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      Mechanisms of haptoglobin protection against hemoglobin peroxidation triggered endothelial damage

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          Abstract

          Extracellular hemoglobin (Hb) has been recognized as a disease trigger in hemolytic conditions such as sickle cell disease, malaria, and blood transfusion. In vivo, many of the adverse effects of free Hb can be attenuated by the Hb scavenger acute-phase protein haptoglobin (Hp). The primary physiologic disturbances that can be caused by free Hb are found within the cardiovascular system and Hb-triggered oxidative toxicity toward the endothelium has been promoted as a potential mechanism. The molecular mechanisms of this toxicity as well as of the protective activities of Hp are not yet clear. Within this study, we systematically investigated the structural, biochemical, and cell biologic nature of Hb toxicity in an endothelial cell system under peroxidative stress. We identified two principal mechanisms of oxidative Hb toxicity that are mediated by globin degradation products and by modified lipoprotein species, respectively. The two damage pathways trigger diverse and discriminative inflammatory and cytotoxic responses. Hp provides structural stabilization of Hb and shields Hb's oxidative reactions with lipoproteins, providing dramatic protection against both pathways of toxicity. By these mechanisms, Hp shifts Hb's destructive pseudo-peroxidative reaction to a potential anti-oxidative function during peroxidative stress.

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          Most cited references 25

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          Hydroperoxide metabolism in mammalian organs.

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            A tissue-scale gradient of hydrogen peroxide mediates rapid wound detection in zebrafish

            Barrier structures (e.g. epithelia around tissues, plasma membranes around cells) are required for internal homeostasis and protection from pathogens. Wound detection and healing represent a dormant morphogenetic program that can be rapidly executed to restore barrier integrity and tissue homeostasis. In animals, initial steps include recruitment of leukocytes to the site of injury across distances of hundreds of micrometers within minutes of wounding. The spatial signals that direct this immediate tissue response are unknown. Due to their fast diffusion and versatile biological activities, reactive oxygen species (ROS), including hydrogen peroxide (H2O2), are interesting candidates for wound-to-leukocyte signalling. We probed the role of H2O2 during the early events of wound responses in zebrafish larvae expressing a genetically encoded H2O2 sensor1. This reporter revealed a sustained rise in H2O2 concentration at the wound margin, starting ∼3 min after wounding and peaking at ∼20 min, which extended ∼100−200 μm into the tail fin epithelium as a decreasing concentration gradient. Using pharmacological and genetic inhibition, we show that this gradient is created by Dual oxidase (Duox), and that it is required for rapid recruitment of leukocytes to the wound. This is the first observation of a tissue-scale H2O2 pattern, and the first evidence that H2O2 signals to leukocytes in tissues, in addition to its known antiseptic role.
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              The clinical sequelae of intravascular hemolysis and extracellular plasma hemoglobin: a novel mechanism of human disease.

              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. 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. 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. 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.
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                Author and article information

                Journal
                Cell Death Differ
                Cell Death Differ
                Cell Death and Differentiation
                Nature Publishing Group
                1350-9047
                1476-5403
                November 2013
                30 August 2013
                1 November 2013
                : 20
                : 11
                : 1569-1579
                Affiliations
                [1 ]Institute of Anesthesiology, University Hospital , Zurich, Switzerland
                [2 ]Division of Internal Medicine, University Hospital , Zurich, Switzerland
                [3 ]Electron Microscopy Center (EMEZ), ETH Zurich, Switzerland
                [4 ]Laboratory of Physical Chemistry, ETH Zurich, Switzerland
                [5 ]Center for Evolutionary Medicine (ZEM), University of Zurich , Zurich, Switzerland
                Author notes
                [* ]Division of Internal  Medicine,  University Hospital ,  CH-8091, Zurich, Switzerland. Tel: +41 44 255 1111; E-mail: dominik.schaer@ 123456usz.ch
                [6]

                These authors contributed equally to this work.

                Article
                cdd2013113
                10.1038/cdd.2013.113
                3792434
                23995229
                Copyright © 2013 Macmillan Publishers Limited

                This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-sa/3.0/

                Categories
                Original Paper

                Cell biology

                endothelial damage, peroxidation, haptoglobin, hemoglobin

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