PZH-induced activation of caspase-3, caspase-9, p21, p53, cleaved-PARP and regulation pro-apoptotic protein Bax. The relative optical densities were indicated in B and D. Cells were treated with 250, 500 and 750 µg/mL PZH for 24 h and then were lyzed for the determination of the indicated protein levels by western blot. Actin was used as internal control. * p < 0.05, ** p < 0.01 vs. control group. Data are mean ± SD. (A) Protein expresion of Bax, caspase-3 and caspase-9; (B) The relative optical densities of Bax, caspase-3 and caspase-9; (C) Protein expresion of p21, p53 and cleaved-PARP; (D) The relative optical densities of p21, p53 and cleaved-PARP.