A Commensal Bifidobacterium longum Strain Prevents Gluten-Related Immunopathology in Mice through Expression of a Serine Protease Inhibitor.

Microbiota-modulating strategies, including probiotic administration, have been tested for the treatment of chronic gastrointestinal diseases despite limited information regarding their mechanisms of action. We previously demonstrated that patients with active celiac disease have decreased duodenal expression of elafin, a human serine protease inhibitor, and supplementation of elafin by a recombinant Lactococcus lactis strain prevents gliadin-induced immunopathology in the NOD/DQ8 mouse model of gluten sensitivity. The commensal probiotic strain Bifidobacterium longum NCC2705 produces a serine protease inhibitor (Srp) that exhibits immune-modulating properties. Here, we demonstrate that B. longum NCC2705, but not a srp knockout mutant, attenuates gliadin-induced immunopathology and impacts intestinal microbial composition in NOD/DQ8 mice. Our results highlight the beneficial effects of a serine protease inhibitor produced by commensal B. longum strains.IMPORTANCE Probiotic therapies have been widely used to treat gastrointestinal disorders with variable success and poor mechanistic insight. Delivery of specific anti-inflammatory molecules has been limited to the use of genetically modified organisms, which has raised some public and regulatory concerns. By examining a specific microbial product naturally expressed by a commensal bacterial strain, we provide insight into a mechanistic basis for the use of B. longum NCC2705 to help treat gluten-related disorders.

Oral administration of Parabacteroides distasonis antigens attenuates experimental murine colitis through modulation of immunity and microbiota composition.

Commensal bacteria have been shown to modulate the host mucosal immune system. Here, we report that oral treatment of BALB/c mice with components from the commensal, Parabacteroides distasonis, significantly reduces the severity of intestinal inflammation in murine models of acute and chronic colitis induced by dextran sulphate sodium (DSS). The membranous fraction of P. distasonis (mPd) prevented DSS-induced increases in several proinflammatory cytokines, increased mPd-specific serum antibodies and stabilized the intestinal microbial ecology. The anti-colitic effect of oral mPd was not observed in severe combined immunodeficient mice and probably involved induction of specific antibody responses and stabilization of the intestinal microbiota. Our results suggest that specific bacterial components derived from the commensal bacterium, P. distasonis, may be useful in the development of new therapeutic strategies for chronic inflammatory disorders such as inflammatory bowel disease.

Declining Use of Corticosteroids for Crohn's Disease Has Implications for Study Recruitment: Results of a Pilot Randomized Controlled Trial.

BACKGROUND: Corticosteroids (CS) have been used extensively to induce remission in Crohn's disease (CD); however, they are associated with severe side effects. We hypothesized that the administration of an exclusive enteral nutrition (EEN) formula to CS would lead to increased CD remission rates and to decreased CS-related adverse events. We proposed to undertake a pilot study comparing EEN and CS therapy to CS alone to assess decrease symptoms and inflammatory markers over 6 weeks. AIM: The overall aim was to assess study feasibility based on recruitment rates and acceptability of treatment in arms involving EEN. METHODS: The pilot study intended to recruit 100 adult patients with active CD who had been prescribed CS to induce remission as part of their care. The patients were randomized to one of three arms: (i) standard-dose CS; (ii) standard-dose CS plus EEN (Modulen 1.5 kcal); or (iii) short-course CS plus EEN. RESULTS: A total of 2009 CD patients attending gastroenterology clinics were screened from October 2018 to November 2019. Prednisone was prescribed to only 6.8% (27/399) of patients with active CD attending outpatient clinics. Of the remaining 372 patients with active CD, 34.8% (139/399) started or escalated immunosuppressant or biologics, 49.6% (198/399) underwent further investigation and 8.8% (35/399) were offered an alternative treatment (e.g., antibiotics, surgery or investigational agents in clinical trials). Only three patients were enrolled in the study (recruitment rate 11%; 3/27), and the study was terminated for poor recruitment. CONCLUSION: The apparent decline in use of CS for treatment of CD has implications for CS use as an entry criterion for clinical trials.

Nutritional profile of rodent diets impacts experimental reproducibility in microbiome preclinical research.

