Stereoselective determination of ginsenosides Rg3 and Rh2 epimers in rat plasma by LC-MS/MS: application to a pharmacokinetic study

Abstract

We developed and validated an accurate and sensitive LC-MS/MS method for the simultaneous quantitation of ginsenoside Rg3 and Rh2 epimers (R-Rg3, S-Rg3, R-Rh2, and S-Rh2) in rat plasma. Analytes were extracted from 0.1 mL aliquots of rat plasma by liquid-liquid extraction, using 2 mL of ethyl acetate. In this assay, dioscin (500 ng/mL) was used as an internal standard. Chromatographic separation was conducted using an Acclaim RSLC C18 column (150 × 2.1 mm, 2.2 μm) at 40°C, with a gradient mobile phase consisting of 0.1% formic acid in distilled water and in acetonitrile, a flow rate of 0.35 mL/min, and a total run time of 20 min. Detection and quantification were performed using a mass spectrometer in selected reaction-monitoring mode with negative electrospray ionization at m/z 783.4 → 161.1 for R-Rg3 and S-Rg3, m/z 621.3 → 161.1 for R-Rh2 and S-Rh2, and m/z 867.2 → 761.5 for the internal standard. For R-Rg3 and S-Rg3, the lower limit of quantification was 5 ng/mL, with a linear range up to 500 ng/mL; for R-Rh2 and S-Rh2, the lower limit of quantification was 150 ng/mL, with a linear range up to 6000 ng/mL. The coefficient of variation for assay precision was less than 10.5%, with an accuracy of 86.4-112%. No relevant cross-talk or matrix effect was observed. The method was successfully applied to a pharmacokinetic study after oral administration of 400 mg/kg and 2000 mg/kg of BST204, a fermented ginseng extract, to rats. We found that the S epimers exhibited significantly higher plasma concentrations and area under curve values for both Rg3 and Rh2. This is the first report on the separation and simultaneous quantification of R-Rg3, S-Rg3, R-Rh2, and S-Rh2 in rat plasma by LC-MS/MS. The method should be useful in the clinical use of ginseng or its derivatives.