Gut microbiota modulate neurobehavior through changes in brain insulin sensitivity and metabolism

Effects of gallic acid and physical training on liver damage, force, and anxiety in obese mice: Hepatic modulation of Sestrin 2 (SESN2) and PGC-α expression

Obesity and overweight are multifactorial diseases affecting more than one-third of the world's population. Physical inactivity contributes to a positive energy balance and the onset of obesity. Exercise combined with a balanced diet is an effective non-pharmacological strategy to improve obesity-related disorders. Gallic acid (GA), is a natural endogenous polyphenol found in a variety of fruits, vegetables, and wines, with beneficial effects on energetic homeostasis. The present study aims to investigate the effects of exercise training on obese mice supplemented with GA. Animal experimentation was performed with male Swiss mice divided into five groups: ST (standard control), HFD (obese control), HFD + GA (GA supplement), HFD + Trained (training), and HFD + GA + Trained (GA and training). The groups are treated for eight weeks with 200 mg/kg/body weight of the feed compound and, if applicable, physical training. The main findings of the present study show that GA supplementation improves liver fat, body weight, adiposity, and plasma insulin levels. In addition, animals treated with the GA and a physical training program demonstrate reduced levels of anxiety. Gene expression analyses show that Sesn2 is activated via PGC-1α independent of the GATOR2 protein, which is activated by GA in the context of physical activity. These data are corroborated by molecular docking analysis, demonstrating the interaction of GA with GATOR2. The present study contributes to understanding the metabolic effects of GA and physical training and demonstrates a new hepatic mechanism of action via Sestrin 2 and PGC-1α.

Dietary polyphenols regulate appetite mechanism via gut-brain axis and gut homeostasis

Nowadays, due to the rise of fast-food consumption, the metabolic diseases are increasing as a result of high-sugar and high-fat diets. Therefore, there is an urgent need for natural, healthy and side-effect-free diets in daily life. Whole grain supplementation can enhance satiety and regulate energy metabolism, effects that have been attributed to polyphenol content. Dietary polyphenols interact with gut microbiota to produce intermediate metabolites that can regulate appetite while also enhancing prebiotic effects. This review considers how interactions between gut metabolites and dietary polyphenols might regulate appetite by acting on the gut-brain axis. In addition, further advances in the study of dietary polyphenols and gut microbial metabolites on energy metabolism and gut homeostasis are summarized. This review contributes to a better understanding of how dietary polyphenols regulate appetite via the gut-brain axis, thereby providing nutritional references for citizens' dietary preferences.

Transcutaneous vagus nerve stimulation modulates depression-like phenotype induced by high-fat diet via P2X7R/NLRP3/IL-1β in the prefrontal cortex

BACKGROUND

Depression is a common psychiatric disorder in diabetic patients. Depressive mood associated with obesity/metabolic disorders is related to the inflammatory response caused by long-term consumption of high-fat diets, but its molecular mechanism is unclear. In this study, we investigated whether the antidepressant effect of transcutaneous auricular vagus nerve stimulation (taVNS) in high-fat diet rats works through the P2X7R/NLRP3/IL-1β pathway.

METHODS

We first used 16S rRNA gene sequencing analysis and LC-MS metabolomics assays in Zucker diabetic fatty (ZDF) rats with long-term high-fat diet (Purina #5008) induced significant depression-like behaviors. Next, the forced swimming test (FST) and open field test (OFT) were measured to evaluate the antidepressive effect of taVNS. Immunofluorescence and western blotting (WB) were used to measure the microglia state and the expression of P2X7R, NLRP3, and IL-1β in PFC.

RESULTS

Purina#5008 diet induced significant depression-like behaviors in ZDF rats and was closely related to purine and inflammatory metabolites. Consecutive taVNS increased plasma insulin concentration, reduced glycated hemoglobin and glucagon content in ZDF rats, significantly improved the depressive-like phenotype in ZDF rats through reducing the microglia activity, and increased the expression of P2X7R, NLRP3, and IL-1β in the prefrontal cortex (PFC).

CONCLUSION

The P2X7R/NLRP3/IL-1β signaling pathway may play an important role in the antidepressant-like behavior of taVNS, which provides a promising mechanism for taVNS clinical treatment of diabetes combined with depression.

Induction of autism-related behavior in male mice by early-life vitamin D deficiency: association with disruption of the gut microbial composition and homeostasis

Vitamin D deficiency (VDD) during early life emerges as a potential risk factor for autism spectrum disorder (ASD). Individuals with autism commonly exhibit lower vitamin D (VD) levels compared to the general population, and VD deficiency is prevalent during pregnancy and lactation. Moreover, gastrointestinal comorbidity, prevalent in ASD patients, correlates closely with disruptions in the gut microbiota and altered intestinal permeability. Therefore, it is fascinating and significant to explore the effects of maternal VD deficiency during pregnancy and lactation on the maturation of the gut microbiota of the offspring and its relevance to autism spectrum disorders. In this study, we established maternal pregnancy and lactation VD-deficient mouse models, employed shotgun macrogenomic sequencing to unveil alterations in the gut microbiome of offspring mice, and observed autism-related behaviours. Furthermore, fecal microbial transplantation (FMT) reversed repetitive and anxious behaviours and alleviated social deficits in offspring mice by modulating the gut microbiota and increasing short-chain fatty acid levels in the cecum, along with influencing the concentrations of claudin-1 and occludin in the colon. Our findings confirm that VDD during pregnancy and lactation is a risk factor for autism in the offspring, with disturbances in the structure and function of the offspring's gut microbiota contributing at least part of the effect. The study emphasises the importance of nutrition and gut health early in life. Simultaneously, this study further demonstrates the effect of VDD on ASD and provides potential ideas for early prevention and intervention of ASD.

Anti-obesity potentiality of Lactiplantibacillus plantarum E2_MCCKT isolated from a fermented beverage, haria: a high fat diet-induced obese mice model study

Obesity is a growing epidemic worldwide. Several pharmacologic drugs are being used to treat obesity but these medicines exhibit side effects. To find out the alternatives of these drugs, we aimed to assess the probiotic properties and anti-obesity potentiality of a lactic acid bacterium E2_MCCKT, isolated from a traditional fermented rice beverage, haria. Based on the 16S rRNA sequencing, the bacterium was identified as Lactiplantibacillus plantarum E2_MCCKT. The bacterium exhibited in vitro probiotic activity in terms of high survivability in an acidic environment and 2% bile salt, moderate auto-aggregation, and hydrophobicity. Later, E2_MCCKT was applied to obese mice to prove its anti-obesity potentiality. Adult male mice (15.39 ± 0.19 g) were randomly divided into three groups (n = 5) according to the type of diet: normal diet (ND), high-fat diet (HFD), and HFD supplemented with E2_MCCKT (HFT). After four weeks of bacterial treatment on the obese mice, a significant reduction of body weight, triglyceride, and cholesterol levels, whereas, improvements in serum glucose levels were observed. The bacterial therapy led to mRNA up-regulation of lipolytic transcription factors such as peroxisome proliferator-activated receptor-α which may increase the expression of fatty acid oxidation-related genes such as acyl-CoA oxidase and carnitine palmitoyl-transferase-1. Concomitantly, both adipocytogenesis and fatty acid synthesis were arrested as reflected by the down-regulation of sterol-regulatory element-binding protein-1c, acetyl-CoA carboxylase, and fatty acid synthase genes. In protein expression study, E2_MCCKT significantly increased IL-10 expression while decreasing pro-inflammatory cytokine (IL-1Ra and TNF-α) expression. In conclusion, the probiotic Lp. plantarum E2_MCCKT might have significant anti-obesity effects on mice.

Insulinemic potential of lifestyle is associated with depression and anxiety in adults: A large community-based study

BACKGROUND

We aimed to investigate the association between an empirical lifestyle index for hyperinsulinemia (ELIH), empirical lifestyle index for insulin resistance (ELIR), and depression and anxiety in an adult Iranian population.

METHODS

In this cross-sectional study, a total of 6450 participants, aged 35-65 years were recruited as part of the MASHAD cohort study. Dietary intakes were assessed using a validated food frequency questionnaire (FFQ). Depression and anxiety were screened using Beck Depression Inventory (BDI) and Beck Anxiety Inventory (BAI). ELIH and ELIR were calculated using dietary intake, body mass index, and physical activity information. Multivariable ordinal logistic regression models were applied to determine the association between ELIH, ELIR, and depression and anxiety severity.

