Esophageal barrier function and tight junction expression in healthy subjects and patients with gastroesophageal reflux disease: functionality of esophageal mucosa exposed to bile salt and trypsin in vitro

The epithelial barrier theory and its associated diseases

The prevalence of many chronic noncommunicable diseases has been steadily rising over the past six decades. During this time, over 350,000 new chemical substances have been introduced to the lives of humans. In recent years, the epithelial barrier theory came to light explaining the growing prevalence and exacerbations of these diseases worldwide. It attributes their onset to a functionally impaired epithelial barrier triggered by the toxicity of the exposed substances, associated with microbial dysbiosis, immune system activation, and inflammation. Diseases encompassed by the epithelial barrier theory share common features such as an increased prevalence after the 1960s or 2000s that cannot (solely) be accounted for by the emergence of improved diagnostic methods. Other common traits include epithelial barrier defects, microbial dysbiosis with loss of commensals and colonization of opportunistic pathogens, and circulating inflammatory cells and cytokines. In addition, practically unrelated diseases that fulfill these criteria have started to emerge as multimorbidities during the last decades. Here, we provide a comprehensive overview of diseases encompassed by the epithelial barrier theory and discuss evidence and similarities for their epidemiology, genetic susceptibility, epithelial barrier dysfunction, microbial dysbiosis, and tissue inflammation.

Epithelial barrier dysfunction, type 2 immune response, and the development of chronic inflammatory diseases

The prevalence of many chronic noncommunicable diseases has been steadily rising over the past six decades. During this time, humans have been increasingly exposed to substances toxic for epithelial cells, including air pollutants, laundry and dishwashers, household chemicals, toothpaste, food additives, microplastics, and nanoparticles, introduced into our daily lives as part of industrialization, urbanization, and modernization. These substances disrupt the epithelial barriers and lead to microbial dysbiosis and cause immune response to allergens, opportunistic pathogens, bacterial toxins, and autoantigens followed by chronic inflammation due to epigenetic mechanisms. Recent evidence from studies on the mechanisms of epithelial barrier damage has demonstrated that even trace amounts of toxic substances can damage epithelial barriers and induce tissue inflammation. Further research in this field is essential for our understanding of the causal substances and molecular mechanisms involved in the initiation of leaky epithelial barriers that cascade into chronic inflammatory diseases.

Genetic evidence causally linking gastroesophageal reflux disease to cholecystitis: a two-sample mendelian randomization study

BACKGROUND

Gastroesophageal reflux disease (GERD) and cholecystitis share overlapping symptoms, including belching, acid reflux, and heartburn. Despite this, the causal relationship between these two conditions remains unclear. This study aimed to investigate the causal link between GERD and cholecystitis using a Mendelian randomization (MR) approach.

METHODS

A two-sample MR analysis was conducted using the inverse variance weighted (IVW), weighted median, weighted mode, and MR-Egger method to assess the causal effects of GERD on the cholecystitis risk. Genome-wide association studies (GWASs) on GERD (N cases = 129080; N controls = 473524) and cholecystitis (N cases = 1930; N controls =359264) were obtained from the IEU Open GWAS project. Various techniques were employed to assess pleiotropy and heterogeneity.

RESULTS

Seventy-seven single nucleotide polymorphisms from GERD GWASs were selected as instrumental variables (IVs). The primary IVW method revealed a significant association between GERD and an increased risk of cholecystitis (odds ratio = 1.004; 95% confidence interval = 1.003-1.005, p = 2.68 × 10- 9). The absence of heterogeneity and pleiotropy in the data supports the reliability of the results.

CONCLUSIONS

GERD was positively associated with the risk of cholecystitis. This study provides insights into potential avenues for the development of prevention strategies and treatment options for cholecystitis in patients with GERD. These findings contribute to our understanding of the complex interplay between GERD and cholecystitis.

Linking GERD and the Peptide Bombesin: A New Therapeutic Strategy to Modulate Inflammatory, Oxidative Stress and Clinical Biochemistry Parameters

Gastroesophageal reflux disease (GERD) represents one of the most prevalent foregut illnesses, affecting a large portion of individuals worldwide. Recent research has shown that inflammatory mediators such as cytokines, chemokines, and enzymes are crucial for causing esophageal mucosa alterations in GERD patients. It seems likely that the expression of various cytokines in the esophageal mucosa also induces oxidative stress by increasing the production of reactive oxygen species (ROS) and reactive nitrogen species (RNS). As humoral agents and peptidergic neurotransmitters that may support the enterogastric axis, bombesin and its related bombesin-like peptide, GRP (gastrin releasing peptide), have not been fully investigated. Therefore, considering all these assumptions, this study aimed to evaluate the influence of bombesin in reestablishing biochemical markers linked with inflammation and oxidative/nitrosative stress in GERD pathological settings. C57BL/6 mice were alternatively overfed and fasted for 56 days to induce GERD and then treated with bombesin (0.1, 0.5, and 1 mg/kg intraperitoneally) once daily for 7 days, and omeprazole was used as the positive control. After 7 days of treatment, gastric pain and inflammatory markers were evaluated. Abdominal pain was significantly reduced following bombesin administration, which was also successful in diminishing inflammatory and oxidative/nitrosative stress markers in a manner overlapping with omeprazole. Moreover, bombesin was also able to appreciably modulate gastric pH as a result of the restoration of gastric homeostasis. Overall, these observations indicated that the upregulation of bombesin and interconnected peptides is a promising alternative approach to treat GERD patients.

Effect of Vitamin D on the Proliferation and Barrier of Atrophic Vaginal Epithelial Cells

Atrophic vaginitis is very common in postmenopausal women due to declining estrogen levels. Vitamin D plays an important role in promoting epithelial cell proliferation, migration and adhesion. We established a rat model of ovariectomy (OVX) induced atrophic vaginitis with the aim of investigating the effects of Vitamin D supplementation on the vaginal epithelial barrier. The results showed that ovariectomised rats had significantly higher vaginal pH, reduced Lactobacillus, significantly lower uterine and vaginal weights, and lower vaginal epithelial PCNA, occludin, and E-cadherin mRNA expression compared with sham-operated rats. Vitamin D supplementation could reduce the vaginal pH, promote the proliferation and keratinization of vaginal epithelial cells, enhance the expression of PCNA mRNA in vaginal tissues, and improve the vaginal and uterine atrophy. Vitamin D can also increase the expression of E-cadherin and occludin proteins in vaginal tissues, maintain the integrity of the vaginal epithelium, increase the number of Lactobacillus, and reduce pathogenic bacterial infections. In vitro experiments demonstrated that 1,25(OH)2D3 could promote the proliferation and migration of VK2/E6E7 vaginal epithelial cells and increase the expression of E-cadherin protein. In conclusion, we demonstrated that Vitamin D can regulate the expression of vaginal epithelial tight junction proteins, promotes cell proliferation, and improves vaginal atrophy due to estrogen deficiency.

Esophageal Mucosal Admittance: A New Technique to Diagnose Gastroesophageal Reflux Disease - Is It Feasible?

Purpose

Esophageal mucosal admittance (MA) is a promising diagnostic method for gastroesophageal reflux disease (GERD). We conducted a study to describe the esophageal MA in patients with reflux symptoms and determine its diagnostic accuracy.

