Preparation of spray-dried powders of lysozyme for pulmonary delivery using liposomes as a carrier

Abstract

The purpose of this study was to develop and optimize the spray drying process for preparing spray-dried lysozyme-loaded liposomal powders with adequate properties for possible application in pulmonary delivery. Extruded liposomes were prepared from hydrogenated soybean phosphatidylcholine (HPC) with and without cholesterol (Chol). The extruded liposomes was then mixed with mannitol and lysozyme solutions and spray-dried into liposomal powders. The effects of HPC/mannitol ratio, presence of glycine as anti-adherent and HPC/Chol ratio on the properties of the spray-dried powders and the reconstituted liposomes were investigated. The spray-dried powders produced were characterized with respect to morphology, thermal property and crystallinity using scanning electron microscopy, differential scanning calorimetry and X-ray diffraction, respectively. Physicochemical properties of reconstituted liposomes, including encapsulation efficiency and size distribution, were evaluated after the powders were re-hydrated at physiologically relevant conditions. The most feasible formulation was further used for process optimization. The effects of spray drying process factors (inlet temperature, feed rate and total solid content) on the properties (yield, moisture content, particle size and entrapment efficiency) of the powders were investigated using the factorial design followed by the central composite design. The results indicated that the spray drying process was feasible in producing lysozyme-loaded liposomal powders. The process had no destructive effect on the stability of the major structural phospholipid. Degree of particle aggregation was strongly dependent on the composition of the powder. Though glycine could improve the yield in the collector of spray dryer, high amounts of glycine resulted in fusion of particles that prevented liposome formation upon reconstitution. At the lipid to mannitol ratio of 1:1, an increase in Chol resulted in a reduction of the size of the reconstituted liposomes. Entrapment of lysozyme in liposomes, on the other hand, increased with Chol content. After reconstitution with Hepes Buffered Saline, pH 7.4 at 37 ºC, the powders spontaneously formed liposomes. Lysozyme was efficiently entrapped into the reconstituted liposomes. Biological activity of lysozyme was not affected by the spray drying process. However, some structural changes were evident. From the optimization study, the results indicated that the spray drying factors had a significant influence on the yield, the particle size and the entrapment efficiency of the powders. The optimum condition selected gave the liposomal powders with process yield of 60.46 %, mass median diameter of 6.00 m and entrapment efficiency of 13.83 g LSZ/mg lipid.