title: Antithrombotic properties of Ixolaris, a potent inhibitor of the extrinsic pathway of the coagulation cascade.
abstract: Ixolaris is a two-Kunitz tick salivary gland protein identified in Ixodes scapularis that presents extensive sequence homology to 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, complex formation is mediated by the FXa heparin-binding exosite, which may also results in decreased FXa activity into the prothrombinase complex. In this report, we show that recombinant (125)I-ixolaris 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 ixolaris 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 microg/kg and 10 microg/kg, respectively. 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 microg/kg) did not affect the aPTT, while the PT was increased by approximately 0.4-fold at the highest ixolaris concentration. Remarkably, effective antithrombotic doses of ixolaris (20 microg/kg) was not associated with bleeding which was significant only at higher doses of the anticoagulant (40 microg/kg). Our experiments demonstrate that ixolaris is an effective and possibly safe antithrombotic agent in vivo.
authors.affiliation: Instituto de Bioquímica Médica, Centro de Ciências da Saúde, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil. robsonqm@bioqmed.ufrj.br
authors.forename: Rômulo A
authors.initials: RA
authors.lastname: Nazareth
authors.forename: Luana S
authors.initials: LS
authors.lastname: Tomaz
authors.forename: Susana
authors.initials: S
authors.lastname: Ortiz-Costa
authors.forename: Geórgia C
authors.initials: GC
authors.lastname: Atella
authors.forename: José M C
authors.initials: JM
authors.lastname: Ribeiro
authors.forename: Ivo M B
authors.initials: IM
authors.lastname: Francischetti
authors.forename: Robson Q
authors.initials: RQ
authors.lastname: Monteiro
mesh_terms: D000818:Animals; D001777:Blood Coagulation / Q000187:drug effects*; D001780:Blood Coagulation Tests; D004305:Dose-Response Relationship, Drug; D005170:Factor X / Q000037:antagonists & inhibitors*; D005343:Fibrinolytic Agents / Q000493:pharmacokinetics / Q000494:pharmacology; D006801:Humans; D007457:Iodine Radioisotopes / Q000493:pharmacokinetics; D010599:Pharmacokinetics; D051381:Rats; D017208:Rats, Wistar; D012471:Salivary Proteins and Peptides / Q000493:pharmacokinetics / Q000494:pharmacology*; D013927:Thrombosis / Q000188:drug therapy / Q000517:prevention & control; D013987:Ticks
chemical_list: D005343:Fibrinolytic Agents; D007457:Iodine Radioisotopes; C455900:Ixolaris protein, Ixodes scapularis; D012471:Salivary Proteins and Peptides; D005170:Factor X