Estrogenic biological activity and underlying molecular mechanisms of green tea constituents

Green tea is produced from the tea plant Camellia sinensis without fermentation, and contains characteristic constituents, which are associated with health-promoting effects such as physiological, immunological, neurological and psychological effects, and protective effects against diseases, such as cancer, cardiovascular diseases and diabetes. Catechins, such as catechin, epicatechin, epigallocatechin, epicatechin-3-O-gallate and epigallocatechin-3-O-gallate, and other green tea constituents, such as anthocyanidins, flavan-3-ols, flavonols, phenolic acids/depsides and caffeine/vitamins, are associated with many biological activities and cell signaling through interactions with specific proteins and signaling pathways. Among the activities and pathways induced or mediated by green tea constituents, estrogen action was focused on through a comprehensive literature search. Estrogenic activity was evaluated by animal tests, cell assay, ligand-binding assay, protein assay, reporter-gene assay, transcription assay and yeast two-hybrid assay. Furthermore, health benefits, such as bone protection/bone regeneration, cardioprotection and neuroprotection, have been reported as the potential applications of the estrogenic activity of green tea constituents, whereas their anti-estrogenic activity has been discussed in association with cancer treatment and chemoprevention. Controversial results about their mixed estrogenic/anti-estrogenic/non-estrogenic and biphasic activity, and associated toxicity require further detailed studies to clarify the benefits and risks.