Identification of metabolites of palmatine in rats after oral administration using ultra-high-performance liquid chromatography/quadrupole time-of-flight mass spectrometry

RATIONALE: Palmatine (PAL), a protopalmatine alkaloid, is an active constituent in a number of medicinal plants. In order to obtain a comprehensive and systematic metabolic profile of PAL, we investigated its metabolites in plasma, liver tissue, bile, urine, and feces samples after intragastrical administration to Sprague-Dawley rats with a dose of 100 mg/kg/day. METHODS: In this study, a rapid and sensitive method by ultra-high-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC/QTOF-MS), and Metabolynx (TM) software with the mass defect filter (MDF) technique was developed for screening and identification of the metabolites. The structural elucidation of the metabolites was performed by comparing their molecular weights and fragment ions with those of the parent drug. RESULTS: As a result, a total of 58 metabolites were identified in rat biological samples including 46 metabolites in urine, 18 metabolites in plasma, 34 metabolites in bile, 26 metabolites in liver tissue, and 10 metabolites in feces. Among them, six major metabolites were fully confirmed using reference standards and others were identified by retention time, accurate mass and fragment ions. CONCLUSIONS: These results indicated that phase I reactions (demethylation and hydroxylation) and phase II reaction (glucuronidation and sulfation) were the main metabolic pathways of PAL in vivo. This research enhances our understanding of metabolism of PAL in rats, and provides useful information on the action mechanism of PAL. Copyright (C) 2017 John Wiley & Sons, Ltd.