Antibiotics-induced depletion of mice microbiota induces changes in host serotonin biosynthesis and intestinal motility

Effect of the gut microbiota and their metabolites on postoperative intestinal motility and its underlying mechanisms

Gut microbiota is closely related to human health and disease because, together with their metabolites, gut microbiota maintain normal intestinal peristalsis. The use of antibiotics or opioid anesthetics, or both, during surgical procedures can lead to dysbiosis and affect intestinal motility; however, the underlying mechanisms are not fully known. This review aims to discuss the effect of gut microbiota and their metabolites on postoperative intestinal motility, focusing on regulating the enteric nervous system, 5-hydroxytryptamine neurotransmitter, and aryl hydrocarbon receptor.

Postnatal 14D is the Key Window for Mice Intestinal Development- An Insight from Age-Dependent Antibiotic-Mediated Gut Microbial Dysbiosis Study

The postnatal period is one of the critical windows for the structure-function development of the gastrointestinal tract and associated mucosal immunity. Along with other constituent members, recent studies suggest the contribution of gut microbiota in maintaining host health, immunity, and development. Although the gut microbiota's role in maintaining barrier integrity is known, its function in early life development still needs to be better understood. To understand the details of gut microbiota's effects on intestinal integrity, epithelium development, and immune profile, the route of antibiotic-mediated perturbation is taken. Mice on days 7(P7D), 14(P14D), 21(P21D) and 28(P28D) are sacrificed and 16S rRNA metagenomic analysis is performed. The barrier integrity, tight junction proteins (TJPs) expression, intestinal epithelial cell (IEC) markers, and inflammatory cytokines are analyzed. Results reveal a postnatal age-related impact of gut microbiota perturbation, with a gradual increase in the relative abundance of Proteobacteria and a reduction in Bacteroidetes and Firmicutes. Significant barrier integrity disruption, reduced TJPs and IECs marker expression, and increased systemic inflammation at P14D of AVNM-treated mice are found. Moreover, the microbiota transplantation shows recolonization of Verrucomicrobia, proving a causal role in barrier functions. The investigation reveals P14D as a critical period for neonatal intestinal development, regulated by specific microbiota composition.

Impact of the gut microbiome on nicotine's motivational effects and glial cells in the ventral tegmental area in male mice

A link between gut dysbiosis and the pathogenesis of brain disorders has been identified. A role for gut bacteria in drug reward and addiction has been suggested but very few studies have investigated their impact on brain and behavioral responses to addictive drugs so far. In particular, their influence on nicotine's addiction-like processes remains unknown. In addition, evidence shows that glial cells shape the neuronal activity of the mesolimbic system but their regulation, within this system, by the gut microbiome is not established. We demonstrate that a lack of gut microbiota in male mice potentiates the nicotine-induced activation of sub-regions of the mesolimbic system. We further show that gut microbiota depletion enhances the response to nicotine of dopaminergic neurons of the posterior ventral tegmental area (pVTA), and alters nicotine's rewarding and aversive effects in an intra-VTA self-administration procedure. These effects were not associated with gross behavioral alterations and the nicotine withdrawal syndrome was not impacted. We further show that depletion of the gut microbiome modulates the glial cells of the mesolimbic system. Notably, it increases the number of astrocytes selectively in the pVTA, and the expression of postsynaptic density protein 95 in both VTA sub-regions, without altering the density of the astrocytic glutamatergic transporter GLT1. Finally, we identify several sub-populations of microglia in the VTA that differ between its anterior and posterior sub-parts, and show that they are re-organized in conditions of gut microbiota depletion. The present study paves the way for refining our understanding of the pathophysiology of nicotine addiction.

Arctiin alleviates functional constipation by enhancing intestinal motility in mice

Functional constipation (FC), a common symptom that is primarily associated with intestinal motility dysfunction, is a common problem worldwide. Arctiin (Arc) is a lignan glycoside isolated from the Chinese herbal medicine Arctium lappa L., which is a health food in China. The present study aimed to evaluate the laxative effects of Arc against FC in mice. A model of FC induced by loperamide (5 mg/kg) was established in male Institute of Cancer Research (ICR) mice. Arc was administered at a dose of 100 mg/kg as a protective agent. The faecal status, intestinal motility and histological analyses were evaluated. Furthermore, the levels of gastrointestinal motility-associated neurotransmitters, such as motilin (MTL), nitric oxide (NO), and brain-derived neurotrophic factor (BDNF) and the protective effect of Arc on interstitial cells of Cajal (ICC) were assessed. Arc treatment reversed the loperamide-induced reduction in faecal number and water content and the intestinal transit ratio in ICR mice. Histological analysis confirmed that Arc administration mitigated colonic injury. Moreover, Arc treatment increased levels of motilin and brain-derived neurotrophic factor while decreasing nitric oxide levels and ICC injury in the colon of FC mice. Arc decreased inflammation induction and aquaporin expression levels. Owing to its pro-intestinal motility property, Arc was shown to have a protective effect against FC and may thus serve as a promising therapeutic strategy for the management of FC.

Polyunsaturated fatty acids-rich dietary lipid prevents high fat diet-induced obesity in mice

Diet is the primary factor affecting host nutrition and metabolism, with excess food intake, especially high-calorie diets, such as high-fat and high-sugar diets, causing an increased risk of obesity and related disorders. Obesity alters the gut microbial composition and reduces microbial diversity and causes changes in specific bacterial taxa. Dietary lipids can alter the gut microbial composition in obese mice. However, the regulation of gut microbiota and host energy homeostasis by different polyunsaturated fatty acids (PUFAs) in dietary lipids remains unknown. Here, we demonstrated that different PUFAs in dietary lipids improved host metabolism in high-fat diet (HFD)-induced obesity in mice. The intake of the different PUFA-enriched dietary lipids improved metabolism in HFD-induced obesity by regulating glucose tolerance and inhibiting colonic inflammation. Moreover, the gut microbial compositions were different among HFD and modified PUFA-enriched HFD-fed mice. Thus, we have identified a new mechanism underlying the function of different PUFAs in dietary lipids in regulating host energy homeostasis in obese conditions. Our findings shed light on the prevention and treatment of metabolic disorders by targeting the gut microbiota.

Bifidobacterium bifidum CCFM1163 Alleviated Cathartic Colon by Regulating the Intestinal Barrier and Restoring Enteric Nerves

Cathartic colon (CC), a type of slow-transit constipation caused by the long-term use of stimulant laxatives, does not have a precise and effective treatment. This study aimed to evaluate the ability of Bifidobacterium bifidum CCFM1163 to relieve CC and to investigate its underlying mechanism. Male C57BL/6J mice were treated with senna extract for 8 weeks, followed by a 2-week treatment with B. bifidum CCFM1163. The results revealed that B. bifidum CCFM1163 effectively alleviated CC symptoms. The possible mechanism of B. bifidum CCFM1163 in relieving CC was analyzed by measuring the intestinal barrier and enteric nervous system (ENS)-related indices and establishing a correlation between each index and gut microbiota. The results indicated that B. bifidum CCFM1163 changed the gut microbiota by significantly increasing the relative abundance of Bifidobacterium, Faecalibaculum, Romboutsia, and Turicibacter as well as the content of short-chain fatty acids, especially propionic acid, in the feces. This increased the expression of tight junction proteins and aquaporin 8, decreased intestinal transit time, increased fecal water content, and relieved CC. In addition, B. bifidum CCFM1163 also increased the relative abundance of Faecalibaculum in feces and the expression of enteric nerve marker proteins to repair the ENS, promote intestinal motility, and relieve constipation.

