Antibiotic-induced dysbiosis of the microbiota impairs gut neuromuscular function in juvenile mice

T cells regulate intestinal motility and shape enteric neuronal responses to intestinal microbiota

How the gut microbiota and immune system maintain intestinal homeostasis in concert with the enteric nervous system (ENS) remains incompletely understood. To address this gap, we assessed small intestinal transit, enteric neuronal density, enteric neurogenesis, intestinal microbiota, immune cell populations and cytokines in wildtype and T-cell deficient germ-free mice colonized with specific pathogen-free (SPF) microbiota, conventionally raised SPF and segmented filamentous bacteria (SFB)-monocolonized mice. SPF microbiota increased small intestinal transit in a T cell-dependent manner. SPF microbiota increased neuronal density in the myenteric and submucosal plexuses of the ileum and colon, similar to conventionally raised SPF mice, independently of T cells. SFB increased neuronal density in the ileum in a T cell-dependent manner, but independently of T cells in the colon. SPF microbiota stimulated enteric neurogenesis (Sox2 expression in enteric neurons) in the ileum in a T cell-dependent manner, but in the colon this effect was T cell-independent. T cells regulated nestin expression in the ENS. SPF colonization increased Th17 cells, RORγT+ Treg cells, and IL-1β and IL-17A levels in the ileum and colon. By neutralizing IL-1β and IL-17A, we observed that they control microbiota-mediated enteric neurogenesis but were not involved in the regulation of motility. Together, these findings provide new insights into the microbiota-neuroimmune dialog that regulates intestinal physiology.

Sex-dependent alteration of the enteric neuromuscular function after antibiotic-induced dysbiosis in juvenile mice and effect of Lactocaseibacillus rhamnosus GG

Perturbations of the gastrointestinal (GI) microbiota (i.e. dysbiosis) in early life may induce vulnerability of the enteric nervous system (ENS), contributing to early onset GI disorders, such as irritable bowel syndrome (IBS). Probiotics, such as Lacticaseibacillus rhamnosus GG (LGG), may improve pediatric digestive disorders; however, the mechanisms involved, including effects on the ENS, are not yet fully understood. In this study, the long-lasting consequences of antibiotic-induced dysbiosis on intestinal neuromuscular function, as well as the effect of LGG, were evaluated in juvenile female and male mice. One week after antibiotic treatment cessation, broad-spectrum antibiotic treatment induced significant taxonomic changes in both sexes compared to untreated control animals. These changes appeared earlier and involved more potentially harmful bacterial taxa in females than in males. LGG effectively prevented alterations in microbial communities in both sexes, with a more pronounced protective effect in males. Dysbiosis reduced transit efficiency, nitrergic relaxations, and tachykinergic contractions only in females, with no significant effect of LGG in this group. In both sexes, dysbiosis decreased cholinergic contractions; however, LGG restored the excitatory responses to control levels only in males. In summary, early antibiotic-induced dysbiosis in juvenile mice leads to persistent effects during late adolescence on both gut microbiota composition and neuromuscular function. These alterations are more pronounced and less responsive to LGG treatment in females. The findings underscore the critical role of the enteric microbiota in early-life development of functional gastrointestinal disorders with sex-specific features, such IBS.

Antibiotic-induced decrease of bacterial load in guinea pig intestine reduces α2-adrenoceptor expression and activity in peristaltic motor inhibition

BACKGROUND AND PURPOSE

The use of analgosedatives in critically ill patients carries the risk of impairing gastrointestinal (GI) propulsion and could thereby lead to sepsis. The gut microbiota can influence GI motility, but whether GI microbial dysbiosis modifies GI peristalsis impairment by analgosedative drugs has not yet been analysed. This question was addressed in the guinea pig small intestine following a decrease of bacterial load by antibiotic pretreatment.

EXPERIMENTAL APPROACH

Guinea pigs were enorally (within the mouth) pretreated with meropenem, neomycin and vancomycin, and antibiotic-induced decrease of bacterial load was confirmed by 16S rDNA sequencing. Peristalsis in the isolated guinea pig small intestine was evaluated by determining the pressure threshold at which a peristaltic wave is triggered. The expression of factors that may be relevant to communication between GI microbiota and the motor system was examined at the mRNA (quantitative (q)PCR]) and/or protein (enzyme-linked immunosorbent assay [ELISA]) level.

KEY RESULTS

Antibiotic treatment disturbed the small intestinal microbiome as shown by decrease of bacterial load and reduced alpha diversity. Microbial dysbiosis did not affect peristalsis at baseline but blunted the ability of α2 agonists to inhibit peristalsis, while the anti-peristaltic effects of sufentanil, midazolam, neostigmine and propofol were inconsistently affected. These functional alterations were complemented by a decreased expression of α2-adrenoceptors, toll-like receptors (TRL) 3, 4 & 7, IFN-γ and iNOS.

CONCLUSION AND IMPLICATIONS

Antibiotic-induced decrease of bacterial load in the small intestine selectively blunts the ability of α2 agonists to impair peristalsis. This effect is explained by decreased α2-adrenoceptor expression, which may arise from TLR down-regulation in the dysbiotic gut.

Toll-like receptor 4 deficiency ameliorates experimental ileitis and enteric neuropathy: Involvement of nitrergic and 5-hydroxytryptaminergic neurotransmission

BACKGROUND AND PURPOSE

Inflammatory bowel disease (IBD) patients display genetic polymorphisms in toll-like receptor 4 (TLR4) genes, contributing to dysregulate enteric nervous system (ENS) circuits with increased levels of 5-HT and alteration of the neuroimmune crosstalk. In this study, we investigated the impact of TLR4 signalling on mouse ENS dysfunction caused by dextran sulphate sodium (DSS)-induced ileitis.

EXPERIMENTAL APPROACH

Male C57BL/6J (wild-type [WT]) and TLR4-/- mice (10 ± 2 weeks old) received 2% DSS in drinking water for 5 days and then were switched to 3-day regular drinking water. Histological analysis and proinflammatory cytokine mRNA levels were assessed in ileal samples. Gut motility was evaluated by changes in transit of a fluorescent-labelled marker and isometric neuromuscular responses of ileal full-thickness segments to receptor and non-receptor-mediated stimuli. Alterations in ENS architecture were assessed by confocal immunohistochemistry in longitudinal muscle-myenteric plexus whole-mount preparations.

KEY RESULTS

In WT mice, DSS treatment caused delayed gastrointestinal transit, ileal myenteric neurodegeneration, reactive gliosis and release of proinflammatory cytokines. Enhanced cholinergic and tachykinergic excitatory tone, increased inducible nitric oxide synthase (iNOS)-mediated relaxation, and changes in 5-HT2A and 5-HT3 receptor-mediated responses were observed during ileitis in WT mice. TLR4 deficiency reversed most of the functional and morphological abnormalities.

CONCLUSION AND IMPLICATIONS

Our results demonstrate that TLR4 activity influences the severity of ileitis, neuroglial plasticity, gut motility, and nitrergic and 5-HTergic neurotransmissions. The neuroimmune interaction between TLR4 and 5-HT observed in our study appears to be a potential pharmacological target to treat ENS dysfunction implicated in IBD onset/progression.

Tryptophan and Its Metabolite Serotonin Impact Metabolic and Mental Disorders via the Brain-Gut-Microbiome Axis: A Focus on Sex Differences

The crisis of metabolic and mental disorders continues to escalate worldwide. A growing body of research highlights the influence of tryptophan and its metabolites, such as serotonin, beyond their traditional roles in neural signaling. Serotonin acts as a key neurotransmitter within the brain-gut-microbiome axis, a critical bidirectional communication network affecting both metabolism and behavior. Emerging evidence suggests that the gut microbiome regulates brain function and behavior, particularly through microbial influences on tryptophan metabolism and the serotonergic system, both of which are essential for normal functioning. Additionally, sex differences exist in multiple aspects of serotonin-mediated modulation within the brain-gut-microbiome axis, affecting feeding and affective behaviors. This review summarizes the current knowledge from human and animal studies on the influence of tryptophan and its metabolite serotonin on metabolic and behavioral regulation involving the brain and gut microbiome, with a focus on sex differences and the role of sex hormones. We speculate that gut-derived tryptophan and serotonin play essential roles in the pathophysiology that modifies neural circuits, potentially contributing to eating and affective disorders. We propose the gut microbiome as an appealing therapeutic target for metabolic and affective disorders, emphasizing the importance of understanding sex differences in metabolic and behavioral regulation influenced by the brain-gut-microbiome axis. The therapeutic targeting of the gut microbiota and its metabolites may offer a viable strategy for treating serotonin-related disorders, such as eating and affective disorders, with potential differences in treatment efficacy between men and women. This review would promote research on sex differences in metabolic and behavioral regulation impacted by the brain-gut-microbiome axis.

