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.

Development of a new multi-walled carbon nanotube (MWCNT) aerosol generation and exposure system and confirmation of suitability for conducting a single-exposure inhalation study of MWCNT in rats.

Because the primary route of human exposure to multi-walled carbon nanotube (MWCNT) is via inhalation, a new dry MWCNT aerosol generation and exposure system for whole-body inhalation exposure using a cyclone and sieve has been developed. The system was tested for operational performance at 0.2, 1 and 5 mg/m(3). Additionally, it was examined whether this system can be employed in animal whole-body inhalation studies by exposing rats to MWCNT aerosol for 6 h at 5 mg/m(3). The system could consistently provide aerosols with a similar particle size distribution and configuration at all the target exposure concentrations. Almost all MWCNTs were fibrous, and the presence of many well-dispersed, nano-sized particles was confirmed. Additionally, the animal study revealed that large amounts of MWCNTs were inhaled into the lung, resulting in an inflammatory response, with increased LDH and albumin levels, and granulomatous change. Therefore, the aerosol generation and exposure system appears useful for MWCNT inhalation studies using rats.

Two-week Toxicity of Multi-walled Carbon Nanotubes by Whole-body Inhalation Exposure in Rats.

To evaluate pulmonary toxicity of multi-walled carbon nanotubes (MWCNTs), F344 rats of both sexes were exposed by inhalation to 0.2, 1 or 5 mg/m(3) MWCNT aerosol for 6 h/day, 5 days/week for 2 weeks using a whole-body exposure system. At the end of the 2-week exposure period, one-half of the rats were necropsied, and at the end of an additional 4-week postexposure period, the remaining rats were necropsied. MWCNTs were deposited in the lungs of all MWCNT-exposed groups and mostly remained in the lungs throughout the 4-week postexposure period. Granulomatous changes in the lung were found in the rats exposed to 5 mg/m(3) MWCNTs, and these changes were slightly aggravated at the end of the 4-week postexposure period. In the bronchoalveolar lavage fluid (BALF), the numbers of neutrophils, percentages of bi- and multinucleated alveolar macrophages, levels of ALP activity and concentrations of total protein and albumin were elevated in the rats exposed to 1 and 5 mg/m(3) MWCNTs. At the end of the 4-week postexposure period, the values of the BALF parameters tended to remain elevated. In addition, goblet cell hyperplasias in the nasal cavity and nasopharynx were observed in the rats exposed to 1 and 5 mg/m(3) MWCNTs, but these lesions had largely regressed by the end of the postexposure period. Based on the histopathological and inflammatory changes, the no-observed-adverse-effect level (NOAEL) for inhalation of MWCNTs for 2 weeks was 0.2 mg/m(3).

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.

Pulmonary toxicity of intratracheally instilled multiwall carbon nanotubes in male Fischer 344 rats.

In order to assess pulmonary toxicity of multiwall carbon nanotubes (MWCNT), male F344 rats were intratracheally instilled with MWCNT suspension at a dose of 40 or 160 µg/head or α-quartz particles as a positive control at a dose of 160 µg/head and sacrificed for lung histopathology and bronchoalveolar lavage (BAL) fluid analyses on Day 1, 7, 28 or 91 after instillation. Well-dispersed MWCNT brought about dose- or time-dependent changes in lung weight, total proteins, albumin, lactate dehydrogenase and alkaline phosphatase in the BAL fluid, and pulmonary lesions including inflammation, Type II cell hyperplasia, microgranulomas and fibrosis. Phagocytosed and free forms of MWCNT were found in both bronchiolar and alveolar spaces. MWCNT deposition in the bronchus-associated lymphoid tissue gradually increased after instillation. Persistent infiltration of macrophages, transient infiltration of inflammatory cells primarily composed of neutrophils, microgranulomas associated with macrophages engulfing MWCNT, Type II cell hyperplasia and fibrosis with alveolar wall thickening as well as number of multinucleated alveolar macrophages increased dose-dependently. The MWCNT-induced lesions were more potent on Day 91 than the α-quartz-induced ones at an equal mass dose. The present results for intratracheally instilled MWCNT were extrapolated to potential inhalation exposure of humans to MWCNT at workplaces based on several assumptions.

Pulmonary toxicity induced by intratracheal instillation of coarse and fine particles of cerium dioxide in male rats.

In order to examine the short-, medium- and long-term effects of cerium dioxide particles of different sizes on the lung, 10-wk-old male Wistar rats were administered a physiological saline solution with a suspension of coarse or fine particles of cerium dioxide at 34 mg/kg body weight by a single intratracheal instillation. Lungs were examined with cellular and biochemical analyses of the bronchoalveolar lavage (BAL) fluid and histopathology on different days after the instillation. Geometric mean and geometric standard deviation of the diameter were 3.90 microm +/- 1.93 for the coarse (Ce-C) particles, and 0.20 microm +/- 1.20 for the fine (Ce-F) particles. There were no lesions in the lung in the Ce-C-instilled group at any time point after the instillation. The instillation of Ce-F particles primarily induced inflammation, granulomas, mobilization and impairment of alveolar macrophages (AMs), and pulmonary alveolar proteinosis, together with very slight degrees of Type II epithelial cell hyperplasia and of collagen deposition. The pulmonary toxicity of Ce-F-instilled rats was found to be markedly enhanced in sharp contrast to that of Ce-C-instilled rats on the basis of equal mass concentration, suggesting clear dependence of the pulmonary toxicity on numbers and sizes of particles. Causative factors for the pulmonary alveolar proteinosis are discussed with reference to the impaired AMs.

