Single-walled carbon nanotubes induce airway hyperreactivity and parenchymal injury in mice

Inhalation of single-walled carbon nanotubes (SWCNTs) has raised serious concerns related to potential toxic effects in the respiratory system. This study examined possible SWCNT-induced toxic mechanisms in vivo in mice. The results indicated that a single intratracheal instillation of SWCNTs could induce airway hyperreactivity and airflow obstruction and confirmed previous findings of granulomatous changes in the lung parenchyma that persisted from 7 days to 6 months after exposure. The irreversible lung pathology and functional airway alterations in the mouse model mimicked obstructive airway disease in humans. Transcriptomic analysis showed that SWCNTs might up-regulate proteinases (cathepsin K and matrix metalloproteinase [MMP]12), chemokines C-C motif ligands (CCL2 and CCL3), and several macrophage receptors (Toll-like receptor 2, macrophage scavenger receptor 1). Pathway analyses showed that NF-κB-related inflammatory responses and downstream signals affecting tissue remodeling dominated the pathologic process. The NF-κB inhibitor pyrrolidine dithiocarbamate attenuated SWCNT-induced airway hyperreactivity, chronic airway inflammation, and MMP12 and cathepsin K expression when administered in vivo, whereas a cathepsin K inhibitor could partially reduce airway hyperreactivity and granulomatous changes in the SWCNT-treated group. The up-regulation of cathepsin K and MMP12 by SWCNTs was further confirmed via in vitro coculture of bronchoalveolar macrophages with lung epithelial/mesenchymal cells but not in macrophages without coculture, indicating that SWCNT-induced MMP12 and cathespin K were cell-type specific and cell-cell interaction dependent. In conclusion, exposure to SWCNTs may cause irreversible obstructive airway disease. Nanotoxicogenomics uncovered novel mechanisms underlying SWCNT-induced lung diseases, implicating MMP12 and cathepsin K in the pathologic injury as potential biomarkers or therapeutic targets.