Novel Eicosapentaenoic Acid-derived F3-isoprostanes as Biomarkers of Lipid Peroxidation

Isoprostanes (iPs) are prostaglandin (PG) isomers generated by free radical-catalyzed peroxidation of polyunsaturated fatty acids (PUFAs). Urinary F-2-iPs, PGF(2 alpha) isomers derived from arachidonic acid (AA) are used as indices of lipid peroxidation in vivo. We now report the characterization of two major F-3-iPs, 5-epi-8,12-iso-iPF(3 alpha)-VI and 8,12-iso-iPF(3 alpha)-VI, derived from the omega-3 fatty acid, eicosapentaenoic acid (EPA). Although the potential therapeutic benefits of EPA receive much attention, a shift toward a diet rich in omega-3 PUFAs may also predispose to enhanced lipid peroxidation. Urinary 5-epi-8,12-iso-iPF(3 alpha)-VI and 8,12-iso-iPF(3 alpha)-VI are highly correlated and unaltered by cyclooxygenase inhibition in humans. Fish oil dose-dependently elevates urinary F-3-iPs in mice and a shift in dietary omega-3/omega-6 PUFAs is reflected by an increasing slope [m] of the line relating urinary 8, 12-iso-iPF(3 alpha)-VI and 8,12-iso-iPF(2 alpha)-VI. Administration of bacterial lipopolysaccharide evokes a reversible increase in both urinary 8,12-iso-iPF(3 alpha)-VI and 8,12-iso-iPF(2 alpha)-VI in humans on an ad lib diet. However, while excretion of the iPs is highly correlated (R-2 median = 0.8), [m] varies by an order of magnitude, reflecting marked inter-individual variability in the relative peroxidation of omega-3 versus omega-6 substrates. Clustered analysis of F-2- and F-3-iPs refines assessment of the oxidant stress response to an inflammatory stimulus in vivo by integrating variability in dietary intake of omega-3/omega-6 PUFAs.