Introduction

The pathophysiological mechanism involved in irritable bowel syndrome (IBS) is thought to be multifactorial, involving the gut-brain axis and the immune system. Despite this complexity, dietary restriction of fermentable oligo-, dis-, mono- saccharides, and polyols (FODMAPs) has become the first line of treatment, improving symptoms in up to 80% of patients (1). FODMAPs are poorly absorbed in the small intestine and serve as a substrate for the colonic microbiota, which has been proposed as a key mediator of FODMAP tolerance and symptom development. Considering that both the gut microbiota and the (in)tolerance to individual FODMAPs are highly personalised (2), there is a growing need to understand the host-microbiota interactions underlying individual responses to FODMAP restriction and intake. This personalised interplay may be key to more targeted dietary interventions for IBS.

Aims & Methods

We aimed to disentangle the role of the gut microbiota in FODMAP tolerance by exploring microbial dynamics upon restriction and reintroducing individual FODMAPs. To this end, we performed 16S rRNA gene sequencing of over 1,700 faecal samples from 463 IBS patients participating in two clinical trials: a) The DOMINO trial (3), where primary-care patients underwent a FODMAP-lowering diet and b) A cohort of 117 tertiary-care patients underwent a strict FODMAP-restriction followed by a blinded re-introduction of 6 FODMAPs powders (2). Response to the diet was defined as a reduction of at least 50 points on the IBS symptom severity scale. Linear and logistic mixed models were used to assess the relation between the microbiome, response to dietary intervention, host genetics and 32 blood and faecal parameters.

Results

Participants with dysbiotic microbiota at baseline were shown to be less likely to respond to the dietary restriction (p-value=0.01). These participants also showed higher levels of fecal calprotectin, secretory IgA and eosinophil-derived neurotoxin, suggesting immune activation in this subgroup of IBS patients (p-value<0.05). In both cohorts, limiting FODMAP intake was associated with decreased Bifidobacterium abundance (FDR<0.01). Moreover, a dose-dependent effect was observed as depletion was less severe in the FODMAP-lowering DOMINO diet. This effect was independent of response and IBS subtype. Furthermore, total bacterial biomass did not change during the restriction or the reintroduction period. However, we found 25 significant associations between individual FODMAPs and gut bacteria. The reintroduction of galacto-oligosaccharides and fructans restored the levels of Bifidobacterium, while polyols increased the abundance of Anaerostipes, regardless of participants’ tolerance (FDR<0.05). In addition, we observed distinct dynamics in the gut microbiota associated with the tolerance of specific FODMAPs, although they did not reach significance after multiple testing corrections at the current sample size. For example, participants intolerant to sorbitol showed an increase in Alistipes upon exposure to this compound (p-value<0.05, FDR>0.05).

Conclusion

Our results suggest that microbiota composition at baseline influences the clinical response to FODMAP restriction. A low-FODMAP diet does not induce drastic changes in the microbiome composition, although we confirmed the negative impact of dietary restriction on the abundance of Bifidobacterium. However, the less restrictive DOMINO diet results in a milder depletion, suggesting that moderate FODMAP reduction may better preserve beneficial microbiota while still offering symptom relief. Finally, we found evidence for a link between microbial dynamics and FODMAP tolerance, although this needs to be confirmed in larger cohorts.

References

(1) Staudacher HM, Whelan K The low FODMAP diet: recent advances in understanding its mechanisms and efficacy in IBS Gut 2017;66:1517-1527.
(2) Van den Houte K, Colomier E, Routhiaux K, Mariën Z, Schol J, Van den Bergh J, Vanderstappen J, Pauwels N, Joos A, Arts J, Caenepeel P, De Clerck F, Matthys C, Meulemans A, Jones M, Vanuytsel T, Carbone F, Tack J. Efficacy and Findings of a Blinded Randomized Reintroduction Phase for the Low FODMAP Diet in Irritable Bowel Syndrome. Gastroenterology. 2024
(3) Carbone F, Van den Houte K, Besard L DOMINO Study Collaborators, et al Diet or medication in primary care patients with IBS: the DOMINO study - a randomised trial supported by the Belgian Health Care Knowledge Centre (KCE Trials Programme) and the Rome Foundation Research Institute Gut 2022;71:2226-2232.

