Using in vitro iron deposition on asbestos to model asbestos bodies formed in human lung

Our plain-English summary of Using in vitro iron deposition on asbestos to model asbestos bodies formed in human lung, by Z. Shen, D. Bosbach, M.F. Hochella, et al (Chemical Research in Toxicology, 2000).

The study

• Authors: Z. Shen, D. Bosbach, M.F. Hochella, D.L. Bish, M.G. Williams, R.F. Dodson, A.E. Aust
• Journal: Chemical Research in Toxicology
• Published: 2000;13(9):913-21
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Recent studies have shown that iron is an important factor in the chemical activity of asbestos and may play a key role in its biological effects. The most carcinogenic forms of asbestos, crocidolite and amosite, contain up to 27% iron by weight as part of their crystal structure. These minerals can acquire more iron after being inhaled, thereby forming asbestos bodies. Reported here is a method for depositing iron on asbestos fibers in vitro which produced iron deposits of the same form as observed on asbestos bodies removed from human lungs. Crocidolite and amosite were incubated in either FeCl(2) or FeCl(3) solutions for 2 h. To assess the effect of longer-term binding, crocidolite was incubated in FeCl(2) or FeCl(3) and amosite in FeCl(3) for 14 days. The amount of iron bound by the fibers was determined by measuring the amount remaining in the incubation solution using an iron assay with the chelator ferrozine. After iron loading had been carried out, the fibers were also examined for the presence of an increased amount of surface iron using X-ray photoelectron spectroscopy (XPS). XPS analysis showed an increased amount of surface iron on both Fe(II)- and Fe(III)-loaded crocidolite and only on Fe(III)-loaded amosite. In addition, atomic force microscopy revealed that the topography of amosite, incubated in 1 mM FeCl(3) solutions for 2 h, was very rough compared with that of the untreated fibers, further evidence of Fe(III) accumulation on the fiber surfaces. Analysis of long-term Fe(III)-loaded crocidolite and amosite using X-ray diffraction (XRD) suggested that ferrihydrite, a poorly crystallized hydrous ferric iron oxide, had formed. XRD also showed that ferrihydrite was present in amosite-core asbestos bodies taken from human lung. Auger electron spectroscopy (AES) confirmed that Fe and O were the only constituent elements present on the surface of the asbestos bodies, although H cannot be detected by AES and is presumably also present. Taken together for all samples, the data reported here suggest that Fe(II) binding may result from ion exchange, possibly with Na, on the fiber surfaces, whereas Fe(III) binding forms ferrihydrite on the fibers under the conditions used in this study. Therefore, fibers carefully loaded with Fe(III) in vitro may be a particularly appropriate and useful model for the study of chemical characteristics associated with asbestos bodies and their potential for interactions in a biosystem.

In plain English

In this laboratory study, the authors coated crocidolite and amosite asbestos with iron to mimic asbestos bodies from human lungs. Fibers were soaked in ferrous (Fe(II)) or ferric (Fe(III)) chloride for 2 hours, or 2 hours daily for 14 days (crocidolite in either, amosite only Fe(III)). These were compared with amosite asbestos bodies from the lung of a deceased 68-year-old insulator. Crocidolite bound more Fe(II) than amosite, which did not bind Fe(II) well. After 1 mM ferric chloride, both fibers' surface iron-to-silicon ratios were 2.5 times those of untreated fibers. Amosite in 1 mM ferric chloride showed surface bumps of about 1 to 5 nanometers; amosite in 500 µM ferrous chloride was no rougher than untreated amosite. X-ray diffraction found signs of ferrihydrite, a poorly crystallized iron oxide, on long-term Fe(III)-loaded fibers and lung asbestos bodies. Asbestos body surfaces showed only iron and oxygen, plus carbon contamination; the method cannot detect hydrogen, presumed present. The authors concluded that carefully Fe(III)-loaded fibers may usefully model asbestos body chemistry. They noted the loading conditions were not physiological.