Short-chain fatty acids mediate gut microbiota-brain communication and protect the blood-brain barrier integrity

The human gut, with a complex community of microbes, is essential for maintaining overall health. This gut microbiota engages in two-way communication with the central nervous system, collectively known as the gut microbiota-brain axis. Alterations in gut microbiota have been associated with various neurological disorders, and disruptions to the blood-brain barrier (BBB) may be crucial, though the exact mechanisms remain unknown. In the current study, we investigated the impacts of short-chain fatty acids (SCFAs) on the integrity of the BBB, which was compromised by orally administered antibiotics in rhesus monkeys and C57BL/6n mice. Our results showed that SCFA supplementation notably enhanced BBB integrity in rhesus monkeys with gut dysbiosis. Similar outcomes were observed in mice with gut dysbiosis, accompanied by decreased cortical claudin-5 mRNA levels. In particular, propionate, but not acetate or butyrate, could reverse the antibiotic-induced BBB permeability increase in mice. Additionally, in vitro studies demonstrated that propionate boosted the expression of tight junction proteins in brain endothelial cells. These results suggest that the propionate can maintain BBB integrity through a free fatty acid receptor 2-dependent mechanism. This study offers new insights into the gut-brain axis and underscores potential therapeutic targets for interventions based on gut microbiota.

Buttermilk and Whey as Functional Foods to Ameliorate Clindamycin-Induced Changes in Mouse Intestine: Modulation of Intestinal Motility and Toll-like Receptors Expression

Antibiotic treatment is one of the main causes of intestinal dysbiosis, leading, in turn, to other intestinal alterations given the multiple relationships of the microbiota with gut health. Whey and buttermilk are two by-products from the dairy industry with numerous bioactive components. This study aimed to assess the potential of two formulas, containing a mixture of lactoferrin, milk fat globule membrane (MFGM), and whey or buttermilk, to reverse the negative effects of clindamycin on gut motility, Toll-like receptors (TLRs) expression, and oxidative stress in the intestine. For this purpose, a murine model of intestinal dysbiosis was established by clindamycin treatment. Male C57BL/6 mice were treated with saline (Control), clindamycin (Clin), a formula containing whey (F1), or buttermilk (F2) supplemented with lactoferrin and MFGM, Clin+F1, or Clin+F2. Clin delayed the whole gut transit, reduced the response to acetylcholine, decreased TLR2 expression, and increased TLR4 expression in the intestine. F1 and F2 formulas reversed the effects of Clin, restoring TLR2 receptor levels and normalizing intestinal dysmotility. These results indicate that whey- and buttermilk-based formulas supplemented with lactoferrin and MFGM could be used as functional foods to prevent or treat motility disorders and restore some components of the immune system after antibiotic treatment.

From Fundamentals to Innovation in Alzheimer's Disease: Molecular Findings and Revolutionary Therapies

Alzheimer's disease (AD) is a global health concern and the leading cause of dementia in the elderly. The prevalence of this neurodegenerative condition is projected to increase concomitantly with increased life expectancy, resulting in a significant economic burden. With very few FDA-approved disease-modifying drugs available for AD, there is an urgent need to develop new compounds capable of impeding the progression of the disease. Given the unclear etiopathogenesis of AD, this review emphasizes the underlying mechanisms of this condition. It explores not only well-studied aspects, such as the accumulation of Aβ plaques and neurofibrillary tangles, but also novel areas, including glymphatic and lymphatic pathways, microbiota and the gut-brain axis, serotoninergic and autophagy alterations, vascular dysfunction, the metal hypothesis, the olfactory pathway, and oral health. Furthermore, the potential molecular targets arising from all these mechanisms have been reviewed, along with novel promising approaches such as nanoparticle-based therapy, neural stem cell transplantation, vaccines, and CRISPR-Cas9-mediated genome editing techniques. Taking into account the overlap of these various mechanisms, individual and combination therapies emerge as the future direction in the AD strategy.

Virus-Triggered Autoimmunity Was Associated With Hirschsprung's Disease Through Activation of Innate Immunity

Background: Hirschsprung's disease (HSCR) is a congenital enteric nervous system (ENS) disorder. Genetics cannot explain most sporadic cases. To explore the relationship between pathogen infection, autoantibodies, innate immune, and HSCR. Methods: Pathogen microarray was conducted in the serum of the prospective neonatal abdominal distension (NAD) cohort, consisting of 56 children followed for at least 6 months until the final diagnosis of HSCR was determined or excluded. We conducted an autoantibody microarray in an HSCR cohort, which is comprised of diagnosed HSCR patients (HSCR) and healthy control subjects (HC). RNA-seq of colon tissues from aganglionic and ganglionic segments of HSCR patients was performed. Results: Experimental results show that the serum lgM and lgG of enterovirus 71 (EV71) were significantly higher in HSCR than in the gastrointestinal dysfunction (GI) group, with a prediagnose value reaching area under the curve (AUC) over 0.76. We discovered that a group of autoantibodies were significantly higher in HSCR including neuronal pentraxin 1 (NPTX1), amyloid, neuron lysate, and myelin-associated oligodendrocytic basic protein (MOBP) than that in the HC group. These four autoantibodies could distinguish HSCR from the HC group, with a combined AUC of over 0.90 using both serum IgG and IgM. Further analysis showed that wide activation of innate immune pathways, including toll-like receptor (TLR) signaling pathway, neutrophil-to-lymphocyte ratio (NLR) signaling pathway, red cell distribution width to lymphocyte ratio (RLR) signaling pathway, and cyclic adenosine monophosphate (cAMP) signaling pathway in aganglionic compared to ganglionic segments of HSCR. Conclusion: This study suggested that virus-triggered autoimmunity may contribute to HSCR through activation of innate immunity, which facilitates the diagnosis and prevention of HSCR.

Intergenerational neurotoxicity of polystyrene nanoplastics in offspring mice is mediated by dysfunctional microbe-gut-brain axis

Nanoplastics (NPs) are ubiquitous in daily life, posing potential risks to the environment and human. While their negative effects on parental organisms have been extensively studied, intergenerational effects are still in the early stages of investigation. Here, we aimed to investigate the impact of maternal exposure to an environmentally relevant level of polystyrene NPs (PSNPs, 100 nm) during gestation and lactation (∼32 days, 50 μg/mouse/day) on neurotoxicity mediated by the microbe-gut-brain axis in offspring mice. Maternal PSNPs exposure significantly increased brain TNF-α level and microglia by 1.43 and 1.48 folds respectively, compared to control, accompanied by nuclear pyknosis and cell vacuolization in cortex and hippocampus. Targeted neurotransmitter metabolomics analysis revealed dysregulation in dopamine and serotonin metabolism. Specifically, dopamine levels increased significantly from 0.007 ng/L to 0.015 ng/L, while N-acetylseroton and 3,4-dihydroxyphenylacetic acid decreased significantly from 0.002 and 0.929 ng/L to 0.001 and 0.680 ng/L, respectively. Through a combination of 16S rRNA sequencing and biochemical analysis, we discovered that maternal PSNPs exposure led to a depletion of anti-inflammatory bacteria and an enrichment of pro-inflammatory bacteria resulting in intestinal barrier damage, elevated levels of lipopolysaccharide in blood, and subsequent activation of neuroinflammation. Meanwhile, gut bacteria dysbiosis interfered with communication between gut and brain by dysregulating neurotransmitter synthesis, as evidenced by significant associations between neurotransmitter-related bacteria (Akkermansia, Family_XIII_AD3011_group, Lachnoclostridium) and dopamine/serotonin related metabolites. Furthermore, transcriptional alterations in dopamine and serotonin related pathways were observed in the enteric nervous system, suggesting abnormal signal transduction from gut to brain contributes to neurotoxicity. This study provides new insights into NPs-induced neurotoxicity within the context of microbe-gut-brain axis and highlights the risk of cerebral dysfunction in offspring with maternal NPs exposure.

