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Background: There is a debate currently about whether different chemical forms of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are absorbed in an identical way. The objective of this study was to investigate the response of the omega-3 index, the percentage of EPA þ DHA in red blood cell membranes, to supplementation with two different omega-3 fatty acid (n-3 FA) formulations in humans. Design: The study was conducted as a double-blinded placebo-controlled trial. A total of 150 volunteers was randomly assigned to one of the three groups: (1) fish oil concentrate with EPA þ DHA (1.01 g þ 0.67 g) given as reesterified triacylglycerides (rTAG group); (2) corn oil (placebo group) or (3) fish oil concentrate with EPA þ DHA (1.01 g þ 0.67 g) given as ethyl ester (EE group). Volunteers consumed four gelatine-coated soft capsules daily over a period of six months. The omega-3 index was determined at baseline (t 0 ) after three months (t 3 ) and at the end of the intervention period (t 6 ). Results: The omega-3 index increased significantly in both groups treated with n-3 FAs from baseline to t 3 and t 6 (Po0.001). The omega-3 index increased to a greater extent in the rTAG group than in the EE group (t 3 : 186 versus 161% (Po0.001); t 6 : 197 versus 171% (Po0.01)). Conclusion: A six-month supplementation of identical doses of EPA þ DHA led to a faster and higher increase in the omega-3 index when consumed as triacylglycerides than when consumed as ethyl esters.

Oxylipins, the oxidation products of unsaturated fatty acids (FA), are potent endogenous mediators being involved in regulation of various biological processes such as inflammation, pain and blood coagulation. Compared to oxylipins derived from arachidonic acid (AA) by cyclooxygenase action, i.e. prostanoides, only limited information is available about the endogenous levels of hydroxy-, epoxy- and dihydroxy-FA of linoleic acid (LA), AA, α-linolenic acid (ALA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in humans. Particularly, it is unknown how metabolic disorders affect endogenous oxylipin levels in humans. Therefore, in the present study we compared the serum concentrations of 44 oxylipins in 20 normolipidemic with 20 hyperlipidemic (total cholesterol > 200 mg/dl; LDL-C > 130 mg/dl; TG > 150 mg/ml) men (age 29–51 y). The serum concentration varied strongly among subjects. For most hydroxy-, epoxy- and dihydroxy-FA the concentration were comparable to those of plasma reported in earlier studies. Despite the significant change in blood lipid levels the hyperlipidemic group showed only minor differences in oxylipin levels. The hyperlipidemic subjects had a slightly higher serum concentration of 8,9-DiHETrE, 5-HEPE, 10,11-DiHDPE, and a lower concentration of 12,13-DiHOME, 12-HETE, 9,10-DiHODE, and 12,13-DiHODE compared to normolipidemic subjects. Overall the hydroxy-, epoxy- and dihydroxy-FA levels were not changed suggesting that mild combined hyperlipidemia has no apparent effect on the concentration of circulating oxylipins. By contrast, serum levels of several hydroxy-, epoxy-, and dihydroxy-FA are dependent on the individual status of the parent FA. Particularly, a strong correlation between the EPA content in the erythrocyte membrane and the serum concentration of EPA derived oxylipins was observed. Given that the synthesis of EPA from other n3-FA in humans is low, this suggests that oxylipin levels can be directly influenced by the diet.

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