title: Effect of excess alpha-hemoglobin chains on cellular and membrane oxidation in model beta-thalassemic erythrocytes.
abstract: While red cells from individuals with beta thalassemias are characterized by evidence of elevated in vivo oxidation, it has not been possible to directly examine the relationship between excess alpha-hemoglobin chains and the observed oxidant damage. To investigate the oxidative effects of unpaired alpha-hemoglobin chains, purified alpha-hemoglobin chains were entrapped within normal erythrocytes. These "model" beta-thalassemic cells generated significantly (P < 0.001) greater amounts of methemoglobin and intracellular hydrogen peroxide than did control cells. This resulted in significant time-dependent decreases in the protein concentrations and reduced thiol content of spectrin and ankyrin. These abnormalities correlated with the rate of alpha-hemoglobin chain autoxidation and appearance of membrane-bound globin. In addition, alpha-hemoglobin chain loading resulted in a direct decrease (38.5%) in catalase activity. In the absence of exogenous oxidants, membrane peroxidation and vitamin E levels were unaltered. However, when challenged with an external oxidant, lipid peroxidation and vitamin E oxidation were significantly (P < 0.001) enhanced in the alpha-hemoglobin chain-loaded cells. Membrane bound heme and iron were also significantly elevated (P < 0.001) in the alpha-hemoglobin chain-loaded cells and lipid peroxidation could be partially inhibited by entrapment of an iron chelator. In contrast, chemical inhibition of cellular catalase activity enhanced the detrimental effects of entrapped alpha-hemoglobin chains. In summary, entrapment of purified alpha-hemoglobin chains within normal erythrocytes significantly enhanced cellular oxidant stress and resulted in pathological changes characteristic of thalassemic cells in vivo. This model provides a means by which the pathophysiological effects of excess alpha-hemoglobin chains can be examined.
authors.affiliation: Children's Hospital Oakland Research Institute, California 94609.
authors.forename: M D
authors.initials: MD
authors.lastname: Scott
authors.forename: J J
authors.initials: JJ
authors.lastname: van den Berg
authors.forename: T
authors.initials: T
authors.lastname: Repka
authors.forename: P
authors.initials: P
authors.lastname: Rouyer-Fessard
authors.forename: R P
authors.initials: RP
authors.lastname: Hebbel
authors.forename: Y
authors.initials: Y
authors.lastname: Beuzard
authors.forename: B H
authors.initials: BH
authors.lastname: Lubin
mesh_terms: D000640:Amitrole / Q000494:pharmacology; D000975:Antioxidants / Q000494:pharmacology; D003676:Deferoxamine / Q000494:pharmacology; D003911:Dextrans / Q000494:pharmacology; D004907:Erythrocyte Deformability / Q000187:drug effects; D004910:Erythrocyte Membrane / Q000378:metabolism*; D004912:Erythrocytes / Q000737:chemistry*; D005978:Glutathione / Q000097:blood; D006418:Heme / Q000378:metabolism; D006454:Hemoglobins / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D007501:Iron / Q000378:metabolism; D015227:Lipid Peroxidation; D013058:Mass Spectrometry; D008565:Membrane Proteins / Q000378:metabolism; D010084:Oxidation-Reduction; D010545:Peroxides / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D017086:beta-Thalassemia / Q000097:blood*
chemical_list: D000975:Antioxidants; D003911:Dextrans; D006454:Hemoglobins; D008565:Membrane Proteins; D010545:Peroxides; D017382:Reactive Oxygen Species; D006418:Heme; D007501:Iron; D005978:Glutathione; D003676:Deferoxamine; D000640:Amitrole