the involvement of superoxide as an intermediate. The proposed overall scheme for auto-oxidation of melanin consists of one-electron reduction of molecular oxygen to superoxide anion, followed by reduction of superoxide to H2O2 and oxidation of superoxide to O2, and spontaneous dismutation of superoxide to equimolar H2O2 and O2. The data indicate that DOPA melanin can act as a pseudo-dismutase; it is able to oxidize and reduce superoxide anion, albeit the oxidation of superoxide to O2 seems to be the dominant process, accounting for approximately 80% of the reaction between superoxide anion and DOPA melanin. Auto-oxidation of melanin may be an important, ratelimiting process in coupled reactions in which melanin acts as an electron transfer agent. An example is the melanincatalyzed oxidation of NADH and p-phenyldiamine (Van Woert, 1968). Oxidation of NADH by melanin was later confirmed in an independent study (Gan et al., 1974), which also showed that proteins associated with the melanin polymer (either in natural melanoproteins or in synthetic model systems) efficiently inhibited electron transfer reactions of
THE PHYSICAL PROPERTIES OF MELANINS
melanin. An inhibition of the electron transfer ability of DOPA melanin has also been observed for several different drugs upon binding to melanin (Debing et al., 1988). As the degree of inhibition correlated with the extent of binding and did not show any consistent dependence on the chemical nature of the drugs, the inhibitory effect of the drugs was explained by simple shielding of the redox active sites in melanin. It should be emphasized that the oxidizing equivalents for regeneration of melanin, in its electron transfer reactions, can be provided not only by oxygen, but also by other electron-accepting molecules such as ferricyanide (Gan et al., 1976). Another oxidation reaction catalyzed by melanin has been reported by Baich and Schloz (1989): in the presence of synthetic and natural melanins, glycine was oxidized to glyoxylic acid and formic acid. It was not clear from this study, however, what exactly was the role of melanin and whether possible products of reduction of oxygen, such as superoxide and H2O2, were also involved in the oxidation of glycine.
Photoreactivity of Melanin Ultraviolet and visible light can significantly modify the physicochemical properties of melanin. The most noticeable examples of the effects of light in melanin are photoinduced free radicals and photomodification of the redox properties of melanin. Illumination of melanin samples in the EPR spectrometer resonant cavity at room temperature causes a reversible enhancement of the free radical signal of melanin (Cope et al., 1963; Ostrovsky and Kayushin, 1963; Stratton and Pathak, 1968). Steady-state spectra for light-induced radicals observed during continuous photolysis, obtained by subtracting the intrinsic (dark) spectrum from the composite spectrum, revealed that the intrinsic and light-induced species differed in several EPR parameters: line width, g-factor, and microwave saturation (Felix et al., 1979). After termination of the irradiation, the signal decayed with second-order kinetics, suggesting that recombination was the primary process responsible for the termination of the photoinduced radical (Fig. 16.8). As second-order kinetics are typically observed for free radicals
in solutions, the data seem to indicate that the free radicals in melanin at ambient temperature have a substantial degree of molecular mobility. Time-resolved EPR measurements also revealed a new transient species formed in photoirradiated melanin samples (Felix et al., 1979). This species, unlike the “usual” photoinduced radicals, decayed rapidly (in milliseconds) at both ambient and cryogenic temperature, and had an EPR spectrum with a time profile that indicated the occurrence of chemically induced dynamic electron polarization. The data were interpreted in terms of the involvement of a triplet state intermediate. Such interpretation, however, seems inconsistent with the results of recent studies of melanin photodynamics using femtosecond laser flash photolysis and nanosecond photo-acoustic calorimetry (Forrest and Simon, 1998; Nofsinger et al., 2001). The authors failed to detect any long-lived transients with triplet-like properties. On the other hand, the observed very fast repopulation of the melanin ground state was a clear indication of a very efficient mechanism of energy dissipation due to internal conversion. The increased efficiency of melanin for absorbing light at shorter wavelengths suggests that photoformation of melanin free radicals may be a wavelength-dependent phenomenon. Action spectra for photogeneration of free radicals from bovine eye melanin and synthetic DOPA melanin showed a strong wavelength dependence in the 230–600 nm wavelength range (Sarna and Sealy, 1984b). Quantum yields for the steady-state formation of radicals were generally low; for DOPA melanin, the quantum yield reached the value 0.01 only at the shortest wavelengths studied, and it was well below 0.001 in the visible range. The efficiency of production of radicals from natural eumelanin was about three times greater than for synthetic melanin. As action spectra for the production of radicals differed from the optical absorption spectra, it was concluded that the chromophore(s) most active in free radical production were not the major chromophore(s) that absorb light, particularly in the visible range. A new intriguing interpretation of the spectral dependence of the photoinduced formation of melanin radicals was proposed by
Fig. 16.8. Time-resolved changes in the intensity of EPR spectrum of photoinduced free radicals in melanin from bovine eye choroid (A), and second-order plot of the data (B); [R◊] denotes transient free radical concentration. Reproduced from Felix et al. (1979), with permission.
[R·]-1 (arbitrary units)
Light Off 8 7 6 5 4 3 2 1 B
5
10
15 20 time / s
25
30
A Light On
5s
329
CHAPTER 16
Nofsinger et al. (1999). Comparing optical properties of different particle-size fractions of Sepia melanin with the reported spectral dependence of photoformation of melanin radicals, Nofsinger et al. (1999) found striking similarities between the absorption spectrum of the lowest molecular size fraction examined (MW < 1000) and the action spectrum for the photogeneration of melanin radicals. The role of small melanin particles in photogeneration of radicals was further substantiated by photo-acoustic data for different size fractions using an excitation wavelength of 351 nm. Thus, the data revealed that, although the percentage of the absorbed energy that was released as heat by the MW > 10 000, 10 000 > MW > 3000, 3000 > MW > 1000, and MW < 1000 eumelanin fractions was above 90 for the first two fractions, it became about 80 for the third fraction and only about 40 for the smallest molecular weight fraction. The authors concluded that the photochemical properties of melanin are determined by the presence of small molecular size constituents that, unlike the larger melanin particles, retain high photoreactivity. Although the interpretation proposed by Nofsinger et al. (1999) is very attractive and seems probable considering the role of different size aggregates in the structure of melanin (Clancy and Simon, 2001), it remains to be determined how representative the smallest particles are among the building blocks of natural melanin. Photoionization and photohomolysis of melanins occur in the wavelength range 240–300 nm (Kalyanaraman et al., 1984). This was inferred from spin trapping experiments, in which melanin was irradiated in the EPR resonant cavity in the presence of the spin trap 5,5-dimethyl-1-pyrroline-1-oxide (DMPO). In the absence of oxygen, irradiation of the melanin samples resulted in the formation of characteristic spin adducts, DMPO–H◊, product of the interaction of DMPO with either H◊ or eaq–. Photoirradiation of melanin leads to the production of both reducing and oxidizing equivalents on the polymer, which below 400 nm seem to originate from a common precursor (or precursors) (Sarna et al., 1985a). The data indicate that irradiation of melanin with light enhances melanin’s reducing and oxidizing power. In aerated aqueous samples, photoexcitation of melanin leads to an enhanced consumption of molecular oxygen and the formation of superoxide anion and hydrogen peroxide (Felix et al., 1978b; Korytowski et al., 1987; Rózanowska et al., 1995; Sarna et al., 1980b; Tomita et al., 1984). Action spectra and quantum yields for photoinduced consumption of oxygen have been determined for eumelanins and pheomelanins using EPR oximetry (Sarna and Sealy, 1984a; Sarna et al., 1984). The results of these studies indicate that the reduction of oxygen induced in melanin by visible light has a low yield: the quantum yield in the visible range is below 0.001 and reaches 0.01 only at 230–220 nm. Action spectra for photoconsumption of oxygen by eumelanin and pheomelanin are comparable with each other and exhibit similarities to the action spectra for anaerobic photogeneration of free radicals in melanin (Fig. 16.9). Using EPR spin trapping, Rózanowska 330
Fig. 16.9. Action spectra for melanin free radical photoproduction (dotted line) and for oxygen photoconsumption (broken line) by eumelanins. For comparison, an apparent optical absorption spectrum of dopa melanin (solid line) is also shown. Reproduced from Sarna and Sealy (1984b), with permission.
et al. (2002) demonstrated a significant generation of superoxide anion when melanosomes, isolated from human retinal pigment epithelium, were irradiated with blue light. The authors also showed that such an aerobic photoreactivity of the human RPE melanosomes increased with the age of the donors. Although the data suggest an increased pro-oxidizing activity of RPE melanin in RPE from older individuals, at this point it is unclear whether this intriguing observation has any biological implications. A very interesting study regarding the ability of eumelanin to photogenerate reactive oxygen species was recently published by Nofsinger et al. (2002). Using a simple spectrophotometric technique, the authors observed that the efficiency of cytochrome c reduction, used to monitor the photogeneration of superoxide by different molecular size fractions of Sepia melanin, was an order of magnitude higher for the smallest unaggregated oligomers than that characteristic of the bulk pigment. The reduced efficiency of aggregated melanin to photogenerate superoxide anion and hydrogen peroxide was attributed to the decrease in surface concentration of melanin redox active sites upon aggregation. Using the nitroblue tetrazolium–superoxide dismutase assay, the action spectrum for photoproduction of superoxide from aerated aqueous solutions of pheomelanin was determined (Chedekel et al., 1980). In contrast to the results cited above, these results indicated higher quantum yields for the photogeneration of superoxide even in the visible range. The quantitative aspects of this work should be considered with significant caution, however; it is important to realize that nitroblue tetrazolium can be reduced by many electron donors (including melanin itself), and even the inhibitory effects of
THE PHYSICAL PROPERTIES OF MELANINS
superoxide dismutase may not be used as a specific indicator of primary formation of superoxide anion (Aulair and Voisin, 1985). A model for interfacial photoinduced electron transfer between melanin and oxygen molecules has been proposed by Crippa (2001). It involves adsorption of dioxygen on melanin solid surface and light-induced carriers. The process depends on the surface fractal characteristics and is described by the Marcus theory for electron transfer reactions. Prolonged aerobic photolysis of pheomelanin is accompanied by loss of a major melanin chromophore (Chedekel et al., 1977). Although a role for superoxide anion, hydrogen peroxide, and hydroxyl radicals in the photodestruction of pheomelanin was postulated (Chedekel et al., 1978), the mechanism of the observed phenomena has not been established. Although pheomelanin was viewed as being a particularly photolabile type of melanin (Chedekel et al., 1977), a comparative study of photobleaching of eumelanin and pheomelanin suggested that eumelanin was actually more susceptible to aerobic photodegradation (Wolfram and Albrecht, 1987). Bleaching of DOPA melanin induced by its aerobic illumination from near ultraviolet and visible radiation has been studied as a function of pH, concentration of exogenous hydrogen peroxide, oxidation state of melanin, and the presence of copper ions (Korytowski and Sarna, 1990). Based on detection of characteristic products of salicylate hydroxylation (2,3- and 2,5-dihydroxybenzoic acids), the formation of hydroxyl radicals in photolyzed melanin samples has been demonstrated. It was suggested that redox active metal ions that are bound to melanin might be involved in the generation of hydroxyl radicals via Fenton-type processes (Korytowski et al., 1987). Indeed, using direct EPR measurements of copper(II) complexes with melanin, it has been shown that copper(I) bound to melanin was rapidly oxidized by either H2O2 or oxygen (Korytowski and Sarna, 1990). It has been concluded that photobleaching of melanin involves two distinct stages: reversible oxidation of the hydroquinone moieties of melanin followed by irreversible reactions of the monomers that lead to degradation of the melanin polymer. An interesting melanin-mediated photo-oxidation of ascorbate has been reported (Glickman and Lam, 1992; Glickman et al., 1993). It was demonstrated that melanin granules that were isolated from retinal pigment epithelium of bovine eyes induced nonenzymatic oxidation of ascorbate when illuminated with a continuous-wave argon-ion laser. The photooxidation of ascorbate was explained in terms of two processes — one that might be mediated by melanin-induced oxygen radicals and another that was due to interaction of ascorbate with the free radicals of melanin. However, in a more recent study, it has been demonstrated that melanin acts predominantly as an electron transfer agent in the photooxidation of ascorbate, while the ultimate electron acceptor is molecular oxygen (Rózanowska et al., 1997). The results of the latter study also suggested that the primary electron transfer between ascorbate and melanin involved photoinduced melanin radicals.
Antioxidant Properties The discovery of free radical properties of melanin led to a hypothesis that melanin might act as a free radical trap, thereby protecting cells from the effects of free radicals formed in biological oxidation–reduction reactions (Mason et al., 1960). A growing body of experimental evidence suggests that the cellular melanin may be an important antioxidant system (Bustamante et al., 1993; Ostrovsky et al., 1987; PorebskaBudny et al., 1992; Reszka et al., 1998; Scalia et al., 1990; Slawinska et al., 1983; Stepien et al., 2000; also reviewed by Sarna, 1992). As the term “antioxidant” is not always used very rigorously in biomedical literature, it may be useful to define it. Following the definition given by Halliwell and Gutteridge (1989), we will consider an antioxidant as “any substance that, when present at low concentration compared to those of an oxidizable substrate, significantly delays or inhibits oxidation of that substrate.” Thus, melanin may act as an antioxidant by: 1 scavenging initiating radicals; 2 deactivating electronically excited oxidizing species such as singlet molecular oxygen (1O2); 3 sequestering redox active metal ions such as iron and copper (metal ions that are bound to melanin may be less efficient in generating diffusible damaging free radicals and/or decomposing lipid peroxides to form propagating radicals); 4 chain breaking, i.e. scavenging intermediate radicals such as peroxyl and alkoxyl. There is a fairly extensive but amorphous literature on potential antioxidant properties of melanin. The following is aimed at being an indicative, rather than a comprehensive, review of this subject. The antioxidant properties of melanin have been examined by studies of the abilities of melanin to quench electronically excited dye molecules, scavenge reactive free radicals, and sequester redox active metal ions. Using laser flash photolysis and EPR oximetry as well as conventional absorption and fluorescence spectroscopy, it has been shown that binding of two cationic dye molecules, tetra(N-methyl-4-pyrridyl)porphyrin and tetra(4-N,N,N,Ntrimethyl-anilinium)porphyrin, was accompanied by a broadening of their absorption band, fluorescence quenching, triplet state quenching, and reduction in the dye-photosensitized oxygen consumption (Bielec et al., 1986). For anionic dyes such as tetra(4-sulfonatophenyl)porphyrin, there was no binding and, consequently, melanin had little or no effect on the absorption, fluorescence, and triplet states of the dyes and on their photosensitizing abilities (Fig. 16.10). Thus, complexing of positively charged dye molecules via ionic interaction can lead to a very efficient deactivation of their electronically excited states and, as a result, to complete loss of the dyephotosensitizing activity. If not quenched, the dye molecules, via type I or type II photosensitized oxidation reactions, could oxidize many substrate molecules and generate potentially cytotoxic species such as singlet molecular oxygen, superoxide anion, hydrogen peroxide, and hydroxyl radicals (Bensasson et al., 1993; Nonell, 1994). An interaction of melanin with potentially photosensitizing molecules was later confirmed for 331
CHAPTER 16 A 1.0 emission intensity (relative units)
(a) absorbance
0.8 0.6 0.4 0.2
(c)
emission intensity (relative units)
absorbance
1.0 0.8 0.6 0.4 0.2
300 400 500 600 700 λ(nm)
(b) 8 6 4 2
(d) 8 6 4 2 500
600 700 λ(nm)
800
B 1.0 (–∆[O2]/∆t)/mmol dm–3 min–1
(a)
(b)
0.1
0.01
0.001 10
100
1000 10 melanin/mg cm–3
100
1000
Fig. 16.10. The effects of complexation of a positively charged porphyrin dye by synthetic melanin on the optical properties of the dye (top) and its photosensitizing ability (bottom). (A) Optical absorption (a and c) and fluorescence emission (b and d) spectra of an anionic (a and b) and a cationic (c and d) porphyrin in the presence of cysteinyldopa melanin (broken lines) and its absence (solid lines). (B) Oxygen consumption rates photosensitized by the anionic porphyrin (open symbols) and cationic porphyrin (solid symbols) are plotted as a function of concentration of dopa melanin (a) and cysteinyldopa melanin (b). Reprinted from Bielec et al. (1986), with kind permission from the Royal Society of Chemistry, UK.
ground-state complexes with cationic porphyrins (Ito et al., 1992) and demonstrated for the singlet excited state of 8methoxypsoralen (Losi et al., 1993). The mechanism of the quenching of excited states of melanin bound to tetra(4N,N,N,N-trimethylanilinium)porphyrin was studied recently by femtosecond absorption and picosecond emission spectroscopies (Ye et al., 2003). It has been concluded that such a binding facilitates an ultrafast energy transfer from the excited 332
porphyrin molecule to melanin. The excited energy is then rapidly converted into heat. Because of its speed, the process involves only singlet excited states with no triplet state formation. Melanin can also be an efficient quencher of singlet oxygen (Sarna et al., 1985b; Sealy et al., 1984). The rate constants of the interaction of 1O2 (generated by a Rose Bengal photosensitized reaction) with synthetic DOPA and cysteinyldopa melanins and natural melanins have been determined under steady-state conditions, using EPR oximetry. The data indicate that chemical quenching of 1O2 by melanin is a rapid reaction, with the corresponding rate constants of 1.3 ¥ 105 mg/ml/s and 6 ¥ 105 mg/ml/s for DOPA melanin and cysteinyldopa melanin respectively. Natural melanins interacted significantly slower with 1O2. This is not unexpected, considering the particulate form of such melanins; as singlet oxygen was generated uniformly in the sample volume, the aggregated melanin had little chance to interact with most molecules of 1O2 before they deactivated via competing processes. Similar values for the apparent rate constants for the interaction of synthetic melanins with 1O2 have been obtained most recently by direct time-resolved detection of the singlet oxygen after pulse laserinduced generation of 1O2 (Wielgus et al., unpublished). Superoxide anion is another “reactive oxygen species” that may be involved, directly or indirectly, in damage of key cellular constituents (Fridovich, 1983). Superoxide is a product of one-electron reduction of molecular oxygen and can be generated by the interaction of oxygen with suitable electron donors with one-electron reduction potential that is more negative than –0.16 V (Koppenol and Butler, 1985). One of the first reports indicating that melanin can scavenge superoxide anion appeared some 20 years ago (Goodchild et al., 1984). Unfortunately, the experimental details of this study were very sparse. The superoxide scavenging ability of eumelanins was subsequently demonstrated by direct EPR measurements of the characteristic EPR signal of frozen alkaline solutions of H2O2 and NaIO4 in the absence and presence of increasing amounts of melanin (Geremia et al., 1984). This method has been refined by the addition of acetone to the reacting mixture (Sichel et al., 1991). It must be stressed, however, that the free radical scavenging properties of melanin were tested by this method under extreme conditions (pH 13), which are not directly relevant in biological systems. Using stopped-flow EPR measurements of the induced melanin free radical signal and dimethyl sulfoxide (DMSO)/KO2 as the source of superoxide anion, its interaction with DOPA melanin and melanin from bovine eye choroid has been observed, and the rate constant of the interaction has been calculated (Korytowski et al., 1986). The superoxide-induced melanin radicals decayed with an effective bimolecular rate constant of 0.8–5.1 ¥ 104 mg/ml/s. The apparent rate of the interaction of melanin with superoxide has been determined from the observed inhibition of the DMPO–O2H radical adduct formed in the superoxidegenerating system in the presence of superoxide dismutase (SOD) and/or melanin. The rate constant was calculated to be
THE PHYSICAL PROPERTIES OF MELANINS Table 16.1. Apparent second-order rate constants of interaction of melanin with singlet oxygen and free radicals mg/ml/s. Species
Melanin DM
O2(1Dg) O2•¯ • OH
1.3 ¥ 105*
•
0.018 x 104‡ 7.3 ¥ 104‡
OOCH2OH CH2OH CH3 •CHOH
•
3
(2.0†–3.3‡) ¥ 10 107‡
– aq
6.7 ¥ 104‡ 1.7 ¥ 106‡
N3•
104–105‡ 1.2 ¥ 106‡
e CO2•¯
DMT
CDM
BEM
RHM
6.0 ¥ 105*
0.06 ¥ 105*
0.3 ¥ 105*
3
3
10 †
10 † 0.7 ¥ 107‡ 1.3 ¥ 104‡ 1.1 ¥ 106‡ 6
0.4 ¥ 10 ‡
0.8 ¥ 106‡ 2.4 ¥ 106‡ 1.5 ¥ 106‡
*Data obtained by EPR oximetry under steady-state illumination in the presence of Rose Bengal as the sensitizer. †Data obtained by direct EPR measurements and EPR spin trapping using DMSO/KO2 as the source of O2. ‡Data obtained by pulse radiolysis. DM, auto-oxidative DOPA melanin; DMT, DOPA melanin synthesized in the presence of tyrosinase; CDM, cysteinyldopa melanin; BEM, melanin from bovine eye choroid; RHM, red hair melanin.
4 ¥ 105/M/s, assuming a molecular weight of 200 for the DOPA melanin monomer unit. A similar value for the rate constant of DOPA melanin interaction with superoxide anion in fully aqueous media has been obtained by independent measurements using the pulse radiolysis method (6.5 ¥ 105/M/s) (Sarna et al., 1986). This powerful method has also been used for the determination of rate constants of the interaction of several different melanins with radicals from water radiolysis (Table 16.1). In addition, it has been shown that superoxide anion interacts with DOPA melanin predominantly by reducing it. Perhaps the most comprehensive study to date of the interaction of DOPA and cysteinyldopa melanins with a variety of oxidizing and reducing radicals has been published by Rózanowska et al. (1999). The authors, using pulse radiolysis to generate specifically selected free radicals, observed either directly or indirectly their interaction with both synthetic melanins. The results showed that the efficiency of the interaction depended, in a complex way, on the redox potential, the electric charge, and the lifetime of the radicals. Repetitive pulsing experiments, in which the free radicals, probing the melanin redox sites, were generated from four different viologens, indicated that the eumelanin model had more reduced than oxidized groups accessible to reaction with the radicals. Oxidation of DOPA melanin by oxidizing radicals appeared to be easier than that of cysteinyldopa melanin. Although with many radicals studied, melanin interacted via a simple one-electron process, the reaction of both melanins with the strongly oxidizing peroxyl radical from carbon tetrachloride involved radical addition. A very efficient scavenging by cysteinyldopa melanin of peroxyl radicals generated from hydroxyethyl and hydroxymethyl radicals with the corresponding rate constant 2.6 ¥ 106/M/s (3.5 ¥ 104/M/s for DOPA melanin) suggests that
melanin in vivo might be able to participate in chain breaking by scavenging intermediate radicals that are involved in the propagation of the peroxidation process (Dunford et al., 1995). Both synthetic melanins were good scavengers of carbon-centered radicals with corresponding rate constants in the range 107–108/M/s. The results of the reviewed investigations are consistent with melanin being an efficient scavenger of strongly oxidizing (and reducing) free radicals and a quencher of singlet molecular oxygen. It is rather unlikely, however, that these properties of melanin play a key role in the antioxidant action of the pigment. Unless “site-specific” formation of reactive free radicals or singlet oxygen is considered, natural melanin is a very inefficient scavenger and quencher of such short-lived species. This is because of the limited lifetime of randomly generated reactive species. These species would interact with many constituents of the pigmented cell before having a chance to diffuse to the proximity of the melanosomes (or pigment granules), where they would then need to penetrate the melanosome (pigment granule) surface and interact with the active groups in the polymer. A special case, in which the free radical scavenging and singlet oxygen quenching abilities of melanin might be of importance, is “site-specific” formation of such species, i.e. if the generation of reactive, short-lived species is predominantly within the melanin granule (melanosome) or in its proximity. This could happen if copper, iron, or manganese ions bound to melanin were redox activated and exposed to oxygen or H2O2, or when photosensitizing molecules, associated with the melanin granule (melanosome), were activated by light in the presence of oxygen. Under such circumstances, melanin would act as a very powerful antioxidant, and very little reactive species would escape the scavenging and quenching action of the melanin. 333
CHAPTER 16
Perspectives The complexities of melanins, due to their physical–chemical properties and inherent heterogeneity, make it difficult, at least at this time, to reach very specific conclusions as to the properties and structure of melanins. In spite of these limitations, some very useful generalizations can be drawn. It is necessary, however, to use a variety of different methods to try to characterize melanins and to recognize that, inevitably, the conclusions reached by the use of a single method need to be confirmed by other, independent methods. The physical state and experimental conditions of melanins can have profound effects on the apparent properties of the melanin. The most important variables of this type include the state of hydration of the molecule (it might be argued suc334
A 100
DMPO-OH (%)
80
60
40
20
0 0.0
0.2
0.4
0.6
0.8
1.0
DA-melanin (mg/ml) B
Rate of DMPO-OH formation (arb. units)
Melanin principally exerts its antioxidant activity by binding redox active metal ions. This has been demonstrated in model studies with DOPA melanin (Pilas et al., 1988) and dopamine melanin (Zareba et al., 1995). The data indicate that iron ions that are bound to melanin are inefficient catalysts for H2O2-dependent generation of free hydroxyl radicals (Fig. 16.11). Even though melanin complexes with ferrous ions are readily oxidized by H2O2 and oxygen, very few OH radicals leak out of the melanin polymer, as shown by EPR spin trapping and HPLC electrochemical detection of salicylate hydroxylation products. Ferric ions, on the other hand, after binding to melanin, become significantly more difficult to reduce by mild reductants. Sequestration of iron ions has been identified as a major mechanism for the inhibitory effects of melanin on lipid peroxidation (Korytowski et al., 1995), and an important role of the degree of iron binding to melanin on the antioxidant/pro-oxidant actions of melanin in protection against chemically and photochemically induced peroxidation of lipids has been considered in an independent study (Krol and Liebler, 1998). Melanin may lose part of its antioxidant activity, or even become pro-oxidant, when its metal ion-binding capacity is exceeded, or if redox active metal ions, present in melanotic systems, are bound to strong chelators (such as EDTA). The basal rate of lipid peroxidation induced by iron, which was enhanced by dopamine melanin (Ben-Shachar et al., 1991), may be explained by the inability of the melanin to complex all ferric ions. Under the conditions employed by the authors of the cited paper, it seems that the dopamine melanin was saturated with iron ions. Similar phenomena are probably involved in a recently reported pro-oxidant action of DOPA melanin in lipid peroxidation (Sotomatsu et al., 1994). An enhanced formation of hydroxyl radicals, observed in model systems containing ferric ions complexed with EDTA, induced by DOPA melanin (Pilas et al., 1988) and dopamine melanin (Zareba et al., 1995), can be explained by the reducing power of melanin, which is able to reduce and thereby activate ferric ions chelated by EDTA and, hence, drive a Fenton reaction (Fig. 16.11).
6
4
2
0 0.0
0.2
0.4
0.6
0.8
1.0
Melanin (mg/ml) Fig. 16.11. The effects of synthetic dopamine melanin on the generation of free hydroxyl radicals by a Fenton system. (A) shows the inhibitory effect of melanin when ferrous ions were complexed by a weak chelator such as citrate (open triangles); on the other hand, melanin exhibited a negligible effect if Fe(II) was chelated by a strong chelator such as DTPA (solid triangles). (B) illustrates the activating role of melanin, when ferric ions were present in the form of complexes with DTPA (solid circles) and with citrate (open circles). The inhibitory effect of melanin is expressed as normalized maximum levels of the DMPO–◊OH spin adduct formed (A) or its rate of formation (B). Reprinted from Zareba et al. (1995), with kind permission of Elsevier Science-NL.
cessfully that studies on dried melanins will usually have limited validity), the pH, and the present and past history of redox conditions for the sample. Another important consideration is the method of purification of the melanin. It is now recognized that treatment of melanin with strong acids or
THE PHYSICAL PROPERTIES OF MELANINS
alkali may irreversibly modify the physicochemical properties of the melanin polymer. Different melanins can have very different properties. The most important variables are the nature of the monomeric units, especially whether these include cysteine-containing subunits. As a consequence, there are at least three quite different types of naturally occurring melanins: eumelanin, pheomelanin, and neuromelanin. The biological effects and/or roles of melanin are significantly affected by interactions with metal ions as a result of the binding of metal ions by the melanin; the interactions affect the properties of both the metal ions and the melanin. Even though melanin can bind a variety of different types of molecules (with different forces being involved), the most common and important is binding of metal ions and organic cations via electrostatic interaction. In vivo it is likely that some melanins, perhaps most, have proteins associated with them and that these affect the properties of the melanin. The proteins probably include those associated with the synthesis of melanin (tyrosine and related enzymes, except for neuromelanin) and proteins derived from the immediate environment, especially from the melanosomes. The redox character of melanin is very complex and is greatly affected by the nature of the melanin and its environment. In order to understand the extent and even the direction of redox reactions that will occur, it is essential to specify the conditions, including the type of melanin, metal ions that are present, proteins associated with the melanin, the redox state of the melanin, pH, and the presence of other redox active species such as molecular oxygen. The ability of melanin to quench electronically excited states of certain photosensitizing dye molecules, scavenge reactive free radicals, and sequester redox active metal ions makes the pigment an efficient antioxidant. The occurrence of lipids with melanins is very incompletely understood. Melanins are unique biopolymers with persistent free radicals and a distinct EPR signal. Many of the EPR characteristics and the associated free radical and redox reactions occurring in the presence of melanins can be explained on the basis of a dynamic redox equilibrium involving quinones, hydroquinones, and semiquinones in the monomeric units of the melanin. The optical properties of melanin are very incompletely understood in spite of the extensive and often productive studies that have been carried out. In particular, we do not yet have a satisfactory and full explanation for the absorption spectrum of melanins and the biological significance of the photochemistry associated with melanins. Irradiation of melanin with ultraviolet or visible light generates transient free radicals and enhances redox reactivity of the electron exchange groups of melanin. Although intriguing, there is at present no fully satisfactory theory or evidence for melanin to have amorphous semiconducting and related properties. Much is known about melanin through the use of sophisticated physical and chemical approaches, and it is likely that continued progress will be made, eventually resulting in a thorough understanding of this important class of biopolymers.
Acknowledgments The work was supported in part by NIH (grant ROIEY 13722) and by the State Committee for Scientific Research.
References Adhyaru, B. B., N. G. Akhmedov, A. R. Katritzky, and C. R. Bowers. Solid-state NMR spectroscopy characterization of sepia melanin, sepia free acid, and human hair melanin in comparison with several model compounds. Magn. Res. Chem. 41:466–474, 2003. Aime, S., and P. R. Crippa. 13C solid-state cross polarization magicangle spinning nuclear magnetic resonance spectra of natural and synthetic melanins. Pigment Cell Res. 1:355–357, 1988. Aime, S., M. Fasano, E. Terreno, and C. J. Groombridge. NMR studies of melanins: Characterization of a soluble melanin free acid from Sepia ink. Pigment Cell Res. 4:216–221, 1991. Anderson, R. R., R. J. Margolis, S. Watenabe, T. Flotte, G. J. Hruza, and J. S. Dover. Selective photothermolysis of cutaneous pigmentation by Q-switched Nd:YAG laser pulses at 1064, 532 and 355 nm. J. Invest. Dermatol. 93:28–32, 1989. Arnaud, R., G. Perbet, A. Deflandre, and G. Lang. Electron spin resonance of melanin from hair. Effects of temperature, pH and light irradiation. Photochem. Photobiol. 38:161–168, 1983. Aulair, C., and E. Voisin. Nitroblue tetrazolium reduction. In: CRC Handbook of Methods for Oxygen Radical Research, R.A. Greenwald (ed.). Boca Raton: CRC Press, 1985, pp. 123–132. Baich, A., and J. Schloz. The formation of glyoxylate from glycine by melanin. Biochem. Biophys. Res. Commun. 159:1161–1164, 1989. Balasubramanian, D., and C. Mohan Raa. Applications of photoacoustics to biology: some specific systems and methods. Can. J. Phys. 64:1132–1135, 1986. Bardani, L., M. G. Bridelli, M. Carbucicchio, and P. R. Crippa. Comparative Mössbauer and infrared analysis of iron-containing melanins. Biochim. Biophys. Acta 713:8–15, 1982. Barden, H., and K. R. Brizzee. The histochemistry of lipofuscin and neuromelanin. In: Advances in the Biosciences, vol. 64, E. A. Totaro, P. Glees, and F. A. Pisanit (eds). Oxford: Pergamon Press, 1987, pp. 339–392. Bazelon, M., and G. M. Fenichel. Studies on neuromelanin I. A melanin system in the human adult brainstem. Neurology 17:512–519, 1967. Bensasson, R. V., E. J. Land, and T. G. Truscott. Excited States and Free Radicals in Biology and Medicine. Contributions from Flash Photolysis and Pulse Radiolysis. Oxford: Oxford University Press, 1993. Ben-Shachar, D., P. Riederer, and M. B. H. Youdim. Iron–melanin interaction and lipid peroxidation: implications for Parkinson’s disease. J. Neurochem. 57:1609–1614, 1991. Bielec, J., B. Pilas, T. Sarna, and T. G. Truscott. Photochemical studies of porphyrin-melanin interactions. J. Chem. Soc. Farad. Trans. 82:1469–1474, 1986. Bilinska, B., K. Stepien, and T. Wilczok. Infrared spectroscopy of melanins and melanoproteins. Studia Biophys. 122:47–55, 1987. Blois, M. S., A. B. Zahlan, and J. E. Maling. Electron spin resonance studies of some natural melanins. Biophys. J. 4:471–490, 1964. Bochenek, K., and E. Gudowska-Nowak. Fundamental building blocks of eumelanins: electronic properties of indolequinone dimers. Chem. Phys. Lett. 373:532–538, 2003a. Bochenek, K., and E. Gudowska-Nowak. Electronic properties of random polymers: modelling optical spectra on melanins. Acta Phys. Pol. B. 34:2775–2791, 2003b. Boulton, M., F. Docchio, P. Dayhaw-Barker, R. Ramponi, and R. Cubeddu. Age-related changes in the morphology, absorption and fluorescence of melanosomes and lipofuscin granules of the retinal pigment epithelium. Vision Res. 39:1291–1303, 1990.
335
CHAPTER 16 Braslavsky, S. E. Photoacoustic and photothermal methods applied to the study of radiationless deactivation processes in biological systems and in substances of biological interest. Photochem. Photobiol. 43:667–675, 1986. Bridelli, M. G., R. Capelletti, and P. R. Prota. Infrared spectroscopy of eye and synthetic melanins at various values of pH and hydration. Physiol. Chem. Phys. 12:233–240, 1980. Bridelli, M. G., P. R. Crippa, and F. Ugozzoli. X-ray diffraction studies on melanins in lyophylized melanosomes. Pigment Cell Res. 3:187–191, 1990. Bruenger, F. W., B. J. Stover, and D. R. Atherton. The incorporation of various metal ions into in vivo- and in vitro-produced melanin. Radiat. Res. 32:1–12, 1967. Bustamante, J., L. Bredeston, G. Malanga, and J. Mordoh. Role of melanin as a scavenger of active oxygen species. Pigment Cell Res. 6:348–353, 1993. Carstam, R., C. Brinck, A. Hindemith-Augustsson, H. Rorsman, and E. Rosengren. The neuromelanin of the human substantia nigra. Biochim. Biophys. Acta 1097:152–160, 1991. Chedekel, M. R., P. W. Post, R. M. Deibel, and M. Kalus. Photodestruction of phaeomelanin. Photochem. Photobiol. 26:651–653, 1977. Chedekel, M. R., S. K. Smith, P. W. Post, A. Pokora, and D. L. Vessell. Photodestruction of pheomelanin: Role of oxygen. Proc. Natl. Acad. Sci. USA 75:5395–5399, 1978. Chedekel, M. R., P. P. Agin, and R. M. Sayre. Photochemistry of pheomelanin: Action spectrum for superoxide production. Photochem. Photobiol. 31:553–555, 1980. Chedekel, M. R., A. B. Ahene, and L. Zeise. Melanin standard method: empirical formula 2. Pigment Cell Res. 5:240–246, 1992a. Chedekel, M. R., B. L. Murr, and L. Zeise. Melanin standard method: empirical formula. Pigment Cell Res. 5:143–147, 1992b. Cheng, J., S. C. Moss, and M. Eisner. X-ray characterization of melanins — II. Pigment Cell Res. 7:263–273, 1994a. Cheng, J., S. C. Moss, M. Eisner, and P. Zschack. X-ray characterization of melanins — I. Pigment Cell Res. 7:255–262, 1994b. Chio, S. S. 1977. X-ray diffraction and ESR studies on amorphous melanin. PhD Dissertation. University of Houston, Houston, TX. Chio, S.-S., J. S. Hyde, and R. C. Sealy. Temperature-dependent paramagnetism in melanin polymers. Arch. Biochem. Biophys. 199:133–139, 1980. Chio, S. S., J. S. Hyde, and R. C. Sealy. Paramagnetism in melanins: pH dependence. Arch. Biochem. Biophys. 215:100–106, 1982. Clancy, C. M. R., and J. D. Simon. Ultrastructural organization of eumelanin from Sepia officinalis measured by atomic force microscopy. Biochemistry 40:13353–13360, 2001. Clancy, C. M. R., J. B. Nofsinger, R. K. Hanks, and J. D. Simon. A hierarchical self-assembly of eumelanin. J. Phys. Chem. B. 104:7871–7873, 2000. Clark, M. B., Jr., J. A. Gardella, Jr., T. M. Schultz, D. G. Patil, and L. S. Salvati, Jr. Solid-state analysis of eumelanin biopolymers by electron spectroscopy for chemical analysis. Anal. Chem. 62:949–956, 1990. Cope, F. W., R. J. Sever, and B. D. Polis. Reversible free radical generation in the melanin granules of the eye by visible light. Arch. Biochem. Biophys. 100:171–177, 1963. Cotzias, G. C., P. S. Papavasiliou, and S. T. Miller. Manganese in melanin. Nature 201:1228–1229, 1964. Crippa, P. R. Oxygen adsorption and photoreduction of fractal melanin particles. Coll. Surf. B. Biointerfaces 20:315–319, 2001. Crippa, P. R., and C. Viappiani. Photoacoustic studies of nonradiative relaxation of excited states in melanin. Eur. Biophys. J. 17:299–305, 1990. Crippa, P. R., V. Cristofoletti, and N. Romeo. A band model for melanin deduced from optical absorption and photoconductivity experiments. Biochim. Biophys. Acta 538:164–170, 1978. Crippa, P. R., F. Martini, and C. Viappiani. Direct evidence of elec-
336
tron–phonon interaction in melanins. J. Photochem. Photobiol. B 11:371–375, 1991. D’Amato, R. J., Z. P. Lipman, and S. H. Snyder. Selectivity of the parkinsonian neurotoxin MPTP: Toxic metabolite MPP+ binds to neuromelanin. Science 231:987–989, 1986. Debing, I., A. P. Ijzerman, and G. Vauquelin. Melanosome binding and oxidation–reduction properties of synthetic L-dopa-melanin as in vitro tests for drug toxicity. Mol. Pharmacol. 33:470–476, 1988. Deibel, R. M. B., and M. R. Chedekel. Biosynthetic and structural studies on pheomelanin, 2. J. Am. Chem. Soc. 106:5884–5888, 1984. Docchio, F., M. E. Boulton, R. Cubeddu, R. Ramponi, and P. DayhawBorker. Age-related changes in the fluorescence of melanin and lipofuscin granules of the retinal pigment epithelium. A time fluorescence study. Photochem. Photobiol. 54:247–253, 1991. Dontsov, A. E., R. D. Glickman, and M. A. Ostrovsky. Retinal pigment epithelium pigment granules stimulate the photo-oxidation of unsaturated fatty acids. Free Rad. Biol. Med. 26:1436–1446, 1999. Duff, G. A., J. E. Roberts, and N. Foster. Analysis of the structure of synthetic and natural melanins by solid-phase NMR. Biochemistry 27:7112–7116, 1988. Dunford, R., E. J. Land, M. Rozanowska, T. Sarna, and T. G. Truscott. Interaction of melanin with carbon- and oxygen-centered radicals from methanol and ethanol. Free Rad. Biol. Med. 19:735–740, 1995. Edge, E., E. J. Land, M. Rozanowska, T. Sarna, and T. G. Truscott. Carotenoid radical–melanin interactions. J. Phys. Chem. B 104:7193–7196, 2000. Eisner, M. The physical and chemical properties of eye melanin and their relationship to photoprotection. In: Fidenza: Occhio e Radiazioni Solari. Technologie Fotoprotethive e Funzione Visire, M. Cordella, and C. Macaluso (eds). Mattioli: Casa Ed., 1992, pp. 60–77. Elleder, M., and Borovansky, J. Autofluorescence of melanins induced by ultraviolet radiation and near ultraviolet light. A histochemical and biochemical study. Histochem. J. 33:273–281, 2001. Enochs, W. S., M. J. Nilges, and H. M. Swartz. Purified human neuromelanin, synthetic dopamine melanin as a potential model pigment, and the normal human substantia nigra: characterization by electron paramagnetic resonance spectroscopy. J. Neurochem. 61:68–79, 1993a. Enochs, W. S., M. J. Nilges, and H. M. Swartz. A standardized test for the identification and characterization of melanins using electron paramagnetic resonance (EPR) spectroscopy. Pigment Cell Res. 6:91–99, 1993b. Enochs, W. S., T. Sarna, L. Zecca, P. A. Riley, and H. M. Swartz. The roles of neuromelanin, binding of metal ions and oxidative cytotoxicity in the pathogenesis of Parkinson’s disease: a hypothesis. J. Neural Transm. Park. Dis. Dement. Sect. 7:83–100, 1994. Feeney-Burns, L. The pigments of the retinal pigment epithelium. Curr. Topics Eye Res. 2:119–178, 1980. Feeney-Burns, L., R. P. Burns, and C.-L. Gao. Age-related macular changes in humans over 90 years old. Am. J. Ophthalmol. 109:265–278, 1990. Felix, C. C., and R. C. Sealy. Electron spin resonance characterization of radicals from 3,6-dihydroxyphenylalanine: semiquinone anions and their metal chelates. J. Am. Chem. Soc. 103:2831–2836, 1981. Felix, C. C., J. S. Hyde, T. Sarna, and R. C. Sealy. Interactions of melanin with metal ions. Electron spin resonance evidence for chelate complexes of metal ions with free radicals. J. Am. Chem. Soc. 100:3922–3926, 1978a. Felix, C. C., J. S. Hyde, T. Sarna, and R. C. Sealy. Melanin photoreaction in aerated media: Electron spin resonance evidence of production of superoxide and hydrogen peroxide. Biochem. Biophys. Res. Commun. 84:335–341, 1978b.
THE PHYSICAL PROPERTIES OF MELANINS Felix, C. C., J. S. Hyde, and R. C. Sealy. Photoreactions of melanin: A new transient species and evidence for triplet state involvement. Biochem. Biophys. Res. Commun. 88:456–461, 1979. Figge, F. H. Melanin: a natural reversible oxidation–reduction system and indicator. Proc. Soc. Exp. Biol. Med. 41:127–129, 1939. Forrest, S. E., and J. D. Simon, Wavelength-dependent photoacoustic calorimetry study of melanin. Photochem. Photobiol. 68:296–298, 1998. Forrest, S. E., W. C. Lam, D. P. Millar, J. B. Nofsinger, and J. D. Simon. A model for the activated energy transfer within eumelanin aggregates. J. Phys. Chem. B. 104:811–814, 2000. Fork, D. C., and S. K. Herbert. The application of photoacoustic techniques to studies of photosynthesis. Photochem. Photobiol. 57:207–220, 1993. Fridovich, I. Superoxide radical: an endogenous toxicant. Annu. Rev. Pharmacol. Toxicol. 23:239–257, 1983. Froncisz, W., T. Sarna, and J. S. Hyde. Cu2+ probe of metal-ion binding sites in melanin using electron paramagnetic resonance spectroscopy. Arch. Biochem. Biophys. 202:289–303, 1980. Galazka-Friedman, J., E. R. Bauminger, A. Friedman, M. Barcikowska, D. Hechel, and I. Nowik. Iron in parkinsonian and control substantia nigra — a Mössbauer spectroscopy study. Mov. Disord. 11:8–16, 1996. Gallas, J. M., and M. Eisner. Fluorescence of melanin-dependence upon excitation wavelength and concentration. Photochem. Photobiol. 45:595–600, 1987. Gallas, J. M., R. G. Allen, E. T. Schmeisser, M. Eisner, and P. Talley. Thermal properties of melanin determined from photoacoustic techniques. USAFSAM-TR-87-37:1–11, 1988. Gallas, J. M., K. C. Littrell, S. Seifert, G. W. Zajac, and P. Thiyagarajan. Solution structure of copper ion-induced molecular aggregates of tyrosine melanin. Biophys. J. 77:1135–1142, 1999. Gallas, J. M., G. W. Zajac, T. Sarna, and P. L. Stotter. Structural differences in unbleached and mildly-bleached synthetic tyrosinederived melanins identified by scanning probe microscopies. Pigment Cell. Res. 13:99–108, 2000. Galvâo, D. S., and M. J. Caldas. Polymerization of 5,6-indolequinone: a view into the band structure of melanins. J. Chem. Phys. 88:4088–4091, 1988. Galvao, D. S., and M. J. Caldas. Theoretical investigation of model polymers for eumelanins. I. Finite and infinite polymers. J. Chem. Phys. 92:2630–2636, 1990a. Galvao, D. S., and M. J. Caldas. Theoretical investigation of model polymers for eumelanins. II. Isolated defects. J. Chem. Phys. 93:2848–2853, 1990b. Gan, E. V., H. F. Haberman, and I. A. Menon. Oxidation of NADH by melanin and melanoproteins. Biochim. Biophys. Acta 370:62–69, 1974. Gan, E. V., H. F. Haberman, and I. A. Menon. Electron transfer properties of melanin. Arch. Biochem. Biophys. 173:666–672, 1976. Garcia-Borrón, J. C., M. D. Saura, F. Solano, J. L. Iborra, and J. A. Lozano. FT-IR spectroscopy of natural melanins isolated from Harding–Passey mouse melanoma. Physiol. Chem. Phys. Med. NMR 17:211–218, 1985. Geremia, E. C., R. Corsaro, R. Bonomo, R. Giardinelli, P. Pappalardo, A. Venella, and G. Sichel. Eumelanins as free radical trap and superoxide dismutase activity in Amphibia. Comp. Biochem. Physiol. A Physiol. 79:67–69, 1984. Gerlach, M., A. X. Trautwein, L. Zecca, M. B. H. Youdim, and P. Riederer. Mossbauer spectroscopic studies of purified human neuromelanin isolated from the substantia nigra. J. Neurochem. 65:923–926, 1995. Glickman, R. D., and K.-W. Lam. Oxidation of ascorbic acid as an indicator of photooxidative stress in the eye. Photochem. Photobiol. 55:191–196, 1992. Glickman, R. D., R. Sowell, and K.-W. Lam. Kinetic properties of
light-dependent ascorbic acid oxidation by melanin. Free Rad. Biol. Med. 15:453–457, 1993. Goodchild, N., L. Kwock, and P.-S. Lin. Melanin: A possible cellular superoxide scavenger. In: Oxygen and Oxy-Radicals in Chemistry and Biology, M. A. J. Rodgers, and E. L. Powers (eds). New York: Academic Press, 1984, pp. 645–648. Grady, F. J., and D. C. Borg. Electron paramagnetic resonance studies on melanins. I. The effect of pH on spectra at Q band. J. Am. Chem. Soc. 90:2949–2952, 1968. Graham, D. G. Oxidative pathways for catecholamines in the genesis of neuromelanin and cytotoxic quinones. Mol. Pharmacol. 14:633–643, 1978. Hach, P., J. Duchon, and J. Borovansky. Ultrastructure and biochemical characteristics of isolated melanosomes. Folia Morphol. 25:407–410, 1977. Halliwell, B., and J. H. C. Gutteridge. Free Radicals in Biology and Medicine. Oxford: Clarendon Press, 1989. Hearing, V. J. Unraveling the melanocyte. Am. J. Hum. Genet. 52:1–7, 1993. Hearing, V. J., and K. Tsukamoto. Enzymatic control of pigmentation in mammals. FASEB J. 5:2902–2909, 1991. Hearing, V. J., P. Phillips, and M. A. Lutzner. The fine structure of melanogenesis in coat color mutants of the mouse. J. Ultrastruct. Res. 43:88–106, 1973. Herve, M., J. Hirschinger, P. Granger, P. Gilard, A. Deflandre, and N. Goetz. A 13C solid-state NMR study of the structure and autooxidation process of natural and synthetic melanins. Biochim. Biophys. Acta 1204:19–27, 1994. Hintz, P., and B. Kalyanaraman. Metal ion-induced activation of molecular oxygen in pigmented polymers. Biochim. Biophys. Acta 883:41–45, 1986. Huang, J. S., J. S. Sung, M. Eisner, S. C. Moss, and J. M. Gallas. The fractal structure and the dynamics of aggregation of synthetic melanin in low pH aqueous solutions. J. Chem. Phys. 90:25–29, 1989. Hyde, J. S., and W. K. Subczynski. Spin-label oximetry. In: Spin Labelling: Theory and Applications, L. J. Berliner, and J. Reuben (eds). New York: Plenum Press, 1989, pp. 399–425. Il’ichev, Y. V., and J. D. Simon. Building blocks of eumelanin: relative stability and excitation energies of tautomers of 5,6-dihydroxyindole and 5,6-indolequinone. J. Phys. Chem. B 107:7162–7171, 2003. Ito, S. Reexamination of the structure of eumelanin. Biochim. Biophys. Acta 883:155–161, 1986. Ito, S. Advances in chemical analysis of melanins. In: The Pigmentary System, Physiology and Pathophysiology, Chapter 31, J. J. Nordlund, R. E. Boissy, V. J. Hearing, R. A. King, and J.-P. Ortonne (eds). New York: Oxford University Press, 1998, pp. 439–450. Ito, S., and K. Fujita. Microanalysis of eumelanin and pheomelanin in hair and melanomas by chemical degradation and liquid chromatography. Anal. Biochem. 144:527–536, 1985. Ito, S., and K. Jimbow. Quantitative analysis of eumelanin and pheomelanin in hair and melanomas. J. Invest. Dermatol. 80:268–272, 1983. Ito, S., and K. Wakamatsu. Melanin chemistry and melanin precursors in melanoma. J. Invest. Dermatol. 92:261S–265S, 1989. Ito, S., and K. Wakamatsu. Quantitative analysis of eumelanin and pheomelanin in humans, mice, and other animals: a comparative review. Pigment Cell Res. 16:523–531, 2003. Ito, A. S., E. C. Azzellini, S. C. Silva, O. Serra, and A. G. Szabo. Optical absorption and fluorescence spectroscopy studies of ground state melanin–cationic porphyrin complexes. Biophys. Chem. 45:79–89, 1992. Jacques, S. L., and D. McAuliffe. The melanosome: threshold temperature for explosive vaporization and internal absorption coefficient during pulsed laser irradiation. Photochem. Photobiol. 53:769–775, 1991.
337
CHAPTER 16 Jastrzebska, M. M., K. Stepien, J. Wilczok, M. Porebska-Budny, and T. Wilczok. Semiconductor properties of melanins prepared from catecholamines. Gen. Physiol. Biophys. 9:373–383, 1990. Jastrzebska, M. M., H. Isotalo, J. Paloheimo, and H. Stubb. Electrical conductivity of synthetic dopa-melanin polymer for different hydration states and temperatures. J. Biometeorol. Sci. Polym. 7:577–586, 1995. Jastrzebska, M., A. Kocot, and L. Tajber. Photoconductivity of synthetic dopa-melanin polymer. J. Photochem. Photobiol. B Biol. 66:201–206, 2002a. Jastrzebska, M., A. Kocot, J. K. Vij, J. Zalewska-Rejdak, and T. Witecki. Dielectric studies on charge hopping in melanin polymer. J. Mol. Struct. 606:205–210, 2002b. Jimbow, K., O. Oikawa, S. Sugiyama, and T. Takeuchi. Comparison of eumelanogenesis in retinal and follicular melanocytes. J. Invest. Dermatol. 73:278–284, 1979. Jimbow, K., Y. Miyake, K. Homma, K. Yasuda, Y. Izumi, A. Tsutsumi, and S. Ito. Characterization of melanogenesis and morphogenesis of melanosomes by physicochemical properties of melanin and melanosomes in malignant melanoma. Cancer Res. 44:1128–1134, 1984. Kalyanaraman, B., C. C. Felix, and R. C. Sealy. Photoionization and photohomolysis of melanins: An electron spin resonance–spin trapping study. J. Am. Chem. Soc. 106:7327–7330, 1984. Katritzky, A. R., N. G. Akhmedov, S. N. Denisenko, and O. V. Denisko. 1H NMR spectroscopic characterization of solutions of Sepia melanin, Sepia melanin free acid and human hair melanin. Pigment Cell Res. 15:93–97, 2002. Kochanska-Dziurowicz, A. A., T. Wilczok, and A. Bogacz. Interaction of Fe3+ ions with synthetic and natural melanins. A Mössbauer spectroscopy study. Studia Biophys. 109:87–93, 1985. Kollias, N., and A. Baqer. Spectroscopic characteristics of human melanin in vivo. J. Invest. Dermatol. 85:38–42, 1985. Kollias, N., and A. H. Baqer. Absorption mechanisms of human melanin in the visible, 400–720 nm. J. Invest. Dermatol. 89:384–388, 1987. Kollias, N., R. M. Sayre, L. Zeise, and M. R. Chedekel. Photoprotection by melanin. J. Photochem. Photobiol. B 9:135–160, 1991. Kono, R. Structural characterization of sepia melanosome and sepia melanin by ultrasonic measurement. In: Structure and Function of Melanin, vol. 1, K. Jimbow (ed.). Sapporo: Fuji-shoin Co., 1984, pp. 14–17. Kono, R., and K. Jimbow. The structure of B16 and Harding–Passey melanosomes characterized by ultrasonic measurement. In: Structure and Function of Melanin, vol. 2, K. Jimbow (ed.). Sapporo: Fuji-shoin Co., 1985, pp. 11–18. Kono, R., and H. Yoshizaki. Ultrasonic study of aging in hydrated diethylamine melanin. In: Structure and Function of Melanin, vol. 4, K. Jimbow (ed.). Sapporo: Fuji-Shoin Co., 1987, pp. 24–31. Koppenol, W. H., and J. Butler. Energetics of interconversion reactions of oxyradicals. Adv. Free Rad. Biol. Med. 1:91–131, 1985. Korytowski, W., and T. Sarna. Bleaching of melanin pigments. Role of copper ions and hydrogen peroxide in autooxidation and photooxidation of synthetic DOPA-melanin. J. Biol. Chem. 265:12410–12416, 1990. Korytowski, W., P. Hintz, R. C. Sealy, and B. Kalyanaraman. Mechanism of dismutation of superoxide produced during autoxidation of melanin pigments. Biochem. Biophys. Res. Commun. 131:659–665, 1985. Korytowski, W., B. Kalyanaraman, I. A. Menon, T. Sarna, and R. C. Sealy. Reaction of superoxide anions with melanins: electron spin resonance and spin trapping studies. Biochim. Biophys. Acta 882:145–153, 1986. Korytowski, W., B. Pilas, T. Sarna, and B. Kalyanaraman. Photoinduced generation of hydrogen peroxide and hydroxyl radicals in melanins. Photochem. Photobiol. 45:185–190, 1987. Korytowski, W., T. Sarna, and M. Zareba. Antioxidant action of neu-
338
romelanin: The mechanism of inhibitory effect on lipid peroxidation. Arch. Biochem. Biophys. 319:142–148, 1995. Korzhova, L. P., E. V. Frolova, and I. Romakow. A spectrofluorometric method of recording oxidation products of eumelanin destruction. Vopr. Med. Khim. 35:139–143, 1989. Kozikowski, S. D., L. J. Wolfram, and R. R. Alfano. Fluorescence spectroscopy of eumelanins. J. Quantum Electronics QE20:1379–1382, 1984. Krol, E. S., and Liebler, D. C. Photoprotective actions of natural and synthetic melanins. Chem. Res. Toxicol. 11:1434–1440, 1998. Kurtz, S. K., S. D. Kozikowski, and L. J. Wolfram. Non-linear optical and electro-optical properties of biopolymers. In: Electro-Optic and Photorefractive Materials, P. Gunter (ed.). New York: SpringerVerlag, 1987, pp. 110–130. Larsson, B. S. The toxicology and pharmacology of melanins. In: The Pigmentary System, Physiology and Pathophysiology, Chapter 27, J. J. Nordlund, R. E. Boissy, V. J. Hearing, R. A. King, and J.-P. Ortonne (eds). New York: Oxford University Press, 1998, pp. 373–389. Larsson, B., and H. Tjälve. Studies on the melanin affinity of metal ions. Acta Physiol. Scand. 104:479–484, 1978. Larsson, B., and H. Tjalve. Studies on the mechanism of drug-binding to melanin. Biochem. Pharmacol. 28:1181–1187, 1979. Larsson, B., A. Oskarsson, and H. Tjälve. Binding of paraquat and diquat on melanin. Exp. Eye Res. 25:353–359, 1977. Leigh, J. S., Jr. ESR rigid-lattice line shape in a system with two interacting spins. J. Chem. Phys. 52:2608–2612, 1970. Lillie, R. D., and H. M. Fullmer. Endogenous pigments. The melanins. In: Histopathologic Technic and Practical Histochemistry, R. D. Lillie, and H. M. Fullmer (eds). New York: McGraw-Hill Book Co., 1976, pp. 522–527. Lindquist, N. G. Accumulation of drugs on melanin. Acta Radiol. Diagn. 325:1–92, 1973. Lindquist, N. G., and S. Ullberg. Autoradiography of 35S-chlorpromazine: accumulation and retention in melanin-bearing tissues. In: Phenothiazines and Structurally Related Drugs, S. Forrest, C. J. Carr, and E. Usdin (eds). New York: Raven Press, 1974, pp. 413–423. Lindquist, N. G., B. S. Larsson, and A. Lydén-Sokolowski. Autoradiography of [14C]paraquat or [14C]diquat in frogs and mice: Accumulation in neuromelanin. Neurosci. Lett. 93:1–6, 1988. Link, E. M., I. Brown, R. N. Carpenter, and J. S. Mitchell. Uptake and therapeutic effectiveness of 125I and 211At-methylene blue for pigmented melanoma in an animal model system. Cancer Res. 49:4332–4337, 1989. Littrell, K. C., J. M. Gallas, G. W. Zajac, and P. Thiyagarajan. Structural studies of bleached melanin by synchrotron small-angle X-ray scattering. Photochem. Photobiol. 77:115–120, 2003. Liu, Y., and Simon, J. D. Isolation and biophysical studies of natural eumelanins: applications of imaging technologies and ultrafast spectroscopy. Pigment Cell Res. 16:606–618, 2003a. Liu, Y., and Simon, J. D. The effect of preparation procedures on the morphology of melanin from the ink sac of Sepia officinalis. Pigment Cell Res. 16:606–618, 2003b. Liu, Y., V. R. Kempf, J. B. Nofsinger, E. E. Weinert, M. Rudnicki, K. Wakamatsu, S. Ito, and J. D. Simon. Comparison of the structural and physical properties of human hair eumelanin following enzymatic or acid/base extraction. Pigment Cell Res. 16:355–365, 2003. Liu, Y., L. Hong, V. R. Kempf, K. Wakamatsu, S. Ito, and J. D. Simon. Ion-exchange and adsorption of Fe(III) by Sepia melanin. Pigment Cell Res. 17:262–269, 2004. Longnet-Higgins, H. C. On the origin of free radical property of melanin. Arch. Biochem. Biophys. 86:231–232, 1960. Losi, A., R. Bedotti, L. Brancaleon, and C. Viappiani. Porphyrin–melanins interaction: effect on fluorescence. J. Photochem. Photobiol. B 81:69–76, 1993.
THE PHYSICAL PROPERTIES OF MELANINS Lukiewicz, S., K. Reszka, and Z. Matuszak. Simultaneous electrochemical-electron spin resonance (SEESR) studies on natural and synthetic melanins. Bioelectrochem. Bioenerg. 7:153–165, 1980. Lydén, A., U. Bondesson, B. S. Larsson, and N. G. Lindquist. Melanin affinity of 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine, an inducer of chronic parkinsonism in humans. Acta Pharmacol. Toxicol. 53:429–432, 1983. Lydén, A., B. S. Larsson, and N. G. Lindquist. Melanin affinity of manganese. Acta Pharmacol. Toxicol. 55:133–138, 1984. Mann, D. M. A., and P. O. Yates. Lipoprotein pigments — their relationship to ageing in the human nervous system. II. The melanin content of pigmented nerve cells. Brain 97:489–498, 1974. Marsden, C. D. Brain melanin. In: Pigments in Pathology, M. Wollman (ed.). New York: Academic Press, 1969, pp. 395–420. Mason, H. S., D. J. E. Ingram, and B. Allen. The free radical property of melanin. Arch. Biochem. Biophys. 86:225–230, 1960. McGinness, J. E. Mobility gaps: a mechanism for band gaps in melanins. Science 177:896–997, 1972. McGinness, J. E., and P. Proctor. The importance of the fact that melanin is black. J. Theor. Biol. 39:677–678, 1973. McGinness, J. E., P. Corry, and P. Proctor. Amorphous semiconductor switching in melanins. Science 183:853–854, 1974. Meredith, P., and J. Riesz. Radiative relaxation quantum yields for synthetic eumelanin. Photochem. Photobiol. 79:211–216, 2004. Miyake, Y., and Y. Izumi. Chemico-physical properties of melanin. In: Structure and Funtion of Melanin, vol. 1, K. Jimbow (ed.). Sapporo: Fuji-shoin Co., 1984, pp. 3–13. Miyake, Y., Y. Izumi, K. Yasuda, and K. Jimbow. Chemico-physical properties of melanin (II). In: Structure and Function of Melanin, vol. 2, K. Jimbow (ed.). Sapporo: Fuji-shoin Co., 1985, pp. 3–10. Miyake, Y., Y. Izumi, A. Tsutsumi, and K. Jimbow. Chemico-physical properties of melanin (IV). In: Structure and Function of Melanin, vol. 4, K. Jimbow (ed.). Sapporo: Fuji-shoin Co., 1987, pp. 32–43. Monks, T. J., R. P. Hanzlik, G. M. Cohen, D. Ross, and D. G. Graham. Contemporary issues in toxicology. Quinone chemistry and toxicity. Toxicol. Appl. Pharmacol. 112:2–16, 1992. Moore, T. A. Photoacoustic spectroscopy and related techniques to biological materials. Photochem. Photobiol. Rev. 7:187–221, 1983. Nicolaus, R. A. Melanins. Paris: Hermann Press, 1968. Nilges, M. J. Advances in physical analysis of melanins. In: The Pigmentary System, Physiology and Pathophysiology, Chapter 32, J.J. Nordlund, R. E. Boissy, V. J. Hearing, R. A. King, and J.-P. Ortonne (eds). New York: Oxford University Press, 1998, pp. 451–459. Nofsinger, J. B., and Simon, J. D. Relaxation of sepia eumelanin is affected by aggregation. Photochem. Photobiol. 74:31–37, 2001. Nofsinger, J. B., S. E. Forest, and J. D. Simon. Explanation for the disparity among absorption and action spectra of eumelanin. J. Phys. Chem. B. 103:11428–11432, 1999. Nofsinger, J. B., S. E. Forest, L. M. Eibest, K. A. Gold, and J. D. Simon. Probing the building blocks of eumelanins using scanning electron microscopy. Pigment Cell Res. 13:179–184, 2000. Nofsinger, J. B., T. Ye, and J. D. Simon. Ultrafast non-radiative relaxation dynamics of eumelanin. J. Phys. Chem. Biol. 105:2864–2866, 2001. Nofsinger, J. B., Y. Liu, and J. D. Simon. Aggregation of eumelanin mitigates photogeneration of reactive oxygen species. Free Rad. Biol. Med. 32:720–730, 2002. Nonell, S. Reactive oxygen species. In: Photobiology in Medicine. NATO ASI Series A: Life Sciences, G. Jori, R. H. Pottier, M. A. J. Rodgers, and T. G. Truscott (eds). New York: Plenum Press, 1994, pp. 29–50. Novellino, L., A. Napolitano, and G. Prota. Isolation and characterization of mammalian eumelanins from hair and irides. Biochim. Biophys. Acta 1475:295–306, 2000. Odh, G., R. Carstam, J. Paulson, A. Wittbjer, E. Rosengren, and H. Rorsman. Neuromelanin of the human substantia nigra: A mixed-type melanin. J. Neurochem. 62:2030–2036, 1994.
Okazaki, M., K. Kuwata, Y. Miki, S. Shiga, and T. Shiga. Electron spin relaxation of synthetic melanin and melanin-containing tissues studied by electron spin echo and electron spin resonance. Arch. Biochem. Biophys. 242:197–205, 1985. Osak, W., K. Tkacz, J. Slawinski, and H. Czternastek. Dielectric relaxation in synthetic melanin. Biopolymers 28:1875–1883, 1989a. Osak, W., K. Tkacz, H. Czeternastek, and J. Slawinski. I-V characteristics and conductivity of melanin. Biopolymers 28:1885–1890, 1989b. Ostrovsky, M. A., and L. P. Kayushin. ESR study of retina under lighting. Dokl. Akad. Nauk. SSSR 151:986–988, 1963. Ostrovsky, M. A., N. L. Sakina, and A. E. Dontsov. An antioxidant role of ocular screening pigments. Vision Res. 27:893–899, 1987. Ozeki, H., S. Ito, K. Wakamatsu, and T. Hirobe. Chemical characterization of hair melanins in various coat-color mutants of mice. J. Invest. Dermatol. 105:361–366, 1995. Pasenkiewicz-Gierula, M., and R. C. Sealy. Analysis of the ESR spectrum of synthetic dopa melanin. Biochim. Biophys. Acta 884:510–516, 1986. Peter, M. G., and H. Förster. On the structure of eumelanins: Identification of constitutional patterns by solid-state NMR spectroscopy. Angew. Chem. Int. Ed. Engl. 28:741–743, 1989. Pilas, B., and T. Sarna. Quantative determination of melanin in pigmented cells by electron spin resonance spectroscopy. In: Proceedings of the 12th International Pigment Cell Conference, Giessen, 1983, J. Bagnara, S. N. Klaus, E. Paul, and M. Schartl (eds). Tokyo: University of Tokyo Press, 1985, pp. 97–103. Pilas, B., T. Sarna, B. Kalyanaraman, and H. M. Swartz. The effect of melanin on iron associated decomposition of hydrogen peroxide. Free Rad. Biol. Med. 4:285–293, 1988. Porebska-Budny, M., N. L. Sakina, K. B. Stepien, A. E. Dontsov, and T. Wilczok. Antioxidative activity of synthetic melanins. Cardiolipin liposome model. Biochim. Biophys. Acta 1116:11–16, 1992. Potts, A. M., and P. C. Au. The photoconductivity of melanin. Agressologie 9:225–229, 1968. Potts, A. M., and P. C. Au. The affinity of melanin for inorganic ions. Exp. Eye Res. 22:487–491, 1976. Powell, B. J., T. Baruah, N. Bernstein, K. Brake, R. H. McKenzie, P. Meredith, and M. R. Pederson. A first-principles density-functional calculation of the electronic and vibrational structure of the key melanin monomers. J. Chem. Phys. 120:8608–8615, 2004. Prota, G. Progress in the chemistry of melanins and related metabolites. Med. Res. Rev. 8:525–556, 1988. Prota, G. Melanins and Melanogenesis. San Diego: Academic Press, 1992. Prota, G., M. D’Ischia, and A. Napolitano. The chemistry of melanins and related metabolites. In: The Pigmentary System, Physiology and Pathophysiology, Chapter 24, J. J. Nordlund, R. E. Boissy, V. J. Hearing, R. A. King, and J.-P. Ortonne (eds). New York: Oxford University Press, 1998a, pp. 307–332. Prota, G., D.-N. Hu, M. R. Vincensi, S. A. McCormick, and A. Napolitano. Characterization of melanins in human irides and cultured uveal melanocytes from eyes of different colors. Exp. Eye Res. 67:293–299, 1998b. Pullman, A., and B. Pullman. The band structure of melanins. Biochim. Biophys. Acta 54:384–385, 1961. Pullman, A., and B. Pullman. Quantum Biochemistry. New York: Interscience Publications, 1963. Reszka, K. J., and C. F. Chignell. EPR and spin-trapping investigation of free radicals from the reaction of 4-methoxybenzendiazonium tetrafluroborate with melanin and melanin precursors. J. Am. Chem. Soc. 115:7752–7760, 1993. Reszka, K. J., Z. Matuszak, and C. F. Chignell. Lactoperoxidasecatalyzed oxidation of melanin by reactive nitrogen species derived from nitrite (NO2–): an EPR study. Free Rad. Biol. Med. 25:208–216, 1998.
339
CHAPTER 16 Rorsman, H., G. Agrup, C. Hansson, A.-M. Rosengren, and E. Rosengren. Detection of phaeomelanins. In: Pigment Cell: Biologic Basis of Pigmentation, vol. 4, S. Klaus (ed.). Basel: Karger, 1979, pp. 244–252. Rosencwaig, A., and A. Gersho. Theory of photoacoustic effect with solids. J. Appl. Phys. 47:64–69, 1976. Rózanowska, M., J. Jarvis-Evans, W. Korytowski, M. E. Boulton, J. M. Burke, and T. Sarna. Blue light-induced reactivity of retinal age pigment. In vitro generation of oxygen-reactive species. J. Biol. Chem. 270:18825–18830, 1995. Rózanowska, M., A. Bober, J. M. Burke, and T. Sarna. The role of retinal pigment epithelium melanin in photoinduced oxidation of ascorbate. Photochem. Photobiol. 65:472–479, 1997. Rózanowska, M., T. Sarna, E. J. Land, and T. G. Truscott. Free radical scavenging properties of melanin interaction of eu- and pheomelanin models with reducing and oxidising radicals. Free Rad. Biol. Med. 26:518–525, 1999. Rózanowska, M., W. Korytowski, B. Rózanowski, C. Skumatz, M. E. Boulton, J. M. Burke, and T. Sarna. Photoreactivity of aged human RPE melanosomes: A comparison with lipofuscin. Invest. Ophthalmol. Vis. Sci. 43:2088–2096, 2002. Sarna, T. Properties and function of the ocular melanin — a photobiophysical view. J. Photochem. Photobiol. B 12:215–258, 1992. Sarna, T., and S. Lukiewicz. Electron spin resonance (ESR) studies on living cells. II. Normal development of amphibians. Folia Histochem. Cytochem. 9:193–202, 1971. Sarna, T., and M. Rozanowska. Phototoxicity of the eye. In: Photobiology in Medicine, G. Jori, R. H. Pottier, M. A. J. Rodgers, and T. G. Truscott (eds). New York: Plenum Press, 1994, pp. 125–141. Sarna, T., and R. C. Sealy. Photoinduced oxygen consumption in melanin systems. Action spectra and quantum yields for eumelanin and synthetic melanin. Photochem. Photobiol. 39:69–74, 1984a. Sarna, T., and R. C. Sealy. Free radicals from eumelanins: Quantum yields and wavelength dependence. Arch. Biochem. Biophys. 232:574–578, 1984b. Sarna, T., and H. M. Swartz. Identification and characterization of melanin in tissues and body fluids. Folia Histochem. Cytochem. 16:275–286, 1978. Sarna, T., and H. M. Swartz. Interaction of melanin with oxygen (and related species). In: Atmospheric Oxidation and Antioxidants, vol. III, G. Scott (ed.). Amsterdam: Elsevier, 1993, pp. 129–169. Sarna, T., J. S. Hyde, and H. M. Swartz. Ion exchange in melanin: an electron spin resonance study with lanthanide probes. Science 192:1132–1134, 1976. Sarna, T., W. Froncisz, and J. S. Hyde. Cu2+ probe of metal-ion binding sites in melanin using electron paramagnetic resonance spectroscopy. II. Natural melanin. Arch. Biochem. Biophys. 202:304–313, 1980a. Sarna, T., A. Duleba, W. Korytowski, and H. Swartz. Interaction of melanin with oxygen. Arch. Biochem. Biophys. 200:140–148, 1980b. Sarna, T., W. Korytowski, M. Pasenkiewicz-Gierula, and E. Gudowska. Ion-exchange studies in melanins. In: Proceedings of the 11th International Pigment Cell Conference, Sendai, 1980, M. Seiji (ed.). Tokyo: University of Tokyo Press, 1981, pp. 23–29. Sarna, T., I. A. Menon, and R. C. Sealy. Photoinduced oxygen consumption in melanin systems — II. Action spectra and quantum yields for pheomelanins. Photochem. Photobiol. 39:805–809, 1984. Sarna, T., W. Korytowski, and R. C. Sealy. Nitroxides as redox probes of melanins: Dark-induced and photoinduced changes in redox equilibria. Arch. Biochem. Biophys. 239:226–233, 1985a. Sarna, T., I. A. Menon, and R. C. Sealy. Photosensitization of melanin: a comparative study. Photochem. Photobiol. 42:529–532, 1985b. Sarna, T., B. Pilas, E. J. Land, and T. G. Truscott. Interaction of radicals from water radiolysis with melanin. Biochim. Biophys. Acta 883:162–167, 1986.
340
Sarna, T., J. M. Burke, W. Korytowski, M. Rózanowska, C. M. B. Skumatz, A. Zareba, and M. Zareba. Loss of melanin from human RPE with aging: possible role of melanin photooxidation. Exp. Eye Res. 76:89–98, 2003. Scalia, M., E. Geremia, C. Corsaro, C. Santoro, D. Baratta, and G. Sichel. Lipid peroxidation in pigmented and unpigmented liver tissues: Protective role of melanin. Pigment Cell Res. 3:115–119, 1990. Shima, T., T. Sarna, H. M. Swartz, A. Stroppolo, R. Gerbasi, and L. Zecca. Binding of iron to neuromelanin of human substantia nigra and synthetic melanin: an electron paramagnetic resonance spectroscopy study. Free Rad. Biol. Med. 23:110–119, 1997. Sealy, R. C. Free radicals in melanin formation, structure and reactions. In: Free Radicals in Molecular Biology, Aging and Disease, D. Armstrong, R. S. Sohal, R. G. Cutler, and T. F. Slater (eds). New York: Raven Press, 1984, pp. 67–75. Sealy, R. C., C. C. Felix, J. S. Hyde, and H. M. Swartz. Structure and reactivity of melanins: influence of free radicals and metal ions. In: Free Radicals in Biology, W. A. Pryor (ed.). New York: Academic Press, 1980, pp. 209–259. Sealy, R. C., J. S. Hyde, C. C. Felix, I. A. Menon, G. Prota, H. M. Swartz, S. Persad, and H. F. Haberman. Novel free radical in synthetic and natural pheomelanins: Distinction between dopa melanins and cysteinyldopa melanins by ESR spectroscopy. Proc. Natl. Acad. Sci. USA 79:2885–2889, 1982a. Sealy, R. C., J. S. Hyde, C. C. Felix, I. A. Menon, and G. Prota. Eumelanins and pheomelanins: characterization by electron spin resonance spectroscopy. Science 217:545–547, 1982b. Sealy, R. C., T. Sarna, E. J. Wanner, and K. Reszka. Photosensitization of melanin: An electron spin resonance study of sensitized radical production and oxygen consumption. Photochem. Photobiol. 40:453–459, 1984. Seiji, M. Melanosomes 1980. In: Pigment Cell: Proceedings of the XIth International Pigment Cell Conference, M. Seiji (ed.). Tokyo: University of Tokyo Press, 1981, pp. 3–13. Sichel, G., C. Corsaro, M. Scalia, A. J. Di Billio, and R. P. Bonomo. In vitro scavenger activity of some flavonoids and melanins against O2. Free Rad. Biol. Med. 11:1–8, 1991. Simonovic, K. K., and A. Pirie. Barium content of different parts of the choroid of the bovine eye. Nature 199:1007, 1963. Slawinska, D., J. Slawinski, and L. Ciesla. The inhibition of peroxyradical-induced chemiluminescence by melanins. Physiol. Chem. Phys. Med. NMR 15:209–222, 1983. Sotomatsu, A., M. Tanaka, and S. Hirai. Synthetic melanin and ferric ions promote superoxide anion-mediated lipid peroxidation. FEBS Lett. 342:105–108, 1994. Stark, K. B., J. M. Gallas, G. W. Zajac, M. Eisner, and J. T. Golab. Spectroscopic study and simulation from recent structural models for eumelanin: II. Oligomers. J. Phys. Chem. Biol. 107:11558– 11562, 2003. Stepien, K. B., and T. Wilczok. Studies of the mechanism of chloroquine binding to synthetic dopa-melanin. Biochem. Pharmacol. 31:3359–3365, 1982. Stepien, K., A. Zajdel, A. Wilczok, T. Wilczok, A. Grzelak, A. Mateja, M. Soszynski, and G. Bartosz. Dopamine-melanin protects against tyrosine nitration, tryptophan oxidation and Ca(2+)-ATPase inactivation induced by peroxynitrite. Biochim. Biophys. Acta 1523:189–195, 2000. Stratton, K., and M. A. Pathak. Photoenhancement of the electron spin resonance signal from melanins. Arch. Biochem. Biophys. 123:477–483, 1968. Strzelecka, T. A band model for synthetic dopa-melanin. Physiol. Chem. Phys. 14:219–222, 1982a. Strzelecka, T. Semiconductor properties of natural melanins. Physiol. Chem. Phys. 14:223–231, 1982b. Strzelecka, T. A hypothetical structure of melanin and its relation to biology. Physiol. Chem. Phys. 14:233–237, 1982c.
THE PHYSICAL PROPERTIES OF MELANINS Szpoganicz, B., S. Gidanian, P. Kong, and P. Farmer. Metal binding by melanins: studies of colloidal dihydroxyindole-melanin, and its complexation by Cu(II) and Zn(II) ions. J. Inorg. Biochem. 89:45–53, 2002. Swartz, H. M., T. Sarna, and L. Zecca. Modulation by neuromelanin of the availability and reactivity of metal ions. Ann. Neurol. 32:S69S75, 1992. Swartz, H. M., G. Bacic, B. Friedman, F. Goda, O. Y. Grinberg, P. J. Hoopes, J. Jiang, J. Liu, T. Nakashima, T. O’Hara, and T. Walczak. Measurements of pO2 in vivo, including human subjects, by electron paramagnetic resonance. In: Oxygen Transport to Tissue XVI, M. C. Hogan, O. Mathieu-Costello, D. C. Poole, and P. D. Wagner (eds). New York: Plenum Press, 1994, pp. 119–128. Thathachari, Y. T., and M. S. Blois. Physical studies on melanins: II. X-ray diffraction. Biophys. J. 9:77–89, 1969. Thompson, A., E. J. Land, M. R. Chedekal, K. V. Subbarao, and T. G. Truscott. A pulse radiolysis investigation of the oxidation of the melanin precursors 3,4-dihydroxyphenylalanine (DOPA) and cysteinylDOPAs. Biochim. Biophys. Acta 843:49–57, 1985. Toda, K., M. A. Pathak, T. B. Fitzpatrick, W. C. Quevedo, F. Morikawa, and Y. Nakayam. Skin color, its ultrastructure and its determining mechanism. In: Pigment Cell, vol. 1, V. Riley, V. J. McGovern, and P. Russel (eds). Basel: S. Karger, 1973, pp. 61–81. Tomita, Y., A. Hariu, C. Kato, and M. Seiji. Radical production during tyrosinase reaction, DOPA-melanin formation, and photoirradiation of DOPA-melanin. J. Invest. Dermatol. 82:573–576, 1984. Trukhan, E. M., N. F. Perevozchikov, and M. A. Ostrovskii. Photoconductivity of the pigment epithelium of the eye. Biofizika 15:1052–1055, 1970. Trukhan, E. M., V. N. Deryabkin, and M. A. Ostrovskii. Investigations of the photoconductivity of the pigment epithelium of the eye. Biofizika 18:413–416, 1973. Valkovic, V., D. Miljanic, R. M. Wheeler, R. B. Liebert, T. Zabel, and G. C. Phillips. Variation in trace metal concentrations along single hairs as measured by proton induced X-ray emission photometry. Nature 243:543–544, 1973. Van Woert, M. H. Reduced nicotinamide-adenine dinucleotide oxidation by melanin: inhibition by phenothiazines. Proc. Soc. Exp. Biol. Med. 129:165–171, 1968. Van Woert, M. H., and L. M. Ambani. Biochemistry of neuromelanin. Adv. Neurol. 5:215–223, 1974. Vitkin, I. A., J. Woolsey, B. C. Wilson, and R. R. Anderson. Optical and thermal characterization of natural (Sepia officinalis) melanin. Photochem. Photobiol. 59:455–462, 1994. Vsevolodov, E. B., S. Ito, K. Wakamatsu, I. I. Kuchina, and I. F. Latypov. Comparative analysis of hair melanins by chemical and electron spin resonance methods. Pigment Cell Res. 4:30–34, 1991. Wakamatsu, K., S. Ito, and T. Nagatsu. Cysteinyldopamine is not incorporated into neuromelanin. Neurosci. Lett. 131:57–60, 1991. Watanabe, S., R. R. Anderson, S. Brorson, G. Dalickas, J. G.
Fujimoto, and T. J. Flotte. Comparative studies of femtosecond to microsecond laser pulses on selective cell injury in skin. Photochem. Photobiol. 53:757–762, 1991. Wielgus, A., J. Bielec, and T. Sarna. Direct time-resolved measurements of quenching of singlet oxygen by synthetic melanins. Unpublished. Wilczok, T., B. Bilinska, E. Buszman, and M. Kopera. Spectroscopic studies of chemically modified synthetic melanins. Arch. Biochem. Biophys. 231:257–262, 1984. Wolf, K. Melanocyte-keratinocyte interactions in vivo. The fate of melanosomes. Yale J. Biol. Med. 46:384–396, 1973. Wolfram, L. J., and L. Albrecht. Chemical and photo-bleaching of brown and red hair. J. Soc. Cosmet. Chem. 82:179–191, 1987. Wróbel, D., A. Planner, I. Hanyz, A. Wielgus, and T. Sarna. Melanin–porphyrin interaction monitored by delayed luminescence and photoacoustics. J. Photochem. Photobiol. B Biol. 41:45–52, 1997. Ye, T., and J. D. Simon. Ultrafast spectroscopic study of pheomelanin: implications on the mechanism of superoxide anion formation. J. Phys. Chem. Biol. 106:6133–6135, 2002. Ye, T., and J. D. Simon. Comparison of the ultrafast absorption dynamics of eumelanin and pheomelanin. J. Phys. Chem. B 107:11240–11244, 2003. Ye, T., T. Sarna, and J. D. Simon. Ultrafast energy transfer from bound tetra(4-N,N,N,N-trimethylanilinium)porphyrin to synthetic dopa and cysteinyldopa melanins. Photochem. Photobiol. 77:1–4, 2003. Zajac, G. W., J. M. Gallas, J. Cheng, M. Eisner, S. C. Moss, and A. E. Alvarado-Swaisgood. The fundamental unit of synthetic melanin: a verification by tunneling microscopy of X-ray scattering results. Biochim. Biophys. Acta 1199:271–278, 1994. Zareba, M., A. Bober, W. Korytowski, L. Zecca, and T. Sarna. The effect of a synthetic neuromelanin on yield of free hydroxyl radicals generated in model systems. Biochim. Biophys. Acta 1271:343–348, 1995. Zareba, M., M. W. Raciti, M. M. Henry, T. Sarna, and J. M. Burke. Oxidative stress in ARPE-19 cultures: Do melanosomes offer cytoprotection? Free Rad. Biol. Med., 2005, in press. Zecca, L., and H. M. Swartz. Total and paramagnetic metals in human substantia nigra and its neuromelanin. J. Neural Transm. Park. Dis. Dement. Sect. 5:203–213, 1993. Zecca, L., C. Mecacci, R. Seraglia, and E. Parati. The chemical characterization of melanin contained in substantia nigra of human brain. Biochim. Biophys. Acta 1138:6–10, 1992. Zecca, L., R. Pietra, C. Goj, C. Mecacci, D. Radice, and E. Sabbioni. Iron and other metal in neuromelanin; substantia nigra and putamen of human brain. J. Neurochem. 62:1097–1101, 1994. Zeise, L., and M. R. Chedekel. Melanin standard method: titrimetric analysis. Pigment Cell Res. 5:230–239, 1992. Zeise, L., B. L. Murr, and M. R. Chedekel. Melanin standard method. Particle description. Pigment Cell Res. 5:132–142, 1992.
341
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
17
Photobiology of Melanins Antony R. Young
Summary Exposure to ultraviolet radiation (UVR) results in long-term deleterious effects such as skin cancer. A well-recognized short-term consequence of UVR is increased skin pigmentation. Skin color is one of most conspicuous ways in which humans vary, yet many aspects regarding the function of melanin remain controversial. Pigmentation, whether constitutive or facultative, has been widely viewed as photoprotective, largely because darkly pigmented skin is at a lower risk of photocarcinogenesis than fair skin. Research is increasingly suggesting that the relationship between pigmentation and photoprotection may be far more complex than previously assumed. For example, photoprotection against erythema and DNA damage has been shown to be independent of the level of induced pigmentation in human white skin types. Growing evidence now suggests that UVR-induced DNA photodamage, and its repair, is one of the signals that stimulates melanogenesis. These findings suggest that tanning may be a measure of inducible DNA repair capacity, and it is this rather than pigment per se that results in the lower incidence of skin cancer observed in darker skinned individuals. This is supported by some studies that suggest that repeated UVR exposure in skin types IV, who tan well, results in faster DNA repair in comparison with skin types II, who tan poorly. It has been suggested that epidermal pigmentation may in fact be the mammalian equivalent of a bacterial SOS response.
Introduction The color of human skin is largely determined by its epidermal melanin content, whether this melanin is constitutively expressed or induced by UVR from the sun or a tanning device. Melanin production, or melanogenesis, occurs in highly specialized dendritic melanocytes that account for about 1% of epidermal cells. Each basal layer melanocyte is associated with about 36 keratinocytes and one Langerhans cell, and this is known as the epidermal melanin unit (EMU) (Fitzpatrick and Breathnach, 1963). Melanogenesis is described in detail in Chapter 14. The composition of melanin, the end-product of melanogenesis that is transferred to adjacent keratinocytes, is still incompletely understood but is a variable mixture of lighter/reddish/yellowish alkali-soluble, sulfur-containing pheomelanin and darker brownish/blackish insoluble eumelanin. In both cases, the rate-limiting step is the oxidation of tyrosine by tyrosinase in a series of reactions known as the Raper–Mason pathway. Eumelanogenesis leads 342
to the formation of indole derivatives that include 5,6dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA), formed from the oxidation of the 1,4 addition product of tyrosinase-generated dopaquinone. Intermediates in pheomelanogenesis include cysteinyldopas. Indole and cysteinyldopa precursors and their related o-methyl derivatives are released into the epidermis during periods of melanogenic activity induced by UVR or psoralen plus UVA (PUVA). Their lipophilic nature suggests a long half-life in lipophilic dermal and epidermal tissue. Skin color is a consequence of the mix of melanin types and possibly also the way that melanin is packaged in melanosomes, highly specialized melanocyte-derived organelles that are used for the transfer of melanin to keratinocytes via the melanocyte dendrites. Caucasian melanosomes have a long axis of about 400 nm and tend to occur in groups of 3–8, whereas Negroid melanosomes are much longer (800 nm length) and exist singly (Kollias et al., 1991). Melanocyte density is independent of race (Halaban et al., 2003) but varies with body site, with densities ranging from 2000/mm2 in the head or forearm to 1000/mm2 elsewhere. Recent studies indicate that the distribution of melanosomes within keratinocytes (Thong et al., 2003) and melanosome size (Alaluf et al., 2003) play a role in skin color. Melanocyte numbers in non-sunexposed skin show an age-related decline with an approximately 8–10% reduction per decade (Halaban et al., 2003). There is considerable intercellular chemical communication between melanocytes and keratinocytes and, to lesser extent, fibroblasts, neurons, mast cells, and other skin cells. Keratinocytes produce a wide range of mitogenic [e.g. basic fibroblast growth factor (bFGF), transforming growth factor (TGF)a] and inhibitory [e.g. interleukin (IL)1, IL6, TGFb] factors for melanocytes. In addition, the proliferation of melanocytes, melanogenesis, and the transfer of pigment also rely on hormonal controls [a-melanocyte-stimulating hormone (MSH), sex hormones), agouti signal protein, and inflammatory mediators in skin (Chu et al., 2003; Gilchrest et al., 1996). The melanocyte plasma membrane is also thought to be a primary UVR target with the release of membrane-bound factors, such as arachidonic acid and diacylglycerol (DAG), leading to activation of tyrosinase via a protein kinase C (PKC)-mediated pathway (Gilchrest et al., 1996). The behavior of isolated melanocytes in vitro is different from their behavior as part of an EMU. For example, recent studies have shown that the pheomelanin/eumelanin ratio is regulated by keratinocytes (Duval et al., 2002). However, it has also been reported that melanosomes from different skin types maintain their melanin type preferences in
PHOTOBIOLOGY OF MELANINS
melanocytes stimulated with tyrosine in vitro (van Nieuwpoort et al., 2004).
The Effects of Solar UVR on Human Skin The detrimental effects of solar UVR (~295–400 nm) on the skin are well established and are usually categorized as either acute or chronic. Acute effects include DNA (Bykov et al., 1999) and oxidative damage (Sander et al., 2004), mutation (Ziegler et al., 1994), immunosuppression (Ullrich, 2000), and erythema (sunburn) (Harrison and Young, 2002). Molecular biology is increasingly showing that UVR induces the expression of a large number of genes, the physiological consequence of which is poorly understood. Tanning is also an acute effect, and it is debatable whether this is a detrimental or beneficial effect. The chronic effects include skin cancers, which are thought to be a consequence of mutation and immunosuppression (Ullrich, 2002; Ziegler et al., 1994), and photoaging, which is thought to be a consequence of the induction of matrix metalloproteinases (MMPs) (Fisher et al., 2002). Skin darkening in response to solar UVR occurs via two distinct mechanisms: immediate pigment darkening (IPD) and delayed tanning (DT). Both processes are influenced by genetic factors and are more pronounced with darker constitutive pigmentation. The action spectrum for IPD shows a broad peak in the UVA region (Irwin et al., 1993) and is completely different from the action spectrum for DT (Parrish et al., 1982), which indicates that they are mechanistically different processes. There is a range of non-invasive optical techniques to measure skin pigmentation in vivo, but all have disadvantages of various types (Stamatas et al., 2004) and none is in routine use. IPD starts during UV irradiation as a grayish coloration that gradually fades to a brown color over a period of minutes to days depending on UVR dose and individual complexion. These changes are not due to new melanin synthesis but rather oxidation of pre-existing melanin and redistribution of melanosomes from a perinuclear to a peripheral dendritic location (Routaboul et al., 1999). The color change may be so subtle as to be almost undetectable in fair-skinned individuals but is easily observed in skin types IV (or darker). The transient nature of IPD has made understanding of this phenomenon difficult. In vivo reflectance spectroscopy showed a UVA (365 nm) dose-dependent induction of IPD with increased absorbance between 620 and 720 nm (Rosen et al., 1990), similar to that expected from increased native melanin. However, at shorter wavelengths (410–610 nm), the absorbance is less than expected from increased native melanin. Significantly, no photoprotective effect for IPD has been established; hence, its biological function remains unknown. DT, which results from melanogenesis, is associated with increased melanocyte activity and proliferation. It is evident
3–4 days after UVR exposure and is maximal from 10 days to 3–4 weeks depending on complexion and UVR dose. It may take several weeks for the skin to return to its base constitutive color. UVA-induced DT is two or three orders of magnitude less efficient per unit dose than UVB and has an earlier onset, often directly after IPD. Furthermore, it has a different pathophysiology (Eller and Gilchrest, 2000; Lavker and Kaidbey, 1982) that, unlike UVB, is oxygen dependent. The only widely recognized beneficial effect of solar UVR exposure is epidermal vitamin D photosynthesis. Sunlight is believed to be the body’s major source of vitamin D as few people consume enough food that is naturally rich in vitamin D to meet their dietary requirements. Solar UVB (295–310 nm) converts 7-dehydrocholesterol in the skin to vitamin D3 (cholecalciferol), a prohormone with no intrinsic biological activity. Vitamin D3 is metabolized in the liver to 25-hydroxyvitamin D (25(OH)D). Plasma levels of this metabolite are the hallmark for determining vitamin D status as it is used as the substrate for producing the biologically active steroid hormone 1,25-dihydroxyvitamin D. In temperate regions, there is insufficient UVB in the winter months to synthesize vitamin D, and therefore there is a seasonal variation in plasma 25-(OH)D concentrations, with winter levels dependent upon the amount of vitamin D stored in adipose tissue during the previous summer (Devgun et al., 1981; Vieth et al., 2001; Webb et al., 1988). Maintenance of optimal levels of 25(OH)D are essential for bone health, but some epidemiological and intervention trials suggest that vitamin D deficiency may increase the risk of some internal malignancies and autoimmune disorders (Zittermann, 2003).
Skin Chromophores and Their Relationship to Photobiology The UVR-absorbing properties of skin depend on its natural chromophores, which include DNA, amino acids, urocanic acid, and melanins and their precursors (Young, 1997). Absorption of UVR energy by chromophores may initiate photochemical events that are the basis of all skin photobiology. Chromophores, especially those in the upper epidermis, may also attenuate UVR and thus protect the structure beneath from photodamage. For example, nonsolar UVC radiation (100–280 nm) causes very little damage to DNA in cells of the basal layer because of its attenuation by DNA in the cells above and urocanic acid in the stratum corneum (Chadwick et al., 1995). In contrast, solar-range UVB and UVA radiation readily results in damage to DNA of keratinocytes and melanocytes in the basal layer of human skin in vivo (Young et al., 1998a). The emission spectrum of the sun is rich in UVA (315–400 nm) radiation with UVB (280–315 nm) radiation accounting for less than 5% of total UVR content under most conditions. However, because most skin chromophores are primarily UVB absorbers, it is that part of the solar spectrum 343
CHAPTER 17
that causes most of the biological effects described above. For example, action spectrum (wavelength dependence) studies have shown that UVB is three to four orders of magnitude more effective per unit physical dose (J/cm2) than UVA for DNA photodamage (Young et al., 1998b), erythema (Parrish et al., 1982; Young et al., 1998b), tanning (Parrish et al., 1982), and skin cancer in mice (de Gruijl, 1995). However, UVA may be more important for indirect damage to cells caused by oxidative stress. This is caused by reactive oxygen species (ROS) that are generated when UVA (and also UVB) (Sander et al., 2004) is absorbed by as yet poorly defined chromophores that may include flavins and porphyrins. The chromophore(s) for melanogenesis have not been established with certainty, but there is an increasing body of indirect and direct evidence that supports a major role for DNA (Eller and Gilchrest, 2000). Human studies have shown that the action spectra for DNA photodamage, as assessed by cyclobutane pyrimidine dimers (CPD), and tanning are very similar (Parrish et al., 1982; Young et al., 1998b) as shown in Figure 17.1. This suggests that the photochemical event that initiates tanning may be a consequence of DNA photodamage. Figure 17.2 summarizes some of the photobiological events that initiate melanogenesis.
1.0
Skin Type and Melanin The skin’s constitutive melanin content and its melanogenic response to solar UVR form part of the basis of the skin type clinical classification shown in Table 17.1. This scheme was originally devised to optimize UVR doses in phototherapy. Sensitivity to sunburn is routinely evaluated by minimal erythema dose (MED) determination, the MED being the lowest dose (J/cm2) of UVR that will cause erythema assessed at 24 h. In general, tanning capacity is inversely related to MED, but there is a considerable degree of MED overlap within white skin types I–IV (Harrison and Young, 2002). In other words, MED is not a reliable index for predicting skin type. Investigators have determined the quantitative and qualitative melanin content in human hair and skin in vivo and, in some cases, after skin exposure to UVR (for a review, see Ito and Wakamatsu, 2003). The first study of epidermis in vivo was by Thody et al. (1991) in skin types I, II, and III, in which there was a positive correlation between skin type and eumelanin but not pheomelanin. However, the ratio of eumelanin/pheomelanin shows considerable variation, especially in skin types II and III. The level of tanning by PUVA
Upper Epidermis TT Basal Layer TT
Log10 Relative Effect
0.0
MMD
–1.0
–2.0
–3.0 270
290
310
330
350
Membrane Damage
370
CPD
Wavelength (nm) Fig. 17.1. Human action spectra for epidermal DNA photodamage (TT = thymine dimers; data from Young et al., 1998b) and tanning expressed as minimal melanogenic dose (MMD) assessed at 7–14 days (data from Parrish et al., 1982). The TT action spectra show epidermal layer dependence at wavelengths less than 300 nm, probably because of marked UVR attenuation by epidermal chromophores at these wavelengths. These TT and MMD spectra are very similar, which suggests that DNA is an important chromophore for melanogenesis and in particular DNA from the upper epidermis. This suggests the possibility that damage to keratinocytes, with the release of melanogenic factors (see Fig. 17.2), may be more important than direct damage to melanocytes that reside in the basal layer region.
344
Keratinocyte Factors
DNA Repair
Fig. 17.2. Multiple photobiological events initiate melanin synthesis. These include DNA photodamage (CPD) and its repair, membrane damage, and factors from other epidermal cells, especially keratinocytes.
PHOTOBIOLOGY OF MELANINS Table 17.1. Classification of human skin types with respect to relative response to acute and long-term solar exposure. Skin type
Susceptibility to sunburn
Constitutive skin color
Facultative tanning ability
Susceptibility to skin cancer
I II III IV V VI
High High Moderate Low Very low Very low
White White White Olive Brown Black
Very poor Poor Good Very good Very good Very good
High High Moderate Low Very low Very low
was correlated with eumelanin but not pheomelanin. Alaluf et al. (2001) evaluated melanin content in sun-protected and -exposed sites of skin types V and IV. In comparison with DHICA and DHI eumelanins, pheomelanin content was very low. Solar exposure enhanced eumelanin content, in particular predominant DHI eumelanin, but had no effect on pheomelanin levels. In further studies, these authors (Alaluf et al., 2002) assessed epidermal melanin content in five different ethnic groups using alkali solubility as a means of separating the lighter pheomelanin and DHICA eumelanin from the darker DHI eumelanin on sun-protected and -exposed skins. The difference in total melanin content between the lightest European skin and the darkest African skins was only about twofold in both skin sites, which is consistent with previously reported skin type-dependent differences in tyrosinase activity (Iwata et al., 1990; Pomerantz and Ances, 1975). The data also showed that darker skin was associated with greater quantities of alkali-insoluble melanins, and lighter skins were associated with greater quantities of alkali-soluble melanins. The level of melanin, however assessed, was always higher (P < 0.01) in all study populations on sun-exposed sites by factors ranging from 1.3 to 1.9, with the differences in alkalisoluble melanin (1.3–1.5) being smaller than those of alkaliinsoluble melanin (1.5–1.9). The 1.8-fold difference in total melanin in sun-exposed and -protected African skin is about the same as the differences in African and European skin on their respective sun-protected and -exposed sites. The darker skins have the lowest values when the data are expressed as % alkali-soluble melanin, and this is reduced slightly (1.2–1.3) by sun exposure in African and Indian skins only. Overall, these data support a role for eumelanin in sun tolerance as indicated by skin type. However, they also show that skin type differences in skin color and the degree of photoprotection are unlikely to be accounted for by differences in melanin alone, and Alaluf et al. (2002) have suggested that this may also be related to melanosome size.
Photoprotection by Melanin The primary function of skin melanin has not yet been established. A number of roles have been proposed that include photoprotection, thermoregulation, antibiotic, cation chelator,
free radical sink, and by-product of the scavenging of the superoxide radical in the skin by tyrosinase (Giacomoni, 1995; Hill and Hill, 2000; Morison, 1985). It is often stated that melanin is photoprotective because people with constitutively pigmented skins [e.g. types V (brown) or VI (black)] or skin that tans well (e.g. Mediterranean type IV) have much lower incidences of skin cancer that white-skinned people who tan poorly if at all (e.g. types I and II). Indeed, epidemiological studies confirm an inverse correlation between skin cancer incidence and pigmentation with age-adjusted male cancer incidence at 3.4 per 100 000 for blacks and 232.6 per 100 000 for Caucasian whites in the USA (Scotto and Fraummeni, 1982). At its simplest, this argument assumes that melanin or melanogenesis is the only factor that determines the level of a given photobiological response, e.g. skin cancer, to a given physical dose of UVR. However, there is clear evidence that this is not the case. For example, skin types I/II are more readily immunosuppressed than skin types III/IV when compared on the basis of physical or erythemal dose (Kelly et al., 2000). These studies showed that suberythemal doses of solar simulated radiation (SSR) suppressed the sun-sensitive skin types I/II but erythemal doses were necessary to suppress the sun-tolerant skin types III/IV. Furthermore, there is evidence for skin type-dependent differences in responses to oxidative stress (Kerb et al., 1997), which is thought to play a role in cancer (Sander et al., 2004). A photoprotective role for melanin, particularly against skin cancer, was first proposed by Home (1820). The Darwinian argument to support this hypothesis would require skin cancer to interfere with reproduction and child-rearing. Blum (1961) dismissed this argument and noted that nonmelanoma skin cancers generally occur after the reproductive age and are rarely fatal. Malignant melanomas are more fatal but account for only 4% of skin cancers and also usually occur after reproduction. Studies in Nigerian albinos show that, even in an extreme solar environment, skin cancer did not result in death below the age of 25 years (Okoro, 1975). In 2000, a landmark study examined the relationship between UVR levels, skin reflectance (a marker of melanin), vitamin D, and folate levels at different latitudes (Jablonski and Chaplin, 2000). Predicted skin reflectance based on UVR levels was noted to correlate closely, and a strong correlation between skin reflectance, absolute latitude, and UVR was
345
CHAPTER 17
demonstrated. It was concluded that the gradient between UVR and constitutive pigmentation was a compromise between the beneficial effect of vitamin D photosynthesis and the deleterious effect of folate photolysis that would interfere with reproduction. In reality, little is in fact known about the relationship between solar UVR and vitamin D status. Population surveys have shown that vitamin D deficiency is more common among institutionalized, elderly individuals with pigmented skin and those who habitually cover the skin with clothing (BischoffFerrari et al., 2004; Devgun et al., 1981; Vieth et al., 2001). Suberythemal UVB is a potent stimulus of vitamin D synthesis in white-skinned subjects in vivo, who show a ninefold increase in circulating vitamin D3 after a single whole-body exposure of about 0.75 MED (Matsuoka et al., 1989, 1990, 1991). Skin pigmentation is believed to greatly reduce the UVR-mediated synthesis of vitamin D3, with black subjects (n = 1) requiring at least a sixfold greater UVR dose to increase circulating levels of vitamin D3 than whites (n = 2) (Clemens et al., 1982). This finding, based on a very small study, was not confirmed in a later study. Matsuoka and colleagues (1991) found a significant association between skin color and vitamin D3 synthesis in different ethnic groups (n = 8) with white > Oriental > Asian > black, but reported only a twofold difference in vitamin D3 synthesis between white and black skin. The same skin type trend was seen for serum 25(OH)D levels, but it did not reach significance and no skin type effect was seen for serum 1,25 dihydroxyvitamin D. It should be noted that the single UVR challenge dose used in this study could readily be achieved after 10-min exposure to noonday UK summer sunlight. Therefore, it is unlikely that differences in cutaneous vitamin D3 synthesis would result in vitamin D deficiency in pigmented individuals. This conclusion is supported by Stamp et al. (1975), who showed that increases in serum 25(OH)D were similar in white (n = 4), Asian (n = 2), and black subjects (n = 1) after three daily exposures to the same physical UVR dose, and by Brazerol et al. (1988), who also found similar increases in 25(OH)D in white (n = 13) and black (n = 7) subjects exposed to suberythemal whole-body UVR twice a week for 6 weeks. It is possible that a higher incidence of vitamin D deficiency in subjects with pigmented skin results from other factors such as behavior or diet. For example, in the UK, low vitamin D status is relatively more common among Asians, especially children, adolescents, and women. A combination of factors, including the type of vegetarian diet, low calcium intake, and limited solar exposure, appears to underlie the risk (Hamson et al., 2003; Stamp, 1975). Some studies have attempted to determine the photoprotective properties of melanin against specific endpoints in human skin in vivo, and these are reviewed below. It must also be noted that melanogenesis and stratum corneum thickening occur concurrently during the normal tanning response, and this must be borne in mind when considering photoprotection by melanin alone. Although photoprotection may be considered to be a passive physical process, e.g. the attenuation of 346
UVR by melanin and/or stratum corneum thickening, as is the case with conventional sunscreens, it may also be considered as an active enzymatic process, e.g. as a means by which DNA repair is enhanced or ROS are inactivated. For example, chimeric epidermal reconstructs with melanocytes from one skin type added to keratinocyte cultures of a different skin type suggest keratinocyte/melanocyte interaction with both cell types regulating antioxidant defense in a skin typedependent way (Bessou-Touya et al., 1998).
Optical Properties of Melanin and Associated Molecules The absorption spectra of monocysteinyldopas (5-S-cysteinyldopa, 2-S-cysteinyldopa, 6-S-cysteinyldopa) show a maximum at 292 nm, whereas indoles, their methyl derivatives, and 2,5S-S¢-dicysteinyldopa show maxima at 302–330 nm (Kollias et al., 1991). Diffuse spectroscopy has been used to calculate melanin absorption in vivo by comparing normal with melanin-depleted skin in the same vitiligo patient. This approach reveals a maximum at 335 nm, with a steep decline at shorter wavelengths. Absorption is also noted within the visible range (400–800 nm). Differences in pigmentation induced by various bands of UVR (UVB, UVA, and PUVA) have also been analyzed using in vivo reflectance spectroscopy by comparing the results of tanned and untanned skin in the same individuals (Kollias et al., 1994). UVB- and PUVAinduced melanin showed an absorption peak at 305 nm whereas UVA resulted in a 360-nm-centered loss in UVR absorption with a concomitant relative increase in the absorption of visible light. These data suggest that different stimuli induce different pathways of melanogenesis. Interestingly, derivatives in the eumelanogenesis pathway such as DHI and DHICA also showed significant absorption in the solar UVR range (the latter in particular showing strong UVA absorption), and hence could possibly be classified as photoprotective. The particulate nature of melanin results in scattering as well as absorption of UVR. Studies on the cuttle fish melanin particles (size range 20–300 nm) found that the reported level of scatter in the wavelengths 580–633 nm did in fact correspond to the levels predicted (Vitkin et al., 1994). Melanosomes measuring ≥ 300-nm diameter mainly cause forward scatter of UVR in contrast to the smaller particles such as melanin dust found in keratinocytes (< 30 nm), which display symmetrical scattering profiles (Chedekel et al., 1995).
Erythema In the field, Cripps (1981) assessed the protection factor afforded by a Wisconsin (~45∞N) summer tan (obtained over 3.5 months) in skin types II, III, and IV by comparing the SSR MED on tanned and untanned buttock skin. Protection factors were 2.4 ± 0.65 (SD), 2.45 ± 0.5, and 2.1 ± 0.22, respectively, with a mean of 2.33 ± 0.05. Although not stated, it is presumed that tanning was according to skin type, and it seems that better tans did not afford any better protection against erythema. In laboratory studies, Sheehan et al. (1998)
PHOTOBIOLOGY OF MELANINS
induced tanning in skin types II and III with repeated suberythemal exposure to SSR. Photoprotection was evaluated by assessing the MED on untanned and tanned sites, included tanned sites that had had the stratum corneum removed by tape stripping. As expected, the tanning response in skin type III was greater than that in skin type II, but there was no significant difference in the level of photoprotection with a protection factor of about 2 in both skin types. Thus, the degree of photoprotection could not be correlated with the level of the tan. Removal of the stratum corneum generally reduced the level of photoprotection by about 20%, which suggested that the stratum corneum was relatively unimportant in the tanning response. In a comparable later study but without the tape-stripping component, Sheehan et al. (2002) used a similar protocol in skin types II and IV. Despite the difference in the tanning response, the protection factor against erythema, assessed by MED determination, was again of the order of 2 with no difference between the skin types. Overall, the data of Sheehan et al. (1998, 2002) in skin types II, III, and IV show that the degree of photoprotection against erythema was very similar but could not be correlated with the level of tan, as was presumed to be the case in the field study by Cripps (1981). This suggests that other, as yet undefined, inducible forms of photoprotection may be in operation and that the level of melanin may be of less importance. Ha et al. (2003) used reflectance spectroscopy to assess the relationship between acute UVB-induced erythema and constitutive pigmentation. Regression analyses for a given UVB dose (119–300 mJ/cm2) were done on a panel of individuals and showed an inverse relationship, but that slope depends on the dose used. Although these data show that constitutive melanin is photoprotective, they also suggest that this protection is less effective at higher UVB doses. Gniadecka et al. (1996) specifically assessed the photoprotective role of the stratum corneum in vitiliginous and normal adjacent skin (skin type not specified) that had had no UVR exposure for 3 months. Sensitivity to erythema was compared with the thickness of the stratum corneum and the viable epidermis as well as pigmentation assessed by a reflectance device. Overall, the authors concluded that the stratum corneum accounted for almost two-thirds of the photoprotection of normal skin and was therefore more important than pigmentation, and that the thickness of the viable epidermis was not important in photoprotection.
DNA Photodamage UVR induces structural changes in DNA that include the formation of potentially mutagenic CPD and pyrimidine (6–4) pyrimidone photoproducts ((6–4) pp). Human studies have shown that epidermal CPD and ((6–4) pp) are readily induced with suberythemal exposure of SSR, UVB, and UVA (Chadwick et al., 1995; Young et al., 1998a, b). There is increasing evidence that epidermal DNA is a major chromophore for many of the acute and long-term effects of solar exposure (Young, 1996). Photodamage to DNA may result in highly characteristic gene mutations, e.g. p53 which is thought to be the initial
step in nonmelanoma skin cancer (Brash et al., 1996). Furthermore, there is also considerable evidence that DNA photodamage, especially CPD, initiates many of the immunological effects of UVR (Yarosh, 2004). Given the significance of DNA photodamage, it is not surprising that living organisms have developed highly effective DNA repair mechanisms. Studies in our laboratory and by others have shown that, after a single exposure of SSR, ((6–4) pp) repair in human skin in situ is relatively rapid and that CPD repair is much slower with many lesions persisting for at least 24 h (Bykov et al., 1999; Young et al., 1996). Such slow repair also means that lesion induction may be cumulative if skin is exposed to UVR the following day, as is the case in “real life.” There is also evidence that cytosinecontaining lesions (C = C, C = T) are repaired more rapidly than those with thymine only (T = T) (Bykov et al., 1999; Xu et al., 2000). Apart from the DNA repair response, it might also be expected that photoprotection by melanin would include protection against DNA photodamage in situ. One study compared the SSR induction of T = T in white and black skin ex vivo and came to the conclusion that constitutive pigmentation afforded DNA protection factors of 2–4 (Strickland et al., 1988). Bykov et al. (2000) reported an inverse relationship between constitutive pigmentation in white-skinned people and UVB-induced epidermal DNA photodamage. Tadokoro et al. (2003) reported fewer CPD in skins with high levels of constitutive melanin after a dose of about 1 MED. Some studies have assessed the ability of UVRinduced pigmentation in white skin to protect epidermal cells from CPD by a subsequent challenge dose of UVR. Gange et al. (1985) reported that UVB- and UVA-induced tans, in people who tanned well, resulted in protection factors of about 2–3 against the induction of epidermal CPD by UVB. Sheehan et al. (2002) treated skin types II and IV with 0.65 MED SSR for 2 weeks and exposed SSR-treated and untreated skin to 2 MED SSR 1 week after the last tanning treatment. An analysis of the data, taking into account CPD caused by the tanning treatment, showed that pigmentation was associated with a DNA protection factor of about 2–3. Surprisingly, despite the superior tan in skin type IV, the level of photoprotection was not significantly higher than in skin type II. Assessment of photoprotection against erythema was also made, and the protection factors for erythema and CPD were virtually identical, as might be expected in that DNA is the chromophore for erythema. These data are in contrast to those of Gange et al. (1985) who, as stated above, reported that comparable UVB- and UVA-induced tans gave comparable protection against UVB-induced CPD, but that only the UVB tan resulted in protection against UVB-induced erythema with a protection factor of 3. These data, as do those of Tadokoro et al. (2003) described above, suggest a lack of relationship between DNA photodamage and erythema. In a study of skin explants taken from habitually sunexposed skin from two people of skin type III, Kobayashi et al. (1998) showed an inverse relationship between the level of melanin in supranuclear caps and UVB-induced DNA photodamage in the corresponding keratinocytes. The authors 347
CHAPTER 17
showed DNA protection factors ranging from just over 1 to about 5. Barker et al. (1995) compared the UVB dose–responses for CPD in vitro in human melanocytes of different skin types. Melanocytes from skin types IV–VI showed much more tyrosinase activity and melanin than those from skin types I and II. However, the dose–response data show a relatively modest difference in CPD from a single UVB exposure that suggests a protection factor of less than 2. Melanocytes and adjacent basal layer keratinocytes in untanned human skin in situ show similar sensitivity to the induction of CPD by UVB and UVA, suggesting no inherent differences in sensitivity to DNA photodamage (Young et al., 1998a). In combination, the data from these two studies would suggest that melanocytes have no great advantage over keratinocytes in terms of photoprotection from DNA damage. Studies on reconstructed human skin with and without melanocytes from skin types II and III showed that the presence of melanocytes had no effect on the induction of CPD or ((6–4) pp) (Cario-Andre et al., 2000). This is perhaps not surprising, as melanin was not detected in the preparations. However, the presence of melanocytes inhibited the formation of apoptotic sunburn cells (SBC) that are considered to be a means of eliminating keratinocytes with mutagenic and therefore carcinogenic potential (Ziegler et al., 1994). In theory, a reduction in SBC is likely to enhance skin cancer risk. These data suggest that melanocytes might influence the effects of UVR in ways that are unrelated to melanin production. Rijken et al. (2004) compared the effects of a single 2-MED exposure of fluorescent SSR on white buttock skin (types I, II, and III) with comparable physical (i.e. suberythemal) doses on black buttock skin (type VI) in vivo. Subjective assessment of CPD by immunostaining showed comparable levels of CPD in all volunteers in the suprabasal epidermis when sampled immediately after irradiation. CPD was also seen in the basal epidermis and the dermis in the white skin types but not in skin type VI. Fisher et al. (2002) also reported similar differential of epidermal CPD in skin types I/III and V/VI after exposure to UVB plus UVA II (approximately fourfold higher doses in darker skin types) and UVA I (110 J/cm2 in both skin type groups) when samples were taken 24 h after irradiation, which allows time for repair. Both these studies also showed a reduction in other indicators of photodamage (e.g. induction of matrix metalloproteinases, infiltrating neutrophils) in black skin compared with white. Overall, these data suggest that melanin is photoprotective of basal layer DNA, but the experimental design does not provide any indication of the level of protection. However, the data of Fisher et al. (2002) could also be explained by possible skin type differential repair. Overall, several human studies suggest that the acute photoprotection afforded by constitutive and induced pigmentation against DNA photodamage in keratinocytes and melanocytes and erythema is equivalent to wearing a sunscreen with a sun protection factor (SPF) of 2–3. The generally comparable results with DNA photodamage and erythema provide additional evidence that DNA is an impor-
348
tant chromophore for erythema. Protection factors of 2–3 should result in a 50–60% reduction in biologically effective dose. Such a reduction, if maintained over long periods, would be significant in terms of long-term risk of skin cancer. However, the maintenance of a tan requires repeated exposure to UVR, from either the sun or an artificial source, and it is likely that this is associated with the accumulation of epidermal DNA photodamage (Sheehan et al., 2002) that may minimize the benefits of the protection. There are conflicting data about the role of a tan in affording protection against malignant melanoma in women, with Weinstock et al. (1991) suggesting that a tan may afford protection and Holly et al. (1995) reporting no benefit.
Is UVR-induced Melanogenesis an Indicator of DNA Repair? Extensive data suggest that DNA damage per se or DNA repair intermediates initiate melanogenesis, as summarized in Figure 17.2. Several studies have examined the effect of thymine dinucleotides (pTpT), as a model for thymine dimers, on pigmentation. Cloudman S91 mice melanoma cell lines show increased pigmentation in response to UVR. A sevenfold increase in melanin content was also observed after treatment with 50 mm of pTpT for 4 days compared with diluent-treated controls (Eller et al., 1994). Significantly, treatment of cells with pdApdA (a dinucleotide rarely seen as a photoproduct) showed only modest increases in melanin content of 20–30%. These results suggest that the response is specific to UVRinduced DNA damage products. However, agents that induce single-strand DNA breaks are also able to stimulate melanogenesis in vitro (Eller et al., 1996). Cells treated with pTpT displayed not only an increase in melanin content, but also a two- to threefold rise in mRNA for tyrosinase. Interestingly, a rise in tyrosinase levels was noted within 4 h of the addition of pTpT, which is well before mRNA changes were detectable. It would thus appear that pTpT influences gene expression at both the mRNA and the protein level (Eller et al., 1994). In addition to these in vitro studies, in vivo experiments on shaved guinea-pig skin have demonstrated that the topical application of pTpT twice daily for 5 days was able to induce a visible tanning after 1 week, reaching a maximum 1–2 weeks later. When skin sections were examined histologically, they demonstrated the presence of melanin, primarily in the basal epithelial layers, but also in suprabasal caps over nuclei (Eller et al., 1994). This is analogous to the picture seen in the human tanning response. The significance of the dipyrimidine form in inducing a tanning response was verified by Pedeux et al. (1998). Induction of pigmentation in human melanocyte and melanoma cells was demonstrable in response to the dinucleotide pTpT but not the monomer pT alone. Addition of pTpT in concentrations capable of inducing a pigmentary response was not cytotoxic to the cells, and no increase in apoptosis was observed. Treated melanoma cell lines did however show a
PHOTOBIOLOGY OF MELANINS
temporary arrest in the S phase of the cell cycle 24 h after the addition of pTpT, with resumption to normal cycling by 48 h. The mechanism and significance of this phenomenon are yet to be understood. The capacity of DNA photoproducts to induce pigmentation varies with oligonucleotide length and base composition. Although initial studies were largely carried out on pTpT, other DNA fragments are also able to stimulate pigmentation. For example, the p9-mer oligonucleotide pGpApGpTp ApTpGpApG and the p7-mer pApGpTpApTpGpA stimulated melanogenesis in Cloudman S91 murine melanoma cells by up to 800% compared with controls, whereas the p5-mer pCpApTpApC had no effect (Hadshiew et al., 2001). T4 endonuclease V (T4N5) is a bacterial phage enzyme which, apart from catalyzing the rate-limiting step in excision of CPDs, has no other recognized function (Grossman et al., 1988). T4N5 has been shown to accelerate repair of CPD in both cultured cells (Ceccoli et al., 1989; Yarosh et al., 1992) and intact skin (Yarosh, 1990). The effects of this enzyme on pigmentation following UVR have been studied in vitro. Both murine S91 melanoma cells and human melanocytes demonstrated greater melanogenesis (with an almost doubling of melanin content) when treated with T4N5 after irradiation compared with treatment with either diluent alone or heatinactivated enzyme (Gilchrest et al., 1993). These results suggest that accelerated and extensive excision of CPD enhances tanning. A photoprotective effect of DNA fragments has been shown in animal studies. Guinea pigs were treated with topical application of pTpT for 1 month to induce tanning (Gilchrest and Eller, 1999). Their shaved skin was then exposed to a previously determined 6 MED of UVB, and biopsies were taken from both UV-irradiated treated and untreated skin at the height of sunburn reaction (24 h after irradiation). Fontana Mason staining revealed higher melanin content in pTpT treated compared with untreated skin. Routine hematoxylin and eosin staining revealed extensive epidermal necrosis with intraepidermal blistering in UV-irradiated untreated skin. In contrast, pTpT-treated irradiated skin showed no histological damage and was almost indistinguishable from unirradiated skin apart from slight increases in basilar and suprabasilar melanin. Thus, it was concluded that pTpT was fully protective to 6 MED. This capacity of small DNA fragments, especially pTpT, to induce protective tanning responses in the absence of DNA damage has far-reaching therapeutic implications. Topical application of these products may potentially be used to provide a photoprotective tan without the harmful effects of UVR. Sheehan et al. (2002) reported that 10 repeated weekday doses of 0.65 MED SSR resulted in more cumulative CPD in skin type IV than in skin type II, almost certainly because skin types IV have higher MEDs than skin types II. When skin biopsies were examined 1 week after treatment, there was a nonsignificant reduction in lesions in skin type II but significant loss in skin type IV. These data suggest better DNA repair
in skin type IV, which is in accordance with the hypothesis that tanning is associated with DNA repair (Gilchrest and Eller, 1999). Such a hypothesis would suggest that the inverse relationship between skin type and skin cancer, as indicated in Table 17.1, is a consequence of DNA capacity rather than, or as well as, the ability of melanin to act as a photoprotective agent. Recent data suggest that aMSH, associated with the tanning process especially eumelanogenesis (Thody and Graham, 1998), may enhance repair of UVR-induced DNA damage (Böhm et al., 2004).
Mechanism of pTpT-induced Tanning Repair of DNA photolesions requires cell cycle arrest prior to replication and mitosis (Murray, 1992). The tumor suppressor gene p53, known as guardian of the genome, plays a vital role in the repair of DNA and apoptosis. pTpT directly activates p53, with treated cells demonstrating reduced proliferative rates and upregulation of p53-mediated p21, a protein known to mediate cell cycle arrest (Eller et al., 1997). Nuclear translocation of p53 was also observed, a known indicator of p53 activation. Thus, the data unequivocally suggest that pTpT acts at least partially via induction of p53, which regulates tyrosinase gene expression (Khlgation et al., 2002). It has been hypothesized that the DNA photodamage to the telomere 3¢ overhang (TTAGGG) may be a specific trigger for the cellular defense responses to UVR (Eller et al., 2003) and that this is the reason why oligonucleotides with homology (i.e. TT) to this sequence are able to induce such responses as p53 activation.
Melanin Synthesis may be a Damage Response System Although the major DNA photoproducts CPD and 6–4PP are excised by a well-recognized family of DNA repair proteins, the metabolic fate of the excised photoproduct containing a single-stranded DNA (ssDNA) fragment is relatively understudied. In bacterial studies, however, it has been demonstrated that ssDNA plays an important role in photoprotection. Single-strand DNA in prokaryote systems generated from DNA damage/repair interacts and activates a protease, the Rec A protein. Rec A is then responsible for the lifting of repression of over 40 genes important in DNA repair, replication, and cell survival (Courcelle and Hanawalt, 2003). This phenomenon, known as the SOS response, not only increases bacterial survival after irradiation, but also enhances resistance to subsequent UVR-induced DNA damage. Thus, repeat exposure to a sublethal dose of UVR in these bacteria would result in more efficient repair of DNA damage and enhanced survival (Crowley and Hanawalt, 1998). It has been postulated that tanning may form part of a mammalian SOS response (Eller and Gilchrest, 2000).
Immunosuppression by UVR There is considerable evidence that UVR-induced immunosuppression may play a role in skin cancer, and animal studies
349
CHAPTER 17
also suggest a role for susceptibility to infectious disease (Sleijffers et al., 2002). There have been two human studies on the photoprotective effects of melanin on UVR-induced immunosuppression (Selgrade et al., 2001; Vermeer et al., 1991), and both came to the conclusion that pigmentation, even in dark-skinned people, had no effect on the ability of UVR to suppress the induction phase of the contact hypersensitivity (CHS) response, which is regarded as a model for some of the photoimmunological events that are important in skin cancer. The reasons for this are not known, but one explanation would be that a superficial chromophore such as stratum corneum urocanic acid (UCA) is more important than epidermal DNA. Mouse studies have shown that photoimmunosuppression is initiated via either DNA or UCA depending on the viability of the antigen (Kim et al., 2003).
Photosensitization by Molecules Associated with Melanogenesis It has been reported that albinos, who have tyrosinasedeficient melanocytes (i.e. not producing melanin), are prone to nonmelanoma skin cancers but not malignant melanoma (Streutker et al., 2000). This suggests the possibility of melanogenesis-related photosensitization in malignant melanoma. Several in vitro studies have identified photosensitizing properties of melanins or their intermediates (Hill, 1992; Kvam and Dahle, 2004). 5-SCD photobinds to native DNA after exposure to 300-nm radiation and also induced single-strand breaks (SSB) in DNA (Koch and Chedekel, 1986). More recently, it has been reported that 5-SCD is photochemically unstable in the presence of UVA radiation and oxygen (Costantini et al., 1994) and that the eumelaninsoluble precursor DHICA sensitizes DNA SSB with 313-nm exposure, especially in the presence of oxygen (Routaboul et al., 1995). Kipp and Young (1999) showed that the addition of DHICA to human keratinocytes increased their sensitivity to UVA-induced SSB by the generation of ROS. Kvam and Tyrrell (1999) concluded that melanogenesis, but not melanin itself, was associated with oxidative base damage in human melanoma cells. Wenczl et al. (1998) compared the UVA sensitivity of melanocytes from skin type I and skin type IV that had been induced to synthesize melanins by a high concentration of l-tyrosine in the culture medium. The ratio of pheomelanin to total melanin remained the same in skin type IV, but relatively more pheomelanin was induced in skin type I. This was associated with an increase in UVA-induced SSB in DNA. In recent in vivo studies in different mouse strains, Takeuchi et al. (2004) have reported that melanins, in particular pheomelanin, are UVB and UVA photosensitizers in mammalian skin in vivo. It should be stressed that the clinical significance, if any, of these reactions is unknown, but they clearly demonstrate the photobiological potential of melanogenesis intermediates, and it is therefore possible that pheomelanin plays a role in the susceptibility of skin types to skin cancer and other types of photodamage. 350
Pheomelanin
Photosensitization
Eumelanin
Photoprotection
Fig. 17.3. Solar UVR activates melanocytes to initiate the synthesis of a mix of pheomelanin or eumelanin in specialized organelles called melanosomes (represented by the oval structures). The balance of melanin type depends on genetic factors such as skin type. Pheomelanin and eumelanin and their precursors interact in different ways with solar UVR. Pheomelanogenesis may favor photosensitization via ROS, whereas eumelanin is more likely to favor photoprotection.
Perspectives Exposure to solar UVR, especially UVB, results in epidermal DNA photodamage such as CPD that, if unrepaired, can result in mutation, immunosuppression, and consequent skin cancer, especially in people who do not tan readily. Despite concerted public health campaigns and increased awareness of the hazards of UVR, the incidence of skin cancer continues to rise in white-skinned populations. Indeed, a tan is still widely regarded as a desirable sign of health and well-being, especially by the young, and is often justified by its photoprotective properties, which are relatively modest even in those who tan well. The level of photoprotection may ultimately depend on the ratio of pheomelanin to eumelanin as indicated in Figure 17.3, as there is experimental evidence to suggest that pheomelanin may be associated with photosensitization.
PHOTOBIOLOGY OF MELANINS
There is increasing evidence that melanogenesis is initiated by CPD and its repair and may therefore be seen as a biomarker for DNA repair capacity which, in white-skinned people at least, may be more important in skin cancer prevention than in optical photoprotection. The relationship between DNA damage/repair potentially has major therapeutic implications given that topical application of small DNA fragments may induce melanogenesis and a measure of photoprotection, without the harmful effects of UVR. In effect, this may make a skin type II respond more like a skin type IV, and this is an area for further research from which there may be significant public health benefit.
References Alaluf, S., A. Heath, N. Carter, D. Atkins, H. Mahalingam, K. Barrett, R. Kolb, and N. Smit. Variation in melanin content and composition in type V and VI photoexposed and photoprotected human skin: the dominant role of DHI. Pigment Cell Res. 14:337–347, 2001. Alaluf, S., D. Atkins, K. Barrett, M. Blount, N. Carter, and A. Heath. Ethnic variation in melanin content and composition in photoexposed and photoprotected human skin. Pigment Cell Res. 15:112–118, 2002. Alaluf, S., K. Barrett, M. Blount, and N. Carter. Ethnic variation in tyrosinase and TYRP1 expression in photoexposed and photoprotected human skin. Pigment Cell Res. 16:35–42, 2003. Barker, D., K. Dixon, E. E. Medrano, D. Smalara, S. Im, D. Mitchell, G. Babcock, and Z. A. Abdel-Malek. Comparison of the responses of human melanocytes with different melanin contents to ultraviolet B irradiation. Cancer Res. 55:4041–4046, 1995. Bessou-Touya, S., M. Picardo, V. Maresca, J. E. Surleve-Bazeille, C. Pain, and A. Taieb. Chimeric human epidermal reconstructs to study the role of melanocytes and keratinocytes in pigmentation and photoprotection. J. Invest. Dermatol. 111:1103–1108, 1998. Bischoff-Ferrari, H. A., T. Dietrich, E. J. Orav, and B. DawsonHughes. Positive association between 25-hydroxy vitamin D levels and bone mineral density: a population-based study of younger and older adults. Am. J. Med. 116:634–639, 2004. Blum, H. F. Does the melanin pigment of human skin have adaptive value? An essay in human ecology and the evolution of race. Q. Rev. Biol. 36:50–63, 1961. Böhm, M., I. Wolff, T. E. Scholzen, S. J. Robinson, E. Healy, T. A. Luger, T. Schwarz, and A. Schwarz. Alpha-melanocyte-stimulating hormone protects from ultraviolet radiation-induced apoptosis and DNA damage. J. Biol. Chem. 280:5795–5802, 2005. Brash, D. E., A. Ziegler, A. S. Jonason, J. A. Simon, S. Kunala, and D. J. Leffell. Sunlight and sunburn in human skin cancer: p53, apoptosis, and tumor promotion. J. Invest. Dermatol. Symp. Proc. 1:136–142, 1996. Brazerol, W. F., A. J. McPhee, F. Mimouni, B. L. Specker, and R. C. Tsang. Serial ultraviolet B exposure and serum 25 hydroxyvitamin D response in young adult American blacks and whites: no racial differences. J. Am. Coll. Nutr. 7:111–118, 1988. Bykov, V. J., J. M. Sheehan, K. Hemminki, and A. R. Young. In situ repair of cyclobutane pyrimidine dimers and 6–4 photoproducts in human skin exposed to solar simulating radiation. J. Invest. Dermatol. 112:326–331, 1999. Bykov, V. J., J. A. Marcusson, and K. Hemminki. Effect of constitutional pigmentation on ultraviolet B-induced DNA damage in fairskinned people. J. Invest. Dermatol. 114:40–43, 2000. Cario-Andre, M., C. Pain, Y. Gall, J. Ginestar, O. Nikaido, and A. Taieb. Studies on epidermis reconstructed with and without melanocytes: melanocytes prevent sunburn cell formation but not
appearance of DNA damaged cells in fair-skinned caucasians. J. Invest. Dermatol. 115:193–199, 2000. Ceccoli, J., N. Rosales, J. Tsimis, and D. B. Yarosh. Encapsulation of the UV-DNA repair enzyme T4 endonuclease V in liposomes and delivery to human cells. J. Invest. Dermatol. 93:190–194, 1989. Chadwick, C. A., C. S. Potten, O. Nikaido, T. Matsunaga, C. Proby, and A. R. Young. The detection of cyclobutane thymine dimers, (6–4) photolesions and the Dewar photoisomers in sections of UVirradiated human skin using specific antibodies, and the demonstration of depth penetration effects. J. Photochem. Photobiol. B 28:163–170, 1995. Chedekel, M. R. Photophysics and photochemistry of melanin. In: Melanin: Its Role in Human Photoprotection, L. Zeise, M. R. Chedekel, T. B. Fitzpatrick (eds). Overland Park, KA: Valdenmar Publishing Company, 1985, pp. 11–22. Chu D. H., A. R. Haake, K. Holbrook, and C. A. Loomis. The structure and development of skin. In: Dermatology in General Medicine, I. M. Freedburg, A. Z. Eisen, K. Wolff, K. F. Austen, L. A. Goldsmith, and S. I. Katz (eds). New York: McGraw-Hill, 2003, pp. 58–88. Clemens, T. L., J. S. Adams, S. L. Henderson, and M. F. Holick. Increased skin pigment reduces the capacity of skin to synthesise vitamin D3. Lancet 1:74–76, 1982. Costantini, C., M. d’Ischia, A. Palumbo, and G. Prota. Photochemistry of 5-S-cysteinyldopa. Photochem. Photobiol. 60:33–37, 1994. Courcelle, J., and P. C. Hanawalt. RecA-dependent recovery of arrested DNA replication forks. Annu. Rev. Genet. 37:611–646, 2003. Cripps, D. J. Natural and artificial photoprotection. J. Invest. Dermatol. 77:154–157, 1981. Crowley, D. J., and P. C. Hanawalt. Induction of the SOS response increases the efficiency of global nucleotide excision repair of cyclobutane pyrimidine dimers, but not 6–4 photoproducts, in UVirradiated Escherichia coli. J. Bacteriol. 180:3345–3352, 1998. de Gruijl, F. R. Action spectrum for photocarcinogenesis. Recent Results Cancer Res. 139:21–30, 1995. Devgun, M. S., C. R. Paterson, B. E. Johnson, and C. Cohen. Vitamin D nutrition in relation to season and occupation. Am. J. Clin. Nutr. 34:1501–1504, 1981. Duval, C., N. P. Smit, A. M. Kolb, M. Regnier, S. Pavel, and R. Schmidt. Keratinocytes control the pheo/eumelanin ratio in cultured normal human melanocytes. Pigment Cell Res. 15:440–446, 2002. Eller, M. S., and B. A. Gilchrest. Tanning as part of the eukaryotic SOS response. Pigment Cell Res. 13 Suppl. 8:94–97, 2000. Eller, M. S., M. Yaar, and B. A. Gilchrest. DNA damage and melanogenesis. Nature 372:413–414, 1994. Eller, M. S., K. Ostrom, and B. A. Gilchrest. DNA damage enhances melanogenesis. Proc. Natl. Acad. Sci. USA 93:1087–1092, 1996. Eller, M. S., T. Maeda, C. Magnoni, D. Atwal, and B. A. Gilchrest. Enhancement of DNA repair in human skin cells by thymidine dinucleotides: evidence for a p53-mediated mammalian SOS response. Proc. Natl. Acad. Sci. USA 94:12627–12632, 1997. Eller, M. S., G. Z. Li, R. Firoozabadi, N. Puri, and B. A. Gilchrest. Induction of a p95/Nbs1-mediated S phase checkpoint by telomere 3¢ overhang specific DNA. FASEB J. 17:152–162, 2003. Fisher, G. J., S. Kang, J. Varani, Z. Bata-Csorgo, Y. Wan, S. Datta, and J. J. Voorhees. Mechanisms of photoaging and chronological skin aging. Arch. Dermatol. 138:1462–1470, 2002. Fitzpatrick, T. B., and A. S. Breathnach. [The epidermal melanin unit system.] Dermatol. Wochenschr. 147:481–489, 1963. Gange, R. W., A. D. Blackett, E. A. Matzinger, B. M. Sutherland, and I. E. Kochevar. Comparative protection efficiency of UVA- and UVB-induced tans against erythema and formation of endonuclease-sensitive sites in DNA by UVB in human skin. J. Invest. Dermatol. 85:362–364, 1985. Giacomoni, P. U. Open questions in photobiology. III. Melanin and photoprotection. J. Photochem. Photobiol. B 29:87–89, 1995. Gilchrest, B. A., and M. S. Eller. DNA photodamage stimulates
351
CHAPTER 17 melanogenesis and other photoprotective responses. J. Invest. Dermatol. Symp. Proc. 4:35–40, 1999. Gilchrest, B. A., H. Y. Park, M. S. Eller, and M. Yaar. Mechanism of ultraviolet light-induced pigmentation. Photochem. Photobiol. 63:1–6, 1996. Gilchrest, B. A., S. Zhai, M. S. Eller, D. B. Yarosh, and M. Yaar. Treatment of human melanocytes and S91 melanoma cells with the DNA repair enzyme T4 endonuclease V enhances melanogenesis after ultraviolet irradiation. J. Invest. Dermatol. 101:666–672, 1993. Gniadecka, M., H. C. Wulf, N. N. Mortensen, and T. Poulsen. Photoprotection in vitiligo and normal skin. A quantitative assessment of the role of stratum corneum, viable epidermis and pigmentation. Acta Derm. Venereol. 76:429–432, 1996. Grossman, L., P. R. Caron, S. J. Mazur, and E. Y. Oh. Repair of DNA-containing pyrimidine dimers. FASEB J. 2:2696–2701, 1988. Ha, T., H. Javedan, K. Waterston, L. Naysmith, and J. L. Rees. The relationship between constitutive pigmentation and sensitivity to ultraviolet radiation induced erythema is dose-dependent. Pigment Cell Res. 16:477–479, 2003. Hadshiew, I. M., M. S. Eller, F. P. Gasparro, and B. A. Gilchrest. Stimulation of melanogenesis by DNA oligonucleotides: effect of size, sequence and 5¢ phosphorylation. J. Dermatol. Sci. 25:127–138, 2001. Halaban, R., D. N. Herbert, and D E. Fisher. Biology of melanocytes. In: Dermatology in General Medicine, I. M. Freedburg, A. Z. Eisen, K. F. Wolff, K. F. Austen, L. A. Goldsmith, and S. I. Katz (eds). New York: McGraw-Hill, 2003, pp. 127–148. Hamson, C., L. Goh, P. Sheldon, and A. Samanta. Comparative study of bone mineral density, calcium, and vitamin D status in the Gujarati and white populations of Leicester. Postgrad. Med. J. 79:279–283, 2003. Harrison, G. I., and A. R. Young. Ultraviolet radiation-induced erythema in human skin. Methods 28:14–19, 2002. Hill, H. Z. The function of melanin or six blind people examine an elephant. Bioessays 14:49–56, 1992. Hill, H. Z., and G. J. Hill. UVA, pheomelanin and the carcinogenesis of melanoma. Pigment Cell Res. 13 Suppl. 8:140–144, 2000. Holly, E. A., D. A. Aston, R. D. Cress, D. K. Ahn, and J. J. Kristiansen. Cutaneous melanoma in women. I. Exposure to sunlight, ability to tan, and other risk factors related to ultraviolet light. Am. J. Epidemiol. 141:923–933, 1995. Home E. On the black rete mucosum of the Negro being a defence against the scorching effect of the sun’s rays. Phil. Trans. R. Soc. London Biol. 110:1–7, 1820. Irwin, C., A. Barnes, D. Veres, and K. Kaidbey. An ultraviolet radiation action spectrum for immediate pigment darkening. Photochem. Photobiol. 57:504–507, 1993. Ito, S., and K. Wakamatsu. Quantitative analysis of eumelanin and pheomelanin in humans, mice, and other animals: a comparative review. Pigment Cell Res. 16:523–531, 2003. Iwata, M., T. Corn, S. Iwata, M. A. Everett, and B. B. Fuller. The relationship between tyrosinase activity and skin color in human foreskins. J. Invest. Dermatol. 95:9–15, 1990. Jablonski, N. G., and G. Chaplin. The evolution of human skin coloration. J. Hum. Evol. 39:57–106, 2000. Kelly, D. A., A. R. Young, J. M. McGregor, P. T. Seed, C. S. Potten, and S. L. Walker. Sensitivity to sunburn is associated with susceptibility to ultraviolet radiation-induced suppression of cutaneous cell-mediated immunity. J. Exp. Med. 191:561–566, 2000. Kerb, R., J. Brockmoller, T. Reum, and I. Roots. Deficiency of glutathione S-transferases T1 and M1 as heritable factors of increased cutaneous UV sensitivity. J. Invest. Dermatol. 108:229–232, 1997. Khlgatian, M. K., I. M. Hadshiew, P. Asawanonda, M. Yaar, M. S. Eller, M. Fujita, D. A. Norris, and B. A. Gilchrest. Tyrosinase gene expression is regulated by p53. J. Invest. Dermatol. 118:126–132, 2002.
352
Kim, T. H., A. M. Moodycliffe, D. B. Yarosh, M. Norval, M. L. Kripke, and S. E. Ullrich. Viability of the antigen determines whether DNA or urocanic acid act as initiator molecules for UVinduced suppression of delayed-type hypersensitivity. Photochem. Photobiol. 78:228–234, 2003. Kipp, C., and A. R. Young. The soluble eumelanin precursor 5,6dihydroxyindole-2-carboxylic acid enhances oxidative damage in human keratinocyte DNA after UVA irradiation. Photochem. Photobiol. 70:191–198, 1999. Kobayashi, N., A. Nakagawa, T. Muramatsu, Y. Yamashina, T. Shirai, M. W. Hashimoto, Y. Ishigaki, T. Ohnishi, and T. Mori. Supranuclear melanin caps reduce ultraviolet induced DNA photoproducts in human epidermis. J. Invest. Dermatol. 110:806–810, 1998. Koch, W. H., and M. R. Chedekel. Photoinitiated DNA damage by melanogenic intermediates in vitro. Photochem. Photobiol. 44:703–710, 1986. Kollias, N., R. M. Sayre, L. Zeise, and M. R. Chedekel. Photoprotection by melanin. J. Photochem. Photobiol. B 9:135–160, 1991. Kollias, N., A. Baqer, and I. Sadiq. Minimum erythema dose determination in individuals of skin type V and VI with diffuse reflectance spectroscopy. Photodermatol. Photoimmunol. Photomed. 10:249–254, 1994. Kvam, E., and R. M. Tyrrell. The role of melanin in the induction of oxidative DNA base damage by ultraviolet A irradiation of DNA or melanoma cells. J. Invest. Dermatol. 113:209–213, 1999. Kvam, E., and J. Dahle. Melanin synthesis may sensitize melanocytes to oxidative DNA damage by ultraviolet A radiation and protect melanocytes from direct DNA damage by ultraviolet B radiation. Pigment Cell Res. 17:549–550, 2004. Lavker, R. M., and K. H. Kaidbey. Redistribution of melanosomal complexes within keratinocytes following UV-A irradiation: a possible mechanism for cutaneous darkening in man. Arch. Dermatol. Res. 272:215–228, 1982. Matsuoka, L. Y., J. Wortsman, J. G. Haddad, and B. W. Hollis. In vivo threshold for cutaneous synthesis of vitamin D3. J. Lab. Clin. Med. 114:301–305, 1989. Matsuoka, L. Y., J. Wortsman, J. G. Haddad, and B. W. Hollis. Skin types and epidermal photosynthesis of vitamin D3. J. Am. Acad. Dermatol. 23:525–526, 1990. Matsuoka, L. Y., J. Wortsman, J. G. Haddad, P. Kolm, and B. W. Hollis. Racial pigmentation and the cutaneous synthesis of vitamin D. Arch. Dermatol. 127:536–538, 1991. Morison, W. L. What is the function of melanin? Arch. Dermatol. 121:1160–1163, 1985. Murray, A. W. Creative blocks: cell-cycle checkpoints and feedback controls. Nature 359:599–604, 1992. Okoro, A. N. Albinism in Nigeria. A clinical and social study. Br. J. Dermatol. 92:485–492, 1975. Parrish, J. A., K. F. Jaenicke, and R. R. Anderson. Erythema and melanogenesis action spectra of normal human skin. Photochem. Photobiol. 36:187–191, 1982. Pedeux, R., N. Al Irani, C. Marteau, F. Pellicier, R. Branche, M. Ozturk, J. Franchi, and J. F. Dore. Thymidine dinucleotides induce S phase cell cycle arrest in addition to increased melanogenesis in human melanocytes. J. Invest. Dermatol. 111:472–477, 1998. Pomerantz, S. H., and I. G. Ances. Tyrosinase activity in human skin. Influence of race and age in newborns. J. Clin. Invest. 55:1127–1131, 1975. Rijken, F., P. L. Bruijnzeel, H. van Weelden, and R. C. Kiekens. Responses of black and white skin to solar-simulating radiation: differences in DNA photodamage, infiltrating neutrophils, proteolytic enzymes induced, keratinocyte activation, and IL-10 expression. J. Invest. Dermatol. 122:1448–1455, 2004. Rosen, C. F., S. L. Jacques, M. E. Stuart, and R. W. Gange. Immediate pigment darkening: visual and reflectance spectrophotometric analysis of action spectrum. Photochem. Photobiol. 51:583–588, 1990.
PHOTOBIOLOGY OF MELANINS Routaboul, C., C. L. Serpemtini, P. Msika, J.-P. Cesarini, and N. Paillous. Photosensitization of supercoiled DNA damage by 5–6dihydroxyindole-2-carboxylic acid, a precursor of eumelanin. Photochem. Photobiol. 62:469–475, 1995. Routaboul, C., A. Denis, and A. Vinche. Immediate pigment darkening: description, kinetic and biological function. Eur. J. Dermatol. 9:95–99, 1999. Sander, C. S., H. Chang, F. Hamm, P. Elsner, and J. J. Thiele. Role of oxidative stress and the antioxidant network in cutaneous carcinogenesis. Int. J. Dermatol. 43:326–335, 2004. Scotto, J. K., and F. Fraummeni. Skin cancer (other than melanoma). In: Cancer Epidemiology and Prevention, D. Schottenfeld, and F. Fraummeni (eds). Philadelphia: Saunders, 1982, pp. 996–1011. Selgrade, M. K., M. V. Smith, L. J. Oberhelman-Bragg, G. J. LeVee, H. S. Koren, and K. D. Cooper. Dose response for UV-induced immune suppression in people of color: differences based on erythemal reactivity rather than skin pigmentation. Photochem. Photobiol. 74:88–95, 2001. Sheehan, J. M., C. S. Potten, and A. R. Young. Tanning in human skin types II and III offers modest photoprotection against erythema. Photochem. Photobiol. 68:588–592, 1998. Sheehan, J. M., N. Cragg, C. A. Chadwick, C. S. Potten, and A. R. Young. Repeated ultraviolet exposure affords the same protection against DNA photodamage and erythema in human skin types II and IV but is associated with faster DNA repair in skin type IV. J. Invest. Dermatol. 118:825–829, 2002. Sleijffers, A., J. Garssen, and H. van Loveren. Ultraviolet radiation, resistance to infectious diseases, and vaccination responses. Methods 28:111–121, 2002. Stamatas, G. N., B. Z. Zmudzka, N. Kollias, and J. Z. Beer. Noninvasive measurements of skin pigmentation in situ. Pigment Cell Res. 17:618–626, 2004. Stamp, T. C. Factors in human vitamin D nutrition and in the production and cure of classical rickets. Proc. Nutr. Soc. 34:119–130, 1975. Streutker, C. J., D. McCready, K. Jimbow, and L. From. Malignant melanoma in a patient with oculocutaneous albinism. J. Cutan. Med. Surg. 4:149–152, 2000. Strickland, P. T., M. Bruze, and J. Creasey. Cyclobuta-dithymidine induction by solar-simulating UV radiation in human skin. I. Protection by constitutive pigmentation. Photodermatology 5:166–169, 1988. Tadokoro, T., N. Kobayashi, B. Z. Zmudzka, S. Ito, K. Wakamatsu, Y. Yamaguchi, K. S. Korossy, S. A. Miller, J. Z. Beer, and V. J. Hearing. UV-induced DNA damage and melanin content in human skin differing in racial/ethnic origin. FASEB J. 17:1177–1179, 2003. Takeuchi, S., W. Zhang, K. Wakamatsu, S. Ito, V. J. Hearing, K. H. Kraemer, and D. E. Brash. Melanin acts as a potent UVB photosensitizer to cause an atypical mode of cell death in murine skin. Proc. Natl. Acad. Sci. USA 101:15076–15081, 2004. Thody, A. J., E. M. Higgins, K. Wakamatsu, S. Ito, S. A. Burchill, and J. M. Marks. Pheomelanin as well as eumelanin is present in human epidermis. J. Invest. Dermatol. 97:340–344, 1991. Thody, A. J., and A. Graham. Does alpha-MSH have a role in regulating skin pigmentation in humans? Pigment Cell Res. 11:265–274, 1998. Thong, H. Y., S. H. Jee, C. C. Sun, and R. E. Boissy. The patterns of melanosome distribution in keratinocytes of human skin as one determining factor of skin colour. Br. J. Dermatol. 149:498–505, 2003. Ullrich, S. E. Photoimmune suppression and photocarcinogenesis. Front. Biosci. 7:d684–d703, 2002. van Nieuwpoort, F., N. P. Smit, R. Kolb, H. van der Meulen,
H. Koerten, and S. Pavel. Tyrosine-induced melanogenesis shows differences in morphologic and melanogenic preferences of melanosomes from light and dark skin types. J. Invest. Dermatol. 122:1251–1255, 2004. Vermeer, M., G. J. Schmieder, T. Yoshikawa, J. W. van den Berg, M. S. Metzman, J. R. Taylor, and J. W. Streilein. Effects of ultraviolet B light on cutaneous immune responses of humans with deeply pigmented skin. J. Invest. Dermatol. 97:729–734, 1991. Vieth, R., D. E. Cole, G. A. Hawker, H. M. Trang, and L. A. Rubin. Wintertime vitamin D insufficiency is common in young Canadian women, and their vitamin D intake does not prevent it. Eur. J. Clin. Nutr. 55:1091–1097, 2001. Vitkin, I. A., J. Woolsey, B. C. Wilson, and R. R. Anderson. Optical and thermal characterization of natural (Sepia officinalis) melanin. Photochem. Photobiol. 59:455–462, 1994. Webb, A. R., L. Kline, and M. F. Holick. Influence of season and latitude on the cutaneous synthesis of vitamin D3: exposure to winter sunlight in Boston and Edmonton will not promote vitamin D3 synthesis in human skin. J. Clin. Endocrinol. Metab. 67:373–378, 1988. Weinstock, M. A., G. A. Colditz, W. C. Willett, M. J. Stampfer, B. R. Bronstein, M. C. Mihm, Jr, and F. E. Speizer. Melanoma and the sun: the effect of swimsuits and a “healthy” tan on the risk of nonfamilial malignant melanoma in women. Am. J. Epidemiol. 134:462–470, 1991. Wenczl, E., G. P. Van der Schans, L. Roza, R. M. Kolb, A. J. Timmerman, N. P. Smit, S. Pavel, and A. A. Schothorst. (Pheo)melanin photosensitizes UVA-induced DNA damage in cultured human melanocytes. J. Invest. Dermatol. 111:678–682, 1998. Xu, G., E. Snellman, V. J. Bykov, C. T. Jansen, and K. Hemminki. Effect of age on the formation and repair of UV photoproducts in human skin in situ. Mutat. Res. 459:195–202, 2000. Yarosh, D., L. G. Alas, V. Yee, A. Oberyszyn, J. T. Kibitel, D. Mitchell, R. Rosenstein, A. Spinowitz, and M. Citron. Pyrimidine dimer removal enhanced by DNA repair liposomes reduces the incidence of UV skin cancer in mice. Cancer Res. 52:4227–4231, 1992. Yarosh, D. B. Topical application of liposomes. J. Photochem. Photobiol. B 6:445–449, 1990. Yarosh, D. B. DNA repair, immunosuppression, and skin cancer. Cutis 74:10–13, 2004. Young, A. R. The molecular and genetic effects of ultraviolet radiation on skin cells. In: Photodermatology, J. L. M. Hawk (ed.). London: Arnold, 1996, pp. 25–42. Young, A. R. Chromophores in human skin. Phys. Med. Biol. 42:789–802, 1997. Young, A. R., C. A. Chadwick, G. I. Harrison, J. L. Hawk, O. Nikaido, and C. S. Potten. The in situ repair kinetics of epidermal thymine dimers and 6–4 photoproducts in human skin types I and II. J. Invest. Dermatol. 106:1307–1313, 1996. Young, A. R., C. S. Potten, O. Nikaido, P. G. Parsons, J. Boenders, J. M. Ramsden, and C. A. Chadwick. Human melanocytes and keratinocytes exposed to UVB or UVA in vivo show comparable levels of thymine dimers. J. Invest. Dermatol. 111:936–940, 1998a. Young, A. R., C. A. Chadwick, G. I. Harrison, O. Nikaido, J. Ramsden, and C. S. Potten. The similarity of action spectra for thymine dimers in human epidermis and erythema suggests that DNA is the chromophore for erythema. J. Invest. Dermatol. 111:982–988, 1998b. Ziegler, A., A. S. Jonason, D. J. Leffell, J. A. Simon, H. W. Sharma, J. Kimmelman, L. Remington, T. Jacks, and D. E. Brash. Sunburn and p53 in the onset of skin cancer. Nature 372:773–776, 1994. Zittermann, A. Vitamin D in preventive medicine: are we ignoring the evidence? Br. J. Nutr. 89:552–572, 2003.
353
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
18
Toxicological Aspects of Melanin and Melanogenesis Edward J. Land, Christopher A. Ramsden, and Patrick A. Riley
Summary 1 The major contributor to surface pigmentation in vertebrates is melanin. The precise structure of melanin is not clear, but it comprises conjugated indolic moieties that endow the material with strong light-absorptive properties. Eumelanins are dark brown or black, whereas pheomelanins are lighter variant molecules incorporating sulfur atoms. 2 Mammalian melanin is derived from tyrosine by a series of reactions that initially involve oxidation to dopaquinone. The enzyme responsible for this step is tyrosinase, which is synthesized by specialized dendritic cells derived embryologically from the neural crest. Tyrosinase is active in specialized organelles within these melanocytes, and pigment is laid down on a protein stroma in these melanosomes. The fully melanized organelles (melanin granules) are distributed to adjacent cells by partial cytophagy. 3 From the toxicological standpoint, there are two main facets of the pigmentation process that demand attention. One is the process of melanogenesis, in which chemically reactive intermediates are generated that are potentially harmful to melanocytes and may also have toxic effects on adjacent tissues. The other relates to the properties of the product, melanin. Although some cells, such as the pigment epithelium of the retina, retain melanin, the pigment is generally transferred to adjacent recipient cells. Consequently, many of the toxicological sequelae associated with the properties of melanin are observed in epithelial cells. 4 Melanogenesis involves a metabolic pathway, the regulation of which is complex. The crucial enzyme is tyrosinase, a protein with an active site containing two copper atoms that bind molecular oxygen. Regulation of pigmentation incorporates signaling pathways that control the synthesis, posttranslational modification, metal incorporation, routing to organelles, and distribution to melanosomes of the enzyme. The mechanism of tyrosine oxidation requires the copper atoms at the active center to be in the reduced state, and the biochemical regulation of this step depends on the indirect formation of dopa from dopaquinone. The indirect reactions involve spontaneous cyclization of dopaquinone to form cyclodopa, which acts as a reductant in the eumelanogenic pathway, and this is in competition with nucleophilic addition of cysteine to dopaquinone to form cysteinyldopa in the 354
pheomelanic pathway. In this system, cysteinyldopa acts as a reductant of dopaquinone to yield dopa as the autoactivating substrate for tyrosinase. 5 The reactivity of dopaquinone and other intermediate orthoquinones formed during the biogenesis of melanin poses a threat to the survival of melanocytes, in particular by depleting melanogenic cells of antioxidant defenses such as glutathione. Several mechanisms have evolved that provide some protection against this cytotoxic hazard. These include the segregation of melanogenesis in membrane-bound organelles to minimize diffusion of reactive intermediates into the cytosol, and the presence of quinone reductases and catechol-O-methyl transferases in the cytoplasm. 6 Because of their relatively low population density, melanocytes are particularly susceptible to cytotoxic elimination. The visible result of this is depigmentation of epidermal structures, including hair. A wide array of stimuli associated with oxidative stress has been shown to cause local depigmentation by melanocyte depletion. 7 Melanogenesis has been exploited for both diagnostic and therapeutic purposes, mainly in connection with malignant melanoma. Detection of nascent melanin by radiolabeled probes that are incorporated by reaction with quinone intermediates has permitted localization of melanogenic tumors, and a similar principle has been applied to target radiotherapy to melanomas. 8 The introduction of analog substrates for tyrosinase has been pursued as a possible melanoma-targeting strategy. The first-generation analogs were based on 4-hydroxyanisole which, by virtue of its noncyclizing and lipophilic side-chain, results in the formation of a more stable and diffusible orthoquinone product when oxidized by tyrosinase. A more recent development has been to attach to cyclizable tyrosinase substrates known cytotoxic moieties that are released by hydrolysis on cyclization of the quinone oxidation product. 9 In relation to the toxicology of melanin, there has been continued interest in the selective uptake and binding of many materials including metals and a variety of xenobiotics, especially organic amines. The binding mechanisms in the case of cations are largely due to the carboxyl anion content of the pigment, and this also accounts for some of the binding capacity for other agents, including pharmaceuticals, although charge transfer and hydrophobic interactions are also involved.
TOXICOLOGICAL ASPECTS OF MELANIN AND MELANOGENESIS
10 The kinetics of uptake by and release of materials from melanin have been investigated by several techniques. The equilibrium conditions seem to favor the notion that, at relatively low concentrations of potentially noxious agents, melanin acts primarily as a cytoprotective pigment by sequestering harmful chemicals. Combined with the exfoliation of epithelial cells, this may even constitute an important excretory pathway for the organism, especially of heavy metals and, possibly, some carcinogens. 11 However, in tissues where melanin is retained, the accumulation of material during chronic exposure may be related to the induction of specific lesions in pigmented tissue. This appears to be the case in the eye where melanin-affinic drugs may cause retinopathies and cataract formation. Similarly, neurotoxicity in pigmented regions of the central nervous system may be related to the selective accumulation of certain harmful agents, as in parkinsonism. 12 Selective accumulation may constitute a therapeutic advantage. For example, the storage of local anesthetics in inner ear melanin has proved useful in the treatment of severe tinnitus. Similarly, it has been proposed that selective uptake by melanin of psoralens is advantageous in PUVA treatment of psoriasis. Melanin binding of methylene blue has been advocated as a targeting strategy for radiotherapy of melanoma using labels such as radioiodine or astatine-211, and some interesting results have been published of the use of neutron capture therapy of melanoma using boron-10 incorporated into melanin-binding agents. In addition, biological monitoring or forensic investigation of exposure to a variety of agents including industrial chemicals, drugs, or illicit narcotics has been facilitated by examination of pigmented hair samples in which these agents are accumulated.
Introduction Definition of Melanin and Description of Types The predominant surface pigmentation of vertebrates is melanin. Despite the widespread usage since it was first introduced in the eighteenth century, the term “melanin” covers a range of polymers with uncertain structure. It is now widely held that the variability of structure is the consequence of the incorporation of several precursors into the final polymer. In general, however, eumelanin, a black or yellow pigment, is predominantly an indolic polymer which is highly conjugated. The polymer possesses redox properties, an anionic character, and powerful metal-chelating properties. The physical properties of melanins include photon absorption, electron exchange, and cation binding as well as photon–phonon coupling, and are dealt with elsewhere. The chemical reactivity of the precursor intermediates permits the generation of polymers that incorporate other compounds, including especially thiol compounds, which form addition products with quinones and may modify the size and properties of the final polymer. Melanins with high sulfur content are generally reddish and are known as pheomelanins.
Location of Melanin Melanins are found in cutaneous structures. In humans, there is marked pigmentation of the epidermis and epidermal structures such as the hair. The important extracutaneous sites include the eye where there are two melanized structures: the iris and the retina. The choroidal pigment is synthesized by melanocytes, whereas the retinal melanin is synthesized and retained by the cells of the retinal pigment epithelium (RPE). Another site in which melanin is found is in the inner ear. Melanin is also found in the central nervous system (CNS) where it is present in the extrapyramidal nuclei, in particular the substantia nigra. The process involved in the formation of CNS melanin is apparently not dependent on tyrosinase-catalyzed oxidation and thus differs from the general group of these pigments. Melanocytes are found in the meninges, and melanin has been reported in many other locations.
Synthesis In vertebrates, most melanin is synthesized by melanocytes. These neural crest-derived dendritic cells uniquely express features that permit the biosynthesis of melanin. The only other cells that are normally able to do this in mammals are the cells of the RPE. In both cases, the process of melanogenesis involves the synthesis of tyrosinase and related enzymes, which are active in intracellular organelles (melanosomes) where the melanin polymer is formed and deposited on matrix proteins to form a melanin granule. It is likely that the process evolved from a more primitive system in which tyrosinase was exported by a secretory mechanism to act on external substrates present in the microenvironment. This mechanism seems to be an important defensive mechanism in plants and insects, both from an antibiotic point of view and also because of the structural reinforcement that is added by the polymer. A good example of this is the formation of the insect exoskeleton in which hardening is dependent on the action of tyrosinase. In higher animals, although the melanin-generating reactions are still topologically exterior to the cytosol, melanogenesis has been enabled to take place in cytoplasmic organelles by the fusion of enzyme-containing vesicles with matrix vesicles, which either contain the substrate or are able to concentrate it. The details of the segregation of the contents of the vesicles and the processes involved in their fusion have yet to be fully established. In some cells, these melanized granules are retained, for example in the RPE and dermal melanocytes and melanophores in fish and amphibia. But in the epidermis and associated structures such as hair, pigment is transferred to the adjacent keratocytes. The melanin granules that are transferred to recipient cells exhibit no tyrosinase activity so that, in the process of melanization, the enzyme is inactivated. Examination of enzyme activity in different granule fractions derived from melanocytes shows that there is virtually no tyrosinase activity in fully melanized melanosomes. This implies that the enzyme is inactivated by its product. It was shown by Wood and Ingraham (1965) that covalent binding of 14C-labeled 355
CHAPTER 18
phenol to tyrosinase occurs, and this is likely to be due to the interaction of the enzymatically derived orthoquinone with nucleophilic groups of the enzyme protein (Brooks and Dawson, 1966). Studies by Dietler and Lerch (1982) on Neurospora tyrosinase, however, indicated that the amount of binding was too small to account for the inactivation of the enzyme. They gave evidence that there was loss of copper from the enzyme, and it is possible that the metal-chelating property of melanin is responsible for the removal of copper from the active site. An oxidative modification of one of the tyrosinase histidine residues (His-306) was also noted, which may have been due to hydroxyl radical attack.
Distribution Transfer of melanin granules may take place singly, but the most frequent distribution process involves the wholesale transfer of subportions of the melanocyte cytoplasm to surrounding cells by phagocytosis of melanocyte dendrites — a process known as cytocrine transfer. Redistribution of melanin granules in the recipient cells then takes place by membrane fusion. Degradation of melanin is very slow or nonexistent, and turnover depends on the pigment being shed with the cells that have taken up the melanin, e.g. in keratinized epidermis such as the stratum corneum and hair. Secondary depigmentation may therefore accompany conditions in which there is a local increase in epidermal desquamation such as in eczema. Such a mechanism might also be responsible for the hypopigmentation of leprosy and the hypomelanotic macules that are found in association with tuberous sclerosis. In RPE, where the melanin is retained, what turnover occurs appears to involve incorporation of melanosomes into autophagosomes where melanin may contribute to the composition of lipofuscin granules.
Properties Despite many careful studies of melanins, the details of the composition of the pigment is still unclear. In principle, melanins are regarded as complex aggregates of oligomers composed principally of dihydroxyindoles and related oxidation intermediates of the melanogenic pathway. Melanins exhibit three fundamental properties: (1) strong photon absorption across a broad spectrum; (2) facile redox exchange properties; and (3) the capacity to bind chemicals. The binding may give rise to pronounced accumulation of drugs and other chemicals in melanin-containing tissues, especially after chronic exposure, and the melanin-affinic uptake in pigmented tissues is one of the strongest retention mechanisms in the body. Chloroquine, for example (Lindquist, 1973), and N,N-bis-acetanilidedimethylamine (Lyttkens et al., 1984) have been found in marked concentrations in the melanin of the eye 1 year after a single intravenous injection of a trace dose in pigmented mice (Fig. 18.1). The melanin affinity of certain drugs, e.g. phenothiazine derivatives and chloroquine, has turned out to be a main factor in the etiology of lesions affecting the pigmentary system of the body, but it also creates opportunities for tar356
Fig. 18.1. Whole-body autoradiogram of a pigmented mouse (C57BL) 1 year after a single intravenous injection of 3H-N,N-bisacetanilidedimethylamine (QX-572). Note the significant retention of label in the uveal tract of the eye, whereas no radioactivity can be detected in other organs.
geted therapy of malignant melanoma and other diseases, directly or indirectly related to the pigment cells.
Biological Function In man, normal levels of pigmentation differ between races and reflect quantitative differences in the constitutive rates of melanogenesis (Robins, 1991). The explanation given for the relative lack of epidermal pigment in less equatorial populations is based on the idea of the evolutionary value of a diminished light barrier in permitting the light-assisted synthesis of vitamin D in less strongly illuminated regions of the globe (Loomis, 1967). Whatever the genetically determined level of melanization, it is regulated by the control of a number of processes, including access of melanocytes to the skin, which may be important in modifying the degree of regional pigmentation, the nutritional and microenvironmental conditions of melanocytes, and the hormonal regulation of the rate of melanogenesis. In mammals, there does not appear to be direct neural control of pigment cells that permits the spectacular camouflage or communication displays of fish, amphibia, and some reptiles. These rapid reversible changes depend on alterations in the dispersal of melanin granules that are synthesized in and retained by melanophores. Melanophores in frogs are responsive to melanocyte-stimulating hormone (MSH), which binds to cell surface receptors that cause a rise in intracellular cyclic adenosine monophosphate (cAMP). The rise in cAMP causes granular dispersion in melanophores. In
TOXICOLOGICAL ASPECTS OF MELANIN AND MELANOGENESIS
mammals, a rise in cAMP is associated with increased tyrosinase synthesis. Camouflage and communication depends on pigment patterning and, in vertebrates, this is largely determined by the distribution of melanocytes. Relatively little is known about the microenvironmental conditions that regulate access of melanocyte precursors to the skin. The astounding migratory range of neural crest cells and the remarkable phenotypic repertoire of their differentiation products are evidence of the many possible mechanisms that could be implicated in modifying the extent of local pigmentation. Diminished migration into the skin of premelanocytes (melanoblasts) seems to account for the dorsoventral gradient of pigmentation in many vertebrates, and failure to colonize certain regions of the skin may give rise to certain patterns of depigmentation. Some forms of striping or mottling seem to be brought about in this way, for example the patterns resulting from X-chromosome inactivation. Other mechanisms, perhaps involving processes that influence the survival of melanocytes, seem to be involved in patterns of depigmentation or lack of pigmentation such as those in zebra stripes. These phenomena are genetically determined, and pathological variants of them are found in lethal white spotting in mice, which is associated with the megacolon pathology resulting from failure of migration of neural crest ganglion cell precursors in the large gut, and also in Waardenburg syndrome (Waardenburg, 1951), in which there is combined deafness and segmental cranial pigment deficiency due to the failure of neural crest cell migration. The segmental lack of pigment in piebaldism may represent a similar process, although the phenomenon may be viewed as a congenital variant of vitiligo. A good deal of emphasis has been given to the UVR protection afforded by epidermal melanin. Certainly, there is a strong inverse correlation between sunburn susceptibility and the degree of skin pigmentation, and the incidence of skin cancer is much lower in blacks than in whites. Pigmentation of the epidermis and associated structures is probably a manifestation of an evolutionarily significant property unrelated to the light absorption of melanin. It has been suggested that melanin could act as an excretory route for heavy metals. This may be of particular importance to marine mammals and other species with a significant dietary intake of shellfish, and may have proved to be an evolutionary advantage during the littoral evolution of Homo sapiens (Riley, 1992, 1994, 1995). However, eye pigmentation is probably a good example of the exploitation of the photon-absorbing property of melanin to increase visual acuity. Consequently, loss of melanin in the eye, for example in ocular albinism, constitutes a serious problem. The evolutionary benefit of melanin in other sites is unclear. In the inner ear, melanin may act as a phonon absorber, or its action may depend on its chelating properties. One possibility might be that the melanin serves as a device for the local regulation of endogenous cations, such as Ca2+ (Meyer zum Gottesberge-Orsulakova, 1985). Another conceivable function is that melanin is a reservoir for melanin-affinic biogenic
amines, such as dopamine, epinephrine (adrenaline), and norepinephrine (noradrenaline) (Lindquist, 1973), or endogenous polyamines, e.g. spermidine (Tjälve et al., 1981). As far as xenobiotics are concerned, it is tempting to consider melanin as a protective chemical filter. The presence of melanin in some very sensitive tissues evidently favors this hypothesis. The melanin would protect these or adjacent tissues by keeping potentially harmful substances bound and slowly releasing them in low, nontoxic concentrations (especially transient, high-concentration peaks of noxious chemicals are limited by the adsorption to melanin). In the eye, for example, the melanin is located in close proximity to the receptor cells, and the nutrients from the capillary bed of the choroid are filtered through the choroidal melanocytes and the pigment epithelium before reaching the retinal receptors for nourishment. A similar situation exists in the inner ear, because the receptors (the hair cells) are located relatively close to the melanin of the stria vascularis in the cochlea and in the vestibular ampullae. In the brain, neuromelanin is present in nerve cells in the extrapyramidal system, mainly in the substantia nigra and locus coeruleus, and the neuromelanin may be involved in chemical protection. Korytowski et al. (1995), for example, have provided strong experimental support for the idea that the neuromelanin from human substantia nigra can act as a natural antioxidant by sequestering redox-active metal ions. Under certain circumstances, however, the possible protection mechanism may be a threat to the pigment cell, as chronic exposure to certain toxic substances with melanin affinity may cause selective adverse effects in the melanin-containing tissues, as discussed in a subsequent section.
Modification of Melanin Cosmetically, the most important category of depigmentation is the “bleaching” of melanin in hair and in the epidermis. Bleaching of hair is generally achieved by the action of hydrogen peroxide. As has been mentioned previously, melanin is a powerful chelator of transition metals such as iron and copper. In the presence of hydrogen peroxide, these metals catalyze the Fenton reaction, which leads to the generation of hydroxyl radicals: H2O2 + Fe2+ Æ Fe3+ + HO– + HO◊ Hydroxyl radicals are highly reactive and attack any vicinal molecule at diffusion-controlled rates. Thus, melanin exposed to hydrogen peroxide is subjected to a high-density attack by hydroxyl radicals, which results in multiple scission of the polymer (Korytowski and Sarna, 1990). As the melanin is hydroxylated and broken down into shorter segments, the low-energy, photon absorption properties associated with the highly conjugated polymer are lost, and the peroxide-treated tissue (e.g. hair) becomes lighter in hue. Hydroxyl radical attack is also able to damage keratin, so there is some danger to the structural integrity of hair, but the relatively selective effect on melanin is dependent on transitional metal binding to the pigment. A similar approach cannot be used to 357
CHAPTER 18
depigment the epidermis because of the cytotoxic effect of peroxide-derived hydroxyl radicals which damage the skin. An alternative approach to epidermal depigmentation has been employed based on chemical reduction of epidermal melanin. It is known that the optical properties of melanin are affected by the redox status of the polymer because the photon absorption is a function of the number of carbonyl groups. Theoretically, therefore, increasing the reducing environment of the melanin will diminish its light-absorbing properties. The reverse of this process underlies the “immediate pigment darkening” (IPD) that occurs on exposure of melanin to blue or ultraviolet light. This results from an oxidation reaction in which electrons in the melanin are raised to an excited state by high-energy photon absorption and donated to oxygen. Oxidation of the melanin increases the number of carbonyls in the polymer and results in enhanced absorption of low-energy photons (the so-called “bathochromic” effect). The phenomenon is prevented by ischemia during exposure, and IPD is an oxygen-requiring phenomenon. Electron spin resonance spectroscopy of melanin during irradiation shows that there is an increase in the semiquinone content of the polymer. This may come about either by partial reduction of oxygen to form superoxide and the corresponding semiquinone or by delocalization of electrons in the melanin polymer which is facilitated by an increase in the oxidation state. To some extent, a reducing environment exists naturally in the cytoplasm of cells that are recipients of melanin, but it can be augmented, at least in the upper layers of the epidermis, by the external application of creams containing reducing agents such as ascorbic acid or hydroquinone. The main problems associated with this approach concern the uncertain levels of skin penetration of the agents and, in the case of hydroquinone, the complications introduced by the ability of this compound to form covalent addition products with melanin and melanogenic intermediates.
Toxicological Aspects In this chapter, we attempt to summarize the toxicological aspects of melanins and melanogenesis. We distinguish between the process of pigment formation and the properties of the product and, in particular, between cells that elaborate melanin, and are thus prone to the toxic effects of melanogenic intermediates, and cells that are recipients of melanin, which are susceptible to toxicological hazards arising from the properties of the pigment. Melanogenesis has long been recognized as a potential source of cytotoxicity because of the reactivity of the intermediates formed, and several mechanisms are involved in protecting melanogenic cells from damage. We outline potentially hazardous reactions of melanogenic intermediates such as orthoquinones and discuss the mechanisms that have evolved to protect melanocytes. In this context, we discuss the idea of utilizing melanogenesis as a targeted cytotoxic strategy in the treatment of disseminated melanoma. 358
As noted above, melanin has structural properties that endow it with a range of chemical reactivity with toxicological implications. Notably, the high degree of conjugation of the pigment makes it a strong absorber of photons, and part of its protective function results from its photochemical reactivity. Also, the balance between quinone and hydroquinone functions, with the equilibrium permitting intermediate semiquinone steady-state conditions, makes melanin a facile redox exchanger able to act either in a protective mode or as a source of damage. In addition, the presence of anionic functions, such as carboxyl groups, makes melanin a cationic exchanger. The tendency of van der Waals’ stacked ring structures and the presence of nitrogen-containing heterocyclic rings (in the form of indoles or indolines) give rise to the possibility of hydrophobic interactions and charge transfer complexes, thus enabling melanins to act as a sink or depot of a wide range of xenobiotics. We discuss these reactivities in relation to the toxicology of melanin-containing tissues including the eye, ear, and brain in addition to the skin. Finally, we mention attempts to employ melanin-directed toxicology in various therapeutic modalities including melanoma treatment.
Melanogenesis Surface pigmentation by melanin is the result of a chain of events beginning with the migration of neural crest precursors to populate the epidermis and its associated structures, such as hair bulbs, with melanoblasts which undergo differentiation to give rise to the melanocyte population of the skin. Melanocytes possess the specialized cytoplasmic organization and the biosynthetic apparatus to generate melanin. In vertebrates, the stages involved in surface pigmentation include: (1) migration of pigment cell precursors from the neural crest; (2) clonal population of the skin by melanocytes; (3) induction of melanogenic genes; (4) synthesis of melanogenic enzymes and matrix components; (5) post-translational processing of melanogenic proteins; (6) fusion of vesicles to form melanosomes; (7) control of tyrosinase and related melanogenic enzymes: (8) control of post-tyrosinase modification of the synthetic pathway; (9) transfer of pigment granules to recipient cells; and (10) modification of melanin.
Melanocyte Origin, Migration, and Differentiation Relatively little is known about the control of migration of pigment cell precursors. Clearly, the process involves the expression of genes in both the migrating cells and those tissues that are invaded by melanoblasts that control motility and direction. Failure of the appropriate inductive effects results in abnormalities. One such is the premature cessation of migration, which is probably the origin of dermal accumulations of pigment cells as in Mongolian spots. Another example of significance in human pathology is Waardenburg syndrome in which there is a combination of defects including cranial depigmentation ascribable to failure of immigration of neural crest cells.
TOXICOLOGICAL ASPECTS OF MELANIN AND MELANOGENESIS
Dispersion of cells from the neural crest has been clarified by the studies of Mintz (1967) using chimeric mice composed of cells carrying different coat color genes mixed at the blastocyst stage. She concluded that the various striping patterns observed in the mice conformed to a basic distribution of pigment cell precursors into 34 independent regions, i.e. 17 bands on either side of the midline. This implies that all the melanocytes responsible for hair color in mice are derived from 34 cells whose descendants migrate to specific areas of the skin. Further diversification can take place within these clonal areas, accounting for the finer grain patterning exhibited by Xchromosome inactivation (Lyon, 1963) such as in the case of the X-linked genes “dappled”, “brindled,” and “mottled” (Modp, Mob–, Mo), which inhibit pigmentation possibly by reducing the viability of melanocytes expressing the allele. Spotting, piebaldness, or variegation of pigmentation also occur in animals with normal coat color genes and in distributions that do not correspond with the clonal pattern of melanocyte migration. In these cases, there is evidence that the melanoblasts are influenced by the local tissue environment and either fail to enter a region or fail to survive or are not induced to express their differentiated function (Mayer, 1967). The skin can be regarded as a mosaic of zones in which different titers of a factor influencing melanocyte development exist. Spotting genes may therefore determine the distribution of such factors. Some of these effects may, however, reflect abnormal levels of sensitivity of melanocytes to environmental factors. Phenomena related to this are considered elsewhere. During embryogenesis, melanoblasts migrate to sites where they will later synthesize pigment. During this migratory and proliferative phase, no melanogenesis occurs, and the onset of melanin synthesis is the result of a differentiation process in which the biosynthetic apparatus for melanin production is induced. It is important to note that melanogenesis is in no way a “terminal” differentiation either in RPE or in epidermal melanocytes as fully melanized cells are able to proliferate. It seems likely therefore that the genetic controls of melanogenesis are separate from those that determine the degree of expression of melanogenesis. However, experimental systems involving isolated melanocytes have demonstrated that rapidly proliferating cells often become progressively less pigmented. This phenomenon is principally the consequence of pigment dilution. Manifestly, if the cytoplasmic expansion necessary for cell doubling is more rapid than the rate of melanin synthesis, the amount of pigment per cell will be progressively diminished at each cell division. Conversely, any agent that reduces or arrests proliferation will increase the degree of pigmentation even if no direct effect is exerted on the rate of melanogenesis (Riley, 1987). Care is therefore necessary in ascribing changes in the level of pigmentation to “differentiation” or expression of a differentiated phenotype (Abdel-Malek et al., 1992; Abe et al., 1987; Durkacz et al., 1992; Fisher et al., 1985; Kiguchi et al., 1990; Lauharanta et al., 1985; Orlow et al., 1990; Osman et al., 1985; Sunkara et al., 1985).
Having entered the region to be pigmented, the melanoblasts are converted to active melanocytes by the induction of melanin synthesis. A good deal is known not only about tyrosinase and related genes, but also about the regulatory regions of the genome that control their expression. However, at present, the details of the operation of the transcriptional controls remain to be elucidated. Nevertheless, several studies have demonstrated the action of a wide range of agents that appear to stimulate or inhibit transcription of melanogenic genes, in particular tyrosinase. The main stimulatory pathway involves activation of protein kinase A (PKA) through a cAMP-dependent mechanism. Another hormonal effect on melanogenesis (possibly acting at the transcriptional level) is through the catecholamine receptor pathway. Burchill and Thody (1986) showed that the specific D2 receptor agonist LY 171555 inhibited tyrosinase activity in explanted hair bulbs, an effect blocked by sulpiridine, a D2 receptor antagonist. In the case of MSH, the pathway involves MSH receptor-linked G protein activation. The direct action of UVB on melanocytes appears to be cAMP independent (Friedmann and Gilchrest, 1987), and it appears that the stimulating action of prostaglandin E1 may be cAMP independent, although it does raise cAMP levels in Cloudman S91 cells (Abdel-Malek et al., 1987). Inhibitory effects on melanogenesis at the transcriptional level have been observed in the case of a variety of agents including lactic acid (Ando et al., 1993), linoleic acid (Ando et al., 1990), retinoic acid, interleukin (IL)-6, IL1a, tumor necrosis factor (TNF)a (Swope et al., 1991), and epidermal cell-derived thymocyteactivating factor (ETAF) (Swope et al., 1989). It is possible that several of these agents exert their effects through the intermediacy of aPKC (Oka et al., 1993), which may in turn interfere with the stimulatory action of PKA. There is evidence that the stimulatory action of 12-O-tetradecanoylphorbol-13acetate (TPA) is by down-regulation of aPKC (Carsberg et al., 1994) and, conversely, 1-oleoyl-2-acetyl glycerol and linoleate (Ando et al., 1990) exert their inhibitory action by stimulation of aPKC. Undoubtedly, when the transcriptional controls are better comprehended, the complex interactions by which normal melanogenesis is regulated will become clearer.
Melanogenesis — Pathway and Regulation Physiological Control of Melanogenesis Although the entire process of pigment formation involves many complex interactions, including vesicle trafficking and fusion, the intercession of tyrosinase-related proteins, and matrix generating processes, it is clear from the depigmentation of albinism that the crucial element of the melanogenic pathway is the action of the principal oxidizing enzyme, tyrosinase. At present, relatively little is known about the control of expression or the requirement of the tyrosinase-related proteins TRP-1 and TRP-2. The function of TRP-1 is unknown, 359
CHAPTER 18
but TRP-2 has an enzymatic action in catalyzing the conversion of dopachrome to its tautomer 5,6-dihydroxyindole-2carboxylic acid and thus plays a part in the melanogenic pathway. The suggestion has been made that the biosynthesis of melanin in melanosomes is dependent on the cooperative action of tyrosinase and the tyrosinase-related proteins in the form of a physical aggregate (Orlow et al., 1994). Thus, the efficiency of the process could be modified by changes in the composition of the aggregate structure. If this model of melanogenesis is correct, then control of pigmentation may be exerted by components without catalytic activity. Whether this proves to be the case remains to be seen. An interesting observation is the apparent inverse correlation between tyrosinase and TRP-2 activity in MSH-stimulated melanocytes (Martínez-Liarte et al., 1992), which suggests that our present comprehension of the regulatory mechanisms of melanogenesis is extremely tenuous. It is a moot point whether, under normal circumstances, there exists a physiological regulator of tyrosinase activity that acts by preventing access of the substrate to the enzyme (see Chen and Chavin, 1975). As several products of the process of melanogenesis bear a close resemblance to the substrates for both tyrosinase and TRP-2, it would not be surprising if there is some element of feedback inhibition by competition between products and initial or intermediate substrates. Such a phenomenon has been shown in an in vitro system (Wilczek and Mishima, 1995), and a compound having the property of inhibiting tyrosinase has been extracted from melanoma cells (Chian and Wilgram, 1967). The lack of melanogenesis in extramelanosomal sites has been ascribed to binding to tyrosinase of an inhibitor that is diluted or inactivated when the enzyme is taken up by premelanosomes (Hearing and Jiménez, 1987; Martinez et al., 1987). Kameyama et al. (1989) have obtained a highly stable inhibitor of melanogenesis from nonpigmented cells that acts directly on tyrosinase. At present, the identity of this inhibitor is not known (Kameyama et al., 1995), but it may correspond with that isolated from human skin xenografts by Farooqui et al. (1995).
Tyrosinase Tyrosinase (EC 1.14.18.1) is a copper-containing enzyme that catalyzes the oxidation of monohydric phenols and dihydric phenols (catechols) to their corresponding orthoquinones. In vertebrates (and also some invertebrate species), the major natural substrate is tyrosine, which is oxidized with the utilization of molecular oxygen to dopaquinone. Mammalian tyrosinase has an amino acid composition consistent with the DNA sequence established by Kwon et al. (1988), Terao et al. (1989), and Yamamoto et al. (1989), which predicts a protein of 515 amino acids with a molecular mass of 58.5 kDa after cleavage of the leading peptide. This structure includes a hydrophobic transmembrane domain of 23 amino acids and a further 37 amino acids that may act as a signal peptide. Proteolytic cleavage of the transmembrane portion of the enzyme gives an expected molecular weight of about 53 kDa for the unmodified “soluble” form of tyrosinase. 360
This corresponds closely with the lower molecular weight range of the unglycosylated form of the enzyme as ascertained by several laboratories (Burnett, 1971; Hearing et al., 1981).
Substrate Specificity Although the details of the three-dimensional arrangement of the substrate binding site of tyrosinase remain to be confirmed by X-ray crystallographic analysis, it is clear from amino acid sequence data and, by inference, from the structure of the closely related copper protein hemocyanin, that the active site is situated in a hydrophobic pocket into which the phenyl ring of the substrate can be inserted. As tyrosinase is stereospecific, it must be assumed that there are secondary binding domains for the carboxyl and amino groups of tyrosine that exclude binding by the d-isomer. The carboxyl binding site may recognize the carbonyl group (hydrogen bond acceptor) or, if the carboxyl group is ionized at the relevant pH, forms an ionic bond with the negatively charged oxygen. As the amino group of the tyrosine side-chain is unlikely to be protonated under normal conditions, this group may form one (or two) hydrogen bonds with a vicinal acceptor group on the enzyme. The third restriction is presumably spatial because otherwise free rotation of the asymmetrical b carbon would permit the accommodation of either optical isomer of tyrosine. There is also a spatial restriction imposed by the distance between the phenyl ring and the groups on the side-chain conferring specificity of binding and by the maximum size of the substituents at the a carbon of the side-chains. Compounds resembling ltyrosine may act as competitive inhibitors of tyrosinase (e.g. l-phenylalanine) or may themselves be melanogenic substrates (e.g. l-dopa or l-dopamine). A large number of compounds have been investigated as potential substrates for tyrosinase-catalyzed oxidation. Analysis of the data (mostly obtained with tyrosinase from Agaricus bisporus) suggests that a carboxyl or carbonyl groups prevent substrate binding, but the enzyme is apparently tolerant of many side-chain variations. Shortened side-chains (e.g. –CH3 or –C2H5) permit binding to and oxidation of phenols by the enzyme. Many of the shortened side-chain phenols are oxidized more rapidly than tyrosine (Naish-Byfield et al., 1991). Although they may be effective as competitors of tyrosine binding to the enzyme, the majority of these agents are not competitive inhibitors of melanogenesis but exert their depigmenting effect by a cytotoxic action on melanocytes. Generally speaking, the rate of phenol (or catechol) oxidation is determined by the relative ease of electron loss from the phenolic ring so that side-chain substituents that are electron donating in nature increase the tyrosinase-catalyzed oxidation rate (Passi and Nazzaro-Porro, 1981; Passi et al., 1987; Riley, 1975). For example, a methoxy side-chain results in a rapid tyrosinase-catalyzed oxidation, the rate of which exceeds tyrosine oxidation by several fold. Conversely, electronwithdrawing substituents can greatly reduce the oxidation rate. Trifluoromethylphenol is not oxidized by tyrosinase (Riley et al., 1997), whereas the hydrogen-containing analog
TOXICOLOGICAL ASPECTS OF MELANIN AND MELANOGENESIS
p-cresol is a rapidly oxidized substrate. In vitro, trifluoromethylphenol is a competitive inhibitor of tyrosine oxidation, i.e. it competes for occupancy of the substrate binding site but is not itself oxidized. An interesting possibility concerns agents that may bind to the secondary (side-chain) binding sites of tyrosinase and prevent access of the substrate to the active site. Of these, the simplest is probably glycine because its structure (CH2(NH2)COOH) would enable it to occupy the secondary binding site of tyrosinase without impinging on the active site pocket. The same considerations apply to l-alanine (CH3CH(NH2)COOH). Other amino acids could also be considered in this category, but structural considerations suggest that there could be several impediments to their binding to the enzyme. Recently, there has been interest in novel cyclic peptide inhibitors of tyrosinase (Morita et al., 1994a, b). It is interesting to note that glycine is a component of the tripeptide glutathione (GSH) and that some of the influence of GSH on tyrosinase activity (Jara et al., 1988) might be mediated by competitive substrate binding. If binding to either the amino or the carboxyl “receptor” sites were sufficient significantly to block the access of tyrosine to the active site, a host of potential competitive inhibitors is presented including agents such as polyamines and carboxylic acids. Among these could be counted dicarboxylic acids such as azelaic acid (Nazzaro-Porro and Passi, 1978), although the structural requirements with respect to the number of carbons separating the carboxyl groups imply that additional criteria need to be satisfied.
H2NCSCSNH2
dithio-oxamide
HSCH2CHOHCHOHCH2SH dithiothreitol (DTT) (CH3CH2)2NCSSH
diethyldithiocarbamate (DDC)
CH3CHSHCHSHOH
2,3-dithiopropanol
(CH3)2NCH2CH2SH
2-mercaptoethyldimethylamine (MEDA)
HSCH2CH2NH2
cysteamine
HSCH2CHNH2COOH
cysteine
Fig. 18.2. Structural formulae of some potential copper-chelating agents.
Copper Incorporation The essential requirement for copper at the active site of tyrosinase was shown by Keilin and Mann (1938) and Kubowitz (1938). Their studies demonstrated that tyrosinase activity was inhibited by agents such as carbon monoxide, cyanide, diethyldithiocarbonate, and salicylaldoxime that react with copper and render it incapable of binding oxygen (see above). This inhibition was reversible by the addition of excess copper salts to the preparation. Later work by Lerner et al. (1950) and Nelson and Dawson (1955) demonstrated that the copper requirement was general and applied not only to tyrosinases of plant origin but also to the mammalian enzyme. It is now widely agreed that, although there are some differences in the detailed structure of the enzyme on an evolutionary scale (Morrison et al., 1994), the family of tyrosinases all possess copper at the active site probably with a configuration closely similar to that found in the enzyme from Neurospora crassa studied by Lerch and colleagues (Lerch, 1981, 1988; Winkler et al., 1981). In this model, the active site contains two copper atoms bound to histidine residues of the protein and positioned about 3.6 Å apart. The evidence reviewed by Mason (1956) indicated that monohydric phenol oxidation depended on these copper atoms being in the Cu(I) state in order to bind molecular oxygen (Mason, 1955). If oxygen binding is prevented, the enzyme is inactive against phenolic substrates such as tyrosine. It seems likely that oxygen binding is prevented by copper chelation by cyanide
Fig. 18.3. Structural formulae of 8-hydroxyquinoline and analogs.
and carbon monoxide, and it is possible that, if there is no impediment to access, dithiol reagents such as diethyldithiocarbonate and dithiothreitol can form inhibitory complexes with the active site copper atoms (Fig. 18.2). It has been reported that thioredoxin and 2,3-dithiopropanol inhibit tyrosinase by forming bis-cysteinate complexes with one of the copper atoms at the active site by a mechanism involving reduction of a disulfide bridge between cysteine residues located vicinal to the active site (Wood and Schallreuter, 1991). Searle (1970, 1972) demonstrated that local applications of the copper-binding agent 8-hydroxyquinoline produced striking patterns of hair depigmentation in C57Bl mice. A similar effect was exhibited by 8-hydroxyquinaldine (Fig. 18.3). Depigmentation was confined to hair in the growth phase, and 361
CHAPTER 18
Fig. 18.4. Structural formulae of some substrate analog tyrosinase inhibitors.
hair clippings showed that the affected hair was completely devoid of melanin except for occasional dark tips. Cessation of application was followed by the regrowth of normally pigmented hair, demonstrating that the inhibition of melanogenesis was not due to cytotoxic obliteration of the hair bulb melanocytes. 8-Hydroxyquinoline is widely used as an analytical reagent for copper and has antiseptic properties ascribed to its copper-chelating action (Albert, 1985). It seems likely that its depigmenting action is related to rendering tyrosinase copper deficient or binding to the active site. This latter alternative may be favored by the failure of other copper chelators to produce a similar effect; perhaps surprisingly, dithio-oxamide, 2,2¢-biquinoline, and 2,9-dimethyl-1,10phenanthroline (Fig. 18.3) produced no depigmentation. However, these agents, although efficient copper-binding compounds, do not possess a phenolic group and are less likely to gain access to the active site of tyrosinase. Another group of tyrosinase inhibitors includes agents that are able to bind to the active site copper atoms but are able to release only one electron. This group includes mimosine, a naturally occurring pyridone analog of dopa (Hashiguchi and Takahashi, 1977), kojic acid, a Streptomyces-derived antibiotic with pronounced depigmenting activity (Mishima et al., 1988), and tropolone (Kahn and Andrawis, 1985) (see Fig. 18.4). Early observations on the inhibitory effects of carboxylic acids on tyrosinase were interpreted, on the basis of their pHdependent effects, to act by interaction with the histidine ligands of the active site copper atoms (Krüger, 1955). It is difficult to envisage the circumstances in which such a reaction could occur, although compounds having such an action may be included in the group of weak inhibitors in the classification of Wilcox et al. (1985). Relatively powerful carboxylic acid inhibitors include substrate analogs such as benzoic acid, which probably act by occupying the substrate binding site. Benzyl hydroxamic acid (Rich et al., 1978) probably acts as an inhibitor by a mechanism similar to that of phenylalanine 362
and tryptophan (Chakraborty and Chakraborty, 1993). Another melanogenic inhibitor, phenylthiourea, acts in a noncompetitive manner on tyrosinase (Laskin and Piccinini, 1986), suggesting that it belongs to the class of “post-tyrosinase” inhibitors. This also probably applies to the histamine H2 agonists related to nordimaprit (S-(2-(N,N-dimethylamine)ethyl)isothiourea). A series of analogs was examined by Fechner et al. (1993), some of which had depigmenting activity despite increasing the level of tyrosinase activity. Some of the depigmenting action of these compounds was ascribable to a cytotoxic effect (see above). Conversely, the histamine H2 antagonists, cimetidine and ranitidine, were shown to stimulate tyrosinase activity and melanogenesis in B16 cells (Ucar, 1991). Melanogenesis inhibitors of unknown function include two compounds isolated from Streptomyces. These agents, known as OH-3984 K1 and K2, inhibit melanogenesis in B16 melanoma cells at low concentrations by a mechanism that is not thought to involve a direct action on tyrosinase (Komiyama et al., 1993). Currently, little is known about the details of copper insertion into the active site of the enzyme. It is possible that it occurs during protein synthesis in association with the three-dimensional folding of the polypeptide chain. However, the relatively large distances between the putative copperchelating histidine residues make it more likely that the apoenzyme is synthesized first, followed by metal insertion. It is unclear how the copper is transported to the requisite site, or where and how it is added to the apotyrosinase (Martinez et al., 1987). Free copper ions are normally kept at very low concentrations in the cell by scavenging by metallothionein. There may be specific pathways for the delivery of copper to enzymecontaining vesicles. Inhibition of such a mechanism could comprise a hitherto unexplored regulatory mechanism for melanogenesis. As the copper binding is by coordination bonds, it is conceivable that other metals could be incorporated into the enzyme. For example, it has been proposed that the active site of TRP-2 normally contains coordinated zinc atoms (Solano et al., 1994) and, in view of the structural similarity between tyrosinase and TRP-2, there seems to be no obvious structural impediment to the occupancy of the metal binding site by metal ions of appropriate size. Whether competition for the copper binding site of tyrosinase by exposure to high concentrations of metal ions such as iron, nickel, or cobalt influences the activity of the enzyme is not clear. However, Jara et al. (1990) have evidence that high concentrations of zinc are inhibitory to tyrosinase.
Glycosylation The major post-translational modification of the enzyme consists of asparagine-linked glycosylation producing an almost continuous spectrum of isoenzymes on electrophoresis (Ferrini et al., 1987). Carbohydrate addition increases the molecular weight to about 65 kDa (Hearing and Jiménez, 1989), which is consistent with the trypsin-treated material extracted from human melanoma cells (IGR1) by Wittbjer et al. (1990). The shorthand nomenclature of the main molecular forms of mam-
TOXICOLOGICAL ASPECTS OF MELANIN AND MELANOGENESIS
malian tyrosinase permits the stages in its synthesis and distribution to be summarized in the following terms: T3 = unglycosylated, newly translated tyrosinase complete with transmembrane domain [molecular weight (MW) ~58 kDa]; T1 = fully glycosylated enzyme with transmembrane domain (MW ~73 kDa); T1¢ and T2 = partially glycosylated forms of T3; T4 = soluble glycosylated tyrosinase (probably the active form in melanosomes, MW ~65 kDa). At present, little is known about the possible carbohydrate signals that may be involved in the protein sorting in the Golgi region of the cell. What is clear is that inhibition of glycosylation by a variety of agents results in inhibition of melanogenesis. Some of these effects may be exerted by modification of the carbohydrate moieties of the matrix proteins of premelanosomes, but the major feature of melanocytes treated with glycosylation inhibitors is loss of T3. This suggests that an important function of glycosylation is to prevent degradation of newly synthesized enzyme, although Imokawa and Mishima (1984) reported that the effect of glucosamine (a glycosylation inhibitor) was unmodified by the protease inhibitors phenylmethylsulfonyl fluoride (PMSF) or leupeptin. It is not clear to what extent the glycosylation of tyrosinase affects proteolytic attack at specific sites or the general degradation of the protein by masking vulnerable peptide bonds. It seems likely that the release of the soluble enzyme from the membrane-bound form is required as an activation step after fusion with matrix granules of the coated vesicles carrying the bound form of the enzyme. This activation process envisages proteolytic cleavage, the specificity of which may be ensured by glycosylation of other vulnerable sites. An important series of studies by Imokawa and Mishima have demonstrated the depigmenting action of a wide range of glycosylation inhibitors of varying degrees of specificity (Imokawa, 1990; Imokawa and Mishima, 1984, 1985, 1986). In brief, these show that tunicamycin and glucosamine produce reversible loss of melanogenesis associated not only with loss of sialic acid-rich T1 but also with a reduction in T3. These changes are associated with alteration in mannose-specific binding of tyrosinase to the lectin concanavalin A. Recovery of melanogenesis can be interrupted by deoxynojirimycin, castanospermine, swainsonine, and monensin, which inhibit carbohydrate chain elongation at different points (Imokawa, 1990). More recently, Terao et al. (1992) have investigated the effect of some novel glycosylation inhibitors on pigmentation in cultured melanocytes. The compound BMY-28565 inhibited melanogenesis without diminishing the levels of tyrosinase messenger RNA. Although degradation of the unglycosylated protein is the most probable explanation for the reported data, some misrouting of partially glycosylated enzyme cannot be excluded.
Effect of Thiols The regulatory action of thiols with regard to melanogenesis has been the subject of comment for many years. De Léobardy and Labesse (1934) reported some reduction in skin pigmentation in a patient with Addison’s disease treated by daily
injections with 100 mg of cysteine. Although this effect might have resulted from interference with the course of the disease, some other publications report the direct depigmenting action on skin or hair of relatively simple thiols. Cysteamine and 2mercaptoethyldimethylamine (MEDA) were shown to cause depigmentation in black goldfish (Chavin and Schlesinger, 1966) and in black guinea-pig skin (Pathak et al., 1966). Frenk et al. (1968) and Bleehen et al. (1968) found that MEDA was more effective than cysteamine. There are at least four mechanisms that might be invoked to explain these results: (1) thiols will bind to the copper atoms at the active site of tyrosinase and inhibit the enzyme; (2) there are 14 cysteine residues in the mammalian T4 tyrosinase according to the sequence published by Kwon et al. (1988). Some of these may be involved in intramolecular disulfide bridge, modification of which could have significant mechanistic sequelae; (3) thiols react with quinone intermediates of melanogenesis (see below) to modify the product; (4) some thiols may interfere with glutathione generation of the cell and render melanocytes vulnerable to the action of melanogenic intermediates. In addition, an effect of glutathione on recovery of melanogenesis in glucosamine-treated cells was reported by Imokawa (1989), suggesting that quite low concentrations (0.2 mM) of glutathione (GSH) are able to block the translocation of tyrosine to premelanosomes. In this context, it is of interest (and, perhaps, of significance) to note the existence of a cysteine residue in the cytosolic portion of the enzyme. If this intracytoplasmic “tail” acts as a signal peptide that determines the specificity of organelle fusion, it may be that access of tyrosinase to premelanosomes can be indirectly controlled by the redox status of the cell. Halprin and Ohkawara (1966) claimed that differences in the skin color of negroes and Caucasians were inversely proportional to their glutathione level. Benedetto et al. (1981, 1982) reported that the skin levels of reduced glutathione and glutathione reductase were inversely related to the darkness of the melanin in tortoiseshell (tricolor) guinea pigs. It seems likely that these latter effects are largely due to the posttyrosinase modification of melanogenesis, i.e. the production of pheomelanin by combination of thiol compounds with dopaquinone (see below). However, direct effects on enzyme activity may play a part in the regulation of melanogenesis. Thioredoxin reductase has been implicated in such a function (Wood et al., 1995), possibly by the action of reduced thioredoxin in altering the tyrosinase conformation by reducing intramolecular disulfide bonds and, in this connection, it has been shown that thioredoxin reductase is susceptible to inactivation by UVA and UVB (Schallreuter and Wood, 1989), thus suggesting a mechanism for light-stimulated tyrosinase activity. Richter and Clisby (1941) investigated the action on black rats of phenylthiourea. Although 1–2 mg was usually lethal, tolerance could be built up to a dose, administered in the drinking water, of 18 mg per day. After 27 days of administration, graying of the hair was seen. This occurred first behind the neck, then spread along the back and around the head, 363
CHAPTER 18
but the top of the head remained black. Normal pigmentation of the hair returned when the dosage was discontinued. Dieke (1947) studied the effects of three thioureas on black rats that had their hair clipped on one side only. Phenylthiourea in the drinking water again produced almost complete depigmentation of the hair at doses of 25 mg/kg, without affecting hair growth. Thiourea at 200 mg/kg had no effect on hair growth or pigmentation, whereas a-naphthylthiourea, given in the diet, suppressed hair growth, leaving the skin unpigmented. The effects of a-naphthylthiourea, but not those of phenylthiourea, were reversed by cysteine. Although thyroid hormone is of importance in pigmentation, both phenylthiourea and the ineffective thiourea produced similar degrees of hyperplasia and loss of colloid in the thyroid glands of treated animals, supporting the view that phenylthiourea causes depigmentation by inhibiting tyrosinase, which it does in vitro more effectively than thiourea. Phenylthiourea has also been tested as an inhibitor of repigmentation in regenerating fins of the platyfish Xiphophorus (Kull et al., 1954).
Tyrosinase Activity Phase I Melanogenesis, Divergence and the Lag Period The initial step in the biogenesis of melanin consists of the oxidation of tyrosine to dopaquinone (DQ), and this oxidation, together with a set of related reactions, is known as phase I melanogenesis (see Fig. 18.5). Since the first edition of this volume was published, new data on the rates of the chemical reactions involved in phase I melanogenesis have been obtained by pulse radiolysis. The orthoquinone, dopaquinone, formed by the action of tyrosinase on tyrosine, is very susceptible to spontaneous intramolecular and intermolecular nucleophilic attack (Land et al., 2004). Intramolecular Michael addition of the amino group in the side-chain of dopaquinone (reaction A, Fig. 18.5) leads to cyclization, resulting in the formation of cyclodopa. This indoline is rapidly oxidized by residual dopaquinone in a redox exchange (reaction B, Fig. 18.5), giving rise to the corre-
COOH NH2
HO tyrosine
tyrosinase
HO
O
A
COOH
COOH N H cyclodopa
HO
NH2
O
HO N
NH2
HO
COOH NH2
O H 2N
dopa
dopachrome
S
O
COOH
COOH
NH2
COOH 5-S-cysteinyldopa
D
O
COOH
HO HO H2N
dopaquinone
B
HO
C
S
COOH 5-S-cysteinyldopaquinone E
EUMELANIN HO
COOH
PHEOMELANIN
NH2
N HOOC
S
benzothiazine
364
O
F
COOH NH2
N HOOC
S
quinonimine
Fig. 18.5. Reactions of phase I melanogenesis and corresponding rate constants. The rate constants for the spontaneous reactions are as follows: A. 3.8/s (Land et al., 2003c); B. 5.3 ¥ 106/M/s (Land et al., 2003c); C. 3 ¥ 107/M/s (Thompson et al., 1985); D. 8.8 ¥ 105/M/s (Land and Riley, 2000); E. 10/s (Napolitano et al., 1999); F. 5/s (Napolitano et al., 1999).
TOXICOLOGICAL ASPECTS OF MELANIN AND MELANOGENESIS
sponding aminochrome, dopachrome. This redox exchange yields concurrently the catechol, dopa, which is essential to reduce the active site of tyrosinase, allowing it to become active as a phenol oxidase. Tertiary amine analogs of dopaquinone also cyclize but, in this case, yield indolium olate betaines that do not undergo redox exchange to form the corresponding aminochrome and enzyme-activating catechol (Clews et al., 2000; Cooksey et al., 1997). The fact that these tertiary amine derivatives of tyrosine are not oxidized by inactivated tyrosinase provides strong evidence that direct enzymatic catechol formation does not occur under normal conditions. The indirect formation of dopa accounts for the features of the “lag period” observed in vitro for tyrosinasecatalyzed oxidation of tyrosine, during which the rate of oxidation slowly accelerates to reach the maximum velocity. During this lag time, the concentration of catechol formed by the disproportionation of dopaquinone and cyclodopa gradually becomes sufficient to reduce all the inactive mettyrosinase to active deoxy-tyrosinase (Land et al., 2003a). Other factors influencing tyrosinase activation have been elucidated by pulse radiolysis studies of a series of secondary quinone amines (Land et al., 2003b). Such studies showed that the failure of tertiary amine-derived betaines to undergo redox exchange results from the absence of a second exchangeable proton. Intermolecular nucleophilic addition of cysteine to dopaquinone results in the formation of mainly 5-Scysteinyldopa (reaction C, Fig. 18.5) which, like cyclodopa, can undergo redox exchange with residual dopaquinone (reaction D, Fig. 18.5) yielding, initially, 5-S-cysteinyldopaquinone. Over a few tenths of a second, the latter isomerizes spontaneously to a benzothiazine via a metastable quinonimine (reactions E and F, see Fig. 18.5). Both eumelanogenesis and pheomelanogenesis stem from dopaquinone, and the divergent pathways of biogenesis may be described by the balance between the rate constants of the nonenzymatic reactions involved in the initial steps. Taking dopachrome and cysteinyldopaquinone as representative of the divergent pathways, it is possible to derive an “index of divergence” between eumelanogenesis and pheomelanogenesis using the experimentally determined rate constants of reactions A, B, C, and D. From the ratio of the products of the first two rate constants of eumelanogenesis (A and B) and pheomelanogenesis (C and D), it can be deduced that a crossover value for switching between predominance of
eumelanogenesis to predominance of pheomelanogenesis occurs when the cysteine concentration is 7.6 ¥ 10–7 M (Land et al., 2003c). As emphasized above, the essential oxidative step in melanogenesis consists of the tyrosinase-catalyzed generation of orthoquinones, the most reactive of which is dopaquinone. It has been proposed that some subsequent oxidations in the melanogenic pathway may be brought about by redox exchange reactions with dopaquinone and that therefore the regulation of the levels of dopaquinone is crucial to the control of melanogenesis (Riley, 1993). As the reduction product of dopaquinone is dopa, which is rapidly reoxidized by tyrosinase, factors affecting the abundance of dopaquinone exert an important influence on melanin biosynthesis. The formation of dopa is of particular significance in relation to the activation of tyrosinase. Tyrosinase with the active site copper atoms in the oxidized [Cu(II)] state is unable to bind molecular oxygen and therefore cannot catalyze the oxidation of tyrosine. According to the “recruitment” hypothesis, the activity of tyrosinase is enhanced by the reduction of met-tyrosinase, which is accomplished by electron donation from dopa (Fig. 18.6). As dopa is formed as an intermediate product of tyrosine oxidation, this process is considered to account for the “lag” or induction period observed when monophenolic substrates, such as tyrosine, are oxidized by tyrosinase. This view is supported by the action of increasing tyrosine concentrations in lengthening the lag period, which argues that there is competition with the reducing substrate (dopa) for the substrate binding site. Also, the pH dependency of the effect is consistent with met-tyrosinase reduction being inhibited by increasing proton concentrations (Naish-Byfield and Riley, 1992). The generation of dopa in a tyrosine–tyrosinase reaction system is the result of the spontaneous reductive cyclization of dopaquinone to form cyclodopa, which is rapidly oxidized by redox exchange with dopaquinone to yield dopachrome and dopa (reaction B, Fig. 18.5). This process was first described by Evans and Raper in 1937, and the kinetics of the redox exchange were established by pulse radiolysis by Chedekel et al. (1984). Thus, dopa is formed effectively by the disproportionation of the tyrosine oxidation product dopaquinone (Fig. 18.5). Dopaquinone may undergo a redox exchange resulting in the oxidation of a reducing agent, which does not readily form a melanoid polymer. Compounds in this category include
Fig. 18.6. Schematic outline of dopa oxidation by electron donation to the copper atoms in met-tyrosinase.
365
CHAPTER 18
ascorbate and hydroquinone, although the details of the chemistry are not straightforward. It has even been suggested that metal ions could be oxidized by such a mechanism (Palumbo et al., 1987). If the activation of tyrosinase is regulated by the prevalence of dopa, then removal of dopa would constitute an important regulator of melanogenesis. It has been suggested that dopa methylation by the enzyme catechol-O-methyl transferase (COMT) may play such a role (Smit et al., 1994). Catechol methylation (Westerhof et al., 1987) plays a dual role in promoting removal and excretion of catechols and in preventing their oxidation (either enzymatic or auto-oxidation) to the potentially toxic quinone derivatives.
Biochemical Control of Tyrosinase Activity Oxidation of tyrosine to the corresponding orthoquinone involves an ortho hydroxylation and a dehydrogenation and takes place in a single step. For this reaction to occur, the active site must be oxygenated. Oxygen is bound in a peroxy conformation to the two copper atoms at the active site. This oxygen binding can only occur when the copper atoms are in the reduced form [Cu(I)]. This is because each copper atom at the active site of the enzyme donates an electron to molecular oxygen, resulting in the peroxy conformation. The peroxy group forms coordination bonds with the resultant Cu(II) copper atoms. This arrangement is usually indicated as a symmetrical binding with partial coordination bonds to the two copper atoms. Tyrosinase with oxidized copper atoms [Cu(II)] is unable to bind oxygen and is inactive toward tyrosine because its oxidation requires oxygen insertion into the ring (Mason et al., 1955). In this form, it is known as met-tyrosinase, by analogy with met-hemoglobin. The investigations of Lerch (1981) and Solomon and Lowery (1993) have demonstrated the reaction mechanism of monohydric phenol oxidation. This consists of a cycle in which deoxy-tyrosinase first binds molecular oxygen and subsequently the substrate is coordinated to the copper atoms at the active site. A series of proton exchanges results in oxygen insertion in the phenolic ring (Mason et al., 1955), and electron donation from the copper atoms yields the orthoquinone and one molecule of water. In this process, the deoxyenzyme is regenerated. The cycle involved in catechol oxidation is different. Coordination of the catechol to the copper atoms to which oxygen is already coordinated results in the breakdown of the complex with transfer of electrons from catechol to the oxygen to give the corresponding orthoquinone and two hydroxyl ions, leaving the copper of the enzyme in the oxidized (met) state. The met-enzyme is able to coordinate a further molecule of a catecholic substrate and oxidize it to the orthoquinone by electron donation to the cupric copper atoms, regenerating the Cu(I) form of deoxy-tyrosinase that is able to bind molecular oxygen. There are, therefore, two potentially competing oxidation cycles catalyzed by tyrosinase. In both cases, the substrate binding site is the same, involving the two copper atoms, and the products in each case are orthoquinone 366
and water. As, in the first stage of catechol oxidation, two hydroxyl ions are formed and in the second-stage reaction two protons are generated, there is the potential for a pH dependency of the reaction rate, which has complications regarding the lag period, and hence the maximum velocity of monophenol oxidation. There is evidence that newly synthesized tyrosinase is routed to lysosome-like vesicles, and it has been argued that the natural microenvironment of the enzyme contains a high proton concentration (Bhatnagar et al., 1993; Devi et al., 1987, 1989). It may be that pH shifts contribute to the physiological regulation of melanogenesis and the matter has not finally been resolved. An interesting phenomenon is the stimulation of tyrosinase activity in vivo by polyamine antimetabolites (Kapyaho et al., 1985). This may indicate that polyamines inhibit melanogenesis by a lysosomotropic action, although arguments have been advanced in refutation of this proposal. Kapyaho and Janne (1983) showed that stimulation of melanogenesis by 2-difluoromethylornithine (DFMO) was suppressed by putrescine, whereas MSH-stimulated tyrosinase activity was unaffected, arguing for an effect on transcriptional control.
Reactions of Intermediates and the Hazard to Melanocyte Survival An important aspect of the melanogenic pathway involves addition reactions. There are several reactive orthoquinone intermediates that can take part in such reactions, but dopaquinone is particularly susceptible to attack by nucleophiles such as thiol compounds. When these reactions are confined to the melanosomes, they merely constitute aspects of the formation of different variants of melanin. But, should the intermediates leak into the melanocyte cytosol, reductive addition reactions may constitute a cytotoxic hazard to melanocytes, as pointed out by Hochstein and Cohen (1963). There is evidence that some catecholic compounds formed by reductive addition are capable of being reoxidized by tyrosinase but whether they act directly as reducing substrates for the enzyme or are oxidized secondarily by a dopa-DQ redox cycle is not clear, although some in vitro evidence favors direct substrate action. Under conditions in which only small amounts of dopa are available, the addition of a suitable thiol reagent (e.g. cysteine, GSH) is a mechanism for accelerating tyrosine oxidation by the provision of a reducing substrate able to recruit mettyrosinase (Naish and Riley, 1989; Naish-Byfield et al., 1994). Such a process may underlie some aspects of the physiological control of melanogenesis by agencies modifying the access of thiols, such as glutathione, to the melanosomes. This mechanism appears to be implicated in the control of melanogenesis, e.g. in agouti hair, and may have other, more general significance. Conditions in which there is a relative thiol deficiency, such as in cystinosis (Lignac–Fanconi syndrome), may therefore exhibit hypomelanosis by virtue of interference with a thiol-dependent activating mechanism for tyrosinase. The reoxidation of catecholic thiol adducts by tyrosinase appears to be the basis of the synthesis of pheomelanins
TOXICOLOGICAL ASPECTS OF MELANIN AND MELANOGENESIS
(Prota, 1980, 1992). This pathway has been well characterized in the case of the benzothiazine-based pigments found in red chicken feathers, and a similar, though partial, process is regarded as the route to the sulfur-containing red–brown melanins, although the details remain unclear in most cases. It is likely that the diminished absorption of red light by pheomelanins is a reflection of shorter polymer length and the relative paucity of carbonyl groups in the fully oxidized form of the pigment. This implies that immediate pigment darkening (IPD) is a less prominent feature of pheomelanins with the concomitant generation of free radical products. An inhibitory action on melanogenesis by several 2-aryl-1,3thiazolidines has been shown by Napolitano et al. (1991). The main material studied was 2(2-hydroxyphenyl)-1,3thiazolidine-4-carboxylic acid, which prevented equimolar concentrations of tyrosine from tyrosinase-catalyzed conversion to melanin by the formation of a colorless product identified as b-(7-(3-carboxy-5-hydroxy-3,4-dihydro-2H-1,4benzothiazinyl) alanine. This was formed through an intermediate adduct. The authors conclude that 1,3-thiazolidines inhibit melanogenesis by trapping the tyrosinase-generated dopaquinone by the thiol-containing Schiff’s base arising from cleavage of the thiazolidine ring, followed by hydrolysis and ring closure to form a colorless product. An interesting aspect of the reaction of dopaquinone with thiols is the observation that certain thiourea derivatives selectively bind to nascent melanin. By analogy with the reaction of cysteine, glutathione, and dithiothreitol (DTT) with DQ, the process consists predominantly of thiolate ion addition to the 2- or 5-position of the ring. This has been confirmed in the case of thiourea (Palumbo et al., 1990). Few studies have examined the kinetic or regulatory effects of the binding of these compounds. Their major interest has been in connection with their use as carriers of radioisotopes (Broxterman et al., 1983), which can be used to label sites of active melanogenesis.
Protective Mechanisms It is likely that the evolutionary development of pigmentation, which includes the retention of the oxidative enzymes in the cell (as opposed to their secretion as occurs in lower eukaryotes), necessitated the fusion of the tyrosinase-containing vesicles with another membrane-bound structure in which the process of melanogenesis could be contained. In normal circumstances, the membrane surrounding these organelles (melanosomes) serves to isolate the diffusible water-soluble reactive products such as orthoquinones from the cytosol. The formation of melanosomes involves the fusion of at least two vesicular components, one that contains stromal material that forms the framework for subsequent melanin deposition and the other containing tyrosinase and associated melanogenic enzymes. Clearly, this fusion is a potential target for both physiological and pathological inhibition of melanogenesis. At present, little is known about the controlling processes. It is possible that modification of vesicular membrane structure and fluidity or cytoskeletal elements could
interfere with normal fusion. This might account for some of the actions of retinoic acid (Orlow et al., 1990; Ortonne, 1992), although the melanogenic inhibition exhibited in UVBstimulated melanocytes exposed to both cis- and trans-retinoic acid has been shown to be associated with diminished tyrosinase (and TRP-1) synthesis (Romero et al., 1994). Also, some effects of flavonoid extracts of St John’s wort on melanogenesis have been reported (Sattler and Schutt, 1994), which might act through an effect on vesicular membranes. Another potential control point is the intramelanosomal availability of the melanogenic substrate. A study of tyrosine transport in a human melanoma cell line (SK-mel 23) by Pankovich and Jimbow (1991) showed that tyrosine uptake is largely through system L transport, which supplies the tyrosine for both protein synthesis and melanogenesis. Tyrosine uptake by cells was inhibited by the analog substrate 4-Scysteinylphenol and by tryptophan as well as the specific system L inhibitor 2-amino-bicyclo-2,2,1-heptane-2-carboxylic acid. Similar data were published by Jara et al. (1991). Although this mechanism is responsible for the cellular uptake of tyrosine, there may be separate permeases to regulate the access of tyrosine to the melanosome because the process is more analogous to amino acid export. Outward diffusion of potentially cytotoxic products of melanogenesis is thought to be minimal in normal melanocytes, although the existence of melanogens in the blood and urine suggests that some leakage does occur, or that there is extramelanosomal catechol oxidation. There are several cytosolic processes that are invoked as cytoprotective mechanisms and have been reviewed by Smit et al. (2000). The intermediates that may reach the cytosol consist essentially of quinones liberated directly or are generated by oxidation from hydroquinones that leak through the melanosomal membrane. The main pathway of quinone detoxification is by quenching by glutathione with the formation of S-glutathionyl adducts, which are subsequently degraded. In some cells, quinone reductase (DT-diaphorase) may be invoked as a defense mechanism (see Smit et al., 2000). However, one of the major defense mechanisms appears to involve the inactivation of dihydroxyindoles by O-methylation. This pathway, first demonstrated by Axelrod and Lerner in 1963, is catalyzed by the enzyme catechol-O-methyl transferase. It was suggested that this methylation might act as a regulatory mechanism in melanogenesis, but the location of the enzyme outside the melanosome makes this unlikely. However, as a protective mechanism, O-methylation of catechols is likely to be important not only in preventing the formation of reactive orthoquinones but also in interrupting the possibility of free radical reactions generated by one-electron redox cycling involving semiquinones. There is direct evidence that O-methylation is related to the degree of melanogenesis (Smit et al., 1990, 1994). Elimination pathways probably involve glucuronidation and sulfonation as these derivatives of indoles are found in urine (Pavel et al., 1986), but it is likely that this is largely due to hepatic metabolism of the methylated derivatives formed in melanogenic cells. 367
CHAPTER 18
Toxicological Aspects of Melanogenesis In the context of acquired loss of pigmentation, there are good reasons to believe that the initiation of vitiligo may result from damage to melanocytes produced by a local factor. A model of vitiliginous depigmentation is provided by the cytotoxic action of a range of phenolic compounds. The first reported incidence of local depigmentation in man shown to be the result of phenols was in Negroes working in a tanning factory (Oliver et al., 1940). They developed patchy depigmentation of the hands and forearms due to contact with the monobenzyl ether of hydroquinone, which was used as an antioxidant in the production of the rubber gloves with which they were issued. Although the original authors demonstrated the absence of dopa-positive cells in the depigmented zones, it was initially assumed that the effect on melanogenesis was the result of competitive inhibition of tyrosinase (Denton et al., 1952; Lea, 1951; Lorincz, 1950; Peck and Sobotka, 1941). In an extensive survey of locally applied antioxidants, Brun (1961) showed that 4-hydroxyanisole (monomethyl ether of hydroquinone) had a powerful depigmenting action, and studies of this compound, its structural isomers, and a range of related phenols (Riley, 1969a, b) demonstrated that the depigmentation was the consequence of a cytotoxic action on melanocytes. Moreover, 4-hydroxyanisole (4HA) was shown to be a rapidly oxidized substrate of tyrosinase and the cytotoxic action to be due to one or more of the oxidation products (Riley, 1970, 1975). Subsequent investigations have established that the principal cytotoxic species is the corresponding orthoquinone (Naish et al., 1988a, b), which probably initiates melanocyte damage by thiol depletion (Cooksey et al., 1995). An account of these studies is to be found in Riley (1985) and Searle and Riley (1991). Because of the possibility that this tyrosinase-mediated cytotoxicity could provide a targeting mechanism for systemic antimelanoma treatment (Riley, 1970, 1984, 1991), there have been many studies of tyrosine analogs, and several alternative candidate compounds have been investigated (Jimbow et al., 1989; Mascagna et al., 1992). In the early work that demonstrated the cytotoxicity of tyrosine analogs (Riley, 1969a, b, 1970), attention was drawn to the potential hazard posed to the cell by the normal process of melanogenesis, as pointed out by Hochstein and Cohen (1963), and the consequent importance of the containment of the process in melanosomes (Borovansky et al., 1991; Riley, 1975). This led to the mistaken belief in some circles that a cytotoxic action on melanocytes could be achieved by augmentation of melanogenesis by the supply of normal tyrosinase substrates such as dopa and, in vitro, melanocytes exposed to relatively high concentrations of dopa are damaged (Wick, 1977). This effect is due to the oxidation products of dopa (i.e. dopaquinone or DHI) being formed in the medium, partly by auto-oxidation (Picardo et al., 1987) and partly by the action of small amounts of tyrosinase secreted by the cells. Some of the toxic effects elicited by this process may result from the generation of reactive oxygen species such as hydrogen peroxide (Kable and Parsons, 1988; Karg et al., 1991). 368
It has also to be borne in mind that dopa-like catechols may have significant pharmacological effects and that alternative metabolism may result in a plethora of toxic effects unrelated to melanogenesis (Inoue et al., 1990; Passi et al., 1987; Riley, 1984). There is no evidence of cytotoxic action or depigmentation by normal melanogenic substrates in vivo; no case of depigmentation has been recorded among patients receiving long-term, high-dosage l-dopa for the treatment of Parkinson disease. Of the wide range of phenols and catechols that are oxidized by tyrosinase (briefly reviewed by Prota, 1992), only a few exhibit significant melanocytotoxicity. In general, these are agents with side-chains that do not permit facile cyclization, that do not impede diffusion through phospholipid membranes, and that endow the quinone resulting from tyrosinase-catalyzed oxidation with an appropriate level of reactivity with regard to nucleophiles (Cooksey et al., 1992, 1995). Such materials are potential depigmenting agents, producing their effects by depleting the population of melanocytes in the epidermis or hair bulbs.
Diagnostic and Therapeutic Exploitation of Melanogenesis Detection of Nascent Melanin Some melanin-affinic substances, mainly thioureylenes, have turned out to be selectively accumulated solely in nascent melanin (reviewed by Larsson, 1991). The most studied substance in this regard is 2-thiouracil, and Whittaker (1971) was the first to demonstrate the incorporation into the melanin of the retinal pigment cell epithelium of chick embryo in vitro; he also found that the incorporation was tyrosinasedependent. By autoradiography, it was subsequently demonstrated that thiouracil accumulates strongly in the pigmented structures of murine fetal eyes in vivo, where the rate of melanin synthesis is high, whereas in the adult eye, where melanin synthesis is relatively low, only minute amounts of thiouracil were found (Dencker et al., 1979). The uptake in melanin was thus related to the melanin synthesis rather than to the occurrence of preformed melanin — thiouracil is lacking ordinary affinity to melanin (Dencker et al., 1981). Extended studies in melanoma-bearing mice demonstrated a corresponding uptake of thiouracil in the growing melanin of melanotic, but not of amelanotic, melanoma (Dencker et al., 1982). The specific localization of thiouracil and its analogous thioureylenes in nascent melanin has mainly focused interest on the possibility of targeted melanoma therapy, but the uptake may also implicate certain toxicological risks in connection with high-dose administration (see below). The sulfur ligand of thiouracil is apparently of crucial importance for the uptake in melanin, as uracil, which lacks sulfur, and 2-benzylthiouracil, where the sulfur is blocked, do not attach to the melanin (Olander et al., 1983). The thiouracil seems to be incorporated into the melanin structure as a false precursor, presumably through a nucleophilic attack on inter-
TOXICOLOGICAL ASPECTS OF MELANIN AND MELANOGENESIS
Fig. 18.7. Conjugation of 2-thiouracil with dopaquinone giving 6-S-thiouracildopa (3,4dihydroxy-6-(4¢-hydroxypyrimidinyl-2¢thio)-phenylalanine) — cf. Palumbo et al. (1990).
mediates of the melanin synthetic pathway, but the detailed biochemical mechanism behind the incorporation is still unclear. Palumbo et al. (1990) have shown previously that thiouracil is bound covalently to dopaquinone with the formation on 6-S-thiouracildopa (Fig. 18.7), and they concluded that the incorporation into melanin might be due to inglobation of the 6-S-thiouracildopa adduct within the structure of the melanin. More recently, they found that 6-S-thiouracildopa is rapidly oxidized by the melanogenic enzyme tyrosinase to a yellow chromophore, which ultimately forms an insoluble brown pigment (Palumbo et al., 1994). They also provided evidence for the ability of thiouracil to affect melanogenesis by the interaction with melanin intermediates beyond the dopaquinone stage, suggesting other possible modes for the incorporation into melanin. Recent studies in vitro have shown that, besides the thioureylenes, thioamides, 2-mercaptothiazoles, and 2mercaptoxazoles also interact with intermediates of the melanin synthetic pathway, which strongly indicates possible incorporation into growing melanin (Mårs and Larsson, 1995). A complicating finding, however, was that some of these substances acted as tyrosinase inhibitors which, in principle, might counteract the incorporation in vivo.
Toxicology of Nascent Melanin Toxicological risks associated with the incorporation of thioureylenes into nascent melanin, for example in growing fetal pigmented tissues, or in tanning skin and hair follicles, have been poorly evaluated so far. A change in the physicochemical properties of melanins, resulting from a significant incorporation of thioureylenes, might in principle impair the protective role of melanin (see above). In preliminary experiments, it has been found that the uptake of thiouracil and thiourea in synthetic dopa-melanin substantially increases the solubility (B. Larsson, unpublished results) and, with regard to the ability of melanin to oxidize nicotinamide adenine dinucleotide (NADH) (Gan et al., 1976; Van Woert, 1967), it has been demonstrated that the incorporation of thiouracil markedly decreases the oxidative capacity of the melanin in a dose-related manner (Larsson and Mårs, 1994). There are some indications on adverse effects in the living organism connected with the incorporation of thiouracil into growing melanin. Whittaker (1966) reported that thiouracil may cause a specific anomalous gigantism of the melanin granules in the otolith cells of ascidian larvae, reared throughout
embryogenesis in the presence of the drug, and the morphological changes were also accompanied by lighter color of the pigment granules. It is also known that propylthiouracil and methimazol, which are incorporated into melanin (Larsson et al., 1982; Olander et al., 1983), may cause loss or depigmentation of hair in humans (Goodman et al., 1985), indicating a toxic effect in the hair follicles where the rate of melanin synthesis is normally high.
Toxicity of Analog Substrates As discussed above, the potential hazard to melanogenic cells from extramelanosomal leakage of reactive intermediates is, in normal circumstances, contained by quenching mechanisms in the cytosol. However, the steady state may be disturbed by alterations in the propensity of intermediates to diffuse out of the melanosomes as a result of changes in concentration or diffusibility. This appears to be the case for a range of analog substrates for tyrosinase, of which 4-hydroxyanisole (4-HA) is a well-established example. The lack of a cyclizable sidechain increases the stability of the lipophilic quinone product of tyrosinase-catalyzed oxidation aiding its outward diffusion. Several studies have concluded that the major cytotoxic pathway involves the depletion of cellular GSH and attack on crucial nucleophiles, such as the cysteine residues in proteins with thiol-dependent functions (Cooksey et al., 1987, 1995, 1996; Land et al., 1990; Riley et al., 1997). The shortcomings of this approach as a possible anti-melanoma treatment seem to reside in the need for very elevated drug doses to overcome the cellular defenses and, recently, an alternative possibility has been investigated using analog substrates for tyrosinase that release cytotoxic drugs on cyclization of the derived quinone (Riley, 2003). This chemotherapeutic modality, known as melanocyte-directed, enzyme-activated prodrug therapy (MDEPT), is currently under development (Jordan et al., 1999, 2001).
Depigmentation Depigmentation may be either partial or complete, but the difference between hypopigmentation and total depigmentation may not distinguish between the mechanisms involved. Depigmentation may also be generalized or segmental. Of the pathologically significant depigmentations, the congenital category includes generalized depigmentation such as is found in those cases of albinism in which tyrosinase is totally inactive, the lesions being characterized by the presence of melanocytes that 369
CHAPTER 18
contain melanosomes but are not pigmented. In the segmental depigmentation characteristic of piebaldism, melanocytes are absent in the depigmented zones, but tyrosinase activity is normal in the cells in the pigmented areas. Generalized hypopigmentation is associated with phenylketonuria and, to a lesser extent, with cystinosis and homocysteinuria. These lesions are characterized by normal melanocytes with normal tyrosinase activity but in which the total amount of melanin synthesized is much reduced. Phenylketonuria was described by Følling in 1934 and was one of the earliest recognized disorders of amino acid metabolism. The basic lesion is a reduction in phenylalanine hydroxylase activity, and the conversion of phenylalanine to tyrosine proceeds at only about 1/10th of the normal rate in affected individuals (Coleman, 1962). The condition is inherited as a recessive trait and is characterized by decreased pigmentation of the hair and eyes (Fitzpatrick et al., 1961). If untreated, the condition is associated with mental deficiency (Jervis, 1937). The evidence that tyrosine acts as an inducer for tyrosinase (Wilde, 1955) is not strong and, therefore, the suggestion that the high phenylalanine concentrations in these patients may be responsible for depigmentation by repression of tyrosinase synthesis is probably not correct. Coleman (1962) has shown that a molar excess of phenylalanine over tyrosine as high as 70-fold is necessary to produce detectable inhibition of pigment synthesis by tyrosinase. As it is likely that it is the raised concentrations of phenylalanine found in untreated phenylketonuria that are responsible for the dilution of pigmentation in these patients, it may be proposed that the inhibition is brought about by preventing access of tyrosine to the melanosome (Farishian and Whittaker, 1980). Recent evidence has suggested the existence of melanosomal permeases responsible for the uptake and concentration of tyrosine in these organelles, and the similarity in structure of tyrosine and phenylalanine might suggest that inhibition of the permease is the means by which pigment dilution in these cases is brought about. In cystinosis, another inherited metabolic disorder, there is accumulation of cysteine in tissues, and this is associated with hypopigmentation of the skin and eye (Stenson et al., 1983). It is not clear what the mechanism of inhibition of pigment synthesis is, but it is possible that it involves the direct inhibition of tyrosinase by chelation of the copper at the active site of the enzyme. Homocystinuria, an abnormality of methionine metabolism, usually caused by a deficiency in cystathione synthetase, is also associated with hypopigmentation (Ortonne et al., 1983). Affected patients have blond hair, blue eyes, and fair skin. It is not clear whether the inhibition of melanin synthesis that is exhibited by these patients results from an effect on tyrosinase activity or an interaction with dopaquinone (see below). Among the acquired pathological depigmentations are the segmental depigmentation characterized by the partial or complete absence of melanocytes in the affected areas. This condition is known as vitiligo. The predisposition to this type
370
of depigmentation is inherited as an autosomal dominant trait and may be regarded as the acquired version of piebaldism. Although the degree of hypomelanosis is not strictly correlated with the total number of surviving melanocytes in the skin, complete depigmentation is associated with the total loss of functional melanocytes in the affected area. These have been designated absolute and relative vitiligo, respectively, depending on the complete or relative absence of dopa-positive melanocytes in the otherwise normal epidermis (Jarrett and Szabo, 1956). Vitiligo, like albinism, has been recognized for over 2000 years, and descriptions of it occur in the Indian sacred book Atharva Veda. There are many references to white skin in the writings of Buddhism, Islam, and Shintoism. It is likely that vitiligo was the cause of the depigmentation incorrectly referred to as leprosy in translations of the Hebrew Scriptures and, possibly as a result of this, patients with vitiligo were stigmatized as outcasts in many societies. Many vitiligo patients are acutely self-conscious of their cosmetic disfigurement, and Pandit Nehru regarded vitiligo as one of the conditions requiring urgent attention in India. Although vitiligo is more evident in the more darkly pigmented races, it is a disease affecting all ethnic groups with a prevalence of approximately 1%. Once the lesions appear, they tend to spread, and there is usually little chance of effective repigmentation, although strenuous efforts using photosensitizers have been made. Vitiligo generally occurs at sites of friction and trauma and in hyperpigmented areas. The segmental distribution is sometimes very dramatic. Although the pathogenesis of the condition is not well understood, there are two main etiological proposals: one based on the demonstration in some cases of autoantibodies to melanocytes, suggesting that the loss of melanocytes in certain areas is the result of an autoimmune reaction; the alternative is that the loss of melanocytes is due to an autotoxic mechanism resulting from the inability of the melanocytes to detoxify the intermediates of melanogenesis. A third proposal combining these two hypotheses would be that the initiation of the abnormality is caused by an autotoxic action resulting in the release of neoantigens from the melanocytes and the elicitation of a secondary autoimmune response by the host. Such a proposal would enable an immunological distinction to be made between melanocytes in different locations and would therefore account for the nonhomogeneous distribution of the lesions. Acquired pathological hypopigmentations should include the generalized hypopigmentation associated with hypopituitarism, in which there seems to be a generalized loss of MSH and adrenocorticotropic hormone (ACTH) stimulation of the melanocyte population with consequent reduction in overall tyrosinase expression. A number of agents have been reported to have depigmenting action on skin and hair. In some cases, the action may be indirect through the stimulation of inflammatory or immune reactions but, in the majority of instances, the mech-
TOXICOLOGICAL ASPECTS OF MELANIN AND MELANOGENESIS
anism is unknown. Spillane (1963) reported that the muscle relaxant mephensin caused reversible bleaching of hair in some patients, and local depigmentation has been described after intravenous administration of aldhesine (Coote and Abeysiri, 1979). Frenk (1980) described depigmentation from unidentified components of adhesive plaster, and reversible perioral depigmentation attributed to an ingredient of toothpaste (Mathias et al., 1980) has been reported. Poulsen (1981) reported reversible loss of hair pigment in patients taking the tranquilizer dexirosine. Acquired segmental hypopigmentations include a large group of conditions in which localized nutrition is compromised or where there is significant local ischemia. This condition occurs, for example, in chronic hypovascularization of the epidermis as in scleroderma and other collagen diseases. Acute ischemia is also sufficient to cause depigmentation. During experiments on cattle, Findlay and Jenkinson (1964) observed that a single injection of epinephrine (adrenaline) caused the local growth of white hair, and a similar observation was made in rats by Shelley and Ohman (1969). The effect in each instance was ascribed to the intense vasoconstriction caused by the epinephrine injection. Selye (1967) showed that ischemia produced by clamping skinfolds of rats for 8 h was sufficient to cause the regrowth of white hair at the site. A similar interpretation was put forward by Arnold et al. (1975) for the depigmenting effect of 33% triamcinolone in view of the powerful vasoconstricting effect of fluorinated steroids. The relatively low population density of melanocytes and their normally limited rate of proliferation in the adult may render them sensitive to damage. There is evidence that the melanocyte population is especially sensitive to low temperatures, and depigmentation by clamping or freezing is often used for branding animals. It is possible that the selective loss of pigmented hair is responsible for the many anecdotal reports of hair graying or whitening overnight. Ephraim (1959) reviewed a collection of cases of sudden hair whitening that were preceded by stressful experiences such as shipwrecks, railway catastrophes, and terrifying battle experiences and others by neurological disorders such as seizures, strokes, and brain injury. The beard of St Thomas More became white on the night before his execution, and the hair of Ludovicio Sforza is alleged to have turned white after his capture by Louis XII. It is reputed that Marie Antoinette’s hair turned white after the insults and abuse suffered by her family on their enforced return to Paris during the French Revolution. The most reasonable explanation for this phenomenon is that whitening is due to the selective loss of pigmented hair. Jelinek (1972) has shown that hair loss in alopecia areata is frequently confined to the pigmented hairs with white hairs remaining intact. One may postulate that the various traumas involved result in a prolonged peripheral vasoconstriction affecting the arterioles of the upper dermis followed by severe reperfusion injury damaging the pigmented hair bulbs.
