Comparative cytotoxicity study of rock wool and chrysotile by cell magnetometric evaluation

Our plain-English summary of Comparative cytotoxicity study of rock wool and chrysotile by cell magnetometric evaluation, by Y. Kudo, M. Watanabe, M. Okada, et al (Inhalation Toxicology, 2003).

The study

• Authors: Y. Kudo, M. Watanabe, M. Okada, H. Shinji, M. Niitsuya, T. Satoh, Y. Sakai, N. Kohyama, M. Kotani, Y. Aizawa
• Journal: Inhalation Toxicology
• Published: 2003;15(13):1275-95
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Rock wool (RW), a type of man-made mineral fiber (MMMF), is a building material used as an asbestos substitute for heat insulation, fire resistance, and reinforcement. RW is included in group 3 of the IARC classification. In the present study, the cytotoxicity of RW was investigated by cell magnetometry, enzyme assay, DNA ladder detection, and electron microscopic morphological evaluation in comparison with chrysotile fibers (CF). Specimens were prepared by 18-h incubation of Fischer rat alveolar macrophages in the presence of RW fibers as the study material, CF as positive control, and phosphate-buffered saline (PBS) as negative control, together with a relaxation indicator, Fe3O4, except for morphological evaluation, followed by additional procedures of external magnetization and subsequent 20-min remanent magnetic field measurement for magnetometric evaluation, and macrophage DNA extraction for evaluating possible apoptosis by DNA ladder detection. In magnetometry, relaxation, a marker of cytotoxicity, was rapid in both the RW- and PBS-treated groups, while it was delayed in both the long and short CF-treated groups. Differences in percent lactate dehydrogenase (LDH) release between the RW-treated group and PBS-treated group were not significant, but those between the RW-treated group and short CF-treated group were statistically significant. A DNA ladder was not detected in any of the study groups. Electron micrographs showed that RW did not cause any change, but CF caused changes in macrophages. Thus, magnetometric measurements suggested no cytotoxicity of RW. We plan, in the future, to evaluate the safety of RW by magnetometric measurement and morphological observation of the lungs in in vivo inhalation experiments.

In plain English

In this laboratory study, the authors compared rock wool, a man-made mineral fiber used as an asbestos substitute, with chrysotile asbestos. Lung macrophages (defense cells) from male Fischer rats were incubated for 18 hours with rock wool at 50, 100 or 150 µg/ml, long or short chrysotile at 50 µg/ml, or salt solution as a control. Data came from six rats. Tests included cell magnetometry, release of the enzyme LDH, DNA ladder testing for apoptosis, and electron microscopy. In magnetometry, rock wool-treated cells behaved like controls, while both chrysotile groups showed delayed relaxation, which the authors treat as a marker of cell damage. LDH release was 13.7% to 15.1% with rock wool, 14.0% in controls, 21.6% with long chrysotile and 34.28% with short chrysotile. The rock wool versus short chrysotile difference was statistically significant. No DNA ladder appeared in any group. Short chrysotile caused the most visible cell damage, and rock wool caused no apparent degeneration of the cell interior. The authors concluded rock wool was less cytotoxic than chrysotile after short exposure.

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) experiment on rat alveolar macrophages, comparing rock wool with chrysotile asbestos (positive control) and phosphate-buffered saline (negative control)
• Who was studied: Alveolar macrophages collected by lung lavage from male Fischer rats (F344/N Slc, about 200 to 250 g); data from six rats
• Exposure: Rock wool fibers (mean length 16.5 µm, mean diameter 1.80 µm) at 50, 100 and 150 µg/ml. Long or short chrysotile fibers at 50 µg/ml as positive controls. Phosphate-buffered saline as negative control. Incubation lasted 18 hours.
• Main results:
  • In magnetometry, relaxation was rapid in the saline and rock wool groups and delayed in both chrysotile groups. Differences between the rock wool and chrysotile groups were statistically significant (p less than 0.05).
  • Remanent magnetic field at 20 minutes was 33.9 ± 1.57% in the saline group. In the rock wool groups it was 34.2 ± 2.12%, 31.2 ± 2.51% and 34.3 ± 1.26% at 50, 100 and 150 µg/ml. In the long and short chrysotile groups it was 46.4 ± 0.80% and 64.1 ± 3.73%.
  • The 2-minute decay constant was smaller in the long chrysotile group (2.518 ± 0.081 × 10 to the minus 3 per second) and the short chrysotile group (1.559 ± 0.231) than in the saline group (3.245 ± 0.342) and the rock wool groups (2.808, 3.105, 2.956).
  • Percent LDH release was 14.0 ± 1.76% in the saline group and 13.7 ± 2.03%, 13.9 ± 1.96% and 15.1 ± 2.06% in the rock wool 50, 100 and 150 µg/ml groups.
  • Percent LDH release was 21.6 ± 4.60% in the long chrysotile group and 34.28 ± 5.27% in the short chrysotile group.
  • The rock wool versus saline difference in LDH release was not significant. The rock wool versus short chrysotile difference was statistically significant.
  • No DNA fragmentation (a sign of apoptosis) was seen in the saline, rock wool or chrysotile groups.
  • Under electron microscopy, rock wool was seen in macrophage cytoplasm without apparent degeneration.
  • Short chrysotile caused more cytoplasmic vacuolization than long chrysotile, and more cells with condensed nuclei.
• The authors' conclusion: The authors concluded that the cytotoxicity of rock wool was lower than that of chrysotile after short exposure, and that this suggested rock wool was relatively safe, in line with its IARC classification. They planned in vivo inhalation studies.
• Limitations the authors state:
  • The authors stated that chromosomal aberration was not measured, and that the apoptosis-inducing potential of short, thin rock wool fibers still needs investigation.
  • The findings apply to short exposure in cells. The authors planned further evaluation in in vivo inhalation tests.

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Mineral Fiber, IARC Classification, Alveolar Macrophage, Macrophage, Apoptosis, Lactate Dehydrogenase (LDH).

Related studies

• Cytotoxicity study of rock wool by cell magnetometric evaluation — Y. Kudo, M. Kotani, et al. (2009)
• Cytotoxicity study of high temperature wool (HT wool) by cell magnetometric evaluation — Y. Kudo, M. Kotani, et al. (2010)
• Magnetometric evaluation of the effects of man-made mineral fibers on the function of macrophages using the macrophage cell line RAW 264.7 — K. Shibata, Y. Kudo, et al. (2007)
• Magnetometric evaluation for the effect of chrysotile on alveolar macrophages — T. Keira, M. Okada, et al. (1998)
• Mechanism of refractory ceramic fiber- and rock wool-induced cytotoxicity in alveolar macrophages — K.A. Kim, W.K. Lee, et al. (2001)
• Cytotoxicity and solubility evaluation of two types of whiskers by cell magnetometry — Y. Kudo, Y. Aizawa (2011)

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