Comparative chemopreventive mechanisms of green tea, black tea and selected polyphenol extracts measured by in vitro bioassays

Abstract

Black tea extracts (hot aqueous, polyphenols and theaflavins) and green tea extracts (hot aqueous, polyphenols, epicatechin, epicatechin gallate, epigallocatechin and epigallocatechin gallate) were tested in nine standardized cell culture assays for comparative cancer chemopreventive properties. Most black and green tea extracts strongly inhibited neoplastic transformation in mouse mammary organ cultures, rat tracheal epithelial cells and human lung tumor epithelial cells. Nearly all tea fractions strongly inhibited benzo[a]pyrene adduct formation with human DNA. Induction of phase II enzymes, glutathione-S-transferase and quinone reductase, were enhanced by nearly all tea fractions, while glutathione was induced by only a few fractions. Ornithine decarboxylase activity was inhibited by nearly all the green tea fractions, but none of the black tea fractions. 12-O-tetradecanoylphorbol-13-acetate-induced free radicals were inhibited by most tea fractions. These results provide strong evidence of both anti-mutagenic, anti-proliferative and anti-neoplastic activities for both black and green tea extracts. Such anticancer mechanisms may well be responsible for the cancer preventive efficacies seen in both experimental and human studies.

Protective effect of green tea on the risks of chronic gastritis and stomach cancer

“…5 Green tea polyphenols may affect carcinogenesis because of their antioxidative activities, ability to inhibit nitrosation reactions, modulation of carcinogen-metabolizing enzymes, trapping of ultimate carcinogens and the ability to inhibit cell proliferation-related activities. 6 From in vitro and animal studies, 7,8 polyphenolic extracts from green tea have been shown to enhance the activities of phase II detoxifying enzymes, Glutathione-s-tranferases.…”

Prospective cohort comparison of flavonoid treatment in patients with resected colorectal cancer to prevent recurrence

“…Flavonoids are good candidates for primary and secondary prevention of colorectal cancer, since numerous in vitro studies and animal work report on their beneficial activities in terms of suppression of cancer proliferation, antioxidative and antiangiogenetic properties [24] . Epidemiological investigations [22,25,26] , in vivo and in vitro experiments [31][32][33][34][35] and one clinical intervention study [29] support this concept. Other authors could not find protective effects of flavonoids on colorectal cancer incidence [21,27,36] .…”

The Potential Role of Chemoprevention in the Management of Non-Muscle Invasive Bladder Urothelial Carcinoma

“…The polyphenols found in green tea are potent antioxidants; they also inhibit ornithine decarboxylase which is an enzyme that promotes tumor proliferation via nucleic acid regulation (Steele, Kelloff et al 2000). The incidence of UC in Asian populations with increased tea consumption is lower than in North America; a weak inverse relationship between tea intake and UC has been reported in one epidemiological study (Kemberling, Hampton et al 2003).…”