In vitro characterization of 6-Coumarin loaded solid lipid nanoparticles and their uptake by immunocompetent fish cells

Abstract The primary aim of the present work was to evaluate the in vitro uptake of 6-Coumarin (6COUM) loaded solid lipid nanoparticles (SLN) by two gilthead seabream (Sparus aurata L.) cell types: an established cell line (SAF-1 cells) and the primary cultures of head-kidney (HK)--the main haemopoietic organ in fish, equivalent to mammalian bone marrow--leucocytes. For this purpose, after the physicochemical characterization of SLN, the uptake by those immunocompetent fish cells was evaluated using flow cytometry and confocal microscopy. Concomitantly, the uptake of 6-COUM loaded {SLN} was compared with that achieved with 6-COUM loaded pectin microparticles (MPs), which were selected as a competitor of the delivery carriers. After {SLN} and {MP} physicochemical characterization, the results demonstrated that SAF-1 cells were able to internalize high percentages of 6-COUM {SLNs} when incubated for 4, 8 and 24 h, with the highest {SLN} concentration tested (10 ?g/ml). The ability of {HK} leucocytes to internalize {SLN} was also found to vary depending on both incubation time and {SLN} concentration. The highest values of {HK} leucocytes internalizing {SLN} particles (around 16%) were detected at the maximum {SLN} concentration (20 ?g/ml) at incubation times of 4 or 8 h. Conversely, {HK} leucocytes were unable to internalize {MPs} at any tested concentration and incubation time. A possible mechanism explaining the uptake into cells is proposed. The present work constitutes the first approximation to consider {SLN} as nanocarriers for delivering biologically active substances to fish.