Bile acid cocktail (BAC) induces similar changes in the expression of ion transporter MRNA in cultured esophageal epithelial cells (EEC) as observed in biopsies of Barrett's esophagus (BE).

Introduction: Bile acids are thought to have an important role in the mucosal injury of the esophagus and though acid extruding mechanisms can be key factors of the defense. We aimed to determine the effect of a BAC on the activity of ion transporters and the expression of their mRNA in cultured EECs and compare these results with the observations obtained in biopsy samples of patients with BE. Patients, methods: In confluent monolayers of CP-A EECs intracellular pH (pHi) was measured with a fluorescent dye and Na+/H+ exchangers (NHEs), Na+/HCO3- cotransporter (NBC), Cl-/HCO3- exchanger (AE) activities were determined with the ammonium pulse technique. To mimic the chronic conditions of reflux disease in vitro cells were treated by 10- minutes pulses of bile acid cocktail three times a day for 7 days. For the assessment of mRNA expression changes in the acid-base transporters quantitative real time PCR (qRT- PCR) was used. Ten patients with BE were enrolled. Biopsies were obtained from the metaplastic mucosa and also form the squamous epithelium. The mRNA expression level of NHE-1, NHE-2, NBC and AE (Slc26a6, Slc26a3) were determined with qRT- PCR. Results: Treatment of CP-A cells with 0.5 mM bile acid cocktail inhibited the activity of NHE and NBC while it stimulated the HCO3- secretion through AE. Chronic treatment of CP-A cells with bile acid cocktail induced a significant increase in the mRNA expression of NHE-1, NHE-2, NBC, Slc26a6 compared to the untreated cells. Evaluation of esophageal biopsies for the mRNA expression levels of acid/base transporters revealed significantly higher expression levels of NHE-1, NHE-2, NBC, Slc26a6 and Slc26a3 in the Barrett's epithelium compared to the squamous mucosa. Conclusions: Acute exposure of bile acids inhibited the activity of acid-extruding mechanism in EEC. The increased mRNA expression levels of acid/base transporters after chronic bile acid treatment of EECs and the similar pattern observed in the Barrett's epithelium support the pathophysiological role of biliary reflux and suggest that the observed alterations are part of the mucosal defense against bile acid induced injury.