The communication mechanism of the gut-brain axis and its effect on central nervous system diseases: A systematic review

Gut microbiota is involved in intricate and active metabolic processes the host's brain function, especially its role in immune responses, secondary metabolism, and symbiotic connections with the host. Gut microbiota can promote the production of essential metabolites, neurotransmitters, and other neuroactive chemicals that affect the development and treatment of central nervous system diseases. This article introduces the relevant pathways and manners of the communication between the brain and gut, summarizes a comprehensive overview of the current research status of key gut microbiota metabolites that affect the functions of the nervous system, revealing those adverse factors that affect typical communication between the brain-gut axis, and outlining the efforts made by researchers to alleviate these neurological diseases through targeted microbial interventions. The relevant pathways and manners of communication between the brain and gut contribute to the experimental design of new treatment plans and drug development. The factors that may cause changes in gut microbiota and affect metabolites, as well as current intervention methods are summarized, which helps improve gut microbiota brain dialogue, prevent adverse triggering factors from interfering with the gut microbiota system, and minimize neuropathological changes.

Preclinical Evaluation of Sodium Butyrate's Potential to Reduce Alcohol Consumption: A Dose-Escalation Study in C57BL/6J Mice in Antibiotic-Enhanced Binge-Like Drinking Model

INTRODUCTION

In our earlier efforts to establish gut-brain axis during alcohol use disorder (AUD), we have demonstrated that supplementation of C57BL/6J male mice with 8 mg/mL sodium butyrate, a major short-chain fatty acid, in drinking water reduced ethanol intake and neuroinflammatory response in antibiotic (ABX)-enhanced voluntary binge-like alcohol consumption model, drinking in the dark (DID).

METHODS

To further evaluate the preclinical potential of SB, we have set a dose-escalation study in C57BL/6J male mice to test effects of ad libitum 20 mg/mL SB and 50 mg/mL SB and their combinations with ABX in the DID procedure for 4 weeks. Effects of these SB concentrations on ethanol consumption and bodily parameters were determined for the duration of the treatments. At the end of study, blood, liver, and intestinal tissues were collected to study any potential adverse effects ad to measure blood ethanol concentrations.

RESULTS

Increasing SB concentrations in the drinking water caused a loss in the protective effect against ethanol consumption and produced adverse effects on body and liver weights, reduced overall liquid intake. The hypothesis that these effects were due to aversion to SB smell/taste at these high concentrations were further tested in a follow up proof-of-concept study with intragastric gavage administration of SB. The higher gavage dose (320 mg/kg) caused reduction in ethanol consumption without any adverse effects.

CONCLUSION

Overall, these findings added more support for the therapeutic potential of SB in management of AUD, given a proper form of administration.

INTRODUCTION

In our earlier efforts to establish gut-brain axis during alcohol use disorder (AUD), we have demonstrated that supplementation of C57BL/6J male mice with 8 mg/mL sodium butyrate, a major short-chain fatty acid, in drinking water reduced ethanol intake and neuroinflammatory response in antibiotic (ABX)-enhanced voluntary binge-like alcohol consumption model, drinking in the dark (DID).

METHODS

To further evaluate the preclinical potential of SB, we have set a dose-escalation study in C57BL/6J male mice to test effects of ad libitum 20 mg/mL SB and 50 mg/mL SB and their combinations with ABX in the DID procedure for 4 weeks. Effects of these SB concentrations on ethanol consumption and bodily parameters were determined for the duration of the treatments. At the end of study, blood, liver, and intestinal tissues were collected to study any potential adverse effects ad to measure blood ethanol concentrations.

RESULTS

Increasing SB concentrations in the drinking water caused a loss in the protective effect against ethanol consumption and produced adverse effects on body and liver weights, reduced overall liquid intake. The hypothesis that these effects were due to aversion to SB smell/taste at these high concentrations were further tested in a follow up proof-of-concept study with intragastric gavage administration of SB. The higher gavage dose (320 mg/kg) caused reduction in ethanol consumption without any adverse effects.

CONCLUSION

Overall, these findings added more support for the therapeutic potential of SB in management of AUD, given a proper form of administration.

Environmental, socioeconomic, and health factors associated with gut microbiome species and strains in isolated Honduras villages

Despite a growing interest in the gut microbiome of non-industrialized countries, data linking deeply sequenced microbiomes from such settings to diverse host phenotypes and situational factors remain uncommon. Using metagenomic data from a community-based cohort of 1,871 people from 19 isolated villages in the Mesoamerican highlands of western Honduras, we report associations between bacterial species and human phenotypes and factors. Among them, socioeconomic factors account for 51.44% of the total associations. Meta-analysis of species-level profiles across several datasets identified several species associated with body mass index, consistent with previous findings. Furthermore, the inclusion of strain-phylogenetic information modifies the overall relationship between the gut microbiome and the phenotypes, especially for some factors like household wealth (e.g., wealthier individuals harbor different strains of Eubacterium rectale). Our analysis suggests a role that gut microbiome surveillance can play in understanding broad features of individual and public health.

Neuroinflammation, neurodegeneration and alteration of spatial memory in BALB/c mice through ampicillin-induced gut dysbiosis; NOS2 and NFL involvement in a microbiota-gut-brain axis model

We aimed to investigate ampicillin (AMP) mechanisms in microbiota-gut-brain axis. We evaluated its effect on two gut and brain regions and behavioral performances. We administred AMP (1 g/l) to BALB/c mice for 21 days. Then, we analyzed body weigth change, stool consistency scoring, gut length, intestinal microbiota composition, nitric oxide synthase 2 (NOS2) expression and tissue integrity. We subsequently evaluated NOS2, GFAP, CD68 and NFL cerebral expression and spatial memory.Interestingly, our data showed gut microbiota disruption, NOS2 upregulation and tissue damage, associated to cerebral NOS2, GFAP, CD68 and NFL over-expression and behavioral alteration. Antiobiotic therapy should be prescribed with great caution.

Autism spectrum disorders and the gastrointestinal tract: insights into mechanisms and clinical relevance

Autism spectrum disorders (ASDs) are recognized as central neurodevelopmental disorders diagnosed by impairments in social interactions, communication and repetitive behaviours. The recognition of ASD as a central nervous system (CNS)-mediated neurobehavioural disorder has led most of the research in ASD to be focused on the CNS. However, gastrointestinal function is also likely to be affected owing to the neural mechanistic nature of ASD and the nervous system in the gastrointestinal tract (enteric nervous system). Thus, it is unsurprising that gastrointestinal disorders, particularly constipation, diarrhoea and abdominal pain, are highly comorbid in individuals with ASD. Gastrointestinal problems have also been repeatedly associated with increased severity of the core symptoms diagnostic of ASD and other centrally mediated comorbid conditions, including psychiatric issues, irritability, rigid-compulsive behaviours and aggression. Despite the high prevalence of gastrointestinal dysfunction in ASD and its associated behavioural comorbidities, the specific links between these two conditions have not been clearly delineated, and current data linking ASD to gastrointestinal dysfunction have not been extensively reviewed. This Review outlines the established and emerging clinical and preclinical evidence that emphasizes the gut as a novel mechanistic and potential therapeutic target for individuals with ASD.

Probiotics for functional constipation in children: an overview of overlapping systematic reviews

Background

This overview of systematic reviews (SRs) and meta-analysis (MAs) aimed to systematically collate, appraise and synthesize evidence of probiotics for functional constipation (FC) in children.

Methods

SRs/MAs of probiotics for FC in children were systematic identified by searching Cochrane Library, PubMed, Embase, and Web of science. Assessment of Multiple Systematic Reviews 2 (AMSTAR-2), Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA), and Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) were unitized by two reviewers independently to assess the methodological quality, reporting quality, and quality of evidence, respectively.

Results

Seven SRs/MAs met the eligibility criteria and were included in this study. According to AMSTAR-2, a very low methodological quality assessment was given to the included SRs/MAs due to the limitations of items 2, 4 and 7. For the PRISMA statement, the overall quality of reporting was unsatisfactory due to the lack of reporting on protocol, risk of bias across studies, synthesis of results, and additional analysis. According to GRADE, the quality of evidence for outcomes was rated as very low to moderate.

Conclusions

Probiotics may be beneficial in improving FC in children. Because of limitations and inconsistent conclusions, further rigorous, normative and comprehensive SRs/MAs are needed to provide robust evidence for definitive conclusions.

