Cationic solid lipid nanoparticles (SLN) are promising nonviral gene delivery carriers suitable for systemic administration. The objective of this study was to investigate the relationship between the composition of cationic SLN and their ability to condense plasmid DNA (pDNA) and to transfer it in neuroblastoma cells. The SLN were prepared by using stearic acid and stearylamine as lipid core along with Esterquart 1 (EQ1) or Protamine obtaining two samples (SLN-EQ1 and SLN-Protamine, respectively). The cationic SLN were freeze-dried after preparation and their physical-chemical properties, including the surface composition and the transfection efficiency were investigated. The results showed that the two samples had similar size, zeta potential and pDNA binding properties but SLN-Protamine were able to condense pDNA more efficaciously than SLN-EQ1 forming smaller and less positive complexes. SLN-Protamine:pDNA complexes demonstrated to be less cytotoxic and more efficient in the transfection of Na1300 cell line than SLN-EQ1:pDNA. These findings were attributed to the different surface composition of the two samples and in particular to the localization of the Protamine on the surface of the particle while EQ1 in the lipid core. In conclusion the results here suggest that not only the z-potential but also the surface composition may affect the pDNA condensation proprieties and thus the transfection efficiency of nonviral gene nanocarriers.
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