Cell viability assay

Cell viability was evaluated using the MTT assay. In brief, ARPE-19 cells at a density of 1×10⁴ cells/well were incubated with or without SAL (12.5–100 µg/ml) for 24 h and then treated with 200 µM H₂O₂ for 6 h. Next, 50 µl of MTT solution (5 mg/ml; Sigma-Aldrich; Merck KGaA, Darmstadt, Germany) was added into each well, and the plate was incubated for 4 h at 37°C. Then the supernatant was removed and 100 µl DMSO (Sigma-Aldrich; Merck KGaA) was added to dissolve formazan. The absorbance was read at 490 nm using an enzyme linked immunosorbent assay plate reader (Olympus, Tokyo, Japan). The experiment was performed in triplicate.