title: In vitro metabolism of dorzolamide, a novel potent carbonic anhydrase inhibitor, in rat liver microsomes.
abstract: The in vitro metabolism of dorzolamide, a potent carbonic anhydrase inhibitor, was investigated using liver microsomes from Sprague-Dawley rats. The liver microsomes metabolized dorzolamide to an N-deethylated form, whereas N-deethylation of dorzolamide was not detected in 10,000g supernatant from the small intestine, brain, heart, lung, kidney and spleen, or the cytosol fraction of liver. The dorzolamide N-deethylase activity was not detected without an NADPH-generating system and was inhibited by classical inhibitors for cytochrome P450, metyrapone and n-octylamine. Orphenadrine and diphenhydramine (specific inhibitors for CYP2B1/2), diethyldithiocarbamate, disulfiram and isoniazid (inhibitors for CYP2E1), troleandomycin (inhibitor for CYP3A), and testosterone inactivated dorzolamide N-deethylase activity. On the other hand, ajmalicine, a specific inhibitor for CYP2D1, did not inhibit the reaction. With phenobarbital-induced microsomes, 66%, 72%, 36%, and 53% of the 2 beta-, 6 beta-, 16 alpha-, and 16 beta-testosterone hydroxylase activities were inhibited by 5 mM dorzolamide, respectively, whereas the 2 alpha-hydroxylase activity was not inactivated. Antisera against rat CYP2B1, CYP2E1, and CYP3A2 suppressed dorzolamide N-deethylase activity by 52%, 43% and 46%, respectively, whereas only 18% and 15% of the activity were inhibited by anti-CYP1A1 and anti-CYP4A1 antibodies, respectively. Analysis of the N-deethylase reactions using Eadie-Scatchard plots showed high- and low-affinity components in rat liver microsomes. The high-affinity reaction was induced with phenobarbital and dexamethasone, but not with 3-methylcholanthrene. These results suggest that CYP2B, CYP2E1, and CYP3A subfamilies are involved in the dorzolamide N-deethylation in rat liver microsomes.
authors.affiliation: Development Research Laboratories, Banyu Pharmaceutical Co. Ltd, Saitama, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Hasegawa
authors.forename: K
authors.initials: K
authors.lastname: Hara
authors.forename: T
authors.initials: T
authors.lastname: Kenmochi
authors.forename: S
authors.initials: S
authors.lastname: Hata
mesh_terms: D000818:Animals; D002257:Carbonic Anhydrase Inhibitors / Q000378:metabolism*; D003577:Cytochrome P-450 Enzyme System / Q000502:physiology; D003640:Dealkylation; D007527:Isoenzymes / Q000502:physiology; D008297:Male; D008862:Microsomes, Liver / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013449:Sulfonamides / Q000378:metabolism*; D013876:Thiophenes / Q000378:metabolism*
chemical_list: D002257:Carbonic Anhydrase Inhibitors; D007527:Isoenzymes; D013449:Sulfonamides; D013876:Thiophenes; D003577:Cytochrome P-450 Enzyme System; C062765:dorzolamide