Response to DNA Damage in Lung Injury and Repair

Oxygen is a valuable therapeutic agent in treatment of respiratory and cardiovascular disorders. Like other drugs, however, oxygen has a therapeutic window: high concentrations are toxic to the lung, and humans and experimental animals exposed to Fi02 >60% may develop fatal acute lung injury. The toxicity of oxygen is presumed to occur because of increased generation of reactive oxygen radicals which attack and modify cellular macromolecules including lipids, proteins, and nucleic acids.

Damage to cellular DNA is of particular interest, because oxidative DNA damage can trigger necrosis, apoptosis, and cell cycle arrest. These processes are prominent in animals models of oxygen toxicity. Interestingly, however, the amount and type of DNA damage provoked by elevated inspired oxygen concentrations has not been rigorously studied. Reactive oxygen species can attack both the phospho-diester backbone of DNA (leading to strand breaks) as well as the nitrogenous bases (leading to potentially mutagenic base alterations), but it is not clear which, if either, of these effects occurs in the native lung.

We hypothesize that pulmonary oxygen toxicity may be triggered by oxidative DNA damage. We are therefore quantifying the amount and types of DNA damage occurring in the lungs of mice and cultured cells exposed to elevated inspired oxygen concentrations ("hyperoxia"). We are finding distinct types of DNA damage in different cell populations within the mouse lung, and also finding marked differences in the way different primary cell types respond in vitro to hyperoxia.

Oxidative DNA damage activates an abundant, ubiquitous nuclear enzyme, poly (ADP-ribose) polymerase (PARP). Although under normal circumstances PARP activation facilitates DNA repair, in conditions of extreme oxidative stress, PARP activation can lead to cell death. We are therefore testing the hypothesis that PARP activation- triggered by the aforementioned oxidative DNA damage- may be involved in pulmonary oxygen toxicity. We are investigating PARP activation in using tissue culture and mouse models of oxygen toxicity.