Abstract
Background/Objectives: Alveolar macrophages represent the main path of defense in the peripheral pulmonary tissue, though their role in chronic inflammatory lung diseases shows that their protective function can turn pathological. This study focused on developing a system to passively target the release of the pro-inflammatory cytokine TNF-α through the local delivery of siRNA. Methods: An inhalable aspherical microparticle made up of mesoporous silica nanoparticles, crosslinked by an electrostatic LbL-system embedding the siRNA, was developed. Results: Through testing with the NGI, adequate aerodynamic properties with an MMAD as low as 3.37 µm could be determined, with a GSD as low as 1.46, suggesting a relatively small size distribution even during inhalation. To further understand the interaction of the microrods with the lung parenchyma and the resident cells, the disintegration of the rods in different simulant body fluids, their toxicity, and the cell uptake through dTHP-1 and A549 were observed. This showed slow but continuous disintegration, no toxicity in A549 cells, and high microrod uptake by dTHP-1 cells. To demonstrate the effect of the delivered siRNA on the release of TNF-α, ELISAs were carried out, establishing an inhibitory effect of the siRNA-carrying microcarrier system compared to those without siRNA or loaded with scrambled siRNA. To increase the efficacy of the siRNA, chloroquine as an endosomal escape-enhancing compound was loaded onto the mesoporous silica nanoparticles. This resulted in a significant improvement in siRNA inhibition. Conclusions: The developed formulation is able to reach the targeted structure and inhibit the secretion of TNF-α, with CQ increasing the inhibitory effect of the siRNA.