Nitric Oxide, and S-Nitrosothiols

The activity of EDRF has subsequently been largely attributed to the elaboration of nitric oxide (NO) by the endothelium (Ignarro et al., 1987b  

Copyright 1995 by Academic Press, Inc. All rights of reproduction in any form reserved. 

Other investigators, however, have noted inconsistencies between EDRF and NO in several important biological actions. For example, proximal and distal canine coronary artery segments respond uniformly to EDRF, but not to NO (Hoefner et al., 1989). NO consistently relaxes nonvascular smooth muscle, whereas EDRF does not (Shikano etal., 1987). One group of investigators has observed that the in vivo half-life of NO (approximately 0.1 sec) is significantly shorter than the ex vivo half-life of EDRF (6-30 sec) (Kelm and Schrader, 1990). 

Stable adducts of nitric oxide and thiol functional groups Derive from low-molecular-weight and protein thiols Form only in the presence of oxygen in physiological systems Undergo transnitrosation reactions 

The physiological relevance of RSNOs has been confirmed by our observation that the predominant form of NO in mammalian plasma is that of an adduct between NO and serum albumin, S-nitrosoalbumin (Stamler etal., 1992c). S-Nitrosoalbumin possesses EDRF-like properties in vivo, including vasorelaxation and platelet inhibition (Keaney et al., 1993). Human plasma contains approximately 1 /xM concentrations of RSNOs, the preponderant form of which is S-nitrosoalbumin by contrast, the plasma concentration of free NO is approximately 3 nM (Stamler et al., 1992c). Based on these observations, we have proposed that S-nitrosoalbumin serves as a comparatively long-lived plasma reservoir of NO through which the concentration of this reactive short-lived diatomic radical can be buffered (Stamler et al., 1992c). 

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X.J. Zhang, Y. Kislyak, J. Lin, A. Dickson, L. Cardosa, M. Broderick, and H. Fein, Nanometer size electrode for nitric oxide and S-nitrosothiols measurement. Electrochem. Commun. 4, 11-16 (2002). 

Campbell DL, Stamler JS, Strauss HC. 1996. Redox modulation of L-type calcium channels in ferret ventricular myocytes. Dual mechanism regulation by nitric oxide and S-nitrosothiols. J Gen Physiol 108 277-293. 

Hwang, S., Meyerhoff, M.E. Polyurethane with tethered copper (II)-cyclen complex preparation, characterization and catalytic generation of nitric oxide from S-nitrosothiols. Biomaterials 29(16), 2443-2452 (2008)... 

The spontaneous reaction of nitric oxide with thiols is slow at physiological pH and the final product under anaerobic conditions is not a nitrosothiol (Pryor et al., 1982). The reaction is slow because it involves the conjugate base of the thiol (R—S"). At pH 7.0, the oxidation of cysteine by nitric oxide required 6 hr to reach completion and yields RSSR and N 2O as the products. The synthetic preparation of nitrosothiols usually involves the addition of nitrosonium ion from acidified nitrite to the thiol, or oxidation of the thiol with nitrogen dioxide under anaerobic conditions in organic solvents. Nitric oxide will form nitrosothiols by reaction with ferric heme groups, such as found in metmyoglobin or methemoglobin (Wade and Castro, 1990). It is also possible that nitrosyldioxyl radical also reacts with thiols to form a nitrosothiol. 

Motterlini, R., Foresti, R., Bassi, R., Calabrese, V., Clark, J. E. and Green, C. J. Endothelial heme oxygenase-1 induction by hypoxia modulation by inducible nitric oxide synthase and S-nitrosothiols. Journal of Biological Chemistry 27S 13613-13620 2000. 

Marzinzig M, Nussler A K, Stadler J, et al. (1997). Improved methods to measure end products of nitric oxide in biological fluids nitrite, nitrate and S-nitrosothiols. Nitric Oxide Biol. Chem. 1 177-189. 