RESULTS

In a fully adjusted model, participants with the highest ELIH quartile had a higher odds of more severe depression and anxiety compared to those in the lowest category (OR = 1.44; 95 % CI = 1.22-1.71 and OR = 1.62; 95 % CI = 1.37-1.25, respectively). Participants with the highest ELIR had higher odds of more severe depression and anxiety compared to those in the lowest category (OR = 1.22; 95 % CI = 1.04-1.43 and OR = 1.21; 95 % CI = 1.03-1.42, respectively).

LIMITATIONS

The assessment of dietary intake and mental health by questionnaires may increases the rate of misclassification. Due to the study's cross-sectional nature, causal relationships cannot be established.

CONCLUSION

There was a significant positive association between the hyperinsulinemia and insulin resistance potential of lifestyle and severity of depression and anxiety among Iranian adults.

Correlation between symptoms and cognitive function changes in patients with primary insomnia and pathways in gut microbiota

Background

Primary insomnia (PI) refers to syndromes of difficulty falling asleep, poor sleep quality, early awakening, and difficulty falling asleep after waking up. Although there have been numerous studies, the specific etiology and pathogenesis of PI are still misunderstanding. In recent years, the gut microbiota has been proved to be involved in the metabolism of many mental disorders. But the specific mechanisms of its involvement in PI have not been fully elucidated. This study aims to explore the relationship between the gut microbiota and the symptoms, cognitive function changes in PI.

Methods

In this study, the gut microbiota of PI patients and healthy controls was profiled by performing stool 16s rRNA gene sequencing. The co-occurrence network was constructed by using Weight Gene Co-expression Network Analysis (WGCNA) algorithm. The correlation between gut microbiota associated pathways and traits in PI were predicted.

Results

WGCNA results demonstrated several Operational Taxonomic Units (OTU) modules are correlated to symptoms. By using PICRUSt2 software, we predicted the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways of microbiota in modules. For instance, sleep efficiency may be correlated with the presence of Insulin signaling pathway, Flavonoid biosynthesis, Ascorbate and aldarate metabolism, Nitrotoluene degradation, Biotin metabolism, RNA polymerase and Chlorocyclohexane and chlorobenzene degradation. Total sleep time may be correlated with the presence of Tyrosine metabolism, Propanoate metabolism, Carbon fixation pathways in prokaryotes, Carotenoid biosynthesis, Systemic lupus erythematosus, Nitrotoluene degradation and Biosynthesis of unsaturated fatty acids. The severity of insomnia may be correlated with Insulin signaling pathway, Flavonoid biosynthesis, Ascorbate and aldarate metabolism, Nitrotoluene degradation, Biotin metabolism and RNA polymerase. Change of name score in Montreal Cognitive Assessment (MoCA) may be correlated with Tyrosine metabolism, Propanoate metabolism, Carbon fixation pathways in prokaryotes, Carotenoid biosynthesis, Systemic lupus erythematosus, Nitrotoluene degradation, Biosynthesis of unsaturated fatty acids, Apoptosis, Steroid hormone biosynthesis, Geraniol degradation, Protein digestion and absorption and Bisphenol degradation in Gut Microbiota (GM).

Conclusion

This study revealed the potential relationships between gut microbiota and PI. By using pathway prediction and enrichment analysis, we concluded many metabolic pathways may associated with some important traits of insomnia patients, including sleep efficiency, severe insomnia, total sleep time and change of name score in MoCA. The metabolic pathways include Insulin signaling pathway, Flavonoid biosynthesis, Ascorbate and aldarate metabolism, Nitrotoluene degradation, Biotin metabolism, RNA polymerase and Chlorocyclohexane, chlorobenzene degradation, Tyrosine metabolism, Propanoate metabolism, Carbon fixation pathways in prokaryotes, Carotenoid biosynthesis, Systemic lupus erythematosus, Biosynthesis of unsaturated fatty acids, Apoptosis, Steroid hormone biosynthesis, Geraniol degradation, Protein digestion and absorption and Bisphenol degradation.Our study demonstrated that PI patients demonstrate significant changes in gut microbiota, which will help delineate the relationship between gut microbiota and syndromes of PI.

Gut microbiota-derived short-chain fatty acids ameliorate methamphetamine-induced depression- and anxiety-like behaviors in a Sigmar-1 receptor-dependent manner

Methamphetamine (Meth) abuse can cause serious mental disorders, including anxiety and depression. The gut microbiota is a crucial contributor to maintaining host mental health. Here, we aim to investigate if microbiota participate in Meth-induced mental disorders, and the potential mechanisms involved. Here, 15 mg/kg Meth resulted in anxiety- and depression-like behaviors of mice successfully and suppressed the Sigma-1 receptor (SIGMAR1)/BDNF/TRKB pathway in the hippocampus. Meanwhile, Meth impaired gut homeostasis by arousing the Toll-like receptor 4 (TLR4)-related colonic inflammation, disturbing the gut microbiome and reducing the microbiota-derived short-chain fatty acids (SCFAs). Moreover, fecal microbiota from Meth-administrated mice mediated the colonic inflammation and reproduced anxiety- and depression-like behaviors in recipients. Further, SCFAs supplementation optimized Meth-induced microbial dysbiosis, ameliorated colonic inflammation, and repressed anxiety- and depression-like behaviors. Finally, Sigmar1 knockout (Sigmar1-/-) repressed the BDNF/TRKB pathway and produced similar behavioral phenotypes with Meth exposure, and eliminated the anti-anxiety and -depression effects of SCFAs. The activation of SIGMAR1 with fluvoxamine attenuated Meth-induced anxiety- and depression-like behaviors. Our findings indicated that gut microbiota-derived SCFAs could optimize gut homeostasis, and ameliorate Meth-induced mental disorders in a SIGMAR1-dependent manner. This study confirms the crucial role of microbiota in Meth-related mental disorders and provides a potential preemptive therapy.

Exploratory Study of Gastrointestinal Redox Biomarkers in the Presymptomatic and Symptomatic Tg2576 Mouse Model of Familial Alzheimer's Disease: Phenotypic Correlates and Effects of Chronic Oral d-Galactose

The gut might play an important role in the etiopathogenesis of Alzheimer's disease (AD) as gastrointestinal alterations often precede the development of neuropathological changes in the brain and correlate with disease progression in animal models. The gut has an immense capacity to generate free radicals whose role in the etiopathogenesis of AD is well-known; however, it remains to be clarified whether gastrointestinal redox homeostasis is associated with the development of AD. The aim was to (i) examine gastrointestinal redox homeostasis in the presymptomatic and symptomatic Tg2576 mouse model of AD; (ii) investigate the effects of oral d-galactose previously shown to alleviate cognitive deficits and metabolic changes in animal models of AD and reduce gastrointestinal oxidative stress; and (iii) investigate the association between gastrointestinal redox biomarkers and behavioral alterations in Tg2576 mice. In the presymptomatic stage, Tg2576 mice displayed an increased gastrointestinal electrophilic tone, characterized by higher lipid peroxidation and elevated Mn/Fe-SOD activity. In the symptomatic stage, these alterations are rectified, but the total antioxidant capacity is decreased. Chronic oral d-galactose increased the antioxidant capacity and reduced lipid peroxidation in the Tg2576 but had the opposite effects in the wild-type animals. The total antioxidant capacity of the gastrointestinal tract was associated with greater spatial memory. Gut redox homeostasis might be involved in the development and progression of AD pathophysiology and should be further explored in this context.

The interconnection between obesity and executive function in adolescence: The role of the gut microbiome

In the United States, adolescent obesity is a growing epidemic associated with maladaptive executive functioning. Likewise, data link the microbiome to obesity. Emerging microbiome research has demonstrated an interconnection between the gut microbiome and the brain, indicating a bidirectional communication system within the gut-microbiome-brain axis in the pathophysiology of obesity. This narrative review identifies and summarizes relevant research connecting adolescent obesity as it relates to three core domains of executive functioning and the contribution of the gut microbiome in the relationship between obesity and executive functions in adolescence. The review suggests that (1) the interconnection between obesity, executive function, and the gut microbiome is a bidirectional connection, and (2) the gut microbiome may mediate the neurobiological pathways between obesity and executive function deficits. The findings of this review provide valuable insights into obesity-associated executive function deficits and elucidate the possible mediation role of the gut microbiome.

Theabrownin inhibits obesity and non-alcoholic fatty liver disease in mice via serotonin-related signaling pathways and gut-liver axis

INTRODUCTION

Non-alcoholic fatty liver disease (NAFLD) with obesity seriously threats public health. Our previous studies showed that dark tea had more potential on regulating lipid metabolism than other teas, and theabrownin (TB) was considered to be a main contributor to the bioactivity of dark tea.

