Polyunsaturated fatty oxygen

AH the bis- and tri-unsaturated prostanoids display sensitivity to atmospheric oxygen similar to that of polyunsaturated fatty acids and Hpids. As a result, exposure to the air causes gradual decomposition although the crystalline prostanoids ate less prone to oxygenation reactions than PG oils or solutions. 

Animal cells can modify arachidonic acid and other polyunsaturated fatty acids, in processes often involving cyclization and oxygenation, to produce so-called local hormones that (1) exert their effects at very low concentrations and (2) usually act near their sites of synthesis. These substances include the prostaglandins (PG) (Figure 25.27) as well as thromboxanes (Tx), leukotrienes, and other hydroxyeicosanoic acids. Thromboxanes, discovered in blood platelets (thrombocytes), are cyclic ethers (TxBg is actually a hemiacetal see Figure 25.27) with a hydroxyl group at C-15. 

Gardner, H.W. (1989). Oxygen radical chemistry of polyunsaturated fatty acids. Free Rad. Biol. Med. 7, 65-86. 

Figure 17.2 Lipid peroxidation scheme. LH, a polyunsaturated fatty acid LOOM, lipid hydroperoxide LOH, lipid alcohol L, lipid radical LOO, lipid hydroperoxyl radical LO, lipid alkoxyl radical. Initiation the LH hydrogen is abstracted by reactive oxygen (e.g. lipid alkyl radical, lipid alkoxy radical, lipid hydroperoxyl radical, hydroxy radical, etc.) to produce a new lipid alkyl radical, L. Propagation the lipid alkyl, alkoxyl or hydroperoxyl radical abstracts hydrogen from the neighbouring LH to generate a new L radical.

The ability of free or immobilized lipoxygenase to introduce oxygen derived from the air into polyunsaturated fatty acids in media containing organic solvent and aqueous buffer has been investigated [9,56]. The influence of many parameters was tested upon the degree of oxygenation in biphasic systems [36,108]. 

The stimulus for the recent surge of activity in this previously dormant area of organic chemistry can be traced to the prostaglandin connection . That is to the discovery that saturated bicyclic peroxides are key intermediates in the biosynthesis of prostaglandins and other physiologically active substances by the enzymatic oxygenation of polyunsaturated fatty acids. 

Nitric oxide and peroxynitrite contribute to oxidative damage 569 Production of eicosanoids from polyunsaturated fatty acids such as arachidonic acid may generate reactive oxygen species 570 Brain antioxidant defenses modify ischemia-reperfusion injury 570 Reactive oxygen species may modify both the excitotoxic and the apoptotic components of ischemic brain damage 570... 

FIGURE 32-6 Lipid peroxidation leads to fragmentation or oxidation of polyunsaturated fatty acids (PUFA). HO, hydroxyl radical LO, lipid alkoxylradical LOO, lipid peroxyl radical 0 2, superoxide radical O, atomic oxygen radical. (From Hall in [3].)... 

Oxidation to CO of biodiesel results in the formation of hydroperoxides. The formation of a hydroperoxide follows a well-known peroxidation chain mechanism. Oxidative lipid modifications occur through lipid peroxidation mechanisms in which free radicals and reactive oxygen species abstract a methylene hydrogen atom from polyunsaturated fatty acids, producing a carbon-centered lipid radical. Spontaneous rearrangement of the 1,4-pentadiene yields a conjugated diene, which reacts with molecular oxygen to form a lipid peroxyl radical. 

Vitamin E may be indicated in some rare forms of anemia such as macrocytic, megaloblastic anemia observed in children with severe malnutrition and the hemolytic anemia seen in premature infants on a diet rich in polyunsaturated fatty acids. Also anemia s in malabsorption syndromes have shown to be responsive to vitamin E treatment. Finally, hemolysis in patients with the acanthocytosis syndrome, a rare genetic disorder where there is a lack of plasma jS-lipoprotein and consequently no circulating alpha tocopherol, responds to vitamin E treatment. In neonates requiring oxygen therapy vitamin E has been used for its antioxidant properties to prevent the development retrolental fibroplasia. It should be noted that high dose vitamin E supplements are associated with an increased risk in allcause mortality. 

---