Diabetes is a common disorder associated with significant clinical sequelae, including atherosclerosis. Up to three-fourths of all deaths among diabetics are due to coronary heart disease (CHD) and risk factors for CHD are particularly prevalent in diabetics. Despite this observation, epidemiologic data suggest that traditional risk factors for atherosclerosis explain only 25% of the excess CHD in diabetes. This project is based on the hypothesis that the increased incidence of CHD in diabetes is due, in part, to accelerated atherogenic modification of low-density lipoprotein (LDL) by oxidation. The objective of this project, therefore, is to determine the mechanism(s) of excess LDL oxidation in diabetes. We will pursue this objective by examining the role in LDL oxidation of two cardinal features of diabetes, hyperglycemia and dyslipidemia. We will first characterize the effect(s) of glucose on the LDL particle that may impair its resistance to oxidation. Three different systems of LDL oxidation will be investigated: metal ions (Cu2+, Fe3+), aqueous peroxyl radicals, and cultured vascular cells in order to gain insight into the mechanism(s) responsible for a glucose effect. Mechanism(s) will be identified by measuring the effects of glucose on metal ion binding to and reduction by LDL, and assessing the role of preformed lipid hydroperoxides and specific reactive oxygen species in LDL oxidation. We will next determine if known glucose-mediated effects on vascular cell metabolism result in enhanced cellular LDL oxidation. Effects of glucose on the cellular capacity to modify LDL will be characterized by exploring relevant mechanisms (i.e., cellular production of superoxide, nitric oxide [NO], reduced thiol, and cellular reduction of transition metal ions) and the signaling processes involved. Since vascular cell dysfunction caused, in part, by oxidized LDL (ox-LDL) is also important in the pathophysiology of atherosclerosis, we will characterize the effect of glucose on specific cellular responses to ox-LDL, including endothelial cell NO production and, monocyte adhesion, and macrophage uptake of ox-LDL. In the final aim of this project, we will investigate the effects of diabetes-related dyslipidemia on LDL oxidation. Specifically, we will determine LDL compositional changes that are associated with diabetic dyslipidemia and relate these changes to LDL oxidative resistance. Relevant findings from these experiments will be modeled using reconstituted LDL to identify molecular mechanisms. In this manner, we anticipate identifying the precise mechanism(s) of excess LDL oxidation in diabetes, which may result in novel treatments for diabetic vascular disease.
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