Effect of IS on caspase-3/7 activity. Caspase-3/7 activity was analyzed using a Promega Caspase Glo 3/7 kit (described in the Materials and Methods) Caspase-3/7 activity peaked at 6 h at 1 mM IS. IS increased caspase- 3/7 activity, but probenecid (20 mM), an OAT inhibitor, attenuated IS- induced caspase-3/7 activity, which is similar to an antioxidant effect. The data represent the mean ± SEM (n = 6 for each group). *P < 0.05 vs. control cells at each time point.