Formation of F-ring isoprostane-like compounds (F3-isoprostanes) in vivo from eicosapentaenoic acid

Eicosapentaenoic acid (EPA, C20: 5, omega-3) is the most abundant polyunsaturated fatty acid (PUFA) in fish oil. Recent studies suggest that the beneficial effects of fish oil are due, in part, to the generation of various free radical-generated non-enzymatic bioactive oxidation products from omega-3 PUFAs, although the specific molecular species responsible for these effects have not been identified. Our research group has previously reported that pro-inflammatory prostaglandin F-2-like compounds, termed F-2-isoprostanes (IsoPs), are produced in vivo by the free radical-catalyzed peroxidation of arachidonic acid and represent one of the major products resulting from the oxidation of this PUFA. Based on these observations, we questioned whether F-2-IsoP-like compounds (F-3-IsoPs) are formed from the oxidation of EPA in vivo. Oxidation of EPA in vitro yielded a series of compounds that were structurally established to be F-3-IsoPs using a number of chemical and mass spectrometric approaches. The amounts formed were extremely large (up to 8.7 + 1.0 mu g/mg EPA) and greater than levels of F-2-IsoPs generated from arachidonic acid. We then examined the formation of F-3-IsoPs in vivo in mice. Levels of F-3-IsoPs in tissues such as heart are virtually undetectable at baseline, but supplementation of animals with EPA markedly increases quantities up to 27.4 + 5.6 ng/g of heart. Interestingly, EPA supplementation also markedly reduced levels of pro-inflammatory arachidonate-derived F-2-IsoPs by up to 64% ( p < 0.05). Our studies provide the first evidence that identify F-3-IsoPs as novel oxidation products of EPA that are generated in vivo. Further understanding of the biological consequences of F-3-IsoP formation may provide valuable insights into the cardioprotective mechanism of EPA.