The lack of reproducibility of animal experimental results between laboratories, particularly in studies investigating the microbiota, has raised concern among the scientific community. Factors such as environment, stress and sex have been identified as contributors, whereas dietary composition has received less attention. This study firstly evaluated the use of commercially available rodent diets across research institutions, with 28 different diets reported by 45 survey respondents. Secondly, highly variable ingredient, FODMAP (Fermentable Oligo-, Di-, Mono-saccharides And Polyols) and gluten content was found between different commercially available rodent diets. Finally, 40 mice were randomized to four groups, each receiving a different commercially available rodent diet, and the dietary impact on cecal microbiota, short- and branched-chain fatty acid profiles was evaluated. The gut microbiota composition differed significantly between diets and sexes, with significantly different clusters in ß-diversity. Total BCFA were highest (p = 0.01) and SCFA were lowest (p = 0.03) in mice fed a diet lower in FODMAPs and gluten. These results suggest that nutritional composition of commercially available rodent diets impact gut microbiota profiles and fermentation patterns, with major implications for the reproducibility of results across laboratories. However, further studies are required to elucidate the specific dietary factors driving these changes.

Effect of Bifidobacterium infantis NLS super strain in symptomatic coeliac disease patients on long-term gluten-free diet - an exploratory study.

Bifidobacterium infantis NLS super strain (B. infantis NLS-SS) was previously shown to alleviate gastrointestinal symptoms in newly diagnosed coeliac disease (CD) patients consuming gluten. A high proportion of patients following a gluten-free diet experiences symptoms despite dietary compliance. The role of B. infantis in persistently symptomatic CD patients has not been explored. The aim of the study was to evaluate the effect of B. infantis NLS-SS on persistent gastrointestinal symptoms in patients with CD following a long-term GFD. We conducted a randomised, cross-over, double-blind, placebo-controlled trial in symptomatic adult CD patients on a GFD for at least two years. After one-week run-in, patients were randomised to B. infantis NLS-SS or placebo for 3 weeks with cross-over after a 2-week wash-out period. We estimated changes (Δ) in celiac symptom index (CSI) before and after treatment. Stool samples were collected for faecal microbiota analysis (16S rRNA sequencing). Gluten immunogenic peptide (GIP) excretion in stool and urine samples was measured at each study period. Eighteen patients were enrolled; six patients were excluded due violations in protocol. For patients with the highest clinical burden, CD symptoms were lower in probiotic than in placebo treatment (P=0.046). B. infantis and placebo treated groups had different microbiota profiles as assessed by beta diversity clustering. In probiotic treated groups, we observed an increase in abundance of B. infantis. Treatment with B. infantis was associated with decreased abundance of Ruminococcus sp. and Bifidobacterium adolescentis. GIP excretion in stools and urine was similar at each treatment period. There were no differences in adverse effects between the two groups. B. infantis NLS-SS improves specific CD symptoms in a subset of highly symptomatic treated patients (GFD). This is associated with a shift in stool microbiota profile. Larger studies are needed to confirm these findings. ClinicalTrials.gov: NCT03271138.

Helminth antigen-based strategy to ameliorate inflammation in an experimental model of colitis.

Inflammatory bowel disease (IBD) is the most common and serious chronic inflammatory condition of the gut. Among the distinct T helper (Th) cell subsets, a Th1 type response is associated predominantly with Crohn's disease (CD) while helminth infections generate a strong Th2 type response. IBD is most prevalent in developed countries but rare in countries where infections with helminths are common. Thus, it has been hypothesized that infection with helminth infection influence the development of CD and recent clinical and experimental studies suggest strongly a beneficial role of helminth infection in IBD. In the present study we examined the effects of rectal submucosal administration of helminth antigens on subsequent experimental colitis. Mice were treated with Trichinella spiralis antigens prior to the induction of dinitrobenzenesulphonic acid (DNBS)-induced colitis and were killed 3 days post-DNBS to assess colonic damage macroscopically, histologically and by myeloperoxidase (MPO) activity, inducible nitric oxide synthase (iNOS) and cytokine levels. Previous treatment with T. spiralis antigens reduced the severity of colitis significantly, as assessed macroscopically and histologically, and reduced the mortality rate. This benefit was correlated with a down-regulation of MPO activity, interleukin (IL)-1beta production and iNOS expression and an up-regulation of IL-13 and transforming growth factor-beta production in colon. These results clearly show a beneficial role of local treatment with helminth antigens for experimental colitis and prompt consideration of helminth antigen-based therapy for IBD instead of infection with live parasites.

