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3,4-Dehydrodebrisoquine, a Novel Debrisoquine Metabolite Formed from 4-Hydroxydebrisoquine That Affects the CYP2D6 Metabolic Ratio

Yueying Zhen, Ondej Slana, Kristopher W. Krausz, Chi Chen, Josef Slavík, Kerry L. McPhail, T. Mark Zabriskie, Frantiek Perlík, Frank J. Gonzalez, and Jeffrey R. Idle

Laboratory of Metabolism, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland (Y.Z., K.W.K., C.C., F.J.G.); Institute of Clinical Pharmacology, University of Bern, Switzerland (J.S., J.R.I.); Department of Pharmaceutical Sciences, Oregon State University, Corvallis, Oregon (K.L.M., T.M.Z.); and Institute of Pharmacology, 1^st Faculty of Medicine, Charles University, Prague, Czech Republic (O.S., F.P., J.R.I.).

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 ß-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.

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