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Photodegradation of Eumelanin and Pheomelanin and Its Pathophysiological Implications.
- Source :
-
Photochemistry and photobiology [Photochem Photobiol] 2018 May; Vol. 94 (3), pp. 409-420. Date of Electronic Publication: 2017 Oct 26. - Publication Year :
- 2018
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Abstract
- Eumelanin is photoprotective for pigmented tissues while pheomelanin is phototoxic. In this review, we summarize current understanding of how eumelanin and pheomelanin structures are modified by ultraviolet A (UVA) and also by visible light and how reactive oxygen species participate in those processes. Alkaline hydrogen peroxide oxidation was employed to characterize eumelanin and benzothiazole-type pheomelanin, giving pyrrole-2,3,5-tricarboxylic acid (PTCA) and thiazole-2,4,5-tricarboxylic acid (TTCA), respectively. Reductive hydrolysis with hydroiodic acid gives 4-amino-3-hydroxyphenylalanine (4-AHP) from the benzothiazine moiety of pheomelanin. The results show that the photoaging of eumelanin gives rise to free PTCA (produced by peroxidation in situ) and pyrrole-2,3,4,5-tetracarboxylic acid (PTeCA, produced by cross-linking). The TTCA/4-AHP ratio increases with photoaging, indicating the conversion of benzothiazine to the benzothiazole moiety. Analysis of those markers and their ratios show that both eumelanin and pheomelanin in human retinal pigment epithelium melanosomes undergo extensive structural modifications due to their lifelong exposure to blue light. Using synthetic melanins, we also found that singlet oxygen, in addition to superoxide anions, is photogenerated and quenched upon UVA irradiation. The (patho)physiological significance of those findings is discussed in relation to the tanning process, to melanomagenesis in the skin and to age-related macular degeneration in the eyes.<br /> (© 2017 The American Society of Photobiology.)
- Subjects :
- Carboxylic Acids chemistry
Eye metabolism
Eye physiopathology
Eye radiation effects
Humans
Hydrogen Peroxide metabolism
Melanins metabolism
Melanins physiology
Melanosomes metabolism
Melanosomes radiation effects
Pyrroles chemistry
Reactive Oxygen Species metabolism
Retinal Pigment Epithelium metabolism
Retinal Pigment Epithelium radiation effects
Skin metabolism
Skin physiopathology
Skin radiation effects
Skin Aging
Thiazoles chemistry
Tyrosine analogs & derivatives
Tyrosine chemistry
Light
Melanins radiation effects
Ultraviolet Rays
Subjects
Details
- Language :
- English
- ISSN :
- 1751-1097
- Volume :
- 94
- Issue :
- 3
- Database :
- MEDLINE
- Journal :
- Photochemistry and photobiology
- Publication Type :
- Academic Journal
- Accession number :
- 28873228
- Full Text :
- https://doi.org/10.1111/php.12837