Surface reactivity and cell responses to chrysotile asbestos nanofibers

Our plain-English summary of Surface reactivity and cell responses to chrysotile asbestos nanofibers, by F. Turci, M. Colonna, M. Tomatis, et al (Chemical Research in Toxicology, 2012).

The study

• Authors: F. Turci, M. Colonna, M. Tomatis, S. Mantegna, G. Cravotto, G. Gulino, E. Aldieri, D. Ghigo, B. Fubini
• Journal: Chemical Research in Toxicology
• Published: 2012;25(4):884-94
• Cited by: 10 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

High aspect-ratio nanomaterials (HARNs) have recently attracted great attention from nanotoxicologists because of their similarity to asbestos. However, the actual risk associated with the exposure to nanosized asbestos, which escapes most regulations worldwide, is still unknown. Nanometric fibers of chrysotile asbestos have been prepared from two natural sources to investigate whether nanosize may modulate asbestos toxicity and gain insight on the hazard posed by naturally occurring asbestos, which may be defined as HARNs because of their dimensions. Power ultrasound was used to obtain nanofibers from two different chrysotile specimens, one from the dismissed asbestos mine in Balangero (Italian Western Alps) and the other from a serpentine outcrop in the Italian Central Alps. Electron microscopy, X-ray diffraction, and fluorescence spectroscopy revealed that the procedure does not affect mineralogical and chemical composition. Surface reactions related to oxidative stress, free radical generation, bioavailability of iron, and antioxidant depletion, revealed a consistent reduction in reactivity upon reduction in size. When tested on A549 human epithelial cells, the pristine but not the nanosized fibers proved cytotoxic (LDH release), induced NO production, and caused lipid peroxidation. However, nanofibers still induced some toxicity relevant oxidative stress activity (ROS production) in a dose-dependent fashion. The reduction in length and a lack of poorly coordinated bioavailable iron in nanochrysotile may explain this behavior. The present study provides a one-step procedure for the preparation of a homogeneous batch of natural asbestos nanofibers and shows how a well-known toxic material might not necessarily become more toxic than its micrometric counterpart when reduced to the nanoscale.

In plain English

This laboratory study tested whether chrysotile asbestos becomes more or less reactive when broken into nanometer-scale fibers. The authors treated two natural chrysotile samples, from Val Malenco in the Italian Central Alps and from the dismissed Balangero asbestos mine, with ultrasound in water. They chose a 3-hour treatment because it shortened the fibers without changing their crystal structure or chemical composition. Afterwards most fibers were shorter than 3 μm. Only 2% of Balangero nanofibers, and no Val Malenco nanofibers, exceeded 5 μm. In cell-free tests, compared per unit of fiber surface, nanofibers released fewer free radicals and less chelator-extractable iron than the original fibers. In human lung epithelial cells (A549), the original fibers increased cell damage, reactive oxygen, lipid peroxidation and nitric oxide. Nanofibers caused significantly less cell damage and reactive oxygen. At the one dose tested for the last two measures (6 μg/cm2), nanofibers caused no significant rise in lipid peroxidation or nitric oxide. However, Balangero nanofibers at the highest dose still raised reactive oxygen above control. The authors concluded that size reduction lowered reactivity in these tests and that studies in other cell lines and in vivo are needed.

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) study: preparation of chrysotile nanofibers by ultrasound, cell-free surface reactivity tests, and tests on a human lung epithelial cell line
• Who was studied: Two natural chrysotile specimens from Italy, one from Val Malenco (Italian Central Alps, CTL-VM) and one from the Balangero dismissed asbestos mine (CTL-BM), tested on human pulmonary epithelial cells (A549 cell line)
• Exposure: Pristine (micrometric) chrysotile was compared with chrysotile nanofibers made by 3 hours of ultrasound (21 kHz, about 2 W/mL). Cells were exposed for 24 h to 3, 6 and 15 μg/cm2 of Balangero fibers or to 6, 15 and 25 μg/cm2 of Val Malenco fibers. Lipid peroxidation and nitric oxide were tested only at 6 μg/cm2.
• Main results:
  • The 3-hour ultrasound treatment did not change the Mg/Si or Fe/Si ratios of either chrysotile sample.
  • After 3 hours of sonication, most fibers of both samples were shorter than 3 μm. Only 2% of nano-CTL-BM fibers were longer than 5 μm, with a maximum length of 7 μm. No nano-CTL-VM fibers were longer than 5 μm. Median lengths were 1.8 μm for nano-CTL-BM and 1.2 μm for nano-CTL-VM.
  • Compared per unit surface, the nanofibers produced about three times fewer hydroxyl radicals than the micrometric fibers. Compared per mass, Balangero nanofibers were less reactive than micrometric Balangero fibers, while Val Malenco nanofibers had similar reactivity.
  • Iron was extracted over 16 days in a solution of ferrozine (an iron chelator) with ascorbic acid, and the results were normalized per unit surface. On that basis, nanofibers had less bioavailable iron than the pristine fibers.
  • Depletion of the antioxidants ascorbic acid and cysteine was lower for Balangero nanofibers than for pristine Balangero fibers. For Val Malenco, there was no significant difference between nano and pristine fibers.
  • In A549 cells, micrometric fibers caused a significant, dose-dependent increase in LDH release (cell damage). This effect was significantly decreased with equal masses of nanofibers.
  • Nanofibers caused significantly lower reactive oxygen species production than micrometric fibers, but this activity did not fully disappear. At 15 μg/cm2, Balangero nanofibers produced significantly more reactive oxygen species than control cells.
  • At 6 μg/cm2 for 24 h, only the micrometric fibers significantly increased lipid peroxidation and nitric oxide (measured as nitrite) production in A549 cells. Nanofibers did not.
• The authors' conclusion: The authors concluded that when chrysotile from both sources was reduced to smaller fibers, its surface reactivity decreased and its potential to cause several adverse responses in a human lung epithelial cell line was attenuated. They attributed this possibly to smaller size and to reduced free radical generation linked to less bioavailable iron. They also concluded that reducing a fiber to the nanosize does not always increase toxicity.
• Limitations the authors state:
  • The authors stated that more studies on other cell lines and in vivo validation are needed to properly evaluate the risk of chrysotile nanofibers in the environment.
  • Surface charge (zeta potential) could be measured only for the nanometric samples, because the pristine fibers were too large for the instrument.

Mines named here

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

• Balangero mine, Balangero, about 20 km north of Turin, Piedmont

All asbestos mines

Topics

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

Medical terms in this study, explained in our Lexicon: Surface Reactivity, Chrysotile, naturally occurring asbestos (NOA), Ultrasound, Serpentine Group, X-Ray Diffraction (XRD), Oxidative Stress, LDH Release.

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