PHOSPHOLIPID-COMPOSITION AND ORGANIZATION IN MODEL BETA-THALASSEMIC ERYTHROCYTES

The membrane phospholipid organization in human red blood cells (RBC) is rigidly maintained by a complex system of enzymes, However, several elements of this system are sensitive to oxidative damage, An importa nt component in the destruction of beta-thalassemic RBC is the generat ion of reactive oxygen species and the release of redox-active iron by the unpaired alpha-hemoglobin chains. Consequently, we hypothesized t hat the presence of this oxidative stress to the RBC membrane could le ad to alterations in membrane lipid organization, Model beta thalassem ic RBC, prepared by the introduction of excess alpha-globin in the cel l, have previously been shown to exhibit structural and functional cha nges almost identical to those observed in beta-thalassemic cells. Aft er 24 hr at 37 degrees C, the model beta thalassemic cells exhibited a significant loss of deformability, as measured by ektacytometric anal ysis, indicative of extensive membrane damage, However, a normal stead y-state distribution of endogenous phospholipids was found, as evidenc ed by the accessibility of membrane phospholipids to hydrolysis by pho spholipases. Similarly, the kinetics of transbilayer movement of spin- labeled phosphatidylserine (PS) and phosphatidylethanolamine (PE) in a ll samples was in the normal range and was not affected by the presenc e of excess alpha-globin chains. In contrast, a faster rate of spin-la beled phosphatidylcholine (PC) transbilayer movement was observed in t hese cells. While control RBC exhibited a complete loss of their initi al (2 mol%) lysophosphatidylcholine (LPC) levels following 24 hr of in cubation at 37 degrees C, 1.5 mol% LPC was still present in model beta -thalassemic cells, suggesting an altered phospholipid molecular speci es turnover, possibly as a result of an increased repair of oxidativel y damaged phospholipids. (C) 1996 Wiley-Liss, Inc.