Glutamine protects mitochondrial structure and function in oxygen toxicity

Glutamine is an important mitochondrial substrate implicated in the protect ion of cells from oxidant injury, but the mechanisms of its action are inco mpletely understood. Human pulmonary epithelial-like (A549) cells were expo sed to 95% O-2 for 4 days in the absence and presence of glutamine. Cell pr oliferation in normoxia was dependent on glutamine, and glutamine deprivati on markedly accelerated cell death in hyperoxia. Glutamine significantly in creased cellular ATP levels in normoxia and prevented the loss of ATP in hy peroxia seen in glutamine-deprived cells. Mitochondrial membrane potential as assessed by flow cytometry with chloromethyltetramethylrosamine was incr eased by glutamine in hyperoxia-exposed A549 cells, and a glutamine dose-de pendent increase in mitochondrial membrane potential was detected. Glutamin e-supplemented, hyperoxia-exposed cells had a higher O-2 consumption rate a nd GSH content. Electron and fluorescence microscopy revealed that, in hype roxia, glutamine protected cellular structures, especially mitochondria, fr om damage. In hyperoxia, activity of the tricarboxylic acid cycle enzyme al pha -ketoglutarate dehydrogenase was partially protected by its indirect su bstrate, glutamine, indicating a mechanism of mitochondrial protection.