Inhibition of carboxypeptidase U (TAFIa) activity improves rt-PA induced thrombolysis in a dog model of coronary artery thrombosis

Abstract

The physiologically most important activator of intravascular fibrinolysis is tissue-type plasminogen activator (t-PA) released from endothelial cells. In man, sympathomimetic drugs increase the systemic concentration of t-PA. It is therefore of interest to investigate whether cardiac sympathetic activation can induce a local t-PA release, which could counteract intra-coronary clot formation.Thrombolytic therapy with recombinant t-PA (rt-PA) is effective in acute myocardial infarction, but the treatment is limited by a fairly slow reperfusion rate and frequent early reocclusions. A potential mechanism behind early reocclusions might be that active thrombin is released from the thrombus during thrombolytic therapy. Thrombin has recently been shown to activate procarboxypeptidase U, which in its active form (CPU) down-regulates endogenous fibrinolysis. Therefore, one way of improving thrombolytic efficacy may be to combine rt-PA with a lowmolecular weight direct thrombin inhibitor, which theoretically could have a pro-fibrinolytic effect, either by inhibition of fibrin-bound thrombin and/or by inhibition of CPU activation. An alternative way may be direct inhibition of CPU.In a porcine model, experimental activation of cardiac sympathetic nerves by electrical stimulation at 1 and 8 Hz induced 5-and 20-fold increase in the release of both total and active t-PA together with frequency-dependent increases in heart rate, blood pressure, and coronary blood flow. The t-PA release was independent of the heart rate and coronary flow response, but local infusion of isoprenaline suggested that part of the t-PA response was mediated by stimulation of β-adrenergic receptors. Next, we studied the combined effect of rt-PA and thrombin inhibitors (melagatran, hirudin and heparin) in a canine model of copper coil-induced coronary thrombosis. The profibrinolytic effect of rt-PA, either measured as patency rate or time-to-patency, was significantly enhanced with the low-molecular weight direct thrombin inhibitor melagatran, but to a lesser degree by hirudin and heparin. In the same model it was shown that active CPU is produced locally in the coronary vascular bed during both thrombus formation and clot lysis. Inhibition of thrombin attenuated CPU formation and improved patency. A similar effect was obtained with a direct inhibitor of CPU.In conclusion, the coronary t-PA response to sympathetic stimulation may constitute a thromboprotective defence mechanism to counteract its prothrombotic effects on the systemic level. Furthermore, direct thrombin and/or CPU inhibition may be potential targets for prevention of thrombus formation via facilitation of the endogenous fibrinolytic system.

Thrombin-Activatable Fibrinolysis Inhibitor Is Activated in an Instant Blood-Mediated Inflammatory Reaction After Intraportal Islet Transplant

“…5 Although definite proof of a causal relation is currently unavailable, it is reasonable to interpret this temporal profile as a rapid increase of TAFIa during the first hour after transplant, indicating that TAFIa favors islet clotting because of its antifibrinolytic activity. [13][14][15] To obviate the effects of IBMIR, some methods of regulating early coagulation, including systemic administration of anticoagulants such as heparin, melagatran, dextran sulfate, and nacystelyn, have been shown to prevent islet-induced coagulation and Hematoxylin-eosin staining of liver biopsies revealed a thrombus formation in many portal veins, some of which contained entrapped rat islets (magnification ×40).…”

The decrease in procarboxypeptidase U (TAFI) concentration in acute ischemic stroke correlates with stroke severity, evolution and outcome

“…Because proCPU is attached at the surface of the thrombus through cross ligation to fibrin by FXIIIa [3], it seems plausible that larger thrombi and thrombus growth would induce more pronounced proC-PU consumption. Additionally, a stronger decrease in proCPU concentration is indicative of more severe CPU generation, which due to its antifibrinolytic activity favours thrombus growth [3][4][5][6][7][8][9][10][11]. These underlying pathophysiological mechanisms may explain the more pronounced decrease in proCPU concentrations in patients with more severe stroke, unfavourable stroke evolution in the first 72 h and poor long-term outcome.…”

“…It can be activated by thrombin, plasmin or the thrombin/thrombomodulin complex, resulting in the active enzyme carboxypeptidase U (CPU, TAFIa), which attenuates fibrinolysis [3][4][5][6][7][8][9][10][11]. In the last years, it has become increasingly apparent from both in vivo and in vitro studies that the proCPU/CPU pathway provides an explicit molecular link between the coagulation and fibrinolytic cascades [3,[11][12][13][14][15][16][17][18].…”

Biochemical Characterization of Bovine Plasma Thrombin-Activatable Fibrinolysis Inhibitor (TAFI)

“…Interestingly, individuals with the more stable Ile 325 variant are apparently more susceptible to meningococcal sepsis [30]. TAFI has been studied in multiple animal models, including dog, rabbit, mouse, and rat [31][32][33][34][35][36]. Intriguingly, the absence of the protein in knock out mice is compatible with murine life [25,37,38].…”