Are We Ready for Detecting α-Synuclein Prone to Aggregation in Patients? The Case of "Protein-Misfolding Cyclic Amplification" and "Real-Time Quaking-Induced Conversion" as Diagnostic Tools

High-Yield α-Synuclein Purification and Ionic Strength Modification Pivotal to Seed Amplification Assay Performance and Reproducibility

Alpha-synuclein seed amplification assays (αSyn-SAAs) have emerged as promising diagnostic tools for Parkinson's disease (PD) by detecting misfolded αSyn and amplifying the signal through cyclic shaking and resting in vitro. Recently, our group and others have shown that multiple biospecimens, including CSF, skin, and submandibular glands (SMGs), can be used to seed the aggregation reaction and robustly distinguish between patients with PD and non-disease controls. The ultrasensitivity of the assay affords the ability to detect minute quantities of αSyn in peripheral tissues, but it also produces various technical challenges of variability. To address the problem of variability, we present a high-yield αSyn protein purification protocol for the efficient production of monomers with a low propensity for self-aggregation. We expressed wild-type αSyn in BL21 Escherichia coli, lysed the cells using osmotic shock, and isolated αSyn using acid precipitation and fast protein liquid chromatography (FPLC). Following purification, we optimized the ionic strength of the reaction buffer to distinguish the fluorescence maximum (Fmax) separation between disease and healthy control tissues for enhanced assay performance. Our protein purification protocol yielded high quantities of αSyn (average: 68.7 mg/mL per 1 L of culture) and showed highly precise and robust αSyn-SAA results using brain, skin, and SMGs with inter-lab validation.

An α-helical peptide-based plasmonic biosensor for highly specific detection of α-synuclein toxic oligomers

BACKGROUND

α-Synuclein (αS) aggregation is the main neurological hallmark of a group of neurodegenerative disorders, collectively referred to as synucleinopathies, of which Parkinson's disease (PD) is the most prevalent. αS oligomers are elevated in the cerebrospinal fluid (CSF) of PD patients, standing as a biomarker for disease diagnosis. However, methods for early PD detection are still lacking. We have recently identified the amphipathic 22-residue peptide PSMα3 as a high-affinity binder of αS toxic oligomers. PSMα3 displayed excellent selectivity and reproducibility, binding to αS toxic oligomers with affinities in the low nanomolar range and without detectable cross-reactivity with functional monomeric αS.

RESULTS

In this work, we leveraged these PSMα3 unique properties to design a plasmonic-based biosensor for the direct detection of toxic oligomers under label-free conditions.

SIGNIFICANCE AND NOVELTY

We describe the integration of the peptide in a lab-on-a-chip plasmonic platform suitable for point-of-care measurements of αS toxic oligomers in CSF samples in real-time and at an affordable cost, providing an innovative biosensor for PD early diagnosis in the clinic.

Tau- and α-synuclein-targeted gold nanoparticles: applications, opportunities, and future outlooks in the diagnosis and therapy of neurodegenerative diseases

The use of nanomaterials in medicine offers multiple opportunities to address neurodegenerative disorders such as Alzheimer's and Parkinson's disease. These diseases are a significant burden for society and the health system, affecting millions of people worldwide without sensitive and selective diagnostic methodologies or effective treatments to stop their progression. In this sense, the use of gold nanoparticles is a promising tool due to their unique properties at the nanometric level. They can be functionalized with specific molecules to selectively target pathological proteins such as Tau and α-synuclein for Alzheimer's and Parkinson's disease, respectively. Additionally, these proteins are used as diagnostic biomarkers, wherein gold nanoparticles play a key role in enhancing their signal, even at the low concentrations present in biological samples such as blood or cerebrospinal fluid, thus enabling an early and accurate diagnosis. On the other hand, gold nanoparticles act as drug delivery platforms, bringing therapeutic agents directly into the brain, improving treatment efficiency and precision, and reducing side effects in healthy tissues. However, despite the exciting potential of gold nanoparticles, it is crucial to address the challenges and issues associated with their use in the medical field before they can be widely applied in clinical settings. It is critical to ensure the safety and biocompatibility of these nanomaterials in the context of the central nervous system. Therefore, rigorous preclinical and clinical studies are needed to assess the efficacy and feasibility of these strategies in patients. Since there is scarce and sometimes contradictory literature about their use in this context, the main aim of this review is to discuss and analyze the current state-of-the-art of gold nanoparticles in relation to delivery, diagnosis, and therapy for Alzheimer's and Parkinson's disease, as well as recent research about their use in preclinical, clinical, and emerging research areas.

Wake and non-rapid eye movement sleep dysfunction is associated with colonic neuropathology in Parkinson's disease

STUDY OBJECTIVES

The body-first Parkinson's disease (PD) hypothesis suggests initial gut Lewy body pathology initially propagates to the pons before reaching the substantia nigra, and subsequently progresses to the diencephalic and cortical levels, a disease course presumed to likely occur in PD with rapid eye movement sleep behavior disorder (RBD). We aimed to explore the potential association between colonic phosphorylated alpha-synuclein histopathology (PASH) and diencephalic or cortical dysfunction evidenced by non-rapid eye movement (NREM) sleep and wakefulness polysomnographic markers.

METHODS

In a study involving 43 patients with PD who underwent clinical examination, rectosigmoidoscopy, and polysomnography, we detected PASH on colonic biopsies using whole-mount immunostaining. We performed a visual semi-quantitative analysis of NREM sleep and wake electroencephalography (EEG), confirmed it with automated quantification of spindle and slow wave features of NREM sleep, and the wake dominant frequency, and then determined probable Arizona PD stage classifications based on sleep and wake EEG features.

RESULTS

The visual analysis aligned with the automated quantified spindle characteristics and the wake dominant frequency. Altered NREM sleep and wake parameters correlated with markers of PD severity, colonic PASH, and RBD diagnosis. Colonic PASH frequency also increased in parallel to probable Arizona PD stage classifications.

CONCLUSIONS

Colonic PASH is strongly associated with widespread brain sleep and wake dysfunction, suggesting an extensive diffusion of the pathologic process in PD. Visual and automated analyses of polysomnography signals provide useful markers to gauge covert brain dysfunction in PD.

CLINICAL TRIAL

Name: SYNAPark, URL: https://clinicaltrials.gov/study/NCT01748409, registration: NCT01748409.

The Spreading and Effects of Human Recombinant α-Synuclein Preformed Fibrils in the Cerebrospinal Fluid of Mice

Parkinson's disease (PD) patients harbor seeding-competent α-synuclein (α-syn) in their cerebrospinal fluid (CSF), which is mainly produced by the choroid plexus (ChP). Nonetheless, little is known about the role of the CSF and the ChP in PD pathogenesis. To address this question, we used an intracerebroventricular (icv) injection mouse model to assess CSF α-syn spreading and its short- and long-term consequences on the brain. Hereby, we made use of seeding-competent, recombinant α-syn preformed fibrils (PFF) that are known to induce aggregation and subsequent spreading of endogenous α-syn in stereotactic tissue injection models. Here, we show that icv-injected PFF, but not monomers (Mono), are rapidly removed from the CSF by interaction with the ChP. Additionally, shortly after icv injection both Mono and PFF were detected in the olfactory bulb and striatum. This spreading was associated with increased inflammation and complement activation in these tissues as well as leakage of the blood-CSF barrier. Despite these effects, a single icv injection of PFF didn't induce a decline in motor function. In contrast, daily icv injections over the course of 5 days resulted in deteriorated grip strength and formation of phosphorylated α-syn inclusions in the brain 2 months later, whereas dopaminergic neuron levels were not affected. These results point toward an important clearance function of the CSF and the ChP, which could mediate removal of PFF from the brain, whereby chronic exposure to PFF in the CSF may negatively impact blood-CSF barrier functionality and PD pathology.

