The use of animal models for studies on asbestos bioeffects

Our plain-English summary of The 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, vol. 330, pp. 795-797 (Workshop: Laboratory Models for Chronic Toxicity Testing) (1979)
• Type of article: Conference paper
• 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

J M G Davis of the Institute of Occupational Medicine, Edinburgh, wrote this workshop paper. It reviewed animal studies of inhaled asbestos to judge which species best reproduces human disease. Guinea pigs, rabbits, hamsters, gerbils, cats and vervet monkeys developed lung fibrosis in these studies, but no tumors were reported. Rats developed interstitial pulmonary fibrosis, bronchial carcinomas and occasional mesotheliomas. Rats very rarely formed asbestos bodies; the author was unsure whether this was a serious drawback. The author also summarized recent Edinburgh rat experiments using inhaled chrysotile, crocidolite or amosite for one year. Chrysotile produced more interstitial fibrosis than the amphiboles, all malignant lung tumors occurred in chrysotile-treated rats, and both chrysotile levels showed a marked dose-response effect. The text put fibers longer than 20 µ at approximately 7% in the chrysotile clouds and less than 0.5% in the amphibole clouds, though the table appears to print 20% for chrysotile. The author concluded that the rat was the best available model and that the data strongly supported the idea that long asbestos fibers are 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 / workshop paper on animal models, including a summary of the author's group's earlier rat inhalation experiments (Davis et al., published separately)
• Who was studied: Published inhalation studies in rats, guinea pigs, rabbits, hamsters, gerbils, mice, cats, vervet monkeys and baboons, plus recent rat inhalation studies in Edinburgh
• Exposure: Inhaled asbestos. In the Edinburgh studies, UICC samples of chrysotile, crocidolite and amosite were given at 10 mg/m3 for one year. Chrysotile and crocidolite were also given at lower levels to match the fiber numbers of the amosite cloud.
• Main results:
  • Of the species reviewed, only rats developed interstitial pulmonary fibrosis, bronchial carcinomas and occasional mesotheliomas after asbestos inhalation
  • Guinea pigs developed interstitial pulmonary fibrosis, but no bronchial carcinomas or mesotheliomas were recorded in them
  • In a baboon inhalation study, reported only by personal communication, one pleural mesothelioma had apparently been found five years after inhalation began
  • Asbestos bodies occur only very rarely in rats, unlike in humans and the other species reviewed
  • In the Edinburgh rat studies, both chrysotile clouds produced more interstitial fibrosis than any amphibole cloud, and all malignant lung tumors developed in chrysotile-treated rats
  • The two chrysotile clouds showed a marked dose-response effect for both fibrosis and malignancy
  • The prose states that, by scanning electron microscope, the chrysotile clouds had approximately 7% of fibers over 20 µ in length and the crocidolite and amosite clouds less than 0.5%. Table 1 as scanned appears to give 20% for each chrysotile cloud, so the chrysotile figure is inconsistent within the article.
• The authors' conclusion: The author concluded that the rat is the best available animal model for asbestos studies, and that the Edinburgh data strongly support the idea that long asbestos fibers are much more dangerous than short ones
• Limitations the authors state:
  • It is uncertain whether the rat's inability to form asbestos bodies is a serious disadvantage for reproducing human tissue reactions
  • The lowest dose tested in the rat injection studies (0.5 mg) is large compared with what a human lung could accumulate from the urban environment, so experiments with much lower doses are needed

Topics

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

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