Inflammatory effects of nanosized titanium dioxide and carbon nanotube pulmonary exposure

Common materials acquire new properties when manufactured in the nanoscale. The same properties that are responsible for the exciting new possibilities are also a cause for some concern. The high surface area to volume ratio is a feature of engineered nanomaterials (ENM) that causes the amount of surface area to dominate their possible effects. In the case of carbon nanomaterials and other fibers, also the shape and length of the particle play important roles. The two ENM studied in this thesis, nanosized titanium dioxide (TiO2) and carbon nanotubes (CNT), are among the most widely used ENM in the world which means that they hold a high potential of occupationa l and possible customer exposure. Inhalation is the most likely exposure route in occupational settings. For this reason, inhalation exposure of mice was the main route of administration. The study settings were chosen to mimic occupational exposure as far as possible. Different immunological parameters were examined in the lungs of the exposed mice, such as the influx of different leucocytes, expression of cytokine and chemokine messenger molecules and changes in the lung tissue. The results from TiO2 studies indicated that even a normally inert material when nanosized may become inflammogenic. In addition, even small changes in the structure, or even a coating, may modify radically the nature of a material. Exposure to most nanosized TiO2 caused only modest to no inflammation, whereas a silica (SiO2) coated TiO2 triggered an inflammation characterized by pulmonary neutrophilia and mRNA expression of neutrophil chemoattractant CXCL1 and proinflammatory TNF-α. In tissues and bronchoalveolar lavage (BAL), TiO2 was readily engulfed by macrophages. In a model of allergic asthma, it was found that exposure to both nanosized and larger TiO2 seemed to prevent asthmatic symptoms. This underlines the importance of bearing in mind the heterogeneity of the human population when assessing the toxicity of ENM. CNT have raised some serious concerns in the scientific community and the media due to their similarity in structure to asbestos. Here, a remarkable new type of eosinophilic inflammation was observed in long rigid CNT exposed mice after a week of inhalation to these particles. This inflammation was characterized by strong eosinophilia, goblet cell hyperplasia, Th2 type cytokines and increased airway hyper-responsiveness to methacholine. All of the above symptoms have previously been described as symptoms of classical asthma. Transcriptomic analyses revealed radical up-regulation of innate immunity and cytokine/chemokine pathways. There were also roles found for mast cells and alveolar macrophages in orchestrating the inflammation. Lastly in the only exposure conducted by aspiration, mice were exposed to two long CNT (rigid/R and tangled/T) and to crocidolite asbestos. From a few hours to 28 days after a single exposure, there was a striking inflammatory cascade starting with macrophages and neutrophils, progressing to eosinophilic inflammation and eventually terminating as granulomas, goblet cell hyperplasia, Charcot-Leyden-like crystals and the mRNA expression of IL-1β, TGF-β, TNF-α and IL-13. The most dramatic inflammation was seen in the R/CNT group, followed by asbestos with T/CNT being clearly more weakly inflammogenic. In summary, inhalation exposure especially to certain fibrous nanomater ia ls seems to cause strong pulmonary inflammation. This may put exposed individuals at risk of developing lung diseases. In addition to the material of the nanoparticle, two important factors in risk evaluation are the shape of the particle and the possible modification made (e.g. coating) to the particle. The model of allergic asthma demonstrated that an underlying inflammatory condition can greatly affect the inflammatory outcome seen after nanopartic le exposure. The results of this thesis help to understand the underlying mechanisms in nanoparticle induced pulmonary inflammation.