Identification of the Major Urinary Metabolite of the F2-isoprostane 8-iso-prostaglandin F2alpha in Humans

F2-isoprostanes are prostaglandin-like products of nonenzymatic lipid peroxidation. Measurement of levels of endogenous unmetabolized F2-isoprostanes has proven to be a valuable approach to assess oxidative stress in vivo. However, measurement of levels of urinary metabolites of F2-isoprostanes in timed urine collections offers an advantage over measuring unmetabolized F2-isoprostanes, e. g. in a plasma sample, in that it can provide an integrated index of isoprostane production over time. Therefore, we sought to identify the major urinary metabolite in humans of one of the more abundant F2-isoprostanes produced, 8-iso-prostaglandin F2alpha (8-iso-PGF2alpha). 20 microCi of tritiated 8-iso-PGF2alpha was infused over 1 h into a male volunteer. 75% of the infused radioactivity was excreted into the urine during the following 4.5 h and was combined with urine collected for 4 h from a rhesus monkey following infusion of 500 microg of unlabeled 8-iso-PGF2alpha. Urinary metabolites were isolated and purified by adsorption chromatography and high pressure liquid chromatography. The major urinary metabolite, representing 29% of the total extractable recovered radioactivity in the urine, was structurally identified by gas chromatography and mass spectrometry as 2,3-dinor-5, 6-dihydro-8-iso-prostaglandin F2alpha. The identification of 2, 3-dinor-5,6-dihydro-prostaglandin F2alpha as the major urinary metabolite of 8-iso-prostaglandin F2alpha provides the basis for the development of methods of assay for its quantification as a means to obtain an integrated assessment of oxidative stress status in humans.