Effect of surface functionalizations of multi-walled carbon nanotubes on neoplastic transformation potential in primary human lung epithelial cells

Our plain-English summary of Effect of surface functionalizations of multi-walled carbon nanotubes on neoplastic transformation potential in primary human lung epithelial cells, by T.A. Stueckle, D.C. Davidson, R. Derk, et al (Nanotoxicology, 2017).

The study

• Authors: T.A. Stueckle, D.C. Davidson, R. Derk, P. Wang, S. Friend, D. Schwegler-Berry, P. Zheng, N. Wu, V. Castranova, Y. Rojanasakul, L. Wang
• Journal: Nanotoxicology
• Published: 2017;11(5):613-624
• Cited by: 16 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Functionalized multi-walled carbon nanotube (fMWCNT) development has been intensified to improve their surface activity for numerous applications, and potentially reduce toxic effects. Although MWCNT exposures are associated with lung tumorigenesis in vivo, adverse responses associated with exposure to different fMWCNTs in human lung epithelium are presently unknown. This study hypothesized that different plasma-coating functional groups determine MWCNT neoplastic transformation potential. Using our established model, human primary small airway epithelial cells (pSAECs) were continuously exposed for 8 and 12 weeks at 0.06 μg/cm2 to three-month aged as-prepared-(pMWCNT), carboxylated-(MW-COOH), and aminated-MWCNTs (MW-NHx). Ultrafine carbon black (UFCB) and crocidolite asbestos (ASB) served as particle controls. fMWCNTs were characterized during storage, and exposed cells were assessed for several established cancer cell hallmarks. Characterization analyses conducted at 0 and 2 months of aging detected a loss of surface functional groups over time due to atmospheric oxidation, with MW-NHx possessing less oxygen and greater lung surfactant binding affinity. Following 8 weeks of exposure, all fMWCNT-exposed cells exhibited significant increased proliferation compared to controls at 7 d post-treatment, while UFCB- and ASB-exposed cells did not differ significantly from controls. UFCB, pMWCNT, and MW-COOH exposure stimulated significant transient invasion behavior. Conversely, aged MW-NHx-exposed cells displayed moderate increases in soft agar colony formation and morphological transformation potential, while UFCB cells showed a minimal effect compared to all other treatments. In summary, surface properties of aged fMWCNTs can impact cell transformation events in vitro following continuous, occupationally relevant exposures.

In plain English

This laboratory study tested whether surface coatings on multi-walled carbon nanotubes change their ability to push human lung cells toward cancer-like behavior. The authors exposed primary human small airway epithelial cells continuously for 8 and 12 weeks to 0.06 micrograms per square centimeter of uncoated, carboxylated or aminated nanotubes (aged three months), ultrafine carbon black, or crocidolite asbestos. During storage the nanotube coatings were largely lost to oxidation. The aminated nanotubes kept the least surface oxygen and bound the most protein. After 8 weeks, nanotube-exposed cells had more live cells than unexposed cells seven days after reseeding in particle-free medium; asbestos-exposed cells had fewer. Only carbon black and aminated nanotubes increased colonies grown in soft agar, an effect the authors called modest. Aminated nanotubes produced the most Type II foci. Asbestos-exposed cells did not differ from controls in invasion. At 12 weeks, growth ability fell 50-60% in control and carbon black cells and 75-90% in fiber-exposed cells; all stopped growing by 14 weeks. The authors concluded that aged aminated nanotubes caused moderate cell transformation compared with the other nanotubes. They also stated this cell transformation model does not predict asbestos-induced carcinogenesis.

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: Laboratory (in vitro) cell culture experiment with long-term continuous particle exposure, plus physical and chemical characterization of the particles
• Who was studied: Commercially obtained primary human small airway epithelial cells (Lonza), seeded in triplicate in 6-well plates; no human subjects
• Exposure: Continuous exposure for 8 and 12 weeks to 0.06 micrograms per square centimeter of uncoated ('as prepared'), carboxylated or aminated multi-walled carbon nanotubes (aged 3 months), ultrafine carbon black, or crocidolite asbestos (NIEHS standard) as a particle control. Water- and dispersant-exposed cells served as controls.
• Main results:
  • The functionalized nanotubes oxidized during laboratory storage. At 2 months the aminated nanotubes had the least surface oxygen (1.1% oxygen, versus 1.82% for uncoated and 2.6% for carboxylated nanotubes).
  • Aminated nanotubes bound 13-fold more total protein than the control, compared with 5.8-fold for carbon black and the other nanotubes.
  • After 8 weeks of exposure, all nanotube-exposed cells had significantly more live cells than unexposed and carbon black-exposed cells. This was measured at Day 7 after reseeding in particle-free medium.
  • In the same assessment, crocidolite asbestos exposure reduced the number of live cells.
  • At 12 weeks, passage control and carbon black cells showed a significant 50-60% reduction in proliferation ability, while all fiber particle exposed cells showed a 75 to 90% loss.
  • All passaged cells lost proliferation ability and showed senescence by 14 weeks in culture.
  • At 8 weeks, only carbon black- and aminated nanotube-exposed cells had significantly more soft agar colonies. The authors described the effect as modest.
  • Aminated nanotube-exposed cells showed the highest number of Type II foci in the morphological transformation assay.
  • At 8 weeks, carbon black, uncoated and carboxylated nanotube-exposed cells showed a significant 2- to 4-fold increase in invasion ability.
  • Aminated nanotube- and asbestos-exposed cells did not differ from passage control cells in invasion and migration at 8 weeks.
• The authors' conclusion: The authors concluded that laboratory aging caused oxidation and convergence of the nanotubes' surface properties. They concluded that 8 weeks of exposure to aged aminated nanotubes, which had less surface oxygen, caused moderate cell transformation compared with uncoated and carboxylated nanotubes.
• Limitations the authors state:
  • Because the coatings were unstable, the study could not assess freshly made functionalized nanotubes.
  • Soft agar colony counts were low compared with the authors' earlier work with another nanotube type (MWCNT-7).
  • Colonies could not be successfully re-established as clones in culture.
  • The mechanism of the aminated nanotube effect is unknown.
  • The authors stated that, based on this and earlier studies, this cell transformation model does not predict asbestos-induced carcinogenesis.

Topics

Medical terms in this study, explained in our Lexicon: Tumorigenesis, Epithelium, Crocidolite.

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