Polyunsaturated fatty acid formation

Uauy R, Mena P. Wegher B. Nieto S, Salem N Jr. Long chain polyunsaturated fatty acid formation in neonates effect of gestational age and intrauterine growth. Pediatr Res 2000 47(1) 127-135. 

Since subcellular membranes in brain cells contain high amounts of polyunsaturated fatty acids, formation of a single carbon-centered radical within a membrane can lead to peroxidation of... 

Kendrick, A. Ratledge, C. (1996). Cessation of polyunsaturated fatty acid formation in four selected filamentous fimgi when grown on plant oils. J. Am. Oil Chem. Soc., 73, 431-435. 

The precursor for polyunsaturated fatty acid formation in plants and algae is oleate. The next double bond is introduced at the 12,13-position (A12 desaturase) to form linoleate followed by desaturation at the 15,16-position (A15 desaturase) to form a-linolenic acid (all cw-9,12,15-18 3) as summarized in Figure 3.13. With the exception of some Cyanobacteria, a-linolenic acid is the most common fatty acid found in plants and freshwater algae. In marine algae, highly unsaturated 20C acids are predominant, the principal of which (arachidonic and eicosapentaenoic) are made by the pathways shown in Figure 3.13. 

The pathway for polyunsaturated fatty acid formation in plants which was discussed above (Figure 3.14) is probably that used by the majority of plants. It has been termed the eukaryotic pathway because it involves the participation of extra-chloroplastic compartments and particularly because 18C fatty acids are esterified in the sn-2 position of participating lipids (as they would be in other eukaryotes like animals). By contrast, desaturation (and formation of chloroplast lipids) continues within the chloroplast in some plants and such mechanisms are termed prokaryotic. For the latter desaturations, monogalactosyldiacylglycerol is used as substrate - allowing the formation of a-linolenate and, also, hexadecatrienoate (16 3) at its sn-2 position. An example of a plant operating the prokaryotic pathway would be spinach (see Table 6.6). However, the most important point to stress is that for all plants, polyunsaturated fatty acids are made on complex lipid substrates. 

Light and photosynthetic electron transport convert DPEs into free radicals of undetermined stmcture. The radicals produced in the presence of the bipyridinium and DPE herbicides decrease leaf chlorophyll and carotenoid content and initiate general destmction of chloroplasts with concomitant formation of short-chain hydrocarbons from polyunsaturated fatty acids (37,97). 

Organisms differ with respect to formation, processing, and utilization of polyunsaturated fatty acids. E. coli, for example, does not have any polyunsaturated fatty acids. Eukaryotes do synthesize a variety of polyunsaturated fatty acids, certain organisms more than others. For example, plants manufacture double bonds between the A and the methyl end of the chain, but mammals cannot. Plants readily desaturate oleic acid at the 12-position (to give linoleic acid) or at both the 12- and 15-positions (producing linolenic acid). Mammals require polyunsaturated fatty acids, but must acquire them in their diet. As such, they are referred to as essential fatty acids. On the other hand, mammals can introduce double bonds between the double bond at the 8- or 9-posi-tion and the carboxyl group. Enzyme complexes in the endoplasmic reticulum desaturate the 5-position, provided a double bond exists at the 8-position, and form a double bond at the 6-position if one already exists at the 9-position. Thus, oleate can be unsaturated at the 6,7-position to give an 18 2 d5-A ,A fatty acid. 

Fischer S Dietary polyunsaturated fatty acids and eicosanoid formation in humans. Adv Lipid Res 1989 23 169. 

The reason for the cholesterol-lowering effect of polyunsaturated fatty acids is still not fully understood. It is clear, however, that one of the mechanisms involved is the up-regulation of LDL receptors by poly-and monounsaturated as compared with saturated fatty acids, causing an increase in the catabolic rate of LDL, the main atherogenic lipoprotein. In addition, saturated fatty acids cause the formation of smaller VLDL particles that contain relatively more cholesterol, and they are utilized by extrahepatic tissues at a slower rate than are larger particles—tendencies that may be regarded as atherogenic. 

