A new assay for the determination of low-molecular-weight nitrosothiols (nitrosoglutathione), NO, and nitrites by using a specific and sensitive solid-state amperometric gas sensor

No hemoglobin but NO: the icefish (Chionodraco hamatus) heart as a paradigm

The role of nitric oxide (NO) in cardio-vascular homeostasis is now known to include allosteric redox modulation of cell respiration. An interesting animal for the study of this wide-ranging influence of NO is the cold-adapted Antarctic icefish Chionodraco hamatus, which is characterised by evolutionary loss of hemoglobin and multiple cardio-circulatory and subcellular compensations for efficient oxygen delivery. Using an isolated, perfused working heart preparation of C. hamatus, we show that both endogenous (L-arginine) and exogenous (SIN-1 in presence of SOD) NO-donors as well as the guanylate cyclase (GC) donor 8Br-cGMP elicit positive inotropism, while both nitric oxide synthase (NOS) and sGC inhibitors, i.e. L-NIO and ODQ, respectively, induce significant negative inotropic effects. These results therefore demonstrate that under basal working conditions the icefish heart is under the tonic influence of a NO-cGMP-mediated positive inotropism. We also show that the working heart, which has intracardiac NOS (shown by NADPH-diaphorase activity and immunolocalization), can produce and release NO, as measured by nitrite appearance in the cardiac effluent. These results indicate the presence of a functional NOS system in the icefish heart, possibly serving a paracrine/autocrine regulatory role.

Selective liberation of NO from S-nitrosocysteine with potassium thiocyanate, as monitored by an amperometric sensor

S-Nitrosocysteine (CysNO) releases either NO (in the presence of divalent cations) or NO+ (in the presence of chelating agents). NO+ is then transferred to peptides or protein SH groups to form high-mass nitrosothiols. The aim of this work was the development of a specific reaction between thiocyanate (SCN-) and CysNO. This reaction selectively liberates NO from CysNO in the presence of high-mass nitrosothiols. Free NO is measured with an amperometric sensor. We examine with this system the transnitrosylation reaction between CysNO and BSA at low molecular ratios and could assay nitrites, SNO-BSA, and CysNO in the incubation mixture without any preliminary purification steps.

Electrochemical assay for determining nitrosyl derivatives of human hemoglobin: nitrosylhemoglobin and S-nitrosylhemoglobin

Nitric oxide (NO) is an important biological regulator. It can bind to heme iron and form NO+, involved in the synthesis of S-nitrosothiols (-SNOs). NO reacts with human hemoglobin (Hb) to produce the derivatives: S-nitrosylhemoglobin (-SNOHb) and nitrosylhemoglobin (HbNO). At neutral pH values, free NO does not react directly with the -SH groups of Hb. The reductive nitrosylation of Fe(III) heme upon reaction with NO has long been studied, but it is not yet completely known. To quantify the reaction of NO with Hb, we developed a new, sensitive (nanomolar concentration range) electrochemical assay to selectively measure HbNO and -SNOHb. The assay also allows the monitoring of free NO during the reaction with human Fe(III)Hb and Fe(II)HbO(2).

Formation of nitrosothiols from gaseous nitric oxide at pH 7.4

Nitric oxide (NO) is generated in biological systems and plays important roles as a regulatory molecule. Its ability to bind to haem iron is well known. Moreover, it may lose an electron, forming the nitrosonium ion, involved in the synthesis of S-nitrosothiols (SNOs). It has been suggested that S-nitrosohaemoglobin (-SNO Hb) and low molecular weight SNOs may act as reservoirs of NO. SNOs are formed in vitro, at strongly acidic pH values; however, the mechanism of their formation at neutral pH values is still debated. In this paper we report the anaerobic formation of SNOs (both high- and low-molecular weight) from low concentrations of NO at pH 7.4, provided Hb is also present. We propose a reaction mechanism entailing the participation of Fehaem in the formation of NO(+) and the transfer of NO(+) either to Cysbeta(93) of Hb or to glutathione; we show that this reaction also occurs in human RBCs.

