Functions and tocopherol content of blood platelets from elderly people after low intake of purified eicosapentaenoic acid

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.

Moderate intake of docosahexaenoic acid raises plasma and platelet vitamin E levels in cystic fibrosis patients

Patients with cystic fibrosis have increased oxidative stress and impaired antioxidant systems. Moderate intake of docosahexaenoic acid (DHA) may favor the lowering of oxidative stress. In this randomized, double-blind, cross-over study, DHA or placebo capsules, were given daily to 10 patients, 5mg/kg for 2 weeks then 10mg/kg DHA for the next 2 weeks (or placebo). After 9 weeks of wash-out, patients took placebo or DHA capsules. Biomarkers of lipid peroxidation and vitamin E were measured at baseline, and after 2 and 4 weeks of treatment in each phase. The proportions of DHA increased both in plasma and platelet lipids after DHA supplementations. The lipid peroxidation markers did not significantly decrease, in spite of a trend, after the first and/or the second dose of DHA but plasma and platelet vitamin E amounts increased significantly after DHA supplementation. Our findings reinforce the antioxidant potential of moderate DHA intake in subjects displaying increased oxidative stress.

Effect of Male Sex and Obesity on Platelet Arachidonic Acid in Spontaneous Hypertensive Heart Failure Rats

Sexual dimorphism is observed in the progression to congestive heart failure and, ultimately, in longevity in spontaneously hypertensive heart failure (SHHF) rats. As platelet activation may impact development of cardiovascular diseases, we studied the effects of obesity and sex on platelet polyunsaturated fatty acid (PUFA) profile and its relationship to platelet aggregation in 6-month-old SHHF rats. After a 24-hr fast, blood was obtained for measurement of platelet phospholipid omega-6 (n-6) and omega-3 (n-3) PUFA. Collagen-induced platelet aggregation was measured by whole-blood impedance aggregometry. Obese male (OM) SHHF had significantly more platelet arachidonic acid (AA) and total n-6 PUFA than lean males (LMs), lean females (LFs), or obese females (OFs). Platelet aggregation was enhanced in males compared to females, with OMs by 45% compared to OFs and with LMs by 28% compared to LFs. Though no difference was found between OFs and LFs, platelet agregation was increased in OMs by 20% compared to LMs. Though not significantly different, lag time to initiate platelet aggregation tended to be shortest in OMs and then, in Increasing duration, LMs, LFs, and OFs, suggesting that Platelets from male rats were quicker to aggregate than those from females. Platelet aggregation was correlated with platelet AA and total n-6 PUFA content. There was no relationship between n-3 PUFA and platelet aggregation. In SHHF rats, elevated AA and n-6 PUFA levels in platelets are associated with Chanced platelet aggregation. This relationship is potentiated by obesity and male sex.

Fruitflow®: the first European Food Safety Authority-approved natural cardio-protective functional ingredient

Hyperactive platelets, in addition to their roles in thrombosis, are also important mediators of atherogenesis. Antiplatelet drugs are not suitable for use where risk of a cardiovascular event is relatively low. It is therefore important to find alternative safe antiplatelet inhibitors for the vulnerable population who has hyperactive platelets in order to reduce the risk of cardiovascular disease. Potent antiplatelet factors were identified in water-soluble tomato extract (Fruitflow^®), which significantly inhibited platelet aggregation. Human volunteer studies demonstrated the potency and bioavailability of active compounds in Fruitflow^®. Fruitflow^® became the first product in Europe to obtain an approved, proprietary health claim under Article 13(5) of the European Health Claims Regulation 1924/2006 on nutrition and health claims made on foods. Fruitflow^® is now commercially available in different countries worldwide. In addition to its reduction in platelet reactivity, Fruitflow^® contains anti-angiotensin-converting enzyme and anti-inflammatory factors, making it an effective and natural cardio-protective functional food.

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.

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".

Long-chain omega-3 fatty acids eicosapentaenoic acid and docosahexaenoic acid and blood pressure: a meta-analysis of randomized controlled trials

BACKGROUND

Although a large body of literature has been devoted to examining the relationship between eicosapentaenoic and docosahexaenoic acids (EPA+DHA) and blood pressure, past systematic reviews have been hampered by narrow inclusion criteria and a limited scope of analytical subgroups. In addition, no meta-analysis to date has captured the substantial volume of randomized controlled trials (RCTs) published in the past 2 years. The objective of this meta-analysis was to examine the effect of EPA+DHA, without upper dose limits and including food sources, on blood pressure in RCTs.

