Curcumin protects retinal pigment epithelial cells against oxidative stress via induction of heme oxygenase-1 expression and reduction of reactive oxygen

To determine whether curcumin induces expression of the defensive enzyme heme oxygenase-1 (HO-1) and protects cells against oxidative stress in cultured human retinal pigment epithelial cells. Effective concentrations and toxicities of curcumin were determined after 3 h of curcumin treatment with the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Confluent human retinal pigment epithelium cell lines (ARPE-19) were preincubated with curcumin and oxidatively challenged with H(2)O(2). HO-1 expression was determined with western blot analysis. To confirm the protective role of HO-1 in oxidative stress, small interfering RNA (siRNA) against HO-1 or inhibitor of HO-1 was treated with curcumin in retinal pigment epithelium cells. Intracellular levels of reactive oxygen species (ROS) were measured with flow cytometry and confocal microscopy. Apoptosis was evaluated with Annexin V-fluoroscein isothiocyanate staining. Curcumin had little cytotoxicity at concentrations less than 30 μM, and HO-1 expression was the highest at the 15 μM concentration. At this concentration, curcumin also increased the cytoprotective effect against the oxidative stress of H(2)O(2) through the reduction of ROS levels in human retinal pigment epithelial cells. Curcumin's effect on the reduction of ROS was mediated by the increase in HO-1 expression. Curcumin upregulated the oxidative stress defense enzyme HO-1 and may protect human retinal pigment epithelial cells against oxidative stress by reducing ROS levels.