The purpose of this study was to examine the feasibility of using 13C NMR spectroscopy to analyze urinary metabolites produced following coadministration of two structurally similar carbon-13-labeled compounds to rodents. Acrylonitrile (AN) and acrylamide (AM) are used in the chemical industry to manufacture plastics and polymers. These compounds are known to produce carcinogenic, reproductive, or neurotoxic effects in laboratory animals. The potential for human exposure to AN and AM occurs in manufacturing facilities and environmentally. Male F344 rats and B6C3F1 mice were coadministered po [1,2,3-13C]AN (16-17 mg/kg) and [1,2,3-13C]AM (21-22 mg/kg) after 0 or 4 days of administration of unlabeled AN or AM. Urine was collected for 24 h following administration of the 13C-labeled compounds and analyzed by 13C NMR spectroscopy. Rats and mice excreted metabolites derived from glutathione (GSH) conjugation with AM or AN or derived from GSH conjugation with the epoxides cyanoethylene oxide (CEO) or glycidamide (GA). GA and its hydrolysis product were also detected in the urine of rats and mice. For mice, an increased urinary excretion of total AN- and total AM-derived metabolites (p < 0.05) on repeated coadministration suggested a possible increase in metabolism via oxidation. In addition, mice had an increased (p < 0.05) percentage of dose excreted as metabolites derived from GSH conjugation with AM, AN, CEO, or GA after five exposures as compared with one exposure that may be related to a significant increase in the synthesis of GSH or an increase in glutathione transferase activity. The only significant (p < 0.05) increase between one and five exposures for the rat was in the percentage of metabolites produced following conversion of AM to GA. The use of 13C NMR spectroscopy has provided a powerful methodology for elucidation of the metabolism of two 13C-labeled chemicals administered simultaneously.

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1,3-Butadiene (BD) is used in the production of synthetic rubber and other resins. Carcinogenic effects have been observed in laboratory animals exposed to BD, with mice being more sensitive than rats. Metabolic oxidation of butadiene to epoxides is believed to be a crucial step in the initiation of tumors by BD. However, limited information is available that describes the in vivo metabolism of BD. Male Sprague-Dawley rats and B6C3F1 mice were exposed to 800 ppm [1,2 3,4-13C]butadiene for 5 h, and urine was collected during and for 20 h following exposure. Urinary metabolites were characterized using 1- and 2-dimensional methods of NMR spectroscopy. Three metabolites previously detected in vivo, N-acetyl-S-(2-hydroxy-3-butenyl)-L-cysteine, N-acetyl-S-(1-(hydroxymethyl)-2-propenyl)-L-cysteine, and N-acetyl-S-(3,4-dihydroxybutyl)-L-cysteine, were present in both rat and mouse urine, accounting for 87% and 73% of the total metabolites excreted, respectively. A fourth metabolite, previously detected in vitro, 3-butene-1,2-diol, was also present in both rat and mouse urine and comprised 5% and 3% of the total metabolites excreted, respectively. An additional metabolite detected only in mouse urine that is derived from glutathione conjugation with epoxybutene was identified as S-(1-(hydroxymethyl)-2-propenyl)-L-cysteine (4%). N-Acetyl-S-(1-hydroxy-3-butenyl)-L-cysteine (4%), detected in mouse urine, is a thiohemiacetal product of 3-butenal. Additionally, mice excreted N-acetyl-S-(3-hydroxypropyl)-L-cysteine (5%) and N-acetyl-S-(2-carboxyethyl)-L-cysteine (5%), which could be derived from further metabolism of N-acetyl-S-(3,4-dihydroxybutyl)-L-cysteine or from glutathione conjugation with acrolein. Mice excreted N-acetyl-S-(1-(hydroxymethyl)-3,4-dihydroxypropyl)-L-cysteine (5%), which could be derived from glutathione conjugation with diepoxybutane (BDE), while rats excreted 1,3-dihydroxypropanone (5%), which may be derived from hydrolysis of BDE. These studies indicate that reactive aldehydes are produced as metabolites of BD in vivo, in addition to the reactive monoepoxide and diepoxide of BD. The greater toxicity of BD in mice compared with rats may be attributed to the greater ability of rats to detoxify BDE via hydrolysis, and/or to the production of reactive aldehydes.