Abstract
The in vitro metabolism of [14C]bicifadine by hepatic microsomes and hepatocytes from mouse, rat, monkey, and human was compared using radiometric high-performance liquid chromatography and liquid chromatography/tandem mass spectrometry. Two main metabolic pathways were identified in all four species. One pathway was an NADPH-dependent pathway in which the methyl group was oxidized to form a hydroxymethyl metabolite (M2). Its formation was inhibited in human microsomes only by quinidine, a CYP2D6 inhibitor. In incubations with individual cDNA-expressed human cytochromes P450, M2 was formed only by CYP2D6 and CYP1A2, with CYP2D6 activity 6-fold greater than that of CYP1A2. M2 was oxidized further to the carboxylic acid metabolite (M3) by hepatocytes from all four species. The second major metabolic pathway was an NADPH-independent oxidation at the C2 position of the pyrrolidine ring, forming a lactam metabolite (M12). This reaction was almost completely inhibited in human hepatic microsomes and mitochondria by the monoamine oxidase (MAO)-B-specific inhibitor selegiline. Clorgyline, a specific inhibitor of MAO-A, was less effective in inhibiting M12 formation. Other metabolic pathways of variable significance among the four species included the formation of carbamoyl-O-glucuronide, hydroxymethyl lactam, and carboxyl lactam. Overall, the data indicate that the primary enzymes responsible for the primary metabolism of bicifadine in humans are MAO-B and CYP2D6.
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.107.016055.
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ABBREVIATIONS: MAO, monoamine oxidase; HPLC, high-performance liquid chromatography; P450, cytochrome P450; AO, aldehyde oxidase; DOV 255,828, 5-(4-methylphenyl)-3-azabicyclo[3.1.0]hexan-2-one; DOV 255,833, 5-(4-carboxyphenyl)-3-azabicyclo[3.1.0]hexan-2-one; SK&F 86466, 6-chloro-2,3,4,5-tetrahydro-3-methyl-1H-3-benzazepine; LC, liquid chromatography; LC/MS, liquid chromatography/mass spectrometry; LC/MS/MS, liquid chromatography/tandem mass spectrometry; MS, mass spectrometry; amu, atomic mass unit(s).
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↵ The online version of this article (available at http://dmd.aspetjournals.org) contains supplemental material.
- Received March 30, 2007.
- Accepted September 19, 2007.
- The American Society for Pharmacology and Experimental Therapeutics
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