Gastrointestinal involvement in Parkinson's disease: pathophysiology, diagnosis, and management

Localization Matters: Impacts of PEG-J Localization in Intestinal Levodopa Therapy for Parkinson's Disease

BACKGROUND

Real-world clinical evidence is missing to understand the resorption characteristics of levodopa through duodenal and jejunal parts of the small intestine.

OBJECTIVE

To characterize how different application sites of intestinal levodopa gel would impact on levodopa dosing and clinical outcomes.

METHODS

This multicentre retrospective analysis investigated Parkinson's disease patients (n = 111) and their change in levodopa equivalent dosage when switching from oral treatment to intestinal continuous infusion therapy while stratifying for differences in percutaneous gastrojejunostomy (PEG-J) tube localizations. We analyzed data from patients treated with both levodopa-carbidopa (LCIG) and levodopa-carbidopa-entacapone (LECIG) intestinal gel.

RESULTS

In dichotomic analysis, duodenal and jejunal tube positions showed similar levodopa equivalent dosages changes from baseline (P = 0.143). This was similar when subdividing patients for LCIG and LECIG treatment. In duodenal PEG-J positions, 44.4% of patients showed persistent motor fluctuations compared to 21.9% in jejunal placements (P = 0.026). In duodenal positions, fluctuations most often persisted when the PEG-J tube was placed proximally into the duodenum. In jejunal localizations, several patients displayed a satisfactory outcome from the primary intervention but experienced dislocation of the PEG-J tube to a duodenal position. This was associated with re-emergence of motor fluctuations in a majority of them.

CONCLUSIONS

Our real-world data suggest that LCIG and LECIG are absorbed similarly in both duodenal and jejunal portions of the small intestine. However, clinical data suggest, that jejunal positioning is critical to the stabilization of dopaminergic motor fluctuations.

A novel levodopa-carbidopa three-layer gastroretentive tablet for improving levodopa pharmacokinetics

The narrow absorption window of levodopa and the significant impact of peripheral decarboxylase are the most limiting factors in maintaining prolonged and smooth plasma concentration in patients with Parkinson's disease (PD). Therefore, this study aims to design a novel gastroretentive carbidopa-levodopa three-layer tablet, which consists of an expansion layer, an immediate-release layer, and a sustained-release layer. The expansion layer rapidly expanded with sufficient structural strength and stayed in the beagle's stomach for more than 10 h, delineating excellent gastric retention effects. The immediate-release layer quickly released the drug and the sustained-release layer maintained a stable drug concentration. Importantly, pharmacokinetic data obtained under fed conditions demonstrated that the duration of efficacy of the three-layer tablets was significantly superior to that of the commercially available product Sinemet® CR, with effective levodopa blood levels remaining for up to 12 h. This is expected to offer more convenient clinical medication options for patients with PD.

Epigenetic Biomarkers Driven by Environmental Toxins Associated with Alzheimer's Disease, Parkinson's Disease, and Amyotrophic Lateral Sclerosis in the United States: A Systematic Review

Environmental toxins and epigenetic changes have been linked to neurodegenerative diseases, including Alzheimer's Disease (AD), Parkinson's Disease (PD), and amyotrophic lateral sclerosis (ALS). This paper aimed to (i) identify environmental toxins associated with AD, PD, and ALS, (ii) locate potential industrial sources of toxins in the United States (U.S.), and (iii) assess epigenetic changes driven by exposure to toxins reported by patients. Environmental factors and epigenetic biomarkers of neurodegeneration were compiled from 69 studies in the literature using Preferred Reporting Items for Systematic Reviews and Meta Analyses (PRISMA) and geographic information system approaches. Some 127 environmental toxins have been associated or putatively associated with AD, PD, or ALS, with four toxic metals (As, Cd, Mn, and Hg) common to all three of these neurodegenerative diseases. Environmental toxins associated with epigenetic changes (e.g., DNA methylation) in patients include air pollutants, metals, and organic chemicals (e.g., pesticides, mycotoxins, and cyanotoxins). Geographic analysis showed that study locations (e.g., U.S., Europe, and East Asia) were selected by researchers based on convenience of access rather than exposure risk and disease prevalence. We conclude that several toxins and epigenetic markers shared among neurodegenerative diseases could serve as attractive future targets guiding environmental quality improvements and aiding in early disease detection.

Lewy body diseases and the gut

Gastrointestinal (GI) involvement in Lewy body diseases (LBDs) has been observed since the initial descriptions of patients by James Parkinson. Recent experimental and human observational studies raise the possibility that pathogenic alpha-synuclein (⍺-syn) might develop in the GI tract and subsequently spread to susceptible brain regions. The cellular and mechanistic origins of ⍺-syn propagation in disease are under intense investigation. Experimental LBD models have implicated important contributions from the intrinsic gut microbiome, the intestinal immune system, and environmental toxicants, acting as triggers and modifiers to GI pathologies. Here, we review the primary clinical observations that link GI dysfunctions to LBDs. We first provide an overview of GI anatomy and the cellular repertoire relevant for disease, with a focus on luminal-sensing cells of the intestinal epithelium including enteroendocrine cells that express ⍺-syn and make direct contact with nerves. We describe interactions within the GI tract with resident microbes and exogenous toxicants, and how these may directly contribute to ⍺-syn pathology along with related metabolic and immunological responses. Finally, critical knowledge gaps in the field are highlighted, focusing on pivotal questions that remain some 200 years after the first descriptions of GI tract dysfunction in LBDs. We predict that a better understanding of how pathophysiologies in the gut influence disease risk and progression will accelerate discoveries that will lead to a deeper overall mechanistic understanding of disease and potential therapeutic strategies targeting the gut-brain axis to delay, arrest, or prevent disease progression.

Disrupted Paraventricular Hypothalamic Nucleus Functional Connectivity in Parkinson's Disease With Constipation

BACKGROUND

Constipation is one of the most common non-motor symptoms in patients with Parkinson's disease (PD), which could manifest during the early stage of the disease. However, the etiology of constipation in PD remains largely unknown. Previous studies supported that gastrointestinal dysfunction may be associated with functional connectivity alterations in paraventricular hypothalamic nucleus (PVN). Therefore, this study aimed to investigate the potential contribution of the PVN to the pathogenesis of constipation in a cohort of early-stage patients with PD and to compare brain network organization between PD patients with and without constipation.

METHODS

A total of 66 PD patients (PD with constipation and without constipation) and 30 healthy controls were prospectively enrolled. All participants acquired T1-weighted and resting-state fMRI scans. Then we employed voxel-based morphometry analysis and functional connectivity analysis.

RESULTS

We observed a decreased functional connectivity in the PVN-pontine tegmentum pathway in PD patients with constipation compared to the patients without constipation (p = 0.006, t = 5.37), while we did not find any changes in basal ganglia circuitry between these two groups. In addition, we found that the functional connectivity between PVN and pontine tegmentum was negatively associated with the UPDRS I, II, III and NMSS scores (p < 0.05). Meanwhile, these two types of patients also showed substantial differences in functional connections linking the inferior frontal gyrus and cerebellum with multiple brain regions. We discovered no statistical difference in gray matter volume among these two groups.

CONCLUSIONS

Our study provides further insights into the dysfunctional mechanisms of constipation, suggesting that abnormal PVN functional connectivity may be related to the mechanism of constipation in PD. Meanwhile, the inferior frontal gyrus and cerebellum may be involved in the occurrence of constipation in PD patients.

