Inhibition by lipoxygenase products of TXA2-like responses of platelets and vascular smooth muscle. 14-Hydroxy from 22:6n-3 is more potent than 12-HETE

Omega-3 pleiad: The multipoint anti-inflammatory strategy

Omega 3 (ω3) fatty acids have been described since the 1980s as promising anti-inflammatory substances. Prostaglandin and leukotriene modulation were exhaustively explored as the main reason for ω3 beneficial outcomes. However, during the early 2000s, after the human genome decoding advent, the nutrigenomic approaches exhibited an impressive plethora of ω3 targets, now under the molecular point of view. Different G protein-coupled receptors (GPCRs) recognizing ω3 and its derivatives appear to be responsible for blocking inflammation and insulin-sensitizing effects. A new class of ω3-derived substances, such as maresins, resolvins, and protectins, increases ω3 actions. Inflammasome disruption, the presence of GPR120 on immune cell surfaces, and intracellular crosstalk signaling mediated by PPARγ compose the last discoveries regarding the multipoint anti-inflammatory targets for this nutrient. This review shows a detailed mechanistic proposal to understand ω3 fatty acid action over the inflammatory environment in the background of several chronic diseases.

Specialized Pro-Resolving Lipid Mediators in Neonatal Cardiovascular Physiology and Diseases

Cardiovascular disease remains a leading cause of mortality worldwide. Unresolved inflammation plays a critical role in cardiovascular diseases development. Specialized Pro-Resolving Mediators (SPMs), derived from long chain polyunsaturated fatty acids (LCPUFAs), enhances the host defense, by resolving the inflammation and tissue repair. In addition, SPMs also have anti-inflammatory properties. These physiological effects depend on the availability of LCPUFAs precursors and cellular metabolic balance. Most of the studies have focused on the impact of SPMs in adult cardiovascular health and diseases. In this review, we discuss LCPUFAs metabolism, SPMs, and their potential effect on cardiovascular health and diseases primarily focusing in neonates. A better understanding of the role of these SPMs in cardiovascular health and diseases in neonates could lead to the development of novel therapeutic approaches in cardiovascular dysfunction.

Different Influences of trans Fatty Acids on the Phospholipase A2 and Arachidonic Acid Metabolic Pathway in Hepatocytes

This study investigated the effects of 9t18:1 (representing I-TFAs), 9t16:1, and 11t18:1 (representing R-TFAs) and their mixtures on the normal human hepatocyte LO2 cell function, the possible mechanism of lipid metabolism by lipidomics, and the relationship between phospholipase A2 (PLA2) and the arachidonic acid (AA) metabolic pathway. Here, we found that the damaging effect of 9t18:1 on the LO2 cell function was significantly greater than those of 11t18:1 and 9t16:1 (p < 0.05), and the damaging effects of CHB and HSO were significantly greater than those of HHB and CM (p < 0.05). The lipidomic results showed that TFAs and TFA mixtures caused a significant change in the lipid profiles of LO2 cells, in which the TAG, PL, and OL contents increased significantly. Moreover, 9t18:1 regulated only the protein expression of cPLA2 but did not participate in the AA metabolic pathway, while 11t18:1 and 9t16:1 participated in the COX-2 and CYP450 pathways, respectively.

DHA 12-LOX-derived oxylipins regulate platelet activation and thrombus formation through a PKA-dependent signaling pathway

BACKGROUND

The effects of docosahexaenoic acid (DHA) on cardiovascular disease are controversial and a mechanistic understanding of how this omega-3 polyunsaturated fatty acid (ω-3 PUFA) regulates platelet reactivity and the subsequent risk of a thrombotic event is warranted. In platelets, DHA is oxidized by 12-lipoxygenase (12-LOX) producing the oxidized lipids (oxylipins) 11-HDHA and 14-HDHA. We hypothesized that 12-LOX DHA-oxylipins may be involved in the beneficial effects observed in dietary supplemental treatment with ω-3 PUFAs or DHA itself.

OBJECTIVES

To determine the effects of DHA, 11-HDHA, and 14-HDHA on platelet function and thrombus formation, and to elucidate the mechanism by which these ω-3 PUFAs regulate platelet activation.

METHODS AND RESULTS

DHA, 11-HDHA, and 14-HDHA attenuated collagen-induced human platelet aggregation, but only the oxylipins inhibited ⍺IIbβ3 activation and decreased ⍺-granule secretion. Furthermore, treatment of whole blood with DHA and its oxylipins impaired platelet adhesion and accumulation to a collagen-coated surface. Interestingly, thrombus formation was only diminished in mice treated with 11-HDHA or 14-HDHA, and mouse platelet activation was inhibited following acute treatment with these oxylipins or chronic treatment with DHA, suggesting that under physiologic conditions, the effects of DHA are mediated through its oxylipins. Finally, the protective mechanism of DHA oxylipins was shown to be mediated via activation of protein kinase A.

CONCLUSIONS

This study provides the first mechanistic evidence of how DHA and its 12-LOX oxylipins inhibit platelet activity and thrombus formation. These findings support the beneficial effects of DHA as therapeutic intervention in atherothrombotic diseases.

