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Role of the cellular redox state in modulating acute ethanol toxicity in isolated hepatocytes
1Faculty of Pharmacy, University of Toronto, Ontario, Canada.
Objectives:
To propose a mechanism for ethanol induced hepatocytotoxicity.
Design And Methods:
Hepatocytotoxicity was determined at various concentrations of oxygen and agents involved in NADH metabolism.
Results:
At 1% O2, hepatocytes were nearly 8-fold more susceptible to ethanol than at 95% O2 (carbogen). Cytotoxicity at 1% O2 was enhanced in the presence of glycolytic substrates that generate NADH (e.g., sorbitol or xylitol), and prevented by glycolytic substrates that reoxidise NADH (e.g., fructose or dihydroxyacetone). Susceptibility to ethanol correlated with the cytosolic redox state (lactate; pyruvate ratio). Cytotoxicity also correlated with reactive oxygen species (ROS) formation. Cytotoxicity was averted by ROS scavengers or the ferric chelator desferoxamine but was increased by hydroxylamine, a catalase inhibitor, or by prior glutathione depletion. Ethanol induced cytotoxicity was also decreased by inhibitors of alcohol/aldehyde dehydrogenases or CYP2E1, an alcohol inducible cytochrome P450.
Conclusions:
A cytotoxic mechanism was proposed where the sustained increase in NADH levels, resulting from ethanol metabolism, maintains CYP2E1 in a more reduced state that increases ROS formation.