Antioxidants harmful

Preservatives generally fall into four categories. There are ultravi-olet/UV light absorbers (to prevent light from creating harmful and bad-tasting toxins), color stabilizers, antioxidants, and antimicrobials. 

Figure 6.2 Antioxidants are found in fruit and vegetables, making them important to eat every day. Antioxidants react with potentially harmful free radicals before the free radicals can react with other molecules in the body.

Overproduction of ROS can be harmful. Thus, cells have developed a complex antioxidant defense system to counteract the biological potential of ROS formation [213],... 

Flavonoids protect LDL from oxidation, delaying the onset of lipid peroxidation, however, the prevention of atherosclerosis by flavonoids occurs not only by the inhibition of LDL oxidation, but also by the increase of cellular resistance to harmful effects of the oxidized LDL (de Luis and Aller, 2008). The antioxidant activity of anthocyanidins, as well as their protective role against LDL oxidation, has been well demonstrated in different in vitro systems (Aviram and Fuhrman, 2002 Satue-Gracia and others 1997 Teissedre and others 1996). 

Compartmentation means both spatial separation of potentially harmful but essential compounds (e.g., storage of iron in ferritin) and cell- and tissue-specific distribution of antioxidative compounds, and it serves to prevent uncontrolled oxidation. 

In spite of a high reactivity of 3-carotene in free radical reactions and marked antioxidant effects in in vitro systems, 3-carotene did not show itself as an effective in vivo antioxidant. Furthermore, recent clinical trials suggested that the administration of 3-carotene may be useless or even harmful to patients with heart and some other diseases, especially to smokers. One might suspect that one of the major reasons of toxic in vivo effects of 3-carotene might be the formation of prooxidative compounds during 3-carotene oxidation. In contrast to... 

BHT (2,6-di-tert-butyl-4-methylphenol), a phenolic antioxidant, on reaction with NO under neutral conditions, results in scavenging of the potentially harmful NO via radical reactions [143]. Sodium phenolate under basic conditions undergoes a Traube-type reaction at the ortho-position to produce a cupferron derivative [144]. When the ortho-positions are sterically blocked and the para-position does not bear a proton, cyclohexadienone diazeniumdiolates may be formed (Scheme 3.12) [145]. 

A second mechanism in the. aging of CTPB propellants also exists and proceeds concurrently with the reactions proposed above. It consists of an attack at the reactive points of unsaturation in the backbone polymer, which causes additional crosslinking and hence an increase in propellant modulus, particularly at the surface. The exposed surface of CTPB propellants changes, as indicated by an increase in hardness. Heavy metal ions are particularly harmful, and it was found that an increase from 10 to 80 p.p.m. of iron caused a significant increase in surface hardening by catalytic attack on the double bonds. Antioxidants in general provide sufficient protection for polymer storage. In CTPB propellants the antioxidant selected to protect the double bond is very important. Amine-type antioxidants have provided better surface stability than phenolic compounds. 

At best, then, consumption of green tea beverage or capsules containing the concentrated catechins as a cytoprotective and antioxidant measure is logical and supported by much data. At worst, this is a pleasant custom which appears to do no harm in the vast majority of cases. 

Because the potential benefits outweigh the possibilities of harm, many experts recommend a daily multivitamin that does not exceed the RDA of it component vitamins. Multivitamins ensure an adequate intake for those vitamins—folic acid, vitamin B6, vitamin B12, and vitamin D—that are most likely to be deficient. However, the the evidence is insufficient to recommend for or against the use of supplements of vitamins A, C, or E multivitamins with folic acid or antioxidant combinations for the pre vention of cancer or cardiovascular disease. Most experts recommend against the use of p-carotene supplements, either alone or in combina Don, for the prevention of cancer or cardiovascular disease. 

In neural cells, the redox status is controlled by the thioredoxin (Trx) and glutathione (GSH) systems that scavenge harmful intracellular ROS. Thioredoxins are antioxidants that serve as a general protein disulphide oxidoreductase (Saitoh et al., 1998). They interact with a broad range of proteins by a redox mechanism based on the reversible oxidation of 2 cysteine thiol groups to a disulphide, accompanied by the transfer of 2 electrons and 2 protons. These proteins maintain their reduced state through the thioredoxin system, which consists of NADPH, thioredoxin reductase (TR), and thioredoxin (Trx) (Williams, Jr. et al., 2000 Saitoh et al., 1998). The thioredoxin system is a system inducible by oxidative stress that reduces the disulfide bond in proteins (Fig. 7.4). It is a major cellular redox system that maintains cysteine residues in the reduced state in numerous proteins. 

Many medicinal plants contain chemical compounds called flavonoids. Some evidence suggests that flavonoids, also called bioflavonoids, can have beneficial effects on the body. Flavonoids may be able to help ward off bacteria and viruses and reduce inflammation. They may also be antioxidants, which are molecules that clear the body of harmful chemicals called oxygen free radicals. (Oxygen free radicals are highly reactive molecules that damage cells and have been associated with diseases such as cancer, diabetes, and cardiovascular disease.)... 

The dominant significant contribution of uric acid to TAC of blood plasma, obscuring changes in the concentrations of other antioxidants, makes TAC less sensitive to changes in the concentrations of other antioxidants. Moreover, uric acid may be a prooxidant in some situations (S3) and a harmful metabolite in other cases. Attempts have been made to calculate or measure the urate-independent fraction of TAC (P20). 

Dipyridamole has also been shown to have antioxidant effects (19). Antioxidants act to remove harmful reactive-oxygen species and protect low-density lipoproteins (LDL) from oxidation oxidized LDL plays a key role in the development and propagation of atherosclerosis. The antioxidant effects of dipyridamole may be both direct (by scavenging oxygen and hydroxyl radicals, inhibiting lipid peroxidation and oxidative modification of LDL) (20-22) and indirect (via adenosine, which reduces superoxide anion generation). Dipyridamole has been shown to be a more effective anioxidant than ascorbic acid, alpha-tocopherol, or probucol (22). 

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