Objective Functional dyspepsia (FD) is an extremely common functional gastrointestinal disorder, the pathophysiology of which is poorly understood. We hypothesised that impaired intestinal barrier function is involved in the onset and persistence of this disorder by inducing low-grade inflammation. Therefore, our aim was to evaluate duodenal mucosal integrity and low-grade inflammation in patients with FD. Design Duodenal biopsy specimens were obtained from 15 patients with FD fulfilling the Rome III criteria and 15 age- and gender-matched healthy volunteers. Transepithelial electrical resistance (TEER) and paracellular permeability were measured in Ussing chambers. Expression of cell-to-cell adhesion proteins was evaluated by real-time PCR, western blot and/or immunofluorescence. Numbers of mast cells, eosinophils and intraepithelial lymphocytes were assessed by immunohistochemistry. Results Patients with FD displayed lower TEER and increased paracellular passage compared with healthy controls, which is indicative of impaired mucosal integrity. In addition, abnormal expression of cell-to-cell adhesion proteins at the level of tight junctions, adherens junctions and desmosomes was shown. Furthermore, patients were characterised by the presence of low-grade inflammation, as demonstrated by increased infiltration of mucosal mast cells and eosinophils. A significant association between the expression level of several cell-to-cell adhesion proteins, the extent of increased permeability and the severity of low-grade inflammation was found. Conclusions These findings challenge the classical paradigm that patients with FD show no structural changes in the gastrointestinal tract. We suggest that impaired intestinal barrier function is a pathophysiological mechanism in FD. Thus, restoration of intestinal barrier integrity may be a potential therapeutic target for treating patients with FD.

Background: Increased numbers of mast cells and mast cell activation in distal gut segments are associated with symptom onset and severity in irritable bowel syndrome (IBS). Although upper gut symptoms are common, mast cells have not been thoroughly evaluated in proximal gut in IBS patients. Methods: Jejunal biopsies obtained by Watson’s capsule, aspiration of intestinal fluid and one blood sample were obtained in 20 diarrhoea-predominant patients with IBS (D-IBS) and 14 healthy volunteers (H). Psychological stress (Holmes-Rahe Scale) and depression (Beck’s Depression Inventory) were evaluated at baseline and food and respiratory allergy excluded. Biopsies were processed for H&E staining and microscopic inflammation assessed by counting intraepithelial lymphocytes. Mast cells in lamina propria were counted by immunohistochemistry with CD117 (c-kit). Tryptase concentration was measured in intestinal fluid and serum. Results: D-IBS patients showed higher psychological stress than healthy volunteers (D-IBS: 203 (SD 114) v H: 112 (SD 99); p = 0.019). Immunohistochemical staining of jejunal mucosa revealed mild increase in intraepithelial CD3+ cells in D-IBS patients (D-IBS: 15.3 (SD 5.5; 95% CI 12.7 to 17.9) v H: 10.3 (SD 3.9; 95% CI 8.0 to 12.5); p = 0.006). Moreover, D-IBS patients showed marked increase in mast cells numbers (D-IBS: 34 (SD 9.3); H: 15.3 (SD 4.4) mast cells/hpf; p<0.001) and higher tryptase concentration in jejunal fluid (D-IBS: 0.45 (SD 0.38); H: 0.09 (SD 0.10) µg/l; p = 0.005). Upper gut symptoms were not associated with gender, mast cell counts, jejunal tryptase or basal stress. Conclusion: This jejunal mucosal inflammatory profile may help identify diarrhoea-predominant IBS, a stress-related disorder.

