Evaluation of hazardousness of refractory fibers by cell magnetometry

Our plain-English summary of Evaluation of hazardousness of refractory fibers by cell magnetometry, by Y. Kudo, M. Kotani, Y. Aizawa (The Journal of Toxicological Sciences, 2010).

The study

• Authors: Y. Kudo, M. Kotani, Y. Aizawa
• Journal: The Journal of Toxicological Sciences
• Published: 2010;35(6):807-15
• Cited by: 1 article, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

This study was carried out to assess the cytotoxicity of three kinds of refractory fibers (RFs), RF1, RF2, and RF3, by cell magnetometry, lactate dehydrogenase (LDH) assay and morphological observation by scanning electron microscopy, using a mouse-derived cultured cell line, RAW264.7. As an indicator for cell magnetometry, Fe(3)O(4) was added to RAW264.7 cells. RF1, RF2 and RF3 were each added to an aliquot of this solution to make final concentrations of 250, 500 and 1,000 µg/ml in the experimental group. Phosphate buffered solution was added to make the control solution (n = 6). After culturing for 48 hr, the solution was magnetized from outside using a cell magnetometric apparatus, and the remnant magnetic field was measured for 20 min postmagnetization. In cell magnetometry, a significant delay of relaxation compared to that of the control was observed. In the LDH assay, LDH release into the culture medium was observed by addition of RFs. Furthermore, a quantity-dependent relationship was found between the quantity of RF added and the cytotoxicity in cell magnetometry and LDH assay. Morphological examination revealed incomplete phagocytosis of fibers and a decrease of microvilli in the experimental groups. These results suggest that RFs are cytotoxic to RAW264.7 cells, showing concentration-dependent cytotoxicity, and have a possible risk of cytotoxicity similar to that of asbestos. Further studies by pulmonary magnetometry are necessary to assess the hazardousness of RFs.

In plain English

In this laboratory study, the authors tested three refractory fibers (RF1, RF2, RF3), a type of asbestos substitute, on RAW264.7, a mouse-derived macrophage-like cell line. Cells were exposed for 48 hours to 250, 500 or 1,000 µg/ml of each fiber, or to salt solution (control). Cell magnetometry tracks movement inside cells using iron oxide particles. An LDH test measured cell damage; electron microscopy examined cells. Compared with controls, relaxation (fading of the magnetic signal) at 20 minutes after magnetization was significantly delayed at 500 and 1,000 µg/ml for RF1 and at 1,000 µg/ml for RF2 and RF3. Larger fiber amounts were associated with greater delay. The decay constant did not differ significantly. LDH release was significantly higher at 500 and 1,000 µg/ml for all three fibers, and at 250 µg/ml for RF2. At 1,000 µg/ml, cells partly engulfed fibers and had fewer microvilli. The authors concluded that the fibers were cytotoxic to these cells, with a possible risk of cytotoxicity similar to asbestos. Citing an earlier chrysotile study, they suggested lower cytotoxicity than chrysotile and called for 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: Laboratory (in vitro) cell culture experiment using cell magnetometry, LDH assay and electron microscopy
• Who was studied: RAW264.7, a mouse-derived peritoneal macrophage-like cultured cell line; results expressed for groups of 6 samples (n = 6)
• Exposure: Three refractory fibers (RF1, RF2, RF3), supplied by the Japan Fibrous Materials Research Association and composed mainly of alumina and silica. Mean lengths were 12.0, 11.0 and 11.0 µm and mean widths 0.77, 1.10 and 2.40 µm. Final concentrations were 250, 500 and 1,000 µg/ml for 48 hr, with phosphate buffered saline as the control. Morphology was examined at 1,000 µg/ml only.
• Main results:
  • In cell magnetometry, larger amounts of fiber were associated with greater delay of relaxation (a quantity-effect relationship).
  • Compared with controls, relaxation of the remnant magnetic field at 20 min after magnetization was significantly delayed for RF1 at 500 µg/ml (p less than 0.05) and 1,000 µg/ml (p less than 0.001), for RF2 at 1,000 µg/ml (p less than 0.05), and for RF3 at 1,000 µg/ml (p less than 0.001).
  • No statistically significant difference in the decay constant was found between any fiber-exposed group and the controls.
  • Compared with controls, LDH release (a marker of cell damage) was significantly greater for RF1 at 500 and 1,000 µg/ml (both p less than 0.001). For RF2 it was greater at 250 µg/ml (p less than 0.05), 500 µg/ml (p less than 0.05) and 1,000 µg/ml (p less than 0.001). For RF3 it was greater at 500 µg/ml (p less than 0.05) and 1,000 µg/ml (p less than 0.001).
  • Under scanning electron microscopy of cells exposed to 1,000 µg/ml of fiber, the cells showed fewer microvilli, incomplete phagocytosis (engulfing) of fibers, deformation, and elongation along fibers. Some cells kept a globular shape.
  • Under transmission electron microscopy, fiber-exposed cells showed chromatin aggregation in the nuclei and a slight increase in lysosomes. Fibers were seen in the cytoplasm, but the other cell structures remained relatively normal.
• The authors' conclusion: The authors concluded that, in these cultured cells, the refractory fibers were cytotoxic in a concentration-dependent way and have a possible risk of cytotoxicity similar to that of asbestos. In the discussion, they compared their results with an earlier chrysotile study (Shibata et al., 2007). From that comparison, they suggested that refractory fibers have lower cytotoxicity than chrysotile fibers.
• Limitations the authors state:
  • The authors state that nasal inhalation studies and pulmonary magnetometry are still needed to assess lung toxicity and confirm the safety of refractory fibers; this study used cultured cells only.

Topics

Medical terms in this study, explained in our Lexicon: Lactate Dehydrogenase (LDH), Scanning Electron Microscopy (SEM), LDH Release, Phagocytosis.

Related studies

• 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)
• Cytotoxicity study of rock wool by cell magnetometric evaluation — Y. Kudo, M. Kotani, et al. (2009)
• Comparative cytotoxicity study of rock wool and chrysotile by cell magnetometric evaluation — Y. Kudo, M. Watanabe, et al. (2003)
• Magnetometric evaluation for the effect of chrysotile on alveolar macrophages — T. Keira, M. Okada, et al. (1998)
• Cytotoxicity study of high temperature wool (HT wool) by cell magnetometric evaluation — Y. Kudo, M. Kotani, et al. (2010)
• Cytotoxicity and solubility evaluation of two types of whiskers by cell magnetometry — Y. Kudo, Y. Aizawa (2011)

Browse more research in The Journal of Toxicological Sciences, or return to medical research.