Different cellular responses evoked by natural and stoichiometric synthetic chrysotile asbestos

Our plain-English summary of Different cellular responses evoked by natural and stoichiometric synthetic chrysotile asbestos, by E. Gazzano, E. Foresti, I.G. Lesci, et al (Toxicology and Applied Pharmacology, 2005).

The study

• Authors: E. Gazzano, E. Foresti, I.G. Lesci, M. Tomatis, C. Riganti, B. Fubini, N. Roveri, D. Ghigo
• Journal: Toxicology and Applied Pharmacology
• Published: 2005;206(3):356-64
• Cited by: 28 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The carcinogenic potency of asbestos, including chrysotile, is well established. Several physico-chemical features of the fibers appear implied, such as fibrous habit, size, crystallinity, morphology, and surface active metal ions, where free radical generation may take place. In contrast to other asbestos forms, iron is not a stoichiometric component of chrysotile, but is only present together with other extraneous ions as a magnesium- and silicon-replacing contaminant. To determine the role played by contaminating ions and morphological features of the fibers, a stoichiometric chrysotile with constant structure and morphology was synthesized in hydrothermal conditions. Free radical generation and the effects of these fibers on human lung epithelial A549 cells have been compared to that elicited by a well known toxic natural chrysotile (UICC A, from Rhodesia). After a 24-h incubation, the natural, but not the synthetic, form exerted a cytotoxic effect, detected as leakage of lactate dehydrogenase. Homolytic rupture of a C-H bond and lipoperoxidation in A549 cells took place in the presence of the natural, but not of the synthetic, chrysotile. Antioxidant systems were also affected differently. The pentose phosphate pathway and its regulatory enzyme glucose 6-phosphate dehydrogenase were markedly inhibited only by the natural specimen, which also caused a depletion of intracellular reduced glutathione in A549 cells. These results suggest that metal ions, fiber size and state of the surface play a crucial role in the oxidative stress caused by chrysotile asbestos. Stoichiometric synthetic fibers may thus be proposed as a reference standard (negative control) for toxicological studies.

In plain English

This laboratory study compared two forms of chrysotile asbestos using human lung epithelial cells grown in culture (the A549 cell line) and cell-free chemical tests. One was a natural chrysotile reference sample (UICC A, from Rhodesia). The other was synthetic chrysotile made in the laboratory, which contained only traces of iron and had shorter fibers and a larger surface area. Cells were exposed to each for 24 hours. The natural chrysotile caused a 3-fold increase in leakage of the enzyme LDH, a sign of cell damage. It also increased lipid peroxidation and produced free radicals from formate when ascorbic acid was present. It lowered the activity of an antioxidant pathway (the pentose phosphate pathway and its enzyme G6PD) and reduced the cells' glutathione. The synthetic chrysotile had no significant effect in these tests. The authors concluded that the synthetic chrysotile was not cytotoxic to these cells and did not induce oxidative stress. They proposed it as a negative control for laboratory studies and stated that further work is needed to sort out the role of metal contaminants.

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 (in vitro) experiment on cultured human cells, plus cell-free free radical tests, comparing natural and synthetic chrysotile
• Who was studied: Cultured human lung epithelial cells (A549 cell line), grown to confluence and then incubated for 24 hours with or without the fibers; no people or animals were studied
• Exposure: Natural UICC A (Rhodesian) chrysotile compared with stoichiometric synthetic chrysotile. The synthetic fibers contained only traces of iron. The natural sample contained Fe2O3 2.14% and FeO 0.41% by weight, figures the article takes from earlier published data. Mean fiber length was 2.5 micrometres for the synthetic fibers and 7.0 micrometres for the natural fibers. Surface area was 55 m2/g for the synthetic fibers and 30 m2/g for the natural fibers. Cells were exposed to 6 micrograms per square centimetre of each for 24 hours.
• Main results:
  • Natural UICC A chrysotile caused a 3-fold increase in LDH leakage from A549 cells, a sign of cell damage, compared with untreated control cells (P less than 0.005, n = 8)
  • Synthetic chrysotile caused no cytotoxic effect (no increase in LDH leakage) in A549 cells
  • In cell-free tests, Fenton activity (hydroxyl radical release) was very weak with both forms. With ascorbic acid present, the natural chrysotile generated free radicals from formate and the synthetic chrysotile did not.
  • Lipid peroxidation (measured as TBARS) increased significantly in A549 cells exposed to natural chrysotile. Synthetic chrysotile had no significant effect.
  • Natural chrysotile markedly decreased pentose phosphate pathway activity in A549 cells, both at baseline and when stimulated by menadione. Synthetic chrysotile did not significantly change it.
  • Natural chrysotile, but not synthetic chrysotile, significantly decreased activity of the enzyme G6PD. Neither fiber type significantly changed activity of the enzyme 6PGD.
  • Natural chrysotile lowered intracellular reduced glutathione (GSH) in A549 cells, without an increase in oxidized glutathione (GSSG). Synthetic chrysotile did not deplete GSH.
• The authors' conclusion: The authors concluded that synthetic chrysotile, unlike a similar concentration of natural UICC A chrysotile, was not cytotoxic to A549 cells and did not induce oxidative stress. They proposed stoichiometric synthetic chrysotile as a reference (negative control) for studies of how asbestos causes toxicity.
• Limitations the authors state:
  • The two fiber types also differed in size: the synthetic fibers were shorter. The authors chose not to grind the natural sample to match them, because grinding could alter its properties.
  • The authors stated that a further study is needed, using synthetic fibers with controlled amounts of metal, to determine how much of the difference is due to metal contaminants.

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Carcinogenic, Fibrous Habit, A549 Cells, UICC, Lactate Dehydrogenase (LDH), Glutathione (GSH), Oxidative Stress.

Related studies

• Iron-loaded synthetic chrysotile: a new model solid for studying the role of iron in asbestos toxicity — E. Gazzano, F. Turci, et al. (2007)
• Synthetic hydrosilicate nanotubes induce low pro-inflammatory and cytotoxic responses compared to natural chrysotile in lung cell cultures — T. Skuland, T. Maslennikova, et al. (2020)
• Potential toxicity of nonregulated asbestiform minerals: balangeroite from the western Alps. Part 3: Depletion of antioxidant defenses — E. Gazzano, C. Riganti, et al. (2005)
• Antioxidants prevent the RhoA inhibition evoked by crocidolite asbestos in human mesothelial and mesothelioma cells — E. Aldieri, C. Riganti, et al. (2011)
• Surface reactivity and cell responses to chrysotile asbestos nanofibers — F. Turci, M. Colonna, et al. (2012)
• Long-term instillation to four natural representative chrysotile of China induce the inactivation of P53 and P16 and the activation of C-JUN and C-FOS in the lung tissues of Wistar rats — Y. Luo, J. Deng, et al. (2020)

Browse more research in Toxicology and Applied Pharmacology, or return to medical research.