Mechanisms of Arterial Dysfunction in Type 2 Diabetes Mellitus

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Insulin contributes to the regulation of endothelial function and specifically to the production of nitric oxide (NO). In experimental models of insulin resistance, disturbances in insulin signaling lead to decreased production of NO, but this has not been established in patients with type 2 diabetes mellitus. Several potential mechanisms have emerged that may interfere with insulin signaling and consequently production of NO in patients with type 2 diabetes, including pro-inflammatory cytokines, increased concentrations of free fatty acids (FFA), and over-activity of the Rho kinase pathway. As NO is a potent anti-atherogenic molecule, preservation of NO bioactivity is an important goal in halting the development and progression of vascular disease in patients with type 2 diabetes. Accordingly, this proposal applies insights from basic biology to the clinical setting to define the mechanisms that impair vascular function and identify potential therapeutic targets that may improve vascular function in patients with type 2 diabetes. Each of the three specific aims will seek to determine mechanisms that inhibit insulin-mediated vasodilation in patients with type 2 diabetes by employing pharmacologic probes in placebo-controlled crossover trials. These will modulate FFA concentration (intralipid, acipimox), inhibit inflammation and NFKB activation via kB kinase p (salsalate), and inhibit Rho kinase activity (fasudil). Studies will employ a hyperinsulinemic, euglycemic clamp. Insulin-mediated endothelium-dependent vasodilation (by plethysmography and ultrasonography) and skeletal muscle glucose utilization (by [18F] FDG positron emission tomography) will be measured in vivo. Molecular measures of insulin-signaling (Akt and eNOS phosphorylation in biopsy specimens) will be measured ex vivo in skin biopsy specimens to investigate molecular signals that regulate vascular function. It is anticipated that findings from this investigation will uncover pathophysiologic mechanisms that account for abnormal vascular function and atherosclerosis in patients with type 2 diabetes and identify potential therapeutic targets to reduce the risk of adverse cardiovascular events.