Nanoarchitectonics of Layer-by-Layer (LbL) coated nanostructured lipid carriers (NLCs) for Enzyme-Triggered charge reversal.

HYPOTHESIS: Combined usage of Layer-by-Layer (LbL) coating and alkaline phosphatase (ALP) - responsive charge reversal strategies can improve the cellular internalisation of the colloidal drug delivery systems by also decreasing their cytotoxic effects. EXPERIMENTS: Anionic core NLCs were formed by combining the melt emulsification method and ultrasonication. The resulting core NLCs were coated sequentially first with protamine (Prot NLCs) and then with sodium tripolyphosphate (TPP) or sodium polyphosphate (Graham's salt, PP) generating TPP or PP NLCs, respectively. The developed NLCs were characterised regarding their size and zeta potential. Enzyme-induced charge reversal of the TPP and PP NLCs was evaluated by zeta potential measurements upon their incubation with alkaline phosphatase (ALP). In parallel, time-dependent phosphate release was monitored in the presence of isolated as well as cell-associated ALP. Morphological evaluations were performed by scanning electron microscopy (SEM) studies. Moreover, cell viability and cellular uptake studies were carried out in vitro on Caco-2 cells. FINDINGS: The core NLCs were obtained with a mean size of 272.27 ± 5.23 nm and a zeta potential of -25.70 ± 0.26 mV. Upon coating with protamine, the zeta potential raised to positive values with a total change up to Δ29.3 mV also displaying an increase in particle size. The second layer coating with TPP and PP provided a negative surface charge. Subsequent to ALP treatment, the zeta potential of the TPP and PP NLCs reversed from negative to positive values with total changes of Δ8.56 and Δ7.47 mV, respectively. Conformably, significant amounts of phosphate were released from both formulations. Compared with core NLCs, improved cellular viability as well as increased cellular uptake were observed in case of Prot, TPP and PP NLCs.

Reactive oxygen species (ROS) in colloidal systems: Are "PEG-free" surfactants the answer?

HYPOTHESIS: Evaluation and comparison of polyglycerol- (PG-) and saccharide- (SA-) surfactants as "PEG-free"-alternative for polyethylene glycol- (PEG-) surfactants to tackle autoxidation, reactive oxygen species (ROS) formation and degradation of oxidation-prone active ingredients in colloidal systems. EXPERIMENTS: 30 different surfactants were screened for hydroperoxides (HPO), aldehydes, and acid formation serving as autoxidative markers. In a comparative set-up, selected surfactants of each head group type were investigated for temperature- and photo-induced ROS formation. Oxidation markers, as well as the degradation of ß-carotene as model active ingredient in colloidal systems were monitored. FINDINGS: The screening revealed elevated HPO and aldehyde levels for both PG and PEG surfactants, unlike SA surfactants, suggesting similar autooxidation processes due to their polyether substructure. However, in a comparative set-up, PEG-surfactants showed irrespective of the stress conditions or the colloidal systems at least 4-fold higher HPO and aldehyde concentrations, as well as more pronounced pH drops compared to PG- and SA-surfactants. ß-Carotene oxidation was 40- to 50-fold lower in colloidal systems based on PG- or SA-surfactants, confirming reduced ROS formation by "PEG-free"-surfactants. Moreover, superior autoxidation and degradation stability under oxidative conditions resulted in improved colloidal stability of PG- and SA-surfactant based systems. Hence, "PEG-free"- surfactants represent a causal approach to mitigate autoxidation processes in oxidation-prone pharmaceutical and cosmetic products.

Charge-reversal nanoemulsions: A systematic investigation of phosphorylated PEG-based surfactants.

Surfactants bearing monophosphate esters with PEG of increasing chain length and different lipophilic tail structures were investigated to improve the effectiveness of enzyme triggered charge-converting nanoemulsions. The surfactants PEG-8-stearate, PEG-22-tocopheryl succinate (TPGS), PEG-3-oleate, PEG-9-oleate and PEG-9-lauryl ether were phosphorylated and incorporated in a self-emulsifying drug delivery system (SEDDS) exhibiting a defined PEG corona. To provide a positive zeta potential increasing amounts of the cationic surfactant benzalkonium chloride (BA) were incorporated. The effect of these PEG monophosphate esters (P-PEG-surfactants) was evaluated based on enzyme induced phosphate release and change in zeta potential. Significant enzyme induced charge conversion was observed for all P-PEG-surfactants, showing shifts from Δ3 mV to Δ31 mV. Surfactants comprising the shortest and longest PEG chain showed similar amplitudes (P-PEG-3-oleate: Δ11.9 mV; P-PEG-22-TPGS Δ10.2 mV), whereas P-PEG-8-stearate, P-PEG-9-oleate and P-PEG-9-lauryl ether bearing similarly long PEG chains but different lipophilic tail structures resulted in pronounced differences in amplitudes of Δ10.3 mV, Δ14.5 mV and Δ18.1 mV, respectively. Furthermore, an indirect correlation between the lipophilicity of P-PEG-surfactants and the obtained charge-reversing effect was observed. With the exception of P-PEG-lauryl ether, this charge-reversal effect decreased with increasing BA concentrations. In conclusion, the enzyme induced amplitude of charge conversion of P-PEG-surfactants depends to a high extent on their lipophilic tail structure. Based on this knowledge potent charge-reversal nanoemulsions can be designed.