Antinociceptive effect of VSL#3 on visceral hypersensitivity in a rat model of irritable bowel syndrome: a possible action through nitric oxide pathway and enhance barrier function

The gut microbiota in persistent post-operative pain following breast cancer surgery

Persistent post-surgical pain (PPSP) is defined as pain which continues after a surgical operation in a significant form for at least three months (and is not related to pre-existing painful conditions). PPSP is a common, under-recognised, and important clinical problem which affects millions of patients worldwide. Preventative measures which are currently available include the selection of a minimally invasive surgical technique and an aggressive multimodal perioperative analgesic regimen. More recently, a role for the gut microbiota in pain modulation has become increasingly apparent. This study aims to investigate any relationship between the gut microbiota and PPSP. A prospective observational study of 68 female adult patients undergoing surgery for management of breast cancer was carried out. Stool samples from 45 of these patients were obtained to analyse the composition of the gut microbiota. Measures of pain and state-trait anxiety were also taken to investigate further dimensions in any relationship between the gut microbiota and PPSP. At 12 weeks postoperatively, 21 patients (51.2%) did not have any pain and 20 patients (48.8%) reported feeling pain that persisted at that time. Analysis of the gut microbiota revealed significantly lower alpha diversity (using three measures) in those patients reporting severe pain at the 60 min post-operative and the 12 weeks post-operative timepoints. A cluster of taxa represented by Bifidobacterium longum, and Faecalibacterium prausnitzii was closely associated with those individuals reporting no pain at 12 weeks postoperatively, while Megamonas hypermegale, Bacteroides pectinophilus, Ruminococcus bromii, and Roseburia hominis clustered relatively closely in the group of patients fulfilling the criteria for persistent post-operative pain. We report for the first time specific associations between the gut microbiota composition and the presence or absence of PPSP. This may provide further insights into mechanisms behind the role of the gut microbiota in the development of PPSP and could inform future treatment strategies.

Ghrelin prevents lethality in a rat endotoxemic model through central effects on the vagal pathway and adenosine A2B signaling : Brain ghrelin and anti-septic action

Accumulating evidence suggest that ghrelin plays a role as an antiseptic peptide. The present study aimed to clarify whether the brain may be implicated ghrelin's antiseptic action. We examined the effect of brain ghrelin on survival in a novel endotoxemic model achieved by treating rats with lipopolysaccharide (LPS) and colchicine. The observation of survival stopped three days after chemicals' injection or at death. Intracisternal ghrelin dose-dependently reduced lethality in the endotoxemic model; meanwhile, neither intraperitoneal injection of ghrelin nor intracisternal des-acyl-ghrelin injection affected the mortality rate. The brain ghrelin-induced lethality reduction was significantly blocked by surgical vagotomy. Moreover, intracisternal injection of a ghrelin receptor antagonist blocked the improved survival achieved by intracisternal ghrelin injection or intravenous 2-deoxy-d-glucose administration. Intracisternal injection of an adenosine A2B receptor agonist reduced the lethality and the ghrelin-induced improvement of survival was blocked by adenosine A2B receptor antagonist. I addition, intracisternal ghrelin significantly blocked the colonic hyperpermeability produced by LPS and colchicine. These results suggest that ghrelin acts centrally to reduce endotoxemic lethality. Accordingly, activation of the vagal pathway and adenosine A2B receptors in the brain may be implicated in the ghrelin-induced increased survival. Since the efferent vagus nerve mediates anti-inflammatory mechanisms, we speculate that the vagal cholinergic anti-inflammatory pathway is implicated in the decreased septic lethality caused by brain ghrelin.

Impact of gut-peripheral nervous system axis on the development of diabetic neuropathy

Diabetes is a chronic metabolic disease caused by a reduction in the production and/or action of insulin, with consequent development of hyperglycemia. Diabetic patients, especially those who develop neuropathy, presented dysbiosis, with an increase in the proportion of pathogenic bacteria and a decrease in the butyrate-producing bacteria. Due to this dysbiosis, diabetic patients presented a weakness of the intestinal permeability barrier and high bacterial product translocation to the bloodstream, in parallel to a high circulating levels of pro-inflammatory cytokines such as TNF-α. In this context, we propose here that dysbiosis-induced increased systemic levels of bacterial products, like lipopolysaccharide (LPS), leads to an increase in the production of pro-inflammatory cytokines, including TNF-α, by Schwann cells and spinal cord of diabetics, being crucial for the development of neuropathy.

Activation of basal forebrain cholinergic neurons improves colonic hyperpermeability through the vagus nerve and adenosine A2B receptors in rats

Intestinal barrier dysfunction, a leaky gut, contributes to the pathophysiology of various diseases such as dementia and irritable bowel syndrome (IBS). We recently clarified that orexin, ghrelin, or adenosine A2B signaling in the brain improved leaky gut through the vagus nerve. The present study was performed to clarify whether basal forebrain cholinergic neurons (BFCNs) are implicated in the central regulation of intestinal barrier function. We activated BFCNs using benzyl quinolone carboxylic acid (BQCA), a positive muscarinic M1 allosteric modulator, and evaluated colonic permeability by quantifying the absorbed Evans blue in rat colonic tissue. Intracisternal (not intraperitoneal) injection of BQCA blocked the increased colonic permeability in response to lipopolysaccharide. Vagotomy blocked BQCA-induced improvement of colonic hyperpermeability. Intracisternally administered pirenzepine, a muscarinic M1 selective antagonist, prevented intestinal barrier function improvement by intravenously administered 2-deoxy-d-glucose, central vagal stimulant. Adenosine A2B receptor antagonist but not dopamine or opioid receptor antagonist prevented BQCA-induced blockade of colonic hyperpermeability. Additionally, intracisternal injection of pirenzepine blocked orexin- or butyrate-induced intestinal barrier function improvement. These results suggest that BFCNs improve leaky gut through adenosine A2B signaling and the vagal pathway. Furthermore, BFCNs mediate orexin- or butyrate-induced intestinal barrier function improvement. Since BFCNs play a role in cognitive function and a leaky gut is associated with dementia, the present finding may lead us to speculate that BFCNs are involved in the development of dementia by regulating intestinal barrier function.

Oxytocin acts centrally in the brain to improve leaky gut through the vagus nerve and a cannabinoid signaling in rats

Brain oxytocin plays a role in gastrointestinal functions. Among them, oxytocin acts centrally to modulate gastrointestinal motility and visceral sensation. Intestinal barrier function, one of important gut functions, is also regulated by the central nervous system. Little is, however, known about a role of central oxytocin in the regulation of intestinal barrier function. The present study was performed to clarify whether brain oxytocin is also involved in regulation of intestinal barrier function and its mechanism. Colonic permeability was estimated in vivo by quantifying the absorbed Evans blue in colonic tissue in rats. Intracisternal injection of oxytocin dose-dependently abolished increased colonic permeability in response to lipopolysaccharide while intraperitoneal injection of oxytocin at the same dose failed to block it. Either atropine or surgical vagotomy blocked the central oxytocin-induced improvement of colonic hyperpermeability. Cannabinoid 1 receptor antagonist but not adenosine or opioid receptor antagonist prevented the central oxytocin-induced blockade of colonic hyperpermeability. In addition, intracisternal injection of oxytocin receptor antagonist blocked the ghrelin- or orexin-induced improvement of intestinal barrier function. These results suggest that oxytocin acts centrally in the brain to reduce colonic hyperpermeability. The vagal cholinergic pathway or cannabinoid 1 receptor signaling plays a vital role in the process. The oxytocin-induced improvement of colonic hyperpermeability mediates the central ghrelin- or orexin-induced improvement of intestinal barrier function. We would therefore suggest that activation of central oxytocin signaling may be useful for leaky gut-related diseases such as irritable bowel syndrome and autism.

