Vitamin antioxidant effectivity

A specific role for vitamin E in a required metabolic function has not been found. In addition to its direct antioxidant effects, a-tocopherol has been reported to have specific molecular functions. 

This method is also used to measure ex vivo low-density lipoprotein (LDL) oxidation. LDL is isolated fresh from blood samples, oxidation is initiated by Cu(II) or AAPH, and peroxidation of the lipid components is followed at 234 nm for conjugated dienes (Prior and others 2005). In this specific case the procedure can be used to assess the interaction of certain antioxidant compounds, such as vitamin E, carotenoids, and retinyl stearate, exerting a protective effect on LDL (Esterbauer and others 1989). Hence, Viana and others (1996) studied the in vitro antioxidative effects of an extract rich in flavonoids. Similarly, Pearson and others (1999) assessed the ability of compounds in apple juices and extracts from fresh apple to protect LDL. Wang and Goodman (1999) examined the antioxidant properties of 26 common dietary phenolic agents in an ex vivo LDL oxidation model. Salleh and others (2002) screened 12 edible plant extracts rich in polyphenols for their potential to inhibit oxidation of LDL in vitro. Gongalves and others (2004) observed that phenolic extracts from cherry inhibited LDL oxidation in vitro in a dose-dependent manner. Yildirin and others (2007) demonstrated that grapes inhibited oxidation of human LDL at a level comparable to wine. Coinu and others (2007) studied the antioxidant properties of extracts obtained from artichoke leaves and outer bracts measured on human oxidized LDL. Milde and others (2007) showed that many phenolics, as well as carotenoids, enhance resistance to LDL oxidation. 

The mechanism of prooxidant effect of a-tocopherol in aqueous lipid dispersions such as LDLs has been studied [22], This so-called tocopherol-mediated peroxidation is considered in detail in Chapter 25, however, in this chapter we should like to return once more to the question of possible prooxidant activity of vitamin E. The antioxidant effect of a-tocopherol on lipid peroxidation including LDL oxidation is well established in both in vitro and in vivo systems (see, for example, Refs. [3,4] and many other references throughout this book). However, Ingold et al. [22] suggested that despite its undoubted high antioxidant efficiency in homogenous solution a-tocopherol can become a chain transfer agent in aqueous LDL... 

Huge literature on biological functions of flavonoids and their antioxidant and free radical scavenging activities successfully competes with work on antioxidant effects of vitamins E and C. Flavonoids have been reported to exert multiple biological effects and exhibit antiinflammatory, antiallergic, antiviral, and anticancer activities [85 89], However, considering flavonoids as the inhibitors of free radical-mediated processes, two types of their reactions should be discussed flavonoids as free radical scavengers (antioxidants) and flavonoids as metal chelators. 

This mechanism is now considered to be of importance for the protection of LDL against oxidation stress, Chapter 25.) The antioxidant effect of ubiquinones on lipid peroxidation was first shown in 1980 [237]. In 1987 Solaini et al. [238] showed that the depletion of beef heart mitochondria from ubiquinone enhanced the iron adriamycin-initiated lipid peroxidation whereas the reincorporation of ubiquinone in mitochondria depressed lipid peroxidation. It was concluded that ubiquinone is able to protect mitochondria against the prooxidant effect of adriamycin. Inhibition of in vitro and in vivo liposomal, microsomal, and mitochondrial lipid peroxidation has also been shown in studies by Beyer [239] and Frei et al. [240]. Later on, it was suggested that ubihydroquinones inhibit lipid peroxidation only in cooperation with vitamin E [241]. However, simultaneous presence of ubihydroquinone and vitamin E apparently is not always necessary [242], although the synergistic interaction of these antioxidants may take place (see below). It has been shown that the enzymatic reduction of ubiquinones to ubihydroquinones is catalyzed by NADH-dependent plasma membrane reductase and NADPH-dependent cytosolic ubiquinone reductase [243,244]. 

