Alpha-Synuclein in the Gastrointestinal Tract as a Potential Biomarker for Early Detection of Parkinson's Disease

Parkinson disease therapy: current strategies and future research priorities

Parkinson disease (PD) is the fastest growing neurological disorder globally and poses substantial management challenges owing to progressive disability, emergence of levodopa-resistant symptoms, and treatment-related complications. In this Review, we examine the current state of research into PD therapies and outline future priorities for advancing our understanding and treatment of the disease. We identify two main research priorities for the coming years: first, slowing the progression of the disease through the integration of sensitive biomarkers and targeted biological therapies, and second, enhancing existing symptomatic treatments, encompassing surgical and infusion therapies, with the goal of postponing complications and improving long-term patient management. The path towards disease modification is impeded by the multifaceted pathophysiology and diverse mechanisms underlying PD. Ongoing studies are directed at α-synuclein aggregation, complemented by efforts to address specific pathways associated with the less common genetic forms of the disease. The success of these efforts relies on establishing robust end points, incorporating technology, and identifying reliable biomarkers for early diagnosis and continuous monitoring of disease progression. In the context of symptomatic treatment, the focus should shift towards refining existing approaches and fostering the development of novel therapeutic strategies that target levodopa-resistant symptoms and clinical manifestations that substantially impair quality of life.

Microbiome-based therapies for Parkinson's disease

The human gut microbiome dysbiosis plays an important role in the pathogenesis of Parkinson's disease (PD). The bidirectional relationship between the enteric nervous system (ENS) and central nervous system (CNS) under the mediation of the gut-brain axis control the gastrointestinal functioning. This review article discusses key mechanisms by which modifications in the composition and function of the gut microbiota (GM) influence PD progression and motor control loss. Increased intestinal permeability, chronic inflammation, oxidative stress, α-synuclein aggregation, and neurotransmitter imbalances are some key factors that govern gastrointestinal pathology and PD progression. The bacterial taxa of the gut associated with PD development are discussed with emphasis on the enteric nervous system (ENS), as well as the impact of gut bacteria on dopamine production and levodopa metabolism. The pathophysiology and course of the disease are associated with several inflammatory markers, including TNF-α, IL-1β, and IL-6. Emerging therapeutic strategies targeting the gut microbiome include probiotics, prebiotics, synbiotics, postbiotics, and fecal microbiota transplantation (FMT). The article explored how dietary changes may affect the gut microbiota (GM) and the ways that can affect Parkinson's disease (PD), with a focus on nutrition-based, Mediterranean, and ketogenic diets. This comprehensive review synthesizes current evidence on the role of the gut microbiome in PD pathogenesis and explores its potential as a therapeutic target. Understanding these complex interactions may assist in the development of novel diagnostic tools and treatment options for this neurodegenerative disorder.

The Relationship Between Autonomic Dysfunction and Mood Symptoms in De Novo Parkinson's Disease Patients Over Time

BACKGROUND

Autonomic dysfunction is prevalent in Parkinson's disease (PD) and can worsen quality of life. We examined: (a) whether specific autonomic symptoms were more strongly associated with anxiety or depression in PD and (b) whether overall autonomic dysfunction predicted mood trajectories over a 5-year period.

METHODS

Newly diagnosed individuals with PD (N = 414) from the Parkinson's Progression Markers Initiative completed self-report measures of depression, anxiety, and autonomic symptoms annually. Cross-sectional linear regressions examined relationships between specific autonomic subdomains (gastrointestinal, cardiovascular, thermoregulatory, etc.) and mood. Multilevel modeling examined longitudinal relationships with total autonomic load.

RESULTS

Gastrointestinal symptoms were associated with both higher anxiety (b = 1.04, 95% CI [.55, 1.53], P < .001) and depression (b = .24, 95% CI [.11, .37], P = .012), as were thermoregulatory symptoms (anxiety: b = 1.06, 95% CI [.46, 1.65], P = .004; depression: b = .25, 95% CI [.09, .42], P = .013), while cardiovascular (b = .36, 95% CI [.10, .62], P = .012) and urinary symptoms (b = .10, 95% CI [.01, .20], P = .037) were associated only with depression. Longitudinally, higher total autonomic load was associated with increases in both depression (b = .01, 95% CI [.00, .02], P = .015) and anxiety (b = .04, 95% CI [.01, .06], P < .001) over time, as well as occasion-to-occasion fluctuations (depression: b = .08, 95% CI [.05, .10], P < .001; anxiety: b = .24, 95% CI [.15, .32], P < .001).