Profiling the eicosanoid networks that underlie the anti- and pro-thrombotic effects of aspirin

Aspirin prevents thrombosis by inhibiting platelet cyclooxygenase (COX)-1 activity and the production of thromboxane (Tx)A₂, a pro-thrombotic eicosanoid. However, the non-platelet actions of aspirin limit its antithrombotic effects. Here, we used platelet-COX-1-ko mice to define the platelet and non-platelet eicosanoids affected by aspirin. Mass-spectrometry analysis demonstrated blood from platelet-COX-1-ko and global-COX-1-ko mice produced similar eicosanoid profiles in vitro: for example, formation of TxA₂, prostaglandin (PG) F_2α, 11-hydroxyeicosatraenoic acid (HETE), and 15-HETE was absent in both platelet- and global-COX-1-ko mice. Conversely, in vivo, platelet-COX-1-ko mice had a distinctly different profile from global-COX-1-ko or aspirin-treated control mice, notably significantly higher levels of PGI₂ metabolite. Ingenuity Pathway Analysis (IPA) predicted that platelet-COX-1-ko mice would be protected from thrombosis, forming less pro-thrombotic TxA₂ and PGE₂. Conversely, aspirin or lack of systemic COX-1 activity decreased the synthesis of anti-aggregatory PGI₂ and PGD₂ at non-platelet sites leading to predicted thrombosis increase. In vitro and in vivo thrombosis studies proved these predictions. Overall, we have established the eicosanoid profiles linked to inhibition of COX-1 in platelets and in the remainder of the cardiovascular system and linked them to anti- and pro-thrombotic effects of aspirin. These results explain why increasing aspirin dosage or aspirin addition to other drugs may lessen antithrombotic protection.

Muscle Loss Associated Changes of Oxylipin Signatures During Biological Aging: An Exploratory Study From the PROOF Cohort

Characterizations of the multiple mechanisms determining biological aging are required to better understand the etiology and identify early biomarkers of sarcopenia. Oxylipins refer to a large family of signaling lipids involved in the regulation of various biological processes that become dysregulated during aging. To investigate whether comprehensive oxylipin profiling could provide an integrated and fine characterization of the early phases of sarcopenia, we performed a quantitative targeted metabolomics of oxylipins in plasma of 81-year-old subjects from the PROOF cohort with decreased (n = 12), stable (n = 16), or increased appendicular muscle mass (n = 14). Multivariate and univariate analyses identified significant and concordant changes of oxylipin profiles according to the muscle status. Of note, 90% of the most discriminant oxylipins were derived from EPA and DHA and were increased in the sarcopenic subjects. The oxylipins signatures of sarcopenic subjects revealed subtle activation of inflammatory resolution pathways, coagulation processes, and oxidative stress as well as the inhibition of angiogenesis. Heat maps highlighted relationships between oxylipins and the cardiometabolic health parameters which were mainly lost in sarcopenic subjects. This exploratory study supports that targeted metabolomics of oxylipins could provide relevant and subtle characterization of early disturbances associated with muscle loss during aging.

Oxylipin Profiling of Alzheimer's Disease in Nondiabetic and Type 2 Diabetic Elderly

Oxygenated lipids, called “oxylipins,” serve a variety of important signaling roles within the cell. Oxylipins have been linked to inflammation and vascular function, and blood patterns have been shown to differ in type 2 diabetes (T2D). Because these factors (inflammation, vascular function, diabetes) are also associated with Alzheimer’s disease (AD) risk, we set out to characterize the serum oxylipin profile in elderly and AD subjects to understand if there are shared patterns between AD and T2D. We obtained serum from 126 well-characterized, overnight-fasted elderly individuals who underwent a stringent cognitive evaluation and were determined to be cognitively healthy or AD. Because the oxylipin profile may also be influenced by T2D, we assessed nondiabetic and T2D subjects separately. Within nondiabetic individuals, cognitively healthy subjects had higher levels of the nitrolipid 10-nitrooleate (16.8% higher) compared to AD subjects. AD subjects had higher levels of all four dihydroxyeicosatrienoic acid (DiHETrE) species: 14,15-DiHETrE (18% higher), 11,12 DiHETrE (18% higher), 8,9-DiHETrE (23% higher), and 5,6-DiHETrE (15% higher). Within T2D participants, we observed elevations in 14,15-dihydroxyeicosa-5,8,11-trienoic acid (14,15-DiHETE; 66% higher), 17,18-dihydroxyeicosa-5,8,11,14-tetraenoic acid (17,18-DiHETE; 29% higher) and 17-hydroxy-4,7,10,13,15,19-docosahexaenoic acid (17-HDoHE; 105% higher) and summed fatty acid diols (85% higher) in subjects with AD compared to cognitively healthy elderly, with no differences in the DiHETrE species between groups. Although these effects were no longer significant following stringent adjustment for multiple comparisons, the consistent effects on groups of molecules with similar physiological roles, as well as clear differences in the AD-related profiles within nondiabetic and T2D individuals, warrant further research into these molecules in the context of AD.

In vitro and in vivo bimodal effects of docosahexaenoic acid supplements on redox status and platelet function

Docosahexaenoic acid (DHA) is a prominent nutrient of marine lipids. Together with eicosapentaenoic acid, it is recognized as a protective molecule against atherosclerosis and thrombosis through the regulation of blood cell functions, especially platelets. Its high unsaturation index may however make it prone to peroxidation, which is usually considered as deleterious. This short review takes into consideration this possibility related to DHA concentrations both in vitro and in vivo. It is suggested that protective effects of DHA on platelet activation depend on the reduction of oxidative stress, and appear bimodal with the abolishment of such a protection when DHA is used at relatively high concentrations.

