Regulation Of Gut Motility Research Articles

Role of nitric oxide in determination of large intestinal contractility in neonatal rats

Objectives: Nitric oxide (NO) plays a key role in inhibiting the contractility of gut smooth muscles in various species, and NG-nitro-L-arginine methyl ester (L-NAME) is a critical NO synthase inhibitor. Previous research investigating the role of NO in regulating gut motility focused on adult animals. Therefore, more research is needed to determine their status in the gut of newborns. Our study intended to understand how NO impacts the large gut contractility, in vitro, in rats, both neonates and adults, to get a better insight into the physiological role of NO in regulating large gut motility, particularly in neonates. Materials and Methods: In an organ bath preparation, the segments of a large gut (colon and rectum) were subjected to various concentrations of nitroglycerin (NG) (0.01–100 mM), a NO donor, cumulatively. In another group, pre-treatment with L-NAME (100 mM) was done to evaluate the blocking effect of NO on the contractile tension and frequency. Results: NG induced relaxation in the colon and rectum of adult rats in a similar manner. NG caused significantly greater relaxation in neonates’ rectums than in their colons. In neonatal and adult rats, L-NAME pre-application inhibited NG-induced relaxation in contractile tension. Exposure to different concentrations of NG decreased contractile frequency in adult rats’ colons and rectum. However, L-NAME pre-treatment did not affect the decrease in contractile frequency caused by NG. In neonates, NG caused a concentration-dependent reduction in contractile frequency, and a decrease in contractile frequency in the rectum was more than that in the colon. However, L-NAME pre-treatment did not affect the reduction in contractile frequency caused by NG. Conclusion: Nitrergic mechanisms have possibly been present since birth. The intensity of control by NO may be different in the colon and rectum. The differences in NO sensitivity in adults and neonates demonstrated the changes during development.

A3 INVESTIGATING MACROPHAGE-TISSUE CELL COMMUNICATION AXES IN THE GASTROINTESTINAL TRACT

Abstract Background The gastrointestinal tract boasts the highest concentration of macrophages (MPs) in the body, acting as vital immune sentinels that oversee tissue balance. Three distinct subsets of MPs, namely CCR2+, Tim4+, and CCR2,Tim4 double-negative (DN) MPs, populate distinct gut niches. Their functional specialization suggests unique interactions within their non-hematopoietic tissue microenvironments. Despite their crucial roles, the intricacies of these interactions remain elusive. One recently discovered interaction involves a communication axis between MPs and neurons within the muscularis layer of the gut. Here, neurons secrete Colony Stimulating Factor 1 (CSF1), a survival factor for MPs. These MPs reciprocate by producing Bone Morphogenetic Protein 2 (BMP2), assisting neurons in regulating gut motility. Aims Based on the aforementioned interaction, we hypothesize that BMP2, derived from tissue-resident MPs, might influence functions of other tissue niches, subsequently prompting survival of MP via CSF1 production. Our aims are twofold: (1) Identify the role of BMP2 in gut macrophages; (2) Identify BMP2-responsive CSF1-producing tissue cells within the gut. Methods To discern the roles of MP subsets, we developed a conditional knockout mouse model, targeting Bmp2 expression in MPs. We validated successful Bmp2 deletion(BMP2 KO) through quantitative polymerase chain reaction (qPCR) and an in-situ hybridization immunofluorescence assay (RNAscope). Subsequently, single cell RNA (scRNAseq) was performed, combining samples from both control and KO small intestines. This was done to further confirm BMP2 KO and to identify BMP2-responsive CSF1-producing cells. Flow cytometry was then used to characterize the intestinal MPs in control and KO mice. Results Tim4+ MPs emerged as the primary source of BMP2. Comprehensive analysis using qPCR, RNAscope, and scRNAseq validated the complete KO of BMP2 across all macrophage subsets. The loss of MP-produced BMP2 led to a disruption in MP development. Notably, a marked reduction in DN and Tim4+ MPs was observed following deletion of Bmp2 in MPs, emphasizing the critical role of BMP2-driven CSF1 in sustaining these subsets. CSF1 producing cells co-expressing the cognate BMP receptor in the gut, were predominantly non-hematopoietic tissue cells. Among these, distinct fibroblast populations emerged as a potent but not the sole source of CSF1. Conclusions Our work underscores the involvement of multiple tissue cell populations, revealing an intricate network of interactions that extends beyond fibroblasts. This study unveils the multifaceted nature of tissue-MP interactions and their critical roles in maintaining gut homeostasis. Disturbances of these pathways may pave the way for disease by altering tissue homeostasis. Funding Agencies NSERC

