ROLE OF APOPTOSIS, PROLIFERATING CELL NUCLEAR ANTIGEN AND P53 PROTEININ CHEMICALLY-INDUCED COLON-CANCER IN RATS FED CORNCOB FIBER TREATED WITH THE FUNGUS PLEUROTUS-OSTREATUS

The role of apoptosis proliferative cell nuclear antigen (PCNA) and p5 3 protein in the preventive effects of dietary fiber treated with the fungus Pleurotus ostreatus on rat-colon tumorigenesis was studied. Tum ors were induced by five subcutaneous injections of 1,2-dimethylhydraz ine (DMH), 20 mg/kg rat, once a week. Rats were fed a semi-synthetic f iberfree diet (control) or a high-fiber diet (15%) derived from cornco b treated or non-treated with the fungus. The rats we sacrificed 24 we eks after the first carcinogenic injection. The fungus treated corn-co b significaultly decreased tumor incidence (to 26%) as compared to 44% and 57% in the other dietary groups. The apoptotic index (AI) signifi cantly decreased in malignant tissue as compared to non-tumorous tissu e. PCNA and cytoplasmic content of p53 protein exhibited an increasing trend in malignant tissue as compared to benign tissue (at 15% and 18 %. respectively). The fungus-treated corncob significantly increased t he content of p53 in the cell cytoplasm (to 33%) and its serum levels in tumor-bearing rats (to 38%). The cellular concentration of PCNA dec reased to 61% in tumors obtained from rats fed the fungus-treated corn cob as compared to controls. A high positive correlation was found bet ween tumor grade and p53 protein in the serum (r = 0.97) or in the cel l cytoplasm (r = 0.77). and between tumor grade and PCNA (r = 0.81). A n inverse relationship was found between tumor grade and AI (r = -0.63 ). We found that 15% of corncob fiber alone seems not to be enough to prevent chemically induced tumorigenesis. The corncob fiber (15%) trea ted with the fungus had a significant protective effect against DMH-in duced rat colon cancer, even at 15% and this effect was accompanied by the activation of some cellular mechanisms such as apoptosis, PCNA an d p53 protein activation. Incubation of corncob with the fungus Pleuro tus os. increased the dietary fiber content up to 78%. Thus corncob in hibits colon cancel development, and therefore, may considered of pote ntial use to the public.