Identification of two major F2 isoprostanes, 8,12-iso- and 5-epi-8,12-iso-isoprostane F2α-VI, in human urine

Isoprostanes (iPs) are nonenzymatic, free radical-derived compounds isomeric with enzymatically formed eicosanoids such as prostaglandins, leukotrienes, and thromboxanes. One group formed by the auto-oxidation of arachidonic acid, the F-2-iPs, consists of four classes of isomers of prostaglandin F-2 alpha (PGF(2 alpha)), They are relatively abundant in human urine. This fact, along with their chemical stability and excellent characteristics for quantitation by gas chromatography/mass spectrometry, has made them attractive indices of oxidative stress in humans. We developed a specific assay using gas chromatography/mass spectrometry for the first identified F-2-iP, iPF(2 alpha)-III (previously called 8-iso-PGF(2 alpha) or 8-epi-PGF(2 alpha)), which demonstrated the utility of monitoring a specific isomer, Recently, we described an assay for another isomer, iPF(2 alpha)-VI, which is present in urine in greater concentration than iPF(2 alpha)-III and which is particularly amenable to quantitation, We now describe the identification in human urine of two more isomers, 8,12-iso-iPF(2 alpha)-Vl and 5-epi-8,12-iso-iPF(2 alpha)-VI, using high performance liquid chromatography/tandem mass spectrometry and gas chromatography/mass spectrometry, These compounds are each present in similar to 5-fold greater concentrations than iPF(2 alpha)-VI (similar to 20-fold greater than iPF(2 alpha)-III), They share the unique chemical characteristics of class VI compounds, which make them attractive targets for quantitation by gas chromatography/mass spectrometry and immunoassay development.