METHODS

Random-effects meta-analyses were used to generate weighted group mean differences and 95% confidence intervals (CIs) between the EPA+DHA group and the placebo group. Analyses were conducted for subgroups defined by key subject or study characteristics.

RESULTS

Seventy RCTs were included. Compared with placebo, EPA+DHA provision reduced systolic blood pressure (−1.52mm Hg; 95% confidence interval (CI) = −2.25 to −0.79) and diastolic blood pressure (−0.99mm Hg; 95% CI = −1.54 to −0.44) in the meta-analyses of all studies combined. The strongest effects of EPA+DHA were observed among untreated hypertensive subjects (systolic blood pressure = −4.51mm Hg, 95% CI = −6.12 to −2.83; diastolic blood pressure = −3.05mm Hg, 95% CI = −4.35 to −1.74), although blood pressure also was lowered among normotensive subjects (systolic blood pressure = −1.25mm Hg, 95% CI = −2.05 to −0.46; diastolic blood pressure = −0.62mm Hg, 95% CI = −1.22 to −0.02).

CONCLUSIONS

Overall, available evidence from RCTs indicates that provision of EPA+DHA reduces systolic blood pressure, while provision of ≥2 grams reduces diastolic blood pressure.

Docosahexaenoic and eicosapentaenoic acid supplementation does not exacerbate oxidative stress or intravascular haemolysis in homozygous sickle cell patients

We investigated whether or not Omega-3 long-chain polyunsaturated fatty acid (omega-3 LCPUFA) supplementation exacerbates oxidative stress in homozygous sickle cell patients aged 2 to 14 years. Depending on their age, they received between one and three omega-3 (277.8mg DHA and 39.0mg EPA/capsule) or placebo (high oleic acid sunflower seed oil) capsules for one year. Supplementation increased significantly the levels of the two fatty acids in red cell phosphatidylcholine and phosphatidylethanolamine (p<0.001). The patients who received omega-3 LCPUFA compared with their placebo-taking counterparts had a higher concentration of plasma vitamin E at one year (14.3±2.8 versus 12.3±2.8µmol/l; p<0.001). The two groups had comparable concentrations of the vitamin at six month intervention (10.8±2.2 versus 10.7±2.9µmol/l; p>0.05) and baseline (10.7±3.1 versus 10.7±2.8µmol/l; p>0.05). After six month of intervention, the patients on omega 3 fatty acids had lower GPx-1 (33.5±13.4 versus 46.6 ±17.6, p<0.01) and Cu/Zn-SOD (1070±600 versus 1470±690 p<0.05) activities than at baseline. GPx-1 (33.5±17.6IU/g Hb versus 43.7±13.2IU/g Hb; p<0.01) and Cu/Zn-SOD (1070±600IU/g Hb versus 1360±920IU/g Hb; p>0.05) activities were reduced in the omega 3 compared with the placebo at six month intervention. There was no difference in the activity of either of the enzymes between baseline and six month intervention in the placebo group (p>0.05). This study demonstrates; DHA and EPA supplementation, rather than exacerbating the inherent oxidative stress associated with the disease, seems to provide an antioxidant protection. Hence, it will be safe to provide omega-3 LCPUFA to sickle cell patients to help ameliorate vaso-occlusive and haemolytic crises and membrane fatty acid abnormality.

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.

Increasing intakes of the long-chain omega-3 docosahexaenoic acid: effects on platelet functions and redox status in healthy men

Docosahexaenoic acid (DHA) can prevent cardiovascular events. However, few studies have addressed the effects of DHA on both platelet reactivity and redox status in healthy subjects, and dose-related studies are scarce. The main objectives of the present study were to determine the effects of increasing doses of DHA on platelets and redox status in humans. Twelve healthy male volunteers (aged 53-65 yr) were assigned to consume an intake of successively 200, 400, 800, and 1600 mg/d DHA, as the only omega-3 fatty acid, for 2 wk each dose. Blood and urine samples were collected before and after each dose of DHA and at 8 wk after arrest of supplementation. DHA was incorporated in a dose-response fashion in platelet phospholipids. After supplementation with 400 and 800 mg/d DHA, platelet reactivity was significantly decreased. Platelet vitamin E concentration increased only after 200 mg/d DHA, while p38 MAP kinase phosphorylation decreased. Urinary isoprostane was also significantly lowered after 200 mg/d DHA but was increased after 1600 mg/d. Therefore, supplementation with only 200 mg/d DHA for 2 wk induced an antioxidant effect. It is concluded that low consumption of DHA could be an effective and nonpharmacological way to protect healthy men from platelet-related cardiovascular events.

