Effects of dietary fiber on the rat intestinal mucosa exposed to low dosesof a carcinogen

Background: Changes in morphological and immunohistochemical parameters wer e studied in the mt intestinal mucosa exposed to low doses of a carcinogen and administered with dietary fibers. Methods: Tumors were induced by five subcutaneous injections of 1,2-dimethylhydrazine, 10 mg/kg rat, once a week . Rats were fed a semi-synthetic fiber-free diet (control) or a high-fiber diets (15%) derived from cellulose, tomato peels or white grape. The rats w ere sacrificed 24 week after the first carcinogen's injection. The ileum, c olon and tumors were removed for the study. Areas of the mucosal stroma and of lymph infiltrations, and mitotic index were studied along with morpholo gical parameters. Immunohistochemical parameters included determination of Ki-67 proliferating protein and apoptotic index. Results: Areas of the stro ma in colon tumors increased in rats fed tomato peels. Changes in areas of lymphoid infiltrates were related to the type of diet and tumor presence. L ymphoid infiltrations were found to be highly developed in the colon area c lose to tumors, especially in rats fed the white-grape diet. Mitotic index and Ki-67 protein increased significantly in the colon area close to a tumo r and in tumors themselves without any relation to the fiber varieties cons umed. Changes in the rate of apoptosis were not related to the preventive e ffect of diets: apoptotic index was high in tumors obtained from rats fed t he high-cellulose diet with high tumor-preventive effects and also from rat s fed the high-tomato-peel diet with low tumor-preventive effects Conclusio ns: No morphological changes were found in the ileum of rats exposed to a c arcinogen and fed different dietary fibers. In the colon, a carcinogen even in low concentrations inhibited the lymphoid system in the mucosa located far from the tumor or close to the tumor. An increase in the proliferation rate in the colon close to the tumor may reflect the development of precanc eromatous processes or may be related to the effect of growth factors expre ssed by armor cells. Finding adenoma-like dysplasia near tumors may be poss ible in early stages of the development of new tumors. In addition, activat ion of the lymphoid system of the colon following consumption to specific d ietary fiber may be a mechanism by which fiber protect against cancer.