Eicosanoids in platelets and the effect of their modulation by aspirin in the cardiovascular system (and beyond)

Platelets are important players in thrombosis and haemostasis with their function being modulated by mediators in the blood and the vascular wall. Among these, eicosanoids can both stimulate and inhibit platelet reactivity. Platelet Cyclooxygenase (COX)-1-generated Thromboxane (TX)A₂ is the primary prostanoid that stimulates platelet aggregation; its action is counter-balanced by prostacyclin, a product of vascular COX. Prostaglandin (PG)D₂ , PGE₂ and 12-hydroxyeicosatraenoic acid (HETE), or 15-HETE, are other prostanoid modulators of platelet activity, but some also play a role in carcinogenesis. Aspirin permanently inhibits platelet COX-1, underlying its anti-thrombotic and anti-cancer action. While the use of aspirin as an anti-cancer drug is increasingly encouraged, its continued use in addition to P₂ Y₁₂ receptor antagonists for the treatment of cardiovascular diseases is currently debated. Aspirin not only suppresses TXA₂ but also prevents the synthesis of both known and unknown antiplatelet eicosanoid pathways, potentially lessening the efficacy of dual antiplatelet therapies. LINKED ARTICLES: This article is part of a themed section on Eicosanoids 35 years from the 1982 Nobel: where are we now? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.8/issuetoc.

Oxygenation of polyunsaturated fatty acids and oxidative stress within blood platelets

The oxygenation metabolism of arachidonic acid (ArA) has been early described in blood platelets, in particular with its conversion into the potent labile thromboxane A₂ that induces platelet aggregation and vascular smooth muscle cells contraction. In addition, the primary prostaglandins D₂ and E₂ have been mainly reported as inhibitors of platelet function. The platelet 12-lipoxygenase (12-LOX) product, i.e. the hydroperoxide 12-HpETE, appears to stimulate platelet ArA metabolism at the level of its release from membrane phospholipids through phospholipase A₂ (cPLA₂) and cyclooxygenase (COX-1) activities, the first enzymes in prostanoid production cascade. Also, 12-HpETE may regulate the oxygenation of other polyunsaturated fatty acids (PUFA) by platelets, especially that of eicosapentaenoic acid (EPA). On the other hand, the reduced product of 12-HpETE, 12-HETE, is able to antagonize TxA₂ action. This is even more obvious for the 12-LOX end-products from docosahexaenoic acid (DHA), 11- and 14-HDoHE. In addition, 12-HpETE plays a key role in platelet oxidative stress as observed in pathophysiological conditions, but may be regulated by DHA with a bimodal way according to its concentration. Other oxygenated products of PUFA, especially omega-3 PUFA, produced outside platelets may affect platelet functions as well.

Dietary modulation of oxylipins in cardiovascular disease and aging

Oxylipins are a group of fatty acid metabolites generated via oxygenation of polyunsaturated fatty acids and are involved in processes such as inflammation, immunity, pain, vascular tone, and coagulation. As a result, oxylipins have been implicated in many conditions characterized by these processes, including cardiovascular disease and aging. The best characterized oxylipins in relation to cardiovascular disease are derived from the ω-6 fatty acid arachidonic acid. These oxylipins generally increase inflammation, hypertension, and platelet aggregation, although not universally. Similarly, oxylipins derived from the ω-6 fatty acid linoleic acid generally have more adverse than beneficial cardiovascular effects. Alternatively, most oxylipins derived from 20- and 22-carbon ω-3 fatty acids have anti-inflammatory, antiaggregatory, and vasodilatory effects that help explain the cardioprotective effects of these fatty acids. Much less is known regarding the oxylipins derived from the 18-carbon ω-3 fatty acid α-linolenic acid, but clinical trials with flaxseed supplementation have indicated that these oxylipins can have positive effects on blood pressure. Normal aging also is associated with changes in oxylipin levels in the brain, vasculature, and other tissues, indicating that oxylipin changes with aging may be involved in age-related changes in these tissues. A small number of trials in humans and animals with interventions that contain either 18-carbon or 20- and 22-carbon ω-3 fatty acids have indicated that dietary-induced changes in oxylipins may be beneficial in slowing the changes associated with normal aging. In summary, oxylipins are an important group of molecules amenable to dietary manipulation to target cardiovascular disease and age-related degeneration.NEW & NOTEWORTHY Oxylipins are an important group of fatty acid metabolites amenable to dietary manipulation. Because of the role they play in cardiovascular disease and in age-related degeneration, oxylipins are gaining recognition as viable targets for specific dietary interventions focused on manipulating oxylipin composition to control these biological processes.

In vitro and in vivo bimodal effects of docosahexaenoic acid supplements on redox status and platelet function

Docosahexaenoic acid (DHA) is a prominent nutrient of marine lipids. Together with eicosapentaenoic acid, it is recognized as a protective molecule against atherosclerosis and thrombosis through the regulation of blood cell functions, especially platelets. Its high unsaturation index may however make it prone to peroxidation, which is usually considered as deleterious. This short review takes into consideration this possibility related to DHA concentrations both in vitro and in vivo. It is suggested that protective effects of DHA on platelet activation depend on the reduction of oxidative stress, and appear bimodal with the abolishment of such a protection when DHA is used at relatively high concentrations.

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.

Advances in Our Understanding of Oxylipins Derived from Dietary PUFAs

Oxylipins formed from polyunsaturated fatty acids (PUFAs) are the main mediators of PUFA effects in the body. They are formed via cyclooxygenase, lipoxygenase, and cytochrome P450 pathways, resulting in the formation of prostaglandins, thromboxanes, mono-, di-, and tri-hydroxy fatty acids (FAs), epoxy FAs, lipoxins, eoxins, hepoxilins, resolvins, protectins (also called neuroprotectins in the brain), and maresins. In addition to the well-known eicosanoids derived from arachidonic acid, recent developments in lipidomic methodologies have raised awareness of and interest in the large number of oxylipins formed from other PUFAs, including those from the essential FAs and the longer-chain n-3 (ω-3) PUFAs. Oxylipins have essential roles in normal physiology and function, but can also have detrimental effects. Compared with the oxylipins derived from n-3 PUFAs, oxylipins from n-6 PUFAs generally have greater activity and more inflammatory, vasoconstrictory, and proliferative effects, although there are notable exceptions. Because PUFA composition does not necessarily reflect oxylipin composition, comprehensive analysis of the oxylipin profile is necessary to understand the overall physiologic effects of PUFAs mediated through their oxylipins. These analyses should include oxylipins derived from linoleic and α-linolenic acids, because these largely unexplored bioactive oxylipins constitute more than one-half of oxylipins present in tissues. Because collated information on oxylipins formed from different PUFAs is currently unavailable, this review provides a detailed compilation of the main oxylipins formed from PUFAs and describes their functions. Much remains to be elucidated in this emerging field, including the discovery of more oxylipins, and the understanding of the differing biological potencies, kinetics, and isomer-specific activities of these novel PUFA metabolites.

