Enhanced oxidative stress is implicated in the development of atherosclerosis in humans and animal models. F(2)-isoprostanes are formed in vivo via free radical peroxidation of arachidonic acid, and their quantification has allowed assessment of oxidative stress in vivo. F(2)-isoprostanes associate with lipids, although their distribution in human plasma lipoproteins is unknown. Our aim was to determine the distribution and levels of F(2)-isoprostanes in lipoproteins isolated from human plasma by ultracentrifugation and fast protein liquid chromatography (FPLC). F(2)-isoprostanes were significantly higher in HDL compared with LDL or VLDL after isolation by ultracentrifugation or FPLC. Furthermore, HDL3 particles contained elevated levels of F(2)-isoprostanes compared with HDL2. Platelet activating factor acetylhydrolase (PAF-AH), which hydrolyses esterified F(2)-isoprostanes from phospholipids, was predominantly associated with LDL. Reduced F(2)-isoprostanes in LDL may be related to higher PAF-AH activity in LDL. Paraoxonase 1 (PON-1) activity was associated with HDL2 and may be a contributing factor to the lower F(2)-isoprostanes in HDL2 compared with HDL3. Further studies are required to establish the implications of these findings on HDL function.

Anne Barden, Emilie Mas, Kevin D. Croft, Michael Phillips, Trevor A. Mori

Supplementation with eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) has been reported to reduce lipid peroxidation products formed from arachidonic acid (F₂-isoprostanes) in healthy humans, as well as in those under oxidative stress. α-Linolenic acid (ALA) is a precursor to EPA and DHA; however, its conversion in humans is thought to be inefficient. ALA can also undergo free radical oxidation, forming compounds known as F₁-phytoprostanes, which are found in all plants and are in high concentrations in plant pollens. In this study, we examined the effect of ALA supplementation on plasma and urine F₁-phytoprostane and F₂-isoprostane concentrations in men. Thirty-six nonsmoking men, aged 20–65 y, were recruited from the general population and randomly allocated to consume 9 g/d of either flaxseed oil (62% ALA, 5.4 g/d) or olive oil (placebo) for 4 wk in a parallel design. At baseline and after 4 wk of supplementation, blood samples and a 24-h urine sample were collected for measurement of plasma and urinary F₁-phytoprostanes and F₂-isoprostanes and plasma fatty acids. Compared with the olive oil group, plasma phospholipid ALA was greater (P < 0.0001), as were F₁-phytoprostanes in plasma (P = 0.049) and urine (P = 0.06) in the flaxseed oil group after 4 wk supplementation. Flaxseed oil did not affect plasma or urinary F₂-isoprostanes. The greater plasma F₁-phytoprostane concentration in the flaxseed oil group most likely resulted from the increased plasma concentration of the ALA substrate and/or the F₁-phytoprostane content of the flaxseed oil. Future studies are needed to determine the physiological importance of increased plasma and urine F₁-phytoprostanes and their relevance to heart disease prevention.

Several oxylipins are potent lipid mediators that regulate diverse aspects of health and disease and whose quantitative analysis by liquid chromatography–mass spectrometry (LC-MS) presents substantial technical challenges. As members of the lipidomics community, we developed technical recommendations to ensure best practices when quantifying oxylipins by LC-MS.