CONCLUSION

Findings suggest autonomic dysfunction, particularly gastrointestinal and thermoregulatory symptoms, may be an indicator for elevated anxiety/depression and a potential treatment target early on in PD.

The Golgi complex of dopaminergic enteric neurons is fragmented in a hemiparkinsonian rat model

Since gastrointestinal disorders are early consequences of Parkinson's disease (PD), this disease is clearly not restricted to the central nervous system (CNS), but also significantly affects the enteric nervous system (ENS). Large aggregates of the protein α-synuclein forming Lewy bodies, the prototypical cytopathological marker of this disease, have been observed in enteric nervous plexuses. However, their value in early prognosis is controversial. The Golgi complex (GC) of nigral neurons appears fragmented in Parkinson's disease, a characteristic common in most neurodegenerative diseases. In addition, the distribution and levels of regulatory proteins such as Rabs and SNAREs are altered, suggesting that PD is a membrane traffic-related pathology. Whether the GC of enteric dopaminergic neurons is affected by the disease has not yet been analyzed. In the present study, dopaminergic neurons in colon nervous plexuses behave as nigral neurons in a hemiparkinsonian rat model based on the injection of the toxin 6-OHDA. Their GCs are fragmented, and some regulatory proteins' distribution and expression levels are altered. The putative mechanisms of the transmission of the neurotoxin to the ENS are discussed. Our results support the possibility that GC structure and the level of some proteins, especially syntaxin 5, could be helpful as early indicators of the disease. RESEARCH HIGHLIGHTS: The Golgi complexes of enteric dopaminergic neurons appear fragmented in a Parkinson's disease rat model. Our results support the hypothesis that the Golgi complex structure and levels of Rab1 and syntaxin 5 could be helpful as early indicators of the disease.

The Potentiality of Natural Products and Herbal Medicine as Novel Medications for Parkinson's Disease: A Promising Therapeutic Approach

As the global population ages, the prevalence of Parkinson's disease (PD) is steadily on the rise. PD demonstrates chronic and progressive characteristics, and many cases can transition into dementia. This increases societal and economic burdens, emphasizing the need to find effective treatments. Among the widely recognized causes of PD is the abnormal accumulation of proteins, and autophagy dysfunction accelerates this accumulation. The resultant Lewy bodies are also commonly found in Alzheimer's disease patients, suggesting an increased potential for the onset of dementia. Additionally, the production of free radicals due to mitochondrial dysfunction contributes to neuronal damage and degeneration. The activation of astrocytes and the M1 phenotype of microglia promote damage to dopamine neurons. The drugs currently used for PD only delay the clinical progression and exacerbation of the disease without targeting its root cause, and come with various side effects. Thus, there is a demand for treatments with fewer side effects, with much potential offered by natural products. In this study, we reviewed a total of 14 articles related to herbal medicines and natural products and investigated their relevance to possible PD treatment. The results showed that the reviewed herbal medicines and natural products are effective against lysosomal disorder, mitochondrial dysfunction, and inflammation, key mechanisms underlying PD. Therefore, natural products and herbal medicines can reduce neurotoxicity and might improve both motor and non-motor symptoms associated with PD. Furthermore, these products, with their multi-target effects, enhance bioavailability, inhibit antibiotic resistance, and might additionally eliminate side effects, making them good alternative therapies for PD treatment.

