title: Regioselectivity and enantioselectivity of metoprolol oxidation by two variants of cDNA-expressed P4502D6.
abstract: OBJECTIVE
  The oxidative metabolism of metoprolol was investigated in two human lymphoblastoma cell-lines transfected with variants of cDNA for cytochrome P4502D6.
  
  
  METHODS
  The regioselective and enantioselective features of the oxidations of deuterium-labeled pseudoracemic metoprolol were characterized by GC/MS analysis of the substrate and products.
  
  
  RESULTS
  There were significant differences between the two P4502D6 variants in the formation kinetics of O-demethylmetoprolol and alpha-hydroxymetoprolol. The h2D6-Val microsomes highly favored the formation of the O-demethylmetoprolol regioisomer 6.3:1 and 2.8:1, respectively from (R)-metoprolol-d0 and (S)-metoprolol-d2, while the corresponding ratios for h2D6v2 microsomes were much lower. For both variants, O-demethylmetoprolol formation favored the (R)-substrate 1.5 to 2-fold, while alpha-hydroxymetoprolol formation was non-enantioselective. Similar Km values of metoprolol oxidation, 10-20 microM, were observed for the two microsomal preparations.
  
  
  CONCLUSIONS
  The regioselectivity, enantioselectivity, and Km values for the h2D6-Val microsomes resemble those observed for the native P4502D6 in human liver microsomes, whereas the h2D6v2 microsomes deviated remarkably in regioselectivity.
authors.affiliation: Department of Anesthesiology, University of Washington, Seattle 98195, USA.
authors.forename: D S
authors.initials: DS
authors.lastname: Mautz
authors.forename: D D
authors.initials: DD
authors.lastname: Shen
authors.forename: W L
authors.initials: WL
authors.lastname: Nelson
mesh_terms: D002460:Cell Line; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D018076:DNA, Complementary; D006801:Humans; D007700:Kinetics; D008099:Liver / Q000378:metabolism; D008790:Metoprolol / Q000737:chemistry*; D010084:Oxidation-Reduction
chemical_list: D018076:DNA, Complementary; D003577:Cytochrome P-450 Enzyme System; D008790:Metoprolol