[Inhibitory effects of astragaloside IV on cytochrome P450 enzyme of rat liver microsomes].

To provide a scientific basis for the drug-combination and aim to examine whether astragaloside IV has the impact on the cytochrome P450 enzymes. Tolbutamide, chlorzoxazone, coumarin, nifedipine, and phenacetin were as probe substrates of rat CYP2C9, CYP2E1, CYP2A6, CYP3A4, and CYP1A2, and were incubated in rat liver microsomes with astragaloside IV. Triplicate samples were run to generate IC50 value by incubating P450 probe substrates in the presence of five concentrations of astragaloside IV in the incubation mixture. The K(i) values were determined by fitting the probe substrate at various inhibitor concentrations to the equations for competitive inhibition, noncompetitive inhibition, noncompetitive inhibition, and mixed-type inhibition. IC50 and K(i) values were estimated, and the types of inhibition were determined. Among the five probe substrates, astragaloside IV might not significantly affect CYP2E1, CYP2A6 and CYP1A2-mediated metabolism in rats, but was a competitive inhibitor of CYP2C9 (IC50 35.40 micromol x L(-1), K(i) 42.88 micromol x L(-1)), and was a uncompetitive inhibitor of CYP3A4 (IC50 88.24 micromol x L(-1), K(i) 33.31 micromol x L(-1)). These results suggested that astragaloside IV inhibited CYP2C9 and CYP3A4, which provided useful information for safe and effective use of astragaloside IV.