The contribution of age-related changes in the gut-brain axis to neurological disorders

Trillions of microbes live symbiotically in the host, specifically in mucosal tissues such as the gut. Recent advances in metagenomics and metabolomics have revealed that the gut microbiota plays a critical role in the regulation of host immunity and metabolism, communicating through bidirectional interactions in the microbiota-gut-brain axis (MGBA). The gut microbiota regulates both gut and systemic immunity and contributes to the neurodevelopment and behaviors of the host. With aging, the composition of the microbiota changes, and emerging studies have linked these shifts in microbial populations to age-related neurological diseases (NDs). Preclinical studies have demonstrated that gut microbiota-targeted therapies can improve behavioral outcomes in the host by modulating microbial, metabolomic, and immunological profiles. In this review, we discuss the pathways of brain-to-gut or gut-to-brain signaling and summarize the role of gut microbiota and microbial metabolites across the lifespan and in disease. We highlight recent studies investigating 1) microbial changes with aging; 2) how aging of the maternal microbiome can affect offspring health; and 3) the contribution of the microbiome to both chronic age-related diseases (e.g., Parkinson's disease, Alzheimer's disease and cerebral amyloidosis), and acute brain injury, including ischemic stroke and traumatic brain injury.

Probiotics in Postoperative Pain Management

Postoperative pain is the unpleasant sensory and emotional experience after surgery, its origin being both the inflammatory reaction induced by the surgical trauma on the abdominal wall and the splanchnic pain induced by the activation of nociceptors of the viscera, which are highly sensitive to distension, ischemia, and inflammation. Nowadays, it is well recognized that there is a close relationship between the gut microbiome and pain perception, and that microbiome is highly affected by both anesthesia and surgical manipulation. Thus, efforts to restore the disturbed microbiome via supplementation with beneficial bacteria, namely probiotics, seem to be effective. In this article, the knowledge gained mainly from experimental research on this topic is analyzed, the concluding message being that each probiotic strain works in its own way towards pain relief.

Amyloid-β mediates intestinal dysfunction and enteric neurons loss in Alzheimer's disease transgenic mouse

Alzheimer's disease (AD) is traditionally considered as a brain disorder featured by amyloid-β (Aβ) deposition. The current study on whether pathological changes of AD extend to the enteric nervous system (ENS) is still in its infancy. In this study, we found enteric Aβ deposition, intestinal dysfunction, and colonic inflammation in the young APP/PS1 mice. Moreover, these mice exhibited cholinergic and nitrergic signaling pathways damages and enteric neuronal loss. Our data show that Aβ42 treatment remarkably affected the gene expression of cultured myenteric neurons and the spontaneous contraction of intestinal smooth muscles. The intra-colon administration of Aβ42 induced ENS dysfunction, brain gliosis, and β-amyloidosis-like changes in the wild-type mice. Our results suggest that ENS mirrors the neuropathology observed in AD brains, and intestinal pathological changes may represent the prodromal events, which contribute to brain pathology in AD. In summary, our findings provide new opportunities for AD early diagnosis and prevention.

Pathophysiological Aspects and Therapeutic Armamentarium of Alzheimer's Disease: Recent Trends and Future Development

Alzheimer's disease (AD) is the primary cause of dementia and is characterized by the death of brain cells due to the accumulation of insoluble amyloid plaques, hyperphosphorylation of tau protein, and the formation of neurofibrillary tangles within the cells. AD is also associated with other pathologies such as neuroinflammation, dysfunction of synaptic connections and circuits, disorders in mitochondrial function and energy production, epigenetic changes, and abnormalities in the vascular system. Despite extensive research conducted over the last hundred years, little is established about what causes AD or how to effectively treat it. Given the severity of the disease and the increasing number of affected individuals, there is a critical need to discover effective medications for AD. The US Food and Drug Administration (FDA) has approved several new drug molecules for AD management since 2003, but these drugs only provide temporary relief of symptoms and do not address the underlying causes of the disease. Currently, available medications focus on correcting the neurotransmitter disruption observed in AD, including cholinesterase inhibitors and an antagonist of the N-methyl-D-aspartate (NMDA) receptor, which temporarily alleviates the signs of dementia but does not prevent or reverse the course of AD. Research towards disease-modifying AD treatments is currently underway, including gene therapy, lipid nanoparticles, and dendrimer-based therapy. These innovative approaches aim to target the underlying pathological processes of AD rather than just managing the symptoms. This review discusses the novel aspects of pathogenesis involved in the causation of AD of AD and in recent developments in the therapeutic armamentarium for the treatment of AD such as gene therapy, lipid nanoparticles, and dendrimer-based therapy, and many more.

Understanding the Gut-Brain Axis and Its Therapeutic Implications for Neurodegenerative Disorders

The gut-brain axis (GBA) is a complex bidirectional communication network connecting the gut and brain. It involves neural, immune, and endocrine communication pathways between the gastrointestinal (GI) tract and the central nervous system (CNS). Perturbations of the GBA have been reported in many neurodegenerative disorders (NDDs), such as Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS), among others, suggesting a possible role in disease pathogenesis. The gut microbiota is a pivotal component of the GBA, and alterations in its composition, known as gut dysbiosis, have been associated with GBA dysfunction and neurodegeneration. The gut microbiota might influence the homeostasis of the CNS by modulating the immune system and, more directly, regulating the production of molecules and metabolites that influence the nervous and endocrine systems, making it a potential therapeutic target. Preclinical trials manipulating microbial composition through dietary intervention, probiotic and prebiotic supplementation, and fecal microbial transplantation (FMT) have provided promising outcomes. However, its clear mechanism is not well understood, and the results are not always consistent. Here, we provide an overview of the major components and communication pathways of the GBA, as well as therapeutic approaches targeting the GBA to ameliorate NDDs.

Selenium Mitigates Ammonia-Induced Neurotoxicity by Suppressing Apoptosis, Immune Imbalance, and Gut Microbiota-Driven Metabolic Disturbance in Fattening Pigs

Ammonia could be regarded as one detrimental pollutant with an acrid smell in livestock sheds. So far, the pig breeding industry became the main source of atmospheric ammonia. Previous literature demonstrated that excessive ammonia inhalation might cause a series of physiological damage to multiple organs. Unfortunately, the toxicity mechanisms of gaseous ammonia to the porcine nervous system need further research to elucidate. Selenium (Se) involves in many essential physiological processes and has a mitigative effect on the exogenous toxicant. There were scant references that corroborated whether organic Se could intervene in the underlying toxicity of ammonia to the hypothalamus. In the present study, multi-omics tools, ethology, and molecular biological techniques were performed to clarify the detailed mechanisms of relaxation effects of L-selenomethionine on ammonia poisoning. Our results showed that ammonia inhalation caused the clinical symptoms and the increment of positive apoptosis rate in the hypothalamus with the dysfunction of mitochondrial dynamics factors, while obvious mitochondria structure defects were observed. In parallel, the inflammation medium levels and gut microbes-driven metabolism function were altered to mediate the neurotoxicity in fattening pigs through the initiation of inflammation development. Interestingly, L-selenomethionine could attenuate ammonia toxicity by activating the PI3K/Akt/PPAR-γ pathway to inhibit the mitochondria-mediated apoptosis process, blocking the abnormal immune response and the accumulation of reactive oxygen species in the nucleus. Meanwhile, Se could enhance the production performance of fattening sows. Taken together, our study verified the novel hypothesis for the toxicity identification of aerial ammonia and provided a therapeutic strategy for the treatment of occupational poisoning.

Probiotic lactic acid bacteria alleviate pediatric IBD and remodel gut microbiota by modulating macrophage polarization and suppressing epithelial apoptosis

Introduction

The incidence of pediatric inflammatory bowel disease (PIBD) continues to rise. It was reported that the probiotic lactic acid bacteria Pediococcus pentosaceus (P. pentosaceus) can interfere with intestinal immunity, but it is still unknown whether it can alleviate PIBD and the concrete mechanism of immune regulation is unclear.

Methods

For this study, 3-week-old juvenile mice were selected for modeling the development of PIBD. The mice treated with 2% DSS were randomly divided into two groups, which were given P. pentosaceus CECT8330 and equal amounts of solvent, respectively. The feces and intestinal tissue were collected for the mechanism exploration in vivo. THP-1 and NCM460 cells were used to investigate the effects of P. pentosaceus CECT8330 on macrophage polarization, epithelial cell apoptosis, and their crosstalk in vitro.