Patients and Methods

We recruited 92 patients with ambulatory pH-impedance monitoring, upper gastrointestinal endoscopy, and MA measured by the tissue conductance meter. MA was measured during endoscopy at 5cm (distal esophagus) and 15cm above the Z line (middle esophagus), repeated at least five times at each position, and median MA was obtained. Afterwards, two biopsies were taken 5cm above the Z line for histopathological evaluation using the Esohisto criteria. Patients were classified as GERD or non-GERD according to the 2018 Lyon consensus.

Results

The mean age was 43.2 years, and 42 patients were males. The most common symptoms were regurgitation (75.0%), belching (65.2%), and heartburn (46.7%). Twenty-three (32.3%) were diagnosed with GERD using the Lyon consensus, and 24 (26.1%) had esophagitis on histopathology. The median MA at the distal and middle esophagus was moderately correlated. The median MA at both positions was higher in the GERD group but only statistically significant in the middle esophagus. MA was not associated with pH-impedance parameters and esophagitis on histopathology. The diagnostic model developed using the logistic regression did not have good accuracy.

Conclusion

MA was not different between GERD and non-GERD patients.

Alginates for Protection Against Pepsin-Acid Induced Aerodigestive Epithelial Barrier Disruption

OBJECTIVE

Gastroesophageal reflux disease (GERD) and laryngopharyngeal reflux (LPR) are chronic conditions caused by backflow of gastric and duodenal contents into the esophagus and proximal aerodigestive tract, respectively. Mucosal barrier dysfunction resultant from the synergistic actions of chemical injury and the mucosal inflammatory response during reflux contributes to symptom perception. Alginates effectively treat symptoms of mild to moderate GERD and have recently shown benefit for LPR. In addition to forming a "raft" over gastric contents to reduce acidic reflux episodes, alginates have been found to bind the esophageal mucosa thereby preserving functional barrier integrity measured by transepithelial electrical resistance. The aim of this study was to further examine the topical protective capacity of alginate-based Gaviscon Advance (GA) and Double Action (GDA) against pepsin-acid mediated aerodigestive epithelial barrier dysfunction in vitro.

STUDY DESIGN

Translational.

METHODS

Immortalized human esophageal and vocal cord epithelial cells cultured in transwells were pretreated with liquid formula GA, GDA, matched viscous placebo solution, or saline (control), then treated for 1 h with saline, acid (pH 3-6) or pepsin (0.1-1 mg/ml) at pH 3-6. Endpoint measure was taken of horseradish peroxidase (HRP) allowed to diffuse across monolayers for 2 h.

RESULTS

Pepsin (0.1-1 mg/ml) at pH 3-6 increased HRP flux through cultures pretreated with saline or placebo (p < 0.05); acid alone did not. GA and GDA prevented barrier dysfunction.

CONCLUSIONS

GA and GDA preserved epithelial barrier function during pepsin-acid insult better than placebo suggesting that protection was due to alginate. These data support topical protection as a therapeutic approach to GERD and LPR. Laryngoscope, 132:2327-2334, 2022.

Claudin-1/4 as directly target gene of HIF-1α can feedback regulating HIF-1α by PI3K-AKT-mTOR and impact the proliferation of esophageal squamous cell though Rho GTPase and p-JNK pathway

Immunohistochemical microarray comprising 80 patients with esophageal squamous cell carcinoma (ESCC) and discovered that the expression of CLDN1 and CLDN4 were significantly higher in cancer tissues compared to para-cancerous tissues. Furthermore, CLDN4 significantly affected the overall survival of cancer patients. When two ESCC cell lines (TE1, KYSE410) were exposed to hypoxia (0.1% O₂), CLDN1/4 was shown to influence the occurrence and development of esophageal cancer. Compared with the control culture group, the cancer cells cultured under hypoxic conditions exhibited obvious changes in CLDN1 and CLDN4 expression at both the mRNA and protein levels. Through genetic intervention and Chip, we found that HIF-1α could directly regulate the expression of CLDN1 and CLDN4 in cancer cells. Hypoxia can affect the proliferation and apoptosis of cancer cells by regulating the PI3K-Akt-mTOR pathway. Molecular analysis further revealed that CLDN1 and CLDN4 can participate in the regulation process and had a feedback regulatory effect on HIF-1α expression in cancer cells. In vitro cellular experiments and vivo experiments in nude mice further revealed that changes in CLDN4 expression in cancer cells could affect the proliferation of cancer cells via regulation of Rho GTP and p-JNK pathway. Whether CLDN4 can be target for the treatment of ESCC needs further research.

Tight junctions: from molecules to gastrointestinal diseases

Intestinal epithelium functions as a tissue barrier to prevent interaction between the internal compartment and the external milieu. Intestinal barrier function also determines epithelial polarity for the absorption of nutrients and the secretion of waste products. These vital functions require strong integrity of tight junction proteins. In fact, intestinal tight junctions that seal the paracellular space can restrict mucosal-to-serosal transport of hostile luminal contents. Tight junctions can form both an absolute barrier and a paracellular ion channel. Although defective tight junctions potentially lead to compromised intestinal barrier and the development and progression of gastrointestinal (GI) diseases, no FDA-approved therapies that recover the epithelial tight junction barrier are currently available in clinical practice. Here, we discuss the impacts and regulatory mechanisms of tight junction disruption in the gut and related diseases. We also provide an overview of potential therapeutic targets to restore the epithelial tight junction barrier in the GI tract.

Protective Mechanisms of Liquid Formulations for Gastro-Oesophageal Reflux Disease in a Human Reconstructed Oesophageal Epithelium Model

Purpose

A novel experimental design based on a human-reconstructed oesophageal epithelium (HO2E) model has been applied to quantitively assess the properties of a set of liquid formulations, Device A (Gerdoff^® Protection), Device B (Esoxx^® One), and Device C (Marial^® gel) developed to form a temporary physical barrier on the oesophageal epithelium and modify epithelial permeability so to protect the oesophageal mucosa from refluxate components.

Methods

The formulations were applied to a prewetted HO2E model for 15 min. Then, a 0.5% caffeine solution was applied, and its penetration kinetics was assessed at 1 h and 2 h in acidic environments (pH= 3.3) to mirror exposure of the oesophageal mucosa to acidic reflux in GORD patients. Caffeine permeated into the basolateral compartment (evaluated by HPLC-UV) and Lucifer yellow (LY) permeability were quantified 15 min after application of the caffeine in acidic environments.

Results

At the 15 min timepoint, Device A reduced caffeine permeation by 77.2% and LY flux by 30.4% compared to the untreated control and with a faster mode of action than that of the other liquid formulations. Transepithelial caffeine flux was reduced, albeit with different timing and efficiency, by all three compounds up to the end of the 2 hour experiment. At 1 h, Device A reduced the caffeine flux by 79.2%; Device B, by 67.2%; and Device C, by 37%.

Conclusion

These results confirm the ability of the medical devices tested to interact with the oesophageal epithelium and create a temporary physical protective film for up to 2 hours after their application. The results underline differences in the mechanism of action of the three medical devices, with Device A performing faster than the other formulations. The overall results support the relevance of the reconstructed mucosal model to investigate oesophageal epithelium–product interactions and precisely differentiate liquid formulation performance.

