Double lipoxygenation of polyunsaturated fatty acids of nutritional interest.

Double lipoxygenation of polyunsaturated fatty acids having at least three methylene-interrupted double bonds can be made by two lipoxygenases, e.g. 5- and 12-LOX, or 15-LOX only, followed by reduction of the hydroperoxide products through the glutathione peroxidase action. Several biological activities have been reported for such a double 15-LOX product of docosahexaenoic acid, called protectin DX to differentiate it from protectin D1, a stereo and geometric isomer described for its potent anti-inflammatory potential. The geometric characteristic of the double lipoxygenase products is the conjugated triene E,Z,E (trans,cis,trans), which appears crucial in their biological activities. A focus is also done on single lipoxygenation of mono-hydroxylated products first made by aspirin-treated cyclooxygenase-2. The resulting (R,S)-diOH, E,Z,E conjugated trienes, instead of the (S,S)-diOH isomer in case of double lipoxygenation, seem to be even more active for some biological effects, making biologically relevant the single lipoxygenation in aspirin-treated situations.

Functional fluxolipidomics of polyunsaturated fatty acids and oxygenated metabolites in the blood vessel compartment.

Synthesis of bioactive oxygenated metabolites of polyunsaturated fatty acids and their degradation or transformation products are made through multiple enzyme processes. The kinetics of the enzymes responsible for the different steps are known to be quite diverse, although not precisely determined. The location of the metabolites biosynthesis is diverse as well. Also, the biological effects of the primary and secondary products, and their biological life span are often completely different. Consequently, phenotypes of cells in response to these bioactive lipid mediators must then depend on their concentrations at a given time. This demands a fluxolipidomics approach that can be defined as a mediator lipidomics, with all measurements done as a function of time and biological compartments. This review points out what is known, even qualitatively, in the blood vascular compartment for arachidonic acid metabolites and number of other metabolites from polyunsaturated fatty acids of nutritional value. The functional consequences are especially taken into consideration.

Moderate oral supplementation with docosahexaenoic acid improves platelet function and oxidative stress in type 2 diabetic patients.

Platelets from patients with type 2 diabetes are characterised by hyperactivation and high level of oxidative stress. Docosahexaenoic acid (DHA) may have beneficial effects on platelet reactivity and redox status. We investigated whether moderate DHA supplementation, given as a triglyceride form, may correct platelet dysfunction and redox imbalance in patients with type 2 diabetes. We conducted a randomised, double-blind, placebo-controlled, two-period crossover trial (n=11 post-menopausal women with type 2 diabetes) to test the effects of 400 mg/day of DHA intake for two weeks on platelet aggregation, markers of arachidonic acid metabolism, lipid peroxidation status, and lipid composition. Each two week-period was separated from the other by a six-week washout. Daily moderate dose DHA supplementation resulted in reduced platelet aggregation induced by collagen (-46.5 %, p< 0.001), and decreased platelet thromboxane B2 (-35 %, p< 0.001), urinary 11-dehydro-thromboxane B2 (-13.2 %, p< 0.001) and F2-isoprostane levels (-19.6 %, p< 0.001) associated with a significant increase of plasma and platelet vitamin E concentrations (+20 % and +11.8 %, respectively, p< 0.001). The proportions of DHA increased both in plasma lipids and in platelet phospholipids. After placebo treatment, there was no effect on any parameters tested. Our findings support a significant beneficial effect of low intake of DHA on platelet function and a favourable role in reducing oxidative stress associated with diabetes.

Biological properties of a DHA-containing structured phospholipid (AceDoPC) to target the brain.

1-acetyl,2-docosahexaenoyl-glycerophosphocholine (AceDoPC) has been made to prevent docosahexaenoyl (DHA) to move to the sn-1 position as it rapidly does when present in 1-lyso,2-docosahexaenoyl-GPC (lysoPC-DHA), an efficient DHA transporter to the brain. When incubated with human blood, AceDoPC behaves closer to lysoPC-DHA than PC-DHA in terms of binding to plasma albumin and lipoproteins, and DHA incorporation into platelets and red cells. In addition, AceDoPC prevents more efficiently the deleterious effects of the experimental stroke in rats than does unesterified DHA. Also, AceDoPC inhibits platelet-activating factor-induced human blood platelet aggregation. Overall, AceDoPC might act as an efficient DHA transporter to the brain, and as a neuro-protective agent by itself.

Dose-effect and metabolism of docosahexaenoic acid: pathophysiological relevance in blood platelets.

