title: Identification of the human cytochrome P450 enzymes involved in the in vitro metabolism of artemisinin.
abstract: OBJECTIVE
  The study aimed to identify the specific human cytochrome P450 (CYP450) enzymes involved in the metabolism of artemisinin.
  
  
  METHODS
  Microsomes from human B-lymphoblastoid cell lines transformed with individual CYP450 cDNAs were investigated for their capacity to metabolize artemisinin. The effect on artemisinin metabolism in human liver microsomes by chemical inhibitors selective for individual forms of CYP450 was investigated. The relative contribution of individual CYP450 isoenzymes to artemisinin metabolism in human liver microsomes was evaluated with a tree-based regression model of artemisinin disappearance rate and specific CYP450 activities.
  
  
  RESULTS
  The involvement of CYP2B6 in artemisinin metabolism was demonstrated by metabolism of artemisinin by recombinant CYP2B6, inhibition of artemisinin disappearance in human liver microsomes by orphenadrine (76%) and primary inclusion of CYP2B6 in the tree-based regression model. Recombinant CYP3A4 was catalytically competent in metabolizing artemisinin, although the rate was 10% of that for recombinant CYP2B6. The tree-based regression model suggested CYP3A4 to be of importance in individuals with low CYP2B6 expression. Even though ketoconazole inhibited artemisinin metabolism in human liver microsomes by 46%, incubation with ketoconazole together with orphenadrine did not increase the inhibition of artemisinin metabolism compared to orphenadrine alone. Troleandomycin failed to inhibit artemisinin metabolism. The rate of artemisinin metabolism in recombinant CYP2A6 was 15% of that for recombinant CYP2B6. The inhibition of artemisinin metabolism in human liver microsomes by 8-methoxypsoralen (a CYP2A6 inhibitor) was 82% but CYP2A6 activity was not included in the regression tree.
  
  
  CONCLUSIONS
  Artemisinin metabolism in human liver microsomes is mediated primarily by CYP2B6 with probable secondary contribution of CYP3A4 in individuals with low CYP2B6 expression. The contribution of CYP2A6 to artemisinin metabolism is likely of minor importance.
authors.affiliation: Department of Pharmacy, Division of Biopharmaceutics and Pharmacokinetics, Uppsala University, Sweden.
authors.forename: U S
authors.initials: US
authors.lastname: Svensson
authors.forename: M
authors.initials: M
authors.lastname: Ashton
mesh_terms: D000962:Antimalarials / Q000378:metabolism*; D037621:Artemisinins; D001189:Aryl Hydrocarbon Hydroxylases; D002460:Cell Line; D065702:Cytochrome P-450 CYP2B6; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000145:classification / Q000502:physiology*; D018076:DNA, Complementary / Q000235:genetics; D004347:Drug Interactions; D006801:Humans; D007527:Isoenzymes / Q000235:genetics; D007654:Ketoconazole / Q000494:pharmacology; D008730:Methoxsalen / Q000494:pharmacology; D008862:Microsomes, Liver / Q000201:enzymology / Q000378:metabolism*; D006899:Mixed Function Oxygenases / Q000502:physiology; D009966:Orphenadrine / Q000494:pharmacology; D010089:Oxidoreductases, N-Demethylating / Q000502:physiology; D012044:Regression Analysis; D012717:Sesquiterpenes / Q000378:metabolism*; D013997:Time Factors; D014217:Troleandomycin / Q000494:pharmacology
chemical_list: D000962:Antimalarials; D037621:Artemisinins; D018076:DNA, Complementary; D007527:Isoenzymes; D012717:Sesquiterpenes; D003577:Cytochrome P-450 Enzyme System; C031327:artemisinin; D009966:Orphenadrine; D014217:Troleandomycin; D006899:Mixed Function Oxygenases; D001189:Aryl Hydrocarbon Hydroxylases; C585599:CYP2B6 protein, human; C104464:CYP3A protein, human; D065702:Cytochrome P-450 CYP2B6; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D010089:Oxidoreductases, N-Demethylating; D007654:Ketoconazole; D008730:Methoxsalen