The pain system in oesophageal disorders: mechanisms, clinical characteristics, and treatment

The relationship between amino acids and gastroesophageal reflux disease: evidence from a mendelian randomization analysis combined with a meta-analysis

Background

Gastroesophageal Reflux Disease (GERD), a prevalent gastrointestinal disorder globally, exhibits variable prevalence across regions, with higher frequencies observed in Western nations and lower in Asian countries. Key contributing factors encompass unhealthy eating patterns, tobacco use, consumption of alcohol, excess weight, and obesity, along with health conditions such as gestation and diabetes. Common manifestations include heartburn and a burning discomfort behind the breastbone, which, without appropriate management, can progress to more severe issues like esophagitis and Barrett's esophagus. Approaches to management and prevention primarily involve modifications in lifestyle, pharmacotherapy, and surgical interventions when deemed necessary. Utilizing Omics Mendelian Randomization (OMR) to investigate the causative links between genetic variants and diseases provides insights into the biological underpinnings of gastroesophageal reflux diseasec. It aids in pinpointing novel targets for therapy. The influence of amino acids in gastroesophageal reflux disease demonstrates the complexity, having the potential to both mitigate and intensify symptoms, underscoring the significance of personalized nutrition and therapeutic strategies.

Methods

This study is based on the omics mendelian randomization method, coupled with meta-analysis techniques, to enhance the precision of the research findings. Furthermore, a reverse validation procedure was implemented to validate the association between the positive findings and disease outcomes further. Throughout the study, multiple correction measures were employed to ensure the accuracy and reliability of the results.

Results

Based on our research methodology, we have ultimately discovered that glutamate exacerbates gastroesophageal reflux disease, increasing its risk. The data supporting this includes analysis of 20 amino acids and outcomes from the Finnish database, which showed that glutamate had an odds ratio (OR) for gastroesophageal reflux disease risk of 1.175(95% confidence interval (CI): 1.000 ~ 1.380, P = 0.05), and a beta value of 0.161. Analysis with outcomes from the UK database indicated that glutamate had an OR for gastroesophageal reflux disease risk of 1.399(95% CI: 1.060 ~ 1.847, P = 0.018) and a beta value of 0.336. After conducting a meta-analysis of the MR results and applying multiple corrections, the combined OR of glutamate for gastroesophageal reflux disease risk was 1.227 (95% CI: 1.068 ~ 1.411 P = 0.043); the beta values of the three primary MR outcomes were consistent in direction. Building on the positive results, reverse validation with outcome data from two different database sources for glutamate showed: in the Finngen database, with gastroesophageal reflux disease as the exposure, the Inverse Variance Weighted (IVW) method resulted in a P-value of 0.059; in the IEU database under the same condition, the IVW P-value was 1.433.

Conclusions

Glutamate may increase the risk and exacerbate the progression of gastroesophageal reflux disease through mechanisms such as impacting the nervous system and promoting inflammatory responses. Delving into the role of glutamate in gastroesophageal reflux disease enriches our understanding of the disease's biological mechanisms and may offer new strategies for clinical treatment and nutritional management. This insight can aid in developing healthier dietary plans, thereby benefiting patients.

Nonepithelial Gene Expression Correlates With Symptom Severity in Adults With Eosinophilic Esophagitis

BACKGROUND

The mechanistic basis of the variable symptomatology seen in eosinophilic esophagitis (EoE) remains poorly understood.

OBJECTIVE

We examined the correlation of a validated, patient-reported outcome metric with a broad spectrum of esophageal transcripts to uncover potential symptom pathogenesis.

METHODS

We extracted data from 146 adults with EoE through the Consortium of Eosinophilic Gastrointestinal Disease Researchers. Patients were subgrouped by esophageal dilation history. We compared a validated patient-reported outcome metric, the EoE Activity Index (EEsAI), with a set of transcripts expressed in the esophagus of patients with EoE, the EoE Diagnostic Panel (EDP). We used single-cell RNA sequencing data to identify the cellular source of EEsAI-related EDP genes and further analyzed patients with mild and severe symptoms.

RESULTS

The EEsAI correlated with the EDP total score, especially in patients without recent esophageal dilation (r = -0.31; P = .003). We identified 14 EDP genes that correlated with EEsAI scores (r ≥ 0.3; P < .05). Of these, 11 were expressed in nonepithelial cells and three in epithelial cells. During histologic remission, only four of 11 nonepithelial genes (36%) versus all three epithelial genes (100%) had decreased expression to less than 50% of that in active EoE. Fibroblasts expressed five of 11 nonepithelial EEsAI-associated EDP genes (45%). A subset of nonepithelial genes (eight of 11; 73%), but not EoE-representative genes (none of four; 0%; CCL26, CAPN14, DSG1, and SPINK7), was upregulated in patients with EoE with the highest versus lowest symptom burden.