OBJECTIVES

This in vivo study aims to reveal the effects and molecular mechanisms of TB on NAFLD and obesity, and the role of the gut-liver axis is explored.

METHODS

The histopathological examinations, biochemical tests, and nuclear magnetic resonance were applied to evaluate the effects of TB on NAFLD and obesity. The untargeted metabolomics was used to find the key molecule for further exploration of molecular mechanisms. The 16S rRNA gene sequencing was used to assess the changes in gut microbiota. The antibiotic cocktail and fecal microbiota transplant were used to clarify the role of gut microbiota.

RESULTS

TB markedly reduced body weight gain (67.01%), body fat rate (62.81%), and hepatic TG level (51.35%) in the preventive experiment. Especially, TB decreased body weight (32.16%), body fat rate (42.56%), and hepatic TG level (42.86%) in the therapeutic experiment. The mechanisms of action could be the improvement of fatty acid oxidation, lipolysis, and oxidative stress via the regulation of serotonin-related signaling pathways. Also, TB increased the abundance of serotonin-related gut microbiota, such as Akkermansia, Bacteroides and Parabacteroides. Antibiotics-induced gut bacterial dysbiosis disrupted the regulation of TB on serotonin-related signaling pathways in liver, whereas the beneficial regulation of TB on target proteins was regained with the restoration of gut microbiota.

CONCLUSION

We find that TB has markedly preventive and therapeutic effects on NAFLD and obesity by regulating serotonin level and related signaling pathways through gut microbiota. Furthermore, gut microbiota and TB co-contribute to alleviating NAFLD and obesity. TB could be a promising medicine for NAFLD and obesity.

Lactobacillus rhamnosus Sex-Specifically Attenuates Depressive-like Behavior and Mitigates Metabolic Consequences in Obesity

Background

Patients with diabetes exhibit an increased prevalence for emotional disorders compared with healthy humans, partially due to a shared pathogenesis including hormone resistance and inflammation, which is also linked to intestinal dysbiosis. The preventive intake of probiotic lactobacilli has been shown to improve dysbiosis along with mood and metabolism. Yet, a potential role of Lactobacillus rhamnosus (Lacticaseibacillus rhamnosus 0030) (LR) in improving emotional behavior in established obesity and the underlying mechanisms are unknown.

Methods

Female and male C57BL/6N mice were fed a low-fat diet (10% kcal from fat) or high-fat diet (HFD) (45% kcal from fat) for 6 weeks, followed by daily oral gavage of vehicle or 1 × 108 colony-forming units of LR, and assessment of anxiety- and depressive-like behavior. Cecal microbiota composition was analyzed using 16S ribosomal RNA sequencing, plasma and cerebrospinal fluid were collected for metabolomic analysis, and gene expression of different brain areas was assessed using reverse transcriptase quantitative polymerase chain reaction.

Results

We observed that 12 weeks of HFD feeding induced hyperinsulinemia, which was attenuated by LR application only in female mice. On the contrary, HFD-fed male mice exhibited increased anxiety- and depressive-like behavior, where the latter was specifically attenuated by LR application, which was independent of metabolic changes. Furthermore, LR application restored the HFD-induced decrease of tyrosine hydroxylase, along with normalizing cholecystokinin gene expression in dopaminergic brain regions; both tyrosine hydroxylase and cholecystokinin are involved in signaling pathways impacting emotional disorders.

Conclusions

Our data show that LR attenuates depressive-like behavior after established obesity, with changes in the dopaminergic system in male mice, and mitigates hyperinsulinemia in obese female mice.

Altered Secretion, Constitution, and Functional Properties of the Gastrointestinal Mucus in a Rat Model of Sporadic Alzheimer's Disease

The gastrointestinal (GI) system is affected in Alzheimer's disease (AD); however, it is currently unknown whether GI alterations arise as a consequence of central nervous system (CNS) pathology or play a causal role in the pathogenesis. GI mucus is a possible mediator of GI dyshomeostasis in neurological disorders as the CNS controls mucus production and secretion via the efferent arm of the brain-gut axis. The aim was to use a brain-first model of sporadic AD induced by intracerebroventricular streptozotocin (STZ-icv; 3 mg/kg) to dissect the efferent (i.e., brain-to-gut) effects of isolated central neuropathology on the GI mucus. Morphometric analysis of goblet cell mucigen granules revealed altered GI mucus secretion in the AD model, possibly mediated by the insensitivity of AD goblet cells to neurally evoked mucosal secretion confirmed by ex vivo cholinergic stimulation of isolated duodenal rings. The dysfunctional efferent control of the GI mucus secretion results in altered biochemical composition of the mucus associated with reduced mucin glycoprotein content, aggregation, and binding capacity in vitro. Finally, functional consequences of the reduced barrier-forming capacity of the mucin-deficient AD mucus are demonstrated using the in vitro two-compartment caffeine diffusion interference model. Isolated central AD-like neuropathology results in the loss of efferent control of GI homeostasis via the brain-gut axis and is characterized by the insensitivity to neurally evoked mucosal secretion, altered mucus constitution with reduced mucin content, and reduced barrier-forming capacity, potentially increasing the susceptibility of the STZ-icv rat model of AD to GI and systemic inflammation induced by intraluminal toxins, microorganisms, and drugs.

Identification of drug repurposing candidates for the treatment of anxiety: A genetic approach

Anxiety disorders are a group of prevalent and heritable neuropsychiatric diseases. We previously conducted a genome-wide association study (GWAS) which identified genomic loci associated with anxiety; however, the biological consequences underlying the genetic associations are largely unknown. Integrating GWAS and functional genomic data may improve our understanding of the genetic effects on intermediate molecular phenotypes such as gene expression. This can provide an opportunity for the discovery of drug targets for anxiety via drug repurposing. We used the GWAS summary statistics to determine putative causal genes for anxiety using MAGMA and colocalization analyses. A transcriptome-wide association study was conducted to identify genes with differential genetically regulated levels of gene expression in human brain tissue. The genes were integrated with a large drug-gene expression database (Connectivity Map), discovering compounds that are predicted to "normalise" anxiety-associated expression changes. The study identified 64 putative causal genes associated with anxiety (35 genes upregulated; 29 genes downregulated). Drug mechanisms adrenergic receptor agonists, sigma receptor agonists, and glutamate receptor agonists gene targets were enriched in anxiety-associated genetic signal and exhibited an opposing effect on the anxiety-associated gene expression signature. The significance of the project demonstrated genetic links for novel drug candidates to potentially advance anxiety therapeutics.

Inversely Regulated Inflammation-Related Processes Mediate Anxiety-Obesity Links in Zebrafish Larvae and Adults

Anxiety and metabolic impairments are often inter-related, but the underlying mechanisms are unknown. To seek RNAs involved in the anxiety disorder-metabolic disorder link, we subjected zebrafish larvae to caffeine-induced anxiety or high-fat diet (HFD)-induced obesity followed by RNA sequencing and analyses. Notably, differentially expressed (DE) transcripts in these larval models and an adult zebrafish caffeine-induced anxiety model, as well as the transcript profiles of inherently anxious versus less anxious zebrafish strains and high-fat diet-fed versus standard diet-fed adult zebrafish, revealed inversely regulated DE transcripts. In both larval anxiety and obesity models, these included long noncoding RNAs and transfer RNA fragments, with the overrepresented immune system and inflammation pathways, e.g., the "interleukin signaling pathway" and "inflammation mediated by chemokine and cytokine signaling pathway". In adulthood, overrepresented immune system processes included "T cell activation", "leukocyte cell-cell adhesion", and "antigen processing and presentation". Furthermore, unlike adult zebrafish, obesity in larvae was not accompanied by anxiety-like behavior. Together, these results may reflect an antagonistic pleiotropic phenomenon involving a re-adjusted modulation of the anxiety-metabolic links with an occurrence of the acquired immune system. Furthermore, the HFD potential to normalize anxiety-upregulated immune-related genes may reflect the high-fat diet protection of anxiety and neurodegeneration reported by others.