Development of a hydroxyflavone-labelled 4554W peptide probe for monitoring αS aggregation

Parkinson's is the second most common neurodegenerative disease, with the number of individuals susceptible due to increase as a result of increasing life expectancy and a growing worldwide population. However, despite the number of individuals affected, all current treatments for PD are symptomatic-they alleviate symptoms, but do not slow disease progression. A major reason for the lack of disease-modifying treatments is that there are currently no methods to diagnose individuals during the earliest stages of the disease, nor are there any methods to monitor disease progression at a biochemical level. Herein, we have designed and evaluated a peptide-based probe to monitor αS aggregation, with a particular focus on the earliest stages of the aggregation process and the formation of oligomers. We have identified the peptide-probe K1 as being suitable for further development to be applied to number of applications including: inhibition of αS aggregation; as a probe to monitor αS aggregation, particularly at the earliest stages before Thioflavin-T is active; and a method to detect early-oligomers. With further development and in vivo validation, we anticipate this probe could be used for the early diagnosis of PD, a method to evaluate the effectiveness of potential therapeutics, and as a tool to help in the understanding of the onset and development of PD.

Immunological Features of LRRK2 Function and Its Role in the Gut-Brain Axis Governing Parkinson's Disease

Emerging evidence implicates intestinal involvement in the onset and/or progression on the selective degeneration of dopaminergic neurons characterizing Parkinson's disease (PD). On the one hand, there are studies supporting the Braak hypothesis that holds that pathologic α-synuclein, a hallmark of PD, is secreted by enteric nerves into intestinal tissue and finds its way to the central nervous system (CNS) via retrograde movement in the vagus nerve. On the other hand, there is data showing that cells bearing leucine-rich repeat kinase 2 (LRRK2), a signaling molecule with genetic variants associated with both PD and with inflammatory bowel disease, can be activated in intestinal tissue and contribute locally to intestinal inflammation, or peripherally to PD pathogenesis via cell trafficking to the CNS. Importantly, these gut-centered factors affecting PD development are not necessarily independent of one another: they may interact and enhance their respective pathologic functions. In this review, we discuss this possibility by analysis of studies conducted in recent years focusing on the ability of LRRK2 to shape immunologic responses and the role of α-synuclein in influencing this ability.

A review of the current research on in vivo and in vitro detection for alpha-synuclein: a biomarker of Parkinson's disease

Parkinson's disease is a health-threatening neurodegenerative disease of the elderly with clinical manifestations of motor and non-motor deficits such as tremor palsy and loss of smell. Alpha-synuclein (α-Syn) is the pathological basis of PD, it can abnormally aggregate into insoluble forms such as oligomers, fibrils, and plaques, causing degeneration of nigrostriatal dopaminergic neurons in the substantia nigra in the patient's brain and the formation of Lewy bodies (LBs) and Lewy neuritis (LN) inclusions. As a result, achieving α-Syn aggregate detection in the early stages of PD can effectively stop or delay the progression of the disease. In this paper, we provide a brief overview and analysis of the molecular structures and α-Syn in vivo and in vitro detection methods, such as mass spectrometry, antigen-antibody recognition, electrochemical sensors, and imaging techniques, intending to provide more technological support for detecting α-Syn early in the disease and intervening in the progression of Parkinson's disease.

Duodenal alpha-Synuclein Pathology and Enteric Gliosis in Advanced Parkinson's Disease

BACKGROUND

The role of the gut-brain axis has been recently highlighted as a major contributor to Parkinson's disease (PD) physiopathology, with numerous studies investigating bidirectional transmission of pathological protein aggregates, such as α-synuclein (αSyn). However, the extent and the characteristics of pathology in the enteric nervous system have not been fully investigated.

OBJECTIVE

We characterized αSyn alterations and glial responses in duodenum biopsies of patients with PD by employing topography-specific sampling and conformation-specific αSyn antibodies.

METHODS

We examined 18 patients with advanced PD who underwent Duodopa percutaneous endoscopic gastrostomy and jejunal tube procedure, 4 untreated patients with early PD (disease duration <5 years), and 18 age- and -sex-matched healthy control subjects undergoing routine diagnostic endoscopy. A mean of four duodenal wall biopsies were sampled from each patient. Immunohistochemistry was performed for anti-aggregated αSyn (5G4) and glial fibrillary acidic protein antibodies. Morphometrical semiquantitative analysis was performed to characterize αSyn-5G4⁺ and glial fibrillary acidic protein-positive density and size.

