| dc.description.abstract | The presence of nanoparticles in commercially available products has increased drastically in the last decade. Nanoparticles, which are defined as particles with a diameter range from 1 to 100 nm in at least one dimension, have unique physicochemical properties compared to larger-sized particles of similar chemical composition. This might be due to their small size, large surface area, and surface reactivity. Because there is still limited knowledge on their effect on human health and environment, it is important to characterize their chemical properties and potential toxicity to confirm the safety of nanoparticles. The research group has previously demonstrated that amorphous silica nanoparticles (10 nm and 50 nm) have the potential to elicit marked pro-inflammatory cytokine responses mediated through mitogen-activated protein kinases (MAPKs) in a bronchial cell line (BEAS-2B). Si50 has also been shown to induce cytokine responses through nuclear factor (NF)-κB signaling pathways. In the present thesis, the pro-inflammatory and cytotoxic potential of SiNP of 10 nm and 50 nm size to induce gene expression and cytokine responses of IL-6, IL-8, IL-1β and TNF-α were compared at equal mass concentrations in the same bronchial cell line. Three different cell densities of BEAS-2B cells were used to determine if cytokine responses and cytotoxicity of SiNP-exposed cells were affected by cell density in culture. Furthermore, the involvement of the intracellular signaling pathways NF-κB and PKC in mediating the release of IL-6 and IL-8 were examined. The study showed a size- and concentration-dependent increase in pro-inflammatory responses of IL-6, IL-8, RANTES, TNF-α and IL-1β, as well as cytotoxicity measured as LDH-release in BEAS-2B cells after exposure to Si10 and Si50. Si10 caused a stronger response of both IL-6 and IL-8 compared to Si50 at similar particle concentrations. The SiNP-induced RANTES-, IL-1β- and TNF-α responses were less clearly increased by the nanoparticles compared to IL-6 and IL-8, and with Si10 as most potent on mass basis. For both particle sizes, the pattern of release was similar for IL-6 and IL-8. This was different for RANTES showing different pattern of release between Si10 and Si50. Regarding cell density of BEAS-2B cells, cultures with the intermediate cell density induced the highest cytokine release for Si10. However, the effects of cell density upon exposure to Si50 were less distinct. The relative LDH-release was little affected by cell density. Gene expression showed a greater mRNA expression of IL-6 and IL-8 compared to IL-1β and TNF-α, with a more prolonged up-regulation for Si10 than Si50. The activation of NF-κB through the phosphorylation of p65 and degradation of IκB-α was demonstrated in SiNP-exposed BEAS-2B cells. In addition to this, pre-treatment with inhibition of p65 showed the involvement of NF-κB in the release of IL-6 and IL-8 in Si10- and Si50-exposed cells, as demonstrated by the chemical NF-κB inhibitor PDT-p65, and siRNA against p65. It was also demonstrated by using the broad PKC-inhibitor GF109203X that PKC was partly involved in the induction of IL-6 and IL-8 release in BEAS-2B cells. In conclusion, SiNP caused a size- and concentration-dependent increase in pro-inflammatory responses of IL-6, IL-8, RANTES, TNF-α and IL-1β, as well as LDH-release, with Si10 being more potent than Si50. The cell density was of importance for the cytokine responses, whereas cytotoxicity was little affected. A more prolonged gene expression of IL-6, IL-8, IL-1β and TNF-α was seen for Si10-exposed cells compared to Si50. Both Si10-and Si50 seemed to exert their effects on IL-6 and IL-8 via a mechanism involving NF-κB and possibly PKC. | eng |