Mass, number and size of lung fibres in the pathogenesis of asbestosis in sheep

Our plain-English summary of Mass, number and size of lung fibres in the pathogenesis of asbestosis in sheep, by P. Sébastien, R. Bégin, S. Masse (Journal of Experimental Pathology, 1990).

The study

• Authors: P. Sébastien, R. Bégin, S. Masse
• Journal: Journal of Experimental Pathology
• Published: 1990;71(1):1-10
• Cited by: 12 articles, as counted by NIH iCite
• Read it: PubMed · Free full text

Abstract

After long-term asbestos inhalation, the lung tissue burden is much less for chrysotile (CHRY) than for crocidolite (CRO) exposure. Nonetheless CHRY does not appear to be less fibrogenic. To study mechanisms responsible for the low retention of CHRY and the relationships with fibrogenesis, 15 sheep received a single intratracheal injection of either CHRY or CRO. Exposures in 100 ml saline consisted of 100 mg of 1-micron latex beads for the five control sheep, 100 mg UICC CRO fibres for the five CRO sheep and 100 mg UICC B CHRY fibres for the five CHRY sheep. Bronchoalveolar lavage (BAL) was carried out at months 2, 4, 6 and 8 after exposure and necropsy at month 8. BAL and tissue samples were analysed for fibres by transmission electron microscopy. At month 2, mass concentration in BAL was 108 +/- 30 ng/ml for CRO and 0.6 +/- 0.1 ng/ml for CHRY. BAL CRO decreased afterward but BAL CHRY did not. The mass concentration in the lung at month 8 was 40.6 +/- 8.7 ng/mg dry tissue for CRO and 11.5 +/- 7.0 ng/mg for CHRY. BAL fibrogenic activity at month 8 assessed by macrophage fibronectin production was less than 0.2 ng/10(6) cells/24 h in control sheep, 5 +/- 2 in CRO sheep and 11 +/- 2 in CHRY sheep (P less than 0.05 CRO vs CHRY). Histologic score of tissue injury fibrosis was 0 in control sheep, 1.9 +/- 0.3 in CRO sheep and 2.8 +/- 0.1 in CHRY sheep (P less than 0.05). At necropsy, the number size distribution of fibres per microgram of tissue from the (CRO)/(CHRY) sheep was respectively: (127 +/- 54)/(15 +/- 14) for fibres less than 5 microns, (18 +/- 17)/(32 +/- 14) for fibres greater than 5 microns, (1.6 +/- 8)/(7 +/- 13) for fibres greater than 20 microns. This study documented that the low pulmonary retention of CHRY was largely related to the faster alveolar clearance rate of CHRY mass. Fibrogenicity of CHRY remained higher and appeared to be related at least in part to the preferential retention of long and very long CHRY fibres.

In plain English

This was an animal experiment in 15 male sheep, in three groups of five. Each sheep received one infusion into one lung lobe of 100 mg of UICC crocidolite, UICC B chrysotile, or (for controls) latex beads. By count, the chrysotile sheep received more fibres than the crocidolite sheep. Lung washings were sampled at months 2, 4, 6 and 8, and lungs were examined after the sheep were killed at month 8. Chrysotile was cleared from the lung's air spaces much faster: at month 8, crocidolite sheep held more fibre mass in lung tissue. Yet the chrysotile sheep had higher scores for asbestosis-type lung injury and higher output of fibronectin, a marker of fibrosis activity measured in lung-wash cells. Chrysotile sheep also retained more fibres longer than 5 and 20 micrometres. The authors found that only these long-fibre counts were directly related to disease severity, while retained fibre mass, total count and short-fibre count were inversely related. They concluded that fibrogenicity appeared related at least in part to retention of long and very long fibres. They noted uncertainty about where lung-wash fibres come from.

