SLN are nanocarriers that can be tailored to translocate lipophilic compounds and unload their content into the cells. We studied the distribution of the SLN load within the cytoplasm trying to shed some light on the internalization mechanism and on the force field that acts on the internalized compound within the cell.

Epithelial lung cells were incubated with a non-toxic concentration (0.01mg/ml) of SLN loaded with 6-coumarine, a green fluorescent dye. The distribution of fluorescence within the cytoplasm, increased over time as a function of the distance from the plasma-membrane reaching the maximum in proximity of the nuclear membrane.

Lowering the temperature from 37°C to 4°C caused a 50% decrease of the uptake of the fluorophore suggesting that the uptake is not mediated exclusively by active processes.

Further insights on the origin of the distribution pattern was gained by altering the cell structure through a perturbation of the cytoskeleton. After reaching a steady state perinuclear accumulation condition for the fluorophore, we treated cells with cytochalasinD (2.mM, 1 h) to disintegrate actin boundless, avoiding cytotoxic damage. We found that while in the control condition the ratio between perinuclear and peripheral fluorescence was 5 fold, in presence of cytoD, this value decreased to a plateau level of 1.6, suggesting that the integrity of the cytoskeleton is setting intracellular fluid-dynamics and mechanics condition causing the perinuclear accumulation.