The second brain: The connection between gut microbiota composition and multiple sclerosis

Association of Gastrointestinal Symptoms with Depression and Anxiety in Recruits: A Validation Cross-Sectional Study

INTRODUCTION

Gastrointestinal symptoms as well as depression and anxiety can negatively affect the effectiveness of military training and combat in general. This cross-sectional study aimed to determine the prevalence of gastrointestinal symptoms in recruits and further validate their associations with depression and anxiety.

METHODS

A self-report questionnaire was sent to the recruits in an army in April 2022, which primarily included the Symptom Rating Scale (GSRS) for the assessment of gastrointestinal symptoms, the Bristol Stool Scale (BSS) for stool consistency and shape, the Patient Health Questionnaire-9 (PHQ-9) for depression, and the 7-item Generalized Anxiety Disorder scale (GAD-7) for anxiety. Correlation of gastrointestinal symptoms with depression and anxiety was evaluated.

RESULTS

Overall, 467 recruits were included. Their median age was 21.0 years old (range: 18.0-24.0), and 98.1% of them were male. The proportion of gastrointestinal symptoms, abnormal stools, depression, and anxiety was 69.2% (n = 323), 11.3% (n = 53), 17.6% (n = 82), and 12.2% (n = 57), respectively. The recruits with gastrointestinal symptoms evaluated by GSRS had significantly higher prevalence of depression (P < 0.001) and anxiety (P < 0.001) than those without. GSRS score positively correlated with PHQ-9 (rs = 0.440, P < 0.001) and GAD-7 score (rs = 0.386, P < 0.001).

CONCLUSION

Gastrointestinal symptoms are very common in recruits, and positively correlate with depression and anxiety.

Gut Microbiota Composition Is Causally Linked to Multiple Sclerosis: A Mendelian Randomization Analysis

Accumulating evidence links the microbial communities inhabiting the gut to the pathophysiological processes underlying multiple sclerosis (MS). However, most studies on the microbiome in MS are correlative in nature, thus being at risk of confounding and reverse causality. Mendelian randomization (MR) analyses allow the estimation of the causal relationship between a risk factor and an outcome of interest using genetic variants as proxies for environmental exposures. Here, we performed a two-sample MR to assess the causality between the gut microbiome and MS. We extracted genetic instruments from summary statistics from three large genome-wide association studies (GWASs) on the gut microbiome (18,340, 8959, and 7738 subjects). The exposure data were derived from the latest GWAS on MS susceptibility (47,429 patients and 68,374 controls). We pinpointed several microbial strains whose abundance is linked with enhanced MS risk (Actinobacteria class, Bifidobacteriaceae family, Lactobacillus genus) or protection (Prevotella spp., Lachnospiranaceae genus, Negativibacillus genus). The largest risk effect was seen for Ruminococcus Torques (OR, 2.89, 95% C.I. 1.67-5, p = 1.51 × 10-4), while Akkermansia municiphila emerged as strongly protective (OR, 0.43, 95% C.I. 0.32-0.57, p = 1.37 × 10-8). Our findings support a causal relationship between the gut microbiome and MS susceptibility, reinforcing the relevance of the microbiome-gut-brain axis in disease etiology, opening wider perspectives on host-environmental interactions for MS prevention.

Therapeutic effects and mechanisms of fecal microbiota transplantation on EAE partly through HPA axis-mediated neuroendocrine regulation

Background

The pathogenesis of multiple sclerosis (MS) may be closely related to immune regulation and inflammatory cytokines induced by specific flora. Repairing the intestinal flora may alter the immune response in MS patients, thus opening up novel approaches for the treatment of MS.

Objective

We aimed to test the therapeutic effect of fecal microbiota transplantation (FMT) on experimental autoimmune encephalomyelitis (EAE) and the characteristics of intestinal microbiota composition changes, explore the potential mechanisms of FMT treatment.

