Inhibitory effect of n-3 fish oil fatty acids on cardiac Na+/Ca2+ exchange currents in HEK293t cells

Cardiovascular Benefits of Icosapent Ethyl in Patients With and Without Atrial Fibrillation in REDUCE-IT

Background In REDUCE-IT (Reduction of Cardiovascular Events With Icosapent Ethyl-Intervention Trial), icosapent ethyl (IPE) versus placebo) reduced cardiovascular death, myocardial infarction, stroke, coronary revascularization, or unstable angina requiring hospitalization, but was associated with increased atrial fibrillation/atrial flutter (AF) hospitalization (3.1% IPE versus 2.1% placebo; P=0.004). Methods and Results We performed post hoc efficacy and safety analyses of patients with or without prior AF (before randomization) and with or without in-study time-varying AF hospitalization to assess relationships of IPE (versus placebo) and outcomes. In-study AF hospitalization event rates were higher in patients with prior AF (12.5% versus 6.3%, IPE versus placebo; P=0.007) versus without prior AF (2.2% versus 1.6%, IPE versus placebo; P=0.09). Serious bleeding rates trended higher in patients with (7.3% versus 6.0%, IPE versus placebo; P=0.59) versus without prior AF (2.3% versus 1.7%, IPE versus placebo; P=0.08). With IPE, serious bleeding trended higher regardless of prior AF (interaction P value [Pint]=0.61) or postrandomization AF hospitalization (Pint=0.66). Patients with prior AF (n=751, 9.2%) versus without prior AF (n=7428, 90.8%) had similar relative risk reductions of the primary composite and key secondary composite end points with IPE versus placebo (Pint=0.37 and Pint=0.55, respectively). Conclusions In REDUCE-IT, in-study AF hospitalization rates were higher in patients with prior AF especially in those randomized to IPE. Although serious bleeding trended higher in those randomized to IPE versus placebo over the course of the study, serious bleeding was not different regardless of prior AF or in-study AF hospitalization. Patients with prior AF or in-study AF hospitalization had consistent relative risk reductions across primary, key secondary, and stroke end points with IPE. Registration URL: https://clinicaltrials.gov/ct2/show/NCT01492361; Unique Identifier: NCT01492361.

Bidirectional regulatory effects of Cordyceps on arrhythmia: Clinical evaluations and network pharmacology

Background: Cordyceps is a precious Chinese herbal medicine with rich bio-active ingredients and is used for regulating arrhythmia alongside routine treatments. However, the efficacy and potential mechanisms of Cordyceps on patients with arrhythmia remain unclear.

Methods: Randomized controlled trials of bradycardia treatment with Cordyceps were retrieved from diverse databases and available data. Dichotomous variables were expressed as a risk ratio (RR) with a 95% confidence interval (CI). Continuous variables were expressed as a standardized mean difference (SMD) with a 95% CI. Network pharmacology was used to identify potential targets of Cordyceps for arrhythmia. Metascape was used for gene ontology (GO) and genome (KEGG) pathway enrichment analysis.

Results: Nineteen trials included 1,805 patients with arrhythmia, of whom 918 were treated with Ningxinbao capsule plus routine drugs, and, as a control, 887 were treated with only routine drugs. Six trials reported on bradycardia and the other 13 on tachycardia. Treatment with Cordyceps significantly improved the total efficacy rate in both bradycardia (RR = 1.24; 95% CI, 1.15 to 1.35; P_z <0.00001) and tachycardia (RR = 1.27; 95% CI, 1.17 to 1.39; P_z <0.00001). Cordyceps also had beneficial secondary outcomes. No serious adverse events occurred in patients treated with Cordyceps. The results of KEGG pathway enrichment analysis were mainly connected to adrenergic signaling in cardiomyocytes and the PI3K-Akt signaling pathway. IL6, TNF, TP53, CASP3, CTNNB1, EGF, and NOS3 might be key targets for Cordyceps in the treatment of arrhythmia.

Conclusion: This study confirmed that Cordyceps has a certain positive effect on the treatment of arrhythmia and that its main mechanism may be through the regulation of adrenergic signaling in cardiomyocytes and the PI3K-Akt signaling pathway.

The Cardiac Na+ -Ca2+ Exchanger: From Structure to Function

Ca²⁺ homeostasis is essential for cell function and survival. As such, the cytosolic Ca²⁺ concentration is tightly controlled by a wide number of specialized Ca²⁺ handling proteins. One among them is the Na⁺ -Ca²⁺ exchanger (NCX), a ubiquitous plasma membrane transporter that exploits the electrochemical gradient of Na⁺ to drive Ca²⁺ out of the cell, against its concentration gradient. In this critical role, this secondary transporter guides vital physiological processes such as Ca²⁺ homeostasis, muscle contraction, bone formation, and memory to name a few. Herein, we review the progress made in recent years about the structure of the mammalian NCX and how it relates to function. Particular emphasis will be given to the mammalian cardiac isoform, NCX1.1, due to the extensive studies conducted on this protein. Given the degree of conservation among the eukaryotic exchangers, the information highlighted herein will provide a foundation for our understanding of this transporter family. We will discuss gene structure, alternative splicing, topology, regulatory mechanisms, and NCX's functional role on cardiac physiology. Throughout this article, we will attempt to highlight important milestones in the field and controversial topics where future studies are required. © 2021 American Physiological Society. Compr Physiol 12:1-37, 2021.

Defining the Role of Icosapent Ethyl in Clinical Practice

The health benefit of fish oil, i.e. omega-3 fatty acids (ω-3 FA) has a long history of debate. While there are a number of medications to reduce serum triglyceride levels, none have shown unanimous cardiovascular (CV) benefits. The most recent Reduction of Cardiovascular Events with Icosapent Ethyl-Intervention Trial (REDUCE-IT) assessing the CV outcome of one highly purified prescription ω-3 FA has certainly rejuvenated the debate. While this trial has been regarded as one of the most important landmark trials in preventive cardiology, the tolerability issue in a very high dose (4 g/day, as administered in the trial) is still a matter of concern. This article summarizes the current status and future perspective of icosapent ethyl in clinical practice in light of REDUCE-IT.

Dietary and Pharmacological Fatty Acids and Cardiovascular Health

CONTEXT

The effects of dietary intake of different fatty acids and pharmacological use of fatty acids, specifically long-chain n-3 polyunsaturated fatty acids (LC n-3 PUFAs), on cardiovascular health and atherosclerotic cardiovascular disease (ASCVD) prevention have been examined in a large number of observational studies and clinical trials. This review summarizes recent data and discusses potential mechanisms.

EVIDENCE ACQUISITION

The review is based on the authors' knowledge of the field supplemented by a PubMed search using the terms seafood, fish oil, saturated fatty acids, omega-3 fatty acids, eicosapentaenoic acid, docosahexaenoic acid, polyunsaturated fatty acids, monounsaturated fatty acids, and ASCVD.

EVIDENCE SYNTHESIS

We mainly discuss the recent clinical trials that examine the effects of different types of dietary fatty acids and pharmacological use of n-3 PUFA products on ASCVD prevention and the potential mechanisms.

CONCLUSIONS

While replacement of dietary saturated fat with unsaturated fat, polyunsaturated fat in particular, or intake of LC n-3 PUFA-rich seafood has generally shown benefit for ASCVD prevention and is recommended for cardiovascular benefits, data on effects of n-3 PUFA products on ASCVD health are inconsistent. However, recent clinical trials support benefits of prescription EPA in ASCVD prevention. n-3 PUFAs may contribute to ASCVD prevention through multiple mechanisms, including lowering plasma triglyceride levels, anti-inflammatory effects, antithrombotic effects, and effects on endothelial function.

