Identification of the metabolites of tofacitinib in liver microsomes by liquid chromatography combined with high resolution mass spectrometry

Tofacitinib is an orally available Janus kinase inhibitor. The aim of this study was to investigate the metabolism of tofacitinib in mouse, rat, monkey, and human liver microsomes fortified with β-nicotinamide adenine dinucleotide phosphate tetrasodium salt and uridine diphosphate glucuronic acid. The biotransformation was executed at a temperature of 37°C for 60 min, and the samples were analyzed by ultra-high performance liquid chromatography combined with high-resolution mass spectrometry (UHPLC-HRMS) operated in positive electrospray ionization mode. The structures of the metabolites were elucidated according to their retention times, accurate masses, and MS/MS spectra. Under the current conditions, a total of 13 metabolites, including 1 glucuronide conjugate, were detected and structurally proposed. Oxygenation of the pyrrolopyrimidine ring, oxygenation of piperidine ring, N-demethylation, oxygenation of piperidine ring side chain, and glucuronidation were the primary metabolic pathways of tofacitinib. Among the tested species, tofacitinib showed significant species difference. Compared with other species, rat showed similar metabolic profiles to those of humans. The present study provides some new information regarding the metabolism of tofacitinib in Animals and humans, which would bring us considerable benefits for the subsequent studies focusing on the pharmacological effect and toxicity of this drug.