Effects of Commercial Probiotics on Colonic Sensitivity after Acute Mucosal Irritation

Gastrointestinal pathologies associated with abdominal pain, such as irritable bowel syndrome or inflammatory bowel disease, lack sufficiently effective treatments. In our study we have used a rat model of visceral pain (72 animals; n = 8–13 per experimental group) to analyze the consequences of intracolonic administration of the irritant acetic acid on visceral sensitivity, histology of the colonic wall, and inflammatory response. Moreover, we have studied the possible beneficial effects of a pretreatment with a commercial probiotic (Actimel^®). Contrary to expectations, acetic acid application (7 cm proximal to the anus) decreased the nociceptive response to intracolonic mechanical stimulation, with a slight increase in the histological damage of colonic mucosa. The intensity of these changes depended on the concentration (4% or 0.6%) and the time of application (30 or 60 min). Pretreatment with probiotics (by daily gavage, for 1 week) normalized the values obtained in the visceral sensitivity test but revealed an increase in the number of macrophages. These results suggest a possible activation of inhibitory mechanisms early after colonic irritation, not previously described (which need further experimental confirmation), and the ability of probiotics to normalize the effects of acetic acid. In addition, pretreatment with probiotics has a direct effect on immune functions, stimulating macrophagic activity.

The Effect of Probiotics on Intestinal Tight Junction Protein Expression in Animal Models: A Meta-Analysis

This study investigates the effect of probiotics supplementation on tight junction protein (TJP) expression in animal models by meta-analysis. We estimated the effect of probiotics administration in an animal inflammatory bowel disease model based on 47 collected articles from the databases, including Sciencedirect, Pubmed, Scopus, and Google Scholar. The effect size was analyzed with the standardized mean difference, and the heterogeneity of the effect sizes was assessed using Cochran’s Q test. To explain the heterogeneity, moderate analyses, such as meta-ANOVA and meta-regression, were performed using the mixed effects model. Finally, publication bias was assessed using Egger’s linear regression test. Among the evaluated items, zonula occluden (ZO)-1 showed the highest Q statistics value, and the effect sizes of all items were positive with high significance (p < 0.0001). The I2 value of all items reflected high heterogeneity (in excess of 80%). From the results of the meta-ANOVA, the factors of the heterogeneity found in the probiotics strains were investigated. Lactobacillus reuteri was identified as having the greatest effect on claudin and ZO-1 expression. The publication bias was detected by the Egger’s linear regression test, though it revealed that the occludin and ZO-1 had larger sample sizes than the claudin. In sum, this meta-analysis reveals that probiotics are effective at improving TJP expression in a gut environment of inflammatory bowel disease (IBD)-induced animal model. Our findings will interest IBD patients, as they suggest an area warranting future study.

Probiotics attenuate alcohol-induced muscle mechanical hyperalgesia: Preliminary observations

Alcohol use disorder (AUD) is a major health problem that causes millions of deaths annually world-wide. AUD is considered to be a chronic pain disorder, that is exacerbated by alcohol withdrawal, contributing to a high (∼80%) relapse rate. Chronic alcohol consumption has a marked impact on the gut microbiome, recognized to have a significant effect on chronic pain. We tested the hypothesis that modulating gut microbiota through feeding rats with probiotics can attenuate alcohol-induced muscle mechanical hyperalgesia. To test this hypothesis, rats were fed alcohol (6.5%, 4 days on 3 days off) for 3 weeks, which induced skeletal muscle mechanical hyperalgesia. Following alcohol feeding, at which time nociceptive thresholds were ∼37% below pre-alcohol levels, rats received probiotics in their drinking water, either Lactobacillus Rhamnosus GG (Culturelle) or De Simone Formulation (a mixture of 8 bacterial species) for 8 days; control rats received plain water to drink. When muscle mechanical nociceptive threshold was evaluated 1 day after beginning probiotic feeding, nociceptive thresholds were significantly higher than rats not receiving probiotics. Mechanical nociceptive thresholds continued to increase during probiotic feeding, with thresholds approaching pre-alcohol levels 5 days after starting probiotics; nociceptive threshold in rats not receiving probiotics remained low. After probiotics were removed from the drinking water, nociceptive thresholds gradually decreased in these two groups, although they remained higher than the group not treated with probiotic (21 days after ending alcohol feeding). These observations suggest that modification of gut microbiota through probiotic feeding has a marked effect on chronic alcohol-induced muscle mechanical hyperalgesia. Our results suggest that administration of probiotics to individuals with AUD may reduce pain associated with alcohol consumption and withdrawal, and may be a novel therapeutic intervention to reduce the high rate of relapse seen in individuals with AUD attempting to abstain from alcohol.

Post-inflammatory Abdominal Pain in Patients with Inflammatory Bowel Disease During Remission: A Comprehensive Review

Patients with inflammatory bowel disease often experience ongoing pain even after achieving mucosal healing (i.e., post-inflammatory pain). Factors related to the brain-gut axis, such as peripheral and central sensitization, altered sympatho-vagal balance, hypothalamic-pituitary-adrenal axis activation, and psychosocial factors, play a significant role in the development of post-inflammatory pain. A comprehensive study investigating the interaction between multiple predisposing factors, including clinical psycho-physiological phenotypes, molecular mechanisms, and multi-omics data, is still needed to fully understand the complex mechanism of post-inflammatory pain. Furthermore, current treatment options are limited and new treatments consistent with the underlying pathophysiology are needed to improve clinical outcomes.

Estrous cycle and ovariectomy-induced changes in visceral pain are microbiota-dependent

Visceral hypersensitivity (VH) is a hallmark of many functional gastrointestinal disorders including irritable bowel syndrome and is categorized by a dull, diffuse sensation of abdominal pain. Recently, the gut microbiota has been implicated in VH in male mice, but the effects in females have yet to be explored fully. To this end, we now show that somewhat surprisingly, female germ-free mice have similar visceral pain responses to colorectal distension (CRD) as their conventional controls. However, we show that although sensitivity to CRD is estrous cycle stage-dependent in conventional mice, it is not in germ-free mice. Further, ovariectomy (OVX) induced VH in conventional but not germ-free mice, and induced weight gain regardless of microbiota status. Finally, we show that estrogen-replacement ameliorated OVX-induced VH. Taken together, this study provides evidence for a major role of female sex hormones and the gut microbiota in sensation of visceral pain in females.

Centrally administered butyrate improves gut barrier function, visceral sensation and septic lethality in rats

Short chain fatty acids readily crosses the gut-blood and blood-brain barrier and acts centrally to influence neuronal signaling. We hypothesized that butyrate, a short-chain fatty acid produced by bacterial fermentation, in the central nervous system may play a role in the regulation of intestinal functions. Colonic permeability and visceral sensation was evaluated in rats. Septic lethality was evaluated in a sepsis model induced by subcutaneous administration of both lipopolysaccharide and colchicine. Intracisternal butyrate dose-dependently improved colonic hyperpermeability and visceral nociception. In contrast, subcutaneous injection of butyrate failed to change it. Intracisternal orexin 1 receptor antagonist or surgical vagotomy blocked the central butyrate-induced improvement of colonic hyperpermeability. The improvement of intestinal hyperpermeability by central butyrate or intracisternal orexin-A was blocked by cannabinoid 1 or 2 receptor antagonist. Intracisternal butyrate significantly improved survival period in septic rats. These results suggest that butyrate acts in the central nervous system to improve gut permeability and visceral nociception through cannabinoid signaling. Endogenous orexin in the brain may mediate the reduction of intestinal hyperpermeability by central butyrate through the vagus nerve. We would suggest that improvement of leaky gut by central butyrate may induce visceral antinociception and protection from septic lethality.

Effects of Novel Probiotics in a Murine Model of Irritable Bowel Syndrome

Background/Aims

Dysbiosis is an important factor in the pathogenesis of irritable bowel syndrome (IBS). Several studies have reported promising results using probiotics for the treatment of IBS. This study evaluated the efficacy of novel probiotics isolated from Kimchi, a Korean fermented food, and the feces of healthy Vietnamese people in a murine model of IBS.