The highly unnatural fatty acid profile of cells in culture

The fatty acid profile of cells in culture are unlike those of natural cells with twice the monounsaturated (MUFA) and half the polyunsaturated fatty acids (PUFA) level (Mol%). This is not due to cell lines primarily being derived from cancers but is due to limited access to lipid and an inability to make PUFA de novo as vertebrate cells. Classic culture methods use media with 10% serum (the only exogenous source of lipid). Fetal bovine serum (FBS), the serum of choice has a low level of lipid and cholesterol compared to other sera and at 10% of media provides 2-3% of the fatty acid and cholesterol, 1% of the PUFA and 0.3% of the essential fatty acid linoleic acid (18:2n-6) available to cells in the body. Since vertebrate cell lines cannot make PUFA they synthesise MUFA, offsetting their PUFA deficit and reducing their fatty acid diversity. Stem and primary cells in culture appear to be similarly affected, with a rapid loss of their natural fatty acid compositions. The unnatural lipid composition of cells in culture has substantial implications for examining natural stems cell in culture, and for investigations of cellular mechanisms using cell lines based on the pervasive influence of fats.

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.

Omega-3 Fatty Acid and Cardiovascular Outcomes: Insights From Recent Clinical Trials

PURPOSE OF REVIEW

Omega-3 fatty acids (ω-3 FA) are among the most well-recognized health supplements but their cardiovascular benefits have long been controversial owing to inconsistent results from previous cardiovascular outcomes trials (CVOT). In this article, we provide a short review of existing literature followed by recent randomized clinical trial data, with a discussion of the potential clinical implications of these new findings.

RECENT FINDINGS

Data from the randomized, controlled trial REDUCE-IT, when viewed within the context of other recently published trials ASCEND and VITAL, add to a growing body of evidence on the use of ω-3 FA therapies in the treatment of atherosclerotic cardiovascular disease (ASCVD). Given the different formulations, dosages, and patient populations studied, CVOTs of ω-3 FA have provided valuable insight into the use of these agents in cardioprotection. Current data suggest that higher dosages of pure eicosapentaenoic acid ω-3 FA formulations provide additional benefit in reduction of ASCVD events.

Biological activities of non-enzymatic oxygenated metabolites of polyunsaturated fatty acids (NEO-PUFAs) derived from EPA and DHA: New anti-arrhythmic compounds?

ω3 Polyunsaturated fatty acids (ω3 PUFAs) have several biological properties including anti-arrhythmic effects. However, there are some evidences that it is not solely ω3 PUFAs per se that are biologically active but the non-enzymatic oxygenated metabolites of polyunsaturated fatty acids (NEO-PUFAs) like isoprostanes and neuroprostanes. Recent question arises how these molecules take part in physiological homeostasis, show biological bioactivities and anti-inflammatory properties. Furthermore, they are involved in the circulations of childbirth, by inducing the closure of the ductus arteriosus. In addition, oxidative stress which can be beneficial for the heart in given environmental conditions such as the presence of ω3 PUFAs on the site of the stress and the signaling pathways involved are also explained in this review.

Eicosapentaenoic acid triggers Ca2+ release and Ca2+ influx in mouse cerebral cortex endothelial bEND.3 cells

Eicosapentaenoic acid (EPA), an omega-3 fatty acid abundant in fish oil, protects endothelial cells (EC) from lipotoxicity and triggers EC NO release. The latter is related to an elevation of cytosolic Ca2+. Although EPA has been shown to cause human EC cytosolic Ca2+ elevation, the mechanism is unclear. Microfluorimetric imaging was used here to measure free cytosolic Ca2+ concentration. EPA was shown to cause intracellular Ca2+ release in mouse cerebral cortex endothelial bEND.3 cells; interestingly, the EPA-sensitive intracellular Ca2+ pool(s) appeared to encompass and was larger than the Ca2+ pool mobilized by sarcoplasmic-endoplasmic reticulum Ca2+-ATPase inhibition by cyclopiazonic acid. EPA also opened a Ca2+ influx pathway pharmacologically distinct from store-operated Ca2+ influx. Surprisingly, EPA-triggered Ca2+ influx was Ni2+-insensitive; and EPA did not trigger Mn2+ influx. Further, EPA-triggered Ca2+ influx did not involve Na+-Ca2+ exchangers. Thus, our results suggest EPA triggered unusual mechanisms of Ca2+ release and Ca2+ influx in EC.

Cardioprotective effects of omega 3 fatty acids: origin of the variability

Since 40 years, it is known that omega-3 poly-unsaturated fatty acids (ω3 PUFAs) have cardioprotective effects. These include antiarrhythmic effects, improvements of autonomic function, endothelial function, platelet anti-aggregation and inflammatory properties, lowering blood pressure, plaque stabilization and reduced atherosclerosis. However, recently, conflicting results regarding the health benefits of ω3 PUFAs from seafood or ω3 PUFAs supplements have emerged. The aim of this review is to examine recent literature regarding health aspects of ω3 PUFAs intake from fish or supplements, and to discuss different arguments/reasons supporting these conflicting findings.

Effects of endogenous cannabinoid anandamide on cardiac Na⁺/Ca²⁺ exchanger

Endocannabinoid anandamide (N-arachidonoyl ethanolamide; AEA) has been shown to cause negative inotropic and antiarrhythmic effects in ventricular myocytes. In this study, using whole-cell patch clamp technique, we have investigated the effects of AEA on cardiac Na(+)/Ca(2+) exchanger (NCX1)-mediated currents. AEA suppressed NCX1 with an IC50 value of 4.7 μM. Both inward and outward components of exchanger currents were suppressed by AEA equally. AEA inhibition was mimicked by the metabolically stable analogue, methanandamide (metAEA, 10 μM) while it was not influenced by inhibition of fatty acid amide hydrolase with 1 μM URB597 incubation. The effect of AEA, was not altered in the presence of cannabinoid receptor 1 and 2 antagonists AM251 (1 μM) and AM630 (1 μM), respectively. In addition, inhibition by AEA remained unchanged after pertussis toxin (PTX, 2 μg/ml) treatment or following the inclusion of GDP-β-S (1 mM) in pipette solution. Currents mediated by NCX1 expressed in HEK-293 cells were also inhibited by 10 μM AEA a partially reversible manner. Confocal microscopy images indicated that the intensity of YFP-NCX1 expression on cell surface was not altered by AEA. Collectively, the results indicate that AEA directly inhibits the function of NCX1 in rat ventricular myocytes and in HEK-293 cells expressing NCX1.

Do Omega-3 Fatty Acids Decrease the Incidence of Atrial Fibrillation?

Although atrial fibrillation is a very common medical problem in general population and has a high incidence in the setting of open heart surgery, there are very few therapies to prevent occurrence or recurrence of atrial fibrillation. N-3 polyunsaturated fatty acids have been shown to change basic physiologic properties of the atrial tissue to make it less susceptible to atrial fibrillation. In this review, we first describe basic physiological mechanisms thought to be responsible for these changes and then discuss observational and interventional studies evaluating the use n-3 polyunsaturated fatty acids for primary and secondary prevention of atrial fibrillation in the general population, in subjects undergoing open heart surgery, and in special subgroups of patients.

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.

The use of ω-3 poly-unsaturated fatty acids in heart failure: a preferential role in patients with diabetes

PURPOSE

To review the evidence for a beneficial effect of ω-3 PUFAs in heart failure (HF) and its co-morbidities, their possible preferential effect in diabetes and the potential mechanism for their benefit.

METHODS

We summarize the clinical studies which investigated the use of ω-3 PUFAs in patients with HF with an emphasis on diabetes. We briefly summarize the evidence for an effect of ω-3 PUFAs in patients with coronary artery disease (CAD), atrial fibrillation (AF) and ventricular arrhythmias. We also discuss the proposed mechanisms of ω-3 PUFA action in cardiovascular diseases.

