The impact of indigenous microbes on Parkinson's disease

The interrelationship between intestinal immune cells and enteric α-synuclein in the progression of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder primarily characterized by motor impairment, resulting from the accumulation of α-synuclein and neuronal cell death in the substantia nigra of the midbrain. Emerging evidence suggests that α-synuclein aggregation may originate in the enteric nervous system (ENS) and subsequently propagate to the brain via the vagus nerve. Clinical observations, such as prodromal gastrointestinal dysfunction in PD patients and the increased incidence of PD among individuals with inflammatory bowel disease, support the hypothesis that abnormal intestinal inflammation may contribute to the onset of motor dysfunction and neuropathology in PD. This review examines recent findings on the interplay between intestinal immune cells and α-synuclein aggregation within the framework of gut-originated PD pathogenesis. It begins by discussing evidence linking dysbiosis and intestinal inflammation to α-synuclein aggregation in the ENS. Additionally, it explores the potential role of intestinal immune cells in influencing enteric neurons and α-synuclein aggregation, furthering the understanding of PD development.

Gut-first Parkinson's disease is encoded by gut dysbiome

BACKGROUND

In Parkinson's patients, intestinal dysbiosis can occur years before clinical diagnosis, implicating the gut and its microbiota in the disease. Recent evidence suggests the gut microbiota may trigger body-first Parkinson Disease (PD), yet the underlying mechanisms remain unclear. This study aims to elucidate how a dysbiotic microbiome through intestinal immune alterations triggers PD-related neurodegeneration.

METHODS

To determine the impact of gut dysbiosis on the development and progression of PD pathology, wild-type male C57BL/6 mice were transplanted with fecal material from PD patients and age-matched healthy donors to challenge the gut-immune-brain axis.

RESULTS

This study demonstrates that patient-derived intestinal microbiota caused midbrain tyrosine hydroxylase positive (TH +) cell loss and motor dysfunction. Ileum-associated microbiota remodeling correlates with a decrease in Th17 homeostatic cells. This event led to an increase in gut inflammation and intestinal barrier disruption. In this regard, we found a decrease in CD4 + cells and an increase in pro-inflammatory cytokines in the blood of PD transplanted mice that could contribute to an increase in the permeabilization of the blood-brain-barrier, observed by an increase in mesencephalic Ig-G-positive microvascular leaks and by an increase of mesencephalic IL-17 levels, compatible with systemic inflammation. Furthermore, alpha-synuclein aggregates can spread caudo-rostrally, causing fragmentation of neuronal mitochondria. This mitochondrial damage subsequently activates innate immune responses in neurons and triggers microglial activation.

CONCLUSIONS

We propose that the dysbiotic gut microbiome (dysbiome) in PD can disrupt a healthy microbiome and Th17 homeostatic immunity in the ileum mucosa, leading to a cascade effect that propagates to the brain, ultimately contributing to PD pathophysiology. Our landmark study has successfully identified new peripheral biomarkers that could be used to develop highly effective strategies to prevent the progression of PD into the brain.

Probiotic supplementation has sex-dependent effects on immune responses in association with the gut microbiota in community-dwelling older adults: a randomized, double-blind, placebo-controlled, multicenter trial

BACKGROUND/OBJECTIVES

Probiotics have been suggested as potent modulators of age-related disorders in immunological functions, yet little is known about sex-dependent effects of probiotic supplements. Therefore, we aimed to investigate sex-dependent effects of probiotics on profiles of the gut microbiota and peripheral immune cells in healthy older adults.

SUBJECTS/METHODS

In a randomized, double-blind, placebo-controlled, multicenter trial, healthy elderly individuals ≥ 65 yrs old were administered probiotic capsules (or placebo) for 12 wk. Gut microbiota was analyzed using 16S rRNA gene sequencing and bioinformatic analyses. Peripheral immune cells were profiled using flow cytometry for lymphocytes (natural killer, B, CD4+ T, and CD8+ T cells), dendritic cells, monocytes, and their subpopulations.

RESULTS

Compared with placebo, phylum Firmicutes was significantly reduced in the probiotic group in women, but not in men. At the genus level, sex-specific responses included reductions in the relative abundances of pro-inflammatory gut microbes, including Catabacter and unclassified_Coriobacteriales, and Burkholderia and unclassified Enterobacteriaceae, in men and women, respectively. Peripheral immune cell profiling analysis revealed that in men, probiotics significantly reduced the proportions of dendritic cells and CD14+ CD16- monocytes; however, these effects were not observed in women. In contrast, the proportion of total CD4+ T cells was significantly reduced in women in the probiotic group. Additionally, serum lipopolysaccharide-binding protein levels showed a decreasing tendency that were positively associated with changes in gut bacteria, including Catabacter (ρ = 0.678, P < 0.05) and Burkholderia (ρ = 0.673, P < 0.05) in men and women, respectively.

CONCLUSIONS

These results suggest that probiotic supplementation may reduce the incidence of inflammation-related diseases by regulating the profiles of the gut microbiota and peripheral immune cells in healthy elders in a sex-specific manner.

