Pulmonary effects in rats inhaling size-separated chrysotile asbestos fibres or p-aramid fibrils: differences in cellular proliferative responses

Our plain-English summary of Pulmonary effects in rats inhaling size-separated chrysotile asbestos fibres or p-aramid fibrils: differences in cellular proliferative responses, by D.B. Warheit, M.A. Hartsky, S.R. Frame (Toxicology Letters, 1996).

The study

• Authors: D.B. Warheit, M.A. Hartsky, S.R. Frame
• Journal: Toxicology Letters
• Published: 1996;88(1-3):287-92
• Cited by: 10 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

This study was designed to compare the pulmonary cellular proliferative effects of inhaled, size-separated preparations of chrysotile asbestos fibres with similar aerosol fibre concentrations of para-aramid fibrils. Following fibre preparation, rats were exposed for 2 weeks to aerosols of p-aramid fibrils or chrysotile asbestos fibres at design fibre concentrations of 750 and 400 f/cc. Two week exposures to p-aramid fibrils produced transient pulmonary inflammatory and cell labeling responses in terminal bronchiolar and subpleural regions. Similar to p-aramid, exposure to chrysotile produced a transient increase in neutrophils. In contrast, however, substantial increases compared to controls in pulmonary cell labeling indices were measured on terminal bronchiolar, parenchymal, subpleural, and mesothelial surfaces immediately after exposure, and some increases persisted for 3 months postexposure. In complementary studies we demonstrated that p-aramid is biodegradable in the lungs of exposed rats; in contrast, the clearance of long chrysotile fibres was slow or insignificant, resulting in a pulmonary retention of long chrysotile asbestos fibres. The dimensional changes of asbestos fibres as well as the pulmonary cell labeling data indicate that chrysotile asbestos fibres may produce greater long-term pulmonary effects when compared to inhaled para-aramid fibrils.

In plain English

This was an animal experiment. Groups of male rats breathed either Canadian chrysotile asbestos or p-aramid fibrils (Kevlar) for 6 hours a day, 5 days a week, for two weeks, at two concentrations of each. Measured average concentrations were 458 and 782 fibres per cc for chrysotile and 419 and 772 for p-aramid. The chrysotile had been sieved to favour longer fibres, which raised the median length from 3 to 6 micrometres. Sham-exposed rats served as controls. The researchers examined the lungs for signs of cell division at times from immediately after exposure to 12 months later. P-aramid caused only short-lived increases, in the airways and just beneath the lung surface. In high-dose chrysotile rats, increases were significant in the airways, lung tissue and beneath the lung surface through 3 months, returning to control levels at 6 months. In mesothelial cells covering the lung, increases lasted through 1 month according to the figure legend. Chrysotile fibres recovered from the lungs grew longer on average over time, which suggested that short fibres were cleared and long ones retained. The authors concluded that chrysotile is likely to cause greater long-term lung effects than p-aramid.

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 comparing two fibre types at two concentrations each, with sham-exposed controls and follow-up after exposure
• Who was studied: Male Crl:CD BR rats, 7-8 weeks old, from Charles River Breeding Laboratories (Kingston, New York), plus age-matched sham controls. Lungs were evaluated immediately and at 5 days and 1, 3, 6 and 12 months after exposure. The total number of rats per group is not stated.
• Exposure: Size-separated Canadian chrysotile asbestos, with median fibre length raised from 3 to 6 micrometres, or Kevlar p-aramid fibrils. Exposure was 6 hours a day, 5 days a week, for two weeks. Target concentrations were 400 and 750 fibres longer than 5 micrometres per cc. Final mean concentrations were 458 and 782 f/cc for chrysotile and 419 and 772 f/cc for p-aramid.
• Main results:
  • In chrysotile-exposed rats, cell labeling (a marker of cell division) was significantly increased compared with controls on terminal bronchiolar, parenchymal, subpleural and visceral pleural surfaces, from immediately after exposure through 3 months postexposure.
  • According to the figure legends for terminal bronchiolar, alveolar parenchymal and subpleural cells, the significant increases were in the high-dose chrysotile groups at 0 hours, 5 days, 1 month and 3 months, and returned to control levels at 6 months.
  • For mesothelial cells of the visceral pleura, the figure legend reports significant increases in the high-dose chrysotile groups at 0 hours, 5 days and 1 month, returning to control levels at 6 months.
  • P-aramid fibrils produced only transient increases in cell labeling in airway and subpleural regions, seen immediately after exposure but not 5 days later.
  • In p-aramid-exposed rats, there were no significant increases in labeling of alveolar parenchymal cells or mesothelial cells compared with controls.
  • The median and mean lengths of chrysotile fibres recovered from lung tissue increased over time. This suggested selective clearance of short fibres and little clearance of long fibres.
• The authors' conclusion: The authors concluded that inhaled chrysotile asbestos is likely to produce greater long-term pulmonary toxic effects than para-aramid fibrils.

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Fibril.

Related studies

• Lung proliferative and clearance responses to inhaled para-aramid RFP in exposed hamsters and rats: comparisons with chrysotile asbestos fibers — D.B. Warheit, S.I. Snajdr, et al. (1997)
• A comparative study of the clearance of respirable para-aramid, chrysotile and glass fibres from rat lungs — A. Searl (1997)
• A review of inhalation toxicology studies with para-aramid fibrils — D.B. Warheit (1995)
• Cytotoxic effects of aramid fibres on rat pulmonary macrophages: comparison with chrysotile asbestos — J. Dunnigan, D. Nadeau, et al. (1984)
• The inhalation toxicology of p-aramid fibrils — K. Donaldson (2009)
• Man-made respirable-sized organic fibers: what do we know about their toxicological profiles? — D.B. Warheit, K.L. Reed, et al. (2001)

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