Colonic Gene Expression and Fecal Microbiota in Diarrhea-predominant Irritable Bowel Syndrome: Increased Toll-like Receptor 4 but Minimal Inflammation and no Response to Mesalazine

Abstract

Background/Aims Diarrhea-predominant irritable bowel syndrome (IBS-D) has been previously associated with evidence of immune activation and altered microbiota. Our aim is to assess the effect of the anti-inflammatory agent, mesalazine, on inflammatory gene expression and microbiota composition in IBS-D. Methods We studied a subset of patients (n = 43) from a previously published 12-week radomized placebo-controlled trial of mesalazine. Mucosal biopsies were assessed by immunohistochemistry and reverse transcription-polymerase chain reaction for a range of markers of inflammation, altered permeability, and sensory receptors including Toll-like receptors (TLRs) at randomization after treatment. All biopsy data were compared to 21 healthy controls. Patient’s stool microbiota composition was analysed through 16S ribosomal RNA sequencing. Results We found no evidence of increased immune activation compared to healthy controls. However, we did find increased expression of receptors in both sensory pathways and innate immune response including TLR4. Higher TLR4 expression was associated with greater urgency. TLR4 expression correlated strongly with the expression of the receptors bradykinin receptor B2, chemerin chemokine-like receptor 1, and transient receptor potential cation channel, subfamily A, member 1 as well as TLR4’s downstream adaptor myeloid differentiation factor 88. Mesalazine had minimal effect on either gene expression or microbiota composition. Conclusions Biopsies from a well-characterized IBS-D cohort showed no substantial inflammation. Mesalazine has little effect on gene expression and its previous reported effect on fecal microbiota associated with much greater inflammation found in inflammatory bowel diseases is likely secondary to reduced inflammation. Increased expression of TLR4 and correlated receptors in IBS may mediate a general increase in sensitivity to external stimuli, particularly those that signal via the TLR system.

Metabotropic glutamate receptor-8 relieves neonatal maternal separation-induced visceral hypersensitivity in rats by regulating expression of TNF-α

“…Elevated secretion of pro-inflammatory cytokines has been known to participate in the pathogenesis of VH in neonatal colonic irritation model ( 50 ). Another study showed that Bifco can elevate the level of short-chain fatty acids (SCFAs) and decrease secretion of IL-6 and TNF-α ( 26 ). In the present study, decreased TNF-α mRNA expression and MPO activity were found in the intestinal mucosa of rats treated with (S)-3,4-DCPG.…”

“…Even though robust inflammation may be absent in patients with post-infectious IBS, the number of epithelial T lymphocytes and mast cells is often increased in their gastrointestinal (GI) tract (24), indicating a persistent inflammatory status which may contribute to the pathogenesis of colonic hypersensitivity. Many cytokines such as interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), and interleukin-10 (IL-10) have been known to be associated with the development of IBS (6) and have been well studied in IBS animal models along with signal pathways such as pregnane X receptor (PXR)/nuclear factor kappaB (NF-κB), toll-like receptor 4 (TLR4) (25)(26)(27).…”

Gut Microbiota Shifting in Irritable Bowel Syndrome: The Mysterious Role of Blastocystis sp.

“…In this regard, they reported a significant upregulation of TLR2 and TLR4 in patients with IBS-M together with elevation of IL-8 and IL-1β ( 99 ). Recently, Jalanka et al ( 100 ) analyzed the correlation of the gene expression of TLR4 and correlated receptors in patients with IBS and supported the probable role of a low inflammation due to bacteria in the intestine of patients with IBS. Therefore, it seems that a change in the gut microbiota composition may arrange a chronic inflammation and subsequent IBS.…”

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

“…Based on the observation that 5-aminosalicylic acid was able to reduce release of histamine and prostaglandin D2 from mast cell cultures155 and reduced mast cell counts and histamine release in the rectum of patients with IBS,156 mesalazine was evaluated in two large multicentre trials in patients with IBS, which were both negative 157 158. A post-hoc analysis of the British study also failed to demonstrate increased mast cell counts or a gene expression signature indicative of inflammation in patients with IBS in comparison to healthy controls 159…”

“… 157 158 A post-hoc analysis of the British study also failed to demonstrate increased mast cell counts or a gene expression signature indicative of inflammation in patients with IBS in comparison to healthy controls. 159 …”