Human in Vitro Glutathionyl and Protein Adducts of Carbamazepine-10,11-Epoxide, a Stable and Pharmacologically Active Metabolite of Carbamazepine

Abstract

ABSTRACT:The clinical use of carbamazepine (CBZ), an anticonvulsant, is associated with a variety of idiosyncratic adverse reactions that are likely related to the formation of chemically reactive metabolites. CBZ-10,11-epoxide (CBZE), a pharmacologically active metabolite of CBZ, is so stable in vitro and in vivo that the potential for the epoxide to covalently interact with macromolecules has not been fully explored. In this study, two glutathione (GSH) adducts were observed when CBZE was incubated with GSH in the absence of biological matrices and cofactors (e.g., liver microsomes and NADPH). The chemical reactivity of CBZE was further confirmed by the in vitro finding that [ 14 C]CBZE formed covalent protein adducts in human plasma as well as in human liver microsomes (HLMs) without NADPH. The two GSH adducts formed in the chemical reaction of CBZE were identical to the two major GSH adducts observed in the HLM incubation of CBZ, indicating that the 10,11-epoxidation represents a bioactivation pathway of CBZ. The two GSH adducts were isolated and identified as two diastereomers of 10-hydroxy-11-glutathionyl-CBZ by NMR. In addition, the covalent binding of [ 14 C]CBZE was significantly increased in the HLM incubation upon addition of NADPH, indicating that CBZE can be further bioactivated by HLMs. To our knowledge, this is the first time the metabolite CBZE has been confirmed for its ability to form covalent protein adducts and the identity of the two CBZEglutathionyl adducts has been confirmed by NMR. These represent important findings in the bioactivation mechanism of CBZ.

CYP3A4-Mediated Carbamazepine (CBZ) Metabolism: Formation of a Covalent CBZ-CYP3A4 Adduct and Alteration of the Enzyme Kinetic Profile

“…at ASPET Journals on May 10, 2018 dmd.aspetjournals.org methide, and/or epoxide could be viable reactive metabolites that chemically modify P450s (Madden et al, 1996;Pearce et al, 2002Pearce et al, , 2005Bu et al, 2005) (Scheme 1). Furthermore, although the precise site of this binding remains to be identified, conceivably Cys239 could be a plausible target as in raloxifene-mediated CYP3A4 adduction (Baer et al, 2007).…”

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

“…Several reactive metabolites have been proposed as the reactive species responsible for the idiosyncratic toxicity associated with CBZ, including an arene oxide (Spielberg et al, 1981), 9-acridine carboxaldehyde (Furst et al, 1995), CBZ 10,11-epoxide (Bu et al, 2005), an iminoquinone metabolite (CBZ-IQ) derived from 2-hydroxycarbamazepine (2-OHCBZ) (Ju and Utrecht, 1999), and an o-quinone metabolite (CBZ-quinone) (Lillibridge et al, 1996), which is proposed to form via oxidation of the catechol, 2,3-dihydroxy-carbamazepine (2,3-diOHCBZ) (Fig. 1).…”

Correlation study on expression of GST-π protein in brain tissue and peripheral blood of epilepsy rats induced by pilocarpine

“…Thus, when the GST-π expression or activity increases, the drug excretion is accelerated, which gives rise to drug resistance [10] . Carbamazepine epoxide, diene valproic (VPA) and triketone VPA are major metabolites of many anti-epileptic drugs, such as carbamazepine, sodium valproate, are removed from body via the catalysis of GST-π [11] , resulting significant decrease of drug action. The mechanism of increased GST-π expression in brain tissue and serum is unclear and it might be a systematic response induced by epilepsy or anti-epileptic drugs.…”