Cyanide-induced cytotoxicity to isolated hepatocytes

The responses of various cell functional parameters to potassium cyanide (KCN) were investigated in isolated rat hepatocytes to examine their quantitative and temporal relationship to inhibition of mitochondrial respiration. Both cultures and suspensions of hepatocytes, maintained in hormone-supplemented culture medium at 37 degrees C under an air: CO(2) (95:5) atmosphere, were used in these studies. The earliest and most sensitive change detected was inhibition of O(2) consumption (EC (50) = 78 mu m ); other early changes included depression in ATP and ATP/ADP, inhibition of urea synthesis, and elevation in lactate/pyruvate. The effect on ATP depression at 10 min was reversed by replacement with fresh medium containing no cyanide (t (1 2 )=9 min ). Increased release of lactate dehydrogenase and acid phosphatase occurred much later during the incubation (120 or 240 min) and at much higher KCN concentrations (>/=0.5 mm) than the other changes. These observations are consistent with inhibition of mitochondrial respiration being the initiating or major contributing factor in cyanide-induced cytotoxicity in hepatocytes, but because of the difference in EC(50) values for depression of O(2) consumption and energy-dependent parameters and for intracellular enzyme release, other mechanisms may also contribute to cell death. Reduced glutathione content and lipid peroxidation in the cells, assessed by measuring thiobarbituric acid reactants, were not significantly changed, and the mechanism leading up to cell death remains uncharacterized. The cyanide concentrations in vitro that produced inhibition of O(2) consumption were in the same range as those in blood and liver that inhibited cytochrome oxidase in vivo at lethality. The results in the hepatocyte model, therefore, can explain why the liver is not a target organ in massive, acute cyanide poisoning, in that overt signs develop at higher concentrations and after longer times than are applicable for the death of the animal.