Differential Circulating Levels of Naturally Occurring Antibody to α-Synuclein in Parkinson's Disease Dementia, Alzheimer's Disease, and Vascular Dementia

Alpha-synuclein in peripheral body fluid as a biomarker for Parkinson's disease

OBJECTIVE

Whether alpha-synuclein in peripheral body fluids can be used for the diagnosis of Parkinson's disease (PD) remains in controversy. This study evaluates diagnostic potential of alpha-synuclein for PD in various peripheral body fluids using a meta-analysis approach.

METHODS

Studies published before October 2022 were searched in Web of Science and PubMed databases. The results were computed using the STATA 12.0 statistical software.

RESULTS

In plasma, PD patients exhibited elevated alpha-synuclein levels relative to healthy controls (HCs) [standard mean difference (SMD) = 0.78, 95% confidence interval (CI) = 0.42 to 1.15] with a sensitivity of 0.79 (95% CI: 0.64-0.89) and a specificity of 0.95 (95% CI: 0.90-0.98). Higher plasma alpha-synuclein levels were correlated with longer disease durations, higher Unified Parkinson's Disease Rating Scale motor scores, and higher Hoehn and Yahr stages in PD patients. Plasma neural-derived exosomal alpha-synuclein levels (SMD = 1.82, 95% CI = 0.30 to 3.35), ratio of plasma neural-derived exosomal alpha-synuclein to total alpha-synuclein (SMD = 1.26, 95% CI = 0.19 to 2.33), and erythrocytic alpha-synuclein levels were also increased in PD patients (SMD = 6.57, 95% CI = 3.55 to 9.58). In serum, there was no significant difference in alpha-synuclein levels between PD patients and HCs (SMD = 0.54, 95% CI = - 0.27 to 1.34). In saliva, reduced alpha-synuclein levels were observed in PD patients (SMD = - 0.85, 95% CI = - 1.67 to - 0.04).

CONCLUSIONS

Alpha-synuclein levels in plasma, plasma neural-derived exosome, erythrocyte, and saliva may serve as potential biomarkers for the diagnosis of PD.

Alpha-Synuclein in Peripheral Tissues as a Possible Marker for Neurological Diseases and Other Medical Conditions

The possible usefulness of alpha-synuclein (aSyn) determinations in peripheral tissues (blood cells, salivary gland biopsies, olfactory mucosa, digestive tract, skin) and in biological fluids, except for cerebrospinal fluid (serum, plasma, saliva, feces, urine), as a marker of several diseases, has been the subject of numerous publications. This narrative review summarizes data from studies trying to determine the role of total, oligomeric, and phosphorylated aSyn determinations as a marker of various diseases, especially PD and other alpha-synucleinopathies. In summary, the results of studies addressing the determinations of aSyn in its different forms in peripheral tissues (especially in platelets, skin, and digestive tract, but also salivary glands and olfactory mucosa), in combination with other potential biomarkers, could be a useful tool to discriminate PD from controls and from other causes of parkinsonisms, including synucleinopathies.

The relevance of synuclein autoantibodies as a biomarker for Parkinson's disease

Several studies have investigated if the levels of α-synuclein autoantibodies (α-syn AAb) differ in serum of Parkinson's disease (PD) patients and healthy subjects. Reproducible differences in their levels could serve as a biomarker for PD. The results of previous studies however remain inconclusive. With the largest sample size examined so far, we aimed to validate serum α-syn AAb levels as a biomarker for PD and investigated the presence of AAbs against other synucleins. We performed ELISA and immunoblots to determine synuclein AAb levels in the serum of 295 subjects comprising 157 PD patients from two independent cohorts, 46 healthy subjects, and 92 patients with other neurodegenerative disorders. Although serum α- and β-syn AAb levels were significantly reduced in patients with PD and other neurodegenerative disorders as compared to controls, the AAb levels displayed high inter-and intra-cohort variability. Furthermore, α-syn AAb levels showed no correlation to clinical parameters like age, disease duration, disease severity, and gender, that might also be directed against beta- and gamma-syn. In conclusion, serum synuclein AAb levels do allow the separation of PD from healthy subjects but not from other neurodegenerative disorders. Thus, synuclein AAbs cannot be regarded as a reliable biomarker for PD.

