Protection of retinal pigment epithelial cells from oxidative damage by oltipraz, a cancer chemopreventive agent

Objective. To determine whether oltipraz (4-methyl-5-pyrazinyl-3H-1,2-dithiole-3-thione) protects against oxidative injury in cultured human retinal pigment epithelial (hRPE) cells. Methods. Primary cultured hRPE cells were incubated with various concentrations of oltipraz followed by treatment with the chemical oxidant tert-butylhydroperoxide (tBH). Cell viability was assessed by release of lactate dehydrogenase (LDH) and cleavage of WST-1. Intracellular and mitochondrial levels of glutathione (GSH) were measured by HPLC. Glutathione S-transferase (GST), NADPH-quinone reductase (NQR), and glutathione peroxidase (GPx) were measured by specific enzyme activity assays. Results. Treatment of hRPE cells with oltipraz inhibited tBH-induced cell death in a concentration-dependent manner with significant inhibition at 50 μM. Olitpraz (50 μM) increased GSH levels in hRPE cells by approximately 18% and in hRPE mitochondrial fractions by approximately 50% after 24 hours of exposure. Treatment with oltipraz increased GST and NQR activities by approximately 21% and 11%, respectively. Conclusions. Oltipraz protects hRPE cells against tBH induced injury. The mechanism of protection is likely to include increased cellular and mitochondrial GSH levels and induction of detoxification enzymes, including GST and NQR. Dietary supplementation with oltipraz or other dithiolethiones may help protect the hRPE against oxidant induced injury.