NO in the unbound form has a very short lifetime in the cell but can be stabilized by the formation of complexes, i.e. metal-porphyrin nitrosyls, dinitrosyl-iron complexes and S-nitrosothiols, which are cmisidered to be its biological transporters. Nitric oxide has a very high affinity for iron contained in the active sites of proteins [74]. 

Vanin AF (1998) Dinitrosyl iron complexes and S-nitrosothiols are two possible forms for stabilization and transport of nitric oxide in biological systems. Biochemistry 63 782-793... 

De Man JG, Boeckxstaens GE et al (1995) Comparison of the pharmacological profile of S-nitrosothiols, nitric oxide and the nitreigic nemotransmitter in the canine ileocolonic junction. BrJ Pharmacol 114 1179-1184... 

S-nitrosothiols (RSNO) have emerged as important species in the storage and transport of nitric oxide. As NO donors these S-N compounds have potential medical applications in the treatment of blood circulation problems. 

Mechanism of vascular smooth muscle relaxation by organic nitrates, nitrites, nitroprusside, and nitric oxide evidence for the involvement of S-nitrosothiols as active intermediates. /. Pharmacol. Exp. Then 218 (1981), p. 739-749... 

Alpert, C., Ramdev, N., George, D., Loscalzo, J., Detection of S-nitrosothiols and other nitric oxide derivatives by... 

Tsikas, D., Measurement of physiological S-nitrosothiols a problem child and a challenge, Nitric Oxide 9 (2003), p. 53-55... 

DNICs continue to be a relevant aspect of nitric oxide research and indicate the high affinity of NO for metal centers, especially ferrous ions, when compared with sulfur bound NO complexes, such as S-nitrosothiols. 

The capacity of furoxan derivatives to behave as NO-donors was first demonstrated by Feelisch et al. [19], who showed that furoxan derivatives produce nitric oxide when dissolved in physiological solution in the presence of thiols. Among the reaction products, they isolated nitrite and, in lesser amounts, nitrate, which are the final oxidation products of nitric oxide in aerobic water solution, as well as dioxime derivatives, which are the reduction products of the furoxans. They also evidenced a marked p H -dependent production of S-nitrosothiols. Working with N, AF-diisopropylfuroxan-3,4-dicarboxamide (29, Ipramidil) and an excess of glutathione (GSH), the amount of S-nitrosoglutathione formed increased with increasing pH until pH 9, above which it... 

Despite intense study of the chemical reactivity of the inorganic NO donor SNP with a number of electrophiles and nucleophiles (in particular thiols), the mechanism of NO release from this drug also remains incompletely understood. In biological systems, both enzymatic and non-enzymatic pathways appear to be involved [28]. Nitric oxide release is thought to be preceded by a one-electron reduction step followed by release of cyanide, and an inner-sphere charge transfer reaction between the ni-trosonium ion (NO+) and the ferrous iron (Fe2+). Upon addition of SNP to tissues, formation of iron nitrosyl complexes, which are in equilibrium with S-nitrosothiols, has been observed. A membrane-bound enzyme may be involved in the generation of NO from SNP in vascular tissue [35], but the exact nature of this reducing activity is unknown. 

While it is clear that NO is involved in the EDRF, there is also evidence that conjugation with thiols may occur as intermediates [47]. In 1981, Ignarro observed that NO-donating vasodilators react with cysteine to form S-nit-rosocysteine, an activator of guanylate cyclase, and suggested that the formation of unstable S-nitrosothiols was involved in the biological function of nitric oxide... 

Kots, A. Y., Skurat, A. V., Serienko, E. A., Bulargina, T. V., and Severin, E. S. (1992). Nitric oxide stimulates the cysteine-specific mono(ADP-ribosylation) of glyceralde-hyde-3-phosphate dehydrogenase from human. erythrocytes. FEBS Lett. 300, 9-12. Kowaluk, E. A., and Fung, H. L. (1990). Spontaneous liberation of nitric oxide cannot account for in vitro vascular relaxation by S-nitrosothiols. J. Pharmacol. Exp. Ther. 255,... 

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