Unfermented β-fructan Fibers Fuel Inflammation in Select Inflammatory Bowel Disease Patients

BACKGROUND & AIMS

Inflammatory bowel diseases (IBD) are affected by dietary factors, including nondigestible carbohydrates (fibers), which are fermented by colonic microbes. Fibers are overall beneficial, but not all fibers are alike, and some patients with IBD report intolerance to fiber consumption. Given reproducible evidence of reduced fiber-fermenting microbes in patients with IBD, we hypothesized that fibers remain intact in select patients with reduced fiber-fermenting microbes and can then bind host cell receptors, subsequently promoting gut inflammation.

METHODS

Colonic biopsies cultured ex vivo and cell lines in vitro were incubated with oligofructose (5 g/L), or fermentation supernatants (24-hour anaerobic fermentation) and immune responses (cytokine secretion [enzyme-linked immunosorbent assay/meso scale discovery] and expression [quantitative polymerase chain reaction]) were assessed. Influence of microbiota in mediating host response was examined and taxonomic classification of microbiota was conducted with Kraken2 and metabolic profiling by HUMAnN2, using R software.

RESULTS

Unfermented dietary β-fructan fibers induced proinflammatory cytokines in a subset of IBD intestinal biopsies cultured ex vivo, and immune cells (including peripheral blood mononuclear cells). Results were validated in an adult IBD randomized controlled trial examining β-fructan supplementation. The proinflammatory response to intact β-fructan required activation of the NLRP3 and TLR2 pathways. Fermentation of β-fructans by human gut whole microbiota cultures reduced the proinflammatory response, but only when microbes were collected from patients without IBD or patients with inactive IBD. Fiber-induced immune responses correlated with microbe functions, luminal metabolites, and dietary fiber avoidance.

CONCLUSION

Although fibers are typically beneficial in individuals with normal microbial fermentative potential, some dietary fibers have detrimental effects in select patients with active IBD who lack fermentative microbe activities. The study is publicly accessible at the U.S. National Institutes of Health database (clinicaltrials.gov identification number NCT02865707).

A189 ELUCIDATING THE MECHANISTIC ROLE OF GLP-1R IN THE INFLAMMATORY RESPONSE OF MACROPHAGES AND B CELLS TO DIETARY FIBRES

Background

Both diet and the microbiome have been implicated in the pathogenesis of inflammatory bowel diseases (IBD). Fibre is not digested; it is fermented by microbes in the large bowel. High fibre intake is related to lower risk for the development of IBD, and a high fibre diet is usually recommended for individuals with IBD. However, work in our lab suggests that select dietary fibres may be pro-inflammatory in a pediatric IBD cohort. Importantly, large bowel dysbiosis in IBD could limit the fermentation of dietary fibres, leading to reduced production of beneficial microbiome metabolites as well as an accumulation of intact fibre in the large bowel. These intact fibres may then interact with immune cells residing in the large bowel, through specific receptors, and perpetuate the inflammatory state seen in IBD.

Aims

Based on preliminary findings, we hypothesize that the dietary fibre oligofructose acts through GLP-1R on macrophages and B-cells to regulate the inflammatory environment. We expect to find changes in the expression of cytokines and chemokines, and their receptors.

Methods

Changes in immune cell secretions (ELISA) and the expression of selected inflammatory markers (RT-qPCR) were measured to determine potential pathways involved in response to dietary fibres in vitro. Knockdown of proteins of interest (siRNA) was performed to validate the involvement of these pathways in the inflammatory response to dietary fibres. Cells were treated with oligofructose, oligofructose pre-fermented by bacteria, or no fibre. The involvement of the fibre receptor, GLP-1R, was investigated to understand its connection to pathways identified.

Results

Qiagen RT2 profiler array (human inflammatory cytokines and receptors) and cytokine secretion (ELISA) indicated that in response to oligofructose macrophages have a predominantly pro-inflammatory response while B cells have an anti-inflammatory response. Presence of GLP-1R in large bowel and terminal ileum biopsies collected during endoscopy was higher in IBD (Crohn disease n=7; Ulcerative colitis n=7) than non-IBD patients (n=7), and expression was confirmed on both B-cells and macrophages. Knockdown of GLP-1R (siRNA) significantly reduced the pro-inflammatory response (IL-1β ELISA) with oligofructose application in THP-1 macrophage cells

Conclusions

Improving our understanding of the mechanistic link between dietary fibres and immune response will aid us in developing a model for the interactions of oligofructose with the GLP-1R in B cells and macrophages. Findings from this study may be able to inform dietary interventions, prebiotic/probiotic administration, and drug development for treatment of IBDs.

