Inhibitory Effect of Acacetin, Apigenin, Chrysin and Pinocembrin on Human Cytochrome P450 3A4

Cytochrome P450 3A4 is the most significant enzyme in metabolism of medications. Flavonoids are common secondary plant metabolites found in fruits and vegetables. Some flavonoids can interact with other drugs by inhibiting cytochrome P450 enzymes. Thus, the objective of this study was to determine inhibition kinetics of cytochrome P450 3A4 by flavonoids: acacetin, apigenin, chrysin and pinocembrin. For this purpose, testosterone was used as marker substrate, and generation of the 6 beta-hydroxy metabolite was monitored by high performance liquid chromatography coupled with diode array detector./Cso values, inhibition constants, and rates of inhibition were determined. IC50 values ranged between 0.6 and 11.4 mu M. The strongest inhibitor was chrysin (IC50 0.6 mu M, inhibition constant 0.6 mu M, inhibition rate constant 0.065 min(-1), inhibition efficacy 0.108 min(-1) mu M-1). Compared to other flavonoids analyzed, chrysin's inhibitory effect can be attributed to the hydrophobic nonsubstituted B ring, as well as rigidity of the structure. When foods rich in chrysin are consumed, e.g. honey and propolis, chrysin can cause food-drug interactions. Further in vitro studies are needed to determine the reactive intermediate responsible for inactivation of cytochrome P450 3A4 enzyme, as well as in vivo studies to determine possible clinical significance of this inhibition.