Sub-Cytotoxic Nanoparticle Exposure to Airway Epithelial Cells Causes Alterations in Cellular Signaling

Abstract

There are strong correlations between ultrafine particle deposition in the lung and chronic respiratory illness. The growing prevalence of engineered nanoparticles (ENPs) in society presents a new lung toxicant exposure that has the potential to cause adverse affects in the lung, and specifically, on lung innate immune function. We examined the cytotoxicity of hafnium oxide (HfO2), cerium oxide (CeO2), and silicon oxide (SiO2) ENPs, and their micron-sized equivalents, to cultured human airway epithelial cells (16HBE14o-) in terms of cell death and reduction in paracrine ATP signaling as a measure of one aspect of innate immune function in lung epithelium. We used high-throughput real time cell analysis (RTCA) assays and fluorescent-based Live/Dead assays to evaluate cell death to establish cytotoxic levels of ENPs to airway epithelium. We used RTCA with digital imaging video microscopy to evaluate changes in ATP-induced cell signaling following exposure to low, non-cytotoxic doses of ENPs (10 - 50 mg/L). ENP induced cytotoxicity occurred only at high exposures, whereas acute (24 hr) incubations with ENPs resulted in altered ATP-induced cellular signaling at low doses of ENPs. We conclude that sub-cytotoxic exposures to ENPs can alter a basic innate immune function in lung epithelial cells that could contribute to respiratory disease. Such measurements of toxicity may be better indicators of potential health hazards of ENPs than simple cell death assays.