Characterization of Urinary Metabolites from Sprague-Dawley Rats and B6C3F1 Mice Exposed to [1,2,3,4-¹³C]Butadiene

Abstract

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.

Structure of the 1,4-Bis(2‘-deoxyadenosin-N6-yl)-2S,3S-butanediol Intrastrand DNA Cross-Link Arising from Butadiene Diepoxide in the Human N-ras Codon 61 Sequence

“…These may be further oxidized by cytochrome P450 2E1 or 3A4 to form 1,2:3,4-diepoxybutanes (BDO 2 ) (25,(27)(28)(29)(30)(31). Hydrolysis of BDO mediated by epoxide hydrolase forms 1,2-dihydroxy-3-butenes (29,32,33), which are metabolized by cytochrome P450 to hydroxymethylvinylketone (HMVK) (34). Either BDO 2 or the 1,2-dihydroxy-3-butenes may undergo cytochrome P450-mediated oxidation to form 1,2-dihydroxy-3,4-epoxybutanes (BDE) (29,32,35).…”

Inhibitory potency of 4-carbon alkanes and alkenes toward CYP2E1 activity

“…3,4-Epoxy-1-butene displays a moderate affinity toward CYP2E1 and the binding of secondary metabolites to CYP2E1 seems negligible. 1,2-Butenediol may undergo subsequent oxidation to hydroxymethylvinylketone due to CYP2E1 activity (Krause et al 2001) or become conjugated to glutathione and excreted in the urine (Bechtold et al 1994;Nauhaus et al 1996;Sabourin et al 1992). The reported K m for the 1,2-butenediol reaction (∼ 1 mM) using commercially available HLMs pool is strikingly similar to the K i for 1,2-butenediol toward the CYP2E1 marker reaction (3.8 mM, Table 4), even though different reaction conditions were used in the respective studies with three different HLMs (Krause et al 2001).…”

Major Groove Orientation of the (2S)-N6-(2-Hydroxy-3-buten-1-yl)-2′-deoxyadenosine DNA Adduct Induced by 1,2-Epoxy-3-butene

“… 50 Thus, proximate electrophiles arising from BD metabolism include not only EB, and also DEB, and 1,2-dihydroxy-3,4-epoxybutane (EBD). 55 − 57 Additionally, EBD is metabolized by cytochrome P450 to hydroxymethylvinylketones (HMVK). 58 , 59 …”