Immunotherapy for neurodegenerative diseases: focus on α-synucleinopathies

Neurodegenerative disorders: Mechanisms of degeneration and therapeutic approaches with their clinical relevance

Neurodegenerative disorders (NDs) are expected to pose a significant challenge for both medicine and public health in the upcoming years due to global demographic changes. NDs are mainly represented by degeneration/loss of neurons, which is primarily accountable for severe mental illness. This neuronal degeneration leads to many neuropsychiatric problems and permanent disability in an individual. Moreover, the tight junction of the brain, blood-brain barrier (BBB)has a protective feature, functioning as a biological barrier that can prevent medicines, toxins, and foreign substances from entering the brain. However, delivering any medicinal agent to the brain in NDs (i.e., Multiple sclerosis, Alzheimer's, Parkinson's, etc.) is enormously challenging. There are many approved therapies to address NDs, but most of them only help treat the associated manifestations. The available therapies have failed to control the progression of NDs due to certain factors, i.e., BBB and drug-associated undesirable effects. NDs have extremely complex pathology, with many pathogenic mechanisms involved in the initiation and progression; thereby, a limited survival rate has been observed in ND patients. Hence, understanding the exact mechanism behind NDs is crucial to developing alternative approaches for improving ND patients' survival rates. Thus, the present review sheds light on different cellular mechanisms involved in NDs and novel therapeutic approaches with their clinical relevance, which will assist researchers in developing alternate strategies to address the limitations of conventional ND therapies. The current work offers the scope into the near future to improve the therapeutic approach of NDs.

Immunotherapy: An emerging treatment option for neurodegenerative diseases

Accumulation of misfolded proteins and protein aggregates leading to degeneration of neurons is a hallmark of several neurodegenerative diseases. Therapy mostly relies on symptomatic relief. Immunotherapy offers a promising approach for the development of disease-modifying routes. Such strategies have shown remarkable results in oncology, and this promise is increasingly being realized for neurodegenerative diseases in advanced preclinical and clinical studies. This review highlights cases of passive and active immunotherapies in Parkinson's and Alzheimer's diseases. The reasons for success and failure, wherever available, and strategies to cross the blood-brain barrier, are discussed. The need for conditional modulation of the immune response is also reflected on.

Evolving therapeutic interventions for the management and treatment of Alzheimer's disease

Alzheimer's Disease (AD) patients experience diverse symptoms, including memory loss, cognitive impairment, behavioral abnormalities, mood changes, and mental issues. The fundamental objective of this review is to discuss novel therapeutic approaches, with special emphasis on recently approved marketed formulations for the treatment of AD, especially Aducanumab, the first FDA approved moiety that surpasses the blood-brain barrier (BBB) and reduces amyloid plaques in the brain, thereby reducing associated cognitive decline. However, it is still in the phase IV trial and is to be completed by 2030. Other drugs such as lecanemab are also under clinical trial and has recently been approved by the FDA and is also discussed here. In this review, we also focus on active and passive immunotherapy for AD as well as several vaccines, such as amyloid-beta epitope-based vaccines, amyloid-beta DNA vaccines, and stem cell therapy for AD, which are in clinical trials. Furthermore, ongoing pre-clinical trials associated with AD and other novel strategies such as curcumin-loaded nanoparticles, Crispr/ cas9, precision medicine, as well as some emerging therapies like anti-sense therapy are also highlighted. Additionally, we discuss some off-labeled drugs like non-steroidal anti-inflammatory drugs (NSAID), anti-diabetic drugs, and lithium, which can manage symptoms of AD and different non-pharmacological approaches are also covered which can help to manage AD. In summary, we have tried to cover all the therapeutic interventions which are available for the treatment and management of AD under sections approved, clinical phase, pre-clinical phase or futuristic interventions, off-labelled drugs, and non-pharmacological interventions for AD, offering positive findings and well as challenges that remain.

Antibodies and α-synuclein: What to target against Parkinson's Disease?

Parkinson's Disease (PD) is strongly linked to the aggregation of the protein α-synuclein (α-syn), an intrinsically disordered protein. However, strategies to combat PD by targeting the aggregation of α-syn are challenged by the multiple types of aggregates formed both in vivo and in vitro, the potential influence of chemical modifications and the as yet unresolved question of which aggregate types (oligomeric or fibrillar) are most cytotoxic. Here I briefly review the social history of α-syn, the many efforts to raise antibodies against α-syn and the disappointing results of clinical trials based on such antibodies. Ultimately a thorough understanding of the molecular and mechanistic properties of mAbs towards aggregated species of α-syn is an essential prerequisite for any clinical trial, but this is missing in most cases. I highlight new microfluidic techniques which may address this need and call for a more concerted effort to standardize antibody studies as the basis to allow us to link molecular insights to clinical efficacy.

Transmission-selective muscle pathology induced by the active propagation of mutant huntingtin across the human neuromuscular synapse

Neuron-to-neuron transmission of aggregation-prone, misfolded proteins may potentially explain the spatiotemporal accumulation of pathological lesions in the brains of patients with neurodegenerative protein-misfolding diseases (PMDs). However, little is known about protein transmission from the central nervous system to the periphery, or how this propagation contributes to PMD pathology. To deepen our understanding of these processes, we established two functional neuromuscular systems derived from human iPSCs. One was suitable for long-term high-throughput live-cell imaging and the other was adapted to a microfluidic system assuring that connectivity between motor neurons and muscle cells was restricted to the neuromuscular junction. We show that the Huntington's disease (HD)-associated mutant HTT exon 1 protein (mHTTEx1) is transmitted from neurons to muscle cells across the human neuromuscular junction. We found that transmission is an active and dynamic process that starts before aggregate formation and is regulated by synaptic activity. We further found that transmitted mHTTEx1 causes HD-relevant pathology at both molecular and functional levels in human muscle cells, even in the presence of the ubiquitous expression of mHTTEx1. In conclusion, we have uncovered a causal link between mHTTEx1 synaptic transmission and HD pathology, highlighting the therapeutic potential of blocking toxic protein transmission in PMDs.

Alzheimer's Disease Immunotherapy: Current Strategies and Future Prospects

Alzheimer's disease (AD) is an extremely complex and heterogeneous pathology influenced by many factors contributing to its onset and progression, including aging, amyloid-beta (Aβ) plaques, tau fibril accumulation, inflammation, etc. Despite promising advances in drug development, there is no cure for AD. Although there have been substantial advancements in understanding the pathogenesis of AD, there have been over 200 unsuccessful clinical trials in the past decade. In recent years, immunotherapies have been at the forefront of these efforts. Immunotherapy alludes to the immunological field that strives to identify disease treatments via the enhancement, suppression, or induction of immune responses. Interestingly, immunotherapy in AD is a relatively new approach for non-infectious disease. At present, antibody therapy (passive immunotherapy) that targets anti-Aβ aimed to prevent the fibrillization of Aβ peptides and disrupt pre-existing fibrils is a predominant AD immunotherapy due to the continuous failure of active immunotherapy for AD. The most rational and safe strategies will be those targeting the toxic molecule without triggering an abnormal immune response, offering therapeutic advantages, thus making clinical trial design more efficient. This review offers a concise overview of immunotherapeutic strategies, including active and passive immunotherapy for AD. Our review encompasses approved methods and those presently under investigation in clinical trials, while elucidating the recent challenges, complications, successes, and potential treatments. Thus, immunotherapies targeting Aβ throughout the disease progression using a mutant oligomer-Aβ stimulated dendritic cell vaccine may offer a promising therapy in AD.

