Superoxide anion, the main species of ROS in the development of ARDS induced by oleic acid.

It is believed that reactive oxygen species (ROS) play a very important role in the pathogenesis of acute respiratory distress syndrome (ARDS), but the mechanism has not been so clear, owing to the absence of direct measurable (experimental) data. In majority of the medical studies on free radicals, the analysis of ROS has generally been done by the way of measuring their secondary and breakdown products. In our study, we used electron spin resonance (ESR), a sensitive and accurate technique to detect ROS directly and also used some other sensitive techniques including ultra-weak luminescence and chemical luminescence to identify the species and relative amount of ROS. Furthermore, superoxide dismutase (SOD) was pre-administrated in ARDS rats to verify the results from the above studies and explore the possibility of the clinical application of SOD in ARDS. The spectra of ESR showed that the concentration of ROS increased at 10 min and reached a summit at 30 min after injection of oleic acid (OA), then dropped gradually. The scavenging effects of different scavenging agents on ROS by the analysis of ultra-weak luminescence proved that superoxide anion was the main species of ROS in the development of OA-induced ARDS. Moreover, the results of quantified measure of superoxide anion by chemical luminescence also showed the accordant tendency exhibited in ESR measurement. The pre-treatment of SOD might distinctly inhibit the production of superoxide anion, obviously improve the blood gas status, lung wet/dry ratio and lung/body ratio in ARDS rats. It is suggested that ROS may play a key role in the initiation phase of ARDS, while superoxide anion may be a leading actor in this process and SOD could effectively protect rats from ARDS. These results may provide helpful information for the treatment and prevention of ARDS.