In Vitro Modelling of Barrier Impairment Associated with Gastro-Oesophageal Reflux Disease (GERD)

Purpose

A novel experimental model based on a 3D reconstructed human oesophageal epithelium model (HO2E) has been developed to investigate the structural and functional changes of the oesophageal epithelium following exposure to a solution of HCl 0.1 N (pH = 1.2) mirroring GERD microenvironment condition.

Methods

The barrier structure modification after the exposure to the acid solution on HO2E tissues was investigated immediately after damage induction and after 1 hour post incubation and compared to HO2E tissues exposed to phosphate buffered saline solution. Immunofluorescence (IF) was applied to quantify the expression and localization of barrier function proteins: Claudin-1 (CLDN-1), Claudin-4 (CLDN-4), Zonulin-1 (ZO-1), E-Cadherin and Mucin-1 (MUC1). Barrier functionality was measured by TEER.

Results

In the acidic microenvironment, TEER measurement has shown some limitations and results were not applicable, whereas the evaluation of protein localization and quantification provided clear and robust evidence of the damage which occurred to the epithelium barrier structure. CLDN-4 expression significantly decreased after exposure to acid. ZO-1 protein appeared upregulated immediately after exposure to HCl and was mainly localized in the cytoplasm and not on the cell membrane. This different localization was also observed for CLND-1. CLDN-1, MUC1 and, to a lower extent, ZO-1 expression increased during the post-incubation period.

Conclusion

The relevant tissue biomarkers identified, CLDN-1 and MUC1, can be used to monitor TJ structure and epithelial barrier recovery after acid-induced damage which, in our experimental conditions, were non-destructive and suitable for recovery studies. The established model can be useful to investigate the mechanism of action of formulations acting on this specific pathophysiological condition and/or designed to potentiate the physiological defense mechanisms of oesophageal mucosa.

Measurement of low-grade inflammation of the esophageal mucosa with electrical conductivity shows promise in assessing PPI responsiveness in patients with GERD

A device that can easily measure electrical impedance might be a helpful tool for investigating the pathophysiology of gastroesophageal reflux disease. The first aim of this study was to validate our newly developed bioelectrical admittance measurement (BAM) through in vitro experimentation. The second aim was to investigate whether evaluation of BAM by this measurement differed between patients with heartburn according to their response to proton pump inhibitor (PPI) therapy. Caco-2 cell monolayers and three-dimensional tissues were examined by BAM using a frequency response analyzer. BAM was also used to measure the impedance through cell layers. Subsequently, BAM was performed during endoscopy in 41 patients experiencing heartburn without esophageal mucosal breaks. After 2-wk administration of 20-mg rabeprazole twice daily, patient responses to PPI were classified as "good" or "poor" according to their clinical course. In each patient, histological alterations and gene expression levels of inflammation mediators and tight junction proteins were evaluated. Impedance profiles indicated that monolayer Caco-2 cells on top of eight-layered normal human dermal fibroblasts had the highest magnitude of impedance over the range of frequencies. In vivo results revealed that patients with good responses to PPI displayed significantly higher admittance. Severity of low-grade inflammation was significantly associated with esophageal wall admittance. Moreover, esophageal wall admittance may be more closely related to basal zone hyperplasia than dilatation of intercellular spaces. Thus, BAM may be able to detect abnormalities in the subepithelial layer of the esophagus.NEW & NOTEWORTHY Bioelectrical admittance measurement is a new method to evaluate esophageal mucosal permeability vertically during upper gastrointestinal endoscopy. Measurement of low-grade inflammation of the esophageal mucosa with electrical conductivity shows promise in assessing proton pump inhibitor responsiveness in patients with gastroesophageal reflux disease. As various gastrointestinal diseases are associated with changes in mucosal permeability, bioelectrical admittance measurement is expected to be clinically applied to therapeutic decision-making for these diseases in the future.

Gastroesophageal reflux disease: new approaches to optimizing pharmacotherapy

Proton pump inhibitors (PPIs) are baseline drugs for induction and maintenance of remission in gastroesophageal reflux disease (GERD). PPIs have proven to be highly effective in healing esophageal mucosal lesions and relieving the symptoms of the disease in most cases. However, according to the literature data, the incidence rate of clinical ineffectiveness of PPIs in the form of partial or complete persistence of current symptoms during administration of standard doses of PPIs ranges from 10 to 40%. Optimization of GERD therapy in PPI refractory patients is a significant challenge. In most cases, experts advise to increase a dose / dosage frequency of PPIs, switch to CYP2C19-independent PPIs (rabeprazole, esomeprazole, dexlansoprazole), add an esophagoprotective or promotility agents to therapy. At the same time, these recommendations have a limited effect in some patients, which opens up opportunities for looking for new solutions related to the optimization of GERD therapy. Today there is growing evidence of the relevance of the role of disruption of the cytoprotective and barrier properties of the esophageal mucosa in the genesis of GERD and the formation of refractoriness. Intercellular contacts ensure the integrity of the barrier function of the esophageal mucosa to protect it from various exogenous intraluminal substances with detergent properties. Acid-peptic attack in patients with GERD leads to alteration of the expression of some tight junction proteins in epithelial cells of the esophageal mucosa. The latter leads to increased mucosal permeability, which facilitates the penetration of hydrogen ions and other substances into the submucosal layer, where they stimulate the terminals of nerve fibers playing a role in the induction and persistence of the symptoms of the disease. The above evidence brought up to date the effectiveness study of the cytoprotective drugs with tropism to the gastrointestinal tract, as part of the combination therapy of GERD.

Does Trypsin Oral Spray (Viruprotect®/ColdZyme®) Protect against COVID-19 and Common Colds or Induce Mutation? Caveats in Medical Device Regulations in the European Union

BACKGROUND

nasal or oral sprays are often marketed as medical devices (MDs) in the European Union to prevent common cold (CC), with ColdZyme^®/Viruprotect^® (trypsin/glycerol) mouth spray claiming to prevent colds and the COVID-19 virus from infecting host cells and to shorten/reduce CC symptoms as an example. We analyzed the published (pre)-clinical evidence.

METHODS

preclinical: comparison of in vitro tests with validated host cell models to determine viral infectivity. Clinical: efficacy, proportion of users protected against virus (compared with non-users) and safety associated with trypsin/glycerol.

RESULTS

preclinical data showed that exogenous trypsin enhances SARS-CoV-2 infectivity and syncytia formation in host models, while culture passages in trypsin presence induce spike protein mutants. The manufacturer claims >98% SARS-CoV-2 deactivation, although clinically irrelevant as based on a tryptic viral digest, inserting trypsin inactivation before host cells exposure. Efficacy and safety were not adequately addressed in clinical studies or leaflets (no COVID-19 data). Protection was obtained among 9-39% of users, comparable to or lower than placebo-treated or non-users. Several potential safety risks (tissue digestion, bronchoconstriction) were identified.

CONCLUSIONS

the current European MD regulations may result in insufficient exploration of (pre)clinical proof of action. Exogenous trypsin exposure even raises concerns (higher SARS-CoV-2 infectivity, mutations), whereas its clinical protective performance against respiratory viruses as published remains poor and substandard.

