Thirteen‐week Inhalation Toxicity of Carbon Tetrachloride in Rats and Mice: Kasuke Nagano, et al. Japan Bioassay Research Center, Japan Industrial Safety and Health Association—Subchronic toxicity of carbon tetrachloride (CCl₄) was examined by inhalation exposure of F344 rats and BDF₁ mice of both sexes to 0, 10, 30, 90, 270 or 810 ppm (v/ v) CCl₄ vapor for 13 wk (6 h/d and 5 d/wk). In the high exposure levels at 270 and 810 ppm, altered cell foci in the livers of both rats and mice, and fibrosis and cirrhosis in the rat liver were observed. Hematoxylin and eosin‐stained altered cell foci of rats were recognized as glutathione‐S‐transferase placental form (GST‐P) positive foci, which are preneoplastic lesions of hepatocarcinogenesis. The most sensitive endpoint of CCl₄‐induced toxicity was fatty change with large droplets in rats of both sexes and male mice, and cytoplasmic globules in male mice, as well as increased relative liver weight in male rats. Those endpoints were manifested at 10 ppm and the LOAEL was determined as 10 ppm for the hepatic endpoints in rats and mice. Enhanced cytolytic release of liver transaminases into plasma in rats and mice and its close association with hepatic collapse in mice were observed at medium and high levels of inhalation exposure. Both CCl₄‐induced hematotoxicity and nephrotoxicity were observed in both rats and mice, but those toxicities were manifested at higher exposure concentrations than hepatotoxicity. The LOAEL for the hepatic endpoint and the GST‐P‐stained altered cell foci provide relevant animal data for reconsidering the occupational exposure limit value of 5 ppm for CCl₄ and strengthen the evidence of CCl₄induced hepatocarcinogenicity which is used in its carcinogenicity classification.

Background: In Japan, six workers handling cross-linked water-soluble acrylic acid polymer (CWAAP) at a chemical plant suffered from lung diseases, including fibrosis, interstitial pneumonia, emphysema, and pneumothorax. We recently demonstrated that inhalation of CWAAP-A, one type of CWAAP, causes pulmonary disorders in rats. It is important to investigate dose–response relationships and recoverability from exposure to CWAAPs for establishing occupational health guidelines, such as setting threshold limit value for CWAAPs in the workplace.Methods: Male and female F344 rats were exposed to 0.3, 1, 3, or 10 mg/m³CWAAP-A for 6 h/day, 5 days/week for 13 weeks using a whole-body inhalation exposure system. At 1 h, 4 weeks, and 13 weeks after the last exposure the rats were euthanized and blood, bronchoalveolar lavage fluid, and all tissues including lungs and mediastinal lymph nodes were collected and subjected to biological and histopathological analyses. In a second experiment, male rats were pre-treated with clodronate liposome or polymorphonuclear leukocyte-neutralizing antibody to deplete macrophages or neutrophils, respectively, and exposed to CWAAP-A for 6 h/day for 2 days.Results: CWAAP-A exposure damaged only the alveoli. The lowest observed adverse effect concentration (LOAEC) was 1 mg/m³and the no observed adverse effect concentration (NOAEC) was 0.3 mg/m³. Rats of both sexes were able to recover from the tissue damage caused by 13 weeks exposure to 1 mg/m³CWAAP-A. In contrast, tissue damage caused by exposure to 3 and 10 mg/m³was irreversible due to the development of interstitial lung lesions. There was a gender difference in the recovery from CWAAP-A induced pulmonary disorders, with females recovering less than males. Finally, acute lung effects caused by CWAAP-A were significantly reduced by depletion of alveolar macrophages.Conclusions: Pulmonary damage caused by inhalation exposure to CWAAP-A was dose-dependent, specific to the lung and lymph nodes, and acute lung damage was ameliorated by depleting macrophages in the lungs. CWAAP-A had both a LOAEC and a NOAEC, and tissue damage caused by exposure to 1 mg/m³CWAAP-A was reversible: recovery in female rats was less than for males. These findings indicate that concentration limits for CWAAPs in the workplace can be determined.Graphical

We have previously reported that inhalation exposure to titanium dioxide nanoparticles (TiO2 NPs) for 13 weeks causes early pneumoconiosis lesions in the alveolar region of F344 rats. We defined these characteristic lesions as pulmonary dust foci (PDF). In this report, we re-evaluate and detail the histopathological data regarding particle-induced pneumoconiosis lesions, including progressive lesions of the early PDF lesions, that developed in F344 rats exposed TiO2 NPs by whole body inhalation over a period of two years. Male and female F344 rats were exposed to 0.5, 2, and 8 mg/m3 anatase type TiO2 NPs for 6 h/day, 5 days/week for 104 weeks using a whole-body inhalation exposure system. After the final exposure, the rats were euthanized. In the present study, the collected lungs were re-evaluated macroscopically and histopathologically. Rats exposed to TiO₂ NPs developed macroscopic white lesions, primarily in the subpleural and hilar regions of the lung, which increased in size and number with exposure concentration. Histologically, two lesion types were identified: (1) Fibrotic Pulmonary Dust Foci (fPDF), characterized by collagen deposition, inflammatory infiltration, and disrupted alveolar epithelial differentiation, and (2) Dust Macules (DM), characterized by macrophage accumulation without significant fibrosis or inflammation. fPDFs, but not DMs, were observed after 13 weeks exposure to TiO₂ NPs, indicating that the DM-type pneumoconiosis lesions required a longer time to develop compared to fPDF-type pneumoconiosis lesions. Histopathological analysis revealed that the DM-type pneumoconiosis lesions that developed in rats exposed to TiO₂ NPs were similar to DM-type pneumoconiosis lesions that develop in humans. Inhalation exposure to TiO₂ NPs caused the development of two types of pneumoconiosis lesions in rats with distinct pathological features, fPDFs and DMs. The histopathological similarity of the DM-type pneumoconiosis lesions that developed in rat lung in the present study with the DM-type pneumoconiosis lesions that develop in the human lung adds strong support to the conclusion that humans exposed to airborne TiO₂ NPs are at risk of developing pneumoconiosis.

