Mary B. Engler

Omega-6 Fatty Acids and Risk for Cardiovascular Disease A Science Advisory From the American Heart Association Nutrition Subcommittee of the Council on Nutrition, Physical Activity, and Metabolism; Council on Cardiovascular Nursing; and Council on Epidemiology and Prevention

A large body of literature suggests that higher intakes of omega-6 (or n-6) polyunsaturated fatty acids (PUFAs) reduce risk for coronary heart disease (CHD). However, for the reasons outlined below, some individuals and groups have recommended substantial reductions in omega-6 PUFA intake.1–4 The purpose of this advisory is to review evidence on the relationship between omega-6 PUFAs and the risk of CHD and cardiovascular disease. Omega-6 PUFAs are characterized by the presence of at least 2 carbon-carbon double bonds, with the first bond at the sixth carbon from the methyl terminus. Linoleic acid (LA), an 18-carbon fatty acid with 2 double bonds (18:2 omega-6), is the primary dietary omega-6 PUFA. LA cannot be synthesized by humans, and although firm minimum requirements have not been established for healthy adults, estimates derived from studies in infants and hospitalized patients receiving total parenteral nutrition suggest that an LA intake of ≈0.5% to 2% of energy is likely to suffice. After consumption, LA can be desaturated and elongated to form other omega-6 PUFAs such as γ-linolenic and dihomo-γ-linolenic acids. The latter is converted to the metabolically important omega-6 PUFA arachidonic acid (AA; 20:4 omega-6), the substrate for a wide array of reactive oxygenated metabolites. Because LA accounts for 85% to 90% of the dietary omega-6 PUFA, this advisory focuses primarily on this fatty acid, recognizing that dietary AA, which can affect tissue AA levels,5 may have physiological sequelae.6–8 LA comes primarily from vegetable oils (eg, corn, sunflower, safflower, soy). The average US intake of LA, according to National Health and Nutrition Examination Survey 2001 to 2002 data for adults ≥19 years of age, is 14.8 g/d.9 On the basis of an average intake of 2000 kcal/d, LA intake is 6.7% of energy. AA (≈0.15 g/d) is consumed preformed in meat, …

Flavonoid-Rich Dark Chocolate Improves Endothelial Function and Increases Plasma Epicatechin Concentrations in Healthy Adults

Background: Dark chocolate derived from the plant (Theobroma cacao) is a rich source of flavonoids. Cardioprotective effects including antioxidant properties, inhibition of platelet activity, and activation of endothelial nitric oxide synthase have been ascribed to the cocoa flavonoids. Objective: To investigate the effects of flavonoid-rich dark chocolate on endothelial function, measures of oxidative stress, blood lipids, and blood pressure in healthy adult subjects. Design: The study was a randomized, double-blind, placebo-controlled design conducted over a 2 week period in 21 healthy adult subjects. Subjects were randomly assigned to daily intake of high-flavonoid (213 mg procyanidins, 46 mg epicatechin) or low-flavonoid dark chocolate bars (46 g, 1.6 oz). Results: High-flavonoid chocolate consumption improved endothelium-dependent flow-mediated dilation (FMD) of the brachial artery (mean change = 1.3 ± 0.7%) as compared to low-flavonoid chocolate consumption (mean change = −0.96 ± 0.5%) (p = 0.024). No significant differences were noted in the resistance to LDL oxidation, total antioxidant capacity, 8-isoprostanes, blood pressure, lipid parameters, body weight or body mass index (BMI) between the two groups. Plasma epicatechin concentrations were markedly increased at 2 weeks in the high-flavonoid group (204.4 ± 18.5 nmol/L, p ≤ 0.001) but not in the low-flavonoid group (17.5 ± 9 nmol/L, p = 0.99). Conclusion: Flavonoid-rich dark chocolate improves endothelial function and is associated with an increase in plasma epicatechin concentrations in healthy adults. No changes in oxidative stress measures, lipid profiles, blood pressure, body weight or BMI were seen.

