Acid sensors in the gut: a taste of things to come

Comparison of central and intraesophageal factors between gastroesophageal reflux disease (GERD) patients and those with GERD-related noncardiac chest pain

Gastroesophageal reflux disease (GERD) causes a wide range of symptoms. Some patients present with typical symptoms such as heartburn and regurgitation and others with atypical symptoms such as chest pain. The mechanism responsible for the varying clinical presentation of GERD is still not fully elucidated. The aim of this study was to prospectively evaluate differences in central and local intraesophageal factors between patients with typical GERD symptoms and those with noncardiac chest pain (NCCP). Patients presenting with typical and atypical symptoms suspicious of GERD underwent upper endoscopy and 24-hour pH monitoring with four sensors, each positioned at a different esophageal level. All patients completed GERD symptom, Hospital Anxiety and Depression Scale, and Symptom Stress Rating questionnaires. From January 2006 to December 2009, 50 patients were recruited, 29 with typical symptoms, and 21 with NCCP. Patients with proven GERD and NCCP had higher proximal extension of acid during reflux episodes than patients with typical symptoms. They were found to be older, had a shorter history of symptom onset, worse anxiety scores, and more endoscopic findings compatible with gastritis. Proximal extension of acid during the reflux episodes in patients with GERD presenting with NCCP may play a role in symptom generation.

Non-cardiac chest pain: prevalence of reflux disease and response to acid suppression in an Asian population

BACKGROUND

Gastroesophageal reflux disease is thought to be the commonest cause of 'non-cardiac chest pain'. The use of proton-pump inhibitors resulting in improvement in the chest pain symptom would support this causal association.

OBJECTIVES

To determine the prevalence of gastroesophageal reflux disease in non-cardiac chest pain and the response of chest pain to proton-pump inhibitor therapy.

METHODS

Patients with recurrent angina-like chest pain and normal coronary angiogram were recruited. The frequency and severity of chest pain were recorded. All patients underwent esophagogastroduodenoscopy and 48-h Bravo ambulatory pH monitoring before receiving rabeprazole 20 mg bd for 2 weeks.

RESULTS

The prevalence of gastroesophageal reflux disease was 66.7% (18/27). The improvement in chest pain score was significantly higher in reflux compared to non-reflux patients (P = 0.006). The proportion of patients with complete or marked/moderate improvement in chest pain symptoms were significantly higher in patients with reflux (15/18, 83.3%) compared to those without (1/9, 11.1%) (P < 0.001).

CONCLUSION

The prevalence of gastroesophageal reflux disease in patients with 'non-cardiac chest pain' was high. The response to treatment with proton-pump inhibitors in patients with reflux disease, but not in those without, underlined the critical role of acid reflux in a subset of patients with 'non-cardiac chest pain'.

Origin of and therapeutic approach to cardiac syndrome X: Results of the proton pump inhibitor therapy for angina-like lingering pain trial (PITFALL trial)

AIM: To investigate the frequency of gastroen-terological diseases in the etiology and the efficacy of proton pump inhibitors (PPIs) in the treatment of cardiac syndrome X (CSX) as a subform of non-cardiac chest pain (NCCP).

METHODS: We investigated 114 patients with CSX using symptom questionnaires. A subgroup of these patients were investigated regarding upper gastrointestinal disorders (GIs) and treated with PPI. Patients not willing to participate in investigation and treatment served as control group.

RESULTS: Thirty-six patients denied any residual symptoms and were not further evaluated. After informed consent in 27 of the remaining 78 patients, we determined the prevalence of disorders of the upper GI tract and quantified the effect of treatment with pantoprazole. We found a high prevalence of gastroenterological pathologies (26/27 patients, 97%) with gastritis, gastroesophageal reflux disease (GERD) and acid reflux as the most common associated disorders. If treated according to the study protocol, these patients showed a significant improvement in the symptom score. Patients treated by primary care physicians, not according to the study protocol had a minor response to treatment (n = 19, -43%), while patients not treated at all (n = 26) had no improvement of symptoms (-0%).

CONCLUSION: Disorders of the upper GI tract are a frequent origin of CSX in a German population and can be treated with pantoprazole if given for a longer period.

