Metabolism of acrylonitrile to 2-cyanoethylene oxide in F-344 rat liver microsomes, lung microsomes, and lung cells.

The metabolism of acrylonitrile to the epoxide, 2-cyanoethylene oxide (ANO) was examined in rat liver microsomes, lung microsomes, and isolated enriched lung cell preparations. GC/high resolution MS was used to quantitate ANO in microsomal and cellular extracts by monitoring the fragment ion C2H3N (m/z 41.0265). The limit of detection was 0.05 pmol of ANO/0.5 microliter of standard solution, microsomal extract, or cellular extract injected onto the column, and the linear range of analysis was 0.05 to 12.5 pmol of ANO. Kinetic parameters of Vmax, V/K, and Km were calculated for microsomal ANO formation. Liver microsomes were quantitatively more active than lung microsomes on a mg of protein basis. The Vmax (pmol of ANO formed/min/mg of protein) was 666.61 for liver and 45.07 for lung microsomes. The V/K (pmol of ANO/min/mg of protein/microM) was 12.83 for liver and 0.02 for lung microsomes. The apparent Km was 51.93 microM and 1853.83 microM for liver and lung microsomes, respectively. When calculated as nmol of ANO formed/min/nmol of microsomal P-450, the Vmax for lung was equivalent to the Vmax for liver. ANO formation in the rat lung was cell specific. The rates of metabolism in the Clara cell-enriched fraction, the alveolar type II cell-enriched fraction, and the cell suspension were 2.55, 0.38, and 0.67 pmol of ANO formed/min/mg of protein, respectively. No metabolism was observed in the endothelial (small) cell-enriched fraction or in the alveolar macrophages. The results suggest that the lung contributes to the metabolism and disposition of inhaled acrylonitrile.