Antioxidant roles

In plants, and more specifically in leaves, the antioxidant role of carotenoids is well demonstrated because they quench singlet oxygen as noted earlier. However, the antioxidant role of carotenoids in humans is still under debate. 

Giulivi, C. and Davies, K. (1990). A novel antioxidant role for haemoglobin. The comproportionation of ferryl haemoglobin with oxyhaemoglobin. J. Biol. Chem. 265, 19453-19460. 

Ill. Ramesh B, Pugalendi KV. (2006) Antioxidant role of umbelliferone in STZ- diabetic rats. Life Sci 79 306-310. 

MacDonald, B., Gray, J. 1., and Gibbons, L. N. (1980b). Role of nitrite in cured meat flavor Antioxidant role of nitrite. J. Food Sci. 45, 893-897. 

Gurer, H., Ozgunes, H., Oztezcan, S., and Ercal, N. 1999. Antioxidant role of alpha-lipoic acid in lead toxicity. Tree Radical Biology and Medicine 27(1-2) 75-81. 

For a long time, it was considered that, unlike the other vitamins, vitamin E had no specific functions rather it was the major Upid-soluble, radicaltrapping antioxidant in membranes. Many of its functions can be met by synthetic antioxidants however, some of the effects of vitamin E deficiency in experimental animals, including testicular atrophy and necrotizing myopathy, do not respond to synthetic antioxidants. The antioxidant roles of vitamin E and the trace element selenium are closely related and, to a great extent, either can compensate for a deficiency of the other. The sulfur amino acids (methionine and cysteine) also have a vitamin E-sparing effect. 

The best-established function of vitamin E is as a lipid-soluble antioxidant in plasma lipoproteins and cell membranes. Many of the antioxidant actions are unspecific, and a number of synthetic antioxidants have a vitamin E-sparing effect. There is considerable overlap between the antioxidant roles of vitamin E and selenium (Section 4.3.2). 

As well as its antioxidant role, ascorbate can be a source of hydroxyl and superoxide radicals. At high concentrations, it can reduce molecular oxygen to superoxide, being oxidized to monodehydroascorbate. At lower concentrations of ascorbate, both Fe + and Cu + ions are reduced by ascorbate, yielding monodehydroascorbate. Fe + and Cu+ are readily reoxidized by reaction with hydrogen peroxide to yield hydroxide ions and hydroxyl radicals. Cu+ also reacts with molecular oxygen to yield superoxide. 

One danger is that because herbal medications are not regulated, few if any clinical trials are performed even for safety or efficacy. One example is bilberry. Bilberry fruit is used to treat diabetes and diabetic retinopathy. Although animal models support the antioxidant role in vasoprotection, no well-designed and conducted clinical trials exist.The antioxidant effect may have benefit in AMD, as well. The antioxidant efficacy in bilberry is likely due to the tannin content, which is also found in grapes. 

The antioxidant role of NO comes Ifom its reaction with oxygen, carbon and nitrogen centred radicals and can be seen to have a scavenger role under a range of conditions [112]. This is because of the unpaired electrons of NO which react rapidly with alkoxyl and alkyl hydroperoxyl radicals at near diffusion reaction rates (2x10 M s [113]). It is these reactions that have been suggested to have a modulatory role in enzyme- or metal-catalysed... 

An alternative postulated mechanism of AmB induced cell damage involves oxidative stress with the formation of free radical intermediates [15,16, 79]. Evidence against this hypothesis has been provided by recent studies that evaluated the anti- or pro-oxidant effects of AmB by examining its effects on phospholipid pattern in aortic smooth muscle cells [80] as well as on lipid-peroxidation of cis-Parinaric acid in liposomes [81]. These studies provided evidence for an antioxidant role for AmB rather than a pro-oxidant role and suggesting that oxidative stress is not involved in AmB-induced toxicity. 

Al-Malaika, S. Issenhuth, S. Burdick, D. The antioxidant role of vitamin E in polymers. V. Separation of stereoisomers and characterization of other oxidation products of dl-a-tocopherol formed in polyolefins during melt processing. J. Anal. Appl. Pyrolysis 2001, 73, 491-503. 

In a test-tube method called ORAC (oxygen radical absorbance capacity), freeze-dried agaf powder scored the highest ORAC level yet determined among fruits, a result that incited a storm of marketing literature declaring that a af products have the highest antioxidant health value of any food. The bad news is that there are limitations to that ORAC value as we know it (see Appendix A). Antioxidant properties determined in test tubes are unlikely to have the same antioxidant roles in the human body. Further, the comparisons of aqa ORAC with other fruits are not valid since the fruit preparations were not identical across all tests. 

Both marketers of manufactured superfruit products and the public media have exaggerated the potential antioxidant importance of fruit compounds such as polyphenol pigments (anthocyanins, flavonoids, tannins, catechins, xanthones, and many others). These compounds have antioxidant activity in controlled laboratory conditions, but there is no scientifically confirmed evidence that they have antioxidant roles in the human body. 

The antioxidative role of anthocyanins and flavones in providing stable blue flower colors in the angiosperms has been studied. The leaf anthocyanins and flavones showed a protective effect against UV-B radiation. These protective UV-B flavonoids in angiosperms were mainly kaempferol (9), quercetin (10), cyanidin (51), luteolin (65), and isoorientin C-glycoside (flavone C-glycoside, 66) (Fig. 14) [35]. 

Al-Malaika, S. Ashley, H. Issenhuth, S. The antioxidant role of ot-tocopherol in polymers. I The nature of transformation products of a-tocopherol formed during melt processing of LDPE. J. Polym. Sci. Part A, Polym. Chem. 1994, 32, 3099-3113. 

Loreto F., M. Mannozzi, C. Maris, P. Nascetti, F. Ferranti, and S. Pasqualini Ozone quenching properties of isoprene and its antioxidant role in leaves. Plant Physiol. 126 (2001a) 993-1000. 

Lei, X Cornell University Antioxidative role of glutathione peroxidase in transgenic mice CRISP 2001... 

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