Changes in numbers and dimensions of chrysotile asbestos fibers in lungs of rats following short-term exposure

Our plain-English summary of Changes in numbers and dimensions of chrysotile asbestos fibers in lungs of rats following short-term exposure, by V.L. Roggli, A.R. Brody (Experimental Lung Research, 1984).

The study

• Authors: V.L. Roggli, A.R. Brody
• Journal: Experimental Lung Research
• Published: 1984;7(2):133-47
• Cited by: 85 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Previous studies from this laboratory have demonstrated that in rats exposed briefly to aerosolized chrysotile asbestos, fibers initially deposited in the distal lung impact primarily at bifurcations of alveolar ducts. Subsequently, there is a progressive decrease in the numbers of fibers seen by scanning electron microscopy at the bifurcations with increasing time from initial exposure. The purpose of the present study was to assess the number and dimensions of fibers deposited in the lungs of these rats and to determine how these parameters changed at various intervals after the termination of exposure. This was accomplished using a sodium hypochlorite digestion-concentration technique to recover the fibers on a membrane filter. The numbers and dimensions of the fibers were then assessed using scanning electron microscopy. Utilizing these data, the mass of asbestos retained in the lung was calculated with a newly developed formula. Twenty-three percent of the respirable fraction was deposited in the lungs, and 19% of this amount was still present 31 days after exposure. Over the 31 days, there was a progressive increase (p less than 0.05) in mean fiber length and a significant decrease (p less than 0.05) in the diameter of the population of fibers retained in the lung. Such data should prove useful in attempting to understand the progressive pathogenesis of asbestos-induced interstitial lung disease, which seems to be related, at least in part, to the dimensions of the inhaled fibers.

In plain English

In this animal experiment, young male CD-1 rats breathed chrysotile asbestos in nose-only chambers for one hour at 15 micrograms per liter. Groups of three to six were killed immediately and about 1, 8, 14 and 31 days later. Two sham rats breathed room air. Lung tissue was dissolved in bleach, and recovered fibers were counted and measured by electron microscopy. Of 90 micrograms of respirable chrysotile inhaled, 21 micrograms (23%) was deposited in the lungs; 19% of that remained at 31 days. Fiber numbers and mass fell over time. Recovered fibers had a significantly smaller mean diameter from 8 days on and a significantly greater mean length at 31 days. In standard chrysotile samples, isolation significantly raised fiber counts and lowered mean length and diameter, apparently because small fibrils broke off larger bundles. The authors said the smaller diameters might instead reflect changes in the body making fibers easier to break during processing. They concluded that fiber number and mass decreased and retained fiber dimensions changed significantly, and called for further studies on what this means for asbestos-induced lung disease.

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 with sequential sacrifice of rats after a single 1-hour exposure
• Who was studied: 8-week-old male CD-1 rats. Three to six exposed rats were killed at each time point: immediately, about 1 day (24 to 25 hours), 8 days, 2 weeks and about 1 month (31 days) after exposure. Two sham-exposed rats breathed room air and were killed at 1 month.
• Exposure: Aerosolized chrysotile asbestos (Lot AX3738-M, from Johns-Manville, Quebec, Canada), nose-only, for 1 hour, at a respirable mass concentration of 15 micrograms per liter (15 mg per cubic meter)
• Main results:
  • For the exposed rats, the total respirable mass inhaled during the 1-hour exposure was 90 micrograms, of which 21 micrograms (23%) was deposited in the lungs. The scan prints the unit as 'pg', but the article's own figures (15 micrograms per liter, 0.100 liter per minute, 60 minutes) confirm micrograms.
  • At 31 days after exposure, 19% of the deposited asbestos was still present in the rats' lungs
  • In the exposed rats, fiber concentration per gram of lung and total asbestos mass in both lungs decreased progressively with time after exposure
  • The mean diameter of the population of retained fibers fell from 0.165 micrometers (rats killed immediately) to 0.095 micrometers (rats killed at 31 days). The decrease was first statistically significant (p less than 0.05) at 8 days.
  • The mean length of the population of retained fibers rose from 2.84 micrometers (rats killed immediately) to 6.05 micrometers (rats killed at 31 days). The 31-day group's mean length was significantly greater (p less than 0.05) than all other groups.
  • The authors said their data may show a two-phase clearance process. The values given for the two phases were 4 days and 55 days.
  • In standard chrysotile suspensions, the isolation procedure significantly increased fiber number and decreased fiber length and diameter (p less than 0.05). It caused no detectable change in fiber mass.
  • The authors attributed the change in numbers and dimensions in the standard samples to small fibrils apparently breaking off larger chrysotile fiber bundles
  • The small numbers of fibers found in the two sham-exposed rats were attributed to contamination of reagents or filters
• The authors' conclusion: The authors concluded that, during the period when fibers move from the air spaces into the interstitium or are taken up by alveolar macrophages, fiber number and mass decrease progressively and the dimensions of retained fibers change significantly. They said further studies are needed to understand how this bears on asbestos-induced lung disease.
• Limitations the authors state:
  • The method shares the drawbacks of fiber-counting techniques, such as uneven deposition of fibers on the filter
  • Small changes in the number of long fibers strongly affect mean length and calculated mass. Mass is also very sensitive to diameter measurements.
  • The isolation technique altered fiber numbers and dimensions. The authors could not determine how much it altered fibers recovered from tissue, and said the length increase may be an underestimate.
  • The decrease in fiber diameter might instead reflect changes in the body that made fibers more easily broken by the digestion procedure

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, Short-Term Exposure, Scanning Electron Microscopy (SEM), Sodium Hypochlorite Digestion, Respirable Fraction, Fiber Length, Interstitial Lung Disease.

Related studies

• Clearance and dimensional changes of crocidolite asbestos fibers isolated from lungs of rats following short-term exposure — V.L. Roggli, M.H. George, et al. (1987)
• 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)
• Biopersistences of man-made vitreous fibers and crocidolite fibers in rat lungs following short-term exposures — R.P. Musselman, W.C. Miiller, et al. (1994)
• Evaluation of the deposition, translocation and pathological response of brake dust with and without added chrysotile in comparison to crocidolite asbestos following short-term inhalation: interim results — D.M. Bernstein, R. Rogers, et al. (2014)
• 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)
• Rat lung reactivity to natural and man-made fibrous silicates following short-term exposure — I. Lemaire, P.G. Dionne, et al. (1989)

Browse more research in Experimental Lung Research, or return to medical research.