Katrina M Miranda

Nitric oxide (nitrogen monoxide, NO) plays a veritable cornucopia of regulatory roles in normal physiology. In contrast, NO has also been implicated in the etiology and sequela of numerous neurodegenerative diseases that involve reactive oxygen species (ROS) and nitrogen oxide species (RNOS). In this setting, NO is often viewed solely as pathogenic; however, the chemistry of NO can also be a significant factor in lessening injury mediated by both ROS and RNOS. The relationship between NO and oxidation, nitrosation, and nitration reactions is summarized. The salient factors that determine whether NO promotes, abates, or interconnects these chemistries are emphasized. From this perspective of NO chemistry, the type, magnitude, location, and duration of either ROS or RNOS reactions may be predicted.

A new nitric oxide-releasing material produced with cassava starch is described. The ruthenium nitrosyl complex trans-[Ru(NH3)(4)(isn)NO](BF4)(3) (RuNOisn; isn = isonicotinamide) is able to release NO upon either photolysis or chemical reduction. Impregnating this complex under mild conditions into cassava starch (CS) films produced a NO-delivery platform (CSx-RuNOisn). Spectroscopic analysis of CSx-RuNOisn indicates that the coordination sphere of RuNOisn remains intact during film production. Exposure of CSx-RuNOisn to long wave UV-light (lambda(irr) = 355 nm) leads to NO release and formation of the paramagnetic photoproduct trans-[RuIII(NH3)(4)isn(H2O)](3+) in the CS film. Reaction of this aquaruthenium(III) complex with aqueous nitrite regenerates RuNOisn in the film. Delivery of NO upon photolysis of CSx-RuNOisn was verified by trapping with oxymyoglobin. Moreover, NO release upon chemical reduction was carried out using L-cysteine as a reductant. Cysteine-mediated NO delivery from CSx-RuNOisn persisted for more than 7 h, during which physiologically relevant NO concentrations were liberated. These results suggest that CSx-RuNOisn is a promising candidate for use in biological applications.

PMID: 19531488;PMCID: PMC2755905;Abstract:

It has been previously proposed that nitric oxide (NO) is the only biologically relevant nitrogen oxide capable of activating the enzyme soluble guanylate cyclase (sGC). However, recent reports implicate HNO as another possible activator of sGC. Herein, we examine the affect of HNO donors on the activity of purified bovine lung sGC and find that, indeed, HNO is capable of activating this enzyme. Like NO, HNO activation appears to occur via interaction with the regulatory ferrous heme on sGC. Somewhat unexpectedly, HNO does not activate the ferric form of the enzyme. Finally, HNO-mediated cysteine thiol modification appears to also affect enzyme activity leading to inhibition. Thus, sGC activity can be regulated by HNO via interactions at both the regulatory heme and cysteine thiols. © 2009 by The American Society for Biochemistry and Molecular Biology, Inc.

PMID: 12177414;PMCID: PMC123221;Abstract:

The impact of nitric oxide (NO) synthesis on different biological cascades can rapidly change dependent on the rate of NO formation and composition of the surrounding milieu. With this perspective, we used diaminonaphthalene (DAN) and diaminofluorescein (DAF) to examine the nitrosative chemistry derived from NO and superoxide (O2^-) simultaneously generated at nanomolar to low micromolar per minute rates by spermine/NO decomposition and xanthine oxidase-catalyzed oxidation of hypoxanthine, respectively. Fluorescent triazole product formation from DAN and DAF increased as the ratio of O2^- to NO approached equimolar, then decreased precipitously as O2^- exceeded NO. This pattern was also evident in DAF-loaded MCF-7 carcinoma cells and when stimulated macrophages were used as the NO source. Cyclic voltammetry analysis and inhibition studies by using the N2O3 scavenger azide indicated that DAN- and DAF-triazole could be derived from both oxidative nitrosylation (e.g., DAF radical + NO) and nitrosation (NO⁺ addition). The latter mechanism predominated with higher rates of NO formation relative to O2^-. The effects of oxymyoglobin, superoxide dismutase, and carbon dioxide were examined as potential modulators of reactant availability for the O2^- + NO pathway in vivo. The findings suggest that the outcome of NO biosynthesis in a scavenger milieu can be focused by O2^- toward formation of NO adducts on nucleophilic residues (e.g., amines, thiols, hydroxyl) through convergent mechanisms involving the intermediacy of nitrogen dioxide. These modifications may be favored in microenvironments where the rate of O2^- production is temporally and spatially contemporaneous with nitric oxide synthase activity, but not in excess of NO generation.

PMID: 17222913;PMCID: PMC3501193;Abstract:

Nitroxyl (HNO), the 1-electron reduced and protonated congener of nitric oxide (NO), has received recent attention as a potential pharmacological agent for the treatment of heart failure and as a preconditioning agent for the mitigation of ischemia-reperfusion injury. Interest in the pharmacology and biology of HNO has prompted examination, or in some instances reexamination, of many of its chemical properties. Such studies have provided insight into the chemical basis for the biological effects of HNO, although the biochemical mechanisms for many of these effects remain to be established. In this review, a brief description of the biologically relevant chemistry of HNO is given, followed by a more detailed discussion of the pharmacology and potential toxicology of HNO. © 2006 Elsevier Inc. All rights reserved.