Using yeast RNA as a probe for generation of hydroxyl radicals by earth materials

Our plain-English summary of Using yeast RNA as a probe for generation of hydroxyl radicals by earth materials, by C.A. Cohn, R. Laffers, M.A. Schoonen (Environmental Science & Technology, 2006).

The study

• Authors: C.A. Cohn, R. Laffers, M.A. Schoonen
• Journal: Environmental Science & Technology
• Published: 2006;40(8):2838-43
• Cited by: 22 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Inhalation of certain types of particulate matter can lead to lung disease. The reactivity of these particles and, in part, the pathologic responses that result are dictated by their physicochemical properties. The ability of particles to induce the generation of reactive oxygen species (ROS), especially hydroxyl radicals in vivo, is one property that has been correlated to the development of lung disease. Several minerals, such as quartz and asbestos, are known to generate hydroxyl radicals and cause lung disease, but many other minerals have never been tested. Here, we describe a technique employing yeast RNA as a probe to screen for mineral-generated hydroxyl radicals. The stability of RNA in the presence of hydrogen peroxide, ferrous iron, hydroxyl radicals, and several common minerals (quartz, albite, forsterite, fayalite, hematite, magnetite, coal, and pyrite) was examined. 3'-(p-Aminophenyl) fluorescein (APF) was used to verify mineral generation of ROS. RNA is stable in the presence of hydrogen peroxide, quartz, and albite; while it degrades in the presence of ferrous iron, hydroxyl radicals, and the other minerals. Coal and pyrite are the most reactive both in RNA degradation and hydroxyl radical generation. This noncellular technique provides a straightforward way to compare many different particles simultaneously. Those particles showing reactivity toward RNA using this method are high-priority candidates for further in vitro and possibly in vivo tests.

In plain English

This laboratory study, done without living cells, described a test that uses yeast RNA as a probe to screen mineral particles for production of hydroxyl radicals, a highly reactive form of oxygen. Asbestos was not tested; the authors mention it, when describing other research, as a mineral known to generate these radicals and cause lung disease. The authors mixed RNA with eight earth materials (quartz, albite, forsterite, fayalite, hematite, magnetite, a bituminous coal and pyrite) at equal surface area and measured how much RNA remained. They also used a fluorescent dye, APF, to detect hydrogen peroxide and hydroxyl radicals from the particles. RNA was unchanged with quartz and albite. Forsterite and fayalite degraded RNA about equally, and hematite and magnetite degraded more. Coal and pyrite were the most reactive: with pyrite, less than 10% of the RNA remained after about 30 seconds and none was detected after 30 minutes. Coal and pyrite produced measurable hydroxyl radicals. The authors noted that the method is not a toxicity test and that the particle size used was not relevant to inhalation. They also noted that RNA loss could reflect adsorption to particles rather than breakdown.

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: Noncellular laboratory (chemical) experiment developing and testing a screening technique
• Who was studied: No people or animals. Eight earth-material samples were tested: quartz, albite, forsterite, fayalite, hematite, magnetite, a bituminous coal (from NIST) and pyrite. The natural mineral samples came from Wards. Control experiments used chemical reagents (hydrogen peroxide, ferrous iron, ferric iron, EDTA, and acid to lower pH). Asbestos was not among the materials tested; the authors refer to it only through other studies.
• Exposure: Yeast RNA solutions (1.5 mg/L) were exposed to crushed mineral particles sieved to the 63-38 micron fraction. Each mineral was loaded at an equal total surface area of 0.5 m2/L. For the APF dye tests, loadings were 100 m2/L for the silicates and 10 m2/L for coal and pyrite. The authors state that this particle size is irrelevant to inhalation exposure.
• Main results:
  • In control experiments, RNA was relatively stable at pH 3.5, with only 10% degradation, and similarly stable with hydrogen peroxide. Hydroxyl radicals generated by the Fenton reaction degraded RNA, and the degradation scaled with hydroxyl radical concentration.
  • RNA exposed to quartz and albite remained unchanged throughout the experiment, as did RNA in the control experiments.
  • Forsterite and fayalite degraded RNA nearly equally. Hematite and magnetite degraded more RNA than forsterite and fayalite.
  • Coal and pyrite were the most reactive. With pyrite, less than 10% of the RNA remained after about 30 seconds, and RNA was no longer detected after 30 minutes. The coal sample degraded less RNA than pyrite.
  • In the APF dye tests, all of the minerals produced hydrogen peroxide except quartz and fayalite. Coal and pyrite produced measurable quantities of hydroxyl radicals.
• The authors' conclusion: The authors concluded that the experiments demonstrate yeast RNA can be used as a probe for mineral-generated hydroxyl radicals. They described the method as simple and able to compare several types of particles at once. They also stated that it is not an assay for toxicity and that its results may only infer a potential for toxicity.
• Limitations the authors state:
  • The technique is not a toxicity assay; results may only infer a potential for toxicity.
  • The presence of RNase (an enzyme that breaks down RNA) in mineral slurries would invalidate the results.
  • Loss of RNA may be due to adsorption onto particles rather than degradation.
  • The particle size fraction used is irrelevant to inhalation exposure.
  • The quartz result (no RNA loss) diverges from other studies. The authors attribute this to differences in quartz source, preparation and experiment type, and state that quartz may still be toxic when inhaled.
  • Hydroxyl radicals were not detected from fayalite. The authors suggest this is probably because APF is more sensitive for detecting hydrogen peroxide than hydroxyl radicals.

Topics

Medical terms in this study, explained in our Lexicon: Hydroxyl Radical, Reactive Oxygen Species (ROS), Forsterite, Hematite.

Related studies

• A study of the synergistic interaction of asbestos fibers with cigarette tar extracts for the generation of hydroxyl radicals in aqueous buffer solution — A. Valavanidis, H. Balomenou, et al. (1996)
• Identifying the reactive sites of hydrogen peroxide decomposition and hydroxyl radical formation on chrysotile asbestos surfaces — M. Walter, W.D.C. Schenkeveld, et al. (2020)
• Asbestos catalyzes hydroxyl and superoxide radical generation from hydrogen peroxide — S.A. Weitzman, P. Graceffa (1984)
• Generation of hydroxyl radical by crocidolite asbestos is proportional to surface [Fe3+] — A.J. Ghio, J. Zhang, et al. (1992)
• 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 generation at the solid/liquid interface in iron containing minerals — B. Fubini, L. Mollo, et al. (1995)

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