Background: Many in vitro studies have revealed that the interference of dye molecules in traditional nanoparticlecytotoxicity assays results in controversial conclusions. The aim of this study is to establish an extensiveand systematic method for evaluating biological effects of gold nanoparticles in mammalian cell lines.Methods: We establish the cell-impedance measurement system, a label-free, real-time cell monitoring platformthat measures electrical impedance, displaying results as cell index values, in a variety of mammaliancell lines. Cytotoxic effects of gold nanoparticles are also evaluated with traditional in vitro assays.Results: Among the six cell lines, gold nanoparticles induce a dose-dependent suppression of cell growth withdifferent levels of severity and the suppressive effect of gold nanoparticles was indirectly associated withtheir sizes and cellular uptake. Mechanistic studies revealed that the action of gold nanoparticles is mediatedby apoptosis induction or cell cycle delay, depending on cell type and cellular context. Although redox signalingis often linked to the toxicity of nanoparticles, in this study, we found that gold nanoparticle-mediatedreactive oxygen species generation was not sustained to notably modulate proteins involved in antioxidativedefense system.Conclusion: The cell-impedancemeasurement system, a dye-free, real-time screening platform, provides a reliableanalysis for monitoring gold nanoparticle cytotoxicity in a variety of mammalian cell lines. Furthermore, goldnanoparticles induce cellular signaling and several sets of gene expression to modulate cellular physical processes.General significance: The systematic approach, such as cell-impedance measurement, analyzing the toxicology ofnanomaterials offers convincing evidence of the cytotoxicity of gold nanomaterials
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