Helicobacter hepaticus augmentation triggers Dopaminergic degeneration and motor disorders in mice with Parkinson's disease

Gut dysbiosis contributes to Parkinson's disease (PD) pathogenesis. Gastrointestinal disturbances in PD patients, along with gut leakage and intestinal inflammation, take place long before motor disorders. However, it remains unknown what bacterial species in gut microbiomes play the key role in driving PD pathogenesis. Here we show that Helicobacter hepaticus (H. hepaticus), abundant in gut microbiota from rotenone-treated human α-Synuclein gene (SNCA) transgenic mice and PD patients, initiates α-Synuclein pathology and motor deficits in an AEP-dependent manner in SNCA mice. Chronic Dextran sodium sulfate (DSS) treatment, an inflammatory inducer in the gut, activates AEP (asparagine endopeptidase) that cleaves α-Synuclein N103 and triggers its aggregation, promoting inflammation in the gut and the brain and motor defects in SNCA mice. PD fecal microbiota transplant or live H. hepaticus administration into antibiotics cocktail (Abx)-pretreated SNCA mice induces α-Synuclein pathology, inflammation in the gut and brain, and motor dysfunctions, for which AEP is indispensable. Hence, Helicobacter hepaticus enriched in PD gut microbiomes may facilitate α-Synuclein pathologies and motor impairments via activating AEP.

An open label, non-randomized study assessing a prebiotic fiber intervention in a small cohort of Parkinson's disease participants

A pro-inflammatory intestinal microbiome is characteristic of Parkinson's disease (PD). Prebiotic fibers change the microbiome and this study sought to understand the utility of prebiotic fibers for use in PD patients. The first experiments demonstrate that fermentation of PD patient stool with prebiotic fibers increased the production of beneficial metabolites (short chain fatty acids, SCFA) and changed the microbiota demonstrating the capacity of PD microbiota to respond favorably to prebiotics. Subsequently, an open-label, non-randomized study was conducted in newly diagnosed, non-medicated (n = 10) and treated PD participants (n = 10) wherein the impact of 10 days of prebiotic intervention was evaluated. Outcomes demonstrate that the prebiotic intervention was well tolerated (primary outcome) and safe (secondary outcome) in PD participants and was associated with beneficial biological changes in the microbiota, SCFA, inflammation, and neurofilament light chain. Exploratory analyses indicate effects on clinically relevant outcomes. This proof-of-concept study offers the scientific rationale for placebo-controlled trials using prebiotic fibers in PD patients. ClinicalTrials.gov Identifier: NCT04512599.

Dysfunction of the noradrenergic system drives inflammation, α-synucleinopathy, and neuronal loss in mouse colon

Clinical and pathological evidence revealed that α-synuclein (α-syn) pathology seen in PD patients starts in the gut and spreads via anatomically connected structures from the gut to the brain. Our previous study demonstrated that depletion of central norepinephrine (NE) disrupted brain immune homeostasis, producing a spatiotemporal order of neurodegeneration in the mouse brain. The purpose of this study was 1) to determine the role of peripheral noradrenergic system in the maintenance of gut immune homeostasis and in the pathogenesis of PD and 2) to investigate whether NE-depletion induced PD-like α-syn pathological changes starts from the gut. For these purposes, we investigated time-dependent changes of α-synucleinopathy and neuronal loss in the gut following a single injection of DSP-4 (a selective noradrenergic neurotoxin) to A53T-SNCA (human mutant α-syn) over-expression mice. We found DPS-4 significantly reduced the tissue level of NE and increased immune activities in gut, characterized by increased number of phagocytes and proinflammatory gene expression. Furthermore, a rapid-onset of α-syn pathology was observed in enteric neurons after 2 weeks and delayed dopaminergic neurodegeneration in the substantia nigra was detected after 3-5 months, associated with the appearance of constipation and impaired motor function, respectively. The increased α-syn pathology was only observed in large, but not in the small, intestine, which is similar to what was observed in PD patients. Mechanistic studies reveal that DSP-4-elicited upregulation of NADPH oxidase (NOX2) initially occurred only in immune cells during the acute intestinal inflammation stage, and then spread to enteric neurons and mucosal epithelial cells during the chronic inflammation stage. The upregulation of neuronal NOX2 correlated well with the extent of α-syn aggregation and subsequent enteric neuronal loss, suggesting that NOX2-generated reactive oxygen species play a key role in α-synucleinopathy. Moreover, inhibiting NOX2 by diphenyleneiodonium or restoring NE function by salmeterol (a β2-receptor agonist) significantly attenuated colon inflammation, α-syn aggregation/propagation, and enteric neurodegeneration in the colon and ameliorated subsequent behavioral deficits. Taken together, our model of PD shows a progressive pattern of pathological changes from the gut to the brain and suggests a potential role of the noradrenergic dysfunction in the pathogenesis of PD.

Distinct Patterns of Gene Expression Changes in the Colon and Striatum of Young Mice Overexpressing Alpha-Synuclein Support Parkinson's Disease as a Multi-System Process

BACKGROUND

Evidence supports a role for the gut-brain axis in Parkinson's disease (PD). Mice overexpressing human wild type α- synuclein (Thy1-haSyn) exhibit slow colonic transit prior to motor deficits, mirroring prodromal constipation in PD. Identifying molecular changes in the gut could provide both biomarkers for early diagnosis and gut-targeted therapies to prevent progression.

OBJECTIVE

To identify early molecular changes in the gut-brain axis in Thy1-haSyn mice through gene expression profiling.

METHODS

Gene expression profiling was performed on gut (colon) and brain (striatal) tissue from Thy1-haSyn and wild-type (WT) mice aged 1 and 3 months using 3' RNA sequencing. Analysis included differential expression, gene set enrichment and weighted gene co-expression network analysis (WGCNA).

