Neuronally Derived Extracellular Vesicle α-Synuclein as a Serum Biomarker for Individuals at Risk of Developing Parkinson Disease

Abstract

IMPORTANCENonmotor symptoms of Parkinson disease (PD) often predate the movement disorder by decades. Currently, there is no blood biomarker to define this prodromal phase.OBJECTIVETo investigate whether α-synuclein in neuronally derived serum-extracellular vesicles identifies individuals at risk of developing PD and related dementia.DESIGN, SETTING, and PARTICIPANTSThis retrospective, cross-sectional multicenter study of serum samples included the Oxford Discovery, Marburg, Cologne, and Parkinson’s Progression Markers Initiative cohorts. Participants were recruited from July 2013 through August 2023 and samples were analyzed from April 2022 through September 2023. The derivation group (n = 170) included participants with isolated rapid eye movement sleep behavior disorder (iRBD) and controls. Two validation groups were used: the first (n = 122) included participants with iRBD and controls and the second (n = 263) included nonmanifest GBA1N409S gene carriers, participants with iRBD or hyposmia, and available dopamine transporter single-photon emission computed tomography, healthy controls, and patients with sporadic PD. Overall the study included 199 participants with iRBD, 20 hyposmic participants with available dopamine transporter single-photon emission computed tomography, 146 nonmanifest GBA1N409S gene carriers, 21 GBA1N409S gene carrier patients with PD, 50 patients with sporadic PD, and 140 healthy controls. In the derivation group and validation group 1, participants with polysomnographically confirmed iRBD were included. In the validation group 2, at-risk participants with available Movement Disorder Society prodromal markers and serum samples were included. Among 580 potential participants, 4 were excluded due to alternative diagnoses.EXPOSURESClinical assessments, imaging, and serum collection.MAIN OUTCOME AND MEASURESL1CAM-positive extracellular vesicles (L1EV) were immunocaptured from serum. α-Synuclein and syntenin-1 were measured by electrochemiluminescence. Area under the receiver operating characteristic (ROC) curve (AUC) with 95% CIs evaluated biomarker performance. Probable prodromal PD was determined using the updated Movement Disorder Society research criteria. Multiple linear regression models assessed the association between L1EV α-synuclein and prodromal markers.RESULTSAmong 576 participants included, the mean (SD) age was 64.30 (8.27) years, 394 were male (68.4%), and 182 were female (31.6%). A derived threshold of serum L1EV α-synuclein distinguished participants with iRBD from controls (AUC = 0.91; 95% CI, 0.86-0.96) and those with more than 80% probability of having prodromal PD from participants with less than 5% probability (AUC = 0.80; 95% CI, 0.71-0.89). Subgroup analyses revealed that specific combinations of prodromal markers were associated with increased L1EV α-synuclein levels. Across all cohorts, L1EV α-synuclein differentiated participants with more than 80% probability of having prodromal PD from current and historic healthy control populations (AUC = 0.90; 95% CI, 0.87-0.93), irrespective of initial diagnosis. L1EV α-synuclein was increased in at-risk participants with a positive cerebrospinal fluid seed amplification assay and was above the identified threshold in 80% of cases (n = 40) that phenoconverted to PD or related dementia.CONCLUSIONS AND RELEVANCEL1EV α-synuclein in combination with prodromal markers should be considered in the stratification of those at high risk of developing PD and related Lewy body diseases.

Single-Molecule Protein Analysis by Centrifugal Droplet Immuno-PCR with Magnetic Nanoparticles

“…31−33 The performance of the single-molecule immunoassay was evaluated using α-Syn, a biomarker for neurogenerative diseases. 47,60 Herein, as can be seen from Figure 4b, the limit of detection (LoD) values of 43.36 and 173.02 aM were achieved in buffer and serum, respectively. The dynamic range was determined to be ∼0.1− 1000 fM in buffer and ∼0.5−1000 fM in serum (linear correlation coefficient: > 0.99), respectively.…”

“…In our experiment, the concentration of the targeting molecules (e.g., α-Syn, to be measured) was so low that the possibility of having more than one molecule in one microdroplet (∼50 μm diameter) is negligible. Therefore, our experimental analysis can be called “single-molecule protein analysis” in such a sense. − The performance of the single-molecule immunoassay was evaluated using α-Syn, a biomarker for neurogenerative diseases. , Herein, as can be seen from Figure b, the limit of detection (LoD) values of 43.36 and 173.02 aM were achieved in buffer and serum, respectively. The dynamic range was determined to be ∼0.1–1000 fM in buffer and ∼0.5–1000 fM in serum (linear correlation coefficient: > 0.99), respectively.…”

“…Studies have suggested that serum α-Syn is a biomarker for individuals at the risk of developing PD. 47 All three subtypes (α, β, and γ) of this protein were indicated to have clinical values. 48,49 Furthermore, the phosphorylation of α-Syn was a key indicator of the pathological progression of PD.…”

“…Counting the fluorescent microdroplets led to the ultrasensitive detection of α-synuclein (α-Syn). Studies have suggested that serum α-Syn is a biomarker for individuals at the risk of developing PD . All three subtypes (α, β, and γ) of this protein were indicated to have clinical values. , Furthermore, the phosphorylation of α-Syn was a key indicator of the pathological progression of PD. , For instance, the concentration of phosphorylated α-Syn was reported to be higher in PD patients than in healthy individuals (∼756.8 vs ∼143.4 ng/mL) .…”

Exosomes: potential targets for the diagnosis and treatment of neuropsychiatric disorders

“…Instead of focusing on quantitative levels in body fluids or tissues, detection of pathological neuronal a-syn conformation was targeted in this study [ 89 ]. Recently, another research team found that AD measurements of L1EV-synuclein in combination with specific prodromal markers, such as olfactory or cognitive deficit, possible or definite rapid eye movement sleep behavior disorder (RBD), or the glucocerebrosidase (GBA1) gene status, could be used to help substratify individuals with the highest risk of developing PD and related Lewy body diseases [ 92 ]. To facilitate early diagnosis of neurodegenerative illnesses, another study developed a screening approach that can be used in combination with other recognized subjective evaluation and imaging techniques.…”