A51 INTESTINAL MICROBIOTA DETERMINES ARYL HYDROCARBON RECEPTOR ACTIVATION AND SUSCEPTIBILITY TO COLITIS

Background

Intestinal microbiota, diet, and the immune system have been proposed to contribute to the development of inflammatory bowel diseases (IBD). The aryl hydrocarbon receptor (AhR) is a critical regulator of intestinal immunity and mucosal barrier homeostasis that is activated by agonists such as host and microbial tryptophan metabolites. IBD patients have altered microbiota and reduced AhR agonists in intestinal content resulting in the downregulation of AhR. These findings necessitate further study to understand how diet-microbiota interactions contribute to intestinal inflammation.

Purpose

To study the influence of intestinal microbiota on tryptophan metabolism, AhR activation, and colitis severity.

Method

8- to 10-week-old germ-free C57BL/6 mice were colonized with cecal content of mice harbouring specific pathogen-free (SPF) or a limited and well-defined altered Schaedler flora (ASF) microbiota. Germ-free mice were used as controls. Three weeks following colonization, mucosal injury was induced in a subset of mice with dextran sulfate sodium (DSS) in drinking water for five days followed by two days of water recovery. Activation of AhR was measured in stool using an in vitro AhR luciferase reporter assay. Stool AhR agonists were determined using high-performance liquid chromatography coupled to high-resolution mass spectrometry. Colonic expression of AhR pathway genes Cyp1a1, Il22, Ahrr, Ahr, and Il17 was evaluated by RT-qPCR. Susceptibility to colitis was assessed by analysing stool consistency and stool blood, colonic microscopic damage, immune infiltration by immunohistochemistry, and pro-inflammatory gene expression (NanoString). Fecal microbiota was analysed by 16S rRNA gene sequencing (Illumina).

Result(s)

AhR agonists, AhR activation in vitro, and AhR pathway gene expression were elevated in mice colonized with SPF microbiota in comparison to mice colonized with ASF microbiota and germ-free mice. In ASF-colonized mice, DSS induced more severe inflammation than in SPF-colonized mice, as demonstrated by worsened mucosal injury, greater weight loss, and softer stools. SPF-colonized mice developed less mucosal immune cell infiltration and pro-inflammatory gene signaling.

Conclusion(s)

Our findings suggest that intestinal microbiota composition determines the metabolic capacity to degrade tryptophan into agonists that homeostatically activate AhR. When mucosal injury is induced, mice with elevated microbiota-derived AhR agonists and AhR activation develop less severe mucosal injury and signs of colitis. This study presents a useful tool for evaluating dietary and microbial therapies in the context of a microbiota with impaired tryptophan metabolism.

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CCC, CIHR

Disclosure of Interest

None Declared

A48 OPTIMIZATION OF TRYPTOPHAN-CONTAINING DIETS TO ACTIVATE THE ARYL HYDROCARBON RECEPTOR AND REDUCE SUSCEPTIBILITY TO COLITIS

Background

The intestinal microbiota, diet, and the immune system have all been proposed to contribute to the development of inflammatory bowel disease (IBD). The aryl hydrocarbon receptor (AhR) is a critical regulator of intestinal immunity and mucosal barrier homeostasis that is activated by agonists such as diet-derived microbial tryptophan (Trp) metabolites. Increasing evidence suggests that IBD patients have reduced AhR agonists in intestinal content resulting in the downregulation of AhR-regulated genes. In mice, impaired Trp metabolism and AhR signaling translate to increased intestinal inflammation and injury during colitis. This finding highlights the utility of Trp dietary intervention to reduce the onset and progression of inflammation and injury in IBD.

Aims

To optimize a Trp-enriched diet formulation to increase AhR activation and reduce intestinal inflammation and injury in mouse models of colitis.

Methods

Three diet types with elevated Trp were explored: (1) free amino acid diet with added Trp, (2) purified protein diet with added Trp, and (3) purified high protein diet. Following three weeks of diet consumption by C57BL/6 mice, mucosal injury was induced with 2% dextran sulfate sodium in drinking water (DSS) before sacrifice. Susceptibility to colitis was assessed by analyzing stool consistency and blood, microscopic damage, immune infiltration by immunohistochemistry, and pro-inflammatory gene expression (NanoString). Activation of AhR was measured in feces using an in vitro AhR luciferase reporter assay. Colonic expression of AhR pathway genes Cyp1a1, Il22, Ahrr, and Il17 was evaluated by RT-qPCR. Fecal microbiota was analyzed by 16S rRNA gene sequencing (Illumina).

