Guest Editorial: Eicosapentaenoic Acid: Pleiotrope Extraordinaire?

The word “pleiotropy” is derived from the Greek word pleon, which means “more,” and tropos, which means “way” and refers to when a gene produces two or more unrelated pleiotropic traits. The term “statin pleiotropy” has been used to refer to mechanisms independent of cholesterollowering effects. Statins are indicated for both primary and secondary prevention of coronary heart disease. In a meta-analysis of data from 170,000 participants in 26 randomized trials, for each 38.6mg/ dl decrease in low-density lipoprotein cholesterol (LDL-C), major vascular events were reduced by approximately 22 percent; there was no LDL-C threshold identified.1

In addition to significant LDL-C lowering, independent cholesterol effects of statin include anti-inflammatory, antioxidant, anti-proliferative, and immunomodulatory effects, along with improvement in endothelial function and the fibrinolytic system.2 However, despite the significant benefits of statin therapy there remains considerable residual cardiovascular risk.3

Marine omega-3 fish oils, including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have proven beneficial in lowering triglycerides.4 Purified formulation of eicosapentaenoic acid (EPA) ethyl ester (4 grams/day) has demonstrated results including significant decreases in median placeboadjusted triglycerides, non-high-density lipoprotein cholesterol (HDL-C), verylow- density lipoprotein cholesterol (VLDL), apolipoprotein B (Apo B), and total cholesterol in patients with fasting triglycerides >500 mg/dl and <2,000 mg/dl as seen in the MARINE trial and in statin-treated patients with triglycerides >200 mg/dl and <500 mg/dl in the ANCHOR Study.5–6 However, in the MARINE trial, there was no significant change in the placebo-corrected median LDL-C (-2.3 percent, p=0.677). In the ANCHOR trial, the placebo-corrected median LDL-C decreased by only 6.2 percent (p=0.0067). This effect on LDL-C is different from other studied omega-3 products.7–9

A growing body of evidence has shown that EPA has beneficial impact by separate mechanisms in the cascade of physiological events involved in the development of atherosclerosis beyond lipid lowering, thus suggesting pleiotropic effects of EPA.10 Potential EPA pleiotropic effects were suggested by the results of the Japan EPA Lipid Intervention Study (JELIS).11 In JELIS, 18,645 hypercholesterolemic Japanese patients were randomly assigned to EPA (1.8 grams/day) plus statin or statin alone. Over a mean follow-up of 4.6 years in the statin and EPA group, there was a 19 percent relative reduction in the primary endpoint of major coronary events (p=0.011). While there was a small, yet significant, 5 percent reduction in triglycerides (P<0.0001), there was no significant change in LDL-C or HDL-C. This article will review the potential pleiotropic effects of EPA.

Anti-Inflammatory Effects of EPA

Inflammation is one of the key components of atherosclerosis, and high-sensitivity C-reactive protein (hsCRP) is both proatherogenic and a nonspecific marker of inflammatory disease. HsCRP is an independent cardiovascular disease risk predictor independent of cholesterol levels.12 EPA has been shown in multiple studies to reduce serum levels of hsCRP. In the ANCHOR study,9 4 grams/day of EPA added to statin decreased hsCRP by 22 percent compared to placebo. In patients with metabolic syndrome from the ANCHOR and MARINE trials, EPA 4 grams/ day reduced hsCRP compared to placebo 23 percent (P=0.0003) and 40 percent (P=0.0007), respectively.13

In an open-label trial involving 115 patients with acute myocardial infarction and percutaneous coronary intervention (PCI), 57 patients were randomized to 1.8 grams EPA/day with 58 controls; the primary endpoint was a composite of cardiac death, stroke, re-infarction, ventricular arrhythmia, and paroxysmal atrial fibrillation at one month.14 EPA significantly reduced the primary endpoint (10.5 vs. 29.3 percent; P=0.01). Peak C-reactive protein (CRP) after PCI in the EPA group was significantly lower than in the control group (P<0.01). Furthermore, EPA use was an independent factor related to ventricular arrhythmia until one month (odds ratio 0.29; P=0.04).

