High D-glucose does not affect binding of [alpha]-tocopherol to human erythrocytes

The role of α-tocopherol uptake system in human erythrocyte in the uptake of plasma α-tocopherol has been suggested. However no information is available on α-tocopherol uptake activity of human erythrocytes in the presence of high levels of D-glucose which is known to lead to pathological alterations in different cells including human erythrocytes. Therefore, in order to examine the effect of D-glucose on the binding of α-tocopherol to human erythrocytes, the binding characteristics of α-tocopherol to these cells were established first. Binding of [3H]α-tocopherol to human erythrocytes was both saturable and specific. Scatchard analysis of α-tocopherol binding to these cells showed the presence of two independent classes of binding sites with widely different affinities. The high affinity binding sites had a dissociation constant (Kd1) of 90 nM with a binding capacity (n1) of 900 sites per cell, whereas the low affinity binding sites had a dissociation constant (Kd2) of 5.2 μM and a binding capacity (n2) of 105,400 sites per cell. Trypsin treatment abolished all the α-tocopherol binding activity. Competition for the binding of α-tocopherol to human erythrocytes was effective with other homologues of α-tocopherol (β-tocopherol, γ-tocopherol and δ-tocopherol) and their potency was almost equal to α-tocopherol itself. The order of preference was α-tocopherol > β-tocopherol ≥ γ-tocopherol ≥ δ-tocopherol. Incubation of human erythrocytes with various concentrations of D-glucose did not affect α-tocopherol uptake activity. Our data demonstrate the presence of an α-tocopherol uptake system in human erythrocytes and that the α-tocopherol uptake activity is not modulated by the presence of D-glucose.[PUBLICATION ABSTRACT]