title: Sequential metabolism of secondary alkyl amines to metabolic-intermediate complexes: opposing roles for the secondary hydroxylamine and primary amine metabolites of desipramine, (s)-fluoxetine, and N-desmethyldiltiazem.
abstract: Three secondary amines desipramine (DES), (S)-fluoxetine [(S)-FLX], and N-desmethyldiltiazem (MA) undergo N-hydroxylation to the corresponding secondary hydroxylamines [N-hydroxydesipramine, (S)-N-hydroxyfluoxetine, and N-hydroxy-N-desmethyldiltiazem] by cytochromes P450 2C11, 2C19, and 3A4, respectively. The expected primary amine products, N-desmethyldesipramine, (S)-norfluoxetine, and N,N-didesmethyldiltiazem, are also observed. The formation of metabolic-intermediate (MI) complexes from these substrates and metabolites was examined. In each example, the initial rates of MI complex accumulation followed the order secondary hydroxylamine > secondary amine >> primary amine, suggesting that the primary amine metabolites do not contribute to formation of MI complexes from these secondary amines. Furthermore, the primary amine metabolites, which accumulate in incubations of the secondary amines, inhibit MI complex formation. Mass balance studies provided estimates of the product ratios of N-dealkylation to N-hydroxylation. The ratios were 2.9 (DES-CYP2C11), 3.6 [(S)-FLX-CYP2C19], and 0.8 (MA-CYP3A4), indicating that secondary hydroxylamines are significant metabolites of the P450-mediated metabolism of secondary alkyl amines. Parallel studies with N-methyl-d(3)-desipramine and CYP2C11 demonstrated significant isotopically sensitive switching from N-demethylation to N-hydroxylation. These findings demonstrate that the major pathway to MI complex formation from these secondary amines arises from N-hydroxylation rather than N-dealkylation and that the primary amines are significant competitive inhibitors of MI complex formation.
authors.affiliation: Department of Medicinal Chemistry, University of Washington, Box 357610, Seattle, WA 98195, USA.
authors.forename: Kelsey L
authors.initials: KL
authors.lastname: Hanson
authors.forename: Brooke M
authors.initials: BM
authors.lastname: VandenBrink
authors.forename: Kantipudi N
authors.initials: KN
authors.lastname: Babu
authors.forename: Kyle E
authors.initials: KE
authors.lastname: Allen
authors.forename: Wendel L
authors.initials: WL
authors.lastname: Nelson
authors.forename: Kent L
authors.initials: KL
authors.lastname: Kunze
mesh_terms: D001189:Aryl Hydrocarbon Hydroxylases / Q000378:metabolism*; D065702:Cytochrome P-450 CYP2B6; D065731:Cytochrome P-450 CYP2C19; D051544:Cytochrome P-450 CYP3A / Q000378:metabolism*; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D000072467:Cytochrome P450 Family 2; D003891:Desipramine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D004110:Diltiazem / Q000031:analogs & derivatives* / Q000378:metabolism; D005473:Fluoxetine / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D019811:Hydroxylamine; D006898:Hydroxylamines / Q000378:metabolism; D006900:Hydroxylation; D007099:Imipramine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D008862:Microsomes, Liver / Q000378:metabolism*; D010089:Oxidoreductases, N-Demethylating / Q000378:metabolism; D039181:Steroid 16-alpha-Hydroxylase / Q000378:metabolism
chemical_list: D006898:Hydroxylamines; C523297:N,N-didesmethyldiltiazem; D005473:Fluoxetine; C036691:didesipramine; D019811:Hydroxylamine; C039939:N-hydroxydesipramine; D003577:Cytochrome P-450 Enzyme System; D001189:Aryl Hydrocarbon Hydroxylases; C585599:CYP2B6 protein, human; C450279:CYP2C11 protein, rat; C045793:CYP2C19 protein, human; D065702:Cytochrome P-450 CYP2B6; D065731:Cytochrome P-450 CYP2C19; D051544:Cytochrome P-450 CYP3A; D000072467:Cytochrome P450 Family 2; D039181:Steroid 16-alpha-Hydroxylase; C510163:CYP3A4 protein, human; D010089:Oxidoreductases, N-Demethylating; D004110:Diltiazem; C052825:N-monodemethyldiltiazem; C036139:norfluoxetine; D007099:Imipramine; D003891:Desipramine