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

Omega-3 Fatty Acids and Arrhythmias

The pro- and antiarrhythmic effects of omega-3 polyunsaturated fatty acids (n-3 PUFAs) have been extensively studied in preclinical and human trials. Despite early evidence of an antiarrhythmic role of n-3 PUFA in the prevention of sudden cardiac death and postoperative and persistent atrial fibrillation (AF), subsequent well-designed randomized trials have largely not shown an antiarrhythmic benefit. Two trials that tested moderate and high-dose n-3 PUFA demonstrated a reduction in sudden cardiac death, but these findings have not been widely replicated, and the potential of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) to reduce arrhythmic death in combination, or as monotherapy, remains uncertain. The accumulated clinical evidence does not support supplementation of n-3 PUFA for postoperative AF or secondary prevention of AF. Several large, contemporary, randomized controlled trials of high-dose n-3 PUFA for primary or secondary cardiovascular prevention have demonstrated a small, significant, dose-dependent increased risk of incident AF compared with mineral oil or corn oil comparator. These findings were reproduced with both icosapent ethyl monotherapy and a mixed EPA+DHA formulation. The proarrhythmic mechanism of increased AF in contemporary cohorts exposed to high-dose n-3 PUFA is unknown. EPA and DHA and their metabolites have pleiotropic cardiometabolic and pro- and antiarrhythmic effects, including modification of the lipid raft microenvironment; alteration of cell membrane structure and fluidity; modulation of sodium, potassium, and calcium currents; and regulation of gene transcription, cell proliferation, and inflammation. Further characterization of the complex association between EPA, EPA+DHA, and DHA and AF is needed. Which formulations, dose ranges, and patient subgroups are at highest risk, remain unclear.

Activation of hTREK-1 by polyunsaturated fatty acids involves direct interaction

TREK-1 is a mechanosensitive channel activated by polyunsaturated fatty acids (PUFAs). Its activation is supposed to be linked to changes in membrane tension following PUFAs insertion. Here, we compared the effect of 11 fatty acids and ML402 on TREK-1 channel activation using the whole cell and the inside-out configurations of the patch-clamp technique. Firstly, TREK-1 activation by PUFAs is variable and related to the variable constitutive activity of TREK-1. We observed no correlation between TREK-1 activation and acyl chain length or number of double bonds suggesting that the bilayer-couple hypothesis cannot explain by itself the activation of TREK-1 by PUFAs. The membrane fluidity measurement is not modified by PUFAs at 10 µM. The spectral shift analysis in TREK-1-enriched microsomes indicates a KD,TREK1 at 44 µM of C22:6 n-3. PUFAs display the same activation and reversible kinetics than the direct activator ML402 and activate TREK-1 in both whole-cell and inside-out configurations of patch-clamp suggesting that the binding site of PUFAs is accessible from both sides of the membrane, as for ML402. Finally, we proposed a two steps mechanism: first, insertion into the membrane, with no fluidity or curvature modifications at 10 µM, and then interaction with TREK-1 channel to open it.

CYP2J2-mediated metabolism of arachidonic acid in heart: A review of its kinetics, inhibition and role in heart rhythm control

Cytochrome P450 2 J2 (CYP2J2) is primarily expressed extrahepatically and is the predominant epoxygenase in human cardiac tissues. This highlights its key role in the metabolism of endogenous substrates. Significant scientific interest lies in cardiac CYP2J2 metabolism of arachidonic acid (AA), an omega-6 polyunsaturated fatty acid, to regioisomeric bioactive epoxyeicosatrienoic acid (EET) metabolites that show cardioprotective effects including regulation of cardiac electrophysiology. From an in vitro perspective, the accurate characterization of the kinetics of CYP2J2 metabolism of AA including its inhibition and inactivation by drugs could be useful in facilitating in vitro-in vivo extrapolations to predict drug-AA interactions in drug discovery and development. In this review, background information on the structure, regulation and expression of CYP2J2 in human heart is presented alongside AA and EETs as its endogenous substrate and metabolites. The in vitro and in vivo implications of the kinetics of this endogenous metabolic pathway as well as its perturbation via inhibition and inactivation by drugs are elaborated. Additionally, the role of CYP2J2-mediated metabolism of AA to EETs in cardiac electrophysiology will be expounded.

Lipidome Atlas of the Developing Heart Uncovers Dynamic Membrane Lipid Attributes Underlying Cardiac Structural and Metabolic Maturation

Precise metabolic rewiring during heart organogenesis underlies normal cardiac development. Herein, we utilized high-coverage, quantitative lipidomic approaches to construct lipidomic atlases of whole hearts (861 lipids; 31 classes) and mitochondria (587 lipids; 27 classes) across prenatal and postnatal developmental stages in mice. We uncovered the progressive formation of docosahexaenoyl-phospholipids and enhanced remodeling of C18:2, C20:3, and C20:4 fatty acyl moieties into cardiolipins as cardiac development progresses. A preferential flow of ceramides toward sphingomyelin biosynthesis over complex glycosphingolipid formation was also noted. Using maSigPro and GPclust algorithms, we identified a repertoire of 448 developmentally dynamic lipids and mapped their expression patterns to a library of 550 biologically relevant developmentally dynamic genes. Our combinatorial transcriptomics and lipidomics approaches identified Hadha, Lclat1, and Lpcat3 as candidate molecular drivers governing the dynamic remodeling of cardiolipins and phospholipids, respectively, in heart development. Our analyses revealed that postnatal cardiolipin remodeling in the heart constitutes a biphasic process, which first accumulates polyunsaturated C78-cardiolipins prior to tetralinoleoyl cardiolipin forming the predominant species. Multiomics analyses supplemented with transmission electron microscopy imaging uncovered enhanced mitochondria-lipid droplet contacts mediated by perilipin-5. Our combinatorial analyses of multiomics data uncovered an association between mitochondrial-resident, docosahexaenoic acid-phospholipids and messenger RNA levels of proton-transporting adenosine triphosphate synthases on inner mitochondrial membranes, which adds credence to the membrane pacemaker theory of metabolism. The current findings offer lipid-centric biological insights potentially important to understanding the molecular basis of cardiac metabolic flexibility and disease pathology.

