In vitro studies on the chemical reactivity of 2,4-dichlorophenoxyacetyl- S-acyl-CoA thioester

• Published in: Toxicology and applied pharmacology 2003-03, Vol.187 (2), p.101-109
• Main Authors: Li, Chunze, Grillo, Mark P, Benet, Leslie Z
• Format: Article
• Language: English
• Subjects: 2,4-D; 2,4-Dichlorophenoxyacetic acid; 2,4-Dichlorophenoxyacetic Acid - chemistry; 2,4-Dichlorophenoxyacetic Acid - metabolism; 2,4-Dichlorophenoxyacetic Acid - toxicity; Acyl Coenzyme A - antagonists & inhibitors; Acyl Coenzyme A - metabolism; Acyl-CoA; Animals; Biological and medical sciences; Butyrates - pharmacology; Chromatography, High Pressure Liquid; Covalent binding; Glutathione - chemistry; Glutathione - metabolism; Hepatocytes - metabolism; Herbicides - chemistry; Herbicides - metabolism; Herbicides - toxicity; Humans; Male; Medical sciences; Pesticides, fertilizers and other agrochemicals toxicology; Phenoxyacetates - chemistry; Phenoxyacetates - metabolism; Protein Binding - drug effects; Rats; Rats, Sprague-Dawley; Reactive metabolite; Serum Albumin - chemistry; Serum Albumin - metabolism; Toxicology
• ISSN: 0041-008X; 1096-0333
• DOI: 10.1016/S0041-008X(02)00043-1

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 μM) 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 μM 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- 14C]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.