The Gut and Nonmotor Symptoms in Parkinson's Disease

Precision neurology

Over the past several decades, high-resolution brain imaging, blood and cerebrospinal fluid analyses, and other advanced technologies have changed diagnosis from an exercise depending primarily on the history and physical examination to a computer- and online resource-aided process that relies on larger and larger quantities of data. In addition, randomized controlled trials (RCT) at a population level have led to many new drugs and devices to treat neurological disease, including disease-modifying therapies. We are now at a crossroads. Combinatorially profound increases in data about individuals has led to an alternative to population-based RCTs. Genotyping and comprehensive "deep" phenotyping can sort individuals into smaller groups, enabling precise medical decisions at a personal level. In neurology, precision medicine that includes prediction, prevention and personalization requires that genomic and phenomic information further incorporate imaging and behavioral data. In this article, we review the genomic, phenomic, and computational aspects of precision medicine for neurology. After defining biological markers, we discuss some applications of these "-omic" and neuroimaging measures, and then outline the role of computation and ultimately brain simulation. We conclude the article with a discussion of the relation between precision medicine and value-based care.

Enteric glia as a player of gut-brain interactions during Parkinson's disease

The enteric glia has been shown as a potential component of neuroimmune interactions that signal in the gut-brain axis during Parkinson's disease (PD). Enteric glia are a peripheral glial type found in the enteric nervous system (ENS) that, associated with enteric neurons, command various gastrointestinal (GI) functions. They are a unique cell type, with distinct phenotypes and distribution in the gut layers, which establish relevant neuroimmune modulation and regulate neuronal function. Comprehension of enteric glial roles during prodromal and symptomatic phases of PD should be a priority in neurogastroenterology research, as the reactive enteric glial profile, gastrointestinal dysfunction, and colonic inflammation have been verified during the prodromal phase of PD-a moment that may be interesting for interventions. In this review, we explore the mechanisms that should govern enteric glial signaling through the gut-brain axis to understand pathological events and verify the possible windows and pathways for therapeutic intervention. Enteric glia directly modulate several functional aspects of the intestine, such as motility, visceral sensory signaling, and immune polarization, key GI processes found deregulated in patients with PD. The search for glial biomarkers, the investigation of temporal-spatial events involving glial reactivity/signaling, and the proposal of enteric glia-based therapies are clearly demanded for innovative and intestine-related management of PD.

Elevated serum anti-Saccharomyces cerevisiae antibody accompanied by gut mycobiota dysbiosis as a biomarker of diagnosis in patients with de novo Parkinson disease

BACKGROUND AND PURPOSE

Intestinal inflammation and gut microbiota dysbiosis contribute to Parkinson disease (PD) pathogenesis, and growing evidence suggests associations between inflammatory bowel diseases (IBD) and PD. Considered as markers of chronic gastrointestinal inflammation, elevated serum anti-Saccharomyces cerevisiae antibody (ASCA) levels, against certain gut fungal components, are related to IBD, but their effect on PD is yet to be investigated.

METHODS

Serum ASCA IgG and IgA levels were measured using an enzyme-linked immunosorbent assay, and the gut mycobiota communities were investigated using ITS2 sequencing and analyzed using the Qiime pipeline.

RESULTS

The study included 393 subjects (148 healthy controls [HCs], 140 with PD, and 105 with essential tremor [ET]). Both serum ASCA IgG and IgA levels were significantly higher in the PD group than in the ET and HC groups. Combining serum ASCA levels and the occurrence of constipation could discriminate patients with PD from controls (area under the curve [AUC] = 0.81, 95% confidence interval [CI] = 0.76-0.86) and from patients with ET (AUC = 0.85, 95% CI = 0.79-0.89). Furthermore, the composition of the gut fungal community differed between the PD and HC groups. The relative abundances of Saccharomyces cerevisiae, Aspergillus, Candida solani, Aspergillus flavus, ASV601_Fungi, ASV866_Fungi, and ASV755_Fungi were significantly higher in the PD group, and enriched Malassezia restricta was found in the HC group.

CONCLUSIONS

Our study identified elevated serum ASCA levels and enriched gut Saccharomyces cerevisiae in de novo PD.

Differential Findings on Anorectal Manometry in Patients with Parkinson's Disease and Defecatory Dysfunction

Introduction

Gastrointestinal dysfunction, particularly constipation, is among the most common non-motor manifestations in Parkinson's Disease (PD). We aimed to identify high-resolution anorectal manometry (HR-ARM) abnormalities in patients with PD using the London Classification.

Methods

We conducted a retrospective review of all PD patients at our institution who underwent HR-ARM and balloon expulsion test (BET) for evaluation of constipation between 2015 and 2021. Using age and sex-specific normal values, HR-ARM recordings were re-analyzed and abnormalities were reported using the London Classification. A combination of Wilcoxon rank sum and Fisher's exact test were used.

Results

36 patients (19 women) with median age 71 (interquartile range [IQR]: 69-74) years, were included. Using the London Classification, 7 (19%) patients had anal hypotension, 17 (47%) had anal hypocontractility, and 3 women had combined hypotension and hypocontractility. Anal hypocontractility was significantly more common in women compared to men. Abnormal BET and dyssynergia were noted in 22 (61%) patients, while abnormal BET and poor propulsion were only seen in 2 (5%). Men had significantly more paradoxical anal contraction and higher residual anal pressures during simulated defecation, resulting in more negative recto-anal pressure gradients. Rectal hyposensitivity was seen in nearly one third of PD patients and comparable among men and women.