Bidirectional Effects of Mao Jian Green Tea and Its Flavonoid Glycosides on Gastrointestinal Motility

Mao Jian Tea (MJT) has been generally consumed as a digestive aid for more than a hundred years in the Shanxi province of China. However, determination of its efficacy still remains elusive. This study investigated the effect of Mao Jian Green Tea (MJGT) on gastrointestinal motility. The biphasic effects of the hydro extracts of MJGT on gastric emptying and small intestinal propulsion of rats were identified in vivo; namely, the low (MJGT_L) and medium (MJGT_M) concentrations promoted gastrointestinal motility (p < 0.05), whereas the high concentration (MJGT_H) showed the opposite effect (p < 0.01). The expression levels of the gastric hormones, GAS, MTL and VIP (p < 0.05) were consistent with the gastrointestinal motility variation, with the exception of MTL in MJGT_H group (p > 0.01). Two flavonoids, eriodictyol (0.152 mg/mL) and luteolin (0.034 mg/mL), and the corresponding glycosides eriodictyol-7-O-glucoside (0.637 mg/mL) and luteolin-7-O-glucoside (0.216 mg/mL), dominated the hydro extracts identified by HPLC and UPLC-ESI-MS. These compounds can regulate the muscle strip contractions isolated from the gastrointestinal tissues. Additionally, the different concentrations also influenced the gut microbiota accordingly characterized by 16S rDNA gene sequencing. The MJGT_L boosted several probiotic bacteria, such as Muribaculaceae (1.77-fold), Prevotellaceae (1.85-fold) and Lactobacillaceae (2.47-fold), and suppressed the pathogenic species such as Staphylococcaceae (0.03-fold) that, conversely, was enriched in the MJGT_H group (1.92-fold). Therefore, the biphasic effect indicated that the dosage of the herbal tea should not be overlooked.

Gut Microbial Succession Patterns and Metabolic Profiling during Pregnancy and Lactation in a Goat Model

The maternal gut microbiome affects the duration of pregnancy, delivery, and lactation. It also coordinates the stability of maternal metabolism by regulating and modulating inflammatory cytokines and reproductive hormones. This has been shown in several species; however, the situation in ruminants remains a black box. Here, we aimed to elucidate the relationship between the hindgut microbiota, metabolism, and reproductive hormones in domestic goats (Capra hircus) during nonpregnancy, pregnancy, and lactation stages. The hindgut microbiota was altered during these three stages, with a drastic decrease in the abundance of Family_XIII_AD3011_group in the second and third trimesters of pregnancy. Additionally, a decline in the abundance of Christensenellaceae_R-7_group and Turicibacter was observed from the nonpregnancy stage to late gestation. Family_XIII_AD3011_group and Paeniclostridium were strongly correlated with decreased fecal estradiol and progesterone. Furthermore, we generated a metabolome atlas of the gut and serum from nonpregnancy to lactation to reveal the specific metabolic fingerprints of each physiological stage. Several specific gut metabolites, including carnitine C8:1, γ-aminobutyric acid, and indole-3-carboxylic acid, were negatively correlated with the fecal and serum estradiol concentrations. In contrast, 2'-deoxyinosine, deoxyadenosine, and 5'-deoxyadenosine were positively correlated with the fecal and serum estradiol concentrations. The levels of 2'-deoxyinosine, deoxyadenosine, and 5'-deoxyadenosine in fecal samples were positively correlated with Family_XIII_AD3011_group. Other serum metabolites, such as (±)12-HEPE (hydroxy eicosapentaenoic acid), (±)15-HEPE, (±)18-HEPE, cytidine, uracil, and 5-hydroxyindole-3-acetic acid, were negatively correlated with the serum concentrations of estradiol and progesterone. Finally, Corynebacterium and Clostridium_sensu_stricto_1 in the fecal samples were positively correlated with the abundance of 11,12-EET (epoxy-eicosatrienoic acid), (±)18-HEPE, (±)15-HEPE, and (±)12-HEPE in the serum. IMPORTANCE Our findings revealed that the activity of Family_XIII_AD3011_group and Corynebacterium is strongly correlated with the beneficial regulation of physiological hormones and metabolic changes during pregnancy and lactation. These findings are key for guiding targeted microbial therapeutic approaches to modulate microbiomes in gestating and lactating mammals.

Impact of tuberculosis disease on human gut microbiota: a systematic review

INTRODUCTION

This systematic review evaluates the gut microbiota (GM) status in tuberculosis (TB) patients compared to healthy volunteers due to the disease or its treatment.

AREAS COVERED

We conducted a systematic review of all articles published in PubMed, Web of Science, and Embase that assessed the impact of TB disease and anti-tubercular therapy (ATT) on GM from inception till January 2022 (Protocol registration number in PROSPERO: CRD42021261884). Regarding the microbial diversity indices and taxonomy, we found a significant difference in GM status between the TB and healthy control (HC) groups. We found an overabundance of Phylum Proteobacteria and depletion of some short-chain fatty acid-producing bacteria genera like Bifidobacteria, Roseburia, and Ruminococcus in the TB group. We found that ATT exacerbates the degree of dysbiosis caused by Mycobacteria tuberculosis disease.

EXPERT OPINION

The modulation of GM in TB patients in clinical practice may serve as a promising target to reverse the dysbiosis caused. Moreover, this can optimistically change the TB treatment outcome. We expect that appropriate probiotic supplementation with antimycobacterial treatment during tuberculosis disease will help stabilize the GM throughout the treatment phase and protect the GM from dysbiosis.

Luteolin ameliorates loperamide-induced functional constipation in mice

Functional constipation (FC) is one of the most common gastrointestinal disorders characterized by hard stools and infrequent bowel movements, which is associated with dysfunction of the enteric nervous system and intestinal motility. Luteolin, a naturally occurring flavone, was reported to possess potential pharmacological activities on intestinal inflammation and nerve injury. This study aimed to explore the role of luteolin and its functional mechanism in loperamide-induced FC mice. Our results showed that luteolin treatment reversed the reduction in defecation frequency, fecal water content, and intestinal transit ratio, and the elevation in transit time of FC models. Consistently, luteolin increased the thickness of the muscular layer and lessened colonic histopathological injury induced by loperamide. Furthermore, we revealed that luteolin treatment increased the expression of neuronal protein HuC/D and the levels of intestinal motility-related biomarkers, including substance P (SP), vasoactive intestinal polypeptide (VIP), and acetylcholine (ACh), as well as interstitial cells of Cajal (ICC) biomarker KIT proto-oncogene, receptor tyrosine kinase (C-Kit), and anoctamin-1 (ANO1), implying that luteolin mediated enhancement of colonic function and contributed to the anti-intestinal dysmotility against loperamide-induced FC. Additionally, luteolin decreased the upregulation of aquaporin (AQP)-3, AQP-4, and AQP-8 in the colon of FC mice. In summary, our data showed that luteolin might be an attractive option for developing FC-relieving medications.

