Constipation preceding Parkinson's disease: a systematic review and meta-analysis

Acupuncture for constipation in Parkinson's disease: A systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Parkinson's disease (PD) is the second most common neurological disease worldwide, and there is a potential interaction between PD and constipation. PD constipation often causes significant trouble for patients and seriously affects their quality of life. Acupuncture is widely used for treating constipation and has been clinically proven. However, it is unclear whether the current evidence is sufficient to support acupuncture to improve PD constipation.

METHODS

We searched the Cochrane Central Register of Controlled Trials, Embase, PubMed, Web of Science, China National Knowledge Infrastructure, Wan Fang Data Knowledge Service Platform, and Chinese Scientific Journal Database (VIP database) for randomized controlled trials from inception through July 1, 2023. Randomized controlled trials (RCTs) included acupuncture, sham acupuncture, and medication for PD constipation. Stata 16.0 software and Cochrane RoB2.0 were used for data processing and migration risk analysis.

RESULTS

The 11 studies included a total of 960 patients. The results showed that acupuncture or acupuncture combined with conventional treatment seemed to have advantages in improving complete spontaneous bowel movements (WMD: 1.49, 95% CI: 0.86, 2.11; P < .00001), Patient-Assessment of Constipation Quality of Life questionnaire (WMD: -11.83, 95% CI: -15.67, -7.99; P < .00001), the chronic constipation severity scale (CCS) (SMD: -0.99, 95% CI: -1.40, -0.58; P < .01), and c(RRP) (WMD: 2.13, 95% CI: 0.44, 3.82; P < .05).

CONCLUSION

The present results show that compared with conventional treatment, acupuncture combined with conventional treatment seems to increase the number of spontaneous defecations in PD patients, improve quality of life, increase rectal resting pressure, and alleviate the severity of chronic constipation. Thus, acupuncture has the potential to treat PD constipation. However, due to the study's limitations, higher-quality RCTs are needed for verification.

Aberrant bowel movement frequencies coincide with increased microbe-derived blood metabolites associated with reduced organ function

Bowel movement frequency (BMF) directly impacts the gut microbiota and is linked to diseases like chronic kidney disease or dementia. In particular, prior work has shown that constipation is associated with an ecosystem-wide switch from fiber fermentation and short-chain fatty acid production to more detrimental protein fermentation and toxin production. Here, we analyze multi-omic data from generally healthy adults to see how BMF affects their molecular phenotypes, in a pre-disease context. Results show differential abundances of gut microbial genera, blood metabolites, and variation in lifestyle factors across BMF categories. These differences relate to inflammation, heart health, liver function, and kidney function. Causal mediation analysis indicates that the association between lower BMF and reduced kidney function is partially mediated by the microbially derived toxin 3-indoxyl sulfate (3-IS). This result, in a generally healthy context, suggests that the accumulation of microbiota-derived toxins associated with abnormal BMF precede organ damage and may be drivers of chronic, aging-related diseases.

Helicobacter pylori infection is a risk factor for constipation in patients with Parkinson's disease: A multicenter prospective cohort study

BACKGROUND AND AIMS

Constipation is one of the most common nonmotor symptoms (NMSs) of Parkinson's disease (PD). The infection rate of Helicobacter pylori (HP) is greater in PD patients. This study was a multicenter prospective cohort study in which propensity score matching (PSM) was used to determine whether HP infection was a risk factor for constipation in patients with PD.

METHODS

A total of 932 PD patients with 13C-urea breath test for HP were included in the study. The PSM was estimated with the use of a nonparsimonious multivariate logistic regression model, with HP infection as the dependent variable and all the baseline characteristics as covariates. A total of 697 patients composed the study cohort, including 252 (36.2 %) patients in the HP-positive (HPP) group and 445 (63.8 %) patients in the HP-negative (HPN) group. Before PSM, there were differences in several of the baseline variables between the two groups. After PSM, 250 HPP patients were matched with 250 HPN patients and the standardized differences were less than 0.1 for all variables.

RESULTS

The present results demonstrate that HP infection is a risk factor for constipation in patients with PD [RR (95 % CI) 1.412 (1.155-1.727), P < 0.001]. Subgroup analyses revealed that HP infection was both a risk factor for constipation in Hoehn-Yahr scale (1,1.5) group and Hoehn-Yahr scale (2-5) group [OR (95 % CI) 1.811 (1.079-3.038), P < 0.025; OR (95 % CI) 2.041 (1.177-3.541), P < 0.011].

CONCLUSIONS

The results of our prospective cohort study suggest that Helicobacter pylori infection is a risk factor for constipation in patients with PD.

TRIAL REGISTRATION

ChiCTR2300071631.

Epidemiology of Parkinson's Disease: An Update

PURPOSE OF REVIEW

In recent decades, epidemiological understanding of Parkinson disease (PD) has evolved significantly. Major discoveries in genetics and large epidemiological investigations have provided a better understanding of the genetic, behavioral, and environmental factors that play a role in the pathogenesis and progression of PD. In this review, we provide an epidemiological update of PD with a particular focus on advances in the last five years of published literature.

RECENT FINDINGS

We include an overview of PD pathophysiology, followed by a detailed discussion of the known distribution of disease and varied determinants of disease. We describe investigations of risk factors for PD, and provide a critical summary of current knowledge, knowledge gaps, and both clinical and research implications. We emphasize the need to characterize the epidemiology of the disease in diverse populations. Despite increasing understanding of PD epidemiology, recent paradigm shifts in the conceptualization of PD as a biological entity will also impact epidemiological research moving forward and guide further work in this field.

Formulation and Physical-Chemical Analysis of Functional Muffin Made with Inulin, Moringa, and Cacao Adapted for Elderly People with Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder that affects people's health. Constipation is probably one of the most prominent gastrointestinal symptoms (non-motor symptoms) of PD with devastating consequences. The aim of this research work is to formulate a functional food product, supplemented with inulin, cocoa, and Moringa, which can be an adjuvant in the treatment of constipation. The product was prepared according to a muffin or "Chilean cake" recipe; this basic muffin was prepared with additions of inulin (MI), inulin + cacao (MIC), and inulin + Moringa (MIM). A physical-chemical analysis of the macronutrients and an antioxidant capacity assessment of the samples were conducted, as well as a sensory evaluation performed by a group of people suffering from Parkinson's disease. A statistically significant difference was observed in the soluble (p = 0.0023) and insoluble (p = 0.0015) fiber values between the control samples and all samples. Furthermore, inulin + cacao improved the antioxidant capacity and folate intake compared to the control. Inulin alone has been shown to have antioxidant capacity according to ABTS (262.5728 ± 34.74 μmol TE/g) and DPPH (9.092518 ± 10.43 μmol TE/g) assays. A sensory evaluation showed a preference for the product with inulin and for the product with inulin + cacao, with a 78% purchase intention being reported by the subjects who evaluated the products. The incorporation of inulin and cacao improved the nutritional value of the muffins; the dietary fiber, antioxidant capacity and folate content are some of the features that stood out. A bakery product enriched with inulin, cocoa and Moringa could serve as a nutritional strategy to enhance nutritional value, thus helping in the treatment of constipation.

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.

Generally-healthy individuals with aberrant bowel movement frequencies show enrichment for microbially-derived blood metabolites associated with reduced kidney function

Bowel movement frequency (BMF) has been linked to changes in the composition of the human gut microbiome and to many chronic conditions, like metabolic disorders, neurodegenerative diseases, chronic kidney disease (CKD), and other intestinal pathologies like irritable bowel syndrome and inflammatory bowel disease. Lower BMF (constipation) can lead to compromised intestinal barrier integrity and a switch from saccharolytic to proteolytic fermentation within the microbiota, giving rise to microbially-derived toxins that may make their way into circulation and cause damage to organ systems. However, the connections between BMF, gut microbial metabolism, and the early-stage development and progression of chronic disease remain underexplored. Here, we examined the phenotypic impact of BMF variation in a cohort of generally-healthy, community dwelling adults with detailed clinical, lifestyle, and multi-omic data. We showed significant differences in microbially-derived blood plasma metabolites, gut bacterial genera, clinical chemistries, and lifestyle factors across BMF groups that have been linked to inflammation, cardiometabolic health, liver function, and CKD severity and progression. We found that the higher plasma levels of 3-indoxyl sulfate (3-IS), a microbially-derived metabolite associated with constipation, was in turn negatively associated with estimated glomerular filtration rate (eGFR), a measure of kidney function. Causal mediation analysis revealed that the effect of BMF on eGFR was significantly mediated by 3-IS. Finally, we identify self-reported diet, lifestyle, and psychological factors associated with BMF variation, which indicate several common-sense strategies for mitigating constipation and diarrhea. Overall, we suggest that aberrant BMF is an underappreciated risk factor in the development of chronic diseases, even in otherwise healthy populations.

