Rapid short-term clearance of chrysotile compared with amosite asbestos in the guinea pig

Our plain-English summary of Rapid short-term clearance of chrysotile compared with amosite asbestos in the guinea pig, by A. Churg, J.L. Wright, B. Gilks, et al (The American Review of Respiratory Disease, 1989).

The study

• Authors: A. Churg, J.L. Wright, B. Gilks, L. DePaoli
• Journal: The American Review of Respiratory Disease
• Published: 1989;139(4):885-90
• Cited by: 36 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 003682).

Abstract

Compared with amphibole forms of asbestos, chrysotile asbestos fails to accumulate in lung tissue; the mechanism of this effect is disputed. To investigate this problem, we administered a mixture of the amphibole, amosite, and chrysotile to guinea pigs by intratracheal instillation. At 1 day, 1 week, and 1 month after instillation, animals were killed, and the numbers, types, sizes, and compositions of fibers in the lungs were determined by analytical electron microscopy. Both chrysotile and amosite fiber concentrations decreased with time, but relative chrysotile clearance was significantly greater than amosite clearance. There was no evidence of magnesium leaching from chrysotile fibers of any size at any time. Analysis of fiber lengths and widths showed a time trend toward shorter and narrower fibers (particularly toward fibers of less than 2 microns long and less than 0.025 microns wide) for chrysotile. This effect was not seen for amosite. We conclude that (1) failure of chrysotile accumulation in lung results from preferential chrysotile clearance during the first few days to weeks after exposure; (2) there is no evidence that fiber dissolution plays a role in chrysotile clearance; (3) preferential clearance may be a result of fragmentation and rapid removal of chrysotile fibers.

In plain English

This was an animal experiment. The authors put 1 mg of a mixture of equal weights of amosite and Canadian chrysotile asbestos into the windpipes of female guinea pigs (intratracheal instillation). Counted by fibers, the mixture held about eight times as many chrysotile as amosite fibers. Five or six animals were killed at 1 day, 1 week and 1 month. The fibers in their lungs were counted, measured and chemically analyzed by electron microscopy. Concentrations of both fiber types fell over time, but the ratio of chrysotile to amosite fibers dropped about threefold from the starting mixture to 1 month. The authors found no evidence of magnesium leaching from chrysotile fibers. Chrysotile fibers tended to become shorter and narrower: a larger share of the chrysotile fibers recovered were under 2 microns long and under 0.025 microns wide, even though total chrysotile fell. Amosite did not show this trend. The authors concluded that chrysotile is cleared preferentially in the first days to weeks, that there is no evidence dissolution plays a role, and that fragmentation and rapid removal may explain it. They noted that instillation is unphysiologic.

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: a mixture of amosite and chrysotile was given once by intratracheal instillation, and lung fiber content was measured at three later times
• Who was studied: Hartley strain female guinea pigs weighing 400 g; five or six animals killed at each of 1 day, 1 week and 1 month after exposure (University of British Columbia, Vancouver; study dates not stated)
• Exposure: 1 mg of a mixture of equal weights of amosite and Canadian chrysotile in 0.5 ml saline, given once by intratracheal instillation; by count the mixture contained about eight times as many chrysotile as amosite fibers
• Main results:
  • In the guinea pigs' lungs, concentrations of both chrysotile and amosite fell steadily with time (statistically significant for both)
  • The ratio of chrysotile to amosite fibers fell significantly, about threefold, from the starting mixture to 1 month
  • The chrysotile-to-amosite ratio at 1 month was significantly lower than at all earlier time points (p less than 0.01)
  • No evidence of magnesium leaching was found in chrysotile fibers of any size at any time point
  • Chrysotile fibers showed a trend over time toward shorter and narrower fibers, especially fibers under 2 microns long and under 0.025 microns wide; this was not seen for amosite
  • For chrysotile, the proportion of fibers shorter than 2 microns (as a percentage of fibers found at each time) increased at 1 week and 1 month
  • For amosite, the proportion of fibers shorter than 2 microns was always lower than in the starting mixture
  • Mean chrysotile length jumped at 1 day, which the authors interpreted as very rapid removal of very short fibers after instillation
• The authors' conclusion: The authors concluded that chrysotile fails to accumulate in lung because it is cleared preferentially during the first few days to weeks after exposure. They found no evidence that fiber dissolution plays a role, and they concluded that preferential clearance may result from fragmentation and rapid removal of chrysotile fibers.
• Limitations the authors state:
  • Intratracheal instillation is unphysiologic and produces uneven fiber distribution in the lung
  • Whether this method of giving the fibers affects clearance patterns is not known
  • The measurements could not show which size of chrysotile fiber was fragmenting or in which part of the lung this happened
  • Significant magnesium leaching might occur over periods longer than the 1 month studied

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Amosite, Amphibole Group, Fiber Length.

Related studies

• 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)
• Effects of cigarette smoke on the clearance of short asbestos fibres from the lung and a comparison with the clearance of long asbestos fibres — A. Churg, J.L. Wright, et al. (1992)
• Evaluation of the fate and pathological response in the lung and pleura of brake dust alone and in combination with added chrysotile compared to crocidolite asbestos following short-term inhalation exposure — D.M. Bernstein, R.A. Rogers, et al. (2015)
• Lung cinescintigraphy in the dynamic assessment of ventilation and mucociliary clearance of asbestos cement workers — L. Di Lorenzo, M. Mele, et al. (1996)
• Deposition and clearance of chrysotile asbestos — A. Churg (1994)

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