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Departments of 2 Medicine and 1 Pediatrics, National Jewish Medical and Research Center, Denver, Colorado 80206
Glutamine is an important mitochondrial substrate
implicated in the protection of cells from oxidant injury, but the
mechanisms of its action are incompletely understood. Human pulmonary
epithelial-like (A549) cells were exposed to 95% O2 for 4 days in the absence and presence of glutamine. Cell proliferation in
normoxia was dependent on glutamine, and glutamine deprivation markedly
accelerated cell death in hyperoxia. Glutamine significantly increased
cellular ATP levels in normoxia and prevented the loss of ATP in
hyperoxia seen in glutamine-deprived cells. Mitochondrial membrane
potential as assessed by flow cytometry with
chloromethyltetramethylrosamine was increased by glutamine in
hyperoxia-exposed A549 cells, and a glutamine dose-dependent increase
in mitochondrial membrane potential was detected.
Glutamine-supplemented, hyperoxia-exposed cells had a higher
O2 consumption rate and GSH content. Electron and
fluorescence microscopy revealed that, in hyperoxia, glutamine protected cellular structures, especially mitochondria, from damage. In
hyperoxia, activity of the tricarboxylic acid cycle enzyme
-ketoglutarate dehydrogenase was partially protected by its indirect substrate, glutamine, indicating a mechanism of mitochondrial protection.
human; airway; epithelium; adenosine 5'-triphosphate;
-ketoglutarate dehydrogenase; mitochondrial membrane potential
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