Direct red blood cell effect on thrombosis is dependent on the interaction of tissue factor and calcium with membrane phosphatidylserine.

Abstract

Prior literature has implicated Red Blood Cells (RBCs) in the initiation of thrombosis and suggests that post-transfusion hypercoagulability may occur secondary to the effects of RBCs. Elevated serum tissue factor is a known sequelae of acute trauma. Phosphatidylserine is a pro-thrombotic phospholipid present within the RBC cell membrane. We hypothesized that RBC aggregation is dependent on the interaction between RBC membrane bound (exposed) PS, extracellular calcium, and tissue factor. Human whole blood (WB) was separated into components including red blood cells (RBC) and platelet-rich plasma (PRP). WB, PRP, and RBCs underwent impedance aggregometry utilizing arachidonic acid (AA), ADP, collagen, calcium, and tissue factor (TF)-based agonists. RBCs then underwent impedance aggregometry utilizing combined calcium and TF agonists. RBCs were pre-treated with Annexin V, a known PS blocking agent, and underwent impedance aggregometry with combined calcium and TF agonists to determine if the mechanism of calcium/TF-induced RBC aggregability is dependent on PS. RBCs treated with calcium, TF, calcium+TF, and pre-treated with Annexin V followed by calcium+TF were perfused through an in vitro model of pulmonary microcirculatory flow. RBC aggregation was significantly higher than that of WB and PRP when utilizing a TF agonist, an effect unique to TF. The combination of calcium and TF demonstrated significantly higher RBC aggregation than either agonist alone. Pre-treatment with Annexin V resulted in a significantly reduced aggregability of RBC following treatment with TF + calcium. RBCs aged to 42 days did not exhibit significant change in aggregation. Exposure to calcium and TF significantly reduced time to thrombosis of RBCs perfused through a pulmonary microcirculatory model. Treatment with both TF and calcium synergistically induces RBC aggregation. PS appears to play an integral role in the TF/calcium-based, age-independent RBC aggregation response. RBCs treated with TF + calcium exhibit more rapid thrombus formation in an in vitro model of pulmonary microcirculatory perfusion.Study Type: human sample-based study. basic science paper.