Differential effects of α‐, β‐ and γ‐cyclodextrins on human erythrocytes

Abstract

α‐, β‐ and γ‐cyclodextrins are cyclic hexamers, heptamers, and octamers of glucose, respectively, and thus are hydrophilic; nevertheless, they have the ability to solubilize lipids through the formation of molecular inclusion complexes. The volume of lipophilic space involved in the solubilization process increases with the number of glucose units in the cyclodextrin molecule and, consequently, cyclodextrins were found to have different effects on human erythrocytes: (a) in the induction of shape change from discocyte to spherocyte the potency was observed to be α > γ, but with β‐cyclodextrin hemolysis occurred before the change was complete; (b) in the increase of fluorescence intensity of 1‐anilinonaphthalene‐8‐sulfonate in cyclodextrin‐pretreated membranes, the observed potency was β≫γ > α; (c) in the release of potassium and hemoglobin, the potency was β > α > γ. The potencies of cyclodextrin for solubilizing various components of erythrocytes were α > β≫γ for phospholipids, β≫γ > α for cholesterol and β≫γ > α for proteins. The solubilization potencies were derived from concentration/final‐effect curves. The above processes occurred without entry of solubilizer into the membrane, since (a) β‐[14 C]cyclodextrin did not bind to erythrocytes and (b) cyclodextrins did not enter the cholesterol monolayer. A study of the [3 H]cholesterol in erythrocytes indicated that β‐cyclodextrin extracted this lipid from membrane into a new compartment located in the aqueous phase which could equilibrate rapidly with additional erythrocytes. Therefore, the effects of cyclodextrins differ from those of detergents which first incorporate themselves into membranes then extract membrane components into supramolecular micelles.