Methods

EAE animals were treated with FMT, with the therapeutic effects were evaluated by observing neurological scores and measuring serum levels of cortisol, IL-17, and TLR-2. Fecal microbiome 16S rRNA sequencing was used to profile changes in microbiota composition, and adrenalectomy pretreatment was used to test whether FMT effects were dependent on HPA axis function.

Results

FMT improved neurological function and reduced serum IL-17 to levels that were close to the control group. FMT reestablished intestinal homeostasis by altering the structure of the intestinal flora, increasing the abundance of beneficial flora, and regulating intestinal metabolites. We found that the therapeutic effects of FMT depended partly on the efferent function of the HPA axis; surgical disruption of the HPA axis altered the abundance and diversity of the intestinal flora.

Conclusion

FMT showed a neuroprotective effect on EAE by increasing the abundance of the beneficial flora, rebuilding intestinal homeostasis, reducing IL-17 and cortisol serum levels, and promoting serum TLR-2; the therapeutic effect of FMT on EAE is partly dependent on the HPA axis.

In-silico characterization of GABAT protein found in gut-brain axis associated bacteria of healthy individuals and multiple sclerosis patients

Background

Multiple sclerosis (MS) is a neurodegenerative disease characterized by inflammation and demyelination of neurons. There is evidence to suggest that level of a neurotransmitter gamma-aminobutyric acid (GABA), due to the degradation by γ-aminobutyric acid transaminase (GABAT), is reduced in certain areas of the brain in MS patients. MS is always accompanied by gut bacteria dysbiosis. In healthy individuals, Faecalibacterium sp. while in MS patients A. calcoaceticus, Clostridium sp. and S. typhimurium are found abundantly. Although all these microbes produce GABAT but only in MS patients this enzyme significantly degrades GABA.

Objective

Present study is an attempt to characterize the GABAT protein sequences of these bacteria.

Methodology

Sequences of GABAT protein were retrieved from Uniprot database. Sequences were analyzed by Protparam, Gneg-mPLoc, SOSUI, PFP-FunDSeqE, Pepwheel program, PROTEUS and Alphafold and SAVES servers, MEME suite and HDOCK server.

Results

In healthy individuals gastrointestinal tract (GIT) bacteria, GABAT protein was present in inner-membrane with α helix content (61 and 62%) and β sheet content (5%), 4-helical cytokines functional domains. It has greater number of B-cell epitopes and more complex 3D configuration as compared to MS patients GIT bacterial enzymes.

Conclusion

Present study might enable us to modify the GABAT encoding gene and enzyme through site-directed mutagenesis in pathogenic bacteria thus reducing their potential of causing MS.

The role of short-chain fatty acids in central nervous system diseases: A bibliometric and visualized analysis with future directions

Background

Short-chain fatty acids (SCFAs) are thought to play a key role in the microbe-gut-brain axis and involve in the pathogenesis of a variety of neurological diseases. This study aimed to identify research hotspots and evolution trends in SCFAs in central nervous diseases (CNS) and examine current research trends.

Methods

The bibliometric analysis was performed using CiteSpace, and the results were visualized via network maps.

Results

From 2002 to 2022, 480 publications in the database met the criteria. On the country level, China produced the highest number of publications, while the United States had the highest centrality. On the institutional level, University College Cork contributed to the most publications, and John F. Cryan from this university was the key researcher with considerable academic influence. The article, the role of short-chain fatty acids in microbiota-gut-brain, written by Boushra Dalile et al., in 2019 was the most cited article. Furthermore, the journal Nutrients had the maximum number of publications, while Plos One was the most cited journal. "Gut microbiome", "SCFAs", and "central nervous system" were the three most frequent keywords. Among them, SCFAs had the highest centrality. "Animal model" was the keyword with the highest burst strength, with the latest burst keywords being "social behavior", "pathogenesis", and "insulin sensitive". In addition, the research topics on SCFAs in CNS diseases from 2002 to 2022 mainly focused on following aspects: SCFAs plays a key role in microbe-gut-brain crosstalk; The classification and definition of SCFAs in the field of CNS; Several CNS diseases that are closely related to SCFAs research; Mechanism and translational studies of SCFAs in the CNS diseases. And the hotspots over the past 5 years have gradually increased the attention to the therapeutic potential of SCFAs in the CNS diseases.

