Figure 2. NAC treatment suppresses light-induced oxidative stress. 661W cells/ARPE-19 cells were pretreated with NAC (5 mM for 661W cells and 2.5 mM for ARPE-19 cells) or vehicle and cultured under light/dark conditions for 3 days. (A) The intracellular ROS were stained with DCFH-DA fluorescent probe identified by green fluorescence. Scale bar=50 μm. Relative fluorescence intensities were calculated and compared. (B) The GSH/GSSG ratio was measured with a GSH/GSSG Assay Kit. (C) The HO-1 level was determined with western blotting, and β-actin was referred as an internal control. (D) 661W cells pretreated with 5 mM NAC/vehicle were cultured under light/dark conditions for 3 days. ARPE-19 cells pretreated with 2.5 mM NAC/vehicle were cultured under light/dark conditions for 6 days. The cell death percentage was evaluated with PI/Hoechst staining. Scale bar=100μm. The percentage of cell death was calculated as PI-positive cells/total cells%. Three independent experiments are conducted two weeks apart. The results are presented as the mean± SEM. n (per group) =3, *P < 0.05, **P < 0.01.