Tumor-mediated microbiota alteration impairs synaptic tagging/capture in the hippocampal CA1 area via IL-1β production

Cancer patients often experience impairments in cognitive function. However, the evidence for tumor-mediated neurological impairment and detailed mechanisms are still lacking. Gut microbiota has been demonstrated to be involved in the immune system homeostasis and brain functions. Here we find that hepatocellular carcinoma (HCC) growth alters the gut microbiota and impedes the cognitive functions. The synaptic tagging and capture (STC), an associative cellular mechanism for the formation of associative memory, is impaired in the tumor-bearing mice. STC expression is rescued after microbiota sterilization. Transplantation of microbiota from HCC tumor-bearing mice induces similar STC impairment in wide type mice. Mechanistic study reveals that HCC growth significantly elevates the serum and hippocampus IL-1β levels. IL-1β depletion in the HCC tumor-bearing mice restores the STC. Taken together, these results demonstrate that gut microbiota plays a crucial role in mediating the tumor-induced impairment of the cognitive function via upregulating IL-1β production.

Signalling cognition: the gut microbiota and hypothalamic-pituitary-adrenal axis

Cognitive function in humans depends on the complex and interplay between multiple body systems, including the hypothalamic-pituitary-adrenal (HPA) axis. The gut microbiota, which vastly outnumbers human cells and has a genetic potential that exceeds that of the human genome, plays a crucial role in this interplay. The microbiota-gut-brain (MGB) axis is a bidirectional signalling pathway that operates through neural, endocrine, immune, and metabolic pathways. One of the major neuroendocrine systems responding to stress is the HPA axis which produces glucocorticoids such as cortisol in humans and corticosterone in rodents. Appropriate concentrations of cortisol are essential for normal neurodevelopment and function, as well as cognitive processes such as learning and memory, and studies have shown that microbes modulate the HPA axis throughout life. Stress can significantly impact the MGB axis via the HPA axis and other pathways. Animal research has advanced our understanding of these mechanisms and pathways, leading to a paradigm shift in conceptual thinking about the influence of the microbiota on human health and disease. Preclinical and human trials are currently underway to determine how these animal models translate to humans. In this review article, we summarize the current knowledge of the relationship between the gut microbiota, HPA axis, and cognition, and provide an overview of the main findings and conclusions in this broad field.

The gut microbiota-astrocyte axis: Implications for type 2 diabetic cognitive dysfunction

BACKGROUND

Diabetic cognitive dysfunction (DCD) is one of the most insidious complications of type 2 diabetes mellitus, which can seriously affect the ability to self-monitoring of blood glucose and the quality of life in the elderly. Previous pathological studies of cognitive dysfunction have focused on neuronal dysfunction, characterized by extracellular beta-amyloid deposition and intracellular tau hyperphosphorylation. In recent years, astrocytes have been recognized as a potential therapeutic target for cognitive dysfunction and important participants in the central control of metabolism. The disorder of gut microbiota and their metabolites have been linked to a series of metabolic diseases such as diabetes mellitus. The imbalance of intestinal flora has the effect of promoting the occurrence and deterioration of several diabetes-related complications. Gut microbes and their metabolites can drive astrocyte activation.

AIMS

We reviewed the pathological progress of DCD related to the "gut microbiota-astrocyte" axis in terms of peripheral and central inflammation, intestinal and blood-brain barrier (BBB) dysfunction, systemic and brain energy metabolism disorders to deepen the pathological research progress of DCD and explore the potential therapeutic targets.

CONCLUSION

"Gut microbiota-astrocyte" axis, unique bidirectional crosstalk in the brain-gut axis, mediates the intermediate pathological process of neurocognitive dysfunction secondary to metabolic disorders in diabetes mellitus.

Vancomycin Pretreatment on MPTP-Induced Parkinson's Disease Mice Exerts Neuroprotection by Suppressing Inflammation Both in Brain and Gut

A growing body of evidence implies that gut microbiota was involved in pathogenesis of Parkinson's disease (PD), but the mechanism is still unclear. The aim of this study is to investigate the effects of antibiotics pretreatment on the 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP)-induced PD mice. In this study, vancomycin pretreatment was given by gavage once daily with either vancomycin or distilled water for 14 days to mice, then mice were administered with MPTP (20 mg/kg, i.p) for four times in one day to establish an acute PD model. Results show that vancomycin pretreatment significantly improved motor dysfunction of mice in pole and traction tests. Although vancomycin pretreatment had no effect on dopamine (DA) or the process of DA synthesis, it inhibited the metabolism of DA by suppressing the expression of striatal monoamine oxidase B (MAO-B). Furthermore, vancomycin pretreatment reduced the number of astrocytes and microglial cells in the substantia nigra pars compacta (SNpc) to alleviate neuroinflammation, decreased the expression of TLR4/MyD88/NF-κB/TNF-α signaling pathway in both brain and gut. Meanwhile, vancomycin pretreatment changed gut microbiome composition and the levels of fecal short chain fatty acids (SCFAs). The abundance of Akkermansia and Blautia increased significantly after vancomycin pretreatment, which might be related to inflammation and inhibition of TLR4 signaling pathway. In summary, these results demonstrate that the variation of gut microbiota and its metabolites induced by vancomycin pretreatment might decrease dopamine metabolic rate and relieve inflammation in both gut and brain via the microbiota-gut-brain axis in MPTP-induced PD mice. The neuroprotection of vancomycin pretreatment on MPTP-induced Parkinson's disease mice The alterations of gut microbiota and SCFAs induced by vancomycin pretreatment might not only improve motor dysfunction, but also decrease dopamine metabolism and relieve inflammation in both brain and gut via TLR4/MyD88/NF-κB/TNF-α pathway in MPTP-induced PD mice.

Estradiol-mediated protection against high-fat diet induced anxiety and obesity is associated with changes in the gut microbiota in female mice

Decreased estrogens during menopause are associated with increased risk of anxiety, depression, type 2 diabetes and obesity. Similarly, depleting estrogens in rodents by ovariectomy, combined with a high-fat diet (HFD), increases anxiety and adiposity. How estrogens and diet interact to affect anxiety and metabolism is poorly understood. Mounting evidence indicates that gut microbiota influence anxiety and metabolism. Here, we investigated the effects of estradiol (E) and HFD on anxiety, metabolism, and their correlation with changes in gut microbiota in female mice. Adult C57BL/6J mice were ovariectomized, implanted with E or vehicle-containing capsules and fed a standard diet or HFD. Anxiety-like behavior was assessed and neuronal activation was measured by c-fos immunoreactivity throughout the brain using iDISCO. HFD increased anxiety-like behavior, while E reduced this HFD-dependent anxiogenic effect. Interestingly, E decreased neuronal activation in brain regions involved in anxiety and metabolism. E treatment also altered gut microbes, a subset of which were associated with anxiety-like behavior. These findings provide insight into gut microbiota-based therapies for anxiety and metabolic disorders associated with declining estrogens in menopausal women.

Function of the GABAergic System in Diabetic Encephalopathy

Diabetes is a common metabolic disease characterized by loss of blood sugar control and a high rate of complications. γ-Aminobutyric acid (GABA) functions as the primary inhibitory neurotransmitter in the adult mammalian brain. The normal function of the GABAergic system is affected in diabetes. Herein, we summarize the role of the GABAergic system in diabetic cognitive dysfunction, diabetic blood sugar control disorders, diabetes-induced peripheral neuropathy, diabetic central nervous system damage, maintaining diabetic brain energy homeostasis, helping central control of blood sugar and attenuating neuronal oxidative stress damage. We show the key regulatory role of the GABAergic system in multiple comorbidities in patients with diabetes and hope that further studies elucidating the role of the GABAergic system will yield benefits for the treatment and prevention of comorbidities in patients with diabetes.

The microbiota-gut-brain axis in pathogenesis of depression: A narrative review

The microbiota-gut-brain axis is a bidirectional regulatory pathway between the brain and the gastrointestinal tract, which plays an important role in maintain homeostasis. Gut microbiota could influence the behavior, cognition, stress response and others via the axis. Depression is a complex psychiatric disease, giving rise to heavy social health and economic burden. In recent years, studies have shown that the gut microbiota are closely linked to the pathophysiological processes of depression. In this article, the interaction and its underlying mechanisms between depression and gut microbiota were summarized.

Administration Time and Dietary Patterns Modified the Effect of Inulin on CUMS-Induced Anxiety and Depression

SCOPE

Prebiotics exert anxiolytic and antidepressant effects through the microbiota-gut-brain axis in animal models. However, the influence of prebiotic administration time and dietary pattern on stress-induced anxiety and depression is unclear. In this study, whether administration time can modify the effect of inulin on mental disorders within normal and high-fat diets are investigated.

