Detrimental impact of acid and pepsin on the rate of luminal release of transforming growth factor alpha. Its potential pathogenetic role in the development of reflux esophagitis

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.

Mucin Expression in the Esophageal Malignant and Pre-malignant States: A Systematic Review and Meta-analysis

BACKGROUND

Mucins are heavily glycosylated glycoproteins, synthesized by mucosal surfaces and have an important role in healthy state and malignant diseases. Change in mucins synthesis or secretion may be primary event or secondary to inflammation or carcinogenesis.

AIM

The aim of this study is to assess the current knowledge about mucin expression in esophageal lesions, and to establish a role for different mucin expressions as prognostic markers.

METHOD

English Medical literature searches were conducted for "mucin" and "esophagus." Observational studies were included. Meta-analysis was performed using comprehensive meta-analysis software. Pooled odds ratios (OR) and 95% confidence intervals (CI) were calculated.

RESULTS

In the random-effect model, mucin expression was significantly higher in esophageal lesions than in normal esophageal mucosa with OR=5.456 (95% CI, 1.883-15.807, P=0.002). Measure of heterogeneity, demonstrated in the included studies, was high: Q=287.501, df (Q)=44.00, P<0.0001, I=84.696%. There is a gradient of mucin expression and complexity in esophageal premalignant to malignant lesions, lower in Barrett's mucosa with low grade dysplasia (LGD), increased in high grade dysplasia (HGD), and highest in esophageal adenocarcinoma (EAC). MUC2, MUC3, MUC5AC, and MUC6 expression was higher in EAC than HGD, and higher in HGD than in LGD mucosa. The opposite was found for MUC1 and MUC4.

CONCLUSION

Increased expression of certain mucin genes in esophageal mucosa may be further studied as a potential diagnostic tool, and this may add important information in the surveillance of Barrett's esophagus.

Role of saliva in esophageal defense: implications in patients with nonerosive reflux disease

Background:

It has been previously demonstrated that patients with reflux esophagitis exhibit a significant impairment in the secretion of salivary protective components versus controls. However, the secretion of salivary protective factors in patients with nonerosive reflux disease (NERD) is not explored. The authors therefore studied the secretion of salivary volume, pH, bicarbonate, nonbicarbonate glycoconjugate, protein, epidermal growth factor (EGF), transforming growth factor alpha (TGF-α) and prostaglandin E2 in patients with NERD and compared with the corresponding values in controls (CTRL).

Methods:

Salivary secretion was collected during basal condition, mastication and intraesophageal mechanical (tubing, balloon) and chemical (initial saline, acid, acid/pepsin, final saline) stimulations, respectively, mimicking the natural gastroesophageal reflux.

Results:

Salivary volume, protein and TGF-α outputs in patients with NERD were significantly higher than CTRL during intraesophageal mechanical (P < 0.05) and chemical stimulations (P < 0.05). Salivary bicarbonate was significantly higher in NERD than CTRL group during intraesophageal stimulation with both acid/pepsin (P < 0.05) and saline (P < 0.01). Salivary glycoconjugate secretion was significantly higher in the NERD group than the CTRL group during chewing (P < 0.05), mechanical (P < 0.05) and chemical stimulation (P < 0.01). Salivary EGF secretion was higher in patients with NERD during mechanical stimulation (P < 0.05).

Conclusions:

Patients with NERD demonstrated a significantly stronger salivary secretory response in terms of volume, bicarbonate, glycoconjugate, protein, EGF and TGF-α than asymptomatic controls. This enhanced salivary esophagoprotection is potentially mediating resistance to the development of endoscopic mucosal changes by gastroesophageal reflux.

A distinct salivary secretory response mediated by the esophago-salivary reflex in patients with Barrett's esophagus: its potential pathogenetic implications

PURPOSE

A significantly compromised epidermal growth factor (EGF) secretion by basal parotid saliva may contribute to the development of Barrett's esophagus (BE). The rate of secretion of EGF as well as a wide spectrum of protective factors in total basal and stimulated saliva in BE patients remains to be explored. We therefore studied the rate of secretion of salivary buffers, glycoconjugate, protein, EGF, transforming growth factor α (TGFα) and prostaglandin E₂ (PGE₂), evoked by esophago-salivary reflex, in patients with BE and controls (CTRL).

MATERIAL/METHODS

Salivary secretion was collected during basal condition, mastication, and intraesophageal mechanical and chemical stimulations respectively, mimicking the natural gastroesophageal reflux scenario.