Results

P. pentosaceus CECT8330 obviously alleviated colitis symptoms of juvenile mice, including weight loss, colon length shortening, spleen swelling, and intestinal barrier function. Mechanistically, P. pentosaceus CECT8330 could inhibit intestinal epithelial apoptosis by suppressing the NF-κB signaling pathway. Meanwhile, it reprogramed macrophages from a pro-inflammatory M1 phenotype to an anti-inflammatory M2 phenotype, leading to a decreased secretion of IL-1β which contributes to the reduction in ROS production and epithelial apoptosis. Additionally, the 16S rRNA sequence analysis revealed that P. pentosaceus CECT8330 could recover the balance of gut microbiota, and a significantly increased content of Akkermansia muciniphila was particularly observed.

Conclusion

P. pentosaceus CECT8330 shifts macrophage polarization toward an anti-inflammatory M2 phenotype. The decreased production of IL-1β leads to a reduction in ROS, NF-κB activation, and apoptosis in the intestinal epithelium, all of which help to repair the intestinal barrier and adjust gut microbiota in juvenile colitis mice.

The enteric nervous system

Of all the organ systems in the body, the gastrointestinal tract is the most complicated in terms of the numbers of structures involved, each with different functions, and the numbers and types of signaling molecules utilized. The digestion of food and absorption of nutrients, electrolytes, and water occurs in a hostile luminal environment that contains a large and diverse microbiota. At the core of regulatory control of the digestive and defensive functions of the gastrointestinal tract is the enteric nervous system (ENS), a complex system of neurons and glia in the gut wall. In this review, we discuss 1) the intrinsic neural control of gut functions involved in digestion and 2) how the ENS interacts with the immune system, gut microbiota, and epithelium to maintain mucosal defense and barrier function. We highlight developments that have revolutionized our understanding of the physiology and pathophysiology of enteric neural control. These include a new understanding of the molecular architecture of the ENS, the organization and function of enteric motor circuits, and the roles of enteric glia. We explore the transduction of luminal stimuli by enteroendocrine cells, the regulation of intestinal barrier function by enteric neurons and glia, local immune control by the ENS, and the role of the gut microbiota in regulating the structure and function of the ENS. Multifunctional enteric neurons work together with enteric glial cells, macrophages, interstitial cells, and enteroendocrine cells integrating an array of signals to initiate outputs that are precisely regulated in space and time to control digestion and intestinal homeostasis.

Who's talking to whom: microbiome-enteric nervous system interactions in early life

The enteric nervous system (ENS) is the intrinsic nervous system of the gastrointestinal tract (GI) and regulates important GI functions, including motility, nutrient uptake, and immune response. The development of the ENS begins during early organogenesis and continues to develop once feeding begins, with ongoing plasticity into adulthood. There has been increasing recognition that the intestinal microbiota and ENS interact during critical periods, with implications for normal development and potential disease pathogenesis. In this review, we focus on insights from mouse and zebrafish model systems to compare and contrast how each model can serve in elucidating the bidirectional communication between the ENS and the microbiome. At the end of this review, we further outline implications for human disease and highlight research innovations that can lead the field forward.

The Potential Role of Microorganisms on Enteric Nervous System Development and Disease

The enteric nervous system (ENS), the inherent nervous system of the gastrointestinal (GI) tract is a vast nervous system that controls key GI functions, including motility. It functions at a critical interface between the gut luminal contents, including the diverse population of microorganisms deemed the microbiota, as well as the autonomic and central nervous systems. Critical development of this axis of interaction, a key determinant of human health and disease, appears to occur most significantly during early life and childhood, from the pre-natal through to the post-natal period. These factors that enable the ENS to function as a master regulator also make it vulnerable to damage and, in turn, a number of GI motility disorders. Increasing attention is now being paid to the potential of disruption of the microbiota and pathogenic microorganisms in the potential aetiopathogeneis of GI motility disorders in children. This article explores the evidence regarding the relationship between the development and integrity of the ENS and the potential for such factors, notably dysbiosis and pathogenic bacteria, viruses and parasites, to impact upon them in early life.

Effects of Perinatal Antibiotic Exposure and Neonatal Gut Microbiota

Antibiotic therapy is one of the most important strategies to treat bacterial infections. The overuse of antibiotics, especially in the perinatal period, is associated with long-lasting negative consequences such as the spread of antibiotic resistance and alterations in the composition and function of the gut microbiota, both of which negatively affect human health. In this review, we summarize recent evidence about the influence of antibiotic treatment on the neonatal gut microbiota and the subsequent negative effects on the health of the infant. We also analyze the possible microbiome-based approaches for the re-establishment of healthy microbiota in neonates.

The Role of the Human Microbiome in the Pathogenesis of Pain

Understanding of the gut microbiome's role in human physiology developed rapidly in recent years. Moreover, any alteration of this microenvironment could lead to a pathophysiological reaction of numerous organs. It results from the bidirectional communication of the gastrointestinal tract with the central nervous system, called the gut-brain axis. The signals in the gut-brain axis are mediated by immunological, hormonal, and neural pathways. However, it is also influenced by microorganisms in the gut. The disturbances in the gut-brain axis are associated with gastrointestinal syndromes, but recently their role in the development of different types of pain was reported. The gut microbiome could be the factor in the central sensitization of chronic pain by regulating microglia, astrocytes, and immune cells. Dysbiosis could lead to incorrect immune responses, resulting in the development of inflammatory pain such as endometriosis. Furthermore, chronic visceral pain, associated with functional gastrointestinal disorders, could result from a disruption in the gut microenvironment. Any alteration in the gut-brain axis could also trigger migraine attacks by affecting cytokine expression. Understanding the gut microbiome's role in pain pathophysiology leads to the development of analgetic therapies targeting microorganisms. Probiotics, FODMAP diet, and fecal microbiota transplantation are reported to be beneficial in treating visceral pain.

Direct and indirect mechanisms by which the gut microbiota influence host serotonin systems

Mounting evidence highlights the pivotal role of enteric microbes as a dynamic interface with the host. Indeed, the gut microbiota, located in the lumen of the gastrointestinal (GI) tract, influence many essential physiological processes that are evident in both healthy and pathological states. A key signaling molecule throughout the body is serotonin (5-hydroxytryptamine; 5-HT), which acts in the GI tract to regulate numerous gut functions including intestinal motility and secretion. The gut microbiota can modulate host 5-HT systems both directly and indirectly. Direct actions of gut microbes, evidenced by studies using germ-free animals or antibiotic administration, alter the expression of key 5-HT-related genes to promote 5-HT biosynthesis. Indirectly, the gut microbiota produce numerous microbial metabolites, whose actions can influence host serotonergic systems in a variety of ways. This review summarizes the current knowledge regarding mechanisms by which gut bacteria act to regulate host 5-HT and 5-HT-mediated gut functions, as well as implications for 5-HT in the microbiota-gut-brain axis.

Role of gut microbiota-derived signals in the regulation of gastrointestinal motility

The gastrointestinal (GI) tract harbors trillions of commensal microbes, called the gut microbiota, which plays a significant role in the regulation of GI physiology, particularly GI motility. The GI tract expresses an array of receptors, such as toll-like receptors (TLRs), G-protein coupled receptors, aryl hydrocarbon receptor (AhR), and ligand-gated ion channels, that sense different gut microbiota-derived bioactive substances. Specifically, microbial cell wall components and metabolites, including lipopeptides, peptidoglycan, lipopolysaccharides (LPS), bile acids (BAs), short-chain fatty acids (SCFAs), and tryptophan metabolites, mediate the effect of gut microbiota on GI motility through their close interactions with the enteroendocrine system, enteric nervous system, intestinal smooth muscle, and immune system. In turn, GI motility affects the colonization within the gut microbiota. However, the mechanisms by which gut microbiota interacts with GI motility remain to be elucidated. Deciphering the underlying mechanisms is greatly important for the prevention or treatment of GI dysmotility, which is a complication associated with many GI diseases, such as irritable bowel syndrome (IBS) and constipation. In this perspective, we overview the current knowledge on the role of gut microbiota and its metabolites in the regulation of GI motility, highlighting the potential mechanisms, in an attempt to provide valuable clues for the development of gut microbiota-dependent therapy to improve GI motility.

