title: Identification of rat and human cytochrome P450 forms involved in the metabolism of the thromboxane A2 receptor antagonist (+)-S-145.
abstract: (+)-S-145 [5-(+)-(Z)-7-[(1R, 2S, 3S, 4S)-3-phenylsulfonylaminobicyclo[2.2.1]hept-2-yl]-heptenoic acid] and its beta-oxidized metabolites [two [bisnor or dihydro (DH)-bisnor] or four (tetranor) carbon-shortened products at the carboxyl side chain] are hydroxylated at the C-5 or C-6 position of the bicyclo ring by microsomal monooxygenases. We investigated the oxidative metabolism of (+)-S-145 and its beta-oxidized metabolites with liver microsomes from rats and humans to identify which cytochrome P450 (P450) forms are involved in these reactions. In rats, phenobarbital or dexamethasone treatment significantly increased 5- and 6-hydroxylation activities toward (+)-S-145 and its beta-oxidized metabolites, suggesting the involvement of P4503A forms. Immunoinhibition studies suggested that P4503A2 was mainly responsible for the 5-hydroxylation of (+)-S-145, bisnor, and DH-bisnor and the 6-hydroxylation of bisnor and tetranor. Furthermore, P4502C6, a phenobarbital-inducible 2C form in the rat, was involved in the 6-hydroxylation of (+)-S-145, bisnor, and DH-bisnor. P4502C11, the major constitutive form (male rats), was partly involved in the 5-hydroxylation of DH-bisnor and the 6-hydroxylation of bisnor and DH-bisnor. Reconstitution studies with purified human enzymes and immunoinhibition studies suggest that P4503A4 is primarily involved in the 5-hydroxylation of (+)-S-145 and bisnor and the 6-hydroxylation of tetranor; P4502C9/10 mainly catalyzed the 5-hydroxylation of tetranor and the 6-hydroxylation of (+)-S-145. Results of the present study indicated that the same subfamily P450 forms are responsible for the oxidative metabolism of (+)-S-145 in rats and humans. P4503A enzymes were shown to be involved in the formation of 6-hydroxy tetranor, the main metabolite of S-1452 in vivo.
authors.affiliation: Developmental Research Laboratories, Shionogi & Co., Ltd., Osaka, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Yamaguchi
authors.forename: S
authors.initials: S
authors.lastname: Kirita
authors.forename: T
authors.initials: T
authors.lastname: Baba
authors.forename: J
authors.initials: J
authors.lastname: Aoyama
authors.forename: A
authors.initials: A
authors.lastname: Touchi
authors.forename: R H
authors.initials: RH
authors.lastname: Tukey
authors.forename: F P
authors.initials: FP
authors.lastname: Guengerich
authors.forename: T
authors.initials: T
authors.lastname: Matsubara
mesh_terms: D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D001643:Bridged Bicyclo Compounds / Q000378:metabolism*; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis* / Q000276:immunology; D003907:Dexamethasone / Q000494:pharmacology; D004790:Enzyme Induction / Q000187:drug effects; D005229:Fatty Acids, Monounsaturated / Q000378:metabolism*; D006801:Humans; D006900:Hydroxylation; D007527:Isoenzymes / Q000096:biosynthesis* / Q000276:immunology; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D010634:Phenobarbital / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D017482:Receptors, Thromboxane / Q000037:antagonists & inhibitors*; D011994:Recombinant Proteins / Q000276:immunology / Q000378:metabolism
chemical_list: D000906:Antibodies; D001643:Bridged Bicyclo Compounds; D005229:Fatty Acids, Monounsaturated; D007527:Isoenzymes; D017482:Receptors, Thromboxane; D011994:Recombinant Proteins; C056566:S 145; D003907:Dexamethasone; D003577:Cytochrome P-450 Enzyme System; D010634:Phenobarbital