Pharmacokinetics and metabolism study of isoboldine, a major bioactive component from Radix Linderae in male rats by UPLC-MS/MS

Abstract

Ethnopharmacological relevance: Isoboldine is one of the major bioactive constituents in the total alkaloids from Radix Linderae (TARL) which could effectively alleviate inflammation and joints destruction in mouse collagen-induced arthritis. To better understand its pharmacological activities, we need to determine its pharmacokinetic and metabolic profiles.

Materials and methods: In this study, a sensitive and simple UPLC-MS/MS method was developed and validated for determination of isoboldine in rat plasma. Isoboldine in plasma was recovered by liquid-liquid extraction using 1 mL of methyl tert-butyl ether. Chromatographic separation was performed on a C18 column at 45°C, with a gradient elution consisting of acetonitrile and water containing 0.1% (v/v) formic acid at a flow rate of 0.3 mL/min. The detection was performed on an electrospray triple-quadrupole MS/MS by positive ion multiple-reaction monitoring mode. This newly developed method was successfully applied to a pharmacokinetic study after oral and intravenous dosing in rats. For metabolites identification, isoboldine was orally administered to rats and the metabolite in plasma, bile, urine and feces were characterized by the established UPLC-MS/MS method.

Results: Good linearity (r(2)>0.9956) was achieved in a concentration range of 4.8-2400 ng/mL with a lower limit of quantification of 4.8 ng/mL for isoboldine. The intra- and inter-day precisions of the assay were 1.7-5.1% and 2.2-4.4% relative standard deviation with an accuracy of 91.3-102.3%. A total of five phase II metabolites in rat plasma, bile, urine and feces were characterized by comparing retention time in UPLC, and by molecular mass and fragmentation pattern of the metabolites by mass spectrometry with those of isoboldine.

Conclusion: isoboldine has extremely low oral bioavailability due to the strong first-pass effect by the rats, and glucuronidation and sulfonation were involved in metabolic pathways of isoboldine in rats. These results have paved the way for further clarifying therapeutic ingredients and provided new knowledge regarding pharmacokinetic features of this category of isoquinoline alkaloids.

Keywords: Isoboldine; Metabolite identification; Oral bioavailability; Pharmacokinetics; Radix Linderae; UPLC–MS/MS.