Soybean Saponins Inhibit Cell Proliferation bySuppressing PKC Activation and Induce Differentiation ofHT-29 Human Colon Adenocarcinoma Cells

Soybeans are major dietary sources of saponins, which have been suggested as possible anticarcinogens. This study was performed to determine the effect of soybean saponins on cell proliferation, differentiation, and apoptosis in human colon cancer cells. HT-29 cells were incubated in various concentrations of saponins for 24, 48, and 72 hours. Cell growth and whole cell protein kinase C (PKC) activity were determined. Alkaline phosphatase activity and carcinoembryonic antigen level were measured as markers for cell differentiation. Apoptotic cells were quantified. Study results indicated that soybean saponin treatment decreased cell growth in a concentration-dependent manner, and pre-treatment of the cells with saponins significantly suppressed the 12-O-tetradecanoyl phorbol 13-acetate-stimulated PKC activity. Cells treated with 300 and 600 ppm of saponins significantly increased alkaline phosphatase activity by 146% and 242% of the control, respectively. Also, 4-10 times more carcinoembryonic antigen was produced in cells treated with saponins. However, at all the concentrations used, saponins did not induce apoptosis, although there were slight decreases in apoptotic activity in cells treated with 240 and 600 ppm of soybean saponins. These results suggest that crude soybean saponin extract effectively suppresses PKC activation and induces differentiation, which possibly mediate the growth inhibition of tumor cells. Further experiments, including preclinical efficacy studies, are required to fully evaluate soybean saponins for their chemopreventive properties.