Catechins in tea suppress the activity of cytochrome P450 1A1 through the aryl hydrocarbon receptor activation pathway in rat livers

Polycyclic aromatic hydrocarbons (PAHs) and halogenated aromatic hydrocarbons (HAHs) develop various adverse effects through activation of an aryl hydrocarbon receptor (AhR). The suppressive effects of brewed green tea and black tea on 3-methylcholanthrene (MC)-induced AhR activation and its downstream events were examined in the liver of rats. Ad-libitum drinking of green tea and black tea suppressed MC-induced AhR activation and elevation of ethoxyresorufin O-deethylase activity in the liver, whereas the teas themselves did not induce them. Tea showed a suppressive fashion on the expression of cytochrome P450 1A1 (CYP1A1). Tea suppressed the AhR activation induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) ex vivo. A part of catechins and theaflavins was present in plasma and liver as conjugated and intact forms. The results of this study suggested that active component(s) of tea are incorporated in the liver and suppress the activity of CYP1As through the AhR activation pathway.