Brain-Targeted Liposomes Loaded with Monoclonal Antibodies Reduce Alpha-Synuclein Aggregation and Improve Behavioral Symptoms in Parkinson's Disease

Monoclonal antibodies (mAbs) hold promise in treating Parkinson's disease (PD), although poor delivery to the brain hinders their therapeutic application. In the current study, it is demonstrated that brain-targeted liposomes (BTL) enhance the delivery of mAbs across the blood-brain-barrier (BBB) and into neurons, thereby allowing the intracellular and extracellular treatment of the PD brain. BTL are decorated with transferrin to improve brain targeting through overexpressed transferrin-receptors on the BBB during PD. BTL are loaded with SynO4, a mAb that inhibits alpha-synuclein (AS) aggregation, a pathological hallmark of PD. It is shown that 100-nm BTL cross human BBB models intact and are taken up by primary neurons. Within neurons, SynO4 is released from the nanoparticles and bound to its target, thereby reducing AS aggregation, and enhancing neuronal viability. In vivo, intravenous BTL administration results in a sevenfold increase in mAbs in brain cells, decreasing AS aggregation and neuroinflammation. Treatment with BTL also improve behavioral motor function and learning ability in mice, with a favorable safety profile. Accordingly, targeted nanotechnologies offer a valuable platform for drug delivery to treat brain neurodegeneration.

Cellular mechanisms of fibrin (ogen): insight from neurodegenerative diseases

Neurodegenerative diseases are prevalent and currently incurable conditions that progressively impair cognitive, behavioral, and psychiatric functions of the central or peripheral nervous system. Fibrinogen, a macromolecular glycoprotein, plays a crucial role in the inflammatory response and tissue repair in the human body and interacts with various nervous system cells due to its unique molecular structure. Accumulating evidence suggests that fibrinogen deposits in the brains of patients with neurodegenerative diseases. By regulating pathophysiological mechanisms and signaling pathways, fibrinogen can exacerbate the neuro-pathological features of neurodegenerative diseases, while depletion of fibrinogen contributes to the amelioration of cognitive function impairment in patients. This review comprehensively summarizes the molecular mechanisms and biological functions of fibrinogen in central nervous system cells and neurodegenerative diseases, including Alzheimer's disease, Multiple Sclerosis, Parkinson's disease, Vascular dementia, Huntington's disease, and Amyotrophic Lateral Sclerosis. Additionally, we discuss the potential of fibrinogen-related treatments in the management of neurodegenerative disorders.

Pathological mechanisms of neuroimmune response and multitarget disease-modifying therapies of mesenchymal stem cells in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease characterized by the degeneration of dopaminergic neurons in the substantia nigra (SN); the etiology and pathological mechanism of the disease are still unclear. Recent studies have shown that the activation of a neuroimmune response plays a key role in the development of PD. Alpha-synuclein (α-Syn), the primary pathological marker of PD, can gather in the SN and trigger a neuroinflammatory response by activating microglia which can further activate the dopaminergic neuron's neuroimmune response mediated by reactive T cells through antigen presentation. It has been shown that adaptive immunity and antigen presentation processes are involved in the process of PD and further research on the neuroimmune response mechanism may open new methods for its prevention and therapy. While current therapeutic regimens are still focused on controlling clinical symptoms, applications such as immunoregulatory strategies can delay the symptoms and the process of neurodegeneration. In this review, we summarized the progression of the neuroimmune response in PD based on recent studies and focused on the use of mesenchymal stem cell (MSC) therapy and challenges as a strategy of disease-modifying therapy with multiple targets.

Nanomedicine-driven therapeutic interventions of autophagy and stem cells in the management of Alzheimer's disease

Drug-loaded, brain-targeted nanocarriers could be a promising tool in overcoming the challenges associated with Alzheimer's disease therapy. These nanocargoes are enormously flexible to functionalize and facilitate the delivery of drugs to brain cells by bridging the blood-brain barrier and into brain cells. To date, modifications have included nanoparticles (NPs) coating with tunable surfactants/phospholipids, covalently attaching polyethylene glycol chains (PEGylation), and tethering different targeting ligands to cell-penetrating peptides in a manner that facilitates their entry across the BBB and downregulates various pathological hallmarks as well as intra- and extracellular signaling pathways. This review provides a brief update on drug-loaded, multifunctional nanocarriers and the therapeutic intervention of autophagy and stem cells in the management of Alzheimer's disease.

Natural IgG antibodies to β amyloid are decreased in patients with Parkinson's disease

Natural antibodies (nAbs) against aggregation-prone proteins have been found in healthy normal subjects. These proteins likely have a pathogenetic role in neurodegenerative diseases of ageing. They include the amyloid β (Aβ) protein which may play an important role in Alzheimer's dementia (AD), and α-synuclein, a major determinant of Parkinson's disease (PD). We measured nAbs to Aβ in a group of Italian patients with AD, vascular dementia, non-demented PD patients and healthy elderly controls. We found that Aβ antibody levels in AD were similar to age- and sex-matched controls, but contrary to our expectations, they were significantly reduced in PD. This may identify patients that could be more prone to amyloid aggregation.

Current Advances of Plant-Based Vaccines for Neurodegenerative Diseases

Neurodegenerative diseases (NDDs) are characterized by the progressive degeneration and/or loss of neurons belonging to the central nervous system, and represent one of the major global health issues. Therefore, a number of immunotherapeutic approaches targeting the non-functional or toxic proteins that induce neurodegeneration in NDDs have been designed in the last decades. In this context, due to unprecedented advances in genetic engineering techniques and molecular farming technology, pioneering plant-based immunogenic antigen expression systems have been developed aiming to offer reliable alternatives to deal with important NDDs, including Alzheimer's disease, Parkinson's disease, and multiple sclerosis. Diverse reports have evidenced that plant-made vaccines trigger significant immune responses in model animals, supported by the production of antibodies against the aberrant proteins expressed in the aforementioned NDDs. Moreover, these immunogenic tools have various advantages that make them a viable alternative for preventing and treating NDDs, such as high scalability, no risk of contamination with human pathogens, cold chain free production, and lower production costs. Hence, this article presents an overview of the current progress on plant-manufactured vaccines for NDDs and discusses its future prospects.

Extracellular vesicles in neurodegenerative diseases: A systematic review

Introduction

Extracellular vesicles (EVs) are known to have a significant role in the central nervous system (CNS) and neurodegenerative disease.

Methods

PubMed, Scopus, ISI Web of Science, EMBASE, and Google Scholar were used to identify published articles about EV modifications (2012 to Feb 2022).

Results

In total, 1,435 published papers were identified among the searched articles, with 1,128 non-duplicate publications being identified. Following the screening of titles and abstracts, 214 publications were excluded; following the full-text screening of 93 published articles, another 33 publications were excluded. The remaining 60 studies were considered. The kappa statistic of 0.868 indicated that the raters were highly reliable. Furthermore, the inter-reliability and intra-reliability coefficients were found to be 0.931 and 0.908, respectively, indicating strong reliability and consistency between the eligible studies identified by the raters. A total of 27 relevant studies demonstrated the role of EVs as therapeutic and diagnostic biomarkers in neurodegenerative diseases. Of note, 19 and 14 studies, respectively, found EVs to be pioneering in diagnostic and therapeutic roles.