Disclosure

JT has given Scientific advice to AlfaWassermann, Allergan, Christian Hansen, Danone, Grünenthal, Ironwood, Janssen, Kiowa Kirin, Menarini, Mylan, Neutec, Novartis, Noventure, Nutricia, Shionogi, Shire, Takeda, Theravance, Tramedico, Truvion, Tsumura, Zealand and Zeria pharmaceuticals, has received research support from Shire, Sofar and Tsumura, and has served on the Speaker bureau for Abbott, Allergan, AstraZeneca, Janssen, Kyowa Kirin, Menarini, Mylan, Novartis, Shire, Takeda, Truvion and Zeria. Funding was provided by a Methusalem grant from Leuven University to JT This study was supported by a research grant from the Belgian Health Care Knowledge Centre (KCE).

Introduction

Non-celiac gluten/wheat sensitivity (NCGWS) is characterized by gastrointestinal and extra-intestinal symptoms triggered by gluten/wheat ingestion. Symptoms of NCGWS overlap with those of irritable bowel syndrome (IBS) or functional dyspepsia (FD). Due to diagnostic challenges and symptom overlap, data on the prevalence and predictors of NCGWS among patients with IBS or FD, especially those with refractory symptoms, are limited.

Aims & Methods

This was a prospective, multicentric, double-blind, placebo-controlled, crossover trial conducted from October 2021 to March 2023 in India.This was prospectivly registered with the clinical trials Registry, INDIA (CTRI/2021/10/037323). Adults aged 18–65 years with Rome IV-defined irritable bowel syndrome (IBS) or functional dyspepsia (FD) refractory to standard treatment were enrolled after excluding celiac disease, wheat allergy, and alarm features. Participants underwent a two-step diagnostic protocol. In Step I, patients adhered to a 6-week strict gluten-free diet (GFD) under dietitian supervision. Weekly assessments of gastrointestinal and extra-intestinal symptoms, health-related quality of life (HRQoL), and psychological scores were performed using validated instruments. Gluten responders—defined by ≥30% reduction in one to three primary symptoms—were advanced to Step II: a randomized, double-blind, placebo-controlled gluten challenge with crossover. Subjects received indistinguishable gluten or placebo cookies (8 g/day) for one week, followed by a one-week washout and crossover. A ≥30% symptom difference between gluten and placebo phases confirmed non-celiac gluten/wheat sensitivity (NCGWS). Primary outcome was NCGWS prevalence; secondary outcomes included symptom and HRQoL changes post-GFD and predictors of NCGWS. Statistical analyses included intention-to-treat principles and multivariable regression to identify baseline predictors.

Results

Of the 252 patients screened, 177 were enrolled for 6-week GFD (step I), and 154 patients completed this phase (mean age 41.9±14.2 years, 53.2% males). Eighty two (52.3%) patients responded to GFD, of whom 77 entered step 2 (DBPCGC). Thirty one (20.1%) patients had significant symptom worsening on blinded gluten ingestion, suggesting the presence of NCGWS. Independent predictors of NCGWS were female gender, FD-IBS overlap, headache, fatigue, and anxiety. Significant improvements in gastrointestinal symptoms, health-related quality of life, and psychological scores were observed after GFD in responders. No significant impact of diet sequence was noted.

Conclusion

Introduction

Inflammatory bowel disease (IBD) is characterised by inflammatory flares with excruciating pain, for which effective analgesics are lacking. Cocaine- and amphetamine-regulated transcript (CART) peptide regulates peripheral pain in mice.¹ However, its role in visceral nociception as well as the underlying molecular signalling mechanism in primary sensory neurons remains elusive. CART is highly expressed in TRPV1-positive colon-projecting sensory neurons.² In addition, the enzyme prohormone convertase 1/3, which is involved in processing CART into its bioactive fragment 55-102, is upregulated in colonic biopsies of IBD patients (internal data), suggesting a potential role for the peptide in colonic pain.

