THE METABOLISM OF ACETONITRILE TO CYANIDE BY ISOLATED RAT HEPATOCYTES

The metabolism of saturated nitrites, including acetonitrite, has been assumed to occur by a cytochrome P-450-dependent oxidation at the .alpha.-carbon, yielding a cyanohydrin intermediate which may spontaneously degrade to hydrogen cyanide and an aldehyde. However, results of studies in our laboratory suggest that formaldehyde is not a metabolite of acetonitrile. Since acetonitrile is structurally similar to iodomethane, a substrate for glutathione (GSH) S-transferases, we hypothesized that the metabolism of acetonitrile to cyanide might also occur by a nucleophilic substitution reaction involving GSH. The present studies were conducted to investigate these hypotheses and to further our study of the effects of acetone on acetonitrile metabolism. Female Sprague-Dawley rats were pretreated with buthionine sulfoximine BSO (4 mmol/kg ip, at -4 and -2 hr), cobalt heme (90 .mu.mol/kg sc, at -48 hr), acetone (1960 mg/kg po, at -24 hr), or vehicle, and hepatocytes were isolated after collagenase perfusion of the liver. BSO reduced the cellular GSH content by > 80%, but did not appear to affect the metabolism of acetonitrile: the liberation of cyanide correlated with cytochrome P-450, and not GSH, concentrations. Cobalt heme depleted hepatocellular cytochrome P-450 (-45%) content, decreased cell yield and viability, and resulted in a marked reduction in the metabolism of acetonitrile to cyanide. Cobalt heme did not affect the recovery of sodium cyanide from hepatocyte suspensions. Pretreatment of rats with acetone resulted in a twofold increase in the metabolism of acetonitrile to cyanide. Addition of acetone in vitro inhibited acetonitrile metabolism, with an IC50 of 319 .mu.M. These results suggest that the metabolism of acetonitrile to cyanide occurs by a cytochrome P-40-dependent pathway, and not by a nucleophilic substitution reaction with GSH.