Original Articles
Copyright ©The Author(s) 2000. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Gastroenterol. Oct 15, 2000; 6(5): 699-703
Published online Oct 15, 2000. doi: 10.3748/wjg.v6.i5.699
Chemoprevention of tea on colorectal cancer induced by dimethylhydrazine in Wistar rats
Xu Dong Jia, Chi Han
Xu Dong Jia, Chi Han, Department of Food Toxicology, Institute of Nutrition and Food Hygiene, Beijing 100050, China
Xu Dong Jia, graduated from Chinese Academy of Preventive Medicine in 1999. Now he is pursuing his Ph.D. degree at Chinese Academy of Preventive Medicine, having three papers published.
Author contributions: All authors contributed equally to the work.
Correspondence to: Dr. Chi Han, Department of Food Toxicology, Institute of Nutrition and Food Hygiene, 29 Nanwei Road, Beijing 100050, China
Telephone: 0086-10-63170616 Fax: 0086-10-63011875
Received: May 25, 2000
Revised: June 16, 2000
Accepted: June 23, 2000
Published online: October 15, 2000
Abstract

AIM: To investigate the chemopreventive effects of green tea and tea pigment on 1,2-dimethylhydrazine (DMH)-induced rat colorectal carcinogenesis.

METHODS: Male weaning Wistar rats were randomly allocated into four groups. Rats in the positive control group were given s.c. injection of DMH, once a week for ten weeks; rats in tea-treated groups, with the same DMH treatment as in the positive group, received 2% green tea and 0.1% tea pigments; rats in the negative control group were given s.c. injection of the same volume of saline as well as DMH in the positive group. Animals were sacrified and necropsied at the end of week 16 and week 32.

RESULTS: Aberrant cryptic foci (ACF) were formed in animals in DMH-treated groups at the end 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). At the end of week 32, all rats in DMH group developed large intestinal tumors. The results also 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 with the positive control group (36.63 and 40.36 in the green tea group and tea pigment group, respectively, at the end of the experiment, P < 0.01). ras-p21 expression was also signific antly reduced (2.07 and 2.36 in the colon tumors of rats in the green tea group and tea pigments group, respectively at the end of the experiment, P < 0.01). Furthermore, green tea and tea pigment inhibited the expression of Bcl-2 protein (2, 5, 1, 0 and 2, 4, 1, 0, respectively, at the end of the experiment P < 0.01), and induced expression of Bax protein (0, 1, 3, 4 and 0, 1, 4, 3, respectively, P < 0.01).

CONCLUSION: Chinese green tea drinking inhibited ACF and colonic tumors formation in rats, which showed that tea had a significant chemopreventive effect on DMH-induced colorectal carcinogenesis. Such effects may be due to suppression of cell proliferation and induction of apoptosis in the intestinal crypts.

Keywords: colorectal neoplasms; dimethylhydrazine; tea; apoptosis; aberant crypt foci; rats; proliferating cell nuclear antigen; chemoprevention