Fluoride enhances polystyrene nanoparticles cytotoxicity in colonocytes in vitro model

Human gastrointestinal cells can be exposed to different xenobiotics present in food or drinking water. In this work, we assessed the cytotoxicity of polystyrene nanoparticles (PS-NPs) and how it is impacted by fluoride (F^-) presence. We decided to examine PS-NPs and F^- which can be easily found in drinking water and food. Commercially available amine-modified 100 nm PS-NPs were used in the study. Scanning Electron Microscopy with Electron Dispersive Spectroscopy (SEM-EDS) and Dynamic Light Scattering (DLS) were used to characterize PS-NPs. The colon cell lines (HT-29, Caco-2, CCD 841 CoN) were used. Cytotoxicity of PS-NPs and F^- alone or in co-exposition were assessed with MTT assay in a time- and concentration-dependent manner. Flow cytometry was used to measure reactive oxygen species (ROS) production, cell cycle distribution, and apoptosis analysis. Transmission electron microscopy (TEM) was used to determine whether PS-NPs and/or F^- can cause ultrastructure changes in the cells. We have shown that PS-NPs are cytotoxic to human colon cells in a time- and concentration-dependent manner. PS-NPs did not impact neither intracellular ROS production nor the cells cell cycle distribution. However, if HT-29 cells were co-exposed to PS-NPs and F^-, an increased number of cells in G0/G1 phase and decreased number of cells in G2/M were observed. PS-NPs can cause apoptosis in HT-29 cells, this effect was enhanced if cells were co-exposed to PS-NP and F^-. PS-NPs were internalised by the cells and caused ultrastructure changes. Fluoride itself (1 mM) was not cytotoxic to the cells and did not cause any changes in the ultrastructure of the cells. We have proven that polystyrene nanoparticles can be cytotoxic to human gastrointestinal cells and this effect is enhanced by fluoride.