title: In vitro studies on the chemical reactivity of 2,4-dichlorophenoxyacetyl-S-acyl-CoA thioester.
abstract: 2,4-Dichlorophenoxyacetic acid (2,4-D) is a widely used broadleaf herbicide that has been associated with acute liver toxicity in exposed humans or animals. Chemically reactive metabolites of 2,4-D are proposed as mediators of 2,4-D-induced hepatotoxicity. The aim of the present study was to investigate a novel reactive metabolite of 2,4-D, namely 2,4-dichlorophenoxyacetyl-S-acyl-CoA (2,4-D-CoA), and to determine its involvement in 2,4-D covalent adduct formation. Thus, incubations of synthetic 2,4-D-CoA (106 microM) with GSH (1 mM) in phosphate buffer (pH 7.4) showed 2,4-D-CoA to be able to transacylate the cysteine sulfhydryl of GSH, resulting in the formation of 2,4-D-S-acyl-glutathione (2,4-D-SG) thioester and reaching a concentration of 65 microM after 1 h of incubation. Under similar conditions, 2,4-D-CoA was shown to covalently bind to nucleophilic groups on human serum albumin (HSA, 30 mg/ml), resulting in time-dependent 2,4-D-HSA covalent adduct formation that reached a maximum of 440 pmol/mg HSA after 1 h of incubation. In addition to these studies, incubations of [1-(14)C]2,4-D (1 mM) with rat hepatocytes showed a time-dependent covalent binding of 2,4-D to hepatocyte protein. Inhibition of acyl-CoA formation by trimethylacetic acid (2 mM) decreased the amount of covalent binding to protein in rat hepatocytes by 50%. These results indicate that 2,4-D-CoA thioester is a reactive metabolite of 2,4-D that may contribute to 2,4-D-protein adduct formation in vivo and therefore the associated hepatotoxicity.
authors.affiliation: Department of Biopharmaceutical Sciences, University of California, San Francisco, CA 94143-0446, USA.
authors.forename: Chunze
authors.initials: C
authors.lastname: Li
authors.forename: Mark P
authors.initials: MP
authors.lastname: Grillo
authors.forename: Leslie Z
authors.initials: LZ
authors.lastname: Benet
mesh_terms: D015084:2,4-Dichlorophenoxyacetic Acid / Q000737:chemistry / Q000378:metabolism* / Q000633:toxicity; D000214:Acyl Coenzyme A / Q000037:antagonists & inhibitors / Q000378:metabolism; D000818:Animals; D002087:Butyrates / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid; D005978:Glutathione / Q000737:chemistry / Q000378:metabolism; D022781:Hepatocytes / Q000378:metabolism; D006540:Herbicides / Q000737:chemistry / Q000378:metabolism* / Q000633:toxicity; D006801:Humans; D008297:Male; D010642:Phenoxyacetates / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D012709:Serum Albumin / Q000737:chemistry / Q000378:metabolism
chemical_list: C473625:2,4-dichlorophenoxyacetyl-S-acyl-CoA thioester; D000214:Acyl Coenzyme A; D002087:Butyrates; D006540:Herbicides; D010642:Phenoxyacetates; D012709:Serum Albumin; D015084:2,4-Dichlorophenoxyacetic Acid; D005978:Glutathione