TitleCancer chemopreventive mechanisms of tea against heterocyclic amine mutagens from cooked meat.
Publication TypeJournal Article
Year of Publication1999
AuthorsDashwood RH, Xu M, Hernaez JF, Hasaniya N, Youn K, Razzuk A
JournalProc Soc Exp Biol Med
Volume220
Issue4
Pagination239-43
Date Published1999 Apr
ISSN0037-9727
KeywordsAmines, Animals, Colonic Neoplasms, Cytochrome P-450 Enzyme System, Free Radical Scavengers, Heterocyclic Compounds, Liver, Male, Meat, Mutagenicity Tests, Mutagens, Plant Extracts, Rats, Rats, Inbred F344, Salmonella typhimurium, Tea
Abstract

Cooking meat and fish under normal conditions produces heterocyclic amine mutagens, several of which have been shown to induce colon tumors in experimental animals. In our search for natural dietary components that might protect against these mutagens, it was found that green tea and black tea inhibit the formation of heterocyclic amine-induced colonic aberrant crypt foci (ACF) in the rat. Since ACF are considered to be putative preneoplastic lesions, we examined the inhibitory mechanisms of tea against the heterocyclic amines. In the initial studies using the Salmonella mutagenicity assay, green tea and black tea inhibited according to the concentration of tea leaves during brewing and the time of brewing; a 2-3-min brew of 5% green tea (w/v) was sufficient for >90% antimutagenic activity. N-hydroxylated heterocyclic amines, which are direct-acting mutagens in Salmonella, were inhibited by complete tea beverage and by individual components of tea, such as epigallocatechin-3-gallate (EGCG). Inhibition did not involve enhanced mutagen degradation, and EGCG and other catechins complexed only weakly with the mutagens, suggesting electrophile scavenging as an alternative mechanism. Enzymes that contribute to the metabolic activation of heterocyclic amines, namely microsomal NADPH-cytochrome P450 reductase and N, O-acetyltransferase, were inhibited by tea in vitro. Studies in vivo established that tea also induces cytochromes P450 and Phase II enzymes in a manner consistent with the rapid metabolism and excretion of heterocyclic amines. Collectively, the results indicate that tea possesses anticarcinogenic activity in the colon, and this most likely involves multiple inhibitory mechanisms.

DOI10.1046/j.1525-1373.1999.d01-41.x
Alternate JournalProc. Soc. Exp. Biol. Med.
PubMed ID10202396
PubMed Central IDPMC2268949
Grant ListR01 CA065525 / CA / NCI NIH HHS / United States
R01 CA065525-06A1 / CA / NCI NIH HHS / United States
R29 CA065525 / CA / NCI NIH HHS / United States
CA65525 / CA / NCI NIH HHS / United States