The Acute Toxicity of Mineral Fibres: A Systematic In Vitro Study Using Different THP-1 Macrophage Phenotypes

Our plain-English summary of The Acute Toxicity of Mineral Fibres: A Systematic In Vitro Study Using Different THP-1 Macrophage Phenotypes, by S. Mirata, V. Almonti, D. Di Giuseppe, et al (International Journal of Molecular Sciences, 2022).

The study

• Authors: S. Mirata, V. Almonti, D. Di Giuseppe, L. Fornasini, S. Raneri, S. Vernazza, D. Bersani, A.F. Gualtieri, A.M. Bassi, S. Scarfì
• Journal: International Journal of Molecular Sciences
• Published: 2022;23(5)
• Cited by: 16 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Alveolar macrophages are the first line of defence against detrimental inhaled stimuli. To date, no comparative data have been obtained on the inflammatory response induced by different carcinogenic mineral fibres in the three main macrophage phenotypes: M0 (non-activated), M1 (pro-inflammatory) and M2 (alternatively activated). To gain new insights into the different toxicity mechanisms of carcinogenic mineral fibres, the acute effects of fibrous erionite, crocidolite and chrysotile in the three phenotypes obtained by THP-1 monocyte differentiation were investigated. The three mineral fibres apparently act by different toxicity mechanisms. Crocidolite seems to exert its toxic effects mostly as a result of its biodurability, ROS and cytokine production and DNA damage. Chrysotile, due to its low biodurability, displays toxic effects related to the release of toxic metals and the production of ROS and cytokines. Other mechanisms are involved in explaining the toxicity of biodurable fibrous erionite, which induces lower ROS and toxic metal release but exhibits a cation-exchange capacity able to alter the intracellular homeostasis of important cations. Concerning the differences among the three macrophage phenotypes, similar behaviour in the production of pro-inflammatory mediators was observed. The M2 phenotype, although known as a cell type recruited to mitigate the inflammatory state, in the case of asbestos fibres and erionite, serves to support the process by supplying pro-inflammatory mediators.

In plain English

This laboratory study grew a human cell line, THP-1, into three kinds of macrophage. Macrophages are the immune cells that engulf inhaled particles. These were non-activated M0, pro-inflammatory M1 and alternatively activated M2. The cells were exposed for up to 24 hours to crocidolite, chrysotile and fibrous erionite. All three fibres killed cells. In M0 cells after 24 hours, the MTT test showed crocidolite cell death rates of 57%, 49% and 22% at 100, 50 and 10 µg/mL, relative to untreated cells. Fibre-induced cell death was lower in M2 cells. In a 24-hour membrane-damage test, crocidolite gave results comparable to control cells, while chrysotile and erionite caused cell lysis. All fibres raised reactive oxygen species in every cell type, erionite least, and all caused DNA double-strand breaks. Inside M0 cells, chrysotile released chromium, nickel, cobalt and iron, crocidolite iron, and erionite aluminium. M2 cells, usually seen as anti-inflammatory, produced inflammatory signals with the fibres. The authors concluded that M2 macrophages apparently continue to support local inflammation. They noted that their data cover only early stages of toxicity.

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 study comparing three mineral fibres in a human cell line differentiated into three macrophage types (M0, M1, M2)
• Who was studied: Human THP-1 monocytic cells differentiated into M0 macrophages and then into pro-inflammatory M1 macrophages (with interferon-gamma and LPS) or alternatively activated M2 macrophages (with interleukin 4). No people or animals were studied.
• Exposure: UICC standard crocidolite (South Africa), chrysotile from Balangero (Turin, Italy) and fibrous erionite-Na from Jersey (Nevada, USA)
• Main results:
  • In M0 macrophages after 24 h (MTT test), crocidolite caused cell death rates of 57%, 49% and 22% at 100, 50 and 10 µg/mL, compared with control cells
  • In M0 macrophages (MTT test), chrysotile caused cell death rates of 49%, 46% and 14% at the same three concentrations, compared with control cells
  • In M0 macrophages (MTT test), erionite caused significant cell death (45% and 35%) only at the two highest concentrations (100 and 50 µg/mL)
  • Fibre-induced cytotoxicity was lower in M2 macrophages than in M0 and M1 macrophages
  • In the 24-hour LDH test of membrane damage, crocidolite gave values comparable to control in all three macrophage types
  • Chrysotile and erionite caused significant cell lysis
  • Across M0, M1 and M2 macrophages, intracellular reactive oxygen species rose compared with untreated cells: about 1.6-fold with crocidolite, about 1.4-fold with chrysotile and 1.2 to 1.35-fold with erionite
  • Erionite caused a smaller rise in reactive oxygen species than the two asbestos fibres in all three macrophage types
  • After 24 h, DNA double-strand breaks were significantly increased in all three macrophage types
  • In M0 cells, the ratio of DNA-break foci in treated versus untreated cells was about 17 for crocidolite, 12 for chrysotile and 17.2 for erionite
  • In M0 macrophages, intracellular iron rose 6.1-fold with crocidolite and 4.7-fold with chrysotile
  • In M0 macrophages, intracellular aluminium rose significantly only with erionite (2.6-fold)
  • In chrysotile-treated M0 macrophages, intracellular chromium rose 2.3-fold, nickel 4.8-fold and cobalt 4.6-fold compared with control cells
  • In M0 macrophages, release of the inflammatory signal IL-1β rose 1.6-fold with crocidolite and with erionite, and 11.9-fold with chrysotile
  • M2 macrophages, usually considered anti-inflammatory, produced significant pro-inflammatory cytokines with all three fibres
  • Erionite never increased gene activity (transcription) of the cytokines investigated
• The authors' conclusion: The authors concluded that M2 macrophages, although known as cells recruited to counteract inflammation, apparently continue to support local inflammation when in contact with these mineral fibres
• Limitations the authors state:
  • The data cover only the early stages of toxicity and macrophage activation
  • Further studies are needed that model more advanced states of inflammation, for example in 3D-reconstituted human lung tissue and organoids

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: Macrophage, Alveolar Macrophage, Carcinogenic, erionite, Crocidolite, Chrysotile, Cytokine, Cation.

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• New insights into the toxicity of mineral fibres: A combined in situ synchrotron μ-XRD and HR-TEM study of chrysotile, crocidolite, and erionite fibres found in the tissues of Sprague-Dawley rats — A.F. Gualtieri, N. Bursi Gandolfi, et al. (2017)
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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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