Red blood cells modulate structure and dynamics of venous clot formation in sickle cell disease

Abstract

Sickle cell disease (SCD) is associated with chronic activation of coagulation and an increased risk of venous thromboembolism. Erythrocyte sickling, the primary pathologic event in SCD, results in dramatic morphological changes in red blood cells (RBCs) because of polymerization of the abnormal hemoglobin. We used a mouse model of SCD and blood samples from sickle patients to determine if these changes affect the structure, properties, and dynamics of sickle clot formation. Sickling of RBCs and a significant increase in fibrin deposition were observed in venous thrombi formed in sickle mice. During ex vivo clot contraction, the number of RBCs extruded from sickle whole blood clots was significantly reduced compared with the number released from sickle cell trait and nonsickle clots in both mice and humans. Entrapment of sickled RBCs was largely factor XIIIa–independent and entirely mediated by the platelet-free cellular fraction of sickle blood. Inhibition of phosphatidylserine, but not administration of antisickling compounds, increased the number of RBCs released from sickle clots. Interestingly, whole blood, but not plasma clots from SCD patients, was more resistant to fibrinolysis, indicating that the cellular fraction of blood mediates resistance to tissue plasminogen activator. Sickle trait whole blood clots demonstrated an intermediate phenotype in response to tissue plasminogen activator. RBC exchange in SCD patients had a long-lasting effect on normalizing whole blood clot contraction. Furthermore, RBC exchange transiently reversed resistance of whole blood sickle clots to fibrinolysis, in part by decreasing platelet-derived PAI-1. These properties of sickle clots may explain the increased risk of venous thromboembolism observed in SCD.

Coagulation Status and Venous Thromboembolism Risk in African Americans: A Potential Risk Factor in COVID-19

“… 61 , 62 This morphologic change results in the cells having a higher likelihood of getting lodged in the microvasculature and more prone to aggregate than regular blood cells, causing blood flow obstruction and serving as a nidus for clot formation. 63 These morphological red blood cell changes along with activation of the coagulation system may result in a vaso-occlusive crisis. 64 Individuals with SCD are at a significantly higher risk of developing DVT and PE.…”

Sickle Cell Disease: A Paradigm for Venous Thrombosis Pathophysiology

“…Moreover, adults with wide range of sickling hemoglobinopathies have been associated with the development of VTE, from hemoglobin SS to compound heterozygous states to sickle cell trait [ 13 ]. A curious phenomenon in SCD patients is the increased overall prevalence of pulmonary embolism (PE) that occurs in the absence of detectable extremity deep venous thrombosis (DVT) suggesting either the occurrence of in situ pulmonary thrombosis [ 14 ] or classic thromboembolic PE from clot friability/instability [ 15 ]. In SCD, thrombosis also affects the arterial circulation, leading to devastating complications, such as stroke and silent cerebral infarction [ 16 ], a topic that is beyond the scope of this review.…”

“…The Townes and Berkeley(BERK) sickle mouse models show characteristic features of SCD, including severe anemia, hemolysis, inflammation, and endothelial activation [ 36 , 37 ]. Importantly, they also display biochemical features consistent with the sickle hypercoagulable state (see Table 2 ), e.g., increased thrombin generation [ 38 , 39 ], depletion of the natural anticoagulants [ 28 , 38 ], increased TF expression [ 40 ], and abnormalities in fibrinolytic activity [ 15 ]. Evidence of thrombosis can also be found in multiple organs of sickle cell mice [ 41 ], and hypoxia further enhances thrombosis in their pulmonary vasculature [ 42 ].…”

“…Similarly, endothelial inflammation in SCD leads to increased TF and P-selectin expression and release of vWF that could promote small thrombi within the valve pocket, which, growing slowly over days to weeks, may eventually completely occlude the vessel. Interestingly, the venous thrombus in an IVC stasis model in SCD mice demonstrated ultrastructural differences with higher amounts of fibrinous material and red cell entrapment with extensive sickling [ 15 ]. In ex vivo sickle whole blood clots, the number of RBCs extruded from the clot was also significantly reduced, compared with the number released from sickle cell trait and non-sickle clots in both mice and humans.…”

Vascularized Microfluidics and the Blood–Endothelium Interface

“…While thrombosis and hemostasis is the primary role of the platelet, it is also integral to the inflammatory response [127], maintenance of vascular integrity [123], and angiogenesis [128,129], as well as being implicated in multiple diseases, including sickle cell disease [130], hemolytic uremic syndrome [131] and cardiovascular disease [132]. The function of platelets in both homeostasis and these pathologies is profoundly altered by blood flow dynamics [133], making the use of perfusable microvascular models an ideal in vitro platform for the evaluation of platelet-endothelial interactions and their role in human health and disease.…”