title: Black tea theaflavins suppress dioxin-induced transformation of the aryl hydrocarbon receptor.
abstract: Dioxins cause various adverse effects through transformation of aryl hydrocarbon receptor (AhR). In this study, we investigated whether black tea extract and its components, theaflavins, suppress AhR transformation in vitro. First, we confirmed that black tea extract strongly suppressed AhR transformation compared to green and oolong tea, although the catechin contents did not change significantly among the extracts. Then we isolated four theaflavins as active compounds from black tea leaves. They suppressed 1 nM 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced AhR transformation in a dose-dependent manner. The IC(50) values of theaflavin, theaflavin-3-gallate, theaflavin-3'-gallate, and theaflavin-3,3'-digallate (Tfdg) were 4.5, 2.3, 2.2, and 0.7 muM, respectively. The suppressive effect of Tfdg was observed not only by pre-treatment but also by post-treatment. This suggests that theaflavins inhibit the binding of TCDD to the AhR and also the binding of the transformed AhR to the specific DNA-binding site as putative mechanisms.
authors.affiliation: Division of Life Science, Graduate School of Science and Technology, Kobe University, Hyogo, Japan.
authors.forename: Itsuko
authors.initials: I
authors.lastname: Fukuda
authors.forename: Iwao
authors.initials: I
authors.lastname: Sakane
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Yabushita
authors.forename: Shin-Ichi
authors.initials: S
authors.lastname: Sawamura
authors.forename: Kazuki
authors.initials: K
authors.lastname: Kanazawa
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Ashida
mesh_terms: D000818:Animals; D044946:Biflavonoids / Q000737:chemistry / Q000494:pharmacology*; D002392:Catechin / Q000737:chemistry / Q000494:pharmacology*; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D008297:Male; D000072317:Polychlorinated Dibenzodioxins / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018336:Receptors, Aryl Hydrocarbon / Q000187:drug effects* / Q000378:metabolism; D013662:Tea / Q000737:chemistry*
chemical_list: D044946:Biflavonoids; D000072317:Polychlorinated Dibenzodioxins; D018336:Receptors, Aryl Hydrocarbon; D013662:Tea; C056068:theaflavin; D002392:Catechin