CONCLUSION

The correlation of symptoms and nonepithelial esophageal gene expression substantiates that nonepithelial cells (eg, fibroblasts) likely contribute to symptom severity.

Sex- and gender-specific differences in symptoms and health-related quality of life among patients with gastroesophageal reflux disease

Gastroesophageal Reflux Disease (GERD) is a common chronic gastrointestinal disorder affecting both men and women. Nonerosive reflux disease generally affects more women, whereas GERD complications such as Barrett's esophagus (BE) or esophageal cancer affect more men. The aim of this study was to evaluate sex- and gender-specific symptoms and health-related quality of life (HRQoL) among men and women with GERD. Patients with clinical signs of reflux and completion of 24-hour pH-Impedance testing at the University Hospital Cologne were included into the study. Evaluation of symptoms and HRQoL included the following validated questionnaires: GERD-Health-Related Quality of Life (GERD HRQL), Gastrointestinal Quality of Life Index (GIQLI), and Hospital Anxiety and Depression Scale (HADS). In all, 509 women and 355 men with GERD were included. Men had a significantly higher DeMeester score (60.2 ± 62.6 vs. 43 ± 49.3, P < 0.001) and a higher incidence of BE (18.6 vs. 11.2%, P = 0.006). Women demonstrated significantly higher levels of anxiety (30.9 vs. 14.5%, P = 0.001), more severely impacting symptoms (45.3 ± 11.3 vs. 49.9 ± 12.3, P < 0.001), as well as physical (14.2 ± 5.7 vs. 16.7 ± 5.6, P < 0.001) and social dysfunction (13.3 ± 4.8 vs. 14.8 ± 4.3, P = 0.002). Women further reported a lower HRQoL (85.3 ± 22.7 vs. 92.9 ± 20.8, P < 0.001). Men and women differ on biological, psychological, and sociocultural levels.

Esophageal physiology-an overview of esophageal disorders from a pathophysiological point of view

The esophagus serves the principal purpose of transporting food from the pharynx into the stomach. A complex interplay between nerves and muscle fibers ensures that swallowing takes place as a finely coordinated event. Esophageal function can be tested by a variety of methods, endoscopy, manometry, and reflux monitoring being some of the most important. Regarding pathophysiology, motor disorders, such as achalasia, often cause dysphagia and/or chest pain. Functional esophageal disorders are a heterogeneous group with hypersensitivity as a dominant pathophysiological factor. Gastroesophageal reflux disease often causes symptoms, such as heartburn and regurgitation, and a spectrum of disease, ranging from minimal mucosal damage visible only in the microscope to esophageal ulcers and strictures in the most severe cases. Eosinophilic esophagitis is an immune-mediated condition that can result in significant dysphagia and associated luminal narrowing. In the following, we will provide an overview of the most common esophageal disorders from a combined pathophysiological and clinical view.

Upper Gastrointestinal Sensitization And Symptom Generation

Functional gastrointestinal disorders (FGIDs) are a highly prevalent group of heterogeneous disorders, and their diagnostic criteria are symptom-based, with the absence of anatomical and biochemical abnormalities of the gastrointestinal tract. Chronic visceral symptoms are common both in patients with an identifiable organic disease but also in FGID patients. Patients suffering from upper gastrointestinal functional disorders typically present with various symptoms such as early satiety, postprandial fullness, bloating, nausea, vomiting, and epigastric pain. Considering their increasing prevalence, difficulties in diagnosis, and low quality of life, FGIDs have become an emerging problem in gastroenterology. We aimed to provide an updated summary of pathways involved in visceral sensitization. We examined the recent literature searching for evidence of the most important studies about the mechanisms underlying gastrointestinal symptom generation and sensitization.

Opioid-Induced Constipation and Bowel Dysfunction: A Clinical Guideline

OBJECTIVE

To formulate timely evidence-based guidelines for the management of opioid-induced bowel dysfunction.

SETTING

Constipation is a major untoward effect of opioids. Increasing prescription of opioids has correlated to increased incidence of opioid-induced constipation. However, the inhibitory effects of opioids are not confined to the colon, but also affect higher segments of the gastrointestinal tract, leading to the coining of the term "opioid-induced bowel dysfunction."

METHODS

A literature search was conducted using Medline, EMBASE, and EMBASE Classic, and the Cochrane Central Register of Controlled Trials. Predefined search terms and inclusion/exclusion criteria were used to identify and categorize relevant papers. A series of statements were formulated and justified by a comment, then labeled with the degree of agreement and their level of evidence as judged by the Strength of Recommendation Taxonomy (SORT) system.

