Increased Procoagulant Activity of Red Blood Cells from Patients with Homozygous Sickle Cell Disease and β-Thalassemia

Abstract

SummaryIt has recently been proved that, in vitro, red blood cells (RBCs) from patients with homozygous β-thalassemia behave as procoagulant cells. The procoagulant activity of β-thalassemia RBCs might be the result of an increased exposure of procoagulant phospholipids (i. e. phosphatidylserine) in the outer leaflet of the membrane. In order to test this hypothesis, we compared the catalytic properties of RBCs of patients with β-thalassemia and homozygous sickle cell disease (SS-RBCs) with that of controls. The catalytic parameters (Km, kcat) of prothrombin activation by factor Xa were determined both in the absence and in the presence of RBCs. The turn-over number (kcat) of the reaction was not modified by normal, SS- or (3-thalassemia RBCs. The Km was lower in the presence of normal RBCs (mean value: 9.1 µM) than in the absence of cells (26 µM). The Km measured in the presence of either SS-RBCs (mean value: 1.6 µM) or β-thalassemia RBCs (mean value: 1.5 pM) was significantly lower compared to normal RBCs (p <0.001). No significant difference was observed between SS-RBCs and p-thalassemia RBCs. Annexin V, a protein with high affinity and specificity for anionic phospholipids, inhibited the procoagulant activity of both SS-RBCs and (3-thalassemia RBCs, in a dose-dependent manner. More than 95% inhibition was achieved at nanomolar concentrations of annexin V. These results indicate that the procoagulant activity of both β-thalassemia RBCs and SS-RBCs may be fully ascribed to an abnormal exposure of phosphatidylserine at the outer surface of the red cells.

The hypercoagulable state in thalassemia

“…[57][58][59] A comparison of normal RBCs with those isolated from patients with ␤-TM or ␤-TI by our group suggests that thalassemic RBCs may provide a source of negatively charged phospholipids, which can increase thrombin generation, as measured by prothrombinase assay. 60,61 These results were confirmed in a similar assay using RBCs from splenectomized ␤-TI patients as a source of phospholipids. 19 The procoagulant effect of thalassemic RBCs seems to be due to an increased surface expression of anionic phospholipids such as phosphatidylethanolamine (PE) and phosphatidylserine (PS).…”

“…This was demonstrated by experiments that showed that annexin V, which binds anionic phospholipids, could block the procoagulant effect of isolated thalassemic RBCs. 61 These data suggest that the procoagulant effect of thalassemic RBCs may contribute to the hypercoagulable state in thalassemia by amplifying thrombin generation and initiating platelet activation.…”

“…[89][90][91] Sickle RBCs expressing anionic phospholipid surfaces, manifested by enhanced annexin V binding, have been shown to have a procoagulant effect and are thought to be significant in the pathogenesis of the thrombotic manifestations. 57,58,61,90 In support of this idea, significant reductions in the rates of stroke recurrence in sickle cell patients from 46% to 90% to less than 10% have been achieved by chronic blood transfusions and maintenance of hemoglobin S For personal use only. on May 11, 2018.…”

“…[82][83][84][85][86] Hemostatic abnormalities, including low protein C and protein S levels, and elevated plasma concentrations of TAT, F 1,2 , and D-dimer complexes have been found in sickle cell patients. 61,75,[87][88][89] In addition, chronic platelet activation was indicated by the elevated plasma levels of platelet factor 4 (PF4) and ␤-thromboglobulin (␤-TG) and the expression of P selectin and enhanced binding of annexin V to the SCD platelets. 89 These markers of platelet activation, thrombin generation, and enhanced fibrinolyisis were significantly elevated in asymptomatic subjects with SCD and further increased during episodes of pain.…”

Erythrocyte Alterations and Increased Cardiovascular Risk in Chronic Renal Failure

“…Perturbations in RBC PS exposure are seen as a pathogenic mechanism for the prothrombotic state of beta-thalassemia and sickle cell disease (37). Chronic uremia is associated with an increased risk of thrombotic complications, which may represent the predominant cause of mortality particularly in dialysis patients (38).…”