Funding Agencies

CIHRWeston Foundation

A31 COMPLEX ROLE OF DIETARY FIBERS IN IBD: MICROBES MEDIATE FIBER-INDUCED INFLAMMATION

Background

Dietary fibers pass through the bowel undigested and are fermented within the intestine by microbes, typically promoting gut health. However, many IBD patients describe experiencing sensitivity to fibers. β-glucan, found on the surface of fungal cells during fungal infection, has been shown to bind to fiber receptors, such as Dectin-1, on host immune cells, resulting in a pro-inflammatory response. These fungal fibres share properties with dietary fibers.

Aims

As an altered gut microbial composition has been associated with IBD, we hypothesized that the loss of fiber-fermenting microbes populating the gut in IBD could lead to dietary fibers not being efficiently broken down into their beneficial biproducts (e.g. short chain fatty acids; SCFA), resulting in binding of intact fibers to pro-inflammatory host cell receptors.

Methods

Immune and epithelial cell lines and colonic biopsies cultured ex vivo were incubated with oligofructose or inulin (5g/L), or pre-fermented fibers (24hr anaerobic fermentation). Immune responses were measured by cytokine secretion (ELISA), and expression (qPCR). Barrier integrity was measured by transepithelial resistance (TEER). Food frequency questionnaire (FFQ) data of patient fiber consumption were correlated with gut microbes (shotgun sequencing) and immune responses to fiber in patient biopsies.

Results

Unfermented oligofructose induced IL-1β secretion in leukocytes (macrophage, T cell, neutrophil) and in colon biopsies from pediatric Crohn disease (CD; n=38) and ulcerative colitis (UC; n=20) patients cultured ex vivo, but not in non-IBD patients (n=21). IL-1β secretion was greater in patients with more severe disease. Pre-fermentation of oligofructose by whole-microbe intestinal washes from non-IBD patients or remission patients reduced secretion of IL-1β, while whole microbe intestinal washes from severe IBD patients were unable to ferment oligofructose or reduce cytokine secretion. Fiber effects on IL-1β secretion in biopsies positively correlated with effects on barrier integrity in T84 cells. Fiber-associated immune responses in patient biopsies cultured ex vivo (ELISA) correlated with fiber avoidance (FFQ) and gut microbiome (sequencing) in matching patient samples.

Conclusions

Our findings demonstrate that intolerance and avoidance of prebiotic fibers in select IBD patients is associated with the inability to ferment these fibers, leading to pro-inflammatory immune responses and intestinal barrier disruption. This highlights select disease state scenarios, in which administration of fermentable fibers should be avoided and tailored dietary interventions should be considered in IBD patients.

Funding Agencies

CIHRWeston Foundation

A217 DEFINING THE RELATIONSHIP BETWEEN DIETARY FIBERS AND INFLAMMATORY RESPONSE IN PEDIATRIC INFLAMMATORY BOWEL DISEASES

Background

The incidence rates of inflammatory bowel diseases (IBD), Crohn disease (CD) and ulcerative colitis (UC) are increasing in children. Although the etiology of IBD is poorly understood, factors such as urban lifestyle, diet, increased hygiene, and reduced microbial biodiversity have been implicated as risk factors. Compositional changes and reduced microbial biodiversity have been linked to therapy failure in pediatric IBD. Non-digestible dietary carbohydrates, such as fiber, must undergo fermentation by gut microbiota within the large bowel, producing short chain fatty acids (SCFAs). Animal studies have shown that dietary fibers can inhibit IBD-associated inflammation, and clinical trials have demonstrated that SCFAs can prevent intestinal atrophy and allow for tissue recovery in IBD patients. In disease settings with altered gut microbes, fermentation of dietary fibers may be greatly affected. Unfermented fibers interact with receptors on host immune cells and can induce proinflammatory immune response, production of oxygen species and inflammation, or an inhibition of proinflammatory receptors.

Aims

Based on this rationale, we hypothesize that dysbiosis in the IBD gut leads to decreased fiber fermenting microbes, resulting in reduced SCFA production. This contributes to increased inflammatory responses both in in vitro cell lines, as well as ex vivo patient biopsies. Because intact fibers can bind to host cell receptors, this promotes inflammatory response and continued dysbiosis.

Methods

To assess effects of intact fiber on immune cells, macrophage and T-cell in vitro cultures were used to measure cytokine response to inulin (5mg/mL) and oligofructose (5mg/mL) through ELISAs/qPCR. These cell lines and ex vivo patient biopsies were treated with whole fibers and IL-1β secretion was measured. Fibers were also pre-fermented with microbes of interest or whole microbe patient intestinal washes and used to treat cell lines and patient biopsies.

Results

Whole fibers induced a pro-inflammatory response in macrophage cells but not T-cells, and this pro-inflammatory response was mitigated by pre-fermenting the fibers. Intestinal washes from severe IBD patients were unable to successfully ferment oligofructose or reduce fiber-associated inflammation in macrophage cell lines, whereas washes from remission or non-IBD samples reduced IL-1β. Oligofructose was found to increase IL-1β secretion in UC and CD patient biopsies, but not in non-IBD specimens. This increase was also correlated with disease severity.

