Comparative Effects of Cellulose and Soluble Fibers (Pectin, Konjac Glucomannan, Inulin) on Fecal Water Toxicity toward Caco-2 Cells, Fecal Bacteria Enzymes, Bile Acid, and Short-Chain Fatty Acids

The aim of this study was to compare the effects of cellulose and three soluble dietary fibers, pectin, konjac glucomannan (KGM), and inulin, on the cytotoxicity and DNA damage of fecal water-treated Caco-2 cells, a human colon adenocarcinoma cell line, and to investigate the fecal components that potentially modulate the fecal toxicity, that is, bacterial enzymes, bile acids, and short-chain fatty acids. Six-week-old BALB/cJ mice were randomly allocated to consume an AIN-93 diet that contained no dietary fiber (fiber-free) or 5% (w/w) cellulose, pectin, KGM, and inulin for 3 weeks. Feces were collected during days 18-21. Fecal waters were co-incubated with Caco-2 cells to determine the cytotoxicity and DNA damage. In addition, the fecal bacterial enzymes, bile acids, and short-chain fatty acids were determined. Results indicated that all fiber diets similarly increased the survival rate (%) of fecal water-treated Caco-2 cells as compared with the fiber-free diet. The inhibition of fecal water-induced DNA damage in Caco-2 cells was greater for the pectin and inulin diets than for the cellulose and KGM diets. In contrast, cellulose exerted the greatest inhibitory effect on the fecal beta-glucuronidase activity. Cellulose and all soluble dietary fibers reduced the secondary bile acid concentrations in the fecal water, but only soluble fibers increased the fecal concentrations of short-chain fatty acids, as compared with no fiber. Therefore, this study suggests that all dietary fibers substantially reduced the fecal water toxicity, which is associated with decreased secondary bile acid levels by all fibers, reduced fecal beta-glucuronidase activity by cellulose, and increased short-chain fatty acid levels by soluble dietary fibers.