Suppression of azoxymethane-induced preneoplastic lesions and inhibition of cyclooxygenase-2 activity in the colonic mucosa of rats drinking a crude green tea extract

We determined the effects of a crude green tea extract given as drinking fl uid on the promotion/progression phase of colon carcinogenesis in rats afte r induction of the neoplastic process by azoxymethane. Adult Wistar rats we re given azoxymethane (15 mg/kg ip) once a week for two weeks. One week aft er the second injection, the rats were randomly divided into two groups. On e group (n = 8) received daily prepared aqueous solutions of green tea extr acts (GTE; 0.02% wt/vol), the control group (n = 8) received tap water Afte r six weeks, rats receiving GTE showed a 60% reduction in the number of col onic preneoplastic lesions (aberrant crypts). The number of individual cryp ts per aberrant crypt focus (crypt multiplicity) was significantly reduced in the GTE group; the majority (80%) of the remaining aberrant foci contain ed only one or two preneoplastic crypts. A significant and selective decrea se of cyclooxygenase (COX)-2 activity was observed in the colon of rats rec eiving GTE (23 +/- 3 vs. 117 +/- 30 mU/mg protein in controls), whereas COX -I showed no alterations. Our data demonstrate that GTE reduces COX-2 and s uppresses the formation of colonic preneoplastic lesions. They provide new insights into the mechanism of chemopreventive and anti-inflammatory proper ties of green tea.