Methods

Lactobacillus paracasei DK121 was isolated from Kimchi, and L. salivarius V4 and L. plantarum V7 were isolated from the feces of healthy Vietnamese people residing in Korea. Forty rats were allocated to receive one of the study strains, a mixture of the strains, or the vehicle. After 5 days of administration, the rats were restrained in a cage to induce IBS. The effects of the probiotics on IBS were analyzed by evaluating the stool weights and stool consistency scores.

Results

The primary outcome was analyzed upon the completion of a three-week experiment. The rats in the V7 group showed lower stool weights than those in the control group at week 2 (median: 1.10 [V7] vs. 2.35 [control], p=0.04, Mann-Whitney U-test) and week 3 (median: 1.10 [V7] vs. 2.80 [control], p=0.017). The rats in the DK121 (median: 2.00, p=0.007), V7 (median: 2.00, p=0.004), and mixture (median: 1.50, p=0.001) groups showed better stool consistency scores at week 2 than the control group (median: 3.00).

Conclusions

The novel probiotics have beneficial effects on defecation in a murine model of IBS. Human studies confirming the efficacy are warranted.

A role for gut microbiota in early-life stress-induced widespread muscle pain in the adult rat

Adult rats that experienced neonatal limited bedding (NLB), a form of early-life stress, experience persistent muscle mechanical hyperalgesia. Since there is a growing recognition that the gut microbiome regulates pain and nociception, and that early-life stress produces a long-lasting impact on the gut microbiome, we tested the hypothesis that persistent muscle hyperalgesia seen in adult NLB rats could be ameliorated by interventions that modify the gut microbiome. Adult NLB rats received probiotics, either Lactobacillus rhamnosus GG (10 billion CFU/150 ml) or De Simone Formulation (DSF) (112.5 billion CFU/150 ml mixture of 8 bacterial species), in their drinking water, or non-absorbable antibiotics, rifaximin or neomycin, admixed with cookie dough, to provide 50 mg/kg. Mechanical nociceptive threshold in the gastrocnemius muscle was evaluated before and at several time points after administration of probiotics or antibiotics. Adult NLB rats fed probiotics L. Rhamnosus or DSF, antibiotics, as well as rats fed non-absorbable antibiotics rifaximin or neomycin, had markedly attenuated muscle mechanical hyperalgesia. We hypothesize that persistent skeletal muscle hyperalgesia produced by NLB stress may be, at least in part, due to a contribution of the gut microbiome, and that modulation of gut microbiome using probiotics or non-absorbable antibiotics, may be novel therapeutic approaches for the treatment of chronic musculoskeletal pain.

Activation of central adenosine A2B receptors mediate brain ghrelin-induced improvement of intestinal barrier function through the vagus nerve in rats

Leaky gut that is a condition reflecting intestinal barrier dysfunction has been attracting attention for its relations with many diseases such as irritable bowel syndrome or Alzheimer dementia. We have recently demonstrated that ghrelin acts in the brain to improve leaky gut via the vagus nerve. In the present study, we tried to clarify the precise central mechanisms by which ghrelin improves intestinal barrier function through the vagus nerve. Colonic permeability was estimated in vivo by quantifying the absorbed Evans blue in colonic tissue in rats. Adenosine receptor antagonist, 1,3-dipropyl-8-cyclopentylxanthine (DPCPX), blocked the intracisternal ghrelin-induced improvement of intestinal hyperpermeability while dopamine, cannabinoid or opioid receptor antagonist failed to prevent it. Since DPCPX can block adenosine A1 and adenosine A2B receptors, we examined which subtype is involved in the mechanism. Intracisternal injection of adenosine A2B agonist but not adenosine A1 agonist improved colonic hyperpermeability, while peripheral injection of adenosine A2B agonist failed to improve it. Intracisternal adenosine A2B agonist-induced improvement of colonic hyperpermeability was blocked by vagotomy. Adenosine A2B specific antagonist, alloxazine blocked the ghrelin- or central vagal stimulation by 2-deoxy-d-glucose-induced improvement of intestinal hyperpermeability. These results suggest that activation of adenosine A2B receptors in the central nervous system is capable of improving intestinal barrier function through the vagal pathway, and the adenosine A2B receptors may mediate the ghrelin-induced improvement of leaky gut in a vagal dependent fashion. These findings may help us understand the pathophysiology in not only gastrointestinal diseases but also non-gastrointestinal diseases associated with the altered intestinal permeability.

The Role of Intestinal Microbiota and Mast Cell in a Rat Model of Visceral Hypersensitivity

Background/Aims

To explore the role of intestinal flora and mast cells in visceral hypersensitivity (VH).

Methods

The experimental animals were divided into 4 groups: control group, VH group, VH + VSL#3 group, and VH + ketotifen group. Stool samples were collected from each group (n = 3) for a further analysis using 16S ribosomal DNA gene sequence. Visceral sensitivity was evaluated by abdominal withdrawal reflex (AWR) score. Colon tissues of rats were obtained from each group. Mast cells were detected by toluidine blue staining. The degranulation of mast cells was assessed by transmission electron microscopy.

Results

VH rat model could successfully be induced by acetic acid enema combined with partial limb restraint method. Compared with rats in the control group, AWR score, number of mast cells, and degranulation of mast cells were increased in the VH rats, which could be reduced by administration of ketotifen or probiotic VSL#3. Clostridium sensu stricto 1 abundance was higher in the VH group compared to the control group, which could be restored by application of probiotic VSL#3.

Conclusions

Probiotic VSL#3 decreases visceral sensitivity in VH rats. The mechanism may be related to mast cell and intestinal flora. Change of Clostridium sensu stricto 1 abundance may be a basis for VH observed in irritable bowel syndrome and may be prevented by specific probiotic administration.

Ghrelin acts in the brain to block colonic hyperpermeability in response to lipopolysaccharide through the vagus nerve

Brain ghrelin plays a role in gastrointestinal functions. Among them, ghrelin acts centrally to stimulate gastrointestinal motility and induce visceral antinociception. Intestinal barrier function, one of important gastrointestinal functions, is also controlled by the central nervous system. Little is, however, known about a role of central ghrelin in regulation of intestinal permeability. The present study was performed to clarify whether brain ghrelin is also involved in regulation of intestinal barrier function and its mechanism. Colonic permeability was estimated in vivo by quantifying the absorbed Evans blue in colonic tissue in rats. Intracisternal injection of ghrelin dose-dependently abolished increased colonic permeability in response to LPS while intraperitoneal injection of ghrelin at the same dose or intracisternal injection of des-acyl-ghrelin failed to block it. Carbachol potently attenuated LPS-induced intestinal hyperpermeability, and atropine or bilateral subdiaphragmatic vagotomy prevented the improvement of intestinal hyperpermeability by central ghrelin. Intracisternal (D-Lys3)-GHRP-6, a selective ghrelin receptor antagonist, significantly blocked improvement of intestinal barrier function by intravenously administered 2-deoxy-d-glucose, central vagal stimulant. Intracisternal injection of orexin 1 receptor antagonist, SB-334867 blocked intracisternal ghrelin-induced improvement of colonic hyperpermeability. These results suggest that exogenously administered or endogenously released ghrelin acts centrally to improve a disturbed intestinal barrier function through orexinergic signaling and the vagal cholinergic pathway. Central ghrelin may be involved in the pathophysiology and be a novel therapeutic option in not only gastrointestinal diseases such as irritable bowel syndrome but also non-gastrointestinal diseases associated with the altered intestinal permeability.