Laryngopharyngeal Reflux and Inflammatory Responses in Mucosal Barrier Dysfunction of the Upper Aerodigestive Tract

The upper aerodigestive tract (UAT) is the first line of defense against environmental stresses such as antigens, microbes, inhalants, foods, etc., and mucins, intracellular junctions, epithelial cells, and immune cells are the major constituents of this defensive mucosal barrier. Laryngopharyngeal reflux (LPR) is recognized as an independent risk factor for UAT mucosal disorders, and in this review, we describe the components and functions of the mucosal barrier and the results of LPR-induced mucosal inflammation in the UAT. We discuss the interactions between the refluxate and the mucosal components and the mechanisms through which these damaging events disrupt and alter the mucosal barriers. In addition, we discuss the dynamic alterations in the mucosal barrier that might be potential therapeutic targets for LPR-induced disorders.

The esophageal mucosal barrier in health and disease: mucosal pathophysiology and protective mechanisms

Diseases of the esophagus, such as gastroesophageal reflux (GER), can result in changes to mucosal integrity, neurological function, and the microbiome. Although poorly understood, both age and GER can lead to changes to the enteric nervous system. In addition, the esophagus has a distinct microbiome that can be altered in GER. Mucosal integrity is also at risk due to persistent damage from acid. Diagnostic tools, such as ambulatory pH/impedance testing and esophageal mucosal impedance, can assess short-term and longitudinal GER burden, which can also assess the risk for mucosal compromise. The quality of the mucosal barrier is determined by its intercellular spaces, tight junctions, and tight junction proteins, which are represented by claudins, occludins, and adhesion molecules. Fortunately, there are protective factors for mucosal integrity that are secreted by the esophageal submucosal mucous glands and within saliva that are augmented by mastication. These protective factors have potential as therapeutic targets for GER. In this article, we aim to review diagnostic tools used to predict mucosal integrity, aging, and microbiome changes to the esophagus and esophageal mucosal defense mechanisms.

Pharmacologic treatment of GERD: Where we are now, and where are we going?

The introduction of acid inhibition in clinical practice has revolutionized the management of acid-related diseases, leading to the virtual abolition of elective surgery for ulcer disease and relegating antireflux surgery to patients with gastroesophageal reflux disease (GERD) not adequately managed by medical therapy. Proton pump inhibitors (PPIs) are the antisecretory drugs of choice for the treatment of reflux disease. However, these drugs still leave some unmet clinical needs in GERD. PPI-refractoriness is common, and persistent symptoms are observed in up to 40-55% of daily PPI users. Potassium-competitive acid blockers (P-CABs) clearly overcome many of the drawbacks and limitations of PPIs, achieving rapid, potent, and prolonged acid suppression, offering the opportunity to address many of the unmet needs. In recent years, it has been increasingly recognized that impaired mucosal integrity is involved in the pathogenesis of GERD. As a consequence, esophageal mucosal protection has emerged as a new, promising therapeutic avenue. When P-CABS are used as add-on medications to standard treatment, a growing body of evidence suggests a significant additional benefit, especially in the relief of symptoms not responding to PPI therapy. On the contrary, reflux inhibitors are considered a promise unfulfilled, and prokinetic agents should only be used on a case-by-case basis.

Lubiprostone protects esophageal mucosa from acid injury in porcine esophagus

Esophageal injury from acid exposure related to gastroesophageal reflux disease is a common problem and a risk factor for development of Barrett's esophagus and esophageal adenocarcinoma. Our previous work highlights the benefits of using porcine esophagus to study human esophageal disease because of the similarities between porcine and human esophagus. In particular, esophageal submucosal glands (ESMGs) are present in human esophagus and proximal porcine esophagus but not in rodent esophagus. Although CFTR is expressed in the ducts of ESMGs, very little is known about CFTR and alternate anion channels, including ClC-2, in the setting of acid-related esophageal injury. After finding evidence of CFTR and ClC-2 in the basal layers of the squamous epithelium, and in the ducts of the ESMGs, we developed an ex vivo porcine model of esophageal acid injury. In this model, esophageal tissue was placed in Ussing chambers to determine the effect of pretreatment with the ClC-2 agonist lubiprostone on tissue damage related to acid exposure. Pretreatment with lubiprostone significantly reduced the level of acid injury and significantly augmented the recovery of the injured tissue (P < 0.05). Evaluation of the interepithelial tight junctions showed well-defined membrane localization of occludin in lubiprostone-treated injured tissues. Pretreatment of tissues with the Na⁺-K⁺-2Cl^- cotransporter inhibitor bumetanide blocked lubiprostone-induced increases in short-circuit current and inhibited the reparative effect of lubiprostone. Furthermore, inhibition of ClC-2 with ZnCl₂ blocked the effects of lubiprostone. We conclude that ClC-2 contributes to esophageal protection from acid exposure, potentially offering a new therapeutic target.NEW & NOTEWORTHY This research is the first to describe the presence of anion channels ClC-2 and CFTR localized to the basal epithelia of porcine esophageal mucosa and the esophageal submucosal glands. In the setting of ex vivo acid exposure, the ClC-2 agonist lubiprostone reduced acid-related injury and enhanced recovery of the epithelial barrier. This work may ultimately provide an alternate mechanism for treating gastroesophageal reflux disease.

Toll-like receptor 2 stimulation augments esophageal barrier integrity

BACKGROUND

Germline-encoded innate immune pattern recognition receptors (PRR) are expressed at epithelial surfaces and modulate epithelial defenses. Evidence suggests that stimulation of the Toll-like receptor (TLR) family of PRR may regulate epithelial barrier integrity by upregulating tight junction (TJ) complex protein expression, but it is not known whether this mechanism is utilized in esophageal epithelial cells. TJ complex proteins maintain intact barrier function and are dysregulated in atopic disorders including eosinophilic esophagitis.

METHODS

Pattern recognition receptors expression was assessed in EoE and control primary esophageal epithelial cells, demonstrating robust expression of TLR2 and TLR3. The three-dimensional air-liquid interface culture (ALI) model was used to test whether TLR2 or TLR3 stimulation alters epithelial barrier function using an in vitro model of human epithelium. Transepithelial electrical resistance (TEER) and FITC-Dextran permeability were evaluated to assess membrane permeability. ALI cultures were evaluated by histology, immunohistochemistry, Western blotting, and chromatin immunoprecipitation (ChIP).

RESULTS

TLR3 stimulation did not change TEER in the ALI model. TLR2 stimulation increased TEER (1.28- to 1.31-fold) and decreased paracellular permeability to FITC-Dextran, and this effect was abolished by treatment with anti-TLR2 blocking antibody. TJ complex proteins claudin-1 and zonula occludens-1 were upregulated following TLR2 stimulation, and ChIP assay demonstrated altered histone 4 acetyl binding at the TJP1 enhancer and CLDN1 enhancer and promoter following zymosan treatment, implying the occurrence of durable chromatin changes.

CONCLUSIONS

Our findings implicate the TLR2 pathway as a potential regulator of esophageal epithelial barrier function and suggest that downstream chromatin modifications are associated with this effect.

