The calcification of fibrous pleural lesions produced in guinea-pigs by the injection of chrysotile asbestos dust

Our plain-English summary of The calcification of fibrous pleural lesions produced in guinea-pigs by the injection of chrysotile asbestos dust, by J.M. Davis (British Journal of Experimental Pathology, 1971).

The study

• Author: J.M. Davis
• Journal: British Journal of Experimental Pathology
• Published: 1971;52(3):238-43
• Cited by: 2 articles, as counted by NIH iCite
• Read it: PubMed · Free full text

Abstract

In guinea-pig pleural granulomas produced by the injection of chrysotile asbestos dust, the initial cellular lesions were replaced by old acellular fibrous tissue within 15-18 months. After this period calcification of the fibrous tissue commonly occurred. The first sign of calcification was always the formation among the collagen fibres of large numbers of spherical lamellated bodies. These structures stained positive for acid mucopolysaccharides, and electron-microscope observations showed that they were formed around a core of asbestos dust. Calcium in the form of apatite crystals was also often present in these structures. Shortly after the formation of lamellar bodies the mucopolysaccharide normally present on the collagen fibres, was removed and instead it formed a thick coating around any free asbestos dust in the fibrous area. The first signs of general calcium deposition were seen both in contact with collagen fibres and on the surface of the coated asbestos dust. Eventually calcium deposits filled all the tissue spaces and enclosed collagen, coated asbestos dust and lamellar bodies in a solid mass of calcification.

In plain English

This was an animal experiment at the University of Cambridge. Chrysotile asbestos dust (25 mg in 1 ml of distilled water) was injected into the lower right pleural cavity of guinea-pigs, killed at intervals from 7 days to 4 years later. The article did not state how many animals were used. The injections produced large granulomas and fibrous pleural thickening, and by 18 months the granulomas had usually become fibrous tissue. The first sign of calcification was always the formation of spherical laminated bodies among the collagen fibres. These were first seen about 12-15 months after injection and reached 30-40 micrometres across. All had a core of asbestos dust, and the larger ones contained calcium as apatite crystals. Most animals showed signs of pleural calcification by 18 months. Mucopolysaccharide then moved from the collagen to coat the remaining asbestos fibres, and complete calcification quickly followed. The author concluded that the observations did not show whether asbestos dust was essential for calcification. The author added that they gave no extra information on whether it is essential for producing calcified pleural plaques in humans.

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 (intrapleural injection in guinea-pigs, with light and electron microscope study of the pleural lesions)
• Who was studied: Guinea-pigs (number not stated; described as a larger series than the author's earlier report), killed at intervals from 7 days to 4 years after injection; Department of Pathology, University of Cambridge
• Exposure: A single injection of 25 mg of chrysotile asbestos dust in 1 ml of distilled water into the pleural cavity. The dust was mostly short bundles of fibrous chrysotile under 5 micrometres long.
• Main results:
  • In the guinea-pigs, giant cells were noticeably lost by 6-8 months after injection, and by 18 months the granulomas were usually completely fibrosed.
  • Spherical laminated bodies, the first sign of calcification, were first seen about 12-15 months after dust injection. Most animals showed signs of pleural calcification by 18 months.
  • The laminated bodies often reached 30-40 micrometres in diameter and contained acid mucopolysaccharide.
  • All the laminated bodies had a core of asbestos dust. Under the electron microscope, the larger ones contained calcium in the form of apatite crystals.
  • Shortly after the laminated bodies formed, mucopolysaccharide was lost from the collagen and deposited as a coating about 1-2 micrometres thick on the remaining asbestos fibres.
  • Once all the dust had been coated with mucopolysaccharide, complete calcification of the area quickly followed. Calcium deposits eventually enclosed the collagen, the coated dust and the laminated bodies.
  • Most calcifying areas showed three zones: a central zone of complete calcification, a middle zone of coated dust fibres with little calcium, and an outer zone of unchanged fibrous tissue.
• The authors' conclusion: The author concluded that the observations did not show whether asbestos dust in the old fibrosed granulomas was essential for calcification or only coincidentally involved. The asbestos was responsible for the initial fibrous tissue but may not influence later calcification. The study therefore gave no extra information on whether asbestos dust is essential for the production of calcified pleural plaques in humans, and an electron-microscope study of human plaques would be needed. The author also stated that the findings fit current theories on calcification.
• Limitations the authors state:
  • The observations could not show whether asbestos dust was essential for calcification or whether its presence was coincidental.
  • The author could not determine whether the laminated bodies formed outside cells or whether cells were needed for the initial coating.
  • The smaller laminated bodies were invisible under the light microscope and could not be told apart from cross-sections of laminated asbestos bodies under the electron microscope.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Pleural plaques and thickening.

Medical terms in this study, explained in our Lexicon: Chrysotile, Granuloma, Collagen, Deposition.

Related studies

• Asbestos dust as a nucleation center in the calcification of old fibrous tissue lesions, and the possible association of this process to the formation of asbestos bodies — J.M. Davis (1970)
• The long term fibrogenic effects of chrysotile and crocidolite asbestos dust injected into the pleural cavity of experimental animals — J.M. Davis (1970)
• Epithelial outgrowths from lung tissue following intrapleural injection of asbestos dust in experimental animals — J.M. Davis (1971)
• Prevalence of pleural calcification in persons exposed to asbestos dust, and in the general population in the same district — M. Navrátil, F. Trippé (1972)
• Pleural calcification, pleural mesotheliomas, and bronchial cancers caused by tremolite dust — S. Yazicioglu, R. Ilçayto, et al. (1980)
• The effects of inhaled crocidolites from Transvaal and North-west Cape mines on the lungs of rats and guinea-pigs — S.K. Botham, P.F. Holt (1972)

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