A102 MONOSODIUM GLUTAMATE INCREASES VISCERAL SENSITIVITY IN A MURINE MODEL OF IRRITABLE BOWEL SYNDROME

Background

Over 70% of patients suffering from symptoms of the irritable bowel syndrome (IBS) report that food is the most common trigger. Patients have identified that monosodium glutamate (MSG) is one food component that they suspect can trigger symptoms, but this remains unproven. As a first step towards establishing a potential role, we sought to examine whether there was a plausible mechanism of how MSG ingestion could underlie exaggerated pain signaling in IBS.

Aims

To examine the effects of MSG on visceral sensitivity in a murine model of IBS.

Methods

Balb/c mice were subjected to 6-days of water-avoidance stress (WAS) to create a pre-clinical model for IBS. To assess changes in visceral afferent nerve sensitivity in control and WAS mice, responses to ramp distension (0–60 mmHg), in the absence and presence 10 μM MSG perfused into the intestinal lumen (concentration based on diet analysis of MSG human ingestion), were recorded from afferent nerves innervating the jejunum ex vivo. To quantify these responses, the baseline firing frequency (spikes/second) was subtracted from the maximum response at each distending pressure. The relative distension response was calculated as a percentage of the control distension response (absence of MSG) (Figure 1). Jejunal preparations from the same WAS-treated mice were also used to measure ex vivo changes in mucosal permeability to MSG using Ussing chambers. We also ran the same distension protocol; however, we applied 10 μM MSG directly to the organ bath outside intestine obtained from control mice. This direct application would allow the MSG to have direct access to the nerve terminals without having to traverse the mucosa.

Results

The intraluminal administration of 10 μM MSG significantly increased afferent nerve sensitivity in WAS-treated jejunum but not controls. This response was significantly greater (23%) at pressures between 40 and 60 mmHg (p<0.01) (Figure 1). WAS-treated mouse jejunum was also significantly more permeable to MSG (p<0.05). Furthermore, the application of 10 μM MSG directly to the bath containing healthy jejunum significantly increased by 25% the sensitivity of afferent nerves specifically at 60 mmHg (p<0.01).

Conclusions

Our findings demonstrate that MSG increases visceral sensitivity to distension in our pre-clinical model of IBS. The increased permeability to MSG in WAS tissue and increased distension response in healthy control tissue when MSG is applied directly to the bath rather than intraluminally, suggests that MSG signals to the immune compartment or directly to the afferent nerve terminals. These findings support the rationale for future in vivo studies with this model to further clarify the mechanism.

Funding Agencies

CCC, CIHR

A55 LACK OF EXPERIMENTAL REPRODUCIBILITY IN PRECLINICAL RESEARCH IS INFLUENCED BY THE NUTRITIONAL PROFILE OF STANDARD RODENT CHOWS

Background

Lack of experimental reproducibility, particularly in studies investigating the microbiota, is of growing concern to the scientific community. Factors such as environment, stress, and sex have been identified as contributors, whereas dietary composition has received less attention.

Aims

To profile the use of standard rodent chows in research institutions, analyze the nutrient content of common rodent chows, and assess the impact of different chows on microbiota profiles.

Methods

A survey was conducted to evaluate which rodent chows are used by research institutions worldwide. Seven standard rodent chows were selected for analysis of ingredients, fermentable carbohydrate (FODMAP) and gluten content. FODMAP content was measured by high-performance liquid-chromatography and enzymatic assays, and gluten content was assessed by a commercial kit using G12 antibody. Forty C57BL/6 mice were randomized to 4 groups of 10 mice (5 male, 5 female). Group A was euthanized at baseline. Group B received the breeding institution chow (LabDiet 5066). Group C received ResearchDiets AIN93G (low FODMAP and gluten content). Group D received LabDiet 5001 (high FODMAP and gluten content). After 3 weeks, cecal contents were collected and analyzed by 16S rRNA gene sequencing; short- and branched-chain fatty acids (SCFA, BCFAs) content was also determined.

Results

Twenty-eight different types of rodent chows were reported to be used by 45 international survey respondents. Ingredient composition of the standard chows varied widely, resulting in differences in FODMAP and gluten content. Microbiota analysis of cecal contents revealed that gut microbiota composition was altered by the standard chows, as reflected by significantly different clusters in β-diversity analysis as well as by altered α-diversity. Microbiota diversity was also influenced by sex in Groups A and B (p<0.01). Total SCFA levels were lower (p=0.03) and BCFA levels were higher (p=0.01) in Group C compared to Group B.

