Hydroxyl radical nitric oxide

Polyphenols can act as antioxidants by a number of potential pathways. The most important is likely to be by free radical scavenging, in which the polyphenol can break the radical chain reaction. Polyphenols are effective antioxidants in a wide range of chemical oxidation systems, being capable of scavenging peroxyl radicals, alkyl peroxyl radicals, superoxide, hydroxyl radicals, nitric oxide and peroxynitrate in aqueous and organic environments [121]. This activity is due to the ability of donating an H atom from an aromatic hydroxyl group to a free radical, and the major ability of an aromatic structure to support an unpaired electron by delocalization around the 7i-electron system. Phenolic acids... 

Tea polyphenols have been shown to scavenge reactive oxygen species, such as superoxide radical, singlet oxygen, hydroxyl radical, nitric oxide, nitrogen dioxide, and peroxynitrite, which may play important roles in carcinogenesis. 

Tea polyphenols show profound antioxidative effects in various systems they are strong scavengers of superoxide, hydrogen peroxide, hydroxyl radicals, nitric oxide, and peroxynitrite, the products of various chemical reactions and biological systems. 

Production of nitric oxide (NO ), by hydroxylation of arginine, is a part of normal cell signalling. In addition to being a radical, and hence potentially damaging in its own right, nitric oxide can react with superoxide to form peroxynitrite, which in turn decays to yield the more damaging hydroxyl radical. Nitric oxide was first discovered as the endothelium-derived relaxation factor, and this loss of nitric oxide by reaction with superoxide may be an important factor in the development of hypertension. 

Free radicals produced in vivo include superoxide, the hydroxyl radical, nitric oxide, oxygen-centered organic radicals such as peroxyl and alkoxyl radicals, and sulfur-centered thiyl radicals. Other oxygen-containing reactive species that are not radicals are also formed. These include hydrogen peroxide, peroxynitrite, and hypochlorous acid. While these are not radical species, they are actually or potentially damaging oxidants. The collective term ROS is often used to describe both radical and nonradical species. 

The H + NO2 OH + NO reaction provides an excellent example of the use of laser fluorescence detection for the elucidation of the dynamics of a chemical reaction. This reaction is a protot5q)e example of a radical-radical reaction in that the reagents and products are all open-shell free radical species. Both the hydroxyl and nitric oxide products can be conveniently detected by electronic excitation in the UV at wavelengths near 226 and 308 nm, respectively. Atlases of rotational line positions for the lowest electronic band systems of these... 

Fig. 3. Production of reactive species. (A) ROS can be produced from the weak radical oxygen in the mitochondria and endoplasmic reticulum, by various enzymatic reactions, and from oxyhemoglobin. Normally, nontoxic hydrogen peroxide can give rise to the powerful hydroxyl radical in the presence of transition metals (R5). Oxygen can also be induced to react with biomolecules by transition metals and enzymes. RNS can be produced by reaction of superoxide anion radical with the weak radical nitric oxide. These can react to form the powerful oxidant peroxynitrite/peroxynitrous acid, which can cause formation of other radicals, some with longer lives. See the text for details. SOD, superoxide dismutase. (B) Myeloperoxidase in leukocytes can produce the reactive species hypochlorous acid and tyrosyl radical. Unpaired electrons are indicated by the dense dots and paired electrons by the light ones.

Beckman, J.S., Beckman, T.W., Chen, J., Marshall, P.A. and Freeman, B.A. (1990). Apparent hydroxyl radical production by pjeroxynitrite implications for endothelial injury from nitric oxide and superoxide. Proc. Nad. Acad. Sci. USA 87, 1620-1624. 

Results of a more recent series of investigations suggest that lead may cause hypertension in rats by increasing reactive oxygen species, which act as vasoconstrictors, and decreasing nitric oxide, a vasodilator released by the endothelium. The reactive oxygen species may be the hydroxyl radical, and did not appear to be the superoxide anion (Ding et al. 1998). 

The photooxidation of acrylonitrile by hydroxyl radicals in the presence of nitric oxide has been observed to yield formaldehyde (HCHO) and formyl cyanide (HCOCN) (Hashimoto et al. 1984). 

This mode of superoxide-dependent free radical-mediated damaging activity remains an important one although the nature of the generated reactive species (free hydroxyl radicals or perferryl, or ferryl ions) is still obscure. However, after the discovery of the fact that many cells produce nitric oxide in relatively large amounts (see below), it became clear that there is another and possibly a more portent mechanism of superoxide-induced free radical damage, namely, the formation of highly reactive peroxynitrite. 

Nitric oxide is a physiological substrate for mammalian peroxidases [myeloperoxide (MPO), eosinophil peroxide, and lactoperoxide), which catalytically consume NO in the presence of hydrogen peroxide [60], On the other hand, NO does not affect the activity of xanthine oxidase while peroxynitrite inhibits it [61]. Nitric oxide suppresses the inactivation of CuZnSOD and NO synthase supposedly via the reaction with hydroxyl radicals [62,63]. On the other hand, SOD is able to modulate the nitrosation reactions of nitric oxide [64]. 

Probably, the most convincing proof of free radical mechanism of peroxynitrite reactions is the formation of dityrosine [117,118]. It has been suggested [118] that the nitric dioxide radical is responsible for the formation of both 3-nitrotyrosine and dityrosine (Figure 21.1), however, hydroxyl radicals (which were identified in this system by ESR spectroscopy [119]) may also participate in this process. Pfeiffer et al. [118] proposed that dityrosine is predominantly formed at low fluxes of superoxide and nitric oxide, which corresponds to in vivo conditions, however, this observation was not confirmed by Sawa et al. [117],... 

Peroxynitrite easily oxidizes nonprotein and protein thiyl groups. In 1991, Radi et al. [102] have shown that peroxynitrite efficiently oxidizes cysteine to its disulfide form and bovine serum albumin (BSA) to some derivative of sulfenic acid supposedly via the decomposition to nitric dioxide and hydroxyl radicals. Pryor et al. [124] suggested that the oxidation of methionine and its analog 2-keto-4-thiomethylbutanic acid occurred by two competing mechanisms, namely, the second-order reaction of sulfide formation and the one-electron... 

The constituent of paint, 2-nitropropane, exhibiting genotoxicity and hepatocarcinogeni-city was oxidized by liver microsomes forming nitric oxide, which was identified as a ferrous NO complex [61]. Clement et al. [62] concluded that superoxide may participate in the microsomal oxidation of /Y-hydroxyguanidincs, which produced nitric oxide, urea, and the cyanamide derivative. Caro et al. [63] suggested that the oxidation of ketoxime acetoxime to nitric oxide by microsomes enriched with P-450 isoforms might be mediated by hydroxyl or hydroxyl-like radicals. 

It should be noted that Reaction (4) is not a one-stage process.) Both free radical N02 and highly reactive peroxynitrite are the initiators of lipid peroxidation although the elementary stages of initiation by these compounds are not fully understood. (Crow et al. [45] suggested that trans-ONOO is protonated into trans peroxynitrous acid, which is isomerized into the unstable cis form. The latter is easily decomposed to form hydroxyl radical.) Another possible mechanism of prooxidant activity of nitric oxide is the modification of unsaturated fatty acids and lipids through the formation of active nitrated lipid derivatives. 

W. P., Katsuki, S., Kimura, H., Guanylate cyclase activation by azide, nitro compounds, nitric oxide, and hydroxyl radical and inhibition by... 

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