Effect of Lactobacillus acidophilus on colon carcinogenesis

The effect of dietary supplementation of Lactobacillus acidophiluis on chemically induced colon cancer in Wistar male rats was studied. The control group was fed only lab meal and the experimental group was fed lab meal supplemented with viable L. acidophilus (5 $\times$ 10$\sp8$ cells/day). Following 4 weeks of prefeeding, each rat was injected s.c. with the carcinogen, N-nitrosobis(2-oxopropyl)amine (BOP), once a week for 10 weeks. Ornithine decarboxylase (ODC) activity and cell proliferative rate (CPR) in colonic epithelial tissue were used as markers for colon carcinogenesis. At the 26 week induction study, colon tumor incidence, ODC activity, and CPR for the control group were significantly higher than those for the experimental group. At the end of 40-week study, there were no differences in survival rates and colon tumor incidence between groups. No significant differences in the ODC activity and CPR between groups were also observed. However, there were differences in number and size of colon tumors between groups, the experimental group had less and smaller tumors than the control group had. The results indicated that the supplementation of L. acidophilus in the diet seemed to delay the initiation of chemically induced colon tumor in rats. Since the secondary bile acids formed by the bacterial 7a-dehydroxylation action from the primary bile acids have been implicated as promoters of colon carcinogenesis, the effect of L. acidophilus on the degradation of primary bile acid, chenodeoxycholic acid (CDCA), was studied in vitro. Human fecal inoculum (HFI) and fecal inoculum plus L. acidophilus (HFILA) were incubated in 15 ml of MRS broth containing 800 ug CDCA at 37$\sp\circ$C anaerobically for 24 h. The rate of degradation of CDCA was determined by high-performance liquid chromatography. After 24 h incubation, the pH for HFI and HFILA were 4.8 and 4.5, respectively. The degradation of CDCA was 49% for HFI and 32% for HFILA. The addition of L. acidophilus also suppressed the growth of coliforms and anaerobes. Transformation of CDCA by individual L. acidophilus, E. coli, and C. perfringens were also examined. No transformation by any of these microorganisms was observed. Thus, biotransformation of some primary bile acids is reduced in the presence of L. acidophilus. This result suggests that a high number of L. acidophilus in the intestine may potentially reduce the on-set of colon carcinogenesis