Shigetoshi Aiso

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.

Carcinogenicity and chronic toxicity after inhalation exposure of rats and mice to N,N-dimethylformamide.

Carcinogenicity and Chronic Toxicity after Inhalation Exposure of Rats and Mice to N,N‐Dimethylformamide: Hideki Senoh, et al. Japan Bioassay Research Center—Carcinogenicity and chronic toxicity of N,N‐Dimethylformamide (DMF) were examined by inhalation exposure of groups of 50 rats and 50 mice of both sexes to DMF vapor at a concentration of 0, 200, 400 or 800 ppm (v/v) for 6 h/d, 5 d/wk, for 104 wk. In rats, incidences of hepatocellular adenomas and carcinomas significantly increased in the 400 and 800 ppm‐exposed groups and in the 800 ppm‐exposed group, respectively. The hepatocellular adenoma did not increase significantly in the 400 ppm exposed female rats, but its incidence exceeded a range of historical control data in the Japan Bioassay Research Center (JBRC). In mice, incidences of hepatocellular adenomas and carcinomas significantly increased in all the DMF‐exposed groups. Incidence of hepatoblastomas significantly increased in the 200 and 400 ppm‐exposed male mice, and 4 cases of hepatoblastomas in the 400 ppm‐exposed female mice and the 800 ppm‐exposed male mice exceeded the range of historical control data of the JBRC. Incidences of altered cell foci increased in the liver of exposed rats and mice in an exposure concentration‐related manner, and those foci were causally related to the hepatocellular tumors. Liver weights increased in both rats and mice exposed to DMF at 200 ppm and above. Increased levels of γ‐GTP, ALT, AST and total bilirubin in exposed rats of both sexes and AST and ALT in exposed mice of both sexes were noted. It was concluded that 2‐yr inhalation exposure to DMF increased incidences of hepatocellular adenomas and carcinomas in rats and incidences of hepatocellular adenomas, carcinomas and hepatoblastomas in mice, and that hepatocarcinogenicity of DMF was more potent in mice than in 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—

Carcinogenic activity of Farfugium japonicum and Senecio cannabifolius

The carcinogenicity of Farfugium japonicum and Senecio cannabifolius was studied in ACI rats. In Group I, rats were given a diet containing 20% Farfugium japonicum. Groups II, III, IV and V were given diets containing 8%, 4%, 1% and 0.2% Senecio cannabifolius until the end of the experiment, respectively. The experiment was terminated after 480 days, except for Group V which was terminated 560 days after the start of feeding. Hemangioendothelial sarcoma of the liver and liver cell adenoma were induced in Groups I, IV and V. All rats in Groups II and III died of hepatotoxicity within a short period.

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.

Inhalation carcinogenicity and toxicity of 1,2-dichloropropane in rats

The toxicity and carcinogenicity of 1,2-dichloropropane (DCP) were examined by inhalation exposure of male and female F344 rats to DCP for either 13 wk or 2 years. In the 13-wk study, the DCP concentrations used were 125, 250, 500, 1000, or 2000 ppm (v/v), and in the 2-year study the DCP concentrations were 80, 200, or 500 ppm (v/v). Thirteen-week exposure to DCP induced hyperplasia in the respiratory epithelium and atrophy of the olfactory epithelium at 125 ppm and above. At the higher levels of exposure, hemolytic anemia and lesions of liver and adrenal gland were observed. Two-year exposure to DCP significantly increased incidences of papilloma in the nasal cavity of male and female rats exposed to 500 ppm DCP. In addition, three cases of esthesioneuroepithelioma were observed in the DCP-exposed male rats. Total nasal tumors increased in a concentration-dependent manner. Hyperplasia of the transitional epithelium and squamous cell hyperplasia, both of which were morphologically different from the hyperplasia of the respiratory epithelium observed in the 13-wk exposure study, occurred in a concentration-dependent manner; these lesions are considered to be preneoplastic lesions. Atrophy of the olfactory epithelium, inflammation of the respiratory epithelium, and squamous cell metaplasia were also seen in the 2-year study. These results demonstrate that DCP is a nasal carcinogen in rats. Lifetime cancer risks for humans exposed to DCP in the ambient air and work environment were quantitatively estimated, using both nonthreshold and threshold approaches, with the data obtained from the 2-year study.

Thirteen-week inhalation toxicity of p-dichlorobenzene in mice and rats.