Toward the quantification of α-synuclein aggregates with digital seed amplification assays

The quantification and characterization of aggregated α-synuclein in clinical samples offer immense potential toward diagnosing, treating, and better understanding neurodegenerative synucleinopathies. Here, we developed digital seed amplification assays to detect single α-synuclein aggregates by partitioning the reaction into microcompartments. Using pre-formed α-synuclein fibrils as reaction seeds, we measured aggregate concentrations as low as 4 pg/mL. To improve our sensitivity, we captured aggregates on antibody-coated magnetic beads before running the amplification reaction. By first characterizing the pre-formed fibrils with transmission electron microscopy and size exclusion chromatography, we determined the specific aggregates targeted by each assay platform. Using brain tissue and cerebrospinal fluid samples collected from patients with Parkinson's Disease and multiple system atrophy, we demonstrated that the assay can detect endogenous pathological α-synuclein aggregates. Furthermore, as another application for these assays, we studied the inhibition of α-synuclein aggregation in the presence of small-molecule inhibitors and used a custom image analysis pipeline to quantify changes in aggregate growth and filament morphology.

Protease-Sensitive and -Resistant Forms of Human and Murine Alpha-Synucleins in Distinct Brain Regions of Transgenic Mice (M83) Expressing the Human Mutated A53T Protein

Human neurodegenerative diseases associated with the misfolding of the alpha-synuclein (aS) protein (synucleinopathies) are similar to prion diseases to the extent that lesions are spread by similar molecular mechanisms. In a transgenic mouse model (M83) overexpressing a mutated (A53T) form of human aS, we had previously found that Protein Misfolding Cyclic Amplification (PMCA) triggered the aggregation of aS, which is associated with a high resistance to the proteinase K (PK) digestion of both human and murine aS, a major hallmark of the disease-associated prion protein. In addition, PMCA was also able to trigger the aggregation of murine aS in C57Bl/6 mouse brains after seeding with sick M83 mouse brains. Here, we show that intracerebral inoculations of M83 mice with C57Bl/6-PMCA samples strikingly shortens the incubation period before the typical paralysis that develops in this transgenic model, demonstrating the pathogenicity of PMCA-aggregated murine aS. In the hind brain regions of these sick M83 mice containing lesions with an accumulation of aS phosphorylated at serine 129, aS also showed a high PK resistance in the N-terminal part of the protein. In contrast to M83 mice, old APPxM83 mice co-expressing human mutated amyloid precursor and presenilin 1 proteins were seen to have an aggregation of aS, especially in the cerebral cortex, hippocampus and striatum, which also contained the highest load of aS phosphorylated at serine 129. This was proven by three techniques: a Western blot analysis of PK-resistant aS; an ELISA detection of aS aggregates; or the identification of aggregates of aS using immunohistochemical analyses of cytoplasmic/neuritic aS deposits. The results obtained with the D37A6 antibody suggest a higher involvement of murine aS in APPxM83 mice than in M83 mice. Our study used novel tools for the molecular study of synucleinopathies, which highlight similarities with the molecular mechanisms involved in prion diseases.

Wake and non-rapid eye movement sleep dysfunction is associated with colonic neuropathology in Parkinson's disease

Study Objectives

The body-first Parkinson's disease (PD) hypothesis suggests initial gut Lewy body pathology that propagates to the pons before reaching the substantia nigra, and subsequently progresses to the diencephalic and cortical levels. This disease course may also be the most likely in PD with rapid eye movement sleep behavior disorder (RBD).

Objectives

We aimed to explore the potential association between colonic phosphorylated alpha-synuclein histopathology (PASH) and diencephalic or cortical dysfunction evidenced by non-rapid eye movement (NREM) sleep and wakefulness polysomnographic markers.

Methods

In a study involving 43 patients with PD who underwent clinical examination, rectosigmoidoscopy, and polysomnography, we detected PASH on colonic biopsies using whole-mount immunostaining. We performed a visual semi-quantitative and automated quantification of spindle and slow wave features of NREM sleep, and the wake dominant frequency, and then determined Braak and Arizona stage classifications for PD severity based on sleep and wake electroencephalographic features.

Results

The visual analysis aligned with the automated quantified spindle characteristics and the wake dominant frequency. Altered NREM sleep and wake parameters correlated with markers of PD severity, colonic PASH, and RBD diagnosis. Colonic PASH frequency also increased in parallel to presumed PD Braak and Arizona stage classifications.

Conclusions

Colonic PASH in PD is strongly associated with widespread brain sleep and wake dysfunction, pointing toward likely extensive diffusion of the pathological process in the presumptive body-first PD phenotype. Visual and automated analyses of polysomnography signals provide useful markers to gauge covert brain dysfunction in PD.

Statement of Significance

The presence of gut synucleinopathy in Parkinson's disease can be linked to the body-first hypothesis in its pathophysiology. This study, performed in a cohort of 43 patients with Parkinson's disease that underwent clinical assessment, rectosigmoidoscopy and polysomnography, provides evidence that colonic neuropathology in Parkinson's disease is associated with widespread brain dysfunction, as evaluated by wake and non-rapid eye movement sleep polysomnographic markers. Our results support the assumption of an extensive diffusion of the pathological process to diencephalic and neocortical structures in the presumptive body-first phenotype. They also suggest the use of routine polysomnography in phenotyping patients with Parkinson's disease. Future studies should investigate the brain diffusion pattern and its sleep markers in the hypothesized brain-first phenotype of Parkinson's disease.

Extracellular Vesicles for the Diagnosis of Parkinson's Disease: Systematic Review and Meta-Analysis

Parkinson's disease (PD) biomarkers are needed by both clinicians and researchers (for diagnosis, identifying study populations, and monitoring therapeutic response). Imaging, genetic, and biochemical biomarkers have been widely studied. In recent years, extracellular vesicles (EVs) have become a promising material for biomarker development. Proteins and molecular material from any organ, including the central nervous system, can be packed into EVs and transported to the periphery into easily obtainable biological specimens like blood, urine, and saliva. We performed a systematic review and meta-analysis of articles (published before November 15, 2022) reporting biomarker assessment in EVs in PD patients and healthy controls (HCs). Biomarkers were analyzed using random effects meta-analysis and the calculated standardized mean difference (Std.MD). Several proteins and ribonucleic acids have been identified in EVs in PD patients, but only α-synuclein (aSyn) and leucine-rich repeat kinase 2 (LRRK2) were reported in sufficient studies (n = 24 and 6, respectively) to perform a meta-analysis. EV aSyn was significantly increased in neuronal L1 cell adhesion molecule (L1CAM)-positive blood EVs in PD patients compared to HCs (Std.MD = 1.84, 95% confidence interval = 0.76-2.93, P = 0.0009). Further analysis of the biological sample and EV isolation method indicated that L1CAM-IP (immunoprecipitation) directly from plasma was the best isolation method for assessing aSyn in PD patients. Upcoming neuroprotective clinical trials immediately need peripheral biomarkers for identifying individuals at risk of developing PD. Overall, the improved sensitivity of assays means they can identify biomarkers in blood that reflect changes in the brain. CNS-derived EVs in blood will likely play a major role in biomarker development in the coming years. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