The Genetic Background Is Shaping Cecal Enlargement in the Absence of Intestinal Microbiota

Germ-free (GF) rodents have become a valuable tool for studying the role of intestinal microbes on the host physiology. The major characteristic of GF rodents is an enlarged cecum. The accumulation of mucopolysaccharides, digestion enzymes and water in the intestinal lumen drives this phenotype. Microbial colonization normalizes the cecum size in ex-GF animals. However, whether strain genetics influences the cecal enlargement is unknown. Here we investigated the impact of mouse genetic background on the cecal size in five GF strains frequently used in biomedical research. The cecal weight of GF mice on B6 background (B6J and B6N) represented up to 20% of total body weight. GF NMRI and BALBc mice showed an intermediate phenotype of 5-10%, and those on the C3H background of up to 5%. Reduced cecal size in GF C3H mice correlated with decreased water content, increased expression of water transporters, and reduced production of acidic mucins, but was independent of the level of digestive enzymes in the lumen. In contrast, GF B6J mice with greatly enlarged cecum showed increased water content and a distinct metabolic profile characterized by altered amino acid and bile acid metabolism, and increased acidic mucin production. Together, our results show that genetic background influences the cecal enlargement by regulating the water transport, production of acidic mucins, and metabolic profiles.

Gut Microbial-Derived Metabolites as Immune Modulators of T Helper 17 and Regulatory T Cells

The gut microbiota and its derived metabolites greatly impact the host immune system, both innate and adaptive responses. Gut dysbiosis and altered levels of microbiota-derived metabolites have been described in several immune-related and immune-mediated diseases such as intestinal bowel disease, multiple sclerosis, or colorectal cancer. Gut microbial-derived metabolites are synthesized from dietary compounds ingested by the host or host-produced metabolites, and additionally, some bacterial products can be synthesized de novo. In this review, we focus on the two first metabolites families including short-chain fatty acids, indole metabolites, polyamines, choline-derived compounds, and secondary bile acids. They all have been described as immunoregulatory molecules that specifically affect the adaptive immune system and T helper 17 and regulatory T cells. We discuss the mechanisms of action and the consequences in health and diseases related to these gut microbial-derived metabolites. Finally, we propose that the exogenous administration of these molecules or other compounds that bind to their immunoregulatory receptors in a homologous manner could be considered therapeutic approaches.

Poria cocos Polysaccharide Ameliorated Antibiotic-Associated Diarrhea in Mice via Regulating the Homeostasis of the Gut Microbiota and Intestinal Mucosal Barrier

Poria cocos polysaccharides (PCP) have been validated for several biological activities, including antitumor, anti-inflammatory, antioxidant, immunomodulatory, hepatoprotective and modulation on gut microbiota. In this research, we aim to demonstrate the potential prebiotic effects and the therapeutic efficacies of PCP in the treatment of antibiotic-associated diarrhea (AAD), and confirm the beneficial effects of PCP on gut dysbiosis. Antibiotic-associated diarrhea mice models were established by treating them with broad-spectrum antibiotics in drinking water for seven days. Mice in two groups treated with probiotics and polysaccharide were given Bifico capsules (4.2 g/kg/d) and PCP (250 mg/kg/d) for seven days using intragastric gavage, respectively. To observe the regulatory effects of PCP on gut microbiota and intestinal mucosal barrier, we conducted the following experiments: intestinal flora analysis (16S rDNA sequencing), histology (H&E staining) and tight junction proteins (immunofluorescence staining). The levels of mRNA expression of receptors associated with inflammation and gut metabolism were assessed by real-time reverse transcription-polymerase chain reaction (RT-PCR). The study revealed that PCP can comprehensively improve the clinical symptoms of AAD mice, including fecal traits, mental state, hair quality, etc., similar to the effect of probiotics. Based on histology observation, PCP significantly improved the substantial structure of the intestine of AAD mice by increasing the expression levels of colonic tight junction protein zonula-occludens 1 (ZO-1) and its mRNA. Moreover, PCP not only increased the abundance of gut microbiota, but also increased the diversity of gut microbiota in AAD mice, including alpha diversity and beta diversity. Further analysis found that PCP can modulate seven characteristic species of intestinal flora in AAD mice, including Parabacteroides_distasonis, Akkermansia_muciniphila, Clostridium_saccharolyticum, Ruminoc-occus_gnavus, Lactobacillus_salivarius, Salmonella_enterica and Mucispirillum_schaedleri. Finally, enrichment analysis predicted that PCP may affect intestinal mucosal barrier function, host immune response and metabolic function by regulating the microbiota. RT-PCR experiments showed that PCP can participate in immunomodulatory and modulation on metabolic by regulating the mRNA expression of forkhead-box protein 3 (FOXP3) and G protein-coupled receptor 41 (GPR41). These results indicated that Poria cocos polysaccharide may ameliorate antibiotic-associated diarrhea in mice by regulating the homeostasis of the gut microbiota and intestinal mucosal barrier. In addition, polysaccharide-derived changes in intestinal microbiota were involved in the immunomodulatory activities and modulation of the metabolism.

Outer membrane protein Amuc_1100 of Akkermansia muciniphila alleviates antibiotic-induced anxiety and depression-like behavior in mice

Akkermansia muciniphila is present in the mucus layer of its host gut, and its outer membrane protein Amuc_1100 has a significant ameliorative effect on metabolic disorders and emotional memory aspects of enteritis, obesity, depression, and anxiety in the host. Antibiotics affect gut microbial composition, leading to imbalance and behavioral changes in the gut-brain axis, while probiotics have a protective effect against behavioral changes caused by gut flora disorders. In the present study, a depressed mouse model using a broad-spectrum cocktail mixture resulted in increased anxiety and depression-like behavior, decreased serum and hippocampal levels of 5-hydroxytryptamine (5-HT), and increased serum corticosterone (cort) levels. After application of A. muciniphila and Amuc_1100, anxiety and depression-like behavior in antibiotic-treated mice were significantly alleviated. In addition, the brain derived neurotrophic factor / Tropomyosin receptor kinase B (BDNF/TrkB) signaling pathway was altered, glial fibrillary acidic protein (GFAP) expression increased, and c-Fos protein expression decreased in the hippocampus of antibiotic-treated mice. After treatment with A. muciniphila and Amuc_1100, BDNF and TrkB levels were restored in the hippocampus and cortex. These results suggest that A. muciniphila and Amuc_1100 may alleviate antibiotic-induced anxiety and depression by affecting the BDNF/TrkB signaling pathway.

The intestinal microenvironment shapes macrophage and dendritic cell identity and function

The gut comprises the largest body interface with the environment and is continuously exposed to nutrients, food antigens, and commensal microbes, as well as to harmful pathogens. Subsets of both macrophages and dendritic cells (DCs) are present throughout the intestinal tract, where they primarily inhabit the gut-associate lymphoid tissue (GALT), such as Peyer's patches and isolated lymphoid follicles. In addition to their role in taking up and presenting antigens, macrophages and DCs possess extensive functional plasticity and these cells play complementary roles in maintaining immune homeostasis in the gut by preventing aberrant immune responses to harmless antigens and microbes and by promoting host defense against pathogens. The ability of macrophages and DCs to induce either inflammation or tolerance is partially lineage imprinted, but can also be dictated by their activation state, which in turn is determined by their specific microenvironment. These cells express several surface and intracellular receptors that detect danger signals, nutrients, and hormones, which can affect their activation state. DCs and macrophages play a fundamental role in regulating T cells and their effector functions. Thus, modulation of intestinal mucosa immunity by targeting antigen presenting cells can provide a promising approach for controlling pathological inflammation. In this review, we provide an overview on the characteristics, functions, and origins of intestinal macrophages and DCs, highlighting the intestinal microenvironmental factors that influence their functions during homeostasis. Unraveling the mechanisms by which macrophages and DCs regulate intestinal immunity will deepen our understanding on how the immune system integrates endogenous and exogenous signals in order to maintain the host's homeostasis.

