The Role of Photo-Activated Melanosomes and Cellular Antioxidant Defenses in the Response of RPE Cells to Laser Radiation
Abstract
The pigments of the retinal pigment epithelium, i.e. the intracellular granules of melanin, lipofuscin, and melanolipofuscin, have been shown to catalyze free radical activity, especially when illuminated with visible or ultraviolet light. An important issue is whether these reactions are sufficient to produce oxidative damage in the eye. To address this question, the relative photoreactivity of isolated RPE pigment granules towards polyunsaturated fatty acids has been determined, including the dark as well as the light-stimulated reactions. Hydroperoxide derivatives of docosahexaenoic acid were produced by irradiation with short wavelength (<550 nm) visible light when RPE pigments were present. Although melanosomes exhibited the greatest light-induced activity in these reactions, lipofuscin granules induced peroxidation of fatty acids in the dark. In intact, cultured RPE cells, the existence of pigment-mediated photo-reactions was demonstrated with a fluorescent indicator probe of oxidation, 2%,7'-dichlorofluorescein, that was photooxidized in probe-labeled cells in a wavelength dependent fashion with peak activity in the 450 to 500 nm region. This behavior resembled the action spectrum for melanin reactivity. These findings support the hypotheses that the RPE pigments in general contribute to photooxidative stress in ocular tissue, and that accumulation of lipofuscin pigment specifically contributes to age-related oxidative stress in the RPE.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 2001
- Accession Number
- ADA396415
Entities
People
- Randolph D. Glickman
Organizations
- University of Texas at Austin