Omega-3 polyunsaturated fatty acids and oxygenated metabolism in atherothrombosis

Numerous epidemiological studies and clinical trials have reported the health benefits of omega-3 polyunsaturated fatty acids (PUFA), including a lower risk of coronary heart diseases. This review mainly focuses on the effects of alpha-linolenic (ALA), eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids on some risk factors associated with atherothrombosis, including platelet activation, plasma lipid concentrations and oxidative modification of low-density lipoproteins (LDL). Special focus is given to the effects of marine PUFA on the formation of eicosanoids and docosanoids, and to the bioactive properties of some oxygenated metabolites of omega-3 PUFA produced by cyclooxygenases and lipoxygenases. The antioxidant effects of marine omega-3 PUFA at low concentrations and the pro-oxidant effects of DHA at high concentrations on the redox status of platelets and LDL are highlighted. Non enzymatic peroxidation end-products deriving from omega-3 PUFA such as hydroxy-hexenals, neuroketals and EPA-derived isoprostanes are also considered in relation to atherosclerosis. This article is part of a Special Issue entitled "Oxygenated metabolism of PUFA: analysis and biological relevance".

Docosahexaenoic acid, protectin synthesis: relevance against atherothrombogenesis

DHA is an abundant nutrient from marine lipids: its specific biological effects have been investigated in human volunteers, taking into consideration the dose effects. We report herein that, at dosages below 1 g/d, DHA proved to be effective in lowering blood platelet function and exhibited an 'antioxidant' effect. However, this was no longer the case following 1.6 g/d, showing then a U-shape response. The antioxidant effect has been observed in platelets as well as LDL, of which the redox status is assumed to be crucial in their relationship with atherosclerosis. Second, the oxygenated products of DHA, especially protectins produced by lipoxygenases, have been considered for their potential to affect blood platelets and leucocytes. It is concluded that DHA is an interesting nutrient to reduce atherothrombogenesis, possibly through complementary mechanisms involving lipoxygenase products of DHA.

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.

Thrombin-activated human platelets acutely generate oxidized docosahexaenoic-acid-containing phospholipids via 12-lipoxygenase

Arachidonate-containing oxidized phospholipids are acutely generated by 12-LOX (12-lipoxygenase) in agonist-activated platelets. In the present study, formation of structurally related lipids by oxidation of DHA (docosahexaenoic acid)-containing phospholipids is demonstrated using lipidomic approaches. Precursor scanning reverse-phase LC (liquid chromatography)-MS/MS (tandem MS) identified a new family of lipids that comprise phospholipid-esterified HDOHE (hydroxydocosahexaenoic acid). Two diacyl and two plasmalogen PEs (phosphatidylethanolamines) containing predominantly the 14-HDOHE positional isomer (18:0p/14-HDOHE-PE, 18:0a/14-HDOHE-PE, 16:0a/14-HDOHE-PE and 16:0p/14-HDOHE-PE) were structurally characterized using MS/MS and by comparison with biogenic standards. An involvement of 12-LOX was indicated as purified recombinant human 12-LOX also generated the 14-HDOHE isomer from DHA. Pharmacological studies using inhibitors and recombinant platelet 12-LOX indicate that they form via esterification of newly formed non-esterified HDOHE. HDOHE-PEs formed at significant rates (2-4 ng/4×10(7) cells) within 2-180 min of thrombin stimulation, and their formation was blocked by calcium chelation. In summary, a new family of oxidized phospholipid was identified in thrombin-activated human platelets.

Poxytrins, a class of oxygenated products from polyunsaturated fatty acids, potently inhibit blood platelet aggregation

Docosahexaenoic acid (DHA), an important component of marine lipids, exhibits anti-inflammatory activity related to some of its oxygenated metabolites, such as neuroprotectin/protectin D1 [NPD1/PD1; 10(R),17(S)-dihydroxy-docosa-4Z,7Z, 11E,13E,15Z,19Z-hexaenoic acid] produced through the 15-lipoxygenase pathway. However, other metabolites from DHA can be produced through this pathway, and other polyunsaturated fatty acids (PUFAs) of nutritional value may be oxygenated as well. Their biological activities remain unknown. Isomers of protectin D1 were synthesized using soybean lipoxygenase and tested for their ability to inhibit human blood platelet aggregation. A geometric isomer called PDX, previously described with the 11E,13Z,15E geometry, instead of 11E,13E,15Z in PD1, inhibited platelet aggregation at submicromolar concentrations when induced by either collagen, arachidonic acid, or thromboxane. The inhibition occurred at the level of both the cyclooxygenase activity and thromboxane receptor site. Interestingly, all the metabolites tested exhibiting the E,Z,E-conjugated triene were active, whereas E,E,Z trienes (as in PD1) or all-trans (E,E,E) trienes were inactive. We conclude that PDX and other oxygenated products from PUFAs of nutritional interest, having the E,Z,E-conjugated triene motif and collectively named poxytrins (PUFA oxygenated trienes), might have antithrombotic potential.