Peripheral serotonergic neurons regulate gut motility and anxiety-like behavior

Serotonergic circuits in the central nervous system play important roles in regulating mood and behavior, yet the functions of peripheral serotonergic neurons are less understood. Here, we engineered mice lacking the serotonin-producing enzyme Tph2 in peripheral neurons but with intact Tph2 in central neurons. In contrast to mice lacking Tph2 in all neurons, mice lacking Tph2 in peripheral serotonergic neurons did not exhibit increased territorial aggression. However, similar to the total body Tph2 knockout (KO) mice, the conditional KO animals exhibited reduced gut motility and decreased anxiety-like behavior. These observations reveal that peripheral serotonergic neurons contribute to control of intestinal motility and anxiety-like behavior and suggest that therapeutics targeting this subset of peripheral neurons could be beneficial.

Nitric oxide and ion channels mediate L-cysteine-induced inhibition of colonic smooth muscle contraction.

Previous studies have suggested that L-cysteine regulates gut motility through hydrogen sulfide. However, the mechanisms involved in the L-cysteine-induced response have not been extensively studied. This study aimed to investigate the underlying mechanisms of action of L-cysteine on spontaneous contraction of rat colon. Longitudinal and circular muscle strips from rat middle colon were prepared to measure the spontaneous contractile activities of colon in an organ bath system. Whole-cell voltage-clamp techniques were applied to record the currents of L-type voltage-dependent Ca2+ channels (VDCCs) and voltage-gated K+ channels (Kv) in isolated smooth muscle cells (SMCs) from colon. L-cysteine inhibited the spontaneous contraction of longitudinal and circular muscle strips from the rat colon in a concentration-dependent manner. The inhibition induced by L-cysteine was significantly decreased by inhibitors of H2S synthesis (p < 0.05). Furthermore, the suppression induced by L-cysteine was partially attenuated by tetrodotoxin, L-NNA and glibenclamide (p < 0.05). Whole-cell voltage-clamp recordings showed that L-cysteine caused a remarkable reduction in the peak currents of VDCCs and significantly increased the membrane currents of Kv channels in isolated SMCs (p < 0.05). We concluded that L-cysteine inhibits the contractile activities of smooth muscle strips from the rat colon. The relaxation in response to L-cysteine may be in part mediated by a nitrergic pathway and by inhibiting the VDCCs in combination with a direct activation of the KV channels and KATP channels.

RET Signaling Persists in the Adult Intestine and Stimulates Motility by Limiting PYY Release From Enteroendocrine Cells

RET tyrosine kinase is necessary for enteric nervous system development. Loss-of-function RET mutations cause Hirschsprung disease (HSCR), in which infants are born with aganglionic bowel. Despite surgical correction, patients with HSCR often experience chronic defecatory dysfunction and enterocolitis, suggesting that RET is important after development. To test this hypothesis, we determined the location of postnatal RET and its significance in gastrointestinal (GI) motility. RetCFP/+ mice and human transcriptional profiling data were studied to identify the enteric neuronal and epithelial cells that express RET. To determine whether RET regulates gut motility invivo, genetic, and pharmacologic approaches were used to disrupt RET in all RET-expressing cells, a subset of enteric neurons, or intestinal epithelial cells. Distinct subsets of enteric neurons and enteroendocrine cells expressed RET in the adult intestine. RET disruption in the epithelium, rather than in enteric neurons, slowed GI motility selectively in male mice. RET kinase inhibition phenocopied this effect. Most RET+ epithelial cells were either enterochromaffin cells that release serotonin or L-cells that release peptide YY (PYY) and glucagon-like peptide 1 (GLP-1), both of which can alter motility. RET kinase inhibition exaggerated PYY and GLP-1 release in a nutrient-dependent manner without altering serotonin secretion in mice and human organoids. PYY receptor blockade rescued dysmotility in mice lacking epithelial RET. RET signaling normally limits nutrient-dependent peptide release from L-cells and this activity is necessary for normal intestinal motility in male mice. These effects could contribute to dysmotility in HSCR, which predominantly affects males, and uncovers a mechanism that could be targeted to treat post-prandial GI dysfunction.