Oesophageal afferent pathway sensitivity in non-erosive reflux disease

Patients with non-erosive reflux disease (NERD) report symptoms which commonly fail to improve on conventional antireflux therapies. Oesophageal visceral hyperalgaesia may contribute to symptom generation in NERD and we explore this hypothesis using oesophageal evoked potentials. Fifteen endoscopically confirmed NERD patients (four female, 29-56 years) plus 15 matched healthy volunteers (four female, 23-56 years) were studied. All patients had oesophageal manometry/24-h pH monitoring and all subjects underwent evoked potential and sensory testing, using electrical stimulation of the distal oesophagus. Cumulatively, NERD patients had higher sensory thresholds and increased evoked potential latencies when compared to controls (P = 0.01). In NERD patients, there was a correlation between pain threshold and acid exposure as determined by DeMeester score (r = 0.63, P = 0.02), with increased oesophageal sensitivity being associated with lower DeMeester score. Reflux negative patients had lower pain thresholds when compared to both reflux positive patients and controls. Evoked potentials were normal in reflux negative patients but significantly delayed in the reflux positive group (P = 0.01). We demonstrate that NERD patients form a continuum of oesophageal afferent sensitivity with a correlation between the degree of acid exposure and oesophageal pain thresholds. We provide objective evidence that increased oesophageal pain sensitivity in reflux negative NERD is associated with heightened afferent sensitivity as normal latency evoked potential responses could be elicited with reduced afferent input. Increased oesophageal afferent pain sensitivity may play an important role in a subset of NERD and could offer an alternate therapeutic target.

Mechanisms of heartburn

Heartburn is a typical symptom of GERD. The spectrum of diseases associated with GERD includes reflux esophagitis, Barrett's esophagus and nonerosive reflux disease (NERD). Although acid reflux is the classic cause of heartburn in patients with erosive esophagitis, the relationship between acid and heartburn is far from clear, especially in patients with NERD. Strong evidence exists that weakly acidic reflux and/or non-acid-related events have a significant role in the generation of heartburn. In addition to the role of nonacidic refluxate components, activation of mechanoreceptors and chemoreceptors, and a possible role for central and peripheral sensitization, has been described. Although patients with erosive esophagitis respond well to acid-suppressive therapy, the same does not hold true for those with NERD. NERD represents a major clinical problem, and its management remains a challenge. Discussion of NERD focuses on the mechanisms that cause chest pain in this subgroup of patients. Improved understanding of the pathogenesis underlying heartburn in patients with GERD, in particular those with NERD, will shape our understanding of this condition. Such understanding will serve as a platform for further research and allow additional therapies to be developed for this increasingly encountered clinical condition.

Noncardiac chest pain

Noncardiac chest pain (NCCP) affects approximately 1 quarter of the adult population in the United States. The pathophysiology of the disorder remains to be fully elucidated. Identified underlying mechanisms for esophageal pain include gastroesophageal reflux disease (GERD), esophageal dysmotility, and visceral hypersensitivity. Aggressive antireflux treatment has been the main therapeutic strategy for GERD-related NCCP. NCCP patients with or without spastic esophageal motor disorders are responsive to pain modulators. The value of botulinum toxin injection, endoscopic treatment for GERD, and antireflux surgery in alleviating NCCP symptoms is limited.

Non-cardiac chest pain: an update

Non-cardiac chest pain (NCCP) is very common, affecting up to a quarter of the USA adult population. Recent studies have shown that the disorder has a profound impact on patient's quality of life and is associated with marked increase in utilization of healthcare resources. Non-cardiac chest pain is a heterogeneous disorder with gastrointestinal and non-gastrointestinal causes. After excluding a cardiac cause, most NCCP patients are treated by cardiologists or primary care physicians and only the minority are referred to a gastroenterologist for further work-up. Gastro-oesophageal reflux disease (GORD) is the most common cause for NCCP. The role of oesophageal dysmotility in NCCP has been discounted in recent years. However, visceral hyperalgesia has been shown to play an important role in symptom generation of non-GORD-related NCCP. The main therapeutic interventions in GORD-related NCCP patients are potent antireflux modalities and pain modulators in those with non-GORD-related NCCP.

