An assessment of the fibrogenic potential of very short 4T30 chrysotile by intratracheal instillation in rats

Our plain-English summary of An assessment of the fibrogenic potential of very short 4T30 chrysotile by intratracheal instillation in rats, by I. Lemaire, D. Nadeau, J. Dunnigan, et al (Environmental Research, 1985).

The study

• Authors: I. Lemaire, D. Nadeau, J. Dunnigan, S. Massé
• Journal: Environmental Research
• Published: 1985;36(2):314-26
• Cited by: 34 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Three groups of five rats each received, respectively, a single intratracheal instillation of saline (control), 5 mg of UICC chrysotile B asbestos, and 5 mg of a preparation of very short chrysotile fibers (4T30, 100% less than 8 micron) isolated by a sedimentation procedure. At various intervals after the treatment (1 to 60 days), assessment of lung morphology was performed on each animal. Although the two types of chrysotile fibers have similar chemical composition, structure, and surface charge, the lung tissue reaction differed considerably. Lungs of animals exposed to UICC chrysotile B showed significant pathological alterations as early as 7 days following treatment. The lesions were localized in and around terminal bronchioles and consisted of inflammatory cells, fibroblasts and collagen deposition which distorted and obstructed small airways. Reaction to very short 4T30 chrysotile fibers was quite distinct. Seven days after treatment, lungs of these animals showed alveolar and interstitial accumulation of inflammatory cells. The alveolitis persisted 60 days after treatment and no fibrosis was apparent. It appears that very short 4T30 chrysotile fibers are much less fibrogenic than UICC chrysotile B and that intratracheal instillations in rats may represent a useful mean of rapidly assessing the fibrogenic potential of various dusts. These observations support the concept that fiber length is an important factor for fibrogenicity of asbestos.

In plain English

This animal experiment in Quebec, Canada, compared two kinds of chrysotile asbestos in male Wistar rats. Each rat got one windpipe injection of salt solution (controls), 5 mg of UICC chrysotile B, or 5 mg of very short 4T30 chrysotile. In the short-fiber preparation, none were longer than 8 micrometres and 98% were shorter than 3 micrometres. Lungs were examined from 1 to 60 days later. All animals survived, and saline-treated rats had normal lungs. In rats given chrysotile B, lesions appeared within 7 days. The authors reported bronchiolitis obliterans (scarring and blockage of the smallest airways) from day 7 onward in all of these rats, though another passage says almost all animals per group were affected. Rats given the short fibers developed inflammation in the air sacs (alveolitis) that was still present at 60 days, but no collagen deposits, and their small airways were normal. The authors concluded that the short fibers were less fibrogenic (less likely to cause lung scarring) and that fiber length matters. They noted that two months is a short period and that effects at later times or higher doses were unknown.

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: single intratracheal instillation in rats comparing saline, UICC chrysotile B and very short 4T30 chrysotile, with lung examination at set times afterward
• Who was studied: Male Wistar rats (250-300 g) from Charles River Canada, studied at the Université de Sherbrooke, Quebec. Animals were sacrificed at 1, 7, 14, 21 and 60 days. Table 2 lists 2 to 6 animals examined per group at each time point, while the abstract says five rats per group.
• Exposure: 5 mg of UICC chrysotile B, or 5 mg of very short 4T30 chrysotile isolated from Quebec 4T30 chrysotile by sedimentation. The short preparation had no fibers longer than 8 µm, and 98% of its fibers were smaller than 3 µm. Controls received saline.
• Main results:
  • All animals in all groups survived the exposure period.
  • At days 14 and 21, rats given chrysotile B averaged lower body weight (284-288 g) than saline rats (324-329 g) or short 4T30 rats (308-311 g). This difference was no longer apparent at 60 days.
  • Rats injected with saline showed normal lung morphology at each time point.
  • In rats given UICC chrysotile B, significant lesions appeared within 7 days.
  • The article reports peribronchiolitis and bronchiolitis obliterans from 7 days onward in all animals given UICC chrysotile B. A separate general statement says almost all animals in a particular group were affected by the typical lesions.
  • Fibrotic lesions in the chrysotile B group were not formally quantified. On examination, lung sections at 60 days showed an average of 10 fibrotic foci, compared with 4 at day 7 and none at day 1.
  • In rats given very short 4T30 chrysotile, no collagen deposition was found and the small airways were normal in all animals.
  • In the very short 4T30 group, the alveolitis (inflammation in the air sacs) was still present on days 21 and 60.
• The authors' conclusion: The authors concluded that very short 4T30 chrysotile fibers, despite their large surface area, were less fibrogenic than chrysotile B. In their view, this suggests that fibrogenicity is related to fiber length and not to specific surface area.
• Limitations the authors state:
  • The 2-month observation period may be a relatively short time to assess fibrogenicity.
  • It is unknown whether very short 4T30 fibers would cause fibrosis later or at a higher dose.
  • Because of the way and intensity of exposure, the data do not relate to early lung reactions to low-level asbestos inhalation in humans and animals.
  • The results do not suggest that short fibers cannot cause fibrosis over a long time span in humans.
  • The number and extent of fibrotic lesions were not quantified.

Topics

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

Medical terms in this study, explained in our Lexicon: Fibrogenic, Chrysotile, UICC, Fibroblast, Collagen, Deposition, Interstitial, Fibrosis.

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• An assessment of the fibrogenic potential of two refractory fibres by intraperitoneal injection in rats — G.H. Pigott, J. Ishmael (1981)
• Changes in numbers and dimensions of chrysotile asbestos fibers in lungs of rats following short-term exposure — V.L. Roggli, A.R. Brody (1984)
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