Identification of CYP2C19 inhibitors from phytochemicals using the recombinant human enzyme model.

The aim of the present study was to develop the recombinant insect cell-expressed protein as an in vitro model for inhibitors screening for human cytochrome P450 2C19 (CYP2C19), and to use the model to investigate the inhibition effect of three phytochemicals on CYP2C19 in vitro. Omeprazole was applied as the probe substrate. The estimated inhibitory constant (K(i)) of ticlopidine and fluvoxamine were 0.64 +/- 0.025 microM and 0.29 +/- 0.090 microM, respectively. After co-incubation with ticlopidine or fluvoxamine, the mean omeprazole Michaelis-Menten constant (K(m)) increased from 4.99 +/- 0.22 microM to 16.25 +/- 1.22 microM or 19.20 +/- 1.73 microM, respectively, while omeprazole's mean V(max) did not vary much. Both ticlopidine and fluvoxamine were competitive inhibitors of CYP2C19. The IC50 of three phytochemicals, isoalantolactone, curcumol and schisandrin A was determined as 38.91 microM, 121.0 microM and 86.41 microM, and the K(i) as 5.02 +/- 1.04 microM, 35.84 +/- 8.95 microM, and 4.46 +/- 0.017 microM, respectively. The in vitro model for inhibitor screening established using recombinant CYP2C19 could be used to assess the inhibition potential of drug candidates. Isoalantolactone and schisandrin A are potent inhibitors of CYP2C19, while curcumol is a moderate potent inhibitor of CYP2C19.

Interspecies difference of luteolin and apigenin after oral administration of Chrysanthemum morifolium extract and prediction of human pharmacokinetics.

The aims of the present study were to study the interspecies difference in the pharmacokinetics of luteolin and apigenin occurring in Chrysanthemum morifolium extract (CME) among rats, beagle dogs, mini-pigs, and humans, and compared the human pharmacokinetic parameters with the data predicted from the above three animals. The plasma concentrations of luteolin and apigenin were determined with a RP-HPLC method. An interspecies difference of pharmacokinetics was found, especially between rats and other species, the plasma concentration of luteolin was much lower than that of apigenin in rats, although the content of luteolin in CME was higherthan that of apigenin, whereas the plasma concentration of luteolin was much higher than that of apigenin in dogs, mini-pigs and humans. Animal scale-up of some pharmacokinetic parameters of luteolin and apigenin were also performed after rats, beagle dogs, mini-pigs and humans were orally given CME at dosages of 400 mg/kg, 102 mg/kg, 90 mg/kg, and 20 mg/kg, respectively. Linear relationships were obtained between log mean retention time (MRT) and log species body weight (W) (kg), and log elimination half-life (t1/2) (h) and logW. The corresponding allometric equations were MRT=9.382W(0.1711) (R2 = 0.9999) and t1/2 = 4.811W(0.1093) (R2 = 0.9013) for luteolin, MRT = 12.53W(0.0356) (R2 = 0.9980) and t1/2 = 7.940W(0.0294) (R2 = 0.9258) for apigenin, respectively. The predicted human pharmacokinetic parameters (MRT and t1/2) by an allometric approach were 18.6 h and 7.46 h for luteolin, 14.3 h and 8.95 h for apigenin, respectively, which were close to the values obtained from humans (20 mg CME/kg) in the present study. The study has demonstrated the possibility to extrapolate the pharmacokinetic behavior of flavonoids from animals to humans.