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 single intratracheal (bronchoscopic, into the tracheal lobe) injection, followed by repeated bronchoalveolar lavage and necropsy at month 8
• Who was studied: 15 male sheep weighing 25 to 45 kg, divided into three groups of five (control, crocidolite, chrysotile). The article does not state where or when the experiment was done.
• Exposure: 100 mg of UICC crocidolite fibres or 100 mg of UICC B chrysotile fibres in 100 ml saline. Controls received 100 mg of 1-micrometre latex beads. Chrysotile sheep received a higher number of fibres than crocidolite sheep (Table 1 ratio of crocidolite to chrysotile total fibre number 0.29).
• Main results:
  • In lung lavage fluid at month 2, fibre mass concentration was 108 ± 30 ng/ml in crocidolite sheep and 0.6 ± 0.1 ng/ml in chrysotile sheep. Crocidolite levels decreased afterward; chrysotile levels did not.
  • At month 8, the lavage concentration of crocidolite remained about 10 times that of chrysotile.
  • Fibre mass retained in lung tissue at month 8 (Table 1, mean ± standard error) was 40.6 ± 18.7 ng/mg dried tissue in crocidolite sheep and 11.5 ± 7.0 ng/mg in chrysotile sheep (P less than 0.05).
  • Fibronectin production by lavage cells at month 8 was less than 0.2 ng per million cells per 24 h in control sheep, 5 ± 2 in crocidolite sheep and 11 ± 2 in chrysotile sheep (P less than 0.05, crocidolite vs chrysotile).
  • The histologic score of tissue injury and fibrosis was 0 in control sheep, 1.9 ± 0.3 in crocidolite sheep and 2.8 ± 0.1 in chrysotile sheep (P less than 0.05).
  • Fibres retained per microgram of dried lung tissue (Table 1): total fibres were 156 ± 48 in crocidolite sheep and 49 ± 14 in chrysotile sheep. Fibres shorter than 5 micrometres were 127 ± 54 and 16 ± 14 (both differences P less than 0.05).
  • Long fibres retained per microgram of dried lung tissue (Table 1): fibres longer than 5 micrometres were 18 ± 17 in crocidolite sheep and 32 ± 14 in chrysotile sheep. Fibres longer than 20 micrometres were 1.6 ± 8 and 7.1 ± 13 (both differences P less than 0.05).
  • The authors reported a significant direct relationship between the number of fibres longer than 5 micrometres retained in lung tissue and the intensity of fibrosis, measured by pathologic score or by fibronectin production.
  • Retained fibre mass, total fibre number and short-fibre number were inversely related to the severity of fibrosis.
• The authors' conclusion: The authors concluded that the low lung retention of chrysotile was largely related to faster alveolar clearance of chrysotile mass. They also concluded that chrysotile's higher fibrogenicity appeared to be related at least in part to preferential retention of long and very long chrysotile fibres.
• Limitations the authors state:
  • The authors acknowledged limitations of using lavage fibres to measure alveolar clearance, given uncertainty about where lavage fibres come from.
  • The authors found that lavage and lung-tissue fibre counts correlated well for long crocidolite fibres, less well for short crocidolite fibres, and not at all for chrysotile.

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Crocidolite, Fibrogenic, UICC, Bronchoalveolar Lavage (BAL), Autopsy, Transmission Electron Microscopy (TEM), Macrophage.

Related studies

• Mass and number of fibres in the pathogenesis of asbestos-related lung disease in rats — J.M. Davis, S.T. Beckett, et al. (1978)
• Morphologic features and function of the airways in early asbestosis in the sheep model — R. Bégin, S. Massé, et al. (1982)
• Excessive accumulation of asbestos fibre in the bronchoalveolar space may be a marker of individual susceptibility to developing asbestosis: experimental evidence — R. Bégin, P. Sébastien (1989)
• Assessment of progression of asbestosis in the sheep model by bronchoalveolar lavage and pulmonary function tests — R. Bégin, M. Rola-Pleszczynski, et al. (1983)
• Contributions of experimental asbestosis in sheep to the understanding of asbestosis — R. Bégin, A. Cantin, et al. (1991)
• Biochemical components of bronchoalveolar lavage in early experimental asbestosis of the sheep: phospholipase A2 activity, prostaglandin E2 and proteins — P. Sirois, G. Drapeau, et al. (1983)

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