title: Identification of in vitro and in vivo human metabolites of the new psychoactive substance nitracaine by liquid chromatography coupled to quadrupole time-of-flight mass spectrometry.
abstract: The purpose of this work was to investigate the in vitro metabolism of nitracaine, a new psychoactive substance, using human liver microsome incubations, to evaluate the cytochrome P450 (CYP) enzyme isoforms responsible for the phase-I metabolism and to compare the information from the in vitro experiments with data resulting from an authentic user's urine sample. Accurate mass spectra of metabolites were obtained using liquid chromatography-quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) and were used in the structural identification of metabolites. Two major and three minor phase-I metabolites were identified from the in vitro experiments. The observed phase-I metabolites were formed through N-deethylation, N,N-deethylation, N-hydroxylation, and de-esterification, with CYP2B6 and CYP2C19 being the main enzymes catalyzing their formation. One glucuronidated product was identified in the phase-II metabolism experiments. All of these metabolites are reported for the first time in this study except the N-deethylation product. All the in vitro metabolites except the minor N,N-deethylation product were also present in the human urine sample, thus demonstrating the reliability of the in vitro experiments in the prediction of the in vivo metabolism of nitracaine. In addition to the metabolites, three transformation products (p-nitrobenzoic acid, p-aminobenzoic acid, and 3-(diethylamino)-2,2-dimethylpropan-1-ol) were identified, as well as several glucuronides and glutamine derived of them.
authors.affiliation: Toxicological Center, Department of Pharmaceutical Sciences, University of Antwerp, Universiteitsplein 1, 2610, Wilrijk-Antwerp, Belgium. noelia.negreira@outlook.com.
authors.forename: Noelia
authors.initials: N
authors.lastname: Negreira
authors.affiliation: Toxicological Center, Department of Pharmaceutical Sciences, University of Antwerp, Universiteitsplein 1, 2610, Wilrijk-Antwerp, Belgium.
authors.forename: Juliet
authors.initials: J
authors.lastname: Kinyua
authors.affiliation: Department of Clinical Biology, Universitair Ziekenhuis Brussel, Laarbeeklaan 101, Jette, 1090, Brussel, Belgium.
authors.forename: Nik
authors.initials: N
authors.lastname: De Brabanter
authors.affiliation: Toxicological Center, Department of Pharmaceutical Sciences, University of Antwerp, Universiteitsplein 1, 2610, Wilrijk-Antwerp, Belgium.
authors.forename: Kristof
authors.initials: K
authors.lastname: Maudens
authors.affiliation: Toxicological Center, Department of Pharmaceutical Sciences, University of Antwerp, Universiteitsplein 1, 2610, Wilrijk-Antwerp, Belgium. alexander.vannuijs@uantwerpen.be.
authors.forename: Alexander L N
authors.initials: AL
authors.lastname: van Nuijs
mesh_terms: D002478:Cells, Cultured; D002853:Chromatography, Liquid / Q000379:methods*; D006801:Humans; D008862:Microsomes, Liver / Q000378:metabolism*; D009564:Nitracrine / Q000032:analysis / Q000493:pharmacokinetics*; D011619:Psychotropic Drugs / Q000032:analysis / Q000493:pharmacokinetics*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*
chemical_list: D011619:Psychotropic Drugs; D009564:Nitracrine
keywords: High-resolution mass spectrometry; Human liver microsomes; In vitro metabolism; New psychoactive substance; Nitracaine