Using high-resolution Twin-Ion Metabolite Extraction (HiTIME) mass spectrometry with stable isotope labelling to investigate the metabolism of valproic acid in vivo

Abstract Valproic acid (VPA) is a medication that is widely used in the treatment of epilepsy and bipolar disorder, despite a known potential for liver damage in some patients and a specific risk of teratogenic effects if taken by pregnant women. Here the metabolism of VPA has been investigated in male adult Sprague-Dawley rats using the twin-ion method and HiTIME (High-resolution Twin-Ion Metabolite Extraction) analysis under acute dosing. VPA and 13 C 4 -VPA were administered to rats via intra venous infusion and then blood extracts were analysed by liquid chromatography mass spectrometry (LC-MS). Following HiTIME analysis, 13 high scoring data regions were identified that were not present in control samples and corresponded to VPA together with 12 known VPA metabolites. Tandem mass spectrometry was performed on selected VPA metabolites. Increasing the dose of VPA resulted in an increase in the proportion of phase II metabolites formed at the expense of oxidative phase I products and slight increases in glucuronide conjugates were observed in steady-state treatment groups compared to acute dose groups. A twin ion corresponding to a putative VPA-ascorbate adduct was observed and confirmed via independent synthesis. The origin of twin-ion artefacts detected in LC-MS is also discussed as well as proposed methods to reduce their formation.