The Gut-Brain Axis in Parkinson's Disease

Parkinson's disease (PD) involves both the central nervous system (CNS) and enteric nervous system (ENS), and their interaction is important for understanding both the clinical manifestations of the disease and the underlying disease pathophysiology. Although the neuroanatomical distribution of pathology strongly suggests that the ENS is involved in disease pathophysiology, there are significant gaps in knowledge about the underlying mechanisms. In this article, we review the clinical presentation and management of gastrointestinal dysfunction in PD. In addition, we discuss the current understanding of disease pathophysiology in the gut, including controversies about early involvement of the gut in disease pathogenesis. We also review current knowledge about gut α-synuclein and the microbiome, discuss experimental models of PD-linked gastrointestinal pathophysiology, and highlight areas for further research. Finally, we discuss opportunities to use the gut-brain axis for the development of biomarkers and disease-modifying treatments.

Diagnosis and treatment of autonomic failure, pain and sleep disturbances in Parkinson's disease: guideline "Parkinson's disease" of the German Society of Neurology

BACKGROUND AND OBJECTIVE

Non-motor symptoms frequently develop throughout the disease course of Parkinson's disease (PD), and pose affected individuals at risk of complications, more rapid disease progression and poorer quality of life. Addressing such symptom burden, the 2023 revised "Parkinson's disease" guideline of the German Society of Neurology aimed at providing evidence-based recommendations for managing PD non-motor symptoms, including autonomic failure, pain and sleep disturbances.

METHODS

Key PICO (Patient, Intervention, Comparison, Outcome) questions were formulated by the steering committee and refined by the assigned authors. Recommendations were drafted based on relevant studies, systematic reviews, meta-analyses and high-quality guidelines identified by the literature search. They were subsequently reviewed, revised, and voted by the Guideline Group in online consensus conferences. Consensus was achieved in case of > 75% agreement among the group members. The consensus was considered strong, if agreement was > 95%.

RESULTS

The guideline entails: (i) 10 PICOs and 23 recommendations on the diagnosis and treatment of urogenital, cardiovascular and gastrointestinal autonomic failure; (ii) four PICOs and four recommendations on the possible types of pain in PD individuals, their diagnosis and treatment; (iii) 11 PICOs and 11 recommendations on the screening, diagnosis and treatment of sleep disturbances and excessive daytime sleepiness in PD individuals, as well as on their prognostic implications. Thirty-one out of 38 recommendations achieved a strong consensus.

CONCLUSION

The current German PD guideline provides a practice-oriented and etiology-driven stepwise approach to the diagnosis and treatment of autonomic failure, pain and sleep disturbances in PD individuals.

Optical detection of the spatial structural alteration in the human brain tissues/cells and DNA/chromatin due to Parkinson's disease

Parkinson's disease (PD) is considered one of the most frequent neurological diseases in the world. There is a need to study the early and efficient biomarkers of Parkinson's, such as changes in structural disorders like DNA/chromatin, especially at the subcellular level in the human brain. We used two techniques, Partial wave spectroscopy (PWS) and Inverse Participation Ratio (IPR), to detect the changes in structural disorder in the human brain tissue samples. It was observed from the PWS experiment that there was an increase in structural disorder in Parkinson's disease tissues/cells when compared to normal tissues/cells using mesoscopic light transport theory. Furthermore, the IPR experiment also showed DNA/chromatin structural alterations that have the same trend and support the PWS results. The increase in mass density in the nuclei components, such as DNA/chromatin, can be linked to the aggregation of alpha-synuclein in the substantia nigra of the brain. This protein deposition is considered a significant cause of neuronal death in the brains of PD patients. We also did a histological analysis of brain tissues, which supports our results from dual photonics techniques. The results show that this dual technique is a powerful approach to detect the changes. Our results highlight the potential of the parameter, related to the structural disorder strength, as an efficient biomarker for PD progress, paving the way for research into early disease detection.

Sex specific effects of environmental toxin-derived alpha synuclein on enteric neuronal-epithelial interactions

Background

Parkinson's Disease (PD) is a neurodegenerative disorder with prodromal gastrointestinal (GI) issues often emerging decades before motor symptoms. Pathologically, PD can be driven by accumulation of misfolded alpha synuclein (aSyn) protein in the brain and periphery, including the GI tract. Disease epidemiology differs by sex, with men twice as likely to develop PD. Women, however, experience faster disease progression, higher mortality, and more severe GI symptoms. Gut calcitonin gene related peptide (CGRP) is a key regulator of intestinal contractions and visceral pain. The current study tests the hypothesis that sex differences in GI symptomology in PD are the result of aSyn aggregation altering enteric CGRP signaling pathways.

Methods

To facilitate peripheral aSyn aggregation, the pesticide rotenone was administered intraperitoneally once daily for two weeks to male and female mice. Mice were sacrificed two weeks after the last rotenone injection and immunohistochemistry was performed on sections of proximal colon.

Key Results

Levels of aSyn were heightened in myenteric plexus neurons and a subset of neurons immunoreactive to CGRP in rotenone treated mice. Female mice exhibited 153% more myenteric aSyn, 26% more apical CGRP immunoreactivity, and 66.7% more aSyn in apical CGRP + fibers after rotenone when compared to males. Goblet cell numbers were diminished but the individual cells were larger in the apical regions of crypts in the colons of rotenone treated mice.

Conclusions

This study used a mouse model of PD to uncover sex specific alterations in enteric neuronal and epithelial populations, underscoring the importance of considering sex as a biological variable while investigating prodromal GI symptoms.

KEY POINTS

Mouse model of Parkinson's Disease (PD) was used to investigate sex specific impact of enteric alpha synuclein (aSyn) on colonic goblet cells and CGRP + neurons and fibers. Sex specific alterations in intestinal neuronal and epithelial signaling pathways in response to aSyn provides insight into sex differences in PD etiology and prodromal gastrointestinal symptoms.

Gut-induced alpha-Synuclein and Tau propagation initiate Parkinson's and Alzheimer's disease co-pathology and behavior impairments

Tau interacts with α-Synuclein (α-Syn) and co-localizes with it in the Lewy bodies, influencing α-Syn pathology in Parkinson's disease (PD). However, whether these biochemical events regulate α-Syn pathology spreading from the gut into the brain remains incompletely understood. Here, we show that α-Syn and Tau co-pathology is spread into the brain in gut-inducible SYN103+/- and/or TAU368+/- transgenic mouse models, eliciting behavioral defects. Gut pathology was initially observed, and α-Syn or Tau pathology was subsequently propagated into the DMV or NTS and then to other brain regions. Remarkably, more extensive spreading and widespread neuronal loss were found in double transgenic mice (Both) than in single transgenic mice. Truncal vagotomy and α-Syn deficiency significantly inhibited synucleinopathy or tauopathy spreading. The α-Syn PET tracer [18F]-F0502B detected α-Syn aggregates in the gut and brain. Thus, α-Syn and Tau co-pathology can propagate from the gut to the brain, triggering behavioral disorders.

Systemic determinants of brain health in ageing

Preservation of brain health is a worldwide priority. The traditional view is that the major threats to the ageing brain lie within the brain itself. Consequently, therapeutic approaches have focused on protecting the brain from these presumably intrinsic pathogenic processes. However, an increasing body of evidence has unveiled a previously under-recognized contribution of peripheral organs to brain dysfunction and damage. Thus, in addition to the well-known impact of diseases of the heart and endocrine glands on the brain, accumulating data suggest that dysfunction of other organs, such as gut, liver, kidney and lung, substantially affects the development and clinical manifestation of age-related brain pathologies. In this Review, a framework is provided to indicate how organ dysfunction can alter brain homeostasis and promote neurodegeneration, with a focus on dementia. We delineate the associations of subclinical dysfunction in specific organs with dementia risk and provide suggestions for public health promotion and clinical management.

