Additional histopathologic examination of the lungs from a 3-month inhalation toxicity study with multiwall carbon nanotubes in rats

Our plain-English summary of Additional histopathologic examination of the lungs from a 3-month inhalation toxicity study with multiwall carbon nanotubes in rats, by S. Treumann, L. Ma-Hock, S. Gröters, et al (Toxicological Sciences, 2013).

The study

• Authors: S. Treumann, L. Ma-Hock, S. Gröters, R. Landsiedel, B. van Ravenzwaay
• Journal: Toxicological Sciences
• Published: 2013;134(1):103-10
• Cited by: 19 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

For hazard assessment of multiwalled carbon nanotubes (MWCNTs), a 90-day inhalation toxicity study has been performed with Nanocyl NC 7000 in accordance with OECD 413 test guideline. MWCNTs produced no systemic toxicity. However, increased lung weights, multifocal granulomatous inflammation, diffuse histiocytic and neutrophilic infiltrates, and intra-alveolar lipoproteinosis were observed in lung and lung-associated lymph nodes at 0.5 and 2.5mg/m(3). Additional investigations of the lungs were performed, including special stains for examination of connective tissue, and electron microscopy was performed to determine the location of the MWCNTs. The alveolar walls revealed no increase of collagen fibers, whereas within the microgranulomas a slight increase of collagen fibers was observed. The pleura did not reveal any increase in collagen fibers. Only a slight increase in reticulin fibers in the alveolar walls in animals of the 0.5 and 2.5mg/m(3) concentration group was noted. In the 0.1mg/m(3) group, the only animal revealing minimal granulomas exhibited a minimal increase in collagen within the granuloma. No increase in reticulin was observed. Electron microscopy demonstrated entangled MWCNTs within alveolar macrophages. Occasionally electron dense particles/detritus were observed within membrane-bound vesicles (interpreted as phagosomes), which could represent degraded MWCNTs. If so, MWCNTs were degradable by alveolar macrophages and not persistent within the lung. Inhalation of MWCNTs caused granulomatous inflammation within the lung parenchyma but not the pleura in any of the concentration groups. Thus, there are some similarities to effects caused by inhaled asbestos, but the hallmark effects, namely pleural inflammation and/or fibrosis leading to mesotheliomas, are absent.

In plain English

This animal experiment re-examined lung tissue from rats in an earlier 90-day inhalation study of multiwall carbon nanotubes (MWCNTs, Nanocyl NC 7000) at 0.1, 0.5 and 2.5 mg/m3. No asbestos was tested. The asbestos comparisons drew on other studies. A collagen stain showed no connective-tissue increase in the alveolar walls or pleura. Collagen was minimally increased only inside granulomas, whose incidence was printed as 0/1/10/10 for the control, low, mid and high groups. A reticulin stain showed fibers in the alveolar walls increased minimally to moderately at 0.5 and 2.5 mg/m3, slightly more in females, but not at 0.1 mg/m3. Electron microscopy showed tangled nanotubes inside lung macrophages. Small dense particles might be broken-down nanotubes, but they might also be other material. No pleural lesions regarded as precursors of mesothelioma were seen. The authors concluded that the lung effects seem similar to those of chrysotile asbestos, with granulomas and mild fibrosis but not developing into mesotheliomas or other lung tumors. They noted that the study had no recovery group, and they called for a long-term study of tumor and mesothelioma risk.

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: additional microscopic examination (special connective-tissue stains and transmission electron microscopy) of lungs from a previously published 90-day rat inhalation toxicity study run to the OECD 413 guideline
• Who was studied: Rats in control, 0.1, 0.5 and 2.5 mg/m3 groups. Table 1 lists 10 males and 10 females per group. A separate satellite group of two male rats per concentration group was used for electron microscopy. The rat strain is not stated in this text.
• Exposure: Inhaled aerosols of Nanocyl NC 7000 thin multiwall carbon nanotubes (90% carbon, 10% metal oxide; tubes 5 to 15 nm in diameter and 0.1 to 10 micrometers long) at 0.1, 0.5 and 2.5 mg/m3 for 90 days. No asbestos was administered in this study.
• Main results:
  • Masson's trichrome stain for collagen, compared with control animals: no increase of connective tissue in the alveolar wall or the pleura. There was a minimal focal increase of collagen only in areas of granulomatous inflammation.
  • Granulomatous inflammation, to which the collagen increase was linked, had an incidence printed as 0/1/10/10 (control, low, mid and high concentration groups), with severity rising from minimal (grade 1) to moderate (grade 3).
  • There was no increase in collagen in the alveolar walls or around small to middle airways, and no plaque formation on the pleura.
  • Reticulin fibers showed a minimal to moderate diffuse increase inside the alveolar wall that was concentration-response related in the 0.5 and 2.5 mg/m3 groups.
  • Mean severity of increased reticulin fibers (Table 1) was 0 in controls and at 0.1 mg/m3 for both sexes. At 0.5 and 2.5 mg/m3 it was 1.0 and 1.4 in males and 1.1 and 2.5 in females.
  • Females seemed slightly more susceptible than males, based on slightly higher severity.
  • At 0.1 mg/m3, granuloma formation still occurred, so a no-observed-effect concentration for granulomas could not be established. No increase in reticulin fibers was seen at this concentration.
  • Electron microscopy found MWCNTs inside alveolar macrophages in membrane-bound vesicles, and also free in the alveolar space.
  • Small electron-dense clumps in macrophages could mean the nanotubes were being processed (broken down). The authors presented this as a possibility, not a finding.
  • No pleural lesions regarded as precursors of mesothelioma were observed: no mesothelioma-like fibrosis, no chronic or active inflammation, and no mesothelial hypertrophy or hyperplasia.
• The authors' conclusion: The authors concluded that, from information gathered so far in rat studies with MWCNTs, the lung effects seem similar to those caused by chrysotile asbestos: granulomas and mild fibrosis, but not developing into mesotheliomas or other lung tumors. The chrysotile comparison rests on other researchers' studies, not on asbestos tested here.
• Limitations the authors state:
  • No recovery group was run, so the authors could not show whether the effects were reversible.
  • The electron-dense clumps could not be shown to be degraded nanotubes; they might be digested cell debris or other inhaled substances.
  • Biopersistence and long-term tumor or mesothelioma risk were not studied; the authors said a long-term study would be needed.
  • The hardness of the nanotubes damaged the diamond knife, leaving drag marks in electron-microscopy sections wherever MWCNTs were present.

Topics

Medical terms in this study, explained in our Lexicon: Inflammation, Collagen, Pleura, Granuloma, Alveolar Macrophage, Parenchyma, Fibrosis, Mesothelioma.

Related studies

• Thirteen-week study of toxicity of fiber-like multi-walled carbon nanotubes with whole-body inhalation exposure in rats — T. Kasai, Y. Umeda, et al. (2015)
• Inhalation of rod-like carbon nanotubes causes unconventional allergic airway inflammation — E.M. Rydman, M. Ilves, et al. (2014)
• 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)
• Inhalation toxicity study of disk-shaped potassium octatitanate particles (terracess TF) in rats following 90 days of aerosol exposure — S. Sakai, K. Inada, et al. (2010)
• Structural defects play a major role in the acute lung toxicity of multiwall carbon nanotubes: physicochemical aspects — I. Fenoglio, G. Greco, et al. (2008)
• Pulmonary and pleural toxicity of potassium octatitanate fibers, rutile titanium dioxide nanoparticles, and MWCNT-7 in male Fischer 344 rats — M. Abdelgied, A.M. El-Gazzar, et al. (2019)

Browse more research in Toxicological Sciences, or return to medical research.