Discussion

EVs play an important role in the central nervous system (CNS), aiding in cell-to-cell communication and serving as a diagnostic marker and therapeutic target in a variety of neurodegenerative diseases. EVs are the home of several proteins [including-synuclein (-syn) and tau proteins], lipids, and genetic materials such as DNA and RNA. The presence of novel miRNAs in EVs suggests biomarkers for the diagnosis and screening of neurodegenerative disorders. Furthermore, EVs play an important role in the pathogenesis of such disorders. This systematic review discussed the current state of EVs' role in neurological diseases, as well as some preclinical studies on the therapeutic and diagnostic potential of EVs.

Clinical application of prion-like seeding in α-synucleinopathies: Early and non-invasive diagnosis and therapeutic development

The accumulation and deposition of misfolded α-synuclein (α-Syn) aggregates in the brain is the central event in the pathogenesis of α-synucleinopathies, including Parkinson’s disease, dementia with Lewy bodies, and multiple-system atrophy. Currently, the diagnosis of these diseases mainly relies on the recognition of advanced clinical manifestations. Differential diagnosis among the various α-synucleinopathies subtypes remains challenging. Misfolded α-Syn can template its native counterpart into the same misfolded one within or between cells, behaving as a prion-like seeding. Protein-misfolding cyclic amplification and real-time quaking-induced conversion are ultrasensitive protein amplification assays initially used for the detection of prion diseases. Both assays showed high sensitivity and specificity in detection of α-synucleinopathies even in the pre-clinical stage recently. Herein, we collectively reviewed the prion-like properties of α-Syn and critically assessed the detection techniques of α-Syn-seeding activity. The progress of test tissues, which tend to be less invasive, is presented, particularly nasal swab, which is now widely known owing to the global fight against coronavirus disease 2019. We highlight the clinical application of α-Syn seeding in early and non-invasive diagnosis. Moreover, some promising therapeutic perspectives and clinical trials targeting α-Syn-seeding mechanisms are presented.

Proteinopathies: Deciphering Physiology and Mechanisms to Develop Effective Therapies for Neurodegenerative Diseases

Neurodegenerative diseases (NDs) are a cluster of diseases marked by progressive neuronal loss, axonal transport blockage, mitochondrial dysfunction, oxidative stress, neuroinflammation, and aggregation of misfolded proteins. NDs are more prevalent beyond the age of 50, and their symptoms often include motor and cognitive impairment. Even though various proteins are involved in different NDs, the mechanisms of protein misfolding and aggregation are very similar. Recently, several studies have discovered that, like prions, these misfolded proteins have the inherent capability of translocation from one neuron to another, thus having far-reaching implications for understanding the processes involved in the onset and progression of NDs, as well as the development of innovative therapy and diagnostic options. These misfolded proteins can also influence the transcription of other proteins and form aggregates, tangles, plaques, and inclusion bodies, which then accumulate in the CNS, leading to neuronal dysfunction and neurodegeneration. This review demonstrates protein misfolding and aggregation in NDs, and similarities and differences between different protein aggregates have been discussed. Furthermore, we have also reviewed the disposal of protein aggregates, the various molecular machinery involved in the process, their regulation, and how these molecular mechanisms are targeted to build innovative therapeutic and diagnostic procedures. In addition, the landscape of various therapeutic interventions for targeting protein aggregation for the effective prevention or treatment of NDs has also been discussed.

A Novel C-Type Lectin Receptor-Targeted α-Synuclein-Based Parkinson Vaccine Induces Potent Immune Responses and Therapeutic Efficacy in Mice

The progressive accumulation of misfolded α-synuclein (α-syn) in the brain is widely considered to be causal for the debilitating clinical manifestations of synucleinopathies including, most notably, Parkinson’s disease (PD). Immunotherapies, both active and passive, against α-syn have been developed and are promising novel treatment strategies for such disorders. To increase the potency and specificity of PD vaccination, we created the ‘Win the Skin Immune System Trick’ (WISIT) vaccine platform designed to target skin-resident dendritic cells, inducing superior B and T cell responses. Of the six tested WISIT candidates, all elicited higher immune responses compared to conventional, aluminum adjuvanted peptide-carrier conjugate PD vaccines, in BALB/c mice. WISIT-induced antibodies displayed higher selectivity for α-syn aggregates than those induced by conventional vaccines. Additionally, antibodies induced by two selected candidates were shown to inhibit α-syn aggregation in a dose-dependent manner in vitro. To determine if α-syn fibril formation could also be inhibited in vivo, WISIT candidate type 1 (CW-type 1) was tested in an established synucleinopathy seeding model and demonstrated reduced propagation of synucleinopathy in vivo. Our studies provide proof-of-concept for the efficacy of the WISIT vaccine technology platform and support further preclinical and clinical development of this vaccine candidate.

Novel engineered nanobodies specific for N‐terminal region of alpha‐synuclein recognize Lewy‐body pathology and inhibit in‐vitro seeded aggregation and toxicity

Nanobodies (Nbs), the single‐domain antigen‐binding fragments of dromedary heavy‐chain antibodies (HCAb), are excellent candidates as therapeutic and diagnostic tools in synucleinopathies because of their small size, solubility and stability. Here, we constructed an immune nanobody library specific to the monomeric form of alpha‐synuclein (α‐syn). Phage display screening of the library allowed the identification of a nanobody, Nbα‐syn01, specific for α‐syn. Unlike previously developed nanobodies, Nbα‐syn01 recognized the N‐terminal region which is critical for in vitro and in vivo aggregation and contains many point mutations involved in early PD cases. The affinity of the monovalent Nbα‐syn01 and the engineered bivalent format BivNbα‐syn01 measured by isothermal titration calorimetry revealed unexpected results where Nbα‐syn01 and its bivalent format recognized preferentially α‐syn fibrils compared to the monomeric form. Nbα‐syn01 and BivNbα‐syn01 were also able to inhibit α‐syn‐seeded aggregation in vitro and reduced α‐syn‐seeded aggregation and toxicity in cells showing their potential to reduce α‐syn pathology. Moreover, both nanobody formats were able to recognize Lewy‐body pathology in human post‐mortem brain tissue from PD and DLB cases. Additionally, we present evidence through structural docking that Nbα‐syn01 binds the N‐terminal region of the α‐syn aggregated form. Overall, these results highlight the potential of Nbα‐syn01 and BivNbα‐syn01 in developing into a diagnostic or a therapeutic tool for PD and related disorders.

Terpenoid analogues as putative therapeutic agents towards glutathione peroxidase (GPX4) in neurodegenerative disorders: a dynamic computational approach

Carvacrol, a monoterpenoid phenolic phytochemical, a potent antioxidant, and neuroprotective agent is an emerging neuroprotective agent for neurodegenerative diseases (NDDs). Considering scarce information on carvacrol analogues, we hypothesized an in silico investigation emphasizing their preferential binding towards glutathione peroxidase (GPX4) as a target across different species for evaluating through preclinical to clinical studies (2OBI and 6HN3 for Homo sapiens; 5L71 for Mus musculus). Enrichment analysis suggests that ROC (0.59) and AUC (0.61) values have higher sensitivity and significant number of ranked actives. Extra Precision (XP) of 59 compounds was conducted, followed by molecular dynamics and trajectory analysis. Top three hits were chosen for each target i.e., 101203408, 101419546, 59294 (2OBI); 101419546, 100938426, and 28092 (6HN3); and 12059, 52434, 335 (5L71) implying high docking score. 101419546 is common among 2OBI and 6HN3 targets, indicating a multi-target approach. Trajectory analysis of hits provides a permissible range of RMSD, RMSF, Rgyr (∼1.3-2 Å, ∼0.84-1.09 Å, ∼15.05-15.29 Å). Overlapped dynamically simulated 3D-structures of Apo and complexes display significant conformational changes in RMSD of the complexes (∼1.40-2.0 Å) in contrast to Apo (∼1.3-1.8 Å), suggesting structural stability and compactness of the complexes within 45-90 ns. DCCM and PCA analysis shows positive correlation and residual clustering among residues of complexes. The establishment of firm H-bonding, favorable aromaticity and ADMET profile makes them promising drugs across various GPX4 targets among the species. Studies considering the targets across different species aids in anticipating and discovering a common compound for future NDDs therapeutics from bench to bedside.Communicated by Ramaswamy H. Sarma.

