Abstract

In Parkinson’s disease (PD), alpha-synuclein (a-syn) can be detected in biological fluids including saliva. Although previous studies found reduced a-syn total (a-syntotal) concentration in saliva of PD patients, no studies have previously examined salivary a-syn oligomers (a-synolig) concentrations or assessed the correlation between salivary a-syntotal, a-synolig and clinical features in a large cohort of PD patients. Is well known that a-synolig exerts a crucial neurotoxic effect in PD. We collected salivary samples from 60 PD patients and 40 age- and sex-comparable healthy subjects. PD was diagnosed according to the United Kingdom Brain Bank Criteria. Samples of saliva were analyzed by specific anti-a-syn and anti-oligomeric a-syn ELISA kits. A complete clinical evaluation of each patient was performed using MDS-Unified Parkinson's Disease Rating Scale, Beck Depression Inventory, Montreal Cognitive Assessment and Frontal Assessment Battery. Salivary a-syntotal was lower, whereas a-synolig was higher in PD patients than healthy subjects. The a-synolig/a-syntotal ratio was also higher in patients than in healthy subjects. Salivary a-syntotal concentration negatively correlated with that of a-synolig and correlated with several patients’ clinical features. In PD, decreased salivary concentration of a-syntotal may reflect the reduction of a-syn monomers (a-synmon), as well as the formation of insoluble intracellular inclusions and soluble oligomers. The combined detection of a-syntotal and a-synolig in the saliva might help the early diagnosis of PD.

Highlights

  • Alpha-synuclein (a-syn) is a 140-amino acid protein that is widely expressed in presynaptic terminals of the central nervous system and plays an important role in the pathogenesis of Parkinson’s disease (PD) [1,2]

  • The Mann-Whitney U test showed that α-synolig was significantly higher in the saliva of patients with PD than in that of healthy subjects (z = -7.82; p

  • We found that salivary a-syntotal is significantly lower in patients with PD than in healthy subjects

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Summary

Introduction

Alpha-synuclein (a-syn) is a 140-amino acid protein that is widely expressed in presynaptic terminals of the central nervous system and plays an important role in the pathogenesis of Parkinson’s disease (PD) [1,2]. PD is pathologically characterized by a-syn deposition into neurons and neuronal fibers, which leads to the formation of Lewy Bodies and Lewy Neurities [2,3]. A-syn is prevalently expressed as a monomeric form (a-synmon) [4] and is localized in the cytoplasm and in the cellular nuclei or bound to the synaptic vesicles. In PD, a-synmon aggregates into a-syn oligomers (a-synolig) and the oligomers formation, in turn, is followed by oligomers conversion into mature amyloid fibrils, leading to the formation of Lewy bodies and Lewy neurities [7,8]. Soluble a-synolig are present in larger amounts in brain homogenates of PD patients than in those of healthy subjects [9] and cause neuronal cell death [10], being the main neurotoxic form of a-syn [7,11,12]

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