Advances in diabetes for the millennium: diabetes and the endothelium

The normal endothelium performs the function of vasodilation, platelet inhibition, and the suppression of inflammation through the secretion of nitric oxide (NO) and prostacyclin (PGI2). Endothelial damage through diabetes, hypercholesterolemia, and other atherosclerotic risk factors results in the reduction of NO and PGI2 synthesis and secretion; and these changes turn the blood vessel into a proconstrictor, proaggregatory, and proinflammatory state. Because atherosclerosis is a chronic inflammation of the arterial wall, abnormal endothelial function would predispose the artery to atherogenesis and to a prothrombotic state. Recent studies have demonstrated that insulin exerts an anti-inflammatory effect in addition to inhibiting platelet aggregation and the expression of other prothrombotic factors. These facts challenge the conventional view that insulin is the mediator of atherogenesis in insulin-resistant states of obesity and type 2 diabetes, which are characterized by hyperinsulinemia. Furthermore, insulin has been shown to be anti-inflammatory, antioxidant, and profibrinolytic and cardioprotective in patients with acute myocardial infarction. Insulin is required as an anti-inflammatory hormone with potential antiatherosclerotic effects.