RESULTS

While there is emerging evidence for a beneficial effect of ω-3 PUFA supplementation in patients with HF, the evidence for other indications have been variable and conflicting. In HF patients with diabetes, ω-3 PUFAs may have a preferential therapeutic benefit. Randomized controlled trials did not show considerable beneficial effects of ω-3 PUFAs in other conditions such as CAD and AF. In a diabetic and insulin-resistant state, ω-3 PUFAs bind to the G-protein coupled receptor, GPR120, resulting in reduced cytokine production from inflammatory macrophages and improved signaling in adipocytes, leading to a reduction in insulin resistance.

CONCLUSIONS

There is promising evidence showing that use of ω-3 PUFA supplementation improves clinical outcomes of HF patients with diabetes. Further clinical trials are needed in this regard.

Omega-3 polyunsaturated fatty acids reduce vascular endothelial growth factor production and suppress endothelial wound repair

Long-chain polyunsaturated omega-3 fatty acids (n-3 PUFAs) such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have diverse beneficial effects on cardiovascular diseases and have been used widely as supplements in reducing the risk of cardiovascular diseases. The beneficial effects are believed to be related to the anti-inflammatory and antioxidant action of n-3 PUFA. EPA and DHA can inhibit inflammatory cytokine-induced endothelial activation and reduce endothelial migration and proliferation. Revascularisation is the major therapeutic approach for end-stage cardiovascular diseases, and endothelial migration and proliferation are essential for the success of revascularisation. The aim of this study was to investigate the role of n-3 PUFAs on vascular endothelial wound repair. A scratch-wound repair assay was carried out in cultured human microvascular endothelial cells (HMEC-1) with and without different concentrations of DHA or EPA. The effect of DHA and EPA on HMEC-1 proliferation was examined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. The effect of DHA and EPA on vegf mRNA expression was detected by real-time RT-PCR and vascular endothelial growth factor (VEGF) protein secretion by enzyme-linked immunosorbent assay. DHA and EPA dose-dependently suppressed HMEC-1 cell proliferation and wound repair. DHA and EPA treatment did not induce significant HMEC-1 cell death. The treatment, however, significantly suppressed vegf mRNA expression and protein secretion in both normoxia and hypoxia culture conditions. The addition of exogenous VEGF prevented DHA- and EPA-mediated suppression of HMEC-1 cell proliferation. DHA and EPA have anti-angiogenic effect partially through vegf suppression. The use of DHA and EPA may benefit angiogenic diseases, but may have potential side effects to patients undergoing revascularisation therapy. Further studies will be required to confirm the effect of n-3 PUFAs on vascular repair.

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.

Primary Prevention of Atrial Fibrillation where are we in 2012?

Drugs to alter or delay myocardial remodelling associated with heart failure, hypertension, or inflammation in the post-operative setting, may prevent the development of atrial fibrillation. Current experimental and clinical evidences support specific treatments for defined patient population (i.e. ACE-inhibitors and ARB for chronic heart failure and hypertension expecially with LV hypertrophy; statins, corticosteroids and possibly colchicine after cardiac surgery).

(n-3) fatty acids and cardiovascular health: are effects of EPA and DHA shared or complementary?

Considerable research supports cardiovascular benefits of consuming omega-3 PUFA, also known as (n-3) PUFA, from fish or fish oil. Whether individual long-chain (n-3) PUFA have shared or complementary effects is not well established. We reviewed evidence for dietary and endogenous sources and cardiovascular effects on biologic pathways, physiologic risk factors, and clinical endpoints of EPA [20:5(n-3)], docosapentaenoic acid [DPA, 22:5(n-3)], and DHA [22:6(n-3)]. DHA requires direct dietary consumption, with little synthesis from or retroconversion to DPA or EPA. Whereas EPA is also largely derived from direct consumption, EPA can also be synthesized in small amounts from plant (n-3) precursors, especially stearidonic acid. In contrast, DPA appears principally derived from endogenous elongation from EPA, and DPA can also undergo retroconversion back to EPA. In experimental and animal models, both EPA and DHA modulate several relevant biologic pathways, with evidence for some differential benefits. In humans, both fatty acids lower TG levels and, based on more limited studies, favorably affect cardiac diastolic filling, arterial compliance, and some metrics of inflammation and oxidative stress. All three (n-3) PUFA reduce ex vivo platelet aggregation and DHA also modestly increases LDL and HDL particle size; the clinical relevance of such findings is uncertain. Combined EPA+DHA or DPA+DHA levels are associated with lower risk of fatal cardiac events and DHA with lower risk of atrial fibrillation, suggesting direct or indirect benefits of DHA for cardiac arrhythmias (although not excluding similar benefits of EPA or DPA). Conversely, EPA and DPA, but not DHA, are associated with lower risk of nonfatal cardiovascular endpoints in some studies, and purified EPA reduced risk of nonfatal coronary syndromes in one large clinical trial. Overall, for many cardiovascular pathways and outcomes, identified studies of individual (n-3) PUFA were relatively limited, especially for DPA. Nonetheless, the present evidence suggests that EPA and DHA have both shared and complementary benefits. Based on current evidence, increasing consumption of either would be advantageous compared to little or no consumption. Focusing on their combined consumption remains most prudent given the potential for complementary effects and the existing more robust literature on cardiovascular benefits of their combined consumption as fish or fish oil for cardiovascular benefits.

Eicosapentaenoic acid for the prevention of recurrent atrial fibrillation

BACKGROUND

n-3 polyunsaturated fatty acids, primarily eicosapentaenoic acid (EPA), has been reported to have antiarrhythmic and antiinflammatory effects. The aim of the present study was to examine whether the combination of antiarrhythmic drugs and EPA reduced the frequency of atrial fibrillation (AF) in patients with paroxysmal AF.

METHODS

We studied 50 patients with paroxysmal AF (age, 54 ± 9 years) after excluding the clinical conditions associated with an increased risk of AF. Patients were initially treated with antiarrhythmic drugs for 6 months (the observation period), and thereafter, EPA was added at a dose of 1.8 g/day for 6 months (the intervention period). During a one-year period, patients obtained an ECG recording using a portable device each morning and when arrhythmia-related symptom occurred. The end point was the difference of the AF burden (defined by the days of AF per month) between observation period and intervention period. Plasma EPA and C-reactive protein (CRP) levels were also determined.

RESULTS

There was no significant difference in the AF burden before and after intervention (2.6 ± 2.2 days/months vs. 2.5 ± 2.2 days/months, P = 0.45). Although EPA level was significantly increased (42 ± 15 μg/mL to 120 ± 47 μg/mL, P < 0.001), CRP level was unchanged (1.04 ± 0.69 mg/L to 0.96 ± 0.56 mg/L, P = 0.24) following EPA treatment.

CONCLUSIONS

Treatment of EPA in combination with antiarrhythmic drugs did not reduce the AF burden or the CRP levels in paroxysmal AF patients who had no evidence of substantial structural heart disease.

