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Thromb Haemost 2001; 85(04): 661-666
DOI: 10.1055/s-0037-1615650
Review Articles
Schattauer GmbH

Thrombin Activatable Fibrinolysis Inhibitor (TAFI) Does not Inhibit In Vitro Thrombolysis by Pharmacological Concentrations of t-PA

Mario Colucci
1   Department of Biomedical Sciences, Section of General Pathology, University of Bari
,
Anna M. D’Aprile
1   Department of Biomedical Sciences, Section of General Pathology, University of Bari
,
Alessandra Italia
1   Department of Biomedical Sciences, Section of General Pathology, University of Bari
,
Paolo Gresele
2   Institute of Internal and Vascular Medicine, University of Perugia, Italy
,
John Morser
3   Berlex Biosciences, Richmond, CA, USA
,
Nicola Semeraro
1   Department of Biomedical Sciences, Section of General Pathology, University of Bari
› Author Affiliations
Further Information

Publication History

Received 14 February 2001

Accepted after resubmission 06 November 2000

Publication Date:
08 December 2017 (online)

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Summary

TAFI (thrombin activatable fibrinolysis inhibitor) is a plasma procarboxypeptidase that upon activation inhibits the fibrinolytic process by removing the C-terminal lysines from partially degraded fibrin. The generation of activated TAFI (TAFIa) has been suggested to represent a mechanism of thrombus resistance to thrombolytic therapy. However, the ability of TAFI to inhibit fibrinolysis by pharmacological concentrations of t-PA has not been properly investigated. We used an in vitro model consisting of 125I-fibrin blood clots submerged in auto-logous defibrinated plasma. Upon addition of t-PA (125-5000 ng/ml) and CaCl2 (25 mM), samples were incubated at 37° C, and clot lysis was measured at intervals from the radioactivity released into solution. The role of TAFI was assessed either by neutralizing the generated TAFIa with the specific inhibitor PTI (50 g/ml) or by enhancing TAFI activation through the addition of recombinant soluble thrombomodulin (solulin, 1 μg/ml). In our clot lysis model, activation of TAFI amounted to about 20% of inducible carboxypeptidase activity. Addition of PTI, however, produced a significant increase in the extent of lysis only at concentrations of t-PA equal to or lower than 250 ng/ml. When solulin was added to the plasma surrounding the clot, about 70% of TAFI was activated within 15 min. Under these conditions, inhibition of clot lysis was very marked in samples containing 125 or 250 ng/ml of t-PA, but negligible in those containing pharmacological concentrations of the activator (1000 and 5000 ng/ml). Additional experiments suggest that loss of fibrin-dependence by elevated concentrations of t-PA may be one of the mechanisms explaining the lack of effect of TAFIa. Our data indicate that, under our experimental conditions, clot lysis by pharmacological concentrations of t-PA is not influenced by TAFIa even after maximal activation of this procarboxypeptidase.

Keywords

Thrombus - fibrinolysis - plasminogen activators - carboxypeptidase - thrombin
 

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