Thrombomodulin accelerates activated protein C production and inhibits thrombin generation in the plasma of disseminated intravascular coagulation patients.

Thrombomodulin (TM) has been under development as a medicine for disseminated intravascular coagulation (DIC), and is expected to exhibit strong anticoagulant activity by inhibiting thrombin generation via the acceleration of protein C activation. In the present study, we examined the pharmacological action of TM in plasma obtained from DIC patients. TM was found to inhibit thrombin generation and accelerate activated protein C (APC) production at 0.3-30 TM units/ml in plasma obtained from DIC patients irrespective of their underlying disorders. In addition, there was a positive correlation between the inhibition of thrombin generation and the amount of APC produced. Thrombin generation was inhibited by over 50% when the plasma level of APC was increased by more than 0.2 microg/ml. These results indicate that TM inhibits thrombin generation in plasma obtained from DIC patients by accelerating APC production. Moreover, the results imply that the thrombin generation test may be a good method to speculate the efficacy of TM on every patient before the administration of TM.     

The renin-angiotensin system is involved in the production of plasminogen activator inhibitor type 1 by cultured endothelial cells in response to chylomicron remnants.

Triglyceride-rich lipoproteins have been suggested to promote atherosclerosis. Plasminogen activator inhibitor type 1 (PAI-1) plays an important role in the events of cardiovascular pathophysiology. The renin-angiotensin system influences various vascular functions, including PAI-1 production. We examined whether or not chylomicron remnants increased PAI-1 mRNA and protein production in endothelial cells and whether or not an inhibition of the renin-angiotensin system interfered with this effect. Chylomicron remnants were isolated from functionally hepatectomized rats injected with chylomicrons. Human umbilical vein endothelial cell cultures (HUVECs) were incubated with chylomicron remnants with or without an angiotensin-converting enzyme inhibitor (temocaprilat), an angiotensin II receptor type 1 antagonist (RNH-6270), or an angiotensin II receptor type 2 antagonist (PD123319). Chylomicron remnants increased PAI-1 secretion in HUVECs (0.5 microg/ml; 128.3 +/- 6.1%, the mean +/- SEM) as well as angiotensin II (10 nmol/l; 130.7 +/- 9.5%) in 18 h, as compared with the controls, as well as stimulated PAI-1 mRNA expression to a maximum level at 4 h. Temocaprilat and RNH-6270, but not PD123319, attenuated all of these effects. Chylomicron remnants enhanced nuclear extract binding to a very low-density lipoprotein response element in the PAI-1 promoter region and activated nuclear factor-kappaB. Extracellular signal-regulated kinase (ERK 1/2) was phosphorylated in response to chylomicron remnants. These effects were inhibited by temocaprilat or RNH-6270. In conclusion, chylomicron remnants increased protein secretion and mRNA expression of PAI-1 in HUVECs. Inhibition of the renin-angiotensin system reduced this stimulation.