Nitric oxide in ischemic and reperfused human muscle

BACKGROUND

Biochemical events explaining the pathology of ischemia-reperfusion in the muscle are still debated. Nitric oxide (NO) has been postulated to be implicated in these phenomena, but the short half-life of this compound makes it difficult to measure.

METHODS

In this paper, we used an amperometric solid-sate sensor to measure NO concentrations in frozen human muscles before, during and after a period of ischemia. We also measured cytochrome oxidase activity and malondialdehyde (MDA).

RESULTS

NO increased during ischemia but it soon returned to normal values upon reperfusion. On the other hand, cytochrome oxidase that also decreased in ischemic muscle did not increase during the reperfusion and malondialdehyde only increased during reperfusion, indicating the occurrence of peroxidative reactions in this situation.

CONCLUSIONS

NO is implicated in the ischemia/reperfusion pathology, but it is difficult to relate whether this is connected to cytochrome oxidase activity and malondialdehyde formation, also modified in this ischemia-reperfusion model.

Reaction mechanism between nitric oxide and glutathione mediated by Fe(III) myoglobin

Ferrimyoglobin at pH 7.4 binds nitric oxide to yield nitric oxide adducts. In the presence of glutathione (GSH), nitrosoadducts of Mb(III) react with it to give nitrosoglutathione, whose concentration has been determined with an apparatus based on a specific and sensitive solid-state amperometric gas sensor. The reaction constant between the adduct and glutathione, kGSH = (47 +/- 1) M(-1) x s(-1), obtained by UV-Vis spectroscopy kinetic measurements, is about one-eighth of the constant with OH- determined by other authors. We can explain this fact with the higher nucleophilicity of OH- compared to GSH, due to the bulkiness and charge of the species. It is known that the formation of nitrosothiols starting from nitrite or NO (nitrogen monoxide) and glutathione, in the absence of oxygen, is impossible. Thus, from a biological point of view, it is important to point out that GSH reacts with NO in the presence of ferrimyoglobin, even at physiological pH, to form nitrosoglutathione.

Determination of S-nitrosohemoglobin using a solid-state amperometric sensor

Nitric oxide (NO, nitrogen monoxide), generated in biological systems, plays important roles as a regulatory molecule. Its ability to bind to hemoglobin (Hb) iron is well known. Moreover, it may lose an electron, forming the nitrosonium ion, involved in the synthesis of nitrosothiols (RSNO). It has been suggested that S-nitrosohemoglobin (SNO-Hb) may act as a reservoir of NO. The S-nitrosylation of Hb can be detected after the incubation of CysNO and Hb for 60 min with a molecular ratio (CysNO/hem) of 1:1. Upon increasing the ratio to 10:1, about 50% of total Hb (100% of beta-chain -SH 93) was derivatized in 60 min. In this paper, we describe a new method for the quantitative assay of SNO-Hb, after the liberation of NO by Cu(2+)/Cu(+) and the simultaneous assessment of NO by solid-state amperometric sensor. The assay described by us is sensitive, rapid, easy to perform, and inexpensive. For this reason, we believe that it may represent an important analytical improvement for the study of the S-transnitrosylation reactions between RSNO and the Hb Cys-beta 93 and SNO-Hb and glutathione.

Determination of S-nitrosoglutathione in erythrocytes by capillary zone electrophoresis

A method for separation and quantification of S-nitrosoglutathione in red cell extracts by capillary electrophoresis is reported. The method is based on the direct analysis of the metaphosphoric acid erythrocyte extract containing diethylenetriaminepentaacetic acid. Optimization of the method is briefly discussed. Best results in the shortest time were obtained at 25 degrees C, using a coated capillary, 7 kV applied voltage and phosphate sodium 40 mmol/L (pH 2.2) as running buffer. Reproducibility, detection limits, and recoveries of S-nitrosoglutathione analyses were checked. The results evidenced that S-nitrosoglutathione is formed in erythrocytes treated with S-nitrosocysteine, a transnitrosating agent. Under our experimental conditions, the contemporaneous detection and quantification of reduced and oxidized glutathione present in cell extract could also be performed.