Gut-Brain Axis: Potential Factors Involved in the Pathogenesis of Parkinson's Disease

Gluten and its relationship with inflammation and Parkinson's Disease: A literature review

Parkinson's Disease is a neurodegenerative central nervous system (CNS) disease that primarily affects the dopaminergic cells of the Substantia Nigra in the midbrain and causes a diverse array of symptoms, including dystonia, a loss of balance, difficulty initiating movements, akinesia, muscle spasms, and tremors. It has long been known that environmental and commercial compounds are linked to an increased risk of Parkinson's Disease. Of importance, gluten, a complex polysaccharide, has been hypothesized to cause some of the symptoms related to Parkinson's Disease. It is hypothesized that gluten causes a chronic inflammatory state which may lead to plaque formation and neuronal cell death in the substantia nigra, alongside the symptoms of Parkinson's Disease. This literature review hopes to explore the relationship gluten has as an inflammatory molecule and its role in the production and prolongation of the disease processes in Parkinson's Disease.

Water extract of ginseng alleviates parkinsonism in MPTP-induced Parkinson's disease mice

In this study, we investigated the neuroprotective effect of a water extract of ginseng (WEG) obtained via low-temperature extraction of the brain of mice with Parkinson's disease (PD) and the ameliorative effect on the damaged intestinal system for the treatment of dyskinesia in PD mice. MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) was injected intraperitoneally into male C57BL/6 mice to establish a PD model, and WEG was given via oral gavage. The results indicated that WEG could protect the damaged neuronal cells of the mice brain, inhibit the aggregation of α-synuclein (α-Syn) in the brain, and increase the positive expression rate of tyrosine hydroxylase (TH). WEG significantly improved intestinal damage and regulated intestinal disorders (P<0.05). WEG intervention increased the levels of beneficial bacteria, such as Lactobacillus, and normalized the abundance and diversity of colonies in the intestine of mice. Our results suggested that WEG protected neurons in the brain of PD mice via inhibiting the aggregation of α-Syn in the brain and increasing the positive expression level of TH in the brain. WEG regulated the gut microbiota of mice, improved the behavioral disorders of PD mice, and offered some therapeutic effects on PD mice.

Cold-pressed perilla seed oil: Investigating its protective influence on the gut-brain axis in mice with rotenone-induced Parkinson's disease

Perilla seed oil, derived from a regional plant native to northern Thailand, undergoes cold-pressing to analyze its bioactive components, notably alpha-linolenic acid (ALA). ALA, constituting approximately 61% of the oil, serves as a precursor for therapeutic omega-3 fatty acids, EPA and DHA, with neurodegenerative disease benefits and anti-inflammatory responses. This study administered different concentrations of perilla seed oil to male C57BL/6 mice, categorized as low dose (LP 5% w/w), middle dose (MP 10% w/w), and high dose (HP 20% w/w), along with a fish oil (FP 10% w/w) diet. An experimental group received soybean oil (5% w/w). Over 42 days, these diets were administered while inducing Parkinson's disease (PD) with rotenone injections. Mice on a high perilla seed oil dose exhibited decreased Cox-2 expression in the colon, suppressed Iba-1 microglia activation, reduced alpha-synuclein accumulation in the colon and hippocampus, prevented dopaminergic cell death in the substantia nigra, and improved motor and non-motor symptoms. Mice on a middle dose showed maintenance of diverse gut microbiota, with an increased abundance of short-chain fatty acid (SCFA)-producing bacteria (Bifidobacteria, Lactobacillus, and Faecalibacteria). A reduction in bacteria correlated with PD (Turicibacter, Ruminococcus, and Akkermansia) was observed. Results suggest the potential therapeutic efficacy of high perilla seed oil doses in mitigating both intestinal and neurological aspects linked to the gut-brain axis in PD.