RESULTS

At one month, differential expression (Thy1-haSyn vs. WT) of mitochondrial genes and pathways related to PD was discordant between gut and brain, with negative enrichment in brain (enriched in WT) but positive enrichment in gut. Linear regression of WGCNA modules showed partial independence of gut and brain gene expression changes. Thy1-haSyn-associated WGCNA modules in the gut were enriched for PD risk genes and PD-relevant pathways including inflammation, autophagy, and oxidative stress. Changes in gene expression were modest at 3 months.

CONCLUSIONS

Overexpression of haSyn acutely disrupts gene expression in the colon. While changes in colon gene expression are highly related to known PD-relevant mechanisms, they are distinct from brain changes, and in some cases, opposite in direction. These findings are in line with the emerging view of PD as a multi-system disease.

Footprints of a microbial toxin from the gut microbiome to mesencephalic mitochondria

OBJECTIVE

Idiopathic Parkinson's disease (PD) is characterised by alpha-synuclein (aSyn) aggregation and death of dopaminergic neurons in the midbrain. Recent evidence posits that PD may initiate in the gut by microbes or their toxins that promote chronic gut inflammation that will ultimately impact the brain. In this work, we sought to demonstrate that the effects of the microbial toxin β-N-methylamino-L-alanine (BMAA) in the gut may trigger some PD cases, which is especially worrying as this toxin is present in certain foods but not routinely monitored by public health authorities.

DESIGN

To test the hypothesis, we treated wild-type mice, primary neuronal cultures, cell lines and isolated mitochondria with BMAA, and analysed its impact on gut microbiota composition, barrier permeability, inflammation and aSyn aggregation as well as in brain inflammation, dopaminergic neuronal loss and motor behaviour. To further examine the key role of mitochondria, we also determined the specific effects of BMAA on mitochondrial function and on inflammasome activation.

RESULTS

BMAA induced extensive depletion of segmented filamentous bacteria (SFB) that regulate gut immunity, thus triggering gut dysbiosis, immune cell migration, increased intestinal inflammation, loss of barrier integrity and caudo-rostral progression of aSyn. Additionally, BMAA induced in vitro and in vivo mitochondrial dysfunction with cardiolipin exposure and consequent activation of neuronal innate immunity. These events primed neuroinflammation, dopaminergic neuronal loss and motor deficits.

CONCLUSION

Taken together, our results demonstrate that chronic exposure to dietary BMAA can trigger a chain of events that recapitulate the evolution of the PD pathology from the gut to the brain, which is consistent with 'gut-first' PD.

Gut dysfunction may be the source of pathological aggregation of alpha-synuclein in the central nervous system through Paraquat exposure in mice

BACKGROUND

One of the most common types of neurodegenerative diseases (NDDs) is Lewy body disease (LBD), which is characterized by excessive accumulation of α-synuclein (α-syn) in the neurons and affects around 6 million individuals globally. In recent years, due to the environmental factors that can affect the development of this condition, such as exposure to herbicides and pesticides, so it has become a younger disease. Currently, the vast majority of studies on the neurotoxic effects of paraquat (PQ) focus on the late mechanisms of neuronal-glial network regulation, and little is known about the early origins of this environmental factor leading to LBD.

OBJECTIVE

To observe the effect of PQ exposure on intestinal function and to explore the key components of communicating the gut-brain axis by establishing a mouse model.

METHODS AND RESULTS

In this study, C57BL/6J mice were treated by intraperitoneal injection of 15 mg/kg PQ to construct an LBD time-series model, and confirmed by neurobehavioral testing and pathological examination. After PQ exposure, on the one hand, we found that fecal particle counts and moisture content were abnormal. on the other hand, we found that the expression levels of colonic tight junction proteins decreased, the expression levels of inflammatory markers increased, and the diversity and abundance of gut microbiota altered. In addition, pathological aggregation of α-syn was consistent in the colon and midbrain, and the metabolism and utilization of short-chain fatty acids (SCFAs) were also markedly altered. This suggests that pathological α-syn and SCFAs form the gut may be key components of the communicating gut-brain axis.

CONCLUSION

In this PQ-induced mouse model, gut microbiota disruption, intestinal epithelial barrier damage, and inflammatory responses may be the main causes of gut dysfunction, and pathological α-syn and SCFAs in the gut may be key components of the communicating gut-brain axis.

Intestinal microbiota and neuroinflammation in Parkinson's disease: At the helm of the gut-brain axis

Emerging data suggest that disrupted intestinal microbiota, or dysbiosis, may be responsible for multiple features of Parkinson's disease (PD), from initiation, to progression, to therapeutic response. We have progressed greatly in our understanding of microbial signatures associated with PD, and have gained important insights into how dysbiosis and intestinal permeability promote neurodegeneration through neuroinflammation and Lewy body formation. These insights underscore the potential of microbiota-directed therapies, which include dietary, pharmacologic, and lifestyle interventions.

