Cytotoxicity Study of High Temperature Wool (HT Wool) by Cell Magnetometric Evaluation

Abstract

It has been reported that asbestos causes pulmonary fibrosis and malignant tumors, and many in vitro and in vivo studies have shown its toxicity. Therefore, the use of asbestos has been restricted worldwide, including in Japan [1][2][3] , and many asbestos substitutes have been developed. A variety of man-made vitreous fibers (MMVF) such as rock wool (RW) and glass wool are currently used as asbestos substitutes. Recently, a new type of RW, high-alumina, low-silica stone wool, hightemperature wool (HT wool), has been developed. Its chemical composition is characterized by a high concentration of Al 2 O 3 and a low concentration of SiO 2 , low biopersistence, and a high melting point. These characteristics of HT wool have enabled its use to be broadened to heat insulation and other applications, and it has extensively replaced traditional types of RW. However, since HT wool has only been used for a short time, and the IARC categorizes it as unclassifiable, evaluation of its safety is urgently needed. Since most chemical substances enter the body through the airways and are processed by alveolar macrophages, evaluation of the effects on these cells should be a useful system for screening the physiological effects of chemical substances. Furthermore, alveolar macrophages, due to their phagocytic activity, are suited for the evaluation of insoluble particles such as dust, fibrous substances like asbestos and asbestos substitutes.Cell magnetometry is an application of lung magnetometry, which was first reported by Cohen in 1973 4) . The principle of cell magnetometry is to induce uptake of iron oxide particles (magnetic particles) by phagocytes and to magnetize these particles by applying an external magnetic field, followed by measurement of the strength of the remanence after cessation of external 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 (Fe 3 O 4 ) 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 group...