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.

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.

Effects of surface characteristics of potassium titanate whisker samples on acute lung injury induced by a single intratracheal administration in rats.

We compared in vivo biological effects, focusing on lung inflammatory responses after a single intratracheal administration of two types of well-characterized whiskers: potassium octatitanate and potassium hexatitanate, which have similar fiber sizes and chemical compositions, except their surface morphology. The geometrical mean of length (microm), width (microm), and geometric standard deviation (GSD) are: K(2)Ti(8)O(17) (PT1), 6.0[2.0], 0.35[1.51], having rough surface; K(2)Ti(6)O(13) (PT2), 5.0[2.18], 0.31[1.63], having smooth surface. Sixty male Wistar rats (8 wk old) under anesthesia were injected intratracheally with 2 doses of fibers (0.2 mg/0.5 ml/rat, 1.0 mg/0.5 ml/rat) or the same amount of saline solution (group C). Animals were sacrificed on days 1, 3, and 7 after fiber administration, and then the lung tissue and bronchoalveolar lavage (BAL) were collected. There were no obvious differences among the three groups in the yield of BAL fluid. Total protein concentration in BAL increased significantly from day 1; BAL fucose level increased significantly from day 3 in a dose-dependent manner, which gradually recovered by day 7 in groups PT1 and PT2. BAL total protein and fucose in group PT1 increased significantly compared with those in group PT2 at a dose level of 1.0 mg. A dose-independent increase of beta-glucuronidase activity and decrease of superoxide dismutase activity were observed in both fibers. BAL tumor necrosis factor-alpha (TNF-alpha) increased significantly in animals treated with 1.0 mg dosage of PT1 and PT2 on day 1. However, BAL IL-1beta did not show any marked change during the experimental period in animals treated with both fibers. On day 1, BAL cytokine-induced neutrophil attractants (CINC)/growth-related gene product (GRO) increased significantly in the PT1 group treated with 0.2 and 1.0 mg dosage. On day 3, the group treated with 1.0 mg PT1 showed significant increase of CINC/GRO compared with the group treated with 1.0 mg PT2, which recovered to the control level on day 7. Expression of various chemokine mRNAs (MCP-3, MIP-1alpha, RANTES, and eotaxin) increased in rats treated with PT1 or PT2 on day 1 and/or day 3. Increase of gene expression in the PT1 group was greater than that of the PT2 group at 0.2 mg dosage level. These results suggest that differences in the surface morphology of the whisker fibers of similar length and diameter, density, and chemical composition appear to be related to the facilitation of macrophage phagocytes in the macrophage-derived biological effects in acute lung injury induced by inhaled fibers.

Inflammatory responses and mucus secretion in rats with acute bronchiolitis induced by nickel chloride.

The effects of inhaled particulate matter in the workplace and outdoor environment on sensitive subpopulations are not sufficiently investigated in human and animal models. Thus, animal models for pulmonary diseases are necessary for appropriate risk assessment of toxic materials. We studied biochemical characteristics of an acute inflammatory process induced by inhalation of nickel chloride aerosols in rats. Acute bronchiolitis was induced by inhalation of nickel chloride aerosols for 5 days in Wistar rats according to the method described by Kyono et al. (1999). Deterioration and recovery from inflammatory responses were evaluated by analyzing markers of inflammation in bronchoalveolar lavage (BAL) fluid. Experimental animals were sacrificed during and after the nickel aerosol exposure period. The number of neutrophils markedly increased to approximately 0.5 x 10(3) cells/microl BAL fluid during nickel aerosol exposure, accompanied by increase of total protein, soluble L-selectin, cytokine-induced neutrophil chemoattractant/growth-regulated gene products (CINC/GRO), elastolytic activity, trypsin inhibitory capacity, beta-glucuronidase activity, fucose, and sialic acid in BAL fluid compared with those of the control group. There was correlation between number of leukocytes and soluble L-selectin concentration. The number of pulmonary macrophages in BAL fluid decreased to approximately 15% of those of the control group on the days of nickel aerosol exposure. The level of CINC/GRO recovered to that of the control group on day 3 after cessation of the nickel aerosol exposure. However, other inflammatory markers remained at the elevated levels. Changes in the markers of inflammation during and after the nickel aerosol exposure were consistent with previously reported morphological findings. The results indicated that this animal model is potentially useful as an acute bronchiolitis model.