title: Excretion and identification of methacrylonitrile metabolites in the bile of male F344 rats.
abstract: Methacrylonitrile (MAN) is structurally similar to the known carcinogen acrylonitrile (AN), has similar industrial uses, and is occasionally used as its replacement. In contrast to AN, minimal information is available on the toxicity, carcinogenicity, or metabolism of MAN. Earlier work in this laboratory demonstrated that, in rats, MAN is primarily eliminated in the expired air as unchanged MAN, acetone, and CO2. Two mercapturic acids were identified in the urine of rats and mice treated with MAN. In the present work, the common bile duct of anesthetized rats was cannulated. The animals received a single gavage dose of 58 mg/kg 2-[14C]MAN. Bile was collected before and after MAN administration. Bile flow and MAN-derived radioactivity were determined at each time point. MAN had a minimal effect on bile flow and 4 to 6% of the administered MAN dose was excreted in the bile within 6 hr after dosing. HPLC analysis of bile showed two major metabolites, which were identified as 1-(S-glutathionyl)-2-propanone and 1-(S-glutathionyl)-2-cyanopropane by using NMR spectra and chemical synthesis. The ratio of the two metabolites in MAN-treated rats was approximately 2:1. Pretreatment of rats with sodium phenobarbital caused minimal quantitative or qualitative changes in the biliary excretion of MAN metabolites. In contrast, pretreatment of rats with beta-diethylaminoethyl diphenylpropylacetate before MAN administration resulted in a significant decrease in the ratio of 1-(S-glutathionyl)-2-propanone to 1-(S-glutathionyl)-2-cyanopropane (1:2). These data, especially the identification of 1-(S-glutathionyl)-2-propanone, indirectly demonstrated that MAN is metabolized via an epoxide intermediate (1-cyano-1-methyloxirane). Modulation of MAN metabolism by the P450 modulators suggested that this metabolic pathway is catalyzed via the cytochrome P450 enzymes. This work also confirms that MAN undergoes direct reaction with reduced glutathione via a Michael addition. Because of earlier work demonstrated that AN undergoes similar metabolism, MAN might have a qualitative toxicity profile similar to that of acryonitrile.
authors.affiliation: National Institutes of Health, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709, USA.
authors.forename: B I
authors.initials: BI
authors.lastname: Ghanayem
authors.forename: L T
authors.initials: LT
authors.lastname: Burka
mesh_terms: D000181:Acrylonitrile / Q000378:metabolism; D000818:Animals; D001646:Bile / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008689:Methacrylates / Q000378:metabolism*; D009570:Nitriles / Q000378:metabolism*; D010634:Phenobarbital / Q000494:pharmacology; D011335:Proadifen / Q000494:pharmacology; D051381:Rats; D011916:Rats, Inbred F344; D013997:Time Factors
chemical_list: D008689:Methacrylates; D009570:Nitriles; C008385:methacrylonitrile; D011335:Proadifen; D000181:Acrylonitrile; D010634:Phenobarbital