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

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.