Evidence for the bioactivation of zomepirac and tolmetin by an oxidative pathway: identification of glutathione adducts in vitro in human liver microsomes and in vivo in rats.
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Chen Q, Doss GA, Tung EC, Liu W, Tang YS, Braun MP, Didolkar V, Strauss JR, Wang RW, Stearns RA, Evans DC, Baillie TA, Tang W
Evidence for the bioactivation of zomepirac and tolmetin by an oxidative pathway: identification of glutathione adducts in vitro in human liver microsomes and in vivo in rats.
Drug Metab Dispos. 2006 Jan;34(1):145-51. doi: 10.1124/dmd.105.004341. Epub 2005 Oct 26.
- PubMed ID
- 16251255 [ View in PubMed]
- Abstract
Although zomepirac (ZP) and tolmetin (TM) induce anaphylactic reactions and form reactive acyl glucuronides, a direct link between the two events remains obscure. We report herein that, in addition to acyl glucuronidation, both drugs are subject to oxidative bioactivation. Following incubations of ZP with human liver microsomes fortified with NADPH and glutathione (GSH), a metabolite with an MH+ ion at m/z 597 was detected by LC/MS/MS. On the basis of collision-induced dissociation and NMR evidence, the structure of this metabolite was determined to be 5-[4'-chlorobenzoyl]-1,4-dimethyl-3-glutathionylpyrrole-2-acetic acid (ZP-SG), suggesting that the pyrrole moiety of ZP had undergone oxidation to an epoxide intermediate, followed by addition of GSH and loss of the elements of H2O to yield the observed conjugate. The oxidative bioactivation of ZP most likely is catalyzed by cytochrome P450 (P450) 3A4, since the formation of ZP-SG was reduced to approximately 10% of control values following pretreatment of human liver microsomes with ketoconazole or with an inhibitory anti-P450 3A4 IgG. A similar GSH adduct, namely 5-[4'-methylbenzoyl]-1-methyl-3-glutathionylpyrrole-2-acetic acid (TM-SG), was identified when TM was incubated with human liver microsomal preparations. The relevance of these in vitro findings to the in vivo situation was established through the detection of the same thiol adducts in rats treated with ZP and TM, respectively. Taken together, these data suggest that, in addition to the formation of acyl glucuronides, oxidative metabolism of ZP and TM affords reactive species that may haptenize proteins and thereby contribute to the drug-mediated anaphylactic reactions.
DrugBank Data that Cites this Article
- Drug Enzymes
Drug Enzyme Kind Organism Pharmacological Action Actions Zomepirac Cytochrome P450 3A4 Protein Humans UnknownSubstrateDetails