α-Synuclein Strains and Their Relevance to Parkinson's Disease, Multiple System Atrophy, and Dementia with Lewy Bodies

Like many neurodegenerative diseases, Parkinson's disease (PD) is characterized by the formation of proteinaceous aggregates in brain cells. In PD, those proteinaceous aggregates are formed by the α-synuclein (αSyn) and are considered the trademark of this neurodegenerative disease. In addition to PD, αSyn pathological aggregation is also detected in atypical Parkinsonism, including Dementia with Lewy Bodies (DLB), Multiple System Atrophy (MSA), as well as neurodegeneration with brain iron accumulation, some cases of traumatic brain injuries, and variants of Alzheimer's disease. Collectively, these (and other) disorders are referred to as synucleinopathies, highlighting the relation between disease type and protein misfolding/aggregation. Despite these pathological relationships, however, synucleinopathies cover a wide range of pathologies, present with a multiplicity of symptoms, and arise from dysfunctions in different neuroanatomical regions and cell populations. Strikingly, αSyn deposition occurs in different types of cells, with oligodendrocytes being mainly affected in MSA, while aggregates are found in neurons in PD. If multiple factors contribute to the development of a pathology, especially in the cases of slow-developing neurodegenerative disorders, the common presence of αSyn aggregation, as both a marker and potential driver of disease, is puzzling. In this review, we will focus on comparing PD, DLB, and MSA, from symptomatology to molecular description, highlighting the role and contribution of αSyn aggregates in each disorder. We will particularly present recent evidence for the involvement of conformational strains of αSyn aggregates and discuss the reciprocal relationship between αSyn strains and the cellular milieu. Moreover, we will highlight the need for effective methodologies for the strainotyping of aggregates to ameliorate diagnosing capabilities and therapeutic treatments.

Alpha-synuclein in skin as a high-quality biomarker for Parkinson's disease

Parkinson's disease (PD), the most common neurological motor system disorder, which characterised by the irreversible loss of dopaminergic neurones in the substantia nigra pars compacta, and leads to the deficiency of dopamine in the striatum. Deposited Lewy bodies (LBs) in diseased neurones and nerve terminals are the pathological hallmark of PD, and alpha-synuclein (α-Syn) is the most prominent protein in LBs. The tight association between α-Syn and the molecular pathology of PD has generatly increaed the interest in using the α-Syn species as biomarkers to diagnose early PD. α-Syn is not confined to the central nervous system, it is also present in the peripheral tissues, such as human skin. The assessment of skin α-Syn has the potential to be a diagnostic method that not only has excellent sensitivity, specificity, and reproducibility, but also convenient and acceptable to patients. In this review, we (i) integrate the biochemical, aggregation and structural features of α-Syn; (ii) map the distribution of the α-Syn species present in the brain, biological fluids, and peripheral tissues; and (iii) present a critical and comparative analysis of previous studies that have measured α-Syn in the skin. Finally, we provide an outlook on the future of skin biopsy as a diagnostic approach for PD, and highlight its potential implications for clinical trials, clinical decision-making, treatment strategies as well as the development of new therapies.

Cerebrospinal fluid lipoproteins inhibit α-synuclein aggregation by interacting with oligomeric species in seed amplification assays

BACKGROUND

Aggregation of α-synuclein (α-syn) is a prominent feature of Parkinson's disease (PD) and other synucleinopathies. Currently, α-syn seed amplification assays (SAAs) using cerebrospinal fluid (CSF) represent the most promising diagnostic tools for synucleinopathies. However, CSF itself contains several compounds that can modulate the aggregation of α-syn in a patient-dependent manner, potentially undermining unoptimized α-syn SAAs and preventing seed quantification.

METHODS

In this study, we characterized the inhibitory effect of CSF milieu on detection of α-syn aggregates by means of CSF fractionation, mass spectrometry, immunoassays, transmission electron microscopy, solution nuclear magnetic resonance spectroscopy, a highly accurate and standardized diagnostic SAA, and different in vitro aggregation conditions to evaluate spontaneous aggregation of α-syn.

RESULTS

We found the high-molecular weight fraction of CSF (> 100,000 Da) to be highly inhibitory on α-syn aggregation and identified lipoproteins to be the main drivers of this effect. Direct interaction between lipoproteins and monomeric α-syn was not detected by solution nuclear magnetic resonance spectroscopy, on the other hand we observed lipoprotein-α-syn complexes by transmission electron microscopy. These observations are compatible with hypothesizing an interaction between lipoproteins and oligomeric/proto-fibrillary α-syn intermediates. We observed significantly slower amplification of α-syn seeds in PD CSF when lipoproteins were added to the reaction mix of diagnostic SAA. Additionally, we observed a decreased inhibition capacity of CSF on α-syn aggregation after immunodepleting ApoA1 and ApoE. Finally, we observed that CSF ApoA1 and ApoE levels significantly correlated with SAA kinetic parameters in n = 31 SAA-negative control CSF samples spiked with preformed α-syn aggregates.

CONCLUSIONS

Our results describe a novel interaction between lipoproteins and α-syn aggregates that inhibits the formation of α-syn fibrils and could have relevant implications. Indeed, the donor-specific inhibition of CSF on α-syn aggregation explains the lack of quantitative results from analysis of SAA-derived kinetic parameters to date. Furthermore, our data show that lipoproteins are the main inhibitory components of CSF, suggesting that lipoprotein concentration measurements could be incorporated into data analysis models to eliminate the confounding effects of CSF milieu on α-syn quantification efforts.

Alzheimer's disease: a scoping review of biomarker research and development for effective disease diagnosis

INTRODUCTION

Alzheimer's disease (AD) is regarded as the foremost reason for neurodegeneration that prominently affects the geriatric population. Characterized by extracellular accumulation of amyloid-beta (Aβ), intracellular aggregation of hyperphosphorylated tau (p-tau), and neuronal degeneration that causes impairment of memory and cognition. Amyloid/tau/neurodegeneration (ATN) classification is utilized for research purposes and involves amyloid, tau, and neuronal injury staging through MRI, PET scanning, and CSF protein concentration estimations. CSF sampling is invasive, and MRI and PET scanning requires sophisticated radiological facilities which limit its widespread diagnostic use. ATN classification lacks effectiveness in preclinical AD.

AREAS COVERED

This publication intends to collate and review the existing biomarker profile and the current research and development of a new arsenal of biomarkers for AD pathology from different biological samples, microRNA (miRNA), proteomics, metabolomics, artificial intelligence, and machine learning for AD screening, diagnosis, prognosis, and monitoring of AD treatments.

EXPERT OPINION

It is an accepted observation that AD-related pathological changes occur over a long period of time before the first symptoms are observed providing ample opportunity for detection of biological alterations in various biological samples that can aid in early diagnosis and modify treatment outcomes.