Relationship among Parkinson's disease, constipation, microbes, and microbiological therapy

This comprehensive review elucidates the complex interplay between gut microbiota and constipation in Parkinson's disease (PD), a prevalent non-motor symptom contributing significantly to patients' morbidity. A marked alteration in the gut microbiota, predominantly an increase in the abundance of Proteobacteria and Bacteroidetes, is observed in PD-related constipation. Conventional treatments, although safe, have failed to effectively alleviate symptoms, thereby necessitating the development of novel therapeutic strategies. Microbiological interventions such as prebiotics, probiotics, and fecal microbiota transplantation (FMT) hold therapeutic potential. While prebiotics improve bowel movements, probiotics are effective in enhancing stool consistency and alleviating abdominal discomfort. FMT shows potential for significantly alleviating constipation symptoms by restoring gut microbiota balance in patients with PD. Despite promising developments, the causal relationship between changes in gut microbiota and PD-related constipation remains elusive, highlighting the need for further research in this expanding field.

Parkinson's Disease and Photobiomodulation: Potential for Treatment

Parkinson's disease is the second most common neurodegenerative disease and is increasing in incidence. The combination of motor and non-motor symptoms makes this a devastating disease for people with Parkinson's disease and their care givers. Parkinson's disease is characterised by mitochondrial dysfunction and neuronal death in the substantia nigra, a reduction in dopamine, accumulation of α-synuclein aggregates and neuroinflammation. The microbiome-gut-brain axis is also important in Parkinson's disease, involved in the spread of inflammation and aggregated α-synuclein. The mainstay of Parkinson's disease treatment is dopamine replacement therapy, which can reduce some of the motor signs. There is a need for additional treatment options to supplement available medications. Photobiomodulation (PBM) is a form of light therapy that has been shown to have multiple clinical benefits due to its enhancement of the mitochondrial electron transport chain and the subsequent increase in mitochondrial membrane potential and ATP production. PBM also modulates cellular signalling and has been shown to reduce inflammation. Clinically, PBM has been used for decades to improve wound healing, treat pain, reduce swelling and heal deep tissues. Pre-clinical experiments have indicated that PBM has the potential to improve the clinical signs of Parkinson's disease and to provide neuroprotection. This effect is seen whether the PBM is directed to the head of the animal or to other parts of the body (remotely). A small number of clinical trials has given weight to the possibility that using PBM can improve both motor and non-motor clinical signs and symptoms of Parkinson's disease and may potentially slow its progression.

Gastrointestinal conditions in the multiple sclerosis prodrome

OBJECTIVE

To investigate gastrointestinal (GI)-related physician visits and drug dispensations in the 5 years preceding a first recorded demyelinating event or multiple sclerosis (MS) onset.

METHODS

Using linked administrative and clinical data from British Columbia (1996-2013), Canada, we identified an administrative cohort via a validated algorithm (n = 6863), a clinical cohort diagnosed at a MS clinic (n = 966), and matched controls (administrative cohort: n = 31,865; clinical cohort: n = 4534). In each cohort, the 5 years before a first demyelinating event or MS symptom onset (i.e., index date) were examined. We compared rates of GI-related physician visits and risk of ≥1 GI-related dispensation between MS cases and controls using negative binomial and robust Poisson models. Sex differences were tested using interaction terms.

RESULTS

The administrative cohort MS cases had higher rates of physician visits related to gastritis and duodenitis (adjusted rate/risk ratio (aRR):1.42, 95% CI: 1.10-1.83) and diseases of the esophagus (aRR: 1.46, 95% CI: 1.06-2.02) prior to the index date. MS cases also had greater risk of at least one dispensation for several drug classes, including constipation-related (aRR: 1.82, 95% CI: 1.50-2.22), antiemetics/antinauseants (aRR: 1.64, 95% CI: 1.43-1.89), and propulsives (promotility drugs; aRR: 1.62, 95% CI: 1.47-1.79). Men had a disproportionally higher relative risk for propulsives than women (aRR: men = 2.32, 95% CI: 1.79-3.00; women = 1.54, 95% CI: 1.36-1.72). Several findings were similar in the smaller clinical cohort though none reached statistical significance.

INTERPRETATION

GI-related physician visits and drug dispensations were more common in the 5 years before the first demyelinating event versus matched controls. GI symptoms are a measurable feature of the prodromal or early phase of MS, with a sex difference evident.

U.S. Tax Credits to Promote Practical Proactive Preventative Care for Parkinson's Disease

Persons with Parkinson's disease (PD) and society at large can profit from a strategic investment into a forward leaning, practical, preventative, and proactive multidisciplinary care policy. The American healthcare system is not easily bent to accommodate this type of care, and thus a tax benefit is an attractive option. An individual federal income tax benefit of $6200 each year for every person residing in the US with a diagnosis of PD, could among other offerings provide monthly access to a licensed clinical social worker and access to mental health services. The implementation of more coordinated care has the potential reduce the burden of depression, anxiety, and demoralization. Personal training would also be covered and directed by physical and occupational therapists. The combination of home-based and telemedicine services would have the added benefit of improving access. The tax benefit would also provide access to a dietician. This type of care strategy could be designed to proactively identify early signs of aspiration and urinary tract infections to 'head off' significant morbidity. A $6200/year individual tax benefit for those diagnosed with PD will thus translate into more fall prevention, more care in the home setting, less hospitalizations, less depression, less anxiety, less demoralization, better diets, and less persons placed in nursing facilities. Additionally, this tax benefit will provide the potential for billions of dollars in savings to the healthcare system. A tax benefit for PD is a practical preventative and proactive strategy which can serve to advantage both this generation and the next.

Parkinson's disease and gut microbiota: from clinical to mechanistic and therapeutic studies

Parkinson's disease (PD) is one of the most prevalent neurodegenerative diseases. The typical symptomatology of PD includes motor symptoms; however, a range of nonmotor symptoms, such as intestinal issues, usually occur before the motor symptoms. Various microorganisms inhabiting the gastrointestinal tract can profoundly influence the physiopathology of the central nervous system through neurological, endocrine, and immune system pathways involved in the microbiota-gut-brain axis. In addition, extensive evidence suggests that the gut microbiota is strongly associated with PD. This review summarizes the latest findings on microbial changes in PD and their clinical relevance, describes the underlying mechanisms through which intestinal bacteria may mediate PD, and discusses the correlations between gut microbes and anti-PD drugs. In addition, this review outlines the status of research on microbial therapies for PD and the future directions of PD-gut microbiota research.

Oh my gut! Is the microbial origin of neurodegenerative diseases real?

There is no cure or effective treatment for neurodegenerative protein conformational diseases (PCDs), such as Alzheimer's or Parkinson's diseases, mainly because the etiology of these diseases remains elusive. Recent data suggest that unique changes in the gut microbial composition are associated with these ailments; however, our current understanding of the bacterial role in the pathogenesis of PCDs is hindered by the complexity of the microbial communities associated with specific microbiomes, such as the gut, oral, or vaginal microbiota. The composition of these specific microbiomes is regarded as a unique fingerprint affected by factors such as infections, diet, lifestyle, and antibiotics. All of these factors also affect the severity of neurodegenerative diseases. The majority of studies that reveal microbial contribution are correlational, and various models, including worm, fly, and mouse, are being utilized to decipher the role of individual microbes that may affect disease onset and progression. Recent evidence from across model organisms and humans shows a positive correlation between the presence of gram-negative enteropathogenic bacteria and the pathogenesis of PCDs. While these correlational studies do not provide a mechanistic explanation, they do reveal contributing bacterial species and provide an important basis for further investigation. One of the lurking concerns related to the microbial contribution to PCDs is the increasing prevalence of antibiotic resistance and poor antibiotic stewardship, which ultimately select for proteotoxic bacteria, especially the gram-negative species that are known for intrinsic resistance. In this review, we summarize what is known about individual microbial contribution to PCDs and the potential impact of increasing antimicrobial resistance.

Parkinson's disease patients combined with constipation tend to have higher serum expression of microRNA 29c, prominent neuropsychiatric disorders, possible RBD conversion, and a substandard quality of life

INTRODUCTION

The symptom of constipation has been confirmed as an early diagnose criteria for Parkinson's disease (PD). Furthermore, evidences suggest that pathogenesis of PD initiates in gut, rather than brain. If so, identifying biomarkers for constipation in PD might have potentials to assist early diagnosis and initial treatment.

