Pulmonary dust foci as rat pneumoconiosis lesion induced by titanium dioxide nanoparticles in 13-week inhalation study

• Published in: Particle and fibre toxicology Vol. 19; no. 1; pp. 1 - 58
• Main Authors: Yamano, Shotaro, Goto, Yuko, Takeda, Tomoki, Hirai, Shigeyuki, Furukawa, Yusuke, Kikuchi, Yoshinori, Kasai, Tatsuya, Misumi, Kyohei, Suzuki, Masaaki, Takanobu, Kenji, Senoh, Hideki, Saito, Misae, Kondo, Hitomi, Umeda, Yumi
• Format: Journal Article
• Language: English
• Published: London BioMed Central Ltd 14.09.2022; BioMed Central; BMC
• Subjects: Acute toxicity; Aerosols; Alveoli; Anatase; Biochemistry; Bronchus; Carcinogenicity; Carcinogens; Diagnosis; DNA damage; Dust; Endothelial cells; Exposure; F344 rat; Females; Foci; Health aspects; Hematology; Hyperplasia; Inflammation; Inhalation; Lavage; Lesions; Lung diseases; Lungs; Lymph nodes; Macrophages; Males; Morphology; Nanoparticles; Neutrophils; Occupational exposure; Particle size; Pneumoconiosis; Progenitor cells; Pulmonary dust foci (PDF); Pulmonary lesions; Rat pneumoconiosis; Respiration; Risk factors; Rodents; Sex differences; Side effects; Siderosis; Smoking; Stem cells; Titanium; Titanium dioxide; Titanium dioxide nanoparticles (TiO2 NPs); Toxicity; Toxicity testing; Whole-body inhalation; Japan
• ISSN: 1743-8977; 1743-8977
• DOI: 10.1186/s12989-022-00498-3

Most toxicological studies on titanium dioxide (TiO.sub.2) particles to date have concentrated on carcinogenicity and acute toxicity, with few studies focusing of pneumoconiosis, which is a variety of airspace and interstitial lung diseases caused by particle-laden macrophages. The present study examined rat pulmonary lesions associated with pneumoconiosis after inhalation exposure to TiO.sub.2 nanoparticles (NPs). Male and female F344 rats were exposed to 6.3, 12.5, 25, or 50 mg/m.sup.3 anatase type TiO.sub.2 NPs for 6 h/day, 5 days/week for 13 weeks using a whole-body inhalation exposure system. 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. Numerous milky white spots were present in the lungs after exposure to 25 and 50 mg/m.sup.3 TiO.sub.2 NPs. Histopathological analysis revealed that the spots were alveolar lesions, characterized predominantly by the agglomeration of particle-laden macrophages and the presence of reactive alveolar epithelial type 2 cell (AEC2) hyperplasia. We defined this characteristic lesion as pulmonary dust foci (PDF). The PDF is an inflammatory niche, with decreased vascular endothelial cells in the interstitium, and proliferating AEC2 transformed into alveolar epithelial progenitor cells. In the present study, the AEC2 in the PDF had acquired DNA damage. Based on PDF induction, the lowest observed adverse effect concentration for pulmonary disorders in male and female rats was 12.5 mg/m.sup.3 and 6.3 mg/m.sup.3, respectively. The no observed adverse effect concentration for male rats was 6.3 mg/m.sup.3. There was a sex difference in lung lesion development, with females showing more pronounced lesion parameters than males. Inhalation exposure to TiO.sub.2 NPs caused PDF, an air-space lesion which is an alveolar inflammatory niche containing particle-laden macrophages and proliferating AEC2. These PDFs histopathologically resemble some pneumoconiosis lesions (pulmonary siderosis and hard metal pneumoconiosis) in workers and lung disease in smokers, suggesting that PDFs caused by exposure to TiO.sub.2 NPs in rats are an early pneumoconiosis lesion and may be a common alveolar reaction in mammals.