Conclusions

Our results suggest that the composition of the diet not only significantly impacts gut microbiota profiles and fermentation patterns but may also emphasize sex differences in preclinical studies, with major implications for the reproducibility of results across laboratories.

Funding Agencies

CIHRThe Canadian Nutrition Society

Dietary therapies for functional bowel symptoms: Recent advances, challenges, and future directions

BACKGROUND

Functional gastrointestinal symptoms in irritable bowel syndrome (IBS) and quiescent inflammatory bowel disease (IBD) cause significant morbidity and a reduction in quality of life. Multiple dietary therapies are now available to treat these symptoms, but supporting evidence for many is limited. In addition to a further need for studies demonstrating efficacy and mechanism of action of dietary therapies, the risk of nutritional inadequacy, alterations to the microbiome and changes in quality of life are key concerns requiring elucidation. Identifying predictors of response to dietary therapy is an important goal as management could be tailored to the individual to target specific dietary components, and thereby reduce the level of dietary restriction necessary.

PURPOSE

This review discusses the available dietary therapies to treat symptoms in patients with IBS and patients with quiescent IBD suffering from IBS symptoms, with the aim to understand where current dietary evidence lies and how to move forward in dietary research in this field.

Adding glucose to food and solutions to enhance fructose absorption is not effective in preventing fructose-induced functional gastrointestinal symptoms: randomised controlled trials in patients with fructose malabsorption

BACKGROUND

In healthy individuals, the absorption of fructose in excess of glucose in solution is enhanced by the addition of glucose. The present study aimed to assess the effects of glucose addition to fructose or fructans on absorption patterns and genesis of gastrointestinal symptoms in patients with functional bowel disorders.

METHODS

Randomised, blinded, cross-over studies were performed in healthy subjects and functional bowel disorder patients with fructose malabsorption. The area-under-the-curve (AUC) was determined for breath hydrogen and symptom responses to: (i) six sugar solutions (fructose in solution) (glucose; sucrose; fructose; fructose + glucose; fructan; fructan + glucose) and (ii) whole foods (fructose in foods) containing fructose in excess of glucose given with and without additional glucose. Intake of fermentable short chain carbohydrates (FODMAPs; fermentable, oligo-, di-, monosaccharides and polyols) was controlled.

RESULTS

For the fructose in solution study, in 26 patients with functional bowel disorders, breath hydrogen was reduced after glucose was added to fructose compared to fructose alone [mean (SD) AUC 92 (107) versus 859 (980) ppm 4 h^-1 , respectively; P = 0.034). Glucose had no effect on breath hydrogen response to fructans (P = 1.000). The six healthy controls showed breath hydrogen patterns similar to those with functional bowel disorders. No differences in symptoms were experienced with the addition of glucose, except more nausea when glucose was added to fructose (P = 0.049). In the fructose in foods study, glucose addition to whole foods containing fructose in excess of glucose in nine patients with functional bowel disorders and nine healthy controls had no significant effect on breath hydrogen production or symptom response.

CONCLUSIONS

The absence of a favourable response on symptoms does not support the concomitant intake of glucose with foods high in either fructose or fructans in patients with functional bowel disorders.

An inverse method for determining the spatially resolved properties of viscoelastic-viscoplastic three-dimensional printed materials

A method using experimental nanoindentation and inverse finite-element analysis (FEA) has been developed that enables the spatial variation of material constitutive properties to be accurately determined. The method was used to measure property variation in a three-dimensional printed (3DP) polymeric material. The accuracy of the method is dependent on the applicability of the constitutive model used in the inverse FEA, hence four potential material models: viscoelastic, viscoelastic–viscoplastic, nonlinear viscoelastic and nonlinear viscoelastic–viscoplastic were evaluated, with the latter enabling the best fit to experimental data. Significant changes in material properties were seen in the depth direction of the 3DP sample, which could be linked to the degree of cross-linking within the material, a feature inherent in a UV-cured layer-by-layer construction method. It is proposed that the method is a powerful tool in the analysis of manufacturing processes with potential spatial property variation that will also enable the accurate prediction of final manufactured part performance.