Cytotoxicity and cellular uptake of tri-block copolymer nanoparticles with different size and surface characteristics

Background: Polymer nanoparticles (PNP) are becoming increasingly important in nanomedicine and food-based applications. Size and surface characteristics are often considered to be important factors in the cellular interactions of these PNP, although systematic investigations on the role of surface properties on cellular interactions and toxicity of PNP are scarce. Results: Fluorescent, monodisperse tri-block copolymer nanoparticles with different sizes (45 and 90 nm) and surface charges (positive and negative) were synthesized, characterized and studied for uptake and cytotoxicity in NR8383 and Caco-2 cells. All types of PNP were taken up by the cells. The positive smaller PNP45 (45 nm) showed a higher cytotoxicity compared to the positive bigger PNP90 (90 nm) particles including reduction in mitochondrial membrane potential (Delta psi(m)), induction of reactive oxygen species (ROS) production, ATP depletion and TNF-alpha release. The negative PNP did not show any cytotoxic effect. Reduction in mitochondrial membrane potential (Delta psi(m)), uncoupling of the electron transfer chain in mitochondria and the resulting ATP depletion, induction of ROS and oxidative stress may all play a role in the possible mode of action for the cytotoxicity of these PNP. The role of receptor-mediated endocytosis in the intracellular uptake of different PNP was studied by confocal laser scanning microscopy (CLSM). Involvement of size and charge in the cellular uptake of PNP by clathrin (for positive PNP), caveolin (for negative PNP) and mannose receptors (for hydroxylated PNP) were found with smaller PNP45 showing stronger interactions with the receptors than bigger PNP90. Conclusions: The size and surface characteristics of polymer nanoparticles (PNP; 45 and 90 nm with different surface charges) play a crucial role in cellular uptake. Specific interactions with cell membrane- bound receptors (clathrin, caveolin and mannose) leading to cellular internalization were observed to depend on size and surface properties of the different PNP. These properties of the nanoparticles also dominate their cytotoxicity, which was analyzed for many factors. The effective reduction in the mitochondrial membrane potential (Delta psi(m)), uncoupling of the electron transfer chain in mitochondria and resulting ATP depletion, induction of ROS and oxidative stress likely all play a role in the mechanisms behind the cytotoxicity of these PNP.