Gut Microbiota and Disorders of the Central Nervous System

Bioactive Components in Fruit Interact with Gut Microbes

Fruits contain many bioactive compounds, including polysaccharides, oligosaccharides, polyphenols, anthocyanins, and flavonoids. All of these bioactives in fruit have potentially beneficial effects on gut microbiota and host health. On the one hand, fruit rich in active ingredients can act as substrates to interact with microorganisms and produce metabolites to regulate the gut microbiota. On the other hand, gut microbes could promote health effects in the host by balancing dysbiosis of gut microbiota. We have extensively analyzed significant information on bioactive components in fruits based on Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA). Although the deep mechanism of action of bioactive components in fruits on gut microbiota needs further study, these results also provide supportive information on fruits as a source of dietary active ingredients to provide support for the adjunctive role of fruits in disease prevention and treatment.

Dysbiosis of gut microbiota inhibits NMNAT2 to promote neurobehavioral deficits and oxidative stress response in the 6-OHDA-lesioned rat model of Parkinson's disease

BACKGROUND

New data are accumulating on gut microbial dysbiosis in Parkinson's disease (PD), while the specific mechanism remains uncharacterized. This study aims to investigate the potential role and pathophysiological mechanism of dysbiosis of gut microbiota in 6-hydroxydopamine (6-OHDA)-induced PD rat models.

METHODS

The shotgun metagenome sequencing data of fecal samples from PD patients and healthy individuals were obtained from the Sequence Read Archive (SRA) database. The diversity, abundance, and functional composition of gut microbiota were further analyzed in these data. After the exploration of the functional pathway-related genes, KEGG and GEO databases were used to obtain PD-related microarray datasets for differential expression analysis. Finally, in vivo experiments were performed to confirm the roles of fecal microbiota transplantation (FMT) and upregulated NMNAT2 in neurobehavioral symptoms and oxidative stress response in 6-OHDA-lesioned rats.

RESULTS

Significant differences were found in the diversity, abundance, and functional composition of gut microbiota between PD patients and healthy individuals. Dysbiosis of gut microbiota could regulate NAD⁺ anabolic pathway to affect the occurrence and development of PD. As a NAD⁺ anabolic pathway-related gene, NMNAT2 was poorly expressed in the brain tissues of PD patients. More importantly, FMT or overexpression of NMNAT2 alleviated neurobehavioral deficits and reduced oxidative stress in 6-OHDA-lesioned rats.

CONCLUSIONS

Taken together, we demonstrated that dysbiosis of gut microbiota suppressed NMNAT2 expression, thus exacerbating neurobehavioral deficits and oxidative stress response in 6-OHDA-lesioned rats, which could be rescued by FMT or NMNAT2 restoration.

Microbiota-gut-brain axis impairment in the pathogenesis of stroke: implication as a potent therapeutic target

The human microbiota-gut-brain axis has an enormous role in the maintenance of homeostasis and health. Over the last two decades, it has received concerted research attention and focus due to a rapidly emerging volume of evidence that has established that impairment within the microbiota-gut-brain axis contributes to the development and progression of various diseases. Stroke is one of the entities identified to be associated with microbiota-gut-brain axis impairment. Currently, there are still limitations in the clinical treatment of stroke, and the presence of a non-nervous factor from gut microbiota that can alter the course of stroke presents a novel strategy towards the search for a therapeutic silver bullet against stroke. Hence, the aim herein, was to focus on the involvement of microbiota-gut-brain axis impairment in the pathogenesis stroke as well as elucidate its implications as a potent therapeutic target against stroke. The findings of studies to date have revealed and extended the role microbiota-gut-brain axis impairment in the pathogenesis of stroke, and studies have identified from both clinical and pre-clinical perspectives targets within the microbiota-gut-brain axis and successfully modulated the outcome of stroke. It was concluded that the microbiota-gut-brain axis stands as potent target to salvage the neurons in the ischemic penumbra for the treatment of stroke. Assessment of the microbiota profile and its metabolites status holds enormous clinical potentials as a non-invasive indicator for the early diagnosis and prognosis of stroke.

A Deep Insight into the Correlation Between Gut Dysbiosis and Alzheimer’s Amyloidopathy

Background

Recent research has shown a strong correlation between gut dysbiosis and Alzheimer’s disease (AD).

