Effects of copy center particles on the lungs: a toxicological characterization using a Balb/c mouse model

Evaluation of cytotoxic, genotoxic and inflammatory responses of nanoparticles from photocopiers in three human cell lines

Background

Photocopiers emit nanoparticles with complex chemical composition. Short-term exposures to modest nanoparticle concentrations triggered upper airway inflammation and oxidative stress in healthy human volunteers in a recent study. To further understand the toxicological properties of copier-emitted nanoparticles, we studied in-vitro their ability to induce cytotoxicity, pro-inflammatory cytokine release, DNA damage, and apoptosis in relevant human cell lines.

Methods

Three cell types were used: THP-1, primary human nasal- and small airway epithelial cells. Following collection in a large volume photocopy center, nanoparticles were extracted, dispersed and characterized in the cell culture medium. Cells were doped at 30, 100 and 300 μg/mL administered doses for up to 24 hrs. Estimated dose delivered to cells, was ~10% and 22% of the administered dose at 6 and 24 hrs, respectively. Gene expression analysis of key biomarkers was performed using real time quantitative PCR (RT-qPCR) in THP-1 cells at 5 μg nanoparticles/mL for 6-hr exposure for confirmation purposes.

Results

Multiple cytokines, GM-CSF, IL-1β, IL-6, IL-8, IFNγ, MCP-1, TNF-α and VEGF, were significantly elevated in THP-1 cells in a dose-dependent manner. Gene expression analysis confirmed up-regulation of the TNF-α gene in THP-1 cells, consistent with cytokine findings. In both primary epithelial cells, cytokines IL-8, VEGF, EGF, IL-1α, TNF-α, IL-6 and GM-CSF were significantly elevated. Apoptosis was induced in all cell lines in a dose-dependent manner, consistent with the significant up-regulation of key apoptosis-regulating genes P53 and Casp8 in THP-1 cells. No significant DNA damage was found at any concentration with the comet assay. Up-regulation of key DNA damage and repair genes, Ku70 and Rad51, were also observed in THP-1 cells, albeit not statistically significant. Significant up-regulation of the key gene HO1 for oxidative stress, implicates oxidative stress induced by nanoparticles.

Conclusions

Copier-emitted nanoparticles induced the release of pro-inflammatory cytokines, apoptosis and modest cytotoxicity but no DNA damage in all three-human cell lines. Taken together with gene expression data in THP-1 cells, we conclude that these nanoparticles are directly responsible for inflammation observed in human volunteers. Further toxicological evaluations of these nanoparticles, including across different toner formulations, are warranted.

Lung alterations following single or multiple low-dose carbon black nanoparticle aspirations in mice

Carbon black nanoparticle (CBNP) applications in high doses have been shown to be harmful to the lung. It is postulated that even small, environmentally relevant concentrations induce changes on lung homeostasis. The present study determined the impact of low-dose single and multiple CBNP (Printex 90) applications on mouse alveolar cell metabolism, especially inflammatory and oxidative stress parameters. Nanoparticles were administered to mice by a single or 8 oropharyngeal aspirations at wk 1, 2, 3, 5, 7, 9, 11, and 12 using 7 μg Printex 90, 7 μg DQ12 quartz (positive control), with water vehicle and saline as negative controls. After 2 d or 3 mo lung function was analyzed. Further lung histology, bronchoalveolar lavage fluid (BALF) parameters, and mRNA expression of cytokines and antioxidants enzymes in type II pneumocytes were measured on d 3 or after 3 mo. Single low-dose Printex 90 application induced no marked alterations in lung functions or BALF phospholipid levels but significant decrease in superoxide dismutase 2 and numerically elevated glutathione peroxidase 3 mRNA expression levels in type II pneumocytes. Multiple CBNP applications produced reduced lung function, collagen accumulation, elevated phospholipid levels in BALF, and a massive infiltration of macrophages. Type II pneumocyte mRNA expression of antioxidative enzymes remained unchanged throughout the subchronic experiment, but showed a significant decrease in interleukin (IL)-6Rα mRNA expression. This study demonstrates that an environmentally relevant CBNP concentration induced an acute inflammatory response, an effect that is exacerbated throughout the subchronic duration.