Gut dysbiosis impairs intestinal renewal and lipid absorption in Scarb2 deficiency-associated neurodegeneration

Scavenger receptor class B, member 2 (SCARB2) is linked to Gaucher disease and Parkinson's disease. Deficiency in the SCARB2 gene causes progressive myoclonus epilepsy (PME), a rare group of inherited neurodegenerative diseases characterized by myoclonus. We found that Scarb2 deficiency in mice leads to age-dependent dietary lipid malabsorption, accompanied with vitamin E deficiency. Our investigation revealed that Scarb2 deficiency is associated with gut dysbiosis and an altered bile acid pool, leading to hyperactivation of FXR in intestine. Hyperactivation of FXR impairs epithelium renewal and lipid absorption. Patients with SCARB2 mutations have a severe reduction in their vitamin E levels and cannot absorb dietary vitamin E. Finally, inhibiting FXR or supplementing vitamin E ameliorates the neuromotor impairment and neuropathy in Scarb2 knockout mice. These data indicate that gastrointestinal dysfunction is associated with SCARB2 deficiency-related neurodegeneration, and SCARB2-associated neurodegeneration can be improved by addressing the nutrition deficits and gastrointestinal issues.

Physiopathological Roles of White Adiposity and Gut Functions in Neuroinflammation

White adipose tissue (WAT) and the gut are involved in the development of neuroinflammation when an organism detects any kind of injury, thereby triggering metainflammation. In fact, the autonomous nervous system innervates both tissues, although the complex role played by the integrated sympathetic, parasympathetic, and enteric nervous system functions have not been fully elucidated. Our aims were to investigate the participation of inflamed WAT and the gut in neuroinflammation. Firstly, we conducted an analysis into how inflamed peripheral WAT plays a key role in the triggering of metainflammation. Indeed, this included the impact of the development of local insulin resistance and its metabolic consequences, a serious hypothalamic dysfunction that promotes neurodegeneration. Then, we analyzed the gut-brain axis dysfunction involved in neuroinflammation by examining cell interactions, soluble factors, the sensing of microbes, and the role of dysbiosis-related mechanisms (intestinal microbiota and mucosal barriers) affecting brain functions. Finally, we targeted the physiological crosstalk between cells of the brain-WAT-gut axis that restores normal tissue homeostasis after injury. We concluded the following: because any injury can result not only in overall insulin resistance and dysbiosis, which in turn can impact upon the brain, but that a high-risk of the development of neuroinflammation-induced neurodegenerative disorder can also be triggered. Thus, it is imperative to avoid early metainflammation by applying appropriate preventive (e.g., lifestyle and diet) or pharmacological treatments to cope with allostasis and thus promote health homeostasis.

α-synuclein overexpression and the microbiome shape the gut and brain metabolome in mice

Pathological forms of α-synuclein contribute to synucleinopathies, including Parkinson's disease (PD). Most cases of PD arise from gene-environment interactions. Microbiome composition is altered in PD, and gut bacteria are causal to symptoms in animal models. We quantitatively profiled nearly 630 metabolites in the gut, plasma, and brain of α-synuclein-overexpressing (ASO) mice, compared to wild-type (WT) animals, and comparing germ-free (GF) to specific pathogen-free (SPF) animals (n = 5 WT-SPF; n = 6 ASO-SPF; n = 6 WT-GF; n = 6 ASO-GF). Many differentially expressed metabolites in ASO mice are also dysregulated in human PD patients, including amine oxides, bile acids and indoles. The microbial metabolite trimethylamine N-oxide (TMAO) strongly correlates from the gut to the plasma to the brain in mice, notable since TMAO is elevated in the blood and cerebrospinal fluid of PD patients. These findings uncover broad metabolomic changes that are influenced by the intersection of host genetics and microbiome in a mouse model of PD.

Use of Caenorhabditis elegans to Unravel the Tripartite Interaction of Kynurenine Pathway, UPRmt and Microbiome in Parkinson's Disease

The model organism Caenorhabditis elegans and its relationship with the gut microbiome are gaining traction, especially for the study of neurodegenerative diseases such as Parkinson's Disease (PD). Gut microbes are known to be able to alter kynurenine metabolites in the host, directly influencing innate immunity in C. elegans. While the mitochondrial unfolded protein response (UPRmt) was first characterized in C. elegans in 2007, its relevance in host-microbiome interactions has only become apparent in recent years. In this review, we provide novel insights into the current understanding of the microbiome-gut-brain axis with a focus on tripartite interactions between the UPRmt, kynurenine pathway, and microbiome in C. elegans, and explore their relationships for PD remediations.

Modulatory effects of traditional Chinese medicines on gut microbiota and the microbiota-gut-x axis

The gut microbiota offers numerous benefits to the human body, including the promotion of nutrient absorption, participation in metabolic processes, and enhancement of immune function. Recent studies have introduced the concept of the gut-organ axis, which encompasses interactions such as the gut-brain axis, gut-liver axis, and gut-lung axis. This concept underscores the complex interplay between gut microbiota and various organs and tissues, including the brain, heart, lungs, liver, kidneys, muscles, and bones. Growing evidence indicates that gut microbiota can influence the onset and progression of multi-organ system diseases through their effects on the gut-organ axis. Traditional Chinese medicine has demonstrated significant efficacy in regulating the gastrointestinal system, leveraging its unique advantages. Considerable advancements have been made in understanding the role of gut microbiota and the gut-organ axis within the mechanisms of action of traditional Chinese medicine. This review aims to elucidate the roles of gut microbiota and the gut-organ axis in human health, explore the potential connections between traditional Chinese medicine and gut microbiota, and examine the therapeutic effects of traditional Chinese medicine on the microbiota-gut-organ axis. Furthermore, the review addresses the limitations and challenges present in current research while proposing potential directions for future investigations in this area.

Immune landscape of the enteric nervous system differentiates Parkinson's disease patients from controls: The PADUA-CESNE cohort

BACKGROUND

Gastrointestinal dysfunction has emerged as a prominent early feature of Parkinson's Disease, shedding new light on the pivotal role of the enteric nervous system in its pathophysiology. However, the role of immune-cell clusters and inflammatory and glial markers in the gut pathogenetic process needs further elucidation.

OBJECTIVES

We aimed to study duodenum tissue samples to characterize PD's enteric nervous system pathology further. Twenty patients with advanced PD, six with early PD, and 18 matched controls were included in the PADUA-CESNE cohort.

METHODS

Duodenal biopsies from 26 patients with early to advanced stage PD and 18 age-matched HCs were evaluated for the presence of surface markers (CD3+, CD4+, CD8+, CD20+, CD68+, HLA-DR), presence of misfolded alpha-synuclein and enteric glial alteration (GFAP). Correlation of immulogic pattern and clinical characteristic were analyzed.

RESULTS

The findings validate that in patients with Parkinson's Disease, the activation and reactive gliosis are linked to the neurodegeneration triggered by the presence of misfolded alpha-synuclein in the enteric nervous system. This process intensifies from the initial to the advanced stages of the disease. The clusters of T- and B-lymphocytes in the enteric system, along with the overall expression of HLA-DR in antigen-presenting cells, exceeded those in the control group. Conversely, no differences in terms of macrophage populations were found.

CONCLUSIONS

These findings broaden our understanding of the mechanisms underlying the enteric nervous system's involvement in PD and point to the gastrointestinal system as a potential therapeutic target, especially in the early stages of the disease. Moreover, our results propose a role of T- and B-lymphocytes in maintaining inflammation and ultimately influencing alpha-synuclein misfolding and aggregation.