Supersaturation-Dependent Formation of Amyloid Fibrils

The supersaturation of a solution refers to a non-equilibrium phase in which the solution is trapped in a soluble state, even though the solute’s concentration is greater than its thermodynamic solubility. Upon breaking supersaturation, crystals form and the concentration of the solute decreases to its thermodynamic solubility. Soon after the discovery of the prion phenomena, it was recognized that prion disease transmission and propagation share some similarities with the process of crystallization. Subsequent studies exploring the structural and functional association between amyloid fibrils and amyloidoses solidified this paradigm. However, recent studies have not necessarily focused on supersaturation, possibly because of marked advancements in structural studies clarifying the atomic structures of amyloid fibrils. On the other hand, there is increasing evidence that supersaturation plays a critical role in the formation of amyloid fibrils and the onset of amyloidosis. Here, we review the recent evidence that supersaturation plays a role in linking unfolding/folding and amyloid fibril formation. We also introduce the HANABI (HANdai Amyloid Burst Inducer) system, which enables high-throughput analysis of amyloid fibril formation by the ultrasonication-triggered breakdown of supersaturation. In addition to structural studies, studies based on solubility and supersaturation are essential both to developing a comprehensive understanding of amyloid fibrils and their roles in amyloidosis, and to developing therapeutic strategies.

Charge detection mass spectrometry on human-amplified fibrils from different synucleinopathies

Amyloid fibrils are self-assembled mesoscopic protein aggregates, which can accumulate to form deposits or plaques in the brain. In vitro amplification of fibrils can be achieved with real-time quaking-induced conversion (RT-QuIC). However, this emerging technique would benefit from a complementary method to assess structural properties of the amplification products. This work demonstrates the feasibility of nanospray-charge-detection-mass-spectrometry (CDMS) performed on α-synuclein (αSyn) fibrils amplified from human brains with Parkinson's disease (PD) or Dementia with Lewy bodies (DLB) and its synergistic combination with RT-QuIC.

Alpha-Synuclein Aggregation Pathway in Parkinson's Disease: Current Status and Novel Therapeutic Approaches

Following Alzheimer’s, Parkinson’s disease (PD) is the second-most common neurodegenerative disorder, sharing an unclear pathophysiology, a multifactorial profile, and massive social costs worldwide. Despite this, no disease-modifying therapy is available. PD is tightly associated with α-synuclein (α-Syn) deposits, which become organised into insoluble, amyloid fibrils. As a typical intrinsically disordered protein, α-Syn adopts a monomeric, random coil conformation in an aqueous solution, while its interaction with lipid membranes drives the transition of the molecule part into an α-helical structure. The central unstructured region of α-Syn is involved in fibril formation by converting to well-defined, β-sheet rich secondary structures. Presently, most therapeutic strategies against PD are focused on designing small molecules, peptides, and peptidomimetics that can directly target α-Syn and its aggregation pathway. Other approaches include gene silencing, cell transplantation, stimulation of intracellular clearance with autophagy promoters, and degradation pathways based on immunotherapy of amyloid fibrils. In the present review, we sum marise the current advances related to α-Syn aggregation/neurotoxicity. These findings present a valuable arsenal for the further development of efficient, nontoxic, and non-invasive therapeutic protocols for disease-modifying therapy that tackles disease onset and progression in the future.

Proteomics Challenges for the Assessment of Synuclein Proteoforms as Clinical Biomarkers in Parkinson’s Disease

Parkinson’s disease is a complex neurodegenerative disorder resulting in a multifaceted clinical presentation which includes bradykinesia combined with either rest tremor, rigidity, or both, as well as many non-motor symptoms. The motor features of the disorder are associated with the pathological form of alpha synuclein aggregates and fibrils in Lewy bodies and loss of dopaminergic neurons in the substantia nigra. Parkinson’s disease is increasingly considered as a group of underlying disorders with unique genetic, biological, and molecular abnormalities that are likely to respond differentially to a given therapeutic approach. For this reason, it is clinically challenging to treat and at present, no therapy can slow down or arrest the progression of Parkinson’s disease. There is a clear unmet clinical need to develop reliable diagnostic and prognostic biomarkers. When disease-modifying treatments become available, prognostic biomarkers are required to support a definitive diagnosis and clinical intervention during the long prodromal period as no clinical implications or symptoms are observed. Robust diagnostic biomarkers would also be useful to monitor treatment response. Potential biomarkers for the sporadic form of Parkinson’s disease have mostly included synuclein species (monomer, oligomer, phosphorylated, Lewy Body enriched fraction and isoforms). In this review, we consider the analysis of synuclein and its proteoforms in biological samples using proteomics techniques (immunoassay and mass spectrometry) applied to neurodegenerative disease research.

Fluid Biomarkers in Alzheimer’s Disease and Other Neurodegenerative Disorders: Toward Integrative Diagnostic Frameworks and Tailored Treatments

The diagnosis of neurodegenerative diseases (NDDs) represents an increasing social burden, with the unsolved issue of disease-modifying therapies (DMTs). The failure of clinical trials treating Alzheimer′s Disease (AD) so far highlighted the need for a different approach in drug design and patient selection. Identifying subjects in the prodromal or early symptomatic phase is critical to slow down neurodegeneration, but the implementation of screening programs with this aim will have an ethical and social aftermath. Novel minimally invasive candidate biomarkers (derived from blood, saliva, olfactory brush) or classical cerebrospinal fluid (CSF) biomarkers have been developed in research settings to stratify patients with NDDs. Misfolded protein accumulation, neuroinflammation, and synaptic loss are the pathophysiological hallmarks detected by these biomarkers to refine diagnosis, prognosis, and target engagement of drugs in clinical trials. We reviewed fluid biomarkers of NDDs, considering their potential role as screening, diagnostic, or prognostic tool, and their present-day use in clinical trials (phase II and III). A special focus will be dedicated to novel techniques for the detection of misfolded proteins. Eventually, an applicative diagnostic algorithm will be proposed to translate the research data in clinical practice and select prodromal or early patients to be enrolled in the appropriate DMTs trials for NDDs.

Production of Recombinant Alpha-Synuclein: Still No Standardized Protocol in Sight

Synucleinopathies are a group of neurodegenerative diseases, characterized by the abnormal accumulation of the protein alpha-synuclein (aSyn). aSyn is an intrinsically disordered protein that can adopt different aggregation states, some of which may be associated with disease. Therefore, understanding the transitions between such aggregation states may be essential for deciphering the molecular underpinnings underlying synucleinopathies. Recombinant aSyn is routinely produced and purified from E. coli in many laboratories, and in vitro preparations of aSyn aggregated species became central for modeling neurodegeneration in cell and animal models. Thus, reproducibility and reliability of such studies largely depends on the purity and homogeneity of aSyn preparations across batches and between laboratories. A variety of different methods are in use to produce and purify aSyn, which we review in this commentary. We also show how extraction buffer composition can affect aSyn aggregation, emphasizing the importance of standardizing protocols to ensure reproducibility between different laboratories and studies, which are essential for advancing the field.

