(19c) The Effect of Rigid Red Blood Cells on Platelet Adhesion in Blood Flow: Potential Implications in Sickle Cell Disease

Introduction: Sickle cell disease (SCD) refers to a group of genetic disorders characterized by mutations in the β-subunit of hemoglobin, leading to membrane rigidification and less frequent sickling of the red blood cells (RBCs). The impact of diseased, rigid RBCs on other blood cells, including white blood cells and platelets, in flow is currently not well known. Platelets are responsible for maintaining hemostasis by rapidly plugging any interruptions or injuries in the vasculature, a process known as clotting—a key physiological response to vascular injury to prevent blood loss and damage. Clotting is initiated through damage to the endothelium, or the monolayer of cells that line blood vessels, which causes platelets to activate and bind to the endothelium and exposed underlying extracellular matrix proteins. Adhesion of platelets to the injured vessel is contingent on the ability of platelets to marginate towards the vascular wall. Margination is facilitated through heterogeneous collisions between the typically deformable RBCs in the RBC core and the relatively stiff platelets that are displaced towards the wall. However, platelet margination and adhesion in the presence of diseased or stiffened RBCs has yet to be fully elucidated, despite the increase in vaso-occlusive crises and stroke occurring in SCD patients.

Materials and methods: We utilized an in vitro flow-based system to examine how the extent of rigidification and rigid RBC concentration affect platelet margination and binding to a damaged endothelium model mimicking acute vascular damage. RBCs were removed from the whole blood and artificially rigidified using a peroxide solution. The RBCs were then reconstituted into blood and perfused over the damaged endothelium using a parallel plate flow chamber (PPFC) in a variety of different blood flow patterns and conditions. Platelet adhesion was quantified using fluorescent microscopy and compared to a healthy control.

Results and conclusions: The presence of rigid RBCs in flow drastically increases platelet adhesion under a variety of rigidities and concentrations and is dependent on variables including extent of RBC rigidity, shear rate, and flow pattern. This finding suggests that rigid RBCs may play a major role in disrupting normal hemodynamics and contributing to the pervasive vaso-occlusive crises that occur in many SCD patients. Overall, we will elucidate how rigid RBC-platelet interactions affect platelet binding, a critical step in hemostasis. This study can help determine the mechanism causing vaso-occlusive events in SCD patients and can form the basis of the study of platelet-cell dynamics in the future.