Effects of Aramid, a high strength synthetic fiber, on respiratory cells in vitro

Our plain-English summary of Effects of Aramid, a high strength synthetic fiber, on respiratory cells in vitro, by J.P. Marsh, B.T. Mossman, K.E. Driscoll, et al (Drug and Chemical Toxicology, 1994).

The study

• Authors: J.P. Marsh, B.T. Mossman, K.E. Driscoll, R.F. Schins, P.J. Borm
• Journal: Drug and Chemical Toxicology
• Published: 1994;17(2):75-92
• Cited by: 12 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Industry continues to develop synthetic fibers for new technologies and as replacements for asbestos, a toxic and carcinogenic fiber. To determine whether the in vitro effects of the aromatic polyamide fiber, Aramid (Kevlar, Twaron), resembled those induced by asbestos, fibers were surveyed for (1) cytotoxicity as measured by total cell protein, and (2) proliferative capacity as measured by [3H]thymidine incorporation, colony forming efficiency (CFE), and ornithine decarboxylase (ODC) activity in two target cells of mineral dust-induced lung damage, hamster tracheal epithelial (HTE) cells and rat lung (RL90) fibroblasts. Results of cytotoxicity tests indicated that Aramid was as toxic to HTE and RL90 cells as were crocidolite and chrysotile asbestos when expressed on both an equal mass and equal fiber number basis. In HTE cells, Aramid caused a statistically significant increase in [3H]thymidine incorporation and CFE and produced a dose-dependent induction of ODC enzyme activity. Proliferative effects by asbestos or Aramid were not observed in RL90 fibroblasts. Thus, when tested over a respirable size range, Aramid exhibited many of the same effects on epithelial cells in vitro as did asbestos, including increased radiolabeled nucleotide incorporation into DNA and induction of ODC enzyme activity.

In plain English

This laboratory study compared Aramid, a synthetic asbestos substitute sold as Kevlar and Twaron, with UICC crocidolite and Canadian chrysotile asbestos in cultured cells. The authors used hamster tracheal epithelial (HTE) cells and a rat lung fibroblast line (RL90). The Aramid was a fraction prepared from Twaron pulp, with fibers averaging 6.0 micrometres long and 0.4 micrometres wide. When cell damage was measured by cell protein after 24 hours, Aramid was slightly more toxic to HTE cells than either type of asbestos, and the fibroblasts responded similarly. Results were alike whether doses were counted by weight or by fiber number. At low doses, all three fibers significantly increased colony formation and thymidine uptake into DNA in HTE cells. They also raised activity of the enzyme ornithine decarboxylase (ODC) in these cells, in a dose-dependent way. In fibroblasts, low doses did not raise cell protein or thymidine uptake, and ODC induction could not be detected because activity was extremely low; colony formation was tested only in HTE cells. The authors concluded that Aramid can be mitogenic (growth-stimulating) to respiratory epithelium but not to lung fibroblasts. They stressed the need for rigorous inhalation studies.

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) laboratory experiment comparing Aramid with asbestos
• Who was studied: Cultured cells, not people: hamster tracheal epithelial (HTE) cells from neonatal Syrian hamsters, and a diploid line of rat lung fibroblasts (RL90)
• Exposure: UICC reference crocidolite and Canadian chrysotile asbestos, and Aramid (Twaron pulp, type 1095). The Aramid was prepared by stirring 2.0 g of pulp in 800 ml water and collecting the top 250 ml after 1 hour. Exposures were 24 hours for the protein and thymidine tests, 7 days for colony formation, and 4 hours for ODC.
• Main results:
  • The Aramid preparation had a mean length of 6.0 micrometres, a mean diameter of 0.4 micrometres, a mean aspect ratio of 17.0, and 5.1 x 10^6 fibers per microgram. The authors described its aspect ratio and fiber count as similar to crocidolite (mean length 3.14, diameter 0.15, aspect ratio 24.34, 3.04 x 10^6 fibers per microgram).
  • By cell protein after 24 hours, Aramid was slightly more cytotoxic to HTE cells than crocidolite or chrysotile. RL90 fibroblasts responded to Aramid similarly to HTE cells. Results were similar whether expressed by fiber mass or fiber number.
  • Small amounts of all three fibers caused a slight, significant rise in protein content in HTE cells. RL90 fibroblasts showed no such rise.
  • The colony-forming efficiency assay was carried out only in HTE cells.
  • In HTE colony-forming tests (7 days; 2 experiments, n=4 per group per experiment), all three fibers were toxic. All three also had a significant proliferative effect at low concentrations.
  • Thymidine incorporation into DNA rose significantly in HTE cells after exposure to both types of asbestos and to Aramid. It did not rise in fibroblasts.
  • Asbestos and Aramid increased ODC enzyme activity in HTE cells in a dose-dependent fashion. In RL90 fibroblasts, ODC activity was extremely low and induction could not be detected.
• The authors' conclusion: The authors concluded that their in vitro results suggest Aramid can be mitogenic to respiratory epithelium but not to lung fibroblasts. They stated that the study shows the value of in vitro assays for flagging compounds of potential concern, and emphasized the importance of rigorous inhalation studies.
• Limitations the authors state:
  • The authors noted that judging overall health risk needs factors beyond cell tests, including exposure levels in the workplace and fiber durability, and called for inhalation studies.

Topics

Medical terms in this study, explained in our Lexicon: Carcinogenic, Fibroblast, Crocidolite, Chrysotile.

Related studies

• Induction of c-fos and c-jun proto-oncogenes in target cells of the lung and pleura by carcinogenic fibers — Y.M. Janssen, N.H. Heintz, et al. (1994)
• In vitro assays to predict the pathogenicity of mineral fibers — B.T. Mossman, A.M. Sesko (1990)
• Transfection of a manganese-containing superoxide dismutase gene into hamster tracheal epithelial cells ameliorates asbestos-mediated cytotoxicity — B.T. Mossman, P. Surinrut, et al. (1996)
• 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)
• Use of hamster tracheal organ cultures for assessing the cocarcinogenic effects of inorganic particulates on the respiratory epithelium — B.T. Mossman, J.E. Craighead (1979)
• Lung proliferative and clearance responses to inhaled para-aramid RFP in exposed hamsters and rats: comparisons with chrysotile asbestos fibers — D.B. Warheit, S.I. Snajdr, et al. (1997)

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