Chelators of iron, which are now widely applied for the treatment of patients with thalassemia and other pathologies associated with iron overload, are the intravenous chelator desferal (desferrioxamine) and oral chelator deferiprone (LI) (Figure 19.23, see also Chapter 31). Desferrioxamine (DFO) belongs to a class of natural compounds called siderophores produced by microorganisms. The antioxidant activity of DFO has been studied and compared with that of synthetic hydroxypyrid-4-nones (LI) and classic antioxidants (vitamin E). It is known that chronic iron overload in humans is associated with hepatocellular damage. Therefore, Morel et al. [370] studied the antioxidant effects of DFO, another siderophore pyoverdin, and hydroxypyrid-4-ones on lipid peroxidation in primary hepatocyte culture. These authors found that the efficacy of chelators to inhibit iron-stimulated lipid peroxidation in hepatocytes decreased in the range of DFO > hydroxypyrid-4-ones > pyoverdin. It seems that other siderophores are also less effective inhibitors of lipid peroxidation than DFO [371],... 

Antioxidants are compounds that inhibit autoxidation reactions by rapidly reacting with radical intermediates to form less-reactive radicals that are unable to continue the chain reaction. The chain reaction is effectively stopped, since the damaging radical becomes bound to the antioxidant. Thus, vitamin E (a-tocopherol) is used commercially to retard rancidity in fatty materials in food manufacturing. Its antioxidant effect is likely to arise by reaction with peroxyl radicals. These remove a hydrogen atom from the phenol group, generating a resonance-stabilized radical that does not propagate the radical reaction. Instead, it mops up further peroxyl radicals. In due course, the tocopheryl peroxide is hydrolysed to a-tocopherylquinone. 

N.A. Vaccinium macrocarpon Ait. Anthocyanosides, hippuric acid, vitamins , .103 77 78 80 300 Prevents urinary infection and stones, an antioxidant, effect on clogged heart arteries. 

Sea animals are rich in soluble dietary fibers, proteins, minerals, vitamins, antioxidants, phytochemicals, and polyunsaturated fatty acids, with low caloric value. Polysaccharides from marine animals have been reported to possess biological activities with potential medicinal values in addition to their current status as a source of dietary fibers and prebiotics. Moreover, they have a lot of dietary fiber, which lowers blood cholesterol, and iodine, which improves metabolism, vascular and cardiac action, body temperature, and perspiration regulation, and are effective in... 

Vitamin E [a-tocopherol) Men women 15 mg/d Antioxidant effects Hemorrhagic toxicity... 

Further work on the structural requirements for the antioxidant effect has been performed with micelles and liposomes [ 104]. This group concluded that the antioxidant properties of vitamin E and its model compound without the phytyl side-chain were similar within micelles, liposomes and homogeneous solution but that the phytyl side-chain enhances the retention of vitamin E in liposomes and suppresses the transfer of the vitamin between liposomal membranes. 

Thought to function as antioxidants and also to enhance the antioxidant effects of vitamin C... 

Fat-soluble vitamins, in addition to their antioxidative effects on lipids, appear to exert a general protective effect in animals. Vitamin A and beta-carotenes protect lab animals from toxicity of citral, cyclophosphamide and some hydrocarbons (Seifter et al, (A2.) In related but independent studies, it was observed that high levels of vitamin A inhibit tumorogenesis and that low levels of vitamin A appear to enhance tumorogenesis (Baird, (1 ). vitamin E inhibited chemically-induced carcinogenesis in test systems (Shamberger, ) and also reduced the susceptibility of rats to cigarette smoke (Chow,... 

Since vitamin E is very sensitive to oxidation, stable esters have mainly been used for topical formulations and are considered to be safe.64 As had previously been shown for skin of hairless mice,65 but not for human skin,66 the bioconversion of vitamin E acetate by esterases to vitamin E with its known antioxidant effects has recently also been demonstrated in human skin.48 When supplemented orally a-tocopherol acetate or a-tocopherol succinate get readily hydrolyzed to a-tocopherol in the gut47 with the natural single stereoisomeric form (RRR-a-tocopherol) appearing to have about twice the systemic availability of the synthetic form (all-rac-a-tocopherol)67... 

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. 

MRC Vitamin Study Research Group (1991) Prevention of neural tube defects result of the Medical Research Coundl Vitamin Study. Lancet 338(8760) 131-137 Muthuvel R, Venkataraman P, Krishnamoorthy G, Gunadharini DN, Kanagaraj P, Jone Stanley A, Srinivasan N, Balasubramanian K, Aruldhas MM, Arunakaian J (2006) Antioxidant effect of ascorbic acid on PCB (Aroclor 1254) induced oxidative stress in hypothalamus of rats. Clin Chim Acta 365(l-2) 297-303... 

---