Inhaled carbon nanotubes reach the subpleural tissue in mice

Our plain-English summary of Inhaled carbon nanotubes reach the subpleural tissue in mice, by J.P. Ryman-Rasmussen, M.F. Cesta, A.R. Brody, et al (Nature Nanotechnology, 2009).

The study

• Authors: J.P. Ryman-Rasmussen, M.F. Cesta, A.R. Brody, J.K. Shipley-Phillips, J.I. Everitt, E.W. Tewksbury, O.R. Moss, B.A. Wong, D.E. Dodd, M.E. Andersen, J.C. Bonner
• Journal: Nature Nanotechnology
• Published: 2009;4(11):747-51
• Cited by: 288 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Carbon nanotubes are shaped like fibres and can stimulate inflammation at the surface of the peritoneum when injected into the abdominal cavity of mice, raising concerns that inhaled nanotubes may cause pleural fibrosis and/or mesothelioma. Here, we show that multiwalled carbon nanotubes reach the subpleura in mice after a single inhalation exposure of 30 mg m(-3) for 6 h. Nanotubes were embedded in the subpleural wall and within subpleural macrophages. Mononuclear cell aggregates on the pleural surface increased in number and size after 1 day and nanotube-containing macrophages were observed within these foci. Subpleural fibrosis unique to this form of nanotubes increased after 2 and 6 weeks following inhalation. None of these effects was seen in mice that inhaled carbon black nanoparticles or a lower dose of nanotubes (1 mg m(-3)). This work suggests that minimizing inhalation of nanotubes during handling is prudent until further long-term assessments are conducted.

In plain English

This animal experiment studied carbon nanotubes, not asbestos. The authors exposed male C57BL6 mice (10 per group) once, for 6 hours, by nose-only inhalation, to multi-walled carbon nanotubes at 30 or 1 mg per cubic metre, to carbon black nanoparticles at 30 mg per cubic metre, or to saline, and examined their lungs 1 day to 14 weeks later. One day after exposure, nanotubes were seen in macrophages, other cells and collagen beneath the pleura, the lung's outer lining. The high nanotube dose significantly increased the number of immune-cell clusters on the pleural surface at 1 day and 2 weeks, and also their size. It significantly increased scarring (fibrosis) beneath the pleura at 2 and 6 weeks; 9 out of 10 high-dose mice had fibrotic lesions. These effects were not seen with carbon black or the low dose. The authors noted the lesions were focal and looked different from asbestos-related pleural disease, and that the study could not answer whether nanotubes cause mesothelioma. They concluded that minimizing inhalation of nanotubes during handling would be prudent until longer-term studies are done.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Animal experiment: a single 6-hour nose-only inhalation exposure in mice, with lung tissue examined at several later time points
• Who was studied: Pathogen-free adult male C57BL6 mice aged 6 to 8 weeks, 10 per group. Groups were high-dose nanotubes, low-dose nanotubes, carbon black and saline control. Lungs were collected at 1 day, 2 weeks, 6 weeks or 14 weeks after exposure.
• Exposure: Multi-walled carbon nanotubes made with nickel and lanthanum catalysts, at 30 mg per cubic metre (calculated dose 4 mg/kg) or 1 mg per cubic metre (0.2 mg/kg). Carbon black nanoparticles at 30 mg per cubic metre served as a comparison and saline as the control. Nanotube widths were 10 to 50 nm. No asbestos was used.
• Main results:
  • One day after inhalation, nanotubes were found in macrophages and within cells and the collagen matrix beneath the pleura.
  • In the high-dose nanotube group, the incidence and number of pleural mononuclear cell aggregates (1 to 2 per 10 sections) were significantly increased at 1 day and 2 weeks after exposure.
  • The size of the mononuclear cell aggregates was significantly increased by the high nanotube dose.
  • Fibrotic lesions beneath the pleura occurred in 9 out of 10 mice in the nanotube-exposed group. The fibrosis score was significantly increased by the high dose at 2 weeks and 6 weeks.
  • Fibrotic lesions beneath the pleura were seen only in the high-dose nanotube group. Their maximum thickness was 20 to 70 micrometres, compared with 3 to 15 micrometres for normal tissue beneath the pleura.
  • None of these effects were seen in mice that inhaled carbon black nanoparticles or the lower nanotube dose (1 mg per cubic metre).
  • Some nanotubes remained beneath the pleura for at least 14 weeks, but most appeared to have been cleared by then. Fibrosis and cell aggregates diminished.
• The authors' conclusion: The authors concluded that inhaled multi-walled carbon nanotubes increased pleural mononuclear cell accumulation and fibrosis beneath the pleura in mice. They said these changes could be unique to this type of nanotube and may or may not persist with repeated low-dose occupational exposure. They judged that precautions minimizing inhalation during handling would be prudent until longer-term studies of repeated exposures are done.
• Limitations the authors state:
  • The fibrosis score relied on trichrome staining, which could stain other matrix components and contribute to the observed pleural wall thickness.
  • Most of the tissue beneath the pleura in nanotube-exposed mice was normal; the fibrotic lesions were focal and regional.
  • The study cannot answer whether these nanotubes cause mesothelioma. There was no indication of cancer, and asbestos was not used as a positive control.
  • It is unknown whether other types of multi-walled nanotubes would cause the same response. The nanotubes used contained nickel, and agglomeration could affect deposition and toxicity.
  • Clearance of nanotubes from the tissue was not measured quantitatively.
  • Only a single exposure was studied. The changes may or may not persist under repeated, low-dose occupational exposures.

Topics

Medical terms in this study, explained in our Lexicon: Inflammation, Peritoneum, Fibrosis, Mesothelioma, Macrophage.

Related studies

• Length-dependent pleural inflammation and parietal pleural responses after deposition of carbon nanotubes in the pulmonary airspaces of mice — F.A. Murphy, C.A. Poland, et al. (2013)
• Multiwalled carbon nanotube-induced pulmonary inflammatory and fibrotic responses and genomic changes following aspiration exposure in mice: A 1-year postexposure study — B.N. Snyder-Talkington, C. Dong, et al. (2016)
• A single intratracheal instillation of single-walled carbon nanotubes induced early lung fibrosis and subchronic tissue damage in mice — E.J. Park, J. Roh, et al. (2011)
• Length-dependent retention of carbon nanotubes in the pleural space of mice initiates sustained inflammation and progressive fibrosis on the parietal pleura — F.A. Murphy, C.A. Poland, et al. (2011)
• Comparative proteomics and pulmonary toxicity of instilled single-walled carbon nanotubes, crocidolite asbestos, and ultrafine carbon black in mice — J.G. Teeguarden, B.J. Webb-Robertson, et al. (2011)
• Carbon nanotubes introduced into the abdominal cavity of mice show asbestos-like pathogenicity in a pilot study — C.A. Poland, R. Duffin, et al. (2008)

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