The effects of tert-butyl hydroperoxide- and iron-induced oxidative stress on retinal pigment epithelium physiology and function. Protection by antioxidants and mitochondrial protective compounds

Age-related macular degeneration (AMD), like other age-related diseases, appears to involve oxidative damage, particularly to mitochondria. There is a strong evidence of the oxidative stress involvement in the development age-related diseases, including age-related macular degeneration (AMD). Although the pathogenesis of AMD includes different clinical signs, the degeneration of retinal pigment epithelial (RPE) cells is often observed at the early stages of the disease. RPE cells might be susceptible to oxidative damage because RPE cells are exposed to relatively high oxygen tension, intense illumination from focal light, contain an abundance of photosensitizers, and phagocytose photoreceptor outer segments. There is also an age-associated increase in the levels of oxidative stress in RPE cells. One of the primary targets of oxidative stress in RPE is cellular mitochondria.; We hypothesize that oxidative stress and oxidant-induced mitochondrial damage contribute to the retinal degeneration observed in AMD. We further hypothesize that antioxidants protecting mitochondria may prevent or repair RPE cellular damage and degeneration common to AMD.; I investigated the protective action of the mitochondrial protective antioxidants alpha-lipoic acid (LA), acetyl-L-carnitine (ALC), and N-tert-butylhydroxylamine (NtBHA) against the tert-butyl hydroperoxide (t-BuOOH) and iron-induced oxidative stress in RPE cells. I used techniques of fluorescence microscopy, quantitative fluorescent and colorimetric assays, and high performance liquid chromatography (HPLC) in my studies.; In my studies t-BuOOH treatment promoted increased levels of intracellular oxidants, loss of cellular GSH, mitochondrial damage, and, at high doses, cell death. The studies also suggest that RPE mitochondrial function was important for the maintenance of the rates of outer segment phagocytosis in vitro.; ALCAR pretreatment of hfRPE cells before the t-BuOOH exposure partially reversed the oxidant-induced decrease in mitochondrial DeltaPsi and phagocytic rates in viable RPE cells. LA pretreatment protected RPE cells against the t-BuOOH-induced cell death. The LA protection was associated with lower levels of intracellular reactive oxygen species (ROS), prevention of mitochondrial potential decrease, as well as increased GSH levels and GSH/GSSG ratio.; The model of iron-induced oxidative stress in RPE cells can be particularly relevant for AMD pathology since it has been reported that RPE tissues of AMD-affected patients demonstrate significant increase in total iron concentration. (Abstract shortened by UMI.)...