THALASSEMIC ERYTHROCYTES - CELLULAR SUICIDE ARISING FROM IRON AND GLUTATHIONE-DEPENDENT OXIDATION REACTIONS

Both beta-thalassaemic red blood cells and normal red blood cells (RBC) artificially loaded with unpaired alpha-haemoglobin chains exhibit increased amounts of membrane-bound haem and iron. In the model beta-thalassaemic RBC the amount of free haem and iron was as much as 20 times that which could have been contributed by the entrapped alpha-haemoglobin chains alone, This excess haem/iron arises from destabilization of haemoglobin via reactions between ferric iron (Fe3+), initially contributed by the unpaired ct chains, and cytoplasmic constituents, primarily reduced glutathione (GSH), Indeed, in the presence of Fe3+ (100 mu M) addition of even small amounts of GSH (0.5 nm) to dilute RBC haemolysates (0.15 mg haemoglobin/dl) greatly accelerated methaemoglobin formation, In contrast, lysates from GSH-depleted RBC demonstrated a significantly reduced rate of iron-mediated haemoglobin oxidation which was reversible by addition of GSH, The initiation, and subsequent propagation, of Fe3+-mediated haemoglobin oxidation was significantly inhibited by iron chelators. Finally, Fe3+-driven haemoglobin oxidation was synergized by low amounts of H2O2, an oxidant spontaneously generated in thalassaemic RBC. To summarize, the release of small amounts of free iron from unpaired alpha-haemoglobin chains in the beta-thalassaemic RBC can initiate self-amplifying redox reactions which simultaneously deplete cellular reducing potential (e.g. GSH), oxidize additional haemoglobin, and accelerate the red cell destruction.