Short-term tests for the evaluation of potential cancer risk of modified asbestos fibers

Our plain-English summary of Short-term tests for the evaluation of potential cancer risk of modified asbestos fibers, by M.C. Jaurand, A. Renier, A. Gaudichet, et al (Annals of the New York Academy of Sciences, 1988).

The study

• Authors: M.C. Jaurand, A. Renier, A. Gaudichet, L. Kheuang, L. Magne, J. Bignon
• Journal: Annals of the New York Academy of Sciences
• Published: 1988;534:741-53
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Summary of the article

The authors used short-term in vitro tests to assess the potential carcinogenic potency of Canadian chrysotile fibers that had been chemically modified by a phosphatation process for industrial purposes. They compared these with unmodified chrysotile. Fiber size was measured by optical and electron microscopy. Durability was assessed by electron microprobe analysis of fibers ingested by rabbit alveolar macrophages. Cytotoxicity, chromosomal aberrations and cell transformation were tested in rat pleural mesothelial cells (RPMC), in some experiments with benzo(a)pyrene added.

The two fiber types had similar size distributions. Fibers meeting Stanton's criteria numbered about 3 x 10^6 per microgram, about 15 percent of all fibers. After 24 hours in macrophages, unleached untreated chrysotile fell to about 30 percent. Mean Mg/Si peak ratios were 0.76 for unmodified and 0.94 for modified fibers, against starting values of 0.89 and 0.91. Modified fibers were less cytotoxic: viability with 10 µg/ml of untreated fibers was similar to that with 20 µg/ml of modified fibers. Unmodified chrysotile significantly increased chromosomal aberrations from 7 to 15 µg/ml. The increase with modified fibers was not statistically significant. Both types significantly altered chromosome number. Both increased the transformation index compared with controls. The index fell as more cells were plated.

The authors concluded that the modified fibers were more stable and less cytotoxic and clastogenic per unit weight. Transforming potency appeared equivalent, but the assay was not sufficiently established. Animal experiments were in progress.

PubMed has no abstract for this study, and the article doesn't print one. We wrote this summary from the full article with the help of AI. It is not the authors' wording.

In plain English

This laboratory study compared Canadian chrysotile asbestos with chrysotile chemically modified by a phosphatation process for industrial use. The authors ran short-term tests mainly on cultured rat pleural mesothelial cells, and used rabbit alveolar macrophages (lung scavenger cells) to test whether fibers broke down chemically. Both fiber types had similar sizes. Inside macrophages, untreated chrysotile lost magnesium: the share of unchanged fibers fell to about 30 percent after 24 hours, while the modified fibers stayed more stable. The modified fibers were less toxic to mesothelial cells; 20 µg/ml of them gave about the same cell survival as 10 µg/ml of untreated fibers. Untreated chrysotile significantly increased chromosome damage from 7 to 15 µg/ml; the modified fibers also raised it, but not significantly. Both fiber types altered chromosome numbers and seemed to increase cell transformation to a similar degree, though the authors said this test was not sufficiently established. The authors concluded the two fibers showed no great differences in their effects on these cells, and noted that such tests measure cancer-causing potency, not actual hazard.

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 laboratory study (short-term cell culture tests) comparing unmodified and chemically modified chrysotile fibers
• Who was studied: Cultured rat pleural mesothelial cells (RPMC), passaged 8 to 12 times, used for toxicity, chromosome and transformation tests; rabbit alveolar macrophages obtained by bronchoalveolar lavage, used for fiber durability tests. Laboratories in Créteil and Paris, France.
• Exposure: Canadian chrysotile fibers (supplied by the Société Nationale de l'Amiante, Sherbrooke, Quebec) and the same chrysotile modified by a phosphatation process. Doses in cell tests were roughly 2 to 20 µg/ml. Some transformation experiments also added benzo(a)pyrene at 1 µg/ml.
• Main results:
  • Fiber size: in the culture medium, fibers in the size range Stanton linked to higher cancer potency numbered about 3 x 10^6 per microgram, about 15 percent of all fibers. There were no great differences between the two fiber types.
  • Durability inside alveolar macrophages: for untreated chrysotile, the share of unleached fibers (magnesium-to-silicon ratio at or above 0.8) fell to about 30 percent after 24 hours. Mean ratios after 24 hours were 0.76 plus or minus 0.12 for chrysotile and 0.94 plus or minus 0.09 for modified chrysotile (p less than 0.01). Thirty fibers were analyzed for each type.
  • Toxicity to mesothelial cells: modified chrysotile was less cytotoxic. Cell viability with 10 µg/ml of untreated fibers was of the same order as with 20 µg/ml of modified chrysotile.
  • Untreated chrysotile caused a statistically significant increase in chromosomal aberrations compared with untreated cultures, from 7 µg/ml up to 15 µg/ml. The aberrations were mainly of chromatid type.
  • Modified chrysotile also increased chromosomal aberrations compared with controls, but the increase was not statistically significant.
  • Both fiber types significantly changed chromosome number. Treated cells showed a wider range of chromosome numbers, and cells with about 84 chromosomes appeared.
  • Treated cells formed fewer colonies than untreated cells. The transformation index was higher than in controls at every initial cell density, and was similar for chrysotile and modified chrysotile. The transformation level fell as more cells were plated.
  • With benzo(a)pyrene added, one way of expressing the data suggested a synergistic effect between chrysotile and benzo(a)pyrene. Expressed another way, there was no evident synergy.
• The authors' conclusion: The authors concluded that in vitro testing showed no great differences between modified and unmodified chrysotile in their effects on rat pleural mesothelial cells, but that the modified fibers were more chemically stable in alveolar macrophages. By unit weight, the modified fibers were less cytotoxic and less clastogenic (less damaging to chromosomes). The authors noted that animal experiments were in progress.
• Limitations the authors state:
  • The authors stated that the transformation assay is not sufficiently established.
  • The apparent dependence of the transformation index on cell viability needs further investigation.
  • It is unknown whether cells took up different amounts of the two fiber types.
  • The greater stability of the modified fibers was shown only over a short period of 24 hours.
  • The short-term transformation test may not have allowed the most highly transformed cell type to appear.
  • In vitro tests measure cancer-causing potency, not cancer hazard. Clearance and retention of fibers in the body also matter for assessing risk.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile, Lung cancer.

Medical terms in this study, explained in our Lexicon: Carcinogenic, Chrysotile, Electron Microprobe Analysis, Alveolar Macrophage, Mesothelial Cells, Macrophage.

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