Epithelial HIF-1α/claudin-1 axis regulates barrier dysfunction in eosinophilic esophagitis

Epithelial barrier dysfunction is a significant factor in many allergic diseases, including eosinophilic esophagitis (EoE). Infiltrating leukocytes and tissue adaptations increase metabolic demands and decrease oxygen availability at barrier surfaces. Understanding of how these processes impact barrier is limited, particularly in allergy. Here, we identified a regulatory axis whereby the oxygen-sensing transcription factor HIF-1α orchestrated epithelial barrier integrity, selectively controlling tight junction CLDN1 (claudin-1). Prolonged experimental hypoxia or HIF1A knockdown suppressed HIF-1α-dependent claudin-1 expression and epithelial barrier function, as documented in 3D organotypic epithelial cultures. L2-IL5OXA mice with EoE-relevant allergic inflammation displayed localized eosinophil oxygen metabolism, tissue hypoxia, and impaired claudin-1 barrier via repression of HIF-1α/claudin-1 signaling, which was restored by transgenic expression of esophageal epithelial-targeted stabilized HIF-1α. EoE patient biopsy analysis identified a repressed HIF-1α/claudin-1 axis, which was restored via pharmacologic HIF-1α stabilization ex vivo. Collectively, these studies reveal HIF-1α's critical role in maintaining barrier and highlight the HIF-1α/claudin-1 axis as a potential therapeutic target for EoE.

[Subjective, functional and microbiological parameters of the oral cavity in gastroesophageal reflux patients with acidic and subacidic refluctant]

The aim of the study was to compare dental and periodontal status, oral hygiene, salivation rate, functional parameters of saliva and oral microbiota composition in patients with gastroesophageal reflux disease (GERD) with acidic and subacidic refluctant. The study comprised 69 participants divided in 3 groups: 22 healthy volunteers (controls) and 2 main groups: 25 GERD patients with acidic (group 2) and 22 patients with subacidic refluctant (group 3). Poor dental and periodontal condition was revealed in group 3 patients probably because of aggressive intestinal content reflux in the oral cavity resulting in higher PMA an saliva pH values, Escherichia coli species in oral microbiota and low buffer capacity of saliva. The results show that GERD may be suspected due to oral manifestations thus promoting it's prompt treatment.

Achalasia and associated esophageal cancer risk: What lessons can we learn from the molecular analysis of Barrett's-associated adenocarcinoma?

Idiopathic achalasia and Barrett's esophagus (BE) are preneoplastic conditions of the esophagus. BE increases the risk of esophageal adenocarcinoma (EAC), while achalasia is associated with both EAC and esophageal squamous cell carcinoma (ESCC). However, while the molecular mechanisms underlying the transformation of esophageal epithelial cells in BE are relatively well characterized, less is known regarding these processes in achalasia. Nevertheless, both conditions are associated with chronic inflammation and BE can occur in achalasia patients, and it is likely that similar processes underlie cancer risk in both diseases. The present review will discuss possible lessons that we can learn from the molecular analysis of BE for the study of achalasia-associated cancer and contrast findings in BE with those in achalasia. First, we will describe cellular fate during development of BE, EAC, and ESCC, and consider the inflammatory status of the epithelial barrier in BE and achalasia in terms of its contribution to carcinogenesis. Next, we will summarize current data on genetic alterations and molecular pathways involved in these processes. Lastly, the plausible role of the microbiota in achalasia-associated carcinogenesis and its contribution to abnormal lower esophageal sphincter (LES) functioning, the maintenance of chronic inflammatory status and influence on the esophageal mucosa through carcinogenic by-products, will be discussed.

Epithelial Claudin Proteins and Their Role in Gastrointestinal Diseases

Our bodies are protected from the external environment by mucosal barriers that are lined by epithelial cells. The epithelium plays a critical role as a highly dynamic, selective semipermeable barrier that separates luminal contents and pathogens from the rest of the body and controlling the absorption of nutrients, fluid and solutes. A series of protein complexes including the adherens junction, desmosomes, and tight junctions function as the principal barrier in paracellular diffusion and regulators of intracellular solute, protein, and lipid transport. Tight junctions are composed of a series of proteins called occludins, junctional adhesion molecules, and claudins that reside primarily as the most apical intercellular junction. Here we will review one of these protein families, claudins, and their relevance to gastrointestinal and liver diseases.

Guts and Gall: Bile Acids in Regulation of Intestinal Epithelial Function in Health and Disease

Epithelial cells line the entire surface of the gastrointestinal tract and its accessory organs where they primarily function in transporting digestive enzymes, nutrients, electrolytes, and fluid to and from the luminal contents. At the same time, epithelial cells are responsible for forming a physical and biochemical barrier that prevents the entry into the body of harmful agents, such as bacteria and their toxins. Dysregulation of epithelial transport and barrier function is associated with the pathogenesis of a number of conditions throughout the intestine, such as inflammatory bowel disease, chronic diarrhea, pancreatitis, reflux esophagitis, and cancer. Driven by discovery of specific receptors on intestinal epithelial cells, new insights into mechanisms that control their synthesis and enterohepatic circulation, and a growing appreciation of their roles as bioactive bacterial metabolites, bile acids are currently receiving a great deal of interest as critical regulators of epithelial function in health and disease. This review aims to summarize recent advances in this field and to highlight how bile acids are now emerging as exciting new targets for disease intervention.

Additive Effects of Rebamipide Plus Proton Pump Inhibitors on the Expression of Tight Junction Proteins in a Rat Model of Gastro-Esophageal Reflux Disease

Background/Aims

The aim of this study was to investigate the effects of rebamipide on tight junction proteins in the esophageal mucosa in a rat model of gastroesophageal reflux disease (GERD).

Methods

GERD was created in rats by tying the proximal stomach. The rats were divided into a control group, a proton pump inhibitor (PPI) group, and a PPI plus rebamipide (PPI+R) group. Pantoprazole (5 mg/kg) was administered intraperitoneally to the PPI and PPI+R groups. An additional dose of rebamipide (100 mg/kg) was administered orally to the PPI+R group. Mucosal erosions, epithelial thickness, and leukocyte infiltration into the esophageal mucosa were measured in isolated esophagi 14 days after the procedure. A Western blot analysis was conducted to measure the expression of claudin-1, -3, and -4.

Results

The mean surface area of mucosal erosions, epithelial thickness, and leukocyte infiltration were lower in the PPI group and the PPI+R group than in the control group. Western blot analysis revealed that the expression of claudin-3 and -4 was significantly higher in the PPI+R group than in the control group.

Conclusions

Rebamipide may exert an additive effect in combination with PPI to modify the tight junction proteins of the esophageal mucosa in a rat model of GERD. This treatment might be associated with the relief of GERD symptoms.

A Prospective Study of Eosinophilic Esophagitis and the Expression of Tight Junction Proteins in Patients with Gastroesophageal Reflux Disease Symptoms

Background/Aims

Eosinophilic esophagitis (EoE) is often erroneously diagnosed as gastroesophageal reflux disease (GERD). The aim of this study is to investigate the prevalence of EoE and the expression of tight junction (TJ) proteins in patients with GERD symptoms.

Methods

One hundred patients with GERD symptoms and 10 healthy controls were prospectively studied. Sixty-two patients had symptoms refractory to proton pump inhibitors (PPI). All patients underwent esophageal biopsy. Patients were diagnosed with EoE if the number of eosinophil granulocytes per high-power field was ≥15. Immunohistochemical analysis of TJ proteins (claudin-1, claudin-4, occludin, and zonula occludin-1 [ZO-1]) was performed.

Results

EoE was diagnosed in six of 100 patients (6%) with GERD symptoms and in six patients (9.7%) of 62 patients with PPI-refractory GERD. Only one had typical EoE endoscopic findings. The proportion of ZO-1-positive cells was significantly lower in the lower than in the middle esophagus (56.0%±14.0% vs 66.0%±11.5%, p＜0.05). There were no significant correlations between TJ protein expression and GERD symptoms.

