Uric Acid In Multiple Sclerosis

Presence of NitroTyrosine in cells surrounding plaques indicates that Peroxynitrite may be the cause of Brain lesions in Multiple Sclerosis.

Low levels of Uric Acid, a natural scavenger of Peroxynitrite, were demonstrated in blood of patients with Multiple Sclerosis in comparison with control individuals.

These observations were now extended to 132 sets of twins with one sibling affected by Multiple Sclerosis.

In blood of both Mono- and Dizygotic twins the Uric Acid levels were lower in the twin with the disease than in the healthy twin.

Peroxynitrite, a biological oxidant formed from the reaction of Nitric Oxide (NO) with the superoxide radical, is associated with many Pathologies, including NeuroDegenerative Diseases, such as Multiple Sclerosis (MS).

Gout (HyperUricemic) and MS are almost mutually exclusive, and Uric Acid has therapeutic effects in mice with Experimental Allergic EncephaloMyelitis, an animal disease that models MS.

This evidence suggests that Uric Acid may scavenge Peroxynitrite and/or Peroxynitrite-derived reactive species. Therefore, we studied the kinetics of the reactions of Peroxynitrite with Uric Acid from pH 6.9 to 8.0.

The data indicate that PerOxynitrous Acid (HOONO) reacts with the Uric Acid MonoAnion with k = 155 M^-1 s^-1 (T = 37 degrees C, pH 7.4) giving a pseudo-first-order rate constant in blood Plasma k(U(rate))(/Plasma) = 0.05 s^-1 (T = 37 degrees C, pH 7.4; assuming [Uric Acid](Plasma) = 0.3 mM).

Among the biological molecules in human Plasma whose rates of reaction with Peroxynitrite have been reported, CO₂ is one of the fastest with a pseudo-first-order rate constant k(CO₂)(/Plasma) = 46 s^-1 (T = 37 degrees C, pH 7.4; assuming [CO₂](Plasma) = 1 mM).

Thus Peroxynitrite reacts with CO₂ in human blood Plasma nearly 920 times faster than with uric Acid. Therefore, Uric Acid does not directly scavenge Peroxynitrite because Uric Acid can not compete for Peroxynitrite with CO₂.

The therapeutic effects of Uric Acid may be related to the scavenging of the radicals CO^*_-3 and NO^*₂ that are formed from the reaction of Peroxynitrite with CO₂.

We suggest that trapping secondary radicals that result from the fast reaction of Peroxynitrite with CO₂ may represent a new and viable approach for ameliorating the adverse effects associated with Peroxynitrite in many diseases.

Copyright 2000 Academic Press.

Peroxynitrite (ONOO^-), a toxic product of the free radicals Nitric Oxide and SuperOxide, has been implicated in the PathoGenesis of CNS inflammatory diseases, including Multiple Sclerosis and its animal correlate Experimental AutoImmune EncephaloMyelitis (EAE).

In this study we have assessed the mode of action of Uric Acid (UA), a purine metabolite and ONOO^- scavenger, in the treatment of EAE.

We show that if administered to mice before the onset of clinical EAE, UA interferes with the invasion of inflammatory cells into the CNS and prevents development of the disease.

In mice with active EAE, exogenously administered UA penetrates the already compromized Blood-CNS Barrier, blocks ONOO^--mediated Tyrosine nitration and Apoptotic cell death in areas of inflammation in Spinal Cord tissues and promotes recovery of the animals.

Moreover, UA treatment suppresses the enhanced Blood-CNS Barrier permeability characteristic of EAE.

We postulate that UA acts at two levels in EAE:
1. By protecting the integrity of the Blood-CNS Barrier from ONOO^--induced permeability changes such that cell invasion and the resulting pathology is minimized
2. Through a compromized Blood-CNS Barrier, by scavenging the ONOO^- directly responsible for CNS tissue damage and death.

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 mg/kg 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-gamma 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.

ExtraCellular Purines, including Adenosine and ATP, are potent endogenous ImmunoModulatory Molecules. Inosine, a degradation product of these Purines, can reach high concentrations in the ExtraCellular space under conditions associated with cellular metabolic stress such as Inflammation or Ischemia.

In the present study, we investigated whether ExtraCellular Inosine can affect Inflammatory/Immune processes.

In ImmunoStimulated Macrophages and Spleen Cells, Inosine potently inhibited the production of the ProInflammatory Cytokines TNF-, IL-1, IL-12, Macrophage-Inflammatory Protein-1, and IFN-, but failed to alter the production of the AntiInflammatory Cytokine IL-10.

The effect of Inosine did not require cellular uptake by Nucleoside Transporters and was partially reversed by blockade of Adenosine A1 and A2 receptors. Inosine inhibited Cytokine production by a PostTranscriptional mechanism.

The activity of Inosine was independent of activation of the p38 and p42/p44 Mitogen-activated protein kinases, the phosphorylation of the c-Jun terminal kinase, the degradation of inhibitory factor kappaB, and elevation of IntraCellular cAMP.

Inosine suppressed ProInflammatory Cytokine production and mortality in a mouse endotoxemic model. Taken together, Inosine has multiple AntiInflammatory Effects.