Omega-3 fatty acids and cardiovascular disease: effects on risk factors, molecular pathways, and clinical events

We reviewed available evidence for cardiovascular effects of n-3 polyunsaturated fatty acid (PUFA) consumption, focusing on long chain (seafood) n-3 PUFA, including their principal dietary sources, effects on physiological risk factors, potential molecular pathways and bioactive metabolites, effects on specific clinical endpoints, and existing dietary guidelines. Major dietary sources include fatty fish and other seafood. n-3 PUFA consumption lowers plasma triglycerides, resting heart rate, and blood pressure and might also improve myocardial filling and efficiency, lower inflammation, and improve vascular function. Experimental studies demonstrate direct anti-arrhythmic effects, which have been challenging to document in humans. n-3 PUFA affect a myriad of molecular pathways, including alteration of physical and chemical properties of cellular membranes, direct interaction with and modulation of membrane channels and proteins, regulation of gene expression via nuclear receptors and transcription factors, changes in eicosanoid profiles, and conversion of n-3 PUFA to bioactive metabolites. In prospective observational studies and adequately powered randomized clinical trials, benefits of n-3 PUFA seem most consistent for coronary heart disease mortality and sudden cardiac death. Potential effects on other cardiovascular outcomes are less-well-established, including conflicting evidence from observational studies and/or randomized trials for effects on nonfatal myocardial infarction, ischemic stroke, atrial fibrillation, recurrent ventricular arrhythmias, and heart failure. Research gaps include the relative importance of different physiological and molecular mechanisms, precise dose-responses of physiological and clinical effects, whether fish oil provides all the benefits of fish consumption, and clinical effects of plant-derived n-3 PUFA. Overall, current data provide strong concordant evidence that n-3 PUFA are bioactive compounds that reduce risk of cardiac death. National and international guidelines have converged on consistent recommendations for the general population to consume at least 250 mg/day of long-chain n-3 PUFA or at least 2 servings/week of oily fish.

Fatty acids antagonize bupivacaine-induced I(Na) blockade

Theories regarding the mechanism of intravenous fat emulsion for bupivacaine cardiotoxicity include creation of an intravascular lipid sink into which the cardiotoxic drug is sequestered, an improvement of impaired cardiac metabolism, and restoration of cardiomyocyte function by increasing intracellular calcium. However, work in this area is inconclusive and a more mechanistic explanation is desirable. We used a heterologous expression system (HEK-293 cells) and voltage clamp techniques to study the electrophysiologic effects of bupivacaine, polyunsaturated, and saturated fatty acids on sodium current (I(Na)) in stable cell lines expressing human cardiac sodium channels. Linolenic (polyunsaturated) and stearic (saturated) fatty acids were selected for study as they are components of commonly used lipid infusions. Bupivacaine-induced significant tonic and use dependent I(Na) block, as expected. Linolenic and stearic fatty acids directly modulated I(Na), inducing primarily tonic block. Greater block was seen with linolenic acid as compared with stearic acid. Simultaneous exposure to bupivacaine and fatty acids reduced both the tonic and use dependent block compared with bupivacaine alone. Reduction of bupivacaine-induced I(Na) block was greatest in cells treated with linolenic acid. These results suggest that the salutary effects of intravenous fat emulsion may be, in part, due to a direct modulatory effect of fatty acids on cardiac sodium channels.

Upstream therapies for management of atrial fibrillation: review of clinical evidence and implications for European Society of Cardiology guidelines. Part I: primary prevention

Atrial fibrillation (AF) is associated with significant morbidity and mortality. It is also a progressive disease secondary to continuous structural remodelling of the atria due to AF itself, to changes associated with ageing, and to deterioration of underlying heart disease. Current management aims at preventing the recurrence of AF and its consequences (secondary prevention) and includes risk assessment and prevention of stroke, ventricular rate control, and rhythm control therapies including antiarrhythmic drugs and catheter or surgical ablation. The concept of primary prevention of AF with interventions targeting the development of substrate and modifying risk factors for AF has emerged as a result of recent experiments that suggested novel targets for mechanism-based therapies. Upstream therapy refers to the use of non-antiarrhythmic drugs that modify the atrial substrate- or target-specific mechanisms of AF to prevent the occurrence or recurrence of the arrhythmia. Such agents include angiotensin-converting enzyme inhibitors (ACEIs), angiotensin receptor blockers (ARBs), statins, n-3 (ω-3) polyunsaturated fatty acids, and possibly corticosteroids. Animal experiments have compellingly demonstrated the protective effect of these agents against electrical and structural atrial remodelling in association with AF. The key targets of upstream therapy are structural changes in the atria, such as fibrosis, hypertrophy, inflammation, and oxidative stress, but direct and indirect effects on atrial ion channels, gap junctions, and calcium handling are also applied. Although there have been no formal randomized controlled studies (RCTs) in the primary prevention setting, retrospective analyses and reports from the studies in which AF was a pre-specified secondary endpoint have shown a sustained reduction in new-onset AF with ACEIs and ARBs in patients with significant underlying heart disease (e.g. left ventricular dysfunction and hypertrophy), and in the incidence of AF after cardiac surgery in patients treated with statins. In the secondary prevention setting, the results with upstream therapies are significantly less encouraging. Although the results of hypothesis-generating small clinical studies or retrospective analyses in selected patient categories have been positive, larger prospective RCTs have yielded controversial, mostly negative, results. Notably, the controversy exists on whether upstream therapy may impact mortality and major non-fatal cardiovascular events in patients with AF. This has been addressed in retrospective analyses and large prospective RCTs, but the results remain inconclusive pending further reports. This review provides a contemporary evidence-based insight into the role of upstream therapies in primary (Part I) and secondary (Part II) prevention of AF.

Vagal nerve stimulation in prevention and management of coronary heart disease

Coronary heart disease (CHD) that is due to atherosclerosis is associated with low-grade systemic inflammation. Congestive cardiac failure and arrhythmias that are responsible for mortality in CHD can be suppressed by appropriate vagal stimulation that is anti-inflammatory in nature. Acetylcholine, the principal vagal neurotransmitter, is a potent anti-inflammatory molecule. Polyunsaturated fatty acids (PUFAs) augment acetylcholine release, while acetylcholine can enhance the formation of prostacyclin, lipoxins, resolvins, protectins and maresins from PUFAs, which are anti-inflammatory and anti-arrhythmic molecules. Furthermore, plasma and tissue levels of PUFAs are low in those with CHD and atherosclerosis. Hence, vagal nerve stimulation is beneficial in the prevention of CHD and cardiac arrhythmias. Thus, measurement of catecholamines, acetylcholine, various PUFAs, and their products lipoxins, resolvins, protectins and maresins in the plasma and peripheral leukocytes, and vagal tone by heart rate variation could be useful in the prediction, prevention and management of CHD and cardiac arrhythmias.

Antiarrhythmic effects of free polyunsaturated fatty acids in an experimental model of LQT2 and LQT3 due to suppression of early afterdepolarizations and reduction of spatial and temporal dispersion of repolarization

BACKGROUND

Torsades de pointes (TdP) are induced by early afterdepolarizations (EADs) in the presence of an increased dispersion of repolarization. Free polyunsaturated fatty acids (PUFAs) have been suggested to influence cardiac repolarization.

OBJECTIVE

The purpose of this experimental study was to investigate the electrophysiologic effects of PUFAs in a model of LQT2 and LQT3.

METHODS

We investigated the acute antiarrhythmic potential of α-linolenic acid (ALA), docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA) in a whole-heart model of long QT2 (LQT2) and long QT3 (LQT3) syndrome.

RESULTS

In 123 Langendorff-perfused rabbit hearts, the I(Kr)-blocking drug erythromycin (E; 300 μM) or veratridine (V; 0.5 μM), an inhibitor of sodium channel inactivation, significantly increased monophasic ventricular action potentials (MAPs), thereby mimicking LQT2 and LQT3 syndrome. In atrioventricular-blocked hearts, 8 epicardial and endocardial MAPs demonstrated a significant increase in spatial and temporal dispersion. After lowering potassium concentration, E led to EADs and TdP in 44 and 41 of 53 hearts, respectively. Pretreatment with V led to EAD (TdP) in 39 (32) of 43 hearts. Additional treatment with ALA, DHA, or EPA (10 to 20 μM) in the LQT2 model, randomly assigned to 3 groups, suppressed EAD in 72% of ALA-treated hearts and in all hearts that were treated with EPA or DHA. This led to a reduction of TdP of 67% (ALA) and to complete abolishment of TdP in all hearts that were treated with EPA or DHA. A comparable finding was seen in V-pretreated hearts. In addition, DHA and EPA significantly shortened MAP duration and reduced spatial and temporal dispersion of repolarization (P <.01).

