Antioxidant effectiveness environments

There has been some evidence of a higher antioxidant effect when both flavonoids and a-tocopherol are present in systems like LDL, low-density lipoproteins (Jia et al., 1998 Zhu et al, 1999). LDL will incorporate a-tocopherol, while flavonoids will be present on the outside in the aqueous surroundings. A similar distribution is to be expected for oil-in-water emulsion type foods. In the aqueous environment, the rate of the inhibition reaction for the flavonoid is low due to hydrogen bonding and the flavonoid will not behave as a chain-breaking antioxidant. Likewise, in beer, none of the polyphenols present in barley showed any protective effect on radical processes involved in beer staling, which is an oxidative process (Andersen et al, 2000). The polyphenols have, however, been found to act synergistically... 

Tomato was reported to exert antioxidant activity in some studies (Vinson and others 1998 Kahkonen and others 1999), whereas it showed no antioxidant activity or even acted as a pro-oxidant in others (Gazzani and others 1998). The antioxidant effect of tomato is most probably due to synergism between several compounds and not due to lycopene content alone, as pure lycopene and several other carotenoids act as pro-oxidants in a lipid environment (Al-Saikhan and others 1995 Haila and others 1996). 

The similarity between the CB AO mechanism of phenols and HAS was reported at 25 °C in radiation oxidation of 2,4-dimethylpentane performed in the dark [207]. It was concluded that the respective NOH formed from 28, R = H during the stabilization process was the species responsible for the antioxidant effect (Scheme 27). The NOH is considered to be formed via trapping H by lltNO . The authors declared that i NOR are not involved in the stabilization of the radiation-oxidation of hydrocarbons and have doubts about the importance of the involvement of NOR in the regenerative cycle in an oxygen containing environment. 

Here, finally, we see an action of vitamin C that seems to be an antioxidant effect, along the lines of that described by Tom Kirkwood at the start of this chapter. Neutrophils need this extra protection to survive the wrath of their own assault, as they turn their immediate environment into a battlefield. The effect is a little like soldiers strapping on their gas... 

NO is a potent biological mediator regulating vascular tone, platelet function, leukocyte adhesion, and extravasations of leukocytes, but at high levels it plays critical roles in modulating inflammatory and degenerative diseases (12—15). HNO is an unstable weak acid (pKa=11.4) (16,17), which readily dimerizes to yield N2O (16), and Hke NO displays both prooxidative and antioxidative effects (18—25). Hence, the ability of HXs to serve as HNO-donors and/or NO-donors under oxidizing environments is involved in both the beneficial and injurious activities. 

Watkins, T, Geller, M, Kooyenga, D and Bierenbaum, M (1999) Hypocholesterolemic and antioxidant effect of rice bran oil non-saponifiables in hypercholesterolemic subjects. Environ. Nutr. Interact., 3, 115-122. 

Fryer, M. J. (1992). The antioxidant effects of thylakoid Vitamin E (alpha-tocopherol). Plant Cell Environ., 15,381-392. 

The specific mechanisms by which individual dietary components can alter the cancer process remain poorly understood. However, mechanisms underlying the carcinogenesis process are understood sufficiently so that model systems to evaluate the ability of a specific compound to inhibit or promote processes that may prevent or delay cancer development can be predicted. Phytochemcials can act at a variety of sites relevant to the development of the cancer cells. They may inhibit carcinogen activation, induce hepatic detoxification pathways, exert antioxidant effects/metal chelation properties, enhance immune response, induce apoptosis, and alter hormonal environment. 

Betalains have shown strong antioxidant activities in biological environments such as membranes and LDLs," -" suggesting that the consumption of betalain-colored foods may exert protective effects against certain oxidative stress-related diseases (i.e., cancers) in humans. Beetroot has been used as a treatment for cancer in Europe for several centuries. The high content of betanin in red beetroot (300 to 600 mg/kg) may be the explanation for the purported cancer chemopreventive effects of beets. 

A molecule that has a prooxidant effect can be dehned as a molecule that can react with reactive oxygen species (ROS) to form compounds more deleterious to biomolecules than the ROS alone. Possible prooxidant activity of carotenoids was for the first time mentioned by Burton and Ingold. Since then, many other examples of loss of antioxidant activity or prooxidant activity have been illustrated and reviewed in the literature. Increasing oxygen partial pressure (PO2) and/or carotenoid concentration can convert a carotenoid from antioxidant to prooxidant. Thus, depending on the environment, the same molecule can exert either antioxidant or prooxidant activity. ... 