Melanin Binding Mechanisms The mechanism of the binding, which has turned out to be complex, is dominated by electrostatic forces. Melanins are polyanions with a relatively high content of negatively charged carboxyl groups and ortho-semiquinones at physiological pH (Felix et al., 1978; Ito, 1986; Prota, 1992), and substances with cationic properties such as amines and metal ions are readily bound to the melanin by ionic interaction (Larsson and Tjälve, 1978, 1979). Not only aromatic amines (especially the polycyclic ones) but also aliphatic amines are bound (Tjälve et al., 1981). The ionic binding is apparently strengthened by additional forces, such as van der Waals’ attraction at the close apposition between the aromatic rings of the compounds and the melanin structure, as well as hydrophobic interaction, which may be rather pronounced (Larsson et al., 1988a; Stepien and Wilczok, 1982). In addition, involvement of charge transfer interaction has been indicated for electrondonating substances, mainly phenothiazine derivatives such as chlorpromazine (Larsson and Tjälve, 1979; Potts, 1964a). Using electron paramagnetic resonance spectroscopy and 63 Cu(II) as a probe in vitro, it was shown that synthetic dopamelanin and isolated beef-eye melanin have several different metal ion binding sites (Froncisz et al., 1980; Sarna et al., 1980). At pH 3, the interaction was dominated by a monodentate complex with the carboxylic groups of the melanin but, at higher pH, the binding was rearranged to a more stable mono- or bidentate complex with the carboxylic amine or carboxylic imine groups of the melanin. Other studies have shown that ferric ions bind predominantly to ortho-phenolic hydroxyls of the melanin (Sarna et al., 1980, 1981). The complexity of the binding has been demonstrated by Scatchard analysis, which normally shows that more than one binding class is involved for individual substances, including metal ions, indicating the presence of cooperating binding mechanisms as well as the influence of steric factors (Larsson and Tjälve, 1979). The binding energies are inversely proportional to the percentage binding, according to conformational analyses and molecular graphics used for the modeling of a representative melanin structure (Raghavan et al., 1990). Chlorpromazine, chloroquine, and methylene blue, which are strongly bound to melanin in vitro (Larsson and Tjälve, 1979; Potts, 1964a), accordingly showed the lowest binding energies, whereas the reverse was found for phenol and pyridine, which lack experimentally provable melanin affinity. Ionic interaction, however, was not taken into account in this study. The binding to melanin is normally reversible, but there are some interesting exceptions. Chlorpromazine and chloroquine, for example, are partly irreversibly bound in vitro (Larsson and Tjälve, 1979) and, as mentioned above, significant fractions of chloroquine and N,N-bis-acetanilidedimethylamine are retained in rodent uveal melanin 1 year after
371
CHAPTER 18
injection (see Fig. 18.1). At present, the mechanisms responsible for the irreversible interaction are poorly understood, but one possibility might be covalent binding. Another example concerns certain metal ions (copper, iron, and manganese) accumulated in natural melanin in situ, which cannot be removed by either prolonged acid treatment or exposure to strong chelators (Sarna et al., 1980), possibly because of strong multidentate complex formation. The exploration of the binding mechanisms and binding parameters has preferably been performed in vitro on natural and synthetic eumelanins. A few studies, however, have shown that even synthetic dopamine melanin (Ben-Shachar and Youdim, 1993; D’Amato et al., 1987; Larsson, 1979; Lydén et al., 1983, 1984; Wu et al., 1986), as well as natural human neuromelanin (D’Amato et al., 1987; Lindquist, 1973) and synthetic cysteinyldopa melanin (unpublished results), which is a model of pheomelanin, interact similarly with chemicals. The binding properties thus seem to be a general characteristic of melanins. The variety of chemicals with melanin affinity is large. Various drugs of quite different categories are represented, e.g. psychotropic drugs such as phenothiazines and other neuroleptics and tricyclic antidepressants, drugs for rheumatoid arthritis and malaria, local anesthetics, aminoglycoside antibiotics and so forth, and also other kinds of chemicals, for example herbicides, dyes, alkaloids, and metal ions (Larsson, 1979). The techniques used for in vitro studies of melanin affinity basically emanate from Potts (1964a), who used a suspension of isolated beef-eye melanin, which was incubated with test substance dissolved in buffer. Typically, 2.5 mmol of test substance is mixed with 10 mg of melanin suspended in 7 ml of buffer, pH 7.0. The incubation is performed at room temperature for 45 min, when equilibrium has occurred (cf. Larsson et al., 1977), and the pigment granules are then sedimented by centrifugation at 35 000 ¥ g for 10 min. The concentration of the unbound fraction in the supernatant is measured by spectrophotometry, or impulse counting when radiolabeled substances are used. The difference between the initial concentration of test substance and the remaining concentration in the supernatant gives the fraction bound to the melanin. In principle, any purified natural or synthetic melanin may be used for these studies and, if the test substance is poorly water soluble, buffered 33% ethanol may be used as solvent (Larsson et al., 1988b). Scatchard analysis (Scatchard et al., 1957) has proved to be useful for the estimation of detailed binding parameters, i.e. association constants and the number of binding sites on the melanin (Larsson and Tjälve, 1979). The in vitro model for studying melanin affinity has in most cases proved to be suitable for the prediction of melanin affinity in vivo (cf. below). Potts (1962a, b) was the first to demonstrate that phenothiazines are accumulated in the uveal tract of pigmented experimental animals. Whole-body autoradiography (Dencker et al., 1991; Ullberg et al., 1982) has been the most extensively used technique for mapping melanin affinity in vivo. Autoradiography differs from other biological 372
radioisotope techniques in providing more detailed information on the localization in tissues of a labeled substance, without laborious preselection of samples including risks of contamination. Using whole-body autoradiography, Lindquist and Ullberg (1972) found that chloroquine and chlorpromazine are strongly and selectively accumulated and retained in the melanin-containing tissues of pigmented mice, not only in the uveal tract of the eye, but also in the melanincontaining structures of the inner ear and the skin. A corresponding accumulation in fetal tissues was also demonstrated. In these studies, albino mice were used as controls, and they lacked corresponding uptake of label (Lindquist and Ullberg, 1972). During the following years, the melanin affinity in vivo of a great number of substances has been documented, mainly by autoradiography but also by impulse counting of excised tissue samples (for a review, see Larsson, 1979, 1995; Lindquist, 1973; Lindquist et al., 1987; Lydén-Sokolowski, 1990; Tammela, 1985; Wästerström, 1984). In most studies, pigmented mice have been used, but also rats, guinea pigs, hamsters, monkeys, frogs, and fish have been employed.
Kinetics of Uptake As mentioned above, the accumulation of certain melaninaffinic substances in pigmented tissues may be very pronounced. The highest concentrations in the body are often seen in the pigment cells soon after the injection and, about 2 days after the administration, the concentration of most xenobiotics has normally decreased to low levels due to excretion, except from the pigmented tissues where significant retention persists for weeks or longer. The importance of melanin in hair as a repository of substances to which a subject was exposed is important in both clinical and forensic toxicology. An interesting study by Testorf et al. (2001) employed the displacement from Sepia melanin of tritiated flunitrazepam in vitro as a means of measuring the binding and retention of a group of benzodiazepine tranquilizers. They observed rapid Langmuir binding followed by slower diffusion-limited uptake. They interpreted this as evidence of rapid surface binding with subsequent “bulk” binding. The competition by unlabeled drugs enabled the measurement of amounts of drug bound to melanin at low concentrations. Studies on the melanin affinity in vitro usually give accurate data of the intrinsic interaction, but the corresponding outcome of studies in vivo may still be different. This anomaly is mainly due to the interference of additional kinetic factors such as biotransformation and transfer through membranes. Aminoglycoside antibiotics, for example, have a pronounced melanin affinity in vitro but, because of their relatively high molecular weight, combined with positive charges at physiological pH, they show a marked extracellular biodistribution (with a few exceptions, such as endocytosis in the kidney) and do not reach the melanin in vivo (Larsson et al., 1981). Metal ions also show high melanin affinity in vitro but, in the living organism, rather few metals are accumulated in the pigmented tissues after a single injection (Lydén et al., 1984; Tjälve et al.,
TOXICOLOGICAL ASPECTS OF MELANIN AND MELANOGENESIS
1982), apparently because of membrane barriers or possibly metal binding competition between the melanin and proteins. On the other hand, significant amounts of various metals, e.g. Cu, Mn, Pb, Ti, and Zn, are normally found in pigmented tissues, indicating cumulative accumulation during chronic exposure (Zecca and Swartz, 1993). In this connection, it is of interest that the biodistribution of metals may undergo a considerable change after exposure to chelating agents, due to the formation of lipophilic complexes. Lead, for example, is not accumulated in the pigmented tissues of mice after a single injection but, after coexposure to dithiocarbamates, a pronounced melanin binding, in both fetal and adult eyes, has been found (Danielsson et al., 1984). Other examples are nickel combined with pyridinethione (Jasim and Tjälve, 1986) and thiram (Borg and Tjälve, 1988). The coexposure to metals and chelating agents is a potential toxicological problem, as organic compounds with chelating properties are relatively frequent, e.g. in the chemical industry, as pesticides, and even as drugs. The lipophilic metal complexes also readily pass across the blood–brain barrier, which increases the risk of metal binding to neuromelanin and the induction of central adverse effects. In this regard, recent studies by Tjälve et al. (1995) demonstrated that manganese cations are transported at a constant rate along the primary olfactory neurons of pike into the brain, thus circumventing the blood–brain barrier and gaining direct access to the central nervous system. Manganese is a neurotoxic metal that can induce extrapyramidal motor system dysfunctions in man, apparently associated with occupational inhalation of manganese-containing dusts or fumes.
Toxicology of Melanin-affinic Compounds There are many indications that the long-term accumulation of melanin-affinic drugs in pigmented tissues is a major cause behind the development of chronic lesions in the eye and the inner ear, in the skin, and possibly in the neuromelanincontaining nerve cells of the brain stem. The selective chemical stress on the pigment cells, due to a substantial increase in the local concentration of noxious substances, may also add to, or even be the main cause behind, the early aging processes that often are seen in melanin-containing cells. The most striking example is perhaps the early graying of hair, due to the deterioration of the melanocytes in the hair bulbs. Other examples are senile or presenile impairment of melanized structures in the eye and in the inner ear, with the development of certain types of cataracts or retinopathies, secondary to degeneration of the retinal pigment epithelium, and hearing loss due to strial atrophy. In the substantia nigra of the brain stem, the number of pigmented nerve cells normally decreases at the age of 55–65 years, without impairment of the extrapyramidal system, but an additional loss of neurons, induced by chemicals stored in neuromelanin, may ultimately cause extrapyramidal disturbances such as Parkinson disease or tardive dyskinesia (Lindquist, 1973). Although, in general, the uptake of chemicals by melanin affinity affects recipient cells in which the topological distrib-
ution of melanin in the cytosol renders them more susceptible to their effects, there are reports of melanocyte toxicity. A number of studies have shown that melanocytes are susceptible to damage by mutagens and carcinogens. During early experiments on the antitumor action of alkylating agents, Boyland et al. (1948) noted long-lasting bleaching of hair at the site of injection of nitrogen mustard in mice. A similarly localized depigmentation was found by Schoental (1971) in mice injected subcutaneously with N-methyl-Nnitrosourethane, a potent nitroso-carcinogen, and the injection of the same material intravenously into rabbit ears caused the appearance of depigmented hair over the ear veins, still visible after 18 months. Schoental (1971) suggested that the depigmentation was the result of degeneration of melanocytes. Schoental et al. (1978) found that T2 toxin, a carcinogenic metabolite of some Fusarium species, had a necrotizing action on topical application to the skin of mice and caused lasting depigmentation. Aw and Boyland (1978) found permanent depigmentation of hair in black mice at the site of injection of the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA), which they ascribed to selective melanocyte toxicity and, in later experiments (Aw and Boyland, 1981; Aw et al., 1982), they showed that depigmentation of hair in mice injected subcutaneously with a range of alkylating agents, including chlorambucil, dimethylsulfonate, and methyl nitrosourea, was similar to that produced by phenols and some other substances including chloroform and carbon dioxide snow. Aubert and Bohuon (1970) reported depigmentation of hair in hamsters treated with dibenzanthracene. Animals treated with this agent orally became totally depigmented after about 1 month. These actions are consistent with the view that, as the melanocyte population density is low, pigment cells are particularly sensitive to the toxic action of a wide range of agents. The depigmenting effects of these agents should be distinguished from the mutagenic action of the agents, many of which have been shown to produce hair color alterations in the offspring of treated animals (see, for example, Carr, 1947; Lang, 1978; Russell, 1983; Strong, 1945, 1948). Most studies so far on chemically induced lesions in pigmented tissues have been focused on the eye for two reasons: the eye contains a rather high concentration of melanin, restricted to a few well-visible structures, making the eye a suitable model for the demonstration of melanin affinity in vivo. The other reason is that much of the original knowledge on melanin-related adverse effects of drugs mainly originated from the eye and, to some extent, from the skin and the inner ear. During the last decade, however, more attention has been directed toward central effects, mainly Parkinson disease, related to the neuromelanin.
Toxicological Mechanisms The development of specific lesions in pigment cells is obviously the consequence of a combination of selective retention, resulting from melanin binding, and the toxicity of a particular compound. For example, substances with low toxicity 373
CHAPTER 18
(based on the local molar dose) in practice only very rarely induce lesions, in spite of high melanin affinity, whereas substances with a more expressed or specific toxicity may induce the adverse effects in the pigment cells. The melanin thus serves as a chemical depot, from which the stored substances are released and slowly enter the cytoplasm (the binding is normally reversible), and the degenerative course in the cell is ultimately determined by the intrinsic toxicity of the individual substance. Chloroquine, for example, which induces chorioretinopathy and hearing impairment (cf. below), is known to be an intercalating agent inhibiting various biochemical reactions such as protein synthesis (Roskoski and Jaskunas, 1972) and the digestive activity of lysosomes (Homewood et al., 1972). The toxicity of a particular compound may also depend on biotransformation and possible bioactivation reactions, which may take place within the pigment cell or in its close vicinity. Below, some examples of melanin binding combined with bioactivation are given in connection with the discussion of separate target organs. The mechanism so far discussed is based on the premise that the melanin serves passively as a storing device for the toxic chemicals. There are many indications, however, that the binding per se between a substance and melanin may also change the physicochemical properties of the melanin with modification or impairment of its physiological function, ultimately leading to adverse effects. It has been proposed that an important role of melanins might be the protection of pigment cells from the attack of chemically reactive molecules such as free radicals, electrophilic metabolites, and excited, potentially harmful species induced by photochemical processes (for a review, see Larsson, 1979; Swartz et al., 1992). It is well known, for example, that melanins may participate in redox reactions as an electron transfer agent (Gan et al., 1976), which apparently underlies the protective capacity, but it may also involve the oxidation of drugs with the formation of noxious radical cations (Bolt and Forrest, 1967). The binding of certain chemicals, especially electron-donating molecules such as phenothiazines, may block the redox properties of the melanin, because of charge transfer interaction, with a possible decrease in the protective capacity. On the other hand, it has been proposed that the melanin in the retinal pigment epithelium can exert its scavenging and antioxidant properties by the binding of redox-active metals, e.g. iron, copper, and manganese, and the sequestration of potential photosensitizing agents (Sarna, 1992). Another possibility that has been proposed in various connections seems to be the participation of melanin in redox-cycling reactions with the production of reactive oxygen species such as superoxide anions, hydroxyl radicals, peroxides, or singlet oxygen (Swartz et al., 1992). The redox properties of melanin and its interaction with molecular oxygen have been reviewed (Sarna, 1992). The adverse effects normally have a chronic character, and they are related in most cases to high-dose/long-term exposure. A prominent feature of the lesions is that the histological changes are found initially in the melanin-containing cells, and successively in adjacent tissues such as receptor cells. The 374
onset of the adverse effects is often delayed, and the entire manifestation of the lesions may occur even years after cessation of the offending substance (Burns, 1966). The exposure to various toxic compounds with melanin affinity may also cause additive effects. The histopathological changes (reviewed by Lindquist, 1973) are usually characterized by enlargement of the cells, a marked increase in the number of melanosomes, and pigment deposits. Degeneration of the pigment cells occurs gradually with release of melanosomes and other cellular debris, which migrate into surrounding tissues where secondary side-effects can be induced.
The Skin Pigment deposits in the eye, induced by phenothiazines, may appear together with hyperpigmentation of the skin, the socalled eye–skin syndrome (Greiner and Berry, 1964). Chloroquine has also been reported to induce pigment disturbances in the form of deeply pigmented, usually blue–black macules and bleaching of the hair (Stewart et al., 1968). Excessive pigmentation of illuminated areas of the skin appear routinely in most patients treated with chloroquine during the summer, and the pigmentation slowly and incompletely disappears during the winter (Drew, 1962). These findings indicate the presence of photochemical reactions. The high accumulation in the skin and the hair follicles in pigmented (but not in albino) animals strongly indicates that the pigment disturbances are associated with the accumulation of these drugs in the epidermal melanocytes and the hair follicles (Lindquist, 1973). The main interest in the pathology of the pigment cells of the skin, however, has been focused on malignant melanoma. Melanoma induction is generally considered to be causally connected with UV exposure, combined with certain individual characteristics such as number of nevi, ability to tan, skin color, age, etc. (Evans et al., 1988; MacKie and Aitchison, 1982). According to critical examination of the literature, however, the traditional UV-oriented hypothesis seems not to be fully consistent (Koh et al., 1990), and chemical carcinogenesis has been suggested to be an additional cause of the disease (Larsson et al., 1993; Rampen and Fleuren, 1987). This idea is supported by a number of epidemiological studies on melanoma incidence among workers employed in chemical industries and the like (Albert et al., 1980; Austin and Reynolds, 1986; Barthel, 1985; Heldaas et al., 1987; Magnani et al., 1987; Pell et al., 1978; Thomas and Decoufle, 1979). In autoradiographic studies on the biodistribution of various carcinogenic compounds in experimental animals, a pronounced and specific accumulation of potent carcinogens in the melanin-containing cells has been demonstrated, for example aflatoxin B1 (Larsson et al., 1988a), tobacco-specific N-nitrosamines, benzidine, polycyclic hydrocarbons such as dimethylbenzo-[a]anthracene and benzo[a]pyrene (Larsson et al., 1989a; Roberto et al., 1996), and some mutagenic food pyrolysis products (Bergman, 1985; Brandt et al., 1983, 1989). Most carcinogenic substances, however, are procarcinogens, which need metabolic activation to become car-
TOXICOLOGICAL ASPECTS OF MELANIN AND MELANOGENESIS
cinogenic. It is well known that the epidermis and upper dermis, including hair follicles and sebaceous glands, contain inducible enzymes, e.g. aryl hydrocarbon hydroxylase, capable of bioactivating xenobiotics to electrophilic reactive intermediates (Pannatier et al., 1978). Of particular interest in this respect, it has been found that human melanocytes can metabolize benzo[a]pyrene to a number of metabolites, including the proximate carcinogen benzo[a]pyrene-7,8-diol, which demonstrates the presence of cytochrome p450 IA1,2 in the melanocytes (Agarwal et al., 1991). The combination of the specific retention, due to melanin affinity, and the presence of bioactivating enzymes in pigmented tissues strongly supports the idea of chemical carcinogenesis as an etiological factor in malignant melanoma. There are some reports on chemical induction of melanoma in experimental animals (e.g. Anders et al., 1991; Berkelhammer et al., 1982; Goerttler et al., 1980), but a problem in this regard is that most studies on chemical carcinogenesis have routinely been performed in albino animals, which are refractory to melanin-related risks; this is also a general problem concerning drug-induced adverse effects in pigmented tissues.
Ocular Tissues Chorioretinotoxic effects of phenothiazines were first reported from clinical tests of piperidylchlorophenothiazine (NP-207) (Goar and Fletcher, 1957; Kinross-Wright, 1956). Later on, other phenothiazines such as thioridazine and especially chlorpromazine were found to induce similar side-effects (for a review, see Lindquist, 1973). The effects were dependent on relatively high total doses; thioridazine, for example, was considered to be safe in this respect when used in daily doses of less than 800 mg (Siddall, 1966). Many of the patients who receive high-dose therapy over long periods with phenothiazines, especially chlorpromazine, develop pigment disturbances in the eye characterized by pigment deposits in the lens,
which can grow into irreversible cataracts in the most severe cases (Barsa et al., 1965; Siddall, 1966). Pigment deposits on the cornea and the anterior surface of the iris have also been reported (Edler, 1966). The pigment disturbances in the anterior part of the eye are secondary to damage of the melanincontaining cells of the iris, which gives rise to a release into the aqueous humor of pigment granules that are deposited on the corneal endothelium and the frontal surface of the lens. It is unclear why the pigment deposits on the lens surface may occasionally induce opacities and even cataracts, but one possibility that has hitherto been overlooked is that it might result from a transfer of noxious chemicals, stored on the melanin of the pigment deposits, into the lens parenchyma. Chloroquine is considered to be a more potent chorioretinotoxic substance than the clinically used phenothiazines (Meier-Ruge, 1965; Rubin, 1968). The primary lesions are normally seen in the retinal pigment epithelium, where the cells become significantly enlarged with substantial increase in the number of melanosomes, and pigment-laden cells are successively found in the retina (Bernstein and Ginsberg, 1964; Wetterholm and Winter, 1964). Large pigment deposits occurring in the choroid, ciliary body, and the optic nerve have also been reported (Dale et al., 1965). The basic research on the drug-induced, ocular side-effects were performed during the 1960s, and several studies have since confirmed the results. The chemically induced ocular injuries were better understood when the pronounced melanin affinity of the offending drugs, e.g. chlorpromazine and chloroquine (Fig. 18.8), was revealed (Lindquist, 1973; Lindquist and Ullberg, 1972; Potts, 1962a, b, 1964a, b). The retention of the drugs was always restricted to the pigment layers of the uveal tract (the choroid and the iris stroma) and the pigment epithelium, and was absent from the nonpigmented ocular tissues. No corresponding accumulation was seen in albino animals, which are also considerably less sensitive to the adverse effects. Long-
Fig. 18.8. Whole-body autoradiogram of a pregnant pigmented mouse (C57BL) 24 h after intravenous injection of 14C-chloroquine. The highest concentration of radioactivity is found in the maternal and fetal eyes. Some accumulation can also be seen in the skin, kidney, liver, gastric mucosa, and the pancreas, especially in the pancreatic islets.
375
CHAPTER 18
term oral administration of high doses of chlorpromazine to albino rats, for example, has been found to have no observable effect on the retina (Dewar et al., 1978). Subsequent studies have revealed a great number of drugs with melanin affinity (Larsson, 1979; Menon et al., 1982; Persad et al., 1986; Salazar et al., 1976; Zane et al., 1990), and the significance of the affinity for melanin in the etiology of toxic chorioretinopathy and ocular pigment disturbances has become well established. However, not all melanin-affinic compounds may be related to ocular toxicity. Leblanc et al. (1998) claimed that many drug-related toxic effects on the retina described in humans and animal models are unrelated to melanin binding and that melanin binding and retinal toxicity are separate entities, the toxicity being largely a factor determined by intrinsic tissue toxicity rather than melanin affinity. However, as discussed below, it is clear that slow release of melanin-binding drugs from depots in sites such as the eye is important in the regulation of ocular pharmacology (Salazar-Bookaman et al., 1994). As emphasized by Hu et al. (2002), it is clear that, in some cases, the melanin binding acts as a protective shield, but accumulation of potentially toxic agents by binding to melanin may expose ocular pigmented tissue to increased hazard.
Inner Ear The first demonstration of selective retention of drugs in the inner ear due to melanin affinity was reported by Lindquist and Ullberg (1972), and they concluded that there might be a causal connection between the melanin affinity and chemically induced ototoxic lesions. The melanin of the inner ear is present in melanocytes in the connective tissues of the labyrinth and in the modiolus, in epithelial cells of the stria vascularis in the cochlea, and in the vestibular part, mainly in the planum semilunatum adjacent to the crista ampullaris, and in the walls of the utricle and saccule (for a review, see Lyttkens et al., 1979). For the most part, the melanocytes are localized to well-vascularized areas of apparent metabolic and secretory importance, in close contact with capillaries (Savin, 1965). Stria vascularis and planum semilunatum, for example, are locations for the secretion and absorption of endolymph. It is well documented that the antimalarial agent quinine exerts toxic effects on hearing, which becomes permanent when given in large doses, and developing embryos appear to be exceedingly sensitive (Schuknecht, 1974). Prolonged use of chloroquine, which, like quinine, is a quinoline derivative, in the treatment of arthritis and other chronic diseases may also lead to ototoxicity (Dewar and Mann, 1954). Hart and Naunton (1964) reported ototoxic lesions in children whose mother had been treated with chloroquine throughout the pregnancies. Both chloroquine and quinine are strongly bound to the melanin of the inner ear (Dencker and Lindquist, 1975; Dencker et al., 1973; Lindquist, 1973). It is particularly interesting to note that the otic and the ocular lesions caused by these drugs have typical features in common, such as an association with high-dose/long-term therapy, late onset of the pathological course, and primary lesions induced in the 376
pigment cells. These points of agreement strongly favor the idea that the ototoxic effects are related to the specific uptake and retention of the drugs in melanin. The accumulation of chloroquine and quinine in the stria vascularis and planum semilunatum causes a local disturbance or even degeneration of these areas, with migration and deposits of pigment granules (even into the endolymph and to the organ of Corti), followed by secondary lesions in adjacent tissues, including the hair cells (reviewed by Lindquist, 1973). The degeneration of the stria vascularis and the planum semilunatum may impair the secretion and electrolytic composition of the endolymph (a high K+/Na+ concentration ratio), which is injurious to the hair cells (Johnsson and Hawkins, 1972; Müsebeck, 1963). Both dilation and narrowing of the strial capillaries have been reported in experimental animals treated with quinine (Rüedi, 1951), which is obviously connected with the morphologically close contact between the pigment cells and the blood vessels of the stria vascularis. Aminoglycoside antibiotics constitute another group of ototoxic drugs known to produce lesions in the receptor cells of the cochlea and the vestibular tract (Rüedi, 1951), possibly due to secondary alterations of the endolymph (Johnsson and Hawkins, 1972). According to clinical experience, kanamycin, neomycin, and dihydrostreptomycin exert their deleterious effect mainly in the cochlea, whereas streptomycin and gentamicin preferentially cause vestibular damage (reviewed by Wästerström, 1984). Several of these antibiotics are strongly bound to melanin in vitro (Larsson et al., 1981; Lindquist, 1973), but not in vivo after a single administration (Larsson et al., 1981; Nilsson Tammela and Tjälve, 1986). In these studies, it was found that gentamicin, injected intravenously in mice, was mainly localized in the perilymph and the membranous linings of the cochlea and in the floor of the cochlear duct, and dihydrostreptomycin showed a similar distribution in rats and guinea pigs. The toxicokinetic outcome of chronic exposure is unknown. On the other hand, it has been demonstrated that kanamycin is significantly more ototoxic in pigmented than in albino guinea pigs (Wästerström et al., 1986). Degenerative changes (Johnsson and Hawkins, 1972) and increased pigmentation (Nakamura, 1957) in the stria vascularis in animals given ototoxic antibiotics have also been reported. The results are thus in conflict as regards a possible role of the melanin for the ototoxic effects of aminoglycosides, and the problem needs to be investigated further.
Central Nervous System The observation by Mann and Yates (1983) that the most heavily pigmented nerve cells of the substantia nigra are the first to degenerate in parkinsonian patients strongly indicates that neuromelanin is somehow directly involved in the etiology of the disease. Several factors of importance for the development of parkinsonism have been proposed, e.g. heredity, aging, virus infections, drugs, and other environmental chemicals, but the latter, i.e. chemical factors, are considered to be most likely (for a review, see Lydén-Sokolowski, 1990). Phenothiazines and other neuroleptics, for example, are known
TOXICOLOGICAL ASPECTS OF MELANIN AND MELANOGENESIS
to be associated with extrapyramidal disorders such as parkinsonism, occasionally with irreversible symptoms, and tardive dyskinesia (Richardson and Craig, 1982; Schmidt and Jarcho, 1966). The syndrome has been claimed to be a hyperdopaminergic condition of the postsynaptic dopamine receptors (Carlsson, 1970), but this hypothesis has been questioned, for example by Christensen et al. (1970), who found structural degeneration in both the striatum and the substantia nigra of patients suffering from tardive dyskinesia. Although most phenothiazines are bound to melanin (Larsson, 1979), including chlorpromazine, which has been demonstrated to interact with human neuromelanin (Lindquist, 1973), it is unclear to what extent the melanin affinity is involved in the extrapyramidal disorders. A complicating factor so far has been the difficulty in obtaining suitable animal models for studies of melanin-related central effects. Most experimental animals are poorly pigmented in the substantia nigra and locus coeruleus, and laboratory animals such as mice, rats, guinea pigs, and rabbits have been reported to lack, or have only minute amounts of, neuromelanin (Barden and Levin, 1983; Marsden, 1969). In primates, the concentration of neuromelanin increases with age and with the relation to man, but the general impression in conjunction with histological examination of the brain of relatively young or adolescent monkeys, which are the most commonly used primates for experiments, is the presence of a rather low pigmentation in the substantia nigra. In addition, the use of monkeys for experiments is very expensive and ethically controversial. An animal model of potential interest has turned out to be the frog (Barbeau et al., 1985). In the ventral motor regions of the brain, frogs have pigmented neurons that correspond functionally to the pigmented nerve cells in mammals (Kemali and Gioffré, 1985). The nature of the amphibian neuronal pigment is not clearly understood, but histochemical staining has indicated that it is a melanin (Lydén-Sokolowski et al., 1989). A decisive event in the idea of chemical factors behind the etiology of Parkinson disease was the observation some years ago that drug abusers were affected with severe irreversible motor disturbances, similar to those seen in Parkinson disease, after administration of a synthetic heroin (Langston et al., 1983). Chemical analysis showed that the illicit narcotic preparation was contaminated with 1-methyl-4-phenyl1,2,3,6-tetrahydropyridine (MPTP), which was found to induce selective destruction of the melanin-containing nerve cells of the substantia nigra (reviewed by Lindquist et al., 1987), without involvement of the dopamine receptors of the striatum, as revealed by positron emission tomography (Hartvig et al., 1986). MPTP is strongly bound to melanin in vitro, including synthetic dopamine melanin (Lydén et al., 1983) and human neuromelanin (D’Amato et al., 1987), and to neuromelanin of frogs in vivo (Lindquist et al., 1986). The degree of MPTP-induced neurotoxicity is apparently related to the amount of neuromelanin present in the substantia nigra. Man and other primates are considerably more sensitive to the neurotoxic effects than laboratory animals such as guinea pigs and rats (Chiueh et al., 1983) and mice (Hallman et al., 1984;
Heikkila et al., 1984), which are almost lacking neuromelanin (cf. above). The preferential destruction of pigmented nerve cells by the MPTP is dependent on local bioactivation in the brain. MPTP is oxidized to 1-methyl-4-phenyl-2,3-dihydropyridinium (MPDP+) and ultimately to the pyridinium cation 1-methyl-4-phenylpyridine (MPP+) by monoamine oxidase (Chiba et al., 1984). Owing to its water solubility, MPP+ is retained in the dopaminergic zone of the brain where it is formed (Lydén-Sokolowski et al., 1988). MPP+ is bound to neuromelanin (D’Amato et al., 1986), and it has been shown that MPP+ is the species responsible for the neurotoxic effects (Langston et al., 1984; Markey et al., 1984). It has been found that MPP+ is concentrated in mitochondria by energydependent mechanisms, and that it inhibits NADH oxidation, leading to ATP depletion and possible cell death (Ramsay et al., 1986). At high acute dose levels, this mechanism should apply to all experimental animals, irrespective of the neuronal content of melanin but, at subchronic or chronic exposure to low concentrations, the local storage of MPP+ on the neuromelanin is apparently a prerequisite for the toxic effects (cf. Lindquist et al., 1987). In this connection, it is interesting to note that synthetic dopamine melanin can oxidize MPDP+ to MPP+, with the generation of hydrogen peroxide and hydroxyl radicals (Korytowski et al., 1987, 1988; Wu et al., 1986). The reaction is promoted by iron chelates, and it has been proposed that iron plays an important role in the development of parkinsonism (Ben-Shachar and Youdim, 1993; Zecca and Swartz, 1993). In the search for possible parkinsonism-inducing candidates, interest has been focused on the herbicide paraquat, which is structurally related to MPP+ and shows high melanin affinity (Larsson et al., 1977). Paraquat has been found to induce parkinsonian symptoms in frogs (Barbeau et al., 1985) and, by autoradiography, a selective accumulation of paraquat in the pigmented nerve cells of frogs (Fig. 18.9) has been demonstrated (Lindquist et al., 1988). It has been proposed that paraquat may participate in redox cycling (Johannessen
Fig. 18.9. Whole-body autoradiogram of 14C-paraquat in a frog (Rana temporaria) 1 day after intraperitoneal injection. Accumulation is evident in neuromelanin-containing nerve cells and in melanin-bearing cells in the meninges.
377
CHAPTER 18
et al., 1985), continuously generating noxious oxygen species, which is actually the mechanism for the lung toxicity of paraquat (Bus et al., 1976). During recent years, the main interest has been concentrated on neurotoxic metals. Manganese, for example, is known to induce an extrapyramidal disorder resembling parkinsonism (Mena et al., 1967; Rodier, 1955), with selective injury of the pigmented nerve cells of the substantia nigra (Gupta et al., 1980). Like MPTP, manganese is bound to melanin in experimental animals (Lydén et al., 1984), and it seems likely that the redox properties of manganese (similar to those of iron; see above) are of importance for the neurotoxicity. As mentioned above, neuromelanin may act as an antioxidant as a result of the ability to sequester redox-active metal ions such as iron (Korytowski et al., 1995) but it was also demonstrated that dopamine melanin saturated with ferric ions could enhance the formation of free hydroxyl radicals by redox activation of the ions (Zareba et al., 1995). It was concluded that neuromelanin may become an efficient cytotoxic pro-oxidant under conditions that stimulate the release of accumulated iron.
Fig. 18.10. Detail of an autoradiogram showing the cochlea of a young pigmented hooded rat 4 days after intraperitoneal injection of 3H-N,N-bis-acetanilidedimethylamine (QX-572). There is high uptake of radioactivity in the stria vascularis, basal membrane, and mediolus, corresponding to the presence of melanin.
Exploitation of Melanin Binding Pharmacology Specific accumulation of drugs in melanin-containing tissues has mainly been related to adverse effects, but it also implies certain potential pharmacological benefits. The most obvious example is the possibility of using melanin-affinic compounds for melanoma targeting, which is discussed separately below, but there are other potential applications as well. The basic difference between toxicology and pharmacology is a matter of dose, which means that the combined outcome of the therapeutic index of a drug and the stored concentration on melanin is decisive for a local toxicological vs. pharmacological effect (or even no effect whatever). As mentioned previously, melanin may temporarily protect pigment cells from the noxious effects of chemicals by acting as an adsorbing filter. A corresponding effect, from a pharmacological approach, is illustrated by the melanin-dependent mydriatic effect of atropine after topical application, described by Salazar et al. (1976). They found that atropine, which is bound to melanin, exerts a significantly stronger mydriatic effect in a light human iris than in a dark iris, which was explained on the basis of the accumulation of the atropine on the melanin, giving reduced concentrations of the drug in the vicinity of the muscarinic receptors. They also demonstrated a significantly increased duration of the atropine mydriasis in the pigmented iris compared with an albino iris, which neatly illustrates the significance of a drug depot retained on melanin.
Treatment of Tinnitus The storage of drugs on melanin for local therapeutic effects has not been put into ordinary practice so far, mainly because of the delicate and potentially hazardous balance between 378
toxic and pharmacological dose levels that need to be adjusted, but a few studies have been undertaken according to this principle. Lidocaine, which is a local anesthetic drug, is known to have a mitigating effect on tinnitus (Israel et al., 1982), and it is also bound to melanin, e.g. in the modiolus of the cochlea in rats (Englesson et al., 1976; Lyttkens et al., 1979). A few additional drugs with the combined properties of melanin affinity and alleviating effect on tinnitus have also been identified, viz. bupivacain and chlorpromazine (Lyttkens et al., 1979), tocainide (Larsson et al., 1984), and N,Nbis-acetanilidedimethylamine (QX-572), which is the quaternary analog of lidocaine (Lyttkens et al., 1984), and the results from autoradiographic experiments on rats and clinical trials on patients have indicated a connection between the storage of the drugs on the melanin of the inner ear and the relieving effect on severe tinnitus. A fundamental question discussed in this regard is whether lidocaine reduces tinnitus by a central or a peripheral mechanism of action. To elucidate this problem, the effect of lidocaine on tinnitus was compared with that of QX-572 (Lyttkens et al., 1984). As QX-572 is a quaternary ammonium compound, it does not pass the blood–brain barrier, which eliminates the possibility of a central effect. The results of the investigation, including both autoradiographic experiments as well as clinical studies, showed that the effects of lidocaine and QX-572 on tinnitus are mediated by a peripheral mechanism, apparently related to their accumulation on the inner ear melanin (Fig. 18.10) — both drugs exerted similar mitigating effects on tinnitus and uptake on the melanin of the inner ear, but only lidocaine passed the blood–brain barrier. As indicated above, it is of crucial importance that the therapeutic effects of the local
TOXICOLOGICAL ASPECTS OF MELANIN AND MELANOGENESIS
anesthetics strongly outweighs the toxicity of the drugs. Clinical tests have shown that no acute or chronic functional disturbances on hearing, related to lidocaine, are induced at dose levels of 1000–1500 mg, given at a therapeutic dose rate of 6 mg/kg/h (Englesson et al., 1976).
Photochemotherapy Skin conditions, such as vitiligo and psoriasis, may be treated by photochemotherapy (PUVA), which involves the combined effect of a photosensitizer and UV radiation, especially UVA (Honigsmann et al., 1987). Psoralens are commonly used as photosensitizers, and the acronym PUVA originally referred to the potentiating interaction between orally administered 8methoxypsoralen (methoxsalen) and UVA radiation. Methoxsalen is the most commonly used photosensitizer, but related furocoumarins such as 5-methoxypsoralen and 4,5¢,8trimethylpsoralen are occasionally preferred. PUVA therapy is generally regarded as the most effective and safe method for achieving repigmentation in vitiligo, even though interest in grafting is increasing. The effects of PUVA therapy are characterized by an increased number of viable melanocytes and melanosomes, activation of tyrosinase, and gradual migration of melanocytes at the border of the vitiliginous areas inward to form homogeneous pigmentation of the entire area (reviewed by Honig et al., 1994). The mode of action of the psoralens is not fully understood. According to the classical concept, the psoralens intercalate in the DNA, and the absorption of UVA photons leads in two steps to firm covalent bonding to pyrimidine bases, creating a cross-linked bifunctional photoadduct that inhibits DNA synthesis and delays epidermal cell division (Walter et al., 1973). After cell repair, the melanocytes divide into functionally active cells with enhanced pigmentation, but the full explanation of the beneficial effects in vitiligo is probably complex, with the potential additions of selective destruction of lymphocytes or suppression of an autoimmune response playing some role (Honig et al., 1994). It has also been proposed that PUVA therapy induces the formation of reactive oxygen species, which can damage membranes and cause deleterious metabolic changes (Pathak and Joshi, 1984). More recent studies have shown that PUVA treatment of hairless mice induces cutaneous depletion of GSH (Connor and Wheeler, 1987), and this finding was subsequently supported by experiments in vitro, demonstrating PUVA-induced photooxidation of GSH (d’Ischia et al., 1989), which indicates a direct connection between PUVA therapy and the critical role of GSH in melanogenesis (Prota, 1992). Turning now to the melanin and its possible role in PUVA therapy, it has been demonstrated by autoradiography that methoxsalen is bound to melanin, resulting in pronounced accumulation in the uvea of pigmented rats (Wulf and Hart, 1978). In similar studies on mice, a selective but transient uptake of methoxsalen was found in the pigment cells of the eye and skin, with a decrease in the concentration starting about 4 h after injection (Larsson and Mårs, 1993). The melanin affinity of methoxsalen, which is quite surprising
because the drug lacks functional cationic groups, was also demonstrated in vitro (Larsson and Mårs, 1993). The interaction is probably of hydrophobic character, which should explain the limited retention period after a single injection. By the means outlined above, the storing of methoxsalen on the melanin may in principle improve the outcome of PUVA therapy in pigment cells due to increased local concentrations of the drug but, as the mechanism of action obviously involves DNA cross-linking and other possible biochemical insults (cf. above), the melanin affinity may underlie side-effects as well. It has been reported, for example, that geese and ducks, chronically fed with Ammi majus seeds, which naturally contain 5and 8-methoxypsoralen, may develop uveal atrophy (Barishak et al., 1975) and pigmentary retinopathies (Egyed et al., 1975). These effects may in fact be the result of the interaction between the psoralens and UV radiation, as thorough measurements have shown that 30% UVA (365 nm) is transmitted by the lens (Bachem, 1956). Long-term exposure to PUVA is known to be associated with risks of skin cancer (reviewed by Stern, 1992), and there are a number of case reports that suggest a possible connection between PUVA therapy and melanoma. More extensive epidemiological studies have indicated a slightly higher incidence of melanoma in PUVA-treated patients than expected in the general population, but the increased risk found was not statistically significant (Gupta et al., 1988). It seems to be too early to state whether exposure to PUVA is associated with an increased risk of melanoma or not. Additional exposure to other skin carcinogens, e.g. arsenic or methotrexate, may complicate the assessment of epidemiological studies, and there is also some question as to whether sufficient latency time has passed from first exposure to PUVA for its full carcinogenic effect to be realized.
Monitoring Biological monitoring of the exposure to xenobiotics is in principle subordinated to both toxicology and pharmacology. The main areas so far have been the monitoring of exposure to occupational hazardous chemicals and environmental pollution, individual drug screening, the control of illicit abuse of narcotics and doping, and the analyses of tissue samples in forensic medicine. The body levels of foreign substances in urine and blood samples, which are easily accessible, may normally be determined within only a couple of days after exposure, solely giving information on acute exposure. Screening and quantitative assessment of chronic exposure or intermittent administration, on the other hand, is much more complicated and implies specific retention of a compound in a tissue that has easy access for biopsy and analysis. Hair has proved to meet these requirements for certain organic compounds, mainly because of interaction with melanin and keratin. Metals have been investigated most closely in this connection, and the binding to melanin has been established explicitly in a few studies (Cotzias et al., 1964). Subsequently, however, interest has been more concentrated on the accumulation of organic 379
CHAPTER 18
compounds in the hair, e.g. morphine for the determination of opiate abuse histories (Baumgartner et al., 1979; Marigo et al., 1986). Baumgartner et al. (1979) reported that differences in morphine concentration in sections of hair near the scalp and near the distal end correlated with the length of time the drug had been used, but the mechanism behind the accumulation is still obscure. There are a growing number of reports, however, on melanin affinity as the basis for the uptake, for example of industrial chemicals, monitored by mass spectrometry of hydrolyzed hair samples of workers (Larsson et al., 1988b), detrimental airborne impurities such as nicotine (Ishiyama et al., 1983), and various drugs (Ishiyama et al., 1983; Uematsu et al., 1990; Viala et al., 1983). Recently, a promising technique for the detection of illegal use of the beta-agonist clenbuterol as a repartitioning agent in meat production was developed (Appelgren et al., 1994a; Dürsch et al., 1995). Doses given for this purpose are 5–10 times higher than the therapeutic ones, and the illegal use of the drug has caused several cases of food poisoning (cf. Appelgren et al., 1994a). Clenbuterol is bound to melanin (Appelgren et al., 1994b), and the results from experiments on calves, fed with relevant doses of clenbuterol, have shown that it is possible to detect the drug in hair samples up to 14 days after cessation of the administration (Appelgren et al., 1994a). Most likely, it would be possible to detect the drug until the hair is shed, as the clenbuterol will probably stay in the hair once it has been incorporated. Similar experiments by others have shown that the concentration ratio of clenbuterol between black and white hair of calves is approximately 50:1, illustrating the importance of melanin-related retention (Dürsch et al., 1995).
Applied Toxicity of Melanin-affinic Agents A unique characteristic of melanotic melanoma is the presence of melanin, which may serve as a target for the diagnosis and treatment of the disease. Drugs with melanin affinity, e.g. quinoline derivatives labeled with radioiodine, have been used for melanoma scanning (Beierwaltes et al., 1968; Blois, 1968). A potential problem, however, is the corresponding uptake of label in normal pigmented tissues, for example in the eye and the skin. Some reagents may, however, prove valuable as diagnostic probes. For example, 123I-labeled iodoamphetamine and benzamides have been used successfully (Cohen et al., 1988; Labarre et al., 1999; Moins et al., 2002). In recent years, possible therapeutic application of melaninbinding substances has been attempted using methylene blue (MTB) as carrier of radionuclides (Link, 1992; Link and Carpenter, 1990, 1992; Link et al., 1989). Radioiodinated MTB was demonstrated to be suitable for scintimetric detection of melanoma and, when labeled with the a-emitter astatine-211 (with a half-life of 7.2 h), promising therapeutic effects on human melanotic melanoma xenografts in mice were found. In further studies of the histopathology in melanomabearing mice after the administration of therapeutic doses of 211 At-MTB, it was found that the radiation effects were restricted to the tumor cells, whereas no macro- or microscopic 380
lesions could be observed in normal tissues, including the melanin-containing portion of the eye (Michalowski et al., 1993). This may be explained by the dual contributions of the exposed position of tumor cells in general, due to rapid cell turnover (cf. above), and the finding that the accumulation of 211 At-MTB in the eye is delayed for several hours, i.e. one to two times the half-life of astatine-211 (Link, 1994). Another approach, tried mainly in experimental animals, is the use of radiolabeled melanin precursors, at least as far as melanotic melanoma is concerned, where the melanin formation is usually rather pronounced. Physiological precursors, such as tyrosine, dopa, and dopamine, have been examined with reference to their possible specificity for developing melanin (Blois and Kallman, 1964; Hutton and Pentland, 1976; Meier et al., 1967), but a limitation of this approach has been the uptake of the precursors in the synthesis of proteins and monoamines in normal tissues, which gives poor selectivity for the growing tumoral melanin. Artificial melanin precursors such as the thioureylenes, on the other hand, are more promising melanoma seekers because of their high specificity for nascent melanin (Larsson, 1991). Autoradiographic distribution studies on melanoma-bearing mice have demonstrated a selective and pronounced accumulation of label in the tumors, not only of 2-thiouracil (Fig. 18.11) (Dencker et al., 1979, 1982; Fairchild et al., 1982; Levin et al., 1983), but also of the radioiodinated analogs 5iodo-2-thiouracil and 5-iodo-6-n-propyl-2-thiouracil (Larsson et al., 1982; Van Langevelde et al., 1983), methimazole (Olander et al., 1983), thiourea (Mårs and Larsson, 1996), and 2-mercaptobenzothiazole (Fig. 18.12), but the latter was also found to be a strong tyrosinase inhibitor, which decreases the uptake in melanoma (Mårs and Larsson, 1995). Thiouracil and iodothiouracil are the most explored thioureylenes so far as regards possible clinical application. Their selectivity for melanotic melanoma, including metastases (Fairchild et al., 1982; Yamada et al., 1988), is striking, and the only normal tissue in which a significant accumulation and retention occurs is the thyroid gland as a result of the thyrostatic properties of thioureylenes in general. Uptake in the thyroid is essentially decreased by pretreatment with thyroxine, which acts through a feedback depression of the glandular activity and, if radioiodine is used as label, the uptake of radioactivity in the thyroid is prevented by pretreatment with potassium iodide (Larsson et al., 1982). The accumulation of thiouracil in murine melanoma increases almost linearly with the injected dose up to subtoxic levels, indicating nonsaturable incorporation into the melanin in vivo (Dencker et al., 1982). The clinical use is thus favored, especially when the specific activity of the radiolabeling is high, which is easily obtained with the use of short-lived radioisotopes. Palumbo et al. (1994) reported that the incorporation of thiouracil into melanoma tumors in mice follows very rapid kinetics, with the maximum being reached within 30 min. Previous studies have shown that the highest relative concentration in murine melanoma, compared with normal tissues, is attained at 24–48 h after injection (Dencker et al., 1982). If properly labeled with a clinically useful
TOXICOLOGICAL ASPECTS OF MELANIN AND MELANOGENESIS
Fig. 18.11. Whole-body autoradiogram of a mouse, subcutaneously transplanted with Harding–Passey melanoma, 24 h after two daily intramuscular injections of 14C-thiouracil. Highly selective retention of the radiolabel can be seen in the melanoma (the lower part of the tumor is necrotic). The concentration in normal tissues, such as the liver, kidney, lung, and eye, is relatively low.
2-Thiouracil
Fig. 18.12. Structural formulae of substances that are selectively incorporated into melanoma melanin in vivo.
Methimazole
radionuclide, diagnosis by radioscanning may thus be started soon after the injection, and the optimal time for differential diagnosis should be 1–2 days after the administration. Preparatory clinical studies on iodothiouracil have shown that the uptake in cultured human melanoma cells is time dependent and increases with the melanin content (Broxterman et al., 1983; Larsson et al., 1985). In both mice (Larsson et al., 1985) and Syrian golden hamsters (Franken et al., 1985), carrying transplantable melanoma, the accumulation of radioactivity was demonstrated by gamma scintigraphy after the injection of radioiodinated thiouracil. A couple of clinical pilot trials have also been performed. Franken et al. (1986a) compared the clinical outcome of ocular melanoma detection with 123I-thiouracil and 67Ga-citrate respectively.
5-Iodo-2-thiouracil
Thiourea
5-Dihydroxyboryl-2-thiouracil
2-Mercaptobezothiazole
Using a single eye probe collimator for the eye examinations, they demonstrated a significantly increased uptake of label in 7 out of 10 patients, with no false-positive results, and they concluded that 123I-thiouracil was at least as useful as 67Gacitrate for ocular melanoma diagnosis. A preliminary clinical experiment on gamma scintigraphy of cutaneous melanoma in patients injected with 131I-thiouracil has also been performed (Olander et al., 1991). The scanning was complemented by impulse counting of tumor and skin samples dissected out at surgery. Imaging was unsuccessful because of the use of too low radiodoses, but the results indicated that total doses of the order 150–200 MBq would be enough for the imaging. The extrapolation of data from experimental animal models to malignant melanoma of humans may in principle be 381
CHAPTER 18
unreliable with regard to factors such as the heterogeneity of pigment formation, the rate of proliferation, tumoral blood supply, and necrosis. These factors are usually rather reproducible in experimental melanomas, as distinguished from the tumors of patients, and the main problem of using thiouracils for melanoma targeting in patients is in fact the tendency of the metastases to lose pigmentation and become amelanotic. It has been estimated that about 7% of the primary cutaneous melanoma tumors are amelanotic, whereas 13% of the regional lymph node metastases and 31% of the distant metastases lack melanin (Shaw et al., 1985), but variations may occur between metastatic sites, as well as within single tumors (Watts et al., 1981). Amelanotic melanomas, however, may contain minor amounts of melanin (Sarna and Swartz, 1978) and, in view of this observation, the diagnostic potential of the thiouracils becomes more promising. In addition to melanoma detection, the thiouracils may be used for the assessment of the viability of treated melanoma, for example after X-ray irradiation therapy. In experiments with hamsters carrying ocular melanoma, Franken and coworkers (1986b) demonstrated that the uptake of 125Ithiouracil, after irradiation with 40 Gy X-ray, was reduced by 90% 12 days after the treatment. The results may contribute to a more adequate prognosis, as the regression of choroidal melanoma following radiation therapy is usually slow and may take months during which careful observations are necessary to indicate any possible reaction process (Lommatzsch, 1983). The usefulness of the thioureylenes for treatment of malignant melanoma is a matter of uncertainty, mainly because of the occurrence of amelanotic or poorly pigmented cells or metastases, but a few animal studies have been performed. To evaluate the therapeutic potential of thiouracil, mice transplanted with Harding–Passey melanoma were injected with high radiodoses of 35S-2-thiouracil in two independent studies (Fairchild et al., 1989; Olander, 1988). At total doses ranging from about 2 to 8 MBq/g body weight (Olander, 1988), there was on average a halving of the volume and weight of the tumors compared with untreated controls. At doses of about 18 MBq/g body weight (Fairchild et al., 1989), complete tumor regression with no regrowth was observed in some of the animals. It is clear that the radiodoses in these experiments were extremely high — the corresponding dose for a human patient, weighing 70 kg, would be of the order 130–1300 GBq, but comparable doses are more related to the body surface than to the body weight, which may in practice reduce the radiodoses required for the treatment of patients. The idea of using thiouracil as a vehicle for cytostatic agents has been tested in vitro by Wätjen et al. (1982). They investigated the effects of arotenoids and retinoids as 5-substituents of 2-thiouracil on Cloudman S91 melanoma cells. Despite selective uptake of the adducts in the tumor cells, no toxic effects could be noted. In a pilot study the chemotherapeutic effect of 5-(nitrogen mustard)-2-thiouracil on mice transplanted with Harding–Passey melanoma was tested, but 382
the results of this study were negative too. It might appear at first sight that this approach is doomed to failure, but it deserves to be explored in more detail with other cytotoxic ligands, because the discouraging results so far obtained are very preliminary. Thioureylenes may also be used as carriers of boron-10 for boron neutron capture therapy (BNCT). Boron-10, which is a stable nuclide, readily captures thermal neutrons and undergoes instantaneous nuclear fission into an alpha particle and a lithium ion with pronounced ionizing capacities (for a review, see Carlsson et al., 1992). The technique is based on the irradiation of tumors with a thermal neutron beam from an external source, after the accumulation of a boronated compound in tumor tissue and clearance from surrounding normal tissues. The range of the emitted particles is less than a cell diameter and, because of high linear energy transfer, the particles are very efficient in cell killing. The potential of this approach for melanoma treatment was first recognized by Mishima (1973) using a boronated chlorpromazine derivative for BNCT in melanoma-bearing pigs. Thermal neutrons may reach a distance into the body of about 4 cm, but the target depth may be doubled by the use of epithermal neutrons, which are moderated to thermal energies during the penetration of the top layer of tissue. At present, several reactors with epithermal neutron beams that meet with the clinical requirements as to purity and high flux density of neutrons are available, but the bottleneck of the technique is the poor availability of specific tumor seekers for the delivery of boron-10. Clinical experience of BNCT mainly originates from the treatment of brain tumors (reviewed by Carlsson et al., 1992), but trials on melanoma patients have also been performed. Mishima et al. (1989) used 10B1-p-boronophenylalanine (BPA) as a melanoma seeker, and they reported on successful treatment of a patient suffering from an inoperable malignant melanoma lesion on the left occiput. Additional patients have been treated more recently (Mishima et al., 1992). It was proposed that BPA accumulates selectively similarly to the melanin precursor tyrosine but, according to Coderre et al. (1987), BPA uptake in melanoma is dependent on active amino acid transport rather than melanin synthesis — they reported on accumulation of BPA in both melanotic and amelanotic rodent melanomas. Various thioureylenes have also been boronated and tested for melanoma specificity in experimental animals. 5-Dihydroxyboryl-2-thiouracil (Fig. 18.7) and its 6-propyl derivative, for example, were found to be selectively accumulated in B16 and Harding–Passey melanomas transplanted to mice, and the tumoral boron-10 levels as well as the melanoma/blood concentration ratios were in the range necessary for possible treatment by BNCT (Gabel, 1989; Tjarks, 1989). In these experiments, 10B-enriched preparations were used — naturally occurring boron consists of about 20% boron-10, but precursors for clinical use with an isotopic enrichment to 98–99% boron-10 are commercially available. In other experiments, thioureylenes have been boronated by adduct formation with
TOXICOLOGICAL ASPECTS OF MELANIN AND MELANOGENESIS
decaborane. Studies in vitro have shown that complexes between decaborane and, for example, 5-(diethylamino) methyl-2-thiouracil and 1H-1,2,4-triazole-3-thiol, respectively, are readily incorporated into dopa-melanin during its synthesis (Roberto and Larsson, 1989) and selectively accumulated in melanotic melanoma transplanted in mice (Larsson et al., 1989b). No boronated thioureylenes have come into clinical use so far, but the results from the animal experiments are quite promising and qualify for possible clinical application. As mentioned above, however, the use of boronated thioureylenes is limited to melanotic tumors, but it might be possible to optimize the treatment, i.e. to target all tumor cells, by combining the boronated thioureylenes with other melanoma seekers, e.g. BPA and/or boronated monoclonal antibodies. It should also be stressed that the use of BNCT is generally restricted to the treatment of metastases with limited spread, solitary metastases, and inoperable primary tumors, or to adjuvant therapy. The reason is the practical impossibility of giving whole-body exposure to neutrons (cf. Carlsson et al., 1992) and, as regards generalized melanoma, BNCT has to be combined with other suitable modalities, e.g. surgery, external radiation, or chemotherapy.
Perspectives The highly visible nature of surface pigmentation has made it a topic of interest to biologists for centuries, and the variations in human pigmentation are both remarkable and have many ramifications beyond the biological sphere. It is astounding that, despite the degree of interest in melanin pigmentation and the fact that the major pathway of melanogenesis was elucidated 80 years ago, our comprehension of the process and its control is so tentative. The fact that, in vertebrates, melanogenesis is the prerogative of specialized dendritic cells of neural crest origin is in itself an interesting feature and, in unraveling the mechanisms involved in the biogenesis of melanin, many insights have been gained into the complexities of subcellular organization, particularly with regard to vesicular traffic. Apart from leading to a greater understanding of phenomena associated with underlying systemic disease, the pragmatic importance of understanding the control of pigmentation is connected with the physiological functions of melanin, of which the best known is photoprotection. Modification of the degree of cutaneous pigmentation may be useful in the future, on the one hand providing adequate photoprotection to compulsive sun-bathers and possibly, on the other hand, in reducing the need for vitamin D supplementation of the diet necessary for highly pigmented individuals domiciled in regions of high latitude. Another area that could benefit from advances in the knowledge of melanogenesis is that concerned with cosmetic implications of surface pigmentation, particularly as there tends to be much anxiety created by regional pigmentary changes.
Modification of the degree of pigmentation could have important psychological benefits to patients. The research on melanin-related adverse effects of chemicals is presently most focused on neuromelanin and its possible role in the development of Parkinson disease and other extrapyramidal disorders, especially with regard to the interaction between redox-active metals and neuromelanin. The uptake of chemicals related to MPTP and, for example, neuroleptic drugs on neuromelanin is also of great interest in this respect. As mentioned previously, however, the lack of suitable animal models complicates the experiments, and another serious problem in this connection concerns the incomplete insight into the chemical structure of neuromelanin. Considerable efforts are presently being directed to the latter problem to obtain a reliable neuromelanin model for in vitro experiments. Not only the detailed nature and binding properties of neuromelanin, but also the properties of other extracutaneous melanins such as the melanins of the eye and the inner ear, which are found in both epithelial cells and melanocytes, are presently subjected to more extensive investigations. The binding of carcinogenic substances to melanin, as an etiological factor behind the induction of malignant melanoma, is another area of increasing interest. The role of enzymatic activation of procarcinogens stored on melanin has turned out to be of crucial importance in this connection, and it may be further elucidated by molecular biological or histochemical techniques for the mapping of bioactivating enzymes in pigment cells in situ. A related, and possibly underestimated, problem concerns the significance of photochemical reactions between substances stored on melanin and ultraviolet radiation. The development of melanoma seekers is presently found to be in a dynamic phase, mainly as the result of a better understanding of the mechanisms behind the incorporation of thioureylenes into nascent melanin, and the identification of new derivatives by screening techniques. The pharmacokinetic and dynamic properties of these substances need to be investigated in more detail before clinical application is advisable. Pharmacological applications of melanin affinity, in addition to the development of melanoma seekers, are more speculative. The use of melanin affinity for storage of drugs in pigmented tissues for local treatment of diseases, e.g. tinnitus, is complicated because of the delicate balance between therapeutic and toxic doses that need to be clarified and managed. The possibility of using melanin affinity for biological monitoring, on the other hand, is more realistic and presently subjected to further examinations. An important aspect of the study of pigmentation is the possibility of applying this process to chemotherapy for metastatic melanoma using the unique metabolic pathway of melanogenesis as the targeting modality. It is possible that the apparent sensitivity of melanocytes to freezing and reperfusion damage could be used in a similar way. The commercial advantage of being able to determine the hair color of, for example, wool-bearing animals may prove to be valuable, and 383
CHAPTER 18
advances in knowledge of mechanisms of branding by depigmentation may appeal to those governments wishing to barcode their citizens for easy identification.
Acknowledgments This chapter is based on two precursors: a general chapter on depigmentation by one of us (PAR) and a chapter by the late Bengt Larsson on the toxicology of melanin-affinic agents. We wish to acknowledge the great debt that we owe to Bengt Larsson in providing the firm foundation of his profound understanding of the binding of substances to melanins and his careful, balanced, and comprehensive review of the field.
References Abdel-Malek, Z., V. B. Swope, N. Amornsiripanitch, and J. J. Nordlund. In vitro modulation of proliferation and melanization of S91 melanoma cells by prostaglandins. Cancer Res. 47:3141–3146, 1987. Abdel-Malek, Z., V. B. Swope, J. Pallas, K. Krug, and J. J. Nordlund. Mitogenic, melanogenic and cAMP responses of cultured neonatal human melanocytes to commonly used mitogens. J. Cell. Physiol. 150:416–425, 1992. Abe, H., N. Ohya, K. F. Yamamoto, T. Shibuya, S. Arichi, and S. Odashima. Effects of glycyrrhizin and glycyrrhetinic acid on growth and melanogenesis in cultured B16 melanoma cells. Eur. J. Cancer Clin. Oncol. 23:1549–1555, 1987. Agarwal, R., E. E. Medrano, I. U. Khan, J. J. Nordlund, and H. Mukhtar. Metabolism of benzo(A)pyrene by human melanocytes in culture. Carcinogenesis 12:1963–1966, 1991. Albert, A. Selective Toxicity: The Physicochemical Basis of Therapy, 7th edn. London: Chapman and Hall, 1985, pp. 469–475. Albert, D. M., C. A. Puliafito, A. B. Fulton, N. L. Robinson, Z. N. Zakov, T. P. Dryja, A. B. Smith, E. Egan, and S. S. Leffingwell. Increased incidence of choroidal malignant melanoma occurring in a single population of chemical workers. Am. J. Ophthalmol. 89:323–337, 1980. Anders, A., H. Gröger, F. Anders, C. Zechel, and A. Smith. Discrimination of initiating and promoting carcinogens in fish. Ann. Rech. Vet. 22:273–294, 1991. Ando, H., M. Oka, M. Ichihashi, and Y. Mishima. Protein kinase C and linoleic acid-induced inhibition of melanogenesis. Pigment Cell Res. 3:200–206, 1990. Ando, S., O. Ando, Y. Suemoto, and Y. Mishima. Tyrosinase gene transcription and its control by melanogenic inhibitors. J. Invest. Dermatol. 100:150S–155S, 1993. Appelgren, L.-E., U. Bondesson, E. Fredriksson, C. Ingvast Larsson, and D. S. Jansson. Analysis of hair samples for clenbuterol: A possibility to detect illegal use in calves. In: Proceedings of the 6th International EAVPT Congress, Edinburgh, 1994, P. Lees (ed.). Oxford: Blackwell Scientific Publications, 1994a, p. 272. Appelgren, L.-E., C. Ingvast Larsson, D. S. Jansson, and B. S. Larsson. Pigment affinity of clenbuterol. Distribution studies of labelled clenbuterol in mice using autoradiography. In: Proceedings of the 6th International EAVPT Congress, Edinburgh, 1994, P. Lees (ed.). Oxford: Blackwell Scientific Publications, 1994b, p. 276. Arnold, J., P. Anthonioz, and J. P. Marchand. Depigmenting action of corticosteroids. Experimental study on guinea pigs. Dermatologica 151:274–280, 1975. Aubert, C., and C. Bohuon. Depigmentation of the golden hamster by oral 9,10-dimethyl-1,2-benzanthracene administration. C. R. Acad. Sci. 271:281–284, 1970.
384
Austin, D. F., and P. Reynolds. Occupation and malignant melanoma of the skin. Recent results. Cancer Res. 102:98–107, 1986. Aw, T. C., and E. Boyland. Depigmentation of hair in mice due to intradermal injections of a tumour promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA). IRCS Medical Science: Library Compendium 6:213, 1978. Aw, T. C., and E. Boyland. Depigmentation of hair in mice by chemicals. IRCS Medical Science: Library Compendium 9:29–30, 1981. Aw, T. C., R. G. Bird, and E. Boyland. Histology of chemically induced depigmentation of hair in mice. IRCS Medical Science: Library Compendium 10:403–404, 1982. Axelrod, J., and A. B. Lerner. O-methylation in the conversion of tyrosine to melanin. Biochim. Biophys. Acta 71:650–655, 1963. Bachem, A. Ophthalmic ultraviolet action spectra. Am. J. Ophthalmol. 41:969–975, 1956. Barbeau, A., L. Dallaire, N. T. Buu, J. Poirier, and E. Rucinska. Comparative behavioral biochemical and pigmentary effects of MPTP, MPP+ and paraquat in Rana pipiens. Life Sci. 37:1529–1538, 1985. Barden, H., and S. Levin. Histochemical observations on rodent brain melanin. Brain Res. Bull. 10:847–851, 1983. Barishak, Y. R., A. M. Beemer, M. N. Egyed, A. Shlosberg, and A. Eilat. Histology of the iris in geese and ducks photosensitized by ingestion of ammi majus seeds. Acta Ophthalmol. 53:585–590, 1975. Barsa, J. A., J. C. Newton, and J. C. Saunders. Lenticular and corneal opacities during phenothiazine therapy. J. Am. Med. Assoc. 193:10–12, 1965. Barthel, E. Erhöhte Mortalität an Osophaguskrebs, Magenkrebs und Hautmelanom bei Pestizid-exponierten Schädlingsbekämpfern in der DDR. Arch. Geschwulstforsch. 55:481–488, 1985. Baumgartner, A. M., P. F. Jones, W. A. Baumgartner, and C. T. Black. Radioimmunoassay of hair for determining opiate-abuse histories. J. Nucl. Med. 20:748–752, 1979. Beierwaltes, W. H., L. M. Lieberman, V. M. Varma, and R. E. Counsell. Visualizing human malignant melanoma and metastases. Use of chloroquine analog tagged with iodine 125. J. Am. Med. Assoc. 206:97–102, 1968. Benedetto, J.-P., J.-P. Ortonne, and C. Voulot. Role of thiol compounds in mammalian melanin pigmentation: part I. J. Invest. Dermatol. 77:402–405, 1981. Benedetto, J. P., J. P. Ortonne, C. Voulot, C. Khatchadourian, G. Prota, and J. Thivolet. Role of thiol compounds in mammalian melanin pigmentation. II. Glutathione and related enzymatic activities. J. Invest. Dermatol. 79:422–424, 1982. Ben-Shachar, D., and M. B. H. Youdim. Iron, melanin and dopamine interaction: relevance to Parkinson’s disease. Prog. NeuroPsychopharmacol. Biol. Psychiatr. 17:139–150, 1993. Bergman, K. Autoradiographic distribution of 14C-labeled 3Himidazo(4,5-f)quinoline-2-amines in mice. Cancer Res. 45:1351– 1356, 1985. Berkelhammer, J., R. W. Oxenhandler, R. R. J. Hook, and J. M. Hennessey. Development of a new melanoma model in C57Bl/6 mice. Cancer Res. 42:3157–3163, 1982. Bernstein, H. N., and J. Ginsberg. The pathology of chloroquine retinopathy. Arch. Ophthalmol. 71:238–245, 1964. Bhatnagar, V., S. Anjaiah, N. Puri, B. N. Arudhra Darshanam, and A. Ramaiah. pH of melanosomes of B16 murine melanoma is acidic: its physiological importance in the regulation of melanin biosynthesis. Arch. Biochem. Biophys. 307:183–192, 1993. Bleehen, S. S., M. A. Pathak, Y. Hori, and T. B. Fitzpatrick. Depigmentation of skin with 4-isopropylcatechol, mercaptoamines and other compounds. J. Invest. Dermatol. 50:103–117, 1968. Blois, M. S. Preliminary note. Melanoma detection with radioiodoquine. J. Nucl. Med. 9:492–493, 1968. Blois, M. S. J., and R. F. Kallman. The incorporation of C14 from 3,4-dihydroxyphenylalanine-2¢-C14 into the melanin of mouse melanomas. Cancer Res. 24:863–868, 1964.
TOXICOLOGICAL ASPECTS OF MELANIN AND MELANOGENESIS Bolt, A. G., and I. S. Forrest. Interaction between human melanoprotein and chlorpromazine derivatives II. Spectrophotometric studies. Life Sci. 6:1285–1292, 1967. Borg, K., and H. Tjälve. Effect of thiram and dithiocarbamate pesticides on the gastrointestinal absorption and distribution of nickel in mice. Toxicol. Lett. 42:87–98, 1988. Borovansky, J., P. Mirejovsky, and P. A. Riley. Possible relationship between abnormal melanosome structure and cytotoxic phenomena in malignant melanoma. Neoplasma 38:393–400, 1991. Boyland, E., J. W. Clegg, P. C. Koller, E. Rhoden, and O. H. Warwick. The effect of chloroethylamines on tumours, with special reference to bronchogenic carcinoma. Br. J. Cancer 2:17–29, 1948. Brandt, I., J.-Å. Gustafsson, and J. Rafter. Distribution of the carcinogenic tryptophan pyrolysis product Trp-P-1 in control, 9hydroxyellipticine and beta-naphthoflavone pretreated mice. Carcinogenesis 4:1291–1296, 1983. Brandt, I., B. Kowalski, J.-Å. Gustafsson, and J. Rafter. Tissue localization of the carcinogenic glutamic acid pyrolysis product GLUP-1 in control and beta-naphthoflavone-treated mice and rats. Carcinogenesis 10:1529–1533, 1989. Brooks, D. W., and C. R. Dawson. Aspects of tyrosinase chemistry. In: The Biochemistry of Copper, J. Peisach, P. Aisen, and W. E. Blumberg (eds). New York: Academic Press, 1966, pp. 343–357. Broxterman, H. J., A. van-Langevelde, C. N. Bakker, H. Boer, J. G. Journee-de-Korver, F. M. Kaspersen, H. M. Kakebeeke-Kemme, and E. K. Pauwels. Incorporation of [125I]-5-iodo-2-thiouracil in cultured hamster, rabbit, and human melanoma cells. Cancer Res. 43:1316–1320, 1983. Brun, R. Contribution a l’étude de la depigmentation experimentale. Bull. Inst. Nat. Genevois 61:3–97, 1961. Burchill, S. A., and A. J. Thody. DOPAminergic inhibition of tyrosinase activity in hair follicular melanocytes of the mouse. J. Endocrinol. 111:233–237, 1986. Burnett, J. B. The tyrosinases of mouse melanoma: isolation and molecular properties. J. Biol. Chem. 246:3079–3091, 1971. Burns, R. P. Delayed onset of chloroquine retinopathy. N. Engl. J. Med. 275:693–696, 1966. Bus, J. S., S. Z. Cagen, M. Olgaard, and J. E. Gibson. A mechanism of paraquat toxicity in mice and rats. Toxicol. Appl. Pharmacol. 35:501–513, 1976. Carlsson, A. Biochemical aspects of abnormal movements induced by L-dopa. In: L-Dopa and Parkinsonism, A. Barbeau, and F. H. McDowell (eds). Philadelphia: F. A. Davis Co., 1970, pp. 205–213. Carlsson, J., S. Sjöberg, and B. S. Larsson. Present status of boron neutron capture therapy. Acta Oncol. 31:803–813, 1992. Carr, J. G. Production of mutations in mice by 1:2:5:6dibenzanthracene. Br. J. Cancer 1:152–156, 1947. Carsberg, C. J., H. M. Warenius, and P. S. Friedmann. Ultraviolet radiation-induced melanogenesis in human melanocytes. Effects of modulating protein kinase C. J. Cell Sci. 107:2591–2597, 1994. Chakraborty, A. K., and D. P. Chakraborty. The effect of tryptophan on dopa-oxidation by melanosomal tyrosinase. Int. J. Biochem. 25:1277–1280, 1993. Chavin, W., and W. Schlesinger. Some potent melanin depigmentary agents in the black goldfish. Naturwissenschaften 53:413–414, 1966. Chedekel, M. R., E. J. Land, A. Thompson, and T. G. Truscott. Early steps in the free radical polymerization of 3,4dihydroxyphenylalanine (dopa) to melanin. J. Chem. Soc. Chem. Commun., 1170–1172, 1984. Chen, Y. M., and W. Chavin. Melanogenesis in human melanomas. Cancer Res. 35:606–612, 1975. Chian, L. T. Y., and G. F. Wilgram. Tyrosinase inhibition; its role in suntanning and albinism. Science 155:198–200, 1967. Chiba, K., A. Trevor, and N. Castagnoli, Jr. Metabolism of the neurotoxic tertiary amine, MPTP, by brain monoamine oxidase. Biochem. Biophys. Res. Commun. 120:574–578, 1984.
Chiueh, C. C., S. P. Markey, R. S. Burns, J. Johannessen, D. M. Jacobowitz, and I. J. Kopin. N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, a parkinsonian syndrome causing agent in man and monkey, produces different effects in guinea pig and rat. Pharmacologist 25:131, 1983. Christensen, E., J. E. Möller, and A. Faurbye. Neuropathological investigation of 28 brains from patients with dyskinesia. Acta Psychiatr. Scand. 46:14–23, 1970. Clews, J., C. J. Cooksey, P. J. Garratt, E. J. Land, C. A. Ramsden, and P. A. Riley. Oxidative cyclisation of N,N-dialkylcatechol amines to hetrocyclic betaines via o-quinones: synthetic, pulse radiolytic and enzyme studies. J. Chem. Soc., Perkin Trans. I:4306–4315, 2000. Coderre, J. A., J. D. Glass, R. G. Fairchild, U. Roy, S. Cohen, and I. Fand. Selective targeting of boronophenylalanine to melanoma in BALB/c mice for neutron capture therapy. Cancer Res. 47:6377–6383, 1987. Cohen, M. B., R. E. Saxton, R. R. Lake, R. Cagle, L. S. Graham, A. Nizze, L. S. Yamada, M. Gan, G. Bronca, K. Greenwell, and D. L. Morton. Detection of malignant melanoma with iodine-123iodoamphetamine. J. Nucl. Med. 29:1200–1206, 1988. Coleman, D. L. Effect of genic substitution on the incorporation of tyrosine into the melanin of mouse skin. Arch. Biochem. Biophys. 96:562–568, 1962. Connor, M. J., and L. A. Wheeler. Depletion of cutaneous glutathione by ultraviolet radiation. Photochem. Photobiol. 46:239–245, 1987. Cooksey, C. J., E. J. Land, P. A. Riley, T. Sarna, and T. G. Truscott. On the interaction of anisyl-3,4-semiquinone with oxygen. Free Rad. Res. Commun. 4:131–138, 1987. Cooksey, C. J., K. Jimbow, E. J. Land, and P. A. Riley. Reactivity of orthoquinones involved in tyrosinase-dependent cytotoxicity: differences between alkylthio- and alkoxy-substituents. Melanoma Res. 2:283–293, 1992. Cooksey, C. J., E. J. Land, C. A. Ramsden, and P. A. Riley. Tyrosinase-mediated cytotoxicity of 4-substituted phenols: quantitative structure-thiol-reactivity relationships of the derived o-quinones. Anti-Cancer Drug Des. 10:119–129, 1995. Cooksey, C. J., E. J. Land, F. A. P. Rushton, C. A. Ramsden, and P. A. Riley. Tyrosinase-mediated cytotoxicity of 4-substituted phenols: the use of QSAR to forecast reactivities of thiols towards the derived orthoquinones. Quant. Struct.-Act. Relat. 15:498–503, 1996. Cooksey, C. J., P. J. Garratt, E. J. Land, S. Pavel, C. A. Ramsden, P. A. Riley, and N. P. M. Smit. Evidence of the indirect formation of the catecholic intermediate substrate responsible for the autoactivation kinetics of tyrosinase. J. Biol. Chem. 272: 26226–26235, 1997. Coote, N., and L. U. Abeysiri. Skin depigmentation associated with intravenous anaesthetic agents. Anaesthesia 34:336–338, 1979. Cotzias, G. C., P. S. Papavasiliou, and S. T. Miller. Manganese in melanin. Nature 201:1228–1229, 1964. Dale, A. J. D., E. M. Parkhill, and D. D. Layton. Studies on chloroquine retinopathy in rabbits. J. Am. Med. Assoc. 193:241–243, 1965. D’Amato, R. J., Z. P. Lipman, and S. H. Snyder. Selectivity of the parkinsonian neurotoxin MPTP: Toxic metabolite MPP+ binds to neuromelanin. Science 231:987–989, 1986. D’Amato, R. J., D. F. Benham, and S. H. Snyder. Characterization of the binding of N-methyl-4-phenylpyridine, the toxic metabolite of the parkinsonian neurotoxin N-methyl-4-phenyl-1,2,3,6tetrahydropyridine, to neuromelanin. J. Neurochem. 48:653–658, 1987. Danielsson, B. R. G., A. Oskarsson, and L. Dencker. Placental transfer and fetal distribution of lead in mice after treatment with dithiocarbamates. Arch. Toxicol. 55:27–33, 1984. De Léobardy, J., and A. Labesse. On the treatment of Addison’s disease with cysteine. Presse Med. 42:599–600, 1934. Dencker, L., and N. G. Lindquist. Distribution of labeled chloroquine in the inner ear. Arch. Otolaryngol. 101:185–188, 1975.
385
CHAPTER 18 Dencker, L., N. G. Lindquist, and S. Ullberg. Mechanism of druginduced chronic otic lesions. Role of drug accumulation on the melanin of the inner ear. Experientia 29:1362–1363, 1973. Dencker, L., B. Larsson, K. Olander, S. Ullberg, and M. Yokota. False precursors of melanin as selective melanoma seekers. Br. J. Cancer 39:449–452, 1979. Dencker, L., B. Larsson, K. Olander, S. Ullberg, and M. Yokota. Incorporation of thiouracil and some related compounds into growing melanin. Acta Pharmacol. Toxicol. 49:141–149, 1981. Dencker, L., B. S. Larsson, K. Olander, and S. Ullberg. A new melanoma seeker for possible clinical use: selective accumulation of radiolabeled thiouracil. Br. J. Cancer 45:95–104, 1982. Dencker, L., B. S. Larsson, R. d’Argy, S. Ullberg, and H. Tjälve. Macro- and micro-autoradiography. Pure Appl. Chem. 63:1271– 1277, 1991. Denton, C. R., A. B. Lerner, and T. B. Fitzpatrick. Inhibition of melanin formation by chemical agents. J. Invest. Dermatol. 18:119–134, 1952. Devi, C. C., C. Tripathi, and A. Ramaiah. pH-dependent interconvertible allosteric forms of murine melanoma tyrosinase: physiological implications. Eur. J. Biochem. 166:705–711, 1987. Devi, C. C., R. K. Tripathi, and A. Ramaiah. pH-dependent interconvertible forms of mushroom tyrosinase with different kinetic properties. Pigment Cell Res. 2:8–13, 1989. Dewar, A. J., C. M. Yates, G. Barron, A. Gordon, H. Wilson, and J. Baker. The effects of chronic chlorpromazine administration on the albino rat retina. Toxicol. Appl. Pharmacol. 43:501–506, 1978. Dewar, W. A., and H. M. Mann. Chloroquine in lupus erythematosus. Lancet 1:780, 1954. Dieke, S. H. Pigmentation and hair growth in black rats as modified by chronic administration of thiourea, phenylthiourea and anaphthylthiourea. Endocrinology 40:123–136, 1947. Dietler, C., and K. Lerch. Reaction inactivation of tyrosinase. In: Oxidases and Related Redox Systems, T. E. Kind, M. Morrison, and H. S. Mason (eds). New York: Pergamon Press, 1982, pp. 305– 317. d’Ischia, M., A. Napolitano, and G. Prota. Psoralens sensitize glutathione photooxidation in vitro. Biochim. Biophys. Acta 993: 143–147, 1989. Drew, J. F. Concerning the side effects of antimalarial drugs used in the extended treatment of rheumatic disease. Med. J. Aust. 2: 618–620, 1962. Durkacz, B. W., J. Lunec, H. Grindley, S. Griffin, O. Horner, and A. Simm. Murine melanoma cell differentiation and melanogenesis induced by poly(ADP-ribose) polymerase inhibitors. Exp. Cell Res. 202:287–291, 1992. Dürsch, I., H. H. D. Meyer, and H. Karg. Accumulation of the bagonist clenbuterol by pigmented tissues in rat eye and hair of veal calves. J. Anim. Sci. 73:2050–2053, 1995. Edler, K. Ocular changes associated with chlorpromazine therapy; A preliminary report. Acta Ophthalmol. 44:405–409, 1966. Egyed, M. N., L. Singer, A. Eilat, and A. Shlosberg. Eye lesions in ducklings fed ammi majus seeds. Zbl. Vet.-Med. A 22:764–768, 1975. Englesson, S., B. Larsson, N. G. Lindquist, L. Lyttkens, and J. Stahle. Accumulation of 14C-lidocaine in the inner ear. Acta Otolaryngol. (Stockh.) 82:297–300, 1976. Ephraim, A. I. On sudden or rapid whitening of the hair. Arch. Dermatol. 79:228–235, 1959. Evans, R. D., A. W. Kopf, R. A. Lew, D. S. Rigel, R. S. Bart, R. J. Friedman, and J. K. Rivers. Risk factors for the development of malignant melanoma. Review of case–control studies. J. Dermatol. Surg. Oncol. 14:393–408, 1988. Evans, W. C., and H. S. Raper. The accumulation of L-3,4-dihydroxyphenylalanine in the tyrosine-tyrosinase reaction. Biochem. J. 31: 2162–2170, 1937.
386
Fairchild, R. G., S. Packer, D. Greenberg, P. Som, A. B. Brill, I. Fand, and W. P. McNally. Thiouracil distribution in mice carrying transplantable melanoma. Cancer Res. 42:5126–5132, 1982. Fairchild, R. G., J. A. Coderre, S. Packer, D. Greenberg, and B. H. Laster. Therapeutic effects of S-35-thiouracil in BALB/c mice carrying Harding–Passey melanoma. Int. J. Radiat. Oncol. Biol. Phys. 17:337–343, 1989. Farishian, R. A., and J. R. Whittaker. Phenylalanine lowers melanin synthesis in mammalian melanocytes by reducing tyrosine uptake: implications for pigment reduction in phenylketonuria. J. Invest. Dermatol. 74:85–89, 1980. Farooqui, J. Z., E. Robb, S. T. Boyce, G. D. Warden, and J. J. Nordlund. The isolation of a unique melanogenic inhibitor from human skin xenografts: initial in vitro and in vivo characterization. J. Invest. Dermatol. 104:739–743, 1995. Fechner, G. A., J. J. Jacobs, and P. G. Parsons. Inhibition of melanogenesis in human melanoma cells by novel analogues of the partial histamine (H2) agonist nordimaprit. Biochem. Pharmacol. 46:47–54, 1993. Felix, C. C., J. S. Hyde, T. Sarna, and R. C. Sealy. Interactions of melanin with metal ions. Electron spin resonance evidence for chelate complexes of metal ions with free radicals. J. Am. Chem. Soc. 100:3922–3926, 1978. Ferrini, U., A. M. Mileo, and V. J. Hearing. Microheterogeneity of melanosome bound tyrosinase from the Harding–Passey murine melanoma. Int. J. Biochem. 19:227–234, 1987. Findlay, J. D., and D. M. Jenkinson. Sweat gland function in the Ayrshire calf. Res. Vet. Sci. 5:109–115, 1964. Fisher, P. B., D. R. Prignoli, H. Hermo, I. B. Weinstein, and S. Pestka. Effects of combined treatment with interferon and mezerein on melanogenesis and growth in human melanoma cells. J. Interferon Res. 5:11–22, 1985. Fitzpatrick, T. B., M. Seiji, and A. D. McGugan. Melanin pigmentation. N. Engl. J. Med. 265:328–331, 1961. Franken, N. A. P., A. van Langevelde, J. G. Journée-de Korver, C. N. M. Bakker, R. I. J. Feitsma, J. L. van Delft, J. A. Oosterhuis, and E. K. J. Pauwels. Uptake of 123I-5-iodo-2-thiouracil, a possible radiopharmaceutical for noninvasive detection of ocular melanoma, in melanotic and amelanotic melanomas in hamsters. Nucl. Med. Commun. 6:657–663, 1985. Franken, N. A. P., J. L. van Delft, A. van Langevelde, J. C. Bleeker, D. de Wolff-Rouendaal, J. A. van Best, M. L. BouwhuisHoogerwerf, J. A. Oosterhuis, and E. K. J. Pauwels. Scintimetric detection of choroidal malignant melanoma with (123I)-5-iodo-2thiouracil. Ophthalmologica 193:248–254, 1986a. Franken, N. A. P., A. van Langevelde, E. K. J. Pauwels, J. G. Journée-de Korver, C. N. M. Bakker, and J. A. Oosterhuis. Radioiodine-labelled 5-iodo-2-thiouracil: a potential radiopharmaceutical for establishing the viability of ocular melanoma after radiation therapy. Nucl. Med. Commun. 7:797–809, 1986b. Frenk, E. Irreversible depigmentation of skin following acute contact eczema caused by adhesive plaster. Hautarzt 31:639–643, 1980. Frenk, E., M. A. Pathak, G. Szabo, and T. B. Fitzpatrick. Selective action of mercaptoamines on melanocytes in mammalian skin. Arch. Dermatol. 97:465–477, 1968. Friedmann, P. S., and B. A. Gilchrest. Ultraviolet radiation directly induces pigment production by cultured human melanocytes. J. Cell. Physiol. 133:88–94, 1987. Froncisz, W., T. Sarna, and J. S. Hyde. Cu2+ probe of metal-ion binding sites in melanin using electron paramagnetic resonance spectroscopy. Arch. Biochem. Biophys. 202:289–303, 1980. Gabel, D. Tumor-seeking compounds for boron neutron capture therapy: synthesis and biodistribution. In: Clinical Aspects of Neutron Capture Therapy, R. G. Fairchild, V. P. Bond, and A. D. Woodhead (eds). New York: Plenum Press, 1989, pp. 233– 241.
TOXICOLOGICAL ASPECTS OF MELANIN AND MELANOGENESIS Gan, E. V., H. F. Haberman, and I. A. Menon. Electron transfer properties of melanin. Arch. Biochem. Biophys. 173:666–672, 1976. Goar, E. L., and M. C. Fletcher. Toxic chorioretinopathy following the use of NP 207. Am. J. Ophthalmol. 44:603–608, 1957. Goerttler, K., H. Loehrke, J. Schweizer, and B. Hesse. Two-stage tumorigenesis of dermal melanocytes in the back skin of the Syrian golden hamster using systemic initiation with 7,12dimethylbenz(a)anthracene and topical promotion with 12-otetradecanoylphorbol-13-acetate. Cancer Res. 40:155–161, 1980. Goodman, L. S., A. G. Gilman, T. W. Rall, and T. Murad. Goodman & Gilman’s The Pharmacological Basis of Therapeutics, 7th edn. New York: MacMillan Publishing Co., 1985. Greiner, A., and K. Berry. Skin pigmentation and corneal and lens opacities with prolonged chlorpromazine therapy. Can. Med. Assoc. J. 90:663–665, 1964. Gupta, A. K., R. S. Stern, N. A. Swanson, and T. F. Anderson. Cutaneous melanomas in patients treated with psoralens plus ultraviolet A. A case report and the experience of the PUVA Follow-Up Study. J. Am. Acad. Dermatol. 19:67–76, 1988. Gupta, S. K., R. C. Murthy, and S. V. Chandra. Neuromelanin in manganese-exposed primates. Toxicol. Lett. 6:17–20, 1980. Hallman, H., L. Olson, and G. Jonsson. Neurotoxicity of the meperidine analogue N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine on brain catecholamine neurons in the mouse. Eur. J. Pharmacol. 97:133–136, 1984. Halprin, K. M., and A. Ohkawara. Glutathione and human pigmentation. Arch. Dermatol. 94:355–357, 1966. Hart, C. W., and R. F. Naunton. The ototoxicity of chloroquine phosphate. Arch. Otolaryngol. (Chicago) 80:407–412, 1964. Hartvig, P., N. G. Lindquist, S. M. Aquilonius, R. d’Argy, K. Bergström, U. Bondesson, S. Å. Eckernäs, P. Gullberg, B. S. Larsson, B. Lindberg, H. Lundqvist, B. Lydén, B. Långström, P. Malmborg, K. Någren, and C.-G. Stålnacke. Distribution of 1-methyl-4-phenyl1,2,3,6-tetrahydropyridine in experimental animals studied by positron emission tomography and whole body autoradiography. Life Sci. 38:89–97, 1986. Hashiguchi, H., and H. Takahashi. Inhibition of two copper-containing enzymes, tyrosinase and DOPAmine beta-hydroxylase, by lmimosine. Mol. Pharmacol. 13:362–367, 1977. Hearing, V. J., and M. Jiménez. Mammalian tyrosinase — the critical regulatory control point in melanocyte pigmentation. Int. J. Biochem. 19:1141–1147, 1987. Hearing, V. J., and M. Jiménez. Analysis of mammalian pigmentation at the molecular level. Pigment Cell Res. 2:75–85, 1989. Hearing, V. J., T. M. Ekel, and P. M. Montague. Mammalian tyrosinase: isozymic forms of the enzyme. Int. J. Biochem. 13:99–103, 1981. Heikkila, R. E., A. Hess, and R. C. Duvoisin. Dopaminergic neurotoxicity of 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine in mice. Science 224:1451–1453, 1984. Heldaas, S. S., A. A. Andersen, and S. Langford. Incidence of cancer among vinyl chloride and polyvinyl chloride workers: further evidence for an association with malignant melanoma. Br. J. Ind. Med. 44:278–280, 1987. Hochstein, P., and G. Cohen. The cytotoxicity of melanin precursors. Ann. N. Y. Acad. Sci. 100:876–881, 1963. Homewood, C. A., D. C. Warhurst, W. Peters, and V. C. Baggaley. Lysosomes, pH and the antimalarial action of chloroquine. Nature 235:50–52, 1972. Honig, B., W. L. Morison, and D. Karp. Photochemotherapy beyond psoriasis. J. Am. Acad. Dermatol. 31(5 Pt 1):775–790, 1994. Honigsmann, H., K. Wolff, T. B. Fitzpatrick, and M. A. Pathak. Oral photochemotherapy with psoralens and UVA (PUVA): principles and practice. In: Dermatology in General Medicine, T. B. Fitzpatrick, A. Z. Eisen, and K. Wolff (eds). New York: McGrawHill, 1987, pp. 1533–1588.
Hu, D. N., H. E. Savage, and J. E. Roberts. Uveal melanocytes, ocular pigment epithelium and Muller cells in culture: in vitro toxicology. Int. J. Toxicol. 21: 465–472, 2002. Hutton, I. M., and M. Pentland. Uptake of melanin precursors in mouse melanoma. Clin. Oncol. 2:17–23, 1976. Imokawa, G. Analysis of carbohydrate properties essential for melanogenesis in tyrosinases of cultured malignant melanoma cells by differential carbohydrate processing inhibition. J. Invest. Dermatol. 95:39–49, 1990. Imokawa, G. Analysis of initial melanogenesis including tyrosinase transfer and melanosome differentiation through interrupted melanization by glutathione. J. Invest. Dermatol. 93:100–107, 1989. Imokawa, G., and Y. Mishima. Functional analysis of tyrosinase isozymes of cultured malignant melanoma cells during the recovery period following interrupted melanogenesis induced by glycosylation inhibitors. J. Invest. Dermatol. 83:196–201, 1984. Imokawa, G., and Y. Mishima. Analysis of tyrosinases as asparaginelinked oligosaccharides by concanavalin A lectin chromatography: appearance of a new segment of tyrosinases in melanoma cells following interrupted melanogenesis induced by glycosylation inhibitors. J. Invest. Dermatol. 85:165–168, 1985. Imokawa, G., and Y. Mishima. Importance of glycoproteins in the initiation of melanogenesis: an electron microscopic study of B16 melanoma cells after release from inhibition of glycosylation. J. Invest. Dermatol. 87:319–325, 1986. Inoue, S., S. Ito, K. Wakamatsu, K. Jimbow, and K. Fujita. Mechanism of growth inhibition of melanoma cells by 4-Scysteaminylphenol and its analogues. Biochem. Pharmacol. 39:1077–1083, 1990. Ishiyama, I., T. Nagai, and S. Toshida. Detection of basic drugs (methamphetamine, antidepressants and nicotine) from human hair. J. Forens. Sci. 28:380–385, 1983. Israel, J., J. Connelly, S. McTigue, R. Brummett, and J. Brown. Lidocaine in the treatment of tinnitus aurium. Arch. Otolaryngol. 108:471–473, 1982. Ito, S. Reexamination of the structure of eumelanin. Biochim. Biophys. Acta 883:155–161, 1986. Jara, J. R., P. Aroca, F. Solano, J. H. Martínez-Liarte, and J. A. Lozano. The role of sulfhydryl compounds in mammalian melanogenesis: the effect of cysteine and glutathione upon tyrosinase and the intermediates of the pathway. Biochim. Biophys. Acta 967:296–303, 1988. Jara, J. R., F. Solano, J. C. Garcia-Borron, P. Aroca, and J. A. Lozano. Regulation of distal mammalian melanogenesis. II. The role of metal cations. Biochim. Biophys. Acta 1035:276–285, 1990. Jara, J. R., J. H. Martinez-Liarte, and F. Solano. Inhibition by analogues of L-tyrosine transport by B16/F10 melanoma cells. Melanoma Res. 1:15–21, 1991. Jarrett, A., and G. Szabo. Pathological varieties of vitiligo and response to treatment with meladinine. Br. J. Dermatol. 68:313–326, 1956. Jasim, S., and H. Tjälve. Effect of sodium pyridinethione on the uptake and distribution of nickel, cadmium and zinc in pregnant and non-pregnant mice. Toxicology 38:327–350, 1986. Jelinek, J. E. Sudden whitening of the hair. Bull. N. Y. Acad. Med. 48:1003–1013, 1972. Jervis, G. A. Phenylpyruvic oligophrenia: introductory study of 50 cases of mental deficiency associated with excretion of phenylpyruvic acid. Archs. Neurol. Psychiatr. 38:944–951, 1937. Jimbow, K., T. Miura, S. Ito, and K. Ishikawa. Phenolic melanin precursors provide a rational approach to the design of antitumor agents for melanoma. Pigment Cell Res. 2:34–39, 1989. Johannessen, J. N., C. C. Chiueh, R. S. Burns, and S. P. Markey. Differences in the metabolism of MPTP in the rodent and primate
387
CHAPTER 18 parallel differences in sensitivity to its neurotoxic effects. Life Sci. 36:219–224, 1985. Johnsson, L.-G., and J. E. Hawkins, Jr. Symposium on basic ear research II: Strial atrophy in clinical and experimental deafness. Laryngoscope 82:1105–1125, 1972. Jordan, A. M., T. H. Khan, H. M. I. Osborn, A. Photiou, and P. A. Riley. Melanocyte-directed enzyme pro-drug therapy (MDEPT): development of a targeted treatment for malignant melanoma. Bioorg. Med. Chem. 7:1775–1780, 1999. Jordan, A. M., T. H. Khan, H. Malkin, H. M. I. Osborn, A. Photiou, and P. A Riley. Melanocyte-directed enzyme pro-drug therapy (MDEPT): development of second-generation prodrugs for targeted treatment of malignant melanoma. Bioorg. Med. Chem. 9: 1549–1558, 2001. Kable, E. P. W., and P. G. Parsons. Potency, selectivity, and cell cycle dependence of catechols in human tumour cells in vitro. Biochem. Pharmacol. 9:1711–1715, 1988. Kahn, V., and A. Andrawis. Inhibition of mushroom tyrosinase by tropolone. Phytochemistry 24:905–908, 1985. Kameyama, K., M. Jimenez, J. Muller, Y. Ishida, and V. J. Hearing. Regulation of mammalian melanogenesis by tyrosinase inhibition. Differentiation 42:28–36, 1989. Kameyama, K., C. Sakai, S. Kuge, S. Nishiyama, Y. Tomita, S. Ito, K. Wakamatsu, and V. J. Hearing. The expression of tyrosinase, tyrosinase-related proteins 1 and 2 (TRP1 and TRP2), the silver protein, and a melanogenic inhibitor in human melanoma cells of differing melanogenic activities. Pigment Cell Res. 8:97–104, 1995. Kapyaho, K., and J. Janne. Stimulation of melanotic expression in murine melanoma cells exposed to polyamine antimetabolites. Biochem. Biophys. Res. Commun. 113:18–23, 1983. Kapyaho, K., R. Sinervirta, and J. Janne. Effects of inhibitors of polyamine biosynthesis on the growth and melanogenesis of murine melanoma cells. Cancer Res. 45:1444–1448, 1985. Karg, E., E. Rosengren, and H. Rorsman. Hydrogen peroxide as a mediator of DOPAC-induced effects on melanoma cells. J. Invest. Dermatol. 96:224–227, 1991. Keilin, D., and T. Mann. Polyphenol oxydase. Purification, nature and properties. Proc. R. Soc. London, Ser. B. Biol. Sci. 125:187–204, 1938. Kemali, M., and G. Gioffré. Anatomical localization of neuromelanin in the brains of the frog and tadpole. Ultrastructural comparison of neuromelanin with other melanins. J. Anat. 142:73–83, 1985. Kiguchi, K., F. R. Collart, C. Henning-Chubb, and E. Huberman. Induction of cell differentiation in melanoma cells by inhibitors of IMP dehydrogenase: altered patterns of IMP dehydrogenase expression and activity. Cell Growth Differ. 1:259–270, 1990. Kinross-Wright, V. Clinical trial of a new phenothiazine compound: NP-207. Psychiatr. Res. Rep. 4:89–94, 1956. Koh, H. K., B. E. Kliger, and R. A. Lew. Sunlight and cutaneous malignant melanoma: evidence for and against causation. Photochem. Photobiol. 51:765–779, 1990. Komiyama, K., S. Takamatsu, Y. Takahashi, M. Shinose, M. Hayashi, H. Tanaka, Y. Iwai, S. Omura, and G. Imokawa. New inhibitors of melanogenesis, OH-3984 K1 and K2. I. Taxonomy, fermentation, isolation and biological characteristics. J. Antibiot. 46:1520–1525, 1993. Korytowski, W., and T. Sarna. Bleaching of melanin pigments. Role of copper ions and hydrogen peroxide in autooxidation and photooxidation of synthetic DOPA-melanin. J. Biol. Chem. 265: 12410–12416, 1990. Korytowski, W., C. C. Felix, and B. Kalyanaraman. Mechanism of oxidation of 1-methyl-4-phenyl-2,3-dihydropyridinium (MPDP+). Biochem. Biophys. Res. Commun. 144:692–698, 1987. Korytowski, W., C. C. Felix, and B. Kalyanaraman. Oxygen activation during the interaction between MPTP metabolites and syn-
388
thetic neuromelanin. An ESR-spin trapping, optical, and oxidase electrode study. Biochem. Biophys. Res. Commun. 154:781–788, 1988. Korytowski, W., T. Sarna, and M. Zareba. Antioxidant action of neuromelanin: the mechanism of inhibitory effect on lipid peroxidation. Arch. Biochem. Biophys. 319:142–148, 1995. Krüger, R. C. The inhibition of tyrosinase. Arch. Biochem. Biophys. 57:52–60, 1955. Kubowitz, F. Spaltung und Resynthese der Polyphenoxydase und des Hämocyanins. Biochem. Z. 299:32–57, 1938. Kull, F. C., R. Bonorden, and R. L. Mayer. Inhibition of melanin formation in vivo by 4-chlororesorcinol. Proc. Soc. Exp. Biol. Med. 87:538–540, 1954. Kwon, B. S., M. Wakulchik, A. K. Haq, R. Halaban, and D. Kestler. Sequence analysis of mouse tyrosinase cDNA and the effect of melanotropin on its gene expression. Biochem. Biophys. Res. Commun. 153:1301–1309, 1988. Labarre P., J. Papon, M. F. Moreau, N. Moins, A. Veyre, and J. C. Mandelmont. Evaluation in mice of some iodinated melanoma imaging agents using cryosectioning and multiwire proportional counting. Eur. J. Nucl. Med. 26: 494–498, 1999. Land, E. J., and P. A. Riley. Spontaneous redox reactions of dopaquinone and the balance between the eumelanic and phaeomelanic pathways. Pigment Cell Res. 13: 272–277, 2000. Land, E. J, C. J. Cooksey, and P. A. Riley. Reaction kinetics of 4methoxyorthobenzoquinone in relation to its mechanism of cytotoxicity: a pulse radiolysis study. Biochem. Pharmacol. 39:1133–1135, 1990. Land, E. J., C. A. Ramsden, and P. A. Riley. Tyrosinase autoactivation and the chemistry of ortho-quinone amines. Acc. Chem. Res. 36: 300–308, 2003a. Land, E. J., C. A. Ramsden, P. A. Riley, and G. Yoganathan. Mechanistic studies of catechol generation from secondary quinone amines relevant to indole formation and tyrosinase activation. Pigment Cell Res. 16: 397–406, 2003b. Land, E. J., S. Ito, K. Wakamatsu, and P. A. Riley. Rate constants for the first two chemical steps of eumelanogenesis. Pigment Cell Res. 16: 487–493, 2003c. Land E. J., C. A. Ramsden, and P. A. Riley. Quinone chemistry and melanogenesis. In: Methods in Enzymology, vol. 378, H. Sies, and L. Packer (eds). San Diego: Elsevier Science, 2004, pp. 88–109. Lang, R. Mammalian spot test with moxnidazole, a 5-nitroimidazole. Experientia 34:500–501, 1978. Langston, J. W., P. Ballard, J. W. Tetrud, and I. Irwin. Chronic parkinsonism in humans due to a product of mepiridine-analog synthesis. Science 219:979–980, 1983. Langston, J. W., I. Irwin, E. B. Langston, and L. S. Forno. 1-Methyl4-phenylpyridinium ion (MPP+): identification of a metabolite of MPTP, a toxin selective to the substantia nigra. Neurosci. Lett. 48:87–92, 1984. Larsson, B. Mechanisms of accumulation of foreign substances in melanin: Binding to preformed melanin and incorporation into growing melanin. Acta Univ. Upsaliensis 43:1–52, 1979. Larsson, B. S. Melanin-affinic thioureas as selective melanoma seekers. Melanoma Res. 1:85–90, 1991. Larsson, B. Accumulation of drugs on the melanin in the inner ear. In: Melanin: Its Role in Human Photoprotection, L. Zeise, M. R. Chedekel, and T. B. Fitzpatrick (eds). Overland Park, KS: Valdenmar Publishing Co., 1995, pp. 215–219. Larsson, B. S., and U. Mårs. Selective binding of 8-methoxypsoralen to melanin in vivo and in vitro. Pigment Cell Res. 6:321–322, 1993. Larsson, B. S., and U. Mårs. Reduction of the oxidative capacity of melanins due to interaction with chemicals. Melanoma Res. 4 (Suppl. 2):14, 1994. Larsson, B., and H. Tjälve. Studies on the melanin affinity of metal ions. Acta Physiol. Scand. 104:479–484, 1978.
TOXICOLOGICAL ASPECTS OF MELANIN AND MELANOGENESIS Larsson, B., and H. Tjälve. Studies on the mechanism of drug-binding to melanin. Biochem. Pharmacol. 28:1181–1187, 1979. Larsson, B., A. Oskarsson, and H. Tjälve. Binding of paraquat and diquat on melanin. Exp. Eye Res. 25:353–359, 1977. Larsson, B., M. Nilsson, and H. Tjälve. The tissue-disposition of gentamicin in rats. Acta Pharmacol. Toxicol. 48:269–278, 1981. Larsson, B., K. Olander, L. Dencker, and L. Holmqvist. Accumulation of 125I-labelled thiouracil and propylthiouracil in murine melanotic melanomas. Br. J. Cancer 46:538–550, 1982. Larsson, B., L. Lyttkens, and S.-A. Wästerström. Tocainide and tinnitus: clinical effect and site of action. ORL 46:24–33, 1984. Larsson, B. S., L. Dencker, K. Olander, and A. Roberto. Accumulation of radiolabelled thioamides in malignant melanomas. In: Pigment Cell, J. Bagnara, S. N. Klaus, E. Paul, and M. Schartl (eds). Tokyo: University of Tokyo Press, 1985, pp. 611–615. Larsson, P., B. S. Larsson, and H. Tjälve. Binding of aflatoxin B1 to melanin. Food Chem. Toxicol. 26:579–586, 1988a. Larsson, B. S., U. Bondesson, and A. Roberto. Biological monitoring of industrial chemicals with melanin affinity. Pigment Cell Res. 1:281, 1988b. Larsson, B. S., H. Tjälve, P. Larsson, A. Roberto, I. Brandt, and K. Bergman. Retention of carcinogens in pigmented tissues due to melanin affinity (Abstract, 2nd Meeting of the ESPCR, Uppsala, Sweden, 1989). ESPCR Pigment Cell Bull. Special Issue 43, 1989a. Larsson, B. S., B. Larsson, and A. Roberto. Boron neutron capture therapy for malignant melanoma: an experimental approach. Pigment Cell Res. 2:356–360, 1989b. Larsson, B. S., H. Tjälve, A. Roberto, and U. Mårs. Chemical carcinogenesis and malignant melanoma. Pharmacol. Toxicol. 73 (Suppl. II):39, 1993. Laskin, J. D., and L. A. Piccinini. Tyrosinase isozyme heterogeneity in differentiating B16/C3 melanoma. J. Biol. Chem. 261: 16226–16235, 1986. Lauharanta, J., K. Kapyaho, and L. Kanerva. Changes in threedimensional structure of cultured S91 mouse melanoma cells associated with growth inhibition and induction of melanogenesis by retinoids. Arch. Dermatol. Res. 277:147–150, 1985. Lea, A. J. Effect of hydroquinone monobenzyl ether on melanin formation in vitro. Nature 167:906, 1951. Leblanc, B., S. Jezequel, T. Davies, G. Hanton, and C. Tarada. Binding of drugs to eye melanin is not predictive of ocular toxicity. Regul. Toxicol. Pharmacol., 28:124–132, 1998. Lerch, K. Copper monooxygenases: tyrosinase and dopamine betahydroxylase. In: Metal Ions in Biological Systems, vol. 13, H. Sigel (ed.). New York: Marcel Dekker, 1981, pp. 143–186. Lerch, K. Protein and active-site structure of tyrosinase. In: Advances in Pigment Cell Research, J. T. Bagnara (ed.). New York: Alan R. Liss, 1988, pp. 85–98. Lerner, A. B., T. B. Fitzpatrick, E. Calkins, and W. H. Summerson. Mammalian tyrosinase: the relationship of copper to enzymatic activity. J. Biol. Chem. 187:793–802, 1950. Levin, N., L. Queen, and A. Chalom. Detection of melanomas. Arch. Dermatol. 119:295–299, 1983. Lindquist, N. G. Accumulation of drugs on melanin. Acta Radiol. Diagn. 325:1–92, 1973. Lindquist, N. G., and S. Ullberg. The melanin affinity of chloroquine and chlorpromazine studied by whole body autoradiography. Acta Pharmacol. Toxicol. 31 (Suppl. 2):1–32, 1972. Lindquist, N. G., A. Lydén-Sokolowski, and B. S. Larsson. Accumulation of a parkinsonism-inducing neurotoxin in melanin-bearing neurons: autoradiographic studies on 3H-MPTP. Acta Pharmacol. Toxicol. 59:161–164, 1986. Lindquist, N. G., B. S. Larsson, and A. Lydén-Sokolowski. Neuromelanin and its possible protective and destructive properties. Pigment Cell Res. 1:133–136, 1987.
Lindquist, N. G., B. S. Larsson, and A. Lydén-Sokolowski. Autoradiography of [14C]paraquat or [14C]diquat in frogs and mice: accumulation in neuromelanin. Neurosci. Lett. 93:1–6, 1988. Link, E. M. Biochemical targeting in melanoma. Lancet 340:949–950, 1992. Link, E. M. Targeted radiotherapy of disseminated melanoma with 211 At-methylene blue in preparation for clinical trials. Melanoma Res. 4:32, 1994. Link, E. M., and R. N. Carpenter. 211At-methylene blue for targeted radiotherapy of human melanoma xenografts: treatment of micrometastases. Cancer Res. 50:2963–2967, 1990. Link, E. M., and R. N. Carpenter. 211At-methylene blue for targeted radiotherapy of human melanoma xenografts: treatment of cutaneous tumors and lymph node metastases. Cancer Res. 52:4385–4390, 1992. Link, E. M., I. Brown, R. N. Carpenter, and J. S. Mitchell. Uptake and therapeutic effectiveness of 125I and 211At-methylene blue for pigmented melanoma in an animal model system. Cancer Res. 49:4332–4337, 1989. Lommatzsch, P. K. b-Irradiation of choroidal melanoma with 106 Ru/106Rh application: 16 years’ experience. Arch. Ophthalmol. 101:713–717, 1983. Loomis, W. F. Skin-pigment regulation of vitamin D biosynthesis in man. Science 157:501–503, 1967. Lorincz, A. L. Studies on the inhibition of melanin formation. J. Invest. Dermatol. 15:425–431, 1950. Lydén, A., B. S. Larsson, and N. G. Lindquist. Melanin affinity of manganese. Acta Pharmacol. Toxicol. 55:133–138, 1984. Lydén, A., U. Bondesson, B. S. Larsson, and N. G. Lindquist. Melanin affinity of 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine, an inducer of chronic parkinsonism in humans. Acta Pharmacol. Toxicol. 53:429–432, 1983. Lydén-Sokolowski, A. Melanin binding of MPTP and related substances and manganese. Possible connection with parkinsonism. Acta Univ. Upsaliensis 63:1–52, 1990. Lydén-Sokolowski, A., B. S. Larsson, and N. G. Lindquist. Disposition of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in mice before and after monoamine oxidase and catecholamine reuptake inhibition. Pharmacol. Toxicol. 63:75–80, 1988. Lydén-Sokolowski, A., B. S. Larsson, and N. G. Lindquist. Distribution of 1-(3H)methyl-4-phenyl-1,2,3,6-tetrahydropyridine (3HMPTP) in the frog: uptake in neuromelanin. Pharmacol. Toxicol. 65:252–258, 1989. Lyon, M. F. Attempts to test the inactive-X theory of dosage compensation in mammals. Genet. Res. 4:93–102, 1963. Lyttkens, L., B. Larsson, and S.-A. Wästerström. Local anaesthetics and tinnitus: proposed peripheral mechanism of action of lidocaine. ORL 46:17–23, 1984. Lyttkens, L., B. Larsson, J. Stahle, and S. Englesson. Accumulation of substances with melanin affinity to the internal ear. Adv. Otorhinolaryngol. 25:17–25, 1979. MacKie, R. M., and T. Aitchison. Severe sunburn and subsequent risk of primary cutaneous malignant melanoma in Scotland. Br. J. Cancer 46:955–960, 1982. Magnani, C., D. Coggon, C. Osmond, and E. D. Acheson. Occupation and five cancers: a case–control study using death certificates. Br. J. Ind. Med. 44:769–776, 1987. Mann, D. M. A., and P. O. Yates. Possible role of neuromelanin in the pathogenesis of Parkinson’s disease. Mech. Ageing Dev. 21:193–203, 1983. Marigo, M., F. Tagliaro, C. Poiesi, S. Lafisca, and C. Neri. Determination of morphine in the hair of heroin addicts by high performance liquid chromatography with fluorimetric detection. J. Anal. Toxicol. 10:158–161, 1986. Markey, S. P., N. J. Johannessen, C. C. Chiueh, R. S. Burns, and M. A. Herkenham. Intraneuronal generation of a pyridinium
389
CHAPTER 18 metabolite may cause drug-induced parkinsonism. Nature 311:464–467, 1984. Mårs, U., and B. S. Larsson. New thioureas and related substances intended for melanoma targeting. Pigment Cell Res. 8:194–201, 1995. Mårs, U., and B. S. Larsson. Thiourea as a melanoma targeting agent. Melanoma Res. 6:113–120, 1996. Marsden, C. D. Brain melanin. In: Pigments in Pathology, M. Wollman (ed.). New York: Academic Press, 1969, pp. 395–420. Martinez, J. H., F. Solano, A. Arocas, J. C. García-Borrón, J. L. Iborra, and J. A. Lozano. The existence of apotyrosinase in the cytosol of Harding–Passey mouse melanoma melanocytes and characteristics of enzyme reconstitution by Cu(II). Biochim. Biophys. Acta 923:413–420, 1987. Martínez-Liarte, J. H., F. Solano, J. C. García-Borrón, J. R. Jara, and J. A. Lozano. a-MSH and other melanogenic activators mediate opposite effects on tyrosinase and dopachrome tautomerase in B16/F10 mouse melanoma cells. J. Invest. Dermatol. 99:435–439, 1992. Mascagna, D., G. Ghanem, R. Morandini, M. d’Ischia, G. Misuraca, F. Lejeune, and G. Prota. Synthesis and cytotoxic properties of new N-substituted 4-aminophenol derivatives with a potential as antimelanoma agents. Melanoma Res. 2:25–32, 1992. Mason, H. S. Comparative biochemistry of the phenolase complex. In: Advances in Enzymology, vol. 16, F. F. Nord (ed.). New York: Interscience, 1955, pp. 105–184. Mason, H. S. Structures and functions of the phenolase complex. Nature 177:79–81, 1956. Mason, H. S., W. L. Fowlks, and E. Peterson. Oxygen transfer and electron transport by the phenolase complex. J. Am. Chem. Soc. 77:2914–2915, 1955. Mathias, C. G., H. I. Maibach, and M. A. Conant. Perioral leukoderma simulating vitiligo from use of a toothpaste containing cinnamic aldehyde. Arch. Dermatol. 116:1172–1173, 1980. Mayer, T. C. Pigment cell migration in piebald mice. Dev. Biol. 15:521–535, 1967. Meier, D. A., W. H. Beierwaltes, and R. E. Counsell. Radioactivity from labelled precursors of melanin in mice and hamsters with melanomas. Cancer Res. 27:1354–1359, 1967. Meier-Ruge, W. Experimental investigations of the morphogenesis of chloroquine retinopathy. Arch. Ophthalmol. (Chicago) 73: 540–544, 1965. Mena, I., O. Marin, S. Fuenzalida, and G. C. Cotzias. Chronic manganese poisoning. Clinical picture and manganese turnover. Neurology 17:128–136, 1967. Menon, I. A., S. Persad, H. F. Haberman, C. J. Kurian, and P. K. Basu. A qualitative study of the melanins from blue and brown human eyes. Exp. Eye Res. 34:531–537, 1982. Meyer zum Gottesberge-Orsulakova, A. Pigment und Ionentransport im Vestibularorgan. Laryngo-Rhino-Otologie 64:364–367, 1985. Michalowski, A. S., E. M. Link, and F. Rösch. 211At-methylene blue in targeted radiotherapy of disseminated melanoma: microscopic analysis of tumor vs. normal tissue damage. Pigment Cell Res. 6:314, 1993. Mintz, B. Gene control of mammalian pigmentary differentiation: I. Clonal origin of melanocytes. Proc. Natl. Acad. Sci. USA 58:344–351, 1967. Mishima, Y. Neutron capture treatment of malignant melanoma using a 10B-chlorpromazine compound. In: Pigment Cell, vol. 1, V. Riley (ed.). Basel: S. Karger, 1973, pp. 215–221. Mishima, Y., S. Hatta, Y. Ohyama, and M. Inazu. Induction of melanogenesis suppression: cellular pharmacology and mode of differential action. Pigment Cell Res. 1:367–374, 1988. Mishima, Y., M. Ichihashi, S. Hatta, C. Honda, K. Yamamura, and T. Nakagawa. New thermal neutron capture therapy for malignant melanoma. Melanogenesis-seeking 10B molecule-melanoma cell
390
interaction from in vitro to first clinical trial. Pigment Cell Res. 2:226–234, 1989. Mishima, Y., M. Ichihashi, C. Honda, M. Shiono, T. Nakagawa, H. Obara, J. Shirakawa, J. Hiratsuka, K. Kanda, T. Kobayashi, T. Nozaki, O. Aizawa, T. Sato, H. Karashima, K. Yoshino, and H. Fukuda. Advances in the control of human cutaneous primary and metastatic melanoma by thermal neutron capture therapy. In: Progress in Neutron Capture Therapy for Cancer, B. J. Allen, D. E. Moore, and B. V. Harrington (eds). New York: Plenum Press, 1992, pp. 577–583. Moins, N., M. d’Incam, J. Bonafous, F. Bacin, P. Labarre, M. F. Moreau, D. Mestas, E. Noirault, F. Chossat, E. Bertommier, J. Papon, M. Bayle, P. Suteyrand, J. C. Mandelmont, and A. Veyre. 123 I-N-(2-diethylaminoethyl)-2-iodobenzamide: a potential imaging agent for cutaneous melanoma staging. Eur. J. Nucl. Med. 29:1478–1484, 2002. Morita, H., T. Kayashita, H. Kobata, A. Gonda, K. Takeya, and H. Itokawa. Pseudostellarins D–F, new tyrosinase inhibitory cyclic peptides from Pseudostellaria heterophylla. Tetrahedron 50:9975– 9982, 1994a. Morita, H., H. Kobata, K. Takeya, and H. Itokawa. Pseudostellarin G, a new tyrosinase inhibitory cyclic octapeptide from Pseudostellaria heterophylla. Tetrahedron Lett. 35:3563–3564, 1994b. Morrison, R., K. Mason, and S. Frost-Mason. A cladistic analysis of the evolutionary relationships of the members of the tyrosinase gene family using sequence data. Pigment Cell Res. 7:388–393, 1994. Müsebeck, K. Zum Wirkungsmechanismus der Streptomycinvergiftung des Ohres. Arch. Klin. Exp. Ohren-, NasenKehlkopfheilk. 182:583–587, 1963. Naish, S., and P. A. Riley. Studies on the kinetics of oxidation of 4-hydroxyanisole by tyrosinase. Biochem. Pharmacol. 38:1103– 1107, 1989. Naish, S., C. J. Cooksey, and P. A. Riley. Initial mushroom tyrosinasecatalysed oxidation product of 4-hydroxyanisole is 4-methoxyortho-benzoquinone. Pigment Cell Res. 1:379–381, 1988a. Naish, S., J. L. Holden, C. J. Cooksey, and P. A. Riley. Major primary cytotoxic product of 4-hydroxyanisole oxidation by mushroom tyrosinase is 4-methoxy ortho benzoquinone. Pigment Cell Res. 1:382–385, 1988b. Naish-Byfield, S., and P. A. Riley. Oxidation of monohydric phenol substrates by tyrosinase. An oximetric study. Biochem. J. 288:63–67, 1992. Naish-Byfield, S., C. J. Cooksey, A. M. Latter, C. I. Johnson, and P. A. Riley. In vitro assessment of the structure–activity relationship of tyrosinase-dependent cytotoxicity of a series of substituted phenols. Melanoma Res. 1:273–287, 1991. Naish-Byfield, S., C. J. Cooksey, and P. A. Riley. Oxidation of monohydric phenol substrates by tyrosinase: effect of dithiothreitol on kinetics. Biochem. J. 304:155–162, 1994. Nakamura, F. Electrophysiological and cytochemical study on ototoxicity of dihydrostreptomycin. Ann. Otol. Rhinol. Laryngol. 66:1080–1112, 1957. Napolitano, A., M. d’Ischia, G. Prota, M. Havens, and K. Tramposch. 2-Aryl-1,3-thiazolidines as masked sulfhydryl agents for inhibition of melanogenesis. Biochim. Biophys. Acta 1073:416–422, 1991. Napolitano, A., P. Di Donato, G. Prota, and E. J. Land. Transient quinonimines and 1,4-benzothiazines of phaeomelanogenesis: new pulse radiolytic and spectrophotometric evidence. Free Rad. Biol. Med. 27: 521–528, 1999. Nazzaro-Porro, M., and S. Passi. Identification of tyrosinase inhibitors in cultures of Pityrosporum. J. Invest. Dermatol. 71:205–208, 1978. Nelson, J. H., and C. R. Dawson. Tyrosinase. Adv. Enzymol. Relat. Areas Mol. Biol. 4:99–152, 1955. Nilsson Tammela, M., and H. Tjälve. Whole-body autoradiography of (3H)dihydrostreptomycin in guinea pigs and rats. The labelling
TOXICOLOGICAL ASPECTS OF MELANIN AND MELANOGENESIS of the inner ear in relation to other tissues. Acta Otolaryngol. (Stockh.) 101:247–256, 1986. Oka, M., K. Ogita, N. Saito, and Y. Mishima. Selective increase of the alpha subspecies of protein kinase C and inhibition of melanogenesis induced by retinoic acid in melanoma cells. J. Invest. Dermatol. 100:204S-208S, 1993. Olander, K. Foreign melanin precursors for the detection of melanotic melanoma. Acta Univ. Upsaliensis 146:1–44, 1988. Olander, K., B. S. Larsson, and L. Dencker. Thioamides as false melanin precursors: studies in murine melanomas. Acta Pharmacol. Toxicol. 52:135–142, 1983. Olander, K., B. S. Larsson, U. Ringborg, and P. O. Schnell. Uptake of (131I)thiouracil in tumors of patients with disseminated malignant melanoma: a pilot study. Melanoma Res. 1:391–395, 1991. Oliver, E. A., L. Schwartz, and L. H. Warren. Occupational leukoderma. Arch. Dermatol. 42:993–1004, 1940. Orlow, S. J., A. K. Chakraborty, R. E. Boissy, and J. M. Pawelek. Inhibition of induced melanogenesis in Cloudman melanoma cells by four phenotypic modifiers. Exp. Cell Res. 191:209–218, 1990. Orlow, S. J., B. K. Zhou, A. K. Chakraborty, M. Drucker, S. Pifko-Hirst, and J. M. Pawelek. High-molecular-weight forms of tyrosinase and the tyrosinase-related proteins: evidence for a melanogenic complex. J. Invest. Dermatol. 103:196–201, 1994. Ortonne, J. P. Retinoic acid and pigment cells: a review of in-vitro and in-vivo studies. Br. J. Dermatol. 127:43–47, 1992. Ortonne, J.-P., D. B. Mosher, and T. B. Fitzpatrick. Topics in Dermatology: Vitiligo and Other Hypomelanoses of Hair and Skin. New York: Plenum Publishing Corporation, 1983. Osman, A. M., P. W. Jansen, L. A. Smets, and C. Benckhuijsen. Glucocorticoid receptors and cell cycle progression in human melanoma cell lines. J. Cell. Physiol. 125:306–312, 1985. Palumbo A., M. d’Ischia, G. Misuraca, and G. Prota. Effect of metal ions on the rearrangement of dopachrome. Biochim. Biophys. Acta 925: 203–209, 1987. Palumbo, A., M. d’Ischia, G. Misuraca, A. Iannone, and G. Prota. Selective uptake of 2-thiouracil into melanin-producing systems depends on chemical binding to enzymically generated dopaquinone. Biochim. Biophys. Acta 1036:221–227, 1990. Palumbo, A., A. Napolitano, L. DeMartino, W. D. Vieira, and V. J. Hearing. Specific incorporation of 2-thiouracil into biological melanins. Biochim. Biophys. Acta 1200:271–276, 1994. Pankovich, J. M., and K. Jimbow. Tyrosine transport in a human melanoma cell line as a basis for selective transport of cytotoxic analogues. Biochem. J. 280:721–725, 1991. Pannatier, A., P. Jenner, B. Testa, and C. Etter. The skin as a drugmetabolizing organ. Drug Metab. Rev. 8:319–343, 1978. Passi, S., and M. Nazzaro-Porro. Molecular basis of substrate and inhibitory specificity of tyrosinase: phenolic compounds. Br. J. Dermatol. 104:659–665, 1981. Passi, S., M. Picardo, and M. Nazzaro-Porro. Comparative cytotoxicity of phenols in vitro. Biochem. J. 245:537–542, 1987. Pathak, M. A., and P. C. Joshi. Production of active oxygen species (1O2 and O2◊-) by psoralens and ultraviolet radiation (320–400 nm). Biochim. Biophys. Acta 798:115–126, 1984. Pathak, M. A., E. Frenk, G. Szabo, and T. B. Fitzpatrick. Cutaneous depigmentation. Clin. Res. 14:272, 1966. Pavel, S., H. Elzinga, F. A. J. Muskiet, J. M. Smit, N. H. Mulder, and H. Schraffordt Koops. Eumelanin-related indolic compounds in the urine of treated melanoma patients. J. Clin. Chem. Clin. Biochem. 24:176–173, 1986. Peck, S. M., and H. Sobotka. Effect of monobenzyl hydroquinone on oxidase systems in vivo and in vitro. J. Invest. Dermatol. 4:325–329, 1941. Pell, S., M. T. O’Berg, and B. W. Karrh. Cancer epidemiologic surveillance in the DuPont Company. J. Occup. Med. 20:725–740, 1978.
Persad, S., I. A. Menon, P. K. Basu, and H. F. Haberman. Binding of imipramine, 8-methoxypsoralen and epinephrine to human blue and brown eye melanins. J. Toxicol. Cutan. Ocul. Toxicol. 5:125–132, 1986. Picardo, M., S. Passi, M. Nazzaro-Porro, A. S. Breathnach, C. Zompetta, A. Faggioni, and P. Riley. Mechanism of antitumoral activity of catechols in culture. Biochem. Pharmacol. 36:417–425, 1987. Potts, A. M. The concentration of phenothiazines in the eye of experimental animals. Invest. Ophthalmol. Vis. Sci. 1:522–530, 1962a. Potts, A. M. Uveal pigment and phenothiazine compounds. Trans. Am. Ophthalmol. Soc. 60:517–552, 1962b. Potts, A. M. Reaction of uveal pigment with polycyclic compounds. Invest. Ophthalmol. Vis. Sci. 3:405–416, 1964a. Potts, A. M. Further studies concerning the accumulation of polycyclic compounds on uveal melanin. Invest. Ophthalmol. Vis. Sci. 3:399–404, 1964b. Poulsen, J. Hair loss, depigmentation of hair, ichthyosis, and blepharoconjunctivitis produced by dixyrazine. Acta Derm. Venereol. 61:85–88, 1981. Prota, G. Melanins and Melanogenesis. San Diego: Academic Press, 1992. Prota, G. Recent advances in the chemistry of melanogenesis in mammals. J. Invest. Dermatol. 75:122–127, 1980. Raghavan, P. R., P. A. Zane, and S. L. Tripp. Calculation of drugmelanin binding energy using molecular modeling. Experientia 46:77–80, 1990. Rampen, F. H. J., and E. Fleuren. Melanoma of the skin is not caused by ultraviolet radiation but by a chemical xenobiotic. Med. Hypotheses 22:341–346, 1987. Ramsay, R. R., J. I. Salach, and T. P. Singer. Uptake of the neurotoxin 1-methyl-4-phenylpyridine (MPP+) by mitochondria and its relation to the inhibition of the mitochondrial oxidation of NAD-linked substrates by MPP+. Biochem. Biophys. Res. Commun. 134:743–748, 1986. Rich, P. R., N. K. Wiegand, H. Blum, A. L. Moore, and W. D. Bonner. Studies on the mechanism of inhibition of redox enzymes by substituted hydroxamic acids. Biochim. Biophys. Acta 525:325–337, 1978. Richardson, M. A., and T. J. Craig. The coexistence of parkinsonismlike symptoms and tardive dyskinesia. Am. J. Psychiatr. 139: 341–343, 1982. Richter, C. P., and K. H. Clisby. Graying of hair produced by ingestion of phenylthiocarbamide. Proc. Soc. Exp. Biol. Med. 48: 684–687, 1941. Riley, P. A. Hydroxyanisole depigmentation: in vitro studies. J. Pathol. 97:193–206, 1969a. Riley, P. A. Hydroxyanisole depigmentation: in vivo studies. J. Pathol. 97:185–191, 1969b. Riley, P. A. Mechanism of pigment cell toxicity produced by hydroxyanisole. J. Pathol. 101:163–169, 1970. Riley, P. A. Dendritic cell populations of the epidermis. In: The Physiology and Pathophysiology of the Skin, A. Jarrett (ed.). London: Academic Press, 1975, pp. 1101–1130. Riley, P. A. 4-Hydroxyanisole: Recent Advances in Antimelanoma Treatment. Oxford: IRL Press, 1984. Riley, P.A. Radicals and melanomas. Phil. Trans. R. Soc. London B Biol. Sci. 311:679–689, 1985. Riley, P. A. Biochemical markers of differentiated function in melanocytes. In: Cutaneous Melanoma, V. Veronesi, N. Cascinelli, and M. Santanini (eds). London: Academic Press, 1987, pp. 139–144. Riley, P. A. Melanogenesis: a realistic target for antimelanoma therapy? Eur. J. Cancer 27:1172–1177, 1991. Riley, P. A. Materia melanica: further dark thoughts. Pigment Cell Res. 5:101–106, 1992.
391
CHAPTER 18 Riley, P. A. Mechanistic aspects of the control of tyrosinase activity. Pigment Cell Res. 6:182–185, 1993. Riley, P. A. Photopigmentation. In: Photobiology in Medicine, G. Jori, R. H. Pottier, M. A. J. Rodgers, and T. G. Truscott (eds). New York: Plenum Press, 1994, pp. 99–112. Riley, P. A. The evolution of melanogenesis. In: Melanin: Its Role in Human Photoprotection, L. Zeise, M. R. Chedekel, and T. B. Fitzpatrick (eds). Overland Park, KS: Valdenmar Publishing, 1995, pp. 1–10. Riley, P. A. Melanogenesis and melanoma. Pigment Cell Res. 16: 548–552, 2003. Riley, P. A., C. J. Cooksey, C. I. Johnson, E. J. Land, A. M. Latter, and C. A. Ramsden. Melanogenesis-targeted anti-melanoma prodrug development: effect of side-chain variations on the cytotoxicity of tyrosinase-generated orthoquinones in a model screening system. Eur. J. Cancer 33:135–143, 1997. Roberto, A., and B. S. Larsson. The incorporation of boronated substances into melanin in vitro — an experimental model for melanotic melanoma. Strahlenther. Onkol. 165:165–167, 1989. Roberto, A., B. S. Larsson, and H. Tjälve. Uptake of 7,12-dimethylbenz(a)anthracene and benzo(a)pyrene in melanin-containing tissues. Pharmacol. Toxicol. 79:92–99, 1996. Robins, A. H. Biological Aspects of Human Pigmentation. Cambridge: Cambridge University Press, 1991. Rodier, J. Manganese poisoning in Moroccan miners. Br. J. Ind. Med. 12:21–35, 1955. Romero, C., E. Aberdam, C. Larnier, and J. P. Ortonne. Retinoic acid as modulator of UVB-induced melanocyte differentiation. Involvement of the melanogenic enzymes expression. J. Cell Sci. 107:1095–1103, 1994. Roskoski, R., Jr., and S. R. Jaskunas. Chloroquine and primaquine inhibition of rat liver cell-free polynucleotide-dependent polypeptide synthesis. Biochem. Pharmacol. 21:391–399, 1972. Rubin, M. The antimalarials and the tranquilizers. Dis. Nerv. Syst. 29:67–76, 1968. Rüedi, L. Über die Funktion der Stria vascularis. Pract. Otorhinolaryngol. (Basel) 13:341–352, 1951. Russell, L. B. The mouse spot test as a predictor of heritable genetic change and other end-points. In: Chemical Mutagens: Principles and Methods for their Detection, F. J. De Serres (ed.). New York: Plenum Press, 1983, pp. 95–110. Salazar, M., K. Shimada, and P. N. Patil. Iris pigmentation and atropine mydriasis. J. Pharmacol. Exp. Ther. 197:79–88, 1976. Salazar-Bookaman, M. M., I. Wainer, and P. N. Patil. Relevance of drug–melanin interactions to ocular pharmacology and toxicology. J. Ocul. Pharmacol. 10: 217–239, 1994. Sarna, T. Properties and function of the ocular melanin — a photobiophysical view. J. Photochem. Photobiol. B 12:215–258, 1992. Sarna, T., and H. M. Swartz. Identification and characterization of melanin in tissues and body fluids. Folia Histochem. Cytochem. 16:275–286, 1978. Sarna, T., W. Froncisz, and J. S. Hyde. Cu2+ probe of metal-ion binding sites in melanin using electron paramagnetic resonance spectroscopy. II. Natural melanin. Arch. Biochem. Biophys. 202:304–313, 1980. Sarna, T., W. Korytowski, M. Pasenkiewicz-Gierula, and E. Gudowska. Ion-exchange studies in melanins. In: Proceedings of the 11th International Pigment Cell Conference, Sendai, 1980, M. Seiji (ed.). Tokyo: University of Tokyo Press, 1981, pp. 23–29. Sattler, S., and H. Schutt. Johanniskraut: Ein Rezept der Natur gegen Depressionen. Therapiewoche 44:811–815, 1994. Savin, C. The blood vessels and pigmentary cells of the inner ear. Ann. Otol. Rhinol. Laryngol. 74:611–622, 1965. Scatchard, G., J. S. Coleman, and A. C. Shen. Physical chemistry of protein solutions. VII. The binding of some small anions to serum albumin. J. Am. Chem. Soc. 79:12–20, 1957.
392
Schallreuter, K. U., and J. M. Wood. Thioredoxin reductase in control of the pigmentary system. In: Clinics in Dermatology: Disorders of Pigmentation, R. Mackie (ed.). Philadelphia: J. B. Lippincott, 1989, pp. 92–105. Schmidt, W. R., and L. W. Jarcho. Persistent dyskinesias following phenothiazine therapy. Arch. Neurol. 14:369–377, 1966. Schoental, R. Irreversible depigmentation of hair by N-methyl-Nnitrosourethane. Experientia 27:552–553, 1971. Schoental, R., A. Z. Joffe, and B. Yagen. Irreversible depigmentation of hair by T-2 toxin (a metabolite of Fusarium sporothichoides) and by calcium pantothenate. Experientia 34:763, 1978. Schuknecht, H. F. Pathology of the Ear. Cambridge, MA: Harvard University Press, 1974. Searle, C. E. Depigmentation and coat colour variegation in mice treated with 8-hydroxyquinoline. Experientia 26:944–945, 1970. Searle, C. E. The selective depigmenting action of 8-hydroxyquinoline on hair growth in the mouse. Br. J. Dermatol. 86:472–480, 1972. Searle, C. E., and P. A. Riley. Chemically-induced depigmentation of skin and hair. In: Haar und Haarkrankheiten, C. E. Orfanos (ed.). Stuttgart: Springer-Verlag, 1979, pp. 911–929 [English translation (1991): Hair and Hair Diseases C. E. Orfanos (ed.)]. Selye, H. Ischemic depigmentation. Experientia 23:524, 1967. Shaw, H. M., C. M. Balch, S. J. Soong, G. W. Milton, and W. H. McCarthy. Prognostic histopathological factors in malignant melanoma. Pathology 17:271–274, 1985. Shelley, W. B., and S. Ohman. Epinephrine induction of white hair in ACT rats. J. Invest. Dermatol. 53:155–158, 1969. Siddall, J. R. Ocular toxic changes associated with chlorpromazine and thioridazine. Can. J. Ophthalmol. 1:190–198, 1966. Smit, N. P. M., S. Pavel, A. Kammeyer, and W. Westerhof. Determination of catechol-O-methyl transferase activity in relation to melanin metabolism using high-performance liquid chromatography with fluorometric detection. Anal. Biochem. 190:286–291, 1990. Smit, N., C. Tilgmann, T. Karhunen, R. Slingerland, I. Ulmanen, W. Westerhof, and S. Pavel. O-methylation of L-dopa in melanin metabolism and the presence of catechol-O-methyltransferase in melanocytes. Pigment Cell Res. 7:403–408, 1994. Smit, N. P. M., S. Pavel, and P. A. Riley. Mechanisms of control of the cytotoxicity of orthoquinone intermediates of melanogenesis. In: Role of Catechol Quinone Species in Cellular Toxicity, C. R. Creveling (ed.). Johnson City, TN: F. P. Graham Publishing, 2000, pp. 191–245. Solano, F., J. H. Martinez-Liarte, C. Jimenez-Cervantes, J. C. García-Borrón, and J. A. Lozano. DOPAchrome tautomerase is a zinc-containing enzyme. Biochem. Biophys. Res. Commun. 204: 1243–1250, 1994. Solomon, E. I., and M. D. Lowery. Electronic structure contributions to function in bioorganic chemistry. Science 259:1575–1581, 1993. Spillane, J. D. Brunette to blonde: depigmentation of human hair during oral treatment with mephenesin. Br. Med. J. 1:997–1000, 1963. Stenson, S. M., I. M. Siegel, and R. E. Carr. Infantile cystinosis: ocular findings and pigment dilution of eye and skin. Ophthal. Paediatr. Genet. 3:169–180, 1983. Stepien, K. B., and T. Wilczok. Studies of the mechanism of chloroquine binding to synthetic dopa-melanin. Biochem. Pharmacol. 31:3359–3365, 1982. Stern, R. S. Risks of cancer associated with long-term exposure to PUVA in humans: current status — 1991. Blood Cells 18:91–97, 1992. Stewart, T. W., D. W. Miles, and E. R. Earnshaw. Pigmentation and retinopathy due to chloroquine. Acta. Derm. Venereol. 48:47–52, 1968. Strong, L. C. Genetic analysis of the induction of tumors by methylcholanthrene. XI. Germinal mutations and other sudden biological
TOXICOLOGICAL ASPECTS OF MELANIN AND MELANOGENESIS changes following the subcutaneous injection of methylcholanthrene. Proc. Natl. Acad. Sci. USA 31:290–293, 1945. Strong, L. C. The induction of melanotic tumours and pigmented hair changes in mice by methylcholanthrene. Ann. N. Y. Acad. Sci. Spec. Publ. 4:358–368, 1948. Sunkara, P. S., C. C. Chang, N. J. Prakash, and P. J. Lachmann. Effect of inhibition of polyamine biosynthesis by DL-alpha-difluoromethylornithine on the growth and melanogenesis of B16 melanoma in vitro and in vivo. Cancer Res. 45:4067–4070, 1985. Swartz, H. M., T. Sarna, and L. Zecca. Modulation by neuromelanin of the availability and reactivity of metal ions. Ann. Neurol. 32:S69–S75, 1992. Swope, V. B., Z. A. Abdel-Malek, D. N. Sauder, and J. J. Nordlund. A new role for epidermal cell-derived thymocyte activating factor (ETAF)/IL-1 as an antagonist for distinct epidermal cell function. J. Immunol. 142:1943–1949, 1989. Swope, V. B., Z. A. Abdel-Malek, L. Kassem, and J. J. Nordlund. Interleukins 1a and 6 and tumor necrosis factor-b are paracrine inhibitors of human melanocyte proliferation and melanogenesis. J. Invest. Dermatol. 96:180–185, 1991. Tammela, M. Tissue localization of some organic and inorganic cations. Binding to melanin and cartilage. Acta Univ. Upsaliensis 111:1–42, 1985. Terao, M., L. Tabe, E. Garattini, D. Sartori, M. Studer, and B. Mintz. Isolation and characterization of variant cDNAs encoding mouse tyrosinase. Biochem. Biophys. Res. Commun. 159:848–853, 1989. Terao, M., K. Tomita, T. Oki, L. Tabe, M. Gianni, and E. Garattini. Inhibition of melanogenesis by BMY-28565, a novel compound depressing tyrosinase activity in B16 melanoma cells. Biochem. Pharmacol. 43:183–189, 1992. Testorf, M. F., R. Kronstrand, S. P. Svensson, B. Lundstrom, and J. Ahlner. Characterization of [3H]flunitrazepam binding to melanin. Anal. Biochem. 298: 259–264, 2001. Thomas, T. L., and P. Decoufle. Mortality among workers employed in the pharmaceutical industry. A preliminary investigation. J. Occup. Med. 21:619–623, 1979. Thompson, A., E. J. Land, M. R. Chedekel, K. V. Subbarao, and T. G. Truscott. A pulse radiolysis study of the oxidation of the melanin precursors 3,4-dihydroxyphenylalanine (dopa) and the cysteinyldopas. Biochim. Biophys. Acta 843: 49–57, 1985. Tjälve, H., M. Nilsson, and B. Larsson. Binding of 14C-spermidine to melanin in vivo and in vitro. Acta Physiol. Scand. 112:209–214, 1981. Tjälve, H., M. Nilsson, and B. Larsson. Thallium-201: autoradiography in pigmented mice and melanin-binding in vitro. Acta Pharmacol. Toxicol. 51:147–153, 1982. Tjälve, H., C. Mejàre, and K. Borg-Neczak. Uptake and transport of manganese in primary and secondary olfactory neurons in pike. Pharmacol. Toxicol. 77:23–31, 1995. Tjarks, W. 1989. Borhaltige Thioharnstoffe in der Neutroneneinfangtherapie. PhD Thesis. University of Bremen, Bremen. Ucar, K. The effects of histamine H2 receptor antagonists on melanogenesis and cellular proliferation in melanoma cells in culture. Biochem. Biophys. Res. Commun. 177:545–550, 1991. Uematsu, T., R. Sato, O. Fujimori, and M. Nakashima. Human scalp hair as evidence of individual dosage history of haloperidol. A possible linkage of haloperidol excretion into hair with hair pigment. Arch. Dermatol. Res. 282:120–125, 1990. Ullberg, S., B. Larsson, and H. Tjälve. Autoradiography. In: Biologic Applications of Radiotracers, H. J. Glenn (ed.). Boca Raton, FL: CRC Press, 1982, pp. 55–108. Van Langevelde, A., C. N. M. Bakker, H. J. Broxterman, J. G. Journée-de Korver, F. M. Kaspersen, J. A. Oosterhuis, and E. K. J. Pauwels. Potential radiopharmaceuticals for the detection of ocular melanoma, Part I, 5-iodo-2-thiouracil derivatives. Eur. J. Nucl. Med. 8:45–51, 1983.
Van Woert, M. H. Oxidation of reduced nicotinamide adenine dinucleotide by melanin. Life Sci. 6:2605–2612, 1967. Viala, A., E. Deturmeny, C. Aubert, M. Estadieu, A. Durand, J. P. Cano, and J. Delmont. Determination of chloroquine and monodesethylchloroquine in hair. J. Forens. Sci. 28:922–928, 1983. Waardenburg, P. J. A new syndrome combining developmental anomalies of the eyelids, eyebrows and nose root with pigmentary defects of the iris and head hair and with congenital deafness. Am. J. Hum. Genet. 3:195–253, 1951. Walter, J. F., W. H. Kelsey, and J. Voorlees. Psoralen plus black light inhibits epidermal DNA synthesis. Arch. Dermatol. 107:861–865, 1973. Wästerström, S.-A. Accumulation of drugs on inner ear melanin: therapeutic and ototoxic mechanisms. Scand. Audiol. Suppl. 23: 1–40, 1984. Wästerström, S.-A., G. Bredberg, N. G. Lindquist, L. Lyttkens, and H. Rask-Andersen. Ototoxicity of kanamycin in albino and pigmented guinea pigs. I. A morphological and electrophysiological study. Otolaryngol. Clin. North Am. 7:11–18, 1986. Wätjen, F., O. Buchardt, and E. Langvad. Affinity therapeutics. 1. Selective incorporation of 2-thiouracil derivatives in murine melanomas. Cytostatic activity of 2-thiouracil arotinoids, 2thiouracil retinoids, arotinoids and retinoids. J. Med. Chem. 25:956–960, 1982. Watts, K. P., R. G. Fairchild, D. N. Slatkin, D. Greenberg, S. Packer, H. L. Atkins, and S. J. Hannon. Melanin content of hamster tissues, human tissues and various melanomas. Cancer Res. 41:467–472, 1981. Westerhof, W., S. Pavel, A. Kammeyer, F. D. Beusenberg, and R. Cormane. Melanin-related metabolites as markers of the skin pigmentary system. J. Invest. Dermatol. 89:78–81, 1987. Wetterholm, D. H., and F. C. Winter. Histopathology of chloroquine retinal toxicity. Arch. Ophthalmol. (Chicago) 71:82–87, 1964. Whittaker, J. R. Anomalous differentiation of melanin granules caused by thiouracil. Exp. Cell Res. 44:351–361, 1966. Whittaker, J. R. Biosynthesis of a thiouracil phaeomelanin in embryonic pigment cells exposed to thiouracil. J. Biol. Chem. 246: 6217–6226, 1971. Wick, M. M. L-Dopa methyl ester as a new antitumor agent. Nature 269:512–513, 1977. Wilcox, D. E., A. G. Porras, T. Hwang, K. Lerch, M. E. Winkler, and E. I. Solomon. Substrate analogue binding to the coupled binuclear copper active site in tyrosinase. J. Am. Chem. Soc. 107:4015–4027, 1985. Wilczek, A., and Y. Mishima. Inhibitory effects of melanin monomers, dihydroxyindole-2-carboxylic acid (DHICA) and dihydroxyindole (DHI) on mammalian tyrosinase, with a special reference to the role of DHICA/DHI ratio in melanogenesis. Pigment Cell Res. 8:105– 112, 1995. Wilde, C. E. The role of phenylalanine in the differentiation of neural crest cells. Ann. N. Y. Acad. Sci. 60:1015–1025, 1955. Winkler, M. E., K. Lerch, and E. I. Solomon. Competitive inhibitor binding to the binuclear copper active site in tyrosinase. J. Am. Chem. Soc. 103:7001–7003, 1981. Wittbjer, A., G. Odh, A. M. Rosengren, E. Rosengren, and H. Rorsman. Isolation of soluble tyrosinase from human melanoma cells. Acta Derm. Venereol. (Stockh.) Suppl. 70:291–294, 1990. Wood, B. J. B., and L. L. Ingraham. Labelled tyrosinase from labelled substrate. Nature 205:291–292, 1965. Wood, J. M., and K. U. Schallreuter. Studies on the reactions between human tyrosinase, superoxide anion, hydrogen peroxide and thiols. Biochim. Biophys. Acta 1074:378–385, 1991. Wood, J. M., K. U. Schallreuter Wood, N. J. Lindsey, S. Callaghan, and M. L. G. Gardner. A specific tetrahydrobiopterin binding domain on tyrosinase controls melanogenesis. Biochem. Biophys. Res. Commun. 206:480–485, 1995.
393
CHAPTER 18 Wu, E. Y., K. Chiba, A. J. Trevor, and N. Castagnoli, Jr. Interactions of the 1-methyl-4-phenyl-2,3-dihydropyridinium species with synthetic dopamine-melanin. Life Sci. 39:1695–1700, 1986. Wulf, H. C., and J. Hart. Accumulation of 8-methoxypsoralen in the rat retina. Acta Ophthalmol. 56:284–290, 1978. Yamada, K., B. S. Larsson, A. Roberto, L. Dencker, and S. Ullberg. Selective incorporation of thiouracil into murine metastatic melanomas. J. Invest. Dermatol. 90:873–876, 1988. Yamamoto, H., S. Takeuchi, T. Kudo, C. Sato, and T. Takeuchi. Melanin production in cultured albino melanocytes transfected with mouse tyrosinase cDNA. Jpn. J. Genet. 64:121–135, 1989. Zane, P. A., S. D. Brindle, D. O. Gause, A. J. O’Buck, P. R.
394
Raghavan, and S. L. Tripp. Physicochemical factors associated with binding and retention of compounds in ocular melanin of rats: correlations using data from whole-body autoradiography and molecular modeling for multiple linear regression analyses. Pharmaceut. Res. 7:935–941, 1990. Zareba, M., A. Bober, W. Korytowski, L. Zecca, and T. Sarna. The effect of a synthetic neuromelanin on yield of free hydroxyl radicals generated in model systems. Biochim. Biophys. Acta 1271:343–348, 1995. Zecca, L., and H. M. Swartz. Total and paramagnetic metals in human substantia nigra and its neuromelanin. J. Neural Transm. Park. Dis. Dement. Sect. 5:203–213, 1993.
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
19
Regulation of Pigment Type Switching by Agouti, Melanocortin Signaling, Attractin, and Mahoganoid Gregory S. Barsh
Summary 1 There are two major types of melanin pigment produced by mammalian pigment cells: black/brown eumelanin or red/yellow pheomelanin. Both require the enzymatic oxidation of tyrosine to form dopaquinone. During pheomelanin synthesis, dopaquinone is produced at relatively low levels and becomes incorporated into sulfhydryl derivatives. In contrast, eumelanin synthesis is associated with a high rate of dopaquinone production and subsequent enzymatic oxidation into indole derivatives. Studies based on coat color mutations in laboratory mice have identified several genes that regulate whether melanocytes produce pheomelanin or eumelanin; these genes and their homologs in other species are the subject of this chapter. A focal point for pigment type switching is the Melanocortin 1 receptor (Mc1r) gene (formerly known as Extension), which encodes a seven-transmembrane-domain receptor expressed by hair follicle melanocytes; gain-offunction Mc1r mutations cause exclusive production of eumelanin, whereas loss-of-function mutations cause exclusive production of pheomelanin. The Agouti gene (A) encodes the ligand for the Mc1r and is a paracrine signaling molecule secreted from mesenchymal cells in dermal papillae. Agouti protein inhibits Mc1r function such that gain-of-function Agouti mutations cause exclusive production of pheomelanin, whereas loss-of-function mutations cause exclusive production of eumelanin. Two additional molecules required for Agouti inhibition of Mc1r function are Attractin (Atrn), which acts as an accessory receptor for Agouti protein, and Mahoganoid (Mgrn1), an intracellular protein with E3 ubiquitin ligase activity. 2 The Mc1r is coupled to adenylate cyclase and is named after a family of receptors, Mc1r–Mc5r, that bind peptide ligands such as alpha-melanocyte-stimulating hormone (a-MSH) or adrenocorticotropic hormone (ACTH), which are derived from the same precursor, preproopiomelanocortin (Pomc). Activation of Mc1r by gain-of-function mutations or by addition of a-MSH causes increased accumulation of cyclic adenosine monophosphate (cAMP). However, Pomc is expressed primarily in the brain and pituitary gland, and most evidence suggests that basal levels of Mc1r activity in the absence of stimulatory melanocortin ligands are sufficient to induce
constitutive eumelanin synthesis. In most furry mammals, pigmentation patterns that depend on specific deposition of eumelanin vs. pheomelanin are controlled by dynamic changes in local levels of Agouti protein. In humans, however, a physiologic role for Agouti has not yet been established; the human Mc1r has a relatively high level of constitutive basal activity, and individual differences in the ratio of pheomelanin to eumelanin are controlled mostly by allelic variation of Mc1r. Most humans with red hair and fair skin carry a Mc1r lossof-function mutation; population genetic studies suggest that Mc1r function has been under positive selection in African populations, and that Mc1r-induced red hair and fair skin results mostly from genetic drift. 3 Homologs for Agouti and Mc1r are found in genomes from a variety of distantly related vertebrates, but not in invertebrate or Ascidian genomes. 4 Allelic variants of Agouti or Mc1r associated with altered pigment type switching phenotypes within populations of natural or domestic animals have been identified in sheep, cattle, horses, dogs, cats, pigs, foxes, bears, and several avian species. In addition, domestic cats and Syrian hamsters carry an X-linked coat color mutation referred to as Tortoiseshell or Orange, the effects of which are similar to that of the Mc1r but which is likely to represent a different gene. Finally, domestic dogs carry an autosomal coat color mutation referred to as Dominant Black (K) that affects the same pathway but is distinct from Agouti and Mc1r.
Historical Background Almost 100 years ago, studies by Sewall Wright on color inheritance in guinea pigs laid the groundwork for recognizing that mammalian melanocytes synthesize pigment of two different types, black/brown eumelanin or yellow/red pheomelanin (Wright, 1917a, b). Wright suggested that certain genes such as Agouti (A) or Extension (E) determined which of these two pigment types would be synthesized, while others such as Pink-eyed dilution (P) affected the quality of eumelanin but not that of pheomelanin. As described in Chapter 10, an important landmark in melanin research was the recognition in the 1920s that eumelanin synthesis involved oxidation of tyrosine to form an 395
CHAPTER 19
indole-based polymer, by a process now known as the Raper–Mason pathway. Because pheomelanin is soluble in dilute alkali and has a relatively high cysteine content, it was recognized to have a different chemical structure from eumelanin. Studies in the 1950s suggested that alternative amino acids might underlie differences between eumelanin and pheomelanin, but it is now clear that both pigment types are produced solely from tyrosine, and both depend on tyrosinasecatalyzed formation of dopaquinone. Thus, diversion of dopaquinone into the pheomelanic pathway serves as the fulcrum upon which genes that control eumelanin/pheomelanin switching are balanced (Fig. 19.1A). Interestingly, Sewall Wright suggested a biochemical pathway for pigment synthesis in 1917 that was based solely on genetic data (Wright, 1917a). Although details of his hypothesis later proved incorrect, an essential component — that eumelanin and pheomelanin shared both a common precursor and initial steps of oxidative metabolism — was confirmed nearly 50 years later. While the earliest studies of coat color genetics were carried out with guinea pigs as described above, mice are much better suited to breeding studies and so have provided most of the depth in mammalian pigmentation genetics (Wright, 1917c). This resource has arisen from three different sources. Many coat color variants that previously existed among communities of mouse fanciers or wild mice were incorporated into inbred strains during the early part of this century, such as the nonagouti (a) and tobacco (Etob or Mc1rtob) alleles at the Agouti and Mc1r loci respectively (reviewed by Morse, 1978; Silver, 1995). In addition, a large number of spontaneous mutations have arisen during the propagation of inbred strains, such as the mahogany (Atrnmg) or mahoganoid (Mgrn1md) alleles. Finally, systematic large-scale mutagenesis studies carried out at national laboratories such as Harwell (Lyon, 2002), Oak Ridge (Davis and Justice, 1998; Russell and Russell, 1992), and Neuherberg (Ehling et al., 1985; Favor and Neuhauser-Klaus, 2000) have focused on a small number of specific genes — the so-called specific locus test — and have therefore given rise to a large number of alleles for Agouti, Tyrp1 (formerly known as brown), Tyr (formerly known as albino), Myo5a (formerly known as dilute), Pinkeyed dilute, and Ednrb (formerly known as s or piebald spotting). The large number of mouse coat color mutations developed during the last half of the twentieth century provided the raw materials for classical studies of gene action and interaction, as described carefully and thoughtfully in the similarly titled book by Willys Silvers (Silvers, 1979). As molecular genetic tools became increasingly available in the 1980s and 1990s, most of the “classical” mouse coat color genes were cloned, leading to sophisticated explanations and models for how different genetic pathways give rise to specific cellular, tissue, and organismal phenotypes (Bennett and Lamoreux, 2003). A recurring theme from this work is that many of the genes and pathways used by the pigmentary system in laboratory mice are representative of physiologic processes used by other organ systems in all mammals; thus, studying the biology of mouse 396
Fig. 19.1. Biochemistry and genetics of pigment type switching. (A) In most biologic situations, synthesis of the two different pigment types behaves as a binary switch; either pheomelanin or eumelanin is synthesized, but not both. Genetic requirements and factors thought to “tip” the balance are described in the text. (B) Gene products and symbols are indicated together with their likely positions in melanogenesis. Dct (dopachrome tautomerase) and Tyrp1 (tyrosinase-related protein 1) catalyze oxidation of additional compounds after the formation of dopachrome (see Fig. 19.2A) that contribute to eumelanin. Several lines of evidence indicate that Dct and Tyrp1 are required for eumelanin but not pheomelanin synthesis (Kobayashi et al., 1995; Lamoreux et al., 2001; Prota et al., 1995). The P (Pink-eyed dilution) gene and MATP (membraneassociated transporter) are thought to facilitate the transport of small molecules across the melanosomal membrane as described in Chapter 12. Not shown in the diagram is the observation that P and MATP are required for normal levels of pheomelanin as well as eumelanin; however, studies of different coat color mutants indicate that loss-of-function for the P gene (Lamoreux et al., 2001; Prota et al., 1995) impairs synthesis of eumelanin more so than that of pheomelanin. As described in the text, the mechanism by which Mgrn1 is required for pheomelanin synthesis is not yet clear. One possibility (1) is that Mgrn1 normally inhibits the stimulatory activity of Mc1r, such that, in the absence of Mgrn1, Agouti is unable to overcome increased Mc1r signaling. In addition (2), Mgrn1 may be required to communicate signals brought about by Mc1r inhibition to the biochemical apparatus used for pheomelanin synthesis. (C) Summary of coat color phenotypes for various combinations of loss-of-function (lof) or gain-of-function (gof) mutants.
REGULATION OF PIGMENT TYPE SWITCHING BY AGOUTI
coat color helps to understand many aspects of human biology and disease. In the case of pigment type switching, molecular genetic studies of Agouti and Mc1r revealed that a homologous system in the brain, represented by Agouti-related protein and Mc4r, plays a key role in homeostatic control of energy balance and body weight (reviewed by Barsh and Schwartz, 2002). In addition, recent studies of Attractin and Mahoganoid suggest that studies of pigment type switching will prove helpful in understanding the pathogenesis of certain types of neurodegeneration (reviewed by He et al., 2003a). With increasing amounts of genome sequence and annotation available over the last several years, attention has once again turned to pigmentary genetics in animals outside the laboratory, including those of agricultural significance, such as cattle, horses, sheep, and pigs, and those in which unique aspects of their population history provide insight into the role of pigmentary phenotypes in ecology and evolution, including bananaquits, geese, pocket mice, domestic dogs, and humans (Andersson, 2003; Hoekstra et al., 2004; Kerns et al., 2003; Klungland and Vage, 2003; Mundy et al., 2003; Rees, 2003).
Current Concepts Eumelanin and Pheomelanin One of the most interesting features of this system is that, in many biologic settings regardless of scale, one finds eumelanin or pheomelanin, but not both. Pigment granules are generally classified as eumelanosomes or pheomelanosomes, hair follicle melanocytes switch abruptly and precisely between synthesis of the two pigment types, and color patterns in many different mammals are formed by juxtaposition of hairs that contain exclusively eumelanin or pheomelanin. Spots on a leopard, stripes on a tiger, dorsal–ventral differences in rodent coloration, and facial markings characteristic of many different dog breeds are each caused by regulation of an intercellular signaling mechanism and biochemical pathway that switches between synthesis of eumelanin and pheomelanin. Fundamental differences in chemical composition, ultrastructure, and biogenesis distinguish these two types of pigment and, although the differences are also frequently described in terms of visible reflectance — brownish-black (eumelanin) vs. reddish-yellow (pheomelanin) — this is an oversimplification. In particular, low levels of eumelanin (but an absence of pheomelanin) are characteristic of blond hair in many humans, whereas low levels of pheomelanin (but an absence of eumelanin) are characteristic of cream-colored hair in many animals (Ito, 1993, 2003; Ito and Fujita, 1985; Ito and Wakamatsu, 2003; Lamoreux et al., 2001; Ozeki et al., 1995; Prota et al., 1995). Thus, both the pigment type itself as well as the density and distribution of pigment granules in surrounding cells help to determine overall reflectance qualities; in situations where there are low levels of total melanin, visible characteristics can be deceiving with regard to the underlying type of pigment (Fig. 19.1B).
As described in Chapter 10, both pigment types require the enzymatic oxidation of tyrosine to form dopaquinone (by tyrosinase); however, during pheomelanin synthesis, dopaquinone is produced at relatively low levels and serves as a substrate for nonenzymatic addition of cysteine and redox exchange to produce cysteinyldopaquinone (Fig. 19.2A). In contrast, eumelanin synthesis is associated with a higher rate of dopaquinone production followed by nonenzymatic cyclization and redox exchange to yield dopachrome; subsequent enzymatic oxidation yields additional indole derivatives that serve as the building blocks for eumelanin (Ito, 2003; Land et al., 2003, 2004; Land and Riley, 2000; Ozeki et al., 1997). Thus, from a biochemical perspective, two cardinal characteristics of pheomelanin synthesis are low rates of dopaquinone production and a readily available supply of free cysteine. Indeed, a widely proposed theory to account for the ability of melanocytes to switch between eumelanin and pheomelanin synthesis posits that these features — low levels of tyrosinase activity and high levels of free cysteine — are necessary and sufficient for pheomelanin synthesis (Ito, 1993, 2003; Land et al., 2003, 2004). As initially proposed by Ito and colleagues (Ito, 1993), tyrosinase activity (and, thus, the rate of dopaquinone production) was suggested to be the primary determinant of whether or not dopaquinone gave rise to pheomelanin or eumelanin. In part, this proposal was based on the idea that reduced glutathione could serve as a thiol donor for dopaquinone, and that high levels of dopaquinone would inhibit glutathione reductase. More recently, studies of melanosomal transport indicated that cysteine rather than glutathione was likely to be the source of the thiol in cysteinyldopa (Potterf et al., 1999). Together with sophisticated techniques for measuring the kinetics of reactions with unstable intermediates, a more refined view of melanogenesis was reached (Land et al., 2003; Land and Riley, 2000), in which the ratio of pheomelanin to eumelanin production, or an “index of divergence,” could be estimated from rate constants of individual reactions in solution (Fig. 19.2A). At first glance, this approach predicts that the index of divergence depends only on cysteine availability, with approximately equivalent amounts of pheomelanin and eumelanin being produced at cysteine levels of ~ 1 micromolar, independent of dopaquinone concentration (Land and Riley, 2000). However, the underlying chemistry — in which a common precursor is utilized in a first-order reaction for one pathway but a second-order reaction for the other pathway — means that influx of dopaquinone indirectly controls the ratio of pheomelanin to eumelanin synthesis through its consumption of cysteine. Thus, only if cysteine levels were “clamped,” with influx rates rising and falling to maintain a constant steady-state level, would the ratio of pheomelanin to eumelanin be truly independent of dopaquinone production and, in practice, “the sensitivity of the system to the availability of cysteine is influenced by tyrosine uptake and tyrosinase activity” (Land et al., 2003). Advances in melanin chemistry notwithstanding, the preceding discussion does not adequately explain the abrupt 397
CHAPTER 19
Fig. 19.2. Contribution of cysteine and tyrosinase activity to pigment type switching. (A) As described by Land and Riley (Land et al., 2003; Land and Riley, 2000), formation of cysteinyldopa or cyclodopa from dopaquinone occurs spontaneously, and represents the initial step in pheomelanin or eumelanin synthesis respectively. In subsequent steps, cysteinyldopa or cyclodopa is oxidized to yield cysteinyldopaquinone or dopachrome respectively; both reactions proceed spontaneously and utilize dopaquinone as the oxidizing agent. Rate constants for these reactions in solution (r1–r4) have been measured by Riley and colleagues, and used to generate a model of how alterations in the availability of cysteine and the influx of dopaquinone influence the balance between synthesis of the two pigment types (Land et al., 2003; Land and Riley, 2000). As described in the text, this model predicts that cysteine concentration should exhibit a linear relationship with the relative rates of pheomelanin vs. eumelanin production, but does not easily explain how the “switch” between the two types of pigment occurs abruptly in many biologic situations. (B) The left-hand panel illustrates how changes in levels of Agouti expression are related to pigment synthesis. As Agouti expression increases, Mc1r signaling decreases and, at a midpoint, there is an abrupt switch from eumelanin to pheomelanin synthesis. In general, tyrosinase activity correlates with levels of Mc1r signaling. However, the exact shape of the curve is not known, and is shown here purely for purposes of illustration. In animals that carry a hypomorphic tyrosinase allele such as chinchilla (Tyrch), tyrosinase activity is reduced during the entirety of pigment type switching and, at high levels of Agouti expression, becomes insufficient to support any pigment synthesis. The right-hand panel illustrates this principle. Animals that express high levels of Agouti protein and carry a normal tyrosinase allele are reddish-yellow; animals that express no Agouti protein and carry a hypomorphic tyrosinase allele are black, but animals that express high levels of Agouti protein and carry a hypomorphic tyrosinase allele are cream colored. Quantitative measurements of melanin synthesis by Ito and colleagues support this conclusion (Lamoreux et al., 2001). In the absence of Agouti, the chinchilla mutation reduces total melanin from a level of 0.775 to 0.452 (absorbance 500 units/mg hair), almost all of which is pheomelanin; however, in the presence of Agouti (Ay/a), the chinchilla mutation reduces total melanin from a level of 0.093 to 0.023 (absorbance 500 units/mg hair); the latter value is so low that animals appear almost white. See also Plate 19.1, pp. 494–495.
nature of the “switch” itself, as the relationship between tyrosinase activity and the ratio of eumelanin to pheomelanin production is more logistic than linear (Fig. 19.2B). It also does not speak to the biogenesis of pheomelanosomes vs. eumelanosomes, which differ in their structure as well as in their melanin content. The former tends to be spherical with a granular and/or microvesicular lumen that shows little evidence of internal structure, whereas the latter tends to be 398
ovoid with a highly organized internal structure thought to be based on a proteinaceous matrix (Liu et al., 2004). Other than melanin itself, surprisingly little is known about the molecular anatomy that distinguishes pheomelanosomes from eumelanosomes. As described below, genetic observations point to the existence of components specific to eumelanogenesis vs. pheomelanogenesis that are clearly distinct from the pathways that modulate the switch itself; however, it remains to be deter-
REGULATION OF PIGMENT TYPE SWITCHING BY AGOUTI
mined whether these components act by modulating the formation of dopachrome vs. cysteinyldopaquinone, by modulating specialized aspects of melanosome biogenesis, or both.
Melanocortin Receptors and Agouti Protein Ligands Molecular Genetics and Biology of Melanocortin Signaling Much of our current understanding of melanocortin receptor signaling is based on studies carried out on hormonal control of pigmentation in amphibians and reptiles (Lerner, 1993). Melanin-containing cells in these animals, melanophores, exhibit rapid changes in their absorption of visible light mediated by the intracellular dispersion or aggregation of microscopic pigment granules. This phenomenon underlies the ability of many reptiles and amphibians to adapt to their environmental background, and is mediated by a variety of different receptors for catecholamine, serotonergic, and peptide hormones. Recognition that extracts of mammalian pituitary glands could reproduce this process led to the isolation of aMSH, a 13-amino-acid peptide produced by proteolytic cleavage from a multifunctional larger precursor, Pomc (reviewed by Bertagna, 1994; De Wied and Jolles, 1982; Eberle, 1988). Besides a-MSH, Pomc also gives rise to gamma-MSH (gMSH), ACTH, and beta-endorphin. a-MSH, g-MSH, and ACTH (the melanocortins) each contain a common “core” His–Phe–Arg–Trp sequence thought to be responsible for the binding and activation of one or more of the five melanocortin receptors, Mc1r–Mc5r (reviewed by Cone et al., 1996; Schioth, 2001). These receptors were first isolated by screening human melanoma cDNAs for seven transmembrane receptor genes using a polymerase chain reaction (PCR)-based strategy, and identifying two receptors, Mc1r and Mc2r, that would cause intracellular accumulation of cAMP in response to melanocortin peptides (Chhajlani et al., 1993; Chhajlani and Wikberg, 1992; Mountjoy et al., 1992). Mc3r, Mc4r, and Mc5r were then isolated by sequence similarity; all five receptors couple to adenylate cyclase but exhibit unique patterns of agonist selectivity and tissue-specific expression that account for different biologic roles. Melanocytes express only the Mc1r, which is sometimes referred to as the “a-MSH receptor” even though a-MSH is probably more relevant physiologically to Mc3r and Mc4r activity. Some insects have been reported to produce Pomc-related peptides (Schoofs et al., 1993), but there is no obvious melanocortin receptor apparent among invertebrate genomes. Recent studies indicate that homologs for each of the five mammalian receptors exist in fugu and zebrafish (Klovins et al., 2004; Logan et al., 2003a; Logan et al., 2003b; Ringholm et al., 2002), but there is no obvious melanocortin receptor homolog in Ciona; thus, divergence of a single melanocortin receptor into ancestors of the five currently recognized sub-
types is likely to have occurred in primitive vertebrates between 400 and 500 million years ago.
Biology of Agouti Protein and Agouti-Related Protein Agouti protein is an ~ 18-kDa paracrine signaling molecule that acts as the primary physiologic ligand for the Mc1r, but via inhibition rather than stimulation of adenylate cyclase. The activity of Agouti protein in vitro is most easily measured by pharmacologic antagonism of a-MSH binding or receptor activation; however, as described below, several lines of evidence suggest that Agouti protein normally acts in vivo not as an a-MSH antagonist but instead as an inverse agonist, inhibiting high basal levels of Mc1r signaling that occur in the absence of any ligand. Agouti protein was first isolated by positional cloning of a mouse coat color gene that goes by the same name, in which allelic variation had long been recognized to control pigment type switching (Bultman et al., 1992; Miller et al., 1993). The name Agouti comes from a native South American language, where it refers to the rodent Dasyprocta leporina, also known as Dasyprocta aguti. These rodents, as well as many other furred mammals, display a characteristic pigmentation pattern in which individual hairs contain a subapical band of pheomelanic pigment while the tip and the base contain eumelanic pigment. In many cases, both within and among different species, these so-called “Agouti banded hairs” are present on the dorsal surface, whereas ventral hairs contain mostly pheomelanin. Both patterns — the presence of pheomelanic banding on individual hairs and the presence of ventral hairs that are almost entirely pheomelanic — relate directly to specific spatiotemporal patterns of Agouti gene expression directed by different promoters and untranslated first exons (Vrieling et al., 1994). The banding pattern correlates with transient expression of a “hair cycle-specific” Agouti mRNA isoform during early anagen, causing hair follicle melanocytes to switch from eumelanin synthesis to pheomelanin synthesis, and then back again to eumelanin synthesis. In contrast, the presence of ventral hairs that are entirely pheomelanic correlates with expression of a “ventral-specific” Agouti mRNA isoform throughout almost all of anagen, but in ventral rather in dorsal skin. In laboratory mice, ventral-specific isoforms contain an untranslated first exon, 1A, located approximately 118 kb 5¢ of the translational initiation codon, whereas hair cycle-specific isoforms contain one of two alternative untranslated first exons, 1B or 1C, located approximately 18 kb 5¢ of the translational initiation codon (Fig. 19.3). The situation described above is based on studies in laboratory mice, where the different Agouti mRNA isoforms are subject to independent genetic control and exhibit an additive phenotype (Chen et al., 1996; Vrieling et al., 1994). Thus, animals with banded hair on their dorsal surface and pheomelanic hair on their ventral surface are said to carry the whitebellied Agouti (AW) allele, in which both isoforms are active; animals with banded hair on both dorsal and ventral body 399
CHAPTER 19
Fig. 19.3. Region-specific expression of Agouti. As described in the text, expression of Agouti is controlled by two separate promoters that each have their own 5¢ untranslated first exon or exons. Exons 1A and 1A¢ are expressed throughout the entire hair growth cycle, but only in ventral skin, and therefore account for the pale ventrum observed in mice that carry the AW or at alleles. Exons 1B and 1C are expressed in both dorsum and ventrum, but only in the midphase of the hair growth cycle, and therefore account for the subapical band of pheomelanin present in individual hairs of animals that carry the AW or A alleles. See also Plate 19.2, pp. 494–495.
surfaces are said to carry the Agouti (A) allele, in which hair cycle-specific isoforms are present but the ventral-specific isoform is not; finally, animals with eumelanic hair on their dorsal surface and pheomelanic hair on their ventral surface are said to carry the black-and-tan (at) allele, in which the ventral-specific isoform is present but hair cycle-specific isoforms are not (Fig. 19.3). Both types of isoform are expressed in the dermal papillae of hair follicles (Candille et al., 2004; Millar et al., 1995), and help to confirm the notion, originally suggested from transplantation studies (Silvers and Russell, 1955), that Agouti protein has a small sphere of action limited to the hair follicle within which it is synthesized. Although molecular biologic and genetic studies of pigment type switching in animals other than laboratory mice are not extensive, available evidence suggests that the system described above is conserved across most vertebrate phyla. Loss-of-function Agouti alleles that cause a uniform black coat have been described in the rat (Kuramoto et al., 2001a), the domestic dog (Kerns et al., 2004), the domestic cat (Eizirik et al., 2003), horses (Rieder et al., 2001), and Arctic foxes (Vage et al., 1997); furthermore, canids probably use different Agouti isoforms for specific regions of the body (Kerns et al., 2004). The situation in nonmammalian vertebrates is somewhat more complicated, mainly because studies to date have been based on teleosts, in which a whole-genome duplication took place after divergence from the lineage leading to mammals. However, certain lizards carry Mc1r polymorphisms that correlate with color changes (Rosenblum et al., 2004). Finally, recent studies in goldfish have identified a likely ortholog of Agouti, which acts as an antagonist at the fugu
400
Mc1r, and is expressed in ventral but not dorsal skin (CerdaReverter et al., 2005). It should be noted that fish, amphibians, and reptiles have, in general, a pigmentary system that is more complicated than that of mammals, with multiple types of chromatophores and pigment biosynthetic pathways based on xanthines and pteridines as well as on tyrosine (Bagnara, 2003; Kelsh, 2004; Mellgren and Johnson, 2002). In avians, reddish-yellow feather coloration is caused by pheomelanin (Agrup et al., 1978; Haase et al., 1992, 1995; Prota, 1992; Thomson, 1974) but, surprisingly, pheomelanin has not been identified in fish (Ito and Wakamatsu, 2003), suggesting that the “pigment type switching pathway” in poikilotherms may function more to regulate pigment cell behavior via adenylate cyclase activity than to regulate different types of pigment synthesis. In either case, these observations point to a common theme of melanocortin signaling and pigmentation over 400 million years of evolution, whereby localized expression of Agouti protein gives rise to complex pigmentation patterns that distinguish between ventral and dorsal body surfaces in all vertebrates. Ironically, a role for Agouti signaling in humans and higher primates remains uncertain. The human Agouti gene (also referred to as ASIP for Agouti signaling protein) is capable of stimulating pheomelanin synthesis in transgenic mice, and is expressed at low levels in multiple tissues (Kwon et al., 1994; Wilson et al., 1995). Careful studies of Agouti expression in human skin have not been carried out, but putative regulatory sequences associated with the ventral-specific dog and mouse Agouti mRNA isoforms are also conserved in the human
REGULATION OF PIGMENT TYPE SWITCHING BY AGOUTI
genome (Kerns et al., 2004). Unlike the situation with MC1R (see below), population-based studies have failed to identify polymorphisms of human ASIP that support a definitive role in human pigmentation, although there is some evidence of a weak association between a single nucleotide polymorphism (SNP) in the 3¢ untranslated region (UTR) and different pigmentary phenotypes (Bonilla et al., 2005; Kanetsky et al., 2002; Voisey et al., 2001; Zeigler-Johnson et al., 2004); by the same token, the absence of ASIP sequence variation suggests that the gene has been under positive selection during recent primate evolution. Like many aspects of mouse coat color genetics, studies of pigment type switching have also played an important role in understanding basic aspects of mammalian biology that extend outside the pigmentary system. In particular, a set of unusual Agouti alleles in laboratory mice, including lethal yellow (Ay), viable yellow (Avy), and hypervariable yellow (Ahvy), are caused by genomic rearrangements that cause ubiquitous expression of Agouti protein coding sequence, leading to pleiotropic effects that include obesity, diabetes, and increased body size (Duhl et al., 1994). These observations led to an appreciation of a critical role for Mc3r and Mc4r signaling in energy balance, and the discovery of Agouti-related protein (Agrp), a neuropeptide that marks a key subset of hypothalamic neurons which sense and respond to changes in peripheral energy stores (reviewed by Barsh et al., 2000).
Mc1r Allelic Variation and Pigmentary Phenotypes A role for the a-MSH receptor in pigment type switching was suggested almost 30 years before Mc1r was cloned, based on experiments by Takeuchi and colleagues with organ culture of hair bulb melanocytes taken from mice with pheomelanic hairs (Tamate and Takeuchi, 1964). In cultures from animals carrying the Ay mutation (in which, as now known, Agouti protein is expressed at high levels), production of eumelanin could be stimulated by treatment with dibutyryl cAMP or aMSH. In contrast, in cultures from animals homozygous for the recessive yellow mutation of the Extension locus (e/e), production of eumelanin could be stimulated by dibutyryl cAMP but not by a-MSH. Over the last decade, a large number of molecular genetic studies have been carried out to investigate the role of Mc1r variation in different pigmentary phenotypes. An underlying theme of this work is that loss-of-function Mc1r mutations cause a predominantly pheomelanic color — in mice (Robbins et al., 1993), bears (Ritland et al., 2001), cattle (Joerg et al., 1996; Klungland et al., 1995), pigs (Kijas et al., 1998), horses (Marklund et al., 1996), humans (Valverde et al., 1995), dogs (Everts et al., 2000; Newton et al., 2000), and chickens (Takeuchi et al., 1996) — whereas gain-of-function Mc1r mutations cause a predominantly eumelanic color — in sheep (Vage et al., 1999), cattle (Klungland et al., 1995), pigs (Kijas et al., 1998), foxes (Vage et al., 1997), jaguars and jaguarundis (Eizirik et al., 2003), and several avian species (Ling et al., 2003; Mundy et al., 2003, 2004; Theron et al., 2001).
The Mc1r seems to be a relatively common source of normal pigmentary variation in many different species (Hoekstra et al., 2004; Mundy et al., 2004; Rees, 2003; Rosenblum et al., 2004), and has been a frequent subject of population and evolutionary genetic studies. In several instances, Mc1r polymorphisms have been strongly associated with melanism, in which dark individuals appear in a natural population that is mostly light colored. However, the exact nature of the lightcolored population varies considerably. Jaguars that normally display a striking rosette pattern (Eizirik et al., 2003), pocket mice that normally show Agouti banding (Nachman et al., 2003), and Arctic skuas that normally have pale-colored breast plumage (Mundy et al., 2004) are all changed into melanistic forms in association with Mc1r substitutions. These observations underscore the general theme that pigment type switching can give rise to considerable diversity in both color and pattern. In some of these cases, there is strong evidence that the melanistic forms are under selection, suggesting that mutations that constitutively activate the Mc1r have been used as an adaptive mechanism several times during vertebrate evolution. In contrast to rodents, cats, and birds, humans with dark hair and dark skin appear to have a “normal” MC1R that responds to both agonists and antagonists in vitro, and exhibits little variation in African populations. In fact, African individuals show a surprising paucity of noncoding variation in the MC1R (compared with most other genes), which suggests that “purifying selection” has helped to maintain strong constraint for a functional protein during recent human evolution (Harding et al., 2000; John et al., 2003; Rana et al., 1999). That is not to say that MC1R variation does not help to determine differences in human pigmentation phenotypes. Indeed, MC1R was the first gene identified that clearly influences normal variation in human skin and hair color, but via loss-of-function rather than gain-of-function alterations (Valverde et al., 1995). Chemical analyses show that, in general, black, brown, and blond human hair is composed mostly of eumelanin, with the various shades representing different amounts of melanin and/or different structures and arrangements of melanin granules (Ito and Wakamatsu, 2003; Liu et al., 2004). However, red human hair contains high levels of pheomelanin, and many studies have now shown that most individuals with red hair and fair skin carry one or more loss-of-function MC1R alleles (Box et al., 1997; Flanagan et al., 2000; Naysmith et al., 2004; reviewed by Rees, 2003; Sturm et al., 2003). Loss-of-function MC1R alleles are most common in individuals of European continental ancestry, but population genetic studies show an abundance of different alleles and haplotypes, suggesting that these variants are maintained by genetic drift rather than by selection (Harding et al., 2000; Rana et al., 1999).
Accessory Proteins for Melanocortin Signaling: Attractin and Mahoganoid In addition to Agouti and Extension, studies of the coat color
401
CHAPTER 19
mutations mahogany and mahoganoid implicate additional mechanisms in pigment type switching. Both mahogany and mahoganoid were recognized by their ability to suppress pheomelanin synthesis; animals that would otherwise have hairs banded with eumelanin and pheomelanin — the Agouti phenotype — instead show a dark coat color that is almost all eumelanin if they are homozygous for mahogany or mahoganoid. This phenotype is similar to that caused by lossof-function Agouti mutations or gain-of-function constitutively activating Mc1r mutations (Fig. 19.2) and, a priori, could be explained by decreased production or cell surface binding of Agouti protein, increased production of a-MSH, or defects in the melanocyte enzymes or structural proteins required to produce yellow pigment granules. Double mutant studies helped to distinguish among these alternatives, and to establish a genetic pathway for pigment type switching. The results are summarized in Figure 19.1, and indicate that the genes mutated in mahogany and mahoganoid are genetically downstream of Agouti but genetically upstream of Mc1r (Miller et al., 1997). Positional cloning of the gene mutated in mahogany revealed a cysteine-rich 1428-amino-acid type I transmembrane protein that was widely expressed and whose ectodomain contained several domains characteristic of axon guidance and cell adhesion molecules (Gunn et al., 1999; Nagle et al., 1999). The gene was named Attractin (Atrn) to correspond with its human homolog, discovered by DukeCohan and colleagues as a glycoprotein that would “attract” T lymphocytes to monocytes in vitro (Duke-Cohan et al., 1998, 2000); thus, mutant alleles are now referred to as Atrnmg, Atrnmg-L, and Atrnmg-3J (Gunn et al., 2001). Detailed studies of immune function in Attractin mutant mice have not been described; however, mutant animals develop a progressive neurodegenerative disease with dysmyelination, spongiform degeneration, and motor abnormalities (Gunn et al., 2001; Kuramoto et al., 2001b). Similar phenotypes are apparent in two spontaneous rat mutations of Attractin, zitter (Kuramoto et al., 2001b) and myelin vacuolation (Kuwamura et al., 2002), as well as a hamster mutation, black tremor (Kuramoto et al., 2002). Ironically, both the rat zitter mutation and the mouse mahogany mutation were extensively studied over the last decade for completely different reasons; the fact that the same gene underlies both mutations was recognized only in hindsight. In the case of zitter, mutant rats were discovered because of a pronounced tremor (Rehm et al., 1982), and were examined further because of their potential relevance to the pathogenesis of neurodegeneration (Gomi et al., 1990; Kondo et al., 1991; Kuramoto et al., 1994). However, the zitter mutation was maintained on an albino background; thus, the effects on pigment type switching (and the relationship to Attractin) remained obscure until both genes were cloned. In the case of mahogany, mutant mice were examined further because of a potential involvement in central melanocortin signaling: in Ay animals that express Agouti protein ubiquitously, mahogany suppresses the effects of Agouti on both pigmentation and 402
obesity (Miller et al., 1997). However, the neurodegenerative phenotype of mahogany is not readily apparent, in part because the original Atrnmg allele is hypomorphic, and in part because of modifier genes that ameliorate the tremor in some genetic backgrounds (Gunn et al., 2001). The gene mutated in mahoganoid (the official name of which is Mgrn1) encodes an intracellular C3HC4 RING domain protein that has E3 ubiquitin ligase activity in vitro, but whose normal substrate(s) has(ve) yet to be identified (He et al., 2003b; Phan et al., 2002). Like Attractin mutant mice, Mgrn1 mutant mice develop progressive spongiform degeneration, albeit with milder symptoms. Atrn and Mgrn1 have nearly identical patterns of mRNA expression, and are found in many, although not all, tissues and cell types examined; the two genes also have a similar pattern of evolutionary conservation, with homologs in worms and flies, but not in yeast. Although the molecular pathogenesis of neurodegeneration in Atrn and Mgrn1 mutant mice is still unclear, biochemical and genetic studies indicate that Attractin functions in pigment type switching as an obligate accessory receptor for Agouti protein on melanocytes. In transgenic animals, expression of an Atrn cDNA in melanocytes rescues the mahogany coat color phenotype, but expression in keratinocytes does not. Thus, Atrn function is melanocyte autonomous, as is that of the Mc1r. Furthermore, while the effect of Atrn is to facilitate Agouti-induced pheomelanogenesis, overexpression of Atrn has no effect on coat color by itself, suggesting a permissive rather than an active role in pigment type switching. Finally, structure–function studies have shown that different domains of Agouti protein interact with Atrn and the Mc1r. The cysteine-rich carboxy-terminal domain of Agouti protein binds with high (nanomolar) affinity to the Mc1r. In cultured cells, this interaction is sufficient to inhibit adenylate cyclase activity but, in vivo, the carboxy-terminal domain of Agouti protein has no effect on pigmentation. The positively charged amino-terminal domain of Agouti protein binds to Atrn with low (micromolar) affinity, but no consistent effect on cell behavior or signaling has been reported. However, the interaction is biologically significant, because Agrp, which is similar to Agouti in the carboxy-terminal but not in the amino-terminal domain, does not interact with Atrn in vitro or in vivo: although the effects of Agouti protein on obesity (and pigmentation) are suppressed by mahogany, the effects of Agrp are not. Taken together, these observations suggest that Attractin and Mgrn1 are linked components of a genetic pathway that is conserved among all metazoans, and whose original function may have been to ubiquitinate an as yet unidentified substrate or substrates, likely in response to signals from the extracellular environment. During vertebrate evolution, this pathway was “borrowed” by the Agouti-melanocortin system because ubiquitination of the Mgrn target could facilitate pheomelanin synthesis. According to this hypothesis, the ligand for Atrn is different in melanocytes and neurons, but the target for Mgrn1 ubiquitination is the same; thus, identi-
REGULATION OF PIGMENT TYPE SWITCHING BY AGOUTI
fication of this ligand could provide insight into both pigment type switching and the pathogenesis of neurodegeneration.
Perspectives and Future Directions How Does a Pigment Cell Make Pheomelanin? The foregoing discussion underscores the gap that remains in our understanding of pheomelanin synthesis. Outside the melanocyte, Agouti-induced inhibition of Mc1r signaling is the physiologic signal that normally triggers pheomelanin synthesis, but the way in which Atrn and Mgrn1 fit into this pathway inside the melanocyte is not yet clear. The ~100residue intracellular domain of Atrn is required for its effects on both pigmentation and neuronal function (Kuramoto et al., 2001b), which, together with the similar patterns of expression and evolutionary conservation between Atrn and Mgrn1, suggests that Atrn plays a signaling role by activating or facilitating Mgrn1 activity. However, Mgrn1 (and Atrn) are also genetically upstream of Mc1r inhibition, as animals doubly mutant for Mc1re and either Atrnmg or Mgrn1md are phenotypically identical to single Mc1re mutants. This suggests that Mgrn1 plays a role in the levels, subcellular distribution, and/or signaling activity of Mc1r, perhaps by ubiquitinating a substrate that modulates Mc1r turnover or recycling. It is also unclear how Mc1r inhibition and reduced levels of intracellular cAMP are connected to reduction in tyrosinase activity and availability of premelanosomal cysteine that are thought to be required for cysteinyldopa formation. For tyrosinase, one potential mechanism is based on the observation that Mitf serves as a transcriptional activator of tyrosinase, and that the cAMP–protein kinase A–CREB pathway promotes Mitf expression (Busca and Ballotti, 2000; Gaggioli et al., 2003; Price et al., 1998). However, reduced activity of tyrosinase during pheomelanin synthesis is regulated at the post-translational as well as the transcriptional level (Burchill et al., 1989; Kobayashi et al., 1995), and it is not at all clear that Mitf is downregulated during pheomelanin synthesis in vivo. In addition, hypomorphic alleles of tyrosinase have a much greater effect on dilution of pheomelanin than they do on eumelanin (Fig. 19.2B), but hypomorphic alleles of Mitf do not; thus, regulation of Mitf by cAMP signaling cannot easily explain changes in tyrosinase activity that occur during pigment type switching. Finally, it should be noted that regulation of pheomelanin synthesis in humans differs in several respects from that in mice. In addition to questions about the function, if any, of the human Agouti gene, the inverse relationship between tyrosinase activity and pheomelanin synthesis discovered from studies of mouse coat color mutants is not so obvious in studies of human skin and hair (Burchill et al., 1991). In part, this apparent discrepancy could be explained by differences in the distribution and biology of melanocytes in different skin compartments. In mice, the majority of melanocytes are located within hair follicles; there are a few regions where
melanocytes accumulate outside hair follicles (in both the extrafollicular epidermis and the dermis), and these tend to be in areas where hair follicles are either absent or at low density, such as the footpads, the ears, and the tail. In all these cases, however, pheomelanin is synthesized only by intrafollicular melanocytes; even in Ay/a mice, melanocytes in the dermis or extrafollicular epidermis produce only eumelanin (Fitch et al., 2003; Lamoreux and Russell, 1979; Van Raamsdonk et al., 2004). In human skin, however, hair follicle density over most regions of the body is much less than that of mice; extrafollicular epidermal melanocytes are the major determinant of skin color, and may contain substantial amounts of pheomelanin (Thody et al., 1991). In addition to the questions surrounding what happens between Mc1r inhibition and cysteinyldopa formation, a potential gap exists between cysteinyldopa formation and the production of pheomelanosomes, as additional, as yet unidentified, cellular components may be necessary for biogenesis and/or granule maturation. In particular, there is a series of coat color mutants that, at a whole-animal level, interfere with pheomelanin but not eumelanin synthesis — grizzled, subtle gray, gray lethal, and gray intense — and could lie upstream or downstream of cysteinyldopa formation. Answers to these questions may come, in part, from the molecular identity and characterization of the aforementioned mutations. The gene mutated in gray lethal, Ostm1, encodes a single transmembrane spanning protein that appears to be located in an intracellular compartment (Chalhoub et al., 2003). Its function is not yet clear, although a different group who identified the same gene (and named it Gipn) noted limited sequence similarity with a RING domain and suggested that the protein modulated signaling through Gicoupled receptors by ubiquitination of RGS proteins (Fischer et al., 2003). A related approach would be to perturb tyrosinase activity and/or intracellular cysteine levels artificially (using genetics or small molecules) and ask how such manipulations might affect pigment type switching. An experiment of this sort was reported by Lieberman and colleagues (Lieberman et al., 1996) by knocking out gamma-glutamyl transpeptidase (Ggt), a cell surface enzyme that initiates catabolism of glutathione and, when mutated, leads to cysteine deficiency. Mutant animals have a pleiotropic phenotype that includes alterations of the Agouti coat color pattern, possibly due to defective pheomelanin synthesis. However, previous literature linking Ggt activity to pigment synthesis suggests that changes in Ggt activity regulate overall levels of melanogenesis by modulating tyrosinase (Chaubal et al., 2002; Hu, 1982) and, as described above, the two “cardinal characteristics” of pheomelanin synthesis (Fig. 19.1) are not independent. Identification of additional mutations, such as gray intense and grizzled, and application of additional approaches to perturb (and uncouple) tyrosinase activity from changes in intracellular cysteine availability should lead to a more complete understanding of pheomelanin synthesis and pigment type switching. 403
CHAPTER 19
Mc1r Basal Activity and the Potential Role of a-MSH in Normal Pigmentation As described above, interactions between Agouti protein and Mc1r play a key role in pigment type switching across many different vertebrate phyla. Perhaps surprisingly, the same is not true of the Mc1r ligand, a-MSH. In pharmacologic studies of cultured cells, Agouti (or Agrp) acts as a so-called inverse agonist, inhibiting a relatively high level of basal Mc1r (or Mc4r) signaling in the absence of exogenous a-MSH (Adan and Kas, 2003; Chai et al., 2003; Nijenhuis et al., 2001; Siegrist et al., 1997). Initial physiologic studies of a-MSH biosynthesis and possible effects on pigmentation focused mainly on a-MSH as a possible endocrine hormone produced by the pituitary gland. Exogenous administration of a-MSH causes a switch from pheomelanin to eumelanin synthesis in Ay/a mice (Geschwind, 1966), and increased pituitary-derived a-MSH and/or ACTH are responsible for the darkening of skin that occurs in adrenal insufficiency (Beamer et al., 1994). However, plasma levels of a-MSH do not correlate with alterations in coat color that occur when certain strains of mice carrying Avy darken with age, and hypophysectomy does not cause pheomelanogenesis in nonagouti mice, even though small increases in plasma aMSH levels have dramatic effects on coat color (Geschwind et al., 1972; Thody et al., 1983). Thus, circulating a-MSH probably does not act as a major endocrine hormone in physiologic control of pigment synthesis in the mouse. More recently, a potential role for a-MSH in pigment synthesis has focused on a paracrine or autocrine role (reviewed by Pawelek, 1993; Slominski et al., 1993; Wintzen and Gilchrest, 1996), based on the finding that expression of Pomc RNA can be detected in keratinocytes and melanocytes (Farooqui et al., 1993; Slominski et al., 1992, 1995). In most of these studies, it has been difficult to determine whether the RNA detected actually gives rise to physiologically significant levels of aMSH. Targeted deletion of Pomc causes a lighter coat in A/A mice (Barsh, 1999; Yaswen et al., 1999), presumably due to a slight reduction in a-MSH released from plasma and/or skin, but the same targeted allele in a genetic background with very little Agouti expression has no effect on pigmentation; C57BL/6 animals are almost completely black as a result of exclusive production of eumelanin, and that phenotype is not altered by deleting the Pomc gene (Slominski et al., 2005). The situation in humans is less clear. Congenital deficiency of Pomc in humans is associated with red hair (Krude et al., 1998, 2003a, b), but the small number of affected individuals, the absence of quantitative studies, and the heterogeneity of human populations makes it difficult to compare the pigmentary effects caused by loss-of-function for Pomc with those caused by loss-of-function for Mc1r. In culture, human melanocytes exhibit a robust agonist or antagonist response to a-MSH or Agouti protein, respectively, but transgenic mice carrying the human Mc1r placed under the control of normal mouse regulatory elements exhibit a dose-dependent suppression of Agouti-induced pheomelanin synthesis (Healy et al., 2001). Taken together, these data suggest that the effect of 404
Mc1r signaling on human pigmentation includes contributions from high levels of basal receptor activity as well as Pomcderived agonists, but that the former component accounts for most of the pigmentary variation present in human populations.
Genetics of Pigment Type Switching in Cats and Dogs Given the very high level of conservation among mammalian genomes, and the remarkable utility of laboratory mice as a tool for experimental genetics, it may come as something of a surprise that color variation in other mammals harbors unsolved pigmentary mysteries. Among the most interesting group of coat color phenotypes are those associated with regular patterns of stripes or spots, as in zebras, tigers, leopards, or giraffes. Although chemical or biochemical studies have not been carried out, the components of such patterns are likely to be eumelanin alternating with pheomelanin (as in tigers or leopards), or eumelanin alternating with no pigment (as in zebras) (Searle, 1968). In domestic cats, Tabby is an important determinant of pheomelanin/eumelanin-based coat color patterns, but a homologous allelic series has not been identified in rodents (Robinson, 1991; Searle, 1968). Tabby is thought to take its name from the Attabiah region of Baghdad, which is known for weaving a type of silk with elaborate stripe patterns. The stereotypic Tabby contains stripes of Agouti-banded hair alternating with stripes of black (eumelanic) hair. Genetic segregation analysis carried out by cat breeders suggests that variations on this pattern such as large blotches and/or spots represent an allelic series in which the most dominant allele, Abyssinian (Ta), is associated with no stripes, an intermediate allele, mackerel (T), accounts for tiger stripes, and the most recessive allele, blotched (tb), is associated with large coalescent dark areas (Lomax and Robinson, 1988). Based on the pathway of pigment type switching as described earlier, these observations suggest that the Tabby gene product is normally required for Agouti banding, and that different alleles cause the gene to become inactivated in a pattern in which the largest area of inactivation corresponds to the most recessive allele. From this perspective, the gene mutated in Tabby might encode a protein such as Attractin or Mahoganoid, required for normal Agouti signaling, and the molecular basis of the mutant alleles would account for the intriguing nature of the underlying pattern. Comparative zoologic studies suggest that the same mechanism underlies Tabby patterns in domestic and wild cats (Weigel, 1961). Furthermore, a common variant in domestic cats is the Silver tabby, in which stripes of dark hairs alternate with stripes of cream-colored instead of Agouti-banded or yellow hairs. This phenomenon is reminiscent of chinchilla, in which Agouti-induced inhibition of Mc1r signaling gives rise to an absence of pigment rather than pheomelanin per se (Fig. 19.2B). Whether a similar phenomenon explains alternating patterns of black and white in ungulates, i.e. zebras, is
REGULATION OF PIGMENT TYPE SWITCHING BY AGOUTI
less clear, however, as the Tabby gene is clearly recognized only in the Carnivora. Also well known in domestic cats, Sex-linked orange (O) or tortoiseshell is an oft-cited example for teaching principles of mammalian genetics, as patches of yellow and black hair in Tortoiseshell or Calico cats are a dramatic manifestation of clonal patterns of X-inactivation, found only in females and rare XXY males (Centerwall and Benirschke, 1975; Leaman et al., 1999). In cats, Sex-linked orange is epistatic to nonagouti and therefore somewhat analogous to recessive yellow (Mc1re), but it would be extremely unusual to find that the Mc1r gene is responsible for Sex-linked orange as there are almost no exceptions to the conservation of X-linkage among eutherian mammals. An additional source of pigmentary mysteries is apparent from studies of color variation in domestic dogs. Many breeds with uniform pheomelanic coats such as Golden Retrievers, Irish Setters, or yellow Labrador Retrievers carry a loss-offunction Mc1r allele as in laboratory mice and other mammals (Newton et al., 2000). However, a similar phenotype in other breeds such as Rhodesian Ridgebacks, Dachshunds, Great Danes, Chows, and French Bulldogs is probably caused by an Agouti allele known as fawn (ay) (Berryere et al., 2005). As in laboratory mice, the dog ay allele is dominant to other Agouti alleles associated with eumelanin synthesis such as nonagouti (a) or black-and-tan (at). However, unlike mice carrying a “yellow” allele, the dog ay allele does not cause effects outside the pigmentary system, suggesting an underlying molecular basis in which variation in the hair cycle-specific promoter expands the timing of expression to include all of anagen. One of the most intriguing aspects of pigment type switching in domestic dogs is “dominant black,” in which a uniform eumelanic coat color is inherited in a simple dominant fashion, but is caused by variation in neither Mc1r nor Agouti (Kerns et al., 2003, 2004), and has been referred to as “the K locus” based on kurokami, the Japanese word for black hair. Mc1r is epistatic to K, as Labrador Retrievers homozygous for both dominant black (K) and an Mc1r loss-of-function allele are yellow colored; however, the epistasis relationship between K and Agouti is less certain. Together with Sex-linked orange and Tabby, identification of the K locus may not only further our understanding of pigmentary biology but also provide insight into basic aspects of melanocortin receptor signaling used for a variety of physiologic processes.
References Adan, R. A., and M. J. Kas. Inverse agonism gains weight. Trends Pharmacol. Sci. 24:315–321, 2003. Agrup, G., C. Hansson, H. Rorsman, A. M. Rosengren, and E. Rosengren. 5-S-cysteinyldopa and trichochromes in red feathers. Acta Derm. Venereol. 58:269–270, 1978. Andersson, L. Melanocortin receptor variants with phenotypic effects in horse, pig, and chicken. Ann. NY Acad. Sci. 994:313–318, 2003. Bagnara, J. T. Enigmas of pterorhodin, a red melanosomal pigment of tree frogs. Pigment Cell Res. 16:510–516, 2003. Barsh, G. From Agouti to Pomc — 100 years of fat blonde mice. Nature Med. 5:984–985, 1999.
Barsh, G. S., and M.W. Schwartz. Genetic approaches to studying energy balance: perception and integration. Nature Rev. Genet. 3:589–600, 2002. Barsh, G., T. Gunn, L. He, B. Wilson, X. Lu, I. Gantz, and S. Watson. Neuroendocrine regulation by the Agouti/Agrp-melanocortin system. Endocr. Res. 26:571, 2000. Beamer, W. G., H. O. Sweet, R. T. Bronson, J. G. Shire, D. N. Orth, and M. T. Davisson. Adrenocortical dysplasia: a mouse model system for adrenocortical insufficiency. J. Endocrinol. 141:33–43, 1994. Bennett, D. C., and M. L. Lamoreux. The color loci of mice — a genetic century. Pigment Cell Res. 16:333–344, 2003. Berryere, T. G., J. A. Kerns, G. S. Barsh, and S. M. Schmutz. Association of an Agouti allele with fawn or sable coat color in domestic dogs. Mamm. Genome 16:262–272, 2005. Bertagna, X. Proopiomelanocortin-derived peptides. Endocrinol. Metab. Clin. N. Am. 23:467–485, 1994. Bonilla, C., L. A. Boxill, S. A. Donald, T. Williams, N. Sylvester, E. J. Parra, S. Dios, H. L. Norton, M. D. Shriver, and R. A. Kittles. The 8818G allele of the agouti signaling protein (ASIP) gene is ancestral and is associated with darker skin color in African Americans. Hum. Genet. 116:402–406, 2005. Box, N. F., J. R. Wyeth, L. E. O’Gorman, N. G. Martin, and R. A. Sturm. Characterization of melanocyte stimulating hormone receptor variant alleles in twins with red hair. Hum. Mol. Genet. 6:1891–1897, 1997. Bultman, S. J., E. J. Michaud, and R. P. Woychik. Molecular characterization of the mouse agouti locus. Cell 71:1195–1204, 1992. Burchill, S. A., R. Virden, and A. J. Thody. Regulation of tyrosinase synthesis and its processing in the hair follicular melanocytes of the mouse during eumelanogenesis and phaeomelanogenesis. J. Invest. Dermatol. 93:236–240, 1989. Burchill, S. A., S. Ito, and A. J. Thody. Tyrosinase expression and its relationship to eumelanin and phaeomelanin synthesis in human hair follicles. J. Dermatol. Sci. 2:281–286, 1991. Busca, R., and R. Ballotti. Cyclic AMP a key messenger in the regulation of skin pigmentation. Pigment Cell Res. 13:60–69, 2000. Candille, S. I., C. D. Van Raamsdonk, C. Chen, S. Kuijper, Y. ChenTsai, A. Russ, F. Meijlink, and G. S. Barsh. Dorsoventral patterning of the mouse coat by Tbx15. PLoS Biol. 2:E3, 2004. Centerwall, W. R., and K. Benirschke. An animal model for the XXY Klinefelter’s syndrome in man: tortoiseshell and calico male cats. Am. J. Vet. Res. 36:1275–1280, 1975. Cerda-Reverter, J. M., T. Haitina, H. B. Schioth, and R. E. Peter. Gene structure of the goldfish agouti-signaling protein: a putative role in the dorsal–ventral pigment pattern of fish. Endocrinology 146:1597–1610, 2005. Chai, B. X., R. R. Neubig, G. L. Millhauser, D. A. Thompson, P. J. Jackson, G. S. Barsh, C. J. Dickinson, J. Y. Li, Y. M. Lai, and I. Gantz. Inverse agonist activity of agouti and agouti-related protein. Peptides 24:603–609, 2003. Chalhoub, N., N. Benachenhou, V. Rajapurohitam, M. Pata, M. Ferron, A. Frattini, A. Villa, and J. Vacher. Grey-lethal mutation induces severe malignant autosomal recessive osteopetrosis in mouse and human. Nature Med. 9:399–406, 2003. Chaubal, V. A., S. S. Nair, S. Ito, K. Wakamatsu, and M. V. Mojamdar. Gamma-glutamyl transpeptidase and its role in melanogenesis: redox reactions and regulation of tyrosinase. Pigment Cell Res. 15:420–425, 2002. Chen, Y., D. M. J. Duhl, and G. S. Barsh. Opposite orientations of an inverted duplication and allelic variation at the mouse agouti locus. Genetics 144:265–277, 1996. Chhajlani, V., and J. E. S. Wikberg. Molecular cloning and expression of the human melanocyte stimulating hormone receptor cDNA. FEBS Lett. 309:417–420, 1992.
405
CHAPTER 19 Chhajlani, V., R. Muceniece, and J. E. S. Wikberg. Molecular cloning of a novel human melanocortin receptor. Biochem. Biophys. Res. Commun. 195:866–873, 1993. Cone, R. D., D. Lu, S. Koppula, D. I. Vage, H. Klungland, B. Boston, W. Chen, D. N. Orth, C. Pouton, and R. A. Kesterson. The melanocortin receptors: agonists, antagonists, and the hormonal control of pigmentation. Recent Prog. Horm. Res. 51:287–317; discussion 318, 1996. Davis, A. P., and M. J. Justice. An Oak Ridge legacy: the specific locus test and its role in mouse mutagenesis. Genetics 148:7–12, 1998. De Wied, D., and J. Jolles. Neuropeptides derived from proopiocortin: behavioral, physiological, and neurochemical effects. Physiol. Rev. 62:976–1059, 1982. Duhl, D. M. J., M. E. Stevens, H. Vrieling, P. J. Saxon, M. W. Miller, C. J. Epstein, and G. S. Barsh. Pleiotropic effects of the mouse lethal yellow (A(y)) mutation explained by deletion of a maternally expressed gene and the simultaneous production of agouti fusion RNAs. Development 120:1695–1708, 1994. Duke-Cohan, J. S., J. Gu, D. F. McLaughlin, Y. Xu, G. J. Freeman, and S. F. Schlossman. Attractin (DPPT-L), a member of the CUB family of cell adhesion and guidance proteins, is secreted by activated human T lymphocytes and modulates immune cell interactions. Proc. Natl Acad. Sci. USA 95:11336–11341, 1998. Duke-Cohan, J. S., W. Tang, and S. F. Schlossman. Attractin: a cubfamily protease involved in T cell-monocyte/macrophage interactions. Adv. Exp. Med. Biol. 477:173–185, 2000. Eberle, A. N. The Melanotropins. Chemistry, Physiology and Mechanism of Action. Basel: Karger, 1988. Ehling, U. H., D. J. Charles, J. Favor, J. Graw, J. Kratochvilova, A. Neuhauser-Klaus, and W. Pretsch. Induction of gene mutations in mice: the multiple endpoint approach. Mutat. Res. 150:393–401, 1985. Eizirik, E., N. Yuhki, W. E. Johnson, M. Menotti-Raymond, S. S. Hannah, and S. J. O’Brien. Molecular genetics and evolution of melanism in the cat family. Curr. Biol. 13:448–453, 2003. Everts, R. E., J. Rothuizen, and B. A. van Oost. Identification of a premature stop codon in the melanocyte-stimulating hormone receptor gene (MC1R) in Labrador and Golden retrievers with yellow coat colour. Anim. Genet. 31:194–199, 2000. Farooqui, J. Z., E. E. Medrano, Z. Abdel-Malek, and J. Nordlund. The expression of proopiomelanocortin and various POMC-derived peptides in mouse and human skin. Ann. NY Acad. Sci. 680: 508–510, 1993. Favor, J., and A. Neuhauser-Klaus. Saturation mutagenesis for dominant eye morphological defects in the mouse Mus musculus. Mamm. Genome 11:520–525, 2000. Fischer, T., L. De Vries, T. Meerloo, and M. G. Farquhar. Promotion of G alpha i3 subunit down-regulation by GIPN, a putative E3 ubiquitin ligase that interacts with RGS-GAIP. Proc. Natl Acad. Sci. USA 100:8270–8275, 2003. Fitch, K. R., K. A. McGowan, C. D. van Raamsdonk, H. Fuchs, D. Lee, A. Puech, Y. Herault, D. W. Threadgill, M. Hrabe de Angelis, and G. S. Barsh. Genetics of dark skin in mice. Genes Dev. 17:214–228, 2003. Flanagan, N., E. Healy, A. Ray, S. Philips, C. Todd, I. J. Jackson, M. A. Birch-Machin, and J. L. Rees. Pleiotropic effects of the melanocortin 1 receptor (MC1R) gene on human pigmentation. Hum. Mol. Genet. 9:2531–2537, 2000. Gaggioli, C., R. Busca, P. Abbe, J. P. Ortonne, and R. Ballotti. Microphthalmia-associated transcription factor (MITF) is required but is not sufficient to induce the expression of melanogenic genes. Pigment Cell Res. 16:374–382, 2003. Geschwind, I. I. Change in hair color in mice induced by injection of a MSH. Endocrinology 79:1165–1167, 1966. Geschwind, I. I., R. A. Huseby, and R. Nishioka. The effect of melanocyte-stimulating hormone on coat color in the mouse. Recent Prog. Horm. Res. 28:91–130, 1972.
406
Gomi, H., K. Inui, H. Taniguchi, Y. Yoshikawa, and K. Yamanouchi. Edematous changes in the central nervous system of zitter rats with genetic spongiform encephalopathy. J. Neuropathol. Exp. Neurol. 49:250–259, 1990. Gunn, T. M., K. A. Miller, L. He, R. W. Hyman, R. W. Davis, A. Azarani, S. F. Schlossman, J. S. Duke-Cohan, and G. S. Barsh. The mouse mahogany locus encodes a transmembrane form of human attractin. Nature 398:152–156, 1999. Gunn, T. M., T. Inui, K. Kitada, S. Ito, K. Wakamatsu, L. He, D. M. Bouley, T. Serikawa, and G. S. Barsh. Molecular and phenotypic analysis of Attractin mutant mice. Genetics 158:1683–1695, 2001. Haase, E., S. Ito, A. Sell, and K. Wakamatsu. Melanin concentrations in feathers from wild and domestic pigeons. J. Hered. 83:64–67, 1992. Haase, E., S. Ito, and K. Wakamatsu. Influences of sex, castration, and androgens on the eumelanin and pheomelanin contents of different feathers in wild mallards. Pigment Cell Res. 8:164–170, 1995. Harding, R. M., E. Healy, A. J. Ray, N. S. Ellis, N. Flanagan, C. Todd, C. Dixon, A. Sajantila, I. J. Jackson, M. A. Birch-Machin, and J. L. Rees. Evidence for variable selective pressures at MC1R. Am. J. Hum. Genet. 66:1351–1361, 2000. He, L., A. G. Eldridge, P. K. Jackson, T. M. Gunn, and G. S. Barsh. Accessory proteins for melanocortin signaling: attractin and mahogunin. Ann. NY Acad. Sci. 994:288–298, 2003a. He, L., X. Y. Lu, A. F. Jolly, A. G. Eldridge, S. J. Watson, P. K. Jackson, G. S. Barsh, and T. M. Gunn. Spongiform degeneration in mahoganoid mutant mice. Science 299:710–712, 2003b. Healy, E., S. A. Jordan, P. S. Budd, R. Suffolk, J. L. Rees, and I. J. Jackson. Functional variation of MC1R alleles from red-haired individuals. Hum. Mol. Genet. 10:2397–2402, 2001. Hoekstra, H. E., K. E. Drumm, and M. W. Nachman. Ecological genetics of adaptive color polymorphism in pocket mice: geographic variation in selected and neutral genes. Evol. Int. J. Org. Evol. 58:1329–1341, 2004. Hu, F. Theophylline and melanocyte-stimulating hormone effects on gamma-glutamyl transpeptidase and DOPA reactions in cultured melanoma cells. J. Invest. Dermatol. 79:57–62, 1982. Ito, S. High-performance liquid chromatography (HPLC) analysis of eu- and pheomelanin in melanogenesis control. J. Invest. Dermatol. 100:166S–171S, 1993. Ito, S. The IFPCS presidential lecture: a chemist’s view of melanogenesis. Pigment Cell Res. 16:230–236, 2003. Ito, S., and K. Fujita. Microanalysis of eumelanin and pheomelanin in hair and melanomas by chemical degradation and liquid chromatography. Anal. Biochem. 144:527–536, 1985. Ito, S., and K. Wakamatsu. Quantitative analysis of eumelanin and pheomelanin in humans, mice, and other animals: a comparative review. Pigment Cell Res. 16:523–531, 2003. Joerg, H., H. R. Fries, E. Meijerink, and G. F. Stranzinger. Red coat color in Holstein cattle is associated with a deletion in the MSHR gene. Mamm. Genome 7:317–318, 1996. John, P. R., K. Makova, W. H. Li, T. Jenkins, and M. Ramsay. DNA polymorphism and selection at the melanocortin-1 receptor gene in normally pigmented southern African individuals. Ann. NY Acad. Sci. 994:299–306, 2003. Kanetsky, P. A., J. Swoyer, S. Panossian, R. Holmes, D. Guerry, and T. R. Rebbeck. A polymorphism in the agouti signaling protein gene is associated with human pigmentation. Am. J. Hum. Genet. 70:770–775, 2002. Kelsh, R. N. Genetics and evolution of pigment patterns in fish. Pigment Cell Res. 17:326–336, 2004. Kerns, J. A., M. Olivier, G. Lust, and G. S. Barsh. Exclusion of melanocortin-1 receptor (mc1r) and agouti as candidates for dominant black in dogs. J. Hered. 94:75–79, 2003. Kerns, J. A., J. Newton, T. G. Berryere, E. M. Rubin, J. F. Cheng, S. M. Schmutz, and G. S. Barsh. Characterization of the dog Agouti
REGULATION OF PIGMENT TYPE SWITCHING BY AGOUTI gene and a nonagouti mutation in German Shepherd dogs. Mamm. Genome 15:798–808, 2004. Kijas, J. M., R. Wales, A. Tornsten, P. Chardon, M. Moller, and L. Andersson. Melanocortin receptor 1 (MC1R) mutations and coat color in pigs. Genetics 150:1177–1185, 1998. Klovins, J., T. Haitina, D. Fridmanis, Z. Kilianova, I. Kapa, R. Fredriksson, N. Gallo-Payet, and H. B. Schioth. The melanocortin system in Fugu: determination of POMC/AGRP/MCR gene repertoire and synteny, as well as pharmacology and anatomical distribution of the MCRs. Mol. Biol. Evol. 21:563–579, 2004. Klungland, H., and D. I. Vage. Pigmentary switches in domestic animal species. Ann. NY Acad. Sci. 994:331–338, 2003. Klungland, H., D. I. Vage, L. Gomez-Raya, S. Adalsteinsson, and S. Lien. The role of melanocyte-stimulating hormone (MSH) receptor in bovine coat color determination. Mamm. Genome 6:636–639, 1995. Kobayashi, T., W. D. Vieira, B. Potterf, C. Sakai, G. Imokawa, and V. J. Hearing. Modulation of melanogenic protein expression during the switch from eu- to pheomelanogenesis. J. Cell Sci. 108:2301– 2309, 1995. Kondo, A., Y. Sato, and H. Nagara. An ultrastructural study of oligodendrocytes in zitter rat: a new animal model for hypomyelination in the CNS. J. Neurocytol. 20:929–939., 1991. Krude, H., H. Biebermann, W. Luck, R. Horn, G. Brabant, and A. Gruters. Severe early-onset obesity, adrenal insufficiency and red hair pigmentation caused by POMC mutations in humans. Nature Genet. 19:155–157, 1998. Krude, H., H. Biebermann, and A. Gruters. Mutations in the human proopiomelanocortin gene. Ann. NY Acad. Sci. 994:233–239, 2003a. Krude, H., H. Biebermann, D. Schnabel, M. Z. Tansek, P. Theunissen, P. E. Mullis, and A. Gruters. Obesity due to proopiomelanocortin deficiency: three new cases and treatment trials with thyroid hormone and ACTH4–10. J. Clin. Endocrinol. Metab. 88:4633–4640, 2003b. Kuramoto, T., M. Mori, J. Yamada, and T. Serikawa. Tremor and zitter, causative mutant genes for epilepsy with spongiform encephalopathy in spontaneously epileptic rat (SER), are tightly linked to synaptobrevin-2 and prion protein genes, respectively. Biochem. Biophys. Res. Commun. 200:1161–1168, 1994. Kuramoto, T., T. Nomoto, T. Sugimura, and T. Ushijima. Cloning of the rat agouti gene and identification of the rat nonagouti mutation. Mamm. Genome 12:469–471, 2001a. Kuramoto, T., K. Kitada, T. Inui, Y. Sasaki, K. Ito, T. Hase, S. Kawagachi, Y. Ogawa, K. Nakao, G. S. Barsh, M. Nagao, T. Ushigima, and T. Serikawa. Attractin/mahogany/zitter plays a critical role in myelination of the central nervous system. Proc. Natl Acad. Sci. USA 98:559–564, 2001b. Kuramoto, T., T. Nomoto, A. Fujiwara, M. Mizutani, T. Sugimura, and T. Ushijima. Insertional mutation of the Attractin gene in the black tremor hamster. Mamm. Genome 13:36–40, 2002. Kuwamura, M., M. Maeda, T. Kuramoto, K. Kitada, T. Kanehara, M. Moriyama, Y. Nakane, J. Yamate, T. Ushijima, T. Kotani, and T. Serikawa. The myelin vacuolation (mv) rat with a null mutation in the attractin gene. Lab. Invest. 82:1279–1286, 2002. Kwon, H. Y., S. J. Bultman, C. Loffler, W. J. Chen, P. J. Furdon, J. G. Powell, A. L. Usala, W. Wilkison, I. Hansmann, and R. P. Woychik. Molecular structure and chromosomal mapping of the human homolog of the agouti gene. Proc. Natl Acad. Sci. USA 91: 9760–9764, 1994. Lamoreux, M. L., and E. S. Russell. Developmental interaction in the pigmentary system of mice. I. Interactions between effects of genes on color of pigment and on distribution of pigmentation in the coat of the house mouse (Mus musculus). J. Hered. 70:31–36, 1979. Lamoreux, M. L., K. Wakamatsu, and S. Ito. Interaction of major coat color gene functions in mice as studied by chemical analysis of eumelanin and pheomelanin. Pigment Cell Res. 14:23–31, 2001.
Land, E. J., and P. A. Riley. Spontaneous redox reactions of dopaquinone and the balance between the eumelanic and phaeomelanic pathways. Pigment Cell Res. 13:273–277, 2000. Land, E. J., S. Ito, K. Wakamatsu, and P. A. Riley. Rate constants for the first two chemical steps of eumelanogenesis. Pigment Cell Res. 16:487–493, 2003. Land, E. J., C. A. Ramsden, and P. A. Riley. Quinone chemistry and melanogenesis. Methods Enzymol. 378:88–109, 2004. Leaman, T., R. Rowland, and S. E. Long. Male tortoiseshell cats in the United Kingdom. Vet. Record 144:9–12, 1999. Lerner, A. B. The discovery of melanotropins. A history of pituitary endocrinology. Ann. NY Acad. Sci. 680:1–12, 1993. Lieberman, M. W., A. L. Wiseman, Z. Z. Shi, B. Z. Carter, R. Barrios, C. N. Ou, P. Chevez-Barrios, Y. Wang, G. M. Habib, J. C. Goodman, S. L. Huang, R. M. Lebowitz, and M. M. Matzuk. Growth retardation and cysteine deficiency in gamma-glutamyl transpeptidasedeficient mice. Proc. Natl Acad. Sci. USA 93:7923–7926, 1996. Ling, M. K., M. C. Lagerstrom, R. Fredriksson, R. Okimoto, N. I. Mundy, S. Takeuchi, and H. B. Schioth. Association of feather colour with constitutively active melanocortin 1 receptors in chicken. Eur. J. Biochem. 270:1441–1449, 2003. Liu, Y., L. Hong, K. Wakamatsu, S. Ito, B. Adhyaru, C. Y. Cheng, C. Bowers, and J. Simon. Comparison of structural and chemical properties of human black-hair and red-hair melanosomes. Photochem. Photobiol. 81:135–144, 2004. Logan, D. W., R. J. Bryson-Richardson, K. E. Pagan, M. S. Taylor, P. D. Currie, and I. J. Jackson. The structure and evolution of the melanocortin and MCH receptors in fish and mammals. Genomics 81:184–191, 2003a. Logan, D. W., R. J. Bryson-Richardson, M. S. Taylor, P. Currie, and I. J. Jackson. Sequence characterization of teleost fish melanocortin receptors. Ann. NY Acad. Sci. 994:319–330, 2003b. Lomax, T. D., and R. Robinson. Tabby pattern alleles of the domestic cat. J. Hered. 79:21–23, 1988. Lyon, M. F. A personal history of the mouse genome. Annu. Rev. Genomics Hum. Genet. 3:1–16, 2002. Marklund, L., M. J. Moller, K. Sandberg, and L. Andersson. A missense mutation in the gene for melanocyte-stimulating hormone receptor (MC1R) is associated with the chestnut coat color in horses. Mamm. Genome 7:895–899, 1996. Mellgren, E. M., and S. L. Johnson. The evolution of morphological complexity in zebrafish stripes. Trends Genet. 18:128–134, 2002. Millar, S. E., M. W. Miller, M. E. Stevens, and G. S. Barsh. Expression and transgenic studies of the mouse agouti gene provide insight into the mechanisms by which mammalian coat color patterns are generated. Development 121:3223–3232, 1995. Miller, K. A., T. M. Gunn, M. M. Carrasquillo, M. L. Lamoreux, D. B. Galbraith, and G. S. Barsh. Genetic studies of the mouse mutations mahogany and mahoganoid. Genetics 146:1407–1415, 1997. Miller, M. W., D. M. J. Duhl, H. Vrieling, S. P. Cordes, M. M. Ollmann, B. M. Winkes, and G. S. Barsh. Cloning of the mouse agouti gene predicts a secreted protein ubiquitously expressed in mice carrying the lethal-yellow mutation. Genes Dev. 7:454–467, 1993. Morse, H. C. (ed.) Origins of Inbred Mice. New York: Academic Press, 1978. Mountjoy, K. G., L. S. Robbins, M. T. Mortrud, and R. D. Cone. The cloning of a family of genes that encode the melanocortin receptors. Science 257:1248–1251, 1992. Mundy, N. I., J. Kelly, E. Theron, and K. Hawkins. Evolutionary genetics of the melanocortin-1 receptor in vertebrates. Ann. NY Acad. Sci. 994:307–312, 2003. Mundy, N. I., N. S. Badcock, T. Hart, K. Scribner, K. Janssen, and N. J. Nadeau. Conserved genetic basis of a quantitative plumage trait involved in mate choice. Science 303:1870–1873, 2004.
407
CHAPTER 19 Nachman, M. W., H. E. Hoekstra, and S. L. D’Agostino. The genetic basis of adaptive melanism in pocket mice. Proc. Natl Acad. Sci. USA 100:5268–5273, 2003. Nagle, D. L., S. H. McGrail, J. Vitale, E. A. Woolf, B. J. Dussault, Jr., L. DiRocco, L. Holmgren, J. Montagno, P. Bork, D. Huszar, V. Fairchild-Huntress, P. Ge, J. Keilty, C. Ebeling, L. Baldini, J. Gilchrist, P. Burn, G. A. Carlson, and K. J. Moore. The mahogany protein is a receptor involved in suppression of obesity. Nature 398:148–152, 1999. Naysmith, L., K. Waterston, T. Ha, N. Flanagan, Y. Bisset, A. Ray, K. Wakamatsu, S. Ito, and J. L. Rees. Quantitative measures of the effect of the melanocortin 1 receptor on human pigmentary status. J. Invest. Dermatol. 122:423–428, 2004. Newton, J. M., A. L. Wilkie, L. He, S. A. Jordan, D. L. Metallinos, N. G. Holmes, I. J. Jackson, and G. S. Barsh. Melanocortin 1 receptor variation in the domestic dog. Mamm. Genome 11:24–30, 2000. Nijenhuis, W. A., J. Oosterom, and R. A. Adan. AgRP(83–132) acts as an inverse agonist on the human-melanocortin-4 receptor. Mol. Endocrinol. 15:164–171, 2001. Ozeki, H., S. Ito, K. Wakamatsu, and T. Hirobe. Chemical characterization of hair melanins in various coat-color mutants of mice. J. Invest. Dermatol. 105:361–366, 1995. Ozeki, H., S. Ito, K. Wakamatsu, and I. Ishiguro. Chemical characterization of pheomelanogenesis starting from dihydroxyphenylalanine or tyrosine and cysteine. Effects of tyrosinase and cysteine concentrations and reaction time. Biochim. Biophys. Acta 1336: 539–548, 1997. Pawelek, J. M. Proopiomelanocortin in skin: new possibilities for regulation of skin physiology (editorial; comment). J. Lab. Clin. Med. 122:627–628, 1993. Phan, L. K., F. Lin, C. A. LeDuc, W. K. Chung, and R. L. Leibel. The mouse mahoganoid coat color mutation disrupts a novel C3HC4 RING domain protein. J. Clin. Invest. 110:1449–1459, 2002. Potterf, S. B., V. Virador, K. Wakamatsu, M. Furumura, C. Santis, S. Ito, and V. J. Hearing. Cysteine transport in melanosomes from murine melanocytes. Pigment Cell Res. 12:4–12, 1999. Price, E. R., M. A. Horstmann, A. G. Wells, K. N. Weilbaecher, C. M. Takemoto, M. W. Landis, and D. E. Fisher. alphaMelanocyte-stimulating hormone signaling regulates expression of microphthalmia, a gene deficient in Waardenburg syndrome. J. Biol. Chem. 273:33042–33047, 1998. Prota, G. Melanins and Melanogenesis. San Diego: Academic Press, 1992. Prota, G., M. L. Lamoreux, J. Muller, T. Kobayashi, A. Napolitano, M. R. Vincensi, C. Sakai, and V. J. Hearing. Comparative analysis of melanins and melanosomes produced by various coat color mutants. Pigment Cell Res. 8:153–163, 1995. Rana, B. K., D. Hewett-Emmett, L. Jin, B. H. Chang, N. Sambuughin, M. Lin, S. Watkins, M. Bamshad, L. B. Jorde, M. Ramsay, T. Jenkins, and W. H. Li. High polymorphism at the human melanocortin 1 receptor locus (in process citation). Genetics 151:1547–1557, 1999. Rees, J. L. Genetics of hair and skin color. Annu. Rev. Genet. 37:67–90, 2003. Rehm, S., P. Mehraein, A. P. Anzil, and F. Deerberg. A new rat mutant with defective overhairs and spongy degeneration of the central nervous system: clinical and pathologic studies. Lab. Anim. Sci. 32:70–73, 1982. Rieder, S., S. Taourit, D. Mariat, B. Langlois, and G. Guerin. Mutations in the agouti (ASIP), the extension (MC1R), and the brown (TYRP1) loci and their association to coat color phenotypes in horses (Equus caballus). Mamm. Genome 12:450–455, 2001. Ringholm, A., R. Fredriksson, N. Poliakova, Y. L. Yan, J. H. Postlethwait, D. Larhammar, and H. B. Schioth. One melanocortin 4 and two melanocortin 5 receptors from zebrafish show remarkable conservation in structure and pharmacology. J. Neurochem. 82:6–18, 2002.
408
Ritland, K., C. Newton, and H. D. Marshall. Inheritance and population structure of the white-phased “Kermode” black bear. Curr. Biol. 11:1468–1472, 2001. Robbins, L. S., J. H. Nadeau, K. R. Johnson, M. A. Kelly, L. Rosellirehfuss, E. Baack, K. G. Mountjoy, and R. D. Cone. Pigmentation phenotypes of variant extension locus alleles result from point mutations that alter MSH receptor function. Cell 72:827–834, 1993. Robinson, R. Genetics for Cat Breeders. Oxford: Pergamon, 1991. Rosenblum, E. B., H. E. Hoekstra, and M. W. Nachman. Adaptive reptile color variation and the evolution of the Mc1r gene. Evol. Int. J. Org. Evol. 58:1794–1808, 2004. Russell, L. B., and W. L. Russell. Frequency and nature of specificlocus mutations induced in female mice by radiations and chemicals — a review. Mutat. Res. 296:107–127, 1992. Schioth, H. B. The physiological role of melanocortin receptors. Vitam. Horm. 63:195–232, 2001. Schoofs, L., A. De Loof, S. Matsumoto, S. Jegou, and H. Vaudry. Melanotropic peptides in insects. Ann. NY Acad. Sci. 680:600–602, 1993. Searle, A. G. Comparative Genetics of Coat Color in Mammals. New York: Academic Press, 1968. Siegrist, W., R. Drozdz, R. Cotti, D. H. Willard, W. O. Wilkison, and A. N. Eberle. Interactions of alpha-melanotropin and agouti on B16 melanoma cells: evidence for inverse agonism of agouti. J. Recept. Signal Transduct. Res. 17:75–98, 1997. Silver, L. M. An Introduction to mice. In: Mouse Genetics: Concepts and Applications. New York: Oxford University Press, pp. 3–14, 1995. Silvers, W. K. The Coat Colors of Mice: A Model for Mammalian Gene Action and Interaction. New York: Springer-Verlag, 1979. Silvers, W. K., and E. S. Russell. An experimental approach to action of genes at the agouti locus in the mouse. J. Exp. Zool. 130: 199–220, 1955. Slominski, A., R. Paus, and J. Mazurkiewicz. Proopiomelanocortin expression in the skin during induced hair growth in mice. Experientia 48:50–54, 1992. Slominski, A., R. Paus, and J. Wortsman. On the potential role of proopiomelanocortin in skin physiology and pathology. Mol. Cell. Endocrinol. 93:C1–C6, 1993. Slominski, A., G. Ermak, J. Hwang, A. Chakraborty, J. E. Mazurkiewicz, and M. Mihm. Proopiomelanocortin, corticotropin releasing hormone and corticotropin releasing hormone receptor genes are expressed in human skin. FEBS Lett. 374:113–116, 1995. Slominski, A., P. M. Plonka, A. Pisarchik, J. L. Smart, V. Tolle, J. Wortsman, and M. J. Low. Preservation of eumelanin hair pigmentation in proopiomelanocortin-deficient mice on a nonagouti (a/a) genetic background. Endocrinology 146:1245–1253, 2005. Sturm, R. A., D. L. Duffy, N. F. Box, R. A. Newton, A. G. Shepherd, W. Chen, L. H. Marks, J. H. Leonard, and N. G. Martin. Genetic association and cellular function of MC1R variant alleles in human pigmentation. Ann. NY Acad. Sci. 994:348–358, 2003. Takeuchi, S., S. Suzuki, S. Hirose, M. Yabuuchi, C. Sato, H. Yamamoto, and S. Takahashi. Molecular cloning and sequence analysis of the chick melanocortin 1-receptor gene. Biochim. Biophys. Acta 1306:122–126, 1996. Tamate, H. B., and T. Takeuchi. Action of the e locus of mice in the response of phaeomelanic hair follicles to alpha-melanocyte stimulating hormone in vitro. Science 224:1241–1242, 1964. Theron, E., K. Hawkins, E. Bermingham, R. E. Ricklefs, and N. I. Mundy. The molecular basis of an avian plumage polymorphism in the wild: a melanocortin-1-receptor point mutation is perfectly associated with the melanic plumage morph of the bananaquit, Coereba flaveola. Curr. Biol. 11:550–557, 2001. Thody, A. J., K. Ridley, R. J. Penny, R. Chalmers, C. Fisher, and S. Shuster. MSH peptides are present in mammalian skin. Peptides 4:813–816, 1983.
REGULATION OF PIGMENT TYPE SWITCHING BY AGOUTI Thody, A. J., E. M. Higgins, K. Wakamatsu, S. Ito, S. A. Burchill, and J. M. Marks. Pheomelanin as well as eumelanin is present in human epidermis. J. Invest. Dermatol. 97:340–344, 1991. Thomson, R. H. The pigments of reddish hair and feathers. Angew. Chem. Int. Ed. Engl. 13:305–312, 1974. Vage, D. I., D. S. Lu, H. Klungland, S. Lien, S. Adalsteinsson, and R. D. Cone. A non-epistatic interaction of agouti and extension in the fox, Vulpes vulpes. Nature Genet. 15:311–315, 1997. Vage, D. I., H. Klungland, D. Lu, and R. D. Cone. Molecular and pharmacological characterization of dominant black coat color in sheep. Mamm. Genome 10:39–43, 1999. Valverde, P., E. Healy, I. Jackson, J. L. Rees, and A. J. Thody. Variants of the melanocyte-stimulating hormone receptor gene are associated with red hair and fair skin in humans. Nature Genet. 11:328–330, 1995. Van Raamsdonk, C. D., K. R. Fitch, H. Fuchs, M. H. de Angelis, and G. S. Barsh. Effects of G-protein mutations on skin color. Nature Genet. 36:961–968, 2004. Voisey, J., N. F. Box, and A. van Daal. A polymorphism study of the human Agouti gene and its association with MC1R. Pigment Cell Res. 14:264–267, 2001. Vrieling, H., D. M. Duhl, S. E. Millar, K. A. Miller, and G. S. Barsh. Differences in dorsal and ventral pigmentation result from regional
expression of the mouse agouti gene. Proc. Natl Acad. Sci. USA 91:5667–5671, 1994. Weigel, I. The coat pattern of wild feline species and of the domestic cat from a comparative and evolutionary point of view. Saugertierk. Mitt. (Suppl.) 9, 1961. Wilson, B. D., M. M. Ollmann, L. Kang, M. Stoffel, G. I. Bell, and G. S. Barsh. Structure and function of ASP, the human homolog of the mouse agouti gene. Hum. Mol. Genet. 4:223–230, 1995. Wintzen, M., and B.A. Gilchrest. Proopiomelanocortin, its derived peptides, and the skin. J. Invest. Dermatol. 106:3–10, 1996. Wright, S. Color inheritance in mammals. J. Hered. 8:224–235, 1917a. Wright, S. Color inheritance in mammals. V. The guinea pig. J. Hered. 8:476–480, 1917b. Wright, S. Color inheritance in mammals. II. The mouse. J. Hered. 8:373–378, 1917c. Yaswen, L., N. Diehl, M. B. Brennan, and U. Hochgeschwender. Obesity in the mouse model of pro-opiomelanocortin deficiency responds to peripheral melanocortin. Nature Med. 5:1066–1070, 1999. Zeigler-Johnson, C., S. Panossian, S. M. Gueye, M. Jalloh, D. OforiAdjei, and P. A. Kanetsky. Population differences in the frequency of the agouti signaling protein g.8818aÆG polymorphism. Pigment Cell Res. 17:185–187, 2004.
409
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
20
Human Pigmentation: Its Regulation by Ultraviolet Light and by Endocrine, Paracrine, and Autocrine Factors Zalfa Abdel-Malek and Ana Luisa Kadekaro
Summary
Historical Background
1 Cutaneous pigmentation has cosmetic and cultural implications. Melanin in the skin plays a photoprotective role. 2 The tanning response to sun exposure correlates directly with constitutive melanin content, which in turn is determined by the rate of synthesis in melanocytes, and the rate and manner of melanosome delivery to keratinocytes. Cultured human melanocytes respond to ultraviolet radiation (UVR) with growth arrest and increased melanogenesis; however, melanocytes derived from skin types I or II have a slower recovery from the growth arrest, more cyclobutane pyrimidine dimers, and less melanogenic response than melanocytes from skin types V or VI. 3 Exposure to UVR induces the synthesis of a variety of epidermal cytokines and growth factors, many of which affect the proliferation of melanocytes and/or melanogenesis. 4 Human melanocytes respond to certain inflammatory mediators, which include the immune inflammatory cytokines interleukin-1, -6 and tumor necrosis factor-a, and a variety of eicosanoids. 5 Basic fibroblast growth factor is a paracrine factor that is mitogenic for melanocytes. 6 Endothelin-1 is a keratinocyte-derived factor that stimulates melanocyte proliferation and melanogenesis, and promotes survival after exposure to UVR. 7 The proopiomelanocortin-derived melanotropic peptides, particularly a-melanocyte-stimulating hormone (MSH) and adrenocorticotropic hormone (ACTH), are mitogenic and melanogenic for human melanocytes and function as transducers for the melanogenic effect of UVR and as survival factors for melanocytes. 8 The proopiomelanocortin derivative b-endorphin stimulates the proliferation and melanogenesis of human epidermal and follicular melanocytes. 9 Agouti signaling protein antagonizes the effects of a-MSH on human melanocytes. 10 Human melanocytes are targets for vitamin D3 and are affected by estrogens.
The Role of Melanin
410
Cutaneous pigmentation is a genetic trait that distinguishes humans from different ethnic backgrounds, yet is unique to every individual. The growing interest in understanding how human pigmentation is regulated stems from increasing concern about the photocarcinogenic and photoaging effects of sun exposure and the role of melanin in photoprotection. It also stems from cultural preferences for dark-tanned skin (as in Western societies) or light complexion (as in the Orient). Melanin in the skin is known to reduce the penetration of ultraviolet radiation (UVR) through the epidermal layers and to quench reactive oxygen radicals that contribute to the suninduced DNA damage (Kaidbey et al., 1979; Menon and Haberman, 1977; Morison, 1985). Many epidemiologic studies have shown that the frequency of skin cancers is higher in individuals with lightly pigmented skin than in individuals with dark skin (Epstein, 1983; Sober et al., 1991). The correlation between cutaneous melanin content and the susceptibility to sun-induced carcinogenesis has given skin pigmentation a special significance. With the increase in the frequency of sun-induced skin cancers due to the depletion of the ozone layer, understanding the role of melanin in preventing the photodamaging and carcinogenic effects of sun exposure has become an important public health issue.
Current Concepts Constitutive Pigmentation and the Response to UV Radiation One of the most obvious effects of sun exposure is increased skin darkening (i.e. tanning). This response, however, varies among individuals with different pigmentary phenotypes (i.e. skin types). Those with very light skin (skin types I or II) burn and do not tan, whereas those with dark skin (skin types IV–VI) tan well when exposed to the sun. The pigmentary response, particularly the delayed tanning response that results from the stimulation of melanin synthesis, is determined to a large extent by constitutive melanin content in the skin (Pathak et al., 1980). In addition, this response is affected by a wide variety of hormones and cytokines, the production of
HUMAN PIGMENTATION
UV
Growth arrest Endocrine factors
Melanosomes
e.g.
KC Pituitary gland
Adrenal gland
Ovary
Testis
MC Other tissues
Melanogenesis
Paracrine factors that include: 1) α-MSH and ACTH 2) ET-1 3) ASP 1) + 2), 1) + 3)
cAMP, PKA activity PKC, tyrosine phosphorylation antagonist for α-MSH, other (?) signaling pathway regulation of melanocyte proliferation and function
Fig. 20.1. Schematic representation of the regulation of human melanocytes by sun exposure and hormonal factors.
which is augmented by UVR (Fig. 20.1). It was suggested that the increase in pigmentation following exposure to UVR is a consequence of DNA repair (Eller et al., 1994). If this is the case, then dark skin that tans readily would be expected to be more proficient than lightly pigmented skin in repairing DNA damage. However, unequivocal evidence linking skin pigmentation and DNA repair is not available. So far, only one study has demonstrated that multiple irradiations with UVR enhanced the rate of removal of DNA photoproducts in skin type IV but not in skin type I or II individuals (Sheehan et al., 2002). For decades, it has been recognized that differences in constitutive skin pigmentation are not due to differences in the number of melanocytes among different skin types, but to differences in the melanogenic activity of the melanocyte, the number and size of melanosomes, the type of melanin deposited onto melanosomes, and the donation of mature melanosomes to surrounding keratinocytes (Pathak et al., 1980). In Caucasian skin, several melanosomes are packaged and transferred as a single unit or entity to the keratinocytes. However, in dark skin, melanosomes are larger in size than those in Caucasian skin, and each melanosome is transferred individually from a melanocyte to surrounding keratinocytes. Furthermore, it has been demonstrated that the activity of tyrosinase, the rate-limiting enzyme in the melanogenic pathway, correlated directly with skin pigmentation and melanin content and is higher in melanocytes derived from deeply pigmented skin than in melanocytes from lightly pigmented skin (Abdel-Malek et al., 1994; Halaban et al., 1983;
Iwata et al., 1990). With the discovery of the two melanogenic enzymes, TRP-1 and TRP-2, it became evident that they too contribute to constitutive melanization (Hearing and Tsukamoto, 1991; Jackson, 1988; Vijayasaradhi and Houghton, 1991). Using specific antibodies that recognize tyrosinase, TRP-1, and TRP-2, respectively, it was demonstrated by Western blot analysis that the amount of each of these proteins in cutaneous human melanocytes correlates directly with the pigmentary phenotype from which these melanocytes were derived (Abdel-Malek et al., 1993). Additionally, the levels of tyrosinase, TRP-1, and TRP-2 could be increased or decreased by agents that stimulate or inhibit melanogenesis respectively (Abdel-Malek et al., 1993, 1994, 1995). One of the most obvious effects of sun exposure is skin darkening (i.e. tanning). It was demonstrated years ago that the number of DOPA-positive (i.e. active) melanocytes is significantly higher in chronically sun-exposed skin than in unexposed skin from the same individual (Gilchrest et al., 1979). The first evidence for direct responsiveness of human melanocytes in vitro to UV irradiation was provided by Friedmann and Gilchrest (1987), who demonstrated that these cells responded to UVR from a solar simulator with a dose-dependent decrease in proliferation and increase in pigmentation. Libow et al. (1988) then showed that melanocytes responded to UVR with increased proliferation and melanogenesis. Neither study referred to any differences in the responses of melanocytes with different melanin contents to UVR. We have reported that irradiation of melanocytes with a fractionated 411
CHAPTER 20
dose of UVR (mainly UVB with a minor UVC component) that did not cause cell death resulted in inhibition of melanocyte proliferation as a result of arrest in G2 phase of the cell cycle, and in increased tyrosinase activity and melanin content (Abdel-Malek et al., 1994). These effects were the same in melanocytes derived from different skin types. Yohn et al. (1992) found that melanocytes from white skin were more sensitive to the DNA-damaging effects of UVA light. Barker et al. (1995) compared the responses of human melanocytes derived from different pigmentary phenotypes to a single irradiation with increasing doses of UVR. Melanocytes, regardless of their melanin content, exhibited increased levels of the tumor suppressor gene product p53 and became arrested in G1 phase of the cell cycle following UVR irradiation. However, there were distinct differences between the responses of very lightly (skin type I or II derived) and very heavily (skin type V or VI derived) pigmented melanocytes. Only the latter but not the former demonstrated a melanogenic response following exposure to UVR. Furthermore, lightly pigmented melanocytes had a slower recovery from the UVR-induced G1 arrest, and a more prolonged increase in the p53 protein, and encountered more cyclobutane pyrimidine dimers than heavily pigmented melanocytes. The differences in the induction of DNA photoproducts were corroborated by a study in which the responses to UVR of individuals from different ethnic backgrounds and pigmentary phenotypes were compared in vivo (Tadokoro et al., 2003). In further support of these results, Musk and Parsons (1987) noted that human melanoma cells with a low melanin content were more sensitive to killing by solar irradiation or UVC light than melanoma cells that were more melanotic. Additionally, Kobayashi et al. (1993) demonstrated increased formation of cyclobutane pyrimidine dimers and pyrimidine (6,4) pyrimidone photoproducts following irradiation with UVC radiation in lightly pigmented, compared with heavily pigmented, human melanoma cells. Also, irradiated melanoma cells with a high melanin content were found to be more resistant to cell killing than their less melanotic counterparts. Interestingly, however, no difference in the DNA repair of pyrimidine dimers or (6,4) photoproducts was detected among melanoma cells with different melanin contents. Collectively, these studies clearly illustrate distinct differences in the responses of melanocytes from different skin types to UVR and show that the induction of DNA photoproducts correlates with melanin content. As stimulation of melanogenesis is accompanied by increased transfer of melanosomes to adjacent keratinocytes, and thus increased skin pigmentation and photoprotection, the above results offer an explanation for the differences in the cutaneous responses of individuals with different pigmentary phenotypes to sun exposure and in their susceptibility to the development of skin cancers.
