The specificity of neuroprotection by antioxidants

Using fluorescent dyes for ROS detection and mitochondrial inhibitors of known specificities, we studied ROS production under three conditions where ROS are produced by mitochondria: oxidative glutamate toxicity, state IV respiration induced by oligomycin, and tumor necrosis factor-induced cell death.We demonstrated that there are at least four mitochondrial ROS-generating sites in cells, including the flavin mononucleotide (FMN) group of complex I and the three ubiquinone-binding sites in complexes I, II and III. ROS production from these sites is modulated in an insult-specific manner and the sites are differentially accessible to common antioxidants.The inhibition of ROS accumulation by different antioxidants is specific to the site of ROS generation as well as the antioxidant. This information should be useful for devising new interventions to delay aging or treat ROS-related diseases.The production of reactive oxygen species (ROS) is greatly increased under many conditions of toxic stress [1,2]. However, existing antioxidants appear to be relatively ineffective in combating these problems, either because they cannot reach the site of ROS production, which is frequently within mitochondria, or because of their poor ability to scavenge the damaging ROS. Identifying compounds that directly block mitochondrial ROS production may be a novel way to inhibit oxidative stress, and perhaps delay aging and treat mitochondrial ROS-related diseases. However, it remains a challenge to define both the normal and pathologically relevant sites of ROS formation in the mitochondrial electron transport chain (ETC) and to find clinically useful agents that can minimize mitochondrial ROS production.The mitochondrial ETC is composed of a series of electron carriers (flavoproteins, iron-sulfur proteins, ubiquinone and cytochromes) that are arranged spatially according to their redox potentials and organized into four complexes (Figure 1). Electrons derived from metabolic reducing equi