Saponins from various plant sources have been suggested as possible anticarcinogens. Major dietary sources of saponins include legumes such as soybeans. This study was performed to determine the effect of soybean saponins on aflatoxin B(1)(AFB(1))-induced mutagenicity and AFB(1)-DNA adduct formation using Salmonella typhimurium and human liver hepatoma (HepG2) cells, respectively. Major antioxidants including L-ascorbic acid, alpha-tocopherol, all-trans-retinol, and butylated hydroxytoluene (BHT), previously reported to possess antimutagenic activity, were used as test materials to evaluate the relative effectiveness of saponins. Results indicated antimutagenicity was in the order of BHT > saponins > alpha-tocopherol > L-ascorbic acid. Soybean saponins exerted a significant effect, inhibiting the mutagenicity of AFB(1) by 52%, 64%, and 81% at concentrations of 600, 900, and 1,200 microg per plate, respectively. The amount of tritiated AFB(1) metabolites-DNA adducts formed in HepG2 cells was significantly reduced when cells were preincubated with 10 or 30 microg/ml of test materials. Soybean saponins inhibited AFB(1)-DNA adduct formation by 50.1% at a concentration of 30 microg/ml, whereas L-ascorbic acid and BHT reduced adduct formation by 38.4% and 32.6%, respectively, at the same concentrations. These results indicate that soybean saponins possess not only a significant antimutagenic activity but a strong inhibitory action against carcinogen-induced DNA damages. Soybean saponins possibly block the initiation stage of carcinogenesis, and further studies are required to elucidate the mechanisms of action.

This experiment characterizes the time-dependent changes of phospholipids of liver microsomes, plasma, and triglycerides of adipose tissue when olive oil is substituted for soybean oil in the American Institute of Nutrition 93 Growth (AIN 93G) diet. After 2 weeks of acclimation with 7% soybean oil diet, 108 male Sprague-Dawley rats were randomly assigned to be fed diets with either 7% or 15% soybean oil or olive oil. Fatty acids of adipose, blood plasma, and liver microsomes were analyzed every four days for 4 weeks by gas chromatography. After 6 weeks of feeding, no differences in body weight or body composition were observed. The most profound changes occurred in the proportion of linoleic acid to oleic acid in the three tissues. The feeding regimens increased the ratio of oleic to linoleic acids by 6-to 14-fold in olive oil groups compared with soybean oil groups. The level of arachidonic acid declined in olive oil groups. In contrast, levels of n-3 series long chain fatty acids, eicosapentaenoic and docosahexaenoic acids, were higher in olive oil groups. The peroxidizability index, a measure of unsaturation, declined significantly in groups fed olive oil compared to soybean oil. These data indicate that substantial remodeling in fatty acid composition continues until 18-carbon precursors in adipose depots match the dietary pattern. The rate of change appears to be governed by the fractional exchange rate of adipose tissue, which is limited by the rates of lipolysis and daily fatty acid oxidation.