CONCLUSION

The present study showed for the first time that PUFAs are effective in preventing TdP in an experimental model of LQT2 and LQT3 syndrome due to a reversion of AP prolongation, a reduction of spatial and temporal dispersion of repolarization and a suppression of EAD. The PUFA effect is stronger in LQT2 than in LQT3 syndrome, and the antitorsadogenic effect is more remarkable with DHA and EPA as compared with ALA.

Low levels of the omega-3 index are associated with sudden cardiac arrest and remain stable in survivors in the subacute phase

In previous studies, low blood levels of n-3 fatty acids (FA) have been associated with increased risk of cardiac death, and the omega-3 index (red blood cell (RBC) eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) expressed as weight percentage of total FA) has recently been proposed as a new risk factor for death from coronary artery disease, especially following sudden cardiac arrest (SCA). As blood samples often haven been harvested after the event, the aim of our study was to evaluate the stability of RBC fatty acids following SCA. The total FA profile, including the omega-3 index, was measured three times during the first 48 h in 25 survivors of out-of-hospital cardiac arrest (OHCA), in 15 patients with a myocardial infarction (MI) without SCA and in 5 healthy subjects. We could not demonstrate significant changes in the FA measurements in any of the groups, this also applied to the omega-6/omega-3 ratio and the arachidonic acid (AA)/EPA ratio. Furthermore, we compared the omega-3 index in 14 OHCA-patients suffering their first MI with that of 185 first-time MI-patients without SCA; mean values being 4.59% and 6.48%, respectively (p = 0.002). In a multivariate logistic regression analysis, a 1% increase of the omega-3 index was associated with a 58% (95% CI: 0.25–0.76%) reduction in risk of ventricular fibrillation (VF). In conclusion, the omega-3 index remained stable after an event of SCA and predicted the risk of VF.

Electrophysiological mechanisms of the anti-arrhythmic effects of omega-3 fatty acids

Heart rhythm disorders, or arrhythmias, are a leading cause of morbidity and mortality worldwide. Omega-3 polyunsaturated fatty acids (ω3PUFAs), commonly found in fish oils and plant seeds, have recently emerged as potential anti-arrhythmic agents. The purpose of this review is to summarize the electrophysiological basis of the anti-arrhythmic properties of ω3PUFAs from clinical, animal, and cellular research. Evidence of the anti-arrhythmic effects of ω3PUFAs originated from epidemiological studies that correlated a low incidence of sudden cardiac death with high dietary ω3PUFA intake. Subsequently, multiple clinical trials have confirmed the therapeutic effects of ω3PUFAs in preventing sudden cardiac death and multiple other arrhythmia-related disorders. This has led basic scientists to investigate the effects of ω3PUFAs on several ion channels including sodium, potassium, and calcium channels, as well as Na/Ca exchangers. Therefore, ω3PUFAs may hold promise as safe and effective anti-arrhythmic agents. Nevertheless, further research is needed in areas such as: (1) identifying which form(s) of ω3PUFAs (i.e., phospholipid, triglyceride, or free) is (are) responsible for anti-arrhythmic actions; and (2) developing reproducible methods for delivery so that the appropriate form and concentration may be present at the target site to prevent and treat arrhythmias.

n-3 polyunsaturated fatty acids prevents atrial fibrillation by inhibiting inflammation in a canine sterile pericarditis model

OBJECTIVE

It has been recently reported that atrial fibrillation (AF) is associated with inflammation and inflammatory cytokines, and n-3 polyunsaturated fatty acids (PUFAs) might be of anti-inflammatory effects. This study was to evaluate the anti-inflammatory effect of PUFAs on AF in a canine sterile pericarditis model.

METHODS

20 dogs were randomly assigned to two groups: control group (10 dogs) and PUFA treatment group (10 dogs), in which sterile pericarditis was created by open-chest operation. PUFAs were administered orally (2g/day) 4 weeks before the operation till the end of the study. Before and 2 days after the operation, CRP, IL-6, TNF-α levels, the inducibility and maintenance of AF, the atrial effective refractory period (AERPs), and intra-atrial conduction time were determined.

RESULTS

Before the operation, there were no significant differences in any of the parameters between the two groups. On the second postoperative day, the PUFA group had a lower CRP level (7.6 ± 0.5 vs. 11.7 ± 1.3mg/dl, P<0.0001), a lower IL-6 level (112.0 ± 37.3 vs. 142.0 ± 19.6 pg/ml, P<0.01), a lower TNF-α level (83.3 ± 8.5 vs. 112.4 ± 8.2 pg/ml, P<0.0001), a less AF inducibility (percentage of burst attempts leading to AF episodes: 11 ± 7.4 vs. 28 ± 10.3, P<0.001) and maintenance [median AF duration: 1105 s (655.8-1406.5) vs. 2516.5 s (1187-3361), P<0.05], a longer AERP (133.4 ± 4.1 vs. 129.8 ± 4.3 ms, P<0.05), and a shorter intra-atrial conduction time (46.6 ± 4.4 vs. 51.9 ± 4.8 ms, P<0.05) than the control group.

CONCLUSIONS

Dietary n-3 PUFA supplementation attenuates the inducibility and maintenance of AF in the sterile pericarditis model by reducing the production of proinflammatory cytokines.

Lipoxin A4 may function as an endogenous anti-arrhythmic molecule

Cardiac arrhythmias cause significant morbidity and mortality in patients with coronary heart disease, hypertension, and congestive cardiac failure and in the elderly. Inflammation, oxidative injury, altered myocyte metabolism, extracellular matrix remodeling and fibrosis initiate and perpetuate cardiac arrhythmias, especially atrial fibrillation. Enhanced myeloperoxidase (MPO) activity by infiltrating activated leukocytes could bind to myocardial cells and cause fibrosis resulting in the initiation and progression of arrhythmias. Supplementation of eicosapentaenoic and docosahexaenoic acids (EPA and DHA, respectively) suppresses arrhythmias. EPA and DHA form precursors to anti-inflammatory lipid molecules: lipoxins, resolvins, protectins and maresins that are known to suppress inflammation, have anti-fibrotic actions and inhibit MPO activity. Hence, it is likely that leukocyte and/or myocardial deficiency of EPA and DHA and consequent reduced formation of lipoxins, resolvins, protectins and maresins enhance inflammation and MPO activity that leads to myocardial damage and fibrosis and initiation and progression of cardiac arrhythmias. Based on these evidences, I propose that lipoxins, resolvins and protectins function as endogenous anti-arrhythmic molecules and their stable synthetic analogs could be useful in the management of cardiac arrhythmias.

Cardiovascular effects of marine omega-3 fatty acids

Much evidence shows that the marine omega-3 fatty acids eicosapentaenoic acid and docosahexaenoic acid have beneficial effects in various cardiac disorders, and their use is recommended in guidelines for management of patients after myocardial infarction. However, questions have been raised about their usefulness alongside optimum medical therapies with agents proven to reduce risk of cardiac events in high-risk patients. Additionally, there is some evidence for a possible pro-arrhythmic effect in subsets of cardiac patients. Some uncertainly exists about the optimum dose needed to obtain beneficial effects and the relative merit of dietary intake of omega-3 polyunsaturated fatty acids versus supplements. We review evidence for the effects of omega-3 polyunsaturated fatty acids on various cardiac disorders and the risk factors for cardiac disease. We also assess areas of uncertainty needing further research.

