Comparative Toxicities of Aliphatic Nitriles

Aliphatic nitriles have been postulated to manifest their toxicity through cyanide liberation. We have investigated the signs of toxicity and effect of equitoxic LD50 doses of saturated and unsaturated aliphatic mono- and dinitriles on tissue and blood cyanide levels, tissue glutathione levels and cytochrome c oxidase activities. Signs of toxicity were classified into cholinomimetic effects observed with unsaturated nitriles and central nervous system effects observed with saturated nitriles and potassium cyanide (KCN). Hepatic and blood cyanide levels 1 h after treatment were highest following malononitrile (MCN) and decreased in the order of propionitrile (PCN) greater than KCN greater than butyronitrile greater than acrylonitrile (VCN) greater than allylcyanide greater than greater than fumaronitrile greater than acetonitrile. The order differed in brain where KCN preceded MCN and PCN. Hepatic and brain cytochrome c oxidase were significantly inhibited and corresponded to their cyanide levels. No significant inhibition of cytochrome c oxidase was observed in vitro. VCN was the only nitrile which significantly reduced tissue GSH levels. In conclusion, toxic expression of aliphatic nitriles depends not only upon cyanide release but also on their degree of unsaturation. With unsaturated aliphatic nitriles cyanide release plays a minimal role in their toxicity.