High neutrophil-to-lymphocyte ratio predicts short survival in multiple system atrophy

The neutrophil-to-lymphocyte ratio (NLR), an inflammatory marker, can predict the prognosis of neurodegenerative diseases. However, the significance of NLR for the prognosis of multiple system atrophy (MSA) has not been reported. We aimed to examine the prognostic significance of NLR in MSA. A total of 169 MSA patients and 163 matched healthy controls (HCs) were enrolled. MSA patients were divided into three groups according to the tertiles of their NLR. Kaplan–Meier survival analysis and Cox regression model were used to assessing the effect of NLR on survival. An independent validation cohort of 56 consecutive patients with probable MSA who met the inclusion criteria was included. The NLR was significantly higher in patients with MSA than that in HCs. The survival duration in patients with MSA in group 3 was shorter than that in patients in the other two groups (P = 0.013). In the multivariable Cox regression model, a higher NLR increased the risk of mortality in patients with MSA after adjusting for confounding factors (HR = 1.922, P = 0.035). Additionally, a higher NLR increased the risk of mortality in MSA with predominant cerebellar ataxia (MSA-C) (HR = 2.398, P = 0.033) and in men (HR = 3.483, P = 0.027). The concordance index for the multivariate Cox regression model was more than 0.7 both in the primary cohort and external validation cohort. Patients with MSA had a higher NLR than did HCs. A high NLR increased the risk of mortality with MSA, especially in MSA-C and in men.

Efficacy and immunogenicity of MultiTEP-based DNA vaccines targeting human α-synuclein: prelude for IND enabling studies

Accumulation of misfolded proteins such as amyloid-β (Aβ), tau, and α-synuclein (α-Syn) in the brain leads to synaptic dysfunction, neuronal damage, and the onset of relevant neurodegenerative disorder/s. Dementia with Lewy bodies (DLB) and Parkinson’s disease (PD) are characterized by the aberrant accumulation of α-Syn intracytoplasmic Lewy body inclusions and dystrophic Lewy neurites resulting in neurodegeneration associated with inflammation. Cell to cell propagation of α-Syn aggregates is implicated in the progression of PD/DLB, and high concentrations of anti-α-Syn antibodies could inhibit/reduce the spreading of this pathological molecule in the brain. To ensure sufficient therapeutic concentrations of anti-α-Syn antibodies in the periphery and CNS, we developed four α-Syn DNA vaccines based on the universal MultiTEP platform technology designed especially for the elderly with immunosenescence. Here, we are reporting on the efficacy and immunogenicity of these vaccines targeting three B-cell epitopes of hα-Syn aa85–99 (PV-1947D), aa109–126 (PV-1948D), aa126–140 (PV-1949D) separately or simultaneously (PV-1950D) in a mouse model of synucleinopathies mimicking PD/DLB. All vaccines induced high titers of antibodies specific to hα-Syn that significantly reduced PD/DLB-like pathology in hα-Syn D line mice. The most significant reduction of the total and protein kinase resistant hα-Syn, as well as neurodegeneration, were observed in various brain regions of mice vaccinated with PV-1949D and PV-1950D in a sex-dependent manner. Based on these preclinical data, we selected the PV-1950D vaccine for future IND enabling preclinical studies and clinical development.

ABBV-0805, a novel antibody selective for soluble aggregated α-synuclein, prolongs lifespan and prevents buildup of α-synuclein pathology in mouse models of Parkinson's disease

A growing body of evidence suggests that aggregated α-synuclein, the major constituent of Lewy bodies, plays a key role in the pathogenesis of Parkinson's disease and related α-synucleinopathies. Immunotherapies, both active and passive, against α-synuclein have been developed and are promising novel treatment strategies for such disorders. Here, we report on the humanization and pharmacological characteristics of ABBV-0805, a monoclonal antibody that exhibits a high selectivity for human aggregated α-synuclein and very low affinity for monomers. ABBV-0805 binds to a broad spectrum of soluble aggregated α-synuclein, including small and large aggregates of different conformations. Binding of ABBV-0805 to pathological α-synuclein was demonstrated in Lewy body-positive post mortem brains of Parkinson's disease patients. The functional potency of ABBV-0805 was demonstrated in several cellular assays, including Fcγ-receptor mediated uptake of soluble aggregated α-synuclein in microglia and inhibition of neurotoxicity in primary neurons. In vivo, the murine version of ABBV-0805 (mAb47) displayed significant dose-dependent decrease of α-synuclein aggregates in brain in several mouse models, both in prophylactic and therapeutic settings. In addition, mAb47 treatment of α-synuclein transgenic mice resulted in a significantly prolonged survival. ABBV-0805 selectively targets soluble toxic α-synuclein aggregates with a picomolar affinity and demonstrates excellent in vivo efficacy. Based on the strong preclinical findings described herein, ABBV-0805 has been progressed into clinical development as a potential disease-modifying treatment for Parkinson's disease.

Safety and Tolerability of Active Immunotherapy Targeting α-Synuclein with PD03A in Patients with Early Parkinson's Disease: A Randomized, Placebo-Controlled, Phase 1 Study

Background:

Immunotherapies targeting α-synuclein aim to limit its extracellular spread in the brain and prevent progression of pathology in Parkinson’s disease (PD). PD03A is a specific active immunotherapy (SAIT) involving immunization with a short peptide formulation.

Objective:

This phase 1 study characterized the safety and tolerability of PD03A in patients with early PD. A key secondary objective was to evaluate immunological activity following immunization.

Methods:

This was a phase 1 study of two different doses of PD03A versus placebo in PD patients. Patients were randomized (1:1:1) to receive four priming plus one booster vaccination of PD03A 15μg, PD03A 75μg or placebo and were followed for 52 weeks.

Results:

Overall, 36 patients were randomized, of which 35 received five immunizations and completed the study. All patients experienced at least one adverse event. Transient local injection site reactions affected all but two patients; otherwise most AEs were considered unrelated to study treatment. A substantial IgG antibody response against PD03 was observed with a maximum titer achieved at Week-12. Differences in titers between both active groups versus placebo were statistically significant from the second immunization at Week-8 until Week-52.

Conclusion:

The safety profile and positive antibody response of PD03A supports the further development of active immunotherapeutic approaches for the treatment of PD.

