Characterization of Pharmacokinetics and Oral Bioavailability of Saikosaponin A in Rats Using a Validated UFLC-MS/MS...

Saikosaponin A (SSa) is an oleanane type triterpenoid saponin isolated from Radix Bupleuri (Bupleurum chinense DC). While SSa has demonstrated significant pharmacological activities including anti-inflammatory, antioxidant, and antidepressant effects, its pharmacokinetic profile remains poorly characterized. This study developed and validated a sensitive LC-MS/MS method for quantifying SSa in rat plasma. After acetonitrile-mediated protein precipitation, SSa and the internal standard (IS) were separated on a Waters Acquity BEH C18 column using MS detection operated in negative multiple reaction monitoring (MRM) mode. The assay was linear over the concentration range of 2-1000 ng/mL with satisfactory validation parameters of intra-and inter-day precision (3.50%-10.01%) and accuracy (-5.93% to -2.68%), extraction recovery (73.75%-82.50%), stability, and matrix effect (88.49%-103.64%). Application in pharmacokinetic studies revealed distinct administration-related characteristics. Intravenous administration (5 mg/kg) resulted in high clearance with an elimination half-life (t_1/2) of 2.29 h and was accompanied by hemolysis. Oral administration at doses of 50, 100, and 200 mg/kg showed dose-dependent systemic exposure with consistently low bioavailability (0.04%). The limited absorption is likely attributable to poor gastrointestinal permeability and extensive metabolism mediated by intestinal microbiota and hepatic first-pass effects, as indicated by the extremely low system exposure. These findings provide useful information for optimizing SSa therapeutic applications.