In vitro activity of silicon carbide whiskers in comparison to other industrial fibers using four cell culture systems

Our plain-English summary of In vitro activity of silicon carbide whiskers in comparison to other industrial fibers using four cell culture systems, by N.F. Johnson, M.D. Hoover, D.G. Thomassen, et al (American Journal of Industrial Medicine, 1992).

The study

• Authors: N.F. Johnson, M.D. Hoover, D.G. Thomassen, Y.S. Cheng, A. Dalley, A.L. Brooks
• Journal: American Journal of Industrial Medicine
• Published: 1992;21(6):807-23
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Silicon carbide whiskers (SiCW) and continuous glass filaments are important components of composite materials having potentially widespread use in the automotive, aerospace, and power generation industries. We determined the in vitro activity of three well-characterized samples of silicon carbide whiskers and a continuous glass filament sample in four different cellular assays and compared this to the activities of UICC crocidolite, JM Code 100 glass microfiber, and erionite in the same assay systems. The SiCW had a diameter range of 0.32-0.75 microns and a length range of 4.5-20.1 microns. The SiCW was significantly toxic; on a mass basis, one SiCW sample was more toxic than crocidolite; however, JM Code 100 glass microfiber, which is not toxic in vivo (i.e., it does not cause fibrogenesis or carcinogenesis when inhaled), was also more toxic than crocidolite. The glass filament sample was the least cytotoxic of all the samples tested. On a fiber number basis, all three SiCW samples were more toxic than crocidolite. The results of our study showed that SiCW exhibits significant in vitro biological reactivity. Thus, despite the caution that must be exercised in extrpolating the results of in vitro studies to conclusions about in vivo health effects, SiCW should be considered toxic until further toxicological data are available.

In plain English

This laboratory study compared the effects on cultured cells of three samples of silicon carbide whiskers (a fibrous material used in composite materials) with UICC crocidolite (blue asbestos), JM Code 100 glass microfiber, erionite, and a coarse continuous glass filament, PRD-166. Four cell systems were used: rat alveolar macrophages, rat tracheal epithelial cells, a rat lung epithelial cell line, and A549 human lung cancer cells. All three whisker samples harmed cells in a dose-dependent way. Measured by weight, whisker sample #2 and JM Code 100 ranked as most toxic, above crocidolite. The other two whisker samples ranked below crocidolite but above erionite and PRD-166. Measured by fiber number, all three whisker samples were the most toxic. PRD-166 showed no significant toxicity in any assay. The authors noted that JM Code 100, which has not caused lung tumors or fibrosis in animals that inhaled it, also outranked crocidolite. They urged caution in applying cell results to health effects. They concluded that the whiskers should be considered toxic until further toxicological data are available.

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: In vitro (cell culture) toxicity experiments, with physical and chemical characterization of the test materials
• Who was studied: No human subjects. The cells tested were alveolar macrophages and tracheal epithelial cells taken from female Fischer 344/N rats aged 8-10 weeks, an immortalized rat lung epithelial cell line (LEC), and the A549 human lung carcinoma cell line. The work was done at the Inhalation Toxicology Research Institute, Albuquerque, NM.
• Exposure: Three silicon carbide whisker samples from three suppliers. Their mean diameters ranged from 0.32 to 0.75 micrometres and their mean lengths from 4.5 to 20.1 micrometres. They were compared with UICC crocidolite, JM Code 100 glass microfiber, erionite, and PRD-166 continuous glass filament (ball-milled into powder and fiber forms). Cells were exposed for 20 hours at concentrations of up to 50 micrograms per millilitre.
• Main results:
  • All three silicon carbide whisker samples were toxic to alveolar macrophages in a dose-dependent way. Dose-dependent toxicity was also reported in each of the other three assays.
  • On a mass (weight) basis, across the ranking of the four assays, whisker sample #2 and JM Code 100 were the most cytotoxic materials and were more toxic than crocidolite. Whisker samples #1 and #3 were less toxic than crocidolite or JM Code 100 but more toxic than erionite or PRD-166.
  • When toxicity was based on the number of fibers rather than weight, the three silicon carbide whisker samples were the most toxic of the samples tested.
  • Neither the fiber form nor the powder form of the PRD-166 continuous glass filament showed significant toxicity in any of the four assays.
  • The alveolar macrophage assay appeared to be the least sensitive assay and the A549 assay the most sensitive.
  • The results did not consistently support a role for any single physical or chemical property in the toxicity of the fibers tested.
• The authors' conclusion: The authors concluded that silicon carbide whiskers showed significant biological reactivity in vitro and should be considered toxic until further toxicological data are available. They also considered a chronic inhalation study to be warranted.
• Limitations the authors state:
  • The authors cautioned that results from cell studies cannot be directly extrapolated to health effects in living organisms.
  • The toxicity ranking may be misleading: JM Code 100 glass fibers appeared more toxic than crocidolite in these cells, although animals that inhaled it have not shown increased lung tumors or fibrosis.
  • Comparisons by weight may be misleading because the samples contained very different numbers of fibers per milligram.
  • The in vitro results for erionite did not match human exposure and animal inhalation data.
  • The authors stated that a single toxicity assay is insufficient to describe a material's biological reactivity.

Topics

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

Medical terms in this study, explained in our Lexicon: UICC, Crocidolite, erionite, Carcinogenesis.

Related studies

• The immediate effects of silicon carbide whiskers upon ciliated tracheal epithelium — G.L. Vaughan, J.R. Kennedy, et al. (1991)
• The toxicity, in vitro, of silicon carbide whiskers — G.L. Vaughan, J. Jordan, et al. (1991)
• Toxicity in vitro of some silicon carbides and silicon nitrides: whiskers and powders — I. Svensson, E. Artursson, et al. (1997)
• Pulmonary response, in vivo, to silicon carbide whiskers — G.L. Vaughan, S.A. Trently, et al. (1993)
• The carcinogenicity of WHO fibers of silicon carbide: SiC whiskers compared to cleavage fragments of granular SiC — K. Rödelsperger, B. Brückel (2006)
• Expression of Clara cell secretory protein in the lungs of rats exposed to silicon carbide whisker in vivo — Y. Morimoto, L. Ding, et al. (2003)

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