An original methodology to study polymeric nanoparticle-macrophage interactions: Nanoparticle tracking analysis in cell culture media and quantification of the internalized objects

[Display omitted] Poly(lactic acid) (PLA) and poly(lactic-co-glycolic acid) (PLGA) are among the most employed (co)polymers for the preparation of drug nanocarriers for the treatment of cancer and infectious diseases. Before considering any clinical use, it is necessary to understand the interactions between polymeric nanoparticles (NPs) and their physiological environment, especially immune cells. Here, we propose a simple, yet precise method to assess NPs internalization kinetics in macrophages, based on the direct analysis of the cell culture media after different incubation times. The proof of concept is given here by using fluorescent PLGA NPs. Nanoparticle tracking analysis (NTA) was a method of choice, enabling detecting each individual NP and analyzing its trajectory while in Brownian motion. As compared to dynamic light scattering (DLS), NTA enabled a more precise determination of NP size distribution. The uptake process was rapid: in one hour, around a third of the NPs were internalized. In addition, the internalized NPs were visualized by confocal microscopy. The fluorescent cellular stacks were analyzed using a freely available macro for ImageJ software, Particle_In_Cell-3D. The internalized objects were localized and counted. This methodology could serve for further studies while analyzing the effects of NPs size, shape and surface properties on their interaction with various cell lines.