Eumelanin, Pheomelanin, and Photoprotection Human epidermal melanocytes synthesize the main two forms of melanin, the brown–black eumelanin and the red–yellow pheomelanin. The relative amounts of eumelanin and 412
pheomelanin are an important determinant of constitutive cutaneous pigmentation. The ratio of eumelanin to pheomelanin is substantially higher in melanocytes in dark skin than in melanocytes in lightly pigmented skin, and seems to correlate directly with total melanin content (Kadekaro et al., 2003). It has become evident that regulation of synthesis of these two forms of melanin in human melanocytes is mainly carried out by activation of the melanocortin 1 receptor by its ligands a-MSH or ACTH, or inactivation of the receptor by mutations that disrupt its binding or signaling, or possibly by binding of the physiological antagonist agouti signaling protein (Abdel-Malek et al., 1995; Box et al., 1997; Hunt et al., 1995; Scott et al., 2002a; Smith et al., 1998; Suzuki et al., 1997). Eumelanin is thought to be superior to pheomelanin in its photoprotective properties. Eumelanin is more resistant than pheomelanin to degradation and is more efficient in scavenging reactive oxygen species that are produced by UVR exposure (Bustamante et al., 1993; Menon et al., 1985). Moreover, pheomelanin is thought to contribute to the damaging effects of UVR because it can generate hydroxyl radicals and superoxide anions (Chedekel et al., 1978; Felix et al., 1978). Eumelanin is synthesized and deposited onto elliptical melanosomes, whereas pheomelanin is synthesized in smaller round melanosomes. In situ, elliptical melanosomes in dark skin remain intact throughout the epidermal layers, and form supranuclear caps in keratinocytes, reducing exposure of nuclear DNA to impinging UVR (Pathak et al., 1971). In contrast, in lightly pigmented skin, melanosomes are degraded, and only “melanin dust” is evident in the suprabasal layers. The absence or reduction in melanosomes in the epidermis is expected to compromise the photoprotection of the skin, rendering it more vulnerable to UVR-induced damage, and hence carcinogenesis. Indeed, studies on cultured human melanocytes revealed an inverse relationship between eumelanin content and the ratio of eumelanin to pheomelanin, on one hand, and the induction of DNA photoproducts on the other (Smit et al., 2001; Tadokoro et al., 2003).
Induction of Epidermally Synthesized Factors by UVR Several groups of investigators have demonstrated that exposure to UVR stimulates the synthesis of a variety of hormones, cytokines, and growth factors by epidermal cells. Irradiation of keratinocytes with UVR was shown to increase the synthesis of the cytokines interleukin (IL)-1 and tumor necrosis factor (TNF)-a, and the latter cytokine was found to play an important role in the formation of sunburn cells (i.e. apoptotic keratinocytes) (Köck et al., 1990; Kupper et al., 1987; Oxholm et al., 1988; Urbanski et al., 1992). Human melanocytes in culture also synthesize IL-1a and IL-1b (Swope et al., 1994). Basic fibroblast growth factor (bFGF) is synthesized by keratinocytes, and its synthesis is enhanced by UVR (Halaban, 1988). UV irradiation of keratinocytes in vitro, or human skin in vivo, increased the synthesis of endothelin (ET)1 (Imokawa et al., 1992, 1995; Yohn et al., 1993), as well as
HUMAN PIGMENTATION
proopiomelanocortin and its derivatives, a-melanocyte stimulating hormone (a-melanotropin, a-MSH) and adrenocorticotropic hormone (ACTH), b-lipotropic hormone, and its derivative b-endorphin (Kippenberger et al., 1995; Schauer et al., 1994; Suzuki et al., 2002; Wakamatsu et al., 1997; Wintzen et al., 1996). The synthesis of a-MSH and ACTH by cultured human keratinocytes or melanocytes and the synthesis of ET-1 by cultured human keratinocytes were enhanced by IL-1a. Another factor whose synthesis is increased upon irradiation of the epidermis with UVR is stem cell factor (Hachiya et al., 2001). Prostaglandins (PGs) and leukotrienes are two classes of inflammatory mediators that are derived from the metabolism of arachidonic acid by the cyclooxygenase and lipooxygenase pathways respectively. The levels of prostaglandins D2, E2, and F2a have been found to increase in the skin following irradiation with UVR (Black et al., 1980; Kobza Black et al., 1978). We have found that human melanocytes synthesize PGF2a and the lipooxygenase derivatives LTB4 and 12-HETE (Leikauf et al., 1994). Recently, it was demonstrated that activation of the proteinase-activated receptor 2 (PAR-2) stimulates the synthesis of PGE2 and PGF2a by cultured human keratinocytes (Scott et al., 2004). PAR-2 is an important participant in melanosome transfer from melanocytes and keratinocytes, and is activated by UVR. Thus, UVR seems to increase the production of specific arachidonic acid derivatives indirectly by activating PAR-2. The significance of keratinocyte-derived factors in the regulation of melanocyte function was first demonstrated by the observation that media conditioned by cultured human keratinocytes stimulated the proliferation, melanogenesis, and dendricity of cultured human melanocytes (Gordon et al., 1989). Evidence for the participation of keratinocytes in the response of melanocytes to UVR was provided by the observation that melanogenesis was more markedly stimulated by UVR when melanocytes were cocultured with keratinocytes than when melanocytes were grown in monoculture (Duval et al., 2001). There is also evidence for autocrine regulation of human melanocytes. For example, we have reported that human melanocytes synthesize IL-1a and IL-b, and also PGF2a, LTB4, and 12-HETE (Leikauf et al., 1994). Most of the keratinocyte- and melanocyte-derived factors listed above affect the proliferation and/or melanogenesis of human melanocytes in vitro. Based on these findings, we hypothesize that the response of human melanocytes to sun exposure is direct, as well as indirect through the effects of UVR-induced paracrine and autocrine factors.
IL-1a, IL-1b, IL-6, and TNF-a on cultured human melanocytes (Swope et al., 1991). All four cytokines dosedependently decreased the proliferation and tyrosinase activity, and reduced the levels of tyrosinase, TRP-1, and TRP-2 in human melanocytes, as determined by Western blot analysis (Abdel-Malek et al., 1993). The biological effects of these cytokines on human melanocytes strongly suggest that they potentially function as paracrine factors. Additionally, the demonstration that human melanocytes respond to, and synthesize, IL-1a and IL-1b suggests that these two cytokines function as autocrine, as well as paracrine, regulators of human melanocytes (Swope et al., 1994). As UVR has been shown to stimulate the synthesis of IL-1 and TNF-a by keratinocytes, we speculate that these cytokines might be part of a negative feedback loop that downregulates the pigmentary effect of UVR. Moreover, these primary cytokines induce the synthesis of other cutaneous factors that in turn mediate the response of melanocytes to sun exposure or inflammation. For example, IL-1 has been shown to stimulate the synthesis of ET-1 and b-endorphin by keratinocytes (Imokawa et al., 1992; Wintzen et al., 1996), as well as a-MSH and ACTH by human keratinocytes and melanocytes (Chakraborty et al., 1996; Schauer et al., 1994). Another group of inflammatory mediators is the eicosanoids, metabolites of arachidonic acid. We have shown that PGs affect melanogenesis in murine Cloudman melanoma cells, with the E series (PGE1 and E2) being potent stimulators, whereas PGA1 and PGD2 act as potent inhibitors (AbdelMalek et al., 1987). As for normal human melanocytes, Tomita et al. (1987) reported that they respond to PGE1 with increased melanogenesis and dendrite formation. Recently, it was demonstrated that PGE2 and PGF2a increase the dendricity of human melanocytes, an effect that is expected to increase skin pigmentation by facilitating the transfer of melanosomes to keratinocytes (Scott et al., 2004). An important finding by Morelli et al. (1989) was that leukotrienes (LT) C4 and D4, two metabolites of the lipooxygenase pathway, were mitogenic for human neonatal melanocytes. Medrano et al. (1993) went further to demonstrate that normal adult melanocytes were induced to proliferate and form tight spheroids in the presence of LTC4 in the culture medium. Evidently, LTC4 resulted in loss of contact inhibition in the melanocyte cultures, which led to the speculation that LTC4 plays a role in the induction of early events of malignant transformation.
Role of Basic Fibroblast Growth Factor
Regulation of Human Melanocytes by Paracrine and Autocrine Factors Effects of Inflammatory Mediators The clinical observation of post-inflammatory hyperpigmentation has implicated immune inflammatory mediators in this phenomenon (Nordlund and Abdel-Malek, 1988). We have investigated the effects of the immune inflammatory cytokines
One growth factor that has been amply described as a mitogen for normal human melanocytes and as an autocrine stimulator of human melanoma cell growth is bFGF (Halaban et al., 1988a, b). Basic FGF was the first paracrine factor for human melanocytes to be identified. The mitogenic effect of bFGF was observed when it was present concomitantly with an agent that elevates intracellular cyclic adenosine monophosphate (cAMP) levels (e.g. cholera toxin) (Abdel-Malek et al., 1992; Halaban et al., 1988b). Basic FGF elicited its biological 413
CHAPTER 20
effects by binding to a tyrosine kinase receptor that is expressed on human melanocytes (Pittelkow and Shipley, 1989). Unlike most other keratinocyte-derived growth factors, bFGF is not secreted by keratinocytes, and direct contact of melanocytes with keratinocytes is required for its mitogenic effect.
Endothelins and Human Melanocytes Endothelins represent a family of three related peptides, ET-1, -2, and -3, each of which consists of 21 amino acids and is the product of a distinct gene (Fig. 20.1) (Inoue et al., 1989). These peptides have been shown to be synthesized by, and to influence, many cell types in a paracrine manner (Rubanyi and Polokoff, 1994). Yohn et al. (1993) and Imokawa et al. (1992) showed that ET-1 is produced by human keratinocytes. The latter group also reported that ET-1 is mitogenic and melanogenic for human melanocytes that express specific receptors for ET-1 (Yada et al., 1991). They also showed that ET-1 increases the expression of the two melanogenic enzymes tyrosinase and TRP-1 (Imokawa et al., 1995). The physiological relevance of endothelins to pigmentation is clearly illustrated by the findings that mutations in the genes that encode for ET-3, or the ET-B receptor that binds all three endothelins with a similar affinity, result in piebald spotting and megacolon in mice (Greenstein Baynash et al., 1994; Hosoda et al., 1994). These defects are also evident in humans with Hirschsprung’s disease (Puffenberger et al., 1994). These correlations emphasize the importance of normal ET-3 and ET-B receptor expression in the migration of neural crest derivatives, including the melanocytes, during embryonic development. We have reported that ET-1 interacts synergistically with aMSH and bFGF to stimulate human melanocyte proliferation (Swope et al., 1995). We have also found that ET-3 has identical effects to ET-1 and that both peptides bind the ET receptor on melanocytes with the same affinity (Tada et al., 1998). The latter results suggested that human melanocytes express the ET-B receptor (Tada et al., 1998). Northern blot analysis confirmed that human melanocytes predominantly express ET-B and not ET-A receptors. The production of ET-1 by keratinocytes, particularly in response to UVR and IL-1 treatment, suggests a role for this hormone in mediating the response of melanocytes to sun exposure and inflammation. We have found that ET-1 is an important mediator of the response of human melanocytes to UVR. Treatment of UVirradiated cultured human melanocytes with ET-1 enabled them to overcome the UVR-induced G1 arrest, proliferate, and increase melanin synthesis (Tada et al., 1998). Further evidence for the importance of ET-1 in the response of human melanocytes to UVR was provided by the finding that irradiation of human skin in vivo with UVR resulted in increased expression of ET-1 and tyrosinase genes (Imokawa et al., 1995). Additionally, the stimulatory effect of conditioned medium from UV-irradiated keratinocytes on human melanocytes in vitro was greatly abrogated by a neutralizing
414
antibody to ET-1. Recently, we described a survival effect of ET-1 on UV-irradiated human melanocytes. Treatment of human melanocytes with ET-1 markedly reduced the UVRinduced apoptosis and promoted melanocyte survival (Kadekaro et al., 2003, 2005). Melanocytes have a limited self-renewal capacity, and maintaining their survival is crucial, given their importance in conferring photoprotection to the skin.
Role of Proopiomelanocortin Derivatives: Melanocortins and b-Endorphins The melanocortins are a family of structurally related peptides that include a-, b-, and g-MSH and ACTH, all of which are derived from one precursor peptide, proopiomelanocortin (POMC). In particular, a- and b-MSH have been best known for their melanogenic effects on the integument of many vertebrate species, including mammals (Sawyer et al., 1983). Several decades ago, Lerner and McGuire (1964) reported that injection of humans with high concentrations of a-MSH and b-MSH or ACTH resulted in skin darkening. More recently, Levine et al. (1991) demonstrated that injection of humans with a potent synthetic analog of a-MSH, namely [Nle4,DPhe7]-a-MSH, caused increased pigmentation, mostly in habitually sun-exposed skin. A physiological role for melanocortins in regulating human pigmentation was controversial (Fuller et al., 1993; Halaban et al., 1983). However, with the cloning and characterization of the melanocortin receptors, it became evident that human melanocytes express the melanocortin 1 receptor (MC1R) that binds a-MSH and ACTH with the same affinity (Chhajlani and Wikberg, 1992; Mountjoy, 1994; Suzuki et al., 1996). Using receptor binding assays, Donatien et al. (1992) found that human melanocytes express a low number of MSH receptors, and that receptor expression is upregulated by cholera toxin, but downregulated by 12-Otetradecanoylphorbol-13-acetate (TPA). De Luca et al. (1993) confirmed the presence of MSH receptors on human melanocytes, and showed that these cells respond to a-MSH with increased proliferation, without any change in their pigmentation. Hunt et al. (1994a, b) then reported that human melanocytes respond to a-MSH or ACTH with increased melanogenesis. We have demonstrated that human melanocytes maintained in culture in the absence of any cAMP inducer respond equally to a-MSH and ACTH with an increase in both proliferation and melanogenesis (AbdelMalek et al., 1995; Suzuki et al., 1996). The similarity in the responses of human melanocytes to a-MSH and ACTH confirmed previous pharmacological data obtained using the cloned MC1R, which showed that both hormones have similar binding affinities (Chhajlani and Wikberg, 1992). By comparing the relative affinities of a-, b-, g-MSH, and ACTH for the MC1R and their abilities to stimulate the proliferation and melanogenesis of human melanocytes, we found that aMSH and ACTH were equally potent, b-MSH was less effective than either, and g-MSH was the least effective (Suzuki et al., 1996). These results suggest that a-MSH, ACTH, and
HUMAN PIGMENTATION
possibly b-MSH, but not g-MSH, might have a physiological role in human pigmentation. Using Northern blot analysis, we found that human melanocytes express the mRNA transcript for the MC1, but not for the MC2, MC3, MC4, or MC5R. Additionally, we found that the level of the MC1R transcript was increased by brief treatment with a-MSH or ACTH, but decreased by treatment with the MC1R antagonist agouti signaling protein or exposure to UVR (Scott et al., 2002b; Suzuki et al., 1996). Interestingly, treatment of human melanocytes with ET-1 tremendously increased MC1R mRNA levels (Scott et al., 2002b; Tada et al., 1998). This effect of ET-1 suggests that its regulation of human melanocyte proliferation and melanogenesis is not exclusively mediated by binding to the ET receptors, but also by indirectly enhancing the response to melanocortins via upregulating MC1R expression. The observed increase in MC1R mRNA levels following treatment with its agonists a-MSH or ACTH or with ET-1 is expected to sustain, or even enhance, the response of melanocytes to melanocortins. Treatment of human melanocytes with bestradiol increased the expression of MC1R mRNA and augmented the upregulation of the MC1R mRNA level. This suggests a mechanism by which b-estradiol might increase human pigmentation. Studies on the murine Cloudman S91 melanoma cells concluded that UVR upregulates the expression of the MSH receptor, suggesting that the MSH receptor functions as a transducer of the UVR effects on melanoma cells (Chakraborty and Pawelek, 1993). We have found that treatment of normal human melanocytes with a-MSH immediately after irradiation with UVR results in partial recovery from UVR-induced G1 arrest and stimulation of melanogenesis (Im et al., 1998). Recently, we discovered a novel role for melanocortins as survival factors for human melanocytes (Kadekaro et al., 2003, 2005). We have observed that treatment of human melanocytes with either a-MSH or ACTH promotes survival following irradiation with UVR by inhibiting UVR-induced apoptosis and activating survival pathways that are mediated by Akt and the transcription factor Mitf (Kadekaro et al., 2005). Therefore, melanocortins contribute to photoprotection of the skin by maintaining the survival of the melanocyte in the epidermis and stimulating eumelanin synthesis. In addition to a-MSH and ACTH, another POMC-derived peptide, the opioid peptide b-endorphin, was recently shown to stimulate the proliferation, melanogenesis, and dendricity of epidermal human melanocytes (Kauser et al., 2003). bEndorphin may function as a paracrine and autocrine factor for epidermal melanocytes, because it is expressed in the skin as well as in cultured keratinocytes and melanocytes. Moreover, expression of the m-opiate receptor by melanocytes and keratinocytes was also demonstrated, suggesting that the effects of b-endorphin are directly mediated by activating its own specific receptor. Similar findings have just been reported in human follicular melanocytes, which express m-opiate receptor and respond to b-endorphin with increased melano-
genesis, dendricity, and proliferation (Kauser et al., 2004). These recent findings underscore the significance of POMC in the regulation of human skin and hair pigmentation.
Regulation of Eumelanin and Pheomelanin Synthesis by a-MSH and Agouti Protein Genetic studies on the regulation of mouse coat color revealed that the switch from eumelanin to pheomelanin synthesis by follicular melanocytes is mainly regulated by the extension locus and the agouti locus (Quevedo et al., 1981; Robbins et al., 1993; Silvers, 1979). The extension locus codes for the MC1R which, upon activation by a-MSH, stimulates the synthesis of eumelanin (Robbins et al., 1993). The agouti locus codes for a soluble factor, agouti signaling protein, which is temporally expressed in dermal papilla cells within the hair follicles. In mice, expression of different alleles of the agouti and extension loci determines the amount and distribution of pheomelanin and eumelanin in the hair follicles (Quevedo et al., 1981; Silvers, 1979). Five alleles for the murine MC1R have been characterized and found to alter the binding affinity to a-MSH or the coupling to, and activation of, adenylate cyclase and, ultimately, the extent of eumelanin synthesis in follicular melanocytes (Robbins et al., 1993). Five alleles of the agouti locus have been identified and shown to influence the pigmentary phenotype of mice (Silvers, 1979). The wildtype agouti allele results in a narrow subapical band of hair containing pheomelanin. The agouti protein is known to regulate dorsal and ventral pigmentation in the mouse. The difference between dorsal and ventral pigmentation was found to result from the expression of different isoforms of the agouti gene with different sets of 5¢ untranslated exons (Vrieling et al., 1994). Although the role of the agouti locus in the mouse is well defined, its physiological role in the regulation of human pigmentation is to be explored further. The human MC1R gene is homologous to the extension locus in mice. Activation of the human MC1R by its ligand a-MSH increases eumelanin synthesis (Hunt et al., 1995). The MC1R gene is highly polymorphic, with about 65 different allelic variants identified so far (Box et al., 1997; Smith et al., 1998). Many of these alleles were identified in northern European countries and Australia, with some having strong and others having weak association with red hair phenotype. The alleles that are strongly associated with red hair phenotype, namely Arg151Cys, Arg160Trp, and Asp294His substitutions, result in loss of function of the MC1R, and are highly associated with poor tanning ability and increased risk of melanoma (Palmer et al., 2000; Scott et al., 2002a). Expression of the above three alleles in the homozygous or compound heterozygous state increases the sensitivity of human melanocytes to UVR-induced apoptosis, possibly as a result of the inability of these melanocytes to withstand UVR-induced damage (Kadekaro et al., 2005; Scott et al., 2002a). The extensive polymorphism of the MC1R has suggested its significance in the diversity of constitutive human pigmentation and the response of human melanocytes to UVR.
415
CHAPTER 20
The mouse agouti gene has been cloned, and its product, a 131-amino-acid peptide, has been purified (Bultman et al., 1992). The human homolog for the mouse agouti gene has also been cloned and found to share 85% homology in its nucleotide sequence with the mouse gene (Kwon et al., 1994). The product of the human agouti gene is a 132-amino-acid peptide termed agouti signaling protein (ASP), which has 80% homology with the mouse protein (Kwon et al., 1994). Expression of ASP in transgenic mice resulted in a yellow coat color, thus providing evidence for the function of the human agouti gene in the regulation of pheomelanin synthesis (Wilson et al., 1995). The availability of purified mouse agouti protein and ASP provided the opportunity to investigate their effects and the mechanisms of action on melanocytes. Agouti protein acts as an antagonist for a-MSH on the mouse follicular melanocytes (Takeuchi et al., 1989; Yen et al., 1994). Agouti protein functions as a competitive inhibitor for a-MSH binding to the mouse MC1R that is expressed in heterologous cells or B16 melanoma cells (Blanchard et al., 1995; Lu et al., 1994). It has also been proposed that the agouti protein reduces the availability of a-MSH to its receptor. A third possibility is that ASP binds a specific, yet unidentified, receptor that counteracts the signal transduction pathway induced by a-MSH. Both recombinant human and murine agouti proteins were found to inhibit the a-MSH-induced stimulation of cAMP formation by murine B16 melanoma cells (Blanchard et al., 1995; Wilson et al., 1995). We have investigated the possible effects of the mouse and human agouti proteins on cultured human melanocytes. Both proteins completely blocked the mitogenic and melanogenic effects of a-MSH (Suzuki et al., 1997). ASP competed with aMSH for binding to the MC1R, and blocked the stimulation of cAMP formation by a-MSH in human melanocytes. These results clearly demonstrated that ASP functions as an antagonist of the human MC1R. However, the exact role of ASP in human pigmentation remains to be explored. Unlike the human MC1R gene which is highly polymorphic, only one variant of the human agouti gene has been identified (Kanetsky et al., 2002; Voisey et al., 2001). This argues against the significance of the agouti gene in the diversity of human pigmentation. The antagonistic effects of ASP are predominantly mediated by binding to the MC1R. Studies on primary cultures of follicular melanocytes established from three different isogenic mouse strains, namely C57 BL6 E+/E+ (which expresses the wild-type MC1R), e/e (recessive yellow mice that express lossof-function MC1R), and ESO/ESO (somber mice that express constitutively active MC1R), that cannot be activated by aMSH clearly showed that the effects of agouti are only evident in melanocytes that express functional MC1R (Abdel-Malek et al., 2001). These results argue against the existence of a receptor other than MC1R that mediates the effects of ASP.
Role of Steroid Hormones Many studies have described the responses of melanoma cells 416
to a wide variety of hormones, including the steroid hormones estrogen and glucocorticoids (Abdel-Malek et al., 1988; Bhakoo et al., 1981; Sadoff et al., 1973). Some studies have shown that normal human melanocytes are a target for different steroid hormones (McLeod et al., 1994; Ranson et al., 1988). We and others have investigated the effects of vitamin D3 (cholecalciferol) and its hydroxylated metabolites on human melanocytes (Abdel-Malek et al., 1988; Mansur et al., 1988; Ranson et al., 1988). Interest in this hormone stemmed from the fact that it is synthesized in the skin upon sun exposure, and from the possibility that active hydroxylated vitamin D3 metabolites might mediate the melanogenic effects of UVR (Bikle et al., 1986; Holick, 1981). We found, using Western blot analysis, that human melanocytes express specific receptors for vitamin D3 (Abdel-Malek et al., 1988). We also showed that melanocytes respond to 1,25(OH)2 vitamin D3 with a decrease in tyrosinase activity. A similar, yet less remarkable, effect was observed using 25(OH)vitamin D3, and no effect was produced by cholecalciferol. In contrast, in vivo studies in which 1,25(OH)2 vitamin D3 was applied topically onto mice demonstrated that the hormone increases the number of DOPA-positive melanocytes, indicating an increase in their melanogenic activity. Additionally, 1,25(OH)2 vitamin D3 augmented the melanogenic effect of UVR on murine skin. Contrary to these findings, Mansur et al. (1988) found no effect of 1,25(OH)2 vitamin D3, cholecalciferol, previtamin D3, lumisterol, or provitamin D3 on human melanocytes in vitro. Also, they could not detect any specific binding of vitamin D3 using sucrose density gradient analysis, or receptor binding assays utilizing radiolabeled 1,25(OH)2 vitamin D3. In yet another study, Ranson et al. (1988) reported that human melanocytes bound 1,25(OH)2 vitamin D3 with a high affinity and responded to this hormone with increased tyrosinase activity and stimulation of the activity of 25(OH)D3-24hydroxylase. The differences among these findings could be partially attributed to the differences in the melanocyte culture conditions used by the different investigators. The cutaneous effects of vitamin D3, particularly on human pigmentation, deserve to be reinvestigated, as this hormone is now used clinically, e.g. for the treatment of psoriasis. The effects of sex steroid hormones (androgens and estrogens) on cutaneous pigmentation have been recognized for a long time (Hamilton, 1941; Hamilton and Hubert, 1938). The increased pigmentation of the areola and genitalia has mostly been attributed to these hormones (Snell, 1964). Changes in the levels of female sex hormones during pregnancy have been implicated in the skin darkening seen in melasma (Mosher et al., 1987). Estrogens have also been investigated for their effects on cultured human melanocytes. Ranson et al. (1988) first reported that b-estradiol resulted in a dose-dependent increase in tyrosinase activity that was accompanied by a reduction in cellular proliferation. More recently, the same investigative group again reported similar responses of human melanocytes to 17-b-estradiol, effects that were evident at a concentration as low as 10–11 M (McLeod et al., 1994). Both a- and b-estradiol had similar effects, whereas estriol was less
HUMAN PIGMENTATION
potent than either, and estrone was the least effective. Surprisingly, no specific receptors for estrogens could be detected in melanocytes. Among the different melanocyte lines tested, 65% responded as described above to estrogens, and the response did not correlate with constitutive pigmentation. Whether or not melanocytes from male or female donors differ in their responses to sex hormones is worthy of investigation.
Perspectives Cutaneous pigmentation is a genetically determined trait that is regulated by a complexity of intracellular enzymes and factors. In addition, extracellular endocrine, paracrine, and autocrine factors contribute to the regulation of the melanocyte (Fig. 20.1). A major environmental regulator of cutaneous pigmentation is UVR from sun exposure. It is becoming recognized that the response of melanocytes to UVR is not only direct, but also indirect, as UVR induces the synthesis of a wide array of paracrine and autocrine factors. Molecular and cellular studies, exemplified by the demonstrations that human melanocytes express the MC1R and respond to melanocortins, and that these cells respond to endothelins, provided unequivocal evidence that such factors play a crucial role in the regulation of melanocyte function and response to UVR. The network of cutaneous factors activated by UVR may prove to be critical for the maintenance of genomic stability of human melanocytes in the face of UVR-induced DNA damage, and thus prevention of photocarcinogenesis. The lessons learned from mouse genetic studies linking abnormalities of coat color to specific genetic loci are enabling us to unravel the role of genes coding for particular hormones or their receptors in an array of human pigmentary disorders.
References Abdel-Malek, Z., V. B. Swope, N. Amornsiripanitch, and J. J. Nordlund. In vitro modulation of proliferation and melanization of S91 melanoma cells by prostaglandins. Cancer Res. 47:3141– 3146, 1987. Abdel-Malek, Z. A., R. Ross, J. W. Pike, L. Trinkle, V. Swope, and J. J. Nordlund. Hormonal effects of vitamin D3 on epidermal melanocytes. J. Cell. Physiol. 136:273–280, 1988. Abdel-Malek, Z., V. B. Swope, J. Pallas, K. Krug, and J. J. Nordlund. Mitogenic, melanogenic and cAMP responses of cultured neonatal human melanocytes to commonly used mitogens. J. Cell. Physiol. 150:416–425, 1992. Abdel-Malek, Z., V. Swope, C. Collins, R. Boissy, H. Zhao, and J. Nordlund. Contribution of melanogenic proteins to the heterogeneous pigmentation of human melanocytes. J. Cell Sci. 106: 1323–1331, 1993. Abdel-Malek, Z., V. Swope, D. Smalara, G. Babcock, S. Dawes, and J. Nordlund. Analysis of the UV induced melanogenesis and growth arrest of human melanocytes. Pigment Cell Res. 7:326–332, 1994. Abdel-Malek, Z., V. B. Swope, I. Suzuki, C. Akcali, M. D. Harriger, S. T. Boyce, K. Urabe, and V. J. Hearing. Mitogenic and melanogenic stimulation of normal human melanocytes by melanotropic peptides. Proc. Natl. Acad. Sci. USA 92:1789–1793, 1995.
Abdel-Malek, Z. A., M. C. Scott, M. Furumura, M. L. Lamoreux, M. Ollmann, G. S. Barsh, and V. J. Hearing. The melanocortin 1 receptor is the principal mediator of the effects of agouti signaling protein on mammalian melanocytes. J. Cell Sci. 114:1019–1024, 2001. Barker, D., K. Dixon, E. E. Medrano, D. Smalara, S. Im, D. Mitchell, G. Babcock, and Z. A. Abdel-Malek. Comparison of the responses of human melanocytes with different melanin contents to ultraviolet B irradiation. Cancer Res. 55:4041–4046, 1995. Bhakoo, H. S., R. J. Milholland, R. Lopez, C. Karakousis, and F. Rosen. High incidence and characterization of glucocorticoid receptors in human malignant melanoma. J. Natl. Cancer Inst. 66:21–25, 1981. Bikle, D. D., M. K. Nemanic, E. Gee, and P. Elias. 1,25 Dihydroxyvitamin D3 production by human keratinocytes. J. Clin. Invest. 78:557–566, 1986. Black, A. K., N. Fincham, M. W. Greaves, and C. N. Hensby. Time course changes in levels of arachidonic acid and prostaglandins D2, E2, F2a in human skin following ultraviolet B irradiation. Br. J. Clin. Pharmacol. 10:453–457, 1980. Blanchard, S. G., C. O. Harris, O. R. R. Ittoop, J. S. Nichols, D. J. Parks, A. T. Truesdale, and W. O. Wilkison. Agouti antagonism of melanocortin binding and action in the B16F10 murine melanoma cell line. Biochemistry 34:10406–10411, 1995. Box, N. F., J. R. Wyeth, L. E. O’Gorman, N. G. Martin, and R. A. Sturm. Characterization of melanocyte stimulating hormone receptor variant alleles in twins with red hair. Hum. Mol. Genet. 6:1891–1897, 1997. Bultman, S. J., E. J. Michaud, and R. P. Woychik. Molecular characterization of the mouse agouti locus. Cell 71:1195–1204, 1992. Bustamante, J., L. Bredeston, G. Malanga, and J. Mordoh. Role of melanin as a scavenger of active oxygen species. Pigment Cell Res. 6:348–353, 1993. Chakraborty, A., and J. Pawelek. MSH receptors in immortalized human epidermal keratinocytes: a potential mechanism for coordinate regulation of the epidermal-melanin unit. J. Cell. Physiol. 157:344–350, 1993. Chakraborty, A. K., Y. Funasaka, A. Slominski, G. Ermak, J. Hwang, J. M. Pawelek, and M. Ichihashi. Production and release of proopiomelanocortin (POMC) derived peptides by human melanocytes and keratinocytes in culture: regulation by ultraviolet B. Biochim. Biophys. Acta 1313:130–138, 1996. Chedekel, M. R., S. K. Smith, P. W. Post, A. Pokora, and D. L. Vessell. Photodestruction of pheomelanin: role of oxygen. Proc. Natl. Acad. Sci. USA 75:5395–5399, 1978. Chhajlani, V., and J. E. S. Wikberg. Molecular cloning and expression of the human melanocyte stimulating hormone receptor cDNA. FEBS Lett. 309:417–420, 1992. De Luca, M., W. Siegrist, S. Bondanza, M. Mathor, R. Cancedda, and A. N. Eberle. aMelanocyte stimulating hormone (aMSH) stimulates normal human melanocyte growth by binding to high-affinity receptors. J. Cell Sci. 105:1079–1084, 1993. Donatien, P. D., G. Hunt, C. Pieron, J. Lunec, A. Taïeb, and A. J. Thody. The expression of functional MSH receptors on cultured human melanocytes. Arch. Dermatol. Res. 284:424–426, 1992. Duval, C., M. Regnier, and R. Schmidt. Distinct melanogenic response of human melanocytes in mono-culture, in co-culture with keratinocytes and in reconstructed epidermis, to UV exposure. Pigment Cell Res. 14:348–355, 2001. Eller, M. S., M. Yaar, and B. A. Gilchrest. DNA damage and melanogenesis. Nature 372:413–414, 1994. Epstein, J. H. Photocarcinogenesis, skin cancer and aging. J. Am. Acad. Dermatol. 9:487–502, 1983. Felix, C. C., J. S. Hyde, T. Sarna, and R. C. Sealy. Melanin photoreaction in aerated media: electron spin resonance evidence of production of superoxide and hydrogen peroxide. Biochem. Biophys. Res. Commun. 84:335–341, 1978. Friedmann, P. S., and B. A. Gilchrest. Ultraviolet radiation directly
417
CHAPTER 20 induces pigment production by cultured human melanocytes. J. Cell. Physiol. 133:88–94, 1987. Fuller, B. B., D. Rungta, K. Iozumi, G. E. Hoganson, T. D. Corn, V. A. Cao, S. T. Ramadan, and K. C. Owens. Hormonal regulation of melanogenesis in mouse melanoma and in human melanocytes. Ann. N. Y. Acad. Sci. 680:302–319, 1993. Gilchrest, B. A., F. B. Blog, and G. Szabo. Effects of aging and chronic sun exposure on melanocytes in human skin. J. Invest. Dermatol. 73:141–143, 1979. Gordon, P. R., C. P. Mansur, and B. A. Gilchrest. Regulation of human melanocyte growth, dendricity, and melanization by keratinocyte derived factors. J. Invest. Dermatol. 92:565–572, 1989. Greenstein Baynash, A., K. Hosoda, A. Giaid, J. A. Richardson, N. Emoto, R. E. Hammer, and M. Yanagisawa. Interaction of endothelin-3 with endothelin-B receptor is essential for development of epidermal melanocytes and enteric neurons. Cell 79:1277–1285, 1994. Hachiya, A., A. Kobayashi, A. Ohuchi, Y. Takema, and G. Imokawa. The paracrine role of stem cell factor/c-kit signaling in the activation of human melanocytes in ultraviolet-B-induced pigmentation. J. Invest. Dermatol. 116:578–586, 2001. Halaban, R. Responses of cultured melanocytes to defined growth factors. Pigment Cell Res. Suppl. 1:18–26, 1988. Halaban, R., B. S. Kwon, S. Ghosh, P. Delli-Bovi, and A. Baird. bFGF is an autocrine growth factor for human melanomas. Oncogene Res. 3:177–186, 1988a. Halaban, R., R. Langdon, N. Birchall, C. Cuono, A. Baird, G. Scott, G. Moellmann, and J. McGuire. Basic fibroblast growth factor from human keratinocytes is a natural mitogen for melanocytes. J. Cell Biol. 107:1611–1619, 1988b. Halaban, R., S. H. Pomerantz, S. Marshall, D. T. Lambert, and A. B. Lerner. Regulation of tyrosinase in human melanocytes grown in culture. J. Cell Biol. 97:480–488, 1983. Hamilton, J. B. Significance of sex hormones in tanning of the skin of women. Proc. Soc. Exp. Biol. Med. 40:502–503, 1941. Hamilton, J. B., and G. Hubert. Photographic nature of tanning of the human skin as shown by studies of male hormone therapy. Science 88:481, 1938. Hearing, V. J., and K. Tsukamoto. Enzymatic control of pigmentation in mammals. FASEB J. 5:2902–2909, 1991. Holick, M. F. The cutaneous photosynthesis of previtamin D3: a unique photoendocrine system. J. Invest. Dermatol. 77:51–58, 1981. Hosoda, K., R. E. Hammer, J. A. Richardson, A. G. Baynash, J. C. Cheung, A. Giaid, and M. Yanagisawa. Targeted and natural (piebald-lethal) mutations of endothelin-B receptor gene produce megacolon associated with spotted coat color in mice. Cell 79:1267–1276, 1994. Hunt, G., C. Todd, J. E. Cresswell, and A. J. Thody. a-Melanocyte stimulating hormone and its analogue Nle4DPhe7 a-MSH affect morphology, tyrosinase activity and melanogenesis in cultured human melanocytes. J. Cell Sci. 107:205–211, 1994a. Hunt, G., C. Todd, S. Kyne, and A.J. Thody. ACTH stimulates melanogenesis in cultured human melanocytes. J. Endocrinol. 140:R1–R3, 1994b. Hunt, G., S. Kyne, K. Wakamatsu, S. Ito, and A. J. Thody. Nle4DPhe7 a-melanocyte-stimulating hormone increases the eumelanin: phaeomelanin ratio in cultured human melanocytes. J. Invest. Dermatol. 104:83–85, 1995. Im, S., O. Moro, F. Peng, E. E. Medrano, J. Cornelius, G. Babcock, J. Nordlund, and Z. Abdel-Malek. Activation of the cAMP pathway by a-melanotropin mediates the response of human melanocytes to UVB light. Cancer Res. 58:47–54, 1998. Imokawa, G., Y. Yada, and M. Miyagishi. Endothelins secreted from human keratinocytes are intrinsic mitogens for human melanocytes. J. Biol. Chem. 267:24675–24680, 1992.
418
Imokawa, G., M. Miyagishi, and Y. Yada. Endothelin-1 as a new melanogen: coordinated expression of its gene and the tyrosinase gene in UVB-exposed human epidermis. J. Invest. Dermatol. 105:32–37, 1995. Inoue, A., M. Yanagisawa, S. Kimura, Y. Kasuya, T. Miyauchi, K. Goto, and T. Masaki. The human endothelin family: three structurally and pharmacologically distinct isopeptides predicted by three separate genes. Proc. Natl. Acad. Sci. USA 86:2863–2867, 1989. Iwata, M., T. Corn, S. Iwata, M. A. Everett, and B. B. Fuller. The relationship between tyrosinase activity and skin color in human foreskins. J. Invest. Dermatol. 95:9–15, 1990. Jackson, I. J. A cDNA encoding tyrosinase-related protein maps to the brown locus in mice. Proc. Natl. Acad. Sci. USA 85:4392–4396, 1988. Kadekaro, A. L., R. J. Kavanagh, K. Wakamatsu, S. Ito, M. A. Pipitone, and Z. A. Abdel-Malek. Cutaneous photobiology. The melanocyte vs. the sun: who will win the final round? Pigment Cell Res. 16:434–447, 2003. Kadekaro, A. L., H. Kanto, R. Kavanagh, S. Terzieva, J. Hauser, N. Kobayashi, S. Schwemberger, J. Cornelius, G. Babcock, H. G. Shertzer, G. Scott, and Z. Abdel-Malek. a-Melanocortin and endothelin-1 promote the survival of human melanocytes by activating anti-apoptotic pathways and enhancing the repair of DNA photoproduct. Cancer Res. 65:4292–4299, 2005. Kaidbey, K. H., P. Poh Agin, R. M. Sayre, and A. M. Kligman. Photoprotection by melanin — a comparison of black and Caucasian skin. J. Am. Acad. Dermatol. 1:249–260, 1979. Kanetsky, P. A., J. Swoyer, S. Panossian, R. Holmes, D. Guerry, and T. R. Rebbeck. A polymorphism in the agouti signaling protein gene is associated with human pigmentation. Am. J. Hum. Genet. 70:770–775, 2002. Kauser, S., K. U. Schallreuter, A. J. Thody, C. Gummer, and D. J. Tobin. Regulation of human epidermal melanocyte biology by betaendorphin. J. Invest. Dermatol. 120:1073–1080, 2003. Kauser, S., A. J. Thody, K. U. Schallreuter, C. L. Gummer, and D. J. Tobin. beta-Endorphin as a regulator of human hair follicle melanocyte biology. J. Invest. Dermatol. 123:184–195, 2004. Kippenberger, S., A. Bernd, S. Loitsch, A. Ramirez-Bosca, J. BereiterHahn, and H. Holzmann. a-MSH is expressed in cultured human melanocytes and keratinocytes. Eur. J. Dermatol. 5:395–397, 1995. Kobayashi, N., T. Muramatsu, Y. Yamashina, T. Shirai, T. Ohnishi, and T. Mori. Melanin reduces ultraviolet-induced DNA damage formation and killing rate in cultured human melanoma cells. J. Invest. Dermatol. 101:685–689, 1993. Kobza Black, A., M. W. Greaves, C. N. Hensby, and N. A. Plummer. Increased prostaglandins E2 and F2a in human skin at 6 and 24 h after ultraviolet B irradiation (290–320 nm). Br. J. Clin. Pharmacol. 5:431–436, 1978. Köck, A., T. Schwarz, R. Kirnbauer, A. Urbanski, P. Perry, J. C. Ansel, and T. A. Luger. Human keratinocytes are a source for tumor necrosis factor a: evidence for synthesis and release upon stimulation with endotoxin or ultraviolet light. J. Exp. Med. 172:1609–1614, 1990. Kupper, T. S., A. O. Chua, P. Flood, J. McGuire, and U. Gubler. Interleukin 1 gene expression in cultured human keratinocytes is augmented by ultraviolet irradiation. J. Clin. Invest. 80:430–436, 1987. Kwon, H. Y., S. J. Bultman, C. Löffler, W.-J. Chen, P. J. Furdon, J. G. Powell, A.-L. Usala, W. Wilkison, I. Hansmann, and R. P. Woychik. Molecular structure and chromosomal mapping of the human homolog of the agouti gene. Proc. Natl. Acad. Sci. USA 91: 9760–9764, 1994. Leikauf, G. D., Z. A. Abdel-Malek, V. B. Swope, C. A. Doupnik, and J. J. Nordlund. Constitutive biosynthesis of 12-hydroxy-5,8,10,14eicosatetraenoic acid and 6-keto prostaglandin F1a by human melanocytes and Cloudman S91 melanoma cells. In: Pros-
HUMAN PIGMENTATION taglandins, Leukotrienes and Cancer, S. Hammerstrom, and L. W. Marnett (eds). Boston: Kluwer Academic Press, 1994. Lerner, A. B., and J. S. McGuire. Melanocyte-stimulating hormone and adrenocorticotrophic hormone. Their relation to pigmentation. N. Engl. J. Med. 270:539–546, 1964. Levine, N., S. N. Sheftel, T. Eytan, R. T. Dorr, M. E. Hadley, J. C. Weinrach, G. A. Ertl, K. Toth, and V. J. Hruby. Induction of skin tanning by the subcutaneous administration of a potent synthetic melanotropin. J. Am. Med. Assoc. 266:2730–2736, 1991. Libow, L. F., S. Scheide, and V. A. DeLeo. Ultraviolet radiation acts as an independent mitogen for normal human melanocytes in culture. Pigment Cell Res. 1:397–401, 1988. Lu, D., D. Willard, I. R. Patel, S. Kadwell, L. Overton, T. Kost, M. Luther, W. Chen, R. P. Woychik, W. O. Wilkison, and R. D. Cone. Agouti protein is an antagonist of the melanocyte-stimulatinghormone receptor. Nature 371:799–802, 1994. Mansur, C. P., P. R. Gordon, S. Ray, M. F. Holick, and B. A. Gilchrest. Vitamin D, its precursors, and metabolites do not affect melanization of cultured human melanocytes. J. Invest. Dermatol. 91:16–21, 1988. McLeod, S. D., M. Ranson, and R. S. Mason. Effects of estrogens on human melanocytes in vitro. J. Steroid Biochem. 49:9–14, 1994. Medrano, E. E., J. Z. Farooqui, R. E. Boissy, Y. L. Boissy, B. Akadiri, and J. J. Nordlund. Chronic growth-stimulation of human adult melanocytes by inflammatory mediators in vitro: implications for nevus formation and initial steps in melanocyte oncogenesis. Proc. Natl. Acad. Sci. USA 90:1790–1794, 1993. Menon, I. A., and H. F. Haberman. Mechanisms of action of melanins. Br. J. Dermatol. 97:109–112, 1977. Menon, I. A., S. Persad, N. S. Ranadive, and H. F. Haberman. Photobiological effects of eumelanin and pheomelanin. In: Biological, Molecular and Clinical Aspects of Pigmentation, J. T. Bagnara, S. N. Klaus, E. Paul, and M. Schartl (eds). Tokyo: University of Tokyo Press, 1985, pp. 77–86. Morelli, J. G., J. J. Yohn, M. B. Lyons, R. C. Murphy, and D. A. Norris. Leukotrienes C4 and D4 as potent mitogens for cultured human melanocytes. J. Invest. Dermatol. 93:719–722, 1989. Morison, W. L. What is the function of melanin? Arch. Dermatol. 121:1160–1163, 1985. Mosher, D. B., T. B. Fitzpatrick, J.-P. Ortonne, and Y. Hori. Disorders of pigmentation. In: Dermatology in General Medicine, 3rd edn, vol. 1, T. B. Fitzpatrick, A. Z. Eisen, K. Wolff, I. M. Freedberg, and K. F. Austen (eds). New York: McGraw-Hill, 1987, pp. 794– 876. Mountjoy, K. G. The human melanocyte stimulating hormone receptor has evolved to become “super-sensitive” to melanocortin peptides. Mol. Cell Endocrinol. 102:R7–R11, 1994. Musk, P., and P. G. Parsons. Resistance of pigmented human cells to killing by sunlight and oxygen radicals. Photochem. Photobiol. 46:489–494, 1987. Nordlund, J. J., and Z. A. Abdel-Malek. Mechanisms for postinflammatory hyperpigmentation and hypopigmentation. In: Advances in Pigment Cell Research. Proceedings of the XIII International Pigment Cell Society, J. Bagnara (ed.). New York: Alan R. Liss, 1988, pp. 219–236. Oxholm, A., P. Oxholm, B. Staberg, and K. Bendtzen. Immunohistological detection of interleukin 1-like molecules and tumor necrosis factor in human epidermis before and after UVB-irradiation in vivo. Br. J. Dermatol. 118:369–376, 1988. Palmer, J. S., D. L. Duffy, N. F. Box, J. F. Aitken, L. E. O’Gorman, A. C. Green, N. K. Hayward, N. G. Martin, and R. A. Sturm. Melanocortin-1 receptor polymorphisms and risk of melanoma: Is the association explained solely by pigmentation phenotype? Am. J. Hum. Genet. 66:176–186, 2000. Pathak, M. A., Y. Hori, G. Szabo, and T. B. Fitzpatrick. The photobiology of melanin pigmentation in human skin. In: Biology of Normal and Abnormal Melanocytes, T. Kawamura, T. B.
Fitzpatrick, and M. Seiji (eds). Baltimore: University Park Press, 1971, pp. 149–169. Pathak, M. A., K. Jimbow, and T. Fitzpatrick. Photobiology of pigment cells. In: Phenotypic Expression in Pigment Cells, M. Seiji (ed.). Tokyo: University of Tokyo Press, 1980, pp. 655–670. Pittelkow, M. R., and G. D. Shipley. Serum-free culture of normal human melanocytes: Growth kinetics and growth factor requirements. J. Cell. Physiol. 140:565–576, 1989. Puffenberger, E. G., K. Hosoda, S. S. Washington, K. Nakao, D. deWit, M. Yanagisawa, and A. Chakravarti. A missense mutation of the endothelin-B receptor gene in multigenic Hirschsprung’s disease. Cell 79:1257–1266, 1994. Quevedo, W. C., Jr., R. D. Fleischmann, and T. J. Holstein. Pheomelanogenesis in the mouse: a review of its genetic and developmental features. In: Pigment Cell 1981: Phenotypic Expression in Pigment Cells, M. Seiji (ed.). Tokyo: University of Tokyo Press, 1981, pp. 129–137. Ranson, M., S. Posen, and R. S. Mason. Human melanocytes as a target tissue for hormones: in vitro studies with 1a-25,dihydroxyvitamin D3, a-melanocyte stimulating hormone, and b-estradiol. J. Invest. Dermatol. 91:593–598, 1988. Robbins, L. S., J. H. Nadeau, K. R. Johnson, M. A. Kelly, L. RoselliRehfuss, E. Baack, K. G. Mountjoy, and R. D. Cone. Pigmentation phenotypes of variant extension locus alleles result from point mutations that alter MSH receptor function. Cell 72:827–834, 1993. Rubanyi, G. M., and M. A. Polokoff. Endothelins: molecular biology, biochemistry, pharmacology, physiology, and pathophysiology. Pharmacol. Rev. 46:325–415, 1994. Sadoff, L., J. Winkley, and S. Tyson. Is malignant melanoma an endocrine-dependent tumor? The possible adverse effect of estrogen. Oncology 27:244–257, 1973. Sawyer, T. K., V. J. Hruby, M. E. Hadley, and M. H. Engel. aMelanocyte stimulating hormone: chemical nature and mechanism of action. Am. Zool. 23:529–540, 1983. Schauer, E., F. Trautinger, A. Kock, A. Schwarz, R. Bhardwaj, M. Simon, J. C. Ansel, T. Schwarz, and T. A. Luger. Proopiomelanocortin-derived peptides are synthesized and released by human keratinocytes. J. Clin. Invest. 93:2258–2262, 1994. Scott, M. C., K. Wakamatsu, S. Ito, A. L. Kadekaro, N. Kobayashi, J. Groden, R. Kavanagh, T. Takakuwa, V. Virador, V. J. Hearing, and Z. A. Abdel-Malek. Human melanocortin 1 receptor variants, receptor function and melanocyte response to ultraviolet radiation. J. Cell Sci. 115:2349–2355, 2002a. Scott, M. C., I. Suzuki, and Z. A. Abdel-Malek. Regulation of the human melanocortin 1 receptor expression in epidermal melanocytes by paracrine and endocrine factors, and by UV radiation. Pigment Cell Res. 15:433–439, 2002b. Scott, G., S. Leopardi, S. Printup, N. Malhi, M. Seiberg, and R. Lapoint. Proteinase-activated receptor-2 stimulates prostaglandin production in keratinocytes: analysis of prostaglandin receptors on human melanocytes and effects of PGE2 and PGF2a on melanocyte dendricity. J. Invest. Dermatol. 122:1214–1224, 2004. Sheehan, J. M., N. Cragg, C. A. Chadwick, C. S. Potten, and A. R. Young. Repeated ultraviolet exposure affords the same protection against DNA photodamage and erythema in human skin types II and IV but is associated with faster DNA repair in skin type IV. J. Invest. Dermatol. 118:825–829, 2002. Silvers, W. K. The Coat Colors of Mice. A Model for Mammalian Gene Action and Interaction. New York: Springer-Verlag, 1979. Smit, N. P. M., A. A. Vink, R. M. Kolb, M.-J. S. T. Steenwinkel, P. T. M. van den Berg, F. van Nieuwpoort, L. Roza, and S. Pavel. Melanin offers protection against induction of cyclobutane pyrimidine dimers and 6–4 photoproducts by UVB in cultured human melanocytes. Photochem. Photobiol. 74:424–430, 2001. Smith, R., E. Healy, S. Siddiqui, N. Flanagan, P. M. Steijlen, I.
419
CHAPTER 20 Rosdahl, J. P. Jacques, S. Rogers, R. Turner, I. J. Jackson, M. A. Birch-Machin, and J. L. Rees. Melanocortin 1 receptor variants in Irish population. J. Invest. Dermatol. 111:119–122, 1998. Snell, R. S. Effect of the alpha melanocyte-stimulating hormone of the pituitary on mammalian epidermal melanocytes. J. Invest. Dermatol. 42:337–347, 1964. Sober, A. J., R. A. Lew, H. K. Koh, and R. L. Barnhill. Epidemiology of cutaneous melanoma. An update. Dermatol. Clin. 9:617–629, 1991. Suzuki, I., R. Cone, S. Im, J. Nordlund, and Z. Abdel-Malek. Binding capacity and activation of the MC1 receptors by melanotropic hormones correlate directly with their mitogenic and melanogenic effects on human melanocytes. Endocrinology 137:1627–1633, 1996. Suzuki, I., A. Tada, M. M. Ollmann, G. S. Barsh, S. Im, M. L. Lamoreux, V. J. Hearing, J. Nordlund, and Z. A. Abdel-Malek. Agouti signaling protein inhibits melanogenesis and the response of human melanocytes to a-melanotropin. J. Invest. Dermatol. 108:838–842, 1997. Suzuki, I., T. Kato, T. Motokawa, Y. Tomita, E. Nakamura, and T. Katagiri. Increase of pro-opiomelanocortin mRNA prior to tyrosinase, tyrosinase-related protein 1, dopachrome tautomerase, Pmel17/gp100, and P-protein mRNA in human skin after ultraviolet B irradiation. J. Invest. Dermatol. 118:73–78, 2002. Swope, V. B., Z. A. Abdel-Malek, L. Kassem, and J. J. Nordlund. Interleukins 1a and 6 and tumor necrosis factor-a are paracrine inhibitors of human melanocyte proliferation and melanogenesis. J. Invest. Dermatol. 96:180–185, 1991. Swope, V. B., D. N. Sauder, R. C. McKenzie, R. M. Sramkoski, K. A. Krug, G. F. Babcock, J. J. Nordlund, and Z. A. Abdel-Malek. Synthesis of interleukin-1a and b by normal human melanocytes. J. Invest. Dermatol. 102:749–753, 1994. Swope, V. B., E. E. Medrano, D. Smalara, and Z. Abdel-Malek. Longterm proliferation of human melanocytes is supported by the physiologic mitogens a-melanotropin, endothelin-1, and basic fibroblast growth factor. Exp. Cell Res. 217:453–459, 1995. Tada, A., I. Suzuki, S. Im, M. B. Davis, J. Cornelius, G. Babcock, J. J. Nordlund, and Z. A. Abdel-Malek. Endothelin-1 is a paracrine growth factor that modulates melanogenesis of human melanocytes and participates in their responses to ultraviolet radiation. Cell Growth Differ. 9:575–584, 1998. Tadokoro, T., N. Kobayashi, B. Z. Zmudzka, S. Ito, K. Wakamatsu, Y. Yamaguchi, K. S. Korossy, S. A. Miller, J. Z. Beer, and V. J. Hearing. UV-induced DNA damage and melanin content in human
420
skin differing in racial/ethnic origin. FASEB J. Published online April 8, 2003: express article 10.1096/fj.1002–0865fje, 2003. Takeuchi, T., T. Kobunai, and H. Yamamoto. Genetic control of signal transduction in mouse melanocytes. J. Invest. Dermatol. 92:239S242S, 1989. Tomita, Y., M. Iwamoto, T. Masuda, and H. Tagami. Stimulatory effect of prostaglandin E2 on the configuration of normal human melanocytes. J. Invest. Dermatol. 89:299–301, 1987. Urbanski, A., F. Trautinger, B. Brückler, P. Neuner, T. A. Luger, and T. Schwarz. Injection of a TNFa antiserum reduces sunburn cell formation in murine skin. J. Invest. Dermatol. 98:555(abstract), 1992. Vijayasaradhi, S., and A. N. Houghton. Purification of an autoantigenic 75-kDa human melanosomal glycoprotein. Int. J. Cancer 47:298–303, 1991. Voisey, J., N. F. Box, and A. van Daal. A polymorphism study of the human Agouti gene and its association with MC1R. Pigment Cell Res. 14:264–267, 2001. Vrieling, H., D. M. J. Duhl, S. E. Millar, K. A. Miller, and G. S. Barsh. Differences in dorsal and ventral pigmentation result from regional expression of the mouse agouti gene. Proc. Natl. Acad. Sci. USA 91:5667–5671, 1994. Wakamatsu, K., A. Graham, D. Cook, and A. J. Thody. Characterization of ACTH peptides in human skin and their activation of the melanocortin-1 receptor. Pigment Cell Res. 10:288–297, 1997. Wilson, B. D., M. M. Ollmann, L. Kang, M. Stoffel, G. I. Bell, and G. S. Barsh. Structure and function of ASP, the human homolog of the mouse agouti gene. Hum. Mol. Genet. 4:223–230, 1995. Wintzen, M., M. Yaar, J. P. H. Barbach, and B. A. Gilchrest. Proopiomelanocortin gene product regulation in keratinocytes. J. Invest. Dermatol. 106:673–678, 1996. Yada, Y., K. Higuchi, and G. Imokawa. Effects of endothelins on signal transduction and proliferation in human melanocytes. J. Biol. Chem. 266:18352–18357, 1991. Yen, T. T., A. M. Gill, L. G. Frigeri, G. S. Barsh, and G. L. Wolff. Obesity, diabetes, and neoplasia in yellow A(vy)/- mice: ectopic expression of the agouti gene. FASEB J. 8:479–488, 1994. Yohn, J. J., M. B. Lyons, and D. A. Norris. Cultured human melanocytes from black and white donors have different sunlight and ultraviolet A radiation sensitivities. J. Invest. Dermatol. 99:454–459, 1992. Yohn, J. J., J. G. Morelli, S. J. Walchak, K. B. Rundell, D. A. Norris, and M. R. Zamora. Cultured human keratinocytes synthesize and secrete endothelin-1. J. Invest. Dermatol. 100:23–26, 1993.
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
21
Paracrine Interactions of Melanocytes in Pigmentary Disorders Genji Imokawa
Introduction Over the past two decades since Eisinger and Marko (1982) first established human melanocytes in culture by supplementing them with a tumor promoter, phorbol ester, many cytokines, chemokines, chemicals, and eicosanoids have been discovered to be mitogens and/or melanogens for human melanocytes. In parallel, various kinds of cells in the skin have been shown to produce and secrete or release those growth factors in response to several stimuli, including ultraviolet irradiation. In relation to the tissue localization of cells secreting or releasing those factors and epidermal melanocytes as responders, melanogenic paracrine cytokine networks have been discovered to exist between melanocytes and other types of skin cells, including keratinocytes and fibroblasts, which regulate melanocyte function via the corresponding receptors (Imokawa et al., 1992a, 1995, 1996a, b, c, 1998a, b; Yada et al., 1991). Although these studies have usually used cultured skin cells, they have facilitated research directed toward elucidating regulatory mechanisms involved in melanocyte activation, as seen in several types of experimentally induced hyperpigmentation or in hyperpigmentary disorders. Thus, in vivo studies directed toward identifying intrinsic paracrine cytokines involved in hyperpigmentary disorders have been difficult in the absence of information about whether the up- or downregulation of cytokines and/or chemokines in the lesional skin is responsible for the constitutive activation or inactivation of melanocytes in those lesions. In part, this is due to the wide variety of cytokines or chemokines that are not directly related to melanocyte stimulation but are highly expressed in hyperpigmentary disorders because of the concomitant presence of other types of abnormal epidermal cells in addition to melanocytes. Thus, during our research to identify paracrine cytokines intrinsically involved in experimentally induced hyperpigmentation or those responsible for the stimulatory effects of conditioned medium from cultured keratinocytes or fibroblasts, we used six criteria to determine whether a cytokine is an intrinsic factor involved in epidermal hyperpigmentation, as follows: 1 The cytokine(s) should be highly expressed in the surrounding cells in response to several stimuli. 2 The cytokine(s) should exist in supernatants of cultures or in the epidermis at concentrations sufficient to stimulate melanocytes.
3 The stimulatory effect of culture supernatants on melanocytes should be neutralized by an antibody to the cytokine if it is secretable. 4 The cytokine(s) should have the potential to activate melanocytes at physiological concentrations in vitro. 5 The hyperpigmentation induced should be suppressed by antibodies that inhibit the corresponding receptor or by receptor antagonists in vivo. 6 Mutations in the gene encoding the cytokine or its receptor should produce an aberrant phenotype. According to these six criteria, we have characterized the melanogenic paracrine network in the skin associated with the stimulation of melanocyte function in the epidermis, the activation or inactivation of which leads to the hyper- or hypopigmentation associated with epidermal pigmentary disorders. Figure 21.1 depicts such a melanogenic paracrine network between skin cells, which serves to upregulate melanocyte functions. With respect to melanocyte/keratinocyte interactions, these include endothelin-1 (ET-1) (which is secreted by keratinocytes in response to UVB irradiation) (Imokawa et al., 1992a, 1995; Yada et al., 1991), membrane-bound stem cell factor (mSCF) (which is stimulated in production by keratinocytes in response to UVB irradiation) (Hachiya et al., 2001), granulocyte–macrophage colony-stimulating factor (GM-CSF) (which is secreted by keratinocytes in response to UVA irradiation) (Imokawa et al., 1996c), and growth-related oncogene a (GROa) (which has increased secretion by keratinocytes in response to allergic inflammation) (Imokawa et al., 1998a). With respect to melanocyte/fibroblast interactions, they include soluble-type stem cell factor (sSCF) and hepatocyte growth factor (HGF) (which are secreted by proliferating dermal fibroblasts) (Imokawa et al., 1998b). Consistent with these in vitro findings on melanogenic paracrine cytokine networks, we have found that the upregulation of such networks is intrinsically involved in vivo in the stimulation of melanocyte functions in several hyperpigmentary disorders, such as UVB melanosis (Imokawa et al., 1995), lentigo senilis (LS) (Kadono et al., 2001), seborrheic keratosis (SK) (Manaka et al., 2001; Teraki et al., 1996), Riehl’s melanosis (Imokawa and Kawai, 1987; Imokawa et al., 1992a, 1998a), café-au-lait macules (Okazaki et al., 2003), and dermatofibroma (DF) (Shishido et al., 2001). This chapter focuses on epidermal hyper- or hypopigmentary disorders, including UVB melanosis. The activated paracrine interactions between keratinocytes or fibroblasts and melanocytes responsible for increased pigmentation in the 421
CHAPTER 21
Keratinocyte UVA UVB
Melanocyte GM–CSF
TK–R
Cell response DNA synthesis Melanin synthesis
c–met IL–1α
IL–1 PKA
ET–1
MAPkinase
R Gs cAMP
GROa
Gi
R G
AC
c–met ATP PKC
PLC
Ca
HGF
c–kit bFGF
DG
Inflammation
SCF
IP3 PIP2
mSCF
Aging
c–kit
Fibroblast
Fig. 21.1. Melanogenic paracrine cytokine networks between cultured skin cells.
epidermis are described with special reference to the expression of paracrine cytokines and their corresponding receptors.
Endothelin-1/ETB Receptor Interactions between Keratinocytes and Melanocytes ET-1 was first identified in the culture media of porcine endothelial cells and is a 21-residue peptide with a potent vasoconstrictive activity (Yanagisawa et al., 1988). To date, three distinct genes encoding three closely related peptides, ET1, ET-2, and ET-3, have been identified (Inoue et al., 1989). ETs have been reported to bind to two types of receptors, endothelin A receptor (ETAR) and endothelin B receptor (ETBR), which bind all three ETs with different or similar affinities respectively (Arai et al., 1993; Sakamoto et al., 1993; Sakurai et al., 1990). Our study using ETAR and ETBR antagonists to study the proliferation of ET-stimulated cultured human melanocytes revealed that ETBR is predominantly expressed in human melanocytes, in contrast to the predominant expression of ETAR in human endothelial cells. It has been reported that ETs have hormonal regulatory activities in 422
various types of cells, including melanocytes, and in target organs via a receptor-mediated biochemical mechanism (Brenner et al., 1989; Resink et al., 1989; Reynolds et al., 1989; Watanabe et al., 1989). ET isopeptides are first expressed as corresponding ~200residue inactive prepropolypeptides (prepro-endothelins) that are encoded by distinct genes (Inoue et al., 1989). After removal of their signal peptides during their early processing, the propeptides are cleaved at pairs of basic amino acids to yield the intermediate Big ETs. This early processing step is presumably involved with furin, a prohormone convertase of the constitutive secretory pathway (Laporte et al., 1993). Big ETs are then further cleaved by an endopeptidase termed endothelin-converting enzyme (ECE) at Trp-21-Val-/Ile-22 to produce biologically active ETs, which are mature 21-residue peptides (Yanagisawa et al., 1988). We have recently characterized the properties of ECE-1a in human keratinocytes, which are identical to those in endothelial cells (Hachiya et al., 2002).
UVB Melanosis In 1991, we found for the first time that ET-1 is produced and
Tyrosinase TRP-1 GAPDH β-actin ET-1 bFGF IL-1α TNFα IFNγ
Tyrosinase TRP-1 GAPDH β-actin ET-1 bFGF IL-1α TNFα IFNγ
Fig. 21.2. RT-PCR analysis of UVB (2 MED)exposed human epidermis for tyrosinase, ET-1, IL-1a, and TNFa.
Tyrosinase TRP-1 GAPDH β-actin ET-1 bFGF IL-1α TNFα IFNγ
PARACRINE INTERACTIONS OF MELANOCYTES IN PIGMENTARY DISORDERS
Day 0
Day 2
Day 5
secreted by cultured human keratinocytes and can act as a mitogen and a melanogen for human melanocytes (Imokawa et al., 1992a; Yada et al., 1991). The production and subsequent secretion of ET-1 by human keratinocytes was markedly stimulated by UVB irradiation. This evidence prompted us to investigate the possibility that an accentuated ET-1/ETBR cascade is responsible for the increased pigmentation in the epidermis of UVB melanosis. As expected, in real-time quantitative or semiquantitative reverse transcriptase polymerase chain reaction (RT-PCR) analysis of UVB-exposed human epidermis, as late as 5–7 days after irradiation, there is a significant increase in the expression of ET-1 mRNA transcripts, which is accompanied by an increased expression in mRNA transcripts encoding the key melanogenic enzyme, tyrosinase (Fig. 21.2) (Hachiya et al., 2004; Imokawa et al., 1995, 1997). A little earlier than that, the gene expression of interleukin (IL)-1a (known to be primarily responsible for stimulating ET-1 secretion in UVB-exposed human keratinocytes) is also accentuated in UVB-exposed human epidermis. Consistent with this, ET-1 secretion is also increased in UVB (2 MED)exposed human epidermis in organ culture in concert with the increased secretion of IL-1a, compared with nonUVB-exposed human epidermis. Immunohistochemistry with an antibody to ET-1 demonstrates a marked increase in immunostaining throughout the UVB-exposed epidermis (at 7 days after irradiation) compared with nonUVB-exposed human epidermis (Hachiya et al., 2004) (Fig. 21.3). Real-time quantitative RTPCR analysis demonstrates that levels of ET-1 mRNA transcripts are significantly upregulated with a peak at 7 days after UVB irradiation, and remain at a higher level than before irradiation until 25 days after irradiation. In concert with the increased expression of ET-1, mRNA transcript levels for its receptor, ETBR, are also significantly upregulated with a peak at 7 days after irradiation in the UVB-exposed human epidermis compared with the nonexposed human epidermis. Western blotting analysis also reveals an increased expression of ETBR protein in the UVB-exposed human epidermis at
UVB
NonUVB
Fig. 21.3. Immunohistochemistry of ET-1 in UVB (2 MED)-exposed human forearm skin at 7 days after irradiation (see also Plate 21.1, pp. 494–495).
7 days after irradiation (Hachiya et al., 2004). Interestingly, the expression pattern of the ET-1/ETBR cascade following UVB irradiation is considerably delayed compared with the time course of the expression of SCF, as described below. The time course of the expression of ET-1/ETBR mRNA transcripts is shown in Figure 21.4 in comparison with those encoding SCF/c-KIT (as described below). The preferential role of the late expression of ET-1 following the expression of SCF in stimulating melanogenesis in melanocytes may be substantiated by the fact that the exogenous addition of sSCF stimulates the expression of ETBR in human melanocytes (Hachiya et al., 2004), resulting in acceleration of the binding of ET-1 to its receptor on melanocytes. 423
CHAPTER 21
Analysis UVB irradiation (288 mJ/cm2)
(day)
0
1
ACK2 injection (5 mg/50 ml)
2
3
4
Skin color Numbers of DOPA-positive cells
5
6
7
8
SCF
9
10
25
ET-1
ETBR
C-Kit
Fig. 21.4. The time course of expression of SCF/c-KIT and ET-1/ETBR mRNA transcripts following 2 MED UVB-exposed human epidermis in comparison with tyrosinase expression and pigmentation.
Tyrosinase
Pigmentation
Lentigo Senilis Lentigo senilis (LS) is the skin condition of common aging spots with accentuated epidermal pigmentation. In LS lesional skin, the number of tyrosinase-immunopositive melanocytes is increased twofold over the perilesional epidermis (Kadono et al., 2001). Consistent with the increased amount of tyrosinase within the lesional melanocytes, RT-PCR analysis for tyrosinase mRNA transcripts demonstrates that there is an increased expression of those transcripts (average 2.3-fold, P < 0.005, n = 7) in the lesional epidermis compared with the perilesional controls. As there are some similarities in the histopathology and localized eruptions, which predominantly affect sun-exposed areas in UVB-induced melanosis and in LS, and as among the known keratinocyte-derived cytokines pro424
10 nMET-1 300 ET-1(–) ET-1(+)
Thymidine incorporation (% control)
The specific contribution of the ET-1/ETBR linkage to melanocyte activation in UVB-exposed human epidermis is corroborated by the fact that an extract of M. chamomilla, which is a potent antagonist of the ETBR (Imokawa et al., 1997) and which abrogates ET-1-stimulated DNA synthesis in human melanocytes (Fig. 21.5) but does not inhibit tyrosinase in human melanocytes (Imokawa et al., 1997), is significantly effective in preventing the UVB-induced pigmentation of human forearm skin when applied topically immediately after UVB irradiation (Fig. 21.6) (Imokawa et al., 1997). Taken together, these results strongly suggest that UVB irradiation causes epidermal keratinocytes to produce and secrete ET-1, which triggers melanocytes in their vicinity to transduce intracellular signaling via accentuated ETBR function and leads to the stimulation of melanogenesis in UVB-induced melanosis.
200
100
0 0
3
15
30
M. chamomilla concentration (µg/ml) Fig. 21.5. Inhibitory effect of an M. chamomilla extract on ET-1stimulated DNA synthesis in cultured human melanocytes.
PARACRINE INTERACTIONS OF MELANOCYTES IN PIGMENTARY DISORDERS
duced in response to their proliferation, ET-1 is the only cytokine that has dual stimulatory effects on DNA synthesis and melanogenesis of human melanocytes (Imokawa et al., 1996a; Yada et al., 1991), we examined whether ET production and secretion is accentuated in the epidermis of LS. RTPCR analysis demonstrates accentuated expression of transcripts for ET-1 (average 3.2-fold, P < 0.05, n = 6) n=8 P < 0.01
Pigmentation (dl)
0
0.5% M. chamomilla
5 0%
10 21
28
35
42
Days after UVB irradiation with 2 MED dose Fig. 21.6. The preventive effect of a topically applied M. chamomilla extract on UVB-induced human pigmentation. Pigmentation was measured by a color difference meter and is expressed as delta L.
(Fig. 21.7) and for ETBR (average 6.8-fold, P < 0.05, n = 7) in LS lesional epidermis (Kadono et al., 2001). Consistent with this, immunohistochemistry using antibodies to ET-1 or ETBR demonstrates relatively stronger staining in the lesional epidermis (Fig. 21.8) or melanocytes than in the perilesional epidermis or melanocytes respectively. Our previous study demonstrated that, among more than approximately 50 cytokines or chemokines, only three (IL-1a, IL-1b, and TNFa) are ET-1-inducible cytokines (Imokawa et al., 1992a). In focusing on the mechanism(s) involved in the increased expression of ET-1, this prompted us to determine the expression level of these cytokines in the epidermis of LS (except for IL1b, which is not secreted by keratinocytes). The ET-1inducible cytokine, TNFa, is consistently upregulated in the LS lesional epidermis, as determined at the transcriptional level (average 5.5-fold, P < 0.05, n = 3) and by immunostaining, whereas IL-1a (known as a stimulator of ET-1 secretion in UVB-exposed human keratinocytes) is downregulated (average 0.26-fold, n = 2) at the transcriptional level and by immunohistochemistry (Kadono et al., 2001). In contrast, levels of ECE-1a mRNA transcripts (another factor responsible for stimulating the secretion of ET-1) were not substantially increased in the lesional epidermis. Thus, it seems likely that, in contrast to the increased expression of IL-1a as a factor stimulating ET-1 secretion in UVB melanosis, the increased expression of TNFa triggers the stimulation of ET-1 secretion in the LS lesional epidermis. These findings suggest that an accentuation of the epidermal ET cascade, especially with respect to the expression of ET and the ETBR, which is probably triggered by the stimulated secretion of TNFa, plays an important role in the mechanism involved in the hyperpigmentation of LS.
Seborrheic Keratosis Seborrheic keratosis (SK) is a common benign tumor with
Fluorogram A
Densitometric analysis
Fig. 21.7. RT-PCR analysis of ET-1 mRNA in the epidermis of LS and in perilesional skin. (A) Fluorogram. (B) Densitometric analysis. NL, non-lesional epidermis; L, lesional epidermis of LS. Fluorograms are shown at 35 or 37 cycles of PCR for ET-1 and at 22 or 23 cycles for G3PDH. *P < 0.05.
Relative intensity
B
1.4 1.2 1
* 3.2 fold
0.8 0.6 0.4 0.2 0
Patient
NL L 1
NL L NL L NL L NL L NL L 2 3 4 5 6
NL L NL L NL L intensity 7 8 averaged n=8
425
CHAPTER 21 A
Lesion B
Fig. 21.9. Immunostaining with anti-ET-1 in the epidermis of SK (¥180) (see also Plate 21.3, pp. 494–495). Non-lesion Fig. 21.8. Immunostaining with anti-ET-1 in the epidermis of LS. (A) Lesion (¥180). (B) Nonlesion (¥180). See also Plate 21.2, pp. 494–495.
accentuated epidermal pigmentation, which is thought to develop clinically from LS. In the tumor region, there are increased numbers of dopa-positive melanocytes in concert with an increased expression of tyrosinase mRNA as measured by RT-PCR analysis (Teraki et al., 1996). Based upon the observation that increased levels of melanin-producing melanocytes are located in the vicinity of highly proliferating keratinocytes (as seen in hair follicles), we hypothesized that the proliferating keratinocytes in SK trigger the activation of neighboring melanocytes by secreting melanocyte-stimulating cytokines. Thus, the accentuated melanization observed in SK may be associated with the increased production of ETs by the highly proliferating keratinocytes. Therefore, using RT-PCR and immunohistochemistry, we determined whether the production of ET-1 is accentuated in SK of acanthotic and deeply pigmented types. RT-PCR of ET-1 mRNA demonstrates increased levels of ET-1 mRNA transcripts (average 1.7-fold, P < 0.01, n = 5) in SK compared with levels in the perilesional normal controls, which is accompanied by a similarly accentuated expression of tyrosinase mRNA (average 1.7-fold, P < 0.01, n = 5) (Manaka et al., 2001; Teraki et al., 1996). In parallel, immunohistochemical analysis in SK reveals marked immunostaining for ET-1 in almost all basaloid cells (Fig. 21.9) compared with the perilesional normal epidermis. These findings indicate that, in nonUV-associated hyperpigmentary disorders such as SK, there is an overstimulation of ET production and subsequent secretion by keratinocytes, which results in the activation of melanocytes and leads to hyperpigmentation. Although ET secretion by keratinocytes is stimulated following exposure to UVB (Imokawa et al., 1992a), it is con426
ceivable that the increased pigmentation in SK is not directly related to UV exposure because it also appears in nonUVexposed areas. Therefore, it is of considerable interest to know how the secretion of ET-1 is accentuated in SK epidermis via nonUV-associated mechanisms. The production and secretion of ETs by keratinocytes is known to be generally augmented by several inflammatory cytokines, such as IL-1a or TNFa. In UVB-exposed human keratinocytes (Imokawa et al., 1992a; Tsuboi et al., 1994), IL-1a plays an essential role as an autocrine factor enhancing the production and secretion of ET-1. In UVB-exposed epidermis, IL-1a gene expression is consistently augmented prior to the increase in ET-1 gene expression (Imokawa et al., 1995). In contrast, the role of TNFa in UVB-stimulated ET secretion remains unclear because of the absence of increased gene expression in UVBexposed epidermis (Imokawa et al., 1995), although the exogenous addition of TNFa (10 ng/ml) to human keratinocytes in culture stimulates the transcription and eventual secretion of ET-1 (Tsuboi et al., 1994). Thus, it is of importance to determine whether some endogenous factors (known or unknown) are involved in the increase in ET secretion in SK. For this reason, we focused on ET-inducible factors, including IL-1a and TNFa to assess their expression in SK epidermis at the gene and protein levels. RT-PCR of TNFa mRNA demonstrates an increased expression of TNFa transcripts in SK (average 2.6-fold, n = 5) in comparison with the perilesional normal skin (Manaka et al., 2001), whereas there is a marked increase in ET-1 (average 1.7-fold, n = 5) and tyrosinase mRNA transcripts (average 1.7-fold, n = 5) in the lesional skin of SK. In contrast, there is a marked decrease in IL-1a mRNA transcripts (average 0.43-fold, n = 6) in SK in comparison with perilesional normal skin (Manaka et al., 2001). To confirm changes in the production of TNFa and IL1a in SK, we examined whether the production of these cytokines is reflected by changes in their transcripts. Staining with antibodies against TNFa reveals a distinct positive immunoreactivity throughout the basal layers and along the
PARACRINE INTERACTIONS OF MELANOCYTES IN PIGMENTARY DISORDERS
lower epidermis in SK, whereas there is only a weakly positive staining in the perilesional normal control (Manaka et al., 2001). In contrast, there is decreased staining for IL-1a in SK relative to the perilesional skin (Manaka et al., 2001). As TNFa is a potent stimulator of ET secretion in keratinocytes (Tsuboi et al., 1994), it is conceivable that the high production of TNFa in SK is a major factor responsible for the upregulation of ET secretion, although the precise mechanism leading to the increased secretion of TNFa in SK epidermis remains to be elucidated. In contrast to the ET-stimulatory mechanism involved in UVB-exposed keratinocytes or epidermis, it is unlikely that IL-1a is associated with the increased secretion of ET-1 in SK epidermis. Thus, it should be noted that there is a different secretion pattern for two primary inflammatory cytokines, IL-1a and TNFa, between UVBexposed and SK epidermis, with both cytokines and TNFa only, respectively, being stimulated. The increased secretion of TNFa in SK epidermis may be related to the tumorigenicity of SK epidermal cells. The secretion of ET-1 is regulated biologically by the proteolytic converting enzyme (ECE-1a), which degrades Big ET-1 to yield its active form, ET-1. Thus, the production of the active form of ET depends on the activity of ECE-1a, which is probably based on its expression levels in the epidermis. Although there have been no reports describing the presence of ECE-1a in human epidermis, we attempted to determine whether the same ECE-1a as in endothelial cells is expressed in human keratinocytes, and if there is increased expression of ECE-1a in SK epidermis that might account for the mechanism involved in the increased secretion of ET-1. RTPCR analysis of ECE-1a demonstrates that human keratinocytes in culture express the same ECE-1a transcript as endothelial cells but that the expression level is not altered by UVB exposure at 48 h after irradiation, which is in contrast to the increased expression of ET-1 transcripts (Manaka et al., 2001). Our biochemical characterization of ECE-1a in cultured human keratinocytes demonstrated that it has the same enzymatic properties as human endothelial cells (Hachiya et al., 2002). This suggests that, as in endothelial cells, ECE-1a plays an important role in the processing of ET in human keratinocytes. RT-PCR analysis of ECE-1a mRNA reveals a remarkably accentuated expression of those transcripts in the lesional skin of SK (average 15.2-fold, n = 3) (Manaka et al., 2001). Reactivity with antibodies to ECE-1a demonstrates a diffuse positive staining in basaloid cells and in basal layers of SK, whereas no staining with ECE-1a antibodies could be seen in the perilesional normal controls (Manaka et al., 2001). This strongly suggests that the increased expression of ECE-1a also plays a pivotal role in accelerating the secretion of ET-1 in SK, although the mechanism(s) involved in the accentuated expression of ECE-1a in SK epidermis remain(s) unclear. Thus, these findings suggest that there is a general upregulation of the ET-1 inductive linkage in SK, which triggers the high level of secretion of ET-1. This also indicates that the expression of cytokines and/or enzymes is very similar in LS and SK, except for the expression of ECE1a, which is specifically upregulated
in SK but not in LS. Taken together, our results suggest that at least the accentuated expression of the ET cascade (including ECE-1a) is associated with the stimulation of melanocytes leading to the hyperpigmentation in SK.
Membrane-bound SCF/c-KIT Interactions between Keratinocytes and Melanocytes SCF is known as steel factor, kit ligand, and mast cell growth factor, and is encoded by the steel (Sl) locus; its receptor (ckit) is encoded by the dominant white spotting (W) locus. Mutations in either of these loci elicit very similar phenotypes, which are characterized by the loss of neural crest-derived pigment cells, hematopoietic stem cells, and primordial germ cells (Bernstein et al., 1991; Besmer et al., 1993; Galli et al., 1993; Halaban and Moellmann, 1993; Matsui et al., 1990; Orr-Urtreger et al., 1990; Williams et al., 1992). The involvement of SCF/c-kit signaling in melanocyte development at embryonal stages has been delineated by phenotype analysis of Sl and W mice. Experiments using a monoclonal antibody to c-kit (ACK2), an antagonistic blocker of c-kit function, also demonstrated the importance of SCF/c-kit signaling in the development of murine melanocytes (Nishikawa et al., 1991; Okura et al., 1995; Yoshida et al., 1996). Piebaldism, a disorder presenting at birth that is characterized by amelanotic patches on acral and/or ventral skin surfaces, but apparently lacking detectable defects in germ cells or in the hematologic system, is caused by mutations in the genes encoding c-kit (Ezoe et al., 1995; Giebel and Spritz, 1991; Spritz et al., 1992) or ETBR (Amiel et al., 1996; Puffenberger et al., 1994). Thus, it seems likely that the SCF/c-kit linkage plays a pivotal role in developing and regulating melanocyte survival and function, defects in which lead to hypopigmentation.
UVB Melanosis The interaction of SCF with its receptor, c-kit, is well known to be critical to the survival of melanocytes. However, little is known about the role(s) of SCF/c-kit interactions in regulating epidermal pigmentation. Because no data were available concerning the expression of SCF in human keratinocytes in response to UVB irradiation, we determined whether UVB stimulates the expression of SCF in human keratinocytes at the gene and/or protein levels. Our results showed that the exposure of cultured human keratinocytes and melanocytes to UVB upregulates transcription and protein expression of SCF and c-kit respectively (Hachiya et al., 2001). This prompted us to determine whether the exposure of human epidermis to UVB in vivo stimulates the expression of SCF or c-kit at the gene and/or protein levels. In that study (Hachiya et al., 2001, 2004), human volar forearms of normal volunteers were exposed to UVB radiation at 2 MED. At various times after irradiation, suction blisters were induced at the irradiated sites, and epidermal sheets were removed for subsequent studies. Real-time quantitative RT-PCR analysis of UVB-exposed human epidermis at several 427
CHAPTER 21
A
UVB
Control
B UVB
3 days after 2MED UVB irradiation
Control
Membranebound SCF
31 kD
Soluble SCF
18 kD
UVB
Control
30000 25000 20000 15000 10000 5000 0 Control
B
UVB
A
Recombinant SCF
well to several stimuli (including UVB radiation) to induce hyperpigmentation (Imokawa et al., 1986), we used those guinea pigs as a useful model to determine whether interruption of SCF/c-kit signaling abolishes the UVB-induced pigmentation. Prior to that, we evaluated the cross-reactivity of the c-kit antibody ACK2 (Nishikawa et al., 1991) to brownish guinea pig c-kit by examining the stimulatory effect of murine SCF on the proliferation of bone marrow cells from brownish guinea pigs and the prevention of that effect fol-
Intensity
days after irradiation demonstrates that the expression of SCF mRNA transcripts increases significantly 3 days after the irradiation with a peak on day 5 compared with the nonexposed epidermis, after which SCF levels return to the nonirradiated control level by day 25. In a parallel study, pigmentation levels increased significantly by day 7 and reached a plateau at day 10. Expression of tyrosinase mRNA transcripts did not change by day 3, but had increased at day 5 with a plateau at day 10, which paralleled the time course of pigmentation levels. Tyrosinase protein expression assessed by Western blotting analysis was remarkably augmented 7 days after the UV exposure. This time course of expression of SCF/c-KIT mRNA transcripts is summarized in Figure 21.4 and, when compared with the expression of ET-1/ETBR mRNA transcripts, indicates an earlier expression of SCF mRNA transcripts compared with the ET-1/ETBR linkage. Western blotting analysis of mSCF shows a marked increase in UVB-exposed human epidermis compared with nonexposed epidermis, whereas sSCF is not detectable in either type of epidermis (Fig. 21.10). Immunohistochemistry of UVB-exposed human skin with SCF antibodies shows a strong immunostaining located in the stratum spinosum, accompanied by epidermal hyperplasia, compared with nonexposed epidermis (Fig. 21.11). On the other hand, there was no immunostaining with control nonspecific immunoglobulin G (IgG) in the UVB-exposed epidermis. To verify the contribution of the SCF/c-KIT linkage to melanocyte activation during UVB-induced melanosis, it is important to determine whether blockage of that ligand/receptor interaction would result in inhibition or prevention of the UVB-induced pigmentation. Because brownish guinea pigs have functional melanocytes in their epidermis that respond
A B Fig. 21.10. Membrane-bound SCF is markedly increased by UVB irradiation of human epidermis in vivo. (A) Western blotting. (B) Densitometric analysis.
3 days after 2MED UVB irradiation Anti-SCF
Non-specific IgG
Non UVB
100µm Anti-SCF
Non-specific IgG
UVB
100µm
428
Fig. 21.11. Immunostaining with anti-SCF in the epidermis of UVB (2 MED)-exposed human forearm skin (see also Plate 21.4, pp. 494–495).
PARACRINE INTERACTIONS OF MELANOCYTES IN PIGMENTARY DISORDERS
UVB irradiation (288 mJ/cm2)
0
1 Day 6
Fig. 21.12. The c-kit inhibitory antibody, ACK2, abolishes the UVB-induced pigmentation on the dorsal skin of brownish guinea pigs. Guinea pigs were exposed twice to UVB and then injected subepidermally with ACK2 or purified rat IgG 24 h and 48 h after the final UVB irradiation. See also Plate 21.5, pp. 494–495.
lowing treatment with ACK2. The addition of murine SCF stimulated bone marrow cells to synthesize DNA in a dosedependent manner, and that increase could be completely abrogated by ACK2. Control IgG had no such effect, indicating that ACK2 can inhibit the c-kit receptor function of brownish guinea pigs (Hachiya et al., 2001). Further, immunohistochemistry of brownish guinea-pig skin with an antibody to human c-kit revealed that melanocytes in the epidermis of brownish guinea pigs express that receptor. In order to interrupt SCF binding to c-kit, guinea pigs were exposed twice to UVB at a dose of 288 mJ/cm2 and were then injected subepidermally with 5 mg/50 ml ACK2 (or purified rat IgG as a control) 24 h and 48 h after the second UVB irradiation. When observed 6 days after the first UVB irradiation, treatment with ACK2 remarkably abolished the UVB induction of pigmentation, and the color of the UVB-irradiated skin remained similar to the nonexposed area (measured by a color difference meter), whereas a similar injection with nonspecific IgG did not elicit such inhibition (Fig. 21.12) (Hachiya et al., 2001). When observed 10 days after the first irradiation, the inhibitory effect was only partial and a slight increase in skin pigmentation was measured with the color difference meter (Hachiya et al., 2001). In parallel, the numbers of dopapositive melanocytes are comparable on day 6 in the ACK2-injected site and in the nonexposed area in contrast to significant increases in the numbers of dopa-positive melanocytes in the nonspecific IgG-injected site (Fig. 21.13) (Hachiya et al., 2001). On day 10, the number of melanocytes in the ACK2-treated site had increased slightly, but was still significantly less than in the nonspecific IgG-treated site (Fig. 21.13). Continuous observations of skin color changes revealed that a significant inhibition of pigmentation remained at a level similar to that at day 10 until several weeks after
ACK2 injection (5 mg/50 ml)
3
2
Measurement
4
5
6
7
8
A
B
C
Non UVB
UVB + ACK2
UVB + IgG
9
10 (day)
irradiation. These findings strongly suggest that upregulation of SCF/c-kit signaling between keratinocytes and melanocytes is associated with the increased pigmentation in the UVBexposed skin. One of the most important issues addressed concerning the mode of action of SCF refers to how SCF acts on melanocytes during the upregulation of melanogenesis to stimulate their proliferation and melanization. Thus, the observed inhibition of UVB-induced pigmentation by antibodies to c-kit was complete at day 6 but not at day 10, indicating that SCF functions in an early phase of melanogenic stimulation (Hachiya et al., 2001). This was also corroborated by the increased number of dopa-positive melanocytes at day 10, even in the antibodyinjected site (Fig. 21.13), which was paralleled by the skin color changes, although there was still a significant inhibition in melanocyte number and in skin color at the antibodyinjected site compared with the control. In our experiments using hairless mouse epidermis, the expression of SCF, as measured by immunohistochemistry and by enzyme-linked immunosorbent assay (ELISA) reached a peak as early as 24 h after the second daily irradiation with UVB. This contrasts with the later phase of production and secretion for the UVB pigmentation-associated intrinsic cytokine, ET-1, under similar UVB exposure conditions, which takes as long as 5 days or more (Imokawa et al., 1995). Therefore, it is likely that the incomplete inhibition of pigmentation observed at day 10 following the blockage of SCF/c-kit binding is due to an essential role of the SCF/c-kit signaling in an early phase of melanocyte activation as depicted in Figure 21.4. In the later phases of melanogenesis, ET-1 may play an essential role, as described previously (Imokawa et al., 1995). In conclusion, these findings suggest that, in addition to the ET-1/ETBR signaling, SCF/c-kit signaling is also involved in the 429
Day 6
Mean+SD (n=6)
1400 1200 1000
P250
Ideal body weight, % Fig. 50.4. The incidence of acanthosis nigricans increases as body weight increases. [Reprinted with permission from: Hud, J. A., Jr, J. B. Cohen, J. M. Wagner, and P. D. Cruz, Jr. Prevalence and significance of acanthosis nigricans in an adult obese poulation. Arch. Dermatol. 128:941–944, 1992. Copyright 1992, American Medical Association.]
be further subdivided into type A, type B, and other genetic syndromes. Familial acanthosis nigricans is an autosomal dominant condition that develops before puberty. Lesions usually stabilize after several years, although, in some cases, they may regress. Acral acanthotic anomaly is a type of benign acanthosis nigricans seen occasionally in black or Hispanic people, in whom lesions are limited to the dorsae of the hands and feet (Krishnaram, 1991; Schwartz, 1994). Endocrinopathy-related acanthosis nigricans occurs in insulin-resistant or hyperinsulinemic states, especially obesity, polycystic ovarian syndrome, and noninsulin-dependent diabetes mellitus, as well as Cushing syndrome, Addison disease, streak gonads, male hypogonadism, and hyper- and hypothyroidism. Obesity-related acanthosis nigricans frequently resolves after significant weight loss (Fig. 50.4). The clinical course of acanthosis nigricans follows that of the patient’s insulin resistance with onset of insulin resistance correlating directly with the appearance of acanthosis nigricans (Dunaif et al., 1991; Hardaway and Gibbs, 2002; Matsuoka et al., 1993). Overt diabetes mellitus, however, is not common in this type of acanthosis nigricans (Cruz and Hud 1992; Hud et al., 1992). Two constellations of signs are defined as type A and type B syndromic acanthosis nigricans. Type A syndrome, also known as HAIR-AN syndrome (hyperandrogenemia, insulin resistance, and acanthosis nigricans), appears in early childhood, and generalizes rapidly at the onset of puberty. Virilization, enlarged kidneys and adrenal glands, and accelerated somatic growth are frequently seen. Female patients often are hirsute and have polycystic ovaries. It may be more common in black people (Schwartz, 1994). Type B acanthosis nigricans is characterized by autoimmu909
CHAPTER 50 Table 50.1. Syndromes associated with acanthosis nigricans. Type A syndrome (HAIR-AN syndrome) Type B syndrome Hirschowitz syndrome Ataxia telangiectasia Rabson syndrome Leprechaunism Wilson disease Chondrodystrophy with dwarfism Pyramidal tract degeneration Alström syndrome Crouzon syndrome Capozucca syndrome Streak gonads Rud syndrome Bloom syndrome Pituitary neoplasms Gigantism Acromegaly Familial pineal body hypertrophy
Rabson–Mendenhall syndrome Benign encephalopathy Prader–Willi syndrome Pituitary hypogonadism Stein–Leventhal syndrome Lipoatrophic diabetes mellitus Lawrence–Seip syndrome Bartter syndrome Werner syndrome Lupoid hepatitis Lupus erythematosus Dermatomyositis Scleroderma Hashimoto thyroiditis Phenylketonuria Beare–Stevenson syndrome Costello syndrome Pseudoacromegaly Lawrence–Moon–Bardet–Biedl syndrome
acanthosis nigricans have elevated levels of thyroid stimulating hormone (TSH), growth hormone (GH), melanocytestimulating hormone (MSH), and androgens (Givens et al., 1974; Millard and Gould, 1976; Moller, 1978; Nordlund and Lerner, 1975; Weiss et al., 1995). Type A syndrome generally produces high plasma testosterone levels. Patients with type B syndrome may have circulating antibodies to the insulin receptor, leukopenia, or high anti-DNA antibody titers (Kahn et al., 1976; Moller and Flier, 1991; Schwartz, 1994). Hyperlipidemia is a feature of lipodystrophy in Lawrence–Seip syndrome, frequently the only sign in heterozygotes (Mork et al., 1986; Schwartz, 1994; Seip and Trygstad, 1963). Transforming growth factor-a (TGF-a) may be elevated in both the serum and in the urine, rarely in patients with malignant acanthosis nigricans (Yeh et al., 2000).
Criterion for Diagnosis The criterion for diagnosis of acanthosis nigricans is clinical presentation of pigmented, velvety plaques. The sites affected most commonly are the axilla, nape of the neck, and the groin.
Differential Diagnosis nity, including anti-insulin receptor antibodies. The clinical course of acanthosis nigricans parallels the insulin resistance, which may relapse and remit along with the immunologic disease (Cruz and Hud, 1992). Diabetes mellitus is a typical feature. Premenopausal women may also have hyperandrogenism. Putative autoimmune diseases seen in type B syndrome include systemic lupus erythematosus, Sjögren syndrome, vitiligo, Hashimoto thyroiditis, and scleroderma (Matsuoka et al., 1993; Moller and Flier, 1991; Rendon et al., 1989; Schwartz, 1994). Miscellaneous other rare, benign hereditary conditions with acanthosis nigricans include Lawrence–Seip syndrome (lipodystrophic diabetes), leprechaunism, Hirschowitz syndrome, Rabson–Mendenhall syndrome, and pseudoacromegaly syndrome (Table 50.1). Additionally, a high prevalence of acanthosis nigricans in patients with trisomy 21 has recently been described (Hirschler et al., 2002). Certain medications may induce acanthosis nigricans. These include nicotinic acid, diethylstilbestrol, insulin, glucocorticoids, pituitary extracts, oral contraceptives, methyltestosterone, topical fusidic acid, and triazinate. The cutaneous process may normalize following withdrawal of the offending agent, at least in the case of nicotinic acid (Brown and Winkelmann, 1968; Darmstadt et al., 1991; Mellor-Pita et al., 2002; Teknetzis et al., 1993).
Laboratory Findings and Investigations Laboratory findings vary according to the type of acanthosis nigricans. Patients with benign acanthosis nigricans exhibit elevated fasting plasma insulin levels that are significantly higher than those of nonacanthotic patients (Hidalgo, 2002). Hyperglycemia may occur, particularly in obese patients with noninsulin-dependent diabetes mellitus. Some patients with 910
The main diseases in the differential diagnosis of acanthosis nigricans are Dowling–Degos disease, confluent and reticulated papillomatosis (CRP), Becker nevus, and tinea versicolor. Acanthosis nigricans may occasionally have a similar appearance to hyperkeratotic seborrheic keratoses, melanocytic nevi, linear epidermal nevi, and ichthyosis hystrix. It may also resemble the hyperpigmentation of pellagra, Addison disease, and pemphigus vegetans. Early plaques may have some similarities to atopic dermatitis. Dowling–Degos disease (reticulate pigmented anomaly of the flexures) has a distribution similar to acanthosis nigricans, usually affecting the axilla, groin, and other intertriginous sites with reticulated brown plaques. However, unlike acanthosis nigricans, the lesions have little or no substance. Both demonstrate a normal number of melanocytes histologically; Dowling–Degos disease differs from acanthosis nigricans in its lack of papillomatosis, its follicular involvement, and its elongated rete ridges with melanin deposition at the lower tips. The lesions of CRP may appear on the neck, back, and chest as red papules or brown verrucous plaques, mimicking acanthosis nigricans. However, they are not found on mucous membranes, and rarely appear in the axillae or groin. As noted earlier, Becker nevus, like acanthosis nigricans, is usually a brown plaque with skin thickening. However, it may have coarse hypertrichosis on its surface. Histologically, it is identified by smooth muscle hyperplasia and increased amount of melanin, which are not present in acanthosis nigricans. Tinea versicolor can masquerade as acanthosis nigricans with its brown coloration, especially when it appears in flexural areas, on the sides of the chest, or on the neck. However, unlike acanthosis nigricans, tinea versicolor lesions are barely palpable, and have a reticulated pattern with fine scale. Seborrheic keratoses may be confused with acanthosis nigricans because of their brown, black, or yellow color and
ACQUIRED EPIDERMAL HYPERMELANOSES
hyperkeratotic rough surface; however, they are usually well demarcated, round to oval in shape, and are smaller than acanthosis nigricans lesions. Unlike acanthosis nigricans, their number increases with age. Melanocytic nevi are pigmented, sometimes verrucous lesions which may simulate acanthosis nigricans. They differ from acanthosis nigricans in that these nevi are asymmetric, rarely grow larger than 0.5 to 1.0 cm, and have no predilection for intertriginous areas. Histologically, they are composed of an abnormal number of melanocytes in the dermis, unlike acanthosis nigricans, which usually has a normal number of pigment-producing cells, limited to the epidermis. Epidermal nevi, including linear and verrucous types, can resemble acanthosis nigricans. They both may be flesh-colored, brown, or gray-brown. The nevi appear as verrucous papules which may coalesce into plaques. Other types, such as ichthyosis hystrix, can have a bilateral distribution, giving the appearance of acanthosis nigricans-like symmetry. Unlike acanthosis nigricans, they tend to become inflamed, pruritic, and scaly. They rarely appear after puberty. The thickened, hyperpigmented plaques of pellagra may mimic acanthosis nigricans. Sites such as dorsal hands and neck are common to both. Unlike acanthosis nigricans, lesions may be fissured and may worsen after sun exposure. Pellagra affects areas over bony prominences and scalp, which are uncommon sites of involvement in acanthosis nigricans. Addison disease can cause generalized, diffuse brown hyperpigmentation. In contradistinction to acanthosis nigricans, the lesions are not palpable. Pemphigus vegetans may present with verrucous, hyperpigmented plaques involving both cutaneous and mucous membrane surfaces. Unlike acanthosis nigricans, the lesions are often eroded as well as verrucous. On histologic examination pemphigus is characterized by intraepidermal vesiculation and acantholysis, whereas acanthosis nigricans displays none of these features. Atopic dermatitis can present with poorly-demarcated plaques which may be hyperpigmented. Atopic dermatitis and acanthosis nigricans may affect comparable skin sites, such as the nuchal region and intertriginous areas such as the popliteal and antecubital fossae. However, epithelial disruption distinguishes this from acanthosis nigricans. Unlike acanthosis nigricans, pruritus is a prominent symptom, although acanthosis nigricans lesions may occasionally itch.
Pathology Light Microscopy Acanthosis nigricans lesions have a histologic picture which consists of marked hyperkeratosis, prominent finger-like papillomatosis, varying but mild acanthosis, and minimal melanocytic hyperplasia. The interpapillary crypts contain keratotic material. Slight hyperpigmentation of the basal layer is occasionally present, but the gross color is due to hyperkeratosis, not melanin deposition. Usually, there is no inflammation, but a sparse dermal mononuclear infiltrate may be present (Brown and Winkelmann, 1968; Darmstadt et al., 1991; Krishnaram, 1991). There is no histologic difference
between the benign and malignant types of acanthosis nigricans (Brown and Winkelmann, 1968; Farmer and Hood, 1990).
Immunohistochemistry Glycosaminoglycan deposition in the epidermis and papillary dermis may be present (Rogers, 1991). Hyaluronic acid deposits have been associated with polycystic ovary syndrome, other endocrinopathies, and one case of malignant pheochromocytoma (Matsuoka et al., 1993). Tumors associated with acanthosis nigricans have been shown to express TGF-a and increased numbers of epidermal growth factor (EGF) receptors. TGF-a and EGF share a common receptor, the EGF receptor, which may be present in abnormally high numbers in skin affected with acanthosis nigricans (Ellis et al., 1987; Wilgenbus et al., 1992).
Pathogenesis Growth factors which stimulate keratinocytes and dermal fibroblasts at the level of cell receptors may be the proximate cause of acanthosis nigricans. Insulin and TGF-a are the best studied. In normal concentrations, insulin binds preferentially to its classical receptor, initiating its metabolic and proliferative effects. In high concentrations, as in patients with insulinresistant states, insulin has an increased affinity for insulinlike growth factor-1 (IGF-1) (somatomedin C) receptors (“specificity spillover effect”). IGF-1 receptors are present on keratinocytes; thus insulin is capable of activating IGF-1 receptors, stimulating DNA synthesis and epidermal growth (Uyttendaele et al., 2003). The genetic syndromes associated with acanthosis nigricans, such as lipoatrophic diabetes, leprechaunism, type A syndrome, and Rabson–Mendenhall syndrome, have identifiable heterogeneous mutations in the insulin receptor gene (Accili et al., 1992; Flier et al., 1985; Grasinger et al., 1993; Matsuoka et al., 1993; Schwartz, 1994). These abnormalities are associated with acanthosis nigricans, but do not correlate directly with the individual clinical syndromes (Accili et al., 1992). Obesity, hirsutism, and hyperandrogenism may have additive effects which aggravate insulin resistance (Flier et al., 1985). Unlike benign acanthosis nigricans, which is related to insulin action, malignant acanthosis nigricans probably reflects the effects of ectopic growth factors. Tumor products, such as IGF-1 and TGF-a, stimulate epidermal proliferation by binding to skin IGF-1 and EGF receptors (Ellis et al., 1987; Matsuoka et al., 1987; Wilgenbus et al., 1992). Increased plasma levels of growth factors may be operative in other dermatologic paraneoplastic syndromes, such as the sign of Leser–Trelat, florid cutaneous papillomatosis, tylosis, paraneoplastic pemphigus, acquired hypertrichosis lanuginosa, and pachydermoperiostosis, as well as in acanthosis nigricans (Ive, 1963; Matsuoka et al., 1993; Schwartz, 1994; Schwartz and Burgess, 1978). Medications which cause acanthosis nigricans act via a mechanism which has not yet been elucidated (Rogers, 1991; Schwartz, 1994; Teknetzis et al., 1993). 911
CHAPTER 50
Animal Models Acanthosis nigricans occurs in dogs, most notably dachshunds, but also in German shepherds and Lhasa apsos. The majority suffer from an underlying endocrinopathy, as in humans, although associated malignancy has been found. Gartner induced cutaneous lesions resembling acanthosis nigricans in dogs by removing their adrenal glands and gonads (Bornfors, 1958; Brown and Winkelmann, 1968; Curth and Slanetz, 1939; Schwartz, 1994).
Treatment The primary goal of treatment is to correct the underlying disease which leads to the development of acanthosis nigricans. Regression of acanthosis nigricans can occur with improvement of underlying endocrinopathies. Physical activity, calorie restriction, and weight reduction are all protective against hyperinsulinemia and subsequent acanthosis nigricans (Mukhtar et al., 2001). Insulin therapy is usually not indicated even in patients with insulin resistance, since most patients are not diabetic (Cruz and Hud 1992; Schwartz, 1994). Treatment with octreotide, a synthetic analog of somatostatin, reduces insulin secretion and therefore should theoretically reduce the insulin binding to IGF-1 receptors (Hidalgo, 2002). Because acanthosis nigricans is a cutaneous manifestation of hyperinsulinemia and insulin resistance, its detection could be important as a noninvasive and cost-effective tool in type 2 diabetes mellitus screening (Mukhtar et al., 2001). Specific hormone therapy, such as thyroid replacement, estrogen, oral contraceptives, oral hypoglycemic agents, and recombinant IGF-1, have shown benefit in some patients (Dix et al., 1986; Hardaway and Gibbs, 2002; Matsuoka et al., 1993; Ober 1985; Schwartz 1994). Cyclophosphamide or other immune modulators have been tried in type B acanthosis nigricans (Matsuoka et al., 1993). In patients with malignant acanthosis nigricans, resolution of acanthosis nigricans may occur with chemotherapy. Specifically, chemotherapy is beneficial because it decreases epithelial proliferation (Anderson et al., 1999). Treatment directed at the acanthosis nigricans lesions themselves include topical corticosteroids, oral retinoids, topical tretinoin gel, podophyllin, and emollient creams (Anderson et al., 1999; Darmstadt et al., 1991; Katz 1980; Skiljevic et al., 2001). The vitamin D3 analog, calcipitriol, has been shown to be effective in treating acanthosis nigricans by inhibiting the proliferation of keratinocytes and reducing the hyperkeratosis and papillomatosis (Hidalgo, 2002). The acrochordons associated with acanthosis nigricans can be removed via snipping with curved scissors, cryotherapy, or electrodesiccation (Hidalgo, 2002). In drug-induced acanthosis nigricans, discontinuation of the offending drug may result in acanthosis nigricans regression (Coates et al., 1992). Less conventional treatments have been used as well. One patient achieved palliation of malignant acanthosis nigricans after radiation therapy with two courses of electron beam therapy (Weiss et al., 1995). Oral cyproheptadine has been used to inhibit tumor product release and diminish paraneoplastic acanthosis nigricans (Greenwood and Tring, 1982). A 912
few patients with lipodystrophic diabetes have had improvement of acanthosis nigricans while taking dietary fish oil supplements (Sherertz, 1988). Ketoconazole therapy and dermabrasion have also been suggested (Curth and Gibbs, 1967; Schwartz, 1994; Tercedor et al., 1992).
Prognosis Acanthosis nigricans is a chronic condition. The patient’s prognosis depends upon the underlying pathology which is responsible for the acanthosis nigricans. In malignant acanthosis nigricans, diminution of lesions frequently occurs with excision of related cancers; lesions may reappear with recurrence or metastasis (Schwartz, 1994). The longest time between acanthosis nigricans diagnosis and tumor detection is reported to be 16 years; the interval is usually much shorter (Curth et al., 1962). The malignancies in question are often extremely aggressive; the average survival after detection is two years (Curth et al., 1962; Matsuoka et al., 1993) and the average survival being 12 months (Braverman, 2002). However, many patients who receive early cancer therapy survive, one even as long as 14 years after tumor resection (Brown and Winkelmann, 1968).
References Accili, D., F. Barbetti, A. Cama, H. Kadowaki, T. Kadowaki, E. Imano, R. Levy-Toledano, and S. I. Taylor. Mutations in the insulin receptor gene in patients with genetic syndromes of insulin resistance and acanthosis nigricans. J. Invest. Dermatol. 98(6 Suppl):77S-81S, 1992. Anderson, S. H., M. Hudson-Peacock, A. F. Muller. Malignant acanthosis nigricans: potential role of chemotherapy. Br. J. Dermatol. 141:714–716, 1999. Andreev, V. C. Malignant acanthosis nigricans. Semin. Dermatol. 3:265–272, 1984. Azizi, E., H. Trau, M. Schewach-Millet, V. Rosenberg, S. Schneebaum, and R. Michalevicz. Generalized malignant acanthosis nigricans [letter]. Arch. Dermatol. 116:381, 1980. Bonnekoh, B., A. Wevers, H. Spangenberger, G. Mahrle, and T. Krieg. Keratin pattern of acanthosis nigricans in syndromelike association with polythelia, polycystic kidneys, and syndactyly. Arch. Dermatol. 129:1177–1182, 1993. Bornfors, S. Acanthosis nigricans in dogs: A study of aetiology and medical treatment with special attention to hypophyseal-thyroid function. Acta Endocrinol. Suppl. 37:1, 1958. Braverman, I. M. Skin manifestations of internal malignancy. Clin. Geriatr. Med. 18:1–19, 2002. Brown, J., and R. K. Winkelmann. Acanthosis nigricans: A study of 90 cases. Medicine 47:33–51, 1968. Coates, P., D. Shuttleworth, and A. Rees. Resolution of nicotinic acidinduced acanthosis nigricans by substitution of an analogue (acipimox) in a patient with type V hyperlipidaemia. Br. J. Dermatol. 126:412–414, 1992. Cobenour, W., and J. W. Gamble. Acanthosis nigricans: A review of literature and report of case. J. Oral Surg. 29:48–51, 1971. Cruz, P. D., Jr., and J. A. Hud Jr. Excess insulin binding to insulinlike growth factor receptors: proposed mechanism for acanthosis nigricans. J. Invest. Dermatol. 98(6 Suppl):82S–85S, 1992. Curth, H. O. Cancer associated with acanthosis nigricans: review of literature and report of a case of acanthosis nigricans with cancer of the breast. Arch. Surg. 47:517–552, 1943. Curth, H. O. Significance of acanthosis nigricans. Arch. Dermatol. 66:80, 1952.
ACQUIRED EPIDERMAL HYPERMELANOSES Curth, H. O. The Necessity of Distinguishing Four Types of Acanthosis Nigricans. Berlin: Springer-Verlag, 1968. Curth, H. O. Classification of acanthosis nigricans. Int. J. Dermatol. 15:592–593, 1976. Curth, H. O., and R. G. Gibbs. Benign acanthosis nigricans. Arch. Dermatol. 96:345–346, 1967. Curth, H. O., and C. A. Slanetz. Acanthosis nigricans and cancer of the liver in a dog. Am. J. Cancer 37:216–223, 1939. Curth, H. O., A. W. Hilberg, and G. F. Machacek. The site and histology of the cancer associated with malignant acanthosis nigricans. Cancer 15:364–382, 1962. Darier, J. Dystrophie papillaire et pigmentaire. Ann. Dermatol. Syphiligr. (Paris) 4:865–875, 1893. Darmstadt, G. L., B. K. Yokel, and T. D. Horn. Treatment of acanthosis nigricans with tretinoin. Arch. Dermatol. 127:1139–1140, 1991. de Graciansky, P., C. Grupper, and P. Lefort. Acanthosis nigricans atypique. Bull. Soc. Franc. Dermatol. Syphiligr.:483–484, 1951. Dix, J. H., W. J. Levy, and C. Fuenning. Remission of acanthosis nigricans, hypertrichosis, and Hashimoto’s thyroiditis with thyroxine replacement. Pediatr. Dermatol. 3:323–326, 1986. Dunaif, A., G. Green, R. G. Phelps, M. Lebwohl, W. Futterweit, and L. Lewy. Acanthosis nigricans, insulin action, and hyperandrogenism: clinical, histological, and biochemical findings. J. Clin. Endocrinol. Metab. 73:590–595, 1991. Ellis, D. L., S. P. Kafka, J. C. Chow, L. B. Nanney, W. H. Inmann, M. E. McCadden, and L. E. King. Melanoma growth factors, acanthosis nigricans, the sign of Leser-Trelet, and multiple acrochordons: A possible role for alpha-transforming growth factor in cutaneous paraneoplastic syndromes. N. Engl. J. Med. 317:1582–1587, 1987. Farmer, E. R., and A. F. Hood. Pathology of the Skin. Norwalk, CT: Appleton and Lange, 1990. Fleming, M. G., and S. I. Simon. Cutaneous insulin reaction resembling acanthosis nigricans. Arch. Dermatol. 122:1054–1056, 1986. Flier, J. S., R. C. Eastman, K. L. Minaker, D. Matteson, and J. W. Rowe. Acanthosis nigricans in obese women with hyperandrogenism: Characterization of an insulin-resistant state distinct from the type A and B syndromes. Diabetes 34:101–107, 1985. Givens, J. R., I. J. Kerber, W. L. Wiser, R. N. Andersen, S. A. Coleman, and S. A. Fish. Remission of acanthosis nigricans associated with polycystic ovarian disease and a stromal luteoma. J. Clin. Endocrinol. Metab. 38:437–455, 1974. Grasinger, C. C., R. A. Wild, and I. J. Parker. Vulvar acanthosis nigricans: a marker for insulin resistance in hirsute women. Fertil. Steril. 59:583–586, 1993. Greenwood, R., and F. C. Tring. Treatment of malignant acanthosis nigricans with cyproheptadine. Br. J. Dermatol. 106:705–710, 1982. Gross, G., H. Pfister, B. Hellenthal, and M. Hagedorn. Acanthosis nigricans maligna: Clinical and virological investigations. Dermatologica 168:265–272, 1984. Hardaway, C. A., and N. F. Gibbs. What syndrome is this? RabsonMendenhall syndrome. Pediatr. Dermatol. 19:267–270, 2002. Hidalgo, G. Dermatological complications of obesity. Am. J. Clin. Dermatol. 2:497–506, 2002. Hirschler, V., C. Aranda, A. Oneto, C. Gonzalez, M. Jadzinsky. Is acanthosis nigricans a marker of insulin resistance in obese children? Diabetes Care 25:2353, 2002. Hud, J. A., Jr., J. B. Cohen, J. M. Wagner, and P. D. Cruz Jr. Prevalence and significance of acanthosis nigricans in an adult obese population. Arch. Dermatol. 128:941–944, 1992. Ive, F. A. Metastatic carcinoma of cervix with acanthosis nigricans, bullous pemphigoid and hypertrophic pulmonary osteoarthropathy. Proc. R. Soc. Med. 56:910, 1963. Kahn, C. R., J. S. Flier, R. S. Bar, J. A. Archer, P. Gorden, M. M. Martin, and J. Roth. The syndromes of insulin resistance and acan-
thosis nigricans: Insulin-receptor disorders in man. N. Engl. J. Med. 294:739–745, 1976. Katz, R. A. Treatment of acanthosis nigricans with oral isotretinoin. Arch. Dermatol. 116:110–111, 1980. Kierland, R. R. Acanthosis nigricans: an analysis of data in twentytwo cases and a study of its frequency in necropsy material. J. Invest. Dermatol. 9:299–305, 1947. Krishnaram, A. S. Unilateral nevoid acanthosis nigricans [letter]. Int. J. Dermatol. 30:452–453, 1991. Kroumpouzos, G., G. Avgerinou, and S. R. Granter. Acanthosis nigricans without diabetes during pregnancy. Br. J. Dermatol. 146:925–928, 2002. Kuzuya, H., N. Matsuura, M. Sakamoto, H. Makino, Y. Sakamoto, T. Kadowaki, Y. Suzuki, M. Kobayashi, Y. Akazawa, M. Nomura, Y. Yoshimasa, M. Kasuga, K. Goji, S. Nagataki, H. Oyasu, and H. Imura. Trial of insulinlike growth factor I therapy for patients with extreme insulin resistance syndromes. Diabetes 42:696–705, 1993. Matsuoka, L. Y., J. Goldman, J. Wortsman, D. Kleinsmith, and C. E. Kupchella. Antibodies against the insulin receptor in paraneoplastic acanthosis nigricans. Am. J. Med. 82:1253–1256, 1987. Matsuoka, L. Y., J. Wortsman, and J. Goldman. Acanthosis nigricans. Clin. Dermatol. 11:21–25, 1993. Mellor-Pita, S., M. Yebra-Bango, J. Alfaro-Martinez, and E. Suarez. Acanthosis nigricans: a new manifestation of insulin resistance in patients receiving treatment with protease inhibitors. Clin. Infect. Dis. 34:716–717, 2002. Millard, L. G., and D. J. Gould. Hyperkeratosis of the palms and soles associated with internal malignancy and elevated levels of immunoreactive human growth hormone. Clin. Exp. Dermatol. 1:363–368, 1976. Moller, D. E., and J. S. Flier. Insulin resistance: mechanisms, syndromes, and implications. N. Engl. J. Med. 325:938–948, 1991. Moller, H. Phototoxicity of Dictamnus alba. Contact Derm. 4:264–269, 1978. Mork, N. J., G. Rajka, and J. Halse. Treatment of acanthosis nigricans with etretinate (Tigason) in a patient with LawrenceSeip syndrome (generalized lipodystrophy). Acta Derm. Venereol. 66:173–174, 1986. Mukhtar, Q., G. Cleverley, R. E. Voorhees, and J. W. McGrath. Prevalence of acanthosis nigricans and its association with hyperinsulinemia in New Mexico adolescents. J. Adolesc. Health 28:372–376, 2001. Nordlund, J. J., and A. B. Lerner. On the cause of acanthosis nigricans. N. Engl. J. Med. 293:200, 1975. Ober, K. P. Acanthosis nigricans and insulin resistance associated with hypothyroidism. Arch. Dermatol. 121:229–231, 1985. Pollitzer, S. Acanthosis Nigricans. London: HK Lewis and Co., 1890. Rendon, M. I., P. D. Cruz Jr., R. D. Sontheimer, and P. R. Bergstresser. Acanthosis nigricans: a cutaneous marker of tissue resistance to insulin. J. Am. Acad. Dermatol. 21:461–469, 1989. Robbins, S. L., R. S. Cotran, and V. Kimar. Robbins’ Pathologic Basis of Disease, 4th ed. Philadelphia: Saunders, 1989. Rogers, D. L. Acanthosis nigricans. Semin. Dermatol. 10:160–163, 1991. Schwartz, R. A. Acanthosis nigricans. J. Am. Acad. Dermatol. 31:1–19, 1994. Schwartz, R. A., and G. H. Burgess. Florid cutaneous papillomatosis. Arch. Dermatol. 114:1803–1806, 1978. Seip, M., and O. Trygstad. Generalized lipodystrophy. Arch. Dis. Child. 38:447–453, 1963. Sherertz, E. F. Improved acanthosis nigricans with lipodystrophic diabetes during dietary fish oil supplementation. Arch. Dermatol. 124:1094–1096, 1988. Skiljevic, D. S., M. M. Nikolic, A. Jakovljevic, and D. D. Dobrosavljevic. Generalized acanthosis nigricans in early childhood. Pediatr. Dermatol. 18:213–216, 2001.
913
CHAPTER 50 Stone, O. J. Acanthosis nigricans — decreased extracellular matrix viscosity: cancer, obesity, diabetes, corticosteroids, somatotrophin. Medical Hypotheses 40:154–157, 1993. Stoddart, M. L., K. S. Blevins, E. T. Lee, W. Wang, P. R. Blackett; Cherokee Diabetes Study. Association of acanthosis nigricans with hyperinsulinemia compared with other selected risk factors for type 2 diabetes in Cherokee Indians: the Cherokee Diabetes Study. Diabetes Care 25:1009–1014, 2002. Stuart, C. A., C. J. Pate, and E. J. Peters. Prevalence of acanthosis nigricans in an unselected population. Am. J. Med. 87:269–272, 1989. Stuart, C. A., M. M. Smith, C. R. Gilkison, S. Shaheb, and R. M. Stahn. Acanthosis nigricans among native Americans: an indicator of high diabetes risk. Am. J. Publ. Health 84:1839–1842, 1994. Teknetzis, A., I. Lefaki, D. Joannides, and A. Minas. Acanthosis nigricans-like lesions after local application of fusidic acid. J. Am. Acad. Dermatol. 28:501–502, 1993. Tercedor, J., J. M. Rodenas, M. T. Herranz, A. Vidal, and M. MunozTorres. Effect of ketoconazole in the hyperandrogenism, insulin resistance and acanthosis nigricans (HAIR-AN) syndrome [letter; comment]. J. Am. Acad. Dermatol. 27(5 Pt 1):786, 1992. Uyttendaele, H., T. Koss, et al. Generalized acanthosis nigricans in an otherwise healthy young child. Pediatr. Dermatol. 20:254–256, 2003. Weiss, E., H. Schmidberger, R. Jany, C. F. Hess, and M. Bamberg. Palliative radiotherapy of mucocutaneous lesions in malignant acanthosis nigricans. Acta Oncol. 34:265–267, 1995. Wilgenbus, K., A. Lentner, R. Kuckelkorn, S. Handt, and C. Mittermayer. Further evidence that acanthosis nigricans maligna is linked to enhanced secretion by the tumour of transforming growth factor alpha. Arch. Dermatol. Res. 284:266–270, 1992. Yeh, J. S., S. E. Munn, T. A. Plunkett, P. G. Harper, D. J. Hopster, and A. W. du Vivier. Coexistence of acanthosis nigricans and the sign of Leser-Trelat in a patient with gastric adenocarcinoma: a case report and literature review. J. Am. Acad. Dermatol. 42(2 Pt 2): 357–362, 2000.
Acromelanosis Progressiva
Fig. 50.5. Typical blue-black lesion on the fingers of a child with acromelanosis progressiva.
(Furuya and Mishima, 1962). The mucous membranes and nails are spared (Gonzalez and Vazquez Botet, 1980). One of the children had associated seizures (Furuya and Mishima, 1962) and the other was otherwise normal (Gonzalez and Vazquez Botet, 1980).
Pathology The main pathologic finding is a proliferation of normal melanocytes in the basal epidermis. In some areas, the melanocytes are clustered, but no true nesting is present. Melanin is noted mainly along the basal cell layer of the epidermis with some upward migration of this pigment. The dermis is uninvolved, except for a sparse perivascular mononuclear infiltrate (Gonzalez and Vazquez Botet, 1980).
Norman Levine and Cynthia Burk
Differential Diagnosis Historical background Thomas (1923) first described hyperpigmentation on the dorsal digits in infants, which he called “spitzenpigment.” Bloom made a similar observation in 1950 in a patient with associated hypertrichosis and café-au-lait spots. Weidman (1969) described a 10-year-old child with pigmentation of the fingers and toes, which slowly progressed over several years. Furuya and Mishima (1962) were the first to report a patient whose initial acral pigmentation became more widespread. One additional case, now termed acromelanosis progressiva, has been described (Gonzalez and Vazquez Botet, 1980).
Synonyms Spitzenpigment, acropigmentation, acromelanosis.
Clinical Findings The lesions first appear in early childhood as symmetrical blue-black lesions over the distal digits (Fig. 50.5), toes, and the perianal area. The pigmentation subsequently spreads proximally to the thighs, buttocks, genitals, and abdomen 914
Reticulate acropigmentation of Kitamura bears some resemblance to acromelanosis progressiva. However, it is far more common. It is transmitted via an autosomal dominant mode of inheritance and presents in the first and second decades of life. Like acromelanosis, it presents with acral pigmentation, but it is characterized by a reticulate pattern of hyperpigmented macules. There are no areas of hypopigmentation (Griffiths, 1976). The classic histopathology involves the presence of digitated and filiform elongated rete ridges, with clumps of heavy melanin pigmentation at their tips (Al Hawsawi, 2002). There is also epidermal atrophy and an increase in the number of basal melanocytes (Alfadley, 2000). Acropigmentation of Dohi (Komaya, 1924) presents in infancy and/or early childhood with reticulate hyperpigmented and hypopigmented macules of the dorsa of hands and feet. Acropigmentation of Dohi is most often inherited in an autosomal dominant pattern; however, a few cases have been inherited as an autosomal recessive trait. Histopathologically, there is an increase in melanin pigments at the basal layer and through the epidermis within the areas of hyperpigmentation. In the areas of hypopigmentation, there is a decrease or an
ACQUIRED EPIDERMAL HYPERMELANOSES
absence of melanin pigments. Overall, melanocyte number is unaffected (Alfadley, 2000). Universal acquired melanosis has been described in a neonate with progressive brown pigmentation which eventuated in generalized jet-black skin by age 3 (Ruiz-Maldonado et al., 1978). Electron microscopy showed the pigment to be distributed in a Negroid pattern in spite of the fact that the patient was white.
Pathogenesis The origin of this peculiar pigmentary abnormality is not known. The histologic findings are identical to those of a lentigo, with increased numbers of epidermal melanocytes. Thus, this may be an epidermal hamartoma of melanocytes; the dermal counterpart might be the nevus of Ota, the Mongolian spot, and the blue nevus (Furuya and Mishima, 1962; Gonzalez and Vazquez Botet, 1980).
Treatment and Prognosis No therapies have been described for acromelanosis progressiva. Although long-term follow-up on these few cases has not been reported, there is no mention of spontaneous resolution once the pigment is established.
References Alfadley, A., A. Al Ajlan, B. Hainau, K. T. Pedersen, and I. Al Hoqail. Reticulate acropigmentation of Dohi: a case report of autosomal recessive inheritance. J. Am. Acad. Dermatol. 43:113–117, 2002. Al Hawsawi, K., K. Al Aboud, A. Alfadley, and D. Al Aboud. Kitamura-Dowling Degos disease overlap: a case report. Int. J. Dermatol. 41:518–520, 2002. Bloom, D. Acropigmentation in a child. Arch. Dermatol. 62:475, 1950. Furuya, T., and Y. Mishima. Progressive pigmentary disorder in Japanese child. Arch. Dermatol. 86:412–418, 1962. Gonzalez, J. R., and M. Vazquez Botet. Acromelanosis: A case report. J. Am. Acad. Dermatol. 2:128–131, 1980. Griffiths, W. A. D. Reticulate acropigmentation of Kitamura. Br. J. Dermatol. 95:437–443, 1976. Komaya, G. Pigmentanomalie der extremitaten. Arch. Dermatol. Syphil. 147:389–393, 1924. Ruiz-Maldonado, R., L. Tamayo, and J. Fernandez-Diez. Universal acquired melanosis. Arch. Dermatol. 114:775–778, 1978. Thomas, E. Uber das Spitzen pigment des Kleinekindes. Munch. Med. Wochenschr. 70:1102, 1923. Weidman, A. I. Acropigmentation (acromelanosis): Report of a case. Cutis 5:1119–11120, 1969.
Becker Nevus Norman Levine and Cynthia Burk
Historical Background In 1923, Stokes described a patient with a pigmented hairy plaque, which when biopsied, displayed dermal smooth muscle hyperplasia. Twenty-six years later, Becker (1949) reported almost identical findings. Since 1965, the condition has been named after Becker (Copeman and Wilson-Jones, 1965).
Fig. 50.6. Becker nevus of the trunk (see also Plate 50.2 pp. 494–495).
Synonyms Becker melanosis, pigmented hairy epidermal nevus, nevus pilaris, melanosis naeviformis Becker, nevus tardif de Becker.
Epidemiology Becker nevus occurs in all races; it is four to six times more common in males than in females (Tymen et al., 1981). It occurs in approximately 0.5% of the population (Hsu et al., 2001).
Clinical Findings Becker nevus is characterized by an irregular macule or patch, often with hypertrichosis (Terheyden et al., 1998). The hair associated with Becker nevus usually develops several years after the hyperpigmentation and is often coarse and dark. Becker nevus is most commonly located unilaterally on the shoulder, upper arm, anterior chest, or scapula (Fig. 50.6). However, there have been reports of Becker nevi occurring on the face, neck, and lower extremities. It is often minimally substantive (Copeman and Wilson-Jones, 1965). The lesions typically present during the adolescent years; however, both congenital and familial cases have been reported. Familial cases demonstrate autosomal dominance with incomplete penetrance and variable expressivity (Book et al., 1997). There appears to be a spectrum of disease which includes lesions present at birth with prominent hamartomatous changes of dermal smooth muscle and less skin darkening. These have been called smooth muscle hamartomas or congenital Becker nevus (Berger and Levin 1984; Johnson and Jacobs, 1989; Karo and Gange 1981). The clinical appearance of these lesions closely resembles those of the acquired plaques in adolescent boys. Most Becker nevi occur as isolated defects. However, ipsilateral bony abnormalities, acneiform eruptions (Burgeen and Ackerman, 1978), and breast hypoplasia have been described (Glinick et al., 1983; Lucky et al., 1981) in patients with Becker nevi. In addition, cystic lymphangioma, ipsilateral foot enlargement, pectus carinatum, neurofibroma, segmental odontomaxillary dysplasia, and connective tissue nevus have been 915
CHAPTER 50
described in patients with Becker nevus (Oyler et al., 1997). Skeletal abnormalities such as hemivertebrae, spina bifida occulta, scoliosis, cervical ribs, and minor sternal anomalies have also been associated with Becker nevus. Other associated abnormalities include accessory scrotum, congenital adrenal hyperplasia, supernumerary nipples, aplasia of the ipsilateral pectoralis major muscle, and localized lipoatrophy (SantosJuanes et al., 2002). Lichen planus has also been associated within Becker nevus (Terheyden et al., 1998). The acneiform eruptions are thought to be caused by an increased number of androgen receptors within the affected skin. The onset around puberty, the male predominance, and the hypertrichosis all suggest a critical role of local androgen sensitivity.
Pathology Microscopic examination of a Becker nevus reveals regular acanthosis, papillomatosis, variable hyperkeratosis, increased basal layer pigmentation, dermal thickening, and an absence of nevus cells in the dermis. Hyperplasia of hair follicles and sebaceous glands can also occur as well as lengthening and clubbing of the rete ridges. The number of melanocytes is probably normal (Frenk and Delacre, 1970), but one report suggests that it is increased (Tate et al., 1980). Melanocytes surrounding keratinocytes contain an increased density of pigment granules (Oyler et al., 1997). In the dermis there are hyperplastic smooth muscle fibers which are randomly arranged without relationship to hair follicles (Haneke, 1979). These are almost identical to the changes seen in what has been called smooth muscle hamartoma, many of which have some increased epidermal pigmentation (Berger and Levin 1984; Johnson and Jacobs, 1989). Variable hyperplasia of different cell types may be found in these lesions, such as keratinocytes, fibroblasts, melanocytes, sebaceous and pilar epithelium, nerve cells, and smooth muscle cells (Hsu et al., 2001). There are no nevus cell nests such as one would see in melanocytic nevi.
Criteria for Diagnosis The diagnosis of a Becker nevus is usually made on the following grounds: ∑ sharply demarcated hyperpigmented plaque with coarse hair; ∑ the lesion usually presents or enlarges at the time of puberty; and ∑ pathological examination reveals basilar hyperpigmentation without nests of nevus cells. There are also increased smooth muscle fibers in the dermis.
Differential Diagnosis The differential diagnosis includes those conditions with large hyperpigmented patches and plaques. Congenital hairy nevi can have a similar appearance to the congenital variant of Becker nevus. However, these often lack the sharp margination and have a pebbly surface, which is lacking in Becker nevi. Nevus of Ito presents as a brown-gray patch over the posterior trunk. It differs from a Becker nevus in that it lacks hair 916
and has a poorly demarcated border. The differential diagnosis also includes lichen simplex chronicus, postinflammatory hyperpigmentation, and café-au-lait patch.
Pathogenesis The exact cause of this anomaly is unknown. The basic change in the pigmentary system in these lesions appears to be one of an inability of the melanocytes to be downregulated once stimulatory factors activate them (Urbanek and Johnson, 1978). One such stimulatory influence could be endogenous androgens. Becker nevi often appear at about the time of puberty and share features of other androgen-mediated tissues such as coarse terminal hair growth, smooth muscle hyperplasia, and dermal thickening (Person and Longcope, 1984). Lesional tissue has been shown to contain increased numbers of androgen receptors which may be the cause or the result of increased androgen effects at this localized site (Person and Longcope, 1984).
Treatment A Becker nevus has no medical import; thus treatment is for cosmetic purposes only. If the lesion is small, surgical excision is possible. However, many lesions are too large to permit primary closure. Serial partial excisions are possible in these cases. Laser technology has been introduced in the management of pigmented lesions (Geronemus, 1992; Goldberg, 1993; Nelson and Applebaum, 1992). A single Becker nevus has been treated in this way; the results were difficult to assess from the discussion, but this may be a worthwhile avenue for further investigation (Tse et al., 1994). A Q-switched ruby laser can reduce the hyperpigmentation (Adams, 1997).
Prognosis A Becker nevus is benign and has no potential to undergo malignant degeneration. Once established, it remains for the rest of one’s life. However, there have been reports of the hyperpigmentation fading over a number of years (Hsu et al., 2001).
References Adams, S. P. Dermacase. Becker’s nevus. Can. Fam. Physician. 43:855, 863, 1997. Becker, S. W. Concurrent melanosis and hypertrichosis in distribution of nevus unius lateris. Arch. Dermatol. Syphil. 60:155–160, 1949. Berger, T. G., and M. W. Levin. Congenital smooth muscle hamartoma. J. Am. Acad. Dermatol. 11:709–712, 1984. Book, S. E., A. T. Glass, et al. Congenital Becker’s nevus with a familial association. Pediatr. Dermatol. 14:373–375, 1997. Burgeen, B. L., and A. B. Ackerman. Acneform lesions in Becker’s nevus. Cutis 21:617–619, 1978. Copeman, P. W. M., and E. Wilson-Jones. Pigmented hairy epidermal nevus (Becker). Arch. Dermatol. 92:249–252, 1965. Frenk, E., and T. J. Delacre. Zür ultrastruktur der Beckareschen melanose. Hautarzt 9:397–400, 1970. Geronemus, R. G. Q-switched ruby laser therapy of nevus of Ota. Arch. Dermatol. 128:1618–1622, 1992. Glinick, S. E., J. C. Alper, H. Boggars, and J. A. Brown. Becker’s melanosis: Associated abnormalities. J. Am. Acad. Dermatol. 9:509–511, 1983.
ACQUIRED EPIDERMAL HYPERMELANOSES Goldberg, D. J. Benign pigmented lesions of the skin. Treatment with the Q-switched ruby laser. J. Dermatol. Surg. Oncol. 19:376–379, 1993. Haneke, E. The dermal component of melanosis naeviformis Becker. J. Cutan. Pathol. 6:53–58, 1979. Hsu, S., J. Y. Chen, and P. Subrt. Becker’s melanosis in a woman. J. Am. Acad. Dermatol. 45(6 Suppl): S195–196, 2001. Johnson, M. D., and A. H. Jacobs. Congenital smooth muscle hamartoma: A report of six cases and a review of the literature. Arch. Dermatol. 125:820–822, 1989. Karo, K. R., and R. W. Gange. Smooth-muscle hamartoma: Possible congenital Becker’s nevus. Arch. Dermatol. 117:678–679, 1981. Lucky, A. W., M. Saruk, and A. B. Lerner. Becker’s nevus associated with limb asymmetry. Arch. Dermatol. 117:243, 1981. Nelson, J. S., and J. Applebaum. Treatment of superficial cutaneous pigmented lesions by melanin-specific selective photothermolysis using the Q-switched ruby laser. Ann. Plast. Surg. 29:231–237, 1992. Oyler, R. M., D. A. Davis, and J. T. Woosley. Lymphangioma associated with Becker’s nevus: a report of coincident hamartomas in a child. Pediatr. Dermatol. 14:376–379, 1997. Person, J. R., and C. Longcope. Becker’s nevus: an androgenmediated hyperplasia with increased androgen receptors. J. Am. Acad. Dermatol. 10:235–238, 1984. Santos-Juanes, J., C. Galache, J. R. Curto, M. P. Carrasco, A. Ribas, and J. Sanchez del Rio. Acneiform lesions in Becker’s nevus and breast hypoplasia. Int. J. Dermatol. 41:699–700, 2002. Stokes, J. H. Nevus pilaris with hyperplasia of nonstriated muscle. Arch. Dermatol. Syphil. 7:479–481, 1923. Tate, P. R., S. J. Hodge, and L. G. Owen. A quantitative study of melanocytes in Becker’s nevus. J. Cutan. Pathol. 7:404–409, 1980. Terheyden, P., B. Hornschuh, S. Karl, J. C. Becker, and E. B. Brocker. Lichen planus associated with Becker’s nevus. J. Am. Acad. Dermatol. 38(5 Pt 1): 770–772, 1998. Tse, Y., V. J. Levine, S. A. McClain, and R. Ashinoff. The removal of cutaneous pigmented lesions with the Q-switched ruby laser and the Q-switched neodymium: yttrium-aluminum-garnet laser. A comparative study. J. Dermatol. Surg. Oncol. 20:795–800, 1994. Tymen, R., J. F. Forestier, B. Boutet, and B. Colomb. Nevus tardif de Becker. Ann. Dermatol. Venereol. 108:41–46, 1981. Urbanek, R. W., and W. C. Johnson. Smooth muscle hamartoma associated with Becker’s nevus. Arch. Dermatol. 114:104–106, 1978.
Fig. 50.7. A large isolated café-au-lait spot in a baby.
Fig. 50.8. Small café-au-lait spot on the scrotum.
Café-au-lait macule, circumscribed melanotic macule, hypermelanotic macule, circumscribed hypermelanosis.
included more than 4000 newborns (Tekin et al., 2001). The vast majority of infants with café-au-lait spots have no associated abnormalities. Solitary café-au-lait spots are common in the general population affecting up to a third of normal children; however, multiple lesions are unusual and raise the suspicion of a multiple-system disorder (Landau and Krafchik, 1999). There are several multiorgan disorders which include them, in addition to neurofibromatosis, including McCune–Albright syndrome, tuberous sclerosis, Bloom syndrome, Watson syndrome, and ring chromosome syndrome. The association with café-au-lait spots and ataxia-telangectasia, Silver–Russell syndrome, juvenile xanthogranuloma, and LEOPARD syndrome is less clear but there may be an association.
Epidemiology
Clinical Findings
Café-au-lait spots are a common finding at birth (Alper et al., 1979; Whitehouse, 1966) but the incidence rate depends on the race of the neonate. Café-au-lait spots were noted in 0.3% of Caucasians and 18% of African-Americans in a study that
Café-au-lait spots present as uniformly pigmented tan-brown, oval or round macules or patches. The pigmented border may be either smooth or jagged (Figs 50.7–50.9). Those café-aulait spots associated with McCune–Albright syndrome often
Café-au-lait Spots Norman Levine and Cynthia Burk
Historical Background Although the first written description of café-au-lait spots is lost to history, it first became an important cutaneous sign in the late 1800s when von Recklinghausen first described the neural nature of neurofibromas and others noted café-au-lait macules as a part of the syndrome (Marie and Bernard, 1896).
Synonyms
917
CHAPTER 50
Differential Diagnosis Café-au-lait spots must be distinguished from other conditions which produce pigmented macules. A congenital melanocytic nevus is present at birth and is often uniformly brown. Most of these lesions acquire some substance and/or hair early in life, while café-au-lait spots remain macular throughout life. Becker nevus may present at or near birth and have an almost identical appearance to café-au-lait spots. As the child ages, the lesions acquire coarse hair and may become palpable. The increased dermal smooth muscle seen on skin biopsy clinches the diagnosis of Becker nevus. Nevus spilus is characterized by a light-brown patch, but differs from a café-au-lait spot in that it is stippled with dark-brown macules (Levine, 1995). Ephelides, congenital nevus, lentigo, nevocellular nevus, and segmental pigmented disorder are all other skin lesions to consider in the differential diagnosis (Landau and Krafchik, 1999). There are several related congenital pigmentary abnormalities, collectively called dermal melanosis; these include nevus of Ota, nevus of Ito, Mongolian spot, and perhaps, blue nevus. All of these conditions impart a blue or gray hue to the skin because of the deep dermal melanin deposition, which differentiates them from café-au-lait spots. In darkly pigmented children, it may be very difficult to distinguish blue from brown colors. The most common of these conditions, Mongolian spots almost always resolve in the first few years of life; café-au-lait spots are stable.
Pathogenesis Fig. 50.9. Café-au-lait spot showing a nevoid distribution.
have characteristic jagged edges; those spots associated with neurofibromatosis 1 usually have smooth margins (Cohen et al., 2000). Generally, more lesions are found in areas like the trunk, buttocks, and lower limbs and tend to spare the head, neck, and upper extremities (Cohen et al., 2000). In newborns, lesions are mainly concentrated to the buttock area and range in size from 0.2 cm to 4 cm, whereas in older children lesions are mainly centered on the trunk and can be 1.5–30 cm in size (Landau and Krafchik, 1999).
Pathology Light microscopic examination reveals increased epidermal melanin with normal numbers of melanocytes. Ultrastructural examination shows increased pigment without giant pigment granules (macromelanosomes), which are a feature of the caféau-lait spots that occur in neurofibromatosis.
Criteria for Diagnosis ∑ Lightly pigmented macules or patches. ∑ Fewer than six lesions with a diameter of 1.5 cm or larger.
If present, this is almost pathognomonic of neurofibromatosis (Korf, 1992). 918
The etiology of these congenital lesions is not known. It appears that there are a normal number of melanocytes, which are more active at synthesizing melanin.
Treatment There are no medical indications for treating café-au-lait spots. They have no malignant potential and are usually in locations of little esthetic significance. The Q-switched ruby laser, the Q-switched Nd-YAG laser, and the pulsed dye laser have all recently been used with variable responses (Shimboshi and Kamide, 1997).
Prognosis These innocuous macules and patches increase in size only in proportion to the growth of the child. They may lighten slightly as one ages, but usually remain unchanged throughout adult life.
References Alper, J., L. B. Holmes, and M. C. Mihm Jr. Birthmarks with serious medical significance: nevocellular nevi, sebaceous nevi, and multiple cafe au lait spots. J. Pediatr. 95:696–700, 1979. Carpo, B. G., J. M. Gravelink, and S. V. Gravelink. Laser treatment of pigmented lesions in children. Semin. Cutan. Med. Surg. 18:233– 243, 1999. Cohen, J. B., C. K. Janniger, and R. A. Schwartz. Café-au-lait spots. Cutis 66:22–24, 2000.
ACQUIRED EPIDERMAL HYPERMELANOSES Korf, B. R. Diagnostic outcome in children with multiple cafe au lait spots. Pediatrics 90:924–927, 1992. Landau, M., and B. R. Krafchik. The diagnostic value of café-au-lait macules. J. Am. Acad. Dermatol. 40(6 Pt 1): 877–890, 1999. Levine, N. Pigmentary abnormalities. In: Pediatric Dermatology, 2nd ed., L. A. Schachner, and R. C. Hansen (eds). New York: Churchill Livingstone, 1995, pp. 541–542. Marie, P., and A. Bernard. Presentation d’un malade atteint de neuro-fibromaose generalisée. Bull. Mem. Soc. Med. Hop. Paris 13:200–203, 1896. Shimboshi, T., and R. Kamide. Long term follow-up in treatment of solar lentigo and café-au-lait macules with Q-switched ruby laser. Aesth. Plast. Surg. 21:445–448, 1997. Tekin, M., J. N. Bodurtha, and V. M. Riccardi. Café-au-lait spots: the pediatrician’s perspective. Pediatr. Rev. 22:82–90, 2001. von Recklinghausen, F. D. Ueber die multiplen Fibrome der Haut und ihre Beziehung zu den multiplen Neuromen. Berlin: Hirschwald, 1882. Whitehouse, D. Diagnostic value of café-au-lait spots in children. Arch. Dis. Child. 41:316–319, 1966.
Carcinoid Syndrome Norman Levine and Cynthia Burk
Historical Background The carcinoid syndrome is an uncommon complication of malignant carcinoid tumors, occurring in about 4% of all patients with carcinoid tumors (Wilson, 1970). Since its initial description by Thorsen et al. (1954), over 200 cases have been reported, undoubtedly a low estimate of the total number that have occurred. Recent reports indicate that the estimated annual incidence is between 1 and 8.4/100 000 (Rohaizak and Farndon, 2002).
stenosis/insufficiency, endocardial fibrosis, pulmonary valve stenosis, and rarely, sexual dysfunction, vasospastic angina, retroperitoneal fibrosis, rheumatoid arthritis, and mental status changes. These clinical signs associated with carcinoid tumors are dependent on the monoamine elaborated; these include catecholamines, histamine, bradykinins, adrenocorticotropin, vasopressin, and prostaglandins (Feldman, 1987). The location of the primary tumor dictates the types of symptoms and signs of the syndrome. For example midgut carcinoids are more likely to produce carcinoid syndrome than are foregut tumors, but if carcinoid syndrome does occur with a foregut neoplasm, there is often very profound flushing. Midgut carcinoids are associated with a more transient flush which is more cyanotic in appearance, telangiectasias, cardiac lesions, and pulmonary fibrosis (Kaplan, 1991). Diarrhea occurs with tumors from all locations. Although much is known about these various mediators, it is not entirely clear exactly which one is associated with the various signs and symptoms. The cardinal cutaneous sign of carcinoid syndrome is cutaneous flushing. The color can vary from bright red or violaceous to pink-orange. It is usually limited to the upper torso, neck, and face (Fig. 50.10). Most paroxysms last for only a few minutes, although severe attacks can last much longer and be associated with such intense and widespread flushing that periorbital edema and a decrease in blood pressure can ensue. Most episodes occur randomly, but some patients note that emotional stress, physical exertion, ethanol ingestion, or
Synonyms Carcinoidosis (Weichert, 1970).
Epidemiology Carcinoid syndrome occurs mostly in those patients with malignant carcinoid tumors of the intestinal tract, particularly the small intestine. Rarely, the syndrome may arise from bronchial, stomach, or appendix neoplasms. There is no race or sex predilection for either the primary tumor or for the fullblown syndrome.
Clinical Findings Enterochromaffin cells are embryologically related to thyroid C cells, adrenal medullary cells, and melanocytes, all derived from the neural crest. These cells concentrate amino acid precursors of aromatic amines and produce bioamines; the acronym for these cells is APUD and the tumors are sometimes called “apudomas.” Other such tumors include thyroid adenomas, pituitary adenomas, parathyroid adenomas, and adrenal cortical adenomas. Up to 18% of patients with malignant carcinoid tumors present with the carcinoid syndrome, which may include signs and symptoms of facial flushing with telangiectasia, lacrimation, diarrhea/nausea, bronchospasm/wheezing, tricuspid
Fig. 50.10. Red violaceous flush of carcinoid syndrome (see also Plate 50.3, pp. 494–495).
919
CHAPTER 50
defecation can precipitate an attack (Feingold and Elias, 1988). After years of chronic flushing episodes, many people develop fixed telangiectasias of the face and neck. Cutaneous hyperpigmentation occasionally occurs with carcinoid syndrome. Three different circumstances lead to a change in skin pigment. Carcinoid tumors secrete large amounts of serotonin; the precursor for this amine is tryptophan. When excess tryptophan is diverted for this synthesis, a deficiency of another tryptophan product, niacin, may result which may lead to the clinical signs of pellagra. The eruption of this vitamin deficiency consists of gray-black, keratotic plaques in a photodistribution, localized to the dorsal forearms, legs, and trunk (Castiello and Lynch, 1972). Carcinoid tumors rarely can secrete excess adrenocorticotropic hormone (ACTH). This can result in generalized hyperpigmentation, similar to what is seen in Addison disease (Rodriguez Vaca et al., 1987). The third type of skin pigment change occurs over the forehead, wrists, thighs, and trunk; it consists of yellow-brown, slightly atrophic plaques (Stampien et al., 1993). Many other cutaneous findings have been reported in the carcinoid syndrome. These include pruritus, scleroderma, cutaneous metastases, pyoderma gangrenosum, and erythema annulare centrifugum (Donaldson, 2000; Wilkin and Demis, 1995). A few primary carcinoid tumors of the skin have also been described (Bart et al., 1990; Van Dijk and ten Seldam, 1975).
Criteria for Diagnosis
Pathology
Pathogenesis
Microscopically, carcinoid tumors consist of small round cells in monotonous sheets with uniform nuclei and cytoplasm. They stain positive with argyrophil, argentaffin, chromogranin, and nonspecific enolase. It is difficult to distinguish benign versus malignant carcinoid tumors via pathological appearance alone.
The mediators secreted by the tumor cells are almost certainly responsible for the signs and symptoms of carcinoid syndrome. However, it has been very difficult to correlate specific clinical findings with the effects of a given mediator. One exception to this may be the generalized hyperpigmentation, which seems to be a direct result of excess ACTH secretion (Rodriguez Vaca et al., 1987). Another well-described association is the pellagralike findings in those patients with high circulating levels of serotonin. As noted above, tryptophan is diverted from niacin synthesis to serotonin synthesis, leaving the affected patient with a niacin deficiency state which leads to pellagra. The cutaneous sclerosis associated with the carcinoid syndrome may also be related to an impairment of tryptophan metabolism (Ratnavel et al., 1994). There are several candidates for mediators of the flushing and diarrhea that are so common in these patients. These include histamine, 5-hydroxytryptamine (5-HT), prostaglandins, vasoactive intestinal peptide, glucagon, gastrin, calcitonin, kallikrein, substance P, and substance K (Kaplan, 1991). It is possible that combinations of these mediators are responsible for the clinical findings.
Diagnostic Evaluation Light microscopic examination of flushed skin is nondiagnostic. The hyperpigmented skin reveals increased epidermal melanin. The evaluation of carcinoid syndrome is based on the observation that most of these tumors secrete large amounts of serotonin. This amine is metabolized in the blood to 5hydroxyindoleacetic acid (5-HIAA) which is then excreted through the kidneys. Elevated levels of this metabolite in the urine are highly suggestive of the presence of a carcinoid tumor. Since many foods can affect 5-HIAA excretion, an elimination diet is necessary before this determination is undertaken (Wilkin and Demis, 1995). Selective abdominal vein catheterization with blood sampling for serotonin can localize the site of the tumor and can identify the rare cases where urine 5-HIAA levels are normal (Davis and Rosenberg, 1961; Kuwada, 2000). When clinical findings are equivocal, one can attempt to provoke a flushing episode. Ethanol, pentagastrin, or minute doses of epinephrine may be used for this purpose. 920
∑ Metastatic carcinoid tumor. ∑ Symptom complex of paroxysmal flushing and diarrhea. ∑ Urinary 5-HIAA levels above 15 mg per day (in most
instances).
Differential Diagnosis The differential diagnosis of carcinoid syndrome includes other conditions associated with flushing (Wilkin, 1983). Systemic mastocytosis can produce flushing and diarrhea. Elevated urinary histamine and its metabolites and a normal urinary 5-HIAA clearly separate it from carcinoid syndrome. Menopausal flushing can simulate that seen in those with carcinoid tumors. Often, the same triggers are operative for both processes. The drenching sweats and nighttime episodes are more common in those with menopausal symptoms. If there is any doubt, a urinary 5-HIAA measurement will separate these two entities. Pheochromocytoma is a tumor of the adrenal gland which secretes a catecholamine which can cause occasional episodes of paroxysmal flushing. However, the flushed sensation appears only after an attack of headache, tachycardia, chest pain, and pallor (Wilkin, 1983). Rosacea occurs in individuals who are prone to flush. Facial telangiectasias identical to those noted in carcinoid syndrome are an essential part of the disease. The other clinical manifestations of carcinoid syndrome are absent and urinary 5-HIAA is normal.
Treatment If the carcinoid tumor can be surgically excised, the signs and symptoms of the syndrome can disappear (Rodriguez Vaca et al., 1987). However, great care by the anesthesiologist is needed to prevent a carcinoid crisis with hypotension and
ACQUIRED EPIDERMAL HYPERMELANOSES
cardiac arrest from occurring (RuDusky, 1999). Hepatic resection as well as hepatic artery embolization have been used with a good performance status for removing metastatic disease (Filosso et al., 2002). Although the radiosensitivity of these tumors has not been reported, chemotherapy regimens including the combination of 5-fluorouracil and streptozocin have been tried, with moderate success (Filosso et al., 2002). Thus, it should be used as a late treatment for patients with carcinoid tumors/syndrome. Somatostatin and its longer-acting analogs octreotide and lanreotide are the drugs of choice for managing malignant carcinoid syndrome as they have been proved to improve symptoms and decrease the tumor progression (Ganim and Norton 2000; O’Toole et al., 2000; Filosso et al., 2002; Leong and Pasieka, 2002). Treatment with recombinant interferon-a may control the symptoms of the disease and in some cases increase mean survival time (Filosso et al., 2002). Serotonin antagonists such as methysergide or ondansetron, a 5-HT3 antagonist, can be used to slow gastric emptying and improve both diarrhea and nausea (Wymenga et al., 1998). However, these agents do little for the flushing. Cyproheptadine has antiserotonin and antihistamine effects and is sometimes useful in the treatment of the flush. Clonidine is another agent of value in histamine-mediated flushing. Treatment for the wheezing and bronchospasm should include systemic corticosteroids, but not epinephrine, which could initiate a vasomotor attack in these patients. For the patient who is at risk for the pellagralike reaction, niacin supplementation is essential. Many foods containing tyramine can precipitate a flushing paroxysm; these include tomatoes, eggplant, and avocados. Alcohol and hot, spicy foods can also evoke an attack. The patient should be given a list of the foods to eat in moderation or to avoid altogether.
Prognosis The prognosis depends on the site and the stage of the disease at diagnosis. Rectal and appendageal tumors do not affect survival; lesions in other intestinal sites have a five-year survival of 65% with lymph node involvement and only an 18% survival if there are hepatic metastases, a situation common in the carcinoid syndrome. Once flushing ensues, the median survival is less than three years. Patients with greatly elevated urinary 5-HIAA (greater than 150 mg/day) can expect to live only about 13 months (Kaplan, 1991). Nearly half of all patients with carcinoid tumors who die from the disease succumb to heart failure (Ganim, 2000).
References Bart, R. S., H. Kamino, J. Waisman, A. Lindner, and S. Colen. Carcinoid tumor of skin: report of a possible primary case. J. Am. Acad. Dermatol. 22:366–370, 1990. Castiello, R. J., and P. J. Lynch. Pellagra and the carcinoid syndrome. Arch. Dermatol. 105:574–577, 1972. Davis, R. B., and J. C. Rosenberg. Carcinoid syndrome associated with hyperserotoninemia and normal 5-hydroxyindoleacetic acid excretion. Am. J. Med. 30:167–174, 1961. Donaldson, D. Carcinoid tumours — the carcinoid syndrome and
serotonin (5-HT): a brief review. J. Royal Soc. Health 120:78, 2000. Feingold, K. R., and P. M. Elias. Endocrine–skin interactions. Cutaneous manifestations of adrenal disease, pheochromocytomas, carcinoid syndrome, sex hormone excess and deficiency, polyglandular autoimmune syndromes, multiple endocrine neoplasia syndromes, and other miscellaneous disorders [review]. J. Am. Acad. Dermatol. 19:1–20, 1988. Feldman, J. M. Carcinoid tumors and syndrome. Semin. Oncol. 14:237–260, 1987. Filosso, P. L., E. Ruffini, A. Oliaro, E. Papalia, G. Donati, and O. Rena. Long-term survival of atypical bronchial carcinoids with liver metastases, treated with octreotide. Eur. J. Cardiothorac. Surg. 21:913–917, 2002. Ganim, R. B., and J. A. Norton. Recent advances in carcinoid pathogenesis, diagnosis and management. Surg. Oncol. 9:173–179, 2000. Kaplan, L. M. Endocrine tumors of the gastrointestinal tract and pancreas. In: Harrison’s Principles of Internal Medicine, J. D. Wilson et al. (eds). New York: McGraw-Hill, 1991, pp. 1386–1393. Kuwada, S. K. Carcinoid tumors. Semin. Gastrointest. Dis. 11:157– 161, 2000. Leong, W. L., and J. L. Pasieka. Regression of metastatic carcinoid tumors with octreotide therapy: two case reports and a review of the literature. J. Surg. Oncol. 79:180–187, 2002. O’Toole, D., M. Ducreux, G. Bommelaer, J. L. Wemeau, O. Bouche, Catus F, J. Blumberg, and P. Ruszniewski. Treatment of carcinoid syndrome: a prospective crossover evaluation of lanreotide versus octreotide in terms of efficacy, patient acceptability, and tolerance. Cancer 88:770–776, 2000. Rohaizak, M., and J. R. Farndon. Use of octreotide and lanreotide in the treatment of symptomatic non-resectable carcinoid tumours. Aust. N. Z. J. Surg. 72:635–638, 2002. RuDusky, B. M. Carcinoid — a diagnostic and therapeutic dilemma [comment]. Chest 116:1142–1143, 1999. Ratnavel, R. C., N. P. Burrows, and R. J. Pye. Scleroderma and the carcinoid syndrome. Clin. Exp. Dermatol. 19:83–85, 1994. Rodriguez Vaca, M. D., M. Angel, I. Halperin, J. Freixenet, M. Marti, M. J. Martinez Osaba, J. Sanchez Lloret, A. Palacin, and E. Vilardell. Diagnosis of lung carcinoid with cutaneous hyperpigmentation eight years after bilateral adrenalectomy. J. Endocrinol. Invest. 10:537–540, 1987. Stampien, T. M., I. Thomas, and R. A. Schwartz. Cutaneous pigmentation as a sign of systemic disease. In: Pigmentation and Pigmentary Disorders, N. Levine (ed.). Boca Raton, FL: CRC Press, 1993, pp. 376–377. Thorson, A., G. Biorck, and G. Bjorkman. Malignant carcinoid of the small intestine with metastases to the liver, valvular disease of the right side of the heart (pulmonary stenosis and tricuspid regurgitation without septal defects), peripheral vasomotor symptoms, bronchoconstriction, and an unusual type of cyanosis: A clinical and pathologic syndrome. Am. Heart Assoc. J. 47:795–817, 1954. Van Dijk, C., and L. E. J. ten Seldam. A possible primary cutaneous carcinoid. Cancer 36:1016–1020, 1975. Weichert, R. F. The neural ectodermal origin of the peptide secreting endocrine glands: A unifying concept for the etiology of multiple endocrine adenomatosis and the inappropriate secretion of peptide hormones by non-endocrine tumors. Am. J. Med. 49:232–241, 1970. Wilkin, J. K. Flushing reactions. Rec. Adv. Dermatol. 6:157–187, 1983. Wilkin, J. K., and D. J. Demis. Carcinoidosis (carcinoid syndrome). In: Clinical Dermatology, J. D. Demis (eds). Philadelphia: Lippincott-Raven Publishers, 1995, pp. 1–7. Wilson, H. Carcinoid syndrome. Curr. Probl. Surg. 11:36–41, 1970. Wymenga, A. N., E. G. de Vrieds, M. K. Leijsma, I. P. Kema, and J. H. Kleibeuker. Effects of ondansetron on gastrointestinal symptoms in carcinoid syndrome. Eur. J. Cancer 34:1293–1294, 1998.
921
CHAPTER 50
Confluent and Reticulated Papillomatosis Norman Levine and Cynthia Burk
Historical Background Two French dermatologists, Gougerot and Carteaud (1927, 1932), were the first to report a series of cases of an unusual papillomatous disease. They described three slightly different variants, confluent and reticulated papillomatosis (CRP), punctate, pigmented, verrucous papillomatosis, and nummular and confluent papillomatosis. Only the first variety is seen with any frequency today. Subsequently, this condition was reported in the United States (Wise and Sachs, 1937). Confluent and reticulated papillomatosis has now been seen in all parts of the world. Approximately 50 cases have been reported since 1978 (Lee et al., 1994).
Fig. 50.11. Localized pigmented confluent and reticulated papillomatosis (see also Plate 50.4, pp. 494–495).
Synonyms Cutaneous papillomatosis, CRP of Gougerot and Carteaud, nummular and confluent papillomatosis, papillomatose pigmentee innominee, papillomatose pigmentee confluente et reticulee innominee, atrophie brilliante, parakeratose brilliante (Waisman, 1995).
Epidemiology Early studies reported that CRP was more common in women and in black people (Hamilton et al., 1980). A review of many published studies led the investigators to refute this claim (Lee et al., 1994). They found no difference in the incidence between the sexes or between any racial group. The typical onset is around age 20. Most of the reported cases have been sporadic, although there have been a few familial occurrences (Baden, 1965). Confluent and reticulated papillomatosis is 2.5 times more common in women and two times more common in black people (Hamilton et al., 1980; Montemarano et al., 1996; Solomon and Laude, 1996).
Fig. 50.12. Close-up view of the patient in Figure 50.11.
Clinical Findings A typical patient with CRP presents with 1–2 mm red, verrucous, minimally scaly papules in the inframammary, interscapular, and epigastric region; these enlarge and eventually coalesce into brown plaques (Figs 50.11–50.13). The lesions lead to an accentuation of the natural skin folds on the neck and in the axillae. As the lesions spread peripherally, the advancing borders take on a reticulated appearance (Hamilton et al., 1980; Lee et al., 1994). The mucous membranes, palms, and soles are spared.
Pathology
Fig. 50.13. Extensive confluent and reticulated papillomatosis of Gougerot and Carteaud (see also Plate 50.5, pp. 494–495).
Light microscopic examination reveals variable hyperkeratosis, and a normal basal layer. Epidermal atrophy over the dermal papillary tips may alternate with mild to moderate acanthosis. Papillomatosis is always present. In the dermis, there is a mild perivascular lymphocytic infiltrate, vascular dilatation, and occasional upper dermal edema (Hamilton et al., 1980).
Electron microscopic examination shows an alteration of cornified cell structures showing snake coil-like, or trianglelike stacks, an increase in the Odland bodies in the stratum granulosum, and an increased number of melanosomes in the stratum corneum (Montemarano et al., 1996). There are also an increased number of transitional cells between the stratum
922
ACQUIRED EPIDERMAL HYPERMELANOSES
granulosum and the stratum corneum (Inaloz et al., 2002), an increase in the number of lamellar granules in the granular cell layer, and an increased number of melanosomes in the upper epidermal layers. The basal layer melanocytes appear normal (Chang et al., 1996; Jimbow et al., 1992).
Criteria for Diagnosis The diagnostic features that should make one consider the diagnosis of CRP are as follows (Lee et al., 1994): ∑ Hyperpigmented papules and plaques involving the chest and/or back with a reticulated peripheral margin. ∑ No hyphae suggestive of tinea versicolor present on potassium hydroxide preparation or skin biopsy. ∑ Histologic changes including hyperkeratosis, papillomatosis, acanthosis alternating with mild atrophy, and evidence of mild dermal inflammation and vasodilatation.
Differential Diagnosis The skin diseases to be considered include tinea versicolor, acanthosis nigricans, cutaneous amyloidosis, keratosis follicularis, certain forms of ichthyosis, erythrokeratoderma variabilis, and epidermodysplasia verruciformis. The main condition that must be differentiated from CRP is tinea versicolor. In fact, the two skin problems are so similar clinically, and even mycologically on occasion (Thomsen, 1979), some believe that CRP is, indeed, a variety of tinea versicolor (Roberts and Lachapelle, 1969). The arguments against this notion are discussed in the section on pathogenesis. Although the distribution and morphology of the full-blown lesions is similar, the histologic changes are distinct enough to diagnose these as distinct entities. Acanthosis nigricans can sometimes be confused with CRP. Histopathologically, they are indistinguishable (Ginarte et al., 2002). The lesions of acanthosis nigricans are usually velvety rather than scaly. Although the neck is commonly involved in both diseases, acanthosis nigricans appears prominently in the axillae and groin area while CRP presents on the central back and chest. Mucous membrane lesions can be found in acanthosis nigricans while this does not occur in CRP (Hamilton et al., 1980).
Pathogenesis The etiology of CRP is not known; however, several theories have been proposed. Because of its clinical similarity to tinea versicolor, some consider CRP to be of fungal origin. The response to antifungal agents such as selenium sulfide has also led to this conclusion (Nordby and Mitchell, 1986). However, this agent probably is working in CRP as an inhibitor of keratinization rather than as an antimicrobial drug (Sheth, 1983). Meischer was the first to suggest that CRP was a disorder of keratinization (Meischer, 1954). Many others have voiced this same view since that time (Bruynzeel-Koomen and de Witt, 1984; Jimbow et al., 1992; Lee et al., 1991). Electron microscopic studies have provided strong evidence that this is the case (Jimbow et al., 1992; Lee et al., 1991). Early investigators believed that CRP was associated with
endocrine dysfunction because of its clinical similarity to acanthosis nigricans (Waisman, 1953). There have been occasional cases of CRP appearing in patients with endocrine dysfunction such as Cushing disease, hypothyroidism (Waisman, 1995), diabetes mellitus, obesity, and menstrual irregularities (Chang et al., 1996; Montemarano et al., 1996). The vast majority of cases have no associated endocrine abnormalities, however; thus, this theory is no longer seriously considered. Other theories of causation with little corroborative evidence include photosensitivity (Vassileva et al., 1989), cutaneous amyloidosis (Groh and Schnyder, 1983), genetic factors (Henning and de Wit, 1981), and atopy (Chang et al., 1996).
Treatment Many different therapeutic modalities have been tried in CRP, but most have fallen by the wayside. These include keratolytics, superficial radiation, thyroid replacement, phototherapy, anticholinergic agents, hydroquinone, selenium sulfide, weight reduction, and crude liver extract, presumably for its vitamin A content (Hamilton et al., 1980). The treatment of choice for CRP is minocycline, 100–200 mg per day for weeks to months (Baalbaki, 1993; Chang et al., 1996; Petit et al., 1989; Puig, 1995; Sassolas, 1992). Still, other antibiotics may also be efficacious, including oral fusidic acid (1000 mg daily), clarithromycin (500 mg daily for five weeks), erythromycin (1000 mg daily), and azithromycin (500 mg daily). Complete clearing after treatment with these various antibiotics raises the possibility that reticulated papillomatosis is caused by a bacterial infection (Jang et al., 2001). Retinoids have been used in several patients with CRP; the results are very encouraging. Isotretinoin (Hodge and Ray, 1991; Lee et al., 1994) and etretinate (Baalbaki et al., 1993; Bruynzeel-Koomen and de Witt, 1984; Hirokawa et al., 1994) have both worked well in this disease. Long-term treatment is necessary since relapse occurs promptly after discontinuation of either of these drugs. In addition, topical tacalcitol and calcipotriol (both vitamin D analogs which regulate cell differentiation and inhibit the proliferation of keratinocytes) have been effective (Ginarte et al., 2002).
Prognosis CRP is a chronic disease with a slow, irregular progression. With few exceptions (Thomsen, 1979) there is little tendency for spontaneous resolution.
References Baalbaki, S. A., J. A. Malak, and M. A. al-Khars. Confluent and reticulated papillomatosis. Treatment with etretinate. Arch. Dermatol. 129:961–963, 1993. Baden, H. P. Familial cutaneous papillomatosis. Arch. Dermatol. 92:394–395, 1965. Bruynzeel-Koomen, C., and R. F. E. de Witt. Confluent and reticulated papillomatosis successfully treated with the aromatic etretinate. Arch. Dermatol. 120:1236–1237, 1984. Chang, S. N., S. C. Kim, S. H. Lee, and W. S. Lee. Minocycline treatment for CRP. Cutis 57:454–457, 1996.
923
CHAPTER 50 Ginarte, M., J. M. Fabeiro, and J. Toribio. Confluent and reticulated papillomatosis (Gougerot-Carteaud) successfully treated with tacalcitol [comment]. J. Dermatol. Treat. 13:27–30, 2002. Gougerot, H., and A. Carteaud. Papillomatose pigmentee innominee. Bull. Soc. Franc. Dermatol. Syphiligr. 34:719–721, 1927. Gougerot, H., and A. Carteaud. Neue formen der papillomatose. Arch. Dermatol. Syphil. 165:232–267, 1932. Groh, V., and U. Schnyder. Nosologie der Papillomatose papuleuse confluente et réticulée (Gougerot-Carteaud). Hautarzt 34:81–86, 1983. Hamilton, D., V. Tavafoghi, J. C. Shafer, and G. W. Hambrick Jr. Confluent and reticulated papillomatosis of Gougerot and Carteaud: Its relation to other papillomatoses. J. Am. Acad. Dermatol. 2:401– 410, 1980. Henning, J. P., and R. F. de Wit. Familial occurrence of CRP. Arch. Dermatol. 117:809–810, 1981. Hirokawa, M., M. Matsumoto, and H. Iizuka. Confluent and reticulated papillomatosis: a case with concurrent acanthosis nigricans associated with obesity and insulin resistance. Dermatology 188:148–151, 1994. Hodge, J. A., and M. C. Ray. Confluent and reticulated papillomatosis: response to isotretinoin. J. Am. Acad. Dermatol. 24:654, 1991. Inaloz, H. S., G. K. Patel, and A. G. Knight. Familial CRP. Arch. Dermatol. 138:276–277, 2002. Jang, H. S., C. K. Oh, J. H. Cha, S. H. Cho, K. S. Kwon. Six cases of CRP alleviated by various antibiotics. J. Am. Acad. Dermatol. 44:652–655, 2001. Jimbow, M., O. Talpash, and K. Jimbow. Confluent and reticulated papillomatosis: clinical, light and electron microscopic studies. Int. J. Dermatol. 31:480–483, 1992. Lee, M. P., M. J. Stiller, S. A. McClain, J. L. Shupack, and D. E. Cohen. Confluent and reticulated papillomatosis: Response to high-dose oral isotretinoin therapy and reassessment of epidemiologic data. J. Am. Acad. Dermatol. 31:327–331, 1994. Lee, S. H., E. H. Choi, and W. S. Lee. Confluent and reticulated papillomatosis: a clinical, histopathological, and electron microscopic study. J. Dermatol. 18:725–730, 1991. Meischer, G. Erythrokeratodermia papillaris et reticularis. Dermatologica 108:303–314, 1954. Montemarano, A. D., M. Hengge, P. Sau, and M. Welch. Confluent and reticulated papillomatosis: response to minocycline. J. Am. Acad. Dermatol. 34(2 Pt 1): 253–256, 1996. Nordby, C., and A. Mitchell. Confluent and reticulated papillomatosis responsive to selenium sulfide. Int. J. Dermatol. 25:194–199, 1986. Petit, A., P. Evenou, and J. Civatte. Papillomatose confluente et reticulée de Gougerot et Carteaud: traitment par mynocicline. Ann. Dermatologie Venereologie 116:29–30, 1989. Puig, L., and J. M. de Moragas. Confluent and reticulated papillomatosis of Gougerot and Carteaud: minocycline deserves trial before etretinate [letter]. Arch. Dermatol. 131:109–110, 1995. Roberts, S., and J. Lachapelle. Confluent and reticulate papillomatosis (Gougerot-Carteaud) and Pityrosporum orbiculare. Br. J. Dermatol. 81:841–845, 1969. Sassolas, B., P. Plantin, and G. Guillet. Confluent and reticulated papillomatosis: treatment with minocycline. J. Am. Acad. Dermatol. 26:501–502, 1992. Sheth, R. A. A comparison of miconazole nitrate and selenium disulfide as anti-dandruff agents. Int. J. Dermatol. 22:123–125, 1983. Solomon, B. A., and T. A. Laude. Two patients with CRP: response to oral isotretinoin and 10% lactic acid lotion. J. Am. Acad. Dermatol. 35:645–646, 1996. Thomsen, K. Confluent and reticulated papillomatosis (GougerotCarteaud). Acta Derm. Venereol. Suppl. (Stockh.) 59:185–187, 1979. Vassileva, S., K. Pramatarov, and L. Popova. Ultraviolet light-induced CRP. J. Am. Acad. Dermatol. 21:413–414, 1989.
924
Waisman, M. Cutaneous papillomatosis, pseudoacanthosis nigricans, and benign acanthosis nigricans. South. Med. J. 46:162–169, 1953. Waisman, M. Cutaneous papillomatosis (Gougerot-Carteaud). In: Clinical Dermatology, J. D. Demis (eds). Philadelphia: LippincottRaven Publishers, 1995, pp. 41–45. Wise, F., and W. Sachs. Cutaneous papillomatosis. Arch. Dermatol. Syphil. 36:475–485, 1937.
Cutaneous Amyloidosis Norman Levine and Cynthia Burk
Historical Background In the mid-1800s, Virchow first coined the term “amyloidosis” to describe starchlike substances in the skin and in other organs (Virchow, 1971). He was actually describing the ground substance that surrounded the amyloid fibrils. Since that time, efforts have been made to apply a uniform definition to these fibrils, which have some similarities in spite of greatly differing chemical compositions (Glenner, 1980). It is now known that all amyloids have two common characteristics: (1) they have straight, nonbranching filaments composed of polypeptide chains and a special three-dimensional structure, b-pleating, and (2) they all stain positively with Congo red (Eanes and Glenner, 1968).
Synonym b-fibrilloses.
Epidemiology Cutaneous amyloidosis is seen throughout the world, but is more common among Asians and Latin Americans. People of all ages may be affected but it is far more prevalent during adult life.
Clinical Findings There are several different clinical patterns associated with localized cutaneous amyloid deposition. The most common types are macular and lichen amyloidosis. These are probably variations on the same theme, since there are cases of a mixed picture in the same patient and macular amyloidosis becoming lichenoid over time (Iwasaki et al., 1991; Kibbi et al., 1992). In the purely macular variety, asymptomatic, poorly defined brown to gray-brown macules are found, most commonly in the interscapular area, over the shoulders (Fig. 50.14), on the face, or on the extremities (Black and WilsonJones, 1971; Brownstein and Hashimoto, 1972). The pigmentation may appear in parallel bands; this rippled hyperpigmentation occurs in no other pigmentary disorder other than macular amyloidosis. Lichen amyloidosis presents as pruritic, flesh-colored papules which coalesce into flat-topped (lichenoid), mildly keratotic plaques. The anterior legs (Figs 50.15 and 50.16) and upper back are frequent sites of lichen amyloidosis (Hashimoto and Yoong Onn, 1971). Mixed, or biphasic cutaneous amyloidosis consists of both the macular (Fig. 50.17) and lichenoid variety in the same patient in different lesions
ACQUIRED EPIDERMAL HYPERMELANOSES
Fig. 50.16. Typical hyperpigmented lesions on the thigh.
Fig. 50.14. Interscapular maculopapular and pigmented amyloidosis (see also Plate 50.6, pp. 494–495).
Fig. 50.17. Heavily pigmented macular amyloidosis (see also Plate 50.7, pp. 494–495).
Fig. 50.15. Pigmented cutaneous amyloidosis of the leg.
or in different parts of the same lesion (Brownstein et al., 1973). Another variation of lichen/macular amyloidosis is friction amyloidosis. This has been described after prolonged or vigorous use of nylon brushes or towels (Hashimoto et al., 1987; Macsween and Saihan, 1997; Tanigaki et al., 1985; Wong and Lin, 1988). Chronic rubbing and scratching for whatever reason probably causes the same changes in predisposed individuals. Nodular (tumefactive) amyloidosis usually presents in middle-aged women as one or a few firm, flesh-colored or yellowish papules or nodules on the face, scalp, or extremities.
Minor trauma may result in the lesions becoming hemorrhagic. Although nodular amyloidosis is almost always an isolated finding, it has been noted in a few patients with concomitant Sjögren syndrome (Haneda and Hamamatsu, 1979). Nodular amyloidosis may represent a localized plasma cell dyscrasia that can be associated with a monoclonal gammopathy, multiple myeloma, or lymphoplasmacytoid lymphoma (Badell et al., 1996; Hamzavi and Lui, 1999). Localized macular or biphasic amyloid deposition may be associated with depigmentation surrounded by hyperpigmentation. This is known as vitiliginous amyloidosis (Ishigaki et al., 1977). A similar poikilodermatous variety has also been described in patients with Riehl melanosis (Nagao and Iijima, 1974). Children may develop amyloid deposits in the skin after a severe sunburn. These lesions resemble colloid milia on the face. Adults may have a similar problem on the concha of the ears (Hicks et al., 1988). Both of these processes appear to be examples of actinically induced epidermal damage with 925
CHAPTER 50
amyloid synthesis and deposition. A number of Japanese patients have been described with asymptomatic amyloid deposition of the perianal area. The lesions present as hyperkeratotic linear plaques radiating from the anal verge (Vasily et al., 1978). A rare familial form of generalized macular or lichenoid amyloidosis has been described as an autosomal dominant disease. These patients manifest generalized hyperpigmentation with irregular hypopigmented macules (Yanagihara, 1981).
Electron microscopy of the amyloid deposits reveals filaments that are identical to those seen in AL amyloid, the type noted in systemic amyloidosis. Amyloid deposits preferentially around elastic fibrils. Melanosomes are also found in the amyloid deposits, suggesting that either keratinocytes containing melanosomes or melanocytes themselves undergo degeneration to produce these deposits (Hashimoto, 1995).
Criteria for Diagnosis ∑ Localized skin lesions containing amyloid fibrils ∑ No systemic manifestations of amyloidosis
Associated Disorders Multiple endocrine neoplasia (MEN) type 2a syndrome (Sipple syndrome) is an autosomal dominant phakomatosis characterized by hyperplasia and/or carcinoma of the thyroid gland, hyperplasia of the parathyroid gland and adrenal medulla, and/or pheochromocytoma (Gagel et al., 1988, 1989; Sipple, 1961; Szinnai et al., 2003). A specific mutation has been discovered for this phenotype (Barone et al., 1994; Kousseff, 1995). Many patients with this syndrome also have localized cutaneous amyloidosis (Chabre et al., 1992; Donovan et al., 1989; Gagel et al., 1988; Kousseff et al., 1991; Pacini et al., 1993; Robinson et al., 1992). Pleiotropy appears to be the most likely explanation for this association (Kousseff et al., 1991). Two other associations have been noted. Three patients with notalgia paresthetica, which is a localized peripheral neuropathy of the upper back, have also had amyloid deposition in the pruritic area (Goulden et al., 1994). This probably occurs in the same way as in friction amyloidosis, secondary to chronic rubbing and scratching. Two kindreds have been described with pachyonychia congenita and localized amyloid. The authors hypothesize that both conditions share abnormal keratin dynamics (Tidman et al., 1987).
Differential Diagnosis The differential diagnosis of macular amyloidosis includes conditions which produce macular hyperpigmentation. These include postinflammatory hyperpigmentation, melasma, nevus of Ito, and ashy dermatosis. Both postinflammatory hyperpigmentation and melasma can produce poorly demarcated brown patches. Amyloid is not noted on histologic examination. Although nevus of Ito and ashy dermatosis occur on the upper back, they both have a violaceous hue rather than a brown color. Amyloid is not deposited in these conditions. Lichen amyloidosis must be differentiated from other pruritic processes that produce papules and plaques; these include prurigo nodularis, lichen simplex chronicus, lichen planus, and pretibial myxedema. Although all of these conditions produce lichenoid plaques, only lichen amyloidosis has histologic evidence of dermal amyloid deposition on light microscopy. Nodular amyloidosis has a similar clinical appearance to many localized infiltrative processes such as lymphoma, colloid milium, sarcoidosis, mastocytoma, rheumatoid nodules, gouty tophi, and calcinosis cutis. Histologic examination is usually needed to sort out these possibilities.
Pathogenesis Pathology Light microscopic examination reveals similar lichenoid changes whether the lesions are macules or lichenoid papules. There is hyperkeratosis and variable degrees of keratinocyte degeneration and basal layer destruction. Amorphous eosinophilic material (amyloid) is deposited in a widened papillary dermis. Dermal melanophages and a sparse superficial perivascular infiltrate are also present (Kibbi et al., 1992). The nodular form of cutaneous amyloid differs in that the amyloid deposits extend into the deeper dermis and even the subcutis. Histochemical analysis shows that the amyloids present in the localized forms of amyloidosis contain keratins, presumably derived from epidermal keratinocytes (Ortiz-Romero et al., 1994). This is designated as amyloid K or AK amyloid (Hashimoto, 1984). Thus, most of these amyloid proteins will stain positive with antikeratin antibodies (Hamzavi and Lui, 1999). Nodular amyloid does not contain amyloid K, although other amyloid stains are positive. It is derived from immunoglobulin light chains (Ito et al., 1989), similar to that found in systemic amyloid. 926
Localized cutaneous amyloid fibrils are produced by a filamentous degeneration of keratin-type intermediate filaments (Hashimoto et al., 1987; Kamakiri et al., 1983). These may be apoptotic keratinocytes which drop into the upper dermis (Kamakiri et al., 1983). Specific antikeratin antibodies that react with cutaneous amyloid give further credence to the notion that these deposits originate in the suprabasal layer of the epidermis (Ortiz-Romero et al., 1994). This certainly explains why one might develop localized amyloid deposits after prolonged scratching or rubbing with nylon brushes or with sharp fingernails. Asymptomatic lesions of macular amyloid are more difficult to explain with this logic. Similarly, the cases of localized amyloid that appears in association with MEN 2a syndrome could be ascribed to cutaneous trauma. It seems that there is a genetic component in many cases, which may make one more prone to this disposition of apoptotic keratinocytes.
Treatment Most cases of localized cutaneous amyloidosis respond poorly to therapy. There are a few encouraging reports which tout systemic retinoids as being beneficial for lichen amyloidosis
ACQUIRED EPIDERMAL HYPERMELANOSES
(Helander and Hopsu-Havu, 1986; Marschalko et al., 1988). Low-dose cyclophosphamide has been reported as beneficial in reducing the symptoms of lichen amyloidosis (Paricha et al., 1987). One must weigh the risks of aggressive therapy such as this with the benefits in this relatively innocuous condition. Dermabrasion may successfully debulk cutaneous amyloid deposits and improve pruritus (Wong et al., 1982). Hypopigmenting agents such as hydroquinone are not useful in improving the appearance of the lesions of macular amyloidosis. Topical steroids with or without occlusion have been used for macular amyloidosis with limited success (Macsween and Saihan, 1997). Carbon dioxide laser vaporization has been successful in treating nodular amyloidosis. However, tissue friability and poor hemostasis may be of some concern with these patients (Hamzavi and Lui, 1999). A recent case report documents complete clearing in a patient with lichen amyloidosis and atopic dermatitis after ciclosporin therapy (Behr et al., 2001).
Prognosis The lesions of localized cutaneous amyloidosis seldom regress spontaneously. The course is variable; some people continue to develop new lesions or have old ones expand for years whereas others have only a single, stable patch or plaque.
References Badell, AO, Servitje, J. Graells, Curco N, J. Notario, and J. Peyri. Salivary gland lymphoplasmacytoid lymphoma with nodular cutaneous amyloid deposition and lambda chain paraproteinaemia. Br. J. Dermatol. 135:327–329, 1996. Behr, F. D., N. Levine, and J. Bangert. Lichen amyloidosis associated with atopic dermatitis: clinical resolution with cyclosporine. Arch. Dermatol. 137:553–555, 2001. Barone, V., F. Pacini, E. Martino, A. Loviselli, A. Pinchera, and G. Romeo. Identification of the Cys634 to Tyr mutation of the RET proto-oncogene in a pedigree with multiple endocrine neoplasia type 2A and localized cutaneous lichen amyloidosis. J. Endocrinol. Invest. 17:201–204, 1994. Black, M. M., and E. Wilson-Jones. Macular amyloidosis. Br. J. Dermatol. 84:199–209, 1971. Brownstein, M., and K. Hashimoto. Macular amyloidosis. Arch. Dermatol. 106:50–57, 1972. Brownstein, M. H., K. Hashimoto, and G. Greenwald. Biphasic amyloidosis: link between macular and lichenoid forms. Br. J. Dermatol. 88:25–29, 1973. Chabre, O., F. Labat, N. Pinel, F. Berthod, V. Tarel, and I. Bachelot. Cutaneous lesion associated with multiple endocrine neoplasia type 2A: lichen amyloidosis or notalgia paresthetica? Henry Ford Hosp. Med. J. 40:245–248, 1992. Chang, Y. T., S. F. Tsai, W. J. Wang, C. J. Hong, C. Y. Huang, and C. K. Wong. A study of apolipoproteins E and A-I in cutaneous amyloids. Br. J. Dermatol. 145:422–427, 2001. Donovan, D. T., M. L. Levy, E. J. Furst, B. R. Alford, T. Wheeler, J. A. Tschen, and R. F. Gagel. Familial cutaneous lichen amyloidosis in association with multiple endocrine neoplasia type 2A: a new variant. Henry Ford Hosp. Med. J. 37:147–150, 1989. Eanes, E. D., and G. G. Glenner. X-ray diffraction studies on amyloid filaments. J. Histochem. Cytochem. 16:673–677, 1968. Gagel, R. F., A. H. Tashjian Jr., T. Cummings, N. Papathanasopoulos, M. M. Kaplan, R. A. DeLellis, H. J. Wolfe, and S. Reichlin. The clinical outcome of prospective screening for multiple endocrine neoplasia type 2a: An 18 year experience. N. Engl. J. Med. 318:478–484, 1988.
Gagel, R. F., M. L. Levy, D. T. Donovan, B. R. Alford, T. Wheeler, and J. A. Tschen. Multiple endocrine neoplasia type 2a associated with cutaneous lichen amyloidosis [see comments]. Ann. Intern. Med. 111:802–806, 1989. Glenner, G. G. A retrospective and prospective overview of the investigations on amyloid and amyloidosis: The beta-fibrilloses. Amsterdam: Exerpta Medica, 1980. Goulden, V., A. S. Highet, and H. K. Shamy. Notalgia paraesthetica — report of an association with macular amyloidosis. Clin. Exp. Dermatol. 19:346–349, 1994. Hamzavi, I., and H. Lui. Excess tissue friability during CO2 laser vaporization of nodular amyloidosis. Dermatol. Surg. 25:726–728, 1999. Haneda, S., and T. Hamamatsu. Cutaneous amyloidosis associated with Sjögren’s syndrome. Hifu. Rinsho. 21:81–86, 1979. Hashimoto, K. Progress on cutaneous amyloid. J. Invest. Dermatol. 82:1, 1984. Hashimoto, K. Cutaneous amyloidoses. In: Clinical Dermatology. Hagerstown, Maryland: Williams and Wilkins, 1995, pp. 11–13. Hashimoto, K., and L. L. Yoong Onn. Lichen amyloidosus: Electron microscopic study of a typical case and a review. Arch. Dermatol. 104:648–667, 1971. Hashimoto, K., K. Ito, M. Kumakiri, and J. Headington. Nylon brush macular amyloidosis. Arch. Dermatol. 123:633–637, 1987. Helander, I., and V. K. Hopsu-Havu. Treatment of lichen amyloidosis by etretinate. Clin. Exp. Dermatol. 11:574–577, 1986. Hicks, B. C., P. J. Weber, K. Hashimoto, K. Ito, and D. M. Koreman. Primary cutaneous amyloidosis of the auricular concha. J. Am. Acad. Dermatol. 18:19–25, 1988. Ishigaki, M., T. Fugii, and M. Ohashi. Cutaneous amyloidosis with vitiligo. Jpn. J. Clin. Dermatol. (Tokyo) 31:513, 1977. Ito, K., K. Hashimoto, N. Kambe, and S. Van. Roles of immunoglobulins in amyloidogenesis in cutaneous nodular amyloidosis. J. Invest. Dermatol. 89:415–418, 1989. Iwasaki, K., M. Mihara, S. Nishiura, and S. Shimao. Biphasic amyloidosis arising from friction melanosis. J. Dermatol. 18:86–91, 1991. Kamakiri, M., K. Hashimoto, I. Tsukinaga, T. Kimura, and Y. Miura. Presence of basal lamina-like substance with anchoring fibrils within the amyloid deposits of primary localized cutaneous amyloidosis. J. Invest. Dermatol. 81:153–157, 1983. Kibbi, A. G., N. G. Rubeiz, S. T. Zaynoun, and A. K. Kurban. Primary localized cutaneous amyloidosis. Int. J. Dermatol. 31:95–98, 1992. Kousseff, B. G. Multiple endocrine neoplasia 2 (MEN 2)/MEN 2A (Sipple syndrome). Dermatol. Clin. 13:91–97, 1995. Kousseff, B. G., C. Espinoza, and G. A. Zamore. Sipple syndrome with lichen amyloidosis as a paracrinopathy: pleiotropy, heterogeneity, or a contiguous gene? J. Am. Acad. Dermatol. 25:651–657, 1991. Macsween, R. M., and E. M. Saihan. Nylon cloth macular amyloidosis. Clin. Exp. Dermatol. 22:28–29, 1997. Marschalko, M., J. Daroczy, and G. Soos. Etretinate for the treatment of lichen amyloidosis. Arch. Dermatol. 124:657–659, 1988. Nagao, S., and S. Iijima. Light and electron microscopic study of Riehl’s melanosis: Possible mode of its pigmentary incontinence. J. Cutan. Pathol. 1:165, 1974. Ortiz-Romero, P. L., C. Ballestin-Carcavilla, J. L. Lopez-Estebaranz, and L. Iglesias-Diez. Clinicopathologic and immunohistochemical studies on lichen amyloidosis and macular amyloidosis [letter]. Arch. Dermatol. 130:1559–1560, 1994. Pacini, F., L. Fugazzola, and G. Bevilacqua. Multiple endocrine neoplasia type 2A and cutaneous lichen amyloidosis: Description of a new family. Endocrine. Invest. 16:295–296, 1993. Paricha, J. S. et al. Low dose cyclophosphamide therapy in lichen amyloidosis. Indian J. Dermatol. Venereol. Leprol. 53:273–274, 1987.
927
CHAPTER 50 Robinson, M. F., E. J. Furst, V. Nunziata, M. L. Brandi, J. P. Ferrer, M. J. Martins Bugalho, G. di Giovanni, R. J. Smith, D. T. Donovan, B. R. Alford, J. F. Hejtmancik, V. Colantuoni, L. Quadro, E. Limbert, I. Halperin, E. Vilardell, and R. F. Gagel. Characterization of the clinical features of five families with hereditary primary cutaneous lichen amyloidosis and multiple endocrine neoplasia type 2. Henry Ford Hosp. Med. J. 40:249–252, 1992. Sipple, J. H. The association of pheochromocytoma with carcinoma of thyroid gland. Am. J. Med. 31:163–166, 1961. Szinnai, G., C. Meier, P. Komminoth, U. W. Zumsteg. Review of multiple endocrine neoplasia type 2A in children: therapeutic results of early thyroidectomy and prognostic value of codon analysis. Pediatrics 111:E132–139, 2003. Tanigaki, T., S. Hata, and Y. Kitano. Epidemiological survey of “nylon clothes friction dermatosis” [Japanese]. Nippon Hifuka Gakkai Zasshi 95:1159–1164, 1985. Tidman, M. J., R. S. Wells, and D. M. MacDonald. Pachyonychia congenita with cutaneous amyloidosis and hyperpigmentation — a distinct variant. J. Am. Acad. Dermatol. 16:935–940, 1987. Vasily, D. B., S. G. Bhatia, and S. R. Uhlin. Familial primary cutaneous amyloidosis: Clinical, genetic and immunofluorescent studies. Arch. Dermatol. 114:1173–1176, 1978. Virchow, R. Cellular Pathology. New York: Dover Publications, 1971. Wong, C. K., and C. S. Lin. Friction amyloidosis. Int. J. Dermatol. 27:302–307, 1988. Wong, C.-K., D. Phil, and W.-M. Li. Dermabrasion for lichen amyloidosis. Arch. Dermatol. 118:302–304, 1982. Yanagihara, M. Ano-sacral cutaneous amyloidosis. Jpn. J. Dermatol. 91:463–468, 1981.
Dermatosis Papulosa Nigra Norman Levine and Cynthia Burk
Historical Background While visiting Jamaica and Central America in 1925, Aldo Castellani observed a rather common condition among the adult, indigenous population. He named this condition dermatosis papulosa nigra. A collaborative report with Duval (Castellani and Duval, 1929) established the basic clinical and pathologic findings.
Epidemiology Dermatosis papulosa nigra is seen almost exclusively in the Negroid race (Costa, 1944; Mascaro, 1963; Michael and Seale, 1930, 1933). Occasional cases among Mexicans, Filipinos, Vietnamese, and Europeans have been described (Grimes, 1983).
Clinical Findings The characteristic presentation is one of light-brown to black, well-circumscribed, smooth and rounded (85%), pedunculated (15%), or filiform (rare) papules measuring 0.1–0.5 cm. These papules are most densely located on the central and lateral cheeks with gradual fanning toward the forehead and neck (Fig. 50.18). Rarely, the upper torso is involved. Prepubertal onset is rare, with only one case reported in a 7-yearold (Babapour et al., 1993). There is a gradual increase in size and number of papules, peaking during the sixth decade. Light-skinned black people have a lower prevalence of involvement than those with darker skin. There is a female 928
Fig. 50.18. Small pigmented lesions on the temporal areas.
predominance approaching 2 to 1. Females also tend to have greater numbers of papules. The incidence among black people ranges from 35% (Hairston, 1964) up to 77% (Grimes, 1983). The papules are generally asymptomatic unless traumatized, and itching is seen in only 5% of cases. There appears to be a hereditary basis for this condition; approximately one half of affected individuals report at least one family member with this problem. There are no associated medical conditions.
Pathology Histopathologic examination of the early lesion shows acanthosis with broadening and downward projection of the rete pegs. There are increased numbers of mitotic figures and more pigment in the basal cell. There may be mild spongiosis. As a papule matures, the acanthotic center becomes more pronounced with fusing of the rete pegs. Intraepidermal horn cysts are common (Michael and Seale, 1929). Melanophages are present in the upper dermis. Mild papillary dermal edema and lymphohistiocytic infiltrate may be present, along with immature pilosebaceous structures in the involved and adjacent dermis. The histologic picture is much like that of an acanthotic seborrheic keratosis (Lever and Schaumburg-Lever, 1983).
Differential Diagnosis The differential diagnosis includes other pigmented papules. Pigmented nevi are less numerous, are smoother, and have a distinctive histopathology. Multiple minute digitate hyperkeratoses are not seen on the face (Balus et al., 1988). Adenoma sebaceum in the black may mimic dermatosis papulosa nigra clinically; only by pathologic examination can they be absolutely identified. Verrucae planae are usually less pigmented and often show signs of the isomorphic (Koebner) phenomenon. Histopathology is distinctive. Basal cell nevus syndrome may present with small pigmented papules but the histopathology is diagnostic. Fibroepitheliomas (skin tags) are common on the eyelids and periorbital areas but tend to be more pedunculated, and have much less acanthosis and hyalinization on histologic examination. The differential diagnosis also includes melanocytic nevi, follicular hamartomas, and
ACQUIRED EPIDERMAL HYPERMELANOSES
seborrheic keratoses. Typically, follicular hamartomas have a central umbilication that is not present in dermatosis papulosa nigra (Babapour et al., 1993).
Pathogenesis Although the pathogenesis of dermatosis papulosa nigra is unproved, there appears to be a genetic basis. The appearance at puberty with slow progression would suggest a hormonal effect on the pilosebaceous apparatus.
Treatment The lesions of dermatosis papulosa nigra are benign and generally do not psychologically or socially affect involved individuals. Some consider the papules to be attractive and a form of beauty mark. Various destructive modalities of removal have been reported to be effective and safe (Kenney, 1988). This would include “light abrasive curettage” where the papule is gently abraded with a curette using no anesthesia, allowing the remaining portion of the papule to involute spontaneously (Kauh, 1983). Light electrodesiccation, cryosurgery, shave excision, and chemical cautery can also be used. The carbon dioxide laser in the ultrapulsed mode may also be used to remove these lesions.
References Babapour, R., J. Leach, and H. Levy. Dermatosis papulosa nigra in a young child. Pediatr. Dermatol. 10:356–358, 1993. Balus, L., P. Donati, A. Amantea, and A. S. Breathnach. Multiple minute digitate hyperkeratosis. J. Am. Acad. Dermatol. 18:431– 436, 1988. Castellani, A. Observations on some diseases of Central America. J. Trop. Med. Hygiene 28:149–150, 1925. Castellani, A., and C. W. Duval. Dermatosis papulosa nigra. J. Trop. Med. 32:149–150, 1929. Costa, O. G. Dermatosis papulosa nigra. An. Brasil Dermatol. Sifil. 19:217–219, 1944. Grimes, P. E. Dermatosis papulosa nigra. Cutis 32:385–386, 1983. Hairston, M. A. Dermatosis papulosa nigra. Arch. Dermatol. 89:655– 658, 1964. Kauh, Y. C. A surgical approach for dermatosis papulosa nigra. Int. J. Dermatol. 22:590–592, 1983. Kenney, J. A., Jr. Dermatosis papulosa nigra and seborrheic keratosis. Ala. J. Med. Soc. 17:49–50, 1988. Lever, W. F., and G. Schaumburg-Lever. Histopathology of the Skin, 6th ed. Philadelphia: JB Lippincott Co., 1983. Mascaro, J. M. Castellani’s dermatosis papulosa nigra; historical note. Bull. Soc. Franc. Dermatol. Syphiligr. 70:535–537, 1963. Michael, J. C., and E. R. Seale. Dermatosis papulosa nigra. Arch. Dermatol. Syphil. 20:629–640, 1929. Michael, J. C., and E. R. Seale. Dermatosis papulosa nigra. J. Trop. Med. 33:12–15, 1930. Michael, J. C., and E. R. Seale. Dermatosis papulosa nigra. Arch. Dermatol. Syphil. 20:629–640, 1933.
Ephelides (Freckles) Norman Levine and Cynthia Burk
Introduction Ephelides (freckles) are small tan to dark-brown macules, seen mainly in children, on sun-exposed skin. Because the
Fig. 50.19. Ephelides on sun-exposed areas.
term freckle is sometimes used interchangeably with the term lentigo, there is often considerable confusion within the medical literature about what is actually being described (Jansson, 1958).
Clinical Findings Freckles are genetic in origin, following an autosomal dominant pattern (Jansson, 1958); they are especially common among persons of Celtic (Scottish–Irish–Welsh) ancestry. Freckles are seen only in sun-exposed areas, being most heavily concentrated on the face, upper back, and dorsal forearms (Frederich, 1959; Goldberg and Altman, 1984) (Fig. 50.19). Onset may be at any time but is often early in childhood when outdoor swimming begins. A study of 1456 New South Wales school children revealed an increasing number of freckles with increasing age, suggesting that continued sun exposure increases the degree of freckling (Nicholls, 1968). Boys and girls are equally affected. Redheads are most likely to have freckles (Brues, 1950). Most freckles are small macules, measuring 2–4 mm, but may be larger. Experimental evidence reveals the MFD (minimal freckle dose) to be 6 MED (minimal erythema dose) (Wilson and Kligman, 1982) and may appear after a single sunburn. Freckles help to protect the skin from further ultraviolet (UV) damage (Ito, 1950), and may be considered a sign of photoaging (Holzle, 1992). Freckles are often dynamic lesions. Most sunburn freckles appear after the skin has peeled, normally, within two to four weeks after the sunburn. Photochemotherapy in fair-skinned individuals may lead to frecklelike lesions but they are much more like lentigines, based on histopathology (Kanerva et al., 1984). Melanocytes exposed to radioactive thorium-X solution may lose their capacity to freckle (Breathnach, 1982). Excessive plasma and tissue levels of chloroquine due to renal failure may lead to lightening of the hair and to freckles (Dupre et al., 1985). Ephelides may appear in stretched scars (Breathnach, 1958). Freckles are of clinical significance because of their association with both melanoma (Bataille et al., 2000; Elwood et 929
CHAPTER 50
al., 1985; Evans et al., 1988; Marks, 1989; Scotto and Fears 1987) and nonmelanoma skin cancer (Bastiaens et al., 2001; Hogan et al., 1989, 1990). Recent studies indicate that having freckles is a moderate risk factor for developing cutaneous melanoma (Bakos et al., 2002; Grulich et al., 1996). Freckling is also correlated with increased numbers of nevocellular nevi (Bataille et al., 2000; Coombs et al., 1992; Fritschi et al., 1994; Sigg and Pelloni 1989). Ephelides, malignant melanoma, and nonmelanoma skin cancer are all strongly associated with the MC1R gene which plays an important role in skin pigmentation (Bastiaens et al., 2001). Freckles are seen in individuals with xeroderma pigmentosum. Axillary and intertriginous “frecklelike” macules are important markers in neurofibromatosis, but are not true freckles since they are not induced by ultraviolet light and do not fade. Freckles may be present in Gardner syndrome (Bazex and Bazex, 1978) or the NAME syndrome (Nevi, Atrial myxoma, Myxoid neurofibroma, and Ephelides) (Rolle et al., 1995). Patients with tyrosinase-positive albinism may have freckling due to accumulation of pigment over time (Findlay, 1962). Freckles and abnormalities of the eyebrows may serve as indicators for genetic abnormalities in the development of the teeth and jaws (Ulrich, 1990). Freckles may be related to a change that can occur in pheomelanin exposed to ultraviolet light. This may explain the predominance of freckling among redheads and blondes.
Pathology Light microscopy reveals a normal stratum corneum and Malpighian layer. The basal layer shows increased pigmentation without elongation of the rete pegs. The dermis is normal (Lever and Schaumburg-Lever, 1983). Large numbers of mature melanosomes and dendritic melanocytes as seen in dark-skinned individuals are characteristic (Breathnach, 1957). There seem to be an increased number of melanocytes in freckles compared to adjacent nonpigmented skin (Rhodes et al., 1991). Ultrastructural studies reveal elongated, fully melanized melanosomes with 90 Å (9 nm) striations (Breathnach and Wyllie, 1964).
Differential Diagnosis The clinical diagnosis of freckles is routine when occurring in a fair-skinned, red-headed child and limited to sun-exposed skin. Solar lentigines are the main point of confusion. These lesions tend to occur in older individuals, have a greater spectrum of shape, size, and color, and histologically show elongation of the rete pegs, increased numbers of melanocytes with some degree of cellular atypia, and dermal melanophages. Solar lentigines are slow to fade without therapy.
Treatment Treatment of freckles is for cosmetic reasons only. Application of hydroquinone 2–4% or combination glycolic acid/kojic acid lotion along with maximum UVA blocking sunscreen in the morning and retinoic acid (Goldfarb et al., 1990) in the 930
evening will significantly lighten freckles. Sun avoidance and the use of protective clothing are helpful in speeding the response to treatment. Phenol peeling removes freckles but runs the risk of toxicity and permanent hypopigmentation (Schuhmachers-Brendler, 1955; Zhao, 1992). Skillful use of liquid nitrogen (Kleine-Natrop, 1964) and dermabrasion is effective. Pigment lasers such as the Q-switched alexandrite laser, Q-switched 532 nm neodymium:yttrium aluminum garnet (Nd:YAG), Q-switched ruby (Nelson and Applebaum, 1992) offer an aggressive and effective way to remove freckles (Jang et al., 2000; Suh et al., 2001). Combination therapy of pigmented lasers and chemical peels may be useful in removing freckles (Lee et al., 2002). Intense pulsed light is another possible modality for the treatment of facial freckles (Huang et al., 2002; Kawada et al., 2002).
References Bakos, L. M., Wagner, R. M. Bakos, C. S. Leite, C. L. Sperhacke, K. S. Dzekaniak, and A. L. Gleisner. Sunburn, sunscreens, and phenotypes: some risk factors for cutaneous melanoma in southern Brazil. Int. J. Dermatol. 41:557–562, 2002. Bastiaens, M., J. ter Huurne, N. Gruis, Bergman W, R. Westendorp, B. J. Vermeer, and J. N. Bouwes Bavinck. The melanocortin-1-receptor gene is the major freckle gene. Hum. Mol. Genet. 10:1701– 1708, 2001. Bataille, V., H. Snieder, A. J. MacGregor, P. Sasieni, and T. D. Spector. Genetics of risk factors for melanoma: an adult twin study of nevi and freckles. J. Natl. Cancer Inst. 92:457–463, 2000. Bazex, A., and J. Bazex. Dermatology and polyposis of the gastrointestinal tract. Ann. Dermatol. Venereol. 105:851–858, 1978. Breathnach, A. S. Melanocytic distribution in forearm epidermis of freckled human subjects. J. Invest. Dermatol. 29:253–261, 1957. Breathnach, A. S. Melanocytic pattern of an area of freckled epidermis covering a stretched scar. J. Invest. Dermatol. 31:237–241, 1958. Breathnach, A. S. A long-term hypopigmentation effect of thorium-X on freckled skin. Br. J. Dermatol. 106:19–25, 1982. Breathnach, A. S., and L. M. Wyllie. Electron microscopy of melanocytes and melanosomes in freckled human epidermis. J. Invest. Dermatol. 42:389–394, 1964. Brues, A. M. Linkage of bodybuild with sex, eye colour, and freckling. Am. J. Hum. Genet. 2:215, 1950. Coombs, B. D., K. J. Sharples, K. R. Cooke, D. C. Skegg, and J. M. Elwood. Variation and covariates of the number of benign nevi in adolescents. Am. J. Epidemiol. 136:344–355, 1992. Crowe, F. W. Axillary freckling as a diagnostic aid in neurofibromatosis. Ann. Intern. Med. 61:1142–1143, 1964. Dupre, A., J. P. Ortonne, P. Viraben, and F. Arfeux. Chloroquineinduced hyperpigmentation of hair and freckles, associated with congenital renal failure. Arch. Dermatol. 121:1164–1166, 1985. Elwood, J. M., R. P. Gallagher, and G. P. Hill. Pigmentation and skin reaction to sun as risk factor for cutaneous melanoma: Western Canada Study. Br. Med. J. 288:99–102, 1984. Elwood, J. M., R. P. Gallagher, J. Davidson, and G. B. Hill. Sunburn, suntan and the risk of cutaneous malignant melanoma. Br. J. Cancer 51:543–549, 1985. Evans, R. D., A. W. Kopf, R. A. Lew, D. S. Rigel, R. S. Bart, R. J. Friedman, and J. K. Rivers. Risk factors for the development of malignant melanoma: Review of case-control studies. J. Dermatol. Surg. Oncol. 14:393–408, 1988. Findlay, G. H. On giant dendritic freckles and melanocytic reactions in the skin of the albino Bantu. S. Afr. J. Lab. Clin. Med. 8:68–72, 1962.
ACQUIRED EPIDERMAL HYPERMELANOSES Frederich, H. Beitrag zur Behandlung von Epheliden und Virginum. Medizinische 16:800–801, 1959. Fritschi, L. P., A. McHenry, R. M. Green, L. Green, and V. Siskind. Nevi in schoolchildren in Scotland and Australia. Br. J. Dermatol. 130:599–603, 1994. Goldberg, L. H., and A. Altman. Benign skin changes associated with chronic sunlight exposure. Cutis 34:33–38, 1984. Goldfarb, M. T., C. N. Ellis, and J. J. Voorhees. Topical tretinoin — its use in daily practice to reverse photoaging. Br. J. Dermatol. 122(Suppl. 35):87–91, 1990. Grulich, A. E., V. Bataille, A. J. Swerdlow, J. A. Newton-Bishop, J. Cuzick, P. Hersey, and W. H. McCarthy. Naevi and pigmentary characteristics as risk factors for melanoma in a high-risk population: a case-control study in New South Wales, Australia. Int. J. Cancer 67:485–491, 1996. Hogan, D. J., P. R. Lane, L. Gran, and L. Wong. Risk factors for squamous cell carcinoma of the skin in Saskatchewan, Canada. J. Dermatol. Sci. 1:97–101, 1990. Hogan, O. J., T. To, L. Gran, D. Wong, and P. R. Lane. Risk factors for basal carcinoma. Int. J. Dermatol. 28:591–594, 1989. Holzle, E. Pigmented lesions as a sign of photodamage. Br. J. Dermatol. 127 Suppl 41:48–50, 1992. Huang, Y. L., Y. L. Liao, S. H. Lee, and H. S. Hong. Intense pulsed light for the treatment of facial freckles in Asian skin. Dermatol. Surg. 28:1007–12; discussion p. 1012, 2002. Ito, M. Genetic studies on skin diseases: ephelides, dyschromatosis symmetrica hereditaria and xeroderma pigmentosum. Tohoku J. Exp. Med. 53:69–72, 1950. Jang, K. A., E. C. Chung, et al. Successful removal of freckles in Asian skin with a Q-switched alexandrite laser. Dermatol. Surg. 26:231–234, 2000. Jansson, H. Problems of differentiation of ephelides and lentigines based on analysis of frequency. Hautarzt 7:311–313, 1958. Kanerva, L., K. M. Niemi, and J. Lauharanta. A semiquantitative light and electron microscopic analysis of histopathologic changes in phototherapy-induced freckles. Arch. Dermatol. Res. 276:2–11, 1984. Kawada, A., H. Shiraishi, M. Asai, H. Kameyama, Y. Sangen, Y. Aragane, and T. Tezuka. Clinical improvement of solar lentigines and ephelides with an intense pulsed light source. Dermatol. Surg. 28:504–508, 2002. Kleine-Natrop, H. E. Nitrogen peeling in freckles and skin infection. Hautarzt 15:557–559, 1964. Lee, G. Y., H. J. Kim, and K. K. Wang. The effect of combination treatment of the recalcitrant pigmentary disorders with pigmented laser and chemical peeling. Dermatol. Surg. 28:1120–1123; discussion 1123, 2002. Lever, W. F., and G. Schaumburg-Lever. Histopathology of the Skin, 6th ed. Philadelphia: JB Lippincott Co., 1983. Marks, J. Freckles, moles, melanoma and the ozone layer: a tale of the relationship between humans and their environment. Med. J. Aust. 151:611–613, 1989. Marks, R. Freckles, moles, and melanoma. Aust. Fam. Physician 17:1025, 1988. Nelson, J. S., and J. Applebaum. Treatment of superficial cutaneous pigmented lesions by melanin-specific selective photothermolysis using the Q-switched ruby laser. Ann. Plast. Surg. 29:231–237, 1992. Nicholls, E. M. Genetic susceptibility and somatic mutation in the production of freckles, birthmarks and moles. Lancet 1:71–73, 1968. Rhodes, A. R., L. S. Albert, R. L. Barnhill, and M. A. Weinstock. Suninduced freckles in children and young adults. A correlation of clinical and histopathologic features. Cancer 67:1990–2001, 1991. Rolle, F., E. Cornu, Y. Ghossein, J. M. Bonnetblanc, J. Bensaid, and C. Christides. Cutaneous lentigines, freckles, and atrial myxomas [letter]. Ann. Thorac. Surg. 59:267–268, 1995.
Schuhmachers-Brendler, R. Corrective dermatology: therapy of freckles with phenol ether. Hautarzt 6:499–501, 1955. Scotto, J., and T. R. Fears. The association of solar ultraviolet and skin melanoma incidence among caucasians in the United States. Cancer Invest. 5:275–283, 1987. Sigg, C., and F. Pelloni. Frequency of acquired melanonevocytic nevi and their relationship to skin complexion in 939 schoolchildren. Dermatologica 179:123–128, 1989. Suh, D. H., K. H. Han, and J. H. Chung. The use of Q-switched Nd:YAG laser in the treatment of superficial pigmented lesions in Koreans. J. Dermatol. Treat. 12:91–96, 2001. Ulrich, K. Freckles and dysplasias of the eyebrows as indicators for genetic abnormalities of the development of the teeth and jaws. Stomatol. DDR 40:64–66, 1990. Wilson, P. D., and A. M. Kligman. Experimental induction of freckles by ultraviolet-B. Br. J. Dermatol. 106:401–406, 1982. Zhao, Q. M. [Clinical observation of face peeling treatment for ephelides and phenol excretion in urine]. Chung Hua Cheng Hsing Shao Shang Wai Ko Tsa Chih 8:179–181,247, 1992.
Erythema ab Igne Norman Levine and Cynthia Burk
Synonyms Erythema a colore (Bazex et al., 1963), ephelis ignealis, ephelis ab igne (Abraham, 1902), erythema caloricum, livedo reticularis e calore, Buscke heat melanosis, and toasted skin syndrome.
Clinical Findings Erythema ab igne is a reticulated dermatosis, which is a reaction to chronic, nonburning thermal exposure in the range of 43–47 ∞C. Skin lesions may not appear for three weeks after the heat exposure (Lin et al., 2002). The typical case of erythema ab igne occurs in a person who has repeatedly warmed bare legs in front of an open fireplace, radiator, or heater. Another common setting is the young girl with menstrual cramps who uses a heating pad on the abdomen. Other cases occur in cooks, stokers, blacksmiths, silversmiths, and foundrymen. Anyone with chronic pain, such as low back pain, that uses a heating device may develop erythema ab igne (Dvoretzky and Silverman, 1991). Cases of erythema ab igne have also been reported in individuals who take frequent hot baths, who use heating blankets or hot water bottles, who are in close contact with car heaters, and who use furniture/therapeutic chairs with built-in heating devices (Helm et al., 1997; Lin et al., 2002; Meffert and Davis 1996; Milligan and Graham-Brown 1989). Erythema ab igne may be linked to cancer-related pain secondary to the application of heat for pain relief (MacHale et al., 2000). In each case the skin and subdermal vascular plexus reacts with vasodilatation and hemostasis, forming a reticulated pattern that begins with erythema but in time becomes hyperpigmented (Fig. 50.20). In very chronic cases, the skin develops poikiloderma with epidermal atrophy, telangiectasia, and hyperkeratosis. The pattern on the legs can resemble that of excessive solar damage. There may be some itching or burning; however, most cases are asymptomatic. 931
CHAPTER 50
Fig. 50.20. Extensive involvement of the legs.
Fig. 50.21. Typical reticulated pattern of hyperpigmentation induced by erythema ab igne (see also Plate 50.8, pp. 494–495).
Associated Disorders Erythema ab igne is associated with a slight increase in malignancy when the etiology is due to a hydrocarbon heat source (Lin et al., 2002). Actinic keratoses and squamous cell carcinomas have been reported in a number of cases after a long latent period (Arrington and Lockman 1979; Ashby 1985; Helm et al., 1997). These include cases from the chronic heat of a sunken hearth (irori), and underfloor braziers covered with a quilt (kotatsu). Other cases include those from heated brick beds in northern China (kang cancers) (Laycock, 1948), coal-burning baskets in Kashmir in India (Kangri cancers) (Neve, 1923; Suryanarayan, 1973), peat fire cancers in Ireland (Cross, 1967), and benzene-burning pots in Japan (kairo cancers) (Kligman and Kligman, 1984). There is evidence of a destructive synergism between ultraviolet and infrared radiation (Kligman, 1982). A few cases of coexisting squamous cell carcinoma and Merkel cell carcinoma in an area of erythema ab igne have been reported (Jones et al., 1988; Iacocca et al., 1998). Abdominal erythema ab igne is increasingly being recognized as an important sign in chronic abdominal pain, especially from pancreatic disease (Ashby et al., 1985; Halliday et al., 1986; Mok and Blumgart 1984; Mucklow and Freeman, 1990; Raffle 1984). Erythema ab igne on the flank, back, or the upper abdomen (Fig. 50.21) may be the only cutaneous manifestation of splenomegaly, pancreatitis, peptic ulcer disease, pancreatic pseudocyst or pancreatic cancer (Butler, 1977; Tan and Bertucci, 2000). Other unusual sites such as the thigh, pubic area, and upper back suggest underlying malignancy such as gastric and renal carcinoma as well as bony metastases (Butler, 1977). A few cases of bullous lichen planus arising in an area of erythema ab igne have been reported (Horio and Imamura 1986; Flanagan et al., 1996). In addition, lymphedema has been associated with a hypertrophic or keloidal variant of erythema ab igne (Cox et al., 1996).
Pathology Light microscopic examination of early erythema ab igne shows atrophy of the Malpighian layer, increased epidermal and upper dermal melanin with dermal vasodilatation. 932
Advanced cases show epidermal vacuolation (Wilkinson, 1972), focal hyperkeratosis, and dyskeratosis. There is increased elastosis with fragmented collagen fibers (Johnson and Butterworth, 1971). Epidermal dysplasia within abnormal elastic tissue may also be seen (Cox et al., 1996). There is minimal basophilia and homogenization of elastic fibers which is prominent in solar elastosis (Shahrad and Marks, 1977). Melanophages and hemosiderin are seen in the dermis (Findlayson et al., 1966; Hartzell, 1912). Varying degrees of dermal lymphohistiocytic infiltration are present. Extravasation of red blood cells is inconstant.
Differential Diagnosis Livedo reticularis has a reticulated pattern with erythema but shows no hyperpigmentation. Poikiloderma atrophicans vasculare is more atrophic and telangiectatic and does not show the distinct vascular pattern of erythema ab igne. Majocchi disease tends to be more annular and superficial.
Treatment In early cases there is complete resolution by removal of the offending heating device. More advanced cases may respond somewhat to tretinoin and/or 5-fluorouracil cream (Helm et al., 1997; Sahl and Taira 1992). Associated cutaneous malignancies require surgical removal.
Prognosis Prognosis is good except those cases associated with internal disease or metastatic malignancy.
References Abraham, P. S. Ephelis ab igne. Br. Med. J. 14:100, 1902. Akasaka, T., and S. Kon. Two cases of squamous cell carcinoma arising from erythema ab igne. Nippon. Hifuka. Gakkai. Zasshi. Jpn. J. Dermatol. 99:735–742, 1989. Arrington, J. H., III, and D. S. Lockman. Thermal keratosis and squamous cell carcinoma in situ associated with erythema ab igne. Arch. Dermatol. 115:1226–1228, 1979. Ashby, M. Erythema ab igne in cancer patients. J. R. Soc. Med. 78:925–927, 1985.
ACQUIRED EPIDERMAL HYPERMELANOSES Ashby, M. A., P. Carmochan, and D. M. Tait. Erythema ab igne: a model of hyperthermic skin damage and carcinogenesis in humans? Int. J. Hypertherm. 1:391–393, 1985. Bazex, A. R., R. Salvador, A. Dupre, M. Parant, and B. Christol. Erytheme a calore. Bull. Soc. Franc. Dermatol. Syphiligr. 70:296, 1963. Cox, N. H., W. D. Paterson, and A. W. Popple. A reticulate vascular abnormality in patients with lymphoedema: observations in eight patients. Br. J. Dermatol. 135:92–97, 1996. Cross, F. On a turf (peat) fire cancer: malignant change superimposed on erythema ab igne. Proc. R. Soc. Med. 60:1307–1308, 1967. Dvoretzky, I., and N. R. Silverman. Reticular erythema of the lower back. Erythema ab igne. Arch. Dermatol. 127:405–406,408–409, 1991. Findlayson, G. R., W. M. Sams Jr., and J. G. Smith. Erythema ab igne — a histopathological study. J. Invest. Dermatol. 46:104–107, 1966. Flanagan, N., R. Watson, E. Sweeney, and L. Barnes. Bullous erythema ab igne. Br. J. Dermatol. 134:1159–1160, 1996. Halliday, C. E., A. K. Goka, and M. J. Farthing. Erythema ab igne: a sign of organic disease [letter]. J. R. Soc. Med. 79:249–250, 1986. Hartzell, M. B. Erythema ab igne. J. Cutan. Dis. 30:461, 1912. Helm, T. N., G. T. Spigel, and K. F. Helm. Erythema ab igne caused by a car heater. Cutis 59:81–82, 1997. Horio, T., and S. Imamura. Bullous lichen planus developed on erythema ab igne. J. Dermatol. 13:203–207, 1986. Iacocca, M. V., J. L. Abernethy, C. M. Stefanato, A. E. Allan, J. Bhawan. Mixed Merkel cell carcinoma and squamous cell carcinoma of the skin. J. Am. Acad. Dermatol. 39(5 Pt 2): 882–887, 1998. Johnson, W. C., and T. Butterworth. Erythema ab igne elastosis. Arch. Dermatol. 104:128–131, 1971. Jones, C. S., S. K. Tyring, P. C. Lee, and J. D. Fine. Development of neuroendocrine (Merkel cell) carcinoma mixed with squamous cell carcinoma in erythema ab igne. Arch. Dermatol. 124:110–113, 1988. Kligman, L. H. Intensification of ultraviolet-induced dermal damage by infrared radiation. Arch. Dermatol. Res. 272:229–238, 1982. Kligman, L. H., and A. M. Kligman. Reflections on heat. Br. J. Dermatol. 110:369–375, 1984. Lankisch, P. G., and W. Creutzfeldt. Erythema ab igne (livido reticularis e calorie): a skin manifestation of chronic pancreatic disease. Z. Gastroenterol. 24:119–120, 1986. Laycock, H. T. Kang Cancer. Br. Med. J. 1:982, 1948. Lin, S. J., C. J. Hsu, and H. C. Chiu. Erythema ab igne caused by frequent hot bathing. Acta Derm.Venereol. 82:478–479, 2002. MacHale, J., F. Chambers, and P. R. O’Connell. Erythema ab igne: an unusual manifestation of cancer-related pain. Pain 87:107–108, 2000. Meffert, J. J., and B. M. Davis. Furniture-induced erythema ab igne. J. Am. Acad. Dermatol. 34:516–517, 1996. Milligan, A., and R. A. Graham-Brown. Erythema ab igne affecting the palms. Clin. Exp. Dermatol. 14:168–169, 1989. Mok, D. W. H., and L. H. Blumgart. Erythema ab igne in chronic pancreatic pain: a diagnostic sign. J. R. Soc. Med. 77:299–301, 1984. Mucklow, E. S., and N. V. Freeman. Pancreatic ascites in childhood. Br. J. Clin. Pract. 44:248–251, 1990. Neve, E. F. Kangri-burn cancer. Br. Med. J. 2:1255–1256, 1923. Peterkin, G. A. G. Malignant change in erythema ab igne. Br. Med. J. 2:1599–1602, 1955. Raffle, E. J. Erythema ab igne in chronic pancreatic pain. J. R. Soc. Med. 77:706, 1984. Roth, D., and M. London. Acridine probe study into synergistic DNA denaturing action of heat and ultraviolet light in squamous cells. J. Invest. Dermatol. 69:368–372, 1977. Sahl, W. J., Jr., and J. W. Taira. Erythema ab igne: treatment with 5fluorouracil cream. J. Am. Acad. Dermatol. 27:109–110, 1992.
Shahrad, P., and R. Marks. The wages of warmth: changes in erythema ab igne. Br. J. Dermatol. 97:163–172, 1977. Suryanarayan, C. R. Kangri cancer in Kashmir Valley. J. Surg. Oncol. 5:327–333, 1973. Tan, S., and V. Bertucci. Erythema ab igne: an old condition new again. Can. Med. Assoc. J. 162:77–78, 2000. Wilkinson, D. S. Cutaneous reactions to mechanical and thermal injury. In: Textbook of Dermatology, 2nd ed., A. Rook, D. S. Wilkinson, and F. J. G. Ebling (eds). Oxford: Blackwell Scientific Publications, 1972, pp. 435–436.
Erythema Dyschromicum Perstans Norman Levine and Cynthia Burk
Historical Background In 1957 Ramirez described a group of patients which he called Los Cenicientos (ashen ones). He called the disease dermatosis cenicienta, a reference to Cinderella and her ashen smudges (Knox et al., 1968). Convit et al. suggested the name erythema chromicum figuratum melanodermicum, but in 1961 adopted the term erythema dyschromicum perstans (Convit et al., 1961a, b). Other cases which could possibly be erythema dyschromicum perstans include lichen atypiques on invisibles pigmentogenes (Gougerot, 1935a, b), roseola pigmentosa, pigmentation maculosa multiplex (Ito, 1955), and lichen pigmentosum in Japan, la melanodermite lichenoidea in Ethiopia (Greppi and Soustek, 1966), and lichen planus pigmentosus in India (Bhutani et al., 1974). The term ashy dermatosis of Ramirez is used in English-speaking countries.
Epidemiology Erythema dyschromicum perstans is most commonly seen in persons of intermediate skin color. Most reports come from Central America (Ramirez, 1966, 1967) but cases have been reported worldwide (Koves de Amini and Briceno-Maaz, 1967) and represent all skin types, even fair-skinned Caucasians (Byrne and Berger, 1974; Holst and Mobachen, 1974; Peachy, 1976). There is no gender preference; although most cases are seen in young adults, children as young as 5 years old have been reported (Urano-Suehissa et al., 1984).
Clinical Findings One sees variably sized ashy hyperpigmented patches primarily located on the torso, extremities, and/or face. There is no involvement of the palms, soles, scalp, nails, or mucosa. New cases may have a leading, erythematous edge, but this is normally absent soon afterwards (Convit et al., 1961b). Lesions may vary in color from slate-gray to blue-brown. Peripheral hypopigmentation is often seen in older lesions, which tends to accentuate the inner hyperpigmentation (Fig. 50.22). Wood’s light examination shows no accentuation of the hyperpigmentation. This is to be expected since the pigment is primarily dermal in origin. Individual lesions may be annular or polycyclic with overlapping borders. New lesions may appear in areas which have previously resolved. Oval lesions may follow skin tension lines. Up to 90% of the body may be involved in exceptional cases. There may be mild pruritus but 933
CHAPTER 50
Differential Diagnosis
Fig. 50.22. Blue-brown hyperpigmented macules at the late stage of erythema dyschromicum perstans (see also Plate 50.9, pp. 494–495).
typically the condition is asymptomatic. A unilateral case in a child with positive rheumatoid factor has been reported (Urano-Suehissa et al., 1984). Erythema dyschromicum perstans may occur simultaneously in patients with vitiligo (Osswald et al., 2001). Onset may be abrupt but there is slow progression with less than a 10% chance of spontaneous remission (Palatsi, 1977). General health is not affected and routine laboratory studies are normal.
Pathology Routine histology shows both early and late changes. Early, active lesions show a normal stratum corneum, slightly atrophic epidermis, varying degrees of spongiosis and lymphocytic exocytosis, basal vacuolar degeneration (Ackerman, 1978), and dermal lymphohistiocytic perivascular and/or lichenoid infiltrate. Colloid bodies, which represent degenerated extruded keratinocytes, are frequently seen in the dermis. Dermal hemosiderin may be present. Both increased epidermal melanin and dermal melanophages (melaninosis) (Pathak et al., 1983) are seen. Older lesions lack basal degeneration and a dense dermal infiltrate while dermal pigmentation increases. Split-dopa staining reveals increased numbers of epidermal melanocytes with an arborizing, dendritic proliferation and epidermal pigmentation. Contrarily, S-100 staining reveals the dermal pigmentation to be within melanophages. This dermal pigmentation produces the characteristic blue or ashy-gray color because of scattering and re-emission of blue light. Electron microscopy reveals cytoplasmic vacuoles and melanosome complexes within basal keratinocytes. Desmosomes are retracted. There is no evidence of basement membrane reduplication (Soter et al., 1969). Immunofluorescence studies show variable staining of dermal colloid bodies with IgG, IgM, IgA, C3, and C4 (Kark and Litt, 1980; Novick and Phelps, 1985; Tschen et al., 1980). There may be occasional IgG immunoglobulin staining of the basal and prickle cell layer. All immunofluorescence studies may be negative. 934
The differential diagnosis includes fixed-drug reactions, which may mimic erythema dyschromicum perstans quite convincingly. Histology may be similar but a careful history is diagnostic. The pigmentation of melasma is frequently enhanced by Wood’s light examination. Poikiloderma of Civatte shows significant telangiectasia. A number of clinically similar cases in New Guinea (Bereston, 1946; Wilson, 1946) proved to be due to Triquin, which is a combination of quinacrine, chloroquine, and hydroxychloroquine. Postinflammatory hyperpigmentation from pityriasis rosea has a different clinical course and histology, and resolves in a few weeks. Urticaria pigmentosa has a positive Darier sign. Late pinta has a positive darkfield examination, antitreponemal serology, and responds to penicillin therapy. Maculae cerulae is associated with pediculosis. Macular amyloid can be differentiated by histology. Argyria is more diffuse and histology is diagnostic. Riehl melanosis is associated with irritant and sensitizing topical agents, and lichen planus subtropicus has a distinct photoaccentuated pattern. There have been several cases of lichen planus in conjunction with erythema dyschromicum perstans; there are those that contend that erythema dyschromicum perstans is a subset of lichen planus rather than a form of fixed erythema. Several authors have debated this issue in detail (Berger et al., 1989; Kark and Litt 1980; Naidorf and Cohen 1982; Person and Rogers 1981). There has also been an association with erythema dyschromicum perstans and lichen planopilaris (Metin et al., 2001).
Pathogenesis The etiology of erythema dyschromicum perstans is unknown. However, there is evidence that the immune system plays a crucial role in the development of this condition. The first case from the United States seemed to resolve after treatment of the whipworm Trichuris trichiura with dithiazanine (Stevenson and Miura, 1966). Contact with optical whitener in washing powders has been suspected, but never substantiated (Pinol, 1971). Some have suggested that paraphenylenediamine hair dyes might trigger the condition (Bhutani, 1986). There has been one case with an association with licking ammonium nitrate fertilizer (Jablonska, 1975). Erythema dyschromicum perstans has also been associated with endocrinopathies, Xray contrast studies, and been linked to the hepatitis C virus (Goihman, 1998). Cell adhesion and activation molecules may be involved in the pathogenesis of erythema dyschromicum perstans (Baranda et al., 1997).
Treatment There is no single established therapy for erythema dyschromicum perstans. Various therapies have been tried with limited success such as sun protection, chemical peels, antibiotics, topical and systemic corticosteroids, estrogens, keratolytics, vitamins, isoniazid, griseofulvin, and chloroquine (Goihman 1998; Osswald et al., 2001). Clofazimine may be successful by decreasing the inflammatory component
ACQUIRED EPIDERMAL HYPERMELANOSES
in erythema dyschromicum perstans and by exerting its immunomodulating effects (Baranda et al., 1997). Dapsone is another treatment that may work by regulating the immune responses involved in the pathogenesis of erythema dyschromicum perstans (Goihman, 1998). The Q-switched ruby laser may prove to be useful as it is in nevus of Ota, which also has excessive dermal melanin.
References Ackerman, A. B. Histologic Diagnosis of Inflammatory Skin Diseases. Philadelphia: Lea and Febiger, 1978. Baranda, L. B., Torres-Alvarez, R. Cortes-Franco, B. Moncada, D. P. Portales-Perez, and R. Gonzalez-Amaro. Involvement of cell adhesion and activation molecules in the pathogenesis of erythema dyschromicum perstans (ashy dermatitis). The effect of clofazimine therapy. Arch. Dermatol. 133:325–329, 1997. Bereston, E. S. Lichenoid dermatitis: observation of 200 cases from the dermatology section, Medical Branch, Dewitt General Hospital, Auburn, California. J. Invest. Dermatol. 7:69, 1946. Berger, R. S., T. J. Hayes, and S. L. Dixon. Erythema dyschromicum perstans and lichen planus: Are they related? J. Am. Acad. Dermatol. 21:438–442, 1989. Bhutani, L. K., T. R. Bedi, A. K. Pandhi, and N. C. Nayak. Lichen planus pigmentosus. Dermatologica 149:43–50, 1974. Byrne, D. A., and R. S. Berger. Erythema dyschromicum perstans. Acta Derm. Venereol. 54:65–68, 1974. Convit, J., F. Kerdel-Vegas, and G. Rodriguez. Eritema discromico perstans. Dermatol. Venez. 2:118–164, 1961a. Convit, J., F. Kerdel-Vegas, and G. Rodriguez. Erythema dyschromicum perstans: A hitherto undescribed skin disease. J. Invest. Dermatol. 36:457–462, 1961b. Goihman, Y. Erythema dyschromicum perstans: response to dapsone therapy. Int. J. Dermatol. 37:796, 1998. Gougerot, M. H. Lichen atypiques on invisibles pigmentogenes reveles par des pigmentation. Bull. Soc. Franc. Dermatol. Syphiligr. 42:792–794, 1935a. Gougerot, M. H. Lichen atypiques ou invisibles pigmentogenes. Bull. Soc. Franc. Dermatol. Syphiligr. 42:894–898, 1935b. Greppi, C., and Z. Soustek. Laa melanodermite lichenoide in soggetti etiopici. Minerva Dermatol. 41:153, 1966. Henderson, C. D., J. A. Tschen, and D. G. Schaefer. Simultaneously active lesions of vitiligo and erythema dyschromicum perstans. Arch. Dermatol. 124:1258–1260, 1988. Holst, R., and H. Mobachen. Erythema dyschromicum perstans. Acta Derm. Venereol. 54:69–72, 1974. Ito, M. Pigmentation maculosa multiplex. Tokyo: Kanahara Shuppan, 1955. Jablonska, S. Ingestion of ammonium nitrate as a possible cause of erythema dyschromicum perstans (ashy dermatosis). Dermatologica 150:287–291, 1975. Kark, E. C., and R. L. Litt. Ashy dermatosis: A variant of lichen planus? Cutis 25:631–633, 1980. Knox, J. M., B. G. Dodge, and R. G. Freeman. Erythema dyschromicum perstans. Arch. Dermatol. 97:262–270, 1968. Koves de Amini, E., and T. Briceno-Maaz. Neuvos casos de eritema discrómico perstans: Dermaosis. Cenicienta. Med. Cutánea. 1:353–360, 1967. Metin, A., O. Calka, and S. Ugras. Lichen planopilaris coexisting with erythema dyschromicum perstans. Br. J. Dermatol. 145:522–523, 2001. Naidorf, K. F., and S. R. Cohen. Erythema dyschromicum perstans and lichen planus. Arch. Dermatol. 118:683–685, 1982. Novick, N. L., and R. Phelps. Erythema dyschromicum perstans. Int. J. Dermatol. 10:630–633, 1985. Osswald, S. S., L. H. Proffer, and C. R. Sartori. Erythema
dyschromicum perstans: a case report and review. Cutis 68:25–28, 2001. Palatsi, R. Erythema dyschromicum perstans: A follow-up study from Northern Finland. Dermatologica 155:40–44, 1977. Pathak, M. A., N. P. Sanchez, and T. B. Fitzpatrick. Erythema dyschromicum perstans. In: Biology and Diseases of Dermal Pigmentation, T. B. Fitzpatrick et al. (eds). Tokyo: University of Tokyo Press, 1983, pp. 191–208. Peachy, R. D. E. Ashy dermatosis. Br. J. Dermatol. 94:227–228, 1976. Person, J. R., and R. L. Rogers. Ashy dermatosis: An apoptotic disease? Arch. Dermatol. 117:701–704, 1981. Piñol, A. J. Dermatitis por blaqucadones opticos: Estudio de 103 obervaciones personales. Med. Cutanea Ibero-Lat-Am. 5:249–267, 1971. Piquero-Martin, J., R. Perez-Alfonzo, and V. Abrusci. Clinical trial with clofazimine for treating erythema dyschromicum perstans. Int. J. Dermatol. 28:198–200, 1989. Ramirez, C. O. Los cenicientos, problemo clinico. In: Memoria del Primer Congreso Centroamericano de Dermatologica. San Salvador, 1957; pp. 122–130. Ramirez, C. O. Dermatosis cenicienta: Estudio epidermiológico de 139 casos. Dermatologica (Mexico) 10:133–142, 1966. Ramirez, C. O. The ashy dermatosis (erythema dyschromicum perstans). Cutis 3:244–247, 1967. Soter, N. A., C. Wand, and R. G. Freeman. Ultrastructural pathology of erythema dyschromicum perstans. J. Invest. Dermatol. 52:155, 1969. Stevenson, J. R., and M. Miura. Erythema dyschromicum perstans (ashy dermatosis). Arch. Dermatol. 94:196, 1966. Tschen, J. A., E. A. Tschen, and M. H. McGavran. Erythema dyschromicum perstans. J. Am. Acad. Dermatol. 2:295–302, 1980. Urano-Suehissa, S., H. Tagami, and K. Iwatsuki. Unilateral ashy dermatosis occurring in a child. Arch. Dermatol. 120:1491–1493, 1984. Wilson, D. J. Eczematous and pigmentary lichenoid dermatitis: Atypical lichen planus: Preliminary report. Arch. Dermatol. 54:377–396, 1946.
Erythromelanosis Follicularis Faciei et Colli Norman Levine and Cynthia Burk
Historical Background In 1960 Kitamura et al. described six young Japanese men with the triad of preauricular erythema, hyperpigmentation, and fine follicular papules. Since then, about 33 cases have been described (Kim et al., 2001). Most cases are sporadic (Mishima and Rudner, 1966), but a brother and sister have been reported (Yanez et al., 1993), which suggests an autosomal recessive inheritance (Acay 1993; Perez-Bernal et al., 2000).
Clinical Findings Erythromelanosis follicularis faciei et colli usually begins around the time of puberty, mainly affecting males (Sodaify et al., 1994). Approximately 15 cases have been reported in women (Alcalay et al., 1986; Hodak et al., 1996; Ingber et al., 1986). It is usually bilateral but unilateral cases have been noted (Borkovic et al., 1984). It usually begins in the preauricular area and slowly extends outwardly towards the cheek, neck, and occasionally involves the auricle and eyelid (Seiko 935
CHAPTER 50
Fig. 50.23. Typical lesion of the face and neck. (Courtesy of Dr. Yoon Kee Park and Dr. Sungbin Im.)
Fig. 50.24. Same patient as in Figure 50.23 (see also Plate 50.10, pp. 494–495).
et al., 1991) (Figs 50.23 and 50.24). One sees pinpoint, pale follicular papules interlaced with a ruddy hyperpigmentation (Fig. 50.25) (Whittaker and Griffiths, 1987). Posteriorly, the condition is fairly well circumscribed but anteriorly and inferiorly there is a gradual feathering (Watt and Kaiser, 1981). On diascopy there is blanching of the erythema but not the hyperpigmentation. Wood’s light examination shows accentuation of the hyperpigmentation. Terminal hairs may be enlarged and vellus hairs are lost. Local hyperhidrosis has been described leading to bothersome rusting of eyeglasses (Andersen, 1980). There is often an associated keratosis pilaris of the arms or back. One case had associated calcinosis cutis (Lee and Yang, 1987). Photosensitivity is absent.
melanosomes (Janniger, 1993). A single immunofluorescence study of five patients showed IgM in a granular pattern at the dermoepidermal junction (Alcalay et al., 1986).
Pathology Routine histopathologic examination shows a mounding and perifollicular parakeratosis. Enlarged hair follicles and hair shafts are noted. The hair shaft medulla may show retained cellular debris. There is also basal hyperpigmentation. The dermis contains a mild to moderate superficial perivascular lymphohistiocytic infiltrate with vascular ectasia. Electron microscopic studies reveal homogeneous clumping and enlargement of both melanocytic and keratinocytic 936
Differential Diagnosis The differential diagnosis includes ulerythema oophryogenes which mainly involves the eyebrows, forehead, and cheeks and leads to atrophic scarring with no hyperpigmentation. Keratosis pilaris blanches on diascopy and does not have increased basal pigmentation. Erythrose péribuccale pigmentaire lacks follicular papules and is scaly. Becker melanosis is usually seen on the back or torso and has normal hair structures. Postinflammatory hyperpigmentation, melasma, and berloque dermatitis do not have follicular papules or telangiectasia. Poikiloderma of Civatte involves the lateral neck and upper chest, and shows distinctive sparing under the chin. Follicular papules are not prominent.
Treatment With the exception of topical retinoic acid, which is of minimal value, there have been few proved therapeutic options described. One group recommends 12% ammonium lactate and metronidazole 0.75% gel (Warren and Davis, 1995).
ACQUIRED EPIDERMAL HYPERMELANOSES Seiko, T., S. Takahashi, and M. Morohashi. A case of erythromelanosis follicularis faciei with a unique distribution. J. Dermatol. 18:167–170, 1991. Sodaify, M., S. Baghestani, F. Handjani, and M. Sotoodeh. Erythromelanosis follicularis faciei et colli. Int. J. Dermatol. 33:643–644, 1994. Warren, F. M., and L. S. Davis. Erythromelanosis follicularis faciei in women. J. Am. Acad. Dermatol. 32(5 Pt 2):863–866, 1995. Watt, T. L., and J. S. Kaiser. Erythromelanosis follicularis faciei et colli: a case report. J. Am. Acad. Dermatol. 5:533–534, 1981. Whittaker, S. J., and W. A. Griffiths. Erythromelanosis follicularis faciei et colli. Clin. Exp. Dermatol. 12:33–35, 1987. Yanez, S., J. A. Velasco, and M. P. Gonzalez. Familial erythromelanosis follicularis faciei et colli — an autosomal recessive mode of inheritance. Clin. Exp. Dermatol. 18:283–285, 1993.