Clinical onset of celiac disease after an episode of Campylobacter jejuni enteritis.

The present report describes a young woman with no previous gastrointestinal complaints who was initially diagnosed with postinfective irritable bowel syndrome (IBS) after a confirmed case of Campylobacter jejuni enteritis. However, because of persistent diarrhea, new-onset bloating and the development of iron and vitamin deficiencies, serological markers for celiac disease (CD) were evaluated. A positive tissue transglutaminase immunoglobulin A antibody test and repeat endoscopy with duodenal biopsy showing a Marsh IIIa lesion confirmed the diagnosis of CD. Infectious gastroenteritis is a well-established risk factor for the development of IBS, and there is recent evidence that it could play a role in the initiation and exacerbation of inflammatory bowel disease. The present case suggests that the clinical expression of CD can be unmasked by an acute gastrointestinal infection and supports the hypothesis that environmental factors other than gliadin may play a role in the clinical onset of CD in a genetically susceptible host. The increasing availability of serological testing and upper endoscopy has led to increasingly frequent diagnoses of CD and recognition that it may mimic IBS. The present case findings suggest that CD should be considered in the differential diagnosis of persistent IBS-like symptoms after an episode of infectious gastroenteritis.

The complex task of measuring intestinal permeability in basic and clinical science.

Intestinal permeability is a key feature of intestinal barrier function. Altered intestinal permeability is described in many chronic diseases and may be a risk factor for disease development and a target for emerging therapeutics. Thus, reliable and sensitive methods to measure intestinal permeability in both the clinical and preclinical setting are needed. There is currently a large array of tests to choose from, each with advantages and disadvantages. When possible, a combination of methods should be used. The choice of tests should be based on a deep understanding of intestinal barrier physiology and the recognition of their limitations. This mini-review will highlight the advantages and limitations associated with intestinal permeability tests and will identify current problems in the field and how they can be addressed in the future.

Microbiota and host determinants of behavioural phenotype in maternally separated mice.

Early-life stress is a determinant of vulnerability to a variety of disorders that include dysfunction of the brain and gut. Here we exploit a model of early-life stress, maternal separation (MS) in mice, to investigate the role of the intestinal microbiota in the development of impaired gut function and altered behaviour later in life. Using germ-free and specific pathogen-free mice, we demonstrate that MS alters the hypothalamic-pituitary-adrenal axis and colonic cholinergic neural regulation in a microbiota-independent fashion. However, microbiota is required for the induction of anxiety-like behaviour and behavioural despair. Colonization of adult germ-free MS and control mice with the same microbiota produces distinct microbial profiles, which are associated with altered behaviour in MS, but not in control mice. These results indicate that MS-induced changes in host physiology lead to intestinal dysbiosis, which is a critical determinant of the abnormal behaviour that characterizes this model of early-life stress.

Lactobacillus rhamnosus CNCM I-3690 and the commensal bacterium Faecalibacterium prausnitzii A2-165 exhibit similar protective effects to induced barrier hyper-permeability in mice.

Impaired gut barrier function has been reported in a wide range of diseases and syndromes and in some functional gastrointestinal disorders. In addition, there is increasing evidence that suggests the gut microbiota tightly regulates gut barrier function and recent studies demonstrate that probiotic bacteria can enhance barrier integrity. Here, we aimed to investigate the effects of Lactobacillus rhamnosus CNCM I-3690 on intestinal barrier function. In vitro results using a Caco-2 monolayer cells stimulated with TNF-α confirmed the anti-inflammatory nature of the strain CNCM I-3690 and pointed out a putative role for the protection of the epithelial function. Next, we tested the protective effects of L. rhamnosus CNCM I-3690 in a mouse model of increased colonic permeability. Most importantly, we compared its performance to that of the well-known beneficial human commensal bacterium Faecalibacterium prauznitzii A2-165. Increased colonic permeability was normalized by both strains to a similar degree. Modulation of apical tight junction proteins expression was then analyzed to decipher the mechanism underlying this effect. We showed that CNCM I-3690 partially restored the function of the intestinal barrier and increased the levels of tight junction proteins Occludin and E-cadherin. The results indicate L. rhamnosus CNCM I-3690 is as effective as the commensal anti-inflammatory bacterium F. prausnitzii to treat functional barrier abnormalities.

