Mechanistic Insights Into Gut Microbiome Dysbiosis-Mediated Neuroimmune Dysregulation and Protein Misfolding and Clearance in the Pathogenesis of Chronic Neurodegenerative Disorders

Increasing spatial working memory in mice with Akkermansia muciniphila

Recent research has shown the gut microbiome's impact on memory, yet limitations hinder the identification of specific microbes linked to cognitive function. We measured spatial working memory in individual mice before and after fecal microbiota transplantation (FMT) to develop a targeted analysis that identifies memory-associated strains while minimizing host genetic effects. Transplantation of human fecal into C57BL/6 mice yielded varied outcomes: some mice showed significant improvements while others had negligible changes, indicating that these changes are due to differences in FMT colonization. Metagenomic analysis, stratified by memory performance, revealed a positive correlation between the abundance of Akkermansia muciniphila and improved memory. Moreover, administering two A. muciniphila strains, GMB 0476 and GMB 2066, to wild-type mice elevated spatial working memory via BDNF activation. Our findings indicate that specific gut microbes, particularly A. muciniphila, may modulate memory and represent potential targets for therapeutic intervention in cognitive enhancement.

The roles of functional bacterial amyloids in neurological physiology and pathophysiology: Pros and cons for neurodegeneration

Bacterial biofilms, which are complex communities of microorganisms encapsulated in a self-produced extracellular matrix, play critical roles in various diseases. Recent research has underscored the dualistic nature of amyloids, structural proteins within these biofilms, in human health, particularly highlighting the significant role in neurodegenerative disorders such as Alzheimer's (AD) and Parkinson's disease (PD). These amyloids modulate the immune response by inducing the production of interleukin-10 (IL-10), which plays a role in anti-inflammatory processes. Additionally, they inhibit the aggregation of human amyloids and enhance the integrity of the intestinal barrier. Detrimentally, they exacerbate neuroinflammation by elevating inflammatory cytokines and promoting the aggregation of human amyloid proteins-amyloid-β (Aβ) in AD and α-synuclein (αS) in PD-through a process known as cross-seeding. Moreover, bacterial amyloids have also been shown to stimulate the production of anti-curli/DNA antibodies, which are implicated in the pathogenesis of autoimmune diseases. Given their dualistic nature, bacterial amyloids may, under specific conditions, function as beneficial proteins for human health. This understanding holds promise for the development of targeted therapeutic strategies aimed at modulating bacterial amyloids in the context of neurodegenerative diseases, such as AD and PD.

Therapeutic effects of traditional Chinese medicine Hua-Feng-Dan in a rat model of ischemic stroke involve renormalization of gut microbiota

Hua-Feng-Dan is a traditional Chinese medicine used to treat ischemic stroke, but little is known about its therapeutic mechanism. This study explored whether and how the mechanism involves readjustment of gut microbiota. Rats were subjected to middle cerebral artery occlusion as a model of ischemic stroke or to sham surgery, then treated or not with Hua-Feng-Dan. The different groups of animals were compared in terms of neurological score, cerebral infarct volume, brain edema, brain and gut histopathology to assess stroke severity. They were also compared in terms of indices of intestinal barrier permeability, inflammation and oxidative stress, brain metabolites as well as composition of the gut microbiota and their metabolites. Hua-Feng-Dan significantly reduced cerebral infarct volume and brain water content and improved neurological score, ischemic brain histopathology, and gut histopathology. It partially reversed stroke-induced intestinal barrier disruption and leakage, inflammation, dyslipidemia and oxidative stress, as well as the stroke-induced increase in pathogenic gut microbiota (e.g., Escherichia-Shigella, Enterococcus, Clostridium_innocuum_group) and decrease in beneficial microbiota (e.g., Lachnospiraceae, unclassified__f__Lachnospiracea and Ruminococcus_torques_group). The treatment altered levels of 39 and 38 metabolites produced during gut microbial and brain tissue metabolism respectively, mainly of amino acids, nucleosides, short-chain fatty acids, and essential fatty acids. Levels of factors related to inflammation and intestinal barrier permeability correlated positively with relative abundance of Escherichia-Shigella and Clostridium_innocuum_group, and negatively with 4-(glutamylamino) butanoate, 2-hydroxy-3-methylbutyric acid, dihomo-α-linolenic acid, dihomolinoleic acid, and 10-nitrolinoleic acid. Conversely, levels of 4-(glutamylamino) butanoate, 2-hydroxy-3-methylbutyric acid, and 10-nitrolinoleic acid correlated positively with relative abundance of unclassified__f__Lachnospiracea. Our results suggest that Hua-Feng-Dan may mitigate ischemic stroke injury by renormalizing gut microbiota and restoring gut barrier function, gut metabolism, thereby helping to alleviate inflammatory, neurological damage, and brain metabolic disorders.