Erythrose Péribuccale Pigmentaire of Brocq Norman Levine and Cynthia Burk
Historical Background In 1923, Brocq reported on a case of unusual perioral hyperpigmentation. The next 50 years produced few of a similar condition.
Synonyms
Fig. 50.25. Prominent hyperpigmentation associated with erythema.
References Acay, M. C. Erythromelanosis follicularis faciei et colli: a genetic disorder? Int. J. Dermatol. 32:542, 1993. Alcalay, J., A. Ingber, S. Halevi, M. David, and M. Sandbank. Erythromelanosis follicularis faciei in women. Br. J. Dermatol. 114:267, 1986. Andersen, B. L. Erythromelanosis follicularis faciei et colli. Case reports. Br. J. Dermatol. 102:323–325, 1980. Borkovic, S. P., R. A. Schwartz, and R. S. McNutt. Unilateral erythromelanosis follicularis faciei et colli. Cutis 33:163–168, 1984. Hodak, E., A. Ingber, J. Alcaley, and M. David. Erythromelanosis follicularis faciei in women [comment]. J. Am. Acad. Dermatol. 34:714, 1996. Ingber, A., E. Hodak, and E. Sandbank. A recent case of erythromelanosis follicularis faciei et colli in a female. Z. Hautkrankh. 61:1409–1410, 1986. Janniger, C. K. Erythromelanosis follicularis faciei et colli. Cutis 51:91–92, 1993. Kitamura, K., H. Kato, Y. Mishima, and S. Sonoda. Erythromelanosis follicularis faciei. Hautarzt 11:391–393, 1960. Lee, C. W., and I. S. Yang. Cutaneous calcinosis in erythromelanosis follicularis faciei et colli. Clin. Exp. Dermatol. 12:31–32, 1987. Mishima, Y., and E. Rudner. Erythromelanosis follicularis faciei et colli. Dermatologica 132:269, 1966. Perez-Bernal, A., M. A. Munoz-Perez, and E. Camacho. Management of facial hyperpigmentation. Am. J. Clin. Dermatol. 1:261–268, 2000.
L’erthrose pigmentée péribuccale, melanosis perioralis et peribuccalis (Braun-Falco et al., 1991), erythrosis pigmenta faciei (Korting and Denk, 1976), erythrosis pigmentosa peribuccalis (Cohen, 1948), erythrose péribuccale pigmentaire (Kaminsky and Asrilant, 1959; Tritsch and Greither, 1955), and pigmented peribuccal erythema of Brocq (Everett and Burgdorf, 1992).
Clinical Findings Erythrose péribuccale pigmentaire is most commonly seen in adult women but may rarely be seen in men. The condition affects the central face, especially, the perioral area and usually has a thin, unaffected grenz zone at the vermilion border. The hyperpigmentation may extend down as far as the nasolabialis sulcus (Perez-Bernal et al., 2000). Occasionally, the disorder extends over the jaws and to the temples (Tritsch and Greither, 1955). After recurrent episodes of erythema and a reddishbrown pigmentary response, a gray-brown hyperpigmentation ensues, usually with some degree of telangiectasia (Fig. 50.26). Although there may be considerable variation of erythema and discoloration, the process is fairly stable. There may be loss of vellus hairs. Should significant scaling develop, the condition is called “parakeratose pigmentogene peribuccale.” Although there are no strict diagnostic criteria, the combination of centro-facial, perioral, red-brown or gray-brown hyperpigmentation with a history or clinical evidence of vascular instability and telangiectasia should be sufficient for the diagnosis. Topical corticosteroids and photodynamic substances in some cosmetics may be factors in the development of erythrose péribuccale pigmentaire of Brocq (Perez-Bernal et al., 2000). 937
CHAPTER 50 of facial hyperpigmentation. Am. J. Clin. Dermatol. 1:261–268, 2000. Tritsch, H., and A. Greither. Erythrosis pigmenta of the face. Arch. Dermatol. Syphil. (Berlin) 199:221–227, 1955.
Extracutaneous Neuroendocrine Melanoderma Norman Levine and Cynthia Burk
Historical Background
Fig. 50.26. Typical péribuccale pattern of involvement.
Although there had been over 40 well-documented cases of hyperadrenocorticism occurring in association with neoplasia between 1928 and 1961, the relationship of an increased plasma and tumor tissue ACTH-like substance was not proved until 1961 (Christy, 1961). In 1963 the term “ectopic ACTH syndrome” was first used and the syndrome was clearly defined (Liddle et al., 1963).
Histopathology Light microscopy reveals basal epidermal hyperpigmentation. The dermis shows vascular dilatation, mild superficial perivascular lymphohistiocytic infiltration and melanophages (Obermayer and Becker, 1932).
Clinical Findings
The differential diagnosis includes perioral dermatitis, rosacea, seborrheic dermatitis, and estrogen-driven melasma, with or without complicating factors such as the abuse of topical, fluorinated corticosteroids, petrolatum, or photosensitizing cosmetic agents.
Signs and symptoms may be mild and insidious, delaying early diagnosis and treatment. Approximately 25% of patients with Cushing syndrome have the “ectopic ACTH syndrome.” Hypokalemic alkalosis, weakness, and edema are common; obesity, ecchymosis and striae may also be present. Associated internal disorders include impaired glucose tolerance and oligomenorrhea. Hirsutism, acne, and seborrhea may develop. The hypermelanosis is accentuated in sun-exposed areas (Fig. 50.27), creases, pressure points, oral mucosa, and the genitalia.
Treatment
Pathology
The hyperpigmentation may respond to various combinations of broad-spectrum sunscreen, hydroquinone, kojic acid, azelaic acid (Perez-Bernal et al., 2000), glycolic acid, retinoic acid, chemical peeling, dermabrasion, and laser resurfacing. Wood’s light examination may help guide therapy. Avoidance of sun and ultraviolet lamps is important. Pigmentation usually persists even after the cause has been removed (PerezBernal et al., 2000).
Routine histologic examination shows increased epidermal melanin without increased numbers of melanocytes. Melanin is most concentrated in the basal layer but is also prominent in the stratum malpighii. Dermal melanophages may be present (Lerner, 1955). The histologic picture is similar to that of a naturally darkly pigmented person.
Differential Diagnosis
References Braun-Falco, O. G., H. H. Plewig, K. Wolf, and R. K. Winkelman. Melanosis perioralis et peribuccalis. In: Dermatology, O. BraunFalco et al. (eds). Berlin: Springer-Verlag, 1991, p. 692. Brocq, J. L. L’erthrose pigmentée péri-buccale. Presse Med. 31:720– 728, 1923. Cohen, E. L. Erythrosis pigmentosa peribuccalis. Br. J. Dermatol. 60:203–211, 1948. Everett, M. A., and W. H. C. Burgdorf. Pigmented peribuccal erythema of Brocq. In: Clinical Dermatology, J. Demis (ed.). Philadelphia: J. B. Lippincott, 1992, pp. 11–12. Kaminsky, A., and M. Asrilant. Erythrose peribuccale pigmentaire. Rev. Assoc. Med. Argent. 73:427–429, 1959. Korting, G. W., and R. Denk. Circumscribed hyperpigmentation. In: Dermatology. Philadelphia: JB Lippincott, 1976, p. 381. Obermayer, M. E., and S. W. Becker. Erythrose peribuccale pigmentaire of Brocq: case with capillary and histologic study. Arch. Dermatol. Syphil. 26:444–450, 1932. Perez-Bernal, A., M. A. Munoz-Perez, and E. Camacho. Management
938
Laboratory Findings Laboratory studies show hypokalemia and elevated plasma and urinary 17-OH corticosteroids. Elevated plasma ACTH can arise from a pituitary tumor or from the adrenal gland (Bower and Gordon, 1965). These sources must be ruled out by magnetic resonance imaging (MRI) studies and dexamethasone suppression tests. There is evidence that certain tumors produce peptides which, much like corticotropinreleasing factor, act on the pituitary gland (Al Rustom et al., 1986). The ACTH produced by neoplasms is identical to pituitary ACTH (Liddle et al., 1969). There can also be an MSH action which is distinct from the ACTH action.
Pathogenesis Hyperpigmentation is caused by both ACTH and MSH action on the melanocytes. The most common tumor to cause the “ectopic ACTH syndrome” is bronchogenic oat cell carcinoma (Friedman et al., 1965; Liddle et al., 1969), accounting
ACQUIRED EPIDERMAL HYPERMELANOSES Bower, B. F., and G. S. Gordon. Hormonal effects of nonendocrine tumors. Annu. Rev. Med. 16:83–118, 1965. Christy, N. P. Adrenocorticotropic activity in the plasma of patients with Cushing’s syndrome associated with pulmonary neoplasm. Cancer Res. 1:85–86, 1961. Friedman, M., P. Marshall-Jones, and E. J. Ross. Cushing’s syndrome: Adrenocortical hyperactivity secondary to neoplasms arising outside the pituitary-adrenal system. Q. J. Med. 35:193–214, 1965. Gartner, L. A., and M. L. Voorhess. Adrenocorticotropic hormone-producing thymic carcinoid in a teenager. Cancer 71:106–111, 1993. Lerner, A. B. Melanin pigmentation. Am. J. Med. 19:902–924, 1955. Liddle, G. W., D. P. Island, R. L. Ney, W. E. Nicholson, and N. Shimizu. Nonpituitary neoplasm and Cushing’s syndrome. Arch. Intern. Med. 111:471–475, 1963. Liddle, G. W., W. E. Nicholson, D. P. Island, D. N. Orth, K. Abe, and S. C. Lowder. Clinical and laboratory studies of ectopic hormonal syndromes. Rec. Prog. Hormone Res. 25:283–305, 1969. Lohrenz, F. N., and G. S. Custer. ACTH-producing metastasis from carcinoma of the esophagus. Ann. Intern. Med. 62:1017–1022, 1965. Pearse, A. G. E. The neuroendocrine (APUD) cells of the skin. Am. J. Dermatopathol. 2:121–128, 1980. Upton, G. V., and T. T. Amaturda. Evidence for the presence of tumor peptides with corticotropin-releasing-factor-like activity in the ectopic ACTH syndrome. N. Engl. J. Med. 285:419–424, 1971. Waldrum, H. L., P. G. Burhol, J. A. Johnson, and A. G. Smith. MSHproducing gastric tumor. Acta Hepatogastroenterol. 24:386–388, 1977.
Felty Syndrome and Rheumatoid Arthritis Norman Levine and Cynthia Burk
Historical Background Fig. 50.27. Hyperpigmentation of the face.
for over half of cases. Other tumors include pancreatic carcinoma, esophageal carcinoma (Lohrenz and Custer, 1965), pheochromocytoma, thymoma (Gartner and Voorhess, 1993), ovarian carcinoma, gastric cancer (Waldrum et al., 1977), and various APUD tumors (Azzopardi et al., 1968; Pearse, 1980). The wide variety of causative tumors suggests that there may be a selective loss of repressors allowing ACTH and other active peptides to be produced (Upton and Amaturda, 1971). Additionally, exogenous sources of corticosteroids given for chronic diseases may produce these symptoms.
Treatment Unfortunately, by the time of diagnosis, there is often metastasis and, thus, a poor prognosis. Early diagnosis and treatment allows for the only chance of cure.
References Al Rustom, K., J. Gerard, and G. E. Pierard. Extrapituitary neuroendocrine melanoderma, unique association of extensive melanoderma with macromelanosomes and extrapituitary secretion of a high molecular weight neuropeptide related to pro-opiomelanocortin. Dermatologica 173:157–162, 1986. Azzopardi, J. G., M. C. Path, and E. D. Williams. Pathology of “nonendocrine” tumors associated with Cushing’s Syndrome. Cancer 22:274–286, 1968.
In 1924, while still a resident physician, Augustus Felty reported on his index case and four others from hospital records. The syndrome had been reported in Europe under a variety of names as early as 1896 (Still, 1896; Von Jaksch, 1896). The term Felty syndrome was first used in 1932 (Hanrahan and Miller, 1932), and is characterized by the triad of rheumatoid arthritis, splenomegaly, and leukopenia (neutropenia). Middle-aged individuals with chronic arthritis are most prone to this syndrome, but an occasional child has been reported. Most cases are sporadic but familial cases have been reported (Blendis et al., 1976; Runge et al., 1986). As in rheumatoid arthritis, there are numerous extra-articular manifestations. This syndrome has been extensively reviewed (Bowman, 2002; DeGruchy and Langley, 1961; Sienknecht et al., 1977; Spivak, 1977).
Clinical Findings Felty’s first five cases had hyperpigmentation as a clinical feature — most reports since have not emphasized this. Approximately 20% of Felty’s cases showed some degree of hyperpigmentation. Some may also have a yellow-brown pigmentation of sun-exposed areas (Ruderman, 1968) (Fig. 50.28). When hyperpigmentation is present, the source is generally of two types; vasculitis, especially, of the distal digits can lead to small, pigmented macules. There is general skin fragility in rheumatoid arthritis that leads to easy bruising and 939
CHAPTER 50
Pathology Histologic changes are those of a naturally dark or tanned person. There is increased epidermal melanization. Dermal hemosiderin may be present.
Treatment Treatment of hyperpigmentation in Felty syndrome and rheumatoid arthritis involves control of the primary disease process, sunscreens, and sun avoidance.
References
Fig. 50.28. Hyperpigmentation on sun-exposed areas in a patient with rheumatoid arthritis (see also Plate 50.11, pp. 494–495).
ecchymosis which can result in dermal hemosiderin deposition and iron-induced stimulation of melanocytes (Morgan and Chow, 1993). Rare cases associated with symptomatic porphyria have been described (Eales et al., 1972; Rimington et al., 1972). Medications used to treat arthritic symptoms may lead to hyperpigmentation. Gold therapy can produce a diffuse cutaneous pigmentation. Gold is preferentially taken up by the dermis in ultraviolet-exposed skin. This dermal gold stimulates melanin production leading to photoaccentuated hyperpigmentation (Leonard et al., 1986; Pelachyk et al., 1984). Antimalarial preparations (quinacrine, chloroquine, hydroxychloroquine) may bind to melanin with subsequent cutaneous and mucosal hyperpigmentation (Granstein and Sober, 1981). Methotrexate when taken weekly may induce photosensitivity and result in hyperpigmentation (Toussirot and Wendling, 1999). Busulfan and cyclophosphamide may both induce diffuse hyperpigmentation that is enhanced in sun-exposed areas, especially in patients with dark complexions (Toussirot and Wendling, 1999). Minocycline is used for its immunomodulatory properties in treating rheumatoid arthritis. This drug has also been associated with hyperpigmentation (Langevitz et al., 2000; Ozog et al., 2000). 940
Bennion, S. D. Hyperpigmentation in a patient with Felty’s syndrome and hemochromatosis. J. Assoc. Mil. Dermatol. 9:14–17, 1983. Blendis, L. M., K. L. Jones, E. B. Hamilton, and R. Williams. Familial Felty’s syndrome. Ann. Rheum. Dis. 35:279–281, 1976. Bowman, S. J. Hematological manifestations of rheumatoid arthritis. Scand. J. Rheum. 31:251–259, 2002. DeGruchy, G. C., and G. R. Langley. Felty’s syndrome. Australas. Ann. Med. 10:292–303, 1961. Eales, L., W. G. Sears, K. B. King, M. B. Levey, and C. Rimington. Symptomatic porphyria in a case of Felty’s syndrome, I, Clinical and routine biochemical studies. Clin. Chem. 18:459–461, 1972. Fam, A., and T. Paton. Nail pigmentation after parenteral gold therapy for rheumatoid arthritis. Arthritis Rheum. 27:119–120, 1984. Felty, A. R. Chronic asthma in the adult, associated with splenomegaly and leukopenia: a report of 5 cases of an unusual clinical syndrome. Bull. Johns Hopkins Hosp. 35:16–20, 1924. Granstein, R., and A. Sober. Drug- and heavy metal-induced hyperpigmentation. J. Am. Acad. Dermatol. 5:1–18, 1981. Hanrahan, E. M., Jr., and S. R. Miller. Effect of phlebectomy in Felty’s syndrome. J. Am. Med. Assoc. 99:1247–1249, 1932. Leonard, P., F. Moatamed, J. Ward, M. Piepkorn, E. Adams, and W. Knibbe. Chrysiasis: the role of sun exposure in dermal hyperpigmentation secondary to gold therapy. J. Rheumatol. 13:58–64, 1986. Langevitz, P., A. Livneh, I. Bank, and M. Pras. Benefits and risks of minocycline in rheumatoid arthritis. Drug Saf. 22:405–414, 2000. Lutterloh, C., and P. Shallenberger. Unusual pigmentation developing after prolonged suppressive therapy with quinacrine hydrochloride. Arch. Dermatol. Syphil. 53:349–354, 1946. Morgan, G. J., Jr., and W. S. Chow. Clinical features, diagnosis, and prognosis in rheumatoid arthritis. Curr. Opin. Rheumatol. 5:184– 190, 1993. Ozog, D. M., D. S. Gogstetter, G. Scott, and A. A. Gaspari. Minocycline-induced hyperpigmentation in patients with pemphigus and pemphigoid. Arch. Dermatol. 136:1133–1138, 2000. Pelachyk, J. M., W. F. Bergfeld, and J. T. McMahon. Chrysiasis following gold therapy for rheumatoid arthritis: ultrastructural analysis with x-ray energy spectroscopy. J. Cutan. Pathol. 11:491–494, 1984. Pinals, R. S. Felty’s syndrome. In: Textbook of Rheumatology, 4th ed., W. N. Kelly, C. B. Sledge, E. D. Harris, and S. Ruddy (eds). Philadelphia: WB Saunders, 1993, pp. 924–930. Rimington, C., W. G. Smears, and L. Eales. Symptomatic porphyria in a case of Felty’s syndrome. II. Biochemical investigations. Clin. Chem. 18:462–470, 1972. Ruderman, M., L. M. Miller, and R. S. Pinals. Clinical and serologic observations on 27 patients with Felty’s syndrome. Arthritis Rheum. 11:377–384, 1968. Runge, L. A., F. R. Davey, J. Goldberg, and P. R. Boyd. The inheritance of Felty’s syndrome in a family with several affected members. J. Rheumatol. 13:39–42, 1986. Sams, W., and J. Epstein. The affinity of melanin for chloroquine. J. Invest. Dermatol. 45:482–488, 1965. Sienknecht, C. W., M. B. Urowitz, and W. Pruzanski. Felty’s syn-
ACQUIRED EPIDERMAL HYPERMELANOSES
Fig. 50.29. Melasma-like hyperpigmentation.
Fig. 50.30. Diffuse meloderma.
drome: Clinical and serological analysis of 34 cases. Ann. Rheum. Dis. 36:500, 1977. Spivak, J. L. Felty’s Syndrome: An analytical review. Johns Hopkins Med. J. 141:156–162, 1977. Still, G. F. On a form of chronic joint disease in children. Med. Chirurg. Trans. 80:47–53, 1896. Toussirot, E. and D. Wendling. Methotrexate-induced hyperpigmentation in a rheumatoid arthritis patient. Clin. Exp. Rheumatol. 17: 751, 1999. Von Jaksch, A. Arthritis urica, Megalosplenie and Leukopenie. Dtsch. Med. Wochenschr. 36:634–638, 1896.
Hyperpigmentation Associated with Human Immunodeficiency Virus (HIV) Infection Philippe Bahadoran
Fig. 50.31. Small hyperpigmented macules of the fingertips.
Hyperpigmentation Types Probably Related to HIV Infection and/or its Therapeutics
described and are summarized in Table 50.2. Except for melasmalike pigmentation, that seems to occur alone, the other types of pigmentation are frequently associated with each other (Bendick et al., 1989; Gallais et al., 1992; GrauMassanes et al., 1990; Greenberg and Berger, 1990; Lacour et al., 1991; Langford et al., 1989; Merenich et al., 1989; PoizotMartin et al., 1991; Tadini et al., 1991).
Clinical and Histologic Features Hyperpigmentation occurs frequently in patients with HIV infections, especially in the late stage of the disease. Different patterns of cutaneous (Figs 50.29–50.31), mucosal (Fig. 50.32), and nail (Fig. 50.33) pigmentation have been
941
CHAPTER 50
Histologic and ultrastructural features indicative of melanotic pigmentation are found in most cases, except for clofazimine-induced pigmentation. Melanin is increased in the epidermis, especially in the keratinocytes of the basal layer (Esposito, 1987; Ficarra et al., 1990; Gaddoni et al., 1995; Gallais et al., 1992; Greenberg and Berger, 1990; Gregory and DeLeo, 1994; Hermanns-Lê et al., 1993; Langford et al., 1989). A moderate degree of dermal pigment incontinence is often noted in addition to epidermal pigmentation (Ficarra et al., 1990; Gallais et al., 1992; Greenberg and Berger, 1990; Gregory and DeLeo, 1994; Hermanns-Lê et al., 1993; Langford et al., 1989). There is no melanocyte proliferation, but ultrastructural studies indicate that these cells are activated (Ficarra et al., 1990; Hermanns-Lê et al., 1993; Zhang et al.,
Fig. 50.32. Hyperpigmented lesions of the tongue.
Fig. 50.33. Hyperpigmentation of the nail bed (see also Plate 50.12, pp. 494–495).
Table 50.2. Hyperpigmentation patterns probably related to HIV infection and/or its therapeutics. Hyperpigmentation
Clinical features
References
Facial and photodistributed hyperpigmentation
Light brown macules over the temporal and frontal regions Sometimes more spread, mimicking melasma May even extend to other photoexposed areas Occurs mostly at the late stage of HIV infection Pigmented macules on palms and soles, on dorsal and ventral aspects of fingers, and on finger pads Reported in severely immunocompromised patients Heterogeneous light to dark brown pigmentation Confers a “dirty” aspect Observed in patients with advanced HIV infection Oral pigmentation is the most frequent and is more often macular than diffuse Oral melanotic macules in HIV infection have a rapid progression rate Genital pigmentation was rarely reported Longitudinal melanonychia is the most frequent aspect Horizontal or diffuse nail discoloration is also possible Zidovudine (AZT) is clearly the dominant cause, pigmentation is dose dependent and reversible once AZT is stopped Nail pigmentation also occurs in HIV-positive patients without AZT
Lacour et al., 1993; Gaddoni et al., 1995; Gregory and DeLeo, 1994; Pascual et al., 1996
Acral hyperpigmentation
Diffuse hyperpigmentation
Mucosal hyperpigmentation
Nail hyperpigmentation
942
Bendick et al., 1989; Doutre et al., 1990; Gallais et al., 1992; Merenich et al., 1989 Esposito, 1987; Jing et al., 2000; HermannsLê et al., 1993; Lacour et al., 1991; Poizot-Martin et al., 1991 Cohen and Callen, 1992; Ficarra et al., 1990; Gallais et al., 1992; Greenberg and Berger, 1990; Grau-Massanes et al., 1990; Langford et al., 1989; Tadini et al., 1991 Azon-Masoliver and Mallolas, 1988; Bendick et al., 1989; Chandrasekar, 1989; Don et al., 1990; Furth and Kazakis, 1987; Greenberg and Berger, 1990; Grau-Massanes et al., 1990; Lacour et al., 1988; Panwalker, 1987; Tosti et al., 1990
ACQUIRED EPIDERMAL HYPERMELANOSES
1989). Similar findings, e.g., increase of melanin throughout the nail plate, and dendritic melanocytes, are observed in melanonychia (Greenberg and Berger, 1990; Tosti et al., 1990).
Etiology Hyperpigmentation during the course of HIV infection is rarely secondary to adrenal insufficiency (Dore et al., 1998; Esposito, 1987). Although opportunistic infections can cause adrenal lesions in HIV infection (Bricaire et al., 1998), adrenal function is nonetheless often normal in these patients (Verges et al., 1990). Folate or vitamin B12 deficiency can result in acquired cutaneous or mucosal pigmentation (Fitzpatrick and Ortonne, 1995), and low folate or vitamin B12 plasma levels occur frequently in acquired immune deficiency syndrome (AIDS) (Boudes et al., 1990), but a direct link between hyperpigmentation and vitamin deficiency has not been established in HIV infection. Hyperpigmentation of photoexposed areas in porphyria cutanea tarda was observed in association with AIDS (Pascual et al., 1996), but porphyria cutanea tarda might rather be linked to hepatitis C infection (Castanet et al., 1994). Zidovudine (AZT) was the first nucleoside analog to be approved as antiretroviral medication. AZT is undoubtedly a frequent cause of pigmented nails (Anders and Abele, 1989; Azon-Masoliver and Mallolas, 1988; Chandrasekar, 1989; Don et al., 1990; Furth and Kazakis, 1987; Grau-Massanes et al., 1990; Greenberg and Berger, 1990; Lacour et al., 1988; Panwalker, 1987; Tosti et al., 1990). Nail involvement ranges from toenail only involvement to complete fingernail and toenail involvement, including scattered nail involvement of toes and fingers. Nail pigmentation patterns associated with AZT include entire nail pigmentation, transverse banding, and multiple longitudinal bands. Pigmentation varies from faint blue, dark blue-gray, and brownish discolorations (Ward et al., 2002). AZT may sometimes induce oral pigmentation (Greenberg and Berger, 1990), acral pigmented macules (Bendick et al., 1989; Doutre et al., 1990), and diffuse melanoderma (Hermanns-Lê et al., 1993), but these types of pigmentation are also frequently reported without relation to this drug during the course of HIV infection (Ficarra et al., 1990; Gallais et al., 1992; Granel et al., 1997; Lacour et al., 1991; Langford et al., 1989; Poizot-Martin et al., 1991). As with other drugs, AZT-induced pigmentation is reversible upon discontinuation (Ward et al., 2002). The nail and mucocutaneous pigmentation induced by AZT is due to the deposition of melanin (Greenberg and Berger, 1990). Mice fed AZT exhibit a hyperpigmentation on their tails because of the presence of large quantities of melanin in the epidermis; they are therefore regarded as a possible animal model of AZT-induced hyperpigmentation (Roth et al., 1991). In this model the increased pigmentation is due to increased numbers of melanosomes within epidermal keratinocytes (Obuch et al., 1992). Emtricitabine (FTC) is a recent nucleoside analog used for antiretroviral therapy. Hyperpigmentation, usually affecting either the palms of the hands or the soles
of the feet, was reported on individuals with FTC, and is almost exclusive to patients of African origin (Nelson et al., 2004). Insulin resistance is a side effect in patients with HIV infection who are receiving treatment with protease inhibitors. A case of acanthosis nigricans, in the context of insulinresistance induced by protease inhibitors, was reported recently (Mellor-Pita et al., 2002). Hydroxyurea, a cytotoxic agent used in myeloproliferative disorders, has recently been introduced as an adjunct to antiretroviral therapy. Melanonychia and mucocutaneous hyperpigmentation due to hydroxyurea use in HIV-infected patients have been reported (Joyner et al., 1999; Laughon et al., 2000). High-dose rifabutin (600 mg daily) for mycobacterial infection can induce dark brown skin pigmentation, but not the lower dosage (300 mg daily) used for prophylaxis (Figueras et al., 1998; Smith and Flanigan, 1995). Clofazimine, which is also used for mycobacterial infection, induces skin hyperpigmentation, due to the accumulation in the skin of the drug itself and later of a ceroidlike substance (Granstein and Sober, 1981). Tetracosactide (ACTH), which is used for the treatment of elevated cranial pressure due to cerebral toxoplasmosis, induces a diffuse, Addisonlike hyperpigmentation (Granstein and Sober, 1981). Several drugs used for Kaposi sarcoma treatment — bleomycin, vinblastine, and cyclophosphamide — can cause pigmentary changes (Caumes et al., 1991; Granstein and Sober, 1981). Ketoconazole was suspected of causing cutaneous and oral pigmentation in HIVinfected patients (Langford et al., 1989; Poizot-Martin et al., 1991). Increased plasmatic levels of a-MSH were noted in a patient with severe melanoderma (Gallais et al., 1992). However, when a-MSH was measured in nine patients with AIDS and diffuse melanoderma, only one had an elevated value, which suggests that excessive production of a-MSH is a rare etiology of hyperpigmentation associated with AIDS (Lacour and Ortonne, 1996). In a study that aimed to assess the cutaneous response to UV irradiation in HIV patients each subject underwent an exposure of 6 MED. No significant differences between HIVinfected patients and controls were found for delayed pigmentation (Aubin et al., 1999).
Other Pigmented Dermatoses Occurring in HIV-Infected Patients The following entities are considered separately because erythema dyschromicum perstans and Riehl melanosis may represent the occurrence of otherwise well-defined pigmented dermatoses in the context of HIV infection, whereas in pigmented erythroderma, pigmentation is only a secondary event.
Erythema Dyschromicum Perstans This rare dermatitis was reported twice during the course of HIV infection. The histologic findings of basal cell vacuolization with dermal pigment incontinence confirmed the diagnosis in both cases (Nelson et al., 1992; Venencie et al., 1988). 943
CHAPTER 50
Riehl Melanosis One case of Riehl–melanosis-like facial pigmentation, with a large number of melanophages in the dermis, was reported in a Japanese patient with advanced HIV infection (Hanada et al., 1994).
Pigmented Erythroderma This severe skin disease occurs during the late stage of AIDS, and it is characterized by a pruriginous squamous erythroderma, followed in most patients by intense cutaneous pigmentation (Friedler et al., 1999; Janier et al., 1989; Kaplan et al., 1991; Picard-Dahan et al., 1996). Despite some clinical similarities with Sézary syndrome, histologic and molecular biology studies do not demonstrate features of cutaneous Tcell lymphomas. The cause of this peculiar HIV-associated erythroderma remains unknown. The mechanism of hyperpigmentation is also uncertain, but given the context in which it occurs, a postinflammatory pigmentation seems most likely.
Hypopigmentation HIV–infection-associated vitiligo has rarely been reported (de la Fuente et al., 1991; Duvic et al., 1987; Ivker et al., 1994). In addition, a case of vitiligo in association with HIV where a rising CD4 lymphocyte count due to highly active antiretroviral therapy (HAART) closely correlated with changes in the skin was reported recently (Anthony and Marsden, 2003). On the other hand, infectious causes of hypopigmentation, such as tinea versicolor achromians, post-zoster hypopigmented macules, secondary syphilis, or even leprae, may occur more frequently during the course of HIV infection.
Dysplastic Nevi and Melanoma There have been several case reports of melanoma (McGregor et al., 1992; Rivers et al., 1989; Tyndall et al., 1989; Van Ginkel et al., 1991) and dysplastic nevi (Betlloch et al., 1991; Duvic et al., 1989) among HIV-infected patients. In a comparative study, it was found that the total number of nevi was higher in a group of HIV-infected patients than in controls (Grob et al., 1996). However, patients and controls were not significantly different according to the number of large (equal or larger than 5 mm) or atypical nevi. Additional epidemiological data are warranted to confirm that the frequency or the gravity of melanocytic tumors is increased with HIV infection. Regarding the prognosis, it was reported recently that melanoma patients who were HIV-positive had a significantly shorter disease-free and overall survival compared with HIVnegative melanoma patients. There was an inverse relationship between CD4 cell counts and time to first melanoma recurrence (Rodrigues et al., 2002).
Conclusion Hypermelanosis significantly increases in individuals with HIV infection. Apart from nail pigmentation that is clearly linked with AZT, a defined etiology can rarely be determined for cutaneous and mucosal hyperpigmentation. However, the 944
search for treatable causes and for drug-induced hyperpigmentation must be done carefully in every case of hyperpigmentation occurring in an HIV-infected patient.
References Antony, F. C., and R. A. Marsden. Vitiligo in association with human immunodeficiency virus infection. J. Eur. Acad. Dermatol. Venereol. 17:456–458, 2003. Aubin, F, N. Parriaux, C. Robert, D. Blanc, C. Drobacheff, R. Laurent, and P. Humbert. Cutaneous reaction to ultraviolet irradiation in human-immunodeficiency-virus-infected patients. A casecontrol study. Dermatology 198:256–260, 1999. Azon-Masoliver, A., and J. Mallolas. Zidovudine-induced nail pigmentation. Arch. Dermatol. 124:1570–1571, 1988. Bendick, C., H. Rasokat, and G. Steigleder. Azidothymidine-induced hyperpigmentation of skin and nails. Arch. Dermatol. 125:1285– 1286, 1989. Betlloch, I., C. Amador, E. Chiner, F. Pasquau, J. L. Calpe, and A. Vilar. Eruptive melanocytic nevi in hurnan immunodeficiency virus infection. Int. J. Dermatol. 30:303, 1991. Boudes, P., J. Zittoun, and A. Sobel. Folate, vitamin B 12 and HIV infection. Lancet 335:1401–1402, 1990. Bricaire, F., C. Marche, and D. Zoubi. Adrenocortical lesions and AIDS. Lancet i:881, 1988. Castanet, J., J. P. Lacour, J. Bodokh, S. Bekri, and J. P. Ortonne. Porphyria cutanea tarda in association with human immunodeficiency virus infection: is it related to hepatitis C virus infection? Arch. Dermatol. 130:664–665,1994. Caumes, E., C. Katlama, G. Guermonprez, I. Bournerias, M. Danis, and M. Gentilini. Cutaneous side-effects of bleomycin in AIDS patients with Kaposi’s sarcoma. Lancet 336:1593, 1991. Chandrasekar, P. H. Nail discoloration and human immunodeficiency virus infection. Am. J. Med. 86:506–507, 1989. Cohen, L. M., and J. P. Callen. Oral and labial melanotic macules in a patient infected with human immunodeficiency virus. J. Am. Acad. Dermatol. 26:653–654, 1992. de la Fuente, J., E. Suarez, J. A. Arzuaga, P. Tebas, and J. Lopez de Letona. Vitiligo et SIDA. Nouv. Dermatol. 10:397–398, 1991. Don, P. C., F. Fusco, P. Fried, A. Batterman, F. P. Duncanson, T. H. Lenox, and N. C. Klein. Nail dyschromia associated with zidovudine. Ann. Intern. Med. 112:145–146, 1990. Dore, M. X., A. de La Blanchardiere, P. Lesprit, F. David, J. P. Beressi, J. Fiet, D. Sicard, and J. M. Decazes. Peripheral adrenal insufficiency in AIDS. Rev. Med. Intern. 19:23–28, 1998. Doutre, M.-S., C. Beylot, and J. Beylot. Macules pigmentées des extrémités au cours d’un traitement par zidovudine. Rev. Med. Interne 11:486, 1990. Duvic, M., L. Lowe, R. P. Rapini, S. Rodriguez, and M. L. Levy. Eruptive dysplastic nevi associated with human immunodeficiency infection. Arch. Dermatol. 125:397–401, 1989. Duvic, M., R. Rapimi, W. K. Hoots, and P. W. Mansell. Human immunodeficiency virus-associated vitiligo: expression of autoimmunity with immunodeficiency? J. Am. Acad. Dermatol. 17:656– 662, 1987. Esposito, R. Hyperpigmentation of skin in patients with AIDS. Br. Med. J. 294:840, 1987. Ficarra, G., E. J. Shillitoe, K. Adler-Storthz, D. Gaglioti, M. Di Pietro, R. Riccardi, and G. Forti. Oral melanotic macules in patients infected with human immunodeficiency virus. Oral Surg. Oral Med. Oral Pathol. 70:748–755, 1990. Fitzpatrick, T. B., and J. P. Ortonne. Abnormalities of pigmentation. In: Dermatology in General Medicine, 3rd ed., T. B. Fitzpatrick, A. Z. Eisen, K. Wolff, I. M. Freedberg, and K. F. Austen (eds). New York: McGraw Hill, 1995, p. 962. Figueras, C., L. Garcia, and J. M. Bertran. Hyperpigmentation in a
ACQUIRED EPIDERMAL HYPERMELANOSES patient with AIDS, receiving rifabutin for disseminated Mycobacterium genavense infection. Eur. J. Pediatr.157:612, 1998. Friedler, S., M. T. Parisi, E. Waldo, R. Wieczorek, G. Sidhu, and M. J. Rico. Atypical cutaneous lymphoproliferative disorder in patients with HIV infection. Int. J. Dermatol. 38:111–118, 1999. Furth, P., and A. Kazakis. Nail pigmentation changes associated with azidothymidine (zidovudine). Ann. Intern. Med. 107:350, 1987. Gaddoni, G., L. Baldassari, F. Albertini, and C. Misciali. Melasma and acquired immunodeficiency syndrome (AIDS). J. Eur. Acad. Dermatol. Venereol. 4:44–47, 1995. Gallais, V., J. P. Lacour, C. Perrin, G. Ghanem, J. Bodokh, and J. P. Ortonne. Acral hyperpigmented macules and longitudinal melanonychia in AIDS patients. Br. J. Dermatol. 126:387–391, 1992. Granel, F., F. Truchetet, and M. Grandidier. Longitudinal colored bands, oral and cutaneous pigmentation without taking zidovudine. Ann. Dermatol. Venereol. 124:460–462, 1997. Granstein, R., and A. Sober. Drug- and heavy metal-induced hyperpigmentation. J. Am. Acad. Dermatol. 5:1–18, 1981. Grau-Massanes, F., F. Millan, M. I. Febrer, C. Pujol, V. A. Alegre, M. Salavert, V. Navarro, and A. Aliaga. Pigmented nails and mucocutaneous pigmentation in HIV-positive patients treated with zidovudine. J. Am. Acad. Dermatol. 22:687, 1990. Greenberg, R., and T. Berger. Nail and mucocutaneous hyperpigmentation with azidothymidine therapy. J. Am. Acad. Dermatol. 22: 327–330, 1990. Gregory, N., and V. A. DeLeo. Clinical manifestations of photosensitivity in patients with human immunodeficiency virus infection [editorial]. Arch. Dermatol. 130:630–633, 1994. Hanada, K., I. Hashimoto, T. Baba, T. Tamura, and S. Kishibe. Melanosis Riehl-like facial pigmentation in a Japanese case of AIDS. J. Dermatol. 21:363–366, 1994. Grob, J. J., S. Bastuji-Garin, L. Vaillant, J. C. Roujeau, P. Bernard, B. Sassolas, and J. C. Guillaume. Excess of nevi related to immunodeficiency: a study in HIV-infected patients and renal transplant recipients. J Invest. Dermatol. 107:694–697, 1996. Hermanns-Lê, T., F. Gerardy-Goffin, M. Giet-Lesuisse, and G. E. Pierard. Ultrastructural study of azidothymidine-induced melanoderma in an AIDS patient [in French]. Ann. Pathol. 13:328–331, 1993. lvker, R., M. Goldaber, and M. R. Buchness. Blue vitiligo. J. Am. Acad. Dermatol. 30(5 Pt 2):829–831, 1994. Janier, M., C. Katlama, B. Flageul, F. Vaiensi, 1. Moulonguet, F. Sigaux, D. Dompmartin, and J. Civatte. The pseudo-Sezary syndrome with CD8 phenotype in a patient with the acquired immunodeficiency syndrome. Ann. Intern. Med. 110:738–740, 1989. Jing, W. A retrospective survey of mucocutaneous manifestations of HIV infection in Malaysia: analysis of 182 cases. J. Dermatol. 27:225–232, 2000. Joyner, S., D. Lee, P. Hay, and R. Lau. Hydroxyurea-induced nail pigmentation in HIV patients. HIV Med. 1:40–42, 1999. Kaplan, M. H., W. Hall, M. Susin, S. Pahwa, S. Z. Salahuddin, C. Heilman, J. Fetten, M. Coronesi, and B. F. Farber. Syndrome of severe skin disease, eosinophilia, and dermatopathic lymphadenopathy in patients with HTLV-II complicating human immunodeficiency virus infection. Am. J. Med. 91:300–307, 1991. Lacour, J. P., D. Dubois, and D. Ortonne. Mélanonychies en bandes au cours du traitement par la zidovudine. Ann. Dermatol. Venereol. 155:1091, 1988. Lacour, J. P., V. Gallais, J. Bodokh, G. Ghanem, and J. P. Ortonne. Cutaneous and mucous hyperpigmentation in AIDS [letter, in French]. Presse Med. 20:1686–1690, 1991. Lacour, J. P., G. Ghanem, and J. P. Ortonne. AIDS and pigmentation. In: Proceedings of the 18th World Congress of Dermatology, W. H. C. Burgdorf, and S. I. Katz (eds). New York: Parthenon Publishing Group, 1993, pp. 513–515. Lacour, J. P., and J. P. Ortonne. AIDS, hypermelanosis, melasma and alphaMSH. J. Eur. Acad. Dermatol. Venerol. 6:96–97, 1996.
Langford, A., H. D. Pohle, and H. Gelderblom. Oral hyperpigmentation in HIV infected patients. Oral Surg. Oral Med. Oral Pathol. 67:301–307, 1989. Laughon, S. K., L. L. Shinn, and J. R. Nunley. Melanonychia and mucocutaneous hyperpigmentation due to hydroxyurea use in an HIV-infected patient. Int. J. Dermatol. 39:928–931, 2000. McGregor, J. M., M. Newell, J. Ross, N. Kirkham, D. H. McGibbon, and C. Darley. Cutaneous malignant melanoma and human immunodeficiency virus (HIV) infection: a report of three cases. Br J. Dermatol. 126:516–519, 1992. Mellor-Pita, S., M. Yebra-Bango, J. Alfaro-Martinez, and E. Suarez. Acanthosis nigricans: a new manifestation of insulin resistance in patients receiving treatment with protease inhibitors. Clin. Infect. Dis. 34:716–717, 2002. Merenich, J. A., R. N. Hannon, R. H. Gentry, and S. M. Harrison. Azidothymidine-induced hyperpigmentation mimicking adrenal insufficiency. Am. J. Med. 86:469–470, 1989. Nelson, M. R., A. G. Lawrence, R. C. Staughton, and B. G. Gazzard. Erythema dyschromicum perstans in an HIV antibody-positive man [letter]. Br. J. Dermatol. 127:658–659, 1992. Nelson, M., and M. Schiavone. Emtricitabine (FTC) for the treatment of HIV infection. Int. J. Clin. Pract. 58:504–510, 2004. Obuch, M. L., G. Baker, R. I. Roth, T. S. Yen, J. Levin, and T. G. Berger. Selective cutaneous hyperpigmentation in mice following zidovudine administration. Arch. Dermatol. 28:508–513, 1992. Panwalker, A. P. Nail pigmentation in the acquired immunodeficiency syndrome. Ann. Intern. Med. 107:943–944, 1987. Pascual, C., V. Garcia-Patos, R. Bartralot, R. Pedragosa, M. Capdevila, J. Barbera, and A. Castells. Pigmentation cutanée, seule manifestation d’une porphyrie cutanée tardive chez un malade séropositif pour le VIH 1. Ann. Dermatol. Venereol. 123:262–264, 1996. Picard-Dahan, C., T. Le Guyadec, M. Grossin, N. Féton, M. Raphaël, A. M. Simonpoli, B. Crickx, and S. Belaich. Erythrodermies pigmentées au cours du SIDA: cinq cas. Ann. Dermatol. Venereol. 123:307–313, 1996. Poizot-Martin, I., A. Lafeuillade, C. Dhiver, L. Xeri, R. Bouabdallah, T. Gamby, and J. A. Gastaut. Cutaneo-mucosal hyperpigmentation in AIDS. 4 cases [in French]. Presse Med. 20:632–636, 1991. Rivers, J. K., A. W. Kopf, and A. H. Postel. Malignant melanoma in a man séropositive for the human immunodeficiency virus. J. Am. Acad. Dermatol. 20:1127–1128, 1989. Rodrigues, L. K., B. J. Klencke, K. Vin-Christian, T. G. Berger, R. I. Crawford, J. R. Miller 3rd, C. M. Ferreira, M. Nosrati, and M. Kashani-Sabet. Altered clinical course of malignant melanoma in HIV-positive patients. Arch. Dermatol. 138:765–770, 2002. Roth, R. I., G. Baker, and J. Levin. An animal model for the study of azidothymidine-induced hyperpigmentation. Lab. Invest. 64:437– 439, 1991. Smith, J. F., and T. P. Flanigan. Unusual pigmentation in patients with AIDS who are receiving rifabutin for bacteremia due to Mycobacterium avium/Mycobacterium intracellulare complexe. Clin. Infect. Dis. 21:1515, 1995. Tadini, G., M. D’Orso, M. Cusini, and E. Alessi. Oral mucosa pigmentation: a new side effect of azidothymidine therapy in patients with acquired immunodeficiency syndrome [letter]. Arch. Dermatol. 127:267–268, 1991. Tosti, A., G. Gaddoni, P. A. Fanti, A. D’Antuono, and F. Albertini. Longitudinal melanonychia induced by 3¢azidodeoxythymidine. Dermatologica 180:217–220, 1990. Tyndall, B., R. Finlayson, K. Mutimer, F. A. Billson, V. F. Munro, and D. A. Cooper. Malignant melanoma associated with human immunodeficiency virus infection in three homosexual men. J. Am. Acad. Dermatol. 20:587–591, 1989. Van Ginkel, C. J. W., R. Tjon Lim Sang, J. L. G. Blaauwgeers, J. K. M. Eeftinck Schattenkerk, W. J. Mooi, and H. J. Hulsebosch. Multiple primary malignant melanomas in an HIV-positive man. J. Am. Acad. Dermatol. 24:284–285, 1991.
945
CHAPTER 50
Fig. 50.34. Hyperpigmented melanoacanthoma (see also Plate 50.13, pp. 494–495).
Fig. 50.35. Melanoacanthoma of the oral mucosa.
Venencie, P. Y., Y. Laurian, F. Lemarchand-Venencie, D. Lemay, and F. Verroust. Erythema dyschromicum perstans following human immunodeficiency virus seroconversion in an haemophiliac child. Arch. Dermatol. 124:1013–1014, 1988. Ward, H. A., G. G. Russo, and J. Shrum. Cutaneous manifestations of antiretroviral therapy. J. Am. Acad. Dermatol. 46:284–293, 2002.
Melanoacanthoma Norman Levine and Cynthia Burk
Historical Background In 1927, Bloch (1927) reported a case of an unusual pigmented lesion which he called “melanoepithelioma.” Mishima and Pinkus (1960) coined the term “melanoacanthoma” to describe a benign tumor characterized by proliferating dendritic melanocytes and keratinocytes. They included Bloch’s case but felt that he had failed to clearly identify this entity as separate from a pigmented seborrheic keratosis.
Clinical Findings There are two clinical forms of melanoacanthoma. The first (cutaneous) type is seen mainly in middle-aged to elderly Caucasians of either sex (Delacretaz, 1975; Reaves, 1972); it consists of a solitary, brown or black papule or small to giant-sized plaque (Fig. 50.34) which may be seen in the scalp, neck, back, abdomen, penis, eyelids, or extremities (Delacretaz 1975; Fatahzadeh and Sirois, 2002; Spott et al., 1972; Vion and Merot 1989). There is no malignant potential. These develop slowly and usually have a roughened surface. The second (mucosal) type occurs primarily in young or middle-aged black females (Tomich and Zunt, 1990). Approximately 37 cases of oral melanoacanthoma have been reported between 1978 and 2002 (Fatahzadeh and Sirois, 2002). It occurs on the lips, oropharynx, or oral mucosa (Fig. 50.35), including the hard palate, labial mocosa, alveolar mucosa, and fixed gingival mucosa (Fornatora et al., 2003; Matsuoka et al., 1982; Sexton and Maize 1987). It may be slightly verrucous but, generally, is flat and asymptomatic (Eisen and 946
Fig. 50.36. The clear cells in the mid epidermis are melanocytes.
Voorhees, 1991; Frey et al., 1984; Wright 1988). Pruritus, burning, or pain is infrequent. The lesions are solitary (90%), dark brown, black, or blue-black in color, and are 0.5–6.0 cm in size (Prince et al., 1984). They arise within a few weeks, and usually resolve after biopsy or removal of irritating stimuli. Cheek-biting, smoking, and ill-fitting dentures are the most common irritants. There are no associated medical conditions. Oral melanoacanthoma is unrelated to seborrheic keratosis (Fornatora et al., 2003). The lesion has no malignant potential. Clinical findings are nondiagnostic, thus biopsy is suggested (Fatahzadeh and Sirois, 2002).
Pathology Histopathologic examination of the cutaneous melanoacanthoma reveals a hyperplastic epidermis with papillomatosis, acanthosis, and pseudo-horn cyst formation. The distinguishing characteristic is dendritic melanocytes throughout the basal and all spinous layers (Figs 50.36 and 50.37). Most of the melanin is contained within the melanocytes. Ultrastructural study shows a partial blockage of melanin transfer to the
ACQUIRED EPIDERMAL HYPERMELANOSES
suggest that oral melanoacanthoma is a misnomer and have proposed the term, mucosal melanotic macule, reactive type (Horlick et al., 1988). The fact that these mucosal lesions arise and remit quickly following removal of offending stimuli would support this concept.
Treatment
Fig. 50.37. Close-up view of a dendritic melanocyte (FontanaMasson stain).
keratinocytes (Schlappner et al., 1978). Cells in mitosis may be seen but there is no atypia. Dermal melanophages are present. In the mucosal type, spongiotic intraepithelial vesicles (Zemtsov and Bergfeld, 1989), lymphohistiocytic dermal infiltrate admixed with eosinophils and increased vascularity may be seen (Fornatora et al., 2003). Strong HMB-45 reactivity is present in most cases of oral melanoacanthoma, making the diagnosis of melanoma difficult to exclude (Fornatora et al., 2003).
Differential Diagnosis The pigmented seborrheic keratosis does not have the prominent dendritic melanocytes with heavy pigmentation and melanin transfer blockage; although up to 38% of seborrheic keratosis demonstrate some degree of dendritic melanocytes (Simon et al., 1991). Some seborrheic keratoses show dendritic melanocytes within the islands of basaloid cells. Physiologic pigmentation shows basal hyperpigmentation. Nevocellular nevus (Buchner and Hansen, 1979), blue nevus, melanoma (Lambert et al., 1985, 1987), and pigmented basal cell carcinoma have distinctive pathologic findings. Dermatofibroma is a dermal tumor. The labial melanotic macule shows only increased numbers of melanocytes along the basal cell layer (Weathers et al., 1976). Amalgam tattoos show dermal granules. Kaposi sarcoma in HIV patients is a vascular lesion. Fixed drug eruption may affect the tongue (Tagami, 1973). Smoker’s melanosis is more diffuse than melanoacanthoma (Hedin, 1977).
Pathogenesis The pathogenesis of melanoacanthoma is unknown but it is suggested that the cutaneous melanoacanthoma is an irritated, pigmented seborrheic keratosis (Mevorah and Mishima, 1965; Simon et al., 1991). The mucosal type is a reactive lesion seen in black people due to their physiologic oral pigmentation in association with pigment lability following trauma or irritation. The term “melanoacanthosis” might better fit the clinicopathologic presentation (Tomich and Zunt, 1990). Others
Cutaneous melanoacanthomas may easily be removed surgically. A specimen for pathologic study should be obtained to rule out melanoma (Whitt et al., 1988). Mucosal lesions should also be biopsied since melanoma may be clinically identical to melanoacanthoma. Several oral melanoacanthomas have been reported to regress spontaneously after biopsy (Fatahzadeh and Sirois 2002; Fornatora et al., 2003). Removal of offending irritants generally leads to remission of oral melanoacanthoma.
References Bloch, B. Uber benigne nicht naevoide Melanoepitheliome der Haut nebst Bemerkungen uber das Wesen und die Genese der Dendritenzallon. Arch. Dermatol. Syphil. (Berlin) 153:20–40, 1927. Buchner, A., and L. S. Hansen. Pigmented nevi of the oral mucosa: A clinicopathologic study of 32 new cases and review of 75 cases from the literature. Part I. A clinicopathologic study of 32 new cases. Oral Surg. 48:131–142, 1979. Delacretaz, J. Melana Acanthome. Dermatologica 151:236–240, 1975. Eisen, D., and J. J. Voorhees. Oral melanoma and other pigmented lesions of the oral cavity. J. Am. Acad. Dermatol. 24:527–537, 1991. Fatahzadeh, M., and D. A. Sirois. Multiple intraoral melanoacanthomas: a case report with unusual findings. Oral Surg. Oral Med. Oral Pathol. Oral Radiol. Endodont. 94:54–56, 2002. Fornatora, M. L., R. F. Reich, S. Haber, F. Solomon, and P. D. Freedman. Oral melanoacanthoma: a report of 10 cases, review of the literature, and immunohistochemical analysis for HMB-45 reactivity. Am. J. Dermatopathol. 25:12–15, 2003. Frey, V. M., W. C. Lambert, R. D. Seldin, L. C. Schneider, and M. L. Mesa. Intraoral melanoacanthoma. J. Surg. Oncol. 27:93–96, 1984. Hedin, C. A. Smoker’s melanosis. Arch. Dermatol. 113:1533–1538, 1977. Horlick, H. P., R. R. Walther, D. J. Zagarelli, D. N. Silvers, and Y. D. Eliezri. Mucosal melanotic macule, reactive type: a simulation of melanoma. J. Am. Acad. Dermatol. 19:786–791, 1988. Lambert, M. W., W. C. Lambert, R. A. Schwartz, M. L. Mesa, R. H. Brodkin, A. H. Abbey, G. K. Potter, and W. P. Little Jr. Colonization of nonmelanocytic cutaneous lesions by dendritic melanocytic cells: a stimulant of acral-lentiginous (palmar-plantar-subungualmucosal) melanoma. J. Surg. Oncol. 28:12–18, 1985. Lambert, W. C., M. W. Lambert, M. L. Mesa, L. C. Scheider, C. G. Fischman, A. H. Abbey, R. H. Brodkin, M. D. Elam, W. A. Anderson, and G. K. Potter. Melanoacanthoma and related disorders: Simulants of acral-lentiginous (PPSM) melanoma. Int. J. Dermatol. 26:508–510, 1987. Matsuoka, L. Y., S. Glasser, and S. Barsky. Melanoacanthoma of the lip. Arch. Dermatol. 115:1116, 1979. Matsuoka, L. Y., S. Barsky, S. Barsky, and S. Glasser. Melanoacanthoma of the lip. Arch. Dermatol. 118:290, 1982. Mevorah, B., and Y. Mishima. Cellular response of seborrheic keratosis following croton oil irritation and surgical trauma with special reference to melanoacanthoma. Dermatologica 131:452–464, 1965.
947
CHAPTER 50 Mishima, Y., and H. Pinkus. Benign mixed tumor of melanocytic and malphigian cells. Melanoacanthoma: Its relationship to Bloch’s benign non-nevoid melanoepithelioma. Arch. Dermatol. 81:539– 550, 1960. Prince, C., A. H. Mehregan, K. Hashimoto, and H. Plotnick. Large melanoacanthomas: A report of 5 cases. J. Cutan. Pathol. 11:309– 317, 1984. Reaves, C. E. Melanoacanthoma: A case report and review of the literature. Bull. Assoc. Mil. Dermatol. 22:55–58, 1972. Schlappner, O. L., G. Rowden, T. M. Philips, and Z. Raham. Melanoacanthoma: Ultrastructural and immunological studies. J. Cutan. Pathol. 5:127–141, 1978. Schneider, L. C., M. L. Mesa, and S. M. Haber. Melanoacanthoma of the oral cavity. Oral Surg. 52:284–287, 1981a. Schneider, L. C., M. L. Mesa, and L. Moore. Melanoacanthoma: A ten-year prospective study. J. Oral Pathol. 10:368, 1981b. Sexton, F. M., and J. C. Maize. Melanotic macules and melanoacanthomas of the lip. Am. J. Dermatopathol. 9:438–444, 1987. Simon, P., L. Requena, and Y. E. Sanchez. How rare is melanoacanthoma? Arch. Dermatol. 127:583–584, 1991. Spott, D. A., M. G. Wood, and C. L. Heaton. Melanoacanthoma of the eyelid. Arch. Dermatol. 115:898–899, 1972. Tagami, H. Pigmented macules of the tongue following fixed drug eruption. Dermatologica 147:157, 1973. Tomich, C. E., and J. L. Dorey. Melanoacanthoma of the oral mucosa. Annual Meeting of the American Academy of Oral Pathologists. 1979. Tomich, C. E., and S. L. Zunt. Melanoacanthosis (melanoacanthoma) of the oral mucosa. J. Dermatol. Surg. Oncol. 16:231–236, 1990. Vion, B., and Y. Merot. Melanoacanthoma of the penis shaft: Report of a case. Dermatologica 179:87–89, 1989. Weathers, D. R., R. L. Corio, B. E. Crawford, J. S. Giansanti, and L. R. Page. The labial melanotic macule. Oral Surg. Oral Med. Oral Pathol. 42:196–205, 1976. Whitt, J. C., D. R. Jennings, D. M. Arendt, and J. R. Vinton. Rapidly expanding pigmented lesion of the buccal mucosa. J. Am. Dent. Assoc. 117:620–622, 1988. Wright, J. M. Intraoral melanoacanthomas: a reactive melanocytic hyperplasia: Case report. J. Periodontol. 59:53–55, 1988. Wright, J. M., W. H. Bonnie, D. L. Byrd, and A. R. Dunsworth. Intraoral melanoacanthoma. J. Periodontol. 54:107–111, 1983. Zemtsov, A., and W. F. Bergfeld. Oral melanoacanthoma with prominent spongiotic intraepithelial vesicles. J. Cutan. Pathol. 16:365– 369, 1989.
biologic systems. In 1942, Klaber coined the term “phytophotodermatitis” to specify the skin’s reaction to sunlight after contact with certain plants (Heskel et al., 1983).
Synonyms Berloque dermatitis, “Club Med dermatitis”, phototoxic dermatitis, strimmer rash (“string trimmers’ dermatitis”), “celery burn,” dermatitis bullosa striata pretensis.
Epidemiology Phytophotodermatitis is an inflammatory cutaneous response to plant phototoxic chemicals, known as furocoumarins or psoralens. This in conjunction with ultraviolet light results in hyperpigmentation. The incidence varies geographically with the type of local flora and the likelihood of human–plant contact. The exact incidence of this problem is unknown. Individuals having physical contact with plants containing furocoumarins with subsequent sun exposure are at risk for developing phytophotodermatitis. Field workers, gardeners, chefs, and grocers are most commonly affected. In certain regions of the world, psoralen-containing plant species are endemic or are even used for esthetic foliage (Camm et al., 1976). Unsuspecting nature lovers have had severe consequences after rubbing phototoxic leaves on their skin as an insect repellent (Gawkrodger and Savin, 1983).
Clinical Findings People must be exposed to both psoralen-containing plants and other sources such as perfumes, and ultraviolet A (UVA) light to develop phytophotodermatitis. Psoralen exposure occurs after contact with crushed surfaces or the sap of the culprit plant. For example, sliced fruit permits exposure to psoralens in the peel (Egan and Sterling, 1993). In a typical patient, the first physical finding may be sharply demarcated, hyperpigmented macules or patches within days of exposure (Figs 50.38 and 50.39). The color of the lesions is usually tan or brown (Tunget et al., 1994). They appear at sites of plant
Phytophotodermatitis Norman Levine and Cynthia Burk
Historical Background For 3000 years, the sap of certain roots and flowers has been known to cause skin blistering (Levine, 1993; Moller, 1978). Some oils from these plants produced skin pigmentation, and were applied topically as therapy for vitiligo (Egan and Sterling, 1993). In 1916, Freund described berloque dermatitis, which occurred as a result of skin exposure to oil of bergamot in cologne (Egan and Sterling, 1993). Oppenheim speculated in 1932 that “itching blisters” occurring in meadow sunbathers were the result of photosensitization caused by either an insect in the field or perhaps the chlorophyll in the grass. He named the phenomenon “dermatitis bullosa striata pretensis.” Blum was one of the first to demonstrate that light of specific wavelengths has direct effects on 948
Fig. 50.38. Typical figurate pattern of hyperpigmentation caused by phytophotodermatitis.
ACQUIRED EPIDERMAL HYPERMELANOSES
contact and sun exposure. Hyperpigmentation may be the only clinical sequela if erythema-provoking doses of UVA light are not absorbed. If present, the acute dermatitis occurs within 24–48 hours of exposure (Egan and Sterling, 1993; Heskel et al., 1983), although in one case a 16-day interval between plant contact and sun exposure was reported (Tunget et al., 1994). Involvement is limited to light-exposed areas of skin, most commonly the face, neck, and dorsal aspects of the extremities. Patients may develop linear or bizarre-shaped, erythematous plaques and vesicles at the sites of plant contact. Vesicles may coalesce into bullae coexistent with the erythematous streaks. A mild sunburn-like erythema may be the only acute change. A burning sensation occasionally accompanies the lesions. Pruritus is not a characteristic symptom. Within 3–10 days, denudation of blisters and desquamation occurs (Egan and Sterling, 1993). The patient often has residual hyperpigmentation which may persist up to six months after exposure. Spontaneous resolution of the dermatitis usually occurs; however, one case severe enough to require five days of inpatient treatment has been reported (Gawkrodger and Savin, 1983; Webb and Brooke, 1995). Phototoxicity is a dose-related phenomenon, and should theoretically occur in 100% of individuals receiving the sufficient doses of psoralen and UVA radiation (Harber and Baer, 1972). Failure to elicit such a reaction happens because of variable psoralen content in plants and individual patient factors influencing absorption of phototoxins. Furocoumarin content in plants can vary seasonally and regionally in the same species (Finkelstein et al., 1994; Rook et al., 1992). As phytophotodermatitis is not an allergic or immune-mediated process, it can occur with the first exposure. Compared to the frequency of substrate exposures, dermatitis due to phytophototoxins is quite unusual.
Criteria for Diagnosis ∑ History of contact with psoralen-containing plant with sub-
sequent UVA light exposure. ∑ Physical examination shows hyperpigmented patches, which
may be preceded by linear erythema and vesicles or bullae on sun-exposed areas of skin.
Differential Diagnosis The differential diagnosis of berloque dermatitis includes other causes of hyperpigmentation, eruptions from contact with plants, and those related to sunlight exposure. Given a specific plant-related history, the diagnoses to be considered include irritant contact dermatitis and allergic contact dermatitis. If sun exposure alone precedes the eruption, the etiology may be a medication-induced phototoxic or photoallergic reaction, polymorphous light eruption, lupus erythematosus, pellagra, or suntan. Without a history of plant, perfume, or light exposure, hyperpigmentation may be due to melasma. Other distinctions to be made are between phytophotodermatitis and other vesiculobullous diseases such as
Fig. 50.39. Brown hyperpigmentation caused by application of topical psoralens and indiscriminate exposure to sunlight (see also Plate 50.14, pp. 494–495).
erythema multiforme, bullous pemphigoid, pemphigus vulgaris, and porphyria cutanea tarda. Trauma from physical abuse must be considered in children with linear inflammatory plaques and vesicles (Barradell et al., 1993; Weber, 1999). These patterned skin lesions may look like burns or hand prints. Therefore, it is important to identify phytophotodermatitis by its uniformly dark color, absence of definite dermatomal pattern, and its distribution within the sunlight exposed areas of the skin. Fungal infections and bacterial cellulitis are other diagnoses to rule out. Paederus dermatitis created by crushing the causative beetle over the skin can also mimic phytophotodermatitis (Uslular et al., 2002; Weber et al., 1999). Irritant contact dermatitis from plants may present acutely as vesiculobullous, erythematous, or urticarial lesions. However, chronic hyperpigmentation is not a prominent feature. Unlike phytophotodermatitis, the eruption does not require UVA light exposure (Barradell et al., 1993). Allergic contact dermatitis from plants, unlike phytophotodermatitis, requires prior sensitization. The source of allergen is most commonly the Rhus family of plants. Minimal contact is sufficient to elicit the allergic reaction, while phytophotodermatitis occurs only when significant doses are absorbed. The clinical pattern may be similar, but allergic contact dermatitis may occasionally have more diffuse patchy erythema. Pruritus is almost always present. Medication-induced phototoxic reactions appear similar to an exaggerated sunburn. During the acute phase they may resemble phytophotodermatitis, but prolonged hyperpigmentation is not a feature of drug-induced phototoxic reactions. Drugs implicated in this reaction include amiodarone, doxycycline, thiazides, furosemide, sulfonamides, and phenothiazines. Photoallergic reactions caused by medications may appear identical to phytophotodermatitis. In contrast to berloque dermatitis, prolonged skin tanning in the affected sites is not a feature of this condition. Berloque dermatitis presenting with hyperpigmentation alone may resemble a suntan because of the similar brown 949
CHAPTER 50
patches on sun-exposed skin. However, the two are clinically different in several ways. A suntan has an immediate pigment darkening effect, followed by a delayed darkening which peaks at about 72 hours. Berloque dermatitis pigmentation may appear between 24 and 48 hours, but persists as long as six months. Whereas suntan darkens all exposed skin diffusely, psoralen and UVA light produces well-circumscribed lesions, often with bizarre shapes. Lentigines are tan to dark brown macules which are suninduced and may resemble the lesions of berloque dermatitis. However, each lentigo is rarely larger than 20 mm; multiple lentigines are not confluent. Once present, they do not fade. Melasma is the brown “mask of pregnancy” frequently seen in women either during pregnancy or while taking oral contraceptives. These well-defined macules or patches can be aggravated by sunlight. In contradiction to phytophotodermatitis, melasma appears commonly on the face and has a more reticulated pattern.
Pathology Light Microscopy The histologic picture in the acute, inflammatory stage is that of contact dermatitis. There is epidermal spongiosis with intraepidermal vesicles and a dermal infiltrate. Very mild lesions may show only single-cell epidermal necrosis. In the later phase, there may be hyperkeratosis, slight epidermal thinning, dermal–epidermal junction vacuolization, and parakeratosis. A perivascular lymphohistiocytic infiltrate is present. Hyperpigmentation can be seen in the epidermis and dermis. Pigmentary incontinence in the form of dermal melanin is found both extracellularly and within melanophages (Egan and Sterling, 1993; Heskel et al., 1983; Webb and Brooke, 1995). Increased epidermal melanin, much like that seen with a suntan, is seen in the chronic cutaneous hyperpigmentation phase of berloque dermatitis.
Pathogenesis The plant families known to cause phytophotodermatitis include the Umbelliferae, the Rutaceae, the Moraceae, and the Leguminosae. These include edible vegetables such as celery, parsnip, parsley, dill, carrots, citrus fruits such as limes and oranges, and other plants such as giant hogweed, berryrue, and wild rhubarb (Egan and Sterling, 1993; Tunget et al., 1994). Tobacco, garlic, fig, mustard, buttercup, corn, fennel, angelica, masterwort, atrillal, hot peppers, daffodil bulbs, and hyacinth may also contain natural psoralens (Adams 1998; Bergeson and Weiss 2000; Bollero et al., 2001; Bosch 1997). Psoralens may be found in certain brands of perfumes and cosmetics as well as Saint John’s Wort (Adams, 1998). In experimental studies, high furocoumarin concentrations cause photohemolysis of red blood cells (Bollero et al., 2001). Rarely, reports of wound sepsis and retinal hemorrhages can complicate the course of the illness (Bollero et al., 2001). Psoralens may be phytoalexins, protective compounds made by the plant in response to stress or infection. Skin contact with the plant causes exposure to psoralens, which when activated by UVA light leads to skin inflam950
mation and increased melanocyte activity, producing increased cutaneous pigmentation. Furocoumarins are a group of molecules related to coumarin. They have a double-ringed structure attached to a furan ring. At least 28 furocoumarins are found naturally in plants, but only three are commonly implicated in phytophotodermatitis. These are 8-methoxypsoralen (xanthotoxin or methoxsalen), 5-methoxypsoralen (bergapten), and 4,5¢,8trimethylpsoralen (TMP) (Harber and Baer, 1972; Yurkow and Laskin, 1991). Furocoumarins are chromophores, molecules which absorb radiation. Absorption of one photon increases the energy of the molecule, exciting one electron into a higher orbit, which creates a transiently reactive species. This process photoactivates the furocoumarin. The absorption spectrum specific for each furocoumarin molecule is within the UVA spectrum (320–400 nm). The action spectrum, which specifies the wavelength necessary to provoke furocoumarin phototoxicity, is close to the absorption spectrum, ranging from 312 nm to 406 nm for different molecules (Musajo and Rodighiero, 1970; Yurkow and Laskin, 1991). Skin injury occurs after the furocoumarins traverse the stratum corneum and enter the keratinocytes. Inside the nuclei of these cells, the furocoumarins react with DNA. In the dark, they intercalate between adjacent base pairs in the double helix with weak chemical bonds (Musajo and Rodighiero, 1970). In this circumstance, no permanent reaction takes place. However, a UVA light-activated furocoumarin can bind specifically and covalently to pyrimidine bases. Two monoadducts are possible via this reaction. Cycloaddition can take place between the 5,6positions on thymine or uracil and either the 4¢,5¢- or the 3,4diene on the psoralen. With the addition of a second photon, 3,4-monoadducts covalently cross-link between strands of DNA, forming a bifunctional adduct. This is structurally analogous to interstrand thymine dimerization, preventing strand separation for DNA replication (Harber and Baer, 1972; Musajo and Rodighiero, 1970). This inhibits DNA synthesis and may cause cell death (Ena et al., 1989). In addition to interacting with nucleic acids, psoralens may also bind to cell proteins and membrane lipids. Two types of reactions are postulated to occur: type I, or anoxic reactions, produce DNA and amino acid interactions; type II, or oxygendependent reactions, produce reactive oxygen species, causing membrane lipid damage and cellular destruction. This inflammatory response is not an immune-mediated process, and immunocompetence is not required to develop phytophotodermatitis. Neither ultraviolet light nor psoralen alone produces these effects. Phytophotodermatitis is a dose-dependent reaction. A sufficient psoralen concentration must be present with adequate exposure to UVA light. The dose relationship between UV and psoralens may be synergistic rather than additive (Yurkow and Laskin, 1991). Psoralen absorption influences whether this reaction takes place; this is facilitated by moisture, a thin stratum corneum, and minimal epidermal melanin (Izumi and Dawson, 2002). UV light must be of a wavelength com-
ACQUIRED EPIDERMAL HYPERMELANOSES
patible with the action spectrum of the psoralens. At suberythemogenic doses, the result is hyperpigmentation without inflammation. The hyperpigmentation of berloque dermatitis is caused by stimulation of melanocytes in the basal epidermis and hair follicle infundibulum, inducing melanogenesis. It also causes melanocyte migration into affected areas (Levine, 1993). The mechanism of this effect is unknown. In more severe cases, postinflammatory dermal melanin deposition may be an element of the increased pigmentation as well (Gould et al., 1995).
Treatment Management of acute phytophotodermatitis is aimed at diminishing symptoms and inflammation. Topical corticosteroids are effective in most cases. Cool compresses as well as nonsteroidal anti-inflammatory medications may help reduce pain and erythema. Systemic corticosteroids are rarely required. Hyperpigmentation does not respond to topical corticosteroid therapy (Egan and Sterling, 1993; Tunget et al., 1994). The discoloration does tend to diminish gradually over several months. Long-term prevention requires knowledge of offending substances and avoidance of contact. Perfumes containing oil of bergamot should be avoided when sun exposure is anticipated. Certain work situations, such as grocery store checkout stands, may predispose employees to exposure to celery or limes. Individuals working in these environments may benefit from wearing protective gloves; stores can also institute more protective packaging (Webb and Brooke, 1995).
Prognosis The prognosis for patients who develop phytophotodermatitis is excellent. Spontaneous resolution usually occurs without scarring in three to five days. The chronic sequela consists of sustained hyperpigmentation. This fades after weeks to months (Barradell et al., 1993; Webb and Brooke, 1995). Rarely, hypertrophic scarring can result from severe involvement (Bollero et al., 2001).
References Adams, S. P. Dermacase: Phytophotodermatitis. Can. Fam. Physician 44:503–509, 1998. Barradell, R., A. Addo, A. J. McDonagh, M. J. Cork, and J. K. Wales. Phytophotodermatitis mimicking child abuse. Eur. J. Pediatr. 152:291–292, 1993. Bergeson, P. S., and J. C. Weiss. Picture of the month. Phytophotodermatitis. Arch. Pediatr. Adolesc. Med. 154:201–202, 2000. Bollero, D., M. Stella, A. Rivolin, P. Cassano, D. Risso, and M. Vanzetti. Fig leaf tanning lotion and sun-related burns: case reports. Burns 27:777–779, 2001. Bosch, J. J. Phytophotodermatitis. J. Pediatr. Health Care 11:84, 97–98, 1997. Camm, E., H. W. Buck, and J. C. Mitchell. Phytophotodermatitis from Heracleum mantegazzianum. Contact Dermatitis 2:68–72, 1976. Egan, C. L., and G. Sterling. Phytophotodermatitis: a visit to Margaritaville. Cutis 51:41–42, 1993. Ena, P., G. Dessi, F. Chiarolini, and P. Fabbri. Phytophotodermatitis from a Cachrys species. Contact Dermatitis 20:144–145, 1989.
Finkelstein, E., U. Afek, E. Gross, N. Aharoni, L. Rosenberg, and S. Halevy. An outbreak of phytophotodermatitis due to celery. Int. J. Dermatol. 33:116–118, 1994. Gawkrodger, D. J., and J. A. Savin. Phytophotodermatitis due to common rue (Ruta graveolens). Contact Dermatitis 9:224, 1983. Gould, J. W., M. G. Mercurio, and C. A. Elmets. Cutaneous photosensitivity diseases induced by exogenous agents. J. Am. Acad. Dermatol. 33:551–573, 1995. Harber, L. C., and R. L. Baer. Pathogenic mechanisms of drug-induced photosensitivity. J. Invest. Dermatol. 58:327–342, 1972. Heskel, N. S., R. B. Amon, F. J. Storrs, and C. R. White Jr. Phytophotodermatitis due to Ruta graveolens. Contact Dermatitis 9:278–280, 1983. Izumi, A. K. and K. L. Dawson. Zabon phytophotodermatitis: first case reports due to Citrus maxima. J. Am. Acad. Dermatol. 46(5 Suppl): S146–147, 2002. Levine, N. Pigmentation and Pigmentary Disorders. Boca Raton, FL: CRC Press, 1993. Moller, H. Phototoxicity of Dictamnus alba. Contact Dermatitis 4:264–269, 1978. Musajo, L., and G. Rodighiero. Studies on the photo-C4-cycloaddition reactions between skin-photosensitizing furocoumarins and nucleic acids. Photochem. Photobiol. 11:27–35, 1970. Rook, A., D. S. Wilkinson, and F. J. G. Ebling. Textbook of Dermatology, 5th ed. London: Blackwell Scientific Publications, 1992. Tunget, C. L., S. G. Turchen, A. S. Manoguerra, R. F. Clark, and D. E. Pudoff. Sunlight and the plant: a toxic combination: severe phytophotodermatitis from Cneoridium dumosum. Cutis 54:400– 402, 1994. Uslular, C., H. Kavukcu, D. Alptekin, M. A. Acar, Y. G. Denli, H. R. Memisioglu, and H. Kasap. An epidemicity of Paederus species in Cukurova region. Cutis 69:277–279, 2002. Webb, J. M., and P. Brooke. Blistering of the hands and forearms. Arch. Dermatol. 131:833–834, 1995. Weber, I. C., C. P. Davis, and D. M. Greeson. Phytophotodermatitis: the other “lime” disease. J. Emerg. Med. 17:235–237, 1999. Yurkow, E. J., and J. D. Laskin. Mechanism of action of psoralens: isobologram analysis reveals that ultraviolet light potentiation of psoralen action is not additive but synergistic. Cancer Chemother. Pharmacol. 27:315–319, 1991.
Polyneuropathy, Organomegaly, Endocrinopathy, M Protein, and Skin Changes: POEMS Syndrome James J. Nordlund
Historical Background The first report of a plasma cell dyscrasia associated with polyneuritis was published in 1968 (Shimpo, 1968).
Synonyms The proper name for this syndrome is “Polyneuropathy, Organomegaly, Endocrinopathy, M protein with Skin changes”. The acronym POEMS syndrome (Bardwick et al., 1980) has become the common name.
Epidemiology The first case of POEMS syndrome was reported in the Japanese literature (Shimpo, 1968). It was thought that this 951
CHAPTER 50
syndrome most commonly affected Japanese males. However review of the literature does not seem to substantiate this suggestion (Bardwick et al., 1980). Males and females seem to be affected about equally with some predilection for males (Fam et al., 1986). The median age of 38 patients with POEMS was 51 years (range 32–83 years) (Miralles et al., 1992).
Clinical Description This syndrome is defined as the association of polyneuropathy, organomegaly, endocrinopathy, the presence of an M protein in the serum, and skin changes. Each of the five features has an array of manifestations. The polyneuropathy affects peripheral nerves of both extremities (Bardwick et al., 1980; Ku et al., 1995; Miralles et al., 1992; Romas et al., 1992). The cranial nerves tend to be spared but edema of the optic nerve and papilledema have been reported (Bardwick et al., 1980; Bolling and Brazis, 1990; Romas et al., 1992). One patient reported in the literature had all features of this syndrome but did not have neuropathy (Morrow et al., 1982). Polyneuropathy is not a common feature of most disorders associated with plasma cell dyscrasias. Typically the neuropathy of plasma cell disorders is caused by deposition of amyloid in the nerve (Miralles et al., 1992). Patients with POEMS syndrome have a focal or segmental demyelinating disorder with axonal degeneration (Romas et al., 1992). Both sensory and motor nerves are involved (Ku et al., 1995) and the patient can be disabled from resultant muscle degeneration (Bardwick et al., 1980). Painful dysesthesias and paresthesias are common. Nerve biopsies confirm the loss of myelinated fibers with some nerves showing wallerian degeneration. A small number of axonal fibers showed grossly thickened myelin sheaths. Amyloid was not observed (Romas et al., 1992). Organomegaly most commonly is manifested by hepatomegaly, splenomegaly, and/or lymphadenopathy. The number of affected individuals who have one or more organs enlarged has been reported to be as low as 25% (Miralles et al., 1992) to as high as 67% (Fam et al., 1986). Liver biopsies on some patients were normal in appearance (Bardwick et al., 1980). Endocrine abnormalities are numerous in type. In one series of 38 patients, hypothyroidism, elevated serum prolactin levels, low serum testosterone, impotence, gynecomastia, and/or elevated gonadotropin levels were noted (Miralles et al., 1992). These abnormalities were also noted in a carefully studied two patients (Bardwick et al., 1980). About 65% of affected individuals have some form of endocrine disorder (Fam et al., 1986). Almost all patients reported had a plasma cell abnormality (Miralles et al., 1992). These included plasmacytomas in the skin (Feddersen et al., 1989), lytic or sclerotic tumors in bone (Bardwick et al., 1980; Chan et al., 1990; Miralles et al., 1992; Puig et al., 1985; Romas et al., 1992; Shelley and Shelley, 1987), or benign gammopathies (Miralles et al., 1992; Morrow et al., 1982; Rongioletti et al., 1994). The most
952
Fig. 50.40. Hyperpigmentation of the leg (see also Plate 50.15, pp. 494–495).
Fig. 50.41. Diffuse hyperpigmentation of the dorsum of hands (see also Plate 50.16, pp. 494–495).
common gammopathy is of the IgA form but IgG, l-light chain, and indeterminate monoclonal peaks have been noted. Skin changes were also of multiple types. The most common is a diffuse brown hyperpigmentation observed in about half
ACQUIRED EPIDERMAL HYPERMELANOSES
Fig. 50.42. Close-up view of the pigmentary changes.
Fig. 50.43. Glomeruloid angiomata characteristic of POEMS. Note the diffuse hyperpigmentation commonly observed in patients with POEMS (see also Plate 50.17, pp. 494–495).
of affected individuals (Bardwick et al., 1980; Feddersen et al., 1989; Ishikawa et al., 1987; Miralles et al., 1992; Morrow et al., 1982; Romas et al., 1992; Shelley and Shelley, 1987). The discoloration affects the entire integument including the palms and genitalia (Figs 50.40 and 50.41). There are many other cutaneous abnormalities. The skin has been noted to be thickened and almost sclerodermoid in quality (Fig. 50.42). Hypertrichosis also is common, especially over skin not typically hirsute (Miralles et al., 1992; Shelley and Shelley, 1987). The skin is a common site for tumors of vascular origin. These include angiomata (Kanitakis et al., 1988; Puig et al., 1985), glomeruloid hemangiomata (Fig. 50.43) (Chan et al., 1990; Del Rio et al., 1994; Hudnall et al., 2003; Ishikawa et al., 1987; Kanitakis et al., 1988; Kingdon et al., 2001; Longo et al., 1999; Rongioletti et al., 1994; Obermoser et al., 2003; Scheers et al., 2002; Tsai et al., 2001), and miscellaneous other vascular neoplasms (Tsang et al., 1991). The glomeruloid angiomata have been attributed to herpesvirus 8 by some investigators (Belec et al., 1999a, b; Papo et al., 1999; Tohda et al., 2001; Hudnall et al., 2003). Others have not found this virus in the angiomata (Obermoser et al., 2003; Zumo and Grewal 2002).
often lower than normal. Levels of luteinizing hormone or prolactin are elevated. The serum in most individuals will have an M protein. No one finding is specific. No feature is found in all individuals although neuropathy and the presence of a plasma cell dyscrasia with an associated M protein are very common clinical features.
Histology
References
The histologic features of the pigmentation are not specific. There seems to be increased melanin in the basilar layer of the epidermis (Feddersen et al., 1989; Tsang et al., 1991). Changes related to deposition of mucin-like proteins and the various vascular neoplasms are found in dermatopathology textbooks.
Laboratory Findings There are many laboratory abnormalities because of the multiplicity of the tissues and organs involved by this syndrome. Nerve conduction studies are typical of a demyelinating disorder. Serum levels of sex steroids such as testosterone are
Pathogenesis Elevated levels of interleukin (IL)-1b (Gherardi et al., 1994; Tartour et al., 1994) and IL-6 have been reported (Fukatsu et al., 1992; Gherardi et al., 1994; Mandler et al., 1992; Tartour et al., 1994). The kidneys also have been found to have increased quantities of IL-6 in some of the cells of the glomerulus (Fukatsu et al., 1992). This has led some to propose that elevated cytokines, particularly IL-6, are major factors in causing this syndrome. More recently vascular endothelial growth factor (VEGF) has been identified in the blood of patients with POEMS syndrome (Hashiguchi et al., 2000; Minamitani et al., 2002; Niimi et al., 2000; Soubrier et al., 1999; Watanabe et al., 1996, 1998). It has been proposed as a factor for the formation of the angiomatous lesions in the skin.
Bardwick, P. A., N. J. Zvaifler, G. N. Gill, D. Newman, G. D. Greenway, and D. L. Resnick. Plasma cell dyscrasia with polyneuropathy, organomegaly, endocrinopathy, M protein, and skin changes: the POEMS syndrome. Report on two cases and a review of the literature. Medicine 59:311–322, 1980. Belec, L., F. J. Authier, A. S. Mohamed, M. Soubrier, and R. K. Gherardi. Antibodies to human herpesvirus 8 in POEMS (polyneuropathy, organomegaly, endocrinopathy, M protein, skin changes) syndrome with multicentric Castleman’s disease. Clin. Infect. Dis. 28:678–679, 1999a. Belec, L., A. S. Mohamed, F. J. Authier, M. C. Hallouin, A. M. Soe, S. Cotigny, P. Gaulard, and R. K. Gherardi. Human herpesvirus 8 infection in patients with POEMS syndrome-associated multicentric Castleman’s disease. Blood 93:3643–3653, 1999b.
953
CHAPTER 50 Bolling, J. P., and P. W. Brazis. Optic disk swelling with peripheral neuropathy, organomegaly, endocrinopathy, monoclonal gammopathy, and skin changes (POEMS syndrome). Am. J. Ophthalmol. 109:503–510, 1990. Chan, J. K., C. D. Fletcher, G. A. Hicklin, and J. Rosai. Glomeruloid hemangioma: a distinctive cutaneous lesion of multicentric Castleman’s disease associated with POEMS syndrome. Am. J. Surg. Pathol. 14:1036–1046, 1990. Del Rio, R., M. Alsina, J. Monteagudo, D. Torremorell, U. Gonzalez, J. Luelmo, and J. M. Mascaro. POEMS syndrome and multiple angioproliferative lesions mimicking generalized histiocytomas. Acta Derm. Venereol. 74:388–390, 1994. Fam, A. G., J. D. Rubenstein, and D. H. Cowan. POEMS syndrome. Study of a patient with proteinuria, microangiopathic glomerulopathy, and renal enlargement. Arthritis Rheum. 29:233–241, 1986. Feddersen, R. M., W. Burgdorf, K. Foucar, L. Elias, and S. M. Smith. Plasma cell dyscrasia: a case of POEMS syndrome with a unique dermatologic presentation. J. Am. Acad. Dermatol. 21:1061–1068, 1989. Fukatsu, A., Y. Ito, Y. Yuzawa, F. Yoshida, M. Kato, K. Miyakawa, and S. Matsuo. A case of POEMS syndrome showing elevated serum interleukin 6 and abnormal expression of interleukin 6 in the kidney. Nephron 62:47–51, 1992. Gherardi, R. K., L. Belec, G. Fromont, M. Divine, D. Malapert, P. Gaulard, and J. D. Degos. Elevated levels of interleukin-1 beta (IL-1 beta) and IL-6 in serum and increased production of IL-1 beta mRNA in lymph nodes of patients with polyneuropathy, organomegaly, endocrinopathy, M protein, and skin changes (POEMS) syndrome. Blood 83:2587–2593, 1994. Hashiguchi, T., K. Arimura, K. Matsumuro, R. Otsuka, O. Watanabe, M. Jonosono, Y. Maruyama, I. Maruyama, and M. Osame. Highly concentrated vascular endothelial growth factor in platelets in CrowFukase syndrome. Muscle Nerve 23:1051–1056, 2000. Hudnall, S. D., T. Chen, K. Brown, T. Angel, M. R. Schwartz, and S. K. Tyring. Human herpesvirus-8-positive microvenular hemangioma in POEMS syndrome. Arch. Pathol. Lab. Med. 127:1034–1036, 2003. Ishikawa, O., Y. Nihei, and H. Ishikawa. The skin changes of POEMS syndrome. Br. J. Dermatol. 117:523–526, 1987. Kanitakis, J., H. Roger, M. Soubrier, J. J. Dubost, B. Chouvet, and P. Souteyrand. Cutaneous angiomas in POEMS syndrome. An ultrastructural and immunohistochemical study. Arch. Dermatol. 124:695–698, 1988. Kingdon, E. J., B. B. Phillips, M. Jarmulowicz, S. H. Powis, and M. P. Vanderpump. Glomeruloid haemangioma and POEMS syndrome. Nephrol. Dial. Transplant. 16:2105–2107, 2001. Ku, A., E. Lachmann, R. Tunkel, and W. Nagler. Severe polyneuropathy: initial manifestation of Castleman’s disease associated with POEMS syndrome. Arch. Phys. Med. Rehabil. 76:692–694, 1995. Longo, G., G. Emilia, and U. Torelli. Skin changes in POEMS syndrome. Haematologica 84:86, 1999. Mandler, R. N., D. P. Kerrigan, J. Smart, W. Kuis, P. Villiger, and M. Lotz. Castleman’s disease in POEMS syndrome with elevated interleukin-6. Cancer 69:2697–2703, 1992. Minamitani, S., S. Ohfuji, S. Nishiguchi, S. Shiomi, M. Ogami, T. Matsuo, M. Ohsawa, K. Ohta, and M. Hino. An autopsy case of POEMS syndrome with a high level of IL-6 and VEGF in the serum and ascitic fluid. Intern. Med. 41:233–236, 2002. Miralles, G. D., J. R. O’Fallon, and N. J. Talley. Plasma-cell dyscrasia with polyneuropathy. The spectrum of POEMS syndrome. N. Engl. J. Med. 327:1919–1923, 1992. Morrow, J. S., E. J. Schaefer, D. P. Huston, and S. W. Rosen. POEMS syndrome: studies in a patient with an IgG-kappa M protein but no polyneuropathy. Arch. Intern. Med. 142:1231–1234, 1982. Niimi, H., K. Arimura, M. Jonosono, T. Hashiguchi, M. Kawabata,
954
M. Osame, and I. Kitajima. VEGF is causative for pulmonary hypertension in a patient with Crow-Fukase (POEMS) syndrome. Intern. Med. 39:1101–1104, 2000. Obermoser, G., C. Larcher, J. A. Sheldon, N. Sepp, and B. Zelger. Absence of human herpesvirus-8 in glomeruloid haemangiomas associated with POEMS syndrome and Castleman’s disease. Br. J. Dermatol. 148:1276–1278, 2003. Papo, T., M. Soubrier, A. G. Marcelin, V. Calvez, B. Wechsler, J. M. Huraux, J. C. Piette, and P. Cacoub. Human herpesvirus 8 infection, Castleman’s disease and POEMS syndrome. Br. J. Haematol. 104:932–933, 1999. Puig, L., A. Moreno, P. Domingo, E. Llistosella, and J. M. de Moragas. Cutaneous angiomas in POEMS syndrome. J. Am. Acad. Dermatol. 12:961–964, 1985. Romas, E., E. Storey, M. Ayers, and E. Byrne. Polyneuropathy, organomegaly, endocrinopathy, M-protein and skin change (POEMS) syndrome with IgG kappa paraproteinemia. Pathology 24:217–220, 1992. Rongioletti, F., C. Gambini, and R. Lerza. Glomeruloid hemangioma: a cutaneous marker of POEMS syndrome. Am. J. Dermatopathol. 16:175–178, 1994. Scheers, C., A. Kolivras, A. Corbisier, P. Gheeraert, C. Renoirte, A. Theunis, N. de Saint-Aubain, J. Andre, U. Sass, and M. Song. POEMS syndrome revealed by multiple glomeruloid angiomas. Dermatology 204:311–314, 2002. Shelley, W. B., and E. D. Shelley. The skin changes in the Crow-Fukase (POEMS) syndrome: a case report. Arch. Dermatol. 123:85–87, 1987. Shimpo, S. Solitary plasmacytoma with polyneuritis and endocrine disturbances. Nippon Rinsho 26:2444–2447, 1968. Soubrier, M., C. Sauron, B. Souweine, C. Larroche, B. Wechsler, L. Guillevin, J. C. Piette, H. Rousset, and P. Deteix. Growth factors and proinflammatory cytokines in the renal involvement of POEMS syndrome. Am. J. Kidney Dis. 34:633–638, 1999. Tartour, E., D. Adams, J. F. Besancenot, W. H. Fridman, and M. Schlumberger. Poems syndrome with high interleukin (IL) 6 and IL1 beta serum levels, in a patient with thyroid carcinoma and melanoma. Eur. J. Cancer 30A:893–894, 1994. Tohda, S., N. Murakami, and N. Nara. Human herpesvirus 8 DNA in HIV-negative Japanese patients with multicentric Castleman’s disease and related diseases. Int. J. Mol. Med. 8:549–551, 2001. Tsai, C. Y., C. H. Lai, H. L. Chan, and Tt. Kuo. Glomeruloid hemangioma — a specific cutaneous marker of POEMS syndrome. Int. J. Dermatol. 40:403–406, 2001. Tsang, W. Y., J. K. Chan, and C. D. Fletcher. Recently characterized vascular tumours of skin and soft tissues. Histopathology 19:489–501, 1991. Watanabe, O., K. Arimura, I. Kitajima, M. Osame, and I. Maruyama. Greatly raised vascular endothelial growth factor (VEGF) in POEMS syndrome. Lancet 347: 702, 1996. Watanabe, O., I. Maruyama, K. Arimura, I. Kitajima, H. Arimura, M. Hanatani, K. Matsuo, T. Arisato, and M. Osame. Overproduction of vascular endothelial growth factor/vascular permeability factor is causative in Crow-Fukase (POEMS) syndrome. Muscle Nerve 21:1390–1397, 1998. Zumo, L., and R. P. Grewal. Castleman’s disease-associated neuropathy: no evidence of human herpesvirus type 8 infection. J. Neurol. Sci. 195:47–50, 2002.
Urticaria Pigmentosum and Mastocytosis James J. Nordlund
Historical Background The first report of urticaria pigmentosum was published by
ACQUIRED EPIDERMAL HYPERMELANOSES
Nettleship who suggested that this syndrome was a form of urticaria or hives (Nettleship and Tay, 1869). It was Sangster who later coined the term urticaria pigmentosum (Sangster, 1878). Unna (1887) first suggested that this disorder was an abnormality of cutaneous mast cells. Sézary suggested the term mastocytosis (Sézary et al., 1936) [excerpted from The Skin in Mastocytosis (Soter, 1991)].
Table 50.3. Classification of mastocytosis by organ involvement (Longley et al., 1995).
Synonyms
Group II: Extracutaneous mastocytosis Hematopoietic Gastrointestinal Hepatic Reticuloendothelial Osseous Other
Mastocytosis, bullous mastocytosis, diffuse cutaneous mastocytosis, mastocytoma, systemic mastocytosis, telangiectasia macularis eruptiva perstans.
Epidemiology
Group 1: Cutaneous mastocytosis Solitary mastocytoma Urticaria pigmentosum Diffuse cutaneous mastocytosis Telangiectasia macularis eruptiva perstans
The prevalence of mast cell disease is not known. It has been estimated that less than 1:1000 patients coming to a dermatology clinic have mast cell disease in some form (Longley et al., 1995). There seems to be no predilection for either gender. Many cases are sporadic but there are other reports suggesting an autosomal dominant inheritance (Longley et al., 1995; Soter, 1991). Recent studies on the pathogenesis of the systemic forms suggest that the disease in at least some individuals is caused by a mutation in the c-kit protooncogene and thus inheritable (Boissan et al., 2000; Buttner et al., 1998; Longley and Metcalfe, 2000; Longley et al., 1993, 1996; Nagata et al., 1995; Valent et al., 1999). Gene expression has been studied and several genes and gene products are consistently overexpressed including a tryptase, b tryptase and carboxypeptidase A (Roberts and Oates, 1991; D’Ambrosio et al., 2003).
Clinical Manifestations Urticaria pigmentosum and/or mastocytosis represent a group of disorders caused by abnormalities in mast cells of the skin or other organs. Mast cell disease can be mild, debilitating or fatal. Mast cell disease that affects infants commonly is selflimiting and spontaneously regresses by adolescence. Mast cell disease beginning during adulthood persists and can produce severe systemic signs and symptoms (for reviews see Azana et al., 1994; DiBacco and DeLeo, 1982; Kettelhut and Metcalfe, 1991; Lazarus et al., 1991; Longley et al., 1995; Metcalfe, 1991a; Monheit et al., 1979; Soter, 1991). Many forms of this disease cause hyperpigmentation of the epidermis. There are several classifications of mast cell disorders based on age of onset, severity of symptoms, and organs involved (Azana et al., 1994; Longley et al., 1995; Metcalfe, 1991a; Soter, 1991). The classification by organ systems of Longley will be used for this discussion (Table 50.3). The mastocytoma occurs typically during infancy and presents as an isolated nodule either at birth or developing shortly after. The lesion is typically 1 to several centimeters in diameter and is typically reddish brown or yellowish brown in color. Gentle stroking of the lesion causes it to become erythematous and often edematous, a phenomenon called Darier sign. Occasionally a blister forms following trauma to the
Fig. 50.44. Urticaria pigmentosa with hyperpigmented macules and papules (see also Plate 50.18, pp. 494–495).
lesion. The lesion is benign and may regress spontaneously although some seem to persist into adolescence. Urticaria pigmentosum of childhood typically presents as brownish macules (Fig. 50.44) or papules occurring during infancy. Typically the lesions first appear before the age of 1 955
CHAPTER 50
year (Azana et al., 1994; Kettelhut and Metcalfe, 1991) although they have been noted to form as late as 11 years. The brown hue can vary from reddish to yellow. These spots like the mastocytoma exhibit a Darier sign. The typical lesion is 3–10 mm in diameter. The number of spots can vary from few to hundreds. The child may have itching and occasional blisters (Azana et al., 1994; Longley et al., 1995; Soter, 1991). The lesions are typically on the trunk and spare the extremities and face. They regress spontaneously (Czarnetzki et al., 1988). Adult onset urticaria pigmentosum differs significantly from the childhood form. The lesions first appear during the third or fourth decade of life although the range of onset is throughout adult life. The lesions are similar to those observed in the infantile form of this disease. These lesions tend to persist and cause symptoms of pruritus in many patients and many adults have evidence of systemic involvement, especially bone marrow (Czarnetzki et al., 1988) and liver (Mican et al., 1995) and other organs (Metcalfe, 1991b). Telangiectasia macularis eruptiva perstans is a variant of adult disease characterized by prominent telangiectases typically on the trunk. The lesions are not pigmented but the skin exhibits marked dermographism, i.e., development of hives following stroking of the skin. Like those with diffuse mastocytosis, the skin color can have a mildly pigmented hue. Both adults and children can have diffuse cutaneous mastocytosis (Fig. 50.45). The infant is born with a thickening of the skin (Fig. 50.46). Gentle trauma such as picking up the child can provoke localized urticaria, blisters (Oranje et al., 1991), and systemic symptoms such as wheezing, diarrhea, and hypotension thought to be related to sudden release of large amounts of histamine, prostaglandin D2, heparin, and other mast cell mediators (Roberts and Oates, 1991). The skin often is diffusely pigmented (Fig. 50.47).
Fig. 50.45. Marked hyperpigmentation in a boy with diffuse mastocytosis (see also Plate 50.19, pp. 494–495).
Histology The typical lesions show a dense infiltrate of polygonal, eosinophilic mast cells in the dermis (Anstey et al., 1991; Haas et al., 1995; Oku et al., 1990; Oranje et al., 1991). The mast cells exhibit metachromasia when stained with the toluidine blue technique. The mast cells also stain with a variety of histochemical and immunohistochemical stains including those for tryptase, chymase, and the ligand for c-kit receptor (Haas et al., 1995; Longley et al., 1993). Electron microscopy confirms the abnormalities found by light microscopy (Anstey et al., 1991). The epidermis shows moderate to large amounts of melanin compared to the surrounding normal skin, easily demonstrated by staining the affected and normal skin with the Fontana-Masson silver stain for melanin (Figs 50.48 and 50.49). The number of melanocytes per unit area appears to be normal when epidermal sheets are stained by the dopa techniques (Fig. 50.50). These data suggest that the hyperpigmentation is caused by stimulation of melanocyte function and not alterations in proliferation of the melanocytes.
956
Fig. 50.46. Generalized or diffuse mastocytosis. Note the skin thickening associated with hyperpigmentation (same patient as in Fig. 50.45) (see also Plate 50.20, pp. 494–495).
Laboratory Findings The most important findings are histologic. However analyses of urinary excretory products for histamine and its metabolites, prostaglandin D2 and its metabolites (Roberts and Oates,
ACQUIRED EPIDERMAL HYPERMELANOSES
Fig. 50.49. Fontana-Masson stain of epidermis overlying a mastocytoma. The epidermis contains increased amounts of melanin.
Fig. 50.47. Hyperpigmentation of the face in a patient with diffuse mastocytosis and silver blond hair and very fair skin (see also Plate 50.21, pp. 494–495). A
Fig. 50.48. Fontana-Masson stain of normal skin. B
1991) can be useful. Liver function studies and biopsies (Metcalfe, 1991b; Mican et al., 1995) have been used to confirm systemic disease. The bone marrow often confirms systemic disease (Czarnetzki et al., 1988). X-rays and scans of
Fig. 50.50. (A, B) Dopa stain of epidermis of normal and affected skin. The affected skin has normal numbers of melanocytes but excessive melanin, an indicator of melanogenesis without proliferation of the pigment cells.
957
CHAPTER 50
the bones can confirm marrow involvement (Andrew and Freemont, 1993; Chen et al., 1994).
Criterion for Diagnosis The histologic finding of increased mast cells in the skin confirms the diagnosis of urticaria pigmentosum.
Differential Diagnosis The generalized macules must be distinguished from ephelides that typically occur on sun-exposed skin in contrast with urticaria pigmentosum on the trunk. Nevi and lentigines do not have a positive Darier sign but histology will distinguish easily between the various disorders. Xanthomata and nevoxanthoendothelioma might be difficult to distinguish from urticaria pigmentosum but the histology is definitive for all these disorders. Solitary mastocytoma might be confused with a bug bite although the latter is transient and the former persistent. The systemic mastocytosis with blistering has been confused with Staphylococcus scalded skin syndrome (Oranje et al., 1991).
Pathogenesis The disease is one of mast cells. The signs and symptoms can be attributed to excessive numbers of mast cells in the skin and other organs (Akiyama et al., 1991; DiBacco and DeLeo, 1982; Lazarus et al., 1991; Longley et al., 1995). The precise abnormality producing abnormalities in the mast cell is not well identified. The c-kit protooncogene located on chromosome 12 (Grabbe et al., 1994) codes for a transmembrane tyrosine kinase receptor (Nagata et al., 1995) found on both melanocytes and mast cells (Dippel et al., 1995; Grabbe et al., 1994). The ligand for this receptor is called stem cell factor or SCF. The factor has many functions for hematopoietic cells (Grabbe et al., 1994). Its precise function for melanocytes is not well defined but is capable of stimulating melanogenesis (Longley et al., 1993). However mutations in the c-kit receptor (Longley et al., 1996; Nagata et al., 1995; Valent et al., 1999) have been identified in patients with systemic mastocytosis. An abundance of stem cell factor and its mRNA have been observed in similar patients. Similar studies on urticaria pigmentosum show different staining patterns for stem cell factor but the results do not definitively establish a role for c-kit receptor or stem cell factor in all forms of mastocytosis (Hamann et al., 1995) although c-kit and SCF are well established as causative in some patients with urticaria pigmentosum (Longley et al., 1996; Buttner et al., 1998; Valent et al., 1999; Boissan et al., 2000; Longley and Metcalfe, 2000).
Animal Models A disorder resembling human mastocytosis has been described in both a goat (Khan et al., 1995) and in a group of dogs (O’Keefe et al., 1987).
Treatment There is no good treatment for the pigmentary abnormality 958
associated with this syndrome. In infants the pigmented spots tend to disappear by the middle of teenage years (Soter, 1991). For those with systemic mastocytosis or the adult forms, treatment is directed at controlling the signs and symptoms related to release of mast cell mediators and include antihistamines, cromolyn, and similar agents (Gasior-Chrzan and Falk, 1992; Horan et al., 1990; Metcalfe, 1991c). Photochemotherapy has been used to degranulate the mast cells and prevent symptoms (Smith et al., 1990).
References Akiyama, M., Y. Watanabe, and T. Nishikawa. Immunohistochemical characterization of human cutaneous mast cells in urticaria pigmentosa (cutaneous mastocytosis). Acta Pathol. Jpn. 41:344–349, 1991. Andrew, S. M., and A. J. Freemont. Skeletal mastocytosis. J. Clin. Pathol. 46:1033–1035, 1993. Anstey, A., D. G. Lowe, J. D. Kirby, and M. A. Horton. Familial mastocytosis: a clinical, immunophenotypic, light and electron microscopic study. Br. J. Dermatol. 125:583–587, 1991. Azana, J. M., A. Torrelo, I. G. Mediero, and A. Zambrano. Urticaria pigmentosa: a review of 67 pediatric cases. Pediatr. Dermatol. 11:102–106, 1994. Boissan, M., F. Feger, J. J. Guillosson, and M. Arock. c-Kit and c-kit mutations in mastocytosis and other hematological diseases. J. Leukoc. Biol. 67:135–148, 2000. Buttner, C., B. M. Henz, P. Welker, et al. Identification of activating c-kit mutations in adult-, but not in childhood-onset indolent mastocytosis: a possible explanation for divergent clinical behavior. J. Invest. Dermatol. 111:1227–1231, 1998. Chen, C. C., M. P. Andrich, J. M. Mican, and D. D. Metcalfe. A retrospective analysis of bone scan abnormalities in mastocytosis: correlation with disease category and prognosis. J. Nucl. Med. 35:1471–1475, 1994. Czarnetzki, B. M., G. Kolde, A. Schoemann, S. Urbanitz, and D. Urbanitz. Bone marrow findings in adult patients with urticaria pigmentosa. J. Am. Acad. Dermatol. 18:45–51, 1988. D’Ambrosio, C., C. Akin, Y. Wu, M. K. Magnusson, and D. D. Metcalfe. Gene expression analysis in mastocytosis reveals a highly consistent profile with candidate molecular markers. J. Allergy Clin. Immunol. 112:1162–1170, 2003. DiBacco, R. S., and V. A. DeLeo. Mastocytosis and the mast cell. J. Am. Acad. Dermatol. 7:709–722, 1982. Dippel, E., N. Haas, J. Grabbe, D. Schadendorf, K. Hamann, and B. M. Czarnetzki. Expression of the c-kit receptor in hypomelanosis: a comparative study between piebaldism, naevus depigmentosus and vitiligo. Br. J. Dermatol. 132:182–189, 1995. Gasior-Chrzan, B., and E. S. Falk. Systemic mastocytosis treated with histamine H1 and H2 receptor antagonists. Dermatology 184:149– 152, 1992. Grabbe, J., P. Welker, E. Dippel, and B. M. Czarnetzki. Stem cell factor, a novel cutaneous growth factor for mast cells and melanocytes. Arch. Dermatol. Res. 287:78–84, 1994. Haas, N., K. Hamann, J. Grabbe, B. Algermissen, and B. M. Czarnetzki. Phenotypic characterization of skin lesions in urticaria pigmentosa and mastocytomas. Arch. Dermatol. Res. 287:242– 248, 1995. Hamann, K., N. Haas, J. Grabbe, and B. M. Czarnetzki. Expression of stem cell factor in cutaneous mastocytosis. Br. J. Dermatol. 133:203–208, 1995. Horan, R. F., A. L. Sheffer, and K. F. Austen. Cromolyn sodium in the management of systemic mastocytosis. J. Allergy Clin. Immunol. 85:852–855, 1990. Kettelhut, B. V., and D. D. Metcalfe. Pediatric mastocytosis. J. Invest. Dermatol. 96:15S-18S, 1991.
ACQUIRED EPIDERMAL HYPERMELANOSES Khan, K. N., J. E. Sagartz, G. Koenig, and K. Tanaka. Systemic mastocytosis in a goat. Vet. Pathol. 32:719–721, 1995. Lazarus, G. S., C. Guzzo, R. M. Lavker, G. F. Murphy, and N. M. Schechter. Urticaria pigmentosum: nature’s experiment in mast cell biology. J. Dermatol. Sci. 2:395–401, 1991. Longley, B. J., and D. D. Metcalfe. A proposed classification of mastocytosis incorporating molecular genetics. Hematol. Oncol. Clin. North Am. 14:697–701, viii, 2000. Longley, B. J., Jr., G. S. Morganroth, L. Tyrrell, T. G. Ding, D. M. Anderson, D. E. Williams, and R. Halaban. Altered metabolism of mast-cell growth factor (c-kit ligand) in cutaneous mastocytosis. N. Engl. J. Med. 328:1302–1307, 1993. Longley, B. J., L. Tyrrell, S. Z. Lu, Y. S. Ma, K. Langley, T. G. Ding, T. Duffy, P. Jacobs, L. H. Tang, and I. Modlin. Somatic c-KIT activating mutation in urticaria pigmentosa and aggressive mastocytosis: establishment of clonality in a human mast cell neoplasm. Nat. Genet. 12:312–314, 1996. Longley, J., T. P. Duffy, and S. Kohn. The mast cell and mast cell disease. J. Am. Acad. Dermatol. 32:545–561, 1995. Metcalfe, D. D. Classification and diagnosis of mastocytosis: current status. J. Invest. Dermatol. 96:2S-4S, 1991a. Metcalfe, D. D. The liver, spleen, and lymph nodes in mastocytosis. J. Invest. Dermatol. 96:45S-46S, 1991b. Metcalfe, D. D. The treatment of mastocytosis: an overview. J. Invest. Dermatol. 96:55S-56S (discussion 56S-59S), 1991c. Mican, J. M., A. M. Di Bisceglie, T. L. Fong, W. D. Travis, D. E. Kleiner, B. Baker, and D. D. Metcalfe. Hepatic involvement in mastocytosis: clinicopathologic correlations in 41 cases. Hepatology 22:1163–1170, 1995. Monheit, G. D., T. Murad, and M. Conrad. Systemic mastocytosis and the mastocytosis syndrome. J. Cutan. Pathol. 6:42–52, 1979. Nagata, H., A. S. Worobec, C. K. Oh, B. A. Chowdhury, S. Tannenbaum, Y. Suzuki, and D. D. Metcalfe. Identification of a point mutation in the catalytic domain of the protooncogene c-kit in peripheral blood mononuclear cells of patients who have mastocytosis with an associated hematologic disorder. Proc. Natl. Acad. Sci. U. S. A. 92:10560–10564, 1995. Nettleship, E., and W. Tay. Rare forms of urticaria. Br. Med. J. 2:323–324, 1869. O’Keefe, D. A., C. G. Couto, C. Burke-Schwartz, and R. M. Jacobs. Systemic mastocytosis in 16 dogs. J. Vet. Intern. Med. 1:75–80, 1987. Oku, T., H. Hashizume, R. Yokote, T. Sano, and M. Yamada. The familial occurrence of bullous mastocytosis (diffuse cutaneous mastocytosis). Arch. Dermatol. 126:1478–1484, 1990. Oranje, A. P., W. Soekanto, A. Sukardi, V. D. Vuzevski, A. van der Willigen, and H. M. Afiani. Diffuse cutaneous mastocytosis mimicking staphylococcal scalded-skin syndrome: report of three cases. Pediatr. Dermatol. 8:147–151, 1991. Roberts, L. J., and J. A. Oates. Biochemical diagnosis of systemic mast cell disorders. J. Invest. Dermatol. 96:19S-24S (discussion 24S– 25S), 1991. Sangster, A. An anomalous mottled rash, accompanied by pruritus, factitious urticaria and pigmentation, urticaria pigmentosa(?). Trans. Clin. Soc. London 11:161–163, 1878. Sezary, A., G. Levy-Coblentz, and P. Chauvillon. Dermographisme et mastocytose. Bull. Soc. Franc. Dermatol. Syphiligr. 43:359–361, 1936. Smith, M. L., P. W. Orton, H. Chu, and W. L. Weston. Photochemotherapy of dominant, diffuse, cutaneous mastocytosis. Pediatr. Dermatol. 7:251–255, 1990. Soter, N. A. The skin in mastocytosis. J. Invest. Dermatol. 96:32S–38S (discussion 38S–39S), 1991. Unna, P. G. Beitrage zur Anatomie und Pathogenese der Urticaria simplex und Pigmentosa. Mschr. Prakt. Dermatol. Suppl. Dermatol. Stud. 3:9, 1887. Valent, P., L. Escribano, R. M. Parwaresch, V. Schemmel, L. B. Schwartz, K. Sotlar, W. R. Sperr, and H. P. Horny. Recent advances
in mastocytosis research. Summary of the Vienna Mastocytosis Meeting 1998. Int. Arch. Allergy Immunol. 120:1–7, 1999.
Poikiloderma of Civatte Vlada Groysman and Norman Levine
Historical Background Civatte originally described this disorder appearing in the sunexposed areas of the lateral neck and upper chest as a type of postinflammatory alteration (Civatte, 1923). Over the past several years, it has been noted that this disease is characterized by interfollicular erythema and pigmentation without inflammation.
Synonyms Menopausal solar dermatitis and atrophic degenerative pigmentary dermatitis and Berkshire neck are other names used for this syndrome.
Epidemiology This entity is more common in middle-aged women and in outdoor workers of either gender, particularly those with fair skin (Graham, 1989).
Clinical Findings Poikiloderma of Civatte presents gradually with retiform hyperpigmentation and telangiectasia with progressive epidermal atrophy over the sun-exposed portions of the lateral neck (Fig. 50.51) and upper chest. The submandibular and submental areas are spared. Milder forms are common and those patients often do not seek medical advice. It is usually asymptomatic but occasionally causes burning, itching, and discomfort. Reddish brown reticulated pigmentation with telangiectasia and interspersed atrophic pale spots are found in fairly symmetric pattern on the lateral cheeks and the sides of the neck but sparing the area shaded by the chin. Occasionally, the
Fig. 50.51. Poikilodermatous patches on the lateral aspect of the neck and face (see also Plate 26.1, pp. 494–495).
959
CHAPTER 50
condition becomes so extensive that there is significant cosmetic disfigurement.
Associated Disorders This may occur in the context of other chronic photodermatosis such as actinic keratoses, nonmelanoma skin cancer and photoaging changes elsewhere in sun-exposed skin.
Pathology The epidermis shows atrophy and irregular hyperpigmentation of the basal cell layer. Occasional liquefaction degeneration in the basal cell layer and mild perivascular lymphocytic infiltration in the upper dermis is noted. Pigment incontinence and dermal melanophages are frequently seen. Moderate basophilic degeneration of collagen and solar elastosis are evident.
hormonal milieu in postmenopausal women and genetic predisposition. Photodynamic substances in fragrances and cosmetics have also been implicated in pathogenesis. Kathon CG is a common component of cosmetic products and is made of mixture of methylchloroisothiazolinone and methylisothiazolinone 3:1. In low concentrations, Kathon CG is a cosmetic allergen that plays a role in initiation or continuation of poikiloderma of Civatte (Kumar, 2001; Lee and Lam, 1999). A delayed contact hypersensitivity reaction initiated by allergens may cause basal layer deterioration and melanin incontinence, resulting in reticular hyperpigmentation (Katoulis, 2001). Genetically determined predisposition is also postulated in the pathogenesis of poikiloderma of Civatte as shown by increased susceptibility to UV radiation in certain families. It presents as an autosomal dominant trait with variable penetrance (Katoulis et al., 1999).
Laboratory Findings None.
Criteria for Diagnosis Physical examination and exclusion of other photosensitivity diseases are usually sufficient to make the diagnosis.
Differential Diagnosis The differential diagnosis of poikiloderma of Civatte includes other skin conditions which produce lesions in sun-exposed skin and those which cause poikilodermatous change. Lupus erythematosus may have atrophic lesions in sun-exposed skin. However, the lesions are not as extensive and do not limit themselves to the neck area. Dermatomyositis may have similar lesions to those of lupus erythematosus. Atrophy and telangiectasias may occur on the neck and chest wall. However, there are usually facial lesions, periorbital edema, and a violaceous discoloration of the upper eyelids. Riehl melanosis may occur on the lateral neck and have dyspigmentation. There is no atrophy or telangiectasia in the lesions, however. Berloque dermatitis commonly occurs on the neck, especially after application of certain fragrances. However, the lesions are hyperpigmented without atrophy or telangiectasias. Poikiloderma atrophicans vasculare occurs in the context of peripheral T-cell lymphoma or as an isolated finding and has all of the physical elements of poikiloderma of Civatte, namely, hyperpigmentation, telangiectasia, and atrophy. However, the lesions do not limit themselves to sunexposed areas and are generally much smaller in size. Two pediatric syndromes, Bloom syndrome and Rothmund–Thomson syndrome, produce lesions with poikiloderma. Both present with lesions in early life and have many other cutaneous and systemic findings that allow easy differentiation from poikiloderma of Civatte.
Pathogenesis Chronic exposure to sunlight is an important pathogenic factor (Goldberg and Altman, 1984), as evidenced by distribution on face and neck, in combination with changes in
960
Animal Models None.
Treatment Meticulous sunscreen protection and avoidance of sun exposure is recommended. Topical corticosteroids are not effective in treatment of poikiloderma of Civatte, and should be avoided to prevent the aggravation of cutaneus atrophy. There is also evidence of clinical improvement in patients after complete avoidance of perfumes and cosmetics (Katoulis et al., 2002). Studies indicate that pulsed tunable dye laser (PDL) at 585 nm produces reduction in telangiectasia-induced erythema (Clark and Jiminez-Acosta, 1994; Geronemus, 1990; Haywood and Monk, 1998; Wheeland and Applebaum, 1990). Complications with use of PDL include posttreatment purpura, hypopigmentation, and in some cases scarring. Treatment with potassium titanyl phosphate laser (KTP) at 532 nm offers reduction in both telangiectatic and pigmented lesions (Batta et al., 1999). Treatment of poikilodenma of Civatte with intense pulsed light source, which delivers multiple wavelengths with software managed pulse durations, allows some reduction in both vascular and pigmented lesions with minimal side effects (Goldman, 2001). Argon lasers have also been used in management; however, there is significant risk of scarring (Oldbricht, 1987).
Prognosis Poikiloderma of Civatte progresses with increasing exposures to sunlight. The lesions persist permanently and no spontaneous regression has been reported. In severe cases, there is cosmetic disfigurement.
References Batta, K., C. Hindson, J. A. Cotterill, and I. S. Foulds. Treatment of poikiloderma of Civatte with the potassium titanyl phosphate laser. Br. J. Dermatol. 146:1191–1192, 1999. Clark, R. E., and F. Jiminez-Acosta. Poikiloderma of Civatte. Resolu-
ACQUIRED EPIDERMAL HYPERMELANOSES tion after treatment with pulsed dye laser. N. Carolina Med. J. 55:234–235, 1994. Civatte, A. Poikilodermie reticulee pigmentaire du visage et du col. Ann. Dermatol. Syphiligr. (Paris) 6:605–620, 1923. Geronemus, R. Poikiloderma of Civatte. Arch. Dermatol. 126:547– 548, 1990. Goldberg, L. H., and A. Altman. Benign skin changes associated with chronic sunlight exposure. Cutis 34:33–38, 1984. Goldman, M. P., and R. A. Weiss. Treatment of poikiloderma of Civatte on the neck with an intense pulsed light source. Plast. Reconstr. Surg. 107:1376–1381, 2001. Graham, R. What is poikiloderma of Civatte? Practitioner 233:1210, 1989. Haywood, R. M., and B. E. Monk. Treatment of Poikiloderma of Civatte with the pulsed dye laser: a series of seven cases. J. Cutan. Laser Ther. 1:45–48, 1999. Katoulis, A. C., N. G. Stavrianeas, A. Katsarou, C. Antoniou, S. Georgala, D. Rigopoulos, E. Koumantaki, G. Avgerinou, and A. D. Katsambas. Evaluation of the role of contact sensitization and photosensitivity in the pathogenesis of poikiloderma of Civatte. Br. J. Dermatol. 147:493–497, 2002. Katoulis, A. C., N. G. Stavrianeas, A. Katsarou, C. Antoniou and J. D. Stratigos. Familial cases of poikiloderma of Civatte: genetic implications in its pathogenesis? Clin. Exp. Dermatol. 24:385–387, 1999. Lee, T. Y., and T. H. Lam. Allergic contact dermatitis due to Kathon CG in Hong Kong. Contact Dermatitis 41:41–42, 1999. Raulin, C., B. Greve, and H. Grema. Laser. Surg. Med. 32:78–87, 2003. Sahoo, B., and B. Kumar. Role of methylchloroisothiazolinone/ methylisothiazolinone (Kathon CG) in poikiloderma of Civatte. Contact Dermatitis 44:249, 2001. Wheeland, R. G., and J. Applebaum. Flashlamp-pumped pulsed dye laser therapy for poikiloderma of Civatte. J. Dermatol. Surg. Oncol. 16:12–16, 1990. Fig. 50.52. Pigmented contact dermatitis (Riehl’s melanosis).
Riehl’s Melanosis Scott Bangert and Norman Levine
Historical Background
Clinical Findings
In Vienna during the First World War, Riehl (1917) first described several patients with a gray-brown reticular facial pigmentation, which he attributed to contact with “noxious substances” of wartime living conditions. Hoffman and Habermann (1918) reported similar cases they dubbed “melanodermatitis toxica,” which they believed to be due to an unknown photosensitizing agent in mineral oil. During World War II and afterward, cases of Riehl melanosis were reported in France (Granier, 1943), Austria (Meischer, 1949), and Argentina (Peirini, 1952). Tar exposure producing a low-grade contact dermatitis was believed to be the causative agent. Some 20 years later, a number of cases were reported in Japan. Nakayama (1976) linked this outbreak to cosmetic ingredients and proposed the term “pigmented contact dermatitis.”
Riehl’s melanosis typically affects middle-aged women. Dark skin and ability to tan also appear to be risk factors. Patients typically present with a rapid onset of diffuse, reticular patches of brown-gray hyperpigmentation. The face and neck are primarily involved (Fig. 50.52), especially the forehead, temple, and zygomatic area, although the ears, nape of the neck, and scalp can be involved as well. In addition, use of optical whiteners can produce hyperpigmentation of the hands, forearms, and trunk, although typically this is not as pronounced (Osmundsen, 1970; Pinol-Agiade et al., 1971). Occasionally, patients may demonstrate mild erythema, scaling, or pruritus, although such symptoms are usually absent, and hyperpigmentation occurs without preceding symptoms (Nakagawa et al., 1984). The time course of the condition is variable and may become progressively worse if the causative agent is not removed.
Synonyms
Histopathology
Riehl’s melanosis is also known as pigmented contact dermatitis or female facial melanosis.
The dominant histologic feature of Riehl’s melanosis is liquefaction degeneration of the basal layer of the epidermis
961
CHAPTER 50
resulting in pigment incontinence into the dermis. The papillary dermis contains an infiltrate of lymphocytes and macrophages containing large amounts of melanin, and the basal lamina is prominently thickened. Epidermal melanin may be increased or decreased. While the epidermal change and lymphohistiocytic infiltrate are not as marked, the vacuolar changes and dermal melanosis of Riehl’s melanosis are comparable to other lichenoid dermatoses, including lichen planus and lupus erythematosus (Nakagawa et al., 1984). Such findings suggest that Riehl’s melanosis fits on a continuum of lichenoid dermatoses (Masahiro et al., 2003). It differs from typical contact dermatitis by showing liquefaction rather than spongiosis and by having a less pronounced dermal infiltrate.
Differential Diagnosis Hyperpigmentation produced by other causes can resemble Riehl’s melanosis, including melasma, acquired bilateral nevus of Ota-like macules, pigmented actinic lichen planus, photosensitivity reactions, and berloque dermatitis. Melasama can closely mimic Riehl’s melanosis, and coexistence of the two entities is possible, as cosmetic agents used to cover up the melasma can exacerbate the Riehl condition. In distinguishing between these two entities, it should be noted that melasma typically affects the central face, including the chin, nose, upper lip, and forehead, while Riehl’s melanosis is more prominent in the lateral areas of the face. Pigmented actinic lichen planus is more violaceous in color, and typically presents with overlying scale and elevated borders. Acquired bilateral nevus of Ota-like macules typically usually involve the forehead, eyelids, cheeks, and nose, and may be differentiated from Riehl’s melanosis based on histology. A history of photosensitizer use can help distinguish photosensitivity reactions and berloque dermatitis from Riehl melanosis. Poikiloderma of Civatte, erythrose péribuccale pigmentaire of Brocq, and erythromelanosis follicularis are three facial hyperpigmentation disorders that at one time were considered variants of Riehl’s melanosis, but are now regarded as distinct entities (Katoulis et al., 2002). All three entities present with more erythema than Riehl melanosis. Poikiloderma of Civatte presents with telangiectasias and atrophy, while erythromelanosis has a papular component not present in Riehl’s melanosis. Erythrose péribuccale pigmentaire of Brocq can further be differentiated based on its perioral location.
Pathogenesis While the pathogenesis of Riehl’s melanosis is not entirely clear, it is believed to be primarily due to contact sensitivity to chemical agents found in perfumes and cosmetics. Darkskinned individuals are more commonly affected, possibly because signs of inflammation upon contactant exposure are less visible clinically in these patients (Cotterill et al., 1987). Another explanation for the lack of clinical inflammation of Riehl’s melanosis suggests that the offending agents have an affinity for melanin or react in the presence of melanin, producing a localization of inflammatory cells to melanocytes 962
(Hayakawa et al., 1987). It is not clear how such agents would damage only the basilar epidermal layer without producing other signs of cutaneous injury. Studies to isolate the most common offending agents have suggested several chemicals found in cosmetics including Brilliant Lake Red, I. Sudan, hydroxycitronellal, benzyl salicylate, jasmine, canaga oil, lemon oil, and geraniol (Nakagawa et al., 1984; Rorsman, 1982). It has also been postulated that UV radiation is a pathogenic factor, since combinations of chemicals and UV light produce histologic findings similar to Riehl’s melanosis, and the lesions are typically often distributed in sun-exposed skin. Optic whiteners containing pyrazolone derivatives are believed to be responsible for producing the truncal distribution sometimes seen in this condition (Rorsman, 1982), although this has become less of a problem following its removal from most consumer products (Serrano et al., 1989). Though chemical agents have been seen as causative since Riehl first described it, new cases have been described not linked to chemical exposure. Histologically, Riehl melanosis shows lichenoid changes similar to lichen planus and lupus erythematosus, and it is possible that all three are pathogenically linked. Masahiro et al. (2003) reported a patient with lichen planus and Riehl’s melanosis in separate locations. This patient was patch test negative and no causative agent could be identified, and the authors suggested a common, possibly extrinsic factor, in both conditions. Similarly, Miyoshi and Kodama (1997) reported a patient with concurrent Sjögren syndrome and Riehl’s melanosis. Again, no cause was found for the Riehl’s melanosis, and the patient’s condition improved despite continuing the same cosmetics. The authors suggested the possibility that Riehl’s melanosis could be a cutaneous manifestation of Sjögren syndrome. Both cases suggest that Riehl’s melanosis fits on a continuum of lichenoid immune reactions and may be caused by intrinsic as well as extrinsic factors.
Treatment Removal of the offending agent is necessary to reverse the hyperpigmentation of Riehl’s melanosis. This often necessitates a screen of the ingredients of all cosmetics and perfumes used by the patient, and even then a cause may not be found (Nakagawa et al., 1984). Gradual resolution occurs over the course of one to two years, although use of hydroquinone and tretinoin or glycolic acid may speed the process (Perez-Bernal, 2000). Although lasers have been used effectively in the treatment of melasma, to date, no published reports have studied their use in Riehl’s melanosis. While facial lesions could be expected to respond well, use for the neck lesions would likely produce less satisfactory results.
References Cotterill, J. A., K. S. Ryatt, and R. Greenwood. Prurigo pigmentosa. Br. J. Dermatol. 105:707–710, 1981. Garnier, G. Les pigmentations cervico-faciales de guerre (melanose de Riehl Poikilodermie). Presse Med. August 14:435, 1943. Hayakawa, R., K. Matsunaga, and Y. Arima. Airborne pigmented contact dermatitis due to musk ambrette in incense. Contact Dermatitis 16:96–98, 1987.
ACQUIRED EPIDERMAL HYPERMELANOSES Katoulis, A. C., N. G. Stavrianeas, A. Katsarou, C. Antoniou, S. Georgala, D. Rigopoulos, E. Koumantaki, G. Avgerinou, and A. D. Katsambas. Evaluation of the role of contact sensitization and photosensitivity in the pathogenesis of poikiloderma of Civatte. Br. J. Dermatol. 147:493–497, 2002. Lautenschlager, S., and P. H. Itin. Reticulate, patchy and mottled pigmentation of the neck. Dermatology 197:291–296, 1998. Lee, C. S., and H. W. Lim. Cutaneous diseases in Asians. Dermatol. Clin. 21:669–678, 2003. Meischer, G. Ausspra Uber Melanosis Riehl. Arch. Dermatol. Syphil. 189:301, 1949. Miyoshi, K., and H. Kodama. Riehl’s melanosis-like eruption associated with Sjögren’s syndrome. J. Dermatol. 24:784–786, 1997. Mosher, D. B., T. B. Fitzpatrick, J. P. Ortonne, and Y. Hori. Hypomelanoses and hypermelanoses. In: Dermatology in General Medicine. 5th ed., I. M. Freedberg, A. Z. Eisen, K. Wolff, K. F. Austen, L. A. Goldsmith, S. I. Katz, and T. B. Fitzpatrick (eds). New York: McGraw-Hill, 1999, pp. 1008–1009. Nakagawa, H., S. Matsuo, R. Hayakawa, K. Takahashi, T. Shigematsu, and S. Ota. Pigmented cosmetic dermatitis. Int. J. Dermatol. 23:299, 1984. Osmundsen, P. E. Pigmented contact dermatitis. Br. J. Dermatol. 83:296–298, 1970. Peirini, L. E. Melanosis de Riehl. Arch. Argent. Dermatol. 2:315, 1952. Perez-Bernal, A., M. A. Munoz-Perez, and F. Camacho. Management of facial hyperpigmentation. Am. J. Clin. Dermatol. 1:261–268, 2000. Pinol-Agiade, J., F. Grimalt, and C. Ramaguera. Dermatitis porblanqueadores opticos. Med. Critanea 5:249, 1971. Riehl, G. Veber ein egenaartige melanose. Wien. Klin. Wochenschr. 30:780–781, 1917. Rorsman, H. Riehl’s melanosis. Int. J. Dermatol. 2:75–78, 1982. Seike, M., Y. Hirose, M. Ikeda, and H. Kodama. Coexistence of Riehl’s melanosis and lichen planus. J. Dermatol. 30:132–134, 2003. Serrano, G., C. Pujol, J. Cuadia, S. Gallo, and A. Aliaga. Riehl’s melanosis: pigmented contact dermatitis caused by fragrances. J. Am. Acad. Dermatol. 21:1057–1060, 1989.
Atrophoderma of Pasini et Pierini James J. Nordlund, Norman Levine, Charles S. Fulk, and Randi Rubenzik
Historical Background The first patients with atrophoderma were reported by Pasini in 1923 and Pierini in 1936 (Pierini, 1936; Pierini and Vivoli, 1936). The name atrophoderma of Pasini and Pierini was used by Canizares et al. (1958) when they reviewed a number of additional cases. Since that time, many cases with similar clinical characteristics have been reported.
Synonyms Atrophoderma of Pasini and Pierini is also known as morphea plana atrophica, progressive idiopathic atrophoderma, atrophic scleroderma d’emblée, dyschromic and atrophic scleroderma, atrophoscleroderma superficialis circumscripta (Musgnug, 1995).
Clinical Characteristics This syndrome is characterized by atrophy of the dermis man-
Fig. 50.53. Pigmented atrophoderma of Pasini and Pierini (see also Plate 50.22, pp. 494–495).
ifested by a slight depression of the skin with a very abrupt edge, termed a cliff sign. The atrophic area has normal epidermis which is hyperpigmented in many but not all individuals (Buechner and Rufli, 1994; Iriondo et al., 1987; Poche, 1980). The lesions typically develop during the teenage years or early adulthood. The largest group of patients studied, 34 patients, consisted of 21 females and 13 males (Buechner and Rufli, 1994). The age of onset of the lesions for this group ranged from 7 years to 66 years. The average age was 26 years (males) or 33 years (females). Women are more commonly affected than are men (Buechner and Rufli, 1994). It has never been reported in Asians and only one case of this condition in black people has been described (Murphy et al., 1990). The skin in this syndrome can have a normal color (Iriondo et al., 1987). Typically the lesions are hyperpigmented, often brown in color (Fig. 50.53), suggestive of epidermal hyperpigmentation (Berman et al., 1988; Buechner and Rufli, 1994; Wakelin and James, 1995). The individual lesions are often palm sized, but they may range from a few centimeters in diameter to one where almost the entire back is covered. They are round or oval and are arranged with the long axis parallel to the planes of cleavage. The plaques may be gray, violaceous, or brown (Figs 50.54 and 50.55). In some patients the color has been noted to be bluish to violaceous, which suggests dermal melanosis (Berman et al., 1988; Heymann, 1994; Poche, 1980; Pullara et al., 1984). Deeper blood vesels are faintly visible as if seen through tinted glass (Miller, 1965). Most patients eventually develop multiple lesions, but many may have one or two lesions initially. Usually the lesions affect the trunk and are bilateral, but zosteriform and unilateral distributions have been described (Bourgiois-Spinasse and Grupper, 1969; Buechner and Rufli, 1994; Iriondo et al., 1987; Murphy et al., 1990; Wakelin and James, 1995). Individual lesions may coalesce into oddly shaped plaques. The most common site affected is the back (Buechner and Rufli, 1994). Other areas where lesions are observed are the chest, arms, and abdomen. The face is never involved (Poche, 1980). 963
CHAPTER 50
Associated Disorders Atrophoderma of Pasini and Pierini is often observed in individuals who are otherwise healthy in other respects. However, it also has been observed in association with morphea (Murphy et al., 1990; Pullara et al., 1984; Wakelin and James, 1995) or lichen sclerosis et atrophicus (Heymann, 1994; Wakelin and James, 1995). These associations have been the basis for some authors suggesting that this syndrome is a variant of morphea [for reviews see Poche (1980) and Pullara et al. (1984)].
Histology Fig. 50.54. Typical lesion of the right scapular area (see also Plate 50.23, pp. 494–495).
The histology is not diagnostic and the findings not specific. The epidermis is usually normal but increased amounts of basilar melanin may be noted. The dermis has a mononuclear cell infiltrate. Melanophages may be present. The collagen is decreased in quantity. Elastic fibers seem to be increased but might be due to condensation of the fibers from the loss of collagen (Buechner and Rufli, 1994; Lever and SchaumbergLever, 1991).
Differential Diagnosis The main differential diagnosis is morphea.
Treatment and Prognosis There is no treatment for atrophoderma of Pasini and Pierini. The lesions usually persist for the life of the individual. Some have been noted to resolve spontaneously.
References
Fig. 50.55. Extensive involvement of the arm and shoulder.
On palpation, the plaques feel like normal skin, without any suggestion of sclerosis or a leathery feel (Poche, 1980). Occasionally, there may be some sclerosis in very old lesions. The sclerosis has suggested to some that atrophoderma is a mild variant of morphea (see Morphea and Scleroderma below). 964
Berman, A., G. D. Berman, and R. K. Winkelmann. Atrophoderma (Pasini-Pierini). Findings on direct immunofluorescent, monoclonal antibody, and ultrastructural studies. Int. J. Dermatol. 27:487–490, 1988. Bourgiois-Spinasse, J., and H. Grupper. Atrophodermie de PasiniPierini en band unilaterale. Bull. Soc. Franc. Dermatol. Syphiligr. 76:494–498, 1969. Buechner, S. A., and T. Rufli. Atrophoderma of Pasini and Pierini. Clinical and histopathologic findings and antibodies to Borrelia burgdorferi in thirty-four patients. J. Am. Acad. Dermatol. 30:441–446, 1994. Canizares, O., P. M. Sachs, L. Jaimovich, and V. M. Torres. Idiopathic atrophoderma of Pasini and Pierini. Arch. Dermatol. 77:42–60, 1958. Heymann, W. R. Coexistent lichen sclerosus et atrophicus and atrophoderma of Pasini and Pierini. Int. J. Dermatol. 33:133–134, 1994. Iriondo, M., R. F. Bloom, and K. H. Neldner. Unilateral atrophoderma of Pasini and Pierini. Cutis 39:69–70, 1987. Lever, W. F., and G. Schaumberg-Lever. Histopathology of the Skin. Philadelphia: J. B. Lippincott, 1991. Miller, R. F. Idiopathic atrophoderma. Arch. Dermatol. 92:653–660, 1965. Murphy, P. K., S. R. Hymes, and N. A. Fenske. Concomitant unilateral idiopathic atrophoderma of Pasini and Pierini (IAPP) and morphea. Observations supporting IAPP as a variant of morphea. Int. J. Dermatol. 29:281–283, 1990. Musgnug, R. H. Atrophoderma of Pasini and Pierini. In: Clinical Dermatology, D. J. Demis (ed.). Philadelphia: Lippincott-Raven Publishers, 1995, pp. 21–25.
ACQUIRED EPIDERMAL HYPERMELANOSES Pasini, A. Atrophodermia idiopatica progressiva. G. Ital. Dermatol. Sifilol. 58:785–809, 1923. Pierini, L. E. Atrophoderma idiopathica progressive. Rev. Argent. Dermatsif. 19:322, 1936. Pierini, L. E., and D. Vivoli. Atrofodermia idiopahica progressiva (Pasini). G. Ital. Dermatol. 77:403–409, 1936. Poche, G. W. Progressive idiopathic atrophoderma of Pasini and Pierini. Cutis 25:503–506, 1980. Pullara, T. J., C. W. Lober, and N. A. Fenske. Idiopathic atrophoderma of Pasini and Pierini [review]. Int. J. Dermatol. 23:643–645, 1984. Wakelin, S. H., and M. P. James. Zosteriform atrophoderma of Pasini and Pierini. Clin. Exp. Dermatol. 20:244–246, 1995.
Hyperpigmentation Associated with Scleromyxedema and Gammopathy Kazunori Urabe, Juichiro Nakayama, and Yoshiaki Hori Scleromyxedema was recognized as a distinct entity by Buschke in 1902. It is characterized by woody, nonpitting induration of the skin. The induration is caused by deposition of mucin in the dermis. Scleromyxedema is often associated with a monoclonal gammopathy. The gammopathy is usually an IgG although IgA and IgM have also been reported. The light chains can be either of the kappa or lambda type (Fleishmajer, 1993). Two cases in which abnormal skin pigmentation was noted have been reported. One had localized hyperpigmentation, the other generalized hyperpigmentation. In both cases the mechanism for the excessive production of pigmentation was not identified. The first case described by Kovary (1981) was a 65-yearold woman with high levels of serum IgG. Her skin abnormality began as induration and stiffness of the neck. Within the first year the infiltration had spread to the face, shoulders, upper part of the arms, and thorax. On physical examination of these lesions, nonpitting induration was observed. Localized hyperpigmentation was present on the face and the “V” of the neck. Microscopic examination of the skin biopsy showed a normal epidermis but an acellular fibrosis of the dermis reaching to the subcutaneous fat. Direct immunofluorescent staining did not disclose deposition of immunoglobulins within the affected skin. The second patient (McFadden et al., 1987) was a 56year-old man with hyperlipoproteinemia and cardiovascular disease. He had IgG lambda paraproteinemia without evidence of multiple myeloma. His skin was markedly indurated over the neck and the upper aspect of the trunk, arms, thighs, and lower aspect of the trunk. The legs and feet appeared less involved. He had generalized, light brown pigmentation of the skin that was more pronounced in the indurated skin and less pronounced over the hands, feet, and pubic and genital areas. Leukonychia involving all fingernails was noted. Light microscopic examination of the lesional skin biopsy specimen showed normal epidermis and an increased amount of pigmentation in the basal cell layer. The dermis was notably thickened and fibrotic with separation and swelling of the collagen tissue. Direct immunofluorescent staining failed to show any immunoglobulin or complement deposition in the lesional
skin. Ultrastructural examination showed normal-appearing melanocytes with increased transfer of melanosomes to basal keratinocytes. The melanocytes had morphologic features suggestive of active melanogenesis. Melanosomes in all four stages of melanization were present. In the dermis, melanophages with melanosome complexes were noted. Lipid droplets were seen in the cytoplasm of every third basal keratinocyte or melanocyte.
References Fleishmajer, R. Scleredema and papular mucinosis. In: Dermatology in General Medicine, 4th ed., T. B. Fitzpatrick, A. Z. Eisen, K. Wolff, I. M. Freedberg, and K. F. Austen (eds). New York: McGraw Hill, 1993, pp. 2186–2187. Kovary, P. M., F. Vakilzadeh, E. Macher, H. Zaun, H. Merk, and G. Goerz. Monoclonal gammopathy in scleredema. Arch. Dermatol. 117:536–539, 1981. McFadden, N., K. Ree, E. Soyland, and T. E. Larceny. Scleredema adultorum associated with a monoclonal gammopathy and generalized hyperpigmentation. Arch. Dermatol. 123:629–632, 1987.
Ichthyosis Nigricans, Keratoses, and Epidermal Hyperplasia James J. Nordlund
Introduction The color of the skin is determined by the quantity of melanin in the epidermis. The thickness of the epidermis can alter the quantity of melanin in the epidermis. If the epidermis is acanthotic, the skin will appear darker (see Chapters 27 and 28 on normal and abnormal skin color). This discoloration is observed in a variety of conditions not of pigment cell origin. They include the ichthyoses, hyperkeratoses, and epidermal hyperplasia. In addition the stratum corneum is often abnormal. Light striking the aberrant stratum corneum is not reflected normally. This physical phenomenon also alters the color of such skin and gives it a gray or blue-gray hue.
Clinical Features There are many forms of ichthyoses (Fig. 50.56), all characterized by an excessively thick stratum corneum. This skin has an abnormally dark appearance. The discoloration is present from birth (Figs 50.57–50.59). The epidermis can become thicker at later times in life. The typical adult develops seborrheic keratoses (Figs 50.60 and 50.61). These are discrete papules and plaques that are usually located on the trunk. The lesions vary in size from 1 mm to several centimeters. The lesions have discrete edges and are raised with a velvety, verrucous, or scaly surface. Many are irregularly pigmented (see Figs 50.60 and 50.61). One very pigmented type of seborrheic keratosis is the melanoacanthoma (Lever and Schaumberg-Lever, 1991; Pinkus and Mehregan, 1981) (see section on melanoacanthoma earlier in this chapter). Skin chronically rubbed or scratched thickens. This condi965
CHAPTER 50
Fig. 50.58. Typical clinical appearance of ichthyosis nigricans.
Fig. 50.56. Prominent and extensive hyperpigmentation in a patient with ichthyosis hystrix (see also Plate 50.24, pp. 494–495).
Fig. 50.57. Hyperpigmentation due to epidermal thickening of ichthyosis in a newborn child (see also Plate 50.25, pp. 494–495).
tion is called lichen simplex chronicus. Typically the patient complains of incessant itch. The skin has thickened skin lines. It is hyperpigmented, usually brown in color indicative of epidermal hypermelanosis. However on occasion there is dermal melanosis and the discoloration has a gray hue. 966
Fig. 50.59. Thickened stratum corneum manifested as hyperpigmented scales.
Fig. 50.60. Seborrheic keratosis markedly hyperpigmented.
Histology The histopathology of all ichthyoses is characterized by hyperkeratosis or a thickened stratum corneum (Lever and Schaumberg-Lever, 1991; Pinkus and Mehregan, 1981). Seborrheic keratoses exhibit a great variety in clinical and histo-
ACQUIRED EPIDERMAL HYPERMELANOSES
Fig. 50.61. Heterogeneous pigmentation in a seborrheic keratosis.
logic appearances. All exhibit hyperkeratoses, acanthosis, and papillomatosis (Lever and Schaumberg-Lever, 1991; Pinkus and Mehregan, 1981). Melanocytes can be found in aberrant places. Typically they are located at the dermoepidermal junction. In the seborrheic keratosis, dendritic melanocytes can be seen in the mid-epidermis where they likely contribute to the deeply pigmented appearance. Lichen simplex chronicus exhibits similar histologic features, hyperkeratosis and acanthosis along with other features of dermatitis. It is likely that the hyperkeratosis and acanthosis are responsible for the discoloration typical of this condition. Fig. 50.62. Isolated hyperpigmented morphea.
Treatment and Pathogenesis These conditions are not primarily pigmentary disorders and the discoloration disappears when the epidermal thickening is corrected. For approach to treatment, standard textbooks of dermatology should be consulted.
ratio is about 3 : 1 (Krafchik, 1992; Serup, 1986; Uziel et al., 1994).
References
Clinical Findings
Lever, W. F., and G. Schaumberg-Lever. Histopathology of the Skin. Philadelphia: J. B. Lippincott, 1991. Pinkus, H., and A. H. Mehregan. A Guide to Dermatohistopathology. New York: Appleton-Century-Crofts, 1981.
Morphea and Scleroderma James J. Nordlund
Synonyms Morphea is also labeled localized scleroderma or circumscribed scleroderma.
Epidemiology The prevalence of morphea in the general population is estimated to be about 2–5 per million adults (Uziel et al., 1994). There are no good data for prevalence of morphea in children. Females seem to be affected more commonly than males; the
Morphea, or localized scleroderma, can affect children or adults (Krafchik, 1992; Serup, 1986; Uziel et al., 1994). Five clinical varieties have been described (Lever and SchaumbergLever, 1991): plaque, guttate, linear, segmental, and generalized. The plaque type (Fig. 50.62) is the most common and is characterized by indurated, often pigmented, depressed plaques on the trunk. Guttate lesions often surround the plaques. Widespread lesions on the trunk and extremities are termed generalized morphea (Fig. 50.63). It must be distinguished from scleroderma, which is not generalized morphea but a different disease. The linear form occurs most commonly on the extremities and on the scalp and face. The segmental form affects the face and causes atrophy of the skin, subcutaneous tissue, and muscles. The face is severely deformed. The early lesion of morphea is an erythematous plaque often indurated to palpation. There is a characteristic violet or lilac halo around the edge (Fig. 50.64). As the lesion evolves, the skin atrophies. The epidermis shows minimal changes other 967
CHAPTER 50
in facial hemiatrophy. The affected tissue can be very distorted. Atrophic, bound-down lesions across a joint can interfere with the motion of the limb. In one study of 30 children affected with morphea, 26 had the linear form. The lesions were on the extremity in 19 children and on the face in 7 children. Three had plaque morphea and one had generalized morphea (Uziel et al., 1994). In another study of 58 adults, 38 had the plaque or generalized form and only 20 had lesions on the extremities. Facial hemiatrophy was observed in eight of the adults (Serup, 1986). There seems to be a significant difference in the type of lesions observed in adults and children. There are many pigmentary changes. The earliest lesions have the lilac halo typical of the inflammatory stage of the disease. Hyperpigmentation, usually brown, which is suggestive of epidermal hypermelanosis, is common in all forms of morphea or localized scleroderma. It is especially common in the plaque and generalized variants and in the linear form on the extremities (Serup, 1986). Pigmentary changes are not common in the linear scleroderma on the face (en coup d’sabre). Gray hyperpigmentation suggestive of dermal melanosis and hypopigmentation have also been described (Krafchik, 1992). Pigmentary changes, both hyper- and hypopigmentation, have been associated with progressive systemic sclerosis (scleroderma) (Fig. 50.65).
Associated Findings
Fig. 50.63. Generalized hyperpigmented morphea.
Morphea should be distinguished from scleroderma which is a systemic disorder that clinically differs greatly from morphea. The histologic changes of the two are similar. Lichen sclerosis et atrophicus, a condition that results in atrophy of the epidermis and destruction of the melanocytes, is sometimes found in association with morphea. Some have considered the two disorders to be variable expressions of the same disorder (Tremaine et al., 1990; Uitto et al., 1980). Others consider morphea and lichen sclerosis et atrophicus to be different and not associated (Patterson and Ackerman, 1984). Atrophoderma of Pasini and Pierini is thought by others to be a variant of morphea (Kencka et al., 1995).
Histology
Fig. 50.64. Prominent atrophy and lilac ring.
than pigmentation (described later). There might be mild atrophy. The dermis is firm and the subcutaneous tissue atrophic. The mature plaque is depressed. There can be involvement of the muscles and connective tissue such as seen
968
The histology of early inflammatory lesions differs from that of late sclerotic lesions. Early lesions show thickened collagen and moderately severe inflammatory infiltrates usually composed of mononuclear cells. In later lesions the inflammatory infiltrate is gone and collagen deposition is marked (Lever and Schaumberg-Lever, 1991). The epidermis can be normal or show atrophy. In pigmented lesions there are increased quantities of melanin, which might be apparent only with special stains and when compared to biopsies from uninvolved skin. Lipid droplets are present in the cytoplasm of melanocytes but not in keratinocytes or Langerhans cells. This finding is not unique to morphea (Ortonne et al., 1980). The number of mast cells in the dermis is fewer than normal (Nishioka et al., 1987).
ACQUIRED EPIDERMAL HYPERMELANOSES
Fig. 50.65. Diffuse hyperpigmentation with depigmentation on the neck and upper trunk.
Pathogenesis The cause of morphea is not known. Attempts to document a role for Borrelia burgdorferi have been inconclusive but the weight of evidence seems to suggest that this organism does not have a role in morphea’s cause (Abele and Anders, 1990; Aberer et al., 1991; Meis et al., 1993; Schempp et al., 1993). Organic solvents (Yamakage and Ishikawa, 1982) and eosinophilic fasciitis (Hulshof et al., 1992; Mensing and Schmidt, 1985; Valentini et al., 1988) have been implicated.
Therapy There is no good therapy for morphea. Epidermal pigmentation can be treated with standard lightening agents such as hydroquinone, steroids, and retinoids. There are no published reports on the success of therapy.
References Abele, D. C., and K. H. Anders. The many faces and phases of borreliosis II [review]. J. Am. Acad. Dermatol. 23:401–410, 1990. Aberer, E., H. Klade, and G. Hobisch. A clinical, histological, and
immunohistochemical comparison of acrodermatitis chronica atrophicans and morphea. Am. J. Dermatopathol. 13:334–341, 1991. Hulshof, M. M., B. W. Boom, and B. A. Dijkmans. Multiple plaques of morphea developing in a patient with eosinophilic fasciitis [letter]. Arch. Dermatol. 128:1128–1129, 1992. Kencka, D., M. Blaszczyk, and S. Jablonska. Atrophoderma PasiniPierini is a primary atrophic abortive morphea. Dermatology 190:203–206, 1995. Krafchik, B. R. Localized cutaneous scleroderma [review]. Semin. Dermatol. 11:65–72, 1992. Lever, W. F., and G. Schaumberg-Lever. Histopathology of the Skin. Philadelphia: J. B. Lippincott, 1991. Meis, J. F., R. Koopman, B. van Bergen, G. Pool, and W. Melchers. No evidence for a relation between Borrelia burgdorferi infection and old lesions of localized scleroderma (morphea) [letter]. Arch. Dermatol. 129:386–387, 1993. Mensing, H., and K. U. Schmidt. Diffuse fasciitis with eosinophilia associated with morphea and lichen sclerosus et atrophicus. Acta Derm. Venereol. 65:80–83, 1985. Nishioka, K., Y. Kobayashi, I. Katayama, and C. Takijiri. Mast cell numbers in diffuse scleroderma. Arch. Dermatol. 123:205–208, 1987. Ortonne, J. P., H. Perrot, D. Schmitt, and P. Bioulac. Cutaneous hypermelanosis and intramelanotic lipid droplets. Arch. Dermatol. 116: 301–306, 1980. Patterson, J. A., and A. B. Ackerman. Lichen sclerosus et atrophicus is not related to morphea. A clinical and histologic study of 24 patients in whom both conditions were reputed to be present simultaneously. Am. J. Dermatopathol. 6:323–335, 1984. Schempp, C., H. Bocklage, R. Lange, H. W. Kolmel, C. E. Orfanos, and H. Gollnick. Further evidence for Borrelia burgdorferi infection in morphea and lichen sclerosus et atrophicus confirmed by DNA amplification. J. Invest. Dermatol. 100:717–720, 1993. Serup, J. Assessment of epidermal atrophy in localized scleroderma (morphea). Dermatologica 172:205–208, 1986. Tremaine, R., J. E. Adam, and M. Orizaga. Morphea coexisting with lichen sclerosus et atrophicus. Int. J. Dermatol. 29:486–489, 1990. Uitto, J., D. J. Santa Cruz, E. A. Bauer, and A. Z. Eisen. Morphea and lichen sclerosus et atrophicus. Clinical and histopathologic studies in patients with combined features. J. Am. Acad. Dermatol. 3:271–279, 1980. Uziel, Y., B. R. Krafchik, E. D. Silverman, P. S. Thorner, and R. M. Laxer. Localized scleroderma in childhood: a report of 30 cases. Semin. Arthritis Rheum. 23:328–340, 1994. Valentini, G., R. Rossiello, L. Gualdieri, G. Tirri, J. C. Gerster, and E. Frenck. Morphea developing in patients previously affected with eosinophilic fasciitis. Report of two cases. Rheumatol. Int. 8:235–237, 1988. Yamakage, A., and H. Ishikawa. Generalized morphea-like scleroderma occurring in people exposed to organic solvents. Dermatologica 165:186–193, 1982.
Pigmentary Changes Associated with Addison Disease Cindy L. Lamerson and James J. Nordlund
Historical Background In 1855 Thomas Addison published a monograph entitled On the Constitutional and Local Effects of Disease of the SupraRenal Gland, which presented the characteristics of what is now known as Addison disease.
969
CHAPTER 50
Fig. 50.66. Hyperpigmentation of the dorsum of the feet.
Fig. 50.67. Hyperpigmented palmar creases.
Synonyms Addison disease is also known as hypocorticism, Addison syndrome, suprarenal insufficiency, and hypoadrenalism.
Epidemiology Addison disease is caused by a deficiency of adrenocortical hormones including glucocorticoids such as cortisone, and mineralocorticoids such as aldosterone. Addison is an uncommon disorder affecting approximately 1 in 10 000 individuals (Kong and Jeffcoate, 1994). The characteristic features of the disorder include a generalized brown hyperpigmentation, hypotension, weakness, nausea, vomiting, and diarrhea. There is no age, race, or sexual predilection.
Clinical Findings One of the most striking cutaneous changes in Addison disease is hyperpigmentation of the skin and mucous membranes (Plates 50.26–50.28; Kong and Jeffcoate, 1994; Mulligan and Sowers, 1985; Whitehead et al., 1989; Zelissen et al., 1995). In 20–40% of patients the hyperpigmentation is the presenting symptom of their disease. The pigmentation is a brown or bronze color suggestive of a deep suntan. The hyperpigmentation is generalized in distribution but more accentuated in sun-exposed areas. Often this brown hyperpigmentation is referred to as the persistence of a summer tan. The pigmentation is usually darker in areas prone to trauma (Fig. 50.66) such as palmar creases (Fig. 50.67 and Plate 28.5, pp. 494–495), knees, and elbows, which are subjected to pressure and friction. There is also darker pigmentation in scars (Fig. 50.68). Common areas for deeper pigmentation are the areola (Fig. 50.69), axilla, perineum, and genitalia. Moreover, the linea nigra may become prominent in parous women. Hyperpigmentation of the buccal and gingival mucosa as well as the tongue (Fig. 50.70) may be present as patchy macules and may be a gray blue color. In addition to the hyperpigmentation of the normal skin, melanocytic nevi may darken and lentigines may appear (Braverman, 1981; Nerup, 1974). The hair may darken and gray hairs may regain pigmentation. Longitudinal pigmented bands may be prominent in 970
Fig. 50.68. Hyperpigmented surgical scar.
the nails (Allenby and Snell, 1966; Sterling et al., 1988). The bands are similar to those normally occurring in the nails of individuals with type V or type VI skin. In addition to the pigmentary changes, individuals with Addison disease may have other cutaneous changes, including loss of body hair, especially in the axilla, and fibrosis and calcification of the pinna (Graner, 1985; Haegy, 1982; Ketterer and Frenk, 1995; Kim, 1988; Shimao, 1971).
Associated Disorders Adrenal atrophy is rarely a single disorder. Currently, adrenal disease is most commonly caused by an autoimmune mechanism in which antibodies are thought to destroy the gland. Such individuals commonly have other endocrine abnormalities caused by antibodies. These include thyroid disease, diabetes mellitus, pernicious anemia, and/or gonadal failure (Appel and Holub, 1976; Chen et al., 1996; Inaba and Morii, 1995; Nomura et al., 1994; Zelissen et al., 1995). Other individuals have tuberculosis, systemic fungal infec-
ACQUIRED EPIDERMAL HYPERMELANOSES
Histology The histology of pigmentary changes of Addison disease is not diagnostic. There is no increase in the number of melanocytes. The melanocytes are more active and produce increased amounts of melanin. Increased melanin is visible in the basal layer of the epidermis and upper layers, including the stratum corneum. Melanophages may be present in the upper dermis (Lerner, 1955; Montgomery and O’Leary, 1930).
Pathogenesis
A
B Fig. 50.69. Hyperpigmentation of areolae before treatment (A) that resolved after treatment (B) (see also Plate 50.26A and 50.26B, pp. 494–495).
The adrenal cortex fails to synthesize glucocorticoids appropriately in individuals with Addison disease. Adrenocortical failure is most often a result of atrophy of the gland (Kong and Jeffcoate, 1994; Zelissen et al., 1995), although very rarely the patient might have a defect in the pituitary (Yamamoto et al., 1992). These latter individuals do not exhibit hyperpigmentation. The adrenal gland may be destroyed by a number of mechanisms, including autoimmune antibodies (Chen et al., 1996; Inaba and Morii, 1995; Kong and Jeffcoate, 1994; Nomura et al., 1994; Zelissen et al., 1995), tuberculosis, deep fungi (histoplasmosis and paracoccidiomycosis) (Kong and Jeffcoate, 1994; Nomura et al., 1994; Zelissen et al., 1995), or metastatic carcinoma (Kong and Jeffcoate, 1994). In healthy individuals the adrenal gland is stimulated by adrenocorticotropic hormone (ACTH) secreted by the pituitary gland. ACTH is derived from its precursor, proopiomelanocortin. The adrenal gland synthesizes cortisone that serves to suppress the pituitary function, a feedback mechanism. When the gland is destroyed by any mechanism, there is a disruption of the normal cortisol–pituitary–hypothalamic feedback, and ACTH levels rise. Along with ACTH, other peptides from proopiomelanocortin are also produced in increased quantities. These include b-lipotropin (LPH), g-melanotropin, b-melanotropin, and a-melanotropin. It is thought that the molecules of melanotropin give rise to the pigmentation (Shizume, 1985).
Criteria for Diagnosis and Laboratory Abnormalities
Fig. 50.70. Typical hyperpigmentation of Addison disease (see also Plate 50.27, pp. 494–495).
tions, or metastatic carcinoma (Kong and Jeffcoate, 1994; Nomura et al., 1994; Zelissen et al., 1995). Adrenoleukodystrophy is a cause of adrenal disease in young boys (Kong and Jeffcoate, 1994; Laureti et al., 1996).
Addison disease cannot be diagnosed in the absence of adrenal hypofunction. The clinical manifestations are not specific (Marlette, 1975; Runcie et al., 1986; Strakosch and Gordon, 1978; Whitehead et al., 1989). ACTH stimulation test is used to diagnose adrenal cortical failure. Serum cortisol levels are measured following stimulation with ACTH. If the cortisol levels remain low despite ACTH stimulation, the diagnosis of Addison disease is made. Early in the course of the disease, the test may be negative, so repeat testing may be necessary. Moreover, partially compensated hypoadrenalism may present with skin hyperpigmentation (Whitehead et al., 1989). In approximately 50% of patients, autoantibodies directed against the adrenal gland are present in the patient’s serum (Chen et al., 1996; Nomura et al., 1994; Whitehead et al., 1989; Zelissen et al., 1995). Many other metabolic abnormalities are associated with 971
CHAPTER 50 Table 50.4. Differential diagnosis of generalized brown hyperpigmentation. Exogenous administration of ACTH Nelson syndrome AIDS (resulting from glucocorticoid deficiency at target tissues) (Norbiato et al., 1994) Hyperthyroidism Carcinoid Pheochromocytoma Cirrhosis POEMS syndrome Siemerling–Creuzfeldt disease; adrenoleukodystrophy Drug-induced hyperpigmentation Methotrexate 5-fluorouracil Congenital polychlorinated biphenyl (PCB) poisoning (Miller, 1985)
adrenal insufficiency. Many of these are related to the deficiency of mineralocorticoids such as aldosterone. Such abnormalities include hypoglycemia, hyponatremia, and hyperkalemia, as well as an elevated blood urea nitrogen.
Differential Diagnosis The differential diagnosis of diffuse brown hyperpigmentation of Addison disease is presented in Table 50.4.
Treatment Replacement therapy permits the pigment to fade gradually. Without such treatment the disease will be progressive and lead to the death of the individual. The usual therapy is prednisone and a mineralocorticoid such as fludrocortisone. If treatment is initiated appropriately, the prognosis for the disease is excellent (Shimao, 1971).
References Addison, T. On the Constitutional and Local Effects of Disease of the Supra-Renal Capsules. London: Samuel Highley, 1855, p. 43. Allenby, C. F., and P. H. Snell. Longitudinal pigmentation of the nails in Addison’s disease. Br. Med. J. 5503:1582–1583, 1966. Appel, G. B., and D. A. Holub. The syndrome of multiple endocrine gland insufficiency. Am. J. Med. 61:129–133, 1976. Braverman, I. M. Skin Signs of Systemic Disease, 2nd ed. Philadelphia: W. B. Saunders, 1981, p. 366. Chen, S., J. Sawicka, C. Betterle, M. Powell, L. Prentice, M. Volpato, B. Rees Smith, and J. Furmaniak. Autoantibodies to steroidogenic enzymes in autoimmune polyglandular syndrome, Addison’s disease, and premature ovarian failure. J. Clin. Endocrinol. Metab. 81:1871–1876, 1996. Graner, J. L. Addison, pernicious anemia and adrenal insufficiency. Can. Med. Assoc. J. 133:855–857, 1985. Haegy, J. M. Acute adreno-cortical insufficiency. Eight case reports. Semaine Hopitaux 58:143–147, 1982. Inaba, M., and H. Morii. Polyglandular autoimmune syndrome [review; in Japanese]. Nippon Rinsho 53:974–978, 1995.
972
Ketterer, R., and E. Frenk. Skin changes in endocrine disorders (with the exception of diabetes) [review; in German]. Ther. Umsch. 52:269–274, 1995. Kim, H. W. Generalized oral and cutaneous hyperpigmentation in Addison’s disease. Odonto-Stomatol. Tropicale 11:87–90, 1988. Kong, M. F., and W. Jeffcoate. Eighty-six cases of Addison’s disease. Clin. Endocrinol. 41:757–761, 1994. Laureti, S., G. Casucci, F. Santeusanio, G. Angeletti, P. Aubourg, and P. Brunetti. X-linked adrenoleukodystrophy is a frequent cause of idiopathic Addison’s disease in young adult male patients. J. Clin. Endocrinol. Metab. 81:470–474, 1996. Lerner, A. B. Melanin pigmentation. Am. J. Med. 19:902–924, 1955. Marlette, R. H. Generalized melanoses and nonmelanotic pigmentations of the head and neck. J. Am. Dent. Assoc. 90:141–147, 1975. Miller, R. W. Congenital PCB poisoning: a reevaluation. Environ. Health Perspec. 60:211–214, 1985. Montgomery, H., and P. A. O’Leary. Pigmentation of the skin in Addison’s disease, acanthosis nigricans and hemochromatosis. Arch. Dermatol. Syphil. 21:970–984, 1930. Mulligan, T. M., and J. R. Sowers. Hyperpigmentation, vitiligo, and Addison’s disease. Cutis 36:317–318, 322, 1985. Nerup, J. Addison’s disease: a review of some clinical, pathological and immunological features. Dan. Med. Bull. 21:201–207, 1974. Nomura, K., H. Demura, and T. Saruta. Addison’s disease in Japan: characteristics and changes revealed in a nationwide survey. Intern. Med. 33:602–606, 1994. Norbiato, G., M. Galli, V. Righini, and M. Moroni. The syndrome of acquired glucocorticoid resistance in HIV infection. Ballieres Clin. Endocrinol. Metab. 8:777–787, 1994. Runcie, C. J., C. G. Semple, and S. D. Slater. Addison’s disease without pigmentation. Scott. Med. J. 31:111–112, 1986. Shimao, S. Addison’s disease and problems in hormone therapy: skin hyperpigmentation and hormone therapy. Horumon to Rinsho Clin. Endocrinol. 19:103–107, 1971. Shizume, K. Thirty five years of progress in the study of MSH. Yale J. Biol. Med. 58:561–570, 1985. Sterling, G. B., L. F. Libow, and M. E. Grossman. Pigmented nail streaks may indicate Laugier-Hunziker syndrome. Cutis 42: 325–326, 1988. Strakosch, C. R., and R. D. Gordon. Early diagnosis of Addison’s disease: pigmentation as sole symptom. Aust. N. Z. J. Med. 8:189– 190, 1978. Whitehead, E. M., A. B. Atkinson, D. R. Hadden, J. Weaver, and B. Sheridan. Partially compensated hypoadrenalism presenting with persistent skin pigmentation. J. Endocrinol. Invest. 12:187–191, 1989. Yamamoto, T., J. Fukuyama, K. Hasegawa, and M. Sugiura. Isolated corticotropin deficiency in adults. Report of 10 cases and review of literature [review]. Arch. Intern. Med. 152:1705–1712, 1992. Zelissen, P. M., E. J. Bast, and R. J. Croughs. Associated autoimmunity in Addison’s disease. J. Autoimmun. 8:121–130, 1995.
Pigmentary Changes Associated with Cutaneous Lymphomas Debra L. Breneman
Historical Background The term mycosis fungoides was introduced by Alibert to
ACQUIRED EPIDERMAL HYPERMELANOSES
characterize a patient with a desquamating rash who developed tumors resembling mushrooms. Bazin (1870) described a natural progression from a premycotic phase to tumors. An erythrodermic phase was later described by Besnier and Hallopeau (1892). Sézary and Bouvrain (1938) described the triad of erythroderma, leukemia composed of large mononuclear cells with convoluted nuclei, and lymphadenopathy. This subsequently became known as Sézary syndrome (Taswell and Winkelmann, 1961). It was later shown that some patients with mycosis fungoides developed involvement of the blood and viscera (Clendenning et al., 1964; Epstein et al., 1972). Studies using cytogenetics and cellular immunology showed these diseases represented neoplasms of T lymphocytes (Broome et al., 1973; Crossen et al., 1971). In the vast majority of cases the abnormal cells were found to have functional and phenotypic features of helper T cells (Berger et al., 1979; Kung et al., 1981).
Synonyms The designation, cutaneous T-cell lymphoma, represents a group of neoplasms of T-cells that present with the skin as the initial site of involvement. Mycosis fungoides is the most common type of cutaneous T-cell lymphoma. Other types of cutaneous T-cell lymphoma include Sézary syndrome, adult T-cell leukemia/lymphoma, CD30+ large cell lymphoma, angiocentric T-cell lymphoma, and subcutaneous T-cell lymphoma.
Epidemiology Mycosis fungoides is increasing in incidence. The incidence has been reported to be as high as 0.9 per 100 000 (Chuang et al., 1990). The cause is unknown. Environmental, infectious, and genetic factors have all been postulated to play a role in the development of this disease but these proposals have not been proved (Tuyp et al., 1987).
General Clinical Findings Mycosis fungoides has been reported to occur mostly in older individuals and is rare in children and adolescents (Peters et al., 1990). It has been reported to occur more frequently in blacks and is also more common in men, with male/female ratios variably being reported at 2:1 to 3:1 (Chuang et al., 1990).
Clinical Description of Disease The natural history of mycosis fungoides is variable. Most patients have a protracted preclinical phase and a prolonged survival with little morbidity. Others may have a fulminate course with rapid development of systemic dissemination and death (Bunn and Lamberg, 1979). There are three distinct cutaneous phases which occur in mycosis fungoides (Edelson, 1980). In the patch stage the lesions are flat and nonpalpable. They are often erythematous and may be scaly. They tend to occur on covered portions of
Fig. 50.71. Multiple patches of hypopigmented mycosis fungoides.
the body, and unusual shapes are common. In a variant of the patch phase, poikiloderma vasculare atrophicans, the skin is atrophic with mottled pigmentation and telangiectasia. In the plaque phase of mycosis fungoides the lesions become elevated above the surrounding skin surface. They may be erythematous or violaceous. In heavily pigmented individuals the plaques may be hyperpigmented. They may ulcerate and become secondarily infected. In the tumor phase the lesions become further elevated. The tumors may arise de novo or in pre-existing plaques. Mycosis fungoides may also progress to an exfoliative erythroderma in which the skin is diffusely red and scaly and there is severe pruritus. Mycosis fungoides may disseminate to extracutaneous sites. The sites of dissemination are varied and disease has been identified in virtually every organ system (Rappaport and Thomas, 1974). The lymph nodes are the most common site of extracutaneous involvement. Gross involvement of the peripheral blood generally occurs relatively late in the disease. There is a strong association between gross lymph node or blood involvement and visceral disease. Dissemination may occur late in the disease to the bone marrow, liver, spleen, lungs, bones, central nervous system, and other organs.
Hypopigmentation and Mycosis Fungoides Cutaneous pigmentary changes are well recognized in mycosis fungoides but usually occur either in association with poikiloderma vasculare atrophicans or following treatment and regression of the cutaneous lesions, with a resultant mixed pattern of hypo- and hyperpigmentation (Smith and Sammon, 1978). Additionally, untreated plaques of mycosis fungoides in heavily pigmented individuals commonly are hyperpigmented (Zackheim et al., 1982). Hypopigmented mycosis fungoides (Figs 50.71 and 50.72) was initially described in 1973 (Ryan et al., 1973). To date,
973
CHAPTER 50
lymphoma mimicking porokeratosis have been reported (Hsu et al., 1992). These patients had widespread sharply demarcated macules that clinically resembled disseminated superficial actinic porokeratosis. In one patient the macules were hypopigmented and in the other they were hyperpigmented.
Associated Disorders
Fig. 50.72. Hypopigmented mycosis fungoides characterized by round to irregular hypopigmented patches.
there have been 29 cases reported of hypopigmented mycosis fungoides (Breathnach et al., 1982; Cooper et al., 1992; Dabski et al., 1985; Goldberg et al., 1986; Handfield-Jones et al., 1992; Lambroza et al., 1995; Misch et al., 1987; Ryan et al., 1973; Rustin et al., 1986; Sigal et al., 1987; Smith and Sammon, 1978; Volkenandt et al., 1993; Whitmore et al., 1994; Zackheim et al., 1982). The age of onset of reported cases ranges from 4 to 72 years with most cases beginning before the fourth decade. Eleven cases have been reported with onset of hypopigmented mycosis fungoides under the age of 20 years. This is in contrast to mycosis fungoides in general which more commonly presents in older adults. Hypopigmented mycosis fungoides occurs with equal frequency in men and women (Lambroza et al., 1995). Only one case of hypopigmented mycosis fungoides has been reported in a white patient (Sigal et al., 1987). All other cases have been reported in individuals with brown or black skin (Lambroza et al., 1995). Hypopigmented mycosis fungoides presents clinically as circular or oval areas of hypopigmentation with distinct or indistinct borders. There may be some degree of erythema, scaling, and infiltration. Small islands of normal pigmentation may be present in their center. Patients may present with macular hypopigmentation only or there may be associated erythematous patches, plaques, and papules as well as poikiloderma. Only a few lesions may be present, or most of the body surface may be involved. The hypopigmentation generally involves the trunk and extremities, and only rarely is the face involved. Areas of involvement are often bilaterally symmetric and there may be a progressive loss of pigment over time. Hypopigmented macules appear de novo and are not preceded by erythema, scaling, or induration. Pruritus within lesions is variable. Hypopigmented areas have been reported to be present for up to 20 years prior to presentation. Areas of pigmentary loss are generally hypopigmented but occasionally may appear depigmented. Additionally, two black patients with cutaneous T-cell 974
Poikiloderma vasculare atrophicans and large plaque parapsoriasis both may precede mycosis fungoides, and are felt by some authors to be indistinguishable from early mycosis fungoides (Lindae et al., 1988; Sanchez and Ackerman, 1979). Poikiloderma vasculare atrophicans is characterized by atrophic patches containing hypo- and hyperpigmented macules and telangiectasia. A progression to overt mycosis fungoides may be associated with some degree of induration. The clinical findings of large plaque parapsoriasis may be identical to those found in patch stage mycosis fungoides. These lesions are erythematous to light brown patches which may be atrophic and have a fine superficial scale. Both conditions have a predilection for covered areas of the body. Lymphomatoid papulosis is an entity consisting of recurrent self-healing papulo-nodular lesions that resemble pityriasis lichenoides et varioliformis acuta clinically but lymphoma histologically. Lymphomatoid papulosis most commonly has a benign clinical course lasting for months to decades (Thomsen and Wantzin, 1987). Approximately 25% of patients with lymphomatoid papulosis develop lymphoma with mycosis fungoides being the most commonly associated type (Wantzin et al., 1985). Mycosis fungoides may precede, develop concurrently, or appear after the onset of lymphomatoid papulosis. Follicular mucinosis is a condition of unknown etiology consisting of follicular papules or indurated plaques with hair loss. Histologically there is accumulation of acid mucopolysaccharides in the pilosebaceous unit. A coexisting lymphoma, most commonly mycosis fungoides, occurs in 15% of patients with follicular mucinosis (Lancer et al., 1984). Patients with coexisting follicular mucinosis and mycosis fungoides are generally in the fourth to seventh decades of life.
Other Pigmentary Abnormalities in Mycosis Fungoides Diffuse progressive hyperpigmentation as a manifestation of mycosis fungoides has been reported in one patient (David et al., 1987). The patient, who presented for evaluation of hyperpigmentation and pruritus of simultaneous onset, had widespread, poorly defined, dark brown macules over much of the skin surface. Histologically the hyperpigmented macules showed typical findings of mycosis fungoides. The patient, who had tumor stage disease and lymph node involvement, died of complications of staphylococcal sepsis. In addition to histologic changes typical of mycosis fungoides, a large amount of melanin in the basal layer and giant melanin granules in focal areas throughout the spinous layer were noted.
ACQUIRED EPIDERMAL HYPERMELANOSES
One patient who was subsequently shown to have mycosis fungoides presented with well-defined, blue macules within what appeared to be an eczematous dermatitis (Neuman, 1984). Histologic examination of a blue macule, in addition to changes characteristic of mycosis fungoides, showed marked incontinence of pigment. This may have led to a Tyndall effect producing the bluish discoloration. Four patients have been reported who developed pigmented purpuralike eruptions which progressed to mycosis fungoides (Barnhill and Braverman, 1988; Waisman, 1976). These patients presented with petechial patches with varying degrees of scale, pigmentation, and lichenification. Initial biopsies were consistent with pigmented purpuric dermatosis, and the diagnosis of mycosis fungoides was made following serial skin biopsies.
Routine Histology, Histochemistry, and Immunochemistry
Fig. 50.73. Lower trunk and thighs of patient with mycosis fungoides showing reticulated hyperpigmentation (see also Plate 50.28, pp. 494–495).
Electron microscopy revealed large lymphocytes with cerebriform nuclei in the dermis and epidermis. Melanin granules were seen within the cytoplasm of tumor cells infiltrating the dermis, in typical Lutzner cells, and in nontumoral macrophages. In the epidermis, keratinocytes of the suprabasal layer contained multiple dispersed melanin granules with several giant granules within the cytoplasm. Langerhans cells in the epidermis showed a few aggregated melanin granules. A patient with florid reticulate pigmentation (see Fig 50.73) as a manifestation of mycosis fungoides has been reported (McDonagh et al., 1991). The patient, who had tumors involving the chest and back, died of unrelated causes. In other patients with mycosis fungoides reported with reticulate pigmentation the pigmentary abnormality has been more limited in extent and severity (Brehmer-Andersson, 1976). Histologically within the hyperpigmented areas in this patient, in addition to features typical of mycosis fungoides, pigmentary incontinence and numerous melanophages within the dermis were noted.
The histologic appearance of mycosis fungoides varies with the cutaneous stage of the disease (Nickoloff, 1988). The histologic diagnosis of the patch stage is often difficult and early biopsies may be described as showing a nonspecific chronic dermatitis. In the patch and plaque stages, epidermotropism of lymphocytes is present, often with minimal spongiosis. Infiltration of the epidermis by mononuclear cells without evident spongiosis is strongly suggestive of early cutaneous T-cell lymphoma. Lymphocytes may appear to line up along the dermal–epidermal junction. In the patch stage there is a sparse infiltrate of mononuclear cells in the upper dermis. The lymphocytes may or may not appear to be pleomorphic or hyperchromatic or contain convoluted nuclei. As the clinical lesions become thicker, forming definite plaques, there is a tendency for epidermotropic cells to form Pautrier microabscesses, which are clusters of lymphocytes in the epidermis. A lichenoid and/or perivascular infiltrate is often present. The mononuclear cells may show deeply indented nuclei along with a mixed inflammatory response. In the tumor stage the infiltrate is denser and extends into the subcutaneous fat, and there may be a loss of epidermotropism. There may be varying degrees of transformation with mononuclear cells containing large hyperchromatic nuclei, prominent nucleoli, and frequent mitotic figures. In hypopigmented mycosis fungoides, exocytosis is often moderate and may be so extreme as to simulate pagetoid reticulosis (Lambroza et al., 1995). Dermal involvement may be minimal. Melanin may be reduced or absent, and mild to marked pigmentary incontinence may be seen. Immunocytochemistry studies in lesions of mycosis fungoides generally show predominance of CD4 antigen positive cells. Partial loss of the CD7 antigen is common (Whitmore et al., 1994).
Other Investigations Electron microscopy of hypopigmented mycosis fungoides, in addition to showing focal invasion of the epidermis by atypical lymphocytes, may show enlargement of epidermal 975
CHAPTER 50
intercellular spaces suggestive of intraepidermal edema, and degenerative changes in adjacent melanocytes and keratinocytes in some cases (Breathnach et al., 1982; Misch et al., 1987; Sigal et al., 1987). Degenerative changes present within melanocytes may include extensive cytoplasmic vacuolization, marked dilatation of the rough endoplasmic reticulum, and swelling of mitochondria with loss of cristae. Melanocytes may be incompletely melanized and occasionally may be undergoing disintegration. Occasionally the overall numbers of melanocytes may be reduced. Numbers of melanosomes within keratinocytes may be normal or decreased. Melanin-containing macrophages may be seen in the papillary dermis (Goldberg et al., 1986; Lambroza et al., 1995). By using a specific molecular probe for the malignant lymphoid clone in a patient with mycosis fungoides, hypopigmented lesions, which were previously unclassifiable by conventional microscopy, were found to contain tumor clonespecific DNA. This evidence suggested that the hypopigmented lesions were actually early manifestations of mycosis fungoides (Volkenandt et al., 1993). In another patient with hypopigmented mycosis fungoides, T-cell receptor gene rearrangement analysis was negative (Lambroza et al., 1995). However, gene rearrangement studies are frequently negative in early stage mycosis fungoides.
Criteria for Diagnosis The diagnosis of mycosis fungoides is generally made by light microscopy of hematoxylin and eosin stained sections from involved skin (Nickoloff, 1988). Multiple biopsies obtained over months or years are sometimes necessary to establish the diagnosis. Immunoperoxidase studies and T-cell receptor gene rearrangement analysis are sometimes useful in confirming the diagnosis. Further evaluation includes a thorough physical examination with emphasis on examination of the lymph nodes, liver, and spleen. Peripheral blood studies should include a complete blood count with determination of the white blood cell count and examination of a peripheral smear for the presence of atypical lymphocytes. Additional testing for blood involvement may include lymphocyte flow cytometry and T-cell receptor gene rearrangement analysis in some cases. Other baseline tests usually include serum chemistries and lactic dehydrogenase and a chest X-ray. Additional staging procedures useful in selected patients include computed tomography (CT) scan of the abdomen and pelvis, lymph node biopsy, and bone marrow biopsy (Sausville et al., 1988). Further evaluation of specific organ systems is indicated when involvement is suggested by history, physical examination, or baseline test results.
Differential Diagnosis Mycosis fungoides is a great mimicker and it has been reported to imitate numerous other cutaneous diseases. It is most commonly mistaken for chronic dermatitis. The differential diagnosis of hypopigmented mycosis fungoides includes vitiligo, 976
idiopathic guttate hypomelanosis, tinea versicolor, pityriasis alba, sarcoidosis, leprosy, pityriasis lichenoides chronica, and postinflammatory hypopigmentation.
Pathogenesis Mycosis fungoides represents a monoclonal expansion of helper T cells which in the initial stages have a strong affinity for the epidermis (Heald and Edelson, 1993). The disease may initially remain localized to one area of the skin but with time can progress to involve multiple regions. Subclones that are biologically more malignant exhibit less affinity for the epidermis. They enter a vertical growth pattern and form tumors. Subclones with decreased affinity for the skin may lead to spread to lymph nodes and viscera. The development of hypopigmented mycosis fungoides lesions may be related to melanocyte degeneration and abnormal melanogenesis caused by a nonspecific response to cell injury associated with inflammation (Breathnach et al., 1982). A defect in melanosome transfer has also been postulated as an etiology for the reduced pigment (Goldberg et al., 1986). More than one cause for this pigmentary defect may be operational. A spectrum of abnormal melanogenesis may exist, with pigment cell death as the most extreme expression (Lambroza et al., 1995).
Animal Models A cutaneous lymphoma similar to mycosis fungoides has been described in dogs (Fivenson et al., 1994). Canine mycosis fungoides is a T-cell lymphoma that mimics mycosis fungoides immunophenotypically and ultrastructurally.
Treatments There is an often bewildering array of therapeutic options available for the treatment of mycosis fungoides. Much of the treatment is directed towards skin involvement. Especially in early stage patients, there is no evidence that systemic chemotherapy alters the prognosis. A number of topical therapies are used in treating patients with mycosis fungoides. Very little has been published on the use of topical corticosteroids, although they are routinely used in clinical practice in patients with early stage skin disease or as adjunctive therapy. Two topical chemotherapeutic agents, mechlorethamine hydrochloride and carmustine, are used routinely in mycosis fungoides. Topical mechlorethamine has been used for this disease for more than 30 years, is effective in early disease, and has little toxicity (Vonderheid et al., 1989). Mechlorethamine may be applied either as an aqueous or ointment preparation. Carmustine (BCNU), like mechlorethamine hydrochloride, is an alkylating agent. Carmustine is generally applied in solution form but may also be applied as an ointment. Efficacy rates are similar to those attained with topical mechlorethamine (Zackheim et al., 1992). Both UVB and PUVA phototherapy have been used in treating mycosis fungoides. UVB phototherapy is generally
ACQUIRED EPIDERMAL HYPERMELANOSES
most useful for patients with patch phase skin disease (Resnick and Vonderheid, 1993). PUVA is most useful in patients with patch or plaque phase skin disease (Gilchrest, 1979). Relapse is common when treatment is discontinued. Because neoplastic cells of mycosis fungoides are radiosensitive, radiation is useful in the treatment of this disease. Total skin irradiation allows delivery of high energy electrons to a limited depth of the entire skin surface and prevents systemic toxicity. Total skin irradiation provides the highest complete response rate in patients with early skin disease that can be achieved with any treatment modality (Hoppe et al., 1969). Local radiotherapy is commonly used in treating individual tumors or ulcerating plaques. Advanced mycosis fungoides often requires systemic therapy. Objective response rates of 60–70% have been reported with single agent cytotoxic chemotherapy, but median duration of response is less than six months (Holloway et al., 1992). Single agents which have been used include mechlorethamine, cyclophosphamide, chlorambucil, methotrexate, cisplatin, prednisone, VP16, vincristine, adriamycin, and bleomycin. Newer agents include fludarabine monophosphate, deoxycoformycin, and 2-chlorodeoxyadenosine. Combination chemotherapy utilizes multiple drugs to inhibit different phases of the cell cycle. Objective response rates of 60–100% have been reported in patients with mycosis fungoides treated with combination chemotherapy (Holloway et al., 1992). Other systemic agents which are useful in the treatment of mycosis fungoides include the interferons and the retinoids. Photophoresis, also known as extracorporeal photochemotherapy, is effective in some erythrodermic patients (Holloway et al., 1992). Patients with hypopigmented mycosis fungoides have been reported to develop perifollicular repigmentation within hypopigmented patches with PUVA therapy. This may be followed by clearing both clinically and histologically (Breathnach et al., 1982; Handfield-Jones et al., 1992; Lambroza et al., 1995; Whitmore et al., 1994). Partial or complete repigmentation of hypopigmented mycosis fungoides may result from the use of carmustine (Zackheim et al., 1982), topical mechlorethamine (Goldberg et al., 1986), total skin irradiation, or adjuvant chemotherapy (Lambroza et al., 1995). However, interruption of therapy may result in recurrence of hypopigmentation. Of note, hyperpigmentation may occur as a result of some topical agents used in treating mycosis fungoides. Particularly in dark complexioned persons, hyperpigmentation may follow the topical application of carmustine or mechlorethamine hydrochloride. Hyperpigmentation may also occur with ultraviolet B or PUVA phototherapy (Zackheim et al., 1982).
Prognosis Patients with mycosis fungoides may be divided into three distinct prognostic groups (Sausville et al., 1988). Patients with the best prognosis are those with patch or plaque phase skin disease without involvement of lymph nodes, blood, or
viscera. These patients have a median survival of greater than 12 years. An intermediate prognostic group consists of patients with tumors or erythroderma or those with early involvement of the lymph nodes or blood but without visceral involvement. These patients have a median survival of five years. Poor risk patients are those with visceral disease or effaced lymph nodes. These patients have a median survival of 2.5 years. The long-term prognosis of patients with hypopigmented mycosis fungoides is unknown, particularly since many of these patients present at a younger age than do patients with typical mycosis fungoides. Most patients reported with hypopigmented mycosis fungoides have had indolent disease over limited follow-up periods (Whitmore et al., 1994). One patient, however, developed cutaneous tumors and involvement of axillary lymph nodes, and subsequently died of bone marrow aplasia and septicemia, despite topical and systemic chemotherapy and electron beam therapy (Sigal et al., 1987). Of note, this patient was white, in contrast with most patients with hypopigmented mycosis fungoides who are dark skinned.
References Alibert, J. L. Description des maladies de la peau: Observees à l-hopital St. Louis et exposition des eilleurs methodes Suivies pour leur traitement. Paris: Barrois l’aine et Fils; p. 157, 1806. Barnhill, R. L., and I. M. Braverman. Progression of pigmented purpura-like eruptions to mycosis fungoides: Report of three cases. J. Am. Acad. Dermatol. 19:25–31, 1988. Bazin, E. Leçons sur le traitement des maladies chroniques en général affections de la peau en particulier par l’emploi comparé des eaux minérales de l’hydrothérapie et des moyens pharmaceutiques. Paris: Adrien Delahaye; p. 425, 1870. Berger, C. L., D. Warburton, J. Raafeet, P. LoGerfo, and R. L. Edelson. Cutaneous T-cell lymphoma: Neoplasm of T-cells with helper activity. Blood 53:642–651, 1979. Besnier, E., and H. Hallopeau. On the erythrodermia of mycosis fungoides. J. Cutan. Genito. Urin. Dis. 10:453, 1892. Breathnach, S. M., P. H. McKee, and N. P. Smith. Hypopigmented mycosis fungoides: Report of five cases with ultrastructural observation. Br. J. Dermatol. 106:643–649, 1982. Brehmer-Andersson, E. Mycosis fungoides and its relationship to Sezary syndrome, lymphomatoid papulosis, and primary cutaneous Hodgkin’s disease. Acta Derm. Venereol. Suppl. (Stockh.) 56:1– 142, 1976. Broome, J. D., D. Zucker-Franklin, M. S. Weiner, C. Bianco, and V. Nussenweig. Leukemic cells with membrane properties of thymusderived (T) lymphocytes in a case of Sezary syndrome: morphologic and immunologic studies. Clin. Immunol. Immunopathol. 1:319– 329, 1973. Bunn, P. A., and S. I. Lamberg. Report of the committee on staging and classification of cutaneous T-cell lymphomas. Cancer Treatment Rep. 63:725–728, 1979. Chuang, T.-Y., D. Su, and S. A. Muller. Incidence of cutaneous T-cell lymphoma and other rare skin cancers in a defined population. J. Am. Acad. Dermatol. 23:254–256, 1990. Clendenning, W. E., G. Brecher, and E. J. Van Scott. Mycosis fungoides: Relationship to malignant cutaneous reticulosis and the Sezary syndrome. Arch. Dermatol. 89:785–792, 1964. Cooper, D., M. Jacobson, and R. S. Bart. Hypopigmented macules. Hypopigmented mycosis fungoides (MF). Arch. Dermatol. 128: 1266–1267,1269–1270, 1992.
977
CHAPTER 50 Crossen, P. E., J. E. Mellor, A. G. Finley, R. B. M. Ravich, P. C. Vincent, and F. W. Gunz. The Sezary syndrome: Cytogenetic studies and identification of the Sezary cell as an abnormal lymphocyte. Am. J. Med. 50:24–34, 1971. Dabski, K., H. L. Stoll, and H. Milgrom. Unusual clinical presentation of epidermotropic cutaneous lymphoma: small hypopigmented macules. Int. J. Dermatol. 24:108–115, 1985. David, M., A. Shanon, B. Hazaz, and M. Sandbank. Diffuse progressive hyperpigmentation: An unusual skin manifestation of mycosis fungoides. J. Am. Acad. Dermatol. 16:257–260, 1987. Edelson, R. L. Cutaneous T-cell lymphoma: Mycosis fungoides, Sezary syndrome, and other variants. J. Am. Acad. Dermatol. 2:89–106, 1980. Epstein, E. H., D. L. Levin, J. D. Croft, and M. A. Lutzner. Mycosis fungoides. Survival, prognostic features, response to therapy and autopsy findings. Medicine (Baltimore) 51:61–72, 1972. Fivenson, D. P., G. M. Saed, E. R. Beck, R. W. Dunstan, and P. F. Moore. T-cell receptor cell gene rearrangement in canine mycosis fungoides. Further support for a canine model of cutaneous T-cell lymphoma. J. Invest. Dermatol. 102:227–230, 1994. Gilchrest, B. A. Methoxsalen photochemotherapy for mycosis fungoides. Cancer Treat. Rep. 63:663–667, 1979. Goldberg, D. J., R. S. Schinella, and P. Kechijian. Hypopigmented mycosis fungoides. Speculation about the mechanism of hypopigmentation. Am. J. Dermatopathol. 8:326–330, 1986. Handfield-Jones, S. E., N. P. Smith, and S. M. Breathnach. Hypopigmented mycosis fungoides. Clin. Exp. Dermatol. 17:374–375, 1992. Heald, P. W., and R. L. Edelson. Lymphomas, pseudolymphomas, and related conditions. In: Dermatology in General Medicine, 4th ed., T. B. Fitzpatrick, A. Z. Eisen, K. Wolff, I. M. Freedberg, and K. F. Austen (eds). New York: McGraw-Hill, Inc., 1993, pp. 1285– 1307. Holloway, K. B., F. P. Flowers, and F. A. Ramos-Caro. Therapeutic alternatives in cutaneous T-cell lymphoma. J. Am. Acad. Dermatol. 27:367–378, 1992. Hoppe, R. T., R. S. Cox, Z. Fuks, N. M. Price, M. A. Bagshaw, and E. M. Farber. Electron beam therapy for mycosis fungoides: The Stanford University experience. Cancer Treat. Rep. 63:691–700, 1969. Hsu, W. T., M. B. Toporcer, G. R. Kantor, E. C. Vonderheid, and M. E. Kadin. Cutaneous T-cell lymphoma with porokeratosislike lesions. J. Am. Acad. Dermatol. 27(2 Pt 2):327–330, 1992. Kung, P. C., C. L. Berger, G. Goldstein, P. LoGerfo, and R. L. Edelson. Cutaneous T-cell lymphoma: Characterization by monoclonal antibody. Blood 57:261–266, 1981. Lambroza, E., S. R. Cohen, R. Phelps, M. Lebwohl, I. M. Braverman, and D. DiConstanzo. Hypopigmented variant of mycosis fungoides: Demography, histopathology, and treatment of seven cases. J. Am. Acad. Dermatol. 32:987–993, 1995. Lancer, H. A., B. R. Bronstein, H. Nakagawa, A. K. Bhan, and M. C. Mihm. Follicular mucinosis. J. Am. Acad. Dermatol. 10:760–768, 1984. Lindae, M. L., E. A. Abel, R. T. Hoppe, and G. S. Wood. Poikilodermatous mycosis fungoides and atrophic large plaque parapsoriasis exhibit similar abnormalities of T-cell antigen expression. Arch. Dermatol. 124:366–372, 1988. McDonagh, A. J., D. J. Gawkrodger, A. E. Walker, and P. B. Gray. Reticulate pigmentation in mycosis fungoides. Int. J. Dermatol. 30:658–659, 1991. Misch, K. J., J. A. Maclennan, and R. A. Marsden. Hypopigmented mycosis fungoides. Clin. Exp. Dermatol. 12:53–55, 1987. Neuman, K. Blue polka-dots: An unusual presentation of mycosis fungoides. Cutis 33:373–374, 1984. Nickoloff, B. Light microscopic assessment of 100 patients with
978
patch/plaque stage mycosis fungoides. Am. J. Dermatopathol. 10: 469–477, 1988. Peters, M. S., S. N. Thibodeau, J. W. White, and R. A. Winkelmann. Mycosis fungoides in children and adolescents. J. Am. Acad. Dermatol. 22:1011–1018, 1990. Rappaport, H., and L. B. Thomas. Mycosis fungoides. The pathology of extracutaneous involvement. Cancer 34:1198–1229, 1974. Resnick, K. S., and E. C. Vonderheid. Home UV phototherapy of early mycosis fungoides. Long term follow-up observations in 31 patients. J. Am. Acad. Dermatol. 29:73–77, 1993. Rustin, M. H., M. Griffiths, and C. M. Ridley. The immunopathology of hypopigmented mycosis fungoides. Clin. Exp. Dermatol. 11:332–339, 1986. Ryan, E. A., K. V. Sanderson, P. N. Bartak, and P. D. Sammon. Can mycosis fungoides begin in the epidermis? A hypothesis. Br. J. Dermatol. 88:419–429, 1973. Sanchez, J. L., and A. B. Ackerman. The patch stage of mycosis fungoides. Criteria for histologic diagnosis. Dermatol. Clin. 1:5–26, 1979. Sausville, E. A., J. L. Eddy, R. W. Makuch, A. B. Fischmann, G. P. Schechter, M. Matthews, E. Glatstein, D. C. Ihde, F. Kaye, S. R. Veach, R. Phelps, T. O’Conner, J. B. Trepel, J. D. Kotelingam, A. F. Gazzar, J. D. Minna, and P. A. Bunn. Histopathologic staging at initial diagnosis of mycosis fungoides and the Sezary syndrome. Ann. Intern. Med. 109:372–382, 1988. Sézary, A., and Y. Bouvrain. Erythrodermia avec presence de cellules monstreuses uses dans le derme et le sang circulant. Soc. Dermatol. Syphil. 13:254–260, 1938. Sigal, M., M. Grossin, L. LaRoche, F. Basset, G. Aitkin, J. L. Haziza, and S. Belaich. Hypopigmented mycosis fungoides. Clin. Exp. Dermatol. 12:453–454, 1987. Smith, N. P., and P. D. Sammon. Mycosis fungoides presenting with areas of cutaneous hypopigmentation. Clin. Exp. Dermatol. 3:213– 215, 1978. Taswell, H. F., and R. K. Winkelmann. Sezary syndrome — a malignant reticulemic erythroderma. J. Am. Med. Assoc. 177:465–472, 1961. Thomsen, K., and G. L. Wantzin. Lymphomatoid papulosis. A followup study of 30 patients. J. Am. Acad. Dermatol. 17:632–636, 1987. Tuyp, E., A. Borgoyne, T. Aitchison, and R. MacKie. A case-control study of possible causative factors in mycosis fungoides. Arch. Dermatol. 123:196–200, 1987. Volkenandt, M., H. P. Soyer, L. Cerroni, O. M. Koch, J. Atzpodien, and H. Kerl. Molecular detection of clone-specific DNA in hypopigmented lesions of a patient with early evolving mycosis fungoides. Br. J. Dermatol. 28:423–428, 1993. Vonderheid, E. C., E. T. Tan, A. F. Kantor, L. Shrager, B. Micaily, and E. J. Van Scott. Long term efficacy, curative potential, and carcinogenicity of topical mechlorethamine chemotherapy in cutaneous T-cell lymphoma. J. Am. Acad. Dermatol. 20:416–428, 1989. Waisman, M. Lichen aureus. Arch. Dermatol. 112:696–697, 1976. Wantzin, G. L., K. Thomsen, F. Brandrup, and J. K. Larsen. Lymphomatoid papulosis. Development into cutaneous T-cell lymphoma. Arch. Dermatol. 121:792–794, 1985. Whitmore, S. E., E. Simmons-O’Brien, and F. S. Rotter. Hypopigmented mycosis fungoides. Arch. Dermatol. 130:476–480, 1994. Zackheim, H. S., E. H. Epstein, D. A. Grekin, and N. S. McNutt. Mycosis fungoides presenting as areas of hypopigmentation. J. Am. Acad. Dermatol. 6:340–345, 1982. Zackheim, H. S., E. H. Epstein, and W. R. Crain. Topical carmustine (BCNU) for cutaneous T-cell lymphoma: A 15 year experience in 143 patients. J. Am. Acad. Dermatol. 22:802–810, 1992.
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
51
Hypermelanosis Associated with Gastrointestinal Disorders Sections Porphyria Cutanea Tarda Eun Ji Kwon and Victoria P. Werth Cronkhite–Canada Syndrome Eun Ji Kwon, James J. Nordlund, and Victoria P. Werth Hemochromatosis and Hemosiderosis Joerg Albrecht and Victoria P. Werth Primary Biliary Cirrhosis Joerg Albrecht and Victoria P. Werth Inflammatory Bowel Disease and Pigmentation Joerg Albrecht and Victoria P. Werth Pellagra Eun Ji Kwon and Victoria P. Werth Peutz–Jeghers Syndrome Nancy Burton Esterly, Eulalia Baselga, and Beth A. Drolet
Porphyria Cutanea Tarda
“hereditary porphyria” (Gawkrodger, 1994; Harber and Held, 1993).
Eun Ji Kwon and Victoria P. Werth
Epidemiology Introduction The porphyrias are a group of disorders with a defect in biosynthesis of heme, the oxygen carrier in hemoglobin. While numerous types of porphyria exist, porphyria cutanea tarda (PCT) is the most common and characterized by hyperpigmentation of the integument. The term PCT includes several related disorders, all of which are characterized by uroporphyrinogen decarboxylase (URO-D) deficiency and subsequent systemic accumulation of porphyrin by-products of the heme biosynthesis pathway.
Historical Background In a 1911 publication, Günther originally classified PCT as hematoporphyria chronica. Waldenstrom, in 1937, first used the term porphyria cutanea tarda to describe the findings (Bickers and Frank, 2003). Brunsting (1951) further described the condition in a report out of the Mayo Clinic. The enzyme responsible for all types of PCT is URO-D, which was identified in the 1970s. More recently it has been shown that more than one type of PCT exists (Harber and Held, 1993). The association between porphyrins and photosensitivity has been recognized since 1912, when the German physician Meyer-Betz developed severe phototoxic reaction after self-injection with hematoporphyrin (Sarkany, 2001).
Synonyms Porphyria Some of “acquired phyria,” “acquired
cutanea tarda has been given a number of names. these are “symptomatic cutaneous porphyria,” hepatic porphyria,” “cutaneous hepatic por“hepatic porphyria,” “sporadic porphyria,” porphyria,” “symptomatic porphyria,” and
PCT is the most common of the porphyrias. Its exact prevalence is unknown but estimates of 1 in 25 000 in North America to 1 in 5000 in Czechoslovakia have been proposed (Elder, 1990). There is no racial predilection (Gawkrodger, 1994) and the male to female incidence is about equal (Grossman et al., 1979). PCT has been most often seen in males who consumed heavy amounts of alcohol prior to the use of estrogencontaining birth control pills (de Salamanca et al., 1982). Type I, or sporadic PCT, accounts for about 80% whereas type II, or familial PCT, is responsible for the remaining 20% of patients with this disorder (Gawkrodger, 1994). A third type of PCT has been described in four families in Spain (Gawkrodger, 1994). Type II PCT, (familial), presents at any age, including childhood, whereas the more common type I PCT (sporadic) most often begins in middle age (Gawkrodger, 1994).
Clinical Findings PCT is a photosensitivity disorder in which the most characteristic findings are noted on the exposed skin. Most often a subtle increased skin fragility is noted especially on the dorsal aspects of the hands, although the feet can also be involved (Harber and Held, 1993; Bickers and Frank, 2003). Vesicles and bullae develop on areas of sun exposure and repeated trauma. They frequently rupture and become infected (Figs 51.1 and 51.2). Healing is slow, with scarring, thickening of the skin, and milia formation (Hurley, 1992). Mottled areas of reddish to purple discoloration may remain (Harber and Held, 1993). Pigmentary changes are characteristic clinical signs of PCT (see Fig. 51.3). More frequently in females the face may have 979
CHAPTER 51
Fig. 51.1. Hyperpigmentation and scars on the dorsum of the hand.
Fig. 51.3. Hyperpigmentation and hypertrichosis of the face (see also Plate 51.1, pp. 494–495).
sun-exposed surfaces. These lesions present as yellow to white, waxy, indurated plaques that clinically and histologically resemble morphea or scleroderma (Bickers and Frank, 1993). Calcium may be deposited within these plaques (Harber and Held, 1993).
Associated Disorders
Fig. 51.2. Blister and hyperpigmentation.
a melasmalike periocular mottled dyspigmentation (Harber and Held, 1993). Individuals with PCT usually develop a photodistributed and sometimes widespread brown hyperpigmentation (Harber and Held, 1993). The “tan” may persist into the winter months, and this hyperpigmentation may indicate a flare in disease activity (Held et al., 1989). Rarely the hyperpigmentation may involve only the lower extremities (Held et al., 1989). Other cutaneous findings associated with PCT include hypertrichosis, which is most apparent along the temples and cheeks (Fig. 51.3) (Bickers and Frank, 2003). The pathogenesis of the hypertrichosis is unknown and androgen levels are reported to be normal (Bickers and Frank, 2003). Some patients present with a reddish-purple heliotrope-like coloration of the central face, which may be most prominent periorbitally. Scarring alopecia and onycholysis are other cutaneous findings (Grossman and Poh-Fitzpatrick, 1986). Fluorescence of the teeth and erythrocytes may be noted in some patients (Lim and Poh-Fitzpatrick, 1984). Sclerodermoid plaques have been noted in patients with PCT and they can involve both sun-exposed and non– 980
Iron overload with elevated plasma iron levels can occur in a third to half of individuals with PCT. Increased amounts of iron identified by staining is present in Kupffer cells and hepatocytes (Grossman et al., 1979). Ferrokinetic studies in these individuals have been shown to be normal (Bickers and Frank, 2003). There are numerous hypotheses that suggest a role for iron in the pathogenesis of PCT. However, the mechanism for the development of porphyria and the role of iron remain unclear (Bickers and Frank, 2003). Recent evidence demonstrates an association between PCT and mutations in the hereditary hemochromatosis gene HFE (hemochromatosis, ferrum/iron). Prevalence of the hemochromatosis C282Y mutation in the HFE gene has been found to be increased among British patients with sporadic PCT and North American sporadic and familial PCT patients (Bulaj et al., 2000; Roberts et al., 1997). PCT patients with homozygous genotype for the C282Y mutation have considerably higher iron overload than those heterozygous for the mutation or without the mutation (Bulaj et al., 2000). Homozygosity for the C282Y HFE mutation is a significant susceptibility factor in sporadic and familial PCT, whereas heterozygosity has less effect on the development of PCT (Brady et al., 2000; Bulaj et al., 2000). Increased prevalence of a second milder mutation of the HFE gene, H63D, was found among southern European PCT patients (Sampietro et al., 1998). The role of this mutation in PCT pathogenesis is uncertain. Association between PCT and hepatitis C infection has been made in recent years. Approximately 50% of PCT patients worldwide are infected with HCV (Gisbert et al., 2003), but there is considerable geographical variation in this association. The exact role of HCV infection in PCT is unclear.
HYPERMELANOSIS ASSOCIATED WITH GASTROINTESTINAL DISORDERS
With genotyping at the HFE locus now available through diagnostic laboratories, screening PCT patients for HFE mutations and hepatitis C infection may be useful for early treatment of these PCT-associated conditions. Avoidance of alcohol and estrogen should be encouraged (Bonkovsky et al., 1998; Bulaj et al., 2000; Mendez et al., 1998). Abnormal glucose tolerance tests have been reported in 25–50% of patients with PCT, a third of whom require treatment (Bickers and Frank, 2003; Grossman et al., 1979). Association between HIV and PCT has been described (Cohen et al., 1990; Drobacheff et al., 1998; Gafa et al., 1992; Wissel et al., 1987). PCT has also been associated with benign and malignant hepatic tumors (Gawkrodger, 1994; Grossman and Poh-Fitzpatrick, 1986). Associations with subacute cutaneous and systemic lupus erythematosus, hemodialysis, and Klinefelter syndrome have also been described (Callen and Ross, 1981; Epstein et al., 1973; Kelly, 1992).
Histology Routine staining of a PCT blister generally reveals a noninflammatory subepidermal separation in which the dermal papillae often extend irregularly from the blister floor into the blister cavity. This is termed festooning but is not specific for PCT. Superficial perivascular homogeneous, pale, eosinophilic deposits are noted. PAS staining is recommended because it may reveal thickening of the basement membrane zone around capillaries. In areas of sclerosis the collagen bundles are thickened (Lever and Schaumburg-Lever, 1990). Histology of the hyperpigmented skin has been studied carefully. Hyperpigmented skin tends to have increased epidermal melanin deposits, but no specific or diagnostic changes for PCT. None of the skin biopsies showed fluorescence due to porphyrin or significant hemosiderosis (Tsega et al., 1980). Pigmentary incontinence is not a feature of PCT. Some electron micrograph studies found a tendency for dispersion of single, larger melanosomes. This pattern is similar to black or tanned skin. This is unusual for light-colored skin, which has usually smaller melanosomes dispersed in groups in keratinocytes (Konrad and Wolff, 1973) (see Chapters 27 and 28 on normal and abnormal color of skin). However, other studies have not supported this finding (Held et al., 1989). Direct immunofluorescence often reveals positive staining of IgG and complement in the blood vessel wall and the basement membrane zone. This is thought to result from trapping of this material rather than by immunological mechanisms (Lever and Schaumburg-Lever, 1990).
Laboratory Findings Elevated iron stores and abnormal glucose tolerance test are frequently observed in PCT patients. Occasionally erythrocytosis and cryoglobulinemia are also noted (Bickers and Frank, 2003). Wood’s lamp examination of urine may reveal a characteristic pinkish-red fluorescence due to excretion of increased levels of uroporphyrin (Bickers and Frank, 2003). The porphyrin pattern in PCT has three main features: (1) increased urinary excretion of 8, 7, 6, 5, and 4-carboxy por-
phyrins; (2) a distinctive pattern of excretion of isomer series I and III; and (3) increased fecal excretion of isocoproporphyrin (Harber and Held, 1993). The ratio of uroporphyrin to coproporphyrin in urine is usually greater than 3 to 1 (Bickers and Frank, 2003).
Criteria for Diagnosis PCT diagnosis is suspected due to the presence of the abovementioned typical clinical signs and symptoms. Wood’s light examination of the urine supports these findings. The definitive diagnosis of PCT is confirmed, however, by examination of the porphyrin excretion profile (Harber and Held, 1993).
Differential Diagnosis The differential diagnosis of PCT includes variegate porphyria, pseudoporphyria, hepatoerythropoietic porphyria, hereditary coproporphyria, porphyrin secreting hepatic tumors, and epidermolysis bullosa acquisita. Other conditions which can be confused with PCT are hydroa aestivale, hydroa vacciniforme, scleroderma, morphea, neurotic excoriations, polymorphous light eruption, pemphigus vulgaris, and bullous pemphigoid (Bickers and Frank, 2003; Harber and Held, 1993). Some medications cause fragility of sun-exposed skin. Rarely widespread hyperpigmentation may resemble Addison disease (see Chapter 50) or hemochromatosis (Grossman and Poh-Fitzpatrick, 1986).
Pathogenesis The enzyme responsible for all types of PCT is URO-D. In type I (sporadic) PCT, extrahepatic URO-D levels are normal, but hepatic levels are decreased (Bickers and Frank, 2003). There is no family history of the disorder. Type I PCT is frequently precipitated by environmental factors such as alcohol, estrogens, iron, and polyhalogenated cyclic hydrocarbons (Gawkrodger, 1994). Although alcohol and estrogens appear to trigger PCT in 80% of the cases with type I disorder, the exact mechanism by which these agents cause PCT is not known (Elder, 1990). Acute and chronic alcohol ingestion has been shown to decrease activity of URO-D and ethanol stimulates hepatic aminolevulinic acid (ALA) synthase in PCT patients (Bickers and Frank, 2003; McColl et al., 1981). Also, chronic alcoholism results in increased iron absorption, possibly associated with inherited HFE mutations mentioned above (Bickers and Frank, 2003). Ferrous ions have been shown in vitro to inhibit URO-D activity (Kushner et al., 1972, 1975). It has been suggested that estrogens and chlorinated hydrocarbons (e.g., hexachlorobenzene), acting in a manner similar to that of ferrous ions, inhibit URO-D activity (Bickers and Frank, 2003; Grossman and Poh-Fitzpatrick, 1986). In Type II (familial) PCT, the mode of transmission is autosomal dominant. However, penetrance of type II PCT is low (approximately 20%), and most individuals with inherited defects in URO-D do not develop PCT (Bickers and Frank, 2003; Gawkrodger, 1994). In contrast to type I PCT, there is a reduction in both hepatic and extrahepatic URO-D activity 981
CHAPTER 51
in type II PCT (Gawkrodger, 1994). Like sporadic PCT, decreased URO-D activity is confined to the liver in type III PCT. However, type III PCT is characterized by positive family history (Held et al., 1989). In PCT uroporphyrins and 7-carboxyl porphyrins have been shown to accumulate in the skin (Bickers and Frank, 2003; Grossman and Poh-Fitzpatrick, 1986), but porphyrin may also be synthesized in the skin (Bickers et al., 1977). These cutaneous porphyrins absorb light energy maximally in the Soret band (400–410 nm), which penetrates the epidermis. The absorbed energy is transferred to surrounding molecules and results in hydrogen peroxide or lipid peroxide (Grossman and Poh-Fitzpatrick, 1986). The peroxides damage cellular membranes and disrupt their integrity. This leads to the release of secondary mediators. Repeated insults eventually lead to the chronic skin changes. However, the pathophysiology of the hypertrichosis, sclerodermalike changes, skin fragility, and pigmentation abnormalities are not well understood. Some data have suggested that uroporphyrin I, a porphyrin upregulated in PCT via downstream URO-D deficiency, may contribute to sclerodermalike skin changes because it stimulates collagen synthesis in human fibroblasts (Bickers and Frank, 2003; Grossman and Poh-Fitzpatrick, 1986; Held et al., 1989).
the depletion of excess iron stores often seen in PCT. Depletion of iron may produce improvement in the clinical signs and symptoms by decreasing ALA synthase activity and porphyrin synthesis, reducing inhibition of URO-D activity, lowering iron-overload induced hepatic lipid peroxidation, and minimizing the oxidation of the uroporphyrinogen substrate to nonmetabolizable porphyrins (Bickers and Frank, 2003). In patients where phlebotomy is contraindicated, chloroquine can be used. Chloroquine appears to form a watersoluble complex with porphyrin, thus allowing for excretion (Grossman and Poh-Fitzpatrick, 1986). A recent study indicates PCT patients homozygous for the C282Y HFE mutation respond poorly to chloroquine treatment, while C282Y heterozygosity and compound heterozygosity (C282Y/H63D) do not lessen therapeutic response to chloroquine (Stolzel et al., 2003). Other treatments which have been used include plasmapheresis, cholestyramine, iron chelators, and activated charcoal (Grossman and Poh-Fitzpatrick, 1986; Grossman et al., 1979; Miyauchi et al., 1983). Coexisting HCV and/or HIV infection should be managed appropriately. Treatment with highly active antiretroviral therapy (HAART) alone caused resolution of PCT lesions in a case report of a PCT patient with AIDS and HCV infection (Rich et al., 1999).
Animal Models A zebrafish model with homozygous mutation in the URO-D gene shows a photosensitive porphyria syndrome which can be reversed by transient and germline expression of the wildtype URO-D allele (Wang et al., 1998). Type I PCT has been induced in iron-loaded mice exposed to hexachlorobenzene (Smith and Francis, 1983). Using homologous recombination, Phillips et al. (2001) produced mice with disruption of one allele of the URO-D gene. Increased hepatic porphyrins and hepatic URO-D activity reduction was seen upon treating the URO-D+/- mice with iron-dextran and d-ALA. By breeding HFE-/- mice with URO-D+/- mice, the same authors generated mice heterozygous URO-D and homozygous null HFE genotype. These animals showed PCT-like phenotype without ALA supplementation and dramatically decreased URO-D activity, suggesting HFE-mutation-induced iron overload alone can reduce URO-D activity in URO-D heterozygous mice (Phillips et al., 2001).
Treatment Identification and avoidance of precipitating factors such as alcohol, estrogen, and iron, along with sun avoidance and use of sunscreens, are general measures which should be included in the treatment of PCT (Gawkrodger, 1994). Removal of environmental precipitants alone can result in a slow improvement of the clinical features (Grossman and Poh-Fitzpatrick, 1986). However, most PCT patients receive repeated phlebotomy and oral antimalarials to treat the disease (Bickers and Frank, 2003). Phlebotomy is a widely used and safe procedure for these patients. The efficacy of phlebotomy has been attributed to 982
Prognosis The prognosis of patients with PCT is dependent on treatment and any underlying associated condition (hepatic cancer, HIV, HCV, diabetes, etc.). The pigment disorder slowly clears with treatment with marked improvement after 18–24 months (Grossman et al., 1979).
References Bickers, D. R., and J. Frank. The porphyrias. In: Fitzpatrick’s Dermatology in General Medicine, 6th ed., I. M. Freedberg, A. Z. Eisen, K. Wolff, K. F. Austen, L. A. Goldsmith, and S. Katz (eds). New York: McGraw Hill, Inc., 2003, pp. 1435–1466. Bickers, D. R., L. Keogh, A. B. Rifkind, L. C. Harber, and A. Kappas. Studies in porphyria. VI. Biosynthesis of porphyrins in mammalian skin and in the skin of porphyric patients. J. Invest. Dermatol. 68:5–9, 1977. Bonkovsky, H. L., M. Poh-Fitzpatrick, N. Pimstone, J. Obando, A. Di Bisceglie, C. Tattrie, K. Tortorelli, P. LeClair, M. G. Mercurio, and R. W. Lambrecht. Porphyria cutanea tarda, hepatitis C, and HFE gene mutations in North America. Hepatology 27:1661–1669, 1998. Brady, J. J., H. A. Jackson, A. G. Roberts, R. R. Morgan, S. D. Whatley, G. L. Rowlands, C. Darby, E. Shudell, R. Watson, J. Paiker, M. W. Worwood, and G. H. Elder. Co-inheritance of mutations in the uroporphyrinogen decarboxylase and hemochromatosis genes accelerates the onset of porphyria cutanea tarda. J. Invest. Dermatol. 115:868–874, 2000. Brunsting, L. A., H. L. Mason, and R. A. Aldrich. Adult form of chronic porphyria with cutaneous manifestations. J. Am. Med. Assoc. 146:1207–1212, 1951. Bulaj, Z. J., J. D. Phillips, R. S. Ajioka, M. R. Franklin, L. M. Griffen, D. J. Guinee, C. Q. Edwards, and J. P. Kushner. Hemochromatosis genes and other factors contributing to the pathogenesis of porphyria cutanea tarda. Blood 95:1565–1571, 2000.
HYPERMELANOSIS ASSOCIATED WITH GASTROINTESTINAL DISORDERS Callen, J. P., and L. Ross. Subacute cutaneous lupus erythematosus and porphyria cutanea tarda. J. Am. Acad. Dermatol. 5:269–273, 1981. Cohen, P. R., S. M. Suarez, and V. A. DeLeo. Porphyria cutanea tarda in human immunodeficiency virus-infected patients. J. Am. Med. Assoc. 264:1315–1316, 1990. de Salamanca, R. E., D. Mingo, S. Chinarro, J. J. Munoz, and J. Perpina. Porphyrin-excretion in female estrogen-induced porphyria cutanea tarda. Arch. Dermatol. Res. 274:179–184, 1982. Drobacheff, C., C. Derancourt, H. Van Landuyt, D. Devred, B. de Wazieres, B. Cribier, D. Rey, J. M. Lang, C. Grosieux, B. Kalis, and R. Laurent. Porphyria cutanea tarda associated with human immunodeficiency virus infection. Eur. J. Dermatol. 8:492–496, 1998. Elder, G. H. Porphyria cutanea tarda: A multifactorial disease. In: Recent Advances in Dermatology, vol. 8, R. H. Champion, and R. J. Pye (eds). Edinburgh: Churchill Livingstone, 1990, pp. 55–69. Epstein, J. H., D. L. Tuffanelli, and W. L. Epstein. Cutaneous changes in the porphyrias. Arch. Dermatol. 107:689–698, 1973. Gafa S., A. Zannini, and C. Gabrielli. Porphyria cutanea tarda and HIV infection: effect of zidovudine treatment on a patient. Infection 20:373–374, 1992. Gawkrodger, D. J. The porphyrias. In: Textbook of Dermatology, 5th ed., A. Rook, D. S. Wilkinson, and F. J. G. Ebling (eds). Cambridge: Blackwell Scientific Publications, Inc., 1994, pp. 2304–2308. Gisbert, J. P., L. Garcia-Buey, J. M. Pajares, and R. Moreno-Otero. Prevalence of hepatitis C virus infection in porphyria cutanea tarda: systematic review and meta-analysis. Hepatology 39:620–627, 2003. Grossman, M. E., and M. B. Poh-Fitzpatrick. Porphyria cutanea tarda. Dermatol. Clin. 4:297–309, 1986. Grossman, M. E., D. R. Bickers, M. B. Poh-Fitzpatrick, V. A. Deleo, and B. C. Harber. Porphyria cutanea tarda. Am. J. Med. 67:277–286, 1979. Harber, L. C., and J. L. Held. Porphyria cutanea tarda. In: Clinical Dermatology, 20th ed., D. J. Demis (ed.). Philadelphia: JB Lippincott, 1993, pp. 1–13. Held, J. L., D. N. Silvers, and M. E. Grossman. Hyperpigmentation of the lower extremities associated with porphyria cutanea tarda. Arch. Dermatol. 125:297–298, 1989. Hurley, H. J. The porphyrias. In: Dermatology, 3rd ed., S. L. Moschella, and H. J. Hurley (eds). Philadelphia: WB Saunders, 1992, pp. 1667–1681. Kelly, W. N. Textbook of Internal Medicine, 2nd ed. Philadelphia: JB Lippincott, 1992. Konrad, K., and K. Wolff. Hyperpigmentation, melanosome size, and distribution patterns of melanosomes. Arch. Dermatol. 107:853– 860, 1973. Kushner, J. P., G. R. Lee, and S. Nacht. The role of iron in the pathogenesis of porphyria cutanea tarda. J. Clin. Invest. 51:3044–3051, 1972. Kushner, J. P., D. P. Steinmuller, and G. R. Lee. The role of iron in the pathogenesis of porphyria cutanea tarda. J. Clin. Invest. 56:661– 667, 1975. Lever, W. F., and G. Schaumburg-Lever. Histopathology of the Skin, 7th ed. Philadelphia: JB Lippincott, 1990. Lim, H. W., and M. B. Poh-Fitzpatrick. Hepatoerythropoietic porphyria: A variant of childhood-onset porphyria cutanea tarda. J. Am. Acad. Dermatol. 11:1103–1111, 1984. McColl, K. E., M. R. Moore, G. G. Thompson, and A. Goldberg. Abnormal haem biosynthesis in chronic alcoholics. Eur. J. Clin. Invest. 11:461–468, 1981. Mendez, M., L. Sorkin, M. V. Rossetti, K. H. Astrin, A. M. del C. Batlle, V. E. Parera, G. Aizencang, and R. J. Desnick. Familial porphyria cutanea tarda: characterization of seven novel uroporphyrinogen decarboxylase mutations and frequency of common hemochromatosis alleles. Am. J. Hum. Genet. 63:1363– 1375, 1998.
Miyauchi, S., S. Shiraishi, and Y. Miki. Small volume plasmapheresis in the management of porphyria cutanea tarda. Arch. Dermatol. 119:752–755, 1983. Phillips, J. D., L. K. Jackson, M. Bunting, M. R. Franklin, K. R. Thomas, J. E. Levy, N. C. Andrews, and J. P. Kushner. A mouse model of familial porphyria cutanea tarda. Proc. Natl. Acad. Sci. U. S. A. 98:259–264, 2001. Rich, J. D., E. Mylonakis, R. Nossa, and R. M. Chapnick. Highly active antiretroviral therapy leading to resolution of porphyria cutanea tarda in a patient with AIDS and hepatitis C. Dig. Dis. Sci. 44:1034–1037, 1999. Roberts, A. G., S. D. Whatley, R. R. Morgan, M. Worwood, and G. H. Elder. Increased frequency of the haemochromatosis Cys282Tyr mutation in sporadic porphyria cutanea tarda. Lancet 349:321– 323, 1997. Sampietro, M., A. Piperno, L. Lupica, C. Arosio, A. Vergani, N. Corbetta, I. Malosio, M. Mattioli, A. L. Fracanzani, M. D. Cappellini, G. Fiorelli, and S. Fargion. High prevalence of the His63Asp HFE mutation in Italian patients with porphyria cutanea tarda. Hepatology 27:181–184, 1998. Sarkany, R. P. E. The management of porphyria cutanea tarda. Clin. Exp. Dermatol. 26:225–232, 2001. Smith, A. G., and J. E. Francis. Synergism of iron and hexachlorobenzene inhibits hepatic uroporphyrinogen decarboxylase in inbred mice. Biochem. J. 214:909–913, 1983. Stolzel, U., E. Kostler, D. Schuppan, M. Richter, U. Wollina, M. O. Doss, C. Wittekind, and A. Tannapfel. Hemochromatosis (HFE) gene mutations and response to chloroquine in porphyria cutanea tarda. Arch. Dermatol. 139:309–313, 2003. Tsega, E., B. Damtew, J. W. Landells, A. Besrat, and E. Seyoum. Hyperpigmentation of the face and hands without blisters: porphyria cutanea tarda. Br. J. Dermatol. 103:187–190, 1980. Wang, H., Q. Long, S. D. Marty, S. Sassa, and S. Lin. A zebrafish model for hepatoerythropoietic porphyria. Nat. Genet. 20:239–243, 1998. Wissel, P. S., P. Sordillo, K. E. Anderson, S. Sassa, R. L. Savillo, and A. Kappas. Porphyria cutanea tarda associated with the acquired immune deficiency syndrome. Am. J. Hematol. 25:107–113, 1987.
Cronkhite–Canada Syndrome Eun Ji Kwon, James J. Nordlund, and Victoria P. Werth
Historical Background In 1955 Cronkhite and Canada presented two women with debilitating diarrhea, generalized hair loss, hyperpigmentation of the skin, and onychotrophia. The backs of the hands, fingers, and the body folds were especially pigmented although there was melanin deposition in the oral cavity and much of the integument. The second patient was thought also to have vitiligo. Both patients had polyposis of the intestinal tract (Cronkhite and Canada, 1955).
Synonyms Intestinal polyposis with hyperpigmentation; intestinal polyposis with nail loss
Epidemiology Cronkhite–Canada syndrome is a rare disorder which was first described by Cronkhite and Canada in 1955. As of 2002, only 467 cases have been reported worldwide, with approximately 75% of cases reported from Japan (Goto, 1995; Takakura et al., 2004). The reason for this distribution is not known. The 983
CHAPTER 51
Fig. 51.4. Total alopecia and diffuse hyperpigmentation. (Courtesy of Dr. J. Bazex.)
Fig. 51.5. Extensive hyperpigmentation of the trunk and hands with nail changes (see also Plate 51.2, pp. 494–495). (Courtesy of Dr. J. Bazex.)
estimated male to female ratio is 3:2, with a mean age at onset of 59 years (Daniel et al., 1982). Most cases are sporadic and there seems to be no familial or genetic basis for this syndrome.
1987; Allbritton et al., 1998; Bianchi et al., 1984; Bruce et al., 1999; Casalnuovo et al., 1991; Cronkhite and Canada, 1955; Goto, 1994, 1995; Herzberg and Kaplan, 1990; Lin et al., 1987; Pal et al., 1990). The cause of this pigmentation is not known. There is an increased amount of melanin in the epidermis (Herzberg and Kaplan, 1990; Ortonne et al., 1985), although dermal melanosis has also been described (Ortonne et al., 1985). In one case, the pigmentation began on the pelvic girdle but rapidly spread to other parts of the skin, but in other patients patchy vitiligo has also been reported (Cronkhite and Canada, 1955). Dyspigmentation may persist or resolve after therapy or spontaneously (Daniel et al., 1982).
Clinical Features The main feature is the development of polyps that form throughout the intestinal tract and affecting the mucosa of the stomach, the small and large bowel (Shibuya, 1972). Most of the original cases were adults, although children with intestinal polyposis have been described (Kucukaydin et al., 1992; Scharf et al., 1986). Adults in the ninth decade of life who developed this syndrome have been described (Jones and Paone, 1984). The patient presents with watery diarrhea, protein-losing enteropathy, malnutrition, electrolyte unbalance, hypogeusia, and weight loss. The diarrhea and malabsorption are caused by the loss of fluid from the polyps (Harned et al., 1995; Jenkins et al., 1985). There are many cutaneous manifestations of this syndrome. Patchy hair loss that progresses to almost complete alopecia is common (Fig. 51.4) (Aanestad et al., 1987; Allbritton et al., 1998; Bianchi et al., 1984; Bruce et al., 1999; Casalnuovo et al., 1991; Cronkhite and Canada, 1955; Goto, 1994, 1995; Ortonne et al., 1985; Takakura et al., 2004). The eyebrows, eye lashes, and other body hair can be lost. The hair loss might be due to anagen effluvium. The fingernails and toenails become thin and brittle and later are shed from the ends of the fingers and toes (Fig. 51.5). Subepidermal blisters, keratoacanthoma, and oral erosions also have been observed. Acquired ichthyosis, purpura and ecchymoses, psoriasiform plaques and pruritus all have been observed in the Cronkhite–Canada syndrome (Bianchi et al., 1984). Hair and nail regrowth may occur after treatment, during remission, or spontaneously despite continued active disease (Daniel et al., 1982). A common feature is diffuse distribution of hyperpigmented light-to-dark brownish macules and patches affecting all parts of the integument (see Figs 51.4 and 51.5) (Aanestad et al., 984
Associated Disorders A number of other disorders have been described in association with this syndrome. They include lupus erythematosus (Kubo et al., 1986), hypothyroidism (Pal et al., 1990), tuberculosis (Lin et al., 1987), cataracts (Hutnik and Nichols, 1998; Simcock et al., 1996), portal thrombosis with high titer of antinuclear antibodies and membranous glomerulonephritis (Takeuchi et al., 2003), and zinc deficiency-related taste disturbances (Yoshida and Tomita, 2002). Although gastric and colorectal cancers have been reported among patients with Canada–Cronkhite syndrome (Egawa et al., 2000; Goto and Shimokawa, 1994; Katayama et al., 1985; Malhotra and Sheffield, 1988; Murai et al., 1993; Nagata et al., 2003; Nakatsubo et al., 1997; Rappaport et al., 1986; Satoh et al., 2000; Takeuchi et al., 2003; Watanabe et al., 1999; Yamaguchi et al., 2001), whether Canada–Cronkhite polyps carry malignant potential remains controversial.
Histology The epidermis of the pigmented skin is usually slightly thickened with compact hyperkeratosis and has increased amounts of melanin with normal or slightly increased numbers of melanocytes (Herzberg and Kaplan, 1990; Ortonne et al., 1985). By electron microscopy the melanocytes appear to be activated and have increased melanogenic activity. The
HYPERMELANOSIS ASSOCIATED WITH GASTROINTESTINAL DISORDERS
epidermis may also be atrophic, with only a few hair follicles (Kindblom et al., 1977; Jarnum and Jensen, 1966) and hair shaft miniaturization, as well as follicular dilatation and extensive glycosaminoglycan deposits in the reticular dermis (Allbritton et al., 1998). In the dermis melanophages and some perivascular mononuclear cell infiltrate can be found.
et al., 1993; Scharf et al., 1986, Takakura et al., 2004), but to date the treatment is still empirical.
Prognosis
Radiological or endoscopic examination of the intestinal tract including the stomach, small and large intestines, and the rectum will demonstrate the presence of diffuse polyposis (Harned et al., 1995; Rossi et al., 1981). These changes may cause abnormal gastrointestinal absorption. Patients with serious disease may demonstrate mild to moderate anemia, electrolyte disturbances, and a decrease in total serum protein (Daniel et al., 1982).
Canada–Cronkhite syndrome has traditionally carried a poor prognosis (Canada and Cronkhite, 1955). However, nutritional therapy has been reported to achieve remission for more than 5 years (Daniel et al., 1982), but complete remission with medical treatment is rare (Ward et al., 2002). Surgical treatment is also not universally successful and the longest reported survival after surgical treatment is 15–17.5 years (Daniel et al., 1982). The major causes of death include gastrointestinal bleeding, intussusception, gastrointestinal prolapse, thromboembolic episodes, malnutrition, and massive fluid, protein, and electrolyte losses (Daniel et al., 1982). In some patients the disease is associated with neoplasms in the intestinal tract (Murai et al., 1993) or other organs.
Criteria for Diagnosis
References
Laboratory Findings
The association of diffuse polyposis, protein-losing enteropathy, loss of nails and/or hair with or without hyperpigmentation establishes the diagnosis.
Differential Diagnosis The differential diagnosis includes all syndromes characterized by intestinal polyps (Finan and Ray, 1989; Harned et al., 1995). These include the Peutz–Jeghers syndrome (see later), Gardner syndrome, Bannayan–Riley–Ruvalcaba syndrome, and the Ruvalcaba–Myhre–Smith syndrome.
Pathophysiology The etiology of the disease is unclear. So far no consistent inheritance pattern has been observed. In Japan mental stress and physical fatigue have been identified as important risk factors (Goto, 1995). Reports of patients with antinuclear antibodies (Murata et al., 2000; Takeuchi et al., 2003) and positive response to corticosteroids in many cases suggest an underlying immunological abnormality in the pathogenesis of Canada–Cronkhite syndrome (Canada and Cronkhite, 1955; Daniel et al., 1982). In their first description Cronkhite and Canada attributed the cutaneous changes to severe malnutrition secondary to diarrhea and malabsorption. However, cutaneous changes may precede the gastrointestinal manifestations and may develop independently of gastrointestinal disease activity (Daniel et al., 1982).
Treatment Currently there are no specific therapies for the hyperpigmentation. The bowel disease has been treated surgically. A multitude of medical treatments have been used in Cronkhite–Canada syndrome, including corticosteroids, anabolic steroids, antibiotics, and H1- and H2-receptor blockers, antiplasmin and mesalazine as well as nutritional supplementation (Allbritton et al., 1998; Casalnuovo et al., 1991; Canada and Cronkhite, 1955; Daniel et al., 1982; Jones and Paone, 1984; Kaneko et al., 1991; Kubo et al., 1986; Murai
Aanestad, O., N. Raknerud, S. T. Aase, and G. Narverud. The Cronkhite-Canada syndrome: Case report. Acta. Chirurg. Scand. 153:143–145, 1987. Allbritton, J., E. Simmons-O’Brien, D. Hutcheons, and S. E. Whitmore. Cronkhite-Canada Syndrome: report of two cases, biopsy findings in the associated alopecia, and a new treatment option. Cutis 61:229–232, 1998. Bianchi, C. A., A. Garcia Garcia, and O. Stringa. [Cutaneous manifestations of the malabsorption syndrome]. Med. Cutanea IberoLat-Am. 12:227–235, 1984. Bruce, A., S. N. Ng, H. C Wolfsen, R. C. Smallfridge, and D. P. Lookingbill. Cutaneous clues to Cronkhite-Canada syndrome: a case report. Arch. Dermatol. 135:212, 1999. Casalnuovo, C., M. Ghigliani, A. Avagnina, B. Elsner, and G. Palau. [Cronkhite-Canada syndrome: Report of a case]. Medicina (B. Aires) 51:155–160, 1991. Cronkhite, L. S., and W. J. Canada. Generalized intestinal polyposis: an unusual syndrome of polyposis, pigmentation, alopecia and onychotrophia. N. Engl. J. Med. 252:1011–1015, 1955. Daniel, E. S., S. L. Ludwig, K. J. Lewin, R. M. Ruprecht, G. M. Rajacich, and A. D. Schwabe. The Cronkhite-Canada Syndrome: an analysis of clinical and pathologic features and therapy in 55 patients. Medicine. 61:293–309, 1982. Egawa, T., T. Kubota, Y. Otani, N. Kurihara, S. Abe, M. Kimata, J. Tokuyama, N. Wada, K. Suganuma, Y. Kuwano, K. Kumai, Y. Sugino, M. Mukai, and M. Kitajima. Surgically treated CronkhiteCanada syndrome associated with gastric cancer. Gastric Cancer 3:156–160, 2000. Finan, M. C., and M. K. Ray. Gastrointestinal polyposis syndromes. Dermatol. Clin. 7:419–434, 1989. Goto, A. [Cronkhite-Canada syndrome]. Nippon Rinsho Suppl 6:23–26, 1994. Goto, A. Cronkhite-Canada syndrome: epidemiological study of 110 cases reported in Japan. Nippon Geka Hokan 64:3–14, 1995. Goto, A., and K. Shimokawa. Cronkhite-Canada syndrome associated with lesions predisposing to development of carcinoma. J. Jpn. Soc. Cancer Ther. 29: 1767–77, 1994. Harned, R. K., J. L. Buck, and L. H. Sobin. The hamartomatous polyposis syndromes: clinical and radiologic features. Am. J. Roentgenol. 164:565–571, 1995. Herzberg, A. J., and D. L. Kaplan. Cronkhite–Canada syndrome: Light and electron microscopy of the cutaneous pigmentary abnormalities. Int. J. Dermatol. 29:121–125, 1990.
985
CHAPTER 51 Hutnik, C. M., and B. D. Nichols. Cataracts in systemic diseases and syndromes. Curr. Opin. Ophthalmol. 9:14–19, 1998. Jarnum, S., and H. Jensen. Diffuse gastrointestinal polyposis with ectodermal changes. Gastroenterology 50: 107–118, 1966. Jenkins, D., P. M. Stephenson, and B. B. Scott. The Cronkhite-Canada syndrome: an ultrastructural study of pathogenesis. J. Clin. Pathol. 38:271–276, 1985. Jones, A. F., and D. B. Paone. Canada-Cronkhite syndrome in an 82year-old woman. Am. J. Med. 77:555–557, 1984. Kaneko, Y., H. Kato, Y. Tachimori, H. Watanabe, K. Ushio, H. Yamaguchi, M. Itabashi, and M. Noguchi. Triple carcinomas in Cronkhite-Canada syndrome. Jpn. J. Clin. Oncol. 21:194–202, 1991. Katayama, Y., M. Kimura, and M. Konn. Cronkhite-Canada syndrome associated with a rectal cancer and adenomatous changes in colonic polyps. Am. J. Surg. Pathol. 9:65–71, 1985. Kindblom, L. G., L. Angervall, B. Santesson, and S. Selander. Cronkhite-Canada syndrome. Cancer 39:2651–2657, 1977. Kubo, T., S. Hirose, S. Aoki, T. Kaji, and M. Kitagawa. CanadaCronkhite syndrome associated with systemic lupus erythematosus. Arch. Intern. Med. 146:995–996, 1986. Kucukaydin, M., T. E. Patiroglu, H. Okur, and M. Icer. Infantile Cronkhite-Canada syndrome? Case report. Eur. J. Pediatr. Surg. 2:295–297, 1992. Lin, H. J., Y. T. Tsai, S. D. Lee, K. H. Lai, W. W. Ng, T. N. Tam, H. C. Lin, L. B. Liou, and S. H. Tsay. The Cronkhite-Canada syndrome with focus on immunity and infection: Report of a case. J. Clin. Gastroenterol. 9:568–570, 1987. Malhotra, R., and A. Sheffield. Cronkhite-Canada syndrome associated with colon carcinoma and adenomatous changes in C-C polyps. Am. J. Gastroenterol. 83:772–776, 1988. Murai, N., T. Fukuzaki, T. Nakamura, H. Hayashida, M. Okazaki, K. Fujimoto, and T. Hirai. Cronkhite-Canada syndrome associated with colon cancer: report of a case. Surg. Today 23:825–829, 1993. Murata, I., I. Yoshikawa, M. Endo, M. Tai, C. Toyoda, S. Abe, Y. Hirano, and M. Otsuki. Cronkhite-Canada syndrome: report of two cases. J. Gastroenterol. 35: 706–11, 2000. Nagata, J., H. Kijima, K. Hasumi, T. Suzuki, T. Shirai, and T. Mine. Adenocarcinoma and multiple adenomas of the large intestine, associated with Cronkhite-Canada syndrome. Dig. Liver Dis. 35:434–438, 2003. Nakatsubo, N., R. Wakasa, K. Kiyosaki, K. Matsui, and F. Konishi. Cronkhite-Canada syndrome associated with carcinoma of the sigmoid colon: report of a case. Surg. Today 27:345–348, 1997. Ortonne, J. P., J. Bazex, and P. Berbis. [Cronkhite-Canada disease. Discussion apropos of a case and study of the pigmentation]. Ann. Dermatol. Venereol. 112:951–958, 1985. Pal, A., S. Sen, S. Ghosh, R. Sarkar, and K. N. Jalan. CronkhiteCanada syndrome with hypothyroidism. Indian J. Gastroenterol. 9:229–230, 1990. Rappaport, L. B., H. V. Sperling, and A. Stavrides. Colon cancer in the Cronkhite-Canada syndrome. J. Clin. Gastroenterol. 8:199– 202, 1986. Rossi, A., G. Marconi, U. Camellini, and G. Marchitelli. [Radiological aspect of Peutz-Jeghers syndrome: considerations on a case]. Acta. Biomed. Ateneo. Parmense 52:237–244, 1981. Satoh, H., K. Togashi, F. Konishi, K. Sakuma, and H. Nagai. Diagnosis of neoplastic changes by magnifying colonoscopy in a patient with Cronkhite-Canada syndrome: report of a case. Dig. Endosc. 12:255–258, 2000. Scharf, G. M., J. H. Becker, and N. J. Laage. Juvenile gastrointestinal polyposis or the infantile Cronkhite-Canada syndrome. J. Pediatr. Surg. 21:953–954, 1986. Shibuya, C. An autopsy case of Cronkhite-Canada’s syndrome — generalized gastrointestinal polyposis, pigmentation, alopecia and onychotrophia. Acta. Pathol. Jpn. 22:171–183, 1972.
986
Simcock, P. R., H. J. Zambarakji, and B. R. Muller. Cataract formation in the Cronkhite-Canada syndrome. J. Cataract Refract. Surg. 22:1125–1126, 1996. Takakura, M., A. Hitomi, N. Tsuchihashi, E. Miyazaki, Y. Yoshioka, K. Yoshida, F. Oryo, and T. Sawada. A case of Cronkhite-Canada syndrome markedly improved with mesalazine therapy. Dig. Endosc. 16:74–78, 2004. Takeuchi, Y., M. Yoshikawa, N. Tsukamoto, A. Shiroi, Y. Hoshida, Y. Enomoto, T. Kimura, K. Yamamoto, H. Shiiki, E. Kikuchi, and H. Fukui. Cronkhite–Canada syndrome with colon cancer, portal thrombosis, high titer of antinuclear antibodies, and membranous glomerulonephritis. J. Gastroenterol. 38:791–795, 2003. Ward, E., H. C. Wolfsen, and C. Ng. Medical management of Cronkhite-Canada syndrome. South Med. J. 95:272–274, 2002. Watanabe, T., M. Kudo, H. Shirane, H. Kashida, S. Tomita, A. Orino, A. Todo, and T. Chiba. Cronkhite-Canada syndrome associated with triple gastric cancers: a case report. Gastrointest. Endosc. 50:688–691, 1999. Yamaguchi, K., Y. Ogata, Y. Akagi, T. Sasatomi, K. Ozaki, A. Ohkita, H. Ikeda, and K. Shirouzu. Cronkhite-Canada syndrome associated with advanced rectal cancer treated by a subtotal colectomy: report of a case. Surg. Today 31:521–526, 2001. Yoshida, S., and H. Tomita. A case of Cronkhite–Canada syndrome whose major complaint, taste disturbance, was improved by zinc therapy. Acta. Otolaryngol. Suppl. 546:154–158, 2002.
