Highlights

• Short SWCNTs induced persistent pulmonary inflammation over a 90-day period following instillation.
• Pulmonary inflammation after short MWCNT instillation decreased in a time-dependent manner.
• MWCNT instillation induced greater levels of pleural inflammation than did short SWCNTs.
• Short SWCNTs and MWCNTs underwent lymphatic drainage to the mediastinal lymph nodes after pleural penetration.
• The extent and time-dependent changes of pulmonary and pleural inflammation differed following SWCNT and MWCNT instillations.

Abstract

Relationships between the physical properties of carbon nanotubes (CNTs) and their toxicities have been studied. However, little research has been conducted to investigate the pulmonary and pleural inflammation caused by short-fiber single-walled CNTs (SWCNTs) and multi-walled CNTs (MWCNTs). This study was performed to characterize differences in rat pulmonary and pleural inflammation caused by intratracheal instillation with doses of 0.15 or 1.5 mg/kg of either short-sized SWCNTs or MWCNTs. Data from bronchoalveolar lavage fluid analysis, histopathological findings, and transcriptional profiling of rat lungs obtained over a 90-day period indicated that short SWCNTs caused persistent pulmonary inflammation. In addition, the short MWCNTs markedly impacted alveoli immediately after instillation, with the levels of pulmonary inflammation following MWCNT instillation being reduced in a time-dependent manner. MWCNT instillation induced greater levels of pleural inflammation than did short SWCNTs. SWCNTs and MWCNTs translocated in mediastinal lymph nodes were observed, suggesting that SWCNTs and MWCNTs underwent lymphatic drainage to the mediastinal lymph nodes after pleural penetration. Our results suggest that short SWCNTs and MWCNTs induced pulmonary and pleural inflammation and that they might be transported throughout the body after intratracheal instillation. The extent of changes in inflammation differed following SWCNT and MWCNT instillation in a time-dependent manner.

Graphical abstract

Hypothetical model of SWCNT- or MWCNT-induced pulmonary and pleural inflammation.