NPT520-34 improves neuropathology and motor deficits in a transgenic mouse model of Parkinson's disease

NPT520-34 is a clinical-stage, small molecule being developed for the treatment of Parkinson's disease and other neurodegenerative disorders. The therapeutic potential of NPT520-34 was first suggested by findings from cell-based assays of alpha-synuclein (ASYN) clearance. As reported here, NPT520-34 was subsequently evaluated for therapeutically relevant actions in a transgenic animal model of Parkinson's disease that overexpresses human ASYN and in an acute lipopolysaccharide (LPS)-challenge model using wild-type mice. Daily administration of NPT520-34 to mThy1-ASYN (Line 61) transgenic mice for one or three months resulted in reduced ASYN pathology, reduced expression of markers of neuroinflammation, and improvements in multiple indices of motor function. In an LPS-challenge model using wild-type mice, a single-dose of NPT520-34 reduced LPS-evoked increases in the expression of several pro-inflammatory cytokines in plasma. These findings demonstrate the beneficial effects of NPT520-34 on both inflammation and protein-pathology endpoints, with consequent improvements in motor function in an animal model of Parkinson's disease. These findings further suggest that NPT520-34 may have two complementary actions: (1) to increase the clearance of neurotoxic protein aggregates and (2) to directly attenuate inflammation. NPT520-34 treatment may thereby address two of the predominate underlying pathophysiological aspects of neurodegenerative disorders such as Parkinson's disease.

Immunotherapies for Neurodegenerative Diseases

The current treatments for neurodegenerative diseases are mostly symptomatic without affecting the underlying cause of disease. Emerging evidence supports a potential role for immunotherapy in the management of disease progression. Numerous reports raise the exciting prospect that either the immune system or its derivative components could be harnessed to fight the misfolded and aggregated proteins that accumulate in several neurodegenerative diseases. Passive and active vaccinations using monoclonal antibodies and specific antigens that induce adaptive immune responses are currently under evaluation for their potential use in the development of immunotherapies. In this review, we aim to shed light on prominent immunotherapeutic strategies being developed to fight neuroinflammation-induced neurodegeneration, with a focus on innovative immunotherapies such as vaccination therapy.

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.

Harnessing the immune system for the treatment of Parkinson's disease

Current treatment options for Parkinson's disease (PD) typically aim to replace dopamine, and hence only provide symptomatic relief. However, in the long run, this approach alone loses its efficacy as it is associated with debilitating side effects. Hence there is an unmet clinical need for addressing levodopa resistant symptoms, and an urgency to develop therapies that can halt or prevent the course of PD. The premise that α-syn can transmit from cell-to-cell in a prion like manner has opened up the possibility for the use of immunotherapy in PD. There is evidence for inflammation in PD as is evidenced by microglial activation, as well as the involvement of the peripheral immune system in PD, and peripheral inflammation can exacerbate dopaminergic degeneration as seen in animal models of the disease. However, mechanisms that link the immune system with PD are not clear, and the sequence of immune responses with respect to PD are still unknown. Nevertheless, our present knowledge offers avenues for the development of immune-based therapies for PD. In order to successfully employ such strategies, we must comprehend the state of the peripheral immune system during the course of PD. This review describes the developments in the field of both active and passive immunotherapies in the treatment of PD, and highlights the crucial need for future research for clarifying the role of inflammation and immunity in this debilitating disease.

LRRK2 mediates microglial neurotoxicity via NFATc2 in rodent models of synucleinopathies

Synucleinopathies are neurodegenerative disorders characterized by abnormal α-synuclein deposition that include Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy. The pathology of these conditions also includes neuronal loss and neuroinflammation. Neuron-released α-synuclein has been shown to induce neurotoxic, proinflammatory microglial responses through Toll-like receptor 2, but the molecular mechanisms involved are poorly understood. Here, we show that leucine-rich repeat kinase 2 (LRRK2) plays a critical role in the activation of microglia by extracellular α-synuclein. Exposure to α-synuclein was found to enhance LRRK2 phosphorylation and activity in mouse primary microglia. Furthermore, genetic and pharmacological inhibition of LRRK2 markedly diminished α-synuclein-mediated microglial neurotoxicity via lowering of tumor necrosis factor-α and interleukin-6 expression in mouse cultures. We determined that LRRK2 promoted a neuroinflammatory cascade by selectively phosphorylating and inducing nuclear translocation of the immune transcription factor nuclear factor of activated T cells, cytoplasmic 2 (NFATc2). NFATc2 activation was seen in patients with synucleinopathies and in a mouse model of synucleinopathy, where administration of an LRRK2 pharmacological inhibitor restored motor behavioral deficits. Our results suggest that modulation of LRRK2 and its downstream signaling mediator NFATc2 might be therapeutic targets for treating synucleinopathies.

Safety and immunogenicity of the α-synuclein active immunotherapeutic PD01A in patients with Parkinson's disease: a randomised, single-blinded, phase 1 trial

BACKGROUND

Robust evidence supports the role of α-synuclein pathology as a driver of neuronal dysfunction in Parkinson's disease. PD01A is a specific active immunotherapy with a short peptide formulation targeted against oligomeric α-synuclein. This phase 1 study assessed the safety and tolerability of the PD01A immunotherapeutic in patients with Parkinson's disease.

METHODS

We did a first-in-human, randomised, phase 1 study of immunisations with PD01A, followed by three consecutive study extensions. Patients aged 45-65 years with a clinical diagnosis of Parkinson's disease (≤4 years since diagnosis and Hoehn and Yahr Stage 1 to 2), imaging results (dopamine transporter single photon emission CT and MRI) consistent with their Parkinson's disease diagnosis, and on stable doses of Parkinson's disease medications for at least 3 months were recruited at a single private clinic in Vienna, Austria. Patients were randomly assigned (1:1), using a computer-generated sequence with varying block size, to receive four subcutaneous immunisations with either 15 μg or 75 μg PD01A injected into the upper arms and followed up initially for 52 weeks, followed by a further 39 weeks' follow-up. Patients were then randomly assigned (1:1) again to receive the first booster immunisation at 15 μg or 75 μg and were followed up for 24 weeks. All patients received a second booster immunisation of 75 μg and were followed up for an additional 52 weeks. Patients were masked to dose allocation. Primary (safety) analyses included all treated patients. These four studies were registered with EU Clinical Trials Register, EudraCT numbers 2011-002650-31, 2013-001774-20, 2014-002489-54, and 2015-004854-16.

FINDINGS

32 patients were recruited between Feb 14, 2012, and Feb 6, 2013, and 24 were deemed eligible and randomly assigned to receive four PD01A priming immunisations. One patient had a diagnosis change to multiple system atrophy and was withdrawn and two patients withdrew consent during the studies. 21 (87%) of 24 patients received all six immunisations and completed 221-259 weeks in-study (two patients in the 15 μg dose group and one patient in the 75 μg dose group discontinued). All patients experienced at least one adverse event, but most of them were considered unrelated to study treatment (except for transient local injection site reactions, which affected all but one patient). Serial MRI assessments also ruled out inflammatory processes. Systemic treatment-related adverse events were fatigue (n=4), headache (n=3), myalgia (n=3), muscle rigidity (n=2), and tremor (n=2). The geometric group mean titre of antibodies against the immunising peptide PD01 increased from 1:46 at baseline to 1:3580 at week 12 in the 15 μg dose group, and from 1:76 to 1:2462 at week 12 in the 75 μg dose group. Antibody titres returned to baseline over 2 years, but could be rapidly reactivated after booster immunisation from week 116 onwards, reaching geometric group mean titres up to 1:20218.

INTERPRETATION

Repeated administrations of PD01A were safe and well tolerated over an extended period. Specific active immunotherapy resulted in a substantial humoral immune response with target engagement. Phase 2 studies are needed to further assess the safety and efficacy of PD01A for the treatment of Parkinson's disease.

FUNDING

AFFiRiS, Michael J Fox Foundation.

α-Synuclein in Parkinson's Disease: Does a Prion-Like Mechanism of Propagation from Periphery to the Brain Play a Role?