WITHDRAWN: Progranulin inhibits phospholipase sPLA2-IIA to control neuroinflammation

The authors have withdrawn this manuscript because more work is needed to fully define the role of sPLA2-IIA. Therefore, the authors do not wish this work to be cited as reference for the project. If you have any questions, please contact the corresponding author.

Gut microbiota and Parkinson's disease: potential links and the role of fecal microbiota transplantation

Parkinson's disease (PD) is the second most common neurodegenerative disease worldwide and seriously affects the quality of life of elderly patients. PD is characterized by the loss of dopaminergic neurons in the substantia nigra as well as abnormal accumulation of α-synuclein in neurons. Recent research has deepened our understanding of the gut microbiota, revealing that it participates in the pathological process of PD through the gut-brain axis, suggesting that the gut may be the source of PD. Therefore, studying the relationship between gut microbiota and PD is crucial for improving our understanding of the disease's prevention, diagnosis, and treatment. In this review, we first describe the bidirectional regulation of the gut-brain axis by the gut microbiota and the mechanisms underlying the involvement of gut microbiota and their metabolites in PD. We then summarize the different species of gut microbiota found in patients with PD and their correlations with clinical symptoms. Finally, we review the most comprehensive animal and human studies on treating PD through fecal microbiota transplantation (FMT), discussing the challenges and considerations associated with this treatment approach.

Impact of Physical Activity on Cellular Metabolism Across Both Neurodegenerative and General Neurological Conditions: A Narrative Review

BACKGROUND

Regular physical activity plays a crucial role in modulating cellular metabolism and mitigating the progression of neurodegenerative diseases such as Alzheimer's, Parkinson's, and Multiple Sclerosis.

OBJECTIVE

The objective of this review is to evaluate the molecular mechanisms by which exercise influences cellular metabolism, with a focus on its potential as a therapeutic intervention for neurological disorders.

METHODS

A comprehensive literature review was conducted using peer-reviewed scientific articles, with a focus on the period between 2015 and 2024, to analyze the effects of exercise on mitochondrial function, oxidative stress, and metabolic health.

RESULTS

The findings indicate that exercise promotes mitochondrial biogenesis, enhances oxidative phosphorylation, and reduces reactive oxygen species, contributing to improved energy production and cellular resilience. These metabolic adaptations are associated with delayed disease progression and reduced symptoms in patients with neurodegenerative conditions. Additionally, integrating exercise with nutritional strategies may further enhance therapeutic outcomes by addressing metabolic disturbances comprehensively.

CONCLUSIONS

This review concludes that personalized exercise protocols should be developed to optimize metabolic benefits for patients with neurological diseases, while future research should focus on biomarker development for individualized treatment approaches. These findings highlight the importance of non-pharmacological interventions in managing neurodegenerative diseases.

Resolution of Chronic Inflammation, Restoration of Epigenetic Disturbances and Correction of Dysbiosis as an Adjunctive Approach to the Treatment of Atopic Dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease with multifactorial and unclear pathogenesis. Its development is characterized by two key elements: epigenetic dysregulation of molecular pathways involved in AD pathogenesis and disrupted skin and gut microbiota (dysbiosis) that jointly trigger and maintain chronic inflammation, a core AD characteristic. Current data suggest that failed inflammation resolution is the main pathogenic mechanism underlying AD development. Inflammation resolution is provided by specialized pro-resolving mediators (SPMs) derived from dietary polyunsaturated fatty acids acting through cognate receptors. SPM levels are reduced in AD patients. Administration of SPMs or their stable, small-molecule mimetics and receptor agonists, as well as supplementation with probiotics/prebiotics, demonstrate beneficial effects in AD animal models. Epidrugs, compounds capable of restoring disrupted epigenetic mechanisms associated with the disease, improve impaired skin barrier function in AD models. Based on these findings, we propose a novel, multilevel AD treatment strategy aimed at resolving chronic inflammation by application of SPM mimetics and receptor agonists, probiotics/prebiotics, and epi-drugs. This approach can be used in conjunction with current AD therapy, resulting in AD alleviation.

