Treatment with recombinant ADAMTS13, alleviates hypoxia/reoxygenation-induced pathologies in a mouse model of human sickle cell disease.

BACKGROUND: Sickle cell disease (SCD) is an inherited red blood cell disorder with a causative substitution in the beta-globin gene that encodes beta-globin in hemoglobin. Furthermore, the ensuing vasculopathy in the microvasculature involves heightened endothelial cell adhesion, inflammation, and coagulopathy, all of which contribute to vaso-occlusive crisis (VOC) and the sequelae of SCD. In particular, dysregulation of the von Willebrand factor (VWF) and a disintegrin and metalloproteinase with thrombospondin type 1 motif, member 13 (ADAMTS13) axis has been implicated in human SCD pathology. OBJECTIVES: To investigate the beneficial potential of treatment with recombinant ADAMTS13 (rADAMTS13) to alleviate VOC. METHODS: Pharmacologic treatment with rADAMTS13 in vitro or in vivo was performed in a humanized mouse model of SCD that was exposed to hypoxia/reoxygenation stress as a model of VOC. Then, pharmacokinetic, pharmacodynamic, and behavioral analyses were performed. RESULTS: Administration of rADAMTS13 to SCD mice dose-dependently increased plasma ADAMTS13 activity, reduced VWF activity/antigen ratios, and reduced baseline hemolysis (free hemoglobin and total bilirubin) within 24 hours. rADAMTS13 was administered in SCD mice, followed by hypoxia/reoxygenation stress, and reduced VWF activity/antigen ratios in parallel to significantly (p < .01) improved recovery during the reoxygenation phase. Consistent with the results in SCD mice, we demonstrate in a human in vitro system that treatment with rADAMTS13 counteracts the inhibitory activity of hemoglobin on the VWF/ADAMTS13-axis. CONCLUSION: Collectively, our data provide evidence that relative ADAMTS13 insufficiency in SCD mice is corrected by pharmacologic treatment with rADAMTS13 and provides an effective disease-modifying approach in a human SCD mouse model.

Peroxiredoxin-2: A Novel Regulator of Iron Homeostasis in Ineffective Erythropoiesis.

AIMS: Iron overload (IO) is a life-threatening complication of chronic hemolytic disorders such as ß-thalassemia. IO results in severe cellular oxidative damage, leading to organ failure. Peroxiredoxin-2 (Prx2), a typical 2-cysteine-(Cys)-peroxiredoxin, is an important component of the cytoprotective system, but its response to IO is still to be fully defined. RESULTS: We studied the effects of IO on Prx2-knockout mice (Prx2-/-). The absence of Prx2 enhanced toxicity due to IO on erythropoiesis. We found that IO failed to induce the typical hepcidin (Hamp) upregulation in Prx2-/- mice due to its failure to activate the signal transducer and activator of transcription-3 (STAT3) with intact Jak2 signaling. In Prx2-/- mice, the loss of Hamp response was also observed after administration of a single dose of oral iron. When lipopolysaccharide (LPS) was used to explore IL6-STAT3 activation in Prx2-/- mice, STAT3 activation and Hamp upregulation were once again defective. Treatment with PEP-fusion-recombinant-Prx2 (PEP Prx2) significantly increased STAT3 activation with upregulation of Hamp expression in both IO- and LPS-exposed Prx2-/- mice. We also confirmed the beneficial effects of PEP Prx2 on Hamp expression through STAT3 activation in ß-thalassemic mice. INNOVATION: We propose that Prx2 plays a key role in responding to cytotoxicity of IO, directly targeting STAT3-transcriptional factor in a Jak2-independent fashion and regulating Hamp in response to canonical stimuli. CONCLUSION: Collectively, our data highlight a novel role of Prx2 in iron homeostasis. Prx2 is a key cytoprotector against IO that is induced either by iron supplementation or due to chronic hemolysis as in ß-thalassemia. Prx2 is required to support STAT3 transcriptional activity and regulation of Hamp expression. Antioxid. Redox Signal. 28, 1-14.

Dietary ω-3 fatty acids protect against vasculopathy in a transgenic mouse model of sickle cell disease.

The anemia of sickle cell disease is associated with a severe inflammatory vasculopathy and endothelial dysfunction, which leads to painful and life-threatening clinical complications. Growing evidence supports the anti-inflammatory properties of ω-3 fatty acids in clinical models of endothelial dysfunction. Promising but limited studies show potential therapeutic effects of ω-3 fatty acid supplementation in sickle cell disease. Here, we treated humanized healthy and sickle cell mice for 6 weeks with ω-3 fatty acid diet (fish-oil diet). We found that a ω-3 fatty acid diet: (i) normalizes red cell membrane ω-6/ω-3 ratio; (ii) reduces neutrophil count; (iii) decreases endothelial activation by targeting endothelin-1 and (iv) improves left ventricular outflow tract dimensions. In a hypoxia-reoxygenation model of acute vaso-occlusive crisis, a ω-3 fatty acid diet reduced systemic and local inflammation and protected against sickle cell-related end-organ injury. Using isolated aortas from sickle cell mice exposed to hypoxia-reoxygenation, we demonstrated a direct impact of a ω-3 fatty acid diet on vascular activation, inflammation, and anti-oxidant systems. Our data provide the rationale for ω-3 dietary supplementation as a therapeutic intervention to reduce vascular dysfunction in sickle cell disease.