Abstract
Carboxylic acids may be metabolized to acyl glucuronides and acyl-coenzyme A thioesters (acyl-CoAs), which are reactive metabolites capable of reacting with proteins in vivo. In this study, the metabolic activation of tolmetin (Tol) to reactive metabolites and the subsequent formation of Tol-protein adducts in the liver were studied in rats. Two hours after dose administration (100 mg/kg i.p.), tolmetin acyl-CoA (Tol-CoA) was identified by liquid chromatography-tandem mass spectrometry in liver homogenates. Similarly, the acyl-CoA-dependent metabolites tolmetin-taurine conjugate (Tol-Tau) and tolmetin-acyl carnitine ester (Tol-Car) were identified in rat livers. In a rat bile study (100 mg/kg i.p.), the S-acyl glutathione thioester conjugate was identified, providing further evidence of the formation of reactive metabolites such as Tol-CoA or Tol-acyl glucuronide (Tol-O-G), capable of acylating nucleophilic functional groups. Three rats were treated with clofibric acid (150 mg/kg/day i.p. for 7 days) before dose administration of Tol. This resulted in an increase in covalent binding to liver proteins from 0.9 nmol/g liver in control rats to 4.2 nmol/g liver in clofibric acid-treated rats. Similarly, levels of Tol-CoA increased from 0.6 nmol/g to 4.4 nmol/g liver after pretreatment with clofibric acid, whereas the formation of Tol-O-G and Tol-Tau was unaffected by clofibric acid treatment. However, Tol-Car levels increased from 0.08 to 0.64 nmol/g after clofibric acid treatment. Collectively, these results confirm that Tol-CoA is formed in vivo in the rat and that this metabolite can have important consequences in terms of covalent binding to liver proteins.
Footnotes
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This work was supported in part by National Institutes of Health Grant GM 36633, The Lundbeck Foundation, and grants from The Danish Technical Research Council (56-01-0014) and The Danish Medical Research Council (22-02-340).
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Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
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doi:10.1124/dmd.106.013334.
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ABBREVIATIONS: Tol, tolmetin; Tol-O-G, tolmetin acyl glucuronide; Tol-CoA, tolmetin acyl CoA thioester; Tol-Gly, tolmetin-glycine conjugate; Tol-Tau, tolmetin-taurine conjugate; ESI, electrospray ionization; Tol-Car, tolmetin acyl carnitine ester; Tol-SG, tolmetin acyl-S-glutathione conjugate; Tol-OH, tolmetin hydroxy metabolite; Tol-COOH, tolmetin carboxyl metabolite; HPLC, high-performance liquid chromatography; LC, liquid chromatography; MS, mass spectrometry; MS/MS, tandem mass spectrometry.
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↵1 Current affiliation: Department of Drug Metabolism, Merck Research Labs, West Point, Pennsylvania.
- Received October 28, 2006.
- Accepted February 12, 2007.
- The American Society for Pharmacology and Experimental Therapeutics
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