Potential role of probiotics and prebiotics for the prevention of colorectal cancer

Probiotics are living microorganisms, which upon ingestion in certain numbers, exert health benefits beyond inherent nutrition. Prebiotics are dietary ingredients, which upon ingestion reach the gut to be fermented by the gut flora and cause enhancement of microorganisms, which exert health benefits beyond inherent nutrition. In most cases the probiotic microorganisms are classified as lactic acid producing bacteria, or in the case of prebiotics, additionally also include bacteria which increase the proportion of butyrate in the gut. These type of bacteria maintain positive physiological functions of the gut flora, may aid in alleviating symptoms of lactose intolerance, or affect immune functions. In addition, their participation in decreasing cholesterol serum concentrations or reducing risk for colorectal cancers is a focus of ongoing research. We have been performing mechanistic studies in colon cells in vitro and in vivo to assess protective effects by these microorganisms and some selected metabolites to determine cancer protective properties. It has been found that live, ingested Lactobacilli and Bifidobacteria are efficient in deactivating two carcinogens in the gut of rats. The effects were determined by detecting the modulation of carcinogen induced DNA damage in colon cells following oral application of 7,12-dimethylhydrazine and N-methyl-N'-nitro-N-nitrosoguanidine to Sprague Dawley rats. Also in this test system, lactulose (a synthetic disaccharide, with the properties of prebiotics) was an inhibitor of carcinogen induced DNA damage. Presently, selected metabolites of lactic acid bacteria and of the gut flora are being investigated for their potential to deactivate carcinogens, in order to identify the mechanisms of these protective effects.