Post-infectious ibs following Clostridioides difficile infection; role of microbiota and implications for treatment

Up to 25% of patients recovering from antibiotic-treated Clostridioides difficile infection (CDI) develop functional symptoms reminiscent of Post-Infectious Irritable Bowel Syndrome (PI-IBS). For patients with persistent symptoms following infection, a clinical dilemma arises as to whether to provide additional antibiotic treatment or to adopt a conservative symptom-based approach. Here, we review the literature on CDI-related PI-IBS and compare the findings with PI-IBS. We review proposed mechanisms, including the role of C. difficile toxins and the microbiota, and discuss implications for therapy. We suggest that gut dysfunction post-CDI may be initiated by toxin-induced damage to enteroglial cells and that a dysbiotic gut microbitota maintains the clinical phenotype over time, prompting consideration of microbiota-directed therapies. While Fecal Microbial Transplant (FMT) is currently reserved for recurrent CDI (rCDI), we propose that microbiota-directed therapies may have a role in primary CDI in order to avoid or mitigate futher antibiotic treatment that further disrupts the microbiota and thus prevent PI-IBS. We discuss novel microbial transfer therapies and as they emerge, we recommend clinical trials to determine whether microbial transfer therapy of the primary infection prevents both rCDI and CDI-related PI- IBS.

Oral tryptophan activates duodenal aryl hydrocarbon receptor in healthy subjects: a crossover randomized controlled trial

Background and Aims: Tryptophan is an essential amino acid transformed by host and gut microbial enzymes into metabolites that regulate mucosal homeostasis through Aryl hydrocarbon receptor (AhR) activation. Alteration of tryptophan metabolism has been associated with chronic inflammation, however whether tryptophan supplementation affects the metabolite repertoire and AhR activation under physiologic conditions in humans, is unknown. Methods: We performed a randomized, double blind, placebo-controlled, crossover study in 20 healthy volunteers. Subjects on a low tryptophan background diet were randomly assigned to a 3-week L-tryptophan supplementation (3 g/day) or placebo, and after a 2-week washout switched to opposite interventions. We assessed gastrointestinal and psychological symptoms by validated questionnaires, AhR activation by cell reporter assay, tryptophan metabolites by liquid chromatography and high-resolution mass spectrometry, cytokine production in isolated monocytes by ELISA and microbiota profile by 16S rRNA Illumina technique. Results: Oral tryptophan supplementation was well tolerated, with no changes in gastrointestinal or psychological scores. Compared with placebo, tryptophan increased AhR activation capacity by duodenal contents, but not by feces. This was paralleled by higher urinary and plasma kynurenine metabolites and indoles. Tryptophan had a modest impact on fecal microbiome profiles, and no significant effect on cytokine production. Conclusions: At the doses used in this study, oral tryptophan supplementation in humans induces microbial indole and host kynurenine metabolic pathways in the small intestine, known to be immunomodulatory. The results should prompt tryptophan intervention strategies in inflammatory conditions of the small intestine where the AhR pathway is impaired.

Vasoactive Intestinal Polypeptide Plays a Key Role in the Microbial-Neuroimmune Control of Intestinal Motility

BACKGROUND & AIMS

Although chronic diarrhea and constipation are common, the treatment is symptomatic because their pathophysiology is poorly understood. Accumulating evidence suggests that the microbiota modulates gut function, but the underlying mechanisms are unknown. We therefore investigated the pathways by which microbiota modulates gastrointestinal motility in different sections of the alimentary tract.

METHODS

Gastric emptying, intestinal transit, muscle contractility, acetylcholine release, gene expression, and vasoactive intestinal polypeptide (VIP) immunoreactivity were assessed in wild-type and Myd88-/-Trif-/- mice in germ-free, gnotobiotic, and specific pathogen-free conditions. Effects of transient colonization and antimicrobials as well as immune cell blockade were investigated. VIP levels were assessed in human full-thickness biopsies by Western blot.

RESULTS

Germ-free mice had similar gastric emptying but slower intestinal transit compared with specific pathogen-free mice or mice monocolonized with Lactobacillus rhamnosus or Escherichia coli, the latter having stronger effects. Although muscle contractility was unaffected, its neural control was modulated by microbiota by up-regulating jejunal VIP, which co-localized with and controlled cholinergic nerve function. This process was responsive to changes in the microbial composition and load and mediated through toll-like receptor signaling, with enteric glia cells playing a key role. Jejunal VIP was lower in patients with chronic intestinal pseudo-obstruction compared with control subjects.

CONCLUSIONS

Microbial control of gastrointestinal motility is both region- and bacteria-specific; it reacts to environmental changes and is mediated by innate immunity-neural system interactions. By regulating cholinergic nerves, small intestinal VIP plays a key role in this process, thus providing a new therapeutic target for patients with motility disorders.

The gut protist Tritrichomonas arnold restrains virus-mediated loss of oral tolerance by modulating dietary antigen-presenting dendritic cells

Loss of oral tolerance (LOT) to gluten, driven by dendritic cell (DC) priming of gluten-specific T helper 1 (Th1) cell immune responses, is a hallmark of celiac disease (CeD) and can be triggered by enteric viral infections. Whether certain commensals can moderate virus-mediated LOT remains elusive. Here, using a mouse model of virus-mediated LOT, we discovered that the gut-colonizing protist Tritrichomonas (T.) arnold promotes oral tolerance and protects against reovirus- and murine norovirus-mediated LOT, independent of the microbiota. Protection was not attributable to antiviral host responses or T. arnold-mediated innate type 2 immunity. Mechanistically, T. arnold directly restrained the proinflammatory program in dietary antigen-presenting DCs, subsequently limiting Th1 and promoting regulatory T cell responses. Finally, analysis of fecal microbiomes showed that T. arnold-related Parabasalid strains are underrepresented in human CeD patients. Altogether, these findings will motivate further exploration of oral-tolerance-promoting protists in CeD and other immune-mediated food sensitivities.

Understanding neuroimmune interactions in disorders of gut-brain interaction: from functional to immune-mediated disorders

Functional gastrointestinal disorders-recently renamed into disorders of gut-brain interaction-such as irritable bowel syndrome and functional dyspepsia are highly prevalent conditions with bothersome abdominal symptoms in the absence of structural abnormalities. While traditionally considered as motility disorders or even psychosomatic conditions, our understanding of the pathophysiology has evolved significantly over the last two decades. Initial observations of subtle mucosal infiltration with immune cells, especially mast cells and eosinophils, are since recently being backed up by mechanistic evidence demonstrating increased release of nociceptive mediators by immune cells and the intestinal epithelium. These mediators can activate sensitised neurons leading to visceral hypersensitivity with bothersome symptoms. The interaction between immune activation and an impaired barrier function of the gut is most likely a bidirectional one with alterations in the microbiota, psychological stress and food components as upstream players in the pathophysiology. Only few immune-targeting treatments are currently available, but an improved understanding through a multidisciplinary scientific approach will hopefully identify novel, more precise treatment targets with ultimately better outcomes.

A266 DIET-BASED THERAPIES FOR INTESTINAL DYSFUNCTION INDUCED BY CLOSTRIDIOIDES DIFFICILE INFECTION

Background

Chronic gut dysfunction occurs in up to 25% of patients following antibiotic-treated C. difficile infection (CDI). We developed a humanized mouse model in which germ free mice colonized with microbiota from patients with severe constipation post-CDI developed slow colonic transit, as a result of damage to the Interstitial Cells of Cajal (ICC) network by pro-inflammatory macrophages. Colonic transit, immune activation and the ICC network normalized after fecal microbiota transplantation using samples from healthy mice, as well after treatment with psyllium fiber. Here we explored the long-term effects of psyllium and evaluated the therapeutic potential of pectin and quercetin in this model.

Purpose

1) To investigate the time course of the beneficial effect of psyllium on colonic motility.

2) To explore possible therapeutic properties of flavonoids and pectin.

Method

Germ-free mice were colonized with microbiota from the post-CDI (PCDI) patient or healthy controls (HC). After 3 weeks, the mice were fed for 4-5 weeks with a control diet or diets with 15% psyllium (PSY), 10% pectin (PCT) or 0.05% quercetin (QCT). To evaluate time course of PSY on motility, control diet was administered for 3-weeks following PSY treatment. The bead expulsion test was used to assess colonic motility. Stool samples were collected for microbial profiling, and short and branched-chain fatty acids (SCFA/BCFA) analysis. Macrophages morphology and counts, and ICC network structure were evaluated by immunohistochemistry.

Result(s)

Compared to HC microbiota, colonization with post-CDI microbiota induced slow colonic transit in recipient mice, and this was normalized by PSY (n=13; p=0.02). The benefit of PSY was transient as colonic transit slowed following discontinuation of PSY (p=0.001). The changes in colonic transit were paralleled by switch in macrophages phenotype and damage to the ICC network. Additionally, discontinuation of PSY resulted in a return of microbial diversity (p< 0.001), SCFA/BCFA levels (acetic and propionic acid/ iso-butyric and valeric acid) and specific bacterial species abundances, to values seen in untreated mice colonized with post-CDI microbiota. Microbial analysis predicted potential pathways involved in macrophage polarization, including the synthesis of SCFA/BCFA, degradation of inositol and production of acetylglucosamine.

PCT also normalized slow intestinal transit in mice colonized with post-CDI microbiota (p=0.003), restored phenotype of infiltrating macrophages, and improved the structural integrity of the ICC network. In contrast, QCT failed to improve gut dysfunction in PCDI mice.

Conclusion(s)

Our results suggest that the beneficial effects of psyllium in this model are transient. Dietary pectin, but not quercetin, may also serve as a novel treatment strategy to restore colonic motility and immune homeostasis in humans with severe constipation post-CDI.

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Other

Please indicate your source of funding;

W. Garfield Weston Foundation

Disclosure of Interest

None Declared

A8 MICROBIAL ACTIVATION OF INTESTINAL DENDRITIC CELLS IS CRITICAL FOR THE ESTABLISHMENT OF NORMAL BEHAVIOR

Background

Accumulating evidence suggests that gut microbiota affects brain development and its function. It is well known that compared with conventional mice (SPF), germ-free (GF) mice display higher exploratory behavior, which normalizes after bacterial colonization. However, little is known about the underlying mechanisms and first critical steps initiating microbiota-gut-brain communication, which lead to establishment of normal behavior.

Purpose

To investigate the role of immune system in the establishment of normal behavior after bacterial colonization.

Method

We assessed behavior in GF mice before and after colonization with SPF microbiota, Altered Schaedler Flora (ASF) or the single bacterial strain E. coli JM83, and compared them to SPF mice, using the light-dark preference and tail suspension tests. Levels of brain-derived neurotrophic factor (BDNF) and c-Fos expression were measured by immunofluorescence in the hippocampus and amygdala. Colonic and brain gene expression were assessed using a NanoString technology. The immunodeficient MyD88-/- Ticam1- and SCID mice were used to study the role of the innate and adaptive immune systems. To demonstrate the role of the dendritic cells (DCs), we measured behavior before and after mono-colonization with E. coli JM83 in GF mice treated with cosalane and fingolimod, that inhibit DCs activation and migration, respectively. Brain levels of CD11b, CD11c and CD103 as DCs markers was assessed by immunofluorescence.

Result(s)

Compared to SPF mice, GF mice showed higher exploratory and less depressive-like behavior. The ex-germ-free mice colonized with ASF microbiota, or mono-colonized with E. coli JM83 showed similar normalization of behavior as those colonized with SPF microbiota. Mono-colonization with E. coli reduced both BDNF and c-fos levels in the hippocampus and amygdala. While colonization of GF SCID mice induced same change in behavior as in wild-type mice, GF MyD88-/-Ticam1-/- mice did not alter their behavior. Mono-colonization affected multiple genes in the colon and the brain, associated with innate immunity and neural plasticity. Treatment with both cosalane and fingolimod prevented behavioral changes after colonization, which was paralleled by absence of CD11b+CD103+CD11c+ cells in the brain, otherwise found in high numbers in control mono-colonized mice and absent in germ-free mice.

Conclusion(s)

The innate immune system, through activation and migration of intestinal dendritic cells into the brain, initiates the neuro-immune signaling within the gut-brain axis and leads to normalization of behavior after bacterial colonization. Our findings may impact several psychiatric conditions, in which altered innate immune signaling has been implicated.