The role of gut-derived short-chain fatty acids in Parkinson's disease

The emerging function of short-chain fatty acids (SCFAs) in Parkinson's disease (PD) has been investigated in this article. SCFAs, which are generated via the fermentation of dietary fiber by gut microbiota, have been associated with dysfunction of the gut-brain axis and, neuroinflammation. These processes are integral to the development of PD. This article examines the potential therapeutic implications of SCFAs in the management of PD, encompassing their capacity to modulate gastrointestinal permeability, neuroinflammation, and neuronal survival, by conducting an extensive literature review. As a whole, this article emphasizes the potential therapeutic utility of SCFAs as targets for the management and treatment of PD.

Diagnostic and therapeutic challenges in PD-associated non-motor symptoms: the roles of neurologists and consultant physicians

In addition to their motor symptoms, almost all Parkinson's disease patients report non-motor symptoms (NMS) and, in the later course of the disease, non-motor fluctuations as well. These NMS encompass e.g. neuropsychiatric, gastrointestinal, urogenital, cardiovascular symptoms and pain. For a long time, these symptoms received no or at best very little attention, but there is a growing trend towards their recognition and treatment. Despite this progress, significant gaps remain, particularly due to the sometimes-limited expertise among neurologists regarding these symptoms. The clinical need to consequently treat these NMS raises the question of whether Movement Disorder specialists should and can address them sufficiently or if additional consultant physicians have to be enrolled. Therefore, our objective is to establish benchmarking criteria to outline a potential way forward. Ideally, Movement Disorder specialists should take on greater responsibility when treating non-motor PD symptoms, integrating diagnostic and therapeutic pathways from other medical disciplines where feasible.

Olfactory deficit and gastrointestinal dysfunction precede motor abnormalities in alpha-Synuclein G51D knock-in mice

Parkinson's disease (PD) is typically a sporadic late-onset disorder, which has made it difficult to model in mice. Several transgenic mouse models bearing mutations in SNCA, which encodes alpha-Synuclein (α-Syn), have been made, but these lines do not express SNCA in a physiologically accurate spatiotemporal pattern, which limits the ability of the mice to recapitulate the features of human PD. Here, we generated knock-in mice bearing the G51D SNCA mutation. After establishing that their motor symptoms begin at 9 mo of age, we then sought earlier pathologies. We assessed the phosphorylation at Serine 129 of α-Syn in different tissues and detected phospho-α-Syn in the olfactory bulb and enteric nervous system at 3 mo of age. Olfactory deficit and impaired gut transit followed at 6 mo, preceding motor symptoms. The SncaG51D mice thus parallel the progression of human PD and will enable us to study PD pathogenesis and test future therapies.

Microbiota-gut-brain axis in health and neurological disease: Interactions between gut microbiota and the nervous system

Along with mounting evidence that gut microbiota and their metabolites migrate endogenously to distal organs, the 'gut-lung axis,' 'gut-brain axis,' 'gut-liver axis' and 'gut-renal axis' have been established. Multiple animal recent studies have demonstrated gut microbiota may also be a key susceptibility factor for neurological disorders such as Alzheimer's disease, Parkinson's disease and autism. The gastrointestinal tract is innervated by the extrinsic sympathetic and vagal nerves and the intrinsic enteric nervous system, and the gut microbiota interacts with the nervous system to maintain homeostatic balance in the host gut. A total of 1507 publications on the interactions between the gut microbiota, the gut-brain axis and neurological disorders are retrieved from the Web of Science to investigate the interactions between the gut microbiota and the nervous system and the underlying mechanisms involved in normal and disease states. We provide a comprehensive overview of the effects of the gut microbiota and its metabolites on nervous system function and neurotransmitter secretion, as well as alterations in the gut microbiota in neurological disorders, to provide a basis for the possibility of targeting the gut microbiota as a therapeutic agent for neurological disorders.

Implications of Butyrate Signaling Pathways on the Motor Symptomatology of Parkinson's Disease and Neuroprotective Effects-Therapeutic Approaches: A Systematic Review

Parkinson's Disease (PD) is a prevalent neurodegenerative disorder characterized by motor and non-motor symptoms. Emerging evidence suggests that gut microbiota alterations, specifically involving short-chain fatty acids (SCFAs) like butyrate, may influence PD pathogenesis and symptomatology. This Systematic Review aims to synthesize current research on the role of butyrate in modulating motor symptoms and its neuroprotective effects in PD, providing insights into potential therapeutic approaches. A systematic literature search was conducted in April 2024 across databases, including ScienceDirect, Scopus, Wiley, and Web of Science, for studies published between 2000 and 2024. Keywords used were "neuroprotective effects AND butyrate AND (Parkinson disease OR motor symptoms)". Four authors independently screened titles, abstracts, and full texts, applying inclusion criteria focused on studies investigating butyrate regulation and PD motor symptoms. A total of 1377 articles were identified, with 40 selected for full-text review and 14 studies meeting the inclusion criteria. Data extraction was performed on the study population, PD models, methodology, intervention details, and outcomes. Quality assessment using the SYRCLE RoB tool highlighted variability in study quality, with some biases noted in allocation concealment and blinding. Findings indicate that butyrate regulation has a significant impact on improving motor symptoms and offers neuroprotective benefits in PD models. The therapeutic modulation of gut microbiota to enhance butyrate levels presents a promising strategy for PD symptom management.

Novel strategies in Parkinson's disease treatment: a review

An unprecedented extension of life expectancy observed during the past century drastically increased the number of patients diagnosed with Parkinson's diseases (PD) worldwide. Estimated costs of PD alone reached $52 billion per year, making effective neuroprotective treatments an urgent and unmet need. Current treatments of both AD and PD focus on mitigating the symptoms associated with these pathologies and are not neuroprotective. In this review, we discuss the most advanced therapeutic strategies that can be used to treat PD. We also critically review the shift of the therapeutic paradigm from a small molecule-based inhibition of protein aggregation to the utilization of natural degradation pathways and immune cells that are capable of degrading toxic amyloid deposits in the brain of PD patients.

Validation of the DIGEST-FEES as a Global Outcome Measure for Pharyngeal Dysphagia in Parkinson's Disease

Flexible Endoscopic Evaluation of Swallowing (FEES) is one of two diagnostic gold standards for pharyngeal dysphagia in Parkinson's disease (PD), however, validated global outcome measures at the patient level are widely lacking. The Dynamic Imaging Grade of Swallowing Toxicity for Flexible Endoscopic Evaluation of Swallowing (DIGEST-FEES) represents such an outcome measure but has been validated primarily for head and neck cancer collectives. The objective of this study was, therefore, to investigate the validity of the DIGEST-FEES in patients with PD. Content validity was evaluated with a modified Delphi expert survey. Subsequently, 66 FEES videos in PD patients were scored with the DIGEST-FEES. Criterion validity was determined using Spearman's correlation coefficient between the DIGEST-FEES and the Penetration-Aspiration Scale (PAS), the Yale-Residue-Rating-Scale, the Functional-Oral-Intake-Scale (FOIS), and the swallowing-related Unified-Parkinson-Disease-Rating-Scale (UPDRS) items. Inter-rater reliability was determined using 10 randomly selected FEES-videos examined by a second rater. As a result, the overall DIGEST-FEES-rating exhibited significant correlations with the Yale-Valleculae-Residue-Scale (r = 0.84; p < 0.001), the Yale-Pyriform-Sinus-Residue-Scale (r = 0.70; p < 0.001), the FOIS (r =  - 0.55, p < 0.001), and the UPDRS-Swallowing-Item-Score (r = 0.42, p < 0.001). Further, the DIGEST-FEES-safety subscore correlated with the PAS (r = 0.63, p < 0.001). Inter-rater reliability was high for the overall DIGEST-FEES rating (quadratic weighted kappa of 0.82). Therefore, DIGEST-FEES is a valid and reliable score to evaluate overall pharyngeal dysphagia severity in PD. Nevertheless, the modified Delphi survey identified domains where DIGEST-FEES may need to be specifically adapted to PD or neurological collectives in the future.