Probiotic mixture VSL#3: An overview of basic and clinical studies in chronic diseases

Probiotics are known as “live microorganisms” and have been proven to have a health effect on hosts at the proper dose. Recently, a kind of probiotic mixture including eight live bacterial strains, VSL#3, has attracted considerable attention for its combined effect. VSL#3 is the only probiotic considered as a kind of medical food; it mainly participates in the regulation of the intestinal barrier function, including improving tight junction protein function, balancing intestinal microbial composition, regulating immune-related cytokine expression and so on. The objective of this review is to discuss the treatment action and mechanism for the administration of VSL#3 in chronic diseases of animals and humans (including children). We found that VSL#3 has a therapeutic or preventive effect in various systemic diseases per a large number of studies, including digestive systemic diseases (gastrointestinal diseases and hepatic diseases), obesity and diabetes, allergic diseases, nervous systemic diseases, atherosclerosis, bone diseases, and female reproductive systemic diseases.

The Microbiota-Gut-Brain Axis

The importance of the gut-brain axis in maintaining homeostasis has long been appreciated. However, the past 15 yr have seen the emergence of the microbiota (the trillions of microorganisms within and on our bodies) as one of the key regulators of gut-brain function and has led to the appreciation of the importance of a distinct microbiota-gut-brain axis. This axis is gaining ever more traction in fields investigating the biological and physiological basis of psychiatric, neurodevelopmental, age-related, and neurodegenerative disorders. The microbiota and the brain communicate with each other via various routes including the immune system, tryptophan metabolism, the vagus nerve and the enteric nervous system, involving microbial metabolites such as short-chain fatty acids, branched chain amino acids, and peptidoglycans. Many factors can influence microbiota composition in early life, including infection, mode of birth delivery, use of antibiotic medications, the nature of nutritional provision, environmental stressors, and host genetics. At the other extreme of life, microbial diversity diminishes with aging. Stress, in particular, can significantly impact the microbiota-gut-brain axis at all stages of life. Much recent work has implicated the gut microbiota in many conditions including autism, anxiety, obesity, schizophrenia, Parkinson’s disease, and Alzheimer’s disease. Animal models have been paramount in linking the regulation of fundamental neural processes, such as neurogenesis and myelination, to microbiome activation of microglia. Moreover, translational human studies are ongoing and will greatly enhance the field. Future studies will focus on understanding the mechanisms underlying the microbiota-gut-brain axis and attempt to elucidate microbial-based intervention and therapeutic strategies for neuropsychiatric disorders.

Microbiota: a novel regulator of pain

Among the various regulators of the nervous system, the gut microbiota has been recently described to have the potential to modulate neuronal cells activation. While bacteria-derived products can induce aversive responses and influence pain perception, recent work suggests that "abnormal" microbiota is associated with neurological diseases such as Alzheimer's, Parkinson's disease or autism spectrum disorder (ASD). Here we review how the gut microbiota modulates afferent sensory neurons function and pain, highlighting the role of the microbiota/gut/brain axis in the control of behaviors and neurological diseases. We outline the changes in gut microbiota, known as dysbiosis, and their influence on painful gastrointestinal disorders. Furthermore, both direct host/microbiota interaction that implicates activation of "pain-sensing" neurons by metabolites, or indirect communication via immune activation is discussed. Finally, treatment options targeting the gut microbiota, including pre- or probiotics, will be proposed. Further studies on microbiota/nervous system interaction should lead to the identification of novel microbial ligands and host receptor-targeted drugs, which could ultimately improve chronic pain management and well-being.

Bacterial modulation of visceral sensation: mediators and mechanisms

The potential role of the intestinal microbiota in modulating visceral pain has received increasing attention during recent years. This has led to the identification of signaling pathways that have been implicated in communication between gut bacteria and peripheral pain pathways. In addition to the well-characterized impact of the microbiota on the immune system, which in turn affects nociceptor excitability, bacteria can modulate visceral afferent pathways by effects on enterocytes, enteroendocrine cells, and the neurons themselves. Proteases produced by bacteria, or by host cells in response to bacteria, can increase or decrease the excitability of nociceptive dorsal root ganglion (DRG) neurons depending on the receptor activated. Short-chain fatty acids generated by colonic bacteria are involved in gut-brain communication, and intracolonic short-chain fatty acids have pronociceptive effects in rodents but may be antinociceptive in humans. Gut bacteria modulate the synthesis and release of enteroendocrine cell mediators, including serotonin and glucagon-like peptide-1, which activate extrinsic afferent neurons. Deciphering the complex interactions between visceral afferent neurons and the gut microbiota may lead to the development of improved probiotic therapies for visceral pain.

Mechanisms of Probiotic VSL#3 in a Rat Model of Visceral Hypersensitivity Involves the Mast Cell-PAR2-TRPV1 Pathway

BACKGROUND

Mast cells (MCs), PAR2 and TRPV1, play a key role in the regulation of visceral pain. Several studies have found that probiotics regulate visceral sensitivity.

AIMS

The purpose of the current study was to explore the role of MC-PAR2-TRPV1 in VH and the mechanism of VSL#3 in a rat model of VH.

METHODS

A total of 64 rats were randomly divided into eight groups: Control VH, VH + ketotifen, VH + FSLLRY-NH2, VH + SB366791, VH + VSL#3, VH + VSL#3 + capsaicin, and VH + VSL#3 + SLIGRL-NH2. The rat model of VH was induced by acetic acid enema and the partial limb restraint method. VH was assessed by the abdominal withdrawal reflex score. MCs in colonic tissue were detected by the toluidine blue staining assay. The expression of PAR2 and TRPV1 in DRGs (L6-S1) was measured by immunohistochemistry and Western blotting.

RESULTS

The established VH was abolished by treatment with ketotifen, a mast cell stabilizer FSLLRY-NH2, a PAR2 antagonist SB366791 a TRPV1 antagonist, and probiotic VSL#3 in rats. The administration of ketotifen or probiotic VSL#3 caused a decrease in mast cell number in the colon and decreased PAR2 and TRPV1 expression in DRGs. Intrathecal injection of FSLLRY-NH2 or SB366791 caused decreased expression of PAR2 and/or TRPV1 in DRGs in VH rats. SLIGRL-NH2, a PAR2 agonist, and capsaicin, a TRPV1 agonist, blocked the effects of probiotic VSL#3.

CONCLUSIONS

The probiotic VSL#3 decreases VH in rat model of VH. The mechanism may be related with the mast cell-PAR2-TRPV1 signaling pathway.

Visceral pain: gut microbiota, a new hope?

BACKGROUND

Visceral pain is a complex and heterogeneous disorder, which can range from the mild discomfort of indigestion to the agonizing pain of renal colic. Regulation of visceral pain involves the spinal cord as well as higher order brain structures. Recent findings have linked the microbiota to gastrointestinal disorders characterized by abdominal pain suggesting the ability of microbes to modulate visceral hypersensitivity and nociception to pain.

MAIN BODY

In this review we describe the neuroanatomical basis of visceral pain signaling and the existing evidence of its manipulation exerted by the gut microbiota. We included an updated overview of the potential therapeutic effects of dietary intervention, specifically probiotics and prebiotics, in alleviating hypersensitivity to visceral pain stimuli.

CONCLUSIONS

The gut microbiota dramatically impacts normal visceral pain sensation and affects the mechanisms mediating visceral nociception. Furthermore, manipulation of the gut microbiota using prebiotics and probiotics plays a potential role in the regulation of visceral pain disorders.

A prospective, interventional, randomized, double-blind, placebo-controlled clinical study to evaluate the efficacy and safety of Bacillus coagulans LBSC in the treatment of acute diarrhea with abdominal discomfort

PURPOSE

Increasing resistance towards antibiotics has augmented the use of probiotics for the treatment of diarrhea and associated symptoms. Probiotics are active microorganisms which exert some health benefits when consumed in the right amount. This randomized, double-blind, placebo-controlled clinical trial was conducted on 60 "intention to treat" subjects to evaluate the safety and efficacy of probiotic preparation Lactic Acid Bacillus (LAB containing active ingredient Bacillus coagulans strain LBSC) for the treatment of acute diarrhea with abdominal discomfort.

