title: Characterization of human cytochrome P450 mediated bioactivation of amodiaquine and its major metabolite N-desethylamodiaquine.
abstract: Oxidative bioactivation of amodiaquine (AQ) by cytochrome P450s to a reactive quinoneimine is considered as an important mechanism underlying its idiosyncratic hepatotoxicity. However, because internal exposure to its major metabolite N-desethylamodiaquine (DEAQ) is up to 240-fold higher than AQ, bioactivation of DEAQ might significantly contribute to covalent binding. The aim of the present study was to compare the kinetics of bioactivation of AQ and DEAQ by human liver microsomes (HLM) and to characterize the CYPs involved in bioactivation of AQ and DEAQ.
  
  
  
  Glutathione was used to trap reactive metabolites formed in incubations of AQ and DEAQ with HLM and recombinant human cytochrome P450s (hCYPs). Kinetics of bioactivation of AQ and DEAQ in HLM and involvement of hCYPs were characterized by measuring corresponding glutathione conjugates (AQ-SG and DEAQ-SG) using a high-performance liquid chromatography method.
  
  
  
  Bioactivation of AQ and DEAQ in HLM both exhibited Michaelis-Menten kinetics. For AQ bioactivation, enzyme kinetical parameters were Km, 11.5 ± 2.0 μmol l-1, Vmax, 59.2 ± 3.2 pmol min-1mg-1and CLint, 5.15 μl min-1mg-1. For DEAQ, parameters for bioactivation were Km, 6.1 ± 1.3 μmol l-1, Vmax, 5.5 ± 0.4 pmol min-1mg-1and CLint0.90 μl min-1mg-1. Recombinant hCYPs and inhibition studies with HLM showed involvement of CYP3A4, CYP2C8, CYP2C9 and CYP2D6 in bioactivation.
  
  
  
  The major metabolite DEAQ is likely to be quantitatively more important than AQ with respect to hepatic exposure to reactive metabolites in vivo. High expression of CYP3A4, CYP2C8, CYP2C9, and CYP2D6 may be risk factors for hepatotoxicity caused by AQ-therapy.
authors.affiliation: Division of Molecular Toxicology, Amsterdam Institute for Molecules Medicines and Systems (AIMMS), Department of Chemistry and Pharmaceutical Sciences, Faculty of Sciences, Vrije Universiteit, De Boelelaan 1108, 1081 HZ, Amsterdam, the Netherlands.
authors.forename: Yongjie
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Division of Molecular Toxicology, Amsterdam Institute for Molecules Medicines and Systems (AIMMS), Department of Chemistry and Pharmaceutical Sciences, Faculty of Sciences, Vrije Universiteit, De Boelelaan 1108, 1081 HZ, Amsterdam, the Netherlands.
authors.forename: Nico P E
authors.initials: NP
authors.lastname: Vermeulen
authors.affiliation: Division of Molecular Toxicology, Amsterdam Institute for Molecules Medicines and Systems (AIMMS), Department of Chemistry and Pharmaceutical Sciences, Faculty of Sciences, Vrije Universiteit, De Boelelaan 1108, 1081 HZ, Amsterdam, the Netherlands.
authors.forename: Jan N M
authors.initials: JN
authors.lastname: Commandeur
mesh_terms: D065767:Activation, Metabolic / Q000235:genetics*; D000655:Amodiaquine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics*; D065607:Cytochrome P-450 Enzyme Inhibitors / Q000494:pharmacology; D003577:Cytochrome P-450 Enzyme System / Q000187:drug effects / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism; D006801:Humans; D008862:Microsomes, Liver / Q000201:enzymology*; D011994:Recombinant Proteins / Q000187:drug effects / Q000378:metabolism
chemical_list: D065607:Cytochrome P-450 Enzyme Inhibitors; D011994:Recombinant Proteins; D000655:Amodiaquine; C047386:desethylamodiaquine; D003577:Cytochrome P-450 Enzyme System; D005978:Glutathione
keywords: N-desethylamodiaquine; amodiaquine; bioactivation; glutathione conjugate; human cytochrome P450s