Chronotropic effects and mechanisms of long-chain omega-3 polyunsaturated fatty acids on heartbeat: the latest insights

The roles of the resting heart rate (RHR) have been actively investigated and increasingly recognized in recent decades, because of the growing evidence that fast RHR is associated with and predicts the risk of developing cardiovascular and metabolic disorders, as well as all-cause mortality. Long-chain omega-3 polyunsaturated fatty acids (PUFAs) (eg, eicosapentaenoic acid and docosahexaenoic acid) have been shown to have chronotropic effects on heartbeat in both healthy people and patients with various disease conditions. The aims of this review are (1) to briefly summarize the importance of elevated RHR in disease pathogenesis and mortality; (2) to provide an update on the negative chronotropic effect of omega-3 PUFAs on the heart; (3) to highlight how omega-3 PUFAs regulate heart rate through the autonomic nervous system - a central control mechanism; and (4) to highlight how omega-3 PUFAs modulate the trans-membrane ionic channels in cardiomyocytes - a fundamental mechanism of cardiac automaticity. Eicosapentaenoic acid and docosahexaenoic acid are nutrients derived from some aquatic organisms, and they can also be converted from digested oily seeds and nuts of some terrestrial plants in the body. The consumption of omega-3 PUFAs for RHR reduction represents a lifestyle modification for risk factor management and promises nutritional benefits for public health improvement.

Direct evidence of bradycardic effect of omega-3 fatty acids acting on nucleus ambiguus

Docosahexaenoic acid (DHA) an omega-3 polyunsaturated fatty acid, is an agonist of FFA1 receptor. DHA administration reduces the heart rate via unclear mechanisms. We examined the effect of DHA on neurons of nucleus ambiguus that provide the parasympathetic control of heart rate. DHA produced a dose-dependent increase in cytosolic Ca²⁺ concentration in cardiac-projecting nucleus ambiguus neurons; the effect was prevented by GW1100, a FFA1 receptor antagonist. DHA depolarized cultured nucleus ambiguus neurons via FFA1 activation. Bilateral microinjection of DHA into nucleus ambiguus produced bradycardia in conscious rats. Our results indicate that DHA decreases heart rate by activation of FFA1 receptor on cardiac-projecting nucleus ambiguus neurons.

About the controversies of the cardioprotective effect of n-3 polyunsaturated fatty acids (PUFAs) between animal studies and clinical meta-analyses: a review with several strategies to enhance the beneficial effects of n-3 PUFAs

Several meta-analyses describing the effect of n-3 polyunsaturated fatty acids on the survival rate of the victims of an acute coronary event do not clearly support a beneficial impact of these fatty acids. Yet, animal studies consistently show n-3 PUFA-induced protection against ischemia-reperfusion-induced myocardial injuries. The impact on reperfusion arrhythmias of these PUFAs is more controversial. The literature shows the anti-arrhythmic properties of circulating n-3 PUFAs. However, when these fatty acids are incorporated in the cardiac membrane, they protect the myocardial tissue vis a vis cellular damage but they can be either pro- or anti-arrhythmic during reperfusion, depending on the severity of tissue injuries. The latter elements can explain the lack of beneficial effect observed in the meta-analyses, but a proper use of n-3 PUFAs may provide advantages in terms of survival rate. This review discusses the different results obtained in humans and animals and presents several strategies to enhance the beneficial effects of n-3 PUFAs.

Tumor Necrosis Factor-α in Heart Failure: an Updated Review

PURPOSE OF THE REVIEW

Proinflammatory cytokines are consistently elevated in congestive heart failure. In the current review, we provide an overview on the current understanding of how tumor necrosis factor-α (TNFα), a key proinflammatory cytokine, potentiates heart failure by overwhelming the anti-inflammatory responses disrupting the homeostasis.

RECENT FINDINGS

Studies have shown co-relationship between severity of heart failure and levels of the proinflammatory cytokine TNFα and one of its secondary mediators interleukin-6 (IL-6), suggesting their potential as biomarkers. Recent efforts have focused on understanding the mechanisms of how proinflammatory cytokines contribute towards cardiac dysfunction and failure. In addition, how unchecked proinflammatory cytokines and their cross-talk with sympathetic system overrides the anti-inflammatory response underlying failure. The review offers insights on how TNFα and IL-6 contribute to cardiac dysfunction and failure. Furthermore, this provides a forum to begin the discussion on the cross-talk between sympathetic drive and proinflammatory cytokines and its determinant role in deleterious outcomes.

Proinflammatory Cytokines Mediate GPCR Dysfunction

Proinflammatory reaction by the body occurs acutely in response to injury that is considered primarily beneficial. However, sustained proinflammatory cytokines observed with chronic pathologies such as metabolic syndrome, cancer, and arthritis are detrimental and in many cases is a major cardiovascular risk factor. Proinflammatory cytokines such as interleukin-1, interleukin-6, and tumor necrosis factor α (TNFα) have long been implicated in cardiovascular risk and considered to be a major underlying cause for heart failure (HF). The failure of the anti-TNFα therapy for HF indicates our elusive understanding on the dichotomous role of proinflammatory cytokines on acutely beneficial effects versus long-term deleterious effects. Despite these well-described observations, less is known about the mechanistic underpinnings of proinflammatory cytokines especially TNFα in pathogenesis of HF. Increasing evidence suggests the existence of an active cross-talk between the TNFα receptor signaling and G-protein-coupled receptors such as β-adrenergic receptor (βAR). Given that βARs are the key regulators of cardiac function, the review will discuss the current state of understanding on the role of proinflammatory cytokine TNFα in regulating βAR function.

