Frequent homozygous deletion of Cdkn2a/2b in tremolite-induced malignant mesothelioma in rats.

The onset of malignant mesothelioma (MM) is linked to exposure to asbestos fibers. Asbestos fibers are classified as serpentine (chrysotile) or amphibole, which includes the crocidolite, amosite, anthophyllite, tremolite, and actinolite types. Although few studies have been undertaken, anthophyllite has been shown to be associated with mesothelioma, and tremolite, a contaminant in talc and chrysotile, is a risk factor for carcinogenicity. Here, after characterizing the length and width of these fibers by scanning electron microscopy, we explored the cytotoxicity induced by tremolite and anthophyllite in cells from an immortalized human mesothelial cell line (MeT5A), murine macrophages (RAW264.7), and in a rat model. Tremolite and short anthophyllite fibers were phagocytosed and localized to vacuoles, whereas the long anthophyllite fibers were caught on the pseudopod of the MeT5A and Raw 264.7 cells, according to transmission electron microscopy. The results from a 2-day time-lapse study revealed that tremolite was engulfed and damaged the MeT5A and RAW264.7 cells, but anthophyllite was not cytotoxic to these cells. Intraperitoneal injection of tremolite in rats induced diffuse serosal thickening, whereas anthophyllite formed focal fibrosis and granulomas on peritoneal serosal surfaces. Furthermore, the loss of Cdkn2a/2b, which are the most frequently lost foci in human MM, were observed in 8 cases of rat MM (homozygous deletion [5/8] and loss of heterozygosity [3/8]) by array-based comparative genomic hybridization techniques. These results indicate that tremolite initiates mesothelial injury and persistently frustrates phagocytes, causing subsequent peritoneal fibrosis and MM. The possible mechanisms of carcinogenicity based on fiber diameter/length are discussed.

Lung cancer in a patient with predominantly short tremolite fibers in his lung.

The carcinogenicity of short tremolite fibers in human has not been cleared and has been argued hitherto. A lung cancer patient had worked at a gabbro quarry. Particles isolated from the excised lung parenchyma of the patient were measured for asbestos bodies (ABs) and asbestos fibers (AFs). The concentrations of ABs were 3964 AB/g dry lung, and AFs were 5.60 × 106 fibers/g dry lung (>5 um in length) and 22.5 × 106 fibers/g dry lung (>1 um in length). AFs were mostly tremolite fibers and under 7 um in length (mean length 4.0 um, standard deviation 2.8 um). Almost all fibers were <10 um in length and an aspect ratio (AR) of <20:1 and ≥3:1. The patient had never smoked. His wife, who had worked with him in the quarry, had died of pleural mesothelioma. This study strongly indicates that such short tremolite fibers will induce lung cancer and possibly mesothelioma in human.

Significant relationship between the extent of pleural plaques and pulmonary asbestos body concentration in lung cancer patients with occupational asbestos exposure.

BACKGROUND: The aim of this study was to elucidate whether there is a relationship between the extent of pleural plaques and pulmonary asbestos body concentration (PABC). METHODS: The subjects were 207 lung cancer patients with occupational asbestos exposure. We determined the plaque extent by findings on chest images using our own criteria. PABCs were measured in resected or autopsy lung specimens. RESULTS: There was a significant relationship between plaque extent and PABC. Seventy-five percent of the patients determined to have extensive plaques based on our criteria had a PABC of ≥5,000 asbestos bodies per gram of dry lung tissue, which is one of the certification criteria of lung cancer caused by asbestos for workers' compensation in Japan. CONCLUSIONS: In lung cancer patients, the plaque extent had a significant positive relationship with the PABC. The plaque extent would be useful as a proxy for PABC for lung cancer compensation purposes.

Rat model demonstrates a high risk of tremolite but a low risk of anthophyllite for mesothelial carcinogenesis.

