Major urinary metabolites of 6-keto-prostaglandin F2α in mice

Western diets are enriched in omega-6 vs. omega-3 fatty acids, and a shift in this balance toward omega-3 fatty acids may have health benefits. There is limited information about the catabolism of 3-series prostaglandins (PG) formed from eicosapentaenoic acid (EPA), a fish oil omega-3 fatty acid that becomes elevated in tissues following fish oil consumption. Quantification of appropriate urinary 3-series PG metabolites could be used for noninvasive measurement of omega-3 fatty acid tone. Here we describe the preparation of tritium- and deuterium-labeled 6-keto-PGF(2 alpha) and their use in identifying urinary metabolites in mice using LC-MS/MS. The major 6-keto-PGF(2 alpha) urinary metabolites included dinor-6-keto-PGF(2 alpha) (similar to 10%) and dinor-13, 14-dihydro-6,15-diketo-PGF(1 alpha) (similar to 10%). These metabolites can arise only from the enzymatic conversion of EPA to the 3-series PGH endoperoxide by cyclooxygenases, then PGI(3) by prostacyclin synthase and, finally, nonenzymatic hydrolysis to 6-keto-PGF(2 alpha). The 6-keto-PGF derivatives are not formed by free radical mechanisms that generate isoprostanes, and thus, these metabolites provide an unbiased marker for utilization of EPA by cyclooxygenases.