Kinetics of molecule transfer between lipid vesicles and beta-cyclodextrins

We propose a calorimetric method based on the van't Hoff model of depression of the freezing temperature to investigate slow kinetics involving lipid vesicles (liposomes) and drug-beta-cyclodextrin (Cyd) complexes. Some nonsteroidal antiinflammatory drugs (NSAIDs) were examined and standard phospholipid liposomes were used in our experiments. Three different kinetic processes were investigated: (a) Transfer of drugs from water-soluble Cyd-complexes to void liposomes. (b) Uptake of drugs from the surface of liposomes by free Cyd dissolved in the aqueous phase. (c) Exchange of drugs from loaded to void vesicles, and the effect of free Cyd in enhancing such a transfer. Most experiments were performed both below and above the main transition (melting) temperature of the liposome bilayer, The results show that our technique can be used to follow slow kinetics in such complex systems and is sensitive enough to detect small changes related to chemical structure modifications of the investigated drugs. (C) 1996 Academic Press,Inc