Antioxidants lipid peroxyl radicals

MbFe(IV)=0 and with lipid peroxyl radicals (Castellucio et al, 1995). It may accordingly be concluded that the most relevant single parameter for predicting the antioxidative activity of a new plant phenol would be the standard reduction potential, E . 

Mooradian (1993) has studied the antioxidant properties of 14 steroids in a non-membranous system in which the fluorescence of the protein phycoerythrin was measured in the presence of a lipid peroxyl radical generator (ABAP). Oxidation of the protein produces a fluorescent species. Quenching of fluorescence by a test compound indicates antioxidant activity. Oestrone, testosterone, progesterone, androstenedione, dehydroepian-drosterone, cortisol, tetrahydrocortisone, deoxycorti-... 

The inhibition of lipid (LH) oxidation may be considered as one of the most important chemical reaction mechanisms that could explain the antioxidant function of flavonoids. In general terms, chain-breaking antioxidants (AH) inhibit or retard lipid oxidation (reactions 1-7) by interfering with initiation [generically represented by reaction 1] or with chain propagating reactions (reactions 2 and 3) by readily donating hydrogen atoms to lipid peroxyl radicals (LOO ) or lipid radicals (L ) (reactions 4 and 5) [Frankel, 1998] ... 

The lung also possesses nonenzymatic antioxidants such as vitamin E, beta-carotene, vitamin C, and uric acid. Vitamin E is lipid-soluble and partitions into lipid membranes, where it is positioned optimally for maximal antioxidant effectiveness. Vitamin E converts superoxide anion, hydroxyl radical, and lipid peroxyl radicals to less reactive oxygen metabolites. Beta-carotene also accumulates in cell membranes and is a metabolic precursor to vitamin A. Furthermore, it can scavenge superoxide anion and react directly with peroxyl-free radicals, thereby serving as an additional lipid-soluble antioxidant. Vitamin C is widely available in both extracellular and intracellular spaces where it can participate in redox reactions. Vitamin C can directly scavenge superoxide and hydroxyl radical. Uric acid formed by the catabolism of purines also has antioxidant properties and primarily scavenges hydroxyl radical and peroxyl radicals from lipid peroxidation. 

In the second experiment, mice were irradiated with the highest dose from the dose-response experiment. Concentrations of lipid hydroperoxides and lipophilic antioxidants were measured simultaneously on single skin samples from irradiated and non-irradiated sides of each mouse. The lipid hydroperoxide assay directly measured lipid peroxidation and thus was superior to the TBARS assay, which is indirect. Lipid-peroxyl radicals have been linked to chemically induced cutaneous carcinogenesis [31] as well as to UV-light-induced cutaneous carcinogenesis [32],... 

Cyanidin inhibits epidermal growth factor receptor tyrosine kinase (EGF-RTK), a-glycosidase and COX-1 and COX-2. Delphinidin (3,5,7,3, 4, 5 -hexahydroxyflavylium) also inhibits EGF-RTK. Anthocyanidins and anthocyanins can be anti-inflammatory antioxidants by acting as free radical scavengers. Thus, nasunin (delphinidin-3-(j6-coumaroylrutinoside)-5-glucoside) scavenges OH (hydroxyl), 02 (superoxide) and lipid peroxyl radicals and inhibits lipid peroxidation. 

Tocols are primary antioxidants that scavenge lipid peroxyl radicals (ROO ) by donating hydrogen atoms, and tocopheroxyl radicals (TocO ) may even scavenge another peroxyl radical forming stable products ... 

Quercetin, a highly studied antioxidant flavonoid has the potential to inhibit free radical processes in cells by a) scavenging O2 b) blocking lipid peroxidation c) reacting with peroxyl or lipid peroxyl radicals d) inhibiting formation of HO and e) chelating iron ions. 

Without doubt vitamin E is the most important lipid-soluble chain-breaking antioxidant in the human body. It is able to interact with lipid peroxyl radicals and is also able to react with singlet oxygen. The role of vitamin E as an antioxidant in vivo has been established several times by measuring tissue lipid peroxidation in vitamin E-deficient or in vitamin E-supplemented animals. 

Nitric oxide can both promote and inhibit lipid peroxidation (Hogg and Kalyanaraman (1999). By itself, NO acts as a potent inhibitor of the lipid peroxidation chain reaction by scavenging propagatory lipid peroxyl radicals (formula [81]). It can also inhibit many potential initiators of lipid peroxidation, such as peroxidase enzymes. In the presence of 02 , NO forms peroxynitrite (see equation [46]), a powerful oxidant capable of initiating lipid peroxidation and oxidising lipid soluble antioxidants. 

Isoflavones have been shown to be beneficial in several chronic diseases in which oxidants are involved. Isoflavones are weak antioxidants when tested in vitro in die context of scavenging lipid peroxyl radicals. However, at sites of mflammation proinflammatory oxidants such as peroxynitrite (ONOO"), hypochlorous acid (HOCl), and hypobromous acid (HOBr) are formed that may also react widi isoflavones. We present evidence herein, using reverse-phase HPLC-mass spectrometry and proton NMR, that at concmitrations of diese oxidants formed at these local sites, nitration, chlorination, and bromination of isoflavones occurs. 

Many known antioxidants have been shown to operate by acting as a hydrogen atom donor, thus breaking the chain of lipid peroxidation by quenching intermediate lipid peroxyl radicals which would otherwise go on to propagate the peroxidation process [9], As such, measures of radical scavenging ability are often nsed as a measure of antioxidant power. 

As strong antioxidants and scavengers of superoxide, hydroxyl and peroxyl radicals, tea flavonoids can suppress radical chain reactions and terminate lipid peroxidation (Kumamoto and Sonda, 1998, Yang and Wang, 1993). 

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