In vitro toxicity of asbestos substitutes evaluated by cytomagnetometry

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Recently, some asbestos substitutes have been used in Japan, as health disorders occurred by asbestos had been known. However, such substitutes have not proved their safety yet, and it is important to establish screening methods for evaluating health disorders. Then we examined a few evaluations of health disorders for silicon carbide whisker (SiC), titanium dioxide whisker (TiO_2) and rock wool (RW) not only by cytomagnetometry, but also by LDH release assays, morphological observations and apoptotic observations.Both 20, 40, and 60 μg/ml of SiC and TiO_2 in the culture medium showed that relaxation was delayed dose-dependently and decay constants were smaller than those of negative controls. LDH release assay showed that releasing rates were increased dose-dependently. Morphological observations showed multiple vacuolations in cytosol, degenerations of nuclei, and agglutinations of chromatin. And apoptotic observations by using TUNEL method and DNA ladder method showed slight apoptotic cells in a sample added to SiC.On the other hand, 50, 100, and 150μg/ml of RW did not show delays of relaxation and decreasing of decay constants in comparison with negative controls. Results of LDH release assay, morphological observations including TUNEL method and DNA ladder method, and apoptotic observations supported results of cytomagnetometry.Then, it is found that an acute cytotoxicity of RW to alveolar macrophages is less than that of SiC and TiO_2 in in vitro experiments. In future, we are going to use subculture cells instead of alveolar macrophages obtained from bronchoalveolar lavage, to avoid changes in conditions of experiments. In order to observe a mechanism of relaxation optically, we will examine intracellular movements of magnetized particles after magnetization by using a video-enhanced microscope. In addition, cytotoxic evaluations of asbestos substitutes except SiC, TiO_2 and RW will be examined.