Induction of nitric oxide synthase in vivo and cell injury in rat duodenal epithelium by a water soluble extract of Helicobacter pylori

1 Helicobacter pylori (Hp) infection, which involves the gastric antrum and duodenal mucosa, may be involved in peptic ulceration by stimulating the local release of cytoxic or pro-inflammatory factors. 2 Nitric oxide (NO) is known to be cytotoxic at high concentration. The aim of the present study was therefore to investigate the ability of a water soluble extract of Hp to induce NO synthase in duodenal mucosa and epithelial cells following its administration in vivo in rats and determine its association with cell damage. 3 Administration of Hp water extract (4 ml kg(-1)) led to the expression of the calcium-independent inducible nitric oxide synthase (iNOS) after 4 h in the duodenum, determined as [C-14]-arginine conversion to citrulline. 4 This iNOS activity was not reduced by pretreatment with anti-neutrophil serum (0.4 mi kg(-1), i.p., 3 h before challenge). However, dexamethasone pretreatment (1 mg kg(-1), i.v., 2 h before the extract), or administration of the NO synthase inhibitor N-G-nitro-L-arginine methyl ester (L-NAME, 5 mg kg(-1), i.v., 2.5 h after the extract) reduced this activity. 5 Furthermore, iNOS was expressed in duodenal isolated epithelial cells 4 h after the i.v. challenge with the extract, at a time when the cellular viability was also reduced, as assessed by trypan blue exclusion. 6 Dexamethasone pretreatment, administration of L-NAME, or pretreatment with polymyxin B (1 mg kg(-1), i.v.) which binds endotoxin, reduced both the iNOS activity and epithelial cell damage. 7 The induction of NO synthase by the Hp extract thus results in duodenal epithelial cell injury and such actions could play a role in pathogenesis of peptic ulcer disease.