Protection of rats against 3-butene-1,2-diol-induced hepatotoxicity and hypoglycemia by N-acetyl-l-cysteine.

3-Butene-1,2-diol (BDD), an allylic alcohol and major metabolite of 1,3-butadiene, has previously been shown to cause hepatotoxicity and hypoglycemia in male Sprague-Dawley rats, but the mechanisms of toxicity were unclear. In this study, rats were administered BDD (250 mg/kg) or saline, ip, and serum insulin levels, hepatic lactate levels, and hepatic cellular and mitochondrial GSH, GSSG, ATP, and ADP levels were measured 1 or 4 h after treatment. The results show that serum insulin levels were not causing the hypoglycemia and that the hypoglycemia was not caused by an enhancement of the metabolism of pyruvate to lactate because hepatic lactate levels were either similar (1 h) or lower (4 h) than controls. However, both hepatic cellular and mitochondrial GSH and GSSG levels were severely depleted 1 and 4 h after treatment and the mitochondrial ATP/ADP ratio was also lowered 4 h after treatment relative to controls. Because these results suggested a role for hepatic cellular and mitochondrial GSH in BDD toxicity, additional rats were administered N-acetyl-l-cysteine (NAC; 200 mg/kg) 15 min after BDD administration. NAC treatment partially prevented depletion of hepatic cellular and mitochondrial GSH and preserved the mitochondrial ATP/ADP ratio. NAC also prevented the severe depletion of serum glucose concentration and the elevation of serum alanine aminotransferase activity after BDD treatment without affecting the plasma concentration of BDD. Thus, depletion of hepatic cellular and mitochondrial GSH followed by the decrease in the mitochondrial ATP/ADP ratio was likely contributing to the mechanisms of hepatotoxicity and hypoglycemia in the rat.

Mercapturic acid urinary metabolites of 3-butene-1,2-diol as in vivo evidence for the formation of hydroxymethylvinyl ketone in mice and rats.

3-Butene-1,2-diol (BDD), a major metabolite of 1,3-butadiene (BD), can readily be oxidized to hydroxymethylvinyl ketone (HMVK), a Michael acceptor. In previous studies, 4-(N-acetyl-l-cystein-S-yl)-1,2-dihydroxybutane (DHB), a urinary metabolite of BD that was used to assess human BD exposure, was suggested to be a metabolite of HMVK, but DHB formation from BDD and the formation of the DHB precursor 4-(N-acetyl-l-cystein-S-yl)-1-hydroxy-2-butanone (HB) have not been previously investigated. In the current study, four HMVK-derived mercapturic acids [DHB, HB, 3-(N-acetyl-l-cystein-S-yl)propan-1-ol (POH), and 3-(N-acetyl-l-cystein-S-yl)propanoic acid (PA)] were identified in the urine of mice and rats given BDD (284-2272 micromol/kg, i.p.) based on GC/MS analyses and comparisons with synthetic standards after esterification and silylation of the carboxyl and hydroxyl groups, respectively. The combined amounts of the mercapturic acids excreted after BDD exposure were dose-dependent and were mostly similar between mice and rats given equivalent doses of BDD. The mercapturic acids accounted for a greater fraction of the administered BDD dose as the dose was lowered, suggesting that HMVK formation represents a prominent route for BDD metabolism in both mice and rats. The major mercapturic acid excreted by mice was DHB, whereas rats excreted equivalent amounts of DHB and HB. The levels of POH or PA were significantly lower in both species relative to DHB or HB. The observed species differences in the excretion of DHB and HB were thought to be due to differences in the capacity of mice and rats to reduce HB to DHB.

Species and tissue differences in the toxicity of 3-butene-1,2-diol in male Sprague-Dawley rats and B6C3F1 mice.

3-Butene-1,2-diol (BDD) is a major metabolite of 1,3-butadiene (BD), but the role of BDD in BD toxicity and carcinogenicity remains unclear. In this study, the acute toxicity of BDD was investigated in male Sprague-Dawley rats and B6C3F1 mice. Of the rats given 250 mg/kg BDD, 2 out of 4 died within 24 h; rats experienced hypoglycemia, significant alterations of liver integrity tests, and had lesions in the liver 4 h after treatment, but no lesions were detected in extrahepatic tissues. Rat hepatic GSH and GSSG levels were significantly depleted at both 1 and 4 h after the BDD treatment. Rats administered 200 mg/kg BDD also had liver lesions but no death or hypoglycemia was observed four or 24 h after treatment; these rats had depleted hepatic GSH and GSSG levels at 1 h but not at 4 or 24 h after treatment. Mice administered 250 mg/kg BDD exhibited modest alterations of liver integrity tests, but no death, hypoglycemia, or lesions in any tissue, and hepatic GSH and GSSG levels were depleted at 1 h but not at 4 h. The plasma half-life of BDD was four times longer in rats than in mice. Additional studies in rats showed the depletion of hepatic GSH and GSSG preceded the BDD-induced hypoglycemia and hepatotoxicity. Thus, the long half-life of BDD in rat plasma and the sustained depletion of hepatic GSH and GSSG may in part explain the higher sensitivity of the rat to BDD-induced hepatotoxicity. Furthermore, the results indicate that BDD may play a role in BD-induced toxicity.

Detection of carboxylic acids and inhibition of hippuric acid formation in rats treated with 3-butene-1,2-diol, a major metabolite of 1,3-butadiene.

Epidemiological studies have indicated that 1,3-butadiene exposure is associated with an increased risk of leukemia. In human liver microsomes, 1,3-butadiene is rapidly oxidized to butadiene monoxide, which can then be hydrolyzed to 3-butene-1,2-diol (BDD). In this study, BDD and several potential metabolites were characterized in the urine of male B6C3F1 mice and Sprague-Dawley rats after BDD administration (i.p.). Rats given 1420 micromol kg(-1) BDD excreted significantly greater amounts of BDD relative to rats administered 710 micromol kg(-1) BDD. Rats administered 1420 or 2840 micromol kg(-1) BDD excreted significantly greater amounts of BDD per kilogram of body weight than mice given an equivalent dose. Trace amounts of 1-hydroxy-2-butanone and the carboxylic acid metabolites, crotonic acid, propionic acid, and 2-ketobutyric acid, were detected in mouse and rat urine after BDD administration. Because of the identification of the carboxylic acid metabolites and because of the known ability of carboxylic acids to conjugate coenzyme A, which is critical for hippuric acid formation, the effect of BDD treatment on hippuric acid concentrations was investigated. Rats given 1420 or 2272 micromol kg(-1) BDD had significantly elevated ratios of benzoic acid to hippuric acid in the urine after treatment compared with control urine. However, this effect was not observed in mice administered 1420 or 2840 micromol kg(-1) BDD. Collectively, the results demonstrate species differences in the urinary excretion of BDD and show that BDD administration in rats inhibits hippuric acid formation. The detection of 1-hydroxy-2-butanone and the carboxylic acids also provides insight regarding pathways of BDD metabolism in vivo.