Anti-Gephyrin Antibodies: A Novel Specificity in Patients With Systemic Sclerosis and Lower Bowel Dysfunction.

Autoantibodies are clinically useful in phenotyping patients with systemic sclerosis (SSc). Gastrointestinal (GI) function is regulated by the enteric nervous system (ENS) and commonly impaired in SSc, suggesting that the SSc autoimmune response may target ENS antigens. We sought to identify novel anti-ENS autoantibodies with an aim to clinically phenotype SSc GI dysfunction. Serum from a patient with SSc with GI dysfunction but without defined SSc-associated autoantibodies was used for autoantibody discovery. Immunoprecipitations performed with murine myenteric plexus lysates were on-bead digested, and autoantigens were identified by mass spectrometry. Prevalence was determined, and clinical features associated with novel autoantibodies were evaluated in a SSc cohort using regression analyses. The expression of gephyrin in human GI tract tissue was examined by immunohistochemistry. We identified gephyrin as a novel SSc autoantigen. Anti-gephyrin antibodies were present in 9% of patients with SSc (16/188) and absent in healthy controls (0/46). Anti-gephyrin antibody-positive patients had higher constipation scores (1.00 vs 0.50, P = 0.02) and were more likely to have severe constipation and severe distention/bloating (46% vs 15%, P = 0.005; 54% vs 25%, P = 0.023, respectively). Anti-gephyrin antibody levels were significantly higher among patients with severe constipation (0.04 vs 0.00; P = 0.001) and severe distention and bloating (0.03 vs 0.004; P = 0.010). Severe constipation was associated with anti-gephyrin antibodies even in the adjusted model. Importantly, gephyrin was expressed in the ENS, which regulates gut motility. Gephyrin is a novel ENS autoantigen that is expressed in human myenteric ganglia. Anti-gephyrin autoantibodies are associated with the presence and severity of constipation in patients with SSc.

Colon-Targeted Delivery of Indole Acetic Acid Helps Regulate Gut Motility by Activating the AHR Signaling Pathway.

Intestinal peristalsis is vital for gastrointestinal physiology and host homeostasis and is frequently dysregulated in intestinal disorders. Gut microbiota can regulate gut motility, especially through the tryptophan metabolism pathway. However, the role of indoles as microbial tryptophan metabolites in colonic function requires further exploration. Here, we show that the delivery of indole acetic acid (IAA) targeting the colon can improve gut motility by activating the aryl hydrocarbon receptor (AHR). To achieve colon-targeted delivery, Eudragit S-100 (ES) and chitosan (CS) were used as drug carriers. After optimisation, IAA-loaded ES-coated CS nanoparticles exhibited an encapsulation efficiency of 83% and a drug-loading capacity of 16%. These nanoparticles exhibited pH-dependent characteristics and remained stable in acidic conditions and the upper intestine. In simulated intestinal fluid (pH 7.4) and colonic lumen, considerable amounts of IAA were released after approximately 4 h. Compared with free IAA, the nanoparticles exerted enhanced therapeutic effects on gut movement disorders induced by loperamide. The efficacy of IAA treatment was attributable to the activation of the AHR signalling pathway and increased levels of AHR agonists. Furthermore, the oral administration of IAA-loaded nanoparticles promoted serotonin secretion and maintained the intestinal barrier function. The experimental outcomes demonstrate the efficiency of the proposed colon-specific delivery system and highlight the role of IAA, produced by gut microbiota metabolism, in regulating gut peristalsis through AHR activation.

A CNS circuit that regulates gut motility.

A CNS circuit that regulates gut motility.

Insights on discovery, efficacy, safety and clinical applications of ghrelin receptor agonist capromorelin in veterinary medicine.

Growth hormone and insulin like growth factor-1 plays an important role in the regulation of body composition and metabolism. Growth Hormone is released from the pituitary through a specific G-protein coupled receptor (GPCR) called growth hormone secretagogue receptor 1a expressed in the hypothalamus. Ghrelin is a peptide hormone released from the cells in the stomach, which stimulates appetite and food intake in mammals, regulates gut motility, gastric acid secretion, taste sensation, circadian rhythm, learning and memory, oxidative stress, autophagy, glucose metabolism etc. When the release of the endogenous ligand GHSR-1a, i.e., ghrelin is malfunctioned or stopped, external substitutes are administrated to induce the stimulation of growth hormone and appetite. A class of compound known as ghrelin receptor agonists are developed as an external substitute of ghrelin for regulation and stimulation of growth hormone in frailty, for body weight gain, muscle mass gain, prevention of cachexia and for the treatment of chronic fatigue syndromes. Capromorelin [Entyce™ (Aratana Therapeutics, Leawood, KS, USA)] is the only FDA (Food and Drug Administration) approved (May 2016) drug used for stimulating appetite in dogs and was marketed in the fall of 2017. In 2020, USFDA approved Capromorelin [Elura™ (Elanco US Inc.)] for the management of weight loss in chronic kidney disease of cats. This article reviews the discovery of the ghrelin receptor agonist capromorelin, its efficacy, safety, clinical applications and aims to delineate its further scope of use in veterinary practice.

