Risk factors, DNA damage, and disease progression in Barrett's esophagus

Esophageal adenocarcinoma develops on a background of Barrett's esophagus. A number of risk factors have been linked to both conditions, including gastroesophageal reflux and smoking. However, the molecular mechanisms by which these factors influence disease progression remain unclear. One possibility is that risk factors generate promutagenic DNA damage in the esophagus. The comet assay was used to measure DNA damage in esophageal (Barrett's and squamous) and gastric mucosa of Barrett's patients with (n = 24) or without (n = 50) associated adenocarcinoma or high-grade dysplasia in comparison with control patients (squamous mucosa) without Barrett's esophagus (n = 64). Patients completed a questionnaire detailing exposure to some of the known risk factors for Barrett's esophagus and adenocarcinoma. In Barrett's esophagus patients, DNA damage was higher in Barrett's mucosa compared with normal esophageal and gastric mucosa (P < 0.001). In addition, the highest quartile of DNA damage in Barrett's mucosa was associated with an increased risk (odds ratio, 9.4; 95% confidence interval, 1.1-83.4; P = 0.044) of developing adenocarcinoma or high-grade dysplasia compared with DNA damage levels in the lowest quartile. Smoking was associated with higher DNA damage in squamous epithelium in all patient groups (P < 0.01) and in Barrett's mucosa (P < 0.05) in Barrett's esophagus patients only. In controls only, current reflux was associated with higher DNA damage, whereas anti-inflammatory drug use resulted in lower levels. Collectively, these data imply a genotoxic insult to the premalignant Barrett's mucosa that may explain the genetic instability in this tissue and the progression to adenocarcinoma. There is an indication for a role for smoking in inducing DNA damage in esophageal mucosa but an understanding of the role of reflux requires further investigation.