Simultaneous determination of three sesquiterpene lactones from Herba Inula extract in rat plasma by LC/MS/MS and its application to pharmacokinetic study

A rapid and sensitive liquid chromatography–tandem mass spectrometry method has been developed and validated for the determination of 1-acetoxy-6α-hydroxyeriolanolide, 1β-hydroxyalantolactone and ivangustin from Herba Inula extract in rat plasma. Plasma samples were pretreated by protein precipitation with methanol. Chromatographic separation was accomplished on a TOSOH TSKgel ODS column with mobile phase consisting of methanol and 0.3% formic acid (80:20, v/v). The detection was carried out by multiple-reaction monitoring mode under positive electrospray ionization. The quantification was performed using the transitions of m/z 309.1/185.0 for 1-acetoxy-6α-hydroxyeriolanolide, m/z 249.0/231.1 for 1β-hydroxyalantolactone and ivangustin and m/z 285.0/193.0 for diazepam, respectively. Calibration curves were linear over the concentration range of 4–800 ng/mL for 1-acetoxy-6α-hydroxyeriolanolide, 8–500 ng/mL for 1β-hydroxyalantolactone and ivangustin. The limit of detection (LOD) was 1 ng/mL for 1-acetoxy-6α-hydroxyeriolanolide, 1.6 ng/mL for 1β-hydroxyalantolactone and ivangustin (S/N = 3). The intra-day and inter-day precisions (RSD%) for the three compounds were less than 7.8% and 8.6%, and the accuracy (RE%) ranged from −4.6 to 6.8%. The method was successfully applied to pharmacokinetic studies of the three sesquiterpene lactones after oral administration of 300 mg/kg Herba Inula extract to rats, the t1/2 of 1-acetoxy-6α-hydroxyeriolanolide, 1β-hydroxyalantolactone and ivangustin was 9.65 ± 1.43, 14.88 ± 0.82 and 13.93 ± 2.74 (h). The AUC(0−t) of 1-acetoxy-6α-hydroxyeriolanolide, 1β-hydroxyalantolactone and ivangustin was 1102.46 ± 247.04, 808.92 ± 117.53 and 990.35 ± 275.49 (ng h/mL), respectively.