Impaired non-esterified fatty acid suppression is associated with endothelial dysfunction in insulin resistant subjects

In a recent study, we found a significant association between insulin resistance (IR) and disturbed flow-associated (endothelial-dependent) vasodilation in first-degree relatives of subjects with type 2 diabetes. However, the mechanisms linking insulin resistance and endothelial dysfunction (ED) have not been fully elucidated. Experimental data have pointed out that non-esterified fatty acids (NEFA) have a modulating effect on NO-synthase activity, and therefore on endothelial function. The aim of our study was to evaluate whether insulin resistance associated impaired NEFA suppression is present in subjects with ED. We examined 53 first-degree relatives (FDR) of patients with type 2 diabetes (32 f, 21 m, mean age 35 years). Endothelial function was measured as flow-associated vasodilation (FAD%) of the brachial artery. Insulin sensitivity was evaluated with a standard hyperinsulinemic glucose clamp (insulin infusion rate of 1 mU/kg/min). While under fasting conditions, NEFA did not differ between groups with high or low FAD (0.415 +/- 0.033 vs. 0.394 +/- 0.040 mmol/l; p = n.s.), reduced FAD% was significantly associated with higher non-esterified fatty acids concentrations during steady state of the glucose clamp (0.072 +/- 0.022 vs. 0.039 +/- 0.016 mmol/l; p = 0.04). This association was independent of insulin levels under fasting conditions and during the glucose clamp. in conclusion, our results reveal a significant association between endothelial dysfunction and impaired nonesterified fatty acid suppression in insulin resistant subjects. As insulin resistance of lipolysis is a feature of the insulin resistance syndrome, these results suggest that elevated NEFA concentrations could play a role linking endothelial dysfunction and insulin resistance in vivo.