title: Conclusive identification of the oxybutynin-hydrolyzing enzyme in human liver.
abstract: The aim of this study was to conclusively determine the enzyme responsible for the hydrolysis of oxybutynin in human liver. Hydrolysis in human liver microsomes (HLMs) and human liver cytosol (HLC) followed Michaelis-Menten kinetics with similar K(m) values. In recombinant human carboxylesterase (CES)-expressing microsomes, CES1 was much more efficient than CES2 and yielded a K(m) value more comparable with that found in HLMs or HLC than did CES2. A correlation analysis using a set of individual HLMs, in which both CESs acted independently showed that the hydrolysis rate of oxybutynin, correlated significantly with a CES1 marker reaction, clopidogrel hydrolysis, but not with a CES2 marker reaction, irinotecan (CPT-11) hydrolysis. Chemical inhibition studies using bis-(p-nitrophenyl) phosphate, clopidogrel, nordihydroguaiaretic acid, procainamide, physostigmine, and loperamide revealed that the effects of these compounds in HLMs, HLC, and recombinant CES1-expressing microsomes were similar, whereas those in CES2-expressing microsomes were clearly different. These results strongly suggest that CES1, rather than CES2, is the principal enzyme responsible for the hydrolysis of oxybutynin in human liver.
authors.affiliation: Drug Metabolism Research Laboratories, Drug Discovery Research, Astellas Pharma Inc., 2-1-6 Kashima, Yodogawa-ku, Osaka 532-8514, Japan. yuichiro.sato@astellas.com
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Sato
authors.forename: Aiji
authors.initials: A
authors.lastname: Miyashita
authors.forename: Takafumi
authors.initials: T
authors.lastname: Iwatsubo
authors.forename: Takashi
authors.initials: T
authors.lastname: Usui
mesh_terms: D001711:Biotransformation; D043182:Carboxylesterase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D002265:Carboxylic Ester Hydrolases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D003600:Cytosol / Q000201:enzymology / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D006868:Hydrolysis; D066298:In Vitro Techniques; D008099:Liver / Q000201:enzymology* / Q000378:metabolism; D008333:Mandelic Acids / Q000737:chemistry / Q000493:pharmacokinetics*; D008862:Microsomes, Liver / Q000201:enzymology / Q000378:metabolism; D015394:Molecular Structure; D018727:Muscarinic Antagonists / Q000737:chemistry / Q000493:pharmacokinetics*; D053719:Tandem Mass Spectrometry
chemical_list: D004791:Enzyme Inhibitors; D008333:Mandelic Acids; D018727:Muscarinic Antagonists; D002265:Carboxylic Ester Hydrolases; C474609:CES1 protein, human; C517204:CES2 protein, human; D043182:Carboxylesterase; C005419:oxybutynin