Reactive oxygen species and the brain in sleep apnea.

Rodents exposed to intermittent hypoxia (IH), a model of obstructive sleep apnea (OSA), manifest impaired learning and memory and somnolence. Increased levels of reactive oxygen species (ROS), oxidative tissue damage, and apoptotic neuronal cell death are associated with the presence of IH-induced CNS dysfunction. Furthermore, treatment with antioxidants or overexpression of antioxidant enzymes is neuroprotective during IH. These findings mimic clinical cases of OSA and suggest that ROS may play a key causal role in OSA-induced neuropathology. Controlled production of ROS occurs in multiple subcellular compartments of normal cells and de-regulation of such processes may result in excessive ROS production. The mitochondrial electron transport chain, especially complexes I and III, and the NADPH oxidase in the cellular membrane are the two main sources of ROS in brain cells, although other systems, including xanthine oxidase, phospholipase A2, lipoxygenase, cyclooxygenase, and cytochrome P450, may all play a role. The initial evidence for NADPH oxidase and mitochondrial involvement in IH-induced ROS production and neuronal injury unquestionably warrants future research efforts.