title: Impaired microsomal oxidation of the atypical antipsychotic agent clozapine in hepatic steatosis.
abstract: Hepatic lipid infiltration (steatosis) is a complication of the metabolic syndrome and can progress to nonalcoholic steatohepatitis and severe liver injury. Microsomal cytochrome P450 (P450) drug oxidases are down-regulated in experimental steatosis. In this study we evaluated the separate and combined effects of lipid accumulation and P450 down-regulation on the microsomal oxidation of the antipsychotic agent clozapine (CLZ), the use of which is associated with an increased incidence of the metabolic syndrome. Several important drug oxidizing P450s were down-regulated, and the formation of N-desmethyl-CLZ (norCLZ) and CLZ N-oxide was decreased in microsomal fractions from orotic acid-induced early steatotic rat liver. Inclusion of lipids extracted from steatotic, but not control, liver decreased the free concentration of CLZ in microsomes and suppressed norCLZ formation; CLZ N-oxidation was unchanged. Triglycerides increased in steatotic liver to 15-fold of control, whereas increases in the monounsaturated oleic acid to 10-fold of control and total polyunsaturated and saturated fatty acids to 4- and 5-fold of control also occurred. Addition of triglycerides containing esterified omega-6 and omega-3 fatty acids inhibited the microsomal formation of norCLZ but not that of CLZ N-oxide; triglycerides esterified with unsaturated and monounsaturated fatty acids were inactive. Thus, drug oxidation may be suppressed in steatosis by P450 down-regulation and the accumulation of polyunsaturated fatty esters. In contrast, the activity of the flavin-containing monooxygenase that mediates CLZ N-oxidation was unimpaired. Lipid deposition in livers of patients with the metabolic syndrome may necessitate dosage adjustments for toxic drugs, including CLZ.
authors.affiliation: Pharmacogenomics and Drug Development Group, Faculty of Pharmacy, University of Sydney, New South Wales, Australia.
authors.forename: Wei V
authors.initials: WV
authors.lastname: Zhang
authors.forename: Iqbal
authors.initials: I
authors.lastname: Ramzan
authors.forename: Michael
authors.initials: M
authors.lastname: Murray
mesh_terms: D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000378:metabolism; D003024:Clozapine / Q000031:analogs & derivatives / Q000378:metabolism*; D019388:Cytochrome P-450 CYP1A2 / Q000378:metabolism; D019392:Cytochrome P-450 CYP2E1 / Q000378:metabolism; D051544:Cytochrome P-450 CYP3A / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D000072467:Cytochrome P450 Family 2; D003580:Cytochromes; D005227:Fatty Acids / Q000378:metabolism; D005231:Fatty Acids, Unsaturated / Q000378:metabolism; D005234:Fatty Liver / Q000139:chemically induced / Q000378:metabolism*; D007700:Kinetics; D008055:Lipids / Q000032:analysis / Q000494:pharmacology; D008099:Liver / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism*; D009963:Orotic Acid / Q000494:pharmacology; D010078:Oxazines / Q000378:metabolism; D010084:Oxidation-Reduction / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D039181:Steroid 16-alpha-Hydroxylase / Q000378:metabolism; D014280:Triglycerides / Q000494:pharmacology
chemical_list: D003580:Cytochromes; D005227:Fatty Acids; D005231:Fatty Acids, Unsaturated; D008055:Lipids; D010078:Oxazines; D014280:Triglycerides; C058272:norclozapine; C007649:ethoxyresorufin; D009963:Orotic Acid; D003577:Cytochrome P-450 Enzyme System; D019392:Cytochrome P-450 CYP2E1; D001189:Aryl Hydrocarbon Hydroxylases; C450279:CYP2C11 protein, rat; C017170:Cyp1a2 protein, rat; D019388:Cytochrome P-450 CYP1A2; D051544:Cytochrome P-450 CYP3A; D000072467:Cytochrome P450 Family 2; D039181:Steroid 16-alpha-Hydroxylase; D003024:Clozapine; C079149:clozapine N-oxide