Is there a relationship between combined reflux of gastric and duodenal juice and metaplasia during mucosal healing?
M. Fein (Wursburg), C.G. Bremner (Los Angeles)
Esophageal columnar metaplasia with specialized, intestinal epithelium and goblet cells, i.e. Barrett's esophagus (BE), replaces normal squamous epithelium of the esophagus in 10-20% of the patients with chronic gastroesophageal reflux disease. Patients with BE are at increased risk for developing adenocarcinoma of the esophagus and cardia , which has a rapidly growing incidence in the United States .
The gastric juice refluxing into the esophagus contains gastric secretions (acid and pepsin) as well as biliary and pancreatic secretions (bile salts and trypsin), which have refluxed into the stomach from the duodenum. Combined reflux is defined as reflux containing both gastric and duodenal secretions. The importance of the different components of combined reflux has been studied in animal as well as human studies.
Synergism of gastric and duodenal juice in esophageal mucosal injury
and esophageal columnar metaplasia in animal studies
The interactions of gastric and duodenal juice can be explained based on the pKa values of the constituents of duodenal juice [3-6]. Conjugated bile salts have a pKa of about 2, unconjugated bile salts and trypsin have a pKa close to 7. As a consequence, at pH 2, conjugated bile salts and acid have synergistic effects , while trypsin does not have any effect. At pH 7, trypsin or unconjugated bile salts augment esophageal injury, while conjugated bile salts cause only minimal esophagitis [4, 5]. The constituents of duodenal juice also interact with each other, e.g. unconjugated bile salts significantly increase esophageal mucosal damage caused by trypsin . The synergism of conjugated bile salts and acid is likely to be the main mechanism causing esophageal injury.
The relation of combined reflux and development of esophageal columnar metaplasia after mucosal healing has been investigated in dogs [7-9]. After mucosectomy esophageal columnar metaplasia occurred in dogs with gastroesophageal reflux without inducing increased reflux of duodenal juice [7, 8]. In these models the yield of esophageal columnar metaplasia was dependent on acid reflux, indicating that acid plays an important role in the development of esophageal metaplasia. In a dog model without mucosectomy acid reflux alone did not induce esophageal metaplasia, but metaplasia developed in dogs with surgically induced reflux of gastric and duodenal juice .
Therefore, it appears that reflux of gastric and duodenal juice acts synergistically to cause esophageal injury and columnar metaplasia.
Duodenal juice is a prerequisite for the development of adenocarcinoma
in the rat esophagus
The relationship of combined reflux to the development of esophageal adenocarcinoma, a complication of metaplasia, has been investigated in the rat model [10-14]. It has been shown that rats treated with esophageal specific nitrosamines develop squamous esophageal cancer in a time- and dose-dependent fashion . When the rat esophagus is exposed to a mixture of gastric and duodenal juice by either esophago-jejunostomy  or esophago-duodenostomy  and carcinogen is administered, the yield of tumors at 22-24 weeks post-operatively is increased. There is also a change in histology in that in addition to squamous carcinomas, adenocarcinomas develop. In contrast, when there is an increased esophageal exposure to gastric juice without duodenal juice in rats treated with carcinogen, there is no increase in tumor yield and no adenocarcinomas are found .
The role of gastric juice on tumor development in the rat model of adenocarcinoma was investigated in a recent study . Reflux of duodenal juice was induced and all animals received carcinogen. The prevalence of esophageal adenocarcinoma in rats with duodeno-gastroesophageal reflux was 30%, and 87% in rats with reflux of duodenal juice alone. In further subgroups there was a progressive increase in the prevalence of adenocarcinoma as less gastric juice was permitted to reflux with duodenal juice into the esophagus, indicating that the presence of gastric juice in refluxed duodenal juice protects against the development of esophageal adenocarcinoma.
In conclusion, in the rat model, duodenal juice is a prerequisite for the development of esophageal adenocarcinoma, and gastric juice seems to have a protective effect.
