Ordering of Saturated and Unsaturated Lipid Membranes near Their Phase Transitions Induced by an Amphiphilic Cyclodextrin and Cholesterol

Fragmentation of DMPC Membranes by a Wedge-Shaped Amphiphilic Cyclodextrin into Bicellar-like Aggregates

Small bilayer lipid aggregates such as bicelles provide useful isotropic or anisotropic membrane mimetics for structural studies of biological membranes. We have shown previously by deuterium NMR that a wedge-shaped amphiphilic derivative of trimethyl βcyclodextrin anchored in deuterated DMPC-d27 bilayers through a lauryl acyl chain (TrimβMLC) is able to induce magnetic orientation and fragmentation of the multilamellar membranes. The fragmentation process fully detailed in the present paper is observed with 20% cyclodextrin derivative below 37 °C, where pure TrimβMLC self-assembles in water into large giant micellar structures. After deconvolution of a broad composite ²H NMR isotropic component, we propose a model where the DMPC membranes are progressively disrupted by TrimβMLC into small and large micellar aggregates depending whether they are extracted from the outer or inner layers of the liposomes. Below the fluid-to-gel transition of pure DMPC-d27 membranes (T_c = 21.5 °C), the micellar aggregates vanish progressively until complete extinction at 13 °C, with a probable release of pure TrimβMLC micelles leaving lipid bilayers in the gel phase doped with only a small amount of the cyclodextrin derivative. Bilayer fragmentation between T_c and 13 °C was also observed with 10% and 5% of TrimβMLC, with NMR spectra suggesting possible interactions of micellar aggregates with fluid-like lipids of the P_β' ripple phase. No membrane orientation and fragmentation was detected with unsaturated POPC membranes, which are able to accommodate the insertion of TrimβMLC without important perturbation. The data are discussed in relation to the formation of possible DMPC bicellar aggregates such as those known to occur after insertion of dihexanoylphosphatidylcholine (DHPC). These bicelles are in particular associated with similar deuterium NMR spectra exhibiting identical composite isotropic components which were never characterized before.

New Lipidyl-Cyclodextrins Obtained by Ring Opening of Methyl Oleate Epoxide Using Ball Milling

Bearing grafts based on fatty esters derivatives, lipidyl-cyclodextrins (L-CDs) are compounds able to form water-soluble nano-objects. In this context, bicatenary biobased lipidic-cyclodextrins of low DS were easily synthesized from a fatty ester epoxide by means of alternative methods (ball-milling conditions, use of enzymes). The ring opening reaction of methyl oleate epoxide needs ball-milling and is highly specific of cyclodextrins in solventless conditions. L-CDs are thus composed of complex mixtures that were deciphered by an extensive structural analysis using mainly mass spectrometry and NMR spectroscopy. In addition, as part of their potential use as vectors of active drugs, these products were submitted to an integrity study on in vitro model of the blood-brain-barrier (BBB) and the intestinal epithelium. No toxicity has been observed, suggesting that applications for the vectorization of active ingredients can be expected.