Hemochromatosis and Hemosiderosis Joerg Albrecht and Victoria P. Werth Hemochromatosis is an iron-storage disorder due to an inappropriately high absorption of iron from the duodenum. This leads to iron deposition in various organs with eventual impairment, especially of the liver, pancreas, heart, and pituitary gland. The term hemochromatosis denotes generally genetic hemochromatosis, whereas other diseases associated with iron overload, like thalassemia or sideroblastic anemia, are referred to as secondary iron overload. The term hemosiderosis describes the histologic appearance of increased stainable tissue iron. Hemosiderosis may be associated with secondary iron overload in any tissue, however, the focus of this section will be on cutaneous hemosiderosis.
Hereditary Hemochromatosis Introduction Hemochromatosis is a genetic metabolic disease characterized by an increased iron absorption that causes primary iron overload with organ damage. In the skin hemochromatosis is associated with a bronze or grayish melanocytic dermal and epidermal hyperpigmentation.
Historical Background The disease is also called Troisier–Hanot–Chauffard syndrome after three of its first describers in 1865 (Pietrangelo, 2003). The term hemochromatosis was coined by von Recklinghausen in 1899 to describe a pigmentation which was thought to be derived from the blood.
Epidemiology Hemochromatosis has frequently been described as a disease
HYPERMELANOSIS ASSOCIATED WITH GASTROINTESTINAL DISORDERS
predominantly of the male adult population. However, a recent, large French study has found that the onset of the disease is not later in women, but the authors concede that homozygous hemochromatosis is slightly underexpressed in women (Moirand et al., 1997). The prevalence of the heterozygotic hemochromatosis gene is about 9.2%, and homozygotic carriers make up 0.4% in a northern European population with similar numbers occurring in the white population in North America or Australia. The disease is much rarer in nonwhite patients (Bomford, 2002). Overall only 50% of the homozygous patients show clinical features of hemochromatosis (Olynyk et al., 1999). In spite of this, the number of patients diagnosed has increased significantly over the last decades due to increased awareness and ease of diagnosis (Niederau et al., 1996) and this may influence the epidemiological estimates, which are likely to be corrected upward.
Clinical Description of Disease/Associated Disorders Clinical diagnosis of hemochromatosis is difficult, because the early symptoms are usually nonspecific (Ryan et al., 2002). According to a recent series, around 30% of the diagnosed patients currently present without any clinical symptoms (Adams et al., 1991, 1997; Niederau et al., 1996), but this figure was up to 70% in an American series (Bacon and Sadiq, 1997). Most patients present with nonspecific symptoms like arthralgia, fatigue, abdominal pain, weight loss, or impotence (Adams et al., 1997; Niederau et al., 1996), indicating that gonadal, adrenal or pituitary damage may be early events. The classic clinical tetrad of hemochromatosis (liver disease, diabetes mellitus, cardiac failure, and hyperpigmentation) was only found in 10–20% of patients in large series (Adams et al., 1997). Liver fibrosis rarely develops in patients younger than 40 years. Exceptions are patients who have predisposing cofactors like excessive alcohol consumption (Tavill, 1999). Due to the lack of specific early symptoms hemochromatosis is underdiagnosed and a high incidence of clinical suspicion may be necessary for diagnosis. However, early diagnosis and treatment is vital to improve the prognosis and to avoid liver cirrhosis. Therefore family screening is important to identify family members who may have the disease (Ryan et al., 2002). In spite of the genetic nature of hemochromatosis, the diagnosis is dependent on the phenotype rather than the genotype (Pietrangelo, 2003). Of patients who present with characteristic symptoms, more than 90% have a discoloration of their skin. Because of its insidious onset (Chevrant-Breton et al., 1977) or the mildness of the discoloration (Milder et al., 1980) the skin is usually not the reason medical attention is sought. Patients have a characteristic grayish hue that may seem metallic and has given the disease the name bronze diabetes. The pigmentation is usually diffuse or generalized but may be more pronounced on the face, neck, extensor aspects of the lower forearm, dorsa of the hands, lower legs, genital region, and in scars. Because discolorations may be most prominent in the sun-exposed areas hemochromatosis may be mistaken for a suntan.
More than 95% of symptomatic patients have hepatomegaly at presentation, many of these without laboratory abnormalities. Those patients who develop hepatic cirrhosis have a 30% chance of developing hepatic carcinoma and have a clinical course and clinical symptoms similar to patients with other forms of hepatic cirrhosis. Diabetes mellitus occurs in about 30% of the patients (Niederau et al., 1996), with an increased likelihood in patients who have a family history of diabetes. This suggests that direct damage to the pancreatic islets occurs in combination with a genetic predisposition. Arthropathy has a varying course and age of presentation. Usually it involves the joints of the hand first. The joints to be affected are usually second and third metacarpophalangeal joints, and a progressive polyarthritis involving wrists, hips, ankles, and knees may follow. The arthropathy tends to progress in spite of iron removal or appropriate treatment. Between 5% and 15% of the patients have cardiac involvement (Niederau et al., 1996), which may present with electrocardiographic changes and cardiac arrhythmia. Particularly in young adults cardiac involvement may present as congestive heart failure that quickly leads to death. If other overt manifestations of the underlying disease are absent, the diffuse cardiac enlargement may be misdiagnosed as idiopathic cardiomyopathy. Hypogonadism may be a presenting symptom also. Iron deposits may harm the hypothalamic–pituitary function and lead to reduced production of gonadotropins. Primary testicular dysfunction has been observed as well. The overwhelming number of patients with hereditary hemochromatosis will have the above clinical characteristics, but different forms of hemochromatosis have been described. A number of Italian cases showed a vastly accelerated type of hemochromatosis, called type 2, which primarily affects the heart and the endocrine system, leading to death before the thirtieth birthday (Andrews, 1999; Camaschella et al., 1997). Neonatal hemochromatosis is even more fulminant and leads to neonatal death due to liver failure (Andrews, 1999).
Histology Due to the importance of laboratory test for the diagnosis of hemochromatosis, skin biopsy is now considered only for confirmatory purposes. The site for skin biopsy is of minor relevance since iron deposits can be found in nonpigmented areas as well. It is recommended to avoid biopsy of the legs because venous stasis or prior inflammation may cause ferritin deposits which are independent of hemochromatosis. The most common stain used to detect iron deposits in histologic examinations is Perls Prussian blue, sometimes called Perls acid or ferrocyanide reaction. The pigmentation of hemochromatosis is a combination of hemosiderin and melanin. The epidermis normally is normal in thickness, but atrophy and ichthyosis may be observed. Increased melanin can be found in the basilar and suprabasilar layers. Aside from free hemosiderin around the blood vessels, in the upper dermis, hemosiderin is also found in macrophages and in the basement membrane of eccrine sweat 987
CHAPTER 51
glands. Rarely hemosiderin is observed in the epidermis or within eccrine secretory cells (Chevrant-Breton et al., 1977).
Laboratory Findings Hemochromatosis is most reliably diagnosed by “transferrin saturation” testing. This test can be done in patients older than 1 year. For randomly drawn specimens a saturation of >50% should raise the suspicion of hemochromatosis and should be repeated, although the cut-off point is disputed and may be as low as 45% (Durupt et al., 2000). Fasting saturation values >62% are highly likely to indicate hemochromatosis and are recommended to verify randomly drawn results. Due to diurnal variations the test should be conducted in the morning, after the patient has fasted overnight and consumed no vitamin or mineral supplements for at least 24 hours. Vitamin C supplements or general consumption is particularly relevant since it increases iron absorption in the intestine (Felitti, 1999). Serum ferritin has a good correlation with iron excess in tissue, but its specificity is low because many factors, like inflammation or cytolysis, can influence the results (Pietrangelo, 2003).
Diagnosis The diagnosis of the disease may be based on the classic tetrad of liver cirrhosis, cardiac failure, diabetes, and hyperpigmentation, but in more and more patients the diagnosis is made prior to the development of characteristic symptoms at a stage when the disease presents with uncharacteristic symptoms like weakness. In most patients the diagnosis is probably never made (Nichols and Bacon, 1989). If hemochromatosis is suspected genetic testing should be performed, but due to the low penetrance of the disease the tests will not confirm the diagnosis in the absence of other findings. Additionally liver biopsy or preferably SQUID (supraconducting quantum interference device) may identify increased iron deposition in the liver.
Differential Diagnosis The nonspecific clinical presentation of the disease may indicate a large number of differential diagnoses. Laboratory results indicating an iron storage disease limit this number significantly. Secondary siderosis can develop after multiple transfusions, e.g., due to congenital anemia, or due to alcohol abuse in patients with porphyria. Some of these patients with secondary siderosis may be heterozygotic C282Y gene carriers and this defect may exacerbate their iron storage disease.
Pathogenesis Iron causes the grayish hue that has been described as bronze, but the characteristic tan color of the patients’ skin is caused by increased melanin (Felitti, 1999). Melanocytes seem to be stimulated by the iron in hemochromatosis, but the exact mechanism of this stimulation is currently unknown. It has
988
been postulated that melanocyte stimulation is secondary to tissue injury caused by the iron deposit. Mouse experiments demonstrated increased melanin production when exogenous iron was injected into hairless mice (Tsuji, 1980). Secondary changes of the skin due to hormonal disturbances and liver cirrhosis are frequently observed as well. Hemochromatosis is caused by an increased absorption of iron from the duodenum due to a mutation in the gene controlling the intestine’s mucosal barrier to iron absorption. It can be caused by mutations of multiple genes and at least 5 types of genetic variations have been identified. Type 1 or hereditary hemochromatosis is by far the most common form. It is an autosomal recessive human leukocyte antigen (HLA)linked disorder caused by a mutation of the HFE gene, that leads to a substitution of a tyrosine residue in place of a cysteine at position 282 (C282Y), a mutation that is also common in PCT (see section on PCT earlier in this chapter). More than 80% of the European patients with hemochromatosis are homozygous for this mutation, which is thought to be 2000 years old (Rochette et al., 1999). One other mutation relevant to type 1 hemochromatosis is H63D. This mutation is more widespread outside Europe and seems to be due to a higher proportion of spontaneous mutations and has less penetrance than the C282Y mutation (Bomford, 2002). Type 2 or juvenile hemochromatosis is a rare, autosomal recessive condition caused by an unidentified locus on chromosome 1q. It affects men and women equally. Type 3 is an autosomal recessive trait first described in Southern Italy. Type 4 is associated with the gene ferroportin 1, also known as IREG1 or MTP1, which encodes an intestinal transport molecule. It has been described in three families (Bomford, 2002). Type 5 is a form of autosomal dominant overload that has first been described in Japan. The mutation for this gene encodes the H-subunit of familial iron overload. Other forms of hemochromatosis have been described but not genetically characterized (Bomford, 2002). In spite of these advances in the genetic characterization of hemochromatosis the disease is poorly understood. It is especially puzzling that the variation of phenotype of homozygous patients with a C282Y mutation cannot be explained currently.
Animal Models To date there are two mouse models of hemochromatosis: one is based on a b2-microglobulin knockout (Rothenberg and Voland, 1996) and the second is based on a mutation of the murine analog of the HFE gene (Zhou et al., 1998). Increased iron storage disease has been observed regularly in captive lemurs. The increased incidence of iron storage disease in these animals seems to be due to a relative lack of ironbinding food components like tannins in captive diets (Wood et al., 2003).
Treatment The main aim of the treatment is depletion of the iron stores of the body. This is done by repeated phlebotomy. Initially
HYPERMELANOSIS ASSOCIATED WITH GASTROINTESTINAL DISORDERS
500 mL blood may be drawn weekly until the ferritin is below 20 mg/L. Thereafter four times a year is frequently sufficient. The goal is to keep the hemoglobin about 11–12 g/dL and the ferritin below 50 mL/L. In order to reduce protein losses associated with phlebotomy, erythropheresis is recommended. In general patients are advised to reduce iron absorption, e.g., by drinking black tea with their meals: and to reduce alcohol consumption since alcohol has shown to worsen the prognosis of the disease (Scotet et al., 2003). However, due to the complexity and difficulty of keeping a diet with a low iron content, patients are not usually given specific dietary advice. Regular large doses of vitamin C should be avoided since it increases iron absorption. Deferoxamine is less effective than phlebotomy and is mostly recommended for secondary siderosis after transfusions.
Prognosis The principal causes of death of patients with untreated hemochromatosis are cardiac failure (30%), hepatocellular failure or portal hypertension (25%), and hepatocellular carcinoma (30%). However, untreated cases are rare and patients who are treated before liver damage has occurred have a normal life expectancy.
References Adams, P. C., Y. Deugnier, R. Moirand, and P. Brissot. The relationship between iron overload, clinical symptoms, and age in 410 patients with genetic hemochromatosis. Hepatology 25:162–166, 1997. Adams, P. C., A. E. Kertesz, and L. S. Valberg. Clinical presentation of hemochromatosis: a changing scene. Am. J. Med. 90:445–449, 1991. Andrews, N. C. Disorders of iron metabolism. N. Engl. J. Med. 341:1986–1995, 1999. Bacon, B. R., and S. A. Sadiq. Hereditary hemochromatosis: presentation and diagnosis in the 1990s. Am. J. Gastroenterol. 92:784–789, 1997. Bomford, A. Genetics of haemochromatosis. Lancet 360:1673–1681, 2002. Camaschella, C., A. Roetto, M. Cicilano, P. Pasquero, S. Bosio, L. Gubetta, F. Di Vito, D. Girelli, A. Totaro, M. Carella, A. Grifa, and P. Gasparini. Juvenile and adult hemochromatosis are distinct genetic disorders. Eur. J. Hum. Genet. 5:371–375, 1997. Chevrant-Breton, J., M. Simon, M. Bourel, and B. Ferrand. Cutaneous manifestations of idiopathic hermochromatosis. Study of 100 cases. Arch. Dermatol. 113:161–165, 1977. Durupt, S., I. Durieu, R. Nove-Josserand, L. Bencharif, H. Rousset, and Durand D. Vital. [Hereditary hemochromatosis]. Rev. Med. Interne 21:961–971, 2000. Felitti, V. J. Hemochromatosis: A common, rarely diagnosed disease. Perm. J. 3:10–22, 1999. Milder, M. S., J. D. Cook, S. Stray, and C. A. Finch. Idiopathic hemochromatosis, an interim report. Medicine (Baltimore) 59:34–49, 1980. Moirand, R., P. C. Adams, V. Bicheler, P. Brissot, and Y. Deugnier. Clinical features of genetic hemochromatosis in women compared with men. Ann. Intern. Med. 127:105–110, 1997. Nichols, G. M., and B. R. Bacon. Hereditary hemochromatosis: pathogenesis and clinical features of a common disease. Am. J. Gastroenterol. 84:851–862, 1989.
Niederau, C., R. Fischer, A. Purschel, W. Stremmel, D. Haussinger, and G. Strohmeyer. Long-term survival in patients with hereditary hemochromatosis. Gastroenterology 110:1107–1119, 1996. Olynyk, J. K., D. J. Cullen, S. Aquilia, E. Rossi, L. Summerville, and L. W. Powell. A population-based study of the clinical expression of the hemochromatosis gene. Gastroenterology 341:718–724, 1999. Pietrangelo, A. Haemochromatosis. Gut 52 Suppl 2:ii23–ii30, 2003. Rochette, J., J. J. Pointon, C. A. Fisher, G. Perera, M. Arambepola, D. S. Arichchi, S. De Silva, J. L. Vandwalle, J. P. Monti, J. M. Old, A. T. Merryweather-Clarke, D. J. Weatherall, and K. J. Robson. Multicentric origin of hemochromatosis gene (HFE) mutations. Am. J. Hum. Genet. 64:1056–1062, 1999. Rothenberg, B. E., and J. R. Voland. Beta2 knockout mice develop parenchymal iron overload: A putative role for class I genes of the major histocompatibility complex in iron metabolism. Proc. Natl. Acad. Sci. U. S. A. 93:1529–1534, 1996. Ryan, E., V. Byrnes, B. Coughlan, A. M. Flanagan, S. Barrett, J. C. O’Keane, and J. Crowe. Underdiagnosis of hereditary haemochromatosis: lack of presentation or penetration? Gut 51:108–112, 2002a. Scotet, V., M. C. Merour, A. Y. Mercier, B. Chanu, T. Le Faou, O. Raguenes, G. Le Gac, C. Mura, J. B. Nousbaum, and C. Ferec. Hereditary hemochromatosis: effect of excessive alcohol consumption on disease expression in patients homozygous for the C282Y mutation. Am. J. Epidemiol. 158:129–134, 2003. Tavill, A. S. Clinical implications of the hemochromatosis gene. N. Engl. J. Med. 341:755–757, 1999. Tsuji, T. Experimental hemosiderosis: relationship between skin pigmentation and hemosiderin. Acta. Derm. Venereol. 60:109–114, 1980. Wood, C., S. G. Fang, A. Hunt, W. J. Streich, and M. Clauss. Increased iron absorption in lemurs: quantitative screening and assessment of dietary prevention. Am. J. Primatol. 61:101–110, 2003. Zhou, X. Y., S. Tomatsu, R. E. Fleming, S. Parkkila, A. Waheed, J. Jiang, Y. Fei, E. M. Brunt, D. A. Ruddy, C. E. Prass, R. C. Schatzman, R. O’Neill, R. S. Britton, B. R. Bacon, and W. S. Sly. HFE gene knockout produces mouse model of hereditary hemochromatosis. Proc. Natl. Acad. Sci. U. S. A. 95:2492–2497, 1998.
Hemosiderosis Introduction Hemosiderosis is defined as the histologic equivalent of secondary iron overload, which may be local, i.e., restricted to one organ, or generalized.
Epidemiology The incidence and prevalence of hemosiderosis is unknown due to the multiplicity of associated diseases.
Clinical Description of Disease/Associated Disorders A comprehensive description of changes that lead to cutaneous hemosiderosis is not possible due to the variety of causative conditions. Essentially any condition that is associated with erythrocyte extravasation will cause some hemosiderosis (Fig. 51.6). Therefore any vasculitis or malformation of cutaneous vessels, like pseudo-Kaposi sarcomas or arteriovenous malformations, are histologically associated with iron deposits of variable extent and duration. Medical treatments with ironcontaining drugs, e.g., Monsel solution, may lead to cutaneous
989
CHAPTER 51
hemosiderosis as well (Amazon et al., 1980; Wood and Severin, 1980). The following discussion is therefore not comprehensive but reflects those conditions that have been discussed in the dermatology literature due to their association with hemosiderosis. The most common condition associated with cutaneous hemosiderosis is probably actinic purpura, also called senile or Bateman purpura. This purpura is due to damages of the microvasculature, which are caused by ultraviolet radiationinduced dermal tissue atrophy. Atrophy renders the skin and microvasculature more susceptible to the effects of minor trauma and shearing forces which leads to extravasation of blood components and secondary hemosiderosis (Arya and Kihiczak, 2002; Gilchrest 1996). Local extravasation of erythrocytes also frequently occurs in relation to varicose veins and venous ulcers. This discoloration is associated with the acute disease and usually subsides after the underlying cause has been treated. Varicose dyschromia is a combination of increased melanin production and deposition of hemosiderin. While compression therapy reduces melanocytic pigmentation reliably, the resolution of hemosiderin discoloration is quite variable (Cuttell and Fox, 1982). Hemosiderin deposits usually disappear completely after one year but may persist for more than five years after successful sclerotherapy (Georgiev, 1990; Goldman et al., 1987). Sequential biopsies from chronic venous ulcers have not only shown hemosiderin deposits around the margins but also demonstrated that these are reduced during healing (Herrick et al., 1992). Another disorder associated with cutaneous hemosiderin deposits is targetoid hemosiderotic hemangioma. These hemangiomas are rare benign vascular tumors, usually smaller than 1 cm in diameter which may be annular (Saga, 1981). The lesions may fluctuate and can be swollen and tender. Histologically the differential diagnosis is Kaposi sarcoma (Perrin et al., 1995). Confusingly, given the name, lack of hemosiderin deposits does not exclude the diagnosis of targetoid hemosiderotic hemangioma (Ly et al., 1998). Congenital histiocytosis is a self-healing condition, associated with brown cutaneous papulonodules in newborns which regress within two to four months. The disease may present with massive hemosiderosis, which may give the impression of strong pigmentation (Belajouza-Noueiri et al., 2001). Hemosiderotic fibrohistiocytic lipomatous lesion is a recently described heavily pigmented spindle cell proliferation which occurs within a lipoma and can grow to impressive sizes. The lesions in this small series occurred primarily on the ankles of female patients in their fifties and developed mostly after local trauma. They tend to recur after excision (Marshall-Taylor and Fanburg-Smith, 2000). Hemosiderosis as a generalized secondary iron overload syndrome has a multiplicity of causes and clinical presentations that can be seen in Table 51.1. Hemosiderosis chiefly occurs in the lungs and kidneys and is the result of other disease processes. Pulmonary hemosiderosis caused by recurrent pulmonary hemorrhage occurs as an idiopathic entity 990
Fig. 51.6. Cutaneous hemosiderosis secondary to fracture of the arm.
(Milman and Pedersen, 1998), as part of Goodpasture syndrome, or in severe mitral stenosis. Occasionally, the blood loss from these episodes of hemorrhage into the lungs causes iron-deficiency anemia. Renal hemosiderosis can result from extensive intravascular hemolysis caused by trauma to red blood cells (e.g., chronic disseminated intravascular coagulation, defective or torn heart valve leaflets, prosthetic mechanical heart valves) or in paroxysmal nocturnal hemoglobinuria. In renal hemosiderosis, free hemoglobin is filtered at the glomerulus, e.g., due to hemolysis. Haptoglobin usually binds the free hemoglobin, but when haptoglobin is saturated renal iron deposition occurs. Usually the renal parenchyma is not damaged by these iron deposits, but severe hemosiderinuria may result in iron deficiency (Andrews, 1999; Lim et al., 2000).
Histology Hemosiderosis is not a disease entity but rather a condition in which iron, usually in its ferric state (Fe3+), is deposited in tissue. The most common stain used to detect ferric iron in histology is Perls Prussian blue, sometimes called Perls acid or ferrocyanide reaction.
Laboratory Findings In order to distinguish localized hemosiderosis, e.g., due to actinic purpura, from generalized hemosiderosis, e.g., secondary to multiple infusions, the iron stores of the body have to be evaluated. This is most easily done using serum ferritin as a screening test. In cases of tissue damage and inflammation the increase in ferritin may be misleadingly high, while in scorbutic patients the ferritin may be misleadingly low (Porter, 2001). However, an increased transferrin saturation and serum iron will confirm a diagnosis of iron overload.
Pathogenesis The pathogenesis of hemosiderosis is iron overload caused by an underlying disease or external causes. It may be iatrogenic, e.g., after multiple blood transfusions (Hb SS, thalassemia); or
HYPERMELANOSIS ASSOCIATED WITH GASTROINTESTINAL DISORDERS Table 51.1. Classification of hemosiderosis and hemochromatosis. Primary genetic hemochromatosis Iron overload Congenital hemolytic anemias Increased parental iron intake (rare) Repeated transfusions, e.g., due to defective Hb synthesis (sickle cell disease, thalassemia) Iron dextran IM Increased intestional iron absorption African iron overload Kashin–Bek disease with hemosiderosis (Beers and Berkow, 1999) Localized hemosiderosis Pulmonary (idiopathic) Renal Hepatic (porphyria cutanea tarda) Cutaneous (e.g., actinic purpura)
self-inflicted due to African iron overload (Andrews, 1999). In case of localized hemosiderosis the pathogenesis may be related to extravasation of red blood cells, e.g., after vasculitis or due to chronic actinic vascular damage as in actinic purpura or the application of iron-containing drugs. Trauma or intoxication lead to hemosiderosis due to iron-containing objects, e.g., nails or ammunition. Two patterns of iron overload are usually observed. Iron overload in which the plasma iron content exceeds the transferrin binding capacity will lead to deposits of iron in the parenchyma cells of the liver, the heart, and a subgroup of endocrine tissues. The most typical disease with this type of iron deposition is hereditary hemochromatosis. Iron overload that results from increased catabolism of erythrocytes leads to accumulation of iron in the reticuloendothelial macrophages, which only later spills over to the parenchymal cells. This parenchymal iron overload causes fibrosis and tissue damage that may characterize some forms of hemosiderosis. Iron accumulation in the macrophages only is usually not dangerous (Andrews, 1999).
Animal Models A specific animal model for hemosiderosis does not exist, however, systemic hemosiderosis has been induced in SpragueDawley rats by subcutaneous injection of elemental iron as iron–dextran complex (Pelot et al., 1998). Another way to induce systemic hemosiderosis is through infection and hemolysis. Cullen and Levine (1987) developed a model of Syrian hamsters who were infected by Babesia microti, a malaria-like protozoan usually associated with rodents. The animals did not die but the disease caused intravascular and extravascular hemolysis and marked renal hemosiderosis.
Treatment Treatment of hemosiderosis-associated pigmentary changes will depend on whether the discoloration is primarily due to
hemosiderin or melanin and whether the pigmentation is dermal or epidermal in origin (Briganti et al., 2003). The different treatment options are discussed in more detail in Chapters 59–64 of this book. Transfusion iron overload and iron overload that occurs due to defective erythropoiesis (e.g., in congenital hemolytic anemias or hemoglobinopathies) is usually obvious from the clinical history. Because the transfusions are given due to anemia, phlebotomy may not be possible. Desferrioxamine can be given to effectively reduce iron stores for symptomatic systemic hemosiderosis. The drug is given slowly subcutaneously because boluses are associated with acute systemic side effects. Toxic effects resulting from desferrioxamine therapy are now rare provided the recommended dosing schedules are not exceeded. However, baseline examinations of ears and eyes are recommended. Efficacy must continually be evaluated (usually by urine iron measurement) due to tachyphylaxis that may develop with desferrioxamine therapy. Alternatively, salmon- or rusty colored urine confirms >50 mg/day of iron in the urine (Porter, 2001).
Prognosis The prognosis of hemosiderosis is dependent on the underlying condition.
References Amazon, K., M. J. Robinson, and A. M. Rywlin. Ferrugination caused by Monsel’s solution. Clinical observations and experimentations. Am. J. Dermatopathol. 2:197–205, 1980. Andrews, N. C. Disorders of iron metabolism. N. Engl. J. Med. 341:1986–1995, 1999. Arya V., and G. Kihiczak. Actinic purpura. 2002, www.emedecine. com (accessed February 28, 2004). Belajouza-Noueiri, C., M. Denguezli, H. Selmi, M. Mokni, B. Jomaa, and R. Nouira. [Intense hemosiderin deposits in a case of selfhealing congenital histiocytosis]. Ann. Dermatol. Venereol. 128:238–240, 2001. Briganti, S., E. Camera, and M. Picardo. Chemical and instrumental approaches to treat hyperpigmentation. Pigment Cell Res. 16:101– 110, 2003. Cullen, J. M., and J. F. Levine. Pathology of experimental Babesia microti infection in the Syrian hamster. Lab. Anim. Sci. 37:640– 643, 1987. Cuttell, P. J., and J. A. Fox. The aetiology and treatment of varicose pigmentation. Phlebologie 35:381–389, 1982. Georgiev, M. Postsclerotherapy hyperpigmentations: a one-year follow-up. J. Dermatol. Surg. Oncol. 16:608–610, 1990. Gilchrest, B. A. A review of skin ageing and its medical therapy. Br. J. Dermatol. 135:867–875, 1996. Goldman, M. P., R. P. Kaplan, and D. M. Duffy. Postsclerotherapy hyperpigmentation: a histologic evaluation. J. Dermatol. Surg. Oncol. 13:547–550, 1987. Herrick, S. E., P. Sloan, M. McGurk, L. Freak, C. N. McCollum, and M. W. Ferguson. Sequential changes in histologic pattern and extracellular matrix deposition during the healing of chronic venous ulcers. Am. J. Pathol. 141:1085–1095, 1992. Lim, Y. K., A. Jenner, A. B. Ali, Y. Wang, S. I. Hsu, S. M. Chong, H. Baumman, B. Halliwell, and S. K. Lim. Haptoglobin reduces renal oxidative DNA and tissue damage during phenylhydrazine-induced hemolysis. Kidney Int. 58:1033–1044, 2000.
991
CHAPTER 51 Ly, S., J. Versapuech, B. Vergier, M. Beylot-Barry, and C. Beylot. Guess what! Targetoid hemosiderotic hemangioma. Eur. J. Dermatol. 8:583–585, 1998. Marshall-Taylor, C., and J. C. Fanburg-Smith. Hemosiderotic fibrohistiocytic lipomatous lesion: ten cases of a previously undescribed fatty lesion of the foot/ankle. Mod. Pathol. 13:1192–1199, 2000. Milman, N., and F. M. Pedersen. Idiopathic pulmonary haemosiderosis. Epidemiology, pathogenic aspects and diagnosis. Respir. Med. 92:902–907, 1998. Pelot, D., X. J. Zhou, P. Carpenter, and N. D. Vaziri. Effects of experimental hemosiderosis on pancreatic tissue iron content and structure. Dig. Dis. Sci. 43:2411–2414, 1998. Perrin, C., S. Rodot, J. P. Ortonne, and J. F. Michiels. [Targetoid hemosiderotic hemangioma]. Ann. Dermatol. Venereol. 122:111– 114, 1995. Porter, J. B. Practical management of iron overload. Br. J. Haematol. 115:239–252, 2001. Saga, K. Annular hemosiderotic histiocytoma. J. Cutan. Pathol. 8:251–255, 1981. Wood, C., and G. L. Severin. Unusual histiocytic reaction to Monsel’s solution. Am. J. Dermatopathol. 2:261–264, 1980.
Primary Biliary Cirrhosis Joerg Albrecht and Victoria P. Werth
Introduction Primary biliary cirrhosis (PBC) is a chronic non–pusproducing destructive cholangitis, which is also less commonly named “primary biliary hepatitis (PBH),” “chronic nonsuppurative destructive cholangitis,” and “primary autoimmune cholangitis.”
Epidemiology PBC affects all races but seems to cluster within specific geographic areas. The male/female ratio is 9:1 with a median age of onset of 20 years, with a range from 20 to 90 years. The annual incidence and prevalence for the disease ranges from 2 and 24 cases to 19 and 240 cases per million population (Jones, 2003; Kim et al., 2000; Talwalkar and Lindor, 2003). The reported incidence is highest in areas of the UK and lowest in Canada and Australia, with almost no cases in subSaharan Africa or India. This range of prevalence is probably partly due to environmental factors that may influence disease expression, however, no distinct factors have been identified, although an association with infections has been suggested (Feld and Heathcote, 2003; Gish and Mason, 2001; Prince et al., 2001).
Historical Background In 1857 Thomas Addison (1785–1860) and William Gull described the first cases of what is now recognized as the autoimmune liver disease, PBC. Thomas Addison was born in an area with one of the highest prevalences of PBC yet described, and there is some suggestion from contemporary sources that he himself succumbed to the liver disease (Jones, 2003). 992
Fig. 51.7. Woman with biliary cirrhosis and diffuse hyperpigmentation more pronounced on sun-exposed areas (see also Plate 51.3, pp. 494–495).
Clinical Description of Disease/Associated Disorders Patients with PBC show diffuse darkening of the skin, with accentuation in the sun-exposed areas (Fig. 51.7). The hyperpigmentation is associated with pruritus, jaundice, and subcutaneous lipid deposits around the eyes (xanthelasma) or on joints or tendons (xanthomas). Patients with PBC may also show the typical pigmented corneal rings that are usually associated with Wilson disease (Fleming et al., 1975; Goldstein, 1976). Occasionally PBC is associated with other connective tissue diseases like rheumatoid arthritis, thyroiditis (Hashimoto), or Sjögren syndrome. In 10% the disease shows clinical overlap with CREST syndrome or autoimmune hepatitis, which may distort the clinical picture (Bolognia and Braverman, 2001; Nishio et al., 2000). Currently most patients are diagnosed as having PBC during routine screening. Suspicion may be raised by a twofold or greater level of serum alkaline phosphatase levels with concurrent elevation of the serum 5¢-nucleotidase activity and the g-glutamyl transpeptidase levels, while serum bilirubin is still
HYPERMELANOSIS ASSOCIATED WITH GASTROINTESTINAL DISORDERS
normal. Patients are usually asymptomatic and may remain so for prolonged periods of time; 90% of the patients with symptoms are women between 35 and 60 years. Patients have intense pruritus and fatigue independent of the extent of their liver involvement. The pruritus may initially be limited to the palms and the soles. The other symptoms of the disease are largely related to impaired bile excretion and subsequent hepatocellular failure, and may not occur in patients with a protracted course of the disease. Clinical changes usually associated with PBC are jaundice, hepatomegaly, maldigestion, and portal hypertension with its associated morbidity and mortality.
mately 50% of patients have antinuclear antibodies, sometimes against very specific proteins (nuclear pore membrane protein gp210, transcriptional activator Sp100, inner nuclear membrane protein LBR). Absence of an elevated serum IgM concentration and/or specific autoantibodies argues against PBC. The clinical signs of liver disease are accompanied by characteristic changes in the cholestatic enzymes, such as an increase in alkaline phosphatase, decrease in leukocyte alkaline phosphatase (LAP), as well as increases in bilirubin and g-glutamyl transpeptidase (GGT or g-GT and GGTP or gGTP). Patients usually show hypercholesterolemia as a further consequence of liver disease.
Histology
Diagnosis
Skin histology is rarely warranted, in spite of the hyperpigmentation that is observed in patients with PBC. A histologic and ultrastructural study of PBC has demonstrated that cutaneous pigmentation in PBC is due to the presence of increased amounts of melanin, widely dispersed throughout both epidermis and dermis. The authors observed no deposits of stainable iron, but found unusually high levels of melanosomes in the epidermis. These melanosomes were packaged in large membrane-bound clusters. It remains unclear whether the excess melanin in PBC results from increased melanogenesis or from defective melanin degradation. The authors did not demonstrate hormonal (b-melanocyte-stimulating hormone and adrenocorticotropic hormone) or chemical (bile salt irritation) stimuli that may have increased melanogenesis. The melanocyte to keratinocyte ratio was not significantly higher in PBC when compared to skin from matched sites from control patients with alcoholic cirrhosis or no abnormalities of pigmentation (Mills et al., 1981). Histologic staging of liver disease in PBC is not always straightforward, although a four-stage morphologic classification has been established. Frequently different stages of the disease can be observed in one patient at the same time. Small biopsies may miss this variety of presentations and thus risk misclassification. As a general rule the highest stage in any one patient is considered to represent the clinical stage. Stage I is the earliest recognizable stage and termed nonsuppurative destructive cholangitis. It is a necrotizing inflammatory process of the portal triads characterized by destruction of medium and small bile ducts, and a dense infiltrate of acute and chronic inflammatory cells. These inflammatory cells become less prominent when the number of bile ducts has been reduced and small new bile ducts proliferate (stage II). The progression of the disease leads to a decrease in interlobular ducts, loss of liver cells, and expansion of periportal fibrosis into a network of connective tissue scars (stage III). Stage IV documents liver cirrhosis (Chung and Podolski, 2001).
The diagnosis of primary biliary cirrhosis is only rarely based on the skin changes. Indicators of cholestasis and increases in IgM may point towards the disease, as do positive antimitochondrial antibody (AMA) titers. False-positive AMA results occur, and a number of patients may never develop AMA titers. In some of these latter patients antinuclear or smooth muscle antibodies are present and the disease is described as autoimmune cholangitis, although the histology is identical to PBC and the natural history seems to be similar. Alternatively AMA-negative patients may have primary sclerosing cholangitis and the biliary tract should be evaluated to exclude this condition (Chung and Podolski, 2001). If the diagnosis of PBC has been established the patient should be screened for other associated autoimmune diseases like Sjögren syndrome, thyroiditis, CREST syndrome, or scleroderma, and metabolic disease including bone problems and vitamin deficiency should be investigated (Gish and Mason, 2001).
Differential Diagnosis Based on the hyperpigmentation the most relevant differential diagnosis is POEMS [polyneuropathy: organomegaly (spleen, liver, lymph nodes); endocrinopathies (impotence, gynecomastia); M-protein; and skin changes]. The skin changes of POEMS syndrome include hyperpigmentation, skin thickening, hypertrichosis, and angiomas (Bolognia and Braverman, 2001). The clinical differential diagnosis for diseases of the liver include intrahepatic cholestasis, as seen in cholestatic viral hepatitis or drug-induced jaundice, or extrahepatic cholestasis seen in cholelithiasis, tumors, maw-worms, liver flukes, or stenosis of the common bile duct after laparoscopic cholecystectomy. Pruritus as a basis for differential diagnosis can be associated with diseases of the skin, allergies, PBC or PSC, a variety of intestinal parasites, diabetes, lymphomas, renal insufficiency, polycythemia vera, iron deficiency, senile pruritus, or associated with psychiatric diseases.
Laboratory Findings More than 90% of patients have autoantibodies against specific mitochondrial proteins (AMA), most often the E2 subunits of the oxo-acid dehydrogenase complexes. Approxi-
Pathogenesis PBC is a complex autoimmune disease. More than 90% of the patients have IgG antimitochondral antibodies in the serum 993
CHAPTER 51
that are particularly directed at the pyruvate dehydrogenase complex (PDC); specifically the autoantibody response is directed at the enzyme 2, dihydrolipoamide acetyl transferase (E2), and enzyme 3 building protein (E3BP) components of PDC. It is thought likely that CD8+ cytotoxic T cells with selfPDC derived epitopes are responsible for target cell damage, i.e., the apoptosis of biliary epithelial cells, although direct cytotoxic activity has not been demonstrated. As a reflection of this process lymphocytes are prominent in the portal regions and surround damaged bile duct. These histologic changes associated with PBC resemble graft-versus-host disease and suggest that damage to the bile ducts may be biologically mediated. The pathognomonic liver damage is caused by impaired biliary excretion due to fibrosing obliteration of intrahepatic bile ductules, which causes progressive fibrosis of the liver (Jones, 2003).
gression in individual patients several mathematical models based on clinical, laboratory, and histological criteria have been developed, the most popular of these based on the Mayo Clinic patient population and available on the web (Dickson et al., 1989). In general, the development of portal hypertension indicates a poor prognosis, as does anti-M4 or anti-M8. The serum bilirubin concentration is the best prognostic indicator of all laboratory values. Once the serum bilirubin concentration exceeds 145 mmol/L or there is evidence of ascites, hepatic encephalopathy, or variceal bleeding, patients should be considered for liver transplantation. Prognosis after liver transplantation is excellent with 85–90% survival after one year. Thereafter survival rates are similar to those of healthy patients matched for age and sex (Nishio et al., 2000).
Animal Models
Beswick, D. R., G. Klatskin, and J. L. Boyer. Asymptomatic primary biliary cirrhosis. A progress report on long-term follow-up and natural history. Gastroenterology 89:267–271, 1985. Bolognia, J. L., and I. M. Braverman. Skin manifestations of internal disease. In: Harrison’s Principles of Internal Medicine, 15th ed. E. Braunwald, A. S. Fauci, D. L. Kasper, S. L. Hauser, D. L. Longo, and J. L. Jameson (eds). New York: McGraw-Hill, 2001. Chung, R. T., and D. K. Podolski. Cirrhosis and its complications. In: Harrison’s Principles of Internal Medicine, 15th ed. E. Braunwald, A. S. Fauci, D. L. Kasper, S. L. Hauser, D. L. Longo, and J. L. Jameson (eds). New York: McGraw-Hill, 2001. Dickson, E. R., P. M. Grambsch, T. R. Fleming, L. D. Fisher, and A. Langworthy. Prognosis in primary biliary cirrhosis: model for decision making. Hepatology 10:1–7, 1989. Feld, J. J., and E. J. Heathcote. Epidemiology of autoimmune liver disease. J. Gastroenterol. Hepatol. 18:1118–1128, 2003. Fleming, C. R., E. R. Dickson, R. W. Hollenhorst, N. P. Goldstein, J. T. McCall, and A. H. Baggenstoss. Pigmented corneal rings in a patient with primary biliary cirrhosis. Gastroenterology 69:220–225, 1975. Gish, R. G., and A. Mason. Autoimmune liver disease. Current standards, future directions. Clin. Liver Dis. 5:287–314, 2001. Goldstein, N. P. Letter: Pigmented corneal rings in a patient with primary biliary cirrhosis. Arch. Neurol. 33:372–1976. Jones, D. E. Addison’s other disease: primary biliary cirrhosis as a model autoimmune disease. Clin. Med. 3:351–356, 2003. Jones, D. E., J. M. Palmer, J. A. Kirby, D. J. De Cruz, G. W. McCaughan, J. D. Sedgwick, S. J. Yeaman, A. D. Burt, and M. F. Bassendine. Experimental autoimmune cholangitis: a mouse model of immune-mediated cholangiopathy. Liver 20:351–356, 2000. Kim, W. R., K. D. Lindor, G. R. Locke, III, T. M. Therneau, H. A. Homburger, K. P. Batts, B. P. Yawn, J. L. Petz, L. J. Melton, III, and E. R. Dickson. Epidemiology and natural history of primary biliary cirrhosis in a US community. Gastroenterology 119:1631–1636, 2000. Levy, C., and K. D. Lindor. Current management of primary biliary cirrhosis and primary sclerosing cholangitis. J. Hepatol. 38(Suppl 1):S24–S37, 2003. Mills, P. R., C. J. Skerrow, and R. M. MacKie. Melanin pigmentation of the skin in primary biliary cirrhosis. J. Cutan. Pathol. 8:404–410, 1981. Nishio, A., E. B. Keeffe, H. Ishibashi, and E. M. Gershwin. Diagnosis and treatment of primary biliary cirrhosis. Med. Sci. Monit. 6:181–193, 2000.
Recently an animal model for PBC, i.e., experimental autoimmune cholangitis (EAC) has been developed. To acquire the disease female SJL/J mice have to be sensitized with PDC, i.e., its purified E2/E3BP component. Within five weeks the mice have high titer antibodies and splenic T-cell proliferation, and after 30 weeks a high proportion of the mice have EAC (Jones et al., 2000).
Treatment While there is no specific therapy for PBC, ursodiol has been shown to be beneficial to relieve symptoms. Classic immunosuppressive medications like glucocorticoids, methotrexate, colchicine, azathioprine, ciclosporin, and tacrolimus have been disappointing in controlled trials. Unfortunately the ultimate treatment for PBC still is liver transplantation. The patients have excellent survival, but about 25% will show histologic changes of PBC after five years, which is often asymptomatic (Nishio et al., 2000). While the traditional treatment dogma has been to slow or prevent disease progression, it is now appreciated that at least equal effort should be given to treating symptoms such as fatigue and pruritus, which can dramatically improve the patient’s quality of life (Jones, 2003). A detailed description of symptomatic treatment is beyond the scope of this chapter and the reader is referred to the current medical literature (Levy and Lindor, 2003).
Prognosis PBC is a progressive disease that leads to cirrhosis and liver failure. The time from diagnosis to end-stage liver disease can range from a few months to 20 years, depending upon when the diagnosis is first made. Many patients have a chronic and indolent course of the disease; in the majority of usually elderly patients the risk of developing the disease is very low and these patients may have a normal life expectancy (Jones, 2003; Nishio et al., 2000). However, association with other autoimmune disease generally predicts a worse prognosis (Beswick et al., 1985). In order to calculate the disease pro994
References
HYPERMELANOSIS ASSOCIATED WITH GASTROINTESTINAL DISORDERS Prince, M. I., A. Chetwynd, P. Diggle, M. Jarner, J. V. Metcalf, and O. F. James. The geographical distribution of primary biliary cirrhosis in a well-defined cohort. Hepatology 34:1083–1088, 2001. Talwalkar, J. A., and K. D. Lindor. Primary biliary cirrhosis. Lancet 362:53–61, 2003.
Inflammatory Bowel Disease and Pigmentation Joerg Albrecht and Victoria P. Werth Inflammatory bowel diseases, i.e., Crohn disease and ulcerative colitis, are associated with a number of cutaneous findings of varying frequency (Apgar, 1991). However, the association between inflammatory bowel disease and pigmentation is a tenuous one. There have been repeated reports of correlation between the activity of Crohn disease and vitiligo. In one case the two conditions only coexisted (Monroe, 1976), in a second the diseases showed parallel activity and were both suppressed by the steroid treatment for Crohn disease (McPoland and Moss 1988). A recent epidemiologic study confirmed that the incidence of inflammatory bowel diseases is approximately twice as high in patients with vitiligo as in the general population (Alkhateeb et al., 2003). This, however, is not a very strong association between two autoimmune diseases and it does not imply that vitiligo and inflammatory bowel diseases are associated in a clinically meaningful way.
References Alkhateeb, A., P. R. Fain, A. Thody, D. C. Bennett, and R. A. Spritz. Epidemiology of vitiligo and associated autoimmune diseases in Caucasian probands and their families. Pigment Cell Res. 16:208–214, 2003. Apgar, J. T. Newer aspects of inflammatory bowel disease and its cutaneous manifestations: a selective review. Semin. Dermatol. 10:138–147, 1991. McPoland, P. R., and R. L. Moss. Cutaneous Crohn’s disease and progressive vitiligo. J. Am. Acad. Dermatol. 19:421–425, 1988. Monroe, E. W. Vitiligo associated with regional enteritis. Arch. Dermatol. 112:833–834, 1976.
Pellagra Eun Ji Kwon and Victoria P. Werth
Historical Background Pellagra, derived from the Italian pelle meaning “skin” and agra meaning “dry,” was first described by Gaspar Casal in the Asturias region of Spain in 1735 (Sebrell, 1981). Called “mal de la rosa” among the Asturians for its characteristic erythematous rash on the skin, the disease struck poor peasants who subsisted on a maize-based diet lacking meat intake. Casal speculated that this was a nutritional disease after noting that adding animal products to the peasants’ diet ameliorated symptoms. The nutritional basis of pellagra was established during the 1910s by Joseph Goldberger of the
United States Public Health Service. Through a series of clinical trials on prisoners, Goldberger proved that a diet poor in animal protein caused pellagra and that an animal–proteinrich diet could treat and prevent pellagra. The exact nutritional deficiency was not identified until 1937, when Conrad Elvehjem of the University of Wisconsin demonstrated conclusively that niacin was the key pellagra-preventive factor (Roe, 1973).
Epidemiology Although pellagra is rare in industrialized countries, it is still observed in areas of the world where malnutrition continues to be a problem. In endemic areas it affects individuals of all ages, typically first appearing in children after breastfeeding ceases. Endemic areas include India where millet and corn are primary dietary staples and Asia and Africa where corn (containing a nonabsorbable bound form of niacin) is the primary staple (Nieves and Goldsmith, 2003; Stratigos and Katsambas, 1977). Multiple outbreaks of pellagra have occurred since 1988 in refugee programs in Angola, Ethiopia, Malawi, Nepal, Swaziland, the former Zaire, and Zimbabwe (World Health Organization, 2000). Sporadic cases of pellagra have been reported in developed nations, especially in association with chronic alcoholism, malabsorption disorders, and nutrient–drug interactions (Nieves and Goldsmith, 2003).
Clinical Description of Disease/Associated Disorders Pellagra is characterized by the triad of three Ds — dermatitis, diarrhea, and dementia. The cutaneous lesions are symmetric and appear on sun-exposed areas such as the dorsum of the hands, wrists, and forearms (Fig. 51.8), face, neck, anterior chest, knees, shoulders, and elbows (Figs 51.9 and 51.10) (Miller, 1989). The lesions are precipitated by sunlight, heat, or trauma (Miller, 1989). The disease begins as a dermatitis with well-defined, painful or burning areas of erythema and edema. Erythema on the face may resemble the “butterfly” rash of lupus erythematosus. These lesions may resemble early sunburn and the initial erythema changes to cinnamon-brown in color. However, the rate of tanning is slower than is characteristic in sunburn (Hegyi et al., 2004). Vesicles or bullae can also occur. Later, the lesions, sometimes described as “gooselike,” become hyperpigmented, hyperkeratotic, scaly, variably fissured and crusted (see Fig. 51.10) (Miller, 1989). The dorsal surfaces of the hands are most frequently involved, and referred to as the “glove” or “gauntlet” of pellagra. Lesions on the feet and leg may resemble a “boot.” Casal’s “necklace” refers to the lesions that occur as a wide band around the neck and on the anterior chest. With advanced deficiency state, the skin may become covered with black crusts due to hemorrhages (Nieves and Goldsmith, 2003). Angular cheilosis and stomatitis, glossitis (“beefy” red, smooth or black, atrophic tongue), proctitis, vulvovaginitis, and scrotal dermatitis are common in individuals with pellagra (Miller, 1989). Infants may present with a diaper dermatitis. However, there is evidence suggesting angular 995
CHAPTER 51
Fig. 51.8. Hyperpigmentation scaly fissured dermatitis on the sunexposed areas (see also Plate 51.4, pp. 494–495).
cheilitis and nasolabial seborrhea without other pellagra skin lesions, as well as pellagrous vulvovaginitis and perianal and scrotal lesions are secondary to riboflavin deficiency, rather than niacin insufficiency (Sebrell, 1979). Healing of pellagra lesions occurs centrifugally, as desquamation begins from the center of the lesion and spreads towards the periphery where there is still active inflammation (Nieves and Goldmisth, 2003). Other gastrointestinal symptoms include dysphagia, abdominal pain, nausea, and vomiting (Miller, 1989; Spivak and Jackson, 1977). Neuropsychiatric symptoms include headache, dizziness, weakness, anorexia, depression, anxiety, insomnia, apathy, memory impairment, hallucinations, delusions, and encephalopathy (Miller, 1989; Spivak and Jackson, 1977). In severe and untreated patients, signs of peripheral nerve, posterolateral cord, and pyramidal tract involvement may occur, and patients may enter a stuporous and comatose state before their eventual death (Hegyi et al., 2004; Miller, 1989; Spivak and Jackson, 1977).
Fig. 51.9. Scaly dermatitis involving the face and V of neck in patient with pellagra. The eruption rapidly resolved with proper dietary intake (see also Plate 51.5, pp. 494–495).
Histology The histology of pellagra is nonspecific (Moore et al., 1942). Early lesions may show ballooning degeneration of the epidermis that results in an intraepidermal vesicle or bulla, or marked papillary dermal edema with resultant subepidermal vesicle or bulla (Hendricks, 1991). Later lesions may show hyperkeratosis and parakeratosis, acanthosis that may be psoriasiform, and increased melanin along the basal layer (Moore et al., 1942). The spinous layer may contain vacuolar changes, similar to those observed in acrodermatitis enteropathica and necrolytic migratory erythema. Atrophic sebaceous glands may be seen (Nieves and Goldsmith, 2003). The infiltrate is mononuclear and located in the superficial dermis (Moore et al., 1942). In the papillary dermis there may be dilated blood vessels and red blood cell extravasation (Hendricks, 1991).
996
Fig. 51.10. Pellagra. Scaly dermatitis on the arms of the man in Figure 51.10 (see also Plate 51.6, pp. 494–495).
HYPERMELANOSIS ASSOCIATED WITH GASTROINTESTINAL DISORDERS
Laboratory Findings Patients with pellagra have a low 24-hour urinary excretion of one or both metabolites of niacin, i.e., N1methyl nicotinamide and its 2-pyridone derivative (Russell, 2001). A combined excretion of N1methyl nicotinamide and 2-pyridone lower than 1.5 mg in 24 hours is suggestive of severe niacin deficiency (Hegyi et al., 2004). They may also have increased serum serotonin and its metabolite 5-hydroxyindoleacetic acid. Hypoalbuminemia, macrocytic anemia, hyperuricemia, hypercalcemia, hypokalemia, hypophosphatemia, abnormal liver function tests, and increased serum porphyrin levels may also be present (Spivak and Jackson, 1977; Hegyi et al., 2004).
Diagnosis Diagnosis is made by the presence of typical cutaneous lesions and history of diet deficiencies with or without gastrointestinal and neurologic symptoms. The diagnosis is confirmed if the syndrome disappears when niacin is introduced into the diet.
Differential Diagnosis Drug eruptions, photodermatitis, atopic dermatitis, subacute lupus erythematosus, polymorphous light eruption, pemphigus vulgaris, PCT, and porphyria variegata and deficiencies of other nutrients, such as zinc, may resemble pellagra (Hegyi et al., 2004; Hendricks, 1991). Although kwashiorkor may also mimic pellagra, kwashiorkor is more common in children, and unlike pellagra, involves the hair and nails (Karthikeyan and Thappa, 2002). It is also important to identify pellagratriggering conditions, such as anorexia nervosa, malabsorptive disorders, alcoholism, carcinoid tumor, Hartnup syndrome, and HIV/AIDS (Murray et al., 2001; Pitche et al., 1999; Prousky, 2003; Russell, 2001).
Pathogenesis Pellagra is caused by a deficiency of niacin (nicotinic acid, vitamin B3, pellagra-preventing vitamin) or nicotinamide. Niacin is a substituted pyridine derivative (Henderson, 1983). Nicotinamide is a derivative of nicotinic acid that contains an amide instead of a carboxyl group. It is nutritionally equivalent to nicotinic acid since it is readily deaminated in the body. Sources of niacin include diet and conversion from tryptophan in vivo. Foods abundant in niacin include lean meats, liver, fish, poultry, unrefined and enriched grains and cereals, milk, nuts, and legumes (Stratigos and Katsambas, 1977). Conversion of tryptophan to niacin occurs when there is an abundance of amino acids in the diet. It requires as cofactors vitamin B1, B2, and B6. In the presence of vitamins B2 and B6, 1 mg of niacin is formed from 60 mg of tryptophan. Nicotinic acid and nicotinamide play important roles in metabolism. They are key components of coenzyme I (nicotinamide adenine dinucleotide, or NAD+) and coenzyme II (nicotinamide adenine dinucleotide phosphate, or NADP+.)
These coenzymes participate in oxidation–reduction reactions, and thus participate in carbohydrate, amino acid, and fatty acid metabolism. NAD and NADP are also active in DNA repair and calcium mobilization involving adenosinediphosphate–ribose transfer reactions. Therefore, niacin deficiency has profound negative effects on cellular function throughout the body, especially in tissues with high energy requirements and/or high cellular turnover, such as the brain, intestinal mucosa, and skin (Hendricks, 1991; Russell, 2001). It is hypothesized that niacin deficiency may trigger phototoxic reactions in the skin through the accumulation of kynurenic acid, a photosensitizing by-product of the tryptophan–niacin conversion pathway that is downregulated by nicotinamide (Hendricks, 1991). In addition, NADPH deficiency (secondary to niacin/nicotinamide insufficiency) may lead to increased oxidative damage to the skin by decreasing concentrations of reduced glutathione needed to detoxify H2O2 to H2O (Hendricks, 1991). Decreased levels of reduced glutathione may also be associated with hyperpigmentation. There is evidence in mammalian models that low levels of reduced glutathione and glutathione reductase activity in the melanocyte milieu stimulate eumelanin-type pigment synthesis (Benedetto et al., 1981, 1982; Halprin and Ohkawara, 1966). Inadequate dietary intake of niacin, nicotinamide, or tryptophan can produce pellagra (Stratigos and Katsambas, 1977). Individuals living in cultures with diets rich in maize have historically been at risk for developing pellagra. Although niacin is present in maize in significant amounts, it is in a nonabsorbable form that is bound to peptides and complex carbohydrates. However, niacin in maize may be released in an alkaline environment. In Mexico, where the practice of washing maize with limewater is common, pellagra has not been a public health issue even among the indigent rural population (Stratigos and Katsambas, 1977). Other causes of nutrition deficiency, such as chronic alcoholism, psychiatric disorders, malabsorption (e.g., jejunoileitis, Crohn disease, gastroenterostomy, or subtotal gastrectomy), and eating disorders also place individuals at risk for pellagra (Nieves and Goldsmith, 2003; Prousky, 2003). In addition, increased dietary leucine (as seen in regions in India with leucine-rich millet-based diet) may precipitate pellagra by inhibiting the conversion from tryptophan to niacin (Stratigos and Katsambas, 1977). Pellagra may be secondary to systemic conditions. Carcinoid tumors often precipitate clinical pellagra by converting a large proportion of tryptophan to serotonin, depleting tryptophan available for niacin production. Tryptophan malabsorption is also seen in Hartnup disease, an inherited disorder of intestinal and kidney tryptophan transport (Russell, 2001). In addition, decreased serum levels of tryptophan and pellagralike manifestations have been described among individuals with HIV infection (Murray et al., 2001; Pitche et al., 1999). Deficiencies in other essential vitamins and nutrients, as commonly seen in malnourished individuals, also contribute
997
CHAPTER 51
to pellagra. For example, deficiency in B2 and B6 (cofactors in conversion reaction from tryptophan to niacin) may cause pellagra (Stratigos and Katsambas, 1977). Therefore, it is important to include replacement of all essential nutrients when treating pellagra. Various medications have also been shown to cause pellagra. Isoniazid and 5-fluorouracil are known to inhibit the conversion of tryptophan to niacin. 6-Mercaptopurine triggers pellagra by inhibiting NAD phosphorylase and NAD production (Miller, 1989). Other pellagragenic medications include pyrazinamide, hydantoins, ethionamide, phenobarbital, azathioprine, and chloramphenicol (Hegyi et al., 2004).
Animal Models “Black tongue,” an experimental analog of pellagra in dogs, was cured and prevented, when their diet was supplemented with nicotinamide or niacin (Elvehjem et al., 1938; Goldberger and Tanner, 1922). Dietary niacin deficiency has also been induced in Japanese quails and Weanling Long-Evans rats (Boyonoski et al., 2000; Koh et al., 1998).
Treatment Oral nicotinamide or nicotinic acid supplementation of 100– 200 mg three times daily for five days is used to treat the clinical manifestations of pellagra. Nicotinamide is preferred over niacin because it does not produce a flushing reaction. Parenteral nicotinamide may be used for patients with poor oral toleration (Hendricks, 1991; Russell, 2001). Diet rich in proteins and essential nutrients should accompany nicotinamide supplementation for complete recovery. Identification and management of underlying causes of secondary pellagra is also crucial. The minimal daily requirement of niacin is 4.4 mg/1000 kcal and the recommended daily allowance of niacin is 6.6 mg/1000 kcal (Food and Nutrition Board and National Research Council, 1989). Therefore, multivitamins with at least 15 mg of nicotinamide should be given daily as preventive therapy along with a high-protein diet (Hendricks, 1991). The response to therapy is dramatic. Early cutaneous lesions and cutaneous, gastrointestinal, and neurologic symptoms respond within 24 hours.
Prognosis Prognosis is good with treatment. If untreated, the course is chronic with seasonal exacerbations, and death can occur as a consequence of dehydration or central nervous system involvement (Hendricks, 1991).
References Benedetto, J. P., J. P. Ortonne, C. Voulot, C. Khatchadourian, G. Prota, and J. Thivolet. Role of thiol compounds in mammalian melanin pigmentation. Part I. Glutathione and related enzymatic activities. J. Invest. Dermatol. 77:402–405, 1981. Benedetto, J. P., J. P. Ortonne, C. Voulot, C. Khatchadourian, G. Prota, and J. Thivolet. Role of thiol compounds in mammalian melanin pigmentation. II. Glutathione and related enzymatic activities. J. Invest. Dermatol. 79:422–424, 1982.
998
Boyonoski, A. C., L. M. Gallacher, M. M. ApSimon, R. M. Jacobs, G. M. Shah, G. G. Poirier, and J. B. Kirkland. Niacin deficiency in rats increases the severity of ethylnitrosourea-induced anemia and leukopenia. J. Nutr. 130:1102–1107, 2000. Elvehjem, C. A., R. J. Madden, F. M. Strong, and D. W. Woolley. Isolation and identification of anti-black tongue factor. J. Biol. Chem. 123:137–149, 1938. Goldberger, J., and W. F. Tanner. Amino acid deficiency is probably the primary etiologic factor in pellagra. Public. Health Rep. 37:462–486, 1922. Food and Nutrition Board, and National Research Council. Recommended daily allowances, 10th ed. Washington DC: National Academy of Sciences, 1989. Halprin, K. M., and A. Ohkawara. Glutathione and human pigmentation. Arch. Dermatol. 94:355–357, 1966. Hegyi, J., R. A. Schwartz, and V. Hegyi. Pellagra: Dermatitis, dementia and diarrhea. Int. J. Dermatol. 43:1–5, 2004. Henderson, L. M. Niacin. Annu. Rev. Nutr. 3:289–307, 1983. Hendricks, W. M. Pellagra and pellagralike dermatoses: etiology, differential diagnosis, dermatopathology and treatment. Semin. Dermatol. 10:282–292, 1991. Karthikeyan, K., and D. M. Thappa. Pellagra and skin. Int. J. Dermatol. 41:476–481, 2002. Koh, Y. H., K. H. Choi, and I. K. Park. Effects of niacin deficiency on the levels of soluble proteins and enzyme activities in various tissues of Japanese quail. Int. J. Biochem. Cell. Biol. 30:943–953, 1998. Miller, S. J. Nutritional deficiency and the skin. J. Am. Acad. Dermatol. 21:1–30, 1989. Moore, R. A., T. D. Spies, and Z. K. Cooper. Histopathology of the skin in pellagra. Arch. Dermatol. 46:100–111, 1942. Murray, M. F., M. Langan, and R. R. MacGregor. Increased plasma tryptophan in HIV-infected patients treated with pharmacologic doses of nicotinamide. Nutrition 17:654–656, 2001. Nieves, D. S., and L. A. Goldsmith. Cutaneous changes in nutritional disease. In: Fitzpatrick’s Dermatology in General Medicine, 6th ed. I. M. Freedberg, A. Z. Eisen, K. Wolff, K. F. Austen, L. A. Goldsmith, and S. Katz (eds). New York: McGraw Hill, Inc., 2003, pp. 1399–1411. Pitche, P., K. Kombate, and K. Tchangai-Walla. Prevalence of HIV infection in patients with pellagra and pellagra-like erythemas. Med. Trop. (Mars.) 59:365–367, 1999. Prousky, J. E. Pellagra may be a rare secondary complication of anorexia nervosa: a systematic review of the literature. Altern. Med. Rev. 8:180–185, 2003. Roe, D. A. A Plague of Corn: The Social History of Pellagra. Ithaca, NY: Cornell University Press, 1973. Russell, R. M. Vitamin and trace mineral deficiency and excess. In: Harrison’s Principles of Internal Medicine, 15th ed. E. Braunwald, A. S. Fauci, D. L. Kasper, S. L. Hauser, D. L. Longo, and J. L. Jameson (eds). New York: McGraw-Hill, Inc., 2001, pp. 461–469. Sebrell, W. H. Identification of riboflavin deficiency in human subjects. Fed. Proc. 38:2694, 1979. Sebrell, W. H., Jr. History of pellagra. Fed. Proc. 40:1520–1522, 1981. Spivak, J. L., and D. L. Jackson. Pellagra: an analysis of 18 patients and review of the literature. Johns Hopkins Med. J. 140:295–309, 1977. Stratigos, J. K., and A. Katsambas. Pellagra: a still existing disease. Br. J. Dermatol. 96:99–106, 1977. World Health Organization. Nutrition for Health and Development: A global agenda for combating malnutrition. World Health Organization, 2000. www.who.int//mipfiles/2231/ NHDprogressreport2000.pdf (accessed February 11, 2004).
HYPERMELANOSIS ASSOCIATED WITH GASTROINTESTINAL DISORDERS
Peutz–Jeghers Syndrome Nancy Burton Esterly, Eulalia Baselga, and Beth A. Drolet
Historical Background Peutz–Jeghers syndrome consists of macular mucocutaneous pigmentation and hamartomatous polyps of the gastrointestinal tract. Although delineation of this syndrome has been credited to two physicians of last century, it was actually first described in twin sisters by Sir Jonathan Hutchinson in 1896. Both of these girls had pigmented lesions on the lips. One died of intestinal intussusception at the age of 20 years and the other died of breast cancer at 52 years (Jeghers et al., 1949). Peutz in 1921 reported on seven individuals in three generations of a Dutch family who had pigmented lesions of the lips and oral mucosa as well as intestinal polyposis. He stressed the association of these two findings (Peutz, 1921). Several incomplete descriptions of patients who probably had this disorder were published subsequently. Then in 1949, Jeghers, McKusick, and Katz collected ten of these patients and, in a landmark paper published in the New England Journal of Medicine, they established this disorder as a specific entity distinct from other disorders of abnormal pigmentation and gastrointestinal polyposis.
Fig. 51.11. Multiple pigmented macules on the lower lip of a patient with Peutz–Jeghers syndrome (see also Plate 51.7, pp. 494–495).
Synonyms This syndrome has also been called Peutz–Touraine–Jeghers syndrome, intestinal polyposis type II and periorificial lentiginosis. The last name is an erroneous term because the pigmented lesions are not lentigines.
Epidemiology and Genetics Peutz–Jeghers syndrome has been described throughout the world in individuals of many ethnic groups. It is inherited as a simple mendelian dominant trait with nearly 100% penetrance and variable expressivity (Foley et al., 1988). It has been estimated that 42–64% of cases arise from spontaneous mutations (Salmon and Frieden, 1995). There is no sex predilection (Jeghers et al., 1949). It is said to occur in 1 in 8300–29 000 births (Kitagawa et al., 1995).
Clinical Findings Mucocutaneous pigmented macules are usually the first sign of the disorder and develop in infancy or childhood. Rarely they are present at birth (Jeghers et al., 1949) or develop as late as the seventh decade of life (McKenna et al., 1994). The macules are brown (Fig. 51.11), black or less commonly blueblack. They range in size from 1 mm to 5 mm and have a round, ovoid or irregular configuration and sometimes a stippled appearance (Jeghers et al., 1949). They occur most often on the lips, particularly the lower lip, and on the buccal mucosa (Fig. 51.12). The gingivae, hard palate and, rarely, the tongue are also sites of predilection. The pigmented macules developing on the cutaneous surfaces are most numerous in the perioral area (Fig. 51.13) but the forehead, paranasal, and periorbital skin can also be involved (Kitagawa et al., 1995).
Fig. 51.12. Typical pigmented macules of the oral mucosa in Peutz–Jeghers syndrome (see also Plate 51.8, pp. 494–495).
In these sites the macules may be smaller and darker in color. At times the macules are distributed over the bridge of the nose in a butterfly pattern (Yosowitz et al., 1974). Elsewhere on the body, sites of predilection include the dorsum of the hands and feet, the fingertips (Fig. 51.14) and toe tips, the umbilicus, and the anus (Jeghers et al., 1949; Kitagawa et al., 1995; Lucky, 1988). Longitudinal pigmented bands may be seen in the nails. The cutaneous pigmentation tends to fade in adulthood but the mucosal pigment persists indefinitely. The pigmented macules are considered markers for the more troublesome gastrointestinal polyps. However, both findings can occur independently and the number of skin lesions does not predict the severity of bowel involvement. The intestinal polyps vary in size, distribution, and number but are multiple in 90% of cases (Yosowitz et al., 1974) and can be sessile or pedunculated. They are believed to be hamartomatous and have a specific pathologic pattern consisting of benign glan999
CHAPTER 51
are often bilateral and multifocal (Burdick and Prior, 1982; Dreyer et al., 1994; Giardiello et al., 1987; Hizawa et al., 1993; Spigelman et al., 1989; Trau et al., 1982; Wilson et al., 1986) and appear at a younger age than expected in the general population (Spigelman et al., 1989).
Histology
Fig. 51.13. Perioral pigmented macules.
Fig. 51.14. Small pigmented macules on the fingertips.
dular structures surrounded by branching bundles of smooth muscle that project towards the surface of the polyp forming a treelike pattern (Hizawa et al., 1993; Perzin and Bridge, 1982). The small bowel, particularly the jejunum and ileum, are the most common sites, but polyps also occur in the stomach and colon. Rarely, polyps have been documented in the gallbladder, kidney, bladder, ureter, and nasopharynx (Salmon and Frieden, 1995). Recurrent bouts of colicky abdominal pain due to obstruction or intussusception, bleeding and chronic iron-deficiency anemia due to fecal blood loss are frequent findings. Although the gastrointestinal polyps are benign, there is a 2–3% risk for malignant transformation. The gastric and duodenal mucosa are the most frequent sites for the development of malignancies (Cordts and Chabot, 1983; Hizawa et al., 1993; Perzin and Bridge, 1982). In addition to gastrointestinal malignancies, which may arise from normal mucosa as well as from polyps, patients with Peutz–Jeghers syndrome are predisposed to develop other types of cancer, particularly breast, lung, and pancreatic cancer, adenoma maligna of the uterine cervix and gonadal tumors such as Sertoli cell testicular tumors and ovarian sex cord tumors with annular tubules. These tumors
1000
There are only a few reports of the histologic findings in the pigmented lesions. The cutaneous macules are characterized by mild acanthosis, elongation of the rete ridges, increased melanin in the epidermal basal cell layer, particularly at the tips of the rete ridges, as well as in melanophages in the subpapillary dermis (Kitagawa et al., 1995; Uno and Hori, 1987). Trau described increased numbers of melanocytes in the basal cell layer as well (Trau et al., 1982). However, Yamada, using dopa stains (Yamada et al., 1981), found approximately the same number of melanocytes in affected skin as in normal skin. Yamada et al. (1981) and Kitagawa et al. (1995) agree that the number of melanocytes in the oral lesions is not increased. Banse-Kupin and Douglass (1986) found an increased number of melanocytes with long dendrites filled with melanosomes in the acral macules but did not describe the histologic findings in oral mucosal lesions. Ultrastructural studies of the oral mucosal macules demonstrated large, deeply pigmented melanosomes singly dispersed within keratinocytes (Yamada et al., 1981). Melanophages in the dermis contained partially degraded melanosomes. In contrast, pigmented macules on nonmucosal surfaces contained numerous melanosomes and melanin granules within the dendrites of the melanocytes but few within the keratinocytes, suggesting a pigment blockade. The dendrites of the melanocytes were noted to be exceptionally long and branched compared to those in the normal skin (Yamada et al., 1981). Uno and Hori (1987) described similar findings in macules of both the lips and fingers. The melanocytes were filled with large numbers of fully melanized melanosomes and had elongated dendritic processes. Portions of the dendritic processes were found among the upper epidermal keratinocytes supporting the concept of pigment blockade as characteristic of this disorder. Giant melanosomes have never been reported in Peutz–Jeghers syndrome.
Diagnosis The criteria for diagnosis of Peutz–Jeghers syndrome are clinical because there are no pathognomonic laboratory studies. Approximately 50% of patients will have a positive family history (Kitagawa et al., 1995; Yosowitz et al., 1974). The findings of typical pigmented macules in characteristic locations along with gastrointestinal polyps, recurrent intussusceptions, episodic bouts of colicky abdominal pain, intestinal obstruction, gastrointestinal hemorrhage, and anemia are highly suggestive of the diagnosis (Jeghers et al., 1949; McAllister and Richards, 1977; Yosowitz et al., 1974). The diagnosis is confirmed by radiologic and endoscopic studies of the gastrointestinal tract that demonstrate multiple polyps which have
HYPERMELANOSIS ASSOCIATED WITH GASTROINTESTINAL DISORDERS
distinctive histologic features. In the infant, the identifying mucocutaneous pigmentation may be absent, posing a considerable diagnostic challenge (Howell et al., 1981).
Differential Diagnosis Differential diagnosis includes juvenile polyposis, which is frequently manifest by gastrointestinal bleeding and secondary iron-deficiency anemia but rarely by colicky pain. This syndrome is not characterized by associated pigmented macules (Yosowitz et al., 1974). Two acquired conditions that overlap with Peutz–Jeghers syndrome are Cronkhite–Canada syndrome and Laugier–Hunziker syndrome. In the former, there is gastrointestinal polyposis, but the hyperpigmented macules affect the skin and not the mucosa. In addition there is nail dystrophy and alopecia and onset is usually over the age of 50 years (Daniel et al., 1982). Laugier–Hunziker syndrome is characterized by hyperpigmented macules of the oral mucosa and lips, hyperpigmented streaks in the nails and absence of gastrointestinal polyps (Koch et al., 1987).
Pathogenesis The pathogenesis is poorly understood. It has been suggested that the gene in Peutz–Jeghers syndrome controls growth and differentiation of cells in the gastrointestinal tract because of the development of the hamartomas and complicating neoplasms (Spigelman et al., 1989). The mechanism for the development of increased mucocutaneous pigmentation is unclear.
Treatment Most authors advise conservative management for the bouts of abdominal pain including bed rest, mild sedation and nasogastric suction. Spontaneous reduction of intussusception is common in these patients. However, continued bleeding or progression to obstruction or strangulation of the bowel demands immediate surgical intervention. Multiple enterostomies will permit removal of large numbers of polyps. Resection should be reserved for short segments of bowel containing large or very numerous polyps to preserve as much bowel as possible (McAllister and Richards, 1977; Yosowitz et al., 1974). Because the risk of malignancy is relatively low in the hamartomatous polyps, prophylactic resection of bowel is not indicated (Howell et al., 1981). More aggressive management consisting of endoscopic polypectomy of as many polyps as possible, particularly those in the stomach, duodenum, and colon, and routine radiologic surveillance studies have been advocated by some authors (Foley et al., 1988). The increased risk for extraintestinal malignancy mandates routine mammography, breast examination, and gynecologic surveillance (to include pelvic ultrasound and cervical smears) for early detection of breast, cervical, and ovarian neoplasms in women with this syndrome. Testicular and pancreatic tumors in particular must be watched for in affected males (Foley et al., 1988; Giardiello et al., 1987; Hizawa et al., 1993; Spigelman et al., 1989). According to relative risk analysis, patients with Peutz–
Jeghers syndrome have a significantly greater risk for the development of gastrointestinal and extra-intestinal cancer and death at a relatively young age (Giardiello et al., 1987; Salmon and Frieden, 1995). Premature death from complications of the gastrointestinal polyps may also occur.
References Banse-Kupin, L. A., and M. C. Douglass. Localization of PeutzJeghers macules to psoriatic plaques. Arch. Dermatol. 122:679– 683, 1986. Burdick, D., and J. T. Prior. Peutz-Jeghers syndrome. A clinicopathologic study of a large family with a 27-year follow-up. Cancer 50:2139–2146, 1982. Cordts, A. E., and J. R. Chabot. Jejunal carcinoma in a child. J. Pediatr. Surg. 18:180–181, 1983. Daniel, E. S., S. I. Ludwig, and K. J. Lewin. The Cronkhite–Canada syndrome: an analysis of clinical and pathologic features and therapy in 55 patients. Medicine 61:293–309, 1982. Dreyer, L., W. K. Jacyk, and D. J. du Plessis. Bilateral large-cell calcifying Sertoli cell tumor of the testes with Peutz-Jeghers syndrome: a case report. Pediatr. Dermatol. 11:335–337, 1994. Foley, T. R., T. J. McGarrity, and A. B. Abt. Peutz-Jeghers syndrome: A clinicopathologic survey of the “Harrisburg family” with a 49year follow-up. Gastroenterology 95:1535–1540, 1988. Giardiello, F. M., S. B. Welsh, S. R. Hamilton, G. J. A. Offerhaus, A. M. Gittelsohn, S. V. Booker, A. J. Krush, J. H. Yardley, and G. D. Luk. Increased risk of cancer in the Peutz-Jeghers syndrome. N. Engl. J. Med. 116:1511–1514, 1987. Hizawa, K., M. Iida, T. Matsumoto, N. Kohrogi, H. Kinoshita, T. Yao, and M. Fujishima. Cancer in Peutz-Jeghers syndrome. Cancer 72:2777–2781, 1993. Howell, J., K. Pringle, B. Kirschner, and J. D. Burrington. PeutzJeghers polyps causing colocolic intussusception in infancy. J. Pediatr. Surg. 16:82–84, 1981. Hutchinson, J. Pigmented spots on the lips of twins. Arch. Surg. 7:290, 1896. Jeghers, H., V. A. McKusick, and K. A. Katz. Generalized intestinal polyposis and melanin spots of the oral mucosa, lips and digits: A syndrome of diagnostic significance. N. Engl. J. Med. 241:993– 1005,1031–1036, 1949. Kitagawa, S., B. L. Townsend, and A. A. Hebert. Peutz-Jeghers syndrome. [Review]. Dermatol. Clin. 13:127–133, 1995. Koch, S. E., P. E. LeBoit, and R. B. Odom. Laugier-Hunziker syndrome. J. Am. Acad. Dermatol. 16:431–434, 1987. Lucky, A. W. Pigmentary abnormalities in genetic disorders. Dermatol. Clin. 6:193–203, 1988. McAllister, A. J., and K. F. Richards. Peutz-Jeghers syndrome: Experience with twenty patients in five generations. Am. J. Surg. 134: 717–720, 1977. McKenna, K. E., M. Y. Walsh, and D. Burrows. Pigmentation of Peutz-Jeghers syndrome occurring in psoriatic plaques. Dermatology 189:297–300, 1994. Perzin, K. H., and M. F. Bridge. Adenomatous and carcinomatous changes in hamartomatous polyps of the small intestine (PeutzJeghers syndrome): report of a case and review of the literature. Cancer 49:971–983, 1982. Peutz, J. L. A very remarkable case of familial polyposis of mucous membrane of intestinal tract and nasopharynx accompanied by peculiar pigmentations of skin and mucous membrane. Nederl. Maatsch. N. F. 10:134–146, 1921. Salmon, J. K., and I. J. Frieden. Congenital and genetic disorders of hyperpigmentation. Curr. Probl. Dermatol. 7:145–196, 1995. Spigelman, A. D., V. Murday, and R. K. S. Phillips. Cancer and the Peutz-Jeghers syndrome. Gut 30:1588–1590, 1989.
1001
CHAPTER 51 Trau, H., M. Schewach-Millet, B. K. Fisher, and H. Tsur. Peutz-Jeghers syndrome and bilateral breast carcinoma. Cancer 50:788–792, 1982. Uno, A., and Y. Hori. Disturbance of melanosome transfer in pigmented macules of Peutz-Jeghers syndrome. In: Brown Melanoderma: Biology and Disease of Epidermal Pigment, T. B. Fitzpatrick, M. M. Wick, and K. Toda (eds). New York: Columbia University Press, 1987, pp. 173–278. Wilson, D. M., W. C. Pitts, R. L. Hintz, and R. G. Rosenfeld. Testic-
1002
ular tumors with Peutz-Jeghers syndrome. Cancer 57:2238–2240, 1986. Yamada, K., A. Matsukawa, Y. Hori, and A. Kukita. Ultrastructural studies on pigmented macules of Peutz-Jeghers syndrome. J. Dermatol. 8:367–377, 1981. Yosowitz, P., R. Hobson, and F. Ruymann. Sporadic Peutz-Jeghers syndrome in early childhood. Am. J. Dis. Child. 128:709–712, 1974.
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
52
Acquired and Congenital Dermal Hypermelanosis Sections Sacral Spot of Infancy Sang Ju Lee, Seung-Kyung Hann, and Sungbin Im Nevus of Ota Sang Ju Lee, Seung-Kyung Hann, and Sungbin Im Nevus of Ito Sang Ju Lee, Seung-Kyung Hann, and Sungbin Im Phakomatosis Pigmentovascularis Sang Ju Lee, Seung-Kyung Hann, and Sungbin Im Other Congenital Dermal Melanocytosis Sang Ju Lee, Seung-Kyung Hann, and Sungbin Im Acquired Dermal Melanocytosis Sang Ju Lee, Seung-Kyung Hann, and Sungbin Im Carleton–Biggs Syndrome Sang Ju Lee, Seung-Kyung Hann, and Sungbin Im Acquired Bilateral Nevus of Ota-like Macules (ABNOM) Sang Ju Lee, Seung-Kyung Hann, and Sungbin Im Blue Macules Associated with Progressive Systemic Sclerosis Sang Ju Lee, Seung-Kyung Hann, and Sungbin Im
Sacral Spot of Infancy Sang Ju Lee, Seung-Kyung Hann, and Sungbin Im
Historical Background Professor E. Balz (1885), a German who taught internal medicine at the University of Tokyo, first described blue-black macules on the buttocks of Japanese children and called them Mongolian spots because he believed them to be characteristic of the Asian peoples. The term Mongolian spot persists in common usage although it has no relation to mongolism (Down syndrome). Anthropologic theories have attempted to explain the origin of this spot, and suggest that it was derived from the racial admixture resulting from the Mongolian invasion of Europe (Cordova, 1981). This benign, blue-gray macule is also called the sacral spot or blue-gray macule of infancy.
Clinical Findings Mongolian spots are present at birth or appear soon after. They usually are located over the sacrum (Figs 52.1 and 52.2). The Mongolian spot, a form of dermal melanocytosis, is the most common congenital pigmented lesion. It is present in approximately 80–100% of newborns of Asian and black origin. About 94% of Korean newborns have this spot (Kim and Herr, 1986). They are also seen in about 1 to 15% of Caucasians (Hori and Takayama, 1988; Leung, 1988). The incidence is slightly higher in males than females. Lesions vary in size from 1–2 cm to extensive areas covering most of the
sacrum, buttocks, and back. In the majority of individuals they occupy less than 5% of the body surface area. Lesions are completely macular and usually have indistinct borders. Their color varies from gray to grayish blue to grayish black. Such variability may be noted in a single patient. The most common location is the sacrococcygeal area followed by the lumbar area, buttock, and back. Less common locations include the thorax and abdomen, leg, arm, and shoulder (Leung, 1988) (Fig. 52.3). Rarely, Mongolian spots occur in the scalp area (Leung and Kao, 1999). Occasionally, in extrasacral regions they are termed aberrant Mongolian spots or macular blue nevus. These macules are usually darker than usual lumbosacral spots and sometimes increase in intensity of color with age. These macules should be called macular type of blue nevus rather than “persistent” Mongolian spots (Hori and Takayama, 1988). Some of the macular types of blue nevi have prominent hair growth within them. Ikeda (1981) labeled macular type of blue nevus as the plaque type of blue nevus. White halo may develop around the sacral spot (Bart and Olson, 1991). The natural history of most sacral spots is the intensification of color in the first year of life. They reach maximum size by 2 years of age, followed by gradual disappearance during the first 6–7 years of life. By 10 years of age almost all Mongolian spots have disappeared. The frequency of persistent lesions has been estimated to be 3–4% (Kikuchi, 1982; Leung, 1988).
Associated Disorders In a condition as common as the Mongolian spot, one must 1003
CHAPTER 52
52.1
52.2
Figs. 52.1 and 52.2. Mongolian spots at sacral region (see also Plate 52.1, pp. 494–495).
be cautious in labeling associated abnormalities as more than a coincidence. Nevertheless, a true association appears to exist between extensive Mongolian spots and metabolic disorders. An abnormality of sphingolipid metabolism, GM1 type 1 gangliosidosis, is caused by a deficiency of the enzyme bgalactosidase. Severe developmental delay, facial and peripheral edema, unusual facial features, hepatosplenomegaly, and cherry-red spots of the retina have been observed in these patients. The skin findings in those cases consist of widespread multiple confluent and individual bluish macules varying in size from a few millimeters to several centimeters. The diagnosis is made by demonstration of absence of b-galactosidase activity in peripheral leukocytes and/or skin fibroblasts (Beratis et al., 1989; Selsor and Lesher, 1989; Weissbluth et al., 1981). Grant et al. (1998) investigated a 9-month-old black girl in whom evaluation for extensive Mongolian spots led to an early diagnosis of Hurler syndrome. Hurler syndrome is recognized as the most common and severe form of the mucopolysaccharidoses in infancy. The molecular basis for Hurler syndrome involves a series of specific mutations on the short arm of chromosome 4. These mutations cause an absence of the lysosomal glycosidase a-L-iduronidase, which
1004
is required in the sequential process of dismantling glycosaminoglycans. The partially degraded glycosaminoglycans heparan sulfate and dermatan sulfate are deposited in various organs, producing a wide array of clinical manifestations, including coarse facial features, hypertrichosis, cloudy corneas, progressive mental retardation, and hepatosplenomegaly (Grant et al., 1998). A clinical correlation was suggested between extensive Mongolian spots and Hunter syndrome (Ochiai et al., 2003). Hunter syndrome is an Xlinked disorder characterized by a deficiency of lysosomal iduronate-2-sulfatase, and resultant accumulation of dermatan and heparin sulfate. Both Hurler and Hunter syndromes are progressive in nature, and thus the importance of early diagnosis should be emphasized to prevent progressive, irreversible organ damage. Extensive Mongolian spots is one of the cutaneous findings that provides the clue (Grant et al., 1998; Ochiai et al., 2003). A meningeal tumor of the spine, which was found to be a benign melanocytoma, was described in an adult patient with a persistent Mongolian spot on the back. Another case of neurocutaneous melanosis has been reported in association with extensive slate-gray lesions of dermal melanocytosis and
ACQUIRED AND CONGENITAL DERMAL HYPERMELANOSIS
Fig. 52.3. Aberrant Mongolian spot (macular type of blue nevus) (see also Plate 52.2, pp. 494–495).
a nevus flammeus (Novotny and Urich, 1986). A Hispanic infant with lesions clinically identical to Mongolian spots was found to have a myelomeningocele as well as hydrocephalus. Biopsy of the skin, however, demonstrated an increase in epidermal as well as dermal melanocytes which differed from the usual histology of Mongolian spots (Schwartz et al., 1986). Several papers reported an association of dermal melanocytosis with cleft lip (Bart and Olson, 1991; Inoue et al., 1982; Kurata et al., 1989; Mori et al., 1975) and it is called a “cleft lip-Mongolian spot” (Igawa et al., 1994). A patient with an adult onset sacral spot was reported as “adult onset Mongolian spot” (Carmichael et al., 1993).
Histopathology The etiology of this birthmark is unknown. During fetal life, dermal melanocytes migrate from the neural crest to their designated site at the dermoepidermal junction. Dermal melanocytes are present in the dermis of embryos beginning in
the tenth week, and between the eleventh and fourteenth week these migrate to the epidermis. They gradually disappear from the dermis after the twentieth week. A sacral spot of infancy is thought to be due to a failure of migration of dermal melanocytes to the epidermis and their delayed disappearance from the dermis (Leung et al., 1988). A Japanese anatomist, Morooka, examined fetuses and noted that dermal melanocytes typical of the spots were present at three months of fetal life. Lesions were recognizable macroscopically by seven months gestation (Kikuchi, 1982). Histopathologically the lesions consist of dendritic melanocytes containing melanin granules lying scattered between the collagen bundles in the lower one half to two thirds of the dermis. By electron microscopy these melanocytes contain numerous melanized melanosomes. Also, in most white children, dermal melanocytes can be found histologically in the lumbosacral region but they possess incompletely melanized melanosomes and are not visible clinically. The regression of Mongolian spots is a unique event not seen in other forms of dermal melanocytosis. The mechanism for their disappearance is poorly understood. The ultrastructural examinations show an extracellular sheath enclosing dermal melanocytes. It is less well developed in the Mongolian spot than in the nevus of Ito (Okawa et al., 1979). Inoue et al. (1982) noted that persistent Mongolian spots were enveloped in a fibrous sheath, which is not present in regressing lesions. Halo Mongolian spots have been described rarely. Histologic examination shows a lack of inflammatory infiltrate (Bart and Olson, 1991). Very extensive Mongolian spots may regress more slowly and portions may never disappear completely. Persistent Mongolian spots, also called dermal melanocytic hamartoma, occur in approximately 3–4% of Japanese adults. They are probably analogous to the nevus of Ota or Ito. Persistent lesions are also seen in the nevus pigmentovascularis.
Differential Diagnosis and Management The differential diagnosis of Mongolian spots includes traumatic ecchymosis. Occasionally parents of affected infants have erroneously been accused of child abuse (Smialek, 1980; Dungy, 1982). Other diagnostic considerations include nevi of Ota and Ito as well as large congenital melanocytic nevi. Nevi of Ota and Ito appear from birth to adolescence and usually persist in life. The histology of the Mongolian spot is similar to that of nevi of Ota and Ito. They show wavy, bipolar melanocytes lying parallel to the surface and scattered among the collagen bundles. The melanocytes are located predominantly in the upper dermis in nevi of Ota and Ito, but in the lower dermis in Mongolian spots. Mongolian spots are almost always self-limited and of no clinical importance. No treatment is necessary.
References Balz, E. Die korperlichen Eigneschaften der Japaner. Mitteheil d. deutsch Gesell. f. Natur-u Volkerkunde Ostasiens Bd. 4:H. 32, 1885 (as cited in Morooka, 1931).
1005
CHAPTER 52 Bart, B. J., and C. L. Olson. Congenital halo mongolian spot. J. Am. Acad. Dermatol. 6:1082–1083, 1991. Beratis, N. G., A. Varvarigou-Frimas, S. Beratis, and S. L. Sklower. Angiokeratoma corporis diffusum in GM1 type gangliosidosis, type 1. Clin. Genet. 36:59–64, 1989. Carmichael, A. J., C. Y. Tan, and S. M. Abraham. Adult onset Mongolian spot. Clin. Exp. Dermatol. 18:72–74, 1993. Cordova, A. The mongolian spot. Clin. Pediatr. (Phila.) 20:714–719, 1981. Dungy, C. I. Mongolian spots, day care centers, and child abuse. Pediatrics 69:672, 1982. Grant, B. P., J. S. Beard, F. Castro, M. C. Guiglia, and B. D. Hall. Extensive Mongolian spots in an infant with Hurler syndrome. Arch. Dermatol. 134:108–109, 1998. Hori, Y., and O. Takayama. Circumscribed dermal melanoses: Classification and histologic features. Dermatol. Clin. 6:315–326, 1988. Igawa, H. H., T. Ohura, T. Sugihara, T. Ishikawa, and M. Kumakiri. Cleft lip Mongolian spot: Mongolian spot associated with cleft lip. J. Am. Acad. Dermatol. 30:566–569, 1994. Ikeda, S., A. Makita, and K. Tajima. Clinical and histologic study of blue nevus. In: Biology and Diseases of Dermal Pigmentation, T. B. Fitzpatrick, A. Kukita, F. Morikawa, M. Seiji, A. J. Sober, and K. Toda (eds). Tokyo: University of Tokyo Press, 1981, pp. 95– 106. Inoue, S., I. Kukuchi, and T. Ono. Dermal melanocytosis associated with cleft lip. Arch. Dermatol. 118:443–444, 1982. Kikuchi, I. What is a mongolian spot? Int. J. Dermatol. 21:131–133, 1982. Kim, J. H., and H. Herr. A statistical study of mongolian spot. Korean J. Dermatol. 24:373–379, 1986. Kurata, S., Y. Ohara, S. Itami, Y. Inoue, H. Ichikawa, and S. Takayasu. Mongolian spots associated with cleft lip. Br. J. Plast. Surg. 42:625–627, 1989. Leung, A. K. C. Mongolian spots in Chinese children. Int. J. Dermatol. 27:106–108, 1988. Leung, A. K. C., R. B. Lowry, I. Mitchell, S. Martin, and D. M. Cooper. Klippel-Trenaunay and Sturge-Weber syndrome with extensive Mongolian spots, hypoplastic larynx and subglottic stenosis. Clin. Exp. Dermatol. 13:128–132, 1988. Leung, A. K. C., and C. P. Kao. Extensive Mongolian spots with involvement of the scalp. Pediatr. Dermatol. 16:371–372, 1999. Mori, T., T. Onizuka, and T. Akagawa. Cleft lip nevus. Jpn. J. Plast. Reconstr. Surg. 18:526–527, 1975. Novotny, E. J., and H. Urich. The coincidence of neurocutaneous melanosis and encephalofacial angiomatosis. Clin. Neuropathol. 5:246–251, 1986. Ochiai, T., K. Ito, T. Okada, M. Chin, H. Shichino, and H. Mugishima. Significance of extensive Mongolian spots in Hunter’s syndrome. Br. J. Dermatol. 148:1173–1178, 2003. Okawa, Y., R. Yokota, and A. Yamauchi. On the extracellular sheath of dermal melanocytes in nevus fuscocaeruleus acromiodeltoideus (Ito) and Mongolian spot: an ultrastructural study. J. Invest. Dermatol. 73:224–230, 1979. Schwartz, R. A., N. Cohen-Addad, M. W. Lambert, and W. C. Lambert. Congenital melanocytosis with myelomeningocele and hydrocephalus. Cutis 37:37–39, 1986. Selsor, L. C., and J. L. Lesher. Hyperpigmented macules and patches in a patient with GM1 type gangliosidosis. J. Am. Acad. Dermatol. 20:878–882, 1989. Smialek, J. E. Significance of Mongolian spots. J Pediatr. 97:504–505, 1980. Weissbluth, M., N. B. Esterly, and W. A. Caro. Report of an infant with GM1 type gangliosidosis type 1 and extensive and unusual mongolian spots. Br. J. Dermatol. 104:195–200, 1981.
1006
Nevus of Ota Sang Ju Lee, Seung-Kyung Hann, and Sungbin Im
Historical Background Nevus of Ota is a form of benign melanocytosis located over the first (ophthalmic) and second (maxillary) branches of the trigeminal nerve. It was first described by Ota and Tanino (1939) as naevus fuscocaeruleus ophthalmomaxillaris. Later Fitzpatrick et al. (1956) suggested the term oculodermal melanocytosis. The term nevus of Ota is commonly used to refer to this anomaly.
Epidemiology Most cases of nevus of Ota have been reported in Asia including Japan and Korea. Nevus of Ota occurs in approximately 1 out of 500 people (Hidano et al., 1967). Eighty percent of all reported cases are of females (Geronemus, 1992; Hidano et al., 1967; McDonald and Georgouras, 1992). The ratio of males to females in Korea is 1:2.67 (Lee, 1986). In Japan, 0.4–1% of all patients seen in dermatologic clinics have nevus of Ota (Balmaceda et al., 1993; Hidano et al., 1967). The general prevalence of nevus of Ota in Korea was reported as 0.03% in adolescents. In dermatology clinics in Korea the prevalence was reported as 0.24% (Lee, 1986). It also occurs in Chinese, East Indians, and black and white people (Watanabe and Takahashi, 1994). Nevus of Ota is typically congenital but can be acquired (Balmaceda et al., 1993; Whitmore et al., 1991). Inherited cases are rare. To date only five familial cases of nevus of Ota have been reported (Trese et al., 1981).
Clinical Findings There is a bimodal age of onset: the first (about 50–60% of all cases) in early childhood before the age of 1 year, with the majority present at birth; and the second (40 to 50%) around puberty (Hidano et al., 1967; Lynn et al., 1993; RuizVillaverde et al., 2003). The remainder arise during the first four decades of life (Hidano et al., 1967; Whitmore et al., 1991). The female to male ratio is 4.8:1 in Japan. Some have speculated that a hormonal influence on melanogenesis may play a role in unmasking the nevus and may contribute to the female predominance and bimodal peak age of onset. The intensity of pigmentation may be influenced by fatigue, menstruation, insomnia, and weather (Hidano et al., 1967). In approximately 5% of cases the onset of the nevus is noted after minor trauma such as a contusion or sunburn. However, the relationship between these events and dermal melanocytosis remains unclear (Kopf and Weidman, 1962; Okawa et al., 1979; Whitmore et al., 1991). Clinically an ill-defined, brown, blue-gray or blue-black patchy hyperpigmentation intermingled with small flat brown spots is observed in the distribution of the maxillary and ophthalmic branches of the fifth cranial nerve. Rarely, it involves the third branch of the trigeminal nerve. In 5% of cases, the lesions are bilateral (Hidano, 1985; Hori et al., 1984; Reinke et al., 1974) although bilateral involvement occurs in 5–13%
ACQUIRED AND CONGENITAL DERMAL HYPERMELANOSIS
Fig. 52.5. Ocular hyperpigmentation in a patient with nevus of Ota.
Fig. 52.4. Slate-blue hyperpigmentation of the cheek.
of affected individuals (Kopf and Weidman, 1962). There are individuals with a unilateral nevus of Ito and a bilateral nevus of Ota (Furukawa et al., 1970; Hidano et al., 1965). The nevus of Ito differs from the nevus of Ota only by its distribution. The nevus of Ito affects the supraclavicular, scapular, and deltoid regions. It may occur alone or in association with an ipsilateral or bilateral nevus of Ota (Hidano et al., 1965; Mishima and Mevorah, 1961). The pigmentation is usually poorly demarcated, macular or slight raised and mottled with colors that vary from black to purple, blue-black, slate-blue (Fig. 52.4), purple-brown, or brown (Fitzpatrick et al., 1987; Hidano et al., 1967; Hori and Takayama, 1988; Liesegang, 1994). Slightly raised or nodular areas identical to blue nevi may be present (Dorsey and Montgomery, 1954; Kopf and Weidman, 1962; McDonald and Georgouras, 1992). Focal cellular blue nevi that enlarge can be mistaken for a malignant melanoma (Kersting and Caro, 1956; Yeschua et al., 1975). There are no abnormalities of vascularization or hair (Kopf and Weidman, 1962; Okawa et al., 1979). Ocular involvement in the nevus of Ota occurs approximately in two-thirds of patients (Patel et al., 1998). Hyper-
pigmentation may occur on the sclera (Fig. 52.5), cornea, iris, optic nerve, fundus, extraocular muscles, retrobulbar fat, and periosteum (Balmaceda et al., 1993; Bhattacharya et al., 1973; Hidano et al., 1967; Hori and Takayama, 1988; Liesegang, 1994; McDonald and Georgouras, 1992). The melanocytic infiltration of the iris may manifest as heterochromia iridis. Similar pigment changes can rarely be seen in the mucosal membranes of the head and neck such as pharynx, nasal mucosa, buccal mucosa, tympanic membrane, and hard palate (Balmaceda et al., 1993; Bhattacharya et al., 1973; Hidano et al., 1967; Hori and Takayama, 1988; Liesegang, 1994; McDonald and Georgouras, 1992). The lesion can be found on the eustachian tube, the tympanic membrane (55%), nasal mucosa (28%), pharynx (24%), or on the palate (18%) (Hidano et al., 1967). Pigmented melanocytes also may be found in underlying periosteum, bone, dura mater, and cerebral cortex, the orbicularis and temporalis muscles, or maxillary sinus. Many patients report fluctuation of pigment intensity associated with fatigue, menstruation, insomnia, and weather changes (Hidano et al., 1967; Yoshida, 1952). The brown spots are caused by epidermal hyperpigmentation. The blue-black or slate-gray macules are caused by the presence of dermal melanocytes. Spontaneous regression does not occur. The nevus of Ota has been classified by the extent of the anomaly into four types (Tanino, 1939). Types I–III are unilateral. Type IA or mild orbital type is characterized by light brown or slate spotted pigmentation limited to the upper and lower eyelids. Type IB (mild zygomatic) has discrete brownish purple spots limited to the zygomatic region. Type II (moderate) exhibits deep slate- to brown-purple, relatively dense spotted pigmentation on the eyelids, zygomatic region, and base of the nose. Type III (extensive) is characterized by deep blue to bluish-purple, densely spotted, or almost diffuse pigmentation on the eyelids, zygomatic region, base of the nose and nasal ala, forehead, external ear, post auricular region, and anterior scalp. Type IV (bilateral) involves both sides of the face. Extracutaneous pigmentation is common and affects 1007
CHAPTER 52
the conjunctiva, sclera, and tympanic membrane. Less frequently, the nasal mucosa, palate, pharynx, cornea, iris, uveal tract, and fundus are affected. There are two main complications associated with nevus of Ota: ocular complications and malignancy. The nevus of Ota can develop a number of ocular complications such as melanosis oculi (Teekhasaence et al., 1990), ocular hypertension (Kitagawa et al., 2003), and glaucoma of the involved eye (Kopf and Weidman, 1962; Sang et al., 1977). Abnormalities of ocular pigmentation occur in 49–65% of patients with nevus of Ota (Hidano et al., 1967; Kopf and Weidman, 1962; Tanino, 1939). It is almost always unilateral. Only one case of bilateral ocular involvement has been reported (Dompmartin et al., 1989). In cases of ocular involvement, ipsilateral sclera is always involved, most commonly in the temporal or superior quadrants (Cowan and Balistocky, 1962). Other sites of ocular involvement are the iris (50%), the conjunctiva (40%), the choroid (18%), and the optic nerve and its meningeal sheath (5%) (Cowan and Balistocky, 1962; Tanino, 1940). Melanocytosis of the cornea, the ciliary body, extraocular muscles, orbital fat, and periorbital and orbital bones has been described. Ocular hypertension has been found in patients with nevus of Ota and it is thought to be due to goniodysgenesis, abnormally thick cornea, or infiltration of melanocytic cells into the trabecular meshwork (Kitagawa et al., 2003; Teekhasaenee et al., 1990). Ocular melanocytosis with occlusion of the canal of Schlemm that results in secondary glaucoma has been observed in seven patients (Reinke et al., 1974; Teekhasaenee et al., 1990). Melanoma associated with nevus of Ota was first described by Hulke in 1861. In general, nevus of Ota does not often give rise to malignant melanoma. However, malignant transformation has occurred in 4.6% of 670 cases of nevus of Ota reported in the literature (Miller, 1994; Shaffer et al., 1992). The median age at which the melanoma was detected was 51 years (range 15–72). Melanoma occurs more frequently in white people. Of the 32 reported cases, 28 occurred in white patients, 3 in Japanese and 1 in a black patient. Dutton and colleagues (1984) estimated the incidence of malignancy to be up to 25% for white patients, 1% for black patients, and 0.5% for Asians. The most common site for melanoma is the choroid, followed by the uveal tract (Bordon et al., 1995; Dutton et al., 1984; Hagler and Brown, 1966; Haim et al., 1982; Hartmann et al., 1989; Jay, 1965; Liesegang, 1994; Speakman and Phillips, 1973). Seventeen of 39 individuals had a choroidal melanoma (Albert and Scheie, 1963; Croxatto et al., 1981; Frezzotti et al., 1968; Gonder et al., 1981, 1982; Halasa, 1970; Hulke, 1861; Makley and King, 1967; Mohandessan et al., 1979; Nik et al., 1982; Ray and Schaeffer, 1967; Singh et al., 1988; Ticho et al., 1989; Velazquez and Jones, 1983; Yamamoto, 1969). Conjunctival melanoma has not been reported (Liesegang, 1994). Melanoma can also arise in the skin (Croxatto et al., 1981; Dompmartin et al., 1989; Hartmann et al., 1989; Kopf and Bart, 1982).
1008
Fig. 52.6. Bipolar melanocytes in the dermis cause this abnormality.
A few cases of intracranial melanoma have been reported (Balmaceda et al., 1993; Horsey et al., 1980; Theunissen et al., 1993). Primary melanoma developed in the central nervous system in 23% of affected individuals (Botticelli et al., 1983; Enriquez et al., 1972; Hartmann et al., 1989; Horsey et al., 1980; Sang et al., 1977; Shaffer et al., 1992; Willis, 1967; Yanoff and Zimmerman, 1967). These have involved the dura (Horsey et al., 1980), Meckel’s cave (Botticelli et al., 1983), pineal gland (Enriquez et al., 1973), cortical surfaces (Sang et al., 1977; Willis, 1967), and the optic chiasm (Kojima et al., 1959). Nevus of Ota has also been reported with an ipsilateral plexiform neuroma (Gupta et al., 1986). The cause of the melanoma has not been determined. A causal relationship between nevus of Ota and melanoma has not yet been established.
Histology The epidermis is typically normal. There is a dense population of bipolar melanocytes in the dermis (Hirayama and Suzuki, 1991; Hori et al., 1982; Ishibashi et al., 1990) (Fig. 52.6). These melanocytes are weakly dopa positive, an indication that they retain some capacity to synthesize melanin. On electron microscopy the dermal melanocytes are noted to contain many singly dispersed melanosomes 0.4–0.8 mm in size (Hori et al., 1982). Occasionally giant melanosomes may be seen (Ticho et al., 1989). Most melanosomes are fully melanized. Partially melanized melanosomes are observed rarely if at all. The melanosomes in melanocytes in the basal layer of the epidermis overlying the nevus are small, 0.2–0.3 mm in longest dimension. A lamina lucida and lamina densa can be found around some dermal melanocytes. The dermal melanocytes are surrounded by an extracellular sheath of various thicknesses. The extracellular sheaths are PAS negative and are composed of fine filaments, 2–4 nm in diameter and have a feltlike structure. The thickness of extracellular sheaths differs according to the age of the patient and thickens as the patient gets older. This pattern is similar to that in Mongolian spots
ACQUIRED AND CONGENITAL DERMAL HYPERMELANOSIS
A
B
Fig. 52.7. Nevus of Ota showing intense blush color (A). Total disappearance of the lesion after laser treatment (B) (see also Plate 52.3A and B, pp. 494–495).
except that in nevus of Ota it tends to be more superficial (Maize and Ackerman, 1987; Lever and Schaumburg-Lever, 1983). Merkel cells have also been reported in these lesions (Ono et al., 1984). Although most of the melanocytes lie in the upper third of the reticular dermis, melanocytes also can be found in the papillary dermis and the subcutis tissue around adnexa (Hidano et al., 1965). Hirayama and Suzuki (1991) classified nevus of Ota into five types according to the distribution of dermal melanocytes. These are the superficial (type S), superficial dominant (type SD), diffuse (type Di), deep dominant (type DD), and deep (type De). The histologic types correlated well with the visible color of the nevus. The more brownish lesions represented type S or type SD. The most bluish lesions were type Di, DD or De. Melanophages are rarely observed. The slightly raised or infiltrated areas within the nevus of Ota and Ito show a larger number of elongated, dendritic melanocytes than do non-infiltrated areas. These areas mimic the pathology of a common or cellular blue nevus (Kopf and Weidman,
1962). In the oral mucosa, a more dense concentration of melanocytes are found in the dermis (Mishima and Mevorah, 1961). In ocular tissue, melanocytes may be seen in the episclera, deeper layers of scleral stroma, conjunctiva, iris, and choroid (Fitzpatrick et al., 1956).
Associated Disorders Nevus of Ota has been associated with other disorders such as vascular malformations and/or hemiparesis (Ono et al., 1984). This syndrome is classified as nevus pigmentovascularis (Benson and Rennie, 1992; Reed and Sugarman, 1974). Other reported associations include the Sturge–Weber syndrome (Noreiga-Sanchez et al., 1972), neurosensory hearing loss (Reed and Sugarman, 1974; Alvarez-Cuesta et al., 2002), spinocerebellar degeneration (Whyte and Dekaban, 1976), the Klippel–Trenaunay–Weber syndrome (Furukawa et al., 1970), and intracranial vascular malformations (Keinke et al., 1974). A number of other congenital anomalies including multiple gastrointestinal hemangiomas, intracranial arteriovenous mal-
1009
CHAPTER 52
formation, enlargement of the posterior cranial fossa, von Recklinghausen disease, ipsilateral sensorineural deafness, Down syndrome with unilateral congenital cataract and ipsilateral hemiatrophy of the upper extremity, and familial cerebellar degeneration have been reported in association with the nevus of Ota. Whether these associations are causally related to the nevus of Ota or are incidental findings is not clear.
Pathogenesis Nevus of Ota is thought to represent disorder of neural crest migration (Benson and Rennie, 1992). Melanoblasts normally arise from the neural crest and migrate to the skin, leptomeninges, ocular structures and the internal ear. Deafness has been associated with nevus of Ota (Reed and Sugarman, 1974). Some cells ascend to the dermal–epidermal junction to become branched melanocytes producing melanin. In the nevus of Ota, blue nevus and Mongolian spots, melanocytes are thought to be aberrant and become arrested during migration, remaining in the dermis. This results in a persistent discoloration and cosmetic disfigurement (Maize and Ackerman, 1987; Zimmerman and Becker, 1959).
Treatment The lesion of nevus of Ota persists throughout life. There are no reports of spontaneous regression. The Mongolian spot typically disappears during childhood. With time, the nevus of Ota/Ito may increase in intensity, particularly within the first year of life. Rarely, the lesions may become less apparent during childhood. If ocular pigmentation is present, patients should be followed periodically by an ophthalmologist. It is unnecessary to remove prophylactically stable cutaneous lesions (Kopf and Weidman, 1962). Several aggressive therapies have been used in the past such as surgical excision with or without skin grafting, dermabrasion, and cryotherapy. Surgical treatment causes scarring, but some surgeons have demonstrated good results with a microsurgical technique (Furukawa et al., 1970). Cryotherapy can be effective but success depends on the site of the lesion. It is not reliable and may cause atrophy or scarring if it is applied excessively. Lasers in recent years have also been used to treat successfully the nevus of Ota (Apfelberg et al., 1981). The monochromatic, focused light beam from Q-switched ruby or Q-switched neodymium:yttrium aluminum garnet (Nd:YAG) lasers have been shown to interact selectively with melanin killing the melanocytes (Fig. 52.7). Several reports have proved the safety and efficacy of laser treatments (Geronemus, 1992; Lowe et al., 1993; Taylor et al., 1994; Watanabe and Takahashi, 1994). The treatment of choice is laser therapy with the Q-switched ruby (Charles et al., 1994), Q-switched Nd:YAG, or Q-switched alexandrite layers (al Deeb and Bahou, 1993; Geronemus, 1992; Sawada et al., 1990; Watanabe and Takahashi, 1994; Zimmerman and Becker, 1959). These are helpful in reducing the intensity of pigment with minimal risk of scarring. Watanabe treated a nevus of Ota on 114 patients with good results. Of the 35 patients who 1010
received four or five treatments, 33 had an excellent response (lightening of 80% or more) and 2 had a good response (lightening of 40–80%). The laser treatment of nevus of Ota in children can achieve a good result in fewer sessions and at a lower complication rate than later treatment (Kono et al., 2003). The risk of recurrence after laser treatment is estimated to be between 0.6% and 1.2% (Chan et al., 2001). Dermabrasion can be helpful in some cases. Because most nevi are macular, many patients feel opaque covering agents yield cosmetically acceptable results.
References Albert, D. M., and H. G. Scheie. Naevus of Ota with malignant melanoma of the choroid: Report of a case. Arch. Ophthalmol. 69:774–777, 1963. al Deeb, S. M., and Y. Bahou. A new neurocutaneous syndrome possibly related to Ota’s nevus. J. Neurol. Sci. 118:92–96, 1993. Alvarez-Cuesta, C. C., C. Raya-Aguado, F. Vazquez-Lopez, P. B. Carcia, and N. Perez-Olova. Nevus of Ota associated with ipsilateral deafness. J. Am. Acad. Dermatol. 47:S257–S259, 2002. Apfelberg, D. B., M. R. Moser, H. Lash, and J. Rivers. The argon laser for cutaneous lesions. J. Am. Med. Assoc. 245:2073–2075, 1981. Balmaceda, C. M., M. R. Fetell, J. Powers, J. L. O’Brien, and E. H. Housepian. Nevus of Ota and leptomeningeal melanocytic lesions. Neurology 43:381–386, 1993. Benson, M. T., and I. G. Rennie. Hemi-naevus of Ota: perturbation of neural crest differentiation as a likely mechanism. Graefes Arch. Klin. Exp. Ophthalmol. 230:226–229, 1992. Bhattacharya, S. K., H. S. Girgla, and G. Singh. Nevus of Ota. Int. J. Dermatol. 12:344–347, 1973. Bordon, A. F., M. L. Wray, R. Belfort, I. W. McLean, and M. Burnier. Choroidal malignant melanoma in association with oculodermal melanocytosis in a black patient. Br. J. Ophthalmol. 79:191–192, 1995. Botticelli, A. R., M. Villani, P. Angiori, and L. Peserice. Meningeal melanocytoma of Meckel’s cave associated with ipsilateral Ota nevus. Cancer 51:2304–2310, 1983. Chan, H. H., L. K. Lam, D. S. Wong, R. S. Leung, S. Y. Ying, C. F. Lai, W. S. Ho, and J. K. Chua. Nevus of Ota: a new classification based on the response to laser treatment. Lasers Surg. Med. 28:267–272, 2001. Charles, R. T., J. F. Thomas, G. William, and A. Rox. Treatment of nevus of Ota by Q-switched ruby laser. J. Am. Acad. Dermatol. 30:743–751, 1994. Cowan, T. H., and M. Balistocky. The nevus of Ota or oculodermal melanocytosis. The ocular changes. Arch. Ophthalmol. 65:483– 492, 1962. Croxatto, J. W., D. E. Charles, and E. S. Mallran. Neurofibromatosis associated with nevus of Ota and choroidal melanoma. Am. J. Ophthalmol. 92:578–580, 1981. Dompmartin, A., D. Leroy, D. Labbe, J. B. Letessier, and J. C. Mandard. Dermal malignant melanoma developing from a nevus of Ota. Int. J. Dermatol. 28:535–536, 1989. Dorsey, C. S., and H. Montgomery. Blue nevus and its distinction from Mongolian spot and the nevus of Ota. J. Invest. Dermatol. 22:225–236, 1954. Dutton, J. J., R. L. Anderson, R. L. Schelper, J. J. Purcell, and D. T. Tse. Orbital malignant melanoma and oculodermal melanocytosis: Report of two cases and review of the literature. Ophthalmology 91:497–507, 1984. Enriquez, R., B. Egbert, and J. Bullock. Primary malignant melanoma of central nervous system: Pineal involvement in a patient with nevus of Ota and multiple pigmented skin nevi. Arch. Pathol. 95:392–395, 1972.
ACQUIRED AND CONGENITAL DERMAL HYPERMELANOSIS Enriquez, R., B. Egbert, and J. Bullock. Primary malignant melanoma of the central nervous system: pineal involvement in a patient with nevus of Ota and multiple pigmented skin nevi. Arch. Pathol. 95:392–395, 1973. Fitzpatrick, T. B., R. Zeller, A. Kukita, and H. Kitamura. Ocular and dermal melanocytosis. Arch. Ophthalmol. 56:830–832, 1956. Fitzpatrick, T. B., A. Z. Eisen, K. Wolff, I. M. Freedburg, and K. F. Austen. Dermatology in General Medicine, 3rd ed. New York: McGraw Hill, Inc., 1987, pp. 979–981. Frezzotti, R., R. Guerra, G. P. Dragoni, and P. Bonamsi. Malignant melanoma of the choroid in a case of naevus of Ota. Br. J. Ophthalmol. 52:922–924, 1968. Furukawa, T., A. Igata, Y. Toyokura, and S. Ikeda. Sturge-Weber and Klippel-Trenaunay syndrome with nevus of Ota and Ito. Arch. Dermatol. 102:640–645, 1970. Geronemus, R. G. Q-switched ruby laser therapy of nevus of Ota. Arch. Dermatol. 128:1618–1622, 1992. Gonder, J. R., J. A. Shields, and D. M. Albert. Malignant melanoma of the choroid associated with oculodermal melanocytosis. Ophthalmology 88:372–376, 1981. Gonder, J. R., E. B. Shields, D. M. Albert, J. J. Augsburger, and P. T. Lavin. Uveal malignant melanoma associated with ocular and oculodermal melanocytosis. Ophthalmology 89:953–959, 1982. Gupta, A., J. Ram, and I. S. Jain. Nevus of Ota associated with neurofibromatosis. Ann. Ophthalmol. 18:154–155, 1986. Hagler, W. S., and C. C. Brown. Malignant melanoma of the orbit arising in the nevus of Ota. Trans. Am. Acad. Ophthalmol. Otolaryngol. 70:817–822, 1966. Haim, T., E. Meyer, H. Kerner, and S. Zonis. Oculodermal melanocytosis and orbital malignant melanoma. Ann. Ophthalmol. 14:1132– 1136, 1982. Halasa, A. Malignant melanoma in a case of bilateral nevus of Ota. Arch. Ophthalmol. 84:176–178, 1970. Hartmann, L. C., G. F. Oliver, R. K. Winkleman, T. V. Colby, T. M. Sundt, and B. P. O’Neill. Blue nevus and nevus of Ota associated with dural melanoma. Cancer 64:182–186, 1989. Hidano, A. Acquired, bilateral nevus of Ota-like macules [letter]. J. Am. Acad. Dermatol. 12:368–369, 1985. Hidano, A., H. Kajima, and Y. Endo. Bilateral nevus of Ota associated with nevus of Ito. Arch. Dermatol. 91:357, 1965. Hidano, A., H. Kajima, S. Ikeda, H. Mizutani, H. Miyasato, and M. Niimura. Natural history of nevus of Ota. Arch. Dermatol. 95:187–195, 1967. Hirayama, T., and T. Suzuki. A new classification of Ota’s nevus based on histopathological features. Dermatologica 183:169–172, 1991. Hori, Y., and O. Takayama. Circumscribed dermal melanoses: Classification and histologic features. Dermatol. Clin. 6:315–326, 1988. Hori, Y., K. Oohara, and M. Niimura. Electron microscopy: ultrastructural observations of the extracellular sheath of dermal melanocytes in the nevus of Ota. Am. J. Dermatopathol. 4:245–251, 1982. Hori, Y., M. Kawashima, and K. Oohara. Acquired, bilateral nevus of Ota-like macules. J. Am. Acad. Dermatol. 10:961–964, 1984. Horsey, W. J., J. M. Bilbae, J. Nethencott, R. Myers, and H. J. Hoffman. Oculodermal melanosis complicated by multiple intracranial tumors. Can. J. Neurol. Sci. 7:101–107, 1980. Hulke, J. W. Series of cases of carcinoma of eyeball (case 2). Ophthalmol. Hosp. Res. 3:279–286, 1861. Ishibashi, A., K. Kimura, and A. Kukita. Plaque-type blue nevus combined with lentigo (nevus spilus). J. Cutan. Pathol. 17:241–245, 1990. Jay, B. Malignant melanoma of the orbit in a case of oculodermal melanosis. Br. J. Ophthalmol. 49:359–363, 1965. Keinke, T., K. Kaber, and A. Tosselson. Ota nevus, multiple heman-
giomas, and Takayasu arteritis. Arch. Dermatol. 110:442–450, 1974. Kersting, D. W., and M. R. Caro. Cellular blue nevus of Ota followed for twenty-two years. Arch. Dermatol. 74:59–62, 1956. Kitagawa, K., S. Hayasaka, and Y. Nagaki. Falsely elevated intraocular pressure due to an abnormally thick cornea in a patient with nevus of Ota. Jpn. J. Ophthalmol. 47:142–144, 2003. Kojima, K., C. Natsume, and A. Honda. A melanoma of the optic chiasm occurs in a case of Ota’s nevus and melanosis bulbi. Jpn. J. Clin. Ophthalmol. 13:502–504, 1959. Kono, T., H. H. Chan, A. R. Ercocen, Y. Kikuchi, S. Uezono, S. Iwasaka, T. Isago, and M. Nozaki. Use of Q-switched ruby laser in the treatment of nevus of Ota in different age groups. Lasers Surg. Med. 32:391–395, 2003. Kopf, A. W., and R. S. Bart. Tumor Conference No 42. J. Dermatol. Surg. Oncol. 8:442–445, 1982. Kopf, A. W., and A. I. Weidman. Nevus of Ota. Arch. Dermatol. 85:195–207, 1962. Lee, J. H. A clinical observation about the nevi involving melanocytes in the Korea youth. Korean J. Dermatol. 24:73–78, 1986. Lever, W. F., and G. Schaumburg-Lever. Histopathology of the Skin, 6th ed. Philadelphia: JB Lippincott Co., 1983, pp. 699–700. Liesegang, T. J. Pigmented conjunctival and scleral lesions. Mayo Clin. Proc. 69:151–161, 1994. Lowe, N. J., J. M. Wieder, D. Sawcer, P. Burrows, and M. Chalet. Nevus of Ota: Treatment with high energy fluences of the Qswitched ruby laser. J. Am. Acad. Dermatol. 29:997–1001, 1993. Lynn, A., S. J. Brozena, C. G. Espinoza, and N. A. Fenske. Nevus of Ota acquisita of late onset. Cutis 51:194–196, 1993. Maize, J. C., and B. A. Ackerman. Pigmented Lesions of the Skin. Philadelphia: Lea and Febiger, 1987, pp. 134–137. Makley, T. A., Jr., and C. M. King. Malignant melanoma of the choroid in melanosis oculi. Trans. Am. Acad. Ophthalmol. Otolaryngol. 71:638, 1967. McDonald, R. R., and K. E. Georgouras. Skin disorders in IndoChinese immigrants. Med. J. Aust. 156:847–853, 1992. Miller, M. Follow-up to case report: invasive naevus of Ota. Pathology 26:76, 1994. Mishima, Y., and B. Mevorah. Nevus Ota and nevus Ito in American Negroes. J. Invest. Dermatol. 36:133, 1961. Mohandessan, M., C. Fetkanhour, and R. O’Grady. Malignant melanoma of the choroid in a case of nevus of Ota. Ann. Ophthalmol. 11:189–192, 1979. Nik, N. A., W. B. Glew, and L. E. Zimmerman. Malignant melanoma of the choroid in the nevus of Ota of a black patient. Arch. Ophthalmol. 100:1641–1643, 1982. Noreiga-Sanchez, A., O. N. Markand, and J. H. Herndon. Oculocutaneous melanosis associated with the Sturge-Weber syndrome. Neurology 22:256–262, 1972. Okawa, Y., R. Yokota, and A. Yamauchi. On the extracellular sheath of dermal melanocytes in nevus fuscocaeruleus acromiodeltoideus (Ito) and Mongolian spot: an ultrastructural study. J. Invest. Dermatol. 73:224–230, 1979. Ono, T., K. Mah, and F. Hu. Dermal Merkel cells in the nevus of Ota and leopard syndrome. J. Am. Acad. Dermatol. 11:245–249, 1984. Ota, M., and H. Tanino. The naevus fusco-caeruleus opthalmomaxillaris and its relationship to pigmentary changes in the eye. Jikeikai Med. J. 63:1243–1244, 1939. Patel, B. C., C. A. Egan, R. W. Lucius, J. W. Gerwels, N. Mamalis, and R. L. Anderson. Cutaneous malignant melanoma and oculodermal melanocytosis (nevus of Ota): report of a case and review of the literature. J. Am. Acad. Dermatol. 38:862–865, 1998. Ray, P. E., and E. M. Schaeffer. Nevus of Ota and choroidal melanoma. Surg Ophthalmol 12:130–131, 1967. Reed, W. B., and G. I. Sugarman. Unilateral nevus de Ota with sensorineural deafness. Arch. Dermatol. 109:881–883, 1974. Reinke, T., K. Haber, and A. Josselson. Ota nevus, multiple heman-
1011
CHAPTER 52 gioma, and Takayasu arteritis. Arch. Dermatol. 110:447–450, 1974. Ruiz-Villaverde, R., J. B. Melguizo, A. B. Eisman, and S. S. Ortega. Bilateral Ota naevus. J. Eur. Acad. Dermatol. Venereol. 17:437– 439, 2003. Sang, D. N., D. M. Albert, A. J. Sober, and T. O. McMeekin. Nevus of Ota with contralateral cerebral melanoma. Arch. Ophthalmol. 95:1820–1824, 1977. Sawada, Y., M. Iwata, and Y. Mitsusashi. Nevus pigmentovascularis. Ann. Plast. Surg. 25:142–145, 1990. Shaffer, D., K. Walker, and G. R. Weiss. Malignant melanoma in a Hispanic male with nevus of Ota. Dermatology 185:146–150, 1992. Singh, M., B. Kaur, and H. M. Annuar. Malignant melanoma of the choroid in nevus of Ota. Br. J. Ophthalmol. 72:131–133, 1988. Speakman, J. S., and M. J. Phillips. Cellular and malignant blue nevus complicating oculodermal melanosis. Can. J. Ophthalmol. 8:539–547, 1973. Tanino, H. Uber eine in Japan Haufig vorkommende Navus form: naevus fusco-caeruleus ophthal-maxillaris Ota. Jpn. J. Dermatol. Urol. 46:107–111, 1939. Tanino, H. Uber eine in Japan Haufig vorkommende Navusform: naevus fusco-caeruleus ophthal-maxillaris Ota. Jpn. J. Dermatol. Urol. 47:51–53, 1940. Taylor, C. R., T. J. Flotte, W. Gange, and R. R. Anderson. Treatment of nevus of Ota by Q-switched ruby laser. J. Am. Acad. Dermatol. 30:743–751, 1994. Teekhasaenee, C., R. Ritch, U. Rutnin, and N. Leelawongs. Ocular findings in oculodermal melanocytosis. Arch. Ophthalmol. 108: 1114–1120, 1990. Theunissen, P., G. Spincemaille, M. Pannebakker, and J. Lambers. Meningeal melanoma associated with nevus of Ota: case report and review. J. Clin. Neuropathol. 12:125–129, 1993. Ticho, B. H., M. O. Tso, and S. Kishi. Diffuse iris nevus in oculodermal melanocytosis: A light and electron microscopic study. J. Pediatr. Ophthalmol. Strabismus 26:244–250, 1989. Trese, M. T., T. H. Pettit, R. Y. Foos, and J. Hofbauer. Familial nevus of Ota. Ann. Ophthalmol. 13:855–857, 1981. Velazquez, N., and I. S. Jones. Ocular and oculodermal melanocytosis associated with uveal melanoma. Ophthalmology 90:1472– 1476, 1983. Watanabe, S., and H. Takahashi. Treatment of nevus of Ota with the Q-switched ruby laser. N. Engl. J. Med. 331:1745–1750, 1994. Whitmore, S. E., B. B. Wilson, and P. H. Cooper. Late-onset nevus of Ota. Cutis 48:213–216, 1991. Whyte, M. P., and A. S. Dekaban. Familial cerebellar degeneration with slow eye movements, mental deterioration and incidental nevus of Ota. Dev. Med. Child. Neurol. 18:373–379, 1976. Willis, R. A. Pathology of Tumors. London: Butterworth, 1967, pp. 930. Yamamoto, T. Malignant melanoma of the choroid in nevus of Ota. Ophthalmologica 151:1–10, 1969. Yanoff, M., and L. E. Zimmerman. Histogenesis of malignant melanomas of the uvea. Arch. Ophthalmol. 77:331–336, 1967. Yeschua, R., M. R. Wexler, and Z. Newman. The nevus of Ota: case report. Plast. Reconstr. Surg. 55:229–233, 1975. Yoshida, K. Nevus fusco-caeruleus ophthalmo-maxilaris Ota. Tohoku J. Exp. Med. 55(suppl. 1):34–43, 1952. Zimmerman, A. A., and S. W. Becker. Melanocytes and melanoblasts in fetal negro skin. In: Illinois Monographs in Medical Science. Urbana, IL: University of Illinois Medical Press, 1959, pp. 1–59.
Nevus of Ito Sang Ju Lee, Seung-Kyung Hann, and Sungbin Im The nevus of Ito, first reported by Ito in 1954, is a nevoid 1012
A
B Fig. 52.8. (A, B) Typical clinical appearance of nevus of Ito.
pigmentary anomaly similar to the nevus of Ota in clinical appearance but located on the skin innervated by the posterior supraclavicular and lateral brachiocutaneous nerves (Fig. 52.8). Nevus of Ito typically has flat blue-black or slate-gray macules intermingled with small, flat brown spots. The brown
ACQUIRED AND CONGENITAL DERMAL HYPERMELANOSIS
spots are caused by localized epidermal hyperpigmentation and blue-black or slate-gray macules are caused by the presence of dermal melanocytes. It is usually congenital but may appear in early childhood. It does not disappear with time. It may be associated with nevus of Ota or nevus of flammeus. The latter association is called phakomatosis pigmentovascularis (Furukawa et al., 1970). Histologically the epidermis is normal and the dermis contains numerous bipolar melanocytes. By electron microscopy, the dermal melanocytes contain singly dispersed, fully melanized melanosomes (Hori and Takayama, 1988). The melanocytes are typically surrounded by a sheath of variable thickness. Malignant transformation has been observed in nevus of Ito (van Krieken et al., 1988).
References Furukawa, T., A. Igata, Y. Toyokura, and S. Ikeda. Sturge-Weber and Klippel-Trenaunay syndrome with nevus of Ota and Ito. Arch. Dermatol. 102:640–645, 1970. Hori, Y., and O. Takayama. Circumscribed dermal melanoses: Classification and histologic features. Dermatol. Clin. 6:315–326, 1988. van Krieken, J. H., B. W. Boom, and E. Scheffer. Malignant transformation in a naevus of Ito. A case report. Histopathology 12: 100–102, 1988.
Phakomatosis Pigmentovascularis Sang Ju Lee, Seung-Kyung Hann, and Sungbin Im
Historical Background A pigmented nevus of various types and a vascular nevus commonly occur together (Gilliam et al., 1993; Hasegawa and Yasuhara, 1985; Sawada et al., 1990). Nevus pigmentovascularis, first described in 1920, is a large melanocytic nevus associated with vascular nevus (Fig. 52.9). In 1947, Ota et al. (Hasegawa and Yasuhara, 1985; Sawada et al., 1990) reported a case of nevus pigmentovascularis. He noted the association of nevus flammeus (port wine stain) and pigmented nevi such as a persistent Mongolian spot (dermal melanocytosis), nevus spilus, zosteriform lentiginous nevus, or nevus pigmentosus et verrucous. Some affected individuals might have a nevus anemicus. These anomalies have been associated with multiple granular cell tumors (Gilliam et al., 1993; Guiglia and Prendiville, 1991; Hasegawa and Yasuhara, 1985; Sawada et al., 1990).
Type 1: A combination of a nevus flammeus and nevus pigmentosus and verrucous epidermal nevus. Type 2: A combination of a nevus flammeus and a Mongolian spot with or without nevus anemicus. Type 3: A combination of a nevus flammeus and nevus spilus with or without nevus anemicus. Type 4: A combination of a nevus flammeus, nevus anemicus, and a Mongolian spot with or without nevus anemicus. Recently, the classification of a combination of a cutis marmorata telangiectatica congenita and aberrant Mongolian spots as a new entity in the form of phakomatosis pigmentovascularis (type 5) has been proposed (Enjolras and Mulliken, 2000; Torrelo et al., 2003). Nearly 200 cases have been reported, most of them in Japanese literature. Among 60 cases, 85% were type 2; 5% were type 3; 10% were type 4. However, there has been no Japanese report of type 1 (Happle, 1991; Hasegawa and Yasuhara, 1985; Libow, 1993; Ruiz-Maldonado et al., 1987; Vidaurri-de la Cruz et al., 2003). Phakomatosis pigmentovascularis is frequently observed in females. The male to female ratio is 1:1.34 (Vidaurri-de la Cruz et al., 2003). Although patients may have lesions limited to the skin, extracutaneous abnormalities have been frequently described. Leptomeningeal angiomatosis has been detected in individuals with a port wine stain in the characteristic trigeminal nerve distribution. Glaucoma has been noted in individuals with a facial port wine stain in a trigeminal distribution or with a nevus of Ota affecting the eye. Other abnormalities include soft-tissue hypertrophy, hypoplastic larynx and subglottic stenosis, scoliosis, anemia, venous hypoplasia from the inferior vena cava to the superficial femoral vein, renal anomaly, renal angiomas, moyamoya disease, malignant polyposis, and mental disturbance. Melanosis oculi with mammillations resembling Lisch nodules have also been described (Di Landro et al., 1999; Gilliam et al., 1993; Guiglia and Prendiville, 1991; Huang and Lee, 2000; Happle, 1991; Hasegawa and Yasuhara, 1985; Libow, 1993; Park et al., 2003; Sawada et al., 1990; Tsuruta et al., 1999).
Differential Diagnosis
Synonym Phakomatosis pigmentovascularis pigmentovascularis.
and Yasuhara (1985) have subdivided nevus pigmentovascularis into four subtypes. Each type has been further classified into two subdivisions: (a) cutaneous involvement only, and (b) cutaneous and systemic involvement.
is
also
called
nevus
Clinical Findings Patients with this syndrome have a distinctive association of an extensive nevus flammeus with melanocytic (Figs 52.9– 52.13) or epidermal nevi. The melanocytic lesions may be persistent aberrant Mongolian spots or nevus spilus. Hasegawa
Other syndromes can resemble phakomatosis pigmentovascularis. Patients with type IIb phakomatosis pigmentovascularis can have a nevus flammeus, intracranial and visceral angiomata, and seizure disorders. Such individuals fulfill the clinical criteria for Sturge–Weber syndrome. Patients with phakomatosis pigmentovascularis type IIb may appear to have the Klippel–Trenaunay syndrome. Such individuals have an extensive nevus flammeus associated with lymphangioma and/or hemihypertrophy of the limbs. 1013
52.9
52.11
52.10
52.13
52.12
Figs. 52.9–52.13. Phakomatosis pigmentovascularis illustrating both dermal melanocytosis and nevus flammeus (see also Plates 52.4–52.7, pp. 494–495).
ACQUIRED AND CONGENITAL DERMAL HYPERMELANOSIS
Pathogenesis Like other rare congenital disorders, the pathogenesis of phakomatosis pigmentovascularis has not been clarified. A hypothesis was proposed that a pathogenic factor (drugs, virus, or substances toxic to the nervous system) could have an irritating effect and cause some clones of angioblasts and melanoblasts to proliferate in an aberrant form (Ortonne et al., 1978; Ruiz-Maldonado et al., 1987). Another possible explanation is the “twin spot theory.” Twin spotting is presumed to be caused by different recessive heterozygous mutations whose loci are located on the same chromosome. During embryogenesis, each of two different recessive mutations on one chromosome becomes homozygous in each of the daughter cells by somatic crossing over or false chromosomal cleavage. Therefore, one daughter cell is homozygous for one of two recessive phenotypes, whereas the other is homozygous for the other phenotype. Because the coexistence of nevus flammeus and nevus anemicus is compatible with the “twin spot theory,” phakomatosis pigmentovascularis could be explained by genetic abnormalities in the vasomotor nerve cells and melanocytes, both of which derive from a common neuroectodermal precursor (Happle, 1991, 1999; Park et al., 2003; Torrelo et al., 2003).
References Di Landro, A., G. L. Tadini, L. Marchesi, and T. Cainelli. Phakomatosis pigmentovascularis: A new case with renal angiomas and some considerations about the classification. Pediatr. Dermatol. 16:25–30, 1999. Enjolras, O., and J. B. Mulliken. Vascular malformations. In: Textbook of Pediatric Dermatology, J. Harper (ed.). Oxford: Blackwell Science, 2000, pp. 975–996. Gilliam, A. C., N. K. Ragge, M. I. Perez, and J. L. Bolognia. Phakomatosis pigmentovascularis type IIb with iris mammillations. Arch. Dermatol. 129:340–342, 1993. Guiglia, M. C., and J. S. Prendiville. Multiple granular cell tumors associated with giant speckled lentiginous nevus and nevus flammeus in a child. J. Am. Acad. Dermatol. 24:359–363, 1991. Huang, C., and P. Lee. Phakomatosis pigmentovascularis IIb with renal anomaly. Clin. Exp. Dermatol. 25:51–54, 2000. Happle, R. Allelic somatic mutations may explain vascular twin nevi. Hum. Genet. 86:321–322, 1991. Happle, R. Loss of heterozygosity in human skin. J. Am. Acad. Dermatol. 40;318–321, 1999. Hasegawa, Y., and M. Yasuhara. Phakomatosis pigmentovascularis type IVa. Arch. Dermatol. 121:651–655, 1985. Libow, L. F. Phakomatosis pigmentovascularis type IIIb. J. Am. Acad. Dermatol. 29:305–307, 1993. Ortonne, J. P., D. Flored, J. Coiffet, and X. Cottin. Syndrome de Sturge-Weber associé à une mélanose oculo-cutanée: étude clinique, histologique et ultrastructurale d’ un cas. Ann. Dermatol. Venerol. 105:1019–1031, 1978. Park, J. G., K. Y. Roh, H. J. Lee, S. J. Ha, J. Y. Lee, S. S. Yun, K. W. Lim, K. S. Song, and J. W. Kim. Phakomatosis pigmentovascularis IIb with hypoplasia of the inferior vena cava and the right iliac and femoral veins causing recalcitrant stasis leg ulcers. J. Am. Acad. Dermatol. 49:S167-S169, 2003. Ruiz-Maldonado, R., L. Tamayo, A. M. Laterza, G. Brawn, and A. Lopez. Phakomatosis pigmentovascularis: A new syndrome? Report of four cases. Pediatr. Dermatol. 4:189–196, 1987. Sawada, Y., M. Iwata, and Y. Mitsusashi. Nevus pigmentovascularis. Ann. Plast. Surg. 25:142–145, 1990.
Torrelo, A., A. Zambrano, and R. Happle. Cutis marmorata telangiectatica congenita and extensive Mongolian spots: type 5 phacomatosis pigmentovascularis. Br. J. Dermatol. 148:342–345, 2003. Tsuruta, D., K. Fukai, M. Seto, K. Fujitani, K. Shindo, T. Hamada, and M. Ishii. Phakomatosis pigmentovascularis type IIIb associated with moyamoya disease. Pediatr. Dermatol. 16:35–38, 1999. Vidaurri-de la Cruz., H, L. Tamayo-Sanchez, C. Duran-McKinster, L. Orozco-Covarrubias Mde, and R. Ruiz-Maldonado. Phakomatosis pigmentovascularis II A and II B: clinical findings in 24 patients. J. Dermatol. 30:381–388, 2003.
Other Congenital Dermal Melanocytosis Sang Ju Lee, Seung-Kyung Hann, and Sungbin Im Dermal melanocytosis is characterized by the presence of ectopic melanocytes in the dermis (Jimenez et al., 1994). Dermal melanocytosis is seen in various congenital conditions, mostly in children, and occasionally in adulthood (Hidano and Kaneko, 1991). Congenital dermal melanosis has several morphologic forms, including the Mongolian spot, the blue nevus, the nevus of Ota, and the nevus of Ito (Fukuda et al., 1993). However, a few cases of congenital dermal melanocytosis do not fit into any of the above mentioned entities. This section focuses on the rare variants of congenital dermal melanosis.
Clinical Findings Dermal melanocytosis typically occurs on the face, in the supraclavicular region (Lever, 1976), over the upper part of the back, the neck, breasts, and abdomen (Cole et al., 1950; El Bahrawy, 1922), and less commonly over the sacrum. Other cases do not fit this picture. In reported congenital generalized dermal melanocytosis, a baby girl was born with blue-gray discoloration of almost the entire integument (Fig. 52.13). The face, palms, soles, genital area, and nipples were spared. The pigmentation varied in intensity from one area to another with a few nonpigmented areas on the thigh and abdomen. The margins of the pigmented regions were ill defined (Bashiti et al., 1981). Velez et al. (1992) described a 28-year-old woman with speckled grayblue pigmentation in a segmental pattern on the right side of the trunk, involving several thoracic dermatomes, that was termed congenital segmental dermal melanocytosis. Grezard et al. (1999) reported a 45-year-old woman who was born with grey-blue pigmentation on both sides of the back that subsequently spread along the dermatomes. The latter case of congenital bilateral dermal melanocytosis resembles the former, but with bilateral involvement (Grezard et al., 1999). Krishnan et al. (2003) reported a 31-year-old man with a congenital presentation of a solitary 10 cm ¥ 8 cm sized speckled blue-brown patch.
Histopathology Light microscopic examination of pigmented skin shows 1015
CHAPTER 52
numerous stellate and fusiform melanocytes diffusely distributed throughout the dermis. The cells tend to be oriented parallel to the skin surface and contain particulate brown pigment. Melanocytes are numerous in the middle and lower dermis and occasionally extend into the subcutaneous tissue. There are no melanophages in the dermis. The overlying epidermal melanocytes appear normal in number and morphology. The dopa reaction and the Fontana-Masson stain are positive in virtually all the dermal and epidermal melanocytes. Electron microscopic examination shows the pigmented cells to be typical dermal melanocytes. The cells contained premelanosomes and melanosomes with varying degree of maturation within a same cell. A narrow band of extracellular filamentous material surrounds each melanocyte. In the biopsy specimen from nonpigmented areas, the epidermal melanocytes were present in seemingly normal numbers and the melanin pigment was normal (Bashiti et al., 1981; Grezard et al., 1999; Velez et al., 1992).
Pathogenesis The pathogenesis of persistent dermal melanocytes is uncertain. Dermal melanocytes are presumed by analogy with epidermal melanocytes to arise in the neural crest and migrate onto the skin. It has been suggested that dermal melanocytes are simply melanocytes destined for the epidermis that have remained in the dermis. Because of the lack of information on the determinants of normal migration of epidermal melanocytes, our understanding of these lesions is poor (Bashiti et al., 1981).
References Bashiti, H. M., J. D. Blair, R. A. Triska, and L. Keller. Generalized dermal melanocytosis. Arch. Dermatol. 117:791–793, 1981. Cole, H. N., Jr., W. R. Hubler, and H. J. Lund. Persistent aberrant mongolian spot. Arch. Dermatol. 61:244–260, 1950. El Bahrawy, A. A. Ueba den mongolenfleck bei. Eur. Arch. Dermatol. Syphil. 141:172–192, 1922. Fukuda, M., J. Kitajima, H. Fushida, and T. Hamada. Acquired dermal melanocytosis of the hand: a new clinical type of dermal melanocytosis. J. Dermatol. 20:561–565, 1993. Grezard, P., F. Berard, B. Balme, and H. Perrot. Congenital bilateral dermal melanocytosis with a dermatomal pattern. Dermatology 198:105–106, 1999. Hidano, A., and K. Kaneko. Acquired dermal melanocytosis of the face and extremities. Br. J. Dermatol. 124:96–99, 1991. Jimenez, E., P. Valle, and P. Villegas. Unusual acquired dermal melanocytosis. J. Am. Acad. Dermatol. 30:277–278, 1994. Krishnan, R. S., T. R. Roark, and S. Hsu. Isolated patch of speckled, congenital, pigmented dermal melanocytosis outside the face or acromioclavicular regions. J. Eur. Acad. Dermatol. Venereol. 17:238–239, 2003. Jimenez, E., P. Valle, and P. Villegas. Unusual acquired dermal melanocytosis. J. Am. Acad. Dermatol. 30:277–278, 1994. Lever, W. F. Histopathology of the Skin. Philadelphia: JB Lippincott Co., 1976, p. 777. Velez, A., C. Fuente, I. Belinchon, N. Martin, V. Furio, and E. Sanchez Yus. Congenital segmental dermal melanocytosis in an adult. Arch. Dermatol. 128: 521–525, 1992.
1016
Acquired Dermal Melanocytosis Sang Ju Lee, Seung-Kyung Hann, and Sungbin Im
Historical Background Acquired dermal melanocytosis initially was described by Mevorah et al. in 1977. They reported a 32-year-old Portuguese woman with a bluish spot on her right hand. The lesion had appeared at the age of 11 years.
Clinical and Histological Findings Acquired dermal melanocytosis can occur in adult life. Acquired dermal melanocytosis can be classified into generalized, linear, and localized types on clinical grounds. One case of acquired generalized dermal melanocytosis was a 55-yearold man with a leiomyosarcoma of the rectum and multiple metastatic lesions in the liver. The initial lesions were noticed on the face at the age of 53 years. They extended to the upper extremities and back. On physical examination, there were extensive and multiple blue-gray macules on the face, upper extremities, shoulders, and back. Gray flecks on both palpebral conjunctivae, blue-gray flecks on the palate, and blue and brown pigmentation on the gingiva were also noted (Ono et al., 1991). Pariser and Bluemink (1982) described a case of acquired linear dermal melanocytosis. The lesion began after blunt trauma on the posterior aspect of the lower part of the leg and extended distally for several months. There was no history of an eruption preceding the onset of the hyperpigmentation and the patient had taken no systemic medication before or after the onset of the lesion. The lesion was composed of irregularly shaped 2–8 mm brown macules arranged in a linear fashion with many “skip” areas. The sural nerve innervated the affected area. The authors suggested that trauma preceding the onset of the lesion might have induced nerve reactivity that stimulated melanocytes in the area. Histologically, cells with granular brown cytoplasmic pigment located in the papillary dermis were observed. Pigment granules were stained black by the Fontana-Masson stain. Electron microscopic study showed that dendritic melanocytes were present in the papillary dermis (Pariser and Bluemink, 1982). In 1977, Mevorah et al. described a 32-year-old Portuguese woman with a bluish spot on her right hand that had appeared when she was 11 years. The lesion involved the second finger, part of the dorsum of the hand, and the adjoining distal third of the palm. Clinically this lesion was similar to an aberrant, persistent Mongolian spot. However histologically there was a significant number of melanophages accompanying the dermal melanocytes, features that are not characteristic of the Mongolian spot (Mevorah et al., 1977). Acquired dermal melanocytoses are sometimes classified according to their characteristic clinical appearances. Hori et al. (1984) described cases involving only the face as acquired, bilateral nevus of Ota-like macules. Hidano and Kaneko (1991) described acquired dermal melanocytosis of the face
ACQUIRED AND CONGENITAL DERMAL HYPERMELANOSIS
and extremities. Several cases of acquired dermal melanocytosis distributed only on the extremities without involving the face were described (Fukuda et al., 1993; Kuniyuki, 1997; Mevorah et al., 1977). Ono et al. (1991) reported seven Japanese males with acquired dermal melanocytosis on the upper back as an upper back variant of late onset dermal melanocytosis. Ono et al. (1991) described a male with acquired dermal melanocytosis disseminated on the face, upper limbs, and trunk as generalized type of acquired dermal melanocytosis.
Pathogenesis The pathogenesis of acquired dermal melanocytosis has been proposed to be the reactivation of pre-existing dermal melanocytes or the manifestation of latent dermal melanocytosis triggered by dermal inflammation, atrophy, or degeneration of the epidermis and/or dermis (Hori et al., 1984). Ultraviolet irradiation may increase MSH or endothelins, increasing tyrosinase activity and thus inducing melanogenesis, especially when the lesions are distributed on sun-exposed areas of the face and extremities (Imokawa et al., 1995; Kuniyuki, 1997). Kunachak et al. (1996) postulated that female hormones affect the occurrence of acquired dermal melanocytosis because of the high percentage of women exhibiting these lesions. Recently, Rubin et al. (2001) reported a case of acquired dermal melanocytosis appearing during pregnancy, and suggested estrogen and progesterone may induce onset of acquired dermal melanocytosis.
References Fukuda, M., J. Kitajima, H. Fushida, and T. Hamada. Acquired dermal melanocytosis of the hand: A new clinical type of dermal melanocytosis. J. Dermatol. 20:561–565, 1993. Hidano, A., and K. Kaneko. Acquired dermal melanocytosis of the face and extremities. Br. J. Dermatol. 124:96–99, 1991. Hori, Y., M. Kawashima, K. Oohara, and A. Kukita. Acquired, bilateral nevus of Ota-like macules. J. Am. Acad. Dermatol. 10:961–964, 1984. Imokawa, G., M. Miyagishi, and Y. Yada. Endothelin-1 as a new melanogen: Coordinated expression of its gene and the tyrosinase gene in UVB-exposed human epidermis. J. Invest. Dermatol. 105:32–37, 1995. Kunachak, S., S. Kunachakr, V. Sirikulchayanonta, and P. Leelaudomniti. Dermabrasion is an effective treatment for acquired bilateral nevus of Ota-like macules. Dermatol. Surg. 22:559–562, 1996. Kuniyuki, S. Acquired dermal melanocytosis on the wrist. J. Dermatol. 24:120–124, 1997. Mevorah, B., E. Frenk, and J. Delacretaz. Dermal melanocytosis: Report of an unusual case. Dermatologica 154:107–114, 1977. Ono, S., M. Hori, and K. Yamashita. Generalized type of acquired dermal melanocytosis. Jpn. J. Dermatol. 101:965–971, 1991. Ono, T., K. Egawa, K. Kayashima, and M. Kitoh. Late onset dermal melanocytosis: An upper back variant. J. Dermatol. 18:97–103, 1991. Pariser, R. J., and G. G. Bluemink. Acquired linear dermal melanocytosis: nerve course distribution. Arch. Dermatol. 118:125–128, 1982. Rubin, A. I., S. Van Laborde, and M. J. Stiller. Acquired dermal melanocytosis: Appearance during pregnancy. J. Am. Acad. Dermatol. 45:609–613, 2001.
Carleton–Biggs Syndrome Sang Ju Lee, Seung-Kyung Hann, and Sungbin Im Acquired dermal hyperpigmentation is caused either by the presence of dermal melanocytes (dermal melanocytosis) or by the presence of free melanin in the dermis or within dermal macrophages (dermal melanosis). The etiology of acquired dermal melanocytosis is thought to be reactivation of latent dermal melanocytes or migration of melanocytes into the dermis from the hair bulb. Acquired dermal melanosis occurs in many inflammatory disorders of the epidermis such as lichen planus. In 1948, Carleton and Biggs described a 14-year-old girl who was normal apart from her skin, which was covered with widespread bluish spots. These lesions were not congenital although at birth there was pigmentation on the sclera and iris of the left eye. The girl also had thickening of the skull behind the ears and pronounced ballooning of the posterior cranial fossa. At 3 years of age, a blue spot appeared on her back. At 8 years of age another appeared on her nose and more appeared around the age of 9. Metastatic malignant melanoma was found in the liver and the lymph nodes at the age of 43 years (Levene, 1979). The primary melanoma was not identified. At the autopsy, widespread dermal, visceral, and cranial melanoses were observed. Melanophages were present in visceral and cranial tissue, and melanocytes and melanophages in the dermis. Histologic examination showed the presence of dendritic or bipolar melanocytes scattered through the dermis around blood vessels and sweat ducts.
References Carleton, A., and R. Biggs. Diffuse mesodermal pigmentation with congenital cranial abnormality. Br. J. Dermatol. 60:10–13, 1948. Levene, A. Disseminated dermal melanocytosis terminating in melanoma. Br. J. Dermatol. 101:197–205, 1979.
Acquired Bilateral Nevus of Ota-like Macules (ABNOM) Sang Ju Lee, Seung-Kyung Hann, and Sungbin Im
Clinical and Histologic Findings Acquired bilateral nevus of Ota-like macules (ABNOM), or Hori’s macules, are characterized by development of bilateral blue-brown or slate-gray macules on the face (Fig. 52.14). Blue-brown macules can be found on the sides of the forehead, temples, eyelids, malar areas, and root and alae of the nose. Women are affected more commonly than men (Hori et al., 1984). The ocular and mucosal membranes are not involved. Histologically, bipolar or oval dermal melanocytes that are slightly dopa-positive are found scattered in the upper and middle portions of the dermis. On electron microscopy these dermal melanocytes contain many singly dispersed
1017
CHAPTER 52
ECS
1 mm Fig. 52.15. Electron micrograph of a dermal melanocyte from acquired, bilateral nevus of Ota-like macule. ECS, extracellular sheath, uranyl acetate and lead citrate stain.
References Hori, Y., K. Oohara, and M. Niimura. Electron microscopy: ultrastructural observations of the extracellular sheath of dermal melanocytes in the nevus of Ota. Am. J. Dermatopathol. 4:245– 251, 1982. Hori, Y., M. Kawashima, and K. Oohara. Acquired, bilateral nevus of Ota-like macules. J. Am. Acad. Dermatol. 10:961–964, 1984. Okawa, Y., R. Yokota, and A. Yamauchi. On the extracellular sheath of dermal melanocytes in nevus fuscocaeruleus acromiodeltoideus (Ito) and Mongolian spot: an ultrastructural study. J. Invest. Dermatol. 73:224–230, 1979. Fig. 52.14. Acquired facial blue macules resembling a bilateral nevus of Ota (see also Plate 52.8, pp. 494–495).
Blue Macules Associated with Progressive Systemic Sclerosis Sang Ju Lee, Seung-Kyung Hann, and Sungbin Im
melanosomes that are 0.4–0.8 mm in size and are in stages II, III, and IV of melanization (Fig. 52.15). These melanocytes are surrounded by an extracellular sheath (Hori et al., 1982; Okawa et al., 1979). The epidermis is normal.
Differential Diagnosis These macules can be differentiated clinically and histologically from congenital bilateral nevus of Ota (type IV nevus of Ota), female facial melanosis, Riehl melanosis, and dermal melasma. Congenital bilateral nevus of Ota is usually present at or soon after birth or develops around adolescence. The conjunctivae and the mucosal membrane of the mouth and nose or the tympanic membrane are commonly involved by the nevus of Ota. Dermal melanocytes are not found in facial melanosis, Riehl melanosis, and melasma. The dermal melanocytes of acquired bilateral nevus of Otalike macules may be attributed to the migration of hair bulb melanocytes into the dermis or to the reactivation of latent dermal melanocytes in the affected areas. The latter hypothesis is supported by recent observations confirming the existence of melanoblasts in the dermis of the adult skin. 1018
In progressive systemic sclerosis, brownish hyperpigmentation and depigmentation of the involved areas of the skin are commonly observed and are considered highly suggestive of scleroderma (See Fig. 50.65, Chapter 50, section on Morphea and scleroderma). Blue macules have also been observed, however, on the back, shoulders, and one or both upper portions of the arms in the first four years in the course of the disease. The blue macules consisted mostly of linear blue streaks along with some small blue patches (Hori et al., 1976). Histologically, spindle-shaped and brown pigment-bearing dermal melanocytes can be recognized in the upper two-thirds of the dermis. These dermal melanocytes are widely spaced in the dermis between the connective and elastic tissue fibers. The dopa reaction of the dermal melanocytes in the blue macule is positive. Electron microscopically, many fully melanized melanosomes are present in these dermal melanocytes. A few immature melanosomes may be found. Almost all melanosomes, whatever the stage of melanization, are singly distributed in the cytoplasm (Hori and Takayama, 1988; Stanford and Georgouras, 1996).
ACQUIRED AND CONGENITAL DERMAL HYPERMELANOSIS
References Hori, Y., S. Miyazawa, and S. Nishiyama. “Naevus caeruleus tardus” in association with progressive systemic scleroderma. In: Pigment Cell, V. Riley (ed.). Basel: S Karger, 1976, pp. 273–283.
Hori, Y., and O. Takayama. Circumscribed dermal melanoses: classification and histologic features. Dermatol. Clin. 6:315–326, 1988. Stanford, D. G., and K. E. Georgouras. Dermal melanocytosis: a clinical spectrum. Australas. J. Dermatol. 37:19–25, 1996.
1019
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
53
Mixed Epidermal and Dermal Hypermelanoses and Hyperchromias Sections Melasma Sang Ju Lee, Seung-Kyung Hann, and Sungbin Im Melanosis from Melanoma Sang Ju Lee, Seung-Kyung Hann, and Sungbin Im
Melasma Sang Ju Lee, Seung-Kyung Hann, and Sungbin Im
Clinical Findings Melasma is defined as light to dark brown, purple, irregular hypermelanosis of the face (Fig. 53.1). It develops slowly and is usually symmetric (Newcomer et al., 1961). Although it may occur in men (Vazquez et al., 1988), it is far more common in women particularly those of Hispanic origin (Sanchez et al., 1981) and Asians. Dark-skinned races living in India, Pakistan, and the Middle East tend to develop this problem in the first decade of life (Pathak et al., 1986) but patients from most other races note the onset at puberty or later. The condition may last for many years with relapses during the summer and relative remissions during the winter. The lesions of melasma are strictly limited to sun-exposed skin. The arcuate or polycyclic lesions are brown, gray, or blue macules which coalesce into irregular patches. The lesions may be linear and have a starburst distribution. There are three patterns of distribution of the hyperpigmentation (Sanchez et al., 1981). The most common presentation is in the central facial area observed in about two-thirds of affected individuals. These individuals also have lesions on the forehead, nose, chin, and medial aspects of the cheeks. The “malar pattern” appears in about 20% of patients. Their lesions are limited to the cheeks and nose. Melasma over the ramus of the mandible, called the “mandibular pattern,” occurs in about 15% of patients. Areas off of the face, particularly the forearms, may be involved along with any of these patterns. The hyperpigmentation of melasma can be of two forms. The first is due to increase of epidermal melanin and the color of the affected areas is brown. The other is caused by increased epidermal melanin and deposition of melanin in the dermis. The color is gray-brown or slate. The various types of melasma can be differentiated by Wood’s light examination. Four distinct patterns are identifiable (Sanchez et al., 1981). In the epidermal type, Wood’s light produces an enhancement of the color contrast between affected and normal skin (Gilchrest et al., 1977). This is the most common pattern. In one study 72% of patients mani1020
fested this type of discoloration. Melasma of the dermal type shows no enhancement of color contrast under Wood’s light. There is a mixed dermal–epidermal type in which the Wood’s light examination shows enhancement but no color accentuation in different areas on the same patient. Finally, in very dark-skinned individuals, one cannot see the lesions of melasma under Wood’s light. The light emitted by Wood’s light is absorbed by melanin. In the epidermal type of melasma, the affected sites appear darker because the extra melanin absorbs all the light. For those with dermal pigmentation, there is scattering and reflection of the light from the epidermis that hides the hyperpigmentation visible under normal lighting (Findlay, 1970).
Histopathology There are two types of microscopic finding: an epidermal pattern and a dermal pattern (Sanchez et al., 1981). In the epidermal type, melanin deposition is mainly increased in the basal and suprabasal layers of the epidermis. There may be increased quantities of pigment throughout the epidermis including the stratum corneum. In addition, there is vacuolar degeneration of the basal cells. The dermal type of pigment deposition is characterized by melanin deposition in perivascular macrophages around both the superficial and deep dermal vessels (Sanchez et al., 1981). However, melanophages were present both in melasma and in normal facial skin in some of melasma patients, and melanophages were present in the normal dermis of Japanese skin. Thus, some researchers suggest that the melanophages cannot be a hallmark of the dermal type of melasma (Kang et al., 2002; Ohkuma, 1991). Pigment deposition in the dermal type of melasma is much more prominent than that in the epidermal type. Dopa staining of epidermal preparations shows increased melanin production in epidermal melanocytes in both the epidermal and dermal patterns. The dendrites of the melanocytes contain an increased number of melanosomes (Sanchez et al., 1981). Dopa-positive melanocytes do not increase in number.
Differential Diagnosis Many different conditions can produce increased pigmentation in sun-exposed skin. These include medications such as
MIXED EPIDERMAL AND DERMAL HYPERMELANOSES AND HYPERCHROMIAS
Fig. 53.1. Melasma.
amiodarone, phenothiazines, and heavy metals. However, the pattern of pigmentation is not arcuate or polycyclic as observed in melasma. Inflammatory insults, particularly in dark-skinned people, can lead to postinflammatory hyperpigmentation. Cutaneous lupus erythematosus, other photosensitivity reactions, skin infections, and severe atopic dermatitis all may result in hyperpigmentation but the inflammatory phase is almost always easily noted. This clinical feature differentiates postinflammatory hyperpigmentation from melasma, which has no inflammatory phase. Poikiloderma of Civatte can result in reticulated hyper- and hypopigmented atrophic plaques on the neck and upper chest. This may resemble melasma but the atrophy and telangiectasia seen in this condition are not noted in melasma.
Pathogenesis The cause of melasma is not known but there are a number of factors that may be involved in causing or aggravating the condition. The related condition chloasma occurs during pregnancy and in women on oral contraceptives (Cook et al., 1961; Esoda, 1963; Resnick, 1967). This is the so-called “mask of pregnancy.” The hyperpigmentation often decreases or disappears completely after parturition but may not regress
in women on oral contraceptives until the medication is discontinued (Resnick, 1967). In one study, 87% of patients who developed melasma while on birth control pills also had this problem during a subsequent pregnancy, an observation suggesting that these are individuals susceptible to hormonal stimulation of melanocytes (Sanchez et al., 1981). Both estrogen and progesterone are likely to be involved in inducing melasma. There is a report that a melanocyte stimulating hormone (a-MSH) antigen was highly expressed in the lesional keratinocytes of melasma. Locally produced a-MSH is known to be involved in epidermal skin pigmentation by stimulating tyrosinase activity and melanin synthesis in vivo. It is suggested that a-MSH is involved in the hyperpigmentation of melasma skin (Im et al., 2002). However, it is possible that other hormones such as b-lipotropin, which is secreted by the pituitary gland and is a melanotropic peptide, could play some role. Plasma levels of this hormone do not differ in patients with or without melasma (Smith et al., 1977). There is also a report that thyroid disorders are associated with melasma in women whose pigmentation develops during pregnancy or after ingestion of oral contraceptive drugs (Lutfi et al., 1985). Results of some studies suggest that melasma may be a type of photocontact dermatitis. The allergens were found to be ingredients in cosmetics. Indoor lighting at low intensity over long periods of time seems to elicit a photosensitivity reaction (Verallo-Rowell et al., 2001). Photocontact dermatitis might be a mechanism by which release of a-MSH from keratinocytes is stimulated. The most important exacerbating factor for melasma is exposure to ultraviolet light. In one study of 76 patients, all reported that sun exposure selectively darkened the areas already hyperpigmented by melasma (Sanchez et al., 1981). Individuals whose condition cleared up with therapy often note a recurrence after subsequent sun exposure. Ultraviolet light normally increases melanogenic activity in melanocytes with resulting hyperpigmentation (Pathak et al., 1962). In addition to direct ultraviolet light exposure, accumulated sun exposure is also important to develop melasma. Increased solar elastosis is found in the lesional skin of melasma compared to adjacent perilesional normal skin, suggesting chronic sun exposure (Kang et al., 2002). There may be genetic factors, which make one more prone to develop melasma. Aside from the disease occurring more frequently in certain racial groups, there have been many cases of familial melasma (Sanchez et al., 1981). There is also a report that two identical twins had melasma precipitated by the same trigger factors, i.e., oral contraceptive pills and pregnancy. Both noted accentuation following exposure to ultraviolet light although other members of their family did not have similar problems (Hughes, 1987). It is commonly believed that certain cosmetics can produce hyperpigmentation. Virtually all women who have melasma report the use of cosmetics (Sanchez et al., 1981). These agents have been impugned as causative or at least as contributory factors (Montagna et al., 1980). No specific ingredient in 1021
CHAPTER 53
cosmetic preparations has been implicated and there has never been an experimental reproduction of melasma after the use of any topically applied chemical. Many individuals with melasma attempt to improve their appearance by using coverup makeup. It is quite likely that makeup use is a coincidental event which has no etiologic relationship to the skin disease. A likely scenario for the production of melasma is that clones of melanocytes are activated by ultraviolet light and functionally altered by other factors such as hormones which increase the synthesis of melanin.
Treatment Before embarking on therapy, it is important to determine the clinical/histologic type of melasma. Wood’s lamp examination usually is sufficient to make this determination. If not, a biopsy might be necessary. If the patient has the dermal form of the disease, there is little one can do to bleach the pigment. Since sunlight exacerbates the problem, potent, broad-spectrum sun protection is important to minimize sun-induced hyperpigmentation (Pathak et al., 1986; Vazquez and Sanchez, 1983). Since ultraviolet A (UVA) can enhance melanogenesis, sunscreens that block in that spectrum as well as in the ultraviolet B (UVB) range are necessary. For those patients with the epidermal type of melasma, bleaching agents are useful when used for prolonged periods. Hydroquinone-containing agents in a concentration of 1–4% are the most commonly used bleaching products (Arndt and Fitzpatrick, 1965) (Fig. 53.2A, B). Hydroquinone is not always helpful because of a high incidence of contact dermatitis and postinflammatory hyperpigmentation (Jimbow et al., 1974). To prevent these side effects, corticosteroids are often mixed with hydroquinone as one of the combination therapies (Kligman and Willis, 1975). The combination of 2% hydroquinone and 0.05% or 0.1% tretinoin (retinoic acid) has been used successfully for melasma (Pathak et al., 1986). The combination may be more effective than either 2% hydroquinone or tretinoin alone although irritation is still problematic. Topical tretinoin (0.1%) alone is reported to be effective in fair-skinned women (Griffiths et al., 1993) and black (African-American) patients (Kimbrough-Green et al., 1994), but the time to clinical improvement is long, at least 24 weeks (Griffiths et al., 1993). Combination products containing hydroquinone 4%, fluocinolone acetonide 0.01% and tretinoin 0.025% are available commercially (TriLuma®) and lighten epidermal melasma within two to three months in many patients. The mechanism of action of tretinoin in lightening melasma is not understood although reduction in epidermal melanin perhaps as a result of inhibition of the melanin-forming enzyme tyrosinase (Orlow et al., 1990) might be a factor in clinical improvement. Jimbow (1991) has reported marked improvement without irritation in 9 of 12 cases of melasma treated with topical 4% N-acetyl-4-cysteaminylphenol. Two other novel compounds, arbutin and kojic acid, have been described as beneficial (Maeda and Fukuda, 1991; Mishima, 1992). 1022
A
B Fig. 53.2 Extensive melasma of the cheeks (A). Same patient showing almost complete regression of hyperpigmentation after hydroquinone treatment (B) (see also Plates 53.1A and 53.1B, pp. 494–495).
In the epidermal form of melasma if one can selectively decrease the population of affected melanocytes, skin color can be lightened. This can be accomplished with physical modalities such as liquid nitrogen cryotherapy, CO2 laser vaporization, chemical peeling, and superficial dermabrasion. The risk with all of these procedures is that the resultant skin color will not be a perfect match to the surrounding unaffected skin.
References Arndt, K., and T. Fitzpatrick. Topical use of hydroquinone as a depigmentating agent. J. Am. Med. Assoc. 194:965–967, 1965. Cook, H. H., C. J. Gamble, and A. P. Saherthwaite. Oral contraception by norethynodrel. Am. J. Obstet. Gynecol. 88:437–445, 1961. Esoda, E. C. J. Chloasma from progestational oral contraceptives. Arch. Dermatol. 87:486, 1963. Findlay, G. Blue skin. Br. J. Dermatol. 83:127–134, 1970. Gilchrest, B. A., T. B. Fitzpatrick, R. R. Anderson, and J. A. Parrish. Localization of melanin pigmentation in the skin with Wood’s lamp. Br. J. Dermatol. 96:245–248, 1977. Griffiths, C. E., L. J. Finkel, C. M. Ditre, T. A. Hamilton, C. N. Ellis, and J. J. Voorhees. Topical tretinoin (retinoic acid) improves
MIXED EPIDERMAL AND DERMAL HYPERMELANOSES AND HYPERCHROMIAS melasma. A vehicle-controlled, clinical trial. Br. J. Dermatol. 129:415–421, 1993. Hughes, B. R. Melasma occurring in twin sisters. J. Am. Acad. Dermatol. 17:841, 1987. Im, S., J. Kim, W. Y. On, and W. H. Kang. Increased expression of alpha-melanocyte-stimulating hormone in the lesional skin of melasma. Br. J. Dermatol. 146:165–167, 2002. Jimbow, K. N-acetyl-4-S-cysteaminylphenol as a new type of depigmenting agent for the melanoderma of patients with melasma. Arch. Dermatol. 127:1528–1534, 1991. Jimbow, K., H. Obata, M. A. Pathak, and T. B. Fitzpatrick. Mechanism of depigmentation by hydroquinone. J. Invest. Dermatol. 62:436–449, 1974. Kang, W. H., K. H. Yoon, E. S. Lee, J. Kim, K. B. Lee, H. Yim, S. Sohn, and S. Im. Melasma: histopathological characteristics in 56 Korean patients. Br. J. Dermatol. 146:228–237, 2002. Kimbrough-Green, C. K., C. E. Griffiths, L. J. Finkel, T. A. Hamilton, S. M. Bulengo-Ransby, C. N. Ellis, and J. J. Voorhees. Topical retinoic acid (tretinoin) for melasma in black patients. A vehiclecontrolled clinical trial. Arch. Dermatol. 130:727–733, 1994. Kligman, A. M., and I. Willis. A new formula for depigmenting human skin. Arch. Dermatol. 111:40–48, 1975. Lutfi, R. J., M. Fridmanis, A. L. Misiunas, O. Pafume, E. A. Gonzalez, J. A. Villemur, M. A. Mazzini, and H. Niepomniszcze. Association of melasma with thyroid autoimmunity and other thyroidal abnormalities and their relationship to the origin of the melasma. J. Clin. Endocrinol. Metab. 61:28–31, 1985. Maeda, K., and K. Fukuda. In vitro effectiveness of several whitening cosmetic components in human melanocytes. J. Soc. Cosmet. Chem. 42:361, 1991. Mishima, Y. A post melanosomal era: control of melanogenesis and melanoma growth. Pigment Cell Res. Suppl 2:3–16, 1992. Montagna, W., F. Hu, and K. Carlisle. Reinvestigation of solar lentigines. Arch. Dermatol. 116:1151–1154, 1980. Newcomer, V. D., M. C. Lindbert, and T. H. Stenbert. A melanosis of the face (“chloasma”). Arch. Dermatol. 83:284–297, 1961. Ohkuma, M. Presence of melanophages in the normal Japanese skin. J. Am. Acad. Dermatol. 13: 32–37, 1991. Orlow, S. J., A. K. Chakraborty, and J. M. Pawelek. Retinoic acid is a potent inhibitor of inducible pigmentation in murine and hamster melanoma cell lines. J. Invest. Dermatol. 94:461–464, 1990. Pathak, M. A., F. C. Riley, and T. B. Fitzpatrick. Melanogenesis in human skin following exposure to long-wave ultraviolet and visible light. J. Invest. Dermatol. 39:435–443, 1962. Pathak, M. A., T. B. Fitzpatrick, and E. W. Kraus. Usefulness of retinoic acid in the treatment of melasma. J. Am. Acad. Dermatol. 15:894–899, 1986. Resnick, S. Melasma induced by oral contraceptive drugs. J. Am. Med. Assoc. 199:95, 1967. Sanchez, N. P., M. A. Pathak, S. Sato, T. B. Fitzpatrick, J. L. Sanchez, and M. C. Mihm Jr. Melasma: a clinical, light microscopic, ultrastructural and immunofluorescence study. J. Am. Acad. Dermatol. 4:698–710, 1981. Smith, A. G., S. Shuster, A. J. Thody, and M. Peberky. Chloasma, oral contraceptives, and plasma immunoreactive b-melanocytestimulating hormone. J. Invest. Dermatol. 68:169–170, 1977. Vazquez, M., and J. L. Sanchez. The efficacy of a broad-spectrum sunscreen in the treatment of melasma. Cutis 32:92–96, 1983. Vazquez, M., H. Maldonado, C. Benmaman, and J. L. Sanchez. Melasma in men. A clinical and histologic study. Int. J. Dermatol. 27:25–27, 1988. Verallo-Rowell, V. M., D. Villacarlos-Buatista, N. S. Oropeza, B. Gepaya-Resurreccion, and S. A. Mendoza. Indoor lights used in the photopatch testing of a case-controlled group of melasma and non-melasma patients. In: Skin in the Tropics: Sunscreens and the Hyperpigmentations, V. M. Verallo-Rowell (ed.). Manila: Anvil Press, 2001, pp. 102–131.
Melanosis from Melanoma Sang Ju Lee, Seung-Kyung Hann, and Sungbin Im
Historical Background In 1864 the German pathologist, Ernst Wagner, described a man in his thirties who had developed a melanoma in congenital nevus and subsequently acquired a generalized uniformly bluish-gray discoloration. That paper might have been the first on this subject.
Epidemiology The incidence of noticeable cutaneous melanosis in patients with metastatic melanoma is probably around 1–2%, a figure confirmed by Rorsman et al., who observed three cases in a group of 161 patients in Sweden (Agrup et al., 1979). A truly striking melanosis occurs at a lower frequency. Because the condition is so rare, most publications report only one patient. To date, about 60 cases have been reported in the literature (Böhm et al., 2001; Carruth et al., 2002; Lerner and Moellmann, 1993; Manganoni et al., 1993; Murray et al., 1999; Pec et al., 1993; Tsukamoto et al., 1998).
Clinical Findings By definition this form of discoloration occurs only in individuals with metastatic melanoma. The initial discoloration is usually noted as slate blue, even cerulean blue (Pack and Scharnagel, 1951), and is probably missed in many cases of widely disseminated metastatic melanoma. It develops insidiously. This early bluish coloration is an indication that the melanin deposition begins in the deeper layers of the skin, i.e., the dermis. Later, in those few patients who live to develop a full-blown melanosis, pigment deposition progresses rapidly until the patient is a dark slate color at the time of death (Fig. 53.3). Lerner and Moellmann reviewed the 42 patients reported in the literature: 20 males, 14 females, and 8 whose gender was not recorded. The age range of the women was 20–67 years (mean 40, median 41) and of the men 31–70 years (mean 50, median 49). Three women were pregnant. All patients had widespread metastatic disease. Metastases in the liver, skin, lymph node, spleen, heart, kidney, bone marrow, and gastrointestinal tract were observed with high frequency. Some patients had spectacular showers of hundreds of cutaneous metastases that ranged in size from less that 1 mm2 to larger than 1 cm2. In nearly all patients, light-exposed areas were considerably darker than the covered parts. The conjunctiva and oral mucosa may be involved and even the hair may darken. The melanosis also affects internal epithelia and connective tissues. The urine is usually black or turns black on exposure to air and light. There were no reports of patients with vitiligo (Lerner and Moellmann, 1993). The location of the primary lesions varied (Lerner and Moellmann, 1993). In at least 7, perhaps 10, of the 35 patients for whom the site of origin of the melanoma was reported, the malignant transformation had occurred in congenital nevi, 1023
CHAPTER 53
Increases in the epidermal pigment are not as common. When present, it is located predominantly in the keratinocytes of the stratum basale and the skin color tends toward brown or black. The appearance is that of a normal epidermis, albeit one more darkly pigmented than would be expected on the basis of genetic skin type. Melanocytes may or may not appear to be turned on to produce more melanin. The melanocyte density is thought to be normal.
Differential Diagnosis Some rare conditions are similar in appearance. Legg (1884), more than a century ago, wondered whether his patient with metastatic melanosis had ingested silver nitrate because this man looked as if he were afflicted with argyria. The color of individuals with argyria resembles closely that of individuals afflicted with melanomatosis. Mild melanosis is clearly distinguishable from jaundice. Widespread metastases of the liver can produce a superimposed jaundice. If the adrenal glands have been destroyed by metastases the individual has three causes for hyperpigmentation, excessive melanotropin secretion from the adrenal insufficiency, melanomatosis, and jaundice. Patients with adrenal insufficiency without melanoma do not have melanuria and their skin darkens to brown without developing a bluish hue.
Pathogenesis
Fig. 53.3. Diffuse hypermelanosis in a patient with metastatic malignant melanoma (courtesy of Dr. Aaron Lerner). See also Plate 53.2, pp. 494–495.
none larger than 5–7 cm in its broadest dimension. Two, and perhaps four, patients had unknown primaries. In the two questionable cases, the disease was said to have arisen in one or both adrenal glands. Only one patient had a primary melanoma of the eye. In the remaining cases, the melanoma had developed in an acquired nevus or independently of an existing melanocytic lesion.
Histopathology The findings can be divided into two groups according to the location of the excess pigment, i.e., dermal alone and dermal plus epidermal. Dermal pigment is the hallmark of all melanoma-associated cases of cutaneous melanosis and the cause of the blue hue (Findlay, 1970). The pigment is primarily in macrophages, especially those located in the vicinity of microvessels. In addition, melanin may be found free among the connective tissue fibers, as part of cellular debris or in dermal fibroblasts, endothelial cells, and disseminated melanoma cells when such are present. Melanoma cells have been noted singly or in microscopic tumors in the dermis and in the lumina of dermal blood and lymphatic capillaries (Murray et al., 1999). 1024
In a hypothesis published in 1954, Fitzpatrick et al. suggested that the darkening in generalized melanomatosis in patients with metastatic disease was due to an increase of soluble precursors of melanin produced by the malignant melanocytes (Fitzpatrick et al., 1954). These intermediates diffuse into the circulation, are deposited in the skin and other tissues to produce the melanosis. Some are excreted by the kidneys and darken the urine. Rorsman et al. made the more specific suggestion that trichochromes, and possibly also polymers containing 6-hydroxy-5-methoxyindole-2-carboxylic acid (Rorsman et al., 1986), are deposited in tissues and cause the melanosis (Agrup et al., 1978, 1979; Tsukamoto et al., 1998). Trichochromes are pheomelanic pigments formed from 5-Sand 2-S-cysteinyldopa and are markedly elevated in the sera of patients with generalized melanosis due to melanoma. Silberberg et al. were the first to examine melanotic skin with an electron microscope (Silberberg et al., 1968). They determined that copious amounts of pigment were present in particulate form and that the epidermal component of the melanosis in their patient was due to increased melanogenic activity in melanocytes, possibly assisted by epidermal cytostasis secondary to chemotherapy. A hypothesis proposed in 1974/1980 by Wolff and coworkers suggested that the melanosis may be due in part to pigmented single cell metastases in the dermis and/or epidermis (Konrad and Wolff, 1974; Schuler et al., 1980). A solitary nest of malignant melanocytes has been seen within a small dermal vessel, probably a lymphatic (Murray et al., 1999). However, observations reported by others are not consistent with this
MIXED EPIDERMAL AND DERMAL HYPERMELANOSES AND HYPERCHROMIAS
view (Adrian et al., 1981; Gebhart and Kokoschka, 1981; Rorsman et al., 1986; Steiner et al., 1991). Lerner (1993) hypothesized that the anomalous presence of growth factors that stimulate the proliferation and melanogenic differentiation of normal and malignant melanocytes play a major role in producing the clinical event. Böhm et al. observed the blood levels of a-MSH, hepatocyte growth factor, and endothelin-1 were significantly elevated in the patient with melanosis from melanoma. And they suggested aberrant production of these factors may be responsible not only for activation of the pigment system in diffuse melanosis of metastatic melanoma, but also for increased proliferation, motility, and pigment incontinence of normal and malignant melanocytes (Böhm et al., 2001).
References Adrian, R. M., G. F. Murphy, S. Sato, R. D. Granstein, T. B. Fitzpatrick, and A. J. Sober. Diffuse melanosis secondary to metastatic malignant melanoma. Light and electron microscopic findings. J. Am. Acad. Dermatol. 5:308–318, 1981. Agrup, G., C. Lindbladh, G. Prota, H. Rorsman, A.-M. Rosengren, and E. Rosengren. Trichochromes in the urine of melanoma patients. J. Invest. Dermatol. 70:90–91, 1978. Agrup, G., P. Agrup, C. Hansson, H. Rorsman, and E. Rosengren. Diffuse melanosis and trichochromuria in malignant melanoma. Acta Derm. Venereol. 59:456–457, 1979. Böhm, M., M. Schiller, D. Nashan, R. Stadler, T. A. Luger, and D. Metze. Diffuse melanosis arising from metastatic melanoma: pathogenetic function of elevated melanocyte peptide growth factors. J. Am. Acad. Dermatol. 44:747–754, 2001. Carruth, M. R., G. D. Goldstein, and D. K. Tillman. Localized melanosis in an immunocompromised patient with local metastatic melanoma. Dermatol. Surg. 28:241–3, 2002. Findlay, G. Blue skin. Br. J. Dermatol. 83:127–134, 1970. Fitzpatrick, T. B., H. Montogomery, and A. B. Lerner. Pathogenesis of generalized dermal pigmentation secondary to malignant melanoma and melanuria. J. Invest. Dermatol. 22:163, 1954. Gebhart, W., and E. M. Kokoschka. Generalized diffuse melanosis
secondary to malignant melanoma. In: Pathology of Malignant Melanoma, A. B. Ackerman (ed.). New York: Masson, 1981, pp. 243–249. Konrad, K., and K. Wolff. Pathogenesis of diffuse melanosis secondary to malignant melanoma. Br. J. Dermatol. 91:635, 1974. Legg, J. W. Multiple melanotic sarcomata beginning in the choroid, followed by pigmentation of the skin of the face and hands. Trans. Path. Soc. 35:367–372, 1884. Lerner, A. B., and G. Moellmann. Two rare manifestations of melanomas: generalized cutaneous melanosis and rapid solar induction of showers of small pigmented lesions. A critical review of the literature and presentation of two additional cases. Acta Derm. Venereol. 73:241–250, 1993. Manganoni, A. M., F. Facchetti, A. Lonati, P. Calzavara, and G. De Panfilis. Generalized melanosis associated with malignant melanoma: unusual histologic appearance. Cutis 52:93–94, 1993. Pack, G. T., and I. M. Scharnagel. The prognosis for malignant melanoma in the pregnant woman. Cancer 4:324–334, 1951. Pec, J., L. Plank, E. Minarikova, E. Palencarova, Y. Rollova, Z. Lazarova, S. Auxtova, and L. Lauko. Generalized melanosis with malignant melanoma metastasizing to skin — a pathological study with S-100 protein and HMB-45. Clin. Exp. Dermatol. 18:454–457, 1993. Rorsman, H., P. Agrup, B. Carlen, C. Hansson, N. Jonsson, and E. Rosengren. Trichochromuria in melanosis of melanoma. Acta Derm. Venereol. 6:468–473, 1986. Schuler, G., H. Honigsmann, and K. Wolff. Diffuse melanosis in metastatic melanoma. Further evidence for disseminated single cell metastases in the skin. J. Am. Acad. Dermatol. 3:363–369, 1980. Silberberg, I., A. W. Kopf, and S. L. Gumport. Diffuse melanosis in malignant melanoma. Arch. Dermatol. 97:671, 1968. Steiner, A., K. Rappersberger, V. Groh, and H. Pehamberger. Diffuse melanosis in metastatic malignant melanoma. J. Am. Acad. Dermatol. 24:625–628, 1991. Tsukamoto, K., M. Furue, Y. Sato, O. Takayama, R. Akasu, N. Ohtake, K. Wakamatsu, S. Ito, K. Tamaki, and S. Shimada. Generalized melanosis in metastatic malignant melanoma: the possible role of DOPAquinone metabolites. Dermatology 197:338–342, 1998. Wagner, E. Fall von Combination eines Pigmentkrebses mit einer reinen Pigmentgeschwulst. Arch. Heilkunde 5:280–284, 1864.
1025
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
54
Drug-induced or -related Pigmentation Peter A. Lio and Arthur J. Sober
Cutaneous Pigmentation
Fixed Drug Eruption
Reflection, absorption, and back-scattering of incident light determine the remittance spectrum or color of human skin (Anderson and Parrish, 1981; Findlay, 1970; Jeghers, 1944). Approximately 5% of incident light is reflected off normal stratum corneum. The major visible light chromophores present in human skin include epidermal melanin, intravascular hemoglobin, bilirubin, and carotene. Deposition of strong chromophores into the epidermis (quinacrine) or superficial dermis (tattoo inks) alters the absorption of certain visible light wavelengths and, thus, skin color. Absorptive subtraction of specific wavelengths from the total remittance spectrum is straightforward; however, dermal interactions with incident light are more complex (see Chapters 27 and 28). Visible light that escapes corneal reflection, absorption by epidermal melanin, and epidermal remittance is largely scattered by dermal collagen fibers and absorbed by native intravascular chromophores. Shorter wavelengths of light are backscattered at more superficial dermal layers than longer wavelengths. Deposition of broadly absorbing pigments (melanin, melanin–drug complexes) into deeper layers of the dermis can change the color of dermal remittance. A portion of the penetrating blue light is backscattered in superficial dermal layers, while forward-scattered blue light and longer wavelengths are absorbed by deeply deposited dermal pigments. Therefore, preferential dermal backscattering of shorter wavelengths and deep dermal pigment absorption of longer wavelengths imparts a blue hue to dermal remittance in a phenomenon known as Rayleigh or Tyndall scattering (Bohnert et al., 2000; Prum and Torres, 2003). Increased epidermal melanization absorbs a large percentage of incident and scattered light and diminishes the effect of differential dermal backscattering on skin color. Diffuse dermal deposition of black/brown pigment also masks differential spectral scattering and results in dark-brown, gray, or black coloration. Drugs or chemicals which perturb cutaneous spectral remittance comprise the focus of the ensuing discussion. This section expands upon information previously presented in several reviews (Granstein and Sober, 1981; Kang et al., 1993; Lerner and Sober, 1986, 1988; Levantine and Almeyda, 1973; Sober and Granstein, 1981).
Historical Background
1026
A case of fixed drug eruption was first documented by Bourns in 1889 when he described a patient who developed sharply demarcated hyperpigmented lesions on the lips and tongue after ingesting 20 grains of antipyrine (phenazone). The term fixed drug eruption, l’eruption erythémato-pigmentée fixé, was coined five years later by Brocq when he described three cases of erythematous and pigmented fixed eruptions following administration of antipyrine (Brocq, 1894). In 1919, Goldenberg and Chargin reported the first case of fixed drug eruption in the American literature entitled “Dermatitis medicamentosa (arsphenamin) with pigmentation” (Korkij and Soltani, 1984).
Epidemiology In a series of 446 inpatients with drug eruptions, Kauppinen (1984) showed that 92 patients (21%) manifested fixed drug eruptions, second only to exanthematous eruptions. Although fixed drug eruption can occur at any age, it is most commonly seen in 21–40-year-old adults; fixed drug eruptions occur more often in men than women (Chan, 1984a; Shukla, 1981). A genetic predisposition to fixed drug eruption was suggested by Pellicano et al. (1994) after finding a significantly higher prevalence of B22 and Cw1 major histocompatibility complex (MHC) antigens in 36 unrelated patients with fixed drug eruption. They proposed that a biochemical interaction between offending drugs and these two MHC-I molecules on epidermal cells may render individuals susceptible to fixed drug eruptions. Further research in this vein revealed a strong relation between trimethoprim– sulfamethoxazole-induced fixed drug eruption and the HLA-A30 antigen (Ozkaya-Bayazit and Akar, 2001). These investigators suggested that perhaps susceptibility to fixed drug eruptions is conferred by an as yet unrecognized gene near the HLA-A locus.
Clinical Findings Clinically, fixed drug eruption produces well-circumscribed lesions that recur at fixed sites after each challenge with the offending agent. Although some patients may present with multiple lesions, fixed drug eruption classically appears as a
DRUG-INDUCED OR -RELATED PIGMENTATION
Fig. 54.1. The vesicular phase of fixed drug eruption (see also Plate 54.1, pp. 494–495).
Fig. 54.2. Late stage of fixed drug eruption showing residual brown to black hyperpigmentation (see also Plate 54.2, pp. 494–495).
solitary erythematous macule that subsequently evolves into an edematous dusky red plaque. Vesicles and bullae (Fig. 54.1) with crusting and/or desquamation may develop at a later stage (Korkij and Soltani, 1984). Pruritus and burning are common symptoms; associated constitutional symptoms are rare but have been reported (Sehgal and Gangwani, 1987). The acute phase inflammation spontaneously resolves leaving a brown to violet-brown (Fig. 54.2) to black (Fig. 54.3) hyperpigmented macule that persists for weeks to months and becomes more pronounced with each fixed drug eruption recurrence (Korkij and Soltani, 1984; Sehgal and Gangwani, 1987). Repeated attacks of fixed drug eruption may both increase the size of existing lesions and induce new lesions (Korkij and Soltani, 1984). Fixed drug eruption can occur at any mucocutaneous site; however, predilected areas include the lips, arms, legs, trunk, sacral regions, and genitalia, particularly the glans penis (Sehgal and Gangwani, 1987). Palms, soles, and nail folds can also be involved (Baran and Perrin, 1991; Korkij and Soltani, 1984). Sites of prior pathology, such as insect bites, vascular lesions, herpes zoster, or previous cellulitis may predetermine the site of fixed drug
Fig. 54.3. Blue-black hyperpigmentation from chronic fixed drug eruption.
eruption (Korkij and Soltani, 1984). Recent work by OzkayaBayazit (2003) elucidated preferential site involvement for several specific agents. Notably, co-trimoxazole most frequently produced lesions on genital mucosa, while naproxen induced lesions on the lips with a highly significant association. Fixed drug eruption typically presents one to two weeks after initiating drug therapy, but sensitization may require a few weeks to several years of drug exposure (Korkij and Soltani, 1984). Once a patient is sensitized to a drug, reexposure will cause an eruption within 30 minutes to 8 hours, with a mean of 2.1 hours (Korkij and Soltani, 1984; Sehgal and Gangwani, 1987). Patients with fixed drug eruption may demonstrate a refractory period of weeks to several months during which the offending drug fails to induce a reaction (Korkij and Soltani, 1984). In contrast to the classic form of fixed drug eruption, there are patients who develop a generalized bullous fixed eruption. Also, not all fixed drug eruptions result in hyperpigmentation (Shelley and Shelley, 1987b). The drugs associated with nonpigmenting fixed drug eruptions include pseudoephedrine hydrochloride, tetrahydrozoline hydrochloride, piroxicam, diflunisal, thiopental, iothalamate, and arsphenamine, although case reports exist for other individual agents as well (Benson et al., 1990; Krivda and Benson, 1994; Roetzheim et al., 1991; Shelley and Shelley, 1987b).
Histology Histopathologic features of fixed drug eruption include hydropic degeneration with subsequent pigmentary incontinence, scattered dyskeratotic keratinocytes, and subepidermal bullae (Lever and Schaumburg-Lever, 1990; Masu and Seiji, 1983). The upper dermis usually reveals vascular dilatation, marked edema, and a perivascular inflammatory cell infiltrate consisting of histiocytes, polymorphonuclear leukocytes, and mast cells (Sehgal and Gangwani, 1987). Masu and Seiji have proposed the following mechanism for the development of pigmentary incontinence: (1) lymphocytes migrate into the 1027
CHAPTER 54 Table 54.1. Substances producing fixed drug eruption.* Antimicrobials
Analgesics/antipyretics
Metals/halides
Miscellaneous
Acetarsone Acriflavine
Antimony potassium tartrate Arsenicals
Anthralin Belladonna alkaloids
Amodiaquine Amoxicillin
Acetanilide Acetaminophen (paracetamol) (Zemtsov et al., 1992) Aminopyrine Antipyrine
Bismuth subsalicylate Bromides
Ampicillin (Chan, 1984b)
Aspirin
Gold sodium thiosulfate
Chlorhexidine (Moghadam et al., 1991) Chloroquine phosphate Dapsone Erythromycin (Pigatto et al., 1984) Fluconazole (Morgan and Carmichael, 1994) Griseofulvin (Feinstein et al., 1984)
Cincophen
Iodine
8-Chlorotheophylline Chlorphenesin carbamate (Coskey, 1982) Dextromethorphan (Stubb and Reitamo, 1990b) Diethylstilbestrol
Phenacetin Salicylates Nonsteroidal anti-inflammatory drugs (NSAIDs) Diflunisal Ibuprofen
Mercurial salts Antihistamines Cyclizine
Disulfiram Eosin Ephedrine Epinephrine Ergot
Levamisole Methenamine Metronidazole (Shelley and Shelley, 1987a)
Meclofenamic acid Mefenamic acid (Long et al., 1992) Naproxen (Habbema and Bruynzeel, 1987)
Nystatin p-Aminosalicylic acid Penicillin G
Oxyphenbutazone Phenylbutazone Piroxicam (Stubb and Reitamo, 1990a) Sulindac (Bruce and Odom, 1986) Tolmentin
Dimenhydrinate Diphenhydramine (Dwyer and Dick, 1993) Sedatives/hypnotics Barbiturates Carbamazepine (Shuttleworth and Graham-Brown, 1974) Chloral hydrate Chlordiazepoxide Chlormezanone (Mohamed and Bahru, 1983) Ethchlorvynol (Auerbach, 1965) Lormetazepam (Jafferany and Haroon, 1988) Meprobamate Methaqualone (Slazinski and Knox, 1984) Temazepam (Archer and English, 1988)
Pipemidic acid (Miyagawa et al., 1991) Quinacrine Quinine Rifampin (Mimouni et al., 1990) Streptomycin
Tolphenamic acid (Autio and Stubb, 1993) Cardiac agents Digitalis
Sulfonamides
Hydralazine (Sehgal and Gangwani, 1986) Pentaerythritol tetranitrate
Tetracyclines (Minkin et al., 1969) Trimethoprim (Hughes et al., 1987)
Quinidine Tetraethylammonium
Erythrosin Formaldehyde Heroin (Westerhof et al., 1983) Ipecac (emetine) Isoaminile citrate Iothalamic acid Karaya gum Legumes Oral contraceptives Oxyphenisatin acetate Pamabrom (Nedorost et al., 1991) Papaverine (Kirby et al., 1994) Phenolphthalein Phenothiazine Pseudoephedrine Saccharin Sodium cacodylate Sulfobromophthalein sodium Strychnine sulfate
*Table modified from Korkij and Soltani (1984).
epidermis and attack and injure keratinocytes; (2) dermal macrophages migrate to the epidermis and phagocytose dyskeratotic keratinocytes and their melanin stores; (3) the macrophages return to the dermis and digest all keratinocyte remnants except the melanosomes, which resist degradation and tattoo the dermis (Masu and Seiji, 1983).
Pathogenesis Numerous drugs and substances have been reported to cause 1028
fixed drug eruption (Table 54.1). Fixed drug eruptions have been most commonly associated with analgesics, barbiturates, salicylates, sulfonamides, tetracyclines, antipyrine, chlordiazepoxide, dapsone, oxyphenbutazone, phenolphthalein, and quinine (Olumide, 1979; Shukla, 1981). Although fixed drug eruption is usually due to a single drug, there are patients in whom fixed drug eruption develops following the ingestion of chemically related drugs (cross sensitivity) or unrelated drugs (polysensitivity) (Kawada et al., 1994; Korkij and
DRUG-INDUCED OR -RELATED PIGMENTATION
Soltani, 1984; Mishra et al., 1990). Oral rechallenge is the gold standard for definitive diagnosis of fixed drug eruption; some authors have raised theoretical concerns that peroral provocation could potentially induce either a generalized bullous eruption or an anaphylactic reaction (Alanko et al., 1987; Sehgal and Gangwani, 1987). Occasionally, patch, scratch, or intracutaneous testing is helpful; positive patch tests are frequently seen with phenazone derivatives (antipyrine), barbiturates, and sulfonamides (Alanko et al., 1987; Granstein and Sober, 1981; Korkij and Soltani, 1984; Pigatto et al., 1984; Stubb and Reitamo, 1990b). The pathogenetic mechanism(s) and the factor(s) that contribute to the preferential localization of fixed drug eruption lesions to certain skin sites remains unknown. Studies have failed to demonstrate the presence of the offending drug or its metabolite in affected skin. Several in vivo and in vitro studies implicate an immune pathogenesis. One study reports elevated serum immunoglobulin G (IgG) and IgA, yet normal serum IgM, levels two days after the reappearance of fixed drug eruption. These immunoglobulins return to normal levels three weeks after the disappearance of the lesions (Theodoridis et al., 1977). Immunofluorescence microscopic studies have shown the presence of IgG, C3 and fibrin in intercellular spaces of affected epidermis (Korkij and Soltani, 1984). Wyatt et al. reported that serum samples obtained from active fixed drug eruption could elicit an inflammatory response if injected into a quiescent prior fixed drug eruption site (Wyatt et al., 1972). This serum factor was thermolabile and was thought to represent a protein-conjugated drug derivative; drug alone failed to produce a reaction at either normal or prior fixed drug eruption sites. A study by GimenezCamarasa et al. (1975) supported the presence of a thermolabile serum factor in vitro with a lymphocyte blast transformation assay. Exposure to causative drug alone produced no lymphocyte blast transformation; however, autologous serum from patients with active fixed drug eruption did induce blast transformation, which increased when the offending drug was added to the lymphocyte culture. The clinical course of fixed drug eruption suggests that a cutaneous factor possessing memory function is also involved. Hindsén et al. (1978) found CD8-positive T cells in the epidermis during both the acute and healing phase of fixed drug eruptions, thus suggesting that memory T suppressor/ cytotoxic cells may play an important role in mediating the epidermal damage seen in the fixed drug eruption. Teraki et al. (1994) observed in two patients that within 1.5 hours, oral drug rechallenge induced intense surface expression of intercellular adhesion molecule (ICAM)-1 in only lesional keratinocytes and vascular endothelium. The intensity of ICAM1 expression correlated with the degree of T cell invasion into the epidermis. In vitro studies using skin organ culture showed that tumor necrosis factor a or interferon g stimulated lesional keratinocytes and endothelium to express ICAM-1 more rapidly. This suggests that nonspatially specific drug-induced cytokine expression induces focal, rapid, and intense ICAM1 expression by keratinocytes and endothelial cells that may
activate and home disease-specific T cells to fixed cutaneous sites. Using flow cytometry in both active and inactive lesions, Teraki and Shiohara (2003) proposed that CD8-positive T cells producing interferon g act as effector cells in the epidermal injury process, while CD4-positive T cells produce interleukin (IL)-10 to play a regulatory role. These authors hypothesized that it is the balance between the CD4- and CD8-positive cells which determines activity of the fixed drug eruption. Autotransplantation experiments have yielded variable results. Full-thickness skin transplanted from a fixed lesion into normal skin retains its ability to react for several weeks before reverting to normal; normal skin transplanted into a fixed drug eruption lesion initially does not react but later becomes positive. Since grafted skin eventually adopts the characteristics of its new environment, this would suggest the presence of fixed yet transferable etiologic factors within the cutis or subcutis of reaction sites (Knowles et al., 1936; Korkij and Soltani, 1984).
Treatment Discontinuation of the offending agent is obviously the best treatment for fixed drug eruptions. Corticosteroid therapy may diminish the intensity of the reaction in fixed drug eruption without affecting the temporal course of the disease (Stitzler and Kopf, 1960). Antihistamines have been found to have no effect on fixed drug eruption (Feinstein et al., 1984).
Discoloration of Skin Caused by Metals and Drugs Metals Iron Ferric salt solutions used to treat Rhus dermatitis (Traub and Tennen, 1936), Monsel solution (ferric subsulfate) (Danau and Grosshans, 1981; Olmstead et al., 1980; Wood and Severin, 1979), and industrial exposure to a “pickling” fluid that contained ferric salts dissolved in hydrochloric acid (Hare, 1951) have all caused iron tattooing of the dermis. In these instances, acute spongiotic dermatitis, surgical wounding, or acid exposure disrupted the epidermal barrier and permitted penetration of iron salts. Perls stain highlights iron encrustation of collagen fibers and deposits in dermal macrophages. Cutaneous hyperpigmentation can complicate sclerotherapy of superficial veins. Extravasated red blood cells decompose and release their iron stores that become sequestered as hemosiderin within dermal macrophages. The vast majority of post–sclerotherapy-induced hyperpigmentation resolves within six months to two years. Some patients experience persistent pigmentation which may respond to treatment with the copper vapor laser (Thibault and Wlodarczyk, 1992). Red blood cells can extravasate through the capillary walls when the latter are inflamed. This condition is called capillaritis. Typically the patient notes pinpoint red macules on the skin of the lower legs (Fig. 54.4). The red lesions turn red1029
CHAPTER 54
Fig. 54.4. Hemosiderin pigmentation from chronic capillaritis.
Fig. 54.5. Extensive lichen aureus from iron deposits in the skin (see also Plate 54.3, pp. 494–495).
Fig. 54.6. Slate-gray color most prominent on sun-exposed skin (normal hand for comparison) (see also Plate 54.4, pp. 494–495).
tattoos which have been more problematic (Tope and Shellock, 2002). orange in color and persist indefinitely. If this process is extensive, the skin can acquire an orange color in a disorder known as lichen aureus (Fig. 54.5). The stain or orange color is due to the oxidation of iron to the ferric state. A single case of orange-brown staining of the toenail plates has been reported in a patient whose feet were exposed to rural well water with a high iron content (Olsen and Jatlow, 1984). Prussian blue staining and spectroscopic analysis of nail plate samples confirmed the presence of increased iron. Since the nail discoloration followed the pattern of the proximal nail fold, not the lunula, the authors concluded that iron had penetrated the nail plate from the outside. There was no evidence of systemic iron overload in this patient. Several cases of burning or pain within iron tattoos have been reported during magnetic resonance imaging (MRI) procedures (e.g., Kreidstein et al., 1997). This phenomenon has prompted some radiologists to refuse to perform MRI procedures on individuals with permanent cosmetic tattoos such as eyeliner or blush. A large survey study rebuffs this stance and attempts to delineate between cosmetic tattoos and decorative 1030
Platinum In one case, administration of the chemotherapeutic agent, cisplatin, produced a gray-white line at the gingival margin (Ettinger and Freeman, 1979). Cutaneous pigmentation has not been noted with this drug.
Silver Silver compounds, ingested orally or applied to mucosal surfaces were once popular for the treatment of gastrointestinal, upper respiratory tract, and genitourinary infections. Generalized, slate-gray pigmentation (Figs 54.6 and 54.7) characteristic of argyria often appeared after a few months to 25 years of silver compound use; however, the majority of cases manifested after two to three years of continuous or intermittent administration (Hill and Montgomery, 1941). Generalized argyria tends to be most prominent in sun-exposed areas; the nails (Fig. 54.8), mucous membranes, and sclerae may also be discolored. Occupational exposure to silver refinery furnace fumes has
DRUG-INDUCED OR -RELATED PIGMENTATION
A
B Fig. 54.7. A silvery color to the skin of a man with marked argyria. Discoloration is most noticeable in sun-exposed skin. The hand exhibits normal skin color for comparison (see also Plate 54.5, pp. 494–495).
Fig. 54.8. Azure discoloration of the nail plate from silver deposition (see also Plate 54.6, pp. 494–495).
Fig. 54.9 Routine histologic examination of a specimen from a patient with argyria showing an eccrine gland (A). Polarized demonstrating silver particles (B) especially prominent around the eccrine apparatus.
resulted in significant pulmonary absorption and the eventual development of generalized argyria (Bleehen et al., 1981). Localized pigmentary changes have been noted in both an ungloved hand chronically exposed to silver-containing photographic solution (Buckley, 1963) as well as a burn wound treated with silver sulfadiazine (Dupuis et al., 1985). Biopsy of a pigmented area of the skin of a photo-processing technician demonstrated silver deposition only within the papillary dermis adjacent to eccrine ducts, thus implying that the sweat ducts served as the conduit for percutaneous absorption. Histopathology reveals finely granular black pigment scattered throughout the dermis yet prominently aggregated within the membrana propria of eccrine glands (Fig. 54.9A, B) (Hill and Montgomery, 1941; Mehta et al., 1966). Less striking concentrations of silver grains appear at the dermoepidermal junction, around sebaceous glands and hair follicles, and in the walls of blood vessels. Dark field microscopy renders the silver granules brilliantly refractile. Electron 1031
CHAPTER 54
Fig. 54.11. Discoloration of the hands from chrysiasis; normal hands shown for comparison (see also Plate 54.8, pp. 494–495).
Fig. 54.10. A patient with rheumatoid arthritis treated with gold. Her skin has a lilac discoloration most visible in sun-exposed skin (see also Fig. 54.11 and Plate 54.7, pp. 494–495).
microscopy reveals electron-dense deposits within lysosomal structures of macrophages (Bleehen et al., 1981) and fibroblasts (Mehta et al., 1966). Electron-dense granules have also been found in association with elastic and collagen fibers (Bleehen et al., 1981; Mehta et al., 1966; Prose, 1963). X-ray microanalysis has definitively identified elemental silver in argyric lesions (Bleehen et al., 1981).
Gold The first descriptions of chrysiasis appeared in the 1920s and referred to gold-treated tuberculosis patients who developed blue-gray discoloration of sun-exposed skin (Schmidt, 1941). Today, gold therapy is used primarily as a treatment alternative for rheumatoid arthritis. Chrysiasis typically presents as a photodistributed, blue-gray hyperpigmentation over the face (Fig. 54.10), neck, upper chest, arms, and hands (Fig. 54.11); (Beckett et al., 1982; Schmidt, 1941)]. Gold tattooing of the dermis directly contributes to the cutaneous pigmentation noted in chrysiasis patients. Some data suggest that gold also increases cutaneous melanization (Leonard et al., 1986). Why the pigmentation is most prominent in sun-exposed areas is 1032
not clear although ultraviolet light has been reported to enhance local gold deposition (Leonard et al., 1986; Schmidt, 1941). Administration of greater than 50–150 mg/kg of cumulative gold sodium thiosulfate (20–60 mg/kg gold) predisposes to the development of chrysiasis after a latent phase of months to years. Lower cumulative doses of chrysotherapy result in microscopic deposition of gold in the skin but not gross pigmentary changes (Jeffrey et al., 1975). There are some data to suggest that certain individuals are more susceptible to chrysiasis. Rodriguez-Perez et al. (1994) demonstrated that, among patients with rheumatoid arthritis receiving gold therapy, human leukocyte antigen (HLA)-B27 antigen is associated with the development of chrysiasis. Gold therapy was linked to yellow discoloration of the toenails in a patient who received a cumulative dose of 2.5 g of gold sodium thiomalate (Fam and Paton, 1984). Unlike cutaneous pigmentation which may be permanent (Beckett et al., 1982; Granstein and Sober, 1981), nail discoloration clears as the nail plate grows distally. Light microscopy reveals finely granular black pigment around appendages, vessels, and nerves but not within appendages, the epidermis, or basement membranes (Millard et al., 1988; Schultz Larsen et al., 1984). Epipolarized light microscopy enhances the detection of gold particles. Transmission electron microscopy demonstrates dense particles primarily within macrophage lysosomes. Gold particles appear as both filaments and microtubules in fine crystalline patterns, as dense small and rod-like particles, and as larger irregular crystalline masses. Laser microprobe mass spectroscopy, X-ray microanalysis, and backscattered electron imaging have definitively identified gold within biopsy samples (Millard et al., 1988).
Mercury Early in this century, topical preparations of inorganic mercury compounds, such as ammoniated mercury, mercurous chlo-
DRUG-INDUCED OR -RELATED PIGMENTATION
ride, and mercurous oxide, were applied both as bleaching agents and psoriasis treatments (Burge and Winkelmann, 1970; Young, 1960). Pigmentary changes caused by topical mercurial creams were reported first in 1922 and most recently in 1990 (Burge and Winkelmann, 1970; Dyall-Smith and Scurry, 1990; Goeckermann, 1922; Hollander and Baer, 1929; Kern, 1969; Lamar and Bliss, 1966; Lang, 1988). Industrial cutaneous exposure to mercurial salts has caused not only cutaneous hyperpigmentation but also signs and symptoms of systemic mercury intoxication or hydrargyrosis (Kennedy et al., 1977). Rarely, prolonged application of topical mercurial vanishing creams has resulted in significant systemic absorption. One woman who had applied a relatively high percentage 17.5% mercuric ammonium chloride preparation daily for 18 years presented with perifollicular hyperpigmentation, elevated blood and urine mercury levels, and possible neuropsychiatric toxicity (Dyall-Smith and Scurry, 1990). Mercury-induced hyperpigmentation arises in areas directly contacted by mercurial salts. This pigmentation is most pronounced in skin creases, the periorbital region, and around hair follicles (Burge and Winkelmann, 1970; Dyall-Smith and Scurry, 1990; Kennedy et al., 1977; Lamar and Bliss, 1966). Mercury penetrates the epidermis via its appendages and then crosses the appendageal epithelium into the dermis by an unclear mechanism (Scott, 1959; Witten, 1957). Once in the dermis, mercury ions, presumably, inhibit melanin synthesis by displacing copper from tyrosinase, thus rendering this apoenzyme inactive (Lerner, 1952). However, contrary to mercury’s purported therapeutic indication, long-term use of mercurial creams induces hyperpigmentation as a consequence of heavy metal tattooing of the dermis in conjunction with increased epidermal melanin deposition (Burge and Winkelmann, 1970; Lamar and Bliss, 1966). Routine histopathology and electron microscopy have localized upper dermal metallic granules, free in the dermis, in association with elastic fibers, and within macrophages (Burge and Winkelmann, 1970). Silver stains have revealed increased basal layer epidermal melanin content (Burge and Winkelmann, 1970). Dark field microscopy demonstrates brilliantly refractile granules within the upper dermis as well as in the upper stratum corneum if mercury exposure were relatively recent (Burge and Winkelmann, 1970; Kennedy et al., 1977). Both neutronactivation and analytical electron microscopy have confirmed the presence of elemental mercury in specimens derived from hyperpigmented patients (Burge and Winkelmann, 1970; Kennedy et al., 1977). While neutron-activation spectroscopy must be performed blindly on a bulk sample, analytical electron microscopy allows for simultaneous structural and elemental analysis of discrete particles. Once within dermal macrophages the mercury tattooed areas are unlikely to resolve spontaneously; however, perifollicular deposits may rapidly disappear after stopping topical mercurials (Dyall-Smith and Scurry, 1990). Slate-gray dermal mercury tattoos can be treated with dermabrasion although iatrogenic postinflammatory hyperpigmentation is always a concern (Lang, 1988).
Fig. 54.12. Hyperchromatic margins of the gums from deposition of lead (see also Plate 54.9, pp. 494–495).
Lead Ingestion or inhalation of lead-bearing compounds present in the home or at work accounts for the vast majority of lead intoxication (Bruggenkate et al., 1975). The symptoms of plumbism include lethargy, gastrointestinal distress, peripheral neuritis, and encephalopathy. Eighty percent of patients with chronic lead intoxication present with a characteristic bluegray, Burton line over the marginal gingivae (Fig. 54.12) [(Bruggenkate et al., 1975; Dummett, 1964)]. Bacterially generated hydrogen sulfide may precipitate lead in the gingival tissues. Gingival biopsy has demonstrated dark-brown pigment within the subepithelial connective tissue. Qualitative electron microprobe analysis has confirmed the presence of lead within the Burton lines (Bruggenkate et al., 1975). Gingival pigmentation may be the sole clue to chronic lead toxicity, as reported in an institutionalized patient with precedent mental retardation and pica syndrome (Lockhart, 1981). Calcium ethylenediamine tetraacetic acid, dimercaptoethanol (BAL), and D-penicillamine represent chelating agents employed in the treatment of lead toxicity. Elimination of lead exposure, chelation therapy, and improved oral hygiene may result in the slow resolution of gingival pigmentation (Bruggenkate et al., 1975). While pigmentation of the skin has not been reported with lead intoxication, nail hyperpigmentation has been reported in an infant treated daily with Tao Dan® powder, a leadbearing absorbent compound (Shengda and Dean, 1989). This infant had a significantly elevated blood lead level. Energy dispersive X-ray microanalysis confirmed the presence of lead within the nail plate. Nail plate proteins contain numerous sulfhydryl groups that can avidly bind lead. Discontinuance of the powder resulted in restoration of normal nail plate color.
Bismuth Bismuth compounds have been used to treat venereal disease, psoriasis, lichen planus, and inflammatory gastrointestinal 1033
CHAPTER 54
disorders (Dummett, 1964). Long-term oral or parenteral bismuth administration has produced generalized slate-gray hyperpigmentation, also known as bismuthia, which is often accentuated over the face, neck, and dorsa of the hands (Leuth et al., 1936; Zala et al., 1993). Gingival and oral mucosal hyperpigmentation may accompany cutaneous discoloration. As proposed for lead deposition, oral bacterial flora produce hydrogen sulfide that may precipitate bismuth in the marginal gingivae (Dummett, 1964). Bismuth-induced pigmentation is permanent and may present without the nephropathy, stomatitis, vomiting, diarrhea, and neurologic disorders typical of bismuth poisoning. Chelating agents, such as BAL, are indicated only in patients demonstrating systemic bismuth toxicity and blood bismuth levels greater than 200–300 mg/L (Zala et al., 1993). Biopsy reveals finely granular, non-doubly refractile, dark pigment scattered in the papillary and reticular dermis (Leuth et al., 1936; Zala et al., 1993). Basic qualitative chemical analysis has been used to prove the presence of bismuth in bulk biopsy specimens (Leuth et al., 1936). The staining method of Christeller and Komaya has identified bismuth particles as brown granules on fixed tissue sections (Zala et al., 1993). Although not reported, analytical electron microscopy or laser probe spectroscopy could be used to demonstrate the presence of bismuth.
Semimetals Arsenic Inorganic trivalent arsenic preparations, such as Fowler solution (liquor potasii arsenites or potassium arsenite), have been prescribed for the treatment of psoriasis, folliculitis, lichen planus, pityriasis rubra pilaris, and dermatitis herpetiformis (Cuzick et al., 1982; Levantine and Almeyda, 1973). Injected pentavalent organic arsenic compounds were employed as treatments for syphilis (Sutton, 1923). Water supplies may also be contaminated with arsenic (Cebrian et al., 1983). Prolonged ingestion of inorganic arsenic can result in the development of diffuse macular hyperpigmentation, particularly over the trunk. Within the hyperpigmented macules reside several small islands of normally pigmented skin, which produce a “rain drop” appearance (Fig. 54.13). Arsenical keratoses, particularly over the hands and feet (Fig. 54.14), often accompany the cutaneous hyperpigmentation. One study of patients who had been exposed to arsenic-tainted well water estimated the threshold cumulative dose necessary to induce hyperpigmentation to be 3 g (Cebrian et al., 1983). The latent period between exposure and appearance of pigmentary changes ranges from 1 to 20 years. Bartolome et al. (1999) reported a case of acute arsenic ingestion of between 8 g and 16 g of sodium arsenite by a psychotic woman who subsequently developed erythroderma within five days. Biopsy of the eruption revealed the presence of multiple small pigment granules in and around histiocytes and throughout the collagen fibers of the papillary dermis. These granules stained positively with Fontana-Masson and negatively with periodic
1034
Fig. 54.13. Leucomelanoderma from ingestion of arsenic. Note both hyperpigmented skin and small hypopigmented macules (courtesy of Dr. Claire Beylot).
acid-Schiff and HMB-45, supporting the notion that they represented arsenic deposition at an early stage. Routine histopathologic examination classically reveals basal layer and dermal melanin deposition (Montgomery and Ornsby, 1954). Osborne’s method of staining has demonstrated arsenic-containing crystals within the dermis and epidermis (Montgomery and Ornsby, 1954). Arsenic may promote melanin synthesis by binding sulfhydryl groups, thus liberating copper ions to activate tyrosinase (Levantine and Almeyda, 1973).
Tellurium Tellurium is a heavy element which is used in the vulcanizing of rubber, as a diagnostic test for diphtheria, as an additive to cast iron, steel, and copper, as a glass coloring agent, and as a chemical catalyst (Blackadder and Manderson, 1975). Laboratory exposure of two workers to tellurium hexafluoride gas resulted in characteristic signs of tellurium toxicity, the most distinctive of which is a strong garliclike odor of breath and excreta. Additionally, these exposed workers manifested
DRUG-INDUCED OR -RELATED PIGMENTATION
A
B
Fig. 54.14. Punctate keratoses on the palms (A) and soles (B) of the man with a history of arsenic ingestion taken as a tonic during childhood.
hyperpigmented patches over their face, neck, and finger webs (Blackadder and Manderson, 1975). The skin discoloration faded over several weeks. Biopsy samples were not analyzed.
Tattoos Tattooing involves the implantation of pigmented particles into the dermis (Fig. 54.15) (Morgan, 1974). Commonly used chromophores include: carbon (black), cinnabar, a combination of mercuric and cadmium sulfide (red) (Fig. 54.16), chromium oxide (green) (Figs 54.17 and 54.18), cadmium sulfide (yellow), cobalt (blue) (see Figs 54.17 and 54.18), ferric salts (brown/pink), manganese (purple), and titanium oxide (white). Photoallergic reactions to cadmium sulfide and manganese have been reported (Goldstein, 1967; Nguyen and Allen, 1979). Eczematous and granulomatous reactions to mercury, cobalt, and chromium salts may also complicate cutaneous tattoos (Fig. 54.19) (Beerman and Lane, 1957; Fregert and Rorsman, 1966; Hirsh and Johnson, 1984; McGrouther et al., 1977; Schmidt and Christensen, 1978). Most tattoos are intentional. However, accidental cutaneous
injury may introduce a variety of substances into the dermis. Abrasions from falling on roads or streets often are contaminated with tiny particles of dirt, which may persist indefinitely in the skin, thus producing a traumatic tattoo. For example, a piercing pencil injury may deposit carbon/graphite particles into the dermis and cause a permanent tattoo. Gunpowder (Fig. 54.20) ejected from the end of a gun barrel can penetrate the skin and form a spray of small (1 mm) blue macules and papules. Before the advent of laser therapy, tattoo ablation options were limited to surgical excision, deep dermabrasion, salabrasion, or destruction with topical acids (Morgan, 1974). Use of the Q-switched ruby and neodymium:yttrium aluminum garnet (Nd:YAG) lasers allows for removal of tattoos with reduced dermal scarring (Kilmer and Anderson, 1993; Taylor et al., 1990). Recently, it has been reported that laser treatment of tattoos may trigger local and generalized allergic reactions by liberating pigment antigens from within histiocytes and exposing them to the immune system (Ashinoff et al., 1995). In patients with history of laser-triggered allergy to tattoo pigments, pretreatment with systemic corticosteroids
1035
CHAPTER 54
Fig. 54.15. Professional tattoo.
Fig. 54.16. Professional tattoo illustrating yellows and reds (see also Plate 54.10, pp. 494–495).
and antihistamines can prevent subsequent allergic reactions (Ashinoff et al., 1995). Imiquimod, a topical immune-response modifier, has been shown to be effective in tattoo removal in a guinea pig model when applied soon after application of the tattoo (Solis et al., 2002). Thus, further study may determine a role for this modality, perhaps as an adjunct or alternative to laser tattoo removal.
Carotenoids b-Carotene Carotene, the precursor of vitamin A (provitamin A), is a yellowish lipochrome found in several green, yellow, and orange fruits and vegetables, such as leafy greens, broccoli, carrots, squash, sweet potatoes, oranges, apricots, cantaloupe, mango, and papaya (Lescari, 1981). Cooking, pureeing, or mashing of vegetables liberates carotene crystals from within the plant cell walls and, thus, significantly increases its bioavailability (Lescari, 1981; Micozzi et al., 1988). Carotene is also found in butter, eggs, milk, certain vegetable oils, and purified supplements. About one-third of ingested carotene is absorbed. Some of the absorbed carotene is converted in the small intestine and liver to vitamin A. Since this conversion is slow, carotenemia does not lead to hypervitaminosis A. 1036
Fig. 54.17. Professional tattoo illustrating pinks, blues, greens, and light purples (see also Plate 54.11, pp. 494–495).
Carotenemia refers to a yellow discoloration of the skin (Fig. 54.21) most commonly due to ingestion of excess carotene-bearing foods. Hypothyroidism, diabetes mellitus, hyperlipidemias, and nephrotic syndrome manifest elevated b-lipoproteins, the major carriers of serum carotene, and
DRUG-INDUCED OR -RELATED PIGMENTATION
Fig. 54.18. Artistic tattoo showing multiple colors and shades (see also Plate 54.12, pp. 494–495).
predispose to carotenemia (Lescari, 1981; Stack et al., 1988; Walton et al., 1965). Rare cases of carotenemia are due to inborn errors of metabolism that interfere with conversion of carotene to vitamin A (Jones and Black, 1994; McLaren and Zekian, 1971; Sharvill, 1970). Excess serum carotene is deposited in the skin, with a predilection for the subcutaneous fat and stratum corneum (Greenberg et al., 1958; Lescari, 1981). Sweat, sebum, and urine may contain significant quantities of carotene. Nonkeratinized epithelia do not have an affinity for carotene; thus, unlike jaundice, the sclerae and oral mucous membranes do not display yellow discoloration in carotenemia. Serum carotene concentration above 250 µg/dL results in obvious skin yellowing, first appearing over the palms, soles, nasolabial folds, tip of the nose, and forehead, then progressing to involve the dorsal digits, buttocks, breasts, abdomen, chin, and postauricular areas (Lescari, 1981; Stack et al., 1988). A careful history and physical examination should be able to distinguish carotenemia from jaundice. Serum carotene and bilirubin levels should be measured in equivocal cases. Addition of alcohol to a serum sample will result in an organic
Fig. 54.19. Tattoo with granuloma in skin bearing red colors due to an allergic reaction to cinnabar, a compound made from mercury. The red areas are inflamed.
Fig. 54.20. Gunpowder tattoo.
phase that is yellow in hyperbilirubinemia but clear in carotenemia. Conversely, petroleum ether added to a serum sample will create a yellow organic layer in carotenemia yet a clear organic phase in hyperbilirubinemia (Stack et al., 1988). 1037
CHAPTER 54
Fig. 54.21. Yellow-colored hands from ingestion of beta-carotene causing carotenoderma. Normal hand included for comparison (see also Plate 54.13, pp. 494–495).
Fig. 54.22. Blue-black chromophore deposits in sun-exposed areas of the face of a man taking amiodarone (see also Plate 54.14, pp. 494–495).
In the short term, carotenemia is harmless; however, longstanding carotenemia has been associated with weakness, weight loss, hepatomegaly, neutropenia, hypotension, and amenorrhea. Yellow skin color will return to normal within two to six weeks after dietary retinol restriction. The differential diagnosis of xanthoderma includes lycopenemia (see below) and ingestion or percutaneous absorption of quinacrine, saffron, picric acid, tetryl, and dinitrophenol (Lescari, 1981).
agent does not cause hypervitaminosis A. Retinopathy, hepatitis, cutaneous hypersensitivity, and aplastic anemia have been associated with use of this agent as a tanning pill (Bluhm et al., 1990).
Lycopene Lycopene is an isomer of b-carotene that is found in beets, tomatoes, rose hips, bittersweet berries, and chili beans (Baran and Perrin, 1991). Although the pigmentary change induced by lycopene can mimic carotenemia, lycopenemia usually imbues an orange hue. Since lycopene is a more intensely colored pigment, staining of the skin and fat can occur at serum concentrations lower than that necessary to induce carotenemia. Lycopenemia manifests over the palms and soles, spares the sclerae, but may involve the hard palate. Simultaneous lycopenemia and carotenemia has been reported in patients who ingest large amounts of tomatoes and yellow vegetables (Hughes and Wooten, 1966).
Canthaxanthin Canthaxanthin is a carotenoid present in crustaceans, fish, bird feathers, mushrooms, algae, food dyes, and yellow and orange vegetables (Jackson, 1981). When ingested and deposited in the subcutaneous fat and epidermis, this orangecolored chromophore simulates a tan. Preparations of this pigment, such as Orobronze, have been distributed contrary to the US Food and Drug Administration (FDA) recommendations as oral tanning agents; however, the skin coloration produced by this agent is not protective against ultraviolet radiation. Canthaxanthin has also been used in the management of photosensitivity disorders and vitiligo (Gupta et al., 1988). Since canthaxanthin is not a vitamin A precursor, this 1038
Amiodarone Amiodarone is a diiodinated benzofuran used to suppress both supraventricular and ventricular cardiac arrhythmias. After approximately four months of amiodarone therapy, 30–76% of patients have experienced photosensitivity, predominantly to UVA but some to UVB (Chalmers et al., 1982; Harris et al., 1983a, b; Rappersberger et al., 1989; Roupe et al., 1987; Waitzer et al., 1987; Zachary et al., 1984). Of patients taking amiodarone, 1–10% will develop cutaneous, slate-gray hyperpigmentation after an average of 20 months and a minimum of 160 g of amiodarone therapy (Bucknall et al., 1986; Casillas et al., 1978; Harris et al., 1983a, b; Matheis, 1972; Rappersberger et al., 1989). Over several months to two years after discontinuing amiodarone, the pigmentary changes tend to fade (Matheis, 1972; Rappersberger et al., 1989; Trimble et al., 1983). One patient who had amiodarone-induced facial hyperpigmentation for four years noted complete clearance of this discoloration approximately six months after lowering the dose to 200 mg/day. Subsequently, the patient continued to take amiodarone at this dose for two years without developing recurrent hyperpigmentation (Beukema and Grayboys, 1988). Amiodarone-induced hyperpigmentation is most prominent in sun-exposed areas (Figs 54.22 and 54.23) (Weiss et al., 1984) and may be initiated by a phototoxic reaction (Rappersberger et al., 1989; Trimble et al., 1983; Wanet et al., 1971). Ultraviolet radiation-induced free radical generation may predispose to amiodarone accumulation within dermal cells in sun-exposed areas (Alinovi et al., 1985; Miller and McDonald, 1984). High-performance liquid chromatography has demonstrated levels of amiodarone and its major metabolite, desethylamidarone, to be approximately ten times greater
DRUG-INDUCED OR -RELATED PIGMENTATION
Fig. 54.24. The tibial surface of a patient taking minocycline showing blue discoloration from deposition of the drug chelated with metal ions (see also Plate 54.16, pp. 494–495).
tion with the Q-switched ruby laser. This yielded complete resolution of the pigment after one treatment, with no recurrence after a year of follow-up, despite continuing on amiodarone.
Tetracyclines Minocycline
Fig. 54.23. Close-up of the patient in Fig. 54.22, showing blueblack discoloration of the skin (see also Plate 54.15, pp. 494–495).
in sun-exposed pigmented tissue compared with those in nonexposed skin (Adams et al., 1985; Zachary et al., 1984). Histologically, biopsies disclose yellow-brown refractile granules in the dermis, especially around vessels. Sudan black stain accents the lipid-laden dermal deposits. Electron microscopy localizes electron-dense material to membranebound, lysosomal-like structures within histiocytes, endothelial cells, smooth muscle cells, fibroblasts, pericytes, polymorphonuclear leukocytes, and keratinocytes (Adams et al., 1985; Miller and McDonald, 1984; Trimble et al., 1983; Waitzer et al., 1987; Zachary et al., 1984). Four types of lysosomal deposits have been described: (1) lamellar or myelin figurelike inclusion (most typical), (2) electron dense, (3) membrane-bound electronlucent, and (4) mixed (Waitzer et al., 1987). Within these lysosomal inclusions, electron probe microscopy has disclosed definite iodine peaks, suggesting the presence of amiodarone or a metabolite. Thus, it has been hypothesized that amiodarone accumulation in lysosomes represents a drug-induced lipidosis (Trimble et al., 1983; Waitzer et al., 1987). Although the pigmentation tends to self-resolve after cessation of amiodarone, for some patients this is not possible. Karrer et al. (1999) successfully treated the hyperpigmenta-
Minocycline is a tetracycline derivative frequently employed to treat acne vulgaris. Oxidation turns yellow crystalline minocycline black. At doses of 200 mg/day, vestibular toxicity is the most frequent side effect. However, continuous administration can result in localized blue-black hyperpigmentation of inflamed or previously scarred skin (type I), bluegray pigmentation of previously normal extremity skin (type II) (Fig. 54.24), or diffuse muddy brown discoloration of sunexposed areas (type III) (Argenyi et al., 1987; Basler and Kohnen, 1978; Basset-Séguin et al., 1995; McGrae and Zelickson, 1980; Pepine et al., 1993; Ridgway et al., 1982; Sauer, 1979; Simons and Morales, 1980). Face, lower extremities, and arms are common targets for minocycline-induced pigmentary changes. Nail beds, sclerae, mucous membranes (Fig. 54.25) and teeth (Fig. 54.26) may also be affected (Pepine et al., 1993). Minocycline has been associated with extracutaneous pigmentation of thyroid, cartilage, bones, and brain in humans (Attwood and Dennett, 1976; Gordon et al., 1984) and laboratory animals (Benitz et al., 1967). Pigmentary changes from minocycline have been noted as early as nine weeks after starting minocycline at a dose of 100 mg twice per day (cumulative dose = 12.1 g) (Ridgway et al., 1982). After discontinuing minocycline, the induced pigmentation tends to slowly fade over months to years. Histopathologic findings vary depending on the type of minocycline-induced pigmentation (Argenyi et al., 1987). Biopsies of type I pigmentation have revealed both intra- and extracellular, iron-positive pigment granules within the dermis (Basler and Kohnen, 1978; Fenske et al., 1980). Electron microscopic analysis of the type I pigment granules identifies hemosiderin- and ferritin-like membrane-bound particles as 1039
CHAPTER 54
Similar to the case with amiodarone-induced pigmentation, Q-switched lasers have also proved to be effective at treating minocycline-related pigmentation, particularly that of type II (Green and Freedman, 2001).
Tetracycline
Fig. 54.25. Hyperpigmentation of the oral mucosa from minocycline (see also Plate 54.17, pp. 494–495).
Osteoma cutis is a rare manifestation of acne vulgaris and appears as small blue-gray nodules over the face. Some reports have blamed tetracycline treatment for the appearance of these lesions (Basler et al., 1974; Walter and Macknet, 1979). One acne patient developed osteoma cutis after four years of tetracycline therapy and fluorescence microscopy identified a chromophore consistent with tetracycline (Walter and Macknet, 1979). Furthermore, no new lesions of osteoma cutis developed after tetracycline was discontinued. Whether this association between tetracycline and osteoma cutis is etiologic or coincidental remains to be discerned. In addition, tetracycline has been reported to produce yellow lunulae (Hendricks, 1980).
Methacycline
Fig. 54.26. Discoloration of the teeth (see also Plate 54.18, pp. 494–495).
well as non–membrane-bound inclusions. Type II biopsies have demonstrated predominantly intracellular pigment granules within the dermis and subcutis (Argenyi et al., 1987; McG1rae and Zelickson, 1980; Ridgway et al., 1982). Perls and Fontana-Masson stains show the pigment granules to have characteristics of both iron and melanin. Electron microscopy has identified electron-dense, iron-containing particles in siderosomes, within dermal histiocytes, free within the cytoplasm, or, rarely, scattered among dermal collagen fibers (Sato et al., 1981). Since electron microscopy has not revealed increased numbers of melanosomes and the pigment does not bleach with hydrogen peroxide, it has been hypothesized that the Fontana-Masson stain is detecting an oxidized minocycline metabolite, which has chelated iron and, to a lesser degree, calcium (Argenyi et al., 1987). X-ray analysis of types I and II specimens has found evidence of iron, calcium, sulfur, and chlorine with the pigment granules (Argenyi et al., 1987; Ridgway et al., 1982; Sato et al., 1981). Type III biopsies are remarkable for increased basal layer and dermal melanization without evidence of increased iron deposition (Simons and Morales, 1980). 1040
Methacycline is another tetracycline derivative that has been reported to produce gray-black pigmentation of light-exposed areas of the skin and yellow-brown pigmentation of the conjunctiva in 7/250 patients studied (Walter and Macknet, 1979). Cumulative doses ranged from 420 g to 1575 g over 2–7.5 years. Salient histologic features included moderate basal layer pigmentation, elastotic changes of the upper and intermediate dermis, pigmented macrophages that variably stained positive with Fontana-Masson stain, and refractile dermal granules that stained with von Kossa stain. Electron microscopy defined the basal layer and macrophage pigment as consistent with melanin. Dermal elastic fibers were found to contain streaks of osmiophilic, irregularly shaped granules.
Ochronosis Ochronosis refers to tissue deposition of microscopic, ochrecolored pigment, which when present in the dermis imparts a blue-black hue to the skin. Inherited deficiency of homogentisic acid oxidase results in accumulation of polymerized homogentisic acid in skeletal, cardiovascular, genitourinary, respiratory, ocular, and cutaneous tissues. This inborn error of amino acid metabolism defines alkaptonuria or endogenous ochronosis (Albers et al., 1992). Hydroquinone, phenol, resorcinol, and antimalarial agents represent pharmacologic agents that may induce exogenous ochronosis (Figs 54.27and 54.28).
Phenolic Compounds Topical preparations of hydroquinone serve as popular treatments for epidermal pigmentary disorders, such as melasma (Engasser and Maibach, 1981). Chronic application of hydroquinones in concentrations as low as 2% may result in localized dermal pigmentation that typically presents as well-demarcated, blue-black pigmented facial macules, which are often permanent (Bentley-Philips and Bayles, 1975; Cullison et al., 1983; Dogliotti and Leibowitz, 1979;
DRUG-INDUCED OR -RELATED PIGMENTATION
Fig. 54.27. Localized ochronosis of the face from excessive use of hydroquinone (see also Plate 59.4, pp. 494–495).
Hardwick et al., 1989; Howard and Furner, 1990; Lawrence et al., 1988). Hydroquinone creams have also caused nail plate pigmentation, possibly due to photopolymerization of absorbed hydroquinone into a brown pigment (Arndt and Fitzpatrick, 1965; Mann and Harman, 1983). This nail discoloration disappeared one month after discontinuing hydroquinone creams (Mann and Harman, 1983). Phenol-containing medicaments have produced pigmentary changes in cartilage, skin, sclerae, and urine, that are nearly indistinguishable from endogenous ochronosis (Beddard and Plumtre, 1912; Berry and Peat, 1931; Cullison et al., 1983). Carbolic acid (phenol) dressings used for the treatment of chronic skin ulcers have induced cutaneous ochronosis (Brogren, 1952). Hair tonics containing phenolic compounds have been linked to hyperpigmentation of the scalp and palms (Forman, 1975). Topically applied resorcinol (Howard and Furner, 1990) in acne preparations, in Castellani’s paint, or as a consequence of industrial exposure (Dupre et al., 1979) as well as topical picric acid (Cullison et al., 1983) burn treatments have caused localized ochronosis. Biopsy of hyperpigmented ochronotic areas has revealed dermal deposits of ochre (yellow-brown) pigment as fine gran-
Fig. 54.28. Patient in Fig. 54.27 showing discoloration of the chin from localized ochronosis due to excessive application of hydroquinone.
ules both free and within macrophages (Albers et al., 1992; Attwood and Dennett, 1976; Findlay et al., 1975). Larger crystalline masses of similar pigment are interposed between collagen bundles. These irregularly shaped, crystalline masses represent degenerated collagen fibers interspersed with ochronotic pigment. Pigment granules also have been found within elastic fibers. Larger pigment clumps were more common in areas of solar elastosis, suggesting that solar radiation promoted pigment deposition. By analogy to endogenous ochronosis, it has been proposed that the pigment of exogenous ochronosis also represents polymerized homogentisic acid. Both endogenous and exogenous ochronosis are indistinguishable under the microscope as both manifest as golden brown (ochre) pigment deposits that stain positive with Fontana-Masson and negative with Perls reagents. Unlike melanin, neither endogenous nor exogenous ochronosis bleaches with hydrogen peroxide treatment (Attwood and Dennett, 1976). The phenolic compounds, hydroquinone, picric acid, and phenol may be oxidized and enzymatically converted to hydroxyindole molecules which can polymerize and form ochronotic pigment (Cullison et al., 1041
CHAPTER 54
Fig. 54.29. Patient with atabine-induced lichen planus-like eruption. Note the brown-violaceous discoloration of the skin of the abdomen and the yellow color of the extremities (see also Plate 54.19, pp. 494–495).
1983). Alternatively, it has been suggested that these phenolic compounds may inhibit homogentisic acid oxidase, thus mimicking the mechanism of endogenous ochronosis (Howard and Furner, 1990). Treatment modalities are limited although Kramer et al. (2000) showed some success with the Q-switched ruby laser.
Antimalarials Antimalarial compounds, such as chloroquine, hydroxychloroquine, quinine, quinacrine, amodiaquine (Fig. 54.29) may induce cutaneous hyperpigmentation in 8–25% of patients taking these medicines for longer than three to four months (Bruce et al., 1986; Campbell, 1960; Leigh et al., 1979; Levy, 1982; Ludwig et al., 1963; Lutterloh and Shallenberger, 1946; Sugar and Waddell, 1946; Tuffanelli et al., 1963). Typically, the ochronosis-like, gray to blue-black pigmentation is distributed over the anterior tibiae, face, hard palate, gums, sclerae, and subungual areas. Discoloration of the hard palate is usually the initial manifestation. Quinine shots have produced localized pigmentary changes over the buttocks (Bruce et al., 1986). Discontinuance of the offending agents has led to decreased intensity, but not complete resolution, of the hyperpigmentation. Hydroxychloroquine has been noted to bleach hair in a smaller percentage of individuals (Fig. 54.30). The bleaching is reversible when the medication is discontinued. Histopathologic examination of antimalarial ochronosis has revealed classic ochronotic changes as well as focal staining for melanin and hemosiderin. Since chloroquine has a high affinity for melanin (Sams and Epstein, 1965), it has been proposed that melanin is the pigmented polymer responsible for cutaneous discoloration. In a patient with localized, quinine shot-induced cutaneous pigmentation, reverse-phase highpressure liquid chromatography analysis of a biopsy specimen revealed an oxidized metabolite of quinine (Bruce et al., 1986). The time interval between sampling and the last dose of quinine was approximately 70 years. 1042
Fig. 54.30. Patient taking chloroquine exhibits loss of hair color (see also Plate 54.20, pp. 494–495).
In another patient who developed anterior tibial pigmentation secondary to Atabrine, direct tissue analysis found almost twofold higher levels in a pigmented area than in a nonpigmented area. In addition, fluorescence microscopy demonstrated that pigment granules fluoresced at the same wavelength as pure Atabrine. Thus, several lines of evidence suggest that melanin–antimalarial drug complexes and hemosiderin account for the pigment composition. The presence of melanin within this pigment creates a semantical argument against assigning antimalarial drug-induced pigmentation as a form of ochronosis which, classically, refers to a nonmelanin polymer of phenolic metabolite monomers (Cullison et al., 1983). More commonly than it induces hyperpigmentation, quinacrine imbues a lemon yellow hue to the skin secondary to deposition in the epidermis (Lutterloh and Shallenberger, 1946; Sokol et al., 1982). The discoloration becomes noticeable within 3–10 days of administration. Wood’s lamp examination of the skin and urine demonstrates yellow-green fluorescence. In contrast to jaundice, quinacrine negligibly discolors the sclerae. Yellow discoloration of the skin disappears one to four months after discontinuing the drug.
Clofazimine Clofazimine is a reddish blue, substituted phenazine dye employed to combat multibacillary leprosy as well as other mycobacterial infections, rhinoscleroma, and inflammatory dermatoses (Arbiser and Moschella, 1995). This drug is highly lipophilic and is consumed avidly by macrophages. Within two weeks of taking clofazimine, patients may develop a reddish hue which represents deposition of clofazimine into the skin (Browne, 1965). Due to their ample population of macrophages, active inflammatory lesions absorb clofazimine to a greater degree than normal tissue and, thus, can display a deep red-blue hue (Figs 54.31 and 54.32) (Job et al., 1990; Kossard et al., 1987)]. Initial studies of clofazimine pigmentation revealed subtle evidence of drug deposition in routinely
DRUG-INDUCED OR -RELATED PIGMENTATION
Fig. 54.31. Clofazimine hyperpigmentation. The lighter arm is normal and included for comparison with the deep brown color of the arm of a patient taking clofazimine (see also Plate 54.21, pp. 494–495).
Fig. 54.33. Patient taking thorizine who developed a mauve discoloration on her cheeks and sclera (see also Plate 54.23, pp. 494–495).
processed skin biopsies (Levy and Randall, 1970; Sakurai and Skinsnes, 1970, 1977). However, analysis of frozen sections, which does not expose tissue to organic solvents that can extract clofazimine, demonstrated prominent deposition of vivid red crystals concentrated around vessels in the reticular dermis (Kossard et al., 1987). Chronic administration of clofazimine for months commonly results in a generalized pink-brown discoloration that is accentuated in sun-exposed areas (Mackey and Barnes, 1974). Light microscopy of biopsies from brown areas showed focal, dermal collections of foamy macrophages with diffusely distributed brownish granular pigment (Job et al., 1990). Lipofuscin stains highlighted these pigment granules; melanin and iron stains were negative. Electron microscopy displayed numerous multivesiculated phagolysosomes. These intralysosomal vesicles were lined by a trilamellar membrane and contained electron-dense amorphous granular material and lamellar structures characteristic of lipofuscin. Both subacute and chronic clofazimine-induced cutaneous pigmentation gradually resolve once the drug is discontinued (Job et al., 1990).
Psychotropic Drugs Phenothiazines
Fig. 54.32. The brown arm on the right is that of a patient treated with clofazimine. The normal-colored arm on the left is for comparison (see also Plate 54.22, pp. 494–495).