Primary and secondary prevention of atrial fibrillation with statins and polyunsaturated fatty acids: review of evidence and clinical relevance

Atrial fibrillation (AF) is an increasingly common arrhythmia that now stands at epidemic proportion, with more than 2.3 million people affected in the USA and over 4.5 million people affected in Western Europe. AF is an expression of underlying heart disease and is increasingly associated with hypertension, congestive heart failure, and ischemic heart disease. It is also a progressive disease secondary to continuous structural remodeling of the atria, which relates to AF itself, to changes associated with aging and to progression of the underlying heart disease. Traditionally, AF has been addressed only after it has already presented with pharmacological and nonpharmacological therapies designed for rhythm or rate control (secondary prevention). Although secondary prevention is the most feasible approach at present, the concept of primary prevention of AF with therapies aimed at preventing the development of substrate and correcting the risk factors for AF has emerged as a strategy, which is likely to produce a larger effect in the general population. Recent experiments provided new insights into AF pathophysiology, which generated background for new mechanism-based therapies. Agents targeting inflammation, oxidative injury, atrial myocyte metabolism, extracellular matrix remodeling, and fibrosis have theoretical advantages as novel therapeutic strategies. In this respect, drugs that are not traditionally antiarrhythmic such as angiotensin-converting enzyme inhibitors, angiotensin-receptor blockers, aldosterone antagonists, statins, and omega-3 polyunsaturated fatty acids have shown an antiarrhythmic potential in addition to any treatment effect on the underlying disease. These agents are thought to have an advantage of targeting both the occurrence and progression of the substrate for AF, thus, providing primary and secondary prevention of the arrhythmia. Although first experimental and hypothesis-generating small clinical studies or retrospective analyses have been encouraging, several larger, properly designed, prospective trials have not confirmed earlier observations. This review provides a contemporary evidence-based insight into the possible preventative and reverse remodeling role of statins and polyunsaturated fatty acids in AF.

Association between n-3 fatty acid consumption and ventricular ectopy after myocardial infarction

BACKGROUND

n-3 (omega-3) Fatty acids are associated with a reduced risk of cardiovascular disease; however, the relation between dietary intake of n-3 fatty acids and ventricular arrhythmias has not been investigated among acute post-myocardial infarction (AMI) patients-a group at elevated risk of malignant arrhythmias.

OBJECTIVE

The objective was to examine the association between n-3 fatty acid consumption and ventricular ectopy among AMI patients.

DESIGN

In 260 AMI patients, dietary intake of n-3 fatty acids was assessed by using the Harvard food-frequency questionnaire, and ventricular ectopy was estimated from 24-h electrocardiograph recordings.

RESULTS

A greater intake of n-3 fatty acids (eicosapentaenoic acid + docosahexaenoic acid + docosapentaenoic acid + alpha-linolenic acid) was associated with lower ventricular ectopy (beta = -0.35, P = 0.011), and this effect remained after cardiovascular comorbidities were controlled for (beta = -0.47, P = 0.003). Higher concentrations of both marine-based (eicosapentaenoic acid + docosahexaenoic acid) (beta = -0.21, P = 0.060) and plant-based (alpha-linolenic acid) (beta = -0.33, P = 0.024) fatty acids remained associated with lower ventricular ectopy after cardiovascular comorbidities were controlled for.

CONCLUSION

These findings extend existing evidence linking n-3 fatty acid consumption to a reduced risk of ventricular arrhythmias by showing that a greater intake of n-3 fatty acids may be associated with low ventricular ectopy among AMI patients.

The role of n-3 PUFAs in preventing the arrhythmic risk in patients with idiopathic dilated cardiomyopathy

BACKGROUND

N-3 polyunsaturated fatty acids (n-3 PUFAs) intake is associated with a reduction in sudden cardiac death in patients with ischemic heart disease. Their effects in patients with heart failure caused by idiopathic dilated cardiomyopathy (IDC) are unknown.

METHODS

We compared with placebo the effects of n-3 PUFAs administration in 44 patients with IDC and with frequent or repetitive ventricular arrhythmias at Holter monitoring using a randomized, double-blind design. Arrhythmic risk was assessed by microvolt T-wave analysis (MTWA), signal averaged ECG (SAECG), Holter monitoring, power spectral analysis of heart rate (HR) variability, catecholamine and cytokine plasma levels, at baseline and after 6 months.

RESULTS

At MTWA, 7/12 patients (58%) initially positive became negative after n-3 PUFAs while one patient became positive after placebo (p = 0.019). N-3 PUFAs administration was also associated to normalization of SAECG (11/15 patients, p < 0.0015), decrease in non-sustained ventricular tachycardia (NSVT) episodes (p = 0.0002) and NSVT HR (p = 0.0003), improvement in HR variability and decrease in catecholamine and cytokine plasma levels. The ratio of plasma n-6 PUFAs to n-3 PUFAs decreased from 12.01 to 3.48 after n-3 PUFAs.

CONCLUSIONS

N-3 PUFAs administration is associated with favorable effects on parameters related to arrhythmic risk in patients with idiopathic dilated cardiomyopathy. These results are consistent with antiarrhythmic activity independent from their antiischemic effects.

Essential fatty acids and their metabolites could function as endogenous HMG-CoA reductase and ACE enzyme inhibitors, anti-arrhythmic, anti-hypertensive, anti-atherosclerotic, anti-inflammatory, cytoprotective, and cardioprotective molecules

Lowering plasma low density lipoprotein-cholesterol (LDL-C), blood pressure, homocysteine, and preventing platelet aggregation using a combination of a statin, three blood pressure lowering drugs such as a thiazide, a beta blocker, and an angiotensin converting enzyme (ACE) inhibitor each at half standard dose; folic acid; and aspirin-called as polypill- was estimated to reduce cardiovascular events by approximately 80%. Essential fatty acids (EFAs) and their long-chain metabolites: gamma-linolenic acid (GLA), dihomo-GLA (DGLA), arachidonic acid, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) and other products such as prostaglandins E1 (PGE1), prostacyclin (PGI2), PGI3, lipoxins (LXs), resolvins, protectins including neuroprotectin D1 (NPD1) prevent platelet aggregation, lower blood pressure, have anti-arrhythmic action, reduce LDL-C, ameliorate the adverse actions of homocysteine, show anti-inflammatory actions, activate telomerase, and have cytoprotective properties. Thus, EFAs and their metabolites show all the classic actions expected of the "polypill". Unlike the proposed "polypill", EFAs are endogenous molecules present in almost all tissues, have no significant or few side effects, can be taken orally for long periods of time even by pregnant women, lactating mothers, and infants, children, and adults; and have been known to reduce the incidence cardiovascular diseases including stroke. In addition, various EFAs and their long-chain metabolites not only enhance nitric oxide generation but also react with nitric oxide to yield their respective nitroalkene derivatives that produce vascular relaxation, inhibit neutrophil degranulation and superoxide formation, inhibit platelet activation, and possess PPAR-gamma ligand activity and release NO, thus prevent platelet aggregation, thrombus formation, atherosclerosis, and cardiovascular diseases. Based on these evidences, I propose that a rational combination of omega-3 and omega-6 fatty acids and the co-factors that are necessary for their appropriate action/metabolism is as beneficial as that of the combined use of a statin, thiazide, a beta blocker, and an angiotensin converting enzyme (ACE) inhibitor, folic acid, and aspirin. Furthermore, appropriate combination of omega-3 and omega-6 fatty acids may even show additional benefits in the form of protection from depression, schizophrenia, Alzheimer's disease, and enhances cognitive function; and serve as endogenous anti-inflammatory molecules; and could be administered from childhood for life long.

