title: How good is the neosquamous epithelium?
abstract: OBJECTIVE
  Endoscopic radiofrequency ablation of dysplastic Barrett's esophagus (BE) combined with proton pump inhibitor therapy is commonly utilized for preventing progression of dysplastic BE to esophageal adenocarcinoma. Fundamental to the success of this and all ablative approaches is the healing of the ablated areas of BE with a stratified squamous epithelium referred to as 'neosquamous epithelium' (NSE). Although NSE appears 'normal' endoscopically, the reemergence of BE over time in the previously ablated segments raises the question of the health and integrity of NSE.
  
  
  METHODS
  The health of NSE was recently investigated in endoscopic biopsies in vitro in a group of patients after ablation while on proton pump inhibitors. Biopsies of NSE were compared to upper squamous epithelium (USE) from the same patients morphologically (light microscopy) and with respect to barrier function by measuring electrical resistance and fluorescein flux in mini-Ussing chambers.
  
  
  RESULTS
  Compared to USE, NSE exhibited dilated intercellular spaces and inflammation and defective barrier function by low electrical resistance and high fluorescein flux. Moreover, NSE exhibited downregulation of claudin-4, a highly expressed protein in squamous tight junctions.
  
  
  CONCLUSIONS
  NSE has defective barrier function in part due to downregulation of claudin-4. Since downregulation of claudin-4 increases paracellular permeability to cations, e.g. hydrogen ions, NSE is more vulnerable to attack and damage by acidic and weakly acidic refluxates--a phenomenon that may contribute in part to the reemergence of BE.
authors.affiliation: University of North Carolina at Chapel Hill, Chapel Hill, N.C., USA.
authors.forename: Roy C
authors.initials: RC
authors.lastname: Orlando
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001471:Barrett Esophagus / Q000235:genetics / Q000473:pathology / Q000503:physiopathology; D057167:Claudins / Q000235:genetics / Q000378:metabolism; D017097:Electric Impedance; D004848:Epithelium / Q000473:pathology* / Q000503:physiopathology; D004947:Esophagus / Q000473:pathology; D005786:Gene Expression Regulation; D006801:Humans; D008297:Male; D008875:Middle Aged; D055815:Young Adult
chemical_list: D057167:Claudins