Objective To explore the effect and mechanism of steroidal saponin from Ypsilandra thibetica (YB16) on apoptosis of HCT15 human colon cancer cells.

Methods HCT15 cells were cultured in vitro and treated with YB16 at doses of 0.125 – 16.000 mol/L for 24 hours. The survival rate of HCT15 cells was measured with methyl thiazolyl tetrazolium (MTT) assay. The morphological changes of cells were observed under light microscope. Apoptosis was observed with acridine orange (AO) staining. Changes in cell membrane potential were observed with JC-1 staining. Western blot was used to detect protein expression of B lymphocyto tumor-2 (Bcl-2), poly(ADP-ribose) polymerase (PARP), cleaved-PARP, caspase-3, and cleaved-caspase-3.

Results Compared with that of the control cells, the survival rates of HCT15 cells exposed to various doses of YB16 decreased significantly in a dose-effect manner (P < 0.05) and significantly increased number of the cells with apoptotic characteristics was also observed for the YB16 treated HCT15 cells. Significantly increased expression of Bcl-2 protein (0.542 ± 0.04, 0.351 ± 0.03) and increased expressions of cleaved-PARP (0.647 ± 0.05, 0.686 ± 0.03) and cleaved-caspase-3 protein (0.677 ± 0.03, 0.762 ± 0.04) were detected in the HCT15 cells treated with 0.500 and 1.000 μmol/L YB16 in comparison with those in the control cells (all P < 0.05).

Conclusion YB16 can inhibit the proliferation and promote cell apoptosis of HCT15 cells, which may be related to down-regulation of Bcl-2 protein expression and up-regulation of cleaved-PARP and cleaved-caspase-3 protein expression.