Lutein protects retinal pigment epithelium from cytotoxic oxidative stress

Context: Lutein (LUT) and zeaxanthin (ZEA) are currently under investigation in clinical trials as prophylactic nutritional agents for age-related macular degeneration (AMD). However, dose used in these trials is empirical and not been investigated in in vitro studies. Objective: In this study, we investigated the dose-response effect of LUT and ZEA in protecting retinal pigment epithelium (RPE) from oxidative stress, a common underlying pathology in AMD. Methods: Three thousand cultured human retinal pigment epithelial cells (ARPE-19) were plated in 72-well plate and after 24 h were exposed to increasing concentrations of hydrogen peroxide (H2O2). ARPE-19 cells were exposed to four different concentrations of LUT (0.5, 1, 2 and 4 mu g/mL) and ZEA (0.1, 0.2, 0.4 and 0.8 mu g/mL). After 24 h incubation, cells were subjected to oxidative stress induced with H2O2. Cultures containing saline solution and dichloromethane served as controls. Cell viability was assessed using the WST-1 assay. Pathophysiological pathways were evaluated by measuring caspase-3 levels as an indicator of apoptosis induction. Reactive oxygen species (ROS) levels were measured using dihydrorhodamine-123. Results: Cell viability as a percentage of control was 81.3%, 81.1%, and 88.8% at 0.5, 1, and 2 mu g/ml, respectively of LUT (p<0.001). The maximum cytoprotective effect was seen with LUT at 2 mu g/mL. ZEA did not show any cytoprotective effect at all concentrations used in the study. Caspase-3 showed a corresponding decrease in levels with LUT (1 and 2 mu g/ml). Significant decrease in ROS levels were measured only with LUT at 4 mu g/ml (p = 0.02). Discussion and conclusions: Results from our study provide in vitro data to support the epidemiologic studies, which are currently underway to provide evidence that lutein may act as cofactor that modulates processes implicated in AMD pathogenesis.