METHODS AND RESULTS

Mice subjected to chronic unpredicted mild stress (CUMS) are administered with inulin in the morning (7:30-8:00 am) or evening (7:30-8:00 pm) for 12 weeks. Behavior, intestinal microbiome, cecal short-chain fatty acids, neuroinflammatory responses, and neurotransmitters are measured. A high-fat diet aggravated neuroinflammation and is more likely to induce anxiety and depression-like behavior (p < 0.05). Morning inulin treatment improves the exploratory behavior and sucrose preference better (p < 0.05). Both inulin treatments decrease the neuroinflammatory response (p < 0.05), with a more evident trend for the evening administration. Furthermore, morning administration tends to affect the brain-derived neurotrophic factor and neurotransmitters.

CONCLUSION

Administration time and dietary patterns seem to modify the effect of inulin on anxiety and depression. These results provide a basis for assessing the interaction of administration time and dietary patterns, providing guidance for the precise regulation of dietary prebiotics in neuropsychiatric disorders.

Radix Rehmanniae Praeparata (Shu Dihuang) exerts neuroprotective effects on ICV-STZ-induced Alzheimer's disease mice through modulation of INSR/IRS-1/AKT/GSK-3β signaling pathway and intestinal microbiota

Radix Rehmanniae Praeparata (RRP, Shu Dihuang in Cinese) is widely used as primal medicine in Chinese herbal formula for the treatment of Alzheimer's disease (AD). However, the underlying mechanism of RRP for AD remains unclear. The aim of this study was to investigate the therapeutic effect of RRP on intracerebroventricular injection of streptozotocin (ICV-STZ)-induced AD model mice and its potential mechanism. ICV-STZ mice were continuously gavaged with RRP for 21 days. The pharmacological effects of RRP were evaluated by behavioral tests, brain tissue H&E staining and hippocampal tau protein phosphorylation levels. The expression levels of insulin receptor (INSR), IRS-1, pSer473-AKT/AKT and pSer9-GSK-3β/GSK-3β proteins in hippocampal and cortical tissues were detected by Western-blot method. The 16S rRNA gene sequencing was used to analyze the changes of intestinal microbiota in mice. The compounds in RRP were analyzed by mass spectrometry and their binding ability to INSR proteins was detected by molecular docking. The results showed that RRP ameliorated cognitive dysfunction and neuronal pathological changes of brain tissue in ICV-STZ mice, reduced tau protein hyperphosphorylation, INSR, IRS-1, pSer473-AKT/AKT, and pSer9-GSK-3β/GSK-3β levels in hippocampal and cortical tissues. Meanwhile, RRP reversed ICV-STZ-induced dysregulation of intestinal microbiota in AD mice. Mass spectrometry analysis showed that the RRP consisted mainly of seven compounds, namely Acteoside (Verbascoside), 5-Hydroxymethyl-2-furaldehyde (5-HMF), Apigenin7-O-glucuronide, Icariin, Gallic acid, Quercetin-3β-D-glucoside, and Geniposide. Molecular docking results further indicated that the compounds in RRP have binding ability to INSR protein and potential multiple synergistic effects. RRP ameliorates cognitive dysfunction and brain histopathological changes in AD mice. The mechanism of RRP ameliorating AD may be related to the regulation of INSR/IRS-1/AKT/GSK-3β signaling pathway and intestinal microbiota. This study supports the potential anti-AD efficacy of RRP and initially reveals the pharmacological mechanism of RRP, providing a theoretical basis for further clinical application of RRP.

Sirtuins and redox signaling interplay in neurogenesis, neurodegenerative diseases, and neural cell reprogramming

Since the discovery of Neural Stem Cells (NSCs) there are still mechanism to be clarified, such as the role of mitochondrial metabolism in the regulation of endogenous adult neurogenesis and its implication in neurodegeneration. Although stem cells require glycolysis to maintain their stemness, they can perform oxidative phosphorylation and it is becoming more and more evident that mitochondria are central players, not only for ATP production but also for neuronal differentiation's steps regulation, through their ability to handle cellular redox state, intracellular signaling, epigenetic state of the cell, as well as the gut microbiota-brain axis, upon dietary influences. In this scenario, the 8-oxoguanine DNA glycosylase (OGG1) repair system would link mitochondrial DNA integrity to the modulation of neural differentiation. On the other side, there is an increasing interest in NSCs generation, from induced pluripotent stem cells, as a clinical model for neurodegenerative diseases (NDs), although this methodology still presents several drawbacks, mainly related to the reprogramming process. Indeed, high levels of reactive oxygen species (ROS), associated with telomere shortening, genomic instability, and defective mitochondrial dynamics, lead to pluripotency limitation and reprogramming efficiency's reduction. Moreover, while a physiological or moderate ROS increase serves as a signaling mechanism, to activate differentiation and suppress self-renewal, excessive oxidative stress is a common feature of NDs and aging. This ROS-dependent regulatory effect might be modulated by newly identified ROS suppressors, including the NAD⁺-dependent deacetylase enzymes family called Sirtuins (SIRTs). Recently, the importance of subcellular localization of NAD synthesis has been coupled to different roles for NAD in chromatin stability, DNA repair, circadian rhythms, and longevity. SIRTs have been described as involved in the control of both telomere's chromatin state and expression of nuclear gene involved in the regulation of mitochondrial gene expression, as well as in several NDs and aging. SIRTs are ubiquitously expressed in the mammalian brain, where they play important roles. In this review we summarize the current knowledge on how SIRTs-dependent modulation of mitochondrial metabolism could impact on neurogenesis and neurodegeneration, focusing mainly on ROS function and their role in SIRTs-mediated cell reprogramming and telomere protection.

Gamma-Aminobutyric Acid Promotes Beige Adipocyte Reconstruction by Modulating the Gut Microbiota in Obese Mice

Given the increasing prevalence of obesity, the white-to-beige adipocyte conversion has attracted interest as a target for obesity treatment. Gamma-aminobutyric acid (GABA) treatment can reduce obesity, but the underlying mechanism remains unclear. Here, we aimed to investigate the mechanism by which GABA triggers weight loss by improving the beiging of inguinal white adipose tissue (iWAT) and the role of gut microbiota in this process. The results showed that GABA reduced body weight and adipose inflammation and promoted the expression of thermogenic genes in the iWAT. The 16S rRNA sequence analysis of gut microbiota showed that GABA treatment increased the relative abundance of Bacteroidetes, Akkermansia, and Romboutsia and reduced that of Firmicutes and Erysipelatoclostridium in obese mice. Additionally, serum metabolomic analysis revealed that GABA treatment increased 3-hydroxybutyrate and reduced oxidized lipid levels in obese mice. Spearman's correlation analysis showed that Akkermansia and Romboutsia were negatively associated with the levels of oxidized lipids. Fecal microbiota transplantation analysis confirmed that the gut microbiota was involved in the white-to-beige adipocyte reconstruction by GABA. Overall, our findings suggest that GABA treatment may promote iWAT beiging through the gut microbiota in obese mice. GABA may be utilized to protect obese people against metabolic abnormalities brought on by obesity and gut dysbiosis.

Long-term LDR exposure may induce cognitive impairments: A possible association through targeting gut microbiota-gut-brain axis

Environmental and occupational low-dose radiation (LDR) exposure may be harmful for health but the previous reports regarding effect of LDR on cognition are contradictory. Here we investigated the effect of long-term LDR exposure on cognition. In this study, male Balb/c mice' cognitive functions were tested at 15 weeks after being exposed to 0.5 Gy LDR in 10 fractions at each dose of 0.05 Gy. The results demonstrated that long-term LDR exposure increases escape latency and the time spent in finding exits in mice compared with non LDR exposure. Meanwhile, the inflammation-related proteins including NFκB and p38 also increased. Lipopolysaccharide (LPS) increased and short-chain fatty acid (SCFA) levels decreased following long term LDR exposure. Treatment with microbiota-derived LPS and SCFAs reversed these effects in mice. Furthermore, the gut barrier integrity was damaged in a time-dependent manner with the decreased expression of intestinal epithelial-related biomarkers such as ZO-1 and occludin. Mechanistically, long after exposure to LDR, increased LPS levels may cause cognitive impairment through the regulation of Akt/mTOR signaling in the mouse hippocampus. These findings provide new insight into the clinical applications of LDR and suggest that the gut microbiota-plasma LPS and SCFAs-brain axis may underlie long-term LDR-induced cognition effects.

Multi-omics gut microbiome signatures in obese women: role of diet and uncontrolled eating behavior

BACKGROUND

Obesity and related co-morbidities represent a major health challenge nowadays, with a rapidly increasing incidence worldwide. The gut microbiome has recently emerged as a key modifier of human health that can affect the development and progression of obesity, largely due to its involvement in the regulation of food intake and metabolism. However, there are still few studies that have in-depth explored the functionality of the human gut microbiome in obesity and even fewer that have examined its relationship to eating behaviors.

