Iron-related toxicity of single-walled carbon nanotubes and crocidolite fibres in human mesothelial cells investigated by Synchrotron XRF microscopy

Our plain-English summary of Iron-related toxicity of single-walled carbon nanotubes and crocidolite fibres in human mesothelial cells investigated by Synchrotron XRF microscopy, by F. Cammisuli, S. Giordani, A. Gianoncelli, et al (Scientific Reports, 2018).

The study

• Authors: F. Cammisuli, S. Giordani, A. Gianoncelli, C. Rizzardi, L. Radillo, M. Zweyer, T. Da Ros, M. Salomé, M. Melato, L. Pascolo
• Journal: Scientific Reports
• Published: 2018;8(1):706
• Cited by: 7 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Carbon nanotubes (CNTs) are promising products in industry and medicine, but there are several human health concerns since their fibrous structure resembles asbestos. The presence of transition metals, mainly iron, in the fibres seems also implicated in the pathogenetic mechanisms. To unravel the role of iron at mesothelial level, we compared the chemical changes induced in MeT-5A cells by the exposure to asbestos (crocidolite) or CNTs at different content of iron impurities (raw-SWCNTs, purified- and highly purified-SWCNTs). We applied synchrotron-based X-Ray Fluorescence (XRF) microscopy and soft X-ray imaging (absorption and phase contrast images) to monitor chemical and morphological changes of the exposed cells. In parallel, we performed a ferritin assay. X-ray microscopy imaging and XRF well localize the crocidolite fibres interacting with cells, as well as the damage-related morphological changes. Differently, CNTs presence could be only partially evinced by low energy XRF through carbon distribution and sometimes iron co-localisation. Compared to controls, the cells treated with raw-SWCNTs and crocidolite fibres showed a severe alteration of iron distribution and content, with concomitant stimulation of ferritin production. Interestingly, highly purified nanotubes did not altered iron metabolism. The data provide new insights for possible CNTs effects at mesothelial/pleural level in humans.

In plain English

This was a laboratory study of human mesothelial cells (the MeT-5A line), not of people. The authors exposed the cells to crocidolite asbestos fibres or to single-walled carbon nanotubes with different amounts of leftover iron, each at 5 µg/mL. The nanotubes were raw (under 30% iron by weight), purified (under 15%) or highly purified (under 2% in the article's table). The authors measured cell survival and ferritin, an iron-storage protein. They also used synchrotron X-ray microscopy on 5 to 8 cells per condition to see where iron was. After 24 hours, about 64% of cells survived raw nanotubes and 65% survived crocidolite, compared with more than 80% for purified and highly purified nanotubes. Ferritin in crocidolite-exposed cells was 3 to 10 times control levels at 24 and 48 hours. Raw nanotubes gave a very similar rise, purified nanotubes a much smaller one, and highly purified nanotubes a negligible one. The authors concluded that altered iron metabolism, a key mechanism in asbestos toxicity, also occurs with carbon nanotubes in cells. They added that how the iron increase leads to cell toxicity needs further clarification.

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 laboratory experiment on a human mesothelial cell line, using cell viability tests, a ferritin assay and synchrotron X-ray fluorescence and soft X-ray microscopy
• Who was studied: Human mesothelial MeT-5A cells grown in culture; for the X-ray fluorescence microscopy, 5 to 8 cells were analysed per experimental condition
• Exposure: UICC standard crocidolite asbestos fibres and three single-walled carbon nanotube preparations (raw, under 30 wt% residual iron; purified, under 15 wt%; highly purified, under 2 wt% per Table 1), each at 5 µg/mL for 24 h. Ferritin was also measured after 48 h. Ferrous sulphate (80 µM) was used as an iron control, and untreated cells served as controls.
• Main results:
  • Cell viability was around 64% with raw nanotubes and 65% with crocidolite after 24 h, falling to 58% and 56% respectively after an additional 24 h
  • Purified and highly purified nanotubes left cell viability higher than 80% at both 24 h and 48 h
  • Ferritin in crocidolite-exposed cells was 3 to 10 times that of control cells, at 24 and 48 h respectively
  • Raw nanotubes produced a ferritin rise very similar to that from crocidolite at both time points
  • Purified nanotubes produced a much smaller ferritin rise, and highly purified nanotubes a negligible one
  • In crocidolite-exposed cells, iron maps showed iron-rich segments marking the fibres, most of which appeared to be inside the cells
  • In cells exposed to raw nanotubes, iron maps showed an overall iron increase and iron-rich hot spots inside or around the cells
  • In cells exposed to highly purified nanotubes, the intracellular iron increase was mild and uneven
• The authors' conclusion: The authors concluded that altered iron metabolism, which they describe as a key mechanism in asbestos toxicity, is also a biological effect of carbon nanotubes at the cellular level. They attributed the effect to iron impurities in a dose-dependent manner, implying that high purification minimises it.
• Limitations the authors state:
  • The steps connecting the iron increase to cell toxicity need further clarification
  • The purification steps also changed the nanotubes' solubility in water, which the authors could not exclude as a factor in the different toxicity of the materials
  • The authors had no evidence of where inside the cells the nanotubes were held (lysosomal or phagic vesicles)
  • Raw nanotubes could not be recognised in the X-ray absorption and contrast images

Topics

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

Medical terms in this study, explained in our Lexicon: Crocidolite, Mesothelial Cells, MeT-5A Cells, Ferritin.

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