Oxygen radicals are supposed to be involved in inflammation and cell proliferation. Helicobacter pylori induces decrease in antioxidant defense factors, such as GSH, mucus and constitutive nitric oxide (NO), gastric mucosal injury and inflammation.

Inflammation and injury might be caused by oxidant-mediated expression of inflammatory cytokine interleukin-8 (IL-8) and inflammatory enzymes such as cyclooxtgenase-2 (COX-2) and inducible nitric oxide synthase (iNOS), which were mediated by oxidant-sensitive transcription factors such as nuclear factor-κB (NF-κB) and activator protein-1 (AP-1), possibly with mitogen activated protein kinase (MAPK) activation.

H.Pylori-induced alterations in protein expression demonstrate the involvement of oxidative stress in the pathogenesis of H.Pylori-induced gastric diseases. The differentially expressed genes and proteins may be useful as prognostic indices for gastric diseases associated with H.Pylori infection.

In conclusion, oxygen radicals are produced in gastric epithelial cells infected with H.Pylori, which may reduce the antioxidant defense mechanism and turn on the expression of inflammatory genes, adhesion molecules and mediators stimulating cell proliferation, as well as defensive molecular chaperones in gastric epithelial cells.