Osthole inhibited the activity of CYP2C9 in human liver microsomes and influenced indomethacin pharmacokinetics in rats

Osthol, a pharmacologically active ingredient in various traditional Chinese medicines, is predominantly metabolized by CYP2C9. It may be co-administered with other drugs which are metabolized by CYP2C9 in clinical medicine. However, CYP2C9*1/*2/*3 genotype on the pharmacokinetics of osthole and its metabolic diversity between rat and human are unclear. In this study, we investigated the effects of osthole on enzyme activity of CYP2C11/CYP2C9 in rat liver microsomes (RLMs) and human liver microsomes (HLMs), to distinguish metabolic manner of osthole in different species. Interestingly, we found that osthole inhibits the activity of CYP2C11 in a non-competitive manner in RLMs, while inhibits CYP2C9 activity in a competitive manner in pooled HLMs. Then, the effects of CYP2C9*1/*2/*3 allele on the pharmacokinetics of osthole were identified. In human CYP2C9 isoform, the Ki value of 21.93 mu M (CYP2C9*1), 18.10 mu M (CYP2C9*2), 13.12 mu M (CYP2C9*3) indicate that there are individual differences in the inhibition of osthole on CYP2C9 activity. We investigated how the indomethacin pharmacokinetics was affected by osthole in SD rat. To estimate the area under the curve (AUC), maximum plasma concentration (C-max) and apparent clearance (CL/F), indomethacin (10 mg/kg) was given orally combined with osthole (20 mg/kg) in adult SD rat. We found the value of PK on indomethacin, such as the AUC(0-infinity), was from 176.40 +/- 17.29 to 173.74 +/- 27.69 mu g/ml h(-1), C-max from 9.02 +/- 1.24 to 9.89 +/- 0.82 mu g/ml and CL/F from 0.11 +/- 0.01 to 0.12 +/- 0.04 mg/kg/h which were unsignificantly changed compared with the control groups. However, the T-max was prolonged from 2.00 +/- 0.00 h to 7.33 +/- 1.15 h, and T-1/2 increased from 8.38 +/- 2.30 h to 11.37 +/- 2.11 h. These results indicate that osthole could potentially affect the metabolism of indomethacin in vivo.