Chiral HPLC determination and stereoselective pharmacokinetics of tetrahydroberberine enantiomers in rats.

Tetrahydroberberine (THB), a racemic mixture of (+)- and (-)-enantiomer, is a biologically active ingredient isolated from a traditional Chinese herb Rhizoma corydalis (yanhusuo). A chiral high performance liquid chromatography method has been developed for the determination of THB enantiomers in rat plasma. The enantioseparation was carried out on a Chiral®-AD column using methanol:ethanol (80:20, v/v) as the mobile phase at the flow rate 0.4 ml/min. The ultraviolet detection was set at 230 nm. The calibration curves were linear over the range of 0.01-2.5 μg/ml for (+)-THB and 0.01-5.0 μg/ml for (-)-THB, respectively. The lower limit of quantification was 0.01 μg/ml for both (+)-THB and (-)-THB. The stereoselective pharmacokinetics of THB enantiomers in rats was studied after oral and intravenous administration at a dose of 50 and 10 mg/kg racemic THB (rac-THB). The mean plasma levels of (-)-THB were higher at almost all time points than those of (+)-THB. (-)-THB also exhibited greater C(max), and AUC(0-∞), smaller CL and V(d), than its antipode. The (-)/(+)-enantiomer ratio of AUC(0-∞) after oral and intravenous administration were 2.17 and 1.43, respectively. These results indicated substantial stereoselectivity in the pharmacokinetics of THB enantiomers in rats.