Conclusions

The prevalence of EoE among patients with PPI-refractory GERD is approximately 10%. Regardless of endoscopic findings, esophageal biopsy is crucial in diagnosing EoE. The disruption of ZO-1 expression in the lower esophagus is significantly associated with GERD symptoms.

Evaluation of Esophageal Mucosal Integrity in Patients with Gastroesophageal Reflux Disease

BACKGROUND

Impaired esophageal mucosal integrity plays a role in causing symptoms of gastroesophageal reflux disease (GERD). Recently, the assessment of esophageal baseline impedance (BI) using the multichannel intraluminal impedance-pH (MII-pH) test was suggested as a surrogate technique for the study of esophageal mucosal integrity and was reported to be useful in distinguishing GERD from non-GERD. However, measuring BI requires a 24-h testing period, is complicated, and causes considerable patient discomfort.

SUMMARY

Recently, endoscopy-guided catheters that can measure mucosal impedance (MI) and mucosal admittance (MA), which is the inverse of impedance, were developed, and their usefulness in measuring MI and MA for the diagnosis of GERD has been reported. In these studies, esophageal MI values were significantly lower in patients with GERD than in those without GERD. In contrast, esophageal MA was significantly higher in patients with GERD than in those without. Furthermore, we reported that MA is inversely correlated with BI and correlated with acid exposure time. Key Messages: Endoscopy-guided real-time measurement of MI and MA may allow the estimation of mucosal integrity and may be a useful diagnostic tool for patients with GERD in a manner similar to 24-h MII-pH monitoring.

The Esophageal Epithelial Barrier in Health and Disease

Dysfunction in the esophageal epithelial barrier function is a major source for morbidity. To better understand the pathophysiologic pathways of the diseases associated with barrier dysfunction, including gastroesophageal reflux disease, eosinophilic esophagitis, Barrett's esophagus, and obesity, it is important to understand the esophageal epithelial embryologic development, microscopic anatomy with a special focus on the barrier structure and function, extraepithelial defense mechanisms, and how these change in the diseased state. In recent years, significant progress has been made in elucidating the esophageal barrier structure and function both in vitro and in vivo. This has enhanced the understanding of mechanisms of disease, and may also allow identification of therapeutic targets that can help in the management of these diseases. This review provides a detailed discussion regarding the esophageal epithelial barrier structure and function, the current and historical techniques used to study the barrier, and how it is affected by common esophageal diseases.

TGF-β1 alters esophageal epithelial barrier function by attenuation of claudin-7 in eosinophilic esophagitis

Barrier dysfunction has been implicated in the pathophysiology of eosinophilic esophagitis (EoE). Transforming growth factor-β1 (TGF-β1), a potent pleiotropic molecule, is increased in EoE; however, no study has evaluated its influence on esophageal epithelial barrier. We hypothesized that TGF-β1 regulates barrier dysfunction in EoE. We aimed to determine the role of TGF-β1 in the epithelial barrier in models of EoE. To examine the impact of TGF-β1 on esophageal barrier, immortalized human esophageal epithelial (EPC2-hTERT) cells were exposed to TGF-β1 during the three-dimensional air-liquid interface (3D-ALI) model in vitro. TGF-β1 exposure diminished EPC2-hTERT barrier function as measured by transepithelial electrical resistance (TEER) and 3 kDa Fluorescein isothiocyanate dextran paracellular flux (FITC Flux), and hematoxylin and eosin (H&E) assessment revealed prominent cellular separation. In analysis of epithelial barrier molecules, TGF-β1 led to the specific reduction in expression of the tight-junction molecule, claudin-7 (CLDN7), and this was prevented by TGF-β-receptor I inhibitor. Short hairpin ribonucleic acid (shRNA)-mediated CLDN7 knockdown diminished epithelial barrier function, whereas CLDN7 overexpression resulted in protection from TGF-β1-mediated barrier dysfunction. In pediatric EoE biopsies CLDN7 expression was decreased and altered localization was observed with immunofluorescence analysis, and the TGF-β1 downstream transcription factor, phosphorylated SMAD2/3 (pSMAD2/3), was increased. Our data suggest that TGF-β1 participates in esophageal epithelial barrier dysfunction through CLDN7 dysregulation.

A sequential assessment of the preservation injury in porcine intestines

BACKGROUND

Clinical and experimental evidence strongly suggest that ischemia-reperfusion injury after intestinal transplantation has deleterious short- and long-term effects and finding means to reduce ischemia-reperfusion injury is a major research area. The anatomical and physiological similarities between the human and porcine digestive tract favor its use as a preclinical model for translational research. Intriguingly, no systematic appraisal of the development of the intestinal preservation injury in pigs is available.

MATERIALS AND METHODS

Intestinal procurement was performed in nine pigs using histidine-tryptophan-ketoglutarate solution as preservation fluid. Ileal biopsies were obtained after 8, 14, and 24 h of static cold storage (SCS), and the preservation injury was assessed morphologically (Chiu score) as well as on the molecular level. Tight junction (zonula occludens, claudin-3 and 4, tricellulin, and occludin) and adherens junctions (E-cadherin) proteins were studied using immunofluorescence and Western blot.

RESULTS

Eight hours of SCS induced minimal mucosal changes (Chiu grade 1) that advanced to significant subepithelial edema (Chiu grade 3) after 24 h; progressive Goblet cell depletion was also noted. Apoptosis (studied by cleaved caspase-3 staining significantly increased after 24 h of SCS. Significant molecular changes with decreasing expression of zonula occludens, tricellulin, and occludin were evident already after 8 h of SCS and continuously worsened. Claudin-3 and Claudin-4 and E-cadherin expression remained relatively unaltered during SCS.

CONCLUSIONS

Important molecular alterations precede histologic changes during SCS of the porcine intestine and may be used as more sensitive injury markers than histologic changes in intestinal ischemia and transplantation.

High expression of Claudin-2 in esophageal carcinoma and precancerous lesions is significantly associated with the bile salt receptors VDR and TGR5

BACKGROUND

Claudins are a family of integral membrane proteins and are components of tight junctions (TJs). Many TJ proteins are known to tighten the cell structure and maintain a barrier. Claudin-2 forms gated paracellular channels and allows sodium ions and other small positively charged ions to cross between adjacent cells. Recently, we found that vitamin D receptor (VDR) enhanced Claudin-2 expression in colon and that bile salt receptors VDR and Takeda G-protein coupled receptor5 (TGR5) were highly expressed in esophageal adenocarcinoma (EAC) and precancerous lesions. Here, we examined the expression of Claudin-2 in EAC and precancerous lesions and its association with VDR and TGR5 expression.

METHODS

Claudin-2 expression was examined by immunohistochemistry on tissue microarrays, containing EAC, high grade dysplasia (HGD), low grade dysplasia (LGD), Barrett's esophagus (BE), columnar cell metaplasia (CM), squamous cell carcinoma (SCC), and squamous epithelium (SE) cases. Intensity (0 to 3) and percentage were scored for each case. High expression was defined as 2-3 intensity in ≥ 10% of cells.