Docosahexaenoic acid (DHA) is known as a major nutrient from marine origin. Considering its beneficial effect in vascular risk prevention, the effect of DHA on blood components, especially platelets, will be reviewed here. Investigating the dose-effect of DHA in humans shows that daily intake lower than one gram/day brings several benefits, such as inhibition of platelet aggregation, resistance of monocytes against apoptosis, and reinforced antioxidant status in platelets and low-density lipoproteins. However, higher daily intake may be less efficient on those parameters, especially by losing the antioxidant effect. On the other hand, a focus on the inhibition of platelet aggregation by lipoxygenase end-products of DHA is made. The easy conversion of DHA by lipoxygenases and the formation of a double lipoxygenation product named protectin DX, reveal an original way for DHA to contribute in platelet inhibition through both the cyclooxygenase inhibition and the antagonism of thromboxane A2 action.

Functional lipidomics of oxidized products from polyunsaturated fatty acids.

Because of their high degree of unsaturation, polyunsaturated fatty acids (PUFA) in mammals, with mainly 18, 20 and 22 carbons, can easily be autooxidized, and converted into many oxidized derivatives and degradation products. This short review reports on some of those relevant to the evaluation of oxidative stress in situ. In addition, the enzyme-dependent oxygenation by both dioxygenases and monooxygenases is briefly reviewed by functional and/or metabolic categories, pointing out the structure variety and the analytical approaches.

DHA metabolism: targeting the brain and lipoxygenation.

Docosahexaenoic acid (DHA), the end-product of the metabolism of omega-3 family fatty acids, is the main polyunsaturated fatty acid of the brain, but its accumulation is incompletely understood. This paper reviews how it could accumulate through specific uptake of DHA-containing lysophosphatidylcholine (LysoPC-DHA). DHA migrates very easily from the sn-2 position of LysoPC, which could be considered as the physiological form of polyunsaturated LysoPC, to the sn-1 position, which is much more stable. An approach preventing migration by acetylating the sn-1 position, while retaining the main physico-chemical properties of the carrier, is described. Also, the double lipoxygenation and bond-isomerization of DHA into 10(S),17(S)-docosahexa-4Z,7Z,11E,13Z,15E,19Z-enoic acid, named PDX, by soybean lipoxygenase is described. As in other E,Z,E conjugated trienes, PDX is shown to inhibit human blood platelet aggregation at submicromolar concentrations.

Fatty acid-derived lipid mediators and blood platelet aggregation.

Polyunsaturated fatty acids of nutritional value may affect cell functions after their release from cell lipid storage sites, especially phospholipids, and specific oxygenation by cyclooxygenases, lipoxygenases and cytochrome P(450). The end-products, namely prostanoids, leukotrienes, and mono-, di- and tri-hydroxy derivatives exhibit a variety of biological effects, especially on vascular cells, leukocytes and platelets. This paper reviews some results obtained with blood platelets as target cells, showing that various lipoxygenase end-products, mainly mono- and di-hydroxy derivatives, are inhibitors (IC(50) in microM range) of arachidonic acid-induced aggregation either at the cycloxygenase or thromboxane receptor site level.

Full characterization of PDX, a neuroprotectin/protectin D1 isomer, which inhibits blood platelet aggregation.

Our study aimed to establish the complete structure of the main dihydroxy conjugated triene issued from the lipoxygenation (soybean enzyme) of docosahexaenoic acid, named PDX, an isomer of protectin/neuroprotectin D1 (PD1/NPD1) described by Bazan and Serhan. NMR approaches and other chemical characterization (e.g. GC-MS, HPLC and LC-MS/MS) indicated that PDX is 10(S),17(S)-dihydroxy-docosahexa-4Z,7Z,11E,13Z,15E,19Z-enoic acid. The use of (18)O(2) and mass spectrometry showed that PDX is a double lipoxygenation product. Its structure differs from PD1, with E,Z,E geometry (PDX) instead of E,E,Z (PD1) and S configuration at carbon 10 instead of R. PDX inhibits human blood platelet aggregation at sub-micromolar concentrations.

Pro- and antioxidant activities of docosahexaenoic acid on human blood platelets.

n - 3 polyunsaturated fatty acids may protect against vascular diseases, however, their high accumulation in membranes may increase lipid peroxidation and subsequently induce deleterious effects in patients suffering from oxidative stress. This led us to investigate in vitro the dose-dependent effect of docosahexaenoic acid (DHA) on the redox status of human platelets. We have compared the effect of different DHA concentrations (0.5, 5 and 50 micro mol L(-1)) corresponding to DHA/albumin ratios of 0.01, 0.1 and 1. At the highest concentration, DHA elicited a marked oxidative stress, as evidenced by high malondialdehyde and low vitamin E levels whereas the lowest DHA concentration significantly decreased the malondialdehyde formation, with no change in vitamin E. The proportion of DHA was only increased in plasmalogen phosphatidylethanolamine at low concentration to rise in all phosphatidyl-choline and -ethanolamine subclasses at high concentration. Thus, the results show a biphasic effect of DHA with antioxidant and prooxidant effects at low and high concentrations, respectively, with a possible relationship with the phospholipid subclass in which it accumulates.

