Length-dependent retention of carbon nanotubes in the pleural space of mice initiates sustained inflammation and progressive fibrosis on the parietal pleura

Our plain-English summary of Length-dependent retention of carbon nanotubes in the pleural space of mice initiates sustained inflammation and progressive fibrosis on the parietal pleura, by F.A. Murphy, C.A. Poland, R. Duffin, et al (The American Journal of Pathology, 2011).

The study

• Authors: F.A. Murphy, C.A. Poland, R. Duffin, K.T. Al-Jamal, H. Ali-Boucetta, A. Nunes, F. Byrne, A. Prina-Mello, Y. Volkov, S. Li, S.J. Mather, A. Bianco, M. Prato, W. Macnee, W.A. Wallace, K. Kostarelos, K. Donaldson
• Journal: The American Journal of Pathology
• Published: 2011;178(6):2587-600
• Cited by: 219 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The fibrous shape of carbon nanotubes (CNTs) raises concern that they may pose an asbestos-like inhalation hazard, leading to the development of diseases, especially mesothelioma. Direct instillation of long and short CNTs into the pleural cavity, the site of mesothelioma development, produced asbestos-like length-dependent responses. The response to long CNTs and long asbestos was characterized by acute inflammation, leading to progressive fibrosis on the parietal pleura, where stomata of strictly defined size limit the egress of long, but not short, fibers. This was confirmed by demonstrating clearance of short, but not long, CNT and nickel nanowires and by visualizing the migration of short CNTs from the pleural space by single-photon emission computed tomographic imaging. Our data confirm the hypothesis that, although a proportion of all deposited particles passes through the pleura, the pathogenicity of long CNTs and other fibers arises as a result of length-dependent retention at the stomata on the parietal pleura.

Copyright © 2011 American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved.

In plain English

In this animal experiment, researchers injected carbon nanotubes, a manufactured fiber-shaped material, into the chest (pleural) cavity of mice to test whether fiber length mattered. They compared long, short and short tangled nanotubes with long and shortened amosite asbestos and carbon black. They also tested quartz, coal mine dust, plastic beads and nickel nanowires. Among the nanotubes, asbestos and carbon black, only long-fiber samples significantly increased pleural inflammatory cells at 24 hours. These were long amosite and the two long nanotube samples. Of quartz, coal mine dust and beads, only the 10-micrometre beads did so. One long nanotube sample caused lasting inflammation. It also caused a fibrotic layer on the chest-wall lining (parietal pleura) that thickened from 4 to 24 weeks. With one short tangled sample, mild early inflammation resolved and the lining was normal at 4, 12 and 24 weeks. Imaging showed short nanotubes collecting in chest lymph nodes within 24 hours. Significantly more short than long nickel nanowires reached those nodes. The authors concluded that long fibers are retained at drainage openings (stomata) in the parietal pleura, while short fibers are cleared to the lymph nodes.

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: fibers and particles were injected directly into the pleural space of mice, with follow-up from 24 hours to 24 weeks
• Who was studied: Female C57Bl/6 mice aged 8 weeks, examined at 24 hours, 7 days, 4 weeks, 12 weeks and 24 weeks after injection; Balb/C mice were used for the imaging experiment
• Exposure: Five multiwalled carbon nanotube samples, grouped as long (NTlong1, NTlong2), short and tangled (NTtang1, NTtang2), or short and straight (NTshort). Controls were amosite asbestos enriched for long fibers (LFA), shortened amosite asbestos (SFA) and nanoparticle carbon black. The study also used quartz, coal mine dust, 3- and 10-micrometre polystyrene beads, and short and long nickel nanowires. The dose was 5 micrograms per mouse.
• Main results:
  • At 24 hours, only the samples containing long fibers (long amosite, NTlong1 and NTlong2) significantly increased the total number of cells in pleural lavage fluid.
  • Only mice injected with long nanotubes or long asbestos had significantly more granulocytes (inflammatory cells) than vehicle controls. Mice given short amosite, carbon black or the short nanotube samples did not.
  • In NTlong2-treated mice, granulocyte numbers were greatly reduced by 4 weeks but stayed above vehicle-control and NTtang1 levels up to 24 weeks.
  • At 1 day, inflammatory-cell aggregates were present on the pleural surface with both NTtang1 and NTlong2. By 7 days, the parietal pleura of NTtang1-treated mice looked completely normal.
  • NTlong2-treated mice developed a fibrotic layer over the parietal pleura that kept thickening from 4 to 24 weeks. At 4, 12 and 24 weeks, mice given vehicle control or NTtang1 had a single layer of mesothelial cells with no inflammation.
  • In long-nanotube-treated mice, the fibrosis became about 20 times thicker and contained more collagen between 1 and 24 weeks.
  • At 24 weeks, the marker of dividing cells (Ki-67) was detected along the mesothelium only in NTlong2-treated mice.
  • Quartz, coal mine dust and 3-micrometre beads, all small enough to pass through the stomata, caused no inflammatory response in the pleural space.
  • Among quartz, coal mine dust and the beads, only the 10-micrometre beads, which are too large to pass through the stomata, significantly increased granulocytes at 24 hours.
  • By 24 hours, radiolabeled short nanotubes injected into the pleural space were found almost entirely in the cranial mediastinal lymph nodes.
  • Significantly more nickel nanowires reached the mediastinal lymph nodes in mice given short nanowires than in mice given long nanowires.
  • Long nickel nanowires caused a greater inflammatory response than short nickel nanowires.
• The authors' conclusion: The authors concluded that the length-dependent response is explained by long fibers being retained at stomata in the parietal pleura, while short fibers are cleared to the mediastinal lymph nodes.
• Limitations the authors state:
  • Radiolabeling shortens long nanotubes, so the imaging method could not show retention of long nanotubes; only short nanotubes were imaged.
  • The comparison of short and long carbon nanotubes in lymph nodes was only qualitative, because small nanotubes are hard to count in lymph tissue.
  • The authors could not define a length below which fibers are not retained in the pleura.
  • The doses used were relatively high.
  • The possible route of fibers reaching the pleura through the blood was not investigated.
  • The authors described the nickel nanowire data as necessarily limited.

Topics

Medical terms in this study, explained in our Lexicon: Inflammation, Fibrosis, Parietal Pleura, Mesothelioma, Pleural Cavity, Pleura.

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)
• Asbestos, carbon nanotubes and the pleural mesothelium: a review of the hypothesis regarding the role of long fibre retention in the parietal pleura, inflammation and mesothelioma — K. Donaldson, F.A. Murphy, et al. (2010)
• Inflammation in the pleural cavity following injection of multi-walled carbon nanotubes is dependent on their characteristics and the presence of IL-1 genes — Y.J. Arnoldussen, V. Skaug, et al. (2018)
• Size- and shape-dependent pleural translocation, deposition, fibrogenesis, and mesothelial proliferation by multiwalled carbon nanotubes — J. Xu, D.B. Alexander, et al. (2014)
• Persistent Pleural Lesions and Inflammation by Pulmonary Exposure of Multiwalled Carbon Nanotubes — D. Liao, Q. Wang, et al. (2018)
• Effects of sustained stimulation with multi-wall carbon nanotubes on immune and inflammatory responses in mice — A. Yamaguchi, T. Fujitani, et al. (2012)

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