Alpha 2-antiplasmin supplementation inhibits tissue plasminogen activator-induced fibrinogenolysis and bleeding with little effect on thrombolysis.

Weitz, Jeffrey I.; Leslie, Beverly A.; Hirsh, Jack; Klement, Petr

doi:10.1172/jci116335

Cited by 51 publications

(48 citation statements)

References 30 publications

(27 reference statements)

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“…5F). These results indicate that CPB inhibitors enhance fibrinolysis on the surface of clots (Bouma and Meijers, 2003), whereas effective doses of tPA directly activate plasminogen in circulating blood (Weitz et al, 1993). These results might be related to the low level of bleeding seen with EF6265 in vivo (Fig.…”

Section: Discussionmentioning

confidence: 84%

Enhancement of Fibrinolysis by EF6265 [(S)-7-Amino-2-[[[(R)-2-methyl-1-(3-phenylpropanoylamino)propyl]hydroxyphosphinoyl] methyl]heptanoic Acid], a Specific Inhibitor of Plasma Carboxypeptidase B

Suzuki¹,

Muto²,

Fushihara³

et al. 2004

J Pharmacol Exp Ther

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Plasma procarboxypeptidase B, also known as thrombin-activatable fibrinolysis inhibitor (TAFI), is converted by thrombin into the active enzyme, carboxypeptidase B (CPB)/activated TAFI. Plasma CPB down-regulates fibrinolysis by removing carboxy-terminal lysines, the ligands for plasminogen and tissue-type plasminogen activator (tPA), from partially degraded fibrin. To target thrombosis in a new way, we have identified and optimized a phosphinic acid-containing inhibitor of CPB,heptanoic acid] and determined both the pharmacological profile and pathophysiological role of CPB in rat thrombolysis. EF6265 specifically inhibited plasma CPB activity with an IC 50 (50% inhibitory concentration) of 8.3 nM and enhanced tPA-mediated clot lysis in a concentrationdependent manner. EF6265 decreased detectable thrombi (percentage of glomerular fibrin deposition; control, 98 Ϯ 1.1; EF6265, 0.1 mg/kg, 27 Ϯ 9.1) that had been generated by tissue factor in a rat microthrombosis model with concomitant increases in plasma D-dimer concentration (control, Ͻ0.5 g/ml; EF6265, 0.1 mg/kg, 15 Ϯ 3.5 g/ml). EF6265 reduced plasma ␣2-antiplasmin activity to a lesser extent than tPA. In an arteriovenous shunt model, EF6265 (1 mg/kg) enhanced exogenous tPA-mediated thrombolysis under the same conditions that neither EF6265 nor tPA (600 kIU/kg) alone reduced thrombi. EF6265 (1 and 30 mg/kg) did not affect the bleeding time in rats. Moreover, it did not prolong the bleeding time evoked by tPA (600 kIU/kg). These results confirm that circulating procarboxypeptidase B functions as a fibrinolysis inhibitor's zymogen and validates the use of CPB inhibitors as both an enhancer of physiological fibrinolysis in microcirculation and as a novel adjunctive agent to tPA for thromboembolic diseases while maintaining a small effect on primary hemostasis.Thrombosis-related diseases, including myocardial infarction, cerebral infarction, and disseminated intravascular coagulation are life-threatening and the search for treatments remains challenging. Although thrombolytics including tissue-type plasminogen activator (tPA) or urokinase-type plasminogen activator and anticoagulants including heparin have been developed over the last few decades, the risk of hemorrhaging with these antithrombotic agents restricts their clinical use. The dose of tPA must be high enough to overcome the inhibitory effects of plasminogen activator inhibitor-1 in the plasma, and results in the generation of plasmin in circulating blood (Rijken and Sakharov, 2001). Consequently, these large quantities of generated plasmin can induce thrombolysis and result in hemorrhaging as a side effect (Bloom et al., 1988). Many efforts have therefore been made to identify and develop pharmacologically distinct antithrombotic agents while maintaining a low risk of hemorrhaging.Plasma procarboxypeptidase B (proCPB; EC 3.4.17.20), also known as thrombin-activatable fibrinolysis inhibitor (TAFI) or procarboxypeptidase U, is produced in the liver and Article, publication date, and citation informa...

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Section: Discussionmentioning

confidence: 84%

Enhancement of Fibrinolysis by EF6265 [(S)-7-Amino-2-[[[(R)-2-methyl-1-(3-phenylpropanoylamino)propyl]hydroxyphosphinoyl] methyl]heptanoic Acid], a Specific Inhibitor of Plasma Carboxypeptidase B

Suzuki¹,

Muto²,

Fushihara³

et al. 2004

J Pharmacol Exp Ther

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“…1) were compared by incubating them in plasma in the absence or presence of a plasma clot and measuring B␤1-42 generation as a sensitive index of fibrinogenolysis. Based on our previous work demonstrating that (DD)E-mediated stimulation of systemic plasminogen activation compromises the fibrin specificity of t-PA (12,14,28,29), we examined the possibility that differences in fibrin specificity of the activators reflect the extent to which they are stimulated by (DD)E or Fg. To accomplish this, we compared the kinetics of Pg activation by t-PA to that of the TNK variants in the presence of fibrin, (DD)E, or Fg and determined the affinities of the activators for these fibrin(ogen) derivatives.…”

mentioning

confidence: 99%

Identification of the Mechanism Responsible for the Increased Fibrin Specificity of TNK-Tissue Plasminogen Activator Relative to Tissue Plasminogen Activator

