Chemoprevention against colon cancer by dietary intake of sulforaphane

Background: Sulforaphane (SFN) is a phytochemical compound which belongs to isothiocyanates family found in abundance in broccoli sprouts. SFN induces a variety of antioxidant enzymes via NF-E2-related factor 2-Kelch-like ECH-associated protein 1-mediated pathway, thereby protecting cells from injury induced by various kinds of oxidative stresses. We have previously shown that SFN protects gastric mucosa from oxidative injury induced by H. pylori infection. SFN also down-regulates histone deacetylase (HDAC) activity, thereby inducing apoptosis and inhibiting proliferation of tumor cells in variety of tissues. On the other hand, the incidence of colon cancer has increased in Japan. Since numerous epidemiological studies have shown that colon cancer is inversely associated with intake of anti-oxidant vegetables, we examined whether daily intake of SFN prevents colon tumorigenesis in mice and human subjects. Methods 1. Effects of SFN on Colonic tumorigenesis in Mice Treated with Chemical Carcinogen: Effects of SFN on colonic tumorigenesis were examined in the ICR male mice, pretreated with a chemical carcinogen, azoxymethane (AOM) (15 mg/kg). The mice treated with AOM for 3 or 6 times were fed for 8 or 24 weeks with or without sulforaphane glucosinolates (SGS: 2,200 ppm/kg/day), which is a precursor of SFN. Effects of SGS treatment on formation of the microscopic aberrant crypt foci (ACF) and the macroscopic tumors in colonic mucosa were evaluated. 2. Effects of SFN on formation of Colonic ACF in patients with colonic adenoma: Effects of intake of raw broccoli sprouts (BS), 50 g/day containing 220 mg SGS every other day, for 6 months on changes in the number of ACF in rectal mucosa was examined by colonoscopy in patients with colonic adenoma. 3. Effects of SFN on intestinal microbiota in human subjects: Effects of dietary intake of raw BS, 20 g/day, which contains 88 mg SGS every other day, for 2 weeks on intestinal microbiota in healthy volunteers was assessed by measuring composition of stool bacteria, using a method of terminal restriction fragment length polymorphism flora analysis. In human studies, alfalfa sprouts, which contains no SFN, was used as a placebo control. Results: 1. Daily administration of SGS suppressed formation of microscopic ACF and macroscopic colonic tumors in the AOM-pretreated mice in vivo. 2. Intake of BS for 6 months tended to decrease the number of colonic ACF in patients with colonic adenoma. 3. Intake of BS for 2 weeks increased percentages of Bifidobacterium and Clostridium XVIa, which has been shown to enhance protection of colonic mucosa by increasing butyrate production in colonic lumen. Conclusions: 1. Daily intake of SFN affords chemoprotection against colonic tumors in the mice treated with a chemical carcinogen. 2. The present study further suggests that, in addition to previously reported mechanisms, changes in the intestinal microbiota by SFN intake may also play a role in chemoprevention against colon cancer. Further studies are required to prove this possibility.