Conclusion

Our data affirms the high prevalence of anorectal disorders in PD. Using the London Classification, abnormal expulsion and dyssynergia and anal hypocontractility were the most common findings in PD. Whether the high prevalence of anal hypocontractility in females is directly related to PD or other confounding factors will require further research.

Evaluating the effectiveness of probiotics in relieving constipation in Parkinson's disease: A systematic review and meta-analysis

Objectives

The aim of this study was to evaluate the effects of probiotics on the treatment of constipation in patients with Parkinson's disease (PD) by analyzing data from published randomized clinical trials (RCTs). PD is a neurodegenerative disease characterized by clinical symptoms such as rigidity, bradykinesia, and resting tremor. Constipation is a common complaint reported by PD patients. Probiotics are often used to treat functional constipation. The potential mechanisms behind PD-related constipation include dysfunction of the enteric nervous system due to alpha-synuclein aggregation, dyssynergic contractions of the puborectalis muscle, and alterations of the gut microbiome.

Method

To conduct this study, we searched Scopus, PubMed, and Google Scholar for published articles on PD, probiotics, and constipation. We selected RCTs from 944 studies, and ultimately included 3 RCTs in our meta-analysis. The frequency of bowel movements per week was the only index that could be summarized among the records. We extracted and analyzed the results as means and standard deviations.

Result

We calculated a standardized mean difference (SMD) of 0.92 (95% CI, 0.65 to 1.19; I-squared = 57.0%; p < 0.001) to determine the treatment effect in terms of frequency of bowel movements per week in the RCTs.

Conclusion

Our results show that probiotic intake has beneficial effects on constipation in PD patients. Further research, including multicenter studies, is needed to assess the long-term efficacy and safety of probiotic supplements in neurodegenerative diseases.

How Toll-like receptors influence Parkinson's disease in the microbiome-gut-brain axis

Recently, a large number of experimenters have found that the pathogenesis of Parkinson's disease may be related to the gut microbiome and proposed the microbiome-gut-brain axis. Studies have shown that Toll-like receptors, especially Toll-like receptor 2 (TLR2) and Toll-like receptor 4 (TLR4), are key mediators of gut homeostasis. In addition to their established role in innate immunity throughout the body, research is increasingly showing that the Toll-like receptor 2 and Toll-like receptor 4 signaling pathways shape the development and function of the gut and enteric nervous system. Notably, Toll-like receptor 2 and Toll-like receptor 4 are dysregulated in Parkinson's disease patients and may therefore be identified as the core of early gut dysfunction in Parkinson's disease. To better understand the contribution of Toll-like receptor 2 and Toll-like receptor 4 dysfunction in the gut to early α-synuclein aggregation, we discussed the structural function of Toll-like receptor 2 and Toll-like receptor 4 and signal transduction of Toll-like receptor 2 and Toll-like receptor 4 in Parkinson's disease by reviewing clinical, animal models, and in vitro studies. We also present a conceptual model of the pathogenesis of Parkinson's disease, in which microbial dysbiosis alters the gut barrier as well as the Toll-like receptor 2 and Toll-like receptor 4 signaling pathways, ultimately leading to a positive feedback loop for chronic gut dysfunction, promoting α-synuclein aggregation in the gut and vagus nerve.

Impact of environmental toxicants exposure on gut-brain axis in Parkinson disease

Parkinson disease (PD) is a major public health challenge as many of the current drugs used in its management provide symptomatic relieve without preventing the underlying cause of the neurodegeneration. Similarly, the non-motor complications of PD, especially the gastrointestinal tract (GIT) disturbance increases the disease burden on both the PD patient and caregivers. Different theories have been postulated regarding the mechanisms or pathways involved in PD pathology but gut-brain axis involvement has gained much more momentum. This pathway was first suggested by Braak and colleagues in 2003, where they suggested that PD starts from the GIT before spreading to the brain. However, human exposure to environmental toxicants known to inhibit mitochondrial complex I activity such as rotenone, paraquat and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) are well associated with PD. Several reports have shown that oral exposure of laboratory animals to rotenone causes mitochondria dysfunction, GIT disturbance, overexpression of alpha synuclein and microbiota imbalance. This review focuses on the mechanism(s) through which rotenone induces PD pathogenesis and potential for therapeutic small molecules targeting these processes at the earliest stages of the disease. We also focused on the interaction between the GI microbiota and PD pathology.

The role of nutrition on Parkinson's disease: a systematic review

BACKGROUND

Parkinson's disease (PD) in elderly patients is the second most prevalent neurodegenerative disease. The pathogenesis of PD is associated with dopaminergic neuron degeneration of the substantia nigra in the basal ganglia, causing classic motor symptoms. Oxidative stress, mitochondrial dysfunction, and neuroinflammation have been identified as possible pathways in laboratory investigations. Nutrition, a potentially versatile factor from all environmental factors affecting PD, has received intense research scrutiny.

METHODS

A systematic search was conducted in the MEDLINE, EMBASE, and WEB OF SCIENCE databases from 2000 until the present. Only randomized clinical trials (RCTs), observational case-control studies, and follow-up studies were included.

RESULTS

We retrieved fifty-two studies that met the inclusion criteria. Most selected studies investigated the effects of malnutrition and the Mediterranean diet (MeDiet) on PD incidence and progression. Other investigations contributed evidence on the critical role of microbiota, vitamins, polyphenols, dairy products, coffee, and alcohol intake.

