Cytotoxicity study of rock wool by cell magnetometric evaluation

Our plain-English summary of Cytotoxicity study of rock wool by cell magnetometric evaluation, by Y. Kudo, M. Kotani, Y. Aizawa (Regulatory Toxicology and Pharmacology, 2009).

The study

• Authors: Y. Kudo, M. Kotani, Y. Aizawa
• Journal: Regulatory Toxicology and Pharmacology
• Published: 2009;55(2):151-7
• Read it: PubMed · Publisher

Abstract

The cytotoxicity of rock wool (RW), an asbestos substitute, was evaluated by cell magnetometry. Alveolar macrophages were isolated from male Fisher rats. Following addition of triiron tetraoxide (Fe(3)O(4)) to macrophages, RW was added. Then, the remnant magnetic field strength was measured for 20min after magnetization by an external field. Relaxation, an indicator of decay of cytotoxicity, was observed by cell magnetometry immediately postmagnetization in the group to which RW was added. In general, materials phagocytosed by macrophages are ingested into phagosomes and digested while migrating. This migration of phagosomes occurs by polymerization and depolymerization of the cytoskeleton. As a result of evaluation, relaxation was not delayed by addition of RW, since RW caused no effect on the cytoskeleton. It was suggested that RW has no cytotoxicity as evaluated by cell magnetometry.

In plain English

This laboratory study tested whether rock wool, a man-made vitreous fiber used as an asbestos substitute, damages lung immune cells. The authors took alveolar macrophages from 6 male Fisher rats. For 18 hours they exposed the cells to rock wool at 50, 100 or 150 micrograms per millilitre, to long or short chrysotile asbestos at 50 micrograms per millilitre for comparison, or to buffered salt solution (PBS) without fibers; in the main tests every group also received iron oxide particles. The main test, cell magnetometry, tracks how fast magnetized iron particles inside the cells lose their alignment. The authors treated slower loss, called delayed relaxation, as a sign of cell damage. Twenty minutes after magnetization, 32.9% of the field remained in the salt-solution group, 30.9% to 43.9% in the rock wool groups, and about 66% in both chrysotile groups. Rock wool did not differ significantly from salt solution. Chrysotile differed significantly from rock wool. A test of enzyme leakage from the cells showed a similar pattern. No DNA fragmentation was seen in any group. The authors concluded that, after short-term laboratory exposure, cytotoxicity was less marked with rock wool than with chrysotile.

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 alveolar macrophages, using cell magnetometry, an enzyme (LDH) leakage assay, DNA ladder detection and electron microscopy
• Who was studied: Alveolar macrophages (lung immune cells) obtained by lung lavage from 6 male Fisher rats (F344/N Slc) weighing 200 to 250 g; the study was done at Kitasato University School of Medicine, Japan
• Exposure: Rock wool made by NC Co., Ltd., Japan, at 50, 100 and 150 micrograms per millilitre. Its composition was 39% SiO2, 33% CaO, 14% Al2O3, 5% MgO, 1.8% Fe2O3 and 0.6% S. Positive controls were long and short chrysotile fibers at 50 micrograms per millilitre; the negative control was PBS. Cells were incubated for 18 hours. For magnetometry, the enzyme assay and DNA ladder detection, iron oxide (Fe3O4) at 50 micrograms per millilitre was added to every well, including the PBS control. It was not added for electron microscopy.
• Main results:
  • The remnant magnetic field remaining 20 minutes after magnetization was 32.9 ± 3.6% in the PBS group. In the 50, 100 and 150 micrograms per millilitre rock wool groups it was 30.9 ± 5.7%, 39.7 ± 5.3% and 43.9 ± 7.4%.
  • Relaxation was delayed in the chrysotile groups: 66.2 ± 4.9% (long chrysotile) and 66.4 ± 6.4% (short chrysotile) of the field remained at 20 minutes.
  • There was no significant difference between the PBS and rock wool groups. Differences between the rock wool groups and both chrysotile groups were statistically significant (p less than 0.05).
  • At 2 minutes after magnetization, the decay constant was smaller in both chrysotile groups than in the PBS and rock wool groups. Values were 3.1 ± 0.4 for PBS; 3.1 ± 0.4, 2.6 ± 0.5 and 2.9 ± 0.7 for the rock wool groups; and 1.6 ± 0.1 and 1.2 ± 0.3 for long and short chrysotile. Rock wool did not differ significantly from PBS; it did differ significantly from both chrysotile groups.
  • Percent LDH release was 19.6 ± 2.3% in the PBS group. It was about 15% to 21% in the rock wool groups, and 40.0 ± 4.8% and 42.2 ± 5.3 in the long and short chrysotile groups. Differences between rock wool and chrysotile were significant; differences between PBS and rock wool were not.
  • No DNA fragmentation, which the authors use as a sign of apoptosis (programmed cell death), was seen in the PBS, rock wool or chrysotile groups.
  • By electron microscopy, macrophages exposed to 150 micrograms per millilitre of rock wool showed no apparent degeneration of the cytoplasm. In the chrysotile groups, fibers were broken into small pieces inside vacuoles, and there were more cells with condensed nuclei.
• The authors' conclusion: The authors concluded that cytotoxicity, evaluated mainly by cell magnetometry after short-term exposure in vitro, was less marked with rock wool fibers than with chrysotile. They suggested that rock wool showed no cytotoxicity as evaluated by cell magnetometry, and they planned further in vivo inhalation tests in animals.
• Limitations the authors state:
  • Chromosomal aberration was not measured. The authors said the potential of short, thin rock wool fibers to cause apoptosis still needs evaluation.
  • The rock wool tested was shorter and had lower iron content than the rock wool in another study that found oxidative and genotoxic effects. The authors suggested those different features might explain the different results.

Topics

Medical terms in this study, explained in our Lexicon: Alveolar Macrophage, Macrophage.

Related studies

• Comparative cytotoxicity study of rock wool and chrysotile by cell magnetometric evaluation — Y. Kudo, M. Watanabe, et al. (2003)
• Cytotoxicity study of high temperature wool (HT wool) by cell magnetometric evaluation — Y. Kudo, M. Kotani, et al. (2010)
• Mechanism of refractory ceramic fiber- and rock wool-induced cytotoxicity in alveolar macrophages — K.A. Kim, W.K. Lee, et al. (2001)
• 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)
• Cytotoxicity and solubility evaluation of two types of whiskers by cell magnetometry — Y. Kudo, Y. Aizawa (2011)

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