Scanning electron microscopical investigations of broncho-alveolar casts after intratracheal asbestos fibre instillation

Our plain-English summary of Scanning electron microscopical investigations of broncho-alveolar casts after intratracheal asbestos fibre instillation, by B. Voss, T. Kerenyi, K.M. Müller, et al (International Journal of Hygiene and Environmental Health, 2000).

The study

• Authors: B. Voss, T. Kerenyi, K.M. Müller, M. Wilhelm
• Journal: International Journal of Hygiene and Environmental Health
• Published: 2000;203(2):127-34
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The evaluation of the toxicity of mineral fibres has been tried to achieve in experimental animal models. However, the appearance of fibres in the pleural space could not be explained satisfactorily. Histomorphological examinations showed that intratracheal instillation of asbestos fibres leads to parabronchial and intraalveolar granulomatous tissue reactions and bronchial epithelial regenerations. For further elucidation of the pathogenesis of lung cancer and of mesothelioma the localisation and transport of inhaled fibres is of high interest. Thus, a three dimensional visualization of the structure of rat lungs before and after intratracheal instillation of UICC crocidolite fibres was performed by plastic casts to follow the way of asbestos fibres in the lung tissues and the pleura. The casts allowed to demonstrate airway structures with imprints of epithelial cells and blood vessels of normal and treated animals by scanning electron microscopy. Instilled asbestos fibres transformed bronchial structures and resulted in cystic deformations of the pleural surface. The penetration of single fibres through bronchial trunks and the visceral pleura could be shown for the first time in a three-dimensional topography of the affected tissue. Now, there is support for similar results of histomorphological examinations indicating the possibility that asbestos fibres could penetrate the pleura and migrate into the pleural space. The question if the migration of fibres is a mechanical movement or an active transport is still under discussion.

In plain English

This was an animal experiment in rats. Young male Wistar or Sprague Dawley rats received a single dose of UICC crocidolite asbestos (2 mg per animal) into the windpipe; controls received salt solution only. Groups of 10 rats were killed from 3 days to 12 months later, and their lungs were examined by light and scanning electron microscopy and as plastic casts of airways and blood vessels. Fibres were found mostly in the lower lobe of the treated lung. The authors described erosion of the airway lining, local collagen deposits and, in part, adenomatous lesions. Fibres were seen in the visceral pleura, and after one year the pleura showed cell proliferation and focal fibrous thickening. Six months after instillation some pleural surface cells showed cystic deformations, mainly where fibres had penetrated. Casts showed thickened, deformed airways and, sometimes, a single fibre that possibly had penetrated the pleura. The article gives no counts of affected animals. The authors suggested that fibres reaching the pleural space could be one reason mesothelioma develops. They noted that inhalation studies mimic natural exposure more closely.

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: Animal experiment. Rats were given a single intratracheal instillation of crocidolite or, as controls, saline. Groups were killed at set times, and the lungs were examined by light microscopy, by scanning electron microscopy of tissue sections, and as methacrylate (plastic) casts.
• Who was studied: Specific pathogen-free male white Wistar or Sprague Dawley rats, 10 to 12 weeks old (250 g), obtained from Charles River, Germany. Groups of 10 rats were killed at each time point. In each group, 4 lungs were examined in paraffin sections and 4 were prepared for electron microscopy. Casts were made from adult Sprague Dawley rats. The total number of animals and the study dates are not stated.
• Exposure: UICC crocidolite A2-09 asbestos, 2 mg in 200 µl physiological saline per animal, given as a single intratracheal instillation under pentobarbital anaesthesia. Controls received physiological sodium chloride solution. Most fibres were described as about 2 µm in diameter and 5 µm long, with a length to diameter ratio of 5:1. The comparison symbol before the diameter is lost in the text.
• Main results:
  • In treated rats, crocidolite fibres were detected mostly in the lower lobe of the instilled right or left lung. The opposite lobes remained unaffected.
  • In treated rats, the local fibre burden induced erosions of the bronchial epithelium, accompanied by squamous metaplasia.
  • After 7 days, penetration of fibres led to local collagen deposition in treated rats.
  • In treated rats, epithelial cell proliferation, cellular infiltration of fibre deposits and granuloma formation partially resulted in adenomatous lesions. The tissue deformation was still visible after one year.
  • In histological sections from treated rats, crocidolite fibres were found in the main layer of the visceral pleura and seemed to penetrate its external basement membrane.
  • One year after instillation, mesothelial cells in treated rats proliferated into a multiple cell layer. Submesothelial cells also proliferated, producing a focal fibrous thickening of the visceral pleura.
  • Scanning electron microscopy of tissue sections from treated rats showed penetration of the bronchial wall by long fibres. Control sections showed normal alveoli and bronchi.
  • Six months after instillation, some mesothelial cells on the pleural surface of treated rats had developed cystic deformations, or had become flattened and lost their microvilli coat. This occurred mainly at sites of penetrated fibres.
  • Casts made 6 or 12 months after crocidolite instillation showed a thickened bronchial trunk, with multiple deformations at bifurcations and at sites where fibres had penetrated through the bronchi.
  • In casts from treated rats, remains of the visceral pleural layer sometimes contained a single fibre that possibly could have penetrated the visceral pleura and reached the pleural space.
• The authors' conclusion: The authors concluded that the casts showed crocidolite fibres penetrating the bronchi and visceral pleura. They suggested it is feasible that this routing of fibres, and their accumulation in the space between the pleural layers, could be one reason for the development of mesothelioma.
• Limitations the authors state:
  • Fibres were given by intratracheal instillation. The authors note that inhalation studies mimic natural exposure more closely.
  • There was some evidence that particles could have been retained in the trachea.
  • Fibres seen inside walls or pleura in tissue sections could have been moved there by the cutting knife. The authors give this as the reason they also used plastic casts.

Topics

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

Medical terms in this study, explained in our Lexicon: Lung Cancer, Mesothelioma, UICC, Crocidolite, Pleura, Scanning Electron Microscopy (SEM), Visceral Pleura.

Related studies

• The production of TNF-alpha and IL-1-like activity by bronchoalveolar leucocytes after intratracheal instillation of crocidolite asbestos — X.Y. Li, D. Lamb, et al. (1993)
• A study of the length and diameter of fibres, in lung and in broncho-alveolar lavage fluid, following exposure of rats to chrysotile asbestos — E. Kauffer, J.C. Vigneron, et al. (1987)
• Macrophage phagocytic activity and cell phagocytic capacity following intratracheal instillation of a comixture of asbestos fibers — I. Trosic, M. Matausic-Pisl, et al. (1995)
• Increased 8-hydroxyguanine in DNA and its repair activity in hamster and rat lung after intratracheal instillation of crocidolite asbestos — R. Yamaguchi, T. Hirano, et al. (1999)
• Comparison of functional, biochemical, and morphometric alterations in the lungs of 4 rat strains and hamsters following repeated intratracheal instillation of crocidolite asbestos — D.J. Padilla-Carlin, D.L. Costa (2011)
• MWCNT-7 administered to the lung by intratracheal instillation induces development of pleural mesothelioma in F344 rats — T. Numano, H. Higuchi, et al. (2019)

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