RESULTS

Salivary pH in BE was significantly lower than in controls during mechanical (p<0.001) and chemical stimulations (p<0.001). Bicarbonate and protein outputs in BE were significantly lower during mechanical (p<0.05) and chemical stimulations (p<0.01). The non-bicarbonate and glycoconjugate outputs in BE were lower during chemical stimulation (p<0.05) and during mechanical (p<0.05) and chemical stimulations (p<0.05) respectively. The rate of salivary EGF output in BE was significantly lower during mechanical stimulation (p<0.05). We observed a higher TGFα output during mastication (p<0.05) and PGE2 secretion during basal and masticatory condition (p<0.05) in BE.

CONCLUSIONS

Patients with BE demonstrated significantly compromised salivary pH and rate of secretion of bicarbonate, non-bicarbonate, glycoconjugate, protein and EGF. This impairment could potentially predispose to the development of accelerated esophageal mucosal injury. Potential restoration of this impairment by masticatory stimulation of salivary secretion using sugarless chewing gum justifies further clinical exploration.

Salivary transforming growth factor alpha in patients with Sjögren's syndrome and reflux laryngitis

Introduction

Saliva plays a key role in the homeostasis of the digestive tract, through its inorganic components and its protein growth factors. Sjögren's syndrome patients have a higher prevalence of gastroesophageal reflux disease and laryngopharyngeal reflux. Decreased salivary transforming growth factor alpha levels were observed in dyspeptic patients, but there have been no studies in patients with Sjögren's syndrome and laryngopharyngeal reflux.

Objective

To compare the salivary transforming growth factor alpha levels of patients with Sjögren's syndrome and laryngopharyngeal reflux to those of healthy controls.

Methods

This is a prospective controlled study. Twelve patients with Sjögren's syndrome and laryngopharyngeal reflux and 11 controls were prospectively evaluated. Spontaneous and stimulated saliva samples were obtained to establish salivary transforming growth factor alpha concentrations.

Results

The salivary transforming growth factor alpha levels of patients were significantly higher than those of healthy controls. Five patients with laryngopharyngeal reflux also had erosive esophagitis; their salivary transforming growth factor alpha levels were comparable to controls.

Conclusion

Salivary transforming growth factor alpha level was significantly higher in patients with Sjögren's syndrome and laryngopharyngeal reflux when compared to the control group.

The role of mucin in GERD and its complications

Acid, pepsin and other noxious material reach the esophageal mucosa and interact with the luminal aspect of the squamous epithelium. The first protective barrier to these potentially injurious substances is the mucus buffer layer that covers the mucosa. In healthy people, the esophagus has a protective surface adherent mucus gel barrier. Levels of mucin glycoprotein are considerably increased in response to acid and pepsin. A wide spectrum of mucin genes are expressed in normal esophageal mucosa, squamous cell carcinoma of the esophagus, Barrett epithelium and esophageal adenocarcinoma. The mucins MUC5AC and MUC6 are expressed to a similar degree in Barrett metaplasia and gastric mucosa, as is MUC2 in Barrett intestinal metaplasia and small bowel mucosa. Increased expression of MUC1 is associated with progression from dysplasia to adenocarcinoma of the esophagus. Thus, mucins have an important role in the defense of esophageal mucosa against the acid, pepsin and bile that are present in the refluxate. Changes in the expression of mucins occur in patients with GERD, and might lead to the development of new drugs.

Significant increase of esophageal mucin secretion in patients with reflux esophagitis after healing with rabeprazole: its esophagoprotective potential

Esophageal mucin secretion in patients with reflux esophagitis (RE) is significantly impaired. Rabeprazole augments gastric mucin secretion. We have studied, therefore, the effect of rabeprazole on esophageal mucin secretion in patients with RE. The study was conducted in 15 patients with RE treated with rabeprazole (20 mg QD) for 8 weeks. Esophageal secretions were collected during consecutive infusions of initial NaCl, HCl/Pepsin (HCl/P), and a final NaCl, using a specially designed esophageal catheter, before and after therapy. Mucin was measured using standard methodology. After rabeprazole administration esophageal mucin concentration as well as secretion increased during perfusion with initial saline (P < 0.01), HCl/P (P < 0.02), and concluding saline (P < 0.001). Stimulation of esophageal mucin secretion by rabeprazole may indicate that the mechanisms governing its secretion are similar to those implicated in gastric mucin output. Enhancement of esophageal mucin secretion by rabeprazole may translate into esophagoprotective potential in patients with reflux esophagitis.