Parkinson's disease is associated with low striated esophagus contractility potentially contributing to the development of dysphagia

BACKGROUND

Parkinson's disease (PD) is the second most common neurodegenerative disorder, and more than 80% of PD patients will develop oropharyngeal dysphagia. Despite its striated histology, proximity to airway, and potential negative impact of its dysfunction on bolus transport and airway safety, the contractile function of the striated esophagus in PD patients has not been systematically studied.

METHODS

Using our repository of clinical manometry and the Milwaukee ManoBank, we analyzed high-resolution manometry (HRM) studies of 20 PD patients, mean age 69.1 (range 38-87 years); 30 non-PD patients with dysphagia, mean age 64.0 (44-86 years); and 32 healthy volunteers, mean age 65.3 (39-86 years). Patients with abnormal findings based on Chicago Classification 4.0 were identified. Repeat analysis was performed in 20% of the manometric tracings by a different investigator with inter-rater concordance between 0.91 and 0.99.

KEY RESULTS

The striated esophageal contractile integral in PD patients was significantly lower than that in non-PD dysphagic patients and healthy controls (p = 0.03 and <0.01, respectively). This significant difference persisted after excluding patients with concurrent Chicago Classification motility disorders (p = 0.02 and 0.01, respectively). In both analyses, the distal esophageal contractile integral did not show any significant difference between groups (p = 0.58 and 0.93, respectively).

CONCLUSIONS & INFERENCES

PD is associated with a significant decrease in striated esophagus contractility compared to non-PD and healthy controls. This finding may play a pathophysiologic role in development of dysphagia in this patient population.

Impact of autonomic symptoms on the clinical course of Parkinson's disease

PURPOSE

Patients with Parkinson's disease (PD) exhibit various degrees of autonomic symptoms, which may be associated with Lewy body pathology distributed extensively in the autonomic nervous system. We hypothesized that the severity of autonomic symptoms reflects the severity of PD-related pathology, resulting in poor outcomes. The purpose of this study was to evaluate the impact of autonomic symptoms on PD progression.

METHODS

We conducted a follow-up study among consecutive patients with PD at Dokkyo Medical University Hospital. Patients underwent comprehensive baseline evaluations and were classified into high and low autonomic symptom groups using the Scale for Outcomes in Parkinson's Disease-Autonomic (SCOPA-AUT). The Kaplan‒Meier survival curves were used to analyze the time to discontinuation of their visits because of PD-related endpoints and to evaluate the association with high SCOPA-AUT scores.

RESULTS

Of the 101 patients, 74 (73%) met the inclusion criteria. During the follow-up period (mean 1654 days), 22/74 patients reached PD-related endpoints (death, 4; hospitalization, 9; nursing home institutionalization, 9). PD patients with high SCOPA-AUT scores reached the endpoints faster than those with low SCOPA-AUT scores. A high SCOPA-AUT score, including gastrointestinal, urinary, and thermoregulation domains; high motor symptom scores; and low specific binding ratios (SBRs) on 123I FP-CIT-SPECT (DAT-SPECT) were associated with reaching PD-related endpoints. A high SCOPA-AUT score was associated with reaching the endpoints even after adjustment for covariates.

CONCLUSIONS

Patients with high autonomic symptom scores had a greater risk of reaching PD-related endpoints than patients with low autonomic symptom scores.

[Gastrointestinal disorders in hyperkinetic movement disorders and ataxia]

Disorders of the gastrointestinal tract in patients suffering from hypokinetic movement disorders, and in particular Parkinson's disease, have increasingly been the subject of more intensive neuromedical research. So far, few data are available for patients with hyperkinetic movement disorders and ataxias. This review article summarizes the currently available and relevant publications on this topic. The particular focus is on essential tremor, restless legs syndrome, Huntington's disease and the group of hereditary ataxias. Further intensive research will be necessary in the future to collect detailed information also for these disease symptoms about specific disturbance patterns, in order to understand the underlying pathological pathways and to derive specific treatment approaches.

Alpha Synuclein Toxicity and Non-Motor Parkinson's

Parkinson's disease (PD) is a common multisystem neurodegenerative disorder affecting 1% of the population over the age of 60 years. The main neuropathological features of PD are the loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) and the presence of alpha synuclein (αSyn)-rich Lewy bodies both manifesting with classical motor signs. αSyn has emerged as a key protein in PD pathology as it can spread through synaptic networks to reach several anatomical regions of the body contributing to the appearance of non-motor symptoms (NMS) considered prevalent among individuals prior to PD diagnosis and persisting throughout the patient's life. NMS mainly includes loss of taste and smell, constipation, psychiatric disorders, dementia, impaired rapid eye movement (REM) sleep, urogenital dysfunction, and cardiovascular impairment. This review summarizes the more recent findings on the impact of αSyn deposits on several prodromal NMS and emphasizes the importance of early detection of αSyn toxic species in biofluids and peripheral biopsies as prospective biomarkers in PD.

α-Synuclein Overexpression and the Microbiome Shape the Gut and Brain Metabolome in Mice

Pathological forms of the protein α-synuclein contribute to a family of disorders termed synucleinopathies, which includes Parkinson's disease (PD). Most cases of PD are believed to arise from gene-environment interactions. Microbiome composition is altered in PD, and gut bacteria are causal to symptoms and pathology in animal models. To explore how the microbiome may impact PD-associated genetic risks, we quantitatively profiled nearly 630 metabolites from 26 biochemical classes in the gut, plasma, and brain of α-synuclein-overexpressing (ASO) mice with or without microbiota. We observe tissue-specific changes driven by genotype, microbiome, and their interaction. Many differentially expressed metabolites in ASO mice are also dysregulated in human PD patients, including amine oxides, bile acids and indoles. Notably, levels of the microbial metabolite trimethylamine N-oxide (TMAO) strongly correlate from the gut to the plasma to the brain, identifying a product of gene-environment interactions that may influence PD-like outcomes in mice. TMAO is elevated in the blood and cerebral spinal fluid of PD patients. These findings uncover broad metabolomic changes that are influenced by the intersection of host genetics and the microbiome in a mouse model of PD.

Association of intestinal inflammation and permeability markers with clinical manifestations of Parkinson's disease

INTRODUCTION

Intestinal inflammation and gut microbiota dysbiosis can stimulate degeneration of dopaminergic neurons and development of Parkinson's disease (PD) via the gut-brain axis in certain patients.

METHODS

In a case-control study, fecal markers of intestinal inflammation and permeability were measured using the ELISA method in PD patients and healthy controls. Motor and nonmotor symptoms were assessed using the Movement Disorder Society (MDS) Unified PD Rating Scale, Hoehn & Yahr scale, MDS Non-Motor Symptom Scale, Scales for Outcomes in PD - Autonomic Dysfunction, PD Sleep Scale - 2, Montreal Cognitive Assessment, Beck Anxiety Inventory, and Beck Depression Inventory-II. A correlation was established between the intestinal inflammation and permeability markers and PD symptoms.

RESULTS

Higher levels of beta-defensin 2, zonulin and lactoferrin were recorded in PD patients compared to controls. Calprotectin and secretory immunoglobulin A showed no significant differences. Regression analysis indicated the roles of beta-defensin 2 and lactoferrin in predicting PD likelihood. Calprotectin yielded positive correlations with disease duration, depression, motor fluctuations, and gastrointestinal symptoms; beta defensin 2 with thermoregulation; and secretory immunoglobulin A with depression. Secretory immunoglobulin A showed negative correlation with age and age at disease onset, while zonulin showed negative correlation with the MDS Unified PD Rating Scale total score.

