Nitrated unsaturated fatty acids, such as 10- and 12-nitrolinoleate , cholesteryl nitrolinoleate, and nitrohydroxylinoleate, represent a new class of endogenous lipid-derived signalling molecules. LNO2 isomers serve as potent endogenous ligands for PPARγ and can also decompose or be metabolized to release nitric oxide. 9-Nitrooleate is one of two regioisomers of nitrooleate, the other being 10-nitrooleate (OA-NO2; used for the mixture of isomers), which are formed by nitration of oleic acid in approximately equal proportions in vivo. Peroxynitrite, acidified nitrite, and myeloperoxidase in the presence of H2O2 and nitrite, all mediate the nitration of oleic acid. OA-NO2 is found in human plasma as the free acid and esterified in phospholipids at concentrations of 619 ± 52 nM and 302 ± 369 nM, respectively. OA-NO2 activates PPARγ approximately 7-fold at a concentration of 1 μM and effectively promotes differentiation 3T3-L1 preadipocytes to adipocytes at 3 μM.