Health claims: omega-3 fatty acids and cardiovascular disease

Microalgae as a Potential Source of Bioactive Food Compounds

Microalgae are unicellular, photosynthethic organisms that can grow on diverse aquatic habitatss like ponds, lakes, rivers, oceans, waste water and humid soils. Recently, microalgae are gaining importance as renewable sources of biologically active food compounds such as polysaccharides, proteins, essential fatty acids, biopigments such as chlorophylls, carotenoids, astaxanthin, as well as vitamins and minerals.The bioactive food compounds of microalgae enable them to be part of multitude of applications in numerous industrial products for healthy life and ecosystem. This review article summarizes the applications of biologically active food compounds derived from microalgae as nutraceuticals, healthy dietary supplements, pharmaceuticals and cosmetics. Further, this review article highlights the importance of research focus on the identification and extraction of bioactive food compounds from the huge numbers of microlage that exist in nature for sustainable global food security and economy.

Fish oil supplementation prevents neointima formation in nonhypercholesterolemic balloon-injured rabbit carotid artery by reducing medial and adventitial cell activation

We asked whether balloon-injured neointima formation in the presence of high/low serum cholesterol (CT) levels might be affected by dietary supplementation with fish oil (FO). To test this hypothesis, we examined the differentiation, proliferation, or apoptosis profile of smooth muscle cell (SMC) and adventitial cell response to a mild injury induced via a Fogarty catheter in the carotid artery of adult rabbits that had been fed a standard chow or 0.5% CT-enriched diet starting 4 weeks before the lesion. One week before surgery, animals received FO supplementation. This regimen was continued for the following 3 weeks. The effect of FO on the early proliferative/migratory response of carotid SMCs was also examined in 2- and 7-day-injured normocholesterolemic rabbits. As controls, animals subjected to 3-week endothelial injury and animals kept on a 7-week CT diet were used. Carotid cryosections from the various animal groups were evaluated for morphometry (image analysis), differentiation (immunofluorescence with monoclonal antibodies specific for smooth muscle markers, ie, myosin isoforms, SM22, and fibronectin), proliferation (bromodeoxyuridine incorporation), and apoptosis (terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling). FO treatment significantly reduced the development of intimal thickening in normocholesterolemic rabbits but had no efficacy in the presence of relatively higher serum CT levels. At day 2 (adventitia) and day 7 (neointima, media, and adventitia), the proliferation index of SMCs in FO-treated injured rabbits was markedly lower than in untreated injured controls. Concomitantly with the antiproliferative effect, FO was able to decrease the size of 2 cell types involved in the cell growth response to endothelial injury, namely, the "fetal-type" medial SMC subpopulation and the fibroblast-derived adventitial myofibroblasts. Thus, in our experimental conditions, a low CT level is a permissive condition for FO to prevent neointima formation to a considerable extent. This event is attributable to the early postinjury effect of FO on SMC/adventitial cell proliferation/differentiation patterns.

Dietary polyunsaturated fatty acids, vitamin E and hypoxia/reoxygenation-induced damage to cardiac tissue

Polyunsaturated fatty acids (PUFA), in the form of marine oils, contain a large proportion of n-3 long chain fatty acids and have been recommended as a dietary supplement for patients with ischaemic heart disease. It has also been suggested that consumption of diets rich in polyunsaturated fatty acids renders tissues more susceptible to free radical-mediated lipid peroxidation, a process which has been implicated in the mechanisms by which tissues may become damaged following hypoxia and subsequent reoxygenation. We have examined the effect of supplementation of diets with oils of different PUFA composition and different vitamin E content on the accumulation of fatty acids by rat hearts in comparison with the effects on tissue lipid peroxidation and the response of the heart to a standardised form of oxidative stress. Groups of Wistar rats were fed a vitamin E supplemented (100 mg alpha-tocopherol acetate/kg) diet containing either 10% corn oil, 10% menhaden oil or 10% lard, or a low vitamin E diet (2.5 mg alpha-tocopherol acetate/kg) containing either 10% corn oil, 10% menhaden oil or 10% lard for 82 +/- 3 days. Diets supplemented with menhaden oil had a dramatic effect on the incorporation of n-3 fatty acids into the cardiac tissue and increased the susceptibility of this tissue to lipid peroxidation in vitro. The effect of these changes on damage to isolated hearts subjected to 60 min hypoxia and reoxygenation was examined using a modified Langendorff system. Nutritional manipulation of the tissue fatty acids and vitamin E content had no influence on the release of creatine kinase activity from rat hearts subjected to hypoxia/reoxygenation. Thus these data do not support the hypothesis that consumption of diets rich in polyunsaturated fatty acids renders tissues more susceptible to free radical damage induced by hypoxia/reoxygenation.

