Abstract
Several new glutathione adducts (M3–M7) of trazodone were tentatively identified in human liver microsomal incubations using liquid chromatography-tandem mass spectrometry (LC/MS/MS). Following incubations with trazodone in the presence of glutathione, 1-(3′-chlorophenyl)piperazine (m-CPP), a major circulating and pharmacologically active metabolite of several antidepressants including trazodone, nefazodone, and etoperidone, was trapped with glutathione to afford the corresponding quinone imine-sulfydryl adducts M4 and M5. Two novel glutathione adducts of deschloro-m-CPP and deschloro-trazodone, M3 and M6, were also detected by tandem mass spectrometry. The identities of these m-CPP-derived glutathione adducts were further confirmed by LC/MS/MS analyses of microsomal incubations of m-CPP. To investigate the bioactivation mechanism, a regioisomer of m-CPP, 1-(4′-chlorophenyl)piperazine, was incubated in human liver microsomes. Blockage of bioactivation by 4′-chloro-substitution at least partially suggested that formation of m-CPP-derived glutathione adducts M3, M4, and M5 is mediated by a common quinone imine intermediate. A tentative pathway states that upon formation of the trazodone- and m-CPP-1′,4′-quinone imine intermediates through initial 4′-hydroxylation, glutathione attacks at the chlorine position by an ipso substitution, resulting in 4′-hydroxy-3′-glutathion-deschloro-trazodone (M6) and 4′-hydroxy-3′-glutathion-deschloro-m-CPP (M3), respectively. In contrast to CYP3A4-dependent bioactivation of trazodone itself, formation of M4 was mediated specifically by CYP2D6, as evidenced by cDNA-expressed CYP2D6-catalyzing formation of M4 from m-CPP, strong inhibition of formation of M4 by quinidine, a specific CYP2D6 inhibitor, in both incubations of trazodone and m-CPP with human liver microsomes, and concentration-dependent inhibition of M4 formation by quinidine.
Footnotes
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Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
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doi:10.1124/dmd.107.019471.
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ABBREVIATIONS: 5-HT, 5-hydroxytryptamine; P450, cytochrome P450; m-CPP, 1-(3′-chlorophenyl)piperazine; GSH, glutathione; p-CPP, 1-(4′-chlorophenyl)piperazine; LC/MS/MS, liquid chromatography-tandem mass spectrometry; HPLC, high-performance liquid chromatography; PI, precursor ion; EPI, enhanced product ion; NL, neutral loss; HLM, human liver microsome; CID, collision-induced dissociation.
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↵1 Current affiliation: Department of Drug Metabolism and Pharmacokinetics, Roche Palo Alto, Palo Alto, CA.
- Received October 28, 2007.
- Accepted January 28, 2008.
- The American Society for Pharmacology and Experimental Therapeutics
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