Gut microbiota alteration after cholecystectomy contributes to post-cholecystectomy diarrhea via bile acids stimulating colonic serotonin

Post-cholecystectomy diarrhea (PCD) is highly prevalent among outpatients with cholecystectomy, and gut microbiota alteration is correlated with it. However, how and to what extent changed fecal bacteria contributes to diarrhea are still unrevealed. Humanized gut microbiome mice model by fecal microbiota transplantation was established to explore the diarrhea-inducible effects of gut microbiota. The role of microbial bile acids (BAs) metabolites was identified by UPLC/MS and the underlying mechanisms were investigated with selective inhibitors and antagonists as probes. These mice transplanted with fecal microbiome of PCD patients (PCD mice) exhibited significantly enhanced gastrointestinal motility and elevated fecal water content, compared with these mice with fecal microbiome of NonPCD patients and HC. In analyzing gut microbiota, tryptophan metabolism was enriched in PCD microbiome. In addition, overabundant serotonin in serum and colon, along with elevated biosynthesis gene and reduced reuptake gene, and highly expressed 5-HT receptors (5-HTRs) in colon of PCD mice were found, but not in small intestine. Notably, diarrheal phenotypes in PCD mice were depleted by tryptophan hydroxylase 1 inhibitor (LX1606) and 5-HTRs selective antagonists (alosetron and GR113808). Furthermore, increased microbial secondary BAs metabolites of DCA, HDCA and LCA were revealed in feces of PCD mice and they were found responsible for stimulating 5-HT level in vitro and in vivo. Intriguingly, blocking BAs-conjugated TGR5/TRPA1 signaling pathway could significantly alleviate PCD. In conclusion, altered gut microbiota after cholecystectomy contributes to PCD by promoting secondary BAs in colon, which stimulates colonic 5-HT and increases colon motility.

Gastrointestinal and Microbiome Profiling in Rodent Models of Neurological and Psychiatric Disorders

Mice and other rodent models have been widely used to understand the role of the gut microbiome in various neurological and psychiatric disorders. Here we describe a protocol to characterize the structural and functional phenotype of the rodent gut and to examine the gut microbiota composition through V4 16S rRNA gene sequencing and microbiome profiling. This protocol will have utility for those investigating the gut, and associated microbiota, in a wide range of different rodent models of human disorders.

In vivo functional effects of Weissella confusa VP30 exopolysaccharides on loperamide-induced constipation in rats

In this work, the in vivo functionalities of milk fermented with Weissella confusa VP30 (VP30-EPS) and purified exopolysaccharide (pEPS) from the milk fermented with Weissella confusa VP30 were evaluated for their effect on constipation using an experimental constipated rat model. Rats were randomly divided into four groups: (i) control group (PBS administered normal group), (ii) loperamide treated group (constipation group), (iii) constipation with loperamide plus VP30-EPS (1 g/kg), and (iv) constipation with loperamide plus pEPS (0.6 g/kg) groups. Loperamide treatment induced animal constipation and significantly reduced the frequency of defecation, intestinal transit ratio, and water content of feces. However, all four fecal parameters were improved in both the loperamide plus VP30-EPS and pEPS administered groups as compared to the loperamide group. These results suggest that the addition of VP30-EPS potentially improves the functional laxative effects of commercial products. This study suggests the possibility that VP30-EPS can be applied to fermented and/or functional foods to relieve constipation.

Lentinan improves intestinal inflammation and gut dysbiosis in antibiotics-induced mice

Gut microbiota dysbiosis is already a global problem after antibiotic overuse. This study was to investigate the therapeutic effect of lentinan and the mechanism of recovery of intestinal inflammation on broad-spectrum antibiotic-driven gut microbial dysbiosis in mice. Gut microbiota was elucidated by the Illumina MiSeq platform. Gas chromatography/mass spectrometry was used to investigate short-chain fatty acid content. Colon histology, expression of tight-junction associated proteins and pro-inflammatory cytokines levels were evaluated. The results showed that the gut microbiota of diversity and richness were reduced and various taxonomic levels of the gut microbiota were perturbed after antibiotics gavage. The abundance of Firmicutes and Bacteroidetes shifted to Proteobacteria and increased the relative abundance of harmful microbiota (Parabacteroides and Klebsiella) post-antibiotics, whereas lentinan administration reversed the dysbiosis and increased beneficial microbiota, including S24-7, Lactobacillus, Oscillospira, Ruminococcus and Allobaculum. The concentrations of propionic acid and butyric acid were significantly increased by treatment with lentinan. And lentinan improved colon tissue morphology and reduced pro-inflammatory cytokines via altering NF-κB signaling pathway in antibiotic-driven gut microbial dysbiosis mice. Taken together, the results proved that lentinan can be used as a prebiotic and the result provided a theoretical basis for improving the clinical treatment of broad-spectrum antibiotics side effects.

Interaction between the Gut Microbiota and Intestinal Motility

The gut microbiota is the largest symbiotic ecosystem with the host and has been proven to play an important role in maintaining the stability of the intestinal environment. The imbalance of the gut microbiota is caused by the imbalance between the symbiotic microbiota and the pathogenic microbiota. The commensal microbiome regulates intestinal motility, while the pathogenic microbiome causes intestinal motility disorder, resulting in disease development. Intestinal motility is a relatively general term, and its meaning may include intestinal muscle contraction, intestinal wall biomechanics, intestinal compliance, and transmission. The role of intestinal microecology and intestinal motility are interrelated, intestinal flora disorder mediates intestinal motility, and abnormal intestinal motility affects colonization of the intestinal flora. In this review, we briefly outlined the interaction between gut microbiota and intestinal motility and provided a reference for future studies.

Gut microbiota plays a role in irritable bowel syndrome by regulating 5-HT metabolism

Irritable bowel syndrome (IBS) is a common chronic functional gastrointestinal disorder. Brain-gut-microbiota axis dysfunction is an important pathogenic factor for IBS, in which neurotransmitters and gut microbes play key roles. The gastrointestinal tract contains large amounts of serotonin (5-hydroxytryptamine, 5-HT), a neurotransmitter that has been strongly linked to IBS-related symptoms. More than 90% of serotonin is synthesized in the gut by enterochromaffin cells (ECs), and certain intestinal flora can affect the occurrence and development of IBS by regulating 5-HT and its metabolism. In this review, we will discuss the role of gut microbiota in IBS by regulating 5-HT.

Engineered 5-HT producing gut probiotic improves gastrointestinal motility and behavior disorder

Slow transit constipation is an intractable constipation with unknown aetiology and uncertain pathogenesis. The gut microbiota maintains a symbiotic relationship with the host and has an impact on host metabolism. Previous studies have reported that some gut microbes have the ability to produce 5-hydroxytryptamine (5-HT), an important neurotransmitter. However, there are scarce data exploiting the effects of gut microbiota-derived 5-HT in constipation-related disease. We genetically engineered the probiotic Escherichia coli Nissle 1917 (EcN-5-HT) for synthesizing 5-HT in situ. The ability of EcN-5-HT to secrete 5-HT in vitro and in vivo was confirmed. Then, we examined the effects of EcN-5-HT on intestinal motility in a loperamide-induced constipation mouse model. After two weeks of EcN-5-HT oral gavage, the constipation-related symptoms were relieved and gastrointestinal motility were enhanced. Meanwhile, administration of EcN-5-HT alleviated the constipation related depressive-like behaviors. We also observed improved microbiota composition during EcN-5-HT treatment. This work suggests that gut microbiota-derived 5-HT might promise a potential therapeutic strategy for constipation and related behavioral disorders.

