Antithrombotic properties of Ixolaris, a potent inhibitor of the extrinsic pathway of the coagulation cascade

Rômulo A. Nazareth; Luana S. Tomaz; Susana Ortiz-Costa; Geórgia C. Atella; José M. C. Ribeiro; Ivo M. B. Francischetti; Robson Q. Monteiro

doi:10.1160/TH06-02-0105

Thrombosis and Haemostasis, Table of Contents

Thromb Haemost 2006; 96(01): 7-13
DOI: 10.1160/TH06-02-0105

Blood Coagulation, Fibrinolysis and Cellular Haemostasis

Schattauer GmbH

Antithrombotic properties of Ixolaris, a potent inhibitor of the extrinsic pathway of the coagulation cascade

Rômulo A. Nazareth

¹Instituto de Bioquímica Médica, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil

,

Luana S. Tomaz

¹Instituto de Bioquímica Médica, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil

,

Susana Ortiz-Costa

²Instituto de Nutrição, Centro de Ciências da Saúde, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil

,

Geórgia C. Atella

¹Instituto de Bioquímica Médica, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil

,

José M. C. Ribeiro

³Section of Vector Biology, Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, Maryland, USA

,

Ivo M. B. Francischetti

³Section of Vector Biology, Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, Maryland, USA

,

Robson Q. Monteiro

¹Instituto de Bioquímica Médica, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil

› Author Affiliations

Abstract

Summary

Ixolaris is a two-Kunitz tick salivary gland protein identified in Ixodes scapularis that presents extensive sequence homology t TFPI.It binds to FXa or FX as scaffolds and inhibits tissue factor/ FVIIa complex (extrinsic Xnase). Differently from TFPI, ixolaris does not bind to the active site cleft of FXa. Instead, comple formation is mediated by the FXa heparin-binding exosite,which may also results in decreased FXa activity into the prothrombi nase complex.In this report,we show that recombinant ¹²⁵I-ixo laris interacts with rat and human FX in plasma and prolongs the prothrombin time (PT) and activated partial thromboplastin time (aPTT) in vitro.We have also investigated the effects of ixo laris in vivo, using a venous thrombosis model. Subcutaneous (s.c.) or intravenous (i.v.) administration of ixolaris in rats caused a dose-dependent reduction in thrombus formation, with complete inhibition attained at 20 µg/kg and 10 µg/kg, re spectively. Antithrombotic effects were observed 3 h after s.c. administration of ixolaris and lasted for 24 h thereafter. Ex vivo experiments showed that ixolaris (up to 100 µg/kg) did not affect the aPTT,while the PT was increased by ∼0.4-fold at the hig hest ixolaris concentration. Remarkably, effective antithrom botic doses of ixolaris (20 µg/kg) was not associated with bleed ing which was significant only at higher doses of the anticoagulant (40 µg/kg).Our experiments demonstrate that ixolaris is an effective and possibly safe antithrombotic agen in viv .

Keywords

Anticoagulant - ixolaris - venous thrombosis - factor Xa - tissue factor - tick saliva - Ixodes scapularis

Full Text

References

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