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Synucleinopathies are neurodegenerative diseases characterized by accumulation of misfolded α-synuclein (α-syn) inclusions in neuronal and/or glial cells. Different synucleinopathies may affect different brain regions and cell types. In Parkinson’s disease (PD) and dementia with Lewy bodies (DLB), α-syn deposits predominantly in neuronal Lewy bodies (LBs) and Lewy neurites (LNs), whereas in multiple system atrophy (MSA), α-syn-rich glial cytoplasmic inclusions (GCIs) are found in oligodendrocytes (1). Despite differences in the underlying pathophysiology, synucleinopathies often are misdiagnosed, especially by non-experts in the early-stages, due to the overlapping clinical symptoms (2, 3). Several studies have demonstrated the utility of measuring α-syn in neuronal EVs (nEVs) as a diagnostic biomarker for PD and atypical parkinsonian disorders (4). Recently, our group has shown that α-syn measured in both nEVs and oligodendroglial EVs (oEVs) in the same samples, and in particular the oEV:nEV α-syn concentration ratio, yielded a discriminative model distinguishing between PD and MSA with 89.8% sensitivity and 86.0% specificity and between healthy controls (HC) and MSA with 96.0% sensitivity and 84.3% specificity. In contrast, the model offered moderate separation between PD and HC – 71.4% sensitivity and 62.7% specificity (5).

Background & AimsParkinsonian disorders, such as Parkinson's disease (PD), multiple system atrophy (MSA), dementia with Lewy bodies (DLB), progressive supranuclear palsy (PSP) and corticobasal syndrome (CBS), share early motor symptoms but have distinct pathophysiology. As a result, accurate premortem diagnosis is challenging for neurologists, hindering efforts for disease‐modifying therapeutic discovery. Extracellular vesicles (EVs) contain cell‐state‐specific biomolecules and can cross the blood‐brain barrier to the peripheral circulation, providing a unique central nervous system (CNS) insight. This meta‐analysis evaluated blood‐isolated neuronal and oligodendroglial EVs (nEVs and oEVs) α‐synuclein levels in Parkinsonian disorders.MethodsFollowing PRISMA guidelines, the meta‐analysis included 13 studies. An inverse‐variance random‐effects model quantified effect size (SMD), QUADAS‐2 assessed risk of bias and publication bias was evaluated. Demographic and clinical variables were collected for meta‐regression.ResultsThe meta‐analysis included 1,565 patients with PD, 206 with MSA, 21 with DLB, 172 with PSP, 152 with CBS and 967 healthy controls (HCs). Findings suggest that combined concentrations of nEVs and oEVs α‐syn is higher in patients with PD compared to HCs (SMD = 0.21, p = 0.021), while nEVs α‐syn is lower in patients with PSP and CBS compared to patients with PD (SMD = ‐1.04, p = 0.0017) or HCs (SMD = ‐0.41, p < 0.001). Additionally, α‐syn in nEVs and/or oEVs did not significantly differ in patients with PD vs. MSA, contradicting the literature. Meta‐regressions show that demographic and clinical factors were not significant predictors of nEVs or oEVs α‐syn concentrations.ConclusionThe results highlight the need for standardized procedures and independent validations in biomarker studies and the development of improved biomarkers for distinguishing Parkinsonian disorders.

Synucleinopathies are a group of neurodegenerative diseases including Parkinson’s disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA). These diseases are characterized by the aggregation and deposition of α-synuclein (α-syn) in Lewy bodies (LBs) in PD and DLB or as glial cytoplasmic inclusions in MSA. In healthy brains, only ∼4% of α-syn is phosphorylated at Ser129 (pS129-α-syn), whereas >90% pS129-α-syn may be found in LBs, suggesting that pS129-α-syn could be a useful biomarker for synucleinopathies. However, a widely available, robust, sensitive, and reproducible method for measuring pS129-α-syn in biological fluids is currently missing. We used Meso Scale Discovery (MSD)’s electrochemiluminescence platform to create a new assay for sensitive detection of pS129-α-syn. We evaluated several combinations of capture and detection antibodies and used semisynthetic pS129-α-syn as a standard for the assay at a concentration range from 0.5 to 6.6 × 104 pg/mL. Using the antibody EP1536Y for capture and an anti-human α-syn antibody (MSD) for detection was the best combination in terms of assay sensitivity, specificity, and reproducibility. We tested the utility of the assay for the detection and quantification of pS129-α-syn in human cerebrospinal fluid, serum, plasma, saliva, and CNS-originating small extracellular vesicles, as well as in mouse brain lysates. Our data suggest that the assay can become a widely used method for detecting pS129-α-syn in biomedical studies including when only a limited volume of sample is available and high sensitivity is required, offering new opportunities for diagnostic biomarkers, monitoring disease progression, and quantifying outcome measures in clinical trials.

Extracellular vesicles (EVs), including exosomes, microvesicles, and oncosomes, are nano-sized particles enclosed by a lipid bilayer. EVs are released by virtually all eukaryotic cells and have been shown to contribute to intercellular communication by transporting proteins, lipids, and nucleic acids. In the context of neurodegenerative diseases, EVs may carry toxic, misfolded forms of amyloidogenic proteins and facilitate their spread to recipient cells in the central nervous system (CNS). CNS-originating EVs can cross the blood–brain barrier into the bloodstream and may be found in other body fluids, including saliva, tears, and urine. EVs originating in the CNS represent an attractive source of biomarkers for neurodegenerative diseases, because they contain cell- and cell state-specific biological materials. In recent years, multiple papers have reported the use of this strategy for identification and quantitation of biomarkers for neurodegenerative diseases, including Parkinson’s disease and atypical parkinsonian disorders. However, certain technical issues have yet to be standardized, such as the best surface markers for isolation of cell type-specific EVs and validating the cellular origin of the EVs. Here, we review recent research using CNS-originating EVs for biomarker studies, primarily in parkinsonian disorders, highlight technical challenges, and propose strategies for overcoming them.