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NITRIC OXIDE -OXYGEN RADICAL INTERACTIONS IN NEURODEGENERATION M. Flint Beal, M.D. Dept of Neurology and Neuroscience.Weill Medical College of Cornell University. New York, NY 10021

A role for oxidative damage in the pathogenesis of neurodegeneratwe disease is becoming increasingly apparent. One potential mediator of oxidative damage is peroxyniuite. It has been proposed that mutant superoxide dismutase is associated with familial ALS may more readily react with peroxynitrite to nitrate proteins. Consistent with this we found increased levels of 3.niuotyrosine m the spinal cords of both sporadic and familial ALS patients. Furthermore, we showed increased immunostaining for 3-nitrotyrosine in the anterior horn cells of a mouse model of ALS. Increased 3.nitrotyrosine staining of neurotihrillary tangle bearing neurons has been demonstrated independently by two groups of investigators in Alzheimer’s Disease. ‘Ihere is also evidence of increased 3. nitrotyrosine stammg in the substantia nigra of Parkinson’s Disease patients. Consistent wth this we showed that following administration of MPTP to both mice and baboons, there IS increased 3-nitrotyrosine staining in the substantia nigra. Furthermore, we found that administration of inhibitors of neuronal nitric oxide synthase sigmficantly attenuated the neurotoxicity of MPTP both 1” mu and in baboons. Recent studies confirmed this by demonstrating that mice deficient in neuronal nitric oxide synthase are resistant to MPTP. There is also recent evidence that MPTP administration results in nitration of tyrosine hydroxylase accompamed by reduced activity of this essential enzyme. Administration of neuronal nitric oxide synthase inhibitors also inhibits ammal models of Huntington’s Disease produced by both malonate and 3-nitropropionic acid. More recently, we found that creatine administration to a uansgenic mouse model of amyotmphlc lateral sclerosis both extends survival and reduces 3. nmotyrosine concentrations, which are elevated in the spinal cords of these mice. The present evidence, therefore, implicates oxidative damage and 3-nitrotyrosine in the pathogenesis of neurodegenerative dtseases.

I p-2 I Nitric oxide in mitochondlial function and injury S. Moncada, The Wolfson Institute for Biomedical Research, University College London, Gower Street, London WCIE 6BT. Two enzymes, the soluble guanylyl cyclase and cytochrome c oxidase, have been shown to be exquisitely sensitive to nitric oxide (NO) at low physiological concentrations. Activation of the soluble guanylyl cyclase by endogenotts NO and the consequent increase in the second messenger cyclic GMP are now known to control a variety of biological functions. Cytochrome c oxidase (complex IV, the terminal enzyme of the mitochondtial respiratory chain) is inhibited by NO. We have shown that NO generated by vascular endothelial cells under basal and stimulated conditions modulates the respiration of these cells in response to acute changes in oxygen concentration. This action occurs at the level of complex IV and depends on influx of calcium. Thus, NO plays a physiological role in adjusting the capacity of this enzyme to use oxygen, allowing endothelial cells to adapt to acute changes in their environment. We have, in addition, studied the effect of long-term exposure to NO on different enzymes of the respiratory chain in a variety of cell lines. Our results show that, although NO inhibits complex IV in a way that is always reversible, prolonged exposure to NO results in a gradual and persistent inhibition of complex I that is concomitant with a reduction in the intracellular concentration of reduced glutatbione. This inhibition appears to result from S-nitrosylation of critical thiols in the enzyme complex because it can be immediately reversed by exposing the cells to high intensity light or by replenishment of intracellular reduced glutathione. Furthermore, decreasing the concentration of reduced glutathione accelerates the process of persistent inhibition. Our results suggest that, although NO may regulate cell respiration physiologically by its action on complex IV, long-term exposure to NO leads to persistent inhibition of complex I and potentially to cell pathology.

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