Selected inflammatory conditions of the distal alimentary tract may respond to topical SCFA treatment. The rationale for using SCFA enemas is based on Roediger's (1980) observation that butyrate is the preferred fuel of colonocytes and that SCFA deficiency could lead, in the short term, to mucosal hypoplasia and, in the long term, to colitis. The absence of luminal nutrients is especially evident in the excluded rectum after complete diversion of the faecal stream. Harig et al. (1989) were the first to treat successfully diversion colitis with SCFA irrigation (acetate 60 mM, propionate 30 mM, n-butyrate 40 mM). However, subsequent studies could not reproduce the initial positive data. In distal ulcerative colitis an impaired mucosal oxidation of SCFAs has been described despite their luminal abundance. Pilot studies using either the SCFA mixture or butyrate monotherapy have yielded promising results. However, extended confirmatory studies with a larger sample size have not yet been performed. Preliminary data are also available for the use of SCFA in pouchitis and radiation proctitis. In summary, SCFA topical therapy seems to be a promising option in distinct forms of inflammatory bowel disease; however, the routine use of SCFAs cannot be recommended until their efficacy has been confirmed in larger trials.
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.
Secondary bile acids (BA) may be involved in the pathogenesis of colorectal cancer. In vivo, starch malabsorption has been shown to reduce fecal excretion of secondary BA. The present in vitro study was performed to investigate the effect of starch fermentation on BA metabolism by colonic bacteria. Fecal samples of healthy volunteers were incubated in anaerobic batch cultures for 48 hours with the primary bile acids cholic (0.6 g/l) and chenodeoxycholic acid (0.4 g/l). Media were starch free or enriched with starch (10 g/l). The pH was controlled and held at 6 or 7. In the starch-free incubations, secondary BA were rapidly formed, and degradation of primary to secondary BA was complete within 24 hours. The formation of secondary BA was partially inhibited by the addition of starch to the media. This effect was stronger at pH 6 than at pH 7. Starch was rapidly and completely fermented. In conclusion, this study showed that formation of secondary BA by fecal bacteria is inhibited when starch is simultaneously fermented, an effect that is mainly, but not completely, explained by reduction of pH.
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