Several of the pathways of metabolism of the suspected carcinogen acrylonitrile (AN) were identified previously in this laboratory with the use of subcellular fractions and purified enzymes (Guengerich, F. P., Geiger, L. E., Hogy, L. L., and Wright, P. L., Cancer Res., 41: 4925–4933, 1981). In order to establish the relative contributions of the various pathways leading to activated and detoxicated products, we examined AN metabolism in isolated Fischer 344 rat hepatocytes as a model. Reduced glutathione (GSH) was depleted, and cell viability was lost in an AN concentration-dependent manner. The major GSH adduct formed at all AN concentrations was identified as S-(2-cyanoethyl)GSH using thin-layer and high-performance liquid chromatography. Acid hydrolysis and amino acid analysis of labeled hepatocellular protein revealed S-(2-carboxyethyl)-cysteine as the major adduct formed, indicating direct alkylation of cysteinyl residues by AN. 2-Cyanoethylene oxide accumulated in the hepatocyte incubations but did not appear to contribute extensively to alkylation of GSH or protein. Cyanide, resulting from hydrolysis of 2-cyanoethylene oxide, appeared to be completely converted to thiocyanate, which was identified by gel exclusion chromatography and mass spectrometry of the methyl derivative. The concentration of thiocyanate formed was directly proportional to the concentration of AN used. Cyanide does not appear to play a role in AN-mediated cell death. Alkylation of hepatocellular DNA and RNA and extracellular DNA was not observed to an extent greater than one base in 3.5 × 105. The relative rates of the various pathways were compared, and more than 97% of the metabolites can be accounted for by the described reactions. These results are of use in evaluating the contribution of the various pathways and modes of binding of AN to toxicity and carcinogenicity in liver and extrahepatic target tissues.
This work was supported in part by USPHS Grants ES 02205 and ES 00267.