Asbestos was abundantly used in industry during the last century. Currently, asbestos confers a heavy social burden due to an increasing number of patients with malignant mesothelioma (MM), which develops after a long incubation period. Many studies have been conducted on the effects of the asbestos types that were most commonly used for commercial applications. However, there are few studies describing the effects of the less common types, or minor asbestos. We performed a rat carcinogenesis study using Japanese tremolite and Afghan anthophyllite. Whereas more than 50% of tremolite fibers had a diameter of < 500 nm, only a small fraction of anthophyllite fibers had a diameter of < 500 nm. We intraperitoneally injected 1 or 10 mg of asbestos into F1 Fischer-344/Brown-Norway rats. In half of the animals, repeated intraperitoneal injections of nitrilotriacetate (NTA), an iron chelator to promote Fenton reaction, were performed to evaluate the potential involvement of iron overload. Tremolite induced MM with a high incidence (96% with 10 mg; 52% with 1 mg), and males were more susceptible than females. Histology was confirmed using immunohistochemistry, and most MMs were characterized as the sarcomatoid or biphasic subtype. Unexpectedly NTA showed an inhibitory effect in females. In contrast, anthophyllite induced no MM after an observation period of 550 days. The results suggest that the carcinogenicity of anthophyllite is weaker than formerly reported, whereas that of tremolite is as potent as major asbestos as compared with our previous data.

Mesothelioma carcinogenesis of chrysotile and forsterite compared and validated by intraperitoneal injection in rat.

Asbestos, especially chrysotile, continues to be exposed to humans globally. Hence, it should be disposed properly to prevent asbestos-related diseases, including mesothelioma and lung cancer. This study aimed to verify whether forsterite, a heating product of chrysotile, can cause carcinogenicity, particularly mesothelioma. Forsterite (FO-1000) and enstatite (EN-1500) produced by heating chrysotile at 1000°C and 1500°C, respectively, were subjected. We injected 10 mg of chrysotile, FO-1000, or EN-1500 in rats intraperitoneally and observed the development of peritoneal mesothelioma until 24 months. The incidence of peritoneal mesothelioma in the chrysotile group was 91.2%, whereas in the FO-1000 and EN-1500 groups, peritoneal mesothelioma did not develop. Urinary 8-hydroxy-2'-deoxyguanosine and serum N-ERC/mesothelin concentrations significantly increased in the chrysotile group that developed peritoneal mesothelioma, while they only temporarily changed in the FO-1000 or EN-1500 groups during early treatment. Furthermore, there was a significant homozygous deletion of the CDKN2A/p16 gene in the chrysotile group compared to the control group, in contrast to no significant difference in the FO-1000 and EN-1500 groups. Therefore, this study provides clear evidence that forsterite is a nonmesothelioma carcinogen and suggests that forsterite and enstatite are sufficient substances for chrysotile detoxification.

Iron overload signature in chrysotile-induced malignant mesothelioma.

Exposure to asbestos is a risk for malignant mesothelioma (MM) in humans. Among the commercially used types of asbestos (chrysotile, crocidolite, and amosite), the carcinogenicity of chrysotile is not fully appreciated. Here, we show that all three asbestos types similarly induced MM in the rat peritoneal cavity and that chrysotile caused the earliest mesothelioma development with a high fraction of sarcomatoid histology. The pathogenesis of chrysotile-induced mesothelial carcinogenesis was closely associated with iron overload: repeated administration of an iron chelator, nitrilotriacetic acid, which promotes the Fenton reaction, significantly reduced the period required for carcinogenesis; massive iron deposition was found in the peritoneal organs with high serum ferritin; and homozygous deletion of the CDKN2A/2B/ARF tumour suppressor genes, the most frequent genomic alteration in human MM and in iron-induced rodent carcinogenesis, was observed in 92.6% of the cases studied with array-based comparative genomic hybridization. The induced rat MM cells revealed high expression of mesoderm-specific transcription factors, Dlx5 and Hand1, and showed an iron regulatory profile of active iron uptake and utilization. These data indicate that chrysotile is a strong carcinogen when exposed to mesothelia, acting through the induction of local iron overload. Therefore, an intervention to remove local excess iron might be a strategy to prevent MM after asbestos exposure.

Observation of the same asbestos body by both phase contrast microscope and analytical transmission electron microscope.

The amount of asbestos body (AB) in the human lungs is used as an index to assess asbestos lung cancer (ALC). This study reports a new method to observe the same AB previously observed by analytical transmission electron microscope (ATEM) by phase contrast microscope (PCM) or the contrary order. Four kinds of specimens were prepared from the lung tissue of an asbestos related worker: ordinary PCM specimen (A); PCM specimen (B) of which the cover glass was stripped off and ashed at a low temperature; transmission electron microscope (TEM) specimen (C); and PCM specimen (D) covered a TEM specimen (C) with immersion liquid and cover glass. These specimens were all observed by PCM, and the specimen (C) by analytical TEM (ATEM). The results showed that the TEM specimen (C) is transparent in visible light and we can also see the particles by PCM. The image by PCM of the TEM specimen (C) showed very similar features to that of PCM specimens (A) and (B). Accordingly, we could observe various same particles by both ATEM and PCM. In conclusion, the method observing the same AB by both PCM and ATEM will contribute to standardize the recognition of AB for PCM analysts.