Antioxidant Vitamins C and E Improve Endothelial Function in Children With Hyperlipidemia: Endothelial Assessment of Risk from Lipids in Youth (EARLY) Trial

Background—Hyperlipidemia is associated with endothelial dysfunction, an early event in atherosclerosis and predictor of risk for future coronary artery disease. Epidemiological studies suggest that increased dietary intake of antioxidants reduces the risk of coronary artery disease. The purpose of this study was to determine whether antioxidant vitamin therapy improves endothelial function and affects surrogate biomarkers for oxidative stress and inflammation in hyperlipidemic children. Methods and Results—In a randomized, double-blind, placebo-controlled trial, the effects of antioxidant vitamins C (500 mg/d) and E (400 IU/d) for 6 weeks and the National Cholesterol Education Program Step II (NCEP-II) diet for 6 months on endothelium-dependent flow-mediated dilation (FMD) of the brachial artery were examined in 15 children with familial hypercholesterolemia (FH) or the phenotype of familial combined hyperlipidemia (FCH). Antioxidant vitamin therapy improved FMD of the brachial artery compared with baseline (P <0.001) without an effect on biomarkers for oxidative stress (autoantibodies to epitopes of oxidized LDL, F2-isoprostanes, 8-hydroxy-2′-deoxyguanosine), inflammation (C-reactive protein), or levels of asymmetric dimethylarginine, an endogenous inhibitor of nitric oxide. Conclusions—Antioxidant therapy with vitamins C and E restores endothelial function in hyperlipidemic children. Early detection and treatment of endothelial dysfunction in high-risk children may retard the progression of atherosclerosis.

Omega-3 Polyunsaturated Fatty Acid (Fish Oil) Supplementation and the Prevention of Clinical Cardiovascular Disease: A Science Advisory from the American Heart Association

Multiple randomized controlled trials (RCTs) have assessed the effects of supplementation with eicosapentaenoic acid plus docosahexaenoic acid (omega-3 polyunsaturated fatty acids, commonly called fish oils) on the occurrence of clinical cardiovascular diseases. Although the effects of supplementation for the primary prevention of clinical cardiovascular events in the general population have not been examined, RCTs have assessed the role of supplementation in secondary prevention among patients with diabetes mellitus and prediabetes, patients at high risk of cardiovascular disease, and those with prevalent coronary heart disease. In this scientific advisory, we take a clinical approach and focus on common indications for omega-3 polyunsaturated fatty acid supplements related to the prevention of clinical cardiovascular events. We limited the scope of our review to large RCTs of supplementation with major clinical cardiovascular disease end points; meta-analyses were considered secondarily. We discuss the features of available RCTs and provide the rationale for our recommendations. We then use existing American Heart Association criteria to assess the strength of the recommendation and the level of evidence. On the basis of our review of the cumulative evidence from RCTs designed to assess the effect of omega-3 polyunsaturated fatty acid supplementation on clinical cardiovascular events, we update prior recommendations for patients with prevalent coronary heart disease, and we offer recommendations, when data are available, for patients with other clinical indications, including patients with diabetes mellitus and prediabetes and those with high risk of cardiovascular disease, stroke, heart failure, and atrial fibrillation.

Mechanisms of vasorelaxation induced by eicosapentaenoic acid (20:5n-3) in WKY rat aorta

The vasorelaxant activity of eicosapentaenoic acid (EPA, 20:5n‐3), the omega‐3 polyunsaturated fatty acid, was investigated in isolated Wistar Kyoto (WKY) rat aortae by measuring isometric tension. Eicosapentaenoic acid (1–100 μM) relaxed rat aortae contracted with high K+ (80 mM) or noradrenaline (NA, 1 μM) in a concentration‐dependent manner. Contractions induced by Bay K 8644 or increasing concentrations of calcium were unaffected by EPA. The relaxant effect of EPA (3–100 μM) was significantly inhibited by indomethacin (10 μM), the cyclo‐oxygenase inhibitor, but not by the nitric oxide (NO) synthesis inhibitor, Nω‐nitro‐L‐arginine methyl ester hydrochloride (L‐NAME, 100 μM). Removal of the endothelium did not alter EPA‐induced relaxations. In Ca2+‐free, EGTA 2 mM solution, EPA (10–30 μM significantly inhibited NA‐sustained contractions. Incubation with EPA (5, 10 μM) diminished both NA‐induced (1 μM) phasic and sustained contractions. The vasorelaxant effects of EPA (30 μM) on NA‐induced (1 μM) contractions were significantly inhibited by the K+ channel blocker, glibenclamide (10 μM), but not tetraethylammonium (1 mM). Moreover, indomethacin and glibenclamide combined significantly inhibited EPA‐induced (1–100 μM) responses. These results indicate EPA exerts its endothelium‐independent vasorelaxant effects in WKY rat aortae through production of prostanoids which activate K+ATP channels. Inhibition of Ca2+ mobilization from intracellular pools and influx through the non‐L‐type, but not the L‐type, Ca2+ channel are also possible mechanisms action of EPAs.

