Glutathione-loaded solid lipid nanoparticles based on Gelucire® 50/30: Spectroscopic characterization and interactions with fish cells

A characterization of solid lipid nanoparticles (SLN) produced starting from an emulsion prepared in acidic or neutral medium and based on Gelucire® 50/13 as lipid phase was performed by X-Ray Photoelectron Spectroscopy Analysis (XPS). The smallest particle size and the highest peptide content were observed for GSH-SLN produced in acidic medium [GSH-SLN(HAc)]. XPS analysis demonstrate the absence of GSH from the surface of the SLN and, combined with the observed sustained release kinetics, allowed us to propose the peptide GSH localization within the lipid nanoparticles. Differential Scanning Calorimetry thermograms of the GSH loaded SLN revealed the absence of the melting point peak at 193 °C attributable to the peptide, suggesting the decreased crystallinity of GSH in the lipid Gelucire® 50/13 forming the SLN matrix. SAF-1 cells (fibroblast-like cells derived from the fin) and gilthead seabream leukocytes were incubated in the presence of FITC-SLN. However, confocal microscopy confirmed that both types of cells were unable to internalize SLN. This result may be ascribed to the slightly negative surface-charge of labelled particles which is unfavorable for effective interactions of these essentially neutral particles with fish cells, suggesting, in perspective, the need to modify the carrier system surface in order to target cell fish.