Daily administration of 125 mg of phenothiazine for six months has been shown to be associated with the development of cutaneous hyperpigmentation (Ban et al., 1985), however, most cases appear after daily doses of at least 300 mg for two years (Bond and Yee, 1980; Greiner and Berry, 1964; Haddad, 1977; Zelickson and Zeller, 1964). This pigmentation begins as golden-brown pigmentation over sun-exposed areas and can progress to slate gray-blue–black discoloration. Darker pigmentation most commonly occurs over the face and has been called “magot chinois” (Ey and Rappart, 1956) and “visage mauve” (Fig. 54.33) (Perrot and Bourjala, 1962). Increased epidermal melanin has been described in unexposed 1043
CHAPTER 54
areas (Robins, 1975). Nail bed pigmentation has also been ascribed to phenothiazine use (Satanove, 1965). Lenticular and corneal pigment deposits may be detectable on slit-lamp examination (Bond and Yee, 1980). It has been reported that pigmentary changes are more common in women than in men (Greiner and Berry, 1964), but this contention has been challenged (Ban et al., 1985). The incidence of overall pigmentary changes has been reported to be 1.2–2.9% in patients on chronic phenothiazine therapy (Ananth et al., 1972; Ban et al., 1985; Greiner and Berry, 1964); however, less than 1% develop slate gray-blue–black discoloration (Mathalone, 1965; Robins, 1975; Tredici et al., 1965). Chlorpromazine has been implicated as the most frequent phenothiazine inducer of hyperpigmentation, but haloperidol and levomepromazine have also been blamed (Ban et al., 1985). Initially, phenothiazine-induced pigmentation was thought to be permanent (Gibbard and Lehman, 1966). More recent reports claim that chlorpromazine-induced blue-black pigmentary changes are reversible (Ewing and Einarson, 1981; Lal et al., 1993). One study followed the persistence of blue-black pigmentary changes after chlorpromazine had been discontinued and replaced with other neuroleptics, including alternative phenothiazines. The study demonstrated that 14/15 patients had complete clearing within six months to five years; the remaining patient displayed marked improvement (Lal et al., 1993). D-penicillamine has been used to treat phenothiazine-induced pigmentation (Gibbard and Lehman, 1966), but its side-effect profile, modest efficacy, and recent evidence suggesting the spontaneous reversibility of pigmentation preclude its use. Histopathologic examination reveals golden-brown pigment granules located predominantly around vessels in the papillary and upper reticular dermis (Benning et al., 1988; Satanove, 1965). This pigment stained with Fontana-Masson but not with Perls reagent. Electron microscopy demonstrated membrane-bound, electron-dense inclusions within macrophages, endothelial cells, and Schwann cells (Benning et al., 1988; Hashimoto et al., 1966; Zelickson, 1965). Increased epidermal melanin has also been noted (Hashimoto et al., 1966). Energy-dispersive X-ray microanalysis has detected a significant sulfur peak, which implied the presence of chlorpromazine within these dense inclusions (Benning et al., 1988). Darkly pigmented skin from some affected patients contained a purple substance with a reflectance curve that differed from that of melanin (Satanove, 1965). Perry observed that the major metabolite of chlorpromazine, 7-hydroxychlorpromazine, turns purple on exposure to ultraviolet light, thus potentially explaining why pigmentary changes are most prominent in sun-exposed skin (Perry, 1964). In vitro, chlorpromazine has been shown to bind strongly to melanin (Potts, 1964). Although the exact nature of the intracellular “chlorpromazine bodies” is not known, several points of evidence suggest a composition of drug-metabolite–melanin complexes (Benning et al., 1988). 1044
Fig. 54.34. Localized hyperpigmentation after topical treatment with nitrogen mustard (see also Plate 54.24, pp. 494–495).
Tricyclic Antidepressants Both desipramine (Steele and Ashby, 1993) and imipramine (Hare, 1970; Hashimoto et al., 1991) have been reported to cause slate-gray pigmentation in sun-exposed areas over the face, hands, arms, and neck. Imipramine dosages ranged from 150 mg/day for five years to 300 mg/day for ten years. Desipramine induced pigmentation when given as 450 mg/day for seven years. Biopsies of affected areas demonstrated golden-brown granules in the upper dermis (Hashimoto et al., 1991; Steele and Ashby, 1993). Electron microscopy of a specimen from a patient with imipramine-induced pigmentation demonstrated both increased phagocytosed dermal melanin as well as electron-dense inclusions within dermal histiocytes, fibroblasts, and dendrocytes (Hashimoto et al., 1991). The pigmentation induced by tricyclic antidepressants appears to be caused by both increased dermal melanin as well as distinct inclusions that may represent drug metabolite complexes (Steele and Ashby, 1993).
Chemotherapeutic Agents Several chemotherapeutic agents such as nitrogen mustard (Fig. 54.34) and bleomycin (Figs 54.35 and 54.36) are able to produce mucocutaneous hyperpigmentation by unknown mechanism(s). The pigment responsible for this pigmentation is melanin, with the exception of cisplatin, in which deposition of platinum has been implicated (Ettinger and Freeman, 1979). Recent evidence suggests that fragments of nucleic acid, modeled to mimic repair by-products of ultraviolet–lightinduced DNA damage, can stimulate melanogenesis (Eller et al., 1994). Similarly, it is possible that chemotherapy-induced damage to cutaneous cellular DNA could produce signals that promote melanin synthesis and transport. Chemotherapy can enhance sensitivity to ionizing and ultraviolet radiation and reduce the radiation dose necessary to induce hyperpigmentation (Falkson and Schultz, 1962). Direct melanocyte toxicity may trigger melanogenesis or
DRUG-INDUCED OR -RELATED PIGMENTATION
alter melanosome transport. Some evidence suggests that certain cytotoxic agents can alter keratinocyte melanosome aggregation and, thus alter skin color (Flaxman et al., 1973). The individual agents reported to cause hyperpigmentation are listed in Table 54.2. Note that azidothymidine (AZT) is included in this table. Although AZT is used as an antiretroviral drug, it was originally developed as a chemotherapeutic agent and probably induces hyperpigmentation in a manner similar to other members of this group (Adrian et al., 1980). Discrete hyperpigmentation that correlates to areas covered
by adhesive tape or electrocardiographic leads occurs in chemotherapy patients (Horn et al., 1989; Singal et al., 1991). Thiotepa, cyclophosphamide, etoposide, and carboplatin may be secreted in the sweat, accumulate under occlusion, and influence melanogenesis or melanosome dispersion (Kang et al., 1993).
Fig. 54.35. Flagellate distribution of bleomycin-induced hyperpigmentation (see also Plate 54.25, pp. 494–495).
Fig. 54.36. Pathognomonic clinical appearance of bleomycininduced hyperpigmentation (see also Plate 54.26, pp. 494–495).
Miscellaneous Drugs and Chemicals The details of pigmentary changes induced by additional drugs, chemicals, and dyes are included in Tables 54.3 and 54.4.
Table 54.2. Chemotherapeutics and pigmentation. Agent
Clinical appearance
Ametantrone
Diffuse blue-gray pigmentation
Histopathology/comment
Drug is blue-black aminoanthraquinone dye, which may be responsible for hyperpigmentation Occurs in all patients who receive more than 135 mg/m2 per injection (Loesch et al., 1983) Azidothymidine Mucocutaneous and nail plate pigmentation (Bendick et al., Increased melanin within basal keratinocytes and dermal (AZT) 1989; Furth and Kazakis, 1987; Greenberg and Berger, macrophages 1990) Two weeks of high-dose AZT induced pigmentation in mouse model; increased melanosomes in epidermal melanocytes noted (Obuch et al., 1992) 1,3-Bis(chloroethyl)- Localized hyperpigmentation at site of application Increased number of melanocytes and pigmented 1-nitrosourea keratinocytes (Hilger et al., 1974) (BCNU) Causes hyperpigmentation only when applied topically; first noted on hands of health professionals administering BCNU (Frost and Devita, 1966) May represent postinflammatory hyperpigmentation; however, precedent erythema is not essential (Frost and Devita, 1966) Pigmentation reproduced in hairless mice (Hilger et al., 1974) Bleomycin Linear, “flagellate” pigmented bands over chest, back, finger High bleomycin concentration in skin (Werner and joints, palms, elbows, knees (Lowitz, 1975; Sonntag, Thornberg, 1976) 1972) Associated with minor trauma (Moulin et al., 1970) Increased epidermal melanin, little dermal pigment incontinence (Perrot and Ortonne, 1978)
1045
CHAPTER 54 Table 54.2. Continued. Agent
Busulfan
Cisplatin Cyclophosphamide (Cytoxan)
Clinical appearance
Histopathology/comment
Reticulate pattern in one patient. (Also received cyclophosphamide, vincristine, adriamycin, and methotrexate) (Wright et al., 1990) Pigmented bands in nail bed (one patient also received vinblastine) (Shetty, 1973; Sonntag, 1972) One case localized to fresh striae distensae (also received cisplatin and vincristine) (Tsuji and Sawabe, 1993) 3/19 (Galton, 1953) and 39/788 (Kyle et al., 1961) CML patients developed diffuse brownish pigmentation over face, forearms, trunk, dorsal hands; resolved in three months (Galton, 1953) #207] May mimic Addison disease (Kyle et al., 1961)
Dopa staining of an epidermal sheet has revealed larger melanocytes with complex dendrites and increased tyrosinase activity (Granstein and Sober, 1981) 8–20% incidence of hyperpigmentation (Blum et al., 1973)
Gray-white line at gingival margin (Ettinger and Freeman, 1979) Local or generalized skin and nail plate/bed hyperpigmentation (Romankiewics, 1974; Shah et al., 1978; Solidoro and Saenz, 1966) Brown pigmentation of gingival margin in one patient (Harrison and Wood, 1972) Supravenous hyperpigmentation was noted in a patient who received combination chemotherapy with cyclophosphamide, doxorubicin, vincristine and prednisone (Schulte-Huermann et al., 1994)
Dactinomycin
Generalized hyperpigmentation, most prominent over face (Bronner and Hood, 1983; Ma et al., 1971)
Daunorubicin
Transverse brown-black bands in nail plate (de Marins et al., 1978) Cutaneous hyperpigmentation (not specified)
Dibromomannitol Doxorubicin (Adriamycin)
5-Fluorouracil (systemic)
1046
Brown-black nail pigmentation: horizontal bands (Morris et al., 1977), longitudinal bands (Priestman and James, 1975), and diffuse (Orr and McKernan, 1980) Appears to involve nail plate (Morris et al., 1977) Can involve dorsal finger joints (Orr and McKernan, 1980; Pratt and Shanks, 1974) as well as palms, soles, buccal mucosa (Rothberg et al., 1974), and tongue (Rao et al., 1976) Uniform hyperpigmentation over sun-exposed areas often preceded by erythema (Falkson and Schultz, 1962) One report of hyperpigmentation over infused vein (Hrushesky, 1976) Localized hyperpigmentation of dorsal hands (Perlin and Ahlgren, 1991; Reed and Morris, 1984), palms, soles, and trunk (Cho et al., 1988) Unusual serpentine hyperpigmented streaks over the trunk (Vukelja et al., 1991) Five reported cases of transient corneal striate melanokeratosis following subconjunctival injection (Stank et al., 1990)
Onset of pigmentation after 90–285 mg (Cohen et al., 1973) Increased melanin in basal keratinocytes and dermal macrophages
Speculation that busulfan inactivates sulfhydryl groups, liberates copper, and thus activates tyrosinase (Kyle et al., 1961) Topical busulfan fails to produce hyperpigmentation (Granstein and Sober, 1981) Hyperpigmentation is more likely to be induced in darkskinned patients (Burns et al., 1971)
In five cases of black nail pigmentation, cumulative dose = 1.2–12.3 g over 10 days to 26 weeks 20% of treated neuroblastoma patients manifested hyperpigmentation (Thurman et al., 1964) Pigmentation starts in proximal nail fold suggesting that matrical melanocytes are stimulated (Bronner and Hood, 1983) Resolution 6–12 months after end of treatment (Bronner and Hood, 1983) Incidence of hyperpigmentation reported to be occasional (Karnofsky, 1968) to universal — 18/18 patients (Ma et al., 1971)
5/11 CML patients treated intravenously developed hyperpigmentation (Canellos et al., 1975) Increased epidermal melanization and number of melanocytes (Rothberg et al., 1974) More common in dark-skinned patients (Pratt and Shanks, 1974; Rothberg et al., 1974)
Increased basal layer melanin, scattered dyskeratotic keratinocytes 2–42% treated patients affected (Bateman et al., 1971; Falkson and Schultz, 1962; Hrushesky, 1976) 5-fluorouracil can reduce threshold of ionizing- and ultraviolet-induced cutaneous hyperpigmentation (Falkson and Schultz, 1962; Hum and Bateman, 1975)
DRUG-INDUCED OR -RELATED PIGMENTATION Table 54.2. Continued. Agent
Clinical appearance
Histopathology/comment
Hydroxyurea
Increased pigmentation over back and pressure points that tends to be reversible (Majumdar et al., 1990) Longitudinal band nail hyperpigmentation (Beylot-Barry et al., 1995; Pirard et al., 1994; Vomvouras et al., 1991) Hyperpigmentation tends to be diffuse but is more intense in lesional skin (Epstein and Ugel, 1970; Mandy et al., 1971; Van Scott and Winters, 1970) Pigmentation fades after treatment is discontinued; lesional discoloration is slow to resolve
Lichenoid eruption with secondary hyperpigmentation (Kennedy et al., 1975)
Mechlorethamine
Disaggregation of melanosomes, increased numbers of melanocytes and keratinocyte melanosomes (Flaxman et al., 1973) No alteration in melanosome size
Table 54.3. Miscellaneous inducers of pigmentation. Drug or chemical
Clinical appearance
Ciclosporin
Progressive hyperpigmentation in a renal transplant patient (Brady and Wing, 1989) Brown-gray pigmentation in sun-exposed areas 90% of 122 patients directly exposed to PCBcontaminated cooking oil demonstrated mucocutaneous pigmentation: nose, conjunctiva, oral mucosa, nails (Wong et al., 1982) Prenatal exposure due to contaminated cooking oil has caused congenital pigmentation of face, perineum, genitalia, nail bed and plate, and palms (Gladen et al., 1990) Rare congenital diffuse brown pigmentation (Rogan, 1982) Nail pigmentation in workers exposed to PCBs (Gladen et al., 1990; Reggiani and Bruppacher, 1985) Diffuse hyperpigmentation
Dioxin/polychlorinated biphenyls
Levodopa
Hydantoins (phenytoin and methoin)
Oxprenolol Pefloxacin/norfloxacin
Phenacetin Rifampicin
10% develop hyperpigmentation of face and neck resembling chloasma; no significant associated endocrine abnormalities (Kuske and Krebs, 1964; Levantine and Almeyda, 1972) Prenatal exposure to phenytoin associated with nail hyperpigmentation (Johnson and Goldsmith, 1981) Pigmentation in light- and pressure-exposed areas (Richards, 1985) Blue-black pigmentation of the legs secondary to pefloxacin; resolved in 45 days; recurred after taking closely related norfloxacin (Le Cleach et al., 1995)
Diffuse brown pigmentation (Nanra et al., 1978) Orange-red discoloration of skin, urine, tears after accidental ingestion of 2 g in 18-month-old; resolved by one month (Salazar de Souza et al., 1987)
Histopathology/comments
Basal layer pigmentation (Kikuchi, 1984) Gas chromatography has detected PCBs in skin and subcutaneous fat, perhaps contributing to pigmentation Transplacental exposure possible (Brodkin and Schwartz, 1984; Gladen et al., 1990)
Sign of significant dioxin exposure (Dunagin, 1984)
Deeper color in women than in men; thought that estrogens may increase tyrosinase utilization of levodopa which is a melanogen (Robins, 1979)
Pigmentary abnormalities resolve upon discontinuation Focal dense, dermal, black pigment Perls stain positive Electron microscopy reveals electron-dense particles within dermal histiocytes X-ray microanalysis shows that pigment particles contain iron No dermal melanosomes Lipofuscin pigment (Gloor, 1978)
Modified from Kang et al. (1993) and Lerner and Sober (1986). PCB, polychlorinated biphenyl.
1047
CHAPTER 54 Table 54.4. Nitro compounds, dyes, and tar. Dye
Clinical appearance
Comments
Aniline dyes (Orange II)
Pigmented contact dermatitis of the face
Azo dyes (Sudan I)
Pigmented contact dermatitis of the face
Danthron (Dorbanex)
Red-brown discoloration of skin in perianal and thigh areas (Barth et al., 1984) Yellow-orange pigmentation
Pigment incontinence and hydropic degeneration of the basal layer (Rorsman, 1982) Pigment incontinence and hydropic degeneration of the basal layer (Rorsman, 1982) Staining occurs from this anthraquinone, which is used as a laxative Color change does not involve melanin. Postulated mechanism of action involves reduction of sulfhydryl groups in keratin. Used as a “tanning” agent Chemical was used to treat obesity by means of its mild central nervous system stimulatory action (Cutting et al., 1933) Used in serum amylase determination (Fregert and Trulson, 1980) Henna is derived from Lawsonia inermis and other members of this family. Henna may react with amino acids in the stratum corneum Pigmentation is presumably secondary to direct tissue staining The localization of this yellow dye in the skin has not been determined (Alano and Webster, 1970). Used as urinary tract analgesic Taken by malingering soldiers in World War I to produce a clinically jaundiced appearance. Of note, some of the nitro compounds can cause true chemical hepatitis Staining secondary to nitric acid reacting with aromatic amino acids in proteins (Fregert et al., 1980) Pigment laden dermal macrophages, perivascular infiltrate. Affects workers exposed to tar, oil, pitch and other tar products
Dihydroxyacetone
2,4-Dinitrophenol
Dinitrosalicylic acid
Yellow pigmentation of exposed areas on contact and jaundiced appearance on oral use (Jeghers, 1944) Yellow-stained palms and fingers
Henna (2,4-dihydroxynaphthoquinone)
Reddish-orange coloration
Nitrazepam
Yellow cheeks and soles (Fregert et al., 1980)
Phenazopyridine (Pyridium)
Picric acid
Diffuse yellow color resembling jaundice with scleral pigmentation (Engle and Schoolwerth, 1981) Jaundiced appearance
Sodium nitrate
Yellow staining
Tar melanosis (melanodermatitis toxica)
Postinflammatory reticulate hyperpigmentation secondary to a combination of irritation and phototoxicity (Mosher et al., 1987; Sugai et al., 1977) Canary yellow staining from contact Yellow staining topically
Tetryl Trinitrotoluene, nitric acid, styphnate hexanitrodiphenylamine
Used in explosives (Jeghers, 1944)
Modified from Kang et al. (1993) and Lerner and Sober (1986).
References Adams, P., D. Holt, G. Storey, A. Morley, J. Callaghan, and R. Campbell. Amiodarone and its desethyl metabolite: tissue distribution and morphologic changes during long-term therapy. Circulation 72:1064–1075, 1985. Adrian, R. M., A. F. Hood, and A. T. Skarin. Mucocutaneous reactions to antineoplastic agents. CA Cancer J. Clin. 80:143–157, 1980. Alanko, K., S. Stubb, and S. Reitamo. Topical provocation of fixed drug eruption. Br. J. Dermatol. 116:561–567, 1987. Alano, F., and G. Webster. Acute renal failure and pigmentation due to phenazopyridine. Ann. Intern. Med. 72:89–91, 1970. Albers, S. E., S. J. Brozena, L. F. Glass, and N. A. Fenske. Alkaptonuria and ochronosis: case report and review. J. Am. Acad. Dermatol. 27:609–614, 1992. Alinovi, A., C. Reverberi, M. Melissari, and M. Gabrielli. Cutaneous hyperpigmentation induced by amiodarone hydrochloride. J. Am. Acad. Dermatol. 12:563–566, 1985.
1048
Ananth, J., T. Ban, H. Lehman, and F. Rizvi. A survey of phenothiazine-induced skin pigmentation. Indian J. Psychiatry 14:76–80, 1972. Anderson, R., and J. Parrish. The optics of human skin. J. Invest. Dermatol. 19:13–19, 1981. Arbiser, J., and S. Moschella. Clofazimine: a review of its medical uses and mechanism of action. J. Am. Acad. Dermatol. 32:241–247, 1995. Archer, C., and J. English. Extensive fixed drug eruption induced by temazepam. Clin. Exp. Dermatol. 13:336–338, 1988. Argenyi, Z., W. Bergfeld, R. Tuthill, J. McMahon, J. Ratz, and N. Petroff. Minocycline-related cutaneous hyperpigmentation as demonstrated by light microscopy, electron microscopy and X-ray energy spectroscopy. J. Cutan. Pathol. 14:176–180, 1987. Arndt, K., and T. Fitzpatrick. Topical use of hydroquinone as a depigmentating agent. J. Am. Med. Assoc. 194:965–967, 1965.
DRUG-INDUCED OR -RELATED PIGMENTATION Ashinoff, R., V. Levine, and N. Soter. Allergic reactions to tattoo pigment after laser treatment. Dermatol. Surg. 21:291–294, 1995. Attwood, H., and X. Dennett. A black thyroid and minocycline treatment. Br. Med. J. 2:1109–1110, 1976. Auerbach, R. Fixed drug eruption: Ethchlorvynol. Arch. Dermatol. 92:184, 1965. Autio, P., and S. Stubb. Fixed drug eruption caused by tolphenamic acid. Arch. Dermatol. Venereol. (Stockh.) 73:76, 1993. Ban, T., W. Guy, and W. Wilson. Neuroleptic-induced skin pigmentation in chronic hospitalized schizophrenic patients. Can. J. Psychiatr. 30:406–408, 1985. Baran, R., and C. Perrin. Fixed drug eruption presenting as an acute paronychia. Br. J. Dermatol. 125:592–595, 1991. Barth, J., H. Reshad, C. Darley, and J. Gibson. A cutaneous complication of Dorbanex therapy. Clin. Exp. Dermatol. 9:95–96, 1984. Bartolome, B., S. Cordoba, S. Nieto, J. Fernandez-Herrera, and A. Garcia-Diez. Acute arsenic poisoning: clinical and histopathological features. Br. J. Dermatol. 141:1106–1109, 1999. Basler, R., and P. Kohnen. Localised hemosiderosis as a sequela of acne. Arch. Dermatol. 114:1695–1697, 1978. Basler, R., W. Taylor, and D. Peacor. Post-acne osteoma cutis: X-ray diffraction analysis. Arch. Dermatol. 110:113–114, 1974. Basset-Séguin, N., F. Amauric, G. Barnéon, P. Huet, and J. Guilhou. Pigmentation cutanée à la minocycline: à propos d’un cas. Nouv Dermatol. 14:34–35, 1995. Bateman, J., R. Pugh, D. Cassidy, G. Marshall, and L. Irwin. 5Fluorouracil given once weekly: Comparison of intravenous and oral administration. Cancer 28:907–913, 1971. Beckett, V., J. Doyle, G. Hadley, and K. Spear. Chrysiasis resulting from gold therapy in rheumatoid arthritis: Identification of gold by X-ray microanalysis. Mayo Clin. Proc. 57:773–777, 1982. Beddard, A., and C. Plumtre. A further note on ochronosis associated with carboluria. Q. J. Med. 5:505–507, 1912. Beerman, H., and R. Lane. Tattoo: A survey of some of the literature concerning the medical complications of tattooing. Am. J. Med. Sci. 227:444–450, 1957. Bendick, C., H. Rasokat, and G. Steigleder. Azidothymidine-induced hyperpigmentation of skin and nails. Arch. Dermatol. 125:1285– 1286, 1989. Benitz, K., G. Roberts, and A. Yusa. Morphologic effects of minocycline in laboratory animals. Toxicol. Appl. Pharmacol. 11:150–170, 1967. Benning, T., K. McCormack, P. Ingram, and D. Kaplan. Microprobe analysis of chlorpromazine pigmentation. Arch. Dermatol. 124:1541–1544, 1988. Benson, P., W. Giblin, and D. Douglas. Transient, nonpigmenting fixed drug eruption caused by radiopaque contrast media. J. Am. Acad. Dermatol. 23:379–381, 1990. Bentley-Philips, B., and M. Bayles. Cutaneous reactions to topical application of hydroquinone. S. Afr. Med. J. 49:1391–1395, 1975. Berry, J., and S. Peat. Ochronosis: Report of a case with carboluria. Lancet 2:124–136, 1931. Beukema, W., and T. Grayboys. Spontaneous disappearance of bluegray facial pigmentation during amiodarone therpy. Am. J. Cardiol. 62:1146–1147, 1988. Beylot-Barry, M., B. Vergier, C. Beylot, G. Marit, and A. Broustet. Multiple squamous cell carcinomas after prolonged treatment with hydroxyurea. Eur. J. Dermatol. 5:227–230, 1995. Blackadder, E., and W. Manderson. Occupational absorption of tellurium: a report of two cases. Br. J. Industr. Med. 32:59–61, 1975. Bleehen, S., D. Gould, C. Harrington, T. Durrant, D. Slater, and J. Underwood. Occupational argyria: light and electron microscopic studies and X-ray microanalysis. Br. J. Dermatol. 104:19–26, 1981. Bluhm, R., R. Branch, P. Johnston, and R. Stein. Aplastic anemia associated with canthaxanthin ingested for “tanning” purposes. J. Am. Med. Assoc. 264:141–142, 1990.
Blum, R., S. Carter, and K. Agre. A clinical review of bleomycin: a new antineoplastic agent. Cancer 31:903–914, 1973. Bond, W., and G. Yee. Ocular and cutaneous effects of chronic phenothiazine therapy. Am. J. Hosp. Pharm. 37:74–78, 1980. Bohnert, M., R. Baumgartner, and S. Pollak. Spectrophotometric evaluation of the colour of intra- and subcutaneous bruises. Int. J. Legal. Med. 113:343–348, 2000. Bourns, B. Unusual effects of antipyrine. Br. Med. J. 2:818–820, 1889. Brady, A., and A. Wing. Hyperpigmentation due to cyclosporin therapy. Nephrol. Dial. Transplant. 4:309–310, 1989. Brocq, L. Eruptio erythémato-pigmentée fixé due a l’antipyrine. Ann. Dermatol. Syphiligr. (Paris) 5:308–313, 1894. Brodkin, R., and R. Schwartz. Cutaneous signs of dioxin exposure. Am. Fam. Physician 30:189–194, 1984. Brogren, N. Case of exogenous ochronosis from carbolic acid compresses. Acta. Derm. Venereol. 32:258–260, 1952. Bronner, A., and A. Hood. Cutaneous complications of chemotherapeutic agents. J. Am. Acad. Dermatol. 9:645–663, 1983. Browne, S. Red and black pigmentation developing during treatment of leprosy with B663. Leprosy Rev. 36:17–20, 1965. Bruce, D., and R. Odom. Fixed drug eruption to sulindac. Cutis 38:323–324, 1986. Bruce, S., J. Yschen, and D. Chow. Exogenous ochronosis resulting from quinine injections. J. Am. Acad. Dermatol. 15:357–361, 1986. Bruggenkate, C., E. Cardozo, P. Maaskant, and I. van der Waal. Lead poisoning with pigmentation of the oral mucosa. Oral Surg. 39:747–753, 1975. Buckley, W. Localized argyria. Arch. Dermatol. 81:531–539, 1963. Bucknall, C., B. Keeton, P. Curry, M. Tynan, G. Sutherland, and D. Holt. Intravenous and oral amiodarone for arrhythmias in children. Br. Heart J. 56:278–284, 1986. Burge, K., and R. Winkelmann. Mercury pigmentation. Arch. Dermatol. 102:51–61, 1970. Burns, W. A., W. McFarland, and M. J. Matthews. Toxic manifestations of busulfan therapy. Med. Ann. D. C. 40:567–572, 1971. Campbell, C. Pigmentation of the nail-beds, palate and skin occurring during malarial suppressive therapy with “camoquin.” Med. J. Aust. 1:956–960, 1960. Canellos, G., R. Young, P. Neiman, and V. DeVita. Dibromomannitol in the treatment of chronic granulocytic leukemia: a prospective randomized comparison with busulfan. Blood 45:197–203, 1975. Casillas, J., D. Fernandez Berridi, F. Malpartida de Torres, and Q. Gutierrez. Pigmentación cutánea producida por amiodarona. Rev. Esp. Cardiol. 31:617–623, 1978. Cebrian, M., A. Albores, M. Aguilar, and E. Blakely. Chronic arsenic poisoning in the north of Mexico. Hum. Toxicol. 2:121–133, 1983. Chalmers, R., H. Muston, V. Srinivas, and D. Bennett. High incidence of amiodarone-induced photosensitivity in north-west England. Br. Med. J. 285:341, 1982. Chan, H. Fixed drug eruption: A study of 20 occurrences in Singapore. Int. J. Dermatol. 23:607–609, 1984a. Chan, H. Fixed drug eruption to bacampicillin (ampicillin). Arch. Dermatol. 120:542, 1984b. Cho, K., J. Chung, A. Lee, Y. Lee, N. Kim, and C. Kim. Pigmented macules in patients treated with systemic 5-fluorouracil. J. Dermatol. 15:342–346, 1988. Cohen, I., M. Mosher, E. O’Keefe, and S. Klaus. Cutaneous toxicity of bleomycin therapy. Arch. Dermatol. 107:553–555, 1973. Coskey, R. Fixed drug eruption from chlorphenesin carbamate. J. Am. Med. Assoc. 248:30–31, 1982. Cullison, D., D. Abele, and J. O’Quinn. Localized exogenous ochronosis. J. Am. Acad. Dermatol. 8:882–889, 1983. Cutting, W., H. Mehrtens, and M. Fainter. Actions and uses of dinitrophenol. J. Am. Med. Assoc. 101:193–195, 1933. Cuzick, J., S. Evans, M. Gillman, and D. Price Evans. Medical arsenic and internal malignancies. Br. J. Cancer 45:904–911, 1982.
1049
CHAPTER 54 Danau, D., and E. Grosshans. Mosel’s solution and histological lesions. Am. J. Dermatopathol. 4:418–419, 1981. de Marins, M., A. Hendricks, and G. Soltzner. Nail pigmentation with daunorubicin therapy. Ann. Intern. Med. 89:516–517, 1978. Dogliotti, M., and M. Leibowitz. Granulomatous ochronosis — a cosmetic-induced skin disorder in blacks. S. Afr. Med. J. 56:757–760, 1979. Dummett, C. Oral mucosal discoloration related to pharmacotherapeutics. J. Oral Ther. Pharmacol. 1:106–110, 1964. Dunagin, W. Cutaneous signs of systemic toxicity due to dioxins and related chemicals. J. Am. Acad. Dermatol. 10:688–700, 1984. Dupre, A., J. Bonafe, R. Viraben, and M.-T. Arquie. Idiopathic pigmentation of hands: professional exogenous ochronosis: a new entity? Arch. Dermatol. Res. 266:1–9, 1979. Dupuis, L., N. Shear, and R. Zuker. Hyperpigmentation due to topical application of silver sulfadiazine cream. J. Am. Acad. Dermatol. 6:1112–1114, 1985. Dwyer, C., and D. Dick. Fixed drug eruption caused by diphenhydramine. J. Am. Acad. Dermatol. 29:496–497, 1993. Dyall-Smith, D., and J. Scurry. Mercury pigmentation and high mercury levels from the use of a cosmetic cream. Med. J. Aust. 153:409–410, 1990. Eller, M. S., M. Yaar, and B. A. Gilchrest. DNA damage and melanogenesis. Nature 372:413–414, 1994. Engasser, P., and H. Maibach. Cosmetics and dermatology: Bleaching creams. J. Am. Acad. Dermatol. 5:143–147, 1981. Engle, J., and A. Schoolwerth. Additive nephrotoxicity from roentgenographic contrast media. Its occurrence in phenazopyridine induced renal failure. Arch. Intern. Med. 6:784–786, 1981. Epstein, E., and A. Ugel. Effects of topical mechlorethamine on skin lesions in psoriasis. Arch. Dermatol. 102:504–506, 1970. Ettinger, L., and A. Freeman. The gingival platinum line. Cancer 44:1882–1884, 1979. Ewing, D., and T. Einarson. Loxapine as an alternative to phenothiazine in a case of oculocutaneous skin pigmentation. Am. J. Psychiatr. 138:1631–1632, 1981. Ey, F., and P. Rappart. Les réactions d’intolerance vis-à-vis de la chlorpromazine. Encephale 45:790–792, 1956. Falkson, G., and E. Schultz. Skin changes in patients treated with 5fluorouracil. Br. J. Dermatol. 74:229–235, 1962. Fam, A., and T. Paton. Nail pigmentation after parenteral gold therapy for rheumatoid arthritis. Arthritis Rheum. 27:119–120, 1984. Feinstein, A., E. Sofer, H. Trau, and M. Schewach-Millet. Urticaria and fixed drug eruption in a patient treated with griseofulvin. J. Am. Acad. Dermatol. 10:915–917, 1984. Fenske, N., J. Millns, and K. Greer. Minocycline-induced pigmentation at sites of cutaneous inflammation. J. Am. Med. Assoc. 244:1103–1106, 1980. Findlay, G. Blue skin. Br. J. Dermatol. 83:127–134, 1970. Findlay, G., J. Morrison, and J. Simson. Exogenous ochronosis and pigmented colloid milium from hydroquinone bleaching creams. Br. J. Dermatol. 93:613–622, 1975. Flaxman, B., A. Sosis, and E. Van Scott. Changes in melanosome distribution in caucasoid skin following topical application of nitrogen mustard. J. Invest. Dermatol. 60:321–326, 1973. Forman, L. Pigmentation of the palms and scalp probably due to proprietary hair tonics containing various phenols and phenolic derivatives. Br. J. Dermatol. 93:718, 1975. Fregert, S., and H. Rorsman. Allergic reactions to trivalent chromium compounds. Arch. Dermatol. 93:711–713, 1966. Fregert, S., and L. Trulson. Yellow stained skin from dinitrosalicylic acid. Contact Dermatitis 6:362, 1980. Fregert, S., J. Poulsen, and L. Trulson. Yellow stained skin from sodium nitrate in an etching agent. Contact Dermatitis 6:296, 1980. Frost, P., and V. Devita. Pigmentation due to a new antitumor agent.
1050
Effects of topical application of BCNU. Arch. Dermatol. 94:265–268, 1966. Furth, P., and A. Kazakis. Nail pigmentation changes associated with azidothymidine (zidovudine). Ann. Intern. Med. 107:350, 1987. Galton, D. Myleran in chronic myeloid leukemia. Lancet 264:208– 213, 1953. Gibbard, B., and H. Lehman. Therapy of phenothiazine-produced skin pigmentation: a preliminary report. Am. J. Psychiatry 123:351–352, 1966. Gimenez-Camarasa, J. M., P. Garcia-Calderon, and J. M. De Moragas. Lymphocyte transformation test in fixed drug eruption. N. Engl. J. Med. 292:819–821, 1975. Gladen, B., J. Taylor, T.-C. Wu, N. Ragan, W. Rogan, and C.-C. Hsu. Dermatologic findings in children exposed transplacentally to heatdegraded polychlorinated biphenyls in Taiwan. Br. J. Dermatol. 122:799–808, 1990. Gloor, F. Changing concepts in pathogenesis and morphology of analgesic nephropathy as seen in Europe. Kidney Int. 1:27–33, 1978. Goeckermann, W. A peculiar discoloration of the skin probably resulting from mercurial compounds (calomel) in proprietary face creams. J. Am. Med. Assoc. 79:605–607, 1922. Goldstein, N. Mercury-cadmium sensitivity in tattoos. A photoallergic reaction in red pigment. Ann. Intern. Med. 67:984–989, 1967. Gordon, G., B. Sparano, and A. Kramer. Thyroid gland pigmentation and minocycline therapy. Am. J. Pathol. 117:98–109, 1984. Granstein, R., and A. Sober. Drug- and heavy metal-induced hyperpigmentation. J. Am. Acad. Dermatol. 5:1–18, 1981. Green, D., and K. J. Friedman. Treatment of minocycline-induced cutaneous pigmentation with the Q-switched Alexandrite laser and a review of the literature. J. Am. Acad. Dermatol. 44:342–347, 2001. Greenberg, R., and T. Berger. Nail and mucocutaneous hyperpigmentation with azidothymidine therapy. J. Am. Acad. Dermatol. 22:327–330, 1990. Greenberg, R., T. Cornbleet, and A. Jaffay. Accumulation and excretion of vitamin A-like fluorescent material by sebaceous glands after the oral feeding of various carotenoids. J. Invest. Dermatol. 32:599–604, 1958. Greiner, A., and K. Berry. Skin pigmentation and corneal and lens opacities with prolonged chlorpromazine therapy. Can. Med. Assoc. J. 90:663–665, 1964. Gupta, A., H. Haberman, D. Pawlowski, G. Shulman, and A. Menon. Canthaxanthin. Int. J. Dermatol. 24:528–532, 1988. Habbema, L., and D. Bruynzeel. Fixed drug eruption due to naproxen. Dermatologica 174:184–185, 1987. Haddad, R. Blue skin pigmentation and chlorpromazine. J. Ky. Med. Assoc. 75:124–126, 1977. Hardwick, N., L. van Gelder, and C. van der Merwe. Exogenous ochronosis: an epidemiologic study. Br. J. Dermatol. 120:229–238, 1989. Hare, P. A case of occupational iron pigmentation of the skin. Br. J. Dermatol. 63:63–66, 1951. Hare, P. Visage mauve (? from imipramine). Br. J. Dermatol. 83:420, 1970. Harris, L., W. McKenna, E. Rowland, D. Holt, G. Storrey, and D. Krikler. Side effects of long-term amiodarone therapy. Circulation 67:45–51, 1983a. Harris, L., W. McKenna, E. Rowland, and D. Krikler. Side effects and possible contraindications of amiodarone use. Am. Heart J. 106:916–921, 1983b. Harrison, B., and C. Wood. Cyclophosphamide and pigmentation. Br. Med. J. 2:352, 1972. Hashimoto, K., W. Weiner, J. Albert, and R. Nelson. An electron microscopic study of chlorpromazine pigmentation. J. Invest. Dermatol. 47:296–306, 1966. Hashimoto, K., S. A. Joselow, and M. J. Tye. Imipramine hyperpigmentation: a slate-gray discoloration caused by long-term
DRUG-INDUCED OR -RELATED PIGMENTATION imipramine administration. J. Am. Acad. Dermatol. 25(2 Pt 2):357–361, 1991. Hendricks, A. Yellow lunulae with fluorescence after tetracycline therapy. Arch. Dermatol. 116:438, 1980. Hilger, R., K. Fukuyama, H. Zackheim, and J. Epstein. Increased melanocytes in hairless mice following topical treatment with carmustine (BCNU) and nitrogen mustard (NM). Clin. Res. 22:159A, 1974. Hill, W., and H. Montgomery. Argyria with special reference to the cutaneous histopathology. Arch. Dermatol. 44:588–599, 1941. Hindsén, M., O. Christensen, V. Gruic, and H. Lofberg. Fixed drug eruption: an immunohistochemical investigation of the acute and healing phase. Br. J. Dermatol. 116:351–360, 1987. Hirsh, B., and W. Johnson. Pathology of granulomatous diseases. Int. J. Dermatol. 23:531–538, 1984. Hollander, L., and H. Baer. Discoloration of the skin due to mercury. Arch. Dermatol. Syphil. 20:27–35, 1929. Horn, T., R. Beveridge, M. Egorin, M. Abeloff, and A. Hood. Observations and proposed mechanism of N,N¢,N¢¢-triethylenethiophosphoramide (thiotepa)-induced hyperpigmentation. Arch. Dermatol. 125:524–527, 1989. Howard, K., and B. Furner. Exogenous ochronosis in a MexicanAmerican woman. Cutis 45:180–182, 1990. Hrushesky, W. Serpentine supravenous 5-fluorouracil (NSC-19893) hyperpigmentation. Cancer Treat. Rep. 60:639, 1976. Hughes, B., P. Holt, and R. Marks. Trimethoprim associated fixed drug eruption. Br. J. Dermatol. 116:241–242, 1987. Hughes, J., and R. Wooten. The orange people. J. Am. Med. Assoc. 197:730–731, 1966. Hum, G. J., and J. R. Bateman. 5-Day infusion with 5-fluorouracil (5-FU; NSC-19893) for gastroenteric carcinoma after failure on weekly 5-FU therapy. Cancer Chemotherap. Rep. Part 1 59:1177–1179, 1975. Jackson, R. Quick “suntan” pills in Canada. J. Am. Acad. Dermatol. 4:233, 1981. Jafferany, M., and T. Haroon. Fixed drug eruption with lormetazepam (Noctamid). Dermatologica 177:386, 1988. Jeffrey, D., D. Biggs, J. Percy, and A. Russell. Quantitation of gold in skin in chrysiasis. J. Rheumatol. 2:28–35, 1975. Jeghers, H. Pigmentation of the skin. N. Engl. J. Med. 231:88–100, 1944. Job, C., L. Yoder, R. Jacobson, and R. Hastings. Skin pigmentation from clofazimine therapy in leprosy patients: A reappraisal. J. Am. Acad. Dermatol. 23:236–241, 1990. Johnson, R., and L. Goldsmith. Dilantin digital defects. J. Am. Acad. Dermatol. 5:191–196, 1981. Jones, S., and M. Black. Metabolic carotenemia. Br. J. Dermatol. 131:145, 1994. Kang, S., E. Lerner, A. Sober, and N. Levine. Pigmentary disorders from exogenous causes. In: Pigmentation and Pigmentary Disorders, N. Levine (ed.). Boca Raton: CRC Press, 1993, pp. 417–431. Karnofsky, D. The use of actinomycin in neoplastic disease in adults. In: Actinomycin, S. Waksman (ed.). Manila: Interscience, 1968, pp. 147–162. Karrer, S., U. Hohenleutner, R. M. Szeimies, and M. Landthaler. Amiodarone-induced pigmentation resolves after treatment with the Q-switched ruby laser. Arch. Dermatol. 135:251–253, 1999. Kauppinen, K., and S. Stubb. Drug eruptions: Causative agents and clinical types. Acta Derm. Venereol. 64:320–324, 1984. Kawada, A., M. Hiruma, K. Morimoto, A. Ishibashi, and H. Banba. Fixed drug eruption induced by ciprofloxacin followed by oflaxacin. Contact Dermatitis 31:182–183, 1994. Kennedy, B., R. Smith, and R. Goltz. Skin changes secondary to hydroxyurea therapy. Arch. Dermatol. 111:183–187, 1975. Kennedy, C., E. Molland, K. Henderson, and A. Whiteley. Mercury pigmentation from industrial exposure. Br. J. Dermatol. 96:367–374, 1977.
Kern, A. Mercurial pigmentation. Arch. Dermatol. 99:129–130, 1969. Kikuchi, M. Autopsy of patients with yusho. Prog. Clin. Biol. Res. 137:19–30, 1984. Kilmer, S., and R. Anderson. Clinical use of the Q-switched ruby and Q-switched neodymium:YAG (1064 nm and 532 nm) lasers for treatment of tattoos. J. Dermatol. Surg. Oncol. 19:330–338, 1993. Kirby, K., R. Cohen, and C. Upson. Fixed drug eruption to papaverine. Urology 43:886–887, 1994. Knowles, F., H. Decker, and R. Kandle. Phenolphthalein dermatitis. Arch. Dermatol. 33:227–237, 1936. Korkij, W., and K. Soltani. Fixed drug eruption. A brief review. Arch. Dermatol. 120:520–524, 1984. Kossard, S., D. Emilija, I. McColl, and W. Ryman. Autofluorescence of clofazimine in discoid lupus erythematosus. J. Am. Acad. Dermatol. 17:867–871, 1987. Kramer, K. E., A. Lopez, C. M. Stefanato, and T. J. Phillips. Exogenous ochronosis. J. Am. Acad. Dermatol. 42:869–871, 2000. Kreidstein, M. L., D. Giguere, and A. Freiberg. MRI interaction with tattoo pigments: case report, pathophysiology, and management. Plast. Reconstr. Surg. 99:1717–1720, 1997. Krivda, S., and P. Benson. Nonpigmenting fixed drug eruption. J. Am. Acad. Dermatol. 31:291–292, 1994. Kuske, H., and A. Krebs. Hyperpigmentierungen vom typus des chloasmas mach behandlung mit hydantoin praparaten. Dermatologia 129:121–139, 1964. Kyle, R., R. Schwartz, H. Oliner, and W. Damestek. A syndrome resembling adrenocortical insufficiency associated with long-term busulfan (Myleran) therapy. Blood 18:497–510, 1961. Lal, S., D. Bloom, B. Silver, B. Desjardins, B. Krishman, J. Thavundayil, and T. Thompson. Replacement of chlorpromazine with other neuroleptics: effect on abnormal skin pigmentation and ocular changes. J. Psychiatry Neurosci. 18:173–177, 1993. Lamar, L., and B. Bliss. Localized pigmentation of the skin due to topical mercury. Arch. Dermatol. 93:450–453, 1966. Lang, P. Probable coexisting exogenous ochronosis and mercurial pigmentation managed by dermabrasion. J. Am. Acad. Dermatol. 19:942–946, 1988. Lawrence, N., C. Bilgard, R. Reed, and W. Perret. Exogenous ochronosis in the United States. J. Am. Acad. Dermatol. 18:1207–1211, 1988. Le Cleach, L., O. Chosidow, G. Peytavin, J. P. Berry, S. Boisnic, Y. Le Charpentier, S. Herson, and C. Frances. Blue-black pigmentation of the legs associated with pefloxacin therapy [letter]. Arch. Dermatol. 131:856–857, 1995. Leigh, I., C. Kennedy, J. Ramsey, and W. Henderson. Mepacrine pigmentation in systemic lupus erythematosus. Br. J. Dermatol. 101:147–153, 1979. Leonard, P., F. Moatamed, J. Ward, M. Piepkorn, E. Adams, and W. Knibbe. Chrysiasis: the role of sun exposure in dermal hyperpigmentation secondary to gold therapy. J. Rheumatol. 13:58–64, 1986. Lerner, A. Effect of ions on melanin formation. J. Invest. Dermatol. 18:47–52, 1952. Lerner, E., and A. Sober. Chemicals and pharmacologic agents which cause hyperpigmentation of the skin. In: Brown Melanoderma, T. Fitzpatrick, M. Wick, and K. Toda (eds). Tokyo: University of Tokyo Press, 1986, pp. 215–227. Lerner, E., and A. Sober. Chemicals and pharmacologic agents that cause hyperpigmentation of the skin. Dermatol. Clin. 6:327–337, 1988. Lescari, A. Carotenemia. Clin. Pediatr. (Phila.) 20:25–29, 1981. Leuth, H., D. Sutton, C. McMullen, and C. Muehlberger. Generalized discoloration of skin resembling argyria following prolonged oral use of bismuth. Arch. Intern. Med. 57:1115–1124, 1936. Levantine, A., and J. Almeyda. Drug reactions XX. Cutaneous reactions to anticonvulsants. Br. J. Dermatol. 87:646–648, 1972.
1051
CHAPTER 54 Levantine, A., and J. Almeyda. Drug induced changes in pigmentation. Br. J. Dermatol. 89:105–112, 1973. Lever, W. F., and G. Schaumburg-Lever. Histopathology of the Skin, 7th ed. Philadelphia: JB Lippincott, 1990, pp. 284–285. Levy, H. Chloroquine-induced pigmentation. S. Afr. Med. J. 62:735–737, 1982. Levy, L., and H. Randall. A study of skin pigmentation by clofazimine. Int. J. Lepr. 38:404–416, 1970. Lockhart, P. Gingival pigmentation as the sole presenting sign of chronic lead poisoning in a mentally retarded adult. Oral Surg. 52:143–149, 1981. Loesch, D., D. Von Hoff, J. Kuhn, C. Coltman, F. Tio, T. Claudhuri, J. Bender, and A. Grillo-Lopez. Phase I investigation of ametantrone. Cancer Treat. Rep. 67, 1983. Long, C., A. Finlay, and R. Marks. Fixed drug eruption to mefenamic acid: a report of three cases. Br. J. Dermatol. 126:409–411, 1992. Lowitz, B. Streaking with bleomycin. N. Engl. J. Med. 292:1300–1301, 1975. Ludwig, G., J. Toole, and J. Wood. Ochronosis from quinacrine (Atabrine). Ann. Intern. Med. 59:378–384, 1963. Lutterloh, C., and P. Shallenberger. Unusual pigmentation developing after prolonged suppressive therapy with quinacrine hydrochloride. Arch. Dermatol. Syphil. 53:349–354, 1946. Ma, H., S. Yip, and D. Chun. Actinomycin-D in the treatment of methotrexate-resistant malignant trophoblastic tumors. J. Obstet. Gynaecol. 78:166–171, 1971. Mackey, J., and J. Barnes. Clofazimine in the treatment of discoid lupus erythematosus. Br. J. Dermatol. 91:93–96, 1974. Majumdar, G., S. Heard, and N. Stater. Reversible hyperpigmentation associated with high-dose hydroxyurea. Br. Med. J. 300:1468, 1990. Malacarne, P., and G. Zavagli. Melphalan-induced melanonychia striata. Arch. Dermatol. Res. 258:81–83, 1977. Mandy, S., J. Taylor, and K. Halprin. Topically applied mechlorethamine in the treatment of psoriasis. Arch. Dermatol. 103:272–276, 1971. Mann, R., and R. Harman. Nail staining due to hydroquinone skinlightening creams. Br. J. Dermatol. 108:363–365, 1983. Masu, S., and M. Seiji. Pigmentary incontinence in fixed drug eruptions. Histologic and electron microscopic findings. J. Am. Acad. Dermatol. 8:525–532, 1983. Mathalone, M. Oculocutaneous effects of chlorpromazine. Lancet 2:111–112, 1965. Matheis, H. Amiodarone-pigmentierung. Dermatologica 145:304– 318, 1972. McGrae, J., and M. Zelickson. Skin pigmentation secondary to minocycline therapy. Arch. Dermatol. 116:1262–1265, 1980. McGrouther, D., P. Downie, and W. Thompson. Reactions to red tattoos. Br. J. Plast. Surg. 30:84–85, 1977. McLaren, D., and B. Zekian. Failure of enzymic cleavage of b carotene. Am. J. Dis. Child. 121:278–280, 1971. Mehta, A., K. Dawson-Butterworth, and M. Woodhoude. Argyria, electron microscopic study of a case. Br. J. Dermatol. 78:175–179, 1966. Micozzi, M., E. Brown, P. Taylor, and E. Wolfe. Carotenodermia in men with elevated carotenoid intake from foods and b-carotene supplements. Am. J. Clin. Nutr. 48:1061–1064, 1988. Millard, P., A. Chaplin, V. Venning, C. Wilson, and R. Wallach. Chrysiasis: transmission electron microscopy, laser microprobe mass spectrometry and epipolarized light as adjuncts to diagnosis. Histopathology 13:281–288, 1988. Miller, R., and A. McDonald. Dermal lipofuscinosis associated with amiodarone therapy. Arch. Dermatol. 120:646–649, 1984. Mimouni, A., E. Hodak, and M. Mimouni. Fixed drug eruption following rifampin treatment. DICP 24:947–948, 1990. Minkin, W., H. Cohen, and S. Frank. Fixed drug eruption due to tetracycline. Arch. Dermatol. 100:749, 1969.
1052
Mishra, D., M. Mobashir, and M. Shoaib Zaheer. Fixed drug eruption and cross reactivity between tinidazole and metronidazole. Int. J. Dermatol. 29:740, 1990. Miyagawa, S., Y. Yaashina, S. Hirota, and T. Shirai. Fixed drug eruption due to pipemidic acid. Int. J. Dermatol. 18:59–60, 1991. Moghadam, B., C. Drisko, and R. Gier. Chlorhexidine mouthwash induced fixed drug eruption. Oral Surg. Oral Med. Oral Pathol. 71:431–434, 1991. Mohamed, K., and J. Bahru. Fixed drug eruption caused by chlormezanone. Int. J. Dermatol. 22:548, 1983. Montgomery, H., and O. Ornsby. Diseases of the Skin. Philadelphia: Lea and Febiger, 1954, pp. 713–715. Morgan, B. Tattoos. Br. Med. J. 3:34–35, 1974. Morgan, J., and A. Carmichael. Fixed drug eruption with fluconazole. Br. Med. J. 308:454, 1994. Morris, D., J. Aisner, and P. Wiernik. Horizontal pigmented banding of the nails in association with adriamycin chemotherapy. Cancer Treat. Rep. 61:499–501, 1977. Mosher, D. B., T. B. Fitzpatrick, J.-P. Ortonne, and Y. Hori. Disorders of pigmentation. In: Dermatology in General Medicine, 3rd ed., vol. 1, T. B. Fitzpatrick, A. Z. Eisen, K. Wolff, I. M. Freedberg, and K. F. Austen (eds). New York: McGraw-Hill, Inc.; Section 14. Disorders of Melanocytes, 1987, pp. 794–876. Moulin, G., B. Fiefe, and A. Beyvin. Pigmentation cutanée par là bleomycine. Bull. Soc. Franc. Dermatol. Syphiligr. 77:293–296, 1970. Nanra, R., J. Stuart-Taylor, A. deLeon, and K. White. Analgesic nephropathy: etiology, clinical syndrome and clinicopathologic correlations in Australia. Kidney Int. 13:79–92, 1978. Nedorost, S., J. Taylor, C. Camisa, K. Tomecki, T. Helm, and W. Durkin. Fixed drug eruption from pamabrom. Cleve. Clin. J. Med. 58:33–34, 1991. Nguyen, L., and H. Allen. Reactions to manganese and cadmium in tattoos. Cutis 23:71–72, 1979. Obuch, M. L., G. Baker, R. I. Roth, T. S. Yen, J. Levin, and T. G. Berger. Selective cutaneous hyperpigmentation in mice following zidovudine administration. Arch. Dermatol. 128:508–513, 1992. Olmstead, P., H. Lund, and D. Leonard. Monsel’s solution: A histologic nuisance. J. Am. Acad. Dermatol. 3:492–498, 1980. Olsen, T., and P. Jatlow. Contact exposure to elemental iron causing chromonychia. Arch. Dermatol. 120:102–103, 1984. Olumide, Y. Fixed drug eruption. A lesson in drug usage. Int. J. Dermatol. 18:818–821, 1979. Orr, L., and J. McKernan. Pigmentation with doxorubicin therapy. Arch. Dermatol. 116:273, 1980. Ozkaya-Bayazit, E. Specific site involvement in fixed drug eruption. J. Am. Acad. Dermatol. 49:1003–1007, 2003. Ozkaya-Bayazit, E., and U. Akar. Fixed drug eruption induced by trimethoprim-sulfamethoxazole: evidence for a link to HLA-A30 B13 Cw6 haplotype. J. Am. Acad. Dermatol. 45:712–717, 2001. Pellicano, R., G. Ciavarella, M. Lomuto, and G. Di Giorgio. Genetic susceptibility to fixed drug eruption: Evidence for a link with HLAB22. J. Am. Acad. Dermatol. 30:52–54, 1994. Pepine, M., F. P. Flowers, and F. A. Ramos-Caro. Extensive cutaneous hyperpigmentation caused by minocycline. J. Am. Acad. Dermatol. 28(2 Pt 2):292–295, 1993. Perlin, E., and J. D. Ahlgren. Pigmentary effects from the protracted infusion of 5-fluorouracil. Int. J. Dermatol. 30:43–44, 1991. Perrot, H., and J.-P. Ortonne. Hyperpigmentation after bleomycin therapy. Arch. Dermatol. Res. 261:245–252, 1978. Perrot, P., and J. Bourjala. Cas pour diagnostic; un visage mauve. Bull. Soc. Franc. Dermatol. Syphiligr. 90:631–635, 1962. Perry, T. 7-Hydroxychlorpromazine: Potential toxic drug metabolite. Science 146:81–83, 1964. Pigatto, P., A. Riboldi, F. Riva, and G. Altomare. Fixed drug eruption to erythromycin. Acta Dermatol. Venereol. 64:272–273, 1984.
DRUG-INDUCED OR -RELATED PIGMENTATION Pirard, C., J. Michaux, and A. Bourlond. Mélanonychie en bandes longitudinales et hydroxyureé. Ann. Dermatol. Venereol. 121:106–109, 1994. Potts, A. M. Reaction of uveal pigment with polycyclic compounds. Invest. Ophthalmol. Vis. Sci. 3:405–416, 1964. Pratt, C., and E. Shanks. Hyperpigmentation of nails from doxorubicin. J. Am. Med. Assoc. 228:460, 1974. Priestman, T., and K. James. Adriamycin and longitudinal pigmented banding of fingernails. Lancet i:1337–1338, 1975. Prose, P. An electron microscopic study of human generalized argyria. Am. J. Pathol. 42:293–299, 1963. Prum, R. O., and R. Torres. Structural colouration of avian skin: convergent evolution of coherently scattering dermal collagen arrays. J. Exp. Biol. 206:2409–2429, 2003. Rao, S., A. Potnis, T. Sobrinho, and A. Brown. Pigmentation of the tongue after treatment with adriamycin. Cancer Treat. Rep. 60:1402–1404, 1976. Rappersberger, K., H. Honigsmann, B. Ortel, A. Tanew, K. Konrad, and K. Wolff. Photosensitivity and hyperpigmentation in amiodarone-treated patients: incidence, time course, and recovery. J. Invest. Dermatol. 93:201–209, 1989. Reed, W., and D. Morris. Maculopapular eruption resulting from systemic administration of 5-fluorouracil. Cutis 33:381–382, 1984. Reggiani, G., and R. Bruppacher. Symptoms, signs, and findings in humans exposed to PCBs and their derivatives. Environ. Health Perspec. 60:225–232, 1985. Richards, S. Cutaneous side-effects of beta-adrenergic blocking agents. Australas. J. Dermatol. 26:25–28, 1985. Ridgway, H., T. Sonnex, C. Kennedy, P. Millard, W. Henderson, and S. Gold. Hyperpigmentation associated with oral minocycline. Br. J. Dermatol. 107:95–102, 1982. Robins, A. Melanosis after prolonged chlorpromazine therapy. S. Afr. Med. J. 49:1521–1524, 1975. Robins, A. Melanin pigmentation, women, and levodopa. Arch. Dermatol. 7:817, 1979. Rodriguez-Perez, M., J. Gonzalez-Dominguez, L. Mataran, S. GarciaPerez, and D. Salvatierra. Association of HLA-DR5 with mucocutaneous lesions in patients with rheumatoid arthritis receiving gold sodium thiomalate. J. Rheumatol. 21:41–43, 1994. Roetzheim, R., A. Herold, and D. Van Durme. Nonpigmenting fixed drug eruption caused by diflunisal. J. Am. Acad. Dermatol. 24:1021–1022, 1991. Rogan, W. PCBs and cola-colored babies: Japan 1968, and Taiwan 1979. Teratology 3:259–261, 1982. Romankiewics, J. Cyclophosphamide and pigmentation. Am. J. Hosp. Pharm. 31:1074, 1974. Rorsman, H. Riehl’s melanosis. Int. J. Dermatol. 2:75–78, 1982. Rothberg, H., C. Place, and O. Shteit. Adriamycin (NSC-123127) toxicity: Unusual melanotic reaction. Cancer Treat. Rep. 58:749–751, 1974. Roupe, G., O. Larko, and B. Olsson. Amiodarone photoreactions. Acta Derm. Venereol. 67:76–79, 1987. Sakurai, I., and O. Skinsnes. Lipids in leprosy. II Histochemistry of lipids in human leprosy. Int. J. Lepr. 38:389–403, 1970. Sakurai, I., and O. Skinsnes. Histochemistry of B663 pigmentation: ceroid-like pigmentation in macrophages. Int. J. Lepr. 45:343–354, 1977. Salazar de Souza, J., V. Almeida, and J. Pinheiro. Red child syndrome. Arch. Dis. Child. 62:1181, 1987. Sams, W., and J. Epstein. The affinity of melanin for chloroquine. J. Invest. Dermatol. 45:482–488, 1965. Satanove, A. Pigmentation due to phenothiazines in high and prolonged dosage. J. Am. Med. Assoc. 194:263–268, 1965. Sato, S., G. Murphy, J. Bernhard, M. Mihm, and T. Fitzpatrick. Ultrastructural and X-ray microanalytical observations of minocycline related hyperpigmentation of the skin. J. Invest. Dermatol. 77:264–271, 1981.
Sauer, G. Muddy skin from minocycline. Schoch Letter 29:3, 1979. Schmidt, H., and H. Christensen. Red poster paint tattoo granuloma. Arch. Dermatol. 114:965–966, 1978. Schmidt, O. Chrysiasis. Arch. Dermatol. Syphil. 44:446–452, 1941. Schulte-Huermann, P., M. Zumdick, and T. Ruzicka. Supravenous hyperpigmentation in association with CHOP chemotherapy of a CD30 (Ki-1)-positive anaplastic large-cell lymphoma. Dermatology 191:65–67, 1994. Schultz Larsen, F., H. Boye, and E. Hage. Chrysiasis: electron microscopic studies and X-ray microanalysis. Clin. Exp. Dermatol. 9:174–180, 1984. Scott, A. The behaviour of radioactive mercury and zinc after application to normal and abnormal skin. Br. J. Dermatol. 71:181–189, 1959. Sehgal, V., and M. Gangwani. Hydralazine induced fixed drug eruption. Int. J. Dermatol. 25:394, 1986. Sehgal, V., and O. Gangwani. Fixed drug eruption. Current concepts. Int. J. Dermatol. 26:67–74, 1987. Shah, P., K. Rao, and A. Patel. Cyclophosphamide induced nail pigmentation. Br. J. Dermatol. 98:675–680, 1978. Sharvill, D. Familial hypercarotenemia and hypovitaminosis A. Proc. R. Soc. Med. 63:605–606, 1970. Shelley, W., and E. Shelley. Fixed drug eruption due to metronidazole. Cutis 39:393–394, 1987a. Shelley, W., and E. Shelley. Nonpigmenting fixed drug eruption as a distinctive reaction pattern: Examples caused by sensitivity to pseudoephedrine hydrochloride and tetrahydrozoline. J. Am. Acad. Dermatol. 17:403–407, 1987b. Shengda, H., and D. Dean. Hyperpigmentation of the nail from lead deposition. Int. J. Dermatol. 28:273–275, 1989. Shetty, M. Case of pigmented banding of the nail caused by bleomycin. Cancer Treatment Rep. 61:501–502, 1973. Shukla, S. Drugs causing fixed drug eruptions. Dermatologica 163:160–163, 1981. Shuttleworth, D., and R. Graham-Brown. Fixed drug eruption due to carbamazepine. Clin. Exp. Dermatol. 9:424–426, 1974. Simons, J., and A. Morales. Minocycline and generalized cutaneous pigmentation. J. Am. Acad. Dermatol. 3:244, 1980. Singal, R., W. W. Tunnessen Jr., J. M. Wiley, and A. F. Hood. Discrete pigmentation after chemotherapy. Pediatr. Dermatol. 8:231–235, 1991. Slazinski, L., and D. Knox. Fixed drug eruption due to methaqualone. Arch. Dermatol. 120:1073–1075, 1984. Sober, A., and R. Granstein. Chemical and pharmacologic agents causing dermal pigmentation. In: Biology and Diseases of Dermal Pigmentation, T. Fitzpatrick, A. Kukita, F. Morikawa, M. Seiji, A. Sober, and K. Toda (eds). Tokyo: University of Tokyo Press, 1981, pp. 117–126. Sokol, R., P. Lichtenstein, and M. Farrell. Quinacrine hydrochlorideinduced yellow discoloration of the skin in children. Pediatrics 2:232–231, 1982. Solidoro, A., and R. Saenz. Effects of cyclophosphamide on 127 patients with malignant lymphoma. Cancer Treat. Rep. 50:265–270, 1966. Solis, R. R., D. G. Diven, M. I. Colome-Grimmer, N. Snyder, and R. F. Wagner. Experimental nonsurgical tattoo removal in a guinea pig model with topical imiquimod and tretinoin. Dermatol. Surg. 28:83–86, 2002. Sonntag, G. Bleomycin (NSC-125066): phase I clinical study. Cancer Chemother. Rep. 36:197–205, 1972. Stack, K., M. Churchwell, and R. Skinner. Xanthoderma: Case report and differntial diagnosis. Cutis 41:100–102, 1988. Stank, T., T. Krupin, and M. Feitl. Subconjunctival 5-fluorouracilinduced transient striate melanokeratosis. Arch. Ophthalmol. 108:1210, 1990. Steele, T. E., and J. Ashby. Desipramine-related slate-gray skin pigmentation [letter]. J. Clin. Psychopharmacol. 13:76–77, 1993.
1053
CHAPTER 54 Stitzler, C., and A. Kopf. Fixed drug eruption caused by 8-chlorotheophylline in dramamine with clinical and histologic changes. J. Invest. Dermatol. 34:319–330, 1960. Stubb, S., and S. Reitamo. Fixed drug eruption caused by piroxicam. J. Am. Acad. Dermatol. 22:1111–1112, 1990a. Stubb, S., and S. Reitamo. Fixed drug eruption due to dextromethorphan. Arch. Dermatol. 126:970–971, 1990b. Sugai, T., Y. Tahahashi, and T. Takagi. Pigmented cosmetic dermatitis and coal tar dyes. Contact Dermatitis 3:249–256, 1977. Sugar, H., and W. Waddell. Ochronosis-like pigmentation associated with the use of Atabrine. Ill. Med. J. 89:234–239, 1946. Sutton, R. Diseases of the Skin. St. Louis: Mosby, 1923, pp. 880– 884. Taylor, C., R. Gange, J. Dover, T. Flotte, E. Gonzalez, N. Michaud, and R. Anderson. Treatment of tattoos by Q-switched ruby laser. Arch. Dermatol. 126:893–899, 1990. Teraki, Y., N. Moriya, and T. Shiohara. Drug-induced expression of intercellular adhesion molecule-1 on lesional keratinocytes in fixed drug eruption. Am. J. Pathol. 145:550–560, 1994. Teraki, Y., and T. Shiohara. IFN-gamma-producing effector CD8+ T cells and IL-10-producing regulatory CD4+ T cells in fixed drug eruption. J. Allergy Clin. Immunol. 112:609–615, 2003. Theodoridis, A., R. Tsabaos, C. Sivenas, and J. Capetanakis. Serum immunoglobulins in fixed drug eruption. Acta Derm. Venereol. 57:507–508, 1977. Thibault, P., and J. Wlodarczyk. Postsclerotherapy hyperpigmentation. The role of serum ferritin levels and the effectiveness of treatment with the copper vapor laser. J. Dermatol. Surg. Oncol. 18:47–52, 1992. Thurman, W., D. Fernbach, and M. Sullivan. Cyclophosphamide therapy in childhood neuroblastoma. N. Engl. J. Med. 270:1336–1342, 1964. Tope, W. D., and F. G. Shellock. Magnetic resonance imaging and permanent cosmetics (tattoos): survey of complications and adverse events. J. Magn. Reson. Imaging 15:180–184, 2002. Traub, E., and J. Tennen. Permanent pigmentation following application of iron salts. J. Am. Med. Assoc. 106:1711–1712, 1936. Tredici, I., B. Schiele, and W. McClanahan. The incidence and management of chlorpromazine skin-eye syndrome. Minn. Med. 48:569–574, 1965. Trimble, J., D. Mindelson, B. Fetter, P. Ingram, J. Gallagher, and J. Shelburne. Cutaneous pigmentation secondary to amiodarone therapy. Arch. Dermatol. 119:914–918, 1983. Tsuji, T., and M. Sawabe. Hyperpigmentation in striae distensae after bleomycin treatment. J. Am. Acad. Dermatol. 28:503–505, 1993. Tuffanelli, D., R. Abraham, and E. Dubois. Pigmentation from antimalarial therapy. Arch. Dermatol. 88:419–426, 1963. Van Scott, E., and P. Winters. Responses of mycosis fungoides to intensive external treatment with nitrogen mustard. Arch. Dermatol. 102:507–514, 1970. Vomvouras, S., A. S. Pakula, and J. M. Shaw. Multiple pigmented nail bands during hydroxyurea therapy: an uncommon finding. J. Am. Acad. Dermatol. 24(6 Pt 1):1016–1017, 1991.
1054
Vukelja, S. J., M. W. Bonner, M. McCollough, P. W. Cobb, D. A. Gaule, P. J. Fanucchi, and J. H. Keeling. Unusual serpentine hyperpigmentation associated with 5-fluorouracil. Case report and review of cutaneous manifestations associated with systemic 5-fluorouracil. J. Am. Acad. Dermatol. 25(5 Pt 2):905–908, 1991. Waitzer, S., J. Butany, L. From, W. Hanna, C. Ramsay, and E. Downar. Cutaneous ultrastructural changes and photosensitivity associated with amiodarone activity. J. Am. Acad. Dermatol. 16:779–787, 1987. Walter, J., and K. Macknet. Pigmentation of osteoma cutis caused by tetracycline. Arch. Dermatol. 115:1087–1088, 1979. Walton, K., D. Campbell, and E. Tonks. The significance of alterations in serum lipids in thyroid dysfunction. Clin. Sci. 29:199–215, 1965. Wanet, J., G. Achten, and G. Barchewitz. Amiodarone et dépôts: Etude clinques et histologique. Ann. Dermatol. Venereol. 98:131–140, 1971. Weiss, S., H. Lim, and G. Curtis. Slate-gray pigmentation of sunexposed skin induced by amiodarone. J. Am. Acad. Dermatol. 11:898–900, 1984. Werner, Y., and B. Thornberg. Cutaneous side effects of bleomycin therapy. Acta. Derm. Venereol. 56:155–158, 1976. Westerhof, W., E. Wolters, J. Brookbakker, R. Boelen, and M. Schipper. Pigmented lesions of the tongue in heroin addicts: Fixed drug eruption. Br. J. Dermatol. 109:605–610, 1983. Witten, V. Studies on the mechanism of eczematous contact dermatitis. I. Findings on human skin with radioactive bichloride of mercury. J. Invest. Dermatol. 28:339–346, 1957. Wong, C.-K., C.-J. Chen, P.-C. Cheng, and P.-H. Chen. Mucocutaneous manifestations of polychlorinated biphenyls (PCB) poisoning: a study of 122 cases in Taiwan. Br. J. Dermatol. 107:317–323, 1982. Wood, C., and G. Severin. Unusual histiocytic reactions to Monsel’s solution. Am. J. Dermatopathol. 2:261–264, 1979. Wright, A., S. Bleehen, and A. Champion. Reticulate pigmentation due to bleomycin: light and electron-microscopic studies. Dermatologica 180:255–257, 1990. Wyatt, E., M. Greaves, and J. Sondergaard. Fixed drug eruption (phenolphthalein). Arch. Dermatol. 106:671–673, 1972. Young, E. Ammoniated mercury poisoning. Br. J. Dermatol. 72:449–455, 1960. Zachary, C., D. Slater, D. W. Holt, G. Storrey, and D. MacDonald. The pathogenesis of amiodarone-induced pigmentation and photosensitivity. Br. J. Dermatol. 110:451–456, 1984. Zala, L., T. Hunziker, and L. R. Braathen. Pigmentation following long-term bismuth therapy for pneumatosis cystoides intestinalis. Dermatology 187:288–289, 1993. Zelickson, A. Skin pigmentation and chlorpromazine. J. Am. Med. Assoc. 194:670–672, 1965. Zelickson, A., and H. Zeller. A new and unusual reaction to chlorpromazine. J. Am. Med. Assoc. 188:394–396, 1964. Zemtsov, A., D. Yanase, A. Boyd, and B. Shehata. Fixed drug eruption to Tylenol: Report of two cases and review of the literature. Cutis 50:281–282, 1992.
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
6
Disorders of Pigmentation of the Nails and Mucous Membranes
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
55
The Melanocyte System of the Nail and its Disorders Robert Baran, Christophe Perrin, Luc Thomas, and Ralph Braun
Introduction The presence of melanocyte in normal nails was first demonstrated in 1968 by Higashi and confirmed by the ultrastructural study of Hashimoto in 1971, who identified many dendritic melanocytes containing mature and immature melanosomes in the matrix of the nails of Japanese and black people.
Anatomy The nail is the permanent product of the nail matrix. Its normal appearance and growth depends on the integrity of several components: the surrounding tissues or perionychium and the bony phalanx. Together, these form the nail apparatus or nail unit (Fig. 55.1).
The Nail Melanin Unit Distribution of Melanocytes According to Type of Epithelium The nail apparatus consists of three types of epithelium: 1 an epidermal-type of epithelium localized at the folded dorsal and ventral aspect of the proximal nail fold, the lateral nail folds, and the hyponychium; 2 a stratified epithelium keratinizing via a granular layer but different from the epidermis by virtue of its thinness, and the lack of papillomatosis and sweat glands. This epithelium, called eponychium, covers the ventral aspect of the proximal nail fold; and 3 a stratified epithelium without a granular layer covering both the matrix and the nail bed. The elective and sequential expression of hair keratins at the keratogenous zone of the matrix is responsible for the generation of the nail plate (Perrin et al., 2004). The nail epidermal-type epithelium contains active melanocytes whose distribution and density are identical to those observed in the neighboring epidermis. The nail epithelium corresponding to eponychium, matrix, and the nail bed contains a scattering of quiescent melanocytes that are not detectable with Fontana-Masson stain.
Bicompartmentalization of Melanocytes of the Eponychium Matrix and Nail Bed White people show two types of melanocytic distribution (Perrin et al., 1997): ∑ A compartment of quiescent melanocytes unable to synthesize melanin under normal conditions (Figs 55.2 and 55.3A). These amelanotic melanocytes (dopa-negative) have been demonstrated by immunohistochemical techniques: this reacts with the monoclonal (Mo) antibodies (Ab) TMH1 and MoAb B8G3, which recognize tyrosinase-related protein (TRP) 1, but not with MoAb 5C12 and MoAb 2B7, which recognize tyrosinase. ∑ A compartment of functionally differentiated melanocytes which were first described by Higashi and Saito (1969) as dopa-positive melanocytes (Fig. 54.3B). Immunohistochemical studies (Perrin et al., 1997; Tosti et al., 1994b) have demonstrated that these melanocytes contain a multifunctional enzyme tyrosinase, which catalyzes the initial events of melanogenesis and the other regulatory proteins and is known as tyrosinase-related protein (TRP) I and II. These melanocytes consequently express all the key enzymes necessary for melanin synthesis. In contrast with previously held views (Baran and Kechijian, 1989; Tosti et al., 1994b), the melanocytes of the distal matrix are not more numerous than those of the proximal matrix. Their density is nevertheless low (Perrin et al., 1997): 217/mm2 compared to that of the epidermis. The difference between these matricial zones is solely in the distribution of dormant and potentially active compartments. The melanocytes of the proximal matrix are mainly dormant. In the distal matrix the quiescent melanocytic compartment is reduced whereas the group of functionally differentiated melanocytes is dominant. The melanocytes of both divisions, unlike the epidermal melanocytes, express MoAb HMB-45, which recognizes the glycoprotein P mel-17 present in the immature melanosome. Together these immunohistochemical data suggest that the matrix melanocytes contain premelanosomes and melanosome types 1 and 2 with little or no active production of mature melanosomes. This is in accordance with ultrastructural studies (Hashimoto, 1971), which demonstrated the scarcity of recognizable melanosomes in the Caucasian nail. Perrin et al. have also defined a smaller population of nail bed dormant melanocytes, with approximately 25% of the 1057
CHAPTER 55
Sagittal section through finger nail
Proximal matrix Proximal nail fold Eponychium Cuticle Lunula Nest of pigment producing cells Nail plate Nail
Distal matrix
bed
Hyponychium Distal groove
A
B
A
Fig. 55.1. (A) Anatomy of the nail apparatus. (B) Formation of longitudinal melanonychia (see also Plate 55.1, pp. 494–495).
NP
KZ
B Fig. 55.3. (A) Split epithelial sheet of the nail matrix. Note the arboreal pattern in the proximal matrix (MoAb TMH1). (B) The increased parallel pattern of the ridges in the distal matrix and the beginning of the nail bed (dopa reaction). (Original magnification ¥100.) A
NP
KZ
B Fig. 55.2. (A, B) Frozen vertical sections of proximal matrix stained with (A) MoAb TMH1 reactive to TRP1 and (B) MoAb HMB-45. Note the heterogeneous suprabasal distribution of melanocytes. (Original magnification ¥250.) NP, nail plate; KZ, keratogenous zone.
1058
number of melanocytes formed in the matrix (Fig. 55.4). This differs from De Berker et al.’s (1996a) observation where the nail bed was noted to lack melanocyte markers. This discrepancy may be due to differences in investigation techniques, one of which was the split-skin preparation. The melanocytes of the eponychium are mainly composed of dormant cells. Their density is close to that found in the matrix (C. Perrin, personal data). There is only one ultrastructural study comparing the nail melanocytes according to the skin color type (Hashimoto, 1971). The melanocytes in Japanese nails contained all gradation of maturing melanosomes (the majority being of an immature variety) and transferred melanosomes (often just half-filled with melanin) were regularly seen within the keratinocytes. In the nails of black subjects, most of the melanosomes including transferred melanosomes were mature.
THE MELANOCYTE SYSTEM OF THE NAIL AND ITS DISORDERS
Fig. 55.4. Split epithelial sheet of the nail bed. The long epithelial ridges are aligned longitudinally (MoAb TMH1; original magnification ¥100).
Intraepithelial Distribution of Melanocytes in Eponychium, Matrix, and Nail Bed Melanocytes of the proximal matrix and, to a lesser degree, the distal matrix have a basal as well as suprabasal distribution (Higashi, 1968; Perrin et al., 1997; Tosti et al., 1994b). These false images of migration are explained by the thickness of the basal keratinocytic compartment composed of two to ten layers of basaloid cells (see Fig. 55.2B). This suprabasal location can rise very high, immediately beneath the keratogenous zone and such dendritic melanocytes, expressing HMB45, may pose a problem for interpretation where there is a suspicion of melanoma. Two main aspects should be highlighted (Perrin et al., 1997): (1) there are no melanocytes in the keratogenous zone; and (2) these melanocytes remain isolated from each other without organization into nevus cell nests. We have not found the “small clusters” gathered together as described by Tosti (1994b) neither on normal nail unit specimens nor on the biopsies of longitudinal melanonychia associated histologically with simple melanocytic activation (C. P. personal data). The melanocytes of the hyponychium and of the nail bed retain a basal distribution because of the monocellular nature of the basal layer in these two anatomic regions.
Distinguishing Features between the Nail and Follicular Unit Like the melanocytes of the eponychium and nail bed, melanocytes of the outer root sheath (ORS) of the follicles are L-dopa negative and contain a negligible amount of tyrosinase. However the latter differs from the former by the lack of expression of TRP1 and TRP2 (Horikawa et al., 1996). In addition, although the antigens recognized by HMB-45 and NK-1/beted are the product of the same gene (the silver locus gene, P mel-17), melanocytes of the ORS react with NK1/beted but not with HMB-45 (Horikawa et al., 1996). These data suggest that the melanocytes of eponychium and nail bed have a greater ability to be activated than those of the ORS.
Fig. 55.5. Longitudinal melanonychia (single band) (see also Plate 55.2, pp. 494–495).
Melanocytes of the follicular bulb are different from matrix melanocytes: they have a cyclic activity corresponding to a single type of melanocyte for each stage (Commo and Bernard, 2000). It is likely that the degree of activation of the nail melanocytes is largely due to the varying thicknesses of nail epithelium, the sun protection of the nail plate, and the proximal nail fold. Eponychium and proximal matrix are protected from the sun by the connective and epithelial axis of the proximal nail fold and the nail plate. The latter protects the distal matrix and the nail bed in the same way; the existence of a contingent of potentially active melanocytes in the distal matrix and not in the nail bed is in a large part due to the reduced thickness of the epithelium of the distal matrix compared to the deep epithelial ridges of the nail bed.
Melanonychia The term melanonychia, which means black nail, encompasses a brown to black coloration due to melanin, whereas nonmelanotic hyperplasia refers to coloration due to other substances or blood pigment. Longitudinal melanonychia is characterized by the presence of a single (Fig. 55.5) or 1059
CHAPTER 55 Table 55.1. Drug- and toxin-induced melanonychia. Chemotherapeutics Bleomycin sulfate Busulfan Cyclophosphamide Dacarbazine Daunorubicin hydrochloride Doxorubicin Etoposide 5-fluorouracil Hydroxyurea Melphalan hydrochloride Methotrexate Nitrogen mustard Nitrosurea Tegafur
Fig. 55.6. Longitudinal melanonychia (multiple bands) (see also Plate 55.3, pp. 494–495).
multiple pigmented streaks (Fig. 55.6), tan, brown, black, or blue (Smith et al., 2003), within the nail plate. Transverse melanonychia is not nearly as common (Quinlan et al., 2005). Active melanocytes produce melanin-rich melanosomes, which are transferred via dendrites to keratinocytes of the matrix. As the keratinocytes of the matrix differentiate into nail plate onychocytes, melanin will continuously be enclosed in the growing nail plate to give rise to a longitudinal band. The more proximal the origin, the more superficial is the melanin within the nail. It is therefore possible to identify the site of origin of pigmentation in longitudinal melanonychia within the matrix by staining distal nail plate clippings with Fontana-Masson argentaffin reaction. Longitudinal melanonychia is most common in frequently used fingers.
Topography of the Melanin Pigment within the Nail Plate Longitudinal melanonychia originates more often in the distal matrix (Baran and Kechijian, 1989) because only the distal matrix contains potentially active melanocytes (Perrin et al., 1997). This distal location allows nail surgery without dys1060
Miscellaneous Antimalarials Arsenic, thallium, mercury, PCB Clofazimine Clomipramine, cyclines, roxithromycin, sulfonamide Gold salts Ibuprofen Ketoconazole, fluconazole, amorolfine Fluoride Lamivudine, zidovudine Mepacrine, amodiaquine, chloroquine Phenothiazine Phenytoin Psoralen Steroids, ACTH, MSH Sulfonamide Timolol
trophic sequelae. The biopsy takes into account distal keratin examination after Fontana-Masson stain. Pigment located within the lower third indicates a distal matrix origin. Pigment invading the whole thickness of the nail plate indicates a proximal pigmentary source. There are many causes of longitudinal melanonychia and the differential diagnosis includes numerous conditions (Baran and Kechijian, 1989). The most frequent are listed in Tables 55.1 and 55.2.
Differential Diagnosis of Nail Pigmentation Besides the common causes of endogenous melanin deposition, pigmentation of the nail may be due to bacterial infection, hematoma, etc. ∑ Exogenous hyperchromia (Haneke and Baran, 2001): Usually the brown to black hue does not present as longitudinal melanonychia. Most of the causes such as tobacco, potassium permanganate, silver nitrate, can easily be scratched off. ∑ Bacterial hyperchromia (Haneke and Baran, 2001): Subjects involved in “wet work” are vulnerable to bacterial growth on the nail apparatus. Most bacteria producing a gray to black color belong to the group of Gram-negative pathogens
THE MELANOCYTE SYSTEM OF THE NAIL AND ITS DISORDERS Table 55.2. Nondrug-induced melanonychia due to melanocyte activation. Endocrine diseases
HIV infection Inflammatory nail disorders
Laugier syndrome Peutz–Jeghers syndrome Nonmelanocytic neoplasms
Nutritional Trauma (acute or repeated)
Physical agents
Addison disease, acromegaly, Cushing syndrome Hyperthyroidism, Nelson syndrome, pregnancy Lichen planus, lichen striatus, pustular psoriasis, Hallopeau acrodermatitis Onychomycosis, radiodermatitis, localized scleroderma Systemic lupus erythematosus
Bowen disease, basal cell carcinoma, myxoid pseudocyst Subungual fibrous histiocytoma, warts Folate deficiency, malnutrition, vitamin B12 deficiency Frictional melanonychia, onychotillomania, occupational melanonychia Surgery, cryosurgery, phototherapy, radiation
Idiopathic
(Pseudomonas, Klebsiella and Proteus spp.). The pigmentation usually originates under the junction of the lateral and proximal nail folds or in the lateral nail groove. The color rapidly returns when scraped off. Bacterial culture will confirm the diagnosis. ∑ Subungual hematoma (Haneke and Baran, 2001): This occurs due to single acute and heavy trauma, has a typical history, and does not reach the free edge of the nail. The extravasated erythrocytes from the capillary vessels of the nail bed are incorporated within the growing nail. The dark pigment is positive for blood with the pseudo-peroxidase reaction (Hemostix test). However, an underlying tumor may bleed spontaneously and yield a positive blood test. Repeated minor trauma (friction of shoes) may take on a longitudinal elliptical shape. If the nail is notched with the scalpel at the proximal margin of the spot, distal migration of the hematoma can be accurately measured as the nail plate grows. However, nonmigrating hematomas and foreign bodies do not follow this rule and require more extensive evaluation.
How to Distinguish between Melanin Pigmentation and Nonmelanin Hyperchromia Melanin pigment is visible after hematoxylin and eosin (H&E) stain as brown deposits with multiple granules within onychocytes. Hematic deposits are different and present as patches, more or less pronounced, depending on whether they are due to splinter hemorrhages or a large hematoma. They
are red-brown on H&E stain, greenish on toluidine blue, and negative on Fontana-Masson staining. Due to the lack of hemosiderin, Perls stain is negative. Rarely, examination of the distal nail keratin may show numerous atypical melanocytes scattered among the onychocytes (Haneke and Binder, 1978; Kerl et al., 1984; Kuchelmester et al., 2000). They are the signature of a nail melanoma. Linear melanonychia due to subungual keratosis of the nail bed is a new entity (Baran and Perrin, 1999). After nail avulsion, it appears as a single, prominent, longitudinal keratinized and pigmented mass.
Fungal Melanonychia Histologic examination facilitates the distinction between two main categories: the pigmented dermatophytes and the dematiaceous-type molds, such as Scytalidium dimidiatum, Wangiella dermatitidis, Fusarium solani, Alternaria spp. The dermatophytes, especially Trichophyton rubrum, with a diffusible black pigment produce a mycelium whose hyphae are of homogeneous caliber and regular septae. Often, they are long and straight and are mixed with globular monomorphic arthrospores. Fontana-Masson stains their cytoplasm while their walls remain hyaline (Perrin and Baran, 1997). The dematiaceous molds have irregular morphology and caliber. Their walls are thick and more or less loaded with melanin. They are stained by the Fontana-Masson, which does not stain the cytoplasm (Russel-Bell, 1983). Several types of fungus, especially Trichophyton soudanense and Candida, can produce a pigmentation of the nail by activating melanocytes in the matrix and/or nail bed. However, the black pigmentation sometimes associated with nail Candida infection may remain unexplained. In most cases, clinical examination may differentiate between these entities but dermoscopy is very helpful in difficult cases. It facilitates the identification of small melanin inclusions in the nail plate which resemble tiny gray-black granules on dermoscopic examination. These granules are not seen in hematomas or fungal infections. The latter is frequently associated with a nail dystrophy, which clinically is already suggestive of this diagnosis. Dermoscopically, the pseudopigmentation in fungal infections of the nail is homogeneous and does not always show melanin inclusions. As about two-thirds of ungual melanomas start with brown to black nail pigmentation, the diagnosis of subungual melanonychia must always be included in the differential diagnosis of longitudinal melanonychia.
When Should the Clinician be Suspicious? (Baran and Kechijian, 1989) When longitudinal melanonychia: ∑ begins in a single digit of a person during the fourth to sixth decade of life or later. However, melanonychia due to subungual melanoma has even been observed in children; ∑ develops abruptly in a previously normal nail plate; ∑ becomes suddenly darker or wider (Fig. 55.7); ∑ occurs in the thumb, or index finger, or great toe; 1061
CHAPTER 55
Fig. 55.7. Proximal widening of longitudinal melanonychia (melanoma in situ) (see also Plate 55.4, pp. 494–495).
Fig. 55.8. Melanonychia associated with Hutchinson sign (melanoma) (see also Plate 55.5, pp. 494–495). (Courtesy C. Beylot, France.)
∑ occurs in a person who gives a history of digital trauma;
mandatory. It provides useful information that could aid in determining whether a nail apparatus biopsy should be done.
∑ occurs singly in the digit of a dark-skinned patient, partic-
ularly if the thumb or great toe is affected; ∑ demonstrates blurred, rather than sharp, lateral borders; ∑ occurs in a person who gives a history of malignant
melanoma; ∑ occurs in a person in whom the risk of melanoma is increased (e.g., dysplastic nevus syndrome); ∑ is accompanied by nail dystrophy, such as partial nail destruction or disappearance of the nail plate; ∑ is associated with the Hutchinson sign (Fig. 55.8). This periungual spread of pigmentation is the most important indicator of subungual melanonychia provided the conditions accompanied by the pseudo-Hutchinson sign (Baran and Kechijian, 1996; Fig. 55.9) have been ruled out (Table 55.3); ∑ bands that do not extend distally to the free edge of the nail are unlikely to represent subungual melanoma. However, they may represent metastatic melanoma (Fig. 55.10) or longitudinal melanonychia arising from the nail bed. Nevertheless, despite meticulous evaluation, the etiology of longitudinal melanonychia may remain obscure, perplexing to the physician, and distressing for the adult patient. Dermoscopic examination of longitudinal melanonychia is, therefore,
1062
Dermoscopic Examination of Longitudinal Melanonychia (Ronger et al., 2002) Dermoscopy is a noninvasive method for the differential diagnosis of pigmented lesions of the skin and the early diagnosis of melanoma. It has been shown to increase diagnostic accuracy compared to clinical visual inspection. Dermoscopy uses an immersion technique to render the stratum corneum translucent, and optical magnification. The handheld devices (dermoscopes) are easy to use and relatively inexpensive. Recently, dermoscopy has been found to be useful for the assessment and diagnosis of longitudinal melanonychia. For the examination of the nail apparatus we recommend the use of a gel (cosmetic gel, ultrasound gel) as an immersion liquid. Due to its viscosity, the gel does not wash off and fills the space ideally between the curved nail surface and the plane contact plate of the handheld dermoscope. For evaluation of the pigmentation it may be useful to vary the focus of the device. With dermoscopy the following criteria can be evaluated:
THE MELANOCYTE SYSTEM OF THE NAIL AND ITS DISORDERS
Fig. 55.10. Longitudinal melanonychia that does not reach the free edge (melanoma metastasis) (see also Plate 55.7, pp. 494–495).
Fig. 55.9. Subungual hemorrhage associated with the pseudoHutchinson sign (see also Plate 55.6, pp. 494–495). (Courtesy R. Sinclair, Australia.)
∑ Homogeneous grayish lines with gray pigmentation of the
background: This pattern is usually due to an epithelial hyperpigmentation without melanocytic hyperplasia (lentigo, drug induced pigmentation, ethnic pigmentation, etc.). ∑ Brown background pigmentation: A brown background pigmentation is usually associated with overlying lines (which can be regular or irregular) and is due to prominent melanocytic hyperplasia. ∑ Regular pattern: Brown longitudinal parallel lines with regular coloration, spacing, and thickness (Fig. 55.11). This pattern is usually associated with a brown homogeneous coloration of the background. The color of the lines varies from light brown to black. However the same shade of brown is consistent within the lesion. The spacing between the bands is regular and the thickness of the bands is similar throughout the lesion. ∑ Irregular pattern: Longitudinal brown to black lines with spacing of irregular thickness, spacing and/or coloration, and disruption of the parallelism (Fig. 55.12). This pattern is also associated with a homogeneous brown pigmentation of the background, but in this case the color of the lines varies from light brown to black and in most cases many different colors and shades of brown can be seen in the same nail pigmenta-
tion. The lines vary in their thickness and spacing. In many cases the lines that are supposed to run parallel lose their parallelism and cross each other. Dermoscopy has changed the management of nail pigmentation because it facilitates the differentiation of melanocytic hyperplasia and epithelial pigmentation. If the pattern is irregular, complete excisional biopsy is always recommended for both diagnosis and treatment.
Appropriate Surgical Intervention in Longitudinal Melanonychia No single biopsy method meets the needs of all patients with longitudinal melanonychia. The type of biopsy selected (Baran and Kechijian, 1989) is determined by a range of factors: (1) periungual pigmentation; (2) the location of the band within the nail (median or lateral); (3) the origin of the band in the matrix (proximal or distal); (4) the width of the band. Periungual pigmentation indicates a high risk of malignancy. If there are no other factors to account for this pigmentation, the whole nail apparatus should be removed “en bloc” down to the bone with a 1 mm margin of normal tissue and without cosmetic consideration. When the lateral third of the nail plate is involved, lateral longitudinal excisional biopsy is the preferred method, since the cosmetic outcome is reasonable. When the mid-portion of the nail plate is involved the potential of postoperative dystrophy may be important. To perform the optimal biopsy, it is necessary to identify the origin of melanocytes responsible for the band in the matrix. This may be determined by sampling the free edge of the nail
1063
CHAPTER 55 Table 55.3. Conditions accompanied by pseudo-Hutchinson sign. Condition Benign Illusory pigmentation Ethnic pigmentation
Clinical features
Regressing nevoid melanosis in childhood Subungual hematoma Silver nitrate
Dark color traverses the transparent cuticle and thin nail fold Pigmentation of proximal nail fold in dark-skinned persons; lateral nail folds not involved; longitudinal melanonychia not always present; often exaggerated in thumbs Macular pigmentation of lips, mouth, and genitalia; one or several fingers involved Hyperpigmentation of fingers and toes; macular pigmentation of buccal mucosa and lips Diffuse tanning of both exposed and nonexposed portions of the body; bluish-black discoloration of the mucous membranes of the lips and mouth Reported after treatment of finger dermatitis, psoriasis, and chronic paronychia Polydactylous involvement Polydactylous involvement Polydactylous involvement Polydactylous involvement; zidovudine produces similar pigmentation Friction, nail biting and picking, and boxing Pigment recurrence after biopsy of longitudinal melanonychia in acquired and congenital melanocytic nevi; often striking cytologic atypia after biopsy Monodactylous; initial increase in dyschromia followed by subsequent pigment regression; perplexing disorder Exceptionally, blood spreads to nail folds and hyponychia area For treatment of granulation tissue; may produce a black halo
Malignant Bowen disease
Monodactylous or polydactylous with longitudinal melanonychia
Laugier syndrome Peutz–Jeghers syndrome Addison disease Radiation therapy Malnutrition Minocycline Amlodipine Patients with AIDS Trauma-induced congenital nevus Congenital or acquired nevus
plate and using Masson-Fontana stain. Pigment in the lower part of the nail reflects a distal matrix origin with good cosmesis. In contrast, pigment in the upper portion of the nail reflects an origin in the proximal matrix and carries a high risk of scarring with secondary nail dystrophy following excision. The type of biopsy needed will depend on the width of the longitudinal melanonychia: ∑ For a band less than 3 mm in width, a 3 mm punch biopsy is advised. ∑ For a band 3–6 mm in width, if the pigment arises from distal matrix, a transverse matrix biopsy can be performed while proximal matrix pigment requires an “en bloc” removal and repair, using a U-flap. ∑ For a band greater than 6 mm in width, matrix punch or transverse biopsy is usually adequate as a preliminary investigation. Recently, tangential matrix excision has been suggested (Haneke, 1999). It gives a specimen less than 1 mm thick. This technique may avoid the risk of postoperative nail dystrophy. If the lesion turns out to be malignant, total nail ablation may be performed three days later.
Benign Melanonychia Benign melanonychia presents two problems for the pathologist.
How to Distinguish Simple Melanocyte Activation from Lentigo? The histologic definition of lentigo classically rests on two cri1064
teria: a regular epidermal papillomatosis and an increase of the number of melanocytes arranged in solitary units; it is termed lentigo-nevus when at least one nest is present. The lack of nevus nests and discrete melanocytic hyperplasia are often observed in the setting of a benign melanonychia. The difficulty in distinguishing a simple melanocyte activation from a lentigo in the nail matrix is a classic problem in the literature (Goettmann-Bonvallot et al., 1999; Molina and Sanchez, 1995). In addition, the value of a possible epithelial hyperplasia is debatable because of the high physiologic variability of the matrix papillomatosis. In our practice (C. P. personal data), when the number of melanocytes is close to normal — the most common situation — we use criteria adjusted to the topography and morphology of the melanocytes. Melanocyte activation differs from lentigo by the dendritic aspect of the melanocytes and their suprabasal topography (Fig. 55.13). The lentigo corresponds to melanocytes scattered along the basal membrane. They have a round appearance often with a clear halo of cytoplasmic retraction. The dendritic shapes of the melanocytes in melanocyte activation are sometime well visible when the dendrites are overloaded with melanin granules. However, very often only Fontana-Masson stain or HMB-45 immunoreactivity can display them. The suprabasal topography of these melanocytes provides evidence of their physiologic characteristics which are really different from the basal hamartomatous location of the lentigo. In the proximal matrix, the dendritic melanocytes are found between the second and tenth layer of basaloid cells whereas in the
THE MELANOCYTE SYSTEM OF THE NAIL AND ITS DISORDERS
Fig. 55.11. Benign melanocytic nevus of the thumbnail of a 6-yearold male patient. The background pigmentation is brown, indicating the presence of melanocytic hyperplasia and the pattern of the lines is regular with regard to coloration, spacing, thickness, and parallelism (see also Plate 55.8, pp. 494–495).
Fig. 55.12. Acral lentiginous melanoma of the hallux in a 54-yearold female patient (Clark level II, 0.32 mm). The background pigmentation is also brown, but the lines are irregular in thickness, spacing, and coloration, and show areas of disruption of parallelism (see also Plate 55.9, pp. 494–495).
distal matrix they are limited to the first suprabasal layer.
Characteristic Histologic Features of the Nail Apparatus Nevi Like the plantar nevi, the ungual nevi may mimic a nail melanoma (Clemente et al., 1995). Classically the features that can be mistaken for malignancy are: lentiginous manner of growth; suprabasal migration with nail plate involvement; and a dermal inflammatory response. Two further characteristics of this region should be mentioned: ∑ The symmetric nature of the nevus is often difficult to evaluate because of the frequent extension of the matrix nevi to the ventral aspect of the proximal nail fold and more rarely to the nail bed and to the hyponychium (Coskey et al., 1983, Goettmann-Bonvallot et al., 1999; Tosti et al., 1996). These various regions have differing anatomic architecture, which makes comparative analysis of the lesional edges barely reliable (Fig. 55.14).
Fig. 55.13. Melanocyte activation (HMB-45 staining; original magnification ¥250).
1065
CHAPTER 55
Fig. 55.14. Nail matrix nevus. Note the extension to the eponychium (arrowheads).
In some junctional nevi there is persistence of a basal and suprabasal physiologic dendritic melanocyte contingent (C. P. personal data). This dendritic aspect is regarded as the earliest histologic sign of acral lentiginous melanoma. However, it should be carefully interpreted in the nail apparatus and always linked with nuclear atypias.
Melanoma in Situ The histologic diagnosis of melanoma in situ is sometimes difficult because of the poor quality of the biopsy or because of the inappropriate site of origin. The acral lentiginous type predominates. The presence of nests and/or migration throughout the epithelium and the nail plate indicates an advanced stage and one should look for an invasive focus on serial sections (Kuchelmester et al., 2000). Improvements in the clinical criteria for assessment of the longitudinal melanonychia and in biopsy techniques has enabled the detection of a larger number of incipient acral lentiginous melanomas. The best diagnostic criteria, in this type, are the cytonuclear atypias and the confluence, even focal, of these atypical melanocytes. Melanoma in situ, initially pagetoid, is rare in the nail apparatus whereas a pagetoid contingent within an acral lentiginous melanoma is frequent and may present in up to 50% of cases (Takematsu et al., 1985). Tomizawa (2000) has reported a variant of pagetoid melanoma in situ characterized by a very limited number of melanocytes scattered throughout the whole thickness of the basal compartment, which could be generated from suprabasal melanocytes in the matrix. In fact, serial sections disclose in this variant rare atypical melanocytes in the keratogenous zone and in the nail plate (Perrin, 2000). Nuclear atypias do not pose a problem when they are present as hyperchromatic or clear nuclei of varying size and with prominent nucleoli. Sometimes, the distinctions are more subtle. They may be limited to a minimal increase in nuclei which are of the same size as the keratinocytes. Useful distinguishing features are their angular shape, dense chromatin, 1066
Fig. 55.15. Isolated atypical melanocyte diagnosed at the time of the biopsy as atypical melanocyte hyperplasia and corresponding to acral lentiginous melanoma when the monobloc excision of the whole band was performed (HES ¥400).
polymorphism, and variation in size in different fields. Sometimes the atypical nuclei are so discrete that it is difficult to make a diagnosis with certainty. In these cases greater weight must be given to the clinical features. If there is a resemblance to a melanoma or if there is a widening of the longitudinal band, it is better to use the descriptive term “atypical melanocytic hyperplasia” (Fig. 55.15) and consider a monobloc excision of the band. The age of the patient is important as even slight atypias in a middle-aged patient are much more significant than those in a child (GoettmannBonvallot et al., 1999).
Invasive Melanoma Ungual melanomas are not restricted to the acral lentiginous type. All the types observed elsewhere in the epidermis may be seen. However, the assessment of the level of invasion does not follow the classical rules used for the skin. Clark levels are modified for two reasons: ∑ Because of the unique fibrotendinous structure of the nail dermis, it is often difficult to determine accurately the interface between papillary and reticular dermis. Consequently, the incidence of levels III and IV is increased. ∑ In addition, because of a lack of an anatomic hypodermal layer, level V corresponds to an invasion of the osteocartilaginous structures (Patterson and Helwig, 1980). The Breslow index is also modified by two factors (Perrin, 2000). The epithelium of the matrix and nail bed is devoid of a granular layer. In melanoma an epidermal metaplasia is frequently present which facilitates the calculation of this index. However, this metaplasia may be partial and its thickness very variable from one plane to another. In the physiologic state and compared to the epidermis, the epithelium of the proximal nail fold and of the distal matrix is much thinner. These features are only visible on transverse sections. Longitudinal sections, which are usually performed,
THE MELANOCYTE SYSTEM OF THE NAIL AND ITS DISORDERS
Fig. 55.16. Young child presenting with longitudinal melanonychia — progressive fading — disappearance at age 18. (Courtesy E. Grosshans, France.)
are more difficult to orientate in a vertical plane and the thickness of the epithelium is apparently excessively increased because some sections are tangential. The nail bed epithelium has a papillary design which is more pronounced than that of the epidermis in case of invasion. This architecture of the nail bed may lead to features similar to verrucous melanoma. The Breslow index, used on the epidermis, is not entirely transferable to the nail apparatus because of microanatomic particularities of the nail and sectional artifacts. Further studies are still necessary to ratify the prognosis and therapeutic value of the Breslow index on the nail unit.
Spontaneous Regression of Melanocytic Lesions Longitudinal melanonychia, as a sign of the “nevoid nail area melanosis” observed in Japanese children, may demonstrate spontaneous regression and even disappearance (Kikuchi et al., 1983). The histologic features of these pigmented lesions are lacking. Longitudinal melanonychia from a matrix nevus was also observed to fade with time (Tosti et al., 1994a). Grosshans (1994) reported the complete disappearance of longitudinal melanonychia occurring in a 4-year-old white patient after 14 years (Fig. 55.16).
References Baran, R., and P. Kechijian. Longitudinal melanonychia. Diagnosis and management. J. Am. Acad. Dermatol. 21:1165–1175, 1989. Baran, R., and P. Kechijian. Hutchinson’s sign: A reappraisal. J. Am. Acad. Dermatol. 34:87–90, 1996. Baran, R., and C. Perrin. Linear melanonychia due to subungual keratosis of the nail bed: a report of 2 cases. Br. J. Dermatol. 140:730–733, 1999. Clemente, C., S. Zurrida, C. Bartoli, A. Bono, P. Collini, and F. Rilke. Acrallentiginous naevus of plantar skin. Histopathology 27;549–555, 1995.
Commo, S., and B. A. Bernard. Melanocyte subpopulation turnover during the human hair cycle: an immunohistological study. Pigment Cell Res. 13:253–259, 2000. Coskey, R. J., T. D. Magnell, and E. G. Bernacki. Congenital subungual nevus. J. Am. Acad. Dermatol. 9:747–751, 1983. De Berker, D., R. P. R. Dawber, A. Thody, and A. Graham. Melanocytes are absent from normal nail bed; the basis of a clinical dictum. Br. J. Dermatol. 134:564, 1996.
Goettmann-Bonvallot, S., J. André, and S. Belaich. Longitudinal melanonychia in children: A clinical and histopathologic study of 40 cases. J. Am. Acad. Dermatol. 41:17–22, 1999. Grosshans E. Mélanines, mélanomes. Nouv. Dermatol. 13:497–498, 1994. Haneke E. Operative therapie akraler und subungualer melanoma. In: Operative und onkologische Dermatologie. Fortschritte der operativen und onkologischen Dermatologie 15, R. Rompel, and J. Petres (eds). Berlin: Springer, 1999, pp. 210–144. Haneke, E., and D. Binder. Subuguales Melanome mit streifiger Nagelpigmentierung. Hautarzt 29:389–391, 1978. Haneke, E., and R. Baran. Longitudinal melanonychia. Dermatol. Surg. 27:580–584, 2001. Hashimoto, K. Ultrastructure of the human toenail. J. Invest. Dermatol. 56:235–246, 1971. Higashi, N. Melanocytes of nail matrix and nail pigmentation. Arch. Dermatol. 97:570–574, 1968. Higashi, N., and D. Saito. Horizontal distribution of the dopapositive melanocytes in the nail matrix. J. Investig. Dermatol. 53:163–165, 1969. Horikawa, T., D. A. Norris, T. W. Johnson, T. Zekman, N. Dunscomb, S. D. Bennion, R. L. Jackson, and J. G. Morelli. DOPA-negative melanocytes in the outer root sheath of human hair follicles express premelanosomal antigens but not a melanosomal antigen of the melanosome-associated glycoproteins tyrosinase, TRP-1, and TRP-2. J. Invest. Dermatol. 106:28–35, 1996. Kerl, H., H. Trau, and A. B. Ackerman. Differentiation of melanocytic nevi from malignant melanomas in palms, soles and nail bed solely by signs in the cornified layer of the epidermis. Am. J. Dermatopathol. 6:159–161, 1984. Kikuchi, I., S. Inoue, E. Sakaguchi, and T. Ono. Regressing nevoid nail area melanosis in childhood. Dermatology 186:88–93, 1993. Kuchelmester, C., G. Schaumburg-Lever, and C. Garbe. Acral cutaneous melanoma in Caucasians: clinical features, histopathology and prognosis in 112 patients. Br. J. Dermatol. 143:275–280, 2000. Molina, D., and J. L. Sanchez. Pigmented longitudinal bands of the nail. Am. J. Dermatopathol. 17:539–541, 1995. Patterson, R. H., and E. B. Helwig. Subungual malignant melanoma: A clinical-pathologic study. Cancer 46:2074–2087, 1980. Perrin, C., and R. Baran. Longitudinal melanonychia caused by Trichophyton rubrum. J. Am. Acad. Dermatol. 31:311–316, 1994. Perrin, C., J. F. Michiels, A. Pisani, and J. P. Ortonne. Anatomic distribution of melanocytes in normal nail unit. Am. J. Dermatopathol. 19:462–467, 1997. Perrin, C., L. Langbein, and J. Schweizer. Expression of hair keratins in the adult nail unit: an immunohistochemical analysis of the onychogenesis in the proximal nail fold, matrix and nail bed. Br. J. Dermatol. 151:362–371, 2004. Perrin, Ch. Anatomie microscopique de l’appareil unguéal: histologie et histopathologie. In: L’ongle. Monographie du GEM N° 27, C. Dumontier ed. Paris: Elsevier, 2000, pp. 19–28. Quinlan, K. E., J. J. Janiga, R. Baran, and H. W. Lim. Transverse melanonychia secondary to total skin electron beam therapy: a report of 3 cases. J. Am. Acad. Dermatol. 53:S112–114, 2005. Ronger, S., S. Touzet, C. Ligeron, B. Balme, A. M. Viallard, D. Barrut, C. Colin, and L. Thomas. Dermoscopic examination of nail pigmentation. Arch. Dermatol. 138:1327–1333, 2002. Russel-Bell, B. Characterization of pigmented fungi by melanin staining. Am. J. Dermatopathol. 5:77–81, 1983. Smith, D. F., M. B. Morgan, and M. S. Bettencourt. Longitudinal melanonychia. Arch. Dermatol. 139:1209–1214, 2003. Takematsu, H., M. Obata, Y. Tomita, T. Kato, M. Takahashi, and R. Abe. Subungual melanoma. Cancer 55:2725–2731, 1985. Tomizawa, K. Early malignant melanoma manifested as longitudinal
1067
CHAPTER 55 melanonychia: subungual melanoma may arise from suprabasal melanocytes. Br. J. Dermatol. 143:431–434, 2000. Tosti, A., R. Baran, R. Morelli, P. A. Fanti, and A. Peserico. Progressive fading of longitudinal melanonychia due to a nail matrix melanocytic nevus in a child. Arch. Dermatol. 130:1076–1077, 1994a. Tosti, A., N. Cameli, B. M. Piraccini, P. A. Fanti, and J. P. Ortonne.
1068
Characterization of nail matrix melanocytes with anti-PEP1, antiPEP8, TMH-1, and HMB-45 antibodies. J. Am. Acad. Dermatol. 31:193–196, 1994b. Tosti, A., R. Baran, B. M. Piraccini, N. Cameli, and P. A. Fanti. Nail matrix nevi: A clinical and histopathologic study of twenty-two patients. J. Am. Acad. Dermatol. 34:765–771, 1996.
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
56
Pigmentary Abnormalities and Discolorations of the Mucous Membranes John C. Maize, Jr. and John C. Maize, Sr.
Introduction Pigmentary abnormalities and discolorations of the oral and anogenital mucosa, like those of the cutaneous surface, have a variety of causes and implications. Causes range from benign physiologic pigmentation which may be an incidental finding or a cosmetic concern for an individual to malignant neoplasms that portend a grave prognosis to the patient. This chapter discusses alterations in pigmentation (both hyperpigmentation and hypopigmentation) and color that affect the oral, genital, and anal surfaces, as well as the causes, associated conditions, and treatments.
Normal Melanocyte Numbers in Mucosae
Genital Melanocyte numbers on genital skin are at the upper end of the range of variation of melanocyte density observed regionally on the cutaneous surface in general and is in keeping with the density of melanocytes observed in oral mucosal epithelium and external anal epithelium (Freedberg et al., 1999).
Anal Melanocyte density on external anal skin and the squamous zone of the anal canal is similar to the density of melanocytes elsewhere on the cutaneous surface. Melanocytes are present in transitional zone epithelium of the anal canal but are decreased in number compared with the squamous zone. Melanocytes are present but exceedingly rare in normal colorectal mucosa (Clemmensen and Fenger, 1991).
Hyperpigmentation
Oral Melanocyte number and distribution within the epithelium of the oral mucosa is similar to the epidermis of the cutaneous surface in general. In the epidermis from the cutaneous surface, melanocytes vary in density depending upon the site, with more melanocytes per unit area on skin of the face (1 melanocyte per 4 keratinocytes within the basal epidermis in routine hematoxylin and eosin stained sections) than on the trunk (1:14) (Hicks and Flaitz, 2000). Within the oral gingival mucosa, the melanocyte to keratinocyte ratio is 1:15 (Cicek and Ertas, 2003; Hicks and Flaitz, 2000). The number of melanocytes within the mucosa in light and darkerskinned races is the same (Cicek and Ertas, 2003). Melanocytes in the oral mucosa produce melanin pigment within melanosomes in the cytoplasm as they do elsewhere, but the amount of melanin pigment production is decreased relative to melanocytes in normal skin (Cicek and Ertas, 2003). Variations in pigmentation of the mucosa among racial groups is due to differences in pigment production by melanocytes and to the type and distribution of melanosomes within melanocytes (Cicek and Ertas, 2003). The morphology of normal melanocytes in the mucosa on routinely stained sections is similar to that of melanocytes in the epidermis, with a round, dark nucleus, inconspicuous nucleolus, and often a clear halo around the nucleus. Cytoplasm is usually difficult to appreciate.
Oral There is an array of etiologies for clinically appreciable pigmentation of the oral mucous membranes. Causes include: endogenous chromophores such as blood and hemoglobin, exogenous chromophores (medications, metals, dental amalgam), the pigment melanin, neoplasms (lentigines, nevi, melanomas, benign and malignant vascular neoplasms), and genetic or systemic disorders [acromegaly, Addison disease, Albright syndrome, hemochromatosis, Laugier–Hunziker syndrome, and Peutz–Jeghers syndrome (PJS)]. Each of these categories will be discussed in this section.
Endogenous Chromophores (Blood and Heme) Benign Hemangiomas (Capillary Hemangiomas; Hemangiomas of Infancy; Strawberry Nevi) Hemangiomas are benign proliferative vascular lesions and are the most common tumors of infancy. Girls are more often affected than boys, and premature infants are the most susceptible to developing a hemangioma. Fifty percent of lesions are present congenitally, with the remainder usually presenting in the month after birth. Early lesions may appear telangiectatic or ecchymotic, and rarely, appear to be a hypochromic patch clinically. Lesions subsequently enlarge and become dark red to deep purple nodules or tumors. Lesions can grow rapidly or slowly over a 1069
CHAPTER 56
period of months up to one year of age before stabilizing and then slowly involuting over the next few years to one decade. Lesions on the lip as well as a few other sites such as the nose or parotid gland may not involute. Intraoral hemangiomas can occur and, early on, be confused with a pigmented lesion. With cervicofacial hemangiomas in the beard area of the face including the lip, involvement of the airway can be problematic and may require a tracheotomy. Exact mechanisms controlling lesion development and devolution are not known. Treatment may involve the use of intralesional or systemic corticosteroids, lasers, surgery, or systemic interferon. The mode of therapy depends largely on the exact lesion location as well as size, growth rate, and risk to the patient (Metry and Hebert, 2000). Histopathology Evolving lesions show a proliferation of endothelial cells which may be enlarged and display numerous mitoses. Cells may be arranged in solid aggregates or strands, and vascular lumina may be small, slitlike, and not easily visualized. Later, lesions develop a more obvious lobular pattern of vascular spaces with flattened endothelial cells lining the lumina. Endothelial cells label with standard endothelial cell markers, including CD31 and CD34. Immunoperoxidase staining for GLUT-1 differentiates these lesions from vascular malformations that have no tendency for involution (Weedon, 2002a). Port Wine Stain (Nevus Flammeus) Port wine stains are uncommon congenital vascular malformations usually of the head and neck area, which persist throughout life in most cases. Involvement of the face in the distribution of the V1 branch of the trigeminal nerve is a component of the Sturge–Weber syndrome. Enlargement of the lips can be especially disfiguring as a result of vascular stasis and soft tissue hypertrophy (macrocheilia) (Del Pozo et al., 2004). Intraoral involvement can appear as a dark red–purple patch or plaque and is usually in addition to involvement of the face. Isolated oral involvement must be exceedingly rare if it occurs at all. Histopathology Early lesions demonstrate slight dilation of the vessels of the superficial vascular plexus. With time, vascular channels may become notably distended and congested by erythrocytes. Vessel walls are thin and there is no proliferation of vascular structures (Weedon, 2002b). Trauma (Hemoglobin/Hemosiderin) Hyperchromic lesions on the oral mucosa may sometimes follow trauma with submucosal hemorrhage. Breakdown of red blood cells liberates hemoglobin, which is phagocytized by tissue macrophages. Within the lysosomes of macrophages, hemoglobin is converted by the action of various enzymes into hemosiderin. Siderophages may persist within the area of injury for a prolonged period of time (many months) and be appreciable clinically as a discoloration.
1070
Fig. 56.1. Venous lake of the upper lip. Diascopy will often reveal the vascular nature of these lesions; however, when they thrombose, they may not blanch with pressure and may simulate a melanocytic lesion.
Venous lakes Clinical Venous lakes are common lesions of aged individuals and often affect the lower lip as well as other areas of the head and neck (Fig. 56.1). They are solitary papules usually less than 1 cm in diameter and are clinically dark-blue to black in appearance. A simple clinical test will confirm the diagnosis in many instances: firm digital pressure will compress the lesion and evacuate it; the lesion will then refill with blood slowly when pressure is released. If the lesion is thrombosed, however, it may be firm and noncompressible, clinically mimicking a melanocytic lesion, especially malignant melanoma. Histopathology Biopsy reveals a dilated endothelial-lined vascular space with a single lumen in the upper dermis. The lumen usually contains many erythrocytes (Fig. 56.2). Thrombus may partly or completely fill the space in some lesions (Weedon, 2002c). Malignant Kaposi sarcoma Kaposi sarcoma (KS) is a herpes virusinduced malignant vascular endothelial proliferation caused by human herpes virus-8 (HHV-8) (Drago and Rebora, 1999). There are multiple clinical settings for development of KS: (1) classic type — lesions occurring on the lower legs of elderly men of Mediterranean heritage; (2) endemic type — seen mostly in adult men in central Africa; (3) iatrogenic type — seen in patients with organ transplants or patients who have undergone chemotherapy for lymphoproliferative diseases; and (4) HIV-associated (Drago and Rebora, 1999). Involvement of the oral mucosa is usually seen in patients with HIV-associated KS (Newland et al., 1988), and may be
PIGMENTARY ABNORMALITIES AND DISCOLORATIONS OF THE MUCOUS MEMBRANES
Fig. 56.2. Venous lake histopathology. There is a dilated vascular space congested by erythrocytes. There is partial thrombosis at one edge of the lumen.
Fig. 56.3. Intraoral Kaposi sarcoma. KS on the mucosa may simulate a melanocytic neoplasm. Mucosal KS is most often seen in the setting of human immunodeficiency virus (HIV) disease (see also Plate 56.1, pp. 494–495).
the presenting sign of illness on occasion. Early, or patchstage, lesions, are flat, often irregular, and are dark red or purple in color (Fig. 56.3), whereas nodular lesions of KS may be large, elevated, indurated, and hemorrhagic or black in appearance. Lesions at any stage may be confused clinically with a melanocytic neoplasm, and biopsy may be needed to correctly establish the diagnosis. Histopathology The microscopic features of the neoplasm depend on the stage of development of the lesion. Early lesions of KS are composed of delicate — at times insidious — ramifying vascular channels which make the dermis appear subtly more cellular than normal at scanning magnification.
Fig. 56.4. Kaposi sarcoma histopathology. There is a proliferation of spindled endothelial cells which lack significant cytologic atypia. There are many erythrocytes within the irregular vascular channels formed by the endothelial cells as well as within the intracytoplasmic lumens in some cells.
The mucosal epithelium in patch-stage lesions is unaltered. Delicate spindled endothelial cells may closely hug the dermal collagen bundles, and intraluminal erythrocytes in the vessels between collagen bundles may be mistaken for extravasation if care is not taken. The presence of neoplastic vascular channels which enclose pre-existing vessels may make them appear to protrude or “float” within an empty space, a change classically referred to as the “promontory sign.” As lesions advance, they become more cellular and may even consist of solid-appearing zones of spindled cells (Fig. 56.4). The surface may ulcerate. Cytologically, the spindled cells are not notably atypical in most cases. Intracytoplasmic lumens containing erythrocytes may be appreciated and hyalinized eosinophilic round globules which represent effete erythrocytes may be seen intracellularly and extracellularly. Hemosiderin deposits are common in lesions at all stages of development. The spindled cells label with the typical immunoperoxidase markers of endothelium: CD31, CD34, and factor VIII-related antigen (Newland et al., 1988). Immunoperoxidase staining for human herpes virus 8 (KS herpes virus) is a sensitive and specific confirmatory test (Patel et al., 2004). Treatment In recent years with advances in HIV treatment using highly active antiretroviral therapy (HAART), specific treatment for KS has been largely obviated by the immune reconstitution which HAART therapy promotes, though improvement does take time once therapy is initiated. Breakthrough or nonresponsive cases do still occur. Depending upon the severity of disease, therapy may include the topical retinoid gel alitretinoin, surgery, radiotherapy, interferon or interleukin-2 infusions, or intralesional or systemic chemotherapy with vinblastine. Other chemotherapeutic agents have also
1071
CHAPTER 56
which occurs in Addison disease (see the following section on Addison disease). Hyperpigmentation in acromegaly is due to increased melanin production by melanocytes in response to increased a-melanocyte stimulating hormone (a-MSH) produced by the pituitary (Lenane and Powell, 2000).
Fig. 56.5. Physiologic (racial) pigmentation. There are relatively symmetric hyperpigmented patches on the gingiva of this black patient.
been successfully used as single-drug treatments including chlorambucil, cyclophosphamide, and actinomycin (Sterling and Kurtz, 1998).
Melanin and Melanocytes Benign Physiologic (Racial) Pigmentation Hyperpigmentation of the oral mucosa often occurs as a variant of normal. Clinically appreciated pigmentation of the oral mucosa is rare in white people, but common in darker-skinned individuals (Fig. 56.5). Onset of this so-called physiologic pigmentation is during infancy or puberty (Eisen and Voorhees, 1991). Physiologic pigmentation is present to different degrees among individuals within the same race and within a given individual in different areas of the mouth. The labial gingiva is more commonly affected than the buccal, palatal, or lingual gingiva, and, more specifically, the attached gingiva is most frequently affected, followed in decreasing order by the papillary gingiva, the marginal gingiva, and the alveolar mucosa (Cicek and Ertas, 2003). On physical examination, physiologic pigmentation is almost always bilateral and symmetrical (Dummet and Bolden, 1964). Microscopically, the cause of the pigmentation is attributable to increased pigment production within melanocytes in the hyperpigmented areas and not to a difference in numbers of melanocytes in those areas. Treatment is not required, but may be desired for cosmetic reasons. Surgical, cryosurgical, and laser techniques may result in improvement (Almas and Sadig, 2002; Tal, 1991; Tal et al., 2003). Acromegaly Acromegaly is a disease caused by excessive secretion of human growth hormone by the pituitary, usually due to a hormone-secreting tumor. Roughly 40% of patients with the disease will also develop hyperpigmentation of the face, oral and genital mucosa, scars, and palmar creases. The pattern of hyperpigmentation is very similar to the pattern 1072
Addison Disease One potentially life-threatening cause of mucosal hyperpigmentation is Addison disease. Addison disease is rare, estimated to occur in one person per million population, is more common in women, and is caused by lack of production of cortisol and other steroid hormones by the adrenal glands. Causes of primary hypocortisolism (adrenal failure) can include autoimmune destruction of the adrenal cortex (most common), infections such as tuberculosis or histoplasmosis, or metastatic disease involving the adrenals with destruction of glands. Mucosal pigmentation often occurs in the setting of generalized hyperpigmentation or “tanning,” but may occur in isolation or in the presence of only subtle or slowly developing generalized hyperpigmentation. Other signs and symptoms of Addison disease include hypotension, fatigue/loss of energy, weight loss, and electrolyte imbalances. Pigmentation is due to increased pigment production by melanocytes secondary to stimulation by aMSH, and biopsy would reveal only hyperpigmentation of the basal epidermis without an increase in melanocyte number. aMSH is formed by cleavage of proopiomelanocortin which is released from the pituitary gland in response to low circulating levels of cortisol (failure of negative inhibition). Clinically, the oral pigmentation most commonly presents as multiple blue-black macular pigmented areas involving any of the mucosal surfaces within the mouth. Other signs include accentuation of pigmentation within established scars, development of genital hyperpigmentation, and pigmentation of the nails and palmar creases (Erickson et al., 2000; Lamey et al., 1985). Albright Syndrome (McCune–Albright Syndrome) The features of this syndrome include fibrous dysplasia of one or more bones with associated pain, deformity, and pathological fractures; large hyperpigmented patches with irregular, jagged outlines (“coast of Maine” café-au-lait macules), and, in girls only, precocious puberty. Hyperpigmented macules are most frequent on the trunk and extremities, but they may affect the face and, sometimes, the lip. Biopsy shows a normal number of melanocytes, some of which have macromelanosomes, and hyperpigmentation of the basal epidermis (Champion et al., 1998; Lenane and Powell, 2000). Carney Complex (LAMB Syndrome; NAME Syndrome) Clinical In 1973, Rees and others first reported a patient with numerous brown macules on the skin and a left atrial “endotheliomyxoma” (Rees et al., 1973). Atherton and coworkers (1980) later described a 10-year-old boy with generalized pigmented macules, blue nevi, congenital melanocytic nevi, myxoid cutaneous lesions, and bilateral atrial myxomas. They designated this compilation of findings the NAME syndrome for Nevi, Atrial myxomas, Myxomas of the skin, and
PIGMENTARY ABNORMALITIES AND DISCOLORATIONS OF THE MUCOUS MEMBRANES
Ephelides. In 1984, Rhodes and coworkers described an additional patient with both cutaneous and cardiac lesions. This patient had brown and black macules on the face and vulva that were documented to have increased melanocyte numbers. The authors felt that, in the light of this finding, “lentigines” was a more appropriate designation for these lesions than the term “ephelides” utilized in the acronym NAME, and they proposed the acronym LAMB instead for Lentigines, Atrial myxomas, Mucocutaneous myxomas, and Blue nevi (Rhodes et al., 1984). Carney and coworkers in 1985 reported a syndrome of hyperpigmented macules, cardiac myxomas, and endocrine abnormalities. Carney published several subsequent reports on this syndrome, and the term Carney complex (CNC) has supplanted the terms “LAMB” and “NAME” for this multiple neoplasia syndrome. CNC type 1 has been linked to a mutation in the PRKAR1A gene on chromosome 17q in a large percentage of affected persons, while other cases (type 2) have been linked to a locus on chromosome 2p16 (McKusick, 1986a). Patients with CNC develop brown or black macules of the face, lips and genital skin, multiple blue nevi, atrial myxomas (in up to 75% of cases) and myxomas of the mucosa and skin. The pigmented macules may develop in early childhood. Psammomatous melanotic schwannoma is a distinctive tumor that has been noted to occur in the skin as well as spinal nerve roots, the gastrointestinal tract, and bone of patients with CNC. A variety of endocrine abnormalities may occur in CNC, including acromegaly (in up to 10% of patients), and tumors of various endocrine glands (adrenals, gonads, thyroid) (Pandolfino et al., 2001). The presence of genital pigmented macules, especially black ones, helps distinguish CNC from Peutz–Jeghers syndrome (Rhodes et al., 1984). Also, with Peutz–Jeghers syndrome, pigmented macules appear predominantly on perioral skin and oral mucosa, eyelids, palms, and soles (Rhodes et al., 1984).
entirely dermal collections of two types of melanocytes. One type is heavily pigmented fusiform melanocytes and the other type is large melanocytes with a polygonal shape, a central round nucleus, and abundant cytoplasm. Melanocytes do not demonstrate maturation with dermal descent. Misdiagnosis of these lesions as malignant melanoma is a danger. The melanocytes of EBN, though large, are not atypical (Izquierdo et al., 2001).
Histopathology Biopsy of pigmented macules of the face, lips, or genital skin can show a spectrum of findings. In some instances, there is hyperpigmentation of the basal zone only without an appreciable increase in melanocytes; in other words, they are ephelides. Other lesions may demonstrate not only hyperpigmentation of the basal epidermis, but also a slight increase in melanocyte numbers and are better termed lentigines, though they may lack epidermal changes of elongation and clubbing of rete ridges seen commonly in simple lentigines. Still other lesions have been described with features of junctional or compound melanocytic nevi. One lesion in particular deserves a brief discussion here, and that is the epithelioid blue nevus (EBN). This lesion was originally described as occurring in the context of CNC but has since been noted to occur sporadically in the absence of other stigmata of CNC. EBN tends to occur on the upper back, shoulders, and extremities and clinically the nevi are indistinguishable from other types of blue nevi. Several cases of sporadic EBN have been described on genital mucosa in both men and women. Microscopically, EBN is comprised of
Histopathology Fixed drug eruptions are microscopically distinctive and a specific diagnosis may be rendered if the reaction is captured during an active phase. Because of the acuity of the reaction, there is a basket-woven stratum corneum. There is a bandlike infiltrate of lymphocytes with admixed eosinophils and scattered neutrophils which abuts and may obscure the dermal–epidermal interface. Necrotic keratinocytes are numerous along the junction and melanophages may be sparse or plentiful depending on the skin type of the affected individual and the length of time the reaction has been ongoing. There is also an accompanying mid to deep dermal perivascular infiltrate which is helpful in distinguishing fixed drug reaction from erythema multiforme (Fig. 56.7). Lesions sampled late in the course may demonstrate postinflammatory pigmentary alteration only (Ackerman et al., 1997).
Fixed Drug Eruption Fixed drug eruption is a peculiar hypersensitivity reaction to a medication or ingested compound which recurs repeatedly in the same specific location(s) after each exposure to the offending agent, though new sites in addition to the older ones may be affected each time the reaction recurs. Sensitization to the offending agent is required and the condition may onset after several weeks of exposure initially and more rapidly (within hours) with subsequent exposures. Lesions start as discrete, round to oval erythematous macules or patches but may become indurated or bullous. They often develop a distinctive red-brown or purple-brown color. Although the lesions do not appear initially as pigmented lesions, they do progress to a stage of hyperpigmentation after the acute reaction wanes. Lesions may affect any part of the body, but are particularly common on mucosal surfaces, including the lips (Fig. 56.6), the genital mucosa, and the perianal skin. Lesions are frequently single but may be multiple. The hyperpigmentation is due to melanin incontinence from the interface reaction that occurs in fixed drug eruptions. Repeated exposure to the drug may result in progressive darkening over time. The most common causative agents have been reported to be sulfonamides, tetracyclines, penicillins, nonsteroidal anti-inflammatory agents, and barbiturates. Phenolphthalein was a common offending agent in the past before its removal from laxative preparations and some beverages (English et al., 1997).
Freckles Clinical Freckles are common lesions, and may occur on the vermilion of the lip as they do elsewhere on sun-exposed skin. 1073
CHAPTER 56
Fig. 56.7. Fixed drug eruption histopathology. In this acute lesion, there is confluent epidermal necrosis beneath a basket-weave stratum corneum and there is a bandlike mixed inflammatory infiltrate in the dermis. Note the large number of melanophages.
opment of hepatocellular carcinoma, hyperpigmentation, and diabetes mellitus. Up to 25% of patients may have blue-gray macular hyperpigmentation of the hard palate and attached gingiva. The pigmentation is due to increased melanin pigmentation in the basal layer and not to iron deposition within the tissue (Lenane and Powell, 2000; McKusick, 1986b). Fig. 56.6. Fixed drug eruption. The red-brown pigmentation of the eruption involves the upper cutaneous lip and extends onto the vermilion.
The lower lip is more commonly affected than the upper lip (see Figs 54.1–54.3 and Plates 54.1 and 54.2). Freckles are usually tan to brown macules several millimeters in maximal diameter, but they may be larger. The hallmark of a freckle clinically is that it darkens with increased exposure to sunlight, and fades if exposure is limited (Maize and Ackerman, 1987). Histopathology Freckles show hyperpigmentation of the basal layer of the epidermis. Unlike in solar lentigines, there is no elongation or clubbing of rete ridges. There is no acanthosis of the epidermis which is typically seen in labial melanotic macules (see below). Melanocytes are not increased in number, but they may be mildly enlarged with more prominent dendritic processes in the melanocytes of adjacent unaffected skin (Maize and Ackerman, 1987). Hemochromatosis Hemochromatosis in its classic form is an autosomal recessive disease due to defect in the HFE gene on chromosome 6p21.3. The result is systemic iron overload, which, if untreated, can lead to cirrhosis of the liver and devel1074
Labial Melanotic Macules Clinical Labial melanotic macules are not uncommon brown to blue-black flat lesions which usually occur on the vermilion of the lower lip, but may occur on the upper lip as well (Ho et al., 1993). Although they have also been referred to as labial lentigines, they are morphologically distinct from traditional lentigines and do not evolve into nevi as do some lentigines; therefore, the term melanotic macule is preferred for these lesions (Maize, 1988). Patients with melanotic macules of the lip are prototypically white women about 40 years of age with a slowly appearing (over months to years) asymptomatic macule on the lower lip (Fig. 56.8) (Ho et al., 1993). Men less commonly develop melanotic macules, and these lesions have been noted in black patients as well. Many times, these lesions possess a benign clinical morphology, but some lesions may display features such as asymmetry, border irregularity, color variation, and large size which may simulate melanoma in situ. For this reason, they are a cause for clinical concern and biopsy. Oral and labial melanotic macules have been reported in association with human immunodeficiency virus (HIV) disease (Cohen and Callen, 1992). Some authors have proposed the unitarian view that isolated oral/labial melanotic macules are but one manifestation of Laugier–Hunziker syndrome (Dupre and Viraben, 1990) (see discussion on Laugier–Hunziker syndrome below).
PIGMENTARY ABNORMALITIES AND DISCOLORATIONS OF THE MUCOUS MEMBRANES
Fig. 56.8. Labial melanotic macule. Lesions may be asymmetrical and possess an irregular border, simulating melanoma clinically (see also Plate 56.2, pp. 494–495).
Fig. 56.9. Labial melanotic macule histopathology. There is acanthosis of the epidermis with broad rete ridges which show prominent basilar hyperpigmentation. Melanocytes are not increased. Parakeratosis often overlies these lesions as in this example.
Histopathology Melanotic macules classically show hyperpigmentation of the basal layer principally at the tips of elongated and broadened rete ridges. At times, however, pigmentation may be confluent within the basal epidermis. Epithelial changes include compact orthohyperkeratosis, mild parakeratosis, and hyperplasia manifested by widened and elongated rete ridges. In the lamina propria, features such as telangiectasia, enlarged fibroblasts, and melanophages are characteristically present (Fig. 56.9). Although most sources report that melanotic macules are due to increased melanin pigment alone and not to an increase in melanocytes, some studies have demonstrated a twofold
Fig. 56.10. Laugier–Hunziker syndrome. There are multiple tan to brown macules on the vermilion of the lower lip (see also Plate 56.3, pp. 494–495).
increase in the number of melanocytes in these lesions compared to normal lip mucosa (Sexton and Maize, 1987). Melanocytes in melanotic macules also possess morphologic differences over normal mucosal melanocytes. In the case of melanocytes in melanotic macules, individual melanocytes display a network of long, fine, branching dendrites which intercalate among the keratinocytes of the adjacent basal layer and overlying spinous layer. These dendrites are heavily melanized. Dendritic melanocytic proliferations of the mucosal surfaces must be viewed with caution, as melanomas in situ of the mucosa will at times manifest as a lentiginous proliferation of single units with a predominantly dendritic morphology. In contrast to melanotic macules, however, melanomas in situ display long, coarse dendrites which may extend into the upper reaches of the spinous layer. Also, cytologic atypia is not a feature of the melanocytes in melanotic macules; in melanomas in situ, however, atypia manifested by overall cellular and nuclear enlargement, nuclear hyperchromasia and pleomorphism, and nucleolar enlargement may be marked. It should be understood that some areas within a lesion of melanoma may be deceptively benign appearing and small samples may therefore miss the telltale features required to make the diagnosis. Therefore, any biopsy specimen submitted to exclude melanoma should include areas of induration, erosion, or ulceration if such areas are present in a given lesion (Maize, 1988). Laugier–Hunziker Syndrome Clinical In 1970, Laugier and Hunziker described a condition they termed “essential lenticular melanotic pigmentation of the oral cavity and the lips.” The condition predominantly affects Caucasians and onset is during adulthood. Affected persons can display multiple discrete pigmented macules on virtually any aspect of the oral mucosa and often on multiple surfaces (Figs 56.10 and 56.11). The syndrome has been expanded to include pigmented macules 1075
CHAPTER 56
Fig. 56.12. Peutz–Jeghers syndrome. There are subtle tan macules on the lower lip (see also Plate 56.4, pp. 494–495).
Fig. 56.11. Laugier–Hunziker syndrome. The tongue is also involved in this patient.
or patches on the neck, chest, abdomen, fingers, soles, penis, vulva, vagina, cervix, perineum, and perianal skin as well. Pigmented longitudinal streaks of the nail or pigmentation of the whole nail complete with the Hutchinson sign (pigmentation extending onto the proximal nail fold) have been described. No other organ involvement has been reported in addition to skin and mucosal pigmentation (Veraldi et al., 1991). The unitarian view has been proposed that stipulates that the term “Laugier disease” be used whenever there is a clinically hyperpigmented macule with the histopathologic features of a melanotic macule. Proponents of this view believe that isolated labial melanotic macules, penile lentigines, vulvar melanosis, some lesions of linear melanonychia (those not due to a true melanocytic proliferation), and volar melanotic macules of the palms and soles are merely variant expressions of the classic form of Laugier–Hunziker syndrome (Dupre and Viraben, 1990). Histopathology Biopsy reveals acanthosis of the epidermis, basal layer hyperpigmentation, and pigment incontinence, findings indistinguishable from those of isolated melanotic macules of the lip or genitalia. Melanocytes are normal in number, arrangement within the epidermis, and morphology. Elongated intracytoplasmic melanosomes are present within keratinocytes of the basal epidermis, and it is postulated that there is some functional alteration in melanocytes with respect to melanosome synthesis and transfer to keratinocytes (Veraldi et al., 1991). Treatment Therapy is not required once the diagnosis is established. Laser therapy utilizing lasers effective on melanin 1076
pigment has been successfully performed for improvement of cosmesis (Papadavid and Walker, 2001). Peutz–Jeghers Syndrome PJS is an autosomal dominantly inherited disease, although about 40% of cases are new mutations. The defective gene is SKT11 on chromosome 19p13.3 which encodes a serine-threonine kinase (McKusick, 2004). Patients develop pigmented macules of the oral mucosa, especially the lower lip (Fig. 56.12) and buccal mucosa, smaller pigmented macules (usually less than 1 mm) on the face near the mouth, and pigmented macules on the palms and soles, sometimes with pigmented longitudinal streaking of the nails. The pigmented lesions most commonly arise in the early years of life, though they may be congenital or develop during adulthood. Typically, facial and acral lesions fade over time, though intraoral pigmentation usually persists. In addition to the cutaneous findings, patients develop gastrointestinal polyps mostly in the small intestines, but other areas of the gastrointestinal tract may also be affected. Histopathology Microscopically, the pigmented lesions demonstrate hyperpigmentation of the basal epidermis without an increase in melanocytes. The polyps are usually benign hamartomas, though adenocarcinomas can occur in 2–3% of patients, some of which develop independent of the hamartomatous polyps. There is an increased risk of malignancy developing outside the gastrointestinal tract as well in patients with PJS, especially the breast and ovary. Treatment The skin lesions serve as a hallmark of disease, but they do not require treatment. Lasers effective for skin lesions due to increased melanin pigment have been successfully employed to eliminate lesions in some patients (Kato et al., 1998). Persons affected by PJS must be followed by a gastroenterologist for regular surveillance. Polyps may have to be removed, especially if there are symptoms. Large numbers of
PIGMENTARY ABNORMALITIES AND DISCOLORATIONS OF THE MUCOUS MEMBRANES
Fig. 56.13. Melanoacanthoma. Note the irregular and stippled brown-black macules on the labial mucosa.
Fig. 56.14. Melanoacanthoma histopathology. A scanning view demonstrating the marked hyperplasia of the mucosal epithelium (H&E).
polyps may pose a management problem. Prophylactic colectomy has been employed in some such cases (Champion et al., 1998; Lenane and Powell, 2000). LEOPARD Syndrome (Multiple Lentigines Syndrome) This is an autosomally dominant inherited cardiocutaneous syndrome. The acronym LEOPARD stands for Lentigines, Electrocardiographic conduction abnormalities, Ocular hypertelorism, Pulmonary stenosis, Abnormal genitalia, Retardation of growth, and Deafness. Lentigines are distributed over the lower central face including the lips, neck, trunk, extremities (including palms and soles), and genitalia, but are not present inside the mouth. Cardiac problems may include obstructive cardiomyopathy and mitral regurgitation in addition to electrocardiographic abnormalities. The genetic defect has been identified as a mutation in the gene encoding proteintyrosine phosphatase, nonreceptor type, 11 (PTPN11) on chromosome 12q24.1. Different areas of the same gene are mutated in Noonan syndrome, and, therefore, Noonan syndrome and LEOPARD syndrome are allelic variants of one another (McKusick, 1986c). Histopathology Biopsy of the pigmented lesions shows an increase in single unit melanocytes in the basal epidermis in addition to increased pigmentation of the keratinocytes in the basal layer, i.e., the lesions are true lentigines. In addition, melanocytes contain an abundance of melanosomes which may be substantially enlarged (macromelanosomes) (Nordlund et al., 1973; Weiss and Zelickson, 1977). Melanoacanthoma (Melanoacanthosis) of the Oral Mucosa Clinical Melanoacanthomas are benign pigmented lesions of the oral mucosa which, with rare exception, affect black patients. Lesions more commonly occur in women than in men, and they tend to arise in patients in their teens to late thirties/early forties. The buccal mucosa is most commonly affected in just over half of cases, with the labial mucosa comprising approximately another fifth (Fig. 56.13). Lesions are
brown, black or blue-black in appearance, often with a rough surface, and may simulate nevi or melanoma clinically. Individual lesions may be strikingly large, measuring up to five centimeters in diameter and, rarely, they can diffusely affect the mucosal surfaces. Lesions are often asymptomatic, but they may be painful or pruritic. The etiology of these lesions is not known, but there may be a role for chronic irritation due to physical trauma (e.g., cheek biting, ill-fitting dentures) or cigarette smoking. Lesions usually regress in a matter of weeks after biopsy or after resolution of the trauma or smoking cessation. It has been postulated that black patients with physiologic hyperpigmentation are likely predisposed to reactive changes involving melanocytes inhabiting mucosal epithelium in addition to the more universal reactive changes in keratinocytes as a response to chronic trauma and/or irritation (Maize, 1988; Tomich and Zunt, 1990). Histopathology Lesions demonstrate a hyperplastic epidermis with large, dendritic melanocytes scattered throughout the thickened mucosal epithelium (Figs 56.14–56.17). These melanocytes are fairly evenly distributed within the spinous layer and do not form nests. Melanocytes have abundant melanin pigment granules within their cytoplasm, including within the long, thin dendritic processes extending between keratinocytes of the epithelium. Few pigment granules are transferred to the keratinocytes and it seems as though there is a defect in melanosome transfer from melanocytes to the adjacent keratinocytes. Melanocytes are not increased in number in the basal epidermis and are not atypical in appearance (Tomich and Zunt, 1990). Nevi Melanocytic nevi occur within the mouth as they do elsewhere on the cutaneous surface, though they are uncommon, occurring in about 0.1% of people. All age groups can 1077
CHAPTER 56
Fig. 56.15. Melanoacanthoma histopathology. At higher power, single unit melanocytes are discernable within the thickened spinous layer of the epithelium (H&E).
Fig. 56.17. Melanoacanthoma histopathology. Note the delicate, markedly elongated dendrites of the melanocytes within this melanoacanthoma (Warthin–Starry).
Fig. 56.18. Oral blue nevus. A blue-black papule on the hard palate (see also Plate 56.5, pp. 494–495). Fig. 56.16. Melanoacanthoma histopathology. In sections stained with a silver stain, many more melanocytes are evident scattered as single cells throughout the epithelium.
be affected, but lesions are most commonly noted in young to middle-aged adults. Palatal, gingival, and labial mucosa can be affected, with the palate being the most common location. Most lesions are only several millimeters in diameter, though nevi one centimeter or more in diameter are encountered on occasion. Lesions may be macular, but up to two thirds of lesions are papular. Up to a fifth of mucosal nevi are nonpigmented (Buchner and Hansen, 1979, 1980b). Approximately a third of nevi from oral mucosa are common blue nevi (Figs 55.18–55.20). Congenital pattern nevi, combined nevi, and Spitz nevi have all been reported to occur in the mouth. Microscopic features of these lesions are identical to those occurring elsewhere. 1078
Fig. 56.19. Oral blue nevus histopathology. At scanning power, there is heavy pigmentation of the submucosa.
PIGMENTARY ABNORMALITIES AND DISCOLORATIONS OF THE MUCOUS MEMBRANES
Fig. 56.20. Oral blue nevus histopathology. Higher power reveals the pigment to be within bipolar melanocytes situated between and parallel to collagen bundles of the submucosa.
Smoker’s Melanosis Individuals who smoke tobacco have been observed to have increased pigmentation of the oral mucosal surfaces in general as compared with nonsmokers. However, discrete focal areas of macular hyperpigmentation usually less than 1 cm in diameter on the oral mucosal surface in persons who smoke are referred to as smoker’s melanosis or smoker’s stains, though “melanosis” seems most appropriate since the cause is increased melanin pigment within the mucosal epithelium. The usual locations are the attached labial gingiva and the mandibular interdental papillae. Incidence increases with increasing tobacco use and is seen more commonly in women over 30 years old (Cicek and Ertas, 2003). Malignant Oral Melanoma The subject of oral melanoma has been extensively discussed in numerous articles and texts and will be only briefly reviewed herein for the sake of completeness. Readers are referred to other sources for more detailed discussion (Bongiorno and Arico, 2002; Eisen and Voorhees, 1991; Hicks and Flaitz, 2000; Rapini et al., 1985; Umeda et al., 2002). Clinical Melanoma of the oral cavity is an uncommon neoplasm, though in reported series, the incidence varies from 0.1% to 8% of all melanomas. In some populations, such as the Japanese, oral melanomas constitute a higher percentage of all melanomas than in whites (Umeda et al., 2002). The most common sites of involvement within the mouth are the palate (40%) and the maxillary gingiva (Fig. 56.21). Presentation is quite variable: lesions may develop slowly or quickly; change subtly or dramatically; be pigmented or amelanotic. Most lesions are asymptomatic, but lesions may ulcerate, bleed, and cause pain. The vast majority of oral melanomas develop in patients over 40 years of age and are extremely rare
Fig. 56.21. Intraoral melanoma. The maxillary gingiva is the most common site of development of intraoral melanoma (see also Plate 56.6, pp. 494–495).
prior to age 20 (Eisen and Voorhees, 1991; Rapini et al., 1985). Biopsy of all oral lesions of unknown origin, especially pigmented lesions which are new or changing, is in the patient’s best interest. The prognosis of melanoma occurring in the oral cavity is much more dismal than melanomas on the cutaneous surface, with a survival rate of only 5–15% after 5 years (Bongiorno and Arico, 2002). Whether the particularly poor prognosis of the lesions is due to inherent genetically programmed behavioral differences in melanomas arising on the mucosa, to a delay in detection due to the location, to inadequate surgical treatment, or to a combination of these factors has not been determined. Histopathology Histopathologic features of melanoma in the mouth are variable as they are in the skin. Melanocyte morphology may be spindled, epithelioid, dendritic, or mixed. Single unit melanocytes may predominate and display confluence and pagetoid upward migration. Nests and/or sheets of melanocytes may also be present. Architectural features such as size, symmetry, and circumscription are important in evaluating melanocytic neoplasms of the mucosa as they are in the skin. It is worth mentioning one specific pattern of oral melanoma that is uncommon in cutaneous melanoma (except acral lentiginous types), namely, the dendritic intraepithelial pattern. Caution must be used when prominent dendritic processes are encountered in lesions with increased melanocytes confined to the basal layer of the epithelium. Variability in the thickness of the dendritic processes and the length of the processes can be a hallmark of in situ melanoma at times. Melanocytic processes which extend substantially above the basal and parabasal layers are abnormal and, when coupled with variability in the thickness and length of the dendrites, can be a clue to the diagnosis of in situ melanoma (Figs 56.22 and 56.23). Prognosis of lesions based on depth of invasion as measured 1079
CHAPTER 56
Fig. 56.22. Intraoral melanoma histopathology. This melanoma in situ shows a marked increase in single unit melanocytes within the basal layer of the mucosal epithelium. Note the enlarged and hyperchromatic nuclei and the extension to the portion of the epithelium overlying the papillae of the lamina propria (H&E).
Fig. 56.23. Intraoral melanoma histopathology. Melanocytic proliferations on mucosal surfaces which demonstrate marked dendrites as pictured here should raise suspicion for melanoma in situ (Mart-1).
in millimeters has not been studied as rigorously as in the skin, but some small studies corroborate a worse survival for deeper lesions. No large series have compared survival of patients with oral melanoma versus survival of patients with cutaneous melanoma thickness for thickness. Clark level measurements do not apply to oral melanomas due to the absence of the delineation of a papillary and a reticular dermis as exists in the skin (Eisen and Voorhees, 1991).
Exogenous Chromophores Amalgam Tattoo Dental amalgam used as a filler material in restoration proce1080
Fig. 56.24. Amalgam tattoo. There is dark blue-black macular pigmentation of the buccal mucosa adjacent to a decayed tooth (see also Plate 56.7, pp. 494–495).
Fig. 56.25. Amalgam tattoo histopathology. There are variably sized aggregates of amalgam material in the submucosa with a moderately dense mixed inflammatory infiltrate (H&E).
dures may be traumatically introduced into the tissues of the mouth and result in clinically appreciated blue-black or gray macules (Fig. 56.24). Lesions are most commonly located on the gingiva and alveolar mucosa, but the buccal mucosa can also be affected. Lesions vary in size from 1 mm to 2 cm (Eisen and Voorhees, 1991). The amalgam material may be viewed as radio-opaque material in the tissue on X-ray of the affected area. Although the diagnosis is most often easily made based on the location, appearance and dental history, sometimes biopsy is necessary to confirm the clinical impression. Biopsy reveals the presence of dark granular material within histiocytes, fibroblasts, and endothelial cells and associated with collagen bundles, nerves, or around minor salivary glands (Fig. 56.25). In some instances, the amalgam may be situated
PIGMENTARY ABNORMALITIES AND DISCOLORATIONS OF THE MUCOUS MEMBRANES Table 56.1. Drugs causing discoloration of the oral mucosa, skin, and nails. Drug name
Oral dyschromia (Abdollahi and Radfar, 2003)
Amodiaquine Azidothymidine (AZT; zidovudine) Betel Bleomycin Busulfan Chloroquine Clofazimine Cyclophosphamide Doxorubicin Estrogen/Progestins Heroin (inhaled) Hydroxychloroquine Ketoconazole Mepacrine (Quinacrine) Methyldopa Minocycline Nicotine Nitrogen mustard Phenothiazines Quinidine Quinine
+ + + + + + + + + + + + + + + + + + + + +
(Palate) (Soft palate, gingiva, lips, tongue)
(Palate)
(Mucosa, tongue) (Tongue) (Palate) (Palate) (Tongue)
(Palate)
as large clumps within the lamina propria or the submucosa. Foreign body reactions are sometimes observed (Buchner and Hansen, 1980a). Medications There are a number of drugs which are well documented to cause discoloration of the oral mucosa. Such dyschromic lesions often accompany discolorations of the skin and nails. (See Table 56.1 for a listing of drugs which cause oral mucosal dyschromia.) Azidothymidine (AZT), a medication used in the treatment of HIV infection, can cause rapid onset of mucosal pigmentation as soon as a few weeks after the start of therapy. AZT directly stimulates melanin production in mucosal melanocytes and is not due to medication deposition. AZT pigmentation of oral mucosa, skin, and nails predominantly occurs in dark-skinned patients (Greenberg and Berger, 1990). All of the commonly used antimalarials agents (hydroxychloroquine, chloroquine, and quinacrine) can cause a blue-black hyperchromia of the skin which is accentuated in areas of sun exposure, as well as discoloration of the palatal mucosa and nail (Sontheimer and Provost, 1996). Heavy Metals Ingestion of heavy metals may result in deposition of the metals within the tissues of the oral mucosa and cause visible dyschromia. The classic example is the gingival “lead line” of lead toxicity (plumbism), but there are others. Linear metal deposits within the gingiva have also been described with
Skin dyschromia
Nail dyschromia (Scher and Daniel, 1997)
+ (Sontheimer and Provost, 1996) + (Greenberg and Berger, 1990)
+ +
+ (Bork, 1988) + (Bork, 1988) + (Sontheimer and Provost, 1996) + (Bork, 1988) + (Bork, 1988) + (Bork, 1988) + (Bork, 1988)
+ + +
+ (Sontheimer and Provost, 1996) + + (Sontheimer and Provost, 1996)
+
+ (Bork, 1988) +
+ +
+ (Bork, 1988) + (Conroy et al., 1996) + (Bork, 1988)
+
+ +
+
bismuth, copper, mercury, and thallium. Other metals may also cause oral dyschromia in different locations of the oral mucosa, including arsenic, gold, iron, manganese, silver, tin, and vanadium (Abdollahi and Radfar, 2003).
Genital Benign Vulvar Hyperpigmentation Racial variation of pigmentation may be observed on the genital mucosa as it is in the oral mucosa and is regarded as a normal variant. A number of other causes may result in the benign increase in melanin pigment in genital skin. Hormonal influences such as pregnancy, Cushing disease, Addison disease, and exogenous androgens may cause increased mottled or diffuse macular hyperpigmentation of the genital skin without an increase in melanocytes. Common causes of pigmentary changes elsewhere on the skin may also occur on the genital skin, such as post-inflammatory hyper- (or hypo-) pigmentation (Rock, 1992). Vulvar Lentigines In two studies assessing frequency of pigmented lesions of the vulva, simple lentigines were the most common pigmented lesion seen, being present in 3.5–7% of the study population. Clinically, lentigines are usually less than 5 mm in diameter, are well circumscribed, and may occur on the vulvar skin or the mucosa. Typically, there are a small number of lentigines occurring on the vulva of a given patient, but at times there 1081
Fig. 56.26. Vulvar melanosis. Hyperpigmented brown-black irregular patches are situated near the vaginal introitus (see also Plate 56.8, pp. 494–495).
Fig. 56.27. Vulvar melanosis histopathology. Note the bulbous contour of the rete ridges of the hyperplastic epidermis (H&E).
may be numerous lesions. Microscopically, there are elongated and club-shaped rete ridges and there is hyperpigmentation of the basal epidermis. Increased numbers of melanocytes may be appreciated, but melanocyte atypia is not a feature. Lesions indistinguishable from simple lentigines may also occur in the Carney complex and in the LEOPARD syndrome. Patients with neurofibromatosis may have freckling in the genital area which may be clinically similar to lentiginosis (Rock, 1992). Vulvar Melanosis Hyperpigmented macules which are similar in many ways to the oral labial melanotic macule occur on the vulva of women. Identical lesions have also been reported within the vagina and on the uterine cervix. These lesions tend to occur in women who are between menarche and menopause, though there has been no reported association with abnormal hormonal states or exogenous hormone use. Lesions are often large, being between 10 mm and 45 mm in one reported case series (SisonTorre and Ackerman, 1985), and malignant melanoma is often a clinical consideration in the differential diagnosis of these lesions. Unlike with labial melanotic macules, however, lesions may be multiple in a substantial percentage of affected persons. Involvement of the labia minora is most frequently observed, but lesions may also occur on the labia majora as well as the introitus and perineum (Fig. 56.26). Microscopic features are like those of oral melanotic macules, with epidermal hyperplasia and hyperpigmentation of the basal zone (Figs 56.27 and 56.28). Some reports have mentioned a mild increase in melanocytes which may have prominent, thin, arborizing dendrites, but no nests of melanocytes and no cytologic atypia (Rudolph, 1990). Once the diagnosis is correctly established, treatment is not necessary (Sison-Torre and Ackerman, 1985). Penile Lentigo/Atypical Penile Lentigo Men may have lesions involving the glans penis or penile shaft 1082
Fig. 56.28. Vulvar melanosis histopathology. Hyperpigmentation of the basal epidermis is most prominent at the tips of the broadened rete. There is a mild infiltrate which contains melanophages (H&E).
which clinically and histopathologically are similar to vulvar melanosis and oral melanotic macules (Figs 56.29–56.31). These hyperpigmented macular lesions have been reported under the terms penile lentigo and atypical penile lentigo. Several reports have described slightly increased numbers of single unit melanocytes with dendritic morphology in the basal layer of epidermis. Barnhill and coworkers noted that penile and vulvar lesions differed with respect to the presence of melanocytes with a dendritic morphology. Specifically, all penile lesions they reviewed displayed prominent dendritic melanocytes, whereas vulvar lesions showed little in the way of dendritic melanocytes (Barnhill et al., 1990). In the lesion reported as atypical penile lentigo, melanocytic atypia of some melanocytes was observed. The reported incidence of these
PIGMENTARY ABNORMALITIES AND DISCOLORATIONS OF THE MUCOUS MEMBRANES
Fig. 56.29. Penile lentigo. A markedly irregular patch on the glans penis with variegated tan to dark brown pigmentation (see also Plate 56.9, pp. 494–495).
Fig. 56.31. Penile lentigo histopathology. There is no melanocytic proliferation, merely basilar hyperpigmentation.
Fig. 56.30. Penile lentigo histopathology. There is epidermal hyperplasia with broad rete ridges with hyperpigmentation at the tips of the rete (H&E).
lesions is low and the natural history is not known. As with vulvar melanosis and labial melanotic macules, knowledge of these lesions is important to avoid overtreatment (Maize, 1988). Genital Nevi (Including “Milk Line” Nevi) On the vulva, melanocytic nevi are the second most frequent pigmented lesion after lentigines, occurring in 2% of white women in some studies. All types of nevi which occur on the torso may occur on the vulva: junctional, compound, and intradermal nevi, including atypical (Clark, “dysplastic”) nevi (Rock, 1992). The histopathology of most nevi on the vulva is not unique to the site, but there are special features which can occur in nevi in this location which are important to recognize. The concept of milk line nevi or so-called atypical nevi of special anatomic sites has been propagated fairly recently in the medical literature after the initial description of the
“atypical melanocytic nevus of the genital type” by Wallace Clark and others (Clark et al., 1998), though the recognition of distinctive features of melanocytic nevi occurring on the genitalia in particular predates their work by many years (Maize and Ackerman, 1987). Knowledge of these distinctive changes is important because melanocytic nevi on the genitalia and other special sites such as breast, axilla, and umbilicus may simulate melanoma in situ. The melanocytes within the epidermis in nevi of the genitalia tend to be large with large round or oval nuclei with an open chromatin pattern, and nuclei may show some pleomorphism. There is often a population of melanocytes with abundant, pale staining cytoplasm reminiscent of the dusty melanin pigment observed in some lesions of melanoma. Nests within the epidermis vary in size and shape, but they are often relatively large and are closely spaced (Figs 56.32 and 56.33). Pagetoid scatter may be a minor feature and does not extend beyond the last nest defining the periphery of the lesion. Despite some unsettling cytologic and architectural features, these lesions overall are small, well circumscribed, symmetrical, and lack atypia of the dermal component as do nevi from other locations (Fig. 56.34) (Maize and Ackerman, 1987; Zhou and Crowson, 2003). 1083
CHAPTER 56
Fig. 56.32. Vulvar melanocytic nevus histopathology. There is a compound melanocytic proliferation. Within the epidermis, nests of melanocytes vary in size and shape, and there are zones of confluence (H&E).
Fig. 56.34. Vulvar melanocytic nevus histopathology. Dermal melanocytes are small and uniform in appearance, a reassuring finding (H&E).
elongated and hyperpigmented rete ridges (Lenane and Powell, 2000).
Fig. 56.33. Vulvar melanocytic nevus histopathology. The melanocytes within the epidermis are large with abundant pale cytoplasm (H&E).
Bannayan–Riley–Ruvalcaba Syndrome (BRRS) BRRS is usually an autosomally dominant inherited disease, though sporadic cases do occur. Patients are predominantly male and may have macrocephaly, hypotonia, hyporeflexia, developmental delay, lipomas (cutaneous and/or visceral), hemangiomas, hamartomatous polyps of the intestine, Hashimoto thyroiditis, and pigmented macules of the penis or vulva. Familial cases have been linked to mutations in the PTEN gene on chromosome 10q23.31, the same gene locus as Cowden syndrome. It has been postulated that these two syndromes are merely different phenotypic expressions of a single syndrome, and, therefore, patients with both syndromes should be carefully followed for the development of cancer (McKusick, 1986d). Biopsy of the pigmented genital macules shows a slight increase in melanocytes in the basal layer with 1084
Vulvar Dowling–Degos Disease (Reticulate Pigmented Anomaly of the Flexures) Dowling–Degos disease is usually an autosomally dominant inherited condition which affects the flexural areas including initially the axillae and groin but may later involve the neck, inframammary folds, natal cleft, upper arms, and inner thighs. There have been several cases of Dowling–Degos disease affecting exclusively the vulva. One 55-year-old Japanese woman developed pruritus vulvae which preceded by several years the development of “innumerable pigmented macules on her bilateral vulva.” These were brown to black in color, less than 1 mm in diameter, and symmetrically distributed. Histopathology of lesions of Dowling–Degos disease resembles a reticulated seborrheic keratosis with elongated, hyperpigmented downgrowths from the epidermis and extensions emanating from follicular infundibula. Horn pseudocysts and dilated follicular opening may be seen. There are scattered melanophages in the papillary dermis (Maize and Ackerman, 1987). Laugier–Hunziker Syndrome See discussion of this condition in the section on pigmentary abnormalities of the oral mucosa.
Malignant Vulvar Melanoma Approximately 8–11% of vulvar malignancies are melanomas, and these comprise roughly 2–5% of all melanomas. White people, followed closely by Asians, are most commonly affected, with black people being uncommonly affected. The disease strikes predominantly postmenopausal women aged 50–80 years. Clinical appearance and symptomatology of melanomas of the vulva is not different than melanomas
PIGMENTARY ABNORMALITIES AND DISCOLORATIONS OF THE MUCOUS MEMBRANES
from other body sites, but the depth of invasion of vulvar melanomas is typically greater at discovery. Survival estimates for patients diagnosed with vulvar melanoma range from 36% to 54%. It is not known whether this is attributable entirely to delayed diagnosis by virtue of the hidden and private nature of the location preventing patient knowledge of a new or changing lesion or resulting in a delay in presentation to or examination by a healthcare provider, or if there is also a distinct biologic difference in behavior of genital melanomas (Rock, 1992). Microscopic criteria for a diagnosis of melanoma of the vulva are the same as for elsewhere. Lesions of the genital mucosa may show atypical lentiginous melanocytic proliferation of single unit melanocytes, sometimes with prominent dendrites, as in melanoma of the oral mucosa. Penile Melanoma As in the case of vulvar melanoma, melanoma of the penis is rare: only 1% of all penile malignancies are melanomas. Most patients are between 50 and 70 years of age, with rare cases reported in younger individuals. Two-thirds of cases present as lesions on the glans penis, and ulceration is a frequent finding. Metastasis is present in up to 60% of cases at diagnosis. Lesions may be misdiagnosed as an infection or an inflammatory process initially, delaying appropriate diagnosis and treatment. Clinical and histopathologic criteria for diagnosis of melanoma in general also apply to penile melanoma (English et al., 1997). Pigmented Genital Carcinomas Squamous cell carcinoma in situ (SCCIS), invasive squamous cell carcinoma, and basal cell carcinoma can all occur with pigmented variants. SCCIS as a cause of a pigmented lesion on the vulva occurred with a frequency roughly equal to that of melanocytic nevi in one series (Rock, 1992). Extensive carcinoma in situ of the vulva has been reported which presented as diffuse macular hyperpigmentation with focal ulceration (Rock, 1992). Full-thickness atypia of squamous keratinocytes with enlarged and pleomorphic nuclei, nuclear crowding and loss of polarity, atypical mitotic figures, scattered individually necrotic keratinocytes, and parakeratosis of the stratum corneum are prototypical findings in SCCIS. In pigmented variants, there is abundant melanin pigment in the neoplastic keratinocytes. The microscopic differential diagnosis includes bowenoid papulosis which may be indistinguishable from SCCIS. However, the clinical appearance is distinct, as bowenoid papulosis presents as multiple verrucous tan or brown papules on the genitalia often indistinguishable clinically from condylomata acuminata (Maize and Ackerman, 1987).
Anal Benign Laugier–Hunziker Syndrome See discussion of this condition in the section on pigmentary abnormalities of the oral mucosa.
Malignant Anal Melanoma Melanoma of the anus comprises less than 5% of all anal malignancies and less than 1% of all melanomas. However, the anus is the most frequent site of development of melanoma of the gastrointestinal tract. The most frequently affected group is white women between the ages of 50 and 80 years, although anal melanoma may make up a higher proportion of all melanomas in darker-skinned populations. Melanoma of the anus often causes bleeding or a mass which prompts the patient to seek attention. Importantly, up to 80% of anal melanomas are not appreciably pigmented clinically, and a fifth are amelanotic microscopically as well. Because of this absence of notable pigmentation in many cases, melanomas may be misdiagnosed and treated as hemorrhoids for a while before the correct diagnosis is rendered. Anal melanomas are thicker at diagnosis than melanomas from non-anogenital sites, typically being greater than 1 mm Breslow thickness. The five-year survival rate is under 20% with the median survival between 8 and 23 months. Management of the disease consists of surgical removal of the neoplasm with appropriate margins of normal-appearing tissue. In the past, aggressive surgical management with wide excision and node dissection was advocated, but these procedures did not afford any clear survival benefit over local excision alone. Radiation therapy has been proposed as a reasonable adjunctive measure after surgical removal of the tumor (Kim et al., 2004; Moozar et al., 2003).
Hypopigmentation Genital Vitiligo Vitiligo is an acquired disease due to loss of melanocytes which results in depigmentation of the affected skin. Although the cause is not precisely known, there is evidence supporting an immune-mediated mechanism of melanocyte destruction (Lepe et al., 2003). The disease occurs in all ages and races, and in both sexes and it occurs with greater frequency in individuals with a family history of vitiligo. The disease is especially stigmatizing in darker-skinned individuals and certain cultural groups. Other autoimmune diseases are seen with greater frequency in patients with vitiligo versus patients without vitiligo, including thyroid disease, diabetes mellitus, pernicious anemia, and Addison disease (Alkhateeb et al., 2003; Kenney, 1988). The reasons behind the development of a cytotoxic immune response against melanocytes are not fully understood. Any part of the body may be affected, including the genitalia, and, in some instances there may be exclusive involvement of the genitalia. In such instances, the clinical differential diagnosis may include lichen sclerosus. Chemical leukoderma caused by exposure to agents that are toxic to melanocytes, such as monobenzyl ether of hydroquinone and phenolic compounds, may present with genital depigmentation in some instances and must be considered in the 1085
CHAPTER 56
differential diagnosis as well. The diagnosis is made by careful history. Histopathology The microscopic findings in vitiligo depend upon the stage of disease progression sampled. Early lesions may demonstrate diminished basal layer pigmentation within the epidermis and even some residual melanocytes. Melanophages are present in the papillary dermis and there may be a sparse superficial perivascular inflammatory infiltrate of lymphocytes. Rarely, there may be exocytosis of lymphocytes into the epidermis. In fully developed lesions, there is loss of both melanocytes in the lesional skin and loss of melanin pigment within keratinocytes of the basal layer. Special staining techniques for melanocytes using immunoperoxidase markers such as Melan-A/Mart-1 and the Fontana-Masson stain for melanin pigment may be useful in confirming a loss of melanocytes and a reduction or absence in melanin pigment. Melanophages may or may not be present (Ackerman et al., 1997). Chemical leukoderma is histologically indistinguishable from vitiligo. Treatment Treatment of vitiligo may be most successful if initiated early in the disease process. Topical steroids have been a first-line therapy for many years. Newer topical immune modulators such as topical tacrolimus have shown recent promise in vitiligo therapy (Lepe et al., 2003). Psoralens with ultraviolet A light (PUVA) (both with topically applied psoralens and orally administered psoralens) and narrow-band UVB have been successfully employed for vitiligo therapy, though such treatments may not be practical for genital skin. Treatment employing a 308 nm xenon chloride excimer laser has been useful in some cases of limited vitiligo (Baltas et al., 2002). Melanocyte transfer and skin grafting techniques may restore pigmentation to affected skin (Gupta et al., 2004). Camouflage of affected areas using stains, self-tanning creams, waterproof cosmetics, and tattooing have been utilized to minimize the appearance of lesional skin.
Lichen Sclerosus Clinical White women who are postmenopausal are most commonly affected by lichen sclerosus (LS), but the disease is seen in a wide range of age and in all races. LS often presents as a maddeningly pruritic patch that is erythematous and inflamed during the early stages and eventuates in a depigmented — classically, porcelain white — and atrophic plaque. There are often superimposed secondary changes of lichenification or excoriation. At times, lesions are strikingly purpuric or surmounted by hemorrhagic vesicles and bullae. The vulva surrounding the vaginal introitus is usually the epicenter of the disease, but it may spread centrifugally to surround not only the vaginal opening but also the anus in a pattern likened to a “figure-of-eight.” In advanced disease, there may be extensive scarring and fusion of the vulva with attendant constric1086
Fig. 56.35. Lichen sclerosus of the penis (balanitis xerotica obliterans).
tion of the introitus and concealment of the clitoris. In men, LS (historically termed “balanitis xerotica obliterans” or BXO) is usually confined to the glans penis and foreskin and presents with pruritus, pain, and phimosis. Involvement of the perineum and perianal skin are unusual. LS may occur on nongenital skin also as guttate papules or as large plaques. The clinical appearance of the lesions is similar, with a finely wrinkled, atrophic surface and porcelain-white coloration (Fig. 56.35). Lesions may co-occur with classic lesions of morphea. Rare cases of LS of the oral mucosa have been described. The etiology of the disease is not known. Longstanding genital lesions of LS carry an approximately 5% risk of developing squamous cell carcinoma (Lorenz et al., 1998). Histopathology Lesions of LS share identical histopathologic features irrespective of the site of occurrence. Early lesions demonstrate a bandlike infiltrate of lymphocytes which abuts and focally obscures the dermal–epidermal junction. Injury to the epidermis is seen as vacuolization and squamatization of the basal layer with scattered necrotic keratinocytes along the junction. Exocytosis of lymphocytes into the epidermis during the early phases of disease may simulate mycosis fungoides. Fully developed lesions demonstrate veritable sclerosus of the papillary dermis, often with pronounced edema. The overlying epidermis shows thinning with a flattened rete ridge pattern and
PIGMENTARY ABNORMALITIES AND DISCOLORATIONS OF THE MUCOUS MEMBRANES
there is compact orthohyperkeratosis of the cornified layer. There may be plugging of adnexal openings. A subtle lichenoid infiltrate may be present subjacent to the zone of sclerosus and there is usually a superficial perivascular infiltrate of lymphocytes. Clinically apparent hypopigmentation is due to damage to the basal layer resulting in loss of melanin pigment from basal keratinocytes. Melanophages are often noted in the sclerotic papillary dermis (Carlson et al., 1998). Treatment Ultra-potent topical steroids (class I) such as 0.05% clobetasol propionate are considered first-line therapy for the management of genital LS. Intensive therapy initiated early in the course of disease may prevent untoward sequelae such as scarring and labial fusion. Close monitoring of patients utilizing strong steroids on genital skin is required to prevent unintended side effects. One treatment protocol involves application twice daily for 1 month, then once daily at bedtime for one month, then twice a week at bedtime for three months, then once or twice a week as needed to control symptoms (Lorenz et al., 1998). Less potent steroids may be employed once the disease is under control. Newer therapeutic options such as topical tacrolimus ointment have shown some promise (Ruzicka et al., 2003). Topical testosterone is no longer recommended. For men with phimosis, circumcision is often required.
Melanocytic Nevi in Lichen Sclerosus A rare but potentially vexing problem arises when LS occurs in an area containing a melanocytic neoplasm. When this occurs, melanocytic nevi may clinically, dermoscopically, and microscopically mimic malignant melanoma. Because the disease process in LS affects both the epidermis with damage to the epidermal–dermal interface and the papillary dermis with sclerosis of the collagen bundles, the process affects melanocytic neoplasms in much the same way as partial biopsy or external trauma does: the nevus may take on characteristics of persistent (recurrent) nevi, so-called “pseudomelanoma” change. The criteria which apply to correctly identifying a persistent nevus over a persistent melanoma still apply in this scenario, though the background scarring in a typical persistent nevus is replaced by a background of the classic appearance of LS (pale-pink homogenization of collagen within the papillary dermis, a variable degree of vacuolar alteration of the epidermal–dermal junction with lymphocytes along the junction, and a compact cornified layer with slight to marked hyperplasia). The criteria for identifying nevi within an area of LS are as follows: crisp lateral demarcation of the epidermal component, limited pagetoid scatter, simultaneous presence of zones mimicking melanoma in situ, dermal fibrosis, and areas identifiable as melanocytic nevus with small, uniform and orderly melanocytes within the dermis beneath the area of papillary dermal sclerosus, absence of mitoses in dermal melanocytes, HMB-45 staining limited to epidermal melanocytes and those within the zone of sclerosus (not deeper melanocytes), and a MIB-1(Ki-67) labeling index of less than
10% (Carlson et al., 2002). Care must be taken to avoid diagnosis of these lesions as melanoma with regression. The small size of the process, usually less than 6 mm, is helpful in this regard (Zhou and Crowson, 2003).
Contact Leukoderma Depigmentation of the skin which may be difficult or impossible to distinguish from vitiligo may occur after contact with certain chemical compounds which are cytotoxic to melanocytes. These include monobenzyl ether of hydroquinone and phenolic compounds. History of exposure to these chemical agents is required for diagnosis. Biopsy shows loss of melanocytes and absence of melanin pigmentation within the epidermis as in vitiligo (Reitschel and Pine, 1995).
Leukoderma Syphiliticum Syphilis is a known cause of depigmentation of the skin since ancient times, though leukoderma syphiliticum is not observed frequently today. Leukoderma syphiliticum typically occurs in the skin following the resolution of classic papular lesions of secondary syphilis. The depigmentation classically persists throughout life. Rare cases of leukoderma syphiliticum have been described affecting only the genitalia. On routine microscopy, melanocytes are roughly normal in number and morphologic appearance. On electron microscopy, melanosomes are smaller and less melanized than in normal skin, and they are not distributed throughout the cell in a typical fashion, being more clustered within the cell body and less dispersed within the dendritic processes. Spirochetes are not detectable (Frithz et al., 1982).
Extramammary Paget Disease A rare cause of hypopigmented patches involving the genitalia is extramammary Paget disease. Usually this disease presents as velvety, erythematous or eroded plaques in the groin or anogenital area. Sometimes the plaques are hyperpigmented or, rarely, may present as hypopigmented macules alone or in conjunction with more classic-appearing lesions. Microscopically, there are pale, atypical cells within the epidermis in pagetoid array. These cells label with immunoperoxidase staining methods for carcinoembryonic antigen as well as low molecular-weight keratin (e.g., CAM 5.2). In the hypopigmented areas, melanin pigment is reduced or absent and there are papillary dermal melanophages in these areas. There may or may not be an associated internal malignancy, and appropriate clinical and radiological studies must be performed to exclude the possibility of associated malignancy in all cases (Kakinuma et al., 1994).
References Abdollahi, M., and M. Radfar. A review of drug-induced oral reactions. J. Contemp. Dent. Pract. 4:10–31, 2003. Ackerman, A. B., N. Chongchitnant, J. Sanchez, Y. Guo, B. Bennin, M. Reichel, and M. B. Randall. Histologic Diagnosis of Inflammatory Skin Diseases: An Algorithmic Method Based on Pattern Analysis, Second Edition. Baltimore: Williams & Wilkins, 2003.
1087
CHAPTER 56 Alkhateeb, A., P. R. Fain, A. Thody, D. C. Bennett, and R. A. Spritz. Epidemiology of vitiligo and associated autoimmune diseases in Caucasian probands and their families. Pigment Cell Res. 16: 208–214, 2003. Almas, K., and W. Sadig. Surgical treatment of melanin-pigmented gingiva: an esthetic approach. Indian J. Dent. Res. 13:70–73, 2002. Atherton, D. J., D. W. Pitcher, R. S. Wells, and D. M. MacDonald. A syndrome of various cutaneous pigmented lesions, myxoid neurofibromata and atrial myxoma: the NAME syndrome. Br. J. Dermatol. 103:421–429, 1980. Baltas, E., Z. Csoma, F. Ignacz, A. Dobozy, and L. Kemeny. Treatment of vitiligo with the 308-nm xenon chloride excimer laser. Arch. Dermatol. 138:1619–1620, 2002. Barnhill, R. L., L. S. Albert, S. K. Shama, M. A. Goldenhersh, A. R. Rhodes, and A. J. Sober. Genital lentiginosis: a clinical and histopathologic study. J. Am. Acad. Dermatol. 22:453–460, 1990. Bongiorno, M. R., and M. Arico. Primary malignant melanoma of the oral cavity: case report. Int. J. Dermatol. 41:178–181, 2002. Bork, K. Cutaneous Side Effects of Drugs. Philadelphia: W. B. Saunders, 1988, p. 422. Buchner, A., and L. S. Hansen. Pigmented nevi of the oral mucosa: a clinicopathologic study of 32 new cases and review of 75 cases from the literature. Part I. A clinicopathologic study of 32 new cases. Oral Surg. Oral Med. Oral Pathol. 48:131–142, 1979. Buchner, A., and L. S. Hansen. Amalgam pigmentation (amalgam tattoo) of the oral mucosa. A clinicopathologic study of 268 cases. Oral Surg. Oral Med. Oral Pathol. 49:139–147, 1980a. Buchner, A., and L. S. Hansen. Pigmented nevi of the oral mucosa: a clinicopathologic study of 32 new cases and review of 75 cases from the literature. Part II. Analysis of 107 cases. Oral Surg. Oral Med. Oral Pathol. 49:55–62, 1980b. Carlson, J. A., P. Lamb, J. Malfetano, R. A. Ambros, and M. C. Mihm., Jr. Clinicopathologic comparison of vulvar and extragenital lichen sclerosus: histologic variants, evolving lesions, and etiology of 141 cases. Mod. Pathol. 11:844–854, 1998. Carlson, J. A., X. C. Mu, A. Slominski, K. Weismann, A. N. Crowson, J. Malfetano, V. G. Prieto, and M. C. Mihm, Jr. Melanocytic proliferations associated with lichen sclerosus. Arch. Dermatol. 138:77–87, 2002. Champion, R. H., J. L. Burton, D. A. Burns, and S. M. Breathnach (eds). Rook/Wilkinson/Ebling Textbook of Dermatology. Malden, Massachusetts: Blackwell Science, 1998. Cicek, Y., and U. Ertas. The normal and pathological pigmentation of oral mucous membranes: a review. J. Contemp. Dent. Pract. 4:76–86, 2003. Clark, W. H., Jr., A. F. Hood, M. A. Tucker, and R. M. Jampel. Atypical melanocytic nevi of the genital type with a discussion of reciprocal parenchymal-stromal interactions in the biology of neoplasia. Hum. Pathol. 29(1 Suppl 1):S1–24, 1998. Clemmensen, O. J., and C. Fenger. Melanocytes in the anal canal epithelium. Histopathology 18:237–241, 1991. Cohen, L. M., and J. P. Callen. Oral and labial melanotic macules in a patient infected with human immunodeficiency virus. J. Am. Acad. Dermatol. 26:653–654, 1992. Conroy, E. A., M. O. Liranzo, J. McMahon, W. D. Steck, and R. J. Tuthill. Quinidine-induced pigmentation. Cutis. 57:425–427, 1996. Del Pozo, J., J. M. Pazos, and E. Fonseca. Lower lip hypertrophy secondary to port-wine stain: combined surgical and carbon dioxide laser treatment. Dermatol Surg. 30(2 Pt 1):211–214, 2004. Drago, F., and A. Rebora. The new herpesviruses: emerging pathogens of dermatological interest. Arch. Dermatol. 135:71–75, 1999. Dummet, C. O., and T. E. Bolden. Melanoblasts in gingival irritation. Mil. Med. 129:1191–1197, 1964. Dupre, A., and R. Viraben. Laugier's disease. Dermatologica. 181:183–186, 1990. Eisen, D., and J. J. Voorhees. Oral melanoma and other pigmented
1088
lesions of the oral cavity. J. Am. Acad. Dermatol. 24:527–537, 1991. English, J. C., 3rd, R. A. Laws, G. C. Keough, J. L. Wilde, J. P. Foley, and D. M. Elston. Dermatoses of the glans penis and prepuce. J. Am. Acad. Dermatol. 37:1–24, 1997. Erickson, Q. L., E. J. Faleski, M. K. Koops, and D. M. Elston. Addison’s disease: the potentially life-threatening tan. Cutis 66:72–74, 2000. Freedberg, I. M., A. Z. Eisen, K. Wolff, K. F. Austen, L. A. Goldsmith, S. I. Katz, and T. B. Fitzpatrick (eds). Fitzpatrick’s Dermatology in General Medicine. New York: McGraw-Hill, 1999. Frithz, A., Lagerholm, B., and T. Kaaman. Leukoderma syphiliticum: ultrastructural observations on melanocyte function. Acta Derm. Venereol. 62:521–525, 1982. Greenberg, R. G., and T. G. Berger. Nail and mucocutaneous hyperpigmentation with azidothymidine therapy. J. Am. Acad. Dermatol. 22(2 Pt 2):327–330, 1990. Gupta, S., K. Sandhu, A. Kanwar, and B. Kumar. Melanocyte transfer via epidermal grafts for vitiligo of labial mucosa. Dermatol Surg. 30:45–48, 2004. Hicks, M. J., and C. M. Flaitz. Oral mucosal melanoma: epidemiology and pathobiology. Oral Oncol. 36:152–169, 2000. Ho, K. K., Dervan, P., O’Loughlin, S., and F. C. Powell. Labial melanotic macule: a clinical, histopathologic, and ultrastructural study. J. Am. Acad. Dermatol. 28:33–39, 1993. Izquierdo, M. J., M. A. Pastor, L. Carrasco, C. Moreno, H. Kutzner, O. P. Sangueza, and L. Requena. Epithelioid blue naevus of the genital mucosa: report of four cases. Br. J. Dermatol. 145:496–501, 2001. Kakinuma, H., U. Iwasawa, N. Kurakata, and H. Suzuki. A case of extramammary Paget’s disease with depigmented macules as the sole manifestation. Br. J. Dermatol. 130:102–105, 1994. Kato, S., J. Takeyama, Y. Tanita, and K. Ebina. Ruby laser therapy for labial lentigines in Peutz-Jeghers syndrome. Eur. J. Pediatr. 157:622–624, 1998. Kenney, J. A., Jr. Vitiligo. Dermatol. Clin. 6:425–434, 1988. Kim, K. B., A. M. Sanguino, C. Hodges, N. E. Papadopoulos, O. Eton, L. H. Camacho, L. D. Broemeling, M. M. Johnson, M. T. Ballo, M. I. Ross, J. E. Gershenwald, J. E. Lee, P. F. Mansfield, V. G. Prieto, and A. Y. Bedikian. Biochemotherapy in patients with metastatic anorectal mucosal melanoma. Cancer 100:1478–1483, 2004. Lamey, P. J., F. Carmichael, and C. Scully. Oral pigmentation, Addison's disease and the results of screening for adrenocortical insufficiency. Br. Dent. J. 158:297–298, 1985. Lenane, P., and F. C. Powell. Oral pigmentation. J. Eur. Acad. Dermatol. Venereol. 14:448–465, 2000. Lepe, V., B. Moncada, J. P. Castanedo-Cazares, M. B. Torres-Alvarez, C. A. Ortiz, and A. B. Torres-Rubalcava. A double-blind randomized trial of 0.1% tacrolimus vs 0.05% clobetasol for the treatment of childhood vitiligo. Arch. Dermatol. 139:581–585, 2003. Lorenz, B., R. H. Kaufman, and S. K. Kutzner. Lichen sclerosus. Therapy with clobetasol propionate. J. Reprod. Med. 43:790–794, 1998. Maize, J. C. Mucosal melanosis. Dermatol. Clin. 6:283–293, 1988. Maize, J. C., and A. B. Ackerman. Pigmented Lesions of the Skin. Philadelphia: Lea & Febiger, 1987, p. 328. McKusick, V. A. Carney complex, type 1; CNC1. (3/20/2002) http://www. ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=160980, 1986a. McKusick, V. A. Hemochromatosis; HFE. (5/30/04) http://www.ncbi.nlm. nih.gov/entrez/dispomim.cgi?id=235200, 1986b. McKusick, V. A. LEOPARD syndrome. (8/16/2002) http://www.ncbi.nlm. nih.gov/entrez/dispomim.cgi?id=151100, 1986c. McKusick, V. A. Macrocephaly, multiple lipomas, and hemangiomata.
(4/19/2001) http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id= 153480, 1986d. McKusick, V. A. Peutz–Jeghers syndrome. (1/15/2004) http://www. ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=175200, 2004.
PIGMENTARY ABNORMALITIES AND DISCOLORATIONS OF THE MUCOUS MEMBRANES Metry, D. W., and A. A. Hebert. Benign cutaneous vascular tumors of infancy: when to worry, what to do. Arch. Dermatol. 136: 905–914, 2000. Moozar, K. L., C. S. Wong, and J. Couture. Anorectal malignant melanoma: treatment with surgery or radiation therapy, or both. Can. J. Surg. 46:345–349, 2003. Newland, J. R., D. P. Lynch, and N. G. Ordonez. Intraoral Kaposi’s sarcoma: a correlated light microscopic, altrastructural and immunohistochemical study. Oral Surg. Oral Med. Oral Pathol. 66:48–58, 1988. Nordlund, J. J., A. B. Lerner, I. M. Braverman, and J. S. McGuire. The multiple lentigines syndrome. Arch. Dermatol. 107:259–261, 1973. Pandolfino, T. L., S. Cotell, and R. Katta. Pigmented vulvar macules as a presenting feature of the Carney complex. Int. J. Dermatol. 40:728–730, 2001. Papadavid, E., and N. P. Walker. Q-switched Alexandrite laser in the treatment of pigmented macules in Laugier-Hunziker syndrome. J. Eur. Acad. Dermatol. Venereol. 15:468–469, 2001. Patel, R. M., J. R. Goldblum, and E. D. Hsi. Immunohistochemical detection of human herpes virus-8 latent nuclear antigen-1 is useful in the diagnosis of Kaposi sarcoma. Mod. Pathol. 17:456–460, 2004. Rapini, R. P., L. E. Golitz, R. O. Greer, Jr., E. A. Krekorian, and T. Poulson. Primary malignant melanoma of the oral cavity. A review of 177 cases. Cancer 55:1543–1551, 1985. Rees, J. R., F. G. Ross, and G. Keen. Lentiginosis and left atrial myxoma. Br. Heart J. 35:874–876, 1973. Reitschel, R. L., and J. W. Pine (eds). Fisher’s Contact Dermatitis. Baltimore: Williams & Wilkins, 1995. Rhodes, A. R., R. A. Silverman, T. J. Harrist, and A. R Perez-Atayde. Mucocutaneous lentigines, cardiomucocutaneous myxomas, and multiple blue nevi: the “LAMB” syndrome. J. Am. Acad. Dermatol. 10:72–82, 1984. Rock, B. Pigmented lesions of the vulva. Dermatol. Clin. 10:361–370, 1992. Rudolph, R. I. Vulvar melanosis. J. Am. Acad. Dermatol. 23 (5 Pt 2):982–984, 1990. Ruzicka, T., T. Assmann, and M. Lebwohl. Potential future dermatological indications for tacrolimus ointment. Eur. J. Dermatol. 13:331–342, 2003.
Scher, R. K., and C. R. Daniel. Nails: Therapy, Diagnosis, Surgery, 2nd ed. Philadelphia: W. B. Saunders Company, 1997:205–207. Sexton, F. M., and J. C. Maize. Melanotic macules and melanoacanthomas of the lip. A comparative study with census of the basal melanocyte population. Am. J. Dermatopathol. 9:438–444, 1987. Sison-Torre, E. Q., and A. B. Ackerman. Melanosis of the vulva. A clinical simulator of malignant melanoma. Am. J. Dermatopathol. 7 Suppl:51–60, 1985. Sontheimer, R. D., and T. T. Provost (eds). Cutaneous Manifestations of Rheumatic Diseases. Baltimore: William & Wilkins, 1996. Sterling, J. C., and J. B. Kurtz. In: Rook/Wilkinson/Ebling Textbook of Dermatology, vol. 2. R. H. Champion, J. L. Burton, D. A. Burns, and S. M. Breathnach (eds). Malden, Massachusetts: Blackwell Science, 1998, pp. 1063–1064. Tal, H. A novel cryosurgical technique for gingival depigmentation. J. Am. Acad. Dermatol. 24(2 Pt 1):292–293, 1991. Tal, H., Oegiesser, D., and M. Tal. Gingival depigmentation by erbium:YAG laser: clinical observations and patient responses. J. Periodontol. 74:1660–1667, 2003. Tomich, C. E., and S. L. Zunt. Melanoacanthosis (melanoacanthoma) of the oral mucosa. J. Dermatol. Surg. Oncol. 16:231–236, 1990. Umeda, M., H. Komatsubara, Y. Shibuya, S. Yokoo, and T. Komori. Premalignant melanocytic dysplasia and malignant melanoma of the oral mucosa. Oral Oncol. 38:714–722, 2002. Veraldi, S., S. Cavicchini, C. Benelli, and G. Gasparini. LaugierHunziker syndrome: a clinical, histopathologic, and ultrastructural study of four cases and review of the literature. J. Am. Acad. Dermatol. 25:632–636, 1991. Weedon, D. Skin Pathology, 2nd ed. Philadelphia: Churchill Livingstone, 2002a, p. 1009. Weedon, D. Skin Pathology, 2nd ed. Philadelphia: Churchill Livingstone, 2002b, p. 1003. Weedon, D. Skin Pathology, 2nd ed. Philadelphia: Churchill Livingstone, 2002c, p. 1007. Weiss, L. W., and A. S. Zelickson. Giant melanosomes in multiple lentigines syndrome. Arch. Dermatol. 113:491–494, 1977. Zhou, J. H., and A. N. Crowson. Pathologic quiz case: pigmented lesion on the mons pubis of a 17-year-old girl. Compound nevus with features of milk mine nevus. Arch. Pathol. Lab. Med. 127:e391–e392, 2003.
1089
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
7
Benign Neoplasms of Melanocytes
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
57
Common Benign Neoplasms of Melanocytes Sections Pigmented Spindle Cell Nevi Julie V. Schaffer and Jean L. Bolognia Speckled Lentiginous Nevus (Nevus Spilus) Julie V. Schaffer and Jean L. Bolognia Melanocytic (Nevocellular) Nevi and Their Biology Julie V. Schaffer and Jean L. Bolognia
Pigmented Spindle Cell Nevi Julie V. Schaffer and Jean L. Bolognia
Historical Background In 1975, Reed et al. first proposed that the pigmented spindle cell nevus was a benign melanocytic neoplasm distinct from the usual epithelioid and spindle cell (Spitz) nevus. Distinguishing features included its capacity to produce melanin and its growth in an expansive fashion rather than in an infiltrating pattern (Fig. 57.1) (Reed et al., 1975).
Synonyms Additional names for pigmented spindle cell nevus include pigmented spindle cell nevus of Reed (Cochran et al., 1993), pigmented spindle cell tumor (Ainsworth et al., 1979; Kolde and Vakilzadeh, 1987; Schubert, 1986), pigmented spindle cell tumor of Reed (Gartmann, 1981; Smith, 1983, 1987), Reed’s nevus (Abramovits and Gonzalez-Serva, 1993), Reed’s pigmented spindle cell nevus (Wistuba and Gonzalez, 1990), and pigmented spindle cell nevus of non-Spitz type (Christiansen et al., 1985).
1981; Kolde and Vakilzadeh, 1987; Requena and Sanchez Yus, 1990; Sagebiel et al., 1984; Sau et al., 1993; Schubert, 1986; Smith, 1987) [(Barnhill et al., 1991a) plexiform variant excluded] 184 (48%) were found in this location. The upper extremity represents the next most common site with 25% of pigmented spindle cell nevi occurring in this site (95/386). In one institution, the diagnosis of Spitz nevus was ten times more common than that of pigmented spindle cell nevus (Gartmann, 1981). However, in a retrospective analysis of 247 epithelioid and/or spindle cell nevi excised between 1974 and 1993 at the University of Milan (Dal Pozzo et al., 1997), 21% were pigmented spindle cell nevi, 50% were pigmented Spitz (epithelioid and spindle cell) nevi, and the remaining 29% were “nonpigmented” Spitz nevi. Approximately onehalf of the lesions in the first two groups were located on the lower extremities, whereas those in the third group favored the head and neck; the mean age of patients with pigmented lesions (n = 177, including the 52 pigmented spindle cell nevi) was 14 years, compared with 9 years for those with domeshaped, nonpigmented lesions (n = 70) (Dal Pozzo et al., 1997).
Clinical Presentation Epidemiology/Clinical Findings The vast majority of pigmented spindle cell nevi are acquired and in one study of 40 patients with such lesions, they were reportedly present for 1 month to 3 years with a mean of 9.7 months (Smith, 1987). A mean duration of 6 years was reported in a second series of 22 patients (Requena and Sanchez Yus, 1990). In the six largest series of patients to date (Barnhill et al., 1991a; Gartmann, 1981; Requena and Sanchez Yus, 1990; Sagebiel et al., 1984; Sau et al., 1993; Smith, 1987), these nevi were observed more commonly in women than in men (243 women/395 total) with a combined female : male ratio of 1.6:1. The age at diagnosis ranged from 2 to 60 years (Sagebiel et al., 1984; Sau et al., 1993), but the average age ranged from 16 to 25 years (Barnhill et al., 1991a; Requena and Sanchez Yus, 1990; Sagebiel et al., 1984; Sau et al., 1993; Smith, 1987). The lower extremity is the most common site for pigmented spindle cell nevi and in a total of 386 patients (Barnhill and Mihm, 1989; Gartmann,
The classic presentation for a pigmented clinical cell nevus is a single, darkly pigmented macule or papule on the lower extremity of a young female patient (Cochran et al., 1993; Requena and Sanchez Yus, 1990; Smith, 1987). These nevi can vary in size from 1 mm to 11 mm (Gartmann, 1981; Kolde and Vakilzadeh, 1987; Requena and Sanchez Yus, 1990), but are usually 3 mm to 6 mm in diameter (Requena and Sanchez Yus, 1990; Sau et al., 1984; Smith, 1987). There may be a history of fairly rapid growth (Ainsworth et al., 1979). Pigmented spindle cell nevi tend to be sharply demarcated from the normal surrounding skin (Requena and Sanchez Yus, 1990; Sagebiel et al., 1984; Smith, 1987), although occasionally a pigmented macular halo may be seen (Ainsworth et al., 1979). The well-defined border is a clinical reflection of circumscribed nests of melanocytes and a lack of “trailing off” of single melanocytes as is seen in atypical nevi. The color of pigmented spindle cell nevi can vary from dark brown to black to intense gray or blue (Reed et al., 1093
CHAPTER 57
Pigmented spindle cell nevus
1975; Sau et al., 1984) and their topography has been described as smooth and slightly dome-shaped (Requena and Sanchez Yus, 1990; Smith, 1987). A clinical diagnosis of cutaneous melanoma is fairly common given the dark brown to black color (Barnhill and Mihm, 1989; Requena and Sanchez Yus, 1990), and in two series, the clinical diagnosis of pigmented cell nevus was suspected in up to 10% of cases (Requena and Sanchez Yus, 1990; Smith, 1987). In addition to cutaneous lesions, a pigmented spindle cell nevus of the bulbar conjunctiva has been described, with a clinical differential diagnosis that included ocular melanoma (Seregard, 2000). Lastly, there is one report of agminated lesions (both Spitz and pigmented spindle cell nevi) on the plantar surface of the foot in a 12-year-old African-American girl (Abramovits and Gonzalez-Serva, 1993).
Associated Disorders None.
Histology
Spitz nevus
Melanoma Fig. 57.1. Schematic representation of the growth pattern and histologic features of pigmented spindle cell nevus, Spitz nevus, and melanoma. (Adapted from N. P. Smith. The pigmented spindle cell tumor of Reed: an underdiagnosed lesion. Sem. Diagn. Pathol. 4:75–87, 1987, with permission of the publisher.)
1094
Rather large and elongated compact nests of melanocytes are seen at the dermoepidermal junction and less often in the papillary dermis, overall demonstrating a plate-like architectural pattern (Fig. 57.2A; see also Fig. 57.1A) (Reed et al., 1975; Requena and Sanchez Yus, 1990). In one series of 40 pigmented spindle cell nevi, 18 (45%) were junctional nevi and 22 (55%) were compound nevi (Smith, 1987). It is unusual for the nevus cells to involve the reticular dermis. In one review of 91 cases, only seven had a depth of invasion greater than 0.6 mm (Sagebiel et al., 1984). The individual cells are spindle shaped and highly melanized (Fig. 57.2B and C) (Cochran et al., 1993). In typical pigmented spindle cell nevi, a symmetrical pattern of proliferation is observed (Smith, 1987) and the lateral demarcation is rather sharp (Requena and Sanchez Yus, 1990; Sau et al., 1993; Smith, 1987). Occasionally, a portion of the nevus will be composed of isolated single spindle cells at the dermoepidermal junction (Requena and Sanchez Yus, 1990). Junctional nests have been observed in the dermal portion of eccrine ducts as well as in the infundibulum of hair follicles (Requena and Sanchez Yus, 1990; Sagebiel et al., 1984; Sau et al., 1993; Smith, 1987). Of note, sparse upward growth of individual cells into the overlying epidermis was observed by Sagebiel et al. (1984) in 25 of their 91 cases (27%). Requena and Sanchez Yus (1990) described single cells or small nests in the overlying epidermis in 19 of 22 cases. However, they saw no extension of solitary melanocytes laterally beyond the body of the nevus. Pagetoid melanocytosis, defined as the upward discontinuous extension of melanocytes into the superficial epidermis, was observed by Haupt et al. (1995) in 20% (2/10) of the pigmented spindle cell nevi in their series. In contrast, several authors have stated that there is no pagetoid spread of single melanocytes in these lesions (Cochran et al., 1993; Reed et al., 1975). Cochran et al. (1993) believe that keratinocytes in overlying epidermis that contain abundant melanin may have an appearance similar to pagetoid cells. Multinucleated giant cells with small
COMMON BENIGN NEOPLASMS OF MELANOCYTES
Fig. 57.2. (A) Photomicrograph of pigmented spindle cell nevus demonstrating symmetry, expansile growth pattern, and superficial nature of the nevus (H&E, ¥40). (B, C) Proliferation of uniformappearing, spindle-shaped cells, some of which contain obvious melanin; melanophages are seen at the base of the lesion as well as admixed with the nevus cells (H&E, B, ¥100; C, ¥400).
uniform nuclei have been observed in up to half of the lesions (Sau et al., 1993). In typical pigmented cell nevi, pure collections of large epithelioid cells are not seen nor is pleomorphism or cytologic atypia (Cochran et al., 1993; Requena and Sanchez Yus, 1990; Sagebiel et al., 1984). For example, Sagebiel et al. (1984)
reported uniform nuclei in 97% of their cases with prominent nucleoli in 23%. Although atypical variants of pigmented spindle cell nevi with cytologic atypia and prominent lentiginous melanocytic hyperplasia have been described (Barnhill and Mihm, 1989; Barnhill et al., 1991a), some authors believe that such lesions are better classified as pigmented Spitz nevi (Requena and Sanchez Yus, 1990). In the compound pigmented spindle cell nevi, a decrease in cellular size and cytoplasm content, i.e., maturation, can be seen in the lower portions of the lesions (Barnhill and Mihm, 1989; Requena and Sanchez Yus, 1990; Sagebiel et al., 1984). The presence of typical mitotic figures has been noted by several groups of investigators, but their frequency has varied. In a series of 40 pigmented spindle cell nevi (Smith, 1987) more than one mitosis per 5 high power fields was seen in only four lesions (10%) whereas Sau (1993) reported an average of three mitoses per 10 high-power fields (n = 95). To date, no atypical mitotic figures have been observed (Guillen and Murphy, 1985; Sagebiel et al., 1984; Sau et al., 1993). Some degree of hyperplasia of the epidermis is observed frequently (Cochran et al., 1993; Requena and Sanchez Yus, 1990). Epidermal hyperplasia was observed in 92.5% (37 of 40) of the lesions in one series (Smith, 1987). Pigment is readily apparent in the nests of melanocytes and the keratinocytes of the surrounding epidermis (Wistuba and Gonzalez, 1990). In the darkly pigmented lesions, melanin is seen within macrophages in the papillary dermis as well as in the stratum corneum (Imber, 1990; Requena and Sanchez Yus, 1990). Celleno and Massi (2002) described a variant of junctional pigmented spindle cell nevus with particularly abundant melanophages resembling the “tumoral melanosis” that can be seen upon regression of a cutaneous melanoma. Eosinophilic globules (Kamino bodies) have been identified in pigmented spindle cell nevi and their frequency varies from 10% [4 of 40 (Smith, 1987)] to 32% [7 of 22 (Requena and Sanchez Yus, 1990)] to 80% [8/10 (Wistuba and Gonzalez, 1990)]. Occasionally, the Kamino bodies may be darkly pigmented (Requena and Sanchez Yus, 1990). Some authors state that a lymphoid infiltrate is unusual (Cochran et al., 1993) whereas others state that the majority of pigmented spindle cell nevus have an infiltrate of mononuclear cells at the base of the lesion (Requena and Sanchez Yus, 1990; Sagebiel et al., 1984; Sau et al., 1993; Smith, 1987).
Laboratory Findings and Investigations The measurement of 5-S-cysteinyl dopa levels in a variety of pigmented lesions has revealed a significant difference between pigmented spindle cell nevi and melanomas with levels of £50 ng/mg in pigmented spindle cell nevi and ≥100 ng/mg in melanomas (Takeuchi and Morishima, 1990). Additional information can be gained by staining histologic sections with silver to visualize nucleolar organizer regions. Pigmented spindle cell nevus have fewer nucleolar organizer regions and the majority are organized within well-defined nucleolar clusters (Evans et al., 1991). In contrast, the nucleolar organizer regions in melanomas are widely 1095
CHAPTER 57
dispersed within the nucleus and are often in an extranucleolar location. Several clinicians have advocated the use of epiluminescence microscopy to distinguish pigmented Spitz nevi from cutaneous melanoma. Clues to the diagnosis of pigmented Spitz nevus as opposed to melanoma include a monomorphous appearance, a regular pigment network, bizarre retiform depigmentation in the center of the lesion (i.e., a negative pigment network), a regular distribution of brown globules and black dots, and the lack of pseudopods or radial streaming (Pehamberger et al., 1987; Steiner et al., 1987, 1992). A superficial black network (corresponding to areas of pigmented parakeratosis) represents an additional dermoscopic feature that is seen in approximately 10% of pigmented Spitz nevi (Argenziano et al., 2001). Rubegni et al. (2002) used digital dermoscopic analysis to determine the most useful variables in differentiating pigmented Spitz nevi from cutaneous melanoma, and found that measurements of entropy, red color, and peripheral black areas as well as diameter tended to be higher in the latter lesions. Argenziano et al. (1999) further classified the dermoscopic patterns of pigmented Spitz nevi into three main groups: (1) a starburst pattern characterized by radial streaks on a background of diffuse gray-blue to black pigmentation (50%; particularly common in lesions with classic histologic features of pigmented spindle cell nevi); (2) a globular pattern demonstrating central brown to gray-blue pigmentation and a peripheral rim of large brown globules (25%); and (3) an atypical pattern with irregular pigmentation and structures indistinguishable from those seen in melanoma (25%). Evolution from a globular pattern to a starburst pattern over a period of months has been described in several pigmented Spitz nevi (Piccolo et al., 2003; Pizzichetta et al., 2002). One important pitfall in distinguishing pigmented Spitz nevi from melanomas via dermoscopy is the observation that melanomas occasionally exhibit the globular and starburst patterns (Argenziano et al., 1999). Nevertheless, in a study of 54 pigmented Spitz nevi, the use of dermoscopy improved the accuracy of clinical diagnosis from 56% to 93% (Steiner et al., 1992), and in another study of 26 Spitz nevi, observation via digital videomicroscopy increased clinical diagnostic accuracy from 15% to 58% (Pellacani et al., 2000). Dermoscopy thus represents a useful tool, helping to further characterize individual melanocytic lesions in the context of a thorough history and total cutaneous examination. A definitive diagnosis, however, requires histologic examination (Peris et al., 2002).
Criteria for Diagnosis Elongated compact nests of spindle shaped and heavily melanized melanocytes are seen at the dermoepidermal junction and less often in the papillary dermis with a tendency for neighboring nests to fuse (Reed et al., 1975; Requena and Sanchez Yus, 1990). The growth pattern is expansive as opposed to infiltrating (Reed et al., 1975). In typical pigmented spindle cell nevus, there are uniform nuclei, a uniform cytologic pattern, few if any large epithelioid cells, and no 1096
lateral pagetoid spread of single melanocytes (Reed et al., 1975). Atypical variants can have cellular atypia and prominent lentiginous melanocytic hyperplasia, but retain a symmetric and orderly growth pattern (Barnhill and Mihm, 1989).
Differential Diagnosis Clinically, the differential diagnosis includes atypical nevus and cutaneous melanoma while the major entities in the histologic differential diagnosis are spindle and epithelioid cell (Spitz) nevus and cutaneous melanoma. Although hyperplasia of the epidermis is seen in pigmented spindle cell nevus, it is not to the extent as in a Spitz nevus (Ainsworth et al., 1979; Reed et al., 1975). In addition, infiltration of the reticular dermis in an interstitial pattern is seen in Spitz nevi but not pigmented spindle cell nevi (Imber, 1990). Pigment production is usually more striking in a pigmented spindle cell nevus and substantial numbers of plump epithelioid cells are not seen except in atypical variants (Barnhill et al., 1991a). Pigmented spindle cell nevus can have eosinophilic globules (Kamino bodies), but there is rarely edema in the papillary dermis, a marked vascular proliferation, or a desmoplastic stroma (Gartmann, 1981; Requena and Sanchez Yus, 1990; Sau et al., 1993; Smith, 1987). Also, the cells within a pigmented spindle cell nevus are thought to be more uniform throughout the lesion than the cells of a Spitz nevus (Smith, 1987). However, there are pathologists who believe that the pigmented spindle cell nevus is simply a variant of the Spitz nevus (Echevarria and Ackerman, 1967; Sagebiel et al., 1984; Wistuba and Gonzalez, 1990). In comparison to atypical nevi, the epidermal and dermal components of typical pigmented spindle cell nevus are coterminous (Cochran et al., 1993) and these nevi lack a junctional “shoulder.” There are also more well-defined lateral margins and less stromal changes such as lamellar fibroplasia in pigmented spindle cell nevi (Guillen and Murphy, 1985; Sagebiel et al., 1984). The deep penetrating or plexiform spindle cell nevus is another benign pigmented lesion that is composed of pigmented spindle cells (Barnhill et al., 1991b; Cooper, 1992; Seab et al., 1989). However, as its names imply, the nevus cells extend into the deep reticular dermis and even the subcutis and, because the fascicles involve neurovascular structures and adnexae, a plexiform appearance is observed. In contrast to pigmented spindle cell nevus, cutaneous melanomas are usually asymmetric histologically and not sharply demarcated (Guillen and Murphy, 1985). Typical pigmented spindle cell nevus have no pleomorphism or cellular atypia whereas the atypical variants can have “uniform but worrisome hyperchromatic nuclei” (Reed et al., 1975). However, the cellular atypia is never as marked as in melanoma (Barnhill and Mihm, 1989), i.e., a wide range of nuclear changes is not observed (Reed et al., 1975). If a dermal component is present, maturation of the cells is observed in a pigmented spindle cell nevus as opposed to the complete absence of cytologic maturation at the base of a melanoma (Guillen and Murphy, 1985). Lateral extension of single melanocytes beyond the body of the nevus is characteristic of melanoma,
COMMON BENIGN NEOPLASMS OF MELANOCYTES
but not typical pigmented spindle cell nevus (Requena and Sanchez Yus, 1990). Regression and surface ulceration are also not characteristic features of pigmented spindle cell nevus (Sagebiel et al., 1984; Sau et al., 1993; Smith, 1987). One area of concern is the number of pigmented spindle cell nevi that have been diagnosed as melanoma by pathologists, e.g., greater than 43% (10/23) in one series (Smith, 1987), 50% (5/10) in a second (Wistuba and Gonzalez, 1990), and 27% (23/85) in a third (Sau et al., 1993). The controversial form of cutaneous melanoma known as minimal deviation melanoma has a pigmented spindle cell variant that shares some features with pigmented spindle cell nevus including a monotonous and uniform proliferation of melanocytes, but in this type of minimal deviation melanoma, the tumors are deeper, there is an absence of cellular maturation, and numerous mitoses may be seen (Mérot and Mihm, 1985; Reed et al., 1975). In the spindle cell variants of melanoma, e.g., desmoplastic melanoma, a proliferation of atypical spindle cells is seen in the dermis, but the pattern is infiltrative and is often composed of single cells (Smith, 1987). Lastly, Reed (1985) believes that there is a malignant counterpart to the pigmented spindle cell tumor.
Pathogenesis Unknown.
Animal Models None.
Treatment Given their dark color and frequent location on the lower extremities of women, biopsies of pigmented spindle cell nevus are obtained routinely. However, the clinician must decide whether the entire lesion should be removed surgically. One argument for complete local excision is the need for a thorough histologic examination of the lesion given the number of malignant tumors with spindle cell differentiation (Guillen and Murphy, 1985). Dellon and Farmer (1988) recommended margins of 3 mm to 5 mm of adjacent skin to allow histologic evaluation of the transition zone of normal skin to nevus and to include the few lesions with indistinct borders. Currently, the general consensus is to recommend complete excision (Sau et al., 1993).
Prognosis The pigmented spindle cell nevus is considered a benign neoplasm of melanocytes (Requena and Sanchez Yus, 1990) and, to date, there have been no reports of the development of metastases or a significant local recurrence rate (Guillen and Murphy, 1985). Sau et al. (1993) reported no local recurrences or distant spread in 57 patients followed for an average of 6 years whereas Smith (1987) and Sagebiel et al. (1984) had the same experience with 30 patients followed for a mean of 3 years and 38 patients followed an average of 14 months, respectively. Even in 15 patients (9 of whom had atypical pigmented spindle cell nevus) followed for a mean of 8.8 years,
there were no recurrences (Barnhill et al., 1991a). However, the fact that the majority of lesions were completely excised does influence these results. To date, pigmented spindle cell nevus have not been associated with an increased incidence of a personal or family history of melanoma or the presence of atypical nevi (Barnhill et al., 1991a; Smith, 1987).
References Abramovits, W., and A. Gonzalez-Serva. Multiple agminated pigmented Spitz nevi (mimicking acral lentiginous malignant melanoma and dysplastic nevus) in an African-American girl. Int. J. Dermatol. 32:280–285, 1993. Ainsworth, A. M., R. Folberg, R. J. Reed, and W. H. Clark Jr. Melanocytic nevi, melanocytomas, melanocytic dysplasias and uncommon forms of melanoma. In: Human Malignant Melanoma, W. H. Clark Jr., L. I. Goldman, and M. J. Mastrangelo (eds). New York: Grune and Stratton, 1979, pp. 179–182. Argenzaino, G., M. Scalvenzi, S. Staibano, B. Brunetti, D. Piccolo, M. Delfino, G. de Rosa, and H. P. Soyer. Dermatoscopic pitfalls in differentiating pigmented Spitz naevi from cutaneous melanoma. Br. J. Dermatol. 141:788–793, 1999. Argenziano, G., H. P. Soyer, G. Ferrara, D. Piccolo, R. HofmannWellenhof, K. Peris, S. Staibano, and S. Chimenti. Superficial black network: an additional dermoscopic clue for the diagnosis of pigmented spindle and/or epithelioid cell nevus. Dermatology 203:333–335, 2001. Barnhill, R. L., and M. C. Mihm Jr. Pigmented spindle cell naevus and its variants: distinction from melanoma. Br. J. Dermatol. 121:717– 726, 1989. Barnhill, R. L., M. A. Barnhill, M. Berwick, and M. C. Mihm Jr. The histologic spectrum of pigmented spindle cell nevus: a review of 120 cases with emphasis on atypical variants. Hum. Pathol. 22:52–58, 1991a. Barnhill, R. L., M. C. Mihm Jr., and C. M. Magro. Plexiform spindle cell naevus: a distinctive variant of plexiform melanocytic naevus. Histopathology 18:243–247, 1991b. Celleno, L., and G. Massi. A variant of junctional naevus of epithelioid and spindle cell type rich in melanophages. Acta Dermatol. Venereol. 82:456–459, 2002. Christiansen, P., S. Oster, and H. Sogaard. Pigmented spindle cell nevus of non-Spitz type. Differential diagnosis from malignant melanoma. Ugeskr. Laeger 147:3910–3911, 1985. Cochran, A. J., C. Bailly, P. Eberhard, and D. Dolbeau. Nevi, other than dysplastic and Spitz nevi. Semin. Pathol. 10:3–17, 1993. Cooper, P. H. Deep penetrating (plexiform spindle cell) nevus. J. Cutan. Pathol. 19:172–180, 1992. Dal Pozzo, V., C. Benelli, L. Restano, R. Gianotti, and B.M. Cesana. Clinical review of 247 case records of Spitz nevus (epithelioid cell and/or spindle cell nevus). Dermatology 194:20–25, 1997. Dellon, A. L., and E. R. Farmer. Pigmented Spitz nevus in an adult. Ann. Plast. Surg. 20:128–132, 1988. Echevarria, R., and L. V. Ackerman. Spindle and epithelioid cell nevi in the adult: clinicopathologic report of 26 cases. Cancer 20:175– 189, 1967. Evans, A. T., J. M. Orrell, and A. Grant. Re-evaluating silver-stained nucleolar organizer regions (AgNORs) in problematic cutaneous melanocytic lesions: A study with quantitation and pattern analysis. J. Pathol. 165:61–67, 1991. Gartmann, H. Der pigmentierte Spindelzellentumor (PSCT). Z. Hautkrankh. 56:862–876, 1981. Guillen, F. J., and G. F. Murphy. Capsule dermatopathology: Nevomelanocytic lesions with spindle cell differentiation. J. Dermatol. Surg. Oncol. 11:225–230, 1985. Haupt, H. M., and J. B. Stem. Pagetoid melanocytosis; Histologic features in benign and malignant lesions. Am. J. Surg. Pathol. 19:792–797, 1995.
1097
CHAPTER 57 Imber, M. J. Benign cutaneous lesions potentially misdiagnosed as malignant neoplasms. Semin. Diagn. Pathol. 7:139–145, 1990. Kolde, G., and F. Vakilzadeh. Der pigmentierte Spindelzellentumor. Hautarzt 38:743–745, 1987. Mérot, Y., and M. C. Mihm Jr. Aspect inhabituel et méconnu du mélanome malin cutané: Le mélanome malin a déviation minime. Etude rétrospective de 45 cas. Ann. Dermatol. Venereol. 112:325–336, 1985. Pehamberger, H., A. Steiner, and K. Wolff. In vivo epiluminescence microscopy of pigmented skin lesions. I. Pattern analysis of pigmented skin lesions. J. Am. Acad. Dermatol. 17:571–583, 1987. Pellacani, G., A. M. Cesinaro, and S. Seidenari. Morphological features of Spitz naevus as observed by digital videomicroscopy. Acta Dermatol. Venereol. 80:117–121, 2000. Peris, K., A. Ferrari, G. Argenziano, H. P. Soyer, and S. Chimenti. Dermoscopic classification of Spitz/Reed nevi. Clin. Dermatol. 20:259–262, 2002. Piccolo, D., A. Ferrari, and K. Peris. Sequential dermoscopic evolution of pigmented Spitz nevus in childhood. J. Am. Acad. Dermatol. 49:556–558, 2003. Pizzichetta, M. A., G. Argenziano, G. Grandi, C. de Giacomi, G. Trevisan, and H. P. Soyer. Morphologic changes of a pigmented Spitz nevus assessed by dermoscopy. J. Am. Acad. Dermatol. 47:137–139, 2002. Reed, R. J. The histological variance of malignant melanoma: The interrelationship of histological subtype, neoplastic progression, and biological behaviour. Pathology 17:301–319, 1985. Reed, R. J., H. Ichinose, W. H. Clark, and M. C. Mihm Jr. Common and uncommon melanocytic nevi and borderline melanomas. Semin. Oncol. 2:119–147, 1975. Requena, L., and E. Sanchez Yus. Pigmented spindle cell naevus. Br. J. Dermatol. 123:757–763, 1990. Rubegni, P., A. Ferrari, G. Cevenini, D. Piccolo, M. Burroni, R. Perotti, K. Peris, P. Taddeucci, M. Biagioli, G. Dell’Eva, S. Chimenti, and L. Andreassi. Differentiation between pigmented Spitz naevus and melanoma by digital dermoscopy and stepwise logistic discriminant analysis. Melanoma Res. 11:37–44, 2001. Sagebiel, R. W., E. K. Chinn, and B. M. Egbert. Pigmented spindle cell nevus: Clinical and histologic review of 90 cases. Am. J. Surg. Pathol. 8:645–653, 1984. Sau, P., J. H. Graham, and E. B. Helwig. Pigmented spindle cell nevus. Arch. Dermatol. 120:1615, 1984. Sau, P., J. H. Graham, and E. B. Helwig. Pigmented spindle cell nevus: a clinicopathologic analysis of ninety-five cases. J. Am. Acad. Dermatol. 28:565–571, 1993. Schubert, E. Der pigmentierte Spindelzelltumor (PSCT). Z. Hautkrankh. 61:827–829, 1986. Seab, J. A., Jr., J. H. Graham, and E. B. Helwig. Deep penetrating nevus. Am. J. Surg. Pathol. 13:39–44, 1989. Seregard, S. Pigmented spindle cell naevus of Reed presenting in the conjunctiva. Acta Ophthalmol. Scand. 78:104–106, 2000. Smith, N. P. The pigmented spindle cell tumour of Reed — an underrecognized lesion. Br. J. Dermatol. 109:39, 1983. Smith, N. P. The pigmented spindle cell tumor of Reed: an under diagnosed lesion. Semin. Diagn. Pathol. 4:75–87, 1987. Steiner, A., H. Pehamberger, and K. Wolff. In vivo epiluminescence microscopy of pigmented skin lesions. II. Diagnosis of small pigmented skin lesions and early detection of malignant melanoma. J. Am. Acad. Dermatol. 17:584–591, 1987. Steiner, A., H. Pehamberger, M. Binder, and K. Wolff. Pigmented Spitz nevi: improvement of the diagnostic accuracy by epiluminescence microscopy. J. Am. Acad. Dermatol. 27:697–701, 1992. Takeuchi, M., and T. Morishima. Pigmented spindle cell nevus and pigmented Spitz nevus — clinical and histopathological study on pigmented Spitz nevus, and its differentiation from early melanoma by fluorescence method and measurement of 5-S-CD level in the
1098
lesion [ Japanese]. Nippon Hifuka Gakkai Zasshi 100:1153–1165, 1990. Wistuba, I., and S. Gonzalez. Eosinophilic globules in pigmented spindle cell nevus. Am. J. Dermatopathol. 12:268–271, 1990.
Speckled Lentiginous Nevus (Nevus Spilus) Julie V. Schaffer and Jean L. Bolognia
Historical Background For this particular pigmented lesion, there is a long history of disagreement regarding nomenclature, i.e., “speckled lentiginous nevus” versus nevus spilus. This controversy over terminology dates back to the use of the term “nevus spilus” in the late nineteenth and early twentieth centuries to describe a uniformly pigmented brown patch. Several writings from this period (Besnier et al., 1902; Bulkley, 1842; Duhring, 1883; Hyde and Montgomery, 1901; Kaposi, 1887) are frequently cited to support the argument that use of the term nevus spilus creates confusion (Altman and Banse, 1992; Misago et al., 1993; Pritchett and Pritchett, 1982; Stewart et al., 1978; Vion et al., 1985). These early references contain relatively nonspecific descriptions of the clinical characteristics of a nevus spilus, with no mention of superimposed, more darkly pigmented macules or papules. For example, Bulkley (1842) classified ephelis and nevus spilus as macules, his definition of a macule being a “permanent alteration of the color of the skin, either of its whole surface or some of it only, without elevation or desquamation.” Kaposi (1887) referred to a nevus spilus as a birthmark with a smooth, soft surface without any other skin changes, and Besnier et al. (1902) stated that the description of this lesion was completely confused with that of a lentigo. In 1952, Ito and Hamada reintroduced the term nevus spilus to refer to a hyperpigmented patch with superimposed darker macules. Biopsies were performed in 4 of 21 cases, and no nevus cells were seen (Ito and Hamada, 1952). However, the exact sites within the nevus spilus that were biopsied were not mentioned, and two of the cases may have represented Becker melanosis. Benedict et al. (1968) subsequently defined a nevus spilus as a single light brown patch with a diameter of 1 cm to 20 cm and a clinical appearance similar to that of a caféau-lait macule. Two years later, Cohen et al. (1970) reported 17 patients with the clinical diagnosis of nevus spilus whose lesions were similar in appearance to those described by Ito and Hamada (1952); however, biopsy specimens from both the background hyperpigmentation and the more darkly pigmented speckles contained nevus cells. Then, in the mid1970s, the term “speckled lentiginous nevus” first appeared as a name for pigmented lesions with a background of macular hyperpigmentation containing smaller, darker macules and/or papules (Stewart et al., 1978). It is easy to understand from this historical account why there has been so much confusion over terminology. In a review of MEDLINE citations over the past decade
COMMON BENIGN NEOPLASMS OF MELANOCYTES
(1994–2004), the two terms have been used in a ratio of approximately 1.5 nevus spilus to 1 speckled lentiginous nevus. Proponents of the term nevus spilus point to the Greek root spilos, the translation of which is “spot” (Dorland, 1994; Leider and Rosenblum, 1976), and interpret this word to mean or imply “spotty” (Cohen et al., 1970; Rhodes and Mihm, 1990). The authors and others, however, favor the term speckled lentiginous nevus not only from a historical perspective or because of the correct translation of spilos, but as a means of emphasizing the biologic behavior of this pigmented lesion. A speckled lentiginous nevus can be likened to a melanocytic garden within which a variety of lesions can grow, from junctional nevi to blue nevi to melanoma (Cramer, 2001; Schaffer et al., 2001a). Unfortunately, as recently as 15–20 years ago, a nevus spilus was incorrectly viewed as a lesion with no malignant potential (Rhodes, 1983), and the histologic features of the spots of a nevus spilus are still often described simply as those of a junctional nevus (Elder and Elenitsas, 1997; Kurban et al., 1992). Several authors have pointed out that use of the term speckled lentiginous nevus serves to broaden both the clinical and histologic spectrum (Aloi et al., 1995; Altman and Banse, 1992; Misago et al., 1993; Schaffer et al., 2001a). Lastly, the practice of referring to a smaller lesion as a nevus spilus and a larger lesion as a speckled lentiginous nevus only serves to add to the confusion.
Synonyms Although the majority of cases are described as either speckled lentiginous nevus (Aloi et al., 1995; Betti et al., 1994, 1997a, b, 1999; Ceylan et al., 2003; Crosti and Betti, 1994; Guiglia and Prendiville, 1991; Hofmann et al., 1998; Langenbach et al., 1998a; Marchesi et al., 1993; Misago et al., 1993; Nguyen et al., 1982; Paik et al., 1996; Schaffer et al., 2001a; Stewart et al., 1978; Torrelo et al., 2003a; Vásquez-Doval et al., 1995; Wagner and Cottel, 1989) or nevus spilus (Bielsa et al., 1998; Borrego et al., 1994; Breitkopf et al., 1996; Breuillard et al., 1991; Cohen et al., 1970; Cox et al., 1997; Cramer, 1977; Falo et al., 1994; Frenk et al., 1975; Gerardo et al., 2001; Gold et al., 1999; Grevelink et al., 1997; Hori et al., 1978; Hwang et al., 1997; Ishibashi et al., 1990; Keine et al., 1995; Konrad et al., 1974; Kopf et al., 1985a, b; Krahn et al., 1992; Langenbach et al., 1998b; Mang et al., 2003; Page and Windhorst, 1972; Park et al., 1999; Roma et al., 2000; Rütten and Goos, 1990; Sigg and Pelloni, 1989; Sigg et al., 1990; Skogh and Moi, 1978; Takahashi, 1976; Toppe and Haas, 1988; Weinberg et al., 1998; Welch and James, 1993; Zvulunov, 1995), when the lesion is linear or covers large areas of the body, the terms zosteriform speckled lentiginous nevus (Altman and Banse, 1992; Bolognia, 1991; Pritchett and Pritchett, 1982), speckled zosteriform lentiginous nevus (Simoes, 1981; Stern et al., 1990), zosteriform lentiginous nevus (Johnson, 1973; Matsudo et al., 1973; Ruth et al., 1980; van der Horst and Dirksen, 1981; Vignale et al., 1994), and mosaic speckled lentiginous nevus (Nguyen et al., 1982) have been used. Additional synonyms are nevus on nevus (Guillot
et al., 1991) which is also known as naevus sur naevus (Brufau et al., 1986; Hidano, 1986; Vion et al., 1985) or nevus sobre nevus (Piñol-Aguadé and Peyri Rey, 1973), speckled nevus spilus (Vion et al., 1985), speckled nevus (Nguyen et al., 1982), segmental nevus spilus (Moreno-Arias et al., 2001), nevus spilus zoniforme (Ito and Hamada, 1952), nevus spilus en nappe (Ito and Hamada, 1952), and spotty nevus (Vion et al., 1985). The term dysplastic nevus spilus (Grinspan et al., 1997; Kurban et al., 1992; Rhodes and Mihm, 1990) has been used to describe a speckled lentiginous nevus in which the intraepidermal melanocytes in the speckles have cellular atypia and pleomorphism.
Epidemiology/Clinical Findings In clinical studies involving children and adults, speckled lentiginous nevi have been shown to have a prevalence in the general population similar to that of congenital melanocytic nevi. For example, in a series of 601 consecutive patients who were primarily adults, 2.3% were noted to have a speckled lentiginous nevus >1.5 cm in diameter on total body skin examination (Kopf et al., 1985b). The prevalence rates of speckled lentiginous nevi in three series of children aged 8–16 years (n = 939), 6–15 years (n = 1123), and 6–18 years (n = 1592) were 2.1% (Sigg et al., 1990), 1.8% (Rivers et al., 1995), and 1.3% (McLean and Gallagher, 1995), respectively. However, much lower prevalence rates have been reported in series of newborns. Rhodes and Mihm (1990) observed that only 2/1118 newborns had a clinically evident speckled lentiginous nevus, and no speckled lentiginous nevi were noted in two studies assessing birthmarks in 4641 (Alper and Holmes, 1983) and 1058 (Walton et al., 1976) newborns. Based on these findings, Rhodes and Mihm (1990) concluded that speckled lentiginous nevi are acquired lesions. In contrast, of 26 patients described in four series (Brufau et al., 1986; Cohen et al., 1970; Stewart et al., 1978; Vion et al., 1985), 21 (81%) had lesions that were present at birth or noted during early infancy; these series included small lesions, with at least 40% measuring 9 mm (Hofmann-Wellenhof et al., 1994), but they are often 2 mm to 3 mm in diameter. It is also important to remember that different types of nevi may appear at different points in time. For example, at age 3 years, one child was described as having multiple Spitz nevi within his speckled lentiginous nevus (Prose et al., 1983), but when examined at age 13 years, he had multiple blue and compound nevi within the lesion (personal communication, S. J. Orlow). Occasionally, papules or plaques with the clinical appearance of classic congenital melanocytic nevi may be found admixed with or adjacent to areas with the appearance of a typical speckled lentiginous nevus (i.e., “hybrid” lesions) (Langenbach et al., 1998b; Mang et al., 2003; Saraswat et al., 2003; Schaffer et al., 2001a; Torrelo et al., 2003a) (Fig. 57.6); in such cases, satellite congenital melanocytic nevi may be present (Schaffer et al., 2001a; Torrelo et al., 2003a). Areas with an increased number of terminal hairs have been described within both hybrid (see Fig. 57.6) and conventional speckled lentiginous nevi (Grinspan et al., 1997; Langenbach et al., 1998b; Mang et al., 2003; Prose et al., 1983; Saraswat et al., 2003; Schaffer et al., 2001a). The background hyperpigmentation can range in size from 1 cm to >60 cm in diameter (Crosti and Betti, 1994), but is often 3 cm to 6 cm in diameter (Stewart et al., 1978). In one study of 14 patients with nevus spilus >1.5 cm in diameter, the average size was 4.3 ± 3.5 cm (Kopf et al., 1985b). The color of the background pigmentation can vary from light tan (Stewart et al., 1978) to dark brown, and may darken following sun exposure (Falo et al., 1994; Matsudo et al., 1973). When the background pigmentation is a light tan color, clustering of the speckles may be overlooked (Bolognia, 1991) or a misdiagnosis made, such as agminated nevi or partial unilateral lentiginosis (Figs 57.7 and 57.8). Most commonly, the shape of a speckled lentiginous nevus is oval, but it can be blocklike in configuration with a sharp demarcation at the midline as well as linear. The latter have been described as zosteriform (Altman and Banse, 1992; Bolognia, 1991; Johnson, 1973; Matsudo et al., 1973; Pritchett and Pritchett, 1982; Ruth et al., 1980; Simoes, 1981; Stern et al., 1990; Stewart et al., 1978; van der Horst and Dirksen, 1981) and the linear lesions may follow the lines of Blaschko (Bolognia et al., 1994; Langenbach et al., 1998b; Welch and James, 1993) (Fig. 57.9). Extensive areas of the
COMMON BENIGN NEOPLASMS OF MELANOCYTES
Fig. 57.3. The background hyperpigmentation in this speckled lentiginous nevus was present since early infancy. A biopsy specimen of the largest “speckle” showed a pigmented dermal nevus.
Fig. 57.4. A speckled lentiginous nevus in which the largest erythematous papule had the histologic features of a Spitz nevus. (Courtesy of Yale Residents’ Slide Collection.)
Fig. 57.5. An extensive speckled lentiginous nevus in which junctional, compound, and Spitz nevi developed. (Courtesy of New York University Department of Dermatology Slide Collection.)
Fig. 57.6. Hybrid speckled lentiginous nevus in which plaques with the appearance of classic congenital melanocytic nevi are admixed with smaller macules and papules, all within a tan background patch. Note the areas with an increased density of terminal hairs.
body can be involved in these cases (Betti et al., 1994; Crosti and Betti, 1994; Davis and Shaw, 1964; Hofmann et al., 1998; Nguyen et al., 1982; Tadini et al., 1998; Torrelo et al., 2003a; Welch and James, 1993). Lastly, scleral pigmentation similar to that seen in nevus of Ota can occur when lesions containing blue nevi are located in the periocular area (Brufau et al., 1986; Hofmann et al., 1998), and a divided form of speckled lentiginous nevus that involved both the upper and lower eyelids has been described (Sato et al., 1979). This latter phenomenon reflects the probable timing of nevus formation during embryonic development, occurring after eyelid fusion in the eighth to ninth week of gestation but before eyelid reopening in the sixth month of gestation.
Associated Disorders There have been at least 22 reports of cutaneous melanoma developing within a speckled lentiginous nevus (Bolognia, 1991; Borrego et al., 1994; Breitkopf et al., 1996; Breuillard and Duthoit, 1991; Brufau et al., 1986; Cox et al., 1997; Grinspan et al., 1997; Guillot et al., 1991; Kopf et al., 1985a; Krahn et al., 1992; Kurban et al., 1992; Perkinson, 1957; Rhodes and Mihm, 1990; Rütten and Goos, 1990; Stern et al., 1990; Tadini et al., 1998; Vásquez-Doval et al., 1995; Vignale et al., 1994; Vion et al., 1985; Wagner and Cottel, 1989; Weinberg et al., 1998) (Fig. 57.10). These melanomas were diagnosed at a mean age of 52 years (range 25–79 years), and two patients also fulfilled the clinical criteria for neurofibromatosis type 1 (NF-1) (Perkinson, 1957; Rütten and Goos, 1990). In a few cases, the melanomas have been fatal (Bolognia, 1991; Brufau et al., 1986; Stern et al., 1990; Weinberg et al., 1998) and in one, there were two separate primaries (Krahn et al., 1992). The background speckled lentiginous nevi varied in size from 3 cm in diameter (Wagner and Cottel, 1989) to extensive zosteriform lesions (Bolognia, 1101
CHAPTER 57
Fig. 57.8. A subtle speckled lentiginous nevus that might be overlooked by the clinician.
Fig. 57.7. A. Although the initial clinical impression was agminated nevi, Wood’s lamp examination demonstrated background hyperpigmentation and pointed to the diagnosis of speckled lentiginous nevus; the lesion had been present since birth. B. Agminated compound nevi arising on a background of normally pigmented skin even under Wood’s lamp examination.
1991; Borrego et al., 1994; Guillot et al., 1991; Stern et al., 1990; Tadini et al., 1998), and some had speckles with atypical cytologic features (Bolognia, 1991; Grinspan et al., 1997; Kurban et al., 1992; Rhodes and Mihm, 1990). It has yet to be determined whether the surface area of the speckled lentiginous nevus, the number or type of superimposed nevi, or the presence of atypical cytologic features in the speckles correlates with the risk of developing cutaneous melanoma. Recently, the level of concern regarding speckled lentiginous nevi has become similar to that assigned to classic congenital 1102
Fig. 57.9. An extensive unilateral speckled lentiginous nevus with midline demarcation; note that the upper edge of the nevus follows the lines of Blaschko.
COMMON BENIGN NEOPLASMS OF MELANOCYTES
Fig. 57.10. Speckled lentiginous nevus that extends from the midline of the back (A) onto the left upper arm within the lines of Blaschko (B). The scar from the previous excision of the primary melanoma is seen at the base of the neck (A). A histologic section from one of the atypical nevi within the speckled nevus demonstrates lentiginous hyperplasia of the rete ridges, proliferation of atypical nevus cells, melanophages, and a superficial perivascular infiltrate (C). From Bolognia, J.L. Fatal melanoma arising in a zosteriform speckled lentiginous nevus. Arch. Dermatol. 1991; 127:1240–1241, copyright 1991, American Medical Association.
nevi. From (1992) suggested that speckled lentiginous nevi may actually present a greater risk, noting that of more than 2000 melanomas seen at her pigmented lesion clinic during a 15-year period, more arose from speckled lentiginous nevi (n = 3) than from large classic congenital melanocytic nevi (n = 1). In a study of 105 patients with melanoma and 601 controls, the prevalence of speckled lentiginous nevi >1.5 cm in diameter was not significantly higher in the melanoma group (4.8%) compared with the control group (2.3%) (Kopf et al., 1985a). Based upon the cutaneous findings, there are four major categories within the syndrome complex known as phako-
matosis pigmentovascularis (PPV) (Hasegawa and Yasuhara, 1985): type I, nevus flammeus and epidermal nevus; type II, nevus flammeus and dermal melanocytosis (nevus of Ota, nevus of Ito or aberrant Mongolian spots), with or without nevus anemicus; type III, nevus flammeus and nevus spilus, with or without nevus anemicus; and type IV, nevus flammeus, dermal melanocytosis, and nevus spilus, with or without nevus anemicus. More recently, a fifth category (type V) consisting of cutis marmorata telangiectatica congenita (CMTC) and dermal melanocytosis was proposed (Enjolras and Mulliken, 2000; Torrelo et al., 2003b); a patient with both CMTC and a nevus spilus has also been described (Kudo et al., 1986). 1103
CHAPTER 57
Patients with a nevus spilus, nevus anemicus, and primary lymphedema either with (Steijlen and Kuiper, 1990) or without (Bielsa et al., 1998) an associated capillary malformation have been reported; Bielsa et al. suggested that lymphatic malformations be included in the spectrum of vascular findings in PPV. Each of the PPV categories is subdivided into either cutaneous disease only (a) or cutaneous plus systemic disease (b). Signs and symptoms of the Sturge–Weber syndrome, Klippel–Trenaunay syndrome, and oculodermal melanosis can be seen in the latter group (Guiglia and Prendiville, 1991; Hasegawa and Yasuhara, 1985; Libow, 1993; Sawada et al., 1990; Sigg and Pelloni, 1989; Tsuruta et al., 1999). However, given the confusion over terminology, it should come as no surprise that in at least three reports of PPV, the “nevus spilus” was an extensive, uniformly pigmented patch without nevus cells (Hasegawa and Yasuhara, 1985; Sawada et al., 1990; Tsuruta et al., 1999), while in other reports, the lesions were speckled nevi (Guiglia and Prendiville, 1991; Prigent et al., 1991; Happle and Steijlen, 1989; Libow, 1993; Sigg and Pelloni, 1989; Zahorcsek et al., 1988). In 1996, Happle et al. coined the term “phakomatosis pigmentokeratotica” for a specific “twin nevus” syndrome in which a speckled lentiginous nevus (typically distributed in a “checkerboard” pattern) is associated with an organoid nevus with sebaceous differentiation (most often arranged in a linear pattern following the Blaschko lines); extracutaneous features can include musculoskeletal and neurologic anomalies such as hemiatrophy with muscular weakness, scoliosis, segmental dysesthesia and/or hyperhidrosis, mild mental retardation, and seizures (Boente et al., 2000; Descamps et al., 2000; Hermes et al., 1997; Hill et al., 2003; Kinoshita et al., 2003; Langenbach et al., 1998a; Saraswat et al., 2003; Tadini et al., 1998; Torrelo and Zambrano, 1998). At least three of the patients reported to date had organoid nevus-associated hypophosphatemic vitamin D-resistant rickets (Goldblum and Headington, 1993; Saraswat et al., 2003; Tadini et al., 1998). Several cases that fit the definition of phakomatosis pigmentokeratotica had been previously reported as epidermal or sebaceous nevus syndrome (Goldberg et al., 1987; Goldblum and Headington, 1993; Kopf and Bart, 1980; Misago et al., 1994; Stein et al., 1972; Wollenberg et al., 2002), Feuerstein– Mims neuroectodermal syndrome (Wauschkuhn and Rohde, 1971), and “nevus on nevus” (Brufau et al., 1986; PiñolAguadé and Peyri Rey, 1973). More recently, Happle (2002) defined the “speckled lentiginous nevus syndrome” as the association of this skin lesion with ipsilateral sensory and/or motor neuropathy (Holder et al., 1994; Piqué et al., 1995), spinal muscular atrophy (Hofmann et al., 1998), or muscular hypertrophy (Brufau et al., 1986). Of note, two of these cases were originally reported as partial unilateral lentiginosis, one with clinically apparent background hyperpigmentation more consistent with a diagnosis of speckled lentiginous nevus (Piqué et al., 1995) and the other with no obvious background hyperpigmentation, but multiple blue nevi as well as lentigines within a discrete area on the affected limb (Hofmann et al., 1104
1998). Happle (2002) proposed that this complex of neurologic and musculoskeletal abnormalities, distinct from the findings observed in association with organoid nevi in Schimmelpenning syndrome, is specific to the speckled lentiginous nevus “half” of phakomatosis pigmentokeratotica. Skin lesions with the clinical appearance of zosteriform speckled lentiginous nevi represent the cutaneous findings in the “FACES” syndrome, which is characterized by facial features (e.g., bifid tip of the nose), anorexia, cachexia, eye and skin anomalies (Friedman and Goodman, 1984). This syndrome was described in a mother and two daughters from a family with consanguinity. Additional clinical features included a high-pitched, nasal voice, severe muscle wasting, and musculoskeletal abnormalities. Of note, the skin lesions first appeared at age 7 years in the proband. There is a report of both ichthyosis (presumably X-linked) and a congenital speckled lentiginous nevus in a young man and his maternal grandfather (Crosti and Betti, 1994). Other males (maternal first cousins) in the family had only ichthyosis. In addition, a girl with phakomatosis pigmentokeratotica was noted to have diffuse, ichthyosis-like hyperkeratosis (Tadini et al., 1995). An extensive nevus spilus was also observed in a patient with Ebstein’s disease, which is the eponym for congenital downward displacement of the tricuspid valve into the right ventricle (Hori et al., 1978). Other reported associations with speckled lentiginous nevi include corneal snowflake dystrophy [2/38 patients in one series (Meretoja, 1985)] and adult-onset hearing loss (Nguyen et al., 1982). Although there are at least four reports of patients with segmental NF-1 plus either a speckled lentiginous nevus (Paik et al., 1996) or segmental lentiginosis (Allegue et al., 1989; Roth et al., 1987; Wong et al., 1997), two additional reports of segmental NF-1 in cases with a speckled lentiginous nevus are problematic because the diagnosis of segmental NF-1 is questionable (Finley and Kolbusz, 1993; Selvaag et al., 1994). In one patient, the diagnosis was based solely on the histologic features of a papule present within the speckled lentiginous nevus (Finley and Kolbusz, 1993); i.e., there were no other stigmata of NF. A collection of spindle cells was observed within a fine fibrocollagenous background in the reticular dermis, and the pathologic diagnosis was neurofibroma (no immunohistochemical studies were performed). As pointed out by Trattner and Hodak (1994), the lesion could have been simply a neurotized melanocytic nevus, a type of lesion that has been reported to develop within speckled lentiginous nevi (Hwang et al., 1997; van der Horst and Dirksen, 1981). In the second patient, a malformation of the fifth lumbar vertebra and shortening of the left extremity were seen in association with a speckled lentiginous nevus involving the left lower trunk and lower extremity (Selvaag et al., 1994). Again, there were no other signs of neurofibromatosis, and perhaps the diagnosis was actually SLN syndrome.