CONCLUSIONS

There are still many concerns regarding the association between PD and nutrition, possibly due to underlying genetic and environmental factors. However, there is a body of evidence revealing that correcting malnutrition, gut microbiota, and following the MeDiet reduced the onset of PD and reduced clinical progression. Other factors, such as polyphenols, polyunsaturated fatty acids, and coffee intake, can have a potential protective effect. Conversely, milk and its accessory products can increase PD risk. Nutritional intervention is essential for neurologists to improve clinical outcomes and reduce the disease progression of PD.

Bilateral Subthalamic Nucleus Deep Brain Stimulation Improves Gastric Emptying Time in Parkinson Disease

BACKGROUND

It is well-established that deep brain stimulation (DBS) can improve motor function in those with Parkinson disease (PD); however, its effects on gastrointestinal disorders remain unclear.

METHODS

From January 2019 to December 2020, 26 patients with PD who had undergone subthalamic nucleus (STN) DBS were included in our study. The evaluated items included the pre- and postoperative dose of levodopa, Unified Parkinson's Disease Rating Scale, part III, scores with and without medication and stimulation, and gastric emptying time (expressed as the peak time of carbon-¹³C dioxide excretion in the ¹³C-acetate breath test). Sex-, age-, and body weight-matched controls were recruited to test the gastric emptying time in healthy individuals.

RESULTS

All the patients benefited from DBS. The Unified Parkinson's Disease Rating Scale, part III, scores had decreased from 48.5 ± 13.77 to 25.23 ± 8.59 without medication and 31.23 ± 11.4 to 13.92 ± 5.27 with medication. The levodopa equivalent dose had decreased from 1009.8 ± 291 mg to 707.65 ± 193.79 mg. The gastric emptying time was significantly prolonged in the patients with PD before DBS compared with the healthy control group (29.23 ± 6.58 minutes) and had improved to 35.19 ± 10.14 minutes with medication and 38.07 ± 11.17 minutes without medication after 3 months of STN stimulation. At 6 months postoperatively, the gastric emptying time was 32.3 ± 10.02 minutes without medication and 33.84 ± 10.79 minutes with medication.

CONCLUSIONS

A delayed gastric emptying time is associated with greater PD severity. Antiparkinsonian medications did not affect gastric emptying in patients with PD. STN DBS can improve both movement function and gastrointestinal motility in patients with PD in the long term. The exact mechanism by which DBS improves gastric emptying requires further exploration.

Irritable bowel syndrome and subsequent risk of Parkinson's disease: a nationwide population-based matched-cohort study

BACKGROUND

Gastrointestinal dysfunction (GI) is the most prevalent non-motor symptom of Parkinson's disease (PD), and its role in the risk of PD has been studied. In this study, we tried to evaluate whether irritable bowel syndrome (IBS) increased the risk of PD development stratified by sex, age, and IBS duration using a large nationwide cohort in Korea.

METHODS

Patients aged ≥ 20 years with a primary diagnosis of IBS (ICD-10 codes: G56) more than three times were selected. A randomly matched cohort without IBS was enrolled by exact matching patients for sex, age, socioeconomic status, comorbidities, and year of enrollment to the IBS group with a ratio of 1:3. Cause-specific Cox regression models were used to identify hazards associated with PD development depending on the presence of IBS during the 11-year follow-up period.

RESULTS

In total, 285,064 patients were enrolled in the study: 71,806 in the IBS cohort and 213,258 in the comparison cohort. Cause-specific Cox regression model showed a hazard ratio of 1.436 (95% CI, 1.226-1.682) for PD development in the IBS cohort, which is consistent in both male and female sexes. Subgroup analyses according to age groups showed that IBS increased PD risk only in individuals ≥ 65 years (HR = 1.449, 95% CI, 1.207-1.741).

CONCLUSIONS

We found temporal relationship between IBS and PD at aged ≥ 65 years. There might be a possibility that IBS was an early manifestation of PD, and future studies for causal link between the two diseases to elucidate biomechanism are warranted.

The intestinal luminal sources of α-synuclein: a gastroenterologist perspective

Parkinson's disease is characterized by nonmotor/motor dysfunction, midbrain dopaminergic neuronal death, and α-synuclein (aSN) deposits. The current hypothesis is that aSN accumulates in the enteric nervous system to reach the brain. However, invertebrate, vertebrate, and nutritional sources of aSN reach the luminal compartment. Submitted to local amyloidogenic forces, the oligomerized proteins' cargo can be sensed and sampled by a specialized mucosal cell to be transmitted to the adjacent enteric nervous system, starting their upward journey to the brain. The present narrative review extends the current mucosal origin of Parkinson's disease, presenting the possibility that the disease starts in the intestinal lumen. If substantiated, eliminating the nutritional sources of aSN (eg, applying a vegetarian diet) might revolutionize the currently used dopaminergic pharmacologic therapy.