Excretion of Amyloid-β in the Gastrointestinal Tract and Regulation by the Gut Microbiota

Background: Amyloid-β (Aβ) is important in the etiology of Alzheimer’s disease (AD). Removal of Aβ from the brain is a major strategy for the prevention and treatment of AD. Objective: To clarify whether Aβ 42 can be cleared by intestinal excretion and whether the gut microbiota (GM) can affect the excretory clearance of Aβ 42 in the peripheral blood and intestines. Methods: Male 8-month-old C57BL6 mice were maintained on either normal chow or received broad-spectrum antibiotics in their drinking water for one week. Sterile saline, fluorescein isothiocyanate (FITC), or FITC-Aβ 42 (fluorescein isothiocyanate-labeled amyloid-β 42 peptides) was injected 1 h before FITC, or FITC-Aβ 42 was injected 1 h before sampling. Related changes of Aβ 42 before and after injection were evaluated. Results: FITC-Aβ 42 was injected into mice through the tail vein and could later be detected in feces. Furthermore, the fecal concentrations of FITC-Aβ 42 were higher in mice that had been fed antibiotics to alter their GM than in normal mice. However, the FITC-Aβ 42 concentrations in blood showed the opposite pattern. Conclusion: Aβ 42 can be excreted into the intestinal lumen and is regulated by the GM.

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.

Neonatal antibiotics have long term sex-dependent effects on the enteric nervous system

Infants and young children receive the highest exposures to antibiotics globally. Although there is building evidence that early life exposure to antibiotics increases susceptibility to various diseases including gut disorders later in life, the lasting impact of early life antibiotics on the physiology of the gut and its enteric nervous system (ENS) remains unclear. We treated neonatal mice with the antibiotic vancomycin during their first 10 postnatal days, then examined potential lasting effects of the antibiotic treatment on their colons during young adulthood (6 weeks old). We found that neonatal vancomycin treatment disrupted the gut functions of young adult female and male mice differently. Antibiotic-exposed females had significantly longer whole gut transit while antibiotic-treated males had significantly lower faecal weights compared to controls. Both male and female antibiotic-treated mice had greater percentages of faecal water content. Neonatal vancomycin treatment also had sexually dimorphic impacts on the neurochemistry and Ca2+ activity of young adult myenteric and submucosal neurons. Myenteric neurons of male mice were more disrupted than those of females, while opposing changes in submucosal neurons were seen in each sex. Neonatal vancomycin also induced sustained changes in colonic microbiota and lasting depletion of mucosal serotonin (5-HT) levels. Antibiotic impacts on microbiota and mucosal 5-HT were not sex-dependent, but we propose that the responses of the host to these changes are sex-specific. This first demonstration of long-term impacts of neonatal antibiotics on the ENS, gut microbiota and mucosal 5-HT has important implications for gut function and other physiological systems of the host. KEY POINTS: Early life exposure to antibiotics can increase susceptibility to diseases including functional gastrointestinal (GI) disorders later in life. Yet, the lasting impact of this common therapy on the gut and its enteric nervous system (ENS) remains unclear. We investigated the long-term impact of neonatal antibiotic treatment by treating mice with the antibiotic vancomycin during their neonatal period, then examining their colons during young adulthood. Adolescent female mice given neonatal vancomycin treatment had significantly longer whole gut transit times, while adolescent male and female mice treated with neonatal antibiotics had significantly wetter stools. Effects of neonatal vancomycin treatment on the neurochemistry and Ca2+ activity of myenteric and submucosal neurons were sexually dimorphic. Neonatal vancomycin also had lasting effects on the colonic microbiome and mucosal serotonin biosynthesis that were not sex-dependent. Different male and female responses to antibiotic-induced disruptions of the ENS, microbiota and mucosal serotonin biosynthesis can lead to sex-specific impacts on gut function.

Probiotic coated with glycol chitosan/alginate relieves oxidative damage and gut dysmotility induced by oxytetracycline in zebrafish larvae

Probiotic-based therapy is a promising approach, which can positively modulate bacterial composition and maintain homeostasis. However, exogenous probiotics are easily destroyed by harsh conditions in vivo; thus, their application prospects have been severely limited. Specifically, oxytetracycline (OTC), a broad-spectrum antibiotic widely used in aquaculture, results in adverse intestinal environments, such as dysbacteriosis, oxidative damage, and gut dysmotility. Here, we describe a facile method to apply glycol chitosan/alginate as armor on the surface of probiotics to effectively protect them from the changed enteric environments induced by OTC. The results demonstrated that the coated Lacticaseibacillus rhamnosus GG (LGG) for only 2 h administration could significantly improve the colonization rate of LGG, and the relative abundance of Lacticaseibacillus can reach 80% in OTC-treated larvae intestines. We also explored the specific mechanisms of the coated LGG to diminish reactive oxygen species (ROS) generation and rescue gut dysmotility for OTC treatment, including enhancing the activity of antioxidative enzymes (CAT, SOD and GPx) and increasing 5-HT synthesis. The mitigation effect of the coated LGG for 2 h administration was comparable to that of uncoated LGG for 24 h administration. Encapsulation of LGG with polysaccharides provides a unique application example for generating useful bacterial therapeutics in harsh intestinal environments.

Lactobacillus rhamnosus GG normalizes gut dysmotility induced by environmental pollutants via affecting serotonin level in zebrafish larvae

Intestinal peristalsis is essential for gastrointestinal function, which could maintain the appropriate progression and digestion of food and reduce bacterial aggregation through mixing function. Even though certain ingredients of foodstuff are known to increase or decrease intestinal peristalsis, the role of environmental pollutants on intestinal peristalsis is relatively unknown. Therefore, the effects of four typical environmental pollutants (oxytetracycline, arsenic, polychlorinated biphenyls and chlorpyrifos) on intestinal peristalsis in the zebrafish model and then tested the recovery effect of the constipation-resistant probiotic. The results showed that 4-day environmental pollutants exposures on the zebrafish embryos at 1 day post fertilization clearly decreased the intestinal peristalsis through decreasing the serotonin (5-HT) production and down-regulating the expression of key genes involved in 5-HT synthesis. Pollutants-evoked change of gut motility could be normalized in the presence of Lactobacillus rhamnosus GG (LGG) via increasing 5-HT secretion. Exogenous 5-hydroxytryptophan (100 µg/L) could also rescue the dysfunction of gut motility in pollutants-treated zebrfish. The data identified that LGG normalized disorder of intestinal peristalsis induced by environmental pollutants through increasing 5-HT level. The stimulant effect of LGG on peristalsis may be associated with 5-HT system, which could provide references for the application of probiotics in regulation of gut dysmotility.

Antimicrobial drug use and the risk of glioma: A case-control study

BACKGROUND

The use of antibiotics has been associated with increased risks of various cancers. Comprehensive information on the association of antibiotic use with the risk of glioma is lacking.