Alpha and Beta Synucleins: From Pathophysiology to Clinical Application as Biomarkers

The synuclein family includes three neuronal proteins, named α‐synuclein, β‐synuclein, and γ‐synuclein, that have peculiar structural features. α‐synuclein is largely known for being a key protein in the pathophysiology of Parkinson's disease (PD) and other synucleinopathies, namely, dementia with Lewy bodies and multisystem atrophy. The role of β‐synuclein and γ‐synuclein is less well understood in terms of physiological functions and potential contribution to human diseases. α‐synuclein has been investigated extensively in both cerebrospinal fluid (CSF) and blood as a potential biomarker for synucleinopathies. Recently, great attention has been also paid to β‐synuclein, whose CSF and blood levels seem to reflect synaptic damage and neurodegeneration independent of the presence of synucleinopathy. In this review, we aim to provide an overview on the pathophysiological roles of the synucleins. Because γ‐synuclein has been poorly investigated in the field of synucleinopathy and its pathophysiological roles are far from being clear, we focus on the interactions between α‐synuclein and β‐synuclein in PD. We also discuss the role of α‐synuclein and β‐synuclein as potential biomarkers to improve the diagnostic characterization of synucleinopathies, thus highlighting their potential application in clinical trials for disease‐modifying therapies. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society

Neurodegenerative Disorders of Alzheimer, Parkinsonism, Amyotrophic Lateral Sclerosis and Multiple Sclerosis: An Early Diagnostic Approach for Precision Treatment

Neurodegenerative diseases (NDs) are characterised by progressive dysfunction of synapses, neurons, glial cells and their networks. Neurodegenerative diseases can be classified according to primary clinical features (e.g., dementia, parkinsonism, or motor neuron disease), anatomic distribution of neurodegeneration (e.g., frontotemporal degenerations, extrapyramidal disorders, or spinocerebellar degenerations), or principal molecular abnormalities. The most common neurodegenerative disorders are amyloidosis, tauopathies, a-synucleinopathy, and TAR DNA-binding protein 43 (TDP-43) proteopathy. The protein abnormalities in these disorders have abnormal conformational properties along with altered cellular mechanisms, and they exhibit motor deficit, mitochondrial malfunction, dysfunctions in autophagic-lysosomal pathways, synaptic toxicity, and more emerging mechanisms such as the roles of stress granule pathways and liquid-phase transitions. Finally, for each ND, microglial cells have been reported to be implicated in neurodegeneration, in particular, because the microglial responses can shift from neuroprotective to a deleterious role. Growing experimental evidence suggests that abnormal protein conformers act as seed material for oligomerization, spreading from cell to cell through anatomically connected neuronal pathways, which may in part explain the specific anatomical patterns observed in brain autopsy sample. In this review, we mention the human pathology of select neurodegenerative disorders, focusing on how neurodegenerative disorders (i.e., Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and multiple sclerosis) represent a great healthcare problem worldwide and are becoming prevalent because of the increasing aged population. Despite many studies have focused on their etiopathology, the exact cause of these diseases is still largely unknown and until now with the only available option of symptomatic treatments. In this review, we aim to report the systematic and clinically correlated potential biomarker candidates. Although future studies are necessary for their use in early detection and progression in humans affected by NDs, the promising results obtained by several groups leads us to this idea that biomarkers could be used to design a potential therapeutic approach and preclinical clinical trials for the treatments of NDs.

OUP accepted manuscript

To date, no reliable clinically applicable biomarker has been established for Parkinson's disease. Our results indicate that a long anticipated blood test for Parkinson's disease may be realized. Following the isolation of neuron-derived extracellular vesicles of Parkinson's disease patients and non-Parkinson's disease individuals, immunoblot analyses were performed to detect extracellular vesicle-derived α-synuclein. Pathological α-synuclein forms derived from neuronal extracellular vesicles could be detected under native conditions and were significantly increased in all individuals with Parkinson's disease and clearly distinguished disease from the non-disease state. By performing an α-synuclein seeding assay these soluble conformers could be amplified and seeding of pathological protein folding was demonstrated. Amplified α-synuclein conformers exhibited β-sheet-rich structures and a fibrillary appearance. Our study demonstrates that the detection of pathological α-synuclein conformers from neuron-derived extracellular vesicles from blood plasma samples has the potential to evolve into a blood-biomarker of Parkinson's disease that is still lacking so far. Moreover, the distribution of seeding-competent α-synuclein within blood exosomes sheds a new light of pathological disease mechanisms in neurodegenerative disorders.

Development of HANABI, an ultrasonication-forced amyloid fibril inducer

Amyloid fibrils involved in amyloidoses are crystal-like aggregates, which are formed by breaking supersaturation of denatured proteins. Ultrasonication is an efficient method of agitation for breaking supersaturation and thus inducing amyloid fibrils. By combining an ultrasonicator and a microplate reader, we developed the HANABI (HANdai Amyloid Burst Inducer) system that enables high-throughput analysis of amyloid fibril formation. Among high-throughput approaches of amyloid fibril assays, the HANABI system has advantages in accelerating and detecting spontaneous amyloid fibril formation. HANABI is also powerful for amplifying a tiny amount of preformed amyloid fibrils by seeding. Thus, HANABI will contribute to creating therapeutic strategies against amyloidoses by identifying their biomarkers.

The Concept of α-Synuclein Strains and How Different Conformations May Explain Distinct Neurodegenerative Disorders

In the past few years, an increasing amount of studies primarily based on experimental models have investigated the existence of distinct α-synuclein strains and their different pathological effects. This novel concept could shed light on the heterogeneous nature of α-synucleinopathies, a group of disorders that includes Parkinson's disease, dementia with Lewy bodies and multiple system atrophy, which share as their key-molecular hallmark the abnormal aggregation of α-synuclein, a process that seems pivotal in disease pathogenesis according to experimental observations. However, the etiology of α-synucleinopathies and the initial events leading to the formation of α-synuclein aggregates remains elusive. Hence, the hypothesis that structurally distinct fibrillary assemblies of α-synuclein could have a causative role in the different disease phenotypes and explain, at least to some extent, their specific neurodegenerative, disease progression, and clinical presentation patterns is very appealing. Moreover, the presence of different α-synuclein strains might represent a potential biomarker for the diagnosis of these neurodegenerative disorders. In this regard, the recent use of super resolution techniques and protein aggregation assays has offered the possibility, on the one hand, to elucidate the conformation of α-synuclein pathogenic strains and, on the other hand, to cyclically amplify to detectable levels low amounts of α-synuclein strains in blood, cerebrospinal fluid and peripheral tissue from patients. Thus, the inclusion of these techniques could facilitate the differentiation between α-synucleinopathies, even at early stages, which is crucial for successful therapeutic intervention. This mini-review summarizes the current knowledge on α-synuclein strains and discusses its possible applications and potential benefits.