Aims & Methods

Here, we aimed to test if CART would affect firing of the colon-innervating lumbar splanchnic nerve (LSN) as model of visceral nociception and characterise its effect and signalling pathway in sensory neurons innervating the colon. Studies were performed using tissue from male and female C57BL/6J mice euthanised by cervical dislocation and exsanguination in accordance with Schedule 1 of the Animals (Scientific Procedures) Act 1986. Thoracolumbar dorsal root ganglia (DRG) neurons were dissociated and cultured overnight for Ca²⁺ imaging using Fluo-4 AM as previously described.³ Cells were perfused with extracellular solution (ECS) alone or supplemented with either rat CART 55-102, (20-300nM, ECS), thapsigargin (10mM, DMSO), xestospongin C (1mM, ECS), edelfosine (10mM, ECS), capsaicin (10mM, ethanol) or KCl solution (60mM, ddH₂O) for respective challenge or pre-treatment. All conditions were blinded and randomised. Colorectum with attached lumbar splanchnic nerve was carefully removed and mounted on a tissue bath superfused with Krebs buffer as previously described.³ Rat CART 55-102 was superfused at 5ml/min, resulting in a final concentration of 200nM. Statistical analysis was performed using Student´s t test or ANOVA and Dunnett´s multiple comparisons test. Data is displayed as mean ± SEM.

Results

CART elicited a concentration-dependent increase in intracellular Ca²⁺ in DRG neurons, which at the highest concentration tested (300nM) induced a significant increase in intracellular Ca²⁺ in 29.2 ± 2.98% of DRG neurons relative to 8.35 ± 1.25% of vehicle responders (p < 0.0001). 55.05% of CART-responsive neurons were putative nociceptors due to co-sensitivity to capsaicin. Further investigation revealed a statistically significant reduction in the proportion of CART-sensitive neurons compared to CART (300nM) alone following pre-treatment with edelfosine, a phospholipase C inhibitor (10.5 ± 3.88%, p = 0.006), thapsigargin, a SERCA pump inhibitor (7.25 ± 1.78%, p = 0.001), or xestospongin C, an inositol triphosphate receptor inhibitor (6.74± 1.87%, p = 0.006). Furthermore, tissue bath application of CART (200nM) elicited a marked transient increase in ongoing LSN discharge, which increased from a baseline of 12.8 ± 3.9 (spikes/s) to a peak firing of 19.7 ± 6.1 spikes/s (p = 0.0385).

Conclusion

CART stimulates intracellular Ca²⁺ release in capsaicin-sensitive neurons consistent with a role in pain processing. This response was mediated by the release of Ca²⁺ from intracellular stores such as the endoplasmic reticulum and attenuated by inhibitors of the G_q pathway, suggesting activation of a G_q-coupled GPCR. The pronociceptive activity of CART on nerve firing suggests a potential role in colonic pain. Further research is necessary to identify the role of CART in IBD.

References

1. Ohsawa M, Dun SL, Tseng LF, Chang J, Dun NJ. Decrease of hindpaw withdrawal latency by cocaine- and amphetamine-regulated transcript peptide to the mouse spinal cord. Eur J Pharmacol. Jul 7 2000;399(2-3):165-9. doi:10.1016/s0014-2999(00)00374-5
2. McGuire C, Boundouki G, Hockley JRF, et al. Ex vivo study of human visceral nociceptors. Gut. Jan 2018;67(1):86-96. doi:10.1136/gutjnl-2016-311629
3. Higham JP, Bhebhe CN, Gupta RA, et al. Transcriptomic profiling reveals a pronociceptive role for angiotensin II in inflammatory bowel disease. Pain. Jan 29 2024;doi:10.1097/j.pain.0000000000003159

Disclosure

The PhD research is partially funded by Metrion Biosciences.