Objectives: We performed a cytotoxicity study by cell magnetometry, measured lactate dehydrogenase (LDH) activity by enzyme assay, detected DNA ladder formation, and performed morphological examination by electron microscopy in order to evaluate the safety of high temperature wool (HT wool), an asbestos substitute, using long and short chrysotile fibers (CF) as positive controls and phosphate buffered saline (PBS) as a negative control. Methods: Alveolar macrophages were isolated from male Fisher rats. Following the addition of iron oxide particles (Fe₃O₄) to macrophages, HT wool, long or short CF was added. Then, the remanence strength was measured for 20 min after magnetization by an external field. Percent LDH release was calculated after determining LDH activity. DNA was detected using an apoptosis detection kit. Morphological observation was performed by taking electron micrographs of macrophages in the groups treated with HT wool and long- and short-CF. Results: Rapid relaxation, an indicator of decay of cytotoxicity, was observed by cell magnetometry immediately after magnetization was ended in the groups treated with HT wool and PBS, showing that HT wool causes no harmful effect on the cytoskeleton. The CF-treated groups had higher LDH activity than the PBS- and HT wool-treated groups. No fragmentation of DNA was observed in any group. In morphological observation, cytotoxicity in macrophages was lower in the HT wool-treated groups than in the CF-treated groups. Conclusions: The results suggest that HT wool has no cytotoxicity, as evaluated by cell magnetometry, enzyme assay, DNA ladder detection and morphological examination.

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