Page 66 - Read Online

Page 134 Chalatsa et al. Neuroimmunol Neuroinflammation 2020;7:132-40 I http://dx.doi.org/10.20517/2347-8659.2020.01
[20]
[21]
mass spectrometry , time-resolved fluorescence energy transfer , electrochemiluminescence
[22]
[23]
immunoassay and western blot . In addition, new biochemical assays that can detect α-synuclein
aggregates have emerged, such as Protein-misfolding cyclic amplification and Real-time Quaking-induced
conversion, by taking advantage the ability of α-synuclein to nucleate further aggregation [24-26] . Using
all these different methods, it is important to note that, even though there are variations in the absolute
concentrations measured, the results produced for total (or monomeric) CSF α-synuclein agree on a
reduction in α-synuclein levels in PD patients when compared with control subjects. When oligomeric or
phosphorylated α-synuclein was assessed in the CSF, both forms were found to be increased in PD patients
compared with the controls. However, it is important to note that the of ligands such as ThT may affect the
actual structure of the α-synuclein species.

Even though the above findings are consistent, the diagnostic accuracy (sensitivity and specificity)
remains unsatisfactory either for the detection of the monomeric or the modified forms of α-synuclein.
Additionally, some studies report contradictory results; some have found similar CSF α-synuclein levels
between PD patients and control subjects [27-29] , whereas others have reported increased CSF α-synuclein
levels in samples from AD [30,31] , progressive supranuclear palsy or Creutzfeldt-Jacob patients compared with
[32]
the control group .
A number of factors could explain the observed variability in the results, as well as the differences
reported in the absolute concentrations. First, the immunoassays used are based on divergent antibodies
that recognize different fragments of the protein and with variable affinity. Second, the patient cohorts
show great variability in terms of number, disease stage and clinical symptoms (affected mobility or
dementia) present at the time of CSF collection. Third, the implementation of strict standardized guidelines
concerning collection and storage protocols and allowed blood contamination have only recently started to
be followed. Furthermore, common reference materials are still missing making the interpretation of results
from assay to assay extremely difficult.

The quantification of CSF α-synuclein could aid the differential diagnosis in clinically overlapping
neurodegenerative diseases, as suggested for PD, DLB and AD [33-35] . However, it is unclear whether the
levels of CSF α-synuclein could be correlated with the severity of disease, indicating for example a more
rapid decline in motor performance or the appearance of dementia. Interestingly, recent reports have
shown that simultaneous measurement of α-synuclein levels along with other proteins, such as tau, Aβ
42
and Glucocerebrosidase 1 could be more effective in discriminating PD patients with synucleinopathies
from healthy individuals or those with other neurodegenerative diseases [30,36-38] .

Other biological fluids could also serve as promising candidates for α-synuclein detection and subsequent
PD diagnosis. The majority of reports studying plasma α-synuclein have exhibited increased levels in PD
patients [39-46] relative to control subjects, whereas other studies have reported similar [27,47,48] or decreased
[49]
plasma α-synuclein levels between PD patients and healthy participants. Interestingly, it was found
that plasma levels of phosphorylated α-synuclein were higher in the PD samples than the controls [44,50,51] .
The results obtained from plasma have been controversial, mainly due to the fact that red blood cells
are a major source of α-synuclein and the rest erythrocytes that remain in plasma can be subjected to
[52]
[47]
hemolysis markedly affecting α-synuclein values .
As erythrocytes are the major source of peripheral α-synuclein, a recent report has proposed erythrocytic
α-synuclein as a potential PD biomarker, as it was found that the total and aggregated α-synuclein levels
[53]
were significantly higher in the membrane fraction of PD patients compared to healthy controls . Saliva
α-synuclein has also been considered as a prospective biomarker, as α-synuclein pathology has been found
in submandibular salivary glands [54,55] and saliva α-synuclein could be easily accessible and poorly affected