Design of nanostructured lipid carriers and solid lipid nanoparticles for enhanced cellular uptake

In this study PEG-free and zeta potential changing lipid-based nanocarriers providing enhanced cellular uptake were developed. Nanostructured lipid carriers (NLC), consisting of paraffin wax, caprylic/ capric triglyceride, cetyltrimethylammoniumchloride and either soy lecithin or polyglycerol-4 laurate and solid lipid nanoparticles (SLN) with the same composition but without the liquid lipid content were developed. All formulations exposed a positive surface charge and were then coated with the polyphosphate Graham's salt. Phosphate release from these formulations was evaluated by incubation with intestinal alkaline phosphatase as well as on a Caco-2 monolayer and zeta potentials were measured. Additionally, cellular uptake studies were performed. Within 5 h, a remarkable amount of phosphate was released from all formulations incubated with intestinal alkaline phosphatase. Enzymatically induced phosphate release with intestinal alkaline phosphatase led to a zeta potential shift up to Δ 26 mV. Results of phosphate release and zeta potential change were confirmed on Caco-2 cells. Cellular uptake studies on Caco-2 cells showed an up to 5.6-times higher uptake compared to cells with inhibited phosphatase. According to these results, polyphosphate coating is a powerful tool to obtain lipid-based nanocarriers for enhanced cellular uptake.

Polyphosphate coatings: A promising strategy to overcome the polycation dilemma

AIM

It was the aim of this study to develop a zeta potential changing drug delivery system by decorating lipid-based nanocarriers with a polycationic cell penetrating peptide (CPP) and subsequently masking these cationic substructures with polyphosphates.

METHODS

In order to anchor the CPP poly-l-lysine (PLL) on the surface of the oily droplets of an o/w nanoemulsion, stearic acid was covalently attached to the peptide. The resulting CPP-decorated oily droplets were coated with phytic acid and tripolyphosphate. The elimination of these polyphosphates due to cleavage by alkaline phosphatase was monitored by the release of monophosphate from the surface of the nanocarriers, by the change in zeta potential and by cellular uptake studies on Caco-2 cells.

RESULTS

Polyphosphate coated PLL-decorated nanocarriers exhibited a pronounced conversion of zeta potential from -14.1 mV to +4.2 mV in case of tripolyphosphate coated nanocarriers and from -9.9 mV to -2.6 mV in case of phytic acid coated nanocarriers. The cellular uptake on Caco-2 cells of the polyphosphate coated nanocarriers was 4-fold improved compared to the control nanocarriers. Furthermore, confocal images showed that the majority of nanodroplets distributed in cytoplasm not being internalized into lysosomes.

CONCLUSION

Polyphosphate coating of CPP-decorated nanocarriers seems to be a promising and simple strategy to overcome the polycation dilemma.