Autoxidation lipid

Comparison of equation (9.21) with equations (9.9) and (9.6) reveals the resemblance of nuclear and electron resonance methods. In equation (9.21), P is the so-called Bohr magneton, and the electron g value is a porportionality constant which is dependent upon the magnetic species and its environment. Only unpaired electrons give rise to ESR spectra, and this is why, except in the study of lipid autoxidation, lipids can only be studied through the use of spin labels, which are stable, usually nitroxide, radicals (Fig. 9.26). 

Neff, W.E., Frankel, E.N. and Weisleder, D. High-pressure liquid chromatography of autoxidized lipids II. Hydroperoxy-cyclic peroxides and other secondary products from methyl linolenate. Lipids 16, 439-448 (1981). 

Reddy, K. and Tappel, A.L. (1974) Effect of dietary selenium and autoxidized lipids on glutathione peroxidase system of gastrointestinal tract and other tissues in the rat. J. Nutr. 104, 1069-1078. 

CHAN H w s (1987) Autoxidation of Unsaturated Lipids, London, Academic Press. 

POKORNY j (1987) Major factors affecting the autoxidation of lipids , in Chan El W S, Autoxidation of unsaturated lipids , London, Academic Press, 141-206. 

Interestingly, early examples of carotenoid autoxidation in the literature described the influence of lipids and other antioxidants on the autoxidation of carotenoids." " In a stndy by Budowski et al.," the influence of fat was fonnd to be prooxidant. The oxidation of carotenoids was probably not only cansed by molecnlar oxygen bnt also by lipid oxidation products. This now well-known phenomenon called co-oxidation has been stndied in lipid solntions, in aqueons solntions catalyzed by enzymes," and even in food systems in relation to carotenoid oxida-tion." The inflnence of a-tocopherol on the antoxidation of carotenoids was also stndied by Takahashi et al. ° who showed that carotene oxidation was snppressed as... 

Figure 1.7 Typical zero-order and corresponding second-derivative electronic absorption spectra of ethanol-reconstituted lipid/chloroform extracts of autoxidized model polyunsaturated fatty-acid compounds and inflammatory synovial fluid obtained after (1) reduction with NaBH4 and (2) dehydration with alcoholic H2S04- (a) Methyl linoleate subsequent to autoxidation in air at ambient temperature for a period of 72 h (—), or exposure to a Fenton reaction system containing EDTA (5.75 x 10 mol/dm ), H2O2 (1.14 X 10 mol/dm ) and Fe(ll) (5.75 x IO mol/dm ) as an aqueous suspension (—) (b) as (a) but with methyl linolenate (c) untreated rheumatoid knee-joint synovial fluid.

Chan, H.W.S. and Levett, G. (1977). Autoxidation of methyl linoleate. Separation and analysis of isomeric mixtures of methyl linoleate hydroperoxides and methyl hydrox-ylinoleates. Lipids 12, 99. 

As a reasonable biogenetie pathway for the enzymatic conversion of the polyunsaturated fatty acid 3 into the bicyclic peroxide 4, the free radical mechanism in Equation 3 was postulated 9). That such a free radical process is a viable mechanism has been indicated by model studies in which prostaglandin-like products were obtained from the autoxidation of methyl linolenate 10> and from the treatment of unsaturated lipid hydroperoxides with free radical initiators U). 

Kim, SJ, Nara, E, Kobayashi, H, Terao, J, and Nagao, A, 2001. Formation of cleavage products by autoxidation of lycopene. Lipids 36, 191-199. 

Peroxyl radicals are the species that propagate autoxidation of the unsaturated fatty acid residues of phospholipids (50). In addition, peroxyl radicals are intermediates in the metabolism of certain drugs such as phenylbutazone (51). Epoxidation of BP-7,8-dihydrodiol has been detected during lipid peroxidation induced in rat liver microsomes by ascorbate or NADPH and during the peroxidatic oxidation of phenylbutazone (52,53). These findings suggest that peroxyl radical-mediated epoxidation of BP-7,8-dihydrodiol is general and may serve as the prototype for similar epoxidations of other olefins in a variety of biochemical systems. In addition, peroxyl radical-dependent epoxidation of BP-7,8-dihydrodiol exhibits the same stereochemistry as the arachidonic acid-stimulated epoxidation by ram seminal vesicle microsomes. This not only provides additional... 

The effects of flavonoids on in vitro and in vivo lipid peroxidation have been thoroughly studied [123]. Torel et al. [124] found that the inhibitory effects of flavonoids on autoxidation of linoleic acid increased in the order fustin < catechin < quercetin < rutin = luteolin < kaempferol < morin. Robak and Gryglewski [109] determined /50 values for the inhibition of ascorbate-stimulated lipid peroxidation of boiled rat liver microsomes. All the flavonoids studied were very effective inhibitors of lipid peroxidation in model system, with I50 values changing from 1.4 pmol l-1 for myricetin to 71.9 pmol I 1 for rutin. However, as seen below, these /50 values differed significantly from those determined in other in vitro systems. Terao et al. [125] described the protective effect of epicatechin, epicatechin gallate, and quercetin on lipid peroxidation of phospholipid bilayers. 

Ideally samples from living organisms should be extracted without any delay to prevent autoxidative or enzymic deterioration of their lipid constituents. If this is not feasable the sample should be frozen immediately and stored at — 20 °C in a glass container under nitrogen. Often lipids will be extracted into an organic solvent and during this and subsequent steps in the analytical procedure minimal exposure of the lipids to air, light and heat is very important to prevent oxidation or destruction of the lipids. 

Cosgrove, J. P., Church, D. F., and Pryor, W. A., 1987, The kinetics ofthe autoxidation of polyunsaturated fatty acids, Lipids 22 299-304. 

SCHEME 1. Autoxidation of lipids (RH) is afree radical process yielding hydroperoxides as primary products and many other secondary derivatives... 

Volatile compounds formed by anabolic or catabolic pathways include fatty acid derivatives, terpenes and phenolics. In contrast, volatile compounds formed during tissue damage are typically formed through enzymatic degradation and/ or autoxidation reactions of primary and/or secondary metabolites and includes lipids, amino acids, glucosinolates, terpenoids and phenolics. 

Chan HWS (ed) (1987) Autoxidation of unsaturated lipids. Academic, London... 

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