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) experiment loading iron onto asbestos fibers, with comparison to asbestos bodies recovered from human lung tissue
• Who was studied: Crocidolite and amosite asbestos fibers (laboratory samples), plus amosite asbestos bodies isolated from the lung tissue of one deceased 68-year-old insulator who had adenocarcinoma
• Exposure: Crocidolite or amosite (1 mg/mL) incubated in FeCl2 (100 or 500 µM) or FeCl3 (100 µM or 1 mM) for 2 h. In long-term loading, fibers were exposed 2 h per day, followed by washing, for 14 days: crocidolite in 500 µM FeCl2 or 1 mM FeCl3, amosite in 1 mM FeCl3 only.
• Main results:
  • In 2 h loading, crocidolite bound more Fe(II) than amosite at both FeCl2 concentrations.
  • Amosite did not bind Fe(II) well, and its binding did not depend on the FeCl2 concentration.
  • Corrected for fiber surface area, amosite bound almost twice as much Fe(III) as crocidolite in 2 h.
  • Over 14 days, crocidolite and amosite both bound Fe(III) cumulatively.
  • Crocidolite bound no more Fe(II) after the first 2 h incubation.
  • By XPS, the surface Fe/Si ratio was 1.5 times that of untreated fibers for crocidolite in 500 µM FeCl2, and 2.5 times for both fibers in 1 mM FeCl3.
  • Amosite treated for 2 h in 1 mM FeCl3 showed surface roughening on atomic force microscopy, with relief of about 1 to 5 nm.
  • Amosite loaded from 500 µM FeCl2 showed no surface roughening compared with control and untreated amosite; minor bumps on all of these samples were attributed to natural surface imperfections and adhering mineral dust.
  • X-ray diffraction of the asbestos bodies from human lung showed a broad hump characteristic of 2-line ferrihydrite.
  • The long-term Fe(III)-loaded amosite and crocidolite showed the same weak ferrihydrite hump.
  • The ferrihydrite hump was not seen in the control fibers.
  • Auger analysis of the segmented asbestos bodies from human lung detected only iron and oxygen on the surface, plus adventitious carbon; hydrogen cannot be detected by this method and was presumed present.
• The authors' conclusion: The authors concluded that Fe(II) binding is probably ion exchange, while Fe(III) binding forms ferrihydrite on the fibers. They concluded that fibers carefully loaded with Fe(III) in vitro may be an appropriate and useful model for studying the chemical characteristics of asbestos bodies.
• Limitations the authors state:
  • The iron-loading conditions did not reflect physiological binding conditions.
  • XPS could not be done on the human lung asbestos bodies because too little material was available.
  • The XPS Fe/Si ratios are semiquantitative.
  • AFM images comparing untreated and iron-loaded crocidolite were not conclusive because the fibers are so narrow.
  • The ferrihydrite signals in the XRD patterns were very weak, and weaker still for the laboratory-loaded fibers.
  • The laboratory deposits had not yet formed the large, segmented coatings seen on lung asbestos bodies.

Topics

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

Medical terms in this study, explained in our Lexicon: Deposition, Asbestos Bodies, Carcinogenic, Crocidolite, Amosite, Crystal Structure, X-Ray Diffraction (XRD), Ferrihydrite.

Related studies

• Iron enhances uptake of mineral particles and increases lipid peroxidation in tracheal epithelial cells — B. Keeling, K.Y. Li, et al. (1994)
• Transcriptional activation of inflammasome components by Libby amphibole and the role of iron — J.H. Shannahan, A.J. Ghio, et al. (2012)
• Iron associated with asbestos bodies is responsible for the formation of single strand breaks in phi X174 RFI DNA — L.G. Lund, M.G. Williams, et al. (1994)
• Mobilization of iron from urban particulates leads to generation of reactive oxygen species in vitro and induction of ferritin synthesis in human lung epithelial cells — K.R. Smith, A.E. Aust (1997)
• Activation of UICC crocidolite: the effect of conversion of some ferric ions to ferrous ions — M. Gulumian, D.J. Bhoolia, et al. (1993)
• Iron topochemistry and surface reactivity of amphibole asbestos: relations with in vitro toxicity — A. Pacella, G.B. Andreozzi, et al. (2012)

Browse more research in Chemical Research in Toxicology, or return to medical research.