Purpose

To investigate the relationship between gut dysbiosis, immune system activation, and the onset of AD and to examine current breakthroughs in microbiota-targeted AD therapeutics.

Methods

A review of scientific literature was conducted to assess the correlation between gut dysbiosis and AD and the various factors associated.

Results

Gut dysbiosis produces an increase in harmful substances, such as bacterial amyloids, which makes the gut barrier and blood-brain barrier more permeable. This leads to the stimulation of immunological responses and an increase in cytokines such as interleukin-1β (IL-1β). As a result, gut dysbiosis accelerates the progression of AD.

Conclusion

The review highlights the connection between gut dysbiosis and AD and the potential for microbiota-targeted therapies in AD treatment.

Pictorial Abstract

Exercise training has a protective effect in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine mice model with improved neural and intestinal pathology and modified intestinal flora

Parkinson's disease (PD) is a common neurodegenerative disease with the exact etiology still unclear, but gut microbial disorders are thought to be related to the initiation and progression of it. Exercise training has a significant effect on the intestinal flora, so to investigate the promotion effect of exercise training on Parkinson's disease, we performed a rotarod walking training (5 times a week at 25 rpm for 20 min for 8 weeks) on a chronic mouse model of Parkinson's disease induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and observed the locomotor function of mice, function of dopaminergic neurons, intestinal mucosal barrier condition, intestinal inflammation and the structure and composition of intestinal flora. The results showed in these PD mice, exercise training improved their motility, increased the dopamine (DA) content in the striatum, along with promoted the gene expression of tyrosine hydroxylase and brain-derived neurotrophic factor in the striatum, which suggests this exercise training might protect striatal dopaminergic neurons from MPTP damage; the results also showed exercise training promoted recovery from ileal pathology, reduced the gene expression of intestinal inflammatory factors, and significantly altered the composition and structure of the intestinal flora in these mice.

Intestinal dysbiosis mediates cognitive impairment via the intestine and brain NLRP3 inflammasome activation in chronic sleep deprivation

Growing evidence suggests the involvement of the microbiota-gut-brain axis in cognitive impairment induced by sleep deprivation (SD), however how the microbiota-gut-brain axis work remains elusive. Here, we discovered that chronic SD induced intestinal dysbiosis, activated NLRP3 inflammasome in the colon and brain, destructed intestinal/blood-brain barrier, and impaired cognitive function in mice. Transplantation of "SD microbiota" could almost mimic the pathological and behavioral changes caused by chronic SD. Furthermore, all the behavioral and pathological abnormalities were practically reversed in chronic sleep-deprived NLRP3^-/- mice. Regional knockdown NLRP3 expression in the gut and hippocampus, respectively. We observed that down-regulation of NLRP3 in the hippocampus inhibited neuroinflammation, and ameliorated synaptic dysfunction and cognitive impairment induced by chronic SD. More intriguingly, the down-regulation of NLRP3 in the gut protected the intestinal barrier, attenuated the levels of peripheral inflammatory factors, down-regulated the expression of NLRP3 in the brain, and improved cognitive function in chronic SD mice. Our results identified gut microbiota as a driver in chronic SD and highlighted the NLRP3 inflammasome as a key regulator within the microbiota-gut-brain axis.

New insights into the mechanisms of high-fat diet mediated gut microbiota in chronic diseases

High-fat diet (HFD) has been recognized as a primary factor in the risk of chronic disease. Obesity, diabetes, gastrointestinal diseases, neurodegenerative diseases, and cardiovascular diseases have long been known as chronic diseases with high worldwide incidence. In this review, the influences of gut microbiota and their corresponding bacterial metabolites on the mechanisms of HFD-induced chronic diseases are systematically summarized. Gut microbiota imbalance is also known to increase susceptibility to diseases. Several studies have proven that HFD has a negative impact on gut microbiota, also exacerbating the course of many chronic diseases through increased populations of Erysipelotrichaceae, facultative anaerobic bacteria, and opportunistic pathogens. Since bile acids, lipopolysaccharide, short-chain fatty acids, and trimethylamine N-oxide have long been known as common features of bacterial metabolites, we will explore the possibility of synergistic mechanisms among those metabolites and gut microbiota in the context of HFD-induced chronic diseases. Recent literature concerning the mechanistic actions of HFD-mediated gut microbiota have been collected from PubMed, Google Scholar, and Scopus. The aim of this review is to provide new insights into those mechanisms and to point out the potential biomarkers of HFD-mediated gut microbiota.

