Activated protein C decreases plasminogen activator-inhibitor activity in endothelial cell-conditioned medium

Abstract

Confluent cultures of endothelial cells from human umbilical cord were used to study the effect of activated human protein C (APC) on the production of plasminogen activators, plasminogen activator-inhibitor, and factor VIII-related antigen. Addition of APC to the cells in a serum-free medium did not affect the production of tissue-type plasminogen activator (t-PA) or factor VIII-related antigen; under all measured conditions, no urokinase activity was found. However, less plasminogen activator-inhibitor activity accumulated in the conditioned medium in the presence of APC. This decrease was dose dependent and could be prevented by specific anti-protein C antibodies. No decrease was observed with the zymogen protein C or with diisopropylfluorophosphate-inactivated APC. APC also decreased the t-PA inhibitor activity in endothelial cell-conditioned medium in the absence of cells, which suggests that the effect of APC is at least partly due to a direct effect of APC on the plasminogen activator- inhibitor. High concentrations of thrombin-but not of factor Xa or IXa-- had a similar effect on the t-PA inhibitor activity. The effect of APC on the plasminogen activator-inhibitor provides a new mechanism by which APC may enhance fibrinolysis. The data suggest that activation of the coagulation system may lead to a secondary increase of the fibrinolytic activity by changing the balance between plasminogen activator(s) and its (their) fast-acting inhibitor.

The effects of activated protein C and prostacyclin on arterial oxygenation and protein leakage in the lung and the gut under endotoxaemia in the rat

“…A randomized blinded study showed a reduction in mortality in septic patients (25). The anti‐inflammatory and microcirculatory effects of APC (10–14) may also indirectly counteract an increase in permeability, thus contributing to the apparent reduction of protein leakage in the gut. The ability of APC to cause an increase in the synthesis of PGI 2 through upregulation of COX‐2 synthesis (15, 18) may be of special interest in the context of the present study.…”

“…APC has anti‐thrombotic properties through its inhibition of activated factors V and VIII (10, 11), and from its pro‐fibrinolytic properties through inhibition of the plasminogen activator–inhibitor 1 (12, 13). APC may have direct anti‐inflammatory action – from its interaction with the APC receptor on the endothelium, on immune cells, and on epithelial cells of the airway.…”

Hypoxia induces procoagulant activity in cultured human venous endothelium

“…In addition, it will inactivate factor VIIIa, prevent conversion of VIII to VIIIa, and also possibly neutralize plasminogen activator inhibitor. 26 Other direct endothelial products affecting thrombus formation include tissue-type and urokinase-like plasminogen activator as well as plasminogen activator-inhibitor as mentioned above. Plasminogen activator-inhibitor is one of the major protein products of the endothelial cell and plays a major role in preventing ongoing fibrinolysis, which obviously poses a threat equal to unregulated throm-bosis} a…”

Antiphospholipid syndrome: multiple mechanisms

“…An important modulator of this process is plasminogen activator inhibitor (PAI), which is another endothelial‐derived protein. Activated protein C has been shown to decrease the PAI activity of cultured EC, and may therefore act indirectly as a promoter of fibrinolysis [63,64]. Thus the binding of antibodies to protein C could impair clot degradation.…”