Prevention of experimental allergic encephalomyelitis by targeting nitric oxide and peroxynitrite: Implications for the treatment of multiple sclerosis

Abstract

In this study we provide further evidence associating activated cells of the monocyte lineage with the lesions of multiple sclerosis (MS). Using a combination of immunohistochemistry and reverse transcriptase-dependent in situ polymerase chain reaction analysis, we have identified monocytes expressing inducible nitric oxide synthase (iNOS) to be prevalent in the plaque areas of post mortem brain tissue from patients with MS. In addition, we have obtained evidence of the nitration of tyrosine residues in brain areas local to accumulations of iNOS-positive cells. In parallel studies we have assessed the effects of inhibitors of iNOS induction, as well as scavengers of nitric oxide and peroxynitrite in the experimental allergic encephalomyelitis model. Significant therapeutic effects were seen with the inhibitor of iNOS induction, tricyclodecan-9-xyl-xanthogenate, a nitric oxide scavenger, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, and a peroxynitrite scavenger, uric acid. In particular, treatment with high doses of uric acid virtually prevented clinical symptoms of the disease. Together with our demonstration of the presence of activated macrophages expressing high levels of iNOS and evidence of peroxynitrite formation in brain tissue from patients with MS, these findings are of importance in the development of approaches to treat this disease.

The Peroxynitrite Scavenger Uric Acid Prevents Inflammatory Cell Invasion into the Central Nervous System in Experimental Allergic Encephalomyelitis through Maintenance of Blood-Central Nervous System Barrier Integrity

“…For example, ascorbic acid, another biologically relevant antioxidant, was ϳ15-fold less effective at inhibiting DHR 123 oxidation mediated by ONOO Ϫ elaborated by activated macrophages. More important in the context of nitrotyrosine formation in MS and EAE (1)(2)(3)(4)(5), UA efficiently inhibits ONOO Ϫ -mediated tyrosine nitration in the presence and absence of a source of carbonyl anion. Apart from inactivating ONOO Ϫ , UA does not appear to have any significant effect on in vitro measures of immune and inflammatory cell function relevant to EAE.…”

“…Our approach to examining the contribution of ONOO Ϫ to the pathogenesis of EAE has been to determine whether reagents that interfere with its chemical reactions also inhibit the development or progression of the disease (1,5,15). Table I summarizes the results of a survey of a variety of compounds that have been assessed for the capacity to inhibit oxidation of DHR 123 by ONOO Ϫ produced either chemically by SIN-1 or biologically by LPS-stimulated RAW monocytes.…”

“…Thus, although the etiologies of MS and EAE may differ, the latter provides models in which potential therapeutic strategies against shared pathological attributes can be studied. We have previously demonstrated that the development of clinical signs of EAE in SWX/J14 mice immunized with proteolipid protein peptide (PLP 139 -151 ), as well as PLSJL/F 1 and IFN-␥ receptor knockout mice immunized with myelin basic protein (MBP) can be curtailed by the aggressive administration of uric acid (UA) (1,15), a known ONOO Ϫ scavenger (16,17). UA treatment also promotes the recovery of mice with EAE from clinical signs of the disease (15).…”

“…C entral nervous system lesions containing activated cells of the monocyte lineage and nitrotyrosine residues, evidence of the local formation of peroxynitrite (ONOO Ϫ ), 4 are pathological hallmarks of multiple sclerosis (MS) and experimental allergic encephalomyelitis (EAE) in conventional mouse models (1)(2)(3)(4)(5). In both cases, inflammatory cells producing NO ⅐ (6, 7) as a consequence of the up-regulation of inducible NO synthase (iNOS) (8 -12) are believed to be the primary source of ONOO Ϫ , which is formed by the rapid reaction of NO ⅐ and superoxide.…”

Antioxidants and polyunsaturated fatty acids in multiple sclerosis

“…It was proposed that the mechanism of EAE inhibition in iron-deficient mice involves the delivery and metabolism of iron for optimal CD4 þ T-cell development (Grant et al, 2003). Some investigators have shown iNOS inhibition as well as NO scavenging to suppress EAE (Cross et al, 1994;Zhao et al, 1996;Hooper et al, 1997;Jolivalt et al, 2003), whereas others have shown iNOS inhibition (O'Brien et al, 1999(O'Brien et al, , 2001 or NO donor (Xu et al, 2001) to aggravate or ameliorate EAE, thus not clarifying the exact role for NO .…”