Iron mobilization from asbestos by chelators and ascorbic acid

Our plain-English summary of Iron mobilization from asbestos by chelators and ascorbic acid, by L.G. Lund, A.E. Aust (Archives of Biochemistry and Biophysics, 1990).

The study

• Authors: L.G. Lund, A.E. Aust
• Journal: Archives of Biochemistry and Biophysics
• Published: 1990;278(1):61-4
• Cited by: 73 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The ability of chelators and ascorbic acid to mobilize iron from crocidolite, amosite, medium- and short-fiber chrysotile, and tremolite was investigated. Ferrozine, a strong Fe(II) chelator, mobilized Fe(II) from crocidolite (6.6 nmol/mg asbestos/h) and amosite (0.4 nmol/mg/h) in 50 mM NaCl, pH 7.5. Inclusion of ascorbate increased these rates to 11.4 and 4.9 nmol/mg/h, respectively. Ferrozine mobilized Fe(II) from medium-fiber chrysotile (0.6 nmol/mg/h) only in the presence of ascorbate. Citrate and ADP mobilized iron (ferrous and/or ferric) from crocidolite at rates of 4.2 and 0.3 nmol/mg/h, respectively, which increased to 4.8 and 1.0 nmol/mg/h in the presence of ascorbate. Since ascorbate alone mobilized iron from crocidolite (0.5 nmol/mg/h), the increase appeared to result from additional chelation by ascorbate. Citrate also mobilized iron from amosite (1.4 nmol/mg/h) and medium-fiber chrysotile (1.6 nmol/mg/h). Mobilization of iron from asbestos appeared to be a function not only of the chelator, but also of the surface area, crystalline structure, and iron content of the asbestos. These results suggest that iron can be mobilized from asbestos in the cell by low-molecular-weight chelators. If this occurs, it may have deleterious effects since this could result in deregulation of normal iron metabolism by proteins within the cell resulting in iron-catalyzed oxidation of biomolecules.

In plain English

This was a test-tube experiment, not a study of people or animals. The authors measured how fast iron was released ('mobilized') from five asbestos samples: crocidolite, amosite, medium- and short-fiber chrysotile, and tremolite. The fibers were placed in a pH 7.5 salt solution with iron-binding chemicals (chelators), with or without ascorbic acid (ascorbate). The strong chelator ferrozine released iron from crocidolite at 6.6 nmol per mg of asbestos per hour, rising to 11.4 with ascorbate. From amosite it released 0.4, rising to 4.9 with ascorbate. It released iron from medium-fiber chrysotile (0.6) only with ascorbate, and none from short-fiber chrysotile or tremolite. With crocidolite, citrate and ADP released iron, while histidine, tryptophan, acetate and cysteine did not. With no added chemical, no iron release was detected. Citrate also released iron from amosite, and from medium-fiber chrysotile only in the first two hours. With ferrozine, release of ferrous iron from crocidolite rose as pH fell. The authors concluded that small chelating molecules can release iron from asbestos. They suggested that if this happens inside cells, it could upset normal iron control.

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 (test-tube) laboratory chemistry experiment; no human or animal subjects
• Who was studied: Samples of five forms of asbestos (crocidolite, amosite, medium-fiber chrysotile, short-fiber chrysotile, tremolite) obtained from NIEHS/NTP
• Exposure: Asbestos (1 mg/ml) incubated for up to 36 h with 1 mM chelators. These were ferrozine; the possible physiological chelators citrate, ADP, acetate, cysteine, histidine, phosphate and tryptophan; and the nonbiological EDTA and Tris. Each was tested with or without 1 mM ascorbate, and the effects of pH and buffer type were also tested.
• Main results:
  • Crocidolite with ferrozine: iron released at 6.6 nmol/mg/h. Adding ascorbate increased this 1.7-fold, to 11.4 nmol/mg/h.
  • Amosite with ferrozine: 0.4 nmol/mg/h without ascorbate and 4.9 with ascorbate. This 12-fold rise was the largest increase from ascorbate.
  • Without ascorbate, ferrozine released iron from crocidolite and amosite but not from medium-fiber chrysotile, short-fiber chrysotile or tremolite. With ascorbate, medium-fiber chrysotile released 0.6 nmol/mg/h. With short-fiber chrysotile, the ferrozine-iron complex formed on the fiber but was not released during a 24-h incubation.
  • With no added chemical, no iron release from crocidolite was detected. Ascorbate alone released 0.5 nmol/mg/h.
  • Crocidolite: citrate released iron at 4.2 nmol/mg/h and ADP at 0.3, rising to 4.8 and 1.0 with ascorbate. Because ascorbate alone released iron, the authors attributed the increase to an additive effect of ascorbate.
  • Histidine, tryptophan, acetate, cysteine and phosphate released no iron from crocidolite. However, 50 mM sodium phosphate released iron from crocidolite at 0.9 nmol/mg/h.
  • EDTA released iron from crocidolite at about four times the rate of ferrozine (Table III prints 30.1 and 27.3 nmol/mg/h). Tris released none over 36 h.
  • Citrate (without ascorbate) released iron from amosite at 1.4 nmol/mg/h and from medium-fiber chrysotile at 1.6 nmol/mg/h. Release from medium-fiber chrysotile occurred only in the first 2 h. Citrate released none from short-fiber chrysotile or tremolite.
  • The pH test was run only on ferrous iron [Fe(II)] release from crocidolite by ferrozine. In that test, release went up as pH went down.
  • Compared with 50 mM NaCl, iron release by ferrozine from crocidolite fell when Tris or sodium phosphate buffers were used.
• The authors' conclusion: The authors concluded that a chelator must be present to release iron from asbestos, and that small chelating molecules may release iron from asbestos inside cells. If so, they said, this might disrupt normal iron regulation in the cell.

Topics

Medical terms in this study, explained in our Lexicon: Crocidolite, Amosite, Chrysotile, Tremolite, Crystalline.

Related studies

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• Chemical characterization and reactivity of iron chelator-treated amphibole asbestos — J. Gold, H. Amandusson, et al. (1997)
• 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)
• High dose of ascorbic acid induces cell death in mesothelioma cells — Y. Takemura, M. Satoh, et al. (2010)
• Ascorbic acid modifies the surface of asbestos: possible implications in the molecular mechanisms of toxicity — G. Martra, M. Tomatis, et al. (2003)

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