METHOD

We first identified that microRNA 29c (miR-29c) was dysregulated both in PD and constipation patients through bioinformatics analysis. Then, serological analysis of the expression of miR-29c in 67 PD patients with constipation (PD-C), 51 PD patients without constipation (PD-NC), and 50 healthy controls (HC) was carried out by qPCR. Demographic and clinical features were also compared. Patients in PD-C group were further classified into two groups: those with prodromal stage constipation (PD-C-Pro) (n = 36) and those with clinical stage constipation (PD-C-Clinic) (n = 31), to explore their different characteristics.

RESULTS

The levels of miR-29c in PD-C group were higher than that in PD-NC group, both higher than HC group. PD-C-Pro group's miR-29c levels were statistically higher compared with PD-C-Clinic group's. What is more, PD-C group had higher scores of MDS-UPDRS-I, NMSS, NMSS3, NMSS4, NMSS6, NMSS9, SCOPA-AUT, HAMD, HAMA, RBDSQ, CSS, and PACQOL compared with PD-NC party. Relative to the PD-C-Clinic, patients in PD-C-Pro group had higher MDS-UPDRS-I, NMSS, NMSS3, HAMD, and HAMA scores, and were more likely to have RBD.

CONCLUSION

Our results indicated that miR-29c seems to be an underlying cause for developing constipation in patients with PD and PD-C identifies a group of patients with more severe non-motor impairment, prominent neuropsychiatric disorders, and possible RBD conversion as well as a substandard quality of life. We further confirmed that there is a close relationship between symptoms representing the same pathological origin, especially constipation and RBD.

Metabolic Disturbances in the Gut-brain Axis of a Mouse Model of MPTP-induced Parkinsonism Evaluated by Nuclear Magnetic Resonance

Parkinson's Disease is a synucleinopathy that primarily affects the dopaminergic cells of the central nervous system, leading to motor and gastrointestinal disturbances. However, intestinal peripheral neurons undergo a similar neurodegeneration process, marked by α-synuclein (αSyn) accumulation and loss of mitochondrial homeostasis. We investigated the metabolic alterations in different biometrics that compose the gut-brain axis (blood, brain, large intestine, and feces) in an MPTP-induced mouse model of sporadic Parkinson's Disease. Animals received escalating administration of MPTP. Tissues and fecal pellets were collected, and the metabolites were identified through the untargeted Nuclear Magnetic Resonance spectroscopic (1H NMR) technique. We found differences in many metabolites from all the tissues evaluated. The differential expression of metabolites in these samples mainly reflects inflammatory aspects, cytotoxicity, and mitochondrial impairment (oxidative stress and energy metabolism) in the animal model used. The direct evaluation of fecal metabolites revealed changes in several classes of metabolites. This data reinforces previous studies showing that Parkinson's disease is associated with metabolic perturbation not only in brain-related tissues, but also in periphery structures such as the gut. In addition, the evaluation of the microbiome and metabolites from gut and feces emerge as promising sources of information for understanding the evolution and progression of sporadic Parkinson's Disease.

Constipation in Parkinson's Disease

Constipation is one of the most common gastrointestinal features of Parkinson's disease (PD), occurring in over 50% of all PD patients during the course of their disease. Furthermore, constipation is now recognized as an important, prodromal symptom and may predate the onset of the classical motor symptoms by decades. Thereafter, the prevalence and severity of constipation in PD tend to parallel the course of both motor and nonmotor phenomena such as cognitive decline and depression. Difficult defecation (obstructed defecation, dyssynergia) is the primary pathophysiology underlying constipation and likely reflects involvement by the PD process of one or more of the many skeletal muscle groups that are involved in effecting defecation. Management of constipation in PD may be complicated by several patient factors including dysphagia, cognitive impairment, depression, and weak sphincter tone. While the armamentarium available to those who treat constipation, in general, has expanded considerably in recent years, the evidence supporting any therapy in the management of this symptom in PD has remained slim.

An Overview of Gastrointestinal Dysfunction in Parkinsonian Syndromes

Gastrointestinal (GI) dysfunction is a common nonmotor symptom in Parkinson's disease (PD) as well as other parkinsonian syndromes and may precede the onset of motor symptoms by decades. Involvement of all segments of the GI tract can lead to altered responses to medications and worsened quality of life for patients. While some GI symptoms occur in isolation, others overlap. Therefore, understanding the changes in different segments of the GI tract and how they relate to altered responses to PD treatment can guide both diagnostic and pharmacological interventions. Gut microbiota plays a critical role in immune activity and modulation of the enteric and central nervous systems. Understanding this bidirectional relationship helps to elucidate the pathogenesis of neurodegeneration. This review will describe the current understanding of how GI dysfunction develops in parkinsonian syndromes, common symptoms in PD and related disorders, and available treatments.

Parkinson's disease: Are gut microbes involved?

INTRODUCTION

Parkinson's disease (PD) is a neurodegenerative disorder that affects more than 10 million individuals worldwide. It is characterized by motor and sensory deficits. Research studies have increasingly demonstrated a correlation between Parkinson's disease and alternations in the composition of the gut microbiota in affected patients. Also, the significant role of prebiotics and probiotics in gastrointestinal and neurological conditions is imperative to understand their relation to Parkinson's disease.

METHOD

To explore the scientific interaction of the gut-microbiota-brain axis and its association with Parkinson's disease, a comprehensive narrative review of the relevant literature was conducted. Articles were retrieved systematically from reputable sources, including PubMed, Science Direct, World Health Organization (WHO), and Advanced Google Scholar. Key search terms included are "Parkinson's Disease", "Gut Microbiome", "Braak's Theory", "Neurological Disorders", and "Gut-brain axis". Articles included in our review are published in English and they provide detailed information on the relationship between Parkinson's disease and gut microbiota RESULTS: This review highlights the impact of gut microbiota composition and associated factors on the progression of Parkinson's disease. Evidence-based studies highlighting the existing evidence of the relationship between Parkinson's disease and alteration in gut microbiota are discussed. Consequently, the potential mechanisms by which the gut microbiota may affect the composition of the gut microbiota were revealed, with a particular emphasis on the role of the gut-brain axis in this interplay.

CONCLUSION

Understanding the complex interplay between gut microbiota and Parkinson's disease is a potential implication for the development of novel therapeutics against Parkinson's disease. Following the existing relationship demonstrated by different evidence-based studies on Parkinson's disease and gut microbiota, our review concludes by providing recommendations and suggestions for future research studies with a particular emphasis on the impact of the microbiota-brain axis on Parkinson's disease.

The Poly-Arginine Peptide R18D Interferes with the Internalisation of α-Synuclein Pre-Formed Fibrils in STC-1 Enteroendocrine Cells

In Parkinson's disease (PD), gut inflammation is hypothesised to contribute to α-synuclein aggregation, but gastrointestinal α-synuclein expression is poorly characterised. Cationic arginine-rich peptides (CARPs) are an emerging therapeutic option that exerts various neuroprotective effects and may target the transmission of protein aggregates. This study aimed to investigate endogenous α-synuclein expression in enteroendocrine STC-1 cells and the potential of the CARP, R18D (18-mer of D-arginine), to prevent internalisation of pre-formed α-synuclein fibrils (PFFs) in enteroendocrine cells in vitro. Through confocal microscopy, the immunoreactivity of full-length α-synuclein and the serine-129 phosphorylated form (pS129) was investigated in STC-1 (mouse enteroendocrine) cells. Thereafter, STC-1 cells were exposed to PFFs tagged with Alexa-Fluor 488 (PFF-488) for 2 and 24 h and R18D-FITC for 10 min. After confirming the uptake of both PFFs and R18D-FITC through fluorescent microscopy, STC-1 cells were pre-treated with R18D (5 or 10 μM) for 10 min prior to 2 h of PFF-488 exposure. Immunoreactivity for endogenous α-synuclein and pS129 was evident in STC-1 cells, with prominent pS129 staining along cytoplasmic processes and in perinuclear areas. STC-1 cells internalised PFFs, confirmed through co-localisation of PFF-488 and human-specific α-synuclein immunoreactivity. R18D-FITC entered STC-1 cells within 10 min and pre-treatment of STC-1 cells with R18D interfered with PFF uptake. The endogenous presence of α-synuclein in enteroendocrine cells, coupled with their rapid uptake of PFFs, demonstrates a potential for pathogenic spread of α-synuclein aggregates in the gut. R18D is a novel therapeutic approach to reduce the intercellular transmission of α-synuclein pathology.