Soluble vascular cell adhesion molecule-1 as a biohumoral correlate of atherosclerosis

Vascular cell adhesion molecule-1 (VCAM-1) is a protein expressed on the surface of activated endothelial cells and expressed in early atherosclerosis. Because part of the protein is shed in the circulation and can be detected in peripheral plasma [soluble (s) VCAM-1], we hypothesized that sVCAM-1 may be a circulating marker of the presence and severity of atherosclerosis in humans. We selected 11 patients with essential hypertension plus peripheral vascular disease (PVD) and matched them for age, gender, body mass index, and smoking habits with 11 patients with uncomplicated essential hypertension (UH) and 11 healthy controls. We evaluated plasma concentrations of sVCAM-1 along with those of the soluble form of two other endothelial leukocyte adhesion molecules [sE-selectin and s-intercellular adhesion molecule-1 (sICAM-1)] and other markers of endothelial dysfunction/ damage [s-thrombomodulin, plasminogen activator inhibitor type I, and von Willebrand factor (vWF)]. We also measured insulin, glucose, fibrinogen, total and HDL cholesterol, and the urinary albumin excretion (UAE), which may also be related to atherosclerosis. Results of these assays were related to the echographic assessment of the maximum intima-media thickness (IMTmax) at the carotid bifurcation, as an index of atherosclerosis in the carotids. PVD patients had a clearly elevated IMTmax [2.7 (1.1-3.1) mm, median (range)] compared with both UH patients [1.2 (0.8-2.4) mm] and controls [1 (0.6-2) mm]. sVCAM-1 was clearly higher in PVD patients [990 (273-1808) ng/mL, median (range)] versus 340 (236-975) ng/mL in UH and 386 (204-835) ng/mL in controls, and it separated clinical categories better than sICAM-1, vWF, glucose, insulin, UAE, triglycerides, or total, LDL or HDL cholesterol, sVCAM-1 was also the best biohumoral correlate of IMTmax (R = .59; P < .001) in univariate analysis. Because many of the biohumoral variables assessed were mutually intercorrelated, they were entered in a multivariate analysis to assess their contribution in explaining IMTmax variability. sVCAM-1 remained the only independent predictor of IMTmax and totally abolished the contribution of other variables to IMTmax variability. Thus, sVCAM-1 is a good biohumoral correlate of overt atherosclerosis, independent of underlying hypertension, and may be an in vivo marker of endothelial activation. Its potential value as a surrogate for global risk assessment and its behavior in intervention studies remain to be determined.

Polyunsaturated fatty acids and signalling via phospholipase C-beta and A2 in myocardium