Conclusion

The research of SCFAs in CNS diseases is attracting growing attention. However, there is a lack of cooperation between countries and institutions, and additional measures are required to promote cooperation. The current evidence for an association between SCFAs and CNS diseases is preliminary and more work is needed to pinpoint the precise mechanism. Moreover, large-scale clinical trials are needed in the future to define the therapeutic potential of SCFAs in CNS diseases.

Intestinal Microbiota Reduction Followed by Fasting Discloses Microbial Triggering of Inflammation in Rheumatoid Arthritis

Rheumatoid arthritis (RA) synovitis is dominated by monocytes/macrophages with inflammatory patterns resembling microbial stimulation. In search of triggers, we reduced the intestinal microbiome in 20 RA patients (open label study DRKS00014097) by bowel cleansing and 7-day fasting (≤250 kcal/day) and performed immune monitoring and microbiome sequencing. Patients with metabolic syndrome (n = 10) served as a non-inflammatory control group. Scores of disease activity (DAS28/SDAI) declined within a few days and were improved in 19 of 20 RA patients after breaking the fast (median ∆DAS28 = -1.23; ∆SDAI = -43%) or even achieved remission (DAS28 < 2.6/n = 6; SDAI < 3.3/n = 3). Cytometric profiling with 46 different surface markers revealed the most pronounced phenomenon in RA to be an initially increased monocyte turnover, which improved within a few days after microbiota reduction and fasting. Serum levels of IL-6 and zonulin, an indicator of mucosal barrier disruption, decreased significantly. Endogenous cortisol levels increased during fasting but were insufficient to explain the marked improvement. Sequencing of the intestinal microbiota indicated that fasting reduced potentially arthritogenic bacteria and changed the microbial composition to species with broader metabolic capabilities. More eukaryotic, predominantly fungal colonizers were observed in RA, suggesting possible involvement. This study demonstrates a direct link between the intestinal microbiota and RA-specific inflammation that could be etiologically relevant and would support targeted nutritional interventions against gut dysbiosis as a causal therapeutic approach.

The adaptation model of immunity: A new insight into aetiology and treatment of multiple sclerosis

Current research and drug development for multiple sclerosis (MS) is fully influenced by the self-nonself (SNS) model of immunity, suggesting that breakage of immunological tolerance towards self-antigens expressed in the central nervous system (CNS) is responsible for pathogenesis of MS; thus, immune suppressive drugs are recommended for the management of the disease. However, this model provides incomplete understanding of the causes and pathways involved in the onset and progression of MS and limits our ability to effectively treat this neurological disease. Some pre-clinical and clinical reports have been misunderstood; some others have been underappreciated because of the lack of a theoretical model that can explain them. Also, current immunotherapies are guided according to the models that are not designed to explain the functional outcomes of an immune response. The adaptation model of immunity is proposed to offer a new understanding of the existing data and galvanize a new direction for the treatment of MS. According to this model, the immune system continuously communicates with the CNS through the adaptation receptors (AdRs) and adaptation ligands (AdLs) or co-receptors, signal IV, to support cell growth and neuroplasticity. Alterations in the expression of the neuronal AdRs results in MS by shifting the cerebral inflammatory immune responses from remyelination to demyelination. Therefore, novel therapeutics for MS should be focused on the discovery and targeting of the AdR/AdL axis in the CNS rather than carrying on with immune suppressive interventions.

