Functionalized Surface-Charged SiO2 Nanoparticles Induce Pro-Inflammatory Responses, but Are Not Lethal to Caco-2 Cells

Nanoparticles (NPs) are widely used in food, and analysis of their potential gastrointestinal toxicity is necessary. The present study was designed to determine the effects of silica dioxide (SiO2), titanium dioxide (TiO2), and zinc oxide (ZnO) NPs on cultured THP-1 monocyte-derived macrophages and human epithelial colorectal adenocarcinoma (Caco-2) cells. Exposure to ZnO NPs for 24 h increased the production of redox response species (ROS) and reduced cell viability in a dose-dependent manner in THP-1 macrophages and Caco-2 cells. Although TiO2 and SiO2 NPs induced oxidative stress, they showed no apparent cytotoxicity against both cell types. The effects of functionalized SiO2 NPs on undifferentiated and differentiated Caco-2 cells were investigated using fluorescently labeled SiO2 NPs with neutral, positive, or negative surface charge. Exposure of both types of cells to the three kinds of SiO2 NPs significantly increased their interaction in a dose-dependent manner. The largest interaction with both types of cells was noted with exposure to more negatively surface-charged SiO2 NPs. Exposure to either positively or negatively, but not neutrally, surface-charged SiO2 NPs increased NO levels in differentiated Caco-2 cells. Exposure of differentiated Caco-2 cells to positively or negatively surface-charged SiO2 NPs also upregulated interleukin-8 expression. We conclude that functionalized surface-charged SiO2 NPs can induce pro-inflammatory responses but are noncytotoxic.