Parkinson's disease (PD) is one of the most common neurodegenerative diseases, defined as motor and non-motor symptoms associated with the loss of dopaminergic neurons and a decreased release of dopamine (DA). Currently, PD patients are believed to have a neuropathological basis denoted by the presence of Lewy bodies (LBs) or Lewy neurites (LNs), which mostly comprise α-synuclein (α-syn) inclusions. Remarkably, there is a growing body of evidence indicating that the inclusions undergo template-directed aggregation and propagation via template-directed among the brain and peripheral organs, mainly in a prion-like manner. Interestingly, some studies reported that an integral loop was reminiscent of the mechanism of Parkinson's disease, denoting that α-syn as prionoid was transmitted from the periphery to the brain via specific pathways. Also the systematic life cycle of α-syn in the cellular level is illustrated. In this review, we critically assess landmark evidence in the field of Parkinson's disease with a focus on the genesis and prion-like propagation of the α-syn pathology. The anatomical and cell-to-cell evidences are discussed to depict the theory behind the propagation and transferred pathways. Furthermore, we highlight effective therapeutic perspectives and clinical trials targeting prion-like mechanisms. Major controversies surrounding this topic are also discussed.

Immunotherapies for Aging-Related Neurodegenerative Diseases-Emerging Perspectives and New Targets

Neurological disorders such as Alzheimer's disease (AD), Lewy body dementia (LBD), frontotemporal dementia (FTD), and vascular dementia (VCID) have no disease-modifying treatments to date and now constitute a dementia crisis that affects 5 million in the USA and over 50 million worldwide. The most common pathological hallmark of these age-related neurodegenerative diseases is the accumulation of specific proteins, including amyloid beta (Aβ), tau, α-synuclein (α-syn), TAR DNA-binding protein 43 (TDP43), and repeat-associated non-ATG (RAN) peptides, in the intra- and extracellular spaces of selected brain regions. Whereas it remains controversial whether these accumulations are pathogenic or merely a byproduct of disease, the majority of therapeutic research has focused on clearing protein aggregates. Immunotherapies have garnered particular attention for their ability to target specific protein strains and conformations as well as promote clearance. Immunotherapies can also be neuroprotective: by neutralizing extracellular protein aggregates, they reduce spread, synaptic damage, and neuroinflammation. This review will briefly examine the current state of research in immunotherapies against the 3 most commonly targeted proteins for age-related neurodegenerative disease: Aβ, tau, and α-syn. The discussion will then turn to combinatorial strategies that enhance the effects of immunotherapy against aggregating protein, followed by new potential targets of immunotherapy such as aging-related processes.

Targeting α-synuclein for PD Therapeutics: A Pursuit on All Fronts

Parkinson's Disease (PD) is characterized both by the loss of dopaminergic neurons in the substantia nigra and the presence of cytoplasmic inclusions called Lewy Bodies. These Lewy Bodies contain the aggregated α-synuclein (α-syn) protein, which has been shown to be able to propagate from cell to cell and throughout different regions in the brain. Due to its central role in the pathology and the lack of a curative treatment for PD, an increasing number of studies have aimed at targeting this protein for therapeutics. Here, we reviewed and discussed the many different approaches that have been studied to inhibit α-syn accumulation via direct and indirect targeting. These analyses have led to the generation of multiple clinical trials that are either completed or currently active. These clinical trials and the current preclinical studies must still face obstacles ahead, but give hope of finding a therapy for PD with time.

Friend, Foe or Both? Immune Activity in Alzheimer's Disease

Alzheimer's disease (AD) is marked by the presence of amyloid beta (Aβ) plaques, neurofibrillary tangles (NFT), neuronal death and synaptic loss, and inflammation in the brain. AD research has, in large part, been dedicated to the understanding of Aβ and NFT deposition as well as to the pharmacological reduction of these hallmarks. However, recent GWAS data indicates neuroinflammation plays a critical role in AD development, thereby redirecting research efforts toward unveiling the complexities of AD-associated neuroinflammation. It is clear that the innate immune system is intimately associated with AD progression, however, the specific roles of glia and neuroinflammation in AD pathology remain to be described. Moreover, inflammatory processes have largely been painted as detrimental to AD pathology, when in fact, many immune mechanisms such as phagocytosis aid in the reduction of AD pathologies. In this review, we aim to outline the delicate balance between the beneficial and detrimental aspects of immune activation in AD as a more thorough understanding of these processes is critical to development of effective therapeutics for AD.

Ginkgolic acid promotes autophagy-dependent clearance of intracellular alpha-synuclein aggregates

The accumulation of intracytoplasmic inclusion bodies (Lewy bodies) composed of aggregates of the alpha-synuclein (α-syn) protein is the principal pathological characteristic of Parkinson's disease (PD) and may lead to degeneration of dopaminergic neurons. To date there is no medication that can promote the efficient clearance of these pathological aggregates. In this study, the effect on α-syn aggregate clearance of ginkgolic acid (GA), a natural compound extracted from Ginkgo biloba leaves that inhibits SUMOylation amongst other pathways, was assessed in SH-SY5Y neuroblastoma cells and rat primary cortical neurons. Depolarization of SH-SY5Y neuroblastoma cells and rat primary cortical neurons with KCl was used to induce α-syn aggregate formation. Cells pre-treated with either GA or the related compound, anacardic acid, revealed a significant decrease in intracytoplasmic aggregates immunopositive for α-syn and SUMO-1. An increased frequency of autophagosomes was also detected with both compounds. GA post-treatment 24 h after depolarization also significantly diminished α-syn aggregate bearing cells, indicating the clearance of pre-formed aggregates. Autophagy inhibitors blocked GA-dependent clearance of α-syn aggregates, but not increased autophagosome frequency. Western analysis revealed that the reduction in α-syn aggregate frequency obtained with GA pre-treatment was accompanied by little change in the abundance of SUMO conjugates. The current findings show that GA can promote autophagy-dependent clearance of α-syn aggregates and may have potential in disease modifying therapy.

Clinical implications of extracellular vesicles in neurodegenerative diseases

Introduction: Extracellular vesicles (EVs) released by neural cells play a crucial role in intracellular communication in both physiological and pathological states. Recent studies have shown that the neuropathogenic manifestation of many progressive nervous system diseases including Parkinson's disease (PD), Alzheimer's diseases (AD), and amyotrophic lateral sclerosis (ALS). These diseases are frequently found to be associated with the accumulation of misfolded proteins, exploit EVs for the spread of aggregates to naive cells in a prion-like mechanism. Therefore, characterization of EVs and understanding their mechanism of action could open a window of opportunity to discover biomarkers and therapeutic targets in a disease-specific manner. Areas covered: In this review, we discuss the role of neural cells-derived EVs in normal and disease states. We also highlight their biomedical potential in modern medicine, including the use of circulating EVs as biomarkers for diagnosis with a special focus on newly-identified potential biomarkers in neurodegenerative disease, and novel methodologies in EVs isolation. Expert opinion: Systematic and comprehensive analysis of EVs in different biofluid sources is needed. Considering the potential for tremendous clinical benefits of EVs research in neurodegenerative disease, there is also an urgent need to standardize neural cells-derived EV enrichment protocols for consensus results.

Effects of single and combined immunotherapy approach targeting amyloid β protein and α-synuclein in a dementia with Lewy bodies-like model

INTRODUCTION

Immunotherapeutic approaches targeting amyloid β (Aβ) protein and tau in Alzheimer's disease and α-synuclein (α-syn) in Parkinson's disease are being developed for treating dementia with Lewy bodies. However, it is unknown if single or combined immunotherapies targeting Aβ and/or α-syn may be effective.

