Tatsuya Kasai

Inhalation Carcinogenicity and Chronic Toxicity of Indium-tin Oxide in Rats and Mice

Inhalation Carcinogenicity and Chronic Toxicity of Indium‐tin Oxide in Rats and Mice: Kasuke Nagano, et al. Japan Bioassay Research Center, Japan Industrial Safety and Health Association—

Thirteen-week study of toxicity of fiber-like multi-walled carbon nanotubes with whole-body inhalation exposure in rats

Abstract Cancer development due to fiber-like straight type of multi-walled carbon nanotubes (MWCNTs) has raised concerns for human safety because of its shape similar to asbestos. To set concentrations of MWCNT for a rat carcinogenicity study, we conducted a 13-week whole body inhalation study. F344 male and female rats, 6-week-old at the commencement of the study, were exposed by whole-body inhalation to MWCNT at concentrations of 0, 0.2, 1 and 5 mg/m3 with a generation and exposure system utilizing the cyclone sieve method. Measured concentrations in the exposure chambers were 0.20 ± 0.02, 1.01 ± 0.11 and 5.02 ± 0.25 mg/m3 for 13 weeks. The MMAD (GSD) of MWCNT were 1.4–1.6 μm (2.3–3.0), and mean width and length were 94.1–98.0 nm and 5.53–6.19 μm, respectively, for each target concentration. Lung weights were increased 1.2-fold with 1 mg/m3 and 1.3-fold with 5 mg/m3 in both sexes compared to the controls. In the bronchoalveolar lavage fluid (BALF) analyses, inflammatory parameters were increased concentration-dependently in both sexes from 0.2 mg/m3. Granulomatous changes in the lung were induced at 1 and 5 mg/m3 in females and even at 0.2 mg/m3 in males. Focal fibrosis of the alveolar wall was observed in both sexes at 1 mg/m3 or higher. Inflammatory infiltration in the visceral pleural and subpleural areas was induced only at 5 mg/m3. In conclusion, we determined 0.2 mg/m3 as the low-observed-adverse-effect level (LOAEL) for respiratory tract toxicity in the present inhalation exposure study of rats.

Two- and 13-week inhalation toxicities of indium-tin oxide and indium oxide in rats.

Two‐ and 13‐week Inhalation Toxicities of Indium‐tin Oxide and Indium Oxide in Rats: Kasuke Nagano, et al. Japan Bioassay Research Center, Japan Industrial Safety and Health Association—

Carcinogenicity studies of 1,4-dioxane administered in drinking-water to rats and mice for 2 years

The carcinogenicity of 1,4-dioxane was examined by giving groups of 50 F344/DuCrj rats and 50 Crj:BDF(1) mice of each sex 1,4-dioxane in the drinking-water for 2 years. The concentrations of 1,4-dioxane were 0 (control), 200, 1000 and 5000 ppm (wt./wt.) for rats and 0, 500, 2000 and 8000 ppm for mice. The highest dose levels did not exceed the maximum tolerated dose. In the rat, there was significant induction of nasal squamous cell carcinomas in females and hepatocellular adenomas and carcinomas in males and females, peritoneal mesotheliomas in males, and mammary gland adenomas in females. In the mouse, there was significant induction of hepatocellular tumors in males and females. Two nasal tumors occurring in the 8000 ppm-dosed groups were spontaneously rare and, thus, were attributed to 1,4-dioxane exposure. The present studies provided clear evidence of carcinogenicity in rats and mice. Lifetime cancer risk of humans exposed to 1,4-dioxane through drinking-water was quantitatively estimated with a non-threshold approach by application of a linearized multistage model to dose-carcinogenic response relationships, in addition to a threshold approach for estimation of the tolerable daily intake using no-observed- or lowest-observed-adverse-effect levels of the carcinogenic responses and uncertainty factors.

Two-year inhalation study of carcinogenicity and chronic toxicity of 1,4-dioxane in male rats

Carcinogenicity and chronic toxicity of 1,4-dioxane were examined by inhalation exposure of 50 male F344 rats to 1,4-dioxane vapor at 0 (clean air), 50, 250, or 1250 ppm (v/v) for 6 h/day, 5 days/wk, and 104 wk. Survival rates of 250 and 1250 ppm-exposed groups were decreased near the end of the 2-yr exposure period, due probably to the occurrence of malignant tumors. A statistically significant but marginal decrement of terminal body weight (<10%) was found in the 1250 ppm-exposed group, suggesting slight systemic toxicity. Significant changes in plasma levels of AST, ALT, ALP, and γ-GTP and relative weight of the liver occurred in the 1250 ppm-exposed group. Dose-dependent and statistically significant increases in incidences of nasal squamous cell carcinomas, hepatocellular adenomas, and peritoneal mesotheliomas were found primarily in the 1250 ppm-exposed group. The incidences of renal cell carcinomas, fibroadenomas in the mammary gland, and adenomas in the Zymbal gland were also increased dose-dependently. Preneoplastic lesions occurred in the nasal cavity and liver of the 1,4-dioxane-exposed groups. As nonneoplastic lesions, the significantly increased incidences of nuclear enlargement, atrophy, and respiratory metaplasia in the nasal cavity were noted at 50 ppm and above. A LOAEL (lowest observed adverse effect level) was determined at 50 ppm for the nasal endpoint of general chronic toxicity. This study provides clear evidence of carcinogenicity for 1,4-dioxane in male rats. A cytotoxic-proliferative and in vivo genotoxic mode of action is suggested to operate in 1,4-dioxane-induced carcinogenesis.

