Bile Acid Metabolism by Colonic Bacteria in Continuous Culture: Effects of Starch and pH

Abstract

Secondary bile acids (BA) have been shown to be involved as a promoting agent in the adenoma-carcinoma sequence of colorectal cancer. In previous studies, fermentation of starch has been shown to inhibit the degradation of primary to secondary BA by the colonic microflora. This study was designed to investigate BA metabolism in continuous cultures of mixed fecal bacteria to get further insights into the mechanisms of this inhibition. Fermentation vessels were fed with media containing cholic (0.6 g/l) and chenodeoxycholic acid (0.4 g/l). Cultures were either starch-free or enriched with starch (10 g/ 1). pH was controlled and adjusted to 7.0 or 6.0. Total culture duration was 28 days and concentrations of BA, short-chain fatty acids (SCFA), and starch were measured periodically. At pH 6, significantly more primary BA remained in the media and less secondary BA were produced. Total BA concentrations were lower at pH 7. SCFA concentrations were higher in the vessels supplemented with starch. Starch was completely fermented and not present in significant amounts in any fermentation vial after the first week. These data indicate that bacterial breakdown of primary to secondary BA is inhibited when starch is simultaneously fermented. This effect can be explained by the reduction of pH resulting from SCFA production. Considering these findings, resistant starch which escapes assimilation in the small bowel may be a protective factor against colorectal cancer.

Germinated barley foodstuff, a prebiotic product, ameliorates inflammation of colitis through modulation of the enteric environment

“…27,28 Also, these patients may have higher levels of carcinogenic secondary bile acids and, thus, be more likely to develop cancer on the right side of the colon, where secondary bile acid concentrations are highest. 37,38 Therefore, it is important to investigate whether GBF eliminates bile acids in vivo. In the present study, GBF significantly decreased the total cecal bile acid content in colitis mice compared with the content in the control group.…”

Characterization of the Contents of Ascending Colon to Which Drugs are Exposed After Oral Administration to Healthy Adults

“…In contrast, in the fed state, in 10 out of 12 subjects, primary bile acids were found in higher % content than secondary bile acids, indicating that when more bile acids enter the colon (fed state) the capacity for conversion to secondary bile acids is overwhelmed, resulting in more bile acids quantified in the primary form. Another reason might be that, as in vitro data have shown (42), bacterial breakdown of primary to secondary bile acids is inhibited when carbohydrates are simultaneously fermented. Data of the present study are in line with previous data (43,44) showing that, in ileostomy subjects, excreted bile acids consist of C (70%) and CDC (30%).…”

Rye Bread Improves Bowel Function and Decreases the Concentrations of Some Compounds That Are Putative Colon Cancer Risk Markers in Middle-Aged Women and Men

“…Butyrate is the preferred fuel for colonocytes, especially in the distal colon and may be a protective factor in colon carcinogenesis (Scheppach 1998). SCFA may also decrease the colonic pH and inhibit dehydroxylation of bile acids, thus inhibiting conversion of primary bile acids to secondary bile acids (Christl et al 1997) Bacterial fermentation in the colon produces large amounts of end products, some of which have been shown to be harmful to the colonic epithelium and are putative colon cancer risk markers. Bacterial ␤-glucosidase hydrolyzes plant glycosides to release aglygones, many of which are mutagenic, although some also have anticarcinogenic activity (Rowland 1995).…”