Use of animal models for studies on asbestos bioeffects

Our plain-English summary of Use of animal models for studies on asbestos bioeffects, by J.M.G Davis (1979).

The study

• Author: J.M.G Davis
• Published: Annals of the New York Academy of Sciences p795-798 (1979)
• Type of article: Journal article
• Our copy: from Johns-Manville's own medical library. The article is still under copyright, so we describe it here rather than post it.

In plain English

This short review examined animal studies of asbestos to find the best animal model. From other researchers' inhalation studies, the author reported that rats developed interstitial pulmonary fibrosis, bronchial carcinomas and occasional mesotheliomas. Hamsters, gerbils, cats and monkeys developed lung fibrosis, but no lung tumors were reported. Unlike humans, rats only very rarely form asbestos bodies. It also summarized an Edinburgh study (Davis et al.) in which rats breathed UICC chrysotile, crocidolite or amosite for one year. The author wrote that both chrysotile clouds caused more fibrosis than any amphibole cloud and that all malignant lung tumors were in chrysotile-treated rats. Two unclear table entries in this copy prevent checking these statements independently. Chrysotile groups had 8 bronchial carcinomas at 10 mg/m3 and 2 at 2 mg/m3. The number of rats per group was not given. The text said about 7% of chrysotile fibers exceeded 20 micrometres (the table showed more than 20%), against less than 0.5% for amphibole clouds. The author concluded the rat is the best available model, and saw strong support for long fibers being much more dangerous than short ones.

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: Review of published animal experiments on asbestos, including a summary of a rat inhalation experiment carried out in Edinburgh (Davis et al.)
• Who was studied: Review: rats, guinea pigs, rabbits, hamsters, gerbils, mice, cats, monkeys and baboons in other researchers' studies. Edinburgh experiment: rats (numbers not given). Some batches were killed at fixed timepoints; most were allowed to live their full life span.
• Exposure: Edinburgh experiment: one year of inhalation of UICC samples of chrysotile, crocidolite and amosite at 10 mg/m3. Chrysotile and crocidolite were also given at lower levels (2 and 5 mg/m3 in the table) to match the fiber numbers of the amosite cloud.
• Main results:
  • From the reviewed inhalation studies, rats developed interstitial pulmonary fibrosis, bronchial carcinomas and occasional mesotheliomas.
  • In the reviewed studies, cats and monkeys developed pulmonary fibrosis but no tumors. No pulmonary neoplasms were reported in hamsters, gerbils or mice.
  • Asbestos bodies, common in human lungs, occur only very rarely in rats.
  • Edinburgh rats, per the author's text: both chrysotile clouds produced more interstitial pulmonary fibrosis than any amphibole cloud, and all malignant lung tumors developed in chrysotile-treated animals. These statements cannot be checked independently against this copy of the table because two entries are unclear: the low-dose chrysotile fibrosis value and the amosite carcinoma entry.
  • Chrysotile 10 mg/m3 group: interstitial fibrosis of 9.15% of lung volume 29 months after the start of inhalation, and 8 bronchial carcinomas.
  • Chrysotile 2 mg/m3 group: 2 bronchial carcinomas. The fibrosis value is printed as '186' and cannot be confirmed.
  • The author reported a marked dose-response effect between the two chrysotile clouds for both fibrosis and malignancy.
  • Amosite 10 mg/m3 group: interstitial fibrosis of 2.58% of lung volume at 29 months. The bronchial carcinoma entry is unreadable.
  • Crocidolite groups: fibrosis of 1.38% (10 mg/m3) and 0.76% (5 mg/m3) of lung volume at 29 months, with 0 bronchial carcinomas in each.
  • The text states that, by scanning electron microscopy, crocidolite and amosite clouds had less than 0.5% of fibers longer than 20 micrometres and chrysotile clouds had about 7%. The table as printed gives more than 20% for both chrysotile clouds.
  • The author interpreted the data as strong support for the idea that long asbestos fibers are much more dangerous than short ones, and found fiber mass unimportant.
• The authors' conclusion: The author concluded that the rat represents the best available animal model for asbestos studies.
• Limitations the authors state:
  • Rats rarely form asbestos bodies, and it is uncertain whether this is a serious disadvantage for reproducing human tissue reactions.
  • The lowest dose in the intrapleural injection studies (0.5 mg) is large compared with what a human lung could accumulate from the urban environment, so lower-dose experiments are needed.
  • Primates might respond more like humans, but their high cost would preclude large-scale use.

Topics

Medical terms in this study, explained in our Lexicon: Interstitial, Pulmonary Fibrosis, Carcinoma, Mesothelioma, Fibrosis, Asbestos Bodies, UICC, Chrysotile.

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