METHODS

We performed a large case-control study based on the Clinical Practice Research Datalink (CPRD) GOLD from the United Kingdom. We identified 4423 glioma cases recorded between 1995 and 2020 and matched them to controls (1:10) on the date of diagnosis (i.e., the index date), age, sex, general practice, and number of years of medical history in the database prior to the index date. We conducted conditional logistic regression analyses to calculate odds ratios (ORs) with 95% confidence intervals (CIs). The exposures of interest were the use of antimicrobial drugs, including antibacterial, antiviral, antifungal, antiprotozoal, and anthelmintic drugs with specific subclasses, where possible.

RESULTS

We found no substantially increased risk of glioma after ever-use of antibiotics (OR 1.13, 95% CI 1.03-1.24). The risk did not increase with the increasing number of prescriptions received or with increasing time from first use to cancer diagnosis. The use of polyenes was associated with a weakly decreased risk of glioma (OR 0.81, 95% CI 0.67-0.96).

Leaky Gut in IBD: Intestinal Barrier-Gut Microbiota Interaction

Inflammatory bowel disease (IBD) is a global disease that is in increasing incidence. The gut, which contains the largest amount of lymphoid tissue in the human body, as well as a wide range of nervous system components, is integral in ensuring intestinal homeostasis and function. By interacting with gut microbiota, immune cells, and the enteric nervous system, the intestinal barrier, which is a solid barrier, protects the intestinal tract from the external environment, thereby maintaining homeostasis throughout the body. Destruction of the intestinal barrier is referred to as developing a "leaky gut," which causes a series of changes relating to the occurrence of IBD. Changes in the interactions between the intestinal barrier and gut microbiota are particularly crucial in the development of IBD. Exploring the leaky gut and its interaction with the gut microbiota, immune cells, and the neuroimmune system may help further explain the pathogenesis of IBD and provide potential therapeutic methods for future use.

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.

Antibiotic pretreatment promotes orally-administered triptolide absorption and aggravates hepatotoxicity and intestinal injury in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Triptolide (TP) exhibits extensive pharmacological activity, but its hepatotoxicity and intestinal injury are significant and limit its clinical use.

AIM OF THE STUDY

To investigate the effect of gut microbiota disturbance after antibiotic pretreatment on TP-induced hepatotoxicity, intestinal injury and their mechanism.

MATERIALS AND METHODS

We compared the characteristics of TP-induced hepatotoxicity and intestinal injury in mice with or without antibiotic pretreatment. The levels of cytokines in the serum, immunohistochemistry, and the pharmacokinetics of TP were determined.

RESULT

Antibiotic pretreatment aggravates TP-induced hepatotoxicity and ileum/colon injury. TP induces hepatotoxicity in a dose-dependent manner after antibiotic pretreatment. Serum IL-1β and IL-6 levels were increased in mice given oral TP after antibiotic pretreatment. TP can increase the expression of NLRP3 inflammasome in hepatocytes, and Oral TP after antibiotic pretreatment can significantly enhance its expression, but NLRP3 inflammasome no significant change in colon and ileum. The pharmacokinetic characteristics of TP are altered significantly by antibiotic pretreatment, as shown by a 145.87% increase in C_max, a 155.11% increase in AUC_0-t, a 155.1% increase in relative bioavailability, and a 15.44% delay in MRT. Moreover, TP causes hepatotoxicity in a time-dependent manner.

CONCLUSIONS

Antibiotic pretreatment aggravates triptolide-induced hepatotoxicity and intestinal injury through elevated inflammatory response and promoted triptolide absorption.

The Role of Nutritional Factors in the Modulation of the Composition of the Gut Microbiota in People with Autoimmune Diabetes

Type 1 diabetes mellitus (T1DM) is a disease marked by oxidative stress, chronic inflammation, and the presence of autoantibodies. The gut microbiota has been shown to be involved in the alleviation of oxidative stress and inflammation as well as strengthening immunity, thus its' possible involvement in the pathogenesis of T1DM has been highlighted. The goal of the present study is to analyze information on the relationship between the structure of the intestinal microbiome and the occurrence of T1DM. The modification of the intestinal microbiota can increase the proportion of SCFA-producing bacteria, which could in turn be effective in the prevention and/or treatment of T1DM. The increased daily intake of soluble and non-soluble fibers, as well as the inclusion of pro-biotics, prebiotics, herbs, spices, and teas that are sources of phytobiotics, in the diet, could be important in improving the composition and activity of the microbiota and thus in the prevention of metabolic disorders. Understanding how the microbiota interacts with immune cells to create immune tolerance could enable the development of new therapeutic strategies for T1DM and improve the quality of life of people with T1DM.

Aminoglycoside treatment alters hearing-related genes and depicts behavioral defects in Drosophila

The hearing organ of Drosophila is present within the second segment of antennae. The hearing organ of Drosophila (Johnston's organ [JO]) shares much structural, developmental, and functional similarity with the vertebrate hearing organ (Organ of Corti). JO is evolving as a potential model system to examine the hearing-associated defects in vertebrates. In the vertebrates, aminoglycosides like gentamicin, kanamycin, and neomycin have been known to cause defects in the hearing organ. However, a complete mechanism of toxicity is not known. Taking the evolutionary conservation into account the current study aims to test various concentrations of aminoglycoside on the model organism, Drosophila melanogaster. The current study uses the oral route to check the toxicity of various aminoglycosides at different concentrations (50, 100, 150, 200, and 250 μg ml^{- 1} ). In Drosophila, many foreign particles enter the body through the gut via food. The aminoglycoside treated third instar larvae show defective crawling and sound avoidance behavior. The adult flies release lower amounts of acetylcholine esterase and higher amounts of reactive oxygen species than control untreated animals, accompanied by defective climbing and aggressive behavior. All these behavioral defects are further confirmed by the altered expression level of hearing genes such as nompC, inactive, nanchung, pyrexia. All the behavioral and genetic defects are reported as a readout of aminoglycoside toxicity.

The microbiota-gut-brain axis participates in chronic cerebral hypoperfusion by disrupting the metabolism of short-chain fatty acids

BACKGROUND

Chronic cerebral hypoperfusion (CCH) underlies secondary brain injury following certain metabolic disorders and central nervous system (CNS) diseases. Dysregulation of the microbiota-gut-brain axis can exacerbate various CNS disorders through aberrantly expressed metabolites such as short-chain fatty acids (SCFAs). Yet, its relationship with CCH remains to be demonstrated. And if so, it is of interest to explore whether restoring gut microbiota to maintain SCFA metabolism could protect against CCH.

RESULTS

Rats subjected to bilateral common carotid artery occlusion (BCCAO) as a model of CCH exhibited cognitive impairment, depressive-like behaviors, decreased gut motility, and compromised gut barrier functions. The 16S ribosomal RNA gene sequencing revealed an abnormal gut microbiota profile and decreased relative abundance of some representative SCFA producers, with the decreased hippocampal SCFAs as the further evidence. Using fecal microbiota transplantation (FMT), rats recolonized with a balanced gut microbiome acquired a higher level of hippocampal SCFAs, as well as decreased neuroinflammation when exposed to lipopolysaccharide. Healthy FMT promoted gut motility and gut barrier functions, and improved cognitive decline and depressive-like behaviors by inhibiting hippocampal neuronal apoptosis in BCCAO rats. Long-term SCFA supplementation further confirmed its neuroprotective effect in terms of relieving inflammatory response and hippocampal neuronal apoptosis following BCCAO.

