Homocysteine and its thiolactone may promote apoptotic events in blood platelets in vitro.

The actions of homocysteine and its major metabolite, cyclic thioester, homocysteine thiolactone on endothelial cells, blood platelets, plasmatic fibrinogen and plasminogen--the important major components of haemostasis, regulating the flowing properties of blood--are complex and sometimes controversial. Homocysteine (Hcys) can promote apoptosis in endothelial cells, but the role of Hcys and its thiolactone in the apoptotic process in blood platelets is unknown. In order to study the appearance of apoptosis in platelets after treatment with the reduced form of Hcys or its thiolactone different markers were chosen: annexin V binding (phosphatidylserine exposure), platelet microparticle formation, mitochondrial membrane depolarization and αIIbβ3 expression in vitro. Apoptotic events and platelet activation were measured by a flow cytometer. In gel-filtered platelets treated with different concentrations of the reduced form of Hcys (25, 50 and 100 µM, 10 min) a significant increase of phosphatidylserine exposure (about 37% at the highest concentration, p < 0.001) and platelet microparticle formation were observed. Homocysteine caused also a dose-dependent depolarization of mitochondrial potential. The same apoptotic markers appeared in HTL-treated platelets (0.2 and 1 µM). Moreover, resveratrol (25 µM), a well known antioxidant, distinctly reduced the level of apoptotic markers. The obtained results indicate that Hcys and its thiolactone may promote in vitro apoptotic events in human gel-filtered platelets.