Antibiotic Consumption Patterns in European Countries Are Associated with the Prevalence of Parkinson’s Disease; the Possible Augmenting Role of the Narrow-Spectrum Penicillin

Parkinson’s disease: Parkinson’s disease (PD) is the second-most common neurodegenerative disease, affecting at least 0.3% of the worldwide population and over 3% of those over 80 years old. According to recent research (2018), in 2016, 6.1 million (95% uncertainty interval (UI) 5.0–7.3) individuals had Parkinson’s disease globally, compared with 2.5 million (2.0–3.0) in 1990. The pandemic-like spreading of PD is considered a slow-moving disaster. Most recent studies indicated the possible role of an altered microbiome, dysbiosis, in the development of PD, which occurs long before the clinical diagnosis of PD. Antibiotics are considered as major disruptors of the intestinal flora and we have hypothesized that, as different classes of antibiotics might induce different dysbiosis, certain classes of antibiotics could trigger the PD-related dysbiosis as well. Comparative analyses were performed between the average yearly antibiotic consumption of 30 European countries (1997–2016) and the PD prevalence database (estimated for 2016). We divided the time frame of antibiotic consumption of 1997–2016 into four subsections to estimate the possible time lapse between antibiotic exposure and the prevalence, prevalence change, and PD-related death rates estimated for 2016. Our results indicated that countries with high consumption of narrow-spectrum penicillin experienced a higher increase in PD prevalence than the others. Countries reporting a decline in PD from 1990 to 2016 demonstrated a reduction in the consumption of narrow-spectrum penicillin in this period.

Identification of gut metabolites associated with Parkinson's disease using bioinformatic analyses

BACKGROUND

Parkinson's disease (PD) is a common neurodegenerative disease affecting the movement of elderly patients. Environmental exposures are the risk factors for PD; however, gut environmental risk factors for PD are critically understudied. The proof-of-concept study is to identify gut metabolites in feces, as environmental exposure risk factors, that are associated with PD and potentially increase the risk for PD by using leverage of known toxicology results.

MATERIALS AND METHODS

We collected the data regarding the gut metabolites whose levels were significantly changed in the feces of patients with PD from the original clinical studies after searching the following databases: EBM Reviews, PubMed, Embase, MEDLINE, and Elsevier ClinicalKey. We further searched each candidate metabolite-interacting PD gene set by using the public Comparative Toxicogenomics Database (CTD), identified and validated gut metabolites associated with PD, and determined gut metabolites affecting specific biological functions and cellular pathways involved in PD by using PANTHER tools.

RESULTS

Sixteen metabolites were identified and divided into the following main categories according to their structures and biological functions: alcohols (ethanol), amino acids (leucine, phenylalanine, pyroglutamic acid, glutamate, and tyrosine), short-chain fatty acids (propionate and butyrate), unsaturated fatty acids (linoleic acid and oleic acid), energy metabolism (lactate, pyruvate, and fumarate), vitamins (nicotinic acid and pantothenic acid), and choline metabolism (choline). Finally, a total of three identified metabolites, including butyrate, tyrosine, and phenylalanine, were validated that were associated with PD.

CONCLUSION

Our findings identified the gut metabolites that were highly enriched for PD genes and potentially increase the risk of developing PD. The identification of gut metabolite exposures can provide biomarkers for disease identification, facilitate an understanding of the relationship between gut metabolite exposures and response, and present an opportunity for PD prevention and therapies.

Traumatic spinal cord injury and the contributions of the post-injury microbiome

Spinal cord injuries are an enormous burden on injured individuals and their caregivers. The pathophysiological effects of injury are not limited to the spine and limb function, but affect numerous body systems. Growing observations in human studies and experimental models suggest that the gut microbiome is altered following spinal cord injury. Given the importance of signals derived from the gut microbiome for host physiology, it is possible that injury-triggered dysbiosis subsequently affects aspects of recovery. Here, we review emerging literature on the role of the microbiome following spinal cord injury. Specifically, we highlight findings from both human and experimental studies that correlate taxonomic changes to aspects of injury recovery. Examination of both observational and emerging interventional studies supports the notion that future therapeutic avenues for spinal cord injury pathologies may lie at the interface of the host and indigenous microbes.

Intestinal Barrier Dysfunction in the Absence of Systemic Inflammation Fails to Exacerbate Motor Dysfunction and Brain Pathology in a Mouse Model of Parkinson's Disease

Introduction

Parkinson's disease (PD) is the second most common neurodegenerative disease associated with aging. PD patients have systemic and neuroinflammation which is hypothesized to contribute to neurodegeneration. Recent studies highlight the importance of the gut-brain axis in PD pathogenesis and suggest that gut-derived inflammation can trigger and/or promote neuroinflammation and neurodegeneration in PD. However, it is not clear whether microbiota dysbiosis, intestinal barrier dysfunction, or intestinal inflammation (common features in PD patients) are primary drivers of disrupted gut-brain axis in PD that promote neuroinflammation and neurodegeneration.

Objective

To determine the role of microbiota dysbiosis, intestinal barrier dysfunction, and colonic inflammation in neuroinflammation and neurodegeneration in a genetic rodent model of PD [α-synuclein overexpressing (ASO) mice].

Methods

To distinguish the role of intestinal barrier dysfunction separate from inflammation, low dose (1%) dextran sodium sulfate (DSS) was administered in cycles for 52 days to ASO and control mice. The outcomes assessed included intestinal barrier integrity, intestinal inflammation, stool microbiome community, systemic inflammation, motor function, microglial activation, and dopaminergic neurons.

Results

Low dose DSS treatment caused intestinal barrier dysfunction (sugar test, histological analysis), intestinal microbiota dysbiosis, mild intestinal inflammation (colon shortening, elevated MPO), but it did not increase systemic inflammation (serum cytokines). However, DSS did not exacerbate motor dysfunction, neuroinflammation (microglial activation), or dopaminergic neuron loss in ASO mice.

