Quantification of Major Metabolites of AB-FUBINACA in Solid Tissues Obtained from an Abuser

AB-FUBINACA M3 was reported to be a major metabolite of the drug, but its in vivo concentration in authentic human solid tissues has not been quantified yet. Another metabolite AB-FUBINACA M4 did not receive much attention previously and also has not been quantified yet in any authentic human specimens. The aims of this study are to establish a sensitive method for quantification of M3 and M4 in solid tissues and to compare the metabolite profile of AB-FUBINACA in authentic human specimens in vivo with that produced by human hepatocytes in vitro. The quantification was performed by liquid chromatography (LC)-quadrupole-ion trap-tandem mass spectrometry (MS-MS), and the characterization by LC-quadrupole Orbitrap MS-MS The limits of quantification of M3 were 10 pg/mL and 60 pg/g, and those of M4 were 100 pg/mL and 600 pg/g in urine and tissues, respectively. In the present work, M3 and M4 were identified and quantified in human lung, liver and kidney obtained from a cadaver for the first time; the concentrations of M3 were 226, 255, 202 and 155 pg/mL or g, and those of M4 14,400, 768, 637 and 1,390 pg/mL or g in urine, lung, liver and kidney, respectively. The peak intensity profiles of seven metabolites in these specimens were compared with that produced by human hepatocytes; the top three metabolites in urine specimen were completely different from those of hepatocytes. M3 was reported as the predominant metabolite in several previous works and M4 was listed as a minor metabolite in only one work, but, in this work, M4 has been found to be the major metabolite in all of the authentic urine, lung, liver and kidney specimens. The M3 plus M4 metabolites in lung or kidney were found most recommendable to prove AB-FUBINACA consumption, when urine specimen is lacking.