Effect of Cyclodextrin and Membrane Lipid Structure upon Cyclodextrin–Lipid Interaction

Methyl-β-cyclodextrin (MβCD) can be used to exchange membrane lipids between different vesicles in order to prepare model membrane vesicles with lipid asymmetry. To help define what factors influence lipid exchange, we studied how lipid interaction with cyclodextrins (CDs) was affected by lipid and CD structure. The decrease in light scattering upon CD-induced vesicle solubilization and the change in Förster resonance energy transfer of labeled lipids upon vesicle solubilization and lipid exchange were used to detect phospholipid-CD interaction. Of the CDs examined, MβCD, hydroxypropyl-α-cyclodextrin (HPαCD), and hydroxypropyl-β-cyclodextrin (HPβCD) were the three with the most suitable phospholipid interaction properties. Only MβCD was observed to dissolve lipid vesicles (at least at CD concentrations below 125 mM). Solubilization of lipid vesicles was half complete at 10-80 mM MβCD with progressively higher MβCD concentrations required as phospholipid acyl chain length increased from 14 to 22 carbons. Phospholipid acyl chain unsaturation and lipid headgroup structure also affected the amount of MβCD needed for solubilization. All three CDs studied were able to carry out phospholipid exchange. MβCD, which retained the ability to carry out lipid exchange below MβCD concentrations needed for solubilization, exchanged lipid more efficiently than HPαCD or HPβCD. However, the ability of HPαCD to exchange phospholipids, coupled with its inability to interact with cholesterol, indicates that it will be useful for preparing asymmetric vesicles with controlled amounts of cholesterol.