Aerodynamic performance of lipid-based nanocarrier functionalized by novel mannose derivatives for Rifampicin intramacrophagic delivery

Introduction. Alveolar macrophages (AM) are sites of infection by pathogens such as Mycobacterium tuberculosis. On the basis of the presence of mannose receptors on AM membranes, mannose moieties have been considered as ligands for macrophage active targeting. Mannosylated derivatives were synthesized to decorate the surface of Rifampicin (RIF) loaded Solid Lipid Nanoparticle assemblies (SLNas) for an inhaled anti-tuberculosis (TB) therapy by Dry Powder Inhaler (DPI) device with the goal to relate surface functionality with respirability performance. Methods. Biocompatible lipid components such as fatty acids and their derivatives were processed using the melt emulsification technique. SLNas surface decoration was obtained by means of four newly synthesized mannose derivatives having surfactant effect. The obtained mannosylated carriers were examined for their intrinsic properties (size, morphology and shape, surface charge, bulk and tap density, aerodynamic diameter, physical state of the components, drug loading and in vitro release) associated to respirability features assessed by Next Generation Impactor (NGI). Mannosylation occurrence was investigated using X-ray Photoelectron Spectroscopy for Chemical Analysis. Furthermore, SLNas cytotoxicity, macrophage internalization, and ability to provide RIF intramacrophagic transport were evaluated on J774 cell line by MTT test, flow cytometry, and confocal microscopy. Results and Discussion. SLNas exhibited adequate drug payload, in vitro release, and cell internalization (Fig. 1, Confocal microscopy images of J774 cells incubated for 6 h with Nile Red labeled SLNas after blue nuclei and green lysosome staining) with consequent efficient RIF translocation inside macrophages (about 70%). A relevant increase in drug content within macrophages provided by SLNas compared to free RIF solution (Fig. 2, Intracellular RIF percentage inside J774 cell line) confirmed both RIF difficulty to diffuse across macrophage membranes and SLNas efficacy to promote drug transport into cells. Furthermore, it is noteworthy that the presence of these new surface-active agents reduced powder cohesiveness without impairing respirability (fine particle fraction ranging from 30% to 50%) (Fig. 3, SLNas aerodynamic distribution by NGI upon powder aerosolisation). SLNas proposed in this research can be prepared by a green-technology avoiding organic solvents. Thus, these new SLNas may represent an encouraging opportunity in a perspective of an efficacious anti-TB inhaled therapy