Lipids unsaturated, oxidation

They are widely distributed in vegetable lipids, and in the body fat of animals, though animals cannot synthesize them. They have vitamin E activity and can protect unsaturated lipids against oxidation. Four are found naturally ... 

For the NO studies that show inhibition of lipid peroxidation, we used HL-60 cells made more oxidizable by adding 32 pM docosahexaenoic acid (22 6q)3 ) to the growth media. When unenriched cells were examined, inhibition of oxidation was qualitatively identical, but the magnitude of the effect was less, and therefore more difficult to measure. The effect of lipid unsaturation will be developed below. 

Other biochemical pathways affected by NOx include inhibition of lipid biosynthesis, oxidation of unsaturated fatty acids in vivo, and stimulation of peroxidase activity. 

Unsaturated fatty acids esterified to phospholipids are also targets for lipid peroxidation. Oxidative fragmentation of phospholipids such as l-pahnitoyl-2-arachidonoyl-OT-glycero-3-phosphocholine (PAPC) generates several oxidation products, which mediate... 

Fluorescence techniques are very sensitive. On a molar basis, the amount of malonaldehyde detected by fluorescence is 10 to 1(X) times more sensitive than the colorimetric TB A assay. However, this method is not specific, as it measures complex mixtures resulting from the interactions of oxidized lipids, unsaturated aldehydes and malonaldehyde with proteins, peptides, amino acids, phospholipids, DNA and nucleic acids. These interactions involve oxidized or polymerized species of proteins or amino acids. The fluorescence method provides a non-speciflc but sensitive measure of oxidative deterioration in complex foods such as meats and fish, which are often difficult to analyse for... 

Another mechanism for protecting unsaturated lipids against oxidation in vivo is claimed to be the action of polyamines, particularly spermine and spermidine (Lpvaas, 1991). The molecular structure contains several nitrogen atoms (Figure 3.2), but their action as antioxidants has not been explained. 

Textbooks often refer to the oxidation of food lipids as autoxidation. The prefix auto is defined as self-acting thus the term, autoxidation has been used to describe the ability of lipids to oxidize by the self perpetuating generation of ftee radicals from unsaturated fatty acids in the presence of oxygen. Unfortunately, the term autoxidation can be misinterpreted as the ability of lipids to oxidize on their own. This is rarely ftie case in foods since there are normally prooxidants present or environmental conditions that cause and accelerate lipid oxidation. 

Unsaturated lipid substrates are the prime compounds of deterioration in food and cosmetics. They are constituted of mixtures of tri-, di-, and monoacylglycerols, free fatty acids, glycolipids, phospholipids, sterols, and other substances (Chen et ah, 2011). Hydrolysis, polymerization, and isomerization reactions can cause the deterioration of food, and the resulting compounds are harmful to health (Chen et ah, 2011 Ng et ah, 2014). However, the most important reaction that occurs with lipids is oxidation, because lipids are easily oxidized, even by atmospheric oxygen. This process results in the destruction of essential triglycerides and fat-soluble vitamins (A, D, E, and K), which leads to the formation of aldehydes, ketones, and free fatty acids. This is undesirable because the palatability, odor, texture, consistency, appearance, and nutritional value of the food are altered (Takemoto et ah, 2009 Andre et al., 2010). 

Marinova EM, Yanishheva NV. 1994. Effect of lipid unsaturation on the oxidative activity of some phenohc acids. Journal of American Oil Chemists Society, 71 427-434. 

The susceptibility of unsaturated membrane lipids to oxidation by atmospheric oxygen is to an extent mirrored by the ease with which they can be oxidised via enzymatic... 

Steroids (1) are members of a large class of lipid compounds called terpenes that are biogenicaHy derived from the same parent compound, isoprene, C Hg Steroids contain or are derived from the perhydro-l,2-cyclopentenophenanthrene ring system (1) and are found in a variety of different marine, terrestrial, and synthetic sources. The vast diversity of the natural and synthetic members of this class depends on variations in side-chain substitution (primarily at C17), degree of unsaturation, degree and nature of oxidation, and the stereochemical relationships at the ring junctions. 

Mechanisms of lipid peroxidation that have been implicated in atherosclerosis may be pertinent to RA. Cellular lipoxygenase enzymes may promote LDL modification by inserting hydroperoxide groups into unsaturated fetty-acid side chains of the LDL complex (Yla-Herttuala etal., 1990). 15-Lipoxygenase has been implicated as an initiator of LDL oxidation (Cathcart etal., 1991) whilst 5-lipoxygenase does not appear to be involved (Jessup et al., 1991). Products of activated lipoxygenase enzymes within inflammatory synovial fluid surest that this pathway could be activated in RA (Costello etal., 1992). 

Lipids are hydrolyzed by moisture and heat into free fatty acids, though hydrolytic enzymes may be deactivated by extrusion. Also, unsaturated fatty acids may imdergo oxidative rancidity (Camire et al., 1990). 

---