A Small Peptide Increases Drug Delivery in Human Melanoma Cells

Melanoma is the most fatal type of skin cancer and is notoriously resistant to chemotherapies. The response of melanoma to current treatments is difficult to predict. To combat these challenges, in this study, we utilize a small peptide to increase drug delivery to melanoma cells. A peptide library array was designed and screened using a peptide array-whole cell binding assay, which identified KK-11 as a novel human melanoma-targeting peptide. The peptide and its D-amino acid substituted analogue (VPWxEPAYQrFL or D-aa KK-11) were synthesized via a solid-phase strategy. Further studies using FITC-labeled KK-11 demonstrated dose-dependent uptake in human melanoma cells. D-aa KK-11 significantly increased the stability of the peptide, with 45.3% remaining detectable after 24 h with human serum incubation. Co-treatment of KK-11 with doxorubicin was found to significantly enhance the cytotoxicity of doxorubicin compared to doxorubicin alone, or sequential KK-11 and doxorubicin treatment. In vivo and ex vivo imaging revealed that D-aa KK-11 distributed to xenografted A375 melanoma tumors as early as 5 min and persisted up to 24 h post tail vein injection. When co-administered, D-aa KK-11 significantly enhanced the anti-tumor activity of a novel nNOS inhibitor (MAC-3-190) in an A375 human melanoma xenograft mouse model compared to MAC-3-190 treatment alone. No apparent systemic toxicities were observed. Taken together, these results suggest that KK-11 may be a promising human melanoma-targeted delivery vector for anti-melanoma cargo.

Small intestine neuromuscular dysfunction in a mouse model of dextran sulfate sodium-induced ileitis: Involvement of dopaminergic neurotransmission

AIMS

Anomalies in dopaminergic machinery have been shown in inflammatory bowel disease (IBD) patients and preclinical models of IBD. Thus, we aimed to evaluate the impact of dextran sodium sulfate (DSS)-induced ileitis on enteric dopaminergic pathways.

MATERIALS AND METHODS

Male C57/Bl6 mice (10 ± 2 weeks old) received 2% DSS in drinking water for 5 days and were then switched to regular drinking water for 3 days. To measure ileitis severity inflammatory cytokines (IL-1β, TNFα, IL-6) levels were assessed. Changes in ileal muscle tension were isometrically recorded following: 1) cumulative addition of dopamine on basal tone (0.1-1000 μM); ii) 4-Hz electric field stimulation (EFS) in the presence of 30 μM dopamine with/without 10 μM SCH-23390 (dopamine D1 receptor (D1R) antagonist) or 10 μM sulpiride (D2R antagonist). Immunofluorescence distribution of the neuronal HuC/D protein, glial S100β marker, D1R, and dopamine transporter (DAT) were determined in longitudinal-muscle-myenteric plexus whole-mounts (LMMPs) by confocal microscopy. D1R and D2R mRNA transcripts were evaluated by qRT-PCR.

KEY FINDINGS

DSS caused an inflammatory process in the small intestine associated to dysmotility and altered barrier permeability, as suggested by decreased fecal output and enhanced stool water content. DSS treatment caused a significant increase of DAT and D1R myenteric immunoreactivity as well as of D1R and D2R mRNA levels, accompanied by a significant reduction of dopamine-mediated relaxation, involving primarily D1-like receptors.

SIGNIFICANCE

Mouse ileitis affects enteric dopaminergic neurotransmission mainly involving D1R-mediated responses. These findings provide novel information on the participation of dopaminergic pathways in IBD-mediated neuromuscular dysfunction.

Exploring the Effects of Six Weeks of Resistance Training on the Fecal Microbiome of Older Adult Males: Secondary Analysis of a Peanut Protein Supplemented Randomized Controlled Trial

The bacteria inhabiting the gastrointestinal tract contribute to numerous host functions and can be altered by lifestyle factors. We aimed to determine whether a 6-week training intervention altered fecal microbiome diversity and/or function in older males. Fecal samples were collected prior to and following a 6-week twice-weekly supervised resistance training intervention in 14 older Caucasian males (65 ± 10 years, 28.5 ± 3.2 kg/m2) with minimal prior training experience. Participants were randomized to receive a daily defatted peanut powder supplement providing 30 g protein (n = 8) or no supplement (n = 6) during the intervention. Bacterial DNA was isolated from pre-and post-training fecal samples, and taxa were identified using sequencing to amplify the variable region 4 (V4) of the 16S ribosomal RNA gene. Training significantly increased whole-body and lower-body lean mass (determined by dual energy X-ray absorptiometry) as well as leg extensor strength (p < 0.05) with no differences between intervention groups. Overall composition of the microbiome and a priori selected taxa were not significantly altered with training. However, MetaCYC pathway analysis indicated that metabolic capacity of the microbiome to produce mucin increased (p = 0.047); the tight junction protein, zonulin, was measured in serum and non-significantly decreased after training (p = 0.062). Our data suggest that resistance training may improve intestinal barrier integrity in older Caucasian males; further investigation is warranted.

Microbiota and Pain: Save Your Gut Feeling

Recently, a growing body of evidence has emerged regarding the interplay between microbiota and the nervous system. This relationship has been associated with several pathological conditions and also with the onset and regulation of pain. Dysregulation of the axis leads to a huge variety of diseases such as visceral hypersensitivity, stress-induced hyperalgesia, allodynia, inflammatory pain and functional disorders. In pain management, probiotics have shown promising results. This narrative review describes the peripheral and central mechanisms underlying pain processing and regulation, highlighting the role of the gut-brain axis in the modulation of pain. We summarized the main findings in regard to the stress impact on microbiota’s composition and its influence on pain perception. We also focused on the relationship between gut microbiota and both visceral and inflammatory pain and we provided a summary of the main evidence regarding the mechanistic effects and probiotics use.

Establishment and evaluation of a specific antibiotic-induced inflammatory bowel disease model in rats

Physical and chemical methods for generating rat models of enteritis have been established; however, antibiotic induction has rarely been used for this purpose. The present study aimed to establish and evaluate a rat model of inflammatory bowel disease (IBD) using antibiotics. A total of 84 Sprague-Dawley (SD) rats were divided into the following groups, according to the dosage and method of administration of the antibiotics: A, control; B, low-dose clindamycin; C, medium-dose clindamycin; D, high-dose clindamycin; E, low-dose clindamycin, ampicillin and streptomycin; F, medium-dose clindamycin, ampicillin and streptomycin; and G, high-dose clindamycin, ampicillin and streptomycin. Antibiotic administration was stopped on day 7; the modeling period covered days 1-7, and the recovery period covered days 8-15. Half of the animals were dissected on day 11, with the remaining animals dissected on day 15. Food and water intake, body weight and fecal weight were recorded. Intestinal flora was analyzed via microbial culture and quantitative PCR. The content of TNF-α, IL1-β, IL-6 and C-reactive protein (CRP) was assessed in abdominal aorta blood. Colonic and rectal tissues were examined pathologically via hematoxylin-eosin staining to assess leukocyte infiltration and intestinal mucosal changes as indicators of inflammation. Rat weight, food intake, water intake and 2-h fecal weight were significantly different across the experimental groups (P = 0.040, P = 0.016, P<0.001 and P = 0.009, respectively). Microbial cultures revealed no significant differences between group A and B,C (P = 0.546,0.872) but significant differences betwenn group A and the other experimental groups (all P<0.001). Furthermore, significant differences in the levels of Bacteroides, Faecalibacterium prausnitzii and Dialister invisus on day 4 between groups A, C and F (P = 0.033, P = 0.025 and P = 0.034, respectively). Significant differences were detected in the levels of TNF-α, IL1-β, IL-6 and CRP between the groups (all P<0.001). The colonic and rectal pathological inflammation scores of the experimental groups were significantly different compared with group A (B vs. A, P = 0.002; others, all P<0.001). These findings indicated that an antibiotic-induced IBD model was successfully established in SD rats; this animal model may serve as a useful model for clinical IBD research.

Interaction of the Microbiota and the Enteric Nervous System During Development

The gastrointestinal tract contains the enteric nervous system within its walls and a large community of microbial symbionts (microbiota) in its lumen. In recent years, studies have shown that these two systems that lie adjacent to each other interact. This review will summarize new data using mouse models demonstrating the concurrent development of the enteric nervous system and microbiota during key pre- and postnatal stages. It will also discuss the possible roles that microbiota play on influencing enteric nervous system development and implications of antibiotic exposure during developmental windows.

