The relationship of chemical modification of membrane proteins and plasma lipoproteins to reduced membrane fluidity of erythrocytes from diabetic subjects.

The significance of the two most common hallmarks of the diabetic state, hyperglycaemia and hyperlipidaemia, was investigated in terms of disorders of cell membrane dynamics. In order to examine whether the alterations in cell membrane lipid bilayer dynamics are somehow related to protein chemical modifications in plasma low-(LDL) and high-density lipoproteins (HDL) and blood cell membranes, we compared 19 poorly controlled diabetic subjects with 19 age- and sex-matched controls. The extent of (non-enzymatic) glycation, lipid peroxidation and the cholesterol/phospholipid ratio were increased in plasma low density lipoproteins and high density lipoproteins from diabetic patients. The mean steady-state fluorescence polarization values in 1,6-diphenyl-1,3,5-hexatriene-labelled isolated erythrocyte membranes from diabetic subjects were significantly greater than from control subjects (0.186 +/- 0.008 vs 0.173 +/- 0.006, p < 0.001); the fluorescence polarization values in erythrocyte membranes from diabetic and control subjects positively correlated with the extent of membrane protein glycation, lipid peroxidation and the cholesterol content. The cholesterol to phospholipid molar ratios in low density lipoproteins and high-density lipoproteins from diabetic and control subjects correlated significantly with the fluorescence polarization values in erythrocyte membranes from these subjects. Furthermore, the extent of glycation of low density lipoproteins appears to be strongly correlated with the extent of lipoprotein lipid peroxidation (r = 0.789, p < 0.001). The atherosclerotic potential of plasma lipoproteins in diabetes mellitus was discussed in terms of membrane and plasma protein chemical modifications.