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Oxidative Medicine and Cellular Longevity
Volume 2013, Article ID 523652, 11 pages
http://dx.doi.org/10.1155/2013/523652
Review Article

The Haptoglobin-CD163-Heme Oxygenase-1 Pathway for Hemoglobin Scavenging

Department of Biomedicine, University of Aarhus, Ole Worms Alle 3, Building 1170, 8000 Aarhus C, Denmark

Received 20 March 2013; Revised 9 May 2013; Accepted 13 May 2013

Academic Editor: Mohammad Abdollahi

Copyright © 2013 Jens Haugbølle Thomsen et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The haptoglobin- (Hp-) CD163-heme oxygenase-1 (HO-1) pathway is an efficient captor-receptor-enzyme system to circumvent the hemoglobin (Hb)/heme-induced toxicity during physiological and pathological hemolyses. In this pathway, Hb tightly binds to Hp leading to CD163-mediated uptake of the complex in macrophages followed by lysosomal Hp-Hb breakdown and HO-1-catalyzed conversion of heme into the metabolites carbon monoxide (CO), biliverdin, and iron. The plasma concentration of Hp is a limiting factor as evident during accelerated hemolysis, where the Hp depletion may cause serious Hb-induced toxicity and put pressure on backup protecting systems such as the hemopexin-CD91-HO pathway. The Hp-CD163-HO-1 pathway proteins are regulated by the acute phase mediator interleukin-6 (IL-6), but other regulatory factors indicate that this upregulation is a counteracting anti-inflammatory response during inflammation. The heme metabolites including bilirubin converted from biliverdin have overall an anti-inflammatory effect and thus reinforce the anti-inflammatory efficacy of the Hp-CD163-HO-1 pathway. Future studies of animal models of inflammation should further define the importance of the pathway in the anti-inflammatory response.