METHODS

In an attempt to advance our knowledge of the gut-microbiome-brain axis in the obese phenotype, we thoroughly characterized the gut microbiome signatures of obesity in a well-phenotyped Italian female cohort from the NeuroFAST and MyNewGut EU FP7 projects. Fecal samples were collected from 63 overweight/obese and 37 normal-weight women and analyzed via a multi-omics approach combining 16S rRNA amplicon sequencing, metagenomics, metatranscriptomics, and lipidomics. Associations with anthropometric, clinical, biochemical, and nutritional data were then sought, with particular attention to cognitive and behavioral domains of eating.

RESULTS

We identified four compositional clusters of the gut microbiome in our cohort that, although not distinctly associated with weight status, correlated differently with eating habits and behaviors. These clusters also differed in functional features, i.e., transcriptional activity and fecal metabolites. In particular, obese women with uncontrolled eating behavior were mostly characterized by low-diversity microbial steady states, with few and poorly interconnected species (e.g., Ruminococcus torques and Bifidobacterium spp.), which exhibited low transcriptional activity, especially of genes involved in secondary bile acid biosynthesis and neuroendocrine signaling (i.e., production of neurotransmitters, indoles and ligands for cannabinoid receptors). Consistently, high amounts of primary bile acids as well as sterols were found in their feces.

CONCLUSIONS

By finding peculiar gut microbiome profiles associated with eating patterns, we laid the foundation for elucidating gut-brain axis communication in the obese phenotype. Subject to confirmation of the hypotheses herein generated, our work could help guide the design of microbiome-based precision interventions, aimed at rewiring microbial networks to support a healthy diet-microbiome-gut-brain axis, thus counteracting obesity and related complications.

Target Metabolites to Slow Down Progression of Amyotrophic Lateral Sclerosis in Mice

Microbial metabolites affect the neuron system and muscle cell functions. Amyotrophic lateral sclerosis (ALS) is a multifactorial neuromuscular disease. Our previous study has demonstrated elevated intestinal inflammation and dysfunction of the microbiome in patients with ALS and an ALS mouse model (human-SOD1^G93A transgenic mice). However, the metabolites in ALS progression are unknown. Using an unbiased global metabolomic measurement and targeted measurement, we investigated the longitudinal changes of fecal metabolites in SOD1^G93A mice over the course of 13 weeks. We further compared the changes of metabolites and inflammatory response in age-matched wild-type (WT) and SOD1^G93A mice treated with the bacterial product butyrate. We found changes in carbohydrate levels, amino acid metabolism, and the formation of gamma-glutamyl amino acids. Shifts in several microbially contributed catabolites of aromatic amino acids agree with butyrate-induced changes in the composition of the gut microbiome. Declines in gamma-glutamyl amino acids in feces may stem from differential expression of gamma-glutamyltransferase (GGT) in response to butyrate administration. Due to the signaling nature of amino acid-derived metabolites, these changes indicate changes in inflammation, e.g., histamine, and contribute to differences in systemic levels of neurotransmitters, e.g., γ-Aminobutyric acid (GABA) and glutamate. Butyrate treatment was able to restore some of the healthy metabolites in ALS mice. Moreover, microglia in the spinal cord were measured by IBA1 staining. Butyrate treatment significantly suppressed the IBA1 level in the SOD1^G93A mice. Serum IL-17 and LPS were significantly reduced in the butyrate-treated SOD1^G93A mice. We have demonstrated an inter-organ communications link among microbial metabolites, neuroactive metabolites from the gut, and inflammation in ALS progression. The study supports the potential to use metabolites as ALS hallmarks and for treatment.

(-)-Epicatechin mitigates anxiety-related behavior in a mouse model of high fat diet-induced obesity

Mounting evidence demonstrates that consumption of high fat diet (HFD) and subsequent development of obesity leads to alterations in cognition and mood. While obesity can affect brain function, consumption of select dietary bioactives may help prevent obesity-related cognitive decline. This study investigated the capacity of the dietary flavonoid (-)-epicatechin (EC) to mitigate HFD-induced obesity-associated alterations in memory and mood. Healthy 8-week old male C57BL/6J mice were maintained on either a control diet (10 kCal% from fat) or a HFD (45 kCal% from fat) and were supplemented with EC at 2 or 20 mg/kg body weight (B.W.) for a 24 week period. Between week 20 and 22, anxiety-related behavior, recognition memory, and spatial memory were measured. Underlying mechanisms were assessed by measuring the expression of selected genes in the hippocampus and by 16S rRNA sequencing and metabolomic analysis of the gut microbiota. 24 weeks of HFD feeding resulted in obesity, which was not affected by EC supplementation. HFD-associated increase in anxiety-related behavior was mitigated by EC in a dose-response manner and was accompanied by increased hippocampal brain-derived neurotrophic factor (BDNF), as well as partial or full restoration of glucocorticoid receptor, mineralocorticoid receptor and 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) expression. Higher EC dosage (20 mg/kg B.W.) also restored aberrant Lactobacillus and Enterobacter abundance altered by HFD and/or the associated obesity. Together, these results demonstrate how EC mitigates anxiety-related behaviors, revealing a connection between BDNF- and glucocorticoids-mediated signaling. Our findings link changes in the hippocampus and the gut microbiota in a context of HFD-induced obesity and anxiety.

Overcoming Anxiety Disorder by Probiotic Lactiplantibacillus plantarum LZU-J-TSL6 through Regulating Intestinal Homeostasis

Lactiplantibacillus plantarum LZU-J-TSL6 with high γ-aminobutyric acid (GABA) production (3.838 g/L) was screened and isolated from the Chinese fermented food snack “Jiangshui”. The improvement effect on anxiety disorder was explored using mice as animal models. In vitro results revealed that LZU-J-TSL6 had the potential to colonize the intestine (p < 0.01) and the anxiety-like behavior of the mice after seven days’ gavage with LZU-J-TSL6 was significantly improved (p < 0.01) when compared to the model group. LZU-J-TSL6 was able to effectively increase the GABA content in the mice hippocampus (p < 0.0001) and restore some markers related to anxiety such as brain-derived neurotrophic factor (BDNF), glial fibrillary acidic protein (GFAP), and 5-hydroxytryptamine (5-HT). Simultaneously, it had a certain repair effect on Nissl bodies and colon tissue in mice hippocampus. In addition, LZU-J-TSL6 increased the relative abundance of beneficial bacteria Bacteroides and Muribaculum, thereby regulating the imbalance of intestinal microbiota caused by anxiety disorder. It also affects the nerve pathway and intestinal mucosal barrier by increasing the content of glutamine and γ-aminobutyric acid and other related metabolites, thereby improving anxiety. Therefore, the GABA-producing Lactobacillus plantus LZU-J-TSL6 can be used as a probiotic to exert an indirect or direct anti-anxiety effect by maintaining the balance of the intestinal environment, producing related metabolites that affect nerve pathways and repair the intestinal mucosal barrier. It can be used as an adjuvant treatment to improve anxiety disorders.

Realgar Alleviated Neuroinflammation Induced by High Protein and High Calorie Diet in Rats via the Microbiota-Gut-Brain Axis

Purpose: Gastrointestinal heat retention syndrome (GHRS) often occurs in adolescents, resulting into nervous system injury. Realgar, an arsenic mineral with neuroprotective effect, has been widely used to treat GHRS. However, its mechanism of action remains unknown. Methods: A GHRS rat model was established using a high protein and high calorie diet. We performed macroscopic characterization by assessing bowel sounds, hot/cold preference, anal temperature, and fecal features. Atomic fluorescence spectroscopy was employed to evaluate brain arsenic level while hippocampal ultrastructural changes were analyzed using transmission electron microscopy. In addition, inflammatory cytokines and BBB breakdown were analyzed by western blotting, immunofluorescence assays, and immunohistochemistry staining. We also evaluated hippocampal metabolites by LC-MS while fecal microorganisms were assessed by 16S rDNA sequencing. Results: Our data showed that the high protein and high calorie diet induced GHRS. The rat model depicted decreased bowel sounds, increased fecal characteristics score, preference for low temperature zone, and increased anal temperature. In addition, there was increase in inflammatory factors IL-6, Iba-1, and NF-κB p65 as well as reduced BBB structural protein Claudin-5 and Occludin. The data also showed appearance of hippocampus metabolites disorder and fecal microbial imbalance. Realgar treatment conferred a neuroprotective effect by inhibiting GHRS-specific characteristics, neuroinflammatory response, BBB impairment, metabolites disorder, and microbial imbalance in the GHRS rat model. Conclusion: Taken together, our analysis demonstrated that realgar confers a neuroprotective effect in GHRS rats through modulation of the microbiota-gut-brain axis.

