Dispersion medium modulates oxidative stress response of human lung epithelial cells upon exposure to carbon nanomaterial samples

Our plain-English summary of Dispersion medium modulates oxidative stress response of human lung epithelial cells upon exposure to carbon nanomaterial samples, by E. Herzog, H.J. Byrne, M. Davoren, et al (Toxicology and Applied Pharmacology, 2009).

The study

• Authors: E. Herzog, H.J. Byrne, M. Davoren, A. Casey, A. Duschl, G.J. Oostingh
• Journal: Toxicology and Applied Pharmacology
• Published: 2009;236(3):276-81
• Cited by: 71 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Due to their large specific surface area, the potential of nanoparticles to be highly reactive and to induce oxidative stress is particularly high. In addition, some types of nanoparticles contain transition metals as trace impurities which are known to generate reactive oxygen species (ROS) in biological systems. This study investigates the potential of two types of single-walled carbon nanotube samples, nanoparticulate carbon black and crocidolite asbestos to induce ROS in lung epithelial cells in vitro. Carbon nanotube and carbon black samples were used as produced, without further purification or processing, in order to best mimic occupational exposure by inhalation of airborne dust particles derived from carbon nanomaterial production. Intracellular ROS were measured following short-term exposure of primary bronchial epithelial cells (NHBE) and A549 alveolar epithelial carcinoma cells using the redox sensitive probe carboxydichlorofluorescin (carboxy-DCFDA). The oxidative potential of agglomerated nanomaterial samples was compared following dispersion in cell culture medium with and without foetal calf serum (FCS) supplement. In addition, samples were dispersed in dipalmitoylphosphatidylcholine (DPPC), the major component of lung surfactant. It could be illustrated that in vitro exposure of lung epithelial cells to carbon nanomaterial samples results only in moderate or low oxidative stress under the exposure conditions employed. However, cell responses are strongly dependent on the vehicle used for dispersion. Whereas the presence of DPPC increased intracellular ROS formation, FCS seemed to protect the cells from oxidative insult.

In plain English

This was a laboratory (in vitro) study of reactive oxygen species (ROS) formation in two human lung epithelial cell types: primary bronchial cells (NHBE) and the A549 alveolar type II carcinoma line. Cells were exposed for 1 hour to 50 micrograms per millilitre of HiPco single-walled carbon nanotubes, arc discharge single-walled carbon nanotubes, P90 carbon black, or UICC crocidolite asbestos, dispersed in culture medium (with or without foetal calf serum) or in DPPC, the main component of lung surfactant. ROS were measured with the carboxy-DCFDA probe by flow cytometry. In NHBE cells, particles and asbestos dispersed in culture medium alone did not induce ROS; after dispersion in DPPC the reported increases over DPPC-free medium were 1.5-fold (HiPco), 2.2-fold (arc discharge), 3.8-fold (P90) and 1.4-fold (asbestos), although the authors stated there was no statistically significant increase in asbestos toxicity. In A549 cells in serum-free medium, HiPco nanotubes raised ROS significantly (1.9-fold) while the 1.1-fold arc discharge change was not significant; with FCS added, no ROS response could be detected for any particle. N-acetyl-L-cysteine pre-treatment inhibited ROS formation. The authors concluded responses depended strongly on the dispersion vehicle.

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 measuring intracellular reactive oxygen species in two human lung epithelial cell types
• Who was studied: Human A549 alveolar type II carcinoma cells and normal human primary bronchial epithelial cells (NHBE), seeded at 3x10^4 cells/well; experiments in duplicate with two replicates each
• Exposure: 1 hour exposure to 50 micrograms per millilitre (25 micrograms per square centimetre) of HiPco SWCNT (10 wt.% iron catalyst residues), arc discharge SWCNT (under 1 wt.% nickel and yttrium catalysts), P90 carbon black (mean diameter 14 nm) or UICC crocidolite asbestos, dispersed in culture medium with or without FCS, or in DPPC/PBS; hydrogen peroxide 500 micromolar as positive control
• Main results:
  • In NHBE cells, particles or asbestos dispersed in cell culture medium did not induce ROS formation, unlike hydrogen peroxide
  • In NHBE cells, dispersion in DPPC gave significant ROS increases relative to control for all four materials, with P90 carbon black the most active
  • In NHBE cells, DPPC dispersion increased ROS formation compared with DPPC-free medium by factors of 1.5 (HiPco SWCNT), 2.2 (arc discharge SWCNT), 3.8 (P90) and 1.4 (crocidolite asbestos)
  • The authors stated in the Discussion that the DPPC-related increase for asbestos was not statistically significant, and attributed this to asbestos already being well dispersed in culture medium
  • In standard growth media, A549 cells responded significantly to HiPco SWCNT only, and not to any other particle
  • In A549 cells, HiPco and arc discharge SWCNT in FCS-free medium increased ROS by factors of 1.9 and 1.1; with FCS added no ROS response was detected for any particle
  • In A549 cells, DPPC dispersion increased ROS most for P90 (90% increase over particles in medium without FCS); increases for the two SWCNT samples were not statistically significant
  • Pre-treatment with the antioxidant N-acetyl-L-cysteine inhibited ROS formation in NHBE cells after both particle and hydrogen peroxide exposure, and also in A549 cells
  • Despite much higher metal impurity content in HiPco SWCNT, no correlation between cellular response and metal content was observed
• The authors' conclusion: The authors concluded that exposure of lung epithelial cells to carbon nanomaterials produced only moderate or low oxidative stress under these conditions, that ROS production from carbon nanomaterials was always higher than from asbestos, and that responses depended strongly on the dispersion vehicle, with DPPC increasing and FCS appearing to protect against ROS formation
• Limitations the authors state:
  • The authors noted the carboxy-DCFDA assay detects only certain types of ROS, so further assays and endpoints would be needed for a full picture of oxidative stress
  • The authors stated that any contribution of lipid peroxidation to the observed effects remained under investigation
  • The authors stated that whether improved dispersion increases particle uptake by cells would need further investigation

Topics

Medical terms in this study, explained in our Lexicon: Oxidative Stress, Reactive Oxygen Species (ROS), Crocidolite, Occupational Exposure, Short-Term Exposure, Carcinoma.

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