CONCLUSION

Our results demonstrate that modulating the gut microbiome via FMT can ameliorate BCCAO-induced gut dysbiosis, cognitive decline, and depressive-like behaviors, possibly by enhancing the relative abundance of SCFA-producing floras and subsequently increasing SCFA levels. Video abstract.

Transcript and blood-microbiome analysis towards a blood diagnostic tool for goats affected by Haemonchus contortus

The Alpine goat (Capra aegagrus hircus) is parasitized by the barber pole worm (Haemonchus contortus). Hematological parameters from transcript and metagenome analysis in the host are reflective of infestation. We explored comparisons between blood samples of control, infected, infected zoledronic acid-treated, and infected antibody (anti-γδ T cells) treated wethers under controlled conditions. Seven days post-inoculation (dpi), we identified 7,627 transcripts associated with the different treatment types. Microbiome measurements at 7 dpi revealed fewer raw read counts across all treatments and a less diverse microbial flora than at 21 dpi. This study identifies treatment specific transcripts and an increase in microflora abundance and diversity as wethers age. Further, F/B ratio reflect health, based on depression or elevation above thresholds defined by the baseline of non-infected controls. Forty Alpine wethers were studied where blood samples were collected from five goats in four treatment groups on 7 dpi and 21 dpi. Transcript and microbiome profiles were obtained using the Partek Flow (St. Louis, Missouri, USA) software suites pipelines. Inflammation comparisons were based on the Firmicutes/Bacteriodetes ratios that are calculated as well as the reduction of microbial diversity.

A Computational Model of Bacterial Population Dynamics in Gastrointestinal Yersinia enterocolitica Infections in Mice

Simple Summary

Computational modeling of bacterial infection is an attractive way to simulate infection scenarios. In the long-term, such models could be used to identify factors that make individuals more susceptible to infection, or how interference with bacterial growth influences the course of bacterial infection. This study used different mouse infection models (immunocompetent, lacking a microbiota, and immunodeficient models) to develop a basic mathematical model of a Yersinia enterocolitica gastrointestinal infection. We showed that our model can reflect our findings derived from mouse infections, and we demonstrated how crucial the exact knowledge about parameters influencing the population dynamics is. Still, we think that computational models will be of great value in the future; however, to foster the development of more complex models, we propose the broad implementation of the interdisciplinary training of mathematicians and biologists.

Abstract

The complex interplay of a pathogen with its virulence and fitness factors, the host’s immune response, and the endogenous microbiome determine the course and outcome of gastrointestinal infection. The expansion of a pathogen within the gastrointestinal tract implies an increased risk of developing severe systemic infections, especially in dysbiotic or immunocompromised individuals. We developed a mechanistic computational model that calculates and simulates such scenarios, based on an ordinary differential equation system, to explain the bacterial population dynamics during gastrointestinal infection. For implementing the model and estimating its parameters, oral mouse infection experiments with the enteropathogen, Yersinia enterocolitica (Ye), were carried out. Our model accounts for specific pathogen characteristics and is intended to reflect scenarios where colonization resistance, mediated by the endogenous microbiome, is lacking, or where the immune response is partially impaired. Fitting our data from experimental mouse infections, we can justify our model setup and deduce cues for further model improvement. The model is freely available, in SBML format, from the BioModels Database under the accession number MODEL2002070001.

Impact of antibiotics on the human microbiome and consequences for host health

It is well established that the gut microbiota plays an important role in host health and is perturbed by several factors including antibiotics. Antibiotic-induced changes in microbial composition can have a negative impact on host health including reduced microbial diversity, changes in functional attributes of the microbiota, formation, and selection of antibiotic-resistant strains making hosts more susceptible to infection with pathogens such as Clostridioides difficile. Antibiotic resistance is a global crisis and the increased use of antibiotics over time warrants investigation into its effects on microbiota and health. In this review, we discuss the adverse effects of antibiotics on the gut microbiota and thus host health, and suggest alternative approaches to antibiotic use.

Gut microbiota-motility interregulation: insights from in vivo, ex vivo and in silico studies

The human gastrointestinal tract is home to trillions of microbes. Gut microbial communities have a significant regulatory role in the intestinal physiology, such as gut motility. Microbial effect on gut motility is often evoked by bioactive molecules from various sources, including microbial break down of carbohydrates, fibers or proteins. In turn, gut motility regulates the colonization within the microbial ecosystem. However, the underlying mechanisms of such regulation remain obscure. Deciphering the inter-regulatory mechanisms of the microbiota and bowel function is crucial for the prevention and treatment of gut dysmotility, a comorbidity associated with many diseases. In this review, we present an overview of the current knowledge on the impact of gut microbiota and its products on bowel motility. We discuss the currently available techniques employed to assess the changes in the intestinal motility. Further, we highlight the open challenges, and incorporate biophysical elements of microbes-motility interplay, in an attempt to lay the foundation for describing long-term impacts of microbial metabolite-induced changes in gut motility.

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.

Antibiotic-induced gut dysbiosis leads to activation of microglia and impairment of cholinergic gamma oscillations in the hippocampus

Antibiotics are widely applied for the treatment of bacterial infections, but their long-term use may lead to gut flora dysbiosis and detrimental effects on brain physiology, behavior as well as cognitive performance. Still, a striking lack of knowledge exists concerning electrophysiological correlates of antibiotic-induced changes in gut microbiota and behavior. Here, we investigated changes in the synaptic transmission and plasticity together with behaviorally-relevant network activities from the hippocampus of antibiotic-treated mice. Prolonged antibiotic treatment led to a reduction of myeloid cell pools in bone marrow, circulation and those surveilling the brain. Circulating Ly6C^hi inflammatory monocytes adopted a proinflammatory phenotype with increased expression of CD40 and MHC II. In the central nervous system, microglia displayed a subtle activated phenotype with elevated CD40 and MHC II expression, increased IL-6 and TNF production as well as with an increased number of Iba1 + cells in the hippocampal CA3 and CA1 subregions. Concomitantly, we detected a substantial reduction in the synaptic transmission in the hippocampal CA1 after antibiotic treatment. In line, carbachol-induced cholinergic gamma oscillation were reduced upon antibiotic treatment while the incidence of hippocampal sharp waves was elevated. These alterations were associated with the global changes in the expression of neurotrophin nerve growth factor and inducible nitric oxide synthase, both of which have been shown to influence cholinergic system in the hippocampus. Overall, our study demonstrates that antibiotic-induced dysbiosis of the gut microbiome and subsequent alteration of the immune cell function are associated with reduced synaptic transmission and gamma oscillations in the hippocampus, a brain region that is critically involved in mediation of innate and cognitive behavior.

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.

Enteric Microbiota-Mediated Serotonergic Signaling in Pathogenesis of Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is a chronic functional disorder that affects the gastrointestinal tract. Details regarding the pathogenesis of IBS remain largely unknown, though the dysfunction of the brain-gut-microbiome (BGM) axis is a major etiological factor, in which neurotransmitters serve as a key communication tool between enteric microbiota and the brain. One of the most important neurotransmitters in the pathology of IBS is serotonin (5-HT), as it influences gastrointestinal motility, pain sensation, mucosal inflammation, immune responses, and brain activity, all of which shape IBS features. Genome-wide association studies discovered susceptible genes for IBS in serotonergic signaling pathways. In clinical practice, treatment strategies targeting 5-HT were effective for a certain portion of IBS cases. The synthesis of 5-HT in intestinal enterochromaffin cells and host serotonergic signaling is regulated by enteric resident microbiota. Dysbiosis can trigger IBS development, potentially through aberrant 5-HT signaling in the BGM axis; thus, the manipulation of the gut microbiota may be an alternative treatment strategy. However, precise information regarding the mechanisms underlying the microbiota-mediated intestinal serotonergic pathway related to the pathogenesis of IBS remains unclear. The present review summarizes current knowledge and recent progress in understanding microbiome–serotonin interaction in IBS cases.