Results

AhR activation in vitro and colonic AhR pathway gene expression were elevated in mice fed diets containing added Trp (1 & 2) in comparison to mice fed a high protein diet (3). While all DSS-treated mice developed colitis, mice fed a purified protein diet with added Trp (2) were protected from severe colitis and developed less microscopic damage, immune cell infiltration, and pro-inflammatory gene signalling. Enriched Trp concentrations in the form of free amino acid (1) and high protein (3) diets were not associated with protection from inflammation and injury during colitis.

Conclusions

Our findings suggest that the addition of Trp to a conventional diet (2) may increase microbial tryptophan metabolites to ameliorate colitis severity and intestinal homeostasis through AhR activation. Despite having similar Trp concentrations, a Trp-enriched free amino acid diet (1) and a high protein diet (3) do not improve colitis severity. Thus, both the diet formulation and the availability of Trp should be considered when designing dietary interventions for the treatment of colitis through AhR activation.

Funding Agencies

CCC, CIHRFarncombe Family Digestive Health Research Institute, Douglas Family Chair in Gastroenterology Research, Biocodex Microbiota Foundation

A23 DIETARY PROTEIN AND AMINO ACID COMPOSITIONS INFLUENCE MICROBIOTA, INTESTINAL PERMEABILITY, AND SUSCEPTIBILITY TO COLITIS

Background

Environmental factors, such as alterations in diet and microbiota, have been linked to inflammatory bowel diseases (IBD). The incidence of IBD is rising, particularly in Canada and other industrialized nations that consume western-style diets high in fat and protein. While most dietary proteins and amino acids are absorbed in the small intestine, substantial amounts can enter the colon for microbial metabolism and to exert effects on intestinal tissue and immune cells. Prospective cohort studies suggest that diets high in protein are associated with an increased risk of IBD. However, the role of excess dietary protein and amino acids in IBD pathogenesis is not clear.

Aims

To study whether and how consumption of diets high in protein or amino acids influences intestinal inflammation, colitis severity, and intestinal microbiota.

Methods

To assess the influence of dietary protein composition on colitis severity, specific pathogen-free C57BL/6 mice were fed isocaloric casein-based purified diets containing low (7%), normal (14%), or high (35%) protein (HPD). Mice were also fed an amino acid-defined diet (AAD) with amino acid and ingredient composition matched to the normal protein diet. Following three weeks of diet consumption ad libitum, mice were continued on the same diet and mucosal injury was induced with 2% dextran sulfate sodium (DSS; 5 days) followed by water (2 days) before sacrifice. Mice were monitored daily for clinical signs of colitis. Susceptibility to colitis was assessed by analysing stool consistency and blood, microscopic scoring (Cooper score), and by immunohistochemistry of colon tissue. Fecal microbiota (16S rRNA Illumina), intestinal permeability (Ussing chambers), proinflammatory gene expression (NanoString and RT-qPCR), and bacterial translocation (plating) were analysed.

Results

Following DSS exposure, mice fed HPD and AAD experienced greater weight loss, bacterial translocation to the spleen, stool blood, and diarrhea compared to mice fed the normal protein control diet. While all DSS-treated mice developed colitis, HPD and AAD fed mice also developed greater histologic damage, intestinal permeability, and innate immune cell infiltration. Cytokine profiling revealed that AAD is associated with significant up-regulation of IL-18 during colitis. Principle coordinates analysis based on Bray-Curtis dissimilarities demonstrates distinct shifts in the fecal microbiota of mice fed HPD and AAD.

Conclusions

These results suggest that excess dietary protein and amino acids are associated with more severe colitis and microbiota alterations in the DSS model. Previous studies demonstrate that IL-18 is up-regulated in IBD patients. Its overexpression may incite inflammation by stimulating cytokine signalling through NFκB and modify microbial community structure by regulating antimicrobial peptides.

Funding Agencies

CIHRFarncombe Family Digestive Health Research Institute, Douglas Family Chair in Gastroenterology Research

A48 COLITIS FAVORS THE EXPANSION OF BACTERIA THAT ACTIVATE PAR2 AMPLIFYING INFLAMMATORY RESPONSE

Background

Proteolytic imbalance has been described in patients with inflammatory bowel disease (IBD) and in different models of experimental colitis. Although the proteases reported to be increased are mainly from the host, the role of bacterial proteases has recently emerged, as they can promote inflammation, in part, through activation of Protease-activated receptors (PARs). PAR2 deficient mice are resistant to inflammation and PAR2 activation affects multiple aspects of the tissue response to injury. However, PAR2 communicates with other receptors such as toll-like and other PARs, which are important in multiple immune signaling pathways. Thus, the direct implication of PAR2 in colitis, and specifically the activation of the external domain by microbial proteases, remains unclear.