Duodenal Carbonic Anhydrase: Mucosal Protection, Luminal Chemosensing, and Gastric Acid Disposal

The duodenum serves as a buffer zone between the stomach and jejunum. Over a length of only 25 cm, large volumes of strong acid secreted by the stomach must be converted to the neutral-alkaline chyme of the hindgut lumen, generating large volumes of CO2, which the duodenum then absorbs. The duodenal mucosa consists of epithelial cells connected by low-resistance tight junctions, forming a leaky epithelial barrier. Despite this high permeability, the epithelial cells, under intense stress from luminal mineral acid and highly elevated P(CO2), maintain normal functioning. Furthermore, the duodenum plays an active role in foregut acid-base homeostasis, absorbing large amounts of H+ and CO2 that are recycled by the gastric parietal cells. Prompted by the high expression of cytosolic and membrane carbonic anhydrase (CAs) in duodenal epithelial cells, and the intriguing observation that CA activity appears to augment cellular acid stress, we formulated a novel hypothesis regarding the role of CA in duodenal acid absorption, epithelial protection, and chemosensing. In this review, we will describe how luminal CO2/H+ traverses the duodenal epithelial cell brush border membrane, acidifies the cytoplasm, and is sensed in the subepithelium.

The pathophysiology of non-cardiac chest pain

Various underlying mechanisms have been described in patients with non-cardiac chest pain (NCCP). By far, gastroesophageal reflux disease (GERD) is the most common cause and thus requires initial attention when patients with NCCP are managed. Esophageal dysmotility can be demonstrated in 30% of the NCCP patients, but appears to play a very limited role in symptom generation. A significant number of patients with NCCP lack any evidence of GERD and have been consistently shown to have reduced perception thresholds for pain. Peripheral and/or central sensitization have been suggested to be responsible for visceral hypersensivity in NCCP patients. Further understanding of the underlying mechanisms for pain in patients with NCCP will likely improve our current therapeutic approach.

Acid-sensing pathways in rat gastrointestinal mucosa

The gastrointestinal mucosa serves as the interface between the luminal contents, including nutrients and injurious substances, and submucosal structures. Secreted gastric acid is one of the principal injurious components of the luminal contents. To be protected against harm from this acid, the epithelium has an "early warning" system that can activate potent defense mechanisms. We studied the mechanisms that defend the epithelium against luminal acid-induced injury, including the regulation of epithelial intracellular pH (pHi), blood flow, and mucus gel secretion in the perfused rat duodenum, and the pathways involved in the activation and regulation of these mechanisms. Physiological concentrations of luminal acid acidified the epithelial cells and increased blood flow (hyperemic response) and mucus gel thickness. The hyperemic response to acid was abolished by inhibitors of the Na+/H+ exchange, vanilloid receptors (VR), calcitonin gene-related peptide (CGRP) receptors, and nitric oxide (NO) synthase, and also by sensory afferent denervation, but not by pretreatment with a nonselective cyclooxygenase (COX) inhibitor. Mucus secretion in response to luminal acid was delayed by an interruption to the capsaicin pathway, which includes VR, capsaicin-sensitive afferent nerves, CGRP, and NO, and was abolished by COX inhibition. These observations support the hypothesis that the capsaicin pathway is an acid-sensing pathway that promotes hyperemia and mucus secretion in response to luminal acid. The COX pathway is a secondary regulatory system for mucus secretion. A similar acid-sensing capsaicin pathway is also present in the colon, suggesting that the gastrointestinal mucosa "tastes" luminal acidity through epithelial-VR communication.

Chest pain of esophageal origin

Chest pain of esophageal origin is the most common atypical/extraesophageal manifestation of gastroesophageal reflux disease (GERD). We are increasingly recognizing the important role of the cardiologist in making the diagnosis. Studies continue to focus on the mechanisms of pain in this challenging group of patients. Factors that determine the development and persistence of visceral hypersensitivity are currently under investigation. Invasive diagnostic studies have been replaced by therapeutic trials or empirical therapies. Proton pump inhibitors have been demonstrated to be the most effective treatment for GERD-related noncardiac chest pain (NCCP). Pain modulators remain the primary therapy for non-GERD-related NCCP. Sertraline is the first selective serotonin reuptake inhibitor to demonstrate a significant improvement in chest pain symptoms.