Conclusion

Disruption of the intestinal barrier without overt intestinal inflammation is not associated with worsening of PD-like behavior and pathology in ASO mice.

T cells, α-synuclein and Parkinson disease

The notion that autoimmune responses to α-synuclein may be involved in the pathogenesis of this disorder stems from reports that mutations in α-synuclein or certain alleles of the major histocompatibility complex (MHC) are associated with the disease and that dopaminergic and norepinephrinergic neurons in the midbrain can present antigenic epitopes. Here, we discuss recent evidence that a defined set of peptides derived from α-synuclein act as antigenic epitopes displayed by specific MHC alleles and drive helper and cytotoxic T cell responses in patients with PD. Moreover, phosphorylated α-synuclein may activate T cell responses in a less restricted manner in PD. While the roles for the acquired immune system in disease pathogenesis remain unknown, preclinical animal models and in vitro studies indicate that T cells may interact with neurons and exert effects related to neuronal death and neuroprotection. These findings suggest that therapeutics that target T cells and ameliorate the incidence or disease severity of inflammatory bowel disorders or CNS autoimmune diseases such as multiple sclerosis may be useful in PD.

Mitochondria-Microbiota Interaction in Neurodegeneration

Alzheimer’s and Parkinson’s are the two best-known neurodegenerative diseases. Each is associated with the excessive aggregation in the brain and elsewhere of its own characteristic amyloid proteins. Yet the two afflictions have much in common and often the same amyloids play a role in both. These amyloids need not be toxic and can help regulate bile secretion, synaptic plasticity, and immune defense. Moreover, when they do form toxic aggregates, amyloids typically harm not just patients but their pathogens too. A major port of entry for pathogens is the gut. Keeping the gut’s microbe community (microbiota) healthy and under control requires that our cells’ main energy producers (mitochondria) support the gut-blood barrier and immune system. As we age, these mitochondria eventually succumb to the corrosive byproducts they themselves release, our defenses break down, pathogens or their toxins break through, and the side effects of inflammation and amyloid aggregation become problematic. Although it gets most of the attention, local amyloid aggregation in the brain merely points to a bigger problem: the systemic breakdown of the entire human superorganism, exemplified by an interaction turning bad between mitochondria and microbiota.

The gut-brain axis and Parkinson disease: clinical and pathogenetic relevance

Gastrointestinal disorders are one of the most significant non-motor problems affecting people with Parkinson disease (PD). Pathogenetically, the gastrointestinal tract has been proposed to be the initial site of pathological changes in PD. Intestinal inflammation and alterations in the gut microbiota may contribute to initiation and progression of pathology in PD. However, the mechanisms underlying this "gut-brain" axis in PD remain unclear. PD patients can display a large variety of gastrointestinal symptoms, leading to reduced quality of life and psychological distress. Gastrointestinal disorders can also limit patients' response to medications, and consequently negatively impact on neurological outcomes. Despite an increasing research focus, gastrointestinal disorders in PD remain poorly understood and their clinical management often suboptimal. This review summarises our understanding of the relevance of the "gut-brain" axis to the pathogenesis of PD, discusses the impact of gastrointestinal disorders in patients with PD, and provides clinicians with practical guidance to their management.

Influence of probiotic bacteria on gut microbiota composition and gut wall function in an in-vitro model in patients with Parkinson's disease

We report here the potential role of a 4-strain probiotic suspension for use with patients with Parkinson's disease (PD). Stool samples from a group of three patients with diagnosed PD were used to create microbiotas in an in-vitro gut model. The effects of dosing with an oral probiotic suspension (Symprove) on bacterial composition and metabolic activity in the microbiotas was evaluated over 48 h and compared with healthy controls. Additionally, the effect of probiotic dosing on epithelial tight-junction integrity, production of inflammatory markers and wound healing were evaluated in cell culture models. In general, the relative proportions of the main bacterial phyla in the microbiotas of PD patients differed from those of healthy subjects, with levels of Firmicutes raised and levels of Bacteroidetes reduced. Dosing with probiotic resulted in a change in bacterial composition in the microbiotas over a 48 h period. Several other indicators of gut health changed upon dosing with the probiotic; production of short chain fatty acids (SCFAs) and lactate was stimulated, levels of anti-inflammatory cytokines (IL-6, IL-10) increased and levels of pro-inflammatory cytokines and chemokines (MCP-1 and IL-8) decreased. Tight junction integrity was seen to improve with probiotic dosing and wound healing was seen to occur faster than a control. The data suggest that if development and/or progression of PD is influenced by gut microbiota dysbiosis then supplementation of the diet with a properly formulated probiotic may be a useful adjunct to standard treatment in clinic.

The Effects of Consuming White Button Mushroom Agaricus bisporus on the Brain and Liver Metabolome Using a Targeted Metabolomic Analysis

A targeted metabolomic analysis was performed on tissues derived from pigs fed diets supplemented with white button mushrooms (WBM) to determine the effect on the liver and brain metabolome. Thirty-one pigs were fed a grower diet alone or supplemented with either three or six servings of freeze-dried WBM for six weeks. Tissue metabolomes were analyzed using targeted liquid chromatography-mass spectrometry (LC-MS) combined with chemical similarity enrichment analysis (ChemRICH) and correlated to WBM-induced changes in fecal microbiome composition. Results indicated that WBM can differentially modulate metabolites in liver, brain cortex and hippocampus of healthy pigs. Within the glycero-phospholipids, there was an increase in alkyl-acyl-phosphatidyl-cholines (PC-O 40:3) in the hippocampus of pigs fed six servings of WBM. A broader change in glycerophospholipids and sphingolipids was detected in the liver with a reduction in several lipid species in pigs fed both WBM diets but with an increase in amino acids known as precursors of neurotransmitters in the cortex of pigs fed six servings of WBM. Metabolomic changes were positively correlated with increased abundance of Cryomorphaceae, Lachnospiraceae, Flammeovirgaceae and Ruminococcaceae in the microbiome suggesting that WBM can also positively impact tissue metabolite composition.