Acute Administration of Fish Oil Inhibits Triggered Activity in Isolated Myocytes From Rabbits and Patients With Heart Failure

Background— Fish oil reduces sudden death in patients with prior myocardial infarction. Sudden death in heart failure may be due to triggered activity based on disturbed calcium handling. We hypothesized that superfusion with ω3-polyunsaturated fatty acids (ω3-PUFAs) from fish inhibits triggered activity in heart failure.

Methods and Results— Ventricular myocytes were isolated from explanted hearts of rabbits with volume- and pressure-overload–induced heart failure and of patients with end-stage heart failure. Membrane potentials (patch-clamp technique) and intracellular calcium (indo-1 fluorescence) were recorded after 5 minutes of superfusion with Tyrode’s solution (control), ω-9 monounsaturated fatty acid oleic acid (20 μmol/L), or ω3-PUFAs (docosahexaenoic acid or eicosapentaenoic acid 20 μmol/L). ω3-PUFAs shortened the action potential at low stimulation frequencies and caused an ≈25% decrease in diastolic and systolic calcium (all P <0.05). Subsequently, noradrenalin and rapid pacing were used to evoke triggered activity, delayed afterdepolarizations, and calcium aftertransients. ω3-PUFAs abolished triggered activity and reduced the number of delayed afterdepolarizations and calcium aftertransients compared with control and oleic acid. ω3-PUFAs reduced action potential shortening and intracellular calcium elevation in response to noradrenalin. Results from human myocytes were in accordance with the findings obtained in rabbit myocytes.

Conclusion— Superfusion with ω3-PUFAs from fish inhibits triggered arrhythmias in myocytes from rabbits and patients with heart failure by lowering intracellular calcium and reducing the response to noradrenalin.

Na+/Ca2+ exchangers: three mammalian gene families control Ca2+ transport

Mammalian Na+/Ca2+ exchangers are members of three branches of a much larger family of transport proteins [the CaCA (Ca2+/cation antiporter) superfamily] whose main role is to provide control of Ca2+ flux across the plasma membranes or intracellular compartments. Since cytosolic levels of Ca2+ are much lower than those found extracellularly or in sequestered stores, the major function of Na+/Ca2+ exchangers is to extrude Ca2+ from the cytoplasm. The exchangers are, however, fully reversible and thus, under special conditions of subcellular localization and compartmentalized ion gradients, Na+/Ca2+ exchangers may allow Ca2+ entry and may play more specialized roles in Ca2+ movement between compartments. The NCX (Na+/Ca2+ exchanger) [SLC (solute carrier) 8] branch of Na+/Ca2+ exchangers comprises three members: NCX1 has been most extensively studied, and is broadly expressed with particular abundance in heart, brain and kidney, NCX2 is expressed in brain, and NCX3 is expressed in brain and skeletal muscle. The NCX proteins subserve a variety of roles, depending upon the site of expression. These include cardiac excitation-contraction coupling, neuronal signalling and Ca2+ reabsorption in the kidney. The NCKX (Na2+/Ca2+-K+ exchanger) (SLC24) branch of Na+/Ca2+ exchangers transport K+ and Ca2+ in exchange for Na+, and comprises five members: NCKX1 is expressed in retinal rod photoreceptors, NCKX2 is expressed in cone photoreceptors and in neurons throughout the brain, NCKX3 and NCKX4 are abundant in brain, but have a broader tissue distribution, and NCKX5 is expressed in skin, retinal epithelium and brain. The NCKX proteins probably play a particularly prominent role in regulating Ca2+ flux in environments which experience wide and frequent fluctuations in Na+ concentration. Until recently, the range of functions that NCKX proteins play was generally underappreciated. This situation is now changing rapidly as evidence emerges for roles including photoreceptor adaptation, synaptic plasticity and skin pigmentation. The CCX (Ca2+/cation exchanger) branch has only one mammalian member, NCKX6 or NCLX (Na+/Ca2+-Li+ exchanger), whose physiological function remains unclear, despite a broad pattern of expression.

Epithelial Na+ channel stimulation by n-3 fatty acids requires proximity to a membrane-bound A-kinase-anchoring protein complexed with protein kinase A and phosphodiesterase

Essential polyunsatured fatty acids have been shown to modulate enzymes, channels and transporters, to interact with lipid bilayers and to affect metabolic pathways. We have previously shown that eicosapentanoic acid (EPA, C20:5, n-3) activates epithelial sodium channels (ENaCs) in a cAMP-dependent manner involving stimulation of cAMP-dependent protein kinase (PKA). In the present study, we explored further the mechanism of EPA stimulation of ENaC in A6 cells. Fluorescence resonance energy transfer experiments confirmed activation of PKA by EPA. Consistent with our previous studies, EPA had no further stimulatory effect on amiloride-sensitive transepithelial current (INa) in the presence of CPT-cAMP. Thus, we investigated the effect of EPA on cellular pathways which produce cAMP. EPA did not stimulate adenylate cyclase activity or total cellular cAMP accumulation. However, membrane-bound phosphodiesterase activity was inhibited by EPA from 2.46 pmol/mg of protein/min to 1.3 pmol/mg of protein/min. To investigate the potential role of an A-kinase-anchoring protein (AKAP), we used HT31, an inhibitor of the binding between PKA and AKAPs as well as cerulenin, an inhibitor of myristoylation and palmitoylation. Both agents prevented the stimulatory effect of EPA and CPT-cAMP on INa and drastically decreased the amount of PKA in the apical membrane. Colocalization experiments in A6 cells cotransfected with fluorescently labeled ENaC beta subunit and PKA regulatory subunit confirmed the close proximity of the two proteins and the membrane anchorage of PKA. Last, in A6 cells transfected with a dead mutant of Sgk, an enzyme which up-regulates ENaCs, EPA did not stimulate Na+ current. Our results suggest that stimulation of ENaCs by EPA occurs via SGK in membrane-bound compartments containing an AKAP, activated PKA, and a phosphodiesterase.

Metabolic regulation of sodium-calcium exchange by intracellular acyl CoAs

The sodium-calcium exchanger (NCX) is a critical mediator of calcium homeostasis. In the heart, NCX1 predominantly operates in forward mode to extrude Ca(2+); however, reverse-mode NCX1 activity during ischemia/reperfusion (IR) contributes to Ca(2+) loading and electrical and contractile dysfunction. IR injury has also been associated with altered fat metabolism and accumulation of long-chain acyl CoA esters. Here, we show that acyl CoAs are novel, endogenous activators of reverse-mode NCX1 activity, exhibiting chain length and saturation dependence, with longer chain saturated acyl moieties being the most effective NCX1 activators. These results implicate dietary fat composition as a plausible determinant of IR injury. We further show that acyl CoAs may interact directly with the XIP (exchanger inhibitory peptide) sequence, a known region of anionic lipid modulation, to dynamically regulate NCX1 activity and Ca(2+) homeostasis. Additionally, our findings have broad implications for the coupling of Ca(2+) homeostasis to fat metabolism in a variety of tissues.

Antiarrhythmic effects of omega-3 fatty acids

Fish oil, and omega-3 fatty acids in particular, have been found to reduce plasma levels of triglycerides and increase levels of high-density lipoprotein in patients with marked hypertriglyceridemia, and a pharmaceutical-grade preparation has recently received approval from the US Food and Drug Administration to market for this purpose. However, in both bench research studies and clinical trials, evidence for clinically significant antiarrhythmic properties has also been detected in association with omega-3 fatty acid intake. Arguably the most significant finding in this data set was the reduction in the incidence of sudden death in survivors of myocardial infarction in the Gruppo Italiano per lo Studio della Sopravvivenza nell'Infarto Miocardico (GISSI)-Prevenzione trial and the subsequent recommendation for administration of fish oil as part of the postinfarction regimen in Europe. This article reviews in detail the basic and clinical research studies of fish oil as an antiarrhythmic entity, the forms of preparation and/or administration that appear to possess these properties and those that do not, the types of arrhythmias (ventricular ectopy and atrial fibrillation as well as ventricular tachyarrhythmias) that have been beneficially affected by fish oil administration, and the presumed and known mechanisms by which the beneficial actions are exerted.