Neuromodulation and the Gut-Brain Axis: Therapeutic Mechanisms and Implications for Gastrointestinal and Neurological Disorders

The gut-brain axis (GBA) represents a complex, bidirectional communication network that intricately connects the gastrointestinal tract with the central nervous system (CNS). Understanding and intervening in this axis opens a pathway for therapeutic advancements for neurological and gastrointestinal diseases where the GBA has been proposed to play a role in the pathophysiology. In light of this, the current review assesses the effectiveness of neuromodulation techniques in treating neurological and gastrointestinal disorders by modulating the GBA, involving key elements such as gut microbiota, neurotrophic factors, and proinflammatory cytokines. Through a comprehensive literature review encompassing PubMed, Google Scholar, Web of Science, and the Cochrane Library, this research highlights the role played by the GBA in neurological and gastrointestinal diseases, in addition to the impact of neuromodulation on the management of these conditions which include both gastrointestinal (irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), and gastroesophageal reflux disease (GERD)) and neurological disorders (Parkinson's disease (PD), Alzheimer's disease (AD), autism spectrum disorder (ASD), and neuropsychiatric disorders). Despite existing challenges, the ability of neuromodulation to adjust disrupted neural pathways, alleviate pain, and mitigate inflammation is significant in improving the quality of life for patients, thereby offering exciting prospects for future advancements in patient care.

From the Gut to the Brain: Is Microbiota a New Paradigm in Parkinson's Disease Treatment?

Parkinson's disease (PD) is recognized as the second most prevalent primary chronic neurodegenerative disorder of the central nervous system. Clinically, PD is characterized as a movement disorder, exhibiting an incidence and mortality rate that is increasing faster than any other neurological condition. In recent years, there has been a growing interest concerning the role of the gut microbiota in the etiology and pathophysiology of PD. The establishment of a brain-gut microbiota axis is now real, with evidence denoting a bidirectional communication between the brain and the gut microbiota through metabolic, immune, neuronal, and endocrine mechanisms and pathways. Among these, the vagus nerve represents the most direct form of communication between the brain and the gut. Given the potential interactions between bacteria and drugs, it has been observed that the therapies for PD can have an impact on the composition of the microbiota. Therefore, in the scope of the present review, we will discuss the current understanding of gut microbiota on PD and whether this may be a new paradigm for treating this devastating disease.

Analyzing the bibliometrics of brain-gut axis and Parkinson's disease

Background

Parkinson's disease (PD), characterized by the loss of dopaminergic neurons, is a progressive neurodegenerative disorder. Recent research has revealed a significant connection between gut microbiota and PD. To gain insight into research interests, disciplinary contexts, and potential future directions, a comprehensive bibliometric analysis was conducted on the brain-gut axis and PD literature published between 2014 and 2023.

Methods

Relevant literature records were gathered from the Web of Science Core Collection on August 11, 2023. The data were then analyzed by Biblioshiny R packages and VOSviewer (version 1.6.19).

Results

The dataset revealed an upward trend in annual scientific publications on the brain-gut axis and PD, with an annual growth rate of 50.24%. China, the United States, and Italy were the top three most productive countries/regions. The journal "International Journal Of Molecular Sciences" published the most articles, while "Movement Disorders" received the highest number of citations. Professor Keshavarzian A emerged as the most prolific author, while Professor Scheperjans F held the highest h-index. Keyword analysis highlighted "alpha-synuclein" as the most frequent term, with "mouse model," "inflammation," and "risk" as emerging research topics. Additionally, "central nervous system" and "intestinal bacterial overgrowth" attracted increasing attention.

Conclusion

This study examined current trends and hotspots in the bibliometric landscape of the brain-gut axis and PD research. Future research directions should explore the functional and metabolic activities of gut microbiota. Additionally, transitioning from observational to interventional study designs offers the potential for personalized interventions and disease prediction. These findings can guide researchers in navigating the latest developments and shaping the future directions of this field.

Microbiota, Tryptophan and Aryl Hydrocarbon Receptors as the Target Triad in Parkinson's Disease-A Narrative Review

