Development of a Short-Term Inhalation Test in the Rat Using Nano-Titanium Dioxide as a Model Substance

Abstract

Evidence suggests that short-term inhalation studies may provide comparable prediction of respiratory tract toxicity to 90-day studies, presenting the opportunity to save time and resources in screening inhalation toxicity of test substances. The aim of this study was to develop a short-term inhalation test that could be employed to provide early evidence on respiratory tract effects which might occur from long-term exposure to aerosols of nano-materials. Male Wistar rats were exposed to aerosols of 0 (control), 2, 10 and 50 mg/m³ nano-titanium dioxide (TiO₂) by inhalation for 6 h/day for 5 days. Necropsies were performed either immediately after the last exposure or after 3 and 16 days post exposure (study days 5, 8 and 21, respectively). Treatment with nano-TiO₂ resulted in morphological changes in the lung, with 50 mg/m³ nano-TiO₂ producing an increase in lung weight. Lung inflammation was associated with dose-dependent increases in bronchoalveolar lavage fluid (BALF) total cell and neutrophil counts, total protein content, enzyme activities and levels of a number of cell mediators. No indications of systemic effects could be found by measurement of appropriate clinical pathology parameters. Cell replication (determined by incorporation of 5-bromo-2′-deoxyuridine) was increased at all nano-TiO₂ dose levels in large/medium bronchi and terminal bronchioles. The effects on the parameters measured were most prominent either on study day 5 or 8, with some endpoints returning to control levels by day 21. Overall, the pulmonary effects of nano-TiO₂ observed in this short-term study were comparable to those previously reported in subchronic inhalation studies.

This work was supported in part by the EU project NanoSafe2 and the BMBF (German Federal Ministry of Education and Research) project NanoCare. We thank ILSI/HESI for providing the test material and the respective characterization data. We thank Professor Brian G. Lake for preparation of this manuscript.