Background-Hemolytic diseases are characterized by enhanced intravascular hemolysis resulting in heme-catalyzed reactive oxygen species generation, which leads to endothelial dysfunction and oxidative damage. Hemopexin (Hx) is a plasma heme scavenger able to prevent endothelial damage and tissue congestion in a model of heme overload. Here, we tested whether Hx could be used as a therapeutic tool to counteract heme toxic effects on the cardiovascular system in hemolytic diseases. Methods and Results-By using a model of heme overload in Hx-null mice, we demonstrated that heme excess in plasma, if not bound to Hx, promoted the production of reactive oxygen species and the induction of adhesion molecules and caused the reduction of nitric oxide availability. Then, we used β-thalassemia and sickle cell disease mice as models of hemolytic diseases to evaluate the efficacy of an Hx-based therapy in the treatment of vascular dysfunction related to heme overload. Our data demonstrated that Hx prevented heme-iron loading in the cardiovascular system, thus limiting the production of reactive oxygen species, the induction of adhesion molecules, and the oxidative inactivation of nitric oxide synthase/nitric oxide, and promoted heme recovery and detoxification by the liver mainly through the induction of heme oxygenase activity. Moreover, we showed that in sickle cell disease mice, endothelial activation and oxidation were associated with increased blood pressure and altered cardiac function, and the administration of exogenous Hx was found to almost completely normalize these parameters. 12,13,16 In hemolytic diseases, the high rate of hemolysis results in the saturation and depletion of the plasma Hb/heme scavenging systems 17 and leads to a buildup of Hb and heme in the circulation that mediates pro-oxidant and proinflammatory effects on vessel endothelial cells.
Conclusions-Hemopexin
18Although many mechanisms contribute to the complex pathophysiology of hemolytic diseases as SCD and β-thalassemia, a unifying theme is represented by the dysfunction of the vascular endothelium and the highly pro-oxidant plasma environment. 1,[19][20][21][22] SCD is characterized by recurring episodes of painful vasoocclusion, leading to ischemia/reperfusion injury and organ damage.6,23 Endothelial dysfunction, inflammation, and activated monocytes, neutrophils, platelets, and dense red cells all contribute to sickle cell crisis.4,23 β -Thalassemia is frequently complicated by thromboembolic events resulting from coagulation abnormalities and damaged red cells exposing phosphatidylserine, to which endothelial activation and oxidative stress strongly contribute. 3,23,24 Moreover, severe forms of SCD and β-thalassemia require a blood transfusion regimen that further increases the amount of circulating Hb/heme, thus exacerbating oxidative stress. 25,26 Although an iron chelation therapy is routinely associated with a transfusion regimen, 27,28 no heme chelation therapy has been developed to date that specifically prevents heme-induced endot...
