A novel cyclodextrin-lipid complex method for formulating asymmetric liposomes and the complexation and asymmetry validations

Liposomes have long been explored as versatile drug delivery systems. Recently, achieving and maintaining asymmetry of liposomes has been the focus of liposomal research. This research aims to provide a novel method for formulating asymmetric liposomes, it focuses on development and optimization of asymmetric liposomes using a cyclodextrin (CD)-lipid exchange method, firstly created by E. London and coworkers, the innovative method has not yet in any publications. The method involves dissolving cyclodextrin in HEPES buffer. The lipid is then dissolved in methanol and added in dropwise approach to cyclodextrin solution. Complexation of the lipid and cyclodextrin is confirmed by several methods involving: infrared spectroscopy which showed shifts of some peaks and disappearance of others, thermogravimetric analysis, differential scanning calorimetry, and nuclear magnetic resonance (the spectra were different compared to the raw materials and physical mixtures). Large unilamellar vesicles (acceptor) are formulating with required lipids via thin film method. Finally, equal volumes of the cyclodextrin-lipid complex and acceptor vesicles suspension are mixed using a shaking water bath (22 °C) for 45mins-1 hour to allow lipid exchange, then asymmetric liposomes, via centrifugation at 15,000RPM at 4 °C for 1 hour, were collected from the rest of vehicle containing the CD-complex on. The asymmetry of liposomes was confirmed by using zetapotential and fluorescence quenching methods. The study showed more stable liposomes compared to those prepared by the conventional method. In future, those asymmetric liposomes prepared by the cyclodextrin-lipid complexation method will be evaluated for their encapsulation efficiency for both small and large drug molecules.