Up-regulation of PAI-1 synthesis by insulin and proinsulin in HEP G2 cells but not in endothelial cells

Abstract

Summary Increased plasminogen activator inhibitor 1 (PAI-1) plasma levels have been described in patients with ischemic heart disease. Although the regulation of PAI-1 production is still not completely understood, the important role of metabolic factors has been suggested. Clinical and biochemical changes found in the ‘syndrome X’ are significantly correlated to plasma PAI-1 levels. Intact proinsulin and its derivates have been observed in plasma and shown to possess immunological reactivity similar to that of insulin in conventional radioimmunoassay. PAI activity has been shown in diabetic patients to better correlate with plasma levels of proinsulin and split products than with insulin. These data question the existing relationship between insulin, proinsulin, and cellular PAI-1 production. We have compared the effect of insulin and proinsulin on PAI-1 synthesis by Hep G2 cells, and endothelial cells from human umbilical vein and porcine aorta. Our results indicated that proinsulin and insulin increased PAI-1 synthesis by Hep G2 cells. Nevertheless the proinsulin-induced up-regulation always represented 2 to 4% of the insulin's effect, on a molar basis. Conversely to previous reports we cannot demonstrate an effect of proinsulin or insulin on PAI-1 synthesis by endothelial cells irrespective of their origin. Therefore, in so far as in vitro results can be extrapolated to the in vivo situation in insulin resistant patients, and in so far as insulin and precursors play a role in PAI-1 synthesis regulation in these patients, elevated PAI-1 levels observed in insulin resistant and/or coronary heart disease patients might be the result of increased synthesis of PAI-1 localized at the hepatocyte level.