Effects of soy isoflavones on aberrant crypt foci and DNA damage in colon of rats treated with dimethylhydrazine

Abstract

Soy isoflavones have received considerable attention for the potential role in reducing the risk of cancers. We previously observed significant reduction in the number of colonic aberrant crypt foci and expression of cyclooxygenase‐2 in rats which were fed soy isoflavones after injection of dimethylhydrazine (DMH) for 12 weeks. In this study, we investigated whether feeding soy isoflavones before and during treatment with DMH affects aberrant crypt foci formation and DNA damage in colon. Four weeks old Sprague Dawley male rats were fed AIN93‐based experimental diets supplemented with 0 (control diet), 50 or 500 mg soy isoflavones per kg diet for 8 weeks, and received subcutaneous injections of DMH (20mg/kg body weight) twice per week for 4 weeks while maintaining experimental diets. Then all the groups were given the control diet for another 6 weeks. Colon cells were isolated and subjected to the alkaline single cell gel electrophoresis. DNA damage was determined by measuring tail lengths of the cells with fluorescence microscope. There was no significant difference in weight gains and food efficiencies among groups. Numbers of total aberrant crypts and aberrant crypt foci of colon tended to be lower in the rats pre‐fed soy isoflavones as compared with the control group. DNA damages of colonic cells were insignificant among the groups. Being considered that rats were sacrificed at only 6 weeks after DMH treatment, the results indicate that intake of soy isoflavones before and during DMH treatment may reduce formation of aberrant crypt foci in colon, which was irrelevant to colonic cell DNA damage. This research was supported by RIC program of MCIE.