n-3 Fatty acids and cardiovascular disease: navigating toward recommendations

Variability in the Clinical Effects of the Omega-3 Polyunsaturated Fatty Acids DHA and EPA in Cardiovascular Disease-Possible Causes and Future Considerations

Cardiovascular disease (CVD) that includes myocardial infarction and stroke, is the leading cause of mortality worldwide. Atherosclerosis, the primary underlying cause of CVD, can be controlled by pharmacological and dietary interventions, including n-3 polyunsaturated fatty acid (PUFA) supplementation. n-3 PUFA supplementation, primarily consisting of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), has shown promise in reducing atherosclerosis by modulating risk factors, including triglyceride levels and vascular inflammation. n-3 PUFAs act by replacing pro-inflammatory fatty acid types in cell membranes and plasma lipids, by regulating transcription factor activity, and by inducing epigenetic changes. EPA and DHA regulate cellular function through shared and differential molecular mechanisms. Large clinical studies on n-3 PUFAs have reported conflicting findings, causing confusion among the public and health professionals. In this review, we discuss important factors leading to these inconsistencies, in the context of atherosclerosis, including clinical study design and the differential effects of EPA and DHA on cell function. We propose steps to improve clinical and basic experimental study design in order to improve supplement composition optimization. Finally, we propose that understanding the factors underlying the poor response to n-3 PUFAs, and the development of molecular biomarkers for predicting response may help towards a more personalized treatment.

Activity, Expression, and Substrate Preference of the Δ(6)-Desaturase in Slow- or Fast-Growing Rabbit Genotypes

In the present paper liver fatty acid Δ(6) desaturation (fads2) activity was analyzed in two rabbit strains with slow- (S, 27.5 g/day) or fast-growing (F, 48.5 g/day) rate. The fatty acid profile of the liver showed a different PUFA profile in the two strains with a lower n-6/n-3 ratio in the S rabbits. The expression of fads2 was 2-fold higher in S than in F rabbits, whereas enzyme activity was higher in F and more oriented toward the desaturation of linoleic acid (90%). In contrast, S showed a higher preference for linolenic acid (38.9 vs 10%). This study identified a single difference in the fads2 amino acid sequence between these two strains. Such a difference consists in the substitution of Gly104 to Ser104 in the sequence of F fads2. These results indicate for the first time that genetic selection for performance may affect the preference for PUFA toward desaturation of linoleic/linolenic acid.

Fortification of pork loins with docosahexaenoic acid (DHA) and its effect on flavour

Pork is traditionally low in docosahexanoic acid (DHA, C22:6n-3) and deficient in omega-3 fats for a balanced human diet. DHA as triglycerides was commercially prepared from the microalgae Schizochytrium and injected into fresh pork loins. Treatments of a mixed brine control (CON), 3.1% sunflower oil in mixed brine (SF) and a 3.1% DHA oil in mixed brine (DHA) were injected into pork loins at 10 mL/100 g and grilled at 205°C. After cooking, the CON and SF pork loins contained 0.03 to 0.05 mg DHA/g of pork and the DHA injected loins contained approximately 1.46 mg DHA/g. This also changed the fatty acid profile of omega-6: omega-3 from, 5 to 1 in the CON pork, to a ratio of 1.7 to 1 in DHA pork. The appearance, odor, oxidation rates and sensory taste, as judged by a trained panel, determined the DHA injected meat to be, 'slightly desirable’ and gave lower 'off flavour’ scores, relative to the CON and SF injected pork. Pork can be fortified with DHA oil to 146 mg/100 g serving, which would meet half the recommended daily omega 3 fatty acid requirements for adult humans and would be desirable in taste.

Cardiovascular risk factors among prisoners: an integrative review

BACKGROUND AND AIM

Incarceration is characterized by inequalities in disease burden and an increased risk for cardiovascular disease (CVD). The aim of this review was to critique published empirical research studies on cardiovascular risk factors among prisoners and to summarize and synthesize current knowledge and findings across these studies.

DESIGN AND REVIEW METHOD

An integrative review of the studies was conducted. Cooper's five stage method was used as a framework to guide data collection, analysis, and synthesis. Quality appraisal of retrieved studies was done using a combined evaluation tool for quantitative research studies and a checklist. The following databases were searched: CINAHL, MEDLINE, PubMed, Cochrane, Indigenous Studies Portal (iPortal), Native Health Database, Criminal Justice Abstracts, and PsychInfo using keywords. Inclusion criteria were used to select published papers.