Effects of pumaprazole (BY841), a novel reversible proton pump antagonist, and of omeprazole, on intragastric acidity before and after cure of Helicobacter pylori infection.

BACKGROUND: Omeprazole produces a higher intragastric pH in the presence of Helicobacter pylori infection than after cure. AIM: To investigate whether this effect also occurs with pumaprazole (BY841), a reversible proton pump antagonist which, in contrast to omeprazole, does not require activation in the acid compartment of the parietal cell. METHODS: In a randomized, crossover, double-blind study, 24-h intragastric pH was measured in 13 H. pylori-positive subjects before and after a 1-week course of omeprazole (20 mg o.d.) or of pumaprazole (100 mg b.d.). The studies were repeated after the infection was cured. RESULTS: In the absence of drug administration, the median 24-h pH values before cure (median 2.0, 90% CI: 1.2-3.2) did not differ from those after cure (median 1.5, 90% CI: 1.3-2.2; P = 0.115). The 24-h pH values were higher before cure of the infection than after during both pumaprazole (6.0, 4.8-6.7 vs. 4.3, 2.6-5.7; P = 0.002) and omeprazole (5.8, 4.0-6.2 vs. 3.6, 2.8-5; P = 0.004). Both before and after cure, there were no significant differences between the two drugs with respect to acid inhibition over the 24-h period. The median decrease in acid inhibition after cure of the infection (calculated as the difference in H+ activity in mmol/L) during pumaprazole (median 0.05, 90% CI: 6 x 10-4- 2.3) was no different from that during omeprazole (median 0.2, 90% CI: 3 x 10-3-1.5; P = 0.6). CONCLUSIONS: Both before and after cure of H. pylori infection, pumaprazole raised the intragastric pH over a 24-h period to a similar degree as omeprazole. H. pylori infection similarly augments the pH-increasing effect of both drugs. This effect is related to H. pylori infection and not to an increased activation of acid inhibitory agents in the parietal cell compartment.

The effect of intra-gastric acidity and flora on the concentration of N-nitroso compounds in the stomach.

BACKGROUND: Correa's hypothesis proposes that gastric carcinogenesis is due to atrophic gastritis and hypochlorhydria which permit gastric bacterial colonization, the reduction of dietary nitrates to nitrites and the formation of potentially carcinogenic N-nitroso compounds (NOCs). OBJECTIVE: To test the hypothesis that omeprazole-induced hypochlorhydria is associated with increased intra-gastric concentrations of nitrate-reducing bacteria (NRB), nitrites and NOCs. DESIGN: Single-blind study in healthy volunteers. PARTICIPANTS: Fourteen healthy subjects (seven female, mean age 24 years), free of Helicobacter pylori infection, received a one-week course of placebo followed by a two-week course of omeprazole, 20 mg daily. METHODS: Fasted gastric samples, aspirated using a sterile double-lumen nasogastric tube at the end of the 1 st week (placebo) and the 2nd and 3rd weeks (omeprazole), were cultured aerobically and anaerobically; gastric pH and intra-gastric concentrations of nitrates, nitrites and NOCs were also determined. RESULTS: After weeks 1, 2 and 3, the intra-gastric concentrations of nitrate-reducing bacteria exceeded 10(5) colony-forming units (c.f.u.)/ml in 3, 7 and 9 subjects, respectively (P > 0.05). A gastric pH greater than 4.0 was associated with increased NRB (P < 0.05); however, neither increased gastric pH nor increased NRB, alone or in combination, was associated with increased intra-gastric concentrations of nitrites or NOCs (P > 0.05). CONCLUSIONS: A two-week increase in gastric pH in healthy, H. pylori-negative subjects was associated with increased intra-gastric concentrations of nitrate-reducing bacteria but not of nitrites or N-nitroso compounds. These data suggest that reduced gastric acid secretion is not a necessary precursor to the formation of carcinogenic N-nitroso compounds and that other mechanisms should be invoked to explain gastric carcinogenesis.

