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Ammonia-induced apoptosis is accelerated at higher pH in gastric surface mucous cells
Hideo Suzuki1, Akinori Yanaka, Takeshi Shibahara
1Department of Gastroenterology, Institute of Clinical Medicine, University of Tsukuba, Ibaraki 305-8575, Japan.
Abstract:
Gastric luminal ammonia produced by Helicobacter pylori has been shown to cause gastric mucosal injury. This study was conducted to examine the mechanisms by which gastric luminal ammonia causes apoptosis of gastric epithelial cells. Monolayers of GSM06 cells, developed from murine gastric surface mucous cells, were cultured in the absence or presence of 10-30 mM NH(4)Cl at ambient pH of 5.0, 6.0, and 7.0. In the presence of luminal NH(4)Cl, GSM06 cells showed 1) cell shrinkage and nuclear chromatin condensation, 2) DNA fragmentation into oligonucleosomes, 3) leakage of cytochrome c into cytosolic fraction without affecting bax expression, and 4) increases in activity of caspases-3 and -9. These changes were accentuated when the cells were cultured at pH 7.0. In the absence of NH(4)Cl, none of these changes was detected at any pH examined. These results suggest that gastric luminal ammonia, at concentrations detected in H. pylori-infected subjects, induces apoptosis of gastric epithelial cells by release of cytochrome c from mitochondria, followed by activation of caspases-9 and -3, especially at higher ambient pH.
Insights
Gastric ammonia from Helicobacter pylori induces gastric epithelial cell apoptosis. This programmed cell death involves mitochondrial cytochrome c release and caspase activation, particularly at higher pH levels.
Area of Science:
- Cell Biology
- Gastroenterology
- Molecular Biology
Background:
- Helicobacter pylori infection is a major cause of gastric mucosal injury.
- Gastric luminal ammonia, a byproduct of H. pylori, is implicated in this damage.
Purpose of the Study:
- To investigate the molecular mechanisms by which gastric luminal ammonia induces apoptosis in gastric epithelial cells.
- To elucidate the role of pH in ammonia-induced apoptosis.
Main Methods:
- Cultured murine gastric surface mucous cells (GSM06) with varying concentrations of ammonium chloride (NH4Cl).
- Assessed cellular changes including morphology, DNA fragmentation, cytochrome c release, and caspase activity.
- Examined effects across different ambient pH levels (5.0, 6.0, and 7.0).
Main Results:
- Ammonium chloride induced characteristic apoptotic features: cell shrinkage, nuclear condensation, and DNA fragmentation.
- Cytochrome c was released into the cytosol, activating caspases-9 and -3.
- These apoptotic events were significantly enhanced at a higher ambient pH of 7.0.
Conclusions:
- Gastric luminal ammonia triggers apoptosis in gastric epithelial cells via the mitochondrial pathway.
- The process involves cytochrome c release and subsequent caspase activation.
- Elevated pH exacerbates ammonia-induced apoptosis, suggesting a pH-dependent mechanism relevant to H. pylori infections.