Loss of phospholipid membrane asymmetry and sialylated glycoconjugates from erythrocyte surface in haemoglobin E β-thalassaemia

This study aimed to investigate any correlation between the extent of phosphatidylserine (PS) asymmetry and sialylated glycoconjugate levels with the faster clearance of circulating erythrocytes in haemoglobin E (HbE) beta-thalassaemia. Erythrocytes from peripheral blood samples of different HbE beta-thalassaemia patients showed loss of PS asymmetry measured by annexin V binding using flow cytometry. Maximum PS exposure was found when HbE was 50-60% and HbF was < 20% indicating a possible correlation with severity of the disease. Separation of erythrocytes into aged and younger cells showed higher loss of PS asymmetry in the younger erythrocytes of HbE beta-thalassaemia patients when compared with normal blood, where PS asymmetry was lost only in the older cells. Sialylated glycoconjugate measurement using the lectins wheatgerm agglutinin and pokeweed mitogen showed loss of sialic acid and N-acetyl-D-glucosamine-bearing glycoproteins in the order normal < homozygous E < HbE beta-thalassaemic upon ageing. A possible correlation was found between the loss of PS asymmetry with HbE level and the reduction of glycophorins from the cell surface, mediated by membrane vesiculation. A more facilitated vesiculation process in HbE beta-thalassaemic erythrocytes could lead to faster shedding of glycophorin-containing microvesicles, leaving highly PS-exposed erythrocytes accessible to phagocytes.