Identification of the stable and reactive metabolites of tetrahydropiperine using ultrahigh‐performance liquid chromatography combined with diode‐array detection and high‐resolution mass spectrometry

Rationale Tetrahydropiperine is one of the natural arylpentanamide compounds isolated from Piper nigrum L., which has been demonstrated to have insecticidal activity. The aim of this study was to investigate the metabolic profiles of tetrahydropiperine in mouse, rat, dog, monkey and human hepatocytes. Methods The in vitro metabolism of tetrahydropiperine was elucidated via incubation with hepatocytes for 2 h at 37°C. The samples were analyzed using ultrahigh‐performance liquid chromatography combined with diode‐array detection and high‐resolution tandem mass spectrometry operated in positive electrospray ionization mode. The structures of the metabolites were characterized using their retention times and their tandem mass spectrometric product ions. Results A total of 20 metabolites were detected and their structures were proposed. These metabolites were formed mainly through the following pathways: (1) 1,3‐benzodioxole ring opening to form a catechol derivative (M12), which was prone to glucuronidation (M6 and M8), methylation (M17) and glutathione (GSH)‐derived conjugation through an ortho ‐quinone intermediate (M4) or via an aldehyde intermediate (M7); (2) dehydrogenation to form a piperanine (M15), which was subsequently subject to hydroxylation (M2 and M5) and GSH conjugation (M10 and M11) via Michael addition; (3) hydroxylation (M13, M14, M16, M18 and M19); and (4) direct GSH conjugation through an aldehyde intermediate (M3). Conclusions The major metabolic pathways of tetrahydropiperine were hydroxylation, dehydrogenation, methylation, GSH conjugation and glucuronidation. Tetrahydropiperine was bioactivated through ortho ‐quinone, Michael receptor and aldehyde intermediates.