Lower levels of erythrocyte membrane fluidity in diabetic patients. A spin label study

The dynamic properties of intact erythrocyte membrane in diabetic patients were investigated by means of electron spin resonance using three stearic acid spin labels (SAL): 5-, 12-, and 16-SAL. Significantly lower levels of erythrocyte membrane fluidity were revealed with 16-SAL as a probe in diabetic patients when compared with normal controls. However, there were no significant differences in fluidity values using 5- or 12-SAL between the two groups. Therefore, it became obvious that the decrease in fluidity was located in deeper sites (hydrophobic region) of the erythrocyte double membrane in diabetic patients. It was strongly suggested that changes in the membrane cholesterol to phospholipid molar ratios are not a principal factor contributing to the fluidity change. A significant increase of sphingomyelin and decrease of phosphatidylethanolamine were found in the erythrocyte membrane of diabetic patients and an alteration in membrane phospholipid classes and their acyl-chains could conceivably be related to the fluidity change. There were no significant correlations between change in membrane fluidity and most plasma lipids, plasma lecithin-cholesterol acyl-transferase activities, erythrocyte glycosylated hemoglobin, erythrocyte adenosine triphosphate, fasting blood glucose or duration of the disease. Plasma cholesterol of high-density lipoprotein showed a significant negative correlation with the membrane fluidity values. Some of the possible factors contributing to and the significance of the lower levels of erythrocyte membrane fluidity were discussed in conjunction with both metabolic and clinical aspects in diabetic patients.