Helicobacter pylori induces apoptosis in gastric epithelial cells through inducible nitric oxide

Background: Gastric mucosal injury by Helicobacter pylori has been suggeste d to be mediated by various cytokines induced by this organism. Nitric oxid e (NO) is an important effector molecule involved in immune regulation and defence. To clarify the mechanisms by which H. pylori induces gastric mucos al cell injury, we examined whether H. pylori induces gastric epithelial de ath via NO production. Methods: Cytotoxic and non-cytotoxic strains of H. pylori were used. The de ath of MKN45 cells caused by H. pylori was examined by the 3-(4,5-dimethyl- thiazole-2yl)-2,5-diphenyl tetrazolium bromide (MTT) assays. Aminoguanidine was used to inhibit inducible nitric oxide synthase (iNOS) activity. Expre ssion of iNOS mRNA was determined by the reverse transcriptase-polymerase c hain reaction and the DNA fragmentation analysis was performed by using aga rose gel electrophoresis. Results: The MTT assay revealed that neither viable H. pylori nor other com ponents of the microorganism induced cell death. Both preincubation of MKN4 5 cells with interferon-gamma for 6 h and coculture with TNF-alpha signific antly increased the cytotoxicity of H. pylori. Both cytotoxic and non-cytot oxic strains of H. pylori induced cell death. Expression of iNOS mRNA was o bserved in MKN45 cells at 6, 8 and 12 h after H. pylori inoculation. The cy totoxicity of H. pylori was inhibited by aminoguanidine and DNA fragmentati on analysis showed that H. pylori induced apoptosis. Conclusions: These findings suggested that viable H. pylori induces apoptos is of gastric epithelial cells via nitric oxide. Our study indicated that i NOS expression plays an important role in gastric cell injury. (C) 2000 Bla ckwell Science Asia Pty Ltd.