Overview of diet and autoimmune demyelinating optic neuritis: a narrative review

This review summarizes the cellular and molecular underpinnings of autoimmune demyelinating optic neuritis (ADON), a common sequela of multiple sclerosis and other demyelinating diseases. We further present nutritional interventions tested for people with multiple sclerosis focusing on strategies that have shown efficacy or associations with disease course and clinical outcomes. We then close by discuss the potential dietary guidance for preventing and/or ameliorating ADON.

The oral microbiome in autoimmune diseases: friend or foe?

The human body is colonized by abundant and diverse microorganisms, collectively known as the microbiome. The oral cavity has more than 700 species of bacteria and consists of unique microbiome niches on mucosal surfaces, on tooth hard tissue, and in saliva. The homeostatic balance between the oral microbiota and the immune system plays an indispensable role in maintaining the well-being and health status of the human host. Growing evidence has demonstrated that oral microbiota dysbiosis is actively involved in regulating the initiation and progression of an array of autoimmune diseases.Oral microbiota dysbiosis is driven by multiple factors, such as host genetic factors, dietary habits, stress, smoking, administration of antibiotics, tissue injury and infection. The dysregulation in the oral microbiome plays a crucial role in triggering and promoting autoimmune diseases via several mechanisms, including microbial translocation, molecular mimicry, autoantigen overproduction, and amplification of autoimmune responses by cytokines. Good oral hygiene behaviors, low carbohydrate diets, healthy lifestyles, usage of prebiotics, probiotics or synbiotics, oral microbiota transplantation and nanomedicine-based therapeutics are promising avenues for maintaining a balanced oral microbiome and treating oral microbiota-mediated autoimmune diseases. Thus, a comprehensive understanding of the relationship between oral microbiota dysbiosis and autoimmune diseases is critical for providing novel insights into the development of oral microbiota-based therapeutic approaches for combating these refractory diseases.

The role of the gut microbiota and fecal microbiota transplantation in neuroimmune diseases

The gut microbiota plays a key role in the function of the host immune system and neuroimmune diseases. Alterations in the composition of the gut microbiota can lead to pathology and altered formation of microbiota-derived components and metabolites. A series of neuroimmune diseases, such as myasthenia gravis (MG), multiple sclerosis (MS), neuromyelitis optica spectrum disorders (NMOSDs), Guillain-Barré syndrome (GBS), and autoimmune encephalitis (AIE), are associated with changes in the gut microbiota. Microecological therapy by improving the gut microbiota is expected to be an effective measure for treating and preventing some neuroimmune diseases. This article reviews the research progress related to the roles of gut microbiota and fecal microbiota transplantation (FMT) in neuroimmune diseases.

Key role of the gut-microbiota-brain axis via the subdiaphragmatic vagus nerve in demyelination of the cuprizone-treated mouse brain

Multiple sclerosis (MS) is the most common demyelinating disease that attacks the central nervous system. Dietary intake of cuprizone (CPZ) produces demyelination resembling that of patients with MS. Given the role of the vagus nerve in gut-microbiota-brain axis in development of MS, we performed this study to investigate whether subdiaphragmatic vagotomy (SDV) affects demyelination in CPZ-treated mice. SDV significantly ameliorated demyelination and microglial activation in the brain compared with sham-operated CPZ-treated mice. Furthermore, 16S ribosomal RNA analysis revealed that SDV significantly improved the abnormal gut microbiota composition of CPZ-treated mice. An untargeted metabolomic analysis demonstrated that SDV significantly improved abnormal blood levels of metabolites in CPZ-treated mice compared with sham-operated CPZ-treated mice. Notably, there were correlations between demyelination or microglial activation in the brain and the relative abundance of several microbiome populations, suggesting a link between gut microbiota and the brain. There were also correlations between demyelination or microglial activation in the brain and blood levels of metabolites. Together, these data suggest that CPZ produces demyelination in the brain through the gut-microbiota-brain axis via the subdiaphragmatic vagus nerve.

