Increase of uric acid and purine compounds in biological fluids of multiple sclerosis patients

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Abstract

Objectives

In this study, the concentrations of uric acid, purine profile and creatinine in samples of cerebrospinal fluid and serum of multiple sclerosis (MS) patients were measured by HPLC and compared with corresponding values recorded in patients without MS (cerebrospinal fluid) and healthy subjects (serum).

Design and methods

All samples were deproteinized with ultrafiltration (which ensures minimal sample manipulation and efficient protein removal) and then assayed for the synchronous HPLC separation of uric acid, hypoxanthine, xanthine, inosine, adenosine, guanosine and creatinine.

Results

The values of all compounds assayed were significantly higher in both biological fluids of MS patients with respect to values measured in controls. In particular, serum hypoxanthine, xanthine, uric acid and sum of oxypurines were, respectively, 3.17, 3.11, 1.23 and 1.27-fold higher in these patients than corresponding values recorded in controls (p < 0.001).

Conclusions

Differently from what previously reported, we here demonstrate that all purine compounds, including uric acid, are elevated in biological fluids of MS patients. Reinforced by the trend observed for creatinine, this corroborates the notion of sustained purine catabolism, possibly due to imbalance in ATP homeostasis, under these pathological conditions. These results cast doubt on the hypothesis that uric acid is depleted in MS because of increased oxidative stress, rather suggesting that this disease causes a generalized increase in purine catabolism. As observed in other pathological states, uric acid, purine compounds and creatinine, can be considered markers of metabolic energy imbalance rather than of reactive oxygen species, even in MS.

Introduction

The neurodegenerative demyelinating disorder known as multiple sclerosis (MS) affects the central nervous system through autoimmune pathogenetic mechanisms. Several studies have postulated that reactive oxygen species (ROS) and reactive nitrogen species (RNS) might play a key role in the disease development by contributing to myelin and oligodendroglia degeneration, characteristics of MS [1], [2]. ROS and RNS production is physiologically buffered by several enzymatic (superoxide dismutase, catalase, glutathione peroxidase, etc.) and non-enzymatic (glutathione, ascorbic acid, α-tochopherol, coenzyme Q10, uric acid, etc.) low molecular weight antioxidants. When ROS and RNS are generated in amounts exceeding the scavenging capacity, cells and tissues undergo oxidative and nitrosative stresses. Both phenomena are frequently encountered in various pathological states such as tissue ischemia and reperfusion [3], head injury [4], diabetes [5] and various neurodegenerative disorders [6], [7] including MS [1], [2]. In particular, a major pathophysiological role for peroxynitrite (ONOOradical dot) has been suggested on the basis of data obtained either in experimental autoimmune encephalomyelitis (EAE), the animal model of MS, or in patients suffering from MS. In fact, the administration of ONOOradical dot scavengers had beneficial effects in EAE rats [8], whilst an increase in nitrotyrosine (one of the main biomarkers of ONOO. formation) was detected in cerebrospinal fluid (CSF) of MS patients [9]. On the other hand, several studies highlighted clear biochemical signs indicative of sustained oxidative stress in CSF and plasma of MS patients [10].

The general tendency is to attribute the responsibility for ROS and RNS overproduction to the inflammatory cell population characteristic of MS [11]. However, it has recently been demonstrated that mitochondria of glial cells of EAE rats can generate such conspicuous ROS and RNS overflows as to compromise severely even their mitochondrial functions, including their capacity for oxidative phosphorylation [12], [13]. Since this phenomenon has clearly been demonstrated to occur much earlier than the activation of the inflammatory processes, it is plausible that mitochondria, similarly to other acute [14], [15] and chronic [16], [17] cerebral pathological states, are key organelles in the pathological processes that underlie the evolution of MS.

In the attempt to find out reliable biochemical markers of diagnostic and/or prognostic value, several compounds detectable in bodily fluids (plasma/serum, CSF, urine) were measured in MS patients, including uric acid. As far as this product of purine catabolism is concerned, the results of several clinical studies gave no unanimous findings, showing either significant decrease (interpreted as a biochemical evidence of oxidative/nitrosative stress occurrence in MS), or no differences when comparing the circulating uric acid levels of MS patients and controls (for schematic tables reporting the to date available literature on this controversial issue, see [18] and [19]).

With the aim of clarifying this conflicting point, we studied 48 MS patients in which CSF and serum were assayed for uric acid, purine metabolites and creatinine. The values of the various compounds recorded in MS patients were compared with those obtained in a group of 48 non-cerebral patients (CSF) and in a group of 48 healthy control subjects (serum).

Section snippets

Patient selection and assessment of clinical disability

Forty-eight MS patients were included in this study (Table 1). They were assessed clinically using the Extended Disability Status Scale score (EDSS) [20], [21]. Patients were classified into relapsing remitting (RR), secondary progressive (SP) or primary progressive (PP), as described elsewhere [22]. The control groups consisted of 48 healthy volunteers (serum) and 48 patients (CSF) with non-inflammatory neurological diseases who underwent a lumbar puncture for non-specific sensory symptoms and

Results

The characteristics of both the MS patients and the control groups are summarized in Table 1. As expected, there was a significant difference in the degree of disability between the different MS subgroups, with SP and PP MS patients being more disabled than RR MS patients on the EDSS (p < 0.001).

Discussion

The data reported in the present study suggest that MS patients may suffer from a cell energy metabolism deficit that can be evidenced in biological fluids (CSF and serum). The profile of compounds directly (uric acid, hypoxanthine, xanthine, inosine, guanosine, adenosine) or indirectly (creatinine) reflecting the imbalance between ATP production and consumption was similarly altered in both CSF and serum of MS patients with respect to corresponding values detected in control groups.

As far as

Acknowledgments

This work has been supported in part by research funds of Catania University, of Catholic University of Rome “Sacro Cuore”, and by MIUR – PRIN 2007JBHZ5F grant.

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