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

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 HCO₃^--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. Copyright (C) 2000 Elsevier Science B.V.