In Barrett's epithelial cells, weakly acidic bile salt solutions cause oxidative DNA damage with response and repair mediated by p38

Abstract

The frequency of esophageal adenocarcinoma is rising despite widespread use of proton pump inhibitors (PPIs), which heal reflux esophagitis but do not prevent reflux of weakly acidic gastric juice and bile in Barrett's esophagus patients. We aimed to determine if weakly acidic (pH 5.5) bile salt medium (WABM) causes DNA damage in Barrett's cells. Because p53 is inactivated frequently in Barrett's esophagus and p38 can assume p53 functions, we explored p38's role in DNA damage response and repair. We exposed Barrett's cells with or without p53 knockdown to WABM, and evaluated DNA damage, its response and repair, and whether these effects are p38 dependent. We also measured phospho-p38 in biopsies of Barrett's metaplasia exposed to deoxycholic acid (DCA). WABM caused phospho-H2AX increases that were blocked by a reactive oxygen species (ROS) scavenger. WABM increased phospho-p38 and reduced bromodeoxyuridine incorporation (an index of S phase entry). Repair of WABM-induced DNA damage proceeded through p38-mediated base excision repair (BER) associated with reduction-oxidation factor 1-apurinic/apyrimidinic endonuclease I (Ref-1/APE1). Cells treated with WABM supplemented with ursodeoxycholic acid (UDCA) exhibited enhanced p38-mediated responses to DNA damage. All of these effects were observed in p53-intact and p53-deficient Barrett's cells. In patients, esophageal DCA perfusion significantly increased phospho-p38 in Barrett's metaplasia. WABM exposure generates ROS, causing oxidative DNA damage in Barrett's cells, a mechanism possibly underlying the rising frequency of esophageal adenocarcinoma despite PPI usage. p38 plays a central role in oxidative DNA damage response and Ref-1/APE1-associated BER, suggesting potential chemopreventive roles for agents like UDCA that increase p38 activity in Barrett's esophagus.