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Free Radic Biol Med. 2013 Aug;61:265-72. doi: 10.1016/j.freeradbiomed.2013.04.026. Epub 2013 Apr 25.

Immuno-spin trapping of heme-induced protein radicals: Implications for heme oxygenase-1 induction and heme degradation.

Author information

  • 1Free Radical Metabolism Group, Laboratories of Toxicology and Pharmacology, National Institute of Environmental Health Sciences, 111 T.W. Alexander Drive, Research Triangle Park, NC 27709, USA. Electronic address: kumara10@niehs.nih.gov.
  • 2Free Radical Metabolism Group, Laboratories of Toxicology and Pharmacology, National Institute of Environmental Health Sciences, 111 T.W. Alexander Drive, Research Triangle Park, NC 27709, USA.
  • 3Laboratory of Structural Biology, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709, USA.
  • 4Department of Environmental Health Sciences, University of South Carolina, Columbia, SC 29208, USA.

Abstract

Heme, in the presence of hydrogen peroxide, can act as a peroxidase. Intravascular hemolysis results in a massive release of heme into the plasma in several pathophysiological conditions such as hemolytic anemia, malaria, and sickle cell disease. Heme is known to induce heme oxygenase-1(HO-1) expression, and the extent of induction depends on the ratio of albumin to heme in plasma. HO-1 degrades heme and ultimately generates the antioxidant bilirubin. Heme also causes oxidative stress in cells, but whether it causes protein-radical formation has not yet been studied. In the literature, two purposes for the degradation of heme by HO-1 are discussed. One is the production of the antioxidant bilirubin and the other is the prevention of heme-dependent adverse effects. Here we have investigated heme-induced protein-radical formation, which might have pathophysiological consequences, and have used immuno-spin trapping to establish the formation of heme-induced protein radicals in two systems: human serum albumin (HSA)/H2O2 and human plasma/H2O2.We found that excess heme catalyzed the formation of HSA radicals in the presence of hydrogen peroxide. When heme and hydrogen peroxide were added to human plasma, heme was found to oxidize proteins, primarily and predominantly HSA; however, when HSA-depleted plasma was used, heme triggered the oxidation of several other proteins, including transferrin. Thus, HSA in plasma protected other proteins from heme/H2O2-induced oxidation. The antioxidants ascorbate and uric acid significantly attenuated protein-radical formation induced by heme/H2O2; however, bilirubin did not confer significant protection. Based on these findings, we conclude that heme is degraded by HO-1 because it is a catalyst of protein-radical formation and not merely to produce the relatively inefficient antioxidant bilirubin.

Copyright © 2013 Elsevier Inc. All rights reserved.

KEYWORDS:

Heme; Nitrone adducts; Oxidative stress; Peroxidase; Protein oxidation; Protein radical

PMID:
23624303
[PubMed - in process]
PMCID:
PMC3851609
Free PMC Article
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