RESULTS

From a list of 10,832 potentially relevant studies, 33 citations were identified for review. Screening the reference lists of the pertinent papers identified additional publications. Current definitions, prevalence, and mechanism of opioid-induced bowel dysfunction were reviewed, and a treatment algorithm and statements regarding patient management were developed to provide guidance on clinical best practice in the management of patients with opioid-induced constipation and opioid-induced bowel dysfunction.

CONCLUSIONS

In recent years, more insight has been gained in the pathophysiology of this "entity"; new treatment approaches have been developed, but guidelines on clinical best practice are still lacking. Current knowledge is insufficient regarding management of the opioid side effects on the upper gastrointestinal tract, but recommendations can be derived from what we know at present.

Adam, Eve and the reflux enigma: age and sex differences across the gastro-oesophageal reflux spectrum

INTRODUCTION

We present demographic differences across the gastro-oesophageal reflux disease (GORD) spectrum in a UK District General Hospital.

PATIENTS AND METHODS

Data were prospectively collected over 37 years. At endoscopy patients were categorized as: erosive oesophagitis (EO), Barrett's oesophagus (BO) or nonerosive reflux disease (NER). Analysis 1: comparison of EO, BO and NER 1977-2001 when the database for GORD without BO closed. Analysis 2: demographic differences in oesophageal adenocarcinoma (OAC) in total BO population diagnosed 1977-2011.

RESULTS

GORD 1977-2001 (n=11 944): sex, male predominance in EO and BO but not NER; male : female ratios, 1.81, 1.65, 0.87, respectively (P<0.0001); mean age at presentation, EO 54 years, BO 62 years, NER 50 years; women were older than men by 10, 7 and 6 years, respectively.BO 1977-2011: prevalent OAC, 87/1468 (6%); male : female ratio, 4.1 (P<0.0001); incident OAC, 54/1381 (3.9%); male : female ratio, 3.5 (P<0.0001). Among all BO, more men developed OAC (3 vs. 0.9%). Within each sex, proportion of OAC higher among men (4.9 vs. 2.3%); at OAC diagnosis women were slightly but not significantly older (69.9 vs. 72.3 years, P=0.322).

CONCLUSION

Two views may explain our findings. First, women have either milder reflux, or reduced mucosal sensitivity hence reflux remains silent for longer. Alternatively, women genuinely develop reflux later, that is, are more protected and for longer from developing GORD and its complications. Early evidence is emerging that female sex hormones may indeed have a protective role in GORD during the reproductive period. We suggest reflux and its consequences may be an example of 'protection' conferred on Eve.

Patients with Barrett's esophagus are hypersensitive to acid but hyposensitive to other stimuli compared with healthy controls

BACKGROUND

Esophageal hyposensitivity has been observed in Barrett's esophagus and may contribute to its pathophysiology. However, studies are few, in particular those assessing different sensory modalities. We aimed to compare esophageal sensitivity to multimodal stimulation in patients with Barrett's esophagus and in healthy controls.

METHODS

Twenty-three patients with Barrett's esophagus and 12 healthy controls were examined. A multimodal probe was placed in the lower esophagus. Mechanical, thermal, and electrical stimulation was applied followed by an acid perfusion test with 0.1 N hydrochloric acid.

KEY RESULTS

Compared with controls, patients were hyposensitive to mechanical distension, heat, and electrical stimulation (all P<.05), but hypersensitive to acid (mean tolerated acid volume 57% lower, P=.001). A linear correlation between acid hypersensitivity and lower baseline impedance was found (P<.001). Patients had longer esophageal acid exposure time than controls (median acid exposure time 18 vs 5%, P=.03). Asymptomatic patients (no reflux symptoms at baseline) were hyposensitive to mechanical distension, electrical stimulation, and acid perfusion (all P<.05) compared with symptomatic patients.

CONCLUSIONS & INFERENCES

Patients with Barrett's esophagus exhibited acid hypersensitivity but hyposensitivity to other stimuli. Lower mucosal baseline impedance, a likely surrogate marker for impaired mucosal integrity, may explain the selective hypersensitivity to acid. On the other hand, the concurrent hyposensitivity may theoretically be explained by changes in central pain modulation. Patients with Barrett's esophagus seem to compose symptomatic and asymptomatic subgroups, showing different esophageal sensory profiles.

The Role of Esophageal Hypersensitivity in Functional Esophageal Disorders

The Rome IV diagnostic criteria delineates 5 functional esophageal disorders which include functional chest pain, functional heartburn, reflux hypersensitivity, globus, and functional dysphagia. These are a heterogenous group of disorders which, despite having characteristic symptom profiles attributable to esophageal pathology, fail to demonstrate any structural, motility or inflammatory abnormalities on standard clinical testing. These disorders are associated with a marked reduction in patient quality of life, not least considerable healthcare resources. Furthermore, the pathophysiology of these disorders is incompletely understood. In this narrative review we provide the reader with an introductory primer to the structure and function of esophageal perception, including nociception that forms the basis of the putative mechanisms that may give rise to symptoms in functional esophageal disorders. We also discuss the provocative techniques and outcome measures by which esophageal hypersensitivity can be established.

