Antitumorigenic effects of several food proteins in a rat model with coloncancer and their reverse correlation with plasma bile acid concentration

In order to obtain information on the preventive effects of various food pr oteins against colonic cancer, six groups of azoxymethane-initiated mature Fischer rats (n=10) were fed respective diets different in protein sources such as bovine milk casein (casein), high-molecular-weight fraction from pr otolytic digest of soy protein isolate (soybean HMF), hen's yolk defatted p rotein (yolk protein), wheat gluten and codfish meat, which had been supple mented with sodium deoxycholate (hereinafter, DCA) as a cancer promoter exc ept for an additional DCA-unfed casein group. All of the living rats at che ckpoints during the feeding period were examined by the use of a bronchus f iberscope for colonic tumor incidence at 6 wk intervals between the 10th an d 34th wk, from which both blood and feces samples were taken at times of e ndoscopy. Tumorigenesis in the colon was perceived by endoscopy at wk 22 in the group fed DCA casein only and at wk 28 in the other groups except the DCA-unfed casein group. At wk 34. both soybean HMF and yolk: protein groups ranked inferior to the DCA-unfed group in tumor incidence. When plasma ste roid or lipid concentration was plotted against tumor incidence at wk 28 or 34, positive correlations were found between plasma bile acid concentratio n and tumor incidence at both weeks. With the exception of the DCA-unfed ca sein group, plasma bile acid concentration was reversely correlated to feca l bile acid excretion. Taken altogether, these results suggest that bile ac ids at higher concentrations in the plasma may serve as risk: factors of co lon tumor incidence.