Hyperglycemia-Induced Metabolic Reprogramming Mediates a Proatherogenic Phenotype in Healthy Human Monocytes

Abstract

Introduction: Poor glycemic control is considered an important contributor to cardiovascular disease in patients with diabetes. Episodic hyperglycemia as a surrogate for glycemic variability promotes monocyte adhesion and increases the prevalence of proinflammatory monocytes within atherosclerotic plaques of patients with diabetes. We previously found that acute hyperglycemia-induced a pro-inflammatory phenotype and promoted the development of foamy monocytes by increasing total cholesterol deposition, cholesterol ester, and free cholesterol content by enhancing oxidized LDL uptake. However, the mechanism by which acute hyperglycemia induces monocyte cholesterol deposition and inflammation remains unknown. Methods: Monocytes isolated from healthy individuals (age range 20–40; n=5) were cultured in low (5mM) or high (16.7mM) glucose conditions with or without a glycolysis inhibitor (2-deoxyglucose, 2DG, 5 mM) or an endoplasmic reticulum stress inhibitor (4-phenylbutyric acid, PBA; 20mM) for 6 hrs. After treatment, cytokine release, oxidized LDL uptake, and metabolic assays using Seahorse Technology were performed. Results: Healthy human monocytes exposed under high glucose conditions showed a pro-atherosclerotic phenotype with higher levels of the pro-inflammatory cytokines, TNFα(median of differences 6.34 pg/ml, p=0.002) and IL1β(12.04 pg/ml, p=0.003), and increased oxidized LDL uptake (5062ug Dil-Ox LDL/mg, p=0.001). Furthermore, hyperglycemia resulted in higher levels of glycolysis (basal glycolysis 12.94 pmol/min, p=0.01; basal proton efflux rate 15.5 pmol/min, p=0.03) and mitochondrial respiration (percentage of respiratory capacity 16pmol/min p=0.04), suggesting a significant alteration in the metabolic programming of these monocytes. Treatment with 2-DG or PBA attenuated the pro-atherosclerotic phenotype induced by hyperglycemia, promoting a reduction of cytokine release, a reduction of oxidized LDL uptake, and near normalization of the glycolic rate and mitochondrial respiration, stabilizing cellular bioenergetics. Conclusions: Altogether, our results suggest that monocyte ER stress in response to acute hyperglycemia promotes a hypermetabolic state characterized by a proinflammatory and proatherogenic monocyte phenotype. Therefore, acute hyperglycemia is a potential mechanism promoting atherosclerosis in patients with type 2 diabetes.