Crosstalk between neurological, cardiovascular, and lifestyle disorders: insulin and lipoproteins in the lead role

Insulin resistance and impaired lipoprotein metabolism contribute to a plethora of metabolic and cardiovascular disorders. These alterations have been extensively linked with poor lifestyle choices, such as consumption of a high-fat diet, smoking, stress, and a redundant lifestyle. Moreover, these are also known to increase the co-morbidity of diseases like Type 2 diabetes mellitus and atherosclerosis. Under normal physiological conditions, insulin and lipoproteins exert a neuroprotective role in the central nervous system. However, the tripping of balance between the periphery and center may alter the normal functioning of the brain and lead to neurological disorders such as Alzheimer's disease, Parkinson's disease, stroke, depression, and multiple sclerosis. These neurological disorders are further characterized by certain behavioral and molecular changes that show consistent overlap with alteration in insulin and lipoprotein signaling pathways. Therefore, targeting these two mechanisms not only reveals a way to manage the co-morbidities associated with the circle of the metabolic, central nervous system, and cardiovascular disorders but also exclusively work as a disease-modifying therapy for neurological disorders. In this review, we summarize the role of insulin resistance and lipoproteins in the progression of various neurological conditions and discuss the therapeutic options currently in the clinical pipeline targeting these two mechanisms; in addition, challenges faced in designing these therapeutic approaches have also been touched upon briefly.

Gut microbes and food reward: From the gut to the brain

Inappropriate food intake behavior is one of the main drivers for fat mass development leading to obesity. Importantly the gut microbiota-mediated signals have emerged as key actors regulating food intake acting mainly on the hypothalamus, and thereby controlling hunger or satiety/satiation feelings. However, food intake is also controlled by the hedonic and reward systems leading to food intake based on pleasure (i.e., non-homeostatic control of food intake). This review focus on both the homeostatic and the non-homeostatic controls of food intake and the implication of the gut microbiota on the control of these systems. The gut-brain axis is involved in the communications between the gut microbes and the brain to modulate host food intake behaviors through systemic and nervous pathways. Therefore, here we describe several mediators of the gut-brain axis including gastrointestinal hormones, neurotransmitters, bioactive lipids as well as bacterial metabolites and compounds. The modulation of gut-brain axis by gut microbes is deeply addressed in the context of host food intake with a specific focus on hedonic feeding. Finally, we also discuss possible gut microbiota-based therapeutic approaches that could lead to potential clinical applications to restore food reward alterations. Therapeutic applications to tackle these dysregulations is of utmost importance since most of the available solutions to treat obesity present low success rate.

Fecal microbiota transplantation in the metabolic diseases: Current status and perspectives

With the development of microbiology and metabolomics, the relationship between the intestinal microbiome and intestinal diseases has been revealed. Fecal microbiota transplantation (FMT), as a new treatment method, can affect the course of many chronic diseases such as metabolic syndrome, malignant tumor, autoimmune disease and nervous system disease. Although the mechanism of action of FMT is now well understood, there is some controversy in metabolic diseases, so its clinical application may be limited. Microflora transplantation is recommended by clinical medical guidelines and consensus for the treatment of recurrent or refractory Clostridium difficile infection, and has been gradually promoted for the treatment of other intestinal and extraintestinal diseases. However, the initial results are varied, suggesting that the heterogeneity of the donor stools may affect the efficacy of FMT. The success of FMT depends on the microbial diversity and composition of donor feces. Therefore, clinical trials may fail due to the selection of ineffective donors, and not to faulty indication selection for FMT. A new understanding is that FMT not only improves insulin sensitivity, but may also alter the natural course of type 1 diabetes by modulating autoimmunity. In this review, we focus on the main mechanisms and deficiencies of FMT, and explore the optimal design of FMT research, especially in the field of cardiometabolic diseases.

Linking circadian rhythms to microbiome-gut-brain axis in aging-associated neurodegenerative diseases

Emerging evidence suggests that both disruption of circadian rhythms and gut dysbiosis are closely related to aging-associated neurodegenerative diseases. Over the last decade, the microbiota-gut-brain axis has been an emerging field and revolutionized studies in pathology, diagnosis, and treatment of neurological disorders. Crosstalk between the brain and gut microbiota can be accomplished via the endocrine, immune, and nervous system. Recent studies have shown that the composition and diurnal oscillation of gut microbiota are influenced by host circadian rhythms. This provides a new perspective for investigating the microbiome-gut-brain axis. We aim to review current understanding and research on the dynamic interaction between circadian rhythms and the microbiome-gut-brain axis. Furthermore, we will address the possible neurodegenerative disease contribution through circadian rhythms and microbiome-gut-brain axis crosstalk.

A Reciprocal Link Between Gut Microbiota, Inflammation and Depression: A Place for Probiotics?

Depression is a severe mental disorder that places a significant economic burden on public health. The reciprocal link between the trillions of bacteria in the gut, the microbiota, and depression is a controversial topic in neuroscience research and has drawn the attention of public interest and press coverage in recent years. Mounting pieces of evidence shed light on the role of the gut microbiota in depression, which is suggested to involve immune, endocrine, and neural pathways that are the main components of the microbiota-gut-brain axis. The gut microbiota play major roles in brain development and physiology and ultimately behavior. The bidirectional communication between the gut microbiota and brain function has been extensively explored in animal models of depression and clinical research in humans. Certain gut microbiota strains have been associated with the pathophysiology of depression. Therefore, oral intake of probiotics, the beneficial living bacteria and yeast, may represent a therapeutic approach for depression treatment. In this review, we summarize the findings describing the possible links between the gut microbiota and depression, focusing mainly on the inflammatory markers and sex hormones. By discussing preclinical and clinical studies on probiotics as a supplementary therapy for depression, we suggest that probiotics may be beneficial in alleviating depressive symptoms, possibly through immune modulation. Still, further comprehensive studies are required to draw a more solid conclusion regarding the efficacy of probiotics and their mechanisms of action.

Antibiotic-induced microbiome depletion remodels daily metabolic cycles in the brain

The gut microbiome influences cognition and behavior in mammals, yet its metabolic impact on the brain is only starting to be defined. Using metabolite profiling of antibiotics-treated mice, we reveal the microbiome as a key input controlling circadian metabolic cycles in the brain. Intra and inter-region analyses characterise the influence of the microbiome on the suprachiasmatic nucleus, containing the central clockwork, as well as the hippocampus and cortex, regions involved in learning and behavior.

Gut Microbiota Regulate Pancreatic Growth, Exocrine Function, and Gut Hormones

Growing evidence indicates an important link between gut microbiota, obesity, and metabolic syndrome. Alterations in exocrine pancreatic function are also widely present in patients with diabetes and obesity. To examine this interaction, C57BL/6J mice were fed a chow diet, a high-fat diet (HFD), or an HFD plus oral vancomycin or metronidazole to modify the gut microbiome. HFD alone leads to a 40% increase in pancreas weight, decreased glucagon-like peptide 1 and peptide YY levels, and increased glucose-dependent insulinotropic peptide in the plasma. Quantitative proteomics identified 138 host proteins in fecal samples of these mice, of which 32 were significantly changed by the HFD. The most significant of these were the pancreatic enzymes. These changes in amylase and elastase were reversed by antibiotic treatment. These alterations could be reproduced by transferring gut microbiota from donor C57BL/6J mice to germ-free mice. By contrast, antibiotics had no effect on pancreatic size or exocrine function in C57BL/6J mice fed the chow diet. Further, 1 week vancomycin administration significantly increased amylase and elastase levels in obese men with prediabetes. Thus, the alterations in gut microbiota in obesity can alter pancreatic growth, exocrine function, and gut endocrine function and may contribute to the alterations observed in patients with obesity and diabetes.

The gut microbiome and mental health: advances in research and emerging priorities

The gut microbiome exerts a considerable influence on human neurophysiology and mental health. Interactions between intestinal microbiology and host regulatory systems have now been implicated both in the development of psychiatric conditions and in the efficacy of many common therapies. With the growing acceptance of the role played by the gut microbiome in mental health outcomes, the focus of research is now beginning to shift from identifying relationships between intestinal microbiology and pathophysiology, and towards using this newfound insight to improve clinical outcomes. Here, we review recent advances in our understanding of gut microbiome-brain interactions, the mechanistic underpinnings of these relationships, and the ongoing challenge of distinguishing association and causation. We set out an overarching model of the evolution of microbiome-CNS interaction and examine how a growing knowledge of these complex systems can be used to determine disease susceptibility and reduce risk in a targeted manner.

