Simultaneous determination of imperatorin and its metabolites in vitro and in vivo by a GC-MS method: application to a bioavailability and protein binding ability study in rat plasma.

In this study, a simple and sensitive gas chromatography-mass spectrometry method was developed for the study of bioavailability and protein binding and the metabolism of imperatorin in rat. The results showed that the pharmacokinetics of imperatorin after intravenous and oral administration in rats exhibited linear characteristics. The absolute bioavailability of imperatorin was calculated as ~3.85, ~33.51 and ~34.76% for 6.25, 12.5 and 25 mg/kg, respectively. The low bioavailability of imperatorin may be attributed to the poor absorption or extensive metabolism. The phase I metabolites of imperatorin formed in vitro by rat liver microsomes were studied, and two metabolites were isolated and identified as xanthotoxol and heraclenin. Following oral administration of imperatorin, one metabolite (heraclenin) was detected in rat plasma, and two potential metabolites (xanthotoxol and heraclenin) were detected in rat urine. However, none of potential metabolites was detected in rat feces and bile. The results showed that the metabolites of imperatorin were excreted by kidney, and heraclenin was associated with an active component. Demethylation and oxygenization were the main metabolic pathways. In vitro plasma protein binding of imperatorin was 90.1 and 92.6% for the spiked rat plasma concentrations of 1.0 and 50.0 µg/mL, respectively, indicating that imperatorin showed slow distribution into the intra- and extracellular space.