Gut-brain axis and neurodegeneration: mechanisms and therapeutic potentials

This paper reviews the effects of gut microbiota in regulating neurodegenerative diseases through controlling gut-brain axis. Specific microbial populations and their metabolites (short-chain fatty acids and tryptophan derivatives) regulate neuroinflammation, neurogenesis and neural barrier integrity. We then discuss ways by which these insights lead to possible interventions - probiotics, prebiotics, dietary modification, and fecal microbiota transplantation (FMT). We also describe what epidemiological and clinical studies have related certain microbiota profiles with the courses of neurodegenerative diseases and how these impact the establishment of microbiome-based diagnostics and individualized treatment options. We aim to guide microbial ecology research on this key link to neurodegenerative disorders and also to highlight collaborative approaches to manage neurological health by targeting microbiome-related factors.

Gut microbiota dysbiosis contributes to α-synuclein-related pathology associated with C/EBPβ/AEP signaling activation in a mouse model of Parkinson's disease

JOURNAL/nrgr/04.03/01300535-202409000-00042/figure1/v/2024-01-16T170235Z/r/image-tiff Parkinson's disease is a neurodegenerative disease characterized by motor and gastrointestinal dysfunction. Gastrointestinal dysfunction can precede the onset of motor symptoms by several years. Gut microbiota dysbiosis is involved in the pathogenesis of Parkinson's disease, whether it plays a causal role in motor dysfunction, and the mechanism underlying this potential effect, remain unknown. CCAAT/enhancer binding protein β/asparagine endopeptidase (C/EBPβ/AEP) signaling, activated by bacterial endotoxin, can promote α-synuclein transcription, thereby contributing to Parkinson's disease pathology. In this study, we aimed to investigate the role of the gut microbiota in C/EBPβ/AEP signaling, α-synuclein-related pathology, and motor symptoms using a rotenone-induced mouse model of Parkinson's disease combined with antibiotic-induced microbiome depletion and fecal microbiota transplantation. We found that rotenone administration resulted in gut microbiota dysbiosis and perturbation of the intestinal barrier, as well as activation of the C/EBP/AEP pathway, α-synuclein aggregation, and tyrosine hydroxylase-positive neuron loss in the substantia nigra in mice with motor deficits. However, treatment with rotenone did not have any of these adverse effects in mice whose gut microbiota was depleted by pretreatment with antibiotics. Importantly, we found that transplanting gut microbiota derived from mice treated with rotenone induced motor deficits, intestinal inflammation, and endotoxemia. Transplantation of fecal microbiota from healthy control mice alleviated rotenone-induced motor deficits, intestinal inflammation, endotoxemia, and intestinal barrier impairment. These results highlight the vital role that gut microbiota dysbiosis plays in inducing motor deficits, C/EBPβ/AEP signaling activation, and α-synuclein-related pathology in a rotenone-induced mouse model of Parkinson's disease. Additionally, our findings suggest that supplementing with healthy microbiota may be a safe and effective treatment that could help ameliorate the progression of motor deficits in patients with Parkinson's disease.

The involvement of effector memory CD4+ T cells in mediating the impact of genus Oscillibacter gut microbiota on Alzheimer's disease: a Mendelian randomization study

Objective

This study aimed to investigate the causal relationship between gut microbiota characteristics (207 taxa and 205 pathways) and Alzheimer's disease and determine and quantify the role of immune cells as potential mediators.