New Concepts of the Interplay Between the Gut Microbiota and the Enteric Nervous System in the Control of Motility

Propulsive gastrointestinal (GI) motility is critical for digestive physiology and host defense. GI motility is finely regulated by the intramural reflex pathways of the enteric nervous system (ENS). The ENS is in turn regulated by luminal factors: diet and the gut microbiota. The gut microbiota is a vast ecosystem of commensal bacteria, fungi, viruses, and other microbes. The gut microbiota not only regulates the motor programs of the ENS but also is critical for the normal structure and function of the ENS. In this chapter, we highlight recent research that has shed light on the microbial mechanisms of interaction with the ENS involved in the control of motility. Toll-like receptor signaling mechanisms have been shown to maintain the structural integrity of the ENS and the neurochemical phenotypes of enteric neurons, in part through the production of trophic factors including glia-derived neurotrophic factor. Microbiota-derived short-chain fatty acids and/or single-stranded RNA regulates the synthesis of serotonin in enterochromaffin cells, which are involved in the initiation of enteric reflexes, among other functions. Further evidence suggests a crucial role for microbial modulation of serotonin in maintaining the integrity of the ENS through enteric neurogenesis. Understanding the microbial pathways of enteric neural control sheds new light on digestive health and provides novel treatment strategies for GI motility disorders.

Enteric neuroimmune interactions coordinate intestinal responses in health and disease

The enteric nervous system (ENS) of the gastrointestinal (GI) tract interacts with the local immune system bidirectionally. Recent publications have demonstrated that such interactions can maintain normal GI functions during homeostasis and contribute to pathological symptoms during infection and inflammation. Infection can also induce long-term changes of the ENS resulting in the development of post-infectious GI disturbances. In this review, we discuss how the ENS can regulate and be regulated by immune responses and how such interactions control whole tissue physiology. We also address the requirements for the proper regeneration of the ENS and restoration of GI function following the resolution of infection.

Hyaluronan: A Neuroimmune Modulator in the Microbiota-Gut Axis

The commensal microbiota plays a fundamental role in maintaining host gut homeostasis by controlling several metabolic, neuronal and immune functions. Conversely, changes in the gut microenvironment may alter the saprophytic microbial community and function, hampering the positive relationship with the host. In this bidirectional interplay between the gut microbiota and the host, hyaluronan (HA), an unbranched glycosaminoglycan component of the extracellular matrix, has a multifaceted role. HA is fundamental for bacterial metabolism and influences bacterial adhesiveness to the mucosal layer and diffusion across the epithelial barrier. In the host, HA may be produced and distributed in different cellular components within the gut microenvironment, playing a role in the modulation of immune and neuronal responses. This review covers the more recent studies highlighting the relevance of HA as a putative modulator of the communication between luminal bacteria and the host gut neuro-immune axis both in health and disease conditions, such as inflammatory bowel disease and ischemia/reperfusion injury.

The Pivotal Role of Microbiota in Modulating the Neuronal-Glial-Epithelial Unit

The enteric nervous system (ENS) consists of enteric neurons and enteric glial cells (EGCs) and controls the function of the epithelial barrier. Thus, a novel concept of neuronal-glial-epithelial unit in the gut was put forward by analogy with neuronal-glial-endothelial unit in the brain. The environment in the gastrointestinal (GI) tract is complex as it harbours millions of bacteria, which extensively attach with intestinal epithelium. The cross-talk between the neuronal-glial-endothelial unit and microbiota plays a pivotal role in modulating the epithelial barrier's permeability, intestinal development and immune response. And evidence shows dysbiosis is the potent risk factor in the pathologic process of Parkinson's disease (PD) and inflammatory bowel disease (IBD). In this review, we summarize the compelling results in favor of microbiota serving as the key modulator in the neuronal-glial-epithelial unit development and function, with profound effects on intestinal homeostasis.

Intestinal microbiota shapes gut physiology and regulates enteric neurons and glia

BACKGROUND

The intestinal microbiota plays an important role in regulating gastrointestinal (GI) physiology in part through interactions with the enteric nervous system (ENS). Alterations in the gut microbiome frequently occur together with disturbances in enteric neural control in pathophysiological conditions. However, the mechanisms by which the microbiota regulates GI function and the structure of the ENS are incompletely understood. Using a mouse model of antibiotic (Abx)-induced bacterial depletion, we sought to determine the molecular mechanisms of microbial regulation of intestinal function and the integrity of the ENS. Spontaneous reconstitution of the Abx-depleted microbiota was used to assess the plasticity of structure and function of the GI tract and ENS. Microbiota-dependent molecular mechanisms of ENS neuronal survival and neurogenesis were also assessed.

RESULTS

Adult male and female Abx-treated mice exhibited alterations in GI structure and function, including a longer small intestine, slower transit time, increased carbachol-stimulated ion secretion, and increased intestinal permeability. These alterations were accompanied by the loss of enteric neurons in the ileum and proximal colon in both submucosal and myenteric plexuses. A reduction in the number of enteric glia was only observed in the ileal myenteric plexus. Recovery of the microbiota restored intestinal function and stimulated enteric neurogenesis leading to increases in the number of enteric glia and neurons. Lipopolysaccharide (LPS) supplementation enhanced neuronal survival alongside bacterial depletion, but had no effect on neuronal recovery once the Abx-induced neuronal loss was established. In contrast, short-chain fatty acids (SCFA) were able to restore neuronal numbers after Abx-induced neuronal loss, demonstrating that SCFA stimulate enteric neurogenesis in vivo.

CONCLUSIONS

Our results demonstrate a role for the gut microbiota in regulating the structure and function of the GI tract in a sex-independent manner. Moreover, the microbiota is essential for the maintenance of ENS integrity, by regulating enteric neuronal survival and promoting neurogenesis. Molecular determinants of the microbiota, LPS and SCFA, regulate enteric neuronal survival, while SCFA also stimulates neurogenesis. Our data reveal new insights into the role of the gut microbiota that could lead to therapeutic developments for the treatment of enteric neuropathies. Video abstract.

Influence of Tilia tomentosa Moench Extract on Mouse Small Intestine Neuromuscular Contractility

Functional gastrointestinal disorders (FGIDs) are characterized by abdominal pain, bloating and bowel disturbances. FGID therapy is primarily symptomatic, including treatment with herbal remedies. Flower extract of Tilia tomentosa Moench (TtM) is occasionally used as an anti-spasmodic in popular medicine. Since its effect on intestinal response is unknown, we evaluated the influence of TtM extract on small intestine contractility. Ileal preparations from C57BL/6J mice were mounted in organ baths to assess changes in muscle tension, following addition of TtM extract (0.5–36 μg/mL) or a vehicle (ethanol). Changes in contractile response to receptor- and non-receptor-mediated stimuli were assessed in ileal preparations pretreated with 12 μg/mL TtM. Alterations in the enteric nervous system neuroglial network were analyzed by confocal immunofluorescence. Increasing addition of TtM induced a marked relaxation in ileal specimens compared to the vehicle. Pretreatment with TtM affected cholinergic and tachykininergic neuromuscular contractions as well as K⁺-induced smooth muscle depolarization. Following incubation with TtM, a significant reduction in non-adrenergic non-cholinergic-mediated relaxation sensitive to Nω-Nitro-L-arginine methyl ester hydrochloride (pan-nitric oxide synthase inhibitor) was found. In vitro incubation of intestinal specimens with TtM did not affect the myenteric plexus neuroglial network. Our findings show that TtM-induced intestinal relaxation is mediated by nitric oxide pathways, providing a pharmacological basis for the use of TtM in FGIDs.

The gut microbiota mediates the protective effects of anserine supplementation on hyperuricaemia and associated renal inflammation

Hyperuricaemia is a disease associated with elevated serum uric acid content, which has emerged rapidly in recent decades. The drugs used to treat clinical hyperuricaemia have side effects, and their safety is poor. However, anserine is a natural carnosine derivative that shows an anti-hyperuricaemic effect. A previous study demonstrated that anserine inhibits uric acid synthesis and promotes uric acid excretion, but there is no evidence regarding the effect of anserine from the perspective of the gut microbiota. In this study, the anti-hyperuricaemic and anti-inflammatory effects of anserine were explored in a diet-induced hyperuricaemic mouse model. Anserine alleviated hyperuricaemia and renal inflammation phenotypes, inhibited uric acid biosynthesis, promoted uric acid excretion, and inhibited NLRP3 inflammasome and TLR4/MyD88/NF-κB signalling pathway activation. The results showed that the anti-hyperuricaemic effect of anserine was dependent on the gut microbiota in the germ-free mice experiment. Furthermore, anserine treatment reversed gut microbiota dysbiosis, repaired the intestinal epithelial barrier and increased short-chain fatty acid production. Moreover, the anti-hyperuricaemic effect of anserine was transmissible by transplanting the faecal microbiota from anserine-treated mice, indicating that the protective effects were at least partially mediated by the gut microbiota. Thus, we identified a new and safe prebiotic material to alleviate hyperuricaemia and provided ideas for the development of oligopeptides.

