Abstract
In view of the lack of information on the extent to which tea beverages inhibit the activity of human cytochrome P 450 3A (CYP 3A), we investigated their effect on the midazolam 1'-hydroxylation activity of CYP 3A contained in human liver microsomes. “Grapefruit (white)” was used as a positive control, and “Valencia Orange”, as a negative control. All the tea beverages tested significantly inhibited the midazolam 1'-hydroxylation activity of CYP 3A in a concentration-dependent manner and inhibition was particularly marked for Katekin 600® and Banso-reicha® (5.0%, v/v). The potency of the inhibitory effects was similar to that of grapefruit. The inhibitory effects on the activity of CYP 3A were enhanced by pre-incubation of tea samples (2.5%, v/v) with microsomal fractions for 5 to 30 min in a preincubation period-dependent manner. These results suggest that Katekin 600® and Banso-reicha® contain mechanism-based inhibiting agents. Further, the inhibitory effects on CYP 3A of green tea beverages seemed to be enhanced by catechins with the enhancement depending on the catechin concentration indicated on the label.
In conclusion, we found that there were ingredients that inhibited CYP 3A activity in all of the tea beverages, and they were probably catechins.
