Decrease of red cell membrane fluidity and -SH groups due to hyperglycemic conditions is counteracted by alpha-lipoic acid.
Human red cell membranes (ghosts) were treated by 5 min of incubation with fasting or hypo- and hyperglycemic concentrations of D-glucose. This simulation of nondiabetic or diabetic conditions revealed an influence on membrane fluidity and on protein -SH reactivity. Protein -SH groups, measured with Ellman's reagent, generally behave in the same way as membrane fluidity determined with diphenylhexatriene. Maximal values were obtained with 5 mM D-glucose, whereas decrease was observed above 10 mM D-glucose. Addition of alpha-lipoic acid (4 nmol/mg protein) resulted in a significant increase in membrane fluidity and titratable -SH groups at glucose concentrations of 10 mM and above. Dithiothreitol diminished titrable-SH groups and did not restore membrane fluidity. 2-Mercaptopropionylglycine was only effective in restoration of -SH groups. By contrast to D-glucose, other sugars such as L-glucose, D-fructose, or sucrose revealed no comparable changes on membrane fluidity and titratable membrane -SH groups between concentrations of 5 and 10 mM. The hyperglycemic effects of D-glucose were corroborated with isolated, reconstituted membrane proteins and erythrocyte glucose carrier, indicating that, in general, the observed divergent biochemical/biophysical changes of the red cell membrane are influenced by the glucose transport protein GluT1. The natural R-form and the S-form of alpha-lipoic acid were compared with racemic R-/S-forms for their efficiencies in alterations of red cell membrane fluidity. Decreased fluidities in presence of 10 mM glucose were found to be influenced in differentiated ways: the S-form was highly active in increasing fluidity at 4 nmol/mg and increasingly less active up to 20 nmol/mg protein. By contrast the R-form of lipoic acid was moderately efficient in increasing fluidity through a larger concentration range between 4 and 80 nmol/mg protein.
Hofmann
M
M
Gustav-Embden-Zentrum der Biologischen Chemie, Universitätsklinikum Frankfurt, Frankfurt am Main, Germany.
Mainka
P
P
Tritschler
H
H
Fuchs
J
J
Zimmer
G
G
D004229:Dithiothreitol / Q000494:pharmacology; D004910:Erythrocyte Membrane / Q000502:physiology*; D005454:Fluorescence Polarization; D005947:Glucose / Q000378:metabolism; D051272:Glucose Transporter Type 1; D006021:Glycophorins / Q000378:metabolism; D006801:Humans; D006943:Hyperglycemia / Q000503:physiopathology*; D008560:Membrane Fluidity / Q000187:drug effects*; D008565:Membrane Proteins / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D013438:Sulfhydryl Compounds / Q000032:analysis / Q000494:pharmacology*; D008063:Thioctic Acid / Q000494:pharmacology*; D008625:Tiopronin / Q000494:pharmacology
D051272:Glucose Transporter Type 1; D006021:Glycophorins; D008565:Membrane Proteins; D009004:Monosaccharide Transport Proteins; C495677:SLC2A1 protein, human; D013438:Sulfhydryl Compounds; D008063:Thioctic Acid; D008625:Tiopronin; D005947:Glucose; D004229:Dithiothreitol