Perspective: Low Risk of Parkinson's Disease in Quasi-Vegan Cultures May Reflect GCN2-Mediated Upregulation of Parkin

Mitochondrial dysfunction in dopaminergic neurons of the substantia nigra (SN) appears to be a key mediating feature of Parkinson's disease (PD), a complex neurodegenerative disorder of still unknown etiology. Parkin is an E3 ubiquitin ligase that promotes mitophagy of damaged depolarized mitochondria while also boosting mitochondrial biogenesis-thereby helping to maintain efficient mitochondrial function. Boosting Parkin expression in the SN with viral vectors is protective in multiple rodent models of PD. Conversely, homozygosity for inactivating mutations of Parkin results in early-onset PD. Moderate protein plant-based diets relatively low in certain essential amino acids have the potential to boost Parkin expression by activating the kinase GCN2, which in turn boosts the expression of ATF4, a factor that drives transcription of the Parkin gene. Protein-restricted diets also upregulate the expression of PINK1, a protein that binds to the outer membrane of depolarized mitochondria and then recruits and activates Parkin. This effect of protein restriction is mediated by the downregulation of the kinase activity of mammalian target of rapamycin complex 1; the latter suppresses PINK1 expression at the transcriptional level. During the 20th century, cultures in East Asia and sub-Sahara Africa consuming quasi-vegan diets were found to be at notably decreased risk of PD compared with the USA or Europe. It is proposed that such diets may provide protection from PD by boosting Parkin and PINK1 expression in the SN. Other measures that might be expected to upregulate protective mitophagy include supplemental N-acetylcysteine (precursor for hydrogen sulfide) and a diet rich in spermidine-a polyamine notably high in corn.

The Contribution of Gut Microbiota-Brain Axis in the Development of Brain Disorders

Different bacterial families colonize most mucosal tissues in the human organism such as the skin, mouth, vagina, respiratory, and gastrointestinal districts. In particular, the mammalian intestine hosts a microbial community of between 1,000 and 1,500 bacterial species, collectively called "microbiota." Co-metabolism between the microbiota and the host system is generated and the symbiotic relationship is mutually beneficial. The balance that is achieved between the microbiota and the host organism is fundamental to the organization of the immune system. Scientific studies have highlighted a direct correlation between the intestinal microbiota and the brain, establishing the existence of the gut microbiota-brain axis. Based on this theory, the microbiota acts on the development, physiology, and cognitive functions of the brain, although the mechanisms involved have not yet been fully interpreted. Similarly, a close relationship between alteration of the intestinal microbiota and the onset of several neurological pathologies has been highlighted. This review aims to point out current knowledge as can be found in literature regarding the connection between intestinal dysbiosis and the onset of particular neurological pathologies such as anxiety and depression, autism spectrum disorder, and multiple sclerosis. These disorders have always been considered to be a consequence of neuronal alteration, but in this review, we hypothesize that these alterations may be non-neuronal in origin, and consider the idea that the composition of the microbiota could be directly involved. In this direction, the following two key points will be highlighted: (1) the direct cross-talk that comes about between neurons and gut microbiota, and (2) the degree of impact of the microbiota on the brain. Could we consider the microbiota a valuable target for reducing or modulating the incidence of certain neurological diseases?

Spectrum of Non-Motor Symptoms in Parkinson's Disease

Parkinson's disease is predominantly classified as a movement disorder. Beyond the textbook definition of rigidity, tremors, and bradykinesia, Parkinson's disease encompasses an entire entity of non-motor symptom complexes that can precede the motor features by many years. Despite their significant clinical importance, the awareness of non-motor symptoms is quite negligible. Sleep disorders, gastrointestinal dysfunction, olfactory disturbances, anxiety, and depressive episodes are some of the most common non-motor presentations. The wide-spread occurrence of olfactory symptoms and the low cost of the assessment, is favoring olfactory dysfunction as a potential biomarker in Parkinson's. Sleep disorders may manifest before the motor and autonomic symptoms and might be linked to concomitant sleeping disorders like insomnia, REM sleep disorders, restless leg syndrome, narcolepsy, or obstructive sleep apnea. Non-motor symptoms can deteriorate the quality of life in Parkinson's patients. Early detection of non-motor symptoms can help in the diagnosis of Parkinson's disease and can fairly improve the survival and prognosis of these patients.

Fisetin Regulates Gut Microbiota and Exerts Neuroprotective Effect on Mouse Model of Parkinson's Disease

Previous studies have reported the anti-oxidant, anti-inflammatory, and anti-cancer effects of fisetin. However, the therapeutic efficacy of fisetin in Parkinson’s disease (PD) is unclear. In this study, we demonstrated that fisetin could markedly alleviate 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced dopaminergic neurodegeneration in mice. To confirm the reported correlation between gut microbiota and PD, the bacterial DNA in the fresh feces of mice from each group was subjected to 16S rRNA (V3 and V4 regions) sequencing. The results revealed that fisetin changed the number, diversity, and distribution of gut microbiota in MPTP-induced mice model of PD. The alpha and beta diversity analyses showed that the fisetin intervented MPTP group gut microbiota exhibited a significantly higher abundance of Lachnospiraceae and a significantly lower abundance of uncultured_bacterium_g_Escherichia-Shigella and uncultured_bacterium_g_Bacillus than the MPTP group gut microbiota. These findings indicated that fisetin exerts a neuroprotective effect on neurodegeneration by altering the composition and diversity of gut microbiota. Thus, fisetin could be a potential novel therapeutic for PD.

