Comparison of the effect of homocysteine in the reduced form, its thiolactone and protein homocysteinylation on hemostatic properties of plasma.

Mechanisms involved in the relationship between hyperhomocysteinemia and hemostatic process are still unclear. In the literature there are few papers describing studies on the effects of homocysteine (Hcys) on proteins that participate in blood coagulation and fibrinolysis in human. The aim of our study was to establish and compare the influence of a reduced form of Hcys (at final doses of 0.01 - 1 mM) and the most reactive form of Hcys - its cyclic thioester, homocysteine thiolactone (HTL, 0.1 - 1 μM) on the clot formation (using whole human plasma and purified fibrinogen) and the fibrin lysis. Moreover, the aim of our study was to explain the effect of plasma protein modifications (S- and N-homocysteinylation) on selected parameters of hemostasis. We observed that HTL, like its precursor, a reduced form of Hcys stimulated polymerization of fibrinogen, but this process was not dose-dependent. In the presence of HTL (at the lowest tested concentration - 0.1μM) the increase was about 55%. Our present results also demonstrated that Hcys in the reduced form (0.01 - 1 mM) and HTL at lower doses than Hcys (0.1 - 1 μM) reduced the fibrin lysis in whole human plasma. Our results reported that HTL, like the reduced form of Hcys (at concentrations corresponding to concentrations in plasma during hyperhomocysteinemia) induced modifications of hemostatic plasma proteins, and the consequence of these modifications may be alteration in protein structure associated with changes of hemostatic functions.