Oxysterol-induced toxicity in R28 and ARPE-19 cells

Studies have shown an intimate relationship between cholesterol and retinal diseases; we examined the effects of cholesterol oxides on cultured cells. Using the rat retinal precursor cell line R28 and the human RPE cell line ARPE-19, we investigated the potential cytotoxicity of cholesterol oxides. Cultured R28 and ARPE-19 cells were treated with either 25-hydroxycholesterol and 7-ketocholesterol (0-50 μg/ml). Cell viability was determined by the WST-1 colorimetric assay. Production of reactive oxygen intermediate (ROI) was assessed by a fluorescent probe-based assay (2′,7′-dichlorodihydrofluorescein diacetate [H₂DCFDA]). To detect the presence of apoptosis, DNA fragmentation gel analysis and Hoescht nuclear staining were performed. Both cholesterol oxides tested were toxic in a time- and dose-dependent fashion to the two cell lines used in this study. Treatment of R28 cells with either 25-hydroxycholesterol or 7-ketocholesterol at a concentration of 25 μg/ml resulted in greater than 50% loss of cell viability after 24 h. ARPE-19 cells were slightly less affected, with a loss of cell viability of approximately 20% and 40% after 24 h-exposure of 25-hydroxycholesterol and 7-ketocholesterol, respectively. DNA fragmentation and chromatin condensation demonstrated apoptotic events occurring in 7-ketocholesterol-treated cells. The fluorescent assay for ROI production showed that after an hour of exposure to 7-ketocholesterol, R28 cells responded with increased levels of ROIs, whereas no immediate production of ROIs were detected with treated ARPE-19 cells. These in vitro findings provide evidence that cholesterol oxides can directly damage cultured retinal and RPE cells. The oxysterol-induced oxidative stress in these cells may be a factor in the pathology of retinal degenerative diseases.