Potential Roles of n-3 PUFAs during Skeletal Muscle Growth and Regeneration

Omega-3 polyunsaturated fatty acids (n-3 PUFAs), which are commonly found in fish oil supplements, are known to possess anti-inflammatory properties and more recently alter skeletal muscle function. In this review, we discuss novel findings related to how n-3 PUFAs modulate molecular signaling responsible for growth and hypertrophy as well as the activity of muscle stem cells. Muscle stem cells commonly known as satellite cells, are primarily responsible for driving the skeletal muscle repair process to potentially damaging stimuli, such as mechanical stress elicited by exercise contraction. To date, there is a paucity of human investigations related to the effects of n-3 PUFAs on satellite cell content and activity. Based on current in vitro investigations, this review focuses on novel mechanisms linking n-3 PUFA’s to satellite cell activity and how they may improve muscle repair. Understanding the role of n-3 PUFAs during muscle growth and regeneration in association with exercise could lead to the development of novel supplementation strategies that increase muscle mass and strength, therefore possibly reducing the burden of muscle wasting with age.

Associations of the serum long-chain n-3 PUFA and hair mercury with resting heart rate, peak heart rate during exercise and heart rate recovery after exercise in middle-aged men

Long-chain n-3 PUFA from fish have been associated with lower risk of CVD. Fish may also contain methylmercury, which may attenuate the inverse associations of the long-chain n-3 PUFA. However, the mechanisms underlying these associations are not fully known. We evaluated the associations of the serum long-chain n-3 PUFA (EPA, DPA and DHA) and hair Hg with resting heart rate (HR), peak HR during cycle ergometer exercise and HR recovery after exercise. A total of 1008 men from the population-based Kuopio Ischaemic Heart Disease Risk Factor Study, aged 42-60 years and free of CVD, were studied. After multivariate-adjustments in ANCOVA, higher serum total long-chain n-3 PUFA concentration was associated with lower resting HR (extreme-quartile difference 2·2 beats/min; 95 % CI 0·2, 4·1, P trend across quartiles=0·02), but not with peak HR or HR recovery. Associations were generally similar when EPA, DPA and DHA were evaluated individually, except for DPA, which was also associated with better HR recovery after exercise (extreme-quartile difference 2·1 beats/min; 95 % CI 0·1, 4·2, P trend=0·06). Higher hair Hg content had a trend towards lower peak HR after adjusting for the long-chain n-3 PUFA (P trend=0·05), but it only slightly attenuated the associations of the serum long-chain n-3 PUFA with HR. These findings suggest that higher serum long-chain n-3 PUFA concentrations are associated with lower resting HR in middle-aged men from Eastern Finland, which may partially explain the potential cardioprotective effect of fish intake.

Therapeutic potential of omega-3 fatty acid-derived epoxyeicosanoids in cardiovascular and inflammatory diseases

Numerous benefits have been attributed to dietary long-chain omega-3 polyunsaturated fatty acids (n-3 LC-PUFAs), including protection against cardiac arrhythmia, triglyceride-lowering, amelioration of inflammatory, and neurodegenerative disorders. This review covers recent findings indicating that a variety of these beneficial effects are mediated by "omega-3 epoxyeicosanoids", a class of novel n-3 LC-PUFA-derived lipid mediators, which are generated via the cytochrome P450 (CYP) epoxygenase pathway. CYP enzymes, previously identified as arachidonic acid (20:4n-6; AA) epoxygenases, accept eicosapentaenoic acid (20:5n-3; EPA) and docosahexaenoic acid (22:6n-3; DHA), the major fish oil n-3 LC-PUFAs, as efficient alternative substrates. In humans and rodents, dietary EPA/DHA supplementation causes a profound shift of the endogenous CYP-eicosanoid profile from AA- to EPA- and DHA-derived metabolites, increasing, in particular, the plasma and tissue levels of 17,18-epoxyeicosatetraenoic acid (17,18-EEQ) and 19,20-epoxydocosapentaenoic acid (19,20-EDP). Based on preclinical studies, these omega-3 epoxyeicosanoids display cardioprotective, vasodilatory, anti-inflammatory, and anti-allergic properties that contribute to the beneficial effects of n-3 LC-PUFAs in diverse disease conditions ranging from cardiac disease, bronchial disorders, and intraocular neovascularization, to allergic intestinal inflammation and inflammatory pain. Increasing evidence also suggests that background nutrition as well as genetic and disease state-related factors could limit the response to EPA/DHA-supplementation by reducing the formation and/or enhancing the degradation of omega-3 epoxyeicosanoids. Recently, metabolically robust synthetic analogs mimicking the biological activities of 17,18-EEQ have been developed. These drug candidates may overcome limitations of dietary EPA/DHA supplementation and provide novel options for the treatment of cardiovascular and inflammatory diseases.

Modulation of heart rate and heart rate variability by n-3 long chain polyunsaturated fatty acids: Speculation on mechanism(s)

Heart rate (HR) and heart rate variability (HRV) are valuable markers of health. Although the underlying mechanism(s) are controversial, it is well documented that n-3 long chain polyunsaturated fatty acid (LCPUFA) intake improves HR and HRV in various populations. Autonomic modulation and/or alterations in cardiac electrophysiology are commonly cited as potential mechanisms responsible for these effects. This article reviews existing evidence for each and explores a separate mechanism which has not received much attention but has scientific merit. Based on presented evidence, it is proposed that n-3 LCPUFAs affect HR and HRV directly by autonomic modulation and indirectly by altering circulating factors, both dependently and independently of the autonomic nervous system. The evidence for changes in cardiac electrophysiology as the mechanism by which n-3 LCPUFAs affect HR and HRV needs strengthening.

