> salicylamide is an antagonist of the aryl hydrocarbon ...
Black tea theaflavins suppress dioxin-induced transformation of the
aryl hydrocarbon receptor.
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. PMID: 15914905
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