Dual Roles of Helicobacter pylori NapA in Inducing and Combating Oxidative Stress

Abstract

Neutrophil-activating protein (NapA) has been well documented to play roles in human neutrophil recruitment and in stimulating host cell production of reactive oxygen intermediates (ROI). A separate role for NapA in combating oxidative stress within H. pylori was implied by studies of various H. pylori mutant strains. Here, physiological analysis of a napA strain was the approach used to assess the iron-sequestering and stress resistance roles of NapA, its role in preventing oxidative DNA damage, and its importance to mouse colonization. The napA strain was more sensitive to oxidative stress reagents and to oxygen, and it contained fourfold more intracellular free iron and more damaged DNA than the parent strain. Pure, iron-loaded NapA bound to DNA, but native NapA did not, presumably linking iron levels sensed by NapA to DNA damage protection. Despite its in vitro phenotype of sensitivity to oxidative stress, the napA strain showed normal (like that of the wild type) mouse colonization efficiency in the conventional in vivo assay. By use of a modified mouse inoculation protocol whereby nonviable H. pylori is first inoculated into mice, followed by (live) bacterial strain administration, an in vivo role for NapA in colonization efficiency could be demonstrated. NapA is the critical component responsible for inducing host-mediated ROI production, thus inhibiting colonization by the napA strain. An animal colonization experiment with a mixed-strain infection protocol further demonstrated that the napA strain has significantly decreased ability to survive when competing with the wild type. H. pylori NapA has unique and separate roles in gastric pathogenesis.

Helicobacter pyloridefense against oxidative attack

“…Deficiency of a range of antioxidant enzymes, including Hp-SOD, KatA, Hp-Tpx, and AhpC, results in a compensatory increase in NapA production (76), suggesting that it may function as a secondary antioxidant that becomes important when other defenses are overwhelmed. This is supported by the fact that NapA mutant strains of H. pylori are able to colonize mice normally (99), indicating that the enzyme is not required for survival and that some functional redundancy may be present. Although the precise mechanism of its antioxidant activity is unknown, it is possible that the iron-sequestering properties of NapA may help prevent secondary ROS formation from superoxide (99).…”

“…This is supported by the fact that NapA mutant strains of H. pylori are able to colonize mice normally (99), indicating that the enzyme is not required for survival and that some functional redundancy may be present. Although the precise mechanism of its antioxidant activity is unknown, it is possible that the iron-sequestering properties of NapA may help prevent secondary ROS formation from superoxide (99). When ironloaded, NapA can also bind to DNA with great affinity and, therefore, may play a role in protecting DNA from oxidative damage.…”

Detection and evaluation of antibodies against neutrophil-activating protein of Helicobacter pylori in patients with gastric cancer

“…ROS production is significantly decreased in gastric mucosa of patients with H pylori successfully eradicated [33] . It has also been shown that HP-NAP can be involved in extravasation of leukocytes, and ROS can play a role in the carcinogenic process in gastric mucosa during chronic H pylori infection [34,35] , indicating that HP-NAP may be a risk factor for H pylori-associated gastric cancer.…”

Global transcriptional analysis of Mycoplasma hyopneumoniae following exposure to hydrogen peroxide

“…In Helicobacter pylori NapA plays a dual role in pathogenesis: in colonization and in protection against oxidative damage (Wang et al, 2006). As a protein that binds iron, it may thus serve as a primitive siderophore for mycoplasmas, although in previous work, napA was not transcriptionally responsive to changes in iron concentration in M. hyopneumoniae (Madsen et al, 2006b) as has been shown in other bacterial pathogens (Mey et al, 2005).…”