RESULTS AND CONCLUSION

A total of 12 studies that met the inclusion criteria were identified and analyzed. Hypertension, among other CVD risk factors such as smoking, physical inactivity and obesity, was one of the three most common CVD risk factors found in prisoners. Women and young offenders had a higher prevalence of hypercholesterolemia. Identifying prevalent risks factors among prisoners might influence the development of CVD prevention strategies that are specifically directed to at risk prisoners.

The omega-3 fatty acid nutritional landscape: health benefits and sources

Dietary fatty acids (FA) are increasingly recognized as major biologic regulators and have properties that relate to health outcomes and disease. The longer chain, more bioactive (n-6) (or omega-6) FA and (n-3) (or omega-3) FA share similar elongation and desaturation enzymes in their conversion from the essential (n-6) FA, linoleic acid, and (n-3) FA, α-linolenic acid (ALA). Conversion from these essential FA is very inefficient. However, now for the (n-3) FA series, soy oil can be enriched with (n-3) stearidonic acid (SDA) to allow for much more efficient conversion to longer chain EPA. EPA and the longer chain DHA possess distinct physical and biological properties that generally impart properties to cells and tissue, which underlie their ability to promote health and prevent disease. Although active in a number of areas of human biology, mechanisms of action of EPA and DHA are perhaps best defined in cardiovascular disease. There is concern that to reach the intake recommendations of EPA and DHA, their supply from cold water fish will be insufficient. Gaps in understanding mechanisms of action of (n-3) FA in a number of health and disease areas as well as optimal sources and intake levels for each need to be defined by further research. Because of the inefficient conversion of ALA, the appearance of SDA in enriched soy oil offers a biologically effective and cost effective approach to providing a sustainable plant source for (n-3) FA in the future.

Effect of ALA-enriched food supply on cardiovascular risk factors in males

The outcome of a total dietary approach using a wide range of n-3 polyunsaturated fatty acids (PUFA) enriched food items on cardiovascular diseases called for further investigation. The study objective was to assess the effect of an ALA-enriched food supply on cardiovascular risk factors in healthy males. A dietary intervention (single-blind field trial with pre- and post-measurements) was performed with 59 healthy males in a Belgian prison. Over a period of 12 weeks they were supplied with an n-3 enriched diet (containing 6.5 g n-3 PUFA/day compared to 4 g n-3 PUFA/day in the standard diet) that was substituted for their regular diet, increasing mainly the alpha-linolenic acid intake (from 2.8 to around 5 g/day). The results indicated no impact on subjects waist circumference, weight and BMI or systolic blood pressure. In contrast, the diastolic blood pressure significantly decreased during the intervention period (from 74.6 +/- 8.2 to 71.7 +/- 10.1 mmHg; P < 0.02). Moreover, the HDL-cholesterol level increased in non-smoking participants (from 0.97 +/- 0.25 to 1.06 +/- 0.23 mmol/l; P < 0.03). In summary, the study demonstrated that enrichment of commonly eaten food items with n-3 fatty acids provides the opportunity to increase the n-3 fatty acid intake and to decrease the n-6/n-3 ratio which results in a decreasing diastolic blood pressure and an increase of HDL-cholesterol (in non-smokers).

n-3 fatty acids reduce arterial LDL-cholesterol delivery and arterial lipoprotein lipase levels and lipase distribution

OBJECTIVE

We previously reported that saturated fat (SAT)-enriched diets increase arterial cholesteryl ester (CE) deposition, especially from LDL-selective uptake (SU), and this was associated with increased arterial lipoprotein lipase (LpL). We now question how n-3 fatty acid rich diets influence arterial cholesterol delivery and arterial LpL levels.

METHODS AND RESULTS

C57BL/6 mice were fed chow or eucaloric high-fat diets enriched in SAT or fish oil (n-3) for 12 weeks, and then injected with double radiolabeled or fluorescent-labeled human LDL to separately trace LDL-CE and LDL-apoB uptake. SAT and n-3 diets increased plasma cholesterol levels similarly; n-3 diets lowered plasma triglyceride concentrations. SAT increased arterial LDL-SU with significantly higher CE infiltration into aortic media. In contrast, n-3 markedly reduced total LDL uptake and CE deposition and abolished SU with LDL localized only in aortic intima. Disparate patterns of CE deposition between diets were consistent with distribution of arterial LpL-SAT diets induced higher LpL levels throughout the aorta; n-3 diets decreased LpL levels and limited LpL expression to the aortic intima.