The Emerging Landscape of Natural Small-molecule Therapeutics for Huntington's Disease

Huntington's disease (HD) is a rare and fatal neurodegenerative disorder with no diseasemodifying therapeutics. HD is characterized by extensive neuronal loss and is caused by the inherited expansion of the huntingtin (HTT) gene that encodes a toxic mutant HTT (mHTT) protein having expanded polyglutamine (polyQ) residues. Current HD therapeutics only offer symptomatic relief. In fact, Food and Drug Administration (FDA) approved two synthetic small-molecule VMAT2 inhibitors, tetrabenazine (1) and deutetrabenazine (2), for managing HD chorea and various other diseases in clinical trials. Therefore, the landscape of drug discovery programs for HD is evolving to discover disease- modifying HD therapeutics. Likewise, numerous natural products are being evaluated at different stages of clinical development and have shown the potential to ameliorate HD pathology. The inherent anti-inflammatory and antioxidant properties of natural products mitigate the mHTT-induced oxidative stress and neuroinflammation, improve mitochondrial functions, and augment the anti-apoptotic and pro-autophagic mechanisms for increased survival of neurons in HD. In this review, we have discussed HD pathogenesis and summarized the anti-HD clinical and pre-clinical natural products, focusing on their therapeutic effects and neuroprotective mechanism/s.

The role of gut microbiota in gout: Is gut microbiota a potential target for gout treatment

Numerous studies have demonstrated that gut microbiota is essential for the host's health because it regulates the host's metabolism, endocrine, and immune systems. In recent years, increasing evidence has shown that gut microbiota plays a role in the onset and progression of gout. Changes in the composition and metabolism of the gut microbiota, result in abnormalities of uric acid degradation, increasing uric acid generation, releasing pro-inflammatory mediators, and intestinal barrier damage in developing gout. As a result, gout therapy that targets gut microbiota has drawn significant interest. This review summarized how the gut microbiota contributes to the pathophysiology of gout and how gout affects the gut microbiota. Additionally, this study explained how gut microbiota might serve as a unique index for the diagnosis of gout and how conventional gout treatment medicines interact with it. Finally, prospective therapeutic approaches focusing on gut microbiota for the prevention and treatment of gout were highlighted, which may represent a future avenue in gout treatment.

“Iron triangle” of regulating the uterine microecology: Endometrial microbiota, immunity and endometrium

The uterus is the core place for breeding new life. The balance and imbalance of uterine microecology can directly affect or even dominate the female reproductive health. Emerging data demonstrate that endometrial microbiota, endometrium and immunity play an irreplaceable role in regulating uterine microecology, forming a dynamic iron triangle relationship. Up to nowadays, it remains unclear how the three factors affect and interact with each other, which is also a frontier topic in the emerging field of reproductive tract microecology. From this new perspective, we aim to clarify the relationship and mechanism of the interaction of these three factors, especially their pairwise interactions. Finally, the limitations and future perspectives of the current studies are summarized. In general, these three factors have a dynamic relationship of mutual dependence, promotion and restriction under the physiological or pathological conditions of uterus, among which the regulatory mechanism of microbiota and immunity plays a role of bridge. These findings can provide new insights and measures for the regulation of uterine microecology, the prevention and treatment of endometrial diseases, and the further multi-disciplinary integration between microbiology, immunology and reproductive medicine.