Effects of docosahexaenoic acid on some megakaryocytic cell gene expression of some enzymes controlling prostanoid synthesis

Beneficial effects of docosahexaenoic acid (DHA) intake in the prevention of cardiovascular diseases are known, and platelets play a crucial role in cardiovascular complications. However, high doses of DHA may increase lipid peroxidation and induce deleterious effects, notably in platelets. This led us to investigate the effect of DHA on gene expression of some enzymes controlling redox status and prostanoid formation in human megakaryoblastic cells (MEG-01 cell line). MEG-01 cells were incubated in presence of DHA (10 and 100 micromol/L) for 6h. DHA enrichment up-regulated glutathione peroxidase-1 and thromboxane synthase mRNA. DHA increased gene catalase expression and up-regulated PPAR beta/delta and PPAR gamma mRNA in presence of high concentration of DHA. In conclusion, our results support an antioxidant mechanism of DHA. The effects of DHA on cellular redox status could, with others, provide an explanation for the beneficial influence of low consumption of DHA on cardiovascular events.

Generic and product-specific health claim processes for functional foods across global jurisdictions

Worldwide consumer interest in functional foods and their potential health benefits has been increasing over the past 10 y. To respond to this interest, regulatory bodies have developed guidelines for assessing health claims on functional foods. The objective of this article is to investigate the type and amount of evidence needed in various jurisdictions on a worldwide basis to substantiate both generic and product-specific health claims. Two types of health claims were examined using separate case studies. Analysis of generic health claims was highlighted by (n-3) fatty acids and their relation to heart health; whereas examination of product-specific health claims was conducted using probiotics and their association with gastrointestinal well-being. Results showed a common core for use of convincing high-quality human data, especially in the form of randomized controlled trials (RCT), but there was significant variability in the type and amount of scientific evidence needed to substantiate health claims, both generic and product specific, across different jurisdictions. Product-specific claims tended to use human RCT as the main basis for claims, whereas generic claims tended to base their statements on a wider spectrum of literature.

Dietary fatty acid composition rather than vitamin E supplementation influence ex vivo cytokine and eicosanoid response of porcine alveolar macrophages

This study examined the influence of different dietary fat sources (animal fat, sunflower oil, and fish oil) and supplementation of vitamin E (85, 150 and 300 mg all-rac-alpha-tocopheryl acetate/kg diet) on the ex vivo synthesis of eicosanoids and cytokines by porcine alveolar macrophages. Supplementation of vitamin E provoked an increase in the concentration of alpha-tocopherol of the macrophages irrespective of fat sources. Fish oil increased the macrophage n-3 content with 100% and 40%, and reduced the n-6 with 60% and 53% in comparison with sunflower oil and animal fat, respectively. Fish oil decreased the production of TNF-alpha, IL-8, LTB4, and PGE2 (but not IL-6) relative to the other dietary fat sources, and no difference was observed between sunflower oil and animal fat. Positive correlations were found between the n-6 fatty acid content and the production of PGE2, and the PGE2 production was positively correlated with TNF-alpha and IL-8. Negative correlations were found between the n-3 PUFA content and the concentration of PGE2, TNF-alpha and IL-8. In conclusion, dietary fish oil supplemented at a level of 5%, but not supplemental vitamin E, influenced the inflammatory responses of alveolar macrophages isolated from weaned pigs relatively to animal fat and sunflower oil.

The independent effects of eicosapentaenoic acid and docosahexaenoic acid on cardiovascular risk factors in humans

PURPOSE OF REVIEW

This review details the independent effects of purified eicosapentaenoic acid and docosahexaenoic acid on cardiovascular risk factors in humans. We report data from the recent literature and our own controlled clinical trials which compared the independent effects of these fatty acids in individuals at increased risk of cardiovascular disease, namely overweight hyperlipidaemic men and treated-hypertensive, type 2 diabetic men and women. We discuss the biological effects of these fatty acids and the potential mechanisms through which they may affect cardiovascular disease risk factors.

