Ricard Farré

Short exposure of oesophageal mucosa to bile acids, both in acidic and weakly acidic conditions, can impair mucosal integrity and provoke dilated intercellular spaces.

Background: Severe duodeno-gastro-oesophageal reflux (DGOR) is a risk factor for oesophagitis and Barrett’s oesophagus. Patients with non-erosive reflux disease (NERD) have a slight increase in DGOR. Patients with gastro-oesophageal reflux disease (GORD), who are taking proton pump inhibitors (PPIs), still have reflux but of weakly acidic pH and persistence of bile. In these two groups of patients, heartburn might be due to increased oesophageal mucosal permeability and dilated intercellular spaces (DIS). We aimed to assess whether experimental short exposure of the oesophageal mucosa to bile acids, in low concentrations (at acidic, weakly acidic and neutral conditions) can increase mucosal permeability and provoke DIS. Methods: Rabbit oesophageal mucosa was studied in diffusion and Ussing chambers. We assessed the effects of different solutions containing bile acids, applied to the mucosal side, on transepithelial electrical resistance (RT) and permeability to fluorescein. The diameter of intercellular spaces was assessed by using transmission electron microscopy. Results: Incubation of oesophageal mucosa with acidic solutions (pH 2.0) containing a range of bile acids (0.5–5 mmol/l) markedly decreased RT and increased mucosal permeability. Weakly acidic solutions (pH 5.0), and to some extent neutral solutions (pH 7.4), containing some bile acids also decreased RT and increased permeability, although the effects were much less marked and in some combinations no effect was seen. Exposure to bile acids provoked DIS in acid and weakly acidic conditions but not in neutral (pH 7.4) solutions. Conclusions: Experimental short exposure of the oesophageal mucosa to solutions with a bile acid concentration and acidity similar to that observed in the gastric contents of patients with NERD or ERD, and who are taking PPIs, may impair oesophageal mucosal integrity and even induce dilated intercellular spaces. Such a situation could, theoretically, underlie the occurrence and/or persistence of symptoms in these patients.

The Capsaicin Receptor TRPV1 Is a Crucial Mediator of the Noxious Effects of Mustard Oil

Mustard oil (MO) is a plant-derived irritant that has been extensively used in experimental models to induce pain and inflammation. The noxious effects of MO are currently ascribed to specific activation of the cation channel TRPA1 in nociceptive neurons. In contrast to this view, we show here that the capsaicin receptor TRPV1 has a surprisingly large contribution to aversive and pain responses and visceral irritation induced by MO. Furthermore, we found that this can be explained by previously unknown properties of this compound. First, MO has a bimodal effect on TRPA1, producing current inhibition at millimolar concentrations. Second, it directly and stably activates mouse and human recombinant TRPV1, as well as TRPV1 channels in mouse sensory neurons. Finally, physiological temperatures enhance MO-induced TRPV1 stimulation. Our results refute the dogma that TRPA1 is the sole nocisensor for MO and motivate a revision of the putative roles of these channels in models of MO-induced pain and inflammation. We propose that TRPV1 has a generalized role in the detection of irritant botanical defensive traits and in the coevolution of multiple mammalian and plant species.

Evaluation of oesophageal mucosa integrity by the intraluminal impedance technique

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.

Acid and weakly acidic solutions impair mucosal integrity of distal exposed and proximal non-exposed human oesophagus

Background Oesophageal mucosa dilated intercellular spaces (DIS) may be important for symptom perception in non-erosive reflux disease (NERD). Patients with NERD might have DIS even in the proximal oesophagus. We aimed to assess the effect of oesophageal perfusions with acid and weakly acidic solutions on ‘exposed’ and ‘non-exposed’ oesophageal mucosa and its relationship to symptoms in healthy subjects. Methods 14 healthy volunteers underwent upper gastrointestinal endoscopy with biopsies at 3 and 13 cm proximal to the oesophagogastric junction (OGJ). In following sessions, subjects received 30 min perfusions with neutral, weakly acidic, acidic and acidic-bile acid solutions at 5 cm above the EGJ (separated 4 weeks). Biopsies were taken 20 min after perfusions. Electron microscopy was used to measure DIS. Subjects scored heartburn during perfusions using a visual analogue scale. Results (1) Oesophageal perfusion with acid solutions, with or without bile acids, provoked DIS in the ‘exposed’ oesophageal mucosa; (2) oesophageal perfusion with weakly acidic solutions provoked identical changes to those observed after perfusion with acid solutions; (3) distal oesophageal perfusions not only provoked changes in the ‘exposed’ but also in the more proximal ‘non-exposed’ mucosa; and (4) in spite of the presence of perfusion-induced DIS, most healthy subjects did not perceive heartburn during the experiments. Conclusions The human oesophageal mucosa is very sensitive to continuous exposure with acidic and weakly acidic solutions. In spite of the presence of intraluminal acid and DIS, healthy subjects did not experience heartburn, suggesting that NERD patients should have other critical factors underlying their symptoms.