Shedding light on biological sex differences and microbiota-gut-brain axis: a comprehensive review of its roles in neuropsychiatric disorders

Women and men are suggested to have differences in vulnerability to neuropsychiatric disorders, including major depressive disorder (MDD), generalized anxiety disorder (GAD), schizophrenia, eating disorders, including anorexia nervosa, and bulimia nervosa, neurodevelopmental disorders, such as autism spectrum disorder (ASD), and neurodegenerative disorders including Alzheimer’s disease, Parkinson’s disease. Genetic factors and sex hormones are apparently the main mediators of these differences. Recent evidence uncovers that reciprocal interactions between sex-related features (e.g., sex hormones and sex differences in the brain) and gut microbiota could play a role in the development of neuropsychiatric disorders via influencing the gut–brain axis. It is increasingly evident that sex–microbiota–brain interactions take part in the occurrence of neurologic and psychiatric disorders. Accordingly, integrating the existing evidence might help to enlighten the fundamental roles of these interactions in the pathogenesis of neuropsychiatric disorders. In addition, an increased understanding of the biological sex differences on the microbiota–brain may lead to advances in the treatment of neuropsychiatric disorders and increase the potential for precision medicine. This review discusses the effects of sex differences on the brain and gut microbiota and the putative underlying mechanisms of action. Additionally, we discuss the consequences of interactions between sex differences and gut microbiota on the emergence of particular neuropsychiatric disorders.

The human microbiome is a unique set of organisms affecting health via the gut–brain axis.

Neuropsychiatric disorders, eating disorders, neurodevelopmental disorders, and neurodegenerative disorders are regulated by the microbiota–gut–brain axis in a sex-specific manner.

Understanding the role of the microbiota–gut–brain axis and its sex differences in various diseases can lead to better therapeutic methods.

Varied Composition and Underlying Mechanisms of Gut Microbiome in Neuroinflammation

The human gut microbiome has been implicated in a host of bodily functions and their regulation, including brain development and cognition. Neuroinflammation is a relatively newer piece of the puzzle and is implicated in the pathogenesis of many neurological disorders. The microbiome of the gut may alter the inflammatory signaling inside the brain through the secretion of short-chain fatty acids, controlling the availability of amino acid tryptophan and altering vagal activation. Studies in Korea and elsewhere highlight a strong link between microbiome dynamics and neurocognitive states, including personality. For these reasons, re-establishing microbial flora of the gut looks critical for keeping neuroinflammation from putting the whole system aflame through probiotics and allotransplantation of the fecal microbiome. However, the numerosity of the microbiome remains a challenge. For this purpose, it is suggested that wherever possible, a fecal microbial auto-transplant may prove more effective. This review summarizes the current knowledge about the role of the microbiome in neuroinflammation and the various mechanism involved in this process. As an example, we have also discussed the autism spectrum disorder and the implication of neuroinflammation and microbiome in its pathogenesis.

Changes in gut microbiota composition with age and correlations with gut inflammation in rats

Increasing evidences indicate that gut microbiota composition is associated with multiple inflammatory diseases. However, little is known about how gut microbiota changes with age and correlations with gut inflammation at sexual maturity stage of healthy individuals. Elucidating the dynamic changes of gut microbiota in healthy individuals at the sexual maturity stage and correlations with gut inflammation can provide clues for early risk assessment of gut diseases at the sexual maturity stage. Here, the shift in gut bacteria and its relationship with gut inflammation at the sexual maturity stage were explored. Sprague–Dawley rats at the sexual maturity stage were used in this study. 16S rRNA gene sequencing was performed to decipher gut bacteria shifts from the 7th week to the 9th week, and enzyme-linked immunosorbent assay (ELISA) was used to measure gut inflammation and gut barrier permeability. We found an increase in bacterial richness with age and a decrease in bacterial diversity with age. The gut bacteria were primarily dominated by the phyla Firmicutes and Bacteroides and the genus Prevotella. The relative abundance of Firmicutes increased with age, and the relative abundance of Bacteroides decreased with age. There was a positive correlation between body weight and the Firmicutes:Bacteroides ratio. More and more gut microbiota participated in the host gut inflammation and barrier permeability regulation with age. Ruminococcus was the only gut bacteria participated in gut inflammation and barrier permeability regulation both in the 7th week and the 15th week. These results provide a better understanding of the relationship between gut bacteria and gut inflammation in sexually mature rats and show that Ruminococcus may be a potential indicator for early risk assessment of gut inflammation.

Insulin action in the brain: cell types, circuits, and diseases

Since its discovery over 100 years ago, insulin has been recognized as a key hormone in control of glucose homeostasis. Deficiencies of insulin signaling are central to diabetes and many other disorders. The brain is among the targets of insulin action, and insulin resistance is a major contributor to many diseases, including brain disorders. Here, we summarize key roles of insulin action in the brain and how this involves different brain cell types. Disordered brain insulin signaling can also contribute to neuropsychiatric diseases, affecting brain circuits involved in mood and cognition. Understanding of insulin signaling in different brain cell types/circuits and how these are altered in disease may lead to the development of new therapeutic approaches to these challenging disorders.

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

The human gut microbiota is a complex, dynamic, and highly diverse community of microorganisms. Beginning as early as in utero fetal development and continuing through birth to late-stage adulthood, the crosstalk between the gut microbiome and brain is essential for modulating various metabolic, neurodevelopmental, and immune-related pathways. Conversely, microbial dysbiosis – defined as alterations in richness and relative abundances – of the gut is implicated in the pathogenesis of several chronic neurological and neurodegenerative disorders. Evidence from large-population cohort studies suggests that individuals with neurodegenerative conditions have an altered gut microbial composition as well as microbial and serum metabolomic profiles distinct from those in the healthy population. Dysbiosis is also linked to psychiatric and gastrointestinal complications – comorbidities often associated with the prodromal phase of Parkinson’s disease (PD) and Alzheimer’s disease (AD). Studies have identified potential mediators that link gut dysbiosis and neurological disorders. Recent findings have also elucidated the potential mechanisms of disease pathology in the enteric nervous system prior to the onset of neurodegeneration. This review highlights the functional pathways and mechanisms, particularly gut microbe-induced chronic inflammation, protein misfolding, propagation of disease-specific pathology, defective protein clearance, and autoimmune dysregulation, linking gut microbial dysbiosis and neurodegeneration. In addition, we also discuss how pathogenic transformation of microbial composition leads to increased endotoxin production and fewer beneficial metabolites, both of which could trigger immune cell activation and enteric neuronal dysfunction. These can further disrupt intestinal barrier permeability, aggravate the systemic pro-inflammatory state, impair blood–brain barrier permeability and recruit immune mediators leading to neuroinflammation and neurodegeneration. Continued biomedical advances in understanding the microbiota-gut-brain axis will extend the frontier of neurodegenerative disorders and enable the utilization of novel diagnostic and therapeutic strategies to mitigate the pathological burden of these diseases.

Effects of chronic triclosan exposure on social behaviors in adult mice

Triclosan (TCS), a newly identified environmental endocrine disruptor (EED) in household products, has been reported to have toxic effects on animals and humans. The effects of TCS exposure on individual social behaviors and the potential underlying mechanisms are still unknown. This study investigated the behavioral effects of 42-day exposure to TCS (0, 50, 100 mg/kg) in drinking water using the open field test (OFT), social dominance test (SDT), social interaction test (SIT), and novel object recognition task (NOR). Using 16S rRNA sequencing analysis and transmission electron microscopy (TEM), we observed the effects of TCS exposure on the gut microbiota and ultrastructure of hippocampal neurons and synapses. Behavioral results showed that chronic TCS exposure reduced the social dominance of male and female mice. TCS exposure also reduced social interaction in male mice and impaired memory formation in female mice. Analysis of the gut microbiota showed that TCS exposure increased the relative abundance of the Proteobacteria and Actinobacteria phyla in female mice. Ultrastructural analysis revealed that TCS exposure induced ultrastructural damage to hippocampal neurons and synapses. These findings suggest that TCS exposure may affect social behaviors, which may be caused by altered gut microbiota and impaired plasticity of hippocampal neurons and synapses.