Progressive LDL Reduction to Very Low Levels Improves Dimeric Nitric Oxide Synthase, Nitric Oxide Bioavailability and Reduces Peroxynitrite in Endothelial Cells during Hyperglycemia

Abstract

Circulating levels of glucose and LDL influence Endothelial Cell (EC) function in a highly interactive manner as evidenced by nitric oxide production and coupling of endothelial Nitric Oxide Synthase (eNOS) dimer. Here, we report on the status of eNOS function in Human Umbilical Vein Endothelial Cells (HUVECs) cultured under normo- and hyperglycemic (250 mg/dL) condition followed by exposure to increasing LDL concentrations (10-150 mg/dL). Production of bioavailable, cytoprotective NO and cytotoxic peroxynitrite (ONOO^-) were measured in endothelium with nanosensors. Coupling efficiency of dimeric eNOS was measured using immunochemistry. The ratio of cytoprotective NO and cytotoxic ONOO^- concentrations ([NO]/[ONOO^-]) was used as a marker for eNOS and endothelial function. The normal ratio for [NO]/[ONOO^-] is 2.5-5.0. A ratio of 1.0 or below is an indicator of modest to severe endothelial dysfunction. Under normoglycemic conditions (up to 100 mg/dL glucose) [NO]/[ONOO^-] can reach the 0.50 value with the LDL concentration of about 110 mg/dL, while in hyperglycemia (250 mg/dL glucose), the 0.50 value was reached at about 50 mg/dL. Reduction of LDL down to 50 mg/dL, in hyperglycemia, helps prevent severe dysfunction in endothelium by enhancing eNOS dimerization, increasing NO production and decreasing the concentration of cyctotoxic ONOO^-, which may significantly reduce CV risk factors.