Autoimmunity, immunodeficiency and mucosal infections: chronic intestinal inflammation as a sensitive indicator of immunoregulatory defects in response to normal luminal microflora.

Despite the fact that target antigens and the genetic basis of several autoimmune diseases are now better understood, the initial events leading to a loss of tolerance towards self-components remain unknown. One of the most attractive explanations for autoimmune phenomena involves various infections as possible natural events capable of initiating the process in genetically predisposed individuals. The most accepted explanation of how infection causes autoimmunity is based on the concept of "molecular mimicry" (similarity between the epitopes of an autoantigen and the epitopes in the environmental antigen). Infectious stimuli may also participate in the development of autoimmunity by inducing an increased expression of stress proteins (hsp), chaperones and transplantation antigens, which leads to abnormal processing and presentation of self antigens. Superantigens are considered to be one of the most effective bacterial components to induce inflammatory reactions and to take part in the development and course of autoimmune mechanisms. It has long been known that defects in the host defense mechanism render the individual susceptible to infections caused by certain microorganisms. Impaired exclusion of microbial antigens can lead to chronic immunological activation which can affect the tolerance to self components. Defects in certain components of the immune system are associated with a higher risk of a development of autoimmune disease. The use of animal models for the studies of human diseases with immunological pathogenesis has provided new insights into the influence of immunoregulatory factors and the lymphocyte subsets involved in the development of disease. One of the most striking conclusion arising from work with genetically engineered immunodeficient mouse models is the existence of a high level of redundancy of the components of the immune system. However, when genes encoding molecules involved in T cell immunoregulatory functions are deleted, spontaneous chronic inflammation of the gut mucosa (similar to human inflammatory bowel disease) develops. Surprisingly, when such immunocompromised animals were placed into germfree environment, intestinal inflammation did not develop. Impairment of the mucosal immune response to the normal bacterial flora has been proposed to play a crucial role in the pathogenesis of chronic intestinal inflammation. The use of immunodeficient models colonized with defined microflora for the analysis of immune reactivity will shed light on the mode of action of different immunologically important molecules responsible for the delicate balance between luminal commensals, nonspecific and specific components of the mucosal immune system.

Intestinal microbiota influence the early postnatal development of the enteric nervous system.

BACKGROUND: Normal gastrointestinal function depends on an intact and coordinated enteric nervous system (ENS). While the ENS is formed during fetal life, plasticity persists in the postnatal period during which the gastrointestinal tract is colonized by bacteria. We tested the hypothesis that colonization of the bowel by intestinal microbiota influences the postnatal development of the ENS. METHODS: The development of the ENS was studied in whole mount preparations of duodenum, jejunum, and ileum of specific pathogen-free (SPF), germ-free (GF), and altered Schaedler flora (ASF) NIH Swiss mice at postnatal day 3 (P3). The frequency and amplitude of circular muscle contractions were measured in intestinal segments using spatiotemporal mapping of video recorded spontaneous contractile activity with and without exposure to lidocaine and N-nitro-L-arginine (NOLA). KEY RESULTS: Immunolabeling with antibodies to PGP9.5 revealed significant abnormalities in the myenteric plexi of GF jejunum and ileum, but not duodenum, characterized by a decrease in nerve density, a decrease in the number of neurons per ganglion, and an increase in the proportion of myenteric nitrergic neurons. Frequency of amplitude of muscle contractions were significantly decreased in the jejunum and ileum of GF mice and were unaffected by exposure to lidocaine, while NOLA enhanced contractile frequency in the GF jejunum and ileum. CONCLUSIONS & INFERENCES: These findings suggest that early exposure to intestinal bacteria is essential for the postnatal development of the ENS in the mid to distal small intestine. Future studies are needed to investigate the mechanisms by which enteric microbiota interact with the developing ENS.

