Oxidative denaturation of red blood cells in thalassemia.
We believe that on the basis of all available data, severe oxidative damage occurs in alpha- and beta-thalassemic RBCs, as depicted schematically in Fig 6. The differences in the severity and pattern of the oxidative damage may be related to the type and, perhaps, quantity of precipitated globin chains. The detrimental effect of the excess chains is multifold. In the process of globin-chain precipitation, free radicals are generated. The end product of the precipitated hemoglobin chains is heme, from which eventually iron and globin are liberated. Globin chains have been found to interact and disrupt the RBC membrane, damaging the cytoskeleton. The role of heme has not yet been studied in detail in thalassemic RBCs. However, there is some evidence that it participates in damaging RBCs in other types of hemoglobinopathies. Excess of iron is known to be a catalyst of peroxidation via the Fenton reaction, causing damage to the various RBC membrane components (lipids, proteins, etc). The denatured hemaglobin, in the form of hemichromes, aggregates with protein 3, forming Actual proof of excessive free radical production in thalassemia is still warranted. It will not be easy to document since the amount of superoxide dismutase in RBCs is above and beyond that required for neutralizing excess amount of superoxide. The more active radicals, particularly hydroxyl free radical, are difficult to measure because they are so active an interact immediately with any given substrate in their vicinity. In addition, we have to better understand the finding of excess membrane lipids in thalassemic RBCs and whether there are changes in the formation and propagation of lipid peroxidation in these cells compared with normal RBCs. Regarding the proteins, further understanding is required concerning the exact type and sites of oxidation that occurs in the beta-thalassemia 4.1 protein, and whether the damage found in alpha-thalassemia is due to oxidation of ankyrin itself or its entrapment within the complex of the precipitated hemichromes of beta chains. What is the role of the different globin chain oxidation and precipitation in generating such different cytoskeletal protein alterations? Another point that needs to be elucidated is the role of different kinds of antibodies that are attached to the newly exposed antigenic sites on the thalassemic RBC membranes.(ABSTRACT TRUNCATED AT 400 WORDS)
Shinar
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Magen David Adom Blood Services Center, Tel Hashomer, Israel.
Rachmilewitz
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EA
D004912:Erythrocytes / Q000378:metabolism*; D005914:Globins / Q000378:metabolism; D006418:Heme / Q000502:physiology; D006420:Hemeproteins / Q000378:metabolism; D006801:Humans; D007501:Iron / Q000097:blood; D008563:Membrane Lipids / Q000097:blood; D008565:Membrane Proteins / Q000097:blood; D010084:Oxidation-Reduction; D013789:Thalassemia / Q000097:blood*
D006420:Hemeproteins; D008563:Membrane Lipids; D008565:Membrane Proteins; C001332:hemichrome; D006418:Heme; D005914:Globins; D007501:Iron