Peroxynitrite reactivity

Peroxynitrite is a nonspecific oxidant that reacts with all classes of biomolecules depleting low-molecular-weight antioxidants, initiating lipid peroxidation, damaging nucleic acids and proteins. Its reactions are much slower than those of the hydroxyl radical but are faster than those of hydrogen peroxide. Comparison of peroxynitrite reactivity with various amino acid residues of human serum albumin have shown that cysteine, methionine, and tryptophan are the most reactive... 

Groves, J. T. Peroxynitrite reactive, invasive and enigmatic. Current Opinion in... 

Groves, J.T. (1999). Peroxynitrite Reactive, invasive and enigmatic. Curr. Opin. Chem. Biol. 3, 226-235. 

We examine here a number of reaction pathways for nitric oxide, with the emphasis on assessing their biological relevance. To date, the fastest reaction for nitric oxide with clear toxicological significance is that with superoxide to produce ONOO" (Huie and Padmaja, 1993). Thus, the chemistry and reactivity of ONOO" are discussed at length. In addition, the interaction between ONOO" and nitric oxide is examined with respect to its effects on nitric oxide half-life as well as effects on peroxynitrite reactivity toward phenol. Reaction mechanisms are proposed to account for the nitrated, hydroxylated, and nitrosated phenolic products seen. 

At physiological pH, ONOO- protonates to peroxynitrous acid (ONOOH) which disappears within a few seconds, the end product being largely nitrate. The chemistry of peroxynitrite/peroxynitrous acid is extremely complex, although addition of ONOO to cells and tissues leads to oxidation and nitration of proteins, DNA and lipids with a reactivity that is comparable to that of hydroxyl radicals. 

Peroxynitrite (ONOO-) is a cytotoxic reactive species that is formed by the reaction of nitric oxide and superoxide. Methods for measuring the scavenging capacity of peroxynitrite usually depend on either the inhibition of tyrosine nitration or the inhibition of dihydrorhodamine 123 (DHR) oxidation to rhodamine 123 (MacDonalds-Wicks and... 

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. 

Reaction of nitric oxide with superoxide is undoubtedly the most important reaction of nitric oxide, resulting in the formation of peroxynitrite, one of the main reactive species in free radical-mediated damaging processes. This reaction is a diffusion-controlled one, with the rate constant (which has been measured by many workers, see, for example, Ref. [41]), of about 2 x 109 1 mol-1 s-1. Goldstein and Czapski [41] also measured the rate constant for Reaction (11) ... 

On the other hand, in accord with the free radical mechanism peroxynitrite is dissociated into free radicals, which are supposed to be genuine reactive species. Although free radical mechanism was proposed as early as in 1970 [111], for some time it was not considered to be a reliable one because a great confusion ensued during the next two decades because of misinterpretations of inconclusive experiments, sometimes stimulated by improper thermodynamic estimations [85]. The latest experimental data supported its reliability [107-109]. Among them, the formation of dityrosine in the reaction with tyrosine and 15N chemically induced dynamic nuclear polarization (CIDNP) in the NMR spectra of the products of peroxynitrite reactions are probably the most convincing evidences (see below). 

It has been suggested that there are three major pathways for peroxynitrite to react with various substrates. With a pK value for peroxynitrite equal to 6.8 [103], peroxynitrite exists in the ionized or nonionized form depending on pH. Furthermore, the reactivity of peroxynitrite depends on its cis- and trans-conformations. Correspondingly, the following mechanisms for peroxynitrite decomposition have been proposed ... 

The reaction of peroxynitrite with the biologically ubiquitous C02 is of special interest due to the presence of both compounds in living organisms therefore, we may be confident that this process takes place under in vivo conditions. After the discovery of this reaction in 1995 by Lymar [136], the interaction of peroxynitrite with carbon dioxide and the reactions of the formed adduct nitrosoperoxocarboxylate ONOOCOO has been thoroughly studied. In 1996, Lymar et al. [137] have shown that this adduct is more reactive than peroxynitrite in the reaction with tyrosine, forming similar to peroxynitrite dityrosine and 3-nitrotyrosine. Experimental data were in quantitative agreement with free radical-mediated mechanism yielding tyrosyl and nitric dioxide radicals as intermediates and were inconsistent with electrophilic mechanism. The lifetime of ONOOCOO was estimated as <3 ms, and the rate constant of Reaction (42) k42 = 2 x 103 1 mol 1 s 1. 

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... 

Thus the competition between stimulatory and inhibitory effects of NO depends on the competition between two mechanisms the direct interaction of NO with free radicals formed in lipid peroxidation and the conversion of NO into peroxynitrite or other reactive NO metabolites. Based on this suggestion, Freeman and his coworkers [42-44] concluded that the prooxidant and antioxidant properties of nitric oxide depend on the relative concentrations of NO and oxygen. It was supposed that the prooxidant effect of nitric oxide originated from its reaction with dioxygen and superoxide ... 

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. 

Reactive nitrogen species are another factor of free radical damage in rheumatoid arthritis, although their role is less studied than that of oxygen radicals. Stichtenoth and Frolich [242] pointed out that the inhibition of nitric oxide synthesis had beneficial effects in humans. Mazzetti et al. [243] found that IL-1(3 stimulated NO production in RA chondrocytes. We demonstrated that NO synthase of RA neutrophils generated the enhanced amount of peroxynitrite [234]. Nitric oxide and oxygen radicals are also important inducers of death of human osteoarthritic synoviocytes [244]. 

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. 

Possel et al. [104] also concluded that DCFH is more sensitive to peroxynitrite oxidation than DHR. Unfortunately, both compounds are oxidized by other reactive species (for example, DCFH by superoxide and DHR by HOC1), and therefore, their use for peroxynitrite detection must be confirmed by the other methods. 

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