Figure 3. Cell viability and heme oxygenase-1 (HO-1) expression in human retinal pigment epithelial cells between curcumin pretreatment and control dimethyl sulfoxide (DMSO) groups with various H₂O₂ concentrations. A: Cell viability measured with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Human retinal pigment epithelial cells (ARPE-19) cells pretreated with 15 μM curcumin showed more cell viability than those from the control DMSO group. The difference was highest in 1000 μM H₂O₂. *p<0.05 . The percentage of live cells among the total cells was calculated from three separate experiments. B: HO-1 protein expression was measured with western blot analysis. The plus sign means pretreatment with 15 μM curcumin. HO-1 expression was higher in the curcumin-pretreated group under treatment of H₂O₂ compared to the control group. β-actin served as the standard. Results were quantified with densitometry. The image for HO-1 was shown from more than three separate experiments.