New insights on the biomineralisation process developing in human lungs around inhaled asbestos fibres

Our plain-English summary of New insights on the biomineralisation process developing in human lungs around inhaled asbestos fibres, by F. Bardelli, G. Veronesi, S. Capella, et al (Scientific Reports, 2017).

The study

• Authors: F. Bardelli, G. Veronesi, S. Capella, D. Bellis, L. Charlet, A. Cedola, E. Belluso
• Journal: Scientific Reports
• Published: 2017;7:44862
• Cited by: 15 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Once penetrated into the lungs of exposed people, asbestos induces an in vivo biomineralisation process that leads to the formation of a ferruginous coating embedding the fibres. The ensemble of the fibre and the coating is referred to as asbestos body and is believed to be responsible for the high toxicological outcome of asbestos. Lung tissue of two individuals subjected to prolonged occupational exposure to crocidolite asbestos was investigated using synchrotron radiation micro-probe tools. The distribution of K and of elements heavier than Fe (Zn, Cu, As, and Ba) in the asbestos bodies was observed for the first time. Elemental quantification, also reported for the first time, confirmed that the coating is highly enriched in Fe (~20% w/w), and x-ray absorption spectroscopy indicated that Fe is in the 3+ oxidation state and that it is present in the form of ferritin or hemosiderin. Comparison of the results obtained studying the asbestos bodies upon removing the biological tissue by chemical digestion and those embedded in histological sections, allowed unambiguously distinguishing the composition of the asbestos bodies, and understanding to what extent the digestion procedure altered their chemical composition. A speculative model is proposed to explain the observed distribution of Fe.

In plain English

This laboratory study examined asbestos bodies, which are asbestos fibres coated with an iron-rich layer that forms inside the lung. The tissue came from forensic autopsies of two former workers of an asbestos plant in North-West Italy that made fibre-reinforced cement products. Both workers had pulmonary asbestosis. One also had pleural mesothelioma and the other had lung cancer. The fibres were crocidolite. The authors used synchrotron X-ray methods and electron microscopy on two kinds of sample: bodies freed by chemically digesting the tissue, and bodies still inside tissue sections. The outer coating held about 14% iron by weight, similar to a ferritin standard. The inner part held two to almost three times as much, about 27 to 39%. The iron was in the 3+ form and matched a ferritin standard. Copper, zinc, arsenic and barium were found on the extracted bodies. Barium was not detected in bodies left in tissue, and the authors said this would suggest it was introduced during digestion. Phosphorus, potassium and calcium sat in the coating but were removed by digestion. The authors concluded the coatings are mainly ferritin and/or hemosiderin. They proposed a model of coating formation that they called speculative.

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 analysis of autopsy lung tissue (two cases) using synchrotron X-ray fluorescence and X-ray absorption spectroscopy, plus electron microscopy
• Who was studied: Lung tissue from two former workers of an asbestos plant in North-West Italy, collected after forensic autopsy. Both had pulmonary asbestosis; case A also had pleural mesothelioma and case B also had lung cancer.
• Exposure: Occupational exposure at a plant producing fibre-reinforced cement products (90% cement, 10% asbestos); fibres in the lungs identified as crocidolite
• Main results:
  • In both cases, the number of asbestos bodies per gram of dry lung tissue was well above the European Respiratory Society guideline level that indicates high occupational exposure
  • Iron in asbestos bodies (both extracted and embedded in tissue) was about 300 times higher than in the surrounding lung tissue and about 1000 times higher than in a bovine liver reference
  • Iron in the outer part of the asbestos bodies was similar to the ferritin standard, about 14% by weight
  • The inner part of the asbestos bodies contained two to almost three times as much iron as the outer part, about 27 to 39% by weight
  • Iron in the coating was in the 3+ oxidation state and in the form of ferritin or hemosiderin
  • Copper, zinc, arsenic and barium were detected on asbestos bodies extracted by digestion, at 0.02 to 0.3% by weight
  • Barium was not detected (or was below the 0.001% detection limit) in asbestos bodies embedded in tissue sections; the authors said this would suggest it was introduced during the digestion procedure
  • Phosphorus, potassium and calcium were associated with the coating of asbestos bodies but were dissolved and removed by chemical digestion
• The authors' conclusion: The authors concluded that hematite and metallic iron are absent or present well below 5%, and that the asbestos bodies are mainly composed of ferritin and/or hemosiderin. They also proposed a speculative model to explain the iron distribution.
• Limitations the authors state:
  • The proposed model of how asbestos bodies change over time is speculative and cannot be confirmed in laboratory time-scale experiments
  • Copper, zinc and arsenic could not be confirmed in tissue-embedded bodies, so their presence on extracted bodies may partly reflect contamination during digestion
  • Elements lighter than iron were not quantified because of calibration problems
  • Ferritin and hemosiderin are difficult to tell apart

Topics

The National Library of Medicine indexes this study under subjects our site covers: Asbestosis.

Medical terms in this study, explained in our Lexicon: Asbestos Body Formation, Occupational Exposure, Crocidolite, Asbestos Bodies, Ferritin.

Related studies

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• Deposition of inhaled asbestos and man-made mineral fibres in the respiratory tract — A. Morgan (1995)
• 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)
• Stability of mineral fibres in contact with human cell cultures. An in situ μXANES, μXRD and XRF iron mapping study — S. Pollastri, A.F. Gualtieri, et al. (2016)
• Human exposure to trace elements and PCDD/Fs around a hazardous waste landfill in Catalonia (Spain) — M. Herrero, J. Rovira, et al. (2020)
• Asbestos dust as a nucleation center in the calcification of old fibrous tissue lesions, and the possible association of this process to the formation of asbestos bodies — J.M. Davis (1970)

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