Supercoiled plasmid DNA as a model target for assessing the generation of free radicals at the surface of fibres

Our plain-English summary of Supercoiled plasmid DNA as a model target for assessing the generation of free radicals at the surface of fibres, by K. Donaldson, P.S. Gilmour, P.H. Beswick (Experimental and Toxicologic Pathology, 1995).

The study

• Authors: K. Donaldson, P.S. Gilmour, P.H. Beswick
• Journal: Experimental and Toxicologic Pathology
• Published: 1995;47(4):235-7
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The ability of respirable amosite and crocidolite asbestos, refractory ceramic fibres (RCFs) and man made vitreous fibres (MMVFs) to cause free radical injury to plasmid, phiX174 RFI DNA was assessed. The amosite and crocidolite asbestos caused substantial damage to the DNA and, in the main, the free radicals responsible for the asbestos-mediated DNA damage were hydroxyl radicals as determined by inhibition with mannitol. Asbestos fibre-mediated damage to the DNA was completely ameliorated by the chelation of fibre-associated iron by pre-treatment of fibres with desferrioxamine-B, confirming the importance of iron in the production of free radicals. MMVFs and RCFs produced modest free radical damage to the DNA, which was prevented by mannitol but not by iron chelation.

In plain English

This was a short laboratory experiment on fibre samples, not a study of people or animals. The authors incubated a circular type of DNA (plasmid DNA) with equal numbers of fibres: amosite asbestos, crocidolite asbestos, four refractory ceramic fibres (RCFs) and four man-made vitreous fibres (MMVFs). They then measured the proportions of different plasmid DNA forms, which served as an indication of damage by free radicals (highly reactive molecules). The asbestos fibres caused the greatest damage. The man-made fibres caused marginal damage, which reached statistical significance for the RCFs but not for the MMVFs. Mannitol, which removes a free radical called the hydroxyl radical, reduced the damage caused by both asbestos types. Pre-treating the asbestos fibres with desferrioxamine-B, a chemical that binds iron, reduced the asbestos damage. The article's summary describes this as completely ameliorated. The small damage from the man-made fibres was prevented by mannitol but not by binding iron. The authors concluded that the disease-causing activity of these asbestos fibres may be related to hydroxyl radical damage to molecules such as DNA, via iron.

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 using plasmid DNA as a target for fibre-generated free radicals
• Who was studied: fibre samples, not people: amosite asbestos (as used in an earlier study), and crocidolite asbestos, refractory ceramic fibres (RCF) 1, 2, 3 and 4 and man-made vitreous fibres (MMVF) 10, 11, 21 and 22 from the TIMA Fibre Repository, tested on phiX174 plasmid DNA
• Exposure: 290 ng of plasmid DNA incubated for 8 hours at 37 degrees C with each fibre type at an equal number of 616,600 WHO fibres (longer than 5 micrometres, under 3 micrometres in diameter, aspect ratio over 3 to 1) in 20 microlitres of solution. Some tests added mannitol (final 4 mM). Others used fibres pre-treated with 10 mM desferrioxamine-B, which were then transferred together with the desferrioxamine-B.
• Main results:
  • Damage was assessed from the proportions of the plasmid DNA forms, which the authors used as an indication of free radical damage.
  • The asbestos fibres (amosite and crocidolite) caused the greatest DNA damage. The man-made fibres produced marginal damage.
  • The damage from the man-made fibres was consistent but small. It did not reach statistical significance for MMVFs but did for RCFs.
  • Mannitol (4 mM), a hydroxyl radical scavenger, reduced the DNA damage caused by long amosite and crocidolite fibres.
  • Pre-treating the asbestos fibres with desferrioxamine-B, which binds (chelates) iron, reduced the asbestos-caused DNA damage. The article's summary describes this as complete amelioration.
  • The modest damage from MMVFs and RCFs was prevented by mannitol but not by iron chelation.
• The authors' conclusion: The authors concluded that the disease-causing (pathogenic) activity of these asbestos fibres may be related to their ability to cause hydroxyl radical-mediated damage to macromolecules, particularly DNA, via iron. They also concluded that iron does not play a role in the free radical activity of RCFs and MMVFs in this model.

Topics

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

Medical terms in this study, explained in our Lexicon: Amosite, Crocidolite, Vitreous, Hydroxyl Radical.

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)
• Free radical activity of natural and heat treated amphibole asbestos — C. Otero Areán, F. Barceló, et al. (2001)
• 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)
• 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 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 of industrial fibers: role of iron in oxidative stress and activation of transcription factors — P.S. Gilmour, D.M. Brown, et al. (1997)

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