Influence of exercise on visceral pain: an explorative study in healthy volunteers

Background and objectives

Contradictory results have been found about the effect of different exercise modalities on pain. The aim of this study was to investigate the early effects of aerobic and isometric exercise on different types of experimental pain, including visceral pain, compared to an active control condition.

Methods

Fifteen healthy subjects (6 women, mean [standard deviation] age 25 [6.5] years) completed 3 interventions consisting of 20 minutes of aerobic cycling, 12 minutes of isometric knee extension and a deep breathing procedure as active control. At baseline and after each intervention, psychophysical tests were performed, including electrical stimulation of the esophagus, pressure pain thresholds and the cold pressor test as a measure for conditioned pain modulation. Participants completed the Medical Outcome Study Short-Form 36 and State-Trait Anxiety Inventory prior to the experiments. Data were analyzed using two-way repeated measures analysis of variance.

Results

No significant differences were found for the psychophysical tests after the interventions, compared to baseline pain tests and the control condition.

Conclusion

No hypoalgesic effect of aerobic and isometric exercise was found. The evidence for exercise-induced hypoalgesia appears to be not as consistent as initially thought, and caution is recommended when interpreting the effects of exercise on pain.

Understanding the sensory irregularities of esophageal disease

Symptoms relating to esophageal sensory abnormalities can be encountered in the clinical environment. Such sensory abnormalities may be present in demonstrable disease, such as erosive esophagitis, and in the ostensibly normal esophagus, such as non-erosive reflux disease or functional chest pain. In this review, the authors discuss esophageal sensation and the esophageal pain system. In addition, the authors provide a primer concerning the techniques that are available for investigating the autonomic nervous system, neuroimaging and neurophysiology of esophageal sensory function. Such technological advances, whilst not readily available in the clinic may facilitate the stratification and individualization of therapy in disorders of esophageal sensation in the future.

Management of chronic visceral pain

Despite marked differences in underlying pathophysiology, the current management of visceral pain largely follows the guidelines derived from the somatic pain literature. The effective management of patients with chronic visceral pain should be multifaceted, including both pharmacological and psychological interventions, thereby providing a mechanism-orientated approach to treatment. Patients can frequently become disenfranchised, and subsequently disengaged, with healthcare providers leading to repeated consultations. Thus, a key aspect of management is to break this cycle by validating patients' symptoms, adopting an empathic approach and taking time to educate patients. To optimize treatment and outcomes in chronic visceral pain we need to move away from approaches exclusively based on dealing with peripheral nociceptive input toward more holistic strategies, taking into account alterations in central pain processing.

Randomized clinical trial: efficacy and safety of PPC-5650 on experimental esophageal pain and hyperalgesia in healthy volunteers

OBJECTIVE

Gastroesophageal reflux disease (GERD) is a common condition associated with symptoms as heart burn, regurgitation, chest pain, and gastrointestinal discomfort. PPC-5650 is a new pharmacological agent that can modulate acid-sensing ion channel activity, potentially leading to reduction in the pain signal. In healthy volunteers the esophagus was sensitized with acid to mimic GERD with the aims: 1) to assess the efficacy of a single bolus of PPC-5650 locally applied to the esophagus using multimodal pain stimulations, and 2) to assess the safety profile of PPC-5650.

MATERIALS AND METHODS

The study was a randomized, double-blinded, placebo-controlled, crossover trial in healthy males. Esophageal electrical, thermal, mechanical, and chemical stimulations were performed, pain perception was rated, and referred pain areas were drawn. Sensitization was induced by intraluminal esophageal acid perfusions. Adverse events were registered.

RESULTS

Twenty-five healthy males completed the study (mean age 23.4 ± 2.0 years). About 90 min after drug administration, PPC-5650 increased the volume tolerated at moderate pain during mechanical stimulation compared to placebo (difference 13.5, 95% CI: 0.58-26.47, p = 0.04), but there was no effects on thermal-, electrical-, and chemical-induced pain (all p > 0.05). PPC-5650 did not affect referred pain areas to any stimulation (all p > 0.05). Ten participants reported adverse events during the placebo treatment period, and nine participants reported adverse events during the PPC-5650 treatment period (p = 0.8).

CONCLUSION

Sensitization to mechanical stimulation of the esophagus was reduced by PPC-5650 compared to placebo. The overall safety and tolerability of PPC-5650 was acceptable. Thus, PPC-5650 may play a role in the future treatment of patients with GERD.