The modified glucose clearance test: a novel non-invasive method for differentiating non-erosive reflux disease and erosive oesophagitis

BACKGROUND

Impaired salivary secretion has been reported to cause abnormal acid clearance from the oesophagus in gastro-oesophageal reflux disease (GERD). However, few studies have explained the differences between non-erosive reflux disease (NERD) and erosive oesophagitis (EO) with respect to salivary secretion. Aim To elucidate these differences, we measured salivary secretion by using the modified glucose clearance test (mGCT).

METHODS

All subjects completed endoscopic examinations, the frequency scale for the symptoms of GERD questionnaire and the mGCT comprising a resting GCT (measured as RGC time) and a chewing-stimulated GCT (SGC time).

RESULTS

Resting glucose clearance time was 18.5 min in control group and significantly longer in NERD and EO groups (28.5 and 39.0 min respectively). SGC time was 6.1 min in control group and 7.2 min in NERD group and significantly longer in EO group (10.2 min) than in the control and NERD groups.

CONCLUSIONS

In the EO group, both resting and stimulated salivary secretions were less than in control group. However, in the NERD group, resting salivary secretion was decreased, but stimulated salivary secretion was similar to that of the control group. Therefore, these results may help in explaining the differences in the pathogenesis of NERD and EO.

Significant enhancement of esophageal pre-epithelial defense by tegaserod: implications for an esophagoprotective effect

BACKGROUND & AIMS

Tegaserod, a serotonin 5-hydroxytryptamine (5-HT)4 receptor agonist, is thought to stimulate intestinal secretions. The aim of the current study was to assess the effect of tegaserod vs placebo on salivary and esophageal protective factors in patients with gastroesophageal reflux disease (GERD).

METHODS

This study was a randomized, double-blind, placebo-controlled, cross-over trial in 38 GERD patients treated with tegaserod 6 mg twice a day vs placebo. Salivary samples were collected basally and during mastication. In addition, in 32 GERD patients, salivary and esophageal secretions also were collected during infusion of NaCl, HCl/pepsin, and NaCl in a consecutive fashion using a specially designed esophageal catheter. Saliva and esophageal perfusates were assessed for the pH, volume, content of buffers, protein, mucin, epidermal growth factor (EGF), transforming growth factor alpha (TGFalpha), and prostaglandin E (PGE)2 and analyzed statistically.

RESULTS

Salivary flow rates during administration of tegaserod increased over corresponding values during both basal conditions (P < .01) and mastication (P < .001). The rate of secretion of salivary bicarbonate and nonbicarbonate buffers also increased in basal conditions (P < .001 and P < .01, respectively) and during mastication (P < .05 and P = .05). Salivary EGF increased during mastication (P < .05), whereas PGE2 and TGF alpha increased in basal conditions (P < .05 and P < .01). Esophageal perfusate volumes increased during administration of tegaserod in basal conditions (P < .05), whereas esophageal EGF secretion increased after mucosal exposure to HCl/pepsin and subsequent final perfusion with NaCl (P < .05).

CONCLUSIONS

Significant stimulatory impact of 5-HT4 agonist on several salivary protective factors as well as esophageal EGF secretion may have esophagoprotective implications in patients with GERD and may help to address new therapies in the future.

The potential role of the esophageal pre-epithelial barrier components in the maintenance of integrity of the esophageal mucosa in patients with endoscopically negative gastroesophageal reflux disease

OBJECTIVE

Patients with gastroesophageal reflux disease (GERD) accompanied by erosive reflux esophagitis (RE) exhibit an impairment within the esophageal pre-epithelial barrier protective components that may facilitate the development and/or progression of the mucosal injury. Little is known, however, whether such impairment is a general phenomenon affecting all patients with GERD or whether this is a characteristic feature only of patients with erosive RE. We therefore studied the rate of secretion of esophageal inorganic and organic protective factors in patients with endoscopically negative [E (-)] GERD and compared these results with the corresponding values in asymptomatic volunteers (CTRL).

METHODS

The study was conducted on 33 white asymptomatic volunteers and 10 white patients with a long history of GERD confirmed by 24-h pH monitoring and a grossly negative upper endoscopy. Esophageal secretion was collected during mucosal exposure to NaCl, HCl, HC/pepsin and NaCl using the esophageal perfusion catheter. In collected samples all investigated parameters were measured.

RESULTS

The pH of esophageal secretion and its content of bicarbonate, EGF, and PGE2 in patients with E (-) GERD and asymptomatic volunteers were similar. Unexpectedly, the rate of esophageal glycoconjugate (predominantly mucin) secretion was significantly higher in patients with E (-) GERD than in controls during perfusion with HCl (p < 0.05). Furthermore, secretion of protein in patients with E (-) GERD was significantly higher than in the control group during the mucosal exposure to HCl/Pepsin (p < 0.05). The nonbicarbonate buffer secretion during perfusion with HCl and HCl/Pepsin as well as the rate of esophageal TGFalpha output during infusion of final saline in patients with E (-) GERD were significantly lower than in CTRL group (p < 0.05).

