Oxidative stress: role of mitochondria and protection by glutathione.

Increasing evidence has unraveled a dual functional role of mitochondria as suppliers of the energy required for cell viability, and critical players in the pathway leading to cell death. Consequence of their physiological role in the oxidative phosphorylation is the generation of reactive oxygen species (ROS) as byproducts of the consumption of molecular oxygen in the electron transport chain. Superoxide anion and hydrogen peroxide produced during aerobic respiration are precursors of hydroxyl radical by the participation of transition metals. Glutathione (GSH) in mitochondria is the only defense available to metabolize hydrogen peroxide. A small fraction of the total cellular pool of GSH is sequestered in mitochondria by the action of a carrier that transports GSH from cytosol to the mitochondrial matrix. Recent evidence position mitochondria as subcellular targets of cytokines leading to overproduction of ROS induced by ceramide, a lipid intermediate of cytokine action. Chronic ethanol-fed cells are selectively depleted of GSH in mitochondria due to a defective operation of the carrier responsible for the transport of GSH from cytosol into the mitochondrial matrix. Its limitation sensitizes alcohol hepatocytes to the prooxidant effects of cytokines and prooxidants generated by the oxidative metabolism of ethanol. One of the mechanisms leading to the onset of selective defect in the mitochondrial transport of GSH induced by chronic ethanol exposure is mediated by decreased fluidity of the mitochondrial inner membrane. Its fluidization by SAM treatment normalizes the steady state levels of GSH in mitochondria contributing to withstand the oxidative stress derived by the oxidative metabolism of ethanol.