Amorphous silica nanoparticles show concentration and time-dependent toxicity on Human HaCaT Cells

Abstract

Background: The wide use of nanomaterials in medicine and biology and the unknown cytotoxicity of some nanoparticles heighten the demand for health and safety guidelines. The creation of these guidelines relies on experimental investigation to inform guidelines to eliminate the risk of exposure from newly synthesized nanoparticles. Skin contact of nanoparticles can cause skin cancer; therefore, the focus of this study was to identify the cytotoxicity of these particles to skin cells in an in vitro model. Methods: The toxicity of 12-nm amorphous silica (SiO2) nanoparticles following 4, 24 and 48h exposure was investigated using a human keratinocyte cell line (HaCaT) with [3-(4,5- dimethylthiazol-2yl)-diphenyltetrazolium bromide] (MTT) and crystal violet assays. Eleven concentrationsof 12-nm SiO2 ranging between 0.05-10 mg/mL were tested. Results: At 4, 24 and 48h exposure, a dose dependent increase in cell killing with increasing concentration were observed when screened with the MTT assay. At 24h for concentrations ≥ 2 mg/mL, relative survival decreased when assayed by the MTT assay and relative cell number decreased when assayed with the crystal violet assay. After 48htreatment, cytotoxicity was observed at every treatment concentration assessed with the MTT and crystal violet assays. The level of cytotoxicity was also time dependent (4, 24, 48h)at every concentration. The level ofcytotoxicity after 48h treatment was equal to or less than that of cell population streated for 24h. Conclusion: Silica nanoparticles are toxic to cultured human skin cells at a concentration as low as 0.05 mg/mL for 48h treatment when screen by the crystal violet assay. When nanoparticles of consistent structure and surface area are used to treat human cells in culture, results varied between two well recognised colourimetric bioassays. However, with both assays, silica nanoparticles are toxic to human skin cells in vitro and toxicity is both concentration dependent and time dependent.

Keywords: Silica particles, nanoparticles, occupational health, HaCaT cells