Comparative pharmacokinetics of timosaponin B-II and timosaponin A-III after oral administration of Zhimu–Baihe herb-pair, Zhimu extract, free timosaponin B-II and free timosaponin A-III to rats

The aim of this study was to compare the pharmacokinetics of timosaponin B-II and timosaponin A-III in rat plasma after oral administration of Zhimu–Baihe herb-pair, Zhimu extract, free timosaponin B-II and free timosaponin A-III. After addition of internal standard (IS) ginsenoside Rh1, plasma samples were pretreated by protein precipitation. Chromatographic separation was carried out on a SHISEIDO CAPCELL PAK C18 column (100 mm × 3 mm i.d., 3.0 μm) with the mobile phase consisting of acetonitrile and 0.05% (v/v) formic acid by linear gradient elution. The detection was performed on an Agilent G1946D single quadrupole mass spectrometer with negative electrospray ionization (ESI) interface in select-ion-monitoring (SIM) mode. The following ions: m/z 919 for timosaponin B-II, m/z 739 for timosaponin A-III and m/z 683 for the IS were used for quantitative determination. Good linearity was achieved over the concentration ranged from 4.0–793.3 ng/mL to 3.9–781.3 ng/mL for the two saponins. The precision of the in vivo study was evaluated by intra- and inter-day assays and the percentages of relative standard deviation were all within 15%. The plasma concentrations of timosaponin B-II and timosaponin A-III in rats at designated time periods were successfully determined using this fully validated method, and statistically significant differences (p < 0.5) in pharmacokinetic parameters including AUC0−t, AUC0−∞ and MRT (mean residence time) were obtained. Compared to these pharmacokinetic parameters after oral administration of Zhimu extract and monomer solution, higher peak concentration (Cmax is higher), slower elimination (MRT is longer) and larger AUC values could be observed after giving Zhimu–Baihe herb-pair in our study. Therefore, this result not only elucidated the steady and long-lasting pharmacological properties but also revealed the practical value of the compatibility of herb-pair remedy.