Katrina M Miranda

PMID: 12208370;Abstract:

The mechanisms that control the biological signaling and toxicological properties of the nitrogen oxide species nitroxyl (HNO) are largely unknown. The ingress and intracellular reactivity of nitroxyl-derived species were examined using Angeli's salt (AS), which decomposes initially to HNO and nitrite at physiologic pH. Exposure of 4,5-diaminofluorescein (DAF) to AS resulted in fluorescent product formation only in the presence of molecular oxygen. Kinetic analysis and the lack of signal from a nitric oxide (NO)-sensitive electrode suggested that these processes did not involve conversion of HNO to NO. On an equimolar basis, bolus peroxynitrite (ONOO^-) exposure generated only 15% of fluorescent product formation observed from AS decomposition. Moreover, infusion of synthetic ONOO^- at a rate comparable to AS decomposition resulted in only 4% of the signal. Quenching of AS-mediated product formation within intact human MCF-7 breast carcinoma cells containing DAF by addition of urate to buffer suggested involvement of an oxidized intermediate formed from reaction between HNO and oxygen. Conversely, intact cells competitively sequestered the HNO-derived species from reaction with DAF in solution. These data show this intermediate to be a long-lived diffusible species. Relative product yield from intracellular DAF was decreased 5- to 8-fold when cells were lysed immediately prior to AS addition, consistent with the partitioning of HNO and/or derived species into the cellular membrane, thereby shielding these reactive intermediates from either hydrolysis or cytoplasmic scavenger pools. These findings establish that oxygen-derived species of nitroxyl can readily penetrate and engage the intracellular milieu of cells and suggest this process to be independent of NO and ONOO^- intermediacy. The substantial facilitation of oxygen-dependent nitroxyl chemistry by intact lipid bilayers supports a focusing role for the membrane in modulation of cellular constituents proteins by this unique species.

PMID: 12054463;Abstract:

The nitroxyl (HNO) donor Angeli's salt (Na2N2O3; AS) is cytotoxic in vitro, inducing double strand DNA breaks and base oxidation, yet may have pharmacological application in the treatment of cardiovascular disease. The chemical profiles of AS and synthetic peroxynitrite (ONOO^-) in aerobic solution were recently compared, and AS was found to form a distinct reactive intermediate. However, similarities in the chemical behavior of the reactive nitrogen oxide species (RNOS) were apparent under certain conditions. Buffer composition was found to have a significant and unexpected impact on the observed chemistry of RNOS, and varied buffer conditions were utilized to further distinguish the chemical profiles elicited by the RNOS donors AS and synthetic ONOO^-. Addition of HEPES to the assay buffer significantly quenched oxidation of dihydrorhodamine (DHR), hydroxylation of benzoic acid (BA), and DNA damage by both AS and ONOO^-, and oxidation and nitration of hydroxyphenylacetic acid by ONOO^-. Additionally, H2O2 was produced in a concentration-dependent manner from the interaction of HEPES with both the donor intermediates. Interestingly, clonogenic survival was not affected by HEPES, indicating that H2O2 is not a contributing factor to in vitro cytotoxicity of AS. Variation in RNOS reactivity was dramatic with significantly higher relative affinity for the AS intermediate toward DHR, BA, DNA, and HEPES and increased production of H2O2. Further, AS reacted to a significantly greater extent with the unprotonated amine form of HEPES while the interaction of ONOO^- with HEPES was pH-independent. Addition of bicarbonate only altered ONOO^- chemistry. This study emphasizes the importance of buffer composition on chemical outcome and thus on interpretation and provides further evidence that ONOO^- is not an intermediate formed between the reaction of O2 and HNO produced by AS. © 2002 Elsevier Science (USA). All rights reserved.

PMID: 11396476;Abstract:

The Janus face of nitric oxide (NO) has prompted a debate as to whether NO plays a deleterious or protective role in tissue injury. There are a number of reactive nitrogen oxide species, such as N2O3 and ONOO^-, that can alter critical cellular components under high local concentrations of NO. However, NO can also abate the oxidation chemistry mediated by reactive oxygen species such as H2O2 and O2^- that occurs at physiological levels of NO. In addition to the antioxidant chemistry, NO protects against cell death mediated by H2O2, alkylhydroperoxides, and xanthine oxidase. The attenuation of metal/peroxide oxidative chemistry, as well as lipid peroxidation, appears to be the major chemical mechanisms by which NO may limit oxidative injury to mammalian cells. In addition to these chemical and biochemical properties, NO can modulate cellular and physiological processes to limit oxidative injury, limiting processes such as leukocyte adhesion. This review will address these aspects of the chemical biology of this multifaceted free radical and explore the beneficial effect of NO against oxidative stress.

The redox siblings nitroxyl (HNO) and nitric oxide (NO) have often been assumed to undergo casual redox reactions in biological systems. However, several recent studies have demonstrated distinct pharmacological effects for donors of these two species. Here, infusion of the HNO donor Angeli's salt into normal dogs resulted in elevated plasma levels of calcitonin gene-related peptide, whereas neither the NO donor diethylamine/NONOate nor the nitrovasodilator nitroglycerin had an appreciable effect on basal levels. Conversely, plasma cGMP was increased by infusion of diethylamine/NONOate or nitroglycerin but was unaffected by Angeli's salt. These results suggest the existence of two mutually exclusive response pathways that involve stimulated release of discrete signaling agents from HNO and NO. In light of both the observed dichotomy of HNO and NO and the recent determination that, in contrast to the O-2/O-2(-) couple, HNO is a weak reductant the relative reactivity of HNO with common biomolecules was determined. This analysis suggests that under biological conditions, the lifetime of HNO with respect to oxidation to NO, dimerization, or reaction with O-2 is much longer than previously assumed. Rather, HNO is predicted to principally undergo addition reactions with thiols and ferric proteins. Calcitonin gene-related peptide release is suggested to occur via altered calcium channel function through binding of HNO to a ferric or thiol site. The orthogonality of HNO and NO may be due to differential reactivity toward metals and thiols and in the cardiovascular system, may ultimately be driven by respective alteration of cAMP and cGMP levels.

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.