Soybean saponins inhibit cell proliferation by suppressing PKC activation and induce differentiation of HT-29 human colon adenocarcinoma cells

Soybeans are major dietary sources of saponins, which have been suggested a s possible anticarcinogens. This study was performed to determine the effec t of soybean saponins on cell proliferation, differentiation, and apoptosis in human colon cancer cells. HT-29 cells were incubated in various concent rations of saponins for 24, 48, and 72 hours. Cell growth and whole cell pr otein kinase C (PKC) activity were determined. Alkaline phosphatase activit y and carcinoembryonic antigen level were measured as markers for cell diff erentiation. Apoptotic cells were quantified. Study results indicated that soybean saponin treatment decreased cell growth in a concentration-dependen t manner, and pretreatment of the cells with saponins significantly suppres sed the 12-O-tetradecanoyl phorbol 13-acetate-stimulated PKC activity. Cell s 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 c ells treated with 240 and 600 ppm of soybean saponins. These results sugges t that crude soybean saponin extract effectively suppresses PKC activation and induces differentiation, which possibly mediate the growth inhibition o f tumor cells. Further experiments, including preclinial efficacy studies, are required to fully evaluate soybean saponins for their chemopreventive p roperties.