Uptake Kinetics, Uptake Pathways and Cytotoxicity of SiO 2-Nanoparticles Interacting with HeLa and HUVEC Cells

Abstract

The question whether nanoparticles (NPs) are toxic to humans has attracted increasing attention during the last years. As NPs have unique chemical and physical properties they are extensively used in industry and added to commercial products. One commonly used type are silica-nanoparticles (SiO2-NPs). They occur e.g. as carriers in catalysis, drug delivery systems or food additives leading to a constant exposure of humans. Therefore a strong need for more detailed and systematic investigations exists concerning NP uptake into human cells and the resulting impact on cellular viability.To gain a closer insight into NP-cell interaction and fundamental mechanisms of cytotoxicity we determined the uptake efficiency and uptake pathways of SiO2-NPs in HeLa and HUVEC cells by live-cell-imaging and correlated the results with observed cytotoxic effects. First, the SiO2-NPs were extensively characterized concerning size, shape and labeling. We then incubated SiO2-NPs with cells for varying time periods and monitored the NP uptake by highly sensitive spinning-disc-confocal-microscopy. By measuring stacks of confocal cross-sections of individual living cells and subsequent 3D reconstructions and digital image alanysis, NPs that are in contact with the cell membrane and NPs localized inside the cytoplasm can be differentiated and quantified. We furthermore investigated the NP uptake while blocking individual uptake pathways with specific inhibitors. Thereby we gained valuable information about the uptake pathways used by the NPs. We found that both HeLa and HUVEC cells internalized the SiO2-NPs via the clathrin dependant pathway. Interestingly the NP uptake by HUVEC cells is significantly more efficient compared to HeLa cells. We furthermore compared the cytotoxic response of both cell lines to the SiO2-NPs and found that this difference in uptake efficiency is reflected by the toxic response.