CONCLUSIONS

n-3 rich diets decrease arterial total LDL delivery and abrogate LDL-SU in parallel with changing arterial wall LpL expression and distribution.

Conclusions and recommendations from the symposium, Beyond Cholesterol: Prevention and Treatment of Coronary Heart Disease with n-3 Fatty Acids

After the symposium "Beyond Cholesterol: Prevention and Treatment of Coronary Heart Disease with n-3 Fatty Acids," faculty who presented at the conference submitted manuscripts relating to their conference topics, and these are presented in this supplement. The content of these manuscripts was reviewed, and 2 conference calls were convened. The objective was to summarize existing evidence, gaps in evidence, and future research needed to strengthen recommendations for specific intakes of n-3 fatty acids for different conditions relating to cardiovascular disease. The following 2 questions were the main items discussed. What are the roles of n-3 fatty acids in primary versus secondary prevention of coronary heart disease? What are the roles of n-3 fatty acids in hypertriglyceridemia, in the metabolic syndrome and type 2 diabetes, and in sudden cardiac death, cardiac arrhythmias, and vulnerable plaque? Each area was summarized by using 2 general categories: 1) current knowledge for which general consensus exists, and 2) recommendations for research and policy. Additional references for these conclusions can be found in the articles included in the supplement.

Impact of communication on consumers' food choices

Consumers' food choices and dietary behaviour can be markedly affected by communication and information. Whether the provided information is processed by the receiver, and thus becomes likely to be effective, depends on numerous factors. The role of selected determinants such as uncertainty, knowledge, involvement, health-related motives and trust, as well as message content variables, are discussed in the present paper based on previous empirical studies. The different studies indicate that: uncertainty about meat quality and safety does not automatically result in more active information search; subjective knowledge about fish is a better predictor of fish consumption than objective knowledge; high subjective knowledge about functional foods as a result of a low trusted information source such as mass media advertising leads to a lower probability of adopting these foods in the diet. Also, evidence of the stronger impact of negative news as compared with messages promoting positive outcomes of food choices is discussed. Finally, three audience-segmentation studies based on consumers' involvement with fresh meat, individuals' health-related-motive orientations and their use of and trust in fish information sources are presented. A clear message from these studies is that communication and information provision strategies targeted to a specific audience's needs, interests or motives stand a higher likelihood of being attended to and processed by the receiving audience, and therefore also stand a higher chance of yielding their envisaged impact in terms of food choice and dietary behaviour.

How relevant is the ratio of dietary n-6 to n-3 polyunsaturated fatty acids to cardiovascular disease risk? Evidence from the OPTILIP study

PURPOSE OF REVIEW

There has been much debate over the practical utility of the dietary ratio of n-6 to n-3 polyunsaturated fatty acids in optimizing the benefits of n-3 fatty acids (C18-C22) on cardiovascular health. This review examines the supporting evidence from the OPTILIP study within the context of the emerging consensus on the value of this dietary metric.

RECENT FINDINGS

The question of whether the ratio of n-6/n-3 polyunsaturated fatty acids or total amounts of dietary polyunsaturated fatty acids is of more importance to cardiovascular health has been addressed recently in a randomly controlled trial (OPTILIP) and in a stable isotope tracer study. These two studies were independently unanimous in concluding that the ratio of n-6/n-3 polyunsaturated fatty acids is of no value in modifying cardiovascular disease risk. The latter study also showed that the absolute amounts of dietary linoleic acid and alpha-linolenic acid are of relevance to the efficiency of conversion of alpha-linolenic acid to eicosapentaenoic acid and docosahexaenoic acid.

SUMMARY

This review should help to settle any outstanding controversy over the dietary ratio of n-6/n-3 polyunsaturated fatty acids. It reinforces current recommendations to increase the consumption of preformed eicosapentaenoic acid/docosahexaenoic acid in fish, and supports dietary measures to increase and decrease intakes alpha-linolenic acid and linoleic acid, respectively, to promote the endogenous synthesis of these longer chain n-3 polyunsaturated fatty acids.

Fish consumption is a safe solution to increase the intake of long-chain n-3 fatty acids

OBJECTIVES

Dietary intake of long-chain (LC) n-3 PUFA in developed countries is low compared with recommendations. Fish is naturally rich in LC n-3 PUFA, but is also a dietary source of heavy metals and organic pollutants. We investigated whether the recommendation for LC n-3 PUFA could be reached through fish consumption, without exceeding the provisional tolerable weekly intake of methylmercury (MeHg) and the tolerable weekly intake (TWI) of dioxin-like compounds. Also, the contribution of margarines enriched with LC n-3 PUFA was assessed.

