In Vivo Mechanistic Studies on the Metabolic Activation of 2-Phenylpropionic Acid in Rat
- Leslie Z. Benet, Department of Biopharmaceutical Sciences, 513 Parnassus Ave, S-926, University of California, San Francisco, California 94143-0446. E-mail:benet{at}itsa.ucsf.edu
Abstract
Two alternative metabolic pathways, acyl glucuronidation and acyl-CoA formation, are implicated in the generation of reactive acylating metabolites of carboxylic acids. Here, we describe studies that determine the relative importance of these two pathways in the metabolic activation of a model substrate, 2-phenylpropionic acid (2-PPA), in vivo in rats. Male Sprague-Dawley rats were pretreated with and without (−)-borneol (320 mg/kg i.p.), an inhibitor of acyl glucuronidation, or trimethylacetic acid (TMA, 500 mg/kg i.p.), an inhibitor of acyl-CoA formation, before receiving 2-PPA (racemic, 130 mg/kg). After administration of 2-PPA, livers were collected over a 2-h period and analyzed for 2-PPA acyl glucuronidation and 2-PPA-CoA formation by high-performance liquid chromatography. Covalent binding was measured by scintillation counting of washed liver protein precipitates. Results showed that pretreatment with TMA led to a 49% decrease in covalent binding of 2-PPA to liver proteins, when a 64% decrease in the exposure of 2-PPA-CoA was observed. Conversely, 95% inhibition of acyl glucuronidation by (−)-borneol, led to a 23% decrease in covalent binding to protein. These results suggest that metabolic activation by 2-PPA-CoA formation contributes to covalent adduct formation to protein in vivo to a greater extent than metabolic activation by acyl glucuronidation for this model substrate.
Footnotes
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↵1 Present address: Pharmacia Corporation, Global Drug Metabolism, Kalamazoo, MI 49007-4940.
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This work was supported in part by National Institute of Health Grant GM-36633. A preliminary account of this work was presented at the XIVth World Congress of Pharmacology (International Union of Pharmacology), July 2002 (San Francisco, CA).
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DOI: 10.1124/jpet.102.043174
- Abbreviations:
- GSH
- glutathione
- 2-PPA
- 2-phenylpropionic acid
- 2-PPA-1-O-G
- 2-PPA-1-O-acyl glucuronides
- 2-PPA-CoA
- 2-PPA-S-acyl CoA
- TMA
- trimethylacetic acid
- TMA-CoA
- TMA-S-acyl-CoA thioester
- HPLC
- high-performance liquid chromatography
- ACN
- acetonitrile
- CNS
- central nervous system
- AUC
- area under the curve
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- Received August 15, 2002.
- Accepted December 19, 2002.
- The American Society for Pharmacology and Experimental Therapeutics
