Preparation and evaluation of controlled release microparticles for respiratory protein therapy

A series of microparticle formulations, designed for controlled release pulmonary therapy, were evaluated in terms of their physical properties, aerosol performance, lung epithelial cell toxicity, and controlled release profile. A protein, bovine serum albumin (BSA) was chosen as a model macromolecule active ingredient which was coprocessed, using spray drying, with varying concentrations of the release modifier, polyvinyl alcohol (PVA). The spray dried microparticles were tested for their physico-chemical characteristics (e.g., size distribution, morphology and density), in vitro aerosolisation performance using a 5-stage Marple Miller Impactor (MMI) and in vitro release profiles by a custom-built diffusion cell (in 100 mL phosphate buffer pH 7.4). The toxicity of PVA on lung epithelial cells was investigated using a human alveolar basal epithelium A549 cell line. Analysis of the particle size data indicated that all the spray dried BSA/PVA samples had similar size distributions with a median particle diameter (d0.5) across all samples of 2.79 ± 0.11 µm. All formulations had relatively good aerosolisation performance when compared to conventional dry powder inhalation (DPI) formulations although increasing PVA percentage had a negative effect on the aerosol performance in vitro. Analysis of the difference and similarity factors for the release profiles indicated significant differences with respect to PVA concentration. Furthermore, cell toxicity analysis indicated PVA to have limited effect on cell viability after 24 h exposure. A series of protein-based inhalation formulations have been developed and tested, and shown to be suitable for controlled release in the respiratory tract.