Methods

Gut microbiota characteristics (207 taxa and 205 pathways) were obtained from the NHGRI-EBI GWAS Catalog project, while Alzheimer's disease data and 731 immune cell characteristics were obtained from the IEU Open GWAS project. Two-sample Mendelian randomization (MR) was conducted to determine whether gut microbiota characteristics (207 taxa and 205 pathways) were causally related to Alzheimer's disease. Furthermore, two-step MR was employed to quantify the proportion of the effect of immune cell characteristics mediated by gut microbiota characteristics (207 taxa and 205 pathways) on Alzheimer's disease.

Results

A total of 17 immune cell characteristics were identified as potential mediators for 13 gut microbiota influencing Alzheimer's disease, with Effector Memory CD4+ T-cell Absolute Count accounted for 8.99% of the causal relationship between genus Oscillibacter and Alzheimer's disease.

Conclusion

In summary, our research confirms a causal relationship between gut microbiota and Alzheimer's disease, with immune cells contributing to a significant portion of the effect. However, the full mediators of gut microbiota's impact on Alzheimer's disease remain unclear. Further investigation is warranted to explore additional potential risk factors acting as mediators.

The Brain-Gut Axis, an Important Player in Alzheimer and Parkinson Disease: A Narrative Review

Neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD), are severe age-related disorders with complex and multifactorial causes. Recent research suggests a critical link between neurodegeneration and the gut microbiome, via the gut-brain communication pathway. This review examines the role of trimethylamine N-oxide (TMAO), a gut microbiota-derived metabolite, in the development of AD and PD, and investigates its interaction with microRNAs (miRNAs) along this bidirectional pathway. TMAO, which is produced from dietary metabolites like choline and carnitine, has been linked to increased neuroinflammation, protein misfolding, and cognitive decline. In AD, elevated TMAO levels are associated with amyloid-beta and tau pathologies, blood-brain barrier disruption, and neuronal death. TMAO can cross the blood-brain barrier and promote the aggregation of amyloid and tau proteins. Similarly, TMAO affects alpha-synuclein conformation and aggregation, a hallmark of PD. TMAO also activates pro-inflammatory pathways such as NF-kB signaling, exacerbating neuroinflammation further. Moreover, TMAO modulates the expression of various miRNAs that are involved in neurodegenerative processes. Thus, the gut microbiome-miRNA-brain axis represents a newly discovered mechanistic link between gut dysbiosis and neurodegeneration. MiRNAs regulate the key pathways involved in neuroinflammation, oxidative stress, and neuronal death, contributing to disease progression. As a direct consequence, specific miRNA signatures may serve as potential biomarkers for the early detection and monitoring of AD and PD progression. This review aims to elucidate the complex interrelationships between the gut microbiota, trimethylamine-N-oxide (TMAO), microRNAs (miRNAs), and the central nervous system, and the implications of these connections in neurodegenerative diseases. In this context, an overview of the current neuroradiology techniques available for studying neuroinflammation and of the animal models used to investigate these intricate pathologies will also be provided. In summary, a bulk of evidence supports the concept that modulating the gut-brain communication pathway through dietary changes, the manipulation of the microbiome, and/or miRNA-based therapies may offer novel approaches for implementing the treatment of debilitating neurological disorders.

A randomized, double-blinded, placebo-controlled clinical trial on Lactobacillus-containing cultured milk drink as adjuvant therapy for depression in irritable bowel syndrome

