Effect of Synthetic Vitreous Fiber Exposure on TMEM16A Channels in a Xenopus laevis Oocyte Model

Our plain-English summary of Effect of Synthetic Vitreous Fiber Exposure on TMEM16A Channels in a Xenopus laevis Oocyte Model, by M. Zangari, G. Zabucchi, M. Conti, et al (International Journal of Molecular Sciences, 2024).

The study

• Authors: M. Zangari, G. Zabucchi, M. Conti, P. Lorenzon, V. Borelli, A. Constanti, F. Dellisanti, S. Leone, L. Vaccari, A. Bernareggi
• Journal: International Journal of Molecular Sciences
• Published: 2024;25(16)
• Read it: PubMed · Publisher · Free full text

Abstract

Many years ago, asbestos fibers were banned and replaced by synthetic vitreous fibers because of their carcinogenicity. However, the toxicity of the latter fibers is still under debate, especially when it concerns the early fiber interactions with biological cell membranes. Here, we aimed to investigate the effects of a synthetic vitreous fiber named FAV173 on the Xenopus laevis oocyte membrane, the cell model we have already used to characterize the effect of crocidolite asbestos fiber exposure. Using an electrophysiological approach, we found that, similarly to crocidolite asbestos, FAV173 was able to stimulate a chloride outward current evoked by step membrane depolarizations, that was blocked by the potent and specific TMEM16A channel antagonist Ani9. Exposure to FAV173 fibers also altered the oocyte cell membrane microvilli morphology similarly to crocidolite fibers, most likely as a consequence of the TMEM16A protein interaction with actin. However, FAV173 only partially mimicked the crocidolite fibers effects, even at higher fiber suspension concentrations. As expected, the crocidolite fibers' effect was more similar to that induced by the co-treatment with (Fe3+ + H2O2), since the iron content of asbestos fibers is known to trigger reactive oxygen species (ROS) production. Taken together, our findings suggest that FAV173 may be less harmful that crocidolite but not ineffective in altering cell membrane properties.

In plain English

This laboratory experiment used egg cells (oocytes) from African clawed frogs (Xenopus laevis), not people. The authors compared ground FAV173, a rock wool synthetic vitreous fiber, with crocidolite asbestos. They measured the cells' membrane electrical properties and examined their surface by electron microscopy. Crocidolite at 15 µg/mL lowered the resting membrane potential to 67% of that of untreated cells, while FAV173 needed 400 µg/mL for a similar drop. The FAV173 effect stayed short-lived even at 600 µg/mL, while crocidolite at 45 µg/mL still acted after 2 hours. Both fibers increased voltage-evoked currents with a pattern typical of TMEM16A chloride channels. Crocidolite (15 µg/mL) did so more strongly than FAV173 (200 µg/mL): 222% versus 162% of control at minus 80 mV. The TMEM16A blocker Ani9 partly reversed the FAV173 effect. In a high-calcium bath, FAV173 narrowed the cell-surface projections (microvilli) without changing their density. Crocidolite, tested in a normal bath, reduced microvilli density. The authors concluded that FAV173's effect appears TMEM16A-dependent, like crocidolite's, but less severe. They noted that the high FAV173 concentrations used had no real biological or clinical significance.

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 oocytes (electrophysiological voltage-clamp recordings and scanning electron microscopy)
• Who was studied: Oocytes (stage VI) from sexually mature female Xenopus laevis frogs, University of Trieste, Italy. Numbers of cells varied by experiment. For example, the current measurements used n = 32 crocidolite-treated cells from 5 batches and n = 53 FAV173-treated cells from 7 batches.
• Exposure: Ground rock wool FAV173 at 15 to 400 µg/mL, and also 600 µg/mL. Analytical standard UICC crocidolite (South Africa) at 15 µg/mL and 45 µg/mL. Iron (Fe3+, 400 µM) plus hydrogen peroxide (1 mM), used to mimic fiber iron and reactive oxygen species. Treatments lasted roughly 5 to 120 minutes.
• Main results:
  • Crocidolite (15 µg/mL) reduced resting potential to 67 ± 4% and membrane resistance to 65 ± 4% of control cells. FAV173 gave similar effects only at 400 µg/mL for resting potential (reduced to 66 ± 4% of control) and at 200 µg/mL for membrane resistance.
  • The FAV173 effect on resting potential was transient even at 600 µg/mL. The crocidolite effect at 45 µg/mL was still present after 2 hours.
  • Both fibers increased evoked current amplitude, and the crocidolite effect (15 µg/mL) was stronger than the FAV173 effect (200 µg/mL). At minus 80 mV, currents were 222 ± 25% of control with crocidolite and 162 ± 10% with FAV173. At +40 mV, they were 173 ± 17% with crocidolite and 132 ± 7% with FAV173. The authors described TMEM16A channels as possible mediators.
  • In the high-calcium bath, the TMEM16A blocker Ani9 partially reversed the FAV173 effect on currents. The authors took this as suggesting a contribution of TMEM16A channel activity.
  • In the high-calcium bath, FAV173 (200 µg/mL) reduced microvilli diameter from 74.32 ± 1.68 nm to 64.06 ± 1.80 nm without altering their density. Crocidolite (15 µg/mL), tested in the normal bath, reduced microvilli density from 15.31 ± 0.58 to 11.32 ± 0.30 per µm2. The crocidolite decrease in diameter had p = 0.06.
  • In cells treated with cytochalasin D, which blocks actin polymerization, FAV173 only slightly depolarized the resting potential (−26.69 ± 2.12 mV, n = 13). Crocidolite depolarized it to −8.75 ± 0.95 mV (n = 12). Ani9 prevented the crocidolite effect.
• The authors' conclusion: The authors concluded that the electrical changes caused by FAV173 in frog oocytes appear to depend on TMEM16A channel activation, as with crocidolite, but are less severe. They suggested that the oocyte model merits consideration for safety screening of asbestos replacement fibers.
• Limitations the authors state:
  • The oocyte model makes it difficult to study the inside of the cell after fiber contact, because dense granules hide organelles and fibers.
  • The crocidolite concentration used was higher than that accumulated in the lungs of exposed people.
  • The high FAV173 concentrations used had no real biological or clinical significance.
  • The possibility that FAV173 pierces the membrane is based only on electrical observations.

Topics

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

Medical terms in this study, explained in our Lexicon: Vitreous, Crocidolite, Reactive Oxygen Species (ROS).

Related studies

• Xenopus laevis Oocytes as a Model System for Studying the Interaction Between Asbestos Fibres and Cell Membranes — A. Bernareggi, E. Ren, et al. (2015)
• 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)
• Asbestos Fibers Enhance the TMEM16A Channel Activity in Xenopus Oocytes — A. Bernareggi, M. Zangari, et al. (2023)
• Refractory ceramic fibers (RCFs) induce germline aneuploidy in Drosophila oocytes — C.J. Osgood (1994)
• Differential in vitro cellular response induced by exposure to synthetic vitreous fibers (SVFs) and asbestos crocidolite fibers — G. Cardinali, D. Kovacs, et al. (2006)
• Synthetic vitreous fibers: a review of toxicology research and its impact on hazard classification — T.W. Hesterberg, G.A. Hart (2001)

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