Radical reactions lipids

Nishi, J., Ogura, R, Sugiyama, M., Hidaka, T. and Kohno, M. (1991). Involvement of active oxygen in lipid peroxide radical reaction of epidermal homogenate following ultra-violet light exposure. J. Invest. Dermatol. 97, 115-119. 

Further research is required to establish whether free-radical-induced damage is a primary event in diabetes. Tissue damage, which is associated with inactivation of antioxidants and release of metal ions that are potent catalysts of free radical reactions, can lead to lipid peroxidation. This raises the possibility that the diabetic process itself or other frctors may increase free-radical activity following direct tissue damage. 

The photochemiluminiscence (PCL) assay was initially used by Popov and others (1987). Popov and Lewin (1994 1996) have extensively studied this technique to determine water-soluble and lipid-soluble antioxidants. The PCL assay measures the antioxidant capacity, toward the 02 radical, in lipidic and water phase. This method allows the quantification of both the antioxidant capacity of hydrophilic and/or lipophilic substances, either as pure compounds or complex matrices from different origin synthetic, vegetable, animal, human, etc. The PCL method is based on an approximately 1,000-fold acceleration of the oxidative reactions in vitro by the presence of an appropriate photosensitizer. The PCL is a very quick and sensitive method. Chua and others (2008) used this assay to determine the antioxidant potential of Cin-namomum osmophloeum, whereas Kaneh and Wang and others (2006) determined the antioxidant capacity of marigold flowers. The antioxidant activity of tree nut oil extracts was also assessed by this method (Miraliakbari and Shahidi 2008). 

Rodenas et al. [77] studied PMN-stimulated lipid peroxidation of arachidonic acid. As MDA formation was inhibited both with L-arginine (supposedly due to the formation of excess NO) and DTPA (an iron ion chelator), it was concluded that about 40% of peroxidation was initiated by hydroxyl radicals formed via the Fenton reaction and about 60% was mediated by peroxynitrite. However, it should be noted that the probability of hydroxyl radical-initiated lipid peroxidation is very small (see above). Phagocyte-mediated LDL oxidation is considered below. 

It is generally thought that NO interferes with lipid peroxidation by providing alternative ways to chain termination (Rubbo et al, 1995 Rubbo et al, 1994). For example, radical-radical reactions between NO and LOO, LO and L radicals, as shown below, likely occur ... 

Homolytic cleavage of covalent bonds is an alternative means of generating free radicals. This may be assisted by the addition of an electron as in the case of carbon tetrachloride activation. The electron may be donated by cytochrome P-450, allowing the loss of chloride ion and the production of a trichloromethyl radical (Fig. 4.7). This can initiate other radical reactions by reacting with oxygen or unsaturated lipids. 

Schoneich C, Dillinger U, von Bruchhausen F, Asmus K-D (1992) Oxidation of polyunsaturated fatty adds and lipids through thiyl and sulfonyl radicals reaction kinetics, and influence of oxygen and structure of thiyl radicals. Arch Biochem Biophys 292 456-467 Schuchmann H-P, von Sonntag C (1981) Photolysis at 185 nm of dimethyl ether in agueous solution Involvement of the hydroxymethyl radical. J Photochem 16 289-295 Schuchmann H-P, von Sonntag C (1997) Fleteroatom peroxyl radicals. In Alfassi ZB (ed) Peroxyl radicals. Wiley, Chichester, pp 439-455... 

Fig. 7.3 Reactions showing the generation of ROS during lipid peroxidation and oxidative stress. Hydroxyl radical ( OH) lipid radical ( lipid), peroxyl radical (lipid-OO ) lipid peroxide (lipid-OOH) nitric oxide ( NO) nitrogen dioxide (N02) peroxynitrite anion (ONOO-) hypochlorous acid (HOC1), and hydrogen peroxide (H202)...

B23. Burlakova, E. B., and Dziuba, N. M., Synthetic inhibitors and natural antioxidants. II. The antioxidative activity of liver lipids of irradiated mice and die radioprotective effect of inhibitors of free radical reactions. Biofizika 11, 54—57 (1966). 

A product with a higher melting point is necessary for consumer acceptance. In addition, triacylglycerides that are more unsaturated tend to spoil more rapidly. This spoilage is due to oxidation caused by radical reactions. (This is an example of the au-toxidation process described in Section 21.8 and the Focus On box Vitamin E and Lipid Autoxidation on page 937. The hydrogens on the allylic carbons of unsaturated fatty acid residues are more readily abstracted because the resulting radicals are stabilized by resonance, so these compounds oxidize and spoil faster.) However, there is a trade-off, because it has been demonstrated that saturated fats have more deleterious health consequences than unsaturated fats do. 

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