Histology In the areas of background hyperpigmentation, a variable
COMMON BENIGN NEOPLASMS OF MELANOCYTES
degree of lentiginous hyperplasia of the epidermis is observed, as is increased pigmentation of the basal layer, i.e., histologic findings similar to those of a lentigo simplex (Altman and Banse, 1992; Betti et al., 1997a; Crosti and Betti, 1994; Hermes et al., 1997; Hofmann et al., 1998; Pritchett and Pritchett, 1982; Stewart et al., 1978; Tadini et al., 1998). An increase in the number of active melanocytes also has been reported (Crosti and Betti, 1994; Hofmann et al., 1998; Matsudo et al., 1973; Ruth et al., 1980; Stewart et al., 1978; Takahashi, 1976). Occasionally, early nesting of nevus cells is seen within biopsy specimens of the background hyperpigmentation, which is sometimes referred to as nevus incipiens (Altman and Banse, 1992; Cohen et al., 1970; Prose et al., 1983). Histologic findings in biopsy specimens of the speckles can vary from lentiginous melanocytic hyperplasia and junctional theques at the tips of elongated rete ridges (macular lesions) to ordinary compound and dermal nevi (Altman and Banse, 1992; Betti et al., 1994, 1997a; Bielsa et al., 1998; Ceylan et al., 2003; Cramer, 1977; Crosti and Betti, 1994; Hermes et al., 1997; Langenbach et al., 1998a; Maize and Ackerman, 1987; Misago et al., 1994; Nguyen et al., 1982; Pock et al., 1991; Rhodes and Mihm, 1990; Roma et al., 2000; Simoes, 1981; Stewart et al., 1978; Tadini et al., 1998; Torrelo et al., 2003a). Collections of nevus cells around and within adnexal structures, nerves and/or blood vessels as well as between collagen bundles in the reticular dermis, representing characteristic findings of congenital melanocytic nevi, also may be present (Betti et al., 1994, 1997a; Casanova et al., 1996; Kopf et al., 1985b; Langenbach et al., 1998b; Maize and Ackerman, 1987; Mang et al., 2003; Saraswat et al., 2003; Schaffer et al., 2001a; Weinberg et al., 1998). In addition, the histologic features of Spitz nevus (Akasaka et al., 1993; Aloi et al., 1995; Betti et al., 1997b; Hofmann-Wellenhof et al., 1994; Vion et al., 1985; Woerdeman, 1984), dysplastic nevus (Bolognia, 1991; Grinspan et al., 1997; Kurban et al., 1992; Rhodes and Mihm, 1990; Wollenberg et al., 2002), or blue nevus (Betti et al., 1997a, 1999; Hofmann et al., 1998; Hori et al., 1978; Ishibashi et al., 1990; Korting, 1967; Langenbach et al., 1998a; Marchesi et al., 1993; Misago et al., 1993, 1994; Park et al., 1999; Pock et al., 1991; Toppe and Haas, 1988) can be seen. There are several reports of neurotized nevi developing within a speckled lentiginous nevus (Finley and Kolbusz, 1993; Hwang et al., 1997; van der Horst and Dirksen, 1981). Dermal melanophages also may be seen in the absence of an inflammatory infiltrate (Nguyen et al., 1982; Ruth et al., 1980). Speckled lentiginous nevi that contain blue nevi may occasionally have additional hamartomatous components other than melanocytic nevi, e.g., hyperplastic eccrine glands and ducts in the papillary dermis [Betti et al., 1997a; see section on Pilar neurocristic hamartoma (Chapter 58)], basaloid proliferation (Betti et al., 1999), and hyperplasia of arrector pili muscles (Park et al., 1999). These observations suggest that, as neural crest derivatives, melanocytes in the dermis may potentially have a “mesenchymal” role contributing to the
induction of epithelial proliferations. Cases in which a nevus sebaceus was completely superimposed on a speckled lentiginous nevus have also been described (Kopf and Bart, 1980; Langenbach et al., 1998a; Misago et al., 1994); these met the definition of phakomatosis pigmentokeratotica, and pigmented basal cell carcinomas eventually developed in two of the lesions (Langenbach et al., 1998a; Misago et al., 1994).
Laboratory Findings and Investigations Electron microscopic studies have shown the junctional theques in speckled lentiginous nevi to be composed of Mishima B-type cells with primarily fully melanized melanosomes and a few premelanosomes (Matsudo et al., 1973; Ruth et al., 1980). In addition, macromelanosomes have been seen within the melanocytes and keratinocytes of speckled lentiginous nevus (Frenk et al., 1975; Konrad et al., 1974; Pritchett and Pritchett, 1982; Rhodes and Mihm, 1990). Analysis by flow cytometry of a “dysplastic” nevus spilus in which a melanoma arose showed aneuploidy in the DNA of the melanoma as well as one of the pigmented lesions (a lentiginous junctional dysplastic nevus with slight atypia) within the nevus spilus (Kurban et al., 1992). The background hyperpigmentation and the remainder of the speckles (junctional and compound dysplastic nevi with slight to focally moderate atypia) were diploid. A systemic evaluation is recommended if the patient has other cutaneous features suggestive of PPV III or IV, e.g., nevus flammeus, nevus anemicus, and dermal melanocytosis (Guiglia and Prendiville, 1991; Happle and Steijlen, 1989; Hasegawa and Yasuhara, 1985; Libow, 1993; Sigg and Pelloni, 1989; Toda, 1986; Zahorcsek et al., 1988). The presence or absence of signs and symptoms such as seizures, mental retardation, glaucoma, and limb hypertrophy determines whether the diagnosis is PPV IIIa or IVa (cutaneous disease only) versus PPV IIIb or IVb (cutaneous plus systemic disease). If the patient has an extensive speckled lentiginous nevus and/or an associated organoid nevus, an evaluation focusing on the neurologic and musculoskeletal systems is warranted to assess for features of the speckled lentiginous nevus syndrome and phakomatosis pigmentokeratotica (see above) (Happle, 2002; Tadini et al., 1998).
Criteria for Diagnosis Diagnosis is based on the presence of a patch of hyperpigmentation which contains a variable number of smaller macules and/or papules that are usually more darkly pigmented. Biopsy specimens of the speckles demonstrate lentiginous melanocytic hyperplasia, collections of nevus cells, or dermal melanocytes. Of note, nevus cells may be present in biopsy specimens of the background hyperpigmentation (Altman and Banse, 1992; Cohen et al., 1970; Prose et al., 1983); this argues against using the histologic features of the background as a primary criterion for the diagnosis of this pigmented lesion (Kurban et al., 1992). 1105
CHAPTER 57
Differential Diagnosis The major entity in the differential diagnosis of the earliest stage of a speckled lentiginous nevus, the patch of hyperpigmentation, is a café-au-lait macule (Cohen et al., 1970). Agminated melanocytic nevi may be confused with a speckled lentiginous nevus, but in the former the background skin is not hyperpigmented. The clinician can use a Wood’s lamp to confirm the presence or absence of background hyperpigmentation. In partial unilateral lentiginosis, multiple lentigines are grouped together within an area of normal skin, and there is often a sharp demarcation at the midline (Cappon, 1948; Micali et al., 1994; Pickering, 1973; Schaffer et al., 2001b; Thompson and Diehl, 1980; Trattner and Metzker, 1993); the pigmented macules typically appear during childhood and undergo a gradual wavefront extension over months to years. Biopsy specimens demonstrate the histologic features of lentigines, e.g., an increase in the melanin content and lentiginous hyperplasia of the epidermis. Occasionally, small nests of nevus cells may be seen at the tips of the rete ridges (Marchesi et al., 1992), forming a ‘‘jentigo” pattern. One problem is the use by a few authors of the term “partial unilateral lentiginosis” to describe clustered lentigines within a patch of hyperpigmentation (Piqué et al., 1995). This may be due to the misconception that the speckles in a speckled lentiginous nevus cannot be lentigines. There are a few reports of patients with both types of lesions, speckled lentiginous nevus and segmental lentiginosis (Betti et al., 1997b; Crosti and Betti, 1994). When the histologic features of the speckles are those of Spitz nevi, one must be aware of the confusion in the literature regarding terminology. The term “agminated Spitz nevi” has been used to refer to clusters of nevi in an area of normally pigmented skin (Abramovits and Gonzalez-Serva, 1993; Krakowski et al., 1981; Orita et al., 1986) as well as clusters of nevi on a background of hyperpigmentation (Böer et al., 2001; Brownstein, 1972; Bullen et al., 1995; Duperrat and Dufourmentel, 1959; Goldberg et al., 1989; Grupper and Tubiana, 1955; Herd et al., 1994; Kopf and Andrade, 1966; Lancer et al., 1983; Palazzo and Duray, 1988; Quirino et al., 1996; Sourriel et al., 1969), even when the latter are admixed with other types of melanocytic nevi (Renfro et al., 1989). Several authors have advanced the notion that multiple Spitz nevi within a hyperpigmented patch represent a subtype of speckled lentiginous nevus (Akasaka et al., 1993; HofmannWellenhof et al., 1994; Woerdeman, 1984), and the present authors agree with this unifying concept, reserving the term “agminated Spitz nevi” to a cluster of nevi arising within an area of normally pigmented skin. The eccrine-centered nevus and the spotted grouped pigmented nevus (types I and II) represent variants of congenital melanocytic nevi in which speckles occur in a perifollicular and/or perieccrine distribution (Drut et al., 1999; Mishima, 1973; Morishima et al., 1976) (Fig. 57.11). Confusion has occurred because the term “spotted grouped pigmented nevus” has been used to describe speckled lentiginous nevi (Morishima et al., 1976; Sato et al., 1979). However, these 1106
Fig. 57.11. A speckled lentiginous nevus that overlaps clinically with a spotted grouped nevus.
two forms of nevi may simply represent ends of a spectrum since, in our opinion, both are subtypes of congenital nevi. There is also an example of a patient with a widespread speckled lentiginous nevus in which some of the grouped nevi appeared on a tan background patch, while others did not (Betti et al., 1994). In a biopsy specimen of a brown papule from normally pigmented skin, nevus cells were observed around and within adnexal structures, nerves, and blood vessels as well as splayed between collagen bundles, as in a congenital nevus (Betti et al., 1994). Additional confusion arises from the use of the terms “zosteriform melanocytic nevus” to describe large café-au-lait lesions that histologically lack nevus cells (Alper and Holmes, 1983) and “zosteriform lentiginous nevus” to describe lesions more compatible with linear and whorled nevoid hypermelanosis or epidermal nevi (Port et al., 1978). Also, the term speckled lentiginous nevus has been used to describe agminated nevi that are not within a tan or brown background patch (Maize and Ackerman, 1987). Although scattered lentigines within areas of postinflammatory hyperpigmentation can appear as psoriatic plaques, resolve, and resemble nevus spilus clinically (Burrows et al., 1994; Helland and Bang, 1980; Hofmann et al., 1977; Skogh and Moi, 1978), there is usually no difficulty separating these two entities.
Pathogenesis The speckled lentiginous nevus has been described as a “field defect.” Rhodes and Mihm (1990) suggested that speckled lentiginous nevi may be due to a defect in the melanoblasts that populate a localized area of the skin, and considered the possible influence of environmental and genetic factors. Other authors have raised the possibility of mosaicism as an explanation for zosteriform speckled lentiginous nevi (Davis and Shaw, 1964). Both extensive speckled lentiginous nevi and large classic congenital melanocytic nevi typically have a mosaic pattern of distribution, with the former lesions tending to either have a blocklike configuration (“checkerboard”; type
COMMON BENIGN NEOPLASMS OF MELANOCYTES
2) or follow Blaschko lines (type 1), and the latter usually having a patchy pattern without midline separation (type 4) (Happle, 1993). Interestingly, there are a few reports of familial occurrence of speckled lentiginous nevi (Crosti and Betti, 1994; Suzuki et al., 1990) and classic congenital nevi (Danarti et al., 2003). Recently, the concept of paradominant inheritance has been proposed to explain the genetic basis of speckled lentiginous nevi, classic congenital melanocytic nevi, and other conditions (e.g., Klippel–Trenaunay syndrome, Sturge–Weber syndrome, nevus anemicus, and organoid nevi) that are characterized by a mosaic distribution of lesions and occurrence that is primarily sporadic, but occasionally familial (Danarti et al., 2003; Happle, 2002). Zygotes that are homozygous for a paradominant mutation die during early embryogenesis, whereas individuals who are heterozygous are phenotypically normal; this allows a mutant gene to be transmitted without clinical expression through many generations. The trait only becomes manifest when a somatic mutation in a developing embryo results in loss of heterozygosity, thereby forming a population of cells that is homozygous for the mutation. Happle and Steijlen (1989) and Tadini et al. (1998) proposed the genetic concept of twin spotting (didymosis) for patients with PPV or PPK who have a nevus flammeus plus a speckled lentiginous nevus or an organoid nevus plus a speckled lentiginous nevus, respectively. The presumption is that the nevus flammeus (or the organoid nevus) and the speckled lentiginous nevus are caused by different recessive mutations, and that the two genes reside at different sites on the same chromosome (Fig. 57.12). If an embryo is a double heterozygote, then, following DNA replication, somatic crossing over can result in two populations of cells, each homozygous for one of two recessive mutations (Happle and Steijlen, 1989).
Animal Models None.
Treatment A common strategy for longitudinal care is baseline photographic documentation followed by serial clinical observation for the development of macules or papules with atypical features or signs suggestive of cutaneous melanoma. Any such change would prompt the performance of a biopsy. The patient and family also should be educated regarding the clinical signs of melanoma. In general, speckled lentiginous nevi are much easier to follow clinically than classic congenital nevi, which are often dark brown or black, thicker throughout, and covered by dense terminal hairs. In addition, to date, there have been no reports of the development of melanoma within the dermal component of speckled lentiginous nevi as there have been for classic congenital nevi. Some authors have advocated dermatoscopy or digital epiluminescence microscopy as aids in longitudinal clinical evaluation of speckled lentiginous nevi (Johr and Binder, 2000; Johr et al., 1998). An alternative is surgical excision (Casanova et al., 1996;
A
B
C
D
E Fig. 57.12. Mechanism of non-allelic twin spotting in an embryo that is doubly heterozygous for two different recessive mutations at neighboring loci. A pair of homologous chromosomes (A) undergoes semiconservative replication (B). Crossing-over occurs, with exchange of the region carrying the two mutations (C); as a result, each chromosome is composed of two different chromatids (D). The random assortment of the chromatids during mitosis may result in two different daughter cells, each homozygous for one of the mutations (E). Recently, heterozygous germline mutations in the VG5Q gene on chromosome 5q13, which encodes a potent angiogenic factor, were identified in a subset of patients with Klippel–Trenaunay syndrome (Tian et al., 2004). As twin spotting is thought to explain the association of Klippel–Trenaunay syndrome with speckled lentiginous nevi in patients with PPV IIIb or IVb, this finding implies that genes involved in the pathogenesis of speckled lentiginous nevi may potentially be located on chromosome 5q.
Page and Windhorst, 1972; Rhodes, 1996), but because a speckled lentiginous nevus represents a “field defect,” the entire area of hyperpigmentation has to be removed in order to avoid recurrence, usually resulting in a scar of significant size. Several groups have reported use of the Q-switched ruby, 1107
CHAPTER 57
Q-switched neodymium:yttrium-aluminum-garnet (Nd:YAG), or Q-switched alexandrite laser to treat both the background hyperpigmentation and the speckles within a speckled lentiginous nevus (Grevelink et al., 1997; Moreno-Arias et al., 2001; Nehal et al., 1996; Nelson and Applebaum, 1992; Taylor and Anderson, 1993; Tse et al., 1994). Grevelink et al. (1997) reported >80% lightening in 6/6 patients (mean age 30 years; range 15–42 years) who received one to five treatments with the Q-switched ruby laser; one patient was noted to develop hyperpigmentation at the periphery of the lesion, and focal recurrences occurred after two and three years in the two patients for whom follow-up information was available. In three of the patients in this study, a comparison of test sites treated with the Q-switched ruby versus the Q-switched Nd:YAG showed 0–30% and 50–80% lightening, respectively. Specific details are available for four other patients treated with the Q-switched ruby laser (Nehal et al., 1996; Taylor and Anderson, 1993; Tse et al., 1994). Post treatment, both hypo- and hyperpigmentation were observed, as were return of the background pigmentation (n = 1), lack of response despite seven treatments (n = 1), and partial (25–60%) improvement (n = 2; one patient was also treated with the Q-switched Nd:YAG laser). In the single case reported to date, only 50% lightening was seen after 16 treatments with the Q-switched alexandrite laser (Morena-Arias et al., 2001). Lastly, 50–75% clearance was observed after four sessions with intense pulsed light in the four patients reported thus far (Gold et al., 1999; Moreno-Arias and Ferrando, 2001). In general, it appears that the background component of a speckled lentiginous nevus, like the café-au-lait macule, is particularly resistant to treatment and prone to recurrence (Hruza, 1997). From a cosmetic standpoint, although Grevelink et al. (1997) had more encouraging shortterm results than the other groups, the durability of the response remains to be seen. Moreover, from a medical standpoint, laser treatment of the nevi within a speckled lentiginous nevus is as controversial as it is for the treatment of other melanocytic nevi.
Prognosis In the past, speckled lentiginous nevi (especially those of relatively small size) were often assigned the same level of concern as a café-au-lait macule or lentigo, and routine longitudinal observation was not advised. More recently, following multiple reports of the development of cutaneous melanoma within these lesions and mounting evidence of their congenital nature, the level of concern has become more or less proportional to that given to a classic congenital nevus of the same size. It remains to be seen whether the surface area of the speckled lentiginous nevus, the number or type of nevi contained within the lesion, or the presence of atypical cytologic features in the speckles will correlate with the risk of developing cutaneous melanoma.
References Abramovits, W., and A. Gonzalez-Serva. Multiple agminated pig-
1108
mented Spitz nevi (mimicking acral lentiginous malignant melanoma and dysplastic nevus) in an African-American girl. Int. J. Dermatol. 32:280–285, 1993. Akasaka, T., Y. Imamura, and S. Kon. Multiple agminated juvenile melanoma arising on a hyperpigmented macule. J. Dermatol. 20:638–642, 1993. Allegue, F., A. España, J. M. Fernández-García, and A. Ledo. Segmental neurofibromatosis with contralateral lentiginosis. Clin. Exp. Dermatol. 14:448–450, 1989. Aloi, F., C. Tomasini, and M. Pippione. Agminated Spitz nevi occurring within a congenital speckled lentiginous nevus. Am. J. Dermatopathol. 17:594–598, 1995. Alper, J. C., and L. B. Holmes. The incidence and significance of birthmarks in a cohort of 4,641 newborns. Pediatr. Dermatol. 1:58–68, 1983. Altman, D. A., and L. Banse. Zosteriform speckled lentiginous nevus. J. Am. Acad. Dermatol. 27:106–108, 1992. Benedict, P. H., G. Szabó, T. B. Fitzpatrick, and S. J. Sinesi. Melanotic macules in Albright’s syndrome and in neurofibromatosis. J. Am. Med. Assoc. 205:618–626, 1968. Besnier, E., L. Brocq, and L. Jacquet. La Pratique Dermatologique. Paris: Masson et Cie, 1902, p. 565. Betti, R., E. Inselvini, and C. Crosti. Extensive unilateral speckled lentiginous nevus. Am. J. Dermatopathol. 16:554–556, 1994. Betti, R., E. Inselvini, M. Palvarini, and C. Crosti. Agminate and plaque-type blue nevus combined with lentigo, associated with follicular cyst and eccrine changes: a variant of speckled lentiginous nevus. Dermatology 195:387–390, 1997a. Betti, R., E. Inselvini, M. Palvarini, and C. Crosti. Agminated intradermal Spitz nevi arising on an unusual speckled lentiginous nevus with localized lentiginosis: A continuum? Am. J. Dermatopathol. 19:524–527, 1997b. Betti, R., E. Inselvini, and C. Crosti. Blue nevi and basal cell carcinoma within a speckled lentiginous nevus. J. Am. Acad. Dermatol. 41:1039–1041, 1999. Bielsa, I., C. Paradelo, M. Ribera, and C. Ferrándiz. Generalized nevus spilus and nevus anemicus in a patient with a primary lymphedema: A new type of phakomatosis pigmentovascularis? Pediatr. Dermatol. 15:293–295, 1998. Böer, A., M. Wolter, L. Kneisel, and R. Kaufmann. Multiple agminated Spitz nevi arising on a café-au-lait macule: Review of the literature with contribution of another case. Pediatr. Dermatol. 18:494–497, 2001. Bolognia, J. L. Fatal melanoma arising in the zosteriform speckled lentiginous nevus. Arch. Dermatol. 127:1240–1241, 1991. Bolognia, J., S. Orlow, and S. A. Glick. Lines of Blaschko. J. Am. Acad. Dermatol. 31:157–190, 1994. Boente, M. C., N. Pizzi de Parra, M. Larralde de Luna, H. B. Bonet, A. Santos Munoz, V. Parra, P. Gramajo, S. Moreno, and R. A. Asial. Phacomatosis pigmentokeratotica: Another epidermal nevus syndrome and a distinctive type of twin spotting. Eur. J. Dermatol. 10:190–194, 2000. Borrego, L., J. Hernandez Santana, O. Baez, and B. Hernandez Hernandez. Naevus spilus as a precursor of cutaneous melanoma: report of a case and literature review. Clin. Exp. Dermatol. 19:515–517, 1994. Breitkopf, C., K. Ernst, and M. Hundeiker. Neubildungen auf naevus spilus. Hautarzt 47:759–762, 1996. Breuillard, F., and D. Duthoit. Mélanome malin in situ sur naevus spilus. Rev. Eur. Dermatol. 3:476–478, 1991. Brownstein, W. E. Multiple agminated juvenile melanoma. Arch. Dermatol. 106:89–91, 1972. Brufau, C., M. Moran, and M. Arrnijo. Naevus sur naevus: A propos de 7 observations, trois associées a d’autres dysplasies, et une à un mélanome malin invasif. Ann. Dermatol. Venereol. 113:409–418, 1986.
COMMON BENIGN NEOPLASMS OF MELANOCYTES Bulkley, H. D. Lecture on the classification and diagnosis of diseases of the skin. N. Y. Med. Gaz. 2:97–107, 1842. Bullen, R., S. N. Snow, P. O. Larson, L. H. Kircik, S. Nychay, and P. Briggs. Multiple agminated Spitz nevi: Report of two cases and review of the literature. Pediatr. Dermatol. 12:156–158, 1995. Burrows, N. P., S. Handfield-Jones, B. E. Monk, R. A. Sabroe, J. M. Geraghty, and P. G. Norris. Multiple lentigines confined to psoriatic plaques. Clin. Exp. Dermatol. 19:380–382, 1994. Cappon, D. Case of unilateral lentigines with mental deficiency. Br. J. Dermatol. 60:371–374, 1948. Casanova, D., J. Bardot, J. P. Aubert, L. Andrac, and G. Magalon. Management of nevus spilus. Pediatr. Dermatol. 13:233–238, 1996. Ceylan, C., F. Özdemir, G. Öztürk, T. Akalin, and I. Kilinç.Tuberous sclerosis associated with multiple speckled lentiginous nevi. J. Eur. Acad. Dermatol. 17:601–619, 2003. Cohen, H. I., W. Minkin, and S. B. Frank. Nevus spilus. Arch. Dermatol. 102:433–437, 1970. Cox, N. H., A. Malcolm, and E. D. Long. Superficial spreading melanoma and blue naevus within naevus spilus — ultrastructural assessment of giant pigment granules. Dermatology 194:213–216, 1997. Cramer, H. J. Beitrag zur histopathologie des naevus spilus. Zentralbl. Allg. Pathol. Pathologische Anat. 121:122–128, 1977. Cramer, S. F. Speckled lentiginous nevus (nevus spilus): The roots of the “melanocytic garden.” Arch. Dermatol. 137:1654–1655, 2001. Crosti, C., and R. Betti. Inherited extensive speckled lentiginous nevus with ichthyosis: Report of a previously undescribed association. Arch. Dermatol. 130:393–395, 1994. Danarti, R., A. König, and R. Happle. Large congenital melanocytic nevi may reflect paradominant inheritance implying allelic loss. Eur. J. Dermatol. 13:430–432, 2003. Davis, D. G., and M. W. Shaw. An unusual human mosaic for skin pigmentation. N. Engl. J. Med. 270:1384–1389, 1964. Descamps, V., B. Lebrin-Vignes, J. Wendling, S. Belaïch, and B. Crickx. Phacomatosis pigmentokeratotica: Mosaïcisme associant un naevus sur naevus géant et un hamartome verruco-sébacé: Un example de “twin spotting.” Ann. Dermatol. Venereol. 127:4S99, 2000. Dorland, W. A. N. Dorland’s Medical Dictionary. Philadelphia, PA: W. B. Saunders Co., 1994, p. 1557. Drut, R., R. M. Drut, and M. Cohen. Adnexal-centered giant congenital melanocyte nevus with extensive ganglioneuromatous component and trisomy 7. Pediatr. Dev. Pathol. 2:473–477, 1999. Duhring, L. A. A Practical Treatise on Diseases of the Skin, 3rd ed. Philadelphia, PA: J. B. Lippincott, 1883, p. 376. Duperrat, B., C. Doufourmentel. Etude du melanoma juvenile d’après 40 cas personels. Minerva Dermatol. 34:190–193, 1959. Elder, D., and R. Elenitsas. Benign pigmented lesions and malignant melanoma. In: Lever’s Histopathology of the Skin, 8th ed., D. Elder, R. Elenitsas, C. Jaworsky, and B. Johnson (eds). Philadelphia, PA: Lippincott-Raven Publishers, 1997, pp. 632–633. Enjolras, O., and J. B. Mulliken. Vascular malformations. In: Textbook of Pediatric Dermatology, J. Harper, A. Oranje, and N. Prose (eds). Oxford: Blackwell Science, 2000, pp. 975–976. Falo, L. D., Jr., A. J. Sober, and R. L. Barnhill. Evolution of a naevus spilus. Dermatology 189:382–383, 1994. Finley, E. M., and R. V. Kolbusz. Segmental neurofibromatosis clinically appearing as a nevus spilus. Int. J. Dermatol. 32:358–360, 1993. Frenk, E., B. Mevorah, and J. Delacretaz. Seltenere melanozyten- und neavuszellnaevi. Hautarzt 26:619–624, 1975.
Friedman, E., and R. M. Goodman. The “FACES” syndrome: A new syndrome with unique facies, anorexia, cachexia, and eye and skin lesions. J. Craniofac. Genet. Dev. Biol. 4:227–231, 1984. From, L. Congenital nevi — Let’s be practical. Pediatr. Dermatol. 9:345–346, 1992. Gold, M. H., T. D. Foster, and M. W. Bell. Nevus spilus successfully treated with an intense pulsed light source. Dermatol. Surg. 25:254–255, 1999. Goldberg, L. H., S. A. B. Collins, and D. M. Siegel. The epidermal nevus syndrome: Case report and review. Pediatr. Dermatol. 4:27–33, 1987. Goldberg, N. S., L. R. Shapiro, S. S. Weiss, and W. Szaniawski. Agminated Spitz nevus in a boy with blepharophimosis syndrome. Cutis 44:385–387, 1989. Goldblum, J. R., and J. T. Headington. Hypophosphatemic rickets and multiple spindle and epithelioid nevi associated with linear nevus sebaceus syndrome. J. Am. Acad. Dermatol. 29:109–111, 1993. Grevelink, J. M., S. González, R. Bonoan, C. Vibhagool, and E. Gonzalez. Treatment of nevus spilus with the Q-switched ruby laser. Dermatol. Surg. 23:365–369, 1997. Grinspan, D., A. Casala, J. Abulafia, J. Mascotto, and M. Allevato. Melanoma on dysplastic nevus spilus. Int. J. Dermatol. 36:499– 502, 1997. Grupper, C., and R. Tubiana. Mélanome juvenile de Spitz ou pseudomélanome. Bull. Soc. Franc. Dermatol. Syphil. 62:300–302, 1955. Guiglia, M. C., and J. S. Prendiville. Multiple granular cell tumors associated with giant speckled lentiginous nevus and nevus flammeus in a child. J. Am. Acad. Dermatol. 24:359–363, 1991. Guillot, B., D. Bessis, G. Barnéon, S. Monpoint, and J. J. Guilhou. Malignant melanoma occurring on a “naevus on naevus.” Br. J. Dermatol. 124:610–611, 1991. Happle, R. Mosaicism in human skin: Understanding the patterns and mechanisms. Arch. Dermatol. 129:1460–1470, 1993. Happle, R. Speckled lentiginous nevus syndrome: delineation of a new distinct neurocutaneous phenotype. Eur. J. Dermatol. 12:133–135, 2002. Happle, R., and P. M. Steijlen. Phacomatosis pigmentovascularis gedeutet als ein phänomen der zwillingsflecken. Hautarzt 40:721– 724, 1989. Happle, R., R. Hoffmann, L. Restano, R. Caputo, and G. Tadini. Phacomatosis pigmentokeratotica: A melanocytic-epidermal twin nevus syndrome. Am. J. Med. Genet. 65:363–365, 1996. Hasegawa, Y., and M. Yasuhara. Phakomatosis pigmentovascularis type IVa. Arch. Dermatol. 121:651–655, 1985. Helland, S., and G. Bang. Nevus spilus-like hyperpigmentation in psoriatic lesions during PUVA therapy. Acta Derm. Venereol. 60: 81–83, 1980. Herd, R. M., S. M. Allan, L. Biddlestone, P. K. Buxton, and K. M. Mclaran. Agminate Spitz naevi arising on hyperpigmented patches. Clin. Exp. Dermatol. 19:483–486, 1994. Hermes, B., B. Cremer, R. Happle, and B. M. Henz. Phacomatosis pigmentokeratotica: A patient with the rare melanocytic-epidermal twin nevus syndrome. Dermatology 194:77–79, 1997. Hidano, A. Naevus sur naevus et naevus spilus. Ann. Dermatol. Venereol. 113:845, 1986. Hill, V. A., R. H. Felix, P. S. Mortimer, and J. I. Harper. Phacomatosis pigmentokeratotica. J. R. Soc. Med. 96:30–31, 2003. Hofmann, C., G. Plewig, and O. Braun-Falco. Ungewöhnliche nebenwirkungen bei oraler photochemotherapie (PUVA-therapie) der psoriasis. Hautarzt 28:583–588, 1977. Hofmann, U. B., P. Ogilvie, W. Mullges, E.-B. Brocker, and H. Hamm. Congenital unilateral speckled lentiginous blue nevi with asymmetric spinal muscular atrophy. J. Am. Acad. Dermatol. 39:326–329, 1998. Hofmann-Wellenhof, R., H. P. Soyer, J. Smolle, and H. Kerl. Spitz’s
1109
CHAPTER 57 nevus arising on a nevus spilus. Dermatology 189:265–268, 1994. Holder, J. E., R. A. C. Graham-Brown, and R. D. R. Camp. Partial unilateral lentiginosis associated with blue naevi. Br. J. Dermatol. 130:390–393, 1994. Hori, M., G. Satomi, K. Yanagisawa, and H. Imamura. A case of giant nevus spilus with various pigment flecks associated with Ebstein’s disease. Jpn. J. Clin. Dermatol. (Tokyo) 32:1011–1014, 1978. Hruza, G. J. Commentary: Treatment of nevus spilus with the Qswitched ruby laser. Dermatol. Surg. 23:369–370, 1997. Hwang, S. M., E. H. Choi, W. S. Lee, S. I. Choi, and S. K. Ahn. Nevus spilus (speckled lentiginous nevus) associated with a nodular neurotized nevus. Am. J. Dermatopathol. 19:308–311, 1997. Hyde, J. N., and F. H. Montgomery. A Practical Treatise on Diseases of the Skin, 6th ed. Philadelphia, PA: Lea Brothers, 1901, p. 467. Ishibashi, A., K. Kimura, and A. Kukita. Plaque-type blue nevus combined with lentigo (nevus spilus). J. Cutan. Pathol. 17:241–245, 1990. Ito, M., and Y. Hamada. VIII: Nevus spilus en nappe. Tohoku J. Exp. Med. 55:44–48, 1952. Johnson, B. L. Zosteriform lentiginous nevus. Arch. Dermatol. 108:856, 1973. Johr, R. H., and M. Binder. Management of nevus spilus — a better way. Pediatr. Dermatol. 17:491–492, 2000. Johr, R. H., L. S. Schachner, and W. Stoltz. Management of nevus spilus. Pediatr. Dermatol. 15:407–410, 1998. Kaposi, M. Pathologie und Therapie der Hautkrankheiten. Wein: Urban & Schwartzenberg, 1887, p. 583. Keine, P., J. P. Brodersen, and R. Folster-Holst. “Blaue” variante eines naevus spilus. Hautarzt 46:349–351, 1995. Kinoshita, K., H. Shinkai, and A. Utani. Phacomatosis pigmentokeratotica without extracutaneous abnormalities. Dermatology 207: 415–416, 2003. Konrad, K., H. Honigsmann, and K. Wolff. Naevus spilus — ein pigmentnaevus mit Riesenmelanosomen. Klinik, histologie und ultrastruktur. Hautarzt 25:585–593, 1974. Kopf, A. W., and R. Andrade. Benign juvenile melanoma. In: Year Book of Dermatology, A. W. Kopf, and R. Andrade (eds). Chicago: Year Book Medical Publishers Inc., 1966, pp. 7–52. Kopf, A. W., and R. S. Bart. Tumor conference: Combined organoid and melanocytic nevus. J. Dermatol. Surg. Oncol. 6:28–30, 1980. Kopf, A. W., L. J. Levine, D. S. Rigel, R. J. Friedman, and M. Levenstein. Congenital-nevus-like nevi, nevi spili, and cafè-au-lait spots in patients with malignant melanoma. J. Dermatol. Surg. Oncol. 11:275–280, 1985a. Kopf, A. W., L. J. Levine, D. S. Rigel, R. J. Friedman, and M. Levenstein. Prevalence of congenital naevus like nevi, nevi spili and café-au-lait spots. Arch. Dermatol. 121:766–769, 1985b. Korting, G. W. Über nachbarschaftliches vorkommen von blauen naevus und pigmentnaevus in isoleiter wie disserninierter weise. Z. Haut Geschlechtskrankh. 42:1–4, 1967. Krahn, G., E. Thoma, and R. U. Peter. Zwei superfiziell spreitende maligne melanome auf naevus spilus. Hautarzt 43:32–34, 1992. Krakowski, A., E. Tur, and S. Brenner. Multiple agminated juvenile melanoma: a case with a sunburn history, and a review. Dermatologica 163:270–275, 1981. Kudo, T., M. Kitabatake, and H. Ishikawa. [A case of cutis marmorata telangiectatica congenita and naevus spilus with moyamoya disease.] [Japanese] Hifuka No Rinsho 40:905–909, 1986. Kurban, R. S., F. I. Preffer, A. T. Sober, M. C. Mihm Jr., and R. L. Barnhill. Occurrence of melanoma in “dysplastic” nevus spilus: report of case and analysis by flow cytometry. J. Cutan. Pathol. 19:423–428, 1992.
1110
Lancer, H. A., J. E. Muhlbauer, and A. J. Sober. Multiple agminated spindle cell nevi: unique clinical presentation and review. J. Am. Acad. Dermatol. 8:707–711, 1983. Langenbach, N., U. Hohenleutner, and M. Landthaler. Phacomatosis pigmentokeratotica: Speckled-lentiginous nevus in association with nevus sebaceus. Dermatology 197:377–380, 1998a. Langenbach, N., A. Pfau, M. Landthaler, and W. Stolz. Naevi spili, café-au-lait spots and melanocytic naevi aggregated alongside Blaschko’s lines, with a review of segmental melanocytic lesions. Acta Derm. Venereol. 78:378–380, 1998b. Leider, M., and M. Rosenblum. A Dictionary of Dermatological Words, Terms and Phrases. West Haven, CT: Dome Laboratories, 1976, pp. 300–301, 384. Libow, L. F. Phakomatosis pigmentovascularis type IIIb. J. Am. Acad. Dermatol. 29:305–307, 1993. Maize, J. C., and B. A. Ackerman. Pigmented Lesions of the Skin. Philadelphia: Lea and Febiger, 1987, pp. 73–162. Mang, R., T. Ruzicka, and M. Megahed. Ungewöhnliche klinische präsentationen melanozytärer nävi. Hautarzt 54:370–372, 2003. Marchesi, L., L. Naldi, A. Di Landro, L. Cavalieri d’Oro, A. Brevi, and T. Cainelli. Segmental lentiginosis with jentigo histologic pattern. Am. J. Dermatopathol. 14:323–327, 1992. Marchesi, L., L. Naldi, A. Parma, F. Locati, and T. Cainelli. Agminate blue nevus combined with lentigo. A variant of speckled lentiginous nevus? Am. J. Dermatopathol. 15:162–165, 1993. Matsudo, H., W. B. Reed, D. Homme, W. Bartok, and R. Horowitz. Zosteriform lentiginous nevus. Arch. Dermatol. 107:902–905, 1973. McLean, D. I., and R. P. Gallagher. “Sunburn” freckles, café-au-lait macules, and other pigmented lesions of schoolchildren: the Vancouver Mole Study. J. Am. Acad. Dermatol. 32:565–570, 1995. Meretoja, J. Inherited corneal snowflake dystrophy with oculocutaneous pigmentation disturbances and other symptoms. Ophthalmologica 191:197–205, 1985. Micali, G., M. R. Nasca, D. Innocenzi, and D. Lembo. Agminated lentiginosis: Case report and review of the literature. Pediatr. Dermatol. 11:241–245, 1994. Misago, N., Y. Narisawa, and H. Kohda. A combination of speckled lentiginous nevus with patch-type blue nevus. J. Dermatol. 20:643– 647, 1993. Misago, N., Y. Narisawa, T. Nishi, and H. Kohda. Association of nevus sebaceus with an unusual type of “combined nevus”. J. Cutan. Pathol. 21:76–81, 1994. Mishima, Y. Eccrine-centered nevus. Arch. Dermatol. 107:59–61, 1973. Moreno-Arias, G. A., and J. Ferrando. Intense pulsed light for melanocytic lesions. Dermatol. Surg. 27:397–400, 2001. Moreno-Arias, G. A., F. Bulla, J. J. Vilata-Corell, and A. CampsPresneda. Treatment of widespread segmental nevus spilus by Qswitched alexandrite laser (755 nm, 100 nsec). Dermatol. Surg. 27:841–843, 2001. Morishima, T., M. Endo, I. Imagawa, and S. Morioka. Clinical and histopathological studies on spotted grouped pigmented nevi with special reference to eccrine-centered nevus. Acta Derm. Venereol. 56:345–351, 1976. Nehal, K. S., V. J. Levine, and R. Ashinoff. The treatment of benign pigmented lesions with the Q-switched ruby laser: A comparative study using the 5.0- and 6.0-mm spot size. Dermatol. Surg. 22:683–686, 1996. Nelson, J. S., and J. Applebaum. Treatment of superficial cutaneous pigmented lesions by melanin-specific selective photothermolysis using the Q-switched ruby laser. Ann. Plast. Surg. 29:231–237, 1992. Nguyen, K. Q., D. L. Pierson, and O. G. Rodman. Mosaic speckled lentiginous nevi. Cutis 30:65–68, 1982.
COMMON BENIGN NEOPLASMS OF MELANOCYTES Orita, M., K. Obara, T. Irimajiri, and M. Kobayashi. Multiple agminate juvenile melanoma. Dermatologica 172:58–61, 1986. Page, E. V., and D. B. Windhorst. Unusual nevus (nevus spilus). Arch. Dermatol. 105:115, 1972. Paik, S.-C., J.-H. Shim, J.-D. Lee, B.-K. Cho, and C.-W. Kim. Bilateral segmental neurofibromatosis with speckled lentiginous nevus. Int. J. Dermatol. 35:360–361, 1996. Palazzo, J. P., and P. H. Duray. Congenital agminated Spitz nevi: immunoreactivity with a melanoma-associated monoclonal antibody. J. Cutan. Pathol. 15:166–170, 1988. Park Y. M., H. Kang, and B. K. Cho. Plaque-type blue nevus combined with nevus spilus and smooth muscle hyperplasia. Int. J. Dermatol. 38:775, 1999. Perkinson, N. G. Melanoma arising in a café-au-lait spot of neurofibromatosis. Am. J. Surg. 93:1018–1020, 1957. Pickering, J. G. Partial unilateral lentiginosis with associated developmental abnormalities. Guys Hospital Rep. 122:361–370, 1973. Piñol-Aguadé, J., and J. Peyri Rey. Nevus sobre nevus. Med. Cutan. Ibero Lat. Am. 7:85–93, 1973. Piqué, E. P., A. Aguilar, M. C. Fariña, M. A. Gallego, P. Escalonilla, and L. Requena. Partial unilateral lentiginosis: report of seven cases and review of the literature. Clin. Exp. Dermatol. 20:319–322, 1995. Pock, L., J. Trnka, F. Vosmik, and F. Zaruba. Systematized progradient multiple combined melanocytic and blue nevus. Am. J. Dermatopathol. 13:282–287, 1991. Port, M., J. Courniotes, and M. Podwal. Zosteriform lentiginous naevus with ipsilateral rigid cavus foot. Br. J. Dermatol. 98:693– 698, 1978. Prigent, F., A. Kahn, C. Martinet, and T. Saigot. Phacomatose pigmento-vasculaire IIIa. Ann. Dermatol. Venereol. 118:531–533, 1999. Pritchett, R. M., and P. S. Pritchett. Zosteriform speckled lentiginous nevus with giant melanosomes. Cutis 30:329–334, 1982. Prose, N. S., E. Heilman, Y. M. Felman, F. Tanzer, and J. Silber. Multiple benign juvenile melanoma. J. Am. Acad. Dermatol. 9:236–242, 1983. Quirino, A. P., F. Azevedo, and M. B. Monteiro. Nevus de Spitz multiples agminés. Ann. Dermatol. Venereol. 123:S145, 1996. Renfro, L., J. M. Grant-Kels, and S. A. Brown. Multiple agminate Spitz nevi. Pediatr. Dermatol. 6:114–117, 1989. Rhodes, A. R. Pigmented birthmarks and precursor melanocytic lesions of cutaneous melanoma identifiable in childhood. Pediatr. Clin. North Am. 30:435–463, 1983. Rhodes, A. R. Nevus spilus: A potential precursor of cutaneous melanoma worthy of aggressive surgical excision? Pediatr. Dermatol. 13:250–252, 1996. Rhodes, A. R., and M. C. Mihm Jr. Origin of cutaneous melanoma in a congenital dysplastic nevus spilus. Arch. Dermatol. 126:500– 505, 1990. Rivers, J. K., R. MacLennan, J. W. Kelly, A. E. Lewis, B. J. Tate, S. Harrison, and W. H. McCarthy. The eastern Australian childhood nevus study prevalence of atypical nevi, congenital nevus-like nevi, and other pigmented lesions. J. Am. Acad. Dermatol. 32:957–963, 1995. Roma, P., H. Sanjeev, and K. Bhusan. Generalized naevus spilus: A rare entity? J. Eur. Acad. Dermatol. 14:430, 2000. Roth, M. R., R. Martinez, and W. D. James. Segmental neurofibromatosis. Arch. Dermatol. 123:917–920, 1987. Rütten, A., and M. Goos. Nevus spilus with malignant melanoma in a patient with neurofibromatosis. Arch. Dermatol. 126:539–540, 1990. Ruth, W. K., J. D. Shelbourne, and B. V. Jegasothy. Zosteriform lentiginous nevus. Arch. Dermatol. 116:476, 1980. Saraswat, A., S. Dogra, A. Bbansali, and B. Kumar. Phakomatosis pigmentokeratotica associated with hypophosphataemic vitamin
D-resistant rickets: improvement in phosphate homeostasis after partial laser ablation. Br. J. Dermatol. 148:1074–1076, 2003. Sato, S., H. Kato, and A. Hidano. Divided nevus spilus and divided form of spotted grouped pigmented nevus. J. Cutan. Pathol. 6:507–512, 1979. Sawada, Y., M. Iwata, and Y. Mitsusashi. Nevus Pigmentovascularis. Ann. Plast. Surg. 25:142–145, 1990. Schaffer, J. V., S. J. Orlow, R. Lazova, and J. L. Bolognia. Speckled lentiginous nevus: Within the spectrum of congenital melanocytic nevi. Arch. Dermatol. 137:172–178, 2001a. Schaffer, J. V., R. Lazova, and J. L. Bolognia. Partial unilateral lentiginosis with ocular involvement. J. Am. Acad. Dermatol. 44:387–390, 2001b. Selvaag, E., P. Thune, and T. E. Larsen. Segmental neurofibromatosis presenting as a giant naevus spilus. Acta Derm. Venereol. 74:327, 1994. Sigg, C., and F. Pelloni. Oligosymptomatic form of Klippel-Trenaunay-Weber syndrome associated with giant nevus spilus. Arch. Dermatol. 125:1284–1285, 1989. Sigg, C., F. Pelloni, and U. W. Schnyder. Frequency of congenital nevi, nevi spili and café-au-lait spots and their relation to nevus count and skin complexion in 939 children. Dermatologica 180:118–123, 1990. Simoes, G. A. Speckled zosteriform lentiginous nevus. J. Am. Acad. Dermatol. 4:236–238, 1981. Skogh, M., and H. Moi. Naevus-spilus-artige hyperpigmentierungen bei psoriasis. Hautarzt 29:607, 1978. Sourriel, P., C. Beylot, and X. Carrard. Mélanome de Spitz (forme multiple agminée). Bull. Soc. Franc. Dermatol. Syphil. 76:77–79, 1969. Stein, K. M., E. Shumunes, and M. Thew. Neurofibromatosis presenting as the epidermal nevus syndrome. Arch Dermatol. 105:229–232, 1972. Steijlen, P. M., and J. P. Kuiper. Phacomatose vasculaire pigmentée. Phlébologie 43:34–35, 1990. Stern, J. B., H. M. Haupt, and C. M. Aaronson. Malignant melanoma in a speckled zosteriform lentiginous nevus. Int. J. Dermatol. 29:583–584, 1990. Stewart, D. M., J. Altman, and A. H. Mehregan. Speckled lentiginous nevus. Arch. Dermatol. 114:895–896, 1978. Suzuki, K., H. Ishizake, and H. Takahashi. [Phacomatosis pigmentovascularis IIIb associated with porokeratosis, acanthosis nigricans and endocrinopathy in brother and sister.] [Japanese] Skin Res. (Hifu) 32:65–70, 1990. Tadini, G., E. Ermacora, and G. Carminati. Unilateral speckledlentiginous naevus, contralateral verrucous epidermal naevus, and diffuse ichthyosis-like hyperkeratosis: an unusual example of twin spotting? Eur. J. Dermatol. 5:659–663, 1995. Tadini, G., L. Restano, R. Gonzales-Perez, M. A. Gonzales-Ensenat, M. A. Vincente-Villa, S. Cambiaghi, P. Marchettini, M. Mastrangelo, and R. Happle. Phacomatosis pigmentokeratotica: Report of new cases and further delineation of the syndrome. Arch. Dermatol. 134:333–337, 1998. Takahashi, M. Studies on café au lait spots in neurofibromatosis and pigmented macules of nevus spilus. Tohoku J. Exp. Med. 118:255– 273, 1976. Taylor, C. R., and R. R. Anderson. Treatment of benign pigmented epidermal lesions by Q-switched ruby laser. Int. J. Dermatol. 32:908–912, 1993. Thompson, G. W., and A. K. Diehl. Partial unilateral lentiginosis. Arch. Dermatol. 116:356, 1980. Tian, X.-L., R. Kadaba, S.-A. You, M. Liu, A. A. Timur, L. Yang, Q. Chen, P. Szafranski, S. Rao, L. Wu, D. E. Housman, P. E. DiCorleto, D. J. Driscoll, J. Borrow, and Q. Wang. Identification of an angiogenic factor that when mutated causes susceptibility to Klippel-Trenaunay syndrome. Nature 427:640–645, 2004.
1111
CHAPTER 57 Toda, K. Phacomatosis pigmentovascularis Ota. In: Biology and Diseases of Epidermal Pigmentation, T. B. Fitzpatrick, M. M. Wick, and K. Toda (eds). Tokyo: University of Tokyo Press, 1986. pp. 179–181. Toppe, F., and N. Haas. Naevus spilus géant avec naevus bleus. A propros d’un cast. Ann. Dermatol. Venereol. 115:703–707, 1988. Torrelo, A., and A. Zambrano. What syndrome is this: Phakomatosis pigmentokeratotica (Happle). Pediatr. Dermatol. 15:321–323, 1998. Torrelo, A., I. de Prada, A. Zambrano, and R. Happle. Extensive speckled lentiginous nevus associated with giant congenital melanocytic nevus: An unusual example of twin spotting? Eur. J. Dermatol. 13:534–536, 2003a. Torrelo, A., A. Zambrano, and R. Happle. Cutis marmorata telangiectatica congenita and extensive mongolian spots: type 5 phacomatosis pigmentovascularis. Br. J. Dermatol. 148:342–345, 2003b. Trattner, A., and A. Metzker. Partial unilateral lentiginosis. J. Am. Acad. Dermatol. 29(5 Pt 1):693–695, 1993. Trattner, A., and E. Hodak. Segmental neurofibromatosis clinically appearing as a nevus spilus. Int. J. Dermatol. 33:75, 1994. Tse, Y., V. J. Levine, S. A. McClain, and R. Ashinoff. The removal of cutaneous pigmented lesions with the Q-switched ruby laser and the Q-switched neodymium: yttrium-aluminum-garnet laser. A comparative study. J. Dermatol. Surg. Oncol. 20:795–800, 1994. Tsuruta, D., K. Fukai, M. Seto, K. Fujitani, K. Shindo, T. Hamada, and M. Ishii. Phakomatosis pigmentovascularis type IIIb associated with moyamoya disease. Pediatr. Dermatol. 16:35–38, 1999. van der Horst, J. C., and H. J. Dirksen. Zosteriform lentiginous naevus. Br. J. Dermatol. 104:104–105, 1981. Vásquez-Doval, J., M. A. Sola, F. Contreras-Mejuto, P. Redondo, J. Soto, and E. Quintanilla. Malignant melanoma developing in a speckled lentiginous nevus. Int. J. Dermatol. 34:637–638, 1995. Vignale, R. A., J. Espasandin, and H. Deneo. Melanoma extensivo superficial en nevo lentiginoso zosteriforme moteado. Med. Cut. Ibero. Lat. Am. 22:365–368, 1994. Vion, B., S. Belaïch, M. Grossin, and J. Préaux. Les aspects évolutifs du naevus sur naevus. Revue de la littérature à propos de 7 observations. Ann. Dermatol. Venereol. 112:813–819, 1985. Wagner, R. F., Jr., and W. I. Cottel. In situ malignant melanoma arising in a speckled lentiginous nevus. J. Am. Acad. Dermatol. 20:125–126, 1989. Walton, R. G., A. H. Jacobs, and A. J. Cox. Pigmented lesions in newborn infants. Br. J. Dermatol. 95:389–396, 1976. Wauschkunh, J., and B. Rohde. Systematisierte talgdüsen-, pigmentund epitheliale naevi mit neurologischer symptomatik: FeuersteinMimsches neuroektodermales syndrom. Hautarzt 22:10–13, 1971. Weinberg, J. M., P. J. Schutzer, R. M. Harris, I. A. Tangoren, S. Sood, and R. I. Rudolph. Melanoma arising in nevus spilus. Cutis 61:287–289, 1998. Welch, M. L., and W. D. James. Widespread nevus spilus. Int. J. Dermatol. 32:120–122, 1993. Woerdeman, M. J. Multiple agminate juvenile melanoma in a naevusspilus-like hyperpigmented area. Br. J. Dermatol. 110:119–120, 1984. Wollenberg, A., C. Butnaru, and T. Oppel. Phacomatosis pigmentokeratotica (Happle) in a 23-year-old man. Acta Derm. Venereol. 82:55–57, 2002. Wong, S. S. Bilateral segmental neurofibromatosis with partial unilateral lentiginosis. Br. J. Dermatol. 136:380–383, 1997. Zahorcsek, Z., A. Schmelas, and I. Schneider. Progrediente zirkumskripte lentiginose–Phakomatosis pigmentovascularis III/A. Hautarzt 39:519–523, 1988. Zvulunov, A. Segmental neurofibromatosis versus giant nevus spilus. Acta Derm. Venereol. 75:408, 1995.
1112
Melanocytic (Nevocellular) Nevi and Their Biology Julie V. Schaffer and Jean L. Bolognia
Definitions Melanocytic nevi (moles) are benign proliferations of a type of melanocyte known as a “nevus cell” (Magana-Garcia and Ackerman, 1990). The two major differences between ordinary melanocytes that reside in the basal layer of the epidermis and nevus cells are: (1) nevus cells cluster as nests within the lower epidermis and/or dermis, whereas epidermal melanocytes are evenly dispersed as single units; and (2) nevus cells do not have dendritic processes (with the exception of those within blue nevi). Both melanocytes and nevus cells are capable of producing the pigment melanin. Melanocytic nevi can be acquired or congenital, banal or atypical (“dysplastic”). The names applied to acquired nevi reflect the location of the nests of melanocytes; i.e., nests are at the dermal–epidermal junction in junctional nevi, in the dermis in intradermal nevi, and at both sites in compound nevi. Clinically, with progressive migration of melanocytes from the dermal–epidermal junction into the dermis, nevi become more elevated and less pigmented (Clark et al., 1984; Lund and Stobbe, 1949). Atypical nevi are benign acquired melanocytic nevi that share, usually to a lesser degree, some of the clinical features of melanoma (i.e., asymmetry, border irregularity, color variability, and diameter ≥6 mm). Considerable controversy has surrounded terms such as “dysplastic nevus,” and the 1992 National Institutes of Health Consensus Conference recommended the use of the more clinically descriptive term “atypical nevus.” They also recommended that these lesions be described histologically as “nevi with architectural disorder,” with specification of the degree of melanocytic atypia present. Of note, however, several studies have found that clinical and histologic atypia in melanocytic nevi are not highly correlated (Annessi et al., 2001; Klein and Barr, 1990). There are several other variants of melanocytic nevi, such as blue nevi and Spitz nevi, that have specific clinical, histologic, and molecular characteristics (see below). In addition to the basic clinicopathologic subtypes of melanocytic nevi, distinct patterns of nevus morphology can be observed. For example, some individuals tend to develop multiple melanocytic nevi with a particular clinical appearance, e.g., uniformly pink in color, light brown with central brown-black pigmentation, or targetoid (i.e., cockarde nevi) (Schaffer et al., 2001). This results in a predominant type of nevus, or “signature nevus.” The presence of signature nevi suggests that the nevi on a given individual are “programmed,” with nevus morphology depending on genetic as well as environmental factors. Indeed, McGregor et al. (1999) found a significantly higher degree of concordance in the color, size, symmetry, border irregularity, and edge distinctness of nevi (as assessed by quantitative computer image analysis) in monozygotic than dizygotic twins, with genetic influences esti-
COMMON BENIGN NEOPLASMS OF MELANOCYTES
mated to account for 40–80% of variation in these morphologic features.
Molecular Pathogenesis Clonality Molecular investigations have provided evidence that acquired nevi are clonal, and therefore represent true neoplasms rather than hamartomas (Hui et al., 2001; Maitra et al., 2002; Robinson et al., 1998). Polymerase chain reaction-based analysis of the human androgen receptor gene on the X chromosome demonstrated a nonrandom pattern of inactivation in 74%, 91%, and 89% of acquired junctional (26/34), compound (10/11), and intradermal (8/9) nevi from female patients, respectively (Hui et al., 2001; Robinson et al., 1998). The presence of nontumor cells within a specimen may lead to a “false” polyclonal result in a monoclonal lesion, potentially accounting for the lower proportion of junctional nevi found to be monoclonal (as it is difficult to separate these nevus cells from the surrounding epidermis). Together with other technical issues, this may also explain the inability of an earlier study using similar methodology to demonstrate clonality in nevi (Harada et al., 1997). More recently, Maitra et al. (2002) analyzed five chromosomal regions in samples obtained from banal acquired melanocytic nevi via laser capture microdissection, and found loss of heterozygosity in 75% of the nevi (9/12). Hui et al. (2001) emphasized that although the finding of monoclonality verifies the neoplastic nature of nevi, it does not necessarily imply a first step in the development of melanoma or even a precursor state, as suggested by others (Maitra et al., 2002; Robinson et al., 1998). Only one of six congenital melanocytic nevi analyzed in the aforementioned studies was found to be clonal (Hui et al., 2001; Maitra et al., 2002; Robinson et al., 1998). As discussed above, this may represent false polyclonal results due to the intimate admixture of congenital nevus cells with normal dermal elements. However, an alternative explanation, as previously proposed by Ackerman (1993), is that congenital nevi are polyclonal lesions more correctly classified as hamartomas.
Molecular and Cellular Features Several molecular and cellular features differentiate nevus cells from ordinary melanocytes. These include production of basic fibroblast growth factor, a lack of induction of apoptosis when exposed to transforming growth factor b in culture, and a higher intrinsic potential for adhesion (e.g., nesting) and migration (Alanko and Saksela, 2000; Mengeaud et al., 1996; Uead et al., 1994). The expression of E-cadherin, the major mediator of adhesion between epidermal melanocytes and keratinocytes, is relatively strong in junctional nevus cells, but decreases with depth in dermal nevus cells (with the exception of those in blue nevi) (Gontier et al., 2004; Herlyn et al., 2000; Krengel et al., 2004). This suggests that a reduction in keratinocyte control may play a role in the migration of nevus cells from the dermal–epidermal junction into the dermis. Some authors have proposed that breakdown of the basement
membrane by proteolytic enzymes such as matrix metalloproteinases represents another factor in the exodus of junctional nevus cells (Gontier et al., 2003; Krengel et al., 2002); however, both dermal nevi and invasive melanomas are surrounded by and able to synthesize basement membrane material, leading others to postulate that the basement membrane accompanies rather than acts as a barrier to melanocyte movement (Schaumburg-Lever et al., 2000). Compared with ordinary melanocytes, nevus cells at or near the dermal–epidermal junction exhibit increased expression of tyrosinase related protein 1 (TYRP1; involved in melanin biosynthesis) and gp100/Pmel-17 (a marker of melanocyte activation), detected by the MEL-5 and HMB-45 immunohistochemical stains, respectively (Clarkson et al., 2001; Meije et al., 2000). The expression of these proteins diminishes deeper in the dermis in banal nevi, congenital nevi, and most Spitz nevi, but not in blue nevi and some atypical nevi (Bergman et al., 1995; Shah et al., 1997; Skelton et al., 1991; Wood et al., 1991). Nevus cells undergo a process of “maturation” (also referred to as “atrophy”) as they descend into the dermis, associated with a decrease in the size and number of most cellular constituents, lower bcl-2 expression, increased apoptosis, and fewer proliferating cell nuclear antigen (PCNA)- or Ki-67-positive cells (Table 57.2) (Clark et al., 1984; Goovaerts and Buyssens, 1988; Li et al., 2000; MoralesDucret et al., 1995; Sprecher et al., 1999; Tokuda et al., 1994). In addition, dermal descent is often accompanied by Schwannian differentiation and increased expression of nerve growth factor receptor (Argenyi et al., 1996; Clark et al., 1984; Fullen et al., 2001; Goovaerts and Buyssens, 1988; Kanik et al., 1996; Smolle et al., 1988).
Genetic Features Analysis of somatic mutations in melanocytic nevi has provided further insight into their pathogenesis. Gain-of-function mutations in the BRAF gene, which encodes a serine/ threonine kinase in the mitogen-activated protein kinase (MAPK) signaling cascade (Fig. 57.13), have recently been identified in almost three-quarters of banal melanocytic nevi (184/256; particularly intradermal and papillomatous compound variants) and more than one third of primary cutaneous melanomas (170/452; see Table 57.2) (Cohen et al., 2004; Edwards et al., 2004; Kumar et al., 2004; Maldonado et al., 2003; Omholt et al., 2003; Pollock et al., 2003; Reifenberger et al., 2004; Sasaki et al., 2004; Sekulic et al., 2004; Shinozaki et al., 2004; Uribe et al., 2003; Yazdi et al., 2003). This implicates activation of the MAPK pathway as an important step in tumorigenesis rather than malignancy (Arbiser, 2003). Of note, a single phosphomimetic substitution (V599E) accounts for >90% of the activating BRAF mutations in melanocytic tumors, and “ultraviolet (UV) signature” (e.g., pyrimidine dimer) mutations have not been found (Kumar et al., 2004; Pollock et al., 2003; Uribe et al., 2003). BRAF mutations are seen most often in melanomas that occur on intermittently sun-exposed skin, and infrequently in those that arise on chronically sun-exposed skin, on mucous membranes, or 1113
1114
10 76 78 60 9 0 38 38
Nevi Junctional Compound Intradermal Congenital Blue Spitz Atypical Primary melanomas 30 ≥100 >50 ≥100 ≥46 >100 >50
Atypical nevi of greater importance than total number of nevi Roush et al., 1988 246/134 ≥16 Augustsson et al., 1991a 121/378 ≥150 105/181 ≥25 Halpern et al., 1991 Bataille et al., 1996 426/416 ≥100 Tucker et al., 1997 716/1014 ≥100 Bataille et al., 1998 117/163 UK ≥46 Landi et al., 2001 183/179 ≥52 Bakos et al., 2002 103/206 ≥30
Relative risk* (95% CI)
Number of atypical nevi
Relative risk† (95% CI)
12.1 (2.7–53.9) 9.8 (2.5–38.6) M: 13.9 (2.7–71) F: 6.7 (2.9–15) 13.7 (4.9–38.4) 14.9(5.8–38.4)§ 7.6 (3.5–16.2) 10.1 (3.1–22.9) 7.4 (2.9–18.6)‡ 6.9 (1.6–30.3)‡§ 12.7 (4.9–33.5)‡§ 9.5 (5.4–16.8)‡§ 46.5 (11.4–190.8)‡§ 12.7 (4.8–33.3)‡
NR ≥6 ≥3 >1 ≥3 ≥5 ≥1 ≥5 NR ≥3 NR NR NR
NR 6.3 (1.9–21.5) M: 4.5 (0.8–26) F: 4.4 (1.5–13) 2.6 (1.3–5.4) NS 6.1 (2.3–16.1) 2.4 (0.5–11.4) 2.9 (0.9–9.3)‡ NR 4.6 (2.0–10.7)‡# NR NR NR
1.2 (0.7–2.0) 2.6 (1.1–6.1) 6.5 (3.0–14.1)‡§ 3.1 (P10
5
5 8
>10
3
>5
>6 8
1.3
5
11
10
Size (cm)
Blue plaque, overlying blue-white nodules, satellite papule# Blue plaque with gray-brown papules; background tan patch
Gray-blue plaque, superimposed nodule
Pigmented lesion Area of alopecia with subtle pigmentation, 5 superimposed nodules
Bluish patch
Bluish plaque
Pigmented nodule with satellite papules Pigmented lesion Bluish nodules, macules, and papules Pigmented papules
Black macules w/in a blue patch Blue-black plaque with satellite nodules
Rows of peripilar blue, black, and brown papules
Clinical features
+
+
NR
+ +
NR
NR
+
NR NR
+
+
+
+
NR
+
NR
NR +
+
NR
NR
NR NR
NR
NR
NR
NR
NR
+
NR
NR +
+
+
NR
NR NR
NR
NR
NR
NR
Melanocytes surrounding: Adnexae* Vessels Nerves
NR
+
+ + (also enlarged, tortuous nerves and tactoid bodies) + (also tactoid bodies)
NR
NR
NR + (also tactoid bodies) NR
NR
NR
NR
+
Schwannian differentiation
NR
Mucinous with CD34+ spindle cells, dilated vessels, mast cells NR
NR Mucinous with CD34+ spindle cells, floretlike giant cells, dilated vessels, mast cells
NR
NR
NR
NR NR
NR
Fibrous; melanophages
NR
Collagenous; scattered melanophages
Stromal features
Grouped hyperplastic eccrine glands and ducts in the papillary dermis; ruptured epidermoid cyst
Moderate regular acanthosis; no hair follicles NR
NR Elongated, wide rete ridges; alopecia with rare dystrophic follicles
NR
Focal lentiginous epidermal hyperplasia; Aberrant basaloid follicular structures in the dermis NR
Basaloid proliferation in the dermis NR NR
NR
Mild epidermal hyperplasia with hyperkeratosis, horn cysts, and basilar hyperpigmentation NR
Epithelial features
—
—
—
+ (50) —
+ (67)
+ (35)
+ (25)
+ (11) + (12)
—
+ (65)
—
—
Melanoma** (age in y)
*Perifollicular and perieccrine distribution. †Following the distribution of the long thoracic nerve. ‡Excluded case 3 from Pearson et al. (features suggestive of a neurotized congenital melanocytic nevus) and case 1 from Smith et al. (no melanocytic component). #Clinically apparent melanocytic infiltration of underlying muscle, nearby nerves, the parotid gland, and regional lymph nodes (the latter limited to the capsule). §Variant of speckled lentiginous nevus consisting of an “agminate and plaque-type blue nevus combined with lentigo, associated with follicular cyst and eccrine changes” that was noted to have features of a PNH; because PNH was not the overall diagnosis, this case was not included in tabulations of the clinical and histologic features of PNH. **Melanoma variant termed “cutaneous malignant melanotic neurocristic tumor.” PNH, pilar neurocristic hamartoma; DM, dermal melanocytosis; BN, blue nevus; NH, neurocristic hamartoma; NCH, neurocristic cutaneous hamartoma; NR, not reported.
Betti et al., 1997
NCH
Smith et al., 1998‡; Mebish et al., 1998
Crowson et al., 1996/ Resnik et al., 1994 Pearson et al., 1996‡
NH
PNH and DM BN with features of PNH PNH
Kikuchi et al., 1983
Pathy et al., 1993
PNH
Tutill et al., 1982
Diagnosis
Table 58.2. Clinical and histologic features of neurocristic hamartomas.
CHAPTER 58
Fig. 58.8. Pilar neurocristic hamartoma with clustering of blue, black, and brown macules and papules.
Fig. 58.9. Close-up of the papules in Fig. 58.8, showing their rowlike perifollicular arrangement. (From Tuthill, R. J., W. H. Clark, Jr., and A. Levine. Pilar neurocristic hamartoma: its relationship to blue nevus and equine melanotic disease. Arch. Dermatol. 118:592–596, 1982, with permission from the publisher.)
11–67 years; mean = 35 years for the subset of lesions that were congenital) (Pathy et al., 1993; Pearson et al., 1996). Although malignant blue nevi develop in a similar age range and, as noted above, share a predilection for the scalp, they tend to have increased cytologic atypia and more aggressive behavior (Connelly and Smith, 1991; Goldenhersh et al., 1988). Lastly, in contrast with CMMNTs, more than half of melanomas originating in large CMN develop before the age of 5 years (Marghoob et al., 1996).
epithelioid melanocytes containing variable amounts of fine brown pigment. These melanocytes were diffusely positive with HMB-45 immunohistochemical staining (Mezebish et al., 1998; Smith et al., 1998). In 8/13 cases, 4 of which were referred to as pilar neurocristic hamartomas (see Table 58.2), a prominent perifollicular and/or perieccrine distribution of such melanocytes was noted (Bevona et al., 2003; Crowson et al., 1996; Kikuchi et al., 1983; Pathy et al., 1993; Pearson et al., 1996; Smith et al., 1998; Tuthill et al., 1982); the melanocytes were described as “streaming along” the connective tissue sheath of the hair follicle (Kikuchi et al., 1983), “wrapped around” hair follicles and eccrine glands (Pathy et al., 1993), “investing” adnexal structures in whorls and fascicles (Pearson et al., 1996), and “invad[ing]” the adventitial dermis of the hair follicle (Bevona et al., 2003). Tuthill et al. (1982) argued that the combination of a striking accumulation of melanocytes around adnexal structures and only a few scattered pigmented spindle cells in the dermis between the hair follicles distinguished the pilar neurocristic hamartoma from patch- and plaque-type blue nevi (see below). However, most lesions subsequently reported as pilar neurocristic hamartoma or neurocristic hamartoma also had fascicles, cords, and/or sheets of spindled or epithelioid melanocytes elsewhere in the dermis, in some cases surrounding blood vessels and/or nerves and extending into the subcutaneous fat, fascia, and even muscle (Bevona et al., 2003; Pearson et al., 1996; Smith et al., 1998). One patient had benign pigmented spindle cells within the capsule of regional lymph nodes (Bevona et al., 2003). Neuroid structures showing schwannian differentiation were seen in 6/13 cases of neurocristic hamartoma (Bevona et al., 2003; Pearson et al., 1996; Smith et al., 1998; Tuthill et al., 1982; see Table 58.2). Several cases demonstrated abnormal epithelial elements such as basaloid or eccrine proliferations (Crowson et al., 1996; Betti et al., 1997), aberrant basaloid follicular structures (Pearson et al., 1996), and dystrophic follicles (Smith et al., 1998). These observations, together with a diffusely CD34-positive lesional stroma (Mezebish et al., 1998), suggest that neurocristic derivatives in the dermis may have a “mesenchymal” role in influencing the induction of appendageal epithelial development.
Laboratory Findings There are no laboratory findings that are specific for neurocristic hamartoma, except perhaps the histologic finding of pigmented dermal melanocytes, particularly in a periadnexal distribution, in combination with evidence of schwannian differentiation.
Histology Cases reported as neurocristic hamartoma have shown considerable histologic heterogeneity, with different proportions, distributions, and types of melanocytic, schwannian, stromal, and epithelial components (Bevona et al., 2003; see Table 58.2). Nonetheless, all of the lesions demonstrated to some degree a dermal proliferation of dendritic spindled and/or 1160
Differential Diagnosis The major considerations in the differential diagnosis are patch- and plaque-type blue nevi. Patch-type blue nevi present as blue-gray patches that histologically demonstrate a more prominent proliferation of pigmented dendritic dermal melanocytes than Mongolian spots. In plaque-type blue nevi, the
RARE BENIGN NEOPLASMS OF MELANOCYTES
lesions are elevated and are often composed of a cluster of papules and nodules on a blue-gray background (Busam et al., 2000, Pittman and Fisher, 1976). As noted above, these entities have a predilection for the trunk rather than the scalp. Like pilar neurocristic hamartomas, some plaque-type blue nevi demonstrate a periappendageal accumulation of pigmented spindle cells (Tsoïtis et al., 1983; Velez et al., 1993; Wen, 1997), although this is typically in the setting of diffuse infiltration of the interfollicular reticular dermis. In a study of biopsy specimens submitted for routine histologic examination, Misago (2000) found that 63% of cellular blue nevi (5/8) and 9% of common blue nevi (10/112) showed evidence of peripheral nerve sheath differentiation. Some of the lesions were histologically indistinguishable from a neurocristic hamartoma, but clinical information was not available. Smith et al. (2001) reported four cases of congenital cellular blue nevi with diffuse expression of CD34. They proposed that these lesions, which measured 3–6 cm in diameter and were found on the head, neck, and upper back, arose from primitive cells derived from the neural crest and fell within the spectrum of neurocristic hamartomas. Other neoplasms consisting of a combination of cell types derived from the neural crest have been described. For example, Karcioglu et al. (1977) reported an “ectomesenchymoma” showing ganglionic, schwannian, melanocytic, and rhabdomyoblastic differentiation that presented as a tumor on the face of an infant. Misago et al. (1999) observed a slowly enlarging blue-black plaque on the upper arm of a middleaged woman; histologically, the lesion demonstrated both dermal melanocytosis and the features of an immature nerve sheath myxoma.
Pathogenesis and Animal Models A neurocristic hamartoma is thought to result from the aberrant development of pluripotent neural crest cells after their migration to the skin (Mezebish et al., 1998; Pearson et al., 1996). Neural crest cells normally give rise to melanocytes, neurosustentacular cells (e.g., Schwann cells) and, particularly in cephalic areas, neuromesenchymal cells (Reed, 1983). The latter can serve a fibrogenic function, and may also influence the development of epithelial structures such as hair follicles and eccrine glands. Neurocristic hamartomas would fall within a spectrum defined by blue nevi at one end and schwannomas at the other. “Equine melanotic disease” is a disorder characterized by a progressive growth of nodules composed of melanin-laden cells in the dermis of the skin and other tissues. It is seen in horses that turn dappled gray then white as they age (Levene, 1971; Tuthill et al., 1982). Histologically, collections of pigmented spindle cells are observed around hair follicles and sweat glands. Because of the overlap in gross and histologic features, Tuthill et al. (1982) proposed that pilar neurocristic hamartoma was related to equine melanotic disease. However, in contrast with the pilar neurocristic hamartoma, the latter often progresses to involve lymph nodes and viscera and occasionally disseminates rapidly.
Treatment A conservative approach would be to treat neurocristic hamartomas in a manner similar to that advocated for CMN and cellular blue nevi. Any clinically significant change in the lesion would necessitate performance of a biopsy to exclude the possible development of a cutaneous melanoma. Surgical excision could be considered for reasons of cosmesis or for lesions thought to be at increased risk of malignancy and/or too difficult to follow clinically, e.g., those on the scalp.
Prognosis The development of a melanoma in more than half of the 13 reported patients with neurocristic hamartomas is concerning. Most of these individuals had lesions on the scalp, a site where the closely related cellular blue nevus is known to have an especially high risk for transformation to a malignant blue nevus (Goldenhersh et al., 1988). Longitudinal observation, perhaps aided by photography, and education of the patient regarding the clinical signs of malignant degeneration are indicated. If feasible, considering the size of the lesion, patients with a neurocristic hamartoma on the scalp should be given the option of surgical excision.
References Bastian, B. C., J. Xiong, I. J. Frieden, M. L. Williams, P. Chou, K. Busam, D. Pinkel, and P. E. LeBoit. Genetic changes in neoplasms arising in congenital melanocytic nevi: Differences between nodular proliferations and melanomas. Am. J. Pathol. 161:1163–1169, 2002. Betti, R., E. Inselvini, M. Palvarini, and C. Crosti. Agminate and plaque-type blue nevus combined with lentigo, associated with follicular cyst and eccrine changes: A variant of speckled lentiginous nevus. Dermatology 195:387–390, 1997. Bevona, C., Z. Tannous, and H. Tsao. Dermal melanocytic proliferation with features of a plaque-type blue nevus and neurocristic hamartoma. J. Am. Acad. Dermatol. 49:924–929, 2003. Busam, K. J., J. M. Woodruff, R. A. Erlandson, and M. S. Brady. Large plaque-type blue nevus with subcutaneous cellular nodules. Am. J. Surg. Pathol. 24:92–99, 2000. Clark, W. H., Jr., D. E. Elder, and D. Guerry. Dysplastic nevi and malignant melanoma. In: Pathology of the Skin, E. R. Farmer, and A. F. Hood (eds). Norwalk: Appleton and Lange, 1990, pp. 684–756. Connelly, J., and J. L. Smith Jr. Malignant blue nevus. Cancer 67:2653–2657, 1991. Crowson, A. N., C. M. Magro, and W. H. Clark, Jr.. Pilar neurocristic hamartoma. J. Am. Acad. Dermatol. 34:715, 1996. Goldenhersh, M. A., R. C. Savin, R. L. Barnhill, and K. S. Stenn. Malignant blue nevus. J. Am. Acad. Dermatol. 19:712–722, 1988. Grichnik, J. M., A. R. Rhodes, and A. J. Sober. Benign neoplasias and hyperplasias of melanocytes. In: Fitzpatrick’s Dermatology in General Medicine, 6th ed., I. M Freedberg, A. Z. Eisen, K. Wolff, K. F. Austen, L. A. Goldsmith, and S. I. Katz (eds). New York: McGraw-Hill, Inc., 2003, pp. 897–899. Hartmann, L. C., F. Oliver, R. K. Winkelmann, T. V. Colby, T. M. Sundt, and B. P. O’Neill. Blue nevus and nevus of Ota associated with dural melanoma. Cancer 64:182–186, 1989. Jimenez, E., P. Valle, and P. Villegas. Unusual acquired dermal melanocytosis. J. Am. Acad. Dermatol. 30:277–278, 1994.
1161
CHAPTER 58 Karcioglu, Z., A. Someren, and S. J. Mathes. Ectomesenchymoma: A malignant tumor of migratory neural crest (ectomesenchyme) remnants showing ganglionic, schwannian, melanocytic and rhabdomyoblastic differentiation. Cancer 39:2486–2496, 1977. Kikuchi, I., S. Inoue, I. Taketomi, and T. Ono. Two cases of nevus fuscocaeruleus with pain, including a case of pilar neurocristic hamartoma. J. Dermatol. 10:275–280, 1983. Levene, A. Equine melanotic disease. Tumori 57:133–168, 1971. Marghoob, A. A., S. P. Schoenbach, A. W. Kopf, S. J. Orlow, R. Nossa, and R. S. Bart. Large congenital melanocytic nevi and the risk for the development of malignant melanoma: a prospective study. Arch. Dermatol. 132:170, 1996. Mevorah, B., E. Frenk, and J. Delacretaz. Dermal melanocytosis: Report of an unusual case. Dermatologica 154:107–114, 1977. Mezebish, D., K. Smith, J. Williams, P. Menon, J. Crittenden, and H. Skelton. Neurocristic cutaneous hamartoma: A distinctive dermal melanocytosis with an unknown malignant potential. Mod. Pathol. 11:573–578, 1998. Misago, N. The relationship between melanocytes and peripheral nerve sheath cells (part II): Blue nevus with peripheral nerve sheath differentiation. Am. J. Dermatopathol. 22:230–236, 2000. Misago, N., Y. Narisawa, T. Inoue, and N. Yonemitsu. Unusually differentiating immature nerve sheath myxoma in association with dermal melanocytosis. Am. J. Dermatopathol. 21:55–62, 1999. Pathy, A. L., T. N. Helm, D. Elston, W. F. Bergfeld, and R. J. Tuthill. Malignant melanoma arising in a blue nevus with features of pilar neurocristic hamartoma. J. Cutan. Pathol. 20:459–464, 1993. Pearson, J. P., S. Weiss, and J. T. Headington. Cutaneous malignant melanotic neurocristic tumors arising in neurocristic hamartomas:
1162
A melanocytic tumor morphologically and biologically distinct from common melanoma. Am. J. Surg. Pathol. 20:665–677, 1996. Pittman, J. L., and B. K. Fisher. Plaque-type blue nevus. Arch. Dermatol. 112:1127–1128, 1976. Reed, R. J. Neuromesenchyme: The concept of a neurocristic effector cell for dermal mesenchyme. Am. J. Dermatopathol. 5:385–395, 1983. Resnik, K. S., G. R. Kantor, G. H. Telang, and N. R. Howe. Ichthyosis. Basal cell carcinoma. Granuloma annulare. Self-assessment examination of the American Academy of Dermatology. J. Am. Acad. Dermatol. 30:153–156, 1994. Smith, K. J., D. Mezebish, J. Williams, M. L. Elgart, and H. G. Skelton. The spectrum of neurocristic cutaneous hamartoma: clinicopathologic and immunohistochemical study of three cases. Ann. Diagn. Pathol. 2:213–223, 1998. Smith, K. J., M. Germain, J. Williams, and H. G. Skelton. CD34positive cellular blue nevi. J. Cutan. Pathol. 28:145–150, 2001. Tsoïtis, G., C. Kanitakis, and E. Kapetis. Naevus blue multinodulaire en plaque, superficiel et neuroïde. Ann. Dermatol. Venereol. 110:231–235, 1983. Tuthill, R. J., W. H. Clark Jr., and A. Levene. Pilar neurocristic hamartoma: its relationship to blue nevus and equine melanotic disease. Arch. Dermatol. 118:592–596, 1982. Velez, A., E. del-Rio, C. Martin-de-Hijas, V. Furio, E. Sanchez Yus. Agminated blue nevi: Case report and review of the literature. Dermatology 186:144–148, 1993. Wen, S. Y. Plaque-type blue nevus: Review and an unusual case. Acta Derm. Venereol. (Stockh.) 77:458–459, 1997. Wlotzke, U., U. Hohenleutner, R. Hein, R.-M. Szeimies, and M. Landthaler. Maligner infiltrierender blauer nävus vom plaque-typ: Fallbericht und übersicht. Hautarzt 45:860–864, 1995.
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
8
Treatment of Pigmentary Disorders
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
59
Topical Treatment of Pigmentary Disorders Rebat M. Halder and James J. Nordlund
Hyperpigmentation Successful treatment of hyperpigmentation depends on the identification of the mechanism for the abnormal color (see Chapter 28 for discussion of pathophysiology). Many disorders are caused by deposition of excessive quantities of melanin in the epidermis. Some of these conditions are amenable to lightening with applications of topical agents that interfere with production of melanin by the melanocyte. Melasma responds rather well to topical therapies. Café-au-lait macules do not respond as easily but with higher concentrations of lightening agents, can be made to fade. Other disorders are manifestations of deposition of melanin within the dermis. The melanin can be located between collagen bundles or within macrophages called dermal melanosis (see Chapter 28). Or melanocytes replete with melanin can be located in the dermis, a phenomenon called dermal melanocytosis. Melanin within the dermis cannot be treated by applications of topical agents. All of the available topical agents such as hydroquinone function either by blocking production of melanin or enhancing its desquamation. Thus no condition characterized by the presence of melanin within the dermis can be treated topically. Dermal melanin can be treated successfully only with lasers (Chapter 64). Epidermis that is abnormally thick such as is seen in ichthyosis nigricans (Chapters 27 and 28), seborrheic keratoses, or lentigines (Chapters 27 and 28) does not respond to topical treatment with lightening agents that block synthesis of melanin. Some of these conditions might respond to retinoids that will return the structure of the epidermis back to a normal condition. Still other conditions are caused by deposition of extraneous materials in the dermis. Hemosiderin, medications, heavy metals or tattoo dyes (Chapter 54) all are examples of foreign substances located in the dermis that cause hyperpigmentation. None of these are treated with lightening agents and some may require laser therapy (Chapter 64). The chemical agents described below are useful for those conditions caused by excessive production of melanin in the epidermis such as melasma, solar lentigines, postinflammatory hyperpigmentation, and for similar conditions. Congenital forms of hyperpigmentation such as café-au-lait spots do not respond readily to topical or systemic therapy. They must be treated with lasers although the probability of success is mod-
erate. It is critical in prescribing topical agents to understand how they alter the color of skin.
Hydroquinone Hydroquinone is the best known and studied lightening agent. Often it is labeled a bleach, a misnomer that suggests it produces its effects on the skin by modification of the melanin polymer. Rather it functions as an inhibitor of melanin synthesis (Arndt and Fitzpatrick, 1965; Fitzpatrick et al., 1966). More recent studies suggest that it might block formation of melanin by alteration of cellular metabolism (Penney et al., 1984; Smith et al., 1988). In cell cultures hydroquinone inhibits the synthesis of DNA and RNA. The inhibition seems to be dependent on the presence and activity of tyrosinase rather than melanin content of the cell (Penney et al., 1984; Smith et al., 1988). Thus hydroquinone is not a useful agent for altering the color of melanin already deposited within the epidermis or dermis. It can be used to retard or stop production of new melanin in many conditions such as melasma (Grimes, 1995) or postinflammatory hyperpigmentation. Hydroquinone is available in the United States in 2%, 3%, and 4% concentrations in a variety of diluents. The 4% seems to be more effective than the 2%. The agents are applied sparingly twice daily (Figs 59.1 and 59.2). Hydroquinone by itself is a weak therapeutic agent. It generally must be applied for prolonged periods of time for an effect to be seen, usually three to six months (Engasser and Maibach, 1981) (Fig. 59.3). Hydroquinone has been used in combination with other medications such as steroids and retinoids (see below). Its efficacy seems enhanced by combining it with these other preparations. Hydroquinone has been used successfully for many forms of epidermal hyperpigmentation. The classic condition is melasma. This condition may be caused by both epidermal and dermal melanosis. Only the epidermal component responds to applications of hydroquinone. A 3% hydroalcoholic solution of hydroquinone was used to treat 46 women with melasma. The investigators noted that 40 women (87%) improved significantly (Sanchez and Vazquez, 1982). Commercially available combinations such as TriLuma® that contains hydroquinone, tretinoin, and fluocinolone acetonide have been effective in lightening conditions such as melasma. Hydroquinone has been used to prevent hyperpigmentation following procedures such as laser treatments or surgery (Fulton, 1991; Gilchrest and Goldwyn, 1981; Ho et al., 1995). 1165
CHAPTER 59
Fig. 59.1. Boy with hyperpigmented skin in a graft used to treat a thermal burn (see also Plate 59.1, pp. 494–495).
Fig. 59.3. An African American woman with hypopigmented skin from daily applications of hydroquinone. Her normal color is visible as dark streaks on her cheeks and chin (see also Plate 59.3, pp. 494–495). Fig. 59.2. Pigmentation has disappeared following daily applications of 4% hydroquinone for nine months (see also Plate 59.2, pp. 494–495).
It seems to work best when used in combination with other topical agents (see section on Combination therapy below). Hydroquinone is remarkably safe although minor toxicity has been described. Some have suggested that it causes depigmentation by destruction of the melanocyte (Kersey and Stevenson, 1981; Markey et al., 1989). However the capacity of hydroquinone to destroy melanocytes and cause depigmentation is debated. It is well documented that derivatives of hydroquinone with aliphatic or aromatic side chains do cause depigmentation [for review of this controversy see Cummings and Nordlund (1995)]. It has been noted that hydroquinone and its chemical derivatives must not be confused or considered simple variations of each other (BentleyPhillips and Bayles, 1975). The major side effect of hydroquinone is localized ochronosis associated with formation of colloid milium (Camarasa and Serra-Baldrich, 1994; Diven et al., 1990; Findlay and de Beer,
1166
1980; Findlay et al., 1975; Hardwick et al., 1989; Hoshaw et al., 1985; Hull and Procter, 1990; Jordaan and Mulligan, 1990; Jordaan and Van Niekerk, 1991; Lawrence et al., 1988; Tidman et al., 1986; Weiss et al., 1990) (Fig. 58.4). Ochronosis seems to occur in those individuals who use a hydroquinone preparation for excessively prolonged periods of time, usually one or more years and who are exposed to intense sunlight. Hydroquinone also has been reported to alter the color of nails (Coulson, 1993; Mann and Harman, 1983).
Azelaic Acid Azelaic acid is a dicarboxylic acid with nine carbons. It has been proposed that it can lighten skin by inhibiting the activity of the tyrosinase enzyme necessary for melanin production by interruption of the oxidative systems of the melanocyte (Nazzaro-Porro, 1987). This agent first was introduced as a therapy for lentigo maligna, a precursor of melanoma (Breathnach et al., 1989a,b; Fitton and Goa, 1991; Nazzaro-Porro et al., 1989; Rodriguez Prieto et al., 1993). Because it does not destroy the malignancy which can spread and cause the demise of the patient, azelaic acid is no longer used for the treatment
TOPICAL TREATMENT OF PIGMENTARY DISORDERS
caused by physical or photochemical agents, and lentigo maligna melanoma and other disorders characterized by abnormal proliferation of melanocytes. Its mechanism of action is to inhibit DNA synthesis and mitochondrial enzymes, thereby inducing direct cytotoxic effects toward the melanocyte (Smith et al., 1988). Topical azelaic acid has no depigmentation effect on normally pigmented skin, freckles, senile lentigines, and nevi. This specificity may be attributed to its selective effects on abnormal melanocytes. Azelaic acid can be used for postinflammatory hyperpigmentation in acne (Rodriguez Prieto et al., 1993). Free radicals are believed to contribute to hyperpigmentation, and azelaic acid acts by reducing free radical production (Weinstein et al., 1991). Azelaic acid 20% is currently available in the United States and is only indicated for the treatment of acne, although it has off-label use for hyperpigmentation. In the treatment of melasma, a 24-week study in South America found that a 20% concentration of azelaic acid was equivalent to 2% hydroquinone (Weiss et al., 1988). In the Philippines, a study found that 20% concentration of azelaic acid was better than 2% hydroquinone (Snellman et al., 2004).
Topical Steroids
Fig. 59.4. Localized ochronosis from prolonged and excessive use of hydroquinone (see also Plate 59.4, pp. 494–495).
of lentigo maligna. More recently it has been used for treatment of conditions like melasma. It is available in a 20% concentration for application twice daily. Its success in treating melasma is controversial. Some investigators have found it useful (Balina and Graupe, 1991; Piquero Martin et al., 1988; Rigoni et al., 1989; Verallo-Rowell et al., 1989) but others have reported little success with this agent (Duteil and Ortonne, 1992; Mayer-da Silva et al., 1987; Pathak et al., 1985). It is not clear why the results are discrepant. One report suggests that azelaic acid is useful for treatment of acropigmentation of Kitamura (Kameyama et al., 1992). Azelaic acid cream is applied once or twice daily to the hyperpigmented skin. The treatment must be continued for many months. Often this agent is used in combination with one or several of the other lightening agents including hydroquinone, tretinoin, and/or steroids. Its use originated from the findings that Pityrosporum spp. can oxidize unsaturated fatty acids to dicarboxylic acids, which competitively inhibit tyrosinase. Azelaic acid was initially developed as a topical drug with therapeutic effects for the treatment of acne. Because of its effect on tyrosinase, however, it has also been used to treat melasma, lentigo maligna, and other disorders of hyperpigmentation (Ho et al., 1995; Smith et al., 1988) (28,66). Azelaic acid has been reported to be effective for hypermelanosis
Topical steroids have been used for treatment of various hyperpigmentary disorders. The mechanism by which they produce a lightening of the skin is not known. However, it is well established that injection of steroids into the skin causes hypopigmentation (Fig. 59.5). The loss of color is transient, but indicates steroids might be useful in treating pigmentary disorders. It has been suggested that they might have a direct effect on the synthesis of melanin. Melanocytes are known to respond to a variety of chemical mediators like prostaglandins and leukotrienes. Steroids might alter melanocyte function by inhibition of prostaglandin or cytokine production by various cells of the epidermis. Steroids have been combined with tretinoin and hydroquinone in one of the most effective of all therapies for hyperpigmentation (Kligman and Willis, 1975). Topical steroids can be used alone as a modality for epidermal hyperpigmentation. It is hypothesized that corticosteroids suppress the biosynthetic and secretory functions of melanocytes, thus suppressing melanin production without causing destruction of the melanocyte (Kligman and Willis, 1975). High potency steroids can inhibit melanin formation but cause significant side effects, such as epidermal thinning, telangiectasia, acne, form eruption, and increased thickness of vellus hair. Generally midpotency steroids are prescribed such as triamcinolone acetonide 0.1%, desonide 0.05%, or similar steroid. Steroids are applied once or twice daily until the skin returns to normal color, a process that often takes many months or a year.
Topical Retinoids The use of tretinoin was first suggested as a combination therapy (Kligman and Willis, 1975) in which tretinoin was
1167
CHAPTER 59
Fig. 59.6. Melasma in an Asian woman (see also Plate 59.6, pp. 494–495).
Fig. 59.5. Marked hypopigmentation of the epidermis caused by injections of steroids into the skin. The hypopigmentation follows the route of lymphatics. The hypopigmentation is reversible (see also Plate 59.5, pp. 494–495).
considered to function to enhance penetration of hydroquinone. Later tretinoin was recognized to have effects on the pigmentary system of its own. It has been used successfully as a topical treatment for solar lentigines and photodamage (Bulengo-Ransby et al., 1993; Griffiths et al., 1993, 1994; Humphreys et al., 1996; Kimbrough-Green et al., 1994; Leyden et al., 1989; Lowe et al., 1994; Olsen et al., 1992; Ortonne, 1992; Pathak et al., 1986; Rafal et al., 1992; Tadaki et al., 1993; Weinstein et al., 1991; Weiss et al., 1988). Tretinoin can be used for treatment of any form of epidermal hyperpigmentation. It might function in several ways including enhancing desquamation of preformed melanin and inhibition of tyrosinase thereby inhibiting melanin synthesis. Retinoids applied topically or taken orally also might have beneficial effects on those forms of hyperpigmentation caused by abnormal keratinization such as is found in various forms of ichthyosis or acanthosis nigricans. This agent is applied once or twice daily until the skin returns to its normal color. Because it is irritating for many individuals, the dose must be adjusted to prevent inflammation. Inflammation might cause an increase in the hyperpigmentation, especially in those with dark skin. Results of recent studies suggest that tretinoin is useful for the treatment of melasma (Griffiths et al., 1993) (Figs 59.6 and 59.7). A group of 38 women participated in the study. 1168
Fig. 59.7. The melasma has responded to applications of hydroquinone and tretinoin (see also Plate 59.7, pp. 494–495).
Nineteen were in the tretinoin treated group. Of these, 13 reported significant improvement compared to one in the control group. However, many reported irritation from the tretinoin. In another study of melasma in black patients, the investigator found that tretinoin alone produced significant improvement in a third of subjects compared with 10% in the control group. Irritation including desquamation and erythema was noted in 88% of subjects (Kimbrough-Green et al., 1994). Not all studies have confirmed the usefulness of tretinoin for melasma (Tadaki et al., 1993). Tretinoin has been used successfully for treatment of postinflammatory hyperpigmentation caused by acne, dermatitis, and abrasions (Bulengo-Ransby et al., 1993). Although tretinoin can be effective as monotherapy for hyperpigmentation and melasma, it requires 20- to 40-week treatment periods. Darker-skinned people who develop dermatitis from tretinoin may develop postinflammatory hyperpigmentation secondary to the dermatitis. In a randomized clinical trial, the efficacy of adapalene 0.1% was found to be comparable with that of tretinoin 0.05% cream in the treatment of melasma (mainly epidermal
TOPICAL TREATMENT OF PIGMENTARY DISORDERS
type). The results showed fewer side effects and greater acceptability among patients using adapalene (Dogra et al., 2002).
Kojic Acid Kojic acid (5-hydroxy-2(hydroxymethyl)-4-pyrone) is a naturally occurring hydrophilic fungal derivative, evolved from certain species of Acetobacter, Aspergillus, and Penicillium, and used in the treatment of hyperpigmentation disorders (Weiss et al., 1990). It acts by inhibiting the production of free tyrosinase with efficacy similar to hydroquinone (Cabanes et al., 1994). In Japan, kojic acid has been increasingly used in skin care products. This is because, until recently, topically applied kojic acid at 1% concentration had not exhibited any sensitizing activity (Wong and Jimbow, 1991). More recent long-term Japanese studies, however, have shown that kojic acid has the potential for causing contact dermatitis and erythema (Wong and Jimbow, 1991).
N-Acetyl-5-cysteaminylphenol This compound is a thioether that recently has been described as a useful agent for the treatment of epidermal hyperpigmentation (Ito et al., 1987; Jimbow, 1991; Pankovich et al., 1990; Wong and Jimbow, 1991). It is not yet available in North America. Results of studies on black mice suggest that the chemical is capable of completely inhibiting melanin production within the hair follicle (Wong and Jimbow, 1991). NAcetyl-5-cysteaminylphenol acts to decrease intracellular glutathione by stimulating pheomelanin rather than eumelanin. The agent has been used to treat women with melasma (Jimbow, 1991). Of the 12 women treated, one showed complete resolution of the condition. In addition eight showed marked improvement and the others moderate improvement. There were no clinical failures. Improvement of melanoderma in patients with melasma was evident after two to four weeks of daily application of N-acetyl-4-cysteaminylphenol. The investigators observed that the number of melanosomes and quantity of melanin in the keratinocytes decreased significantly following therapy (Jimbow, 1991).
tated the epidermal penetration of the hydroquinone. The tretinoin-induced irritation was reduced by the corticosteroid. The first triple combination topical therapy approved by the US Food and Drug Administration for melasma is a modified formulation comprising fluocinolone acetonide, hydroquinone 4%, and tretinoin 0.05% (TriLuma®). In studies of patients with melasma, 78% had complete or near clearing after eight weeks of therapy. Similar results and favorable safety profile were seen in a 12-month study.
Arbutin Arbutin, which is the b-D-glupyranoside derivative of hydroquinone, is a naturally occurring plant-derived compound that has been used for postinflammatory hyperpigmentation (Boissy et al., 2005; Halder and Richard, 2004; Hori et al., 2004). It is effective in the treatment of disorders of hyperpigmentation characterized by hyperactive melanocytes (Boissy et al., 2005; Halder and Richard, 2004; Hori et al., 2004). The action of arbutin is dependent on its concentration. Higher concentrations are more efficacious than lower concentrations, but they may also result in a paradoxical hyperpigmentation (Boissy et al., 2005; Halder and Richard, 2004; Hori et al., 2004). In comparative in vitro studies of various compounds used to improve the appearance of disorders of hyperpigmentation, arbutin was found to be less toxic than hydroquinone. A dose-dependent reduction in tyrosinase activity and melanin content in melanocytes was also demonstrated.
Licorice Extract Licorice extract is not yet available in North America, but has been used in other parts of the world, particularly in Egypt. Its mechanism of action is similar to that of kojic acid. The main component of the hydrophobic fraction of licorice extract is glabridin. Studies investigating the inhibitory effects of glabridin on melanogenesis and inflammation have shown that it inhibits tyrosinase activity of these cells. No effect on DNA synthesis was detectable.
Mequinol Combination Therapy The most effective preparation for the treatment of epidermal hyperpigmentation is a combination of hydroquinone, a steroid, and tretinoin (Kligman and Willis, 1975). The combination strongly inhibits the production of melanin without destruction of the melanocytes (Kligman and Willis, 1975). It is likely that the three agents each work in different ways. A common preparation is 4% hydroquinone, tretinoin 0.05%, and triamcinolone acetonide 0.1% (or desonide 0.05%) each applied separately (Gilchrest and Goldwyn, 1981; Ho et al., 1995; Pathak et al., 1986). Each medication is applied twice daily if tolerated. Even with triple therapy, it is necessary to continue treatment for many months. The first published study of combination therapy used tretinoin 0.1%, hydroquinone 5%, and dexamethasone 0.1% for postinflammatory hyperpigmentation (Kligman and Willis, 1975). Tretinoin was shown to reduce the atrophy of the corticosteroid and facili-
The chemical 4-hydroxyanisole in combination with tretinoin 0.01% has been shown to inhibit production of melanin (Colby et al., 2003; Kasraee et al., 2003). Recently it has been introduced as a chemical agent (Solagé®) for the treatment of solar lentigines (Fleischer et al., 2000). Patients report significant lightening of solar lentigines after several months of treatment (Fleischer et al., 2000; Colby et al., 2003). The effects of the combination retinoid and mequinol was superior to either agent used individually.
Hypopigmentation Hypopigmentation is defined as a paucity of melanin within the epidermis (Chapter 28). Depigmentation is defined as complete absence of melanin. Depigmentation usually is due to absence of melanocytes such as is found in vitiligo or piebald1169
CHAPTER 59
ism. Occasionally the blockage of the melanin pathway is so severe that the skin appears depigmented despite the presence of melanocytes. This phenomenon is seen in the tyrosinase related forms of oculocutaneous albinism (Chapter 31). There are few agents to repigment skin that has a paucity or absence of melanin or melanocytes. The agents are limited to topical steroids useful for acquired hypomelanoses and various forms of phototherapy. Phototherapy includes exposure to broadband ultraviolet (UV) B which has a spectrum of 290–320 nm or narrowband UV 309–311 nm (see Chapter 59). Narrowband UV has been introduced in recent years for treatment of a variety of dermatological conditions (Baron and Stevens 2003; Grundmann-Kollmann et al., 2004; Mori et al., 2004; Ohe et al., 2004; Saricaoglu et al., 2003; Schiffner et al., 2002; Snellman et al., 2004). These spectra are most effective for causing tanning. UVB is used with variable success to enhance melanin formation in skin that is hypopigmented such as pityriasis alba (Chapter 37). It has little effect on depigmentation. Hypopigmentation can be caused by several mechanisms. Some conditions are acquired and are due to suppression of melanin formation like pityriasis alba. It is possible that the inhibition of melanin formation is related to inflammation within the epidermis. These conditions respond to topical steroids. The choice of steroid seems critical. Potent steroids suppress inflammation but also might directly block the melanization process (see Fig. 59.5). Thus intermediate potency steroids like desonide seem optimal for treatment of pityriasis alba. The congenital variants like a nevus depigmentosus (Chapter 32) or genetic forms like the ash leaf (Chapter 32), or albinism spot are due to an intrinsic defect within the melanocyte and are not responsive to any therapy. Other forms of hypopigmentation are caused by absence of melanocytes. Such conditions include vitiligo and piebaldism. PUVA or psoralens and exposure to ultraviolet A (320–400 nm) and narrow band UVB (309–311 nm) (see Chapter 61) are excellent stimuli for enhancing melanin formation and for proliferation of melanocytes within hair follicles. The efficacy of PUVA or narrow band UVB in conditions characterized by absence of interfollicular melanocytes depends on the availability of a reservoir of melanocytes in hair follicles to migrate into the depigmented skin for repigmentation to occur (see Chapters 30 and 60). Piebald skin lacks melanocytes within the interfollicular epidermis but also within the follicles. Patients with piebaldism do not respond to PUVA or other forms or therapy although pigmented patches at times spontaneously gain pigmentation. Surgical transplant of melanocytes is the most effective way to repigment piebald skin. Currently the logistics and expense of transplantation make this approach impractical. In contrast vitiliginous skin can respond to PUVA or applications of topical therapy (Chapter 30). PUVA also has been used to treat conditions like the hypomelanoses. Patients with some hypomelanoses have a very mottled appearance to their skin. PUVA for individuals
1170
with pityriasis alba or similar conditions usually does not resolve the problem. The normal skin darkens more than the abnormal skin. The contrast can be even more severe after therapy than before. Some hypomelanoses are not caused by abnormalities of the pigment system. The normal color of the skin is determined by other factors such as the vascular supply or the quantity of collagen in the dermis. The nevus anemicus appears hypopigmented but is a vascular anomaly that cannot respond to therapies described in this section. Similarly collagen deposition can give a whitish appearance to the skin. The collagen causes the epidermis to appear white. Examination of such skin with Wood’s light confirms that melanin is present and that the abnormality is dermal. A biopsy is rarely necessary but can confirm the diagnosis. Such abnormalities do not respond to therapies described in this section.
Depigmentation and Use of Monobenzone Monobenzone is the only agent available in the United States and in some European countries for the treatment of vitiligo that is too extensive to repigment (Chapter 30). Monobenzone is a chemical that can destroy epidermal melanocytes and leave the epidermis depigmented. For that reason it is never used for treating hyperpigmented conditions like melasma or postinflammatory hyperpigmentation (Figs 59.8–59.10). The goal of treatment for these latter conditions is inhibition of the synthesis of melanin so that the color of the skin returns to normal. Although monobenzone is a potent inhibitor of melanin synthesis, its capacity to destroy melanocytes makes it useless except for completing the loss of pigment in those with vitiligo. The best is for an individual to have their own normal skin color. The worst is having two colors. The second best is losing
Fig. 59.8. An African American woman incorrectly treated with monobenzone for melasma. She has depigmentation of the face that is not readily repigmented (see also Plate 59.8, pp. 494–495).
TOPICAL TREATMENT OF PIGMENTARY DISORDERS
Fig. 59.9. Depigmentation of the hand by improper use of monobenzone.
Fig. 59.11. Woman with vitiligo too extensive to repigment (see also Plate 59.9, pp. 494–495).
Fig. 59.10. Depigmentation of the forearm from improper use of monobenzone. The photo illustrates the confetti depigmentation from use of this agent.
all one’s color so that the skin color is uniform although depigmented. Thus the optimal therapy for those with vitiligo is repigmentation of the skin. However that is not always possible. For those with vitiligo that is unresponsive to repigmentation or too extensive for repigmentation, monobenzone can produce a uniform depigmented state that is cosmetically very attractive (Figs 59.11 and 59.12) (Mosher et al., 1977). The individual has a very young appearance because the usual spots such as keratoses and lentigines associated with aging do not mar depigmented skin. Monobenzone is available as a 20% cream. It can be purchased from pharmaceutical companies. It is more readily obtained at this time from pharmacists who formulate the preparation. The patient applies the cream on a small spot once daily for a week to ensure that he or she has no allergy to the chemical, the most common side effect (Nordlund et al., 1985). If there is no inflammation, the cream is applied to the pigmented skin twice daily. Loss of pigment occurs slowly over
months to a year or longer. The pigment fades imperceptibly. Usually the person applies the monobenzone to the hands, arms, neck, and face first. When these areas are depigmented the person can then depigment the legs and thighs. Later the trunk can also be treated although most individuals choose to stop when the exposed skin is depigmented. The resulting skin has an attractive, healthy pink color and is not white. At times the commercially available monobenzone is ineffective. It can be used under occlusion or the concentration can be increased to 30%. These maneuvers can be successful at times in depigmentation in a patient whose skin is resistant. Occasionally a patient who has successfully undergone depigmentation suddenly regains much or most of his or her pigmentation back, generally following a sunburn. This is very alarming and requires the patient to start depigmentation again. The repigmentation might be so extensive that the person might choose to try repigmentation. For patients in whom itching and burning occur, a 5% cream is used initially. The concentration is increased every 2–3 months until the 20% preparation is tolerated. Many allergic individuals cannot tolerate any concentration of monobenzone (Chapter 30). They must stop the treatment and there is no substitute medication. Once depigmentation is
1171
CHAPTER 59
Fig. 59.12. Woman in Figure 59.11 properly treated with monobenzone to remove remaining pigment. Her appearance is excellent (see also Plate 59.10, pp. 494–495).
complete, no maintenance is needed except an occasional retreatment may be required for focal areas of repigmentation that may appear particularly after sun exposure. The individual using monobenzone should not allow the cream to touch others. They should avoid direct contact for an hour after applying. Many individuals choose to apply the cream after children go to school and early in the evening to avoid contact with the spouse.
References Arndt, K., and T. Fitzpatrick. Topical use of hydroquinone as a depigmentating agent. J. Am. Med. Assoc. 194:965–967, 1965. Balina, L. M., and K. Graupe. The treatment of melasma. 20% azelaic acid versus 4% hydroquinone cream. Int. J. Dermatol. 30:893–895, 1991. Baron, E. D., and S. R. Stevens. Phototherapy for cutaneous T-cell lymphoma. Dermatol. Ther. 16:303–310, 2003. Bentley-Phillips, B., and M. A. Bayles. Cutaneous reactions to topical application of hydroquinone. Results of a 6-year investigation. S. Afr. Med. J. 49:1391–1395, 1975. Boissy, R. E., M. Visscher, and M. A. DeLong. Deoxyarbutin: a novel reversible tyrosinase inhibitor with effective in vivo skin lightening potency. Exp. Dermatol. 14:601–608.
1172
Breathnach, A. C., M. Nazzaro-Porro, S. Passi, and G. Zina. Azelaic acid therapy in disorders of pigmentation [review]. Clin. Dermatol. 7:106–119, 1989a. Breathnach, A. S., E. J. Robins, M. Nazzaro-Porro, S. Passi, and M. Picardo. Hyperpigmentary disorders–mechanisms of action. Effect of azelaic acid on melanoma and other tumoral cells in culture [review]. Acta Derm. Venereol. Suppl. (Stockh.) 143:62–66, 1989b. Bulengo-Ransby, S. M., C. E. Griffiths, C. K. Kimbrough-Green, L. J. Finkel, T. A. Hamilton, C. N. Ellis, and J. J. Voorhees. Topical tretinoin (retinoic acid) therapy for hyperpigmented lesions caused by inflammation of the skin in black patients. N. Engl. J. Med. 328:1438–1443, 1993. Cabanes, J., S. Chazarra, and F. Garcia-Carmona. Kojic acid, a cosmetic skin whitening agent, is a slow-binding inhibitor of catecholase activity of tyrosinase. J. Pharm. Pharmacol. 46:982–985, 1994. Camarasa, J. G., and E. Serra-Baldrich. Exogenous ochronosis with allergic contact dermatitis from hydroquinone. Contact Dermatitis 31:57–58, 1994. Colby, S. I., E. H. Schwartzel, F. J. Huber, A. Highton, D. J. Altman, W. W. Epinette, and E. Lyon. A promising new treatment for solar lentigines. J. Drugs Dermatol. 2:147–152, 2003. Coulson, I. H. “Fade out” photochromonychia. Clin. Exp. Dermatol. 18:87–88, 1993. Cummings, M. P., and J. J. Nordlund. Chemical leukoderma: fact or fancy. Am. J. Contact Dermatitis 6:122–127, 1995. Diven, D. G., E. B. Smith, R. A. Pupo, and M. Lee. Hydroquinoneinduced localized exogenous ochronosis treated with dermabrasion and CO2 laser. J. Dermatol. Surg. Oncol. 16:1018–1022, 1990. Dogra, S., A. J. Kanwar, and D. Parsad. Adaplene in the treatment of melasma: a preliminary report. J. Dermatol. 29:539–540. Duteil, L., and J. P. Ortonne. Colorimetric assessment of the effects of azelaic acid on light-induced skin pigmentation. Photodermatol. Photoimmunol. Photomed. 9:67–71, 1992. Engasser, P., and H. Maibach. Cosmetics and dermatology: Bleaching creams. J. Am. Acad. Dermatol. 5:143–147, 1981. Findlay, G. H., and H. A. de Beer. Chronic hydroquinone poisoning of the skin from skin-lightening cosmetics. A South African epidemic of ochronosis of the face in dark-skinned individuals. S. Afr. Med. J. 57:187–190, 1980. Findlay, G., J. Morrison, and J. Simson. Exogenous ochronosis and pigmented colloid milium from hydroquinone bleaching creams. Br. J. Dermatol. 93:613–622, 1975. Fitton, A., and K. L. Goa. Azelaic acid. A review of its pharmacological properties and therapeutic efficacy in acne and hyperpigmentary skin disorders. Drugs 41:780–798, 1991. Fitzpatrick, T. B., K. A. Arndt, A. M. El Mofty, and M. A. Pathak. Hydroquinone and psoralens in the therapy of hypermelanosis and vitiligo. Arch. Dermatol. 93:589–600, 1966. Fleischer, A. B., Jr., E. H. Schwartzel, S. I. Colby, and D. J. Altman. The combination of 2% 4-hydroxyanisole (Mequinol) and 0.01% tretinoin is effective in improving the appearance of solar lentigines and related hyperpigmented lesions in two double-blind multicenter clinical studies. J. Am. Acad. Dermatol. 42:459–467, 2000. Fulton, J. E., Jr. The prevention and management of postdermabrasion complications. J. Dermatol. Surg. Oncol. 17:431–437, 1991. Gilchrest, B. A., and R. M. Goldwyn. Topical chemotherapy of pigment abnormalities in surgical patients. Plast. Reconstr. Surg. 67:435–439, 1981. Griffiths, C. E., L. J. Finkel, C. M. Ditre, T. A. Hamilton, C. N. Ellis, and J. J. Voorhees. Topical tretinoin (retinoic acid) improves melasma. A vehicle-controlled, clinical trial. Br. J. Dermatol. 129:415–421, 1993. Griffiths, C. E., M. T. Goldfarb, L. J. Finkel, V. Roulia, M. Bonawitz, T. A. Hamilton, C. N. Ellis, and J. J. Voorhees. Topical tretinoin (retinoic acid) treatment of hyperpigmented lesions associated with
TOPICAL TREATMENT OF PIGMENTARY DISORDERS photoaging in Chinese and Japanese patients: a vehicle-controlled trial. J. Am. Acad. Dermatol. 30:76–84, 1994. Grimes, P. E. Melasma: Etiologic and therapeutic considerations. Arch. Dermatol. 131:1453–1457, 1995. Grundmann-Kollmann, M., R. Ludwig, T. M. Zollner, F. Ochsendorf, D. Thaci, W. H. Boehncke, J. Krutmann, R. Kaufmann, and M. Podda. Narrowband UVB and cream psoralen-UVA combination therapy for plaque-type psoriasis. J. Am. Acad. Dermatol. 50:734–739, 2004. Halder, R. M. and G. M. Richards. Topical agents used in the management of hyperpigmentation. Skin Ther. Lett. 9:1–3. Hardwick, N., L. van Gelder, and C. van der Merwe. Exogenous ochronosis: an epidemiologic study. Br. J. Dermatol. 120:229–238, 1989. Ho, C., Q. Nguyen, N. J. Lowe, M. E. Griffin, and G. Lask. Laser resurfacing in pigmented skin. Dermatol. Surg. 21:1035–1037, 1995. Hori, I., K. Nihei, and I. Kubo. Structural mechanism for depigmenting mechanism of arbutin. Phytother. Res. 18:475–479. Hoshaw, R. A., K. G. Zimmerman, and A. Menter. Ochronosislike pigmentation from hydroquinone bleaching creams in American blacks. Arch. Dermatol. 121:105–108, 1985. Hull, P. R., and P. R. Procter. The melanocyte: an essential link in hydroquinone-induced ochronosis. J. Am. Acad. Dermatol. 22:529–531, 1990. Humphreys, T. R., V. Werth, L. Dzubow, and A. Kligman. Treatment of photodamaged skin with trichloroacetic acid and topical tretinoin. J. Am. Acad. Dermatol. 34:638–644, 1996. Ito, Y., K. Jimbow, and S. Ito. Depigmentation of black guinea pig skin by topical application of cysteaminylphenol, cysteinylphenol, and related compounds. J. Invest. Dermatol. 88:77–82, 1987. Jimbow, K. N-acetyl-4-S-cysteaminylphenol as a new type of depigmenting agent for the melanoderma of patients with melasma. Arch. Dermatol. 127:1528–1534, 1991. Jordaan, H. F., and R. P. Mulligan. Actinic granuloma-like change in exogenous ochronosis: case report. J. Cutan. Pathol. 17:236–240, 1990. Jordaan, H. F., and D. J. Van Niekerk. Transepidermal elimination in exogenous ochronosis. A report of two cases. Am. J. Dermatopathol. 13:418–424, 1991. Kameyama, K., M. Morita, K. Sugaya, S. Nishiyama, and V. J. Hearing. Treatment of reticulate acropigmentation of Kitamura with azelaic acid: an immunohistochemical and electron microscopic study. J. Am. Acad. Dermatol. 26:817–820, 1992. Kasraee, B., F. Handjani, and F. S. Aslani. Enhancement of the depigmenting effect of hydroquinone and 4-hydroxyanisole by alltrans-retinoic acid (tretinoin): the impairment of glutathionedependent cytoprotection? Dermatology 206:289–291, 2004. Kersey, P., and C. J. Stevenson. Vitiligo and occupational exposure to hydroquinone from servicing self-photographing machines. Contact Dermatitis 7:285–287, 1981. Kimbrough-Green, C. K., C. E. Griffiths, L. J. Finkel, T. A. Hamilton, S. M. Bulengo-Ransby, C. N. Ellis, and J. J. Voorhees. Topical retinoic acid (tretinoin) for melasma in black patients. A vehiclecontrolled clinical trial. Arch. Dermatol. 130:727–733, 1994. Kligman, A. M., and I. Willis. A new formula for depigmenting human skin. Arch. Dermatol. 111:40–48, 1975. Lawrence, N., C. Bilgard, R. Reed, and W. Perret. Exogenous ochronosis in the United States. J. Am. Acad. Dermatol. 18:1207–1211, 1988. Leyden, J. J., G. L. Grove, M. J. Grove, E. G. Thorne, and L. Lufrano. Treatment of photodamaged facial skin with topical tretinoin. J. Am. Acad. Dermatol. 21:638–644, 1989. Lowe, P. M., J. Woods, A. Lewis, A. Davies, and A. J. Cooper. Topical tretinoin improves the appearance of photo damaged skin. Australas. J. Dermatol. 35:1–9, 1994. Mann, R., and R. Harman. Nail staining due to hydroquinone skinlightening creams. Br. J. Dermatol. 108:363–365, 1983.
Markey, A. C., A. K. Black, and R. J. Rycroft. Confetti-like depigmentation from hydroquinone. Contact Dermatitis 20:148–149, 1989. Mayer-da Silva, A., H. Gollnick, E. Imcke, and C. E. Orfanos. Azelaic acid vs. placebo: effects on normal human keratinocytes and melanocytes. Electron microscopic evaluation after long-term application in vivo. Acta Derm. Venereol. 67:116–122, 1987. Mori, M., P. Campolmi, L. Mavilia, R. Rossi, P. Cappugi, and N. Pimpinelli. Monochromatic excimer light (308 nm) in patch-stage IA mycosis fungoides. J. Am. Acad. Dermatol. 50:943–945, 2004. Mosher, D. B., J. A. Parrish, and T. B. Fitzpatrick. Monobenzyl ether of hydroquinone: A retrospective study of treatment of 18 vitiligo patients and a review of the literature. Br. J. Dermatol. 97:669–679, 1977. Nazzaro-Porro, M. Azelaic acid. J. Am. Acad. Dermatol. 17:1033– 1041, 1987. Nazzaro-Porro, M., S. Passi, G. Zina, and A. S. Breathnach. Ten years experience of treating lentigo maligna with topical azelaic acid. Acta. Derm. Venereol. 143(Suppl):4957, 1989. Nordlund, J. J., B. Forget, J. Kirkwood, and A. B. Lerner. Dermatitis produced by applications of monobenzone in patients with active vitiligo. Arch. Dermatol. 121:1141–1145, 1985. Ohe, S., K. Danno, H. Sasaki, T. Isei, H. Okamoto, and T. Horio. Treatment of acquired perforating dermatosis with narrowband ultraviolet B. J. Am. Acad. Dermatol. 50:892–894, 2004. Olsen, E. A., H. I. Katz, N. Levine, J. Shupack, M. M. Billys, S. Prawer, J. Gold, M. Stiller, L. Lufrano, and E. G. Thorne. Tretinoin emollient cream: a new therapy for photodamaged skin. J. Am. Acad. Dermatol. 26:215–224, 1992. Ortonne, J. P. Retinoic acid and pigment cells: A review of in-vitro and in-vivo studies. Br. J. Dermatol. 127:43–47, 1992. Pankovich, J. M., K. Jimbow, and S. Ito. 4-S-cysteaminylphenol and its analogues as substrates for tyrosinase and monoamine oxidase. Pigment Cell Res. 3:146–149, 1990. Pathak, M. A., E. R. Ciganer, M. Wick, A. J. Soger, W. A. Farinelli, and T. B. Fitzpatrick. An evaluation of the effectiveness of azelaic acid as a depigmenting and chemotherapeutic agent. J. Invest. Dermatol. 85:222–228, 1985. Pathak, M. A., T. B. Fitzpatrick, and E. W. Kraus. Usefulness of retinoic acid in the treatment of melasma. J. Am. Acad. Dermatol. 15:894–899, 1986. Penney, K. B., C. J. Smith, and J. C. Allen. Depigmenting action of hydroquinone depends on disruption of fundamental cell processes. J. Invest. Dermatol. 82:308–310, 1984. Piquero Martin, J., J. Rothe de Arocha, and D. Beniamini Loker. [Double-blind clinical study of the treatment of melasma with azelaic acid versus hydroquinone] [Spanish]. Med. Cutan. IberoLat-Am. 16:511–514, 1988. Rafal, E. S., C. E. Griffiths, C. M. Ditre, L. J. Finkel, T. A. Hamilton, C. N. Ellis, and J. J. Voorhees. Topical tretinoin (retinoic acid) treatment for liver spots associated with photodamage. N. Engl. J. Med. 326:368–374, 1992. Rigoni, C., P. Toffolo, R. Serri, and R. Caputo. [Use of a cream based on 20% azelaic acid in the treatment of melasma] [Italian]. G. Ital. Dermatol. Venereol. 124:I-VI, 1989. Rodriguez Prieto, M. A., P. Manchado Lopez, I. Ruiz Gonzalez, and D. Suarez. Treatment of lentigo maligna with azelaic acid. Int. J. Dermatol. 32:363–364, 1993. Sanchez, J. L., and M. Vazquez. A hydroquinone solution in the treatment of melasma. Int. J. Dermatol. 21:55–58, 1982. Saricaoglu, H., S. K. Karadogan, E. B. Baskan, and S. Tunali. Narrowband UVB therapy in the treatment of lichen planus. Photodermatol. Photoimmunol. Photomed. 19:265–267, 2003. Schiffner, R., J. Schiffner-Rohe, M. Gerstenhauer, M. Landthaler, F. Hofstadter, and W. Stolz. Dead Sea treatment – principle for outpatient use in atopic dermatitis: safety and efficacy of synchronous
1173
CHAPTER 59 balneophototherapy using narrowband UVB and bathing in Dead Sea salt solution. Eur. J. Dermatol. 12:543–548, 2002. Smith, C. J., K. B. O’Hare, and J. C. Allen. Selective cytotoxicity of hydroquinone for melanocyte-derived cells is mediated by tyrosinase activity but independent of melanin content. Pigment Cell Res. 1:386–389, 1988. Snellman, E., T. Klimenko, and T. Rantanen. Randomized half-side comparison of narrowband UVB and trimethylpsoralen bath plus UVA treatments for psoriasis. Acta Derm. Venereol. 84:132–137, 2004. Tadaki, T., M. Watanabe, K. Kumasaka, Y. Tanita, T. Kato, H. Tagami, I. Horii, T. Yokoi, Y. Nakayama, and A. M. Kligman. The effect of topical tretinoin on the photodamaged skin of the Japanese. Tohoku J. Exp. Med. 169:131–139, 1993. Tidman, M. J., J. J. Horton, and D. M. MacDonald. Hydroquinoneinduced ochronosis: light and electronmicroscopic features. Clin. Exp. Dermatol. 11:224–228, 1986. Verallo-Rowell, V. M., V. Verallo, K. Graupe, L. Villafuerte, and M.
1174
Garcia-Lopez. Double-blind comparison of azelaic acid and hydroquinone in the treatment of melasma. Acta Derm. Venereol. 143(Suppl):58–61, 1989. Weinstein, G. D., T. P. Nigra, P. E. Pocha, R. C. Savan, A. Allan, K. Benik, E. Jeffes, L. Lufrano, and E. G. Thorne. Topical tretinoin for treatment of photodamaged skin: a multicenter study. Arch. Dermatol. 127:659–665, 1991. Weiss, J. S., C. N. Ellis, J. T. Headington, T. Tincoff, T. A. Hamilton, and J. J. Voorhees. Topical tretinoin improves photoaged skin. A double-blind vehicle-controlled study [published errata appear in J. Am. Med. Assoc. 259:3274, 1988 and 260:926, 1988]. J. Am. Med. Assoc. 259:527–532, 1988. Weiss, R. M., E. del Fabbro, and P. Kolisang. Cosmetic ochronosis caused by bleaching creams containing 2% hydroquinone [letter]. S. Afr. Med. J. 77:373, 1990. Wong, M., and K. Jimbow. Selective cytotoxicity of N-acetyl-4-S-cysteaminylphenol on follicular melanocytes of black mice. Br. J. Dermatol. 124:56–61, 1991.
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
60
Chemophototherapy of Pigmentary Disorders Rebat M. Halder and James J. Nordlund
Psoralens and PUVA
Oral Psoralen Therapy
Plant extracts combined with natural sunlight have been used for thousands of years to successfully treat hypopigmentation and vitiligo in Egypt and India (Danielssen, 1966; Ortonne et al., 1983). The plants are Ammi majus in Egypt and Psoralea corylifolia in India (Singh et al., 1974). Several crystalline compounds, including ammodin (8-methoxypsoralen, 8MOP) and bergapten (5-methoxypsoralen, 5-MOP) were isolated from the powder of Ammi majus in 1947 (el-Mofty, 1948). Other psoralens such as trioxsalen (4,5¢,8 trimethylpsoralen, TMP) were developed later. Currently psoralen photochemotherapy is the most widely used and most effective therapy available for repigmentation in vitiligo and other disorders of hypopigmentation although it is not a panacea for any of these conditions. In the United States, photochemotherapy can be administered either systemically or topically. Oral 5-MOP is being used in other countries (Beretti et al., 1989; Hann et al., 1991). The combination of Psoralen and UltraViolet A has been given the acronym PUVA. Psoralens are furocoumarins consisting of a double-ringed coumarin moiety to which a furan group is attached (Fitzpatrick et al., 1966; Parrish et al., 1976; Pathak et al., 1984). The furan ring is joined at its 3¢2¢ bond to the 6,7 bond of the coumarin in a linear fashion. Psoralens are photoactive and have no known effects on their own (Kao and Yu, 1992). For psoralens to be active they must be combined with ultraviolet A (UVA). Psoralens absorb photons forming short-lived, high-energy compounds. The exact mechanism by which photosensitivity occurs following PUVA therapy is not exactly known. However, two distinct independent photoreactions take place when psoralen-treated skin is exposed to UVA light. The type I photoreaction is oxygen independent and forms monofunctional and bifunctional bonds called adducts between the psoralen and DNA. Type II reactions are oxygen dependent and form similar adducts. Psoralen reactions are predominately type I. Those psoralens that form bifunctional adducts generally cause photosensitization. Psoralens are metabolized in the liver where there is saturable, first pass metabolism which reduces the amount of active drug reaching the systemic circulation (Pathak et al., 1984). Metabolism of 8-MOP and TMP have been identified but data on their activity are sparse. 8-MOP induces drugmetabolizing enzymes in the liver as well as cytochrome P450, effects not caused by TMP.
Currently, oral 8-MOP is available in the United States in a liquid formulation contained inside a soft gelatin capsule (Oxsoralen Ultra‘). This preparation is much better absorbed than the previous commercial form that was a crystalline powder inside a hard gelatin capsule. TMP is available in the United States as a tablet (Trisoralen‘). Because of better absorption, the liquid formulation of 8-MOP produces an earlier peak in blood and tissues and is much more photosensitizing than the crystalline powder formulation. Psoralens are absorbed in the small intestine and absorption is decreased by high-fat meals. TMP is highly insoluble in water, less than 8MOP. TMP is poorly absorbed in the small intestine. Measurements of serum levels of psoralen indicate that there is great variability in absorption of TMP by an individual from day to day and from person to person (Chakrabarti et al., 1982). Because of the poor absorption of TMP, it is a poor photosensitizer in oral tablet formulation. TMP has a higher binding affinity to serum proteins than 8-MOP. The binding causes lower tissue concentrations of TMP in the skin. As a general principle TMP is not the agent of choice for oral PUVA (Bleehen, 1972; Kligman and Goldstein, 1973). PUVA therapy for vitiligo is a protracted, time consuming process to which the patient should be committed (el-Mofty et al., 1994). The response rate is moderate. PUVA treatment for other hypopigmentary disorders such as progressive macular hypopigmentation does not require prolonged times. Relative contraindications to PUVA include some ocular disorders, liver dysfunction, young age, small areas of depigmentation, prior history of skin cancers, and prior exposure to cutaneous carcinogens (Nordlund et al., 1996). Absolute contraindications include pregnancy, aphakia, liver failure, photosensitive disorders like lupus erythematosus, depigmentation confined to glabrous skin, and depigmentation confined to skin with white hairs (see also Chapter 30) (Nordlund et al., 1996). In general children are not good candidates for systemic psoralen therapy. Age under 12 years is considered a relative contraindication for oral PUVA therapy (Halder et al., 1987). However, exceptions are made for children with very extensive involvement for which topical PUVA or topical steroid therapy is impractical and for whom the vitiligo is debilitating (Figs 60.1 and 60.2). For children under age 12 years, TMP is sometimes substituted for 8-MOP because TMP is a 1175
CHAPTER 60
Fig. 60.1. Child with extensive vitiligo before therapy with oral PUVA.
Fig. 60.2. Child in Figure 60.1 after treatment with oral PUVA showing excellent repigmentation.
weaker photosensitizer and the margin of safety is greater, lessening the risk of phototoxicity. TMP metabolism is not as dependent on drug-metabolizing enzymes in the liver as is 8-MOP. These enzymes are not fully developed in young children. In adults and some children with vitiligo, 8-MOP, especially in the liquid form (Oxsoralen-Ultra‘), is the most effective drug for PUVA therapy. There are two ways to administer PUVA. The first recommends higher doses of Oxsoralen and lower doses of UVA. The second uses lower doses of psoralen and higher doses of UVA. It is not known whether the two are biologically and biochemically identical but the clinical outcomes of the two forms of therapy seem to be equivalent. For high-dose psoralen therapy, the recommended dosage of 8-MOP (as Oxsoralen-Ultra) is 0.4–0.5 mg/kg ingested 1.5 hours prior to exposure to UVA light. Initial UVA exposure is based on skin type. For skin types I–III, an initial dose of 0.5 J/cm2 of UVA is given whereas for skin types IV–VI, 1.0 J/cm2 is administered. At subsequent treatments increments of 0.25–0.5 J/cm2 are added until persistent, moderate, asymptomatic erythema is maintained between treatments. At that stage, no further increments in UVA dosage are given. Treat-
ments are given two to three times weekly but never on consecutive days. A maximum treatment exposure usually ranges between 1.0 J/cm2 and 4.0 J/cm2. The dose is individualized for each patient and determined by the appearance of erythema. For the second type PUVA called low-dose psoralen therapy, the patient takes 10 mg Oxsoralen-Ultra and is exposed to 4 J UVA. The dose of UVA is increased 1–2 J per treatment until erythema is noted. If the dose of UVA is over 16 J, the patient is given 20 mg of Oxsoralen-Ultra. The dose of UVA is started at 4 J and increased until erythema is noted. The final dose of UVA is usually large, around 14–20 J. The risk of serious burns from inadvertent exposure to UVA in sunlight is minimal in the second form of PUVA utilizing low doses of Oxsoralen (Figs 60.3 and 60.4). Regardless of the method utilized, the course of PUVA should be continued for at least three to four months before the therapy is considered unsuccessful. If repigmentation is not observed in four months, the PUVA probably should be discontinued and tried again at a later time. If repigmentation does occur manifested by perifollicular pigmentation, it should be continued until no further progress is noted. Sunlight must be used with great caution when using 8-MOP (heliotherapy)
1176
PHOTOTHERAPY OF PIGMENTARY DISORDERS
Fig. 60.3. A young man before treatment with PUVA (see also Plate 60.1, pp. 494–495).
because the quantity of UVA reaching the earth’s surface varies widely from hour to hour and day to day. Physicians properly trained can give heliotherapy with 8-MOP but must titrate the exposure to sunlight carefully to avoid burns. In those children selected for oral PUVA therapy, TMP is given in a dosage of 0.6 mg/kg ingested two hours prior to UVA exposure. UVA exposure is determined just as for 8MOP by titrating the amount of UVA to produce erythema. For adults who choose heliotherapy, TMP can be substituted for 8-MOP. It is poorly absorbed and less photosensitizing. The results of treatment seem to be less satisfactory than those with 8-MOP. TMP is taken at a dosage of 0.6–0.8 mg/kg two hours prior to sunlight exposure. Exposure should begin with five minutes of mid-day summer sun. Subsequent exposures are increased in increments of five minutes with each treatment until moderate asymptomatic erythema is achieved. Usually the maximum exposure will be 30–45 minutes. Treatments are done two to three times per week but not on consecutive days. There are important precautions to be taken with oral PUVA therapy, especially if the individual is taking larger doses of 8-MOP. These precautions include the avoidance of
Fig. 60.4. The young man in Figure 60.3 approximately 25 months after treatment with low-dose psoralen PUVA. The response is excellent. Note that glabrous skin on the hands and umbilicus did not respond (see also Plate 60.2, pp. 494–495).
unnecessary exposure to sunlight from the time of ingestion of the medication until sunset of the same day to prevent the risk of developing a burn. Patients should wear UVA blocking, wraparound sunglasses for 12–24 hours after ingestion of psoralen to protect the eyes from psoralen-induced photodamage. Studies have not found an increase in incidence of premature cataracts in vitiligo patients treated with PUVA therapy. Human eyelid skin blocks completely the penetration of UVA. Following oral PUVA therapy, patients must apply a broad spectrum sunscreen to sun-exposed areas of treated skin. Although the incidence of squamous cell carcinoma of the skin has been found to be increased in patients with psoriasis treated with PUVA, skin cancers have not been observed in patients with vitiligo (see Chapter 30 for discussion of skin cancer and vitiligo). Acute side effects of oral PUVA therapy include nausea from the psoralen. This is particularly a problem with higher doses of psoralen. Patients receiving psoralens are subject to severe, blistering burns that are very painful and long-lasting. Many patients note fatigue after each treatment, pruritus, and 1177
CHAPTER 60
Fig. 60.5. Vitiligo before treatment with topical PUVA.
Fig. 60.6. The same skin as in Figure 59.5 during treatment with topical PUVA (see also Plate 60.3, pp. 494–495).
headaches. Generally these are tolerable. Because of the immediate and long-term toxicity of PUVA, the prescribing physician should be familiar with this form of treatment.
Topical PUVA Therapy Topical PUVA therapy for vitiligo is indicated in adults with less than 20% skin surface involvement and for children of any age (Grimes et al., 1982). It can also be used by patients in whom oral PUVA therapy is contraindicated. Topical PUVA seems to avoid some of the potential side effects associated with oral PUVA therapy but has other toxicities that limit its usefulness (Figs 60.5–60.7). Topical PUVA therapy is difficult to use because of the extreme photosensitivity associated with application of psoralens to the skin (Kanof, 1955; Kelly and Pinkus, 1955). Severe blistering burns are common in patients treated with topical PUVA. However, topical PUVA therapy for vitiligo is safe and effective if used judiciously by those properly trained (Fulton et al., 1969; Parrish et al., 1971). Adverse reactions
1178
Fig. 60.7. The patient in Figures 60.5 and 60.6 after successful treatment with topical PUVA.
PHOTOTHERAPY OF PIGMENTARY DISORDERS
are minimized by careful monitoring of the dose of UVA irradiation. Thus, topical PUVA therapy for vitiligo should never be used with natural sunlight (heliotherapy). Topical psoralens are not usually dispensed to patients to avoid inadvertent misuse of these potent agents. Various studies have determined that 0.1% or 0.01% concentration of 8-MOP is optimal for topical PUVA therapy for vitiligo (Grimes et al., 1982; Halder, 1991). One percent Oxsoralen (8-MOP) is diluted to 0.1% or 0.01% concentration in one of the following vehicles: alcohol, propylene glycol, Aquaphor, or acid mantle cream. The formulated cream is applied thinly and sparingly with a cotton-tipped swab within the margins of a vitiliginous patch by the dermatologist, nurse, or medical assistant. Patients who are reliable can be taught how to apply properly the medication in the physician’s office. Because it dries quickly, the alcohol or propylene glycol vehicle is preferred for areas that will be covered with clothing soon after application. Acid mantle cream or Aquaphor is preferred on the face to prevent the Oxsoralen from dripping and causing undesired hyperpigmentation. Normal skin surrounding a depigmented patch is not treated. After an interval of 30 minutes the painted areas are exposed to UVA. Maximal penetration of the psoralen into the epidermis occurs within this time (Arora and Willis, 1976). The initial dose of UVA depends on the skin type. The dose is 0.12 J/cm2 in those with types I–III skin and 0.25 J/cm2 for those with darker skin (Nordlund et al., 1996). The dose is increased by that amount at every other treatment until a mild erythema is produced. Adverse reactions to topical PUVA are common and include excessive erythema and edema, blistering, or extreme pruritus. Treatments must be discontinued until the reactions subside (usually one to two weeks). At reinstitution of therapy, UVA doses are decreased to half the previous value. Blistering may be due to using a preparation of Oxsoralen that is too concentrated, exposure to too much UVA, failure to wash the areas after the treatment or exposure to sunlight following treatment. Blistering can be treated by carefully incising the blister roof, draining the fluid, but leaving the blister roof intact and applying a sterile dressing. Other phototoxic side effects of topical PUVA therapy include itching and hyperkeratosis of treated skin. A mild topical steroid cream, such as desonide, can be used for the itching on facial areas. Triamcinolone acetonide can be used on other areas. Urea or lactic acid containing creams or lotions can soften hyperkeratotic skin. Since topical Oxsoralen is not absorbed through the skin in appreciable amounts (Coleman et al., 1988), risks of premature cataract formation or liver toxicity are thought to be nil. However, there have been isolated reports of elevated liver transaminases with topical PUVA (Park et al., 1994). Topical PUVA is also an acceptable treatment for children too young for oral PUVA. Children as young as 2 years of age have been successfully treated with topical PUVA. The child must be able to stay in the PUVA box for a sufficient time to develop an erythema. Topical or oral
PUVA therapy should never be used in combination due to the much increased risk of severe phototoxic reactions.
Results of PUVA Therapy There are many reports on the results of treatment of vitiligo with topical and oral PUVA therapy. With both forms of therapy there is some degree of repigmentation in 60–80% of patients (Grimes, 1993). Cosmetically acceptable repigmentation ranges from 11% to 60% depending on the criteria used but results of most studies indicate that 40–60% of individuals respond to a course of PUVA (see Figs 60.1–60.7). Complete repigmentation occurs in 20–25% of patients treated. Some investigators suggest that those who fail the first course of therapy be given a second course six months later. A higher percentage regain some pigment, possibly as high as 70%. PUVA therapy, either topical or oral, is not a panacea for the treatment of vitiligo or other pigmentary disorders but is the most effective treatment currently available. Why some patients respond to PUVA therapy and others do not is unknown. The permanence of repigmentation in vitiligo has been reported to be high (Kenney, 1971) but it has been stated that loss of new pigmentation will occur unless the area has completely repigmented. This suggestion has not been substantiated by careful studies. There are factors that influence the response to treatment. Psoralen dosage, either topical or oral, in excessive amounts producing severe erythema or blistering does not give better results. It may decrease the rate of repigmentation. Increased frequency of treatment does not increase response rate but may increase the risk of phototoxic reactions. A good response correlates best with duration of continuous treatment. The course must be at least three to four months. If pigment is developing in the vitiliginous skin, the therapy should be continued until no further progress is noted. Age of the patient is unrelated to response although some have suggested that the younger the patient, the earlier and greater the amount of repigmentation (Grimes, 1993). However this suggestion is still controversial. The site of the lesion is an important factor in determining response to therapy. In most studies, the face and neck respond the best with a 60–70% response with full repigmentation (Grimes, 1993). Areas that characteristically respond poorly are glabrous skin such as the lips, parts of the hands and fingers, feet, toes, ankles, palms, soles, and nipples (see Figs 60.3 and 60.4) (see Chapter 30). This poor response is due to lack of hair follicles that serve as a reservoir of melanocytes. White (not gray) hair itself in an area of vitiligo is also associated with a poor response to therapy (see Figs 60.8 and 60.9). The white color of the hair is an indicator that the reservoir has been destroyed by the vitiliginous process. The extent of vitiligo and duration of disease are not related to the response to PUVA therapy. The activity of the disease can be
1179
CHAPTER 60
Fig. 60.8. White hair in a patch of vitiligo. This skin has lost its reservoir of melanocytes and cannot respond to medical therapies but can be treated with surgical therapies described in Chapter 63.
considered a bad prognostic sign for repigmentation if the disease is spreading rapidly. PUVA does not halt the progression of depigmentation, particularly if the disease is spreading rapidly. Slowly spreading vitiligo can respond to PUVA. It has been suggested that patients with darker skin types, i.e., IV–VI, obtain a better response to PUVA therapy (Grimes et al., 1983). The reason for this is unknown but may be related to a residual pool of melanocytes that may aid in repigmentation. It also might be related to the greater need for patients with dark skin to regain color. Although skin cancer has been reported to be higher in incidence in psoriatic patients treated with PUVA, this has not been the case in vitiligo (Halder et al., 1995; Harrist et al., 1984). The mechanism by which PUVA stimulates proliferation and migration of melanocytes is not known. In normal skin PUVA causes an increase in the number of melanocytes and stimulates melanogenesis (Becker, 1967). Light microscopy (dopa reaction) and scanning electron microscopy have shown proliferation of melanocytes in hair follicles and perifollicular areas in repigmenting vitiligo (Ortonne et al., 1979, 1980). Proliferation of melanocytes within hair follicles has been documented by [3H]-thymidine labeling. The melanocyte reservoir probably resides in the middle and/or lower parts of the outer root sheaths of the hair follicles (Cui et al., 1991; Horikawa et al., 1996). The melanocytes migrate upward along the surface of the outer root sheet to the epidermis where they spread radially. Repigmentation also occurs at the margins of a lesion. It is not known if the mechanism for this type of repigmentation is migration of melanocytes from a marginal follicular reservoir or from uninvolved interfollicular epidermis. It is not known if PUVA stimulates melanocyte proliferation and migration directly or indirectly. Results of recent studies suggest that immune cytokines and inflammatory mediators like leukotriene C4 (LTC4) and transforming growth factor a (TGFa) are potent mitogens for melanocytes (Morelli et al., 1989, 1992). 1180
Fig. 60.9. Depigmented skin in person with vitiligo responding to PUVA. Note that the skin with pigmented terminal hairs responds well, that with white terminal hairs did not respond. The case shows the importance of the reservoir of melanocytes in the follicles (see also Plate 60.4, pp. 494–495).
Khellin and UVA Light (KUVA) Khellin (4,9-dimethoxy-7-methyl-5H-furo[3,2-g][1]-benzophyran-5-one) is a furanochrome isolated from the seeds of the plant Ammi visnaga and has a nucleus that is a structural isomer of the psoralen nucleus (Abdel-Fattah et al., 1982). In the 1940s and 1950s, khellin was used for the treatment of angina pectoris and asthma because of its relaxing effect on smooth muscle via ganglionic blockade. Promising results from limited clinical trials using khellin and natural sunlight to treat vitiligo were first reported in 1982. Daily treatments consisting of 100 mg of khellin administered orally 45 minutes prior to exposure to mid-day sunlight for 15 minutes for four months resulted in 40% of the patients regaining at least 50% repigmentation. Serious side effects were not observed. In another study, patients were exposed three times per week to artificial UVA 2.5 hours after ingesting 100 mg of khellin (Ortel et al., 1988). Each patient received a constant UVA dose per treatment at 10 J/cm2 for skin types II and III and 15 J/cm2 for skin type IV. At least 70% repigmentation was achieved in 41% of the patients who had received 100–200 treatments. This success rate was noted to be comparable to the rate obtained with PUVA using 8-MOP or TMP. Limited success was also reported using a topical 2% solution of khellin although the number of patients was too small to be significant (Orecchia and Perfetti, 1992). Glabrous skin without a melanocyte reservoir did not respond to khellin. Phototoxic erythema was not observed with either topical or oral khellin even at high doses of irradiation. The lack of severe phototoxicity makes khellin a useful drug for home treatments or heliotherapy. Khellin has other short-term side effects. Systemically administered khellin produces nausea, hypotension, or loss of appetite in 30% of patients. These effects usually subsided after two weeks of treatments. In 25% of the patients, signif-
PHOTOTHERAPY OF PIGMENTARY DISORDERS
icant increases in liver transaminases require cessation of treatment (Ortel et al., 1988). These abnormalities spontaneously revert to normal. A marked but reversible increase in liver transaminases was reported in one patient after five weeks of topical applications of khellin (as a 2% solution) to one extremity (Duschet et al., 1989). One case of pseudoallergic reaction to orally administered khellin was reported consisting of a generalized urticarial reaction (Jung and Fingerhut, 1988). Although no long-term clinical side effects were noted after 12–15 months of therapy, the potential for such effects exists since khellin can induce formation of monofunctional adducts and cross-links with DNA and exhibits photogenotoxic properties. Compared with the psoralens, however, khellin produces photoadducts less efficiently than psoralens (Cassuto et al., 1977; Morliere et al., 1988). Like the psoralens, khellin induces an increased tolerance to natural sunlight in vitiliginous skin after a few months, but unlike the psoralens, it does not enhance the tanning properties of UVA in normal skin. Khellin is not approved for use in the United States by the Food and Drug Administration.
Phenylalanine and UVA (Phe-UVA) L-Phenylalanine (l-phe), an essential amino acid normally found in dietary protein, has been reported to induce repigmentation of vitiligo when given orally followed by UVA exposure. Repigmentation was reported in more than 90% of patients treated for six to eight months on a twice weekly regimen. Each individual received an oral dose of l-phe, 50 mg/kg, 30–45 minutes prior to UVA exposure (Cormane et al., 1985). In 26.3%, there was “dense” repigmentation and in 46% there was 50–90% repigmentation (Schulpis et al., 1989). When l-phe at 50 mg/kg was combined with sunlight, a follicular pattern of repigmentation was reported in 81% of cases (Kuiters et al., 1986). Oral phe-UVA was compared with combined oral and topical phe-UVA using a 10% cream of lphe applied to affected areas 20 minutes before UVA exposure (Antoniou et al., 1989). Although blood levels of l-phe were comparable in both groups, 90% of the patients treated with the combined oral and topical mode had greater than 75% repigmentation compared with 45% of the patients on oral treatment alone. The total dose of UVA required was also lower with the combined treatment mode. More recently the protocol was revised to daily intake of l-phe with UVA exposure two to three times per week. Side effects were not encountered in any of the above studies while an increased tolerance of vitiliginous skin to sunlight was observed. The repigmented areas remained stable after one year. Contraindications to phe-UVA include phenylketonuria, impaired liver and kidney function, premalignant and malignant skin lesions, pregnancy, breastfeeding, a history of using arsenates, a history of exposure to ionizing radiation, topical medications such as tar, light-induced dermatoses, autoimmune diseases, significant actinic damage, and cardiovascular disorders.
Although the mechanism by which phe-UVA causes repigmentation is not known, it is probably not related to increased tyrosine formation because no repigmentation was obtained when oral tyrosine was combined with UVA (Cormane et al., 1985). There are many speculations. One proposed mechanism is based on the finding that l-phe reduces an antibody response that might diminish an autoimmune-mediated destruction of melanocytes while allowing UVA or sunlight to stimulate proliferation of melanocytes (Ryan and Carver, 1964). Other suggested mechanisms include the stimulatory effect of UVA and l-phe or one of its metabolites on melanocyte activity and melanosome formation, and a shift in Langerhans cell subpopulations that results in an altered immune response (Cormane et al., 1985).
References Abdel-Fattah, A., M. N. Aboul-Enein, G. M. Wassel, and B. S. El-Menshawi. An approach to the treatment of vitiligo by khellin. Dermatologica 165:136–140, 1982. Antoniou, C., H. Schulpis, T. Michas, A. Katsambas, N. Frajis, S. Tsagaraki, and J. Stratigos. Vitiligo therapy with oral and topical phenylalanine with UVA exposure. Int. J. Dermatol. 28:545–547, 1989. Arora, S. K., and I. Willis. Factors influencing methoxsalen phototoxicity in vitiliginous skin. Arch. Dermatol. 112:327–332, 1976. Becker, S. Psoralen phototherapeutic agents. J. Am. Med. Assoc. 202:120–122, 1967. Beretti, B., D. Grupper, B. Bermejo, A. Borenstein, Y. Charpentier, D. Edelson, A. Thioly-Bensoussan, and R. Triller. PUVA 5-MOP + phenylalanine in the treatment of vitiligo. Study of 125 patients: preliminary results. In: Psoralens: Past, Present and Future of Photochemoprotection and Other Biological Activities. T. B. Fitzpatrick, P. Forlot, M. Pathak, and F. Urbach (eds). Paris: John Libbey Eurotext, 1989, pp. 103–108. Bleehen, S. S. Treatment of vitiligo with oral 4,5¢,8-trimethylpsoralen (Trisoralen). Br. J. Dermatol. 86:54–60, 1972. Cassuto, E., N. Gross, E. Bardwell, and P. Howard-Flanders. Genetic effects of photoadducts and photocross-links in the DNA of phage lambda exposed to 360 nm light and trimethylpsoralen or khellin. Biochim. Biophys. Acta 475:589–600, 1977. Chakrabarti, S. G., P. E. Grimes, H. R. Minus, J. A. Kenney Jr., and T. K. Pradhan. Determination of trimethylpsoralen in blood, ophthalmic fluids and skin. J. Invest. Dermatol. 79:374–377, 1982. Coleman, W. R., N. J. Lowe, M. David, and R. M. Halder. Palmoplantar psoriasis: Experience with 8-methoxypsoralen soaks plus ultraviolet A with the use of a high-output metal halide device. J. Am. Acad. Dermatol. 20:1078–1082, 1988. Cormane, R. H., A. H. Siddiqui, W. Westerhof, and R. B. Schutgens. Phenylalanine and UVA light for the treatment of vitiligo. Arch. Dermatol. Res. 277:126–130, 1985. Cui, J., L. Shan, and G. Wang. Role of hair follicles in the repigmentation of vitiligo. J. Invest. Dermatol. 97:410–416, 1991. Danielssen, B. 1966. Quoted in Goldman, L., R. S. Moraites, and K. W. Kitzmiller. White spots in biblical times. Arch. Dermatol. 93:744–753, 1966. Duschet, P., T. Schwartz, M. Pusch, and F. Gschnait. Marked increase of liver transaminases after khellin and UVA therapy. J. Am. Acad. Dermatol. 21:592–594, 1989. el-Mofty, A. M. A preliminary clinical report on the treatment of leucodermia with Ammi majus Linn. J. Egypt. Med. Assoc. 31:651, 1948. el-Mofty, A. M., H. el Sawalhy, and M. el Mofty. Clinical study of a new preparation of 8-methoxypsoralen in photochemotherapy. Int. J. Dermatol. 33:588–592, 1994.
1181
CHAPTER 60 Fitzpatrick, T. B., K. A. Arndt, A. M. El Mofty, and M. A. Pathak. Hydroquinone and psoralens in the therapy of hypermelanosis and vitiligo. Arch. Dermatol. 93:589–600, 1966. Fulton, J. E., Jr., J. Leyden, and C. Papa. Treatment of vitiligo with topical methoxsalen and blacklite. Arch. Dermatol. 100:224–229, 1969. Grimes, P. E. Vitiligo. An overview of therapeutic approaches. Dermatol. Clin. 11:325–338, 1993. Grimes, P. E., H. R. Minus, S. G. Chakrabarti, J. Enterline, R. Halder, J. E. Gough, and J. A. Kenney Jr. Determination of optimal topical photochemotherapy for vitiligo. J. Am. Acad. Dermatol. 7:771– 778, 1982. Grimes, P. E., H. R. Minus, R. M. Halder, J. Enterline, and J. A. Kenny. Vitiligo: Racial variations in the response to topical photochemotherapy [abstract]. J. Invest. Dermatol. 80:367, 1983. Halder, R. M. Topical PUVA therapy for vitiligo. Dermatol. Nurs. 3:178–180,198, 1991. Halder, R. M., P. E. Grimes, C. A. Cowan, J. A. Enterline, S. G. Chakrabarti, and J. A. Kenney Jr. Childhood vitiligo. J. Am. Acad. Dermatol. 16:948–954, 1987. Halder, R. M., E. F. Battle, and E. M. Smith. Cutaneous malignancies in patients treated with psoralen photochemotherapy (PUVA) for vitiligo [letter]. Arch. Dermatol. 131:734–735, 1995. Hann, S. K., M. Y. Cho, S. Im, and Y. K. Park. Treatment of vitiligo with oral 5-methoxypsoralen. J. Dermatol. 18:324–329, 1991. Harrist, T. J., M. A. Pathak, D. B. Mosher, and T. B. Fitzpatrick. Chronic cutaneous effects of long-term psoralen and ultraviolet radiation therapy in patients with vitiligo. Natl. Cancer Inst. Monogr. 66:191–196, 1984. Horikawa, T., D. A. Norris, T. W. Johnson, T. Zekman, N. Dunscomb, S. D. Bennion, R. L. Jackson, and J. G. Morelli. DOPA-negative melanocytes in the outer root sheath of human hair follicles express premelanosomal antigens but not a melanosomal antigen or the melanosome-associated glycoproteins tyrosinase, TRP-1 and TRP2. J. Invest. Dermatol. 106:28–35, 1996. Jung, E. G., and W. Fingerhut. Pseudoallergic reaction from Khellin in photochemotherapy of vitiligo: a case report. Photodermatology 5:235–236, 1988. Kanof, N. B. Melanin formation in vitiliginous skin under the influence of external applications of 8-methoxypsoralen. J. Invest. Dermatol. 24:5, 1955. Kao, C. H., and H. S. Yu. Comparison of the effect of 8-methoxypsoralen (8-MOP) plus UVA (PUVA) on human melanocytes in vitiligo vulgaris and in vitro. J. Invest. Dermatol. 98:734–740, 1992. Kelly, E. W., Jr., and H. Pinkus. Local application of 8-methoxypsoralen in vitiligo. J. Invest. Dermatol. 25:453, 1955. Kenney, J. A., Jr. Vitiligo treated by psoralens: A long-term follow-up study of the permanency of repigmentation. Arch. Dermatol. 103:475, 1971. Kligman, A. M., and F. P. Goldstein. Ineffectiveness of trioxsalen as an oral photosensitzer. Arch. Dermatol. 107:413–414, 1973.
1182
Kuiters, G. R., J. M. Hup, A. H. Siddiqui, and R. H. Cormane. Oral phenylalanine loading and sunlight as source of UVA irradiation in vitiligo on the Caribbean island of Curacao NA. J. Trop. Med. Hygiene 89:149–155, 1986. Morelli, J. G., J. J. Yohn, M. B. Lyons, R. C. Murphy, and D. A. Norris. Leukotrienes C4 and D4 as potent mitogens for cultured human melanocytes. J. Invest. Dermatol. 93:719–722, 1989. Morelli, J. G., J. Kincannon, J. J. Yohn, T. Zekman, W. L. Weston, and D. A. Norris. Leukotriene C4 and TGF-alpha are simulators of human melanocyte migration in vitro. J. Invest. Dermatol. 98:290–295, 1992. Morliere, P., H. Honigsmann, D. Averbeck, M. Dardalhon, G. Huppe, B. Ortel, R. Santus, and L. Dubertret. Phototherapeutic, photobiologic, and photosensitizing properties of khellin. J. Invest. Dermatol. 90:720–724, 1988. Nordlund, J. J., P. E. Grimes, R. M. Halder, and H. R. Minus. Guidelines of care for vitiligo. J. Am. Acad. Dermatol. 35:620–626, 1996. Orecchia, G., and L. Perfetti. Photochemotherapy with topical khellin and sunlight in vitiligo. Dermatology 184:120–123, 1992. Ortel, B., A. Tanew, and H. Honigsmann. Treatment of vitiligo with khellin and ultraviolet A. J. Am. Acad. Dermatol. 18:693–701, 1988. Ortonne, J. P., D. M. MacDonald, A. Micoud, and J. Thivolet. PUVAinduced repigmentation of vitiligo: a histochemical (split-DOPA) and ultrastructural study. Br. J. Dermatol. 101:1–12, 1979. Ortonne, J. P., D. Schmitt, and J. Thivolet. PUVA-induced repigmentation of vitiligo: scanning electron microscopy of hair follicles. J. Invest. Dermatol. 74:40–42, 1980. Ortonne, J.-P., D. B. Mosher, and T. B. Fitzpatrick. Topics in Dermatology: Vitiligo and Other Hypomelanoses of Hair and Skin. New York: Plenum Medical Book Company, 1983, pp. 129–461. Park, Y. M., T. Y. Kim, H. O. Kim, and C. W. Kim. Reproducible elevation of liver transaminases by topical 8-methoxypsoralen. Photodermatol. Photoimmunol. Photomed. 10:261–263, 1994. Parrish, J. A., M. A. Pathak, and T. B. Fitzpatrick. Prevention of unintentional overexposure in topical psoralen treatment of vitiligo. Arch. Dermatol. 104:281–283, 1971. Parrish, J. A., T. B. Fitzpatrick, C. Shea, and M. A. Pathak. Photochemotherapy of vitiligo. Use of orally administered psoralens and a high-intensity long-wave ultraviolet light system. Arch. Dermatol. 112:1531–1534, 1976. Pathak, M. A., D. B. Mosher, and T. B. Fitzpatrick. Safety and therapeutic effectiveness of 8-methoxypsoralen, 4,5,8-trimethylpsoralen and psoralen in vitiligo. Natl. Cancer Inst. Monogr. 66:165–173, 1984. Ryan, W. L., and M. J. Carver. Inhibition of antibody synthesis by L-phenylalanine. Science 143:479–480, 1964. Schulpis, C. H., C. Antoniou, T. Michas, and J. Strarigos. Phenylalanine plus ultraviolet light: Preliminary report of a promising treatment for childhood vitiligo. Pediatr. Dermatol. 6:332–335, 1989. Singh, G., Z. Ansari, and R. N. Dwivedi. Letter: Vitiligo in ancient Indian medicine. Arch. Dermatol. 109:913, 1974.
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
61
UVB Therapy for Pigmentary Disorders Thierry Passeron and Jean-Paul Ortonne
Introduction Ultraviolet (UV) A and B phototherapies are both widely used in dermatology. UVA radiation includes electromagnetic waves with wavelengths between 320 nm and 400 nm. It is used with systemic or topical psoralens, which selectively absorbs the radiation [psoralen and UVA (PUVA) therapy]. The main action of PUVA on biologic systems is the inhibition of DNA synthesis due to photoadducts formed between psoralen and pyrimidine bases in the nucleic acid. Although for a long time PUVA was considered to be the phototherapy of choice, its potential side effects — including cutaneous cancers (Garland et al., 2003; Lindelof et al., 1999; Stern, 2001; Stern et al., 1997) — mean that many authors recommend the use of UVB therapy instead.
Sources of UVB UVB wavelengths are between 290 nm and 320 nm. Unlike UVA, no prior photosensitization is required for efficacy. Initially broadband UVB therapy (290–320 nm) was based on the use of copper vapor lamps. Later, studies with monochromatic irradiations showed that the spectrum of action of phototherapy in psoriasis was optimal when UVB wavelengths of between 300 nm and 313 nm were used (Parrish, 1981). So, the concept of selective UVB phototherapy was developed, leading to narrowband UVB (NB-UVB) therapy (around 311 nm), which is widely used in dermatology today. Data now confirm that NB-UVB is more efficient than broadband UVB, with a better risk:benefit ratio (Tjioe et al., 2003); however, it is reserved for skin disorders that affect more than 20% of the body surface area. In the past few years, some devices have been developed that selectively deliver UVB to smaller surface areas, allowing surrounding healthy skin to be preserved (Leone et al., 2003; Menchini et al., 2003; Tanghetti and Gillis, 2003a). At the same time, excimer lasers have begun to be used for pigmentary disorders (Esposito et al., 2004; Ostovari et al., 2004; Spencer et al., 2002; Taneja et al., 2003). This type of laser represents the latest advance in the field of selective phototherapy. It emits a wavelength of 308 nm and capitalizes on the physical properties of lasers: monochromatic light; possibility of delivering high fluencies; and selectivity of the treatment. Because it represents an interesting new approach and to date few prospective studies have been performed with this type of laser (especially in pigmentary disorders), studies with long-term follow-up are needed.
Moreover, the high cost of this device has limited its use to a few dermatological centers.
Photobiological Effects of UVB Radiation The mechanisms by which UVB radiation exerts its activity on skin are still not well known. Immunomodulatory effects are the best understood. Animal models have shown that low doses of UVB are able to induce local immunosuppression and high doses can induce systemic immunosuppression (Miyauchi and Horio, 1995; Miyauchi-Hashimoto and Horio, 1996; Toews et al., 1980). UVB radiation acts directly on the antigen-presenting cells by depleting Langerhans cells from the epidermis and impairing antigen-presenting functions (Toews et al., 1980). UVB also works on keratinocytes; after UVB irradiation, the keratinocytes produce many cytokines, such as interleukin (IL)-1, IL10, tumor necrosis factor a (TNF-a), prostaglandin E2 or a-melanocytic stimulating hormone (aMSH). The injection of recombinant TNF-a intracutaneously at the site of sensitization suppresses the induction of contact hypersensitivity, whereas antibodies to TNF-a reverse UVBinduced immunosuppression (Yoshikawa and Streilein, 1990). Pre-treatment of Langerhans cells with IL-10 impairs their ability to present antigen to T helper (Th)1 clones, while antigen-presenting capacity to Th2 clones was not altered (Enk et al., 1993). a-MSH and prostaglandin E2 may also be involved in UV-induced immunosuppression (Luger et al., 1999; Shreedhar et al., 1998). One of the most important photobiological effects of UVB is the induction of apoptosis of T lymphocytes. T cells seem to be affected by UV radiation to a greater extent than do B lymphocytes. The mechanism of action is still not well known, but direct lesions on lymphocytic DNA and expression of Fas ligand on the surface of the keratinocytes could both be involved (Gutierrez-Steil et al., 1998). The exact photobiological effects of the 308 nm excimer laser radiation on skin have not so far been investigated. It is probable that they are similar to those produced by NB-UVB phototherapy. However, it has been shown that the apoptotic dose 50 (apoptosis in 50% of the T cells) is 95 mJ/cm2 with the 308 nm excimer laser and 320 mJ/cm2 with NB-UVB light (Novak et al., 2002). Irradiating at 200 mJ/cm2 with the 308 nm excimer laser induces apoptosis in 59–65% of T cells. This efficiency gain could allow the cumulative dose necessary to obtain clinical results to be reduced, thus limiting the side effects of the phototherapy. However, the need for long-term follow-up is obvious, and the risk that the 308 nm excimer 1183
CHAPTER 61
laser might have long-term mutagenic effects cannot be excluded. Finally, decreased numbers of natural killer cells (Toda et al., 1986), decrease in the expression of adhesion molecules on vascular endothelial cells (Yamawaki et al., 1996), and suppression of the degranulation and secretion of histamine by mast cells (Danno et al., 1986) have also been reported, and may contribute to the immunomodulatory effects of UVB phototherapy. Immunomodulating effects explain the efficacy of UVB therapy on inflammatory disorders such as psoriasis and atopic dermatitis. Apoptosis of T cell infiltrate is also very useful in pityriasis lichenoides and mycosis fungoides. These photobiological effects probably also play an important role in the treatment of autoimmune pigmentary disorders such as vitiligo. Indeed, recent work on the autoimmune origin of vitiligo underlines the importance of the immunomodulatory effect of UVB in the treatment of vitiliginous lesions (Ongenae et al., 2003). The stimulation of migration and proliferation of melanocytes from the hair follicle niche is necessary and essential to obtain repigmentation — including in vitiligo. This stimulation is so far not fully understood, although many studies have demonstrated the direct and indirect action of UVB in melanogenesis. DNA damage and the formation of thymidine dimers directly induced by UVB irradiation of melanocytes have been shown to enhance pigmentation (Eller and Gilchrest, 2000). The increase of a-MSH receptors (Chakraborty et al., 1999) and the formation of nitric oxide (Romero-Graillet et al., 1997), also induced by UVB irradiation, also promote melanogenesis. However, the indirect action of the cytokines secreted by the keratinocytes is probably the major component in this stimulation (Hirobe et al., 2002). This indirect action of UVB could explain its increased efficiency in inducing repigmentation by comparison with UVA, even though UVA radiation can penetrate deeper into the dermis and directly stimulate the melanocytes located in the hair follicle niche.
Vitiligo There is increasing evidence that UVB therapy is superior to UVA in treating vitiligo. Many studies have demonstrated the efficiency of PUVA therapy in this indication; however, there are specific contraindications associated with it and a higher risk of side effects, including skin carcinomas (Garland et al., 2003; Lindelof et al., 1999; Stern, 2001; Stern et al., 1997). It is important to note that long-term follow-up of UVB therapy is much more limited than UVA, but, by means of a dose–response model, it has been calculated that long-term NB-UVB therapy may carry substantially less risk for skin cancer than PUVA therapy (Slaper et al., 1986). A metaanalysis of the literature concludes that UVB therapy is the most effective and safe therapy for generalized vitiligo (Njoo et al., 1998). However, comparison of all of the studies must
1184
be undertaken carefully, as great variability is apparent in the patient population (particularly localization, age, and skin type) and in the duration of treatment.
Broadband UVB Only a few studies have evaluated the use of broadband UVB therapy in the treatment of vitiligo. In the first, 8 of the 14 patients (57.1%) showed repigmentation of at least 75% at the end of 12 months of treatment (Koster and Wiskemann, 1990). However, these results were essentially obtained in Fitzpatrick skin types IV–VI. These interesting results are not confirmed by a recent intraindividual comparative study that showed 22% of patients treated by NB-UVB achieved a repigmentation of at least 75% after 12 months of treatment against none with broadband UVB (Anke Hartmann, 2004). The latter study involved only ten patients, and the localization of the treated lesions was different between the two groups (upper part of the body for NB-UVB and lower part for broadband).
Narrowband UVB First results obtained with NB-UVB were also very promising. In a retrospective study, five of the seven treated patients achieved more than 75% repigmentation following a mean of 19 treatments (Scherschun et al., 2001). In an open trial involving 51 children with generalized vitiligo, 53% of the patients showed at least 75% repigmentation after 1 year of twice-weekly NB-UVB treatment (Njoo et al., 2000). On the other hand, in another study only two of nine patients achieved 75% repigmentation after 12 months of treatment (Anke Hartmann, 2004). In a larger study, 5 of 60 patients (8%) achieved 75% repigmentation after three months of treatment and 32 of the 51 other patients (63%) showed at least 75% repigmentation after 12 months of treatment (Westerhof and Nieuweboer-Krobotova, 1997). In the last few years, new devices for delivering UVB light have been developed to treat localized vitiligo. An open study with NB-UVB micro-phototherapy has shown 510 of 734 patients (69.5%) achieving more than 75% of repigmentation after 12 months of treatment (Menchini et al., 2003). No sideeffects were reported. The device produces a focused beam of NB-UVB, which allows selective treatment of the vitiligo lesions. However, these promising results have to be confirmed in a control prospective study. Another approach was developed using a 308 nm monochromatic excimer lamp. In a pilot study, 12 of 37 patients (32.4%) showed more than 75% repigmentation after three months of treatment and 18 patients (48.6%) after six months (Leone et al., 2003). Side effects were limited to transient erythema. These results are encouraging and seem to be similar to those obtained with 308 nm excimer lasers. The use of a lamp instead of a laser decreases the cost of the device and allows larger surfaces to be treated; however, the device does not use a coherent light and selective treatment with sparing of healthy surrounding skin is not possible.
UVB THERAPY FOR PIGMENTARY DISORDERS
308 nm Excimer Laser The efficiency of the 308 nm excimer laser in the treatment of vitiligo was first reported by Baltas et al. (2001). Since then, many studies have shown the potential of this device in the treatment of vitiligo (Baltas et al., 2002; Esposito et al., 2004; Ostovari et al., 2004; Spencer et al., 2002; Taneja et al., 2003). Only low fluencies are used (starting at between 50 mJ/cm2 and 200 mJ/cm2). Sessions were carried out two or three times a week for one to six months depending on the series. The number of lesions which showed repigmentation at the end of the treatment was excellent (79–100%). However, except in one study, the percentage of treated lesions achieving at least 75% repigmentation was about 30%. Among the factors which influence the therapeutic response, localization of the lesions plays a key role. In their study, Taneja et al. (2003) obtained at least 75% repigmentation in all lesions situated on the face versus none on the hands or the feet. In our series, we found significant statistically inferior results for “UV resistant” areas (extremities and bony protuberances) by comparison with the rest of the body (Ostovari et al., 2004). The stability of the repigmentation with time has so far been difficult to evaluate, as follow-up of the patients is poor or nil; however, one recent series showed an absence of depigmentation of the treated lesions after one year (Esposito et al., 2004). Finally, patients’ tolerance of the treatment is usually good; side effects are limited to erythema and rare bullous lesions. Thus, the 308 nm excimer laser appears to be an efficient and well-tolerated treatment for localized vitiligo.
Combination Therapies Interest in combination treatments was first demonstrated with the combination of UVA and topical steroids. In a prospective, randomized, controlled, left–right comparison study, it was shown that the combination of UVA and fluticasone propionate was much more effective than UVA or topical steroid alone (Westerhof et al., 1999). To the best of our knowledge, the combination of UVB therapy with topical steroids has not yet been evaluated, although some series have studied the association of UVB and other synergistic drugs. Oxidative stress has been shown to be involved in the pathogenesis of vitiligo. Pseudocatalase has the ability to remove hydrogen peroxide and so could be interesting in the treatment of vitiligo. The combination of topical pseudocatalase with UVB showed promising results in a pilot study (complete repigmentation on the face and the dorsum of the hands in 90% of patients) (Schallreuter et al., 1995). Unfortunately, these results were not confirmed in a recent study (Patel et al., 2002). The occurrence of repigmentation of vitiligo in patients treated with calcipotriol (a vitamin D3 analog) for psoriasis has suggested that it might be efficacious in treating vitiligo. The use of calcipotriol with sun or PUVA therapy has provided some interesting rates of repigmentation. However, the results are controversial (Baysal et al., 2003; Ermis et al., 2001; Parsad et al., 1998). To date, only one study with calcipotriol and UVB has been reported. The results confirmed
the efficiency of NB-UVB and its superiority over broadband UVB for treating vitiligo, but also showed that the combination of calcipotriol with UVB had no enhancing effect on repigmentation (Anke Hartmann, 2004). Tacrolimus ointment has recently shown some interesting results in the treatment of vitiligo (Lepe et al., 2003). However, the best results were achieved in sun-exposed areas. Two recent studies have evaluated if the combination of a 308 nm excimer laser and topical tacrolimus could be synergistic. These compared the efficiency of a 308 nm excimer combined with tacrolimus ointment with excimer laser monotherapy (Passeron et al., 2004) or excimer laser monotherapy associated with placebo ointment (Kawalek et al., 2004). In both cases, a total of 24 sessions were completed, and tacrolimus ointment 0.1% was applied twice a day. The results were similar and showed that the combined treatment was more efficient than laser used alone. Tolerance was good and side effects were limited to constant erythema, tingling, and rare bullous lesions. These encouraging results are corroborated by two other reports associating UVB light and topical tacrolimus (Castanedo-Cazares et al., 2003; Tanghetti and Gillis, 2003b). However, the increased risk of skin cancers — promoted by the association of two immunosuppressive treatments — cannot be excluded. In the meanwhile, until long-term follow-up is available, this association should be reserved to control studies.
Other Hypopigmented Disorders Postsurgical Leukoderma Although no prospective studies have been conducted as yet, two cases of post-resurfacing leukoderma have been successfully treated with a 308 nm excimer laser (Friedman and Geronemus, 2001). An improvement of at least 75% was obtained in eight sessions in the first case and in ten sessions in the second one, without any depigmentation after one month follow-up. In one other case of persistent laser-induced hypopigmentation after tattoo removal, repigmentation was achieved in 40 sessions using a 308 nm excimer laser (Gundogan et al., 2004). In all cases, no adverse events were noted and the selectivity of the treatment prevented perilesional hyperpigmentation.
Hypopigmented Mycosis Fungoides UVB phototherapy is one of the best treatments available for cutaneous T lymphomas. Hypopigmentation can occur in mycosis fungoides and in Sézary syndrome. The use of NBUVB therapy has been shown to both improve the lymphocytic infiltrate and hypopigmentation (Akaraphanth et al., 2000; Gathers et al., 2002).
Mature Hypopigmented Striae An open prospective study on 75 patients evaluated the repigmentation of mature hypopigmented striae with a 308 nm
1185
CHAPTER 61
excimer laser (Goldberg et al., 2003). Increased pigmentation was observed after eight sessions, leading to esthetic improvements for 80% of patients. The absence of a control group and the weakness of the evaluation methods moderate these encouraging results, especially as maintenance sessions will probably be necessary to sustain the results. However, this technique remains one of the few possible therapeutic approaches for this frequent esthetical problem.
References Akaraphanth, R., M. C. Douglass, and H. W. Lim. Hypopigmented mycosis fungoides: treatment and a 6(1/2)-year follow-up of 9 patients. J. Am. Acad. Dermatol. 42(1 Pt 1):33–39, 2000. Anke Hartmann, C. L., H. Hamm, E.-B. Bröcker, and U. B. Hofmann. Narrow-band UVB311 nm vs. broad-band UVB therapy in combination with topical calcipotriol vs. placebo in vitiligo. Int. J. Dermatol. 44:736–742, 2005. Baltas, E., Z. Csoma, F. Ignacz, A. Dobozy, and L. Kemeny. Treatment of vitiligo with the 308-nm xenon chloride excimer laser. Arch. Dermatol. 138:1619–1620, 2002. Baltas, E., P. Nagy, B. Bonis, Z. Novak, F. Ignacz, G. Szabo, Z. Bor, A. Dobozy, and L. Kemeny. Repigmentation of localized vitiligo with the xenon chloride laser. Br. J. Dermatol. 144:1266–1267, 2001. Baysal, V., M. Yildirim, A. Erel, and D. Kesici. Is the combination of calcipotriol and PUVA effective in vitiligo? J. Eur. Acad. Dermatol. Venereol. 17:299–302, 2003. Castanedo-Cazares, J. P., V. Lepe, and B. Moncada. Repigmentation of chronic vitiligo lesions by following tacrolimus plus ultravioletB-narrow-band. Photodermatol. Photoimmunol. Photomed. 19:35–36, 2003. Chakraborty, A. K., Y. Funasaka, A. Slominski, J. Bolognia, S. Sodi, M. Ichihashi, and J. M. Pawelek. UV light and MSH receptors. Ann. N. Y. Acad. Sci. 885:100–116, 1999. Danno, K., K. Toda, and T. Horio. Ultraviolet-B radiation suppresses mast cell degranulation induced by compound 48/80. J. Invest. Dermatol. 87:775–778, 1986. Eller, M. S., and B. A. Gilchrest. Tanning as part of the eukaryotic SOS response. Pigment Cell Res. 13(Suppl 8):94–97, 2000. Enk, A. H., V. L. Angeloni, M. C. Udey, and S. I. Katz. Inhibition of Langerhans cell antigen-presenting function by IL-10. A role for IL-10 in induction of tolerance. J. Immunol. 151:2390–2398, 1993. Ermis, O., E. Alpsoy, L. Cetin, and E. Yilmaz. Is the efficacy of psoralen plus ultraviolet A therapy for vitiligo enhanced by concurrent topical calcipotriol? A placebo-controlled double-blind study. Br. J. Dermatol. 145:472–475, 2001. Esposito, M., R. Soda, A. Costanzo, and S. Chimenti. Treatment of vitiligo with the 308 nm excimer laser. Clin. Exp. Dermatol. 29:133–137, 2004. Friedman, P. M., and R. G. Geronemus. Use of the 308-nm excimer laser for postresurfacing leukoderma. Arch. Dermatol. 137:824– 825, 2001. Garland, C. F., F. C. Garland, and E. D. Gorham. Epidemiologic evidence for different roles of ultraviolet A and B radiation in melanoma mortality rates. Ann. Epidemiol. 13:395–404, 2003. Gathers, R. C., L. Scherschun, F. Malick, D. P. Fivenson, and H. W. Lim. Narrowband UVB phototherapy for early-stage mycosis fungoides. J. Am. Acad. Dermatol. 47:191–197, 2002. Goldberg, D. J., D. Sarradet, and M. Hussain. 308-nm Excimer laser treatment of mature hypopigmented striae. Dermatol. Surg. 29:596–598; discussion 598–599, 2003. Gundogan, C., B. Greve, I. Hausser, and C. Raulin. [Repigmentation of persistent laser-induced hypopigmentation with an excimer laser following tattoo removal]. Hautarzt 55:549–552, 2004.
1186
Gutierrez-Steil, C., T. Wrone-Smith, X. Sun, J. G. Krueger, T. Coven, and B. J. Nickoloff. Sunlight-induced basal cell carcinoma tumor cells and ultraviolet-B-irradiated psoriatic plaques express Fas ligand (CD95L). J. Clin. Invest. 101:33–39, 1998. Hirobe, T., R. Furuya, S. Akiu, O. Ifuku, and M. Fukuda. Keratinocytes control the proliferation and differentiation of cultured epidermal melanocytes from ultraviolet radiation Binduced pigmented spots in the dorsal skin of hairless mice. Pigment Cell Res. 15:391–399, 2002. Kawalek, A. Z., J. M. Spencer, and R. G. Phelps. Combined excimer laser and topical tacrolimus for the treatment of vitiligo: a pilot study. Dermatol. Surg. 30(2 Pt 1):130–135, 2004. Koster, W., and A. Wiskemann. [Phototherapy with UV-B in vitiligo]. Z. Hautkr. 65:1022–1024, 1029, 1990. Leone, G., P. Iacovelli, A. Paro Vidolin, and M. Picardo. Monochromatic excimer light 308 nm in the treatment of vitiligo: a pilot study. J. Eur. Acad. Dermatol. Venereol. 17:531–537, 2003. Lepe, V., B. Moncada, J. P. Castanedo-Cazares, M. B. Torres-Alvares, C. A. Ortiz, and A. B. Torres-Rubalcava. A double-blind randomized trial of 0.1% tacrolimus vs 0.05% clobetasol for the treatment of childhood vitiligo. Arch. Dermatol. 139:581–585, 2003. Lindelof, B., B. Sigurgeirsson, E. Tegner, O. Larko, A. Johannesson, B. Berne, B. Ljunggren, T. Andersson, L. Molin, E. NylanderLundqvist, and L. Emtestam. PUVA and cancer risk: the Swedish follow-up study. Br. J. Dermatol. 141:108–112, 1999. Luger, T. A., T. Schwarz, H. Kalden, T. Scholzen, A. Schwarz, and T. Brzoska. Role of epidermal cell-derived alpha-melanocyte stimulating hormone in ultraviolet light mediated local immunosuppression. Ann. N. Y. Acad. Sci. 885:209–216, 1999. Menchini, G., E. Tsoureli-Nikita, and J. Hercogova. Narrow-band UV-B micro-phototherapy: a new treatment for vitiligo. J. Eur. Acad. Dermatol. Venereol. 17:171–177, 2003. Miyauchi, H., and T. Horio. Ultraviolet B-induced local immunosuppression of contact hypersensitivity is modulated by ultraviolet irradiation and hapten application. J. Invest. Dermatol. 104:364–369, 1995. Miyauchi-Hashimoto, H., and T. Horio. Suppressive effect of ultraviolet B radiation on contact sensitization in mice. II. Systemic immunosuppression is modulated by ultraviolet irradiation and hapten application. Photodermatol. Photoimmunol. Photomed. 12:137–144, 1996. Njoo, M. D., P. I. Spuls, J. D. Bos, W. Westerhof, and P. M. Bossuyt. Nonsurgical repigmentation therapies in vitiligo. Meta-analysis of the literature. Arch. Dermatol. 134:1532–1540, 1998. Njoo, M. D., J. D. Bos, and W. Westerhof. Treatment of generalized vitiligo in children with narrow-band (TL-01) UVB radiation therapy. J. Am. Acad. Dermatol. 42(2 Pt 1):245–253, 2000. Novak, Z., B. Bonis, E. Baltas, I. Ocsovszki, F. Ignacz, A. Dobozy, and L. Kemeny. Xenon chloride ultraviolet B laser is more effective in treating psoriasis and in inducing T cell apoptosis than narrowband ultraviolet B. J. Photochem. Photobiol. B 67:32–38, 2002. Ongenae, K., N. Van Geel, and J. M. Naeyaert. Evidence for an autoimmune pathogenesis of vitiligo. Pigment Cell Res. 16:90–100, 2003. Ostovari, N., T. Passeron, W. Zakaria, E. Fontas, J. C. Larouy, J. F. Blot, J. P. Lacour, and J. P. Ortonne. Treatment of vitiligo by 308nm excimer laser: an evaluation of variables affecting treatment response. Lasers Surg. Med. 35:152–156, 2004. Parrish, J. A.. Phototherapy and photochemotherapy of skin diseases. J. Invest. Dermatol. 77:167–171, 1981. Parsad, D., R. Saini, and N. Verma. Combination of PUVAsol and topical calcipotriol in vitiligo. Dermatology 197:167–170, 1998. Passeron, T., N. Ostovari, W. Zakaria, E. Fontas, J. C. Larrouy, J. P. Lacour, and J. P. Ortonne. Topical tacrolimus and the 308-nm excimer laser: a synergistic combination for the treatment of vitiligo. Arch. Dermatol. 140:1065–1069, 2004.
UVB THERAPY FOR PIGMENTARY DISORDERS Patel, D. C., A. V. Evans, and J. L. Hawk. Topical pseudocatalase mousse and narrowband UVB phototherapy is not effective for vitiligo: an open, single-centre study. Clin. Exp. Dermatol. 27:641–644, 2002. Romero-Graillet, C., E. Aberdam, M. Clement, J. P. Ortonne, and R. Ballotti. Nitric oxide produced by ultraviolet-irradiated keratinocytes stimulates melanogenesis. J. Clin. Invest. 99:635–642, 1997. Schallreuter, K. U., J. M. Wood, K. R. Lemke, and C. Levenig. Treatment of vitiligo with a topical application of pseudocatalase and calcium in combination with short-term UVB exposure: a case study on 33 patients. Dermatology 190:223–229, 1995. Scherschun, L., J. J. Kim, and H. W. Lim. Narrow-band ultraviolet B is a useful and well-tolerated treatment for vitiligo. J. Am. Acad. Dermatol. 44:999–1003, 2001. Shreedhar, V., T. Giese, V. W. Sung, and S. E. Ullrich. A cytokine cascade including prostaglandin E2, IL-4, and IL-10 is responsible for UV-induced systemic immune suppression. J. Immunol. 160:3783–3789, 1998. Slaper, H., A. A. Schothorst, and J. C. van der Luen. Risk evaluation of UVB therapy for psoriasis: comparison of calculated risk for UVB therapy and observed risk in PUVA-treated patients. Photodermatology 3:271–283, 1986. Spencer, J. M., R. Nossa, and J. Ajmeri. Treatment of vitiligo with the 308-nm excimer laser: a pilot study. J. Am. Acad. Dermatol. 46:727–731, 2002. Stern, R. S. The risk of melanoma in association with long-term exposure to PUVA. J. Am. Acad. Dermatol. 44:755–761, 2001. Stern, R. S., K. T. Nichols, and L. H. Vakeva. Malignant melanoma in patients treated for psoriasis with methoxsalen (psoralen) and ultraviolet A radiation (PUVA). The PUVA Follow-Up Study. N. Engl. J. Med. 336:1041–1045, 1997. Taneja, A., M. Trehan, and C. R. Taylor. 308-nm excimer laser for the treatment of localized vitiligo. Int. J. Dermatol. 42:658–662, 2003.
Tanghetti, E., and P. R. Gillis. Photometric and clinical assessment of localized UVB phototherapy systems for the high-dosage treatment of stable plaque psoriasis. J. Cosmet. Laser Ther. 5:101–106, 2003a. Tanghetti, E. A., and P. R. Gillis. Clinical evaluation of B Clear and Protopic treatment for vitiligo. Lasers Surg. Med. 32(S15): 37, 2003b. Tjioe, M., T. Smits, P. C. van de Kerkhof, and M. J. Gerritsen. The differential effect of broad band vs narrow band UVB with respect to photodamage and cutaneous inflammation. Exp. Dermatol. 12:729–733, 2003. Toda, K., Y. Miyachi, N. Nesumi, J. Konishi, and S. Imamura. UVB/PUVA-induced suppression of human natural killer activity is reduced by superoxide dismutase and/or interleukin 2 in vitro. J. Invest. Dermatol. 86:519–522, 1986. Toews, G. B., P. R. Bergstresser, and J. W. Streilein. Epidermal Langerhans cell density determines whether contact hypersensitivity or unresponsiveness follows skin painting with DNFB. J. Immunol. 124:445–453, 1980. Westerhof, W., and L. Nieuweboer-Krobotova. Treatment of vitiligo with UV-B radiation vs topical psoralen plus UV-A. Arch. Dermatol. 133:1525–1528, 1997. Westerhof, W., L. Nieuweboer-Krobotova, P. G. Mulder, and E. J. Glazenburg. Left-right comparison study of the combination of fluticasone propionate and UV-A vs. either fluticasone propionate or UV-A alone for the long-term treatment of vitiligo. Arch. Dermatol. 135:1061–1066, 1999. Yamawaki, M., S. Futamura, and T. Horio. UVB radiation suppresses the TNF-alpha-induced expression of E-selectin and ICAM-1 on cultured human umbilical vein endothelial cells. J. Dermatol. Sci. 13:11–17, 1996. Yoshikawa, T., and J. W. Streilein. Tumor necrosis factor-alpha and ultraviolet B light have similar effects on contact hypersensitivity in mice. Reg. Immunol. 3:139–144, 1990.
1187
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
62
Sunscreens and Cosmetics James J. Nordlund and Rebat M. Halder
Sunscreens The cutaneous pigmentary system is markedly affected by electromagnetic radiation. There are two spectra of ultraviolet light that stimulate production of pigmentation in the skin, the process called tanning. They are ultraviolet A (UVA) defined as the spectrum from 320 nm to 400 nm and ultraviolet B (UVB) defined as the spectrum from 290 nm to 320 nm. Ultraviolet C (UVC) is the spectrum from 290 nm to 250 nm. UVC is emitted by the sun but is absorbed by the ozone layer and none reaches the surface of the earth. In contrast large amounts of UVB strike the earth. There is about 1000-fold more UVA in sunlight than UVB. Suntan is caused by two mechanisms: immediate pigment darkening and the production of melanin (Agin et al., 1985; Porges et al., 1988). Immediate pigment darkening is thought to be due mainly to oxidation of the melanin polymer (Beitner and Wennersten, 1985; Honigsmann et al., 1986) within the skin although rearrangement of melanosomes within keratinocytes might also be involved (Lavker and Kaidbey, 1982). It occurs within minutes after exposure to ultraviolet light and reverses within 24 hours after exposure is stopped (Porges et al., 1988). In contrast delayed tanning dependent on melanin synthesis takes several days but persists for prolonged periods of time, up to many weeks (Porges et al., 1988). UVA is especially efficient in causing immediate pigment darkening (Irwin et al., 1993; Kaidbey and Barnes, 1991; Lavker and Kaidbey, 1982; Porges et al., 1988) but can cause melanin synthesis as well. UVB is responsible for delayed tanning that starts about 72 hours after exposure to sunlight. It is caused by enhanced synthesis of melanin and transfer of melanosomes into the surrounding keratinocytes. The mechanisms responsible for stimulating melanin formation are complex. Because sunlight can profoundly affect melanin production and skin color, it is used to treat skin conditions of hypopigmentation like vitiligo and pityriasis alba. It is also important to prevent sunlight from penetrating to skin that is hyperpigmented, such as melasma (Balina and Graupe, 1991; Pathak et al., 1986; Vazquez and Sanchez, 1983; Verallo-Rowell et al., 1989). The best way to stop sunlight from penetrating the skin is by application of sunscreens. The potency of sunscreen or its ability to prevent ultraviolet light from penetrating the epidermis can be measured (Lowe and Frielander, 1995). The potency is called Sun Protective Factor or SPF. An SPF of 2 means that it takes twice as long for a sunburn to develop in the treated skin than in untreated skin. That is, the sunscreen absorbed about half of 1188
the incident light. An SPF of 4 means that it takes four times more exposure to sun to develop a burn in treated skin than in unprotected skin. About a quarter of the incident light penetrates the epidermis. Sunscreens have potencies of 50 and higher. An SPF of 25 absorbs all but 4% of the sunlight. A sunscreen with an SPF of 50 absorbs all but 2% of the ultraviolet light. Practically the difference is not important. Thus a sunscreen with an SPF of 20–25 is considered to have maximum practical protection. The SPF is a measure only of absorption of UVB. Most UVA penetrates through the sunscreen although a moderate amount of the shorter UVA in the 320–340 nm spectrum is absorbed (Cole, 1994; Diffey and Farr, 1991; Gange et al., 1986; Leenutaphong, 1992; Lowe et al., 1987; Roelandts, 1991). There is one chemical called parasol available for protection against UVA (Anonymous, 1989, 1993; Leenutaphong, 1992; Lowe and Frielander, 1995). There are few commercial products containing UVB screens and parasol for complete protection against the effects of UVA and UVB (Anonymous, 1993). Despite this, it is important for those being treated with conditions of hyperpigmentation such as melasma to use sunscreens to block some of the tanning effects of sunlight. Those with depigmenting conditions such as vitiligo, piebaldism, and albinism must use sunscreen to prevent burning. These individuals have lost the sun-protective effects of the pigmentary system. Their skin requires some other form of protection against the burning effects of sunlight. Clothing can be an excellent sunscreen but is not practical during the hot summer months. Sunscreen can act as a substitute for protective clothes. Treatment of individuals with hyperpigmentation such as melasma (Balina and Graupe, 1991; Pathak et al., 1986; Vazquez and Sanchez, 1983; Verallo-Rowell et al., 1989) requires the use of sunscreens. Postinflammatory hyperpigmentation on exposed skin also is benefited by applications of sunscreens (Bekhor, 1995; Ho et al., 1995; Leenutaphong, 1992; Pathak et al., 1986).
Other Therapies for Pigmentary Disorders Cosmetics In darker-skinned individuals cover-up cosmetics (Dermablend, Covermark) can hide the vitiligo area with remarkable color matching and are often used between treatments with other modalities (Figs 62.1 and 62.2). Because they can be rubbed off easily, they are best used on areas that are subject to minimal contact such as the face. Camouflage stains
SUNSCREENS AND COSMETICS
Fig. 62.1. A woman with extensive vitiligo.
Fig. 62.2. Woman in Figure 62.1 after application of cosmetics. Her appearance is excellent.
(Vitadye, Dyoderm), on the other hand, have the advantage of being long-lasting but usually do not offer exact color matching and may interfere with treatment using UV light. They are best used for limited areas that are subject to constant friction. Many women wear cosmetics daily to cover pigmentary blemishes. Many cosmetics contain sunscreens. These combination products seem especially useful to protect the skin from pigmentary changes.
Cole, C. Multicenter evaluation of sunscreen UVA protectiveness with the protection factor test method. J. Am. Acad. Dermatol. 30:729–736, 1994. Diffey, B. L., and P. M. Farr. Sunscreen protection against UVB, UVA and blue light: an in vivo and in vitro comparison [published erratum appears in Br. J. Dermatol. 125:609, 1991]. Br. J. Dermatol. 124:258–263, 1991. Gange, R. W., A. Soparkar, E. Matzinger, S. H. Dromgoole, J. Sefton, and R. DeGryse. Efficacy of a sunscreen containing butyl methoxydibenzoylmethane against ultraviolet A radiation in photosensitized subjects. J. Am. Acad. Dermatol. 15:494–499, 1986. Ho, C., Q. Nguyen, N. J. Lowe, M. E. Griffin, and G. Lask. Laser resurfacing in pigmented skin. Dermatol. Surg. 21:1035–1037, 1995. Honigsmann, H., G. Schuler, W. Aberer, N. Romani, and K. Wolff. Immediate pigment darkening phenomenon. A reevaluation of its mechanisms. J. Invest. Dermatol. 87:648–652, 1986. Irwin, C., A. Barnes, D. Veres, and K. Kaidbey. An ultraviolet radiation action spectrum for immediate pigment darkening. Photochem. Photobiol. 57:504–507, 1993. Kaidbey, K. H., and A. Barnes. Determination of UVA protection factors by means of immediate pigment darkening in normal skin. J. Am. Acad. Dermatol. 25:262–266, 1991. Lavker, R. M., and K. H. Kaidbey. Redistribution of melanosomal complexes within keratinocytes following UV-A irradiation: a possible mechanism for cutaneous darkening in man. Arch. Dermatol. Res. 272:215–228, 1982. Leenutaphong, V. Evaluating the UVA protection of commercially available sunscreens. J. Med. Assoc. Thai. 75:619–624, 1992.
References Agin, P. P., D. L. Desrochers, and R. M. Sayre. The relationship of immediate pigment darkening to minimal erythemal dose, skin type, and eye color. Photodermatology 2:288–294, 1985. Anonymous. Photoplex — a broad spectrum sunscreen. Med. Lett. Drugs Ther. 31:59–60, 1989. Anonymous. Shade UVAGuard — a second broad-spectrum sunscreen. Med. Lett. Drugs Ther. 35:53–54, 1993. Balina, L. M., and K. Graupe. The treatment of melasma. 20% azelaic acid versus 4% hydroquinone cream. Int. J. Dermatol. 30:893–895, 1991. Beitner, H., and G. Wennersten. A qualitative and quantitative transmission electronmicroscopic study of the immediate pigment darkening reaction. Photodermatology 2:273–278, 1985. Bekhor, P. S. The role of pulsed laser in the management of cosmetically significant pigmented lesions [Review]. Australas. J. Dermatol. 36:221–223, 1995.
1189
CHAPTER 62 Lowe, N. J., and J. Frielander. Prevention of photodamage with sunprotection and sunscreens. In: Photodamage, B. A. Gilchrest (ed.). Cambridge, MA: Blackwell Science, Inc., 1995, p. 295. Lowe, N. J., S. H. Dromgoole, J. Sefton, T. Bourget, and D. Weingarten. Indoor and outdoor efficacy testing of a broad-spectrum sunscreen against ultraviolet A radiation in psoralen-sensitized subjects. J. Am. Acad. Dermatol. 17:224–230, 1987. Pathak, M. A., T. B. Fitzpatrick, and E. W. Kraus. Usefulness of retinoic acid in the treatment of melasma. J. Am. Acad. Dermatol. 15:894–899, 1986. Porges, S. B., K. H. Kaidbey, and G. L. Grove. Quantification of visible
1190
light-induced melanogenesis in human skin. Photodermatology 5:197–200, 1988. Roelandts, R. Which components in broad-spectrum sunscreens are most necessary for adequate UVA protection? J. Am. Acad. Dermatol. 25:999–1004, 1991. Vazquez, M., and J. L. Sanchez. The efficacy of a broad-spectrum sunscreen in the treatment of melasma. Cutis 32:92–96, 1983. Verallo-Rowell, V. M., V. Verallo, K. Graupe, L. Villafuerte, and M. Garcia-Lopez. Double-blind comparison of azelaic acid and hydroquinone in the treatment of melasma. Acta Derm. Venereol. 143(Suppl):58–61, 1989.
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
63
Surgical Treatments of Pigmentary Disorders Rebat M. Halder and James J. Nordlund
Repopulation of Melanocytes by Grafting The possibility of treating vitiligo or other forms of depigmentation with “exchange grafts” using the patient’s own clinically normal skin was first recognized in 1952 (Spencer and Tolmach, 1952). Since then, various adaptations of this basic concept have evolved into rather promising additions to the armamentarium for the treatment of depigmentation. Successful repigmentation using these modalities is dependent on proper case selection of patients, especially those with vitiligo. Most importantly, only patients in whom the vitiligo is stable (no progression within four to six months) should be considered as good candidates for transplantation. In this respect, patients with segmental vitiligo are ideal candidates because this type of vitiligo, once established, tends not to progress. Many of these individuals have white hairs within the patch, an indication that the reservoir of melanocytes is destroyed (see Chapter X). Following these selection criteria usually yields relatively high success rates.
Autologous Epidermal Grafting This technique was described in a report published in 1964. It was found that viable epidermis could be separated from dermis in vivo by induction of suction blister by applying negative pressure at 200 mm Hg to the skin for three to four hours (Kiistala and Mustakallio, 1964). Dermal epidermal separation occurs through the level of the lamina lucida. Successful repigmentation of vitiliginous skin was achieved when the resulting melanocyte-bearing blister top was used as a graft, dermal side down, and placed onto recipient area of depigmentation previously denuded by blistering via suction, applications of liquid nitrogen, or by topical UVA (Falabella, 1989; Kiistala and Mustakallio, 1964; Koga, 1988; Suvanprakorn et al., 1985). Pigmentation usually develops in three to six months. There may be areas of achromic fissures between grafts in the recipient areas. Koebnerization at donor sites has been reported in conjunction with depigmentation of transplanted grafts in patients with unstable vitiligo (Hatchome et al., 1990). This technique has been used to treat leukoderma following burns, vitiligo, and piebaldism. Results of treatment of segmented vitiligo are better than of treatment of generalized vitiligo (Koga, 1988). However, most physicians do not have the mechanical apparatus needed for the production of the
blisters at the donor site. Although this technique is time consuming and requires special equipment, its attractive features include the lack of scarring in both donor and recipient sites and the regeneration of new pigmented skin at donor sites. The same sites can be used as a source of melanocytes every few months.
Autologous Thin Thiersch Grafting The application of these thin split-thickness grafts in the treatment of vitiligo was first introduced in 1964 (Behl, 1964). Strips of these grafts obtained using the scalpel or dermatome are placed onto recipient sites prepared in a similar manner or by dermabrasion. Achromic areas ranging in size from 6 cm2 to 100 cm2 were treated. Patients were satisfied with the results in more than 85% of cases although objective evaluations were not done. The same method was reported as successful in over 2500 patients treated for vitiligo over a 20-year period (Behl, 1984, 1985; Behl and Bhatia, 1973). Larger areas were grafted with an average of 180–300 cm2 done at one time. Post-burn leukoderma was treated in 32 patients by using 0.1–0.2 mm thin split-thickness grafts obtained by hand dermatome (Taki et al., 1985). All patients responded with 95–100% repigmentation. Recently the technique of thin splitthickness grafts has been modified for the treatment of vitiligo with the harvesting of grafts by mechanical dermatome with excellent results (Kahn and Cohen, 1995; Kahn et al., 1993). This technique has also been used to successfully treat vitiligo of the lip (Chitale, 1991). The advantage of this technique is it allows the grafting of large areas in a relatively short time. However, this must be weighed against the need for general anesthesia and the risk of hypertrophic scarring of both donor and recipient sites (Falabella, 1989).
Suction Blister Grafts Separation of viable epidermis from dermis can be accomplished via the production of suction blisters at 200 mm Hg negative pressure in three to four hours (Kiistala, 1968; Kiistala and Mustakallio, 1964). This finding was adapted to the treatment of achromic areas of skin where pigmented epidermis is harvested by this technique and is used to cover achromic areas that have been prepared by denuding them with liquid nitrogen blisters (Falabella, 1971, 1984). Melanocytes are contained within the top of 2–2.5 cm suction blisters. The tops of these blisters are removed with iris scissors and are directly applied to the denuded area of achromic skin. These are placed in a mosaic type of pattern. Healing 1191
CHAPTER 63
Fig. 63.1. Minigrafts placed in a depigmented patch on the ankle of a young man have successfully repigmented the area.
occurs in seven days in both donor and grafted sites. Grafted areas are covered with Telfa dressing and elastic bandages. Pigmentation usually develops in three to six months. There may be areas of achromic fissures between grafts in the recipient areas. This technique has been used to treat leukoderma following burns, vitiligo, and piebaldism. Results of treatment of segmented vitiligo are better than of nonsegmented vitiligo (Koga, 1988). An advantage of suction blister grafts is that scarring is minimal, as the dermis is left intact in both donor and recipient sites. However, most physicians do not have the mechanical apparatus needed for the production of the blisters at the donor site.
Autologous Minigrafts This technique was initially reported in one patient for the treatment of depigmentation secondary to a thermal burn. The investigators used a 2 mm punch to obtain grafts from normally pigmented skin that were transplanted into the achromic patch (Orentreich and Selmanowitz, 1972). The technique was subsequently reported to be successful in repigmenting leukodermic areas of the scalp in a patient with scarring alopecia secondary to discoid lupus erythematosus (Lobuono and Shatin, 1976) (Fig. 63.1). This technique was later found to be of benefit in two patients with vitiligo who also received PUVA therapy (Bonafe et al., 1983). This technique has been refined over the years (Falabella, 1978, 1983, 1984, 1986, 1987, 1988, 1989) and presently can be used for stable cases of leukoderma including segmental or localized vitiligo (Fig. 63.1). Post-burn achromia, piebaldism, post-dermabrasion achromia, and depigmentation from monobenzyl ether of hydroquinone can be treated by this technique (Selmanowitz, 1979; Selmanowitz et al., 1977). This technique places islands of normally pigmented skin within achromic or depigmented areas from burns or vitiligo (Falabella, 1989). The islands of pigment enlarge up to 25 times the original surface area of a 1 mm or 2 mm punch graft. A 1192
gradual process of pigment migration takes place during a period of three to six months (Falabella, 1989). The actual technique involves the harvesting of 1.2–2.0 mm punch grafts from the pigmented donor site, usually an area on the lower back below the waistline (Falabella, 1988). They can be harvested virtually next to each other. A 2 ¥ 2 cm area can yield up to 100 minigrafts. The grafts are placed 3–4 mm from each other in the recipient site where the site is prepared by making defects with the same size punch. The grafts are embedded by manual compression with saline soaked gauze and are held in place by Steri strips (cover strips) which are removed in seven days. PUVA therapy given subsequent to autologous minigrafting can hasten the repigmentation process (Skouge et al., 1992). Complications of this technique include cobblestoning, infection at the donor or recipient site, and koebnerization of the donor site. The success of autologous minigrafting is high, if the patient is selected carefully.
Autologous Mini Punch Grafts This technique is analogous to hair transplantation in that skin punches are used. The concept of donor dominance, however, is not applicable to vitiligo since viable transplanted grafts can lose their pigment even in cases where vitiligo appears stable. In 1972, 2 mm punch grafts of normally pigmented skin were used to repigment leukodermic skin (Orentreich and Selmanowitz, 1972). Grafts of 10 ¥ 3 mm with PUVA have been used by others to successfully repigment vitiliginous skin (Bonafe et al., 1983). The technique was refined by using 1.2–1.25 mm full thickness punch grafts placed 4–5 mm apart into comparable-sized recipient sites (Falabella, 1986, 1988). This graft size was found to minimize both the “cobblestoning” (trap door) effect and the cosmetic damage to the donor site that is especially prominent with larger-sized grafts, while containing enough pigment source to stimulate the spotty perifollicular repigmentation that is typically seen with spontaneous repigmentation or repigmentation with PUVA. The extent of maximal pigment spread is approximately four to five times the diameter of the graft and is reached after about four to six months without adjunctive therapy with PUVA (Figs 63.2–63.8). Resumption of the preoperative course of PUVA two weeks postoperatively can shorten this period to two to three months. Histologic studies have shown that the pigmentation that develops around either epidermal or punch grafts consists of normal melanin content and functional melanocytes (Falabella, 1988; Suvanprakorn et al., 1985).
Transplantation of Cultured Autologous Melanocytes The technique of transplanting melanocyte-containing cultures of cells has the theoretical advantage of potentially treating large areas using cells harvested from a small piece of donor skin by expanding the culture in vitro. Its major disadvantage lies in the complexities and cost of the culture systems and equipment required to achieve the culture. Thus
SURGICAL TREATMENTS OF PIGMENTARY DISORDERS
Fig. 63.2. Vitiligo on the forehead before grafting with 1 mm punches (see also Plate 63.1, pp. 494–495).
Fig. 63.3. The skin in Figure 63.2 immediately after the placement of grafts (see also Plate 63.2, pp. 494–495).
Fig. 63.5. The cheek of a woman before grafting with 1 mm punches.
Transplantation of Autologous Pure Melanocyte Culture
Fig. 63.4. The skin in Figures 63.2 and 63.3 after spread of the pigmentation showing excellent response (see also Plate 63.3, pp. 494–495).
this technique is impractical for most dermatologists. Also of concern is the uncertainty about what, if any, effects the chemicals used in culturing the cells have on the melanocytes and subsequently on the patient.
Melanocytes have been observed to survive and proliferate in a medium containing phorbol esters (Eisinger and Marko, 1982). Later, methods were developed to successfully grow melanocytes from individuals with vitiligo (Lerner, 1988; Lerner et al., 1987; Medrano and Nordlund, 1990). These techniques permitted the expansion of a small number of melanocytes into a sufficient number of cells to repigment large areas of depigmented skin. Cultured melanocytes are injected into blisters raised on achromic skin either by suction or by using a combination of liquid nitrogen and a heated oscillating disk. Although the number of cases treated in this way is small, it appears that successful repigmentation does occur. It has been noted that for success the vitiligo should be stable and the melanocyte suspension must contain about 5 ¥ 105 cells/1 cm blister. There is no pigment spread beyond the transplanted area and the color match was perfect. Ultrastructural studies showed that the transplanted melanocytes had localized to the basal layer of the epidermis and were producing and transferring pigment as in the adjacent “normal” 1193
CHAPTER 63
Fig. 63.6. The cheek of the woman in Figure 63.5 immediately after placement of 1 mm punch grafts.
Fig. 63.7. The skin in Figures 63.5 and 63.6 after partial repigmentation.
Fig. 63.8. The skin in Figures 63.5–63.7 after complete repigmentation.
Fig. 63.9. The hand of a patient with vitiligo before treatment with autologous melanocytes grown in culture.
skin (Lerner et al., 1990) (Figs 62.9–62.12). Subsequent to the initial reports of the success of melanocyte transplants for vitiligo, others have had similar successful results (Falabella et al., 1989, 1992; Gauthier and Surleve-Bazeille, 1992; Lontz
et al., 1994; Olsson and Juhlin, 1993; Olsson et al., 1994; Plott et al., 1989; Zachariae et al., 1993). This technique was initially limited by the fact that tissue plasminogen activator (TPA), the essential ingredient for
1194
SURGICAL TREATMENTS OF PIGMENTARY DISORDERS
grow well in the presence of TPA. However, the more recent reports have used growth modifiers other than TPA.
Transplantation of Autologous Melanocyte and Keratinocyte Cocultures
Fig. 63.10. The hand of the patient in Figure 63.9 after transplantation of cultured melanocytes. (Courtesy of Dr. Aaron Lerner.)
Melanocytes can be cultured in the presence of keratinocytes. Such cultures can be used to repigment areas of skin depigmented by diseases or injuries. One report emphasized that melanocytes proliferate despite the lack of “growth enhancers, feeder layers, or hormones” like phorbol esters in the culture medium (Boyce and Ham, 1983). After confluence and differentiation of the culture in about 21 days, the sheet of cells is detached from the culture flask, transferred to a layer of petrolatum gauze, and grafted onto recipient sites previously denuded with liquid nitrogen. With subsequent pigment spread, satisfactory repigmentation and color match have been achieved. Although only primary cultures have been used for grafting, each of these cultures yielded a sheet of cells that was estimated to be ten times the size of the original donor specimen. It is reasonable to assume that with subculturing, further expansion can be obtained. Another study used the culture medium MCDB-153 which was found to support the clonal growth of melanocytes and keratinocytes while inhibiting the growth of fibroblasts (Brysk et al., 1989; Plott et al., 1989). With this culture technique, 50-fold expansion of cells could be achieved in 10–14 days with a melanocyte to keratinocyte ratio of 1:10. The cells were plated on collagen-coated membranes and, once the culture reached 50–70% confluence in about two weeks, the entire composition was then grafted onto dermabraded vitiliginous skin. Repigmentation occurred in three of four cases reported and covered 40–90% of each vitiliginous area with perfect color match and subsequent spreading of pigment beyond the graft margins. The presence of viable melanocytes in the grafted skin was confirmed in both methods by biopsy.
Other Surgical Treatments Micropigmentation
Fig. 63.11. The hand of a patient with vitiligo (see also Plate 63.4, pp. 494–495).
expansion of pure melanocyte cultures, is also a potent tumor promoter and therefore poses long-term risks (Brysk et al., 1989). Furthermore, it was noted that melanocytes from vitiligo patients, unlike those from normal people, did not
The practice of tattooing goes back to prehistoric times. In 1987, the first application of the process in the treatment of vitiligo using nonallergenic iron oxide pigments was reported (Halder et al., 1989). This was an adaptation of the technique of permanent eyeliner tattooing (Patipa, 1987; Patipa et al., 1986). This form of treatment is recommended for limited areas that are not only refractory to other treatments but are also deemed by the patient to be especially cosmetically bothersome. These areas usually include exposed areas on the face such as the lips (Figs 63.13 and 63.14), hands (Figs 63.15 and 63.16), and forearms, but occasionally include more private areas such as the nipples. The results are permanent although some fading will occur with time, requiring an occasional touch-up in one to two years. Patients receiving this treatment nonetheless are very pleased with both their appearance and the convenience 1195
CHAPTER 63
Fig. 63.14. The lips in Figure 63.13 treated with micropigmentation (tattooing). The stark area of depigmentation is no longer visible. The color match is good (see also Plate 63.7, pp. 494–495).
Fig. 63.12. The hand of the patient in Figure 63.11 after successful grafting of cultured melanocytes (see also Plate 63.5, pp. 494–495). (Courtesy of Dr. Aaron Lerner.)
Fig. 63.13. Depigmentation on the lips of an African American patient with vitiligo (see also Plate 63.6, pp. 494–495).
of being able to go about their daily activities without the hassle associated with the use of cover-up cosmetics. The best results in terms of color match and pigment retention are obtained when micropigmentation is performed on soft, thin pigmented skin such as that of the lips and nipples. 1196
Fig. 63.15. The hand of an African American with depigmentation from vitiligo.
Fig. 63.16. The hand in Figure 63.15 after micropigmentation (tattooing) showing an excellent cosmetic response.
Although the potential for koebnerization is real, it has not been reported. The most common complication of tattooing of the lips is herpes simplex. This infection can be prevented by prophylactic treatment with acyclovir.
SURGICAL TREATMENTS OF PIGMENTARY DISORDERS
References Behl, P. N. Treatment of vitiligo with homologous thin Thiersch’s skin grafts. Curr. Med. Pract. 8:218, 1964. Behl, P. N. Repigmentation of leukoderma. J. Dermatol. Surg. Oncol. 10:669–670, 1984. Behl, P. N. Repigmentation of segmental vitiligo by autologous minigrafting. J. Am. Acad. Dermatol. 12:118–119, 1985. Behl, P. N., and R. K. Bhatia. Treatment of vitiligo with autologous thin Thiersch’s grafts. Int. J. Dermatol. 12:329–331, 1973. Bonafe, J. L., J. Lassere, J. P. Chavoin, J. P. Baro, and R. Jeune. Pigmentation induced in vitiligo by normal skin grafts and PUVA stimulation: a preliminary study. Dermatologica 166:113–116, 1983. Boyce, S. T., and R. G. Ham. Calcium-regulated differentiation of normal human epidermal keratinocytes in chemically defined clonal culture and serum-free serial culture. J. Invest. Dermatol. 81:33s– 40s, 1983. Brysk, M. M., R. C. Newton, S. Rajaraman, T. Plott, E. Barlow, T. Bell, P. Penn, and E. B. Smith. Repigmentation of vitiliginous skin by cultured cells. Pigment Cell Res. 2:202–207, 1989. Chitale, V. R. Overgrafting for leukoderma of the lower lip: a new application of an already established method. Ann. Plast. Surg. 26:289–290, 1991. Eisinger, M., and O. Marko. Selective proliferation of normal human melanocytes in vitro in the presence of phorbol ester and cholera toxin. Proc. Natl. Acad. Sci. U. S. A. 79:2018–2022, 1982. Falabella, R. Epidermal grafting: An original technique and its application in achromic and granulating areas. Arch. Dermatol. 104:592–600, 1971. Falabella, R. Repigmentation of leukoderma by minigrafts of normally pigmented, autologous skin. J. Dermatol. Surg. Oncol. 4:916–919, 1978. Falabella, R. Repigmentation of segmental vitiligo by autologous minigrafting. J. Am. Acad. Dermatol. 9:514–521, 1983. Falabella, R. Repigmentation of leukoderma by autologous epidermal grafting. J. Dermatol. Surg. Oncol. 10:136–144, 1984. Falabella, R. Repigmentation of stable leukoderma by autologous minigrafting. J. Dermatol. Surg. Oncol. 12:172–179, 1986. Falabella, R. Postdermabrasion leukoderma. J. Dermatol. Surg. Oncol. 13:44–48, 1987. Falabella, R. Treatment of localized vitiligo by autologous minigrafting. Arch. Dermatol. 124:1649–1655, 1988. Falabella, R. Grafting and transplantation of melanocytes for repigmenting vitiligo and other types of leukoderma. Int. J. Dermatol. 28:363–369, 1989. Falabella, R., C. Escobar, and I. Borrero. Transplantation of in vitrocultured epidermis bearing melanocytes for repigmenting vitiligo. J. Am. Acad. Dermatol. 21:257–264, 1989. Falabella, R., C. Escobar, and I. Borrero. Treatment of refractory and stable vitiligo by transplantation of in vitro cultured epidermal autografts bearing melanocytes. J. Am. Acad. Dermatol. 26(2 Pt 1):230–236, 1992. Gauthier, Y., and J. E. Surleve-Bazeille. Autologous grafting with noncultured melanocytes: a simplified method for treatment of depigmented lesions. J. Am. Acad. Dermatol. 26(2 Pt 1):191–194, 1992. Halder, R. M., H. N. Pham, J. Y. Breadon, and B. A. Johnson. Micropigmentation for the treatment of vitiligo. J. Dermatol. Surg. Oncol. 15:1092–1098, 1989. Hatchome, N., T. Kato, and H. Tagami. Therapeutic success of epidermal grafting in generalized vitiligo is limited by the Koebner phenomenon. J. Am. Acad. Dermatol. 22:87–91, 1990. Kahn, A. M., and M. J. Cohen. Vitiligo: treatment by dermabrasion and epithelial sheet grafting. J. Am. Acad. Dermatol. 33:646–648, 1995. Kahn, A. M., M. J. Cohen, L. Kaplan, and A. Highton. Vitiligo: treat-
ment by dermabrasion and epithelial sheet grafting — a preliminary report. J. Am. Acad. Dermatol. 28:773–774, 1993. Kiistala, U. Suction blister device for separation of viable epidermis from dermis. J. Invest. Dermatol. 50:129–137, 1968. Kiistala, U., and K. K. Mustakallio. In vivo separation of epidermis by production of suction blisters. Lancet 1:144, 1964. Koga, M. Epidermal grafting using the tops of suction blisters in the treatment of vitiligo. Arch. Dermatol. 124:1656–1658, 1988. Lerner, A. B. Repopulation of pigment cells in patients with vitiligo. Arch. Dermatol. 124:1701–1702, 1988. Lerner, A. B., R. Halaban, S. N. Klaus, and G. E. Moellmann. Transplantation of human melanocytes. J. Invest. Dermatol. 89:219–224, 1987. Lerner, A. B., R. Halaban, and D. Leffell. Melanocytes in culture from patients with disorders of hypopigmentation [abstract]. In: Proceedings of the XIVth International Pigment Cell Conference, Y. Mishima (ed.). Kobe, Japan: International Pigment Cell Society, 1990, p. 100. Lobuono, P., and H. Shatin. Transplantation of hair bulbs and melanocytes into leukodermic scars. J. Dermatol. Surg. Oncol. 2:53–55, 1976. Lontz, W., M. J. Olsson, G. Moellmann, and A. B. Lerner. Pigment cell transplantation for treatment of vitiligo: a progress report. J. Am. Acad. Dermatol. 30:591–597, 1994. Medrano, E. E., and J. J. Nordlund. Successful culture of adult human melanocytes from normal and vitiligo donors. J. Invest. Dermatol. 95:441–445, 1990. Olsson, M. J., and L. Juhlin. Repigmentation of vitiligo by transplantation of cultured autologous melanocytes. Acta Derm. Venereol. 73:49–51, 1993. Olsson, M. J., G. Moellmann, A. B. Lerner, and L. Juhlin. Vitiligo: repigmentation with cultured melanocytes after cryostorage. Acta Derm. Venereol. 74:226–228, 1994. Orentreich, N., and V. J. Selmanowitz. Autograft repigmentation of leukoderma. Arch. Dermatol. 105:734–736, 1972. Patipa, M. Eyelid tattooing. Dermatol. Clin. 5:335, 1987. Patipa, M., F. A. Jakobiew, and W. Krebs. Light and electron microscopic findings with permanent eyeliner. Ophthalmologica 93:1361, 1986. Plott, R. T., M. M. Brysk, R. Newton, S. S. Raimer, and S. Rajaraman. A surgical treatment for vitiligo: Transplantation of autologous cultured epithelial grafts. J. Dermatol. Surg. Oncol. 15:1161– 1166, 1989. Selmanowitz, V. J. Pigmentary correction of piebaldism by autografts. II. Pathomechanism and pigment spread in piebaldism. Cutis 24:66–71, 1979. Selmanowitz, V. J., A. D. Rabinowitz, N. Orentriech, and E. Wenk. Pigmentary correction of piebaldism by autografts. J. Dermatol. Surg. Oncol. 3:615–622, 1977. Skouge, J. W., W. L. Morison, R. V. Diwan, and S. Rotter. Autografting and PUVA. A combination therapy for vitiligo. J. Dermatol. Surg. Oncol. 18:357–360, 1992. Spencer, G. A., and J. A. Tolmach. Exchange grafts in vitiligo. J. Invest. Dermatol. 19:1, 1952. Suvanprakorn, P., S. Dee-Ananlap, C. Pongsomboon, and S. N. Klaus. Melanocyte autologous grafting for the treatment of leukoderma. J. Am. Acad. Dermatol. 13:968–974, 1985. Taki, T., S. Kozuka, Y. Izawa, T. Usuda, M. Hiramatsu, T. Matsuda, K. Yokoo, Y. Fukaya, M. Tsubone, and J. Aoka. Surgical treatment of skin depigmentation caused by burn injuries. J. Dermatol. Surg. Oncol. 11:1218–1221, 1985. Zachariae, H., C. Zachariae, B. Deleuran, and P. Kristensen. Autotransplantation in vitiligo: Treatment with epidermal grafts and cultured melanocytes. Acta Derm. Venereol. 73:46–48, 1993.
1197
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
64
Laser Treatment of Pigmentary Disorders Rebat M. Halder, Lori M. Hobbs, and James J. Nordlund
Development of lasers adapted for medical and dermatological uses has been remarkable during the past decade. The field of dermatology has benefited greatly. The treatment of many pigmentary disorders had been difficult or not feasible in the past but lasers have provided a successful treatment modality for some of these conditions. The use of lasers for the treatment of pigmentary disorders is based on the theory of selective photothermolysis (Anderson et al., 1993; Murphy et al., 1983). This theory proposes that the specific spectrum of light emitted by a particular laser is selectively absorbed by a cell or tissue type. That cell or tissue type is selectively damaged or destroyed by the heat energy of the laser utilized. Several lasers emit monochromatic light that is preferentially absorbed by melanin. Specific destruction of melanocytes or dispersion of melanin by these light beams is the probable mechanism for their successful use. Melanin has a very broad absorption spectrum that includes ultraviolet, visible, and near infrared wavelengths (Spicer and Goldberg, 1996). The curve of absorption is highest in the ultraviolet spectrum and lowest in the infrared (Spicer and Goldberg, 1996). The lasers currently used for the treatment of pigmented lesions include the pigmented lesion dye laser, copper vapor laser, Q-switched ruby laser, Q-switched alexandrite laser, Q-switched neodymium:yttrium aluminum garnet (Nd:YAG) laser, continuous wave Nd:YAG laser, frequency doubled Q-switched Nd:YAG laser, and the carbon dioxide laser. The carbon dioxide laser emits continuous radiation with a wavelength of 10 600 nm. Low fluence irradiation (3.0– 4.4 J cm2) is optimal for treating pigmented lesions. The beam causes nonselective thermal damage to the entire epidermis and the melanocytes within. It has been used successfully to treat solar lentigines (Bailin et al., 1980; Dover et al., 1988; Groot et al., 1986). In one series 121 lesions were treated. Six weeks later 12 lentigines had cleared completely, 81 lightened substantially, and 28 were unchanged. There were atrophic changes in two lesions. There are other lasers discussed below that can more effectively treat solar lentigines. Tattoos were formerly treated with the carbon dioxide laser (Spicer and Goldberg, 1996). The infrared beam of the carbon dioxide laser causes coagulation necrosis extending into the reticular dermis. This laser causes changes in the texture of the epidermis and sometimes obvious scarring. Other lasers are now used to treat tattoos. The argon laser (488–514 nm) emits a blue-green light. It is a continuous wave laser and penetrates 1–2 mm in the skin. 1198
It produces heat from high energy fluences required to penetrate melanin in the epidermis (Neumann et al., 1992). Nonspecific destruction of epidermis including the resident melanocytes and papillary dermis can occur. With this laser skin texture changes and scarring are common and are permanent. Hypopigmentation may develop following treatments with this laser. Many benign pigmented lesions have been treated with the argon laser including lentigines, ephelides, café-au-lait spots, blue nevi, nevus of Ota, epidermal nevi, pigmented seborrheic keratosis, melasma, and postinflammatory hyperpigmentation (Brauner et al., 1991; McBurney, 1993; Ohshiro et al., 1980; Trelles et al., 1992). The effectiveness of the argon laser in the treatment of these lesions is variable. Published reports are for the most part anecdotal. Café-au-lait macules and Becker nevi respond poorly (Dover et al., 1990). Recent studies show that freezing of solar lentigines with liquid nitrogen was superior to that of the carbon dioxide or argon laser (Stern et al., 1994). Lentigo maligna has been treated with the argon laser but has recurred (Arndt, 1984, 1986). The pigmented lesion dye laser (PLDL) (500–520 nm) produces a green light. The optimal chromophore is melanin at 510 nm. Light from the PLDL penetrated only to a depth of 0.25–0.5 mm, thus it is best suited for superficial pigment. Benign epidermal pigmented lesions that respond are solar lentigines, ephelides, café-au-lait macules, some seborrheic keratoses, dermatosis papulosa nigra, Becker nevi, some cases of epidermal melasma, and superficial postinflammatory hyperpigmentation (Alster, 1993; Fitzpatrick et al., 1993a; Grekin et al., 1993; Yasuda et al., 1991). Café-au-lait macules do not always clear completely following treatment with this laser (Alster, 1995a). It is not effective in the treatment of deep dermal pigmented lesions such as nevus of Ota, dermal melasma, and dermal melanosis following inflammatory processes (Fitzpatrick et al., 1993a; Grekin et al., 1993). The Q-switched ruby laser (694 nm) emits a red light and causes selective destruction to pigment-containing cells by damaging melanized melanosomes (Hruza et al., 1991; Polla et al., 1987). It is melanin and not hemoglobin that preferentially absorbs 694 nm light. Blue-black and green tattoo pigments also absorb this wavelength well (Dover et al., 1989; Kilmer and Anderson, 1993). The pulse duration of the Q-switched ruby laser is 20–50 ns which is shorter than the estimated 50–100 ns thermal relaxation time of melanosomes (Sherwood et al., 1989) resulting in selective photothermolysis of these organelles (Dawber and Wilkinson,
LASER TREATMENT OF PIGMENTARY DISORDERS
1986). The depth of penetration of light from the Q-switched ruby laser is deep, about 2–3 mm. Lesions that have been treated successfully with this laser include solar lentigines, ephelides, café-au-lait macules, nevus of Ota, melasma and postinflammatory hyperpigmentation, penile lentigines and labial lentigines, Becker nevi, and seborrheic keratoses (Goldberg and Nychay, 1995; Grevelink et al., 1992; Levins and Anderson, 1995; Nelson and Applebaum, 1992; Ono et al., 1993). The rate of response is variable. Solar lentigines and ephelides respond well to one treatment. Café-au-lait macules respond less well and require more than one treatment (Dover et al., 1993). Often it is impossible to completely and permanently clear café-au-lait macules and recurrence of pigmentation is common within 6–12 months (Goldberg, 1993a,b; Grossman et al., 1995). They may become hyperpigmented before clearing and hypopigmentation or mottled pigmentation may occur. The response of Becker nevi is similar. Nevus of Ota responds to treatment by the Q-switched ruby laser. In one series 57% of patients achieved a good response after one treatment (Geronemus, 1992a,b; Taylor et al., 1994; Tse et al., 1994). Biopsy confirmed that dendritic melanocytes were destroyed to a depth of 2.6 mm (Tse et al., 1994). Melasma has a variable response to the Q-switched ruby laser. Most studies report poor results with recurrences common soon after treatment (Goldberg, 1993a,b). Those patients who have the epidermal variant of melasma and who have lighter complexions may respond better as well as those who have shown partial response to previous hydroquinone therapy (Dover et al., 1993). Sunscreens must be used after Qswitched laser therapy for melasma. Postinflammatory hyperpigmentation can occur. Labial and periorbital lentigines in Peutz–Jeghers syndrome have been successfully treated with the Q-switched ruby laser (Ashinoff and Geronemus, 1992; DePadova-Elder and Milgraum, 1994; Ohshiro et al., 1980). Caution must be taken when treating pigmented lesions in darker skin types with the Q-switched ruby laser. Because of increased amounts of melanin present, higher amounts of laser energy are absorbed within the epidermis (Taylor and Anderson, 1994). This may lead to erosions, hyperpigmentation, and hypopigmentation as well as texture changes such as atrophy or depression. The red light of the Q-switched ruby laser is absorbed well by blue-black and green tattoo ink. Tattoos containing these dyes are effectively removed (Achauer et al., 1994; Lowe et al., 1994; Reid et al., 1990, 1993; Scheibner et al., 1990; Taylor et al., 1990, 1991). Other colors are removed less efficiently. Amateur tattoos require fewer treatment sessions than do professional tattoos (Kilmer and Anderson, 1993). Because the 694 nm wavelength of the Q-switched ruby laser is absorbed well by melanin, damage to melanocytes can occur leading to hypopigmentation and hyperpigmentation and rarely even to depigmentation (Dover et al., 1993; Kilmer et al., 1993b). Otherwise, scarring is minimal in the treatment of tattoos by the Q-switched ruby laser. Q-switched ruby laser at exposure doses below the threshold for melanosomal disruption has not been found efficacious in treating vitiligo
Fig. 64.1. A tattoo before laser ablation (see also Plate 64.1, pp. 494–495).
despite instances of hyperpigmentation observed when applied in the treatment of other skin conditions (Renfro and Geronemus, 1992). The Q-switched Nd:YAG laser has a wavelength of 1064 nm and can effectively remove black tattoo ink (Figs 63.1 and 63.2) (Anderson and Dover, 1989; Kilmer and Anderson, 1993; Kilmer et al., 1993b; Levine and Geronemus, 1993). Other colors are removed less efficiently. Because of the long wavelength emitted, the disruption to melanincontaining cells is minimal, so that pigmentary changes are less than with the Q-switched ruby laser (Dover et al., 1993). Temporary texture changes can occur but scarring is rare. A frequency-doubling crystal can be added to the Qswitched Nd:YAG laser which halves the wavelength from 1064 nm to 532 nm (Kilmer et al., 1994). This wavelength is visible green light that is absorbed well by red tattoo ink. Thus, the frequency-doubled Nd:YAG laser can better treat red tattoos than the Q-switched ruby laser or the 1064 nm ND:YAG laser (Kilmer et al., 1993a). However, since this wavelength is also absorbed well by melanin, side effects of hypopigmentation, hyperpigmentation and blistering similar to the Q-switched ruby laser can occur. Also since it does not penetrate into the dermis as deeply as the Q-switched ruby laser, deeper dermal pigmented lesions cannot be treated. The Q-switched Nd:YAG set at 532 nm is very effective at removing lentigines with no scarring (Figs 63.3 and 63.4) (Kilmer 1199
CHAPTER 64
Fig. 64.3. Solar lentigines before laser ablation.
Fig. 64.2. The tattoo in Figure 64.1 treated with a Nd:YAG laser set at 1064 nm (see also Plate 64.2, pp. 494–495). Note the laser removal of black pigmentation in Fig. 64.1. However, the green pigment is not removed by Nd:YAG laser.
et al., 1994). Café-au-lait macules exhibit a variable response (Figs 63.5 and 63.6). The copper vapor laser emits green light at 511 nm and yellow light at 578 nm. A filter provides choice of wavelength (Thibault and Wlodarczyk, 1992). The 511 nm wavelength is used for pigmented lesions. Lentigines and ephelides respond well. Scarring and pigmentary sequelae are uncommon (Neumann et al., 1993). However, other treatment modalities can be used to treat these lesions as well (Dinehart et al., 1993; McMeekin, 1992). Café-au-lait macules have a variable response. The copper vapor laser has been used in treating post-sclerotherapy hyperpigmentation with good results even though the pigment is hemosiderin and not melanin (Thibault and Wlodarczyk, 1992). The Q-switched alexandrite laser (755 nm) has been used successfully in the treatment of blue and black tattoos without long-term pigmentary changes (Alster, 1995b; Fitzpatrick and Goldman, 1994; Fitzpatrick et al., 1992, 1993b; Stafford and Tan, 1995; Stafford et al., 1995). In particular, bright-colored 1200
Fig. 64.4. Hands in Figure 64.4 three months after treatment with a Nd:YAG laser set at 532 nm.
Fig. 64.5 Café-au-lait spot before laser ablation (see also Plate 64.3, pp. 494–495).
ink such as in teal-colored tattoos are amenable to treatment by Q-switched alexandrite laser. The longer wavelength of the Q-switched alexandrite laser penetrates deeper into the skin without disrupting epidermal melanocytes. Such an advantage
LASER TREATMENT OF PIGMENTARY DISORDERS
References
Fig. 64.6 Café-au-lait spot in Figure 64.5 after four treatments with a Nd:YAG laser set at 532 nm. The hyperpigmentation has been removed (see also Plate 64.4, pp. 494–495).
has also enhanced the treatment of deeper dermal melanocytes of the nevus of Ota by the Q-switched alexandrite laser (Alster and Williams, 1995) with very good results without scarring or pigmentary changes. The broadband light source, the intense pulse light (IPL), has been used to treat a variety of pigmented and vascular lesions, as well as unwanted hair and rhytids. The IPL emits a polychromatic light between 515 nm and 1200 nm. Depending upon the intended target and the photo type of the patient, cut-off filters are employed to allow the proper spectrum of light to selectively target the intended chromophore. For example, higher cut-off filters are used to reduce the absorption of melanin and provide a better safety margin when treating darker photo types. The pulse duration of the IPL systems is in the millisecond domain. Single, double, and triple pulses can be utilized. Multiple pulses are often necessary to divide the energy of high fluences. The delay time between pulses varies between 1 millisecond and 300 milliseconds. The delay time follows the principle of thermokinetic selectivity and allows smaller nonselective targets to be protected by cooling down between pulses, and selective larger targets to retain heat, resulting in precise thermal damage. A variety of pigmented disorders can be treated with the IPL (Raulin, 2003). These disorders range from lentigines, nevi of Ota and Ito, café-au-lait macules, postinflammatory hyperpigmentation, melasma, and even traumatic tattoos. Multiple treatments with the IPL are generally required to achieve the desired clinical outcome. The cutaneous response after treatment with the IPL is generally mild to transient erythema and edema lasting for a few hours. When used properly, scarring and permanent dyspigmentation are rare (Greve and Raulin, 2002). Darker photo types and persons who are tanned may experience more adverse events such as transient purpura, crusting, and dyspigmentation. With the use of the IPL, it is crucial to warn patients that unwanted hair loss can occur at the treatment site.
Achauer, B. M., J. S. Nelson, V. M. Vander Kam, and R. Applebaum. Treatment of traumatic tattoos by Q-switched ruby laser. Plast. Reconstr. Surg. 93:318–323, 1994. Alster, T. Treatment of benign epidermal pigmented lesions with the 510 nm pulsed dye laser. Lasers Surg. Med. 5:55, 1993. Alster, T. S. Complete elimination of large cafe-au-lait birthmarks by the 510 nm pulsed dye laser. Plast. Reconstr. Surg. 96:1660–1664, 1995a. Alster, T. S. Q-switched alexandrite laser (755 nm) treatment of professional and amateur tattoos. J. Am. Acad. Dermatol. 33:69–73, 1995b. Alster, T. S., and C. M. Williams. Treatment of nevus of Ota by the Q-switched alexandrite laser. Dermatol. Surg. 21:592–596, 1995. Anderson, R. R., and J. S. Dover. Selective photothermolysis of cutaneous pigmentation by Q-switched Nd:YAG laser pulses at 1064, 532, and 355 nm. J. Invest. Dermatol. 93:28–32, 1989. Anderson, R. R., P. C. Levins, and J. M. Grevelink. Lasers in dermatology. In: Dermatology in General Medicine, 4th ed., T. B. Fitzpatrick, A. Z. Eisen, K. Wolff, I. M. Freedberg, and K. F. Austen (eds). New York: McGraw-Hill, 1993, p. 1755. Arndt, K. A. Argon laser treatment of lentigo maligna. J. Am. Acad. Dermatol. 10:953–957, 1984. Arndt, K. A. New pigmented macule appearing four years after argon laser treatment of lentigo maligna. J. Am. Acad. Dermatol. 14: 1092, 1986. Ashinoff, R., and R. G. Geronemus. Q-switched ruby laser treatment of labial lentigos. J. Am. Acad. Dermatol. 27(5 Pt 2):809–811, 1992. Bailin, P. L., J. R. Ratz, and H. L. Levine. Removal of tattoos by CO2 laser. J. Dermatol. Surg. Oncol. 6:997–1001, 1980. Brauner, G., A. Schlifman, and B. Cosman. Evaluation of argon laser surgery in children under 13 years of age. Plast. Reconstr. Surg. 87:37–43, 1991. Dawber, R. P. R., and J. D. Wilkinson. Physical and surgical procedures. In: Textbook of Dermatology, 4th ed., vol. 3, A. Rook, D. S. Wilkinson, F. J. G. Ebling, R. H. Champion, and J. L. Burton (eds). Oxford: Blackwell Scientific, 1986, pp. 2575–2607. DePadova-Elder, S. M., and S. S. Milgraum. Q-switched ruby laser treatment of labial lentigines in Peutz-Jeghers syndrome. J. Dermatol. Surg. Oncol. 20:830–832, 1994. Dinehart, S. M., M. Waner, and S. Flock. The copper vapor laser for treatment of cutaneous vascular and pigmented lesions. J. Dermatol. Surg. Oncol. 19:370–375, 1993. Dover, J. S., B. R. Smoller, R. S. Stern, S. Rosen, and K. A. Arndt. Low-fluence carbon dioxide laser irradiation of lentigines. Arch. Dermatol. 124:1219–1224, 1988. Dover, J. S., R. J. Margolis, L. L. Polla, S. Watanabe, G. J. Hruza, J. A. Parrish, and R. R. Anderson. Pigmented guinea pig skin irradiated with Q-switched ruby laser pulses: Morphologic and histologic findings. Arch. Dermatol. 125:43–49, 1989. Dover, J. S., K. A. Arndt, R. G. Geronemus, S. M. Olbricht, J. M. Noe, and R. S. Stern. Illustrated Cutaneous Laser Surgery, A Practioner’s Guide, vol. 73. Norwalk, CT: Appleton and Lange, 1990, p. 106. Dover, J. S., S. L. Kilmer, and R. R. Anderson. What’s new in cutaneous laser surgery. Keio J. Med. 42:165–168, 1993. Fitzpatrick, R. E., and M. P. Goldman. Tattoo removal using the alexandrite laser. Arch. Dermatol. 130:1508, 1994. Fitzpatrick, R. E., J. Ruiz-Esparza, and M. P. Goldman. The alexandrite laser for tattoos: a preliminary report. Lasers Surg. Med. 12:72, 1992. Fitzpatrick, R. E., M. P. Goldman, and J. Ruiz-Esparza. Laser treatment of benign pigmented epidermal lesions using a 300 nsecond pulse and 510 nm wavelength. J. Dermatol. Surg. Oncol. 19:341– 347, 1993a.
