Uric acid, the naturally occurring product of purine metabolism, is a strong peroxynitrite scavenger, as demonstrated by the capacity to bind peroxynitrite but not nitric oxide (NO) produced by lipopolysaccharide-stimulated cells of a mouse monocyte line. In this study, we used uric acid to treat experimental allergic encephalomyelitis (EAE) in the PLSJL strain of mice, which develop a chronic form of the disease with remissions and exacerbations. Uric acid administration was found to have strong therapeutic effects in a dose-dependent fashion. A regimen of four daily doses of 500 mg͞kg uric acid was required to promote long-term survival regardless of whether treatment was initiated before or after the clinical symptoms of EAE had appeared. The requirement for multiple doses is likely to be caused by the rapid clearance of uric acid in mice which, unlike humans, metabolize uric acid a step further to allantoin. Uric acid treatment also was found to diminish clinical signs of a disease resembling EAE in interferon-␥ receptor knockout mice. A possible association between multiple sclerosis (MS), the disease on which EAE is modeled, and uric acid is supported by the finding that patients with MS have significantly lower levels of serum uric acid than controls. In addition, statistical evaluation of more than 20 million patient records for the incidence of MS and gout (hyperuricemic) revealed that the two diseases are almost mutually exclusive, raising the possibility that hyperuricemia may protect against MS.The induction of the nitric oxide synthase isoform (NOS-2) in the central nervous system (CNS) commonly associated with cells of the macrophage͞monocyte lineage is a characteristic feature of experimental allergic encephalomyelitis (EAE) (see refs. 1-7 for examples). Moreover, production of the free radical nitric oxide (NO) in CNS tissue of mice has been correlated with the development of clinical signs of the disease (2, 7). The contribution of NO in the etiology of EAE has been confirmed in mice that were immunized with proteolipid protein peptide but failed to develop EAE when treated with a compound that inactivates NO (8).It remains unproven whether NO, which has a short half-life in vivo, exerts a toxic effect on CNS cells directly or through the formation of a more toxic compound, the production of which is directly related to the induction of elevated NO levels in brain tissue. Peroxynitrite (ONOO Ϫ ), a potent oxidant that is formed by the rapid combination of NO with superoxide (O2 Ϫ ), can be formed in an inflammatory response (9) and can cause a variety of toxic effects, including lipid peroxidation (10) and tyrosine nitration (11,12). It therefore has been suggested that peroxynitrite is responsible for a significant proportion of the inflammatory damage attributed to NO (12).We have shown that treatment with uric acid, a naturally occurring compound that selectively binds and inactivates peroxynitrite (13), inhibits the onset of clinical disease in an acute, aggressive form of mouse EAE,...

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.

Purpose: This study is directed at identifying the cell source(s) of immunomodulatory cytokines in highgrade gliomas and establishing whether the analysis of associated markers has implications for tumor grading.Experimental Design: Glioma specimens classified as WHO grade II-IV by histopathology were assessed by gene expression analysis and immunohistochemistry to identify the cells producing interleukin (IL)-10, which was confirmed by flow cytometry and factor secretion in culture. Finally, principal component analysis (PCA) and mixture discriminant analysis (MDA) were used to investigate associations between expressed genes and glioma grade.Results: The principle source of glioma-associated IL-10 is a cell type that bears phenotype markers consistent with M2 monocytes but does not express all M2-associated genes. Measures of expression of the M2 cell markers CD14, CD68, CD163, and CD204, which are elevated in high-grade gliomas, and the neutrophil/myeloid-derived suppressor cell (MDSC) subset marker CD15, which is reduced, provide the best index of glioma grade.Conclusions: Grade II and IV astrocytomas can be clearly differentiated on the basis of the expression of certain M2 markers in tumor tissues, whereas grade III astrocytomas exhibit a range of expression between the lower and higher grade specimens. The content of CD163 þ cells distinguishes grade III astrocytoma subsets with different prognosis.