Radical oxidation reactions of the purine moiety of 2'-deoxyribonucleosides and DNA by iron-containing minerals

Our plain-English summary of Radical oxidation reactions of the purine moiety of 2'-deoxyribonucleosides and DNA by iron-containing minerals, by M. Berger, M. de Hazen, A. Nejjari, et al (Carcinogenesis, 1993).

The study

• Authors: M. Berger, M. de Hazen, A. Nejjari, J. Fournier, J. Guignard, H. Pezerat, J. Cadet
• Journal: Carcinogenesis
• Published: 1993;14(1):41-6
• Cited by: 34 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The radical oxidation capability of several classes of iron minerals, including biotite, hematite, magnetite, minette, nemalite, pyrite, vivianite and two chrysotiles (asbestos), was investigated by using a double experimental approach. One involved the electron spin resonance spin-trapping measurement of organic radicals obtained by the reaction of activated oxygen species, released upon incubation of the minerals in phosphate buffered solutions with formate used as the target molecule. In addition, the formation of mineral-mediated oxidation purine decomposition products, including 7,8-dihydro-8-oxo-2'-deoxyguanosine and 7,8-dihydro-8-oxo-2'-deoxyadenosine, was searched within nucleosides and DNA by using specific and sensitive HPLC electrochemical assays. Emphasis was placed on the mechanistic aspects of the radical oxidation reactions involved in the formation of the two C(8) hydroxylated purine decomposition products.

In plain English

This was a laboratory chemistry study done in France. No people or animals were studied. The authors tested whether iron-containing minerals placed in water produce oxidizing chemicals, and whether those chemicals damage DNA building blocks. The materials were:

• two chrysotile asbestos samples from the UICC
• nemalite from a Quebec chrysotile mine
• air-aged pyrite, vivianite and biotite
• the Lorraine iron ore called 'minette'
• hematite and magnetite
• dissolved ferrous sulfate

They measured two oxidation products, 8-OHdGuo and 8-OHdAdo, in single nucleosides and in calf thymus DNA. Air-aged pyrite, nemalite and ferrous sulfate were the most active on nucleosides. The two chrysotiles, hematite, magnetite and minette showed weak activity. In DNA, 8-OHdGuo was produced by pyrite (60 ng per 100 micrograms of DNA), vivianite (26 ng) and nemalite (15 ng). None was detected with either chrysotile. No 8-OHdAdo was detected in DNA with any mineral tested. The authors said the DNA results agreed with the nucleoside results. They noted that the reaction mechanism is not fully understood. They also said other DNA oxidation products were likely formed but were not measured.

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, in vitro) chemistry experiment: radical-trapping (electron spin resonance) measurement of formate oxidation, and HPLC electrochemical detection of oxidized purine nucleosides in single nucleosides and isolated DNA
• Who was studied: No human or animal subjects. Mineral samples: two UICC chrysotiles (A from Zimbabwe, B from Canada), nemalite from a Quebec chrysotile mine, biotite, hematite, magnetite, 'minette' (Lorraine iron ore), air-aged pyrite, vivianite, and ferrous sulfate. Targets: the nucleosides dAdo and dGuo, and calf thymus DNA.
• Exposure: Incubation with iron-containing minerals, including chrysotile asbestos. For the nucleoside and DNA tests, 1 mg of mineral was added to the solution, typically for 10 minutes.
• Main results:
  • Air-aged pyrite, nemalite and ferrous sulfate were the most efficient at producing 8-OHdAdo and 8-OHdGuo from single nucleosides.
  • The two chrysotiles, hematite, magnetite and minette showed weak activity on nucleosides. Vivianite and, to a lesser extent, biotite showed intermediate activity.
  • The weak result for the chrysotiles was not explained by the chrysotiles binding the nucleosides.
  • In calf thymus DNA, 8-OHdGuo was formed per 100 micrograms of DNA by air-aged pyrite (60 ng; 0.323% of guanine residues), vivianite (26 ng; 0.132%) and nemalite (15 ng; 0.081%), according to Table IV.
  • No 8-OHdGuo was detected in DNA exposed to chrysotile A or chrysotile B.
  • No 8-OHdAdo was detected in DNA with any of the minerals tested.
  • Among the six more active solids, ability to oxidize formate correlated with ability to form 8-OHdAdo (R = 0.98).
  • For comparison, 4.25 Gy of gamma rays produced only 0.56 ng of 8-OHdGuo in calf thymus DNA under the same concentration conditions.
• The authors' conclusion: The authors concluded that the DNA results agreed with the minerals' activity toward single nucleosides. They also said the ratio of 8-OHdAdo to 8-OHdGuo should give information about the kind of oxidizing conditions involved.
• Limitations the authors state:
  • The mechanism of the hydroxylation reactions is not yet completely understood.
  • Other oxidation products of DNA bases are likely produced but were not measured.

Topics

Medical terms in this study, explained in our Lexicon: Hematite, Chrysotile.

Related studies

• Free radical generation at the solid/liquid interface in iron containing minerals — B. Fubini, L. Mollo, et al. (1995)
• Microsomal lipid peroxidation and oxy-radicals formation are induced by insoluble iron-containing minerals — M. Fontecave, M. Jaouen, et al. (1990)
• Participation of nitric oxide and iron in the oxidation of DNA in asbestos-treated human lung epithelial cells — C.C. Chao, S.H. Park, et al. (1996)
• Effect of mineral particles containing iron on primary cultures of rabbit tracheal epithelial cells: possible implication of oxidative stress — C. Guilianelli, A. Baeza-Squiban, et al. (1993)
• Iron from a geochemical viewpoint. Understanding toxicity/pathogenicity mechanisms in iron-bearing minerals with a special attention to mineral fibers — A.F. Gualtieri, G.B. Andreozzi, et al. (2019)
• Chemical differences between long and short amosite asbestos: differences in oxidation state and coordination sites of iron, detected by infrared spectroscopy — A. Graham, J. Higinbotham, et al. (1999)

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