Effect of zearalenone (ZEA) on activation of caspase-3 and caspase-8. Activity of caspase-3 and caspase-8 of HL-60 (A) and U937 (B) cells treated for 24 h with various concentrations of ZEA were measured using specific substrate analogs as described in Materials and methods. Data represent mean values ± S.E.M. from three independent experiments. *, p < 0.05, compared to control.