Investigation of the alterations induced in erythrocyte membrane physical characteristics of non-insulin-dependent type II diabetic Patients: an ESR study

Abstract

The physical and dynamic properties of intact erythrocyte membranes of two groups, diabetic patients treated by diet alone (27 women and 41 men, 40–75 years old) and healthy subjects (controls) (25 women and 35 men, 35–75 years old) were investigated by electron spin resonance (ESR) spectroscopy. 5-doxyl stearic acid (5-DSA) and 4-maleimido-2,2,6,6-tetramethyl-piperidine-1-oxyl (MAL-6) are employed as spin labels throughout the experiments. While 5-DSA monitors the membrane surface region and gives information about the order of lipids in this region through the order parametersS′, MAL-6 binds thiol groups S-H to the membrane protein and gives information about possible protein conformational changes. Order parameters were calculated from room temperature spectra recorded for intact erythrocytes labeled with 5-DSA and the values of 0.682±0.004 and 0.666±0.004 were obtained for diabetic patients and controls, respectively. Variations of theh(−1),h(0),h(+1) and 2A11 parameters in the temperature range of 10–50 °C were also studied and fairly different behaviors were observed for both groups, especially for theh(−1) parameter. Line intensitiesW andS characterizing the concentrations of weakly and strongly immobilized MAL-6 species bound to S-H groups of intact erythrocyte membrane proteins were used to calculate theW/S ratios. They were found to be 34.1±1.9 and 30.5±2.4 for diabetic patients and controls, respectively. While line intensitiesT, those of theM1=−1 high-field resonance line associated with the weakly immobilized S-H sites, of both groups exhibit a very similar microwave saturation behavior in the range of 0.5–20 mW, line intensitiesW of both groups saturated differently. Variations of line intensitiesS, W andT with temperature were also investigated in the temperature range of 10–50 °C and characteristic differences were observed to exist between two groups implying a less fluid erythrocyte membrane for diabetic patients. Increases in the order parameterS′ and in theW/S ratio are considered as major factors attributable to the alteration in the physical and dynamic properties of erythrocyte membrane in the diabetic state.