Eicosapentaenoic acid: Difference between revisions

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'''Eicosapentaenoic acid''' ('''EPA'''; also '''icosapentaenoic acid''') is an [[omega-3 fatty acid]]. In physiological literature, it is given the name 20:5(n-3). It also has the [[trivial name]] '''timnodonic acid'''. In chemical structure, EPA is a [[carboxylic acid]] with a 20-[[carbon]] chain and five ''[[Cis-trans isomerism|cis]]'' [[double bond]]s; the first double bond is located at the third carbon from the omega end.

EPA is a [[polyunsaturated fatty acid]] (PUFA) that acts as a precursor for [[prostaglandin-3]] (which inhibits [[platelet aggregation]]), [[thromboxane-3]], and [[leukotriene-5]] [[eicosanoid]]s. EPA is both a precursor and the [[Hydrolysis|hydrolytic]] [[Metabolism|breakdown]] product of eicosapentaenoyl ethanolamide (EPEA: [[Carbon|C]]₂₂[[Hydrogen|H]]₃₅[[Biological functions of nitric oxide|NO]]₂; 20:5,n-3).  Although studies of [[fish oil]] supplements, which contain both [[docosahexaenoic acid]] (DHA) and EPA, have failed to support claims of preventing [[Myocardial infarction|heart attacks]] or [[stroke]]s, a recent multi-year study of Vascepa ([[Ethyl group|ethyl]] [[eicosapentaenoate]], the [[Ethyl group|ethyl]] [[ester]] of the [[free fatty acid]]), a prescription drug containing only EPA, was shown to reduce heart attack, stroke, and cardiovascular death by 25% relative to a placebo in those with statin-resistant hypertriglyceridemia.

==Sources==

EPA is obtained in the human diet by eating [[oily fish]], e.g., [[cod]] liver, [[herring]], [[mackerel]], [[salmon]], [[menhaden]] and [[sardine]], various types of edible [[algae]], or by taking supplemental forms of fish oil or algae oil. It is also found in human [[breast milk]].

Fish, like most vertebrates, can synthesize very little EPA from dietary [[alpha-linolenic acid]] (ALA). Because of this extremely low conversion rate, fish primarily obtain it from the [[algae]] they consume. It is available to humans from some non-animal sources (e.g., commercially, from ''[[Yarrowia lipolytica]]'', and from [[microalgae]] such as ''Nannochloropsis oculata'', ''Monodus subterraneus'',  ''Chlorella minutissima'' and ''[[Phaeodactylum tricornutum]]'', which are being developed as a commercial source). EPA is not usually found in higher plants, but it has been reported in trace amounts in [[Portulaca oleracea|purslane]]. In 2013, it was reported that a genetically modified form of the plant [[Camelina sativa|camelina]] produced significant amounts of EPA.

The human body converts a portion of absorbed [[alpha-linolenic acid]] (ALA) to EPA. ALA is itself an essential fatty acid, and humans need an appropriate supply of it. The efficiency of the conversion of ALA to EPA, however, is much lower than the absorption of EPA from food containing it. Because EPA is also a [[Precursor (chemistry)|precursor]] to [[docosahexaenoic acid]] (DHA), ensuring a sufficient level of EPA on a diet containing neither EPA nor DHA is harder both because of the extra metabolic work required to synthesize EPA and because of the use of EPA to metabolize into DHA. Medical conditions like [[diabetes mellitus|diabetes]] or certain allergies may significantly limit the human body's capacity for metabolization of EPA from ALA.

== Forms ==

Commercially available dietary supplements are most often derived from fish oil and are typically delivered in the triglyceride, ethyl ester, or phospholipid form of EPA. There is debate among supplement manufacturers about the relative advantages and disadvantages of the different forms. One form found naturally in algae, the polar lipid form, has been shown to have improved bioavailability over the ethyl ester or triglyceride form. Similarly, DHA or EPA in the [[lysophosphatidylcholine]] (LPC) form was found to be more efficient than triglyceride and [[phosphatidylcholine]]s (PC) in a 2020 study.

