The effect of NS-398, a selective cyclooxygenase-2 inhibitor, in human gastric mucosa biopsy during H. Pylori infection

Background: The integrity of the gastrointestinal mucosa depends on the interplay of various protective and damaging factors to which this mucosa is exposed. The balance of prostanoids and nitric oxide (NO) originated from cyclooxygenase-2 (COX-2) and inducible nitric-oxide (iNOS) is important in maintain integrity of gastric mucosa during inflammatory states. Nitric oxide is an important messenger, which not only plays an important physiological role in many systems and cells, but also contributes to the pathogenesis of many conditions, including cancer. Although the gastric mucosal integrity in inflammatory states can be modulate by the concerted action of endogenous NO and PGs, little is known of the cross talk effects between them. The cross talk represents an important mechanism by which the initial inflammatory response can be amplified or attenuated. H. pylori infection recognized as one of the most common chronic infections in humans and its colonization of gastric epithelium results in a chronic gastritis, gastric cancer, and gastric B cell lymphoma. In order to understand relationship between COX-2 and iNOS we examined the effect of 1400W and NS 398 inhibitors of iNOS and COX-2 on the levels of NO and PGE2 and expression of iNOS and COX-2 proteins in human gastric biopsies during H. pylori infection. Methods: A total of 20 subjects with dyspepsia undergoing upper gastrointestinal endoscopy were analysed. Gastric biopsies were taken from the antral mucosa for culture and histological examination. Helicobacter colonization was diagnosed by identification of characteristic curved or spiral bacilli. A pool of 1 or 2 biopsies for patient (n. 11 H. pylori positive and n. 9 H. pylori negative) were incubated at 37 in the medium with/without inhibitors of iNOS and COX-2. Following a 24 h incubation, levels of NO and PGE2 were measured into the medium whereas protein levels were measured in the biopsies. The expression of COX-2 and iNOS protein was evaluated by western blot analysis. Results: All patients (n.11) with H. pylori infection showed chronic active gastritis and a marked expression of COX-2 and i-NOS proteins. They produced also a significant increase of nitrite and PGE2, as a consequence of iNOS and COX-2 activation, compared with patients without H pylori infection. Expression of COX-2 and iNOS protein was absent and the level of nitrite and PGE2 was low in all gastric mucosa of non infected patients and with normal mucosa (n. 9). Addition of NS-398 inhibited significantly the rise observed in H pylori positive patients of both NO and PGE2, while no difference was evident in the group of H pylori negative. iNOS specific inhibitor, 1400W, had no significant effect on the concentration of H pylori positive gastric mucosal PGE2, whereas the level of NO was significantly inhibited. After addition of drugs no difference was observed in the COX-2 and iNOS protein level as determined by densitometry. Conclusions: We observed that COX-2 inhibitor may modulate the iNOS pathway suggesting that COX-2 activity and/or its products may be related to the functional activation of i-NOS but not to the expression of i-NOS protein.