Intrinsic effect of anionic and cationic liposomes and the effect of encapsulation of CpG C and Poly (I:C) in lipid nanoparticles on osteo-immunomodulation.

Abstract

The initial inflammatory phase has been shown crucial for initiation of the healing cascade in bone regeneration. The modulation of the local inflammatory environment has been proposed as a promising strategy for improved bone formation after surgical intervention with bone biomaterials. The induction of mild inflammation through microbial stimuli was recently found to be involved in osteo-immunomodulation. Bacterial stimuli or pathogen associated molecular patterns act through pathogen recognition receptors. It is though that isolated pathogen recognition receptor ligands could induce a similar immune response, while being more applicable in a clinical setting. Stimulation with synthetically developed nucleic acid based pattern recognition receptor ligands Poly(I:C) and CpG oligodeoxynucleotide type C were found to increase an early osteogenic marker in human mesenchymal stem cells. The receptors for these ligands are located intracellular. A suitable lipid based carrier system is used in this research for potential optimization of the biological activity of these synthetic pathogen recognition receptor ligands. With the high level of crosstalk between the immune and skeletal system it is expected that intrinsic immune modulation of the lipid carrier system can influence osteogenic capacity. The first part of this research focussed on the intrinsic osteo-immunomodulatory effects of anionic and cationic liposomes as a lipid based carrier system. Both anionic and cationic liposomes could induce a similar inflammatory response in macrophages, as well as a dose dependant NF-κB activation in RAW-Blue™ cells. However the early osteogenic marker ALP activity, was not increased for anionic or cationic liposomes in human mesenchymal stem cells. The second part of the research focussed on the osteo-immunomodulatory effect of Poly(I:C) and CpG oligodeoxynucleotide type C encapsulated in a lipid carrier. The encapsulation of nucleic acid based drugs like Poly(I:C) and CPG oligodeoxynucleotide type C is more efficient using lipid nano particles as a lipid carrier system. Encapsulation of CPG oligodeoxynucleotide type C in the lipid nano particle showed an increase in ALP activity in human mesenchymal stem cells compared to its free form. Encapsulation of Poly (I:C) did not show a significant increase compared to its free form. All the formulations of lipid nanoparticles could induce a similar inflammatory response in human macrophages. Interestingly, the empty lipid nanoparticle could induce almost a similar response from macrophages compared to lipid nanoparticles encapsulating Poly (I:C) and CpG oligodeoxynucleotide type C. Macrophage TNF-a production was similar for all lipid nanoparticle formulations, only IL-6 and IL-10 production were slightly increased due to transfection of the encapsulated pattern recognition ligands.