Carboxylated short single-walled carbon nanotubes but not plain and multi-walled short carbon nanotubes show in vitro genotoxicity

Our plain-English summary of Carboxylated short single-walled carbon nanotubes but not plain and multi-walled short carbon nanotubes show in vitro genotoxicity, by M. Mrakovcic, C. Meindl, G. Leitinger, et al (Toxicological Sciences, 2015).

The study

• Authors: M. Mrakovcic, C. Meindl, G. Leitinger, E. Roblegg, E. Fröhlich
• Journal: Toxicological Sciences
• Published: 2015;144(1):114-27
• Cited by: 21 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Long carbon nanotubes (CNTs) resemble asbestos fibers due to their high length to diameter ratio and they thus have genotoxic effects. Another parameter that might explain their genotoxic effects is contamination with heavy metal ions. On the other hand, short (1-2 µm) CNTs do not resemble asbestos fibers, and, once purified from contaminations, they might be suitable for medical applications. To identify the role of fiber thickness and surface properties on genotoxicity, well-characterized short pristine and carboxylated single-walled (SCNTs) and multi-walled (MCNTs) CNTs of different diameters were studied for cytotoxicity, the cell's response to oxidative stress (immunoreactivity against hemoxygenase 1 and glutathione levels), and in a hypoxanthine guanine phosphoribosyltransferase (HPRT) assay using V79 chinese hamster fibroblasts and human lung adenocarcinoma A549 cells. DNA repair was demonstrated by measuring immunoreactivity against activated histone H2AX protein. The number of micronuclei as well as the number of multinucleated cells was determined. CNTs acted more cytotoxic in V79 than in A549 cells. Plain and carboxylated thin (<8 nm) SCNTs and MCNTs showed greater cytotoxic potential and carboxylated CNTs showed indication for generating oxidative stress. Multi-walled CNTs did not cause HPRT mutation, micronucleus formation, DNA damage, interference with cell division, and oxidative stress. Carboxylated, but not plain, SCNTs showed indication for in vitro DNA damage according to increase of H2AX-immunoreactive cells and HPRT mutation. Although short CNTs presented a low in vitro genotoxicity, functionalization of short SCNTs can render these particles genotoxic.

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In plain English

This laboratory study tested short carbon nanotubes, not asbestos, on cells grown in dishes. The authors noted that long nanotubes resemble asbestos fibers. They studied short ones that might be used in medicine. Both single-walled and multi-walled nanotubes were tested in plain and carboxylated (chemically modified) forms, and the multi-walled ones came in three diameters. The cells were Chinese hamster lung cells (V79) and human lung adenocarcinoma cells (A549). The authors measured cell viability, oxidative stress, gene mutations, a DNA-damage marker, micronuclei and cells with several nuclei. Thin and carboxylated nanotubes reduced cell viability more, and V79 cells were more sensitive. In V79 cells, mutations rose significantly with carboxylated single-walled nanotubes at all three tested concentrations, and with plain single-walled nanotubes at the highest. The DNA-damage marker rose significantly only in A549 cells given the highest concentration of carboxylated single-walled nanotubes. No nanotube significantly increased micronuclei. The authors concluded that short nanotubes generally showed low potential to damage genetic material, but that functionalization might make short single-walled nanotubes genotoxic. They noted the doses are less representative of workers' exposures.

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) laboratory experiment
• Who was studied: Two cell lines, no people: V79 Chinese hamster lung fibroblasts and A549 human lung adenocarcinoma (alveolar type II) cells. The work was done in Graz, Austria.
• Exposure: Short carbon nanotubes (0.5 to 2 micrometers long), bought from Cheap Tubes Inc. They were plain or carboxylated single-walled nanotubes 1 to 2 nm in diameter (SCNT, SCNTc), and plain or carboxylated multi-walled nanotubes less than 8 nm, 20 to 30 nm, and more than 50 nm in diameter. No asbestos was tested.
• Main results:
  • V79 cells: viability was significantly reduced at 100 or more (units printed as mg/ml) of SCNTc and MCNT8, and at 200 of MCNT8c, MCNT20c and MCNT50c.
  • A549 cells: viability was significantly reduced at 100 or more of SCNTc and at 200 of MCNT8, MCNT20c and MCNT50c.
  • HPRT gene mutation test in V79 cells: mutation rates rose significantly with SCNTc at 50 to 200 and with plain SCNT at 200.
  • DNA-damage marker (H2AX-stained cells) in A549 cells: numbers were low after nanotube treatment. Only cells given 200 of SCNTc showed a significant increase.
  • Oxidative stress marker HO-1 in A549 cells: no significant increase, except with SCNTc at 200.
  • Glutathione (an antioxidant) in A549 cells fell significantly with 25 and 50 of SCNTc, MCNT8c and MCNT50c. There were no significant changes in V79 cells.
  • Micronuclei in V79 cells: 25 to 200 of nanotubes did not significantly increase them.
  • Micronuclei in A549 cells: no significant increase with 50 to 200 of nanotubes.
  • Neither cell line showed an obvious increase in multinucleated cells after nanotube exposure.
  • Both cell lines took up single-walled nanotubes to a smaller degree than multi-walled nanotubes.
• The authors' conclusion: The authors concluded that short carbon nanotubes in general showed a low genotoxic potential, but that functionalization might render short single-walled nanotubes genotoxic. They considered interference with cellular DNA repair the most probable mechanism.
• Limitations the authors state:
  • The concentrations were chosen to simulate medical uses and are less representative of workers' exposures.
  • The positive mutation result could be a false positive caused by damage to targets other than DNA, specific to this test system.
  • Staining for DNA-repair and oxidative-stress proteins was done only in the human A549 cells, not in the hamster V79 cells.

Topics

Medical terms in this study, explained in our Lexicon: Genotoxicity, Oxidative Stress, Glutathione (GSH), Fibroblast, Lung Adenocarcinoma, A549 Cells, Micronuclei.

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