Xenopus laevis Oocytes as a Model System for Studying the Interaction Between Asbestos Fibres and Cell Membranes

Our plain-English summary of Xenopus laevis Oocytes as a Model System for Studying the Interaction Between Asbestos Fibres and Cell Membranes, by A. Bernareggi, E. Ren, V. Borelli, et al (Toxicological Sciences, 2015).

The study

• Authors: A. Bernareggi, E. Ren, V. Borelli, F. Vita, A. Constanti, G. Zabucchi
• Journal: Toxicological Sciences
• Published: 2015;145(2):263-72
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The mode of interaction of asbestos fibres with cell membranes is still debatable. One reason is the lack of a suitable and convenient cellular model to investigate the causes of asbestos toxicity. We studied the interaction of asbestos fibres with Xenopus laevis oocytes, using electrophysiological and morphological methods. Oocytes are large single cells, with a limited ability to endocytose molecular ligands; we therefore considered these cells to be a good model for investigating the nature of asbestos/membrane interactions. Electrophysiological recordings were performed to compare the passive electrical membrane properties, and those induced by applying positive or negative voltage steps, in untreated oocytes and those exposed to asbestos fibre suspensions. Ultrastructural analysis visualized in detail, any morphological changes of the surface membrane caused by the fibre treatment. Our results demonstrate that Amosite and Crocidolite-type asbestos fibres significantly modify the properties of the membrane, starting soon after exposure. Cells were routinely depolarized, their input resistance decreased, and the slow outward currents evoked by step depolarizations were dramatically enhanced. Reducing the availability of surface iron contained in the structure of the fibres with cation chelators, abolished these effects. Ultrastructural analysis of the fibre-exposed oocytes showed no evidence of phagocytic events. Our results demonstrate that asbestos fibres modify the oocyte membrane, and we propose that these cells represent a viable model for studying the asbestos/cell membrane interaction. Our findings also open the possibly for finding specific competitors capable of hindering the asbestos-cell membrane interaction as a means of tackling the long-standing asbestos toxicity problem.

© The Author 2015. Published by Oxford University Press on behalf of the Society of Toxicology. All rights reserved. For Permissions, please e-mail: [email protected].

In plain English

This was a laboratory experiment on frog egg cells, not people. The researchers tested whether egg cells (oocytes) of the frog Xenopus laevis could serve as a model for studying how asbestos fibres interact with cell membranes. They exposed the cells to standard amosite or crocidolite asbestos samples, or to wollastonite, a non-asbestos mineral used for comparison. They measured the cells' electrical properties and examined them by electron microscopy. Compared with untreated cells, amosite and crocidolite changed the membranes' electrical properties. Membrane resistance fell from 0.95 megohms in 102 untreated cells to 0.79 in 68 amosite-treated cells and 0.66 in 84 crocidolite-treated cells. These changes appeared within 5 to 10 minutes. Wollastonite caused no significant changes in 7 cells. Crocidolite injected inside cells did not change their electrical membrane properties, at least in the short term. Treating crocidolite with iron-binding chemicals abolished its effects on the resting membrane properties. Under the microscope, researchers never saw cells engulfing fibres. The authors concluded these cells are a suitable model but said it is unclear how the changes relate to asbestos toxicity.

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 experiment on isolated frog egg cells (oocytes), using electrical recordings and light and electron microscopy
• Who was studied: Mature (stage VI) oocytes taken from adult female Xenopus laevis frogs. Electrical recordings: 102 untreated cells, 68 amosite-treated, 84 crocidolite-treated and 7 wollastonite-treated. The number of frogs, the study location and the dates are not stated.
• Exposure: Standard UICC samples of South African amosite and crocidolite asbestos, suspended in solution and applied to the cells for 5 to 120 minutes at several concentrations. Wollastonite, a non-asbestos silicate, served as a control. In separate experiments, crocidolite was injected inside the cells, and crocidolite was pre-treated with iron-binding chemicals (DFO, EDTA, AFC).
• Main results:
  • Compared with untreated cells, amosite- and crocidolite-treated cells were depolarized and had lower membrane resistance. Membrane resistance was 0.95 plus or minus 0.03 megohms in untreated cells (n = 102), 0.79 plus or minus 0.03 in amosite-treated cells (n = 68) and 0.66 plus or minus 0.03 in crocidolite-treated cells (n = 84).
  • After 5 minutes of exposure, 58% of amosite-treated and 64% of crocidolite-treated cells already showed changes.
  • Wollastonite caused no statistically significant changes in membrane properties (n = 7).
  • The effect increased with dose and was more evident with crocidolite than with amosite.
  • When stepped voltages were applied, amosite-treated and especially crocidolite-treated cells showed a large increase in slow outward electrical currents.
  • Crocidolite injected inside the cells (10 cells, compared with 7 cells injected with salt solution only) did not change their electrical membrane properties, at least in the short term; recordings were made 30 minutes after injection.
  • Pre-treating crocidolite with iron-binding chemicals abolished its effects on the resting membrane properties and only partly reduced its effect on the slow outward currents.
  • In hundreds of electron-microscope sections, no fibres were seen being engulfed by the cells. Fibres were seen in contact with the membrane surface, and the cells' surface projections (microvilli) appeared thicker and more numerous than in untreated cells.
• The authors' conclusion: The authors concluded that frog oocytes can be a suitable model for studying how asbestos fibres interact with cell membranes. They proposed that amosite and crocidolite, by sticking to and/or crossing the membrane, create a non-specific pore through which ions flow. They also concluded that the effects appear not to depend on the cells taking up the fibres.
• Limitations the authors state:
  • The authors stated that it is unclear how the observed membrane changes relate to asbestos toxicity.
  • The authors did not investigate which type of ion current made up the increased outward current.
  • The authors could not completely rule out that the fibres act on the inside of the cell.
  • The authors had no explanation for the changes seen on the outer surface of the eggs.
  • Identifying asbestos fibres in the electron-microscope sections was sometimes difficult.

Topics

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

Medical terms in this study, explained in our Lexicon: Amosite, Crocidolite, Cation, Standing.

Related studies

• On the mechanism of the electrophysiological changes and membrane lesions induced by asbestos fiber exposure in Xenopus laevis oocytes — A. Bernareggi, G. Conte, et al. (2019)
• Effect of Synthetic Vitreous Fiber Exposure on TMEM16A Channels in a Xenopus laevis Oocyte Model — M. Zangari, G. Zabucchi, et al. (2024)
• Asbestos Fibers Enhance the TMEM16A Channel Activity in Xenopus Oocytes — A. Bernareggi, M. Zangari, et al. (2023)
• The crocidolite fibres interaction with human mesothelial cells as investigated by combining electron microscopy, atomic force and scanning near-field optical microscopy — L. Andolfi, E. Trevisan, et al. (2013)
• Refractory ceramic fibers (RCFs) induce germline aneuploidy in Drosophila oocytes — C.J. Osgood (1994)
• Studies using lectins to determine mineral interactions with cellular membranes — B.T. Mossman, L. Jean, et al. (1983)

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