Silica Nanoparticle‐induced Cytokine Responses in BEAS‐2B and HBEC3‐KT Cells: Significance of Particle Size and Signalling Pathways in Different Lung Cell Cultures

Abstract

We have previously reported that silica nanoparticles (SiNPs) of nominal size 50 nm (Si50) induce the pro-inflammatory cytokines CXCL8 and IL-6 in BEAS-2B cells, via mechanisms involving MAPK p38, TACE-mediated TGF-α release and the NF-κB pathway. In this study, we examined whether these findings are cell specific or might be extended to another epithelial lung cell model, HBEC3-KT, and also to SiNPs of a smaller size (nominal size of 10 nm; Si10). The TEM average size of Si10 and Si50 was 10.9 and 34.7 nm, respectively. The surface area (BET) of Si10 was three times higher than for Si50 per mass unit. With respect to hydrodynamic size (DLS), Si10 in exposure medium showed a higher z-average for the main peak than Si50, indicating more excessive agglomeration. Si10 strongly induced CXCL8 and IL-6, as assessed by ELISA and RT-PCR, and was markedly more potent than Si50, even when adjusted to equal surface area. Furthermore, Si10 was far more cytotoxic, measured as lactate dehydrogenase (LDH) release, than Si50 in both epithelial cell cultures. With respect to signalling pathways, Western analysis and experiments with and without inhibition of MAPK, TACE and NF-κB (synthetic inhibitors) revealed that p38-phosphorylation, TACE-mediated TGF-α release and NF-κB activation seem to be important triggering mechanisms for both Si50 and Si10 in the two different lung epithelial cell cultures. In conclusion, the identified signalling pathways are suggested to be important in inducing cytokine responses in different epithelial cell types and also for various sizes of silica nanoparticles.

Pro-inflammatory effects of crystalline- and nano-sized non-crystalline silica particles in a 3D alveolar model

“…IL-1β release is due to silica particle-induced activation of the inflammasome due to uptake of particles causing destabilization of the lysosomal membrane [12,16,18,63,64]. Furthermore, we have in previous studies found that SiNPs also are able to induce gene expression and release of IL-1α and IL-1β in lung epithelial cells at rather low concentrations [11]. Interestingly, IL-1α and IL-1β are both known to be critical paracrine (and endocrine) mediators of inflammation linked to lung [34,60,65,66] and cardiovascular disease [35,36].…”

“…Both types of particles induce cytotoxic, genotoxic and pro-inflammatory acute responses [1,4,8]. In previous studies we have investigated SiNP-induced cytotoxicity, cytokine gene expression and release as well as underlying signalling pathways involved, in lung epithelial cells and macrophages in mono-cultures [11][12][13][14].…”

Synthetic hydrosilicate nanotubes induce low pro‐inflammatory and cytotoxic responses compared to natural chrysotile in lung cell cultures

“…The hydrosilicate NTs and chrysotile were dissolved in PBS with 0.15% BSA to final concentration of 2 mg/mL, and sonicated on ice for 20 minutes to a final energy of 7056 J. The silica NP solution sized 10 nm (Si10) was diluted in PBS with 0.15% BSA after a sonication step . Characterization of Si10 was done in a previous study …”

“…The cells were exposed as described in our previous study. 23 THP-1 monocytes were maintained in RPMI-1640 with 10% FBS at a cell density of 0.5 mill/ml and differentiated to macrophage-like cells (THP-1 macrophages) by exposing to PMA. THP-1 cells were seeded three days before exposure on a 35-mm 6-well plate at a cell density of 0.5 mill/mL or 1 × 10 5 cells on a 96-microwell culture plate in RPMI-1640 with 10% FBS.…”

“…Synthetic hydrosilicate NTs of different median lengths from 0.2 to 5 µm were made and compared with natural chrysotile. Silica nanoparticles of 10 nm size (Si10) were included as a positive control . Our main hypothesis was that synthetic hydrosilicate NTs of short length and with a minor metal contamination had little or no cytotoxic and pro‐inflammatory potential.…”