Cytotoxicity and reactive oxygen species generation from aggregated carbon and carbonaceous nanoparticulate materials

Our plain-English summary of Cytotoxicity and reactive oxygen species generation from aggregated carbon and carbonaceous nanoparticulate materials, by K.M. Garza, K.F. Soto, L.E. Murr (International Journal of Nanomedicine, 2008).

The study

• Authors: K.M. Garza, K.F. Soto, L.E. Murr
• Journal: International Journal of Nanomedicine
• Published: 2008;3(1):83-94
• Cited by: 54 articles, as counted by NIH iCite
• Read it: PubMed · Free full text

Abstract

We have investigated the cytotoxicity and reactive oxygen species (ROS) generation for indoor and outdoor soots: candle, wood, diesel, tire, and natural gas burner soots--along with surrogate black carbon, various multiwall carbon nanotube aggregate materials, TiO2 (anatase) and chrysotile asbestos as reference materials. All soots were observed utilizing TEM and FESEM to be composed of aggregated, primary spherules (20-80 nm diameter) forming complex, branched fractal structures. These spherules were composed of intercalated, turbostratic arrangements of curved graphene fragments with varying concentrations ofpolycyclic aromatic hydrocarbon (PAH) isomers. In vitro cultures with an immortalized human lung epithelial carcinoma cell line (A549) treated with these materials showed decreased cell viability and variations in ROS production, with no correlations to PAH content. The data demonstrate that soots are cytotoxic and that cytotoxicity is not related to PAH content but is related to ROS generation, suggesting that soot induces cellular oxidative stress and that cell viability assays can be indicators of ROS production.

In plain English

This was a laboratory study using a human lung cancer cell line (A549). The cells were exposed to indoor and outdoor soots from candles, wood, diesel, burning tires and natural gas burners. They were also exposed to black carbon and multiwall carbon nanotube materials. Chrysotile asbestos and titanium dioxide (anatase) served as reference (positive control) materials. The authors examined the particles by electron microscopy. After 48 hours they measured cell death and reactive oxygen species (ROS), a marker of oxidative stress. Some results were combined from their earlier studies. All soots were made of tiny spherules 20 to 80 nm across, clumped into branched aggregates. Chrysotile asbestos caused cell death similar to natural gas soot and a commercial nanotube material, while titanium dioxide caused little. Chrysotile, black carbon and a commercial nanotube material produced what the authors called significant ROS. ROS did not correlate with the soots' PAH content, but showed a qualitative correlation with cell death. The authors concluded that soots are cytotoxic and produce ROS, neither related to PAH content. They cautioned that the apparent cell-death ranking carries no real quantitative significance.

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 experiment combined with electron microscopy characterization of the particles; some data are drawn from the authors' earlier studies
• Who was studied: A549, an immortalized human lung carcinoma (epithelial cancer) cell line grown in culture plates. No people or animals were studied.
• Exposure: Soots (candle, wood, diesel, tire, yellow-flame and blue-flame natural gas) were collected on glass fiber filters, which were placed in contact with the cells. Commercial black carbon, two multiwall carbon nanotube materials, TiO2 (anatase) and chrysotile asbestos were added to the cells at 5 µg/mL. All exposures lasted 48 hours. Only chrysotile asbestos and TiO2 served as reference (positive control) materials.
• Main results:
  • Under the electron microscope, all soots consisted of primary spherules 20 to 80 nm in diameter forming branched, fractal-like aggregates.
  • Electron microscope images of a chrysotile asbestos aggregate and a carbon nanotube aggregate collected above a natural gas kitchen burner showed, in the authors' description, essentially identical nanotube structure and dimensions.
  • Cell death increased in this order over 48 hours: candle, wood, diesel, tire and natural gas soots, black carbon, and commercial arc-evaporation-produced nanotubes.
  • Chrysotile asbestos produced a cell-death response similar to natural gas combustion particles and the commercial nanotube material.
  • TiO2 (anatase) produced little cytotoxic response.
  • Chrysotile asbestos, black carbon and a commercial nanotube material produced what the authors called significant ROS, judged against a hydrogen peroxide reference. Other soots produced ROS below the hydrogen peroxide reference.
  • Black carbon gave the strongest ROS response relative to the hydrogen peroxide reference.
  • ROS production from blue-flame natural gas soot was comparable to that from tire soot.
  • ROS production did not correlate with total PAH content of the soots, which was measured in an earlier study.
  • ROS production showed a qualitative correlation with cell death.
• The authors' conclusion: The authors concluded that soot particles (including black carbon) are cytotoxic and produce ROS, that neither effect is related to PAH content, and that carbon and carbonaceous nanoparticles induce oxidative stress at various levels. They added that cell viability assays can be indicative of ROS production.
• Limitations the authors state:
  • The authors stated that the apparent toxicity ranking from the short 48-hour assays has no real quantitative significance.
  • The amount of soot on the filters varied with collection times and concentrations.
  • The authors noted it is difficult to prove that different cell lines respond similarly using dye-based assays; the trends are at least qualitative.
  • The authors' suggested mechanism (graphene fragment edges as sites promoting ROS) is speculative.

Topics

Medical terms in this study, explained in our Lexicon: Reactive Oxygen Species (ROS), Chrysotile, Carcinoma, Oxidative Stress.

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• Reactive oxygen species a double-edged sword for mesothelioma — S. Benedetti, B. Nuvoli, et al. (2015)
• Mobilization of iron from urban particulates leads to generation of reactive oxygen species in vitro and induction of ferritin synthesis in human lung epithelial cells — K.R. Smith, A.E. Aust (1997)
• Production of reactive oxygen intermediates by human macrophages exposed to soot particles and asbestos fibers and increase in NF-kappa B p50/p105 mRNA — R. Oettinger, K. Drumm, et al. (1999)

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