The in vitro cytotoxicity of asbestos fibers: I. P388D1 cells

Acute cytotoxicity of mineral fibres observed by time-lapse video microscopy

Inhalation of mineral fibres is associated with the onset of an inflammatory activity in the lungs and the pleura responsible for the development of fatal malignancies. It is known that cell damage is a necessary step for triggering the inflammatory response. However, the mechanisms by which mineral fibres exert cytotoxic activity are not fully understood. In this work, the kinetics of the early cytotoxicity mechanisms of three mineral fibres (i.e., chrysotile, crocidolite and fibrous erionite) classified as carcinogenic by the International Agency for Research on Cancer, was determined for the first time in a comparative manner using time-lapse video microscopy coupled with in vitro assays. All tests were performed using the THP-1 cell line, differentiated into M0 macrophages (M0-THP-1) and exposed for short times (8 h) to 25 μg/mL aliquots of chrysotile, crocidolite and fibrous erionite. The toxic action of fibrous erionite on M0-THP-1 cells is manifested since the early steps (2 h) of the experiment while the cytotoxicity of crocidolite and chrysotile gradually increases during the time span of the experiment. Chrysotile and crocidolite prompt cell death mainly via apoptosis, while erionite exposure is also probably associated to a necrotic-like effect. The potential mechanisms underlying these different toxicity behaviours are discussed in the light of the different morphological, and chemical-physical properties of the three fibres.

Comparative Cytotoxicity Study of Rock Wool and Chrysotile by Cell Magnetometric Evaluation

Rock wool (RW), a type of man-made mineral fiber (MMMF), is a building material used as an asbestos substitute for heat insulation, fire resistance, and reinforcement. RW is included in group 3 of the IARC classification. In the present study, the cytotoxicity of RW was investigated by cell magnetometry, enzyme assay, DNA ladder detection, and electron microscopic morphological evaluation in comparison with chrysotile fibers (CF). Specimens were prepared by 18-h incubation of Fischer rat alveolar macrophages in the presence of RW fibers as the study material, CF as positive control, and phosphate-buffered saline (PBS) as negative control, together with a relaxation indicator, Fe3O4, except for morphological evaluation, followed by additional procedures of external magnetization and subsequent 20-min remanent magnetic field measurement for magnetometric evaluation, and macrophage DNA extraction for evaluating possible apoptosis by DNA ladder detection. In magnetometry, relaxation, a marker of cytotoxicity, was rapid in both the RW- and PBS-treated groups, while it was delayed in both the long and short CF-treated groups. Differences in percent lactate dehydrogenase (LDH) release between the RW-treated group and PBS-treated group were not significant, but those between the RW-treated group and short CF-treated group were statistically significant. A DNA ladder was not detected in any of the study groups. Electron micrographs showed that RW did not cause any change, but CF caused changes in macrophages. Thus, magnetometric measurements suggested no cytotoxicity of RW. We plan, in the future, to evaluate the safety of RW by magnetometric measurement and morphological observation of the lungs in in vivo inhalation experiments.

Differences in the effects of fibrous and particulate titanium dioxide on alveolar macrophages of Fischer 344 rats

Alveolar macrophages are considered to play a major role in the pathophysiology of lung diseases caused by exposure to various kinds of pathogens and particles. In this study, the cytotoxic effect of different shapes of titanium dioxide (TiO(2)) was evaluated on macrophages using a unique magnetometry method and was compared with conventional methods of lactate dehydrogenase (LDH) release, apoptosis measurement, and morphological observations. Alveolar macrophages obtained from Fischer rats (F344) by bronchoalveolar lavage were incubated in vitro for 18 h with Fe(3)O(4) as a magnetometric indicator and fibrous and particulate forms of TiO(2) as test materials. In the control and particulate exposed group, rapid attenuation of the residual magnetic field, so-called "relaxation," was observed immediately after cessation of the external magnetic field. In comparison, a delay of relaxation was observed in alveolar macrophages exposed to fibrous TiO(2). LDH released into serum-free medium induced by exposure to TiO(2) increased significantly in a concentration-dependent manner in macrophages exposed to fibrous TiO(2), while negligible LDH release was observed in macrophages exposed to particulate TiO(2). The DNA ladder detection method and morphological examination detected no apoptosis in macrophages exposed to 60 micro g/ml of fibrous or particulate TiO(2). Electron microscopic examination revealed vacuolar changes and cell surface damage in macrophages exposed to fibrous TiO(2), but no significant changes in macrophages exposed to particulate TiO(2). The results of magnetometry, LDH release, and electron microscopy suggest that cytotoxicity of TiO(2) depends on the shape of the material.

