Abstract
The aim of this study was to develop and evaluate a zeta potential changing nanoemulsion (NE) containing polyoxyethylene (9) nonylphenol monophosphate ester (PNPP) as emulsifier.2% (v/v) of PNPP and 0.18% (5 μM) of cetyltrimethylammonium bromide (CTAB) were incorporated into the lipophilic NE preconcentrate (PEG-40 castor oil, glyceryl tricaprylate/tricaprate, propylene glycol dicaprylocaprate, propylene glycol monolaurate, highly purified diethylene glycol monoethyl ether; 20/20/10/30/20, v/v). After diluting the lipophilic preconcentrate, resulting NE was analyzed regarding droplet size, polydispersity index (PDI), storage stability and zeta potential change after incubation with intestinal alkaline phosphatase (IAP). Phosphate release due to cleavage by IAP was quantified by malachite green assay and toxicity as well as cellular uptake behavior on Caco-2 cells was determined. The NE containing PNPP and CTAB displayed a droplet size of 113 nm and a PDI of 0.20. It was stable over 4 h. A zeta potential change from −33.7 to +8.2 mV was observed due to cleavage of phosphate groups by isolated IAP. PNPP could be identified as non-toxic up to concentrations of 0.01% (v/v). Furthermore, an enhanced cellular uptake of the NE changing its zeta potential on Caco-2 cells was determined. Therefore, PNPP seems to be a promising tool for the development of zeta potential changing NE.
Highlights
Nanoemulsions (NE) are isotropic dispersions of two non-miscible liquids with droplet sizes in the nanometric range
Alkaline phosphatase from calf intestine with an activity of approximately 3000 U·mg−1 protein, whereby 1 unit catalyzes the hydrolysis of 1 μmol of 4nitrophenyl phosphate per minute at 37 °C in DEA buffer pH 9.8, was purchased from SERVA Electrophoresis GmbH, Germany
Sigma-Aldrich, Austria was the supplier of phosphatase inhibitor cocktail 2
Summary
Nanoemulsions (NE) are isotropic dispersions of two non-miscible liquids with droplet sizes in the nanometric range. In case of o/w NE an oily phase is dispersed in an aqueous medium and stabilized by appropriate surfactants. They can be prepared by “high-energy” techniques such as ultrasonication and high-pressure homogenization or alternatively be designed as self-emulsifying systems. As the oily droplets showed high potential as nanocarriers for oral drug delivery, the pharmaceutical industry discovered NE as useful formulation tool [1,2,3]. After crossing the mucus barrier, a positive zeta potential is preferred to enhance cellular uptake via ionic attraction of these nanocarriers with the negatively charged cell surface [9,10,11]. Anionic nanocarriers with the ability to shift their zeta potential to positive once having reached the absorption membrane hold great promise as delivery systems
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