Metformin prevents colonic barrier dysfunction by inhibiting mast cell activation in maternal separation‐induced IBS‐like rats

Abstract

Background Intestinal barrier dysfunction is a key etiologic factor of irritable bowel syndrome (IBS). Metformin improves intestinal barrier function, although the underlying mechanism has yet to be fully explained. This study evaluates the protective effect of metformin on colonic barrier integrity and explores the underlying cellular mechanisms. Methods IBS‐like rats were induced by maternal separation. Metformin was administered daily by gavage at 08:30, and rat pups were then separated from their mother. Visceral hyperalgesia and depression‐like behaviors were evaluated by colorectal distension, sucrose preference tests, and forced swimming tests. Intestinal integrity was analyzed using sugar probes and transmission electron microscopy. Inflammatory factors and the levels of corticotropin‐releasing factor were assessed by PCR and ELISA. The number of mast cells was evaluated by toluidine blue staining. Protein expression and localization were determined using Western blot and immunochemistry. Key Results Metformin pretreatment (a) reduced visceral hypersensitivity to colorectal distension, immobility time and enhanced sucrose consumption; (b) decreased urine lactulose/mannitol ratio and sucralose output; (c) inhibited the dilation of tight junction and prevented claudin‐4 translocation; (d) inhibited mast cell activation and downregulated the expression of IL‐6, IL‐18, tryptase, PAR‐2, and ERK activation; (e) inhibited claudin‐4 phosphorylation at serine sites and interactions between clau‐4 and ZO‐1. Conclusions & Inferences Metformin may block mast cell activation to reduce PAR‐2 expression and subsequently inhibit ERK activation and clau‐4 phosphorylation at serine sites to normalize the interaction of clau‐4 and ZO‐1 and clau‐4 distribution. Metformin may be clinically beneficial for patients with IBS or IBS‐like symptoms.

A Pilot Study of Clinical Evaluation and Formation Mechanism of Irritable Bowel Syndrome-like Symptoms in Inflammatory Bowel Disease Patients in Remission

“…18 Visceral hypersensitivity could be reduced by blocking MC activation in IBS-like rat models. 35 In this study, we focused on the relationship between MCs and IBS-like symptoms in IBD patients. The present study found that colonic MCs in IBD-IBS patients were significantly more active than those patients without IBS-like symptoms, especially in CD-IBS + patients.…”

Maternal separation in rodents: a journey from gut to brain and nutritional perspectives

“…Indeed, adult MS rodents show greater immobility time in these tests compared with controls (42,53,58,59,61,62,66,75–91) . MS has been associated with decreased sucrose preference (69,71,75–77,79–81,83,87,92–96) and decreased social behaviour with a conspecific (67,72,93,97–99) . The effects of MS are not limited to the above alterations of emotional behaviours; numerous studies also report that MS exacerbates motivation for alcohol and drugs of abuse (see (100) for review).…”

“…Interestingly, early-life adversity has been shown to affect enteric nervous system development in a sex-dependent manner, with females being more sensitive than males (255) . MS also produces increased intestinal motility in response to stress, as evidenced by reduced total transit time and increased number of faecal pellets (81,256–260) . It has been extensively reported that MS rats display visceral hyperalgesia during colorectal distension (51,67,140,144,146,147,180,220,256,257,259–283) .…”

“…Moreover, MS rats show more colonic damage after dextran sulphate sodium or 2,4,6-trinitrobenzenesulphonic acid-induced colitis than non-stressed animals and as a result, they also lose more weight, indicating that they are more sensitive to experimental colitis (305–307) . There is mounting evidence that MS produces long-term gut paracellular and transcellular hyper-permeability to ions and macromolecules (81,262,272,276,299,302,306,308–311) . Remarkably, stress-induced intestinal hyperpermeability appears to be glucocorticoid-dependent, as it is evoked by the synthetic glucocorticoid dexamethasone and prevented by administration of a GR antagonist, similarly to an inhibitor of the myosin light chain kinase controlling epithelial cytoskeleton contraction (221) .…”

“…Indeed, MS animals show an infiltration of immune cells (i.e. polymorphonuclear neutrophils) (262,305) and an increase in mucosal mast cell density (81,253,262,271,308) . MS also increases the expression of numerous cytokines including IL-6, IL-1β, TNFα, IFNγ, IL-4, IL-2 and IL-22 in the colonic mucosa (42,64,262,268,276,278,286,303,305,313) .…”