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CIHR, Other

Please indicate your source of funding;

Balsam Family Foundation

Disclosure of Interest

None Declared

A62 IDENTIFICATION OF SPECIFIC COLONIC DEEP MUSCLE LAYER MACROPHAGES SUBSETS BY THE CD64 (FCΓRI) MARKER

Background

Although intestinal muscle layer macrophages have been suggested to play an important role in the colonic transit by interacting with the myenteric plexus neurons, they have not been fully characterized. CD64 (FcγRI) is one of the most generally used markers for intestinal macrophages, but several studies suggested existence of a subpopulation of macrophages that lack CD64. In addition, the muscle layer macrophage subsets currently identified are considered to be same in the small intestine and colon, although this has not been formally tested.

Purpose

In this study, we aim to identify and characterize the subsets of muscle layer macrophages by CD64 marker. We hypothesize that colon specific CD64-macrophages have a different role from CD64+ conventional macrophages.

Method

The muscle layers of small intestine (ileum) and colon were separated from SPF mice and cells from each muscle layer were analyzed by flow cytometry and fluorescent staining. The muscle layer macrophages were gated withCD45+, F4/80+, CD11b+ and Ly6c-, and analyzed with CD64 and MHCⅡmarkers by flow cytometry. In additional experiments, fluorescent staining with CD64 and F4/80 was assessed in whole-mount tissue of the separated muscle layer.

Result(s)

Within the macrophage population from the colon muscle layer, we found not only CD64+ cells, a conventional marker of macrophage, but also CD64- cell population (CD45+, F4/80+, CD11b+, Ly6c-). However, in the small intestine, this CD64- cell population was barely detectable. In addition, colonic CD64+ cells had mostly high expression of MHCⅡ marker, while CD64- cells had low expression of MHCⅡ. A similar pattern was found when we examined intestinal and colonic tissues by immunofluorescent staining.

Conclusion(s)

We identified a colon-specific CD64- subset of macrophage in muscle layer. Additional experiments are needed to characterize their immunomodulatory properties.

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None

Disclosure of Interest

None Declared

CLIINICAL PRACTICE

A45 FIBER-FREE DIET REDUCES BACTEROIDES ABUNDANCE AND PREVENTS MUCUS DEGRADATION IN MICE COLONIZED WITH MICROBIOTA FROM PATIENTS WITH GENERALIZED ANXIETY DISORDER

Background

Generalized anxiety disorder (GAD) is a debilitating condition with a lifetime prevalence of 4-7% worldwide. We have previously found that compared to healthy controls, GAD patients had lower reported fiber intake, increased gastrointestinal symptoms; and enrichment of Bacteroides genus as well as carbohydrate metabolism pathways (as determined by PICRUSt2, correlated to Bacteroides abundance). Bacteroides are known for its ability to degrade a wide variety of host polysaccharides, such as the intestinal mucus, which could lead to local and systemic inflammation. In this regard, GAD patients had higher C-reactive protein (CRP) compared to healthy controls (p=0.049).

Purpose

To investigate whether a fiber-free diet could decrease Bacteroides abundance and prevent damage of the mucus layer reducing anxiety-behavior in mice with GAD microbiota.

Method

Two germ-free NIH Swiss mouse breeding pairs were colonized with GAD microbiota using patients’ stool samples and kept on either fiber-free or 10 % inulin (fiber) diet. Offspring were weaned at week 3 and psychometric tests were performed at 10 weeks of age. After sacrifice, samples for histology (mucus layer thickness determination), blood (CRP ELISA determination) and stool (Illumina 16S rRNA gene sequencing) were collected. The microbiota data was analyzed following the pipelines of dada2 and by mean comparisons, correlation, AncomBC using R software (v.1.2.1335). Multiple comparison results were corrected allowing 5% of FDR.

Result(s)

Beta diversity analysis showed that parent and offspring’s (n=24 fiber-supplemented and n=14 fiber-free groups) microbiota was similar to the GAD donor. The most differentially abundant bacterial taxon was Bacteroides uniformis, which was decreased in the fiber-free group (p.adj= 0.003). Furthermore, fiber-free diet reduced the overall Bacteroides abundance by half compared to the donor and fiber-supplemented mice group. This led to a thickening (p.adj=0.027) of the mucus layer, increasing from 30 µm (fiber-supplemented diet) to 60 µm in the fiber-free diet group. B. uniformis was negatively correlated to the mucus layer thickness (R= -0.81; p.adj=0.26), although not statistically significant, likely due to a low n number (n=4). We only found a statistical trend for higher CRP levels and anxiety-like behavior in the fiber-supplemented group. This might be because fiber supplementation has several beneficial effects that can counteract the proposed increase in anxiety-like behavior fromBacteroides. Despite that, we found a significant correlation between B. uniformis and time mice spent in the dark (indicative of anxiety-like behavior) in the light preference test.

Conclusion(s)

Our data suggests that Bacteroides abundance, specifically Bacteroides uniformis, contributes to the degradation of the mucus layer and potentially triggers low grade gut inflammation and anxiety-like behavior.

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CIHR

Disclosure of Interest

None Declared

A19 INVESTIGATING MECHANISMS THAT DRIVE SYMPTOMS IN IRRITABLE BOWEL SYNDROME PATIENTS WITH PERCEIVED GLUTEN SENSITIVITY

Background

Patients with irritable bowel syndrome (IBS) often report gastrointestinal symptoms after consuming wheat and gluten-containing foods. It is, however, unclear whether gluten is the main driver of symptoms, as other immunogenic peptides, such as amylase trypsin inhibitors (ATI), poorly digestible fiber (inulin, part of FODMAP) or even the nocebo effect may contribute to symptom generation.

Purpose

To evaluate whether whole wheat containing ATIs and/or purified gluten trigger gastrointestinal symptoms compared to nocebo in patients with IBS adopting a gluten-free diet (GFD).

Method

We conducted a double-blind, randomized, nocebo-controlled crossover study in adult IBS patients (Rome IV criteria) who previously perceived improvement of symptoms while on a GFD. The study was approved by the Hamilton Research Ethics Board (HiREB #4367). Participants were challenged for 7 days with whole wheat, purified gluten, and nocebo (gluten-free flour) added to low FODMAP cereal bars. Each challenge was followed by a 2-week washout. Patients remained on a GFD throughout the study, diet adherence was assessed by a dietitian and stool gluten immunogenic peptides (GIP; Biomedal). Gastrointestinal symptoms were assessed by IBS Symptom Severity Score (IBS-SSS); increases >50 points were considered a significant worsening. Blood samples were collected to assess immune markers and celiac (HLA DQ2, DQ8 and DQ7) genotype. Statistical comparisons used Friedman rank sum tests and paired Wilcoxon signed rank tests.

Result(s)

Twenty-nine IBS patients (27 female, mean age=42, SD=14.4 years) were enrolled in the study; 1 dropped. Similar proportions of patients reacted symptomatically to wheat (11/28, 39.3%), gluten (10/28, 35.7%) and nocebo (8/28, 28.6%). However, there was an overall significant increase in IBS symptoms after wheat (+39.5 on IBS-SSS; p=0.030) but not after gluten (+27.5; p=0.051) or nocebo (+5.5; p=0.236) challenges (Figure 1). Ten participants experienced IBS-SSS symptoms >175 during baseline and did not worsen further during the challenges. TNF-α trended from 1.35 pg/mL after nocebo, 1.47 pg/mL after gluten, to 1.57 pg/mL after wheat; however, this was not significant. Baseline adherence to a GFD was rated excellent in 19 (68%), good in 6 (21%), and fair in 3 (11%) participants. Median GIP levels were 0.584 µg/g after wheat, 0.432 µg/g after gluten, and 0.095 µg/g after nocebo; p<0.0001. Celiac predisposition genes were present in 19/24 participants (10/24 had DQ2, 2/24 had DQ8, and 9/24 had DQ7).

Image

Conclusion(s)

IBS patients self-reporting wheat or gluten sensitivity had worse symptoms after whole wheat, but not purified gluten or nocebo challenge. However, similar proportions of IBS patients reacted to each intervention, suggesting that central mechanisms play an important role in symptom genesis. Furthermore, one third of patients had high symptoms during a GFD and did not react to wheat or gluten challenges, suggesting that other mechanisms are driving their IBS symptoms.

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CIHR, Other

Please indicate your source of funding;

Society for the Study of Celiac Disease (Nestle); Canadian Digestive Health Foundation

Disclosure of Interest

None Declared

A265 TEMPORAL DYNAMICS OF SYMPTOMS AND GUT MICROBIOTA IN EPISODES OF IRRITABLE BOWEL SYNDROME

Background

Irritable bowel syndrome (IBS) is a disorder of gut-brain axis that manifests with chronic abdominal pain, altered bowel habits, and frequent psychiatric comorbidities. Despite mounting evidence showing gut microbiota composition and associated metabolites being altered in IBS, the mechanisms by which they drive the symptoms are unclear. We have previously shown that several IBS symptoms co-occur, that their severity vary among IBS subtypes (10.1093/jcag/gwab049.050), and that several bacterial taxa are differentially modulated during periods of symptom flares and remission. Here we investigate whether the changes in gut microbiome and bacterial metabolites are linked to symptom occurrence and severity.

Purpose

To investigate temporal associations of IBS symptoms with gut microbiota profiles and metabolites.

Method

16S rRNA gene sequencing was performed on stool samples of 28 IBS patients (IBS-D n=20, IBS-C n=8) and 10 healthy controls (HC), collected weekly over a period of 25 weeks, during which gut and mood symptoms were recorded (total of 950 samples). Correlations between principal ordinates obtained from symptom scores and microbiota beta diversity were studied using Procrustes analysis in R. Metabolomics was performed by Mass Spectrometry and analysed using MetaboAnalyst 5.0. Statistical significance was set at p<0.05.

Result(s)

Significant correlation was found between the symptom scores and microbiota beta diversity ordinates over time in 7 patients (5 IBS-D and 2 IBS-C subjects) out of 28 IBS patients. Metabolomics performed on samples selected based on Procrustes analysis and symptom severity scores of individual subjects showed that several pathways are altered in IBS patients (both subtypes) compared to HC, including primary bile acid biosynthesis, beta alanine metabolism, pyrimidine and histidine metabolism. Furthermore, during symptom flares, ornithine, citrulline and gluconic acid vary in IBS-D, while amino acids cysteine, methionine, threonine, and glycine vary in IBS-C subjects.

Conclusion(s)

Our results suggest that IBS symptoms and changes in gut microbiota composition and metabolites must be studied in conjunction, in order to understand the mechanisms underlying IBS pathophysiology. We found that same pathways are altered in IBS subjects irrespective of their subtype, suggestive of a basal metabolic shift in IBS patients. This shift may make them sensitive to further gut microbial modulation of carbohydrate and protein metabolism in IBS-D and IBS-C subjects, respectively, leading to symptom flares. Further analyses are needed to investigate these metabolites and associated bacteria, as they can help identifying subsets of patients with specific disease mechanisms. This will be a steppingstone in moving away from symptom-based subtyping towards mechanism-based grouping and developing effective treatment strategies accordingly.

Disclosure of Interest

None Declared

A53 FECAL BIOACTIVE PHOSPHOLIPIDS AS TRIGGERS OF INTESTINAL HYPERSENSITIVITY IN IRRITABLE BOWEL SYNDROME

Background

Chronic abdominal pain is the most common complaint of patients with gastrointestinal disorders. Its treatment is of limited efficacy as the pathophysiology is poorly understood. The gut microbiome has been shown to affect host physiology, including the neural system function, and growing evidence suggests that it plays an important role in pain perception. Gut microbiota produces a large variety of molecules that can regulate pain perception, such as histamine or bioactive lipids. Phospholipid mediators (PLM) are signaling molecules linked to neurogenic pain as by-products of inflammatory processes in mammals. But it is unknown whether bacteria can produce PLM and whether they play any role in visceral hyperalgesia.

Purpose

To investigate whether PLM are present in stool of patients with chronic abdominal pain, and whether they have potential to induce visceral hypersensitivity.

Method

Stool samples from 27 patients with irritable bowel syndrome (IBS) were collected both during periods of severe and minimal/no pain. The fecal concentration of two PLM (lipid A and lipid B) was determined by ELISA. The passage of lipid A and lipid B through the intestinal barrier was determined ex vivo using Ussing chambers and in vivo by their intracolonic instillation, and their levels assessed in the serosal compartment and the serum, respectively, by ELISA. We used primary cultures of sensory neurons from the dorsal root ganglia (DRG) of conventional mice (SPF) to study the neuronal activation in vitro. Calcium mobilization in DRG sensory neurons was measured by an inverted fluorescence microscope using a fluorescent probe Fluo-4 (1mM) after stimulation with different concentration of lipid A or lipid B. Visceral sensitivity in vivo after intracolonic instillation of combined lipids A and B was evaluated by colorectal distension.

