Figure 3. The ARPE19 cells (an immortal retinal pigment epithelial cell line from a 19-year-old donor) were treated with melatonin (M) at different concentrations. After 1 h, 24 h, and 48 h culture, 0.5 mM H₂O₂ (H) was added and cultured for 24 h. Cells cultured with H₂O₂ alone were used as the controls. Cell viability was evaluated by the microculture tetrazoline test and expressed as percentages of controls (mean±SD in triplicate tests). Error bars represent SD A: Pretreatment with low concentrations of melatonin at 10⁻¹⁰ M (M-10) for 1 h, 24 h, and 48 h significantly protected cells against H₂O₂. B: Pretreatment with high concentrations of melatonin at 10⁻⁶ M (M-6) obtained similar results. The difference between cells cultured with and without melatonin at both high and low concentrations was statistically significant at all three different pretreatment periods. *p<0.05, compared with the controls.