Impact of bacteria in dairy products and of the intestinal microflora on the genotoxic and carcinogenic effects of heterocyclic aromatic amines

This article gives a short overview on the present state of knowledge of th e effects of the intestinal microflora on the health hazards of heterocycli c aromatic amines (HAs). Results of single cell gel electrophoresis assays with conventional, germ free and human flora associated rats indicate that the presence of intestinal microorganisms strongly enhances the induction o f DNA-damage in colon and liver cells by IQ. Furthermore, it was found that supplementation of the feed with Lactobacilli attenuates the induction of colon cancer by this same amine. These recent findings suggest that the int estinal microflora and lactic acid bacilli in dairy products strongly affec t the health risks of HAs. Nevertheless, most previous experiments with HAs focused on the involvement of mammalian enzymes in the biotransformation o f these compounds and only a few articles are available which concern inter actions of bacteria with HAs. Some of these studies suggested that the form ation of directly mutagenic hydroxy-metabolites of the amines by fecal bact eria might be an important activation pathway but it turned out that the hy droxy-derivative of IQ is not genotoxic in mammalian cells and does not cau se colon cancer in laboratory rodents. There is some evidence that hydrolys is of HA-metabolites by bacterial beta -glucuronidase might play a role in the activation of HAs but experimental data are scarce and no firm conclusi ons can be drawn at present. The most important detoxification mechanism ap pears to be the direct binding of the HAs to the cell walls of certain bact erial strains contained in fermented foods. It was shown that these effects do also take place under physiologically relevant conditions. Overall, it seems that intestinal bacteria play a key role in the activation and detoxi fication of HAs which has been an area of research long ignored. The elucid ation of these mechanisms may enable the development of biomarkers for colo n cancer risk and nutritional strategies of protection. (C) 2001 Elsevier S cience B.V. All rights reserved.