METHODS

The Test-A arm (n = 30) was on B. coagulans LBSC [2 billion/g] and Placebo-B arm (n = 30) was on the carrier. The primary outcomes were the time to last unformed stool (TTLUS), number of unformed stools, change in severity of abdominal pain, time to complete resolution of abdominal discomfort, complete remission of diarrhea, and quality of life (QoL). The secondary outcomes were physical examination and vitals, hematological analysis, and assessment of reported adverse events (AEs) or serious adverse events (SAEs).

RESULTS

Trial data showed that the LAB was well-tolerated by participants at the dose provided. The LAB was effective in recovering from acute diarrhea with abdominal pain and discomforts and exhibited improved cluster of QoL. No AEs or SAEs were reported during the trial.

CONCLUSIONS

It is evident that the test drug, i.e., LAB (B. coagulans strain LBSC) is safe and effective for improving the pathophysiological conditions related to acute diarrhea and abdominal discomfort evaluated through stage-II clinical trial.

The Protective Effect of Melissa officinalis L. in Visceral Hypersensitivity in Rat Using 2 Models of Acid-induced Colitis and Stress-induced Irritable Bowel Syndrome: A Possible Role of Nitric Oxide Pathway

Background/Aims

The aim of present study is to estimate the effects of Melissa officinalis L. (MO) on visceral hypersensitivity (VH), defecation pattern and biochemical factors in 2 experimental models of irritable bowel syndrome (IBS) and the possible role of nitric oxide.

Methods

Two individual models of IBS were induced in male Wistar-albino rats. In the acetic acid model, the animals were exposed to rectal distension and abdominal withdrawal reflex, and the defecation patterns were determined. In the restraint stress model, the levels of TNF-α, myeloperoxidase, lipid peroxidation, and antioxidant powers were determined in the (removed) colon. Rats had been treated with MO, L-NG-nitroarginine methyl ester (L-NAME), aminoguanidine (AG), MO + AG, or MO + L-NAME in the mentioned experimental models.

Results

Hypersensitive response to rectal distension and more stool defecation in control rats have been observed in comparison to shams. MO-300 significantly reduced VH and defecation frequency in comparison to controls. VH and defecation pattern did not show significant change in AG + MO and L-NAME + MO groups compared to controls. Also, significant reduction in TNF-α, myeloperoxidase, thiobarbituric acid reactive substances (TBARS), and an increase in antioxidant power in MO-300 group was recorded compared to controls. AG + MO and L-NAME + MO groups showed a reverse pattern compared to MO-300 group.

Conclusions

MO can ameliorate IBS by modulating VH and defecation patterns. Antioxidant and anti-inflammatory properties along with its effect on the nitrergic pathway seem to play important roles in its pharmacological activity.

Glucagon-like peptide-1 analog, liraglutide, improves visceral sensation and gut permeability in rats

BACKGROUND AND AIM

A glucagon-like peptide-1 analog, liraglutide, has been reported to block inflammatory somatic pain. We hypothesized that liraglutide attenuates lipopolysaccharide (LPS)-induced and repeated water avoidance stress (WAS)-induced visceral hypersensitivity and tested the hypothesis in rats.

METHODS

The threshold of the visceromotor response induced by colonic balloon distention was measured to assess visceral sensation. Colonic permeability was determined in vivo by quantifying the absorbed Evans blue spectrophotometrically, which was instilled in the proximal colon for 15 min. The interleukin-6 level in colonic mucosa was also quantified using ELISA.

RESULTS

Subcutaneously injected LPS (1 mg/kg) reduced the visceromotor response threshold after 3 h. Liraglutide (300 μg/kg subcutaneously) at 15 h and 30 min before injecting LPS eliminated LPS-induced allodynia. It also blocked the allodynia induced by repeated water avoidance stress for 1 h for three consecutive days. Neither vagotomy nor naloxone altered the antinociceptive effect of liraglutide, but N^G -nitro-L-arginine methyl ester, a nitric oxide synthesis inhibitor, blocked it. LPS increased colonic permeability and the interleukin-6 level, and the analog significantly inhibited these responses.

CONCLUSIONS

This study suggests that liraglutide blocked LPS-induced visceral allodynia, which may be a nitric oxide-dependent response, and was probably mediated by inhibiting pro-inflammatory cytokine production and attenuating the increased gut permeability. Because the LPS-cytokine system is considered to contribute to altered visceral sensation in irritable bowel syndrome, these results indicate the possibility that liraglutide can be useful for treating this disease.

Wuji Wan Formula Ameliorates Diarrhea and Disordered Colonic Motility in Post-inflammation Irritable Bowel Syndrome Rats by Modulating the Gut Microbiota

Emerging evidence suggests that gut microbiota contribute to the treatment of post-inflammatory irritable bowel syndrome (PI-IBS). Our previous studies have demonstrated that a Chinese formula, Wuji Wan, has the ability to mitigate abdominal pain and diarrhea in PI-IBS rats. However, little is known about the underlying mechanism and whether the gut microbiota mediate the effect of Wuji Wan on PI-IBS. Thus, the aim of this study was to determine whether Wuji Wan mitigated PI-IBS by modifying the gut microbiota. PI-IBS was induced in Sprague-Dawley rats by enema using 4% acetic acid and restraint stress. Rats were fed water, Wuji Wan extract (630 mg/kg) or pinaverium bromide (13.5 mg/kg). Our data showed that Wuji Wan effectively ameliorated abdominal pain, colonic motility abnormality and visceral hypersensitivity. Analysis of the fecal microbiota showed that Wuji Wan could reverse the reduction in richness of the gut microbiota and significantly increase the relative abundances of Akkermansia, Bacteroides, and Parasutterella; however, Lactobacillus and Prevotella were markedly decreased in the PI-IBS rats. Moreover, Wuji Wan promoted goblet cell proliferation in the colonic mucosa by increasing the release of mucin, up-regulating the distribution of tight junction proteins Occludin and ZO-1 and down-regulating the expression of MLCK in colonic epithelial cells. These findings suggest that Wuji Wan may remit IBS by modulating the gut microbiota and stabilizing the gut mucosal barrier, indicating that the use of a classical formula of Traditional Chinese Medicine (TCM) that exhibits a prebiotic effect may be a promising strategy for PI-IBS treatment.

Critical Evaluation of Animal Models of Gastrointestinal Disorders

Preclinical research remains an important tool for discovery and validation of novel therapeutics for gastrointestinal disorders. While in vitro assays can be used to verify receptor-ligand interactions and test for structural activity of new compounds, only whole-animal studies can demonstrate drug efficacy within the gastrointestinal system. Most major gastrointestinal disorders have been modeled in animals; however the translational relevance of each model is not equal. The purpose of this chapter is to provide a critical evaluation of common animal models that are being used to develop pharmaceuticals for gastrointestinal disorders. For brevity, the models are presented for upper gastrointestinal disorders involving the esophagus, stomach, and small intestine and lower gastrointestinal disorders that focus on the colon. Particular emphasis is used to explain the face and construct validity of each model, and the limitations of each model, including data interpretation, are highlighted. This chapter does not evaluate models that rely on surgical or other non-pharmacological interventions for treatment.

Isomalto-oligosaccharides ameliorate visceral hyperalgesia with repair damage of ileal epithelial ultrastructure in rats

Background

Treatment of irritable bowel syndrome (IBS) with probiotics has achieved effectiveness to a certain extent. Whether prebiotics will work is still unclear. This study aimed to investigate the therapeutic effects of the prebiotic isomalto-oligosaccharides (IMO) on visceral hypersensitivity (VHS) in rats and to explore potential mechanism.