Evaluation of sensitivity of fluorescence-based asbestos detection by correlative microscopy.

Fluorescence microscopy (FM) has recently been applied to the detection of airborne asbestos fibers that can cause asbestosis, mesothelioma and lung cancer. In our previous studies, we discovered that the E. coli protein DksA specifically binds to the most commonly used type of asbestos, chrysotile. We also demonstrated that fluorescent-labeled DksA enabled far more specific and sensitive detection of airborne asbestos fibers than conventional phase contrast microscopy (PCM). However, the actual diameter of the thinnest asbestos fibers visualized under the FM platform was unclear, as their dimensions were below the resolution of optical microscopy. Here, we used correlative microscopy (scanning electron microscopy [SEM] in combination with FM) to measure the actual diameters of asbestos fibers visualized under the FM platform with fluorescent-labeled DksA as a probe. Our analysis revealed that FM offers sufficient sensitivity to detect chrysotile fibrils as thin as 30-35 nm. We therefore conclude that as an analytical method, FM has the potential to detect all countable asbestos fibers in air samples, thus approaching the sensitivity of SEM. By visualizing thin asbestos fibers at approximately tenfold lower magnifications, FM enables markedly more rapid counting of fibers than SEM. Thus, fluorescence microscopy represents an advanced analytical tool for asbestos detection and monitoring.

Effectiveness of serum megakaryocyte potentiating factor in evaluating the effects of chrysotile and its heated products on respiratory organs.

Chrysotile (CH), the most common form of asbestos, is rendered less toxic by heating it at 1000°C and converting it to forsterite (FO-1000). However, further safety tests are needed to evaluate human health risk of these materials. It has been reported that serum concentrations of megakaryocyte potentiating factor N-ERC/mesothelin become elevated in patients with mesotheliomas caused by asbestos exposure. In this study, a single 2mg dose of CH or FO-1000 was intratracheally administered to rats. Within 180days after the administrations, serum N-ERC/mesothelin concentrations, levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG) in lung tissues and pathological changes in respiratory organs were determined. In the CH group, a significant increase in serum N-ERC/mesothelin concentrations was observed immediately after intratracheal administration, and the elevation lasted for 30days. In lung tissues, positive staining for 8-OHdG in bronchioles, alveolar epithelium, inflammatory cells, and granulomas was evidence of a marked DNA oxidative damage. Furthermore, measurements of 8-OHdG in lung tissues based on the HPLC-ECD method suggested that serum N-ERC/mesothelin concentrations tended to increase when there are significant DNA damages in lung tissues. In contrast, in the FO-1000 group, a marked rise in serum N-ERC/mesothelin concentrations occurred only in the early phase (1-7days) after intratracheal administration. Similarly, FO-1000 induced elevation of 8-OHdG in lung tissues was transient and modest compared with those of the CH-treated animals. In both the CH and FO-1000 groups, we observed significant correlations between serum N-ERC/mesothelin concentrations and lung 8-OHdG concentrations (r=0.559, p=0.001 for the CH group; r=0.516, p=0.01 for the FO-1000 group). In summary, we demonstrated the possibility of using serum N-ERC/mesothelin concentrations as a useful biomarker for early phase exposure to either CH or FO-1000.

Asbestos conceives Fe(II)-dependent mutagenic stromal milieu through ceaseless macrophage ferroptosis and ß-catenin induction in mesothelium.

