Cutting edge: urease release by Helicobacter pylori stimulates macrophage inducible nitric oxide synthase.

Inducible NO synthase (iNOS) expression and production of NO are both up-regulated with Helicobacter pylori infection in vivo and in vitro. We determined whether major pathogenicity proteins released by H. pylori activate iNOS by coculturing macrophages with wild-type or mutant strains deficient in VacA, CagA, picB product, or urease (ureA(-)). When filters were used to separate H. pylori from macrophages, there was a selective and significant decrease in stimulated iNOS mRNA, protein, and NO(2)(-) production with the ureA(-) strain compared with wild-type and other mutants. Similarly, macrophage NO(2)(-) generation was increased by H. pylori protein water extracts of all strains except ureA(-). Recombinant urease stimulated significant increases in macrophage iNOS expression and NO(2)(-) production. Taken together, these findings indicate a new role for the essential H. pylori survival factor, urease, implicating it in NO-dependent mucosal damage and carcinogenesis.

Helicobacter pylori induces macrophage apoptosis by activation of arginase II.

Helicobacter pylori infection induces innate immune responses in macrophages, contributing to mucosal inflammation and damage. Macrophage apoptosis is important in the pathogenesis of mucosal infections but has not been studied with H. pylori. NO derived from inducible NO synthase (iNOS) can activate macrophage apoptosis. Arginase competes with iNOS by converting L-arginine to L-ornithine. Since we reported that H. pylori induces iNOS in macrophages, we now determined whether this bacterium induces arginase and the effect of this activation on apoptosis. NF-kappa B-dependent induction of arginase II, but not arginase I, was observed in RAW 264.7 macrophages cocultured with H. pylori. The time course of apoptosis matched those of both arginase and iNOS activities. Surprisingly, apoptosis was blocked by the arginase inhibitors N(omega)-hydroxy-L-arginine or N(omega)-hydroxy-nor-L-arginine, but not by the iNOS inhibitor N-iminoethyl-L-lysine. These findings were confirmed in peritoneal macrophages from iNOS-deficient mice and were not dependent on bacterial-macrophage contact. Ornithine decarboxylase (ODC), which metabolizes L-ornithine to polyamines, was also induced in H. pylori-stimulated macrophages. Apoptosis was abolished by inhibition of ODC and was restored by the polyamines spermidine and spermine. We also demonstrate that arginase II expression is up-regulated in both murine and human H. pylori gastritis tissues, indicating the likely in vivo relevance of our findings. Therefore, we describe arginase- and ODC-dependent macrophage apoptosis, which implicates polyamines in the pathophysiology of H. pylori infection.