Remote loading of diclofenac, insulin and fluorescein isothiocyanate labeled insulin into liposomes by pH and acetate gradient methods

Remote loading of the model drugs diclofenac, insulin and fluorescein isoth iocyanate labeled insulin (FITC-insulin) into liposomes by formation of tra nsmembrane gradients were examined. A trapping efficiency of almost 100% wa s obtained for liposomal diclofenac, by the calcium acetate gradient method , whereas liposomes prepared by the conventional reverse-phase evaporation vesicle method had 1-8% trapping efficiencies. Soybean-derived sterol was a better stabilizer of the dipalmitoylphosphatidylcholine bilayer membrane t han cholesterol, as shown from trapping efficiencies and drug release. The pH gradient method resulted in a 5-50% of FITC-insulin liposomal trapping e fficiency, while insulin could not be loaded by this method. Liposomes rele ased calcein in response to insulin, showing insulin interacts with the lip osomal membrane in the presence of a transmembrane gradient. The present wo rk has demonstrated a remote loading method for weak acids such as diclofen ac into liposomes by the acetate gradient method. From the result of remote loading of FITC-insulin into liposomes by the pH gradient method, this met hod may be available for the preparation of liposomal peptides. (C) 1999 El sevier Science B.V. All rights reserved.