Cruciferous vegetables, secondary metabolites of glucosinolates, and colon cancer risk in rats.

摘要

This thesis project examined the effects of cruciferous vegetables on markers of chemically-induced colon cancer. Rats were fed diets containing phenethyl isothiocyanate and indole-3-carbinol, secondary metabolites of glucosinolates found in watercress and cabbage, respectively, for two weeks prior to carcinogen treatment. Eight weeks after the second dose of carcinogen rats were killed and colon and livers were collected. Rats fed diets containing indole-3-carbinol had lower number of aberrant crypt foci (ACF), a putative cancer marker, than rats fed the basal diet. Apoptosis and cell proliferation, as well as cytochrome P450 2E1 (CYP2E1) activity were not significantly different among groups. In a subsequent experiment, rats were fed diets containing lyophilized green cabbage (10%), red cabbage (10%), or watercress (4%). All vegetables were stored at -18°C for up to six months before the start of the experiment. There were no differences among groups in ACF number, ACF mucin expression, CYP2E1, CYP1A, or quinone reductase activities. Glutathione S-transferase (GST) activity was significantly decreased by the green and red cabbage diets compared to the basal diet. A final experiment was conducted to examine the effects of fresh cruciferous vegetables on markers of colon cancer risk. Rats were fed fresh watercress (10%), broccoli (14.4%), and cabbage (22.6%) for twelve weeks. The carcinogen was administered on weeks two and three, and 18-24 hours prior to termination. All vegetable diets significantly decreased ACF number by approximately 40%. Sialomucin-producing foci and mucin-depleted foci, thought to indicate ACF more likely to progress to tumors, were significantly reduced in the vegetable groups compared to the basal diet. No significant differences were found among groups in mucosal apoptosis and cell proliferation labeling indices. CYP1A, CYP2E1, GST, and QR activities were not significantly different among groups. It was concluded that feeding fresh but not lyophilized cruciferous vegetables reduces colon cancer risk in rats and the mechanisms of protection do not appear to involve hepatic carcinogen metabolism, as assessed by measurement of P450 enzymes and the detoxification enzymes GST and QR. This project indicates that cruciferous vegetables can reduce colon cancer risk, but that method of processing must be considered.