A novel mechanism of acid and bile acid-induced DNA damage involving Na+/H+ exchanger: implication for Barrett's oesophagus.
OBJECTIVE
Barrett's oesophagus is a premalignant disease associated with oesophageal adenocarcinoma. The major goal of this study was to determine the mechanism responsible for bile acid-induced alteration in intracellular pH (pH(i)) and its effect on DNA damage in cells derived from normal oesophagus (HET1A) or Barrett's oesophagus (CP-A).


METHODS
Cells were exposed to bile acid cocktail (BA) and/or acid in the presence/absence of inhibitors of nitric oxide synthase (NOS) or sodium-hydrogen exchanger (NHE). Nitric oxide (NO), pH(i) and DNA damage were measured by fluorescent imaging and comet assay. Expression of NHE1 and NOS in cultured cells and biopsies from Barrett's oesophagus or normal squamous epithelium was determined by RT-PCR, immunoblotting or immunohistochemistry.


RESULTS
A dose dependent decrease in pH(i) was observed in CP-A cells exposed to BA. This effect of BA is the consequence of NOS activation and increased NO production, which leads to NHE inhibition. Exposure of oesophageal cells to acid in combination with BA synergistically decreased pH(i). The decrease was more pronounced in CP-A cells and resulted in >2-fold increase in DNA damage compared to acid treatment alone. Examination of biopsies and cell lines revealed robust expression of NHE1 in Barrett's oesophagus but an absence of NHE1 in normal epithelium.


CONCLUSIONS
The results of this study identify a new mechanism of bile acid-induced DNA damage. We found that bile acids present in the refluxate activate immediately all three isoforms of NOS, which leads to an increased NO production and NHE inhibition. This consequently results in increased intracellular acidification and DNA damage, which may lead to mutations and cancer progression. Therefore, we propose that in addition to gastric reflux, bile reflux should be controlled in patients with Barrett's oesophagus.
Goldman
Aaron
A
Arizona Cancer Center, University of Arizona, USA.
Shahidullah
Mohammad
M
Goldman
David
D
Khailova
Ludmila
L
Watts
George
G
Delamere
Nicholas
N
Dvorak
Katerina
K
D001471:Barrett Esophagus / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D001647:Bile Acids and Salts / Q000494:pharmacology*; D027682:Cation Transport Proteins / Q000096:biosynthesis / Q000235:genetics; D002460:Cell Line; D004249:DNA Damage; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D004789:Enzyme Activation / Q000187:drug effects; D004947:Esophagus / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D006851:Hydrochloric Acid / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D009569:Nitric Oxide / Q000502:physiology; D019001:Nitric Oxide Synthase / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers / Q000096:biosynthesis / Q000235:genetics* / Q000502:physiology
D001647:Bile Acids and Salts; D027682:Cation Transport Proteins; D012333:RNA, Messenger; C490998:SLC9A1 protein, human; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D006851:Hydrochloric Acid