Asbestos fibres and man made mineral fibres: induction and release of tumour necrosis factor-alpha from rat alveolar macrophages

Our plain-English summary of Asbestos fibres and man made mineral fibres: induction and release of tumour necrosis factor-alpha from rat alveolar macrophages, by A.G. Ljungman, M. Lindahl, C. Tagesson (Occupational and Environmental Medicine, 1994).

The study

• Authors: A.G. Ljungman, M. Lindahl, C. Tagesson
• Journal: Occupational and Environmental Medicine
• Published: 1994;51(11):777-83
• Cited by: 12 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objectives: Mounting evidence suggests that asbestos fibres can stimulate alveolar macrophages to generate the potent inflammatory and fibrogenic mediator, tumour necrosis factor-alpha (TNF-alpha), and that this may play an important part in the onset and development of airway inflammation and lung fibrosis due to asbestos fibre inhalation. Little is known, however, about the ability of other mineral fibres to initiate formation and release of TNF-alpha by alveolar macrophages. Therefore the effects of different fibres (crocidolite, chrysotile A, chrysotile B, two man made mineral fibres (MMVF 21 and MMVF 22), a ceramic fibre (RCF 1), and a silicon carbide whisker fibre (SiCwh)) on formation and release of TNF-alpha by rat alveolar macrophages were examined.

Methods: Cells were isolated and incubated at 37 degrees C with the different fibres, or with culture medium alone (controls), and the amounts of TNF-alpha messenger RNA (mRNA) in the cells and TNF-alpha bioactivity released into the culture medium were measured at different time points.

Results: Significantly (P < 0.05 v control) increased amounts of TNF-alpha mRNA were found in cells exposed to crocidolite, chrysotile A, chrysotile B, MMVF 21, RCF 1, or SiCwh for 90 minutes, and significantly (P < 0.05 v control) increased activities of TNF-alpha were found in the medium of macrophages exposed to crocidolite, chrysotile A, chrysotile B, or MMVF 21 for four hours.

Conclusion: These observations suggest that not only natural mineral fibres but also certain man made mineral fibres are able to induce the formation and release of TNF-alpha by alveolar macrophages in vitro.

In plain English

This was a laboratory study of cells, not of people. The authors took alveolar macrophages (immune cells from the lung's air spaces) from male Wistar rats. They exposed the cells for 90 minutes or four hours to 100 micrograms per millilitre of one of seven fibres: crocidolite, chrysotile A, chrysotile B, a rock wool (MMVF 21), a slag wool (MMVF 22), a kaolin ceramic fibre (RCF 1) or silicon carbide whiskers. They then measured TNF-alpha, which the authors describe as an inflammatory and fibrogenic mediator. They measured it both as messenger RNA inside the cells and as activity released into the culture fluid. At 90 minutes, TNF-alpha messenger RNA was significantly higher than in unexposed cells for every fibre except the slag wool. At four hours, released TNF-alpha activity was significantly higher for chrysotile A, chrysotile B, crocidolite and the rock wool, but not for the slag wool, the ceramic fibre or the silicon carbide whiskers. The authors concluded that certain man made fibres, not only natural mineral fibres, can induce TNF-alpha in rat macrophages in vitro. They said the biological implications were unclear and that studies in living animals are needed.

