Metabolic pathways of 1-butyl [3-13C]acrylate. Identification of urinary metabolites in rat using nuclear magnetic resonance and mass spectroscopy

1-Butylacrylate, an industrial monomer, is rapidly metabolized by carboxylesterase-catalyzed hydrolysis to acrylic acid and 1-butanol. Acrylic acid enters the intermediary metabolism and is efficiently degraded to carbon dioxide as the metabolic end product. To obtain a virtually complete metabolic pattern, rats were dosed by a single intraperitoneal dose of 1 mmol/kg 1-butyl [3-13C]acrylate. The urine was then analyzed by a one-dimensional 1H-detected and two-dimensional 1H-13C shift-correlated heteronuclear multiple-quantum NMR experiment. In this experiment, three urinary metabolites, namely, 3-hydroxypropanoic acid, N-acetyl-S-(2-carboxyethyl)cysteine, and N-acetyl-S-(2-carboxyethyl)cysteine sulfoxide, were identified comparing their 1H and 13C chemical shifts with those of authentic standards. In another experiment, to enhance minor metabolic pathways, rats were dosed with 0.25 mmol/kg of a carboxylesterase inhibitor, tri-o-tolyl phosphate, prior to 0.5 mmol/kg butyl [3-13C]acrylate. Under these conditions, N-acetyl-S-(2-carboxyethyl)cysteine, N-acetyl-S-[2-(butoxycarbonyl)-ethyl]cysteine, and N-acetyl-S-(2-carboxyethyl)cysteine sulfoxide were found in urine. No metabolites which would arise from a possible metabolic activation of 1-butyl acrylate to 1-butyl oxiranecarboxylate and its subsequent hydrolysis or glutathione conjugation were found. It is estimated that any metabolite amounting to more than 1% of the dose should be detected under these conditions. To study the routes by which BA enters the intermediary metabolism, incorporation of the label into urinary carboxylic acids was followed by GC/MS. Significant enrichment was found in 3-hydroxypropanoic acid and citric and isocitric acid but not in lactic acid.