Synergic effect of glucose and insulin in stimulating plasminogen activator inhibitor 1 (pai-1) expression and secretion in human vascular smooth muscle cells (vSMC)

Increased PAI-1 levels are among the causes for accelerated atherosclerosis in NIDDM. We have demonstrated that glucose and insulin could independently increase PAI-1 secretion and activity in vSMC in culture. Since NIDDM patients are often characterized by both hyperglycemia and tiyperinsulinemia, aim of this study was to observe the effect of combining insulin and glucose on PAI-1 expression and secretion in vSMC culture. Therefore, we cultured arterial vSMC explanted from human umbilical cord and exposed them to increased concentrations of glucose (5, 12, 20, 30 mM) in the absence or in the presence of 0.5 nM insulin, and to increasing concentrations of insulin (0.1, 0.5, 1.0 and 10.0 nM) in the absence or in the presence of 12 mM glucose. After 24 hrs, PAI-1 antigen levels (double antibody ELISA) in the cultured medium(CM) were measured. PAI-1 expression (Northern blot) was evaluated at 5 and 20 mM glucose (with or without 0.5 nM inulin) and at 0.1 and 0.5 insulin (with or without 12 mM glucose).Addition of 0.5 nM insulin to the CM increased glucose-induced PAI-1 secretion at each glucose concentration (by 60, 136, 130 and 110 % respectively) addition of 20 mM glucose increased PAI-1 expression by 55% without and by 125% with 0.5 nM insulin. Addition of 12 mM glucose to the CM resulted in a slight but significant increase in insulininduced PAI-1 secretion at each insulin concentration (by 5, 18, 33 and 24% respectively).0.5 nM insulin increased PAI-1 expression by 53% without and by 120% with 12 mM glucose. Glucose and insulin have a synergic effect in stimulating PAI-1 expression and secretion in vSMC.Therefor, in NIDDM, hyperinsulinemia could worsen the detrimental effect of hyperglicemia on local fibrinolysis and viceversa.