Free radical activity of natural and heat treated amphibole asbestos

Our plain-English summary of Free radical activity of natural and heat treated amphibole asbestos, by C. Otero Areán, F. Barceló, I. Fenoglio, et al (Journal of Inorganic Biochemistry, 2001).

The study

• Authors: C. Otero Areán, F. Barceló, I. Fenoglio, B. Fubini, F.X. Llabrés i Xamena, M. Tomatis
• Journal: Journal of Inorganic Biochemistry
• Published: 2001;83(2-3):211-6
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The amphibole minerals amosite and crocidolite were subjected to calcination and to hydrothermal treatment in order to study the effect of these heat treatments on the ability of the minerals to trigger formation of free radicals, which is known to be a main factor causing asbestosis and other asbestos-induced diseases. Free radical activity of the natural and heat treated minerals was studied by using supercoiled DNA (pUC18 plasmid) as a target molecule, and also by means of EPR spectroscopy. It was shown that after calcination of the natural minerals at 1073 K their free radical activity was strongly decreased These results, which may have relevant consequences for asbestos technology, were correlated with concomitant alteration of the structure and surface chemistry of the minerals during calcination.

In plain English

This was a laboratory study of two amphibole asbestos minerals, amosite and crocidolite, using standard reference samples from the Union Internationale Contre le Cancer (UICC). No people, animals or cells were studied. The authors calcined (heated) portions of the minerals for 2 hours at 673 K or 1073 K, or heated them in water under pressure for 3 days at 473 K. They then measured how strongly each sample triggered free radicals, using damage to a test DNA molecule (pUC18 plasmid) and a radical-detection method (EPR spectroscopy). Untreated minerals alone caused little DNA damage. The control kept 95% of its DNA in the intact (supercoiled) form, compared with 88% for amosite and 90% for crocidolite. With ascorbic acid and hydrogen peroxide added, intact DNA was 15% for both untreated minerals and 12 to 25% after the lower-temperature treatments. After heating at 1073 K, which also changed the minerals' crystal structure, it was 55% for amosite and 47% for crocidolite. The authors concluded that heating at 1073 K significantly lowered the minerals' capacity to trigger free radical generation. The DNA-damage values were averages of three runs, reported without standard deviations.

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 (cell-free) experiment on mineral samples. Natural and heat-treated minerals were tested for free radical activity using a plasmid DNA strand-break assay and EPR spin-trapping, with X-ray diffraction used to check for structural changes.
• Who was studied: Standard reference samples of amosite and crocidolite from the Union Internationale Contre le Cancer (UICC). No human or animal subjects.
• Exposure: Amosite and crocidolite (amphibole asbestos), either untreated or heat treated. Calcination was for 2 h at 673 K or at 1073 K. Hydrothermal treatment was in autoclaves with distilled water for 3 days at 473 K. Samples were tested with plasmid DNA alone, with ascorbic acid (1.5 mM), with hydrogen peroxide (3 mM), or with ascorbic acid plus hydrogen peroxide (0.1 mM).
• Main results:
  • Crystal structure: X-ray diffraction showed no changes after calcination at 673 K or after hydrothermal treatment. Calcination at 1073 K completely changed the diffraction pattern of amosite and produced new diffraction lines for crocidolite.
  • Minerals alone: the untreated minerals caused only a small percentage of DNA strand breaks. Supercoiled DNA went from 95% in the blank control to 88% (amosite) or 90% (crocidolite). The small variations after heat treatments were described as hardly significant.
  • With ascorbic acid: both untreated minerals reduced supercoiled DNA by about 50% (to 46% for amosite and 51% for crocidolite). Only prior calcination at 1073 K appeared to mitigate the damage (88% for amosite and 80% for crocidolite).
  • With hydrogen peroxide alone (3 mM): DNA damage increased (supercoiled DNA 70% to 80% across samples), but much less than with ascorbic acid and hydrogen peroxide together.
  • With ascorbic acid plus hydrogen peroxide: after calcination at 1073 K, supercoiled DNA remaining was 55% for amosite and 47% for crocidolite. This compared with 12% to 25% for the natural minerals or after the lower-temperature treatments.
  • Only single-strand DNA breaks were produced; double-strand breaks were never observed.
  • EPR: calcination at 673 K did not reduce the hydroxyl radical signal, and a small reduction appeared after hydrothermal treatment. Calcination at 1073 K left amosite with no EPR signal and crocidolite with only a very weak signal.
• The authors' conclusion: The authors concluded that calcination of amosite and crocidolite at 1073 K significantly lowered their capacity to trigger free radical generation. This applied both with ascorbic acid added and with ascorbic acid and hydrogen peroxide together. They described it as tempting to correlate this decrease with the thermal transformation of the minerals' structure.
• Limitations the authors state:
  • DNA-assay experiments were done in triplicate, and the Table 1 values are averages reported without standard deviations. Repeat measurements under the same conditions varied by up to 5%.
  • The small activity of the natural minerals without reducing agents made any conclusion about the effect of heat treatments in that condition uncertain.
  • The new crystal phases formed after calcination at 1073 K were not unambiguously identified.
  • Ascorbic acid could not be used in the EPR experiments because the ascorbate radical signal interfered.
  • The DNA assay and EPR results did not fully agree for the 1073 K samples. The authors suggested this could be due to lower sensitivity of the EPR method.
  • Hydrogen peroxide concentrations in the body are unlikely to be much above micromolar level, whereas 3 mM was needed for significant DNA damage without ascorbic acid.

Topics

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

Medical terms in this study, explained in our Lexicon: Amphibole Asbestos, Amphibole Group, Amosite, Crocidolite.

Related studies

• Detection of surface free radical activity of respirable industrial fibres using supercoiled phi X174 RF1 plasmid DNA — P.S. Gilmour, P.H. Beswick, et al. (1995)
• Supercoiled plasmid DNA as a model target for assessing the generation of free radicals at the surface of fibres — K. Donaldson, P.S. Gilmour, et al. (1995)
• Free radical generation in the toxicity of inhaled mineral particles: the role of iron speciation at the surface of asbestos and silica — I. Fenoglio, L. Prandi, et al. (2001)
• Free radical activity associated with the surface of particles: a unifying factor in determining biological activity? — K. Donaldson, P.H. Beswick, et al. (1996)
• Tobacco smoke: involvement of reactive oxygen species and stable free radicals in mechanisms of oxidative damage, carcinogenesis and synergistic effects with other respirable particles — A. Valavanidis, T. Vlachogianni, et al. (2009)
• Cytokine and free radical responses of alveolar macrophages in vitro to asbestos fibres — L.C. Mongan, T. Jones, et al. (2000)

Browse return to medical research.