Different pieces of the same puzzle: a multifaceted perspective on the complex biological basis of Parkinson's disease

The biological basis of the neurodegenerative movement disorder, Parkinson's disease (PD), is still unclear despite it being 'discovered' over 200 years ago in Western Medicine. Based on current PD knowledge, there are widely varying theories as to its pathobiology. The aim of this article was to explore some of these different theories by summarizing the viewpoints of laboratory and clinician scientists in the PD field, on the biological basis of the disease. To achieve this aim, we posed this question to thirteen "PD experts" from six continents (for global representation) and collated their personal opinions into this article. The views were varied, ranging from toxin exposure as a PD trigger, to LRRK2 as a potential root cause, to toxic alpha-synuclein being the most important etiological contributor. Notably, there was also growing recognition that the definition of PD as a single disease should be reconsidered, perhaps each with its own unique pathobiology and treatment regimen.

The Endotoxin Hypothesis of Parkinson's Disease

The endotoxin hypothesis of Parkinson's disease (PD) is the idea that lipopolysaccharide (LPS) endotoxins contribute to the pathogenesis of this disorder. LPS endotoxins are found in, and released from, the outer membrane of Gram-negative bacteria, for example in the gut. It is proposed that gut dysfunction in early PD leads to elevated LPS levels in the gut wall and blood, which promotes both α-synuclein aggregation in the enteric neurons and a peripheral inflammatory response. Communication to the brain via circulating LPS and cytokines in the blood and/or the gut-brain axis leads to neuroinflammation and spreading of α-synuclein pathology, exacerbating neurodegeneration in brainstem nuclei and loss of dopaminergic neurons in the substantia nigra, and manifesting in the clinical symptoms of PD. The evidence supporting this hypothesis includes: (1) gut dysfunction, permeability, and bacterial changes occur early in PD, (2) serum levels of LPS are increased in a proportion of PD patients, (3) LPS induces α-synuclein expression, aggregation, and neurotoxicity, (4) LPS causes activation of peripheral monocytes leading to inflammatory cytokine production, and (5) blood LPS causes brain inflammation and specific loss of midbrain dopaminergic neurons, mediated by microglia. If the hypothesis is correct, then treatment options might include: (1) changing the gut microbiome, (2) reducing gut permeability, (3) reducing circulating LPS levels, or (4) blocking the response of immune cells and microglia to LPS. However, the hypothesis has a number of limitations and requires further testing, in particular whether reducing LPS levels can reduce PD incidence, progression, or severity. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Cognitive heterogeneity in Parkinson's disease: A mechanistic view

Cognitive impairment occurs in most individuals with Parkinson's disease (PD), exacting a high toll on patients, their caregivers, and the healthcare system. In this review, we begin by summarizing the current clinical landscape surrounding cognition in PD. We then discuss how cognitive impairment and dementia may develop in PD based on the spread of the pathological protein alpha-synuclein (aSyn) from neurons in brainstem regions to those in the cortical regions of the brain responsible for higher cognitive functions, as first proposed in the Braak hypothesis. We appraise the Braak hypothesis from molecular (conformations of aSyn), cell biological (cell-to-cell spread of pathological aSyn), and organ-level (region-to-region spread of aSyn pathology at the whole brain level) viewpoints. Finally, we argue that individual host factors may be the most poorly understood aspect of this pathological process, accounting for substantial heterogeneity in the pattern and pace of cognitive decline in PD.

Gastrointestinal Dysfunction in Parkinson's Disease: Neuro-Gastroenterology Perspectives on a Multifaceted Problem

Patients with Parkinson's disease (PD) face a multitude of gastrointestinal (GI) symptoms, including nausea, bloating, reduced bowel movements, and difficulties with defecation. These symptoms are common and may accumulate during the course of PD but are often under-recognized and challenging to manage. Objective testing can be burdensome to patients and does not correlate well with symptoms. Effective treatment options are limited. Evidence is often based on studies in the general population, and specific evidence in PD is scarce. Upper GI dysfunction may also interfere with the pharmacological treatment of PD motor symptoms, which poses significant management challenges. Several new less invasive assessment tools and novel treatment options have emerged in recent years. The current review provides an overview and a practical approach to recognizing and diagnosing common upper and lower GI problems in PD, e.g., dyspepsia, gastroparesis, small bowel dysfunction, chronic constipation, and defecatory dysfunction. Management aspects are discussed based on the latest evidence from the PD and general populations, with insights for future research pertaining to GI dysfunction in PD.

Targeting the microbiota-mitochondria crosstalk in neurodegeneration with senotherapeutics

Neurodegenerative diseases are a group of age-related disorders characterized by a chronic and progressive loss of function and/or structure of synapses, neurons, and glial cells. The etiopathogenesis of neurodegenerative diseases is characterized by a complex network of intricately intertwined pathophysiological processes that are still not fully understood. Safe and effective disease-modifying treatments are urgently needed, but still not available. Accumulating evidence suggests that gastrointestinal dyshomeostasis and microbial dysbiosis might play an important role in neurodegeneration by acting as either primary or secondary pathophysiological factors. The research on the role of microbiota in neurodegeneration is in its early phase; however, accumulating evidence suggests that dysbiosis might promote neurodegenerative diseases by disrupting mitochondrial function and inducing mitochondrial dysfunction-associated senescence (MiDAS), possibly due to bidirectional crosstalk based on the common evolutionary origin of mitochondria and bacteria. Cellular senescence is an onco-supressive homeostatic mechanism that results in an irreversible cell cycle arrest upon exposure to noxious stimuli. Senescent cells resist apoptosis via senescent cell anti-apoptotic pathways (SCAPs) and transition into a state known as senescence-associated secretory phenotype (SASP) that generates a cytotoxic proinflammatory microenvironment. Cellular senescence results in the adoption of a detrimental vicious cycle driven by dysbiosis, mitochondrial dysfunction, inflammation, and oxidative stress - a pathophysiological positive feedback loop that results in neuroinflammation and neurodegeneration. Detrimental effects of MiDAS might be prevented and abolished by mitochondria-targeted senotherapeutics, a group of drugs specifically designed to alleviate senescence by inhibiting SCAPs (senolytics), or inhibiting SASP (senomorphics).

Machado Joseph disease severity is linked with gut microbiota alterations in transgenic mice

Emerging evidence suggests the presence of bidirectional interactions between the central nervous system and gut microbiota that may contribute to the pathogenesis of neurodegenerative diseases. However, the potential role of gut microbes in forms of spinocerebellar ataxia, such as the fatal neurodegenerative disease Machado Joseph disease (MJD), remains unexplored. Here, we examined whether gut microbiota alterations may be an early disease phenotype of MJD. We profiled the gut microbiota of male and female transgenic MJD mice (CMVMJD135) expressing human ATXN3 with expanded CAG repeats (133-143 CAG) at pre-symptomatic, symptomatic and well-established stages of the disease (7, 11 and 15 weeks of age, respectively). We compared these profiles with the gut microbiota of male and female wild-type (WT) littermate control mice at same ages. Correlation network analyses were employed to explore the relevance of microbiota changes to disease progression. The results demontrated distinct sex-dependent effects in disease development whereby male MJD mice displayed earlier motor impairments than female MJD mice. The gut microbiota community structure and composition also demonstrated sex-specific differences between MJD and WT mice. In both male and female MJD mice, the shifts in the microbiota were present by 7 weeks, before the onset of any symptoms. These pre-symptomatic microbial changes correlated with the severity of neurological impairments present at later stages of the disease. Previous efforts towards developing treatments for MJD have failed to yield meaningful outcomes. Our study reports a novel relationship between the gut microbiota and MJD development and severity. Elucidating how gut microbes are involved in MJD pathogenesis may offer new and efficacious treatment strategies for this currently untreatable disease.

The link between increased Desulfovibrio and disease severity in Parkinson's disease

Parkinson's disease (PD), a progressive and incurable neurodegenerative disease, has taken a huge economic toll and medical burden on our society. Increasing evidence has shown a strong link between PD and the gut microbiome, but studies on the relationship between the gut microbiome and the severity of PD are limited. In this study, 90 fecal samples were collected from newly diagnosed and untreated patients with PD (n = 47) and matched healthy control subjects (n = 43). The 16S rRNA amplicon and shotgun metagenomic sequencing was performed, aiming to uncover the connection between the gut microbiome and disease severity in PD. The results showed that Desulfovibrio was significantly increased in PD compared to healthy controls and positively correlated with disease severity. The increase in Desulfovibrio was mainly driven by enhanced homogeneous selection and weakened drift. Moreover, through metagenome-assembled genomes (MAGs) analysis, a Desulfovibrio MAG (MAG58) was obtained which was also positively correlated with disease severity. MAG58 possesses a complete assimilatory sulfate reduction pathway and a near-complete dissimilatory sulfate reduction pathway to produce hydrogen sulfide which may influence the development of PD. Based on these results, a potential pathogenic mechanism was presented to illustrate how the increased Desulfovibrio accelerates the development of PD by producing excessive hydrogen sulfide. The present study highlighted the vital role of Desulfovibrio in the development of PD, which may provide a new target for the diagnosis and treatment of PD. KEY POINTS: • The evidence for the link between increased Desulfovibrio and disease severity in PD • A Desulfovibrio MAG was obtained which was correlated with PD • A model was presented to illustrate how increased Desulfovibrio causes PD.