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.

Gender-specific fatty acid profiles in platelet phosphatidyl-choline and -ethanolamine

Previous studies suggested that women synthesise docosahexaenoic acid (DHA) more efficiently from their precursors than men. This study investigated the relationship between diet, platelet phospholipids fatty acids and gender. Dietary intake and platelet phosphatidyl-choline (PC) and phosphatidylethanolamine (PE) fatty acids were determined in Caucasian 40 men and 34 women. Absolute and %energy intakes of arachidonic acid (AA), eicosapentaenoic acid (EPA), and DHA, and the ratios of total n-6/n-3 PUFA and linoleic/alpha-linolenic acids did not differ between the sexes. However, women had higher DHA in PC (1.19 vs 1.05 wt%, p<0.05) and PE (3.62 vs 3.21 wt%, p<0.05) than men. Also EPA (1.10 vs 0.93 wt%, p<0.05) was higher in women's PE. Conversely, men had elevated AA and total n-6 fatty acids in PC. The higher platelet DHA levels and lower platelet AA/EPA and AA/DHA ratios in women of child-bearing age compared with men, may lead to less platelet aggregation and vaso-occlusion.

n-3 polyunsaturated fatty acids and coronary thrombosis

Studies of Greenland Eskimos showed that a very high intake of marine n-3 fatty acids markedly inhibited platelet reactivity and suggested that intake of these fatty acids might prevent coronary thrombosis. Later studies with lower, more practical doses of n-3 fatty acids also have shown a platelet inhibitory effect of n-3 fatty acids, albeit fairly marginal. Furthermore, n-3 fatty acids have little effect on measures of blood coagulability and may slightly decrease fibrinolysis. In animal models, n-3 fatty acids often have been shown to inhibit thrombosis, but again the doses have tended to be very high. Finally, there has been little effect of (low-dose) n-3 fatty acids in clinical trials in humans on the incidence of myocardial infarction. Overall, there is little evidence for a major antithrombotic effect of practical doses of n-3 fatty acids on coronary thrombosis. This does not exclude a beneficial effect of n-3 fatty acids on coronary heart disease as suggested from clinical trials, but the major effect may be antiarrhythmic rather than antithrombotic.

The influence of fish, meat and polyunsaturated fat intakes on platelet phospholipid polyunsaturated fatty acids in male Melbourne Chinese and Caucasian

OBJECTIVE

The aims of this study were to investigate (1) platelet phospholipid (PL) polyunsaturated fatty acid (PUFA) composition in subjects who were the Melbourne Chinese migrants, compared with those who were the Melbourne Caucasians and (2) the relationship between platelet PL PUFA and intake of fish, meat and PUFA.

DESIGN

Cross-sectional comparison of the Melbourne Chinese and Caucasians.

SETTING

Free-living male subjects.

SUBJECTS

Ninety-seven Melbourne Chinese migrants and 78 Melbourne Caucasians who were recruited in Melbourne.

OUTCOME MEASURES

Dietary intake was assessed using a semi-quantitative food frequency questionnaire. The platelet PUFA was measured by gas-liquid chromatography.

RESULTS

The Melbourne Chinese had significantly higher proportions of platelet PL 20:5n-3 (P=0.006), 22:6n-3 (P<0.0001), total n-3 (P=0.027) and 22:5n-6 (P=0.0002), and a significantly higher intake of fish (P=0.012) and white meat (P=0.0045) compared with the Melbourne Caucasians. In addition, the Melbourne Chinese had significantly lower proportions of 20:3n-6 (P=0.023), 20:4n-6 (P<0.002), 22:4n-6 (P<0.0001), total n-6 (P=0.037), 22:5n-3 (P<0.0001) and ratio of n-6/n-3 (P=0.011), and a significantly lower intake of red and total meat (P<0.0001) than the Melbourne Caucasians. Fish consumption was significantly positively correlated with platelet PL 20:5n-3 and 22:6n-3, and significantly negatively correlated with 22:5n-3 (P<0.05). Meat consumption was significantly positively correlated with 22:5n-3 and significantly negatively correlated with 22:5n-6, 20:5n-3 and 22:6n-3 (P<0.05). Dietary PUFA intake was significantly positively correlated with 20:3n-6, 22:4n-6 and 22:5n-3, and significantly negatively correlated with 22:5n-6, 20:5n-3 and 22:6n-3 (P<0.05).

CONCLUSIONS

Compared with Caucasians, the Melbourne Chinese had a significantly higher level of platelet PL n-3 PUFA, which might contribute to the low CVD mortality in this population. Platelet PL 20:5n-3 and 22:6n-3 were significantly positively correlated with fish intake, and negatively significantly correlated with dietary intake of meat and PUFA, while 22:5n-3 was significantly positively correlated with dietary meat and PUFA intake, and significantly negatively correlated with fish intake. Dietary intake of PUFA and fish are potential confounding factors for assessing the effects of meat consumption on platelet PL individual PUFA. Dietary intake of PUFA and meat did not influence the incorporation of fish long chain n-3 PUFA to platelet PL in this study population.

SPONSORSHIP

Palm Oil Research Institute of Malaysia, Meat Research Corporation Australia.

