Association of Misfolded α-Synuclein Derived from Neuronal Exosomes in Blood with Parkinson's Disease Diagnosis and Duration

Abstract

Background: Misfolded α-synuclein can be detected in blood samples of Parkinson's disease (PD) patients by a seed amplification assay (SAA), but the association with disease duration is not clear, yet.

Objective: In the present study we aimed to elucidate whether seeding activity of misfolded α-synuclein derived from neuronal exosomes in blood is associated with PD diagnosis and disease duration.

Methods: Cross-sectional samples of PD patients were analyzed and compared to samples of age- and gender-matched healthy controls using a blood-based SAA. Presence of α-synuclein seeding activity and differences in seeding parameters, including fluorescence response (in arbitrary units) at the end of the amplification assay (F60) were analyzed. Additionally, available PD samples collected longitudinally over 5-9 years were included.

Results: In the cross-sectional dataset, 79 of 80 PD patients (mean age 69 years, SD = 8; 56% male) and none of the healthy controls (n = 20, mean age 70 years, SD = 10; 55% male) showed seeding activity (sensitivity 98.8%). When comparing subgroups divided by disease duration, longer disease duration was associated with lower α-synuclein seeding activity (F60: p < 0.001). In the longitudinal analysis 10/11 patients showed a gradual decrease of α-synuclein seeding activity over time.

Conclusions: This study confirms the high sensitivity of the blood-based α-synuclein SAA applied here. The negative association of α-synuclein seeding activity in blood with disease duration makes this parameter potentially interesting as biomarker for future studies on the pathophysiology of disease progression in PD, and for biologically oriented trials in this field.

Keywords: Parkinson’s disease; alpha-synuclein; biomarker.

Fig. 1

α-Synuclein seeding in Parkinson’s disease cohorts (n = 79). A) α-Synuclein seeding in Parkinson’s disease cohorts with different disease duration (n = 79). The boxplots indicate the median (range) Thioflavin T signal intensity after 60 hours (in arbitrary units) of the four different Parkinson’s disease duration groups. B) Scatter diagram showing the correlation of α-synuclein seeding (Thioflavin T signal intensity after 60 hours) and disease duration in all analyzed individuals with Parkinson’s disease (n = 79). F60, Thioflavin T signal intensity after 60 hours; PD, Parkinson’s disease.

Fig. 2

Longitudinal α-synuclein seeding of individuals with Parkinson’s disease. Presentation of longitudinal values of the α-synuclein seed amplification assay in n = 11 individuals with Parkinson’s disease at three timepoints. α-Synucleins seeding is displayed as Thioflavin T signal intensity after 60 hours (F60). Each colored line represents longitudinal values of one individual with Parkinson’s disease (mean of both replicates, error bars indicate the standard deviation of both replicates). F60, Thioflavin T signal intensity after 60 hours.

Fig. 3

Examples of longitudinal seeding in Parkinson’s disease. Both boxes show individual seeding curves of one individual with Parkinson’s disease measured at three different timepoints (shown are both replicates). The x-axis displays the hours of the α-synuclein seed amplification assay, the y-axis displays the increasing Thioflavin T signal intensity. hrs, hours; ThT, Thioflavin T.