Parkinson's disease and translational research

Parkinson’s disease (PD) is diagnosed when patients exhibit bradykinesia with tremor and/or rigidity, and when these symptoms respond to dopaminergic medications. Yet in the last years there was a greater recognition of additional aspects of the disease including non-motor symptoms and prodromal states with associated pathology in various regions of the nervous system. In this review we discuss current concepts of two major alterations found during the course of the disease: cytoplasmic aggregates of the protein α-synuclein and the degeneration of dopaminergic neurons. We provide an overview of new approaches in this field based on current concepts and latest literature. In many areas, translational research on PD has advanced the understanding of the disease but there is still a need for more effective therapeutic options based on the insights into the basic biological phenomena.

Kolaviron protects against nigrostriatal degeneration and gut oxidative damage in a stereotaxic rotenone model of Parkinson's disease

The asymptomatic and clinical stages of Parkinson's disease (PD) are associated with comorbid non-motor symptoms including gastrointestinal (GI) dysfunction. Although the neuroprotective and gastroprotective roles of kolaviron (KV) have been reported independently, whether KV-mediated GI-protective capacity could be beneficial in PD is unknown. We therefore investigated the modulatory effects of KV on the loss of dopaminergic neurons, locomotor abnormalities, and ileal oxidative damage when rats are lesioned in the nigrostriatal pathway. KV treatment markedly suppressed the behavioral deficit and apomorphine-induced rotations associated with rotenone lesioning. KV attenuated the loss of nigrostriatal dopaminergic neurons and perturbations in the striatal glucose-regulated protein (GRP78) and X-box binding protein 1 (XBP1) levels. Ileal epithelial injury following stereotaxic rotenone infusion was associated with oxidative stress and marked inhibition of acetylcholine esterase activity and reduced expression of occludin in the crypt and villi. While KV treatment attenuated the redox imbalance in the gut and enhanced occludin immunoreactivity, acetylcholinesterase activity was not affected. Our data demonstrate ileal oxidative damage as a characteristic non-motor gut dysfunction in PD while showing the potential dual efficacy of KV in the attenuation of both neural defects and gut abnormalities associated with PD.

Assessing the Beneficial Effects of the Immunomodulatory Glycan LNFPIII on Gut Microbiota and Health in a Mouse Model of Gulf War Illness

The microbiota’s influence on host (patho) physiology has gained interest in the context of Gulf War Illness (GWI), a chronic disorder featuring dysregulation of the gut–brain–immune axis. This study examined short- and long-term effects of GWI-related chemicals on gut health and fecal microbiota and the potential benefits of Lacto-N-fucopentaose-III (LNFPIII) treatment in a GWI model. Male C57BL/6J mice were administered pyridostigmine bromide (PB; 0.7 mg/kg) and permethrin (PM; 200 mg/kg) for 10 days with concurrent LNFPIII treatment (35 μg/mouse) in a short-term study (12 days total) and delayed LNFPIII treatment (2×/week) beginning 4 months after 10 days of PB/PM exposure in a long-term study (9 months total). Fecal 16S rRNA sequencing was performed on all samples post-LNFPIII treatment to assess microbiota effects of GWI chemicals and acute/delayed LNFPIII administration. Although PB/PM did not affect species composition on a global scale, it affected specific taxa in both short- and long-term settings. PB/PM elicited more prominent long-term effects, notably, on the abundances of bacteria belonging to Lachnospiraceae and Ruminococcaceae families and the genus Allobaculum. LNFPIII improved a marker of gut health (i.e., decreased lipocalin-2) independent of GWI and, importantly, increased butyrate producers (e.g., Butyricoccus, Ruminococcous) in PB/PM-treated mice, indicating a positive selection pressure for these bacteria. Multiple operational taxonomic units correlated with aberrant behavior and lipocalin-2 in PB/PM samples; LNFPIII was modulatory. Overall, significant and lasting GWI effects occurred on specific microbiota and LNFPIII treatment was beneficial.

Norepinephrine depleting toxin DSP-4 and LPS alter gut microbiota and induce neurotoxicity in α-synuclein mutant mice

This study examined the genetic mutation and toxicant exposure in producing gut microbiota alteration and neurotoxicity. Homozygous α-synuclein mutant (SNCA) mice that overexpress human A53T protein and littermate wild-type mice received a single injection of LPS (2 mg/kg) or a selective norepinephrine depleting toxin DSP-4 (50 mg/kg), then the motor activity, dopaminergic neuron loss, colon gene expression and gut microbiome were examined 13 months later. LPS and DSP-4 decreased rotarod and wirehang activity, reduced dopaminergic neurons in substantia nigra pars compacta (SNpc), and SNCA mice were more vulnerable. SNCA mice had 1,000-fold higher human SNCA mRNA expression in the gut, and twofold higher gut expression of NADPH oxidase (NOX2) and translocator protein (TSPO). LPS further increased expression of TSPO and IL-6 in SNCA mice. Both LPS and DSP-4 caused microbiome alterations, and SNCA mice were more susceptible. The altered colon microbiome approximated clinical findings in PD patients, characterized by increased abundance of Verrucomicrobiaceae, and decreased abundance of Prevotellaceae, as evidenced by qPCR with 16S rRNA primers. The Firmicutes/Bacteroidetes ratio was increased by LPS in SNCA mice. This study demonstrated a critical role of α-synuclein and toxins interactions in producing gut microbiota disruption, aberrant gut pro-inflammatory gene expression, and dopaminergic neuron loss.