In the era of a steadily increasing lifespan, neurodegenerative diseases among the elderly present a significant therapeutic and socio-economic challenge. A properly balanced diet and microbiome diversity have been receiving increasing attention as targets for therapeutic interventions in neurodegeneration. Microbiota may affect cognitive function, neuronal survival and death, and gut dysbiosis was identified in Parkinson's disease (PD). Tryptophan (Trp), an essential amino acid, is degraded by microbiota and hosts numerous compounds with immune- and neuromodulating properties. This broad narrative review presents data supporting the concept that microbiota, the Trp-kynurenine (KYN) pathway and aryl hydrocarbon receptors (AhRs) form a triad involved in PD. A disturbed gut-brain axis allows the bidirectional spread of pro-inflammatory molecules and α-synuclein, which may contribute to the development/progression of the disease. We suggest that the peripheral levels of kynurenines and AhR ligands are strongly linked to the Trp metabolism in the gut and should be studied together with the composition of the microbiota. Such an approach can clearly delineate the sub-populations of PD patients manifesting with a disturbed microbiota-Trp-KYN-brain triad, who would benefit from modifications in the Trp metabolism. Analyses of the microbiome, Trp-KYN pathway metabolites and AhR signaling may shed light on the mechanisms of intestinal distress and identify new targets for the diagnosis and treatment in early-stage PD. Therapeutic interventions based on the combination of a well-defined food regimen, Trp and probiotics seem of potential benefit and require further experimental and clinical research.

Insights into Antimicrobial and Anti-Inflammatory Applications of Plant Bioactive Compounds

Plants have long been thought to contribute to health promotion due to their fiber and phenolic content, as well as their inherent biological potential. The bioactive derivatives of medicinal plants are a valuable resource in the fight against serious diseases all around the world. The present review focuses on the current state of knowledge on the usage and medicinal applications of plant bioactives. Issues concerning the effect of aromatic plant derivatives on human gut microbiota and their antimicrobial and anti-inflammatory potentials are discussed and worth further exploring.

Role of enteric glia and microbiota-gut-brain axis in parkinson disease pathogenesis

The microbiota-gut-brain axis or simple gut-brain axis (GBA) is a complex and interactive bidirectional communication network linking the gut to the brain. Alterations in the composition of the gut microbiome have been linked to GBA dysfunction, central nervous system (CNS) inflammation, and dopaminergic degeneration, as those occurring in Parkinson's disease (PD). Besides inflammation, the activation of brain microglia is known to play a central role in the damage of dopaminergic neurons. Inflammation is attributed to the toxic effect of aggregated α-synuclein, in the brain of PD patients. It has been suggested that the α-synuclein misfolding might begin in the gut and spread "prion-like", via the vagus nerve into the lower brainstem and ultimately to the midbrain, known as the Braak hypothesis. In this review, we discuss how the microbiota-gut-brain axis and environmental influences interact with the immune system to promote a pro-inflammatory state that is involved in the initiation and progression of misfolded α-synuclein proteins and the beginning of the early non-motor symptoms of PD. Furthermore, we describe a speculative bidirectional model that explains how the enteric glia is involved in the initiation and spreading of inflammation, epithelial barrier disruption, and α-synuclein misfolding, finally reaching the central nervous system and contributing to neuroinflammatory processes involved with the initial non-motor symptoms of PD.

Amyloid Protein Cross-Seeding Provides a New Perspective on Multiple Diseases In Vivo

Amyloid protein cross-seeding is a peculiar phenomenon of cross-spreading among different diseases. Unlike traditional infectious ones, diseases caused by amyloid protein cross-seeding are spread by misfolded proteins instead of pathogens. As a consequence of the interactions among misfolded heterologous proteins or polypeptides, amyloid protein cross-seeding is considered to be the crucial cause of overlapping pathological transmission between various protein misfolding disorders (PMDs) in multiple tissues and cells. Here, we briefly review the phenomenon of cross-seeding among amyloid proteins. As an interesting example worth mentioning, the potential links between the novel coronavirus pneumonia (COVID-19) and some neurodegenerative diseases might be related to the amyloid protein cross-seeding, thus may cause an undesirable trend in the incidence of PMDs around the world. We then summarize the theoretical models as well as the experimental techniques for studying amyloid protein cross-seeding. Finally, we conclude with an outlook on the challenges and opportunities for basic research in this field. Cross-seeding of amyloid opens up a new perspective in our understanding of the process of amyloidogenesis, which is crucial for the development of new treatments for diseases. It is therefore valuable but still challenging to explore the cross-seeding system of amyloid protein as well as to reveal the structural basis and the intricate processes.

