Inhalation of rod-like carbon nanotubes causes unconventional allergic airway inflammation

Our plain-English summary of Inhalation of rod-like carbon nanotubes causes unconventional allergic airway inflammation, by E.M. Rydman, M. Ilves, A.J. Koivisto, et al (Particle and Fibre Toxicology, 2014).

The study

• Authors: E.M. Rydman, M. Ilves, A.J. Koivisto, P.A. Kinaret, V. Fortino, T.S. Savinko, M.T. Lehto, V. Pulkkinen, M. Vippola, K.J. Hämeri, S. Matikainen, H. Wolff, K.M. Savolainen, D. Greco, H. Alenius
• Journal: Particle and Fibre Toxicology
• Published: 2014;11:48
• Cited by: 74 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Carbon nanotubes (CNT) represent a great promise for technological and industrial development but serious concerns on their health effects have also emerged. Rod-shaped CNT are, in fact, able to induce asbestos-like pathogenicity in mice including granuloma formation in abdominal cavity and sub-pleural fibrosis. Exposure to CNT, especially in the occupational context, happens mainly by inhalation. However, little is known about the possible effects of CNT on pulmonary allergic diseases, such as asthma.

Methods: We exposed mice by inhalation to two types of multi-walled CNT, rigid rod-like and flexible tangled CNT, for four hours a day once or on four consecutive days. Early events were monitored immediately and 24 hours after the single inhalation exposure and the four day exposure mimicked an occupational work week. Mast cell deficient mice were used to evaluate the role of mast cells in the occurring inflammation.

Results: Here we show that even a short-term inhalation of the rod-like CNT induces novel innate immunity-mediated allergic-like airway inflammation in healthy mice. Marked eosinophilia was accompanied by mucus hypersecretion, AHR and the expression of Th2-type cytokines. Exploration of the early events by transcriptomics analysis reveals that a single 4-h exposure to rod-shaped CNT, but not to tangled CNT, causes a radical up-regulation of genes involved in innate immunity and cytokine/chemokine pathways. Mast cells were found to partially regulate the inflammation caused by rod-like CNT, but also alveaolar macrophages play an important role in the early stages.

Conclusions: These observations emphasize the diverse abilities of CNT to impact the immune system, and they should be taken into account for hazard assessment.

In plain English

This was an animal inhalation experiment in mice. The authors exposed mice in a whole-body chamber to aerosols of two multi-walled carbon nanotubes, rigid rod-like CNT (rCNT, Mitsui XNRI MWNT-7; 6.2-8.2 mg/m3) or flexible tangled CNT (tCNT, Cheap Tubes; 17.5-18.5 mg/m3), for 4 hours on one day or on four consecutive days, with samples taken immediately or 24 hours afterwards; C57BL/6 mice received rCNT or tCNT, while BALB/c mice and mast-cell-deficient KitW-sh mice received rCNT. After the four-day exposure, rCNT reduced alveolar macrophages and caused marked eosinophil recruitment in bronchoalveolar lavage and lung tissue, goblet cell activation (PAS+ cells), airway hyperresponsiveness to metacholine in BALB/c mice, up-regulation of Il-13 and Il-5 with down-regulation of Ifn-gamma, and increased Ccl11, Ccl24 and Ccl17; tCNT produced no comparable eosinophilia. Microarray analysis after a single 4-hour exposure showed 776 differentially expressed genes specific to rCNT versus 109 specific to tCNT, with innate immunity and cytokine/chemokine pathways induced by rCNT only. In mast-cell-deficient mice, Il-13 and Il-4 expression was significantly lower, while goblet cell activation was unchanged.

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 inhalation experiment in mice, including transcriptomic (microarray) analysis and use of mast cell deficient mice
• Who was studied: Female C57BL/6, BALB/c and mast cell deficient KitW-sh mice, 7-8 weeks old, studied in Finland (Finnish Institute of Occupational Health); C57BL/6 mice were exposed to rCNT or tCNT, BALB/c and KitW-sh mice to rCNT; group sizes reported per figure (n = 4-20)
• Exposure: Whole-body inhalation of aerosolized rod-like multi-walled carbon nanotubes (rCNT, Mitsui XNRI MWNT-7, 6.2-8.2 mg/m3) or tangled multi-walled carbon nanotubes (tCNT, Cheap Tubes, 17.5-18.5 mg/m3), 4 hours once or on four consecutive days; endotoxin levels below 0.022 EU/mg
• Main results:
  • In C57BL/6 mice exposed 4 h/day for 4 days, rCNT decreased alveolar macrophages and increased inflammatory cells, especially eosinophils, in BAL and lung tissue; tCNT caused no significant change in these cell types
  • rCNT-exposed mice showed macrophages undergoing 'frustrated phagocytosis' and foreign-body giant cells; these were not seen after tCNT
  • BALB/c mice exposed to rCNT for 4 h/day on 4 consecutive days showed enhanced airway hyperresponsiveness to metacholine on day 5
  • In C57BL/6 mice, mucin-producing goblet cells were activated in the lungs after rCNT but not after tCNT
  • In lung tissue after rCNT: Il-13 and Il-5 mRNA up-regulated, Ifn-gamma down-regulated, and Ccl11, Ccl24 and Ccl17 up-regulated; tCNT had no effect on Il-13, Ifn-gamma and Ccl24, suppressed Il-5 and elevated Ccl11 and Ccl17
  • In mast cell deficient KitW-sh mice after 4-day rCNT exposure, eosinophil numbers were significantly higher than in wild type, neutrophils and PAS+ cells did not differ significantly, and Il-13 expression was highly mast-cell dependent
  • Microarray after a single 4-h exposure: 776 differentially expressed genes specific to rCNT versus 109 specific to tCNT (linear FC > |1.5|, post hoc adjusted P-value = 0.01)
  • At 4 h, rCNT induced innate immunity pathways (NOD-like receptor, Toll-like receptor, chemokine and cytokine-cytokine receptor pathways), while these pathways were not activated or were down-regulated after tCNT
  • Early cytokine source: Il-1beta and Tnf-alpha were produced mainly by alveolar macrophages (BAL cells), while Il-33 and Ccl17 were expressed in BAL cells and in other lung tissue cells
• The authors' conclusion: The authors concluded that inhalation of rod-like CNT can induce a novel innate immunity mediated allergic-like airway inflammation in addition to previously described asbestos associated pathologies, that different CNT differ markedly in their effects, and that this should be taken into account in risk assessment and protective measures
• Limitations the authors state:
  • The authors stated that more knowledge on long term effects, clinical impacts and dose-response relationships is needed before solid conclusions on CNT risks can be drawn
  • The authors stated they could not completely exclude a role for group 2 innate lymphoid cells, as their functions and markers are not completely clear
  • The authors noted that assessing CNT health effects in vivo is complex and results are difficult to compare across studies because of differing exposure methods, organisms and material properties

Topics

Medical terms in this study, explained in our Lexicon: Inflammation, Granuloma, Fibrosis, Cytokine, Macrophage.

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