Potential of Prebiotic Butyrogenic Fibers in Parkinson's Disease

Gut Microbiota Metabolite Messengers in Brain Function and Pathology at a View of Cell Type-Based Receptor and Enzyme Reaction

The human gastrointestinal (GI) tract houses a diverse microbial community, known as the gut microbiome comprising bacteria, viruses, fungi, and protozoa. The gut microbiome plays a crucial role in maintaining the body's equilibrium and has recently been discovered to influence the functioning of the central nervous system (CNS). The communication between the nervous system and the GI tract occurs through a two-way network called the gut-brain axis. The nervous system and the GI tract can modulate each other through activated neuronal cells, the immune system, and metabolites produced by the gut microbiome. Extensive research both in preclinical and clinical realms, has highlighted the complex relationship between the gut and diseases associated with the CNS, such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. This review aims to delineate receptor and target enzymes linked with gut microbiota metabolites and explore their specific roles within the brain, particularly their impact on CNS-related diseases.

Dietary fiber supplementation increases Drosophila melanogaster lifespan and gut microbiota diversity

Dietary fiber has been shown to have multiple health benefits, including a positive effect on longevity and the gut microbiota. In the present study, Drosophila melanogaster has been chosen as an in vivo model organism to study the health effects of dietary fiber supplementation (DFS). DFS extended the mean half-life of male and female flies, but the absolute lifespan only increased in females. To reveal the underlying mechanisms, we examined the effect of DFS on gut microbiota diversity and abundance, local gut immunity, and the brain proteome. A significant difference in the gut microbial community was observed between groups with and without fiber supplementation, which reduced the gut pathogenic bacterial load. We also observed an upregulated expression of dual oxidase and a modulated expression of Attacin and Diptericin genes in the gut of older flies, possibly delaying the gut dysbiosis connected to the age-related gut immune dysfunction. Brain proteome analysis showed that DFS led to the modulation of metabolic processes connected to mitochondrial biogenesis, the RhoV-GTPase cycle, organelle biogenesis and maintenance, membrane trafficking and vesicle-mediated transport, possibly orchestrated through a gut-brain axis interaction. Taken together, our study shows that DFS can prolong the half-life and lifespan of flies, possibly by promoting a healthier gut environment and delaying the physiological dysbiosis that characterizes the ageing process. However, the RhoV-GTPase cycle at the brain level may deserve more attention in future studies.

Gut-directed therapy in Parkinson's disease

Parkinson's disease (PD) is a common and slow-progressing neurodegenerative disorder characterized by motor and non-motor symptoms, including gastrointestinal (GI) dysfunctions. Over the last years, the microbiota-gut-brain (MGB) axis is emerging as a bacterial-neuro-immune ascending pathway that contributes to the progression of PD. Indeed, PD patients are characterized by changes in gut microbiota composition, alterations of intestinal epithelial barrier (IEB) and enteric neurogenic/inflammatory responses that, besides determining intestinal disturbances, contribute to brain pathology. In this context, despite the causal relationship between gut dysbiosis, impaired MGB axis and PD remains to be elucidated, emerging evidence shows that MGB axis modulation can represent a suitable therapeutical strategy for the treatment of PD. This review provides an overview of the available knowledge about the beneficial effects of gut-directed therapies, including dietary interventions, prebiotics, probiotics, synbiotics and fecal microbiota transplantation (FMT), in both PD patients and animal models. In this context, particular attention has been devoted to the mechanisms by which the modulation of MGB axis could halt or slow down PD pathology and, most importantly, how these approaches can be included in the clinical practice.

A comprehensive review on the pharmacological role of gut microbiome in neurodegenerative disorders: potential therapeutic targets

Neurological disorders, including Alzheimer and Parkinson's, pose significant challenges to public health due to their complex etiologies and limited treatment options. Recent advances in research have highlighted the intricate bidirectional communication between the gut microbiome and the central nervous system (CNS), revealing a potential therapeutic avenue for neurological disorders. Thus, this review aims to summarize the current understanding of the pharmacological role of gut microbiome in neurological disorders. Mounting evidence suggests that the gut microbiome plays a crucial role in modulating CNS function through various mechanisms, including the production of neurotransmitters, neuroactive metabolites, and immune system modulation. Dysbiosis, characterized by alterations in gut microbial composition and function, has been observed in many neurological disorders, indicating a potential causative or contributory role. Pharmacological interventions targeting the gut microbiome have emerged as promising therapeutic strategies for neurological disorders. Probiotics, prebiotics, antibiotics, and microbial metabolite-based interventions have shown beneficial effects in animal models and some human studies. These interventions aim to restore microbial homeostasis, enhance microbial diversity, and promote the production of beneficial metabolites. However, several challenges remain, including the need for standardized protocols, identification of specific microbial signatures associated with different neurological disorders, and understanding the precise mechanisms underlying gut-brain communication. Further research is necessary to unravel the intricate interactions between the gut microbiome and the CNS and to develop targeted pharmacological interventions for neurological disorders.

The Gut Microbiota in Parkinson Disease: Interactions with Drugs and Potential for Therapeutic Applications

The concept of a 'microbiota-gut-brain axis' has recently emerged as an important player in the pathophysiology of Parkinson disease (PD), not least because of the reciprocal interaction between gut bacteria and medications. The gut microbiota can influence levodopa kinetics, and conversely, drugs administered for PD can influence gut microbiota composition. Through a two-step enzymatic pathway, gut microbes can decarboxylate levodopa to dopamine in the small intestine and then dehydroxylate it to m-tyramine, thus reducing availability. Inhibition of bacterial decarboxylation pathways could therefore represent a strategy to increase levodopa absorption. Other bacterial perturbations common in PD, such as small intestinal bacterial overgrowth and Helicobacter pylori infection, can also modulate levodopa metabolism, and eradication therapies may improve levodopa absorption. Interventions targeting the gut microbiota offer a novel opportunity to manage disabling motor complications and dopa-unresponsive symptoms. Mediterranean diet-induced changes in gut microbiota composition might improve a range of non-motor symptoms. Prebiotics can increase levels of short-chain fatty acid-producing bacteria and decrease pro-inflammatory species, with positive effects on clinical symptoms and levodopa kinetics. Different formulations of probiotics showed beneficial outcomes on constipation, with some of them improving dopamine levels; however, the most effective dosage and duration and long-term effects of these treatments remain unknown. Data from faecal microbiota transplantation studies are preliminary, but show encouraging trends towards improvement in both motor and non-motor outcomes.This article summarises the most up-to-date knowledge in pharmacomicrobiomics in PD, and discusses how the manipulation of gut microbiota represents a potential new therapeutic avenue for PD.

Intermittent fasting associated with coconut oil (Cocos nucifera L.) alters gut-liver axis parameters in diet-induced obese rats

OBJECTIVE

The aim of this article is to investigate the effect of intermittent fasting, associated or not with coconut oil intake, on the gut-liver axis of obese rats.