Ruminal Microbes Exhibit a Robust Circadian Rhythm and Are Sensitive to Melatonin

Gut hormones are not only able to regulate digestive, absorptive, and immune mechanisms of the intestine through biological rhythms, but impact the host through their interactions with intestinal microorganisms. Whether hormones in ruminal fluid have an association with the ruminal ecology is unknown. Objectives of the study were to examine relationships between the diurnal change in ruminal hormones and microbiota in lactating cows, and their associations in vivo and in vitro. For the in vivo study, six cows of similar weight (566.8 ± 19.6 kg), parity (3.0 ± 0.0), and milk performance (8,398.7 ± 1,392.9 kg/y) were used. They were adapted to natural light for 2 weeks before sampling and fed twice daily at 07:00 a.m. and 14:00 p.m. Serum, saliva, and ruminal fluid samples were collected at 02:00, 10:00, and 18:00 on the first day and 06:00, 14:00, and 22:00 on the second day of the experimental period. The concentrations of melatonin (MLT), growth hormone (GH), and prolactin (PRL) were measured via radioimmunoassay, whereas amplicon sequencing data were used to analyze relative abundance of microbiota in ruminal fluid. JTK_CYCLE analysis was performed to analyze circadian rhythms of hormone concentrations as well as the relative abundance of microbiota. For the in vitro study, exogenous MLT (9 ng) was added into ruminal fluid incubations to investigate the impacts of MLT on ruminal microbiota. The results not only showed that rumen fluid contains MLT, but the diurnal variation of MLT and the relative abundance of 9% of total rumen bacterial operational taxonomic units (OTUs) follow a circadian rhythm. Although GH and PRL were also detected in ruminal fluid, there was no obvious circadian rhythm in their concentrations. Ruminal MLT was closely associated with Muribaculaceae, Succinivibrionaceae, Veillonellaceae, and Prevotellaceae families in vivo. In vitro, these families were significantly influenced by melatonin treatment, as melatonin treatment increased the relative abundance of families Prevotellaceae, Muribaculaceae while it reduced the relative abundance of Succinivibrionaceae, Veillonellaceae. Collectively, ruminal microbes appear to maintain a circadian rhythm that is associated with the profiles of melatonin. As such, data suggest that secretion of melatonin into the rumen could play a role in host-microbe interactions in ruminants.

Parkinson's disease and the gut: Models of an emerging relationship

Parkinson's disease (PD) is a common neurodegenerative disease characterized by a progressive loss of fine motor function that impacts 1-2 out of 1,000 people. PD occurs predominately late in life and lacks a definitive biomarker for early detection. Recent cross-disciplinary progress has implicated the gut as a potential origin of PD pathogenesis. The gut-origin hypothesis has motivated research on gut PD pathology and transmission to the brain, especially during the prodromal stage (10-20 years before motor symptom onset). Early findings have revealed several possible triggers for Lewy pathology - the pathological hallmark of PD - in the gut, suggesting that microbiome and epithelial interactions may play a greater than appreciated role. But the mechanisms driving Lewy pathology and gut-brain transmission in PD remain unknown. Development of artificial α-Synuclein aggregates (α-Syn preformed fibrils) and animal disease models have recapitulated features of PD progression, enabling for the first time, controlled investigation of the gut-origin hypothesis. However, the role of specific cells in PD transmission, such as neurons, remains limited and requires in vitro models for controlled evaluation and perturbation. Human cell populations, three-dimensional organoids, and microfluidics as discovery platforms inch us closer to improving existing treatment for patients by providing platforms for discovery and screening. This review includes a discussion of PD pathology, conventional treatments, in vivo and in vitro models, and future directions. STATEMENT OF SIGNIFICANCE: Parkinson's Disease remains a common neurodegenerative disease with palliative versus causal treatments. Recently, the gut-origin hypothesis, where Parkinson's disease is thought to originate and spread from the gut to the brain, has gained traction as a field of investigation. However, despite the wealth of studies and innovative approaches to accelerate the field, there remains a need for in vitro tools to enable fundamental biological understanding of disease progression, and compound screening and efficacy. In this review, we present a historical perspective of Parkinson's Disease pathogenesis, detection, and conventional therapy, animal and human models investigating the gut-origin hypothesis, in vitro models to enable controlled discovery, and future outlooks for this blossoming field.

