Investigation on the early events of apoptosis in senescent erythrocytes with special emphasis on intracellular free calcium and loss of phospholipid asymmetry in chronic renal failure

Background: The pathophysiological link between increased blood concentrations of factors responsible for the derangement and erythrocyte membrane functions in chronic renal failure (CRF) patients are not thoroughly elucidated. We studied the erythrocyte characteristics and phospholipid asymmetry loss in CRF patients with different grades of uremia and also examined the involvement of intracellular free Ca2+ in early events of apoptosis in uremic erythrocytes. Methods: The studied population consisted of 90, age and sex matched control subjects (Group I) and 238 CRF cases divided into 3 groups (Group II, III and IV) according to urea concentrations and complexity of secondary complications. Erythrocyte membrane fluidity determined by binding of MC540. Intracellular free Ca2+ concentration was determined by the 2-wavelength method by using fluorescent calcium-sensitive probe FURA-2AM. Measurement of erythrocyte phosphatidylserine exposure by flow cytometry using Annexin V-FITC. Results: Cholesterol shedding increased with increasing severity of uremic complications. Erythrocytes from Group II show mild echinocyte or formation of spicules on the erythrocyte membrane surface whereas in Group III and IV they were echinocytic. Binding of MC540 was significantly higher with progression of uremic complications. Surface charge of uremic erythrocyte membrane was significantly reduced when compared with control subjects. Intracellular free Ca2+ was positively correlated with binding of MC540 and surface hydrophobicity. The phosphatidylserine exposure of erythrocytes was significantly higher (p<0.001) in uremic patients when compared with controls. Conclusions: Phosphatidylserine (PS) exposure erythrocytes were significantly increased in uremic patients when compared with controls. Uremic complications predisposes to membrane damages in erythrocytes. (c) 2007 Elsevier B.V. All rights reserved.