METHODS

A total of 50 rats were divided into five groups: control, obese, obese with intermittent fasting, obese with intermittent fasting plus coconut oil, and obese with caloric restriction. The rats were induced to obesity with a high-sugar diet for 17 wk. The respective interventions were carried out in the last 4 wk.

RESULTS

The groups with intermittent fasting protocols had reduced total cholesterol (on average 54.31%), low-density lipoprotein (on average 53.39%), and triacylglycerols (on average 23.94%) versus the obese group; and the obese with intermittent fasting plus coconut oil group had the highest high-density lipoprotein compared with all groups. The obese with intermittent fasting plus coconut oil and obese with caloric restriction groups had lower metabolic load compared with the other groups. The obese group had high citric and succinic acid concentrations, which affected the hepatic tricarboxylic acid cycle, while all the interventions had reduced concentrations of these acids. No histologic changes were observed in the intestine or liver of the groups.

CONCLUSION

Intermittent fasting, especially when associated with coconut oil, had effects comparable with caloric restriction in modulating the parameters of the gut-liver axis.

Relationship Between Short-chain Fatty Acids and Parkinson's Disease: A Review from Pathology to Clinic

Parkinson's disease (PD) is a complicated neurodegenerative disease, characterized by the accumulation of α-synuclein (α-syn) in Lewy bodies and neurites, and massive loss of midbrain dopamine neurons. Increasing evidence suggests that gut microbiota and microbial metabolites are involved in the development of PD. Among these, short-chain fatty acids (SCFAs), the most abundant microbial metabolites, have been proven to play a key role in brain-gut communication. In this review, we analyze the role of SCFAs in the pathology of PD from multiple dimensions and summarize the alterations of SCFAs in PD patients as well as their correlation with motor and non-motor symptoms. Future research should focus on further elucidating the role of SCFAs in neuroinflammation, as well as developing novel strategies employing SCFAs and their derivatives to treat PD.

Iron toxicity, ferroptosis and microbiota in Parkinson's disease: Implications for novel targets

Parkinson's Disease (PD) is a progressive neurodegenerative disease characterized by loss of dopaminergic neurons in substantia nigra pars compacta (SNpc). Iron (Fe)-dependent programmed cell death known as ferroptosis, plays a crucial role in the etiology and progression of PD. Since SNpc is particularly vulnerable to Fe toxicity, a central role for ferroptosis in the etiology and progression of PD is envisioned. Ferroptosis, characterized by reactive oxygen species (ROS)-dependent accumulation of lipid peroxides, is tightly regulated by a variety of intracellular metabolic processes. Moreover, the recently characterized bi-directional interactions between ferroptosis and the gut microbiota, not only provides another window into the mechanistic underpinnings of PD but could also suggest novel interventions in this devastating disease. Here, following a brief discussion of PD, we focus on how our expanding knowledge of Fe-induced ferroptosis and its interaction with the gut microbiota may contribute to the pathophysiology of PD and how this knowledge may be exploited to provide novel interventions in PD.

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

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

Butyrate Protects and Synergizes with Nicotine against Iron- and Manganese-induced Toxicities in Cell Culture

Toxic exposures to heavy metals, such as iron (Fe) and manganese (Mn), can result in long-range neurological diseases and are therefore of significant environmental and medical concerns. We have previously reported that damage to neuroblastoma-derived dopaminergic cells (SH-SY5Y) by both Fe and Mn could be prevented by pre-treatment with nicotine. Moreover, butyrate, a short chain fatty acid (SCFA) provided protection against salsolinol, a selective dopaminergic toxin, in the same cell line. Here, we broadened the investigation to determine whether butyrate might also protect against Fe and/or Mn, and whether, if combined with nicotine, an additive or synergistic effect might be observed. Both butyrate and nicotine concentration-dependently blocked Fe and Mn toxicities. Ineffective concentrations of nicotine and butyrate, when combined, provided full protection against both Fe and Mn. Moreover, the effects of nicotine but not butyrate could be blocked by mecamylamine, a non-selective nicotinic antagonist. On the other hand, the effects of butyrate, but not nicotine, could be blocked by beta-hydroxy butyrate, a fatty acid-3 receptor antagonist. These results not only provide further support for neuroprotective effects of both nicotine and butyrate but also indicate distinct mechanisms of action for each one. Furthermore, potential utility of butyrate and nicotine combination against heavy metal toxicities is suggested.

Gut microbiota-derived short chain fatty acids act as mediators of the gut-brain axis targeting age-related neurodegenerative disorders: a narrative review

Neurodegenerative diseases associated with aging are often accompanied by cognitive decline and gut microbiota disorder. But the impact of gut microbiota on these cognitive disturbances remains incompletely understood. Short chain fatty acids (SCFAs) are major metabolites produced by gut microbiota during the digestion of dietary fiber, serving as an energy source for gut epithelial cells and/or circulating to other organs, such as the liver and brain, through the bloodstream. SCFAs have been shown to cross the blood-brain barrier and played crucial roles in brain metabolism, with potential implications in mediating Alzheimer's disease (AD) and Parkinson's disease (PD). However, the underlying mechanisms that SCFAs might influence psychological functioning, including affective and cognitive processes and their neural basis, have not been fully elucidated. Furthermore, the dietary sources which determine these SCFAs production was not thoroughly evaluated yet. This comprehensive review explores the production of SCFAs by gut microbiota, their transportation through the gut-brain axis, and the potential mechanisms by which they influence age-related neurodegenerative disorders. Also, the review discusses the importance of dietary fiber sources and the challenges associated with harnessing dietary-derived SCFAs as promoters of neurological health in elderly individuals. Overall, this study suggests that gut microbiota-derived SCFAs and/or dietary fibers hold promise as potential targets and strategies for addressing age-related neurodegenerative disorders.

Identification of acacia gum fermenting bacteria from pooled human feces using anaerobic enrichment culture

Commercial acacia gum (AG) used in this study is a premium-grade free-flowing powder. It is a gummy exudate composed of arabinogalactan branched polysaccharide, a biopolymer of arabinose and galactose. Also known as food additive, acacia gum (E414), which is presently marketed as a functional dietary fiber to improve overall human gut health. The health effects may be related to the luminal pH regulation from the short-chain fatty acids (SCFA) production. Studies suggested that amylolytic and butyrogenic pathways are the major factors determining the SCFA outcome of AG in the lower gut. However, the primary bacteria involved in the fermentation have not been studied. This study aimed to investigate the putative primary degraders of acacia gum in the gut ecosystem. Isolation and identification of gum-fermenting bacteria were performed through enrichment culture fermentation. The experiment was conducted in an anaerobic chamber for 144 h in three stages. The study was conducted in triplicate using an anaerobic chamber system. This culture system allows specific responses to support only bacteria that are responsible for gum fermentation among the gut microbiota. Five bacterial strains were isolated and found to be gum-fermenting bacteria. Based on the 16s RNA sequence, the isolates matched to butyrate-producing Escherichia fergusonii, ATCC 35469.