CONCLUSIONS

Fecal markers differed in PD patients compared to controls and correlated with age, disease duration, and some nonmotor symptoms. Future studies should identify the subgroups of PD patients that are likely to develop intestinal inflammation.

Dysphagia in Parkinson's disease: A bibliometric and visualization analysis from 2002 to 2022

Background

Dysphagia, or difficulty swallowing, is a prevalent complication of Parkinson's disease (PD), which can significantly impair quality of life. Despite the numerous studies on dysphagia in PD published in various journals, there remains a dearth of bibliometric analysis within this domain. This study thus aims to examine the global patterns of research on dysphagia after PD over the past 20 years, employing a visual analysis.

Material and methods

This investigation aimed to gather pertinent publications concerning dysphagia in PD from the SCI-Expanded database of the Web of Science Core Collection (WoSCC), covering the period from 2002 to 2022. To dissect and visually represent the collated corpus, we harnessed the capacities of CiteSpace, VOSviewer and R software for meticulous bibliometric scrutiny.

Results

The bibliometric study encompassed a total of 692 publications. Within the scope of autocratic nations, the USA emerged as the leading country in the quantity of research outputs. The University of Florida stood out as the most prolific academic entity, with Troche MS being the foremost author, contributing to 21 publications. The journal "Dysphagia" featured as the prime venue for publication. Key trending terms identified over the last 20 years include "Parkinson's disease," "dysphagia," "oropharyngeal dysphagia," and "prevalence."

Conclusion

Bibliometric analysis on dysphagia in PD offers a detailed overview of the development of scholarly publications, enabling scholars to grasp the current state of research within their field. It also serves as a benchmark for shaping future research directions.

Systematic approach to contextualize findings of flexible endoscopic evaluation of swallowing in neurogenic dysphagia- towards an integrated FEES report

Flexible endoscopic evaluation of swallowing (FEES) is one of the most important methods for instrumental swallowing evaluation. The most challenging part of the examination consists in the interpretation of the various observations encountered during endoscopy and in the deduction of clinical consequences. This review proposes the framework for an integrated FEES-report that systematically moves from salient findings of FEES to more advanced domains such as dysphagia severity, phenotypes of swallowing impairment and pathomechanisms. Validated scales and scores are used to enhance the diagnostic yield. In the concluding part of the report, FEES-findings are put into the perspective of the clinical context. The potential etiology of dysphagia and conceivable differential diagnoses are considered, further diagnostic steps are proposed, treatment options are evaluated, and a timeframe for re-assessment is suggested. This framework is designed to be adaptable and open to continuous evolution. Additional items, such as novel FEES protocols, pathophysiological observations, advancements in disease-related knowledge, and new treatment options, can be easily incorporated. Moreover, there is potential for customizing this approach to report on FEES in structural dysphagia.

Attitudes Toward the Adoption of Remote Patient Monitoring and Artificial Intelligence in Parkinson's Disease Management: Perspectives of Patients and Neurologists

OBJECTIVE

Early detection of Parkinson's Disease (PD) progression remains a challenge. As remote patient monitoring solutions (RMS) and artificial intelligence (AI) technologies emerge as potential aids for PD management, there's a gap in understanding how end users view these technologies. This research explores patient and neurologist perspectives on AI-assisted RMS.

METHODS

Qualitative interviews and focus-groups were conducted with 27 persons with PD (PwPD) and six neurologists from Finland and Italy. The discussions covered traditional disease progression detection and the prospects of integrating AI and RMS. Sessions were recorded, transcribed, and underwent thematic analysis.

RESULTS

The study involved five individual interviews (four Italian participants and one Finnish) and six focus-groups (four Finnish and two Italian) with PwPD. Additionally, six neurologists (three from each country) were interviewed. Both cohorts voiced frustration with current monitoring methods due to their limited real-time detection capabilities. However, there was enthusiasm for AI-assisted RMS, contingent upon its value addition, user-friendliness, and preservation of the doctor-patient bond. While some PwPD had privacy and trust concerns, the anticipated advantages in symptom regulation seemed to outweigh these apprehensions.

DISCUSSION

The study reveals a willingness among PwPD and neurologists to integrate RMS and AI into PD management. Widespread adoption requires these technologies to provide tangible clinical benefits, remain user-friendly, and uphold trust within the physician-patient relationship.

CONCLUSION

This study offers insights into the potential drivers and barriers for adopting AI-assisted RMS in PD care. Recognizing these factors is pivotal for the successful integration of these digital health tools in PD management.

Effects of microbiome-based interventions on neurodegenerative diseases: a systematic review and meta-analysis

Neurodegenerative diseases (NDDs) are characterized by neuronal damage and progressive loss of neuron function. Microbiome-based interventions, such as dietary interventions, biotics, and fecal microbiome transplant, have been proposed as a novel approach to managing symptoms and modulating disease progression. Emerging clinical trials have investigated the efficacy of interventions modulating the GM in alleviating or reversing disease progression, yet no comprehensive synthesis have been done. A systematic review of the literature was therefore conducted to investigate the efficacy of microbiome-modulating methods. The search yielded 4051 articles, with 15 clinical trials included. The overall risk of bias was moderate in most studies. Most microbiome-modulating interventions changed the GM composition. Despite inconsistent changes in GM composition, the meta-analysis showed that microbiome-modulating interventions improved disease burden (SMD, - 0.57; 95% CI - 0.93 to - 0.21; I2 = 42%; P = 0.002) with a qualitative trend of improvement in constipation. However, current studies have high methodological heterogeneity and small sample sizes, requiring more well-designed and controlled studies to elucidate the complex linkage between microbiome, microbiome-modulating interventions, and NDDs.

Gut-Initiated Alpha Synuclein Fibrils Drive Parkinson's Disease Phenotypes: Temporal Mapping of non-Motor Symptoms and REM Sleep Behavior Disorder

Parkinson's disease (PD) is characterized by progressive motor as well as less recognized non-motor symptoms that arise often years before motor manifestation, including sleep and gastrointestinal disturbances. Despite the heavy burden on the patient's quality of life, these non-motor manifestations are poorly understood. To elucidate the temporal dynamics of the disease, we employed a mouse model involving injection of alpha-synuclein (αSyn) pre-formed fibrils (PFF) in the duodenum and antrum as a gut-brain model of Parkinsonism. Using anatomical mapping of αSyn-PFF propagation and behavioral and physiological characterizations, we unveil a correlation between post-injection time the temporal dynamics of αSyn propagation and non-motor/motor manifestations of the disease. We highlight the concurrent presence of αSyn aggregates in key brain regions, expressing acetylcholine or dopamine, involved in sleep duration, wakefulness, and particularly REM-associated atonia corresponding to REM behavioral disorder-like symptoms. This study presents a novel and in-depth exploration into the multifaceted nature of PD, unraveling the complex connections between α-synucleinopathies, gut-brain connectivity, and the emergence of non-motor phenotypes.

Neuroimmune Connectomes in the Gut and Their Implications in Parkinson's Disease

The gastrointestinal tract is the largest immune organ and it receives dense innervation from intrinsic (enteric) and extrinsic (sympathetic, parasympathetic, and somatosensory) neurons. The immune and neural systems of the gut communicate with each other and their interactions shape gut defensive mechanisms and neural-controlled gut functions such as motility and secretion. Changes in neuroimmune interactions play central roles in the pathogenesis of diseases such as Parkinson's disease (PD), which is a multicentric disorder that is heterogeneous in its manifestation and pathogenesis. Non-motor and premotor symptoms of PD are common in the gastrointestinal tract and the gut is considered a potential initiation site for PD in some cases. How the enteric nervous system and neuroimmune signaling contribute to PD disease progression is an emerging area of interest. This review focuses on intestinal neuroimmune loops such as the neuroepithelial unit, enteric glial cells and their immunomodulatory effects, anti-inflammatory cholinergic signaling and the relationship between myenteric neurons and muscularis macrophages, and the role of α-synuclein in gut immunity. Special consideration is given to the discussion of intestinal neuroimmune connectomes during PD and their possible implications for various aspects of the disease.