Lipids regulate peripheral serotonin release via gut CD1d

The crosstalk between the immune and neuroendocrine systems is critical for intestinal homeostasis and gut-brain communications. However, it remains unclear how immune cells participate in gut sensation of hormones and neurotransmitters release in response to environmental cues, such as self-lipids and microbial lipids. We show here that lipid-mediated engagement of invariant natural killer T (iNKT) cells with enterochromaffin (EC) cells, a subset of intestinal epithelial cells, promoted peripheral serotonin (5-HT) release via a CD1d-dependent manner, regulating gut motility and hemostasis. We also demonstrated that inhibitory sphingolipids from symbiotic microbe Bacteroides fragilis represses 5-HT release. Mechanistically, CD1d ligation on EC cells transduced a signal and restrained potassium conductance through activation of protein tyrosine kinase Pyk2, leading to calcium influx and 5-HT secretion. Together, our data reveal that by engaging with iNKT cells, gut chemosensory cells selectively perceive lipid antigens via CD1d to control 5-HT release, modulating intestinal and systemic homeostasis.

Gut Microbiome-Brain Alliance: A Landscape View into Mental and Gastrointestinal Health and Disorders.

Gut microbiota includes a vast collection of microorganisms residing within the gastrointestinal tract. It is broadly recognized that the gut and brain are in constant bidirectional communication, of which gut microbiota and its metabolic production are a major component, and form the so-called gut microbiome-brain axis. Disturbances of microbiota homeostasis caused by imbalance in their functional composition and metabolic activities, known as dysbiosis, cause dysregulation of these pathways and trigger changes in the blood-brain barrier permeability, thereby causing pathological malfunctions, including neurological and functional gastrointestinal disorders. In turn, the brain can affect the structure and function of gut microbiota through the autonomic nervous system by regulating gut motility, intestinal transit and secretion, and gut permeability. Here, we examine data from the CAS Content Collection, the largest collection of published scientific information, and analyze the publication landscape of recent research. We review the advances in knowledge related to the human gut microbiome, its complexity and functionality, its communication with the central nervous system, and the effect of the gut microbiome-brain axis on mental and gut health. We discuss correlations between gut microbiota composition and various diseases, specifically gastrointestinal and mental disorders. We also explore gut microbiota metabolites with regard to their impact on the brain and gut function and associated diseases. Finally, we assess clinical applications of gut-microbiota-related substances and metabolites with their development pipelines. We hope this review can serve as a useful resource in understanding the current knowledge on this emerging field in an effort to further solving of the remaining challenges and fulfilling its potential.

Lipid sensing by gut CD1d calibrates peripheral serotonin release

Abstract The crosstalk between the immune and the neuroendocrine system is critical for intestinal homeostasis and gut-brain communications. However, it remains unclear how immune cells participate in gut sensation of hormones release in response to environmental cues, such as self and microbial lipids. We show here that lipid-mediated engagement of invariant natural killer T (iNKT) cells with enterochromaffin (EC) cells, a subset of intestinal epithelial cells, promotes peripheral serotonin (5-HT) release via a CD1d-dependent manner, regulating gut motility and hemostasis. CD1d ligation on EC cells transduces a reverse signal and restrains potassium conductance, leading to calcium influx and 5-HT secretion. Together, we show that by coupling with iNKT cells, gut chemosensory cells perceive lipid antigens via CD1d to calibrate 5-HT release, modulating intestinal and systemic physiology.

Macrophages regulate gastrointestinal motility through complement component 1q.