Memorable Food: Fighting Age-Related Neurodegeneration by Precision Nutrition

Healthcare systems worldwide are seriously challenged by a rising prevalence of neurodegenerative diseases (NDDs), which mostly, but not exclusively, affect the ever-growing population of the elderly. The most known neurodegenerative diseases are Alzheimer's (AD) and Parkinson's disease, multiple sclerosis, and amyotrophic lateral sclerosis, but some viral infections of the brain and traumatic brain injury may also cause NDD. Typical for NDD are the malfunctioning of neurons and their irreversible loss, which often progress irreversibly to dementia and ultimately to death. Numerous factors are involved in the pathogenesis of NDD: genetic variability, epigenetic changes, extent of oxidative/nitrosative stress, mitochondrial dysfunction, and DNA damage. The complex interplay of all the above-mentioned factors may be a fingerprint of neurodegeneration, with different diseases being affected to different extents by particular factors. There is a voluminous body of evidence showing the benefits of regular exercise to brain health and cognitive functions. Moreover, the importance of a healthy diet, balanced in macro- and micro-nutrients, in preventing neurodegeneration and slowing down a progression to full-blown disease is evident. Individuals affected by NDD almost inevitably have low-grade inflammation and anomalies in lipid metabolism. Metabolic and lipid profiles in NDD can be improved by the Mediterranean diet. Many studies have associated the Mediterranean diet with a decreased risk of dementia and AD, but a cause-and-effect relationship has not been deduced. Studies with caloric restriction showed neuroprotective effects in animal models, but the results in humans are inconsistent. The pathologies of NDD are complex and there is a great inter-individual (epi)genetic variance within any population. Furthermore, the gut microbiome, being deeply involved in nutrient uptake and lipid metabolism, also represents a pillar of the gut microbiome-brain axis and is linked with the pathogenesis of NDD. Numerous studies on the role of different micronutrients (omega-3 fatty acids, bioactive polyphenols from fruit and medicinal plants) in the prevention, prediction, and treatment of NDD have been conducted, but we are still far away from a personalized diet plan for individual NDD patients. For this to be realized, large-scale cohorts that would include the precise monitoring of food intake, mapping of genetic variants, epigenetic data, microbiome studies, and metabolome, lipidome, and transcriptome data are needed.

Dysregulation of the Gut-Brain Axis, Dysbiosis and Influence of Numerous Factors on Gut Microbiota Associated Parkinson's Disease

BACKGROUND

Parkinson's disease (PD) has been one of the substantial social, medical concerns and, burdens of the present time. PD is a gradually devastating neurodegenerative disorder of the neurological function marked with α-synucleinopathy affecting numerous regions of the brain-gut axis, as well as the central, enteric, and autonomic nervous system. Its etiology is a widely disputed topic.

OBJECTIVE

This review emphasizes to find out the correlation among the microbial composition and the observable disturbances in the metabolites of the microbial species and its impact on the immune response, which may have a concrete implication on the occurrence, persistence and, pathophysiology of PD via the gut-brain axis.

METHODS

An in-depth research and the database was developed from the available peer-reviewed articles to date (March 2020) utilizing numerous search engines like PubMed, MEDLINE and, other internet sources.

RESULTS

Progressively increasing shreds of evidence have proved the fact that dysbiosis in the gut microbiome plays a central role in many neurological disorders, such as PD. Indeed, a disordered microbiome-gut-brain axis in PD could be focused on gastrointestinal afflictions that manifest primarily several years prior to the diagnosis, authenticating a concept wherein the pathological pathway progresses from the intestine reaching the brain.

CONCLUSION

The microbiota greatly affects the bidirectional interaction between the brain and the gut via synchronized neurological, immunological, and neuroendocrine mechanisms. It can be concluded that a multitude of factors discussed in this review steadily induce the onset of dysbacteriosis that may exacerbate the etiologic mechanism of Parkinson's disease.

Gut-Brain Axis and Neurodegeneration: State-of-the-Art of Meta-Omics Sciences for Microbiota Characterization

Recent advances in the field of meta-omics sciences and related bioinformatics tools have allowed a comprehensive investigation of human-associated microbiota and its contribution to achieving and maintaining the homeostatic balance. Bioactive compounds from the microbial community harboring the human gut are involved in a finely tuned network of interconnections with the host, orchestrating a wide variety of physiological processes. These includes the bi-directional crosstalk between the central nervous system, the enteric nervous system, and the gastrointestinal tract (i.e., gut-brain axis). The increasing accumulation of evidence suggest a pivotal role of the composition and activity of the gut microbiota in neurodegeneration. In the present review we aim to provide an overview of the state-of-the-art of meta-omics sciences including metagenomics for the study of microbial genomes and taxa strains, metatranscriptomics for gene expression, metaproteomics and metabolomics to identify and/or quantify microbial proteins and metabolites, respectively. The potential and limitations of each discipline were highlighted, as well as the advantages of an integrated approach (multi-omics) to predict microbial functions and molecular mechanisms related to human diseases. Particular emphasis is given to the latest results obtained with these approaches in an attempt to elucidate the link between the gut microbiota and the most common neurodegenerative diseases, such as multiple sclerosis (MS), Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS).

The gut microbiome in Parkinson's disease: A culprit or a bystander?