Butyrate protects and synergizes with nicotine against iron- and manganese-induced toxicities in cell culture: Implications for neurodegenerative diseases

Toxic exposures to heavy metals, such as iron (Fe) and manganese (Mn), can result in long-range neurological diseases and are therefore of significant environmental and medical concerns. We have previously reported that damage to neuroblastoma-derived dopaminergic cells (SH-SY5Y) by both Fe and Mn could be prevented by pre-treatment with nicotine. Moreover, butyrate, a short chain fatty acid (SCFA) provided protection against salsolinol, a selective dopaminergic toxin, in the same cell line. Here, we broadened the investigation to determine whether butyrate might also protect against Fe and/or Mn, and whether, if combined with nicotine, an additive or synergistic effect might be observed. Both butyrate and nicotine concentration-dependently blocked Fe and Mn toxicities. The ineffective concentrations of nicotine and butyrate, when combined, provided full protection against both Fe and Mn. Moreover, the effects of nicotine but not butyrate could be blocked by mecamylamine, a non-selective nicotinic antagonist. On the other hand, the effects of butyrate, but not nicotine, could be blocked by beta-hydroxy butyrate, a fatty acid-3 receptor antagonist. These results not only provide further support for neuroprotective effects of both nicotine and butyrate but indicate distinct mechanisms of action for each one. Furthermore, potential utility of the combination of butyrate and nicotine against heavy metal toxicities is suggested.

Parkinson's disease: Are gut microbes involved?

INTRODUCTION

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

METHOD

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

CONCLUSION

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

Dihydromyricetin Protects Against Salsolinol-Induced Toxicity in Dopaminergic Cell Line: Implication for Parkinson's Disease

Parkinson's disease (PD) is a progressive neurodegenerative disease associated with loss of dopaminergic neurons in the substantia nigra pars compacta. Although aging is the primary cause, environmental and genetic factors have also been implicated in its etiology. In fact, the sporadic nature of PD (i.e., unknown etiology) renders the uncovering of the exact pathogenic mechanism(s) or development of effective pharmacotherapies challenging. In search of novel neuroprotectants, we showed that butyrate (BUT), a short-chain fatty acid, protects against salsolinol (SALS)-induced toxicity in human neuroblastoma-derived SH-SY5Y cells, which are considered an in-vitro model of PD. Dihydromyricetin (DHM), a flavonoid derived from Asian medicinal plant, has also shown effectiveness against oxidative damage and neuroinflammation, hallmarks of neurodegenerative diseases. Here we show that pretreatment of SH-SY5Y cells with DHM concentration-dependently prevented SALS-induced toxicity and that a combination of DHM and BUT resulted in a synergistic protection. The effects of both DHM and BUT in turn could be completely blocked by flumazenil (FLU), a GABA_A antagonist acting at benzodiazepine receptor site, and by bicuculline (BIC), a GABA_A antagonist acting at orthosteric site. Beta-hydroxybutyrate (BHB), a free fatty acid 3 (FA3) receptor antagonist, also fully blocked the protective effect of DHM. BHB was shown previously to only partially block the protective effect of BUT. Thus, there are some overlaps and some distinct differences in protective mechanisms of DHM and BUT against SALS-induced toxicity. It is suggested that a combination of DHM and BUT may have therapeutic potential in PD. However, further in-vivo verifications are necessary.

Impact of caloric restriction on the gut microbiota

Caloric restriction (CR) and related time-restricted diets have been popularized as means of preventing metabolic disease while improving general well-being. However, evidence as to their long-term efficacy, adverse effects, and mechanisms of activity remains incompletely understood. The gut microbiota is modulated by such dietary approaches, yet causal evidence to its possible downstream impacts on host metabolism remains elusive. Herein, we discuss the positive and adverse influences of restrictive dietary interventions on gut microbiota composition and function, and their collective impacts on host health and disease risk. We highlight known mechanisms of microbiota influences on the host, such as modulation of bioactive metabolites, while discussing challenges in achieving mechanistic dietary-microbiota insights, including interindividual variability in dietary responses as well as other methodological and conceptual challenges. In all, causally understanding the impact of CR approaches on the gut microbiota may enable to better decode their overall influences on human physiology and disease.

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.

Gut-oriented disease modifying therapy for Parkinson's disease

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

The effects of microbiota abundance on symptom severity in Parkinson's disease: A systematic review

Introduction

Parkinson's disease (PD) is neurodegenerative disease with a multifactorial etiopathogenesis with accumulating evidence identifying microbiota as a potential factor in the earliest, prodromal phases of the disease. Previous research has already shown a significant difference between gut microbiota composition in PD patients as opposed to healthy controls, with a growing number of studies correlating gut microbiota changes with the clinical presentation of the disease in later stages, through various motor and non-motor symptoms. Our aim in this systematic review is to compose and assess current knowledge in the field and determine if the findings could influence future clinical practice as well as therapy in PD.

Methods

We have conducted a systematic review according to PRISMA guidelines through MEDLINE and Embase databases, with studies being selected for inclusion via a set inclusion and exclusion criteria.

Results

20 studies were included in this systematic review according to the selected inclusion and exclusion criteria. The search yielded 18 case control studies, 1 case study, and 1 prospective case study with no controls. The total number of PD patients encompassed in the studies cited in this review is 1,511.

Conclusion

The link between gut microbiota and neurodegeneration is a complex one and it depends on various factors. The relative abundance of various microbiota taxa in the gut has been consistently shown to have a correlation with motor and non-motor symptom severity. The answer could lie in the products of gut microbiota metabolism which have also been linked to PD. Further research is thus warranted in the field, with a focus on the metabolic function of gut microbiota in relation to motor and non-motor symptoms.

Altered gut microbiome diversity and function in patients with propionic acidemia

Propionic acidemia (PA) is an inherited metabolic disorder of propionate metabolism, where the gut microbiota may play a role in pathophysiology and therefore, represent a relevant therapeutic target. Little is known about the gut microbiota composition and activity in patients with PA. Although clinical practice varies between metabolic treatment centers, management of PA requires combined dietary and pharmaceutical treatments, both known to affect the gut microbiota. This study aimed to characterize the gut microbiota and its metabolites in fecal samples of patients with PA compared with healthy controls from the same household. Eight patients (aged 3-14y) and 8 controls (4-31y) were recruited from Center 1 (UK) and 7 patients (11-33y) and 6 controls (15-54y) from Center 2 (Austria). Stool samples were collected 4 times over 3 months, alongside data on dietary intakes and medication usage. Several microbial taxa differed between patients with PA and controls, particularly for Center 1, e.g., Proteobacteria levels were increased, whereas butyrate-producing genera, such as Roseburia and Faecalibacterium, were decreased. Most measured microbial metabolites were lower in patients with PA, and butyrate was particularly depleted in patients from Center 1. Furthermore, microbiota profile of these patients showed the lowest compositional and functional diversity, and lowest stability over 3 months. As the first study to map the gut microbiota of patients with PA, this work represents an important step forward for developing new therapeutic strategies to further improve PA clinical status. New dietary strategies should consider microbial propionate production as well as butyrate production and microbiota stability.