Interaction of lipid oxidation products and amino compounds. Amino acids and primary amines may be involved in other reactions which could lead to the formation of compounds having the potential to undergo N-nitrosation. Malonaldehyde, produced as a result of oxidation of lipids, particularly polyunsaturated fatty acids, has been shown to react with amino acids to produce... 

Chan, P.H. and Fishman, R.A. (1980). Transient formation of superoxide radicals in polyunsaturated fatty acid-induced brain swelling. J. Neurochem. 33, 1004-1007. 

Oxidative damage to membrane polyunsaturated fatty acids leads to the formation of numerous lipid peroxidation products, some of which can be measured as index of oxidative stress, including hydrocarbons, aldehydes, alcohols, ketones, and short carboxylic acids. 

Dietary polyunsaturated fatty acids (PUFAs), especially the n-3 series that are found in marine fish oils, modulate a variety of normal and disease processes, and consequently affect human health. PUFAs are classified based on the position of double bonds in their lipid structure and include the n-3 and n-6 series. Dietary n-3 PUFAs include a-linolenic acid, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) whereas the most common n-6 PUFAs are linoleic acid, y-linolenic acid, and arachidonic acid (AA). AA is the primary precursor of eicosanoids, which includes the prostaglandins, leukotrienes, and thromboxanes. Collectively, these AA-derived mediators can exert profound effects on immune and inflammatory processes. Mammals can neither synthesize n-3 and n-6 PUFAs nor convert one variety to the other as they do not possess the appropriate enzymes. PUFAs are required for membrane formation and function... 

Geyeregger, R. et al., Polyunsaturated fatty acids interfere with formation of the immunological synapse, J Leukoc Biol, 77, 680, 2005. 

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. 

These reactions are of the utmost importance in ensuring the formation of the polyunsaturated fatty acids that are essential for health (see below). 

Although these are termed essential fatty acids, they are, in fact, precursors for the major polyunsaturated fatty acids that have essential roles in the body but are present only in small amounts in the diet. Linoleic acid is converted, via elongation and desaturation reactions, to dihomo-y-linolenic (20 3n-6) and then to arachidonic (20 4n-6) acid. a-Linolenic is converted to eicosapentaenoic (20 5n-3) and then docosahexae-noic (22 6n-3). The pathways for formation of these latter fatty acids, from their dietary precursors, are presented in Figures 11.11 and 11.12. Full details of one pathway are provided, as an example, in Appendix 11.4. For comparison of the two pathways, they are presented side by side in Figure 11.13. 

There is some evidence that, in these patients, the interconversion between the polyunsaturated fatty acids is disturbed, which restricts the formation of eicosapentaenoic and docosahexaenoic acids. Such children are less likely to have been breastfed (breast milk contains these omega-3 fatty acids) they are more likely to suffer from allergies associated with essential fatty acid deficiency and also dry skin and hair and the membranes of the erythrocytes contain less omega-3 fatty acids compared with normal children. So far, the results of supplementation of the diet of these children with this disorder have not been conclusive. 

Polyunsaturated fatty acids Polyunsaturated fatty acids are provided in the triacylglycer-ols on phospholipids in the feeds. They are required for synthesis of phospholipids, which are required for formation of new membranes in proliferating cells, and as precursors for fat signalling molecules that are important in control of proliferation (see below). 

Liu, X., Yamada, N., Maruyama, W., and Osawa, Y. (2008b). Formation of dopamine adducts derived from brain polyunsaturated fatty acids Mechanism for Parkinson s disease.. Biol. Chem. 283,34887-34895. 

Hydroperoxide formation by the ene reaction path may lead to formation of conjugated double bonds in polyunsaturated fatty acids (see Section V.A) this reaction is concurrent with POV increase. An increase of the CDV, as measured from the absorbance at 233 nm, therefore indicates oxidation of polyunsaturated lipids. A strong correlation exists between CDV predicted from the absorbance in the 1100 to 2200 nm NIR region and CDV determined by the Ti Ia-64 AOCS official method , by UV spectrophotometry at 233 nm. The method was applied to determine CDV for oxidized soybean oil. A secondary absorption maximum of lesser intensity appears in the 260-280 mn range, and is assigned to ketone dienes . 

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