Cytotoxicity induced by exposure to natural and synthetic tremolite asbestos: an in vitro pilot study

Our plain-English summary of Cytotoxicity induced by exposure to natural and synthetic tremolite asbestos: an in vitro pilot study, by A. Pugnaloni, F. Giantomassi, G. Lucarini, et al (Acta Histochemica, 2013).

The study

• Authors: A. Pugnaloni, F. Giantomassi, G. Lucarini, S. Capella, A. Bloise, R. Di Primio, E. Belluso
• Journal: Acta Histochemica
• Published: 2013;115(2):100-12
• Cited by: 12 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Mineral fibers are potential carcinogens to humans. In order to help clarify the etiology of the pathological effects of asbestos, cellular reactions to natural and synthetic asbestos fibers were compared using a lung alveolar cancer cell line (A549 epithelial cells), considered the first target of inhaled micro-environmental contaminants. Natural asbestos tremolite (NAT) fibers were collected from rocks in NW Italy. Synthetic asbestos tremolite (SAT) was iron-free and therefore considered as standard tremolite. Both fibers, subjected to mineralogical characterization by X-ray powder diffractometry, electron microscopy and energy dispersive spectrometry, fell within the definition of respirable and potentially carcinogenic fibers. Several signs of functional and structural cell damage were found after treatment with both fibers, documented by viability, motility, and morphological perturbations. Phalloidin labeling showed irregular distribution of cytoskeletal F-actin, whereas immunohistochemical investigations showed abnormal expression of VEGF, Cdc42, β-catenin, assessed as risks indicators for cancer development. Both fibers caused significant loss of viability, even compared to UICC crocidolite, but, while SAT fibers exerted a more direct cytotoxic effect, survival of damaged cells expressing high VEGF levels was detected after NAT contact. This in vitro pilot study outlines potential health risks of NAT fibers in vivo related to their iron content, which could trigger signaling networks connected with cell proliferation and neoplastic transformation.

Copyright © 2012 Elsevier GmbH. All rights reserved.

In plain English

This was a laboratory pilot study, not a study of people. It tested how two kinds of tremolite asbestos affected A549 cells, a human lung cancer cell line grown in culture. Natural tremolite (NAT) came from serpentine rock near Brachiello in Val d'Ala in the NW Italian Alps and contained some iron. Synthetic tremolite (SAT) was made in a laboratory and contained no iron. UICC crocidolite was used for comparison in the viability test. That test measured treated cultures against untreated ones. After 24 hours, viability was 66.8% of control for NAT, 42.3% for SAT and 64% for crocidolite. After 48 hours it was 21.4%, 10.2% and 53% of control. Both tremolites reduced the share of healthy cells and reduced cell movement, and both increased the share of dead (necrotic) cells. The changes in healthy and necrotic cells were larger with SAT. NAT produced more apoptotic cells and stronger staining for VEGF, a growth-factor protein. The authors concluded that SAT seemed more directly toxic, while NAT might carry a higher risk of cell transformation after exposure in the body. Only one dose was tested.

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) pilot study, combined with mineralogical characterization of the fibers
• Who was studied: A549 cells, a human lung cancer (type II alveolar epithelial) cell line; untreated cells served as controls; each experiment was performed three times in triplicate
• Exposure: Natural asbestos tremolite (NAT) from serpentine rock near Brachiello, Val d'Ala (NW Italian Alps), containing some iron. Iron-free synthetic asbestos tremolite (SAT). UICC crocidolite as a comparison in the viability (MTT) assay. Suspensions were applied at a single concentration of 50 per ml of medium (the unit symbol is lost in the text; the article calls this a medium dose between the standard 10 and 100 per ml). Cells were exposed for 24 or 48 hours.
• Main results:
  • MTT viability at 24 h, expressed as a percentage of the untreated control reading: 66.8% (NAT), 42.3% (SAT) and 64% (crocidolite). The authors report significant differences versus controls and between NAT and SAT.
  • MTT viability at 48 h, as a percentage of control: 21.4% (NAT), 10.2% (SAT) and 53% (crocidolite).
  • Healthy cells at 24 h: 90% control, 56% NAT, 42.31% SAT. Necrotic cells at 24 h: 2.2%, 36.2%, 55.43%. Healthy cells at 48 h: 89%, 42%, 33.5%. Necrotic cells at 48 h: 6.04%, 49.4%, 62.3%.
  • Apoptotic cells increased more after NAT. At 48 h they were 8.54% (NAT), 4.34% (SAT) and 2.3% (control).
  • Surviving NAT- and SAT-treated cells lost motility at 24 h, with greater reductions at 48 h.
  • F-actin (cytoskeleton) staining appeared irregular in treated cells. Differences in the proportion of stained cells were not significant at 24 h but were significant at 48 h, when only 8% of NAT cells showed membrane staining.
  • VEGF-positive cells at 24 h: 63% control, 91% NAT, 78% SAT. At 48 h: 75%, 90%, 81%. Staining was stronger in NAT cells.
  • Cdc42-positive cells decreased after both treatments: at 24 h 80% control, 35% NAT, 30% SAT; at 48 h 95%, 15%, 20%.
  • Beta-catenin at the cell membrane decreased after NAT (40% vs 60% of control cells at 24 h) and was not detected after SAT (0% at 24 and 48 h).
• The authors' conclusion: The authors concluded that SAT appeared to cause more direct cytotoxic effects through necrosis. They concluded that NAT might exert a toxic effect with a higher risk of cell transformation after in vivo exposure, and they suggested that iron in the natural fibers might contribute. They wrote that their findings highlight the risk of NAT exposure for workers and people living near tremolite outcrops.
• Limitations the authors state:
  • Only a single (medium) fiber dose was tested. The authors intend future work with different doses and with primary lung and mesothelial cells rather than this cancer cell line.

Topics

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

Medical terms in this study, explained in our Lexicon: Tremolite, Mineral Fiber, Etiology, Carcinogenic, UICC, Crocidolite.

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