Rodents are widely used to study the toxicity of chemicals; however, differences between species indicate that the results from rodents are not always directly transferable to humans. The health of workers exposed to various chemicals and particulates at high doses or for long periods is at risk. Respiratory bronchioles and lobular structures, which are demarcated by interlobular septa, are key sites for occupational lung diseases such as pneumoconiosis; however, these structures vary among animal species. Understanding these differences is crucial for studying the pathology of human occupational lung diseases. However, there is a lack of reviews focusing on these structures in different species. This review explores the lung anatomy of various mammals and its functional importance in disease to connect animal studies with human occupational lung diseases. Our results indicate that artiodactyls, especially small pig breeds and goats, are ideal for research because their respiratory bronchioles and lobular structures are similar to those of humans. This review aims to enhance the use of experimental animal data and improve our understanding of human occupational lung diseases, thereby facilitating early disease detection, treatment, and prevention.

Background: Recently in Japan, six workers at a chemical plant that manufactures resins developed interstitial lung diseases after being involved in loading and packing cross-linked water-soluble acrylic acid polymers (CWAAPs). The present study focused on assessing lung damage in rats caused by workplace-relevant inhalation exposure to CWAAP and investigated the molecular and cellular mechanisms involved in lung lesion development. Methods: Using a whole-body inhalation exposure system, male F344 rats were exposed once to 40 or 100 mg/m³ of CWAAP-A for 4 h or to 15 or 40 mg/m³ of CWAAP-A for 4 h per day once per week for 2 months (9 exposures). In a separate set of experiments, male F344 rats were administered 1 mg/kg CWAAP-A or CWAAP-B by intratracheal instillation once every 2 weeks for 2 months (5 doses). Lung tissues, mediastinal lymph nodes, and bronchoalveolar lavage fluid were collected and subjected to biological and histopathological analyses. Results: A single 4-h exposure to CWAAP-A caused alveolar injury, and repeated exposures resulted in regenerative changes in the alveolar epithelium with activation of TGFβ signaling. During the recovery period after the last exposure, some alveolar lesions were partially healed, but other lesions developed into alveolitis with fibrous thickening of the alveolar septum. Rats administered CWAAP-A by intratracheal instillation developed qualitatively similar pulmonary pathology as rats exposed to CWAAP-A by inhalation. At 2 weeks after intratracheal instillation, rats administered CWAAP-B appeared to have a slightly higher degree of lung lesions compared to rats administered CWAAP-A, however, there was no difference in pulmonary lesions in the CWAAP-A and CWAAP-B exposed rats examined 18 weeks after administration of these materials. Conclusions: The present study reports our findings on the cellular and molecular mechanisms of pulmonary disease in rats after workplace-relevant inhalation exposure to CWAAP-A. This study also demonstrates that the lung pathogenesis of rats exposed to CWAAP-A by systemic inhalation was qualitatively similar to that of rats administered CWAAP-A by intratracheal instillation. Graphical

Carcinogenicity of 1,1,1-trichloroethane (TCE) was examined by an inhalation exposure of F344 rats and BDF1 mice of both sexes to TCE at 0, 200, 800 or 3200 ppm for 6 h/d, 5 d/week for 104 weeks. In male rats, the incidences of bronchiolo-alveolar adenomas and peritoneal mesotheliomas were significantly increased in the 800 and 3200 ppm-exposed groups, respectively. The incidence of bronchiolo-alveolar adenomas in the 3200 ppm-exposed groups exceeded the range of historical control data in the Japan Bioassay Research Center. In female rats, the tumor incidences were not increased in any organs of the TCE-exposed groups. In male mice, a significant positive trend with dose was shown for incidences of bronchiolo-alveolar carcinomas, combined incidences of bronchiolo-alveolar adenomas/carcinomas and hepatocellular adenomas. The incidence of Harderian gland adenomas was significantly increased in the 3200 ppm-exposed group, and malignant lymphomas of spleen at this highest dose exceeded the range of historical control data. In female mice, the combined incidence of bronchiolo-alveolar adenomas/carcinomas was significantly increased in the 3200 ppm-exposed group, and the incidences of hepatocellular adenomas and combined incidences of hepatocellular adenomas/carcinomas were significantly increased in the 200, 800 and 3200 ppm-exposed groups with dose dependence except the combined incidence of hepatocellular adenomas/carcinomas in the 200 ppm-exposed group. The incidences of bronchiolo-alveolar adenomas in the 3200 ppm-exposed group and combined incidences of hepatocellular adenomas/carcinomas in the 200 ppm-exposed groups exceeded the ranges of historical control data. Thus, this study provided clear evidence of inhalation carcinogenicity for TCE in both rats and mice.