a-, P-and y-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 a > y, but with P-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 / 3 9 y > a; (c) in the release of potassium and hemoglobin, the potency was P > a > y. The potencies of cyclodextrin for solubilizing various components of erythrocytes were a > P 9 y for phospholipids, P 9 y > a for cholesterol and $-y > a for proteins. The sohbilizdtion potencies were derived from concentration/ final-effect curves. The above processes occurred without entry of solubilizer into the membrane, since (a) p-]cyclodextrin did not bind to erythrocytes and (b) cyclodextrins did not enter the cholesterol monolayer. A study of the [3H]cholesterol in erythrocytes indicated that P-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.a-, P-and y-cyclodextrins are cyclic oligomers of glucose consisting of six, seven, and eight D-glucopyranose units, respectively, linked by a-glycosidic bonds. The number of these units determines the dimension of the torus-shaped hydrophobic cavity in which guest molecules of SUitdbk size and low polarity can be accomodated in rapidly established equilibria [I].The solubilization of lipophilic compounds by cyclodextrins has many uses in the biomedical field. Thus, solubilization with cyclodextrins of acyl coenzymes A was used in the study of fatty acid synthetase [2], in the partial replacement of serum in cell culture [3] and in assisting organisms to metabolize toxic lipophiles [4]. Cyclodextrins were also widely used both in oral and parenteral formulations of drugs [S, 61. The dissolution of lipids by cyclodextrins may be of use in the study of cell membranes and as an alternative to the use of detergents. The possibility to introduce cyclodextrins as a research tool in membrdne studies and the necessity to gather additional data in support of parenteral use of cyclodextrins led us to investigate the interaction of all three cyclodextrins with human erythrocytes. Previously, hemolysis by cyclodextrins and their methyl derivatives was investigated [7, 81. In this study, a broader investigation was m...

The sterol binding agent 2-hydroxypropyl-beta-cyclodextrin is shown to be a convenient and useful experimental tool to probe intracellular pathways of cholesterol transport. Biochemical and cytochemical studies reveal that cyclodextrin specifically removes plasma membrane cholesterol. Depletion of plasma membrane sphingomyelin greatly accelerated cyclodextrin-mediated cholesterol removal. Cholesterol arriving at the plasma membrane from lysosomes and the endoplasmic reticulum was also removed by cyclodextrin. Cellular cholesterol esterification linked to the mobilization of cholesterol from lysosomes was strongly attenuated by cyclodextrin, suggesting that the major portion of endocytosed cholesterol is delivered from lysosomes to the endoplasmic reticulum via the plasma membrane. Evidence for translocation of lysosomal cholesterol to the endoplasmic reticulum by a plasma membrane-independent pathway is provided by the finding that cyclodextrin loses its ability to suppress esterification when plasma membrane sphingomyelin is depleted. The Golgi apparatus appears to play an active role in directing the relocation of lysosomal cholesterol to the plasma membrane since brefeldin A also abrogated cyclodextrin-mediated suppression of cholesterol esterification. Using cyclodextrin we further show that attenuated esterification of lysosomal cholesterol in Niemann-Pick C cells reflects defective translocation of cholesterol to the plasma membrane that may be linked to abnormal Golgi trafficking.