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/m3 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/m3 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/m3 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/m3 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/m3.

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

Abstract 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/m3. 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/m3. 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.

Acute and Subchronic Inhalation Toxicity of Chloroform in Rats and Mice

Acute and Subchronic Inhalation Toxicity of Chloroform in Rats and Mice: Tatsuya Kasai, et al. Japan Bioassay Research Center—In order to better characterize acute and subchronic toxicities of chloroform and to provide its basic toxicity data for risk assessment of humans exposed to chloroform in work and living environments, mice and rats of both sexes were exposed by inhalation to chloroform at different concentrations from 500 to 8,000 ppm for 6 h/d x 5 d/ wk X 2 wk and from 12 to 400 ppm for 6 h/d x 5 d/wk x 13 wk. The kidneys, liver and nasal cavity were primarily damaged by the inhalation exposure. Acute death occurred at 12 ppm in male mice, 1,000 ppm in female mice and 2,000 ppm in male and female rats. The 13‐wk exposures induced renal lesions in male mice, hepatic and nasal lesions in female mice and renal, hepatic and nasal lesions in male and female rats. Susceptibility to the acute and subchronic toxicities was higher in male mice than female mice, and higher in mice than in rats. No‐observed‐adverse‐ effect‐levels (NOAELs) and lowest‐observed‐adverse‐ effect‐levels (LOAELs) were determined for the renal, hepatic and nasal endpoints of animals exposed to chloroform for 13 wk. For the hepatic endpoint, NOAEL was 100 ppm in male mice, 50 ppm in female mice and female rats and 100 ppm in male rats. For the renal endpoint, LOAEL was 12 ppm in male mice, and NOAEL was 25 ppm in male rats and 100 ppm in female rats. For the nasal endpoint, LOAEL was 12 ppm and 25 ppm in the mice and the rats of both sexes, respectively.

Carcinogenicity and Chronic Toxicity in Rats and Mice Exposed to Chloroform by Inhalation

Carcinogenicity and Chronic Toxicity in Rats and Mice Exposed to Chloroform by Inhalation: Seigo Yamamoto, et al. Japan Bioassay Research Center—A bioassay study of carcinogenicity and chronic toxicity of chloroform was undertaken by inhalation exposures of groups of 50 F344 rats and 50 BDF1 mice of both sexes to chloroform for 6 h/d x 5 d/ wk X 104 wk. The exposure concentration was 0 (control), 10, 30 or 90 ppm for rats and 0, 5, 30 or 90 ppm for mice. Combined incidences of renal cell adenomas and carcinomas, and of hepatocellular adenomas and carcinomas increased in the exposed male and female mice, respectively. Incidences of atypical tubule hyperplasia, cytoplasmic basophilia and nuclear enlargement in the kidneys and fatty change in the liver increased in the exposed male mice. Increased incidence of altered cell foci in the exposed female mice was causally related to the hepatocellular adenomas and carcinomas. No significantly increased incidence of the kidney or liver tumors was observed in the exposed rats of either sex. Increased incidences of nuclear enlargement and dilatation of tubular lumen were found in the kidneys of exposed rats. No‐ observed‐adverse‐effect‐levels (NOAELs) for the biologically significant endpoint were determined from the dose‐response relationships of the present datasets. The NOAEL for the histopathological endpoint of the kidneys resulted in 5 ppm for mice and 10 ppm for rats. An occupational exposure limit for chloroform was discussed in light of the NOAELs.

The increases in relative mRNA expressions of inflammatory cytokines and chemokines in splenic macrophages from rats exposed to multi-walled carbon nanotubes by whole-body inhalation for 13 weeks

Abstract Background: The toxicity of multi-walled carbon nanotubes (MWCNT) may be related to the immune system. The objective of this study was to obtain information for immunotoxic mechanisms of MWCNT in situ. Methods: Using whole-body inhalation, male and female rats were exposed to 0, 0.2, 1 or 5 mg MWCNT/m3 for 13 weeks. Thereafter, spleens were recovered from the rats. Real-time PCR was done to assess expression of TNFα, IL-1β, IL-6, IL-10, MCP-1 and MIP-1α mRNA in the splenic macrophages; splenic T-lymphocytes were examined for IL-2 and TGF-β1 mRNA expression. Results: The relative expression of IL-1β mRNA in the cells from female rats exposed to 5 mg MWCNT/m3 was significantly higher than that in control cells. For IL-6 and IL-10, cells from rats in the 0.2 and 5 mg MWCNT/m3 had significantly higher mRNA expressions than did cells from controls. Expression of IL-1β, IL-6 and TNFα genes in cells from males in all exposure groups were higher than in control cells. Expression of MIP-1α in the cells from female 5-mg group was significantly higher than that in cells in the control. Only IL-2 was expression reduced, i.e. cells from male and female rats in all MWCNT groups had significantly lower mRNA expressions than control cells. Conclusions: Systemic inflammation would likely occur in rats (or other hosts) exposed to MWCNT via inhalation due to increases in the expression of inflammatory cytokines in splenic macrophages. Moreover, decreases in IL-2 expression in T-lymphocytes may be critical to the potential reductions in anti-tumor responses in MWCNT-exposed hosts.