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However it is essential for many metabolic functions. ARA is an important component of human fat and is also found in abundance in the brain, liver, muscles and glandular tissue.In the absence of sufficient dietary linoleic acid or in an inability to synthesize arachidonic acid from LA (18:2 ω-6), dietary source of ARA becomes essential for the body to carry on its biochemical processes. In animals like cats, having very limited capability for converting LA (18:2 ω-6) into ARA, its dietary intake becomes essential.
Structure and properties of arachidonic acid
ARA is an organic carboxylic acid characterized by the presence of carboxyl group. ARA is a weak acid and its boiling point is 169-171 °C. Its molecular formula is C20H32O2. It has a 20-carbon chain and four cis-double bonds. Located at the sixth carbon from the omega end is the first double bond.Its IUPAC Systematic name is (5Z,8Z,11Z,14Z)-Icosa-5,8,11,14-tetraenoic acid. It is also known as all-cis-5,8,11,14-Eicosatetraenoic acid.
The chemical structure of arachidonic acid is:
Arachidonic acid synthesis and cascade
The ARA derived from dietary linoleic acid is esterified into the phospholipid fats of the cell membranes. Phosphatidylethanolamine, phosphatidylcholine, and phosphatidylinositides are the very important phospholipids in which arachidonic acid is present. ARA cascade has more than 20 different signalling paths affecting a wide range of biochemical processes. The functions involving the central nervous system and the inflammatory response are very significant.Inflammatory stimuli generate four types of phospholipase enzymes. Phospholipid is degraded by these enzymes to form arachidonic acid which is oxygenated and modified to form eicosanoids. These eicosanoids produced from ARA are inflammation promoters. Eicosanoids are a range of biologically active compounds including prostaglandins, thromboxanes, and leukotrienes.
In the brain, the ARA present as phospholipids of the neuron cell membranes is released by phospholipidase enzyme which is activated by the neurohormones, neuromodulators or neurotransmitters. ARA as such can affect the activity of the neuron's ion channels and protein kinases. ARA may also be metabolized to form eicosanoids like EETs, neuroprotectin D and some endocannabinoids.
Arachidonic acid, inflammation and prostaglandins
Inflammatory process is the primary component of a number of diseases and disorders like arthritis, hay fever, allergies, periodontitis, asthma, atherosclerosis, cardiovascular diseases, rheumatoid arthritis and gallbladder carcinoma. Though ARA are required for normal body functions and immune processes, too much arachidonic acid presence in the body itself becomes a problem due to over reaction of the inflammatory process for repair and healing.In the presence of inflammatory stimuli, eicosanoids including prostaglandins, thromboxanes and leukotrienes are produced through the COX (cyclooxgenase) and LOX (lipoxygenase) enzyme conversion process. These pro-inflammatory eicosanoids mediate and regulate the whole range of inflammatory processes like blood clotting, platelet aggregation, platelet agglutination, vasoconstriction, leukocyte chemotaxis, inducement of pro-inflammatory cytokines, chemotactic cytokines production, and other immune functions.
Arachidonic acid supplements and bodybuilding
During exercise and bodybuilding after the work out there is damage to muscle tissue. The damaged tissue has to be repaired and new muscle tissue has to be grown through protein synthesis. Arachidonic acid is an integral part of the anabolic process of repair and healing. This is brought about by its mediating and regulating metabolic products like prostaglandins.In resistance training use of its supplement has been very promising with streamlined after workout inflammation, repair, recovery and growth of the muscle tissues involved. There is increased endurance, peak power and faster recovery with the use of ARA supplements during bodybuilding. In bodybuilding training stagnation situations like decline in muscle growth, lack of strength gains, delayed-onset muscle soreness (DOMS also known as muscular mechanical hyperalgesia), with reduced Arachidonic acid levels have been encountered. ARA is the primary building block for the synthesis of dienolic prostaglandins (such as PGE2 and PGF2). PGE2 and PGF2 are closely associated with protein synthesis and muscle cell repair, regeneration and growth.
The use of ARA supplements in healthy people with doses as high as 1,500-1,700mg per day has been found to have no side effects. In people with inflammatory diseases and in pregnant women ARA supplementation is not recommended. Arachidonic acid supplements are being commercially manufactured from the fungus Mortierella alpina.
Arachidonic acid health benefits
As discussed earlier, ARA is vital for the function of the nervous system. Like DHA, neurological health depends on optimum levels of ARA levels in the brain. ARA is involved in protecting the brain from oxidative stress. It is also involved in the growth and repair of neurons. ARA is also involved in the early neurological development and its supplementation in infants has improved their intelligence. ARA deficiency has been associated with Alzheimer’s disease and bipolar disorder. ARA supplementation in the early stages of Alzheimer’s disease is found to reduce the symptoms and progress of the disease. ARA is involved in the building of muscle tissue.Arachidonic acid food sources
Most of the human requirement of arachidonic acid is synthesized from dietary linoleic acid. LA is obtained from vegetable oils and animal fats. ARA is also directly obtained from animal organs, poultry, eggs, meat and fish. Animal livers, brains and kidneys are rich sources of arachidonic acid.Most of the meats (muscles) including poultry contain high amounts of ARA. Eggs are also good sources of ARA. Among the fish catfish and tilapia are found to contain high levels of ARA. Other coldwater fish and fish oils though contain some amounts of arachidonic acid, they are also rich in omega-3 fats which counter the inflammation causing omega-6 fats.
On the other hand, dairy products, fruits, vegetables, grains and nuts have very small amounts of ARA. Most of the vegetable oils have very high levels of LA (18:2 ω-6) which can be desaturated and lengthened to form arachidonic acid.
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