In vitro glycation of red blood cell proteins: high levels of glucose lower lipid fluidity of erythrocyte membranes.

Human erythrocyte proteins, incubated in vitro in the presence of various concentrations of glucose, undergo nonenzymatic glycosylation, as evidenced by thiobarbituric chemical procedure. In vitro incubation of normal blood cells with glucose gave rise to levels of protein-bound glucose as well as of anisotropy values similar to those found in diabetic patients. There was a linear correlation between the amount of lysine-bound glucose of total hemoglobin or membrane proteins and membrane fluidity (r = 0.904 and r = 0.902 respectively). The time course of the reaction is linear for the first hours, and the rate of glycation depends on the glucose concentration in the medium: at a glucose concentration of 28 mmol/l up to 37.4 nmoles of glucose is bound per mg of erythrocyte membrane proteins. Hyperbolic curvature of both time and glucose concentration dependencies were revealed for the glycosylation of hemoglobin and membrane proteins as well as for membrane fluidity alterations. As demonstrated by the finding of 5-hydroxymethylfurfuraldehyde augmentation, higher glucose concentrations result in elevated glycation of both blood cell membrane proteins and hemoglobin, followed by the increase of membrane diphenylhexatriene anisotropy, thus resembling by consequences the affection of blood proteins by chronic hyperglycaemia in diabetes mellitus.