28-Day Rat Inhalation Study – How Systems Toxicology Complements OECD Inhalation Studies

      Kogel, U.; Schlage, W. K.; Martin, F.; Ansari, S.; Xiang, Y.; Meurrens, K.; Vanscheeuwijck, P.; Hoeng, J.; Peitsch, M. C.
      Conference date
      Jun 30, 2013
      Conference name
      International Congress of Toxicology (ICT) 2013

      OECD 28-day rat inhalation studies are designed to characterize test article toxicity. We augmented the OECD study with transcriptomics analysis to evaluate molecular perturbations at the sites of histopathological impact. Rats were exposed for 28 days to filtered air, or to a low, medium, or high concentration of mainstream smoke from the 3R4F reference cigarette. Free lung cells and inflammatory mediators were determined in bronchoalveolar lavage fluid. A strong increase in neutrophil and macrophage counts concomitant with an increase in chemokines and cytokines indicated an inflammatory response. Histopathological evaluation of the respiratory tract revealed the usual smoke-related and dose-dependent adaptive changes in airways and inflammatory responses in lung. Transcriptomics data was generated from three areas of major histological impact: Respiratory Nasal Epithelium (RNE), Respiratory Epithelium of main Bronchus, and Lung Parenchyma. Systems response profiles demonstrated dose-dependency in the number of differentially expressed genes which were mainly related to inflammation, oxidative and ER stress, cell growth, and xenobiotic metabolism for all three tissues. Using our novel Computational-Modeling Approach that is based on causal models of Tissue-Specific Biological Networks, gene fold-changes were translated into Network Perturbation Amplitude (NPA) scores. Major perturbations were found in networks related to inflammation, cell stress, cell proliferation, and senescence. Corresponding to the histological changes, the stress-related response was more pronounced in the nasal and bronchial epithelia, while the inflammatory responses were more pronounced in the lung parenchyma. NPA scores of three exemplary sub-networks from the Inflammatory Processes Network showed agreement to the histopathological findings and resolved cell-type specific signaling contributions. In conclusion, observed histopathological endpoints correlated well with the perturbation of their associated biological networks, thus providing support for the applicability of this approach as a powerful tool to investigate disease mechanisms in vivo and to develop a Systems Biology-Based Risk Assessment for Modified Risk Tobacco Products. Also presented at: PMI-hosted Scientific Symposium Seoul 2013 PMI-hosted Scientific Symposium Interlaken 2013