Beneficial effects of butyrate on brain functions: A view of epigenetic

Brain functions are influenced by the presence, activity, and metabolism of the gut microbiota through the gut-microbiota-brain (GMB) axis. The consumption of a fiber-rich diet increases the content of short-chain fatty acids (SCFAs) from bacterial fermentation in the colon. Among SCFAs, butyrate stands out because of its wide array of biological functions, such as ability to influence brain functions. Pharmacologically, sodium butyrate (NaB) regulates gene expression in the brain, where it has several beneficial effects ranging from neurodegenerative diseases to behavioral disorders through inhibitors of histone deacetylases (HDACis). In this context, we review the mechanisms of action of the two types of butyrate on brain functions, with an emphasis on the epigenetic approach. Both types of butyrate are potentially interesting for the prevention and adjuvant therapy of neurological and psychological disorders due to their neuroprotective functions. However, further studies are needed to investigate the possible neuroepigenetic effects of butyrate derived from bacterial fermentation.

Butyrate: Connecting the gut-lung axis to the management of pulmonary disorders

Short-chain fatty acids (SCFAs) are metabolites released by bacterial components of the microbiota. These molecules have a wide range of effects in the microbiota itself, but also in host cells in which they are known for contributing to the regulation of cell metabolism, barrier function, and immunological responses. Recent studies indicate that these molecules are important players in the gut-lung axis and highlight the possibility of using strategies that alter their intestinal production to prevent or treat distinct lung inflammatory diseases. Here, we review the effects of the SCFA butyrate and its derivatives in vitro and in vivo on murine models of respiratory disorders, besides discussing the potential therapeutic use of butyrate and the other SCFAs in lung diseases.

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

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

Agathobaculum butyriciproducens Shows Neuroprotective Effects in a 6-OHDA-Induced Mouse Model of Parkinson's Disease

Parkinson's disease (PD) is the second-most prevalent neurodegenerative disease and is characterized by dopaminergic neuronal death in the midbrain. Recently, the association between alterations in PD pathology and the gut microbiota has been explored. Microbiota-targeted interventions have been suggested as a novel therapeutic approach for PD. Agathobaculum butyriciproducens SR79^T (SR79) is an anaerobic bacterium. Previously, we showed that SR79 treatment induced cognitive improvement and reduced Alzheimer's disease pathologies in a mouse model. In this study, we hypothesized that SR79 treatment may have beneficial effects on PD pathology. To investigate the therapeutic effects of SR79 on PD, 6-hydroxydopamine (6-OHDA)-induced mouse models were used. D-Amphetamine sulfate (d-AMPH)-induced behavioral rotations and dopaminergic cell death were analyzed in unilateral 6-OHDA-lesioned mice. Treatment with SR79 significantly decreased ipsilateral rotations induced by d-AMPH. Moreover, SR79 treatment markedly activated the AKT/GSK3β signaling pathway in the striatum. In addition, SR79 treatment affected the Nrf2/ARE signaling pathway and its downstream target genes in the striatum of 6-OHDA-lesioned mice. Our findings suggest a protective role of SR79 in 6-OHDA-induced toxicity by regulating the AKT/Nrf2/ARE signaling pathway and astrocyte activation. Thus, SR79 may be a potential microbe-based intervention and therapeutic strategy for PD.

Microbiome-Based Therapies in Parkinson's Disease: Can Tuning the Microbiota Become a Viable Therapeutic Strategy?

Progressive neurodegenerative disorders such as Parkinson's disease (PD) have continued to baffle medical science, despite strides in the understanding of their pathology. The inability of currently available therapies to halt disease progression is a testament to an incomplete understanding of pathways crucial to disease initiation, progression and management. Science has continued to link the activities and equilibrium of the gut microbiome to the health and proper functioning of brain neurons. They also continue to stir interest in the potential applications of technologies that may shift the balance of the gut microbiome towards achieving a favourable outcome in PD management. There have been suggestions that an improved understanding of the roles of the gut microbiota is likely to lead to the emergence of an era where their manipulation becomes a recognized strategy for PD management. This review examines the current state of our journey in the quest to understand how the gut microbiota can influence several aspects of PD. We highlight the relationship between the gut microbiome/microbiota and PD pathogenesis, as well as preclinical and clinical evidence evaluating the effect of postbiotics, probiotics and prebiotics in PD management. This is with a view to ascertaining if we are at the threshold of discovering the application of a usable tool in our quest for disease modifying therapies in PD.

Evaluating Opicapone as Add-on Treatment to Levodopa/DDCI in Patients with Parkinson's Disease

COMT (catechol-O-methyltransferase) inhibitors are key therapeutic agents in the management of motor fluctuations (MF) in patients with Parkinson's disease (PD). As levodopa/DDCI add-on therapy, their main benefit lies in increasing ON-time and reducing OFF-time for PD patients in the middle stages of the disease. Two of the three available COMT inhibitors, tolcapone and entacapone, have been approved for over two decades. Opicapone, a third-generation COMT inhibitor approved in 2016, was designed with the aim of overcoming specific challenges of the earlier generation compounds, specifically hepatotoxicity and short effect duration. This review aims at highlighting the specific properties and characteristics of opicapone, namely combining efficacy with good tolerability as demonstrated in the registration studies and since then confirmed under real-world conditions. Opicapone has been shown to be effective in patients with early, as well as late motor fluctuations. Whilst patients in the earlier Hoehn and Yahr stages benefit more than patients in later stages, the incidence of dyskinesia in patients with recent onset MF is around half that of patients with more established fluctuations. With the added advantage of a once-daily administration, this particular COMT inhibitor provides a simple, yet effective therapy for patients with Parkinson's disease and MF.

Propionic acid beneficially modifies osteoporosis biomarkers in patients with multiple sclerosis

Background

The impact of the gut and its microbiota are increasingly appreciated in health and disease. Short-chain fatty acids (SCFAs) are among the main metabolites synthesized from bacterial fermentation. Recently, we showed the anti-inflammatory and potentially neuroprotective effect of propionic acid (PA) in multiple sclerosis (MS). Osteoporosis is one of the most common co-morbidities for MS patients with limited therapeutic options available. Osteoporosis is closely linked to an imbalance of cells of the immune system and an immune-mediated impact on bone structure via the gut has been shown. Interestingly, intake of SCFA leads to bone mass increase and concomitant reduction of inflammation-induced bone loss in mice.

Objective

To determine the impact of PA supplementation on markers of bone metabolism in MS patients.

Methods

We investigated the influence of 14 days supplementation with PA on bone metabolism in 20 MS patients. To this end, β-CrossLaps and osteocalcin, established markers of bone metabolism, were measured in serum before and after PA intake and correlated with phenotypic and functional immunodata.

Results

Supplementation with PA induced a significant increase in serum levels of osteocalcin, a surrogate marker for bone formation. Levels of β-CrossLaps, a marker for bone resorption, were significantly decreased after therapy. Regulatory T-cell (Treg) numbers and suppressive capacity positively correlated with serum levels of osteocalcin while Th17 cell numbers showed an inverse correlation. Our findings are in line with animal studies showing that SCFA induced increased bone formation and reduced bone resorption.

