| Abstract: | 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 important component in the destruction of β-thalassemic RBC is the generation of reactive oxygen species and the release of redox-active iron by the unpaired α-hemoglobin chains. Consequently, we hypothesized that the presence of this oxidative stress to the RBC membrane could lead to alterations in membrane lipid organization. Model β thalassemic RBC, prepared by the introduction of excess α-globin in the cell, have previously been shown to exhibit structural and functional changes almost identical to those observed in β-thalassemic cells. After 24 hr at 37°C, the model β thalassemic cells exhibited a significant loss of deformability, as measured by ektacytometric analysis, indicative of extensive membrane damage. However, a normal steady-state distribution of endogenous phospholipids was found, as evidenced by the accessibility of membrane phospholipids to hydrolysis by phospholipases. Similarly, the kinetics of transbilayer movement of spin-labeled phosphatidylserine (PS) and phosphatidylethanolamine (PE) in all samples was in the normal range and was not affected by the presence of excess α-globin chains. In contrast, a faster rate of spin-labeled phosphatidylcholine (PC) transbilayer movement was observed in these cells. While control RBC exhibited a complete loss of their initial (2 mol%) lysophosphatidylcholine (LPC) levels following 24 hr of incubation at 37°C, 1.5 mol% LPC was still present in model β-thalassemic cells, suggesting an altered phospholipid molecular species turnover, possibly as a result of an increased repair of oxidatively damaged phospholipids. © 1996 Wiley-Liss, Inc. |
