To study the effect of oxidative stress on expression of OGC and DIC, the cells were exposed to H2O2 at varying doses (50, 100, 200, 300 μM) for 24 hours, and varying durations (2, 4, 6, 8, 24 hours) with 200 μM H2O2. To identify dose and time-dependent inhibition of OGC and DIC expression by chemical inhibitors, cells were incubated with phenylsuccinic acid (PS) and butylmalonic acid (BM; Sigma-Aldrich Corp., St. Louis, MO, USA) in varying doses (2, 5, 10 mM) for 24 hours, and varying durations (2, 4, 6, 8, 24 hours) with a single 5 mM dose of either PS or BM, respectively. Cells were also treated with 5 mM PS or BM, in the presence or absence of 2 mM GSH-MEE (Sigma-Aldrich Corp.) for 24 hours. To identify the effect of competitive inhibitors of the two transporters, cells were treated with a 5 mM dose of either dimethyl 2-oxoglutarate or diethyl malate for 24 hours. All inhibition studies were performed with RPE cells in serum-free medium containing 0.1% dimethyl sulfoxide.