Methods

Water avoidance stress (WAS) was used to induce VHS in rats. The score for the abdominal withdrawal reflex (AWR) was determined while colorectal distension and compared between VHS group and control group in order to validate VHS preparation. Rats with VHS were then divided into an IMO-treated group (intragastric 5% IMO, 2 mL/d, 14 days) and a water-control group (intragastric water). After treatment, AWR score and intestinal transit rate (ITR) were determined, stool culture was performed, the ultrastructure of the ileum epithelium was observed with scanning electron microscopy (SEM), and serum cytokines were measured.

Results

WAS significantly increased AWR score responding to colorectal distension, and lowered the pain threshold. IMO treatment improved VHS with a reduction in AWR score on graded colorectal distension and an increase in pain threshold. SEM showed damages on the ileal epithelial ultrastructure in VHS rats, which was attenuated by IMO treatment. ITR, fecal microbiota and serum cytokine levels were comparable among control group, water-control group, and IMO-treated rats.

Conclusion

In this randomized placebo-controlled study, the results showed that IMO ameliorated WAS-induced visceral hyperalgesia in rats, this effect may be attributed to the repair of damages on intestinal epithelial ultrastructure.

The Role of the Gastrointestinal Microbiota in Visceral Pain

A growing body of preclinical and clinical evidence supports a relationship between the complexity and diversity of the microorganisms that inhabit our gut (human gastrointestinal microbiota) and health status. Under normal homeostatic conditions this microbial population helps maintain intestinal peristalsis, mucosal integrity, pH balance, immune priming and protection against invading pathogens. Furthermore, these microbes can influence centrally regulated emotional behaviour through mechanisms including microbially derived bioactive molecules (amino acid metabolites, short-chain fatty acids, neuropeptides and neurotransmitters), mucosal immune and enteroendocrine cell activation, as well as vagal nerve stimulation.The microbiota-gut-brain axis comprises a dynamic matrix of tissues and organs including the brain, autonomic nervous system, glands, gut, immune cells and gastrointestinal microbiota that communicate in a complex multidirectional manner to maintain homeostasis and resist perturbation to the system. Changes to the microbial environment, as a consequence of illness, stress or injury, can lead to a broad spectrum of physiological and behavioural effects locally including a decrease in gut barrier integrity, altered gut motility, inflammatory mediator release as well as nociceptive and distension receptor sensitisation. Centrally mediated events including hypothalamic-pituitary-adrenal (HPA) axis, neuroinflammatory events and neurotransmitter systems are concomitantly altered. Thus, both central and peripheral pathways associated with pain manifestation and perception are altered as a consequence of the microbiota-gut-brain axis imbalance.In this chapter the involvement of the gastrointestinal microbiota in visceral pain is reviewed. We focus on the anatomical and physiological nodes whereby microbiota may be mediating pain response, and address the potential for manipulating gastrointestinal microbiota as a therapeutic target for visceral pain.

Altered gastrointestinal microbiota in irritable bowel syndrome and its modification by diet: probiotics, prebiotics and the low FODMAP diet

Irritable bowel syndrome (IBS) is a functional bowel disorder characterised by abdominal pain or discomfort with disordered defecation. This review describes the role of the gastrointestinal (GI) microbiota in the pathogenesis of IBS and how dietary strategies to manage symptoms impact on the microbial community. Evidence suggests a dysbiosis of the luminal and mucosal colonic microbiota in IBS, frequently characterised by a reduction in species of Bifidobacteria which has been associated with worse symptom profile. Probiotic supplementation trials suggest intentional modulation of the GI microbiota may be effective in treating IBS. A smaller number of prebiotic supplementation studies have also demonstrated effectiveness in IBS whilst increasing Bifidobacteria. In contrast, a novel method of managing IBS symptoms is the restriction of short-chain fermentable carbohydrates (low fermentable oligosaccharides, disaccharides, monosaccharides and polyols (FODMAP) diet). Studies consistently demonstrate clinical effectiveness of the low FODMAP diet in patients with IBS. However, one unintentional consequence of this dietary intervention is its impact on the microbiota. This leads to an interesting paradox; namely, increasing luminal Bifidobacteria through probiotic supplementation is associated with a reduction in IBS symptoms while in direct conflict to this, the low FODMAP diet has clinical efficacy but markedly reduces luminal Bifidobacteria concentration. Given the multifactorial aetiology of IBS, the heterogeneity of symptoms and the complex and diverse nature of the microbiome, it is probable that both interventions are effective in patient subgroups. However combination treatment has never been explored and as such, presents an exciting opportunity for optimising clinical management, whilst preventing potentially deleterious effects on the GI microbiota.

Stress and the Microbiota-Gut-Brain Axis in Visceral Pain: Relevance to Irritable Bowel Syndrome

Visceral pain is a global term used to describe pain originating from the internal organs of the body, which affects a significant proportion of the population and is a common feature of functional gastrointestinal disorders (FGIDs) such as irritable bowel syndrome (IBS). While IBS is multifactorial, with no single etiology to completely explain the disorder, many patients also experience comorbid behavioral disorders, such as anxiety or depression; thus, IBS is described as a disorder of the gut-brain axis. Stress is implicated in the development and exacerbation of visceral pain disorders. Chronic stress can modify central pain circuitry, as well as change motility and permeability throughout the gastrointestinal (GI) tract. More recently, the role of the gut microbiota in the bidirectional communication along the gut-brain axis, and subsequent changes in behavior, has emerged. Thus, stress and the gut microbiota can interact through complementary or opposing factors to influence visceral nociceptive behaviors. This review will highlight the evidence by which stress and the gut microbiota interact in the regulation of visceral nociception. We will focus on the influence of stress on the microbiota and the mechanisms by which microbiota can affect the stress response and behavioral outcomes with an emphasis on visceral pain.

Probiotic for irritable bowel syndrome in pediatric patients: a randomized controlled clinical trial

Background:

Irritable bowel syndrome (IBS) is a common gastrointestinal disorder in children. Recently, probiotics have been suggested as a treatment option for gastrointestinal disorders. The most effective species and the most appropriate doses are still unknown.

Objective:

The aim of this study was to assess the effects of Lactobacillus GG (LGG) for treating IBS in pediatric patients.

Methods:

In a controlled, double blind, randomized trial, patients with IBS diagnosed by Rome III criteria from August 2012 to September 2012 at Dr. Sheikh Hospital, Mashhad University of Medical Sciences, Iran, were assigned to one of two groups, i.e., intervention and control groups. For four weeks, the intervention group received a probiotic in capsule form that contained LGG at a concentration of 1×10¹⁰ cfu/ml bacteria. For the same period, the control group received a placebo capsule that had the same shape and color but only contained inulin, which also was present in the LGG capsules. The primary outcome was any change in the severity of the patients’ pain, and we used a five-point Likert scale to evaluate the severity of their pain. Secondary outcomes were ghanges of the functional scale, stool patterns, and associated problems.

Results:

Fifty-two patients participated in the study, and 26 patients were assigned randomly to each of the two groups. The severity of the patients’ pain decreased significantly in the intervention group after one, two, three, and four weeks of treatment, as indicated by P-values of 0.01, 0.00, 0.00, and 0.00, respectively. Also, there was significant improvement in the functional scale after two weeks of treatment (P-value ≤ 0.00).

Conclusion:

Lactobacillus GG at a concentration of 1×10¹⁰ cfu/ml for a period of four weeks can lessen the severity of the patients’ pain and improve the functional scale in patients with irritable bowel syndrome. Probiotics can have therapeutic effects for IBS patients.

Animal models of gastrointestinal and liver diseases. Animal models of visceral pain: pathophysiology, translational relevance, and challenges

Visceral pain describes pain emanating from the thoracic, pelvic, or abdominal organs. In contrast to somatic pain, visceral pain is generally vague, poorly localized, and characterized by hypersensitivity to a stimulus such as organ distension. Animal models have played a pivotal role in our understanding of the mechanisms underlying the pathophysiology of visceral pain. This review focuses on animal models of visceral pain and their translational relevance. In addition, the challenges of using animal models to develop novel therapeutic approaches to treat visceral pain will be discussed.

