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A novel mechanism of acid and bile acid-induced DNA damage involving Na+/H+ exchanger: implication for Barrett's oesophagus
  1. Aaron Goldman1,
  2. Mohammad Shahidullah2,
  3. David Goldman3,
  4. Ludmila Khailova4,
  5. George Watts1,
  6. Nicholas Delamere2,
  7. Katerina Dvorak3
  1. 1Arizona Cancer Center, University of Arizona, USA
  2. 2Department of Physiology, University of Arizona, USA
  3. 3Department of Cell Biology and Anatomy, University of Arizona, USA
  4. 4Department of Pediatrics, University of Arizona, USA
  1. Correspondence to Dr Katerina Dvorak, Department of Cell Biology and Anatomy, 1501 N. Campbell Avenue, University of Arizona, Tucson, AZ 85724, USA; kdvorak{at}email.arizona.edu

Abstract

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 (pHi) and its effect on DNA damage in cells derived from normal oesophagus (HET1A) or Barrett's oesophagus (CP-A).

Design 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), pHi 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 pHi 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 pHi. 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.

  • Barrett's oesophagus
  • bile acids, nitric oxide, sodium hydrogen exchanger
  • acid-load

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Footnotes

  • Funding This work was supported by the GI SPORE grant CA95060 from NCI and NIH grant EY06951. Microarray data were generated by the Arizona Cancer Center Genomics Shared Service, supported by NCI grant CA023074-26.

  • Competing interests None.

  • Patient consent All tissue samples obtained for this study originate from the GI SPORE, HSC: #02-0785-01. Patient consent forms as required by the SPORE have been obtained and are housed at the VA hospital in Tucson, Arizona.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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