Stewart¹,

Fredenburgh²,

Leslie³

et al. 2000

Journal of Biological Chemistry

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TNK-tissue plasminogen activator (TNK-t-PA), a bioengineered variant of tissue-type plasminogen activator (t-PA), has a longer half-life than t-PA because the glycosylation site at amino acid 117 (N117Q, abbreviated N) has been shifted to amino acid 103 (T103N, abbreviated T) and is resistant to inactivation by plasminogen activator inhibitor 1 because of a tetra-alanine substitution in the protease domain (K296A/H297A/R298A/R299A, abbreviated K). TNK-t-PA is more fibrin-specific than t-PA for reasons that are poorly understood. Previously, we demonstrated that the fibrin specificity of t-PA is compromised because t-PA binds to (DD)E, the major degradation product of cross-linked fibrin, with an affinity similar to that for fibrin. To investigate the enhanced fibrin specificity of TNK-t-PA, we compared the kinetics of plasminogen activation for t-PA, TNK-, T-, K-, TK-, and NK-t-PA in the presence of fibrin, (DD)E or fibrinogen. Although the activators have similar catalytic efficiencies in the presence of fibrin, the catalytic efficiency of TNK-t-PA is 15-fold lower than that for t-PA in the presence of (DD)E or fibrinogen. The T and K mutations combine to produce this reduction via distinct mechanisms because T-containing variants have a higher K M , whereas K-containing variants have a lower k cat than t-PA. These results are supported by data indicating that T-containing variants bind (DD)E and fibrinogen with lower affinities than t-PA, whereas the K and N mutations have no effect on binding. Reduced efficiency of plasminogen activation in the presence of (DD)E and fibrinogen but equivalent efficiency in the presence of fibrin explain why TNK-t-PA is more fibrin-specific than t-PA. Tissue-type plasminogen activator (t-PA)1 is a trypsin-like serine protease that initiates fibrinolysis by converting plasminogen (Pg) to plasmin (1). Plasmin then solubilizes fibrin, yielding fibrin degradation products. Through a positive feedback mechanism, fibrin enhances its own degradation by stimulating t-PA-mediated Pg activation (2). To enhance this reaction, fibrin binds t-PA and Pg, thereby increasing the catalytic efficiency of t-PA-mediated Pg activation 1000-fold over that in the absence of fibrin (2-6). In contrast to the potent stimulatory effect of fibrin, fibrinogen (Fg) produces only modest enhancement in the catalytic efficiency of Pg activation by t-PA (2, 7, 8). Because it preferentially activates Pg in the presence of fibrin rather than Fg, t-PA is designated a fibrin-specific plasminogen activator. Despite its apparent fibrin specificity, t-PA causes systemic fibrinogenolysis and ␣ 2 -antiplasmin consumption when given to patients (9, 10). Recently, we demonstrated that the fibrin specificity of t-PA is compromised because (DD)E, the major degradation product of cross-linked fibrin (11), stimulates Pg activation by t-PA to a similar extent as fibrin (11)(12)(13). This occurs because, like fibrin, (DD)E also binds t-PA and Pg with high affinity, thereby enhancing their interaction (14). As a potent stimulato...

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“…Administration of t-PA produces an increase in both the amount and duration of bleeding from cut wounds. In animal studies, the administration of a molar excess of a 2 -PI inhibited this process and returned the duration and quantity of skin bleeding towards control values [1]. This site specificity of the human serine protease inhibitor a 2 -PI ensures that haemostasis is maintained and physiological or appropriate, clot lysis is not inhibited.…”

Section: Mechanism Of Actionmentioning

confidence: 90%

“…However, if plasmin is generated in an appropriate bound position on the fibrin strand, usually via the action of tissue type plasminogen activator (t-PA), then a 2 -PI will only partially inhibit this plasmin. It is therefore apparent that a 2 -PI is a powerful inhibitor of free plasmin, associated with 'pathological' fibrinolysis, but does not act as an antifibrinolytic agent for 'appropriate' or 'physiological' fibrinolysis [1].…”

Section: Mechanism Of Actionmentioning

confidence: 99%

The current place of aprotinin in the management of bleeding

Royston

2014

Anaesthesia

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SummaryThere is a considerable difference between the mechanism of action of the lysine analogues, tranexamic acid and epsilon-aminocaproic acid, and the serine protease inhibitor aprotinin. Aprotinin acts to inactivate free plasmin, but with little effect on bound plasmin, whereas the lysine analogues are designed to prevent excessive plasmin formation by fitting into plasminogen's lysine-binding site to prevent the binding of plasminogen to fibrin. Aprotinin is associated with a reduction in bleeding and transfusion requirements following major surgery, and has a dose-response profile, compared with no dose-response effect in the one study investigating tranexamic acid in cardiac surgical patients. Following its withdrawal in 2007, which is explained in detail in this review, the regulators have now licensed aprotinin for myocardial revascularisation only, which is relatively low-risk for bleeding.

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Alpha 2-antiplasmin supplementation inhibits tissue plasminogen activator-induced fibrinogenolysis and bleeding with little effect on thrombolysis.

Cited by 51 publications

References 30 publications

Enhancement of Fibrinolysis by EF6265 [(S)-7-Amino-2-[[[(R)-2-methyl-1-(3-phenylpropanoylamino)propyl]hydroxyphosphinoyl] methyl]heptanoic Acid], a Specific Inhibitor of Plasma Carboxypeptidase B

Enhancement of Fibrinolysis by EF6265 [(S)-7-Amino-2-[[[(R)-2-methyl-1-(3-phenylpropanoylamino)propyl]hydroxyphosphinoyl] methyl]heptanoic Acid], a Specific Inhibitor of Plasma Carboxypeptidase B

Identification of the Mechanism Responsible for the Increased Fibrin Specificity of TNK-Tissue Plasminogen Activator Relative to Tissue Plasminogen Activator

The current place of aprotinin in the management of bleeding

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