Soy isoflavones and saponins provide modest protection from colon cancer in a mouse model

Abstract

Colon cancer risk is highly correlated with dietary factors. We have systematically investigated soy protein and bioactive compounds found in soy, isoflavones (IF) and saponins (SAP), using a mouse model of colon cancer. In previous studies we found soy IF were protective of azoxymethane (AOM)-induced tumors in C57Black/J mice and that soy protein reduced tumor burden compared to casein. In two experiments we attempted to verify these findings and separate the effects of SAP from soy protein and IF. In study 1, female, ovariectomized C57B/J mice were fed diets containing soy protein depleted of IF and SAP, soy+IF, soy+SAP, or soy+IF+SAP. In study 2, similar mice were fed diets containing soy flour prepared from soybeans that were high, moderate or low in naturally occurring IF and SAP. All mice were treated once per wk for 6 wks with IP injection of 10 mg AOM/kg body weight and continued on the study for 35 wks. At termination all organs were removed and weighed and colon examined for tumors. Tumor incidence in study 1 was 46, 46, 30 and 45% for mice fed soy, soy+IF, soy+SAP and soy+IF+SAP, hence a slight decrease in mice fed SAP but not IF. In study 2, tumor incidence was 33, 29 and 21% in mice fed soy flour with low, moderate and high IF+SAP, hence a slight negative correlation with IF+SAP concentration. Overall, the protective effects of soy IF and SAP on colon tumor incidence were modest in this animal model. However, preliminary evidence suggests IF may inhibit cyclooxygenase-2 expression in mouse colon thereby providing a potential protective mechanism. Funding provided by USDA-CSREES.