Asbestos is still a social burden worldwide as a carcinogen causing malignant mesothelioma. Whereas recent studies suggest that local iron reduction is a preventive strategy against carcinogenesis, little is known regarding the cellular and molecular mechanisms surrounding excess iron. Here by differentially using high-risk and low-risk asbestos fibers (crocidolite and anthophyllite, respectively), we identified asbestos-induced mutagenic milieu for mesothelial cells. Rat and cell experiments revealed that phagocytosis of asbestos by macrophages results in their distinctive necrotic death; initially lysosome-depenent cell death and later ferroptosis, which increase intra- and extra-cellular catalytic Fe(II). DNA damage in mesothelial cells, as assessed by 8-hydroxy-2'-deoxyguanosine and γ-H2AX, increased after crocidolite exposure during regeneration accompanied by ß-catenin activation. Conversely, ß-catenin overexpression in mesothelial cells induced higher intracellular catalytic Fe(II) with increased G2/M cell-cycle fraction, when p16INK4A genomic loci localized more peripherally in the nucleus. Mesothelial cells after challenge of H2O2 under ß-catenin overexpression presented low p16INK4A expression with a high incidence of deletion in p16INK4A locus. Thus, crocidolite generated catalytic Fe(II)-rich mutagenic environment for mesothelial cells by necrotizing macrophages with lysosomal cell death and ferroptosis. These results suggest novel molecular strategies to prevent mesothelial carcinogenesis after asbestos exposure.

Forsterite exposure causes less oxidative DNA damage and lung injury than chrysotile exposure in rats.

Chrysotile (CH) is a pathogenic waste building material that can potentially be rendered innocuous via conversion to forsterite (FO) by heating at high temperatures. We compared the ability of FO and CH to cause oxidative DNA damage and lung injury. A single 1-mg intratracheal dose of CH or FO was administered to rats. Significant changes were observed 3 to 7 days after CH injection in alveolar macrophages, neutrophils, eosinophils, lymphocytes, total protein, and lactate dehydrogenase. High concentrations of 8-hydroxy-29-deoxyguanosine (8-OHdG) were also observed in the macrophages, other infiltrating inflammatory cells, granulomas, and in bronchiolar and alveolar epithelial cells. The overexpression of 8-OHdG was limited to airway epithelial and inflammatory cells surrounding the fibrotic foci 540 days after injection, indicating that the inflammatory effects of CH were persistent yet decreased with time. Compared to the CH group, acute lung inflammation observed in the FO group was less apparent and exhibited no progressive fibrosing lesions. The expression of 8-OHdG was transient and weak in the bronchiolar epithelial cells as well as in the inflammatory cells, consistent with low concentrations of 8-OHdG observed in the lungs. These findings confirm that FO causes significantly less inflammation and oxidative DNA damage in the lungs than CH.

Mesothelioma in a worker who spun chrysotile asbestos at home during childhood.

BACKGROUND: Malignant mesothelioma has a long latency period and more commonly found in those exposed to amphibole than chrysotile asbestos. METHOD: A 35 years old asbestos worker in an asbestos textile plant in Chongqing, China, developed mesothelioma after only 4 years of employment. He was born and bred in a company residence of an asbestos plant and manually spun asbestos thread during school age. In the plant, not amphibole but only chrysotile has been used. RESULTS: Diagnosis of malignant mesothelioma was confirmed by comprehensive approaches including gross appearance, histology, histochemistry, and immunocytochemistry. In the lung and tumor tissues, huge number of tremolite with exceptional chrysotile was observed despite the reverse proportion in the work environment. DISCUSSION: Residential exposure and home spinning of asbestos seemed contributed to the early development of mesothelioma in this subject. Although only chrysotile was used and contamination of tremolite was low in the work environment, chrysotile seemed to be cleared leaving tremolite remain in the tissue. CONCLUSION: Chrysotile with little contamination of tremolite can lead to early development of malignant mesothelioma when heavily exposed from childhood at a company residence with household exposure. There can be several mechanisms for tremolite to remain in the lung tissue, far exceeding chrysotile in number.

Microstructures and biological influence of environmental exposure of asbestos.

Asbestos minerals are thin fiber type of minerals and honorably said as "the minerals of the miracle" because of their valuable natures even in the strategic field. On the other hand, the relation between asbestos exposure and diseases such as lung cancer and malignant mesothelioma was proved around 1970 by epidemiology and an animal experiment in relation to their microstructures. Here, microstructures of chrysotile asbestos, a mainstream of asbestos substances, are shown. It is also shown that in what kinds of environment people are exposed to asbestos and what kinds of biological or epidemical things happen after asbestos exposure. Many kinds of fibrous materials as the substitutes of asbestos are described in relation to their carcinogenicity.

Characteristics and modifying factors of asbestos-induced oxidative DNA damage.

