GLUCOSE AND INSULIN INDEPENDENTLY REDUCE THE FIBRINOLYTIC POTENTIAL OF HUMAN VASCULAR SMOOTH-MUSCLE CELLS IN CULTURE

Hyperglycaemia and hyperinsulinaemia have both been related to acceler ated atherosclerosis in non-insulin-dependent diabetes mellitus (NIDDM ). Plasma fibrinolytic potential is reduced in NIDDM and it is known t hat glucose and insulin can modulate plasminogen activator inhibitor ( PAI-1) and tissue-plasminogen activator (t-PA) secretion and can there fore regulate local fibrinolysis. Vascular smooth muscle cells (vSMC) play an important role in the development of atherosclerotic lesions; however, the role of insulin and glucose in regulating PAI-1 and t-PA production in VSMC is presently not known. Therefore, we cultured arte rial vSMC explanted from human umbilical cords and exposed them to inc reasing concentrations of glucose (5, 12, 20, 27, 35 mmol/l) or insuli n (0.1, 0.5, 1, 10 nmol/l) in a serum free medium. After 24 h, PAI-1 a nd t-PA antigens and activity were evaluated in the culture medium; in cells exposed to 20 mmol/l glucose and to 0.5 nmol/l insulin PAI-1 ge ne expression was also evaluated. An increase in PAI-1 antigen was obs erved at each glucose concentration (by 138, 169, 251 and 357% as comp ared to 5 mmol/l glucose) which was paralleled by an increase in PAI-1 activity. t-PA concentration was also increased by glucose but its ac tivity was sharply reduced. An increase in PAI-1 antigen was detected at each insulin level (by 121, 128, 156 and 300 % as compared to no in sulin). PAI-1 activity was slightly increased at the lowest insulin co ncentrations but markedly increased by 10 nmol/l insulin. t-PA antigen was also increased by insulin; however, its activity was markedly red uced at each concentration. As compared to control cells, PAI-1 mRNA w as increased by 2.5 and 2.0 fold by 20 mmol/l glucose and 0.5 nmol/l i nsulin, respectively. We conclude that in human vSMC both glucose and insulin can affect the fibrinolytic balance so as to reduce fibrinolyt ic potential. This might contribute to decreased local fibrinolysis an d thereby might accelerate the atherothrombotic process in NIDDM subje cts.