Actions and Mechanisms of Polyunsaturated Fatty Acids on Voltage-Gated Ion Channels

Polyunsaturated fatty acids (PUFAs) act on most ion channels, thereby having significant physiological and pharmacological effects. In this review we summarize data from numerous PUFAs on voltage-gated ion channels containing one or several voltage-sensor domains, such as voltage-gated sodium (Na_V), potassium (K_V), calcium (Ca_V), and proton (H_V) channels, as well as calcium-activated potassium (K_Ca), and transient receptor potential (TRP) channels. Some effects of fatty acids appear to be channel specific, whereas others seem to be more general. Common features for the fatty acids to act on the ion channels are at least two double bonds in cis geometry and a charged carboxyl group. In total we identify and label five different sites for the PUFAs. PUFA site 1: The intracellular cavity. Binding of PUFA reduces the current, sometimes as a time-dependent block, inducing an apparent inactivation. PUFA site 2: The extracellular entrance to the pore. Binding leads to a block of the channel. PUFA site 3: The intracellular gate. Binding to this site can bend the gate open and increase the current. PUFA site 4: The interface between the extracellular leaflet of the lipid bilayer and the voltage-sensor domain. Binding to this site leads to an opening of the channel via an electrostatic attraction between the negatively charged PUFA and the positively charged voltage sensor. PUFA site 5: The interface between the extracellular leaflet of the lipid bilayer and the pore domain. Binding to this site affects slow inactivation. This mapping of functional PUFA sites can form the basis for physiological and pharmacological modifications of voltage-gated ion channels.

Omega-3 Polyunsaturated Fatty Acids: The Way Forward in Times of Mixed Evidence

Almost forty years ago, it was first hypothesized that an increased dietary intake of omega-3 polyunsaturated fatty acids (PUFA) from fish fat could exert protective effects against several pathologies. Decades of intense preclinical investigation have supported this hypothesis in a variety of model systems. Several clinical cardiovascular studies demonstrated the beneficial health effects of omega-3 PUFA, leading medical institutions worldwide to publish recommendations for their increased intake. However, particularly in recent years, contradictory results have been obtained in human studies focusing on cardiovascular disease and the clinical evidence in other diseases, particularly chronic inflammatory and neoplastic diseases, was never established to a degree that led to clear approval of treatment with omega-3 PUFA. Recent data not in line with the previous findings have sparked a debate on the health efficacy of omega-3 PUFA and the usefulness of increasing their intake for the prevention of a number of pathologies. In this review, we aim to examine the controversies on the possible use of these fatty acids as preventive/curative tools against the development of cardiovascular, metabolic, and inflammatory diseases, as well as several kinds of cancer.

Circulating omega-6 polyunsaturated fatty acids and total and cause-specific mortality: the Cardiovascular Health Study

BACKGROUND

Although omega-6 polyunsaturated fatty acids (n-6 PUFA) have been recommended to reduce coronary heart disease (CHD), controversy remains about benefits versus harms, including concerns over theorized proinflammatory effects of n-6 PUFA. We investigated associations of circulating n-6 PUFA including linoleic acid (the major dietary PUFA), γ-linolenic acid, dihomo-γ-linolenic acid, and arachidonic acid, with total and cause-specific mortality in the Cardiovascular Health Study, a community-based U.S. cohort.

METHODS AND RESULTS

Among 2792 participants(aged ≥65 years) free of cardiovascular disease at baseline, plasma phospholipid n-6 PUFA were measured at baseline using standardized methods. All-cause and cause-specific mortality, and total incident CHD and stroke, were assessed and adjudicated centrally. Associations of PUFA with risk were assessed by Cox regression. During 34 291 person-years of follow-up (1992-2010), 1994 deaths occurred (678 cardiovascular deaths), with 427 fatal and 418 nonfatal CHD, and 154 fatal and 399 nonfatal strokes. In multivariable models, higher linoleic acid was associated with lower total mortality, with extreme-quintile hazard ratio =0.87 (P trend=0.005). Lower death was largely attributable to cardiovascular disease causes, especially nonarrhythmic CHD mortality (hazard ratio, 0.51; 95% confidence interval, 0.32-0.82; P trend=0.001). Circulating γ-linolenic acid, dihomo-γ-linolenic acid, and arachidonic acid were not significantly associated with total or cause-specific mortality (eg, for arachidonic acid and CHD death, the extreme-quintile hazard ratio was 0.97; 95% confidence interval, 0.70-1.34; P trend=0.87). Evaluated semiparametrically, linoleic acid showed graded inverse associations with total mortality (P=0.005). There was little evidence that associations of n-6 PUFA with total mortality varied by age, sex, race, or plasma n-3 PUFA. Evaluating both n-6 and n-3 PUFA, lowest risk was evident with highest levels of both.

CONCLUSIONS

High circulating linoleic acid, but not other n-6 PUFA, was inversely associated with total and CHD mortality in older adults.

Influence of polyunsaturated fatty acids on blood pressure, resting heart rate and heart rate variability among French Polynesians

OBJECTIVE

To analyze the associations between marine n-3 polyunsaturated fatty acids (PUFAs) and blood pressure (BP), resting heart rate (HR), and heart rate variability (HRV) in a population highly exposed to methylmercury through the diet.

METHODS

Concentrations of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) in erythrocytes membranes were measured in 180 French Polynesian adults (≥18 years) residing in Tubuai, which is a community with a traditional lifestyle, or Papeete, which has a modern lifestyle. HRV was measured using a 2-hour ambulatory electrocardiogram (Holter). Resting HR and BP were measured using standardized protocols and pulse pressure (PP) was calculated as systolic BP - diastolic BP. The associations between n-3 PUFAs and the dependent variables were studied using simple and multiple linear regressions.

RESULTS

Increasing DHA concentration was associated with lower resting HR (β = -2.57, p = 0.005) and diastolic BP (β = -1.96, p = 0.05) and higher HRV in multivariable models. Specifically, DHA was associated with high frequency (HF; β = 0.19, p = 0.02) and the square root of the mean squared differences of successive R-R intervals (difference between two consecutive R waves; rMSSD; β = 0.08, p = 0.03), which are specific indices of the parasympathetic activity of the autonomic nervous system.

