Lysosome mediates toxicological effects of polyethyleneimine-based cationic carbon dots

Cationic carbon dots (CDs) have been recently described as nucleic acid carriers with high in vitro and in vivo transfection efficiency and imaging properties. However, developing nanoparticles (NPs) for biomedical applications requires assessing their safety. In the present study, we characterized the cell uptake and trafficking, as well as the cell viability loss, oxidative stress, inflammation, and mitochondrial and lysosomal perturbations evoked by cationic CDs prepared by microwave-assisted pyrolysis of citric acid and high molecular weight branched polyethyleneimine (bPEI25k), using THP-1-derived macrophages. CDs were rapidly internalized by cells and addressed to the lysosomes after their cell entry. The NPs induced a dose- and time-dependent loss in cell viability that was associated with oxidative stress and IL-8 release. The CDs triggered also a dose-dependent loss in lysosome integrity, mitochondrial dysfunction, and NLRP3 inflammasome activation. Inhibition of the lysosomal protease cathepsin B significantly reduced CD-induced mitochondrial dysfunction and NLRP3 inflammasome activation, suggesting a pivotal role of the lysosome in the toxicological effects of the NPs. Our study provides for the first time a mechanistic pathway for the toxicological effects of bPEI25k-based cationic CDs.