Oxidative stress levels and dynamic changes in mitochondrial gene expression in a radiation-induced lung injury model

The purpose of this study was to set up a beagle dog model, for radiation-induced lung injury, that would be able to supply fresh lung tissues in the different injury phases for research into oxidative stress levels and mitochondrial gene expression. Blood serum and tissues were collected via CT-guided core needle biopsies from dogs in the various phases of the radiation response over a 40-week period. Levels of reactive oxygen species (ROS) and manganese superoxide dismutase 2 (MnSOD) protein expression in radiation-induced lung injury were determined by in situ immunocytochemistry; malondialdehyde (MDA) content and reductase activity in the peripheral blood were also tested; in addition, the copy number of the mitochondrial DNA and the level of function of the respiratory chain in the lung tissues were assessed. ROS showed dynamic changes and peaked at 4 weeks; MnSOD was mainly expressed in the Type II alveolar epithelium at 8 weeks; the MDA content and reductase activity in the peripheral blood presented no changes; the copy numbers of most mitochondrial genes peaked at 8 weeks, similarly to the level of function of the corresponding respiratory chain complexes; the level of function of the respiratory chain complex III did not peak until 24 weeks, similarly to the level of function of the corresponding gene Cytb. Radiation-induced lung injury was found to be a dynamically changing process, mainly related to interactions between local ROS, and it was not associated with the levels of oxidative stress in the peripheral blood. Mitochondrial genes and their corresponding respiratory chain complexes were found to be involved in the overall process.