In type 2 diabetes, rosiglitazone therapy for insulin resistance ameliorates endothelial dysfunction independent of glucose control

OBJECTIVE - Insulin resistance is an independent risk factor for arteriosclerosis and cardiovascular mortality. However, the mechanism by which insulin resistance contributes to arteriosclerosis is unknown. Conceivably, endothelial dysfunction could be involved. Therefore, we asked whether therapy for insulin resistance ameliorates any endothelial dysfunction. RESEARCH DESIGN AND METHODS - We performed a double-blind cross-over trial of 12 patients with recently diagnosed type 2 diabetes. They received rosiglitazone 4 mg b.i.d. for 12 weeks and nateglinide 60 mg b.i.d. for the same number of weeks in random order. To assess the degree of endothelial dysfunction, we used venous occlusion plethysmography. We studied vasodilation in response to acetylcholine (ACh) with and without exogenous insulin. The agents were infused into the brachial artery. Furthermore, we determined insulin resistance by euglycemic clamp. RESULTS - Glycemic control was comparable under rosiglitazone and nateglinide. Rosiglitazone ameliorated insulin resistance by 60% compared with nateglinide. ACh response was significantly increased after rosightazone treatment (maximum forearm blood flow 12.8 +/- 1.3 vs. 8.8 +/- 1.3 ml/100 ml after rosightazone and nateglinide, respectively; P < 0.05) but did not attain the level of healthy control subjects (14.0 +/- 0.7 ml/100 ml). Coinfusion of exogenous insulin increased ACh response further in the rosiglitazone group. N-monomethyl-L-arginine-acetate (L-NMMA), an antagonist of nitric oxide synthase, largely prevented the increased vasodilation after rosightazone, regardless of the presence or absence of insulin. Insulin sensitivity and blood flow response were found to be correlated (P < 0.01). CONCLUSIONS - Insulin resistance is a major contributor toward endothelial dysfunction in type 2 diabetes. Both endothelial dysfunction and insulin resistance are amenable to treatment by rosiglitazone.