Is fecal microbiota transplantation (FMT) an effective treatment for patients with functional gastrointestinal disorders (FGID)?

BACKGROUND

Despite its high prevalence and significant effect on quality of life, the etiology of functional gastrointestinal disorders (FGID), and specifically irritable bowel syndrome (IBS), has yet to be fully elucidated. While alterations in immunity, motility, and the brain-gut axis have been implicated in disease pathogenesis, the intestinal microbiota are increasingly being shown to play a role and numerous studies have demonstrated significant differences from normal in the intestinal flora of patients with FGID, and between types of FGID. Fecal microbiota transplantation (FMT) is a curative therapy for Clostridium difficile infection (CDI), a disease hallmarked by intestinal dysbiosis, and FMT is now being explored as a means to also restore intestinal homeostasis in FGID.

PURPOSE

This review aims to investigate the role of intestinal microbiota in the pathogenesis of FGID, the implications of FMT for the treatment of FGID, and the challenges encountered in measuring response to a specific intervention in patients with FGID.

Stress-induced visceral pain: toward animal models of irritable-bowel syndrome and associated comorbidities

Visceral pain is a global term used to describe pain originating from the internal organs, which is distinct from somatic pain. It is a hallmark of functional gastrointestinal disorders such as irritable-bowel syndrome (IBS). Currently, the treatment strategies targeting visceral pain are unsatisfactory, with development of novel therapeutics hindered by a lack of detailed knowledge of the underlying mechanisms. Stress has long been implicated in the pathophysiology of visceral pain in both preclinical and clinical studies. Here, we discuss the complex etiology of visceral pain reviewing our current understanding in the context of the role of stress, gender, gut microbiota alterations, and immune functioning. Furthermore, we review the role of glutamate, GABA, and epigenetic mechanisms as possible therapeutic strategies for the treatment of visceral pain for which there is an unmet medical need. Moreover, we discuss the most widely described rodent models used to model visceral pain in the preclinical setting. The theory behind, and application of, animal models is key for both the understanding of underlying mechanisms and design of future therapeutic interventions. Taken together, it is apparent that stress-induced visceral pain and its psychiatric comorbidities, as typified by IBS, has a multifaceted etiology. Moreover, treatment strategies still lag far behind when compared to other pain modalities. The development of novel, effective, and specific therapeutics for the treatment of visceral pain has never been more pertinent.

Effect of berberine on visceral hypersensitivity in a rat model of irritable bowel syndrome

AIM: To evaluate the effect of berberine (BBR) on visceral hypersensitivity in a rat model of irritable bowel syndrome (IBS) and explore the underlying mechanism.

METHODS: IBS was induced in rats by maternal separation. After berberine intervention, visceral sensitivity was evaluated using the score of abdominal withdrawal reflex (AWR). Defecation parameters were evaluated by restraint stress procedure. The levels of 5-hydroxytryptamine (5-HT) in the colon and interleukin-6 (IL-6) in plasma were determined by ELISA.

RESULTS: Compared with normal control rats, the score of AWR, defecation parameters, and levels of 5-HT and IL-6 were significantly increased in rats treated with normal saline, pinaverium or BBR (P < 0.05); however, these indexes were significantly lower in the pinaverium and BBR groups than in the normal saline group (P < 0.05), and in the BBR group than in the pinaverium group (P < 0.05).

CONCLUSION: BBR has a protective effect on visceral hypersensitivity in rats with IBS via mechanisms possibly related to IL-6 and 5-HT.

Antinociceptive and antidiarrheal effects of pioglitazone in a rat model of diarrhoea-predominant irritable bowel syndrome: role of nitric oxide

Irritable bowel syndrome (IBS) is a prevalent disease characterized by abdominal pain and abnormal bowel habits. Pioglitazone is a peroxisome proliferator-activated receptor (PPAR) γ agonist and, although it is mostly used as an antidiabetic agent, it has been reported to have analgesic effects. Nitric oxide (NO), a gaseous molecule that mediates many of the effects of pioglitazone, has been implicated in the pathophysiology of IBS. The aim of the present study was to investigate the effects of pioglitazone on symptoms in a rat model of diarrhoea-predominant IBS (D-IBS).and to determine the role of NO in these effects. Diarrhoea-predominant IBS was induced by intracolonic instillation of acetic acid. Pioglitazone (2 mg/kg, i.p.) was administered on Days 7, 9 and 11 after acetic acid instillation. To investigate the mechanism involved in pioglitazone action, rats were also administered either the PPARγ antagonist GW9662 (3 mg/kg, i.p.), the NO synthase (NOS) inhibitor N(G) -nitro-l-arginine methyl ester (l-NAME; 10 mg/kg, i.p.) or the NO precursor l-arginine (250 mg/kg, i.p.) along with pioglitazone. Visceral hypersensitivity, nociceptive thresholds, defecation frequency, stool form, serum and colon NO production and inducible (i) NOS activity were assessed 1 h after the final injection of pioglitazone or dimethylsulphoxide (used as the vehicle). Pioglitazone reduced visceral hypersensitivity and defecation frequency, increased nociceptive thresholds, NO production and iNOS activity and shifted stool form towards hard stools in D-IBS rats. These effects of pioglitazone were significantly reversed by l-NAME, but not GW9662. l-Arginine augmented the effects of pioglitazone. In conclusion, pioglitazone alleviates symptoms in a rat model of D-IBS through an NO-dependent mechanism.

The microbiota-gut-brain axis in functional gastrointestinal disorders

Functional gastrointestinal disorders (FGIDs) are highly prevalent and pose a significant burden on health care and society, and impact patients' quality of life. FGIDs comprise a heterogeneous group of disorders, with unclear underlying pathophysiology. They are considered to result from the interaction of altered gut physiology and psychological factors via the gut-brain axis, where brain and gut symptoms are reciprocally influencing each other's expression. Intestinal microbiota, as a part of the gut-brain axis, plays a central role in FGIDs. Patients with Irritable Bowel Syndrome, a prototype of FGIDs, display altered composition of the gut microbiota compared with healthy controls and benefit, at the gastrointestinal and psychological levels, from the use of probiotics and antibiotics. This review aims to recapitulate the available literature on FGIDs and microbiota-gut-brain axis.

Antinociceptive effect of berberine on visceral hypersensitivity in rats

AIM: To assess the protective effect of berberine administration and the role of nitric oxide (NO) in visceral hypersensitivity.

METHODS: Fifty male Sprague-Dawley rats were randomly assigned to five groups. An inflammatory bowel disease model was induced in rats by intracolonic instillation of 1 mL 4% acetic acid at 8 cm proximal to the anus for 30 s and restraint stress. After subsidence of inflammation on day 7 of the experiment, the rats were subjected to rectal distension, performed by a balloon (6-Fr, 2 mm external diameter, disposable silicon balloon-urethral catheter for pediatric use) which was rapidly inflated with increasing volumes of prewarmed (37 °C) water (0.1, 0.2, 0.3, 0.4, 0.6, 0.8 and 1 mL) for 30 s at four-minute intervals, and then the abdominal withdrawal reflex (AWR) and the level of fecal output were measured, respectively. AWR scores either 0, 1, 2, 3 or 4 were obtained by blinded observers. Rats had been pretreated with berberine or aminoguanidine (NO synthetase inhibitor) or berberine + aminoguanidine before measurement.

