Quantification of oxymatrine in rat plasma by UPLC-MS/MS to support the pharmacokinetic analyses of oxymatrine-loaded polymersomes

Abstract

Oxymatrine (OM) is an alkaloid extracted from a Chinese herb that has been found to possess anti-hepatic fibrosis effects. To support a pharmacokinetic study for OM-loaded polymersome-based poly(ethylene glycol)-b-poly(ε-caprolactone) (mPEG-b-PCL) in rats, a rapid, highly selective ultra-performance liquid chromatography-tandem mass spectrometry method (UPLC-MS/MS) to quantify OM in rat plasma was developed and validated. Tetrahydropalmatine was employed as the internal standard (IS). Protein precipitation with acetonitrile was used for preparation of plasma samples. OM and the IS were separated on an ACQUITY UPLC™ BEH C18 column (2.1 mm × 50 mm i.d., 1.7 μm), with a gradient elution of acetonitrile and 0.1% formic acid (aq), within a run time of 2.5 min. Tandem mass detection was carried out using electrospray ionization (ESI) in positive ion-selected multiple reaction monitoring (MRM) mode. The peak area of the m/z 265.20 → 148.07 transition of OM was evaluated versus that of the m/z 356.15 → 192.07 transition of the IS to generate the standard curve. In plasma, the linear range was 4–1000 ng mL⁻¹, with a lower limit of quantitation (LLOQ) of 4.0 ng mL⁻¹ for OM using 100 μL of plasma. The intra- and inter-day precision (RSD) were <8.8%, and the relative accuracy (RE) was from −1.6% to 8.2%. The extraction recoveries were, on average, 79.92% for OM and 79.2% for the IS. Matrix effects and stability were investigated and found to be acceptable at all three concentration levels. This assay was applied to support a pharmacokinetic study of OM-loaded polymersomes in rats after intravenous administration.