EPA also has been shown to decrease pentraxin-3. Pentraxin-3, unlike hsCRP, is more specific for local vascular inflammation and is produced by macrophages and smooth muscle cells in atherosclerotic plaque.15,16 EPA also has been shown to decrease cyclic adenosine monophosphate (cAMP) responsive element binding protein 1, hypoxiainducible factor 1 alpha and interleukin-6 (IL-6) and increase the anti-inflammatory cytokine, IL-10.17,18

 EPA’s Specialized Proresolving Mediators (SPM), Including Resolvins (Rv) E1, E2, E3

Chronic, unrelenting inflammation is characteristic of many metabolic disorders and diseases, including cardiovascular disease. The resolution of inflammation is a complex process and our body has evolutionarily conserved SPMs that are derived from omega-3 polyunsaturated fatty acids; these include resolvins, maresins, and protectins. Resolvin Es (RvEs) are di-or tri-hydroxyl metabolites of EPA. The first resolvin described was RvE1, which is formed from the conversion of EPA to 18R-hydroperoxyeicosapentaenoic acid by acetylated cyclooxygenase-2 (COX-2) or cytochrome P450 enzymes, which then is converted to RvE1 by 5-LOX.19 RvEs have a crucial role in resolving inflammation. RvE1 enhances phagocytosis-induced polymorphonuclear leukocyte (PMN) apoptosis and accelerates the resolution of pulmonary inflammation.20 RvE1 also decreases PMN transendothelial migration and generation of superoxide.21,22 RvE1 specifically interacts with leukotriene B4 receptor (LTB4), BLT1, and ChemR23 to regulate inflammation.23 Thus, EPA-derived RvE1 decreases LTB4 proinflammatory signals such as activation of NF-kB. There also is evidence that RvE1 is involved with the clotting mechanism during inflammation. Human platelets express ChemR23. RvE1 blocks ADP and thromboxanestimulated platelet aggregation; these regulatory actions on ADP are ChemR23- dependent.24,25 Recently, in a study in which ApoE*3 Leiden mice were fed a hypercholesterolemic diet for nine weeks, RvE1 was found to attenuate atherogenesis alone and when combined with statin therapy; there was no effect on cholesterol levels.26 Also, demonstrating its ability to resolve inflammation, RvE1 has been reported to protect against 2-, 4-, 6-trinitrobenzene sulfonic acid-induced colitis, as well as both prevent and restore bone loss in the inflammatory bone disease periodontitis.27,28

Endothelial Function

EPA has a beneficial effect on endothelial function. Vascular endothelial dysfunction is characterized by the impaired release of nitric oxide (NO), which regulates vasomotor tone. In human umbilical vein endothelial cells exposed to oxidized LDL (ox-LDL), EPA improved the balance between NO and toxic reactive oxygen species (ROS), acting synergistically with statins.29 EPA inhibits glucose-induced membrane cholesterol crystalline domain formation through a potent antioxidant mechanism.30 These antioxidant effects may be related to EPA’s ability to intercalate into the lipid membrane bilayer because of its hydrophobicity. Once in the bilayer, it may interfere with the propagation of ROS and thereby preserve membrane lipid structural organization.30 Recently, EPA was shown to reduce the oxidation of small dense LDL, LDL, and VLDL; it also was demonstrated that there was a synergistically greater reduction of oxidation in the presence of atorvastatin active metabolite than with either EPA or atorvastatin metabolite alone.31 Clinically, in the ANCHOR and MARINE trials, utilizing EPA 4 grams/day decreased ox-LDL 13.3 percent (p< 0.0001), 6.6 percent (p=0.055), respectively.32 EPA (1.8 grams/ day for six months) added to a statinimproved endothelial function as measured by the duration of reactive hyperemia in patients with type 2 diabetes mellitus (P=0.01) and by flow-mediated dilatation in patients with coronary heart disease (CHD) (p=0.02).33,34 EPA (1.8grams/day for three months) restored endotheliumdependent vasodilation in hyperlipidemic patients to a level comparable to that observed in normolipidemic controls.35

Conclusions

EPA has myriad non-lipid beneficial pleiotropic effects, including reduction of inflammatory markers, mitigation of oxidative stress and improvement of endothelial function. In addition, EPA’s metabolite RvE1 improves the resolution of inflammation. We are eagerly awaiting the results of the ongoing randomized, placebo-controlled Reduction of Cardiovascular Events with EPA-Intervention Trial (REDUCE-IT) (NCT01492361), which is testing the effect of prescription-strength, highpurity EPA added to statin therapy in reducing cardiovascular (CV) events in high-risk patients with persistently high triglycerides. This study should more definitively clarify the clinical effect of EPA in reducing CV risk. Will EPA be the pleiotrope extraordinaire?

Disclosure statement: Viet Le was a sub-investigator of the EVAPORATE Study for Amarin. Dr. Nelson has received speaker honoraria from Amarin, Kowa, Amgen, Arbotz, Regenerson, and Boston Heart Diagnostics. Dr. Nelson is on the advisory committee for Amarin, and owns stock in Amarin and Amgen.