Closing the knowledge gap on the composition of the asbestos bodies

Our plain-English summary of Closing the knowledge gap on the composition of the asbestos bodies, by F. Bardelli, C. Giacobbe, P. Ballirano, et al (Environmental Geochemistry and Health, 2023).

The study

• Authors: F. Bardelli, C. Giacobbe, P. Ballirano, V. Borelli, F. Di Benedetto, G. Montegrossi, D. Bellis, A. Pacella
• Journal: Environmental Geochemistry and Health
• Published: 2023;45(7):5039-5051
• Cited by: 2 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Asbestos bodies (AB) form in the lungs as a result of a biomineralization process initiated by the alveolar macrophages in the attempt to remove asbestos. During this process, organic and inorganic material deposit on the foreign fibers forming a Fe-rich coating. The AB start to form in months, thus quickly becoming the actual interface between asbestos and the lung tissue. Therefore, revealing their composition, and, in particular, the chemical form of Fe, which is the major component of the AB, is essential to assess their possible role in the pathogenesis of asbestos-related diseases. In this work we report the result of the first x-ray diffraction measurements performed on single AB embedded in the lung tissue samples of former asbestos plant workers. The combination with x-ray absorption spectroscopy data allowed to unambiguously reveal that Fe is present in the AB in the form of two Fe-oxy(hydroxides): ferrihydrite and goethite. The presence of goethite, which can be explained in terms of the transformation of ferrihydrite (a metastable phase) due to the acidic conditions induced by the alveolar macrophages in their attempt to phagocytose the fibers, has toxicological implications that are discussed in the paper.

© 2023. The Author(s).

In plain English

This laboratory study examined asbestos bodies: asbestos fibers in the lungs coated with iron-rich layers of minerals and proteins. The tissue was taken after death from the lungs of two former workers of an asbestos-cement plant in Piedmont, North-Western Italy. The workers were exposed mainly to chrysotile, but also to crocidolite and amosite. Tissue fragments each holding one asbestos body were cut out, and the bodies, still embedded in tissue, were studied by synchrotron x-ray diffraction (three bodies) and x-ray absorption spectroscopy (eight bodies). The uncoated core of one body matched crocidolite, and its coating matched goethite, an iron oxyhydroxide. Across four regions of a representative body, the best spectroscopy fit put about 68 percent (plus or minus 8) of the iron as ferrihydrite and about 31 percent (plus or minus 7) as goethite. A test showed the tissue-fixation steps did not turn ferrihydrite into goethite. The authors concluded that goethite suggests the bodies were exposed to pH far from neutral. Citing other studies, they suggested goethite may add to the bodies' toxicity, but said further research is needed.

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 study of post-mortem human lung tissue using synchrotron x-ray diffraction and x-ray absorption spectroscopy on single asbestos bodies embedded in tissue, plus thermodynamic calculations
• Who was studied: Non-cancerous lung tissue, taken post-mortem from the lower lobes, of two former workers of an asbestos-cement plant in Piedmont, North-Western Italy (operated 1946 to 1982). Case A: 81-year-old male, 27 years of exposure, asbestosis (grade 3), pleural plaques and pleural mesothelioma. Case B: 80-year-old female, more than 10 years of exposure, asbestosis (grade 4), pleural plaques and lung cancer.
• Exposure: Prolonged occupational exposure to asbestos in an asbestos-cement plant, mainly chrysotile, but also crocidolite and amosite
• Main results:
  • Tissue fragments about 100 µm across, each containing a single asbestos body, were cut from 10 µm-thick tissue sections with a laser micro-dissector, so the bodies were measured while still embedded in the tissue
  • X-ray diffraction was performed on different regions of three asbestos bodies
  • The diffraction pattern from the uncoated inner fiber of a representative asbestos body matched the UICC crocidolite reference
  • The diffraction pattern from the iron coating of the same representative asbestos body matched the reference pattern of goethite
  • X-ray absorption spectra were acquired for eight asbestos bodies. For four regions of a representative body, the best fit of the iron spectrum was about 68 plus or minus 8 percent ferrihydrite and about 31 plus or minus 7 percent goethite. These are proportions of the iron present as each form, not of the whole body.
  • Adding hematite to the fit gave a contribution of about 2 percent. Because no hematite was seen by diffraction, the authors considered this likely an artifact of the fitting.
  • Synthetic ferrihydrite put through the same fixation protocol as the tissue showed no goethite. The authors took this as confirmation that sample preparation did not change the iron form.
  • Thermodynamic calculations indicated that ferrihydrite should evolve into goethite, hematite and magnetite. Because only ferrihydrite and goethite were observed, the authors suggested that the rate of transformation (kinetic control) plays a role.
• The authors' conclusion: The authors concluded that iron in the asbestos bodies is present as ferrihydrite and goethite. They proposed that goethite formed from ferrihydrite under acidic conditions, created as macrophages repeatedly tried to engulf the fibers, so the bodies were likely exposed to pH far from neutral. Citing other studies on goethite's toxicity, they suggested goethite may contribute to the cytotoxic properties of asbestos bodies.
• Limitations the authors state:
  • The authors stated that further research is needed to support the idea that goethite contributes to the cytotoxic properties of asbestos bodies

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 Bodies, Alveolar Macrophage, X-Ray Diffraction (XRD), Ferrihydrite, Goethite.

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