Conclusion

In addition to its immune regulatory, disease-modifying effect on MS disease course, supplementation with PA beneficially influences serum levels of β-CrossLaps and osteocalcin and may thus also protect against osteoporosis, a common co-morbidity in MS.

Therapeutic Benefits and Dietary Restrictions of Fiber Intake: A State of the Art Review

Throughout history, malnutrition and deficiency diseases have been a problem for our planet’s population. A balanced diet significantly influences everyone’s health, and fiber intake appears to play a more important role than previously thought. The natural dietary fibers are a category of carbohydrates in the constitution of plants that are not completely digested in the human intestine. High-fiber foods, such as fruits, vegetables and whole grains, have consistently been highly beneficial to health and effectively reduced the risk of disease. Although the mode of action of dietary fiber in the consumer body is not fully understood, nutritionists and health professionals unanimously recognize the therapeutic benefits. This paper presents the fiber consumption in different countries, the metabolism of fiber and the range of health benefits associated with fiber intake. In addition, the influence of fiber intake on the intestinal microbiome, metabolic diseases (obesity and diabetes), neurological aspects, cardiovascular diseases, autoimmune diseases and cancer prevention are discussed. Finally, dietary restrictions and excess fiber are addressed, which can cause episodes of diarrhea and dehydration and increase the likelihood of bloating and flatulence or even bowel obstruction. However, extensive studies are needed regarding the composition and required amount of fiber in relation to the metabolism of saprotrophic microorganisms from the enteral level and the benefits of the various pathologies with which they can be correlated.

Dual-Hit Model of Parkinson's Disease: Impact of Dysbiosis on 6-Hydroxydopamine-Insulted Mice-Neuroprotective and Anti-Inflammatory Effects of Butyrate

Recent evidence highlights Parkinson’s disease (PD) initiation in the gut as the prodromal phase of neurodegeneration. Gut impairment due to microbial dysbiosis could affect PD pathogenesis and progression. Here, we propose a two-hit model of PD through ceftriaxone (CFX)-induced dysbiosis and gut inflammation before the 6-hydroxydopamine (6-OHDA) intrastriatal injection to mimic dysfunctional gut-associated mechanisms preceding PD onset. Therefore, we showed that dysbiosis and gut damage amplified PD progression, worsening motor deficits induced by 6-OHDA up to 14 days post intrastriatal injection. This effect was accompanied by a significant increase in neuronal dopaminergic loss (reduced tyrosine hydroxylase expression and increased Bcl-2/Bax ratio). Notably, CFX pretreatment also enhanced systemic and colon inflammation of dual-hit subjected mice. The exacerbated inflammatory response ran in tandem with a worsening of colonic architecture and gut microbiota perturbation. Finally, we demonstrated the beneficial effect of post-biotic sodium butyrate in limiting at once motor deficits, neuroinflammation, and colon damage and re-shaping microbiota composition in this novel dual-hit model of PD. Taken together, the bidirectional communication of the microbiota–gut–brain axis and the recapitulation of PD prodromal/pathogenic features make this new paradigm a useful tool for testing or repurposing new multi-target compounds in the treatment of PD.

Dihydromyricetin Protects Against Ethanol-Induced Toxicity in SH-SY5Y Cell Line: Role of GABAA Receptor

Toxicity induced by binge alcohol drinking, particularly in adolescent and young adults, is of major medical and social consequence. Recently, we reported that butyrate, a short chain fatty acid, can protect against ethanol (ETOH)-induced toxicity in an in vitro model. In this study, we sought to evaluate the potential effectiveness of dihydromyricetin (DHM), a natural bioactive flavonoid, alone or in combination with butyrate in the same model. Exposure of SH-SY5Y cells for 24 h to 500 mM ETOH resulted in approximately 40% reduction in cell viability, which was completely prevented by 0.1 μM DHM. Combinations of DHM and butyrate provided synergistic protection against alcohol toxicity. Whereas butyrate effect was shown to be mediated primarily through fatty acid receptor 3 activation, DHM protection appears to be mediated primarily via benzodiazepine receptor site of GABA_A receptor. This is based on the finding that DHM's effect could be completely prevented by pretreatment with flumazenil, a selective antagonist at this site, but not by bicuculline, a selective antagonist at the actual GABA_A receptor binding site. These findings suggest potential utility of DHM alone or in combination with butyrate against ETOH-induced toxicity.

Metabolomic Fingerprint of Behavioral Changes in Response to Full-Spectrum Cannabis Extracts

Numerous existing full-spectrum cannabis extract products have been used in clinical trials for the treatment of various diseases. Despite their efficacy, the clinical use of some of these full-spectrum cannabis extracts is limited by behavioral side effects such as cognitive dysfunction and impaired motor skills. To better understand what constitutes cannabis-induced behavioral effects, our objective was to identify a novel panel of blood-based metabolites that are predictive, diagnostic, and/or prognostic of behavioral effects.

At 8 weeks of age, male rats were randomly assigned to groups and were gavage fed with full-spectrum cannabis extract (tetrahydrocannabinol/cannabidiol (THC/CBD) along with all other cannabis compounds, 15 mg/kg), broad-spectrum cannabis extract (CBD along with all other cannabis compounds, 15 mg/kg), or vehicle oil. Four hours after being gavage fed, behavioral assessments were determined using the open field test and the elevated plus maze. Following these assessments, serum was collected from all rats and the serum metabolites were identified and quantified by LC–MS/MS and 1H NMR spectroscopy.

We found that only rats treated with full-spectrum cannabis extract exhibited behavioral changes. Compared to vehicle-treated and broad-spectrum extract–treated rats, full-spectrum extract–treated rats demonstrated higher serum concentrations of the amino acid phenylalanine and long-chain acylcarnitines, as well as lower serum concentrations of butyric acid and lysophosphatidylcholines. This unique metabolomic fingerprint in response to cannabis extract administration is linked to behavioral effects and may represent a biomarker profile of cannabis-induced behavioral changes. If validated, this work may allow a metabolomics-based decision tree that would aid in the rapid diagnosis of cannabis-induced behavioral changes including cognitive impairment.

The Mediterranean Diet as a Source of Bioactive Molecules with Cannabinomimetic Activity in Prevention and Therapy Strategy

The endocannabinoid system is a complex lipid signaling network that has evolved to be a key regulator of pro-homeostatic pathways for the organism. Its involvement in numerous processes has rendered it a very suitable target for pharmacological studies regarding metabolic syndrome, obesity and other lifestyle-related diseases. Cannabinomimetic molecules have been found in a large variety of foods, most of which are normally present in the Mediterranean diet. The majority of these compounds belong to the terpene and polyphenol classes. While it is known that they do not necessarily act directly on the cannabinoid receptors CB1 and CB2, their ability to regulate their expression levels has already been shown in some disease-related models, as well as their ability to modulate the activity of other components of the system. In this review, evidence was gathered to support the idea that phytocannabinoid dietary intake may indeed be a viable strategy for disease prevention and may be helpful in maintaining the health status. In an era where personalized nutrition is becoming more and more a reality, having new therapeutic targets could become an important resource.

