Katrina M Miranda

PMID: 10222043;Abstract:

The primary product of the interaction between nitric oxide (NO) and superoxide (O2/^-) is peroxynitrite (ONOO^-), which is capable of either oxidizing or nitrating various biological substrates. However, it has been shown that excess NO or O2/^- can further react with ONOO^- to form species which mediate nitrosation. Subsequently, the controlled equilibrium between nitrosative and oxidative chemistry is critically dependent on the flux of NO and O2/^-. Since ONOO^- reacts not only with NO and O2/^- but also with CO2, the effects of bicarbonate (HCO3/^-) on the biphasic oxidation profile of dihydrorhodamine-123 (DHR) and on the nitrosation of both 2,3- diaminonaphthalene and reduced glutathione were examined. Nitric oxide and O2/^- were formed with DEA/NO [NaEt2NN(O)NO] and xanthine oxidase, respectively. The presence of HCO3/^- did not alter either the oxidation profile of DHR with varying radical concentrations or the affinity of DHR for the oxidative species. This suggests that the presence of CO2 does not affect the scavenging of ONOO^by either NO or O2/^-. However, an increase in the rate of DHR oxidation by ONOO^- in the presence of HCO3/^- suggests that a CO2-ONOO^- adduct does play a role in the interaction of NO or O2/^- with a product derived from ONOO^-. Further examination of the chemistry revealed that the intermediate that reacts with NO is neither ONOO^- nor cis-HOONO. It was concluded that NO reacts with both trans-HOONO and a CO2 adduct of ONOO^- to form nitrosating species which have similar oxidation chemistry and reactivity with O2/^- and NO.

PMID: 16540401;Abstract:

Nitroxyl (HNO) exhibits unique pharmacological properties that often oppose those of nitric oxide (NO), in part due to differences in reactivity toward thiols. Prior investigations suggested that the end products arising from the association of HNO with thiols were condition-dependent, but were inconclusive as to product identity. We therefore used HPLC techniques to examine the chemistry of HNO with glutathione (GSH) in detail. Under biological conditions, exposure to HNO donors converted GSH to both the sulfinamide [GS(O)NH 2] and the oxidized thiol (GSSG). Higher thiol concentrations generally favored a higher GSSG ratio, suggesting that the products resulted from competitive consumption of a single intermediate (GSNHOH). Formation of GS(O)NH2 was not observed with other nitrogen oxides (NO, N 2O3, NO2, or ONOO^-), indicating that it is a unique product of the reaction of HNO with thiols. The HPLC assay was able to detect submicromolar concentrations of GS(O)NH2. Detection of GS(O)NH2 was then used as a marker for HNO production from several proposed biological pathways, including thiol-mediated decomposition of S-nitrosothiols and peroxidase-driven oxidation of hydroxylamine (an end product of the reaction between GSH and HNO) and N^G-hydroxy-l-arginine (an NO synthase intermediate). These data indicate that free HNO can be biosynthesized and thus may function as an endogenous signaling agent that is regulated by GSH content.

PMID: 12177417;PMCID: PMC123192;Abstract:

A potential of about-0.8 (±0.2) V (at 1 M versus normal hydrogen electrode) for the reduction of nitric oxide (NO) to its one-electron reduced species, nitroxyl anion (³NO^-) has been determined by a combination of quantum mechanical calculations, cyclic voltammetry measurements, and chemical reduction experiments. This value is in accord with some, but not the most commonly accepted, previous electrochemical measurements involving NO. Reduction of NO to ¹NO^- is highly unfavorable, with a predicted reduction potential of about -1.7 (±0.2) V at 1 M versus normal hydrogen electrode. These results represent a substantial revision of the derived and widely cited values of +0.39 V and -0.35 V for the NO/³NO^-and NO/¹NO^- couples, respectively, and provide support for previous measurements obtained by electrochemical and photoelectrochemical means. With such highly negative reduction potentials, NO is inert to reduction compared with physiological events that reduce molecular oxygen to superoxide. From these reduction potentials, the pKa of ³NO^- has been reevaluated as 11.6 (±3.4). Thus, nitroxyl exists almost exclusively in its protonated form, HNO, under physiological conditions. The singlet state of nitroxyl anion, ¹NO^-, is physiologically inaccessible. The significance of these potentials to physiological and pathophysiological processes involving NO and O2 under reductive conditions is discussed.

PMID: 11165873;Abstract:

The physiological function of nitric oxide (NO) in the defense against pathogens is multifaceted. The exact chemistry by which NO combats intracellular pathogens such as Listeria monocytogenes is yet unresolved. We examined the effects of NO exposure, either delivered by NO donors or generated in situ within ANA-1 murine macrophages, on L. monocytogenes growth. Production of NO by the two NONOate compounds PAPA/NO (NH2(C3H6) (N[N(O)NO]C3H7)) and DEA/NO (Na(C2H5)2N[N(O)NO]) resulted in L. monocytogenes cytostasis with minimal cytotoxicity. Reactive oxygen species generated from xanthine oxidase/hypoxanthine were neither bactericidal nor cytostatic and did not alter the action of NO. L. monocytogenes growth was also suppressed upon internalization into ANA-1 murine macrophages primed with interferon-γ (INF-γ) + tumor necrosis factor-α (TNF-α or INF-γ + lipid polysaccharide (LPS). Growth suppression correlated with nitrite formation and nitrosation of 2,3-diaminonaphthalene elicited by stimulated murine macrophages. This nitrosative chemistry was not dependent upon nor mediated by interaction with reactive oxygen species (ROS), but resulted solely from NO and intermediates related to nitrosative stress. The role of nitrosation in controlling L. monocytogenes was further examined by monitoring the effects of exposure to NO on an important virulence factor, Listeriolysin O, which was inhibited under nitrosative conditions. These results suggest that nitrosative stress mediated by macrophages is an important component of the immunological arsenal in controlling L. monocytogenes infections. © 2001 Elsevier Science Inc.

PMID: 10830872;Abstract:

Nitric oxide (NO) has been shown to be a key bioregulatory agent in a wide variety of biological processes, yet cytotoxic properties have been reported as well. This dichotomy has raised the question of how this potentially toxic species can be involved in so many fundamental physiological processes. We have investigated the effects of NO on a variety of toxic agents and correlated how its chemistry might pertain to the observed biology. The results generate a scheme termed the chemical biology of NO in which the pertinent reactions can be categorized into direct and indirect effects. The former involves the direct reaction of NO with its biological targets generally at low fluxes of NO. Indirect effects are reactions mediated by reactive nitrogen oxide species, such as those generated from the NO/O2 and NO/O2^- reactions, which can lead to cellular damage via nitrosation or oxidation of biological components. This report discusses several examples of cytotoxicity involved with these stresses. (C) 2000 Elsevier Science Inc.