Cholecystokinin (CCK): a neuromodulator with therapeutic potential in Alzheimer's and Parkinson's disease

Cholecystokinin (CCK) is a neuropeptide modulating digestion, glucose levels, neurotransmitters and memory. Recent studies suggest that CCK exhibits neuroprotective effects in Alzheimer's disease (AD) and Parkinson's disease (PD). Thus, we review the physiological function and therapeutic potential of CCK. The neuropeptide facilitates hippocampal glutamate release and gates GABAergic basket cell activity, which improves declarative memory acquisition, but inhibits consolidation. Cortical CCK alters recognition memory and enhances audio-visual processing. By stimulating CCK-1 receptors (CCK-1Rs), sulphated CCK-8 elicits dopamine release in the substantia nigra and striatum. In the mesolimbic pathway, CCK release is triggered by dopamine and terminates reward responses via CCK-2Rs. Importantly, activation of hippocampal and nigral CCK-2Rs is neuroprotective by evoking AMPK activation, expression of mitochondrial fusion modulators and autophagy. Other benefits include vagus nerve/CCK-1R-mediated expression of brain-derived neurotrophic factor, intestinal protection and suppression of inflammation. We also discuss caveats and the therapeutic combination of CCK with other peptide hormones.

Predictors for early-onset psychotic symptoms in patients newly diagnosed with Parkinson's disease without psychosis at baseline: A 5-year cohort study

AIMS

To investigate the risk factors for early-onset psychosis in Parkinson's disease (PD) in a cohort of patients from the Parkinson's Progression Markers Initiative.

METHODS

Longitudinal data on motor and non-motor features, dopamine transporter (DAT) imaging, and cerebrospinal fluid (CSF) measurements were collected. The survival probability of psychotic symptoms, potential risk factors for psychosis development over a 5-year follow-up period, and the performance of the prediction model were evaluated.

RESULTS

Among the 338 newly diagnosed patients with PD, 83 developed psychotic symptoms. Gastrointestinal autonomic dysfunction, presence of probable rapid-eye-movement sleep behavior disorder, and the ratio Aβ42: total-tau could independently predict onset of psychosis in PD (hazard ratio (HR) = 1.157, 95% confidence interval (CI) 1.022-1.309, p = 0.021, HR = 2.596, 95% CI 1.287-5.237, p = 0.008, and HR = 0.842, 95% CI 0.723-0.980, p = 0.027, respectively). The combined model integrating baseline clinical predictors, DAT imaging, and CSF measurements achieved better sensitivity than the clinical predictors alone (area under the curve = 0.770 [95% CI 0.672-0.868] vs. 0.714 [95% CI 0.625-0.802], p = 0.098).

CONCLUSION

We identified clinical and CSF predictors of early-onset psychosis in patients with PD. Our study provides evidence and implications for prognostic stratification and therapeutic approaches for PD psychosis.

Evaluation of bidirectional gut-brain axis and anorectal function in Parkinson's disease with constipation

BACKGROUND

Parkinson's disease (PD) is a neurodegenerative movement disorder with prodromal and highly prevalent gastrointestinal (GI) symptoms, especially constipation. Although PD models suggest gut-brain axis dysfunction, the mechanistic underpinnings and their correlation with GI symptoms are poorly understood.

AIM

To examine the bidirectional gut-brain axis function in PD and correlate it with constipation severity, PD duration, and severity.

METHODS

Rectal sensory thresholds and afferent cortical evoked potentials (CEP) were assessed using a 4-ring EMG electrode probe. Efferent anal and rectal motor evoked potentials (MEPs) were obtained following transcranial and lumbosacral magnetic stimulation. Bowel symptoms were assessed by prospective stool diary. The CEP and MEP latencies, rectal sensory thresholds, and anorectal sensorimotor data were compared between PD subjects and age-adjusted healthy subjects.

KEY RESULTS

Twenty-five PD subjects with constipation (F/M = 6/19) and 20 healthy subjects (F/M = 14/6) were enrolled. The first and pain sensation thresholds were higher in PD subjects than healthy subjects (p < 0.002) but lost significance after adjustment for age. Age-adjusted rectal CEP and right-sided cortico-anal MEP latencies were prolonged in PD subjects compared to healthy subjects (p < 0.04). Also, half (4 of 8) age-adjusted spino-anal and rectal MEP latencies in PD subjects were significantly longer. In multivariate linear analysis, first rectal sensation and right-sided MEP latencies showed moderate correlation with constipation severity.

CONCLUSIONS & INFERENCES

Parkinson's disease is associated with significant bidirectional gut-brain axis dysfunction as evidenced by prolonged afferent and efferent neuronal signaling. Constipation severity in PD is correlated to abnormal rectal sensation and lateralized disturbance of efferent brain-gut signaling.

Therapeutics for neurodegenerative diseases by targeting the gut microbiome: from bench to bedside

The aetiologies and origins of neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS) and Huntington's disease (HD), are complex and multifaceted. A growing body of evidence suggests that the gut microbiome plays crucial roles in the development and progression of neurodegenerative diseases. Clinicians have come to realize that therapeutics targeting the gut microbiome have the potential to halt the progression of neurodegenerative diseases. This narrative review examines the alterations in the gut microbiome in AD, PD, ALS and HD, highlighting the close relationship between the gut microbiome and the brain in neurodegenerative diseases. Processes that mediate the gut microbiome-brain communication in neurodegenerative diseases, including the immunological, vagus nerve and circulatory pathways, are evaluated. Furthermore, we summarize potential therapeutics for neurodegenerative diseases that modify the gut microbiome and its metabolites, including diets, probiotics and prebiotics, microbial metabolites, antibacterials and faecal microbiome transplantation. Finally, current challenges and future directions are discussed.

Microbiota-gut-brain axis and its therapeutic applications in neurodegenerative diseases

The human gastrointestinal tract is populated with a diverse microbial community. The vast genetic and metabolic potential of the gut microbiome underpins its ubiquity in nearly every aspect of human biology, including health maintenance, development, aging, and disease. The advent of new sequencing technologies and culture-independent methods has allowed researchers to move beyond correlative studies toward mechanistic explorations to shed light on microbiome-host interactions. Evidence has unveiled the bidirectional communication between the gut microbiome and the central nervous system, referred to as the "microbiota-gut-brain axis". The microbiota-gut-brain axis represents an important regulator of glial functions, making it an actionable target to ameliorate the development and progression of neurodegenerative diseases. In this review, we discuss the mechanisms of the microbiota-gut-brain axis in neurodegenerative diseases. As the gut microbiome provides essential cues to microglia, astrocytes, and oligodendrocytes, we examine the communications between gut microbiota and these glial cells during healthy states and neurodegenerative diseases. Subsequently, we discuss the mechanisms of the microbiota-gut-brain axis in neurodegenerative diseases using a metabolite-centric approach, while also examining the role of gut microbiota-related neurotransmitters and gut hormones. Next, we examine the potential of targeting the intestinal barrier, blood-brain barrier, meninges, and peripheral immune system to counteract glial dysfunction in neurodegeneration. Finally, we conclude by assessing the pre-clinical and clinical evidence of probiotics, prebiotics, and fecal microbiota transplantation in neurodegenerative diseases. A thorough comprehension of the microbiota-gut-brain axis will foster the development of effective therapeutic interventions for the management of neurodegenerative diseases.

