Context The efficient sequestration of hemoglobin by the red blood cell membrane and the presence of multiple hemoglobin clearance mechanisms suggest a critical need to prevent the buildup of this molecule in the plasma. A growing list of clinical manifestations attributed to hemoglobin release in a variety of acquired and iatrogenic hemolytic disorders suggests that hemolysis and hemoglobinemia should be considered as a novel mechanism of human disease. Evidence Acquisition Pertinent scientific literature databases and references were searched through October 2004 using terms that encompassed various aspects of hemolysis, hemoglobin preparations, clinical symptoms associated with plasma hemoglobin, nitric oxide in hemolysis, anemia, pulmonary hypertension, paroxysmal nocturnal hemoglobinuria, and sickle-cell disease. Evidence Synthesis Hemoglobin is released into the plasma from the erythrocyte during intravascular hemolysis in hereditary, acquired, and iatrogenic hemolytic conditions. When the capacity of protective hemoglobin-scavenging mechanisms has been saturated, levels of cell-free hemoglobin increase in the plasma, resulting in the consumption of nitric oxide and clinical sequelae. Nitric oxide plays a major role in vascular homeostasis and has been shown to be a critical regulator of basal and stress-mediated smooth muscle relaxation and vasomotor tone, endothelial adhesion molecule expression, and platelet activation and aggregation. Thus, clinical consequences of excessive cell-free plasma hemoglobin levels during intravascular hemolysis or the administration of hemoglobin preparations include dystonias involving the gastrointestinal, cardiovascular, pulmonary, and urogenital systems, as well as clotting disorders. Many of the clinical sequelae of intravascular hemolysis in a prototypic hemolytic disease, paroxysmal nocturnal hemoglobinuria, are readily explained by hemoglobin-mediated nitric oxide scavenging. Conclusion A growing body of evidence supports the existence of a novel mechanism of human disease, namely, hemolysis-associated smooth muscle dystonia, vasculopathy, and endothelial dysfunction.

Eculizumab is an effective therapy for PNH.

BACKGROUND The up-regulation of P-selectin in endothelial cells and platelets contributes to the cell–cell interactions that are involved in the pathogenesis of vaso-occlusion and sickle cell–related pain crises. The safety and efficacy of crizanlizumab, an antibody against the adhesion molecule P-selectin, were evaluated in patients with sickle cell disease. METHODS In this double-blind, randomized, placebo-controlled, phase 2 trial, we assigned patients to receive low-dose crizanlizumab (2.5 mg per kilogram of body weight), high-dose crizanlizumab (5.0 mg per kilogram), or placebo, administered intravenously 14 times over a period of 52 weeks. Patients who were receiving concomitant hydroxyurea as well as those not receiving hydroxyurea were included in the study. The primary end point was the annual rate of sickle cell–related pain crises with high-dose crizanlizumab versus placebo. The annual rate of days hospitalized, the times to first and second crises, annual rates of uncomplicated crises (defined as crises other than the acute chest syndrome, hepatic sequestration, splenic sequestration, or priapism) and the acute chest syndrome, and patient-reported outcomes were also assessed. RESULTS A total of 198 patients underwent randomization at 60 sites. The median rate of crises per year was 1.63 with high-dose crizanlizumab versus 2.98 with placebo (indicating a 45.3% lower rate with high-dose crizanlizumab, P = 0.01). The median time to the first crisis was significantly longer with high-dose crizanlizumab than with placebo (4.07 vs. 1.38 months, P = 0.001), as was the median time to the second crisis (10.32 vs. 5.09 months, P = 0.02). The median rate of uncomplicated crises per year was 1.08 with high-dose crizanlizumab, as compared with 2.91 with placebo (indicating a 62.9% lower rate with high-dose crizanlizumab, P = 0.02). Adverse events that occurred in 10% or more of the patients in either active-treatment group and at a frequency that was at least twice as high as that in the placebo group were arthralgia, diarrhea, pruritus, vomiting, and chest pain. CONCLUSIONS In patients with sickle cell disease, crizanlizumab therapy resulted in a significantly lower rate of sickle cell–related pain crises than placebo and was associated with a low incidence of adverse events. (Funded by Selexys Pharmaceuticals and others; SUSTAIN ClinicalTrials.gov number, NCT01895361.)

The terminal complement inhibitor eculizumab was recently shown to be effective and well tolerated in patients with paroxysmal nocturnal hemoglobinuria (PNH). Here, we extended these observations with results from an open-label, nonplacebo-controlled, 52-week, phase 3 clinical safety and efficacy study evaluating eculizumab in a broader PNH patient population. Eculizumab was administered by intravenous infusion at 600 mg every 7 ؎ 2 days for 4 weeks; 900 mg 7 ؎ 2 days later; followed by 900 mg every 14 ؎ 2 days for a total treatment period of 52 weeks. Ninety-seven patients at 33 international sites were enrolled. Patients treated with eculizumab responded with an 87% reduction in hemolysis, as measured by lactate dehydrogenase levels (P < .001). Baseline fatigue scores in the FACIT-Fatigue instrument improved by 12.2 ؎ 1.1 points (P < .001). Eculizumab treatment led to an improvement in anemia. The increase in hemoglobin level occurred despite a reduction in transfusion requirements from a median of 8.0 units of packed red cells per patient before treatment to 0.0 units per patient during the study (P < .001). Overall, transfusions were reduced 52% from a mean of 12.3 to 5.9 units of packed red cells per patient. Forty-nine patients (51%) achieved transfusion independence for the entire 52-week period. Improvements in hemolysis, fatigue, and transfusion requirements with eculizumab were independent of baseline levels of hemolysis and degree of thrombocytopenia. Quality of life measures were also broadly improved with eculizumab treatment. This study demonstrates that the beneficial effects of eculizumab treatment in patients with PNH are applicable to a broader population of PNH patients than previously studied. This trial is registered at

The complement system provides critical immunoprotective and immunoregulatory functions but uncontrolled complement activation can lead to severe pathology. In the rare hemolytic disease paroxysmal nocturnal hemoglobinuria (PNH), somatic mutations result in a deficiency of glycosylphosphatidylinositol-linked surface proteins, including the terminal complement inhibitor CD59, on hematopoietic stem cells. In a dysfunctional bone marrow background, these mutated progenitor blood cells expand and populate the periphery. Deficiency of CD59 on PNH red blood cells results in chronic complement-mediated intravascular hemolysis, a process central to the morbidity and mortality of PNH. A recently developed, humanized monoclonal antibody directed against complement component C5, eculizumab (Soliris; Alexion Pharmaceuticals Inc., Cheshire, CT, USA), blocks the proinflammatory and cytolytic effects of terminal complement activation. The recent approval of eculizumab as a first-in-class complement inhibitor for the treatment of PNH validates the concept of complement inhibition as an effective therapy and provides rationale for investigation of other indications in which complement plays a role.