Gut Microbiota Modification via Glucagon-like Peptide-1 with Beneficial Neuroprotective Effects

BACKGROUND: In recent decades, it has been shown that the association between intestinal bacterial imbalance (dysbiosis) and various diseases such as type 2 diabetes can play a role in the development of Alzheimer's and Parkinson's diseases. In this study, the beneficial effects of intestinal microbiota glucagon-like peptide 1 (GLP-1) in cognitive disorders were investigated. METHODS: PubMed-Medline, Web of Science, and Scopus were searched to identify experimental studies based on the bacterial strains along with GLP-1 1 expression in preventing or reducing cognitive impairment. Of the 233 studies, six were eligible for inclusion, and the Systematic Review Centre for Laboratory animal Experimentation (SYRCLE) risk of bias tool was used to evaluate the risk of bias in individual studies. RESULTS: The results showed that intestinal expression of GLP-1 1 could reduce the intestinal pathogenic genus such as Enterobacteriaceae and was obviously associated with a greater number of beneficial genera such as Lactobacillus and Akkermansia. Also, the neuroprotective effects of Clostridium butyricum with GLP-1 1 in a mice were approved. Therefore, the modulation of the intestinal microbiota, mediated by an increase in the intestinal GLP-1 1 level, consequently improved cognitive function. CONCLUSION: In this review, we have indicated that the gut microbiota, by stimulating the expression of the intestinal hormones like GLP-1 1, and also with a beneficial effect in inhibiting some involved genes in inflammation, can declined the development of cognitive disorders.

Microbiota shaping — the effects of probiotics, prebiotics, and fecal microbiota transplant on cognitive functions: A systematic review

BACKGROUND

Dementia is a chronic progressive neurological disease affecting millions of people worldwide, and represents a relevant economic burden for healthcare systems. Although its pathogenesis is still unknown, recent findings have reported that a dysregulated gut-brain axis communication, a fundamental relationship mediated by several host and microbial molecules, is associated with cognitive disorders. In addition, gut microbiota manipulation reduces neuroinflammation, improving cognitive function by restoring the functional gut-brain axis.

AIM

To better define the effects of probiotics, prebiotics, synbiotics, and fecal microbiota transplant (FMT) on cognitive function.

METHODS

We performed a literature search of human randomized clinical trials to examine the effects of the administration of probiotics, prebiotics, synbiotics, or FMT on cognition outcomes in healthy or sick people of every age, sex, and nationality. We systematically searched Embase, Medline/PubMed, Cochrane Library, central and clinicaltrials.gov databases with a combination of comprehensive terms related to cognition and gut microbiota manipulation. Then we carefully reviewed and synthesized the data by type of study design and setting, characteristics of the studied population, kind of intervention (strain type or mixture type, dosage, and frequency of administration), control treatment, inclusion and exclusion criteria, follow-up duration, and cognitive or memory outcomes.

RESULTS

After examining the titles and abstracts, the initial literature screening identified 995 articles, but we added 23 papers in our systematic review. The analyses of these selected studies highlighted that both probiotic supplementation and FMT improved cognitive function regardless of the type and posology of administration and the adopted cognitive tests and questionnaires. We found that most of the studies conducted in healthy people showed a significant positive effect of the intervention on at least one of the performed cognitive tests. Regarding unhealthy subjects, while FMT and especially probiotic administration had multiple beneficial effects on different cognitive functions, supplementation with prebiotics did not provide any cognitive improvement.

CONCLUSION

Probiotic supplementation and FMT may represent a promising strategy to restore gut eubiosis and enhance the cognitive functions of healthy people and patients with neurological disorders.

Decoding the Role of Gut-Microbiome in the Food Addiction Paradigm

Eating behaviour is characterised by a solid balance between homeostatic and hedonic regulatory mechanisms at the central level and highly influenced by peripheral signals. Among these signals, those generated by the gut microbiota have achieved relevance in recent years. Despite this complex regulation, under certain circumstances eating behaviour can be deregulated becoming addictive. Although there is still an ongoing debate about the food addiction concept, studies agree that patients with eating addictive behaviour present similar symptoms to those experienced by drug addicts, by affecting central areas involved in the control of motivated behaviour. In this context, this review tries to summarise the main data regarding the role of the gut microbiome in eating behaviour and how a gut dysbiosis can be responsible for a maladaptive behaviour such as “food addiction”.

