In vitro inhibition of CYP1A and CYP3A by phenolic compounds from bilberry (Vaccinium myrtillus), in male and female porcine liver microsomes

Abstract: Bilberry fruit (Vaccinium myrtillus) is a rich source of bioactive compounds, including flavonols and phenolic acids. At least some of these compounds were shown to be metabo-lized in the liver by cytochrome P450 (CYP450) enzyme system, which is also important in the metabolism of pharmaceuticals. Several flavonols (a flavonoid subgroup) such as quer-cetin, myricetin, isorhamnetin and rutin have been reported to integrate with CYP450, i.e. by inhibition. Thus, a possibility of bilberry interaction with pharmaceutical metabolism should be carefully studied. Gender-related differences of such interactions should also be considered given that CYP450 genes in male and female are differentially expressed. He-patic microsomes are useful in vitro model commonly used at early stages of drug develop-ment to identify potential food-drug or drug-drug interactions. Pig is increasingly used as an animal model for human biomedical studies. The comparability of hepatic CYP450 between pigs and humans as well as easy availability of porcine livers from abattoirs make porcine microsomes an attractive model to study gender-related differences in food-drug interac-tions. The aim of this study was to evaluate the inhibitory effect of selected phenolic compounds from bilberry fruit on the activities of CYP1A and CYP3A in porcine hepatic microsomes. Five flavonols and four phenolic acids were selected for the study. This selection was based on two criteria, abundance in bilberry and potential interaction with CYP450. To estimate CYP1A and CYP3A activities, the probe substrates 7-ethoxyresorutin and 7-benzyloxy-4-triflouromethylcoumarin (BFC) were used, respectively. This study demonstrated that CYP3A activity was non-competitively inhibited by myri-cetin in male pigs only (Ki=112.7) and-, competitively by isorhamnetin in both male (Ki=71.2) and female pigs (Ki=93.7). CYP1A activity was competitively inhibited by my-ricetin in male (Ki=2.5) and female pigs (Ki=4.6) and by isorhamnetin in male (Ki=99.9) and in female pigs (Ki=10.8). Inhibition mode of CYP1A by quercetin differed between genders being competitive in male (Ki=0.2) and irreversible in female pigs (IC50=1.3). In conclusion, this study suggests that the activity of hepatic CYP450 1A and 3A are inhibited by the flavonols myricetin, isorhamnetin and querctin. Moreover, this study pro-vides first evidence of gender-related differences in this inhibition.