Dietary prevention of azoxymethane-induced colon carcinogenesis with rice-germ in F344 rats

The modifying effect of dietary administration of defatted rice-germ and ga mma-aminobutyric acid (GABA)-enriched defatted rice-germ on azoxymethane (A OM)-induced colon carcinogenesis was investigated in two experiments with m ale F344 rats. In the first experiment (the pilot study), the effects of th e defatted rice-germ, the GABA-enriched defatted rice-germ and rice-germ on AOM-induced (15 mg/kg body wt once a week for 3 weeks) formation of aberra nt crypt foci (ACF) were examined. The latter two preparations (2.5% in the diet) significantly inhibited ACF formation (P < 0.005). In the second exp eriment, a longterm study of the effects of rice-germ was done. One group w as treated with AOM alone, four groups received the carcinogen and were fed the diets containing 2.5% rice-germ or 2.5% GABA-enriched defatted rice-ge rm for 5 (initiation phase) or 30 weeks (post-initiation phase), two groups were treated with rice-germ or GABA-enriched defatted rice-germ alone and one group was kept on the basal diet, At the termination of the study, diet ary exposure to rice-germ during the initiation phase significantly reduced the incidence of colonic adenocarcinoma (71 versus 29%, P < 0.01), GABA-en riched defatted rice-germ or rice-germ during the post-initiation phase als o decreased the frequency of colonic adenocarcinoma (71 versus 20%, GABA-en riched defatted rice-germ feeding, P < 0.01; 27%, rice-germ feeding, P < 0. 01). These data suggest that constituents of rice-germ are possible dietary preventatives for human colon cancers.