Parkinson disease-associated cognitive impairment

Parkinson disease (PD) is the second most common neurodegenerative disorder, affecting >1% of the population ≥65 years of age and with a prevalence set to double by 2030. In addition to the defining motor symptoms of PD, multiple non-motor symptoms occur; among them, cognitive impairment is common and can potentially occur at any disease stage. Cognitive decline is usually slow and insidious, but rapid in some cases. Recently, the focus has been on the early cognitive changes, where executive and visuospatial impairments are typical and can be accompanied by memory impairment, increasing the risk for early progression to dementia. Other risk factors for early progression to dementia include visual hallucinations, older age and biomarker changes such as cortical atrophy, as well as Alzheimer-type changes on functional imaging and in cerebrospinal fluid, and slowing and frequency variation on EEG. However, the mechanisms underlying cognitive decline in PD remain largely unclear. Cortical involvement of Lewy body and Alzheimer-type pathologies are key features, but multiple mechanisms are likely involved. Cholinesterase inhibition is the only high-level evidence-based treatment available, but other pharmacological and non-pharmacological strategies are being tested. Challenges include the identification of disease-modifying therapies as well as finding biomarkers to better predict cognitive decline and identify patients at high risk for early and rapid cognitive impairment.

Proteomic Profile of Saliva in Parkinson's Disease Patients: A Proof of Concept Study

Parkinson’s disease (PD) is a progressive neurodegenerative disorder. It affects many organs. Lewy bodies—a histopathological “hallmark” of PD—are detected in about 75% of PD submandibular gland samples. We hypothesize that saliva can be a source of biomarkers of PD. The aim of the study was to evaluate and compare the salivary proteome of PD patients and healthy controls (HC). Salivary samples from 39 subjects (24 PD patients, mean age 61.6 ± 8.2; 15 HC, mean age 60.9 ± 6.7) were collected. Saliva was collected using RNA-Pro-Sal kits. Label-free LC-MS/MS mass spectrometry was performed to characterize the proteome of the saliva. IPA analysis of upstream inhibitors was performed. A total of 530 proteins and peptides were identified. We observed lower concentrations of S100-A16, ARP2/3, and VPS4B in PD group when compared to HC. We conclude that the salivary proteome composition of PD patients is different than that of healthy controls. We observed a lower concentration of proteins involved in inflammatory processes, exosome formation, and adipose tissue formation. The variability of expression of proteins between the two groups needs to be considered.

Single-Molecule Counting Coupled to Rapid Amplification Enables Detection of α-Synuclein Aggregates in Cerebrospinal Fluid of Parkinson's Disease Patients

α-Synuclein aggregation is a hallmark of Parkinson's disease and a promising biomarker for early detection and assessment of disease progression. The prospect of a molecular test for Parkinson's disease is materializing with the recent developments of detection methods based on amplification of synuclein seeds (e.g. RT-QuIC or PMCA). Here we adapted single-molecule counting methods for the detection of α-synuclein aggregates in cerebrospinal fluid (CSF), using a simple 3D printed microscope. Single-molecule methods enable to probe the early events in the amplification process used in RT-QuIC and a precise counting of ThT-positive aggregates. Importantly, the use of single-molecule counting also allows a refined characterization of the samples and fingerprinting of the protein aggregates present in CSF of patients. The fingerprinting of size and reactivity of individual aggregate shows a unique signature for each PD patients compared to controls and may provide new insights on synucleinopathies in the future.

Genetic Architecture and Molecular, Imaging and Prodromic Markers in Dementia with Lewy Bodies: State of the Art, Opportunities and Challenges

Dementia with Lewy bodies (DLB) is one of the most common causes of dementia and belongs to the group of α-synucleinopathies. Due to its clinical overlap with other neurodegenerative disorders and its high clinical heterogeneity, the clinical differential diagnosis of DLB from other similar disorders is often difficult and it is frequently underdiagnosed. Moreover, its genetic etiology has been studied only recently due to the unavailability of large cohorts with a certain diagnosis and shows genetic heterogeneity with a rare contribution of pathogenic mutations and relatively common risk factors. The rapid increase in the reported cases of DLB highlights the need for an easy, efficient and accurate diagnosis of the disease in its initial stages in order to halt or delay the progression. The currently used diagnostic methods proposed by the International DLB consortium rely on a list of criteria that comprises both clinical observations and the use of biomarkers. Herein, we summarize the up-to-now reported knowledge on the genetic architecture of DLB and discuss the use of prodromal biomarkers as well as recent promising candidates from alternative body fluids and new imaging techniques.

Treating Parkinson's Disease with Antibodies: Previous Studies and Future Directions

Parkinson's disease is a neurodegenerative disorder mainly characterized by the degeneration of dopaminergic neurons in the substantia nigra. Degenerating neurons contain abnormal aggregates called Lewy bodies, that are predominantly composed of the misfolded and/or mutated alpha-synuclein protein. Post-translational modifications, cellular stress, inflammation and gene mutations are thought to trigger its pathological misfolding and aggregation. With alpha-synuclein pathology being strongly associated with dopaminergic neuronal toxicity, strategies aimed to reduce its burden are expected to be beneficial in slowing disease progression. Moreover, multiple sources of evidence suggest a cell-to-cell transmission of pathological alpha-synuclein in a prion-like manner. Therefore, antibodies targeting extra- or intracellular alpha-synuclein could be efficient in limiting the aggregation and transmission. Several active and passive immunization strategies have been explored to target alpha-synuclein. Here, we summarize immunotherapeutic approaches that were tested in pre-clinical or clinical studies in the last two decades in an attempt to treat Parkinson's disease.

Biomarkers for Alzheimer's disease-preparing for a new era of disease-modifying therapies

Clinical trial results presented in 2019 suggest that antibody-based removal of cerebral amyloid β (Aβ) plaques may possibly clear tau tangles and modestly slow cognitive decline in symptomatic Alzheimer's disease (AD). Although regulatory approval of this approach is still pending, preparing the healthcare system for the advent of disease-modifying therapies against AD is imperative. In particular, it will be necessary to identify the most suitable biomarkers to facilitate appropriate treatment of AD. Here, we give an update on recent developments in fluid and imaging biomarkers for AD-related pathologies and discuss potential approaches that could be adopted to screen for and clarify the underlying pathology in people seeking medical advice because of cognitive symptoms. We succinctly review recent data regarding biomarkers for Aβ and tau pathology, neurodegeneration, synaptic dysfunction, and inflammation, highlight the need for further research into common copathologies, and suggest how different biomarkers could be used (most likely in combination) to facilitate the development and clinical implementation of novel drug candidates against AD.

CSF and Blood Biomarkers in Neuroinflammatory and Neurodegenerative Diseases: Implications for Treatment

Neuroinflammatory and neurodegenerative diseases are characterized by the interplay of a number of molecular pathways that can be assessed through biofluids, especially cerebrospinal fluid and blood. Accordingly, the definition and classification of these disorders will move from clinical and pathological to biological criteria. The consequences of this biomarker-based diagnostic and prognostic approach are highly relevant to the field of drug development. Indeed, in view of the availability of disease-modifying drugs, fluid biomarkers offer a unique opportunity for improving the quality and applicability of results from clinical trials. Herein, we discuss the benefits of using fluid biomarkers for patient stratification, target engagement, and outcome assessment, as well as the most recent developments in neuroinflammatory and neurodegenerative diseases.

