The oxidation of glutathione by nitroprusside: Changes in glutathione in intact erythrocytes during incubation with sodium nitroprusside as detected by 1H spin echo NMR spectroscopy

S-Nitrosothiols: Materials, Reactivity and Mechanisms

The article provides a comprehensive view of S-nitrosothiols, chemical behaviour, the pathways leading to their synthesis, their spectral properties, analytical methods of detection and determination, chemical and photochemical reactivity, kinetic aspects and suggested mechanisms. The structure parameters of S-nitrosothiols and the parent thiols are analysed with respect to their effect on the strengthening or weakening the S–NO bond, and in consequence on the S-nitrosothiol stability. This depends also on the ease of S–S bond formation in the product disulphide. These structural features seem to be crucial both to spontaneous as well as to Cu-catalysed decomposition. Principal emphasis is given here to the S-nitrosothiols’ ability to act as ligands and to the effect of coordination on the ligand properties. The chemical and photochemical behaviours of the complexes are described in more detail and their roles in chemical and biochemical systems are discussed.

The aim of the article is to demonstrate that the contribution of S-nitrosothiols to chemical and biochemical processes is more diverse than supposed hitherto. Nevertheless, their role is predictable and, based on the correlation between structure and reactivity, many important mechanisms of biochemical processes can be interpreted and various applications designed.

Direct NMR detection of the unstable “red product” from the reaction between nitroprusside and 2-mercaptosuccinic acid

First NMR characterization of the unstable “red product” produced from the reaction between nitroprusside and organic thiolates.

Kinetics and mechanism of the oxidation of glutathione by hexacyanoferrate (III) in aqueous solution

A detailed kinetic study of the oxidation of glutathione by Fe(CN)6(3)- was performed as a function of pH, temperature, and pressure. The pH profile indicates a maximum pH independent rate in the pH range 5 to 8, which is ascribed to the oxidation of the monoanionic form of glutathione. The activation parameters for the oxidation process in this pH range are characterized by significantly negative delta V# (-22 cm3 mol-1) values. The latter value is in good agreement with that calculated theoretically on the basis of the Marcus-Hush-Stranks relationships, and can be ascribed to a large volume collapse associated with the outer-sphere reduction of Fe(CN)6(3-) to Fe(CN)6(4-).

The interaction of sodium nitroprusside with peripheral white blood cells in vitro: a rationale for cyanide release in vivo

Isolated monocytes and polymorphonuclear leukocytes release the cyanide anion from the hypotensive agent, sodium nitroprusside. The proposed mechanism involves the production of hydrogen peroxide which oxidizes the substitution inert d6 iron(II) transition metal complex to a labile d5 iron(III) complex. Consequently, the release of cyanide becomes more favoured. This mechanism is supported by the chemical release of the cyanide anion from sodium nitroprusside in vitro by hydrogen peroxide and the demonstrated ability of monocytes and polymorphonuclear leukocytes to generate hydrogen peroxide ex vivo when chemically stimulated by the nitroprusside anion. The results suggest that within a clinical environment white cell counts and cell activation induced as a consequence of disease processes may be important for predicting the toxicity of sodium nitroprusside.

Spin echo nuclear magnetic resonance studies on intact erythrocytes: changes in cellular metabolism as a consequence of carbimazole therapy

OBJECTIVE

Because the exact mechanism of action of carbimazole is uncertain, nuclear magnetic resonance (NMR) spectroscopy was used to investigate cellular changes in erythrocytes from Graves' patients following a course of carbimazole therapy.

DESIGN

NMR spectroscopy was carried out using intact erythrocytes obtained from Graves' patients prior to and at 2 and 12 months after carbimazole treatment. The data were correlated with thyroid hormone and antibody levels.

PATIENTS

Twenty patients (four males; 16 females) with newly diagnosed and previously untreated Graves' disease were enrolled into the study. Assessments were made prior to the commencement of therapy and after 2 and 12 months on treatment. Of the 20 patients assessed at 0 and 2 months only 12 completed the study.

MEASUREMENTS

The oxidation-reduction balance of erythrocyte glutathione was measured directly using 1H spin echo NMR spectroscopy of intact cells. Thyroid hormone and antibody levels were measured using reported methods.

RESULTS

At 2 and 12 months a significant (P < 0.01) oxidation of the erythrocyte glutathione was observed. Of the four thyroid related markers (T3, T4, TRAb and TSH) assessed in this study both T3 (P < 0.001) and TRAb (P < 0.001) were observed to correlate with the NMR observed changes in glutathione. However, in-vitro experiments indicated that carbimazole does not affect red cell glutathione directly.

CONCLUSIONS

A model is presented which uses the hydrated iodium cation (I+), the natural product of T4 conversion to T3, as a chemical oxidant which can produce the observed clinical alteration in intracellular glutathione in ex-vivo erythrocytes. It is suggested that a major factor in the action of carbimazole in Graves' disease may be to stimulate the function of the deiodinase enzymes.

Clinical analysis in intact erythrocytes using 1H spin echo NMR

A new method of clinical analysis based on 1H spin echo NMR spectroscopy is presented. It is capable of providing information on six metabolites within viable erythrocytes, directly and without any preparative procedures prior to analysis except for cell separation and washing. Erythrocytes from patients with rheumatoid arthritis and Graves' disease are compared with cells obtained from healthy volunteers. The NMR detectable species in the cytosol of the cells are glutathione, ergothioneine, choline, creatine, glycine, lactate and to a lesser extent alanine and valine. Significant differences are observed between the ergothioneine pools in the rheumatoid group (P less than 0.01) compared to the control group. The glutathione: di-glutathione ratio can be assessed from the ratio, g2 to g4, taken from different signals in the glutathione molecule. The total concentration of glutathione present is easily assessed qualitatively but is more difficult to quantitate.