Respiratory exposure to asbestos has been linked with mesothelioma in humans. However, its carcinogenic mechanism is still unclear. Here we studied the ability of chrysotile, crocidolite and amosite fibers to induce oxidative DNA damage and the modifying factors using four distinct approaches. Electron spin resonance analyses revealed that crocidolite and amosite containing high amounts of iron, but not chrysotile, catalyzed hydroxyl radical generation in the presence of H(2)O(2), which was enhanced by an iron chelator, nitrilotriacetic acid, and suppressed by desferal. Natural iron chelators, such as citrate, adenosine 5'-triphosphate and guanosine 5'-triphosphate, did not inhibit this reaction. Second, we used time-lapse video microscopy to evaluate how cells cope with asbestos fibers. RAW264.7 cells, MeT-5 A and HeLa cells engulfed asbestos fibers, which reached not only cytoplasm but also the nucleus. Third, we utilized supercoiled plasmid DNA to evaluate the ability of each asbestos to induce DNA double strand breaks (DSB). Crocidolite and amosite, but not chrysotile, induced DNA DSB in the presence of iron chelators. We cloned the fragments to identify break sites. DSB occurred preferentially within repeat sequences and between two G:C sequences. Finally, i.p. administration of each asbestos to rats induced not only formation of nuclear 8-hydroxy-2'-deoxyguanosine in the mesothelia, spleen, liver and kidney but also significant iron deposits in the spleen. Together with the established carcinogenicity of i.p. chrysotile, our data suggest that asbestos-associated catalytic iron, whether constitutional or induced by other mechanisms, plays an important role in asbestos-induced carcinogenesis and that chemoprevention may be possible through targeting the catalytic iron.

Behavior of rock wool in rat lungs after exposure by nasal inhalation.

To evaluate the safety of rock wool (RW) fibers, we examined the biopersistence of RW fibers in the lungs of rats, based on the changes of fiber number and fiber size in the length and width, in a nose-only inhalation exposure study. Twenty male Fischer 344 rats (6 to 10 wk old) were exposed to RW fibers at a fiber concentration of 70.6 (20.4) fiber/m(3) and a dispersion density of 30.4 (6.6) mg/m(3) [arithmetic mean (SD)] continuously for 3 h daily for 5 consecutive days. Five rats each were sacrificed shortly after exposure ended (baseline group) and at 1, 2, and 4 wk after exposure, and their lung tissues were ashed by a low temperature plasma-asher. The numbers and sizes of fibers in the ash samples were determined using a phase contrast microscope and a computed image analyzer. The fiber numbers in the lungs at 4 wk after exposure had significantly decreased from the baseline value, i. e. shortly after exposure (p<0.05). The half-lives of RW fibers calculated using the one-compartment model were 32 d for total fibers and 10 d for fibers longer than 20 microm in length. Fiber number was 53.6% of the baseline at 4 wk after exposure (baseline group=100%). Likewise, fiber sizes had significantly decreased at 4 wk after exposure (p<0.05), probably because fibers had been dissolved in body fluid, phagocytosed by alveolar macrophages or discharged from the body by mucociliary movement. In future studies, it will be necessary to examine the carcinogenicity of RW fibers through long-term inhalation studies.

Field evaluation of mercury vapor analytical methods: comparison of the "double amalgam method" and ISO 17733.

In this study, a gold amalgam method called the "Double amalgam method" was compared with the ISO 17733 method for mercury vapor analysis method. In terms of sensitivity and ease of operation, the amalgamation method is superior to the oxidation method. Two parallel samplings were carried out in this research at a button battery factory, where the mercury vapor level in the air was about 0.001 mg/m3 and at a fluorescent lamp factory, where the mercury vapor level was about 0.015 mg/m3. In the both cases, the measured values of the two showed good agreement with each other. As these two workplaces represent typical mercury levels in industries today, the double amalgam method is applicable to working environment measurement.

Lung disorders of workers exposed to rush smear dust in China.