Constipation and pain in Parkinson's disease: a clinical analysis

Parkinson's Disease (PD) is a neurodegenerative disorder characterized by both motor and non-motor symptoms (NMS). Among NMS, constipation and pain are both highly prevalent and debilitating affecting up to 80% of PD patients and impairing their quality of life. Here, we investigated the relationship between constipation and pain in PD patients. This is a retrospective study assessing the relationship between pain and constipation in a PD patient population from a clinical database of patients attending the outpatient clinic of the movement disorders division, Neurology Unit of Policlinico Tor Vergata, in Rome. Subjects were assessed with the Unified Parkinson's Disease Rating Scale (UPDRS) part III, Hoehn and Yahr (H&Y) stage, King's Parkinson's Disease Pain Scale (KPPS), Brief Pain Inventory (BPI), Non-Motor Symptoms Scale (NMSS) and Beck Depression Inventory (BDI). Patients were further divided in two groups (Group 1, 32 patients with constipation and Group 2, 35 PD patients without constipation) ANOVA and ANCOVA analysis were used to compare the two groups. PD patients with constipation had significantly higher pain severity and pain interference, as measured by the BPI scale and higher total KPPS score, fluctuation-related pain, nocturnal pain, and radicular pain when compared to PD patients without constipation. This study highlights for the first time a possible interplay between constipation and pain in PD that deserves further investigations.

Green rooibos (Aspalathus linearis) promotes gut health: insight into mechanisms

ETHNOPHARMACOLOGICAL RELEVANCE

Paralleling the increasing incidence of gastrointestinal disorders world-wide, therapeutic investigations of nutraceuticals to promote gastrointestinal health are gaining popularity. Although anecdotally well-known for its gut health promoting potential, sparse scientific evidence supports this action of Aspalathus linearis (Burm.f.) R. Dahlgren - or rooibos - at the gastrointestinal epithelial level.

AIM OF THE STUDY

Traditionally, rooibos is considered to exert antispasmodic, anti-inflammatory, and anti-nociceptive effects in the gut. However, the direct effect on intestinal epithelium is unknown. Thus, to assess the validity of anecdotal claims, two larval zebrafish models were utilized to evaluate effects of rooibos on intestinal health.

MATERIALS AND METHODS

Firstly, a larval zebrafish model of gastrointestinal inflammation (2-day TNBS-exposure) was employed. Co-administration of 6α-methylprednisolone served as an internal treatment control. Assessments included live imaging techniques and post-mortem immunofluorescent staining of epithelial tight junction proteins. In addition, whole body H2O2 and prostaglandin E2 assays were performed. Secondly, a gastrointestinal motility assay was performed, with known pro- and anti-kinetic mediators to assess the effect of rooibos to alter functional outcome in vivo.

RESULTS

Aqueous and ethanol extracts of green rooibos rescued TNBS-induced reductions in neutral red stained length of larval mid-intestines. Subsequent experiments confirmed the rescue capacity of the aqueous green rooibos extract regarding whole body oxidative and inflammatory status. Concerning tight junction proteins, only the aqueous green rooibos extract - and not prednisolone - normalized both zona occludens-1 and occludin expression levels when compared the TNBS group. In terms of gastrointestinal motility, the aqueous green rooibos extract significantly reduced the extent of gut motility dysregulation achieved by kinetic modulators.

CONCLUSIONS

Data indicates the potential of a 2 mg/ml aqueous extract of green rooibos to improve gastrointestinal integrity and functionality in vivo, suggesting beneficial effects of rooibos may already occur at the level of the gut. This provides some evidence to support indigenous knowledge.

Advancements in Genetic and Biochemical Insights: Unraveling the Etiopathogenesis of Neurodegeneration in Parkinson's Disease

Parkinson's disease (PD) is the second most prevalent neurodegenerative movement disorder worldwide, which is primarily characterized by motor impairments. Even though multiple hypotheses have been proposed over the decades that explain the pathogenesis of PD, presently, there are no cures or promising preventive therapies for PD. This could be attributed to the intricate pathophysiology of PD and the poorly understood molecular mechanism. To address these challenges comprehensively, a thorough disease model is imperative for a nuanced understanding of PD's underlying pathogenic mechanisms. This review offers a detailed analysis of the current state of knowledge regarding the molecular mechanisms underlying the pathogenesis of PD, with a particular emphasis on the roles played by gene-based factors in the disease's development and progression. This study includes an extensive discussion of the proteins and mutations of primary genes that are linked to PD, including α-synuclein, GBA1, LRRK2, VPS35, PINK1, DJ-1, and Parkin. Further, this review explores plausible mechanisms for DAergic neural loss, non-motor and non-dopaminergic pathologies, and the risk factors associated with PD. The present study will encourage the related research fields to understand better and analyze the current status of the biochemical mechanisms of PD, which might contribute to the design and development of efficacious and safe treatment strategies for PD in future endeavors.

Microglia and Microbiome-Gut-Brain Axis

The mammalian gut contains a community of microorganisms called gut microbiome. The gut microbiome is integrated into mammalian physiology, contributing to metabolism, production of metabolites, and promoting immunomodulatory actions. Microglia, the brain's resident innate immune cells, play an essential role in homeostatic neurogenesis, synaptic remodeling, and glial maturation. Microglial dysfunction has been implicated in the pathogenesis of several neuropsychiatric disorders. Recent findings indicate that microglia are influenced by the gut microbiome and their derived metabolites throughout life. The pathways by which microbiota regulate microglia have only started to be understood, but this discovery has the potential to provide valuable insights into the pathogenesis of brain disorders associated with an altered microbiome. Here, we discuss the recent literature on the role of the gut microbiome in modulating microglia during development and adulthood and summarize the key findings on this bidirectional crosstalk in selected examples of neuropsychiatric and neurodegenerative disorders. We also highlight some current caveats and perspectives for the field.

Contribution of the Dynamic Intestinal Absorption Model (Diamod) to the Development of a Patient-Centric Drug Formulation

Compound X is a weak basic drug targeting the early stages of Parkinson's disease, for which a theoretical risk assessment has indicated that elevated gastric pH conditions could potentially result in reduced plasma concentrations. Different in vitro dissolution methodologies varying in level of complexity and a physiologically based pharmacokinetic (PBPK) absorption model demonstrated that the dissolution, solubility, and intestinal absorption of compound X was indeed reduced under elevated gastric pH conditions. These observations were confirmed in a crossover pharmacokinetic study in Beagle dogs. As a result, the development of a formulation resulting in robust performance that is not sensitive to the exposed gastric pH levels is of crucial importance. The dynamic intestinal absorption MODel (Diamod), an advanced in vitro gastrointestinal transfer tool that allows to study the gastrointestinal dissolution and interconnected permeation of drugs, was selected as an in vitro tool for the formulation optimization activities given its promising predictive capacity and its capability to generate insights into the mechanisms driving formulation performance. Different pH-modifiers were screened for their potential to mitigate the pH-effect by decreasing the microenvironmental pH at the dissolution surface. Finally, an optimized formulation containing a clinically relevant dose of the drug and a functional amount of the selected pH-modifier was evaluated for its performance in the Diamod. This monolayer tablet formulation resulted in rapid gastric dissolution and supersaturation, inducing adequate intestinal supersaturation and permeation of compound X, irrespective of the gastric acidity level in the stomach. In conclusion, this study describes the holistic biopharmaceutics approach driving the development of a patient-centric formulation of compound X.