Objectives: The aim of this study was to clarify the chronic toxicological effects of indium-tin oxide (ITO) and indium oxide (In 2O3) on laboratory animals. Methods: Male Syrian golden hamsters were intratracheally administered 3 mg/kg or 6 mg/kg of ITO particles, or 2.7 mg/kg or 5.4 mg/kg of In 2O3 particles, containing 2.2 mg/kg or 4.5 mg/kg of indium, twice a week, for 8 wk. Control hamsters were given vehicle of distilled water only. The hamsters were euthanized serially up to 78 wk after the final instillation and the toxicological effects were determined. Results: Body weight gain was significantly suppressed in the ITO 6 mg/kg-treated hamsters compared with the control group, but not in the ITO 3 mg/kg-treated or In 2O3-treated hamsters. Relative lung weights among all the indium-treated groups were significantly increased compared to that in the control group throughout the observation period. The serum indium concentration among all the indium-treated groups gradually increased up to the end of the observation period. Histopathologically, foci of slight to severe pulmonary inflammatory response with diffuse alveolar or bronchiolar cell hyperplasia, expansion of the alveolar spaces and interstitial fibrotic proliferation were present in all the indium-treated hamsters and the severity of these lesions worsened with the passage of time. Lung benign adenomas were only manifest in 3 out of 15 of the ITO 6 mg/kg-treated hamsters. Conclusions: The present results clearly demonstrate that ITO and In 2O3 particles caused chronic pulmonary toxicity when repeated intratracheal instillations were given to hamsters.
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