Synergism of gastric and duodenal juice in reflux disease
Clinical studies confirm the presence of duodenal juice in the esophagus of patients with reflux disease particularly in those with advanced disease [16-20]. Many of these studies have been conducted with a fiber-optic spectrophotometer measuring the amount of bilirubin (Bilitec 2000, Synectics, Stockholm, Sweden), an important advancement in the evaluation of duodenal juice in the stomach or esophagus. By combining this technique with simultaneous pH-monitoring, synergistic effects of gastric and duodenal juice were consistently reported. Patients with Barrett's esophagus have a significant higher concentration of both acid and bilirubin in the esophagus compared to patients with erosive reflux esophagitis [16-18].
The specific relationship between acid and bilirubin exposure has been emphasized in several studies. After subtotal gastrectomy esophagitis developed only, if reflux of duodenal juice was combined with acid reflux , indicating that duodenal juice on its own does not cause mucosal injury. On the other hand, acid reflux without duodenal juice is not injurious to the esophageal mucosa as shown in patients with esophagitis, which healed after subtotal gastrectomy and Roux-en-Y reconstruction despite the presence of acid reflux . A synergism of the components of combined reflux was also shown for the development of complications of Barrett's esophagus, i.e. the appearance of ulcers or strictures, or dysplasia. Patients with Barrett's esophagus and complications had a higher acid and bilirubin exposure to the esophagus and higher gastric bile acid concentrations compared to patients with Barrett's esophagus without complications [20, 22].
In a recent study 100 patients with reflux disease, documented by an increased esophageal exposure to acid, were evaluated with regard to their acid and bilirubin exposure to the esophagus, and the presence of erosive esophagitis, Barrett's esophagus and complications of Barrett's esophagus . Patients, who had an esophageal acid exposure time greater than 10% of the total study period, had significantly more esophagitis or Barrett's esophagus when they had reflux of duodenal juice. The number of patients with esophagitis or Barrett's esophagus was not related to reflux of duodenal juice when the acid exposure time was less than 10% of the total study period. This relationship again emphasizes a synergistic interaction of combined reflux in reflux disease. In this study acid and bilirubin exposure in patients with Barrett's esophagus was also compared (Table I).
Patients with dysplasia had a significantly higher bilirubin exposure time compared to patients with uncomplicated Barrett's, while the acid exposure time of all three groups was similar. This provides evidence that duodenal juice not only enhances the mucosal injury and the potential to get columnar metaplasia, but also may play a role in the development of dysplasia.
The role of combined reflux in the development of esophageal adenocarcinoma is still uncertain. There are reports of patients who have developed an adenocarcinoma following total gastrectomy without any reflux of gastric juice. Epidemiological studies have clearly established that patients with reflux disease have an increased risk for the development of esophageal adenocarcinoma . Based on the finding in the rat model that the acidic gastric juice has a protective effect against the development of esophageal adenocarcinoma, it has been questioned whether the development of esophageal cancer is due to reflux that has been ineffectively controlled, or due to an effective acid suppression that increases the detrimental effects of duodenal juice .
In conclusion, it has been well documented that there is a synergism of gastric and duodenal juice ("combined reflux") resulting in esophagitis, Barrett's metaplasia, and dysplasia. It is likely, that duodenal juice, and not gastric juice is the major factor for the progression from metaplasia to dysplasia to cancer. This encourages the effective reduction of esophageal exposure to all noxious components in the therapy of gastroesophageal reflux disease.
Implications on therapy
Medical therapy aims primarily to reduce esophageal acid exposure and does not correct the underlying abnormality of a defective lower esophageal sphincter. Champion et al.  showed that 20 mg omeprazole taken twice daily suppressed not only esophageal acid reflux, but also reflux of duodenal content. However, reflux of duodenal juice still continued to exceed the normal range in 4 of 9 patients and it is unclear if this reduction would protect against the progression of disease. If treated medically, these patients require lifelong use of high dosages of proton pump inhibitors. Concerns about long-term use of acid suppressant therapy emerge from the rat study mentioned above, and a clinical study demonstrating the development of atrophic gastritis in patients treated with high dosages of acid suppressant therapy . Nevertheless, medical therapy is adequate for patients with contraindications for surgery.
Surgical therapy can correct the underlying defect in reflux disease, i.e. an incompetence of the lower esophageal sphincter, and abolish esophageal exposure to all noxious components. Superior results in comparison to medical therapy in the control of the complications of reflux disease have been documented in randomized trials for patients with well documented reflux disease [26, 27]. However, the selection of patients for surgical treatment is critical to achieve an excellent outcome.
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