Previous studies indicated that diets high in soybean-based foods are associated with reduced cancer incidence. Possible anticarcinogens in soybeans include saponins, protease inhibitors, and isoflavones. The present study was performed to examine the effects of soybean saponins on the growth and oxidative stress makers of human liver cancer cells (HepG2) exposed to a peroxide, and to compare their activities with major dietary antioxidants. Cells were treated with t-BHP (tert-butylhydroperoxide), and then incubated with soybean saponins, L-ascorbic acid, α-tocopherol (300, 600, and 1200μg/plate) or selenium (0.05, 0.1 and 0.2μg/plate) for 48 hours. Cells treated with t-BHP for 45 min had a increased level (46%) of thiobarbituric acid reactive substances (TBARS), while cell growth and enzyme activities were not changed. Soybean saponins and all of the antioxidants used significantly decreased cell growth in a dose-dependent manner (p＜0.05), and soybean saponins exhibited the highest cell growth inhibition. The cellular contents of TBARS were significantly reduced by soybean saponins and antioxidants treatment (p＜0.05). Cellular α-tocopherol content was increased in cells treated with L-ascorbic acid and α-tocopherol, although L-ascorbic acid showed a minor increase compared to α-tocopherol. The activity of SOD (superoxide dismutase) was slightly, but significantly, increased in cells treated with L-ascorbic acid and α-tocopherol. However, no dose-dependent effects was observed. Cellular GPx (glutathione peroxide) activity was increased in cells incubated with selenium, L-ascorbic acid, and α-tocopherol in a dose-dependent manner. Soybean saponins and all of the antioxdants used were effective in enhancing GST (glutathione S-transferase) activity with no dose-dependent effect.These results suggest that soybean saponins and major dietary antioxidants inhibit cancer cell growth possibly by reducing t-BHP-induced oxidative stress in HepG2 cells. Further mechanistic investigations on anticancer activities of soybean saponins is required.

Keywords: Soybean, Saponin, tert-butylhydroperoxide, Oxidative stress, Liver cancer