SWCNT suppress inflammatory mediator responses in human lung epithelium in vitro

Our plain-English summary of SWCNT suppress inflammatory mediator responses in human lung epithelium in vitro, by E. Herzog, H.J. Byrne, A. Casey, et al (Toxicology and Applied Pharmacology, 2009).

The study

• Authors: E. Herzog, H.J. Byrne, A. Casey, M. Davoren, A.G. Lenz, K.L. Maier, A. Duschl, G.J. Oostingh
• Journal: Toxicology and Applied Pharmacology
• Published: 2009;234(3):378-90
• Cited by: 65 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Single-walled carbon nanotubes have gained enormous popularity due to a variety of potential applications which will ultimately lead to increased human and environmental exposure to these nanoparticles. This study was carried out in order to evaluate the inflammatory response of immortalised and primary human lung epithelial cells (A549 and NHBE) to single-walled carbon nanotube samples (SWCNT). Special focus was placed on the mediating role of lung surfactant on particle toxicity. The toxicity of SWCNT dispersed in cell culture medium was compared to that of nanotubes dispersed in dipalmitoylphosphatidylcholine (DPPC, the main component of lung lining fluid). Exposure was carried out for 6 to 48 h with the latter time-point showing the most significant responses. Moreover, exposure was performed in the presence of the pro-inflammatory stimulus tumour necrosis factor-alpha (TNF-alpha) in order to mimic exposure of stimulated cells, as would occur during infection. Endpoints evaluated included cell viability, proliferation and the analysis of inflammatory mediators such as interleukin (IL)-8, IL-6, TNF-alpha and macrophage chemoattractant protein-1 (MCP-1). Crocidolite asbestos was included as a well characterised, toxic fibre control. The results of this study showed that HiPco SWCNT samples suppress inflammatory responses of A549 and NHBE cells. This was also true for TNF-alpha stimulated cells. The use of DPPC improved the degree of SWCNT dispersion in A549 medium and in turn, leads to increased particle toxicity, however, it was not shown to modify NHBE cell responses.

In plain English

This laboratory study tested whether single-walled carbon nanotubes (HiPco SWCNT) trigger or suppress inflammatory mediators in cultured human lung epithelial cells, with crocidolite asbestos (UICC) as a comparison fibre. A549 alveolar type II carcinoma cells and normal human bronchial epithelial cells (NHBE) were exposed for up to 48 hours to 0.195 to 50 micrograms per millilitre of particles in culture medium or DPPC, with and without TNF-alpha stimulation; 48-hour results are presented. Medium-dispersed SWCNT did not reduce A549 or NHBE viability, but lowered IL-8 promoter activity to 64% of control, IL-8 protein by up to 40%, IL-6 by 27% and MCP-1 by more than 40% in A549 cells; in NHBE cells IL-8 fell 22% and IL-6 36%. In unstimulated A549 cells, asbestos dispersed in culture medium slightly increased IL-8 and IL-6, whereas DPPC-dispersed asbestos decreased them by up to 50% and 20%; asbestos also decreased MCP-1 by up to 40% and reduced viability by up to 20%. The authors concluded that SWCNT suppressed inflammatory mediators and that DPPC improved SWCNT dispersion in A549 medium, increasing toxicity.

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 on two human lung epithelial cell types, with asbestos as comparison fibre
• Who was studied: Human A549 alveolar type II carcinoma cells (including stably transfected IL-8 and IL-6 reporter gene lines) and normal human primary bronchial epithelial cells (NHBE, passages 3-7), in culture
• Exposure: HiPco single-walled carbon nanotubes (10 wt.% iron catalyst residues, diameters 0.8-1.2 nm, BET 487.15 m2/g) and UICC crocidolite asbestos (BET 5.6 m2/g), dispersed in culture medium or in DPPC/PBS, at 0.195 to 50 micrograms per millilitre for 6, 24 and 48 hours, with or without rh-TNF-alpha (10 ng/ml) or LPS-PA stimulation
• Main results:
  • In A549-IL8 reporter cells, culture-medium dispersed SWCNT reduced IL-8 promoter activation to 64% of control, with significant decreases from 12.5 micrograms per millilitre
  • IL-8 mRNA in A549 cells exposed to 50 micrograms per millilitre SWCNT fell 30% at 6 h and 40% at 24 h versus unexposed controls
  • In unstimulated A549 cells at 48 h, SWCNT reduced IL-8 protein by up to 40%, IL-6 by 27% and MCP-1 by more than 40%
  • In unstimulated NHBE cells at 48 h, SWCNT reduced IL-8 by 22% and IL-6 by 36%; in rh-TNF-alpha stimulated NHBE cells the reductions were 51% and 64%
  • Crocidolite asbestos in A549 cells inhibited MCP-1 release by up to 40%, while IL-8 and IL-6 protein slightly increased at 48 h when the asbestos was dispersed in culture medium; in NHBE cells IL-8 decreased by up to 11% and IL-6 was unaffected
  • In unstimulated A549 cells, DPPC-dispersed asbestos decreased IL-8 and IL-6 by up to 50% and 20%, whereas increases of around 20% were seen without DPPC
  • Exposure of A549 or NHBE cells to asbestos caused loss of cell viability of up to 20%, whereas medium-dispersed SWCNT did not reduce A549 or NHBE viability; DPPC-dispersed SWCNT caused significant cytotoxicity in A549 cells
  • DPPC dispersion increased SWCNT suspension in A549 medium and increased suppression of IL-8, IL-6 and MCP-1 in A549 cells, but did not alter NHBE responses
• The authors' conclusion: The authors concluded that HiPco SWCNT exposure suppressed inflammatory mediators (IL-8, IL-6, MCP-1) in both A549 and NHBE cells in vitro, that SWCNT showed both similarities and differences to crocidolite asbestos so that risk assessment needs further comparative studies, and that DPPC improved SWCNT dispersion in A549 medium leading to increased particle toxicity
• Limitations the authors state:
  • The authors stated no definite conclusion could be drawn about whether HiPco SWCNT act in an asbestos-like manner
  • The authors noted it remained unknown why DPPC dispersion modified the A549 inflammatory response to asbestos, and that further physical and chemical characterisation of DPPC-particle interactions is needed
  • DLS could not be used for further analysis because SWCNT samples were highly polydispersed and precipitated
  • Medium-dispersed SWCNT incubated with TNF-alpha standard reduced measured protein by 20%, so some decreases may reflect adsorption of TNF-alpha onto the particles
  • There is no reliable human in vitro model for type I epithelial cells, so type II cells were used as a substitute

Topics

The National Library of Medicine indexes this study under subjects our site covers: Crocidolite.

Medical terms in this study, explained in our Lexicon: Epithelium, Environmental Exposure, Lung Lining Fluid, Necrosis, Macrophage, Crocidolite.

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