A study of the synergistic interaction of asbestos fibers with cigarette tar extracts for the generation of hydroxyl radicals in aqueous buffer solution

Our plain-English summary of A study of the synergistic interaction of asbestos fibers with cigarette tar extracts for the generation of hydroxyl radicals in aqueous buffer solution, by A. Valavanidis, H. Balomenou, I. Macropoulou, et al (Free Radical Biology & Medicine, 1996).

The study

• Authors: A. Valavanidis, H. Balomenou, I. Macropoulou, I. Zarodimos
• Journal: Free Radical Biology & Medicine
• Published: 1996;20(6):853-8
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Several models attempt to explain the synergistic increase in lung cancer among workers exposed to asbestos fibers, who were smokers at the same time. It is known that reactive oxygen species (ROS) are important mediators in asbestos-induced diseases, especially cancer. We studied quantitatively the formation of ROS (by spin trapping with DMPO) in aqueous buffer suspensions containing crocidolite (UICC), chrysotile (UICC and commercial, long fibers) alone, and in combination with aqueous cigarette tar extracts. It was observed that asbestos and cigarette tar act in a cooperative or synergistic way in the generation of hydroxyl radical spin adducts. Grinding of asbestos fibers and addition of EDTA (iron chelator) enhanced the intensity of the ESR signal. This enhancement progressed with time, probably due to the reaction of the extracted iron with the slow released hydrogen peroxide from tar extracts. It was observed a fivefold increase in the ESR signal (for crocidolite and aqueous tar extracts) in the formation of hydroxyl radicals via an iron-catalyzed Fenton reaction. These experimental results are suggest to be strong evidence to the fact that lung cancer has been found in asbestos workers exposed to high concentrations of fibers in the working environment who were smokers, and only rarely in nonsmokers.

In plain English

This was a laboratory report from the University of Athens. It tested whether cigarette tar extracts increased the hydroxyl radicals (a reactive form of oxygen) produced by asbestos in buffer solution. No people or animals were studied. The samples were ground UICC crocidolite, UICC chrysotile and long-fiber chrysotile from a Greek mine. They added tar extracts from five Greek cigarettes and measured radicals by ESR. With tar, ground crocidolite gave approximately 5 times its signal without tar after 10 minutes, rising another 30% over 50 minutes. UICC chrysotile showed a twofold increase with tar. Ground chrysotile gave very low signals compared with ground crocidolite at 30 minutes, but with tar and EDTA both UICC samples reached similar signals by about 40 minutes. EDTA, an iron-binding chemical, raised signals further for both fiber types. Superoxide dismutase strongly inhibited radical formation. The authors concluded asbestos and tar acted cooperatively or synergistically. They suggested this was strong evidence related to lung cancer occurring in smoking asbestos workers exposed to high fiber concentrations at work, and only rarely in nonsmokers; the experiment measured no cancer.

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 (test-tube) chemistry experiment using spin trapping and electron spin resonance (ESR) to measure hydroxyl radical generation; published as a brief communication
• Who was studied: No human or animal subjects. The samples were UICC reference crocidolite, UICC chrysotile, and commercial long-fiber chrysotile from the Zidani mine, Northwest Greece, plus aqueous tar extracts from five Greek commercial cigarettes. Measurements were repeated three times.
• Exposure: Freshly ground crocidolite or chrysotile (ground for 2, 4 and 5 min; 10 mg in 2 ml buffer, pH 7.4) alone or mixed with fresh aqueous extracts of tar from five filtered cigarettes (15 mg tar, 0.7 mg nicotine each), with or without EDTA
• Main results:
  • For crocidolite (UICC) ground for 5 min, the ESR signal with tar extract after 10 min incubation was approximately 5 times higher than without tar extract
  • For crocidolite plus tar, the signal increased by a further 30% over another 50 min
  • For chrysotile (UICC) under the same conditions, the signal with tar was twofold higher than without tar
  • The authors observed cooperative or synergistic action of asbestos and tar in generating hydroxyl radical spin adducts
  • In the grinding tests, chrysotile samples, even after grinding, gave very low ESR signal intensity compared with ground crocidolite after incubation for 30 min
  • With both EDTA and tar extract added, UICC chrysotile gave a signal very similar to that of crocidolite; both reached similar intensity after about 40 min
  • Adding EDTA to ground asbestos plus tar extract enhanced the signal further for both crocidolite and chrysotile
  • Without tar, EDTA increased the crocidolite signal by 50% in 30 min, while chrysotile showed only a slight increase
  • Superoxide dismutase (SOD) strongly inhibited hydroxyl radical formation
• The authors' conclusion: The authors concluded that asbestos and cigarette tar act cooperatively or synergistically to generate hydroxyl radicals. They suggested their results were strong evidence related to the fact that lung cancer has been found in asbestos workers exposed to high fiber concentrations in the working environment who were smokers, and only rarely in nonsmokers. This was their interpretation; the experiment measured no cancer in people.
• Limitations the authors state:
  • Experimental values differed by 20-30%, partly because of differences in grinding
  • Tar extracts had to be very fresh to be active, and the amount of tar in the cigarettes may influence activity

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Zidani asbestos mine, Zidani, Kozani, Greece

All asbestos mines

Topics

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

Medical terms in this study, explained in our Lexicon: Hydroxyl Radical, Lung Cancer, Reactive Oxygen Species (ROS), Crocidolite, UICC, Chrysotile, Fenton Reaction.

Related studies

• Role of oxidants in DNA damage. Hydroxyl radical mediates the synergistic DNA damaging effects of asbestos and cigarette smoke — J.H. Jackson, I.U. Schraufstatter, et al. (1987)
• Synergistic effects of mineral fibres and cigarette smoke on the production of tumour necrosis factor by alveolar macrophages of rats — Y. Morimoto, M. Kido, et al. (1993)
• Cigarette smoke augments asbestos-induced alveolar epithelial cell injury: role of free radicals — D.W. Kamp, M.J. Greenberger, et al. (1998)
• Cigarette smoke increases the penetration of asbestos fibers into airway walls — D. McFadden, J. Wright, et al. (1986)
• 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)
• Asbestos catalyzes hydroxyl and superoxide radical generation from hydrogen peroxide — S.A. Weitzman, P. Graceffa (1984)

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