Pulmonary toxicity and genotoxicity of carbon nanotubes in rats, a subacute inhalation study.

Due to their physical and chemical properties, carbon nanotubes (CNTs) are among the most promising nanomaterials in terms of industrial use. In order to assess their toxicological properties, inhalation experiments performed in laboratory rodents remain the most suitable and reliable approach. We have performed sub-acute inhalation experiments in female Sprague Dawley with two CNTs: the “long and thick” NM-401 and the “short and thin”NM-403. Animals were exposed in nose-only chambers to these aerosols 6 hours/day, 5 days/week for 4 weeks. CNT aerosols were generated at a concentration of 0.5 and 1.5 mg/m3 using an acoustic generator. Aerosols were fully characterized in terms of mass- and number-concentration; number- and mass-size distribution as well as morphology.
Tissues were collected 3, 30, 90 and 180 days after the end of the exposure period. At the highest dose, both CNTs induced pulmonary inflammatory response 3 days after the end of exposure, this was demonstrated by an important neutrophilia in the broncho-alveolar lavage fluid (BALF) which however decreased overtime. Despite the presence of NM-401 within the lung, no significant histopathological changes were found; for NM-403 samples are still under evaluation. The genotoxicity of these nanomaterials was also assessed using the multiple-organ comet assay. Despite the presence of inflammation, no increase in DNA damage in lung or BALF cells as well as in liver, spleen or leukocytes was found. Additional experiments including cytokines expression are underway and may help to determine whether these two CNTs with different length and diameter may have distinct toxicological profiles.