Human mini-brains for reconstituting central nervous system disorders

Neurological disorders in the central nervous system (CNS) are progressive and irreversible diseases leading to devastating impacts on patients' life as they cause cognitive impairment, dementia, and even loss of essential body functions. The development of effective medicines curing CNS disorders is, however, one of the most ambitious challenges due to the extremely complex functions and structures of the human brain. In this regard, there are unmet needs to develop simplified but physiopathologically-relevant brain models. Recent advances in the microfluidic techniques allow multicellular culture forming miniaturized 3D human brains by aligning parts of brain regions with specific cells serving suitable functions. In this review, we overview designs and strategies of microfluidics-based human mini-brains for reconstituting CNS disorders, particularly Alzheimer's disease (AD), Parkinson's disease (PD), traumatic brain injury (TBI), vascular dementia (VD), and environmental risk factor-driven dementia (ERFD). Afterward, the applications of the mini-brains in the area of medical science are introduced in terms of the clarification of pathogenic mechanisms and identification of promising biomarkers. We also present expanded model systems ranging from the CNS to CNS-connecting organ axes to study the entry pathways of pathological risk factors into the brain. Lastly, the advantages and potential challenges of current model systems are addressed with future perspectives.

The theoretical problems of "prodrome" and "phenoconversion" in neurodegeneration

The recognition of and approach to prodromal symptoms, those which manifest before a diagnosis can be ascertained at the bedside, are of increasing interest in neurodegenerative research. A prodrome is conceived of as an early window into a disease, a critical time when putative disease-modifying interventions may be best suited for examination. Several challenges affect research in this area. Prodromal symptoms are highly prevalent in the population, can be nonprogressive for years or decades, and exhibit limited specificity in predicting conversion versus nonconversion into a neurodegenerative category within a time window feasible for most longitudinal clinical studies. In addition, there is a large range of biological alterations subsumed within each prodromal syndrome, forced to converge into the unifying nosology of each neurodegenerative disorder. Initial prodromal subtyping efforts have been developed but given the scarcity of prodrome-to-disease longitudinal studies, it is not yet clear whether any prodromal subtype can be predicted to evolve into the corresponding subtype of manifesting disease - a form of construct validity. As current subtypes generated from one clinical population are not faithfully replicated to others, it is likely that, lacking biological or molecular anchors, prodromal subtypes may only be applicable to the cohorts within which they were developed. Furthermore, as clinical subtypes have not aligned with a consistent pattern of pathology or biology, such might also be the fate of prodromal subtypes. Finally, the threshold defining the change from prodrome to disease for most neurodegenerative disorders remains clinical (e.g., a motor change in gait becoming noticeable to a clinician or measurable with portable technologies), not biological. As such, a prodrome can be viewed as a disease state not yet overt to a clinician. Efforts into identifying biological subtypes of disease, regardless of clinical phenotype or disease stage, may best serve future disease-modifying therapeutic strategies deployed not for a prodromal symptom but for a defined biological derangement as soon as it can be determined to lead to clinical changes, prodromal or not.

α-Synuclein induces prodromal symptoms of Parkinson's disease via activating TLR2/MyD88/NF-κB pathway in Schwann cells of vagus nerve in a rat model

BACKGROUND

Increasing evidence suggests that patients with Parkinson's disease (PD) present with peripheral autonomic dysfunction (AutD) that even precedes motor deficits, through which α-synuclein can spread to the central nervous system. However, the pathological mechanisms underlying AutD in prodromal PD remain unclear. Here, we investigated the role of α-synuclein and its interplay with the activation of Schwann cells (SCs) of the vagus nerve in AutD.

METHODS

Rats were subjected to injection with adeno-associated viruses containing the human mutated A53T gene (AAV-A53T) or an empty vector into the left cervical vagus nerve and evaluated for gastrointestinal symptoms, locomotor functions, intestinal blood flow, and nerve electrophysiology. Further, we examined the impact of α-synucleinopathy on vagus nerves, SCs, and central nervous system neurons using electron microscopy, immunofluorescence, immunohistochemistry, and western blot. Finally, the role of Toll-like receptor 2 (TLR2) in regulating the neuroinflammation in the vagus nerve via MyD88 and NF-κB pathway was determined using genetic knockdown.

RESULTS

We found that rats injected with AAV-A53T in the vagus nerve exhibited prominent signs of AutD, preceding the onset of motor deficits and central dopaminergic abnormalities by at least 3 months, which could serve as a model for prodromal PD. In addition, reduced intestinal blood flow and decreased nerve conduction velocity were identified in AAV-A53T-injected rats, accompanied by disrupted myelin sheaths and swollen SCs in the vagus nerve. Furthermore, our data demonstrated that p-α-synuclein was deposited in SCs but not in axons, activating the TLR2/MyD88/NF-κB signaling pathway and leading to neuroinflammatory responses. In contrast, silencing the TLR2 gene not only reduced inflammatory cytokine expression but also ameliorated vagal demyelination and secondary axonal loss, consequently improving autonomic function in rats.

CONCLUSIONS

These observations suggest that overexpression of α-synuclein in the vagus nerve can induce symptoms of AutD in prodromal PD, and provide support for a deeper understanding of the pathological mechanisms underlying AutD and the emergence of effective therapeutic strategies for PD.

Sodium butyrate ameliorates gut dysfunction and motor deficits in a mouse model of Parkinson's disease by regulating gut microbiota

Background

A growing body of evidence showed that gut microbiota dysbiosis might be associated with the pathogenesis of Parkinson's disease (PD). Microbiota-targeted interventions could play a protective role in PD by regulating the gut microbiota-gut-brain axis. Sodium butyrate (NaB) could improve gut microbiota dysbiosis in PD and other neuropsychiatric disorders. However, the potential mechanism associated with the complex interaction between NaB and gut microbiota-gut-brain communication in PD needs further investigation.

Methods

C57BL/6 mice were subjected to a rotenone-induced PD model and were treated intragastrically with NaB for 4 weeks. The gut function and motor function were evaluated. The α-synuclein expression in colon and substantia nigra were detected by western blotting. Tyrosine hydroxylase (TH)-positive neurons in substantia nigra were measured by immunofluorescence. Moreover, gut microbiota composition was analyzed by 16S rRNA sequencing. Fecal short chain fatty acids (SCFAs) levels were determined by liquid chromatography tandem mass spectrometry (LC-MS). The levels of glucagon like peptide-1 (GLP-1) in tissues and serum were evaluated using enzyme-linked immunosorbent assay (ELISA).

Results

NaB ameliorated gut dysfunction and motor deficits in rotenone-induced mice. Meanwhile, NaB protected against rotenone-induced α-synuclein expression in colon and substantia nigra, and prevented the loss of TH-positive neurons. In addition, NaB could remodel gut microbiota composition, and regulate gut SCFAs metabolism, and restore GLP-1 levels in colon, serum, and substantia nigra in PD mice.

Conclusion

NaB could ameliorate gut dysfunction and motor deficits in rotenone-induced PD mice, and the mechanism might be associated with the regulation of gut microbiota dysbiosis.

Faecal metabolite deficit, gut inflammation and diet in Parkinson's disease: Integrative analysis indicates inflammatory response syndrome

BACKGROUND

Gut-brain axis is widely implicated in the pathophysiology of Parkinson's disease (PD). We take an integrated approach to considering the gut as a target for disease-modifying intervention, using continuous measurements of disease facets irrespective of diagnostic divide.

METHODS

We characterised 77 participants with diagnosed-PD, 113 without, by dietary/exogenous substance intake, faecal metabolome, intestinal inflammation, serum cytokines/chemokines, clinical phenotype including colonic transit time. Complete-linkage hierarchical cluster analysis of metabolites discriminant for PD-status was performed.