The structure-activity relationship of lipoxygenase products of long-chain polyunsaturated fatty acids: effects on human platelet aggregation

The effect of hydroperoxy and hydroxy derivatives of various fatty acids on human platelet aggregation was determined to delineate potencies and structure-activity function. In this regard, the 22-carbon n-3 fatty acids are the most potent inhibitors in comparison to the n-6 lipoxygenase derivatives. Submicromolar levels of the docosapentaenoic (22:5) and especially docosahexaenoic (22:6) n-3 hydroperoxy and hydroxy derivatives specifically antagonize the platelet aggregating effect to arachidonic acid (AA, 20:4n-6) but not that of ADP or collagen. Chain length (22-C > 20-C), double-bond position (n-3 > n-6), and double-bond number (6 > 5 > 4) influence the degree of inhibition of AA-induced aggregation of human platelets. Moreover, significant differences in potency were associated with specific structural aspects of 22:6n-3 lipoxygenase derivatives of 22:6n-3 as follows: functional group (OOH > OH) and positional isomer (14-OOH, 14-OH, 20-OOH > 11-OOH, 17-OOH > 10-OOH > 11-OH, 8-OOH, 7-OOH > 4-OOH).

Dietary n - 3 polyunsaturated fatty acids modify Syrian hamster platelet and macrophage phospholipid fatty acyl composition and eicosanoid synthesis: a controlled study

The aim of this study was to determine the effects of varying intakes of dietary n - 3 polyunsaturated fatty acids (PUFA) on the fatty acyl composition and arachidonic acid metabolite synthesis of platelets and macrophages in Syrian hamsters consuming diets that were strictly controlled for n - 6 PUFA content. Animals consumed highly controlled diets which were not supplemented with n - 3 PUFA (control) or supplemented with 0.4%, 0.8% or 2% (w/w) n - 3 fatty acids. The content of n - 3 PUFA in cellular phospholipids increased progressively with the intake of n - 3 PUFA, while n - 6 PUFA, including arachidonic acid, decreased despite the constant intake of 18:2(n - 6); this latter effect was more substantial in macrophages than in platelets. The synthesis by stimulated macrophages of prostaglandin E2, 6-keto-prostaglandin F1 alpha, thromboxane B2 and 11- and 15-hydroxyeicosatetraenoic acids decreased with the intake of 0.8% n - 3 PUFA to 30-50% of the control values. Little effect of diets on platelet aggregation and eicosanoid synthesis was observed reflecting the limited effect on platelet arachidonic acid content. The synthesis of 12-hydroxyeicosapentaenoic acid by stimulated platelets increased with n - 3 PUFA consumption in a dose-dependent fashion. Circulating triacylglycerols and HDL-cholesterol were decreased only in animals consuming 2% n - 3 PUFA. The strict control of n - 6 PUFA intake allows the determination of the effects of n - 3 PUFA intake on the measured parameters without confounding effects of other dietary lipids.

Distribution and metabolism of arachidonic and docosahexaenoic acids in rat pineal cells. Effect of norepinephrine

The time-course incorporation of 10 microM [14C]arachidonic (AA) and docosahexaenoic (DHA) acids into glycerolipids was studied in rat pineal cells. The incorporation of both labeled fatty acids into total lipids was approximately equal, but their distribution profiles among the various cell lipids showed marked differences. The esterification of [14C]DHA in the neutral lipids, triacylglycerols (TAG) and cholesterol esters (CE), was 2-fold higher than that of [14C]AA whereas the opposite could be observed in total phospholipids (PL). The order of incorporation into PL was phosphatidylcholine (PC) > phosphatidylinositol (PI) = phosphatidylethanolamine (PE) for [14C]AA and PC = PE for [14C]DHA, the incorporation of both fatty acids being not detected in phosphatidylserine (PS) and that of DHA not in PI. When using 0.5 microM [3H] fatty acids, the respective distribution patterns resembled that of fatty acids at 10 microM, except for a lower proportion in TAG. The stimulation of 3H-labeled cells by 100 microM norepinephrine induced a 170% increase of basal release of [3H]AA into the medium, while [3H]DHA was virtually not released. However, the analysis of cell labeling revealed that both [3H] fatty acid levels were decreased in PL and increased in TAG. These findings suggest different involvement for AA and DHA in the pineal function. The preferential incorporation of DHA in TAG suggests that TAG might play an important role in the pineal enrichment with DHA. The absence of DHA release after NE stimulation, which however cannot be ascertained, may raise the question of the role of DHA in NE transduction.

Inhibition by n-3 fatty acids of arachidonic acid metabolism in a primary culture of astroglial cells

Docosahexaenoic acid (22:6 n-3) was present in low concentrations in a primary culture of rat brain astroglial cells, when compared to brain cortex. We have thus supplemented these cells with this fatty acid and investigated the effects of its incorporation in cell phospholipids on the conversion of arachidonic acid, 20:4 n-6, through the cyclo and lipoxygenase pathways, after cell stimulation. Docosahexaenoic acid-enriched cells produced less thromboxane B2 and 6-keto-Prostaglandin F1 alpha and markedly less 12-hydroxyeicosatetraenoic acid than unsupplemented cells, after stimulation with the Ca(2+)-ionophore A23187. The production of 15-hydroxyeicosatetraenoic acid from arachidonic acid was slightly increased in docosahexaenoic acid-supplemented cells. We have also supplemented these cells with eicosapentaenoic acid (20:5 n-3) and, in addition to accumulation of this fatty acid in cell phospholipids, we found elevation of 22:5 n-3 and some increment of 22:6, confirming that glial cells are able to convert eicosapentaenoic acid to the long chain, more unsaturated derivatives. In conclusion, n-3 fatty acids, when supplemented to glial cells, appear to modulate the arachidonic acid cascade and to be converted through the elongation and desaturation pathways.

