Cyto-genotoxicity of amphibole asbestos fibers in cultured human lung epithelial cell line: role of surface iron

Our plain-English summary of Cyto-genotoxicity of amphibole asbestos fibers in cultured human lung epithelial cell line: role of surface iron, by R.K. Srivastava, M. Lohani, A.B. Pant, et al (Toxicology and Industrial Health, 2010).

The study

• Authors: R.K. Srivastava, M. Lohani, A.B. Pant, Q. Rahman
• Journal: Toxicology and Industrial Health
• Published: 2010;26(9):575-82
• Cited by: 22 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The present investigations correlate the potentials of the reactive oxygen species (ROS) generation and the cyto-genotoxicity of amphibole asbestos fibers (amosite, crocidolite and tremolite) with their surface iron, under in vitro controlled conditions, using A549 cells (human lung epithelial cell line). The mobilizable surface iron was measured by Atomic Absorption Spectroscopy; the production of ROS was investigated using 2, 7 dichloro-dihydrofluorescein-diacetate (DCFH-DA) dye; for cytotoxicity assessment, the intracellular organelles specific damages were measured, using 3-(4, 5 dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide salt (MTT) assay; and, the genotoxic potential of amphibole fibers was determined by cytokinesis block micronucleus (CBMN) assay. In the study, highest amount of ROS was generated by crocidolite followed by tremolite and minimum with amosite. In MTT assay, the time- and concentration-dependent decrease in percent cell viability was recorded with all the three amphibole fibers, tremolite being most cytotoxic, followed by crocidolite, and then amosite. In genotoxicity assay, an increase in the frequency of micronuclei (MNi) in binucleated (BN) cells was observed, where crocidolite was most genotoxic, followed by tremolite, and amosite the least.The comparison of results depicts a clear trend of cyto-genotoxic potential paralleling the ROS generation, suggesting a definite role of oxidative stress in fiber-induced toxicity. However, amosite contains maximum surface iron (28%), followed by crocidolite (27%), and tremolite carrying least (as contaminant) or no iron, the mobilizable surface iron is maximum in crocidolite followed by amosite and is minimum in tremolite. The mobilizable iron somewhat corresponds with the ROS generation capacity of these fibers. This shows that the surface iron could be mainly responsible for amphibole asbestos-induced ROS toxicity; though it may not be the only factor responsible, other factors like shape and size etc., also play role in amphibole asbestos-induced toxicity.

In plain English

This was a laboratory (in vitro) experiment in which the authors compared three amphibole asbestos fibers — amosite, crocidolite and tremolite — in A549 cells, a human lung epithelial cell line. Fibers were crushed, sieved and suspended; mobilizable surface iron was released with the chelator deferoxamine and measured by atomic absorption spectroscopy; reactive oxygen species (ROS) were measured with DCFH-DA dye, cell viability by MTT assay, and chromosome damage by the cytokinesis-block micronucleus assay. Chelator-mobilized iron was 76.16 nmol/mg fiber for crocidolite, 58.24 for amosite and 0.65 for tremolite, the increase over water being significant (p less than 0.001) for crocidolite and amosite but not tremolite. ROS production rose with concentration and fell with longer exposure; crocidolite gave the most ROS and amosite the least. Cell viability fell with dose and time, tremolite being most cytotoxic, then crocidolite, then amosite. Micronuclei increased up to 1.0 microgram/mL, most with crocidolite. The authors concluded that ROS generation correlated with the observed cyto-genotoxicity.

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 cell-culture experiment comparing three amphibole fibers in a human lung epithelial cell line, with chemical measurement of mobilizable surface iron
• Who was studied: A549 human lung epithelial cell line (described by the authors as non-small lung cell carcinoma-derived), cells of passage number 25 to 30
• Exposure: amosite and crocidolite (from Gujrat Composite Pvt Ltd, India) and tremolite (Rajasthan, India) fibers; 2-40 micrograms/mL for 24, 48 and 72 hours (viability), 0.25-10.0 for 6, 12 and 24 hours (ROS), 0.5-10.0 for 24 hours (micronuclei)
• Main results:
  • Iron mobilized by deferoxamine (mean + SD, nmol/mg fiber): crocidolite 76.16 + 3.66, amosite 58.24 + 6.78, tremolite 0.65 + 0.16; in water 0.035, 0.029 and 0.00 respectively
  • The rise in mobilized iron with chelator over water was statistically significant for crocidolite and amosite but not for tremolite
  • ROS production in all three fibers rose with concentration and fell with longer exposure time
  • ROS ranking: crocidolite highest, tremolite next, amosite least
  • Cytotoxicity (MTT) fell with dose and time for all three fibers; tremolite most cytotoxic, then crocidolite, then amosite
  • Micronucleus induction in A549 cells: crocidolite greatest at 0.5-1.0 micrograms/mL, then tremolite, then amosite
  • Micronuclei in binucleated and mononucleated cells were maximal at 1.0 micrograms/mL and fell at higher concentrations; amosite gave slightly fewer but still significant micronuclei (p less than 0.001)
• The authors' conclusion: The authors concluded that all three amphibole fibers produced time- and dose-dependent cytotoxicity, genotoxicity and ROS generation in A549 cells, that ROS generation could be correlated with the cyto-genotoxicity, and that differential surface iron could be correlated with iron mobility and toxic response, though other factors such as shape and size also play a role
• Limitations the authors state:
  • The authors stated that mobilizable surface iron is not the only contributor to ROS generation, with fiber shape and size also contributing
  • The authors noted that internalized iron is not the only source of ROS and that physical dimensions of fibers play a large role

Topics

Medical terms in this study, explained in our Lexicon: Genotoxicity, Amphibole Asbestos, Reactive Oxygen Species (ROS), Amosite, Crocidolite, Tremolite, A549 Cells, Damages.

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