Inhibitory effect of Bifidobacterium longum cultures on the azoxymethane-induced aberrant crypt foci formation and fecal bacterial beta-glucuronidase.

Abstract

Epidemiologic and experimental studies suggest that consumption of fermented milk products and lactic bacterial cultures that are used to ferment the dairy products, decrease the incidence of certain types of cancer. The present study was designed to determine the effect of lyophilized cultures of Bifidobacterium longum (B. longum), a lactic bacteria, on the azoxymethane (AOM)-induced preneoplastic lesions such as aberrant crypt foci (ACF) formation in the colon and on fecal bacterial beta-glucuronidase activity in male F344 rats. At 5 weeks of age, groups of animals were fed the AIN-76A (control) and the experimental diets containing 1.5% and 3% lyophilized cultures of B. longum. At 10 weeks of age, all animals received sc injection of AOM dissolved in normal saline at a dose rate of 20 mg/kg body wt, once weekly for 2 weeks. The animals were necropsied 6 weeks after the last AOM injection, and the ACF were visualized under light microscopy in the formalin-fixed, unsectioned methylene blue-stained colons where they were distinguished by their increased size, more prominent epithelial cells, and pericryptal space. The cecal contents were analyzed for bacterial beta-glucuronidase activity. The feeding of lyophilized cultures of B. longum significantly inhibited the ACF formation (53%) and the crypt multiplicity in the colon. A significant decrease in the fecal bacterial beta-glucuronidase was also observed in the animals fed the diets containing Bifidobacterium supplements as compared with control diet. These results demonstrate that B. longum in diet influences the metabolic activity of certain types of intestinal microflora that are involved in the production of beta-glucuronidase. Furthermore, the findings also suggest that B. longum supplements inhibit ACF formation, an early preneoplastic marker of malignant potential in the process of colon carcinogenesis.