RESULTS

Claudin-2 was highly expressed in 77% EAC (86/111), 38% HGD (5/13), 61% LGD (17/28), 46% BE (18/39), 45% CM (29/65), 88% SCC (23/26), and 14% SE (11/76). It was significantly more highly-expressed in EAC, SCC and glandular lesions than in SE and more in EAC than in BE and CM. A significant association was found between Claudin-2 expression and VDR and TGR5 expression. No significant association was found between expression of Claudin-2 and age, gender, grade, stage, or patients' survival time in EAC and SCC.

CONCLUSIONS

We conclude that Claudin-2 expression is significantly associated with bile acid receptors VDR and TGR5 expression. Our studies identify a novel role of a tight junction protein in the development and progression of esophageal mucosal metaplasia, dysplasia and carcinoma.

Gastrointestinal mucosal barrier function and diseases

The gastrointestinal mucosal barrier plays an essential role in the separation of the inside of the body from the outside environment. Tight junctions (TJs) are the most important component for construction of a constitutive barrier of epithelial cells, and they regulate the permeability of the barrier by tightly sealing the cell-cell junctions. TJ proteins are represented by claudins, occludin, junctional adhesion molecules, and scaffold protein zonula occludens. Among these TJ proteins, claudins are the major components of TJs and are responsible for the barrier and the polarity of the epithelial cells. Gastrointestinal diseases including reflux esophagitis, inflammatory bowel disease, functional gastrointestinal disorders, and cancers may be regulated by these molecules, and disruption of their functions leads to chronic inflammatory conditions and chronic or progressive disease. Therefore, regulation of the barrier function of epithelial cells by regulating the expression and localization of TJ proteins is a potential new target for the treatment of these diseases. Treatment strategies for these diseases might thus be largely altered if symptom generation and/or immune dysfunction could be regulated through improvement of mucosal barrier function. Since TJ proteins may also modify tumor infiltration and metastasis, other important goals include finding a good TJ biomarker of cancer progression and patient prognosis, and developing TJ protein-targeted therapies that can modify patient prognosis. This review summarizes current understanding of gastrointestinal barrier function, TJ protein expression, and the mechanisms underlying epithelial barrier dysregulation in gastrointestinal diseases.

Biomarkers of Reflux Disease

Gastroesophageal reflux disease (GERD) encompasses an array of disorders unified by the reflux of gastric contents. Because there are many potential disease manifestations, esophageal and extraesophageal, there is no single biomarker of the entire disease spectrum; a set of GERD biomarkers that each quantifies specific aspects of GERD-related pathology might be needed. We review recent reports of biomarkers of GERD, specifically in relation to endoscopically negative esophageal disease and excluding conventional pH-impedance monitoring. We consider histopathologic biomarkers, baseline impedance, and serologic assays to determine that most markers are based on manifestations of impaired esophageal mucosal integrity, which is based on increased ionic and molecular permeability, and/or destruction of tight junctions. Impaired mucosal integrity quantified by baseline mucosal impedance, proteolytic fragments of junctional proteins, or histopathologic features has emerged as a promising GERD biomarker.

A weakly acidic solution containing deoxycholic acid induces esophageal epithelial apoptosis and impairs integrity in an in vivo perfusion rabbit model

Impaired esophageal mucosal integrity may be an important contributor in the pathophysiology of gastroesophageal reflux disease (GERD). Nevertheless, the effect of potentially harmful agents on epithelial integrity is mainly evaluated in vitro for a short period of time and the possible induction of epithelial apoptosis has been neglected. Our objective was to assess the effect of an acidic and weakly acidic solution containing deoxycholic acid (DCA) on the esophageal epithelium in an in vivo rabbit model of esophageal perfusion and to evaluate the role of the epithelial apoptosis. The esophagus of 55 anesthetized rabbits was perfused for 30 min with different solutions at pH 7.2, pH 5.0, pH 1.0, and pH 5.0 containing 200 and 500 μM DCA. Thereafter, animals were euthanized immediately or at 24 or 48 h after the perfusion. Transepithelial electrical resistance, epithelial dilated intercellular spaces, and apoptosis were assessed in Ussing chambers, by transmission electron microscopy, and by TUNEL staining, respectively. No macroscopic or major microscopic alterations were observed after the esophageal perfusions. The acidic and weakly acidic solution containing DCA induced similar long-lasting functional impairment of the epithelial integrity but different ultrastructural morphological changes. Only the solution containing DCA induced epithelial apoptosis in vivo and in vitro in rabbit and human tissue. In contrast to acid, a weakly acidic solution containing DCA induces epithelial apoptosis and a long-lasting impaired mucosal integrity. The presence of apoptotic cells in the esophageal epithelium may be used as a marker of impaired integrity and/or bile reflux exposure.

Estrogen Enhances Esophageal Barrier Function by Potentiating Occludin Expression

BACKGROUND

We recently demonstrated that a female sex hormone, estrogen, suppressed esophageal epithelial injury in a reflux esophagitis model of rat, suggesting that estrogen may play an important role in controlling the progress of the gastro-esophageal reflux disease spectrum. However, the precise mechanism of the action is unclear.

AIM

To investigate the potential role of estrogen in the esophageal barrier function.

METHODS

Male rabbits were pretreated with either continuous release 17β-estradiol or placebo, and the excised esophageal mucosa was subjected to Ussing chamber experiments after the 2-week pre-treatment. The mucosal side of the chamber was perfused with luminal irritants (HCl or acidified sodium nitrite), while the basal side was perfused by modified Krebs buffer. The epithelial barrier function was evaluated by the transmembrane resistance and the epithelial permeability. The intercellular space of the epithelium was investigated with transmission electron microscopy and the expression of tight junction protein, occludin, claudin-1, and claudin-4, with immunoblotting.

RESULTS

Estrogen pre-treatment significantly attenuated the decrease in the transmembrane resistance and the increase in the epithelial permeability induced by luminal irritants. Furthermore, the dilation of the intercellular space induced by luminal HCl was significantly alleviated by 17β-estradiol administration. The baseline occludin expression was significantly potentiated by 17β-estradiol administration.

CONCLUSIONS

This is the first study showing an enhancement of the esophageal barrier function by 17β-estradiol administration. The lack of the protective effect of estrogen could be responsible for the male predominance of erosive reflux esophagitis.

Bile Salts at Low pH Cause Dilation of Intercellular Spaces in In Vitro Stratified Primary Esophageal Cells, Possibly by Modulating Wnt Signaling

BACKGROUND

The presence of dilated intercellular spaces in the stratified squamous lining of the esophagus is the pathognomonic feature of reflux esophagitis secondary to gastroesophageal reflux disease (GERD). In addition to stomach acid, bile salts are major constituents of gastroesophageal refluxate. The aim of our study was to determine the effect of bile salts cocktail at different pHs on epithelial junctions in an in vitro transwell model of stratified esophageal squamous epithelium.

DISCUSSION

Human telomerase reverse transcriptase (hTERT) immortalized primary esophageal EPC1 cells were grown on polyester transwell surfaces in calcium-enriched media. The cells exhibited gradual stratification into an 11-layered squamous epithelium over 7 days, together with epithelial barrier function as indicated by increased transepithelial electrical resistance (TEER). This stratified epithelium demonstrated well-formed tight junctions, adherens junctions, and desmosomes as visualized by immunofluorescence and electron microscopy. When exposed to short pulses of bile salts at pH 5, but not either condition alone, there was loss of stratification and decrease in TEER, concomitant with disruption of adherens junctions, tight junctions, and desmosomes, leading to the appearance of dilated intercellular spaces. At the cellular level, bile salts at pH 5 activated the Wnt pathway (indicated by increased β-catenin Ser552 phosphorylation).

