Inflammatory Cytokines Contribute to Asbestos-Induced Injury of Mesothelial Cells

Our plain-English summary of Inflammatory Cytokines Contribute to Asbestos-Induced Injury of Mesothelial Cells, by M.M. Acencio, B. Soares, E. Marchi, et al (Lung, 2015).

The study

• Authors: M.M. Acencio, B. Soares, E. Marchi, C.S. Silva, L.R. Teixeira, V.C. Broaddus
• Journal: Lung
• Published: 2015;193(5):831-7
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: Several diseases have been related to asbestos exposure, including the pleural tumor mesothelioma. The mechanism of pleural injury by asbestos fibers is not yet fully understood. The inflammatory response with release of mediators leading to a dysregulation of apoptosis may play a pivotal role in the pathophysiology of asbestos-induced pleural disease.

Objective: To determine whether pro-inflammatory cytokines produced by asbestos-exposed pleural mesothelial cells modify the injury induced by the asbestos.

Methods: Mouse pleural mesothelial cells (PMC) were exposed to crocidolite or chrysotile asbestos fibers (3.0 μg/cm(2)) for 4, 24, or 48 h and assessed for viability, necrosis and apoptosis, and the production of cytokines IL-1β, IL-6 and macrophage inflammatory protein-2 (MIP-2). Cells exposed to fibers were also treated with antibodies anti-IL-1β, anti-IL-6, anti- IL-1β+anti-IL-6 or anti-MIP-2 or their irrelevant isotypes, and assessed for apoptosis and necrosis. Non-exposed cells and cells treated with wollastonite, an inert particle, were used as controls.

Results: Mesothelial cells exposed to either crocidolite or chrysotile underwent both apoptosis and necrosis and released cytokines IL-1β, IL-6 and MIP-2. In the crocidolite group, apoptosis and the levels of all cytokines were higher than in the chrysotile group, at comparable concentrations. Neutralization of IL-1β andIL-6, but not MIP-2, inhibited apoptosis and necrosis, especially in the cells exposed to crocidolite fibers.

Conclusions: Both crocidolite and chrysotile asbestos fibers induced apoptosis and produced an acute inflammatory response characterized by elevated levels of IL-1β, IL-6 and MIP-2 in cultured mouse PMC. IL-1β and IL-6, but not MIP-2, were shown to contribute to asbestos-induced injury, especially in the crocidolite group.

In plain English

This laboratory study, done in São Paulo, Brazil, used pleural mesothelial cells (cells lining the chest cavity) taken from mice and grown in culture. The asbestos exposure took place in the dish, not in people or live animals. The cells were exposed to crocidolite or chrysotile asbestos at 3.0 micrograms per square centimeter for 4, 24 or 48 hours. Untreated cells, and cells exposed to wollastonite (described as an inert particle), served as controls. Both asbestos types reduced the share of living cells, causing both apoptosis (programmed cell death) and necrosis. Both also raised levels of the inflammatory signaling proteins IL-1β, IL-6 and MIP-2. Crocidolite caused more apoptosis than chrysotile at 24 hours (21.7% vs 13.4% of cells) and 48 hours (27.2% vs 20.2%), but no significant difference in necrosis was found between the fibers. The signaling proteins alone, without asbestos, did not increase cell death. Blocking IL-1β reduced apoptosis with both fibers, blocking IL-6 reduced necrosis with both fibers, and blocking MIP-2 had no effect. The authors concluded that asbestos-exposed mesothelial cells produce cytokines that contribute to asbestos toxicity, creating a "toxic positive feedback loop."

