Early response of the visceral pleura following asbestos exposure: an ultrastructural study

Our plain-English summary of Early response of the visceral pleura following asbestos exposure: an ultrastructural study, by R.F. Dodson, J.O. Ford (Journal of Toxicology and Environmental Health, 1985).

The study

• Authors: R.F. Dodson, J.O. Ford
• Journal: Journal of Toxicology and Environmental Health
• Published: 1985;15(5):673-86
• Cited by: 15 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The acute in vivo response of the visceral pleura following intracheal instillation of amosite asbestos was examined by light microscopy and by transmission and scanning electron microscopy in the guinea pig model. Asbestos fibers were observed close to the pleura in all time periods but were never found within the pleura or subpleural regions proper. Thus, pleural changes occurred in the absence of direct fiber contact. Morphological changes in the pleural and subpleural areas were seen as early as 2 h after exposure and were associated with pathological alterations of the underlying parenchyma. The normally squamous mesothelial cells became pleomorphic in experimental animals, ranging from slightly cuboidal, to protruding "columnar-like" cells, to more bizarre forms. While many organelles remained unaltered, an increase in vacuolization in portions of the pleura indicated localized and advanced intracellular responses. Beginning at 4 h postexposure, varied numbers of particulate-free macrophages were seen on the pleural surface, and were considered an extension of the inflammatory response occurring in the underlying parenchyma. Early proliferation of the mesothelial cells, in limited areas of the pleura, and cytoplasmic extensions into the pleural space were also observed. Distortions of the basal lamina and smooth-muscle bundles accompanied the morphological changes in the pleural cells. A trend toward normality was observed in the longer time frames, but some areas of pleural change persisted through 3 mo postexposure.

In plain English

In this laboratory experiment, the authors placed a single 25-mg dose of amosite asbestos in saline directly into the windpipe of young adult guinea pigs. Control animals received saline only. Two exposed animals and one control were examined at each time point, from 2 hours to 3 months, using light and electron microscopy of the visceral pleura, the thin lining that covers the lungs. Asbestos fibers were seen in the lung close to the pleura at every time point, but they were never found within the pleura or the tissue just beneath it. Even so, pleural changes appeared as early as 2 hours. Normally flat lining cells took on irregular shapes, and some areas showed extensive vacuoles. From 4 hours, small areas of extra cell layers appeared, and macrophages carrying no particles gathered on the pleural surface. Most changes were linked to collapse or blockage of the underlying lung. By 1 and 3 months most of the pleura had returned to a single layer of flat cells, but some changed areas remained. The authors concluded that pleural changes occurred within 2 hours and that some persisted through 3 months.

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 (guinea pigs), examined by light microscopy and by transmission and scanning electron microscopy, with saline-injected controls
• Who was studied: Young adult Hartley-Duncan guinea pigs from the University of Texas Health Center at Tyler colony. Three animals per time period (two exposed, one saline control), examined at 2 or 4 hours; 1, 2, 3, 4, 5, 6 or 7 days; or 1 or 3 months after instillation
• Exposure: A single intratracheal instillation of 25 mg of commercial grade amosite asbestos in 0.5 ml of physiological saline. In the prepared sample, 92% of fibers were under 10 micrometres long and the average width was under 0.4 micrometres
• Main results:
  • In exposed animals, asbestos fibers were seen close to the pleura at all time periods but were never found within the pleura or subpleural regions; pleural changes occurred in the apparent absence of fibers in the immediate area
  • In exposed animals, changes in the pleural and subpleural regions were seen as early as 2 hours after exposure and continued to various degrees through 3 months
  • Most pleural changes in exposed animals were associated with alteration of the underlying lung due to atelectasis (collapse) or blockage of alveoli by phagocytes and exudate; mesothelial cells in these regions became pleomorphic, from slightly cuboidal to protruding 'columnar-like' to more bizarre forms
  • Beginning 2 hours after exposure, and more often at later times, portions of the mesothelium in exposed animals showed extensive vacuolization of multiple adjacent cells; such extensive regions were never seen in control animals
  • In exposed animals, limited proliferation of the mesothelial layer was first noted at 4 hours and was more extensive by 5 days
  • In exposed animals, macrophages appeared on the pleural surface as early as 4 hours and were particularly numerous at 5 and 6 days; no particulates were noted in mesothelial cells, surface macrophages, or the subpleural connective tissue
  • In exposed animals, the basal lamina and smooth-muscle bundles beneath the pleura were distorted, from 2 hours through 7 days after exposure
  • At 1 and 3 months, most of the pleural surface in exposed animals had reverted to a single layer of relatively flat cells; where lung collapse remained, the adjacent pleura still showed cuboidal, vacuolated forms; no particulates were seen in pleural or subpleural regions
• The authors' conclusion: The authors concluded that acute changes in the visceral pleura occurred as early as 2 hours after intratracheal asbestos exposure, followed a pattern similar in intensity to inflammation in the underlying lung, and trended toward normal, though alterations in some pleural regions persisted through 3 months. They suggested that vacuolization may result from chemically mediated stimuli rather than direct fiber contact.
• Limitations the authors state:
  • Mitotic figures (dividing cells) were not observed; the authors note that their absence at these sampling intervals cannot be used to exclude proliferation of mesothelial cells

Topics

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

Medical terms in this study, explained in our Lexicon: Visceral Pleura, Asbestos Exposure, Amosite, Scanning Electron Microscopy (SEM), Pleura, Parenchyma, Mesothelial Cells, Pleomorphic.

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