Alterations in Organization of Phospholipids in Erythrocytes as Factor in Adherence to Endothelial Cells in Diabetes Mellitus

Erythrocytes from patients with diabetes mellitus exhibit increased adherence to cultured human vascular endothelial cells. We investigated the alterations in erythrocyte surface characteristics that may contribute to their abnormal adherence. The organization of phospholipids in the lipid bilayer, as determined by phospholipase A₂ treatment and chemical labeling with fluorescamine and trinitrobenzene sulfonic acid (TNBS), is altered in erythrocytes from diabetic patients. Specifically, 12–18% of phosphatidylserine in diabetic erythrocytes (n = 25) is accessible to phospholipase A₂ hydrolysis and TNBS labeling, compared to none in normal subjects. These results suggest either a loss in lipid asymmetry or in vivo destabilization of erythrocyte membranes in diabetic patients, causing increased accessibility to phospholipase A₂ degradation. The dye merocyanine 540 (MC-540), which is sensitive to the packing of lipids in the bilayer of the membrane, revealed more binding and fluorescence in erythrocytes from diabetic patients than in those from normal subjects. On flow cytometric analysis, 64.5 ± 17.0% red blood cells (RBCs) in diabetic patients, compared to 35.1 ± 25.9% RBCs in normal subjects, showed positive MC-540 binding, indicating significant (P < .001) differences in the packing of lipids in the external leaflet of the bilayer. The results of our study suggest that a loss of lipid asymmetry and/or less ordered packing in the outer leaflet of the diabetic erythrocyte membrane may be responsible for the increased propensity of erythrocytes to adhere to vascular endothelium.