RECENT FINDINGS

A cardioprotective effect for omega3 fatty acids is supported by prospective studies demonstrating an inverse association between fish intake and coronary heart disease mortality. Data from secondary prevention trials support a reduction in ventricular fibrillation as a primary mechanism for the decreased incidence of myocardial infarction. Clinical trials and experimental studies have shown that omega3 fatty acids have many other potentially important antiatherogenic and antithrombotic effects. Omega-3 fatty acids lower blood pressure and heart rate, improve dyslipidaemia, reduce inflammation, and improve vascular and platelet function. These favourable effects have until recently been primarily attributed to the omega3 fatty acid eicosapentaenoic acid, which is present in large amounts in fish oil. Controlled studies in humans now demonstrate that docosahexaenoic acid, although often present in lower quantities, has equally important anti-arrhythmic, anti-thrombotic and anti-atherogenic effects.

SUMMARY

Available evidence strongly suggests that eicosapentaenoic acid and docosahexaenoic acid have differing haemodynamic and anti-atherogenic properties. The effects of the two fatty acids may also differ depending on the target population.

Influence of very low dietary intake of marine oil on some functional aspects of immune cells in healthy elderly people

Ageing is a multifactorial process involving decreased antioxidant defences and immune functions. n-3 Polyunsaturated fatty acids have been associated with human health benefits, especially against inflammatory and autoimmune diseases. However, their immunomodulatory effects were usually observed with high dosages (>2 g/d) known to increase lipid peroxidation. In contrast, very low doses, that may prevent lipid peroxidation, might affect the immune system differently. To study the latter hypothesis further, we investigated whether the supplementation of healthy elderly people with very low doses of marine oil (MO), a docosahexaenoate (DHA)- and eicosapentaenoate (EPA)-rich triacylglycerol, was able to affect lymphocyte proliferation and biochemical markers known to be altered with age. In a randomized, double-blind design, twenty healthy elderly subjects were assigned to a placebo group (600 mg sunflower oil/d) or to a group consuming 600 mg MO/d providing 150 mg DHA + 30 mg (EPA) for 6 weeks. At day 42, the proliferative responses of lymphocytes to several mitogens were significantly (P<0.01) decreased in the MO group compared with control values. This was accompanied by a slight lowering of their cytosolic cyclic nucleotide phosphodiesterase (PDE) activity, a marked and significant (P<0.05) increase of their particulate PDE activity (+56-57 %) and a slight but significant (P<0.05) increase in cyclic nucleotide intracellular levels. At the same time, the glutathione peroxidase activity was markedly and significantly (P<0.01) depressed in the MO group. None of these modifications could be seen in the placebo group. Collectively, these results demonstrate that even very low doses of n-3 fatty acids are sufficient to affect the immune responses of elderly subjects.

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.

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.

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.

Involvement of lipid peroxidation in platelet signalling

A well-known signalling pathway in blood platelets consists in the release of arachidonic acid (AA) from membrane phospholipids and its specific oxygenation into bioactive derivatives. In particular, cyclic prostaglandin endoperoxides and thromboxane A2 are potent inducers of platelet functions and are produced in greater amounts when the level of lipid hydroperoxides is higher than normal, as 'physiological concentrations' of such peroxides activate the cyclooxygenation of AA. In this context, a lower activity of platelet glutathione peroxidase (GPx), the key-enzyme for the degradation of lipid hydroperoxides, has been reported in aging, which will ensure a longer life span to those peroxides. Accordingly, the biosynthesis of pro-aggregatory prostanoids is elevated in platelets from the elderly. On the other hand, fatty acids from marine origin have been recognized as inhibitors of platelet functions, and they may alter the redox status of cells. They may for instance increase the platelet GPx activity, an effect that can be prevented by antioxidants. Overall, these data point out the relevance of the redox status in platelet functions.

Fish oil source differentially affects rat immune cell alpha-tocopherol concentration