Irritable bowel syndrome (IBS) is frequently linked with coexisting mental illnesses. Our previous study discovered that 32.1% of IBS patients had subthreshold depression (SD), placing them at higher risk of developing major depression. Gut microbiota modulation through psychobiotics was found to influence depression via the gut-brain axis. However, the efficacy of lessening depression among IBS patients remains ambiguous. The study's aim was to investigate the roles of cultured milk drinks containing 109 cfu Lactobacillus acidophilus LA-5 and Lactobacillus paracasei L. CASEI-01 on depression and related variables among IBS participants with SD. A total of 110 IBS participants with normal mood (NM) and SD, were randomly assigned to one of four intervention groups: IBS-NM with placebo, IBS-NM with probiotic, IBS-SD with placebo, and IBS-SD with probiotic. Each participant was required to consume two bottles of cultured milk every day for a duration of 12 weeks. The following outcomes were assessed: depression risk, quality of life, the severity of IBS, and hormonal changes. The depression scores were significantly reduced in IBS-SD with probiotic and placebo from baseline (p < 0.001). Only IBS-SD with probiotic showed a significant rise in serotonin serum levels (p < 0.05). A significantly higher life quality measures were seen in IBS-SD with probiotic, IBS-SD with placebo, and IBS-NM with placebo (p < 0.05). All groups, both placebo and probiotic, reported significant improvement in IBS severity post-intervention with a higher prevalence of remission and mild IBS (p < 0.05). Dual strains lactobacillus-containing cultured milk drink via its regulation of relevant biomarkers, is a potential anti-depressive prophylactic agent for IBS patients at risk.

Identification of Muscle Strength-Related Gut Microbes through Human Fecal Microbiome Transplantation

The gut microbiome is well known for its influence on human physiology and aging. Therefore, we speculate that the gut microbiome may affect muscle strength in the same way as the host's own genes. To demonstrate candidates for gut microbes affecting muscle strength, we remodeled the original gut microbiome of mice into human intestinal microbiome through fecal microbiome transplantation (FMT), using human feces and compared the changes in muscle strength in the same mice before and three months after FMT. After comparing before and after FMT, the mice were divided into three groups based on the observed changes in muscle strength: positive, none, and negative changes in muscle strength. As a result of analyzing the α-diversity, β-diversity, and co-occurrence network of the intestinal microbial community before and after FMT, it was observed that a more diverse intestinal microbial community was established after FMT in all groups. In particular, the group with increased muscle strength had more gut microbiome species and communities than the other groups. Fold-change comparison showed that Eisenbergiella massiliensis and Anaeroplasma abactoclasticum from the gut microbiome had positive contributions to muscle strength, while Ileibacterium valens and Ethanoligenens harbinense had negative effects. This study identifies candidates for the gut microbiome that contribute positively and those that contribute negatively to muscle strength.

The Crucial Role of the Interstitial Cells of Cajal in Neurointestinal Diseases

Neurointestinal diseases result from dysregulated interactions between the nervous system and the gastrointestinal (GI) tract, leading to conditions such as Hirschsprung's disease and irritable bowel syndrome. These disorders affect many people, significantly diminishing their quality of life and overall health. Central to GI motility are the interstitial cells of Cajal (ICC), which play a key role in muscle contractions and neuromuscular transmission. This review highlights the role of ICC in neurointestinal diseases, revealing their association with various GI ailments. Understanding the functions of the ICC could lead to innovative perspectives on the modulation of GI motility and introduce new therapeutic paradigms. These insights have the potential to enhance efforts to combat neurointestinal diseases and may lead to interventions that could alleviate or even reverse these conditions.

Identification of the Intestinal Microbes Associated with Locomotion

Given the impact of the gut microbiome on human physiology and aging, it is possible that the gut microbiome may affect locomotion in the same way as the host's own genes. There is not yet any direct evidence linking the gut microbiome to locomotion, though there are some potential connections, such as regular physical activity and the immune system. In this study, we demonstrate that the gut microbiome can contribute differently to locomotion. We remodeled the original gut microbiome of mice through fecal microbiota transplantation (FMT) using human feces and compared the changes in locomotion of the same mice before and three months after FMT. We found that FMT affected locomotion in three different ways: positive, none (the same), and negative. Analysis of the phylogenesis, α-diversities, and β-diversities of the gut microbiome in the three groups showed that a more diverse group of intestinal microbes was established after FMT in each of the three groups, indicating that the human gut microbiome is more diverse than that of mice. The FMT-remodeled gut microbiome in each group was also different from each other. Fold change and linear correlation analyses identified Lacrimispora indolis, Pseudoflavonifractor phocaeensis, and Alistipes senegalensis in the gut microbiome as positive contributors to locomotion, while Sphingobacterium cibi, Prevotellamassilia timonensis, Parasutterella excrementihominis, Faecalibaculum rodentium, and Muribaculum intestinale were found to have negative effects. This study not only confirms the presence of gut microbiomes that contribute differently to locomotion, but also explains the mixed results in research on the association between the gut microbiome and locomotion.

