The carbohydrate crystalean and colonic microflora modulate expression of glutathione S-transferase subunits in colon of rats

Background Glutathione S-transferases (GSTs)* are an important class of pha se II, predominantly detoxifying, enzymes. The supergene family is composed of several isoenzymes, hetero- and homodimers, with tissue specific distri bution and levels of expression. The hypothesis is that a higher expression of individual proteins within a specific tissue may be associated with a d ecreased burden of exposure to reactive carcinogens and ultimately with a d ecreased cancer risk in this tissue. Aims of the study Since nutrition is expected to contribute to the gene exp ression, it was the aim of this study to investigate the impact of dietary factors, especially resistant starch, and of the gut microflora, which may be influenced by diet, on the GSTs in colon cells of rats. Methods For this, a technique using high pressure liquid chromatography was established with which for the first time GST isoenzymes were analysed in colon cells and compared to the levels of the corresponding proteins in the liver of the same rat. Results It was found that colon cells contain mainly GST pi and low amounts of mu but not GST alpha. In contrast, the predominant form of GSTs in the liver was alpha, then mu and hardly any pi. Altogether, liver cells had app roximately tenfold more total GSTs than colon cells. The feeding of "Crysta lean", a retrograded, high amylose starch which alters the fermentation pro file and the composition of the microflora, led to higher levels of GST pi in the colon. Furthermore, the comparison of GSTs in colon cells of germ-fr ee rats revealed they were much lower than those observed in rats with conv entional microflora. Conclusions These findings clearly demonstrate that the gut bacteria, or th eir metabolic products, enhance GST expression. The studies support the hyp othesis that nutrition - by affecting the gut flora - may induce this poten tially protective and important class of phase II enzymes in important tumo r target cells.