Neoplastic-like transformation effect of single-walled and multi-walled carbon nanotubes compared to asbestos on human lung small airway epithelial cells

Our plain-English summary of Neoplastic-like transformation effect of single-walled and multi-walled carbon nanotubes compared to asbestos on human lung small airway epithelial cells, by L. Wang, T.A. Stueckle, A. Mishra, et al (Nanotoxicology, 2014).

The study

• Authors: L. Wang, T.A. Stueckle, A. Mishra, R. Derk, T. Meighan, V. Castranova, Y. Rojanasakul
• Journal: Nanotoxicology
• Published: 2014;8(5):485-507
• Cited by: 52 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Accumulating evidence indicates that carbon nanotubes (CNTs) are biopersistent and can cause lung damage. With similar fibrous morphology and mode of exposure to asbestos, a known human carcinogen, growing concern has arisen for elevated risk of CNT-induced lung carcinogenesis; however, relatively little is known about the long-term carcinogenic effect of CNT. Neoplastic transformation is a key early event leading to carcinogenesis. We studied the ability of single- and multi-walled CNTs to induce neoplastic transformation of human lung epithelial cells compared to asbestos. Long-term (6-month) exposure of the cells to occupationally relevant concentrations of CNT in culture caused a neoplastic-like transformation phenotype as demonstrated by increased cell proliferation, anchorage-independent growth, invasion and angiogenesis. Whole-genome expression signature and protein expression analyses showed that single- and multi-walled CNTs shared similar signaling signatures which were distinct from asbestos. These results provide novel toxicogenomic information and suggest distinct particle-associated mechanisms of neoplasia promotion induced by CNTs and asbestos.

In plain English

This was a laboratory (in vitro) study. The authors continuously exposed human small airway epithelial cells (SAECs, immortalised with hTERT) for 6 months to a sub-toxic dose of dispersed ultrafine carbon black (UFCB), single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT, Mitsui MWNT-7) or crocidolite asbestos, with surfactant-dispersant and saline passage controls. After exposure, SWCNT- and MWCNT-exposed cells showed greater colony-forming efficiency and Type III foci than dispersant control cells, and SWCNT-, MWCNT- and asbestos-exposed cells proliferated more at 48 hours than saline, dispersant and UFCB cells. In soft agar, SWCNT and MWCNT cells showed a 2.2-fold increase in colonies over dispersant controls and asbestos cells a 1.3-fold increase over saline controls. SWCNT and MWCNT cells showed a 4.7-fold increase in 48-hour invasion and a 2–2.5-fold increase in 24-hour migration compared with control cells; asbestos cells showed increased invasion but no statistically significant change in migration compared with dispersant controls. Whole-genome profiling showed SWCNT and MWCNT signatures resembling each other and differing from asbestos cells, which showed pro-inflammatory signalling.

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: In vitro laboratory study: subchronic (6-month) continuous exposure of a human lung epithelial cell line to nanoparticles and asbestos, with cell behaviour assays, whole-genome microarray profiling, rtPCR and Western blotting
• Who was studied: Human small airway epithelial cells (SAECs) immortalised with hTERT, cultured in triplicate; no human subjects
• Exposure: Six months of continuous culture exposure to dispersed ultrafine carbon black, SWCNT (HiPCO, acid-treated), MWCNT (Mitsui MWNT-7) or crocidolite asbestos at the dose printed as 0.02 mg/cm2 (equivalent to 0.1 mg/ml); crocidolite had a mean length of 10 micrometres, mean diameter of 0.21 micrometres and surface area of 9.8 m2/g; CNTs and UFCB were dispersed in the lung surfactant Survanta
• Main results:
  • SWCNT- and MWCNT-exposed cells had greater colony-forming efficiency and morphological transformation (Type III foci) than dispersant control cells
  • At 48 hours, SWCNT-, MWCNT- and asbestos-exposed cells proliferated significantly more than saline, dispersant and UFCB cells
  • Anchorage-independent growth in soft agar: 2.2-fold increase for SWCNT and MWCNT cells over dispersant controls; 1.3-fold increase for asbestos cells over saline controls
  • SWCNT and MWCNT cells showed a 4.7-fold increase in 48-hour invasion and a 2–2.5-fold increase in 24-hour migration compared with control cells
  • Asbestos-exposed cells showed a significant increase in invasion but no statistically significant change in migration compared with dispersant cells
  • Conditioned media from SWCNT, MWCNT, asbestos and saline cells increased endothelial tube formation, while UFCB and parental SAEC media decreased it, compared with dispersant control cells
  • UFCB-exposed cells had significantly fewer cells than controls, which the authors read as reduced ability to attach and proliferate
  • Gene expression: SWCNT and MWCNT cells showed altered apoptosis, cancer-related and decreased inflammatory signalling, differing from the pro-inflammatory signalling of asbestos and saline cells; principal component analysis explained 75.8% of variance in the first three components
  • Protein expression: SWCNT, MWCNT and asbestos cells over-expressed cFOS, c-Myc and PPAR-gamma, and under-expressed the tumour suppressors Inhibin alpha and p53
• The authors' conclusion: The authors concluded that their study provided new evidence of CNT-associated neoplastic-like transformation of lung epithelial cells after long-term in vitro exposure that differed from crocidolite asbestos, with asbestos cells dominated by pro-inflammatory signalling and CNT cells by decreased innate immune and NF-kB signalling
• Limitations the authors state:
  • The authors stated that caution is needed in interpreting and applying the results of their chronic in vitro model
  • The SAEC-hTERT cells used show drops in p16 expression after continuous long-term passage
  • The culture system lacked cells such as macrophages that release pro-inflammatory cytokines, which must be considered when interpreting the down-regulation of inflammation genes in CNT-exposed cells
  • Only three of the four major criteria for neoplastic transformation were met, as in vivo tumour formation after injection was not tested

Topics

Medical terms in this study, explained in our Lexicon: Carcinogenesis, Carcinogenic, Angiogenesis.

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