CONCLUSION

DHA was associated with lower BP and resting HR and higher HRV among French Polynesians who are also exposed to high methylmercury levels.

n-3 fatty acids and cardiovascular disease: the story is not over yet

A large body of evidences suggest a beneficial role of n-3 poly-unsaturated fatty acids (n-3 PUFAs) on cardiovascular disease, but recent observations and meta-analyses have raised doubts on their real efficacy. Many of these analyses, however, should be interpreted with caution, because of methodological shortcomings, heterogeneity of population, variability of drug dose and composition and other interpretation issues, and are not able to convincingly confute the results of the major clinical trials. Indeed, they demonstrated the efficacy of n-3 PUFAs at least in particular subset of individuals, such as post-acute myocardial infarction patients, at high risk of ventricular arrhythmias. The utilization of n-3 poly-unsaturated fatty acids in the current clinical practice should not be withheld, yet.

The effects of omega-3 polyunsaturated fatty acids on cardiac rhythm: a critical reassessment

Although epidemiological studies provide strong evidence for an inverse relationship between omega-3 polyunsaturated fatty acids (n-3 PUFAs) and cardiac mortality, inconsistent and often conflicting results have been obtained from both animal studies and clinical prevention trials. Despite these heterogeneous results, some general conclusions can be drawn from these studies: 1) n-PUFAs have potent effects on ion channels and calcium regulatory proteins that vary depending on the route of administration. Circulating (acute administration) n-3 PUFAs affect ion channels directly while incorporation (long-term supplementation) of these lipids into cell membranes indirectly alter cardiac electrical activity via alteration of membrane properties. 2) n-3 PUFAs reduce baseline HR and increase HRV via alterations in intrinsic pacemaker rate rather than from changes in cardiac autonomic neural regulation. 3) n-3 PUFAs may be only effective if given before electrophysiological or structural remodeling has begun and have no efficacy against atrial fibrillation. 5) Despite initial encouraging results, more recent clinical prevention and animal studies have not only failed to reduce sudden cardiac death but actually increased mortality in angina patients and increased rather than decreased malignant arrhythmias in animal models of regional ischemia. 6) Given the inconsistent benefits reported in clinical and experimental studies and the potential adverse actions on cardiac rhythm noted during myocardial ischemia, n-3 PUFA must be prescribed with caution and generalized recommendations to increase fish intake or to take n-3 PUFA supplements need to be reconsidered.

Do omega-3 polyunsaturated fatty acids reduce risk of sudden cardiac death and ventricular arrhythmias? A meta-analysis of randomized trials

INTRODUCTION

Omega-3 polyunsaturated fatty acids (PUFA) have demonstrated to have antiarrhythmic properties. However, randomized studies have shown inconsistent results.

OBJECTIVE

We aimed to analyze the effect of omega-3 PUFA on preventing potentially fatal ventricular arrhythmias and sudden cardiac death.

METHODS

Randomized trials comparing omega-3 PUFA to placebo and reporting sudden cardiac death (SCD) or first implanted cardioverter-defibrillator (ICD) event for ventricular tachycardia or fibrillation were included in this study. A meta-analysis using a random effects model was performed and results were expressed in terms of Odds Ratio (OR) and 95% Confidence Interval (CI) after evaluating for interstudy heterogeneity using I(2). The reported data were extracted on the basis of the intention-to-treat principle.

RESULTS

A total of 32,919 patients were included in nine trials; 16,465 patients received omega-3 PUFA and 16,454 received placebo. When comparing omega-3 PUFA to placebo, there was nonsignificant risk reduction of SCD or ventricular arrhythmias (OR = 0.82 [95% CI: 0.60-1.21], p = 0.21 I(2) = 49.7%).

CONCLUSION

Dietary supplementation with omega-3 PUFA does not affect the risk of SCD or ventricular arrhythmias.

Supplementary health benefits of linoleic Acid by improvement of vaginal cornification of ovariectomized rats

PURPOSE

This study aimed to evaluate the possible estrogenic activity of some ingredients of Nigella sativa including Linoleic acid and Gama-Linolenic acid by vaginal cornification assay.

METHODS

Forty ovariectomized (OVX) rats, aged 16 weeks were allotted randomly to five groups: negative control (taking 1 ml olive oil/ day); positive control (taking 0.2 mg/kg/day Conjucated Equine Estrogen-CEE); experimental groups (taking 50 mg/kg/day Linoleic acid or 10 mg/kg/day Gamma Linolenic acid or 15mg/kg/day Thymoquinone ). All of supplements administered via intragastric gavage for 21 consecutive days. To assess estrogen like activity, vaginal smear was examined daily and serum estradiol was measured at baseline, after 10 days and at the end of experiment.

RESULTS

The significant occurrence of vaginal cornification cell (p<0.05) after Linoleic acid supplementation indicated estrogenic activity of Linoleic acid which was in consistency with serum estradiol level, but this effect was not as much as CEE. Gama-Linolenic acid also exist a few cornified cell in smear which was not significantly differ from those control group.

CONCLUSION

Linoleic acid showed the beneficial effects on OVX rats' reproductive performance, thereby indicating its beneficial role in the treatment of the postmenopausal symptoms.