RESULTS

Longer colonic transit was linked to deficits in faecal short-chain-fatty acids outside PD, to a 'tryptophan-containing metabolite cluster' overall. Phenotypic cluster analysis aggregated colonic transit with brady/hypokinesia, tremor, sleep disorder and dysosmia, each individually associated with tryptophan-cluster deficit. Overall, a faster pulse was associated with deficits in a metabolite cluster including benzoic acid and an imidazole-ring compound (anti-fungals) and vitamin B3 (anti-inflammatory) and with higher serum CCL20 (chemotactic for lymphocytes/dendritic cells towards mucosal epithelium). The faster pulse in PD was irrespective of postural hypotension. The benzoic acid-cluster deficit was linked to (well-recognised) lower caffeine and alcohol intakes, tryptophan-cluster deficit to higher maltose intake. Free-sugar intake was increased in PD, maltose intake being 63% higher (p = .001). Faecal calprotectin was 44% (95% CI 5%, 98%) greater in PD [p = .001, adjusted for proton-pump inhibitors (p = .001)], with 16% of PD-probands exceeding a cut-point for clinically significant inflammation compatible with inflammatory bowel disease. Higher maltose intake was associated with exceeding this calprotectin cut-point.

CONCLUSIONS

Emerging picture is of (i) clinical phenotype being described by deficits in microbial metabolites essential to gut health; (ii) intestinal inflammation; (iii) a systemic inflammatory response syndrome.

Advances in the Pharmacological and Non-pharmacological Management of Non-motor Symptoms in Parkinson's Disease: An Update Since 2017

BACKGROUND

Non-motor symptoms (NMS) are an important and ubiquitous determinant of quality of life in Parkinson's disease (PD). However, robust evidence for their treatment is still a major unmet need.

OBJECTIVE

This study aimed to provide an updated review on advances in pharmacological, nonpharmacological, and exercise-based interventions for NMS in PD, covering the period since the publication of the MDS Task Force Recommendations.

METHODS

We performed a literature search to identify pharmacological, non-pharmacological, and exercise-based interventions for NMS in PD. As there are recent reviews on the subject, we have only included studies from the 1st of January 2017 to the 1st of December 2021 and limited our search to randomised and non-randomised (including open-label) clinical trials.

RESULTS

We discuss new strategies to manage NMS based on data that have become available since 2017, for instance, on the treatment of orthostatic hypotension with droxidopa, several dopaminergic treatment options for insomnia, and a range of non-pharmacological and exercise-based interventions for cognitive and neuropsychiatric symptoms, pain, and insomnia and excessive sleepiness.

CONCLUSION

Recent evidence suggests that targeted non-pharmacological treatments, as well as some other NMS management options, may have a significant beneficial effect on the quality of life and need to be considered in the pathways of treatment of PD.

Gut-oriented disease modifying therapy for Parkinson's disease

Neuropathology studies have shown that the pathognomonic feature of Parkinson's disease (PD), one of the most common neurodegenerative disorders, may start from the gut enteric nervous system and then spread to the central dopaminergic neurons through the gut-brain axis. With the advent of metagenomic sequencing and metabolomic analysis, a plethora of evidence has revealed different gut microbiomes and gut metabolites in patients with PD compared with unaffected controls. Currently, although dopaminergic treatments and deep brain stimulation can provide some symptomatic benefits for motor symptoms of the disease, their long-term use is problematic. A mechanism-targeted therapy to halt the neurodegeneration is lacking. The recently observed gut microenvironmental changes in the early stages of the disease play a vital role in the PD pathogenesis. Patients whose disease begins in the gut may benefit most from interventions that target the gut microenvironments. In this review, we will summarize the current studies demonstrating multifunctional roles of gut microbiota in the gut-brain axis of PD and the currently available evidence for targeting the gut microbiota as a novel approach to potential disease-modifying therapy in PD.

REM sleep behavior disorder correlates with constipation in de novo Chinese Parkinson's disease patients

BACKGROUND

Constipation, rapid eye movement sleep behavior disorder (RBD) and hyposmia are common prodromal symptoms of Parkinson's disease (PD), and they may represent two distinct types of disease origin, from the body or the brain. Our study aimed to compare the clinical characteristics of de novo PD patients with and without constipation and identify which prodromal symptoms were associated with constipation.

METHODS

A total of 111 de novo, drug-naïve Chinese PD patients were consecutively enrolled from Jan 2017 to Sept 2021. Patients were classified into PD with and without constipation based on item 5 of the Scales for Outcomes in Parkinson's disease-Autonomic Dysfunction (SCOPA-AUT). The demographic data, motor, and non-motor symptoms were compared between the two groups. The associated factors of constipation were analyzed by the multivariate logistic regression analysis.

RESULTS

In total, 44.1% (n = 49) of de novo PD patients had constipation. PD patients with constipation were older (p = 0.028), had higher proportions of Hoehn and Yahr (H-Y) stage [Formula: see text] 2 (p = 0.002), clinical possible RBD (cpRBD) (p = 0.002) and depression (p = 0.023), as well as marginal increase of hyposmia (p = 0.058) and freezing of gait (p = 0.069). After adjusting for H-Y stage and other confounding factors, cpRBD (OR = 3.508, p = 0.009), rather than hyposmia or depression, was closely related to constipation in de novo Chinese PD patients.

CONCLUSIONS

RBD is closely associated with constipation in de novo Chinese PD patients. Our results support the theory that prodromal symptoms that represent the same pathological origin are closely related to each other.

Inflammatory microbes and genes as potential biomarkers of Parkinson's disease

As the second-largest neurodegenerative disease in the world, Parkinson's disease (PD) has brought a severe economic and medical burden to our society. Growing evidence in recent years suggests that the gut microbiome may influence PD, but the exact pathogenesis of PD remains unclear. In addition, the current diagnosis of PD could be inaccurate and expensive. In this study, the largest meta-analysis currently of the gut microbiome in PD was analyzed, including 2269 samples by 16S rRNA gene and 236 samples by shotgun metagenomics, aiming to reveal the connection between PD and gut microbiome and establish a model to predict PD. The results showed that the relative abundances of potential pro-inflammatory bacteria, genes and pathways were significantly increased in PD, while potential anti-inflammatory bacteria, genes and pathways were significantly decreased. These changes may lead to a decrease in potential anti-inflammatory substances (short-chain fatty acids) and an increase in potential pro-inflammatory substances (lipopolysaccharides, hydrogen sulfide and glutamate). Notably, the results of 16S rRNA gene and shotgun metagenomic analysis have consistently identified five decreased genera (Roseburia, Faecalibacterium, Blautia, Lachnospira, and Prevotella) and five increased genera (Streptococcus, Bifidobacterium, Lactobacillus, Akkermansia, and Desulfovibrio) in PD. Furthermore, random forest models performed well for PD prediction based on 11 genera (accuracy > 80%) or 6 genes (accuracy > 90%) related to inflammation. Finally, a possible mechanism was presented to explain the pathogenesis of inflammation leading to PD. Our results provided further insights into the prediction and treatment of PD based on inflammation.

Aggregation of alpha-synuclein in enteric neurons does not impact function in vitro

Recent evidence implicates a gut-first pathogenesis in the enteric nervous system (ENS) within a portion of PD patients, yet in vitro investigations have primarily focused on the central nervous system. Here, the preformed fibril (PFF) PD model is applied with co-administered groups of butyrate and lipopolysaccharide to model the effects of the local gut microbiome. Significant PFF uptake and retention occur in isolated rat enteric neurons compared to untreated controls resulting in increasing immunostained aggregate conformation-specific, alpha-synuclein (a-Syn) average intensity between 6 µg PFF and untreated controls. Cortical neurons significantly retain PFFs with an increase in aggregated a-Syn average intensity within all dosages. Differences in growth cone morphology but not dynamics in PFF-treated ENS cultures occur. Electrophysiological recordings via a microelectrode array (MEA) indicate no overall difference in spontaneous spike rate. However, only untreated controls respond to PD-relevant dopamine stimulus, while 1 µg PFF and control populations respond to stimulus with ENS-abundant acetylcholine. Finally, no differences in substance P levels-correlated with PD and neurodegeneration-are observed. Overall, these findings suggest the ENS retains PFF dosage absent acute loss in function, however, does experience changes in growth cone morphology and dopamine-stimulated activity.