Disorders of the enteric nervous system - a holistic view

The enteric nervous system (ENS) is the largest division of the peripheral nervous system and closely resembles components and functions of the central nervous system. Although the central role of the ENS in congenital enteric neuropathic disorders, including Hirschsprung disease and inflammatory and functional bowel diseases, is well acknowledged, its role in systemic diseases is less understood. Evidence of a disordered ENS has accumulated in neurodegenerative diseases ranging from amyotrophic lateral sclerosis, Alzheimer disease and multiple sclerosis to Parkinson disease as well as neurodevelopmental disorders such as autism. The ENS is a key modulator of gut barrier function and a regulator of enteric homeostasis. A 'leaky gut' represents the gateway for bacterial and toxin translocation that might initiate downstream processes. Data indicate that changes in the gut microbiome acting in concert with the individual genetic background can modify the ENS, central nervous system and the immune system, impair barrier function, and contribute to various disorders such as irritable bowel syndrome, inflammatory bowel disease or neurodegeneration. Here, we summarize the current knowledge on the role of the ENS in gastrointestinal and systemic diseases, highlighting its interaction with various key players involved in shaping the phenotypes. Finally, current flaws and pitfalls related to ENS research in addition to future perspectives are also addressed.

Effect of Vitamin A Supplementation on Growth Performance, Serum Biochemical Parameters, Intestinal Immunity Response and Gut Microbiota in American Mink (Neovison vison)

Simple Summary

Vitamin A is critical throughout life, but utilization of vitamin A often results in local and systemic toxicity. This study investigated the effect of vitamin A supplementation on mink growth and health. The results show that vitamin A deficiency decreased the ADG, villus height, villus height/crypt depth ratio and mRNA expression levels of IL-22, Occludin and ZO-1. Vitamin A supplementation increased the diversity of jejunum bacteria, decreased the ratio of Firmicutes to Bacteroidetes and increased the relative abundance of Akkermansia and Lachnospiraceae NK4A136 group.

Abstract

This experiment investigated the effect of vitamin A supplementation on growth, serum biochemical parameters, jejunum morphology and the microbial community in male growing-furring mink. Thirty healthy male mink were randomly assigned to three treatment groups, with 10 mink per group. Each mink was housed in an individual cage. The mink in the three groups were fed diets supplemented with vitamin A acetate at dosages of 0 (CON), 20,000 (LVitA) and 1,280,000 IU/kg (HVitA) of basal diet. A 7-day pretest period preceded a formal test period of 45 days. The results show that 20,000 IU/kg vitamin A increased the ADG, serum T-AOC and GSH-Px activities, villus height and villus height/crypt depth ratio (p < 0.05). The mRNA expression levels of IL-22, Occludin and ZO-1 in the jejunum of mink were significantly higher in the LVitA group than those in the CON and HVitA groups (p < 0.05). Vitamin A supplementation increased the diversity of jejunum bacteria, decreased the ratio of Firmicutes to Bacteroidetes and increased the relative abundance of Akkermansia, uncultured bacterium f Muribaculaceae, Allobaculum, Lachnospiraceae NK4A136 group, Rummeliibacillus and Parasutterella. The comparison of potential functions also showed enrichment of glycan biosynthesis and metabolism, transport and catabolism pathways in the vitamin A supplementation groups compared with the CON group. In conclusion, these results indicate that dietary vitamin A supplementation could mediate host growth by improving intestinal development, immunity and the relative abundance of the intestinal microbiota.

Gut Microbiota May Mediate the Influence of Periodontitis on Prediabetes

Mounting evidence has shown that periodontitis is associated with diabetes. However, a causal relationship remains to be determined. Recent studies reported that periodontitis may be associated with gut microbiota, which plays an important role in the development of diabetes. Therefore, we hypothesized that gut microbiota might mediate the link between periodontitis and diabetes. Periodontitis was induced by ligatures. Glycemic homeostasis was evaluated through fasting blood glucose (FBG), serum glycosylated hemoglobin (HbA1c), and intraperitoneal glucose tolerance test. Micro-computed tomography and hematoxylin and eosin staining were used to evaluate periodontal destruction. The gut microbiota was analyzed using 16S ribosomal RNA gene sequencing and bioinformatics. Serum endotoxin, interleukin (IL) 6, tumor necrosis factor α (TNF-α), and IL-1β were measured to evaluate the systemic inflammation burden. We found that the levels of FBG, HbA1c, and glucose intolerance were higher in the periodontitis (PD) group than in the control (Con) group (P < 0.05). When periodontitis was eliminated, the FBG significantly decreased (P < 0.05). Several butyrate-producing bacteria were decreased in the gut microbiota of the PD group, including Lachnospiraceae_NK4A136_group, Eubacterium_fissicatena_group, Eubacterium_coprostanoligenes_group, and Ruminococcaceae_UCG-014 (P < 0.05), which were negatively correlated with serum HbA1c (P < 0.05). Subsequently, the gut microbiota was depleted using antibiotics or transplanted through cohousing. Compared with the PD group, the levels of HbA1c and glucose intolerance were decreased in the gut microbiota-depleted mice with periodontitis (PD + Abx) (P < 0.05), as well as the serum levels of endotoxin and IL-6 (P < 0.05). The serum levels of IL-6, TNF-α, and IL-1β in the PD + Abx group were higher than those of the Con group (P < 0.05). Antibiotics exerted a limited impact on the periodontal microbiota. When the PD mice were cohoused with healthy ones, the elevated FBG and HbA1c significantly recovered (P < 0.05), as well as the aforementioned butyrate producers (P < 0.05). Thus, within the limitations of this study, our data indicated that the gut microbiota may mediate the influence of periodontitis on prediabetes.

Dopamine Transporter Genetic Reduction Induces Morpho-Functional Changes in the Enteric Nervous System

Antidopaminergic gastrointestinal prokinetics are indeed commonly used to treat gastrointestinal motility disorders, although the precise role of dopaminergic transmission in the gut is still unclear. Since dopamine transporter (DAT) is involved in several brain disorders by modulating extracellular dopamine in the central nervous system, this study evaluated the impact of DAT genetic reduction on the morpho-functional integrity of mouse small intestine enteric nervous system (ENS). In DAT heterozygous (DAT^+/-) and wild-type (DAT^+/+) mice (14 ± 2 weeks) alterations in small intestinal contractility were evaluated by isometrical assessment of neuromuscular responses to receptor and non-receptor-mediated stimuli. Changes in ENS integrity were studied by real-time PCR and confocal immunofluorescence microscopy in longitudinal muscle-myenteric plexus whole-mount preparations (). DAT genetic reduction resulted in a significant increase in dopamine-mediated effects, primarily via D1 receptor activation, as well as in reduced cholinergic response, sustained by tachykininergic and glutamatergic neurotransmission via NMDA receptors. These functional anomalies were associated to architectural changes in the neurochemical coding and S100β immunoreactivity in small intestine myenteric plexus. Our study provides evidence that genetic-driven DAT defective activity determines anomalies in ENS architecture and neurochemical coding together with ileal dysmotility, highlighting the involvement of dopaminergic system in gut disorders, often associated to neurological conditions.

The role of gut dysbiosis in Parkinson's disease: mechanistic insights andtherapeutic options

Parkinson's disease is a common neurodegenerative disease in which gastrointestinal symptoms may appear prior to motor symptoms. The gut microbiota of patients with Parkinson's disease shows unique changes, which may be used as early biomarkers of disease. Alteration in gut microbiota composition may be related to the cause or effect of motor or non-motor symptoms, but the specific pathogenic mechanisms are unclear. The gut microbiota and its metabolites have been suggested to be involved in the pathogenesis of Parkinson's disease by regulating neuroinflammation, barrier function and neurotransmitter activity. There is bidirectional communication between the enteric nervous system and the central nervous system, and the microbiota-gut-brain axis may provide a pathway for the transmission of α-synuclein. We highlight recent discoveries and alterations of the gut microbiota in Parkinson's disease, and highlight current mechanistic insights on the microbiota-gut-brain axis in disease pathophysiology. We discuss the interactions between production and transmission of α-synuclein and gut inflammation and neuroinflammation. In addition, we also draw attention to diet modification, use of probiotics and prebiotics and fecal microbiota transplantation as potential therapeutic approaches that may lead to a new treatment paradigm for Parkinson's disease.