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: Laboratory (in vitro) experiment on cultured mouse cells
• Who was studied: Pleural mesothelial cells collected from anesthetized mice by washing out the pleural cavity, then grown in culture. The work was done at the Heart Institute (InCor), University of São Paulo Medical School, Brazil. The number of mice is not stated.
• Exposure: Crocidolite asbestos and chrysotile asbestos, each at 3.0 μg/cm2, for 4, 24 or 48 hours. The chrysotile came from Minaçu, Goiás, Brazil. Median fiber length was 19 μm for crocidolite and 27 μm for chrysotile. Wollastonite at 6.0 μg/cm2 and culture medium alone served as controls. Separate cells were exposed to each cytokine alone for 48 hours. Antibodies blocking IL-1β, IL-6, both together, or MIP-2 were added to asbestos-exposed cells.
• Main results:
  • Both crocidolite and chrysotile significantly reduced the viability of mesothelial cells compared with non-exposed controls or wollastonite-exposed cells. Both necrosis and apoptosis contributed to the loss.
  • Apoptosis, measured by flow cytometry, was higher with crocidolite than with chrysotile. At 24 h it was 21.7 ± 3.0% vs 13.4 ± 1.9% (p less than 0.001). At 48 h it was 27.2 ± 1.2% vs 20.2 ± 1.5% (p = 0.033).
  • A second method (DNA fragmentation staining) also showed more apoptosis with crocidolite than with chrysotile. At 24 h it was 22.1 ± 3.4% vs 13.7 ± 1.9% (p less than 0.001). At 48 h it was 26.7 ± 1.2% vs 19.8 ± 1.4% (p = 0.003).
  • Both fibers increased necrosis. No statistically significant difference in necrosis was found between crocidolite and chrysotile at any measured time point.
  • IL-1β, IL-6 and MIP-2 were significantly higher at all time points in asbestos-exposed cells than in negative controls. Crocidolite produced higher IL-1β than chrysotile at 24 h (56.9 ± 16.5 vs 39.5 ± 13.9 pg/ml). It also produced higher IL-6 and MIP-2 than chrysotile at all time points.
  • Cells exposed to the cytokines alone for 48 h, without asbestos, showed no increase in apoptosis or necrosis.
  • In crocidolite-exposed cells, blocking IL-1β reduced apoptosis at 24 h (17.3 ± 2.7% vs 21.7 ± 3.0%; p = 0.020) and at 48 h (21.8 ± 1.0% vs 27.2 ± 1.2%). Blocking IL-6 reduced apoptosis at 48 h (24.5 ± 1.1% vs 27.2 ± 1.2%; p = 0.001).
  • In chrysotile-exposed cells, only blocking IL-1β reduced apoptosis. At 24 h it was 10.7 ± 1.5% vs 13.4 ± 1.9% (p = 0.013). At 48 h it was 16.2 ± 1.2% vs 20.2 ± 1.5% (p = 0.002).
  • Combining the IL-1β and IL-6 blockers did not reduce apoptosis significantly more than either blocker alone.
  • Blocking IL-6 reduced necrosis in both the crocidolite and chrysotile groups at 24 h and 48 h. Blocking IL-1β or MIP-2 had no effect on necrosis.
  • The MIP-2 blocker and the control (irrelevant) antibodies had no effect on asbestos-induced apoptosis or necrosis. The data were not shown.
• The authors' conclusion: The authors concluded that, even without other cell types present, mesothelial cells exposed to asbestos fibers produce cytokines that contribute to asbestos toxicity, establishing what they called a toxic positive feedback loop.
• Limitations the authors state:
  • The authors acknowledged that other cytokines, not measured in this study, are likely also produced.

Topics

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

Medical terms in this study, explained in our Lexicon: Cytokine, Mesothelial Cells, Asbestos Exposure, Mesothelioma, Apoptosis, Crocidolite, Chrysotile, Necrosis.

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• Distinctive profile of alveolar macrophage-derived cytokine release induced by fibrogenic and nonfibrogenic mineral dusts — I. Lemaire, S. Ouellet (1996)
• SWCNT suppress inflammatory mediator responses in human lung epithelium in vitro — E. Herzog, H.J. Byrne, et al. (2009)
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• Cytokine and free radical responses of alveolar macrophages in vitro to asbestos fibres — L.C. Mongan, T. Jones, et al. (2000)

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