Thalassaemic erythrocytes: cellular suicide arising from iron and glutathione‐dependent oxidation reactions?

Summary. Both β‐thalassaemic red blood cells and normal red blood cells (RBC) artificially loaded with unpaired α‐haemoglobin chains exhibit increased amounts of membrane‐bound haem and iron. In the model β‐thalassaemic RBC the amount of free haem and iron was as much as 20 times that which could have been contributed by the entrapped α‐haemoglobin chains alone. This excess haem iron arises from destabilization of haemoglobin via reactions between ferric iron (Fe 3+ ), initially contributed by the unpaired a chains, and cytoplasmic constituents, primarily reduced glutathione (GSH). Indeed, in the presence of Fe 3+ (100μM) addition of even small amounts of GSH (0‐5 mM) 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 Fe 3+ ‐mediated haemoglobin oxidation was significantly inhibited by iron chelators. Finally, Fe 3+ ‐driven haemoglobin oxidation was synergized by low amounts of H 2 O 2 , an oxidant spontaneously generated in thalassaemic RBC. To summarize, the release of small amounts of free iron from unpaired α‐haemoglobin chains in the β‐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.