Efficacy of Bifidobacterium breve NCC2950 against DSS-induced colitis is dependent on bacterial preparation and timing of administration.

Probiotics have been proposed as a therapy for inflammatory bowel disease, but variations in strains, formulations, and protocols used in clinical trials have hindered the creation of guidelines for their use. Thus, preclinical insight into the mechanisms of specific probiotic strains and mode of administration would be useful to guide future clinical trial design. In this study, live, heat inactivated (HI), and spent culture medium preparations of the probiotic Bifidobacterium breve NCC2950 were administered to specific pathogen free C57BL/6 mice before or during colitis, as well as before colitis reactivation. Five days of 3.5% dextran sulphate sodium in drinking water was used to induce colitis. Pretreatment with live B. breve reduced disease severity, myeloperoxidase activity, microscopic damage, cytokine production, interleukin (IL)-12/IL-10 ratio, and lymphocyte infiltration in the colon. B. breve did not attenuate on-going colitis. After acute colitis, disease symptoms were normalised sooner with live and HI B. breve treatment; however, reactivation of colitis was not prevented. These findings indicate that the efficacy of a probiotic to modulate intestinal inflammation is dependent on the formulation as well as state of inflammation when administered. Overall, live B. breve was most efficacious in preventing acute colitis. Live and HI B. breve also promoted recovery from diarrhoea and colon bleeding after a bout of acute colitis.

Bifidobacterium longum NCC3001 inhibits AH neuron excitability.

BACKGROUND: Bifidobacterium longum (B. longum) NCC3001 can affect behavior and brain biochemistry, but identification of the cellular targets needs further investigation. Our hypothesis was that the communication with the brain might start with action on enteric sensory neurons. METHODS: Ileal segments from adult mice were used to create a longitudinal muscle-myenteric-plexus preparation to expose sensory after-hyperpolarizing (AH) neurons in the myenteric plexus to allow access with microelectrodes. The intrinsic excitability of AH neurons was tested in response to the perfusion of conditioned media (B. longum culture supernatant) or unconditioned media (growth medium, MRS). KEY RESULTS: B. longum conditioned medium significantly reduced the excitability of AH neurons compared to perfusion with the unconditioned medium. Specifically, a reduction was seen in the number of action potentials fired per depolarizing test pulse, the instantaneous and time-dependent input resistances and the magnitude of the hyperpolarization-activated cationic current (Ih ). CONCLUSIONS & INFERENCES: The probiotic B. longum reduces excitability of AH sensory neurons likely via opening of potassium channels and closing of hyperpolarization-activated cation channels.

Altered colonic function and microbiota profile in a mouse model of chronic depression.

BACKGROUND: Depression often coexists with the irritable bowel syndrome (IBS) which is characterized by alterations in gut function. There is emerging evidence that the microbial composition (microbiota) of the gut is altered in IBS, but the basis for this is poorly understood. The aim of this study was to determine whether the induction of chronic depression results in changes in the colonic function and in its microbial community, and to explore underlying mechanisms. METHODS: Bilateral olfactory bulbectomy (OBx) was used to induce depression-like behavior in mice. Colonic function was assessed by measuring muscle contractility, pellet excretion, c-fos activity, and serotonin levels. Microbiota profiles were obtained using denaturing gradient gel electrophoresis (DGGE). The hypothalamic-pituitary axis (HPA) was assessed by the hypothalamic expression of corticotropin-releasing hormone (CRH). In separate studies, mice without OBx received CRH via intracerebroventricular (ICV) infusion for 4 weeks prior to assessing colonic function and microbiota profiles. KEY RESULTS: Olfactory bulbectomy mice demonstrated chronic depression- and anxiety-like behaviors associated with elevated central CRH expression and increases in c-Fos activity, serotonin levels, and motility in the colon. These changes were accompanied by an altered intestinal microbial profile. Central CRH administration produced similar changes in behavior and motility and altered the microbiota profile in the colon. CONCLUSIONS & INFERENCES: The induction of chronic depression alters motor activity and the microbial profile in the colon likely via activation of the HPA. These findings provide a basis for linking the behavioral and gastrointestinal manifestations of IBS.

