Glucose and insulin independently reduce the fibrinolytic potential of human vascular smooth muscle cells in culture

Abstract

Hyperglycaemia and hyperinsulinaemia have both been related to accelerated atherosclerosis in non-insulin-dependent diabetes mellitus (NIDDM). Plasma fibrinolytic potential is reduced in NIDDM and it is known that glucose and insulin can modulate plasminogen activator inhibitor (PAI-1) and tissue-plasminogen activator (t-PA) secretion and can therefore 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 arterial vSMC explanted from human umbilical cords and exposed them to increasing concentrations of glucose (5, 12, 20, 27, 35 mmol/l) or insulin (0.1, 0.5, 1, 10 nmol/l) in a serum free medium. After 24 h, PAI-1 and 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 gene expression was also evaluated. An increase in PAI-1 antigen was observed at each glucose concentration (by 138, 169, 251 and 357% as compared 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 activity 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 insulin). PAI-1 activity was slightly increased at the lowest insulin concentrations but markedly increased by 10 nmol/l insulin. t-PA antigen was also increased by insulin; however, its activity was markedly reduced at each concentration. As compared to control cells, PAI-1 mRNA was increased by 2.5 and 2.0 fold by 20 mmol/l glucose and 0.5 nmol/l insulin, respectively. We conclude that in human vSMC both glucose and insulin can affect the fibrinolytic balance so as to reduce fibrinolytic potential. This might contribute to decreased local fibrinolysis and thereby might accelerate the atherothrombotic process in NIDDM subjects.

Elevated Levels of Acute-Phase Proteins and Plasminogen Activator Inhibitor-1 Predict the Development of Type 2 Diabetes

“…It may be noteworthy that previous reports (including the present one) have shown a weaker cross-sectional relation of PAI-1 to glycemia as compared with body weight, insulinemia, and insulin resistance. It has been suggested that glucose (as well as insulin) may regulate PAI-1 gene expression in vascular smooth muscle cells (24). However, it should be noted that the associations as shown do not necessarily reflect causality.…”

Selective Insulin Resistance Affecting Nitric Oxide Release But Not Plasminogen Activator Inhibitor-1 Synthesis in Fibroblasts From Insulin-Resistant Individuals

“…In vascular wall cells, insulin has been shown to be able to increase leukocytes adhesion molecule expression, 7 endothelin synthesis, 8 vascular smooth cells migration, 6 and PAI-1 transcription and release. 9 All these effects can be considered as proatherogenic. However, several insulin actions can be viewed as antiatherogenic, such as the NOdependent insulin-mediated vasodilation.…”

Advanced glycation endproducts inhibit prostacyclin production and induce plasminogen activator inhibitor-1 in human microvascular endothelial cells

“…The amounts of immunoreactive PAI-1 released into media were measured by ELISA (Imulyse PAI-1; Biopool, Umea Ê , Sweden), according to the supplier's recommendation. Since PAI-1 complexed to u-PA or t-PA is scarcely detectable by this method, the values represent free PAI-1 levels [26]. To determine the biological activity of PAI-1, EC were treated with serum-free medium in the presence or absence of 50 mg/ml AGE for 24 h. Then, the conditioned medium was assayed for anti-fibrinolytic activity in the presence of u-PA (3.8 units/ml), 20 mg/ml plasminogen and the chromogenic plasmin substrates (60 mmol/l D-Val-Leu-Lys p -nitroanilide).…”