Reduction of Nanoparticle Load in Cells by Mitosis but Not Exocytosis

The long-term fate of biomedically relevant nanoparticles (NPs) at the single cell level after uptake is not fully understood yet. We report that lysosomal exocytosis of NPs is not a mechanism to reduce the particle load. Biopersistent NPs such as nonporous silica and gold remain in cells for a prolonged time. The only reduction of the intracellular NP number is observed via cell division, e.g., mitosis. Additionally, NP distribution after cell division is observed to be asymmetrical, likely due to the inhomogeneous location and distribution of the NP-loaded intracellular vesicles in the mother cells. These findings are important for biomedical and hazard studies as the NP load per cell can vary significantly. Furthermore, we highlight the possibility of biopersistent NP accumulation over time within the mononuclear phagocyte system.