Katrina M Miranda

PMID: 21033665;PMCID: PMC2984372;Abstract:

Here we describe a novel caged form of the highly reactive bioeffector molecule, nitroxyl (HNO). Reacting the labile nitric oxide (NO)- and HNO-generating salt of structure iPrHN-N(O)=NO^-Na⁺ (1, IPA/NO) with BrCH2OAc produced a stable derivative of structure iPrHN-N(O)=NO-CH2OAc (2, AcOM-IPA/NO), which hydrolyzed an order of magnitude more slowly than 1 at pH 7.4 and 37 °C. Hydrolysis of 2 to generate HNO proceeded by at least two mechanisms. In the presence of esterase, straightforward dissociation to acetate, formaldehyde, and 1 was the dominant path. In the absence of enzyme, free 1 was not observed as an intermediate and the ratio of NO to HNO among the products approached zero. To account for this surprising result, we propose a mechanism in which base-induced removal of the N-H proton of 2 leads to acetyl group migration from oxygen to the neighboring nitrogen, followed by cleavage of the resulting rearrangement product to isopropanediazoate ion and the known HNO precursor, CH3-C(O)-NO. The trappable yield of HNO from 2 was significantly enhanced over 1 at physiological pH, in part because the slower rate of hydrolysis for 2 generated a correspondingly lower steady-state concentration of HNO, thus, minimizing self-consumption and enhancing trapping by biological targets such as metmyoglobin and glutathione. Consistent with the chemical trapping efficiency data, micromolar concentrations of prodrug 2 displayed significantly more potent sarcomere shortening effects relative to 1 on ventricular myocytes isolated from wild-type mouse hearts, suggesting that 2 may be a promising lead compound for the development of heart failure therapies. © 2010 American Chemical Society.

PMID: 20729216;PMCID: PMC2930750;

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.