The human microbiome in disease and pathology

This narrative review seeks to examine the relationships between bacterial microbiomes and infectious disease. This is achieved by detailing how different human host microbiomes develop and function, from the earliest infant acquisitions of maternal and environmental species through to the full development of microbiomes by adulthood. Communication between bacterial species or communities of species within and outside of the microbiome is a factor in both maintenance of homeostasis and management of threats from the external environment. Dysbiosis of this homeostasis is key to understanding the development of disease states. Several microbiomes and the microbiota within are used as prime examples of how changes in species composition, particularly at the phylum level, leads to such diverse conditions as inflammatory bowel disease (IBD), type 2 diabetes, psoriasis, Parkinson's disease, reflux oesophagitis and others. The review examines spatial relationships between microbiomes to understand how dysbiosis in the gut microbiome in particular can influence diseases in distant host sites via routes such as the gut-lung, gut-skin and gut-brain axes. Microbiome interaction with host processes such as adaptive immunity is increasingly identified as critical to developing the capacity of the immune system to react to pathogens. Dysbiosis of essential bacteria involved in modification of host substrates such as bile acid components can result in development of Crohn's disease, small intestine bacterial overgrowth, hepatic cancer and obesity. Interactions between microbiomes in distantly located sites are being increasingly being identified, resulting in a 'whole of body' effect by the combined host microbiome.

Targeting α-Synuclein in Parkinson's Disease by Induced Pluripotent Stem Cell Models

Parkinson's disease (PD) is a progressive, neurodegenerative disorder characterized by motor and non-motor symptoms. To date, no specific treatment to halt disease progression is available, only medication to alleviate symptoms can be prescribed. The main pathological hallmark of PD is the development of neuronal inclusions, positive for α-synuclein (α-syn), which are termed Lewy bodies (LBs) or Lewy neurites. However, the cause of the inclusion formation and the loss of neurons remain largely elusive. Various genetic determinants were reported to be involved in PD etiology, including SNCA, DJ-1, PRKN, PINK1, LRRK2, and GBA. Comprehensive insights into pathophysiology of PD critically depend on appropriate models. However, conventional model organisms fall short to faithfully recapitulate some features of this complex disease and as a matter-of-fact access to physiological tissue is limiting. The development of disease models replicating PD that are close to human physiology and dynamic enough to analyze the underlying molecular mechanisms of disease initiation and progression, as well as the generation of new treatment options, is an important and overdue step. Recently, the establishment of induced pluripotent stem cell (iPSC)-derived neural models, particularly from genetic PD-variants, developed into a promising strategy to investigate the molecular mechanisms regarding formation of inclusions and neurodegeneration. As these iPSC-derived neurons can be generated from accessible biopsied samples of PD patients, they carry pathological alterations and enable the possibility to analyze the differences compared to healthy neurons. This review focuses on iPSC models carrying genetic PD-variants of α-syn that will be especially helpful in elucidating the pathophysiological mechanisms of PD. Furthermore, we discuss how iPSC models can be instrumental in identifying cellular targets, potentially leading to the development of new therapeutic treatments. We will outline the enormous potential, but also discuss the limitations of iPSC-based α-syn models.

The Gut-Brain Axis and Its Relation to Parkinson's Disease: A Review

Parkinson's disease is a chronic neurodegenerative disease characterized by the accumulation of misfolded alpha-synuclein protein (Lewy bodies) in dopaminergic neurons of the substantia nigra and other related circuitry, which contribute to the development of both motor (bradykinesia, tremors, stiffness, abnormal gait) and non-motor symptoms (gastrointestinal issues, urinogenital complications, olfaction dysfunction, cognitive impairment). Despite tremendous progress in the field, the exact pathways and mechanisms responsible for the initiation and progression of this disease remain unclear. However, recent research suggests a potential relationship between the commensal gut bacteria and the brain capable of influencing neurodevelopment, brain function and health. This bidirectional communication is often referred to as the microbiome-gut-brain axis. Accumulating evidence suggests that the onset of non-motor symptoms, such as gastrointestinal manifestations, often precede the onset of motor symptoms and disease diagnosis, lending support to the potential role that the microbiome-gut-brain axis might play in the underlying pathological mechanisms of Parkinson's disease. This review will provide an overview of and critically discuss the current knowledge of the relationship between the gut microbiota and Parkinson's disease. We will discuss the role of α-synuclein in non-motor disease pathology, proposed pathways constituting the connection between the gut microbiome and the brain, existing evidence related to pre- and probiotic interventions. Finally, we will highlight the potential opportunity for the development of novel preventative measures and therapeutic options that could target the microbiome-gut-brain axis in the context of Parkinson's disease.