A Gutsy Move for Cell-Based Regenerative Medicine in Parkinson's Disease: Targeting the Gut Microbiome to Sequester Inflammation and Neurotoxicity

Pharmaceuticals and cell-based regenerative medicine for Parkinson’s disease (PD) offer palliative relief but do not arrest the disease progression. Cell therapy has emerged as an experimental treatment, but current cell sources such as human umbilical cord blood (hUCB) stem cells display only partial recapitulation of mature dopaminergic neuron phenotype and function. Nonetheless, stem cell grafts ameliorate PD-associated histological and behavioral deficits likely through stem cell graft-secreted therapeutic substances. We recently demonstrated the potential of hUCB-derived plasma in enhancing motor capabilities and gastrointestinal function, as well as preventing dopaminergic neuronal cell loss, in an 1-methyl-4-phenyl-1,2,3,6-tetrahydro-pyridine (MPTP) rodent model of PD. Recognizing the translational need to test in another PD model, we now examined here the effects of an intravenously transplanted combination of hUCB and plasma into the 6-hydroxydopamine (6-OHDA) lesioned adult rats. Animals received three separate doses of 4 × 10⁶ hUCB cells with plasma beginning at 7 days after stereotaxic 6-OHDA lesion, then behaviorally and immunohistochemically evaluated over 56 days post-lesion. Whereas vehicle-treated lesioned animals exhibited the typical 6-OHDA neurobehavioral symptoms, hUCB and plasma-treated lesioned animals showed significant attenuation of motor function, gut motility, and nigral dopaminergic neuronal survival, combined with diminished pro-inflammatory microbiomes not only in the nigra, but also in the gut. Altogether these data support a regenerative medicine approach for PD by sequestering inflammation and neurotoxicity through correction of gut dysbiosis.

Parkinson's disease and the non-motor symptoms: hyposmia, weight loss, osteosarcopenia

Non-motor symptoms (NMSs) are common in Parkinson's disease (PD) and can precede, sometimes for several years. NMSs include, other than gastrointestinal symptoms like constipation and dysphagia, also hyposmia, weight loss and osteosarcopenia. These three NMSs seem to be inter-related and affect patients' health and quality of life. Unfortunately, patients with these symptoms usually are not initially seen by a neurologist, and by the time they are consulted, nearly ~ 80% of the dopaminergic neurons in the substantia nigra have died. To date, no guidelines exist for screening, assessment and management of NMSs in general. A better understanding of these specific NMSs, likely in the context of others, will make it possible to approach and optimise the treatment of the motor symptoms thereby enhancing the welfare of PD patients. Identifying the NMSs could be very helpful, and among them, hyposmia, weight loss and osteosarcopenia may play an important role in solving the limitations in the diagnosis of PD. A strict collaboration between general practitioners, clinicians, geriatricians and neurologists can be one approach towards the diagnosis of pre-PD. Waiting until the motor symptoms develop and the patient is finally visited by the neurologist could be too late, considering the catastrophic prognosis of the disease.

The pharmacological management of constipation in patients with Parkinson's disease: a much-needed relief

INTRODUCTION

Constipation is common in patients with Parkinson's disease (PD). Due to the considerable negative outcomes of constipation, significant efforts have been made to prevent and manage chronic constipation in these patients.

AREAS COVERED

Herein, the authors review some of the known pathophysiological causes for slow gastrointestinal (GI) transit in PD patients and the different pharmacological options. All relevant clinical and experimental data found through online databases were included. Bulking agents, osmotic and stimulant laxatives, chloride channel activators, ghrelin agonists, 5-HT4 receptor agonists, and probiotics are some of the proposed medicinal agents. of the authors further review the evidence on alpha-synuclein and botulinum neurotoxin in these patients. It should be noted, however, that some of these interventions are required to be further validated.

EXPERT OPINION

Reduction of GI transit and dysfunction of the anorectum is obvious in PD, affecting the incidence of constipation and thus, quality of life (QOL). Furthermore, due to an inadequate and delayed absorption of oral anti PD medications, dose adjustments and changes in the route of administration are recommended.

What is strain in neurodegenerative diseases?

Neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease, are characterized by the aggregation of misfolded proteins, including Aβ, tau and α-synuclein. It is well recognized that these misfolded proteins are able to self-propagate and spread throughout the nervous system and cause neuronal injury in a way that resembles prion disease. These disease-specific misfolded proteins demonstrate unique features, including the seeding barrier, the conformational memory effect, strain selection and strain evolution, based on the presence of various strains. However, the accurate definition of the term strain remains to be clarified. Here, a clear interpretation is proposed by a retrospective of its history in prion research and the recent progress in neurodegeneration research. Furthermore, the causes contributing to the genesis of various strains are also summarized. Deeper insight into strains helps us to understand the phenomena we observe in this field and it also enlightens us on the elusive mechanisms and management of neurodegeneration.

Gastrointestinal dysfunction in Parkinson's disease

BACKGROUND

Gastrointestinal (GI) dysfunction is prevalent in Parkinson's disease (PD). Symptoms are evident throughout the disease course, affect the length of the GI tract and impact on patient quality of life and management. We clarify real-life differences in the frequency and severity of GI symptoms in a cohort of PD and healthy control (HC) subjects.

METHODS

103 PD patients were compared to 81 HC subjects. Outcome measures collected from validated questionnaires included constipation severity, upper and lower GI symptoms and physical activity.

