Abstract
Considerable unexplained intersubject variability in the debrisoquine metabolic ratio (urinary debrisoquine/4-hydroxydebrisoquine) exists within individual CYP2D6 genotypes. We speculated that debrisoquine was converted to as yet undisclosed metabolites. Thirteen healthy young volunteers, nine CYP2D6*1 homozygotes [extensive metabolizers (EMs)] and four CYP2D6*4 homozygotes [poor metabolizers (PMs)] took 12.8 mg of debrisoquine hemisulfate by mouth and collected 0- to 8- and 8- to 24-h urines, which were analyzed by gas chromatography-mass spectrometry (GCMS) before and after treatment with β-glucuronidase. Authentic 3,4-dehydrodebrisoquine was synthesized and characterized by GCMS, liquid chromatography-tandem mass spectrometry, and 1H NMR. 3,4-Dehydrodebrisoquine is a novel metabolite of debrisoquine excreted variably in 0- to 24-h urine, both in EMs (3.1–27.6% of dose) and PMs (0–2.1% of dose). This metabolite is produced from 4-hydroxydebrisoquine in vitro by human and rat liver microsomes. A previously unstudied CYP2D6*1 homozygote was administered 10.2 mg of 4-hydroxydebrisoquine orally and also excreted 3,4-dehydrodebrisoquine. EMs excreted 6-hydroxydebrisoquine (0–4.8%) and 8-hydroxydebrisoquine (0–1.3%), but these phenolic metabolites were not detected in PM urine. Debrisoquine and 4-hydroxydebrisoquine glucuronides were excreted in a highly genotype-dependent manner. A microsomal activity that probably does not involve cytochrome P450 participates in the further metabolism of 4-hydroxydebrisoquine, which we speculate may also lead to the formation of 1- and 3-hydroxydebrisoquine and their ring-opened products. In conclusion, this study suggests that the traditional metabolic ratio is not a true measure of the debrisoquine 4-hydroxylation capacity of an individual and thus may, in part, explain the wide intragenotype variation in metabolic ratio.
Footnotes
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Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
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Supported by the National Cancer Institute Intramural Research Program (F.J.G.). J.R.I. is grateful to U.S. Smokeless Tobacco Company for a grant for collaborative research.
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doi:10.1124/dmd.105.008920.
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ABBREVIATIONS: MR, metabolic rate; EM, extensive metabolizer; IM, intermediate metabolizer; P450, cytochrome P450; PM, poor metabolizer; UM, ultrarapid metabolizer; GCMS, gas chromatography-mass spectrometry; LC-MS/MS, liquid chromatography-tandem mass spectrometry; UPLC-TOFMS, ultra-performance liquid chromatography-coupled time-of-flight mass spectrometry.
- Received December 12, 2005.
- Accepted June 12, 2006.
- The American Society for Pharmacology and Experimental Therapeutics
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