Omega-6 Fatty Acids and Risk for Cardiovascular Disease

The long-chain marine n–3 fatty acids have been reported to be cardio protective over many years and many mechanisms of action have been proposed. Up through the first decade of the 21st century, nearly all n–3 randomized trials were positive, but beginning in 2010 several trials were published that did not show a benefit of these fatty acids on clinical cardiovascular endpoints. There is a wealth of epidemiologic evidence for a cardiac benefit for the n–3 fatty acids that appears to contradict the findings of the randomized trials. This chapter will review both trial and prospective cohort study data which, in the aggregate, continues to support the view that n–3 fatty acids are heart healthy.

Genetics and Genomics for the Prevention and Treatment of Cardiovascular Disease: Update A Scientific Statement From the American Heart Association

Cardiovascular diseases (CVDs) are a major source of morbidity and mortality worldwide. Despite a decline of ≈30% over the past decade, heart disease remains the leading killer of Americans.1 For rare and familial forms of CVD, we are increasingly recognizing single-gene mutations that impart relatively large effects on individual phenotype. Examples include inherited forms of cardiomyopathy, arrhythmias, and aortic diseases. However, the prevalence of monogenic disorders typically accounts for a small proportion of the total CVD observed in the population. CVDs in the general population are complex diseases, with several contributing genetic and environmental factors. Although recent progress in monogenic disorders has occurred, we have seen a period of intense investigation to identify the genetic architecture of more common forms of CVD and related traits. Genomics serves several roles in cardiovascular health and disease, including disease prediction, discovery of genetic loci influencing CVD, functional evaluation of these genetic loci to understand mechanisms, and identification of therapeutic targets. For single-gene CVDs, progress has led to several clinically useful diagnostic tests, extending our ability to inform the management of afflicted patients and their family members. However, there has been little progress in developing genetic testing for complex CVD because individual common variants have only a modest impact on risk. The study of the genomics of complex CVDs is further challenged by the influence of environmental variables, phenotypic heterogeneity, and pathogenic complexity. Characterization of the clinical phenotype requires consideration of the clinical details of the diseases and traits under study. This update expands the prior scientific statement on the relevance of genetics and genomics for the prevention and treatment of CVDs.2 In the earlier report, we focused on the current status of the field, which consisted of predominantly family-based linkage studies and single-gene or mendelian mutations of relatively large phenotypic effect …

Omega-3 fatty acids: role in cardiovascular health and disease.

Dietary omega-3 polyunsaturated fatty acids, eicosapentaenoic and docosahxaenoic acids, play an important role in cardiovascular health and disease. Clinical trials provide substantial evidence to support current dietary recommendations for omega-3 fatty acids in cardiovascular disease management. The cardioprotective benefits of omega-3 fatty acids may be attributed to multiple physiological effects on lipids, blood pressure, vascular function, cardiac rhythms, platelet function, and inflammatory responses. The metabolism of omega-3 fatty acids, physiological effects, and clinical considerations with current dietary recommendations and sources of omega-3 fatty acids are presented.

