The effect of tegaserod on esophageal submucosal glands bicarbonate and mucin secretion

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.

Gastroesophageal reflux symptoms not responding to proton pump inhibitor: GERD, NERD, NARD, esophageal hypersensitivity or dyspepsia?

Gastroesophageal reflux (GER) is a common gastrointestinal process that can generate symptoms of heartburn and chest pain. Proton pump inhibitors (PPIs) are the gold standard for the treatment of GER; however, a substantial group of GER patients fail to respond to PPIs. In the past, it was believed that acid reflux into the esophagus causes all, or at least the majority, of symptoms attributed to GER, with both erosive esophagitis and nonerosive outcomes. However, with modern testing techniques it has been shown that, in addition to acid reflux, the reflux of nonacid gastric and duodenal contents into the esophagus may also induce GER symptoms. It remains unknown how weakly acidic or alkaline refluxate with a pH similar to a normal diet induces GER symptoms. Esophageal hypersensitivity or functional dyspepsia with superimposed heartburn may be other mechanisms of symptom generation, often completely unrelated to GER. Detailed studies investigating the pathophysiology of esophageal hypersensitivity are not conclusive, and definitions of the various disease states may overlap and are often confusing. The authors aim to clarify the pathophysiology, definition, diagnostic techniques and medical treatment of patients with heartburn symptoms who fail PPI therapy.

Novel therapeutics for gastro-esophageal reflux symptoms

Approximately 20-30% of patients with gastro-esophageal reflux symptoms report inadequate symptom relief while on proton-pump inhibitor therapy. The mechanisms involved are failure of the antireflux barrier (transient lower esophageal sphincter relaxations), high proximal extent of the refluxate, esophageal hypersensitivity and impaired mucosal integrity. Persisting acid or nonacid reflux can be demonstrated in 40-50% of cases, suggesting that there is room for antireflux therapy in these patients. New antireflux compounds have been shown to decrease the occurrence of transient lower esophageal sphincter relaxations. The most promising classes of compounds are GABA type B agonists and metabotropic glutamate receptor 5 antagonists, which can reduce both reflux episodes and symptoms, but the development of these compounds has been abandoned for either safety issues or lack of efficacy. Esophageal hypersensitivity and impaired mucosal integrity may prove to be relevant therapeutic targets in the future.

The role of the 5-hydroxytryptamine pathway in reflux-induced esophageal mucosal injury in rats

BACKGROUND

Dysfunction of the 5-hydroxytryptamine (5-HT) signaling pathway can lead to gastrointestinal motility and secretion abnormalities and to visceral hypersensitivity. The aim of this study is to investigate the role of 5-HT in reflux-induced esophageal mucosal injury.

METHODS

Fifty 8-week-old male Sprague-Dawley (SD) rats were randomly divided into a gastroesophageal reflux (GER) model group (30 rats) and a sham surgery control group (20 rats). Four weeks after surgery, the esophageal mucosa was collected for histological evaluation, 5-HT concentrations, and 5-HT selective reuptake transporter (SERT) mRNA and 5-HT4 receptor (5-HT4R) protein expressions.

RESULTS

Twenty-seven rats in the GER model group survived, and three rats died. Histologically, in the GER model group, 20 rats had reflux esophagitis (RE group), and 7 rats had non-erosive reflux disease (NERD group). The 5-HT levels in the esophageal tissue from the RE group were significantly higher than those from the control and NERD groups. Both the RE and NERD groups showed significant increases in SERT mRNA expression of the esophageal mucosa than that of the controls, and the SERT mRNA level in the RE group was significantly higher than that in the NERD group. The 5-HT4R protein level of the esophageal mucosa in the RE group was significantly lower than that in the controls and the NERD group.

CONCLUSIONS

We conclude that a 5-HT signaling pathway disorder could be a major factor in the pathogenesis of GER and RE.

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.

New pharmacologic approaches in gastroesophageal reflux disease

This article highlights current and emerging pharmacological treatments for gastroesophageal reflux disease (GERD), opportunities for improving medical treatment, the extent to which improvements may be achieved with current therapy, and where new therapies may be required. These issues are discussed in the context of current thinking on the pathogenesis of GERD and its various manifestations and on the pharmacologic basis of current treatments.

Advances in drug therapy for gastroesophageal reflux disease

The incidence of gastroesophageal reflux disease (GERD) is increasing drastically in China. GERD could probably cause reflux esophagitis, chronic cough, asthma, Barrett's esophagus and adenocarcinoma, and frequently affects health-related quality of life. The use of proton pump inhibitors (PPIs) provides effective symptomatic relief in most patients; however, some patients appear refractory to the treatment with PPIs. The long term use of PPIs might also cause adverse effects, such as interstitial nephritis, fracture and small intestinal bacterial overgrowth. Many new drugs for GERD have emerged recently. This article reviews the advances in drug therapy for GERD.

Medical treatment of GORD. Emerging therapeutic targets and concepts

Approximately 20-30% of patients with gastro-oesophageal reflux symptoms report inadequate symptom relief while on PPI therapy. Persisting acid or non-acid reflux can be demonstrated in 40-50% of them suggesting that there is room for anti-reflux therapy in these patients. New anti-reflux compounds aim at decreasing the occurrence of transient lower oesophageal sphincter relaxations (TLOSRs) which represent the main mechanism of all types of reflux. The most promising classes of compounds are GABA(B) agonists and mGluR5 antagonists which have been shown to reduce both reflux episodes and symptoms and are currently under evaluation in phase II and III clinical trials. Compounds that target TLOSR activity represent a promising new therapeutic option for patients who suffer from GORD symptoms. These drugs will probably be developed as add-on therapy in combination with PPIs provided the tolerability and safety issues are resolved.

New pharmacologic approaches in gastroesophageal reflux disease

This article highlights current and emerging pharmacological treatments for gastroesophageal reflux disease (GERD), opportunities for improving medical treatment, the extent to which improvements may be achieved with current therapy, and where new therapies may be required. These issues are discussed in the context of current thinking on the pathogenesis of GERD and its various manifestations and on the pharmacologic basis of current treatments.

Evolving issues in the management of reflux disease?

PURPOSE OF REVIEW

Gastroesophageal reflux disease (GERD) is a common chronic disorder often successfully treated, although there are several evolving issues in management. We reviewed the issues related to unmet needs over the past 12 months.

RECENT FINDINGS

A substantial number of patients fail to respond adequately to once or even twice daily proton pump inhibitor (PPI). There is no standard definition of PPI failure in GERD; a universally accepted definition for treatment success is also not available. Differentiation between erosive esophagitis and nonerosive reflux disease can be made but requires endoscopy; but studies still confuse functional heartburn and nonerosive reflux disease, which impacts management. Acid reflux plays an important role in GERD pathogenesis and the precise role of acid requires more studies of differences between erosive esophagitis and nonerosive reflux disease symptom generation and the implication of nocturnal acidification. Several possible mechanisms may explain GERD refractory to PPIs.

SUMMARY

Management of PPI nonresponders remains a challenge. Objective and precise evaluation of symptoms and treatment response requires study in high-quality trials. New therapeutic approaches are under investigation to answer unmet needs and improve erosive esophagitis healing rates and symptom control.