Abstract 476: Attenuated Activities of Mitochondria in Vascular Endothelial Cells Exposed to Oxidized or Glycated Low Density Lipoprotein

Abstract

Hyperglycemia and dyslipoproteinemia are two major biochemical markers of diabetes. Elevated low density lipoprotein (LDL) is a classical risk factor for atherosclerotic cardiovascular disease. Our previous studies demonstrated that oxidized LDL (ox-LDL) and glycated LDL (gly-LDL) increased the generation of reactive oxygen species (ROS) in vascular endothelial cells. ROS is implicated in endothelial dysfunction and diabetic vascular complications. Mitochondria are an important source of ROS in the body. We hypothesize that ox-LDL or gly-LDL might affect the activity of mitochondrial respiratory chain. We evaluated the activities of mitochondrial respiratory chain complexes in porcine aortic endothelial cells (PAEC) using OROBORS oxygraph. The oxygraph was used as a highly sensitive tool to evaluate mitochondrial complex activity in freshly harvested and digitonin-permeabilized PAEC (for Complex I, the rotenone-sensitive oxidation of glutamate + malate in the presence of ADP; Complex II, antimycin A-sensitive oxidation of succinate; Complex IV, potassium cyanide-sensitive oxidation of ascorbate + TMPD). The oxygen consumption in Complex I, II and IV of PAEC was significantly decreased by >12 h of incubation with LDL, ox-LDL or gly-LDL compared to control cultures. Attenuated activity of succinate cytochrome C reductase was detected in EC treated with LDL, ox-LDL or gly-LDL for 24 h. Decreased levels of respiratory control ratio were detected in EC treated with LDL or ox-LDL for 6 h, but not for 2 h, compared to control. Impaired activity of mitochondrial complexes can cause electron leakage in the respiratory chain and substantially increase ROS formation. The findings suggest that oxidized or glycated LDL attenuates mitochondrial activities in vascular EC, which may contribute to increased ROS generation and endothelial dysfunction induced by the atherogenic lipoproteins (supported by operating grants from Canadian Institute of Health Research and Canadian Diabetes Association).