Calcium-mediated mechanisms of eicosapentaenoic acid-induced relaxation in hypertensive rat aorta*

We have previously demonstrated the vasorelaxant properties of the omega-3 fatty acid, eicosapentaenoic acid (EPA), in normotensive and spontaneously hypertensive rat (SHR) aorta, although the mechanism(s) of action are not fully understood. Because endothelial dysfunction and increased intracellular free calcium concentration ([Ca2+]i) are seen in hypertensive rat aorta, we investigated the potential role of Ca2+ signaling, endothelium and derived factors, and the opening of potassium (K+) channels in EPA-induced relaxation. In the presence of extracellular Ca2+, EPA induced significant relaxations at >10 micromol/L (P<.01) in norepinephrine (NE) (10(-6) mol/L)-contracted aortic rings and at 30 micromol/L (P<.001) in high K+ (80 mmol/L)-contracted aortic rings. In the absence of extracellular Ca2+, EPA (10 to 30 micromol/L) inhibits the tonic component of NE-induced contraction (P<.0001). The relaxant properties of EPA in SHR aorta appear specific to Ca2+ release from an internal storage site associated with NE-induced tonic contraction. Further studies with the use of fura-2 to measure [Ca2+]i in cultured vascular smooth muscle (VSM) cells from SHR aorta indicated that EPA (30 micromol/ L)-pretreatment attenuated angiotensin II (50 nmol/ L)-induced Ca2+ transient by 95%, suggesting that an inhibitory effect on the Ca2+ signaling may underlie EPA-induced relaxation of the vessel preparation. In addition, EPA per se induced an increase in [Ca2+li with a duration of approximately 20 min in VSM cells, and the effect was not altered by removal of extracellular Ca2+. There was no increase in the level of inositol-1,4,5-trisphosphate in response to EPA (30 micromol/L). The actions of EPA are independent of endothelium-derived factors, cyclooxygenase metabolites, and activation of K+ channels since endothelium removal, N(omega)-nitro-L-arginine methyl ester hydrochloride, (L-NAME, 100 micromol/L), indomethacin (10 micromol/L), tetraethylammonium (1 mmol/L), and glibenclamide (10 micromol/L) did not affect EPA-induced vasodilation in NE-precontracted aortic rings. These results suggest that EPA directly modulates intracellular Ca2+ signaling in VSM cells, and that this may contribute to the vasorelaxant effect and, at least in part, the blood pressure-lowering effect of fish oil.

Docosahexaenoic Acid-Induced Vasorelaxation in Hypertensive Rats: Mechanisms of Action

The authors investigated the vasorelaxant properties of the omega-3 fatty acid, docosahexaenoic (DHA, 22:6n-3), and the possible involvement of endothelium-derived nitric oxide, prostanoids, opening of K+ channels, and/or modulation of calcium-mediated events. Isolated aorta from male spontaneously hypertensive rats (SHR) (age 16-17 weeks) were used to measure isometric tension. DHA-induced (1-100 mol/l) relaxation was examined following contraction to norepinephrine (NE) (10– 6 mol/l) or high-K+ (80 mmol/l) solution in the presence and absence of various inhibitors and calcium-containing solution. DHA acid induced a significant vasorelaxant effect in both NE and high-K+-induced contracted SHR aortic rings, although DHA relaxations were greater in high-K+-induced contracted rings. In the absence of extracellular calcium, DHA (5-30 mol/l) inhibited the initial phasic and sustained components of NE-induced contraction under different conditions. Inhibition of nitric oxide synthesis by N•-nitro-L-arginine methyl ester hydrochloride (100 mol/l) had no effect on DHA relaxations; however, indomethacin or nifedipine caused significant inhibition at• 30 mol/l DHA. The K+ channel blocker, glibenclamide, but not tetraethyl-ammonium, also had an inhibitory effect on DHA-induced relaxation. These results indicate that DHA’s vasorelaxant actions in SHR aorta are independent of endothelium-derived nitric oxide; however, at DHA concentrations• 30 mol/l, vasodilatory prostanoids that activate AT Psensitive K+ channels (KATP) may be involved. At lower concentrations, DHA-induced relaxation appears to be attributed to modulation of intracellular Ca2+release and L-type Ca2+channels in vascular smooth muscle cells. The vasorelaxant properties of DHA may contribute, in part, to the blood pressure–lowering effect of dietary fish oil in this hypertensive model.