Triton X-100 inhibits L-type voltage-operated calcium channels

Triton X-100 (TX-100) is a nonionic detergent frequently used at millimolar concentrations to disrupt cell membranes and solubilize proteins. At low micromolar concentrations, TX-100 has been reported to inhibit the function of potassium channels. Here, we have used electrophysiological and functional techniques to examine the effects of TX-100 on another class of ion channels, L-type voltage-operated calcium channels (VOCCs). TX-100 (30 nmol·L(-1) to 3 μmol·L(-1)) caused reversible concentration-dependent inhibition of recombinant L-type VOCC (CaV 1.2) currents and of native L-type VOCC currents recorded from rat vascular smooth muscle cells and cardiac myocytes, and murine and human pancreatic β-cells. In functional studies, TX-100 (165 nmol·L(-1) to 3.4 μmol·L(-1)) caused concentration-dependent relaxation of rat isolated mesenteric resistance arteries prestimulated with phenylephrine or KCl. This effect was independent of the endothelium. TX-100 (1.6 μmol·L(-1)) inhibited depolarization-induced exocytosis in both murine and human isolated pancreatic β-cells. These data indicate that at concentrations within the nanomolar to low micromolar range, TX-100 significantly inhibits L-type VOCC activity in a number of cell types, an effect paralleled by inhibition of cell functions dependent upon activation of these channels. This inhibition occurs at concentrations below those used to solubilize proteins and may compromise the use of solutions containing TX-100 in bioassays.

Reduction of heart rate by omega-3 fatty acids and the potential underlying mechanisms

An elevated resting heart rate is one of the strongest predictors of cardiovascular mortality and is independently associated with sudden cardiac death (SCD). Agents capable of reducing heart rate without significant side effects are therefore of particular interest for the prevention of SCD. Recent human and animal studies have shown that omega-3 fatty acids can reduce heart rate. Our work has shown that omega-3 fatty acids significantly reduce membrane electrical excitability of the cardiac myocyte by lowering its resting membrane potential and the duration of the refractory period through inhibition of ion channels. We propose that these actions may be the underlying mechanisms for the omega-3 fatty acid-induced reduction of heart rate observed in both humans and animals. The heart rate-lowering capability of omega-3 fatty acids may contribute to their preventive effect against SCD.

Polyunsaturated Fatty acids in atrial fibrillation: looking for the proper candidates

Atrial fibrillation (AF) is the most common sustained arrhythmia encountered in clinical practice with growing prevalence in developed countries. Several medical and interventional therapies, such as atrial specific drugs and pulmonary vein isolation, have demonstrated prevention of recurrences. However, their suboptimal long-term success and significant rate of secondary effects have led to intensive research in the last decade focused on novel alternative and supplemental therapies. One such candidate is polyunsaturated fatty acids (PUFAs). Because of their biological properties, safety, simplicity, and relatively cheap cost, there is a special clinical interest in omega-3 PUFAs as a possible antiarrhythmic agent. Obtained from diets rich in fish, they represent one of the current supplemental therapies. At the cellular level, an increasing body of evidence has shown that n-3 PUFAs exert a variety of effects on cardiac ion channels, membrane dynamic properties, inflammatory cascade, and other targets related to AF prevention. In this article, we review the current basic and clinical evidence pertinent to n-3 PUFAs in AF treatment and prevention. We also discuss controversial outcomes among clinical studies and propose specific subsets of AF patients who will benefit most from n-3 PUFAs.

Serum long-chain n-3 polyunsaturated fatty acids, mercury, and risk of sudden cardiac death in men: a prospective population-based study

Objectives

Fish consumption has been associated with reduced risk of cardiovascular diseases (CVD), especially sudden cardiac death (SCD). Fish is the major source of long-chain n-3 polyunsaturated fatty acids (PUFA) eicosapentaenoic acid and docosahexaenoic acid. It is also a major source of methylmercury, which was associated with increased risk of CVD in this study population. Impact of interaction between long-chain n-3 PUFA and methylmercury on the SCD risk is unknown.

Methods

A total of 1857 men from the prospective, population-based Kuopio Ischaemic Heart Disease Risk Factor study, aged 42–60 years and free of CVD at baseline in 1984–1989, were studied. Serum long-chain n-3 PUFA was used as the marker for long-chain n-3 PUFA intake and hair mercury as the marker for mercury exposure.

Results

During the mean follow-up of 20.1 years, 91 SCD events occurred. In the multivariate Cox proportional hazards regression models, serum long-chain n-3 PUFA concentration was not associated with the risk of SCD until hair mercury was accounted for; then the hazard ratio (HR) in the highest vs. lowest tertile was 0.54 [95% confidence interval (CI) 0.32 to 0.91, p for trend  = 0.046]. When the analyses were stratified by hair mercury content, among those with lower hair mercury, each 0.5 percentage unit increase in the serum long-chain n-3 PUFA was associated with HR of 0.77 (95% CI 0.64 to 0.93), whereas no association was seen among those with higher hair mercury (p for interaction  = 0.01). Among the individual long-chain n-3 PUFA, docosahexaenoic acid was most strongly associated with the risk.

Conclusion

High exposure to mercury may reduce the benefits of long-chain n-3 PUFA on SCD.

Why Do We Still Need Large Scale Clinical Trial: The Case of n-3 PUFA

After the first reports about a protective effect on coronary heart disease (CHD) published more than 40 years ago, wide interest in the therapeutic use of n-3 polyunsaturated fatty acids (n-3 PUFA) aroused. Since then, many studies and meta-analyses have reported a significantly reduced risk of CHD and CV death due to fish and n-3 PUFA intake. Some of the overviews reported a significant reduction of risk of sudden cardiac death, all-cause death, and nonfatal CV events. On the other side, recent clinical trials had mixed findings, raising concern about the consistency of the evidence on n-3 PUFA. We critically reviewed recent large clinical trials reporting data on the antiarrhythmic effects of n-3 PUFA in different clinical settings, i.e., patients with CHD, heart failure, with implantable cardioverter defibrillator, and at risk of atrial fibrillation, in order to summarize the results which are available up to date and possibly give "substantiated" fuel to the debate on the conflicting results of n-3 PUFA.

