An ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was established to determine hirsutine and hirsuteine in rat plasma. Pharmacokinetics of hirsutine and hirsuteine in rats after intravenous or oral administration has been investigated using this developed UPLC-MS/MS method, and bioavailability of the two drugs was calculated. Diazepam was used as internal standard, and UPLC BEH column (2.1 mm × 50 mm, 1.7 μm) was used at temperature of 40°C. The mobile phase was composed of acetonitrile and water (containing 0.1% formic acid) at a gradient elution flow rate of 0.4 mL/min. Nitrogen was used as desolvation gas (800 L/h) and conical gas (50 L/h). The multiple reaction monitoring (MRM) model was applied to quantitatively analyze hirsutine m/z 369 → 226, hirsuteine m/z 367 → 169.9, and diazepam (internal standard) m/z 285.1 → 193.3. Rat plasma samples were deproteinized using acetonitrile prior to UPLC-MS/MS analysis. Within the concentration range of 1-200 ng/mL, the linearity of hirsutine and hirsuteine in plasma was good (r > 0.995), and the lower limit of quantitation was 1 ng/mL. Relative standard deviations of intra-day precision for hirsutine and hirsuteine were ≤6.1% and ≤5.9%, respectively, and those of inter-day precision were ≤6% and ≤7.7%. Accuracy for hirsutine and hirsuteine ranged between 92.3% and 104.8%. Bioavailability of hirsutine and hirsuteine was 4.4% and 8.2%, respectively. The method is sensitive and fast with good selectivity and was successfully applied in the pharmacokinetic studies after intravenous and oral administration of hirsutine and hirsuteine.
Aims: CYP2C19 is an important member of the cytochrome P450 enzyme superfamily. We recently identified 31 CYP2C19 alleles in the Han Chinese population. The aim of this study was to assess the catalytic activities of these allelic isoforms and their effects on the metabolism of fluoxetine in vitro. Methods: The wild-type and 30 CYP2C19 variants were expressed in insect cells and each variant was characterized using fluoxetine as the substrate. Reactions were performed at 37°C with 20-1,000 µmol/L substrate for 30 min. By using ultra-high performance liquid chromatography-mass spectrometry to detect the products, the kinetic parameters Km, Vmax, and intrinsic clearance (Vmax/Km) of norfluoxetine were determined. Results: Among the CYP2C19 variants tested, T130M showed similar intrinsic clearance (Vmax/Km) values with CYP2C19*1, while the intrinsic clearance values of other variants were significantly decreased (from 9.56 to 77.77%). In addition, CYP2C19*3 and *35FS could not be detected because they have no detectable enzyme activity. Conclusion: In China, the assessment of CYP2C19 variants in vitro offers valuable information relevant to the personalized medicine for CYP2C19-metabolized drug.
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