•Pharmacokinetics of emodin and its glucuronidation were investigated by LC–MS/MS method.•The comparison of bioavailability and pharmacokinetics between emodin alone and in combination with piperine were carried out.•Piperine significantly improved the in vivo bioavailability of emodin via the inhibition of its glucuronidation.Emodin (1,3,8-trihydroxy-6-methylanthraquinone) has been widely used as a traditional medicine and was shown to possess a multitude of health-promoting properties in pre-clinical studies, but its bioavailability was low due to the extensive glucuronidation in liver and intestine, hindering the development of emodin as a feasible chemopreventive agent. In this study, piperine, as a bioenhancer, was used to enhance the bioavailability of emodin by inhibiting its glucuronidation. The pharmacokinetic profiles of emodin after oral administration of emodin (20 mg/kg) alone and in combination with piperine (20 mg/kg) to rats were investigated via a validated LC/MS/MS method. As the in vivo pharmacokinetic studies had indicated, the AUC and Cmax of emodin were increased significantly after piperine treatment, and the glucuronidation of emodin was markedly inhibited. Our study demonstrated that piperine significantly improved the in vivo bioavailability of emodin and the influence of piperine on the pharmacokinetics of emodin may be attributed to the inhibition of glucuronidation of emodin. Further research is needed to investigate the detailed mechanism of improved bioavailability of emodin via its combination with piperine.

•The ex vivo stability of bilobalide was investigated for the first time.•Effective strategies to stabilize bilobalide in rat blood and plasma were developed.•An LC–MS/MS method for determining bilobalide in rat plasma was fully validated.•An LOQ of 5.0 ng/mL was achieved with consumption of only 20 μL of plasma.The ex vivo instability of bilobalide containing three γ-lactone rings has been paid less attention by researchers who developed bioanalytical methods for bilobalide. In the present study, a sensitive LC–MS/MS method for the determination of bilobalide in rat plasma was developed with special consideration of ex vivo bilobalide stability. Several important factors affecting the stability of bilobalide in sampling and handling procedures were investigated. To prevent the ex vivo degradation of bilobalide, EDTA instead of heparin was used as an anticoagulant as well as an esterase inhibitor for blood collection and the separation of plasma was performed at 4 °C. 20 μL of plasma sample was acidified with 0.1 M hydrochloric acid, and then extracted with ethyl ether–methylene chloride (2:1, v/v). The extract was chromatographed on a Thermo Hypersil GOLD (100 mm × 2.1 mm, 5 μm) column using acetonitrile–10 mM ammonium acetate–formic acid (90:10:0.4, v/v/v) as the mobile phase. The analyte and the internal standard (ginkgolide B) were detected by selected reaction monitoring mode via negative electrospray ionization. The method was fully validated and proved to be linear over a concentration range of 5.0–5000 ng/mL. The intra- and inter-day precisions were less than 5.2% and the accuracy was within 92.5–101%. The extraction recoveries ranged from 80.7% to 86.7%. The proposed method was successfully applied to a preclinical pharmacokinetic study of bilobalide in rats after intragastric administration of a single dose of bilobalide at 7, 14 and 28 mg/kg.

A rapid and sensitive liquid chromatography-tandem mass spectrometric method (LC–MS–MS) has been developed for simultaneous determination of 20(R)-25-methoxyl-dammarane-3,12,20-triol (25-OCH3-PPD) and its active metabolite, 20(R)-dammarane-3,12,20,25-tetrol (25-OH-PPD) in beagle dog’s plasma. Diazepam was employed as an internal standard. Sample preparation involved a liquid–liquid extraction with diethyl ether and dichloromethane (3:2, v/v). Chromatographic separation was achieved on a Phenomenex C18 material (50 × 2.0 mm i.d., 4 μm) using methanol–water-formic acid (124:26:0.3, v/v/v) as the mobile phase at a flow rate of 0.25 mL min−1. The present method exhibited good linearity over the concentration range of 2–500 ng mL−1 for 25-OCH3-PPD and 2–60 ng mL−1 for 25-OH-PPD. The lower limit of quantification was 2 and 2 ng mL−1 for 25-OCH3-PPD and 25-OH-PPD, respectively. The intra- and inter-day precision values for 25-OCH3-PPD and 25-OH-PPD met the requirements of the FDA guidance, and the accuracy (RE) ranged from −4.1 to 5.6% calculated from QC samples. No endogenous compound was found to interfere with the analysis. 25-OCH3-PPD and 25-OH-PPD were stable during all storage, pretreatment and analytical periods. The validated method was successfully used to study the pharmacokinetics of 25-OCH3-PPD in beagle dogs after oral administration at a dose of 12 mg kg−1.