RESULTS

PD patients were three-times more likely to experience constipation than HC subjects, (78.6% vs 28.4%), exhibited a fourfold increase in constipation severity and formed harder stools. PD patients also reported increased symptoms of indigestion, nausea, excessive fullness and bloating, compared to the HCs. A higher mean Leeds Dyspepsia Questionnaire score for PD patients (8.3 (standard deviation (SD) 7.7) vs 4.6 (SD 6.1), p = 0.001)) indicated increased symptom severity. Chronic pain was more frequently reported and correlated with constipation and upper GI dysfunction, being more prevalent and severe in women. Physical activity was notably decreased in the PD cohort (1823.6 (± 1693.6) vs 2942.4 (± 2620.9) metabolic equivalent-minutes/week, p = 0.001) and correlated with constipation severity. PD therapies were associated with increased fullness and bloating and harder stools.

CONCLUSIONS

PD patients report more prevalent and severe GI dysfunction, although our cohort comprised of many later-stage participants. Earlier recognition of GI dysfunction in PD provides the opportunity to direct treatment for chronic pain and constipation, promote physical activity and rationalise PD therapies for optimal patient care.

"Photobiomics": Can Light, Including Photobiomodulation, Alter the Microbiome?

Objective: The objective of this review is to consider the dual effects of microbiome and photobiomodulation (PBM) on human health and to suggest a relationship between these two as a novel mechanism. Background: PBM describes the use of low levels of visible or near-infrared (NIR) light to heal and stimulate tissue, and to relieve pain and inflammation. In recent years, PBM has been applied to the head as an investigative approach to treat diverse brain diseases such as stroke, traumatic brain injury (TBI), Alzheimer's and Parkinson's diseases, and psychiatric disorders. Also, in recent years, increasing attention has been paid to the total microbial population that colonizes the human body, chiefly in the gut and the mouth, called the microbiome. It is known that the composition and health of the gut microbiome affects many diseases related to metabolism, obesity, cardiovascular disorders, autoimmunity, and even brain disorders. Materials and methods: A literature search was conducted for published reports on the effect of light on the microbiome. Results: Recent work by our research group has demonstrated that PBM (red and NIR light) delivered to the abdomen in mice, can alter the gut microbiome in a potentially beneficial way. This has also now been demonstrated in human subjects. Conclusions: In consideration of the known effects of PBM on metabolomics, and the now demonstrated effects of PBM on the microbiome, as well as other effects of light on the microbiome, including modulating circadian rhythms, the present perspective introduces a new term "photobiomics" and looks forward to the application of PBM to influence the microbiome in humans. Some mechanisms by which this phenomenon might occur are considered.

Gut Vibes in Parkinson's Disease: The Microbiota-Gut-Brain Axis

Background

The complexity of the pathogenic mechanisms underlying neurodegenerative disorders such as Parkinson's disease (PD) is attributable to multifactorial changes occurring at a molecular level, influenced by genetics and environmental interactions. However, what causes the main hallmarks of PD is not well understood. Recent data increasingly suggest that imbalances in the gut microbiome composition might trigger and/or exacerbate the progression of PD.

Objective

The present review aims to (1) report emerging literature showing changes in microbiota composition of PD patients compared to healthy individuals and (2) discuss how these changes may initiate and/or perpetuate PD pathology.

Methods

We analyzed 13 studies published from 2015 and included in this review. Altered microbial taxa were compiled in a detailed table summarizing bacterial changes in fecal/mucosal samples. The methodology was systematically reviewed across the articles and was also included in a table to facilitate comparisons between studies.

Results

Multiple studies found a reduction in short-chain fatty-acid-producing bacteria that can rescue neuronal damage through epigenetic mechanisms. Overall, the studies showed that changes in the gut microbiota composition might influence colonic inflammation, gut permeability, and α-synuclein aggregation, contributing to the neurogenerative process.

Conclusion

Further studies with larger cohorts and high-resolution sequencing methods are required to better define gut microbiota changes in PD. Furthermore, additional longitudinal studies are required to determine the causal link between these changes and PD pathogenesis as well as to study the potential of the intestinal microbiota as a biomarker.

The relationship between inflammatory bowel disease and Parkinson's disease: true or fiction?

Gastrointestinal (GI) symptoms can precede by many years the motor symptoms of Parkinson's disease (PD) and these patients can show some degree of inflammation associated with abnormal aggregates of alpha-synuclein in the GI tract. The abnormal accumulation of alpha-synuclein and the spreading of the aggregates from the gut to the brain might be promoted by inflammation, rising the hypothesis of a possible relationship between inflammatory bowel disease and PD. Many population-based studies have explored this association, but they have found conflicting results. It is essential to clarify this hypothesis and to try to elucidate the milestones of this relationship. There is no clear concordance between the results and the interpretation of different previous findings, probably due to many confounding factors such as drugs with anti-inflammatory activity, surgery, genetic predisposition and also selection bias. If there is a real association between both diseases, gastroenterologists and neurologists should be able to detect possible triggers of the disease or on the other hand, protective factors, that may be considered in clinical practice.