Impact of Gastrointestinal Symptoms on Health-Related Quality of Life in an Australian Parkinson’s Disease Cohort

Background. Gastrointestinal symptoms (GIS) in people with Parkinson’s disease (PwP) are often underreported and may remain untreated. Constipation is a common nonmotor symptom that can adversely affect health-related quality of life (QoL); however, the impact of other GIS has not been adequately investigated. Objectives. To investigate the relationship between QoL and constipation using the Bristol Stool Chart, bowel movement frequency, and a perceived constipation measure; and to explore the relationship between QoL and other GIS in an Australian PD cohort. Methods. The impact of constipation and other GIS on QoL, as measured using the PDQ-39 scale, was assessed in a cohort of 144 (89 males, 55 females) clinic-attending PwP. Constipation was assessed using the Bristol Stool Chart as well as a composite constipation measure, and the Gastrointestinal Symptom Rating Scale (GSRS) was used to rate other GIS. Covariate corrected linear regression models were utilised to determine significant associations between GIS and QoL scores. Results. Individual and combined constipation measures were significantly associated with poorer QoL ( $p=0.032$ and $p=0.002$ , respectively). Analysis of GSRS symptom domains showed that in addition to symptoms of gastrointestinal hypomotility, a number of other symptoms such as increased eructation and increased flatus were also associated with poorer QoL. Conclusions. The findings point to the importance of GIS as contributor to health-related QoL in PwP. A better understanding of the relationship between GIS and QoL will help facilitate the development of more effective screening and treatment programs to improve symptom management and QoL for PwP.

Interactions between gut microbiota and Parkinson's disease: The role of microbiota-derived amino acid metabolism

Non-motor symptoms (NMS) of Parkinson's disease (PD), such as constipation, sleep disorders, and olfactory deficits, may emerge up to 20 years earlier than motor symptoms. A series of evidence indicates that the pathology of PD may occur from the gastrointestinal tract to the brain. Numerous studies support that the gut microbiota communicates with the brain through the immune system, special amino acid metabolism, and the nervous system in PD. Recently, there is growing recognition that the gut microbiota plays a vital role in the modulation of multiple neurochemical pathways via the “gut microbiota-brain axis” (GMBA). Many gut microbiota metabolites, such as fatty acids, amino acids, and bile acids, convey signaling functions as they mediate the crosstalk between gut microbiota and host physiology. Amino acids' abundance and species alteration, including glutamate and tryptophan, may disturb the signaling transmission between nerve cells and disrupt the normal basal ganglia function in PD. Specific amino acids and their receptors are considered new potential targets for ameliorating PD. The present study aimed to systematically summarize all available evidence on the gut microbiota-derived amino acid metabolism alterations associated with PD.

Gut microbiome and Parkinson's disease: Perspective on pathogenesis and treatment

BACKGROUND

Parkinson's disease (PD) is a disease of ⍺-synuclein aggregation-mediated dopaminergic neuronal loss in the substantia nigra pars compacta, which leads to motor and non-motor symptoms. Through the last two decades of research, there has been growing consensus that inflammation-mediated oxidative stress, mitochondrial dysfunction, and cytokine-induced toxicity are mainly involved in neuronal damage and loss associated with PD. However, it remains unclear how these mechanisms relate to sporadic PD, a more common form of PD. Both enteric and central nervous systems have been implicated in the pathogenesis of sporadic PD, thus highlighting the crosstalk between the gut and brain.

AIM

of Review: In this review, we summarize how alterations in the gut microbiome can affect PD pathogenesis. We highlight various mechanisms increasing/decreasing the risk of PD development. Based on the previous supporting evidence, we suggest how early interventions could protect against PD development and how controlling specific factors, including our diet, could modify our perspective on disease mechanisms and therapeutics. We explain the strong relationship between the gut microbiota and the brain in PD subjects, by delineating the multiple mechanisms involved inneuroinflammation and oxidative stress. We conclude that the neurodetrimental effects of western diet (WD) and the neuroprotective effects of Mediterranean diets should be further exploredin humans through clinical trials. Key Scientific Concepts of Review: Alterations in the gut microbiome and associated metabolites may contribute to pathogenesis in PD. In some studies, probiotics have been shown to exert anti-oxidative effects in PD via improved mitochondrial dynamics and homeostasis, thus reducing PD-related consequences. However, there is a significant unmet need for randomized clinical trials to investigate the effectiveness of microbial products, probiotic-based supplementation, and dietary intervention in reversing gut microbial dysbiosis in PD.

Gut microenvironmental changes as a potential trigger in Parkinson's disease through the gut-brain axis

Parkinson's disease (PD) is the second most common neurodegenerative disease attributed to the synergistic effects of genetic risk and environmental stimuli. Although PD is characterized by motor dysfunction resulting from intraneuronal alpha-synuclein accumulations, termed Lewy bodies, and dopaminergic neuronal degeneration in the substantia nigra, multiple systems are involved in the disease process, resulting in heterogenous clinical presentation and progression. Genetic predisposition to PD regarding aberrant immune responses, abnormal protein aggregation, autophagolysosomal impairment, and mitochondrial dysfunction leads to vulnerable neurons that are sensitive to environmental triggers and, together, result in neuronal degeneration. Neuropathology studies have shown that, at least in some patients, Lewy bodies start from the enteric nervous system and then spread to the central dopaminergic neurons through the gut-brain axis, suggesting the contribution of an altered gut microenvironment in the pathogenesis of PD. A plethora of evidence has revealed different gut microbiomes and gut metabolites in patients with PD compared to unaffected controls. Chronic gut inflammation and impaired intestinal barrier integrity have been observed in human PD patients and mouse models of PD. These observations led to the hypothesis that an altered gut microenvironment is a potential trigger of the PD process in a genetically susceptible host. In this review, we will discuss the complex interplay between genetic factors and gut microenvironmental changes contributing to PD pathogenesis.

The microbiome-gut-brain axis in Parkinson disease - from basic research to the clinic

Evidence for a close bidirectional link between the brain and the gut has led to a paradigm shift in neurology, especially in the case of Parkinson disease (PD), in which gastrointestinal dysfunction is a prominent feature. Over the past decade, numerous high-quality preclinical and clinical publications have shed light on the highly complex relationship between the gut and the brain in PD, providing potential for the development of new biomarkers and therapeutics. With the advent of high-throughput sequencing, the role of the gut microbiome has been specifically highlighted. Here, we provide a critical review of the literature on the microbiome-gut-brain axis in PD and present perspectives that will be useful for clinical practice. We begin with an overview of the gut-brain axis in PD, including the potential roles and interrelationships of the vagus nerve, α-synuclein in the enteric nervous system, altered intestinal permeability and inflammation, and gut microbes and their metabolic activities. The sections that follow synthesize the proposed roles of gut-related factors in the development and progression of, in responses to PD treatment, and as therapeutic targets. Finally, we summarize current knowledge gaps and challenges and delineate future directions for the field.

Gut Microbiota: A Novel Therapeutic Target for Parkinson’s Disease

Parkinson’s disease (PD) is the second most common neurodegenerative disease characterized by motor dysfunction. Growing evidence has demonstrated that gut dysbiosis is involved in the occurrence, development and progression of PD. Numerous clinical trials have identified the characteristics of the changed gut microbiota profiles, and preclinical studies in PD animal models have indicated that gut dysbiosis can influence the progression and onset of PD via increasing intestinal permeability, aggravating neuroinflammation, aggregating abnormal levels of α-synuclein fibrils, increasing oxidative stress, and decreasing neurotransmitter production. The gut microbiota can be considered promising diagnostic and therapeutic targets for PD, which can be regulated by probiotics, psychobiotics, prebiotics, synbiotics, postbiotics, fecal microbiota transplantation, diet modifications, and Chinese medicine. This review summarizes the recent studies in PD-associated gut microbiota profiles and functions, the potential roles, and mechanisms of gut microbiota in PD, and gut microbiota-targeted interventions for PD. Deciphering the underlying roles and mechanisms of the PD-associated gut microbiota will help interpret the pathogenesis of PD from new perspectives and elucidate novel therapeutic strategies for PD.

Exploring the Causal Effect of Constipation on Parkinson’s Disease Through Mediation Analysis of Microbial Data

Background and Aims

Parkinson’s disease (PD) is a worldwide neurodegenerative disease with an increasing global burden, while constipation is an important risk factor for PD. The gastrointestinal tract had been proposed as the origin of PD in Braak’s gut–brain axis hypothesis, and there is increasing evidence indicating that intestinal microbial alteration has a role in the pathogenesis of PD. In this study, we aim to investigate the role of intestinal microbial alteration in the mechanism of constipation-related PD.

Methods

We adapted our data from Hill‐Burns et al., in which 324 participants were enrolled in the study. The 16S rRNA gene sequence data were processed, aligned, and categorized using DADA2. Mediation analysis was used to test and quantify the extent by which the intestinal microbial alteration explains the causal effect of constipation on PD incidence.

