title: Identification of the human cytochrome P450 isoforms mediating in vitro N-dealkylation of perphenazine.
abstract: OBJECTIVE
  To identify the human cytochrome P450 (CYP) isoforms mediating the N-dealkylation of the antipsychotic drug perphenazine in vitro and estimate the relative contributions of the CYP isoforms involved.
  
  
  METHODS
  cDNA-expressed CYP isoforms were used to identify the isoforms that are able to mediate the N-dealkylation of perphenazine, which is considered a major metabolic pathway for the drug. Using human liver microsomal preparations (HLM), inhibition studies were carried out to establish the relative contributions of the CYP isoforms involved in the N-dealkylation reaction.
  
  
  RESULTS
  CYP isoforms 1A2, 3A4, 2C8, 2C9, 2C18, 2C19 and 2D6 were able to mediate the N-dealkylation of perphenazine. Reaction velocities and their relative abundance in HLM suggested that CYP1A2, 3A4, 2C19 and 2D6 were the most important contributors to N-dealkylation. Apparent Km values of CYP1A2 and CYP2D6 were in the range 1-2 microM, and Km values of CYP2C19 and CYP3A4 were 14 microM and 7.9 microM, respectively. Ketoconazole inhibition of N-dealkylation mediated by a mixed HLM indicated that CYP3A4 accounted for about 40% of perphenazine N-dealkylation at therapeutically relevant concentrations. The contribution of the CYP isoforms 1A2, 2C19 and 2D6 amounted to 20-25% each as measured by the percentage inhibition obtained by addition of furafylline, fluvoxamine or quinidine, respectively. HLM-mediated N-dealkylation of perphenazine accounted for 57% of the total amount of substrate consumed during incubation.
  
  
  CONCLUSIONS
  The present in vitro study suggests that CYP isoforms 1A2, 3A4, 2C19 and 2CD6 are primarily involved in the N-dealkylation of perphenazine. The relatively modest role of CYP2D6 is at variance with in vivo studies, which indicate a greater contribution of this isoform. Alternative metabolic pathways, corresponding to 43% of the HLM-mediated metabolism of the drug, may depend more strongly on CYP2D6.
authors.affiliation: Institute for Basic Psychiatric Research, Department of Biological Psychiatry, Psychiatric University Hospital, Skovagervej 2, DK-8240 Risskov, Denmark. viol1907@post3.tele.dk
authors.forename: O V
authors.initials: OV
authors.lastname: Olesen
authors.forename: K
authors.initials: K
authors.lastname: Linnet
mesh_terms: D000478:Alkylation; D014150:Antipsychotic Agents / Q000378:metabolism*; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000145:classification / Q000235:genetics / Q000378:metabolism; D008862:Microsomes, Liver / Q000201:enzymology* / Q000378:metabolism; D010546:Perphenazine / Q000378:metabolism*; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000145:classification / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D014150:Antipsychotic Agents; D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D011994:Recombinant Proteins; D003577:Cytochrome P-450 Enzyme System; D010546:Perphenazine