Katrina M Miranda

PMID: 17045928;Abstract:

Generation of peroxynitrite (ONOO^-) as a result of altered redox balance has been shown to affect cardiac function; however, inconsistencies in the data exist, particularly for myocardial contractility. The hypothesis that the cardiac impact of ONOO^- formation depends on its site of generation, intravascular or intramyocardial, was examined. Cardiac contractility was assessed by pressure-volume analysis to delineate vascular versus cardiac changes on direct infusion of ONOO^- into the right atria of conscious dogs both with normal cardiac function and in heart failure. Additionally, ONOO^- was administered to isolated murine cardiomyocytes to mimic in situ cardiac generation. When infused in vivo, ONOO^- had little impact on inotropy but led to systemic arterial dilation, likely as a result of rapid decomposition to NO2^- and NO3^-. In contrast, infused ONOO^- was long lived enough to abolish β-adrenergic (dobutamine)-stimulated contractility/relaxation, most likely through catecholamine oxidation to aminochrome. When administered to isolated murine cardiomyocytes, ONOO^- induced a rapid reduction in sarcomere shortening and whole cell calcium transients, although neither decomposed ONOO^- or NaNO2 had any effect. Thus, systemic generation of ONOO^- is unlikely to have primary cardiac effects, but may modulate cardiac contractile reserve, via blunted β-adrenergic stimulation, and vascular tone, as a result of generation of NO2^- and NO3^-. However, myocyte generation of ONOO^- may impair contractile function by directly altering Ca²⁺ handling. These data demonstrate that the site of generation within the cardiovascular system largely dictates the ability of ONOO^- to directly or indirectly modulate cardiac pump function. © 2006 Elsevier Inc. All rights reserved.

3-Nitrotyrosyl adducts in proteins have been detected in a wide range of diseases. The mechanisms by which reactive nitrogen oxide species may impede protein function through nitration were examined by using a unique model system, which exploits a critical tyrosyl residue in the fluorophoric pocket of recombinant green fluorescent protein (GFP). Exposure of purified GFP suspended in phosphate buffer to synthetic peroxynitrite in either 0.5 or 5 muM steps resulted in progressively increased 3-nitrotyrosyl immunoreactivity concomitant with disappearance of intrinsic fluorescence (IC50 approximate to 20 muM). Fluorescence from an equivalent amount of GFP expressed within intact MCF-7 tumor cells was largely resistant to this bolus treatment (IC50 > 250 muM). The more physiologically relevant conditions of either peroxynitrite infusion (1 muM/min) or de novo formation by simultaneous, equimolar generation of nitric oxide (NO) and superoxide (e.g., 3-morpholinosydnonimine; NONOates plus xanthine oxidase/hypoxanthine, menadione, or mitomycin C) were examined. Despite robust oxidation of dihydrorhodamine under each of these conditions, fluorescence decrease of both purified and intracellular GFP was not evident regardless of carbon dioxide presence, suggesting that oxidation and nitration are not necessarily coupled. Alternatively, both extra- and intracellular GFP fluorescence was exquisitely sensitive to nitration produced by heme-peroxidase/hydrogen peroxide-catalyzed oxidation of nitrite. Formation of nitrogen dioxide (NO2) during the reaction between NO and the nitroxide 2-phenyl-4,4,5,5-tetramethylimidazole-1-oxyl 3-oxide indicated that NO2 can enter cells and alter peptide function through tyrosyl nitration. Taken together, these findings exemplified that heme-peroxidase-catalyzed formation of NO2 may play a pivotal role in inflammatory and chronic disease settings while calling into question the significance of nitration by peroxynitrite.

PMID: 15579020;Abstract:

Nitric oxide has emerged as one of the most important and diverse players in physiology. This small diatomic radical stunned researchers because of its existence and unique biological properties in human physiology. Over the last two decades it was found that NO often has fickle behavior in pathophysiological mechanisms. Where benefiting the host in one case yet inducing and augmenting injury in another. This has lead to confusion in is NO good or bad? Much of the answers to this dichotomy lies in the chemistry of NO and its related nitrogen oxide species. To help understand the complex chemistry with perspective to biology, a discussion on the chemical biology of NO is useful. The chemical biology defines the relevant chemical reaction of NO and nitrogen monoxide in the context of the biological conditions. We discuss in this article the chemistry of nitrogen oxide with different types of biological motifs. Reaction of NO with metal complexes and radicals require low concentration, where formation of reactive nitrogen oxide species require considerably higher amounts and generally are isolated to specific microenvironments in vivo. Though many reactive nitrogen oxide species are formed from chemical reactions with NO, there are several which appear to not require NO to be present, HNO and NO2. These two species have unique physiological effects and represent additional complexity to this biological picture. From this discussion, a picture can be formed concerning the possible chemical dynamics, which can be plausible in different biological mechanisms. © 2004 Bentham Science Publishers Ltd.

PMID: 21235346;PMCID: PMC3070000;Abstract:

The importance of nitric oxide in mammalian physiology has been known for nearly 30 years. Similar attention for other nitrogen oxides such as nitroxyl (HNO) has been more recent. While there has been speculation as to the biosynthesis of HNO, its pharmacological benefits have been demonstrated in several pathophysiological settings such as cardiovascular disorders, cancer, and alcoholism. The chemical biology of HNO has been identified as related to, but unique from, that of its redox congener nitric oxide. A summary of these findings as well as a discussion of possible endogenous sources of HNO is presented in this review. © 2011 Mary Ann Liebert, Inc.