Free hemoglobin induction of pulmonary vascular disease: evidence for an inflammatory mechanism
ABSTRACT Cell-free hemoglobin (Hb) exposure may be a pathogenic mediator in the development of pulmonary arterial hypertension (PAH), and when combined with chronic hypoxia the potential for exacerbation of PAH and vascular remodeling is likely more pronounced. We hypothesized that Hb may contribute to hypoxia-driven PAH collectively as a prooxidant, inflammatory, and nitric oxide (NO) scavenger. Using programmable micropump technology, we exposed male Sprague-Dawley rats housed under room air or hypoxia to 12 or 30 mg per day Hb for 3, 5, and 7 wk. Blood pressure, cardiac output, right ventricular hypertrophy, and indexes of pulmonary vascular remodeling were evaluated. Additionally, markers of oxidative stress, NO bioavailability and inflammation were determined. Hb increased pulmonary arterial (PA) pressure, pulmonary vessel wall stiffening, and right heart hypertrophy with temporal and dose dependence in both room air and hypoxic cohorts. Hb induced a modest increase in plasma oxidative stress markers (malondialdehyde and 4-hydroxynonenal), no change in NO bioavailability, and increased lung ICAM protein expression. Treatment with the antioxidant Tempol attenuated Hb-induced pulmonary arterial wall thickening, but not PA pressures or ICAM expression. Chronic exposure to low plasma Hb concentrations (range = 3-10 μM) lasting up to 7 wk in rodents induces pulmonary vascular disease via inflammation and to a lesser extent by Hb-mediated oxidation. Tempol demonstrated a modest effect on the attenuation of Hb-induced pulmonary vascular disease. NO bioavailability was found to be of minimal importance in this model.
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ABSTRACT: The development of oxygen (O2)-carrying blood substitutes has evolved from the goal of replicating blood O2 transport properties to that of preserving microvascular and organ function, reducing the inherent or potential toxicity of the material used to carry O2, and treating pathologies initiated by anemia and hypoxia. Furthermore, the emphasis has shifted from blood replacement fluid to "O2 therapeutics" that restore tissue oxygenation to specific tissues regions. This review covers the different alternatives, potential and limitations of hemoglobin-based O2 carriers (HBOCs) and perfluorocarbon-based O2 carriers (PFCOCs), with emphasis on the physiologic conditions disturbed in the situation that they will be used. It describes how concepts learned from plasma expanders without O2-carrying capacity can be applied to maintain O2 delivery and summarizes the microvascular responses due to HBOCs and PFCOCs. This review also presents alternative applications of HBOCs and PFCOCs namely: 1) How HBOC O2 affinity can be engineered to target O2 delivery to hypoxic tissues; and 2) How the high gas solubility of PFCOCs provides new opportunities for carrying, dissolving, and delivering gases with biological activity. It is concluded that the development of current blood substitutes has amplified their applications horizon by devising therapeutic functions for O2 carriers requiring limited O2 delivery capacity restoration. Conversely, full, blood-like O2-carrying capacity reestablishment awaits the control of O2 carrier toxicity.ASAIO journal (American Society for Artificial Internal Organs: 1992) 07/2013; 59(4):337-354. DOI:10.1097/MAT.0b013e318291fbaa · 1.39 Impact Factor
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ABSTRACT: Hemolysis occurs in many hematologic and non-hematologic diseases. Extracellular hemoglobin (Hb) has been recognized to trigger specific pathophysiologies that are associated with adverse clinical outcomes in patients with hemolysis, such as acute and chronic vascular disease, inflammation, thrombosis and renal impairment. Among the molecular characteristics of extracellular Hb, translocation of the molecule into the extravascular space, oxidative and nitric oxide reactions, hemin release and molecular signaling effects of hemin appear to be the most critical. Limited clinical experience with a plasma-derived haptoglobin product in Japan and more recent preclinical animal studies suggest that the natural Hb and hemin scavenger proteins haptoglobin (Hp) and hemopexin (Hpx) have a strong potential to neutralize the adverse physiologic effects of Hb and hemin. This includes conditions that are as diverse as red blood cell transfusion, sickle cell disease, sepsis and extracorporeal circulation. This perspective reviews the principal mechanisms of Hb and hemin toxicity in different disease states, updates how the natural scavengers efficiently control these toxic moieties, and explores critical issues in the development of human plasma-derived Hp and Hpx as therapeutics for patients with excessive intravascular hemolysis.Blood 12/2012; 121(8). DOI:10.1182/blood-2012-11-451229 · 10.43 Impact Factor
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ABSTRACT: Objective: Release of hemoglobin (Hb) with hemolysis causes vascular dysfunction. New evidence implicates Hb-induced nuclear factor kappa beta (NFκB) and hypoxia inducible factor (HIF) activation, which may be under the control of a Toll-like receptor (TLR)-signaling pathway. Nearly all TLR signaling pathways activate the myeloid differentiation primary response gene 88 (MyD88) that regulates NFκB. We hypothesized that the differing transition states of Hb influence endothelial cell permeability by NFκB activation and HIF regulation through a MyD88 dependent pathway. Methods and results: In cultured human microvascular endothelial cells (HMEC-1), we examined the effect of Hb in the ferrous (HbFe2+), ferric (HbFe3+), and ferryl (HbFe4+) transition states on NFκB and HIF activity. HIF-1α and HIF-2α mRNA up-regulation, monolayer permeability, F-actin formation, and expression of zona occluden-1 (Z0-1) in the presence or absence of NFκB, MyD88, or HIF inhibition were also measured. Finally, the effects of TLR-4 inhibition or superoxide dismutase (SOD) and catalase were tested. Our data showed that cell free Hb, in each transition state, induced NFκB and HIF activity, up regulated HIF-1α and HIF-2α mRNA, and increased HMEC-1 permeability and F-actin formation. Blockade of either MyD88 or NFκB attenuated Hb-induced HIF activity, the up-regulation HIF-1α and HIF-2α mRNA, HMEC-1 permeability and F-actin formation. Inhibition of HIF activity had less of an effect on Hb-induced monolayer permeability. SOD and catalase also attenuated these endpoints. TLR-4 inhibition had no effect. Conclusion: Our results demonstrate that Hb-induced NFκB and HIF are regulated by MyD88 activation or Hb transition state induced ROS formation, which influences HMEC-1 permeability.American Journal of Respiratory Cell and Molecular Biology 05/2013; DOI:10.1165/rcmb.2012-0440OC · 4.11 Impact Factor