Factoring-in agglomeration of carbon nanotubes and nanofibers for better prediction of their toxicity versus asbestos

Our plain-English summary of Factoring-in agglomeration of carbon nanotubes and nanofibers for better prediction of their toxicity versus asbestos, by A.R. Murray, E.R. Kisin, A.V. Tkach, et al (Particle and Fibre Toxicology, 2012).

The study

• Authors: A.R. Murray, E.R. Kisin, A.V. Tkach, N. Yanamala, R. Mercer, S.H. Young, B. Fadeel, V.E. Kagan, A.A. Shvedova
• Journal: Particle and Fibre Toxicology
• Published: 2012;9:10
• Cited by: 91 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Carbon nanotubes (CNT) and carbon nanofibers (CNF) are allotropes of carbon featuring fibrous morphology. The dimensions and high aspect ratio of CNT and CNF have prompted the comparison with naturally occurring asbestos fibers which are known to be extremely pathogenic. While the toxicity and hazardous outcomes elicited by airborne exposure to single-walled CNT or asbestos have been widely reported, very limited data are currently available describing adverse effects of respirable CNF.

Results: Here, we assessed pulmonary inflammation, fibrosis, oxidative stress markers and systemic immune responses to respirable CNF in comparison to single-walled CNT (SWCNT) and asbestos. Pulmonary inflammatory and fibrogenic responses to CNF, SWCNT and asbestos varied depending upon the agglomeration state of the particles/fibers. Foci of granulomatous lesions and collagen deposition were associated with dense particle-like SWCNT agglomerates, while no granuloma formation was found following exposure to fiber-like CNF or asbestos. The average thickness of the alveolar connective tissue--a marker of interstitial fibrosis--was increased 28 days post SWCNT, CNF or asbestos exposure. Exposure to SWCNT, CNF or asbestos resulted in oxidative stress evidenced by accumulations of 4-HNE and carbonylated proteins in the lung tissues. Additionally, local inflammatory and fibrogenic responses were accompanied by modified systemic immunity, as documented by decreased proliferation of splenic T cells ex vivo on day 28 post exposure. The accuracies of assessments of effective surface area for asbestos, SWCNT and CNF (based on geometrical analysis of their agglomeration) versus estimates of mass dose and number of particles were compared as predictors of toxicological outcomes.

Conclusions: We provide evidence that effective surface area along with mass dose rather than specific surface area or particle number are significantly correlated with toxicological responses to carbonaceous fibrous nanoparticles. Therefore, they could be useful dose metrics for risk assessment and management.

In plain English

This was a laboratory experiment in mice. Female C57BL/6 mice received a single pharyngeal aspiration of single-walled carbon nanotubes (SWCNT, 40 micrograms per mouse), carbon nanofibers (CNF, 120 micrograms per mouse), UICC crocidolite asbestos (120 micrograms per mouse) or PBS, and were examined 1, 7 and 28 days later (six mice per group). On day 1, neutrophils in lavage fluid rose about 150-fold after CNF and 700-fold after SWCNT versus controls, while asbestos produced a delayed peak of 675-fold on day 7. Lung collagen on day 28 increased 3-fold after CNF, 2.8-fold after asbestos and 5.8-fold after SWCNT. Granulomas formed only around dense SWCNT agglomerates, not after CNF or asbestos. All three materials raised oxidative stress markers (4-HNE, protein carbonyls); splenic T cell proliferation was decreased on day 28 after CNF and after asbestos, whereas after SWCNT it fell about 15% on day 7 and returned to control values by day 28. Calculated effective surface area correlated with day-1 neutrophil counts and lavage protein (r = 0.997, p less than 0.05), whereas correlations with BET specific surface area were not statistically significant.

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: controlled mouse pharyngeal aspiration study with 1, 7 and 28 day follow-up
• Who was studied: Specific pathogen-free adult female C57BL/6 mice, 8-10 weeks old, six per group, housed and exposed at NIOSH facilities; sacrificed on days 1, 7 and 28 after exposure
• Exposure: Single pharyngeal aspiration of SWCNT (40 micrograms/mouse; 99.7% elemental carbon, 0.23% iron), CNF (120 micrograms/mouse; 98.6% elemental carbon, 1.4% iron) or UICC standard crocidolite asbestos (120 micrograms/mouse; 18% iron)
• Main results:
  • Neutrophil (PMN) influx on day 1: about 150-fold above control for CNF and 700-fold for SWCNT; asbestos showed a delayed peak of 675-fold on day 7
  • BAL total protein (lung permeability) after CNF: 1.86-, 1.75- and 1.14-fold increases on days 1, 7 and 28
  • BAL total protein after SWCNT: up to 3.75-, 2.5- and 2.6-fold of control on days 1, 7 and 28
  • Lung collagen at day 28: 3-fold (CNF), 2.8-fold (asbestos) and 5.8-fold (SWCNT) versus controls
  • No granuloma formation was found after exposure to fiber-like CNF or asbestos
  • SWCNT agglomerates induced granuloma formation in the lung
  • Oxidative stress markers: 4-HNE rose 6- and 4-fold after CNF (days 1 and 7), 9.5-, 10.0- and 6.0-fold after SWCNT (days 1, 7, 28), and 11-fold after asbestos only at day 28; protein carbonyls rose 4.8, 3.5, 3.5-fold after SWCNT and about 1.8-fold after CNF and asbestos
  • Splenic T cell proliferation ex vivo: no significant change after CNF at day 7 but decreased at day 28; SWCNT caused about a 15% decrease at day 7 that returned to control values by day 28
  • At day 28 splenic T cell proliferation was suppressed in both CNF- and asbestos-treated animals
  • Correlations with effective surface area that reached statistical significance were day-1 PMN counts and day-1 total protein in BAL fluid
  • Effective surface area versus day-1 PMN counts: r = 0.997, p < 0.05 (the same coefficient was reported for day-1 BAL protein)
  • With specific surface area measured by BET, correlations with pulmonary outcomes were not statistically significant, for example alveolar wall thickness at day 28 (r = 0.995, p > 0.05)
  • Calculated effective surface areas: 138 m2/g for SWCNT bundles, about 21 m2/g for CNF and 8.3 m2/g for asbestos; delivered effective surface area was about 5.8-fold (SWCNT) and 2.6-fold (CNF) that of asbestos
• The authors' conclusion: The authors concluded that CNF, SWCNT and asbestos all caused inflammation, lung damage and fibrosis (mass-based potency SWCNT greater than CNF, which was greater than or equal to asbestos), that specific surface area and particle number did not predict biological responses, and that calculated effective surface area of agglomerated nanomaterials, along with mass dose, could be useful for predicting pulmonary responses
• Limitations the authors state:
  • The authors state that the carcinogenic potential of CNF and other longer-term outcomes were not addressed and remain for future study
  • The authors note that effective surface area was a theoretical estimate derived from geometric modelling of agglomerates rather than a direct measurement

Topics

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

Medical terms in this study, explained in our Lexicon: Aspect Ratio (Length-to-diameter ratio), naturally occurring asbestos (NOA), Inflammation, Fibrosis, Oxidative Stress, Fibrogenic, Collagen, Deposition.

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