Abstract

BackgroundAsbestos has been reported to cause pulmonary fibrosis, and its use has been banned all over the world. The related industries are facing an urgent need to develop a safer fibrous substance. Rock wool (RW), a kind of asbestos substitute, is widely used in the construction industry. In order to evaluate the safety of RW, we performed a nose-only inhalation exposure study in rats. After one-month observation period, the potential of RW fibers to cause pulmonary toxicity was evaluated based on lung magnetometry findings, pulmonary biopersistence, and pneumopathology.MethodsUsing the nose-only inhalation exposure system, 6 male Fischer 344 rats (6 to 10 weeks old) were exposed to RW fibers at a target fiber concentration of 100 fibers/cm3 (length [L] > 20 μm) for 6 hours daily, for 5 consecutive days. As a magnetometric indicator, 3 mg of triiron tetraoxide suspended in 0.2 mL of physiological saline was intratracheally administered after RW exposure to these rats and 6 unexposed rats (controls). During one second magnetization in 50 mT external magnetic field, all magnetic particles were aligned, and immediately afterwards the strength of their remanent magnetic field in the rat lungs was measured in both groups. Magnetization and measurement of the decay (relaxation) of this remanent magnetic field was performed over 40 minutes on 1, 3, 14, and 28 days after RW exposure, and reflected cytoskeleton dependent intracellular transport within macrophages in the lung. Similarly, 24 and 12 male Fisher 344-rats were used for biopersistence test and pathologic evaluation, respectively.ResultsIn the lung magnetometric evaluation, biopersistence test and pathological evaluation, the arithmetic mean value of the total fiber concentration was 650.2, 344.7 and 390.7 fibers/cm3, respectively, and 156.6, 93.1 and 95.0 fibers/cm3 for fibers with L > 20 μm, respectively. The lung magnetometric evaluation revealed that impaired relaxation indicating cytoskeletal toxicity did not occur in the RW exposure group. In addition, clearance of the magnetic tracer particles was not significantly affected by the RW exposure. No effects on lung pathology were noted after RW exposure.ConclusionThese findings indicate that RW exposure is unlikely to cause pulmonary toxicity within four weeks period. Lung magnetometry studies involving long-term exposure and observation will be necessary to ensure the safety of RW.

Highlights

  • Asbestos has been reported to cause pulmonary fibrosis, and its use has been banned all over the world

  • Pulmonary fibrosis has occurred in rats experimentally exposed to Rock wool (RW), but no development of lung tumors was noted [1]

  • We have evaluated the cytotoxicity of chrysotile, a type of asbestos, as well as RW and other man-made vitreous fibers (MMVFs), by cell magnetometry that was originally devised in our laboratory [8,9,10,11,12]

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Summary

Introduction

Asbestos has been reported to cause pulmonary fibrosis, and its use has been banned all over the world. Rock wool (RW), a kind of asbestos substitute, is widely used in the construction industry. Rock wool (RW) is a kind of asbestos substitute and is widely used in the construction industry, in particular for fire-resisting insulation, thermal insulation, and acoustic absorption. The primary feature of this method is that this is an in vivo test of the living organism, and the proper function of the main defense cell in the lung (macrophages) can be non-invasively monitored. Using this method, we can obtain knowledge about the intracellular movement of alveolar macrophages, after making them to ingest magnetic particles, by measuring the remanent magnetic field strength in the lung after external magnetization. Since the ingested magnetic particles remain in the phagosomes, intracellular movement of the phagosomes can be detected by measurement of remnant magnetic field [5,6,7]

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