In vivo microdialysis with LC–MS for analysis of spinosin and its interaction with cyclosporin A in rat brain, blood and bile

Spinosin, a major bioactive herbal ingredient isolated from Semen Ziziphi Spinosae, plays an important role in sedation and hypnosis. However, the pharmacokinetic behavior of spinosin in special sites has not been reported. Microdialysis (MD) technique, as a continuous, realtime monitoring sampling technique, is very suitable for the evaluation of the disposition of diverse drugs. To obtain more useful information on spinosin, an in vivo microdialysis sampling technique with High Performance Liquid Chromatography–mass spectrograph (HPLC–MS) method was developed to investigate the pharmacokinetics of spinosin and its interaction with cyclosporin A (CsA) in the brain, blood and bile of rats. The method was validated in terms of selectivity, linearity and sensitivity, and showed advantages in monitoring the pharmacokinetic behavior of drugs. The results revealed that CsA has obvious effects on the pharmacokinetic process of spinosin. When co-administered, the area under the curve (AUC) of spinosin in blood, bile and brain increased from 205.70 to 673.51 mg min/L, 7.77 × 104 to 1.25 × 105 mg min/L, and 2.09 to 5.58 mg min/L, respectively. The t1/2 values of spinosin in blood, bile and brain also changed from 48.07 to 95.04 min, from 97.20 to 152.21 and from 42.18 to 73.83 min, respectively. These results demonstrated that the CsA decreased the efflux of spinosin through the inhibition of P-glycoprotein (P-gp) efflux transporter and it might be used as a group of P-gp substrate. Other transporters or pathways may also be involved in the metabolism of spinosin.

► Analysis of hepatobiliary excretion and brain metabolism is important to understanding drug metabolism.
► Technical difficulties limited spinosin analysis in rat blood, bile and brain.
► A microdialysis technique with HPLC–MS method was developed to investigate the pharmacokinetics of unbound spinosin in the brain, blood and bile dialysate of rats, this method can be conveniently and sensitively applied to monitor the pharmacokinetic behavior of drugs.