New findings on acrylonitrile metabolism

The mechanism of the metabolic pathway of acrylonitrile to cyanide (and subsequently to thiocyanate which is excreted in the urine) was already previously confirmed by our work in vitro as well as in vivo. This metabolic route of AN via glycidonitrile and glycolaldehyde cyanohydrin is not the dominant pathway in the total balance of AN metabolism and does not elucidate the fate of the predominant amount of AN. By means of AN labelled with 14C on the nitrile group it was confirmed that, when different routes of administration are used, AN forms in the rat the main portion of radioactivity excreted in the urine in "non-thiocyanate" metabolites. Based on reflection on the reactivity of AN the assumption was expressed that possible metabolites of AN may be S-(2-cyanoethyl)cysteine (CEC) or N-acetyl-S-(2-cyanoethyl)cysteine (AcCEC), so called AN-mercapturic acid. Both these substances were synthetized in our laboratory and used as standards on paper chromatography of urine of animals exposed to AN. Evidence was provided that the main metabolite of AN in rats and rabbits is AcCEC. In the urine of rats 8 hours following administration of AN-14CN in addition to AcCEC another metabolite appears the structure of which was not elucidated so far. By means of preparative paper chromatography of the methylene chloride extract of rabbit urine obtained after subcutaneous injection of AN it proved possible to isolate AcCEC in the form of its dicyclohexyammonium salt. This salt did not produce a depression of the melting point with the synthetically prepared standard. This proved unequivocally the identity of the two substances.