Ethanol potentiates hypoxic liver injury: role of hepatocyte Na + overload

Abstract

Centrilobular hypoxia has been suggested to contribute to hepatic damage caused by alcohol intoxication. However, the mechanisms involved are still poorly understood. We have investigated whether alterations of Na + homeostasis might account for ethanol-mediated increase in hepatocyte sensitivity to hypoxia. Addition of ethanol (100 mmol/l) to isolated rat hepatocytes incubated under nitrogen atmosphere greatly stimulated cell death. An increase in intracellular Na + levels preceded cell killing and Na + levels in hepatocytes exposed to the combination of ethanol and hypoxia were almost twice those in hypoxic cells without ethanol. Na + increase was also observed in hepatocytes incubated with ethanol in oxygenated buffer. Ethanol addition significantly lowered hepatocyte pH. Inhibiting ethanol and acetaldehyde oxidation with, respectively, 4-methylpyrazole and cyanamide prevented this effect. 4-methylpyrazole, cyanamide as well as hepatocyte incubation in a HCO 3 −-free buffer or in the presence of Na +/H + exchanger blocker 5-( N, N-dimethyl)-amiloride also reduced Na + influx in ethanol-treated hepatocytes. 4-methylpyrazole and cyanamide similarly prevented ethanol-stimulated Na + accumulation and hepatocyte killing during hypoxia. Moreover, ethanol-induced Na + influx caused cytotoxicity in hepatocytes pre-treated with Na +,K +-ATPase inhibitor ouabain. Also in this condition 4-methylpyrazole and 5-( N, N-dimethyl)-amiloride decreased cell killing. These results indicate that ethanol can promotes cytotoxicity in hypoxic hepatocytes by enhancing Na + accumulation.