CONCLUSION

In conclusion, in our in vitro transwell model bile salts at pH 5, but not bile salts or media at pH 5 alone, modulate Wnt signaling, disrupt different junctional complexes, and cause increased permeability of stratified squamous esophageal epithelium. These changes approximate the appearance of dilated intercellular space similar to that found in GERD patients.

Altered Esophageal Mucosal Structure in Patients with Celiac Disease

Background/Aim. Reflux symptoms (RS) are common in patients with celiac disease (CD), a chronic enteropathy that affects primarily the small intestine. We evaluated mucosal integrity and motility of the lower esophagus as mechanisms contributing to RS generation in patients with CD. Methods. We enrolled newly diagnosed CD patients with and without RS, nonceliac patients with classical reflux disease (GERD), and controls (without RS). Endoscopic biopsies from the distal esophagus were assessed for dilated intercellular space (DIS) by light microscopy and electron microscopy. Tight junction (TJ) mRNA proteins expression for zonula occludens-1 (ZO-1) and claudin-2 and claudin-3 (CLDN-2; CLDN-3) was determined using qRT-PCR. Results. DIS scores were higher in patients with active CD than in controls, but similar to GERD patients. The altered DIS was found even in CD patients without RS and normalized after one year of a gluten-free diet. CD patients with and without RS had lower expression of ZO-1 than controls. The expression of CLDN-2 and CLDN-3 was similar in CD and GERD patients. Conclusions. Our study shows that patients with active CD have altered esophageal mucosal integrity, independently of the presence of RS. The altered expression of ZO-1 may underlie loss of TJ integrity in the esophageal mucosa and may contribute to RS generation.

Inhibition of p38 MAPK activation attenuates esophageal mucosal damage in a chronic model of reflux esophagitis

BACKGROUND

Reflux esophagitis (RE) is one of the common gastrointestinal diseases that are increasingly recognized as a significant health problem. This study was designed to investigate the role of p38 mitogen-activated protein kinase (MAPK) in experimental chronic RE model of rats.

METHODS

Chronic acid RE rats were induced by fundus ligation and partial obstruction of the pylorus and treated with SB203580 (a p38 MAPK inhibitor, i.p., 1 mg/kg/day) for 14 days.

KEY RESULTS

Immunohistochemical staining and Western blotting results revealed the activation of p38 MAPK signaling in the esophagus mucosa 14 days post injury. Through gross and histological assessment, we found that inhibition of p38 MAPK activation by SB203580 attenuated esophageal mucosal damage in RE rats. Inhibition of p38 MAPK activation in RE rats attenuated esophageal barrier dysfunction, through enhancing the expression of tight junction proteins and reducing the expression of matrix matalloproteinases-3 and -9. Inhibition of p38 MAPK activation in RE rats reduced CD68-positive cells in esophagus mucosa and mRNA levels of tumor necrosis factor (TNF)-α, interleukin (IL)-6, and IL-1β in esophagus and protein levels of TNF-α, IL-6, and IL-1β in serum. In addition, we found that inhibition of p38 MAPK activation in RE rats suppressed protein expression of inducible nitric oxide synthase and reduced formation of nitric oxide (NO), 3-nitrotyrosin, and malondialdehyde in esophagus.

CONCLUSIONS & INFERENCES

Inhibition of p38 MAPK activation attenuated esophageal mucosal damage in acid RE rats, possibly by modulating esophageal barrier function and regulating inflammatory cell recruitment, and the subsequent formation of cytokines, NO, and reactive oxygen species.

Distinct afferent innervation patterns within the human proximal and distal esophageal mucosa

Little is known about the mucosal phenotype of the proximal human esophagus. There is evidence to suggest that the proximal esophagus is more sensitive to chemical and mechanical stimulation compared with the distal. This may have physiological relevance (e.g., in prevention of aspiration of gastroesophageal refluxate), but also pathological relevance (e.g., in reflux perception or dysphagia). Reasons for this increased sensitivity are unclear but may include impairment in mucosal barrier integrity or changes in sensory innervation. We assessed mucosal barrier integrity and afferent nerve distribution in the proximal and distal esophagus of healthy human volunteers. In 10 healthy volunteers baseline proximal and distal esophageal impedance was measured in vivo. Esophageal mucosal biopsies from the distal and proximal esophagus were taken, and baseline transepithelial electrical resistance (TER) was measured in Ussing chambers. Biopsies were examined immunohistochemically for presence and location of calcitonin gene-related peptide (CGRP)-immunoreactive nerve fibers. In a further four healthy volunteers we investigated for colocalization of CGRP and protein gene product (PGP) 9.5 immunoreactivity in nerve fibers. Baseline impedance was higher in the proximal than in the distal esophagus [2,936 Ω (SD578) vs. 2,229 Ω (SD821); P = 0.03], however, baseline TER was not significantly different between them. Mucosal CGRP-immunoreactive nerves were found in the epithelium of both proximal and distal esophagus, but were located more superficially in the proximal mucosa compared with the distal [11.5 (SD7) vs. 21.7 (SD5) cell layers from lumen, P = 0.002] 19% of proximal, and 10% of distal mucosal PGP-immunoreactive fibers colocalized with CGRP. PGP-immunoreactive fibers were also significantly closer to the luminal surface in the proximal compared with the distal esophagus (P < 0.001). We conclude that mucosal barrier integrity is similar in proximal and distal esophagus, but proximal mucosal afferent nerves are in a more superficial location. The enhanced sensitivity to reflux-evoked symptoms of the proximal esophagus most likely has an anatomical basis.

Luminal solutions protect mucosal barrier during extended preservation

BACKGROUND

Mucosal barrier injury during intestinal preservation (IP) and transplantation favors life-threatening infections. Luminal delivery of solutions containing amino acids or polyethylene glycols (PEGs) may improve preservation results and reduce this injury. We tested if solutions containing glutamine and PEG influence the mucosal injury.

MATERIALS AND METHODS

Rat intestines were perfused and stored in Viaspan-University of Wisconsin solution. Before IP, a PEG 3350 solution was introduced intraluminally alone (group 1) or supplemented with 40 mmol/L L-glutamine (group 2). Controls underwent vascular flush alone (group 3). Preservation injury was evaluated after 8, 14, and 24 h by histology and goblet cell count. Tight-junction proteins zonula occludens-1, claudin-3, claudin-4, and caveolin-1 were studied by immunofluorescence. Maltase and caspase-3 activity were also analyzed.

RESULTS

Group 1 showed mild edema at 8 h and mucosal disruption by 24 h; these features were greatly improved in group 2 where continuous mucosa was found after 24 h of IP. Intestines in group 3 did worse at all time points with subepithelial edema (Park/Chiu grade 3) and marked goblet cell depletion; caspase-3 activity was lowest in group 2. Tight-junction proteins varied continuously during IP; zonula occludens-1 expression and colocalization with claudins decreased significantly in group 3 but not in other groups. Claudin-3 was distinctly localized in the membrane, but stained diffuse, cytoplasmic at later time-points. Claudin-4 changed to a cytoplasmic granular pattern. No caveolin-1 colocalization was observed.

CONCLUSIONS

Luminal PEG and glutamine delay epithelial breakdown and preserve several important mucosal features during extended IP.