Pathophysiologic role of redox status in blood platelet activation. Influence of docosahexaenoic acid.

Decrease of platelet glutathione peroxidase activity results in increased life span of lipid hydroperoxides, especially the 12-lipoxygenase product of arachidonic acid, 12-HpETE. Phospholipase A2 activity is subsequently enhanced with the release of arachidonic acid, which results in higher thromboxane formation and platelet function. Docosahexaenoic acid may either potentiate platelet lipid peroxidation or lower it when used at high or low concentrations, respectively. In the case of slowing down lipid peroxidation, docosahexaenoic acid was specifically incorporated in plasmalogen ethanolamine phospholipids. This could have a relevant pathophysiologic role in atherothrombosis.

Role of polyunsaturated fatty acids in the inhibitory effect of human adipocytes on osteoblastic proliferation.

As previously reported, the association of bone loss with an increase in bone marrow adipose volume may be related to the inhibition of human osteoblastic cell proliferation in the presence of human adipocytes. In the osteoblastic supernatant, fatty acid composition varied after coculture with mature adipocytes, with a marked increase in the proportion of docosahexaenoic acid (22:6 n-3; DHA) (+90 +/- 8%). This suggests that polyunsaturated fatty acids (PUFA) may contribute to the inhibitory effect of adipocytes on osteoblastic cell proliferation. The purpose of the present study was to evaluate the effects of two PUFA, DHA and arachidonic acid (20:4 n-6; AA), on the proliferation of primary human osteoblastic (hOB) cells and human osteosarcoma cell line, MG-63. The effects of cholesterol and oleic acid, a monounsaturated FA (18:1 n-9; OA), both being present in adipocyte lipidic vacuoles, were also investigated. At between 10 and 50 micromol/L, DHA and AA induced a significant dose-dependent decrease in hOB cell proliferation (p < 0.0001 and p < 0.006 for DHA and AA, respectively) when compared with control hOB cells exposed to the vehicle (bovine serum albumin). This inhibition reached -50% with 50 micromol/L of DHA or 20 micromol/L of AA. This effect was not related to cell apoptosis, as shown by terminal deoxynucleotidyltransferase-mediated dUTP-fluorescein nick end labeling (TUNEL) and Hoechst dye staining. In contrast, OA and cholesterol had no effect on hOB cell proliferation, even at a high concentration (200 micromol/L). Similar results were observed with regard to MG-63 cell proliferation. In addition, flow cytometric analysis showed that the number of hOB cells in the S phase of the cycle was twofold lower when treated with 50 micromol/L of DHA or AA. In vitro results indicate that mature adipocytes may contribute to age-related bone loss through the release of polyunsaturated fatty acids, which impair osteoblastic proliferation.

12(S)-Hydroperoxy-eicosatetraenoic acid increases arachidonic acid availability in collagen-primed platelets.

Lipid hydroperoxides have been reported to regulate cell function and eicosanoid formation. The aim of the present study was to determine the effect of 12(S)-hydroperoxy-eicosatetraenoic acid [12(S)-HPETE], the platelet 12-lipoxygenase-derived hydroperoxide of arachidonic acid (AA), on the availability of nonesterified AA, which represents a rate-limiting step in the biosynthesis of eicosanoids. The coincubation of human platelets with concentrations of 12(S)-HPETE below 50 nM and subthreshold concentrations (STC) of collagen (less than 0.24 microg/ml) significantly enhanced platelet aggregation and the formation of thromboxane B(2), the stable catabolite of the potent aggregating agent thromboxane A(2). In addition, the nonesterified endogenous AA concentration increased by 3-fold. Arachidonoyl-containing molecular species concentrations of 1,2-diacyl-glycero-3-phosphocholine, 1-alkyl-2-acyl-glycero-3-phosphocholine, and 1-alkenyl-2-acyl-glycero-3-phosphoethanolamine decreased specifically in response to 12(S)-HPETE, whereas no significant changes were observed within 1,2-diacyl-glycero-3-phosphoethanolamine and 1,2-diacyl-glycero-3-phosphoinositol molecular species. The 12(S)-HPETE-induced increase in nonesterified AA was fully prevented by arachidonoyl trifluoromethyl ketone, an inhibitor of cytosolic phospholipase A(2) (cPLA(2)), and cPLA(2) was translocated to membranes and phosphorylated in platelets incubated with 12(S)-HPETE. In conclusion, these results indicate that nanomolar concentrations of 12(S)-HPETE could play a significant role in controlling the level of endogenous AA and the formation of thromboxane, thereby potentiating platelet function.

