Resumo

Ureases (EC 3.5.1.5), nickel-dependent enzymes that hydrolyze urea into ammonia and CO2, are synthesized by plants, fungi and bacteria. Urease produced by Helicobacter pylori (HPU), an etiological agent of gastric ulcers and cancer, is considered a virulence factor since its ureolytic activity enables the bacterium to survive in the acidic medium of the stomach. Gastric colonization by H. pylori is usually accompanied by an intense infiltration of polymorphonuclear leukocytes, macrophages and lymphocytes. The degree of mucosal damage correlates with an intense neutrophil infiltration. It is well known that platelets participate in the inflammatory response by modulating the activity of other inflammatory cells and ischemic lesions due to vascular insufficiency may lead to ulcers within the gastric mucosa. Previous data of our group showed that HPU: 1) induces platelet aggregation independent of its ureolytic activity, requiring ADP secretion through the lipoxygenase pathway; 2) induces paw edema in a dose- and time-dependent manner, with an intense neutrophil infiltration. In this work, we used a recombinant urease produced in Escherichia coli to evaluate biological effects independent of its enzyme activity. In platelets, our results indicate that HPU interacts with the membrane glycoprotein VI, a well known receptor for collagen, which triggers a signaling cascade requiring metabolites of the platelet 12-lipoxygenase pathway. In human neutrophils, 100 nM rHPU induced extracellular production of ROS, and inhibited their apoptosis (40.5% compared to control), altering the levels of Bcl-XL and Bad proteins. HPU-induced neutrophil chemotaxis was 88% of that observed for fMLP, a strong chemoattractant used as positive control. These effects of rHPU persisted in the absence of enzyme activity. rHPU-induced paw edema, neutrophil chemotaxis and apoptosis inhibition reverted in the presence of the lipoxygenase inhibitors esculetin or AA861. Neutrophils exposed to rHPU had increased content of lipoxygenase(s) and no alteration of cyclooxygenase(s) level(s). Conclusion: Our data indicate that HPU, besides allowing the bacterial survival in the stomach, could play an important role in the pathogenesis of the gastrointestinal inflammatory disease caused by H. pylori.