Synuclein in neurodegeneration

Neurodegenerative diseases are a heterogeneous group of disorders characterized by gradual progressive neuronal loss in the central nervous system. Unfortunately, the pathogenesis of many of these diseases remains unknown. Synucleins are a family of small, highly charged proteins expressed predominantly in neurons. Following their discovery, much has been learned about their structure, function, interaction with other proteins and role in neurodegenerative disease over the last two decades. One of these proteins, α-Synuclein (α-Syn), appears to be involved in many neurodegenerative disorders. These include Parkinson's disease (PD), dementia with Lewy bodies (DLB), Rapid Eye Movement Sleep Behavior Disorder (RBD) and Pure Autonomic Failure (PAF), i.e., collectively termed α-synucleinopathies. This review focuses on α-Syn dysfunction in neurodegeneration and assesses its role in synucleinopathies from a biochemical, genetic and neuroimaging perspective.

Unraveling Pathophysiological Mechanisms of Parkinson's Disease: Contribution of CSF Biomarkers

Diagnosis of Parkinson's disease (PD) relies on clinical history and physical examination, but misdiagnosis is common in early stages. Identification of biomarkers for PD may allow for early and more precise diagnosis and provide information about prognosis. Developments in analytical chemistry allow for the detection of a large number of molecules in cerebrospinal fluid (CSF), which are known to be associated with the pathogenesis of PD. Given the pathophysiology of PD, CSF α-synuclein species have the strongest rationale for use, also providing encouraging preliminary results in terms of early diagnosis. In the field of classical Alzheimer's disease (AD) biomarkers, low CSF Aβ₄₂ levels have shown a robust prognostic value in terms of development of cognitive impairment. Other CSF biomarkers including lysosomal enzymes, neurofilament light chain, markers of neuroinflammation and oxidative stress, although promising, have not proved to be reliable for diagnostic and prognostic purposes yet. Overall, the implementation of CSF biomarkers may give a substantial contribution to the optimal use of disease-modifying drugs.

From Seeds to Fibrils and Back: Fragmentation as an Overlooked Step in the Propagation of Prions and Prion-Like Proteins

Many devastating neurodegenerative diseases are driven by the misfolding of normal proteins into a pathogenic abnormal conformation. Examples of such protein misfolding diseases include Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, amyotrophic lateral sclerosis, and prion diseases. The misfolded proteins involved in these diseases form self-templating oligomeric assemblies that recruit further correctly folded protein and induce their conversion. Over time, this leads to the formation of high molecular and mostly fibrillar aggregates that are increasingly inefficient at converting normal protein. Evidence from a multitude of in vitro models suggests that fibrils are fragmented to form new seeds, which can convert further normal protein and also spread to neighboring cells as observed in vivo. While fragmentation and seed generation were suggested as crucial steps in aggregate formation decades ago, the biological pathways involved remain largely unknown. Here, we show that mechanisms of aggregate clearance—namely the mammalian Hsp70–Hsp40–Hsp110 tri-chaperone system, macro-autophagy, and the proteasome system—may not only be protective, but also play a role in fragmentation. We further review the challenges that exist in determining the precise contribution of these mechanisms to protein misfolding diseases and suggest future directions to resolve these issues.

Significance of Blood and Cerebrospinal Fluid Biomarkers for Alzheimer's Disease: Sensitivity, Specificity and Potential for Clinical Use

Alzheimer's disease (AD) is the most common type of dementia, affecting more than 5 million Americans, with steadily increasing mortality and incredible socio-economic burden. Not only have therapeutic efforts so far failed to reach significant efficacy, but the real pathogenesis of the disease is still obscure. The current theories are based on pathological findings of amyloid plaques and tau neurofibrillary tangles that accumulate in the brain parenchyma of affected patients. These findings have defined, together with the extensive neurodegeneration, the diagnostic criteria of the disease. The ability to detect changes in the levels of amyloid and tau in cerebrospinal fluid (CSF) first, and more recently in blood, has allowed us to use these biomarkers for the specific in-vivo diagnosis of AD in humans. Furthermore, other pathological elements of AD, such as the loss of neurons, inflammation and metabolic derangement, have translated to the definition of other CSF and blood biomarkers, which are not specific of the disease but, when combined with amyloid and tau, correlate with the progression from mild cognitive impairment to AD dementia, or identify patients who will develop AD pathology. In this review, we discuss the role of current and hypothetical biomarkers of Alzheimer's disease, their specificity, and the caveats of current high-sensitivity platforms for their peripheral detection.

Circulating Exosome microRNAs as Diagnostic Biomarkers of Dementia

Dementia is a syndrome of acquired cognitive impairment that leads to a significant decline in a patient’s daily life, ability to learn, and the ability to communicate with others. Dementia occurs in many diseases, including Alzheimer’s disease (AD), dementia with Lewy bodies, frontotemporal dementia, and Parkinson’s disease dementia (PDD). Although the analysis of biomarkers in the cerebrospinal fluid (CSF) and peripheral blood physicochemical analysis can indicate neurological impairment, there are currently no sensitive biomarkers for early clinical diagnosis of dementia or for identifying the cause of dementia. Previous studies have suggested that circulating micro (mi)RNAs may be used as biomarkers for diagnosing neurological disorders. However, miRNAs are susceptible to interference by other components in the peripheral circulation, bringing into question the diagnostic value of circulating miRNAs. Exosomes secreted by most cell types contain proteins, mRNAs, and miRNAs that are closely associated with changes in cellular functions. Exosome miRNAs (ex-miRNAs) are highly stable and resistant to degradation. Therefore, these may serve as useful biomarkers for the early clinical diagnosis of dementia. Here, we review studies of ex-miRNAs that commonly cause clinical dementia and explore whether ex-miRNAs may be used as early diagnostic biomarkers of dementia.

Alpha Synuclein Connects the Gut-Brain Axis in Parkinson's Disease Patients - A View on Clinical Aspects, Cellular Pathology and Analytical Methodology

Parkinson’s disease (PD) is marked by different kinds of pathological features, one hallmark is the aggregation of α-synuclein (aSyn). The development of aSyn pathology in the substantia nigra is associated to the manifestation of motor deficits at the time of diagnosis. However, most of the patients suffer additionally from non-motor symptoms, which may occur already in the prodromal phase of the disease years before PD is diagnosed. Many of these symptoms manifest in the gastrointestinal system (GIT) and some data suggest a potential link to the occurrence of pathological aSyn forms within the GIT. These clinical and pathological findings lead to the idea of a gut-brain route of aSyn pathology in PD. The identification of pathological aSyn in the intestinal system, e.g., by GIT biopsies, is therefore of highest interest for early diagnosis and early intervention in the phase of formation and propagation of aSyn. However, reliable methods to discriminate between physiological and pathological forms of enteral aSyn on the cellular and biochemical level are still missing. Moreover, a better understanding of the physiological function of aSyn within the GIT as well as its structure and pathological aggregation pathways are crucial to understand its role within the enteric nervous system and its spreading from the gut to the brain. In this review, we summarize clinical manifestations of PD in the GIT, and discuss biochemical findings from enteral biopsies. The relevance of pathological aSyn forms, their connection to the gut-brain axis and new developments to identify pathologic forms of aSyn by structural features are critically reviewed.