RESULTS: The rats in the placebo group showed a hypersensitive response to rectal distension (2.69 ± 0.08 vs 1.52 ± 0.08, P = 0.000) and defecated more frequently than those in the control group (5.0 ± 0.16 vs 0.44 ± 0.16, P = 0.000). Comparing the berberine with placebo group, the AWR scores were reduced for all distension volumes and were significant at 0.2-1 mL (1.90 ± 0.08 vs 2.69 ± 0.08, P = 0.000), while the numbers of hard pellets, soft pellets, formless stools, and total fecal output in the placebo group were significantly larger than in the berberine group (5.0 ± 0.16 vs 2.56 ± 0.16, P = 0.000). Administration of aminoguanidine or berberine + aminoguanidine before VH score measurement reversed the antinociceptive effect of berberine (2.52 ± 0.08 vs 1.90 ± 0.08, P = 0.000; 2.50 ± 0.08 vs 1.90 ± 0.08, P = 0.000). The numbers of hard pellets, soft pellets, formless stool, and total of fecal output in aminoguanidine group were significantly larger than the corresponding values in control group, berberine group, and berberine + aminoguanidine group (4.81 ± 0.16 vs 0.44 ± 0.16, P = 0.000; 4.81 ± 0.16 vs 2.56 ± 0.16, P = 0.000; 4.81 ± 0.16 vs 3.75 ± 0.16, P = 0.000). The berberine and berberine + aminoguanidine groups showed reduced defecation, but aminoguanidine alone did not reduce defecation (2.56 ± 0.16 vs 4.81 ± 0.16, P = 0.000; 3.75 ± 0.16 vs 4.81 ± 0.16, P = 0.000).

CONCLUSION: Berberine had an antinociceptive effect on visceral hypersensitivity, and NO might play a role in this effect.

Consumption of fermented milk product with probiotic modulates brain activity

BACKGROUND & AIMS

Changes in gut microbiota have been reported to alter signaling mechanisms, emotional behavior, and visceral nociceptive reflexes in rodents. However, alteration of the intestinal microbiota with antibiotics or probiotics has not been shown to produce these changes in humans. We investigated whether consumption of a fermented milk product with probiotic (FMPP) for 4 weeks by healthy women altered brain intrinsic connectivity or responses to emotional attention tasks.

METHODS

Healthy women with no gastrointestinal or psychiatric symptoms were randomly assigned to groups given FMPP (n = 12), a nonfermented milk product (n = 11, controls), or no intervention (n = 13) twice daily for 4 weeks. The FMPP contained Bifidobacterium animalis subsp Lactis, Streptococcus thermophiles, Lactobacillus bulgaricus, and Lactococcus lactis subsp Lactis. Participants underwent functional magnetic resonance imaging before and after the intervention to measure brain response to an emotional faces attention task and resting brain activity. Multivariate and region of interest analyses were performed.

RESULTS

FMPP intake was associated with reduced task-related response of a distributed functional network (49% cross-block covariance; P = .004) containing affective, viscerosensory, and somatosensory cortices. Alterations in intrinsic activity of resting brain indicated that ingestion of FMPP was associated with changes in midbrain connectivity, which could explain the observed differences in activity during the task.

CONCLUSIONS

Four-week intake of an FMPP by healthy women affected activity of brain regions that control central processing of emotion and sensation.

Probiotics can alleviate cardiopulmonary bypass-induced intestinal mucosa damage in rats

BACKGROUND

Cardiopulmonary bypass (CPB) is commonly applied to support circulation during heart surgery but frequently causes adverse effects.

AIMS

The purpose of this study was to examine the potential of probiotics to improve small intestinal mucosa barrier function after CPB.

METHODS

Twenty-four adult male SD rats were randomly divided into sham-operated (S), CPB-operated (CPB), and probiotic-fed (Y) groups. Diamine oxidase (DAO) activity and concentrations of D-lactic acid, endotoxin, TNFα, and IL-6 were measured in portal vein blood. IgA concentrations were determined in plasma and the small intestine. Vena cava blood and tissue samples were used to monitor bacterial growth. Intestinal epithelial ultrastructure was analyzed by transmission electron microscopy (TEM). Occludin and ZO-1 expression levels in the intestinal epithelium were detected by western blotting and immunohistochemistry, respectively.

RESULTS

D-lactic acid, endotoxin, TNFα and IL-6 levels, DAO activity, and bacterial translocation rate were increased (P < 0.05) in CPB and Y compared to the S group. The above indices were relatively lower (P < 0.05) in Y than in CPB. Plasma and small intestinal IgA levels were significantly lower (P < 0.05) in CPB, while in Y they were significantly increased (P < 0.05) but lower than in S (P < 0.05). These results were confirmed by TEM. Consistently, occludin and ZO-1 expression levels were significantly higher in Y than in CPB (P < 0.05) but still lower compared to S (P < 0.05).

CONCLUSION

Pre-administration of probiotics can improve, to some extent, intestinal barrier function after CPB in rats, and this effect is likely related to inhibition of the CPB-induced inflammatory response, improvement in local intestinal immune function, and increased expression of intestinal epithelial tight junction proteins.

In Vivo and In Vitro Antinociceptive Effect of Fagopyrum cymosum (Trev.) Meisn Extracts: A Possible Action by Recovering Intestinal Barrier Dysfunction

Fagopyrum cymosum (Trev.) Meisn (Fag) is a herb rhizome which has been widely used to treat diseases. To investigate the effects and mechanisms of the Fag on irritable bowel syndrome (IBS), in vivo neonatal pups maternal separation (NMS) combined with intracolonic infusion of acetic acid (AA) was employed to establish IBS rat models. Fag reduced their visceral hyperalgesia and the whole gut permeability, ameliorated colonic mucosa inflammation and injury, and upregulated the expression of decreased tight junction proteins (TJs) of claudin-1, occludin, and ZO-1 (except ZO-2) in colonic epithelium. Caco-2 monolayer cells were incubated with TNF-α and IFN-γ   in vitro to establish an epithelial barrier dysfunction model whose transepithelial electrical resistance (TER) depended more on dose of Fag than that of the controls, and whose TJs levels were lower than those of the controls. Fag upregulated the NP-40 insoluble and soluble components of the four TJs markedly in a dose-dependent manner. These data suggest that Fag alleviated the hyperalgesia of IBS rats by reducing intestinal inflammation and enhancing mucosal epithelial function after regulating the structure and function of TJs.

Probiotics in the management of functional bowel disorders: promise fulfilled?

Irritable bowel syndrome (IBS) and chronic constipation (CC) are common problems worldwide and are associated with significant impact on activities of daily living and quality of life. Recent interest, in IBS in particular, has focused on the potential roles of the microbiota and its interaction with the host's immune system. Recently, high-quality clinical trials have been performed on prebiotics and probiotics in IBS or CC. Although strategies that seek to modify the microbiota, such as the use of probiotics, offer much promise in IBS and CC, more high-quality trials and, studies of longer duration are required.

Probiotics use to treat irritable bowel syndrome

INTRODUCTION

Irritable bowel syndrome (IBS) is a common chronic gastrointestinal (GI) tract disorder with significant disability and a considerable financial burden to health service due to the consumption of resources including investigations, physician time, and cost of treatment. Despite availability of multiple treatment options, there is still poor functional recovery.

AREAS COVERED

Probiotics has been investigated as a promising treatment for IBS, and have demonstrated beneficial effects in some patients. There are many clinical trials investigating the therapeutic benefits of probiotics in IBS but most of them are heterogenic in terms of dose or species used and clinical endpoints. However, recent major meta-analyses revealed benefits of probiotics in patients with IBS. Inhibition of binding of pathogenic bacteria to intestinal epithelial cells, enhancing barrier function of intestinal epithelial, acidification of the colon, suppression of the growth of pathogens, modulation of immunity, inhibition of visceral hypersensitivity, alteration in mucosal response to stress, and improvement of bowel dysmotility are among mechanisms that probiotics may act. Most commonly used probiotics come from the genera Bifidobacterium and Lactobacillus but other species are in trial.

EXPERT OPINION

Although further studies are still needed, current evidences are almost enough to convince experts that probiotics are efficient in the treatment of IBS.