Gastro-esophageal reflux disease to Barrett's

Abstract

Thesis (Ph. D.)--University of Rochester. Department of Biology, 2014.Background: Esophageal Adenocarcinoma (EAC) affects about 18000 of the US population with annual mortality around 15000. Barrett’s esophagus (BE) is the single most important risk factor for the development of esophageal adenocarcinoma. The pathogenesis of BE is believed to be driven by protracted reflux of gastric and duodenal contents into the lower esophagus through an incompetent lower esophageal sphincter (LES) in patients with gastro-esophageal reflux disease (GERD), and as a result the esophageal stem cells are transcommitted to a columnar phenotype in the presence of the reflux environment. Bile acids, along with gastric acid at pH 2-4, are the chief components of reflux. Methods: We compared expression of squamous differentiation markers in biopsies taken from normal squamous esophagus and BE. We also treated primary esophageal cells in monolayer culture with bile acid cocktail and looked at the differentially expressed genes compared to control. In order to simulate gastro-esophageal reflux in vitro we developed a 3-D transwell culture model to grow primary esophageal cells in stratified culture. Subsequently, we used this model to demonstrate the morphological and molecular effects of simulated reflux condition on this stratified epithelium in vitro. Results: Our data indicate that a combination of bile acid and gastric acid at pH5 reduces squamous differentiation in primary esophageal cells as an initial step in EGFR-mediated dedifferentiation that enables mucosal repair in response to reflux injury. We have attributed the observed squamous dedifferentiation to the unionized unconjugated and thus intracellular bile acid pool. Our data demonstrate that bile acid at pH5, but not either alone, disrupts tight junction complexes and causes increased permeability of stratified squamous esophageal epithelium. These changes approximate the appearance of dilated intercellular spaces (DIS) similar to that found in GERD patients. These findings provide novel insights into the molecular mechanisms underlying the adaptive responses of the esophageal epithelium to reflux-mediated injury. Conclusion: To extend the relevance of this study in the clinical setting, acid suppression therapy likely will not prevent DIS formation and subsequent initiation of inflammatory response in esophageal epithelium as long as the patient is refluxing bile salts at a less acidic pH. In the majority of clinical situations, long term acid suppression in patients with GERD raises the gastric pH to 4-6. This facilitates the burgeoning of intestinal microflora and increases bacterial deconjugation of bile acid, causing the predominance of unconjugated bile acid refluxing into the esophagus at a pH around 5. Taking parallels from the in vitro results shown in this dissertation, we can conclude that the refluxing cocktail thus formed might be putting patients at risk to bile acid induced altered cellular differentiation