Mechanism of protein C-dependent clot lysis: role of plasminogen activator inhibitor

Abstract

The mechanism by which activated protein C stimulates fibrinolysis was studied in a simple radiolabeled clot lysis assay system containing purified tissue-type plasminogen activator, bovine endothelial plasminogen activator inhibitor (PAI), plasminogen, 125I-fibrinogen and thrombin. Fibrinolysis was greatly enhanced by the addition of purified bovine activated protein C; however, in the absence of PAI, activated protein C did not stimulate clot lysis, thus implicating this inhibitor in the mechanism. In clot lysis assay systems containing washed human platelets as a source of PAI, bovine-activated protein C-dependent fibrinolysis was associated with a marked decrease in PAI activity as detected using reverse fibrin autography. Bovine-activated protein C also decreased PAI activity of whole blood and of serum. In contrast to the bovine molecule, human-activated protein C was much less profibrinolytic in these clot lysis assay systems and much less potent in causing the neutralization of PAI. This species specificity of activated protein C in clot lysis assays reflect the known in vivo profibrinolytic species specificity. When purified bovine-activated protein C was mixed with purified PAI, complex formation was demonstrated using immunoblotting techniques after polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. These observations suggest that a major mechanism for bovine protein C- dependent fibrinolysis in in vitro clot lysis assays involves a direct neutralization of PAI by activated protein C.

Viscoelastic and aggregometric point‐of‐care testing in patients with septic shock – cross‐links between inflammation and haemostasis

“…Thrombomodulin usually binds thrombin with subsequent loss of its procoagulant activity as well as activating protein C. aPC represents a potent inactivator of FVa and FVIIIa . Moreover, aPC enhances fibrinolysis by neutralisation of plasminogen activator inhibitor type‐1 . Therefore, a loss of aPC activity leads to impaired fibrin removal due to an inhibition of the fibrinolytic system.…”

Extrahepatic Expression and Regulation of Protein C in the Mouse

“…4 It may also stimulate fibrinolysis 4 by reducing the activity of plasminogen activator inhibitor-1. 5,6 The physiological importance of PC is demonstrated by the observations that life-threatening thrombotic complications occur in infants with homozygous PC deficiency, 7 and that patients with heterozygous PC deficiency have a high incidence of venous thrombosis. 8 Moreover, administration of neutralizing monoclonal antibodies to PC induces thrombosis in mice, 9 and infusion of APC prevents the lethal effects of Escherichia coli in baboon models of Gram-negative sepsis 10 and is an effective treatment for certain forms of human septic shock.…”

A review of hyperfibrinolysis in cats and dogs

“…TAFI decreases plasminogen activation; attenuates positive feedback from plasmin; and, at high concentrations, also directly inhibits plasmin (Mosnier & Bouma 2006, Foley et al 2013. The anticoagulant, pro-fibrinolytic enzyme activated protein C neutralises PAI-1 and attenuates the production of TAFI (Sakata et al 1986, Bajzar et al 1996.…”