Increased alpha-synuclein tear fluid levels in patients with Parkinson's disease

The objective of the study was to estimate if altered levels of alpha-synuclein can be detected in tear fluid of patients with Parkinson’s disease (PD). Therefore, tear fluid samples of 75 PD patients, 75 control subjects and 31 atypical Parkinsonian patients were collected and analyzed in triplicates using an ultra-sensitive single molecule array (SIMOA) system and applying a human alpha-synuclein immunoassay. In PD, levels of total soluble alpha-synuclein were significantly increased compared to control subjects (p = 0.03; AUC PD vs. controls 0.60). There was no difference comparing PD patients stratified by Hoehn & Yahr stages and atypical Parkinsonian syndromes stratified by tauopathies and non-PD-synucleinopathies against each other (p > 0.05). In conclusion, alpha-synuclein can be detected and quantified in tear fluid, revealing small but significant differences in total alpha-synuclein levels between PD and control subjects. Tear fluid can be collected non-invasively and risk-free, therefore presenting a promising source for further biomarker research.

Analysis of Protein Conformational Strains-A Key for New Diagnostic Methods of Human Diseases

α-Synuclein is a naturally unfolded protein which easily aggregates and forms toxic inclusions and deposits. It is associated with several neurodegenerative diseases, including Parkinson’s disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA). These diseases, called synucleinopathies, have overlapping symptoms but require different methods of treatment. There are no reliable approaches for early diagnoses of these diseases, and as a result, the treatment begins late, and the disorders are often misdiagnosed. Recent studies revealed that α-synuclein forms distinctive spatial structures or strains at the early steps of these diseases, which may be used for early diagnosis. One of these early diagnostic methods called PMCA (protein misfolding cyclic amplification) allows identification of the distinct α-synuclein strains specific for different human diseases. The method is successfully used for differential diagnosis of patients with PD and MSA.

Novel approaches to counter protein aggregation pathology in Parkinson's disease

The primary neuropathological characteristics of the Parkinsonian brain are the loss of nigral dopamine neurons and the aggregation of alpha synuclein protein. Efforts to development potentially disease-modifying treatments have largely focused on correcting these aspects of the condition. In the last decade treatments targeting protein aggregation have entered the clinical pipeline. In this chapter we provide an overview of ongoing clinical trial programs for different therapies attempting to reduce protein aggregation pathology in Parkinson's disease. We will also briefly consider various novel approaches being proposed-and being developed preclinically-to inhibit/reduce aggregated protein pathology in Parkinson's.

An update on fluid biomarkers for neurodegenerative diseases: recent success and challenges ahead

Over the last twenty years, the characterization of Alzheimer's disease (AD) patients has progressed from a description of clinical symptomatology followed by neuropathological findings at autopsy to in vivo pathophysiological signatures using cerebrospinal fluid (CSF) and positron emission tomography (PET). Additionally, CSF biomarkers now reflect synaptic pathology, axonal injury and neuroinflammation. Novel techniques are capable of measuring proteins of pathophysiological importance at femtomolar concentrations in blood (e.g. amyloid, tau species and neurofilaments), which enable screening of large populations in the near future. This will be essential for secondary prevention trials and clinical management. However, common diseases such as dementia with Lewy bodies, Parkinson's disease and frontotemporal dementias, are still without reliable diagnostic biomarkers, although emerging techniques show promising pilot results for some of these diseases. This is likely to change in the next few years, which will be crucial to stratify populations enrolling in clinical trials, since pathologies often coexist.

α-Synuclein real-time quaking-induced conversion in the submandibular glands of Parkinson's disease patients

BACKGROUND

Identification of a peripheral biomarker is a major roadblock in the diagnosis of PD. Immunohistological identification of p-serine 129 α-synuclein in the submandibular gland tissues of PD patients has been recently reported.

OBJECTIVE

We report on a proof-of-principle study for using an ultra-sensitive and specific, real-time quaking-induced conversion assay to detect pathological α-synuclein in the submandibular gland tissues of PD patients.

METHODS

The α-synuclein real-time quaking-induced conversion assay was used to detect and quantify pathological α-synuclein levels in PD, incidental Lewy body disease, and control submandibular gland tissues as well as in formalin-fixed paraffin-embedded sections.

RESULTS

We determined the quantitative seeding kinetics of pathological α-synuclein present in submandibular gland tissues from autopsied subjects using the α-synuclein real-time quaking-induced conversion assay. A total of 32 cases comprising 13 PD, 3 incidental Lewy body disease, and 16 controls showed 100% sensitivity and 94% specificity. Interestingly, both PD and incidental Lewy body disease tissues showed 100% concordance for elevated levels of pathological α-synuclein seeding activity compared to control tissues. End-point dilution kinetic analyses revealed that the submandibular gland had a wide dynamic range of pathological α-synuclein seeding activity.

CONCLUSIONS

Our results are the first to demonstrate the utility of using the real-time quaking-induced conversion assay on peripherally accessible submandibular gland tissues and formalin-fixed paraffin-embedded tissue sections to detect PD-related pathological changes with high sensitivity and specificity. Additionally, the detection of seeding activity from incidental Lewy body disease cases containing immunohistochemically undetected pathological α-synuclein demonstrates the α-synuclein real-time quaking-induced conversion assay's potential utility for identifying prodromal PD in submandibular gland tissues. © 2019 International Parkinson and Movement Disorder Society.

Biomarkers for Parkinson's Disease: How Good Are They?

Parkinson's disease (PD) is a complex neurodegenerative disorder with no cure in sight. Clinical challenges of the disease include the inability to make a definitive diagnosis at the early stages and difficulties in predicting the disease progression. The unmet demand to identify reliable biomarkers for early diagnosis and management of the disease course of PD has attracted a lot of attention. However, only a few reported candidate biomarkers have been tried in clinical practice at the present time. Studies on PD biomarkers have often overemphasized the discovery of novel identity, whereas efforts to further evaluate such candidates are rare. Therefore, we update the new development of biomarker discovery in PD and discuss the standard process in the evaluation and assessment of the diagnostic or prognostic value of the identified potential PD biomarkers in this review article. Recent developments in combined biomarkers and the current status of clinical trials of biomarkers as outcome measures are also discussed. We believe that the combination of different biomarkers might enhance the specificity and sensitivity over a single measure that might not be sufficient for such a multiplex disease.

Seeded propagation of α-synuclein aggregation in mouse brain using protein misfolding cyclic amplification

α-Synuclein (α-syn) protein aggregation is associated with several neurodegenerative disorders collectively referred to as synucleinopathies, including Parkinson's disease. We used protein misfolding cyclic amplification (PMCA) to study α-syn aggregation in brain homogenates of wild-type or transgenic mice expressing normal (D line) or A53T mutant (M83 line) human α-syn. We found that sonication-incubation cycles of M83 mouse brain gradually produce large quantities of SDS-resistant α-syn aggregates, involving both human and mouse proteins. These PMCA products, containing partially proteinase K-resistant α-syn species, are competent to accelerate the onset of neurologic symptoms after intracerebral inoculation to young M83 mice and to seed aggregate formation of α-syn following PMCA, including in D and wild-type mouse brain substrates. PMCA seeding activity in the M83 diseased brain correlates positively with regions mostly targeted by the α-syn pathology in this model. Our data indicate that similar to prions, PMCA can reproduce some characteristics of α-syn aggregation and seeded propagation in vitro in a complex milieu. This opens new opportunities for the molecular study of synucleinopathies.-Nicot, S., Verchère, J., Bélondrade, M., Mayran, C., Bétemps, D., Bougard, D., Baron, T. Seeded propagation of α-synuclein aggregation in mouse brain using protein misfolding cyclic amplification.