Evaluating biomarkers of neuronal degeneration and neuroinflammation in CSF of patients with multiple sclerosis–osteopontin as a potential marker of clinical severity

Abstract

Biomarkers capable of predicting the clinical course and the rate of disease progression in multiple sclerosis are currently unavailable. Our objective was to examine if the levels of proteins associated with axonal and neuronal degeneration (Tau, p-Tau and β-amyloid_1-42) and T-cell-mediated autoimmunity (osteopontin) are altered in the cerebrospinal fluid (CSF) of MS patients, and to assess their potential in reflecting the clinical severity and predicting the progression and clinical evolution of early MS. The CSF samples collected from patients presenting with different clinical forms of MS were evaluated by enzyme-linked immunosorbent assays. The patients were regularly followed-up and their clinical status was re-evaluated 5 years after sampling. The results demonstrated that while CSF levels of Tau, p-Tau and β-amyloid_1-42 did not differ between MS and Control groups, the levels of osteopontin were significantly elevated in MS patients. This increase was associated with the presence of a relapse and correlated with clinical severity, which findings were independent of age and blood–CSF barrier function. However, none of the examined protein levels differed significantly between groups with different clinical evolutions and no positive correlations with clinical progression could be detected. We conclude that Tau, p-Tau and β-amyloid_1-42 are inappropriate as biomarkers in MS. This is the first report on CSF osteopontin as an independent marker of clinical severity in definite MS.

Introduction

Multiple sclerosis (MS) is a chronic, progressive central nervous system (CNS) disorder, characterized by inflammation, demyelination, axonal damage and eventually neurodegeneration. MS affects women approximately 2–3 times as often as men. The course of the disease can vary in a broad range and finding a proper way to predict disease progression is in focus of biomarker research [1]. 85% of the patients has a clinical course of relapsing–remitting form (RR) characterized by recurrent acute exacerbations, which tend to leave more and more residual symptoms and lead to permanent disability after 20–40 years of disease progression, eventually resulting in death due to severe complications. A portion of patients remains in clinically isolated syndrome (CIS) for years without a subsequent relapse. Primary progressive MS (PP) presents with continuous progression and with a lack of remissions. This subtype represents ~ 10% of all cases; however, the pathomechanism of this form is suggested to be distinct, involving remarkable oligodendroglia degeneration [2], [3].

There are no currently available biomarkers that can predict disease progression and future clinical manifestation of the disease at the time of its first presentation [1]. Identifying proper markers with relevant clinical predictive value is eagerly awaited, as such tools would help clinicians determine which patients need more intensive therapeutic approaches early in their clinical course. It can be hypothesized that proteins released into the cerebrospinal fluid (CSF) during axonal and neuronal injury can be useful as biomarkers in reflecting disease severity and/or predicting the clinical outcome of early MS patients. The main axonal candidates include human microtubule-associated protein Tau, a phosphoprotein that is involved in the polymerization and stabilization of axons and has essential roles in intraneuronal transport processes [4]. Accordingly, a number of small studies have been published examining the CSF levels of Tau in MS, which however demonstrated rather contradictory results [5], [6], [7], [8], [9], [10]. Some of these studies also examined the CSF levels of hyperphosphorylated Tau (p-Tau) and β-amyloid_1-42 as markers of potentially altered protein processing in association with neuronal degeneration. The findings of such studies were similarly contradictory [7], [8], [9], [10]. Osteopontin (OPN), an inflammatory protein associated with the preferential differentiation of T helper 17 (Th17) lymphocytes, has recently gained attention as a potentially useful biomarker in the CSF of MS patients [11], [12], [13], [14]. OPN has also been implicated in neurodegeneration [15], [16]; however, its roles are not yet fully elucidated.

In the present study, our objective was to examine if the levels of Tau, p-Tau, β-amyloid_1-42 and OPN are indeed altered in the CSF of MS patients from our Caucasian population, with additional focus on whether these proteins could serve as biomarkers in reflecting the clinical severity of MS and/or predicting the progression and future clinical manifestation of the disease at its first presentation.