Particle and Fibre Toxicology. Vol. 10, Iss. 39, 42, August 2013
Evaluation of cytotoxic, genotoxic and inflammatory responses of nanoparticles from photocopiers in three human cell lines
Riassunto
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 mug/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 mug nanoparticles/mL for 6-hr exposure for confirmation purposes.
Results Multiple cytokines, GM-CSF, IL-1beta, IL-6, IL-8, IFNgamma, MCP-1, TNF-alpha and VEGF, were significantly elevated in THP-1 cells in a dose-dependent manner. Gene expression analysis confirmed up-regulation of the TNF-alpha gene in THP-1 cells, consistent with cytokine findings. In both primary epithelial cells, cytokines IL-8, VEGF, EGF, IL-1alpha, TNF-alpha, 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.
Commento
Le fotocopiatrici sono alcuni tra i dispositivi elettronici più comunemente utilizzati negli ambienti lavorativi e sono, durante i processi di stampaggio e di manutenzione, una potenziale fonte di esposizione indoor a campi elettromagnetici a bassa frequenza e ad inquinanti tossici come ozono, biossido di azoto e composti volatili di natura particellare. La composizione chimica di questi ultimi è rappresentata da una complessa miscela di sostanze organiche semi volatili ed ossidi metallici inorganici, costituiti prevalentemente da silicio, zolfo, titanio, ferro, cromo, nichel e zinco, che vengono usati come additivi e la cui concentrazione è variabile a seconda del tipo di toner utilizzato.
La tossicologia di questi elementi emessi in forma nano particellare è poco conosciuta ed il tema ha ricevuto la dovuta attenzione, in letteratura, solo di recente.
I pochi studi sul tema, effettuati negli ultimi anni, hanno riportato significativi livelli di genotossicità, danni al DNA ed aberrazioni cromosomiche nei lavoratori professionalmente esposti. In uno studio del 2012 Khatri e collaboratori hanno dimostrato che singole esposizioni a breve termine (6 ore), in un centro di stampaggio con livelli di esposizione modesti (medie giornaliere di 5,000-30,000 particelle/cm3), sono state in grado di indurre aumenti statisticamente significativi dello stress ossidativo sistemico e dell'infiammazione delle vie aeree superiori.
Nella presente ricerca i medesimi autori arricchiscono ulteriormente l’argomento, studiando gli effetti dei composti volatili nanoparticellari emessi dalle fotocopiatrici su tre linee cellulari umane delle vie aeree superiori.