A cascade of thromboembolic processes in a patient with paroxysmal nocturnal haemoglobinuria terminated by treatment with eculizumab

Neutrophil activation and nucleosomes as markers of systemic inflammation in paroxysmal nocturnal hemoglobinuria: effects of eculizumab

BACKGROUND

Paroxysmal nocturnal hemoglobinuria (PNH) is characterized by complement-mediated hemolysis and a high risk of life-threatening venous and arterial thrombosis. Uncontrolled complement activation and the release of cell-free heme may result in systemic inflammation, neutrophil activation, and the release of procoagulant neutrophilic proteases. Eculizumab, an antibody to complement factor C5, inhibits hemolysis and reduces thrombotic risk.

OBJECTIVES

To study neutrophil activation and nucleosome levels in relation to thrombosis in PNH patients before and during treatment with eculizumab.

PATIENTS/METHODS

In 51 untreated PNH patients, including 20 patients before and after commencing eculizumab treatment, we have assessed neutrophil activation by measuring elastase-α1 -antitrypsin (EA) complexes and circulating nucleosomes, as established markers for systemic inflammation and cell death.

RESULTS

Nucleosomes (median; range; 95% confidence interval [CI]), but not EA complexes, were higher in PNH patients with a history of thrombosis (16; 7-264; 0.3-94 U mL(-1) , n = 12) than in those without (6; 6-35; 7-11 U mL(-1) , n = 39) or controls (8; 6-23; 7-12 U mL(-1) , n = 17). EA complexes, but not nucleosomes, decreased promptly and markedly upon eculizumab treatment. EA complexes (estimated marginal means; 95% CI) remained low at ≥ 12 weeks (50; 34-67) compared with baseline (12; -6 to 29).

CONCLUSIONS

The increased nucleosome levels in PNH patients with a history of thrombosis suggest systemic inflammation and/or cell death. Neutrophil activation markers did not differ between patients with and without a history of thrombosis and healthy controls. Interestingly, basal neutrophil activation in PNH patients significantly decreases on treatment with eculizumab, indicating that neutrophil activation is C5a driven.

Alterations in markers of coagulation and fibrinolysis in patients with Paroxysmal Nocturnal Hemoglobinuria before and during treatment with eculizumab

BACKGROUND

Paroxysmal Nocturnal Hemoglobinuria is characterized by complement-mediated hemolysis and an increased thrombosis risk. Eculizumab, an antibody to complement factor C5, reduces thrombotic risk via unknown mechanisms. Clinical observations suggest that eculizumab has an immediate effect.

OBJECTIVES

A better understanding of the mechanism via which eculizumab reduces thrombotic risk by studying its pharmacodynamic effect on coagulation and fibrinolysis.

METHODS

We measured microparticles (MP), tissue factor (TF) activity, prothrombin fragment 1+2 (F1+2), D-dimer and simultaneously thrombin and plasmin generation in 55 PNH patients. In 20 patients, parameters were compared before and during eculizumab treatment (at 1 and 2hours, 1, 4 and≥12weeks after commencement).

RESULTS

Patients with a history of thrombosis had elevated D-dimers (p=0.02) but not MP. Among patients on anticoagulants, those with thrombosis had higher F1+2 concentrations (p=0.003). TF activity was undetectable in plasma MP. Unexpectedly, thrombin peak height and thrombin potential were significantly lower in PNH patients than in healthy controls. Fibrinolysis parameters were normal. During eculizumab treatment D-dimer levels significantly decreased after 1hour (p=0.008) and remained decreased at≥12weeks (p=0.03). F1+2 (p=0.03) and thrombin peak height (p=0.02) in patients not on anticoagulants significantly decreased at≥week 12. MP remained unchanged.

CONCLUSIONS

Eculizumab induces an immediate decrease of D-dimer levels but not of other markers. The decrease in thrombin peak height and F1+2 suggests that eculizumab reduces thrombin generation. Elevated D-dimer levels in untreated PNH patients with a history of thrombosis suggest possible value in predicting thrombotic risk.

Eculizumab: a review of its use in paroxysmal nocturnal haemoglobinuria

Eculizumab is a humanized monoclonal antibody indicated for the treatment of paroxysmal nocturnal haemoglobinuria (PNH). It binds specifically and with high affinity to the complement protein C5, thereby preventing the formation of the terminal complement complex C5b-9, which mediates cell lysis. In patients with PNH, eculizumab inhibits terminal complement mediated intravascular haemolysis. In clinical trials of PNH patients, eculizumab reduced intravascular haemolysis compared with baseline and placebo, as determined by significantly decreased lactate dehydrogenase (LDH) levels. Significant reductions in LDH levels were achieved within the first week of treatment, with near normal levels achieved at week 2 and maintained throughout longer term treatment, including periods of up to 36 months. Eculizumab achieved rapid and sustained efficacy, regardless of baseline LDH levels or platelet counts. In adults with PNH, eculizumab treatment for 26 weeks achieved stabilization of haemoglobin levels in significantly more patients than placebo treatment, and reduced the requirement for packed red cell transfusions to a significantly greater extent than placebo. Half of all patients in the eculizumab group became transfusion independent compared with no patients in the placebo group. Eculizumab was also associated with significant improvements in fatigue and health-related quality-of-life scores in several trials. Over the long term, the survival of PNH patients treated with eculizumab was normalized. Eculizumab was generally well tolerated in clinical trials of PNH patients, including treatment periods of up to 5.5 years. The risk of Neisseria meningitidis is increased with eculizumab and patients must be vaccinated prior to treatment and monitored throughout. Thus, eculizumab, the first targeted terminal complement inhibitor, provides an effective and generally well tolerated treatment for PNH patients, who have previously been without adequate treatment options.

Mechanisms and clinical implications of thrombosis in paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare acquired disease characterized by a clone of blood cells lacking glycosyl phosphatidylinositol (GPI)-anchored proteins at the cell membrane. Deficiency of the GPI-anchored complement inhibitors CD55 and CD59 on erythrocytes leads to intravascular hemolysis upon complement activation. Apart from hemolysis, another prominent feature is a highly increased risk of thrombosis. Thrombosis in PNH results in high morbidity and mortality. Often, thrombosis occurs at unusual locations, with the Budd–Chiari syndrome being the most frequent manifestation. Primary prophylaxis with vitamin K antagonists reduces the risk but does not completely prevent thrombosis. Eculizumab, a mAb against complement factor C5, effectively reduces intravascular hemolysis and also thrombotic risk. Therefore, eculizumab treatment has dramatically improved the prognosis of PNH. The mechanism of thrombosis in PNH is still unknown, but the highly beneficial effect of eculizumab on thrombotic risk suggests a major role for complement activation. Additionally, a deficiency of GPI-anchored proteins involved in hemostasis may be implicated.