An abnormality of the physical properties of the cell membrane may underlie the defect that unites the clinical and biochemical abnormalities found in subjects with
diabetic nephropathy. The cell membrane is linked both structurally and functionally with the cytoskeleton. The fluorescence anisotropy, a measure of membrane fluidity, was studied at baseline and after modulation of
cytoskeletal proteins by
thiol group alkylation with
N-ethylmaleimide (NEM).
1,6-diphenyl-1,3,5-hexatriene (DPH) was used to assess anisotropy in the deep hydrophobic regions of the
lipid bilayer and
trimethylammonium-diphenylhexatriene (
TMA-DPH) was used to assess the superficial, relatively hydrophilic regions. We compared 17 subjects with
insulin-dependent diabetes mellitus (
IDDM) and nephropathy with 17 control subjects with
IDDM and 24 non-diabetic control subjects. Median
TMA-DPH anisotropy (0.271 (0.239-0.332) vs 0.269 (0.258-0.281) vs 0.275 (0.246-0.287)) and DPH anisotropy (0.221 (0.193-0.261) vs 0.227 (0.197-0.253) vs 0.226 (0.193-0.245)) were similar in erythrocytes from the three groups. However after alkylation of
protein thiol groups with NEM clear differences emerged. In the control subjects with and without
IDDM there was a significant fall in
TMA-DPH anisotropy compared to the subjects with
diabetic nephropathy in whom the addition of NEM had no effect (deltaTMA-DPH anisotropy -0.005 (-0.020 - +0.006) vs -0.005 (-0.011 - +0.016) vs +0.002 (-0.010 - +0.008) p < 0.001). This finding was confirmed when the deep regions of the
lipid bilayer were assessed using DPH (deltaDPH anisotropy -0.017 (-0.029 - -0.007.) vs -0.015 (-0.029 - +0.001) vs + 0.003 (-0.021 - +0.018) p < 0.001). We conclude that cytoskeletal modulation of the physical properties of the
cell membrane lipids by
proteins is abnormal in subjects with
diabetic nephropathy. Such an abnormality could explain some of the clinical and metabolic abnormalities found in this condition.