Oestradiol-induced changes in the composition of phospholipid classes of quail oviduct: specific replacement of arachidonic acid by docosahexaenoic acid in alkenylacyl-glycerophosphoethanolamine

The phospholipid composition and the molecular species of the major subclasses of ethanolamine and choline glycerophospholipids were determined during the natural or oestradiol-induced development of the quail oviduct. The phospholipid concentration increased significantly during oviduct development, and the proportion of ethanolamine glycerophospholipids (EPL) remained constant while that of choline glycerophospholipids increased. The immature oviduct contained the majority of its endogenous arachidonic acid mass (71%) in EPL, mainly in alkenylacyl-glycerophosphoethanolamine (alkenylacyl-GPE) (49% of the total). Oestrogen treatment induced the depletion of 20:4,n-6 specifically from this pool, which indicates the biological importance of 20:4,n-6 molecular species in alkenylacyl-GPE as substrates for the oviduct phospholipases activated by oestradiol, and suggests that this EPL subclass is involved in the oestrogen-induced cell proliferation. Another striking result was the marked increase in 22:6,n-3 EPL molecular species following the oestradiol treatment and more particularly the strict substitution of 20:4,n-6 by 22:6,n-3 in alkenylacyl-GPE. We speculate that alkenylacyl-GPE molecular species containing 22:6,n-3 may participate in the arrest of oestrogen-induced proliferation.

Lipoxygenase stimulating effects of hydroxylated docosahexaenoates produced by human platelets

Human platelet suspensions are capable of lipoxygenating docosahexaenoic acid (22:6n3) to an 11(S)-OH-, 14(S)-OH- or 17(S)-OH-22:6n3. The structure and stereochemical purity of these derivatives were confirmed by GC/MS and chiral phase LC analysis. The purified OH-22:6n3 positional isomers which are formed by human platelets were capable of inducing a concentration-dependent contractile response in the guinea-pig lung parenchymal strip at sub-micromolar concentrations. OH-22:6n3 may act in part through stimulation of leukotriene (LT) production as an increase in peptidyl-LT levels (LTC4, LTD4 and LTE4) occurred during the OH-22:6n3-induced contraction in this preparation. Both specific lipoxygenase inhibitors (caffeic acid, 20 uM and NDGA, 50 uM) and a LT receptor antagonist (FPL55712, 20 uM) significantly inhibited the contractile response. Moreover, the OH-22:6n3 positional isomers induced a concentration-dependent increase in LTB4 and LTC4 production in the guinea-pig chopped lung preparation. Other hydroxylated fatty acids and parent fatty acids which were tested (12-OH-20:4n6, 5-OH-20:4n6, 12-OH-20:5n3, 20:5n3 and 22:6n3) did not significantly contract this airway smooth muscle preparation or alter LT production. The hydroxylated 22:6n3 metabolites may modulate airway smooth muscle function in part through the release of peptidyl-LTs from the guinea-pig lung.

Vascular relaxation to omega-3 fatty acids: comparison to sodium nitroprusside, nitroglycerin, papaverine, and D600

The vasorelaxant activity of the omega-3 fatty acids--docosahexaenoic (DHA) and eicosapentaenoic (EPA) acids--in comparison with other known vasodilators--sodium nitroprusside, nitroglycerin, papaverine, and D600--were studied in the isolated rat aorta. The relaxant responses of these vasodilators and fatty acids at concentrations of 1-100 microM were assessed in aortic rings contracted with norepinephrine (NE 10(-6) M) or with KCl (30 mM). Cyclic nucleotide enhancers (sodium nitroprusside, nitroglycerin, papaverine) were more effective in producing relaxation, regardless of the contractile mechanism, i.e., alpha-adrenoceptor stimulation or depolarization. In contrast, the omega-3 fatty acids produced augmented relaxation in NE-contracted vessels. Relaxations produced by DHA (15 +/- 2% to 45 +/- 10%) were similar to D600 (16 +/- 2% to 60 +/- 7%) in NE-contracted rings, but not in KCl contracted rings. The responses to D600 and DHA in KCl-contracted vessels were 79 +/- 2% to 104 +/- 3% and 5 +/- 1% to 21 +/- 3%, respectively. In another set of experiments, the effects of omega-3 fatty acids in the presence of albumin were examined; no significant differences in the induced relaxant responses were noted. These results suggest that the mechanisms of vascular relaxation, such as cyclic nucleotide elevation and calcium antagonism of potential-operated channels, are different from those induced by the omega-3 fatty acids.

12-HETE inhibits the binding of PGH2/TXA2 receptor ligands in human platelets

12(S)-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE), the end-lipoxygenase product of arachidonic acid in platelets has been previously shown to prevent PGH2/TxA2-induced aggregation. From the present study, we show that 12-HETE inhibits the binding of [125I]-PTA-OH, a thromboxane antagonist, to platelet membranes with an IC50 of 8 microM. This value is in accordance with previously reported 12-HETE concentrations required to prevent the aggregation induced by TxA2 mimetics, the methano analogues of PGH2, U44069 and U46619. When [3H]-U44069 was used as a thromboxane agonist to label intact platelets, 12-HETE also inhibited its binding. We conclude that part of the inhibitory effect of 12-HETE on PGH2/TxA2-induced aggregation might be the result of interacting with PGH2/TxA2 receptor sites.

Stereochemical analysis of hydroxylated docosahexaenoates produced by human platelets and rat brain homogenate

The stereochemical configuration of hydroxylated products of docosahexaenoic acid (22:6w3) formed by human platelets and rat brain homogenate were characterized for the first time. Chiral phase HPLC was employed along with autooxidized 22:6w3 as reference material. The 14- and 11-hydroxy 22:6w3 (HDHE) products produced by human platelets were in the S configuration. Rat brain homogenate produced all of the ten possible positional isomers when incubated with 22:6w3. Their retention behavior on the reversed and chiral phase HPLC columns and GC/MS/EI analysis indicated that they were 20-, 17-, 16-, 14-, 13-, 11-, 10-, 8-, 7- and 4-HDHE. However, stereochemical analysis revealed that each positional isomer was a racemic mixture, suggesting that these were not formed by lipoxygenation but mainly by peroxidation process.

