Oxidative and cytotoxic stress induced by inorganic granular and fibrous particles

Our plain-English summary of Oxidative and cytotoxic stress induced by inorganic granular and fibrous particles, by S. Helmig, D. Walter, J. Putzier, et al (Molecular Medicine Reports, 2018).

The study

• Authors: S. Helmig, D. Walter, J. Putzier, H. Maxeiner, S. Wenzel, J. Schneider
• Journal: Molecular Medicine Reports
• Published: 2018;17(6):8518-8529
• Cited by: 10 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The hazards of granular and fibrous particles have been associated with the generation of reactive oxygen species (ROS), which in turn is often associated with physicochemical properties exhibited by these particles. In the present study, the ability of various types of fibrous and granular dusts to generate oxidative stress, and their cytotoxicity, was investigated. Biopersistent granular dusts employed in the present study included micro‑ and nanosized titanium dioxide with rutile or anatase crystal structure modifications. Additionally, glass fibres, chrysotile and crocidolite asbestos representative of fibrous dust were selected. Detailed characterisation of particles was performed using scanning electron microscopy, and the effect of exposure to these particles on cell viability and intracellular ROS generation was assessed by PrestoBlue and 2',7'‑dichlorofluorescein assays, respectively. A549 human lung epithelial adenocarcinoma cells were exposed to increasing concentrations (0.1‑10 µg/cm2) of particles and fibres for 24 h. Subsequently, the gene expression of X‑linked inhibitor of apoptosis (XIAP), superoxide dismutase (SOD)1 and SOD2 were analysed by reverse transcription‑quantitative polymerase chain reaction. All investigated granular particles induce ROS production in A549 lung carcinoma cells within 24 h. Hematite increased ROS production in a dose‑dependent manner. A concentration of >1 µg/cm2 TiO2 na with its disordered surface, demonstrated the greatest ability to generate ROS. Therefore, the crystalline surface structure of the particle may be considered as a determinant of the extent of ROS induction by the particle. Fibrous particle compared with granular particles were associated with a lower ability to generate ROS. Glass fibres did not significantly increase ROS production in A549 cells, but elevated gene expression of SOD2 was observed. The results demonstrated that in general, the ability of particles to generate ROS depends on their number and crystal phase. Therefore, the present study helps to understand the cause of particle toxicity.

In plain English

This was a laboratory study on cells, not on people. The authors exposed A549 human lung cancer cells for 24 hours to 0.1 to 10 µg/cm2 of chrysotile and crocidolite asbestos, glass wool insulation fibres, three forms of titanium dioxide, and nanosized hematite (an iron oxide). They measured cell survival, reactive oxygen species (ROS, reactive molecules that can contribute to oxidative stress) inside cells, and mRNA levels of antioxidant-related genes. Chrysotile and crocidolite markedly reduced cell viability at 5 µg/cm2 or more. Glass fibres and the granular particles did not. All granular particles significantly raised ROS. Fibres raised ROS less than granular particles, and glass fibres caused no significant increase. ROS did not differ significantly between chrysotile and crocidolite. SOD2 gene expression (mRNA) was significantly higher than in unexposed cells after chrysotile (P=0.001), crocidolite (P=0.030) and glass fibres (P=0.005). The authors concluded that fibres induce less ROS because they are larger, fewer and have less surface area. They added that the slower settling of asbestos fibres should be considered. They noted their ROS test could not separate oxidants made by the particles from those made by cells.

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) cell culture experiment comparing exposed cells with unexposed control cells
• Who was studied: A549 human lung epithelial adenocarcinoma cell line (lung cancer cells with characteristics of alveolar type II cells), studied in a laboratory in Giessen, Germany
• Exposure: UICC Rhodesian chrysotile asbestos and UICC South African crocidolite asbestos as reference fibres; glass fibres from commercial glass wool insulation; microsized titanium dioxide anatase, nanosized titanium dioxide anatase and rutile; nanosized hematite. Doses were 0.1 to 10 µg/cm2 for 24 hours. Gene expression tests used 1 µg/cm2 of fibres and 100 ng/cm2 of granular particles.
• Main results:
  • Chrysotile and crocidolite markedly reduced viability of the A549 cells at concentrations of 5 µg/cm2 or more
  • No loss of cell viability was seen with glass fibres
  • All granular particles (titanium dioxide forms and hematite) significantly increased ROS in the cells within 24 hours
  • ROS generation differed significantly between nanosized titanium dioxide anatase and nanosized titanium dioxide rutile (P=0.02)
  • All fibrous particles induced ROS at a lower level than the granular particles
  • ROS generation did not differ significantly between chrysotile and crocidolite asbestos
  • Glass fibres did not significantly increase ROS at any concentration compared with controls
  • Compared with unexposed control cells, SOD2 gene expression (mRNA level) was significantly increased after chrysotile (P=0.001), crocidolite (P=0.030), glass fibres (P=0.005), hematite (P=0.037) and nanosized titanium dioxide rutile (P less than 0.001)
  • In the settling test, about 30% of crocidolite fibres had settled onto the cell layer after 240 minutes, compared with more than 70% of chrysotile fibres
• The authors' conclusion: The authors concluded that fibrous particles induce ROS at a much lower level than granular particles because they are larger, fewer in number and have less surface area. They added that for crocidolite and chrysotile the lower sinking rate under the experimental conditions should also be considered.
• Limitations the authors state:
  • The ROS test (DCF) cannot distinguish oxidants generated by the particles themselves from oxidants generated by the cells
  • ROS was measured only after 24 hours of incubation, which the authors say may explain the lower ROS levels seen with fibres

Topics

Medical terms in this study, explained in our Lexicon: Reactive Oxygen Species (ROS), Oxidative Stress, Crystal Structure, Chrysotile, Crocidolite, Scanning Electron Microscopy (SEM), Adenocarcinoma, Apoptosis.

Related studies

• Pulmonary oxidative stress, inflammation and cancer: respirable particulate matter, fibrous dusts and ozone as major causes of lung carcinogenesis through reactive oxygen species mechanisms — A. Valavanidis, T. Vlachogianni, et al. (2013)
• Oxidative stress-mediated cytotoxicity and apoptosis induction by TiO2 nanofibers in HeLa cells — K.M. Ramkumar, C. Manjula, et al. (2012)
• Mitochondria-derived reactive intermediate species mediate asbestos-induced genotoxicity and oxidative stress-responsive signaling pathways — S.X. Huang, M.A. Partridge, et al. (2012)
• Cytotoxicity, oxidative stress and genotoxicity induced by glass fibers on human alveolar epithelial cell line A549 — V. Rapisarda, C. Loreto, et al. (2015)
• Exposure to nano-size titanium dioxide causes oxidative damages in human mesothelial cells: The crystal form rather than size of particle contributes to cytotoxicity — K. Hattori, K. Nakadate, et al. (2017)
• Cultured airway epithelium responses to mineral particles: role of the oxidative stress — C. Guilianelli, A. Baeza-Squiban, et al. (1996)

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