Preparation, characterization, and evaluation of chitosan-based nanoparticles as CpG ODN carriers

Chitosan-based particles are desirable materials for drug delivery because of their muco-adhesiveness in tissues, biocompatibility, low toxicity and effectiveness in antigen transport. It is still a challenge to prepare chitosan-based particles with high stability and by an effective method. Here we developed chitosan-based nanoparticles for the delivery of toll-like receptor 9 ligands, cytosine-phosphate-guanine oligodeoxynucleotides (CpG ODNs), which can induce the change from Th-2 type to Th-1 type immune response. Because of the low tolerance to DNase and less uptake into the cells of the free CpG ODNs, the development of positively charged carriers is necessary for the effective delivery of CpG ODNs into immune cells. Chitosan nanoparticles were prepared by ionic gelation, and the nanoparticles size and surface charge were measured by dynamic light spectroscopy and zeta potential analyzer, respectively. The synthesized chitosan nanoparticles showed two dispersion peaks, at 196 ± 29 nm and 1.33 ± 0.36 μm, with a zeta potential of +3.3 ± 0.4 mV. The toxicity of the chitosan nanoparticles to murine RAW264 macrophages was measured by formazan dye assay utilizing the water-soluble tetrazolium salt WST-8. Our chitosan nanoparticles exhibited no cytotoxicity to RAW264 cells. Finally, we evaluated the immunostimulatory activity of CpG ODNs loaded on chitosan nanoparticles using human peripheral blood mononuclear cells. CpG ODNs significantly enhanced the secretion level of interleukin-6 and interferon-γ by cells compared to the free CpG ODNs. These results indicated that chitosan nanoparticles could be a good candidate for the delivery of CpG ODNs.