A quantitative study of exocytosis of titanium dioxide nanoparticles from neural stem cells

Abstract

Nanoparticles (NPs) have been widely studied and applied in biomedicine and other fields. It is important to know the basic process of interaction between NPs and cells in terms of cellular endocytosis and exocytosis. However, little attention has been paid to the cellular exocytosis of NPs. Herein, using a multi-step cellular subculture method, we ascertain quantitatively the endocytosis and exocytosis of widely used TiO₂ NPs using the neural stem cells (NSC) as a cellular model and ICP-AES as an analytic measure. Irrespective of the type and dose of TiO₂ NPs, approximately 30% of the total TiO₂ NPs entered NSCs after 48 h incubation. In the first 24 h after removing TiO₂NPs, from the culture medium, about 35.0%, 34.6% and 41.7% of NP1 (50 nm), NP2 (30 nm) and NTs (nanotubes, 100 nm × 4–6 nm) were released (exocytosed) from cells, respectively. The release decreased over time, and became negligible at 72 h. Exocytosis did not happen during cell division. In addition, our results suggested that both endocytosis and exocytosis of TiO₂NPs were energy-dependent processes, and NPs uptake by cells was influenced by serum proteins. Furthermore, we achieved primary dynamic confocal imaging of the exocytosis, allowing tracking of TiO₂ NPs from NSCs. These findings may benefit studies on nanotoxicology and nanomedicine of TiO₂ NPs.