Dietary n-6 and n-3 polyunsaturated fatty acids (PUFAs) have potent biological effects on the blood(cells), the vasculature and they myocardium. In the epidemiological studies in which the benefit from the regular ingestion of n-3 PUFAs was reported, the responsible mechanisms remain obscure. A great deal of the PUFA-effect can be explained by the known interference with the eicosanoid metabolism. Many processes, believed to be involved in atherogenesis such as adhesion and infiltration of bloodcells (in)to the vasculature, platelet aggregation, secretion of endothelium-derived factors and mitogenic responses of vascular smooth muscle cells are partially mediated by receptor-activated phospholipases C-beta and A2. As PUFAs take part at many steps of the signalling pathways, the latter could represent important action sites to beneficially interfere with atherogenesis. In this brief review, we have discussed the results of studies on the influence of alteration of PUFA composition of the membrane phospholipids or of exogenously administered non-esterified PURAs on phospholipid signalling. For convenience, we have mainly focused our discussion on those studies available on the myocardium. By changing the PUFA composition of the phospholipids, the endogenous substrates for the membrane-associated phospholipase C-beta and A2 are changed. This is accompanied by changes in their hydrolytic action on these substrates resulting in altered products (the molecular species of 1,2-diacylglycerols and the non-esterified PUFAs) which on their turn evoke changes in events downstream of the signalling cascades: activation of distinct protein kinase C isoenzymes, formation of distinct eicosanoids and non-esterified PUFA effects on Ca2+ channels. It has also become more clear that the membrane physicochemical properties, in terms of fluidity and cholesterol content of the bilayer, might undergo changes due to altered PUFA incorporation into the membrane phospholipids. The latter effects could have consequences for the receptor functioning, receptor-GTP-binding protein coupling, GTP-binding protein-phospholipase C-beta or A2 coupling as well. It should be noted that most of these studies have been carried out with cardiomyocytes isolated from hearts of animals on PUFA diet or incubation of cultured cardiomyocytes with non-esterified PUFAs in the presence of albumin. Studies need to be performed to prove that the PUFA-diet induced modulations of the phospholipid signalling reactions do occur in vivo and that these effects are involved in the mechanism of beneficial effects of dietary PUFAs on the process of atherosclerosis.

Can we recommend fish oil for hypertension?

1. The ability of the n-3 fatty acids in fish oil to lower blood pressure has been established. Dietary fish oil supplementation is effective in mild hypertension and, in certain cases, as an adjunct therapy in drug-treated hypertension. Efficacy may be enhanced by restricting sodium intake. 2. The overall benefit of fish oil in hypertension, however, has not yet been fully evaluated. We still need further information on the relative efficacy of individual omega-3 fatty acids and on additional cardiovascular benefits and possible disadvantages of increasing their consumption.

Do fish oils prevent restenosis after coronary angioplasty?

BACKGROUND

The omega-3 polyunsaturated fatty acids derived from fish oils have been shown to modulate many factors believed to affect the pathogenesis of atherosclerosis. Because certain features of restenosis following angioplasty mimic some of the early changes of atherogenesis, some researchers have suggested that fish oil might prevent restenosis following angioplasty. We report the effects of omega-3 fatty acids on the rate of restenosis following percutaneous intraluminal coronary angioplasty (PTCA).

METHODS AND RESULTS

From August 1989 through September 1992, 551 patients were randomized to start receiving a daily dietary supplement of ten 1.0-g capsules containing 80.6% ethyl esters of omega-3 fatty acids providing 4.1 g eicosapentaenoic acid (EPA) and 2.8 g docosahexaenoic acid (DHA) for 6 months or an equal amount of an ethyl ester of corn oil. Four hundred seventy subjects who were well matched for risk factors completed successful angioplasty of one or multiple lesions in native coronary vessels and constituted the study cohort, of whom 447 were evaluable at 6 months after PTCA. The criteria for restenosis were that the quantitative coronary angiography at 6 months show a > 30% increase in narrowing at the stenosis site or loss of at least half of the gain achieved at the time of PTCA and final restenosis with < 50% luminal diameter remaining. In 93% of the patients, the end point was determined by angiography and in all except 1% of these by quantitative coronary angiography. Compliance with the fish oil supplement was good as judged by incorporation of EPA and DHA in plasma and red blood cell phospholipids. The restenosis rate among analyzable patients was 46% for corn oil and 52% for fish oil (P = .37). The addition of 200 mg alpha-tocopherol for all subjects during the study had no effect on restenosis rates.

CONCLUSIONS

This was the largest of such trials to date, and a supplement of 8 g/d of omega-3 fatty acids failed to prevent the usual high rate of restenosis after PTCA. No adverse effects were attributable to this large daily supplement of omega-3 fatty acids.

