Open Access Research

Comparison of non-crystalline silica nanoparticles in IL-1β release from macrophages

Wiggo J Sandberg1, Marit Låg1, Jørn A Holme1, Bernd Friede2, Maurizio Gualtieri13, Marcin Kruszewski45, Per E Schwarze1, Tonje Skuland1 and Magne Refsnes1*

Author Affiliations

1 Norwegian Institute of Public Health, Division of Environmental Medicine, P.O. Box 4404, Nydalen, Oslo, N-0403, Norway

2 Elkem AS, Silicon Materials, P.O. Box 8126, Vaagsbygd, Kristiansand, 4675, Norway

3 Present address: Research Centre POLARIS, Department of Environmental Science, University Milano-Bicocca, Piazza della Scienza 1, Milan, 20126, Italy

4 Institute of Nuclear Chemistry & Technology, Warsaw, Poland

5 Independent Laboratory of Molecular Biology, Institute of Rural H, Jaczewskiego 2, Lublin, 20-950, Poland

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Particle and Fibre Toxicology 2012, 9:32  doi:10.1186/1743-8977-9-32

Published: 10 August 2012

Abstract

Background

Respirable crystalline silica (silicon dioxide; SiO2, quartz) particles are known to induce chronic inflammation and lung disease upon long-term inhalation, whereas non-crystalline (amorphous) SiO2 particles in the submicrometre range are regarded as less harmful. Several reports have demonstrated that crystalline, but also non-crystalline silica particles induce IL-1β release from macrophages via the NALP3-inflammasome complex (caspase-1, ASC and NALP3) in the presence of lipopolysaccharide (LPS) from bacteria. Our aim was to study the potential of different non-crystalline SiO2 particles from the nano- to submicro-sized range to activate IL-1β responses in LPS-primed RAW264.7 macrophages and primary rat lung macrophages. The role of the NALP3-inflammasome and up-stream mechanisms was further explored in RAW264.7 cells.

Results

In the present study, we have shown that 6 h exposure to non-crystalline SiO2 particles in nano- (SiNPs, 5–20 nm, 50 nm) and submicro-sizes induced strong IL-1β responses in LPS-primed mouse macrophages (RAW264.7) and primary rat lung macrophages. The primary lung macrophages were more sensitive to Si-exposure than the RAW-macrophages, and responded more strongly. In the lung macrophages, crystalline silica (MinUsil 5) induced IL-1β release more potently than the non-crystalline Si50 and Si500, when adjusted to surface area. This difference was much less pronounced versus fumed SiNPs. The caspase-1 inhibitor zYVAD and RNA silencing of the NALP3 receptor reduced the particle-induced IL-1β release in the RAW264.7 macrophages. Furthermore, inhibitors of phagocytosis, endosomal acidification, and cathepsin B activity reduced the IL-1β responses to the different particles to a similar extent.

Conclusions

In conclusion, non-crystalline silica particles in the nano- and submicro-size ranges seemed to induce IL-1β release from LPS-primed RAW264.7 macrophages via similar mechanisms as crystalline silica, involving particle uptake, phagosomal leakage and activation of the NALP3 inflammasome. Notably, rat primary lung macrophages were more sensitive with respect to silica-induced IL-1β release. The differential response patterns obtained suggest that silica-induced IL-1β responses not only depend on the particle surface area, but on factors and/or mechanisms such as particle reactivity or particle uptake. These findings may suggest that bacterial infection via LPS may augment acute inflammatory effects of non-crystalline as well as crystalline silica particles.

Keywords:
Non-crystalline and crystalline silica particles; Particle size; Macrophages; Inflammation; IL-1β; NALP3 inflammasome; Particle uptake; Phagosomal destabilization