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== Biosynthesis ==

=== Aerobic eukaryote pathway ===

Aerobic eukaryotes, specifically microalgae, [[moss]]es, [[Fungus|fungi]], and most animals (including humans), perform biosynthesis of EPA usually occurs as a series of desaturation and elongation reactions, catalyzed by the sequential action of desaturase and elongase [[enzyme]]s. This pathway, originally identified in ''Thraustochytrium'', applies to these groups:

# a desaturation at the sixth carbon of [[α-Linolenic acid|alpha-linolenic acid]] by a [[delta 6 desaturase|Δ6 desaturase]] to produce [[stearidonic acid]] (SDA, 18:4 ω-3),  

# elongation of the [[stearidonic acid]] by a Δ6 elongase to produce [[eicosatetraenoic acid]] (ETA, 20:4 ω-3),  

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=== Polyketide synthase pathway ===

[[File:LA--) EPA.pdf|thumb|upright=1.5|α-linolenic acid to EPA via PKS]]

The proposed polyketide synthesis pathway of EPA in ''Shewanella'' (a marine bacterium) is a repetitive reaction of reduction, dehydration, and condensation that uses acetyl coA and malonyl coA as building blocks. The mechanism of α-linolenic acid to EPA involves the condensation of malonyl-CoA to the pre-existing α-linolenic acid by KS. The resulting structure is converted by NADPH dependent reductase, KR, to form an intermediate that is dehydrated by the DH enzyme. The final step is the NADPH-dependent reduction of a double bond in trans-2-enoly-ACP via ER enzyme activity. The process is repeated to form EPA.

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==Clinical significance==

{{Further|Essential fatty acid interactions}}

The US [[National Institute of Health]]'s MedlinePlus lists medical conditions for which EPA (alone or in concert with other ω-3 sources) is known or thought to be an effective treatment. Most of these involve its ability to lower [[inflammation]].

Intake of large doses (2.0 to 4.0 g/day) of long-chain omega-3 fatty acids as prescription drugs or dietary supplements are generally required to achieve significant (> 15%) lowering of triglycerides, and at those doses the effects can be significant (from 20% to 35% and even up to 45% in individuals with levels greater than 500&nbsp;mg/dL).

Dietary supplements containing EPA and DHA lower triglycerides in a dose dependent manner; however, DHA appears to raise [[low-density lipoprotein]] (the variant which drives atherosclerosis, sometimes inaccurately called "bad cholesterol") and [[LDL-C]] values (a measurement/estimate of the cholesterol mass within LDL-particles), while EPA does not. This effect has been seen in several [[Meta-analysis|meta-analyses]] that combined hundreds of individual clinical trials in which both EPA and DHA were part of a high dose omega-3 supplement, but it is when EPA and DHA are given separately that the difference can be seen clearly. For example, in a study by Schaefer and colleagues of Tufts Medical School, patients were given either 600&nbsp;mg/day DHA alone, 600 or 1800&nbsp;mg/day EPA alone, or placebo for six weeks. The DHA group showed a significant 20% drop in triglycerides and an 18% increase in LDL-C, but in the EPA groups modest drops in triglyceride were not considered statistically significant and no changes in LDL-C levels were found with either dose.

Omega-3 fatty acids, particularly EPA, have been studied for their effect on [[autistic spectrum disorder]] (ASD). Some have theorized that, since omega-3 fatty acid levels may be low in children with autism, supplementation might lead to an improvement in symptoms. While some uncontrolled studies have reported improvements, well-controlled studies have shown no statistically significant improvement in symptoms as a result of high-dose omega-3 supplementation.

In addition, studies have shown that omega-3 fatty acids may be useful for treating [[Depression (mood)|depression]].

EPA and DHA [[ethyl ester]]s (all forms) may be absorbed less well, thus work less well, when taken on an empty stomach or with a low-fat meal.

== Notes ==

{{notelist}}

== External links ==

* [http://www.ebi.ac.uk/pdbe-srv/PDBeXplore/ligand/?ligand=EPA  EPA bound to proteins] in the [[Protein Data Bank|PDB]]

*[https://pubchem.ncbi.nlm.nih.gov/compound/5283450 Eicosapentaenoyl Ethanolamide]; [[Anandamide]] (20:5, n-3); EPEA. - [[PubChem]]

{{Eicosanoids}}

{{Fatty acids}}

{{Mood stabilizers }}

{{二次利用|date=27 March 2024}}

[[Category:Fatty acids]]

[[Category:Alkenoic acids]]

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