Chemoprevention of tea on colorectal cancer induced by dimethylhydrazine in Wistar rats

AIM To investigate the chemopreventiveeffects of green tea and tea pigment on 1,2-dimethylhydrazine(DMH)-induced rat colorectalcarcinogenesis.METHODS Male weaning Wistar rats wererandomly allocated into four groups.Rats in thepositive control group were given s.c.injectionof DMH,once a week for ten weeks;rats in tea-treated groups,with the same DMH treatment asin the positive group,received 2% green tea and0.1% tea pigments;rats in the negative controlgroup were given s.c.injection of the samevolume of saline as well as DMH in the positivegroup.Animals were sacrified and necropsied atthe end of week 16 and week 32.RESULTS Aberrant cryptic foci(ACF)wereformed in animals in DMH-treated groups at theend of week 16.Compared to the DMH group,green tea and tea pigments groups had less ACF(148.25 and 204.25,respectively,P<0.01).Atthe end of week 32,all rats in DMH groupdeveloped large intestinal tumors.The resultsalso showed that DMH increased labeling index(LI)of proliferating cell nuclear antigen(PCNA)of intestinal mucosa and the expression of ras-p21.However,in the tea-treated groups,PCNA-LI was significantly reduced as compared withthe positive control group(36.63 and 40.36 inthe green tea group and tea pigment group,respectively,at the end of the experiment,P<0.01).ras-p21 expression was alsosignificantly reduced(2.07 and 2.36 in the colontumors of rats in the green tea group and teapigments group,respectively at the end of theexperiment,P<0.01).Furthermore,green tea and tea pigment inhibited the expression of Bcl-2protein(2,5,1,0 and 2,4,1,0,respectively,at the end of the experiment P<0.01),andinduced expression of Bax protein(0,1,3,4and 0,1,4,3,respectively,P<0.01).CONCLUSION Chinese green tea drinkinginhibited ACF and colonic tumors formation inrats,which showed that tea had a significantchemopreventive effect on DMH-inducedcolorectal carcinogenesis.Such effects may bedue to suppression of cell proliferation andinduction of apoptosis in the intestinal crypts.