In recent years, large-scale metagenomics projects such as the Human Microbiome Project placed the gut microbiota under the spotlight of research on its role in health and in the pathogenesis several diseases, as it can be a target for novel therapeutical approaches. The emerging concept of a microbiota modulation of the gut-brain axis in the pathogenesis of neurodegenerative disorders has been explored in several studies in animal models, as well as in human subjects. Particularly, research on changes in the composition of gut microbiota as a potential trigger for alpha-synuclein (α-syn) pathology in Parkinson's disease (PD) has gained increasing interest. In the present review, we first provide the basis to the understanding of the role of gut microbiota in healthy subjects and the molecular basis of the gut-brain interaction, focusing on metabolic and neuroinflammatory factors that could trigger the alpha-synuclein conformational changes and aggregation. Then, we critically explored preclinical and clinical studies reporting on the changes in gut microbiota in PD, as compared to healthy subjects. Furthermore, we examined the relationship between the gut microbiota and PD clinical features, discussing data consistently reported across studies, as well as the potential sources of inconsistencies. As a further step toward understanding the effects of gut microbiota on PD, we discussed the relationship between dysbiosis and response to dopamine replacement therapy, focusing on Levodopa metabolism. We conclude that further studies are needed to determine whether the gut microbiota changes observed so far in PD patients is the cause or, instead, it is merely a consequence of lifestyle changes associated with the disease. Regardless, studies so far strongly suggest that changes in microbiota appears to be impactful in pathogenesis of neuroinflammation. Thus, dysbiotic microbiota in PD could influence the disease course and response to medication, especially Levodopa. Future research will assess the impact of microbiota-directed therapeutic intervention in PD patients.

A gut bacterial amyloid promotes α-synuclein aggregation and motor impairment in mice

Amyloids are a class of protein with unique self-aggregation properties, and their aberrant accumulation can lead to cellular dysfunctions associated with neurodegenerative diseases. While genetic and environmental factors can influence amyloid formation, molecular triggers and/or facilitators are not well defined. Growing evidence suggests that non-identical amyloid proteins may accelerate reciprocal amyloid aggregation in a prion-like fashion. While humans encode ~30 amyloidogenic proteins, the gut microbiome also produces functional amyloids. For example, curli are cell surface amyloid proteins abundantly expressed by certain gut bacteria. In mice overexpressing the human amyloid α-synuclein (αSyn), we reveal that colonization with curli-producing Escherichia coli promotes αSyn pathology in the gut and the brain. Curli expression is required for E. coli to exacerbate αSyn-induced behavioral deficits, including intestinal and motor impairments. Purified curli subunits accelerate αSyn aggregation in biochemical assays, while oral treatment of mice with a gut-restricted amyloid inhibitor prevents curli-mediated acceleration of pathology and behavioral abnormalities. We propose that exposure to microbial amyloids in the gastrointestinal tract can accelerate αSyn aggregation and disease in the gut and the brain.

Diet in Parkinson's Disease: Critical Role for the Microbiome

Background: Parkinson's disease (PD) is the most common movement disorder affecting up to 1% of the population above the age of 60 and 4–5% of those above the age of 85. Little progress has been made on efforts to prevent disease development or halt disease progression. Diet has emerged as a potential factor that may prevent the development or slow the progression of PD. In this review, we discuss evidence for a role for the intestinal microbiome in PD and how diet-associated changes in the microbiome may be a viable approach to prevent or modify disease progression.

Methods: We reviewed studies demonstrating that dietary components/foods were related to risk for PD. We reviewed evidence for the dysregulated intestinal microbiome in PD patients including abnormal shifts in the intestinal microbiota composition (i.e., dysbiosis) characterized by a loss of short chain fatty acid (SCFA) bacteria and increased lipopolysaccharide (LPS) bacteria. We also examined several candidate mechanisms by which the microbiota can influence PD including the NLRP3 inflammasome, insulin resistance, mitochondrial function, vagal nerve signaling.

Results: The PD-associated microbiome is associated with decreased production of SCFA and increased LPS and it is believed that these changes may contribute to the development or exacerbation of PD. Diet robustly impacts the intestinal microbiome and the Western diet is associated with increased risk for PD whereas the Mediterranean diet (including high intake of dietary fiber) decreases PD risk. Mechanistically this may be the consequence of changes in the relative abundance of SCFA-producing or LPS-containing bacteria in the intestinal microbiome with effects on intestinal barrier function, endotoxemia (i.e., systemic LPS), NLRP3 inflammasome activation, insulin resistance, and mitochondrial dysfunction, and the production of factors such as glucagon like peptide 1 (GLP-1) and brain derived neurotrophic factor (BDNF) as well as intestinal gluconeogenesis.

Conclusions: This review summarizes a model of microbiota-gut-brain-axis regulation of neuroinflammation in PD including several new mechanisms. We conclude with the need for clinical trials in PD patients to test this model for beneficial effects of Mediterranean based high fiber diets.

Bacterial Metabolites Mirror Altered Gut Microbiota Composition in Patients with Parkinson's Disease

Increasing evidence is supporting the hypothesis of α-synuclein pathology spreading from the gut to the brain although the exact etiology of Parkinson's disease (PD) is unknown. Furthermore, it has been proposed that inflammation, via the gastrointestinal tract, potentially through infections, may contribute to α-synuclein pathogenesis, and thus to the risk of developing PD. Recently, many studies have shown that PD patients have an altered microbiota composition compared to healthy controls. Inflammation in the gut might drive microbiota alterations or vice versa. Many studies focused on the detection of biomarkers of the etiology, onset, or progression of PD however also report metabolites from bacterial origin. These metabolites might reflect the bacterial composition and as well play an important role in immune homeostasis, ultimately affecting the progression of PD. Besides the bacterial metabolites, pharmacological treatment of PD might play a crucial role during the progression and thus treatment of the disease on the immune system. This review aims to establish a link between the microbial composition with the observed alterations of bacterial metabolites and their impact on the immune system, which could have influential effect in onset, progression and etiology of PD.