Constitutive biosynthesis of plasminogen activator inhibitor type-1 (PAI-1) by cultured human aortic endothelial cells independent of insulin

BACKGROUNDBoth tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor type-1 (PAI-1) are synthesized by vascular endothelium, whereas hepatocytes synthesize PAI-1 but not t-PA. Non-insulin-dependent diabetes mellitus (NIDDM) is associated with decreased fibrinolytic activity in blood secondary to increased PAI-1 activity, and the increase in PAI-1 activity is correlated with the magnitude of elevation of plasma immunoreactive insulin. To determine whether the increased PAI-1, known to be associated with accelerated coronary artery disease in non-diabetic subjects, is a consequence of direct effects of insulin on endothelial cells, we performed the present study with primary cultures of human aortic endothelial cells. METHODSEndothelial cells isolated from human aortas from donor hearts for transplantation were grown to confluence and exposed to selected concentrations of agonists. Accumulation of t-PA and PAI-1 in conditioned media was quantified, as was PAI-1 activity. RESULTSInsulin at pharmacologic concentrations did not alter either PAI-1 or t-PA production by the human aortic endothelial cells, although insulin stimulated PAI-1 synthesis in human hepatoma (Hep G2) cells as expected. Transforming growth factor-β (TGF-β) stimulated endothelial cell PAI-1 production markedly, indicating that the cells could respond positively to stimulation in vitro. PAI-1 activity in the conditioned media was zero under all conditions, which was indicative of the rapid inactivation and degradation of PAI-1 known to occur in media devoid of vitronectin. CONCLUSIONSThe decreased fibrinolytic activity in blood seen in patients with NIDDM appears to reflect direct effects of insulin or its precursor on hepatocytes rather than on endothelial cells