Free radical generation in the toxicity of inhaled mineral particles: the role of iron speciation at the surface of asbestos and silica

Our plain-English summary of Free radical generation in the toxicity of inhaled mineral particles: the role of iron speciation at the surface of asbestos and silica, by I. Fenoglio, L. Prandi, M. Tomatis, et al (Redox Report, 2001).

The study

• Authors: I. Fenoglio, L. Prandi, M. Tomatis, B. Fubini
• Journal: Redox Report
• Published: 2001;6(4):235-41
• Cited by: 56 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Free radical generation at the particle/biological fluid interface is one of the chemical processes that contributes to pathogenicity. In order to investigate the role played by iron, fibres of crocidolite asbestos have been modified by thermal treatments to alter their surface iron content. Two radical mechanisms, HO* from H2O2 and cleavage of a C-H bond, which are both active on the original fibres, have been tested on the modified fibres. C-H cleavage is dependent on Fe(II) abundance and location and is suppressed by surface oxidation while HO* release appears independent of the oxidation state of iron. Quartz specimens with different levels of iron impurities have been tested in a similar manner. A commercially available quartz (Min-U-Sil 5) containing trace levels of iron is also active in both tests, but reactivity is not fully suppressed by treatment with desferrioxamine, which should remove/inactivate iron. The radical yield attained is close to the level produced by a pure quartz dust, suggesting the presence of active sites other than iron. Ascorbic acid reacts with both crocidolite and quartz, with subsequent depletion of the level of antioxidant defences when particle deposition occurs in the lung lining layer. Following treatment with ascorbic acid the radical yield increases with quartz, but decreases with asbestos. Selective removal of iron and silicon from the surface may account for the differences in behaviour of the two particulates.

In plain English

This was a laboratory chemistry study done in test tubes, without cells, animals or people. The authors examined how iron on particle surfaces affects the release of free radicals (highly reactive molecules) from crocidolite asbestos and quartz dust suspended in water. Crocidolite fibres were heated to 400°C either in a vacuum or in air. Heating in vacuum raised the ferrous iron that a chemical could pull from the fibres, from 1.3 to 29 nmol/mg. It also increased one radical reaction, breaking a carbon-hydrogen bond, about 3-fold, while heating in air fully stopped that reaction. The other reaction, hydroxyl radical release from hydrogen peroxide, appeared independent of ferrous iron content. The vacuum effect faded after about 7 days in air. In the hydroxyl radical test, a commercial quartz (Min-U-Sil) was more active than a very pure quartz. After treatment with an iron-removing chemical, its activity fell to the pure quartz's level. Ascorbic acid (vitamin C) increased radical yield from quartz but decreased it from asbestos, and was used up by both. The authors concluded that particle-derived radicals may be one factor in these materials' ability to cause disease.

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: Cell-free laboratory chemistry experiment: free radical release from particle suspensions measured by spin trapping and EPR spectroscopy
• Who was studied: No people or animals. The samples were UICC crocidolite asbestos fibres, a commercial quartz dust (Min-U-Sil 5, with trace iron, 0.075% as Fe2O3) and a pure quartz dust (99.999% SiO2). The work was done at the Università di Torino, Italy.
• Exposure: Crocidolite fibres heated at 400°C in vacuum or in air, and treated with iron chelators (ferrozine, desferrioxamine). Quartz dusts with differing iron content, one treated with desferrioxamine. Both crocidolite and quartz incubated with ascorbic acid. Radical release tested with hydrogen peroxide and with formate.
• Main results:
  • Iron removed from crocidolite over 3 days (nmol/mg). Total iron removed by desferrioxamine: original 155, heated in air 145, heated in vacuo 130. Ferrous iron removed by ferrozine: original 1.3, heated in air 1.1, heated in vacuo 29.
  • For crocidolite, carbon-hydrogen bond cleavage in formate (requiring ferrous iron) was about 3-fold higher in vacuum-heated fibres than in the original fibres, and fully inhibited in air-heated fibres.
  • For crocidolite, hydroxyl radical release in the presence of hydrogen peroxide (Fenton-like reaction) appeared independent of ferrous iron content.
  • In vacuum-heated crocidolite left in air, radical yield fell back to the level of the original fibres after about 7 days.
  • In the hydroxyl radical test, commercial Min-U-Sil quartz was the most active sample. After desferrioxamine treatment, its activity fell to the level of the pure quartz dust.
  • Carbon-hydrogen bond cleavage occurred with the commercial quartz but not with the pure quartz. Desferrioxamine completely inhibited it in the commercial quartz.
  • After treatment with ascorbic acid, radical yield increased with quartz and decreased with crocidolite.
  • The ascorbyl radical signal disappeared after 6 days from both the crocidolite and the quartz suspensions, which the authors took to mean that ascorbate had been totally consumed by reaction with the solid.
• The authors' conclusion: The authors concluded that crocidolite and quartz both release free radicals in a sustained way, so particle-derived reactive oxygen species may be one of the factors contributing to their pathogenicity.

Topics

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

Medical terms in this study, explained in our Lexicon: Crocidolite, Deposition.

Related studies

• Free radical generation at the solid/liquid interface in iron containing minerals — B. Fubini, L. Mollo, et al. (1995)
• Generation of hydroxyl radical by crocidolite asbestos is proportional to surface [Fe3+] — A.J. Ghio, J. Zhang, et al. (1992)
• Free radical activity of natural and heat treated amphibole asbestos — C. Otero Areán, F. Barceló, et al. (2001)
• Enhanced generation of free radicals from phagocytes induced by mineral dusts — V. Vallyathan, J.F. Mega, et al. (1992)
• Free radical activity associated with the surface of particles: a unifying factor in determining biological activity? — K. Donaldson, P.H. Beswick, et al. (1996)
• Free radical activity of synthetic vitreous fibers: iron chelation inhibits hydroxyl radical generation by refractory ceramic fiber — D.M. Brown, C. Fisher, et al. (1998)

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