Antioxidant properties of melanin in retinal pigment epithelial cells.
The retinal pigment epithelium (RPE) is a monolayer of highly pigmented cells lining the inner aspect of Bruch's membrane. This pigmentation is due to eumelanin and a possible antioxidant role of melanin is reported here. The photo-oxidation of A2E, a constituent of RPE lipofuscin, leads to the sequential addition of up to nine oxygen atoms and/or the addition or loss of two hydrogen atoms. These photo-oxidations were investigated in the presence and absence of either calf or human RPE melanin in A2E-laden RPE cells. It was found that calf melanin was protective against the photo-oxidation of A2E, with an inhibition of oxidation of up to 50% in the case of the addition of two oxygen atoms. Calf melanin was also protective against blue light-induced damage to RPE cells. In addition this ability appears to decrease in humans as they grow older. With aging, a melanin-lipofuscin complex called melanolipofuscin forms. It is suggested that the oxidation or photo-oxidation of A2E in vivo may contribute to the age-related deterioration of the anti-oxidant role of RPE melanin and lead to various retinal disorders, such as age-related macular degeneration.
Wang
Z
Z
Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL, USA.
Dillon
J
J
Gaillard
E R
ER
D000818:Animals; D000975:Antioxidants / Q000378:metabolism*; D002417:Cattle; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D008027:Light; D008062:Lipofuscin / Q000737:chemistry / Q000378:metabolism; D008268:Macular Degeneration / Q000473:pathology; D008543:Melanins / Q000378:metabolism*; D010084:Oxidation-Reduction; D010857:Pigment Epithelium of Eye / Q000166:cytology / Q000378:metabolism* / Q000473:pathology; D012164:Retinal Diseases / Q000473:pathology; D013997:Time Factors
D000975:Antioxidants; D008062:Lipofuscin; D008543:Melanins