Soyasaponin I, III, and Soyasapogenol B Inhibit Proliferation and Modulate PKC Expression in Caco-2 Human Colon Cancer Cells

Group B saponins, the predominant form of saponins in heat-treated soy products, have been shown to possess hypocholesterolemic, antimutagenic, and anticarcinogenic properties. Previous studies have evaluated crude mixtures of soyasaponins, but studies evaluating a single purified soyasaponin as an anticarcinogenic agent are limited. The goal of this study is to examine the effects of purified soyasaponins I and III as well as their aglycone form, soyasapogenol B, as anticarcinogenic agents on the human colon adenocarcinoma cell line (Caco-2). Experiments were conducted to examine the effects of purified soyasaponins on cell proliferation, Protein Kinase C (PKC) activity, and cell morphology in Caco-2 cell cultures. Treatment of cells with soyasaponins I and III at concentrations of 0.3-0.9 mg/ml significantly reduced viable cell numbers after 48 and 72 hours of exposure by 8.6-65.3% (p < 0.05). Soyasapogenol B at a concentration of 0.15 mg/ml significantly reduced viable cell numbers after 24 hours by 62.4% (p < 0.05). Cell morphology changes demonstrated that as concentrations and lipophilicity of soyasaponins increased, cell membranes became rougher and more irregular. Treatment of cells for 72 hours significantly reduced the amount of PKC activity by 9-40% (p < 0.05). Results indicate that purified soyasaponins I, III and soyasapogenol B can suppress Caco-2 colon cancer cell proliferation. These findings suggest that purified group B soyasaponins and their final metabolite soyasapogenol B may be a colon-cancer suppressive component of soy that warrants further examination as a potential nutraceutical or functional food.