Development of a liquid chromatography-mass spectrometry method for the determination of ursolic acid in rat plasma and tissue: application to the pharmacokinetic and tissue distribution study.

A fast and sensitive liquid chromatography-mass spectrometry method was developed for the determination of ursolic acid (UA) in rat plasma and tissues. Glycyrrhetinic acid was used as the internal standard (IS). Chromatographic separation was performed on a 3.5 μm Zorbax SB-C18 column (30 mm × 2.1 mm) with a mobile phase consisting of methanol and aqueous 10 mM ammonium acetate using gradient elution. Quantification was performed by selected ion monitoring with (m/z)(-) 455 for UA and (m/z)(-) 469 for the IS. The method was validated in the concentration range of 2.5 - 1470 ng mL(-1) for plasma samples and 20 - 11760 ng g(-1) for tissue homogenates. The intra- and inter-day assay of precision in plasma and tissues ranged from 1.6% to 7.1% and 3.7% to 9.0%, respectively, and the intra- and inter-day assay accuracy was 84.2 - 106.9% and 82.1 - 108.1%, respectively. Recoveries in plasma and tissues ranged from 83.2% to 106.2%. The limits of detections were 0.5 ng mL(-1) or 4.0 ng g(-1). The recoveries for all samples were >90%, except for liver, which indicated that ursolic acid may metabolize in liver. The main pharmacokinetic parameters obtained were T(max) = 0.42 ± 0.11 h, C(max) = 1.10 ± 0.31 μg mL(-1), AUC = 1.45 ± 0.21 μg h mL(-1) and K(a) = 5.64 ± 1.89 h(-1). The concentrations of UA in rat lung, spleen, liver, heart, and cerebellum were studied for the first time. This method is validated and could be applicable to the investigation of the pharmacokinetics and tissue distribution of UA in rats.