INHIBITION OF ASTROCYTE GLUTAMATE UPTAKE BY REACTIVE OXYGEN SPECIES -ROLE OF ANTIOXIDANT ENZYMES

Background: The recent literature suggests that free radicals and reac tive oxygen species may account for many pathologies, including those of the nervous system. Materials and Methods: The influence of various reactive oxygen species on the rate of glutamate uptake by astrocytes was investigated on monolayers of primary cultures of mouse cortical astrocytes. Results: Hydrogen peroxide and peroxynitrite inhibited glu tamate uptake in a concentration-dependent manner. Addition of copper ions and ascorbate increased the potency and the efficacy of the hydro gen peroxide effect, supporting the potential neurotoxicity of the hyd roxyl radical. The free radical scavenger dimethylthiourea effectively eliminated the inhibitory potential of a mixture containing hydrogen peroxide, copper sulphate, and ascorbate on the rate of glutamate tran sport into astrocytes. The inhibitory effect of hydrogen peroxide on g lutamate uptake was not altered by the inhibition of glutathione perox idase, whereas the inhibition of catalase by sodium azide clearly pote ntiated this effect. Superoxide and nitric oxide had no effect by them selves on tile rate of glutamate uptake by astrocytes. The absence of an effect of nitric oxide is not due to an inability of astrocytes to respond to this substance, since the same cultures did respond to nitr ic oxide with a sustained increase in cytoplasmic free calcium. Conclu sion: These results confirm that reactive oxygen species have a potent ial neurotoxicity by means of impairing glutamate transport into astro cytes, and they suggest that preventing the accumulation of hydrogen p eroxide in the extracellular space of the brain, especially during con ditions that favor hydroxyl radical formation, could be therapeutic.