Polyunsaturated fatty free radical oxidation

Polyunsaturated fatty acids are oxidized by enzymatic and nonenzymatic pathways. Nonenzymatic oxidation is a free-radical mediated peroxidation. It is a chain reaction providing a continuous supply of free radicals that initiate further peroxidation. The whole process can be depicted as follows [21] ... 

Abstract. The significance of free radical oxidation of phospholipids in tissues of animals with experimental atherosclerosis was investigated. By using modem physico-chemical methods an elevated content of polyunsaturated fatty acids and other lipids peroxides was discovered in the blood and the aorta of rabbits with experimental atheromatosis. The human blood demonstrated a low level of protective enzymatic systems and a high content of products secondary to peroxidal oxidation of the lipids. The mechanism accounting for the action of lipids peroxides on the vascular wall resulting in the formation of atheromatous plaques is considered. 

Amino acid residues are potential targets of free radical oxidation and nitration. Carbonyl derivatives of proteins may be formed by the interaction of protein amino acid side chains, mainly cysteine, histidine, and lysine residues with reactive aldehydes, such as HNE and ONE generated by peroxidation of PUFAs (polyunsaturated fatty acids). Amino acid and peptide biomarkers of oxidative stress are typically focused on specific proteins related to disease pathology. For instance, the oxidation of histidine and methionine are typically discussed in (3-amyloid plaque formation and HNE-derived histidine adducts are the main focus of modifications on low-density lipoprotein (LDL) (An-nangudi et al., 2008). However, there are several specific examples of general biomarkers of oxidative stress that include endogenous histidine containing dipeptides such as carnosine and anserine as well as the very stable o,o -dityrosine. These will be discussed below. 

Figure 45-6. Interaction and synergism between antioxidant systems operating in the lipid phase (membranes) of the cell and the aqueous phase (cytosol). (R-,free radical PUFA-00-, peroxyl free radical of polyunsaturated fatty acid in membrane phospholipid PUFA-OOH, hydroperoxy polyunsaturated fatty acid in membrane phospholipid released as hydroperoxy free fatty acid into cytosol by the action of phospholipase Aj PUFA-OH, hydroxy polyunsaturated fatty acid TocOH, vitamin E (a-tocopherol) TocO, free radical of a-tocopherol Se, selenium GSH, reduced glutathione GS-SG, oxidized glutathione, which is returned to the reduced state after reaction with NADPH catalyzed by glutathione reductase PUFA-H, polyunsaturated fatty acid.)...

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. 

The E vitamins consist of eight naturally occurring tocopherols, of which a-tocopherol is the most active (Figure 28.28). The primary function of vitamin E is as an antioxidant in prevention of the nonenzymic oxidation of cell components (for example, polyunsaturated fatty acids) by molec ular oxygen and free radicals. 

Precautions should be taken to prevent oxidation during lipid analysis. Polyunsaturated fatty acids in lipid samples are easily attacked by active oxygen species (e.g., free radicals), exacerbated by the presence of strong light and metal ions. Therefore, it is arule of thumb while working with lipids that samples should be handled in a way that minimizes contact with air, light, and metals. To accomplish this, handle samples in glass vessels, use Teflon-lined or coated materials, and maintain the samples... 

---