Bone-Derived Modulators That Regulate Brain Function: Emerging Therapeutic Targets for Neurological Disorders

Bone has traditionally been regarded as a structural organ that supports and protects the various organs of the body. Recent studies suggest that bone also acts as an endocrine organ to regulate whole-body metabolism. Particularly, homeostasis of the bone is shown to be necessary for brain development and function. Abnormal bone metabolism is associated with the onset and progression of neurological disorders. Recently, multiple bone-derived modulators have been shown to participate in brain function and neurological disorders, including osteocalcin, lipocalin 2, and osteopontin, as have bone marrow-derived cells such as mesenchymal stem cells, hematopoietic stem cells, and microglia-like cells. This review summarizes current findings regarding the roles of these bone-derived modulators in the brain, and also follows their involvement in the pathogenesis of neurological disorders. The content of this review may aide in the development of promising therapeutic strategies for neurological disorders via targeting bone.

Changes in the anterior cingulate cortex in Crohn's disease: A neuroimaging perspective

INTRODUCTION

Evidence suggests that Crohn's disease (CD) pathophysiology goes beyond the gastrointestinal tract and is also strongly associated with the brain. In particular, the anterior cingulate cortex (ACC), which plays an integral role in the first brain as part of the default mode network (DMN) and pain matrix, shows abnormalities using multiple neuroimaging modalities. This review summarizes nine related studies that investigated changes in the ACC using structural magnetic resonance imaging, resting-state functional magnetic resonance imaging, and magnetic resonance spectroscopy.

METHODS

An extensive PubMed literature search was conducted from 1980 to August 2020. In a review of the articles identified, particular attention was paid to analysis methods, technical protocol characteristics, and specific changes in the ACC.

RESULTS

In terms of morphology, a decrease in gray matter volume and cortical thickness was observed along with an increase in local gyrification index. In terms of function, functional connectivity (FC) within the DMN was increased. FC between the ACC and the amygdala was decreased. Higher amplitudes of low-frequency fluctuation and graph theory results, including connectivity strength, clustering coefficient, and local efficiency, were detected. In terms of neurotransmitter changes, the concentrations of glutamate increased along with a decrease in gamma-aminobutyric acid, providing a rational explanation for abdominal pain. These changes may be attributed to stress, pain, and negative emotions, as well as changes in gut microbiota.

CONCLUSIONS

For patients with CD, the ACC demonstrates structural, functional, and metabolic changes. In terms of clinical findings, the ACC plays an important role in the onset of depression/anxiety and abdominal pain. Therefore, successful modulation of this pathway may guide treatment.

Mental Disorders Linked to Crosstalk between The Gut Microbiome and The Brain

Often called the second brain, the gut communicates extensively with the brain and vice versa. The conversation between these two organs affects a variety of physiological mechanisms that are associated with our mental health. Over the past decade, a growing body of evidence has suggested that the gut microbiome builds a unique ecosystem inside the gastrointestinal tract to maintain the homeostasis and that compositional changes in the gut microbiome are highly correlated with several mental disorders. There are ongoing efforts to treat or prevent mental disorders by regulating the gut microbiome using probiotics. These attempts are based on the seminal findings that probiotics can control the gut microbiome and affect mental conditions. However, some issues have yet to be conclusively addressed, especially the causality between the gut microbiome and mental disorders. In this review, we focus on the mechanisms by which the gut microbiome affects mental health and diseases. Furthermore, we discuss the potential use of probiotics as therapeutic agents for psychiatric disorders.

Gut dysbiosis and age-related neurological diseases; an innovative approach for therapeutic interventions

The gut microbiota is a complex ecosystem of bacteria, fungi, and viruses that acts as a critical regulator in microbial, metabolic, and immune responses in the host organism. Imbalances in the gut microbiota, termed "dysbiosis," often induce aberrant immune responses, which in turn disrupt the local and systemic homeostasis of the host. Emerging evidence has highlighted the importance of gut microbiota in intestinal diseases, and more recently, in age-related central nervous systems diseases, for example, stroke and Alzheimer's disease. It is now generally recognized that gut microbiota significantly influences host behaviors and modulates the interaction between microbiota, gut, and brain, via the "microbiota-gut-brain axis." Several approaches have been utilized to reduce age-related dysbiosis in experimental models and in clinical studies. These include strategies to manipulate the microbiome via fecal microbiota transplantation, administration of prebiotics and probiotics, and dietary interventions. In this review, we explore both clinical and preclinical therapies for treating age-related dysbiosis.