Result(s)

The concentration of lipid A (p=0.001) and lipid B (p=0.002) in stool was significantly higher in IBS patients when experiencing severe abdominal pain compared to periods of minimal pain. The concentration of lipid A (p=0.03; p=0.07) and lipid B (p=0.018; p=0.018) in the serosal compartment and in the serum, respectively, was higher compared to the control condition. The percentage of neurons responding to lipid A or lipid B was significantly higher compared to the control condition, at all tested concentrations. Finally, combined lipid A and lipid B induced visceral hypersensitivity within 10 minutes (p=0.0433) and 90 minutes (p=0.0020) after intracolonic instillation.

Conclusion(s)

Our data suggest that PLM can be found in stool of patients with abdominal pain, that they cross the colonic barrier and increase visceral sensitivity. Further studies are needed to ascertain whether gut bacteria produce these PLM and investigate the precise mechanisms by which PLM induce hyperalgesia.

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CIHR, Other

Please indicate your source of funding;

Weston Family Foundation

Disclosure of Interest

None Declared

A3 CROHN’S DISEASE PROTEOLYTIC MICROBIOTA ENHANCES INFLAMMATION THROUGH PAR2 PATHWAY IN GNOTOBIOTIC MICE

Background

An imbalance in host proteases has been implicated in inflammatory bowel disease (IBD). Recent evidence implicates microbial proteolytic activity (PA) in ulcerative colitis but whether it also plays a role in Crohn’s disease (CD) remains unclear.

Purpose

We therefore investigated the colitogenic potential and underlying pathways of proteolytic CD microbiota.

Method

Adult germ-free (GF) C57BL/6 mice were colonized with CD microbiota selected based on high (CD-HPA) or low fecal proteolytic activity (CD-LPA), and from healthy controls with LPA (HC-LPA), after which total fecal proteolytic, elastolytic and mucolytic activity were analyzed in the mice. Microbial community was assessed by 16S rRNA gene sequencing. Immune function and colonic injury were investigated by inflammatory gene expression (NanoString) and histology. Colitis severity and underlying pathways were investigated in C57BL/6, Nucleotide-binding Oligomerization Domain-2 knock-out (Nod2^-/-), and Protease-Activated Receptor 2 (PAR2) cleavage resistant mice (R38E-PAR2) subjected to 2% dextran sodium sulfate in drinking water for 5 days followed by 2 days on water.

Result(s)

Colonization with HC-LPA or CD-LPA lowered baseline fecal proteolytic activity compared with GF mice, which was paralleled by lower acute inflammatory cell infiltrate. CD-HPA further increased proteolytic activity compared with GF mice. Fecal supernatants from CD-LPA or HC-LPA colonized mice had lower in vitro PAR2 cleavage compared to supernatants from GF and CD-HPA colonized mice. Several genes, such as Map kinases, Rhoa, Myd88, and Tollip, were increased in GF mice compared to colonized mice. 18 genes related to inflammation and barrier function (e.g., Mapk2k6, Tnf, Claudin1) were differentially expressed between CD-LPA and CD-HPA. CD-HPA mice had lower alpha diversity, distinct microbial profiles, and higher fecal proteolytic activity compared with CD-LPA. Abundance of several beneficial species (e.g., Akkermansia muciniphilia) was decreased while other taxa were increased (e.g., Hungattella hathewayi) in CD-HPA compared to CD-LPA. H. hathewayi as well as the serine protease K04772 were transcriptionally increased in fecal samples from CD-HPA colonized mice. C57BL/6 and Nod2^-/- mice, but not R38E-PAR2 mice, colonized with CD-HPA developed earlier and more severe colitis compared with mice colonized with CD-LPA.

Conclusion(s)

CD proteolytic microbiota is proinflammatory through a PAR2 pathway. H. hathewayi correlates with the proinflammatory phenotype through the serine protease K04772 in this model. The results support a role of microbial PA in CD, which could constitute a biomarker for identifying patients who would benefit from anti-proteolytic therapies.

Disclosure of Interest

None Declared

Crohn's disease proteolytic microbiota enhances inflammation through PAR2 pathway in gnotobiotic mice

Emerging evidence implicates microbial proteolytic activity in ulcerative colitis (UC), but whether it also plays a role in Crohn's disease (CD) remains unclear. We investigated the effects of colonizing adult and neonatal germ-free C57BL/6 mice with CD microbiota, selected based on high (CD-HPA) or low fecal proteolytic activity (CD-LPA), or microbiota from healthy controls with LPA (HC-LPA) or HPA (HC-HPA). We then investigated colitogenic mechanisms in gnotobiotic C57BL/6, and in mice with impaired Nucleotide-binding Oligomerization Domain-2 (NOD2) and Protease-Activated Receptor 2 (PAR2) cleavage resistant mice (Nod2^-/-; R38E-PAR2 respectively). At sacrifice, total fecal proteolytic, elastolytic, and mucolytic activity were analyzed. Microbial community and predicted function were assessed by 16S rRNA gene sequencing and PICRUSt2. Immune function and colonic injury were investigated by inflammatory gene expression (NanoString) and histology. Colonization with HC-LPA or CD-LPA lowered baseline fecal proteolytic activity in germ-free mice, which was paralleled by lower acute inflammatory cell infiltrate. CD-HPA further increased proteolytic activity compared with germ-free mice. CD-HPA mice had lower alpha diversity, distinct microbial profiles and higher fecal proteolytic activity compared with CD-LPA. C57BL/6 and Nod2^-/- mice, but not R38E-PAR2, colonized with CD-HPA had higher colitis severity than those colonized with CD-LPA. Our results indicate that CD proteolytic microbiota is proinflammatory, increasing colitis severity through a PAR2 pathway.

Diet-microbial cross-talk underlying increased visceral perception

Visceral hypersensitivity, a fundamental mechanism of chronic visceral pain disorders, can result from both central or peripheral factors, or their combination. As an important regulator of normal gut function, the gut microbiota has been implicated as a key peripheral factor in the pathophysiology of visceral hypersensitivity. Patients with chronic gastrointestinal disorders, such as irritable bowel syndrome, often present with abdominal pain secondary to adverse reactions to dietary components. As both long- and short-term diets are major determinants of gut microbiota configuration that can result in changes in microbial metabolic output, it is becoming increasingly recognized that diet-microbiota interactions play an important role in the genesis of visceral sensitivity. Changes in pain signaling may occur via diet-induced changes in secretion of mediators by both the microbiota and/or host cells. This review will examine the peripheral influence of diet-microbiota interactions underlying increased visceral sensitivity.

Alterations in fecal β-defensin-3 secretion as a marker of instability of the gut microbiota

Compositional changes in the microbiota (dysbiosis) may be a basis for Irritable Bowel Syndrome (IBS), but biomarkers are currently unavailable to direct microbiota-directed therapy. We therefore examined whether changes in fecal β-defensin could be a marker of dysbiosis in a murine model. Experimental dysbiosis was induced using four interventions relevant to IBS: a mix of antimicrobials, westernized diets (high-fat/high-sugar and high salt diets), or mild restraint stress. Fecal mouse β-defensin-3 and 16S rRNA-based microbiome profiles were assessed at baseline and during and following these interventions. Each intervention, except for mild restraint stress, altered compositional and diversity profiles of the microbiota. Exposure to antimicrobials or a high-fat/high-sugar diet, but not mild restraint stress, resulted in decreased fecal β-defensin-3 compared to baseline. In contrast, exposure to the high salt diet increased β-defensin-3 compared to baseline. Mice exposed to the mix of antimicrobials showed the largest compositional changes and the most significant correlations between β-defensin-3 levels and bacterial diversity. The high salt diet was also associated with significant correlations between changes in β-defensin-3 and bacterial diversity, and this was not accompanied by discernible inflammatory changes in the host. Thus, dietary change or antimicrobial exposure, both recognized factors in IBS exacerbations, induced marked dysbiosis that was accompanied by changes in fecal β-defensin-3 levels. We propose that serial monitoring of fecal β-defensins may serve as a marker of dysbiosis and help identify those IBS patients who may benefit from microbiota-directed therapeutic interventions.

Gut microbiota modulates visceral sensitivity through calcitonin gene-related peptide (CGRP) production

Abdominal pain is common in patients with gastrointestinal disorders, but its pathophysiology is unclear, in part due to poor understanding of basic mechanisms underlying visceral sensitivity. Accumulating evidence suggests that gut microbiota is an important determinant of visceral sensitivity. Clinical and basic research studies also show that sex plays a role in pain perception, although the precise pathways are not elucidated. We investigated pain responses in germ-free and conventionally raised mice of both sexes, and assessed visceral sensitivity to colorectal distension, neuronal excitability of dorsal root ganglia (DRG) neurons and the production of substance P and calcitonin gene-related peptide (CGRP) in response to capsaicin or a mixture of G-protein coupled receptor (GPCR) agonists. Germ-free mice displayed greater in vivo responses to colonic distention than conventional mice, with no differences between males and females. Pretreatment with intracolonic capsaicin or GPCR agonists increased responses in conventional, but not in germ-free mice. In DRG neurons, gut microbiota and sex had no effect on neuronal activation by capsaicin or GPCR agonists. While stimulated production of substance P by DRG neurons was similar in germ-free and conventional mice, with no additional effect of sex, the CGRP production was higher in germ-free mice, mainly in females. Absence of gut microbiota increases visceral sensitivity to colorectal distention in both male and female mice. This is, at least in part, due to increased production of CGRP by DRG neurons, which is mainly evident in female mice. However, central mechanisms are also likely involved in this process.

Changes in signalling from faecal neuroactive metabolites following dietary modulation of IBS pain

OBJECTIVE

Dietary therapies for irritable bowel syndrome (IBS) have received increasing interest but predicting which patients will benefit remains a challenge due to a lack of mechanistic insight. We recently found evidence of a role for the microbiota in dietary modulation of pain signalling in a humanised mouse model of IBS. This randomised cross-over study aimed to test the hypothesis that pain relief following reduced consumption of fermentable carbohydrates is the result of changes in luminal neuroactive metabolites.

DESIGN

IBS (Rome IV) participants underwent four trial periods: two non-intervention periods, followed by a diet low (LFD) and high in fermentable carbohydrates for 3 weeks each. At the end of each period, participants completed questionnaires and provided stool. The effects of faecal supernatants (FS) collected before (IBS FS) and after a LFD (LFD FS) on nociceptive afferent neurons were assessed in mice using patch-clamp and ex vivo colonic afferent nerve recording techniques.

RESULTS

Total IBS symptom severity score and abdominal pain were reduced by the LFD (N=25; p<0.01). Excitability of neurons was increased in response to IBS FS, but this effect was reduced (p<0.01) with LFD FS from pain-responders. IBS FS from pain-responders increased mechanosensitivity of nociceptive afferent nerve axons (p<0.001), an effect lost following LFD FS administration (p=NS) or when IBS FS was administered in the presence of antagonists of histamine receptors or protease inhibitors.

CONCLUSIONS

In a subset of IBS patients with improvement in abdominal pain following a LFD, there is a decrease in pronociceptive signalling from FS, suggesting that changes in luminal mediators may contribute to symptom response.

Biogeographic Variation and Functional Pathways of the Gut Microbiota in Celiac Disease

BACKGROUND & AIMS

Genes and gluten are necessary but insufficient to cause celiac disease (CeD). Altered gut microbiota has been implicated as an additional risk factor. Variability in sampling site may confound interpretation and mechanistic insight, as CeD primarily affects the small intestine. Thus, we characterized CeD microbiota along the duodenum and in feces and verified functional impact in gnotobiotic mice.

METHODS

We used 16S rRNA gene sequencing (Illumina) and predicted gene function (PICRUSt2) in duodenal biopsies (D1, D2 and D3), aspirates, and stool from patients with active CeD and controls. CeD alleles were determined in consented participants. A subset of duodenal samples stratified according to similar CeD risk genotypes (controls DQ2^-/- or DQ2^+/- and CeD DQ2^+/-) were used for further analysis and to colonize germ-free mice for gluten metabolism studies.

