Daily intake of sulphoraphane-rich broccoli sprouts prevents colon tumor formation in mice treated with dextran sodium sulfate and azoxymethane via stimulating nrf2-dependent antioxidant enzymes.

A75

Background and Aim: Sulforaphane protects cells from oxidative injury by activating NF-E2 p45-related factor2 (nrf2) mediated antioxidant enzymes (PNAS, 94:10367, 1997) and prevents tumor formation in froestomach in benzopyrene-treated mice (PNAS 99:7610, 2002). Broccoli sprouts are rich source of sulforaphane glucosinolate (glucoraphanin) which is enzymatically converted to sulforaphane upon ingestion of fresh sprouts. We have previously shown that sulforaphane mitigates high salt diet-induced gastritis in H. pylori-infected mice via activation of nrf2 dependent anti-oxidant enzyme activities (Gastroenterology 124:A5, 2003). However, effects of sulforaphane on colonic mucosa have not previously been reported. The aim of this study is to determine if daily intake of sulforaphane-rich broccoli sprout mitigates dextran sodium sulfate (DSS)-induced colitis and inhibits tumor formation in DSS + azoxymethane(AOM)-treated mice. Methods: Wild type (nrf2+/+) and nrf2-gene knockout type (nrf2-/-) C57BL/6 female mice were treated for 7 days with oral adminstration of 3% DSS with free drinking water, followed by single i.p. injection of 1% AOM. Subsequently, mice were fed with or without broccoli sprouts, which contain 2.5 mmol sulforaphane glucosinolates. Mice were sacrificed at 4 and 8 wks after the AOM treatment. Degree of colitis, incidence of aberrant cript foci (ACF) and polypoid tumors in colonic mucosa were quantitatively evaluated. Antioxidant activity was evaluated by measuring GST-1, and HO-1 mRNA expression by real time RT-PCR. DNA damage was estimated by measuring mucosal level of 8-OHdG. Expressions of TNF-alfa and IL-beta were analyzed by ELISA. Results: : 1. In nrf2+/+ mice, treatment with broccoli sprouts upregulated expression of GST, and HO-1, accompanied by downregulation of TNF-alfa, IL-1beta, and decrease in 8-OHdG production. In nrf2-/- mice these effects of sulforaphane were completely abolished. 2. In nrf2+/+ mice, treatment with broccoli sprouts attenuated DSS-induced colitis, and inhibited subsequent formation of ACF and colon tumors. In nrf2-/-mice, the protective effects of broccoli sprouts against colitis and tumor formation were completely abolished. Conclusion: The present results show that daily intake of sulforaphane-rich broccoli sprouts improves DSS-induced colitis and inhibits colon tumor formation induced by DSS+AOM. Our data further suggest that a diet rich in sulforaphane glucosinolate may be useful in chemoprevention against colon cancer.