Katrina M Miranda

PMID: 19727606;Abstract:

For the past couple of decades nitric oxide (NO) and nitroxyl (HNO) have been extensively studied due to the important role they play in many physiological and/or pharmacological processes. Many researchers have reported important signaling pathways as well as mechanisms of action of these species, showing direct and indirect effects depending on the environment. Both NO and HNO can react with, among others, metals, proteins, thiols and heme proteins via unique and distinct chemistry leading to improvement of some clinical conditions. Understanding the basic chemistry of NO and HNO and distinguishing their mechanisms of action as well as methods of detection are crucial for understanding the current and potential clinical applications. In this review, we summarize some of the most important findings regarding NO and HNO chemistry, revealing some of the possible mechanisms of their beneficial actions. © 2009 The Pharmaceutical Society of Korea.

PMID: 11178938;Abstract:

Numerous methods are available for measurement of nitrate (NO3^-). However, these assays can either be time consuming or require specialized equipment (e.g., nitrate reductase, chemiluminescent detector). We have developed a method for simultaneous evaluation of nitrate and nitrite concentrations in a microtiter plate format. The principle of this assay is reduction of nitrate by vanadium(III) combined with detection by the acidic Griess reaction. This assay is sensitive to 0.5 μM NO3^- and is useful in a variety of fluids including cell culture media, serum, and plasma. S-Nitrosothiols and L-arginine derivatives were found to be potential interfering agents. However, these compounds are generally minor constituents of biological fluids relative to the concentration of nitrate/nitrite. This report introduces a new, convenient assay for the stable oxidation products of nitrogen oxide chemistry in biological samples. © 2001 Academic Press.

The growing evidence that nitroxyl (HNO) has a rich pharmacological potential that differs from that of nitric oxide (NO) has intensified interest in HNO donors. Recently, the diazeniumdiolate (NONOate) based on isopropylamine (IPA/NO; Na[(CH(3))(2)CHNH(N(O)NO)]) was demonstrated to function under physiological conditions as an organic analogue to the commonly used HNO donor Angeli's salt (Na(2)N(2)O(3)). The decomposition mechanism of Angeli's salt is dependent on pH, with transition from an HNO to an NO donor occurring abruptly near pH 3. Here, pH is shown to also affect product formation from IPA/NO. Chemical analysis of HNO and NO production led to refinement of an earlier, quantum mechanically based prediction of the pH-dependent decomposition mechanisms of primary amine NONOates such as IPA/NO. Under basic conditions, the amine proton of IPA/NO is able to initiate decomposition to HNO by tautomerization to the nitroso nitrogen (N(2)). At lower pH, protonation activates a competing pathway to NO production. At pH 8, the donor properties of IPA/NO and Angeli's salt are demonstrated to be comparable, suggesting that at or above this pH, IPA/NO is primarily an HNO donor. Below pH 5, NO is the major product, while IPA/NO functions as a dual donor of HNO and NO at intermediate pH. This pH-dependent variability in product formation may prove useful in examination of the chemistry of NO and HNO. Furthermore, primary amine NONOates may serve as a tunable class of nitrogen oxide donor.

PMID: 12226478;PMCID: PMC130522;Abstract:

The chemical origins of nitrated tyrosine residues (NT) formed in proteins during a variety of pathophysiological conditions remain controversial. Although numerous studies have concluded that NT is a signature for peroxynitrite (ONOO^-) formation, other works suggest the primary involvement of peroxidases. Because metal homeostasis is often disrupted in conditions bearing NT, the role of metals as catalysts for protein nitration was examined. Cogeneration of nitric oxide (NO) and superoxide (O2^-), from spermine/NO (2.7 μM/min) and xanthine oxidase (1-28 μM O2^-/min), respectively, resulted in protein nitration only when these species were produced at approximately equivalent rates. Addition of ferriprotoporphyrin IX (hemin) to this system increased nitration over a broad range of O2^- concentrations with respect to NO. Nitration in the presence of superoxide dismutase but not catalase suggested that ONOO^- might not be obligatory to this process. Hemin-mediated NT formation required only the presence of NO2^- and H2O2, which are stable end-products of NO and O2^- degradation. Ferrous, ferric, and cupric ions were also effective catalysts, indicating that nitration is mediated by species capable of Fenton-type chemistry. Although ONOO^- can nitrate proteins, there are severe spatial and temporal constraints on this reaction. In contrast, accumulation of metals and NO2^- subsequent to NO synthase activity can result in far less discriminate nitration in the presence of an H2O2 source. Metal catalyzed nitration may account for the observed specificity of protein nitration seen under pathological conditions, suggesting a major role for translocated metals and the labilization of heme in NT formation.