Effect of dietary omega-3 polyunsaturated Fatty acids on heart rate and heart rate variability in animals susceptible or resistant to ventricular fibrillation

The consumption of omega-3 polyunsaturated fatty acids (n−3 PUFAs) has been reported to reduce cardiac mortality following myocardial infarction as well as to decrease resting heart rate (HR) and increase HR variability (HRV). However, it has not been established whether n−3 PUFAs exhibit the same actions on HR and HRV in individuals known to be either susceptible or resistant to ventricular fibrillation (VF). Therefore, HR and HRV (high frequency and total R–R interval variability) were evaluated before and 3 months after n−3 PUFA treatment in dogs with healed myocardial infarction that were either susceptible (VF+, n = 31) or resistant (VF−, n = 31) to ventricular tachyarrhythmias induced by a 2-min coronary artery occlusion during the last minute of a submaximal exercise test. HR and HRV were evaluated at rest, during submaximal exercise and in response to acute myocardial ischemia at rest before and after either placebo (1 g/day, corn oil, VF+, n = 9; VF− n = 8) or n−3 PUFA (docosahexaenoic acid + eicosapentaenoic acid ethyl esters, 1–4 g/day, VF+, n = 22; VF−, n = 23) treatment for 3 months. The n−3 PUFA treatment elicited similar increases in red blood cell membrane, right atrial, and left ventricular n−3 PUFA levels in both the VF+ and VF− dogs. The n−3 PUFA treatment also provoked similar reductions in baseline HR and increases in baseline HRV in both groups that resulted in parallel shifts in the response to either exercise or acute myocardial ischemia (that is, the change in these variables induced by physiological challenges was not altered after n−3 PUFA treatment). These data demonstrate that dietary n−3 PUFA decreased HR and increased HRV to a similar extent in animals known to be prone to or resistant to malignant cardiac tachyarrhythmias.

CYP-eicosanoids--a new link between omega-3 fatty acids and cardiac disease?

Fish oil omega-3 fatty acids such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) protect against arrhythmia and sudden cardiac death by largely unknown mechanisms. Recent in vitro and in vivo studies demonstrate that arachidonic acid (AA) metabolizing cytochrome P450-(CYP) enzymes accept EPA and DHA as efficient alternative substrates. Dietary EPA/DHA supplementation causes a profound shift of the cardiac CYP-eicosanoid profile from AA- to EPA- and DHA-derived epoxy- and hydroxy-metabolites. CYP2J2 and other CYP epoxygenases preferentially epoxidize the ω-3 double bond of EPA and DHA. The corresponding metabolites, 17,18-epoxy-EPA and 19,20-epoxy-DHA, dominate the CYP-eicosanoid profile of the rat heart after EPA/DHA supplementation. The (ω-3)-epoxyeicosanoids show highly potent antiarrhythmic properties in neonatal cardiomyocytes, suggesting that these metabolites may specifically contribute to the cardioprotective effects of omega-3 fatty acids. This hypothesis is discussed in the context of recent findings that revealed CYP-eicosanoid mediated mechanisms in cardiac ischemia-reperfusion injury and maladaptive cardiac hypertrophy.

Fish oil for the treatment of cardiovascular disease

Omega-3 fatty acids, which are found abundantly in fish oil, are increasingly being used in the management of cardiovascular disease. It is clear that fish oil, in clinically used doses (typically 4 g/d of eicosapentaenoic acid and docosahexaenoic acid) reduce high triglycerides. However, the role of omega-3 fatty acids in reducing mortality, sudden death, arrhythmias, myocardial infarction, and heart failure has not yet been established. This review will focus on the current clinical uses of fish oil and provide an update on their effects on triglycerides, coronary artery disease, heart failure, and arrhythmia. We will explore the dietary sources of fish oil as compared with drug therapy, and discuss the use of fish oil products in combination with other commonly used lipid-lowering agents. We will examine the underlying mechanism of fish oil's action on triglyceride reduction, plaque stability, and effect in diabetes, and review the newly discovered anti-inflammatory effects of fish oil. Finally, we will examine the limitations of current data and suggest recommendations for fish oil use.

17(R),18(S)-epoxyeicosatetraenoic acid, a potent eicosapentaenoic acid (EPA) derived regulator of cardiomyocyte contraction: structure-activity relationships and stable analogues

17(R),18(S)-epoxyeicosatetraenoic acid [17(R),18(S)-EETeTr], a cytochrome P450 epoxygenase metabolite of eicosapentaenoic acid (EPA), exerts negative chronotropic effects and protects neonatal rat cardiomyocytes against Ca(2+)-overload with EC(50) ≈ 1-2 nM. Structure-activity studies revealed that a cis-Δ(11,12)- or Δ(14,15)-olefin and a 17(R),18(S)-epoxide are minimal structural elements for antiarrhythmic activity whereas antagonist activity was often associated with the combination of a Δ(14,15)-olefin and a 17(S),18(R)-epoxide. Compared with natural material, the agonist and antagonist analogues are chemically and metabolically more robust and several show promise as templates for future development of clinical candidates.

Effect of dietary omega-3 fatty acids on the heart rate and the heart rate variability responses to myocardial ischemia or submaximal exercise

The consumption of omega-3 polyunsaturated fatty acids (n-3 PUFAs) has been reported to decrease resting heart rate (HR) and increase heart rate variability (HRV). However, the effects of n-3 PUFAs on these variables in response to a physiological stress (e.g., exercise or acute myocardial ischemia), particularly in postmyocardial infarction (MI) patients, are unknown. Therefore, HR and HRV (high frequency and total R-R interval variability) were evaluated at rest, during submaximal exercise, and during a 2-min coronary artery occlusion at rest and before and 3 mo after n-3 PUFA treatment in dogs with healed MI (n = 59). The dogs were randomly assigned to either placebo (1 g/day corn oil, n = 19) or n-3 PUFA supplement (docosahexaenoic acid + eicosapentaenoic acid ethyl esters; 1 g/day, n = 6; 2 g/day, n = 12; or 4 g/day, n = 22) groups. The treatment elicited significant (P < 0.01) dose-dependent increases in right atrial n-3 PUFA levels but dose-independent reductions in resting HR and increases in resting HRV. In contrast, n-3 PUFAs did not attenuate the large changes in HR or HRV induced by either the coronary occlusion or submaximal exercise. These data demonstrate that dietary n-3 PUFA decreased resting (i.e., preexercise or preocclusion) HR and increased resting HRV but did not alter the cardiac response to physiologic challenges.

