Contribution of glutamine synthetase to ammonia-induced apoptosis in gastric mucosal cells.
OBJECTIVE
Glutamine synthetase is a key enzyme necessary for ammonia detoxification in the brain, but excessive activation of this enzyme can be cytotoxic to neural cells as a consequence of excessive consumption of ATP and glutamate. The stomach also expresses high levels of glutamine synthetase and this study aimed to investigate a possible pathophysiological role of glutamine synthetase in ammonia-induced gastric mucosal injury.


METHODS
Normal rat gastric mucosal epithelial (RGM-1) cells were treated with ammonia, and a specific glutamine synthetase inhibitor (methionine sulfoximine) was used to assess the action of glutamine synthetase.


RESULTS
Treatment with ammonia induced apoptotic cell death. Increased expression of p21 and Bax, decreased expression of Bcl-2, cytochrome C release from the mitochondria into the cytosol and subsequent activation of caspase-9 and -3 were identified in the cells treated with ammonia, although there was no apparent change in p53 expression. On the other hand, pretreatment with various concentrations of methionine sulfoximine reduced the glutamine synthetase activity in ammonia-treated RGM-1 cells, and prevented the induction of apoptosis and the reduction in intracellular ATP levels in a dose-dependent manner.


CONCLUSIONS
Our results suggested that the energy exhaustion which resulted from an overload of ammonia to glutamine synthetase may have initiated the apoptotic signaling in gastric mucosal cells.
Kubota
Yuuji
Y
Division of Gastroenterology, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan.
Kato
Katsuaki
K
Dairaku
Naohiro
N
Koike
Tomoyuki
T
Iijima
Katsunori
K
Imatani
Akira
A
Sekine
Hitoshi
H
Ohara
Shuichi
S
Matsui
Hiroshi
H
Shimosegawa
Tooru
T
D000255:Adenosine Triphosphate / Q000378:metabolism; D000641:Ammonia / Q000633:toxicity*; D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D018929:Cell Culture Techniques; D045304:Cytochromes c / Q000378:metabolism; D004734:Energy Metabolism; D020869:Gene Expression Profiling; D005974:Glutamate-Ammonia Ligase / Q000494:pharmacology*; D016481:Helicobacter Infections / Q000150:complications; D016480:Helicobacter pylori / Q000472:pathogenicity; D007413:Intestinal Mucosa / Q000473:pathology; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D016159:Tumor Suppressor Protein p53 / Q000096:biosynthesis; D051028:bcl-2-Associated X Protein
C494828:Bax protein, rat; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D016159:Tumor Suppressor Protein p53; D051028:bcl-2-Associated X Protein; D000641:Ammonia; D000255:Adenosine Triphosphate; D045304:Cytochromes c; D005974:Glutamate-Ammonia Ligase