METHODS

Amyloid precursor protein/α-syn tg mice were immunized with AFFITOPEs® (AFF) peptides specific to Aβ (AD02) or α-syn (PD-AFF1) and the combination.

RESULTS

AD02 more effectively reduced Aβ and pTau burden; however, the combination exhibited some additive effects. Both AD02 and PD-AFF1 effectively reduced α-syn, ameliorated degeneration of pyramidal neurons, and reduced neuroinflammation. PD-AFF1 more effectively ameliorated cholinergic and dopaminergic fiber loss; the combined immunization displayed additive effects. AD02 more effectively improved buried pellet test behavior, whereas PD-AFF1 more effectively improved horizontal beam test; the combined immunization displayed additive effects.

DISCUSSION

Specific active immunotherapy targeting Aβ and/or α-syn may be of potential interest for the treatment of dementia with Lewy bodies.

Systemic peptide mediated delivery of an siRNA targeting α-syn in the CNS ameliorates the neurodegenerative process in a transgenic model of Lewy body disease

Neurodegenerative disorders of the aging population are characterized by progressive accumulation of neuronal proteins such as α-synuclein (α-syn) in Parkinson's Disease (PD) and Amyloid ß (Aß) and Tau in Alzheimer's disease (AD) for which no treatments are currently available. The ability to regulate the expression at the gene transcription level would be beneficial for reducing the accumulation of these proteins or regulating expression levels of other genes in the CNS. Short interfering RNA molecules can bind specifically to target RNAs and deliver them for degradation. This approach has shown promise therapeutically in vitro and in vivo in mouse models of PD and AD and other neurological disorders; however, delivery of the siRNA to the CNS in vivo has been achieved primarily through intra-cerebral or intra-thecal injections that may be less amenable for clinical translation; therefore, alternative approaches for delivery of siRNAs to the brain is needed. Recently, we described a small peptide from the envelope protein of the rabies virus (C2-9r) that was utilized to deliver an siRNA targeting α-syn across the blood brain barrier (BBB) following intravenous injection. This approach showed reduced expression of α-syn and neuroprotection in a toxic mouse model of PD. However, since receptor-mediated delivery is potentially saturable, each allowing the delivery of a limited number of molecules, we identified an alternative peptide for the transport of nucleotides across the BBB based on the apolipoprotein B (apoB) protein targeted to the family of low-density lipoprotein receptors (LDL-R). We used an 11-amino acid sequence from the apoB protein (ApoB11) that, when coupled with a 9-amino acid arginine linker, can transport siRNAs across the BBB to neuronal and glial cells. To examine the value of this peptide mediated oligonucleotide delivery system for PD, we delivered an siRNA targeting the α-syn (siα-syn) in a transgenic mouse model of PD. We found that ApoB11 was effective (comparable to C2-9r) at mediating the delivery of siα-syn into the CNS, co-localized to neurons and glial cells and reduced levels of α-syn protein translation and accumulation. Delivery of ApoB11/siα-syn was accompanied by protection from degeneration of selected neuronal populations in the neocortex, limbic system and striato-nigral system and reduced neuro-inflammation. Taken together, these results suggest that systemic delivery of oligonucleotides targeting α-syn using ApoB11 might be an interesting alternative strategy worth considering for the experimental treatment of synucleinopathies.

Antibodies against alpha-synuclein: tools and therapies

Synucleinopathies including Parkinson's disease, dementia with Lewy bodies and multiple system atrophy are characterized by the abnormal accumulation and propagation of α-synuclein (α-syn) pathology in the central and peripheral nervous system as Lewy bodies or glial cytoplasmic inclusions. Several antibodies against α-syn have been developed since it was first detected as the major component of Lewy bodies and glial cytoplasmic inclusions. Over the years, researchers have generated specific antibodies that alleviate the accumulation of intracellular aggregated α-syn and associated pathology in cellular and preclinical models of synucleinopathies. So far, antibodies have been the first choice as tools for research and diagnosis and currently, a wide variety of antibody fragments have been developed as an alternative to full-length antibodies for increasing its therapeutic usefulness. Recently, conformation specific antibody-based approaches have been found to be promising as therapeutic strategies, both to block α-syn aggregation and ameliorate the resultant cytotoxicity, and as diagnostic tools. In this review, we summarize different α-syn specific antibodies and provide their usefulness in tackling synucleinopathies. This article is part of the Special Issue "Synuclein".

Dale Schenk One Year Anniversary: Fighting to Preserve the Memories

It has been a year since we lost Dale Schenk on September 30, 2016. Dale's visionary work resulted in the remarkable discovery in 1999 that an experimental amyloid-β (Aβ) vaccine reduced the neurodegeneration in a transgenic model of Alzheimer's disease (AD). Following Dale's seminal work, several active and passive immunotherapies have since been developed and tested in the clinic for AD, Parkinson's disease (PD), and other neurodegenerative disorders. Here we provide a brief overview of the current state of development of immunotherapy for AD, PD, and other neurodegenerative disorders in the context of this anniversary. The next steps in the development of immunotherapies will require combinatorial approaches mixing antibodies against various targets (e.g., Aβ, α-syn, Tau, and TDP43) with small molecules that block toxicity, aggregation, inflammation, and promote cell survival.

Immune system and new avenues in Parkinson’s disease research and treatment

Parkinson’s disease (PD) is a progressive neurological disorder characterized by degeneration of dopaminergic neurons in the substantia nigra. However, although 200 years have now passed since the primary clinical description of PD by James Parkinson, the etiology and mechanisms of neuronal loss in this disease are still not fully understood. In addition to genetic and environmental factors, activation of immunologic responses seems to have a crucial role in PD pathology. Intraneuronal accumulation of α-synuclein (α-Syn), as the main pathological hallmark of PD, potentially mediates initiation of the autoimmune and inflammatory events through, possibly, auto-reactive T cells. While current therapeutic regimens are mainly used to symptomatically suppress PD signs, application of the disease-modifying therapies including immunomodulatory strategies may slow down the progressive neurodegeneration process of PD. The aim of this review is to summarize knowledge regarding previous studies on the relationships between autoimmune reactions and PD pathology as well as to discuss current opportunities for immunomodulatory therapy.

Emerging Immunotherapies for Parkinson Disease

Symptomatic treatment options for Parkinson disease have steadily improved, and individualized therapeutic approaches are becoming established for every stage of the disease. However, disease-modifying therapy with a causal approach is still unavailable. The central causative role of alpha-synuclein pathology, including its progressive spread to most areas of the CNS, has been widely recognized, and a strong involvement of immune responses has recently been discovered. New immunologic technologies have been shown to effectively prevent the progression of alpha-synuclein pathology in animal models. These approaches have recently been translated into the first human clinical trials, representing a novel starting point for the causal therapy of Parkinson disease. In this review, the pathomechanistic role of alpha-synuclein and its influence on the surrounding cellular environment are analyzed with a strong focus on immune responses and neuroinflammation. The potential of novel immunotherapeutic approaches that reduce the burden of alpha-synuclein pathology in the CNS is critically evaluated, and currently ongoing human clinical trials are presented. The clinical development of these new immunotherapies is progressing rapidly and gives reason to hope that a causal therapy of Parkinson disease could be possible in the foreseeable future.

