Helicobacter pylori-associated ammonia production enhances neutrophil-dependent gastric mucosal cell injury

Abstract

The role of neutrophil and its chlorinated oxidant were investigated in Helicobacter pylori-induced gastric mucosal injury in vitro. Luminol-dependent chemiluminescence (ChL) was used to detect neutrophil-derived oxidants. ChL activity was significantly elevated when neutrophils were incubated in H. pylori, indicating that H. pylori actually elicits oxidative burst of neutrophils. To assess whether H. pylori-activated neutrophils exert the cytotoxicity for gastric mucosal cells, rabbit gastric mucosal cell was monolayered in culture wells and labeled with a fluorescence dye, 2',7'-bis(2-carboxyethyl)-5(6)carboxy-fluorescein, which is retained in the intracellular space as long as the cell membrane is intact. Labeled cells were coincubated with neutrophils and H. pylori. We inferred from the cytotoxicity index (specific %cytotoxicity), which was calculated from fluorometrical measurements of supernatant and lysate, that the mucosal cells were significantly damaged by H. pylori-activated neutrophils. This injury was largely attenuated by eliminating urea from the incubation mixture or by acetohydroxamic acid, a potent urease inhibitor. Additionally, the scavengers of neutrophil-derived oxidants, including taurine, methionine, and catalase, also attenuated this injury. Cultured mucosal cells that were exposed to the solution containing monochloramine (an oxidant yielded by reaction of hypochlorous acid and ammonia) were highly damaged compared with cells exposed to hypochlorous acid or hydrogen peroxide at physiological concentrations. These data suggest that H. pylori-activated neutrophils promote gastric mucosal cell injury and that monochloramine plays a unique and important role in this process.

Susceptibility of Helicobacter pylori and its urease activity to the peroxidase-hydrogen peroxide-thiocyanate antimicrobial system

“…Furthermore, saliva contains OSCN À , the antimicrobial intermediate produced by the system, at an average concentration ranging from 34 to 61 ìM [8,31]. Although the formation of hypochlorous acid by neutrophil-derived MPO has been suggested to serve as a pathogenic factor of H. pylori causing gastric mucosal injury through an in¯amma-tory response [4,5], the system composed of MPO, H 2 O 2 and SCN À kills the bacteria and can at least contribute to host protection against H. pylori in the early stage of infection. The peroxidase system derived from saliva or milk may be active in the oesophagus and the stomach, as it has been shown that peroxidase activity is not rapidly inactivated in gastric juice [43].…”

“…The hydrolysis of urea by cytoplasmic urease results in energy generation in the form of a proton-motive force which drives agellar rotation, allowing bacterial motility in the mucus gel layer of the stomach [1,3]. The formation of monochloramine from ammonia produced by H. pylori urease and neutrophil-derived hypochlorous acid have been suggested to play an important role in gastric mucosal injury [4,5]. Although the precise route of transmission and the natural reservoir of H. pylori remain unknown, recent clinical studies support the existence of gastro±oral and oral±oral pathways of transmission [6].…”

Why is the coexistence of gastric cancer and duodenal ulcer rare? Examination of factors related to both gastric cancer and duodenal ulcer

“…1, 4) Suzuki et al [65] and Murakami et al [66] have reported that H. pylori increases the production of inflammatory cytokines such as IL-1b, IL-2, IL-6, IL-8, and tumor necrosis factor alpha (TNF-a), and that toxic metabolites and lysosomal enzymes released from neutrophils are also responsible for gastric mucosal injury, while Takashima et al [67] reported that decreased acid secretion was accompanied by an elevation of IL-1b messenger RNA levels in the H. pylori-infected gastric mucosa. Esplugues et al [68] and Kondo et al [69] reported that the acidinhibitory effect of IL-1b appears to involve nitric oxide synthesis and may be mediated by the inhibition of gastric histamine mobilization.…”

Molecular Epidemiology of Helicobacter pylori in Brazilian Patients with Early Gastric Cancer and a Review to Understand the Prognosis of the Disease

“…Urease causes damage to the epithelium through the production of ammonia, that, in conjunction with neutrophil metabolites, forms carcinogenic agents that might participate in the development of gastric malignances [30,31]. Ammonia is capable to cause different cell alterations, including swelling of intracellular acidic compartments, alterations of vesicular membrane transport, repression of protein synthesis and ATP production, and cell-cycle arrest [32].…”