Hemopexin Therapy Improves Cardiovascular Function by Preventing Heme-Induced Endothelial Toxicity in Mouse Models of Hemolytic Diseases

Abstract

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...

Hemopexin counteracts systolic dysfunction induced by heme-driven oxidative stress

“…Recently, we showed that, by scavenging heme, Hx prevents heme accumulation in endothelial and immune cells, thus limiting heme toxicity [9,36]. To evaluate whether cardiomyocytes (CMs) may also be affected by pathologic free heme, we treated mouse neonatal CMs with 10 µM heme, in presence of either Hx or Albumin (a low affinity heme-binding protein [17]).…”

“…Heme promotes endothelial dysfunction by inducing the expression of adhesion molecules and reducing nitric oxide (NO) availability, which causes vasoconstriction [9][10][11][12][13][14]. Moreover, heme-derived ROS induce the proliferation of smooth muscle cells, that participate in vasculopathy associated with atherosclerosis and hypertension [15].…”

“…In this way, Hx works as a plasma buffering system to keep circulating heme at very low concentration. Nevertheless, during sustained hemolysis, Hx is fully saturated and free heme levels rise, leading to tissue oxidative damage [9,[20][21][22]. Recent studies have highlighted the potential therapeutic role of exogenous Hx in mouse models of sickle cell disease.…”

“…Recent studies have highlighted the potential therapeutic role of exogenous Hx in mouse models of sickle cell disease. In sickle cell disease mice, exogenous Hx markedly reduces inflammatory vasculopathy, prevents the development of severe acute vaso occlusive events and improves cardiac function [9,23,24]. Given these data, we asked whether the beneficial effect of Hx on the cardiovascular system might be due not only to preservation of vascular homeostasis but also to specific effects on the heart.…”

Increasing serum transferrin to reduce tissue iron overload due to ineffective erythropoiesis

“…18 Gelderman, Baek and co-authors showed that hemopexin as well as haptoglobin supplementation does not alter plasma iron levels or tissue iron loading. 8 This indicates that in the Hbb th3/+ mouse model the rate of intravascular hemolysis does not contribute significantly to hemochromatosis.…”