Naturally occurring autoantibodies against α-synuclein rescues memory and motor deficits and attenuates α-synuclein pathology in mouse model of Parkinson's disease

It has been suggested that aggregation of α-synuclein (α-syn) into oligomers leads to neurodegeneration in Parkinson's disease (PD), but intravenous immunoglobulin (IVIG) which contains antibodies against α-syn monomers and oligomers fails to treat PD mouse model. The reason may be because IVIG contains much low level of antibodies against α-syn, and of which only a small part can penetrate the blood-brain barrier, resulting in an extremely low level of effective antibodies in the brain, and limiting the beneficial effect of IVIG on PD mice. Here, we first isolated naturally occurring autoantibodies against α-syn (NAbs-α-syn) from IVIG. Our further investigation results showed that NAbs-α-syn inhibited α-syn aggregation and attenuated α-syn-induced cytotoxicity in vitro. Compared with vehicles, NAbs-α-syn significantly attenuated the memory and motor deficits by reducing the levels of soluble α-syn, total human α-syn and α-syn oligomers, decreasing the intracellular p-α-syn^ser129 deposits and axonal pathology, inhibiting the microgliosis and astrogliosis, as well as the production of proinflammatory cytokines, increasing the levels of PSD95, synaptophysin and TH in the brain of A53T transgenic mice. These findings suggest that NAbs-α-syn overcomes the deficiency of IVIG and exhibits a promising therapeutic potential for the treatment of PD.

New Perspectives on Roles of Alpha-Synuclein in Parkinson's Disease

Parkinson’s disease (PD) is one of the synucleinopathies spectrum of disorders typified by the presence of intraneuronal protein inclusions. It is primarily composed of misfolded and aggregated forms of alpha-synuclein (α-syn), the toxicity of which has been attributed to the transition from an α-helical conformation to a β-sheetrich structure that polymerizes to form toxic oligomers. This could spread and initiate the formation of “LB-like aggregates,” by transcellular mechanisms with seeding and subsequent permissive templating. This hypothesis postulates that α-syn is a prion-like pathological agent and responsible for the progression of Parkinson’s pathology. Moreover, the involvement of the inflammatory response in PD pathogenesis has been reported on the excessive microglial activation and production of pro-inflammatory cytokines. At last, we describe several treatment approaches that target the pathogenic α-syn protein, especially the oligomers, which are currently being tested in advanced animal experiments or are already in clinical trials. However, there are current challenges with therapies that target α-syn, for example, difficulties in identifying varying α-syn conformations within different individuals as well as both the cost and need of long-duration large trials.

Antibody-based methods for the measurement of α-synuclein concentration in human cerebrospinal fluid - method comparison and round robin study

α‐Synuclein is the major component of Lewy bodies and a candidate biomarker for neurodegenerative diseases in which Lewy bodies are common, including Parkinson's disease and dementia with Lewy bodies. A large body of literature suggests that these disorders are characterized by reduced concentrations of α‐synuclein in cerebrospinal fluid (CSF), with overlapping concentrations compared to healthy controls and variability across studies. Several reasons can account for this variability, including technical ones, such as inter‐assay and inter‐laboratory variation (reproducibility). We compared four immunochemical methods for the quantification of α‐synuclein concentration in 50 unique CSF samples. All methods were designed to capture most of the existing α‐synuclein forms in CSF (‘total’ α‐synuclein). Each of the four methods showed high analytical precision, excellent correlation between laboratories (R² 0.83–0.99), and good correlation with each other (R² 0.64–0.93), although the slopes of the regression lines were different between the four immunoassays. The use of common reference CSF samples decreased the differences in α‐synuclein concentration between detection methods and technologies. Pilot data on an immunoprecipitation mass spectrometry (IP‐MS) method is also presented. Our results suggest that the four immunochemical methods and the IP‐MS method measure similar forms of α‐synuclein and that a common reference material would allow harmonization of results between immunoassays.

Passive Immunotherapies for Central Nervous System Disorders: Current Delivery Challenges and New Approaches

Passive immunotherapy, i.e., the administration of exogenous antibodies that recognize a specific target antigen, has gained significant momentum as a potential treatment strategy for several central nervous system (CNS) disorders, including Alzheimer's disease, Parkinson's disease, Huntington's disease, and brain cancer, among others. Advances in antibody engineering to create therapeutic antibody fragments or antibody conjugates have introduced new strategies that may also be applied to treat CNS disorders. However, drug delivery to the CNS for antibodies and other macromolecules has thus far proven challenging, due in large part to the blood-brain barrier and blood-cerebrospinal fluid barriers that greatly restrict transport of peripherally administered molecules from the systemic circulation into the CNS. Here, we summarize the various passive immunotherapy approaches under study for the treatment of CNS disorders, with a primary focus on disease-specific and target site-specific challenges to drug delivery and new, cutting edge methods.

Inhibition of protein misfolding and aggregation by natural phenolic compounds

Protein misfolding and aggregation into fibrillar deposits is a common feature of a large group of degenerative diseases affecting the central nervous system or peripheral organs, termed protein misfolding disorders (PMDs). Despite their established toxic nature, clinical trials aiming to reduce misfolded aggregates have been unsuccessful in treating or curing PMDs. An interesting possibility for disease intervention is the regular intake of natural food or herbal extracts, which contain active molecules that inhibit aggregation or induce the disassembly of misfolded aggregates. Among natural compounds, phenolic molecules are of particular interest, since most have dual activity as amyloid aggregation inhibitors and antioxidants. In this article, we review many phenolic natural compounds which have been reported in diverse model systems to have the potential to delay or prevent the development of various PMDs, including Alzheimer's and Parkinson's diseases, prion diseases, amyotrophic lateral sclerosis, systemic amyloidosis, and type 2 diabetes. The lower toxicity of natural compounds compared to synthetic chemical molecules suggest that they could serve as a good starting point to discover protein misfolding inhibitors that might be useful for the treatment of various incurable diseases.

Recombinant Antibody Fragments for Neurodegenerative Diseases

BACKGROUND

Recombinant antibody fragments are promising alternatives to full-length immunoglobulins and offer important advantages compared with conventional monoclonal antibodies: extreme specificity, higher affinity, superior stability and solubility, reduced immunogenicity as well as easy and inexpensive large-scale production.

OBJECTIVE

In this article we will review and discuss recombinant antibodies that are being evaluated for neurodegenerative diseases in pre-clinical models and in clinical studies and will summarize new strategies that are being developed to optimize their stability, specificity and potency for advancing their use.

METHODS

Articles describing recombinant antibody fragments used for neurological diseases were selected (PubMed) and evaluated for their significance.

RESULTS

Different antibody formats such as single-chain fragment variable (scFv), single-domain antibody fragments (VHHs or sdAbs), bispecific antibodies (bsAbs), intrabodies and nanobodies, are currently being studied in pre-clinical models of cancer as well as infectious and autoimmune diseases and many of them are being tested as therapeutics in clinical trials. Immunotherapy approaches have shown therapeutic efficacy in several animal models of Alzheimer´s disease (AD), Parkinson disease (PD), dementia with Lewy bodies (DLB), frontotemporal dementia (FTD), Huntington disease (HD), transmissible spongiform encephalopathies (TSEs) and multiple sclerosis (MS). It has been demonstrated that recombinant antibody fragments may neutralize toxic extra- and intracellular misfolded proteins involved in the pathogenesis of AD, PD, DLB, FTD, HD or TSEs and may target toxic immune cells participating in the pathogenesis of MS.

CONCLUSION

Recombinant antibody fragments represent a promising tool for the development of antibody-based immunotherapeutics for neurodegenerative diseases.