Nuclear localization of cationic solid lipid nanoparticles containing Protamine as transfection promoter

Protamine has attracted much attention as DNA condenser and nuclear transfer enhancer although the excess of hydrophilicity and the strong DNA pack restrain its potentialities. In order to overcome this limitation, we added Protamine in the composition of solid lipid nanoparticles (SLN-Protamine) and we compared this carrier with the same kind of SLN containing Esterquat 1 instead of Protamine (SLN-EQ1). Carriers cytotoxicity was assessed on COS-I cells evaluating the cell cycle by propidium iodide test, while the transfection efficiency was studied using pEGFP as plasmid model. The cell penetrating activity of Protamine inside the lipid vectors was evaluated studying cell internalization by confocal microscopy using Red Nile-labeled carriers. SLN-Protamine:pDNA showed a mean diameter five-times smaller than the size of SLN-EQ1:pDNA and a remarkably lesser cytotoxicity. Transfection by SLN-Protamine:pDNA was seven-times more effective compared with the Protamine:pDNA polyplexes while no transfection capacity was observed for SLN-EQ1:pDNA complexes due to their inability to be internalized owing to their larger dimension. Red Nile-SLN-Protamine were localized in endocytic-like vesicles into the nuclear membrane suggesting the inclusion of Protamine in nano-lipophilic systems may enhance the reduction in the complex dimensions, the nuclear pDNA translocation and the pDNA release in the cells.

Graphical abstractNuclear localization of Red Nile-SLN-Protamine:pDNA visualized by confocal microscopy on COS-I cells. The sites of interaction are well recognizable as the white spots enclosed in the yellow squares in (B) (DAPI labeled nuclei), (C) (Red Nile-labeled SLN-Protamine:pDNA) and D (blue and red fluorescence overlap). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)Figure optionsDownload full-size imageDownload as PowerPoint slide