Free arachidonic acid

TBT and TFT are membrane-active molecules, and their mechanism of action appears to be strongly dependent on organotin(IV) lipophilicity. They function as ionophores and produce hemolysis, release Ca(II) from sarcoplasmic reticulum, alter phosphatodylseiine-induced histamine release, alter mitochondrial membrane permeability and perturb membrane enzymes. Organotin(IV) compounds have been shown to affect cell signaling they activate protein kinase and increase free arachidonic acid through the activation of phospholipase... 

The generation of radicals from lipids appear to be dependent on the abstraction of hydrogen by other radicals. Consistent with this idea is the observation that either lipid peroxidation or anoxia can cause a release of free arachidonic acid fix>m culture cells, and this release can be blocked by antioxidants (Braughler et al., 1985, 1988). 

Free arachidonic acid, along with diacylglycerols and free docosahexaenoic acid, is a product of membrane lipid breakdown at the onset of cerebral ischemia, seizures and other forms of brain trauma 585... 

Under physiologic conditions, the balance of membrane lipid metabolism, particularly that of arachidonoyl and docosahexaenoyl chains, favors a very small and tightly controlled cellular pool of free arachidonic acid (AA, 20 4n-3) and docosahexaenoic acid (DHA, 22 6n-3), but levels increase very rapidly upon cell activation, cerebral ischemia, seizures and other types of brain trauma [1, 2], Other free fatty acids (FFAs) in addition to AA, released during cell activation and the initial stages of focal and global cerebral ischemia, are stearic acid (18 0), palmitic acid (16 0) and oleic acid (18 1). 

Free arachidonic acid, along with diacylglycerols and free docosahexaenoic acid, is a product of membrane lipid breakdown at the onset of cerebral ischemia, seizures and other forms of brain trauma. Because polyunsaturated fatty acids are the predominant FFA pool components that accumulate under these conditions, this further supports the notion that fatty acids released from the C2 position of membrane phospholipids are major contributors to the FFA pool, implicating PLA2 activation as the critical step in FFA release [1,2] (Fig. 33-6). 

Artigas F, Romero L, de Montigny C, Blier P. (1996). Acceleration of the effect of selected antidepressant drugs in major depression by 5-HTlA antagonists. Trends Neurosci. 19(9) 378-83. Asakura T, Matsuda M. (1984). Efflux of gamma-aminobutyric acid from and appearance of free arachidonic acid inside synaptosomes. Biochim Biophys Acta. 773(2) 301-7. 

This emphasises the importance of the cell containing sufficient free arachidonic acid for such an exchange to take place. The combination of these two reactions, if they occur simultaneously, is a cycle - the phospholipid/ lysophospholipid cycle (Figure 11.22). 

Figure 1.9. Overview of the biosynthesis of ecosanoids. The 20 carbon fatty acid arachidonic acid is released from cell membrane phospholipids by the actions of phospholipase A2. Free arachidonic acid forms the precursor of prostaglandins and thromboxanes via the multi-enz5une cyclooxygenase pathway, while leukotrienes are formed via the lipoxygenase pathway...

Synthesis of prostaglandins and thromboxanes begins with the oxidative cyclization of free arachidonic acid to yield PGH2 by prostaglandin endoperoxide synthase—a microsomal protein that has two catalytic activities fatty acid cyclooxygenase (COX) and peroxidase. There are two isozymes of the synthase COX-1 and COX-2. Leukotrienes are produced by the 5-lipoxygenase pathway. 

The remainder of the radioactivity is associated with three main phospholipid classes, namely, phosphatidylcholine, phosphatidylethanolamine, and the phosphoinositides, mainly PIP2. Nonetheless, this type of result is commonly attributed to the action of a phospholipase A2, which is activated upon agonist interaction with the platelet. The other presumed product, a lysolecithin, would not be labeled in the above experimental protocol and thus, due to the very small amount formed in the reaction, could not be detected. Though one could potentially label the polar head group of the parent phosphoglycerides, there is little need to do so since the arachidonic acid is associated almost exclusively with the sn-2 ester position on phosphoglycerides. Consequently, the release of free arachidonic acid can be safely attributed to phospholipase A2 activity. While the yield of arachidonic acid is very low, the activation of the cell occurs only over a short time span, anywhere from 5 sec to 1 min. Thus self-control of cell activation is evident. 

Arachidonic acid, a 20-carbon fatty acid, is the primary precursor of the prostaglandins and related compounds (see Figure 39.3). Arachidonic acid is present as a component of the phospholipids of cell membranes, primarily phosphatidyl inositol and other complex lipids.1 Free arachidonic acid is released from tissue phospholipids by the action of phospholipase A2 and other acyl hydrolases, via a process controlled by hormones and other stimuli (see Figure 39.3). There are two major pathways in the synthesis of the eicosanoids from arachidonic acid (see Figure 39.3). 

