DESCRIPTION (Applicant's abstract): The overall aim of this application is to characterize new mechanisms of biological membrane injury resulting form infection with bacterial endotoxin (LPS). The role of free radicals in LPS-induced endotoxemia is becoming well established, however, little is known about the processes involved in the damage to biomembrane lipids by nitrogen dioxide (NO2) radical (a product of nitric oxide oxidation). We have developed a new methodology based on electrospray tandem mass spectrometry, which allows identification and quantification of specific lipid products formed by the reaction of NO2 with arachidonic acid. Preliminary studies have revealed that this reaction generates a complex mixture of lipids containing characteristic products: trans isomers of arachidonic acid and lipids containing nitrogen-carbon bond (nitroeicosanoids). In addition, plasmalogen phospholipids reacted with NO2, which resulted in complete removal of this group of lipids and generation of 1 -lyso-phospholipids. We hypothesize that increased production of NO generates NO2. which is a key radical that targets arachidonic acid and phospholipids. thereby causing membrane injury. Specific aims are to: 1) study relationships between the magnitude of trans-arachidonic acid generation and other markers of free radical damage (isoprostaglandin, nitrite/nitrate, nitrotyrosine); 2) examine the nitration of arachidonic acid and the effects of nitroeicosanoids on NO and cGMP levels in tissues; 3) characterize modifications of plasmalogen phospholipids in endotoxemia. In order to address the role of NO, L-NMA, a NO synthase inhibitor will be used to prevent generation of NO. Uric acid was shown to scavenge NO2, and thus serve as a good probe to study effects of NO2 in LPS-induced injury. Thus these probes will be used to determine the role of NO and NO2 in arachidonic acid isomerization, nitration and plasmalogen degradation. We anticipate that in the long term the proposed studies will provide a foundation for a rational design of new strategies for development of new drugs (inhibitors of lipid isomexization and nitration), and therapies to treat symptoms of sepsis related to the N02-induced cytotoxicity.