RESULTS

Microbiota composition and predicted function in CeD was largely determined by intestinal location. In the duodenum, but not stool, there was higher abundance of Escherichia coli (D1), Prevotella salivae (D2), and Neisseria (D3) in CeD vs controls. Predicted bacterial protease and peptidase genes were altered in CeD and impaired gluten degradation was detected only in mice colonized with CeD microbiota.

CONCLUSIONS

Our results showed luminal and mucosal microbial niches along the gut in CeD. We identified novel microbial proteolytic pathways involved in gluten detoxification that are impaired in CeD but not in controls carrying DQ2, suggesting an association with active duodenal inflammation. Sampling site should be considered a confounding factor in microbiome studies in CeD.

Gut bacteria interact directly with colonic mast cells in a humanized mouse model of IBS

Both mast cells and microbiota play important roles in the pathogenesis of Irritable Bowel Syndrome (IBS), however the precise mechanisms are unknown. Using microbiota-humanized IBS mouse model, we show that colonic mast cells and mast cells co-localized with neurons were higher in mice colonized with IBS microbiota compared with those with healthy control (HC) microbiota. In situ hybridization showed presence of IBS, but not control microbiota, in the lamina propria and RNAscope demonstrated frequent co-localization of IBS bacteria and mast cells. TLR4 and H₄ receptor expression was higher in mice with IBS microbiota, and in peritoneal-derived and bone marrow-derived mast cells (BMMCs) stimulated with IBS bacterial supernatant, which also increased BMMCs degranulation, chemotaxis, adherence and histamine release. While both TLR4 and H₄ receptor inhibitors prevented BMMCs degranulation, only the latter attenuated their chemotaxis. We provide novel insights into the mechanisms, which contribute to gut dysfunction and visceral hypersensitivity in IBS.

Histamine production by the gut microbiota induces visceral hyperalgesia through histamine 4 receptor signaling in mice

The gut microbiota has been implicated in chronic pain disorders, including irritable bowel syndrome (IBS), yet specific pathophysiological mechanisms remain unclear. We showed that decreasing intake of fermentable carbohydrates improved abdominal pain in patients with IBS, and this was accompanied by changes in the gut microbiota and decreased urinary histamine concentrations. Here, we used germ-free mice colonized with fecal microbiota from patients with IBS to investigate the role of gut bacteria and the neuroactive mediator histamine in visceral hypersensitivity. Germ-free mice colonized with the fecal microbiota of patients with IBS who had high but not low urinary histamine developed visceral hyperalgesia and mast cell activation. When these mice were fed a diet with reduced fermentable carbohydrates, the animals showed a decrease in visceral hypersensitivity and mast cell accumulation in the colon. We observed that the fecal microbiota from patients with IBS with high but not low urinary histamine produced large amounts of histamine in vitro. We identified Klebsiella aerogenes, carrying a histidine decarboxylase gene variant, as a major producer of this histamine. This bacterial strain was highly abundant in the fecal microbiota of three independent cohorts of patients with IBS compared with healthy individuals. Pharmacological blockade of the histamine 4 receptor in vivo inhibited visceral hypersensitivity and decreased mast cell accumulation in the colon of germ-free mice colonized with the high histamine-producing IBS fecal microbiota. These results suggest that therapeutic strategies directed against bacterial histamine could help treat visceral hyperalgesia in a subset of patients with IBS with chronic abdominal pain.

Long-term personalized low FODMAP diet in IBS

Irritable bowel syndrome (IBS) patients often resort to dietary interventions to manage their symptoms, as these are frequently exacerbated by various food items. A diet low in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs) is now considered by many a first-line treatment option for IBS, as it has been found to be superior to alternative dietary interventions. However, concerns have been raised as restricting fermentable carbohydrates might result in nutritional deficits or alter composition and function of the gut microbiome in the long term. The study by Staudacher et al., published in this issue of the journal, is the first prospective study to follow IBS patients after completing all three phases of the low FODMAPs diet (restriction, reintroduction, and personalization), demonstrating that this is safe and effective in long-term, when patients are supervised by a dietician. This mini-review provides an up-to-date overview of the use of fermentable carbohydrate's restrictions for symptom management in IBS patients, while summarizing the current knowledge on the possible mechanisms of action behind low fermentable carbohydrate diet efficacy.

A248 THE ROLE OF DIETARY TRYPTOPHAN IN INDOLE AND KYNURENINE PRODUCTION AND IMMUNE MODULATION IN HEALTHY INDIVIDUALS

Background

Natural supplements are widely consumed by the general public, with little evidence of mechanistic support. Tryptophan has gained central attention, being transformed by host and gut microbial enzymes into multiple bioactive metabolites that regulate immunity and mood. Indoles are activators of the aryl hydrocarbon receptor (AhR), crucial for the maintenance of intestinal homeostasis. Tryptophan has been advocated to prevent chronic inflammatory conditions, however the clinical data to support this are missing.

Aims

To investigate clinical, immune, and metabolic parameters in response to tryptophan supplementation, in healthy subjects on a low tryptophan diet.

Methods

We performed a randomized, double blind, placebo-controlled crossover study in 20 healthy volunteers (18 - 75 years old). Subjects were instructed to start a low tryptophan diet and then randomly assigned to a 3-week tryptophan supplementation (3g/day) or placebo, in enteric coated capsules. After a 2-week washout period, subjects crossed over to the opposite intervention arm. Questionnaires were used to assess bowel symptoms, anxiety, depression and stress levels (GSRS, HADS and DASS21, respectively). Stool, urine, blood and duodenal aspirates were collected to measure tryptophan metabolites and cytokines.

Results

Tryptophan supplementation had no changes in gastrointestinal symptoms or behavioral parameters. Compared with placebo, tryptophan increased urinary and plasma levels of indoleamine 2,3-dioxygenase/kynurenine (p= 0.002 and p= 0.02, respectively) and indoles (p= 0.001 and p= 0.01, respectively), suggestive of activation of host and microbial metabolic pathways. Urinary and plasma metabolites were higher than in feces (p=<0.05), suggesting their active absorption in the small intestine. There were no differences in AhR activity in duodenal aspirates or in stool. Although no changes in the cytokine production were detected, serum kynurenine pathway metabolites negatively correlated with IL-8 levels (R=-0.72; p=0.001). Fecal tryptophan metabolites levels positively correlated with anxiety and depression scores, suggesting that the microbial metabolism of dietary tryptophan in the colon impacts host behavior.

Conclusions

Tryptophan supplementation in healthy individuals was safe and had a measurable influence on microbial and host metabolism, mainly kynurenine and indole pathways, with known immunomodulatory properties. Tryptophan was metabolized and absorbed in the small intestine, reflected by the high metabolite levels in plasma and urine. Fecal metabolites correlating with clinical parameters reflect subjects’ long-term diet. Further studies are warranted to study tryptophan supplementation in disorders with altered AhR pathways.

Funding Agencies

CIHR

A144 CHRONIC DSS LEADS TO ALTERED EXPRESSION OF IRAK4/TPL2 PATHWAYS IN UC-COLONIZED MICE

Background

Ulcerative colitis (UC) is one of two forms of inflammatory bowel disease (IBD). The exact cause of IBD is unknown but altered host-microbe interactions and genetic susceptibility are involved in its pathogenesis. Many patients with IBD do not respond to biological therapies targeting single cytokines, therefore new therapies that target common immune pathways are being developed and need to be tested in relevant preclinical models. Previously we have shown that mice colonized with UC microbiota upregulated genes related to inflammation without induction of colitis compared to healthy volunteer-colonized mice. We thus investigated whether IRAK4 and TPL2-induced pathways, new therapeutic targets in development upstream of inflammatory cytokine gene activation, are upregulated in mice colonized with UC microbiota and chronic colitis.

Aims

Our aim was to characterize TPL2 and IRAK4 signalling pathways and T cell phenotypes in UC-colonized mice following chronic low-dose dextran sodium sulfate (DSS) colitis.

Methods

10-16-week-old germ-free C57BL/6 mice were colonized with fecal microbiota from a patient with UC experiencing a flare (n=16). Mice were housed in a gnotobiotic facility during the experiment. Three weeks following colonization, colitis was induced in half of the mice by three cycles (5 d each; 2.0%, 1.5% and 1.5%, respectively) of DSS in drinking water with a 5-d wash-out period between cycles. All mice were fed a control diet (7004, Teklad). Fecal samples were collected weekly. At sacrifice, disease activity (colon length, occult blood in feces, stool consistency, and spleen weight) was measured and colon tissue was collected for histological analysis and RNA sequencing. Mesenteric lymph nodes (MLNs) were acquired for flow cytometry to analyze T cell phenotypes.

Results

In UC-colonized mice, chronic low-dose DSS induced softer feces (p<0.0001), shorter colon length (p<0.0001), and increased spleen weight (p<0.0001), compared with water treated mice. This was paralleled by detectable blood in stool, development of moderate colitis (DSS: 1.9+/-1.4 vs H₂O: 0.5+/-0.2; p<0.02) and higher proportion of IL-17 (p=0.003) and IFN-γ-producing T cells (p=0.06) in MLNs compared with water treated mice. RNA sequencing revealed that inflammatory genes, mainly related to the IRAK4/TPL2 pathway (e.g., Gadd45b, Socs3, Il1b), were significantly increased (p≤0.05) in the colon of mice treated with DSS compared with water.

Conclusions

When challenged with a chronic low-dose chemical injury agent, mice colonized with UC microbiota develop clinical and histological signs of colitis and upregulation of genes involved in inflammation like Gadd45b, Socs3, and Il1b. Thus, this model represents a new valuable tool for preclinical testing of new drug candidates, such as those related to the modulation of IRAK4/TPL2 pathways.

Funding Agencies

CCC

A46 BIOGEOGRAPHIC VARIATION AND FUNCTIONAL PATHWAYS OF THE GUT MICROBIOTA IN CELIAC DISEASE

Background

Genes and gluten are necessary, but insufficient to cause celiac disease (CeD), as risk alleles (DQ2 or DQ8) are prevalent in ~30–40% of the healthy population consuming gluten. Gut microbiota shifts and infections have been proposed as risk modulators. Biogeographic characterization of the microbiota in CeD patients and its functional significance are limited, particularly at the duodenum, the main site of inflammation.

Aims

We studied microbiota composition and predicted function along the gastrointestinal tract and investigated the impact of host genetics and CeD activity.

Methods

We used 16S rRNA gene sequencing (Illumina) and predicted gene function analysis (PICRUSt2), to study the microbiota in duodenal biopsies (D1, D2 and D3), duodenal aspirates, and fecal samples from patients with active CeD (n= 24) (biopsy and serology confirmed) and controls (non-celiac, n= 41). CeD alleles were determined in consented participants using DQ-CD typing. Small intestinal samples from controls (DQ2^-/- = 14; DQ2^+/- = 7) and CeD (DQ2^+/- = 12) were used for further analysis and to colonize C57BL/6 germ-free mice for gluten metabolism studies.

Results

Microbiota community composition and predicted function was mainly determined by intestinal location (P= 0.001). Within the duodenum, but not in stool, CeD patients had increased abundance of opportunistic pathogens. Escherichia coli was increased in D1, Streptococcus pneumoniae in D2, and Neisseria in D3 versus controls. Predicted bacterial protease and peptidase genes were altered in CeD DQ2^+/- patients versus DQ2^-/- controls. In DQ2^+/- controls, fewer predicted bacterial genes were altered compared to CeD DQ2^+/- patients. Impaired capacity to metabolize gluten was confirmed in germ-free mice colonized with microbiota from CeD (DQ2^+/-), but not DQ2^+/- or DQ2^-/- controls.

Conclusions

In the duodenum, CeD is associated with increased opportunistic pathogens and altered bacterial proteolytic profile. These are not determined by genetic predisposition, as CeD and controls with similar genetic background differed in its predicted bacterial proteolytic function, which was confirmed in mice colonized with duodenal microbiota using these cohorts. Our study highlights the need for defining sampling location in studies investigating the role of microbiota in CeD.

Funding Agencies

CAG, CCC, CIHR

A229 GUT MICROBIOTA PROFILES, DIET AND SHORT-CHAIN FATTY ACIDS AS PREDICTORS OF GENERALIZED ANXIETY DISORDER

Background

Generalized anxiety disorder (GAD) is a debilitating chronic condition with a lifetime prevalence of 4–7% worldwide. Both diet and gut microbiota have been previously associated with anxiety.

Aims

To investigate whether bacterial taxa and/or nutrients associate with GAD, and whether they differ from those of healthy controls (HC).