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. 

Peroxide-free arachidonic acid Haemin solution... 

The substrate arachidonic aeid, whieh often leads to formation of inflammatory prostaglandins, is stored in tissues as one of a number of phospholipids these compounds, as the name indicates, comprise complex phosphate-containing esters. The antiinflammatory corticosteroids inhibit the action of the enzyme, phospholipase A2, that frees arachidonic acid. The many undesired effects of those steroids has led to the search for non-steroidal inhibitors of that enzyme. A highly substituted indole derivative has shown good activity as a phospholipase A2 inhibitor. Alkylation of the anion from treatment of indole (32) with benzyl chloride affords the corresponding A-benzylated derivative (33). The methyl ether at the 4 position is then cleaved by means of boron tribromide to yield 34. Alkylation of the enolate from reaction of the phenol with sodium hydride with tert-butylbromoacetate affords the corresponding... 

Additional inflammatory mediators have been detected in cutaneous tissues as a consequence of SM treatment. These include free arachidonic acid (Lefkowitz and Smith, 2002) and its cyclooxygenase (Dachir et al, 2004 Rikimaru et al, 1991) and lipoxygenase products (Tanaka et al, 1997). Furthermore, the increased capillary permeability observed would allow a variety of circulating inflammatory participants, such as complement components, kininogens, etc., to enter the dermal interstitium (Rikimaru et al, 1991). Clearly, vesicant injury involves a host of inflammatory mediators similar to those seen in other types of wounds, where individual cytokines have been singled out as potential therapeutic targets. 

An important structural distinction between IsoPs and cyclo-oxygenase-derived PGs is that the former contain side chains that are predominantly oriented cis to the prostane ring, whereas the latter possess exclusively trans side chains. A second important difference between IsoPs and PGs is that IsoPs are formed in situ esterifled to phospholipids and are subsequently released by a phospholipase(s), whereas PGs are generated only from free arachidonic acid. 

Irvine RF. (1982). How is the level of free arachidonic acid controlled in mammalian cell Biocehm J. 204,3-16. 

Preuss I. And Patscheke H. (1992). Regulation of the concentration of free arachidonic acid in hMnogenates of human platelets. Agents Actitms (Supplements) 37,34-40. 

Figure 8. Effect of free arachidonic acid on the lipopooxidase activity of (I) non-selenic glutathione S-transferase from porcine liver and (2) Se-containing glutathione peroxidase from bovine erythrocytes (substrate - 15 mM 15-hydroperoxyarachidonic acid) [33].

Hydrolysis of 1P3 from membrane lipids yields l-acyl-2-arachidonyl-glycerol, which remains in the piasma membrane. The arachidonate esterified at the 2-po-sition may be hydrolyzed by phospholipase Aj, to yield free arachidonate. The pathway leading to the release of IP3 and arachidonate is show o in Figure 9.98, The events depicted occur in a burst. They occur mainly within a time frame of a minute or so of stimuiation of the cell, Stimulation of the cell can induce an increase in the concentration of free arachidonic acid in the cell. This arachidonate car be used by cyclooxygenase, Cyclooxygenase is a membrane-bound enzyme of the endoplasmic reticulum. The active site faces the cytoplasm. The enzyme Is bifunchonal. It catalyzes the attachment of oxygen moiecuies to arachidonic acid,... 

Filopodia formation and microparticle formation are results of calcium signaling. Filopodia are little feet, extending from the platelet, which allow the platelet to make better contact with the outside environment. Microparticles are tiny vesicles (phospholipid spheres) that are shed from the platelet, allowing the aforementioned docking proteins easier access to a phospholipid surface, and vastly enhancing the rate of activation of further molecules of thrombin. The generation of free arachidonic acid, and consequent formation and release of thromboxane A2 in the surrounding blood, provokes the activation of nearby platelets. 

Figure 6.2. The biosynthesis of prostanoids from arachidonic acid. Free arachidonic acid is converted to the unstable intermediates PGG, and PGH, by cyclooxygenase (COX) enzymes. PGH, is then converted to the five primary prostanoids by specific synthases.

Volterra A, Trotti D, Cassutti P, Tromba C, Salvaggio A, Malangi RC, Racagni G (1992) High sensitivity of glutamate uptake to extracellular free arachidonic acid levels in rat cortical synaptosomes and astrocytes. J Neurochem 59 600-606. 

Burstein S, Budrow J, Debatis M, Hunter SA, Subramanian A (1994) Phospholipase participation in cannabinoid-induced release of free arachidonic acid. Biochem Pharmacol 48 1253-1264... 

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