On the mechanism of cell internalization of chrysotile fibers: an immunocytochemical and ultrastructural study

Our plain-English summary of On the mechanism of cell internalization of chrysotile fibers: an immunocytochemical and ultrastructural study, by W. Malorni, F. Iosi, M. Falchi, et al (Environmental Research, 1990).

The study

• Authors: W. Malorni, F. Iosi, M. Falchi, G. Donelli
• Journal: Environmental Research
• Published: 1990;52(2):164-77
• Cited by: 19 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Human breast carcinoma cells (CG5) and human laryngeal carcinoma cells (HEp-2) were exposed to 10 and 50 micrograms/ml of small (about 5 microns) chrysotile asbestos fibers. Morphological and ultrastructural changes were evaluated by means of immunocytochemistry and by scanning and transmission electron microscopy. Our attention was focused on the mechanisms of cell internalization and on transport of chrysotile fibers. The fibers appeared to penetrate the cell cytoplasm and to be translocated in proximity of the nucleus. Small chrysotile fibers could also be found inside the nucleus of interphase cells. Involvement of the main cytoskeletal components, i.e., microfilaments, intermediate filaments, and microtubules, in the cytotoxicity of chrysotile fibers was also evaluated. Our findings suggest that after fiber penetration, a rearrangement of the cytoskeletal apparatus occurs. It has also been observed that small fibers remain associated with the cytoskeletal framework, which can thus play a role in asbestos intracytoplasmic translocation in epithelial cells. Furthermore, after the cell has completely recovered its morphology, fiber internalization ultimately seems to lead to the formation of giant multinucleated cells. These data could be indicative of an interaction occurring between asbestos fibers and the normal mitotic process. The disturbance of the cell cytoskeleton and the close morphologic contact between asbestos fibers and the cell's nuclear region may be of importance in explaining the well-known carcinogenic effects of asbestos mineral fibers.

In plain English

This laboratory study looked at how chrysotile asbestos fibers enter human cells grown in culture. It did not study people. The authors exposed two human cancer cell lines, breast carcinoma cells (CG5) and laryngeal carcinoma cells (HEp-2), to UICC standard reference chrysotile that had been broken up so that more than 80% of fibers were under 5 micrometers long. They examined the cells with fluorescence and electron microscopy. Only small fibers were studied, and most of the dead cells (90%) contained longer fibers. After 6 hours, fibers were seen in the cytoplasm in 70% of the cell sections examined. Fibers of about 0.5 micrometers were seen inside the nuclear envelope in 20% of thin sections. Fiber entry came with breaks and rearrangements in the cell's internal scaffolding (the cytoskeleton), which appeared to recover by 6 hours. Cells pretreated with cytochalasin B, a substance that breaks down actin, showed no fibers inside. A week after exposure, 30% of cells were giant cells with several nuclei, compared with about 5% of control cells. The authors concluded that their results support an active role of the cytoskeleton in moving chrysotile fibers within cultured epithelial cells.

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) cell culture experiment using immunocytochemistry and scanning and transmission electron microscopy
• Who was studied: Two human cancer cell lines grown in culture: human breast carcinoma cells (CG5) and human laryngeal carcinoma cells (HEp-2). The figures shown are of CG5 cells.
• Exposure: UICC standard reference chrysotile, dispersed by sonication so that more than 80% of fibers were less than 5 micrometers long. The Methods give 50 micrograms per ml for observations at 3 and 6 hours. For long-term treatment, 10 micrograms per ml was given for 24 hours, then cells were kept in fresh medium and observed daily for at least a week. Some cells were pretreated with cytochalasin B (1 micromolar) for 1 hour.
• Main results:
  • Longer fibers (more than 10 micrometers) did not appear to be actively taken into cells. Of the nonviable cells, most (90%) contained the longer fibers. Only viable cells were included in the study.
  • After 3 hours, small fibers were found on the cell surface. After 6 hours, fibers were found in the cytoplasm of 70% of cell sections examined, without a surrounding membrane.
  • In interphase cells, smaller fibers of about 0.5 micrometers were seen inside the nuclear envelope in 20% of thin sections examined. Fibers were also found in nucleoli.
  • After 3 hours of chrysotile treatment, wide breakages in the actin stress fiber network were seen, along with altered arrangement of microtubules and keratin filaments.
  • The cytoskeletal network appeared to have fully recovered after 6 hours of treatment.
  • In cells pretreated with cytochalasin B and then exposed to chrysotile for 3 hours, actin was broken down and no fibers were detected inside the cytoplasm.
  • After a week in fiber-free medium, 30% of exposed cells were giant multinucleated cells, compared with approximately 5% of control cells. Some giant cells were as much as 50 times larger than control cells.
  • After detergent extraction, fibers stayed in close contact with cytoskeletal elements. X-ray microanalysis and diffraction confirmed these were chrysotile fibers.
• The authors' conclusion: The authors concluded that their results support a direct, active involvement of cytoskeletal elements in moving chrysotile fibers within the cytoplasm of cultured epithelial cells. They added that this, together with fibers found in interphase nuclei, might suggest an active contribution of epithelial cells to their own pathological or carcinogenic potential.

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, Carcinoma, Transmission Electron Microscopy (TEM), Translocation, Carcinogenic, Mineral Fiber.

Related studies

• Actin-containing microfilaments of pulmonary epithelial cells provide a mechanism for translocating asbestos to the interstitium — A.R. Brody, L.H. Hill, et al. (1983)
• Alteration of cytoskeletal molecules in a human T cell line caused by continuous exposure to chrysotile asbestos — M. Maeda, Y. Chen, et al. (2013)
• Effects of asbestos and man-made vitreous fibers on cell division in cultured human mesothelial cells in comparison to rodent cells — K. Pelin, P. Kivipensas, et al. (1995)
• Reactive and neoplastic serosal tissue. A light-microscopic, ultrastructural, and immunocytochemical study — J.W. Bolen, S.P. Hammar, et al. (1986)
• Changes in numbers and dimensions of chrysotile asbestos fibers in lungs of rats following short-term exposure — V.L. Roggli, A.R. Brody (1984)
• Long crocidolite asbestos fibers cause polyploidy by sterically blocking cytokinesis — C.G. Jensen, L.C. Jensen, et al. (1996)

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