Functional gastrointestinal disorders (FGIDs) are characterized by chronic complaints arising from disorganized brain-gut interactions leading to dysmotility and hypersensitivity. The two most prevalent FGIDs, affecting up to 16–26% of worldwide population, are functional dyspepsia and irritable bowel syndrome. Their etiopathogenic mechanisms remain unclear, however, recent observations reveal low-grade mucosal inflammation and immune activation, in association with impaired epithelial barrier function and aberrant neuronal sensitivity. These findings come to challenge the traditional view of FGIDs as pure functional disorders, and relate the origin to a tangible organic substrate. The mucosal inflammatory infiltrate is dominated by mast cells, eosinophils and intraepithelial lymphocytes in the intestine of FGIDs. It is well established that mast cell activation can generate epithelial and neuro-muscular dysfunction and promote visceral hypersensitivity and altered motility patterns in FGIDs, postoperative ileus, food allergy and inflammatory bowel disease. This review will discuss the role of mucosal mast cells in the gastrointestinal tract with a specific focus on recent advances in disease mechanisms and clinical management in irritable bowel syndrome and functional dyspepsia.

Background Oesophageal intraluminal impedance is currently used for assessment of reflux in gastro-oesophageal reflux disease (GORD). Oesophageal mucosa integrity may have a key role in heartburn perception in non-erosive reflux disease (NERD). Severe erosive oesophagitis is associated with low impedance baseline. We hypothesised that impedance baseline measurements could be used to evaluate changes in oesophageal mucosa integrity in man. Methods We measured oesophageal impedance baseline before, during and after acid perfusion in rabbits and healthy subjects. Transepithelial resistance (TER) was determined and dilated intercellular spaces (DIS) were assessed in isolated rabbit oesophageal mucosa. Impedance baseline was measured retrospectively at different levels of the oesophagus in impedance-pH recordings from asymptomatic volunteers and patients with GORD. Results In healthy subjects and rabbits, impedance baseline dropped dramatically during perfusion of control solution (pH 7.2) but after perfusion, impedance recovered. In rabbits, after perfusion with saline pH 1.5 and 1.0 impedance values remained a 39.1±7.0% and 63.9±6.5% (p<0.05) lower respectively. There was a positive correlation between in vivo basal impedance and in vitro TER values (r=0.72, p=0.0021). Tissue showed no erosions but both acidic solutions induced DIS. In healthy subjects, after perfusion with saline pH 2.0 and 1.0 the impedance baseline remained lower a 21.9±6.5% and 52.7±5.0%, (p<0.0001) respectively. Patients with GORD have a lower impedance baseline than healthy volunteers at the distal oesophagus. Conclusions Impedance baseline measurements might be used to evaluate the status of the oesophageal mucosa and to study the role of the impaired mucosal integrity in acid-induced heartburn in healthy volunteers and in patients with GORD.

Objective: Recently, the authors demonstrated altered gene expression in the jejunal mucosa of diarrhoea-predominant irritable bowel syndrome patients (IBS-D); specifically, the authors showed that genes related to mast cells and the intercellular apical junction complex (AJC) were expressed differently than in healthy subjects. The aim of the authors here was to determine whether these alterations are associated with structural abnormalities in AJC and their relationship with mast cell activation and IBS-D clinical manifestations. Design: A clinical assessment and a jejunal biopsy were obtained in IBS-D patients (n=45) and healthy subjects (n=30). Mucosal mast cell number and activation were determined by quantifying CD117 ⁺ cells/hpf and tryptase expression, respectively. Expression and distribution of AJC specific proteins were evaluated by western blot and confocal microscopy. AJC ultrastructure was assessed by transmission electron microscopy. Results: Compared with healthy subjects, IBS-D patients exhibited: (a) increased mast cell counts and activation; (b) increased protein expression of claudin-2, reduced occludin phosphorylation and enhanced redistribution from the membrane to the cytoplasm; and (c) increased myosin kinase expression, reduced myosin phosphatase and, consequently, enhanced phosphorylation of myosin. These molecular alterations were associated with ultrastructural abnormalities at the AJC, specifically, perijunctional cytoskeleton condensation and enlarged apical intercellular distance. Moreover, AJC structural alterations positively correlated both with mast cell activation and clinical symptoms. Conclusion: The jejunal mucosa of IBS-D patients displays disrupted apical junctional complex integrity associated with mast cell activation and clinical manifestations. These results provide evidence for the organic nature of IBS-D, a heretofore model disease of functional gastrointestinal disorders.