Role of p53 in the chronic pulmonary immune response to tangled or rod-like multi-walled carbon nanotubes

Our plain-English summary of Role of p53 in the chronic pulmonary immune response to tangled or rod-like multi-walled carbon nanotubes, by K.S. Duke, E.A. Thompson, M.D. Ihrie, et al (Nanotoxicology, 2018).

The study

• Authors: K.S. Duke, E.A. Thompson, M.D. Ihrie, A.J. Taylor-Just, E.A. Ash, K.A. Shipkowski, J.R. Hall, D.A. Tokarz, M.F. Cesta, A.F. Hubbs, D.W. Porter, L.M. Sargent, J.C. Bonner
• Journal: Nanotoxicology
• Published: 2018;12(9):975-991
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The fiber-like shape of multi-walled carbon nanotubes (MWCNTs) is reminiscent of asbestos, suggesting they pose similar health hazards when inhaled, including pulmonary fibrosis and mesothelioma. Mice deficient in the tumor suppressor p53 are susceptible to carcinogenesis. However, the chronic pathologic effect of MWCNTs delivered to the lungs of p53 heterozygous (p53+/-) mice has not been investigated. We hypothesized that p53+/- mice would be susceptible to lung tumor development after exposure to either tangled (t-) or rod-like (r-) MWCNTs. Wild-type (p53+/+) or p53+/- mice were exposed to MWCNTs (1 mg/kg) via oropharyngeal aspiration weekly over four consecutive weeks and evaluated for cellular and pathologic outcomes 11-months post-initial exposure. No lung or pleural tumors were observed in p53+/+ or p53+/- mice exposed to either t- or rMWCNTs. In comparison to tMWCNTs, the rMWCNTs induced the formation of larger granulomas, a greater number of lymphoid aggregates and greater epithelial cell hyperplasia in terminal bronchioles in both p53+/- and p53+/+ mice. A constitutively larger area of CD45R+/CD3+ lymphoid tissue was observed in p53+/- mice compared to p53+/+ mice. Importantly, p53+/- mice had larger granulomas induced by rMWCNTs as compared to p53+/+ mice. These findings indicate that a combination of p53 deficiency and physicochemical characteristics including nanotube geometry are factors in susceptibility to MWCNT-induced lymphoid infiltration and granuloma formation.

In plain English

This animal experiment studied multi-walled carbon nanotubes, not asbestos. The authors tested whether mice missing one copy of the tumor-suppressor gene p53 develop lung or pleural tumors. Normal and p53-deficient mice, in groups of 8 to 14, received tangled nanotubes, rod-like nanotubes or a control solution into the lungs. Nanotubes were given at 1 mg/kg weekly for four weeks. Mice were examined 11 months after the first dose, except that two p53-deficient mice died early and one was euthanized because of lymphoma. No nanotube-related lung tumors, mesothelioma or pleural inflammation were found. In both kinds of mice, rod-like nanotubes produced significantly larger granulomas (inflammatory cell clusters around nanotubes) than tangled ones. They also produced more lymphoid aggregates and more bronchiolar epithelial hyperplasia. p53-deficient mice had more lymphoid tissue in the lung even without exposure. Their granulomas tended to be larger, but not statistically significantly. The authors concluded that losing one p53 copy plays a role in the immune response to nanotubes. They noted that about ten mice per group may be too few to rule out a cancer effect.

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 (chronic study in mice, single endpoint 11 months after first exposure)
• Who was studied: Wild-type and p53 heterozygous (one p53 copy missing) mice on a C57BL/6 background from the Jackson Laboratory, aged 8 to 12 weeks at dosing, studied at North Carolina State University. Group sizes were: wild-type control 10, wild-type tangled 10, wild-type rod-like 8, p53-deficient control 14, p53-deficient tangled 9, p53-deficient rod-like 8.
• Exposure: Tangled multi-walled carbon nanotubes (Helix Material Solutions) or rod-like multi-walled carbon nanotubes (Mitsui MWCNT-7), 1 mg/kg once a week for 4 weeks by oropharyngeal aspiration, a cumulative 4 mg/kg. Controls received the vehicle (0.1% pluronic surfactant solution). No asbestos was given in this study.
• Main results:
  • No nanotube-related lung tumors or mesothelioma were observed. On examination of three stained lung sections per mouse, no pleural inflammation was seen in either genotype.
  • All mice survived to the end except three. Two male p53-deficient mice given rod-like nanotubes died early of unknown causes, and one female p53-deficient mouse given tangled nanotubes was euthanized because of lymphoma.
  • Rod-like nanotubes produced significantly larger lung granuloma area than tangled nanotubes. Rod-like nanotubes also produced significantly more granulomas adjacent to lymphoid tissue, with no notable difference between genotypes.
  • p53-deficient mice exposed to either nanotube showed a trend toward greater granuloma number and total granuloma area than wild-type mice, but the results section states this difference was not statistically significant.
  • The number of lymphoid aggregates increased significantly after rod-like nanotubes, with no difference between genotypes. The share of lung occupied by lymphoid tissue was significantly greater in control p53-deficient mice than in control wild-type mice, and nanotube treatment did not increase it further.
  • Among granulomas from rod-like nanotube exposure, about 25% in wild-type mice and 15% in p53-deficient mice contained dividing (BrdU-positive) cells. This compared with only 5% of granulomas from tangled nanotubes in either genotype.
  • Rod-like nanotubes increased proliferating bronchiolar epithelial cells in both genotypes compared with control or tangled nanotubes, with no difference between genotypes. Papillary hyperplasia was seen in only one p53-deficient mouse given rod-like nanotubes.
  • Fibrosis was mainly within granulomas, and there was no significant difference in airway fibrosis. In the rod-like group, p53-deficient mice had significantly more lung collagen than wild-type mice, but the authors attributed this to a reduction in collagen in wild-type mice given rod-like nanotubes.
  • Levels of osteopontin, TGF-b1 and PDGF-BB in lung lavage fluid were not significantly increased by either nanotube type and did not differ between genotypes. Lavage cell counts showed only slight, non-significant changes.
• The authors' conclusion: The authors concluded that genetic susceptibility (loss of one p53 allele) plays a role in the immune response to multi-walled carbon nanotubes in mice. They also concluded that p53 deficiency and nanotube features, including geometry, are factors in nanotube-induced lymphoid infiltration and granuloma formation.
• Limitations the authors state:
  • About ten mice per group may give insufficient statistical power to establish a negative carcinogenic effect.
  • Only a single chronic time point was assessed.
  • A longer period may be needed for tumors to develop after direct lung exposure.
  • The two nanotubes differed not only in shape but also in length, surface area, surface charge and residual metal catalyst content.
  • Dosing by mass may have delivered different numbers of nanotubes to the lungs.

Topics

Medical terms in this study, explained in our Lexicon: Pulmonary Fibrosis, Mesothelioma, Carcinogenesis, Granuloma.

Related studies

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• 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)
• Epithelial-mesenchymal transition involved in pulmonary fibrosis induced by multi-walled carbon nanotubes via TGF-beta/Smad signaling pathway — T. Chen, H. Nie, 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)
• 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)
• Multi-walled carbon nanotubes directly induce epithelial-mesenchymal transition in human bronchial epithelial cells via the TGF-β-mediated Akt/GSK-3β/SNAIL-1 signalling pathway — M. Polimeni, G.R. Gulino, et al. (2016)

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