Arachidonic acid-metabolizing cytochrome P450 enzymes are targets of {omega}-3 fatty acids

Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) protect against cardiovascular disease by largely unknown mechanisms. We tested the hypothesis that EPA and DHA may compete with arachidonic acid (AA) for the conversion by cytochrome P450 (CYP) enzymes, resulting in the formation of alternative, physiologically active, metabolites. Renal and hepatic microsomes, as well as various CYP isoforms, displayed equal or elevated activities when metabolizing EPA or DHA instead of AA. CYP2C/2J isoforms converting AA to epoxyeicosatrienoic acids (EETs) preferentially epoxidized the ω-3 double bond and thereby produced 17,18-epoxyeicosatetraenoic (17,18-EEQ) and 19,20-epoxydocosapentaenoic acid (19,20-EDP) from EPA and DHA. We found that these ω-3 epoxides are highly active as antiarrhythmic agents, suppressing the Ca(2+)-induced increased rate of spontaneous beating of neonatal rat cardiomyocytes, at low nanomolar concentrations. CYP4A/4F isoforms ω-hydroxylating AA were less regioselective toward EPA and DHA, catalyzing predominantly ω- and ω minus 1 hydroxylation. Rats given dietary EPA/DHA supplementation exhibited substantial replacement of AA by EPA and DHA in membrane phospholipids in plasma, heart, kidney, liver, lung, and pancreas, with less pronounced changes in the brain. The changes in fatty acids were accompanied by concomitant changes in endogenous CYP metabolite profiles (e.g. altering the EET/EEQ/EDP ratio from 87:0:13 to 27:18:55 in the heart). These results demonstrate that CYP enzymes efficiently convert EPA and DHA to novel epoxy and hydroxy metabolites that could mediate some of the beneficial cardiovascular effects of dietary ω-3 fatty acids.

Efficacy of n-3 polyunsaturated fatty acids and feasibility of optimizing preventive strategies in patients at high cardiovascular risk: rationale, design and baseline characteristics of the Rischio and Prevenzione study, a large randomised trial in general practice

BACKGROUND

The optimization of preventive strategies in patients at high risk of cardiovascular events and the evaluation of bottlenecks and limitations of transferring current guidelines to the real world of clinical practice are important limiting steps to cardiovascular prevention. Treatment with n-3 polyunsaturated fatty acids improves prognosis after myocardial infarction, but evidence of this benefit is lacking in patients at high cardiovascular risk, but without a history of myocardial infarction.

METHODS/DESIGN

Patients were eligible if their general practitioner (GP) considered them at high cardiovascular risk because of a cardiovascular disease other than myocardial infarction, or multiple risk factors (at least four major risk factors in non-diabetic patients and one in diabetics).Patients were randomly allocated to treatment with n-3 polyunsaturated fatty acids (1 g daily) or placebo in a double-blind study and followed up for five years by their GPs to assess the efficacy of the treatment in preventing cardiovascular mortality (including sudden death) and hospitalization for cardiovascular reasons. The secondary, epidemiological, aim of the study is to assess whether it is feasible to adopt current guidelines in everyday clinical practice, with a view to optimizing all the available preventive strategies in people at high cardiovascular risk.A nation-wide network of 860 GPs admitted 12,513 patients to the study between February 2004 and March 2007. The mean age was 64 years and 62% were males. Diabetes mellitus plus one or more cardiovascular risk factors was the main inclusion criterion (47%). About 30% of patients were included because of a history of atherosclerotic cardiovascular disease, 21% for four or more risk factors, and less than 1% for other reasons.

DISCUSSION

The Rischio and Prevenzione (R&P) project provides a feasible model to test the efficacy of n-3 polyunsaturated fatty acid therapy in patients at high cardiovascular risk with no history of myocardial infarction, and to assess how to implement recommended preventive strategies in general practice.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00317707.

Cardioprotection by omega-3 fatty acids: involvement of PKCs?

It has been known since the 1970s that an increased consumption of n-3 long chain polyunsaturated fatty acids such as eicosapentaenoic acid and docosahexaenoic acid has cardioprotective effects. Epidemiological studies have reported that this effect is due to the prevention of the arrhythmias responsible for sudden cardiac death. Mechanistically, different hypotheses have been put forward to give an explanation. Among them, there are a direct effect of the polyunsaturated fatty acids on ion channels and/or a modification of the regulation of ion channels by protein kinase C's.

Omega-3 consumption and sudden cardiac death in schizophrenia

People with schizophrenia show a two- to three-fold increased risk to die prematurely. Mortality is accounted for by a combination of factors (patients' life style, suicide, premature cardiovascular disease, metabolic syndromes and, not so often mentioned, sudden death). The cause of sudden death in schizophrenia is unknown, but cardiac arrhythmia plays a potential role. Patients with schizophrenia are at high risk for cardiovascular disease, and some antipsychotics may be associated with cardiovascular adverse events (e.g., electrocardiograph QT interval prolongation), suggesting that this could lead to sudden cardiac death. Animal and clinical studies have shown that omega-3 fatty acids could be useful in the prevention and treatment of schizophrenia. As omega-3 fatty acids have been considered a cardioprotector agent, reducing cardiac arrhythmias and hence sudden cardiac deaths and given their relative safety and general health benefits, our update article summarizes the knowledge by the possible positive effects of omega-3 supplementation and fish consumption against sudden cardiac death in patients with schizophrenia. However, fish species should be selected with caution due to contamination with toxic methylmercury.