We have previously reported that both the source of dietary fish oil and the chemical form of vitamin E supplied in the diet affect the vitamin E status of immune cells in rats. The purpose of this study was to investigate further the effect of fish oil source on immune cell vitamin E status using free alpha-tocopherol (alpha-T) at the AIN recommended level as the sole source of vitamin E. Sixty weanling female rats were fed semipurified, high fat (20 g/100 g) diets containing either tocopherol-stripped lard (LRD), menhaden fish oil (MFO), sardine fish oil (SRD) or cod liver oil (CLO) as the primary lipid source. Endogenous alpha-T concentration was measured and equalized to 150 mg/kg oil by addition of free RRR-alpha-T to each lipid source, allowing for a final concentration of alpha-T in the mixed diet of 30 mg/kg. An additional group of rats was fed LRD without supplemental vitamin E (LRD-) as a negative control. After feeding experimental diets for 5 or 10 wk, tissues were collected for alpha-T analysis by HPLC. After 5 wk, plasma and liver alpha-T (micromol alpha-T/g lipid) were significantly lower in SRD- and CLO-fed rats compared with LRD-fed rats. At 10 wk, only plasma alpha-T in CLO-fed rats remained significantly depressed. Plasma and liver alpha-T concentrations (micromol alpha-T/g lipid) were not significantly lower in MFO-fed rats than LRD-fed rats at either time point. Compared with LRD, feeding MFO to rats for 5 or 10 wk resulted in significantly greater alpha-T content of immune cells. In similar fashion, SRD-fed rats, compared with LRD-fed rats, also had significantly greater alpha-T content in splenocytes at both time points and greater thymocyte alpha-T at 10 wk. In all instances, the alpha-T status of rats fed CLO was indistinguishable from that of rats fed the vitamin E-free diet (LRD-). These data further demonstrate the complexity of the relationship between vitamin E status and dietary (n-3) polyunsaturated fatty acids (PUFA).

Effects of fatty acids on human platelet glutathione peroxidase: possible role of oxidative stress

Highly polyunsaturated fatty acids of the n-3 family are known to be inhibitors of platelet functions, but these fatty acids (FA) may alter the platelet antioxidant status, depending on their concentrations. The present study was aimed to investigate the effect of various FA on glutathione-dependent peroxidase (GPx), the required antioxidant enzyme for degrading FA hydroperoxides. Human platelets were enriched in vitro with either n-3 (18:3, 20.5, or 22.6), n-6 (18:2 or 18:3) FA, 18:1 n-9 or 16:0, and the GPx activity was then measured. It was found that n-3 FA enhanced the GPx activity whereas the others did not affect the enzyme activity. The increased GPx activity was associated with an increased amount of the enzyme measured by Western blotting. The enhanced activity and amount of GPx induced by 22:6n-3, the most potent activator among the n-3 FA, was completely abolished in the presence of cycloheximide at a concentration known to inhibit platelet protein synthesis. Because platelets are devoid of nucleus, which rules out the involvement of transcriptional factors, this suggests that 22:6n-3 might act at a translational level. On the other hand, 22:6n-3 treatment increased the malondialdehyde formation and decreased the vitamin E level in platelets, both events that could be prevented by the antioxidant epicatechin. Because epicatechin also suppressed the enhancement of both the activity and amount of GPx induced by 22:6n-3, we conclude that the increased GPx activity (possibly via protein synthesis) might be associated with an oxidative stress induced by 22:6n-3 and/or 20:4n-6 released from the platelet endogenous pool in the course of the 22:6n-3 enrichment.

Blood cell redox status and fatty acids

Glutathione-dependent peroxidase (GSH-Px) degrades the deleterious hydroperoxides, including those issued from arachidonic acid (AA) by the action of lipoxygenases, into their alcohol counterpart. We report that the hyperactivity of platelets from elderly people and of polymorphonuclear neutrophils from allergic patients, at least partly due to higher formation of thromboxane A2 and leukotriene B4, respectively, is associated with a depressed GSH-Px activity. As we report that n-3 fatty acids may enhance the cell GSH-Px activity, we conclude that the reduction of cell hyperactivity described in response to those fatty acids might be linked to their effect on GSH-Px.

Interactions between arachidonic and eicosapentaenoic acids during their dioxygenase-dependent peroxidation

Eicosapentaenoic acid (EPA), a major polyunsaturated fatty acid of fish has been widely proposed as a potential nutrient for decreasing platelet-endothelial cell interactions and the subsequent atherogenesis and thrombogenesis. This is mainly based upon the decrease of arachidonic acid (AA) oxygenation into bioactive molecules like thromboxane A2. In addition, EPA may be oxygenated into its own active derivatives via cell dioxygenases. We report evidence for the requirement of specific peroxides, adequately provided by AA, to allow EPA to be oxygenated into its bioactive products like prostaglandin I3, a prostacyclin mimetic. On the other hand, we present some data that argue for a decreased basal AA dioxygenation (specific peroxidation) by small concentrations of EPA. The interactions between AA and EPA are then dual, EPA being able to counteract AA oxygenation whereas EPA requires AA to be efficiently oxygenated.

