Effect of ZEA on cell cytotoxicity and apoptotic induction of human leukemic HL-60 and U937 cells. (A) Cell viability of HL-60, U937 and human peripheral blood mononuclear cells using MTT assay. (B) DNA cell cycle analysis of HL-60 and U937 cells treated with ZEA for 24 h. * p < 0.05, compared with control cells. (C) and (D) Histograms of HL-60 and U937 cells treated with ZEA at indicated concentrations, respectively. Cells were stained with PI and subjected to flow cytometer as described in Materials and methods. M1, subdiploid; M2, G1; M3, G2 M.