Mineralogic parameters related to amosite asbestos-induced fibrosis in humans

Our plain-English summary of Mineralogic parameters related to amosite asbestos-induced fibrosis in humans, by A. Churg, J. Wright, B. Wiggs, et al (The American Review of Respiratory Disease, 1990).

The study

• Authors: A. Churg, J. Wright, B. Wiggs, L. Depaoli
• Journal: The American Review of Respiratory Disease
• Published: 1990;142(6 Pt 1):1331-6
• Cited by: 21 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. 003752).

Abstract

We have previously shown that in the lungs of a group of chrysotile miners and millers, grade of interstitial fibrosis (asbestosis) is directly proportional to tremolite fiber or chrysotile fiber concentration but is inversely proportional to mean fiber length and length-related parameters. To compare the effects of the commercial amphibole asbestos amosite on parenchymal fibrosis, we histologically graded fibrosis in four different sites in the lungs of 20 shipyard and insulation workers with heavy amosite exposure and measured by analytic electron microscopy fiber concentration and size in corresponding portions of lung tissue. Fibrosis grade was found to be strongly positively correlated with amosite concentration and negatively correlated with mean fiber size parameters, including fiber length, width, surface area, and mass. A comparison of our present results with our data on the chrysotile miners and millers showed that the regression lines of fibrosis grade versus concentration for amosite, chrysotile, and tremolite were statistically different. These findings indicate that amosite concentration, like chrysotile and tremolite concentration, is closely and directly related to fibrosis at the local lung level. Furthermore, these observations again raise the possibility that short fibers may be more important than is commonly believed in the genesis of fibrosis in man. Last, the concentration comparison data indicate that, fiber for fiber, amosite is more fibrogenic than is chrysotile or tremolite, and indirectly suggest that tremolite is more fibrogenic than is chrysotile.

In plain English

This study examined autopsy lungs from 20 insulators and/or shipyard workers who had heavy exposure to amosite asbestos. In four sites per lung (two upper lobe, two lower lobe), the authors graded interstitial fibrosis (asbestosis) microscopically on a scale of 0 to 4. They used electron microscopy to measure the concentration and size of amosite fibers in matching tissue. Fibrosis grade was positively correlated with amosite concentration (r = 0.62, P < 0.001). It was negatively correlated with mean fiber length, width, surface area and mass, but not significantly with mean aspect ratio: the longer the fibers, the lower the fibrosis grade. The authors compared these results with their earlier study of chrysotile miners and millers. For a given fiber concentration, amosite produced more fibrosis than chrysotile, which produced more than tremolite. The authors argued that, because chrysotile is removed from the lung, tremolite is actually more fibrogenic than chrysotile fiber for fiber. All the workers had also had chrysotile exposure, but too few chrysotile fibers remained to count. The authors noted that their amosite results may therefore be in error, though they judged this not a serious problem.

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: Autopsy lung tissue study. Fibrosis was graded histologically at four sites per lung and compared, using simple regression, with electron microscopy measurements of fiber concentration and size in the same tissue blocks. The results were also compared with the authors' earlier data on chrysotile miners and millers.
• Who was studied: Autopsy lungs from 20 heavily exposed insulators and/or shipyard workers, selected from a larger group to cover a range of fibrosis from none to severe. Mean age was 68 years (SD 9). Mean smoking was 29 pack-years (SD 26). The article does not say where or when the workers worked.
• Exposure: Heavy occupational amosite exposure, confirmed by an initial lung sample. All the workers had historically also had chrysotile exposure, generally at a very high level.
• Main results:
  • In the lung sites of the 20 amosite-exposed workers, fibrosis grade was strongly positively correlated with log amosite fiber concentration (r = 0.62, P < 0.001).
  • Fibrosis grade was significantly negatively correlated with all measured mean fiber size parameters except aspect ratio. Mean fiber mass had r = -0.33 (P < 0.003). Mean fiber length had r = -0.26. The correlation with mean aspect ratio was not significant. The longer the fiber, the lower the fibrosis grade.
  • Fibrosis grade was significantly positively correlated with total fiber length (r = 0.37, P < 0.001), total fiber width and total aspect ratio.
  • The correlation of fibrosis grade with total fiber surface area or total fiber mass was positive but not statistically significant.
  • The authors compared amosite with chrysotile and tremolite data from their earlier study of chrysotile miners and millers. The three regression lines of fibrosis grade against fiber concentration were significantly different (each p < 0.01). For a given fiber concentration, amosite produced more fibrosis than chrysotile, which produced more fibrosis than tremolite. Four chrysotile sites judged to be outliers were dropped from this analysis.
  • For fibrosis grade against mean fiber length, there was no difference between amosite and chrysotile. Tremolite differed significantly from the other fibers (p less than 0.05).
• The authors' conclusion: The authors concluded that, fiber for fiber, amosite was more fibrogenic than chrysotile or tremolite. They argued that because chrysotile is rapidly removed from the lung, much more chrysotile must once have been present than was measured. On that reasoning they concluded that tremolite is actually more fibrogenic than chrysotile on a fiber-for-fiber basis.
• Limitations the authors state:
  • All the workers also had past chrysotile exposure. Most of the chrysotile had disappeared from the lungs, and too few chrysotile fibers remained to count and correlate with fibrosis grade. To the extent that this chrysotile contributed to fibrosis, the amosite results may be in error.
  • The authors judged, from their comparison of the amosite, tremolite and chrysotile data, that the past chrysotile exposure was not a serious problem.
  • The total fiber size parameters correlated strongly with fiber concentration, so in practice they act as a substitute for fiber number.
  • The findings do not explain why asbestosis in humans is concentrated in the lower lung zones.

Topics

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

Medical terms in this study, explained in our Lexicon: Amosite, Fibrosis, Chrysotile, Interstitial Fibrosis, Tremolite, Fiber Length, Amphibole Asbestos, Parenchymal Fibrosis.

Related studies

• Mineralogic correlates of fibrosis in chrysotile miners and millers — A. Churg, J.L. Wright, et al. (1989)
• The distribution of amosite asbestos in the periphery of the normal human lung — A. Churg (1990)
• Long and short fiber amosite asbestos alters at a different extent the redox metabolism in human lung epithelial cells — C. Riganti, E. Aldieri, et al. (2003)
• Spiroergometric parameters at maximal exercise testing assessed functional respiratory impairment in asbestos-induced fibrosis — J. Schneider, R. Arhelger, et al. (2014)
• Rapid short-term clearance of chrysotile compared with amosite asbestos in the guinea pig — A. Churg, J.L. Wright, et al. (1989)
• Fibre distribution in the lungs and pleura of subjects with asbestos related diffuse pleural fibrosis — A.R. Gibbs, M. Stephens, et al. (1991)

Browse more research in The American Review of Respiratory Disease, or return to medical research.