Morais L. OUP accepted manuscript

Recent research has been uncovering the role of the gut microbiota for brain health and disease. These studies highlight the role of gut microbiota on regulating brain function and behavior through immune, metabolic, and neuronal pathways. In this review we provide an overview of the gut microbiota axis pathways to lay the groundwork for upcoming sessions on the links between the gut microbiota and neurogenerative disorders. We also discuss how the gut microbiota may act as an intermediate factor between the host and the environment to mediate disease onset and neuropathology. Based on the current literature, we further examine the potential for different microbiota-based therapeutic strategies to prevent, to modify, or to halt the progress of neurodegeneration.

Disease modifying therapies III: Novel targets

Despite significant research advances, treatment of Parkinson's disease (PD) remains confined to symptomatic therapies. Approaches aiming to halt or reverse disease progression remain an important but unmet goal. A growing understanding of disease pathogenesis and the identification of novel pathways contributing to initiation of neurodegeneration and subsequent progression has highlighted a range of potential novel targets for intervention that may influence the rate of progression of the disease process. Exploiting techniques to stratify patients according to these targets alongside using them as biomarkers to measure target engagement will likely improve patient selection and preliminary outcome measurements in clinical trials. In this review, we summarize a number of PD-related mechanisms that have recently gained interest such as neuroinflammation, lysosomal dysfunction and insulin resistance, while also exploring the potential for targeting peripheral interfaces such as the gastrointestinal tract and its ecosystem to achieve disease modification. We explore the rationale for these approaches based on preclinical studies, while also highlighting the status of relevant clinical trials as well as the promising role biomarkers may play in current and future studies.

Sodium butyrate attenuates rotenone-induced toxicity by activation of autophagy through epigenetically regulating PGC-1α expression in PC12 cells

Short-chain fatty acids (SCFAs) are considered the key molecular link between gut microbiota and pathogenesis of Parkinson's disease (PD). However, the role of SCFAs in PD pathogenesis is controversial. Autophagy is important for the degradation of α-synuclein, which is critical to the development of PD. However, whether SCFAs can regulate autophagy in PD remains unknown. We aimed to investigate the role of SCFAs and explore the potential mechanisms in rat dopaminergic PC12 cells treated with rotenone. Expression levels of α-synuclein, peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) and microtubule-associated protein 1 light chain 3 beta (LC3B)-II were detected by Western blot. Histone acetylation levels at PGC-1α promoter region were measured using chromatin immunoprecipitation-quantitative polymerase chain reaction (ChIP-qPCR). Among the three SCFAs, sodium butyrate (NaB) protected against rotenone-induced toxicity. NaB activated autophagy pathway and reduced rotenone-induced α-synuclein expression through the activation of autophagy. Notably, NaB activated autophagy pathway through upregulating PGC-1α expression. More importantly, NaB promoted the levels of histone 3 lysine 9 acetylation (H3K9Ac) and histone 3 lysine 27 acetylation (H3K27Ac) at PGC-1α promoter region, indicating that NaB promotes PGC-1α expression via histone acetylation modification. In conclusion, NaB can protect against rotenone-induced toxicity through activation of the autophagy pathway by upregulating PGC-1α expression via epigenetic modification.

Sodium Butyrate Protects Against Ethanol-Induced Toxicity in SH-SY5Y Cell Line

Alcohol use disorder (AUD), brought about by excessive alcohol use, is associated with damages to several organs including the brain. Chronic excessive use of alcohol can compromise intestinal integrity, leading to changes in gut microbiota (GM) composition known as dysbiosis. Dysbiosis, by disruption of the gut-brain axis (GBA), further exacerbates the deleterious effects of alcohol. One of the fermentation by-products of GM is butyrate (BUT), a short-chain fatty acid (SCFA) that plays an important role in maintaining homeostasis of the GBA. Alcohol metabolism results in formation of acetaldehyde, a highly reactive compound that reacts with dopamine in the brain to form toxic adducts such as salsolinol. Recent studies indicate potential neuro-protective effects of BUT against various toxicants including salsolinol. Here, we sought to investigate whether BUT can also protect against alcohol toxicity. Pretreatment of neuroblastoma-derived SH-SY5Y cells with 500 mM ethanol (ETOH) for 24 h resulted in approximately 40% reduction in cell viability, which was totally blocked by 10 µM of either BUT or AR 420,626 (AR), a selective fatty acid 3 receptor (FA3R) agonist. The neuro-protective effects of both BUT and AR were significantly (80%) attenuated by beta-hydroxy butyrate (BHB), a selective FA3R antagonist. Interestingly, combination of BUT and AR resulted in synergistic protection against ETOH, which was totally blocked by BHB. These findings suggest potential utility of butyrate and/or FA3R agonists against ETOH-induced toxicity.

Effects of konjac glucomannan with different molecular weights on gut microflora with antibiotic perturbance in in vitro fecal fermentation

This study investigated the effect of konjac glucomannan (KGM) of different molecular weight on fecal microflora against antibiotic disturbance. KGM (~1.8 × 10⁷ Da) was partially hydrolysed with trifluoroacetic acid (TFA) for 10 and 60 min to KGM1 (~2.1 × 10⁴ Da) and KGM2 (7413 Da), respectively. The acid treatment caused significant reduction of intrinsic viscosity, average molecular weight (MW) and particle size of KGM, but brought limited change to the molecular structure. Low-MW KGM2 showed the most significant effect on fecal microflora in the presence of two common antibiotics (ampicillin and clindamycin), by increasing the relative abundance of Bifidobacteriaceae while decreasing the proportion of Enterobacteriaceae. Additionally, both the native and acid-treated KGM counteracted the adverse influence of antibiotics on the production of short chain fatty acids. The results have demonstrated the effect of KGM on gut microbiota with antibiotic disturbance.

Bioderived materials that disarm the gut mucosal immune system: Potential lessons from commensal microbiota

Over the course of evolution, mammals and gut commensal microbes have adapted to coexist with each other. This homeostatic coexistence is dependent on an intricate balance between tolerogenic and inflammatory responses directed towards beneficial, commensal microbes and pathogenic intruders, respectively. Immune tolerance towards the gut microflora is largely sustained by immunomodulatory molecules produced by the commensals, which protect the bacteria from immune advances and maintain the gut's unique tolerogenic microenvironment, as well as systemic homeostasis. The identification and characterization of commensal-derived, tolerogenic molecules could lead to their utilization in biomaterials-inspired delivery schemes involving nano/microparticles or hydrogels, and potentially lead to the next generation of commensal-derived therapeutics. Moreover, gut-on-chip technologies could augment the discovery and characterization of influential commensals by providing realistic in vitro models conducive to finicky microbes. In this review, we provide an overview of the gut immune system, describe its intricate relationships with the microflora and identify major genera involved in maintaining tolerogenic responses and peripheral homeostasis. More relevant to biomaterials, we discuss commensal-derived molecules that are known to interface with immune cells and discuss potential strategies for their incorporation into biomaterial-based strategies aimed at culling inflammatory diseases. We hope this review will bridge the current findings in gut immunology, microbiology and biomaterials and spark further investigation into this emerging field. STATEMENT OF SIGNIFICANCE: Despite its tremendous potential to culminate into revolutionary therapeutics, the synergy between immunology, microbiology, and biomaterials has only been explored at a superficial level. Strategic incorporation of biomaterial-based technologies may be necessary to fully characterize and capitalize on the rapidly growing repertoire of immunomodulatory molecules derived from commensal microbes. Bioengineers may be able to combine state-of-the-art delivery platforms with immunomodulatory cues from commensals to provide a more holistic approach to combating inflammatory disease. This interdisciplinary approach could potentiate a neoteric field of research - "commensal-inspired" therapeutics with the promise of revolutionizing the treatment of inflammatory disease.