Gutting the brain of inflammation: A key role of gut microbiome in human umbilical cord blood plasma therapy in Parkinson's disease model

Current therapies for Parkinson's disease (PD), including L‐3,4‐dihydroxyphenylalanine (L‐DOPA), and clinical trials investigating dopaminergic cell transplants, have generated mixed results with the eventual induction of dyskinetic side effects. Although human umbilical cord blood (hUCB) stem/progenitor cells present with no or minimal capacity of differentiation into mature dopaminergic neurons, their transplantation significantly attenuates parkinsonian symptoms likely via bystander effects, specifically stem cell graft‐mediated secretion of growth factors, anti‐inflammatory cytokines, or synaptic function altogether promoting brain repair. Recognizing this non‐cell replacement mechanism, we examined here the effects of intravenously transplanted combination of hUCB‐derived plasma into the 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP)‐induced rat model of PD. Animals received repeated dosing of either hUCB‐derived plasma or vehicle at 3, 5 and 10 days after induction into MPTP lesion, then behaviourally and immunohistochemically evaluated over 56 days post‐lesion. Compared to vehicle treatment, transplantation with hUCB‐derived plasma significantly improved motor function, gut motility and dopaminergic neuronal survival in the substantia nigra pars compacta (SNpc), which coincided with reduced pro‐inflammatory cytokines in both the SNpc and the intestinal mucosa and dampened inflammation‐associated gut microbiota. These novel data directly implicate a key pathological crosstalk between gut and brain ushering a new avenue of therapeutically targeting the gut microbiome with hUCB‐derived stem cells and plasma for PD.

Parkinson's disease and the gastrointestinal microbiome

Recently, there has been a surge in awareness of the gastrointestinal microbiome (GM) and its role in health and disease. Of particular note is an association between the GM and Parkinson's disease (PD) and the realisation that the GM can act via a complex bidirectional communication between the gut and the brain. Compelling evidence suggests that a shift in GM composition may play an important role in the pathogenesis of PD by facilitating the characteristic ascending neurodegenerative spread of α-synuclein aggregates from the enteric nervous system to the brain. Here, we review evidence linking GM changes with PD, highlighting mechanisms supportive of pathological α-synuclein spread and intestinal inflammation in PD. We summarise existing patterns and correlations seen in clinical studies of the GM in PD, together with the impacts of non-motor symptoms, medications, lifestyle, diet and ageing on the GM. Roles of GM modulating therapies including probiotics and faecal microbiota transplantation are discussed. Encouragingly, alterations in the GM have repeatedly been observed in PD, supporting a biological link and highlighting it as a potential therapeutic target.

Structural Changes Observed in the Piriform Cortex in a Rat Model of Pre-motor Parkinson's Disease

Early diagnosis of Parkinson’s disease (PD) offers perhaps, the most promising route to a successful clinical intervention, and the use of an animal model exhibiting symptoms comparable to those observed in PD patients in the early stage of the disease, may facilitate screening of novel therapies for delaying the onset of more debilitating motor and behavioral abnormalities. In this study, a rat model of pre-motor PD was used to study the etiology of hyposmia, a non-motor symptom linked to the early stage of the disease when the motor symptoms have yet to be experienced. The study focussed on determining the effect of a partial reduction of both dopamine and noradrenaline levels on the olfactory cortex. Neuroinflammation and striking structural changes were observed in the model. These changes were prevented by treatment with a neuroprotective drug, a glucagon-like peptide-1 (GLP1) receptor agonist, exendin-4 (EX-4).

Mediterranean diet adherence is related to reduced probability of prodromal Parkinson's disease

BACKGROUND

The International Parkinson and Movement Disorder Society recently introduced a methodology for probability score calculation for prodromal PD.

OBJECTIVES

To assess the probability of prodromal PD in an older population and investigate its possible association with Mediterranean diet adherence.

METHODS

Data from a population-based cohort study of older adults (HEllenic Longitudinal Investigation of Aging and Diet) in Greece were used. Probability of prodromal PD was calculated according to International Parkinson and Movement Disorder Society research criteria. A detailed food frequency questionnaire was used to evaluate dietary intake and calculate Mediterranean diet adherence score, ranging from 0 to 55, with higher scores indicating higher adherence.

RESULTS

Median probability of prodromal PD was 1.9%, ranging from 0.2 to 96.7% in 1,731 PD-free individuals aged ≥ 65 (41% male). Lower probability for prodromal PD (P < 0.001) in the higher Mediterranean diet adherence groups was noted, driven mostly by nonmotor markers of prodromal PD, depression, constipation, urinary dysfunction, and daytime somnolence. Each unit increase in Mediterranean diet score was associated with a 2% decreased probability for prodromal PD (P < 0.001). Compared to participants in the lowest quartile of Mediterranean diet adherence, those in the highest quartile were associated with a ∼21% lower probability for prodromal PD.

CONCLUSIONS

Adherence to the Mediterranean diet is associated with lower probability of prodromal PD in older people. Further studies are needed to elucidate the potential causality of this association, potential relation of the Mediterranean diet to delayed onset or lower incidence of PD, as well as the underlying neurobiological mechanisms. © 2018 International Parkinson and Movement Disorder Society.

Influence of Commensal Microbiota on the Enteric Nervous System and Its Role in Neurodegenerative Diseases

When thinking about neurodegenerative diseases, the first symptoms that come to mind are loss of memory and learning capabilities, which all resemble hallmarks of manifestation of such diseases in the central nervous system (CNS). However, the gut comprises the largest nervous system outside the CNS that is autonomously active and in close interplay with its microbiota. Therefore, the enteric nervous system (ENS) might serve as an indicator of degenerative pathomechanisms that also affect the CNS. On the other hand, it might offer an entry point for devastating influences from the microbial community or - conversely - for therapeutic approaches via gut commensals. Within the last years, the ENS and gut microbiota therefore have sparked the interest of researchers of CNS diseases and we here report on recent findings and open questions, especially with regard to Alzheimer and Parkinson diseases.