Mechanism of protection of oxidant-injured endothelial cells by glutamine

Glutamine supplementation before oxidant exposure has recently been shown to significantly enhance adenosine triphosphate (ATP) levels and viability in endothelial cells. The aim of this study was to determine if glutamine can help cells after oxidant injury has been initiated and to demonstrate the mechanism of its action. The activity of glyceraldehyde 3-phosphate dehydrogenase was measured in bovine pulmonary artery endothelial cells exposed to H2O2 (0 to 10 mmol/L). Glyceraldehyde 3-phosphate dehydrogenase activity was completely inhibited by 10 mmol/L H2O2 after 1 minute, resulting in inhibition of glycolysis. The endothelial cells were then exposed to 10 mmol/L H2O2, with glutamine (2 mmol/L) being added at different times in relation to the injury. ATP levels were monitored during a 3-hour time course, and short-term viability was measured 6 hours after addition of the oxidant. Significant improvement of endothelial cell ATP levels and short-term viability was seen with addition of glutamine as late as 15 minutes after addition of H2O2. Mitochondrial inhibition with oligomycin (650 nmol/L) abolished the protective effect of glutamine on ATP levels and short-term viability. Cellular survival at 24 hours was not enhanced by glutamine, which suggests that ATP may not be the only factor determining long-term survival after oxidant injury.