N-nitrosamine generation from ingested nitrate via nitric oxide in subjects with and without gastroesophageal reflux

Nitrate ingestion leads to high luminal concentrations of nitric oxide being generated where saliva meets gastric acid. Nitric oxide generates N-nitrosative stress on reacting with oxygen at neutral pH. We aimed to ascertain if luminal nitric oxide exerts nitrosative stress in the human upper gastrointestinal tract, and to assess the influence of acid reflux on this phenomenon.

A silicone tube, segmented every 15 mm and containing phosphate buffer pH 7.4 and the secondary amine morpholine, was inserted into the upper gastrointestinal tract of 16 healthy volunteers and 16 Barrett's esophagus patients. The tube wall has the same permeability properties as an epithelial lipid membrane, allowing passage of gases such as nitric oxide, but not hydrogen ions. After 2 hours, the tube was removed and the concentrations of nitrite and N-nitrosomorpholine in each segment were measured. Healthy volunteers were studied with and without ingestion of (15)N-enriched nitrate and Barrett's esophagus patients were studied with and without stimulation of acid reflux.

In healthy volunteers, N-nitrosomorpholine was generated in the tube sections exposed to gastric acid and increased 2-fold after nitrate. The N-nitrosomorpholine was 77% enriched with (15)N, confirming its source was the ingested nitrate. In the Barrett's patients, generation of N-nitrosomorpholine was shifted proximally with 80% of nitrosative stress occurring within the esophagus during periods of acid reflux.

This study demonstrates the in situ formation of N-nitrosamine from dietary nitrate via nitric oxide. During acid reflux, nitrosative stress occurs almost entirely within the esophagus and may contribute toward carcinogenesis at this site.