Microbes and the gut-brain axis.

BACKGROUND: The 'gut-brain' or 'brain-gut axis', depending on whether we emphasize bottom-up or top-bottom pathways, is a bi-directional communication system, comprised of neural pathways, such as the enteric nervous system (ENS), vagus, sympathetic and spinal nerves, and humoral pathways, which include cytokines, hormones, and neuropeptides as signaling molecules. Recent evidence, mainly arising from animal models, supports a role of microbes as signaling components in the gut-brain axis. AIMS: The purpose of this review is to summarize our current knowledge regarding the role of microbes, including commensals, probiotics and gastrointestinal pathogens, in bottom-up pathways of communication in the gut-brain axis. Although this has clear implications for psychiatric co-morbidity in functional and inflammatory conditions of the gut, the focus of this review will be to discuss the current evidence for a role of bacteria (commensals, probiotics, and pathogens) as key modulators of gut-brain communication. RESULTS & CONCLUSIONS: The strongest evidence for a role of microbes as signaling components in the gut-brain axis currently arises from animal studies and indicate that mechanisms of communication are likely to be multiple. There is need for the concepts generated in animal models to be translated to the human in the future.

The anxiolytic effect of Bifidobacterium longum NCC3001 involves vagal pathways for gut-brain communication.

BACKGROUND: The probiotic Bifidobacterium longum NCC3001 normalizes anxiety-like behavior and hippocampal brain derived neurotrophic factor (BDNF) in mice with infectious colitis. Using a model of chemical colitis we test whether the anxiolytic effect of B. longum involves vagal integrity, and changes in neural cell function. Methods Mice received dextran sodium sulfate (DSS, 3%) in drinking water during three 1-week cycles. Bifidobacterium longum or placebo were gavaged daily during the last cycle. Some mice underwent subdiaphragmatic vagotomy. Behavior was assessed by step-down test, inflammation by myeloperoxidase (MPO) activity and histology. BDNF mRNA was measured in neuroblastoma SH-SY5Y cells after incubation with sera from B. longum- or placebo-treated mice. The effect of B. longum on myenteric neuron excitability was measured using intracellular microelectrodes. KEY RESULTS: Chronic colitis was associated with anxiety-like behavior, which was absent in previously vagotomized mice. B. longum normalized behavior but had no effect on MPO activity or histological scores. Its anxiolytic effect was absent in mice with established anxiety that were vagotomized before the third DSS cycle. B. longum metabolites did not affect BDNF mRNA expression in SH-SY5Y cells but decreased excitability of enteric neurons. CONCLUSIONS & INFERENCES: In this colitis model, anxiety-like behavior is vagally mediated. The anxiolytic effect of B. longum requires vagal integrity but does not involve gut immuno-modulation or production of BDNF by neuronal cells. As B. longum decreases excitability of enteric neurons, it may signal to the central nervous system by activating vagal pathways at the level of the enteric nervous system.

Probiotics effects on gastrointestinal function: beyond the gut?

The digestive tract works through a complex network of integrative functions. At the level of the gut, this integration occurs between the immune, neuromotor and enteroendocrine systems, coordinating the physical and chemical elements of the intestinal barrier in order to facilitate digestion whilst protecting the gut from unwanted components of the luminal contents. Gastrointestinal function is controlled and coordinated by the central nervous system to ensure effective motility, secretion, absorption and mucosal immunity. It follows that perturbations in this complex network could lead to gut dysfunction and symptom generation. Recently, attention has been focused on the emerging hypothesis that gut luminal content contributes to determine normal GI function and on the therapeutic possibilities arising from modulating its impact on gut physiology and immunity using probiotic bacteria. In this issue of Neurogastroenterology and Motility, two papers explore the effect of specific probiotic bacteria on spinal neuronal activation and in vitro muscle contractility. These papers support the notion that the composition of the intestinal microbiota can influence gut neuro-motor function and enhance our understanding on the mechanisms of action underlying the effects of specific probiotics on gut functional disorders.