Participation of nitric oxide and iron in the oxidation of DNA in asbestos-treated human lung epithelial cells

Our plain-English summary of Participation of nitric oxide and iron in the oxidation of DNA in asbestos-treated human lung epithelial cells, by C.C. Chao, S.H. Park, A.E. Aust (Archives of Biochemistry and Biophysics, 1996).

The study

• Authors: C.C. Chao, S.H. Park, A.E. Aust
• Journal: Archives of Biochemistry and Biophysics
• Published: 1996;326(1):152-7
• Cited by: 94 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Treatment of human lung epithelial (A549) cells with crocidolite resulted in the formation of 8-hydroxy-2'-deoxyguanosine (8-OHdG) in the DNA, synthesis of mRNA for the inducible form of nitric oxide synthase (NOS), and increased intracellular nitrite (NO2-), a stable oxidation product of NO. Iron, associated with crocidolite, was involved in both NO2- and 8-OHdG formation. Addition of the NOS inhibitor, aminoguanidine (AG), reduced intracellular NO2- and prevented formation of 8-OHdG in crocidolite-treated cells, suggesting that NO was required in 8-OHdG formation. Addition of an NO-generating compound, diethyltriamine/NO, with AG and crocidolite resulted in recovery of 8-OHdG, further supporting a role for NO in oxidation of deoxyguanosine.

In plain English

This was a laboratory study of human lung cells grown in dishes, not of people. The authors exposed a human lung epithelial cell line (A549) to crocidolite asbestos, which contained 27% iron by weight. They measured oxidative DNA damage (8-OHdG), nitric oxide production (as nitrite), and messenger RNA for inducible nitric oxide synthase (iNOS). Crocidolite was toxic to the cells in a concentration-dependent way, measured as reduced colony-forming ability, and raised 8-OHdG up to 10 times the level in untreated cells. Crocidolite-treated cells made iNOS messenger RNA and significantly more nitrite than untreated cells. Crocidolite with part of its surface iron removed produced at least 60% less 8-OHdG. Adding the nitric oxide synthase inhibitor aminoguanidine lowered nitrite and prevented the crocidolite-related rise in 8-OHdG. Adding a nitric oxide-releasing compound (DETA/NO) brought 8-OHdG partly back up, while DETA/NO alone did not significantly raise 8-OHdG. The authors concluded that both iron and nitric oxide appeared essential for this DNA damage. They suggested that if the same happens in the body, it may lead to tumor formation in exposed lung cells.