The role of Mediterranean diet and gut microbiota in type-2 diabetes mellitus associated with obesity (diabesity)

The human body is made up of 10¹⁴ human cells and 10¹⁵ bacterial cells, forming a combined structure that is described as a "superorganism". Commensal, symbiotic, and pathogenic microorganisms in the human body, many of which are located inside the intestine, affect health conditions and diseases. An important factor contributing to the development of chronic diseases is dysbiosis, which occurs when the number of pathogenic microorganisms increases. Dysbiosis is associated with increased intestinal permeability, endotoxemia (increased LPS), pro-inflammatory cytokine release, energy harvest, and adiposity, thus being involved in the pathogenesis of disorders like diabetes and obesity. Nutritional habits are the most important environmental factor that affects intestinal microbial composition. A dietary pattern that was proven successful in regulating gut microbiota is the renowned Mediterranean diet, which is characterized by high plant-based foods consumption, moderate fish and dairy products consumption, and low red meat consumption. There is an inverse relationship between adherence to the Mediterranean diet and chronic diseases like obesity and diabetes. In addition to the direct effects of the Mediterranean diet on the pathogenesis of these diseases, it can also be effective in preventing these diseases due to its effects on the intestinal microbiota. It is noted that the number of Bifidobacterium and Bacteroides increases the longer one's eating habit adhere to the Mediterranean diet, and the number of Firmicutes decreases, accordingly, thus supporting the symbiotic distribution in the intestinal microbiota.

Anemoside B4 ameliorates experimental autoimmune encephalomyelitis in mice by modulating inflammatory responses and the gut microbiota

BACKGROUND

Anemoside B4 (AB4) is a representative component of Pulsatilla decoction that is used in traditional Chinese medicine for treating inflammatory conditions. It is not known whether AB4 has beneficial effects on multiple sclerosis (MS).

METHODS

In the present study, we examined the preventative and therapeutic effects of AB4, and the possible mechanism by which it protects female mice against experimental autoimmune encephalomyelitis (EAE).

RESULTS

Preventative treatment with AB4 (given orally at 100 and 200 mg/kg for 18 days) reduced the clinical severity of EAE significantly (from 3.6 ± 1.3 to 1.8 ± 1.5 and 1.6 ± 0.6, respectively), and inhibited demyelination and inflammatory infiltration of the spinal cord. In the therapeutic protocol, oral administration of 200 mg/kg AB4 for 21 days after initiation of EAE significantly alleviated disease severity (from 2.6 ± 1.3 to 0.9 ± 0.6) and was as effective as the clinically used drug fingolimod (0.3 ± 0.6). Furthermore, both doses of AB4 significantly inhibited mRNA expression of TNF-α, IL-6, and IL-17, and STAT3 activation, in the spinal cord; and the ex vivo and iv vitro AB4 treatment markedly inhibited secretion of the three cytokines from lymphocytes of EAE mice upon in vitro restimulation. In addition, AB4 reversed the changes in the composition of the intestinal microbiome observed in EAE mice.

CONCLUSION

We reveal for the first time that AB4 protects against EAE by modulating inflammatory responses and the gut microbiota, demonstrating that AB4 may have potential as a therapeutic agent for treating MS in humans.

Probiotics: Protecting Our Health from the Gut

The gut microbiota (GM) comprises billions of microorganisms in the human gastrointestinal tract. This microbial community exerts numerous physiological functions. Prominent among these functions is the effect on host immunity through the uptake of nutrients that strengthen intestinal cells and cells involved in the immune response. The physiological functions of the GM are not limited to the gut, but bidirectional interactions between the gut microbiota and various extraintestinal organs have been identified. These interactions have been termed interorganic axes by several authors, among which the gut-brain, gut-skin, gut-lung, gut-heart, and gut-metabolism axes stand out. It has been shown that an organism is healthy or in homeostasis when the GM is in balance. However, altered GM or dysbiosis represents a critical factor in the pathogenesis of many local and systemic diseases. Therefore, probiotics intervene in this context, which, according to various published studies, allows balance to be maintained in the GM, leading to an individual's good health.