CONCLUSIONS

Our data indicate that patients with E (-) GERD have an esophageal secretory potential, in terms of glycoconjugate and protein, higher than that in asymptomatic controls. This phenomenon in patients with E (-) GERD may, by enhancing the quantity of the esophageal pre-epithelial barrier, help to prevent the development of erosive esophagitis. A significantly lower esophageal secretory response in patients with E (-) GERD in terms of nonbicarbonate buffers and TGFalpha may facilitate the development of GERD symptoms and histological changes of GERD, respectively.

Role of epidermal growth factor (EGF) in oesophageal mucosal integrity

Oesophageal mucosa has well established protective mechanisms, which operate within pre-epithelial, epithelial and post-epithelial compartments. Since refluxed acid and pepsin always act from the luminal side of the mucosa, protective factors like EGF, operating as a part of pre-epithelial defence, are thought to be pivotal in the maintenance of the integrity of the oesophageal mucosa. The significant contribution of salivary EGF to the quality of the oesophageal mucosal barrier has been demonstrated in an experimental setting and in a clinical scenario. Patients with low salivary EGF levels are predisposed to severe oesophageal damage if they develop gastro-oesophageal reflux and are a high-risk group for development of Barrett's oesophagus. Not only the salivary glands but also the human oesophagus has a profound ability to elaborate and release EGF. Some changes in luminal release of EGF during oesophageal mucosal exposure to intraluminal damaging factors imply its role in the oesophageal protective mechanisms. To exert biological effects within the oesophageal mucosal compartment, EGF requires binding to the ligand-binding domain of its receptor. This process results in receptor dimerisation, autophosphorylation and activation of intracellular signal transduction pathways. EGF receptors are localised on the basolateral and luminal aspect of the mucosal cells playing an important role in fast regeneration of oesophageal epithelium through the high mitotic activity of its proliferative zone. An increase in the rate of salivary EGF secretion during masticatory stimulation suggests its potential therapeutic benefit in the treatment of patients with damaged oesophageal mucosa.

Impact of Helicobacter pylori colonization on immunoreactive epidermal growth factor and transforming growth factor-alpha in gastric juice. Its potential pathogenetic implications

Epidermal growth factor (EGF), pivotal in mucosal protection, is partly degraded proteolytically at low pH in the gastric milieu; gastric acid secretion, on the other hand, remains influenced by H. pylori colonization. The aim of this study, therefore, was to evaluate the impact of low pH and H. pylori colonization status on immunoreactive EGF and the other member of EGF-family, immunoreactive transforming growth factor-alpha (TGF-alpha). Eighteen patients with nonulcer dyspepsia (NUD) colonized by H. pylori and 55 NUD patients without H. pylori colonization were investigated. Gastric juice samples were aspirated at the beginning of the endoscopy procedure and immediately placed on ice, and their pH was recorded. The measurement of immunoreactive EGF and TGF-alpha was performed using commercially available radioimmunoassays (RIAs) after adjustment of pH to neutral using an assay buffer. Statistical analysis was performed using sigma-Stat for Windows. The concentration of immunoreactive EGF in patients with NUD colonized by H. pylori was 80% lower (P < 0.02) than in those without H. pylori and in both groups immunoreactive EGF was significantly lower when the pH of gastric juice was below 4.0. The concentration of immunoreactive EGF in H. pylori(+) and H. pylori(-) patients was similar when the pH of aspirated gastric juice was above 4.0. However, with gastric juice pH < 4.0, the EGF concentration was 64% lower in H. pylori(+) patients than H. pylori(-) patients (P < 0.05). In general, the concentration of immunoreactive TGF-alpha in gastric juice was unaffected by H. pylori colonization or pH of gastric juice. It is concluded that: (1) significantly lower immunoreactive EGF concentrations in patients with pH below 4.0 indicate that immunoreactive EGF but not immunoreactive TGF-alpha is affected by an acidic gastric milieu; (2) the further reduction of gastric juice immunoreactive EGF at pH below 4.0 in patients colonized by H. pylori suggests that this microorganism may elaborate factors that accelerate its proteolytic degradation or inhibit its rate of synthesis and/or secretion; and (3) this diminished content of immunoreactive EGF at low pH, especially in patients colonized by H. pylori, may facilitate the development and/or progression of mucosal damage.