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: In vitro laboratory experiment on a cultured human cell line (cell culture study)
• Who was studied: A549 human lung epithelial cell line (described as having characteristics of alveolar epithelial type II cells), obtained from the American Type Culture Collection and studied at Utah State University. No people or animals were studied.
• Exposure: Crocidolite asbestos containing 27% iron by weight. The scanned text prints doses of 1.5, 3.0 and 6.0 'mg/cm2' of culture surface. Other treatments were:
• crocidolite with about 8% of its total (surface) iron removed by desferrioxamine B ('DF crocidolite');
• culture medium with iron (F12) or without iron (F12-Fe);
• the nitric oxide synthase inhibitor aminoguanidine;
• the nitric oxide-releasing compound DETA/NO.
  Exposure lasted 24 hours for DNA measurements and 48 hours for nitrite measurements.
• Main results:
  • Cytotoxicity was measured as relative cloning (colony-forming) ability. Relative survival fell as the crocidolite dose rose: 65 plus or minus 5% at 1.5, 45 plus or minus 5% at 3.0 and 14 plus or minus 4% at 6.0 (per cm2), versus 100% in untreated cells.
  • 8-OHdG per 10^5 deoxyguanosine in the cells' DNA was 1.0 plus or minus 0.4 in untreated cells. In crocidolite-treated cells it was 4.8 plus or minus 2.0 at 1.5, 10.4 plus or minus 2.1 at 3.0 and 10.2 plus or minus 1.7 at 6.0 (all significantly different from control, P less than 0.01). The level stayed constant above 3 per cm2.
  • Crocidolite added to untreated cells just before DNA isolation gave 8-OHdG of 1.2 plus or minus 0.3, versus 1.0 plus or minus 0.4 in controls, which was not a significant elevation. The authors took this as showing that the 8-OHdG increase was not an artifact of the DNA isolation method.
  • Cells treated with DF crocidolite (partly iron-depleted) had at least 60% less 8-OHdG than cells treated with unmodified crocidolite: 3.6 plus or minus 0.1 versus 10.2 plus or minus 1.7 in iron-containing medium, and 1.1 plus or minus 0.1 versus 7.9 plus or minus 1.8 in iron-free medium. The authors reported that the amount of fiber taken up by the cells was approximately the same for both fiber types.
  • In cells treated with DF crocidolite, 8-OHdG was three times higher in iron-containing medium than in iron-free medium.
  • Intracellular nitrite (pmol per 10^6 cells, 48 h) was significantly higher in crocidolite-treated cells than in untreated cells: 384 plus or minus 48 versus 64 plus or minus 13 in iron-containing medium, and 195 plus or minus 47 versus 66 plus or minus 15 in iron-free medium. Removing iron from the fibers (DF crocidolite) lowered nitrite by at least 33%, to 259 plus or minus 26 and 69 plus or minus 22 respectively.
  • Messenger RNA for inducible nitric oxide synthase (iNOS) was detected in crocidolite-treated cells and in cells treated with a cytokine/LPS mixture.
  • Adding aminoguanidine with crocidolite significantly lowered nitrite, but did not eliminate it. Nitrite was 166 plus or minus 30 in iron-containing medium and 89 plus or minus 13 in iron-free medium. 8-OHdG fell to 0.4 plus or minus 0.2 and 0.3 plus or minus 0.1, compared with 10.2 and 7.9 with crocidolite alone.
  • Adding the nitric oxide-releasing compound DETA/NO to cells given crocidolite plus aminoguanidine significantly raised 8-OHdG, to 3.6 plus or minus 1.9 in iron-containing medium and 2.4 plus or minus 1.2 in iron-free medium.
  • DETA/NO alone, without crocidolite, did not significantly raise 8-OHdG (0.7 plus or minus 0.1 and 0.4 plus or minus 0.1), even though nitrite in the cells reached approximately 210 pmol per 10^6 cells.
• The authors' conclusion: The authors concluded that crocidolite treatment of human lung epithelial cells increased nitric oxide synthesis and the formation of the modified DNA base 8-OHdG. They found that both iron and nitric oxide appeared essential for 8-OHdG formation. They suggested that if this occurs in the body, it may lead to tumor formation in asbestos-exposed target cells in the lung.

Topics

Medical terms in this study, explained in our Lexicon: Crocidolite, 8-OHdG.

Related studies

• Regulation of nitric oxide synthase induction by iron and glutathione in asbestos-treated human lung epithelial cells — S.H. Park, A.E. Aust (1998)
• Nitric oxide (NO) synthase activity in the lung and NO synthesis in alveolar macrophages of rats increased on exposure to asbestos — H. Iguchi, S. Kojo, et al. (1996)
• Radical oxidation reactions of the purine moiety of 2'-deoxyribonucleosides and DNA by iron-containing minerals — M. Berger, M. de Hazen, et al. (1993)
• Mobilization of iron from urban particulates leads to generation of reactive oxygen species in vitro and induction of ferritin synthesis in human lung epithelial cells — K.R. Smith, A.E. Aust (1997)
• Iron inhibits the nitric oxide synthesis elicited by asbestos in murine macrophages — E. Aldieri, D. Ghigo, et al. (2001)
• Induction of ferritin synthesis in human lung epithelial cells treated with crocidolite asbestos — R. Fang, A.E. Aust (1997)

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