Evaluation of the effects of inhaled nanoparticles on the central nervous system of mice

In recent years there has been increasing concern that inhalation exposure to ambient particulate matter (PM) can lead to or exacerbate various diseases, which are not limited to the lung and the cardiovascular system, but also extend to other organs and tissues. Several research groups have shown with rodent inhalation studies that PM, and more specifically the fraction of nanoparticles (NP) ( The central focus of in this thesis has been on the hypothesis that inhaled NP play a crucial role in inducing or worsening oxidative stress and inflammation in the CNS, and thereby may contribute to brain pathologies. Oxidative stress and mildly increased inflammation in the brain, which are commonly observed in animal experimental studies, are characteristic for normal brain aging processes. However, they are also featured in various diseases of the CNS including the common neurodegenerative disorders Alzheimer’s disease (AD). The first study addressed the effects of short term (4 h) nose-only inhalation exposure to model carbon NP generated by spark discharge in the lungs and brains of wildtype (WT) and p47phox-/- mice. The p47phox-/- model was used to investigate the role of NADPH oxidase mediated superoxide formation in NP-induced oxidative stress and inflammation. It could be shown that the lungs of p47phox-/- mice are less responsive to NP inhalation than lungs of WT animals. Lung tissue mRNA expression levels of the DNA base excision genes OGG1 and APE-1 were increased upon NP exposure in WT animals but not in the of p47phox-/- mice, reflecting enhanced NADPH oxidase dependent stress and possible DNA damage. However, for the brain, no clear NP-exposure associated contrasts in mRNA or protein marker changes could be detected. The constitutive protein expression of the pro-inflammatory cytokine interleukin-1s was found to differ between the brain homogenates of the shamexposed wildtype and knockout mice. The second study of the project involves a subchronic (i.e. 3 or 13 week) wholebody inhalation study to DEE in an Alzheimer mouse model. For this investigation it was decided to work with B6SJL-Tg (APPSwFlLon, PSEN1*M146L*L286V)6799VAS mice (also referred to as “5xFAD mice”). The female mice of this strain are characterised by the development of histological, neurological as well as functional impairments which are considered to mimic the development and progression of AD in humans. Our study hypothesis is that a subchronic inhalation exposure to combustion derived NP (DEE) leads to an acceleration of these AD-like effects in this mouse model. Therefore, groups of animals were exposed to diluted DEE or HEPA filtered air for 3 or 13 weeks, each 5 days per week, 6 hours per day. At the end of the 3 weeks and 13 weeks exposures, animals were subjected to a series of behavioural tests, i.e. the Y-maze task and X-maze task (both to assess the spatial working memory of mice reflected by the spontaneous alternation) and the string suspension task (to evaluate motor coordination and grip strength). Following, animals were sacrificed and brains were analyzed using histopathological, biochemical and molecular-biological techniques. The hypothesis of this study was that subchronic exposure to NP leads to an acceleration of the age-related onset of AD-like pathology. The results demonstrated deficits in motor condition and/or grip strength as well as increased brain tissue homogenate protein levels of β-amyloid 42 in the NP-exposed 5xFAD mice. Acceleration of β-amyloid 42 plaque deposition in the cortex and hippocampus was also detected. The results of the behaviour tests and histopathology findings indicate, in line with the expectations, the typically age-dependent behavioural deficits and marked plaque-formation in the 5xFAD mice. In conclusion, the results of this thesis are in support of the central nervous system as a major target of environmental nanoparticles, and indicate that long term inhalation exposure may accelerate the pathogenesis of Alzheimer’s disease.