Experimental asbestosis: an investigation of functional and pathological disturbances. II. Results for chrysotile and amosite exposures

Our plain-English summary of Experimental asbestosis: an investigation of functional and pathological disturbances. II. Results for chrysotile and amosite exposures, by D.M. Hiett (British Journal of Industrial Medicine, 1978).

The study

• Author: D.M. Hiett
• Journal: British Journal of Industrial Medicine
• Published: 1978;35(2):135-45
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

ABSTRACT Long-term studies of respiratory function and lung morphology were carried out on control groups of guinea pigs and matched groups exposed by inhalation to asbestos dust. Animals were exposed to aerosols of chrysotile or amosite asbestos containing large numbers of short fibres, for either 9 or 18 days. Resistance and dynamic compliance of the guinea pig respiratory system were measured non-destructively, while the point counting technique was applied to the histological preparations. Under these exposure conditions the extent of pathological and functional changes were not related to differences in duration of exposure. Such changes were more marked, however, in animals exposed at eight rather than three months of age. The measurement of dynamic compliance provided the most sensitive assessment of the functional disturbances, which were more extensive following chrysotile exposure. Progressive peribronchiolar fibrosis developed about 40 weeks after chrysotile exposure at eight months of age, but not until about 70 weeks for animals exposed when three months old. No fibrotic reaction was seen during the 70 weeks of the amosite experiments. The relationships between pathological and functional changes throughout these experiments are discussed, and explanations for the apparent differences in fibrogenicity between chrysotile and amosite are suggested. Early detection of asbestosis may be aided by use of lung function tests known to be sensitive to small airways disease.

In plain English

In this animal experiment, male guinea pigs inhaled chrysotile or amosite aerosols with many short fibres for a single 9- or 18-day period. They were compared with unexposed controls in five experiments lasting 40 to 100 weeks. The author measured breathing function and examined lung tissue. After chrysotile, dynamic compliance (lung stretchiness) first fell below 50% of control values. In all three chrysotile groups it stayed significantly reduced through the analysed period: up to 45 weeks, or 40 weeks for the shortest experiment. Scarring around the small airways (peribronchiolar fibrosis) appeared at 40 and 45 weeks in animals exposed at eight months, and from 70 weeks in one group exposed at three months. Another three-month group showed none during its 40-week experiment. Amosite was followed by shorter-lasting function changes and no apparent collagen formation over the period studied. Under these conditions, exposure length made little difference, while animals exposed at eight months were more affected than those exposed at three months. The author concluded that chrysotile was more fibrogenic than amosite in these experiments, and that tests sensitive to small airways disease may aid early detection of asbestosis.

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 inhalation experiment: exposed guinea pigs compared with matched unexposed controls, with repeated lung function tests and lung tissue examination (point counting) over time
• Who was studied: Male guinea pigs of one strain, in five experiments. Chrysotile C1: 44 exposed, 16 controls, aged 3 months, followed 100 weeks. C2: 16 exposed, 14 controls, 3 months, 40 weeks. C3: 10 exposed, 10 controls, 8 months, 45 weeks. Amosite A1: 12 exposed, 10 controls, 8 months, 70 weeks. A2: 18 exposed, 8 controls, 3 months, 70 weeks. Exposures took place at Reading University and testing at Manchester University. The years of the experiments are not stated.
• Exposure: A single inhalation exposure to an aerosol of chrysotile or amosite asbestos containing large numbers of short fibres, lasting 9 or 18 days. Exposure methods are described in Part I of the study.
• Main results:
  • After chrysotile exposure, compliance in all three chrysotile groups (C1, C2, C3) first fell to less than 50% of control values.
  • Compliance in all three chrysotile groups remained significantly reduced over the period analysed. That analysis covered up to 45 weeks from the start of exposure; the C2 experiment lasted 40 weeks.
  • In the 100-week chrysotile experiment (C1), compliance stayed reduced throughout, with a slight tendency towards further worsening after 80 weeks.
  • Peribronchiolar fibrosis was seen at 40 and 45 weeks in the chrysotile group exposed at 8 months of age (C3).
  • Similar fibrosis was seen from 70 weeks onwards in the chrysotile group exposed at 3 months for 9 days (C1).
  • No fibrosis developed during the 40-week experiment in the chrysotile group exposed at 3 months for 18 days (C2).
  • In the 9-day chrysotile group (C1), the share of lung volume made up of normal alveoli did not fully recover to the control mean during the 100-week experiment. The control mean, reported in Part I, was 94.4%.
  • After amosite exposure, breathing-function disturbances were much less prolonged than after chrysotile.
  • In the amosite groups, occasional large focal dust deposits formed, but with no apparent collagen formation during the period studied.
  • Comparing the two chrysotile groups exposed at 3 months (C1 for 9 days, C2 for 18 days), the longer exposure had little effect on the extent of later changes under the conditions used. One exception: tidal volume was reduced significantly more in the 18-day group.
  • In the amosite experiments, the group exposed at 3 months for 18 days (A2) stayed significantly less affected in compliance than the group exposed at 8 months for 9 days (A1), despite its longer exposure.
• The authors' conclusion: The author concluded that, in these experiments, chrysotile was more fibrogenic than amosite. The author noted that this contrasts with some earlier studies and suggested that differences in fibre length and blocked clearance from the small airways may explain it. The author also concluded that experimental asbestosis can be monitored with simple breathing tests related to tissue findings, and that, regardless of the type of asbestos inhaled, breathing tests sensitive to small airways disease may aid early detection of asbestosis.
• Limitations the authors state:
  • Because of technical difficulties, the first amosite experiment and the third chrysotile experiment were started with 8-month-old rather than 3-month-old animals.
  • The tissue volume analysis was not done for the C2 experiment, because fewer samples were taken.
  • The C3 experiment had too few results for trend analysis of bronchiole changes.
  • Animals at different positions in the exposure chamber showed a gradient of fibre concentration in their breathing disturbances.
  • The author noted that differences in fibre length between the aerosols used by different researchers may cause their findings to disagree.

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Amosite, Point Counting, Fibrosis.

Related studies

• Human and experimental data on translocation of asbestos fibers through the respiratory system — J. Bignon, G. Monchaux, et al. (1979)
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• Experimental lung tumors following specific intrabronchial application of chrysotile asbestos. Longitudinal light and electron microscopic investigations in rats — E. Fasske (1988)
• Quantification of the pathological response and fate in the lung and pleura of chrysotile in combination with fine particles compared to amosite-asbestos following short-term inhalation exposure — D.M. Bernstein, R.A. Rogers, et al. (2011)
• The pathological response and fate in the lung and pleura of chrysotile in combination with fine particles compared to amosite asbestos following short-term inhalation exposure: interim results — D.M. Bernstein, R.A. Rogers, et al. (2010)
• Evaluation of the exposure, dose-response and fate in the lung and pleura of chrysotile-containing brake dust compared to TiO2, chrysotile, crocidolite or amosite asbestos in a 90-day quantitative inhalation toxicology study - Interim results Part 1: Experimental design, aerosol exposure, lung burdens and BAL — D.M. Bernstein, B. Toth, et al. (2020)

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