Comparison of the effects of long-chain omega-3 fatty acid supplementation on plasma levels of free and esterified oxylipins

• 12-week LC n-3 PUFA supplementation led to changes in the overall pattern of both free and total plasma oxylipins.
• EPA-derived hydroxy, epoxy and dihydroxy fatty acids were significantly elevated, while AA-derived metabolites were lowered.
• Changes in concentrations of DHA- and other PUFA-derived oxylipins were minor.
• The ratio between total and free plasma oxylipins remained unchanged.
• Both free and total plasma oxylipins concentrations support similar conclusions regarding the biological effects of LC-n3-PUFA.

IntroductionIt is believed that many of the beneficial effects of long-chain omega-3 polyunsaturated fatty acids (LC n-3 PUFA) are mediated by their oxidized metabolites, the oxylipins. The formation and biological role of many cytochrome P450 and lipoxygenase derived hydroxy, epoxy and dihydroxy FA, particularly of oxylipins esterified in polar lipids and triglycerides remain unclear. In this study, we compared the impact of twelve weeks of LC n-3 PUFA supplementation on the patterns of free and total (sum of esterified and free) hydroxy, epoxy and dihydroxy FAs.Subjects and methodsSubjects (5 male; 5 female) between 46 and 70 years were supplemented with 1.1 g/d of eicosapentaenoic acid (EPA) and 0.74 g/d docosahexaenoic acid (DHA) as ethyl esters. Blood samples were drawn before and after twelve weeks of treatment. Oxylipins in plasma were analyzed by LC–MS directly for free oxylipins and after saponification. Relative FA composition in erythrocyte membranes was analyzed by GC.ResultsLC n-3 PUFA treatment led to a significant increase in EPA (200%) and DHA (23%) in erythrocyte membranes. Of the oxylipins measured in plasma, total and free EPA-derived metabolites were highly increased (70–150%), while total AA-derived metabolites were decreased on average by 30%. There was no effect on DHA-metabolites. Concentrations of total hydroxy and epoxy FAs in plasma were considerably higher compared to free hydroxy and epoxy FAs (up to 350 times), while levels of most free dihydroxy FAs were in a similar range to total dihydroxy FAs. However, the individual ratios between total and free plasma oxylipins remained unchanged after LC n-3 PUFA treatment.Discussion and conclusionsLC n-3 PUFA supplementation causes a shift in the levels of circulating oxylipins, having the strongest impact on EPA-derived epoxy, dihydroxy and hydroxy FA. The unchanged ratio of free and esterified oxylipins in plasma indicates that both concentrations are valuable biomarkers for assessing the individual status of these lipid mediators.