Endothelium, inflammation, and diabetes

The normal endothelium produces a number of vasodilator substances such as nitric oxide (NO) and prostacyclin (PGI2) that regulate vasomotor tone, reduce platelet aggregation, and inhibit the recruitment and activity of inflammatory cells. The functions of vascular endothelial cells are disturbed in diabetic patients. The major cause for mortality and a great percent of morbidity in patients with diabetes mellitus is atherosclerosis. Insulin has recently been shown to stimulate NO release and the expression of NO synthase by the endothelium. Insulin is thus a vasodilator, has anti-platelet activity, and now has been shown to be anti-inflammatory and thus, potentially anti-atherogenic. Similar anti-inflammatory effects of thiazolidenediones (TZDs), troglitazone, and rosiglitazone suggest that they too may have potential anti-atherogenic effects. These effects of insulin and TZDs are of importance since the two major states of insulin resistance, obesity and type 2 diabetes, are associated with a marked increase in atherosclerosis, coronary heart disease, and stroke. These recent observations have extremely important implications for the understanding of the pathogenesis of atherosclerosis in insulin-resistant states and for a rational approach to their comprehensive treatment, including the prevention of atherosclerosis and its complications. This review challenges the previously proposed hypothesis that hyperinsulinemia represents a common pathophysiological pathway of diabetic complications and advances our hypothesis that insulin, through its effect on the endothelium, leucocytes, and platelets, has anti-inflammatory and thus potentially anti-atherogenic properties. Furthermore, through its anti-inflammatory effects, its use improves clinical outcomes in at least two clinical states characterized by profound inflammation-acute myocardial infarction and sepsis.