Interaction of blood cells with the vessel wall in thrombosis

Thrombotic events such as stroke, myocardial infarction, or deep vein thrombosis can be life-threatening; therefore it is important to understand the mechanisms of thrombosis and its correlations with clinical risk factors. It is well known that red blood cells (RBCs) can influence hemostasis and thrombosis by affecting the viscosity and rheological properties of blood. Recent evidence suggests that RBCs may play a more central and active role in some models of experimental thrombosis by interacting directly with the endothelium. It is still unclear, however, if the interaction of RBCs with the endothelial surface is facilitated by other blood components. In order to investigate the interaction of RBCs with endothelium in a defined system in vitro, human umbilical vein endothelial cells (HUVECs) were grown on coverslips and placed in a parallel-plate flow chamber system. Using this system, we tested the hypothesis that RBCs interact directly with ferric chloride-injured endothelium in the absence of other blood components. These experiments demonstrated that RBCs do interact with HUVECs in the flow chamber under both venous and arterial conditions. Using an anti-von Willebrand Factor (VWF) antibody, we demonstrated that the RBC-endothelium interaction is facilitated by VWF in vitro. These findings support a possible active role of RBCs in thrombosis and also demonstrate that RBCs interact with VWF, which was previously unrecognized. Platelets are also known to play an important role in hemostasis and thrombosis, specifically through their interaction with exposed collagen located in the subendothelial matrix that becomes exposed to flowing blood after vascular injury. Platelets may become hyperactive in prothombotic conditions, leading to increased platelet aggregation and thrombotic events. Thrombotic events also increase in the presence of risk factors such as increased age or obesity. Previous data has shown that platelet hydrogen peroxide (H2O2) mediates platelet hyperactivity and that activated platelets from obese mice show increased H2O2 levels. In order to investigate the interactions of platelets with collagen in vitro, the flow chamber system was used with collagen-coated coverslips to study platelet adhesion under arterial and venous conditions. We found that platelets from mice with increased levels of H2O2, due to the genetic deletion of glutathione peroxidase-1 formed larger aggregates than control mice. In preliminary experiments, we observed evidence for increased adhesion and aggregation of platelet from obese mice. These findings confirm the role of H2O2 in platelet hyperactivity and suggest that therapeutic strategies targeted toward lowering platelet H2O2 levels may have the potential to decrease thrombotic complications associated with certain prothrombotic disease states.