Genotoxicity of carbon nanofibers: are they potentially more or less dangerous than carbon nanotubes or asbestos?

Our plain-English summary of Genotoxicity of carbon nanofibers: are they potentially more or less dangerous than carbon nanotubes or asbestos?, by E.R. Kisin, A.R. Murray, L. Sargent, et al (Toxicology and Applied Pharmacology, 2011).

The study

• Authors: E.R. Kisin, A.R. Murray, L. Sargent, D. Lowry, M. Chirila, K.J. Siegrist, D. Schwegler-Berry, S. Leonard, V. Castranova, B. Fadeel, V.E. Kagan, A.A. Shvedova
• Journal: Toxicology and Applied Pharmacology
• Published: 2011;252(1):1-10
• Cited by: 87 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The production of carbon nanofibers and nanotubes (CNF/CNT) and their composite products is increasing globally. CNF are generating great interest in industrial sectors such as energy production and electronics, where alternative materials may have limited performance or are produced at a much higher cost. However, despite the increasing industrial use of carbon nanofibers, information on their potential adverse health effects is limited. In the current study, we examine the cytotoxic and genotoxic potential of carbon-based nanofibers (Pyrograf®-III) and compare this material with the effects of asbestos fibers (crocidolite) or single-walled carbon nanotubes (SWCNT). The genotoxic effects in the lung fibroblast (V79) cell line were examined using two complementary assays: the comet assay and micronucleus (MN) test. In addition, we utilized fluorescence in situ hybridization to detect the chromatin pan-centromeric signals within the MN indicating their origin by aneugenic (chromosomal malsegregation) or clastogenic (chromosome breakage) mechanisms. Cytotoxicity tests revealed a concentration- and time-dependent loss of V79 cell viability after exposure to all tested materials in the following sequence: asbestos>CNF>SWCNT. Additionally, cellular uptake and generation of oxygen radicals was seen in the murine RAW264.7 macrophages following exposure to CNF or asbestos but not after administration of SWCNT. DNA damage and MN induction were found after exposure to all tested materials with the strongest effect seen for CNF. Finally, we demonstrated that CNF induced predominantly centromere-positive MN in primary human small airway epithelial cells (SAEC) indicating aneugenic events. Further investigations are warranted to elucidate the possible mechanisms involved in CNF-induced genotoxicity.

Published by Elsevier Inc.

In plain English

This was a laboratory (in vitro) study comparing carbon nanofibers (Pyrograf-III, 1.4 wt.% iron), UICC crocidolite asbestos (18 wt.% iron) and purified single-walled carbon nanotubes (SWCNT, 0.23 wt.% iron) in cultured cells. Chinese hamster lung fibroblast (V79) cells were exposed at 0, 3, 12 or 48 micrograms per square centimetre for 3 or 24 hours, murine RAW264.7 macrophages were used for particle uptake and free-radical measurement, and primary human small airway epithelial cells (SAEC) were exposed to 2.4 and 24 micrograms per square centimetre of carbon nanofibers. Viability fell with dose and time, most for asbestos, then nanofibers, then SWCNT. Electron spin resonance signals were 4-fold over control for asbestos and 2.5-fold for nanofibers, with SWCNT barely detectable. Comet assay DNA damage and micronucleus induction were found for all three materials. In SAEC, carbon nanofibers produced mainly centromere-positive micronuclei (80% aneugenic events). The authors concluded all three fibrous nanomaterials were genotoxic in vitro, with nanofiber genotoxicity comparable to asbestos and stronger than SWCNT.

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 cell-culture toxicology experiment (cytotoxicity, comet assay, micronucleus test, FISH, electron spin resonance)
• Who was studied: Three cultured cell systems: Chinese hamster lung fibroblast V79 cells, murine RAW264.7 macrophages, and primary human small airway epithelial cells (SAEC)
• Exposure: Carbon nanofibers (Pyrograf-III, PR-24 LHT grade; 1.4 wt.% iron; 60-150 nm diameter), UICC standard crocidolite asbestos (about 18 wt.% iron) and HiPco single-walled carbon nanotubes (0.23 wt.% iron); V79 cells treated at 0 to 48 micrograms per square centimetre for 3 to 24 hours
• Main results:
  • After 24 hours at the two highest concentrations (12 and 48 micrograms per square centimetre) in V79 cells, loss of viability was 38% and 51.5% for asbestos, 26.5% and 36% for carbon nanofibers, and 10% and 22% for SWCNT
  • No cytotoxic effect was seen at the lowest concentration (3 micrograms per square centimetre)
  • In RAW264.7 macrophages, free-radical (ESR) signal intensity was 4-fold over control for asbestos and 2.5-fold over control for carbon nanofibers, while the SWCNT signal was hardly discernable
  • Macrophages internalized carbon nanofibers and asbestos but not carbon nanotubes
  • In V79 cells, 3 hours of CNF at 48 micrograms per square centimetre increased DNA migration, tail length and olive tail moment by 106%, 48% and 201% over vehicle-treated cells
  • At 24 hours, CNF at 3 micrograms per square centimetre significantly increased migrated DNA, tail length and olive tail moment by 45%, 68% and 102%, while CNF at 48 micrograms per square centimetre gave a non-significant elevation of 118%, 88% and 376%
  • No significant differences in DNA damage were found between CNF and SWCNT after 24 hours, and none between CNF and asbestos at any exposure time
  • Micronucleus induction in V79 cells at 12 micrograms per square centimetre was 2.9-fold for CNF, 2.3-fold for asbestos and 1.9-fold for SWCNT versus control; at 48 micrograms per square centimetre it was 2.5-fold for CNF and 2.2-fold for SWCNT
  • In human SAEC, CNF induced both centromere-positive and centromere-negative micronuclei, with aneugenic events predominating (80%)
• The authors' conclusion: The authors concluded that all three fibrous nanomaterials tested were genotoxic in vitro, with carbon nanofiber genotoxicity comparable with asbestos and stronger than SWCNT
• Limitations the authors state:
  • The highest asbestos dose (48 micrograms per square centimetre) was excluded from the DNA damage and micronucleus analyses because cytotoxicity above 50% would interfere with assessing genotoxicity
  • Because primary human cells were used, no background micronucleus rate was detectable in control samples
  • The FISH micronucleus work in SAEC used a different methodology from the V79 micronucleus assay
  • The authors state that further investigation is needed to elucidate the mechanisms of CNF-induced genotoxicity, in vitro and in vivo

Topics

Medical terms in this study, explained in our Lexicon: Genotoxicity, Crocidolite, Fibroblast, Comet Assay, Fluorescence In Situ Hybridization (FISH), Macrophage.

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