Multi-walled carbon nanotubes translocate into the pleural cavity and induce visceral mesothelial proliferation in rats

Our plain-English summary of Multi-walled carbon nanotubes translocate into the pleural cavity and induce visceral mesothelial proliferation in rats, by J. Xu, M. Futakuchi, H. Shimizu, et al (Cancer Science, 2012).

The study

• Authors: J. Xu, M. Futakuchi, H. Shimizu, D.B. Alexander, K. Yanagihara, K. Fukamachi, M. Suzui, J. Kanno, A. Hirose, A. Ogata, Y. Sakamoto, D. Nakae, T. Omori, H. Tsuda
• Journal: Cancer Science
• Published: 2012;103(12):2045-50
• Cited by: 76 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Multi-walled carbon nanotubes have a fibrous structure similar to asbestos and induce mesothelioma when injected into the peritoneal cavity. In the present study, we investigated whether carbon nanotubes administered into the lung through the trachea induce mesothelial lesions. Male F344 rats were treated with 0.5 mL of 500 μg/mL suspensions of multi-walled carbon nanotubes or crocidolite five times over a 9-day period by intrapulmonary spraying. Pleural cavity lavage fluid, lung and chest wall were then collected. Multi-walled carbon nanotubes and crocidolite were found mainly in alveolar macrophages and mediastinal lymph nodes. Importantly, the fibers were also found in the cell pellets of the pleural cavity lavage, mostly in macrophages. Both multi-walled carbon nanotube and crocidolite treatment induced hyperplastic proliferative lesions of the visceral mesothelium, with their proliferating cell nuclear antigen indices approximately 10-fold that of the vehicle control. The hyperplastic lesions were associated with inflammatory cell infiltration and inflammation-induced fibrotic lesions of the pleural tissues. The fibers were not found in the mesothelial proliferative lesions themselves. In the pleural cavity, abundant inflammatory cell infiltration, mainly composed of macrophages, was observed. Conditioned cell culture media of macrophages treated with multi-walled carbon nanotubes and crocidolite and the supernatants of pleural cavity lavage fluid from the dosed rats increased mesothelial cell proliferation in vitro, suggesting that mesothelial proliferative lesions were induced by inflammatory events in the lung and pleural cavity and likely mediated by macrophages. In conclusion, intrapulmonary administration of multi-walled carbon nanotubes, like asbestos, induced mesothelial proliferation potentially associated with mesothelioma development.

© 2012 Japanese Cancer Association.

In plain English

This was a short-term rat experiment from Japan, with cell-culture tests. Ten-week-old male Fisher 344 rats, six per group, had liquid sprayed into their lungs five times over 9 days. Controls got the liquid alone; the other groups got it with one of two multi-walled carbon nanotube products (MWCNT-N, MWCNT-M) or crocidolite asbestos, totaling 1.25 mg of fibers per rat. Six hours after the last dose, nanotube and crocidolite fibers were found in fluid washed from the chest (pleural) cavity, mostly inside macrophages (immune cells). All treated groups developed overgrowth of the lining covering the lung (visceral mesothelium), where the share of cells carrying a cell-division marker was about 10 times the control level. No fibers were found inside these overgrowths. The chest-wall lining (parietal pleura) showed no lesions or fibers. Inflammatory cells in the chest cavity increased. In lab tests, fluid from fiber-exposed macrophages and from treated rats' chest cavities increased growth of human mesothelioma cells. The authors concluded the nanotubes might cause asbestos-like pleural lesions. They noted the spraying method is non-physiological and the dose exceeded a proposed NIOSH limit.

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: Short-term animal experiment, with in vitro cell-culture tests. Fibers were sprayed into rat lungs, crocidolite served as a positive control, and the chest cavity fluid and tissues were examined six hours after the last dose.
• Who was studied: Ten-week-old male Fisher (F344) rats in four groups of six animals each (24 rats), housed at Nagoya City University, Japan.
• Exposure: Two multi-walled carbon nanotube products (MWCNT-N from Nikkiso; MWCNT-7 from Mitsui, called MWCNT-M) or crocidolite asbestos. Each dose was 0.5 mL of a 500 micrograms per mL suspension, sprayed into the lungs once every other day five times over 9 days, for a total of 1.25 mg of fibers per rat. Controls received saline with 0.1% Tween 20.
• Main results:
  • In all three fiber groups, fibers (both nanotube types and crocidolite) were found in cells washed from the pleural cavity, mostly inside macrophage-like cells.
  • Only a few fibers were seen passing directly from the lung through the visceral pleura, and no fibers were found in the parietal pleura.
  • Hyperplastic visceral mesothelial proliferation was seen in all nanotube and crocidolite groups. The PCNA index (the percentage of visceral mesothelial cells positive for the proliferation marker PCNA) was about 10 times that of the control group.
  • No fibers were found within the visceral mesothelial proliferation lesions themselves.
  • No proliferation or other lesions of the parietal mesothelium were observed in any group.
  • In the nanotube and crocidolite groups, the total number of inflammatory cells in the pleural cavity fluid, mostly macrophages, neutrophils and lymphocytes, was significantly increased compared with the control group.
  • In the lab, culture fluid from macrophages exposed to either nanotube type or crocidolite significantly increased the growth of human mesothelioma cells (TCC-MESO1). Concentrated pleural fluid from treated rats had similar effects.
  • Direct exposure of the mesothelioma cells to the nanotubes or crocidolite did not make them grow; it led to cell death.
  • The proportion of cells in the pleural fluid positive for a mesothelial marker was 0.53 to 1.02%, with no difference between groups.
• The authors' conclusion: The authors concluded that both nanotube types, like crocidolite, moved from the lung into the pleural cavity. They found the nanotubes caused visceral mesothelial proliferation and pleural inflammation, which they considered plausibly driven by inflammation and macrophages. In their view, this similarity suggests the nanotubes might cause asbestos-like pleural lesions.
• Limitations the authors state:
  • Spraying or instilling material into the trachea is a non-physiological method. The pressure from spraying may affect how particles move and spread in the lung.
  • The dose was chosen to produce observable lesions and was higher than the carbon nanotube exposure limit proposed by NIOSH. The authors state that time- and dose-dependent experiments are needed.
  • The short experimental period and the limited amount of fibers reaching the pleural cavity may explain why no parietal pleura lesions were seen.
  • The factors in the fluids that caused mesothelial cell growth were not identified.

Topics

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

Medical terms in this study, explained in our Lexicon: Pleural Cavity, Mesothelioma, Peritoneal Cavity, Crocidolite, Alveolar Macrophage, Mediastinal Lymph Nodes, Macrophage, Mesothelium.

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)
• 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)
• 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)
• Comparative carcinogenicity study of a thick, straight-type and a thin, tangled-type multi-walled carbon nanotube administered by intra-tracheal instillation in the rat — D.M. Saleh, W.T. Alexander, et al. (2020)
• 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)
• Osteopontin mRNA expression by rat mesothelial cells exposed to multi-walled carbon nanotubes as a potential biomarker of chronic neoplastic transformation in vitro — S. Sridharan, A. Taylor-Just, et al. (2021)

Browse more research in Cancer Science, or return to medical research.