Silica-coated calcium phosphate nanoparticles for gene silencing of NF-κB p65 by siRNA and their impact on cellular players of inflammation.

The transcription factor NF-κB and its signaling cascade both play key roles in all inflammatory processes. The most critical member of the NF-κB transcription factor family is p65. We investigated the role of cationic silica-coated calcium phosphate nanoparticles (spherical, diameter by SEM 50-60 nm; zeta potential about +26 mV; stabilized by polyethyleneimine) carrying encapsulated siRNA against NF-κB p65 and their influence on inflamed cells. The nanoparticles were taken up by cells of the blood compartment involved in the inflammatory response, particularly by monocytes, and to a lesser extent by endothelial cells and B-cells, but not by T-cells. The particles were found in endolysosomes where they were dissolved at low pH and released the siRNA into the cytoplasm. This was confirmed by dissolution experiments of model nanoparticles in simulated endolysosomal medium (pH 4.7) and by intracellular co-localization studies of double-labeled nanoparticles (using a negatively charged model peptide for siRNA). The encapsulated functional siRNA reverted the p65 gene and protein expression in inflamed monocytes, the main cells in immune response and surveillance, almost back to the non-inflammatory condition. Additionally, the nanoparticles suppressed the pro-inflammatory cytokine expression profiles (TNF-α, IL-6, IFN-β) in inflamed J774A.1 monocytes. Taken together, such nanoparticles can be applied for the treatment of inflammatory diseases.