Methods

Patients with GAD (n=82) and matched HC (n=97) were assessed by validated questionnaires for anxiety (DASS-21), gastrointestinal (GI) symptoms (Rome III, Short-Form Leeds Dyspepsia), and dietary profiles by the Dietary Questionnaire for Epidemiological Studies. We quantified several blood and stool biomarkers, including inflammatory and neuroactive metabolites, as well as short-chain fatty acids. Stool microbiota profiles were assessed by16S rRNA gene sequencing through Illumina. The data was then analyzed following the pipelines of dada2 and by multiple factor analysis (MFA), mean comparisons, correlation, LEfSe and XGBoost using R software (v.1.2.1335). Multiple comparison results were corrected allowing 5% of FDR.

Results

Using MFA to analyze all variables, we identified 3 clusters: one mainly composed of HC (n=99, 91% HC, GI symptoms in 25% of subjects), a second mixed cluster (n=30, 80% GAD, GI symptoms in 80%) and a third cluster mainly composed of GAD patients (n=50, 98% GAD, GI symptoms in 86%). When focusing only on the HCs of cluster 1 (n=90) and GADs of cluster 3 (n=49), we found higher GI symptoms, body mass index, serum C-reactive protein and stool calprotectin levels (adj. p=1.3x10-9, 0.001, 0.017 and 0.017, respectively) and lower concentrations of propionate, butyrate and acetate in GAD compared to HC. GADs also reported overall lower caloric intake (kJ/day; adj. p=1.7x10-4) in the food frequency questionnaire. Fibre (g/day) was the macronutrient most negatively associated with anxiety scores (R=-0.44; adj. p=4.2x10-5). Bacteroides was the only bacterial taxon significantly associated with GAD, as well as with anxiety scores (R=0.31, adj. p=0.003). Interestingly, Bacteroides/fiber ratio was strongly correlated to anxiety scores (R=0.58, adj. p=2.7x10-09). Furthermore, demographic, biomarkers and bacterial taxa data were predictive of the patients’ disease state with 92.8% accuracy. The features that aid the model to predict disease state were Bacteroides/fiber ratio, GI symptoms and stool acetate levels.

Conclusions

Our results suggest that most GAD patients differ in dietary and microbiota profiles from HCs, and that the Bacteroides/fiber ratio, stool acetate and GI symptoms might be good predictors of disease state. Furthermore, these data strongly support the role of microbiota-gut-brain axis in genesis of psychiatric diseases, and they will inform mechanistic studies in gnotobiotic mouse models.

Funding Agencies

NIH

A13 GUT MICROBIOTA MODULATES CGRP PRODUCTION BY DRG NEURONS IN FEMALE MICE

Background

Abdominal pain is a common complaint in patients with chronic gastrointestinal disorders. Accumulating evidence suggests that gut microbiota is an important determinant of gut function, including visceral sensitivity. Germ-free (GF) mice have been shown to display visceral hypersensitivity, which normalizes after colonization. Thus, gut microbiota is involved in the regulation of gut nociception but the underlying mechanisms remain poorly understood.

Aims

To investigate the role of gut microbiota in abdominal pain.

Methods

Method: Adult female and male conventionally raised (SPF) or GF mice were used. Their visceral sensitivity was assessed by visceromotor responses to colorectal distension, at baseline (vehicle: Tween 80 10%, Ethanol 10%, saline 80%) and after intracolonic administration of a TRPV1 agonist capsaicin (30 μg), or a mixture of G-protein coupled receptors agonists (GPCR: bradykinin, histamine and serotonin; 30 μg). Neuronal excitability of dorsal root ganglia (DRG) neurons was assessed by calcium imaging using a fluorescent probe Fluo-4 (1 mM) after stimulation with capsaicin (12.5 nM, 125 nM and 1250 nM) or GPCR agonists (0.3 μM, 3 μM and 30 μM). The neuronal production of substance P (SP) and calcitonin gene-related peptide (CGRP) in response to capsaicin (1250 nM) or GPCR agonists (30 μM) was measured by ELISA.

Results

At baseline, GF male mice exhibited higher responses to colorectal distension compared to SPF males, while SPF and GF females displayed similar visceral sensitivity. In contrast, both intracolonic capsaicin and GPCR agonists increased visceral sensitivity in GF females compared to SPF females, while responses were comparable in male groups.

DRG neuronal activation after stimulation with capsaicin or GPCR agonists was similar in SPF and GF mice of both sexes. While stimulated production of SP by DRG neurons was similar in SPF and GF mice, regardless of sex, the production of CGRP in response to GPCR agonists was higher in GF female than SPF female mice.

Conclusions

Our data suggest that visceral sensitivity in vivo differs according to the gut microbiota status, sex and the activation of TRPV1 and GPCR pathways. At the level of DRG neurons, the absence of gut microbiota does not affect the neuronal activation or production of SP. However, GPCR agonists-stimulated release of CGRP is higher in GF female compared to SPF female mice. All together, our data demonstrate that the gut microbiota modulates visceral sensitivity by regulating the production of CGRP in the sensory neurons, especially in female mice. Further mechanistic studies are needed to investigate the role of gut microbiota in visceral sensitivity.

Funding Agencies

CIHR

A34 GLUTEN-FREE DIET IMPROVES DYSPEPTIC SYMPTOMS IN PATIENTS WITH TYPE 1 DIABETES IN WHOM CELIAC DISEASE WAS EXCLUDED

Background

Patients with type 1 Diabetes Mellitus (T1DM) often suffer from dyspeptic symptoms, such as abdominal pain, bloating, early satiety, nausea and vomiting. T1DM shares genetic risk factors (HLA-DQ2 and DQ8) with celiac disease, an autoimmune disorder caused by an immune reaction to gluten. Patients with concomitant T1DM and celiac disease benefit from a gluten-free diet (GFD), as it improves their symptoms, gastric emptying and small intestinal inflammation. However, it is unknown whether GFD has any benefit in patients with T1DM without celiac disease, who present with symptoms of dyspepsia or gastroparesis.

Aims

To investigate the role of a GFD in the management of moderate to severe dyspeptic symptoms in non-celiac patients with T1DM.

Methods

We enrolled 13 adult T1DM patients, in whom celiac disease was ruled out, suffering from two or more upper GI symptoms. The patients were instructed to adhere to a strict GFD for a period of 1 month, under the supervision of a dietitian. Glycemic levels were monitored by a continuous glucose monitoring device (CGM) for 2 weeks before, and at the end of the GFD period. Standardized questionnaires were used to assess upper GI symptoms (Gastroparesis Cardinal Symptoms Index, Short Form Leeds Dyspepsia questionnaire), general quality of life (Patient Assessment of Upper GI Disorders Quality of Life), and anxiety and depression (Hospital Anxiety Depression scale). Blood samples were collected to assess glycaemia (Hb1Ac) and immune markers. Scintigraphy and videofluoroscopy were used to assess gastric emptying.

Results

After one month on a GFD, T1DM patients reported a significant improvement in nausea (p<0.05), sensation of fullness (p<0.001) and bloating (p<0.0001). Overall dyspepsia symptoms also improved (p<0.01), with 92% of patients reporting decreased dyspepsia scores. Moreover, there was an improvement in the quality of life (p<0.01), and decreased scores of anxiety and depression (p<0.01 and p<0.05, respectively). There were no changes in gastric emptying or glycemic management metrics, such as mean glucose level, time in target, glucose variance or HbA1c levels. Interestingly, one year after the end of the study, 63.6% of participants continued to follow a GFD. The most common reason to remain on a GFD reported by these patients was “because it improved GI symptoms”. Questionnaire data collected at the follow-up demonstrated that the improvement of dyspeptic symptoms persisted after 1 year on GFD (p<0.001).

Conclusions

GFD improves dyspeptic symptoms in T1D patients without concomitant celiac disease, without affecting their glycemic levels or gastric emptying. Although these results need to be validated in a larger study, our data suggest that GFD could be used as a therapeutical tool for T1DM patients grappling with burdensome upper GI symptoms.

Gluten-Free diet improves dyspepsia symptoms in Type 1 Diabetes patients, after 1 month and 1 year

Funding Agencies

CIHR

A6 MECHANISMS UNDERLYING GUT DYSFUNCTION FOLLOWING C. DIFFICILE INFECTION AND IMPLICATIONS FOR TREATMENT

Background

Recent evidence suggests an increasing prevalence of gut dysfunction following C. difficile infection (CDI). The accompanying prolonged antibiotic (AB) exposure likely contributes to chronic gut dysfunction and our ability to induce gut dysfunction in germ free (GF) mice colonized with microbiota from a patient with severe slow transit post CDI (PCDI) supports this notion (10.1093/jcag/gwz047.117). Furthermore, we were able to restore gut function following fecal microbial transfer from healthy murine donors. Our studies have implicated a role for macrophages in the destruction of the Interstitial Cell of Cajal (ICC) network underlying slow colonic transit in the humanized mouse model. These findings prompted us to evaluate microbiota-directed therapy in normalising gut function in this model.

Aims

1)To investigate whether dietary psyllium rescues the development of slow colonic transit (SCT) through modulating host function via microbiota mediated immune mechanisms; and 2)To evaluate the mechanisms underlying the beneficial effects of psyllium

Methods

GF mice were colonized with either microbiota from the PCDI patient or healthy control (HC) for 3 weeks following which PCDI mice were treated with either a control diet or a 15% psyllium diet (PSY). Colonic motility was assessed before and after the diet intervention using the bead expulsion test. Stool samples were collected for microbial profiling, and short and branched-chain fatty acids (SCFA/BCFA) analysis. Colonic muscle layers encompassing myenteric plexus (MP) were collected for gene expression analysis and to evaluate activated macrophages and ICC degeneration using immunohistochemistry.

Results

Microbiota from a PCDI patient induced a SCT phenotype in GF mice (n=13) as compared to mice colonized with HC microbiota (p=0.0002). Psyllium rescued this SCT phenotype in mice (PCDI(n=7) vs.PSY(n=6):p=0.0014). The psyllium-induced rescue was accompanied by normalization of the ICC network and morphological alterations in infiltrating macrophages. This was supported by changes in immune-related gene expression in the MP including CD11b, NOS, Myd88, Mapk1 and NF-κB. Additionally, bacterial composition was different between PCDI and PSY group (p=0.003). SCFAs like acetic and propionic acid were increased, while BCFA like isobutyric and isovaleric acid were decreased following PSY treatment. These alterations in SCFA/BCFA were supported by fluctuations in specific bacteria like Butyricimonas, Phascolarctobacterium and Allistipes.

Conclusions

Our results provide evidence that chronic gut dysfunction following CDI and AB exposure is microbiota-driven. Furthermore, microbiota-directed therapy using psyllium could serve as a novel therapeutic strategy to normalize gut function via microbiota-mediated restoration of immune homeostasis in these patients.

Funding Agencies

W. Garfield Weston Foundation

A14 THE INTESTINAL MICROBIOTA CONTRIBUTES TO AGE-RELATED MEMORY DECLINE

Background

Age-related deterioration of cognitive function and memory capacity occur in both humans and rodents. For example, significant memory deficits have been reported in conventionally raised (SPF) old mice compared to conventionally raised young mice submitted to a spatial memory task (Prevot et al., 2019, Mol Neuropsychiatry 5, 84–97). Microbiota-to-brain signaling is now well established in mice and humans, but the extent to which it influences age-associated memory decline is unknown.

Aims

Our study examines whether the intestinal microbiota contributes to age-associated changes in brain function. We address the specific hypothesis that age-associated cognitive decline is attenuated in the absence of the intestinal microbiota.

Methods

We assessed anxiety-like and depressive-like behavior, locomotor activity and spatial memory performance in young germ-free (GF) mice (2–3 months of age, n=24) and senescent GF mice (13–27 months old, n=22) maintained in axenic conditions, and compared them to conventionally raised (SPF) mice of the same age. Anxiety-like behavior, locomotor activity and depressive-like behavior were measured using the light-dark preference, open-field, and tail suspension tests. We also used the Y-maze test based on a spontaneous alternation task to assess cognition, with the alternation rate as a proxy of spatial working memory. The age-associated inflammation was assessed with IL-6 cytokine plasma concentrations measured by ELISA.