Effects of long-chain polyunsaturated fatty acids on the contraction of neonatal rat cardiac myocytes

Because of the ability of certain long-chain polyunsaturated fatty acids (PUFAs) to prevent lethal cardiac arrhythmias, we have examined the effects of various long-chain fatty acids on the contraction of spontaneously beating, isolated, neonatal rat cardiac myocytes. The omega 3 PUFA from fish oils, eicosapentaenoic acid [EPA; C20:5 (n-3)] and docosahexaenoic acid [DHA; C22:6 (n-3)], at 2-10 microM profoundly reduced the contraction rate of the cells without a significant change in the amplitude of the contractions. The fatty acid-induced reduction in the beating rate could be readily reversed by cell perfusion with fatty acid-free bovine serum albumin. Addition of either oxygenase inhibitors or antioxidants did not alter the effect of the fatty acids. Arachidonic acid [AA; C20:4 (n-6)] produced two different effects on the beating rate, an increase or a decrease, or it produced no change. In the case of the increased or unchanged beating rate in the presence of AA, addition of AA oxygenase inhibitors subsequently reduced the contraction rate. The nonmetabolizable AA analog eicosatetraynoic acid (ETYA) always reduced the beating rate, as did EPA or DHA. Two other PUFAs, linoleic acid [C18:2 (n-6)] and linolenic acid [C18:3 (n-3)] also exhibited similar but less potent effects compared with EPA or ETYA. In contrast, neither the monounsaturated fatty acid oleic acid [C18:1 (n-9)] nor the saturated fatty acids stearic acid (C18:0), myristic acid (C14:0), and lauric acid (C12:0) affected the contraction rate. The inhibitory effect of these PUFAs on the contraction rate was similar to that produced by the class I antiarrhythmic drug lidocaine. The fatty acids that are able to reduce the beating rate, particularly EPA and DHA, could effectively prevent and terminate lethal tachyarrhythmias (contracture/fibrillation) induced by high extracellular calcium concentrations or ouabain. These results suggest that free PUFAs can suppress the automaticity of cardiac contraction and thereby exert their antiarrhythmic effects.

Prevention of ischemia-induced ventricular fibrillation by omega 3 fatty acids

A specially prepared dog model of myocardial infarction was used to test the efficacy of the long-chain polyunsaturated fish oil omega 3 fatty acids eicosapentaenoic (20:5 n-3) and docosahexaenoic (22:6 n-3) acids to prevent ischemia-induced malignant cardiac arrhythmias. The dogs had sustained a prior experimental myocardial infarction from ligation of the left anterior descending coronary artery, and a hydraulic cuff was implanted around the left circumflex artery at that operation. After recovery from that procedure the animals were tested during a treadmill exercise test. With compression of the left circumflex artery sensitive animals will predictably develop ventricular fibrillation (VF). In such prepared dogs an emulsion of fish oil fatty acids was infused i.v. over a 50- to 60-min period just before the exercise-plus-ischemia test, and the effect on development of VF was recorded. The infusion was 100 ml of a 10% (vol/vol) emulsion of a fish oil concentrate containing 70% omega 3 fatty acids with free eicosapentaenoic acid and docosahexaenoic acid composing 33.9% and 25.0% of that total, respectively. Alternatively, some animals similarly received an emulsion containing 5 ml of the free fatty acid concentrate plus 5 ml of a triacylglyerol concentrate containing 65% omega 3 fatty acids with eicosapentaenoic acid and docosahexaenoic acid composing 34.0% and 23.6% of that total, respectively. In seven of eight animals the infusion of the fish oil emulsion completely prevented the acute occurrence of VF in the susceptible animals (P < 0.005). In five of five of these animals the subsequent exercise-plus-ischemia test after a similar infusion of an emulsion in which soy bean oil replaced the fish oil fatty acid concentrates resulted in prompt development of VF. Possible mechanisms for this protective effect of omega 3 fatty acids against exercise and ischemia-induced malignant arrhythmias are considered.