Katrina M Miranda

PMID: 10887204;Abstract:

Dopamine-β-hydroxylase (DβH) is a copper-containing enzyme that uses molecular oxygen and ascorbate to catalyze the addition of a hydroxyl group on the β-carbon of dopamine to form norepinephrine. While norepinephrine causes vasoconstriction following reflex sympathetic stimulation, nitric oxide (NO) formation results in vasodilatation via a guanylyl cyclase- dependent mechanism. In this report, we investigated the relationship between NO and DβH enzymatic activity. In the initial in vitro experiments, the activity of purified DβH was inhibited by the NO donor, diethylamine/NO (DEA/NO), with an IC50 of 1 mM. The inclusion of either azide or GSH partially restored DβH activity, suggesting the involvement of the reactive nitrogen oxide species, N2O3. Treatment of human neuroblastoma cells (SK-N- MC) with diethylamine/NO decreased cellular DβH activity without affecting their growth rate and was augmented by the depletion of intracellular GSH. Coculture of the SK-N-MC cells with interferon-γ and lipopolysaccharide- activated macrophages, which release NO, also reduced the DβH activity in the neuroblastoma cells. Our results are consistent with the hypothesis that nitrosative stress, mediated by N2O3, can result in the inhibition of norepinephrine biosynthesis and may contribute to the regulation of neurotransmission and vasodilatation.

PMID: 15643898;Abstract:

The recent determination that Angeli's salt may have clinical application as a nitrogen oxide donor for treatment of cardiovascular diseases such as heart failure has led to renewed interest in the mechanism and products of thermal decomposition of Angeli's salt under physiological conditions. In this report, several mechanisms are evaluated experimentally and by quantum mechanical calculations to determine whether HNO is in fact released from Angeli's salt in neutral, aerobic solution. The mechanism of product autoxidation is also considered.

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.