Antihemostatic and antithrombotic effects of XC386

Ex-vivo and in-vivo antithrombotic effect of triflavin, an RGD-containing peptide

Triflavin, an Arg-Gly-Asp-containing snake venom peptide, inhibits platelet aggregation through the blockade of fibrinogen binding to the activated platelets. It binds to fibrinogen receptors associated with the glycoprotein IIb/IIIa complex with a Kd value of 7 x 10(-8) M. In this study, we found that 125I-triflavin reached the maximal binding to human platelets within 5 min at 25 degrees C. In addition, when triflavin was intravenously administered at 1.0 mg kg-1 to rabbits, it reversibly impaired the platelet aggregation of platelet-rich plasma caused by ADP (20 microM) ex-vivo over 30 min. The platelet counts of the experimental rabbits remained unchanged. Triflavin was effective in reducing the mortality of ADP-induced acute pulmonary thromboembolism in mice when administered intravenously at a dose of 2 micrograms g-1. Therefore, triflavin was proven to be an effective antithrombotic agent in preventing ADP-induced acute pulmonary thromboembolism in mice and impairing reversibly the platelet function of rabbits when given intravenously.

The effects of leukaemia inhibitory factor on platelet function

Leukaemia inhibitory factor (LIF) is able to promote megakaryocytopoiesis in vitro and elevate platelet counts in vivo, and is a potential new therapeutic agent for the treatment of thrombocytopenia. To determine whether platelets released under conditions of LIF-stimulated megakaryocytopoiesis have intact function, we compared aggregation responses of platelets from mice with constitutively elevated LIF levels (FD/LIF mice) and mice injected with recombinant murine LIF (rmLIF mice) with their respective control mice. We report that ex vivo platelet aggregability and thromboxane B2 release were intact in the LIF-treated mice, and were significantly enhanced in some situations. LIF-treated mice also had significantly increased platelet counts (FD/LIF mice: 1302 +/- 173 x 10(9)/l compared to 1012 +/- 99 x 10(9)/l for FD mice; rmLIF mice: 1460 +/- 193 x 10(9)/l compared to 985 +/- 67 x 10(9)/l for FCS/NS mice), increased platelet volumes and elevated plasma fibrinogen and calcium levels. The platelet hyperreactivity seen in the LIF-treated mice is likely to reflect the larger platelet volumes and/or the effect of plasma components such as fibrinogen, elevated levels of which were due to the concomitant action of LIF as a stimulant of acute phase protein synthesis.