The role of docosahexaenoic acid on visual evoked potentials in one kidney-one clip hypertension

PURPOSE

To investigate the effects of polyunsaturated fatty acid (PUFA) docosahexaenoic acid (DHA) on visual evoked potentials (VEPs) in a one kidney-one clip (1K-1C) hypertension model in rats.

METHODS

Five experimental groups were formed: a control group, a sham group, a group supplemented with DHA, a 1K-1C group, and a 1K-1C + DHA group. The DHA groups were treated for 60 days. In the 1K-1C groups, the right kidney was removed and a silver clip with a 0.2-mm gap was placed on the left renal artery.

RESULTS

The DHA-supplemented rats had lower blood pressure than their respective controls (p < 0.01). The increased brain and retina thiobarbituric acid reactive substances (TBARS) levels in hypertensive rats were abolished by DHA administration. The brain nitrite levels were lower in the DHA, 1K-1C and 1K-1C + DHA groups compared with the control group (p < 0.01), and the retina nitrite level was higher in the 1K-1C + DHA group compared with the DHA and 1K-1C groups (p < 0.01). There was an improvement of P(2), N(2) and P(3) components following DHA supplementation in 1K-1C hypertensive rats compared with the 1K-1C group.

CONCLUSION

The present study suggests that DHA supplementation has the potential to prevent VEP changes caused by an experimental model of hypertension. This state might be related to the lipid peroxidation lowering effect of DHA.

Polyunsaturated fatty acids mobilize intracellular Ca2+in NT2 human teratocarcinoma cells by causing release of Ca2+from mitochondria

In a variety of disorders, overaccumulation of lipid in nonadipose tissues, including the heart, skeletal muscle, kidney, and liver, is associated with deterioration of normal organ function, and is accompanied by excessive plasma and cellular levels of free fatty acids (FA). Increased concentrations of FA may lead to defects in mitochondrial function found in diverse diseases. One of the most important regulators of mitochondrial function is mitochondrial Ca2+([Ca2+]m), which fluctuates in coordination with intracellular Ca2+([Ca2+]i). Polyunsaturated FA (PUFA) have been shown to cause [Ca2+]imobilization albeit by unknown mechanisms. We have found that PUFA but not monounsaturated or saturated FA cause [Ca2+]imobilization in NT2 human teratocarcinoma cells. Unlike the [Ca2+]iresponse to the muscarinic G protein-coupled receptor agonist carbachol, PUFA-mediated [Ca2+]imobilization in NT2 cells is independent of phospholipase C and inositol-1,4,5-trisphospate (IP3) receptor activation, as well as IP3-sensitive internal Ca2+stores. Furthermore, PUFA-mediated [Ca2+]imobilization is inhibited by the mitochondria uncoupler carboxyl cyanide m-chlorophenylhydrozone. Direct measurements of [Ca2+]mwith X-rhod-1 and45Ca2+indicate that PUFA induce Ca2+efflux from mitochondria. Further studies show that ruthenium red, an inhibitor of the mitochondrial Ca2+uniporter, blocks PUFA-induced Ca2+efflux from mitochondria, whereas inhibitors of the mitochondrial permeability transition pore cyclosporin A and bongkrekic acid have no effect. Thus PUFA-gated Ca2+release from mitochondria, possibly via the Ca2+uniporter, appears to be the underlying mechanism for PUFA-induced [Ca2+]imobilization in NT2 cells.

Is fish oil good or bad for heart disease? Two trials with apparently conflicting results

Two successive randomized trials examined the effect of an increased intake of fatty fish, or the use of fish oil supplements, in reducing mortality in men with heart disease. The Diet and Reinfarction Trial (DART) was conducted in 2033 men who were recovering from acute myocardial infarction (MI). Those who were advised to eat fatty fish (or who opted to take fish oil capsules instead) had a 29% reduction in all-cause mortality over the following two years compared with those not so advised. The effect appeared in the first few months of the trial. The Diet and Angina Randomized Trial (DART 2) involved 3114 men with stable angina. Advice to eat fatty fish did not reduce mortality, and taking fish oil capsules was associated with a higher risk of cardiac and sudden death. The adverse effects of fish or fish oil were restricted to men not taking beta-blockers or dihydropyridine calcium-channel blockers, and were greater in those taking digoxin. Evidence from other sources strongly suggests an anti-arrhythmic action of fish oil, particularly after MI or in the presence of acute ischemia. The apparently conflicting results of the two trials may reflect different actions of n-3 fatty acids in acute and chronic conditions, together with different effects of eating fish and taking fish oil capsules. A mechanism is proposed that could account for these findings.

The Antiarrhythmic Effect of n-3 Polyunsaturated Fatty Acids: Modulation of Cardiac Ion Channels as a Potential Mechanism

Sudden cardiac death remains one of the most serious medical challenges in Western countries. Increasing evidence in recent years has demonstrated that the n-3 polyunsaturated fatty acids (PUFAs) can prevent fatal ventricular arrhythmias in experimental animals and probably in humans. Dietary supplement of fish oils or intravenous infusion of the n-3 PUFAs prevents ventricular fibrillation caused by ischemia/reperfusion. Similar antiarrhythmic effects of these fatty acids are also observed in cultured mammalian cardiomyocytes. Based on clinical observations and experimental studies in vitro and in vivo, several mechanisms have been postulated for the antiarrhythmic effect of the n-3 PUFAs. The data from our laboratory and others have shown that the n-3 PUFAs are able to affect the activities of cardiac ion channels. The modulation of channel activities, especially voltage-gated Na(+) and L-type Ca(2+) channels, by the n-3 fatty acids may explain, at least partially, the antiarrhythmic action. It is not clear, however, whether one or more than one mechanism involves the beneficial effect of the n-3 PUFAs on the heart. This article summarizes our recent studies on the specific effects of the n-3 PUFAs on cardiac ion channels. In addition, the effect of the n-3 PUFAs on the human hyperpolarization-activated cyclic-nucleotide-modulated channel is presented.

Pneumolysin-mediated activation of NFkappaB in human neutrophils is antagonized by docosahexaenoic acid

This study was designed to investigate the relationship between influx of extracellular Ca(2+), activation of NFkappaB and synthesis of interleukin-8 (IL-8) following exposure of human neutrophils to subcytolytic concentrations (8.37 and 41.75 ng/ml) of the pneumococcal toxin, pneumolysin, as well as the potential of the omega-3 polyunsaturated fatty acid, docosahexaenoic acid, to antagonize these events. Activation and translocation of NFkappaB were measured using a radiometric electrophoretic mobility shift assay, while influx of extracellular Ca(2+) and synthesis of IL-8 were determined using a radioassay and an ELISA procedure, respectively. Exposure of neutrophils to pneumolysin was accompanied by influx of Ca(2+), activation of NFkappaB, and synthesis of IL-8, all of which were eliminated by inclusion of the Ca(2+)-chelating agent, EGTA (10 m m), in the cell-suspending medium, as well as by pretreatment of the cells with docosahexaenoic acid (5 and 10 microg/ml). The antagonistic effects of docosahexaenoic acid on these pro-inflammatory interactions of pneumolysin with neutrophils were not attributable to inactivation of the toxin, and required the continuous presence of the fatty acid. These observations demonstrate that activation of NFkappaB and synthesis of IL-8, following exposure of neutrophils to pneumolysin are dependent on toxin-mediated influx of Ca(2+) and that these potentially harmful activities of the toxin are antagonized by docosahexaenoic acid.