Aims

To study the role of PAR2 and bacterial proteases in experimental colitis.

Methods

C57BL/6 and protease-resistant PAR2 (R38E-PAR2) mice, in which activation site of PAR2 is missing, were given 3.5% dextran sodium sulfate (DSS) in drinking water for 5 days followed by 2 days of water. Control C57BL/6 (wild-type) and R38E-PAR2 mice received only water. Percent weight change was evaluated along the study. Fecal microbiota (16S Ilumina), expression of proinflammatory genes (Nanostring), gut permeability (Ussing chamber), proteolytic activities (colorimetric assay) and bacterial translocation (plating) were measured in all mice at sacrifice. Inflammation was determined by analyzing stool consistency, fecal blood and by microscopic scores (Cooper score). Bacteria with proteolytic activity were isolated using agar-media with protein as main nutrient and bacterial capacity to release the external domain of PAR2 was tested in cells harbouring luciferase at the PAR2 N terminus.

Results

Wild-type, but not R38E-PAR2 mice, had increased expression of several pro-inflammatory genes, such as tnf, map3k and tlr, gut dysfunction and increased intestinal permeability, increased bacterial translocation into spleen and altered microbiota profiles following DSS treatment. DSS induced colitis in both mouse strains, but clinical and microscopic scores were significantly lower in R38E-PAR2 compared with wild-type mice. DSS increased the abundance of opportunistic pathogens such as Enterococcus and Staphylococcus only in wild-type mice. Proteolytic phenotype of these bacteria, and their capacity to cleave the external domain of PAR2, was confirmed.

Conclusions

Mice lacking the activation site of PAR2 are protected from DSS-induced colitis. DSS treatment leads to expansion of bacteria releasing active proteases, which may mediate injury through PAR2. These results suggest that intestinal injury promotes microbial proteolytic imbalance which in turn, exacerbates inflammation.

Funding Agencies

CAG, CCC, CIHR

Impact of intensive care unit supportive care on the physiology of Ebola virus disease in a universally lethal non-human primate model

Background

There are currently limited data for the use of specific antiviral therapies for the treatment of Ebola virus disease (EVD). While there is anecdotal evidence that supportive care may be effective, there is a paucity of direct experimental data to demonstrate a role for supportive care in EVD. We studied the impact of ICU-level supportive care interventions including fluid resuscitation, vasoactive medications, blood transfusion, hydrocortisone, and ventilator support on the pathophysiology of EVD in rhesus macaques infected with a universally lethal dose of Ebola virus strain Makona C07.

Methods

Four NHPs were infected with a universally lethal dose Ebola virus strain Makona, in accordance with the gold standard lethal Ebola NHP challenge model. Following infection, the following therapeutic interventions were employed: continuous bedside supportive care, ventilator support, judicious fluid resuscitation, vasoactive medications, blood transfusion, and hydrocortisone as needed to treat cardiovascular compromise. A range of physiological parameters were continuously monitored to gage any response to the interventions.

Results

All four NHPs developed EVD and demonstrated a similar clinical course. All animals reached a terminal endpoint, which occurred at an average time of 166.5 ± 14.8 h post-infection. Fluid administration may have temporarily blunted a rise in lactate, but the effect was short lived. Vasoactive medications resulted in short-lived improvements in mean arterial pressure. Blood transfusion and hydrocortisone did not appear to have a significant positive impact on the course of the disease.

Conclusions

The model employed for this study is reflective of an intramuscular infection in humans (e.g., needle stick) and is highly lethal to NHPs. Using this model, we found that the animals developed progressive severe organ dysfunction and profound shock preceding death. While the overall impact of supportive care on the observed pathophysiology was limited, we did observe some time-dependent positive responses. Since this model is highly lethal, it does not reflect the full spectrum of human EVD. Our findings support the need for continued development of animal models that replicate the spectrum of human disease as well as ongoing development of anti-Ebola therapies to complement supportive care.

Electronic supplementary material

The online version of this article (10.1186/s40635-019-0268-8) contains supplementary material, which is available to authorized users.