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: Laboratory (in vitro) experiment on rat lung cells. Fibre-exposed cells were compared with cells exposed to culture medium alone.
• Who was studied: Alveolar macrophages collected by lung washing from male Wistar rats (200-250 g) from a pathogen-free colony, supplied in Sweden. The cell suspension was at least 95% macrophages. There were three to six experiments per condition.
• Exposure: Seven fibres at 100 micrograms per millilitre for 90 minutes or four hours:
• crocidolite, chrysotile A and chrysotile B (International Union Against Cancer standard asbestos fibres)
• MMVF 21 (rock wool)
• MMVF 22 (slag wool)
• RCF 1 (kaolin ceramic fibre)
• silicon carbide whiskers (SiCwh)
  Lipopolysaccharide (LPS, 1 microgram per millilitre) was used as a positive control.
• Main results:
  • TNF-alpha messenger RNA after 90 minutes was significantly increased compared with controls for chrysotile A, chrysotile B, crocidolite, MMVF 21, RCF 1 and silicon carbide whiskers. Values as percentage of control (mean, SEM, number of experiments):
• chrysotile A: 188 (54) (3)
• chrysotile B: 223 (53) (3)
• crocidolite: 178 (22) (4)
• MMVF 21: 139 (16) (3)
• RCF 1: 160 (16) (3)
• silicon carbide whiskers: 151 (20) (3)
  • For MMVF 22 (slag wool), TNF-alpha messenger RNA at 90 minutes was 116% of control (SEM 33, 3 experiments). This was not marked as significant.
  • By four hours, TNF-alpha messenger RNA had returned to baseline for all fibres except chrysotile A, which remained at 151% of control (SEM 20, 5 experiments).
  • Released TNF-alpha activity at four hours was significantly increased compared with controls for chrysotile A, chrysotile B, crocidolite and MMVF 21. Values as percentage of control (mean, SEM, number of experiments):
• chrysotile A: 315 (66) (6)
• chrysotile B: 218 (34) (4)
• crocidolite: 196 (27) (5)
• MMVF 21: 220 (29) (4)
  • At four hours, released TNF-alpha activity was 189% of control for RCF 1 and 162% for silicon carbide whiskers; both were reported as not significant. MMVF 22 was 192% (SEM 39, 4 experiments), also not marked as significant. At 90 minutes, no fibre increased released TNF-alpha activity.
  • The positive control, LPS, significantly increased TNF-alpha messenger RNA at both time points: 416% of control at 90 minutes and 525% at four hours.
• The authors' conclusion: The authors concluded that they had obtained some evidence that not only natural mineral fibres but also certain man made mineral fibres can induce the formation and release of TNF-alpha by alveolar macrophages in vitro. They stated that the biological implications are unclear.
• Limitations the authors state:
  • Fibres were compared by equal quantity (weight), not by equal numbers of fibres.
  • Small amounts of endotoxin (LPS) contamination could not be excluded and may have contributed to TNF-alpha in both exposed and unexposed cells.
  • Absolute TNF-alpha amounts varied between experiments for unclear reasons, so results were expressed as a percentage of each experiment's control.
  • The findings come from cells in vitro; studies in living animals are needed to examine potential toxic effects of man made mineral fibres.

Topics

Medical terms in this study, explained in our Lexicon: Necrosis, Alveolar Macrophage, Fibrogenic, Inflammation, Fibrosis, Crocidolite, Chrysotile, Macrophage.

Related studies

• Synergistic effects of mineral fibres and cigarette smoke on the production of tumour necrosis factor by alveolar macrophages of rats — Y. Morimoto, M. Kido, et al. (1993)
• Iron and reactive oxygen species in the asbestos-induced tumor necrosis factor-alpha response from alveolar macrophages — P.P. Simeonova, M.I. Luster (1995)
• Asbestos-stimulated tumour necrosis factor release from alveolar macrophages depends on fibre length and opsonization — K. Donaldson, X.Y. Li, et al. (1992)
• Bidirectional modulation of TNF-alpha production by alveolar macrophages in asbestos-induced pulmonary fibrosis — S. Ouellet, H. Yang, et al. (1993)
• Asbestos fibers and silica particles stimulate rat alveolar macrophages to release tumor necrosis factor. Autoregulatory role of leukotriene B4 — C.M. Dubois, E. Bissonnette, et al. (1989)
• Distinctive profile of alveolar macrophage-derived cytokine release induced by fibrogenic and nonfibrogenic mineral dusts — I. Lemaire, S. Ouellet (1996)

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