In Vitro Characterization of the Human Liver Microsomal Kinetics and Reaction Phenotyping of Olanzapine Metabolism.
Olanzapine (OLZ) is an atypical antipsychotic used in the treatment of schizophrenia and related psychoses. The metabolism of OLZ is complex and incompletely characterized. This study aimed to elucidate the enzymes and pathways involved in the metabolism of OLZ and to determine the kinetics of OLZ oxidation and glucuronidation by human liver microsomes, recombinant cytochrome P450 (rP450) enzymes, and recombinant UDP-glucuronosyltransferase (rUGT) enzymes. An ultra-performance liquid chromatography-mass spectrometry method was developed and validated to quantify OLZ, its four oxidative metabolites (N-desmethyl-OLZ, 2-hydroxymethyl-OLZ, 7-hydroxy-OLZ, and OLZ-N-oxide), and two N-glucuronides (OLZ-10-N-glucuronide and OLZ-4'-N-glucuronide). Consistent with previous reports, UGT1A4, CYP1A2, and flavin-containing monooxygenase 3 play major roles in catalyzing the formation of OLZ-10-N-glucuronide, 7-hydroxy-OLZ, and OLZ-N-oxide, respectively. In addition, a previously uncharacterized major contribution of CYP2C8 to OLZ-N-demethylation was demonstrated. The kinetics of OLZ metabolite formation (Km and Vmax) by human liver microsomes, rP450 enzymes, and rUGT enzymes were characterized in the presence of bovine serum albumin [2% (w/v)]. Consistent with the known effect of bovine serum albumin on CYP1A2, CYP2C8, and UGT1A4 activities, Km values reported here are lower than previously reported values for OLZ metabolic pathways. In addition to CYP1A2-mediated OLZ-N-demethylation, these results suggest that other P450 enzymes, particularly CYP2C8, contribute significantly to oxidative OLZ metabolism through catalysis of OLZ-N-demethylation.
Department of Clinical Pharmacology and Flinders Centre for Innovation in Cancer, Flinders University School of Medicine, Adelaide, Australia (P.K., T.M.P., M.J.S., J.O.M., A.R.); Department of Pharmacology, Faculty of Science, Mahidol University, Bangkok, Thailand (P.K.); Faculty of Pharmacy, University of Sydney, Sydney, Australia (A.J.M.); and University of Sheffield (Emeritus), Sheffield, United Kingdom (G.T.T.).
Porntipa
P
Korprasertthaworn
Department of Clinical Pharmacology and Flinders Centre for Innovation in Cancer, Flinders University School of Medicine, Adelaide, Australia (P.K., T.M.P., M.J.S., J.O.M., A.R.); Department of Pharmacology, Faculty of Science, Mahidol University, Bangkok, Thailand (P.K.); Faculty of Pharmacy, University of Sydney, Sydney, Australia (A.J.M.); and University of Sheffield (Emeritus), Sheffield, United Kingdom (G.T.T.).
Thomas M
TM
Polasek
Department of Clinical Pharmacology and Flinders Centre for Innovation in Cancer, Flinders University School of Medicine, Adelaide, Australia (P.K., T.M.P., M.J.S., J.O.M., A.R.); Department of Pharmacology, Faculty of Science, Mahidol University, Bangkok, Thailand (P.K.); Faculty of Pharmacy, University of Sydney, Sydney, Australia (A.J.M.); and University of Sheffield (Emeritus), Sheffield, United Kingdom (G.T.T.).
Michael J
MJ
Sorich
Department of Clinical Pharmacology and Flinders Centre for Innovation in Cancer, Flinders University School of Medicine, Adelaide, Australia (P.K., T.M.P., M.J.S., J.O.M., A.R.); Department of Pharmacology, Faculty of Science, Mahidol University, Bangkok, Thailand (P.K.); Faculty of Pharmacy, University of Sydney, Sydney, Australia (A.J.M.); and University of Sheffield (Emeritus), Sheffield, United Kingdom (G.T.T.).
Andrew J
AJ
McLachlan
Department of Clinical Pharmacology and Flinders Centre for Innovation in Cancer, Flinders University School of Medicine, Adelaide, Australia (P.K., T.M.P., M.J.S., J.O.M., A.R.); Department of Pharmacology, Faculty of Science, Mahidol University, Bangkok, Thailand (P.K.); Faculty of Pharmacy, University of Sydney, Sydney, Australia (A.J.M.); and University of Sheffield (Emeritus), Sheffield, United Kingdom (G.T.T.).
John O
JO
Miners
Department of Clinical Pharmacology and Flinders Centre for Innovation in Cancer, Flinders University School of Medicine, Adelaide, Australia (P.K., T.M.P., M.J.S., J.O.M., A.R.); Department of Pharmacology, Faculty of Science, Mahidol University, Bangkok, Thailand (P.K.); Faculty of Pharmacy, University of Sydney, Sydney, Australia (A.J.M.); and University of Sheffield (Emeritus), Sheffield, United Kingdom (G.T.T.).
Geoffrey T
GT
Tucker
Department of Clinical Pharmacology and Flinders Centre for Innovation in Cancer, Flinders University School of Medicine, Adelaide, Australia (P.K., T.M.P., M.J.S., J.O.M., A.R.); Department of Pharmacology, Faculty of Science, Mahidol University, Bangkok, Thailand (P.K.); Faculty of Pharmacy, University of Sydney, Sydney, Australia (A.J.M.); and University of Sheffield (Emeritus), Sheffield, United Kingdom (G.T.T.) andrew.rowland@flinders.edu.au.
Andrew
A
Rowland
D000818:Animals; D014150:Antipsychotic Agents / Q000493:pharmacokinetics*; D001569:Benzodiazepines / Q000493:pharmacokinetics*; D002417:Cattle; D006801:Humans; D007700:Kinetics; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism*; D000077152:Olanzapine; D010641:Phenotype
D014150:Antipsychotic Agents; D001569:Benzodiazepines; D000077152:Olanzapine