Characterization of asbestos fibers in lungs and mesotheliomatous tissues of baboons following long-term inhalation

Our plain-English summary of Characterization of asbestos fibers in lungs and mesotheliomatous tissues of baboons following long-term inhalation, by K. Hiroshima, Y. Murai, Y. Suzuki, et al (American Journal of Industrial Medicine, 1993).

The study

• Authors: K. Hiroshima, Y. Murai, Y. Suzuki, B. Goldstein, I. Webster
• Journal: American Journal of Industrial Medicine
• Published: 1993;23(6):883-901
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Changes in the dimensions of inhaled asbestos fibers in the lung and translocation of intrapulmonary asbestos fibers into mesothelial tissues were investigated in 17 baboons (5 exposed to amosite, 4 to chrysotile, 5 to crocidolite, and 3 unexposed). The animals received different cumulative doses of asbestos by inhalation, followed by varying recovery periods (0-69 months). All asbestos types induced pulmonary asbestosis with severity directly related to the cumulative dose. There were a larger number of asbestos bodies in the lung of the amphibole-exposed animals than in those exposed to chrysotile. A tissue burden study, using transmission electron microscopy on 25-microns paraffin sections, ashed in a low-temperature asher, was performed. Intrapulmonary amosite fibers were shorter in geometric mean length compared with a standard amosite sample (UICC) (3.3 microns). In explanation, it was considered that long fibers might not be able to reach the lower respiratory tract and/or long fibers might be fragmented into shorter fibers. Further, in the amosite-exposed group, the mean length of intrapulmonary fibers increased with the extension of recovery period, suggesting that shorter fibers had been cleared from the lung. The chrysotile standard sample (UICC) had a shorter geometric mean length (1.1 microns) than amosite. The mean length of intrapulmonary chrysotile did not noticeably change with the extension of inhalation and recovery periods; however, the mean width decreased with the extension of these periods. This finding strongly suggested that separation of thick chrysotile fibers had occurred in the lung. The crocidolite standard sample (Transvaal) had a shorter geometric mean length (1.4 microns) than amosite.(ABSTRACT TRUNCATED AT 250 WORDS)

In plain English

This animal experiment examined lung tissue from 17 baboons in inhalation experiments at the National Centre for Occupational Health in South Africa, and tumor tissue from the four that developed mesothelioma. Fourteen inhaled asbestos (5 amosite, 4 chrysotile, 2 Transvaal crocidolite and 3 UICC crocidolite), and 3 were unexposed controls. Fibers were measured by electron microscopy in ashed tissue sections. All three fiber types induced diffuse interstitial fibrosis, with severity related to cumulative dose. Fibrosis was more severe with amphiboles, but those animals mostly had higher doses. Four baboons developed malignant mesothelioma: pleural in two amosite-exposed animals and one UICC crocidolite-exposed animal, and peritoneal in one UICC crocidolite-exposed animal. Amosite fibers in the lung were shorter in geometric mean length (1.9-3.1 micrometers) than the standard sample (3.3 micrometers), and they were longer as the recovery period increased. Chrysotile fibers in the lung were thinner than the standard sample. Electron microscopy found asbestos fibers in all four tumors. No fibers were found in control lungs. The authors concluded that inhaled fibers can be translocated from the lung to the pleura and peritoneum.

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: analysis of lung and tumor tissue from baboons exposed to asbestos by inhalation, using transmission electron microscopy of low-temperature-ashed 25-micrometer sections
• Who was studied: 17 baboons from inhalation experiments in South Africa: 14 exposed (5 amosite, 4 chrysotile, 2 Transvaal crocidolite, 3 UICC crocidolite) and 3 unexposed controls. Tumor tissue came from the 4 that developed mesothelioma.
• Exposure: Inhalation of UICC amosite, Rhodesian chrysotile (UICC chrysotile A), or crocidolite (Transvaal or UICC) in an inhalation chamber 6 hours a day, 5 days a week, followed by varying recovery periods
• Main results:
  • All three asbestos types induced diffuse interstitial fibrosis in the baboon lung, with severity related to cumulative dose
  • Fibrosis was more severe and asbestos bodies more numerous in amphibole-exposed animals than in chrysotile-exposed animals, although the amphibole-exposed animals mostly had higher cumulative doses
  • 4 of 17 baboons developed malignant mesothelioma: pleural in two amosite-exposed animals (#3, #4) and one UICC crocidolite-exposed animal (#13), and peritoneal in one UICC crocidolite-exposed animal (#14)
  • Amosite fibers in the lungs were shorter in geometric mean length (1.9-3.1 micrometers) than the standard amosite sample (3.3 micrometers)
  • In amosite-exposed baboons, mean fiber length in the lung was greater as the recovery period increased
  • Chrysotile fibers in the lungs had geometric mean widths of 0.043-0.063 micrometers, all less than the standard sample (0.11 micrometers)
  • Crocidolite fibers were longer in the lung of the baboon exposed to Transvaal crocidolite for 24 months than in the one exposed for 11 months
  • Fiber dimensions showed no specific tendency to differ among the four interstitial lung sites (peribronchiolar, alveolar septal, subpleural, interlobular connective tissue)
  • Electron microscopy showed asbestos fibers in all four mesothelioma tissues, although none were seen by light microscopy
  • Fiber size in tumor tissue did not differ significantly from the lung in two animals. In the other two, fibers in the tumor were shorter and thinner, with no statistically significant difference in aspect ratio
  • Fragmentation and separation of fibers in the lung were more common for chrysotile than for amosite or crocidolite
  • No asbestos fibers were found in the lungs of the three control baboons
• The authors' conclusion: The authors concluded that their findings strongly suggest fragmentation, separation, and translocation of inhaled fibers are important contributory factors determining the size and distribution of fibers in the lung. They also concluded that the data give evidence that inhaled fibers, amphiboles as well as chrysotile, can be translocated from the lung into the pleura and peritoneum.
• Limitations the authors state:
  • Most chrysotile-exposed baboons died within a few years of first exposure from unknown causes, so only asbestosis could be reported for chrysotile
  • The ashed-section method cannot give the number of fibers per gram of tissue
  • Some very long fibers might be cut when tissue blocks are sectioned
  • Amphibole-exposed animals mostly had higher cumulative doses than chrysotile-exposed animals, which affects the comparison of fibrosis severity
  • The UICC crocidolite standard sample was not characterized because it had not been obtained
  • The authors could not determine whether fiber sizes in the tumors were similar to or different from those in the lung, and say further study is needed

Topics

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

Medical terms in this study, explained in our Lexicon: Translocation, Amosite, Chrysotile, Crocidolite, Cumulative Exposure, Asbestosis, Asbestos Bodies, Amphibole Group.

Related studies

• Malignant mesothelioma induced in baboons by inhalation of amosite asbestos — I. Webster, B. Goldstein, et al. (1993)
• The effects of asbestos-cement dust inhalation on baboons — B. Goldstein, I. Webster, et al. (1978)
• Comparison of Calidria chrysotile asbestos to pure tremolite: final results of the inhalation biopersistence and histopathology examination following short-term exposure — D.M. Bernstein, J. Chevalier, et al. (2005)
• 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)
• Comparison of Calidria chrysotile asbestos to pure tremolite: inhalation biopersistence and histopathology following short-term exposure — D.M. Bernstein, J. Chevalier, et al. (2003)

Browse more research in American Journal of Industrial Medicine, or return to medical research.