Effects of Apple Pectin on Fecal Enzyme Activities and Prostaglandin E2 Levels in Azoxymethane-induced Rat Colon Carcinogenesis

Pectin is a partially methoxylated polymer of ga-lacturonic acid obtained from fruits. Among pectins from various sources, apple pectin exerts stronger bacteriostatic action on Staphylococcus aureus, Streptococcus faecalis, Pseudomonas aeruginosa, or Escherichia coli than does citrus pectin. In this study, we used water-soluble methoxylated pectin from apple. Supplementation of the diet with 20% apple pectin significantly decreased the number of colon tumors and the incidence of such tumors. Interestingly, prostaglandin E2 (PGE2) levels in the distal colonic mucosa of rats fed with 20% apple pectin were lower than the levels in rats fed a basal diet. It is known that PGE2 leads to the modulation of the immune response and the activation of ornithine decarboxylase, which is necessary for the proliferation of tumors. In the group fed apple pectin, fecal β-glucuronidase, considered a key enzyme in the formation of carcinogens in the colonic lumen upon dimethylhydra-zine metabolism, had significantly lower activity than that in the control group during the initiation stage of carcinogenesis. With apple pectin, the concentrations of β-glucosidase and azoreductase were also decreased. The effect of apple pectin on colon carcinogenesis may partially depend on the decrease in PGE2 concentration in the colonic mucosa, and may also be related to the levels of fecal enzyme activities, especially β-glucuronidase, during the initiation stage of carcinogenesis.