Quantification of Usaramine and Its N-oxide Metabolite in Rat Plasma Using Liquid Chromatography-Tandem Mass Spectrometry

Abstract

ABSTRACT A sensitive, fast and robust liquid chromatography tandem mass spectrometry (LC-MS/MS) method was developed and validated for the determination of usaramine (USM) and usaramine N-oxide (UNO) in rat plasma. The separation was conducted on an ACQUITY UPLC BEH C18 Column (50 × 2.1 mm, 1.7 μm), and gradient eluted with mobile phase A (0.1% formic acid with 5 mM ammonium acetate in water) and B (0.1% formic acid in acetonitrile/methanol, 9/1, v/v). The method was linear over the range of 1–2000 ng/mL for both analytes. The validated method was applied to investigate the pharmacokinetic behaviors and sex differences of USM and its N-oxide metabolite in rats. After intravenous administration of USM at 1 mg/kg, the AUC0-t values for USM and UNO were 363 ± 65 and 172 ± 32 ng/mL*h in male rats, respectively, while 744 ± 122 and 30.7 ± 7.4 ng/mL*h in females, respectively. The clearance of USM was significantly higher in male rats than in females (2.77 ± 0.50 vs 1.35 ± 0.19 L/h/kg, p < 0.05). After oral administration of USM at 10 mg/kg, the AUC0-t values of USM and UNO were 1960 ± 208 and 1637 ± 246 ng/mL*h in male rats, respectively, while 6073 ± 488 and 300 ± 62 ng/mL*h in females, respectively. The oral bioavailability of USM in female rats (81.7%) was much higher than in males (54.0%). In conclusion, sex-based differences were observed in the pharmacokinetics, N-oxide metabolism and oral bioavailability of USM.