Gut dysbiosis, defective autophagy and altered immune responses in neurodegenerative diseases: Tales of a vicious cycle

The human microbiota comprises trillions of symbiotic microorganisms and is involved in regulating gastrointestinal (GI), immune, nervous system and metabolic homeostasis. Recent observations suggest a bidirectional communication between the gut microbiota and the brain via immune, circulatory and neural pathways, termed the Gut-Brain Axis (GBA). Alterations in gut microbiota composition, such as seen with an increased number of pathobionts and a decreased number of symbionts, termed gut dysbiosis or microbial intestinal dysbiosis, plays a prominent role in the pathogenesis of central nervous system (CNS)-related disorders. Clinical reports confirm that GI symptoms often precede neurological symptoms several years before the development of neurodegenerative diseases (NDDs). Pathologically, gut dysbiosis disrupts the integrity of the intestinal barrier leading to ingress of pathobionts and toxic metabolites into the systemic circulation causing GBA dysregulation. Subsequently, chronic neuroinflammation via dysregulated immune activation triggers the accumulation of neurotoxic misfolded proteins in and around CNS cells resulting in neuronal death. Emerging evidence links gut dysbiosis to the aggravation and/or spread of proteinopathies from the peripheral nervous system to the CNS and defective autophagy-mediated proteinopathies. This review summarizes the current understanding of the role of gut microbiota in NDDs, and highlights a vicious cycle of gut dysbiosis, immune-mediated chronic neuroinflammation, impaired autophagy and proteinopathies, which contributes to the development of neurodegeneration in Alzheimer's disease, Parkinson's disease, Huntington's disease, multiple sclerosis, amyotrophic lateral sclerosis and frontotemporal lobar degeneration. We also discuss novel therapeutic strategies targeting the modulation of gut dysbiosis through prebiotics, probiotics, synbiotics or dietary interventions, and faecal microbial transplantation (FMT) in the management of NDDs.

The Relationship Between the Gut Microbiome and Neurodegenerative Diseases

Many recent studies have shown that the gut microbiome plays important roles in human physiology and pathology. Also, microbiome-based therapies have been used to improve health status and treat diseases. In addition, aging and neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease, have become topics of intense interest in biomedical research. Several researchers have explored the links between these topics to study the potential pathogenic or therapeutic effects of intestinal microbiota in disease. But the exact relationship between neurodegenerative diseases and gut microbiota remains unclear. As technology advances, new techniques for studying the microbiome will be developed and refined, and the relationship between diseases and gut microbiota will be revealed. This article summarizes the known interactions between the gut microbiome and neurodegenerative diseases, highlighting assay techniques for the gut microbiome, and we also discuss the potential therapeutic role of microbiome-based therapies in diseases.

Novel Pharmacotherapies in Parkinson's Disease

Parkinson’s disease (PD), an age-related progressive neurodegenerative condition, is associated with loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc), which results in motor deficits characterized by the following: akinesia, rigidity, resting tremor, and postural instability, as well as nonmotor symptoms such as emotional changes, particularly depression, cognitive impairment, gastrointestinal, and autonomic dysfunction. The most common treatment for PD is focused on dopamine (DA) replacement (e.g., levodopa = L-Dopa), which unfortunately losses its efficacy over months or years and can induce severe dyskinesia. Hence, more efficacious interventions without such adverse effects are urgently needed. In this review, following a general description of PD, potential novel therapeutic interventions for this devastating disease are examined. Specifically, the focus is on nicotine and nicotinic cholinergic system, as well as butyrate, a short chain fatty acid (SCFA), and fatty acid receptors.

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.

The emerging role of probiotics in neurodegenerative diseases: new hope for Parkinson's disease?

Neurodegenerative disease etiology is still unclear, but different contributing factors, such as lifestyle and genetic factors are involved. Altered components of the gut could play a key role in the gut-brain axis, which is a bidirectional system between the central nervous system and the enteric nervous system. Variations in the composition of the gut microbiota and its function between healthy people and patients have been reported for a variety of human disorders comprising metabolic, autoimmune, cancer, and, notably, neurodegenerative disorders. Diet can alter the microbiota composition, affecting the gut-brain axis function. Different nutraceutical interventions have been devoted to normalizing gut microbiome dysbiosis and to improving biological outcomes in neurological conditions, including the use of probiotics. Preclinical and clinical investigations discussed in this review strengthen the correlation between intestinal microbiota and brain and the concept that modifying the microbiome composition may improve brain neurochemistry, modulating different pathways. This review will discuss the potential use of probiotics for Parkinson's disease prevention or treatment or as adjuvant therapy, confirming that gut microbiota modulation influences different pro-survival pathways. Future investigations in Parkinson's disease should consider the role of the gut-brain axis and additional comprehension of the underlying mechanisms is extremely necessary.

New Avenues for Parkinson's Disease Therapeutics: Disease-Modifying Strategies Based on the Gut Microbiota

Parkinson's disease (PD) is a multifactorial neurodegenerative disorder that currently affects 1% of the population over the age of 60 years, and for which no disease-modifying treatments exist. Neurodegeneration and neuropathology in different brain areas are manifested as both motor and non-motor symptoms in patients. Recent interest in the gut-brain axis has led to increasing research into the gut microbiota changes in PD patients and their impact on disease pathophysiology. As evidence is piling up on the effects of gut microbiota in disease development and progression, another front of action has opened up in relation to the potential usage of microbiota-based therapeutic strategies in treating gastrointestinal alterations and possibly also motor symptoms in PD. This review provides status on the different strategies that are in the front line (i.e., antibiotics; probiotics; prebiotics; synbiotics; dietary interventions; fecal microbiota transplantation, live biotherapeutic products), and discusses the opportunities and challenges the field of microbiome research in PD is facing.

