Peroxynitrite and

Hogg, N., Darley-Usmar, V.M., Graham, A. and Moncada, S. (1993a). Peroxynitrite and atherosclerosis. Biochem. Soc. Trans. 21, 358-362. 

During ischaemia, NOS is activated by calcium influx or by cytokines like tumour necrosis factor (TNF) or by lipopolysaccharide (LPS) and NO is produced in excess. It has been proposed that the excitotoxic effect of glutamate, which contributes to ischaemia-induced neuronal damage, is mediated by increased production of NO via a chain of events that includes increases in intracellular calcium (via glutamate activation of NMDA receptors), calcium activation of NOS, production of NO and peroxynitrite, and induction of lipid peroxidation. In fact, N-nitro-L-atginine, a selective inhibitor of NOS, has been shown to prevent glutamate-induced neurotoxicity in cortical cell cultures (Dawson rf /., 1991). 

Now, we will consider the major reactions of peroxynitrite with biomolecules. It was found that peroxynitrite reacts with many biomolecules belonging to various chemical classes, with the bimolecular rate constants from 10-3 to 10s 1 mol 1 s 1 (Table 21.2). Reactions of peroxynitrite with phenols were studied most thoroughly due to the important role of peroxynitrite in the in vivo nitration and oxidation of free tyrosine and tyrosine residues in proteins. In 1992, Beckman et al. [112] have showed that peroxynitrite efficiently nitrates 4-hydroxyphenylacetate at pH 7.5. van der Vliet et al. [113] found that the reactions of peroxynitrite with tyrosine and phenylalanine resulted in the formation of both hydroxylated and nitrated products. In authors opinion the formation of these products was mediated by N02 and HO radicals. Studying peroxynitrite reactions with phenol, tyrosine, and salicylate, Ramezanian et al. [114] showed that these reactions are of first-order in peroxynitrite and zero-order in phenolic compounds. These authors supposed that there should be two different intermediates responsible for the nitration and hydroxylation of phenols but rejected the most probable proposal that these intermediates should be NO2 and HO. ... 

Other very convincing evidences for free radical-mediated mechanism of decomposition and reactions of peroxynitrite and nitrosoperoxocarboxylate were demonstrated by Lehnig [140] with the use of CIDNP technique. This technique is based on the effects observed exclusively for the products of free radical reactions their NMR spectra exhibit emission characterizing a radical pathway of their formation. Lehnig has found the enhanced emission in the 15N NMR spectra of N03- formed during the decomposition of both peroxynitrite and nitrosoperoxocarboxylate. This fact indicates that N03- was formed from radical pairs [ N02, H0 ] and [ N02, C03 ]. Emission was also observed in the reaction of both nitrogen compounds with tyrosine supposedly due to the formation of radical pair [ N02, tyrosyl ]. 

The functions of mtNOS in mitochondria have been studied (see Chapter 23). Ghafourifar et al. [177] found that the calcium-induced stimulation of mtNOS caused the release of cytochrome c from mitochondria and induced apoptosis. On the other hand, the same group of authors [178] showed that the production of NO by mtNOS and superoxide in mitochondria resulted in the formation of peroxynitrite and stimulated calcium release, indicating the existence of a feedback loop which prevents calcium overload in mitochondria. 

Similar to reactive oxygen species, nitric oxide, peroxynitrite, and other nitrogen oxide species produced by mitochondria are able to stimulate or inhibit apoptosis. Proapoptotic effect of nitric oxide was probably first shown by Albina et al. [138], who demonstrated NO-induced... 

As mentioned earlier, when NO concentration exceeds that of superoxide, nitric oxide mostly exhibits an inhibitory effect on lipid peroxidation, reacting with lipid peroxyl radicals. These reactions are now well studied [42-44]. The simplest suggestion could be the participation of NO in termination reaction with peroxyl radicals. However, it was found that NO reacts with at least two radicals during inhibition of lipid peroxidation [50]. On these grounds it was proposed that LOONO, a product of the NO recombination with peroxyl radical LOO is rapidly decomposed to LO and N02 and the second NO reacts with LO to form nitroso ester of fatty acid (Reaction (7), Figure 25.1). Alkoxyl radical LO may be transformed into a nitro epoxy compound after rearrangement (Reaction (8)). In addition, LOONO may be hydrolyzed to form fatty acid hydroperoxide (Reaction (6)). Various nitrated lipids can also be formed in the reactions of peroxynitrite and other NO metabolites. 

Both vitamin E and vitamin C are able to react with peroxynitrite and suppress its toxic effects in biological systems. For example, it has been shown [83] that peroxynitrite efficiently oxidized both mitochondrial and synaptosomal a-tocopherol. Ascorbate protected against peroxynitrite-induced oxidation reactions by the interaction with free radicals formed in these reactions [84]. 

It has been shown that lung macrophages from patients with systemic sclerosis (SS) produced the elevated levels of nitric oxide, superoxide, and peroxynitrite and expressed the enhanced level of iNOS [281], NAC administration reduced peroxynitrite production and might be possibly recommended for the treatment SS patients. Solans et al. [282] found the significant enhancement of lipid peroxidation in erythrocytes from SS patients. Cracowski et al. [283] showed that in vivo lipid peroxidation was enhanced in scleroderma spectrum disorders including SS and undifferentiated connective tissue disease. 

