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Haptoglobin preserves the CD163 hemoglobin scavenger pathway by shielding hemoglobin from peroxidative modification


Buehler, P W; Abraham, B; Vallelian, F; Linnemayr, C; Pereira, C P; Cipollo, J F; Jia, Y; Mikolajczyk, M; Boretti, F S; Schoedon, G; Alayash, A I; Schaer, D J (2009). Haptoglobin preserves the CD163 hemoglobin scavenger pathway by shielding hemoglobin from peroxidative modification. Blood, 113(11):2578-2586.

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.

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.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:04 Faculty of Medicine > University Hospital Zurich > Clinic and Policlinic for Internal Medicine
05 Vetsuisse Faculty > Veterinary Clinic > Department of Small Animals
Dewey Decimal Classification:610 Medicine & health
Date:12 March 2009
Deposited On:16 Sep 2009 14:42
Last Modified:05 Apr 2016 13:11
Publisher:American Society of Hematology
ISSN:0006-4971
Additional Information:This research was originally published in Blood. BLOOD, 12 MARCH 2009 VOLUME 113, NUMBER 11. Copyright by the American Society of Hematology
Publisher DOI:10.1182/blood-2008-08-174466
PubMed ID:19131549
Permanent URL: http://doi.org/10.5167/uzh-18008

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