The aim of this study was to evaluate the lung disorders of the workers exposed to rush smear dust. A cross sectional study was carried out on 1,709 current workers (788 male, 921 female) in 80 factories. All subjects were asked by questionnaire, and health examination including chest X-ray was conducted for 661 workers in 35 factories. Lung function test was also examined for 119 non-smoking males among 661 subjects. Dust samplings were collected and total and respirable dust concentrations at 127 spots in 35 factories were measured. The geometric mean dust concentration in the workshops was up to 20.00 mg/m(3), and the geometric mean respirable dust concentration reached 8.22 mg/m(3). The mean quartz concentration of accumulated dust was 29.2%. The prevalence of radiographic small opacities profusion category > or = 1/0, according to the ILO 1980 Classification System, was 2.6% among 661 employees. One worker was found to have pneumoconiotic findings of 2/2 profusion accompanied with large opacity. The prevalence of pneumoconiosis (1/0 or more) correlated with cumulative dust exposure (r=0.192, p<0.0001). The similar relationship was found between the prevalence rate of cough or sputa and worksite dust concentration. In non-smokers, a positive association was found between the prevalence of cough and occupational exposure duration (r=0.080, p=0.004). Approximately 19.3% and 34.5% of employees suffered from respiratory impairment for FVC and FEV1.0, respectively. This is the first report of "rush" pneumoconiosis in China. Rush mat workers were found to be at high risk for pneumoconiosis, a preventable disease. Our results showed a dose-response relationship between rush-mat dust level and the prevalence of pneumoconiosis. Similar relationship between the prevalence of cough and sputum and the work duration was found for non-smoking workers but not for smoking workers.

Dissolution of functional materials and rare earth oxides into pseudo alveolar fluid.

The dissolution rates of rare earth oxides and two types of rare earth containing functional materials into water, saline solution, and Gamble's fluid were measured in order to evaluate the biological effects of rare earth-containing functional materials. The tested materials were yttrium, lanthanum, cerium and neodymium oxides, and neodymium-boron-iron magnet alloy (NdBFe) and lanthanum-mish-metal-nickel-cobalt (LmNiCo) hydrogen-containing alloy. The dissolution rates of the rare earth oxides were very low, resulting in concentrations of rare earth elements in the test solutions of the order of ppb. In the most extreme case, Gamble's fluid dissolved 1,400 times more of the rare earth oxides than pure water. Fairly high concentration of neodymium were found in the dissolving fluids, which means that trace neodymium present as an impurity in each rare earth oxide dissolved preferentially. For yttrium oxide, the ratio of neodymium to yttrium that dissolved in the saline solution was greater than 78,000 to 1, taking into account the amount of each that was originally present in the yttrium oxide.

Size- and type-specific exposure assessment of an asbestos products factory in China.

This study describes fibre size and type-specific airborne asbestos exposures in an asbestos product factory. Forty-four membrane filter samples were analysed by scanning electron microscopy to determine the size distribution of asbestos fibres, by workshop. Fibre frequencies of bivariate (length by width) categories were calculated and differences between workshops were tested by analysis of variance. Data were recorded for 13,435 chrysotile and 1075 tremolite fibres. The proportions between size metrics traditionally measured and potentially biologically important size metrics were found to vary in this study from proportions reported in other cohort studies. One, common size distribution was generated for each asbestos type over the entire factory because statistically significant differences in frequency between workshops were not detected. This study provides new information on asbestos fibre size and type distributions in an asbestos factory. The extent to which biologically relevant fibre size indices were captured or overlooked between studies can potentially reconcile currently unexplained differences in asbestos-related disease (ARD) risk between cohorts. The fibre distributions presented here, when combined with similar data from other sites, will contribute to the development of quantitative models for predicting risk and our understanding of the effects of fibre characteristics in the development of ARD.

Evaluation of cellular toxicity of TAFMAG, a natural substitute for asbestos from China.

Asbestos is a very important material for industrial use. However, the need for a substitute for asbestos fiber is currently on the rise due to its high disease causing potential. This study evaluated the potential bio-hazardous effects of TAFMAG, a natural fibrous silicate produced in China, in comparison with chrysotile, a typical toxic asbestos. The physicochemical properties of TAFMAG were very similar to those of chrysotile when it was examined by a scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses. Both of TAFMAG and chrysotile showed high content of magnetite and Fenton activity when compared with wollastonite, a non-asbestos fiber with a known low toxicity. When their cellular toxicity was assessed, TAFMAG showed no or less comparable to that of chrysotile in the hemolysis and lipid peroxidation of erythrocytes, and also on a MTT assay in RLE-6TN, a rat alveolar epithelial cell line. Pre-treatment of fibers with desferrioxamine, an iron chelator, showed that iron content of TAFMAG and chrysotile might be important in their cellular toxicity. These results suggest that TAFMAG is potentially toxic when inhaled into the lung and appropriate laws and regulations should be established for its use.