Later on, other hydroxylamine derivatives such as 1-hydroxy-2,2,6,6-tetramethyl-4-oxo-piperidine (TEMPONEH) and l-hydroxy-3-carboxy-pyrrolidine (CP-3) have been used for superoxide detection [26]. It was found that these spin traps react with both superoxide and peroxynitrite and that they might be applied for quantification of these reactive species [27]. The CP-3 radical is less predisposed to reduction by ascorbic acid and therefore is probably more suitable for superoxide detection in biological systems. 

The formation of peroxynitrite in cells and tissue is frequently characterized by the formation of nitrotyrosine. The formation of nitrotyrosine is not a very specific assay of peroxynitrite detection because the other nitrogen oxide may also take part in this process, but peroxynitrite is undoubtedly the most efficient nitrating agent. (Mechanism of tyrosine nitration by peroxynitrite and other reactive nitrogen compounds has been considered in Chapters 21 and 22.)... 

The other factor affecting the use of organic nitrates is nitrate tolerance, the mechanism of which is unclear. An early explanation of tolerance was thiol depletion [68] but that now seems unlikely as their is an abundance of thiol in most tissue [69]. A more likely explanation is down regulation of the enzymes involved in the biotransformation but few details are available. An interesting suggestion is that GTN induces increased production of superoxide from the vascular wall and tolerance is caused by reaction of NO, produced enzymatically from GTN, with superoxide to give peroxynitrite and then nitrate [70] (Eq. (16)). 

Molsidomine and pirsidomine, are both stable as solids at room temperature in the absence oflight [137]. However the ring opened metabolites SIN-1A and C87-3786 are both photo labile and sensitive to an oxidising environment resulting ultimately in the release of superoxide and NO in stoichiometric quantities [138]. Generation of these two species is an obvious problem due to the resulting formation of peroxynitrite and the generation of OH, which may initiate lipid peroxidation [139-141] (see Eq. (19)). Such concerns over the formation of peroxynitrite from SIN-1A or C87-3786 are warranted since their cytotoxic effects show close consistency with cellular studies doped with neat peroxynitrite [142, 143]. 

It appears likely that oxidative events including mitochondrial dysfunction play a major role in PD. Among the deleterious agents thought to be involved are peroxynitrite and hydroxyl radicals (Yokoyama et ah,... 

As noted above, carnosine has been shown to inhibit protein damage mediated by peroxynitrite and hydroxyl radicals in astroglial cells (Nicoletti et ah, 2007). There is some evidence that carnosine can suppress some of the oxidative damage associated with PD using a model system, and possibly inhibit fibrillization of a-synuclein (Herrera et ah, 2008). 

Analytical methods for ONOO related to the vascular system have been reviewed. Special attention is given to assays involving oxidation of dihydrorhodamine 123 (345) to yield the fluorescent product rhodamine 123 (346, equation 118), luminol (124) CL and nitrotyrosine formation. The reaction of peroxynitrite and carbon dioxide or bicarbonate... 

The stable free radical nitric oxide (NO) has an important role as a biological messenger. The reaction of NO with superoxide (O2 ) forms the powerful oxidant peroxynitrite (ONOO ), and a mechanism for the reaction of ONOO resulting in the abstraction of H from C—H bonds is shown (equations 109, 110). The formation of HO from the spontaneous decomposition of peroxynitrite, and of COJ radicals from CO2 catalyzed decomposition of peroxynitrite, have been demonstrated. ... 

The redox potentials of various oxidants derived from nitric oxide and peroxynitrite are summarized in Table 4. Clearly, as the adducts of molecular oxygen and nitric oxide become more reduced, they form substantially stronger oxidizing agents. In effect, addition of one electron makes these nitrogen oxides more ready to accept the next. The precise pathway of decomposition followed is influenced by what types of target molecules come in contact with peroxynitrite and is... 

Reductions Potentials at pH 7.0 of Nitric Oxide, Peroxynitrite, and Other Secondary Species Derived from Peroxynitrite"... 

Apparent first-order rate constants for peroxynitrite decomposition in various buffers versus pH. When peroxynitrite is fully protonated at acidic pH, the decomposition rate is constant. The breakpoint in the curve identifies the pK, of peroxynitrite since a larger fraction present as an anion slows the rate of decomposition. In 50 mM potassium phosphate, the apparent pK, is at 6.8 and is not affected by temperatute (Koppenol, 1993). The rate of decomposition is not affected hy DMSO, mannitol, or ethanol. As shown in Fig. 28, many buffers can slightly accelerate the decomposition of peroxynitrite and the rate of decomposition reaches a maximum at high buffer concentrations. When these maximal rates are plotted as a function of pH, peroxynitrite exhibits a second pK, of approximately 8.0. 

Although oxygen radicals are destructive to islet cells, the inability of nicotinamide, Probucol, and other free radical scavengers to completely prevent cytokine mediated islet destruction suggests that other cytotoxic mechanisms may be involved in cytokine-induced islet-cell lysis. The possible interactions of superoxide with nitric oxide resulting in the generation of peroxynitrite and hydroxyl radicals may contribute to islet-cell lysis. The chemistry of these free radical interactions, and potential biological roles t)f these toxic radicals are reviewed in this book (see Chapter 1). 

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