Vascular disease is the major cause of morbidity and mortality in diabetes mellitus. While the etiology of vascular disease is multifactorial, endothelial cell (EC) dysfunction is a hallmark of diabetes-associated vascular disease. Substantial evidence indicates that high glucose (HG) concentrations trigger EC dysfunction through the production of reactive oxygen species (ROS). Recently, studies from our laboratory and others identified the conditionally essential amino acid glutamine as a critical regulator of oxidative stress and EC phenotype. In the present study, we investigated the effect of HG concentrations on ECs and determined if glutamine influences the biological actions of HG in these cells. Treatment of human umbilical vein ECs with glucose (5.6-25mM) resulted in a concentration- and time-dependent increase in the production of reactive oxygen species (ROS), whereas mannitol (an osmotic control) minimally affected ROS formation. HG concentrations (25mM) also evoked a time-dependent decrease in EC viability that was paralleled by an increase in apoptosis, as reflected by a rise in annexin V binding and caspase-3 activity. Notably, the administration of glutamine (500μM) inhibits HG-mediated endothelial ROS production and improves EC viability in response to HG levels. Glutamine also induces the expression of heme oxygenase-1 (HO-1) in ECs. However, pharmacological inhibition of HO-1 activity with tin protoporphyrin-IX (10μM) reversed the antioxidant and cytoprotective effect of glutamine in HG-treated ECs. In conclusion, the present study found that glutamine counteracts HG concentration-mediated ROS generation and EC death. Moreover, it demonstrates that the induction of HO-1 by glutamine contributes to the beneficial actions of the amino acid and identifies glutamine as a critical regulator of EC survival in diabetes.
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Supported by the University of Missouri School of Medicine TRIUMPH Initiative Funding.