Psychological stress and corticotropin-releasing hormone increase intestinal permeability in humans by a mast cell-dependent mechanism

Objective Intestinal permeability and psychological stress have been implicated in the pathophysiology of IBD and IBS. Studies in animals suggest that stress increases permeability via corticotropin-releasing hormone (CRH)-mediated mast cell activation. Our aim was to investigate the effect of stress on intestinal permeability in humans and its underlying mechanisms. Design Small intestinal permeability was quantified by a 2 h lactulose–mannitol urinary excretion test. In a first study, 23 healthy volunteers were subjected to four different conditions: control; indomethacin; public speech and anticipation of electroshocks. In a second study, five test conditions were investigated in 13 volunteers: control; after pretreatment with disodium cromoglycate (DSCG); administration of CRH; DSCG+CRH and DSCG+public speech. Results Indomethacin, as a positive comparator (0.071±0.040 vs 0.030±0.022; p<0.0001), and public speech (0.059±0.040; p<0.01), but not the shock protocol increased intestinal permeability. Similarly, salivary cortisol was only increased after public speech. Subgroup analysis demonstrated that the effect of public speech on permeability was only present in subjects with a significant elevation of cortisol. CRH increased the lactulose–mannitol ratio (0.042±0.021 vs 0.028±0.009; p=0.02), which was inhibited by the mast cell stabiliser DSCG. Finally, intestinal permeability was unaltered by public speech with DSCG pretreatment. Conclusions Acute psychological stress increases small intestinal permeability in humans. Peripheral CRH reproduces the effect of stress and DSCG blocks the effect of both stress and CRH, suggesting the involvement of mast cells. These findings provide new insight into the complex interplay between the central nervous system and GI function in man.

Esophageal Dilated Intercellular Spaces (DIS) and Nonerosive Reflux Disease

Esophageal mucosal dilated intercellular spaces (DIS) are frequently observed in patients with nonerosive reflux disease (NERD) and patients with esophagitis. The specificity of DIS is questionable, as it is present in up to 30% of asymptomatic healthy subjects and in patients with other esophageal disorders. DIS occurs in parallel with a drop in potential difference, diminished transepithelial resistance, and increased esophageal mucosal permeability. These alterations arise with exposure to acid and pepsin during gastroesophageal reflux, but the exact pathway of damage to the intercellular junctions remains unclear and seems to be multifactorial. Other noxious contents of the refluxate, such as bile acids, are harmful and DIS can also be induced by acute psychological stress. DIS can be assessed quantitatively with electron microscopy (EM), but it is also recognizable with light microscopy (LM). DIS can disappear after treatment with proton pump inhibitors (PPI); however, this is not the case in all NERD patients. A recent study showed that patients with NERD who are refractory to PPI might still have DIS; and animal experiments showed that persistence of DIS might be due to esophageal mucosal exposure to bile acids and/or psychological stress. In conclusion, DIS is a frequent but nonspecific histological feature of NERD. It can be caused by acid reflux, but bile acids in the refluxate and/or psychological stress can modulate the development or persistence of DIS. Although a causal relationship between DIS and heartburn has been proposed, it still needs to be proven and the underlying mechanisms investigated before considering DIS as a target for treatment of NERD.

Impaired duodenal mucosal integrity and low-grade inflammation in functional dyspepsia

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.

Critical role of stress in increased oesophageal mucosa permeability and dilated intercellular spaces

Background: In patients with non-erosive gastroesophageal reflux disease, heartburn can occur when acid reaches sensory nerve endings through oesophageal-mucosa-dilated intercellular spaces. Stressful life events may increase heartburn perception. In the rat, acute stress increases gastric and intestinal mucosa permeability. We investigated whether acute stress can also increase oesophageal mucosa permeability and contribute to the dilation of mucosa intercellular spaces. Methods: Male Sprague–Dawley rats were submitted to partial restraint stress. Oesophageal mucosa from stressed and control rats was mounted in diffusion chambers. The permeability to 51Cr-EDTA (400 Da), fluorescein isothiocyanate (FITC)-dextran 4000 Da (FD4) and FITC-dextran 20 000 Da (FD20) was assessed after tissue incubation either with Krebs (control) or HCl pH 2.0+ pepsin 1 mg/ml. The diameter of intercellular spaces was assessed using transmission electron microscopy. Results: Acute stress increased faecal output, small-intestinal permeability and glycaemia. Exposure of oesophageal mucosa from control rats to acid-pepsin did not increase permeability to any of the tested molecules. Stress increased the number of submucosal mast cells and, by itself, increased the permeability to the smallest molecule (22.8±7.1 pmol/cm2 vs 5.8±2.1 pmol/cm2) (p<0.001). Exposure of mucosa from stressed rats to acid-pepsin significantly increased permeability to all molecules tested. Electron microscopy showed dilated intercellular spaces only in mucosa from stressed rats (with and without exposure to acid-pepsin). Conclusions: Acute stress can increase, by itself, oesophageal mucosa permeability. There is a potentiation between stress and exposure of the oesophageal mucosa to acid-pepsin, leading to increased permeability and dilated intercellular spaces.

