A novel mechanism of acid and bile acid-induced DNA damage involving Na⁺/H⁺exchanger: implication for Barrett's oesophagus

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 (pH i ) 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), 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.

Dickkopf-1, the Wnt antagonist, is induced by acidic pH and mediates epithelial cellular senescence in human reflux esophagitis

“…Indeed, acid-mediated cellular injury induced Dkk1 overexpression in vitro. This effect was directly linked to acid-mediated DNA damage (14), just as the esophageal epithelial cells respond to alternative inducers of DNA injury such as camptothecin by upregulating Dkk1. In favor of this observation, Dkk1 transcriptional activation has been associated with the p53 tumor suppressor, the activation of which has been reported upon cellular stress accompanied by DNA damage (30,50,52).…”

“…In response to injury, cells will undergo senescence, or they will self-destruct (apoptosis), if the damage cannot be easily repaired. In GERD, squamous epithelial cells are continuously injured by the gastric refluxate, which induces oxidative stress and DNA damage (14,24). As the GERD injury persists, more surface epithelial cells are damaged, and the injury progresses to the deeper layers of the epithelium.…”

“…Characteristically, brain tumor cells respond to DNA damage by elevating Dkk1 expression (44), while activation of IFN-␥ and TNF-␣ signaling pathways has been reported upstream of Dkk1 overexpression in colitis and rheumatoid arthritis (26,49). In reflux esophagitis, the cellular injury is triggered by intraluminal stressors, such as acid and bile, and results in DNA damage (14) and activation of multifaceted inflammatory mechanisms (42). In this study, we emphasized the effect of acid, based on the high Dkk1 levels reported in the normallooking mucosa of esophagitis patients, away from the margins of the reflux-induced lesions/erosions, suggesting that Dkk1 is more likely affected by intraluminal stressors than by inflammatory mediators (2).…”

Does a melatonin supplement alter the course of gastro-esophageal reflux disease?

“…GERD and Barrett's esophagus are identified as major risk factors for esophageal carcinoma. Besides acid reflux, bile reflux can be a clinical challenge due to refractory GERD and it may also play an important role in the progression from Barrett's to adenocarcinoma [5,6] . It is worth drawing attention to studies performed on animal models by Konturek et al [7] .…”

Physiological and pathophysiological investigation of lacrimal and pancreatic ductal epithelial cells

“…Several studies have shown that bile acids induce intracellular acidification in various cell types [68,[95][96][97]. At first step, we have investigated the effect of CDCA and UDCA on basal pH i of pancreatic ducts.…”