Enhanced expression of inducible nitric oxide synthase and nitrotyrosine in gastric mucosa of gastric cancer patients.

Recent studies (K. Komoto et al., Am. J. Gastroenterol., 93: 1271-1276, 1998) have shown that Helicobacter pylori infection is associated with gastric cancer. However, the mechanism of H. pylori in carcinogenesis has not been clarified. H. pylori infection leads to a sustained production of reactive nitrogen species that may contribute to cause DNA damage. In this study, we examined the expression of inducible nitric oxide synthase (iNOS) and nitrotyrosine in gastric mucosa. The expression of iNOS and nitrotyrosine was examined by immunohistochemistry in 93 patients who initially underwent gastric biopsies between 1975 and 1992. Thirty-four individuals were later found to have gastric cancer at least 2 years after the initial biopsies (group A). The other 59 subjects have shown no evidence of gastric cancer during long-term follow-up. Fifty-one of these patients were positive for H. pylori (group B), and eight were negative for H. pylori (group C). The expression of iNOS and nitrotyrosine in the gastric mucosa was significantly higher in H. pylori-positive groups A and B than in H. pylori-negative group C. Among the H. pylori-positive patients, the expression of iNOS and nitrotyrosine was significantly higher in group A than in group B. These results suggest that high production of iNOS and nitrotyrosine in the gastric mucosa infected with H. pylori may contribute to the carcinogenesis of gastric cancer.