Alcohol and mitochondria: A dysfunctional relationship

Mitochondria are intimately involved in the generation of and defense against reactive oxygen species (ROS). Mitochondria are themselves targets of oxidative stress and also contribute to mechanisms by which oxidative stress-related signals control cell fate. Ethanol promotes oxidative stress, both by increasing ROS formation and by decreasing cellular defense mechanisms. These effects of ethanol are prominent in the liver, the major site of ethanol metabolism in the body. The question remains to what extent this contributes to ethanol-dependent tissue damage or the susceptibility of cells to other stressors. In this review, we consider how mitochondrial actions of ethanol influence oxidative stress management of liver cells. Mitochondrial electron transport constitutes the major intracellular source of ROS, and ethanol treatment imposes conditions that promote ROS formation by mitochondria, the effects of which may be enhanced by a decrease in mitochondrial oxidative stress defenses. A significant target of ethanol-related increases in oxidative stress is mitochondrial DNA. Ethanol-induced damage to mitochondrial DNA, if not adequately repaired, impairs mitochondrial function, which further increases oxidative stress in the cell, leading to a vicious cycle of accumulating cell damage that is more apparent with advancing age. Uncontrolled mitochondrial formation of ROS promotes the inappropriate activation of the mitochondrial permeability transition, increasing the sensitivity of cells to other proapoptotic or damage signals. In combination with ethanol-induced defects in mitochondrial function, these alterations may promote both apoptotic and necrotic cell death in response to otherwise benign or beneficial challenges and contribute to the onset or progression of alcohol-induced liver diseases.