Lower levels of lipid peroxidation in human platelets incubated with eicosapentaenoic acid

The modulatory effects of eicosapentaenoic acid (EPA) on platelet arachidonic acid (AA) metabolism were applied to an in vitro model of oxidant stress. Unstimulated normal human blood platelets were first treated with a thiol-oxidizing agent, azodicarboxylic acid bis(dimethylamide) (diamide) (1 microM), and then incubated with a low concentration of EPA (100 nM). Diamide treatment led to a lower alpha-tocopherol content compared to control. Formation of MDA, a marker of the overall lipid peroxidation, as well as formation of 12-hydroxyeicosatetraenoic acid (12-HETE), the 12-lipoxygenase end-product of AA, were both higher in diamide-treated platelets. Subsequent incubation of diamide-treated platelets with EPA counteracted the effects of oxidant stress induced pharmacologically by diamide. Interestingly, EPA prevented the alpha-tocopherol level from falling and the overall lipid peroxidation from increasing as it did during diamide treatment. In particular, incubation of diamide-treated platelets with EPA led to significantly lower amounts of 12-HETE. Conversely, preincubation of platelets with 100 nM EPA protected cells from oxidizing effects induced by diamide treatment, either on the level of lipid peroxides or on the antioxidant status. These results indicate that, in this particular model, EPA permitted platelets to have control levels of tocopherol, MDA and 12-HETE despite diamide treatment. Low concentrations of EPA might have prevented the increase of lipid hydroperoxides and especially the transient accumulation of 12-hydroperoxyeicosatetraenoic acid (12-HPETE).

Effects of dietary fish oil supplementation on platelet aggregability and platelet membrane fluidity in normolipemic subjects with and without high plasma Lp(a) concentrations

The purpose of this study was to compare the relative effect of n-3 fatty acids on plasma lipids and platelet function in normolipemic subjects (n = 8) with plasma Lp(a) levels greater than 30 mg/dl and normolipemic subjects (n = 7) without detectable plasma Lp(a) concentrations. Six weeks of dietary supplementation (3.8 g EPA and 2.9 g DHA/d) significantly reduced (P less than 0.005) plasma TGs in both groups whereas no changes of plasma TC, LDL-C, HDL-C, and Lp(a), respectively, were found. Collagen- or thrombin-stimulated platelet aggregation and collagen- or thrombin-induced TXB2 generation from platelets decreased by approx. 45% in Lp(a)-negative and Lp(a)-positive platelet donors after a 6 week dietary intake. Four more weeks without n-3 supplementation restored the pretreatment values of TGs, platelet aggregability and TXB2 release. The biophysical properties of platelets from normolipemics with and without high plasma Lp(a) concentrations revealed a similar structural order of platelets at 37 degrees C using DPH, TMA-DPH, or 6-AS as fluorescent probes. Also similar temperature-dependent changes in platelet fluidity from 37 degrees C to 17 degrees C were observed in platelet preparations from Lp(a)-positive and Lp(a)-negative subjects. However, no subtle changes in the structural order of platelets due to nutrient intakes were found in all subjects (n = 15, 19-28 yrs) using fluorescence polarization technique. The present data suggest a similar in vitro platelet behaviour from normolipemic subjects with and without high plasma levels of Lp(a) (which is considered a risk for premature atherosclerosis) in contrast to platelet aggregability and platelet fluidity in certain hyperlipidemic stages.

Ingestion of eicosapentaenoic acid-ethyl ester renders rabbit LDL less susceptible to Cu2(+)-catalyzed-oxidative modification

The present study revealed that low density lipoprotein (LDL) obtained from rabbits fed highly purified eicosapentaenoic acid-ethyl ester (EPA-E) (EPA-LDL) was significantly less susceptible to oxidative modification catalyzed by Cu2+ as compared to LDL from rabbits fed a normal diet (control LDL). In a comparison of fatty acid composition of LDL, the contents of EPA and docosapentaenoic acid were significantly increased in EPA-LDL as compared to control LDL. The content of arachidonic acid (AA) was the same in both LDL groups. The contents of total cholesterol, free cholesterol, triglyceride, and phospholipid in LDL were unchanged by EPA-E ingestion. These data raise the possibility that EPA may protect LDL from oxidative modification, leading to a reduction of oxidized LDL in atherosclerotic lesions, and that this may be how EPA exert its anti-atherosclerotic action.