Dual regulation of glutathione peroxidase by docosahexaenoic acid in endothelial cells depending on concentration and vascular bed origin.

Docosahexaenoic acid (DHA) has been reported to elicit oxidative stress, which in turn can induce antioxidant enzymes. Glutathione peroxidase (GPx) has received particular attention in this respect, as this enzyme is specifically required for the degradation of lipid hydroperoxides. Because we previously found that DHA could protect against oxidative stress when used in low amounts, we have compared the effect of a low (10 microM) versus high (100 microM) concentration of DHA on oxidant/antioxidant balance in bovine retinal and bovine aortic endothelial cells (BREC and BAEC). At 100 microM, DHA elicited a marked oxidative stress, as evidenced by high malondialdehyde levels and decreased plasmalogen phosphatidylethanolamine in both cells, and for BAEC only, a decrease of alpha-tocopherol. At 10 microM, DHA induced a slight increase of malondialdehyde in both cells, but did not affect alpha-tocopherol levels, which is indicative of a mild oxidative stress. In BREC, 10 microM DHA slightly but significantly decreased cytosolic GPx (cGPx) activity whereas 100 microM had no effect. In contrast, in BAEC, DHA 10 microM did not affect cGPx activity, whereas 100 microM increased it. The decreased cGPx activity in BREC was associated with a lower level of protein, suggesting a transcriptional and/or posttranscriptional effect. Phospholipid hydroperoxide GPx (PHGPx) activity was not modified by DHA at either concentration in BREC, whereas it was increased in BAEC when using 100 microM. Our results confirm that large amounts of DHA lead to oxidative stress, but do no support an antioxidant action of DHA at low concentration, in endothelium. Nevertheless, we showed that DHA can exert opposite effects on GPx regulation in endothelial cells, with regard to its concentration and to vascular bed origin.

The influence of low intake of n-3 fatty acids on platelets in elderly people.

A total of ten healthy elderly subjects ingested one capsule of 600 mg (corresponding to 150 mg docosahexaenoic acid and 30 mg eicosapentaenoic acid) RO-PUFA triglycerides per day and ten others ingested one capsule of 600 mg sunflower oil as a placebo for 42 days. In the n-3 polyunsaturated fatty acids (PUFA) group, a significant decrease of systolic blood pressure was observed, as well as a trend towards a decrease in both platelet activation and basal formation of thromboxane B(2). Also, a slight but significant increase of docosahexaenoic acid was observed in the phosphatidylethanolamine fraction as well as a significant increase of vitamin E level after the n-3 PUFA intake. Moreover, the basal production of malondialdehyde significantly decreased. No modification was observed for all these parameters in the placebo group. We conclude that a small intake of n-3 PUFA decreased the oxidative stress in platelets of elderly people and could be beneficial in subjects with atherothrombotic tendencies by lowering the cell peroxide tone.

Low concentrations of lipid hydroperoxides prime human platelet aggregation specifically via cyclo-oxygenase activation.

There is mounting evidence that lipid peroxides contribute to pathophysiological processes and can modulate cellular functions. The aim of the present study was to investigate the effects of lipid hydroperoxides on platelet aggregation and arachidonic acid (AA) metabolism. Human platelets, isolated from plasma, were incubated with subthreshold (i.e. non-aggregating) concentrations of AA in the absence or presence of hydroperoxyeicosatetraenoic acids (HPETEs). Although HPETEs alone had no effect on platelet function, HPETEs induced the aggregation of platelets co-incubated with non-aggregating concentrations of AA, HPETEs being more potent than non-eicosanoid peroxides. The priming effect of HPETEs on platelet aggregation was associated with an increased formation of cyclo-oxygenase metabolites, in particular thromboxane A2, and was abolished by aspirin, suggesting an activation of cyclo-oxygenase by HPETEs. It was not receptor-mediated because the 12-HPETE-induced enhancement of AA metabolism was sustained in the presence of SQ29, 548 or RGDS, which blocked the aggregation. These results indicate that physiologically relevant concentrations of HPETEs potentiate platelet aggregation, which appears to be mediated via a stimulation of cyclo-oxygenase activity.