Carbon monoxide neurotoxicity is triggered by oxidative stress induced by ROS production from three distinct cellular sources

Carbon monoxide (CO) poisoning is one of the leading causes of toxic mortality and morbidity. We have studied the generation of reactive oxygen species in cortical neurons in culture in response to toxic doses of CO exposure. Fluorescence microscopy was used to measure the rate of free radical generation, lipid peroxidation, GSH level and also mitochondrial metabolism. We have found that toxic concentrations of CO released from CORM-401 induced mitochondrial depolarisation and inhibition of NADH dependent respiration to a lesser degree than when compared to ischaemia. Energy collapse was not observed within 40 min of CO exposure. We have found that CO induces the generation of reactive oxygen species resulting in lipid peroxidation and a decrease in GSH via three different mechanisms: from mitochondria during the first minutes of CO exposure, from xanthine oxidase at around 20 min exposure due to energy deprivation, and considerable ROS production from NADPH oxidase in the post CO exposure period (re-oxygenation). Inhibition of these different phases with mitochondrial antioxidants, inhibitors of xanthine oxidase, or NADPH oxidase, protected neurons and astrocytes against CO-induced oxidative stress and cell death. The most profound effect was seen during NADPH oxidase inhibition. Thus, oxidative stress has a remarkably significant role in CO-induced neuronal cell death and preventing its occurrence during reoxygenation is of great importance in the consideration of a positive, neurologically protective therapeutic outcome for CO exposed patients.