Peristaltic movement of the intestine propels food down the length of the gastrointestinal tract to promote nutrient absorption. Interactions between intestinal macrophages and the enteric nervous system regulate gastrointestinal motility, yet we have an incomplete understanding of the molecular mediators of this crosstalk. Here, we identify complement component 1q (C1q) as a macrophage product that regulates gut motility. Macrophages were the predominant source of C1q in the mouse intestine and most extraintestinal tissues. Although C1q mediates the complement-mediated killing of bacteria in the bloodstream, we found that C1q was not essential for the immune defense of the intestine. Instead, C1q-expressing macrophages were located in the intestinal submucosal and myenteric plexuses where they were closely associated with enteric neurons and expressed surface markers characteristic of nerve-adjacent macrophages in other tissues. Mice with a macrophage-specific deletion of C1qa showed changes in enteric neuronal gene expression, increased neurogenic activity of peristalsis, and accelerated intestinal transit. Our findings identify C1q as a key regulator of gastrointestinal motility and provide enhanced insight into the crosstalk between macrophages and the enteric nervous system.

Effects and underlying mechanisms of L-arginine on spontaneous muscle contraction of rat colon.

Arginine (Arg), as a basic amino acid, has been reported to be involved in regulation of gut motility. However, the evidence is limited and the underlying mechanism is not fully understood. Our study was conducted to investigate the effects of L-Arg on spontaneous contraction of the longitudinal muscle strip (LMS) of the rat colon and the relevant mechanisms. An organ bath system was used to detect the contractile force of the LMS. Whole-cell voltage-clamp techniques were applied to observe alterations in the currents of large conductance Ca2+-activated K+ (KCa) channels, voltage-dependent potassium (KV) channels, and L-type Ca2+ channels (LTCCs) in smooth muscle cells (SMCs) of the colon. We found that L-Arg within the physiological concentration had no effect on contraction of LMS, while 1mM L-Arg significantly increased both the amplitude and frequency of LMS contractility. And the increase in force was mucosa-dependent, whereas changes in frequency as well as in amplitude were inhibited by atropine. In addition, L-Arg (1mM) activated the LTTCs and inhibited both KCa channels and KV channels on SMCs. Thus, L-Arg above the physiological concentration exerted an excitatory effect on colonic LM contraction, and stimulation by L-Arg was mediated by ACh. In addition, LTCCs, KCa channels, and KV channels on SMCs were involved in the action of L-Arg.

Structural basis for ligand modulation and partial agonism of the 5-HT3R.

Type-3 serotonin receptors (5-HT3Rs) are pentameric ligand gated ion channels that mediate fast synaptic signaling in response to binding of the neurotransmitter serotonin. 5-HT3Rs play a major role in regulating gut motility, secretion, and visceral perception. Hyperactivity of 5-HT3Rs underlies pathologies such as chemotherapy-induced nausea and vomiting, irritable bowel syndrome, depression, anxiety, bipolar disorder, and excessive visceral pain, making it an important drug target. Previous research has resulted in the structures of the 5-HT3AR in complex with the agonist serotonin and setrons, 5-HT3R antagonists. Recently, 5-HT3AR partial agonists have been proposed to treat 5-HT3R pathologies with less severe side effects than full antagonists. However, the molecular mechanisms of partial agonism by orthosteric ligands of the 5-HT3R are still poorly understood. Here we present structures of the 5-HT3AR in complex with two novel orthosteric partial agonists generated from cryo-electron microscopy imaging. Structural stability of the ligand binding poses was assessed by molecular dynamic simulations, and ligand function was assessed by two-electrode voltage clamp in wild type and mutant receptors. Using our ligand-bound models of the 5-HT3AR, we propose structure-based mechanisms for the functional differences between orthosteric partial agonists, full agonist, and antagonists.

Proteolipid protein 1 is involved in the regulation of intestinal motility and barrier function in the mouse.