The role of appendectomy in the development of Parkinson’s disease: a retrospective study in a teaching hospital in Jordan

Background

Parkinson’s disease is a degenerative brain disease related to the accumulation of an abnormally aggregated alpha-synuclein protein. A hypothesis was presumed that this protein will be transported retrogradely from the gastrointestinal tract ultimately leading to the disease. Various epidemiologic studies have shown conflicting results. This study reports the prevalence of appendectomy in Jordanian parkinsonian patients and compares it to controls seen at one major teaching hospital in Jordan. This is a retrospective study of 266 patients compared to a control group of 500 patients randomly selected from the hospital. The prevalence of appendectomy in the 2 groups was studied.

Results

The rate of appendectomy in patients and controls was 26/266 (9.8%) and 27/500 (5.4%), respectively (relative risk 1.30, odds ratio 1.81, χ2, p = 0.026). Appendectomy in the patients was independent of gender (χ2, p = 0.297). Also, there was no difference in patients with and without appendectomy regarding their age, age at diagnosis of PD, and duration of use of levodopa (p = 0.827, 0.960, and 0.688, respectively, Student t test). The mean duration from appendectomy to the diagnosis of the disease varied widely 23 ± 18.7 years, range −12–59 years.

Conclusions

Appendectomy occurred significantly more frequent in patients with Parkinson’s disease than in control. There was no difference regarding the age of onset of disease in the patients with and without appendectomy. Though the appendix in this study seems to have a protective role against the development of the disease, the relationship is quite complex requiring prospective in-depth evaluation.

Exploring the Gut-Brain Axis for the Control of CNS Inflammatory Demyelination: Immunomodulation by Bacteroides fragilis' Polysaccharide A

The symbiotic relationship between animals and their resident microorganisms has profound effects on host immunity. The human microbiota comprises bacteria that reside in the gastrointestinal tract and are involved in a range of inflammatory and autoimmune diseases. The gut microbiota's immunomodulatory effects extend to extraintestinal tissues, including the central nervous system (CNS). Specific symbiotic antigens responsible for inducing immunoregulation have been isolated from different bacterial species. Polysaccharide A (PSA) of Bacteroides fragilis is an archetypical molecule for host-microbiota interactions. Studies have shown that PSA has beneficial effects in experimental disease models, including experimental autoimmune encephalomyelitis (EAE), the most widely used animal model for multiple sclerosis (MS). Furthermore, in vitro stimulation with PSA promotes an immunomodulatory phenotype in human T cells isolated from healthy and MS donors. In this review, we discuss the current understanding of the interactions between gut microbiota and the host in the context of CNS inflammatory demyelination, the immunomodulatory roles of gut symbionts. More specifically, we also discuss the immunomodulatory effects of B. fragilis PSA in the gut-brain axis and its therapeutic potential in MS. Elucidation of the molecular mechanisms responsible for the microbiota's impact on host physiology offers tremendous promise for discovering new therapies.

Gut Microbiota Interaction with the Central Nervous System throughout Life

During the last years, accumulating evidence has suggested that the gut microbiota plays a key role in the pathogenesis of neurodevelopmental and neurodegenerative diseases via the gut-brain axis. Moreover, current research has helped to elucidate different communication pathways between the gut microbiota and neural tissues (e.g., the vagus nerve, tryptophan production, extrinsic enteric-associated neurons, and short chain fatty acids). On the other hand, altering the composition of gut microbiota promotes a state known as dysbiosis, where the balance between helpful and pathogenic bacteria is disrupted, usually stimulating the last ones. Herein, we summarize selected findings of the recent literature concerning the gut microbiome on the onset and progression of neurodevelopmental and degenerative disorders, and the strategies to modulate its composition in the search for therapeutical approaches, focusing mainly on animal models studies. Readers are advised that this is a young field, based on early studies, that is rapidly growing and being updated as the field advances.