Evaluation of hemostasis and endothelial function in patients with paroxysmal nocturnal hemoglobinuria receiving eculizumab

Abstract

Background: Paroxysmal nocturnal hemoglobinuria (PNH) is associated with an increased risk of thrombosis through unknown mechanisms.

Design and methods: We studied 23 patients with PNH, before and after five and 11 weeks of treatment with eculizumab. We examined markers of thrombin generation and reactional fibrinolysis (prothrombin fragment 1+2 (F1+2), D-dimers, and plasmin antiplasmin complexes (P-AP), and endothelial dysfunction tissue plasminogen activator (t-PA), plasminogen activator inhibitor (PAI-1), soluble thrombomodulin (sTM), intercellular adhesion molecule 1 (sICAM-1), vascular cell adhesion molecule (sVCAM-1), endothelial microparticles (EMPs), and tissue factor pathway inhibitor (TFPI).

Results: At baseline, vWF, sVCAM-1, the EMP count, and F1+2 and D-dimer levels were significantly elevated in the patients, including those with no history of clinical thrombosis. Treatment with eculizumab was associated with significant decreases in plasma markers of coagulation activation (F1+2, P=0.012, and D-dimers, P=0.01), and reactional fibrinolysis (P-AP, P=0.0002). Eculizumab treatment also significantly reduced plasma markers of endothelial cell activation (t-PA, P=0.0005, sVCAM-1, P<0.0001, and vWF, P=0.0047) and total (P=0.0008) and free (P=0.0013) TFPI plasma levels.

Conclusions: Our results suggest a new understanding of the contribution of endothelial cell activation to the pathogenesis of thrombosis in PNH. The terminal complement inhibitor, eculizumab, induced a significant and sustained decrease in the activation of both the plasma hemostatic system and the vascular endothelium, likely contributing to the protective effect of eculizumab on thrombosis in this setting.

Figure 1.

Distribution of prothrombin fragment 1+2 (A), D-dimers (B), and P-AP complex (C) plasma levels in the whole cohort (), and in patients without (□) and with anticoagulant treatment () at baseline, and at week 5 and week 11 of eculizumab treatment. Boxes and whisker plots represent the median (full line) and the 25^th and 75^th percentiles (boxes), and the outer whiskers extend to the most extreme data point, which is no more than 1.5 times the interquartile range from the box. Upper and lower limits of normal are indicated, by u and l, respectively.

Figure 2.

Distribution of t-PA (A), sVCAM-1 (B), and vWF Ag (C) plasma levels in the whole cohort (), and in patients without (□) and with anticoagulant therapy () at baseline, and at week 5 and week 11 of eculizumab treatment. Boxes and whisker plots represent the median (full line) and the 25^th and 75^th percentiles (boxes), and the outer whiskers extend to the most extreme data point, which is no more than 1.5 times the interquartile range from the box. Upper and lower limits of normal are indicated, by u and l, respectively.

Figure 3.

Distribution of total TFPI (A) and free TFPI (B) antigen plasma levels in the whole cohort (), and in patients without (□) and with anticoagulant therapy () at baseline, and at week 5 and week 11 of eculizumab treatment. Boxes and whisker plots represent the median (full line) and the 25^th and 75^th percentiles (boxes), and the outer whiskers extend to the most extreme data point, which is no more than 1.5 times the interquartile range from the box. Upper and lower limits of normal are indicated, by u and l, respectively.