These findings, coupled with the fact that Inosine has very low toxicity, suggest that this agent may be useful in the treatment of Inflammatory/Ischemic Diseases.

Uric Acid (UA) is a purine metabolite that selectively inhibits PerOxynitrite-mediated reactions implicated in the pathogenesis of Multiple Sclerosis (MS) and other NeuroDegenerative Diseases.

Serum UA levels are inversely associated with the incidence of MS in humans because MS patients have low Serum UA levels and individuals with HyperUricemia (Gout) rarely develop the disease.

Moreover, the administration of UA is therapeutic in Experimental Allergic Encephalomyelitis (EAE), an animal model of MS. Thus, raising serum UA levels in MS patients, by oral administration of a UA precursor such as Inosine, may have therapeutic value.

We have assessed the effects of Inosine, as well as Inosinic Acid, on parameters relevant to the chemical reactivity of PerOxynitrite and the pathogenesis of EAE.

Both had no effect on chemical reactions associated with peroxynitrite, such as Tyrosine nitration, or on the activation of inflammatory cells in vitro.

Moreover, when mice treated with the Urate oxidase inhibitor Potassium Oxonate were fed inosine or Inosinic Acid, Serum UA levels were elevated markedly for a period of hours, whereas only a minor, transient increase in Serum Inosine was detected.

Administration of Inosinic Acid suppressed the appearance of clinical signs of EAE and promoted recovery from ongoing disease.

The therapeutic effect on animals with active EAE was associated with increased UA, but not Inosine, levels in CNS tissue. We, therefore, conclude that the mode of action of Inosine and Inosinic Acid in EAE is via their metabolism to UA.

Several findings suggest lower levels of Serum Uric Acid in Multiple Sclerosis (MS) patients. The aim of this study is to investigate relationships of Uric Acid Serum levels in Relapse/Remitting (RR) MS patients with clinical activity of disease and Blood-Brain Barrier (BBB) condition.

Sixty-three definite RRMS patients and 40 controls divided into two groups: 20 healthy donors and 20 patients with Other Inflammatory Neurological Diseases (OINDs) were analysed.

By using a quantitative enzymatic assay according to the manufacture's protocol and a commercial Uric Acid standard solution.

Serum Uric Acid levels were measured and the results were standardized. To investigate BBB function, Magnetic Resonance Imaging after administration of Gadolinium was used.

MS patients were found to have significantly lower Serum Uric Acid levels (193.89 +/- 49.05 micromol/l; mean value +/-SD) in comparison with healthy donors (292.7 +/- 58.65 micromol/l; P=0.000) and OIND patients (242.7 +/- 46.66 micromol/l; P=0.001).

We found that MS patients with relapse had significantly lower Serum Uric Acid levels (161.49 +/- 23.61 micromol/l) than MS patients with remission (234.39 +/- 41.96 micromol/l; P=0.000).

And more over, MS patients with BBB disruption had significantly lower Serum Uric Acid levels (163.95 +/- 26.07 micromol/l) than those with normal BBB (252.48 +/- 25.94 micromol/l; P=0.000).

Further, we also found that Serum Uric Acid level independently correlated with disease activity, BBB disruption, and gender.

These results indicate that lower Uric Acid Levels in MS patients are associated with relapse and suggest that uric acid might be beneficial in the treatment of MS.

Several studies indicate that patients with Multiple Sclerosis (MS) have low Serum levels of the endogenous AntiOxidant Uric Acid (UA), although it has not been established whether UA is primarily deficient or secondarily reduced due to its Peroxynitrite scavenging activity.

We measured Serum Urate levels in 124 MS patients and 124 age- and sex-matched controls with Other Neurological Diseases.

In addition, we compared UA levels when MS patients were stratified according to disease activity (by means of clinical examination and MRI), duration, disability and course.

MS patients had significantly lower Serum Urate levels than controls ( p= 0.001). However, UA levels did not significantly correlate with disease activity, duration, disability or course.

Our study favors the view that reduced UA in MS is a primary, constitutive loss of protection against Oxidative agents, which deserves further pathogenetic elucidation aimed at future therapeutic strategies.

The effect of ingesting some Purine-rich foods (Beef Liver, Haddock Fillets and Soybeans) on Uric Acid metabolism was investigated in 18 male subjects with no history of Gout or Kidney Disorder.

In a crossover design, three IsoEnergetic and IsoNitrogenous meals were fed to volunteers during a 3-week period. Only the content of Uricogenic bases (Adenine and HypoXanthine) varied among the test meals.

Ingestion of all experimental meals caused an increase in Serum Uric Acid levels at 120 minutes and this increase was more marked (about twofold) with Haddock and Soybean ingestion.

In all groups, the postprandial Serum Uric Acid levels at 240 minutes were lower than those obtained at 120 minutes, but still remained elevated in comparison to the fasting level.

The test foods had little or no effect on Serum and Urinary Creatinine values. As expected, 24-hour Urinary Uric Acid excretion was similar for the three test meals due to the IsoNitrogenous load of Proteins and Purines.

Assessment of each Purine base content rather than the total Purine content of foods should be considered in future recommendations for HyperUricemic individuals.

Copyright © 1992 by American College of Nutrition. Reprinted by permission.

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