Results

Anxiety-like behavior and depressive-like behavior did not change with the age regardless of the microbial status. However, old SPF mice traveled less distance (866.8 cm) than young SPF mice (1375 cm, p < 0.01) in the open-field. Similarly, old GF mice also traveled less distance (458.9 cm) than young GF mice (875.7 cm, p < 0.0001). In contrast to old SPF mice, old GF mice did not show memory impairment in the spatial memory task. Indeed, old SPF mice displayed lower alternation rate of 58.3%, compared to that found in young SPF mice (76.9%, p < 0.05) while both old and young GF mice had an identical alternation rate of 73.3% ( p > 0.05). In addition, IL-6 plasma levels revealed that old GF mice did not show signs of age-associated inflammation that was evident in old SPF mice (3.68 vs. 13.93 pg/ml, p < 0.05).

Conclusions

We conclude that the absence of age-related memory deficit in old germ-free mice is consistent with a role for the microbiota in age-related cognitive decline, likely mediated via the immune system, as suggested by the absence of age-associated inflammation in germ-free mice. We propose that novel microbiota-targeted therapeutic strategies may prevent or delay the cognitive decline of aging.

Funding Agencies

CIHRBalsam Family Foundation

A51 ROLE OF GUT MICROBIOTA IN THE EPISODIC NATURE OF SYMPTOMS IN IRRITABLE BOWEL SYNDROME

Background

Irritable bowel syndrome (IBS) is a complex functional gastrointestinal disorder with likely heterogenous pathophysiology, multiple symptoms, and comorbidities. Growing evidence shows that the gut microbiota composition and function are altered in IBS patients. However, identifying the critical drivers of clinical expression remains challenging due to the episodic occurrence of IBS symptoms, the inherent variability in composition of gut microbiota across individuals, and high sensitivity of gut microbiota to dietary and environmental cues.

Aims

To identify whether changes in gut microbiota composition accompany or, predict the occurrence of symptoms.

Methods

28 IBS patients (IBS-D n=20, IBS-C n=8) and 10 healthy controls (HC) were followed longitudinally for 25 weeks, collecting stool samples, and recording their symptoms weekly. Stool microbiota profiles were assessed by 16S rRNA gene sequencing using Illumina platform. The sequences were preprocessed, filtered, and annotated using DADA2 and phyloseq pipelines; statistical analyses were performed using FactomineR and microbiomeanalyst packages in R. Statistical significance was set at p<0.05.

Results

Multifactorial analysis of clinical data classified 950 samples in 6 clusters. Distribution of samples among the clusters was based on Bristol stool scale defining symptomatic periods (scores <3 and >4 indicating abnormal stool) and asymptomatic periods (scores 3 or 4), with several gut and mood symptoms varying significantly between the two categories. IBS-D patients, but not IBS-C patients presented with changes in symptoms severity, such as pain, diarrhea, constipation, and anxiety during the symptomatic periods. Depression scores were, however, higher in IBS-C compared to IBS-D patients. In contrast, immune makers such as fecal b-defensin-2 and calprotectin were higher during asymptomatic periods in IBS-D, but not in IBS-C patients. Bacterial diversity profiles differed among IBS patients (IBS-D and IBS-C) and HC, namely Shannon index and Bray-Curtis distance, but they did not change significantly between the symptomatic and asymptomatic periods within each subtype. Despite this, several bacterial taxa unique to each cluster were identified using linear mixed models.

Conclusions

Our results demonstrate the need to study patterns of co-occurrence of IBS symptoms and their severity during symptomatic and asymptomatic periods to better understand the role of identified bacterial taxa in the symptom generation. Identifying their temporal changes and cross-feeding patterns in individual patients will shed light on the underlying mechanistic role of gut microbiota in IBS, which might be otherwise obscured by group generalizations.

Funding Agencies

CIHR

A196 DIARRHEA AS A PRESENTING SYMPTOM OF RELAPSED GRANULOMATOSIS WITH POLYANGIITIS

Background

Granulomatosis with polyangiitis (GPA) is a rare, small-to-medium sized-vessel vasculitis that typically involves the sinus, respiratory, and renal systems. The gastrointestinal (GI) tract is rarely involved, but its exact frequency is poorly characterized. GI symptoms have been reported to occur in up to 10% of acute presentations, and a historic series of 56 autopsies of GPA patients found 24% to have focal necrotizing arteriolitis of the intestine (Storesund, 1998). There are few case reports of colitis associated with GPA. They commonly describe abdominal pain, rectal bleeding, and less frequently, perforation, early in the disease course in conjunction with other classic systems involvement which aid in the diagnosis of GPA.

Aims

We present the case of a 77 year-old woman with lung biopsy-proven cANCA-positive GPA who was found to have colonic vasculitis after she had been in remission for several years.

Methods

Case report and literature review

Results

The patient presented with a 1-month history of progressive back pain, followed by 1 week of severe abdominal pain and watery diarrhea. She was afebrile, with a leukocyte count of 13.8x109/L, C-reactive protein of 213 mg/L, and fecal calprotectin of 669mg/kg. cANCA was strongly positive at 5.4 AI. Computed tomography scan revealed focal inflammatory change at the cecum and terminal ileum. Stool cultures were negative. Colonoscopy showed a polypoid, inflammatory-appearing hard mass at the ileocecal valve with surrounding fragile mucosa. Ileocecal valve biopsies described fibropurulent material and granulation tissue consistent with ulcer bed with surrounding mucosa showing chronic ischemic colitis with various degrees of acute cryptitis. The most likely etiology was speculated by the pathologist to be involvement of the colon by vasculitis, as other etiologies appeared to be ruled out. The patient had mild kidney injury, but no additional lung findings, in contrast to her initial presentation of GPA. She was started on prednisone 50mg/day. Her back pain, abdominal pain, and diarrhea resolved within 1 week, and renal function improved. Currently, there is a plan to start Rituximab for chronic treatment.

Conclusions

Our case of GPA-associated colitis is unique for several reasons. First, most case reports describe rectal bleeding as the presenting symptom of GPA colitis, whereas our patient presented with non-hemorrhagic diarrhea. Second, where available, reports of colitis correlated endoscopically with colonic ulcerations, whereas our patient had an ileocecal mass. Third, most reports present colitis associated with a new diagnosis of GPA, whereas our patient presented with colitis as new GI system involvement with likely inflammatory back pain as the presenting feature of GPA relapse. While a rare feature, colitis secondary to GPA can be considered in the appropriate context.

Funding Agencies

None

Gluten-Free Diet Reduces Symptoms, Particularly Diarrhea, in Patients With Irritable Bowel Syndrome and Antigliadin IgG

BACKGROUND & AIMS

Many patients with irritable bowel syndrome (IBS) perceive that their symptoms are triggered by wheat-containing foods. We assessed symptoms and gastrointestinal transit before and after a gluten-free diet (GFD) in unselected patients with IBS and investigated biomarkers associated with symptoms.

METHODS

We performed a prospective study of 50 patients with IBS (ROME III, all subtypes), with and without serologic reactivity to gluten (antigliadin IgG and IgA), and 25 healthy subjects (controls) at a university hospital in Hamilton, Ontario, Canada, between 2012 and 2016. Gastrointestinal transit, gut symptoms, anxiety, depression, somatization, dietary habits, and microbiota composition were studied before and after 4 weeks of a GFD. HLA-DQ2/DQ8 status was determined. GFD compliance was assessed by a dietitian and by measuring gluten peptides in stool.

RESULTS

There was no difference in symptoms among patients at baseline, but after the GFD, patients with antigliadin IgG and IgA reported less diarrhea than patients without these antibodies (P = .03). Compared with baseline, IBS symptoms improved in 18 of 24 patients (75%) with antigliadin IgG and IgA and in 8 of 21 patients (38%) without the antibodies. Although constipation, diarrhea, and abdominal pain were reduced in patients with antigliadin IgG and IgA, only pain decreased in patients without these antibodies. Gastrointestinal transit normalized in a higher proportion of patients with antigliadin IgG and IgA. Anxiety, depression, somatization, and well-being increased in both groups. The presence of antigliadin IgG was associated with overall reductions in symptoms (adjusted odds ratio compared with patients without this antibody, 128.9; 95% CI, 1.16-1427.8; P = .04). Symptoms were reduced even in patients with antigliadin IgG and IgA who reduced gluten intake but were not strictly compliant with the GFD. In controls, a GFD had no effect on gastrointestinal symptoms or gut function.

CONCLUSIONS

Antigliadin IgG can be used as a biomarker to identify patients with IBS who might have reductions in symptoms, particularly diarrhea, on a GFD. Larger studies are needed to validate these findings. ClinicalTrials.gov: NCT03492333.

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.

Fecal microbiome differs between patients with systemic sclerosis with and without small intestinal bacterial overgrowth

Introduction:

Gastrointestinal manifestations of systemic sclerosis affect up to 90% of patients, with symptoms including diarrhea and constipation. Small intestinal bacterial overgrowth is a condition associated with increased numbers of pathogenic bacteria in the small bowel. While currently unknown, it has been suggested that dysregulation of the fecal microbiota may play a role in the development of systemic sclerosis and small intestinal bacterial overgrowth.

Objectives:

Our study aimed to describe the fecal microbiota of patients with systemic sclerosis and compare it between those with and without a diagnosis of small intestinal bacterial overgrowth. We also compared the fecal microbiota of systemic sclerosis patients with that of healthy controls to understand the association between particular bacterial taxa and clinical gastrointestinal manifestations of systemic sclerosis.

Methods:

A total of 29 patients with systemic sclerosis underwent breath testing to assess for small intestinal bacterial overgrowth, provided stool samples to determine taxonomic assignments, and completed the University of California Los Angeles Scleroderma Clinical Trial Consortium Gastrointestinal Tract 2.0, which details symptoms and quality-of-life factors. Stool samples were compared between systemic sclerosis patients with and without small intestinal bacterial overgrowth, and between patients with systemic sclerosis and a healthy control cohort (n = 20), aged 18–80 years.

Results:

Fecal microbiome analyses demonstrated differences between systemic sclerosis patients with and without small intestinal bacterial overgrowth and differences in the diversity of species between healthy controls and patients with systemic sclerosis. Trends were also observed in anticentromere antibody systemic sclerosis patients, including higher Alistipies indistincus spp. levels associated with increased methane levels of breath gas testing and higher Slakia spp. levels associated with increased rates of fecal soiling.

Conclusions:

Our results suggest that changes to the fecal microbiome occur in patients with small intestinal bacterial overgrowth and systemic sclerosis when compared to healthy controls. As a cross-sectional study, the potential pathophysiologic role of an altered microbiome in the development of systemic sclerosis was not considered and hence needs to be further investigated.

Aryl hydrocarbon receptor ligand production by the gut microbiota is decreased in celiac disease leading to intestinal inflammation

Metabolism of tryptophan by the gut microbiota into derivatives that activate the aryl hydrocarbon receptor (AhR) contributes to intestinal homeostasis. Many chronic inflammatory conditions, including celiac disease involving a loss of tolerance to dietary gluten, are influenced by cues from the gut microbiota. We investigated whether AhR ligand production by the gut microbiota could influence gluten immunopathology in nonobese diabetic (NOD) mice expressing DQ8, a celiac disease susceptibility gene. NOD/DQ8 mice, exposed or not exposed to gluten, were subjected to three interventions directed at enhancing AhR pathway activation. These included a high-tryptophan diet, gavage with Lactobacillus reuteri that produces AhR ligands or treatment with an AhR agonist. We investigated intestinal permeability, gut microbiota composition determined by 16S rRNA gene sequencing, AhR pathway activation in intestinal contents, and small intestinal pathology and inflammatory markers. In NOD/DQ8 mice, a high-tryptophan diet modulated gut microbiota composition and enhanced AhR ligand production. AhR pathway activation by an enriched tryptophan diet, treatment with the AhR ligand producer L. reuteri, or pharmacological stimulation using 6-formylindolo (3,2-b) carbazole (Ficz) decreased immunopathology in NOD/DQ8 mice exposed to gluten. We then determined AhR ligand production by the fecal microbiota and AhR activation in patients with active celiac disease compared to nonceliac control individuals. Patients with active celiac disease demonstrated reduced AhR ligand production and lower intestinal AhR pathway activation. These results highlight gut microbiota-dependent modulation of the AhR pathway in celiac disease and suggest a new therapeutic strategy for treating this disorder.

Novel Fecal Biomarkers That Precede Clinical Diagnosis of Ulcerative Colitis

BACKGROUND & AIMS

Altered gut microbiota composition and function have been associated with inflammatory bowel diseases, including ulcerative colitis (UC), but the causality and mechanisms remain unknown.