Thirteen‐week Inhalation Toxicity of p‐Dichlorobenzene in Mice and Rats: Shigetoshi Aiso, et al. Japan Bioassay Research Center, Japan Industrial Safety and Health Association— Subchronic inhalation toxicity of p‐dichlorobenzene (p‐DCB) was examined by exposing BDF1 mice and F344 rats of both sexes (6 h/d and 5 d/wk) to inhalation of 25, 55, 120, 270 or 600 ppm (v/v) p‐DCB vapor for 13 wk. The exposure to p‐DCB vapor retarded the growth rate in the male mice, and induced hepatotoxicity in the mice and rats of both sexes and renal and hematological toxicity in the male rats. Hepatotoxicity was characterized by increased liver weight, hepatocellular hypertrophy, and increased serum levels of total cholesterol. Liver necrosis and increased serum levels of AST and ALT were observed in the exposed mice, whereas these changes, which indicate hepatocellular death, did not occur in any of the exposed rats. p‐DCB‐induced renal lesions occurred only in the male rats. Hyaline droplets were observed in the proximal tubular epithelial cells, and were stained positively with anti‐α2ν‐globulin, suggesting excessive accumulation of α2ν‐globulin in the epithelial cells. Granular casts were formed in the tubular lumen, resulting from the necrotic desquamation of the renal tubular epithelium. Papillary mineralization in the renal pelvis and increased serum levels of BUN and creatinine were noted. These renal changes indicated α2ν‐globulin nephropathy. Decreases in red blood cell counts, hemoglobin concentration, hematocrit and mean corpuscular volume and increased spleen weight occurred in the exposed male rats. The NOAEL was 120 ppm for the hepatic endpoint in mice and for the renal endpoint in rats. The maximum tolerated dose for a 2‐yr bioassay inhalation study of rodent carcinogenicity was estimated to be 300 ppm, based on the present results.

Hyperplastic nodules of the liver induced in rats fed bracken diet

Hyperplastic nodules (HN) of the liver were induced in Charles River Sprague-Dawley rats (CD rats) and ACI rats fed a diet containing 30% bracken for 260 and 180 days, respectively. HN were also induced in high incidence in CD rats fed a diet containing the carcinogenic fractions of bracken extract.

Thirteen-Week Inhalation Toxicity of 1,4-Dioxane in Rats

Thirteen-week inhalation toxicity of 1,4-dioxane was examined by repeated inhalation exposure of male and female F344 rats to 0 (control), 100, 200, 400, 800, 1600, 3200, or 6400 ppm (v/v) 1,4-dioxane vapor for 6 h/day and 5 days/wk. All the 6400-ppm-exposed males and females died during the first week. Terminal body weight decreased, and relative weights of liver, kidney, and lung increased. AST increased in the 200 ppm-and 3200-ppm-exposed females, and ALT increased in the 3200-ppm-exposed males and females. Nuclear enlargement of nasal respiratory epithelial cells occurring in the 100-ppm-exposed males and females was the most sensitive, followed by the enlarged nuclei in the olfactory, tracheal, and bronchial epithelia. 1,4-Dioxane-induced liver lesions occurred at higher exposure concentrations than the nasal lesions did, and were characterized by single-cell necrosis and centrilobular swelling of hepatocytes in males and females. Glutathione S-transferase placental form (GST-P) positive liver foci were observed in the 1600-ppm-exposed females and 3200-ppm-exposed males and females, which are known as a preneoplastic lesion in rat hepatocarcinogenesis. Plasma levels of 1,4-dioxane increased linearly with an increase in the concentrations of exposure to 400 ppm and above. The enlarged nuclei in the nasal epithelia and the GST-P-positive liver foci were discussed in light of the possible development of nasal and hepatic tumors by long-term inhalation exposure to 1,4-dioxane. A lowest-observed-adverse-effect level (LOAEL) was determined at 100 ppm for the nasal endpoint in both male and female rats.

Carcinogenicity examination of inflorescence of Zingiber mioga Roscoe.

The carcinogenicity of mioga was examined in ACI and Fischer 344 rats. In Experiment I, a test group of ACI rats received diet containing mioga for 365 days, and the control group received normal basal diet. The experiment was terminated 480 days after the start of feeding. In Experiment II, a test group of Fischer 344 rats received diet containing mioga throughout the experiment of 639 days and the control group received normal diet. Female ACI rats in Experiment I developed significantly more urinary bladder tumors than the control group. No carcinogenic activity was observed in males in Experiment I or males or females in Experiment II.