Arachidonic acid availability

Leslie CC. Regulation of arachidonic acid availability for eicosanoid production. Biochem Cell Biol. 2004 82 1-17. 

Lipoxygenation is the major pathway of dioxygenation of arachidonic acid in blood platelets and leads to the 12-5-hydroperoxy acid 12-HPETE and the corresponding 12-hydroxy acid 12-HETE. Several pathways for the synthesis of 12-HETE have been developed. However, despite the availability of this substance, its biological role remains undetermined. 

The occupation of all available coordination sites by phytate suppresses other iron-mediated processes, such as lipid peroxidation ( 0). Figure 6 demonstrates that 0.24 mM phytate prevents the peroxidation of arachidonic acid driven by ascorbic acid and iron, whereas substantial amounts of malondialdehyde arise in the presence of free iron or of an iron-ADP chelate. 

Another commercially available product containing naturally occurring marine products is Formulaid , produced by Martek Biosciences as a nutritional supplement for infant formulas. Formulaid contains two fatty acids, arachidonic acid (ARA) and docosahexaenoic acid (DHA), extracted from a variety of marine microalgae. ARA and DHA are the most abundant polyunsaturated fatty acids found in breast milk, and they are the most important fatty acids used in the development of brain gray matter. They are especially desirable for use in infant formulas because they come from nonmeat sources and can be advertised as vegetarian additives to the product. 

Because of the small amount of natural anandamide available, we were able to record H NMR spectra only. The peaks attributed to double-bond protons (5 5.30 to 5.45, multiplet) were coupled with those of protons that have the chemical shifts of doubly allylic protons (5 2.75 to 2.90, multiplet). Such doubly allylic protons are typically found in all-af, nonconju-gated polyunsaturated fatty acids such as linoleic and arachidonic acids. Three pairs of protons were observed between 5 2.01 and 2.27, which we attributed to two allylic methylene groups and one methylene group a to a carbonyl moiety. Only one methyl group was observed (0.99, triplet). The peaks observed for two protons at 3.42 (N-CH2, triplet), two protons at 3.72 (O-CH2, triplet), and two protons at 2.20 (COCH2, triplet) were... 

COX-1 and COX-2 are the targets of the nonsteroidal anti-inflammatory drugs (NSAID, see Chapter 28). Indirectely the effect of these enzymes is also inhibited by corticosteroids (see also Chapter 26) through a decrease of the availibility of its substrate arachidonic acid by inhibition of phospholipase A2. Relatively new drugs, known as COX-2 selective inhibitors or coxibs (celecoxib, rofecoxib and others), are used as specific inhibitors of COX-2. 

Glucocorticosteroids are the most potent antiinflammatory agents available. They stabilize lysosomal membranes and reduce the concentration of proteolytic enzymes at the site of inflammation. They promote the synthesis of proteins called lipocortins which inhibit phospholipase-A2 and thus inhibit production of arachidonic acid, leukotrienes and prostaglandins. Furthermore, the expression of COX-II and through that the inflammatory effects of the licosanoids is inhibited. Glucocorticosteroids reduce the release of histamine from basophils, decrease capillary permeability and cause vasoconstriction. Glucocorticosteroids stimulate the loss of calcium with the urine and inhibit the resorption of calcium from the gut. 

Pharmacological approaches include the inhibition of release of arachidonic acid by inhibition of phospholipase A2 and the inhibition of acylcarnitine transferase I by and oxfenicine, the latter of which has been shown to prevent or at least delay ischemia-induced uncoupling. There are at present no data available on the possible effects of inhibitors of arachidonic acid release on ischemia-induced uncoupling. 

It is becoming more popular in the US for infant formula manufactures to add fish oils to fortify infant formulae with long-chain polyunsaturated fatty acids, which are critical in early child development because they are necessary for the formation of neural tissues and cells of vascular tissue, but are produced de novo at very low levels from the dietary essential fatty acids Ci8 2, m-3 and Cis 3, co-3. Typically, the long-chain fatty acids, doco-sahexaenoic acid (DHA C22 6) and arachidonic acid (AA C2o 4), were not added to infant formulae available in the US until recently. Many commercial infant formulae manufactures, including Wyeth, Ross and Mead Johnson, now produce infant formulae that are supplemented with DHA and AA. The level of DHA is approximately 0.32%, w/w of fat, and the level of AA is approximately 0.64% w/w of fat. Breast-milk naturally contains small amounts of these long-chain polyunsaturated fatty acids. 

Only little information is available as to the role of arachidonic acid derivatives in VIP-stimulated PRL release. As in the case of TRH, agents that inhibit arachidonic acid generation blunt the PRL response to VIP [122]. 

What is important though is that the double bonds are separated by one and only one single bond. Remember the unsaturated fatty acid, linoleic acid, that you met in Chapter 3 Another fatty acid with even more unsaturation is arachidonic acid. None of the four double bonds in this structure are conjugated since in between any two double bonds there is an sp3 carbon. This means there is no p orbital available to overlap with the ones from the double bonds. The saturated carbon atoms insulate the double bonds from each other. 

Enzymatic assay of lipid hydroperoxides A selective assay has been described for lipid hydroperoxides, based on the cyclooxygenase reaction with a sensitivity in the range of 20-200 pmol (Marshall et al., 1985 Pendleton and Lands, 1987 Lands, 1988). The substrate (15-HPETE) is not, however, commercially available and must therefore be synthesized from purified arachidonic acid by the method of Graft (1982) in which soya bean lipoxygenase is used to catalyse the stereospecific oxygenation of arachidonic acid. 

Purification of arachidonic acid (5,8,11,14-eicosatetraenoic acid) Peroxides are removed from commercially available arachidonic acid by addition of 15 mg of sodium borohydride to 100 mg fatty acid dissolved in 3 ml toluene. The mixture is incubated for 30 min with occasional stirring before addition of 3 ml water and 0.7 ml 1 M citric acid. After vortex-mixing, the phases are separated and the organic phase removed and washed with 1 ml of water. Peroxide free arachidonic acid is dried over anhydrous sodium sulphate and stored at 4°C after addition of 2 ml of 10 mM BHT. 

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