METHODS

We applied 16S ribosomal RNA gene sequencing, shotgun metagenomic sequencing, in vitro functional assays, and gnotobiotic colonizations to define the microbial composition and function in fecal samples obtained from a cohort of healthy individuals at risk for inflammatory bowel diseases (pre-UC) who later developed UC (post-UC) and matched healthy control individuals (HCs).

RESULTS

Microbiota composition of post-UC samples was different from HC and pre-UC samples; however, functional analysis showed increased fecal proteolytic and elastase activity before UC onset. Metagenomics identified more than 22,000 gene families that were significantly different between HC, pre-UC, and post-UC samples. Of these, 237 related to proteases and peptidases, suggesting a bacterial component to the pre-UC proteolytic signature. Elastase activity inversely correlated with the relative abundance of Adlercreutzia and other potentially beneficial taxa and directly correlated with known proteolytic taxa, such as Bacteroides vulgatus. High elastase activity was confirmed in Bacteroides isolates from fecal samples. The bacterial contribution and functional significance of the proteolytic signature were investigated in germ-free adult mice and in dams colonized with HC, pre-UC, or post-UC microbiota. Mice colonized with or born from pre-UC-colonized dams developed higher fecal proteolytic activity and an inflammatory immune tone compared with HC-colonized mice.

CONCLUSIONS

We have identified increased fecal proteolytic activity that precedes the clinical diagnosis of UC and associates with gut microbiota changes. This proteolytic signature may constitute a noninvasive biomarker of inflammation to monitor at-risk populations that can be targeted therapeutically with antiproteases.

A13 A HIGH SALT DIET SYNERGIZES WITH UC MICROBIOTA TO INDUCE A PROINFLAMMATORY IMMUNE TONE IN IMMUNOCOMPETENT GNOTOBIOTIC MICE

Background

The exact cause for inflammatory bowel disease (IBD) is unknown, however, there is consensus that a combination of genetic, environmental, and immune factors, participate in its pathogenesis. Recently, high salt diet (HSD) has been shown to increase the severity of experimental colitis through depletion of lactobacilli in specific pathogen-free mice. However, whether HSD-microbiota interaction occurs in mice colonized with microbiota from patients with IBD, is unknown.

Aims

Our aim was to determine whether mice colonized with microbiota from patients with active ulcerative colitis (UC), one of two forms of IBD, develop more severe inflammation when fed a HSD.

Methods

10–15 week-old germ-free C57BL/6 mice were colonized with fecal microbiota from a healthy control (HC, n=13) or from a patient with UC experiencing a flare (UC, n=13). Colonized mice were housed in ISO positive cages (Techniplast) in a gnotobiotic facility during the experiment. For each group, half of the mice were kept on a control diet (7004, Teklad) and the other half were fed a HSD (7004 supplemented with 4% NaCl) plus 1% NaCl in drinking water for 3 weeks. At sacrifice, colon tissue was collected for histological analysis, RNA sequencing, and flow cytometry. Fecal samples were collected for lipocalin-2 determination.

Results

Colonic polymorphonuclear (PMN) cells were higher in UC compared with HC mice, regardless of diet (p&lt;0.01). In mice fed HSD, UC mice also had higher PMN cell counts than HC mice (p&lt;0.001). Administration of HSD to UC, but not to HC mice, also increased the proportion of α4+IFNg-producing T cells in the colonic lamina propria, compared with UC mice fed control diet (p&lt;0.01). This was paralleled by higher fecal lipocalin-2 in UC mice fed HSD compared with control diet (p&lt;0.05). Targeted analysis of RNA sequencing data revealed that 7 genes, mainly related to the JAK/STAT pathway (i.e., Stat2, Tyk2, Tlr7) were differentially expressed (p≤0.05) between HC and UC mice fed the control diet. A different gene expression signature was found in mice fed HSD compared with control diet, with an increase in proinflammatory genes in UC colonized mice compared to HC colonized mice, such as Il12a and Il6 (p&lt;0.05).

Conclusions

Immunocompetent mice colonized with microbiota from a UC patient in flare spontaneously developed a proinflammatory immune tone, which was exacerbated by HSD. The different pattern of gene induction observed in mice colonized with the microbiota from the same UC donor, but fed HSD, suggests independent and synergistic pathways conducive to inflammation. Future studies will explore the preclinical therapeutic effect of novel drug candidates for the inhibition of such pathways.

Funding Agencies

CCC

A29 NOVEL FECAL BIOMARKERS THAT PRECEDE CLINICAL DIAGNOSIS OF ULCERATIVE COLITIS

Background

Altered gut microbiota composition and function has been associated with inflammatory bowel diseases (IBD) including ulcerative colitis (UC), but causality and mechanisms remain unknown. Most studies have examined patients with active or treated disease and little is known about microbial compositional or functional changes that occur before disease onset.

Aims

We studied a longitudinal cohort of subjects at risk for IBD to define the fecal microbial composition and function in subjects prior to UC onset (pre-UC) and at diagnosis (post-UC), and in matched at-risk subjects that remained healthy.

Methods

Fecal samples were collected from healthy individuals at-risk for IBD (pre-UC; n=13) and subjects were followed longitudinally until UC diagnosis (post-UC, n=9), at which point another fecal sample was collected. Fecal samples from a cohort of matched at-risk individuals that did not develop UC were used as healthy controls (n=48). We applied 16S rRNA gene sequencing, next generation shotgun sequencing, in vitro proteolytic assays and gnotobiotic colonizations to define the microbial composition and proteolytic function in fecal samples.

Results

The microbiota of post-UC subjects clustered separately from pre-UC and HC subjects, based on bray-curtis and unweighted UniFrac, had reduced alpha-diversity, and had reduced abundance of Aldercreutzia compared to pre-UC and HC. In vitro functional analysis revealed increased fecal proteolytic and elastase activity in pre-UC and post-UC samples compared to HC. Metagenomics identified pathways and gene families related to protein metabolism and proteases/peptides that were significantly different between HC and pre-UC samples, suggesting a bacterial component to the pre-UC proteolytic signature. Elastase activity inversely correlated with the relative abundance of Adlercreutzia, and other potentially beneficial taxa, and directly correlated with Bacteroides vulgatus, a known proteolytic taxon. High elastase activity was confirmed in Bacteroides isolates from fecal samples. Bacterial contribution and functional significance of the proteolytic signature was investigated in germ-free adults and litters born from dams colonized with HC, pre-UC or post-UC microbiota. Mice colonized with pre-UC microbiota at adulthood or neonatally developed higher fecal proteolytic activity and an inflammatory immune tone compared with HC colonized mice.

Conclusions

We have identified increased fecal proteolytic activity that precedes clinical diagnosis of UC and associates with gut microbiota changes. This may constitute a non-invasive biomarker of inflammation to monitor at-risk populations that can be targeted therapeutically with anti-proteases.

Funding Agencies

CAG, CCC, CIHR

A238 ABSENCE OF AGE-RELATED MEMORY DECLINE IN GERM-FREE MICE

Background

Age-associated deterioration of cognitive function and memory capacity occur in a variety of mammals, from humans to rodents. For example, significant memory deficits have been reported in conventionally raised (SPF) old mice compared to conventionally raised young mice submitted to a spatial memory task (Prevot et al., Mol Neuropsychiatry 2019). Microbiota to brain signaling is now well established in mice, but the extent to which this influences age-related memory decline is unknown.

Aims

Our project aims to determine whether the intestinal microbiota contributes to age-related changes in brain function. We address the hypothesis that age-related cognitive decline is attenuated in the absence of the intestinal microbiota.

Methods

We studied locomotor behavior and spatial memory performance in young germ-free (GF) mice (2–3 months of age, n=24) and senescent GF mice (13–27 months old, n=22) maintained in axenic conditions, and compared them to conventionally raised (SPF) mice. We used the Y-maze test based on a spontaneous alternations task to assess cognition, with alternation rate as a proxy of spatial working memory performance. The locomotor activity was measured using the open-field test.

Results

GF old mice traveled less distance (458.9 cm) than GF young mice (875.7 cm, p &lt; 0.001) but these differences in locomotor activity did not influence spatial memory performance. Indeed, both GF old and GF young mice had an identical alternation rate of 73.3% (p &gt; 0.05). This contrasted with the memory impairment found in old SPF mice that displayed lower alternation rate of 58.3%, compared to that found in young SPF mice (76.2%, p = 0.13).

Conclusions

We conclude that the absence of age-related memory decline in germ-free mice is consistent with a role for the microbiota in the cognitive decline associated with aging, likely through action on the immune system, well documented in SPF mice (Thevaranjan et al., Cell Host & Microbe 2017). We propose that novel microbiota-targeted therapeutic strategies may delay or prevent the cognitive decline of aging.

Funding Agencies

CIHRBalsam Family Foundation

A9 DORSAL ROOT GANGLIA NEURONAL RESPONSES AND SUBSTANCE P PRODUCTION ARE HIGHER IN MALE MICE

Background

Abdominal pain is a common complaint in patients with chronic gastrointestinal disorders. Accumulating evidence suggests that gut microbiota is an important determinant of gut function, including visceral sensitivity. Germ-free (GF) mice have been shown to display visceral hypersensitivity, which normalizes after colonization. Sex also appears to play a key role in visceral sensitivity, as women report more abdominal pain than men. Thus, both gut bacteria and sex are important in the regulation of gut nociception, but the underlying mechanisms remain poorly understood.

Aims

To investigate the role of gut microbiota and sex in abdominal pain.

Methods

We used primary cultures of sensory neurons from dorsal root ganglia (DRG) of female and male conventionally raised (SPF) or germ-free (GF) mice (7–18 weeks old). To study the visceral afferent activity in vitro, calcium mobilization in DRG sensory neurons was measured by inverted fluorescence microscope using a fluorescent calcium probe Fluo-4 (1mM). Two parameters were considered i) the percentage of responding neurons ii) the intensity of the neuronal response. First, DRG sensory neurons were stimulated by a TRPV1 agonist capsaicin (12.5nM, 125nM and 1.25µM) or by a mixture of G-protein coupled receptors agonist (GPCR: bradykinin, histamine and serotonin; 1µM, 10µM and 100µM). We next measured the neuronal production of substance P and calcitonin gene-related peptide (CGRP), two neuropeptides associated with nociception, in response to capsaicin (1.25µM) or GPCR agonists (100µM) by ELISA and EIA, respectively.

Results

The percentage of neurons responding to capsaicin and GPCR agonists was similar in male and female SPF and GF mice. However, the intensity of the neuronal response was higher in SPF male compared to SPF female in response to capsaicin (125nM: p=0.0336; 1.25µM: p=0.033) but not to GPCR agonists. Neuronal activation was similar in GF and SPF mice of both sexes after administration of capsaicin or GPCR agonists. Furthermore, substance P and CGRP production by sensory neurons induced by capsaicin or GPCR agonists was similar in SPF and GF mice, regardless of sex. However, while the response to capsaicin was similar, the GPCR agonists-induced production of substance P was higher in SPF male mice compared to SPF females (p=0.003). The GPCR agonists-induced production of CGRP was similar in SPF male and female mice.

Conclusions

Our data suggest that at the level of DRG neurons, the absence of gut microbiota does not predispose to visceral hypersensitivity. The intensity of DRG neuronal responses to capsaicin and the GPCR agonists-induced production of substance P are higher in male compared to female mice, in contrast to previously published studies in various models of acute and chronic pain. Further studies are thus needed to investigate the role of sex in visceral sensitivity.

Funding Agencies

CIHR

A8 DIETARY TRYPTOPHAN MODULATES KYNURENINE AND INDOLE PRODUCTION IN HEALTHY INDIVIDUALS

Background

Tryptophan is an essential amino acid that is transformed by host and gut microbial enzymes into multiple bioactive metabolites that regulate immunity, mood and circadian rhythms. In particular, indoles, produced by gut bacterial metabolism of tryptophan, have recently gained central attention. Indoles are activators of the aryl hydrocarbon receptor (AhR), which is crucial for the maintenance of intestinal homeostasis and immunity. Tryptophan supplementation in fortified foods have been advocated to prevent chronic inflammatory conditions, from autism to chronic inflammation. However, whether dietary tryptophan supplementation affects immune function, tryptophan metabolic pathways and gastrointestinal symptoms in healthy subjects, is unknown.

Aims

To assess whether tryptophan supplementation, in healthy subjects on a low tryptophan diet, induces changes in microbiota-derived metabolites (indoles), host cytokine production or gut symptoms.

