Helicobacter pylori Urease Suppresses Bactericidal Activity of Peroxynitrite via Carbon Dioxide Production

Abstract

Helicobacter pylori can produce a persistent infection in the human stomach, where chronic and active inflammation, including the infiltration of phagocytes such as neutrophils and monocytes, is induced. H. pylori may have a defense system against the antimicrobial actions of phagocytes. We studied the defense mechanism of H. pylori against host-derived peroxynitrite (ONOO ؊ ), a bactericidal metabolite of nitric oxide, focusing on the role of H. pylori urease, which produces CO 2 and NH 3 from urea and is known to be an essential factor for colonization. The viability of H. pylori decreased in a time-dependent manner with continuous exposure to 1 M ONOO ؊ , i.e., 0.2% of the initial bacteria remained after a 5-min treatment without urea. The bactericidal action of ONOO ؊ against H. pylori was significantly attenuated by the addition of 10 mM urea, the substrate for urease, whereas ONOO ؊ -induced killing of a urease-deficient mutant of H. pylori or Campylobacter jejuni, another microaerophilic bacterium lacking urease, was not affected by the addition of urea. Such a protective effect of urea was potentiated by supplementation with exogenous urease, and it was almost completely nullified by 10 M flurofamide, a specific inhibitor of urease. The bactericidal action of ONOO ؊ was also suppressed by the addition of 20 mM NaHCO 3 but not by the addition of 20 mM NH 3 . In addition, the nitration of L-tyrosine of H. pylori after treatment with ONOO ؊ was significantly reduced by the addition of urea or NaHCO 3 , as assessed by high-performance liquid chromatography with electrochemical detection. These results suggest that H. pylori-associated urease functions to produce a potent ONOO ؊ scavenger, CO 2 /HCO 3 ؊ , that defends the bacteria from ONOO ؊ cytotoxicity. The protective effect of urease may thus facilitate sustained bacterial colonization in the infected gastric mucosa.

Differential regulation of urease activity in Helicobacter hepaticus and Helicobacter pylori

“…Enzymic degradation of urea by urease results in the production of ammonia and bicarbonate, and both reaction products are thought to play an important part in bacterial pathogenesis. Ammonia serves as nitrogen source and may function in acid resistance (Burne & Chen, 2000;Scott et al, 2002;Williams et al, 1996), whereas bicarbonate may also function in acid resistance as well as in modulating the immune system of the host (Kuwahara et al, 2000;Marcus et al, 2005). Expression of urease in bacteria is controlled by different stimuli, such as urea availability, environmental pH, nitrogen status of the cell, or growth phase (Burne & Chen, 2000).…”

l -Arginine Availability Regulates Inducible Nitric Oxide Synthase-Dependent Host Defense against Helicobacter pylori

“…We have demonstrated that H. pylori induces iNOS and NO production in macrophages (6,(21)(22)(23)47). NO can kill the bacterium in vitro (6,22,30), but H. pylori survives in the human stomach despite detection of iNOS in the infected gastric mucosa (19). It is important to note that even when H. pylori is separated from the mucosal macrophages, NO itself is freely diffusible and can be detected systemically under conditions of infection or other forms of stress where iNOS is upregulated (for a review, see reference 17).…”

Spermine Causes Loss of Innate Immune Response to Helicobacter pylori by Inhibition of Inducible Nitric-oxide Synthase Translation

“…H. pylori can induce iNOS and other innate immune response genes in macrophages even when separated by filter supports or when water extracts are used (6). Although H. pylori-induced NO production can kill the bacterium in vitro (7,9), it survives in the stomach, despite detection of iNOS in infected gastric mucosa (10).…”