Formation of 15-lipoxygenase product from docosahexaenoic acid (22:6w3) by human platelets

The metabolism of docosahexaenoic acid (22:6w3) by 15-lipoxygenase activity of washed human platelets was investigated. Platelets produced 17-hydroxydocosahexaenoic acid (HDHE) when incubated with 22:6w3. Similarly, 15-hydroxyeicosatetraenoic acid (HETE) and 13- and 9-hydroxyoctadecadienoic acids (HODD) were produced when incubated with 20:4w6 and 18:2w6, respectively. However, these products were observed only as minor components in the platelet incubation mixture. Control studies with carefully purified platelets and mononuclear cells indicated that these products were formed by the platelets. Chiral phase HPLC analysis indicated that these compounds were mainly in the S configuration with the exception of the 9-HODD, thus, confirming that a lipoxygenase is responsible for their production. The 9-HODD produced by platelets was a racemic mixture.

Influence of dietary fish on eicosanoid metabolism in man

Two groups of 40 volunteers were given a dietary supplement consisting of 135 g of mackerel or meat (control) paste per day for 6 weeks. Compliance was about 80% in both groups and the daily intake of 20:5(n-3) and 22:6(n-3) from the mackerel supplement was about 1.3 and 2.3 g, respectively. In collagen-activated platelet rich plasma, the potency of blood platelet to produce HHT from arachidonic acid (AA) clearly reduced in the mackerel group, whereas the formation of HHTE from timnodonic acid (TA) increased slightly. Changes in the formation of HHT and HHTE, measured by HPLC, correlated significantly with those of TxB2 and TxB3, respectively, measured by GC/MS. Changes in the formation of the lipoxygenase products HETE (ex AA) and HEPE (ex TA) were qualitatively similar to that seen for the cyclo-oxygenase products, but quantitatively the responses were smaller. Formation of ir TxB2 in clotting blood significantly reduced in the mackerel group. In collagen-activated, citrated whole blood, TxB2 formation tended to be reduced in the mackerel-supplemented volunteers. Mackerel consumption was associated with the formation of considerable amounts of PGI3, as judged from the appearance of 2,3-dinor-delta 17-6-keto-PGF1 alpha in urine. The amount of the major metabolite of PGI2, 2,3-dinor-6-keto-PGF1 alpha was not reduced, or even increased. The daily amount of tetranor prostaglandin metabolites in the urine did not change significantly, which indicates that mackerel supplementation did not alter the formation of prostaglandins E and F.

Albumin-bound docosahexaenoic acid and collagen-induced human platelet reactivity

An in vitro system designed to mimic the effect of various plasma nonesterified (polyunsaturated) fatty acids on platelet function and metabolism was employed. Human platelet aggregation induced by submaximal (1.8 micrograms/ml) collagen stimulation was significantly inhibited by 2 min preincubation with 20 microM albumin-bound docosahexaenoic acid (22:6n-3) (DHA), but not by the other fatty acids tested. [3H]Phosphatidic acid (PA) formation, an indicator of phospholipase C activation following platelet stimulation, was moderately inhibited by eicosapentaenoic acid (20:5n-3), 11,14,17-eicosatrienoic acid (20:3n-3), dihomo-gamma-linolenic acid (20:3n-6), as well as DHA, but not by arachidonic acid (20:4n-6); this inhibition of phospholipase C activation could not explain the differential effect of DHA on platelet aggregation. The decreased production of thromboxane A2 (TxA2), as assessed by [3H]12-hydroxy-5,8,10-heptadecatrienoic acid (HHT) formation, may account for the inhibition of collagen-induced aggregation by 20 microM DHA. Surprisingly, preincubation with 40 microM albumin-bound DHA, even though resulting in greater inhibition of collagen-induced aggregation, had less impact on HHT formation. A small but significant increase in [3H]prostaglandin D2 (PGD2) levels following 3-min collagen stimulation may have contributed to the greater antiaggregatory effect of 40 muM DHA. It is concluded that increased plasma nonesterified DHA may contribute to the dampened platelet activation and altered metabolism following fish oil supplementation of the diet.

The effect of a fish oil diet on the fatty acid composition of individual phospholipids and eicosanoid production by rat platelets

When rats were fed a diet containing chow or fish oil for six weeks, the platelet phospholipid content and percent distribution were similar. In the fish oil fed animals there was a 54, 40, 41, and 24% reduction, respectively, in the levels of 20:4(n-6) in the choline-, ethanolamine-, inositol- and serine-containing glycerophospholipids. Dietary fish oil increased the total (n-3) polyunsaturated fatty acid content in all lipids. This effect was most pronounced in the ethanolamine glycerophospholipids which now contained 26, 11, and 4 nmols of 20:5(n-3), 22:5(n-3), and 22:6(n-3) in 10(9) cells. Ionophore A23187 stimulation of platelets from the chow fed rats resulted in the synthesis of 7, 64, and 3.5 nmols of 12-hydroxy-5,8,10-heptadecatrienoic acid, 12-hydroxy-5,8,10,14-eicosatetraenoic acid and 12-hydroxy-5,8,10,14,17-eicosapentaenoic acid, respectively, from 1 X 10(9) cells. The values from animals fed fish oil were 4, 18, and 27 nmol/10(9) platelets. It was not possible to detect any lipoxygenase products from 22:5(n-3) or 22:6(n-3), even though both acids are readily metabolized by lipoxygenase when added directly to platelets. These findings suggest that 22-carbon (n-3) fatty acids are not liberated when phospholipases are activated by calcium mobilization.