(R)-ketamine as prophylactic and therapeutic drug for neurological disorders: beyond depression

Neurological disorders are the leading cause of disability and the second leading cause of death worldwide. The increasing social and economic burdens of neurological disorders are driven by global population growth and aging. Depression is a common psychiatric symptom in numerous neurological disorders. It is also a risk factor for Alzheimer's disease (AD) and other dementias, Parkinson's disease (PD), and stroke. The rapid-acting and sustained antidepressant actions of (R,S)-ketamine for severe depression was accidentally discovered. Interestingly, (R)-ketamine has greater potency and longer-lasting antidepressant-like effects than (S)-ketamine in rodents. Importantly, its side effects in rodents and humans are lower than those of (R,S)-ketamine and (S)-ketamine. Furthermore, (R)-ketamine could elicit beneficial actions in various rodent models of neurological disorders, including PD, multiple sclerosis (MS), and stroke. In this article, we review the potential of (R)-ketamine as a prophylactic or therapeutic drug for neurological disorders including AD and other dementias, PD, MS, and stroke.

Gut-Brain Axis as a Pathological and Therapeutic Target for Neurodegenerative Disorders

Human lifestyle and dietary behaviors contribute to disease onset and progression. Neurodegenerative diseases (NDDs), considered multifactorial disorders, have been associated with changes in the gut microbiome. NDDs display pathologies that alter brain functions with a tendency to worsen over time. NDDs are a worldwide health problem; in the US alone, 12 million Americans will suffer from NDDs by 2030. While etiology may vary, the gut microbiome serves as a key element underlying NDD development and prognosis. In particular, an inflammation-associated microbiome plagues NDDs. Conversely, sequestration of this inflammatory microbiome by a correction in the dysbiotic state of the gut may render therapeutic effects on NDDs. To this end, treatment with short-chain fatty acid-producing bacteria, the main metabolites responsible for maintaining gut homeostasis, ameliorates the inflammatory microbiome. This intimate pathological link between the gut and NDDs suggests that the gut-brain axis (GBA) acts as an underexplored area for developing therapies for NDDs. Traditionally, the classification of NDDs depends on their clinical presentation, mostly manifesting as extrapyramidal and pyramidal movement disorders, with neuropathological evaluation at autopsy as the gold standard for diagnosis. In this review, we highlight the evolving notion that GBA stands as an equally sensitive pathological marker of NDDs, particularly in Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and chronic stroke. Additionally, GBA represents a potent therapeutic target for treating NDDs.

(R)-ketamine ameliorates the progression of experimental autoimmune encephalomyelitis in mice

Multiple sclerosis (MS) is an immune-mediated neurological disease that attacks the central nervous system, including spinal cord and brain. Experimental autoimmune encephalomyelitis (EAE) is the most commonly used model for MS. Depression is the most prevalent comorbidity in MS patients. We previously demonstrated that (R)-ketamine would be a novel antidepressant without side effects of ketamine. This study was undertaken to investigate whether (R)-ketamine could attenuate disease progression in EAE mouse model. (R)-ketamine (10 mg/kg/day for 15 days) significantly attenuated the reduction of body weight in EAE model mice compared to saline-treated mice. Furthermore, (R)-ketamine ameliorated the clinical EAE scores compared to saline-treated mice. Moreover, (R)-ketamine significantly attenuated the marked increases in the pathological scores, microglial activation, and blood-brain barrier integrity in the spinal cord compared to saline-treated mice. In conclusion, the current study suggests that (R)-ketamine could ameliorate EAE clinical scores and pathological changes in the spinal cord of EAE mice. Therefore, it is likely that (R)-ketamine would be a new potential prophylactic drug for MS.