α-synuclein as an emerging pathophysiological biomarker of Alzheimer's disease

INTRODUCTION

α-syn aggregates represent the pathological hallmark of synucleinopathies as well as a frequent copathology (almost 1/3 of cases) in AD. Recent research indicates a potential role of α-syn species, measured in CSF with conventional analytical techniques, in the differential diagnosis between AD and synucleinopathies (such as DLB). Pioneering studies report the detection of α-syn in blood, however, conclusive investigations are controversial. Ultrasensitive seed amplification techniques, enabling the selective quantification of α-syn seeds, may represent an effective solution to identify the α-syn component in AD and facilitate a biomarker-guided stratification.

AREAS COVERED

We performed a PubMed-based review of the latest findings on α-syn-related biomarkers for AD, focusing on bodily fluids. A dissertation on the role of ultrasensitive seed amplification assays, detecting α-syn seeds from different biological samples, was conducted.

EXPERT OPINION

α-syn may contribute to progressive AD neurodegeneration through cross-seeding especially with tau protein. Ultrasensitive seed amplification techniques may support a biomarker-drug co-development pathway and may be a pathophysiological candidate biomarker for the evolving ATX(N) system to classify AD and the spectrum of primary NDDs. This would contribute to a precise approach to AD, aimed at implementing disease-modifying treatments.

Potential Protein Blood-Based Biomarkers in Different Types of Dementia: A Therapeutic Overview

Abstract:

Biomarkers capable of identifying and distinguishing types of dementia such as Alzheimer's disease (AD), Parkinson's disease dementia (PDD), Lewy body dementia (LBD), and frontotemporal dementia (FTD) have been become increasingly relentless. Studies of possible biomarker proteins in the blood that can help formulate new diagnostic proposals and therapeutic visions of different types of dementia are needed. However, due to several limitations of these biomarkers, especially in discerning dementia, their clinical applications are still undetermined. Thus, the updating of biomarker blood proteins that can help in the diagnosis and discrimination of these main dementia conditions is essential to enable new pharmacological and clinical management strategies, with specificities for each type of dementia. To review the literature concerning protein blood-based AD and non-AD biomarkers as new pharmacological targets and/or therapeutic strategies. Recent findings for protein-based AD, PDD, LBD, and FTD biomarkers are focused on in this review. Protein biomarkers were classified according to the pathophysiology of the dementia types. The diagnosis and distinction of dementia through protein biomarkers is still a challenge. The lack of exclusive biomarkers for each type of dementia highlights the need for further studies in this field. Only after this, blood biomarkers may have a valid use in clinical practice as they are promising to help in diagnosis and in the differentiation of diseases.

The Association Between Plasma α-Synuclein (α-syn) Protein, Urinary Alzheimer-Associated Neuronal Thread Protein (AD7c-NTP), and Apolipoprotein Epsilon 4 (ApoE ε4) Alleles and Cognitive Decline in 60 Patients with Alzheimer's Disease Compared with 28 Age-Matched Normal Individuals

Background

Accumulating evidence has shown that α-synuclein (α-syn) pathology is involved in the pathophysiology of Alzheimer’s disease (AD). This study aimed to investigate the association between the levels of plasma α-syn protein, urinary Alzheimer-associated neuronal thread protein (AD7c-NTP), apolipoprotein epsilon 4 (ApoE ɛ4) alleles and cognitive decline in 60 AD patients compared with 28 age-matched normal controls (NCs) at a single center.

Material/Methods

All participants underwent α-syn, apolipoprotein E (ApoE), AD7c-NTP, cholesterol (CHO), high-density lipoprotein (HDL), low-density lipoprotein (LDL) and triglycerides (TGs) analyses, neuropsychological scale assessments and neuroimaging analysis. Moreover, urine and peripheral blood samples were collected from all participants. The levels of plasma α-syn and AD7c-NTP were assayed using an enzyme-linked immunosorbent assay (ELISA) kit. Other test results were obtained from China-Japan Friendship Hospital.

Results

We found that plasma α-syn levels were significantly different between AD patients and NCs (p=0.045). α-Syn levels were also associated with AD7c-NTP (r=0.231, p=0.03) but not ApoE ɛ4 (Z=−0.147, p=0.883) levels. Neither α-syn [CHO (p=0.432), HDL (p=0.484), LDL (p=0.733) or TGs (p=0.253)] nor AD7c-NTP [CHO (p=0.867), HDL (p=0.13), LDL (p=0.57) or TGs (p=0.678)] had a relationship with lipids.

Conclusions

This study showed that the levels of plasma α-syn protein and urinary AD7c-NTP were significantly increased in AD patients compared with NCs, but not with ApoE alleles or serum lipid levels.