Refractory ceramic fiber: toxicology, epidemiology, and risk analyses--a review

Refractory ceramic fiber (RCF) is an energy-efficient, high-temperature insulation, used principally in industrial furnaces, heaters, and reactors. Prior to the 1980s, there were few publications dealing with the potential health effects of this material. However, with the advent of higher energy costs and the need for thermally efficient high-temperature insulating materials, production of RCF grew rapidly, as did interest in its potential health effects. This article provides a comprehensive and integrated review of the toxicology (in vitro and in vivo), epidemiology, and risk analysis literature of RCF. Based on the available literature, we conclude that an occupational exposure of 0.5 fibers per cubic centimeter (cm(3)) [8-h time-weighted average (8-h TWA)] results in an occupational health risk no greater than 9.1 x 10(-5).

Magnetometric evaluation for the effect of chrysotile on alveolar macrophages

Alveolar macrophages are thought to play an important role in fibrogenesis due to asbestos exposure. In this experiment, we evaluated the effect mainly by unique magnetometry and also by conventional methods such as lactate dehydrogenase (LDH) activity measurement and morphological observations. Alveolar macrophages obtained from Syrian golden hamsters by bronchoalveolar lavages were exposed 18 hours in vitro to Fe3O4 as an indicator for magnetometry and chrysotile for experiments. A rapid decrease of the remanent magnetic field, so called "relaxation", was observed after the cessation of an external magnetic field in macrophages phagocytizing Fe3O4 alone, while relaxation was delayed in those concurrently exposed to chrysotile. Since relaxation is thought due to the cytoskeleton-driven random rotation of phagosomes containing iron oxide particles, chrysotile is considered to interfere with the cytoskeletal function of macrophages. Release of LDH from chrysotile-exposed macrophages into the medium was recognized, but it was not significantly higher than the controls. Apoptosis was negligible in macrophages exposed to chrysotile by the DNA ladder detection, the terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling method and morphological observations. Electron microscopical examinations revealed early necrotic changes in macrophages exposed to chrysotile. These findings indicate that cell magnetometry detects impaired cytoskeletal function due to in vitro exposure to chrysotile.

A semiautomatic image analyzer for cell counts in monolayers. II. Application to toxicity estimation and comparisons between two cell-viability markers, fluorescein diacetate and lactate dehydrogenase

By using an image-analyzer system, toxicological effects of different substances on nonconfluent cells in monolayers can be assessed. The total number of cells and the number of viable cells are semiautomatically counted. Fluorescein diacetate is used as the viability marker. The method was tested by using monolayers of alveolar macrophages from rabbits exposed to manganese dioxide particles. A dose-response curve was obtained from a series of experiments in which the response at a certain dose level can be obtained from cell-counting procedures of the duration of 1 h. The method can be used as a short-term test, testing potentially toxic substances including cytostatic drugs where the viability should be determined. Another example is further given of the use of this technique. The results obtained from it are compared with estimates of the percentage of viable cells assessed by extracellular lactate dehydrogenase from nonexposed and manganese dioxide particle-exposed monolayers of rabbit alveolar macrophages. The two methods both account well for the theoretical relation when the lactate dehydrogenase activity values are corrected for an inactivation of this enzyme with time.