Insulin resistance and thrombosis: a cardiologist's view.

Atherogenesis in the vasculature is accelerated by changes in the dynamic equilibrium between endogenous tissue plasminogen activator and plasminogen activator inhibitor-1 (PAI-1). Increased expression of PAI-1, decreased expression of tissue plasminogen activator, or both can lead to decreased fibrinolytic activity and predispose to thrombosis. Increased concentrations of insulin (and proinsulin) in the plasma increase plasma PAI-1, although the mechanisms of this effect are not known. In addition, it has been observed that basal fibrinolytic activity is decreased in patients with type 2 diabetes; this may accelerate atherosclerosis by exposing vascular luminal wall surfaces to persistent and recurrent thrombi. Abnormalities in the vessel wall appear to contribute to the increased risk. There is also evidence that PAI-1 content is increased in atherosclerotic lesions of patients with type 2 diabetes, suggesting that interventions to reduce insulin resistance and improve glycemic control may improve the fibrinolytic response. Clinical studies in patients with polycystic ovary syndrome (characterized by insulin resistance, hyperinsulinemia, ovarian androgen overproduction, and impaired fibrinolytic capacity) demonstrated that treatment with troglitazone, an insulin-sensitizing agent, can markedly reduce blood levels of PAI-1. There is also clinical evidence that these agents may contribute to regression of intimal medial thickness in patients with type 2 diabetes, providing further indication that antidiabetic interventions may help inhibit the progression of early atherosclerotic lesions.