Carborundum pneumoconiosis. Fibers in the mineral activate macrophages to produce fibroblast growth factors and sustain the chronic inflammatory disease

Our plain-English summary of Carborundum pneumoconiosis. Fibers in the mineral activate macrophages to produce fibroblast growth factors and sustain the chronic inflammatory disease, by R. Bégin, A. Dufresne, A. Cantin, et al (Chest, 1989).

The study

• Authors: R. Bégin, A. Dufresne, A. Cantin, S. Massé, P. Sébastien, G. Perrault
• Journal: Chest
• Published: 1989;95(4):842-9
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Carborundum is a synthetic abrasive manufactured through fusion of high grade silica sand and finely ground carbon in an electric furnace at 2,400 degrees C. It had been considered an inert dust until recently. Two recent epidemiologic studies in Quebec have documented an excess of interstitial lung disease in plant workers and some 30 workers have received workman compensation. Histopathologic lesions have been described in four of the workers. To further investigate the carborundum pneumoconiosis, nine groups of eight sheep were exposed once in the tracheal lobe to either 100 ml saline, 100 mg latex beads in 100 ml saline, 100 mg graphite in 100 ml saline, 100 mg carborundum particles in 100 ml saline, 100 mg ashed carborundum particles in 100 ml saline, 100 mg of quartz (Minusil-5) in 100 ml saline, 100 mg crocidolite fibers in 100 ml saline, 100 mg carborundum fibers in 100 ml saline, and 100 mg ashed carborundum fibers in 100 ml saline solutions. The animals had BAL at two-month intervals and autopsy at month 8. The BAL analyses of cellularity, cytotoxicity and fibrogenicity, in association to necropsy histopathology, documented that all particles except for quartz were inert. The two-carborundum fiber samples produced a similar sustained nodular fibrosing alveolitis and crocidolite asbestos fibers produced a peribronchiolar fibrosing alveolitis of comparable severity. Thus, the major bioactive dusts in the carborundum manufacturing process are quartz particles and the carborundum fibers generated in the process. The latter have fibrogenic activities comparable to asbestos fibers of similar size and are likely to contribute to the pathogenesis of the interstitial lung disease of carborundum workers.

In plain English

This animal experiment in sheep tested dusts from the manufacture of carborundum (silicon carbide), an abrasive. Seventy-two sheep were split into nine groups of eight. Each group had one lung lobe exposed once, either to saline alone or to 100 mg of one material: latex beads, graphite, quartz, crocidolite asbestos fibers, or carborundum particles or fibers, used raw or ashed to burn off surface graphite. Lung washings were analysed every two months, and the lungs were examined at month 8. Lungs exposed to saline, latex, graphite and raw carborundum particles scored 0 for disease. The quartz group scored 2.9, with early silicotic nodules. Crocidolite caused fibrosing inflammation around small airways (score 1.9). Raw and ashed carborundum fibers caused nodular lesions (scores 1.2 and 1.6). The differences among these three fiber groups were not statistically significant. All fiber groups showed raised cell counts in lung washings and raised fibroblast growth activity. The authors concluded that carborundum particles were inert, but that carborundum fibers can start a fibrosing lung disease and can contribute to interstitial lung disease in carborundum plants.

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: sheep given a single exposure in one lung lobe, followed with bronchoalveolar lavage (lung washing) at months 2, 4, 6 and 8 and examined at autopsy at month 8
• Who was studied: 72 sheep weighing 25 to 45 kg, divided into nine groups of eight; the study came from research units in Sherbrooke and Montreal, Quebec, Canada
• Exposure: A single infusion into the tracheal lobe of 100 ml saline alone (control), or 100 mg in 100 ml saline of: latex beads, graphite, raw carborundum (SiC) particles, ashed SiC particles, quartz (Minusil-5), crocidolite fibers, raw SiC fibers, or ashed SiC fibers. The SiC materials and graphite were collected from the Acheson furnaces of two Quebec SiC plants. The SiC fibers averaged 0.27 micrometres (plus or minus 0.27) in diameter and 6.8 micrometres (plus or minus 11.2) in length.
• Main results:
  • Pathologic disease scores at month 8 were 0 plus or minus 0 for the saline, latex, graphite and raw SiC particle groups, and 2.9 plus or minus 1.0 for the quartz group (p less than 0.01 for quartz versus the others).
  • Lungs of sheep exposed to graphite and to raw or ashed SiC particles contained particles, mostly inside macrophages, without cellular reaction. Lungs of the saline and latex groups were normal.
  • In the quartz group, cell counts in lung washings rose early by 500 percent, fell to 250 percent at month 4, and stayed raised to the end. Typical early silicotic nodules were seen at autopsy in all quartz-exposed sheep.
  • Disease scores in the fiber groups were 1.9 plus or minus 0.25 for crocidolite, 1.2 plus or minus 0.21 for raw SiC fibers and 1.6 plus or minus 0.2 for ashed SiC fibers. The differences among the three were not statistically significant (p greater than 0.05).
  • Crocidolite produced lesions around small airways, with granulation tissue containing fibers. SiC fibers produced nodules in the lung tissue made up of multinucleated macrophages, monocytes and a few neutrophils.
  • In all fiber groups, lung-washing cell counts rose after exposure, with a smaller rise in the raw SiC fiber group. Fibronectin production at month 8 was significantly increased, again somewhat less in the raw SiC fiber group.
  • Fibroblast growth activity was significantly increased in all fiber groups.
• The authors' conclusion: The authors concluded that carborundum particles are inert and that, among the non-fibrous particles found on site, only silica appeared potentially responsible for lung injury. They concluded that fibrous SiC has significant biologic activity, can initiate a fibrosing lung disease, and that inhaling SiC fibers can contribute to interstitial lung disease in SiC manufacturing plants. They recommended that workplace monitoring in that industry include airborne fiber levels.
• Limitations the authors state:
  • The authors noted that the slightly lower score for raw compared with ashed SiC fibers (not statistically significant) could reflect an inhibiting effect of surface graphite. It could also reflect less fiber mass in the raw samples, because graphite made up part of the 100 mg weight.

Topics

Medical terms in this study, explained in our Lexicon: Pneumoconiosis, Macrophage, Fibroblast, Interstitial Lung Disease, Crocidolite, Autopsy, Histopathology, Fibrogenic.

Related studies

• In vitro activity of silicon carbide whiskers in comparison to other industrial fibers using four cell culture systems — N.F. Johnson, M.D. Hoover, et al. (1992)
• The toxicity, in vitro, of silicon carbide whiskers — G.L. Vaughan, J. Jordan, et al. (1991)
• The immediate effects of silicon carbide whiskers upon ciliated tracheal epithelium — G.L. Vaughan, J.R. Kennedy, et al. (1991)
• Contemporary issues in fiber toxicology — D.B. Warheit, K.E. Driscoll, et al. (1995)
• Pulmonary reaction to long and short asbestos fibers is independent of fibroblast growth factor production by alveolar macrophages — I.Y. Adamson, D.H. Bowden (1990)
• Pulmonary response, in vivo, to silicon carbide whiskers — G.L. Vaughan, S.A. Trently, et al. (1993)

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