Raw and thermally treated cement asbestos exerts different cytotoxicity effects on A549 cells in vitro

Our plain-English summary of Raw and thermally treated cement asbestos exerts different cytotoxicity effects on A549 cells in vitro, by A. Pugnaloni, G. Lucarini, C. Rubini, et al (Acta Histochemica, 2015).

The study

• Authors: A. Pugnaloni, G. Lucarini, C. Rubini, A. Smorlesi, M. Tomasetti, E. Strafella, T. Armeni, A.F. Gualtieri
• Journal: Acta Histochemica
• Published: 2015;117(1):29-39
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Raw cement asbestos (RCA) undergoes a complete solid state transformation when heated at high temperatures. The secondary raw material produced, high temperatures-cement asbestos (HT-CA) is composed of newly-formed crystals in place of the asbestos fibers present in RCA. Our previous study showed that HT-CA exerts lower cytotoxic cell damage compared to RCA. Nevertheless further investigations are needed to deepen our understanding of pathogenic pathways involving oxidative and nitrative damage. Our aim is to deepen the understanding of the biological effects on A549 cells of these materials regarding DNA damage related proteins (p53, its isoform p73 and TRAIL) and nitric oxide (NO) production during inducible nitric oxide synthase (iNOS)-mediated inflammation. Increments of p53/p73 expression, iNOS positive cells and NO concentrations were found with RCA, compared to HT-CA and controls mainly at 48 h. Interestingly, ferrous iron causing reactive oxygen species (ROS)-mediated DNA damage was found in RCA as a contaminant. HT-CA thermal treatment induces a global recrystallization with iron in a crystal form poorly released in media. HT-CA slightly interferes with genome expression and exerts lower inflammatory potential compared to RCA on biological systems. It could represent a safe approach for storing or recycling asbestos and an environmentally friendly alternative to asbestos waste.

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In plain English

This was a laboratory study using a human cell line, A549, described as human malignant cells with some features of lung alveolar cells. The authors exposed the cells for 24 and 48 hours to raw cement asbestos (RCA, a commercial roofing-slate material containing chrysotile fibers) or to the same material after heating to 1200 °C (HT-CA). They compared both with untreated cells. Both materials were taken up inside the cells. At 48 hours, nuclear p53 staining was found in 50% of RCA-exposed cells, compared with 30% of controls and 25% of HT-CA cells. Nuclear p73 staining was 55% with RCA, compared with 30% and 42%. Cells positive for iNOS, an inflammation-related enzyme, were 90% with RCA at 48 hours, compared with 45% of controls and 43% with HT-CA. Nitric oxide in the culture medium was significantly higher with RCA. TRAIL did not differ among groups. The authors concluded that HT-CA had lower cytotoxic and inflammatory potential than RCA but seemed not completely inert. They cautioned that drawing direct conclusions about its toxicity from this in vitro study would be incautious.

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 comparing raw and heat-treated cement asbestos with untreated control cells, using microscopy, immunohistochemistry and nitric oxide measurement; each experiment was done three times in triplicate
• Who was studied: A549 cells, a human cell line described as malignant cells with some features of alveolar epithelial cells, obtained from the American Type Culture Collection; untreated cultures served as controls
• Exposure: Raw cement asbestos (RCA), a commercial cement asbestos used for outdoor roofing slates and containing chrysotile fibers, and HT-CA, the product of heating cement asbestos to 1200 °C. Both were tested at a single concentration for 24 and 48 hours (the concentration unit is damaged in the text).
• Main results:
  • Both materials were found inside the cells, in the cytoplasm or in lysosome-like vacuoles, at 24 and 48 hours. RCA appeared fibrous; HT-CA appeared as electron-dense granular material.
  • Nuclear p53 staining at 24 hours was significantly higher with RCA (35% of cells) than in controls (25%) or with HT-CA (25%)
  • Nuclear p53 staining at 48 hours was 50% of cells with RCA, compared with 30% of controls and 25% with HT-CA
  • Nuclear p73 staining at 24 hours was 40% of cells with RCA and 45% with HT-CA, compared with 25% of controls
  • Nuclear p73 staining at 48 hours was significantly higher with RCA (55% of cells) than with HT-CA (42%) or in controls (30%)
  • TRAIL was found only in the cytoplasm and did not differ among the groups
  • iNOS-positive cells were significantly more frequent with RCA (75% at 24 hours, 90% at 48 hours) than in controls (45%, 45%) or with HT-CA (55%, 43%)
  • Nitric oxide in the culture medium was significantly higher with RCA (1.8 at 24 hours; 1.2 at 48 hours, printed as '1,2') than in controls and HT-CA cells. Control cells produced a basal level of 1.1 at 24 hours and 0.9 at 48 hours. The unit is printed as 'M', apparently with a symbol lost.
  • Surface analysis found iron at 0.34 weight percent on chrysotile fibers in RCA and 1.23 weight percent on HT-CA
• The authors' conclusion: The authors concluded that HT-CA has lower cytotoxic and inflammatory potential than RCA. They also stated that the transformed product seems not to be completely inert and causes moderate cell damage.
• Limitations the authors state:
  • The authors stated that drawing direct conclusions on the toxicity of the heat-treated material from this in vitro study would be incautious
  • The authors stated that in vivo studies are needed to confirm whether any carcinogenic potential exists
  • The authors stated that whether the amorphous phase in HT-CA is reactive or cytotoxic is undetermined
  • The authors stated that the slight reactivity of HT-CA remains unexplained. They called for further studies comparing it directly with negative controls (Portland or Mg-rich clinker) and positive controls (crocidolite asbestos).

Topics

Medical terms in this study, explained in our Lexicon: A549 Cells, Inducible Nitric Oxide Synthase (iNOS), Inflammation, Reactive Oxygen Species (ROS).

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