Protective role of probiotics and prebiotics in colon cancer

Ingestion of viable probiotics or prebiotics is associated with anticarcino genic effects, one mechanism of which is the detoxification of genotoxins i n the gut. This mechanism was shown experimentally in animals with use of t he rat colon carcinogen 1,2-dimethylhydrazine and by determining endpoints that range from tumorigenesis to induction of DNA damage. Because of the co mplexity of cancer initiation, cancer progression, and the exposure of canc er in the gut, many types of interactions may be envisaged. Notably, some o f our newer studies showed that short-lived metabolite mixtures isolated fr om milk that was fermented with strains of Lactobacillus bulgaricus and Str eptococcus thermophilus are more effective in deactivating etiologic risk f actors of colon carcinogenesis than are cellular components of microorganis ms. Ingestion of prebiotics results in a different spectrum of fermentation products, including the production of high concentrations of short-chain f atty acids. Gut flora, especially after the ingestion of resistant starch, induces the chemopreventive enzyme glutathione transferase ir in the colon of the rat. Together, these factors lead to a reduced load of genotoxic age nts in the gut and to an increased production of agents that deactivate tox ic components. Butyrate is one such protective agent and is associated with lowering cancer risk. It was recently shown that buytrate may inhibit the genotoxic activity of nitrosamides and hydrogen peroxide in human colon cel ls. In humans, the ingestion of probiotics leads to the excretion of urine with low concentrations of components that are genotoxic in human colon cel ls and high concentrations of components that induce oxidized DNA bases.