Cardiovascular risk continuum: implications of insulin resistance and diabetes

Although low-density lipoprotein (LDL) cholesterol is a critically important factor in the development of atherosclerosis, nearly half the patients with coronary artery disease have LDL cholesterol levels within the National Cholesterol Education Program (NCEP) guidelines. Therefore, attention has focused on other modifiable risk factors that could strongly impact the development of coronary artery disease. Type 2 diabetics have a 3-fold increased risk of coronary artery disease; prediabetics, without chronic hyperglycemia, have a 2-fold increased risk compared with normal subjects. Insulin resistance has also been implicated as the cause of atherosclerosis. Insulin resistance is associated with hyperinsulinemia and a constellation of other factors, some of which are themselves independent risk factors for coronary artery disease. These include reduced levels of high-density lipoprotein (HDL) cholesterol, hypertriglyceridemia, increased small dense LDL particles, hypertension, visceral obesity, and increased levels of plasminogen activator inhibitor-1 (PAI-1). Hyperinsulinemia and insulin resistance at the vascular level also may contribute to vascular injury and the atherosclerotic process. Current studies suggest that controlling hyperglycemia, LDL cholesterol, and blood pressure are important to protect the diabetic from atherosclerosis. A key question, particularly in type 2 diabetes, is to define the best regimen for glucose control that will protect the vasculature. Sulfonylureas, metformin, and troglitazone have direct vascular actions. Metformin lowers LDL cholesterol and triglycerides, while troglitazone reverses many of the components associated with the insulin resistance syndrome. Clinical trials focusing on coronary artery disease outcomes are now warranted to prevent coronary artery disease, the major vascular complication and cause of mortality in diabetes.