Arachidonic acid (AA, sometimes ARA) is an omega-6 fatty acid 20:4(?-6). It is the counterpart to the saturated arachidic acid found in peanut oil, (L. arachis – peanut.)^[1]

Chemistry

In chemical structure, arachidonic acid is a carboxylic acid with a 20-carbon chain and four cis double bonds; the first double bond is located at the sixth carbon from the omega end.

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.

Biology

Arachidonic acid is a polyunsaturated fatty acid that is present in the phospholipids (especially phosphatidylethanolamine, phosphatidylcholine and phosphatidylinositides) of membranes of the body's cells, and is abundant in the brain.

It is also involved in cellular signaling as a second messenger.

It is the source of several other molecules with specific roles, as described in the next section.

Synthesis and cascade

Eicosanoid synthesis.

Arachidonic acid is a precursor in the production of eicosanoids:

• the enzymes cyclooxygenase and peroxidase lead to Prostaglandin H2, which in turn is used to produce the prostaglandins, prostacyclin, and thromboxanes.
• the enzyme 5-lipoxygenase leads to 5-HPETE, which in turn is used to produce the leukotrienes.
• arachidonic acid is also used in the biosynthesis of anandamide.

The production of these derivatives and their action in the body are collectively known as the arachidonic acid cascade; see essential fatty acid interactions for more details.

PLA₂ activation

PLA₂, in turn, is activated by ligand binding to receptors, including:

• 5-HT2 receptors ^[2]
• mGLUR1^[2]
• bFGF receptor^[2]
• INF-? receptor^[2]
• INF-? receptor^[2]

Furthermore, any agent increasing intracellular calcium may cause activation of some forms of PLA₂.^[3]

PLC activation

Alternatively, arachidonic acid may be cleaved from phospholipid by phospholipase C (PLC), yielding diacylglycerol (DAG), which subsequently is cleaved by DAG lipase to yield arachidonic acid. ^[2]

Receptors that activate this pathway include:

• A1 receptor^[3]
• D2 receptor^[3]
• ?-2 adrenergic receptor^[3]
• 5-HT1 receptor^[3]

PLC may also be activated by MAP kinase. Activators of this pathway include PDGF and FGF.^[3]

Essential fatty acid

Arachidonic acid in the human body comes from dietary animal sources—meat, eggs, dairy—or is synthesized from linoleic acid.

Arachidonic acid is one of the essential fatty acids required by most mammals. Some mammals lack the ability to—or have a very limited capacity to—convert linoleic acid into arachidonic acid, making it an essential part of their diet. Since little or no arachidonic acid is found in plants, such animals are obligate carnivores; the cat is a common example.^[4][5]

Possible link to Alzheimer's disease

Research based on feeding arachidonic acid to mice suggests a possible link to Alzheimer's disease.^[6]

See also

• Polyunsaturated fat
• Polyunsaturated fatty acid
• Aspirin - inhibits cyclooxygenase enzyme to prevent the conversion of arachidonic acid to other signal molecules

References

1. ↑
2. ↑ ^{a b c d e f} Page 103
3. ↑ ^{a b c d e f}
4. ↑
5. ↑
6. ↑ The Press Association Fatty acid 'link' to Alzheimer's 19 October 2008

External links

• Arachidonic Acid at acnp.org

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