Persistent Pleural Lesions and Inflammation by Pulmonary Exposure of Multiwalled Carbon Nanotubes

Our plain-English summary of Persistent Pleural Lesions and Inflammation by Pulmonary Exposure of Multiwalled Carbon Nanotubes, by D. Liao, Q. Wang, J. He, et al (Chemical Research in Toxicology, 2018).

The study

• Authors: D. Liao, Q. Wang, J. He, D.B. Alexander, M. Abdelgied, A.M. El-Gazzar, M. Futakuchi, M. Suzui, J. Kanno, A. Hirose, J. Xu, H. Tsuda
• Journal: Chemical Research in Toxicology
• Published: 2018;31(10):1025-1031
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Translocation of multiwalled carbon nanotubes (MWCNTs) from the lung to the pleural cavity, deposition of the fibers in the pleural tissue, induction of pleural fibrosis, and mesothelial proliferation have been found in rodents administered MWCNTs by different pulmonary exposure methods. However, whether the translocation and deposition and the subsequent pleural inflammation are associated with the pleural lesions is unclear. In the present study, male F344 rats were given 250 μg of two types of MWCNTs, with crocidolite as a positive control, 2 times/week for 4 weeks by intratracheal spraying. At 24 h and at 3 months after the last spraying, the rats were sacrificed for histological examination of the lung and chest wall; pleural cavity lavage was also collected at sacrifice for observation of pleural inflammatory reactions. The results indicated that intratracheally sprayed MWCNTs, like crocidolite fibers, translocated into the pleural cavity, deposited in the pleura, and induced persistent infiltration of immune cells into the pleural cavity, persistent pleural fibrosis, and mesothelial proliferation. The number of MWCNT fibers detected in the pleural cavity lavage was parallel to the number of infiltrating immune cells, which were mainly composed of macrophages. Analysis of cytokines in the fluids of the pleural cavity lavages by suspension array indicated that levels of IL-2, IL-18, and IP-10 were significantly increased both at 24 h and at 3 months after the last spraying. In vitro proliferation assays revealed that a mixture of IL-2, IL-18, and IP-10, but not any of these cytokines alone, promoted cell proliferation of human fibroblasts and mesothelial cells. These results suggest that translocated and deposited MWCNTs induce subsequent pleural inflammation and that increased IL-2, IL-18, and IP-10 synergistically promote the development of pleural fibrosis and mesothelial proliferation.

In plain English

This was an animal experiment combined with laboratory cell work. Groups of 12 ten-week-old male F344 rats were given 0.5 mL of saline with 0.5% Pluronic F68, or 0.5 mL of 500 micrograms/mL suspensions of two multiwalled carbon nanotubes (MWCNT-1, MWCNT-2) or crocidolite asbestos, by intratracheal spraying twice weekly for four weeks (2 mg total per rat). Six rats per group were killed 24 hours after the last spraying and six at three months. Lung and chest wall tissue and pleural cavity lavage were examined. MWCNTs and crocidolite produced visceral and parietal pleural fibrosis and increased PCNA-positive mesothelial cells at both time points, increased leukocytes (mainly monocytes/macrophages) in the lavage fluid, and fibers were seen in lavage cell pellets under polarized light. Of 20 cytokines measured, only five were detectable, and IL-2, IL-18 and IP-10 were higher in treated groups, though not in every group at every time point: IL-2 at 1 day was 13.05 ± 3.94 pg/mL in MWCNT-1 rats versus non-detectable in controls, but at 3 months it was non-detectable in both MWCNT-1 and control rats. In vitro, only a mixture of the three cytokines increased proliferation of human MRC-5 fibroblasts and Met-5A mesothelial cells.

