EFFECT OF EXCESS ALPHA-HEMOGLOBIN CHAINS ON CELLULAR AND MEMBRANE OXIDATION IN MODEL BETA-THALASSEMIC ERYTHROCYTES

While red cells from individuals with beta thalassemias are characteri zed by evidence of elevated in vivo oxidation, it has not been possibl e 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'' bet a-thalassemic cells generated significantly (P < 0.001) greater amount s of methemoglobin and intracellular hydrogen peroxide than did contro l cells. This resulted in significant time-dependent decreases in the protein concentrations and reduced thiol content of spectrin and ankyr in. These abnormalities correlated with the rate of alpha-hemoglobin c hain 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 challe nged with an external oxidant, lipid peroxidation and vitamin E oxidat ion were significantly (P < 0.001) enhanced in the alpha-hemoglobin ch ain-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 ir on chelator. In contrast, chemical inhibition of cellular catalase act ivity enhanced the detrimental effects of entrapped a-hemoglobin chain s. In summary, entrapment of purified alpha-hemoglobin chains within n ormal erythrocytes significantly enhanced cellular oxidant stress and resulted in pathological changes characteristic of thalassemic cells i n vivo. This model provides a means by which the pathophysiological ef fects of excess alpha-hemoglobin chains can be examined.