Obeticholic acid, a farnesoid X receptor agonist, improves portal hypertension by two distinct pathways in cirrhotic rats.

The farnesoid X receptor (FXR) is a nuclear bile acid receptor involved in bile acid homeostasis, hepatic and intestinal inflammation, liver fibrosis, and cardiovascular disease. We studied the effect of short‐term treatment with obeticholic acid (INT‐747), a potent selective FXR agonist, on intrahepatic hemodynamic dysfunction and signaling pathways in different rat models of cirrhotic portal hypertension (PHT). For this, thioacetamide (TAA)‐intoxicated and bile‐duct–ligated (BDL) rats were used as models. After gavage of two doses of 30 mg/kg of INT‐747 or vehicle within 24 hours, in vivo hemodynamics were assessed. Additionally, we evaluated the direct effect of INT‐747 on total intrahepatic vascular resistance (IHVR) and intrahepatic vascular tone (endothelial dysfunction and hyperresponsiveness to methoxamine) by means of an in situ liver perfusion system and on hepatic stellate cell contraction in vitro. FXR expression and involved intrahepatic vasoactive pathways (e.g., endothelial nitric oxide synthase [eNOS], Rho‐kinase, and dimethylarginine dimethylaminohydrolase [DDAH]) were analyzed by immunohistochemistry, reverse‐transcriptase polymerase chain reaction, or western blotting. In both cirrhotic models, FXR expression was decreased. Treatment with INT‐747 in TAA and BDL reactivated the FXR downstream signaling pathway and decreased portal pressure by lowering total IHVR without deleterious systemic hypotension. In the perfused TAA and BDL cirrhotic liver, INT‐747 improved endothelial vasorelaxation capacity, but not hyperresponsiveness. In both groups, this was associated with an increased eNOS activity, which, in TAA, related to down‐regulation of Rho‐kinase and in BDL to up‐regulation of DDAH‐2. Conclusion: FXR agonist INT‐747 improves PHT in two different rat models of cirrhosis by decreasing IHVR. This hemodynamic effect relates to increased intrahepatic eNOS activity by pathways that differ depending on the etiology of cirrhosis. (Hepatology 2014;59:2286–2298)

Efficacy of Buspirone, a Fundus-Relaxing Drug, in Patients With Functional Dyspepsia

BACKGROUND & AIMS Impaired accommodation and hypersensitivity to gastric distention are believed to be involved in the development of functional dyspepsia (FD). Buspirone, a 5-hydroxytryptamine 1A receptor agonist, relaxes the proximal stomach in healthy individuals. We studied the effects of buspirone on symptoms and mechanisms of FD. METHODS We performed a randomized, double-blind, placebo-controlled, crossover study of 17 patients (13 women; mean age, 38.5 ± 2.4 years). The study included 2 treatment periods of 4 weeks each, separated by a 2-week washout period. In the first period, 7 participants were given buspirone (10 mg, 3 times daily for 4 weeks) and 10 were given placebo 15 minutes before meals; patients switched groups for the second period. We assessed meal-related symptoms and severity, along with gastric sensitivity, accommodation, and emptying (by using barostat and breath tests) before and after 4 weeks of treatment. RESULTS Buspirone significantly reduced the overall severity of symptoms of dyspepsia (7.5 ± 1.3 vs 11.5 ± 1.2 for placebo; P < .005) and individual symptoms of postprandial fullness, early satiation, and upper abdominal bloating, whereas placebo had no significant effect (all P < .05). Buspirone did not alter the rate of gastric emptying of solids or sensitivity to gastric distention, but it significantly increased gastric accommodation, compared with placebo (229 ± 28 vs 141 ± 32 mL, respectively; P < .05), and delayed gastric emptying of liquids (half-life = 64 ± 5 vs 119 ± 24 minutes, respectively). Adverse events were similar when patients were given buspirone or placebo. CONCLUSIONS In patients with FD, 4 weeks of administration of buspirone significantly improved symptoms and gastric accommodation, compared with placebo, whereas gastric emptying of liquids was delayed.