[Mechanism of nano-indium-tin oxide inducing pulmonary alveolar proteinosis in Sprague-Dawley rats]

Objective: To investigate the pathogenesis of pulmonary alveolar proteinosis in rats induced by nano-indium-tin oxide exposure, and to provide a basis for further determining the limit of occupational exposure to indium and developing related protection measures. Methods: In August 2018, a total of 40 specific pathogen-free Sprague-Dawley rats, with an age of 6-8 weeks and a body weight of (200±10) g, were randomly divided into control group, low-dose group (1.2 mg/kg) , middle-dose group (3 mg/kg) , and high-dose group (6 mg/kg) , with 10 rats in each group. After 1 week of routine feeding, the rats were given non-exposed intratracheal instillation twice every week, with an interval of 3 days, for 12 consecutive weeks. Body weight was measured every week during exposure to observe the change in body weight; The rats were anesthetized and sacrificed by chloral hydrate after the exposure ended, and lung tissue and serum were collected; Hematoxylin-eosin staining and periodic acid-Schiff (PAS) staining were performed for lung tissue to observe pathological results; Inductively coupled plasma mass spectrometry was used to measure the serum level of indium; ELISA was used to measure the levels of surfactant protein A (SP-A) , surfactant protein D (SP-D) , and the type II alveolar cell surface antigen Krebs von den Lungen-6 (KL-6) in lung tissue and the serum level of granulocyte-macrophage colony-stimulating factor (GM-CSF) . Results: The pathological results showed that the rats in the control group had basically complete alveolar structure, and after intratracheal instillation of nano indium-tin oxide, uniform, eosinophilic, and unstructured granular substances were observed in the alveolar space of the low-, middle-, and high-dose exposure groups, with macrophage proliferation and an increase in macrophages, especially in the high-dose group. Negative PAS staining was observed in the control group, while substances with positive PAS staining were observed in lung tissue in each exposure group. The three exposure groups had a significantly higher serum level of indium than the control group (P<0.05) . Compared with the control group, the three exposure groups had significant increases in SP-A, SP-D, and KL-6 in lung tissue and a significant reduction in GM-CSF in serum (P<0.05) . Conclusion: Pulmonary alveolar proteinosis in rats may be associated with the destruction of alveolar macrophages caused by nano-indium-tin oxide and the aggregation of pulmonary surfactants due to disorders in the metabolism and clearance of pulmonary surfactants by macrophages.