The effect of sodium carboxymethyl starch with high degree of substitution on defecation

Sodium carboxymethyl starch (CMS-Na), a kind of food additive with high degree of substitution, is also known as a prebiotic. The aim of this study was to determine the effect of CMS-Na on defecation. Constipated mouse model was prepared by loperamide. Normal rats were also used in the study. Short-chain fatty acids in rat feces were detected by gas chromatography. The bacterial communities in rat feces were identified by 16S rDNA gene sequencing. 5-hydroxytryptamine (5-HT) and tryptophan hydroxylase 1 (Tph1) were measured by ELISA. The results showed that CMS-Na increased the fecal granule counts and intestinal propulsion rate in constipated mice. The contents of water, acetic acid, propionic acid and n-butyrate in feces, Tph1 in colon and 5-HT in serum of rats were increased. In addition, CMS-Na shortened the colonic transport time in rats. The 16S rDNA gene sequencing results indicated that CMS-Na increased the relative abundance of Alloprevotella and decreased the proportion of Lactobacillus. However, the biodiversity of the normal intestinal flora was not altered. In conclusion, CMS-Na can promote defecation in constipated mice. The mechanism may be related to the regulation of Alloprevotella and Lactobacillus in colon, the increase of short-chain fatty acids, and the promotion of the synthesis of Tph1 and 5-HT.

Tryptophan-derived serotonin-kynurenine balance in immune activation and intestinal inflammation

Endogenous tryptophan metabolism pathways lead to the production of serotonin (5‐hydroxytryptamine; 5‐HT), kynurenine, and several downstream metabolites which are involved in a multitude of immunological functions in both health and disease states. Ingested tryptophan is largely shunted to the kynurenine pathway (95%) while only minor portions (1%–2%) are sequestered for 5‐HT production. Though often associated with the functioning of the central nervous system, significant production of 5‐HT, kynurenine and their downstream metabolites takes place within the gut. Accumulating evidence suggests that these metabolites have essential roles in regulating immune cell function, intestinal inflammation, as well as in altering the production and suppression of inflammatory cytokines. In addition, both 5‐HT and kynurenine have a considerable influence on gut microbiota suggesting that these metabolites impact host physiology both directly and indirectly via compositional changes. It is also now evident that complex interactions exist between the two pathways to maintain gut homeostasis. Alterations in 5‐HT and kynurenine are implicated in the pathogenesis of many gastrointestinal dysfunctions, including inflammatory bowel disease. Thus, these pathways present numerous potential therapeutic targets, manipulation of which may aid those suffering from gastrointestinal disorders. This review aims to update both the role of 5‐HT and kynurenine in immune regulation and intestinal inflammation, and analyze the current knowledge of the relationship and interactions between 5‐HT and kynurenine pathways.

Gut Microbiota and Neuroplasticity

The accumulating evidence linking bacteria in the gut and neurons in the brain (the microbiota-gut-brain axis) has led to a paradigm shift in the neurosciences. Understanding the neurobiological mechanisms supporting the relevance of actions mediated by the gut microbiota for brain physiology and neuronal functioning is a key research area. In this review, we discuss the literature showing how the microbiota is emerging as a key regulator of the brain's function and behavior, as increasing amounts of evidence on the importance of the bidirectional communication between the intestinal bacteria and the brain have accumulated. Based on recent discoveries, we suggest that the interaction between diet and the gut microbiota, which might ultimately affect the brain, represents an unprecedented stimulus for conducting new research that links food and mood. We also review the limited work in the clinical arena to date, and we propose novel approaches for deciphering the gut microbiota-brain axis and, eventually, for manipulating this relationship to boost mental wellness.

Comparative analysis of microRNA expression profiles in the colons of specific pathogen-free mice and germ-free mice

MicroRNAs play an important role in microbiota-host crosstalk. In this study, we compared microRNA expression in whole colons of specific pathogen-free mice and germ-free mice. Forty-eight microRNAs were differentially expressed by more than 2-fold. Gene ontology analysis of the predicted mRNA targets revealed that the majority of the most significant gene ontology terms were related to GTPases and nerves.

Neurotransmitter Profiles Are Altered in the Gut and Brain of Mice Mono-Associated with Bifidobacterium dentium

BACKGROUND

Accumulating evidence indicates that the gut microbiota can synthesize neurotransmitters as well as impact host-derived neurotransmitter levels. In the past, it has been challenging to decipher which microbes influence neurotransmitters due to the complexity of the gut microbiota.

METHODS

To address whether a single microbe, Bifidobacterium dentium, could regulate important neurotransmitters, we examined Bifidobacteria genomes and explored neurotransmitter pathways in secreted cell-free supernatant using LC-MS/MS. To determine if B. dentium could impact neurotransmitters in vivo, we mono-associated germ-free mice with B. dentium ATCC 27678 and examined fecal and brain neurotransmitter concentrations.

RESULTS

We found that B. dentium possessed the enzymatic machinery to generate γ-aminobutyric acid (GABA) from glutamate, glutamine, and succinate. Consistent with the genome analysis, we found that B. dentium secreted GABA in a fully defined microbial media and elevated fecal GABA in B. dentium mono-associated mice compared to germ-free controls. We also examined the tyrosine/dopamine pathway and found that B. dentium could synthesize tyrosine, but could not generate L-dopa, dopamine, norepinephrine, or epinephrine. In vivo, we found that B. dentium mono-associated mice had elevated levels of tyrosine in the feces and brain.

CONCLUSIONS

These data indicate that B. dentium can contribute to in vivo neurotransmitter regulation.

Interactions between the microbiota and enteric nervous system during gut-brain disorders

For the last 20 years, researchers have focused their intention on the impact of gut microbiota in healthy and pathological conditions. This year (2021), more than 25,000 articles can be retrieved from PubMed with the keywords "gut microbiota and physiology", showing the constant progress and impact of gut microbes in scientific life. As a result, numerous therapeutic perspectives have been proposed to modulate the gut microbiota composition and/or bioactive factors released from microbes to restore our body functions. Currently, the gut is considered a primary site for the development of pathologies that modify brain functions such as neurodegenerative (Parkinson's, Alzheimer's, etc.) and metabolic (type 2 diabetes, obesity, etc.) disorders. Deciphering the mode of interaction between microbiota and the brain is a real original option to prevent (and maybe treat in the future) the establishment of gut-brain pathologies. The objective of this review is to describe recent scientific elements that explore the communication between gut microbiota and the brain by focusing our interest on the enteric nervous system (ENS) as an intermediate partner. The ENS, which is known as the "second brain", could be under the direct or indirect influence of the gut microbiota and its released factors (short-chain fatty acids, neurotransmitters, gaseous factors, etc.). Thus, in addition to their actions on tissue (adipose tissue, liver, brain, etc.), microbes can have an impact on local ENS activity. This potential modification of ENS function has global repercussions in the whole body via the gut-brain axis and represents a new therapeutic strategy.