Conclusions

These results indicate that a lack of fiber-fermenting microbes and presence of whole fibers can lead to pro-inflammatory responses, both in cell lines and patient biopsies. However, the presence of appropriate fermenting microbes can reduce fiber-associated inflammation.

Funding Agencies

CCCWCHRI, Weston Foundation

A15 MICROBES MEDIATE FIBER-INDUCED INFLAMMATION IN IBD

Background

The etiology of inflammatory bowel diseases (IBD) remains unknown, although gut microorganisms and diet have been implicated. Dietary fibers pass through the bowel undigested and are fermented within the intestine by microbes, promoting gut health. However, many IBD patients describe experiencing sensitivity to fibres. Interestingly, fiber receptors on immune cells are able to interact with fibers typically found on the surface of fungal cells (which share properties with dietary fibers), for example, resulting in a paradoxical pro-inflammatory response.

Aims

As an altered microbial composition is a hallmark of IBD, we hypothesized that the loss of fiber fermenting-microbes populating the IBD gut could lead to dietary fibers not being efficiently broken down into their beneficial biproducts, resulting in binding of intact fibers to pro-inflammatory host cell receptors. This can ultimately drive pro-inflammatory responses and a microenvironment that promotes continued dysbiosis and increased pathogenicity of select microbes, as observed in IBD.

Methods

Fiber receptor expression gut was examined using immunohistochemistry and flow cytometry and demonstrated elevated receptor expression due to increased presence of immune cells in IBD patient biopsies. Cytokine secretion, in response to fiber (5mg/mL) or pre-fermented fibers, cultured with microbes of interest, was measured by ELISAs in cell lines in vitro and biopsy tissues cultured ex vivo.

Results

Whole-fibers induced pro-inflammatory cytokine production in macrophage, monocytes, and neutrophils. Specific microbes were capable of fermenting fiber, measured by gas chromatography. Pre-fermentation of fibers by these microbes reduced inflammatory cytokine production. The fiber oligofructose increased IL-1β in pediatric CD (n=44) and UC (n=29) biopsies cultured ex vivo but not in non-IBD (n=25). The increase was greater in patients with more severe disease. Pre-fermentation of oligofructose by bacteria reduced this secretion of IL-1β. Whole-microbe intestinal washes from severe IBD patients were unable to ferment oligofructose or reduce fiber-associated inflammation in macrophage cells compared to remission or non-IBD children. Statistical analysis of food frequency questionnaire (FFQ) data on fiber consumption demonstrated that fiber-associated inflammation in patient biopsies cultured ex vivo (ELISA and qPCR) correlated with fiber avoidance (FFQ).

Conclusions

Comparing in vitro findings to our patient FFQs, intestinal washes (microbe abundance), and detailed patient history will better define the relationship between microbes, dietary fibers, and gut inflammation in IBD. This will allow for tailored dietary intervention through dietary recommendations, prebiotic, and/or probiotic therapies.

Funding Agencies

CCCWeston Foundation, WCHRI

Host immunoglobulin G selectively identifies pathobionts in pediatric inflammatory bowel diseases

BACKGROUND

Inflammatory bowel diseases (IBD) are a group of complex and multifactorial disorders with unknown etiology. Chronic intestinal inflammation develops against resident intestinal bacteria in genetically susceptible hosts. We hypothesized that host intestinal immunoglobulin (Ig) G can be used to identify bacteria involved in IBD pathogenesis.

RESULTS

IgG-bound and -unbound microorganisms were collected from 32 pediatric terminal ileum aspirate washes during colonoscopy [non-IBD (n = 10), Crohn disease (n = 15), and ulcerative colitis (n = 7)], and composition was assessed using the Illumina MiSeq platform. In vitro analysis of invasive capacity was evaluated by fluorescence in situ hybridization and gentamicin invasion assay; immune activation was measured by qPCR. Despite considerable inter-individual variations, IgG binding favored specific and unique mucosa-associated species in pediatric IBD patients. Burkholderia cepacia, Flavonifractor plautii, and Rumminococcus sp. demonstrated increased IgG binding, while Pseudomonas ST29 demonstrated reduced IgG binding, in IBD. In vitro validation confirmed that B. cepacia, F. plautii, and Rumminococcus display invasive potential while Pseudomonas protogens did not.

CONCLUSION

Using IgG as a marker of pathobionts in larger patient cohorts to identify microbes and elucidate their role in IBD pathogenesis will potentially underpin new strategies to facilitate development of novel, targeted diagnostic, and therapeutic approaches. Interestingly, this method can be used beyond the scope of this manuscript to evaluate altered gut pathobionts in a number of diseases associated with altered microbiota including arthritis, obesity, diabetes mellitus, alcoholic liver disease, cirrhosis, metabolic syndrome, and carcinomas.