Kim, H.S. and Lee, B.M., Protective effects of antioxidant supplementation on plasma lipid peroxidation in smokers, J. Toxicol. Environ. Health A, 63, 583, 2001. Gaziano, J.M. et al.. Supplementation with beta-carotene in vivo and in vitro does not inhibit low density lipoprotein oxidation. Atherosclerosis, 112, 187, 1995. Sutherland, W.H.F. et al.. Supplementation with tomato juice increases plasma lycopene but does not alter susceptibility to oxidation of low-density lipoproteins from renal transplant recipients, Clin. Nephrol, 52, 30, 1999. 

However, peroxidation can also occur in extracellular lipid transport proteins, such as low-density lipoprotein (LDL), that are protected from oxidation only by antioxidants present in the lipoprotein itself or the exttacellular environment of the artery wall. It appeats that these antioxidants are not always adequate to protect LDL from oxidation in vivo, and extensive lipid peroxidation can occur in the artery wall and contribute to the pathogenesis of atherosclerosis (Palinski et al., 1989 Ester-bauer et al., 1990, 1993 Yla-Herttuala et al., 1990 Salonen et al., 1992). Once initiation occurs the formation of the peroxyl radical results in a chain reaction, which, in effect, greatly amplifies the severity of the initial oxidative insult. In this situation it is likely that the peroxidation reaction can proceed unchecked resulting in the formation of toxic lipid decomposition products such as aldehydes and the F2 isoprostanes (Esterbauer et al., 1991 Morrow et al., 1990). In support of this hypothesis, cytotoxic aldehydes such as 4-... 

Furthermore, concentrates may also be used as conventional additives in the same polymer or in different polymers. In this way a substantive antioxidant (or modifier) system can be produced with very high effectiveness especially under aggressive environments. In comparison, under such demanding conditions, conventional antioxidants will not only lead to premature failure of the polymer but also to dangerous situations such as in the case in food contact application (packaging), medical uses of polymers (artificial joints), and failure of aircraft tyres where human lifes are at risk. 

The literature on basic- and acid-catalyzed alkylation of phenol and of its derivatives is wide [1,2], since this class of reactions finds industrial application for the synthesis of several intermediates 2-methylphenol as a monomer for the synthesis of epoxy cresol novolac resin 2,5-dimethylphenol as an intermediate for the synthesis of antiseptics, dyes and antioxidants 2,6-dimethylphenol used for the manufacture of polyphenylenoxide resins, and 2,3,6-trimethylphenol as a starting material for the synthesis of vitamin E. The nature of the products obtained in phenol methylation is affected by the surface characteristics of the catalyst, since catalysts having acid features address the electrophilic substitution in the ortho and para positions with respect to the hydroxy group (steric effects in confined environments may however affect the ortho/para-C-alkylation ratio), while with basic catalysts the ortho positions become the... 

Antioxidants are species that accept the reactive byproducts of oxidation reactions. They are typically hindered amines or phenols that accept radicals, inactivating them and preventing further effects of oxidation. The level of antioxidant used in a polymeric item depends on the expected lifetime of the final part, the environment in which the part will be used, and the susceptibility of the polymer to oxidation. Figure 9.7 shows two common antioxidants used in polyolefins. 

At the moment, the role of p53 and its related genes in the regulation of cell growth signaling by carotenoids is not well understood and the results appear controversial. It is possible that several factors may influence the modulatory effects of P-carotene and other carotenoids on p53 levels, including the concomitant presence of smoke, the type and the concentration of the carotenoid, the association with other antioxidants as well as the biological cellular environment. 

Numan IT, Hassan MQ, Stohs SJ. 1990b. Protective effects of antioxidants against endrin-induced lipid peroxidation, glutathione depletion, and lethality in rats. Arch Environ Contam Toxicol 19 302-306. 

NT072 Bagchi, D., E. A. Hassoun, M. Bagchi, and S. J. Stohs. Protective effects of free radical scavengers and antioxidants against smokeless tobacco extract (STE) induced oxidative stress in macrophage J774A.1. Cell cultures. Arch Environ Contam Toxicol 1995 29(3) 424-428. 

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