title: Haptoglobin preserves the CD163 hemoglobin scavenger pathway by shielding hemoglobin from peroxidative modification.
abstract: Detoxification and clearance of extracellular hemoglobin (Hb) have been attributed to its removal by the CD163 scavenger receptor pathway. However, even low-level hydrogen peroxide (H(2)O(2)) exposure irreversibly modifies Hb and severely impairs Hb endocytosis by CD163. We show here that when Hb is bound to the high-affinity Hb scavenger protein haptoglobin (Hp), the complex protects Hb from structural modification by preventing alpha-globin cross-links and oxidations of amino acids in critical regions of the beta-globin chain (eg, Trp15, Cys93, and Cys112). As a result of this structural stabilization, H(2)O(2)-exposed Hb-Hp binds to CD163 with the same affinity as nonoxidized complex. Endocytosis and lysosomal translocation of oxidized Hb-Hp by CD163-expressing cells were found to be as efficient as with nonoxidized complex. Hp complex formation did not alter Hb's ability to consume added H(2)O(2) by redox cycling, suggesting that within the complex the oxidative radical burden is shifted to Hp. We provide structural and functional evidence that Hp protects Hb when oxidatively challenged with H(2)O(2) preserving CD163-mediated Hb clearance under oxidative stress conditions. In addition, our data provide in vivo evidence that unbound Hb is oxidatively modified within extravascular compartments consistent with our in vitro findings.
authors.affiliation: Center for Biologics Evaluation and Research (CBER), US Food and Drug Administration (FDA), Washington, DC, USA.
authors.forename: Paul W
authors.initials: PW
authors.lastname: Buehler
authors.forename: Bindu
authors.initials: B
authors.lastname: Abraham
authors.forename: Florence
authors.initials: F
authors.lastname: Vallelian
authors.forename: Charlotte
authors.initials: C
authors.lastname: Linnemayr
authors.forename: Claudia P
authors.initials: CP
authors.lastname: Pereira
authors.forename: John F
authors.initials: JF
authors.lastname: Cipollo
authors.forename: Yiping
authors.initials: Y
authors.lastname: Jia
authors.forename: Malgorzata
authors.initials: M
authors.lastname: Mikolajczyk
authors.forename: Felicitas S
authors.initials: FS
authors.lastname: Boretti
authors.forename: Gabriele
authors.initials: G
authors.lastname: Schoedon
authors.forename: Abdu I
authors.initials: AI
authors.lastname: Alayash
authors.forename: Dominik J
authors.initials: DJ
authors.lastname: Schaer
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D015703:Antigens, CD / Q000378:metabolism*; D015214:Antigens, Differentiation, Myelomonocytic / Q000378:metabolism*; D002478:Cells, Cultured; D004285:Dogs; D006242:Haptoglobins / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology / Q000502:physiology*; D006419:Heme Oxygenase (Decyclizing) / Q000378:metabolism; D006454:Hemoglobins / Q000737:chemistry / Q000187:drug effects* / Q000378:metabolism*; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D010084:Oxidation-Reduction; D011485:Protein Binding / Q000502:physiology; D055503:Protein Multimerization / Q000187:drug effects; D055550:Protein Stability / Q000187:drug effects; D011956:Receptors, Cell Surface / Q000378:metabolism*; D051116:Receptors, Scavenger / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D000098902:CD163 Antigen
chemical_list: D000596:Amino Acids; D015703:Antigens, CD; D015214:Antigens, Differentiation, Myelomonocytic; D000098902:CD163 Antigen; D006242:Haptoglobins; D006454:Hemoglobins; D011956:Receptors, Cell Surface; D051116:Receptors, Scavenger; D006861:Hydrogen Peroxide; D006419:Heme Oxygenase (Decyclizing)