Gut microbiome plays a vital role in post-stroke injury repair by mediating neuroinflammation

Cerebral stroke is a common neurological disease and often causes severe neurological deficits. With high morbidity, mortality, and disability rates, stroke threatens patients' life quality and brings a heavy economic burden on society. Ischemic cerebral lesions incur pathological changes as well as spontaneous nerve repair following stroke. Strategies such as drug therapy, physical therapy, and surgical treatment, can ameliorate blood and oxygen supply in the brain, hamper the inflammatory responses and maintain the structural and functional integrity of the brain. The gut microbiome, referred to as the "second genome" of the human body, participates in the regulation of multiple physiological functions including metabolism, digestion, inflammation, and immunity. The gut microbiome is not only inextricably associated with dangerous factors pertaining to stroke, including high blood pressure, diabetes, obesity, and atherosclerosis, but also influences stroke occurrence and prognosis. AMPK functions as a hub of metabolic control and is responsible for the regulation of metabolic events under physiological and pathological conditions. The AMPK mediators have been found to exert dual roles in regulating gut microbiota and neuroinflammation/neuronal apoptosis in stroke. In this study, we reviewed the role of the gut microbiome in cerebral stroke and the underlying mechanism of the AMPK signaling pathway in stroke. AMPK mediators in nerve repair and the regulation of intestinal microbial balance were also summarized.

Bacterial DNAemia in Alzheimer's Disease and Mild Cognitive Impairment: Association with Cognitive Decline, Plasma BDNF Levels, and Inflammatory Response

Microbial dysbiosis (MD) provokes gut barrier alterations and bacterial translocation in the bloodstream. The increased blood bacterial DNA (BB-DNA) may promote peripheral- and neuro-inflammation, contributing to cognitive impairment. MD also influences brain-derived neurotrophic factor (BDNF) production, whose alterations contribute to the etiopathogenesis of Alzheimer's disease (AD). The purpose of this study is to measure BB-DNA in healthy elderly controls (EC), and in patients with mild cognitive impairment (MCI) and AD to explore the effect on plasma BDNF levels (pBDNF), the inflammatory response, and the association with cognitive decline during a two-year follow-up. Baseline BB-DNA and pBDNF were significantly higher in MCI and AD than in EC. BB-DNA was positively correlated with pBDNF in AD, plasma Tumor necrosis factor-alpha (TNF-α), and Interleukin-10 (IL-10) levels in MCI. AD patients with BB-DNA values above the 50th percentile had lower baseline Mini-Mental State Examination (MMSE). After a two-year follow-up, AD patients with the highest BB-DNA tertile had a worse cognitive decline, while higher BB-DNA levels were associated with higher TNF-α and lower IL-10 in MCI. Our study demonstrates that, in early AD, the higher the BB-DNA levels, the higher the pBDNF levels, suggesting a defensive attempt; BB-DNA seems to play a role in the AD severity/progression; in MCI, higher BB-DNA may trigger an increased inflammatory response.

Molecular and cellular mechanisms leading to catatonia: an integrative approach from clinical and preclinical evidence

This review aims to describe the clinical spectrum of catatonia, in order to carefully assess the involvement of astrocytes, neurons, oligodendrocytes, and microglia, and articulate the available preclinical and clinical evidence to achieve a translational understanding of the cellular and molecular mechanisms behind this disorder. Catatonia is highly common in psychiatric and acutely ill patients, with prevalence ranging from 7.6% to 38%. It is usually present in different psychiatric conditions such as mood and psychotic disorders; it is also a consequence of folate deficiency, autoimmunity, paraneoplastic disorders, and even autistic spectrum disorders. Few therapeutic options are available due to its complexity and poorly understood physiopathology. We briefly revisit the traditional treatments used in catatonia, such as antipsychotics, electroconvulsive therapy, and benzodiazepines, before assessing novel therapeutics which aim to modulate molecular pathways through different mechanisms, including NMDA antagonism and its allosteric modulation, and anti-inflammatory drugs to modulate microglia reaction and mitigate oxidative stress, such as lithium, vitamin B12, and NMDAr positive allosteric modulators.

