title: UVA-induced oxidative degradation of melanins: fission of indole moiety in eumelanin and conversion to benzothiazole moiety in pheomelanin.
abstract: Eumelanin is photoprotective while pheomelanin is phototoxic to pigmented tissues. Ultraviolet A (UVA)-induced tanning seems to result from the photooxidation of pre-existing melanin and contributes no photoprotection. However, data available for melanin biodegradation remain limited. In this study, we first examined photodegradation of eumelanin and pheomelanin in human black hairs and found that the ratio of Free (formed by peroxidation in situ) to Total (after hydrogen peroxide oxidation) pyrrole-2,3,5-tricarboxylic acid (PTCA) increases with hair aging, indicating fission of the dihydroxyindole moiety. In red hair, the ratio of thiazole-2,4,5-tricarboxylic acid (TTCA) to 4-amino-3-hydroxyphenylalanine (4-AHP) increases with aging, indicating the conversion from benzothiazine to benzothiazole moiety. These photodegradation of melanins were confirmed by UVA (not UVB) irradiation of melanins from mice and human hairs and synthetic eumelanin and pheomelanin. These results show that both eumelanin and pheomelanin degrade by UVA and that Free/Total PTCA and TTCA/4-AHP ratios serve as sensitive indicators of photodegradation.
authors.affiliation: Department of Chemistry, Fujita Health University School of Health Sciences, Toyoake, Aichi, Japan.
authors.forename: Kazumasa
authors.initials: K
authors.lastname: Wakamatsu
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Nakanishi
authors.forename: Narimi
authors.initials: N
authors.lastname: Miyazaki
authors.forename: Ludger
authors.initials: L
authors.lastname: Kolbe
authors.forename: Shosuke
authors.initials: S
authors.lastname: Ito
mesh_terms: D000818:Animals; D052160:Benzothiazoles / Q000737:chemistry / Q000378:metabolism*; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D005260:Female; D006197:Hair / Q000378:metabolism; D006200:Hair Color / Q000528:radiation effects; D006801:Humans; D007211:Indoles / Q000737:chemistry / Q000378:metabolism*; D008543:Melanins / Q000737:chemistry / Q000378:metabolism* / Q000528:radiation effects*; D051379:Mice; D010084:Oxidation-Reduction / Q000528:radiation effects; D013056:Spectrophotometry, Ultraviolet; D014466:Ultraviolet Rays
chemical_list: D052160:Benzothiazoles; D007211:Indoles; D008543:Melanins; C018362:pheomelanin; C041877:eumelanin; C030374:indole; C005465:benzothiazole