RESULTS

Immunoreactivity for aggregated α-Syn was identified in all patients with PD (early and advanced) compared with controls. αSyn-5G4⁺ colocalized with neuronal marker β-III-tubulin. Evaluation of enteric glial cells demonstrated an increased size and density when compared with controls, suggesting reactive gliosis.

CONCLUSIONS

We found evidence of synuclein pathology and gliosis in the duodenum of patients with PD, including early de novo cases. Future studies are required to evaluate how early in the disease process duodenal pathology occurs and its possible contribution to levodopa effect in chronic patients. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

The Neurodegenerative Elderly Syndrome (NES) hypothesis: Alzheimer and Parkinson are two faces of the same disease

Increasing evidence suggests that Alzheimer's disease (AD) and Parkinson's disease (PD) share monoamine and alpha-synuclein (αSyn) dysfunctions, often beginning years before clinical manifestations onset. The triggers for these impairments and the causes leading these early neurodegenerative processes to become AD or PD remain unclear. We address these issues by proposing a radically new perspective to frame AD and PD: they are different manifestations of one only disease we call "Neurodegenerative Elderly Syndrome (NES)". NES goes through three phases. The seeding stage, which starts years before clinical signs, and where the part of the brain-body affected by the initial αSyn and monoamine dysfunctions, influences the future possible progression of NES towards PD or AD. The compensatory stage, where the clinical symptoms are still silent thanks to compensatory mechanisms keeping monoamine concentrations homeostasis. The bifurcation stage, where NES becomes AD or PD. We present recent literature supporting NES and discuss how this hypothesis could radically change the comprehension of AD and PD comorbidities and the design of novel system-level diagnostic and therapeutic actions.

The Interplay between Gut Microbiota and Parkinson's Disease: Implications on Diagnosis and Treatment

The bidirectional interaction between the gut microbiota (GM) and the Central Nervous System, the so-called gut microbiota brain axis (GMBA), deeply affects brain function and has an important impact on the development of neurodegenerative diseases. In Parkinson’s disease (PD), gastrointestinal symptoms often precede the onset of motor and non-motor manifestations, and alterations in the GM composition accompany disease pathogenesis. Several studies have been conducted to unravel the role of dysbiosis and intestinal permeability in PD onset and progression, but the therapeutic and diagnostic applications of GM modifying approaches remain to be fully elucidated. After a brief introduction on the involvement of GMBA in the disease, we present evidence for GM alterations and leaky gut in PD patients. According to these data, we then review the potential of GM-based signatures to serve as disease biomarkers and we highlight the emerging role of probiotics, prebiotics, antibiotics, dietary interventions, and fecal microbiota transplantation as supportive therapeutic approaches in PD. Finally, we analyze the mutual influence between commonly prescribed PD medications and gut-microbiota, and we offer insights on the involvement also of nasal and oral microbiota in PD pathology, thus providing a comprehensive and up-to-date overview on the role of microbial features in disease diagnosis and treatment.

A simple-to-use web-based calculator for survival prediction in Parkinson's disease

Background: To establish and validate a nomogram and corresponding web-based calculator to predict the survival of patients with Parkinson’s disease (PD).

Methods: In this cohort study, we retrospectively evaluated patients (n=497) with PD using a two-stage design, from March 2004 to November 2007 and from July 2005 to July 2015. Predictive variables included in the model were identified by univariate and multiple Cox proportional hazard analyses in the training set.

Results: Independent prognostic factors including age, PD duration, and Hoehn and Yahr stage were determined and included in the model. The model showed good discrimination power with the area under the curve (AUC) values generated to predict 4-, 6-, and 8-year survival in the training set being 0.716, 0.783, and 0.814, respectively. In the validation set, the AUCs of 4- and 6-year survival predictions were 0.85 and 0.924, respectively. Calibration plots and decision curve analysis showed good model performance both in the training and validation sets. For convenient application, we established a web-based calculator (https://tangyl.shinyapps.io/PDprognosis/).

Conclusions: We developed a satisfactory, simple-to-use nomogram and corresponding web-based calculator based on three relevant factors to predict prognosis and survival of patients with PD. This model can aid personalized treatment and clinical decision-making.