The Gut-Brain Axis: Two Ways Signaling in Parkinson's Disease

Parkinson's disease (PD) is a chronic, progressive and second most prevalent neurological disorder affecting the motor system. Cardinal motor impairment and α-synucleinopathy are the characteristic features of PD. Recently, it has been identified that the gut-brain axis is substantially regulated by the gut microbiome (GM) through an immunological, neuroendocrine, and neural mechanism. However, disturbance in the gut-microbiome-brain axis in PD might proceed to gastrointestinal manifestations intermittently leading to the motor system and the PD pathogenesis itself. The gut microbial toxins may induce the production of α-synuclein (α-syn) aggregates in the enteric nervous system (ENS), which may proliferate and propagate in a prion-like-manner through the vagus nerve to the central nervous system (CNS); supporting the hypothesis that, GM might play a pivotal role in PD pathogenesis. Overstimulated innate immune system due to intestinal bacterial overgrowth or gut dysbiosis and the enhanced intestinal permeability may persuade systemic inflammation, while the activation of enteric glial cells and enteric neurons may contribute to α-synucleinopathy. Gut microbiota can bear a significant impact on neurological outcomes such as learning, memory and cognition. In this review paper, we summarize how the alterations in gut microbiota and ENS inflammation are associated with PD pathogenesis. The evidence supporting the causative role played by gut-associated dysbiosis and microbial byproducts, in the onset of PD is also discussed. We have highlighted the landmark discoveries in the field of PD particularly focusing on the gut-brain axis. A better comprehension of the interaction between the gut-brain axis, gut microbiota, and PD can usher in novel therapeutic and diagnostic approaches.

Diet, Microbiota and Brain Health: Unraveling the Network Intersecting Metabolism and Neurodegeneration

Increasing evidence gives support for the idea that extra-neuronal factors may affect brain physiology and its predisposition to neurodegenerative diseases. Epidemiological and experimental studies show that nutrition and metabolic disorders such as obesity and type 2 diabetes increase the risk of Alzheimer's and Parkinson's diseases after midlife, while the relationship with amyotrophic lateral sclerosis is uncertain, but suggests a protective effect of features of metabolic syndrome. The microbiota has recently emerged as a novel factor engaging strong interactions with neurons and glia, deeply affecting their function and behavior in these diseases. In particular, recent evidence suggested that gut microbes are involved in the seeding of prion-like proteins and their spreading to the central nervous system. Here, we present a comprehensive review of the impact of metabolism, diet and microbiota in neurodegeneration, by affecting simultaneously several aspects of health regarding energy metabolism, immune system and neuronal function. Advancing technologies may allow researchers in the future to improve investigations in these fields, allowing the buildup of population-based preventive interventions and development of targeted therapeutics to halt progressive neurologic disability.

Changes in Gastrointestinal Microbiome Composition in PD: A Pivotal Role of Covariates

Altered gut microbiota may trigger or accelerate alpha-synuclein aggregation in the enteric nervous system in Parkinson's disease (PD). While several previous studies observed gut microbiota alterations in PD, findings like diversity indices, and altered bacterial taxa itself show a considerable heterogeneity across studies. We recruited 179 participants, of whom 101 fulfilled stringent inclusion criteria. Subsequently, the composition of the gut microbiota in 71 PD patients and 30 healthy controls was analyzed, sequencing V3–V4 regions of the bacterial 16S ribosomal RNA gene in fecal samples. Our goal was (1) to evaluate whether gut microbiota are altered in a southern German PD cohort, (2) to delineate the influence of disease duration, stage, and motor impairment, and (3) to investigate the influence of PD associated covariates like constipation and coffee consumption. Aiming to control for a large variety of covariates, strict inclusion criteria were applied. Finally, propensity score matching was performed to correct for, and to delineate the effect of remaining covariates (non-motor symptom (NMS) burden, constipation, and coffee consumption) on microbiota composition. Prior to matching altered abundances of distinct bacterial classes, orders, families, and genera were observed. Both, disease duration, and stage influenced microbiome composition. Interestingly, levodopa equivalent dose influenced the correlation of taxa with disease duration, while motor impairment did not. Applying different statistical tests, and after propensity score matching to control for NMS burden, constipation and coffee consumption, Faecalibacterium and Ruminococcus were most consistently reduced in PD compared to controls. Taken together, similar to previous studies, alterations of several taxa were observed in PD. Yet, further controlling for PD associated covariates such as constipation and coffee consumption revealed a pivotal role of these covariates. Our data highlight the impact of these PD associated covariates on microbiota composition in PD. This suggests that altered microbiota may mediate the protective effect of i.e., coffee consumption and the negative effect of constipation in PD.

Faecal Transplantation, Pro- and Prebiotics in Parkinson's Disease; Hope or Hype?

Abstract Faecal microbiome transplantation (FMT) is an attractive technique, because the administration is relatively simple and in general has a mild adverse effect pattern. Moreover, FMT consists of a broad mixture, which could be beneficial, because at this moment it is not known what type of changes in the microbiome are needed. However, except from a few cases no clinical data in Parkinson’s disease (PD) is available yet. There is some indication that FMT might be beneficial in severe constipated PD patients, but the clinical data to support this are very scarce. So, actually there are no good data in the public domain to support FMT at this moment in PD patients. FMT at this moment is a black box with too many unanswered questions, also with respect to safety concerns. Only the administration of species of Lactobacillus and Bifidobacterium over a time period of four to twelve weeks has repeatedly proven to be effective in treating constipation in PD. Also, no solid clinical data are available about the possible effects of probiotic treatment on motor symptoms or progression of PD. Therefore, also probiotic treatments in PD should wait until better clinical data become available, in order to select the right target populations and to have good estimates of the clinical effects to be expected.

Polymannuronic acid prevents dopaminergic neuronal loss via brain-gut-microbiota axis in Parkinson's disease model

The study aims to investigate the potentially neuroprotective effects and underlying mechanisms for brown seaweed polysaccharide of polymannuronic acid (PM) against Parkinson's disease (PD) pathogenesis. PD model mice were pretreated with PM via oral gavage once per day for 4 weeks and the preventative effects of PM against neuronal loss together with its modulation on brain-gut-microbiota axis were systematically explored. The results showed PM administration improved motor functions by preventing dopaminergic neuronal loss in the substantia nigra pars compacta (SNpc) and enhanced contents of striatal homovanillic acid (HVA), serotonin (5-HT), 5-hydroxyindole acetic acid (5-HIAA) and γ-aminobutyric acid (GABA) in PD mice. PM significantly alleviated inflammation in gut, brain and systemic circulation as shown by reduced levels or expressions of pro-inflammatory cytokines concurrently and inhibited mitogen-activated protein kinases (MAPK) signaling pathway in mice colon. Meanwhile, PM greatly improved integrity of intestinal barrier and blood brain barrier (BBB) as indicated by increased expressions of tight junction associated proteins in both mice colon and SNpc. Further studies indicated PM treatment resulted in changes of gut microbial compositions, together with great alterations of digestion and metabolism of dietary proteins and fats, which led to surge increase of fecal short chain fatty acids (SCFAs) in the colon of PD mice. In conclusion, pre-administration of PM could provide neuroprotective effects against PD pathogenesis by suppressing inflammation in gut, brain and systemic circulation, and by improving integrity of intestinal barrier and BBB. PM might modulate brain-gut-microbiota axis, at least in part, via gut microbiota derived SCFAs as mediators.