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Peroxynitrite (PN), the product of nitric oxide (NO) reacted with superoxide, is generated at sites of inflammation. Nitrotyrosine (NT), a marker of PN formation, is abundant in lesions of acute experimental autoimmune encephalomyelitis (EAE), and in active multiple sclerosis (MS) plaques. To determine whether PN plays a role in EAE pathogenesis, mice induced to develop EAE were treated with a catalyst specific for the decomposition of PN. Because this catalyst has no effect upon NO, using it allowed differentiation of PN-mediated effects from NO-mediated effects. Mice receiving the PN decomposition catalyst displayed less severe clinical disease, and less inflammation and demyelination than control mice. Encephalitogenic T cells could be recovered from catalyst-treated mice, indicating that the PN decomposition catalyst blocked the pathogenic action of PN at the effector stage of EAE, but was not directly toxic to encephalitogenic T cells. PN plays an important role distinct from that of NO in the pathogenesis of EAE, a major model for MS.

The formation of the powerful oxidant peroxynitrite (PN) from the reaction of superoxide anion with nitric oxide has been shown to be a kinetically favored reaction contributing to cellular injury and death at sites of tissue inflammation. The PN molecule is highly reactive causing lipid peroxidation as well as nitration of both free and protein-bound tyrosine. We present evidence for the pharmacological manipulation of PN with decomposition catalysts capable of converting it to nitrate. In target cells challenged with exogenously added synthetic PN, a series of metalloporphyrin catalysts (5,10,15,20-tetrakis(2,4,6-trimethyl-3, 3-disulfonatophenyl)porphyrinato iron (III) (FeTMPS); 5,10,15, 20-tetrakis(4-sulfonatophenyl)porphyrinato iron (III) (FeTPPS); 5,10, 15,20-tetrakis(N-methyl-4'-pyridyl)porphyrinato iron (III) (FeTMPyP)) provided protection against PN-mediated injury with EC50 values for each compound 30-50-fold below the final concentration of PN added. Cytoprotection was correlated with a reduction in the level of measurable nitrotyrosine. In addition, we found our catalysts to be cytoprotective against endogenously generated PN in endotoxin-stimulated RAW 264.7 cells as well as in dissociated cultures of hippocampal neurons and glia that had been exposed to cytokines. Our studies thus provide compelling evidence for the involvement of peroxynitrite in cytokine-mediated cellular injury and suggest the therapeutic potential of PN decomposition catalysts in reducing cellular damage at sites of inflammation.