Microspheres containing lipid/chitosan nanoparticles complexes for pulmonary delivery of therapeutic proteins.

Chitosan/tripolyphosphate nanoparticles have already been demonstrated to promote peptide absorption through several mucosal surfaces. We have recently developed a new drug delivery system consisting of complexes formed between preformed chitosan/tripolyphosphate nanoparticles and phospholipids, named as lipid/chitosan nanoparticles (L/CS-NP) complexes. The aim of this work was to microencapsulate these protein-loaded L/CS-NP complexes by spray-drying, using mannitol as excipient to produce microspheres with adequate properties for pulmonary delivery. Results show that the obtained microspheres are spherical and present appropriate aerodynamic characteristics for lung delivery (aerodynamic diameters around 2-3 microm and low apparent tap density of 0.4-0.5 g/cm3). The physicochemical properties of the L/CS-NP complexes are affected by the phospholipids composition. Phospholipids provide a controlled release of the encapsulated protein (insulin), which was successfully associated to the system (68%). The complexes can be easily recovered from the mannitol microspheres upon incubation in aqueous medium, maintaining their morphology and physicochemical characteristics. Therefore, this work demonstrates that protein-loaded L/CS-NP complexes can be efficiently microencapsulated, resulting in microspheres with adequate properties to provide a deep inhalation pattern. Furthermore, they are expected to release their payload (the complexes and, consequently, the encapsulated macromolecule) after contacting with the lung aqueous environment.