Analysis of biological properties of selected elements of haemostasis after treatment with the oxidized form of homocysteine in vitro.

The elevated level of homocysteine (Hcys; hyperhomocysteinemia, in relation to the total plasma Hcys concentration, >15 µM) is associated with different diseases in human, including cardiovascular diseases. In plasma, Hcys occurs in various forms (the reduced Hcys, the oxidized Hcys, homocysteine thiolactone (HTL) and a component of proteins as a result of N- or S-homocysteinylation). The mechanisms by which hyperhomocysteinemia contributes to changes of haemostasis are complex and unclear. The role of different forms of Hcys, which may be involved in the modulation of haemostatic process during hyperhomocysteinemia is also not yet well-known. Our previous works have shown that both Hcys in the reduced form and the most reactive form of Hcys-its thiolactone may modify fibrinolysis, coagulation process and biological activity of blood platelets. The mechanism by which the oxidized Hcys exerts the prothrombotic effect and influences on blood platelets or plasma remains unclear. The aim of our study in vitro was to establish and compare the influence of the oxidized Hcys (at final doses of 0.01-1 mM), the reduced Hcys (at final doses of 0.01-1 mM) and HTL (at final doses of 0.1-1 µM) on selected haemostatic properties of blood platelets (platelet aggregation and platelet microparticle formation measured by flow cytometry) and plasma (fibrin polymerization and lysis). Here, our results indicate that the oxidized Hcys, like the reduced Hcys or HTL-augmented blood platelet aggregation, stimulated polymerization of fibrinogen and reduced the fibrin lysis in plasma. But, we suggest that the most reactive form of Hcys may be HTL (at lower concentrations than Hcys) during hyperhomocysteinemia-induced cardiovascular diseases.