Results

We found 18 bacterial genera and 7 species significantly different between groups of constipated and non-constipated subjects. Among these bacteria, nine genera and four species had a significant mediation effect between constipation and PD. All of them were short-chain fatty acid (SCFA)-producing bacteria that were substantially related to PD. Results from the mediation analysis showed that up to 76.56% of the effect of constipation on PD was mediated through intestinal microbial alteration.

Conclusion

Our findings support that gut dysbiosis plays a critical role in the pathogenesis of constipation-related PD, mostly through the decreasing of SCFA-producing bacteria, indicating that probiotics with SCFA-producing bacteria may be promising in the prevention and treatment of constipation-related PD.

Limitations

1) Several potential confounders that should be adjusted were not provided in the original dataset. 2) Our study was conducted based on the assumption of constipation being the etiology of PD; however, constipation and PD may mutually affect each other. 3) Further studies are necessary to explain the remaining 23.44% effect leading to PD by constipation.

To the Gut Microbiome and Beyond: The Brain-First or Body-First Hypothesis in Parkinson's Disease

There is continued debate regarding Parkinson’s disease etiology and whether it originates in the brain or begins in the gut. Recently, evidence has been provided for both, with Parkinson’s disease onset presenting as either a “body-first” or “brain-first” progression. Most research indicates those with Parkinson’s disease have an altered gut microbiome compared to controls. However, some studies do not report gut microbiome differences, potentially due to the brain or body-first progression type. Based on the etiology of each proposed progression, individuals with the body-first progression may exhibit altered gut microbiomes, i.e., where short-chain fatty acid producing bacteria are reduced, while the brain-first progression may not. Future microbiome research should consider this hypothesis and investigate whether gut microbiome differences exist between each type of progression. This may further elucidate the impact of the gut microbiome in Parkinson’s disease and show how it may not be homogenous across individuals with Parkinson’s disease.

Pharmacological Intervention Targeting FAF1 Restores Autophagic Flux for α-Synuclein Degradation in the Brain of a Parkinson's Disease Mouse Model

α-Synuclein accumulation is implicated in the pathogenesis of neurodegenerative diseases, including Parkinson's disease (PD). Previously, we reported that Fas-associated factor 1 (FAF1), which plays a role in PD pathogenesis, potentiates α-synuclein accumulation through autophagy impairment in dopaminergic neurons. In this study, we show that KM-819, a FAF1-targeting compound, which has completed phase I clinical trials, interferes with α-synuclein accumulation in the mouse brain, as well as in human neuronal cells (SH-SY5Ys). KM-819 suppressed the accumulation of monomeric, oligomeric, and aggregated forms of α-synuclein in neuronal cells. Furthermore, KM-819 restored the turnover rate of α-synuclein in FAF1-overexpressing SH-SY5Y cells, implicating KM-819-mediated reconstitution of the α-synuclein degradative pathway. In addition, KM-819 reconstituted autophagic flux in FAF1-transfected SH-SY5Y cells, also suppressing α-synuclein-induced mitochondrial dysfunction. Moreover, oral administration of KM-819 also interfered with α-synuclein accumulation in the midbrain of mice overexpressing FAF1 via an adeno-associated virus system. Consistently, KM-819 reduced α-synuclein accumulation in both the hippocampus and the midbrain of human A53T α-synuclein transgenic mice. Collectively, these data imply that KM-819 may have therapeutic potential for patients with PD.

Dysautonomia in Parkinson’s Disease: Impact of Glucocerebrosidase Gene Mutations on Cardiovascular Autonomic Control

Evidence from clinical practice suggests that PD patients with the Glucocerebrosidase gene mutations (GBA-PD) are characterized by more severe dysautonomic symptoms than patients with idiopathic PD (iPD). Therefore, an accurate assessment of cardiovascular autonomic control (CAC) is necessary to clarify the role of GBA mutations in the pathophysiology of PD. We evaluated the CAC at rest and during orthostatic challenge of 15 iPD, 15 GBA-PD and 15 healthy controls (CTR). ECG and respiration were recorded in supine position and during active standing. The analysis of Heart Rate Variability (HRV) was performed on ECG recordings using two different approaches, linear spectral analysis and non-linear symbolic analysis. GBA-PD patients presented more frequently an akinetic-rigid phenotype and cognitive dysfunction than iPD patients. Both iPD and GBA-PD group were characterized by a lower spectral HRV than CTR group. At rest, the GBA-PD group was characterized by a lower parasympathetic modulation and a shift of the sympathovagal balance toward a sympathetic predominance compared to the CTR group. Moreover, the GBA-PD patients presented a lower HR increment and a lower or absent reduction of the vagal modulation in response to the active standing than iPD patients. Lastly, the cardiovascular autonomic dysfunction in PD patients was associated with longer disease duration, and with the occurrence of REM sleep behavior disorder and constipation. Our findings suggest a more severe impairment of the CAC in PD patients with GBA mutations. These results and further studies on the role of GBA mutations could allow a stratification based on cardiovascular risk in PD patients and the implementation of specific prevention programs.

Akkermansia muciniphila induces mitochondrial calcium overload and α -synuclein aggregation in an enteroendocrine cell line

The gut microbiota influence neurodevelopment, modulate behavior, and contribute to neurodegenerative disorders. Several studies have consistently reported a greater abundance of Akkermansia muciniphila in Parkinson disease (PD) fecal samples. Therefore, we investigated whether A.muciniphila-conditioned medium (CM) could initiate α-synuclein (αSyn) misfolding in enteroendocrine cells (EEC) — a component of the gut epithelium featuring neuron-like properties. We found that A. muciniphila CM composition is influenced by the ability of the strain to degrade mucin. Our in vitro experiments showed that the protein-enriched fraction of mucin-free CM induces RyR-mediated Ca²⁺ release and increased mitochondrial Ca²⁺ uptake leading to ROS generation and αSyn aggregation. Oral administration of A. muciniphila cultivated in the absence of mucin to mice led to αSyn aggregation in cholecystokinin (CCK)-positive EECs but no motor deficits were observed. Noteworthy, buffering mitochondrial Ca²⁺ reverted the damaging effects observed. These molecular insights offer evidence that bacterial proteins can induce αSyn aggregation in EECs.

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Gut bacterium Akkermansia muciniphila is increased in patients with Parkinson disease

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A. muciniphila-conditioned medium induces mitochondrial Ca²⁺ overload in EECs

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Mitochondrial Ca²⁺ overload leads to ROS generation and αSyn aggregation in vitro

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Buffering mitochondrial Ca²⁺ inhibits A. muciniphila-induced αSyn aggregation

Constipation and Cigarette Smoking Are Independent Influences for Parkinson’s Disease

Background

Tobacco smokers have reduced Parkinson’s disease (PD) risk. Some patients with PD experience constipation long before they develop mobility problems, and constipation is a frequent complaint of people who try to stop smoking. Recently, the gut microbiome has been implicated in PD.

Methods

In the present study, we analyzed the relationship between smoking and constipation in subjects with PD and controls. We wished to determine whether the effects of smoking and constipation were independent or whether they might be interrelated. To evaluate the relationship, we used a cohort of subjects from the UK Biobank (UKB).

Results

In 501,174 subjects, the decreased risk of Parkinson’s disease with increased smoking was significant (p < 0.001, two-tailed Fisher’s exact test). The increased risk of constipation in subjects with PD was significant (p = 0.001, two-tailed Fisher’s exact test). Logistic regression was performed; sex, age, constipation, and smoking were the independent variables, and PD present or absent was the dependent variable. The PD odds ratio (OR) for males was 1.790 (95% confidence interval (CI): 1.629-1.966) times that for females, indicating that PD is more common in men. The risk of PD increased by 1.140 (95% CI: 1.131-1.149) with every year of age. Constipation increased the risk of PD by 4.043 (95% CI: 1.901-8.599). Smoking diminished PD risk by 0.772 (95% CI: 0.690-0.863). Drinking coffee was associated with a reduced risk of PD (OR: 0.815 (95% CI: 0.730-0.909). Drinking tea reduced PD risk by 0.979 (95% CI: 0.962-0.997) for each cup per day. The effects of sex, age, constipation, smoking, drinking coffee, and drinking tea were independent and significant.

Conclusion

Our analysis suggests that the favorable effect of smoking on PD is independent of the detrimental effect of constipation. Smoking reduces PD risk because it not only stimulates the bowel to empty and prevents constipation but also alters the gut microbiome. Another factor, perhaps the tobacco component diterpenoids, may be responsible for the PD risk-reducing effect.