title: Fate of cerium dioxide nanoparticles in endothelial cells: exocytosis.
abstract: Although cytotoxicity and endocytosis of nanoparticles have been the subject of numerous studies, investigations regarding exocytosis as an important mechanism to reduce intracellular nanoparticle accumulation are rather rare and there is a distinct lack of knowledge. The current study investigated the behavior of human microvascular endothelial cells to exocytose cerium dioxide (CeO2) nanoparticles (18.8 nm) by utilization of specific inhibitors [brefeldin A; nocodazole; methyl-β-cyclodextrin (MβcD)] and different analytical methods (flow cytometry, transmission electron microscopy, inductively coupled plasma mass spectrometry). Overall, it was found that endothelial cells were able to release CeO2nanoparticles via exocytosis after the migration of nanoparticle containing endosomes toward the plasma membrane. The exocytosis process occurred mainly by fusion of vesicular membranes with plasma membrane resulting in the discharge of vesicular content to extracellular environment. Nevertheless, it seems to be likely that nanoparticles present in the cytosol could leave the cells in a direct manner. MβcD treatment led to the strongest inhibition of the nanoparticle exocytosis indicating a significant role of the plasma membrane cholesterol content in the exocytosis process. Brefeldin A (inhibitor of Golgi-to-cell-surface-transport) caused a higher inhibitory effect on exocytosis than nocodazole (inhibitor of microtubules). Thus, the transfer from distal Golgi compartments to the cell surface influenced the exocytosis process of the CeO2nanoparticles more than the microtubule-associated transport. In conclusion, endothelial cells, which came in contact with nanoparticles, e.g., after intravenously applied nano-based drugs, can regulate their intracellular nanoparticle amount, which is necessary to avoid adverse nanoparticle effects on cells.
authors.affiliation: Department of Experimental Radiology, Institute of Diagnostic and Interventional Radiology, Jena University Hospital - Friedrich Schiller University Jena, Erlanger Allee 101, 07747 Jena, Germany.
authors.forename: Claudia
authors.initials: C
authors.lastname: Strobel
authors.affiliation: Institute of Anatomy II, Jena University Hospital - Friedrich Schiller University Jena, Teichgraben 7, 07743 Jena, Germany.
authors.forename: Hartmut
authors.initials: H
authors.lastname: Oehring
authors.affiliation: Department of Physics, University of Augsburg, Universitaetsstraße 1, 86159 Augsburg, Germany.
authors.forename: Rudolf
authors.initials: R
authors.lastname: Herrmann
authors.affiliation: Department of Internal Medicine I, Division of Pulmonary Medicine and Allergy/Immunology, Jena University Hospital - Friedrich Schiller University Jena, Erlanger Allee 101, 07747 Jena, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Förster
authors.affiliation: Department of Physics, University of Augsburg, Universitaetsstraße 1, 86159 Augsburg, Germany.
authors.forename: Armin
authors.initials: A
authors.lastname: Reller
authors.affiliation: Department of Experimental Radiology, Institute of Diagnostic and Interventional Radiology, Jena University Hospital - Friedrich Schiller University Jena, Erlanger Allee 101, 07747 Jena, Germany.
authors.forename: Ingrid
authors.initials: I
authors.lastname: Hilger
keywords: Cerium dioxide; Endothelial cells; Exocytosis; Exocytosis inhibitor; Health effects; Nanoparticle