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 in rats (intratracheal spraying) with accompanying in vitro cell proliferation, Western blot and flow cytometry assays
• Who was studied: Groups of 12 ten-week-old male F344 (Fisher 344) rats, housed at Nagoya City University Medical School; half of each group killed 24 h after the last spraying, half at 3 months. Human MRC-5 lung fibroblasts and Met-5A mesothelial cells were used in vitro.
• Exposure: Two vapour-grown multiwalled carbon nanotubes (MWCNT-1, average fiber length 7.41 ± 3.52 μm; MWCNT-2, 4.27 ± 2.88 μm) and crocidolite asbestos (4.45 ± 6.12 μm) as positive control, total 2 mg per rat; vehicle control was saline with 0.5% Pluronic F68
• Main results:
  • MWCNTs and crocidolite caused visceral and parietal pleural fibrosis at both 24 h and 3 months, with significantly increased pleural thickness compared with vehicle-treated control rats
  • Pleural thickness was comparable at 24 h and 3 months for MWCNT-1 and crocidolite, while MWCNT-2 rats had more fibrosis at 3 months than at 24 h
  • PCNA-positive mesothelial cell ratios in visceral and parietal mesothelium were higher in MWCNT- and crocidolite-treated rats than controls at both time points, described by the authors as persistent
  • Leukocytes in pleural cavity lavage fluid were significantly increased in MWCNT- and crocidolite-treated rats, mostly monocytes/macrophages, and slightly lower at 3 months than 24 h
  • MWCNT and crocidolite fibers were seen in pleural cavity lavage cell pellets, and fiber numbers paralleled leukocyte numbers and cytokine levels
  • Of 20 cytokines measured in lavage fluid (pg/mL) only five were detectable; at 1 day IL-2 was 13.05 ± 3.94 (MWCNT-1), 8.90 ± 3.57 (MWCNT-2) and 2.12 ± 1.40 (crocidolite) versus non-detectable in controls, IL-18 was raised only in MWCNT-2 (105.93 ± 32.77 versus 65.16 ± 18.23 in controls), and IP-10 was 7.75 ± 4.21, 7.99 ± 3.88 and 4.44 ± 2.08 versus 1.25 ± 2.13 in controls
  • At 3 months the picture differed by group: IL-2 was non-detectable in both control and MWCNT-1 rats, while MWCNT-2 lavage fluid showed raised IL-18 (78.49 ± 12.87 pg/mL, p less than 0.001 versus control) and IP-10 (6.52 ± 2.61 pg/mL, p less than 0.05 versus control 2.03 ± 2.42)
  • In vitro, IL-2, IL-18 or IP-10 alone up to 50 ng/mL did not promote MRC-5 fibroblast proliferation, but a mixture of the three did, dose-dependently; a similar effect was seen in Met-5A mesothelial cells
• The authors' conclusion: The authors concluded that intratracheally sprayed MWCNTs, like crocidolite, translocate into the pleural cavity and deposit in the pleura, inducing persistent pleural inflammation, fibrosis and mesothelial proliferation, and that the increases in IL-2, IL-18 and IP-10 are associated with these pleural lesions
• Limitations the authors state:
  • The authors noted that cytokines are diluted during pleural cavity lavage, so cytokines that were undetectable in the lavage fluid may still act locally on fibroblasts and mesothelial cells
  • The measured average fiber lengths were longer than those given by the manufacturers, which the authors attributed to short MWCNTs being hard to detect by electron microscopy
  • The authors stated that only obviously thickened regions of the parietal and visceral pleura were measured
  • For histological examination of lavage cell pellets, cells from three rats had to be combined

Topics

The National Library of Medicine indexes this study under subjects our site covers: Crocidolite.

Medical terms in this study, explained in our Lexicon: Inflammation, Translocation, Pleural Cavity, Deposition, Fibrosis, Crocidolite, Pleura, Macrophage.

Related studies

• Size- and shape-dependent pleural translocation, deposition, fibrogenesis, and mesothelial proliferation by multiwalled carbon nanotubes — J. Xu, D.B. Alexander, et al. (2014)
• Multiwalled carbon nanotubes intratracheally instilled into the rat lung induce development of pleural malignant mesothelioma and lung tumors — M. Suzui, M. Futakuchi, et al. (2016)
• 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)
• Stromelysin-2 (MMP-10) facilitates clearance and moderates inflammation and cell death following lung exposure to long multiwalled carbon nanotubes — T.C. Vandivort, T.P. Birkland, et al. (2017)
• Multi-walled carbon nanotubes translocate into the pleural cavity and induce visceral mesothelial proliferation in rats — J. Xu, M. Futakuchi, et al. (2012)
• Threshold Rigidity Values for the Asbestos-like Pathogenicity of High-Aspect-Ratio Carbon Nanotubes in a Mouse Pleural Inflammation Model — D.K. Lee, S. Jeon, et al. (2018)

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