Proteolipid protein 1 (Plp1) is highly expressed in enteric glia, labeling cells throughout the mucosa, muscularis, and the extrinsic innervation. Plp1 is a major constituent of myelin in the central and peripheral nervous systems, but the absence of myelin in the enteric nervous system (ENS) suggests another role for Plp1 in the gut. Although the functions of enteric glia are still being established, there is strong evidence that they regulate intestinal motility and permeability. To interrogate the role of Plp1 in enteric glia, we investigated gut motility, secretomotor function and permeability, and evaluated the ENS in mice lacking Plp1. We studied two time points: ∼3 mo (young) and >1 yr (old). Old Plp1 null mice exhibited increased fecal output, decreased fecal water content, faster whole gut transit times, reduced intestinal permeability, and faster colonic migrating motor complexes. Interestingly, in both young and old mice, the ENS exhibited normal glial and neuronal numbers as well as glial arborization density in the absence of Plp1. As Plp1-associated functions involve mitogen-activated protein kinase/extracellular signal-regulated kinase 1/2 (Mapk/Erk1/2) signaling and Mapk/Erk1/2 are reported to have a regulatory role in intestinal motility, we measured protein expression of Erk1/2 and its active form in the small intestine. Old Plp1 null mice had reduced levels of phosphorylated-Erk1/2. Although Plp1 is not required for the normal appearance of enteric glial cells, it has a regulatory role in intestinal motility and barrier function. Our results suggest that functional changes mediated by Plp1-expressing enteric glia may involve Erk1/2 activation.NEW & NOTEWORTHY Here, we describe that Plp1 regulates gut motility and barrier function. The functional effects of Plp1 eradication are only seen in old mice, not young. The effects of Plp1 appear to be mediated through the Erk1/2 pathway.

The effects of Saccharomyces boulardii on rat colonic hypermotility induced by repeated water avoidance stress and the potential mechanism.

Saccharomyces boulardii (Sb) has been reported to have the potential to regulate gut motility. The aim of this experiment was to explore the possible function of Sb in gut hypermotility elicited by repeated water avoidance stress (WAS). Adult male Wistar rats (N=24) were divided into one of the following three groups: control (C), NS (normal saline) + WAS group (N), and Sb + WAS group (S). A diarrhea-predominant irritable bowel syndrome (IBS-D) model in rats was induced using the WAS method. Gut motility was evaluated by stool pellet expulsion per hour. The contractile activity of the colonic muscle strips was measured using an RM6240 multichannel physiological signal instrument. qRT-PCR and immunohistochemistry were used to assess Toll-like receptor 4 (TLR4) expression in colon tissue. ELISA was used to measure the level of cytokines in the serum and colonic tissue. Also, the microbiota composition was determined using high-throughput 16S rRNA sequencing. The results showed that oral Sb decreased the WAS-induced increased defecation and colonic hypermotility in vivo. Furthermore, Sb also decreased the contractile amplitude of colonic circular muscle (CM) and longitudinal muscle (LM) strips in a dose-dependent manner in vitro. Repeated WAS increased TLR4 expression, but Sb reversed it. Sb also reduced interleukin-6 (IL-6), IL-1β, and interferon-γ (IFN-γ) levels in serum and colonic tissue, while increasing IL-10 levels in colonic tissue. Meanwhile, the rats from the NS + WAS group had decreased microbiota diversity and had lower relative abundances of Patescibacteria, Epsilonbacteraeota, Cyanobacteria, and Turicibacter compared with controls. The rats in the Sb + WAS group showed a tendency to increase the relative abundance of Blautia when compared to control rats and had lower relative abundances of Acidobacteria and Anaerostipes compared with the NS + WAS group. Our findings demonstrated that Sb improved colonic hypermotility in rats, reversed the high-expression of TLR4 in the colon caused by repeated WAS, modulated cytokines in the colon and serum, and altered the gut microbiota, indicating that Sb may be useful for IBS-D.

Role of Hydrogen Sulfide in the Development of Colonic Hypomotility in a Diabetic Mouse Model Induced by Streptozocin.

Hydrogen sulfide (H2S), a novel gasotransmitter, is involved in the regulation of gut motility. Alterations in the balance of H2S play an important role in the pathogenesis of diabetes. This study was conducted to investigate the role of H2S in the colonic hypomotility of mice with streptozotocin (STZ)-induced diabetes. A single intraperitoneal injection of STZ was used to induce the type 1 diabetes model. Male C57BL/6 mice were randomized into a control group and an STZ-treated group. Immunohistochemistry, Western blotting, H2S generation, organ bath studies and whole-cell patch clamp techniques were carried out in single smooth muscle cells (SMCs) of the colon. We found that STZ-induced diabetic mice showed decreased stool output, impaired colonic contractility, and increased endogenous generation of H2S (p < 0.05). H2S-producing enzymes were upregulated in the colon tissues of diabetic mice (p < 0.05). The exogenous H2S donor sodium hydrosulfide (NaHS) elicited a biphasic action on colonic muscle contraction with excitation at lower concentrations and inhibition at higher concentrations. NaHS (0.1 mM) increased the currents of voltage-dependent calcium channels (VDCCs), while NaHS at 0.5 mM and 1.5 mM induced inhibition. Furthermore, NaHS reduced the currents of both voltage-dependent potassium (KV) channels and large conductance calcium-activated potassium (BK) channels in a dose-dependent manner. These results show that spontaneous contraction of colonic muscle strips from diabetic mice induced by STZ was significantly decreased, which may underlie the constipation associated with diabetes mellitus (DM). H2S overproduction with subsequent suppression of muscle contraction via VDCCs on SMCs may contribute in part to the pathogenesis of colonic hypomotility in DM. SIGNIFICANCE STATEMENT: Hydrogen sulfide may exhibit a biphasic effect on colonic motility in mice by regulating the activities of voltage-dependent calcium channels and voltage-dependent and large conductance calcium activated potassium channels. H2S overproduction with subsequent suppression of muscle contraction via VDCCs may contribute to the pathogenesis of colonic hypomotility in diabetes mellitus.

