Abstract

Epidemiologic studies have implicated high-fat diet as a major contributing factor in the develop- ment of human colorectal cancer. Animal model studies have also provided the evidence for the promoting effect of high-fat diet on the 1,2-dimethylhydrazine(DMH)-or azoxymethane(AOM)- induced colorectal tumorigenesis. But there are no reported epidemiologic studies correlation vitamin E consumption with colorectal cancer incidence rates worldwide. In animal model, the effect of vitamin E enriched diet on DMH-or AOM-induced colorectal tumorigenesis still remains controver- sial. The purpose of the present experiment is to elucidate the effect of moderate-fat diet and vitamin E enriched diet on colorectal tumorigenesis in female Wistar rats. The experimental diets, based on regular rat chow obtained from Sam-Yang Oil & Feed Co. Ltd. were as follows: 1) regular diet, 2) 5 % soybean oil added diet, 3) 5% soybean oil and vitamin E (4001U/kg diet) added diet, 4) vitamin E (400 IU/kg diet) added diet. Animals were fed the experimental diet for a 3-week acclimatization period. Each dietary group was divided into two subgroups and all animals received a 5-week course of weekly subcutaneous injection of either DMH (40 mg/kg body weight) or saline-EDTA solution. Animals were fed the experimental diet until the termination of the experiment. Animals were sacrificed 25 weeks after the first injection. All of 73 saline-EDTA treated rats developed no colorectal tumor. Soybean oil added diet group and vitamin E added diet group showed slightly higher incidence (% of animals with tumors) and multiplicity (tumors/animal) of colorectal tumors than the regular diet group did, but soybean oil and vitamin E added diet group showed significantly higher incidence and multiplicity of colorectal tumors than regular diet group did (p<0.025). Tumors were larger (p>0.1), and carcinomas were numerous (p<0.01) in the groups receiving excess vitamin E supplement to their diet. The above results suggest the synergistic interaction between 5% polyunsaturated fat and excess vitamin E in diet on DMH-induced colorectal tumorigenesis in female Wistar rats