Methods

We performed a randomized, double blind, placebo-controlled, crossover study in 20 healthy individuals, between 18 and 75 years old, following a regular diet. Subjects were instructed to start a standardized low tryptophan diet and were randomly assigned to a 3-week tryptophan supplement (3gr/day) or placebo. After a 2-week washout period, subjects were crossed over to the opposite 3-week intervention arm. Self-administered questionnaires (GSRS, DASS21 and HADS) were used to assess gastrointestinal symptoms and mood/anxiety/stress. Stool, urine and blood samples were collected to measure tryptophan metabolites (kynurenine pathway and indoles) and cytokines.

Results

Supplementation of tryptophan was well tolerated and no changes in gastrointestinal symptoms or mood/anxiety were found. Compared with placebo, tryptophan supplementation increased urinary and plasma levels of indoleamine 2,3-dioxygenase (p= 0.002 and p= 0.02, respectively), a key enzyme in the kynurenine pathway, and of several indoles (p= 0.0008 and p= 0.01, respectively), suggestive of activation of microbial and host metabolic pathways. However, there were no measurable changes in the host cytokine production. There was a positive correlation between fecal kynurenine levels and anxiety and depression scores, suggesting that microbial metabolites may impact host behavior in humans.

Conclusions

Dietary tryptophan supplementation in healthy individuals was safe and had a measurable effect on microbial and host metabolism, mainly kynurenine and indole pathways, with known immunomodulatory properties. Although no effects on cytokine production were found, further studies are warranted to investigate tryptophan supplementation in disorders with altered AhR pathway, such as inflammatory bowel disease, metabolic syndrome and celiac disease.

Funding Agencies

None

Saccharomyces boulardii CNCM I-745 modulates the microbiota-gut-brain axis in a humanized mouse model of Irritable Bowel Syndrome

BACKGROUND

Gnotobiotic mice colonized with microbiota from patients with irritable bowel syndrome (IBS) and comorbid anxiety (IBS+A) display gut dysfunction and anxiety-like behavior compared to mice colonized with microbiota from healthy volunteers. Using this model, we tested the therapeutic potential of the probiotic yeast Saccharomyces boulardii strain CNCM I-745 (S. bou) and investigated underlying mechanisms.

METHODS

Germ-free Swiss Webster mice were colonized with fecal microbiota from an IBS+A patient or a healthy control (HC). Three weeks later, mice were gavaged daily with S. boulardii or placebo for two weeks. Anxiety-like behavior (light preference and step-down tests), gastrointestinal transit, and permeability were assessed. After sacrifice, samples were taken for gene expression by NanoString and qRT-PCR, microbiota 16S rRNA profiling, and indole quantification.

KEY RESULTS

Mice colonized with IBS+A microbiota developed faster gastrointestinal transit and anxiety-like behavior (longer step-down latency) compared to mice with HC microbiota. S. bou administration normalized gastrointestinal transit and anxiety-like behavior in mice with IBS+A microbiota. Step-down latency correlated with colonic Trpv1 expression and was associated with altered microbiota profile and increased Indole-3-acetic acid (IAA) levels.

CONCLUSIONS & INFERENCES

Treatment with S. bou improves gastrointestinal motility and anxiety-like behavior in mice with IBS+A microbiota. Putative mechanisms include effects on pain pathways, direct modulation of the microbiota, and indole production by commensal bacteria.

Transcriptional markers of excitation-inhibition balance in germ-free mice show region-specific dysregulation and rescue after bacterial colonization

BACKGROUND

Studies of germ-free (GF) mice demonstrate that gut microbiota can influence behaviour by modulating neurochemical pathways in the brain, and that bacterial colonization normalizes behavioural deficits in GF-mice. Since disrupted GABAergic and glutamatergic signaling are reported in mood disorders, this study investigated the effect of gut microbiota manipulations on EIB-relevant gene expression in the brain.

METHODS

GF Swiss-Webster mice were colonized with E. coli JM83, complex microbiota (specific-pathogen-free; SPF), or no microbiota, and compared with controls (n = 6/group). 21 synaptic genes representing GABAergic, glutamatergic, BDNF, and astrocytic functions were measured in the hippocampus, amygdala, and prefrontal cortex using quantitative PCR. Gene co-expression analysis was used to identify gene modules related to colonization status, and compared by permutation analysis. Gene expression profiles were compared to existing post-mortem cohorts of depressed subjects (n = 28 cases vs 28 controls).

RESULTS

Region-specific alterations in gene expression were observed in GF-mice compared to controls. 58% of all genes (14/24) altered in GF-mice were normalized following SPF-colonization. GF-mice displayed disorganization of gene co-expression networks in all three brain regions (hippocampus, p = 0.0003; amygdala, p = 0.0012; mPFC, p = 0.0069), which was restored by SPF colonization in hippocampus (p v.s. GF = 0.0003, p v.s. control = 0.60). The hippocampal gene expression profile in GF-mice was significantly correlated with that in human depression (ρ = 0.51, p = 0.027), and this correlation was not observed after colonization.

CONCLUSION

Together, we show that the absence of gut microbiota disrupts the expression of EIB-relevant genes in mice, and colonization restores EIB-relevant expression, in ways that are relevant to human depression.

The Risk of Contracting COVID-19 Is Not Increased in Patients With Celiac Disease

The World Health Organization declared coronavirus disease-2019 (COVID-19) a global pandemic in March 2020. Since then, there are more than 34 million cases of COVID-19 leading to more than 1 million deaths worldwide. Numerous studies suggest that celiac disease (CeD), a chronic immune-mediated gastrointestinal condition triggered by gluten, is associated with an increased risk of respiratory infections.^1-3 However, how it relates to the risk of COVID-19 is unknown. To address this gap, we conducted a cross-sectional study to evaluate whether patients with self-reported CeD are at an increased risk of contracting COVID-19.

Derivation and validation of a novel method to subgroup patients with functional dyspepsia: beyond upper gastrointestinal symptoms

BACKGROUND

Conventionally, patients with functional dyspepsia are subgrouped based on upper gastrointestinal symptoms, according to the Rome criteria. However, psychological co-morbidity and extraintestinal symptoms are also relevant to functional gastrointestinal disorders.

AIM

To investigate whether it is possible to subgroup people with functional dyspepsia using factors beyond upper gastrointestinal symptoms.

METHODS

We collected demographic, symptom and psychological health data from adult subjects meeting the Rome III criteria for functional dyspepsia in two secondary care cross-sectional surveys in Canada and the UK. We performed latent class analysis, a method of model-based clustering, to identify specific subgroups (clusters). For each cluster, we drew a radar plot, and compared these by visual inspection, describing cluster characteristics.

RESULTS

In total, 400 individuals met Rome III criteria for functional dyspepsia in the Canadian cohort, and 262 the UK cohort. A four-cluster model was the optimum solution and the characteristics of the clusters were almost identical between the two cohorts. The clusters were defined by a pattern of gastrointestinal symptoms and were further differentiated by the extent of extraintestinal and psychological co-morbidity. Cluster 1 (mean age 46.7 years, 66.7% female) consisted of epigastric pain and nausea with high psychological burden, cluster 2 (mean age 41.5 years, 77.7% female) high overall gastrointestinal symptom severity with high psychological burden, cluster 3 (45.8 years, 67.2% female) oesophageal symptoms and early satiety with low psychological burden, and cluster 4 (mean age 40.4 years, 71.5% female) postprandial fullness with low psychological burden. We validated the model derived using the Canadian study population externally by applying it to the UK dataset. We demonstrated reproducibility; it would perform similarly when applied to a different dataset.

CONCLUSIONS

Latent class analysis identified four distinct functional dyspepsia subgroups characterised by varying degrees of gastrointestinal symptoms, extraintestinal symptoms and psychological co-morbidity. Further research is needed to assess whether they might be used to direct treatment.

Investigation of the Gut Microbiome in Patients with Schizophrenia and Clozapine-Induced Weight Gain: Protocol and Clinical Characteristics of First Patient Cohorts

BACKGROUND

Emerging evidence suggests an important role of the human gut microbiome in psychiatry and neurodevelopmental disorders. An increasing body of literature based on animal studies has reported that the gut microbiome influences brain development and behavior by interacting with the gut-brain axis. Furthermore, as the gut microbiome has an important role in metabolism and is known to interact with pharmaceuticals, recent evidence suggests a role for the microbiome in antipsychotic-induced metabolic side effects in animals and humans.

PURPOSE

Here we present the protocol for a two-phase study investigating the gut microbiome in healthy controls and in patients with schizophrenia treated with antipsychotics.

METHODS

Phase I of our study involves humans exclusively. We recruit 25 patients who are chronically treated with clozapine and compare them with 25 healthy controls matched for age, sex, BMI, and smoking status. A second cohort consists of 25 patients newly starting on clozapine, and a third cohort includes 25 antipsychotic-naive patients. The patients in the second cohort and third cohort are prospectively assessed for up to 6 and 12 weeks, respectively. Phase II of this study will incorporate microbiota humanized mouse models to examine the influence of human fecal transplant on metabolic parameters and the gut-brain axis. Progress and Future Directions: We are underway with the first participants enrolled in all phase I treatment cohorts. This study will contribute to elucidating the role of the gut microbiome in schizophrenia and metabolic side effects. In addition, its results may help to explore potential therapeutic targets for antipsychotic-induced metabolic side effects.

IMAGINE Network's Mind And Gut Interactions Cohort (MAGIC) Study: a protocol for a prospective observational multicentre cohort study in inflammatory bowel disease and irritable bowel syndrome

INTRODUCTION

Gut microbiome and diet may be important in irritable bowel syndrome (IBS), inflammatory bowel disease (IBD) and comorbid psychiatric conditions, but the mechanisms are unclear. We will create a large cohort of patients with IBS, IBD and healthy controls, and follow them over time, collecting dietary and mental health information and biological samples, to assess their gastrointestinal (GI) and psychological symptoms in association with their diet, gut microbiome and metabolome.

METHODS AND ANALYSIS

This 5-year observational prospective cohort study is recruiting 8000 participants from 15 Canadian centres. Persons with IBS who are 13 years of age and older or IBD ≥5 years will be recruited. Healthy controls will be recruited from the general public and from friends or relatives of those with IBD or IBS who do not have GI symptoms. Participants answer surveys and provide blood, urine and stool samples annually. Surveys assess disease activity, quality of life, physical pain, lifestyle factors, psychological status and diet. The main outcomes evaluated will be the association between the diet, inflammatory, genetic, microbiome and metabolomic profiles in those with IBD and IBS compared with healthy controls using multivariate logistic regression. We will also compare these profiles in those with active versus quiescent disease and those with and without psychological comorbidity.

ETHICS AND DISSEMINATION

Approval has been obtained from the institutional review boards of all centres taking part in the study. We will develop evidence-based knowledge translation initiatives for patients, clinicians and policymakers to disseminate results to relevant stakeholders.Trial registration number: NCT03131414.

The gut microbiome and inflammation in obsessive-compulsive disorder patients compared to age- and sex-matched controls: a pilot study

OBJECTIVE

To compare the gut microbiome profile (by way of taxon analysis and indices of β- and α-diversity) and inflammatory markers (C-reactive protein [CRP], interleukin-6[IL-6] and tumour necrosis factor-α [TNF-α]) of obsessive-compulsive disorder (OCD) outpatients and non-psychiatric community controls.

METHODS

We collected morning stool and blood samples from 21 non-depressed, medication-free OCD patients and 22 age- and sex-matched non-psychiatric community controls. Microbiota analysis was performed using Illumina sequencing of the V3 region of 16S rRNA; serum CRP samples were analysed using immunoturbidimetry and plasma IL-6/TNF-α were examined by high-sensitivity ELISA. Multiple comparisons were corrected for using the false discovery rate (α = 0.05).

RESULTS

Compared to controls, the OCD group presented lower species richness/evenness (α-diversity, Inverse Simpson) and lower relative abundance of three butyrate producing genera (Oscillospira, Odoribacter and Anaerostipes). Compared to controls, mean CRP, but not IL-6 and TNF-α, was elevated OCD patients. CRP revealed moderate to strong associations with psychiatric symptomatology.

CONCLUSION

To our knowledge, this is the first investigation of the gut microbiome in OCD. In addition, our findings lend further support for the potential association of inflammation and OCD. These results suggest the gut microbiome may be a potential pathway of interest for future OCD research.