1201
CHAPTER 64 Fitzpatrick, R. E., M. P. Goldman, and J. Ruiz-Esparza. Use of the alexandrite laser (755 nm, 100 nesec) for tattoo pigment removal in an animal model. J. Am. Acad. Dermatol. 28:745–750, 1993b. Geronemus, R. G. Q-switched ruby laser therapy of nevus of Ota. Arch. Dermatol. 128:1618–1622, 1992a. Geronemus, R. G. Q-switched ruby laser therapy of nevus of Ota. Lasers Surg. Med. 4:74, 1992b. Goldberg, D. J. Benign pigmented lesions of the skin. Treatment with the Q-switched ruby laser. J. Dermatol. Surg. Oncol. 19:376–379, 1993a. Goldberg, D. J. Treatment of pigmented and vascular lesions of the skin with the Q-switched Nd: YAG laser (Abstract). Lasers Surg. Med. 13:55, 1993b. Goldberg, D. J., and S. Nychay. Q-switched ruby laser treatment of congenital nevi. Arch. Dermatol. 131:621–623, 1995. Greve B., and C. Raulin. Professional errors caused by lasers and intense pulsed light technology in dermatology and aesthetic medicine. Preventive Strategies and Case Studies. Dermatol. Surg. 28: 156–161, 2002. Grekin, R. C., R. M. Shelton, J. K. Geisse, and I. Frieden. 510-nm pigmented lesion dye laser. Its characteristics and clinical uses. J. Dermatol. Surg. Oncol. 19:380–387, 1993. Grevelink, J. M., H. Liu, C. R. Taylor, and R. R. Anderson. Update on the treatment of benign pigmented lesions with the Q-switched ruby laser. Lasers Surg. Med. Suppl. 4:73, 1992. Groot, D. W., J. P. Arlette, and P. A. Johnston. Comparison of the infrared coagulator and the carbon dioxide laser in the removal of decorative tattoos. J. Am. Acad. Dermatol. 15:518–522, 1986. Grossman, M. E., R. R. Anderson, W. Farinelli, T. J. Flotte, and J. M. Grevelink. Treatment of cafe-au-lait macules with lasers: A clinicopathologic correlation. Arch. Dermatol. 131:1416–1420, 1995. Hruza, G. J., J. S. Dover, T. J. Flotte, M. Goetschkes, S. Watanabe, and R. R. Anderson. Q-switched ruby laser irradiation of normal human skin. Histologic and ultrastructural findings. Arch. Dermatol. 127:1799–1805, 1991. Kilmer, S., and R. Anderson. Clinical use of the Q-switched ruby and Q-switched neodymium:YAG (1064 nm and 532 nm) lasers for treatment of tattoos. J. Dermatol. Surg. Oncol. 19:330–338, 1993. Kilmer, S. L., M. S. Lee, and R. R. Anderson. Treatment of multicolored tattoos with the Q-switched Nd:YAG laser (532 nm); a dose-response study with comparison to the Q-switched ruby laser. Lasers Surg. Med. 5:54, 1993a. Kilmer, S. L., M. S. Lee, J. M. Grevelink, T. J. Flotte, and R. R. Anderson. The Q-switched Nd:YAG laser (1064 nm) effectively treats tattoos: A controlled, dose-response study. Arch. Dermatol. 129:971–978, 1993b. Kilmer, S. L., R. G. Wheeland, D. J. Goldberg, and R. R. Anderson. Treatment of epidermal pigmented lesions with the frequencydoubled Q-switched Nd:YAG laser. A controlled, single-impact, dose-response, multicenter trial. Arch. Dermatol. 130:1515–1519, 1994. Levine, V., and R. G. Geronemus. Tattoo removal with the Q-switched ruby laser and the Nd:YAG laser: a comparative study. Lasers Surg. Med. 5:53, 1993. Levins, P. C., and R. R. Anderson. Q-switched ruby laser for the treatment of pigmented lesions and tattoos [review]. Clin. Dermatol. 13:75–79, 1995. Lowe, N. J., D. Luftman, and D. Sawcer. Q-switched ruby laser: further observations on treatment of professional tattoos. J. Dermatol. Surg. Oncol. 20:307–311, 1994. McBurney, E. I. Clinical usefulness of the argon laser for the 1990s. J. Dermatol. Surg. Oncol. 19:358–362, 1993. McMeekin, T. O. Comparison of Q-switched ruby, pigmented lesion dye laser and copper vapor laser treatment of benign pigmented lesions of the skin. Lasers Surg. Med. 4:74, 1992. Murphy, G. F., R. S. Shepard, B. S. Paul, A. Menkes, R. R. Anderson,
1202
and J. A. Parrish. Organelle-specific injury to melanin-containing cells in human skin by pulsed laser irradiation. Lab. Invest. 49:680– 685, 1983. Nelson, J. S., and J. Applebaum. Treatment of superficial cutaneous pigmented lesions by melanin-specific selective photothermolysis using the Q-switched ruby laser. Ann. Plast. Surg. 29:231–237, 1992. Neumann, R. A., R. M. Knobler, H. Leonhartsberger, and W. Gebhart. Comparative histochemistry of port-wine stains after copper vapor laser (578) nm and argon laser treatment. J. Invest. Dermatol. 99:160–167, 1992. Neumann, R. A., H. Leonhartsberger, K. Bohler-Sommeregger, R. Knobler, E. M. Kokoschka, and H. Honigsmann. Results and tissue healing after copper-vapour laser (at 578 nm) treatment of port wine stains and facial telangiectasias. Br. J. Dermatol. 128:306– 312, 1993. Ohshiro, T., Y. Maruyama, N. Nakajima, and M. Mima. Treatment of pigmentation of the lips and oral mucosa in Peutz-Jeghers syndrome using ruby and argon lasers. Br. J. Plast. Surg. 33:346–349, 1980. Ono, I., H. Gunji, M. Sato, et al. Treatment of pigmented seborrheic keratosis by ruby laser irradiation. Eur. J. Dermatol. 3:206, 1993. Polla, L. L., R. J. Margolis, J. S. Dover, D. Whitaker, G. F. Murphy, S. L. Jacques, and R. R. Anderson. Melanosomes are a primary target of Q-switched ruby laser irradiation in guinea pig skin. J. Invest. Dermatol. 89:281–286, 1987. Reid, W. H., I. D. Miller, M. J. Murphy, J. P. Paul, and J. H. Evans. Q-switched ruby laser treatment of tattoos: a 9-year experience. Br. J. Plast. Surg. 43:663–669, 1990. Raulin C., B. Greve, and H. Grema. IPL technology: a review. Lasers Surg. Med. 32:78–87, 2003. Reid, W. H., P. J. McLeod, and A. Ritchie. Q-switched ruby laser treatment of black tattoos. J. Dermatol. Surg. Oncol. 19:330, 1993. Renfro, L., and R. G. Geronemus. Lack of efficacy of the Q-switched ruby laser in the treatment of vitiligo [letter]. Arch. Dermatol. 128:277–278, 1992. Scheibner, A., G. Kenny, W. White, and R. G. Wheeland. A superior method of tattoo removal using the Q-switched ruby laser. J. Dermatol. Surg. Oncol. 16:1091–1098, 1990. Sherwood, K. A., S. Murray, A. K. Kurban, and O. T. Tan. Effect of wavelength on cutaneous pigment using pulsed irradiation. J. Invest. Dermatol. 92:717–720, 1989. Spicer, M. S., and D. J. Goldberg. Continuing medical education: lasers in dermatology. J. Am. Acad. Dermatol. 34:1–25, 1996. Stafford, T. J., and O. T. Tan. 510-nm pulsed dye laser and alexandrite crystal laser for the treatment of pigmented lesions and tattoos. [Review]. Clin. Dermatol. 13:69–73, 1995. Stafford, T. J., R. Lizek, J. Boll, and O. T. Tan. Removal of colored tattoos with the Q-switched alexandrite laser. Plast. Reconstr. Surg. 95:313–320, 1995. Stern, R. S., J. S. Dover, J. A. Levin, and K. A. Arndt. Laser therapy versus cryotherapy of lentigines: a comparative trial. J. Am. Acad. Dermatol. 30:985–987, 1994. Taylor, C. R., and R. R. Anderson. Ineffective treatment of refractory melasma and post inflammatory hyperpigmentation by Q-switched ruby laser. J. Dermatol. Surg. Oncol. 20:592–597, 1994. Taylor, C., R. Gange, J. Dover, T. Flotte, E. Gonzalez, N. Michaud, and R. Anderson. Treatment of tattoos by Q-switched ruby laser. Arch. Dermatol. 126:893–899, 1990. Taylor, C. R., R. R. Anderson, R. W. Gange, N. A. Michaud, and T. J. Flotte. Light and electron microscopic analysis of tattoos treated by Q-switched ruby laser. J. Invest. Dermatol. 97:131–136, 1991. Taylor, C. R., T. J. Flotte, W. Gange, and R. R. Anderson. Treatment of nevus of Ota by Q-switched ruby laser. J. Am. Acad. Dermatol. 30:743–751, 1994. Thibault, P., and J. Wlodarczyk. Postsclerotherapy hyperpigmenta-
LASER TREATMENT OF PIGMENTARY DISORDERS tion. The role of serum ferritin levels and the effectiveness of treatment with the copper vapor laser. J. Dermatol. Surg. Oncol. 18:47–52, 1992. Trelles, M. A., W. Verkruysse, J. W. Pickering, M. Velez, J. Sanchez, and P. Sala. Monoline argon laser (514 nm) treatment of benign pigmented lesions with long pulse lengths. J. Photochem. Photobiol. B 16:357–365, 1992.
Tse, Y., V. J. Levine, S. A. McClain, and R. Ashinoff. The removal of cutaneous pigmented lesions with the Q-switched ruby laser and the Q-switched neodymium: yttrium-aluminum-garnet laser. A comparative study. J. Dermatol. Surg. Oncol. 20:795–800, 1994. Yasuda, Y., O. T. Tan, A. K. Kurban, et al. Electron microscopic study on black pig skin irradiated with pulsed dye laser (504 nm). Proc. SPIE: Lasers Derm. Tissue Welding 1422:19, 1991.
1203
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
Index
Notes Page numbers in bold refer to tables and those in italics refer to figures. Where genes/proteins from both human and other species are mentioned the gene will be listed under the human gene/protein unless otherwise stated. ABCD1 gene, adrenoleukodystrophy, 772 ABCD syndrome, 146 Abtropfung, 1116 acanthosis nigricans, 907–914 animal models, 912 associated disorders, 910, 910 benign, 909 clinical findings, 908, 908–910, 909 diagnosis/differential diagnosis, 910–911 endocrinopathy-related, 909 epidemiology, 908 familial, 909 historical background, 907–908 laboratory findings/investigations, 910 malignant, 908, 909, 911 obesity-related, 908, 909, 909 pathology/pathogenesis, 911 treatment/prognosis, 912 types, 909–910 N-acetyl-4-S-cystaminylphenol (4-SCAP), 675 achalasis, Rozycki syndrome, 551 achromatous pityriasis faciei, see pityriasis alba achromias, classification, 501 achromic nevus, see nevus depigmentosus acidity, see pH ACK2 (anti-KIT) antibody, 429, 429–430, 430 acoustic neuromas, neurofibromatosis type 2, 813 acquired bilateral nevus of Ota-like macules (ABNOM), 1017–1018, 1018 acquired generalized dermal melanocytosis, 1016 acquired hepatic porphyria, see porphyria cutanea tarda acquired idiopathic benign lentiginosis, see Laugier–Hunziker syndrome acquired leukoderma, see vitiligo vulgaris (vitiligo) acquired leukopathia, see vitiligo vulgaris (vitiligo) acquired linear dermal melanocytosis, 1016 acquired porphyria, see porphyria cutanea tarda acral acanthotic anomaly, 909 acral lentiginous melanoma, 473 Down syndrome, 658 nail, 1063, 1065 acrochordons (skin tags), acanthosis nigricans, 909 acro-dermato-ungual-lacrimal-tooth syndrome (ADULT syndrome), 902 acrogeria, 792, 884–886, 885 acrokeratotic poikiloderma of Weary, see hereditary acrokeratotic poikiloderma acromegaly Carney complex/myxoma syndrome, 855 hyperpigmentation, 1072 acromelanosis albopunctata, see reticulated acropigmentation of Dohi acromelanosis progressiva (acropigmentation), 914, 914–915 acropigmentation of Dohi, 789, 797, 914 acropigmentation of Kitamura, 789, 797 acropigmentation symmetrica of Dohi, see reticulated acropigmentation of Dohi ACTH, see adrenocorticotropic hormone (ACTH) actin filaments, intracellular transport, 37, 38, 38, 171–172
actinic lentigo, see lentigo senilis et actinicus actinic purpura, hemosiderosis, 990 adaptor complex-3 (AP-3), 615 Addison disease adrenoleukodystrophy, 771, 772 associated disorders, 970–971 clinical features, 970, 970, 971 differential diagnosis, 972 epidemiology, 970 histology, 971 hyperpigmentation, 667 laboratory abnormalities, 971–972 melanocytic nevi development, 1126 mucosal hyperpigmentation, 1072 pathogenesis, 971 pigmentary changes, 969–972 treatment, 972 adhesive tape-induced skin discoloration, 1045 adiposogenital syndrome (Fröhlich syndrome), 839 adolescents, skin color, 511–512 adrenal insufficiency, vitiligo vulgaris, 566 adrenergic receptors, color change and, 36–37 adrenocorticotropic hormone (ACTH), 194, 196, 414–415 Addison disease, 971 adrenoleukodystrophy, 771 carcinoid tumors, 920 induction by UVR, 413 adrenoleukodystrophy (ALD), 771–774 adrenomyeloneuropathy (AMN), 771, 772 adriamycin (doxorubicin)-induced skin discoloration, 1046 adult progeria, see Werner syndrome ADULT syndrome (acro-dermato-unguallacrimal-tooth syndrome), 902 AEC syndrome (ankyloblepharon, ectodermal dysplasia), 902 aganglionic megacolon, 145, 146 age/aging disorders associated with, 884–897, see also specific disorders melanocyte senescence, 464–471 melanoma incidence, 473 pigmentation changes, 511, 511–513 premature, ataxia telangiectasia, 621 age spot, see lentigo senilis et actinicus agminated lentigines (AL), 863, 863–867 animal models, 867 associated disorders, 863 clinical description, 865 differential diagnosis, 865, 1106 epidemiology, 865 histopathology, 865 historical background, 864–865, 866 pathogenesis, 865, 867 treatment, 865 agminated Spitz nevi, 1106 agouti protein, 196–198, 199, 399–401 allelic variants, 395 biochemical action, 197 cAMP signaling and, 395 eumelanin vs. pheomelanin biosynthesis, 196–197, 197, 395, 416 evolutionary conservation, 400–401 homologs, 395
human (agouti signaling protein, ASP), 198, 400–401, 416, 514 inverse agonist, see alpha-melanocyte stimulating hormone (a-MSH) isoforms, 399–400 melanocortin receptor binding, 399, 404, 416 MIF relationship, 43 spatiotemporal gene expression, 399–400, 400 AIDS, see HIV infection/AIDS AIM-1, see membrane-associated transport protein (MATP) AK amyloid, 926 albinism, see also ocular albinism (OA); oculocutaneous albinism (OCA); piebaldism/piebald trait auditory abnormalities, 100, 602 clinical features, 571 definition, 600 historical aspects, 8, 599–600 nonmammalian vertebrates, 48, 118 nystagmus, 602 partial (mosaic), see piebaldism/piebald trait visual system abnormalities, 92–93, 571, 600, 600–602 foveal hyperplasia, 601–602 iris pigmentation, 600 optic nerve development, 601–602 retinal pigmentation, 601–602 Albinism Database, 605 albinism–deafness syndrome (Tietz syndrome), 245, 546, 546–547, 630–631 albinoid disorders, 613–621 Albright’s syndrome (disease), see McCune–Albright syndrome alcohol ingestion, porphyria cutanea tarda, 981 alcoholism, centrofacial lentiginosis pathogenesis, 840–841 Alezzandrini syndrome, 559, 725–726, 726, 738 alkaptonuria, see ochronosis allergic contact dermatitis, plants, 949 allergic shiners, 879 allergy testing, progressive macular hypomelanosis, 749 allogeneic bone marrow transplantation (ABMT), melanocytic nevi formation, 1126 all trans retinoic acid (ATRA), see tretinoin (all trans retinoic acid; ATRA) aloesin, 675 alopecia, see also specific types Cronkhite–Canada syndrome, 984, 984 evolutionary significance, 71, 72 thumb deformity and, 904 alopecia areata, 371, 754–756 clinical description, 754, 755 diagnostic criteria, 755 differential diagnosis, 755 Down syndrome, 658 epidemiology, 754 histology, 754–755 historical background, 754 pathogenesis, 755 prognosis, 755–756 sudden whitening of hair, 766 Vogt–Koyanagi–Harada syndrome, 736, 754 alopecia mucinosa, see follicular mucinosis
1205
INDEX alpha-melanocyte stimulating hormone (a-MSH), 414–415 Addison disease, 1072 AIDS patients, 943 amphibian cell differentiation, 117–118 antagonists, 36 binding sites, 762 induction by UVR, 413 iridophore effects, 30, 30–31 melanocortin receptor binding, 399, 404, 415 inverse agonist, see agouti protein as melanocyte mitogen, 448 melasma, 1021 MITF regulation, 246 normal pigmentation role, 404 alveolar rhabdomyosarcoma, pax3 (PAX3) mutations, 144 amalgam tattoo, 1080, 1080–1081 amelanosis, definition, 527 ametantrone-induced skin discoloration, 1045 3-amino-3-hydroxyphenylethylamine (3-AHPEA), 301, 301 4-amino-3-hydroxyphenylethylamine (4-AHPEA), 301, 301, 314 aminoglycoside antibiotics, ototoxicity, 376 3-aminohydroxyphenylalanine (3-AHP), 297, 297, 299–300, 300 4-aminohydroxyphenylalanine (4-AHP), 282, 283, 296–297, 297, 300, 300–301 amiodarone-induced skin discoloration, 1038, 1038–1039, 1039 Ammi majus, 1175 amphibians, see also specific types cellular associations in color change, 40–42 chromatophore development, 115–119 differentiation, 117–118 morphogenesis, 115–117, 116 mutants, 118–119 chromatophores, 108 egg as, 24, 24–25, 25 MSH effects on xanthophores, 31 amyloid, 926 amyloid K, 926 amyloidosis, cutaneous, 924–928 associated disorders, 926 clinical findings, 924–926, 925 diagnosis/differential diagnosis, 926 familial, 926 pathology/pathogenesis, 926 treatment/prognosis, 926–927 anal canal, melanocyte numbers, normal, 1069 analgesics, fixed drug eruption, 1028 anal melanoma, 1085 anal skin, melanocyte numbers, normal, 1069 ancient Greeks, 5 ancient Romans, 5 androgens, melanocyte regulation, 416–417 anemia canities, premature, 659, 666 Fanconi, 776, 776–778 hypopigmentation, 768 iron deficiency, 666 pallor, 530 pernicious, see pernicious anemia Angelman syndrome, 235, 620, 629 anhidrotic ectodermal dysplasia and immunodeficiency (EDA-ID), 877 aniline dyes, skin discoloration, 1048 ankyloblepharon, ectodermal dysplasia (AEC syndrome), 902 anonychia with flexural pigmentation, 789, 797, 873, 874, 902 antibiotics, see also specific drugs confluent and reticulated papillomatosis, 923 fixed drug eruption, 1028 ototoxicity, 376 antigen in melanoma-1 (AIM-1), see membraneassociated transport protein (MATP) antimalarials, hyperpigmentation-induction, 940, 1042, 1042, 1081 anti-melanocyte antibodies, vitiligo vulgaris, 572 antimicrobials, fixed drug eruption, 1028 anti-mitochondrial antibody (AMA) titers, primary biliary cirrhosis, 994 antimonials, post-kala-azar dermatosis, 697 antioxidants depigmentation, 673 melanin as, 72, 311, 331–334, 333, 334, 345 vitiligo vulgaris, 577
1206
antipyretics, fixed drug eruption, 1028 antithyroid antibodies, vitiligo vulgaris, 566 AP2 transcription factor/binding sites, melanoma genetics, 481–482 AP3 (adaptor protein-3), 159–160, 160, 160 AP3B1 gene, Hermansky–Pudlak syndrome type 2, 615 APAF1 mutations, melanoma, 472, 479 apoptosis suppression, melanoma, 472, 481 apudomas, 919 arbutin, 675, 1169 ARF protein, melanoma and, 475, 476 argon laser, 1198 argyria, 525, 1030–1032, 1031 arsenic-induced skin discoloration, 1034, 1034, 1035 arterial dissection, lentiginosis, 868 arthropathy, hereditary hemochromatosis, 987 Asboe–Hansen disease, see incontinentia pigmenti (IP) ascorbate (ascorbic acid), 331, 677 ashen mouse mutant, 173, 174–175 ash-leaf spots, 515, 531, 651, 653, 654, 654 ashy dermatosis of Ramirez, see erythema dyschromicum perstans Aspergillus, pityriasis alba, 700 aspirin, vitiligo vulgaris, 577 ataxia telangiectasia, 621–622 atomic force microscopy, melanins, 312–313, 313–314 atomic weapons, depigmentation due to, 684 atopic dermatitis hyperpigmentation, 911 hypopigmentation, 702–703, 703 ATPases, 37, 183, 233, 237 atrophic degenerative pigmentary dermatitis, see poikiloderma of Civatte atrophic scleroderma d’emblée, see atrophoderma of Pasini et Pierini atrophie brilliante, see confluent and reticulated papillomatosis (CRP) atrophoderma of Pasini et Pierini, 963, 963–965, 964 atrophoscleroderma superficialis circumscripta, see atrophoderma of Pasini et Pierini attractin, 401–403 atypical melanoblastoma, see melanotic ectodermal tumor of infancy atypical melanocytic hyperplasia, 1066, 1066 atypical mole syndrome (AMS), familial melanoma and, 474, 474 atypical nevi, 1112 blue nevus, Carney complex/myxoma syndrome, 857 development, 1127 auditory system albinism, 100, 602 development, 99 melanocytes in, see otic melanocytes toxic lesions, 376 Vogt–Koyanagi–Harada syndrome, 735 autocrine factors human melanocyte regulation, 413–417 melanomas, 490 autocytotoxic hypothesis, vitiligo vulgaris, 574 autoimmunity idiopathic guttate hypomelanosis, 728 vitiligo vulgaris, 565, 572–574 T-cell response, 573 autologous epidermal grafting, 1191 autologous melanocyte and keratinocyte coculture transplantation, 1195 autologous minigrafts, 1192, 1192, 1193, 1194 autologous pure melanocyte culture transplantation, 1193–1195, 1194, 1195, 1196 autologous thin Thiersch grafting, 1191 autonomic nervous system, depigmented skin, 564 auto-oxidation, melanin, 317, 328–329 autosomal recessive ocular albinism (AROA), 605 avian species, see birds axanthic mutants, 118 axillary freckles, 532, 811 azelaic acid (AZA) hyperpigmentation disorders, 1166–1167 mechanism of action, 676, 1167 melasma, 1167
postinflammatory hyperpigmentation, 1167 reticulated acropigmentation of Kitamura, 804 tinea versicolor, 694 azidothymidine (AZT) mucosal discoloration, 1081 skin discoloration, 1045, 1045 azo dyes, skin discoloration, 1048 B7-1, melanoma regression and, 718 B7-2, melanoma regression and, 718 babides, 686 background adaptation, 25–26, 29, 32–33 adaptive mechanisms, 32–33 high vs. low albido environments, 33 morphologic color change, 27–28 physiologic color change, 27 balanitis xerotica obliterans, 1086, 1086 baldness, see alopecia Bannayan–Riley–Ruvalcaba syndrome (BRR), 867–868, 1084 animal models, 868 genital macules, 1084 historical background, 867–868 Barrere, Pierre, 7 Barton, Benjamin, 9 basal cell nevus syndrome (Gorlin Goltz syndrome), 655 basic fibroblast growth factor (bFGF), see fibroblast growth factor-2 (FGF-2) basic helix–loop–helix transcription factors (bHLH), 243, 248 Bateman purpura, 990 Baynham, William, 7 BCL-2 gene/protein deficiency, melanocyte apoptosis, 528 melanoma association, 481 BCNU (carmustine) mycosis fungoides, 976 skin discoloration, 1045 Becker melanosis, see Becker nevus Becker nevus, 915, 915–917 bejel, 688 benign fibrous histiocytoma (dermatofibroma), 433–435 benzathine penicillin, 687, 688 benzothiazines, late pheomelanogenesis, 292, 292–293, 293 Berkshire neck, see poikiloderma of Civatte Berlin syndrome, 780–781 Berloque dermatitis, see phytophotodermatitis 6-beta-alanyl-2-carboxy-4-hydroxybenzothiazide (BTCA), 297, 297 betamethasone, vitiligo vulgaris, 577 big endothelins (big ETs), 422, 427 “bihumoral theory,” 13 bile, as skin pigment, 7 bindhi, chemical depigmentation, 562, 562 biomarkers melanoma, 293–294 replicative senescence, 464 biopterin deficiency, 634 biphasic amyloidosis, 924 bird-headed dwarfism (Seckel syndrome), 657–658 birds eye color, 98, 98–99 melanocyte differentiation, 109, 121–122 melanocyte morphogenesis, 119, 119–121 dynamics, 119–120 mechanism of migration, 120 mutants, 122 birthmarks, see nevi 1,3-bis(chloroethyl)-1-nitrosourea (BCNU), 976, 1045 N,N-bis-acetanilidedimethylamine (QX-572), 378, 378–379 bisisolylmaleimide, 673 bismuthia, 1034 bismuth-induced skin discoloration, 525, 1033–1034 black skin, see also ethnicity; skin types (human) color, early theories, 5–8 inherited patterned lentiginosis, 869 white skin vs., 8 Wood’s light examination, 532 “black tongue,” 998 Blaschko lines, 636–637, 637
INDEX bleaching agents melanin modification, 357–358 melasma, 1022, 1022 bleeding diathesis, Hermansky–Pudlak syndrome, 614 bleomycin-induced skin discoloration, 1045, 1045–1046 blinding filariasis, see onchocerciasis blistering disorders, melanocytic nevi formation, 1121, 1125 BLOC-2, 615 Bloch–Siemens syndrome, see incontinentia pigmenti (IP) Bloch–Sulzberger syndrome, see incontinentia pigmenti (IP) BLOC proteins, 160, 160, 160–161, 615 Bloom syndrome, 806 blue coloration human dermal melanocytes, 69–70 iridophores, 19, 20, 21 “plerodeles blue,” 22, 32 blue-gray macule of infancy, see Mongolian spot blue macules mycosis fungoides, 975 progressive systemic sclerosis, 1018 blue nevi Carney complex/myxoma syndrome, 856, 857 oral mucosa, 1078, 1078, 1079 patch-type, 1160 plaque-type, 1160–1161 speckled lentiginous nevus, 1105 Blumenbach, Johann Friedrich, 7 bone marrow, dyskeratosis congenita, 898 bone morphogenetic proteins (BMPs) avian melanocyte specification, 121 mammalian pigmentary system development, 83 Böök syndrome (PHC syndrome), 661 borderline borderline leprosy, 690 borderline tuberculoid leprosy, 690 boron neutron capture therapy (BNCT), 382–383 Borrelia burgdorferi, morphea, 969 bouba, 686–687 Bourneville disease, see tuberous sclerosis complex (TSC) bowel disorders, hypopigmentation, 665–666 Bowman-Birk protease inhibitor, 678 Boyle, Robert, 6 BRAF gene/protein melanocytic nevi, 1113, 1115 melanoma and, 453, 472, 492 familial, 477 sporadic, 479–480 nevogenesis, 1130 BRCA2 gene/protein, familial melanoma and, 477 breast, Carney complex/myxoma syndrome, 855, 856–857, 858 Breschet, G.H., 8 Breslow index anal melanoma, 1085 ungual melanoma, 1066–1067 BRN2 (N-Oct3; POU3F2) gene, 248 Bronze–Schilder disease, 771–774 Brown, Sir Thomas, 6 buba, 686–687 Buscke heat melanosis, see erythema ab igne busulfan, skin discoloration and, 940, 1046 N-butyldeoxynojirimicin, 673 Byrd, William, 9 C2-ceramide, 673 C57BK/6 MivitMivit mouse model, vitiligo vulgaris, 576, 576 E-cadherin, melanocytic nevi, 1113 N-cadherin, melanoma and, 482 Caenorhabditis elegans, Bannayan–Riley–Ruvalcaba syndrome model, 868 café-au-lait spots (macules: CALMs), 515, 917–919 agminated lentigines, 864 clinical findings, 531–532, 917, 917–918, 918 diagnostic criteria, 918 differential diagnosis, 918 Down syndrome and, 658 epidemiology, 917 familial multiple, 809
genetic epidermal syndromes, 809–823 historical background, 917 laser treatment, 1198, 1200, 1200, 1201 LEOPARD syndrome, 844 McCune–Albright syndrome, 522, 817, 817, 917–918 neurofibromatosis type 1, 435, 810–811, 811, 813 paracrine interactions, 435–437, 436, 440, 441, 441 pathogenesis, 522, 522, 918 pathology, 918 piebaldism, 543 prognosis, 918 Q-switched ruby laser, 1199 Silver–Russell syndrome, 821 solitary, 917 treatment, 918 tuberous sclerosis complex, 654 café noir spots, LEOPARD syndrome, 844 calcipitriol acanthosis nigricans, 912 UVB phototherapy and vitiligo vulgaris, 1185 calcium D-pantetheine-S-sulfonate (PaSSO3Ca), 673 Caldwell, Charles, 8, 9 calphostine, 673 camouflage, melanin and, 75–76 camouflage stains, 1188–1189 cancer, see malignancy; specific cancers Candida infections nail pigmentation, 1061 vitiligo vulgaris, 565 canities definition, 527 premature (premature graying of hair), 659–660 associated disorders, 760 definition, 761 Down syndrome, 658 Fisch syndrome, 659 iron deficiency anemia, 666 mandibulofacial dysostosis, 660 myotonic dystrophy, 661 pernicious anemia, 666 prolidase deficiency, 662 senile, 512, 512, 527, 760–764 animal models, 762 associated disorders, 760 clinical features, 760 diagnosis/differential diagnosis, 761–762 epidemiology, 760 histology, 760–761 historical background, 760 immune tolerance hypothesis, 762 laboratory findings, 761 pathogenesis, 762 prognosis, 763 repigmentation, 762–763 treatment, 762–763 canthaxanthin-induced skin discoloration, 1038 Cantu syndrome, 781 capillaritis, 1029–1030, 1030 capillary hemangiomas, 1069–1070 carate, 687–688 carbolic acid-induced skin discoloration, 1041 carbon baby (universal acquired melanosis), 906 carbon dioxide laser, 1198 7-carboxyl porphyrins, porphyria cutanea tarda, 982 carcinogenesis drug-binding to melanin(s), 373, 374, 383 psoralens and ultraviolet light (PUVA), 582 carcinoid syndrome (carcinoidosis), 919–921 clinical findings, 919, 919–920 pellagra, 998 carcinoid tumors, 920 cardiac anomalies, LEOPARD syndrome, 844–845 cardiac myxomas Carney complex/myxoma syndrome, 854, 854, 856, 858 treatment, 859 cardiac rhabdomyomas, tuberous sclerosis complex, 653 cardiocutaneous syndrome, see LEOPARD syndrome Carleton–Biggs syndrome, 1017
carmustine (BCNU) mycosis fungoides, 976 skin discoloration, 1045 Carney complex/myxoma syndrome associated disorders, 856–857 clinical description/presentation, 846, 856–857 clinical findings, 853–856, 854, 855 diagnosis, 853–856 differential diagnosis, 859 epidemiology, 853 histology, 857–858 histopathology, 1073 historical background, 851, 851–853 laboratory investigations, 858–859 mucosal pigmentation, 1072–1073 pathogenesis, 859 prognosis, 860 treatment, 859–860 carotenemia, 530, 1036–1038, 1038 b-carotene, skin discoloration, 1036–1038, 1038 carotenoids, 19, 22 amphibian egg, 24–25 deficiency, 25 skin discoloration, 1036–1038, 1038 Casal’s necklace, 996 castrated males, skin coloration, 667 cataract, 96, 375 catecholamines, color change (nonmammalian) role, 36–37 cathecols, 675 cativa, 687–688 cats, pigment type switching, 404–405 CD4+ cells melanocytic neoplasia associated hypomelanosis, 716–717 melanoma regression, 718 vitiligo autoimmunity, 573 CD8+ cytotoxic T cells (CTL) melanocytic neoplasia associated hypomelanosis, 716 melanoma-associated depigmentation, 719 melanoma regression, 718 vitiligo autoimmunity, 573 CD8+ T cells, fixed drug eruption, 1029 CDK4 mutations, melanoma, 472, 476 CDKN2A gene/protein atypical mole syndrome, 474 gene products (p16/ARF), 474–475, 475 mutation in familial melanoma, 472, 474–476 nevogenesis, 1129–1130 “celery burns,” see phytophotodermatitis celiac disease, 666 cell adhesion molecules (CAMs) melanoma and, 481–482 pigmentation pattern formation, 45, 47, 112–113 cell–cell interactions, amphibian morphogenesis, 116–117 cell cycle regulation, see also specific molecules melanocyte senescence, 465 melanoma, 453–454 cell death fish pattern formation, 112 melanin-induced, 72 cellular immunity halo nevi, 709–710 tinea versicolor, hypopigmentation pathogenesis, 693–694 Celtic peoples epidermal melanocytes and, 66 melanin content, 74 red hair color, 69 central nervous system (CNS), see also neuromelanin defects hypomelanosis of Ito, 638 Vogt–Koyanagi–Harada syndrome, 735 xeroderma pigmentosum, 890 drug-induced toxicity, 376–378 melanocortin signaling mutants, 402 centrofacial lentiginosis, 837–842 age of onset, 840 animal models, 841 associated disorders, 839 Carney complex/myxoma syndrome vs., 859 clinical description, 838–839, 846 diagnostic criteria, 840 differential diagnosis, 840 epidemiology, 839–840
1207
INDEX historical aspects, 837–838 inheritance, 839 laboratory findings/investigations, 840 neuropsychiatric disorders, 839 pathogenesis, 840–841 alcoholism, 840–841 mechanistic theories, 841 syphilis-induced mutation hypothesis, 840 prevalence, 839 sexual distribution, 839 cerebrovascular anomalies, agminated lentigines, 865 ceroid-lipofuscin, Hermansky–Pudlak syndrome, 615 chaperone proteins, 159–162, 160, 160, 232 Chediak–Higashi syndrome (CHS), 530, 614, 616, 616–617 chaperone protein mutations, 159, 161–162 molecular pathogenesis, 617 “cheetah” phenotype, 1130 chemical melanocytotoxins, 562 chemokines, in pigmentary disorders, 421–444, see also specific molecules chemophototherapy, see photochemotherapy chemotherapy, see also specific agents/treatments drug-binding to melanins, 379, 380–383, 381, 383–384 melanocytic nevi and, 1125–1126 melanoma (see melanoma) mycosis fungoides, 977–978 photochemotherapy (see photochemotherapy) skin discoloration induction, 1044, 1044–1045, 1045, 1045–1047 children, skin color, 511–512 CHK2 gene/protein, familial melanoma and, 477 chloasma, 513, 1021 chloroquine porphyria cutanea tarda, 982 skin discoloration, 982 toxicology of melanin binding, 375 eye, 375–376 ototoxicity, 376 skin, 374 chlorpromazine CNS toxicity and parkinsonism, 377 ocular bodies, 375, 1044 skin discoloration and, 1044 choroid anatomy/structure, 93, 93, 94, 96, 96 development, 91–92 melanocytes, see uveal melanocytes variation in, 96 Christ–Siemens–Touraine syndrome (hypohidrotic ectodermal dysplasia), 901, 902 “chromatic abnormalities,” terminology, 499–503 chromatics, 501, 501 chromatophore(s), 108, see also color change (nonmammalian); specific types adaptive mechanisms, 33–35 amphibian egg as, 24, 24–25, 25 characterization, 14–27 definition/terminology, 11, 12, 14, 14 embryology/development, 11, 12, 42, 51, 52, 76–77 amphibians, 115–119 fish, 109–115 reptiles, 119 extracutaneous, 17, 51–52, 91 functions, 25–28 hormone actions on, 12–13, 32–35, see also individual hormones mechanisms of, 35–37 innervation, 26–27 patterns/patterning, 42–48, 45, 52–53 photosensitive, 35, 52 responses, 27–28 adaptive mechanisms, 33–35 integration, 26 morphologic color change, 27–28 physiologic color change, 27 signaling mechanisms, 26 unknown type, 24 chromatophoromas, 50 chromoheteropia, see heterochromia irides chromometer/chromatometry, 533–534 chromophores human skin color and, 505
1208
melanotic, see melanin(s) nonmelanotic, 501, 505 terminology, 501 UV absorption, 343–344 chronic cyclitis, see heterochromia irides chronic nonsuppurative destructive cholangitis, see primary biliary cirrhosis (PBC) chrysiasis, 525, 1032, 1032 CHS1 gene, Chediak–Higashi syndrome, 616 ciclosporin-induced skin discoloration, 1047 ciliary bodies, 96, 96–97 ciliary epithelium, 97 circumscribed hypermelanosis, see café-au-lait spots (macules: CALMs) circumscribed melanotic macule, see café-au-lait spots (macules: CALMs) circumscribed scleroderma, see morphea cisplatin, skin discoloration, 1030, 1046 Clark levels oral melanoma, 1080 ungual melanoma, 1066 cleft lip-Mongolian spot, 1005 cliff sign, 963 clofazamine hyperpigmentation induction, 943, 1042–1043, 1043 leprosy, 692 clonality, melanocytic nevi, 1113 clonidine, carcinoid syndrome, 921 Clouston syndrome (hidrotic ectodermal dysplasia), 902–903, 903 “Club Med dermatitis,” see phytophotodermatitis clump cells of Kogenei, 97 CMM4 mutations, melanoma, 472, 476 coat, see hair/coat cochlea, melanocytes, 99, 100, 100–101 COL3A1 gene mutations, acrogeria, 885 colitis, Hermansky–Pudlak syndrome, 615 color change (nonmammalian) adaptation to darkness, 33, 33–35, 34 background adaptation, 25–26, 29, 32–33, 33 cellular associations, 40–42, 41 control of, 12–13, 28–35, see also specific hormones adaptive mechanisms, 33–35 mechanisms of hormone action, 35–37 melanophore stimulation, 30–31 pituitary role, 12–13, 28–29 morphologic, 27–28, 28, 29, 31 physiologic, 12, 16, 16, 27 pigment granule translocation, 13, 37–40 subcellular associations, 41–42 compound nevi Carney complex/myxoma syndrome, 857 melanocytic, 1118 computed tomography (CT), Carney complex/myxoma syndrome, 858 confluent and reticulated papillomatosis (CRP), 922–924 clinical features, 910, 922, 922 diagnosis, 923 endocrine dysfunction, 923 epidemiology, 922 pathology/pathogenesis, 922–923 treatment, 923 congenital bilateral dermal melanocytosis, 1015 congenital generalized dermal melanocytosis, 1015 congenital histiocytosis, hemosiderosis, 990 congenital lentiginosis, see LEOPARD syndrome congenital melanocarcinoma, see melanotic ectodermal tumor of infancy congenital nevus, 515 depigmentation halos, 707, 707, 708 congenital poikiloderma with blisters of Kindler–Salamon, see Kindler syndrome congenital poikiloderma with bullous lesions “Weary type,” see hereditary acrokeratotic poikiloderma congenital segmental dermal melanocytosis, 1015 congenital universal hypomelanosis, 624 conservatism, mammalian pigmentary system evolution, 76–78 constitutive skin color (CSC), 65, 507 histological basis, 65–67 UV response, 410–412 contact leukoderma, genital, 1087
contact sensitivity, Riehl’s melanosis, 962 copper ions binding agents, 361, 361–362 melanin binding, 326, 326 Menkes’ kinky hair syndrome, 632 tyrosinase active site, 217–218, 265, 356, 361–362, 365, 365 copper vapor laser, 1200 cortical microadrenomatosis, see primary pigmented nodular adrenal disease corticosteroids injected, hypopigmentation-induction, 1167, 1168 melasma, 678 mycosis fungoides, 976 systemic, vitiligo vulgaris, 580–582 topical combination therapy, 1169 hyperpigmentation disorders, 1167, 1169 hypopigmentation treatment, 1170 lichen sclerosus, 1087 UVB phototherapy and, vitiligo vulgaris, 1185 vitiligo vulgaris, 579–580 cosmetics, 1188–1189 camouflage stains, 1188–1189 cover-up, 1188, 1189 melasma-induction, 1021–1022 Riehl’s melanosis, 962 co-trimoxazole, fixed drug eruption, 1027 coumarins, 675 counseling, vitiligo vulgaris, 583–584 craniofacial–deafness–hand syndrome, 143–144, 544–545 “craw-craw,” 694 “crazy paving stone” dermatitis, kwashiorkor, 664 creole dyschromia, see progressive macular hypomelanosis Crohn’s disease, 995 Cronkhite–Canada syndrome, 983–986 associated disorders, 984 clinical features, 984, 984 epidemiology, 983–984 histology, 984–985 pathophysiology, 985 Cross syndrome, see oculocerebral syndrome with hypopigmentation Crow sign, LEOPARD syndrome, 844 CRP of Gougerot and Carteaud, see confluent and reticulated papillomatosis (CRP) Cruickshank, William, 7 curettage, dermatosis papulosa nigra, 929 Cushing syndrome, 667 Carney complex/myxoma syndrome, 855, 857 pigmented adrenocortical nodular dysplasia, 852–853, 859 treatment, 859 cutaneous hepatic porphyria, see porphyria cutanea tarda cutaneous malignant melanotic neurocristic tumor (CMMNT), 1158, 1160 cutaneous myxomas, Carney complex/myxoma syndrome, 855, 856, 856, 857–858 cutaneous papillomatosis, see confluent and reticulated papillomatosis (CRP) cute, 687–688 cutis trunci variata, see progressive macular hypomelanosis cyanophores, 14, 24 MSH effects, 31 cyanosomes, 24 cyclic AMP (cAMP) signaling adrenergic receptors and, 37 dendrite formation and, 171 melanocortin-1 receptor (Mc1R), 395 agouti protein and, 395 MSH action and, 35–36, 85, 246, 359, 395 tyrosinase and, 403 melanosome translocation, 39 cyclin-dependent kinases (CDKs), see also specific CDKs in aging melanocytes, 465 in melanoma, 454, 472, 474–476 cyclobutane pyrimidine dimers, 344, 347–348, 349 L-cyclodopa (leukodopachrome), 263, 263–264, 284 cyclophosphamide, skin discoloration, 940, 1046
INDEX CYP2D gene/protein, familial melanoma and, 477 cyproheptadine acanthosis nigricans, 912 carcinoid syndrome, 921 cystathionine b synthase deficiency, 529 cystathionine synthase, 626 cysteinyldopamine-melanin, 301, 301–302 cysteinyldopas, 282, 284, 286, 286, 291–292, 292, 354 melanoma markers, 293–294 pigmented spindle cell nevi, 1095 protective roles, 295 thiol source, 397 cystinosis, 370 cytochrome P450, familial melanoma and, 477 cytokines, see also specific molecules human melanocyte regulation, 412, 413 melanoma and, 491–492 in pigmentary disorders, 421–444 cytoskeleton keratinocyte intracellular transport, 182–186 maintenance of melanin cap, 182, 185–186, 186 melanocyte intracellular transport, 13, 37–40, 38, 171–173 cytotoxicity melanin and, 72, see also drug-binding to melanin(s) phototoxicity, 73–74, 334, 334 precursors, 294–295, 295, 366–367 melanocyte sensitivity to, 354, 371 neurotoxicity, 376–378 protective mechanisms, 367, 509–510 dactinomycin-induced skin discoloration, 1046 danthron, skin discoloration, 1048 dapsone, leprosy, 692 Darier sign, 955 Darier–White disease, 647–649, 648 dark dot disease, see Dowling–Degos disease darkness, adaptation to, 33, 33–35, 34, 35 pineal gland role, 33–34 daunorubicin-induced skin discoloration, 1046 Davy, Humphrey, 7 deafness, see hearing loss delayed tanning (DT), 343 Delleman–Oorthuys syndrome (oculocerebrocutaneous syndrome), 630 dendrite formation (melanocytes), 171–173, 173, 176, 176–177, 356 dental defects, hypomelanosis of Ito, 638 dento-oculo-cutaneous syndrome, 903 depigmentation, see also hypomelanosis acquired, 370, 551–598, see also depigmenting agents chemically-induced, 562 drug-induced, 370–371, 582–583, 715, 715–716 monobenzone-induced, 1170, 1170–1172, 1171, 1172 occupational, 669–670 Rozycki syndrome, 551 toxicology, 369–371 Vogt–Koyanagi–Harada syndrome, 735–736 yaws, 686–687 animal, 576–577 confetti-like, 567, 567 confusing terms, 500 congenital, 370 definition, 527 generalized, 369 halos, 707, 707, 708 human skin color evolution, 73–74 lupus erythematosus, 703 melanin modification, 358 melanoma, 566–569, 567, 568 morphological/functional defects, 510 onchocerciasis, 695, 695 pinta, 687 Scarpa triangle, onchocerciasis, 695 segmental, 370, 371, see also piebaldism/piebald trait vitiligo, see vitiligo vulgaris (vitiligo) vitiligo-like, atopic dermatitis, 702, 703 depigmenting agents, 562 bleaching agents, 357–358, 1022 classification, 672 drugs, 370–371, 582–583, 715, 715–716
mechanism of action, 670–671, 672 melanogenic enzyme regulators, 671–677 occupational, 669–670 dermal chromatophore unit, 16–17, 22, 40–41, 41 dermal hyperpigmentation, Mongolian spots, 63, 69 dermal hypoplasia, focal, 645, 646 “dermal light sense,” 13 dermal melanocytes, 63 blue color, 69–70 humans, 69–70 Mongolian spot, 63, 69, 358, 1005 nonhuman mammals, 70 dermal melanocytic hamartoma (persistent Mongolian spot), 1005 dermal melanocytic nevus, 1118 dermal melanocytosis, 523, 524 acquired, 1016–1017 classification, 1016 pathogenesis, 1017 congenital, 1015–1016 clinical findings, 1015 histology, 1015–1016 definition, 1165 dermal melanophores, 11, 14, 16, 16–17, see also specific types extracutaneous, 17 functions, 40–41 mosaic, 42 MSH sensitivity, 17, 28, 29 phyllomedusine melanosomes, 17, 17, 18 structure, 17 dermal melanosis, 522, 523–524 dermal neurofibromas, 812 dermatitis allergic contact, 949 atopic hyperpigmentation, 911 hypopigmentation, 702–703, 703 atrophic degenerative pigmentary, see poikiloderma of Civatte paederus, 949 phototoxic, see phytophotodermatitis pigmented contact, see Riehl’s melanosis dermatitis bullosa striata pretensis, see phytophotodermatitis dermatofibroma, 433–435, 434, 440, 441, 441 dermatomal vitiligo, 500–501 dermatopathia pigmentosa reticularis (DPR), 784–786, 789, 797 clinical findings, 784–785 diagnosis/differential diagnosis, 785, 785–786 genetics, 784 histology, 785 pathogenesis, 786 dermatophyte infection, pigmenting pityriasis alba, 700 dermatosis papulosa nigra, 928, 928–929 dermatospectrometer, 534 dermis, see also entries beginning dermal development, 124 human pigmentation, 69–70 melanoma cell invasion, 490 dermoscopy, 533, 1063 De Sanctis–Cacchione syndrome, 890 desferrioxamine, hemosiderosis, 991 desipramine-induced skin discoloration, 1044 development, see embryology (pigment cells) DHICA oxidase, see tyrosinase-related protein-1 (TYRP-1) diabetes mellitus acanthosis nigricans, 908 hereditary hemochromatosis, 987 vitiligo vulgaris, 564, 566 dibromomannitol-induced skin discoloration, 1046 didymosis (twin spotting), 1015, 1107, 1107, 1130 diethylcarbamazine, onchocerciasis, 696 diffuse lentigo, see LEOPARD syndrome digital malformations, Pierre Robin syndrome, 661 dihydrolipoic acid, 673 2,2¢-dihydroxy-5-5¢-dipropyl-biphenyl (DDB), 677 dihydroxyacetone, skin discoloration, 1048 dihydroxybenzene, see hydroquinone (dihydroxybenzene; HQ)
5,6-dihydroxyindole (DHI), 264, 282, 283, 284 DHICA ratio in late eumelanogenesis, 290–291 melanoma marker, 293 protective role, 295 5,6-dihydroxyindole-2-carboxylic acid (DHICA), 264, 269, 282, 283, 284 DHI ratio in late eumelanogenesis, 290–291 melanoma marker, 293 protective role, 295 5,6-dihydroxyindole-2-carboxylic acid (DHICA) oxidase, see tyrosinase-related protein-1 (TYRP-1) dihydroxyphenylalanine reaction, 534 3,4-dihydroxyphenylalanine (DOPA) staining, see dopa histochemistry N, N¢-dilinoleylcystamine, 676 dilute mouse mutant, 173–174 2,4-dinitrophenol, skin discoloration, 1048 dinitrosalicylic acid, skin discoloration, 1048 dioxin-induced skin discoloration, 1047 discoid lupus erythematosus, pigmentary disturbances, 703, 703 disseminated hypopigmented keratoses, 745–746, 746 pathogenesis, 745–746 DKC1 gene, dyskeratosis congenita, 899 DNA aging/senescence, 468 diagnosis, KIT gene mutations, 142 photodamage, 185, 342, 347–348 action spectra, 344, 344 melanin-induced cell death and, 72 melanogenesis induction, 348–349 ploidy analysis, lentigo simplex, 826 repair, 342 melanogenesis induction, 348–349 skin types and, 411, 412 DNTNBP1 gene, Hermansky–Pudlak syndrome type 7, 616 dogs mycosis fungoides, 976 pigment type switching, 405 dominant-negative mutations, KIT gene, 142 L-dopa formation, 365 oxidation, 262, 263, 266 assay, 272, 274, 274–275 skin discoloration, 1047 L-dopachrome, 263, 264, 274, 284 dopachrome conversion factor (DCF), see tyrosinase-related protein-2 (TYRP-2) dopachrome oxidoreductase, see tyrosinaserelated protein-2 (TYRP-2) dopachrome tautomerase (Dct), see tyrosinaserelated protein-2 (TYRP-2) dopa histochemistry, 155, 534 leprosy, 690–691 pityriasis alba, 700 senile canities, 760–761 dopa-melanin, 289–290, 313 physical properties, 311–341 dopamine-melanins, 301, 301–302 L-dopaquinone, 263, 263, 282, 284, 284 conjugation with 2-thiouracil, 368–369, 369 inhibitory effect, 671 intrinsic reactivity, 285, 285, 354 melanogenesis control by, 285, 285–287 redox exchange, 365–366 thiols and, 367 dorsal spinal line, 881 Dowling–Degos disease, 882–883 clinical features, 803, 882, 882 differential diagnosis, 882–883, 883, 910 histology, 882 historical background, 882 treatment, 883 vulvar, 1084 Down syndrome, 658–659 doxorubicin (adriamycin)-induced skin discoloration, 1046 Drosophila melanogaster, “granule group” mutants, 162 drug-binding to melanin(s), 356, 356, 372, 509–510, see also specific drugs mechanisms of binding, 371–372 pharmacological uses, 378–383 applied toxicity (chemotherapy), 380–383, 381, 383–384
1209
INDEX biological monitoring, 379–380 photochemotherapy, 379 tinnitus treatment, 378, 378–379 toxicity/toxicology, 373–374, 383, see also drug-induced pigmentation changes carcinogenesis, 373, 374, 383 chloroquine, 374, 374, 375–376 CNS, 376–378, 377 eye, 375–376 inner ear, 376 kinetics, 372–373 skin, 374–375 thioureylenes, 368–369, 369 drug-induced phototoxic reactions, 949 drug-induced pigmentation changes, 1026–1054, see also fixed drug eruption; specific drugs depigmentation, 370–371, 582–583 immunotherapy, 715, 715–716 monobenzone, 1170, 1170–1172, 1171, 1172 hyperpigmentation, 940 mycosis fungoides treatment, 977 nails, 1081 oral mucosa, 1081, 1081 “dual filament transport model,” 39 ductal adenomas (breast), Carney complex/myxoma syndrome, 856–857 dye-induced skin discoloration, 1048 dynactin, melanosome trafficking in keratinocytes, 183 dyneins, 185 keratinocyte intracellular transport, 182–186, 184 melanin cap formation, 185–186, 186 melanocyte intracellular transport, 38, 172–173, 174, 183 structure, 182–183 dysacousia, Vogt–Koyanagi–Harada syndrome, 559 dysbindin, 616 dyschromatosis hereditaria, see dyschromatosis universalis hereditaria dyschromatosis universalis hereditaria, 786–788 associated disorders, 786–787 clinical features, 785, 786, 787, 788 pathology, 787 dyschromic and atrophic scleroderma, see atrophoderma of Pasini et Pierini dyskeratosis congenita, 777, 785–786, 898–901 associated findings, 898–899 clinical findings, 898, 899 histology, 899 pathogenesis, 899 prognosis, 899–900 dyskerin, dyskeratosis congenita, 899 dysplastic nevi HIV, 944 melanocytic, 1112 melanoma and, 473, 473, 482 nevus spilus, 1099 dysraphia, centrofacial lentiginosis, 838–839 dystopia canthorum, Waardenburg syndrome, 544 dystrophia bullosa hereditaria, see Mendes da Costa syndrome dystrophia myotonica, 660–661 dystrophie papillaire et pigmentaire, see acanthosis nigricans ear, see also auditory system drug toxicity, 376 melanocytes, see otic melanocytes pigment cells, vitiligo vulgaris, 560 Ebstein’s disease, 1104 echocardiographic screening, Carney complex/myxoma syndrome, 858 ectodermal dysplasia, ectrodactyly, cleft lip and palate (EEC syndrome), 901–902 ectodermal dysplasias, 901–905 abnormal thumbs, 904 classification, 901 hidrotic (Clouston syndrome), 902–903, 903 hypohidrotic, 901, 902 tricho-odonto-onychial type, 903 X-linked anhidrotic, 901, 902 ectomesenchymoma, 1161 ectopic ACTH syndrome, 938–939, 939 eczema, nevus counts, 1126, see also dermatitis
1210
edema, skin, 768 EDN3 gene mutation, Waardenburg syndrome, 544 EDNRB (Ednrb) gene/protein melanocyte morphogenesis, 123–124 mutations, 544, 545 EEC syndrome (ectodermal dysplasia, ectrodactyly, cleft lip and palate), 901–902 EGF motif, tyrosinase gene family, 217 egg, amphibian as chromatophore, 24, 24–25, 25 egr-1, melanoma growth role, 452 electrical properties, melanins, 320–322 electrocardiography (ECG; EKG) abnormalities, LEOPARD syndrome, 844–845, 846 leads, skin discoloration, 1045 electroencephalography (EEG), tuberous sclerosis complex, 655 electron microscopy (EM), 534–535 familial progressive hyperpigmentation, 775 hypermelanocytic punctata et guttata hypomelanosis, 747, 747 Kindler syndrome, 783 leprosy, 691 melanins, 312–313 melanotic ectodermal tumor of infancy, 1152–1153 oculocerebral syndrome with hypopigmentation, 627–628 pityriasis alba, 700 sarcoidosis, 752 senile canities, 761, 761, 762 speckled lentiginous nevus, 1105 tinea versicolor, 693 ultrastructural, 535 Westerhof syndrome, 742–744 electron paramagnetic resonance (EPR) spectroscopy, melanins, 311, 322–325, 323, 328 electron–proton coupling, melanins, 319 electron resonance (ER) spectroscopy, melanins, 299 electrophoresis, enzyme activity assays, 276 Elejalde syndrome, 175 elemental melanin analysis, 298–299, 315 ellagic acid (EA), 676 embryology (pigment cells), 76–77, 108–139, see also melanoblast(s); neural crest; specific genera/species comparative biology, 127 gene regulation, 243–248 growth factors and signal transduction regulating, 445–463, see also specific molecules/pathways historical background, 108–139, 445 mammalian, 78–86, 122–126, 489, 541 genetic disorders, 527–528, 541 identification of biological growth factors, 445–448 murine coat development, 78–82 murine morphogenesis, 123–124 ocular melanocytes, 91–93, 95 otic melanocytes, 99 nonmammalian, 11, 12, 42 amphibians, 115–119 birds, 119, 119–122 organelles, 16, 52 pattern formation, see pattern formation (nonmammalian) reptiles, 119 teleost fish, 109–115 organellogenesis, 16, 52, 155–170, see also melanosome biogenesis pattern formation, 108 stem cells, 489 emtricitabine (FTC), hyperpigmentationinduction, 943 en coup d’sabre, 968 endemic syphilis, 688 endocochlear potential (EP), otic melanocyte role, 100–101 endocrine system, see also hormones; specific components disorders/dysfunction Carney complex/myxoma syndrome, 855 centrofacial lentiginosis, 839 hypomelanosis, 667–668 LEOPARD syndrome, 845
melanonychia, 1061 NAME syndrome, 854 POEMS syndrome, 952 vitiligo and, 564–566 human melanocyte regulation, 411 endoplasmic reticulum (ER), melanosome biogenesis, 155–157 endothelin(s), 422, see also individual types avian melanocyte morphogenesis, 121 fish chromatophore development, 114 mammalian pigmentary system development, 83 as melanocyte mitogens, 446, 491 receptors, 422 B receptor, see endothelin-B (ETB) receptor gene mutations, 145, 146 melanoma and, 453 Waardenburg’s syndrome and, 145, 146 endothelin-1 (ET-1), 421 café-au-lait spots and, 435 fibroblast–melanocyte interactions, 435 inflammatory cytokine induction, 425, 426–427 keratinocyte–melanocyte interactions, 422–427 lentigo senilis, 424–425, 425 seborrheic keratosis, 425–427, 426 UVB melanosis, 422–424, 423, 424, 425 melanocyte regulation, 412–413, 414, 446, 670 endothelin-3 (ET-3), melanocyte regulation, 446, 491 endothelin-B (ETB) receptor, 414, 422 keratinocyte–melanocyte interactions, 422–427 lentigo senilis, 424–425, 425 seborrheic keratosis, 425–427 UVB melanosis, 422–424, 423, 424, 425 melanocyte differentiation/proliferation role, 446 melanoma and, 453 Waardenburg syndrome, 527, 545 endothelin-converting enzyme (ECE), 422, 427 environment adaptation to background, see background adaptation darkness, 33, 33–35, 34, 35 hair/coat color and, 75–76 enzyme assays, 261, 270–276, 272–273, see also specific methods L-dopa oxidation, 272, 274, 274–275 historical background, 270–271 melanin formation, 273, 276 tyrosine hydroxylase, 271, 272 TYRP-2 activity, 273, 275–276 eotaxin, incontinentia pigmenti, 877 ephelides, 515, 515, 929–931 associated conditions, 929–930 axillary, 532, 811 Carney complex/myxoma syndrome, 857 clinical findings, 929, 929–930 differential diagnosis, 930 histopathology, 1074 intertriginous, 810, 811 lentigines vs., 824 lip vermilion, 1073–1074 melanocytic nevi association, 1127 melanoma association, 929–930 NAME syndrome, 853–854, 854 pathology, 930 ephelis ab igne, see erythema ab igne ephelis ignealis, see erythema ab igne ephrins, avian melanocyte morphogenesis, 120 epidermal cysts, normal color, 515–516 epidermal growth factor 2 (EGF2), familial melanoma and, 477 epidermal hypermelanoses, see also individual diseases/disorders acquired, 907–978 congenital, 898–906 melanocytic, 521, 522 melanotic, 521–522, 522 epidermal hyperplasia, pigmented spindle cell nevi, 1095 epidermal melanin unit, 16, 17, 41, 66, 312 epidermal melanocytes evolution, 77–78 extracutaneous vs., 102 human, 65, 65–67 neural crest origin, 122
INDEX epidermal melanophores, 11, 14, 15, 15–16, 41 morphologic color change, 27–28 epidermal nevi, clinical features, 911 epidermal pigmentation, lentigine associated, 824–872 epidermal syndromes (genetic), see also individual disease/disorders aging disorders, 884–897 café-au-lait macules, see café-au-lait spots (macules: CALMs) generalized hyperpigmentation, 771–779 localized hyperpigmentation, 873–883 reticulated hyperpigmentation, 780–808 epidermis, see also entries beginning epidermal development, 124 human, 65, 65, 185, 342, 505, 505, 506, 507 synthesis of pigmentary regulatory factors, 412–413 epidermolysis bullosa (EB) melanocytic nevi formation, 1121, 1125 Mendes da Costa variant, see Mendes da Costa syndrome with mottled pigmentation, 788–790 clinical findings, 788–789, 789, 797 diagnosis/differential diagnosis, 789, 789–790 genetics, 788 histology, 789 pathogenesis, 790 epidermolysis bullosa simplex (EBS), Mendes da Costa variant, see Mendes da Costa syndrome epigenetics, melanocyte aging/senescence, 468 epiloia, see tuberous sclerosis complex (TSC) epiluminescence microscopy, see dermoscopy epinephrine, color change and, 36–37 epithelioid blue nevus (EBN), 1073 eponychium, 1057, 1059 equine melanotic disease, 1161 erbb3 gene/protein, fish chromatophore differentiation, 114 ERK2, MITF-M phosphorylation, 246 erythema minimal dose causing, 344 skin type and, 346–347 erythema ab igne, 931–933, 932 erythema a colore, see erythema ab igne erythema caloricum, see erythema ab igne erythema dyschromicum perstans, 879, 933–935 clinical findings, 933–934, 934 differential diagnosis, 934 epidemiology, 933 HIV, 943 pathology/pathogenesis, 934 erythema streptogenes, see pityriasis alba erythromelanosis follicularis faciei et coli, 935–937, 936, 937 erythrophores, 14, 14, 19–24 migration speed, 39 erythrophoroma, goldfish, 48, 49, 49 differentiation, 49–50, 51 erythrose péribuccale pigmentaire of Brocq, 937–938, 938 erythrosis pigmenta faciei, 937–938, 938 erythrosis pigmentosa peribuccalis, 937–938, 938 esculetin, 675 esculin, 675 essential cutaneo-mucous hyperpigmentation, see Laugier–Hunziker syndrome estrogen melanocyte regulation, 416–417 melanocytic nevi development, 1126 melanogenesis regulation, 195 ethiops, 8 ethnicity, see also skin types (human) eye color, 95, 507 Golger’s rule, 504–505 hair color, 507 MC1R variations, 401 oral mucosa pigmentation, 1072, 1072 skin color and, 63, 65, 66, 66–67, 342, 411, 505–508 chemistry of, 499–500 etretinate confluent and reticulated papillomatosis, 923 Darier–White disease, 649 xeroderma pigmentosum, 892
eumelanin(s), 159, 192, 282, 355, 395 biosynthesis, 193, 263, 263–264, 276–277, 282, 284, 284–285, 342, 365, 397 agouti protein signaling and, 196–197, 197, 395, 416 control, 285, 285–286, 315 early stages, 290, 291 late stages, 290–291, 292 P protein and, 232 brown oculocutaneous albinism, 606 carboxyl content, 296 classification, 287–289, 288 degradation, 295, 295–296, 296, 300 permanganate vs. peroxide oxidation, 302, 302 quantitative analysis, 299–300 ethnic variation in, 506–507 eumelanin/pheomelanin switch (see pigment type switching) functional groups, 315 human hair, 69 human skin, 64–65 hypomelanosis of Ito, 640 isolation, 289 pheomelanin ratio, 350 pheomelanins vs., 298, 298–299, 397 photogeneration of free radicals, 330 photoprotection, 412 structure, 287–289, 288 synthetic, 289–290 eumelanosomes, 159, 312 evolution mammalian pigmentary system, 63–78, 91 hair/coat color, 67–69 human skin color, 64–65, 72–74, 504 melanin adaptations, 63, 72–74 nonhuman primates, 71, 74 radicalism and conservatism in, 76–78 of mammals from reptiles, 63–64, 76–77 MATP gene, 237 melanin and, 357 pigmentary organelles, 41 P protein, 235 tyrosinase gene family, 215 evolutionary conservation agouti protein, 400–401 tyrosinase, 249, 361 excimer laser, 1183 postsurgical leukoderma, 1185 vitiligo vulgaris, 580, 1185 “exclamation mark” hairs, alopecia areata, 755 exocytosis, melanosome transfer to keratinocytes, 177 Experiments and Considerations Touching Colours, 6 extracellular matrix (ECM), amphibian chromatophore morphogenesis, 114–115 extracellular signal-related kinase (ERK) signaling, see mitogen-activated protein kinase (MAPK) signaling cascade extracutaneous melanocytes, 91–107, see also specific types/locations auditory (see otic melanocytes) epidermal vs., 102 historical background, 91 internal organs, 101–102, 102 nonmammalian, 17, 52 ocular (see ocular melanocytes) eye(s), see also choroid; entries beginning oculo-/ ocular; retina; visual system anatomy, 96 chloroquine effects, 375–376 color Drosophila “granule group” mutants, 162 ethnic variation, 507 mammalian, 98 development, 91–93 melanocytes (see ocular melanocytes) protection, oral PUVA, 582, 1177 structure, 93, 93–94, 94, 95 toxicology of melanin-affinic compound, 373 vitiligo vulgaris, 558–560, 559, 560 eyebrows, vitiligo vulgaris, 560 eyelashes, vitiligo vulgaris, 560, 561 eye–skin syndrome, 374 eyewear, protective in PUVA, 582, 1177
FACES syndrome, 1104 facial angiofibromas, tuberous sclerosis complex, 653, 653 facial dermal dysplasia, focal, 904 facial malformations, LEOPARD syndrome, 844 facultative skin color (FSC), 343, 507 histological basis, 65–67 UV response, 410–412 familial atypical multiple mole and melanoma syndrome (FAMMM), 1129, 1131–1132 familial mandibuloacral dysplasia, 790–792, 792 familial melanoma, 472, 474–477 atypical mole syndrome, 474, 474 low-penetrance genes, 477 susceptibility/high-penetrance genes, 474–476 familial multiple café-au-lait spots (neurofibromatosis 6), 809, 813 familial obstructive cardiomyopathy, see LEOPARD syndrome familial progressive hyperpigmentation, 774–776, 906, 914 histology, 775 familial universal or diffuse melanosis, see familial progressive hyperpigmentation Fanconi anemia, 776, 776–778 fatty acids melanogenesis regulation, 200 very long chain (VLCFAs) in adrenoleukodystrophy, 771 Felty syndrome, 939–941, 940 female(s), see also pregnancy facial melanosis, see Riehl’s melanosis human skin color, 513 Fenton reaction, 334, 334, 357–358 ferroportin 1 (IREG1; MTP1) gene, hemochromatosis, 988 fetal hydantoin syndrome, 1152 b-fibrilloses, see amyloidosis, cutaneous fibroblast(s) choroidal, 93, 94 dermatofibroma, 433–435, 434 melanocyte interactions, 433–437 melanocyte mitogen production, 447 melanoma progression, 490, 491 fibroblast growth factor-2 (FGF-2) café-au-lait spots, 435–436 fibroblast–melanocyte interactions, 435–436 human melanocyte regulation, 412, 413–414 mammalian melanocyte requirement, 445–448 melanomas and, 451–453, 490 growth promotion, 451–452 mechanism of action, 452–453 overexpression in tumorigenesis, 491 transcriptional control, 452–453 fibroblast growth factor receptors (FGFRs), 446 in melanoma growth, 451–452 mutations, 447–448 fibroblast growth factors (FGFs) basic (FGF2), see fibroblast growth factor-2 (FGF2) hair follicle growth and, 86 human melanocyte regulation, 412, 413–414 fibrolamellar hepatoma, Carney complex/myxoma syndrome, 857 filopodia, melanocytes, 176, 176–177, 177 Fisch syndrome, 659 fish, see teleost fish Fitzpatrick skin type classification, 506–507, 507 fixed drug eruption, 1026–1029 clinical findings, 1026–1027, 1027 cross sensitivity, 1028 epidemiology, 1026 histology/histopathology, 1027–1028, 1073, 1074 historical background, 1026 mucosal hyperpigmentation, 1073, 1074 nonpigmenting, 1027 pathogenesis, 1028, 1028–1029 polysensitivity, 1028 sensitization, 1027 treatment, 1029 flag sign, kwashiorkor, 664, 665 “flaky paint/enamel paint” rash, kwashiorkor, 664, 665 “floating teeth,” melanotic ectodermal tumor of infancy, 1153 fluconazole, tinea versicolor, 694
1211
INDEX fluorometric assay/analysis melanins, 319, 320 tyrosinase activity, 272, 274 5-fluorouracil-induced skin discoloration, 1046 flushing, carcinoid syndrome, 919–920 focal dermal hypoplasia, 645, 646 folate/folic acid deficiency, 666, 666 hyperpigmentation in HIV, 943 follicular melanocytes, 63, 67–69 bulb, 1059 hair follicle growth regulators and, 86 humans, 68–69 mice, 67–68, 68 regulation of differentiated cells in mice, 85 follicular mucinosis, 702 clinical features, 702, 702 hypopigmentation, 702 mucosis fungoides and, 974 treatment, 702 Fontana–Masson stains, 534 forensic toxicology, 372–373, 379–380 foveal hyperplasia, albinism, 601–602 FOX01A–PAX3 fusions, 144 FoxD3, avian melanocyte specification, 122 framboesia tropica, 686–687 framboesides, 686 frameshift mutations, KIT gene, 142 Franceschetti–Jadassohn syndrome, see Naegeli–Franceschetti–Jadassohn syndrome freckles, see ephelides free fatty acids, melanogenesis regulation, 200 free radicals in melanins, 311, 322–325, 323 inducible vs. intrinsic, 324 photoformation, 329–330, 330 stability, 323 scavengers, 677–678 (see also antioxidants) melanin as, 72, 311, 331–334, 333, 345 freezing, depigmentation, 684 friction amyloidosis, 925 Fröhlich syndrome (adiposogenital syndrome), 839 Fuch’s heterochromic uveitis, 96 fungi non-melanocytic melanins, 301–302 tyrosinase gene family, 214–215 furocoumarins, see psoralens Fusarium solani, melanonychia, 1061 Futcher lines, see pigmentary demarcation lines “gale filarienne,” 694 gamma-glutamyl transpeptidase (Gpt), 403 gammopathy, associated hyperpigmentation, 965 garment nevi, 1148, 1149 Garrod, Sir Archibald, 599 gastrointestinal disorders dyskeratosis congenita and, 898 hypermelanosis and, 979–1002 KIT mutations in, 141, 143 gastrointestinal stromal tumors (GIST), KIT mutations, 141, 143 Gaucher cells, 778 Gaucher disease, 778–779 Gaultier, M., 8 gender, human skin color, 513 generalized bullous fixed eruption, 1027 generalized morphea, 967, 968 generalized nevoid pigmentation, see familial progressive hyperpigmentation gene repression, melanomas, 452–453 genetics, see also individual diseases/disorders hypomelanoses, see hypomelanosis mammalian eye color, 98 mammalian hair pigmentation, 68, 69 mammalian pigmentary system development, 68, 82–85 melanoma (see under melanoma) zebrafish patterning, 47, 113, 115 genitalia abnormalities, LEOPARD syndrome, 845 extramammary Paget disease, 1087 hyperpigmentation, 1081–1085 benign, 1081–1084 malignant, 1084–1085 hypopigmentation, 1085–1087 melanocyte numbers, normal, 1069 nevi, 1083, 1084 pigmented carcinomas, 1085
1212
premature infants, 511 vitiligo vulgaris, 555, 555 gentisic acid (MG), 676 geographic variation in pigmentation, 73–74, 75 glabridin, 678–679, 1169 glaucoma, ocular pigmentation, 96 glomeruloid angiomata, POEMS syndrome, 953, 953 glucocerebrosidase deficiency, Gaucher disease, 778 glucose tolerance tests, porphyria cutanea tarda, 981 glutathione, 676 glutathione-S-transferases, familial melanoma and, 477 GM1 type 1 gangliosidosis, Mongolian spot, 1004 GNAS1 gene, McCune–Albright syndrome, 818 gnetol, 676 goldfish erythrophoroma, 48, 49, 49 differentiation, 49–50, 51 gold-induced skin discoloration, 525, 940, 1032, 1032 gold sodium thiosulfate, chrysiasis, 1032 Golger’s rule, 504–505 Golgi body, role in melanosome biogenesis, 156–157 Goltz’s syndrome, see focal dermal hypoplasia Gordon, John, 8 Gorlin Goltz syndrome (basal cell nevus syndrome), 655 Gottron’s syndrome, see acrogeria goundou, 686 gp100 (Silver/Pmel17), see Pmel-17 gene/protein “granule group” mutants, 162 granulocyte–macrophage colony-stimulating factor (GM-CSF), 421, 435 granulomas, sarcoidosis, 752 gray hair, see canities Griscelli–Prunieras syndrome, 530 Griscelli syndrome (GS), 614, 617–618, 618 melanosome biogenesis and, 159, 162 melanosome trafficking and, 174, 175 molecular pathogenesis, 618 types, 618 Grover disease (transient acantholytic dyskeratosis), 649 growth factors, see also specific growth factors amphibian neural crest cells and, 117 induction by UVR, 412–413 mammalian melanogenesis regulation, 199 mammalian pigmentary system development, 83 melanocyte proliferation/differentiation and, 445–463, 446 identification of, 445–448 melanoma cells, 450–454, 451 autocrine, 490 FGF2 role, 451–452, 490, 491 melanosis from, 1025 paracrine, 491–492 nonmitogenic, 448–450 growth hormone, melanocytic nevi development, 1126 growth-related oncogene a (GROa), 421 keratinocyte–melanocyte interactions, 437–440 melanoma, 490 receptor, 437 Riehl’s melanosis, 437–440, 439 growth retardation, LEOPARD syndrome, 845 guanine, iridophores, 18 guanophores, 12 guidance cues, avian melanoblasts, 120 gumma, 688 gunpowder tattoos, 1035, 1037 guttate leukoderma Darier–White disease, 648 differential diagnosis, 647 hypomelanosis with punctate keratosis of the palms and soles, 646, 647 guttate parapsoriasis (acute pityriasis lichenoides), 703 H63D gene, hemochromatosis, 988 Haber syndrome, 882 HAIR-AN syndrome, 908 hair bulb melanocytes albinism test, 600, 602
alopecia areata, 755 loss, vitiligo vulgaris, 555, 560, 560–561 hair/coat, 63, 67 color, see hair color development, 78–86 embryonic, 78–82 wild-type mice, 78 drug affinity/binding, 372–373, 379–380 evolutionary origin, 77 growth cycle, 67, 80, 80–81 aging/senescence and, 465 growth regulators, 92 hair types, 81 human, see human hair structure, 67, 78, 79 hair color, 63 development embryonic establishment in mice, 78–82 melanoblast migration, 82 wild-type mice, 78 epidermal melanocytes and, 66, 66–67 evolutionary basis environmental factors, 75–76 follicular melanocytes, 67–69 juvenile mammals, 63, 76 primates, 71–72 gray/graying, see canities human, see human hair color white, see leukotrichia (white hair) hair follicles, 67, 79 embryonic development, 81 growth regulators, 92 melanocyte reservoir, vitiligo vulgaris, 560, 577–579, 578 hair shaft diameter, kwashiorkor, 664–665 halides, fixed drug eruption, 1028 Hallerman–Streiff syndrome, 622, 623, 623 halo effect, kwashiorkor, 664 halo nevi, 705–710 clinical features, 706, 706–707, 707, 708 definition, 705 disappearance, 706–707 epidemiology, 705–706 historical aspects, 705 melanoma association, 707–708 multiple, 707, 707 pathogenesis/pathology, 709–710 regression, 709 treatment, 710 vitiligo vulgaris, 558, 558, 708–709 Vogt–Koyanagi–Harada syndrome, 735–736 halo nevus antigens, 709 hamartin, 652 “hanging groin,” onchocerciasis, 695 harderian gland, melanocytes, 101, 102 Harlan, Richard, 8 Hartnup disease, pellagra, 998 Hay–Wells syndrome, 902 hearing loss age-related changes, 468 albinism, 602 Fanconi anemia, 776 mandibulofacial dysostosis, 660 otic melanocytes and, 101 sensorineural LEOPARD syndrome, 844 Waardenburg syndrome, 544 heavy metal excretion, melanin role, 357 heliotherapy, 1176–1177 hemangiomas, 1069–1070 hematoxylin and eosin, 534 hemochromatosis, 986–992 classification, 991 hereditary, 986–989 animal models, 988 associated disorders, 987 clinical features, 987 diagnosis, 988 differential diagnosis, 988 epidemiology, 986–987 historical background, 986 laboratory findings, 988 pathogenesis, 988 treatment, 988–989 histology, 987–988 neonatal, 987 oral mucosa, 1074 types, 987, 988
INDEX hemodialysis patients, lentigo senilis et actinicus, 834–835 hemoglobin, skin color role, 64, 70–71 hemosiderin deposits, 1070, 1071 hemosiderosis, 524, 986, 989–992 animal models, 991 associated disorders, 989–990 classification, 991 clinical features, 989–990, 990 definition, 989 histology, 990–991 oral hyperpigmentation, 1070 pathogenesis, 991 trauma, 990, 990 treatment, 991 hemosiderotic fibrohistocytic lipomatous lesion, 990 Hemostix test, subungual hematoma, 1061 henna, skin discoloration, 1048 hepatic porphyria, see porphyria cutanea tarda hepatitis C infection, porphyria cutanea tarda, 980–981 hepatocyte growth factor (HGF) fibroblast–melanocyte interactions, 433–437 café-au-lait spots, 435–437, 436, 437 dermatofibroma, 433–435 hair follicle growth and, 92 as melanocyte mitogen, 446, 447 nevi and melanoma, 490, 1134 hereditary acrokeratotic poikiloderma, 792–795 clinical features, 783, 785, 792–793, 793 diagnosis/differential diagnosis, 793–794, 794 differential diagnosis, 790 histology, 793 hereditary porphyria, see porphyria cutanea tarda hereditary sclerosing poikiloderma, 795–796 clinical features, 783, 785, 795, 795 diagnosis/differential diagnosis, 795–796, 796 histology, 795 Hermansky–Pudlak syndrome (HPS), 613–616, 614 chaperone protein mutations, 159–160 genetics, 528 histology, 614 molecular pathogenesis, 615 oculocutaneous albinism, 613, 614 phenotypes, 613–615, 614 types, 615–616 herpes zoster hypopigmentation, 697, 697 Vogt–Koyanagi–Harada syndrome, 738 heterochromia, see heterochromia irides heterochromia irides, 756–760 albinism–deafness syndrome, 547 animal models, 758 associated disorders, 757–758 clinical description, 756–757 diagnosis/differential diagnosis, 758 epidemiology, 756 histology, 758 historical background, 756 laboratory findings/investigations, 758 pathogenesis, 758–759 Waardenburg syndrome and, 544 heterochromic cyclitis, see heterochromia irides HFE (hemochromatosis) gene hemochromatosis, 1074 hereditary hemochromatosis, 988 porphyria cutanea tarda, 980, 982 high albido environments, light perception in, 33 high-performance liquid chromatography (HPLC), 535 Hippocrates, 551 Hirschsprung disease, 146–147 piebaldism, 543 Waardenburg syndrome type 4, 545 histidinemia, 623–625 histiocytoma (dermatofibroma), 433–435 HIV infection/AIDS hyperpigmentation associated, 941–946, 942 clinical features, 941, 941–943, 942 etiology, 943 histology, 941–943 Kaposi sarcoma, 1070–1072 labial melanotic macules, 1074 melanoma, 944 vitiligo vulgaris, 572, 573 homeotherms, 12
homocystinuria, 370, 625, 625–626 Hori’s macules, see acquired bilateral nevus of Ota-like macules (ABNOMs) hormones, see also individual hormones mammalian melanocyte regulation, 416–417 melanocytic nevi development, 1126 pigmentary system development, 83 pigmenting (human skin), 513–514 nonmammalian amphibian neural crest cells and, 117 “bihumoral theory,” 13 color change, 11, 12–13, 28–35 mechanisms of, 35–37 melanogenesis regulation, 193–195, 194 pigmentation patterns and, 48, 52–53 sex hormones, see sex hormones Horner syndrome clinical features, 756–757 heterochromia irides, 756–760 ocular pigmentation, 96 horses, pigmentary lesions, 569 HPLC enzyme assay, 272, 274, 275–276 melanin analysis, 298, 299–300, 302 HPS1 gene, Hermansky–Pudlak syndrome type 1, 615 HPS3 gene, Hermansky–Pudlak syndrome type 3, 615 HPS4 gene/protein, Hermansky–Pudlak syndrome type 4, 615–616 HPS5 gene, Hermansky–Pudlak syndrome type 5, 616 HPS6 gene, Hermansky–Pudlak syndrome type 6, 616 HRAS mutations, melanocytic nevi, 1115 human brain, melanocytes, 101 human chimerism, 637 human evolution hair graying/balding and, 72 melanin and adaptation, 72–73 skin color, 64–65, 72–74, 504 human eye color, 98 ethnic variation, 507 human hair, 71–72 Addison disease, 970 age-related changes, 512 ethnic variation, 507 follicles, 79 melanocytes, 68–69 halo nevi, 706 hypertrichosis, 71–72, 980, 980 kwashiorkor, 664–665 Menkes’ kinky hair syndrome, 631–632 structure, 68 vitiligo vulgaris and, 554, 556–557, 560, 560–561, 561 human hair color age-related changes, 512, 512, 659 ethnic variation, 507 genetic hypomelanoses, 657–663 gray/graying (see canities) red (Celtic) phenotype, 66, 69, 415 epidermal melanocytes and, 66 kwashiorkor and, 665 MC1R mutation, 1127 white, see leukotrichia (white hair) human immunodeficiency virus (HIV), see HIV infection/AIDS human leukocyte antigen (HLA) halo nevi, 709 Vogt–Koyanagi–Harada syndrome, 738 human skin color (see human skin color) melanocytic nevi models, 1135, 1136, 1136 Menkes’ kinky hair syndrome, 631 solar radiation effects, 343, 410–412, 411 structure, 65, 65 types, see skin types (human) human skin color, 499, 504–520, see also melanin(s); melanocyte(s) age effects, 511, 511–513 adults, 512 childhood/adolescence, 511–512 premature infants, 511 chemistry, 499–500 constitutive (CSC), 65–67, 410–412, 507 contributing factors, 500 demarcation lines, 514, 514
dermal melanocytes, 69–70 development melanocyte differentiation, 126 melanocyte morphogenesis, 124–125 epidermal melanin unit, 66 epidermal melanocytes, 65, 65–67, 66 evolution of, 64–65, 504 depigmentation, 73–74 melanin and adaptation, 72–73 melanin content, 73–74 facultative (FSC), 65–67, 343, 410–412, 507 glutathione levels and, 363 hemoglobin role, 64, 70–71 histological basis, 65–67 melanin content, 342, 410, 506–507 melanin distribution and, 66, 505, 505 normal, 521, 522 physics of, 500 regulation, 410–420, 411 epidermally-synthesized factors, 412–413 paracrine/autocrine, 413–417 response to UV radiation, 410–412 sex hormones and, 513, 513–514 unusual, 530 variations, 63, 66–67, 342, 499, 504–505, see also ethnicity; skin types (human) ethnicity, 505–508 genetic basis, 237 gray-blue, 530 yellow, 530 yellow-orange, 530 vitamin D synthesis and, 72, 73, 509 Hunter syndrome, Mongolian spot, 1004 Hunter, William, 7 Hurler syndrome, Mongolian spot, 1004 Hutchinson–Gilford syndrome, see progeria Hutchinson sign Laugier–Hunziker syndrome, 1076 melanonychia, 1062, 1062 hydantoin-induced skin discoloration, 1047 hydroquinone (dihydroxybenzene; HQ), 674, 1165–1166 application, 1165 combination therapy, 1169 hyperpigmentation disorders, 1165–1166, 1166 mechanism of action, 1165 melasma treatment, 1022, 1022 ochronosis-induction, 1040, 1041, 1041, 1166, 1167 side effects, 1166 hydroquinone monobenzyl ether (MBEH), 674 6-hydroxy-3,4-dihydrocumarins, 677–678 a-hydroxy acids, 678 4-hydroxyanisole (para-hydroxymethoxybenzene), 369, 675 hydroxychloroquine-induced skin discoloration, 1042, 1042 5-hydroxyindoleacetic acid (5-HIAA), carcinoid syndrome, 920 4-hydroxyphenyl a-D-glucopyranoside (aarbutin), 674 8-hydroxyquinoline (and analogs), 361, 361–362 hydroxyurea, skin discoloration, 943, 1047 hyperchromias, 501, 501 mixed dermal/epidermal, 1020–1025 hyperkeratoses kwashiorkor, 664 warty, 805, 806 hypermelanocytic punctata et guttata hypomelanosis (HPGH), 746–748, 747, 747 hypermelanosis blue (ceruloderma), 521, 522, 522–523, 523 brown, 521 definition, 521 dermal acquired, 1016–1018 congenital, 1003–1019 epidermal (see epidermal hypermelanoses) gastrointestinal disorders and, 979–1002 mixed dermal/epidermal, 521, 1020–1025 universal, 531 hypermelanotic macule, see café-au-lait spots (macules: CALMs) hyperpigmentation, see also specific disorders adrenoleukodystrophy, 772 cytokine involvement, 421–444 drug-induced, 523, 524–526
1213
INDEX familial progressive, 774–776 Fanconi anemia, 776 focal dermal hyperplasia, 645 genital, 1081–1085 kwashiorkor, 664 leprosy, 691 mycosis fungoides, 974–975, 975 oral mucosa, 1069–1081 periorbital, 879, 879–880 piebaldism, 542–543 premature infants, 511 topical treatment, 1165–1169 vulvar, 1081 hyperthyroidism, vitiligo vulgaris, 565–566, 566 hypertrichosis, 71–72 porphyria cutanea tarda, 980, 980 hypoadrenalism, see Addison disease hypochromias, 501, 501 hypocorticism, see Addison disease hypogonadism, pigmentation, 667 hypomelanosis, see also specific types chemical/pharmacologic, 669–685 congenital universal, 624 definition, 527 endemic syphilis, 688 endocrine disorders, 667–668 extracutaneous pigmentation loss, 754–766 genetic acquired depigmentation, 551–598 congenital white spotting, 541–550 defective melanosome biogenesis/transport, 613–621 generalized hypopigmentation, 599–635 hair hypopigmentation, 657–663 immune deficiency, 617–618 localized hypopigmentation, 636–656 infectious, 686–698 inflammatory, 699–704 leprosy, 691 melanocytic neoplasia associated, 705–724 melanocytopenic, 527, 527 acquired, 529 melanopenic, 527, 528 metabolic, 664–667 mosaicism associated, 571–572 nutritional, 664–667 physical agents, 683–685 postinflammatory, 701–704 hypomelanosis of Ito (HI), 636–645 cutaneous symptoms, 637, 638, 638 differential diagnosis, 637–638, 651 exclusion criteria, 637–638 extracutaneous anomalies, 638–639 heterogeneity cytogenic evidence, 639, 640–641 phenotypic evidence, 639, 639 histology, 639–640 historical background, 636 inclusion criteria, 636–637 inheritance, 640, 642 melanin composition, 640 P protein and, 235 terminology, 636 hypomelanosis with punctate keratosis of the palms and soles, 646, 646–647 hypomelanotic macules, idiopathic, 655 hyponychium, 1057, 1059 hypophysis background adaptation, 32–33 morphologic color change, 27 hypopigmentation, see also specific disorders albinism–deafness syndrome, 547 Angelman syndrome, 619–620, 620 atopic dermatitis, 702–703, 703 bowel disorders, 665–666 causes, 1170 Chediak–Higashi syndrome, 613, 616, 616–617 focal dermal hyperplasia, 645, 646 follicular mucinosis, 702, 702 genital, 1085–1087 Griscelli syndrome, 617 Hermansky–Pudlak syndrome, 616 herpes zoster, 697, 697 HIV, 944 kwashiorkor, 664 leprosy, 690, 690, 691 lichen sclerosis et atrophicus, 732 mucous membranes, 1085–1087
1214
mycosis fungoides, 973, 973–974, 974, 975, 976, 977 nutritional causes, 664–666 oculocerebral syndrome with, 627 post-kala-azar dermatosis, 696 P protein and, 235 Prader–Willi syndrome, 620, 620 as therapeutic effect, 670 topical treatment, 1169–1170 Waardenburg syndrome, 545 without hypomelanosis, 767–768 hypopigmented macules, 515 hypopituitarism, pigmentation, 667 hypothalamus, melanogenesis regulation, 194–195 ichthyoses, histology, 966–967 ichthyosis nigrans, keratoses and epidermal hyperplasia, 965–967, 966, 967 idiopathic guttate hypomelanosis (IGH), 726–729 clinical description, 531, 727, 728, 730, 747 diagnostic criteria, 728 differential diagnosis, 728 epidemiology, 727 histochemistry, 727–728 histology, 727–728, 747 historical background, 726–727 pathogenesis, 728 repigmentation, 729 treatment, 728–729 idiopathic lenticular mucocutaneous pigmentation, see Laugier–Hunziker syndrome idiopathic multiple large-macule hypomelanosis, see progressive macular hypomelanosis idiopathic neuraxitis, see Vogt–Koyanagi–Harada syndrome id reaction, yaws, 686 image analysis, 534 imipramine-induced skin discoloration, 1044 imiquimod, xeroderma pigmentosum, 892 immediate pigment darkening (IPD), 343, 358 immune system dyskeratosis congenita and, 898 melanocytes and, 510 UVR effects, 349–350 immunocytochemistry, 534 immunoglobulin(s), fixed drug eruption, 1029 immunoglobulin G (IgG), vitiligo vulgaris, 572 immunohistochemistry acanthosis nigricans, 911 melanotic ectodermal tumor of infancy, 1152–1153 immunomodulators, vitiligo vulgaris, 579–580 immunosuppression melanocytic nevi formation, 1125, 1125–1126 UVR induced, 349–350 impetigo, chronic, see pityriasis alba incontinentia pigmenti (IP) clinical features, 637, 873–875, 874, 875 diagnostic criteria, 876, 877 differential diagnosis, 637, 876 epidemiology, 873 extracutaneous manifestations, 875, 876 genetics, 873 histology, 875–876 historical background, 873 laboratory findings, 876 pathogenesis, 876–877 prognosis, 878 treatment, 877–878 incontinentia pigmenti achromians, see hypomelanosis of Ito (HI) indeterminate leprosy, 690 infants blue-gray macules, see Mongolian spot hemangiomas, 1069–1070 melanotic ectodermal tumor, see melanotic ectodermal tumor of infancy (MNTI) premature, skin color, 511 infections, see also specific infections/organisms hypomelanosis, 686–698 nail, 942, 942 inflammation, see also cytokines; specific mediators of melanocytes and, 74, 412, 413, 510 pigmentation, 670 inflammatory bowel disease, pigmentation, 995
inflammatory mediators, human melanocyte regulation, 412, 413 infrared absorption spectroscopy, melanins, 299, 315 infrared (IR) photography, 533 injury, see trauma INK4A-ARF, see CDKN2A gene/protein “ink-spot” lentigo, see reticulated black solar lentigo “ink-spot” macules, NAME syndrome, 854 innervation, chromatophore(s), 26–27 insulin-like growth factor-1 (IGF-1), melanoma, 490, 491 insulin-like growth factor-1 receptor (IGF-1R), melanoma and, 453 insulin receptor mutations, acanthosis nigricans, 911 intense pulse light (IPL), 1201 intercellular adhesion molecule-1 (ICAM-1), fixed drug eruption, 1029 interferon-g (IFN-g), depigmented skin, 564 interleukin-1a (IL-1a) ET-1 induction, 425, 426–427 GROa induction, 440 induction by UVR, 412, 423 interleukin-1b (IL-1b), induction by UVR, 412, 413 interleukin-1b (IL-1b), POEMS syndrome, 953 interleukin-2 (IL-2), depigmentation induction, 568 interleukin-6 (IL-6), POEMS syndrome, 953 interleukin-8 (IL-8), melanoma, 490 interleukin-8 (IL-8) receptor, 437 “intermedin,” see melanocyte-stimulating hormone (MSH) internal organs, pigmentation, 101–102, 102, see also extracutaneous melanocytes; specific locations nonmammalian, 17, 52 intertriginous freckling, neurofibromatosis type 1, 810, 811 intestinal polyposis type II, see Peutz–Jeghers syndrome intestinal polyposis with hyperpigmentation, see Cronkhite–Canada syndrome intestinal polyposis with nail loss, see Cronkhite–Canada syndrome intracellular pigment transport, see also melanosome trafficking higher vertebrates keratinocytes, 181–186 melanocytes, 65, 171–176 melanogenesis regulation, 199–200 lower vertebrates, 13, 26, 37–40, 38 “dual filament transport model,” 39 speed, 38–39, 39 invertebrates melanogenesis, 193–195 non-melanocytic melanins, 301–302 tyrosinase gene family, 214–215 iodothiouracil, 380, 381, 381 ionizing radiation, depigmentation and, 684 irideterochromia, see heterochromia irides iridomelanophoroma, 48 iridophores, 14, 14, 17, 17, 17–19 adrenergic receptors, 36–37 apparent color and optical properties, 18, 19, 20, 21, 42, 43 avian eye color, 98, 98 leukophores vs., 19 morphologic color change, 27, 31 MSH stimulation, 30, 30–31 physiologic color change, 31 platelet morphology, 18–19, 19, 20, 21 iridosarcoma, 48, 50 iris/iris pigmentation albinism, 600 oculocutaneous albinism type 1, 604 anatomy/structure, 96, 97–98 clump cells of Kogenei, 97 Griscelli syndrome, 617 Lisch nodules in neurofibromatosis, 811, 812, 820 mammalian eye color, 98 melanocyte variation in, 97 nonmammalian eye color, 98, 98–99 pathology, 96 tuberous sclerosis complex, 654 vitiligo vulgaris, 558, 559, 560
INDEX iris pigment epithelium (IPE), 97–98 iritis, vitiligo vulgaris, 559, 560 iron deficiency, anemia, 666 melanin binding, 326–327 overload, porphyria cutanea tarda, 980 skin discoloration and, 1029–1030, 1030 tattoos, 1030 ischemia, depigmentation due to, 371 isolated mucocutaneous melanotic pigmentation (IMMP), 868–869 isomorphic response sunburn, 562–563 vitiligo vulgaris, 562–563, 563 isotretinoin, confluent and reticulated papillomatosis, 923 Ito syndrome, 636 itraconazole, tinea versicolor, 694 ivermectin, onchocerciasis, 696 jaundice carotenemia vs., 1037 melanosis from melanoma vs., 1024 skin color, 530 Jefferson, Thomas, 9 jentigo, 825, 864, 1106 Johanson–Blizzard syndrome, 903 Josselyn, John, 8 junctional nevus, 1112, 1118 Carney complex/myxoma syndrome, 857 juvenile polyposis, 1001 kang cancers, 932 Kangri cancers, 932 Kant, Immanuel, 7–8 Kaposi sarcoma (KS), 1070–1072 histopathology, 1071, 1071 oral mucosa, 1070–1072, 1071 treatment, 1071–1072 kappa-chain deficiency, 631 kathon CG, 960 keratinocyte(s) human, 65, 65 melanin caps, 181–182, 182, 185–186, 186 melanin-induced cell death, 72 melanocyte interactions/regulation, 171, 172, 412–413 mitogen production, 446–447, 447 paracrine factors, 421–444, 422 melanosome acquisition, 65–66, 175–178, 312, 356 melanosome processing, 181–190, see also melanosome trafficking intracellular transport, 181–186, 183, 184 lysosomal processing, 186–187 migration through epidermis, 181 pityriasis alba, 700 keratoses, arsenical, 1034, 1035 keratosis follicularis, see Darier–White disease keratosis follicularis (Darier–White disease), 647–649, 648 ketoconazole, tinea versicolor, 694 khellin, 582, 1180 khellin and UVA light (KUVA), 1180–1181 KIND-1 gene, 783 Kindler syndrome, 781–784 clinical findings, 781–782, 782, 783, 785 differential diagnosis, 783, 783 histology, 782–783 inheritance, 781 pathogenesis, 783 kindlin-1, 783 kinesins, intracellular transport, 38, 172 kinky hair disease, see Menkes’ kinky hair syndrome KIT (Kit) gene/protein functions, 140 human protein, 141 ligand, see stem cell factor (SCF) melanocyte–keratinocyte interactions, 427–433 lentigo senilis, 430, 430–431, 431 UVB melanosis, 423, 424, 427–430, 429 vitiligo vulgaris, 431–433, 432, 433 melanoma and, 453, 481 mutations, 140–143, 141 piebaldism, 543–544 pdgfra gene association, 141 pigmentary system development, 83, 111, 114, 123–124, 446
signal transduction pathway, 140–141 urticaria pigmentosum, 958 Kit ligand (KL), see stem cell factor (SCF) c-Kit tyrosine receptor kinase (c-kitTRK), 83 Klein–Waardenburg syndrome (Waardenburg syndrome type III), 143–144, 544–545 Koebner phenomenon, see isomorphic response kojic acid, 675–676, 1169 kojyl-APPA, 676 Kramer syndrome, see oculocerebral syndrome with hypopigmentation KU-MEL-1, melanoma-associated depigmentation, 719 KUVA therapy, 1180–1181 kwashiorkor, 664–665, 665, 665 labial melanotic macules (lentigines), 1074–1075, 1075 LAMB syndrome, 852, 854, 854, see also Carney complex/myxoma syndrome laminopathies, 791 lamins, 791, 887, 888 Langerhans cell, depigmented skin, 569–570 lareotide, carcinoid syndrome, 921 laser treatment, 1198–1204, see also individual lasers café-au-lait spots, 1198, 1199, 1200, 1200, 1201 ephelides, 930 lentigines, 1200, 1200 lentigo senilis et actinicus, 834 melasma, 1199 nevus of Ota, 1009, 1010, 1199 speckled lentiginous nevus, 1108 tattoos, 1035, 1198, 1199, 1199, 1200 Latanoprost, ocular pigmentation, 96 Laugier disease, see Laugier–Hunziker syndrome Laugier–Hunziker syndrome, 869, 1001, 1075–1076, 1076 lead gingival pigmentation, 1033, 1081 skin discoloration, 1033, 1033 leaden mouse mutant, 173, 175 “lead line,” gingival, 1081 Le Cat, Claude, 8 Leishmania infections, post-kala-azar dermatosis, 696 lens, drug-induced toxicity, 375 lentigines, see also lentiginosis agminated, see agminated lentigines (AL) Carney complex/myxoma syndrome, 855, 856, 857 centrofacial lentiginosis, 838 clinical findings, 825 ephelides vs., 824 generalized (see LEOPARD syndrome) genital, 825, 826 isolated generalized, 869 labial (see labial melanotic macules) laser treatment, 1199, 1200 mucosal, 825 patterned, 827 penile, 825, 826, 1082–1083, 1083 psoriasis, 870 PUVA and, 830, 830, 832, 833, 834 sunbed, 832–833 vulvar, 825, 1081–1082 lentigines, electrocardiographic abnormalities, ocular hypertension, pulmonary stenosis, abnormalities of genitalia, retardation of growth, and deafness, sensorineural type, see LEOPARD syndrome lentiginocardiomyopathic syndrome, see LEOPARD syndrome lentiginosis, 824 arterial dissection, 868 cardiac pre-excitation, 868 centrofacial, see centrofacial lentiginosis eruptive, 869 genital, 825 inherited patterned, in black people, 869 systemic abnormality unknown, 869–870 white, 869–870 lentiginosis profusa, see LEOPARD syndrome lentiginous mosaicism, see agminated lentigines (AL) lentigo benign melanonychia vs., 1064–1065, 1065
maligna, 473, 834, 1166 multiple, see lentigines senilis, see lentigo senilis et actinicus simplex, see lentigo simplex solar, 830–831, 832 lentigo-nevus, 1064 lentigo senilis et actinicus, 829–837 animal models, 833–834 clinical description, 830–832, 831, 832 differential diagnosis, 833 epidemiology, 830 histology, 832–833 historical background, 829 paracrine interactions, 440, 441, 441 ET-1/ETB receptors, 424–425, 425, 426 mSCF/KIT interactions, 430, 430–431, 431 pathogenesis, 833 prevention, 834 prognosis, 834–835 treatment, 834 variants, 830 lentigo simplex, 824–829 animal models, 827 clinical findings, 825, 825–826 course/prognosis, 827 differential diagnosis, 826–827 epidemiology, 824–825 histology/histochemistry, 826 historical background, 824 nail bed, 825 pathogenesis, 827 treatment, 827 lentigo solaris, see lentigo senilis et actinicus “leopard skin,” onchocerciasis, 695 LEOPARD syndrome, 842–851 animal models, 847 associated disorders, 844–845 Carney complex/myxoma syndrome vs., 859 clinical description, 843, 843–844, 844, 1077 diagnosis/differential diagnosis, 846 epidemiology, 843 histology/histochemistry, 845–846, 1077 historical background, 842–843 laboratory findings, 846 pathogenesis, 846–847 treatment, 847 lepromatous leprosy (LL), 689, 690 lepromin skin test, 691 leprosy, 689–692 classification, 689–690 diagnosis, 691 epidemiology, 689 histology, 690–691 historical aspects, 9, 689 hyperpigmentation, 691 hypomelanosis pathogenesis, 691 hypopigmentation, 690, 691 macular hypopigmentation, 571 treatment, 691–692 leptomeninges, melanocytes, 101 l’erthrose pigmentée peri-buccale, see erythrose péribuccale pigmentaire of Brocq leucine zipper, 243 leukemias, ataxia telangiectasia, 621 leukoderma, see also specific types acquired, see vitiligo vulgaris (vitiligo) chemical, 574 classification, 501 piebaldism, 541–543, 542 terminology, 500, 501, 501 leukoderma acquisitum centrifugum, 705, 708, 710 leukoderma punctata, 729–731 animal models, 731 clinical description, 729–730, 730, 747 diagnosis/differential diagnosis, 730–731 histology, 730, 747 pathogenesis, 731 spontaneous partial repigmentation, 731 treatment, 731 leukoderma syphiliticum, 688–689, 689, 1087 leukodermia lenticular disseminada, see idiopathic guttate hypomelanosis leukodopachrome (L-cyclodopa), 263, 263–264 leukopathia, acquired, see vitiligo vulgaris (vitiligo) leukopathia guttata et reticularis symmetrica, see idiopathic guttate hypomelanosis
1215
INDEX leukopathia punctata et reticularis symmetrica, see reticulated acropigmentation of Dohi leukopathie symétrique progressive des extremities, see idiopathic guttate hypomelanosis leukophores, 14, 18–19, 98 leukopigmentary nevus, see halo nevi leukosome, 19 leukotrichia (white hair), 659 sudden whitening, 371, 764–766 associated disorders, 765 clinical features, 764, 765 diagnosis/differential diagnosis, 765 histology, 765 historical background, 764 pathogenesis, 765–766 prognosis/treatment, 766 tuberous sclerosis complex, 654, 654 leukotrienes, human melanocyte regulation, 413 levodopa-induced skin discoloration, 1047 Leydig cell tumor, Carney complex/myxoma syndrome, 858 lichen amyloidosis, 924 lichen aureus, 1030, 1030 lichen nitidus, 731 lichen pigmentosum, see erythema dyschromicum perstans lichen planus, 523, 523 lichen planus pigmentosus, see erythema dyschromicum perstans lichen sclerosis et atrophicus, 731–732, 732, 968 lichen sclerosus (LS), 1086–1087 lichen simplex chronicus, 966, 967 licorice extract, 1169 lidocaine, 378 Li–Fraumeni syndrome, melanoma and, 477 light cells (otic melanocytes), 99–100 light microscopy, 534–535 acanthosis nigricans, 911 chrysiasis, 1032 stains, 534 light responses, RPE melanocytes, 94 light scattering, melanins, 318 lilac rings, morphea, 968, 968 linea nigra, 513, 513 linear morphea, 967 linoleic acid, 677, 678 lipodystrophy, familial mandibuloacral dysplasia, 791 lipophores, 19 b-lipotropin, melasma, 1021 lipoxygenase derivatives, induction by UVR, 413 liquid nitrogen, lentigo senilis et actinicus, 834 liquiritin, 678 Lisch nodules, 810, 811, 812, 820 little leopard, see LEOPARD syndrome Littre, Alexis, 7 livedo reticularis e calore, see erythema ab igne liver fibrosis, hereditary hemochromatosis, 987 liver spot, see lentigo senilis et actinicus LMNA gene, familial mandibuloacral dysplasia, 790 Lorenzo oil, adrenoleukodystrophy, 773 loss-of-function mutations, KIT gene, 142 loss of heterozygosity, melanoma, 480 low albido environments, light perception in, 33 lupus erythematosus, 571, 703, 703 lupus pernio, see sarcoidosis L value, 533 lycopene-induced skin discoloration, 1038 lycopenemia, 1038 lymphokine secretion, defective, melanoma regression, 717 lymphomas ataxia telangiectasia, 621 cutaneous, see mycosis fungoides vitiligo vulgaris, 572 lymphomatoid papulosis, 974 lysosome(s) melanosomes and, 66, 233 biogenesis, 159 processing in keratinocytes, 186–187 RPE melanocytes and, 95 lysosome-associated membrane protein (LAMP-1), 200, 222 lysosome-related organelles (LRO) disorders, 613–621
1216
lysosomes, see lysosome(s) melanosomes, see melanosome(s) LYST gene/protein, 617 Chediak–Higashi syndrome, 617 melanosome biosynthesis, 161–162 macrocheilia, port wine stain, 1070 macromelanocytes, melanoma-associated depigmentation, 714 macromelanosomes, neurofibromatosis type 1, 814 macular amyloidosis, 924 macular blue nevus (aberrant Mongolian spot), 1003 macular degeneration, ocular pigmentation, 96 macular nevus unilateralis, see agminated lentigines (AL) magnesium-1-ascorbate-3-phosphate (MAP), 677 magnetic resonance imaging (MRI) albinism, 601 iron tattoos, 1030 melanotic ectodermal tumor of infancy, 1153 magnetoencephalography, albinism, 601 magot chinosis, 1043, 1043 mahogonoid (Mgrn1), 401–403 major histocompatibility complex (MHC) fixed drug eruption, 1026 melanocytic neoplasia associated hypomelanosis, 716–717 Malassezia furfur, see Pityrosporum orbiculare (ovale) mal de la rosa, see pellagra mal del pinto, 687–688 males, human skin color, 513 malignancy, see also specific cancers/tumors ataxia telangiectasia and, 621 ectopic ACTH syndrome, 938–939 KIT mutations, 142–143 neurofibromatosis type 1 (NF1), 812 nonmammalian vertebrates, 48–50, 49, 51 xeroderma pigmentosum associated, 890, 890, 891 malnutrition, hypopigmentation in, 665–666 Malpighi, Marcello, 6 mammals environmental interactions, 75–76 evolution from reptiles, 63–64, 76–77 eye color, 98 pigmentary system, 63–84 melanin, see melanin pigmentary system (mammalian) mandibuloacral dysplasia (MAD syndrome), 796 mandibulofacial dysostosis (Treacher Collins syndrome), 660 mandrill (Mandrillus sphinx), skin color, 70–71 manganese ions melanin binding, 325–326 neurotoxicity, 378 MAPK, see mitogen-activated protein kinase (MAPK) signaling cascade Marcy, Samuel, 8 MART-1, melanoma regression, 717 mask of pregnancy (chloasma), 513, 1006 mast cell growth factor (MCGF), see stem cell factor (SCF) mast cells café-au-lait spots (macules: CALMs), 437 dermatofibroma, 435 mastocytoma, 141, 143, 955 mastocytosis, 141, 143, 434–435, see also urticaria pigmentosum MATP, see membrane-associated transport protein (MATP) Matricaria chamomilla extract, 678 M-box element, tyrosinase gene family, 218–219, 220–221 MC1R, see melanocortin-1 receptor (MC1R) MCAM expression, melanoma and, 481–482 McCune–Albright syndrome, 817–819 clinical findings, 817, 817–818, 1072 clinical manifestations, 743 pathogenesis, 522, 818 ME20 (Silver/Pmel17), see Pmel-17 gene/protein mechlorethamine mycosis fungoides, 976 skin discoloration, 1047 meladinine, tinea versicolor, 694
melaginina, vitiligo vulgaris, 582 Melan-A/MART-1 protein, 163 melanin(s), 159, 192–193, 193, 282–310, 355, see also melanin pigmentary system (mammalian); melanosome(s); specific types assay, 273, 276, 282, 535 auto-oxidation, 317, 328–329 characterization techniques, 535 chemical analysis, 298–303 chemical properties, 293, 298, 298–299 classification, 287–289, 288 cytotoxicity (see cytotoxicity) degradation, 282, 295, 295–298, 299–300, 302, 303–304, 314, 356 detection of nascent, 368–369 disorders, see also pigmentary anomalies/disorders; specific disorders circumscribed, 531 clinical history, 530–531 diagnosis, 530–535 physical examination, 531–532 removal abnormalities, 530 dispersion agents, 678 drug affinity/binding (see drug-binding to melanin) forensic toxicology, 372–373, 379–380 formation (see melanogenesis) functions, 345, 356–357, 504–505, 508–511 adaptive in mammals, 63, 91, 345 camouflage, 75–76, 357 controversy, 509 human evolution and, 72–74 photoprotection, 72–74, 295, 345–346, 410, 412, 508–509, see also melanin photobiology toxin removal, 509–510 historical aspects, 261–262, 282–283, 311–312 isolation/preparation, 289–290 location, 355 melanoma diagnosis, 293–294, 354 metabolites, 282, 293–295, see also specific metabolites modification, 357–358 molecular weights, 290 morphologic color change, 27–28 ocular, 93, 95, 601, see also retinal pigment epithelium (RPE) other biopolymers vs., 283, 283 otic, 99, 101, 357, see also auditory system photobiology, see melanin photobiology physical properties, 298, 298–299, 311–341, 355, 356 antioxidant, 72, 311, 331–334, 333, 334, 345 band model, 322 cation binding, 311, 324, 325–327, 334, 371–372 electrical conduction, 320–321 energy transfer, 319 free radical centers, 311, 322–325, 329–330, 330 functional groups, 311, 315 optical, 311, 316–320, 317, 319, 346, 522–523 photoreactivity, 329, 329–331, 330, 332 redox reactions, 311, 324, 327–329 P protein interaction, 232 “primary particles,” 312 skin color role, 66, 70–71, 410, 505–507 structures, 287–289, 288, 312–316, 354 supranuclear caps, 181–182, 182, 185–186, 186 synthetic, 289–290, 313 toxicological aspects, 354–355, 371–383 transport, 356, see also intracellular pigment transport; melanosome trafficking melanin-affinic compounds, see drug-binding to melanin(s) melanin-concentrating hormone (MCH), 11, 31–32, 194 melanogenesis regulation, 194–195 “melanin loading,” tinea versicolor, 693 melanin macroglobules (giant melanosomes), familial progressive hyperpigmentation, 775
INDEX melanin photobiology, 329, 329–331, 330, 332, 342–353, see also DNA, photodamage; ultraviolet (UV) radiation DNA damage/repair induced melanogenesis, 348–349 effect of solar UVR on human skin, 343 erythema, 346–347 events initiating melanogenesis, 344, 344 optical properties of melanin, 311, 316–320, 317, 320, 346 photobleaching, 311, 320, 330, 331 photoprotection, 72–74, 295, 345–346, 508–509 effectiveness, 72 eumelanin vs. pheomelanin, 412 SPF, 508 phototoxicity/photosensitization, 73–74, 334, 350 skin chromophores and, 343–344 skin type and, 344–345 melanin pigmentary system (mammalian), see also hair color; skin color; specific components dermal melanocytes, 69–70 development, 78–86, 109, 122–126, 541, see also embryology (pigment cells); melanoblast(s); neural crest differentiation, 125–126 embryonic establishment, 78–82 hair coat of wild-type mice, 78 identification of growth factors, 445–448 morphogenesis, 122–125, 123–125 regulation, 82–85 environmental factors, 75–76 ethnic skin color and, 505–506 evolution of, see evolution follicular melanocytes, 67–69 functional adaptation, 63, 72–74 historical background, 63–64 melanin formation, see melanogenesis melanization inhibitors, 199 ocular, 95–96 melanization-inhibiting factor (MIF), 43–44, 44, 45, 52, 117–118 melanization-stimulating factor (MSF), 44–45 melanoacanthoma (melanoacanthosis), 946–948 cutaneous type, 946, 946 differential diagnosis, 947 mucosal type, 946, 946, 1077, 1077, 1078 pathology/pathogenesis, 946, 946–947, 947 melanoblast(s), 358–359, 489, see also neural crest differentiation, 108–139, 359 amphibians, 117–118 birds, 121–122 fish, 113–115 mammalian, 125–126 reptiles, 119 disorders of, 140–154, 541, see also specific disorders gene regulation, 243–248 MITF, see MITF (mitf) gene/protein growth factors and signal transduction in, 445–463 migration, see melanoblast migration neural crest origin, 108, 359, 541 melanoblast migration, 82, 91–92, 108–139, 359 amphibians, 115–117, 116 birds, 119, 119–121 dorsolateral/lateral, 109 fish, 111–113 mammalian, 82, 122–126 humans, 124–125 mice, 123–124 ocular melanocytes, 91–92 otic melanocytes, 99 reptiles, 119 ventromedial/medial, 109 melanoblastosis cutis linearis, see incontinentia pigmenti (IP) melanocortin-1 (MCR-1), see alpha-melanocyte stimulating hormone (a-MSH) melanocortin-1 receptor (MC1R), 395, 415, 448 accessory proteins, 401–403 basal activity, 404
cyclic AMP signaling, 395 familial melanoma and, 477 gene, 399 allelic variants, 395, 401, 415 human, 415 MC1R mutation, red hair phenotype, 1127 homologs, 395 ligands, see agouti protein; alpha-melanocyte stimulating hormone (a-MSH) molecular biology, 399 melanocyte(s) aging/senescence, 464–471, 469, 511, 511–513, 512 epigenetics, 468 MITF loss, 468 molecular biology/biochemistry, 465–468, 466 mosaicism, 465, 467, 467 signal transduction, 466, 466–467 in vivo studies, 464–465 avian, 98, 98–99, 119, 119–122, see also birds benign neoplasms, 1093–1147, 1148–1162 bipolar, nevus of Ota, 1008, 1008 cell culture, 445–446 autologous transplantation and, 1192–1193 piebaldism, 543 cell death, see also cytotoxicity melanin-induced, 72 protective mechanisms, 367 susceptibility, 354, 371 dendrite formation, 171–173, 173, 176, 356, see also melanosome trafficking development, see embryology (pigment cells) extracutaneous, see extracutaneous melanocytes factors affecting, 191 fibroblast interactions, 433–437 filopodia, 176, 176–177, 177 grafting, 1191–1195 vitiligo vulgaris, 578–579, 583, 583 halo nevi, 709 human, 64–67 dermal, 63, 69–70 epidermal, 65, 65–67, 66 ethnic skin color and, 506 eye color, 98, 507 functions, 508–511 hair color, 507 lifespan, 465–466, 468, 469 morphogenesis, 124–125 regulation of, 410–420, 411 signal transduction in, 449, 450–451 in idiopathic guttate hypomelanosis, 727 immune role, 510 inflammation and, 74 “internal clock,” 762 keratinocyte contacts/interactions, see keratinocyte(s) leprosy and, 690–691 lower vertebrate, see melanophores melanin, see melanin(s) mitogens, 445–463, 446, see also specific growth factors/pathways FGF2 as, 445–448 historical background, 445 identification of, 445–448 a-MSH as, 448 signal transduction, 449, 450–454 transformation and, 491 mouse development, 123–124 differentiation, 125–126 lifespan, 466, 469 nail, 1057–1068, see also nail melanin unit nevus cells vs., 1112 nonhuman primates, 74 nonmitogenic growth factors, 448–450 ocular, see ocular melanocytes organelles, see melanosome(s) otic, see otic melanocytes photolysis, 509 pinta, 688 postnatal disappearance, 528 regulation of differentiated, 85 senile canities, 762
transcriptional regulation, 242–260, see also transcriptional control; specific genes/proteins transformed phenotype, 489–494, see also melanoma vitamin D synthesis, 72, 73, 343, 346, 509 melanocyte differentiation antigen, melanoma regression, 717 melanocyte-directed enzyme-activated prodrug therapy (MDEPT), 369 melanocyte-stimulating hormone (MSH), 11, 28–30, 414–415 Addison disease, 667 a-MSH, see alpha-melanocyte stimulating hormone (aMSH) dendrite formation and, 171 historical aspects, 12–13 human skin color, 513–514 as melanocyte mitogen, 446 melanophore stimulation, 17, 28, 30, 30–31 melanosome trafficking, 30, 175–176, 177 morphologic color change, 27 mutations, mouse coat color, 529 pattern formation and, 48, 48, 52–53 receptors, 36, 52, 85 regulation of differentiated melanocytes in mice, 85 signaling pathway, 35–36, 85, 246, 359, 395 melanocytic nevi, 514, 1112–1147 acquired, 1112, 1115, 1118 environmental factors, 1120–1130, 1122–1123, 1124, 1125 genetic factors, 1120–1130, 1122–1123, 1124 age-related changes, 512–513 children, 1115, 1116, 1117, 1122–1123 clinical features, 911 clonality, 1113 congenital, 1130 cutaneous injury, 1121, 1125, 1125 definitions, 1112–1113 experimental models animals used, 1133, 1134 human skin constructs, 1136, 1136 human skin xenografts, 1135 melanoma association, 1133–1136, 1136 models with dermal origin, 1133 models with epidermal origin, 1133, 1135 transgenic mice, 1135–1136 “field defect theory,” 1116 histogenic origins, 1116 “latitude gradient,” 1116, 1120 melanoma association, 1130–1136, see also melanoma anatomic site relationship, 1132 genetic factors, 1131–1132 models, 1133–1136, 1134, 1136 monitoring, 1133 pathogenesis, 1132–1133 phenotypic risk markers, 1130–1131, 1131 transformation risk, 1132 molecular pathogenesis, 1113–1115, 1114 morphological patterns, 1112 nail, 1063, 1065 natural history, 1115, 1115–1120, 1116, 1117, 1118 oral mucosa, 1077–1078, 1078, 1079, 1120 pathways of evolution, 1116 pigmentary phenotype, 1122–1123, 1124, 1126–1127, 1127 scalp, 1116–1120 sun exposure, 1120–1121 age at exposure, 1121 direct effects, 1121 intermittent, 1120–1121, 1122–1123 latitude, 1121 natural history, 1120 twin studies, 1128–1129 melanocytoma, Mongolian spot, 1004 melanoderma, adrenoleukodystrophy, 772 melanodermatitis toxica (tar melanosis), 1048 melanodermic leukodystrophy, 771–774 melanogenesis, 191–212, 231, 342, 354, 355–356 aging/senescent melanocytes, 467, 467–468 assay, see enzyme assays avian melanocyte specification, 121 biochemical control, 366
1217
INDEX biosynthetic pathways, 192, 193, 213, 231, 282, 284, see also eumelanin; pheomelanin; specific components chemistry, 284–289 dopaquinone regulation, 285, 285–287 enzymology, 261–281 mammalian, 262–264, 263 MITF regulation, 246 phase I, 364, 364–366 switching between, see pigment type switching tyrosinase and related proteins, see tyrosinase gene family cellular vs. subcellular regulation, 192 chromophores, 344 depigmenting drugs and, 670–671 diagnostic utilization of, 368–371 DNA damage/repair induced, 348–349 enzyme regulators, 671–677 factors affecting, 191 historical background, 191–192, 282–283 induction of, 359 inflammation-induced response inhibitors, 678–679 inhibition, 670–671 thiazolidines, 367 tyrosinase glycosylation, 673 invertebrates, 193–195 lower vertebrates, 191, 193–195 hormonal control, 193–195, 194 zebrafish mutants, 47 mammalian, 191, 195–200, 262–264, 284–285, 354 growth factors, 199 hormonal control, 195–198 inhibitory factors, 199 melanosome biosynthesis/transport, 199–200 pH and, 200 proteasome function, 200 substrate availability, 198, 367 UV radiation, 198 melanogenic paracrine network, 421, 422 melanosome transporter proteins and, 230–241 mixed, 282, 287, 287, 350, 350 overview, 192–193 photosensitization and, 350 physiological control, 359–360 recent advances, 290–293 therapeutic utilization of, 368–371 thiol effects, 363–364 toxic intermediates, 366–367 protection from, 367 toxicological aspects, 354, 358–371 melanogenic complex, 222, 261, 269, 277 melanogenic neuroectodermal tumor, see melanotic ectodermal tumor of infancy melanogenic paracrine network, 421, 422 melanoid mutants, 118 melanoma, 489–494 age-related incidence, 473 anal, 1085 animal pigs, 1135 platyfish–swordtail hybrid, 454–455, 1133 biological properties, 490 biomarkers, 293–294 chemotherapy boron neutron capture therapy (BNCT), 382–383 melanin precursor cytotoxicity and, 294–295 resistance, 481, 483, 489 targeting, 354, 380–383, 381, 383–384 therapy-induced depigmentation, 715, 715–716 classification, 473 definition, 472 depigmentation and, see melanoma-associated depigmentation dermal invasion, 490 ephelides association, 929–930 etiology/risk factors, 473–474 familial, 472, 474–477 genetics, 472–488, 1114, see also specific genes/proteins AP2 and, 481–482 APAF1 mutations, 472, 479 apoptosis suppression, 472, 481
1218
BRAF mutations, 472, 477, 479–480, 492 CDK4 mutations, 472, 476 CDKN2A mutations, 472, 474–476, 475 CMM4 mutations, 472, 476 familial melanoma, 474–477 high-penetrance genes, 474–476 loss of heterozygosity, 480 low-penetrance genes, 477 p53 gene/pathway, 477, 478–479 protein tyrosine kinases, 479 PTEN mutations, 472, 480–481 RB gene/pathway, 475, 477, 478 sporadic melanoma, 478–480 telomerase, 482 XP genes and, 476, 833, 891 growth factors/signal transduction in, 450–454, 451, 478–480, 480, 1134 autocrine, 490 cell cycle regulation, 453–454, 474–476, 475 cell surface receptors, 453 FGF2, 451–453, 490, 491 MAPK signaling in, 453–454, 472, 479–480, 480, 492 metastatic cells, 450 paracrine, 491–492 transformation by, 491 halo nevi association, 707–708 historical background, 472 HIV infection and, 944 incidence, 473 Li–Fraumeni syndrome and, 477 melanin-affinic compounds and diagnosis by, 354 induction by, 374–375 targeting by, 380–383, 381, 383–384 melanosis from, 1023–1025, 1024 metastases chemotherapy, 383–384 melanosis, 1023 nail, 1062, 1063 regression, 710 molecular characteristics, 1114 nails, 1066–1067 nevus of Ota, 1008 nonmammalian, 454–455, 1133 oral, 1079, 1079–1080, 1080 penile, 1085 photosensitization, 350 regression, 710–713 clinical features, 711, 711 complete spontaneous, 710 differential diagnosis, 712 epidemiology, 710–711 extent, 711–712 mechanisms, 717–718 pathology, 711, 711–712 prognosis, 712, 712–713 sentinel lymph node involvement, 712 transcriptional control in, 452–453 tumor progression, 473, 473, 489, 490 genetic model, 482–483 “tumor stem cells,” 489–490 TYRP2 expression in, 222–223 UVB and, 473, 491 uveal, 96 viability assessment, 382 vulvar, 1084–1085 xeroderma pigmentosum and, 476, 833, 891 melanoma-associated depigmentation, 566–569, 567, 568, 713–715 “booster function,” 715 cellular mechanism, 719 clinical features, 713, 714 epidemiology, 713 humoral mechanisms, 718–719 mechanisms, 716–719 pathology, 713–714 significance/prognosis, 715 T-cell responses, 544 vitiligo vs., 713–714 melanoma in situ, 1061, 1062, 1066 melanonychia, 1059–1066 benign, 1064–1066 lentigo vs., 1064–1065, 1065 differential diagnosis, 1060–1062, 1061 drug-induced, 1060 fungal, 1061 linear, 1061
longitudinal, 1059–1060, 1060 dermoscopic examination, 1062–1063 spontaneous regression, 1067, 1067 surgical intervention, 1063–1064 melanin/nonmelanin pigment differentiation, 1061 nail plate melanin topography, 1060 non-drug-induced, 1061 striata longitudinalis, 825–826 toxic-induced, 1060 transverse, 1060 melanophages, incontinentia pigmenti, 875–876 melano-phagosome/phagolysosomes distribution in keratinocytes, 181–186 lysosomal processing, 186–187 morphologies, 187 melanophilin, 618 Griscelli syndrome, 162, 174 melanosome biogenesis, 162 melanosome trafficking, 175, 175 melanophores, 14, 14, 15, 15–25, 20, 21, see also color change (nonmammalian); specific types adrenergic receptors, 36–37 avian eye color, 98 darkness adaptation, 34, 35 dermal, see dermal melanophores epidermal, see epidermal melanophores extracutaneous, 17, 52 follicular, 63, 67–69 historical background, 12 melanogenesis regulation, 193–195 pattern formation, see pattern formation (nonmammalian) stimulation of, 30–31 unknown, 24 melanosis, see also specific types paracrine interactions, 440, 441, 441 endothelins in UVB melanosis, 422–424, 423, 424, 425 mSCF/KIT interactions in UVB melanosis, 423, 424, 427–430, 428, 429, 430 Riehl’s (PAN-induced), 437–440, 439, 440 transient neonatal pustular, 905–906, 906 universal acquired, 906 melanosis diffusa congenita, see familial progressive hyperpigmentation melanosis neviformis Becker, see Becker nevus melanosis perioralis et peribuccalis, see erythrose péribuccale pigmentaire of Brocq melanosis universalis hereditaria, see familial progressive hyperpigmentation melanosome(s), see also keratinocyte(s); melanin(s) aging/senescence, 465, 467 architecture, 201 biogenesis, see melanosome biogenesis body distribution variations, 67 darkness adaptation, 34 degradation, 66 abnormalities, 530 ethnic/racial variations, 66, 66–67, 342, 411 intracellular transport, see melanosome trafficking keratinocyte processing of, 181–190 key proteins, 236 LEOPARD syndrome, 846 melanin composition, 312–313 melanization abnormalities, 529 microenvironment, 162–163, 233 nevus of Ota, 1008–1009 ocular choroidal, 93 retention of, 95–96 otic, 99–100 phyllomedusine frogs, 17, 17, 18 porphyria cutanea tarda, 981 stabilization pathway abnormalities, 528–529 transporter proteins, 230–241, 236 historical background, 230–231 MATP, see membrane-associated transport protein (MATP) P protein, see P protein tuberous sclerosis complex, 654 ultrastructure, 312–313 UV-damaged, 72
INDEX melanosome biogenesis, 155–170, 164, 367 “bipartite theory,” 155 disorders of, 159–162, 160, 528–529, 613–621 DOPA histochemistry, 155, 156 melanogenesis regulation and, 199–200 specialization, 162–163 stage I (premelanosomes), 155–157, 156, 157, 164, 231 chaperoning of TYRPs into, 159–162, 160, 232, see also chaperone proteins development and protein trafficking into, 157–159, 158 ER vs. Golgi origin, 155–157 stage II, 155, 156, 164, 231 stage III, 155, 156, 164, 231 melanosome complex formation, aging melanocytes, 467 melanosome trafficking in keratinocytes, 181–186, 183 direction, 185 microtubules, 182, 184–185 molecular motors, 182–186, 184 in melanocytes, 65, 171–176, 183 actin filaments, 37, 38, 38, 171–172 Griscelli syndrome and, 174, 175 melanogenesis regulation, 199–200 melanophilin, 175, 175 microtubules, 37, 38, 171–173 molecular motors, 38–40, 172–173, 174 mouse mutants, 173–176, 174 myosin 5A, 173–174, 175 Rab27A, 174, 175 Rac protein, 171 Rho protein, 171 speed of migration, 38–39, 39 in melanophores, 37–40, 40 transfer abnormalities, 529–530 transfer to keratinocytes, 65–66, 175–178, 312, 356 exocytosis, 177 filopodia and, 176, 176–177, 177 inhibition, 678 molecular mediators, 175–178 MSH role, 175–176, 177 phagocytosis, 178, 181 UVR role, 175–176, 177 melanotic adamantinoma, see melanotic ectodermal tumor of infancy melanotic ameloblastic odontoma, see melanotic ectodermal tumor of infancy melanotic ameloblastoma, see melanotic ectodermal tumor of infancy melanotic anlage tumor, see melanotic ectodermal tumor of infancy melanotic ectodermal tumor of infancy (MNTI), 1148–1157 anatomic locations, 1150, 1151 associated disorders, 1152 bone formation, 1152 central nervous system, 1152, 1155 clinical features, 1150–1152, 1152 diagnosis/differential diagnosis, 1154 epidemiology, 1150 gigantiform variant, 1150 histology, 1152–1153 historical background, 1148 laboratory findings/investigations, 1153–1154 malignant, 1153, 1155 metastases, 1153 neuroblast-like cells, 1152 pathogenesis, 1154–1155 prognosis, 1155–1156 recurrence, 1155 retinal anlage theory, 1154 treatment, 1155 melanotic epithelial odontome, see melanotic ectodermal tumor of infancy melanotic progonoma, see melanotic ectodermal tumor of infancy melanotic tumor of the infantile jaw, see melanotic ectodermal tumor of infancy melanotropin, melanogenesis regulation, 194, 194, 196 melasma, 1020–1023 clinical findings, 1020, 1021 differential diagnosis, 1020–1021 genetics, 1021 histopathology, 1020
pathogenesis, 1021–1022 treatment, 1022, 1022, 1165, 1167, 1168, 1168 hydroquinone, 1165 laser, 1199 types, 1020 melatonin, 11, 13, 194, 514 adaptation to darkness, 33–34 melanogenesis regulation, 195 membrane-associated transport protein (MATP), 163, 230, 231, 235–236, 261, 270 evolution of gene, 237 human skin color variation and, 237 mouse mutants, 235–236 OCA type 4 and, 230, 237, 270, 607 structure and function, 236, 236–237 transporter homologies, 236 memory T-suppressor/cytotoxic cells, fixed drug eruption, 1029 Mendes da Costa syndrome, 789, 796–798, 797 meninges, 101, 559 Menkes’ kinky hair syndrome, 529, 631–633 animal models, 632 clinical features, 631–632 diagnosis/differential diagnosis, 632 epidemiology, 631 histology, 632 investigations, 632 pathogenesis, 632 treatment/prognosis, 633 menopausal solar dermatitis, see poikiloderma of Civatte mequinol, solar lentigines, 1169 Mercurialis, 552 mercury-induced skin discoloration, 525, 1032–1033 Merkel cell, depigmented skin, 570 mesenchymal tissues, melanocytes, 102 metabolic dysfunction, centrofacial lentiginosis, 839 metageria, 792, 886 clinical findings, 886 differential diagnosis, 885, 886 metallothioneins, 678 metals, see also specific metals fixed drug eruption, 1028 melanin binding, 311, 324, 325–327, 371–372 antioxidant properties and, 334 oral mucosa discoloration, 1081 skin discoloration, 523, 524–526, 1029–1030 tyrosinase-related protein-2, binding, 268–269 MET (Met) gene/protein, 446, 447 ligand, see hepatocyte growth factor (HGF) melanocyte–fibroblast interactions, 433–437 melanoma and, 453 methacycline-induced skin discoloration, 1040 methimazole, 677 methoin-induced skin discoloration, 1047 methotrexate, hyperpigmentation-induction, 940 8-methoxypsoralens (8-MOP), 1175 tinea versicolor, 694 vitiligo vulgaris, 580, 581 5-methoxypsoralens (5-MOP), vitiligo vulgaris, 582 1-methy-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) parkinsonism, 377 methylene blue (MTB), 380 methysergide, carcinoid syndrome, 921 Mgrn1 (mahoganoid), 401–403 mice, see also specific mutants Bannayan–Riley–Ruvalcaba syndrome model, 868 coat development, 78–82 coat pigmentation, 67–68, 68, 143, 230–231, 396, 396 mutants, 396 wild-type phenotype, 78, 85 developmental regulation of pigmentation, 82–85 eye color, 231–232 informative mitf alleles, 244–245 melanocyte(s) differentiation, 125–126 lifespan, 466, 469 migration/morphogenesis, 82, 123–124 melanogenesis regulation, 196–197, 395–409 melanosome trafficking, 173–176, 174 mutants, 84, 123, 126
transgenic, melanocytic nevi models, 1135–1136 miconazole, 675 microphthalmia-associated transcription factor, see MITF (mitf) gene/protein micropigmentation (tattooing), 1195–1196, 1196 vitiligo vulgaris, 583 microtrabeculae, 182 microtubule-mediated transport in keratinocytes, 182–186 in melanocytes, 37, 38, 171–173 polarity, 184–185 milk line nevi, 1083 minimal deviation melanoma, 1097 minimal erythema dose (MED), 344 minocycline confluent and reticulated papillomatosis, 923 skin discoloration, 526, 940, 1039–1040, 1040 missense mutations KIT gene, 142 P protein in OCA, 234 tyrosinase in OCA, 223 MITF (mitf) gene/protein, 243–246, 671, 673 aging/senescent melanocytes, 468 fish chromatophore differentiation, 113–114 gene structure, 243, 243–244, 244 promoter, 242, 245–246, 247 informative alleles, 244–245 isoforms, 242, 244, 244 mammalian melanocyte specification, 125–126, 245 mutations Tietz syndrome, 245 Waardenburg syndrome type 2A, 126, 144–145, 245, 544 post-translational regulation, 246, 248 RPE melanocyte development, 92, 252–253 SOX10 and, 247 transcriptional control, 245–246, 247 tyrosinase gene family expression and, 218–219, 220–221, 252 mitogen-activated protein kinase (MAPK) signaling cascade, 449, 450–451 melanocyte aging/senescence, 466, 466–467 melanocytic nevi pathogenesis, 1113, 1115 melanoma and, 453–454, 472, 479–480, 480, 492 mixed melanogenesis, 282, 287, 287, 350, 350 MLPH gene, 175, 618 MMAC1 gene, see PTEN gene/protein molecular motors keratinocyte transport, 182–186 melanocyte transport, 38–40, 40, 172–173, 174 moles, see melanocytic nevi Mongolian spot, 63, 69, 358, 1003–1006 aberrant (macular blue nevus), 1003 adult onset, 1005 associated disorders, 1003–1005 clinical findings, 1003, 1004, 1005 differential diagnosis, 1005 histopathology, 1005 persistent (dermal melanocytic hamartoma), 1005 premature infants, 511 regression, 1003, 1005 monkeys juvenile coat colors, 76 skin color, 74 monobenzone allergy, 582–583, 1171 application, 1171 contraindications, 1170, 1170, 1171 depigmentation, 555, 555, 562, 562, 1170–1172 repigmentation, post-treatment, 1171 vitiligo vulgaris treatment, 582–583, 1171, 1171, 1172 monoclonal antibodies, 534 monocyte-chemoattractive protein-1 (MCP-1), melanoma and, 491 morbus Besnier–Boeck–Schaumann, see sarcoidosis morphea, 967–969 associated findings, 968 clinical findings, 967, 967–968, 968, 969 epidemiology, 967
1219
INDEX histology, 968 pathogenesis, 969 morphea plana atrophica, see atrophoderma of Pasini et Pierini morphologic color change, 27–28, 28, 29, 31 Mortimer’s malady, see sarcoidosis mosaicism aging/senescent melanocyte(s), 465, 467, 467 hypomelanosis of Ito, 636–645 mosaic speckled lentiginous nevus, see speckled lentiginous nevus Moss, Henry, 9 mother yaw, 686 motor proteins, intracellular transport, 38–40, 40, 172–173, 174 mouse, see mice Moynahan’s syndrome, see LEOPARD syndrome MPTP parkinsonism, 377 Mucha–Habermann disease (chronic pityriasis lichenoides), 703 mucous membranes melanocyte numbers, normal, 1069 melanocytic nevi, 1120 normal color, 515–516 pigmentary abnormalities/discolorations, 946, 946, 1069–1089 vitiligo vulgaris, 557–558 multifocal partial unilateral lentiginosis, see agminated lentigines (AL) multiple endocrine neoplasia (MEN) Carney complex/myxoma syndrome vs., 859 MEN type 2a (Sipple syndrome), 926 multiple lentigines syndrome, see LEOPARD syndrome murine models, see mice mycelium, 1061 Mycobacterium lepra, 689, 691 mycosis fungoides, 972–978 animal models, 976 associated disorders, 974–975 clinical features, 973–974 diagnosis/differential diagnosis, 976 disseminated, 973 epidemiology, 973 histology, 975 historical background, 972–973 hyperpigmentation, 974, 975 hypopigmentation, 973, 973–974, 974, 975, 976, 977 macular, 571 UVB phototherapy, 1185 investigations, 975–976 patch stage, 973, 975 pathogenesis, 976 plaque phase, 973 prognosis, 977 treatment, 976–977, 1185 myelin figure, leukoderma punctata, 730 myeloid leukemia, KIT mutations, 141, 143 myosin(s) intracellular transport, 38, 174, 175 myosin 5A, 618 Griscelli syndrome, 162, 176 melanosome trafficking, 173–174, 175 myotonia atrophica, 660–661 myotonia dystrophica (dystrophy), 660–661 MYOVA gene, Griscelli syndrome type 1, 617 myoxin, 529–530 myxoid leiomyomas, Carney complex/myxoma syndrome, 857 myxoid mammary fibroadenomas, 855, 856, 858, 859 myxoma syndrome, see Carney complex/myxoma syndrome Naegeli–Franceschetti–Jadassohn syndrome, 789, 798–799 clinical features, 785, 797, 798, 904 diagnosis/differential diagnosis, 798–799 Naegeli syndrome, see Naegeli–Franceschetti–Jadassohn syndrome naevus fusocaeruleus ophthalmomaxillaris, see nevus of Ota naevus sur naevus, see speckled lentiginous nevus nail(s) absence (anonychia), 789, 797, 873, 874, 902 anatomy, 1057, 1058 bacteria-induced pigmentation, 1060–1061
1220
black (see melanonychia) exogenous pigmentation, 1060 hyperpigmentation HIV infection and, 942, 942 lead-induced, 1033 zidovudine-induced, 943 invasive melanoma, 1066–1067 melanocyte system, 1057–1059, see also nail melanin unit disorders, 1059–1068 nail apparatus (unit), 1057, 1058 nevi, 1065, 1065–1066 nail bed, lentigo simplex, 825 nail matrix, 1057, 1059 biopsy, 1064 removal, 1064 nail melanin unit, 1057–1059 epithelium types, 1057 melanocyte bicompartmentalization, 1057–1058, 1058, 1059 melanocyte distribution, 1057 intraepithelial, 1058, 1059 skin color type, 1058 nail plate, surgery, 1063–1064 NAME syndrome, see also Carney complex/myxoma syndrome clinical features, 852, 852 clinical findings, 853–884, 854 diagnostic criteria, 853–854 historical background, 852 naproxen, fixed drug eruption, 1027 narrow-band spectrophotometers, 533 narrow-band UVB (NBUVB) therapy, 1170, 1183 delivery devices, 1184 vitiligo vulgaris, 580, 1184 National Organization for Albinism and Hypopigmentation (NOAH), 630 natural killer cells (NK), melanocytic neoplasia associated hypomelanosis, 716 natural selection, human skin color, 504 necklace of Venus, 571, 688 neonatal progeroid syndrome of Wiedemann–Rautenstrauch, 822, 886 nerve growth factor (NGF), melanocytes and, 448–450 neural crest, 11, 12, 108, 449, see also melanoblast(s); melanoblast migration depigmentation syndromes, 527 dispersion from, 359 multipotent cells, 109 reptiles, 119 neural hypothesis, vitiligo vulgaris, 575 neural tube, 12, 111, 116 neurocristopathies, 541 neurodegeneration, melanocortin signaling mutants, 402 neuroendocrine melanoderma, extracutaneous, 938–939, 939 neurofibromas, neurofibromatosis type 1, 811, 812, 812 neurofibromatosis, 809–816 animal models, 815 associated disorders, 813 clinical findings, 810, 810–813, 811, 812 diagnosis/differential diagnosis, 814 epidemiology, 810 genetics, 435, 436, 810 histology, 813–814 historical background, 809–810 laboratory investigations, 814 pathogenesis, 814 prenatal diagnosis, 815 treatment, 815 type 1 (NF1) associated tumors, 812 café-au-lait spots, 435–437, 522, 810–811, 811 Carney complex/myxoma syndrome vs., 859 clinical findings, 810, 810–812, 811, 812 diagnosis, 814 gene, 435, 436 histology, 813–814 neurofibromas, 811, 812, 812 with Noonan syndrome, 813, 816–817 piebaldism association, 543 treatment, 815 type 2 (NF2; central, bilateral acoustic), 812–813, 814
type 3 (NF3), 813 type 4 (NF4), 813 type 5 (NF5), see segmental neurofibromatosis type 6 (NF6), 809, 813 type 7 (NF7; late-onset), 813 neurofibromatosis not otherwise specified (NFNOS), 813 neurofibromin, 436, 522, 814 neuroleptics, CNS toxicity and parkinsonism, 376–377 neuromelanin, 301, 312, 314, 373 parkinsonism and, 376–378 nevi, 69, see also specific types age-related changes, 512–513 dysplastic, 473, 473, 482, 944, 1099 genital, 1083, 1084 melanoma association, 473, 473–474, 482 nevocellular nevi, see melanocytic nevi nevoid nail area melanosis, 1067 nevus anemicus, 515, 651, 767–768 associated disorders, 767 clinical features, 767, 768 nevus aversion phenomenon, 1148, 1149, 1150 nevus cells, 1112–1113 “dropping off,” 1116 maturation, 1115–1116 normal melanocyte vs., 1112 nevus depigmentosus, 571, 649–652 associated findings, 650 clinical findings, 649–650, 650, 655 clinical manifestations, 743 diagnosis/differential diagnosis, 650–651 epidemiology, 649 histology, 650 historical background, 649 prognosis, 651 treatment, 651 nevus flammeus, see port wine stain nevus incipiens, 1105 nevus ischemicus, see nevus anemicus nevus of Ito, 1012, 1012–1013 nevus of Ota, 69, 70, 1006–1012 associated disorders, 1009–1010 classification, 1007, 1009 clinical findings, 1006–1008, 1007 complications, 1008 epidemiology, 1006 histology, 1008, 1008–1009 melanoma association, 1008 ocular, 1007, 1007 pathogenesis, 1010 treatment, 1009, 1010 nevus oligemicus, 767 nevus on nevus, see speckled lentiginous nevus nevus pigmentosus systematicus, see incontinentia pigmenti (IP) nevus pigmentovascularis, see phakomatosis pigmentovascularis nevus pilaris, see Becker nevus nevus sobre nevus, see speckled lentiginous nevus nevus spilus, see speckled lentiginous nevus nevus spilus en nappe, see speckled lentiginous nevus nevus spilus zoniforme, see speckled lentiginous nevus nevus tardif de Becker, see Becker nevus nf1 gene, neurofibromatosis type 1, 435, 436, 814 nf2 gene, neurofibromatosis type 2, 813 NFJ syndrome, see Naegeli–Franceschetti–Jadassohn syndrome niacinamide, 678 niacin (nicotinic acid) deficiency, pellagra, 997–998 nicotinamide deficiency, pellagra, 997–998 nitrazepam, skin discoloration, 1048 nitric acid, skin discoloration, 1048 nitrogen mustard-induced skin discoloration, 1044 NOAH (National Organization for Albinism and Hypopigmentation), 630 nobiletin, 676 N-Oct3 (BRN2; POU3F2), 248 nodular (tumefactive) amyloidosis, 925 nodular melanoma, 473 noise-related hearing loss, otic melanocytes and, 101
INDEX nonmammalian pigment cells, 11–62, see also specific types anomalies, 11, 48–50 color change, see color change (nonmammalian) current concepts, 14–51 embryology, 11, 12, 42 growth factors and signal transduction, 454–455 historical background, 11–13 lower vertebrate, see chromatophore(s) melanomas, 454–455 patterns/patterning, 42–48, 45, 52–53 perspectives, 51–53 terminology, 11, 12, 14, 14 nonmelanocytic melanins, 301, 301–302 nonpigmented epithelial cells (NPE), 97 nonsense mutations, KIT gene, 142 Noonan syndrome, 813, 816–817, 846 norepinephrine, color change and, 36–37 norfloxacin-induced skin discoloration, 1047 notalgia paresthetica, amyloidosis, 926 NRAS gene/protein, 480, 1115 nuclear factor kB essential modulator (NEMO), incontinentia pigmenti, 876–877 nuclear magnetic resonance spectroscopy (NMR), melanins, 299, 315–316 nude mouse xenografts, neurofibromatosis type 2, 815 nummular and confluent papillomatosis, see confluent and reticulated papillomatosis (CRP) nystagmus, 602, 627 obesity, acanthosis nigricans, 908, 909, 909 OCA2 gene, 163 occupational pigmentation changes, 669–670, 1030–1031 ochronosis, 526, 1040–1042, 1041 octreotide acanthosis nigricans, 912 carcinoid syndrome, 921 ocular abnormalities, see visual system abnormalities/defects ocular albinism (OA) autosomal recessive, 605 classification, 603 definition, 600 hearing loss, 602 melanosome biogenesis and, 159 type 1 (OA1) gene, 159, 253 X-linked, 529 ocular melanocytes, see also retinal pigment epithelium (RPE) melanocytes; uveal melanocytes development, 91–93 morphology/structures, 93–102 pathological conditions, 96 ocular telangiectasia, 621 oculocerebral hypopigmentation syndrome of Preus, see oculocerebral syndrome with hypopigmentation oculocerebral syndrome with hypopigmentation (OCSH), 626–630 clinical description, 627, 628–629 differential diagnosis, 628–629 electron microscopy, 627–628 epidemiology, 626 hair shaft examination, 628 histology, 627–628 historical background, 626 pathogenesis, 630 treatment/prognosis, 630 oculocerebrocutaneous syndrome (Delleman–Oorthuys syndrome), 630 oculocutaneous albinism (OCA), 222, 234, 602–613 autosomal dominant, 607–608 brown, 606, 607 classification, 602–603, 603 definition, 600 Hermansky–Pudlak syndrome, 613, 614 incidence, 234 prevalence, 603, 603 type 1 (OCA1), 223, 603–605 clinical features, 603–604 molecular pathogenesis, 605 temperature-sensitive, 605 type 1 A (OCA1A), 604, 604
type 1 B (OCA1B), 604, 604 tyrosinase mutations, 222, 223, 603, 605 type 2 (OCA2), 163, 230, 234–235, 270, 605–606 African-American/African individuals, 606, 606 Angelman syndrome, 620 Caucasian individuals, 605–606 molecular pathogenesis, 606 P protein mutations, 230, 234–235, 270, 606 Prader–Willi syndrome, 620 type 3 (OCA3; red; ROCA), 214, 222, 223, 606–607 molecular pathogenesis, 529, 607 ocular features, 607 type 4 (OCA4), 230, 237, 270, 607 MATP mutations, 230, 237, 270, 607 oculocutaneous syndrome, see Vogt–Koyanagi–Harada syndrome Onchocerca volvulus, 694 onchocerciasis, 694–696, 695 onchodermatitis, 694 oncocercomas, 695 oncogenes, KIT as, 142–143 ONC-Xmrk receptor tyrosine kinase, 454–455 ondansetron, carcinoid syndrome, 921 ophthalmologic abnormalities, see visual system abnormalities/defects optical properties iridophores, 18, 19, 20, 21, 43 blue coloration, 19 of melanins, 311, 316–320, 346, 522–523 fluorescence, 319, 320 human skin melanin, 317, 318 photodynamics, 319–320 synthetic melanin, 317, 317–318 optic nerve, albinism, 601–602 optic whiteners, Riehl’s melanosis pathogenesis, 962 oral contraceptives melanocytic nevi development, 1126 melasma-induction, 1021 oral mucosa hyperpigmentation, 1069–1081 drug-induced, 1081, 1081 endogenous chromophores, 1069–1072 exogenous chromophores, 1080–1081 heavy metal-induced, 1081 melanin/melanocytes, 1072–1080 melanocyte numbers, normal, 1069 melanocytic nevi, 1077–1078, 1078, 1079 normal color, 515–516 physiologic (racial) pigmentation, 1072, 1072 organellogenesis, 16, 52, 155–170, see also melanosome biogenesis ortho-quinones cytotoxicity, 294–295, 295, 366–367 intrinsic reactivity, 285, 285, 354 osteoma cutis, tetracycline-induced, 1040 otic melanocytes, 99–101, 100 aging/senescence, 468 development, 99 drug-induced toxicity, 376 functions, 100–101, 357 locations, 99 tinnitus treatment, 378–379 ototoxic drugs, 376 OTX2 gene/protein, 253 ovarian tumors, Carney complex/myxoma syndrome, 857, 859 oxoprenolol-induced skin discoloration, 1047 Oxsoralen UltraTM, 1175 oxygen consumption during melanin photoexcitation, 330, 332 quenching by melanin, 332, 333, 333 redox reactions, 328 oxyresveratrol, 676 p14 (ARF) gene/protein, melanoma and, 475, 476 p16 (INK4A) gene/protein familial melanoma role, 474–476 normal functions, 475, 475–476 sporadic melanoma role, 478 p53 gene/protein familial melanoma role, 477
role in melanogenesis, 349 sporadic melanoma role, 478–479 p63 gene, ectodermal dysplasias, 901 paederus dermatitis, 949 Paget disease, extramammary, 1087 pagetoid melanocytosis, pigmented spindle cell nevi, 1094 pale ear (ep) locus, 615 pallidin, 528 pallid locus mutations, 528 palms, vitiligo vulgaris, 553–554, 554 pancytopenia, Fanconi anemia, 776 pangeria, see Werner syndrome panhypopituitarism, congenital, 667 papillomatose pigmentee confluente et reticulee innominee, see confluent and reticulated papillomatosis (CRP) papillomatose pigmentee innominee, see confluent and reticulated papillomatosis (CRP) paracrine factors melanocyte regulation, 411, 413–417 melanoma formation, 491–492 in pigmentary disorders, 421–444, 422, 441, 441, see also specific disorders pigmentary system development, 83 para-hydroxylated monophenols, 675 parakeratose brilliante, see confluent and reticulated papillomatosis (CRP) parakeratose pigmentogene peribuccale, 937 parangi, 686–687 parapsoriasis, large plaque, 974 paraquat, parkinsonism and, 377, 377–378 parasol, 1188 parkinsonism, 376–378, 377 partial albinism, see piebaldism/piebald trait partial albinism with immunodeficiency syndrome (PAID), 618 partial unilateral lentiginosis (PUL), see agminated lentigines (AL) paru, 686–687 Patch mutant, 126 pattern formation (nonmammalian), 42–48, 45, 52–53 anomalies, 11, 45, 46, 48–50 cell death and, 112 chromophore interactions, 112–113 endogenous integument factors, 42–45, 44, 45 hormonal influences, 48, 52–53 zebrafish, 45–47, 47, 110, 110–111 Pautrier microabscesses, 975 PAX3 (pax3) gene/protein, 126, 246–247 avian melanocyte specification, 122 mutations, 143–144 Waardenburg syndrome, 544 protein product function, 144 SOX10 and, 144 PAX6 (pax6) gene/protein, 253 Peale, Charles, 9 pearl (pe) locus, 615 Pechlin, Johann, 6 pecrolimus, vitiligo vulgaris, 580 pefloxacin-induced skin discoloration, 1047 pellagra, 995–999 animal models, 998 associated disorders, 995–997 clinical features, 911, 996, 996–997 differential diagnosis, 997 epidemiology, 995 glove/gauntlet of, 995–996 histology, 997 laboratory findings, 997 medication-induced, 998 pathogenesis, 997–998 treatment, 998 pemphigus vegetans, 911 penicillin, leukoderma syphiliticum, 689 penile lentigines, 825, 826 atypical penile lentigo, 1082–1083, 1083 penile melanoma, 1085 perinevoid leukoderma, see halo nevi perinevoid vitiligo, see halo nevi periorbital hyperpigmentation, 879, 879–880 periorificial lentiginosis, see Peutz–Jeghers syndrome (PJS) peripheral demyelinating neuropathy, central demyelinating leukodystrophy, Waardenburg syndrome, Hirschsprung disease (PCWH), 545–546
1221
INDEX periungual fibroma, tuberous sclerosis complex, 653, 653 periungual pigmentation, surgery, 1063 pernicious anemia hyperpigmentation, HIV, 943 premature canities, 659, 666 vitiligo vulgaris, 566 peroxidase inhibitors, 677 Peutz–Jeghers syndrome (PJS), 999–1002 cancer predisposition, 1000 clinical findings, 531, 846, 999, 999–1000, 1000 oral mucosa, 1076, 1076–1077 diagnosis/differential diagnosis, 1001 differential diagnosis Carney complex/myxoma syndrome vs., 859 genetics, 999 histopathology, 1000–1001, 1076 treatment, 1001, 1076–1077 Peutz–Touraine–Jeghers syndrome, see Peutz–Jeghers syndrome (PJS) pH effect on melanin binding of metal ions, 325, 371 melanogenesis regulation by, 200 melanosome microenvironment, 162–163, 233 phagocytosis melanosome transfer to keratinocytes, 178, 181, 356 RPE melanocytes, 94–95 phakomatosis pigmentokeratotica, 1104 phakomatosis pigmentovascularis (PPV), 1013–1015 classification, 1013 clinical findings, 1013, 1014, 1103 differential diagnosis, 1013 lentigines, 868 pharmacological nevus, 530 pharyngeal arch abnormalities, mandibulofacial dysostosis, 660 PHC syndrome (Böök syndrome), 661 phenacetin-induced skin discoloration, 1047 phenazopyridine, skin discoloration, 1048 phenolic compound-induced skin discoloration, 1040–1042 phenol oxidases, 261–262 phenolphthalein, fixed drug eruption, 1073 phenothiazines CNS toxicity and parkinsonism, 376–377 skin discoloration due to, 374, 1043, 1043–1044 phenyazonaphthol (PAN) allergy-induced melanosis, 437–440, 438, 439 phenylalanine, 582, 1181 phenylalanine and UVA (Phe-UVA), 1181 phenylketonuria (PKU), 370, 629–630, 633–635, 634 phenylthiourea, tyrosinase inhibition, 362 phenytoin-induced skin discoloration, 1047 pheochromocytoma, 920 pheomelanin(s), 159, 192–193, 282, 355, 395 atypical nevi, 1126 biosynthesis, 193, 263, 263, 276, 282, 284, 284–285, 342, 365, 395, 397 agouti protein signaling and, 196–197, 197, 395, 416 control, 285, 286–287 cysteinyldopa formation, 286, 286 gaps in understanding, 403 late stages, 291–292, 292, 293 P protein and, 232 classification, 287–289, 288 degradation, 296–298, 297, 300 4-AHP as specific marker, 300–301 permanganate vs. peroxide oxidation, 302, 302 quantitative analysis, 299–300 ethnic variation in, 506–507 eumelanin/pheomelanin switch, see pigment type switching eumelanin ratio, 350 eumelanins vs., 298, 298–299, 397 human hair, 68–69 human skin, 65 isolation, 289 photodestruction, 331 photoprotection, 412 solubility, 303, 396 structures, 287–289, 288
1222
synthesis, 85 synthetic, 290 trichochromes, 288, 288, 288–289 wild-type mouse hair, 85 pheomelanosomes, 85, 159, 312 phlebotomy hereditary hemochromatosis, 988–989 porphyria cutanea tarda, 982 phlogiston, 7–8 photo-acoustic spectroscopy, melanins, 318–319 photobiology of melanins, see melanin photobiology photobleaching, melanins, 311, 320, 330, 331 photochemotherapy, 379, 1175–1182 hypopigmentation treatment, 1170 KUVA therapy, 1180–1181 phenylalanine and UVA (Phe-UVA), 1181 PUVA, see psoralens and ultraviolet light A (PUVA) photolysis, melanocyte(s), 509 photoprotection, melanin and, 72–74, 295, 345–346, 412 photoreactivity melanins, 329, 329–331, 330, 332 type I and II reactions, 1175 photoreception, 35, 52 photoreceptor degradation, RPE melanocytes, 94–95 photosensitivity, xeroderma pigmentosum, 889, 889 photosensitization, melanogenesis-related, 350 phototherapy, see photochemotherapy phototoxic dermatitis, see phytophotodermatitis phototoxicity depigmentation, 684 melanin and, 73–74, 334, 334, 350 phototypes, melano-phagolysosome processing, 186 phylloid hypomelanosis, 642, 642–643 phyllomedusine frogs eggs as chromatophores, 24, 24–25, 25 melanosomes, 17, 17, 18 physiologic color change, 12, 27 dermal melanophores, 16, 16 speed, 38–39, 39 physiologic (racial) pigmentation, see ethnicity phytophotodermatitis, 948–951 clinical findings, 532, 948, 948–949 diagnosis/differential diagnosis, 949 dose-dependent reaction, 950 epidemiology, 948 pathology/pathogenesis, 950–951 residual hyperpigmentation, 949 treatment, 951 pian, 686–687 pianides, 686 picric acid, skin discoloration, 1048 piebaldism/piebald trait, 125, 140–143, 427, 446, 541–544 associated conditions, 142–143, 543 clinical features, 541–543, 542, 570–571, 655, 738, 743 genetic diagnosis, 142 genetics, 543–544 histology, 738 homozygous, 543 incidence, 543–544 KIT mutations, 140–142, 141, 142 management, 543, 1170 phenotype, 140 pigmentary anomalies, 542–543 piebald mutant mice, 123–124 Pierre Robin syndrome, 661–662 PIG3.V gene, vitiligo vulgaris, 574 pigmentary anomalies/disorders, 500, see also specific disorders abnormal darkening, 521–526, see also hypermelanosis; hyperpigmentation epidermal thickening, 524, 526 exogenous/endogenous pigment-related, 524–526 exogenous/endogenous related disorders, 523 hemoglobin-related disorders, 523, 524 melanin-related disorders, 521–524 abnormal lightening, 526–530, see also hypomelanosis; hypopigmentation hemoglobin-related disorders, 530 melanin-related disorders, 21–524
chimeras, 45, 46 classification, 501, 501–502, 502 confusing terms, 500–501 definitions, 502 mechanisms, 521–537 melanoblast development and, 140–154 melanosome biogenesis and, 159–162, 160 nonmammalian, 11, 45, 48–50 zebrafish, 47 paracrine interactions, 421–444 pteridine biosynthetic mutants, 21, 25 surgical treatment of, 1191–1197 terminology, 499–503 tyrosinase gene family mutations, 214, 222–223 pigmentary demarcation lines, 514, 880, 880–882 classification, 514, 880, 880–881 histology, 881 pathogenesis, 881 pregnancy, 515 pigmentary dysplasia, see hypomelanosis of Ito (HI) pigmentary glaucoma, 96 pigmentary incontinence, 522, 523–524 pigmentary mosaicism, see hypomelanosis of Ito (HI) pigmentary organelles, 14, see also melanosome(s); specific types evolution, 41 intracellular transport, see intracellular pigment transport organellogenesis, 16, 52, 155–170 subcellular associations, 41–42 unusual, 17, 17, 18, 52 pigmentary spots, normal, 514–515 pigmentation cutaneous, 1026 regulation in humans, 410–420 science of, 5–10 early anatomic discoveries, 5–6 experiments of nature, 8–9 modern research, beginnings of, 10 terminology, 499–503 pigment cells, 11, 108, see also specific types embryology, see embryology evolution, see evolution extracutaneous, see extracutaneous melanocytes mammalian, see melanocyte(s) nonmammalian, see nonmammalian pigment cells “pigment dilution,” 526 pigmented adamantinoma, see melanotic ectodermal tumor of infancy pigmented ameloblastoma, see melanotic ectodermal tumor of infancy pigmented congenital epulis, see melanotic ectodermal tumor of infancy pigmented contact dermatitis, see Riehl’s melanosis pigmented erythroderma, HIV, 944 pigmented hairy epidermal nevus, see Becker nevus pigmented lesion dye laser (PLDL), 1198 pigmented peribuccal erythema of Brocq, see erythrose péribuccale pigmentaire of Brocq pigmented purpura, 524 pigmented retinoblastoma, see melanotic ectodermal tumor of infancy pigmented spindle cell nevi, 1093–1098 clinical features, 1093–1094 diagnosis/differential diagnosis, 1096–1097 epidemiology, 1093 growth pattern, 1094, 1095 histology, 1094, 1094–1095, 1095 historical background, 1093 laboratory findings/investigations, 1095–1096 Spitz nevus vs., 1096 treatment/prognosis, 1097 pigmented spindle cell nevus (tumor) of Reed, see pigmented spindle cell nevi pigmented teratoma, see melanotic ectodermal tumor of infancy pigmented tumor of the jaw of infants, see melanotic ectodermal tumor of infancy
INDEX pigment granule translocation, 356, see also melanosome trafficking color change (nonmammalian), 13, 37–40 pigmenting hormones, 513–514 pigmenting pityriasis alba, 699–700 pigmentophages, 766 pigments, see specific pigments pigment type switching, 395–409, 396, 415–416 accessory proteins, 401–403 agouti protein (see agouti protein) cats, 404–405 dogs, 405 genetic variation and, 395, 401, 404–405 historical background, 395–397 melanocortin signaling, 399, 403 tyrosinase activity vs. cysteine levels in, 397–399, 398, 403 pilar neurocristic hamartoma, 1157–1162 animal models, 1161 associated disorders, 1158, 1160 clinical description, 1158, 1159, 1160 differential diagnosis, 1160–1161 epidemiology, 1158 histology, 1159, 1160 laboratory findings, 1160 malignant transformations, 1158, 1160, 1161 pathogenesis, 1161 treatment/prognosis, 1161 pilomatricomas, myotonic dystrophy, 661 PIMSF, 438, 440, 440 pineal gland, adaptation to darkness, 33–34 pink-eyed dilution (p) gene, see P protein pinta, 687–688 pintids, 686 pituitary, see also specific hormones control of color change (nonmammalian), 12–13, 28–30, 32–33 melanogenesis regulation, lower vertebrates, 194 tumors, Carney complex/myxoma syndrome, 857, 858 pityriasis alba, 699–701 clinical description, 699–700, 700, 750 diagnosis/differential diagnosis, 700–701 vitiligo vulgaris vs., 571 epidemiology, 699 histology, 700, 750 history, 699 laboratory examination, 750 pathogenesis, 700–701 pigmenting, 699–700 treatment, 701 pityriasis alba faciei, see pityriasis alba pityriasis corporis, see pityriasis alba pityriasis impetigo furfuracea, see pityriasis alba pityriasis lichenoides, 703–704 achromic, 703–704 acute (guttate parapsoriasis), 703 chronic (Mucha–Habermann disease), 703 hypopigmentation, 703–704, 704 pityriasis sicca faciei, see pityriasis alba pityriasis simplex faciei, see pityriasis alba pityriasis streptogenes, see pityriasis alba pityriasis versicolor, 750 Pityrosporum orbiculare (ovale), 571, 692 Pityrosporum, progressive macular hypomelanosis, 749 PKA holoenzyme, Carney complex/myxoma syndrome, 853 plaque morphea, 967 platelet-derived growth factor receptor-a (Pdgfra), 126, 141, see also KIT (Kit) gene/protein platelets (reflecting), 18–19, 19, 20, 42 avian eye color, 98, 98 malignancy, 50 platinum-induced skin discoloration, 1030 platyfish-swordtail hybrid, melanoma, 454–455, 1133 “plerodeles blue,” 22, 32 plexiform neurofibromas, 812, 812 plumbism, 1033, 1033, 1081 Pmel-17 gene/protein, 155–157, 252, 261, 269–270, 529 “pocket proteins,” in melanoma, 454 POEMS syndrome, 951–954 clinical features, 952, 952–953 epidemiology, 951–952 pathogenesis, 953
poikiloderma, 782, 783, see also specific types poikiloderma atrophicans, see Rothmund–Thomson syndrome poikiloderma congenitale, see Rothmund–Thomson syndrome poikiloderma of Civatte, 500, 959, 959–961 poikiloderma vasculare atrophicans, 973, 974 poikilotherms, 12 dermal melanophores(cytes), 17 pigmentation patterns, 42–48 point mutations, KIT gene, 142 poliosis, 527, 654 polychlorinated biphenyl-induced skin discoloration, 1047 polyglandular disease, vitiligo vulgaris, 564–565 polyneuropathy, organomegaly, endocrinopathy, M protein and skin changes, see POEMS syndrome polyostotic fibrous dysplasia, 817 polyps Cronkhite–Canada syndrome, 984 Peutz–Jeghers syndrome, 1000, 1001 porphyria cutanea tarda (PCT), 979–983 animal models, 982 associated disorders, 980–981 clinical findings, 979–980, 980 diagnosis/differential diagnosis, 981 epidemiology, 979 histology, 981 laboratory findings, 981 pathogenesis, 981–982 treatment, 982 type I (sporadic), 979, 981 type II (familial), 979, 981–982 port wine stain, 506, 1070 histopathology, 1070 intraoral, 1070 nevus anemicus association, 767 phakomatosis pigmentovascularis, 1013 postinflammatory hyperpigmentation, acne, azelaic acid treatment, 1167 postinflammatory hypopigmentation pityriasis lichenoides, 703–704, 704 psoriasis, 701, 701–702 post-kala-azar dermatosis, 696–697 postzygotic mutations, hypomelanosis of Ito, 640, 642 POU3F2 (BRN2; N-Oct3), 248 P protein, 163, 230, 270 evolution, 235 human skin color variation and, 237 mouse gene (pink-eyed dilution (p) gene), 231–232 mutations, 230, 234–235 oculocutaneous albinism, 528, 606 Prader–Willi syndrome, 629 structure and function, 232–233, 236 transporter homologies, 233 Prader–Willi syndrome (PWS), 620, 620–621 genetic mutation, 629 P protein and, 235 prednisone, vitiligo vulgaris, 577 pregnancy acanthosis nigricans, 908 human skin color and, 513, 513 melanocytic nevi development, 1126 pigmentary demarcation lines, 515, 881 premature aging, ataxia telangiectasia, 621 premature infants, skin color, 511 premelanosomes, 155–157, 159–162, see also melanosome biogenesis prenatal diagnosis KIT gene mutations, 142 neurofibromatosis, 815 primary autoimmune cholangitis, see primary biliary cirrhosis (PBC) primary biliary cirrhosis (PBC), 992–995 animal models, 994 associated disorders, 992 clinical features, 992, 993 diagnosis/differential diagnosis, 993 epidemiology, 992 histology, 992–993 laboratory findings, 993 pathogenesis, 994 prognosis, 994–995 treatment, 994 primary biliary hepatitis (PBH), see primary biliary cirrhosis (PBC)
primary cortical nodular dysplasia, 857, 858 primary pigmented nodular adrenal disease, 857, 858 primates (nonhuman) hair color, 71–72, 74 graying patterns, 71, 71 juvenile coat colors, 76 melanin pigmentation of skin, 74 tylotrich follicles, 70 Pringle disease, see tuberous sclerosis complex (TSC) PRKKAR1A gene mutation, Carney complex/myxoma syndrome, 853, 1073 progeria, 792, 886–888 adult, see Werner syndrome clinical findings, 886–887, 887 differential diagnosis, 885, 887 histology, 887 laboratory investigations, 887 pathogenesis, 887–888 progeroid syndromes, with hyperpigmentation, 792 progesterone melanocytic nevi development, 1126 melanogenesis regulation, 195 progressive cardiomyopathic lentiginosis syndrome, see LEOPARD syndrome progressive idiopathic atrophoderma, see atrophoderma of Pasini et Pierini progressive macular hypomelanosis, 748–751 clinical features, 748–749, 749 diagnosis/differential diagnosis, 749–750, 750 histology, 749 historical background, 748 laboratory findings/investigations, 749 pathogenesis, 750 prognosis/treatment, 750 progressive systemic sclerosis, blue macules, 1018 prolidase deficiency, 662–663 proliferative neurocristic hamartoma, 1157–1158 promontory sign, 1071 proopiomelanocortin (POMC) congenital deficiency, 404 melanogenesis regulation, 399, 414–415 lower vertebrates, 194 mammals, 195–196 Propionibacterium acnes, progressive macular hypomelanosis, 750 prostaglandins human melanocyte regulation, 413 ocular pigmentation, 96 protease-activated receptor 2 (PAR-2), 678 proteasomes, melanogenesis regulation, 200 proteinase-activated receptor-2 (PAR-2) activation, 178 induction by UVR, 413 protein folding, 218, 233 protein interactions, tyrosinase-related proteins, 222 protein kinase C (PKC), melanocyte proliferation role, 446, 450–451 protein malnutrition, kwashiorkor, 664–665 protein sorting, tyrosinase-related proteins, 158, 158–159, 199, 222 protein tyrosine kinases (PTKs), melanoma and, 479 proton pumps, 163, 200, 233, 236 psammomatous melanotic schwannoma, 857, 858, 860, 1073 pseudoatrophic macule, 812 pseudocatalase, 580, 1185 pseudo-Hutchinson sign, 1062, 1062, 1063, 1064 “pseudomelanoma change,” lichen sclerosus, 1087 Psoralea, 1175 psoralens, 379, 950, 1175 hypermelanosis due to, 950, 950 phototherapy, see psoralens and ultraviolet light A (PUVA) phytophotodermatitis, 948 structure, 1175 systemic, vitiligo vulgaris, 580–582 topical, vitiligo vulgaris, 580 psoralens and ultraviolet light A (PUVA), 379 carcinogenicity, 582 children, 1175–1176, 1176, 1177 hypopigmentation treatment, 1170
1223
INDEX lentigines, 830, 830, 832, 833, 834 mechanism of action, 379, 1180 melanoma-induction, 582 mycosis fungoides, 976–977 oral, 1175–1178 contraindications, 1175 high-dose, 1176 low-dose, 1176, 1177 precautions, 1177 side effects, 1177–1178 vitiligo, 1175 psoralens, 1175 repigmentation permanence, 1179 results, 1176, 1177, 1179–1180, 1180 hair color, 1179–1180, 1180 lesion site, 1179–1180 topical, 1178–1179 adverse reactions, 1178–1179 application, 1179 children, 1179 initial dose, 1179 photosensitivity, 1178 vitiligo, 1178, 1178 vitiligo vulgaris, 580–582, 581, 1175 dosage, 581 psoriasis, 701, 701–702, 870 psychotropic drug-induced skin discoloration, 1043–1044 PTEN gene/protein Bannayan–Riley–Ruvalcaba syndrome, 867–868 Cowden syndrome, 867 melanoma and, 472, 480–481 pteridine pigments, 19, 21 autonomy, 21–22 biosynthesis, 21, 23 mutants, 21, 25 pterinosomes, 19, 22, 24 pterorhodin, phyllomedusine frogs, 17, 17, 18 PTPN11 gene, LEOPARD syndrome, 843 pulmonary fibrosis, Hermansky–Pudlak syndrome, 615 pulmonary hemosiderosis, 990 pulmonary valvular dysplasia, LEOPARD syndrome, 845 pulsed tunable dye laser (PDL), poikiloderma of Civatte, 960 punch biopsy, nail, 1064 purines, iridophores, 18 putrefaction, technique, 6 PUVASOL, leukoderma punctata, 729, 731 PUVA therapy, see psoralens and ultraviolet light A (PUVA) pyridine-2,3,4,6-tetracarboxylic acid, 297, 297 pyridoxine, homocystinuria, 626 pyrimidine dimers, 344, 347–348 pyrrole-2,3-dicarboxylic acid (PDCA), 282, 296, 296 pyrrole-2,3,5-tricarboxylic acid (PTCA), 282, 283, 296, 296, 299, 300, 535 Q-switched alexandrite laser, 1200–1201 speckled lentiginous nevus, 1108 Q-switched lasers, 1198–1201, see also specific types speckled lentiginous nevus, 1108 Q-switched Nd:YAG laser, 1199–1200 speckled lentiginous nevus, 1108 tattoo removal, 1199, 1199, 1200 Q-switched ruby laser, 1198–1199 café-au-lait macules, 1199 dark skin types, 1199 nevus of Ota, 1199 speckled lentiginous nevus, 1108 tattoo, 1199 quantum mechanics, melanins, 315, 318 quinacrine-induced skin discoloration, 1042 quinine ototoxicity, 376 skin discoloration, 1042 quinone detoxification pathway, 367 QX-572, 378, 378–379 Rab27A gene/protein, 618 Griscelli syndrome, 162, 174, 618 melanosome biosynthesis, 162 melanosome trafficking, 174–175, 175 Rab GTPases melano-phagolysosome processing, 187
1224
melanosome biogenesis, 162 melanosome trafficking, 174–175 melanosome transfer to keratinocytes, 177 Rac GTPases, melanosome trafficking, 171 racial (physiologic) pigmentation, see ethnicity radial growth phase (RGP) melanoma, 473, 473, 482, 489 dermal invasion, 490 radiation lentigo, 830, 833 radicalism in mammalian pigmentary system evolution, 76–78 radiodermatitis, chronic, depigmentation, 684 radiodermatitis, depigmentation, 684 radiometric assays, 272, 273 radionuclide labeling, 380 RAF mutations, melanoma, 479–480, 492 Raper–Mason pathway, 262–277, 263, 284, 284–285, 342, see also melanogenesis; specific enzymes RAS mutations melanocytic nevi, 1115 melanoma, 453, 479–480, 492 Rayleigh (Tyndall) scattering, 1026 RB (retinoblastoma) gene/protein functions, 475, 475 in melanoma, 454, 475, 477, 478 reactive oxygen species (ROS), see free radicals Recklinghausen disease, clinical manifestations, 743 recombinant interferon-a, carcinoid syndrome, 921 RECQL2 gene, Werner syndrome, 896 RECQL4 gene, Rothmund–Thomson syndrome, 806 red hair phenotype, 69, 415 epidermal melanocytes and, 66 kwashiorkor and, 665 MC1R mutation, 1127 melanocytic nevi association, 1127 redox reactions/agents, 677–678 L-dopaquinone, 365–366 melanins, 311, 324, 327–329 Reed, Alexander, 6 Reed’s nevus, see pigmented spindle cell nevi Reed’s pigmented spindle cell nevus, see pigmented spindle cell nevi reflectance mode confocal microscopy (RCM), 533 reflective spectrophotometry, 533–534 refractosome, 19 renal disease, tuberous sclerosis complex, 656 renal hemosiderosis, 990–991 replicative senescence, 464, 467, 467–468 reptiles, see also specific types chromatophores, 108 iridosarcoma, 50 mammal evolution from, 63–64, 76–77 neural crest and chromatophore development, 119 resorcinol-induced skin discoloration, 1041 resveratrol, 676 rete mucosum, 6–8 RET gene mutations, 146–147, 448 reticulated acropigmentation of Dohi, 799–802 associated disorders, 800 clinical findings, 799–800, 800 diagnosis/differential diagnosis, 800–801, 801 pathology/pathogenesis, 800, 801 reticulated acropigmentation of Kitamura, 802–804, 914 clinical findings, 802, 802–804 diagnosis/differential diagnosis, 803 differential diagnosis, 803 genetics, 802 histology, 803 pathogenesis, 804 reticulated black solar lentigo, 830, 831, 833 reticulated pigmented anomaly of the flexures, see Dowling–Degos disease retina, see also entries beginning retino-/retinal anatomy, 93 drug-induced toxicity, 375–376 pink-eyed dilution (p) gene and, 231–232, 232 retinal anlage tumor, see melanotic ectodermal tumor of infancy retinal choristoma, see melanotic ectodermal tumor of infancy retinal pigment epithelium (RPE), 242, 558 age-related changes, 468, 513
albinism and, 92–93, 601–602 anatomy/structure, 93, 93–94, 95, 96, 97 chloroquine and, 375, 375–376 development, 91–92, 242, 252 melanocytes, see retinal pigment epithelium (RPE) melanocytes melanosomes, 312 optical properties, 320 in premature infants, 511 transcription factors, 252–253 retinal pigment epithelium (RPE) melanocytes, 91 aging/senescence, 468, 513 anatomy/morphology, 93–94 variation in, 97–98 development, 91–93 differentiation, 92 functions, 94–95 retinoblastic teratoma, see melanotic ectodermal tumor of infancy retinoic acid, 199, 367, 678 retinoids confluent and reticulated papillomatosis, 923 topical, hyperpigmentation disorders, 1167–1169 xeroderma pigmentosum, 892 retrotransposons, hypomelanosis of Ito, 642 rheumatoid arthritis, 939–941, 1032, 1032 RhoB gene, 83 Rho GTPases, 83 melanosome trafficking role, 171, 172 rickets, phakomatosis pigmentokeratotica, 1104 Riehl’s melanosis, 438, 961–963 clinical findings, 961, 961 differential diagnosis, 962 histopathology, 961–962 HIV, 944 paracrine interactions, 437–440, 439, 440, 441, 441 pathogenesis, 962 rifabutin, hyperpigmentation-induction, 943 rifampicin in leprosy, 692 skin discoloration due to, 1047 Riley–Smith syndrome, see Bannayan–Riley–Ruvalcaba syndrome (BRR) Riolan, Jean, 5 river blindness, see onchocerciasis Rothmund–Thomson syndrome, 804–808 clinical features, 783, 785, 805, 805–806 diagnosis/differential diagnosis, 806–807, 807 histology, 806 laboratory investigations, 806 management/treatment, 807 pathogenesis, 807 Rozycki syndrome, 551 RPE1 (Silver/Pmel17), 155–157 ruby eye (ru) locus, 616 Rush, Benjamin, 9 Ruvalcaba–Myhre–Smith syndrome, see Bannayan–Riley–Ruvalcaba syndrome (BRR) Ruvalcaba–Zonana–Smith syndrome, see Bannayan–Riley–Ruvalcaba syndrome (BRR) Ruvalcaba–Zonana syndrome, see Bannayan–Riley–Ruvalcaba syndrome (BRR) sacral spot of infancy, see Mongolian spot salamanders chromatophore development, 115–119 color change, 14 light perception in high vs. low albedo environments, 33 neural tube, 116 sandy (sdy) locus, 616 sarcoidosis, 751–753 associated disorders, 752 clinical description, 751–752, 752 diagnosis/differential diagnosis, 753 epidemiology, 751 histology, 752 laboratory findings/investigations, 752 macular hypopigmentation, 571 pathogenesis, 753 prognosis/treatment, 753
INDEX scalp melanocytic nevi, 1116–1120 vitiligo vulgaris, 554, 555 scatter factor, see hepatocyte growth factor (HGF) schwannomas, Carney complex/myxoma syndrome, 855–856, 857, 858, 860 sclera, anatomy, 93 scleroderma, localized, see morphea scleromyxedema, associated hyperpigmentation, 965 sclerosing hemangioma (dermatofibroma), 433–435 sclerotherapy, hyperpigmentation, 1029 Scytalidium dimidiatum, 1061 seasonal variation in pigmentation, 75 seborrheic keratosis, 708, 965, 966, 967 clinical features, 910–911 histology, 967 paracrine interactions, 440, 441, 441 ET-1/ETB receptors, 425–427, 426 Seckel syndrome (bird-headed dwarfism), 657–658 sectorial neurofibromatosis, see segmental neurofibromatosis segmental lentiginosis, see agminated lentigines (AL) segmental morphea, 967 segmental neurofibromatosis, 819–820 agminated lentigines, 867 clinical features, 532, 813, 819, 819 epidemiology, 819 histology, 819 pathogenesis, 820 prognosis/treatment, 820 speckled lentiginous nevus, 1104 segmental nevus spilus, see speckled lentiginous nevus segmental vitiligo, 500–501 segmented heterochromia, iron deficiency anemia, 666 sella turcica, centrofacial lentiginosis, 839 semiconductors, melanin as, 320–322 semimetal-induced skin discoloration, 1034–1035 senescence, see also age/aging associated heterochromatic foci, 468 melanocytes, 464–471, 475 senile purpura, 990 sensorineural hearing loss LEOPARD syndrome, 844 Waardenburg syndrome, 544 serotonin, carcinoid syndrome, 920 Sertoli cell tumors, Carney complex/myxoma syndrome, 858 sex hormones color change (nonmammalian) and, 32 melanocyte regulation, 416–417 melanogenesis regulation, 195 skin color and, 71, 513, 513–514 “threshold theory” and, 82 Sézary syndrome, 973 shagreen patch (connective tissue nevus), 653, 653 Shah-Waardenburg syndrome, see Waardenburg syndrome type 4 (WS4) “Shiro bito,” 551 siderophages, oral mucosa, 1070 siderosis, secondary, 988 Siemens–Bloch pigmented dermatosis, see incontinentia pigmenti (IP) Siemens syndrome, 790 Siemerling–Creutzfeldt disease, 771–774 signaling mechanisms, see also specific pathways chromatophores, 26 melanocytes aging, 466, 466–467 development, 83, 450–451 proliferation and differentiation, 445–463, 449 melanoma cells, 450–454, 451, 474–476, 475, 478–480, 480, 492 FGF2 role, 451–453 signature nevus, 1112 Silver gene, see Pmel-17 gene/protein silver-induced skin discoloration, 1030, 1030–1032, 1031 silver nitrate stains, 534
Silver–Russell syndrome, 820–822 Sinclair swine model, vitiligo vulgaris, 576 Sipple syndrome, amyloidosis and, 926 skeletal abnormalities Becker nevus, 916 dyskeratosis congenita, 898 hypomelanosis of Ito, 638–639 LEOPARD syndrome, 844 Menkes’ kinky hair syndrome, 631–632 Rothmund–Thomson syndrome, 805, 805 skin aging/senescence, 465 chromophores, 343–344 color, see skin color depigmented inflammatory response, 564 physiologic functioning, 564 development melanoblast migration, 82 structural/functional organization, 82 drug-binding to melanin(s), 374–375 evolutionary role, 76 human, see human skin intercellular communication, 342 melanogenic paracrine network, 421, 422 turnover, acceleration, 678 skin cancer, see also specific types immunosuppression and, 349 pigmentation relationship, 345 UVR relationship, 342, 345, 349 skin color, 499, see also melanin; melanin pigmentary system (mammalian) constitutive (CSC), 65–67, 410–412, 507 contributing factors, 500 development, melanoblast migration, 82 facultative (FSC), 65–67, 507 hemoglobin role, 64, 70–71 histological basis, 65–67 human, see human skin color image analysis, 533 melanin role, 70–71, 342 nonhuman primates, 74 mandrill (Mandrillus sphinx), 70–71 physics of, 500 skin myxomas, Carney complex, 855 skin types (human), 506–507, 507 DNA repair and, 411, 412 melanin photobiology and, 344–345, 345, 508–509 physical properties, 509–510 tanning response and, 410, 412 variation in eumelanin:pheomelanin ratios, 412, 506–507 SKT11 gene, Peutz–Jeghers syndrome, 1076 slaty locus, see tyrosinase-related protein-2 (TYRP-2) SLEV1 gene, vitiligo vulgaris, 574 Slit proteins, avian melanocyte morphogenesis, 120–121 SLUG (SNAI2) gene mutation mammalian pigmentary system development, 83 piebaldism and, 142, 543–544 Waardenburg syndrome type 2D, 145, 544 Smith, Samuel Stanhope, 7, 9 smoker’s melanosis, 1079 smooth muscle hamartomas (congenital Becker nevus), 915, 916 Smyth chicken model, vitiligo vulgaris, 577 snake, iridosarcoma, 50 SNAP proteins, melanosome biosynthesis, 162 SNARE proteins melano-phagolysosome processing, 187 melanosome biosynthesis, 160–161, 162 melanosome transfer to keratinocytes, 177 sodium–hydrogen exchangers, 163, 236 sodium nitrate, skin discoloration, 1048 sodium stibogluconate, post-kala-azar dermatosis, 697 sodium thiosulfate, tinea versicolor, 694 solar lentigo, 830–831, 832 solar radiation, see ultraviolet (UV) radiation soles, vitiligo vulgaris, 553–554, 554 somatostatin, carcinoid syndrome, 921 SOS response, 349 SOX10 (Sox10) gene/protein, 247 avian melanocyte specification, 122 fish chromatophore differentiation, 113, 114 MITF and, 247
PAX3 and, 144 Waardenburg syndrome type 3 (WS3), 145 Waardenburg syndrome type 4 (WS4), 146, 247, 545–546 soybean trypsin inhibitor (STI), 678 speckled lentiginous nevus, 515, 869, 870, 1098–1112 associated disorders, 1101–1104 background hyperpigmentation, 1100, 1101, 1102 blue nevi, 1105 clinical features, 1101, 1102 as congenital melanocytic nevus subtype, 1099–1100, 1100 diagnosis/differential diagnosis, 1105–1106, 1106 epidemiology, 1099–1100 eyelids, 1101 histology, 1104–1105 historical background, 1098–1099 hybrid lesions, 1100 laboratory findings/investigations, 1105 lines of Blaschko, 1100, 1102 melanoma development, 1101–1102, 1103, 1105 misdiagnosis, 1100, 1102 pathogenesis, 1106–1107 prognosis, 1108 shape, 1100 terminal hair, 1100, 1101 treatment, 1107–1108 speckled lentiginous nevus syndrome, 1104 speckled nevus (spilus), see speckled lentiginous nevus speckled zosteriform lentiginous nevus, see speckled lentiginous nevus spectrophotometry enzyme assay, 271, 272, 273, 274, 275 melanin analysis, 298, 302–303, 315 sphingosine, 673 spitzenpigment, see acromelanosis progressiva Spitz nevus, pigmented spindle cell nevi vs., 1096 splotch mutant, see PAX3 (pax3) gene/protein sporadic porphyria, see porphyria cutanea tarda spotted grouped pigmented nevus, 1106, 1106 spotting heart disease, see LEOPARD syndrome spotty nevus, see speckled lentiginous nevus squamous cell carcinoma in situ (SCCIS), 1085 Staphylococcus aureus, pityriasis alba, 700 status dysraphicus, centrofacial lentiginosis, 838–839 steel factor (SLF), see stem cell factor (SCF) steely hair disease, see Menkes’ kinky hair syndrome Steinert–Curschmann disease (myotonic dystrophy), 660–661 stem cell factor (SCF) fibroblast–melanocyte interactions, 433–437 café-au-lait macules, 435–437 dermatofibroma, 433–435, 434 mastocytosis, 434–435 keratinocyte–melanocyte interactions, 427–433 lentigo senilis, 430, 430–431, 431 in UVB melanosis, 423, 424, 427–430, 428, 429, 430 vitiligo vulgaris, 431–433, 432, 433 mammalian melanocyte development, 83–85, 124, 427 as melanocyte mitogen, 446, 447, 491 membrane-bound (mSCF), 421, 427–433 receptor (see KIT (Kit) gene/protein) soluble (sSCF), 421, 433–437 urticaria pigmentosum, 958 stem cells, melanoma, 489–490 steroid hormones, see also corticosteroids; sex hormones; specific steroids color change and, 32 melanocyte regulation, 416–417 strawberry nevi, 1069–1070 stress, vitiligo vulgaris, 563 stria, hypopigmented, UVB phototherapy, 1185–1186 stria vascularis, 99, 560 strimmer rash (string trimmer dermatitis), see phytophotodermatitis stromal-derived factor 1a (sdf1a), fish chromatophore morphogenesis, 111–112
1225
INDEX styphnate hexanitrodiphenylamine, skin discoloration, 1048 subcutaneous neurofibromas, 812 subungual hematoma, 1061 subungual tumors, incontinentia pigmenti, 875 suction blister grafts, 1191–1192 sunbed lentigines, 832–833 sunburn, see also erythema amyloid deposits, 925–926 freckles, 831 isomorphic response, 562–563 sun, emission spectra, 343–344, see also ultraviolet (UV) radiation sun exposure atypical nevi, 1127 halo nevi, 705–706 lentigo induction, see lentigo senilis et actinicus pityriasis alba, 700 sun protection factor (SPF), 508, 1188 sunscreens, 508, 1188–1190 melanocytic nevi, 1121 oral PUVA, 1177 potency, 1188 suntans, see tanning superficial spreading melanoma (SSM), 473 superoxide radicals, 330–331, 332–333, 345 suprarenal insufficiency, see Addison disease surgical treatment of pigmentary disorders, 1191–1197, see also specific techniques Sutton nevus, see halo nevi Swiss syndrome, see Carney complex/myxoma syndrome swordtails, melanoma, 454–455, 1133 sympathetic ophthalmia, 738 symptomatic cutaneous porphyria, see porphyria cutanea tarda symptomatic porphyria, see porphyria cutanea tarda synapsids, 76–77 syndrome myxoma, see Carney complex/myxoma syndrome syphilis (secondary), 689 leukoderma, 688–689, 689, 1083 vitiligo vulgaris vs., 571 T4 endonuclease, xeroderma pigmentosum, 892 tacrolimus UVB phototherapy and, vitiligo vulgaris, 1185 vitiligo vulgaris, 580 tanning, 1188, see also facultative skin color (FSC) delayed, 1188 immediate pigment darkening, 1188 variation in ability to, 504, 507–508, 508 targetoid hemosiderotic hemangioma, 990 tar-induced skin discoloration, 1048 tar melanosis (melanodermatitis toxica), 1048 tattoos, 1035–1036, 1036, 1037 ablation, 1035–1036 amalgam, 1080, 1080–1081 colors, 1035 granulomatous reactions, 1035, 1037 laser treatment, 1198, 1199, 1199, 1200 traumatic, 1035 Tay syndrome, 868 T cells halo nevi pathogenesis, 710 vitiligo pathogenesis, 544 teeth, minocycline-induced discoloration, 1039, 1040 telangiectasia macularis eruptiva perstans, 956 teleost fish, see also individual species chromatophores, 15, 19, 108, see also specific types development, 109–115 differentiation, 113–115 light sensitivity, 35 morphogenesis, 111–113 mutants, 47, 113, 114, 115 pigment retention, 110 color pattern formation, 45–47, 47 erythrophoroma, 48, 49, 49 differentiation, 49–50, 51 tellurium toxicity, 1034–1035 telomerase, melanoma genetics, 482
1226
telomeres lengthening, in melanoma, 482 replicative senescence, 464 temperature-sensitive oculocutaneous albinism (OCA), 605 temporary threshold shift (TTS), albinism, 602 TEP1 gene, see PTEN gene/protein TERC gene, dyskeratosis congenita, 899 terminology, 499–503 4-tertiary butylphenol, 675 testicular tumors, 855, 857, 858, 859 treatment, 860 testosterone, 667 tetracosactide (ACTH), hyperpigmentationinduction, 943 tetracycline(s), skin discoloration and, 1039–1040 tetrahydrobiopterin, vitiligo vulgaris, 575 tetryl, skin discoloration, 1048 T helper cells (Th) melanocytic neoplasia-associated hypomelanosis, 716 melanoma-associated depigmentation, 719 melanoma regression, 717 thermal burns, depigmentation, 683, 683–684 thermoregulation, mammalian evolution, 77 thiazole-2,4,5-tricarboxylic acid (TTCA), 282, 297, 297 thiazole-4,5-dicarboxylic acid (TDCA), 297, 297 thiazolidines, melanogenesis inhibition, 367 thioctic acid (a-lipoic acid), 678 thiol compounds, 363–364, 397 thioredoxin, vitiligo vulgaris, 575 thioridazine, retinal toxicology, 375 2-thiouracil, 381 dopaquinone conjugation, 368–369, 369 melanoma targeting, 380, 382 thioureylenes, 381 incorporation into melanin, 368–369 melanoma targeting, 380–383, 381 “threshold theory,” 82 thumb deformity, and alopecia, 904 thymine dimers, melanogenesis induction, 348–349 thymomas, vitiligo vulgaris, 572 thyroid amphibian morphogenesis role, 117 color change (nonmammalian) and, 32 dysfunction, vitiligo vulgaris, 565–566, 566 tumors, Carney complex/myxoma syndrome, 857 thyroxine amphibian morphogenesis, 117 color changes and, 32 Tietz syndrome (albinism–deafness syndrome), 245, 546, 546–547, 630–631 tinea capitis, pigmenting pityriasis alba, 700 tinea versicolor, 692–694 diagnosis/differential diagnosis, 571, 694 electron microscopy studies, 693 epidemiology, 692–693 histology, 693 hypopigmentation, 692, 693 pathogenesis, 693–694 treatment, 694 tinnitus, management, 378, 378–379 tissue plasminogen activator (tPA), melanocyte transplantation, 1194–1195 toasted skin syndrome, see erythema ab igne a-toc, 677 a-tocopherol ferulate (a-Toc-F), 677 toenail plate, orange-brown staining, iron induced, 1030 toxicology, 354–394 melanin, 371–383 melanogenesis, 358–371 TP53 gene, see p53 gene/protein transcriptional control, see also specific genes/proteins historical background, 242–243 melanomas, 452–453 pigment cell development, 243–248 tyrosinase gene family, 218–219, 220, 248–253
transcription factors mammalian pigmentary system development, 83, 450 MITF (see MITF (mitf) gene/protein) tyrosinase gene family control, 218–219 transferrin saturation testing, hereditary hemochromatosis, 988 transgenic mic, melanocytic nevi models, 1135–1136 transient acantholytic dyskeratosis (Grover disease), 649 transient neonatal pustular melanosis, 905–906, 906 transient receptor potential 7 (trmp7), 111 transporter proteins, 230–241, see also specific proteins trauma depigmentation, 684 hemosiderosis, 990, 990 idiopathic guttate hypomelanosis, 728 melanocytic nevi, 1121, 1125, 1125 melanonychia, 1061 oral hyperpigmentation, 1070 tattooing, 1035 thermal burns, depigmentation, 683, 683–684 Treacher Collins syndrome (mandibulofacial dysostosis), 660 Treponema carateum, 686 Treponema endemicum, 688 Treponema pallidum, 686 Treponema pertenue, 686 treponematoses, 686–689, see also individual diseases/disorders tretinoin (all trans retinoic acid; ATRA) combination therapy, 1169 hyperpigmentation disorders, 1167–1169 inflammation–induction, 1168 mechanism of action, 671, 673 melasma, 1168, 1168 melasma treatment, 1022 postinflammatory hyperpigmentation, 1168–1169 side effects, 1168–1169 trichochromes, 288, 288, 288–289 degradation, 297 isolation, 289 melanosis from melanoma, 1024 tricho-oculo-derma-vertebral syndrome, 903 tricho-odonto-onycho-dermal (TOOD) syndrome, 904 tricho-odonto-onychodysplasia, 903 tricho-onycho-hypohidrotic ectodermal dysplasia, 904 Trichophyton rubrum, melanonychia, 1061 Trichophyton sousanense, nail pigmentation, 1061 trichopoliodystrophy, see Menkes’ kinky hair syndrome tricho-rhino-phalangeal syndrome, 903 trichrome vitiligo, 553, 554, 554 tricyclic antidepressant-induced skin discoloration, 1044 triiodothyronine, color changes and, 32 TriLuma®, melasma treatment, 1022, 1169 2,5,6-trimethyl-para-hydroxy-methoxybenzene, 675 4,5¢,8 trimethylpsoralen (TMP), 1175 trimethylpsoralens, 1175 vitiligo vulgaris, 580 trinitrotoluene, skin discoloration, 1048 “tripe palms,” 909 triploidy, hypomelanosis of Ito, 639 triquin, fixed-drug reactions, 934 trisomy 21 (Down syndrome), 658–659 TrisoralenTM, 1175 tristimulus colorimeters, 533 Troisser–Hanot–Chauffard syndrome, see hemochromatosis, hereditary TYRPs (tyrosinase-related proteins), see tyrosinase gene family; specific proteins TYRPS1 gene, tricho-rhino-phalangeal syndrome, 903 L-tryptophan, 264 TSC1 gene, tuberous sclerosis complex, 652 TSC2 gene, tuberous sclerosis complex, 652
INDEX tuberculoid leprosy, 689, 690 tuberin, 652 tuberous sclerosis complex (TSC), 652–656 ash leaf macule (hypomelanotic macule), 531, 651, 653, 654, 654 clinical manifestations, 652–653, 653, 743 cutaneous, 653–654, 747 diagnosis/differential diagnosis, 653, 655 epidemiology, 652 genetics, 652 historical background, 652 laboratory findings/investigations, 655 macules, 638 pathogenesis, 655 pathology, 654–655 pigmentary disorders, 653–654 prognosis/treatment, 655–656 Tu melanoma locus, 454 tumor-infiltrating lymphocytes (TIL), melanoma regression, 717 tumor necrosis factor-a (TNF-a) endothelin induction, 426–427 human melanocyte regulation, 413 induction by UVR, 412 tumors, see malignancy “tumor stem cells,” 489–490 twin spotting (didymosis), 1015, 1107, 1107, 1130 twin studies, melanocytic nevi, 1128–1129 tylotrich follicles, 70, 82 Tyndall (Rayleigh) scattering, 1026 typus maculatus of Mendes da Costa, see Mendes da Costa syndrome tyrosinase, 157, 191–192, 199, 217–219, 242, 249–250, 261, 265–267, 354, 355, 360 acidity and, 200 biochemical control of, 366 in control of melanogenesis, 287, 397, 403 enzyme reactions, 217–218, 261, 262, 262–263, 364, 364–368 assay, 271, 272, 274–275 cytotoxicity and, 366–367, 368 L-dopa oxidation, 262, 263, 266, 272, 274, 274–275 mechanism of action, 265–266, 266, 365, 365 rates, 364 tyrosine hydroxylation, 262, 263, 265, 271, 272, 274, 274 evolutionary conservation, 249, 361 gene structure, 218, 249, 250 historical background, 213–214, 262, 282 inhibition, 673–677 competitive/noncompetitive, 674–676 copper-binding agents, 361, 361–362 shift to pheomelanin synthesis, 676 thiols, 363–364 melanoma marker, 294 mutations, 223–224 oculocutaneous albinism, 605 post-transcription control, 362–363, 676–677 proteasomal regulation, 200 senile canities, 761 structure, 360 active site, 217–218, 261, 265, 356, 361–362 carboxyl sites, 361 glycosylation, 362–363, 673 protein folding/maturation, 218, 233, 363 substrate availability and, 198, 367 substrate specificity, 360–361 targeting to melanosome, 230 transcriptional control, 218–219, 246, 249–250, 671, 673 vitiligo vulgaris and, 573 tyrosinase gene family, 213–229, 242, 248–249, 267, see also specific genes/proteins evolution, 215 historical background, 213–214 invertebrates, 214–215 lower vertebrates, 215 pH and, 162–163 pigmentation disorders and, 214, 222–224 protein interactions, 222, 261, 269, 277 protein sorting/trafficking, 157–159, 158, 164, 199, 222, 232 sequence similarity, 215, 215–217, 216 structural similarity, 217, 217 structure, 157
transcriptional regulation, 248–253 common elements, 221–222 tyrosinase pseudogene, 215 tyrosinase pseudogene (TYRL), 215 tyrosinase-related protein-1 (TYRP-1), 219–220, 242, 250–251, 261, 267 amino acid sequence, 216 avian melanocyte specification, 122 enzyme reaction, 219, 267 evolution, 215 gene structure, 215, 215, 219–220, 250–251, 267 historical background, 214 late eumelanogenesis, 291, 292 melanocytic nevi, 1113 mutations, 220 OCA type 3 and, 214, 222, 606–607 nail melanocytes, 1057 pheomelanogenesis and, 197 protein sorting, 158, 158–159 protein structure, 250, 251 synthesis, 157–158 transcriptional control, 220, 221, 246, 251 tyrosinase-related protein-2 (TYRP-2), 220–221, 242, 251–252, 261, 267–269, 360, 529 activity inhibition, 676 amino acid sequence, 216 homology to tyrosinase, 268 enzyme reaction, 220, 267, 282, 284 assay, 273, 275–276 mechanism of action, 268, 268 evolution, 215 expression in melanoma, 222–223 gene structure, 215, 215, 220, 251 historical background, 214 late eumelanogenesis, 291 mammalian pigmentary system development, 84, 85 metal ion binding sites, 268–269 mutations, oculocutaneous albinism type 3, 529 nail melanocytes, 1057 pheomelanogenesis and, 197 protein sorting, 158, 159 RPE development, 253 synthesis, 157–158 transcriptional control, 220–221, 251–252 tyrosinase-related proteins (TYRPs), see tyrosinase gene family; specific proteins L-tyrosine, 264 deficiency, kwashiorkor, 665 hydroxylation, 262, 263, 264, 265, 354 assay, 271, 272, 274 Tyson, Edward, 8 ulcerative colitis, 666, 995 ultraviolet A (UVA), sunscreen penetration, 1188 ultraviolet B (UVB) immunomodulatory effects, 1183–1184 melanoma risk, 473 melanosis, paracrine interactions in, 440, 441, 441 ET-1/ETB receptor interactions, 422–424, 423, 424, 425 mSCF/KIT interactions, 423, 424, 427–430, 428, 429, 430 photobiological effects, 1183–1184 phototherapy, 1183–1187 broadband, 1183 combination therapies, 1185 hypopigmented mycosis fungoides, 1185 mycosis fungoides, 976–977 narrowband, see narrowband UVB (NB-UVB) therapy postsurgical leukoderma, 1185 stria, hypopigmented, 1185–1186 UVB sources, 1183 vitiligo vulgaris, 1184–1185 solar lentigo, 833 T lymphocyte apoptosis, 1183 ultraviolet B (UVB), delayed tanning, 1188 ultraviolet C (UVC), 1188 ultraviolet (UV) photography, 533 ultraviolet (UV) radiation, see also facultative skin color (FSC); melanin photobiology; tanning; specific wavelengths chromophore absorption, 343–344
dendrite formation and, 171 DNA damage, 185 human skin and, 65, 343, 410–412, 411 idiopathic guttate hypomelanosis, 727, 728 immunosuppression due to, 349–350 induction of epidermally synthesized factors, 412– 413 mammalian melanogenesis and, 198 melanin adaptation to, 72–73 melanoma risk, 473 melanosome transfer to keratinocytes, 175–176, 177 photosensitization, 350 psoriasis treatment, 702 Riehl’s melanosis pathogenesis, 962 skin cancer, 342, 345, 349, 473 skin type, 344–345, 345, 410 tinea versicolor, hypopigmentation pathogenesis, 693 underwhite protein, see membrane-associated transport protein (MATP) unilateral lentigines, see agminated lentigines (AL) universal acquired melanosis (carbon baby), 774–776, 906, 915 upstream regulatory factor 1 (USF1), 248 urocanic acid (UCA), 350 uroporphyrinogen decarboxylase (URO-D) deficiency, 981–982 urticaria pigmentosum, 954–959 adult onset, 956 animal models, 958 of childhood, 955, 955–956 classification, 955 clinical manifestations, 955, 955–956, 957 diagnosis/differential diagnosis, 958 histology, 956, 957 historical background, 954–955 laboratory findings, 956–958 pathogenesis, 958 treatment, 958 uterine tumors, Carney complex/myxoma syndrome, 857 UVB, see ultraviolet B (UVB) uveal melanocytes, 91, 558 age-related changes, 513 anatomy/morphology, 93 variation in, 96–97 development, 91–93 differentiation, 92 ethnic variations, 95 melanoma, 96 uveal tract, 96, 96–97 melanocytes, see uveal melanocytes melanoma, 96 uveitis Fuch’s heterochromic, 96 Vogt–Koyanagi–Harada syndrome, 559, 559 uveoencephalitis, see Vogt–Koyanagi–Harada syndrome uveomeningoencephalitis (syndrome), see Vogt–Koyanagi–Harada syndrome UV light, see ultraviolet (UV) radiation vaccination-induced autoimmune “vitiligo,” 716 vacuolar proton pump, 163, 200 vagabond disease, see vagabond leukomelanoderma vagabond leukomelanoderma, 732–734 clinical description, 532, 733, 733, 733 histology, 733, 733–734 historical background, 732–733 pathogenesis, 734 Vaghbhata, 551–552 vaginal mucosa, normal color, 515–516 VAMP proteins, melano-phagolysosome processing, 187 vanilmandelic acid (VMA), 1153–1154 varicose dyschromia, hemosiderosis, 990 variegated translocation mosaicism, 896 vascular endothelial growth factor (VEGF), 953 vascularity, skin color and, 70–71 vasoconstriction, skin color, 530 Vauzeme, Roussel de, 8 venous lakes, lips, 1070, 1070, 1071 Versalius, 5 vertebrates, see also specific groups/species avian species, see birds
1227
INDEX embryology, see embryology evolution, see evolution intracellular transport, see intracellular pigment transport lower, 11 melanocyte(s), see melanophores melanogenesis, 47, 191, 193–195, 194 tyrosinase gene family, 215 mammals, see mammals nonmammalian albinism, 48, 118 color change, see color change (nonmammalian) malignancy, 48–50, 49, 51 pigment cells, see pigment cells vertical growth phase (VGP) melanoma, 473, 473, 482–483, 489, 490 very long chain fatty acids (VLCFA), adrenoleukodystrophy, 771, 772 Virchow cells, leprosy, 690 “visage mauve,” 1043, 1043 visual acuity, 601, 614 visual evoked potentials (VEPs) albinism, 601 Chediak–Higashi syndrome, 616 Prader–Willi syndrome, 620 visual pigments, photosensitive chromatophores, 35, 52 visual system, see also entries beginning oculo-/ ocular; eye(s); retina defects, see visual system abnormalities/defects development, 91–93 melanocytes, see ocular melanocytes visual system abnormalities/defects, see also specific disorders albinism, see under albinism Alezzandrini syndrome, 725 centrofacial lentiginosis, 839 hypomelanosis of Ito, 638 incontinentia pigmenti, 875 LEOPARD syndrome, 844 melanoma-associated depigmentation, 713 onchocerciasis, 695 Rothmund–Thomson syndrome, 805 Vogt–Koyanagi–Harada syndrome, 735 xeroderma pigmentosum, 890 VIT 1 gene, vitiligo vulgaris, 574 vitamin A supplements, Darier–White disease, 649 vitamin B3 deficiency, 997–998 vitamin B12 deficiency, see pernicious anemia vitamin D (and metabolites) melanocyte regulation, 416 synthesis, 72, 73, 343, 346, 509 vitiliginous amyloidosis, 925 vitiligo vulgaris (vitiligo), 370, 551–584 age of onset, 553 animal models, 576–577 associated conditions, 564–569, 565, 667 Crohn’s disease, 995 Down syndrome, 658 endocrine, 564–566 halo nevi, 558, 558, 708–709 HIV-associated, 944 lupus-associated, 703 psoriasis, 701 skin cancer, 563, 563–564 thyroid dysfunction, 565–566, 566 bilateral, symmetrical (generalized), 553, 553–556, 554 clinical features, 552–553, 730–731, see also alopecia areata cutaneous, 531, 553–557, 655, 738 hearing loss, 101, 560 mucosal depigmentation, 557–558, 558 ocular, 558–560, 559, 560, 757, 757–758 polyglandular dysfunction, 564–565 confusing terms, 500–501 counseling, 583–584 definition, 552 dermatoglyphics, 557 diagnosis/differential diagnosis, 570–572 epidemiology, 552 genetics, 552 genitalia, 555, 555, 1085–1086 hair bulb melanocyte loss, 555, 560, 560–561, see also alopecia areata heterochromia irides, 757–758
1228
histology/histopathology, 563, 569, 569–570, 738, 1086 historical aspects, 9, 551–552 inflammation/inflammatory response, 564, 570 inner ear pigment cells, 560 laboratory findings, 570 lesions hyperpigmented borders, 554, 554 inflammatory, 555 physiologic functioning, 564 medical therapies, 579–582 morphological/functional defects, 510 paracrine interactions, 431–433, 432, 433, 440, 441, 441 pathogenesis, 370, 431, 572–576 autocytotoxic hypothesis, 574 autoimmune hypothesis, 572–574 genetic hypothesis, 574–575 neural hypothesis, 575 pattern of onset, 555 phenolic compounds and, 368 photography, 579 precipitating factors, 562–563 psychologic impact, 561–562 sex differences, 553 spontaneous repigmentation, 556, 556 stress-induced, 563 treatment, 577–584, 1086 age and, 579 chemical depigmentation, 582–583, 1171, 1171, 1172 limitations, 578–579 melanocyte reservoir, 577–579, 578 micropigmentation, 583 photochemotherapy, 579–582 surgical, 583, 583, 1191–1196 UVB phototherapy, 580, 1184–1185 unilateral, asymmetrical (segmented), 553, 556, 556–557, 557, 579, 738 Vogt–Koyanagi–Harada syndrome (VKHS), 734–741 alopecia areata, 736, 754 animal models, 739 associated disorders, 736 clinical features, 559, 559, 560, 735–736, 736, 738 cutaneous, 737 ocular, 735, 736–737, 737 depigmentation, 735–736 diagnosis/differential diagnosis, 737–738 Alezzandrini syndrome vs., 726 dysacousia, 560 epidemiology, 735 histology, 736–737, 738 historical background, 734–735 laboratory findings/investigations, 737 pathogenesis, 738–739 prognosis, 739 “specific antigens,” 739 treatment, 739 Voight lines, see pigmentary demarcation lines vulva hyperpigmentation, 1081 lentigines, 825, 1081–1082 melanoma, 1084–1085 melanosis, 1082, 1082 nevi, 1083, 1084 Waardenburg–Hirschsprung disease (HSCR2), 546 Waardenburg–Shah syndrome (Shah–Waardenburg syndrome), see Waardenburg syndrome type 4 Waardenburg syndrome (WS), 357, 358, 544–546, 738, see also specific types clinical features, 544 genetics, 544 heterochromia irides, 757, 757 historical background, 544 incidence, 544 subtypes, 544–546 Waardenburg syndrome type 1 (WS1), 143–144, 544–545 Waardenburg syndrome type 2 (WS2), 144–145 clinical features, 527, 545 mutation, 527, 630 type 2A (WS2A), 126, 144–145, 245
type 2B (WS2A), 144 type 2C (WS2A), 144 type 2D (WS2A), 145 Waardenburg syndrome type 3 (WS3), 145, 544–545 Waardenburg syndrome type 4 (WS4), 146, 247, 545, 545–547 Wangiella dermatidis, melanonychia, 1061 warty hyperkeratoses, 805, 806 Watson syndrome, 813, 823 Weary–Kindler syndrome, see hereditary acrokeratotic poikiloderma Werner syndrome, 661, 806, 894–897 associated disorders, 895 clinical findings, 792, 894–895, 895 differential diagnosis, 885, 896 genetics, 894 histology, 895 laboratory investigations, 895 pathogenesis, 896 treatment, 896 Westerhof syndrome, 741–744 clinical description, 741–742, 742, 742 diagnosis/differential diagnosis, 743, 744 histopathology, 742, 742–744 white forelock, piebaldism, 570, 655 white hair, see leukotrichia (white hair) white halo, Mongolian spot, 1003 white mutants, 118–119 white pinta, 687 white skin, black skin vs., 8, see also ethnicity; skin types (human) Wnt protein signaling avian melanocyte specification, 121–122 fish chromatophore differentiation, 114 mammalian melanocyte specification, 83, 125, 448 MITF regulation and, 245–246 Wood’s light examination, 531, 532–533 black skin, 532 melasma, 1020 nevus anemicus, 767 nevus depigmentosus, 651 pityriasis alba, 699 tuberous sclerosis complex, 655 vitiligo vulgaris, 553, 554 Woolf syndrome, see albinism–deafness syndrome Woronoff ring, 701, 768 psoriasis, 701 Wright, Sewell, 395–396 WRN, Werner syndrome, 896 xanthelasma, 992 xanthomas, 992 xanthophores, 14, 17, 19–24, 20, 40–41 avian eye color, 98 MSH effects, 31 zebrafish patterning, 47 fate specification, 114–115 X-chromosome inactivation, 357 xenograft, melanocytic nevi models, 1135 Xenopus laevis color change, 29 darkness adaptation, 33, 33–34, 34, 35 morphologic, 27, 28 dermal melanophores, dispersed vs. aggregated, 16 melanophore line, regulation, 455 xeroderma pigmentosum, 889–894 animal models, 892 associated malignancy, 891 clinical findings, 889, 889–891, 890 diagnosis/differential diagnosis, 891 epidemiology, 889 histology, 891 historical background, 889 laboratory findings, 891 lentigines, 831, 890, 891 malignancy association, 890, 890 pathogenesis, 892 pigmentary features, 891 subtypes, 889, 890–891, 892 therapy, 892–893 Xiphophorine Gordon–Kosswig Melanoma System, 48 X-linked albinism–deafness syndrome, 147
INDEX X-ray depigmentation, 684 X-ray diffraction studies, melanin, 313, 314 yaws, 686–687 Yemenite deaf–blind hypopigmentation syndrome, 146 zebra, coat coloration, 75–76 zebrafish chromatophore development, 109–115
differentiation, 113–115 morphogenesis, 111–113 color pattern formation, 45–47, 47 hormonal influences, 48 larval vs. adult, 110, 110–111 molecular genetics, 47 mutants, 47, 111, 113, 114, 115 zidovudine (AZT), hyperpigmentation–induction, 943
Ziehl–Nielsen method, leprosy diagnosis, 691 Ziprkowski–Margolis syndrome, see albinism–deafness syndrome zosteriform lentiginous nevus, see speckled lentiginous nevus zosteriform speckled lentiginosis, see agminated lentigines (AL) zosteriform speckled lentiginous nevus, see speckled lentiginous nevus
1229
The Pigmentary System: Physiology and Pathophysiology, Second Edition Edited by James J. Nordlund, Raymond E. Boissy, Vincent J. Hearing, Richard A. King, William S. Oetting, Jean-Paul Ortonne Copyright © 2006 Blackwell Publishing Ltd
Plate 2.2 (Fig. 2.2)
Plate 2.1 (Fig. 2.1)
Plate 2.4 (Fig. 2.9)
Plate 2.3 (Fig. 2.3)
Plates 2.1–22.2: please refer to text for legends.
Plate 2.5 (Fig. 2.11)
Plate 2.6 (Fig. 2.15)
Plate 2.7 (Fig. 2.16)
Plate 2.8 (Fig. 2.20)
Plate 2.9 (Fig. 2.21)
Plate 2.10 (Fig. 2.22)
Plate 2.11 (Fig. 2.23)
Plate 2.12 (Fig. 2.42)
Plate 2.13 (Fig. 2.44)
Plate 2.14 (Fig. 2.45)
Plate 2.15 (Fig. 2.46)
Plate 2.16 (Fig. 2.47)
Plate 2.17 (Fig. 2.48)
Plate 2.18 (Fig. 2.49)
A
C
Plate 2.19 (Fig. 2.50)
B
Plate 2.20 (Fig. 2.53)
Plate 2.21 (Fig. 2.56)
S
Sinus
C RPE
R Plate 4.1 (Fig. 4.1)
a
b
P
Early larva
Adult
mel
xan irid
mel
mel irid
mel Plate 5.1 (Fig. 5.1)
wild-type
picasso (erbb3)
puma
panther (csf1r)
sparse (kit)
panther (csf1r); sparse (kit)
rose (ednrb1)
panther (csf1r); rose (ednrb1)
sparse (kit); rose (ednrb1)
nacre (mitfa)
leopard (cx40)
jaguar (kir7.1)
Plate 5.2 (Fig. 5.2)
Endoplasmic reticulum Golgi
Tyrosinase
Silver/Pmell7
M ul
t
iv
esi
c ula r / s o r ti ng
bo
o som
el
an
de
os o
me
C o a te
nd
e / p re m
dy
Plate 8.2A (Fig. 8.3A)
Melanoso
e stag me –
II
Clathrins -
Adaptins Molecules for recognition, docking and fusion -
Plate 7.1 (Fig. 7.5)
Plate 8.2B (Fig. 8.3B)
Basement membrane 1 µm
Plate 8.1 (Fig. 8.1)
Plate 8.2C (Fig. 8.3C)
A Tyrosine
Cysteine
Tyrosinase r3
r1
Dopaquinone
Cysteinyldopa r4
Cysteinyldopaquinone
Cyclodopa
r2
Tyrosinase
Dopachrome
Dopa
Eumelanin
Pheomelanin
Level of tyrosinae activity
B Eumelanin
Pheomelanin
Non-mutant (Tyr +)
Tyr ch/Tyr ch Tyr: Ay/a Agouti:
Tyr ch/Tyr ch a/a
+/+ Ay/a
Chinchilla (Tyr ch)
a/a Ay/a Level of Agouti expression Level of Mc1r signaling Plate 19.1 (Fig. 19.2)
light-bellied agouti (AW)
agouti (A)
black-and-tan (at )
Hair cycle: Ventral:
1A
1A¢
Ventralspecific
(100 kb)
1B
1C
ATG
(18 kb)
2
3
4
TGA
Hair cyclespecific
Region-specific promoters
Protein-coding exons
Plate 19.2 (Fig. 19.3)
A
UVB
100mm
Lesion B Non UVB 100mm
Nonlesion
Plate 21.1 (Fig. 21.3) Plate 21.2 (Fig. 21.8)
3 days after 2MED UVB irradiation
Non-specific IgG
Anti-SCF
Non UVB
100mm
Non-specific IgG
Anti-SCF
UVB
100mm
Plate 21.3 (Fig. 21.9)
Plate 21.4 (Fig. 21.11)
UVB irradiation (288 mJ/cm2)
0
1 Day 6
ACK2 injection (5 mg/50 ml)
2
3
Measurement
4
A
non UVB
5
6
7
8
B
C
UVB + ACK2
UVB + IgG
9
10 (day)
Plate 21.5 (Fig. 21.12)
A
A
Lesion B B
Nonlesion Plate 21.6 (Fig. 21.14) Plate 21.7 (Fig. 21.15)
A
B
Nonlesion
Plate 21.8 (Fig. 21.18)
PAN 19 Days
Lesion 16 Days
28 Days
DNCB
28 Days
Plate 21.9 (Fig. 21.21)
A
Plate 22.1 (Fig. 22.1)
19 Days
16 Days
13 Days
7 Days
Cont
1 Day
7 Days
13 Days
1 Day
Cont
B
Growth Factor
ligand GPCR
RTK
K
PTEN
Src
Shc
Ras
PI3
AKT PI3K
Grb2 SOS1 GrB1
STAT RAF PLCγ
PI3K
IKK
BAD GSK3 NFκB β-catenin
MEK
PKC+ Ca+
MAPK
p70S6K
RSK
β-catenin Tcf/Lef CREB MITF
DAG/Ca
RSK STAT NFκB
+
Ras/RAF Rap1/BRAF
Protein MAPK synthesis
RSK
MAPK
PDK1 PKC
Gq/PLCγ
RSK
MAPK
SRF c-Fos, CBP Elk-1 TCF
Plate 26.1 (Figs. 26.1, 50.51) Poikiloderma of Civatte. Differentiation Anti-apoptosis
Proliferation
Plate 22.2 (Fig. 22.2)
Plate 27.1 Greenish discoloration caused by venous engorgement of the areola of a pubescent girl.
Plate 24.1 (Fig. 24.2) Nevocellular nevi.
Plate 27.2 (Fig. 27.4) Nevus flammeus.
Plate 27.3 Nevas anemicus. The hypopigmentation is caused by decreased blood flow.
Plate 27.5 Microvesicular dermatitis affecting exclusively the pigmented skin of a patient with vitiligo.
Plate 27.4 A heavily pigmented Peruvian woman with photodamage (solar elastosis) from intense sun exposure at high altitude.
Plate 27.6 Penile and scrotal hyperpigmentation in a normal neonate. The lower panel shows a dizygotic twin with albinism.
Plate 27.7 Vulvar hyperpigmentation in a newborn infant.
Plate 27.8 (Fig. 27.8) White hair.
Plate 27.11 Type C hypopigmented demarcation line emanating from the nipple.
Plate 27.9 (Fig. 27.9) Linea nigra.
Plate 27.10 Futcher’s type A demarcation line.
Plate 27.12 (Fig. 27.11) Freckles.
Plate 28.1 (Fig. 28.7) Lichen planus.
Plate 28.2 (Fig. 28.8) Hyperpigmented lichen planus. Plate 28.5 Marked hyperpigmentation of the palms of a patient with adrenal insufficiency (normal hands are shown for comparison).
Plate 28.3 (Fig. 28.9) Hemosiderin deposition.
Plate 29.1 (Fig. 29.1) Piebaldism: father and daughter.
Plate 28.4 (Fig. 28.13) Alkaptonuria.
Plate 29.3 (Fig. 29.3) Piebaldism.
Plate 29.2 (Fig. 29.2) Piebaldism.
Plate 29.5 (Fig. 29.5) Waardenburg syndrome type IV.
Plate 29.4 (Fig. 29.4) Waardenburg syndrome type I.
Plate 30.4 (Fig. 30.5) Trichrome vitiligo.
Plate 30.1 (Fig. 30.2) Bilateral vitiligo vulgaris.
Plate 30.5 (Fig. 30.6) Vitiligo on palms.
Plate 30.2 (Fig. 30.3) Segmental vitiligo.
Plate 30.6 (Fig. 30.8) Hyperpigmented borders.
Plate 30.3 (Fig. 30.4) Vitiligo vulgaris.
Plate 30.7 (Fig. 30.10) Vitiligo: raised erythematous borders.
Plate 30.8 (Fig. 30.11) Monobenzone dermatitis.
Plate 30.10 (Fig. 30.16) Segmental vitiligo.
Plate 30.9 (Fig. 30.14) Spontaneous repigmentation.
Plate 30.11 (Fig. 30.18) Depigmentation of gums.
Plate 30.12A (Fig. 30.15) A,B. Segmental vitiligo of chin extending to mouth.
Plate 30.12B (Fig. 30.19)
Plate 30.13 (Fig. 30.21) Vogt–Koyanagi–Harada syndrome.
Plate 30.14 (Fig. 30.22) Uveitis in patient in Plate 30.13.
Plate 30.15 (Fig. 30.23) Iritis in vitiligo patient.
Plate 30.17 (Fig. 30.29) Bindhi depigmentation.
Plate 30.16 (Fig. 30.27) White hairs in vitiligo.
Plate 30.18 (Fig. 30.31) Squamous carcinoma in vitiligo.
Plate 30.19A (Fig. 30.33A) A. Depigmentation in patient with melanoma.
Plate 30.19B (Fig. 30.33B) B. Progressive pigment loss.
Plate 30.20 (Fig. 30.34) Depigmentation with melanoma.
Plate 30.21A (Fig. 30.35A) A,B. Depigmentation of hair associated with metastatic melanoma.
Plate 30.21B (Fig. 30.35B)
Plate 30.22 (Fig. 30.40) Repigmenting vitiligo.
Plate 30.23 (Fig. 30.42) No repigmentation with white hair.
Plate 31.1 (Fig. 31.1) Oculocutaneous albinism type 1A.
Plate 31.2 (Fig. 31.2) Oculocutaneous albinism type 1B.
Plate 31.3 (Fig. 31.3) Oculocutaneous albinism type 2.
Plate 31.4 (Fig. 31.4) Brown oculocutaneous albinism type 2.
Plate 31.6 (Fig. 31.7) Griscelli Syndrome.
Plate 31.5 (Fig. 31.6) Chediak–Higashi syndrome.
Plate 31.7 (Fig. 31.8) Angelman syndrome.
Plate 31.8 (Fig. 31.10) Hellerman–Streiff syndrome.
Plate 31.9 (Fig. 31.12) Homocystinuria.
Plate 31.10 (Fig. 31.13) Oculocerebral syndrome.
Plate 31.11 (Fig. 31.14) Phenylketonuria.
Plate 31.12 (Fig. 31.15) Inborn error of biopterin synthesis.
Plate 31.13 (Fig. 31.16) Brittle hair of patient in Plate 31.12.
Plate 32.2 (Fig. 32.4) Hypomelanosis of Ito.
Plate 32.1 (Fig. 32.2) Hypomelanosis of Ito.
Plate 32.3 (Fig. 32.5) Asymmetric pigmentation.
Plate 32.5 (Fig. 32.9) Focal dermal hypoplasia.
Plate 32.4 (Fig. 32.6) Sweat test of patient in Plate 32.2.
Plate 32.6 (Fig. 32.13) Nevus depigmentosus.
Plate 32.7 (Fig. 32.14) Nevus depigmentosus.
Plate 32.8 (Fig. 32.16) Congenital hypomelanotic nevus.
Plate 32.11 (Fig. 32.19) Periungual fibromata.
Plate 32.9 (Fig. 32.17) Acquired nevus depigmentosus.
Plate 32.12 (Fig. 32.20) Shagreen patch.
Plate 32.10 (Fig. 32.18) Angiofibromata in tuberous sclerosis.
Plate 32.13 (Fig. 32.21) Ash leaf spot.
Plate 32.14 (Fig. 32.22) Leukotrichia of tuberous sclerosis.
Plate 34.2 African child with Kwashiorkor showing hypopigmented skin and light hair. The mother is normally pigmented.
Plate 34.1 (Fig. 34.1) Kwashiorkor.
Plate 34.3 (Fig. 34.2) Hyperpigmentation of folic acid deficiency.
Plate 34.4 Hyperpigmentation of the gums of a patient with folic acid deficiency (courtesy Dr. Fred Miller).
Plate 35.1 (Fig. 35.2) Depigmentation from thermal burn and follicular repigmentation.
Plate 35.2A (Fig. 35.3A) A,B. Pigmentary changes induced by Xray burns.
Plate 34.5 Melasma-like hyperpigmentation associated with folic acid deficiency.
Plate 35.2B (Fig. 35.3B)
Plate 36.1 (Fig. 36.2) Hypopigmentation of leprosy.
Plate 36.3A (Fig. 36.4A) A,B. Tinea versicolor.
Plate 36.2 (Fig. 36.3) Hyper- and hypopigmentation of leprosy. Plate 36.3B (Fig. 36.4B)
Plate 37.1 Typical pityriasis alba on the cheeks of a young boy.
Plate 36.4 (Fig. 36.5) Onchocerciasis. Plate 37.2 (Fig. 37.1) Pityriasis alba.
Plate 36.5 (Fig. 36.6) Post herpes zoster hypopigmentation.
Plate 37.5 (Fig. 37.5) Alopecia mucinosa.
Plate 37.3 (Fig. 37.3) Psoriasis. Plate 37.6 (Fig. 37.6) Atopic dermatitis.
Plate 37.4 (Fig. 37.4) Woronoff ring.
Plate 37.7 Depigmentation on the dorsum of the hands of a patient with scoid lupus erythematosus.
Plate 37.8 (Fig. 37.7) Discoid lupus erythematosus.
Plate 37.9 (Fig. 37.8) Discoid lupus erythematosus.
Plate 37.10 (Fig. 37.9) Pityriasis lichenoides acuta.
Plate 38.1 (Fig. 38.2) Halo nevus.
Plate 38.3 (Fig. 38.4) Halo seborrheic keratoses.
Plate 38.2 (Fig. 38.3) Multiple halo nevi.
Plate 38.4 (Fig. 38.5) Halo congenital nevus.
Plate 38.5 (Fig. 38.6) Depigmented congenital nevus.
Plate 39.1 (Fig. 39.2) Guttate hypomelanosis.
Plate 38.6 (Fig. 38.7) Depigmented congenital nevus.
Plate 39.2 (Fig. 39.6) Lichen sclerosis et atrophicus.
Plate 38.7 (Fig. 38.8) Depigmentation in a melanoma.
Plate 39.3 (Fig. 39.7) Lichen sclerosis et atrophicus.
Plate 40.2 (Fig. 40.4) Progressive macular hypomelanosis.
Plate 40.1 (Fig. 40.2) Hypermelanocytic punctata et guttata hypomelanosis.
Plate 40.3 (Fig. 40.5B) Sarcoidosis.
Plate 41.1 (Fig. 41.1) Regrowing white hair in alopecia areata.
Plate 41.4 (Fig. 41.4) Heterochromia irides.
Plate 41.2 (Fig. 41.2) Heterochromia irides.
Plate 41.3 (Fig. 41.3) Heterochromia irides.
Plate 42.1 (Fig. 42.1) Nevus anemicus.
Plate 43.1 (Fig. 43.1) Hyperpigmentation in Fanconi anemia.
Plate 44.3 (Fig. 44.3) Dyschromatosis universalis hereditaria.
Plate 44.1 (Fig. 44.1) Kindler syndrome.
Plate 44.2 (Fig. 44.2) Kindler syndrome.
Plate 44.4 (Fig. 44.4) Dyschromatosis universalis hereditaria.
Plate 44.5 (Fig. 44.5) Dyschromatosis universalis hereditaria.
Plate 44.7 (Fig. 44.7) Epidermolysis bullosa and mottled hyperpigmentation.
Plate 44.8 (Fig. 44.8) Hereditary acrokeratotic poikiloderma.
Plate 44.6 (Fig. 44.6) Dyschromatosis universalis hereditaria.
Plate 44.9 (Fig. 44.9) Hereditary acrokeratotic poikiloderma.
Plate 44.10 (Fig. 44.10) Hereditary sclerosing poikiloderma.
Plate 44.11 (Fig. 44.11) Hereditary sclerosing poikiloderma.
Plate 44.12 (Fig. 44.12) Acropigmentation of Dohi.
Plate 44.13 (Fig. 44.13) Acropigmentation of Dohi.
Plate 44.14 (Fig. 44.14) Acropigmentation of Dohi.
Plate 44.15 (Fig. 44.15) Acropigmentation of Kitamura.
Plate 44.16 (Fig. 44.16) Acropigmentation of Kitamura.
Plate 44.17 (Fig. 44.17) Acropigmentation of Kitamura.
Plate 44.19 (Fig. 44.19) Rothmund–Thomson syndrome.
Plate 44.18 (Fig. 44.18) Rothmund–Thomson syndrome.
Plate 45.1 (Fig. 45.1) Café-au-lait macules in neurofibromatosis (NF) 1.
Plate 45.2 (Fig. 45.2) Café-au-lait macules in NF1.
Plate 45.5 (Fig. 45.5) Lisch nodules on iris.
Plate 45.3 (Fig. 45.3) Café-au-lait macules in NF1. Plate 45.6 (Fig. 45.6) Plexiform neurofibroma.
Plate 45.4 (Fig. 45.4) Axillary freckling in NF1. Plate 45.7 (Fig. 45.7) McCune–Albright syndrome.
Plate 45.8 (Fig. 45.8) McCune–Albright syndrome.
Plate 45.9 (Fig. 45.9) Segmental neurofibromatosis.
Plate 46.1 (Fig. 46.1) Lentigo simplex.
Plate 46.2 (Fig. 46.2B) PUVA lentigines.
Plate 46.3 (Fig. 46.3) Actinic lentigines.
Plate 46.5 (Fig. 46.5) Eruptive lentigines.
Plate 46.6 (Fig. 46.6) Multiple lentigines (LEOPARD) syndrome.
Plate 46.4 (Fig. 46.4) Actinic lentigines.
Plate 46.7 (Fig. 46.7) LEOPARD syndrome.
Plate 46.10 (Fig. 46.10) Lentigines in Carney complex.
Plate 46.8 (Fig. 46.8) LEOPARD syndrome.
Plate 46.11 (Fig. 46.11) Cardiac myxoma.
Plate 46.9 (Fig. 46.9) LEOPARD syndrome.
Plate 46.14 (Fig. 46.14) Labial lentigines.
Plate 46.12 (Fig. 46.12) Labial lentigines.
Plate 46.15 (Fig. 46.15) Cutaneous myxomata.
Plate 46.13 (Fig. 46.13) Periorbital lentigines.
Plate 46.16 (Fig. 46.16) Zosteriform speckled lentiginosis.
Plate 46.17 (Fig. 46.17) Nevus spilus. Plate 47.2 (Fig. 47.2) Incontinentia pigmenti stage 3.
Plate 47.1 (Fig. 47.1) Incontinentia pigmenti stage 1.
Plate 47.3 (Fig. 47.3) Incontinentia pigmenti stage 4.
Plate 47.4 (Fig. 47.4) Periorbital hyperpigmentation.
Plate 47.7 (Fig. 47.7) Demarcation line type A.
Plate 47.5 (Fig. 47.5) Periorbital hyperpigmentation.
Plate 47.8 (Fig. 47.8) Dowling–Degos disease.
Plate 47.6 (Fig. 47.6) Demarcation line type A.
Plate 47.9 (Fig. 47.9) Dowling–Degos disease.
Plate 48.4 (Fig. 48.8) Werner syndrome.
Plate 48.1 (Fig. 48.1) Progeria.
Plate 48.2 (Fig. 48.2) Xeroderma pigmentosum. Plate 49.1 (Fig. 49.1) Dyskeratosis congenita.
Plate 48.3 (Fig. 48.5) Xeroderma pigmentosum.
Plate 50.1 (Fig. 50.1) Acanthosis nigricans.
Plate 49.2 (Fig. 49.2) Dyskeratosis congenita.
Plate 50.2 (Fig. 50.6) Becker’s nevus.
Plate 49.3 (Fig. 49.4) Clouston syndrome.
Plate 50.3 (Fig. 50.10) Carcinoid syndrome.
Plate 50.4 (Fig. 50.11) Confluent and reticulated papillomatosis.
Plate 50.7 (Fig. 50.17) Macular amyloid.
Plate 50.5 (Fig. 50.13) Confluent and reticulated papillomatosis.
Plate 50.8 (Fig. 50.21) Erythema ab igne.
Plate 50.9 (Fig. 50.22) Erythema dyschromicum perstans.
Plate 50.6 (Fig. 50.14) Macular amyloid.
Plate 50.10 (Fig. 50.24) Erythromelanosis faciei.
Plate 50.11 (Fig. 50.28) Felty syndrome.
Plate 50.12 (Fig. 50.33) Blue nails with HIV.
Plate 50.13 (Fig. 50.34) Melanoacanthoma.
Plate 50.14 (Figs. 28.20, 50.39) Psoralen hyperpigmentation.
Plate 50.17 (Fig. 50.43) Angiomata of POEMS syndrome.
Plate 50.15 (Fig. 50.40) POEMS syndrome.
Figure 50.16 (Fig. 50.41). Hyperpigmentation of POEMS syndrome.
Plate 50.18 (Fig. 50.44) Urticaria pigmentosum.
Plate 50.19 (Fig. 50.45) Diffuse mastocytosis.
Plate 50.20 (Fig. 50.46) Diffuse mastocytosis.
Plate 50.21 (Fig. 50.47) Hyperpigmentation from diffuse mastocytosis.
Plate 50.22 (Fig. 50.53) Atrophoderma of Pasini and Pierini.
Plate 50.23 (Fig. 50.54) Atrophoderma of Pasini and Pierini.
Plate 50.25 (Fig. 50.57) Hyperpigmentation with ichthyosis.
Plate 50.26A (Fig. 50.69A) Addisonian pigmentation before therapy.
Plate 50.24 (Fig. 50.56) Ichthyosis.
Plate 50.26B (Fig. 50.69B) Addisonian pigmentation after therapy.
Plate 50.27 (Fig. 50.70) Addisonian oral hyperpigmentation.
Plate 51.1 (Fig. 51.3) Porphyria cutanea tarda.
Plate 51.2 (Fig. 51.5) Cronkhite–Canada syndrome.
Figure 50.28 (Fig. 50.73) Reticulated hyperpigmentation in mycosis fungoides.
Plate 51.3 (Fig. 51.7) Biliary cirrhosis.
Plate 51.4 (Fig. 51.8) Pellagra.
Plate 51.5 (Fig. 51.9) Pellagra.
Plate 51.6 (Fig. 51.10) Pellagra.
Plate 51.7 (Fig. 51.11) Peutz–Jeghers syndrome.
Plate 51.8 (Fig. 51.12) Peutz–Jeghers syndrome.
Plate 52.2 (Fig. 52.3) Extrasacral blue spots.
Plate 52.1 (Fig. 52.2) Mongolian sacral spot.
Plate 52.3A (Fig. 52.7A) A. Nevus of Ota.
Plate 52.3B (Fig. 52.7B) B. Nevus of Ota laser treated.
Plate 52.5 (Fig. 52.10) Phakomatosis pigmentovascularis.
Plate 52.4 (Fig. 52.9) Phakomatosis pigmentovascularis.
Plate 52.6 (Fig. 52.11) Phakomatosis pigmentovascularis. Plate 52.8 (Fig. 52.14) Acquired facial blue macules.
Plate 52.7 (Fig. 52.13) Phakomatosis pigmentovascularis.
Plate 53.1A (Fig. 53.2A) A. Melasma before therapy.
Plate 53.1B (Fig. 53.2B) B. Melasma after therapy.
Plate 54.1 (Fig. 54.1) Fixed drug eruption.
Plate 53.2 (Fig 53.3) Diffuse melanomatosis.
Plate 54.2 (Fig 54.2) Fixed drug eruption.
Plate 54.3 (Fig. 54.5) Lichen aureus.
Plate 54.5 (Fig. 54.7) Argyria.
Plate 54.4 (Figs 28.10, 54.6) Argyria.
Plate 54.6 (Figs 28.11, 54.8) Blue nails from argyria.
Plate 54.9 (Figs 28.12, 54.12) Gingival lead line.
Plate 54.7 (Figs 28.11, 54.10) Chrysiasis.
Plate 54.10 (Fig. 54.16) Tattoo.
Plate 54.8 (Fig. 54.11) Chrysiasis and normal hand.
Plate 54.11 (Fig. 54.17) Tattoo.
Plate 54.14 (Fig. 54.22) Amiodarone pigmentation.
Plate 54.12 (Fig. 54.18) Tattoo.
Plate 54.13 (Fig. 54.21) Carotenemia.
Plate 54.15 (Fig. 54.23) Amiodarone pigmentation.
Plate 54.16 (Fig. 54.24) Minocycline pigmentation.
Plate 54.19 (Fig. 54.29) Atrabine discoloration.
Plate 54.17 (Fig. 54.25) Minocycline pigmentation. Plate 54.20 (Fig. 54.30) Chloroquine-induced light hair.
Plate 54.18 (Fig. 54.26) Minocycline discoloration of teeth.
Plate 54.21 (Fig. 54.31) Clofazimine pigmentation and normal hand.
Plate 54.24 (Fig. 54.34) Nitrogen mustard hyperpigmentation.
Plate 54.22 (Fig. 54.32) Clofazimine pigmentation.
Plate 54.25 (Fig. 54.35) Bleomycin-induced hyperpigmentation.
Plate 54.23 (Fig. 54.33) Thorizine-induced discoloration.
Plate 54.26 (Fig. 54.36) Bleomycin hyperpigmentation.
Sagittal section through finger nail
Proximal matrix Proximal Nail Fold Eponychium Cuticle Lunula Nest of pigment producing cells Nail plate
Distal matrix
Nail
bed
Hyponychium Distal groove
A
B
Plate 55.1 (Fig. 55.1) Schematic drawing of nail. Plate 55.4 (Fig. 55.7) Longitudinal melanonychia: proximal widening.
Plate 55.2 (Fig. 55.5) Longitudinal melanonychia (single band). Plate 55.5 (Fig. 55.8) Hutchinson sign.
Plate 55.3 (Fig. 55.6) Longitudinal melanonychia (multiple bands).
Plate 55.6 (Fig. 55.9) Pseudo-Hutchinson sign.
Plate 55.8 (Fig. 55.11) Benign nevus.
Plate 55.7 (Fig. 55.10) Longitudinal melanonychia from metastatic melanoma.
Plate 55.9 (Fig. 55.12) Acrolentiginous melanoma.
Plate 56.1 (Fig. 56.3) Oral Kaposi sarcoma.
Plate 56.5 (Fig. 56.18) Blue nevus. Plate 56.2 (Fig. 56.8) Labial melanotic macule.
Plate 56.6 (Fig. 56.21) Gingival melanoma. Plate 56.3 (Fig. 56.10) Laugier–Hunziker syndrome.
Plate 56.4 (Fig. 56.12) Peutz–Jeghers syndrome.
Plate 56.7 (Fig. 56.24) Amalgam tattoo.
Plate 58.1 (Fig. 58.1) Congenital nevus sparing the areola. Plate 56.8 (Fig. 56.26) Vulvar melanosis.
Plate 56.9 (Fig. 56.29) Penile lentigo.
Plate 58.2 (Fig. 58.2) Congenital nevus sparing the areola.
Plate 58.5 (Fig. 58.5) Halos around sacral spots.
Plate 58.3 (Fig. 58.3) Congenital nevus sparing the areola.
Plate 59.1 (Fig. 59.1) Post-graft hyperpigmentation before treatment.
Plate 58.4 (Fig. 58.4) Congenital nevus sparing the genitalia.
Plate 59.2 (Fig. 59.2) Post-graft hyperpigmentation after treatment.
Plate 59.3 (Fig. 59.3) Hypopigmentation from hydroquinone.
Plate 59.4 (Figs 28.14, 54.27, 59.4) Ochronosis from hydroquinone.
Plate 59.6 (Fig. 59.6) Melasma before treatment.
Plate 59.5 (Fig. 59.5) Steroid-induced hypopigmentation.
Plate 59.7 (Fig. 59.7) Melasma after treatment.
Plate 59.8 (Fig. 59.8) Monobenzone-induced depigmentation.
Plate 59.9 (Fig. 59.11) Vitiligo before monobenzone therapy.
Plate 59.10 (Fig. 59.12) Vitiligo after monobenzone therapy.
Plate 60.1 (Figs. 30.43A, 60.3) Vitiligo before PUVA.
Plate 60.2 (Figs. 30.43B, 60.4) Vitiligo after PUVA.
Plate 60.4 (Fig. 60.9) White hair and failure of PUVA.
Plate 60.3 (Fig. 60.6) PUVA repigmentation.
Plate 63.1 (Fig. 63.2) Vitiligo before grafting.
Plate 63.2 (Fig. 63.3) Vitiligo after grafting.
Plate 63.3 (Fig. 63.4) Repigmentation from grafts.
Plate 63.4 (Fig. 63.11) Vitiligo before grafting.
Plate 63.5 (Fig. 63.12) Vitiligo after grafting.
Plate 63.6 (Fig. 63.13) Vitiligo before micropigmentation.
Plate 63.7 (Fig. 63.14) Vitiligo after micropigmentation.
Plate 64.1 (Fig. 64.1) Tattoo before laser removal.
Plate 64.2 (Fig. 64.2) Tattoo after laser removal.
Plate 64.3 (Fig. 64.5) Café-au-lait spot before laser therapy.
Plate 64.4 (Fig. 64.6) Café-au-lait spot after laser therapy.
A
D B
C
E
F
H
G
I
A: These two individuals illustrate the wide range of skin and hair color. [Marianne Greenwood (right) graciously shared the photographs . (from her book Varför Grater Puman?) that compose this frontispiece.] B: Classical Celtic women with blue eyes and red hair. C: Typical Scandinavian with blue eyes. D: Native American. E: A Peruvian girl. F: Himalayan woman and child. G: A Venezuelan woman. H: Two teenagers from New Guinea. I: Man from the New Hebrides Islands. See Chapter 27 for further information.