DESIGN

Published nutrient and contaminant data were used in a probabilistic model to calculate the simultaneous nutrient and contaminant intake for different fish consumption scenarios.

RESULTS

The Belgian recommendation for EPA + DHA (0.3% of total energy intake) can be reached by consuming fatty fish a minimum of twice a week, or by varying between lean and fatty fish a minimum of three times a week. At this fish consumption level, MeHg intake is not an issue of toxicological concern. The intake of dioxin-like compounds approximates the TWI when consuming fatty fish more than twice a week, this being a potential toxicological risk because other food items also contribute to the weekly intake of dioxin-like compounds. Use of margarine enriched with LC n-3 PUFA can help to increase LC n-3 intake, on average by 159 mg/d.

CONCLUSIONS

Combination of regular fish consumption (twice a week) with important contribution of fatty fish species, in combination with regular consumption of margarine enriched with EPA + DHA, can be advised to achieve the recommendation for LC n-3 intake.

n-3 Fatty acids and cardiovascular disease: actions and molecular mechanisms

Cardiovascular disease and atherosclerosis are a leading cause of morbidity and mortality worldwide. Epidemiological studies and randomized control intervention trials have reported that n-3 fatty acids reduce cardiovascular events. A variety of biologic and molecular effects of n-3 fatty acids can modulate the mechanisms of development and progression of atherosclerosis. These include n-3 fatty acid effects on inflammation, cardiac excitability, platelet function, triglyceride blood levels, blood pressure and the stability of atheroma plaques. The molecular mechanisms are still not fully defined; but might involve changes in membrane fluidity, receptor responses and binding to intracellular receptors regulating gene transcription. Understanding and elucidating these mechanisms is important to development of future strategies for prevention and treatment of cardiovascular disease.

(n-3) Long chain PUFA dose-dependently increase oxygen utilization efficiency and inhibit arrhythmias after saturated fat feeding in rats

Fish oil (FO) modifies cardiac membrane phospholipid fatty acid composition to confer increased efficiency of oxygen utilization and antiarrhythmic effects. We tested the capacity of low-dose increments of FO, rich in (n-3) PUFA, to reverse the detrimental pro-arrhythmic and inefficient oxygen usage effects of dietary saturated fat (SAT) [including high ratio of (n-6) PUFA:(n-3) PUFA] during ischemia and reperfusion. Wistar rats were fed an SAT-enriched diet (15.3% fat, including 12% SAT, added by weight) for 6 wk and were then divided into 4 groups (n = 10/group) fed that diet or a 12% fat diet containing 3, 6, or 12% FO in place of SAT for 6 wk. Paced (300/min), erythrocyte-perfused isolated working hearts were subjected to low coronary flow ischemia (15 min) and were then reperfused. At normoxic baseline, external work capacity increased marginally at 6 and 12% FO; however, marked dose-related reductions in oxygen consumption were evident due to FO-dependent reduction in oxygen-energy utilization efficiency and associated reductions in coronary flow and oxygen extraction. Postischemic recovery resulted in lower oxygen consumption, greater oxygen-energy utilization efficiency, reduced coronary release of creatine kinase, and reduced incidence of arrhythmias in all FO groups compared with the SAT group. FO at a dose as low as 3% of total fat dietary supplement effectively reversed the high oxygen requirements and pro-arrhythmic effects of a SAT-rich diet even with continued consumption of SAT (9%) in this ex vivo animal model.

n-3 Fatty acid supplementation and regular moderate exercise: differential effects of a combined intervention on neutrophil function

CVD is associated with a cellular inflammatory/immune response.n-3 PUFA and moderate aerobic exercise independently alter cytokine production and leucocyte function. There is limited evidence for the combined effect of these treatments on immune function, particularly in patients with risk factors for CVD. We hypothesised that exercise would enhance the anti-inflammatory effects ofn-3 PUFA. In a randomised, placebo-controlled study, fifty volunteers were allocated double-blind to consume either sunflower oil (6 g/d, placebo) or DHA-rich fish oil (6 g/d; about 2 gn-3 PUFA; 1·6 g DHA /d) for 12 weeks. Volunteers were further randomised to undertake regular exercise (walking 3 d/week for 45 min at 75 % of maximum heart rate) or maintain their usual physical activity for 12 weeks. Immune functions were assessed in blood taken initially and after 12 weeks. There was no effect on cytokine production by T cells and monocytes. Superoxide anion production from stimulated blood neutrophils was decreased by fish oil (19·5 (sem8·5) %,P = 0·016) but not by exercise, and this change was negatively correlated with the incorporation of DHA into erythrocytes (r–0·385,P = 0·047). Participation in regular exercise maintained neutrophil bactericidal activity, which decreased in non-exercising subjects (2·9 (sem0·7) %,P = 0·013). Neutrophil chemotaxis and adherence were not significantly affected by exercise, oil, or the combination of the two. Thus the combination of moderate exercise and fish-oil supplementation, which reduces cardiovascular risk, may also help to counteract inflammation.