Bile Acid and Gut Microbiota in Irritable Bowel Syndrome.

Gut microbiota and their metabolites like bile acid (BA) have been investigated as causes of irritable bowel syndrome (IBS) symptoms. Primary BAs are synthesized and conjugated in the liver and released into the duodenum. BA biotransformation by gut microbiota begins in the intestine and results in production of a broad range of secondary BAs. Deconjugation is considered the gateway reaction for further modification and is mediated by bile salt hydrolase, which is widely expressed by the gut microbiota. However, gut bacteria that convert primary BAs to secondary BAs belong to a limited number of species, mainly Clostridiales. Like gut microbiota modify BA profile, BAs can shape gut microbiota via direct and indirect actions. BAs have prosecretory effects and regulates gut motility. BAs can also affect gut sensitivity. Because of the vital role of the gut microbiota and BAs in gut function, their bidirectional relationship may contribute to the pathophysiology of IBS. Individuals with IBS have been reported to have altered microbial profiles and modified BA profiles. A significant increase in fecal primary BA and a corresponding decrease in secondary BA have been observed in IBS with predominant diarrhea. In addition, primary BA was positively correlated with IBS symptoms. In IBS with predominant diarrhea, bacteria with reduced abundance mainly belonged to the genera in Ruminococcaceae and exhibited a negative correlation with primary BAs. Integrating the analysis of the gut microbiota and BAs could better understanding of IBS pathophysiology. The gap in this field needs to be further filled in the future.

Saccharomyces boulardii, a yeast probiotic, inhibits gut motility through upregulating intestinal serotonin transporter and modulating gut microbiota

Saccharomyces boulardii (Sb) is a widely used fungal probiotic in treating various digestive diseases, including irritable bowel syndrome (IBS). However, the specific mechanisms of Sb relieving IBS remain unclear. The abnormal serotonin transporter (SERT) / 5-hydroxytryptamine (5-HT) system could cause disordered gastrointestinal sensation and motility, which closely related to IBS pathogenesis. The aim of this study was to explore the effects and mechanisms of Sb on regulating gut motility. Sb supernatant (SbS) was administered to intestinal epithelial cells and mice. SbS upregulated SERT expression via enhancing heparin-binding epidermal growth factor (HB-EGF) release to activate epidermal growth factor receptor (EGFR). EGFR kinase inhibitor treatment or HB-EGF siRNA transfection in cells blocked SbS upregulating SERT. Consistently, SbS-treated mice presented inhibited gut motility, and EGFR activation and SERT upregulation were found. Moreover, 16 S rDNA sequence presented an evident decrease in Firmicutes / Bacteroidetes ratio in SbS group. In genus level, SbS reduced Escherichia_Shigella, Alistipes, Clostridium XlVa, and Saccharibacteria_genera_incertae_sedis, meanwhile, increased Parasutterella. The abundance of Saccharibacteria_genera_incertae_sedis positively correlated with defecation parameters and intestinal 5-HT content. Fecal microbiota transplantation showed that SbS could modulate gut microbiota to influence gut motility. Interestingly, elimination of gut microbiota with antibiotic cocktail did not entirely block SbS regulating gut motility. Furthermore, SbS administration to IBS-D mice significantly upregulated SERT and inhibited gut motility. In conclusion, SbS could upregulate SERT by EGFR activation, and modulate gut microbiota to inhibit gut motility. This finding would provide more evidence for the application of this yeast probiotic in IBS and other diarrheal disorders.