Summary
We measured the absorption spectra of erythrocyte ghosts in the interval of 180-250
nm wavelength and calculated an index order/disorder (Io/d) by the ratio of the absorbances determined at 225 and at 195 nm, i.e. the higher
this ratio, the better the structure order of the erythrocyte membrane proteins examined.
The Io/d was significantly lower in nonregulated diabetics (n=24) than in normals (n=14) (12.14±0.32
versus 14.98±0.20, 2p< 0.001). In diabetics the Io/d correlated inversely with the mean daily plasma glucose (r= -0.51, 2p< 0.02). The
correlation was better with percent stable HbAI (r= -0.62, 2p< 0.005). In 4 initially
non regulated diabetics the Io/d was measured 4-5 times over a two month period while on an appropriate insulin regimen
which resulted in a fair glycemic control. The Io/d and percent stable HbAI slowly and parallely changed towards normal values.
The Io/d was measured also 0, 12, 36, 60, and 108 hours after incubation in vitro of erythrocyte
ghosts at 0, 20, and 37°C at different glucose concentrations (0, 25, and 100 mmol/l).
A decrease in the Io/d was observed, which was more pronounced at the latest times, at 37°C, and at the
highest glucose concentrations. Finally, the incubation of erythrocyte ghosts with
labeled D-(14C)-glucose resulted in a linkage with all membrane proteins, as assessed by the radioactivity
found in all the bands obtained after SDS gel electrophoresis.
Our data suggest that erythrocyte ghosts exposed to an abnormally high glucose concentration,
as in non regulated diabetics, undergo alterations of physico-chemical properties
of membrane proteins.
These alterations can be precisely measured and seem to be a direct consequence not
only of a slow process of glycosylation of membrane proteins, but also of a short-term
interacion between glucose and proteins. The demonstration of such a “glucotoxicity”
could be important to explain the abnormalities reported in the red cells of diabetics.
Key-Words:
Erythrocyte Membranes
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Glycosylation
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Diabetes
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UV Spectra
