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Arachidonic acid ( AA, sometimes ARA) is a polyunsaturated omega−6 fatty acid 20:4(ω−6), or 20:4(5,8,11,14). It is a precursor in the formation of , , and .
Together with omega−3 fatty acids and other omega−6 fatty acids, arachidonic acid provides energy for body functions, contributes to cell membrane structure, and participates in the synthesis of , which have numerous roles in physiology as Cell signaling.
Its name derives from the ancient Greek neologism arachis 'peanut', although peanut oil does not contain any arachidonic acid. Arachidonate is the name of the derived carboxylate anion (conjugate base of the acid), salts, and some esters.
Some chemistry sources define 'arachidonic acid' to designate any of the eicosatetraenoic acids. However, almost all writings in biology, medicine, and nutrition limit the term to all cis-5,8,11,14-eicosatetraenoic acid.
In addition to being involved in cellular signaling as a lipid second messenger involved in the regulation of signaling enzymes, such as Phospholipase C-γ, PLC-δ, and PKC-α, -β, and -γ isoforms, arachidonic acid is a key inflammatory intermediate and can also act as a vasodilator. (Note separate synthetic pathways, as described in section below.)
Arachidonic acid for signaling purposes appears to be derived by the action of group IVA cytosolic phospholipase A2 (cPLA2, 85 kDa), whereas inflammatory arachidonic acid is generated by the action of a low-molecular-weight secretory PLA2 (sPLA2, 14-18 kDa).
Arachidonic acid is a precursor to a wide range of :
The production of these derivatives and their actions in the body are collectively known as the "arachidonic acid cascade"; see Essential fatty acid interactions and the enzyme and metabolite linkages given in the previous paragraph for more details.
Furthermore, any agent increasing intracellular calcium may cause activation of some forms of PLA2.
Receptors that activate this pathway include:
PLC may also be activated by MAP kinase. Activators of this pathway include PDGF and FGF.
A 2009 review indicated that consumption of 5−10% of food energy from omega−6 fatty acids including arachidonic acid may reduce the risk of cardiovascular diseases compared to lower intakes. A 2014 meta-analysis of possible associations between heart disease risk and individual fatty acids reported a significantly reduced risk of heart disease with higher levels of EPA, DHA, and arachidonic acid.
Chemistry
In chemical structure, arachidonic acid is a carboxylic acid with a 20-carbon chain and four cis-; the first double bond is located at the sixth carbon from the omega end.
Biology
Arachidonic acid is a polyunsaturated fatty acid present in the (especially phosphatidylethanolamine, phosphatidylcholine, and phosphatidylinositides) of cell membrane of the body's cells, and is abundant in the brain, muscles, and liver. Skeletal muscle is an especially active site of arachidonic acid retention, accounting for roughly 10–20% of the phospholipid fatty acid content typically.
Biosynthesis and cascade in humans
Arachidonic acid is freed from phospholipid by hydrolysis, catalyzed by the phospholipase A2 (PLA2).
PLA2 activation
PLA2, in turn, is activated by ligand binding to receptors, including:
PLC activation
Alternatively, arachidonic acid may be cleaved from phospholipids after phospholipase C (PLC) cleaves off the inositol trisphosphate group, yielding diacylglycerol (DAG), which subsequently is cleaved by DAG lipase to yield arachidonic acid.
In the body
Cell membranes
Along with other omega−6 and omega−3 fatty acids, arachidonic acid contributes to the structure of cell membranes. When incorporated into , the omega fatty acids affect cell membrane properties, such as permeability and the activity of enzymes and cell-signaling mechanisms.
Brain
Arachidonic acid, one of the most abundant fatty acids in the brain, is present in similar quantities to docosahexaenoic acid, with the two accounting for about 20% of brain fatty-acid content. Arachidonic acid is involved in the early neurological development of infants.
Dietary supplement
Arachidonic acid is marketed as a dietary supplement. A 2019 review of clinical studies investigating the potential health effects of arachidonic acid supplementation of up to 1500 mg per day on human health found there were no clear benefits. There were no in adults of using high daily doses (1500 mg) of arachidonic acid on several of blood chemistry, immune function, and inflammation.
See also
External links
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