Pathways of Carbamazepine Bioactivation in Vitro. III. The Role of Human Cytochrome P450 Enzymes in the Formation of 2,3-Dihydroxycarbamazepine

• Published in: Drug metabolism and disposition Vol. 36; no. 8; pp. 1637 - 1649
• Main Authors: PEARCE, Robin E, WEI LU, YONGQIANG WANG, UETRECHT, Jack P, CORREIA, Maria Almira, LEEDER, J. Steven
• Format: Journal Article
• Language: English
• Published: Bethesda, MD American Society for Pharmacology and Experimental Therapeutics 01.08.2008
• Subjects: Animals; Anticonvulsants - pharmacokinetics; Biological and medical sciences; Biotransformation; Carbamazepine - analogs & derivatives; Carbamazepine - metabolism; Carbamazepine - pharmacokinetics; Chromatography, High Pressure Liquid; Cytochrome P-450 Enzyme System - metabolism; Humans; Mass Spectrometry; Medical sciences; Mice; Microsomes, Liver - enzymology; Pharmacology. Drug treatments; Human; Enzyme; Mood stabilizer; Cytochrome P450; Metabolic activation; Anticonvulsant; Tricyclic compound; Metabolism; Pharmacokinetics; In vitro; Dibenzazepine derivatives; Carbamazepine
• ISSN: 0090-9556; 1521-009X
• DOI: 10.1124/dmd.107.019562

Conversion of the carbamazepine metabolite 3-hydroxycarbamazepine (3-OHCBZ) to the catechol 2,3-dihydroxycarbamazepine (2,3-diOHCBZ) followed by subsequent oxidation to a reactive o -quinone species has been proposed as a possible bioactivation pathway in the pathogenesis of carbamazepine-induced hypersensitivity. Initial in vitro phenotyping studies implicated CYP3A4 as a primary catalyst of 2,3-diOHCBZ formation: 2-hydroxylation of 3-OHCBZ correlated significantly ( r 2 ≥ 0.929, P < 0.001) with CYP3A4/5 activities in a panel of human liver microsomes ( n = 14) and was markedly impaired by CYP3A inhibitors (>80%) but not by inhibitors of other cytochrome P450 enzymes (≤20%). However, in the presence of troleandomycin, the rate of 2,3-diOHCBZ formation correlated significantly with CYP2C19 activity ( r 2 = 0.893, P < 0.001) in the panel of human liver microsomes. Studies with a panel of cDNA-expressed enzymes revealed that CYP2C19 and CYP3A4 were high ( S 50 = 30 μM) and low ( S 50 = 203 μM) affinity enzymes, respectively, for 2,3-diOHCBZ formation and suggested that CYP3A4, but not CYP2C19, might be inactivated by a metabolite formed from 3-OHCBZ. Subsequent experiments demonstrated that preincubation of 3-OHCBZ with human liver microsomes or recombinant CYP3A4 led to decreased CYP3A4 activity, which was both preincubation time- and concentration-dependent, but not inhibited by inclusion of glutathione or N -acetylcysteine. CYP3A4, CYP3A5, CYP3A7, CYP2C19, and CYP1A2 converted [ 14 C]3-OHCBZ into protein-reactive metabolites, but CYP3A4 was the most catalytically active enzyme. The results of this study suggest that CYP3A4-dependent secondary oxidation of 3-OHCBZ represents a potential carbamazepine bioactivation pathway via formation of reactive metabolites capable of inactivating CYP3A4, potentially generating a neoantigen that may play a role in the etiology of carbamazepine-induced idiosyncratic toxicity.