title: N-methyl D-aspartate channels link ammonia and epithelial cell death mechanisms in Helicobacter pylori Infection.
abstract: OBJECTIVE
  Helicobacter pylori infection is a risk factor for gastric cancer. Ammonia/ammonium (A/A) is a cytotoxin generated by H pylori that kills gastric epithelial cells. We investigated whether A/A cytotoxicity occurs by activating N-methyl d-aspartate (NMDA) channels, which results in Ca(2+) permeation and epithelial cell death.
  
  
  METHODS
  Gastric epithelial cells were cultured to confluence and then incubated with A/A and NMDA channel or cell signaling antagonists. Cells were incubated with wild-type H pylori or mutant strains that do not produce A/A. Changes in intracellular Ca(2+) were examined in living cells by confocal microscopy. Biochemical and histochemical techniques were used to examine the relationship between A/A-induced cell death and intracellular levels of Ca(2+).
  
  
  RESULTS
  A/A increased Ca(2+) permeation in gastric epithelial cells; the increase was blocked by NMDA receptor and cell signaling antagonists. Wild-type, but not mutant H pylori, also caused extensive Ca(2+) permeation of gastric epithelial cells, which was blocked when NMDA-receptor expression was repressed. Ca(2+) that entered cells was initially cytoplasmic and activated proteases. Later, the Ca(2+) was sequestered to cytoplasmic vacuoles that are dilatations of the endoplasmic reticulum. Inositol-3-phosphate-dependent release of Ca(2+) from the endoplasmic reticulum and protease activity damaged mitochondria, reduced levels of adenosine triphosphate, and transcriptionally up-regulated cell death effectors. Expression of the NMDA receptor was altered in stomachs of mice infected with H pylori.
  
  
  CONCLUSIONS
  A/A affects gastric epithelial cell viability by allowing excessive Ca(2+) permeation through NMDA channels. NMDA channels might thereby regulate cell survival and death pathways during development of gastric cancers associated with H pylori infection.
authors.affiliation: Department of Surgery, Beth Israel Deaconess Medical Center, Boston, Massachusetts 02215, USA.
authors.forename: Ji Hye
authors.initials: JH
authors.lastname: Seo
authors.forename: James G
authors.initials: JG
authors.lastname: Fox
authors.forename: Richard M
authors.initials: RM
authors.lastname: Peek
authors.forename: Susan J
authors.initials: SJ
authors.lastname: Hagen
mesh_terms: D000641:Ammonia / Q000633:toxicity; D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism*; D016923:Cell Death; D002478:Cells, Cultured; D003603:Cytotoxins / Q000633:toxicity; D004847:Epithelial Cells / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D005753:Gastric Mucosa / Q000166:cytology; D016481:Helicobacter Infections / Q000378:metabolism / Q000382:microbiology*; D016480:Helicobacter pylori / Q000378:metabolism*; D007150:Immunohistochemistry; D051379:Mice; D018613:Microscopy, Confocal; D016202:N-Methylaspartate / Q000494:pharmacology*; D051381:Rats; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism
chemical_list: D003603:Cytotoxins; D016194:Receptors, N-Methyl-D-Aspartate; D016202:N-Methylaspartate; D000641:Ammonia; D002118:Calcium