Comparative review of diets for the metabolic syndrome: implications for nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a significant health problem and affects 70 million adults in the United States (30% of the adult population), and an estimated 20% of these individuals have the most severe form of NAFLD-nonalcoholic steatohepatitis (NASH). The mechanisms underlying disease development and progression are awaiting clarification. Insulin resistance and obesity-related inflammation, among other possible genetic, dietary, and lifestyle factors, are thought to play a key role. A program targeting gradual weight reduction and physical exercise continues to be the gold standard of treatment for all forms of NAFLD. Even though weight loss and dietary and lifestyle changes are recommended as primary treatment for fatty liver, little to no scientific evidence is available on diet and NAFLD. This article reviews the implications of current dietary approaches, including national guidelines and popular weight-loss diets, with a focus on determining the optimal diet to prescribe for NAFLD and NASH patients. The effects of macronutrient content (carbohydrate, fat, and protein ratios) and specific food components, such as soluble fiber, n-3 fatty acids, and fructose, are discussed. The premises, effects, barriers, and issues related to current dietary guidelines and specific diets are discussed, and the question, "Will it work for the pathogenesis of NAFLD and NASH? ", is addressed.

Novel action of n-3 polyunsaturated fatty acids: inhibition of arachidonic acid-induced increase in tumor necrosis factor receptor expression on neutrophils and a role for proteases

OBJECTIVE

Neutrophils and tumor necrosis factor (TNF) play important roles in the pathogenesis of rheumatoid arthritis (RA). Modulation of TNF receptors (TNFRs) may contribute to the regulation of tissue damage, and n-6 polyunsaturated fatty acids (PUFAs) such as arachidonic acid (AA) can increase the expression of TNFRI and TNFRII on neutrophils. Because the n-3 PUFAs are antiinflammatory in RA, we examined whether, as a novel mechanism of action, n-3 PUFAs can antagonize the AA-induced increase in TNFR expression.

METHODS

Human neutrophils were treated with PUFAs and examined for changes in surface expression of TNFRs by flow cytometry. Translocation of protein kinase C (PKC) and activation of ERK-1/2 MAPK were determined by Western blotting. Intracellular calcium mobilization was measured in Fura 2-loaded cells by luminescence spectrometry.

RESULTS

Pretreatment of neutrophils with nanomolar levels of n-3 PUFAs, eicosapentaenoic acid, or docosahexaenoic acid led to a marked inhibition of the AA-induced up-regulation of TNFRs I and II. Such pretreatment, however, did not prevent AA from stimulating the activities of PKC and ERK-1/2, which is required for the actions of AA or its ability to mobilize Ca(2+). Nevertheless, treatment with n-3 PUFAs caused the stimulation of serine proteases that could cleave the TNFRs.

CONCLUSION

These findings suggest a mechanism by which the n-3 PUFAs inhibit the inflammatory response in RA, by regulating the ability of AA to increase TNFR expression. These results help fill the gaps in our knowledge regarding the mechanisms of action of n-3 PUFAs, thus allowing us to make specific recommendations for the use of n-3 PUFAs in the regulation of inflammatory diseases.

Omega-3 fatty acids and prevention of arrhythmias

PURPOSE OF REVIEW

There is now a considerable factual basis from laboratory and clinical trials that omega-3 fatty acids of fish oil will prevent fatal arrhythmias in animals and humans and this is the focus of the review.

RECENT FINDINGS

Several recent trials in humans have strengthened the evidence that omega-3 fatty acids may prevent arrhythmias although this has not been a uniform finding.

SUMMARY

Since there are at present some 400 000 deaths annually in the US alone and millions more worldwide, what has been learned about the antiarrhythmic actions of omega-3 fatty acids has considerable potential public-health benefit.