Inhibition of RPE lysosomal and antioxidant activity by the age pigment lipofuscin

Purpose. To determine whether lipofuscin is detrimental to lysosomal and an tioxidant function in cultured human retinal pigment epithelial (RPE) cells . Methods. Isolated lipofuscin granules were fed to confluent RPE cultures an d the cells maintained in basal medium for 7 days. Parallel cultures were e stablished that did not receive lipofuscin. Cultures were either exposed to visible light (390-550 nm) at an irradiance of 2.8 mW/cm(2) or maintained in the dark at 37 degreesC for up to 24 hours. Cells were subsequently asse ssed for cell viability, lysosomal enzyme activity, and antioxidant capacit y. Results. There was no loss of cell viability during the first 3 hours of li ght exposure, whereas a 10% loss of viability was observed in lipofuscin-fe d cultures after 6 hours' exposure to light. Activities of acid phosphatase , N-acetyl-beta -glucuronidase, and cathepsin D were decreased by Lip to 50 % in lipofuscin-fed cells exposed to light compared with either unfed cells or cells maintained in the dark. There was also a decrease in the antioxid ant potential of RPE cells. Catalase and superoxide dismutase activities de creased by up to 60% and glutathione levels by 28% in light-exposed lipofus cin-fed cells compared with unfed cells or cells maintained in the dark. Conclusions. Lipofuscin has the capacity to reduce the efficacy of the lyso somal and antioxidant systems in RPE cells that may play an important role in retinal ageing and the development of age-related macular degeneration.