Glutamine effects on endothelial and red blood cell metabolism and function in diabetes.

Abstract

Cardiovascular complications are the leading cause of morbidity and mortality in individuals with diabetes, yet strategies that reduce cardiovascular disease (CVD) risk beyond glycemic control remain limited. Endothelial cells and red blood cells (RBCs) become dysfunctional under diabetes-associated hyperglycemia, partly due to increased oxidative stress and impaired vasodilation. These effects may be further influenced by interactions between RBCs and endothelial cells through extracellular vesicles (EVs), which can transfer bioactive cargo that alters endothelial function. Glutamine, the most abundant amino acid in the body, is reduced in individuals with diabetes and has reported antioxidant and anti-inflammatory effects. However, its impact on endothelial cells and diabetic RBCs remains poorly understood. In this thesis, the impact of glutamine on endothelial cells and RBCs was investigated. I showed that glutamine supplementation increased NADPH production and glutathione synthesis in endothelial cells under both normal and hyperglycemic conditions, thereby reducing oxidative stress. Glutamine also systemically altered endothelial metabolism by increasing oxidative respiration, succinate dehydrogenase activity, and UDP-GlcNAc synthesis, while decreasing polyunsaturated fatty acids and one-carbon metabolites. In contrast, RBCs from diabetic subjects showed similar basal ROS levels compared to controls but exhibited reduced antioxidant capacity, evidenced by lower intracellular glutamate and a greater increase in oxidative stress following oxidant exposure. Glutamine supplementation did not improve RBC oxidative stress or enhance glutathione synthesis. Finally, mechanically generated RBC-EVs from diabetic and non-diabetic subjects did not induce oxidative stress or inflammation in endothelial cells, highlighting the potential impact of EV generation methods on their pathological effects. This work increases our understanding of how glutamine impacts endothelial cells and RBCs and suggests that glutamine supplementation alone may have limited beneficial effects. Instead, metabolic engineering of glutamine-related pathways in both endothelial cells and RBCs may be required to optimize therapeutic strategies for CVD.