Cytotoxicity, oxidative stress and genotoxicity induced by glass fibers on human alveolar epithelial cell line A549

Our plain-English summary of Cytotoxicity, oxidative stress and genotoxicity induced by glass fibers on human alveolar epithelial cell line A549, by V. Rapisarda, C. Loreto, C. Ledda, et al (Toxicology in Vitro, 2015).

The study

• Authors: V. Rapisarda, C. Loreto, C. Ledda, G. Musumeci, M. Bracci, L. Santarelli, M. Renis, M. Ferrante, V. Cardile
• Journal: Toxicology in Vitro
• Published: 2015;29(3):551-7
• Cited by: 27 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Man-made vitreous fibers have been widely used as insulation material as asbestos substitutes; however their morphology and composition raises concerns. In 1988 the International Agency for Research on Cancer classified fiberglass, rock wool, slag wool, and ceramic fibers as Group 2B, i.e. possibly carcinogenic to humans. In 2002 it reassigned fiberglass, rock and slag wool, and continuous glass filaments to Group 3, not classifiable as carcinogenic to humans. The aim of this study was to verify the cytotoxic and genotoxic effects and oxidative stress production induced by in vitro exposure of human alveolar epithelial cells A549 to glass fibers with a predominant diameter <3 μm (97%) and length >5 μm (93%). A549 cells were incubated with 5, 50, or 100 μg/ml (2.1, 21, and 42 μg/cm(2), respectively) of glass fibers for 72 h. Cytotoxicity and DNA damage were tested by the MTT and the Comet assay, respectively. Oxidative stress was determined by measuring inducible nitric oxide synthase (iNOS) expression by Western blotting, production of nitric oxide (NO) with Griess reagent, and concentration of reactive oxygen species by fluorescent quantitative analysis with 2',7'-dichlorofluorescein-diacetate (DCFH-DA). The results showed that glass fiber exposure significantly reduced cell viability and increased DNA damage and oxidative stress production in a concentration-dependent manner, demonstrating that glass fibers exert cytotoxic and genotoxic effects related to increased oxidative stress on the human alveolar cell line A549.

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In plain English

This was a laboratory experiment on cells grown in dishes, not a study of people. The authors exposed A549 cells to glass fibers for 72 hours at 5, 50 or 100 micrograms per millilitre. A549 cells are a human cell line taken from a lung (bronchoalveolar) carcinoma that has some features of the cells lining the lung's air sacs. Of the fibers, 97% were under 3 micrometres in diameter and 93% were longer than 5 micrometres. Analysis showed they were borosilicate glass with a high content of silica and boron oxide. Cell survival fell significantly even at the lowest dose and fell further at higher doses. DNA damage also rose with dose. The average percentage of fragmented DNA was 10 in untreated cells, 24 at 5, 65 at 50 and 78 at 100 micrograms per millilitre, and the increase was significant compared with untreated cells. Three markers of oxidative stress also rose in exposed cells: reactive oxygen species, the enzyme iNOS, and nitric oxide. The authors concluded that the glass fibers induced cell damage and DNA damage in these cells, likely through oxidative stress. They noted that results in cell cultures may not be reproduced in living organisms.

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 laboratory experiment: cultured human cells were incubated with glass fibers at three concentrations for 72 hours and compared with untreated control cells
• Who was studied: A549 cells, a human cell line derived from a bronchoalveolar carcinoma with some features of alveolar epithelial type II cells, obtained from the American Type Culture Collection; no human or animal subjects
• Exposure: Glass fibers, 97% with diameter under 3 micrometres and 93% with length over 5 micrometres, at 5, 50 or 100 micrograms per millilitre (2.1, 21 or 42 micrograms per square centimetre) for 72 hours
• Main results:
  • Fiber analysis showed borosilicate glass with high silica (SiO2) and boron oxide (B2O3) content and low alkaline oxide content (Table 1: SiO2 80.6%, B2O3 13.0% by weight)
  • Cell viability (MTT test) was significantly reduced already at the lowest dose (5 micrograms per millilitre), and the effect was concentration-dependent; viability results are shown only in a figure, without numbers in the text
  • In the Comet assay, the percentage of fragmented DNA (TDNA) and the tail moment (TMOM) were significantly increased (p less than 0.001) in fiber-exposed cells compared with control cells after 72 hours
  • Percentage of fragmented DNA (mean plus or minus standard error): control 10 ± 2.3; 5 micrograms per millilitre 24 ± 4.6; 50 micrograms per millilitre 65 ± 12.5; 100 micrograms per millilitre 78 ± 9.8. Tail moment: control 23 ± 1.5; 5 micrograms per millilitre 71 ± 6.4 (higher-dose values are printed ambiguously)
  • Glass fibers induced significant iNOS synthesis and NO and ROS production (Table 3). ROS as percent of control: control 0, 70 ± 9.6, 185 ± 12.5 and 268 ± 9.8 at 5, 50 and 100 micrograms per millilitre. iNOS (arbitrary densitometric units): 0.08 ± 0.01, 1.1 ± 0.06, 1.7 ± 0.05 and 2.1 ± 0.2. NO (micromolar): 2 ± 0.02, 8 ± 0.1, 16 ± 0.5 and 25 ± 2
  • The authors reported a strong inverse correlation between decreased cell viability and increased ROS level; no correlation coefficient is given
• The authors' conclusion: The authors concluded that their findings suggest glass fibers induce cytotoxicity and DNA damage in A549 cells, and that these effects are likely mediated by ROS and RNS generation and oxidative stress
• Limitations the authors state:
  • The authors note that a general limitation of in vitro studies is whether their results are reproducible in vivo, so the effects of exposure in living organisms remain unclear

Topics

Medical terms in this study, explained in our Lexicon: Oxidative Stress, Genotoxicity, Vitreous, Carcinogenic, A549 Cells, Comet Assay, Inducible Nitric Oxide Synthase (iNOS), Reactive Oxygen Species (ROS).

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