Does the Gut Microbial Metabolome Really Matter? The Connection between GUT Metabolome and Neurological Disorders

Herein we gathered updated knowledge regarding the alterations of gut microbiota (dysbiosis) and its correlation with human neurodegenerative and brain-related diseases, e.g., Alzheimer’s and Parkinson’s. This review underlines the importance of gut-derived metabolites and gut metabolic status as the main players in gut-brain crosstalk and their implications on the severity of neural conditions. Scientific evidence indicates that the administration of probiotic bacteria exerts beneficial and protective effects as reduced systemic inflammation, neuroinflammation, and inhibited neurodegeneration. The experimental results performed on animals, but also human clinical trials, show the importance of designing a novel microbiota-based probiotic dietary supplementation with the aim to prevent or ease the symptoms of Alzheimer’s and Parkinson’s diseases or other forms of dementia or neurodegeneration.

Clostridioides difficile and neurological disorders: New perspectives

Despite brain physiological functions or pathological dysfunctions relying on the activity of neuronal/non-neuronal populations, over the last decades a plethora of evidence unraveled the essential contribution of the microbial populations living and residing within the gut, called gut microbiota. The gut microbiota plays a role in brain (dys)functions, and it will become a promising valuable therapeutic target for several brain pathologies. In the present mini-review, after a brief overview of the role of gut microbiota in normal brain physiology and pathology, we focus on the role of the bacterium Clostridioides difficile, a pathogen responsible for recurrent and refractory infections, in people with neurological diseases, summarizing recent correlative and causative evidence in the scientific literature and highlighting the potential of microbiota-based strategies targeting this pathogen to ameliorate not only gastrointestinal but also the neurological symptoms.

Exploring the Paradox of COVID-19 in Neurological Complications with Emphasis on Parkinson’s and Alzheimer’s Disease

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a human coronavirus (HCoV) that has created a pandemic situation worldwide as COVID-19. This virus can invade human cells via angiotensin-converting enzyme 2 (ACE2) receptor-based mechanisms, affecting the human respiratory tract. However, several reports of neurological symptoms suggest a neuroinvasive development of coronavirus. SARS-CoV-2 can damage the brain via several routes, along with direct neural cell infection with the coronavirus. The chronic inflammatory reactions surge the brain with proinflammatory elements, damaging the neural cells, causing brain ischemia associated with other health issues. SARS-CoV-2 exhibited neuropsychiatric and neurological manifestations, including cognitive impairment, depression, dizziness, delirium, and disturbed sleep. These symptoms show nervous tissue damage that enhances the occurrence of neurodegenerative disorders and aids dementia. SARS-CoV-2 has been seen in brain necropsy and isolated from the cerebrospinal fluid of COVID-19 patients. The associated inflammatory reaction in some COVID-19 patients has increased proinflammatory cytokines, which have been investigated as a prognostic factor. Therefore, the immunogenic changes observed in Parkinson's and Alzheimer's patients include their pathogenetic role. Inflammatory events have been an important pathophysiological feature of neurodegenerative diseases (NDs) such as Parkinson's and Alzheimer's. The neuroinflammation observed in AD has exacerbated the Aβ burden and tau hyperphosphorylation. The resident microglia and other immune cells are responsible for the enhanced burden of Aβ and subsequently mediate tau phosphorylation and ultimately disease progression. Similarly, neuroinflammation also plays a key role in the progression of PD. Several studies have demonstrated an interplay between neuroinflammation and pathogenic mechanisms of PD. The dynamic proinflammation stage guides the accumulation of α-synuclein and neurodegenerative progression. Besides, few viruses may have a role as stimulators and generate a cross-autoimmune response for α-synuclein. Hence, neurological complications in patients suffering from COVID-19 cannot be ruled out. In this review article, our primary focus is on discussing the neuroinvasive effect of the SARS-CoV-2 virus, its impact on the blood-brain barrier, and ultimately its impact on the people affected with neurodegenerative disorders such as Parkinson's and Alzheimer's.