The kinetics of thiol-mediated decomposition of S-nitrosothiols

Abstract

The reaction of sulfhydryl (SH)-containing molecules (thiols) with S-nitrosothiols (RSNO) has been shown to be of biological importance. Biologically or therapeutically relevant thiols generally have a pK a value ranging from 8 to 10 for the SH group. In addition, some of these thiols contain a carboxyl group and are acidic, which should be considered in studying the reaction between RSNO and thiols. In the present study, the kinetics of thiol-mediated decomposition of RSNO was investigated in a commonly used phosphate buffer, phosphate buffered saline (PBS; containing 6.9 mM phosphates; buffer capacity = 3.8 mM/pH). The thiols studied can be divided into 2 groups, depending on their pH perturbation capacity. The kinetics was studied using a wide range of thiol concentrations (ie, from 0.1 to 10 mM). A high-performance liquid chromatography (HPLC) method was used to determine RSNO concentrations. The results showed that the acidic thiols, including glutathione, captopril, N-acetylcysteine, and tiopronin, stimulated RSNO decomposition at low millimolar concentrations up to 2 mM. The stimulatory effect, however, became attenuated at concentrations higher than 2 mM in PBS. Increasing the concentration of acidic thiols caused a decrease in solution pH, which was attributable to the inhibitory effect at high thiol concentrations. The effect of thiols on the pH of reaction solution, and the resulting bell-shaped rate profi les, can be predicted by a quantitative analysis, from which a comparison of the intrinsic reactivity toward RSNO, among 8 thiols, was possible. The intrinsic reactivity in general followed the Brønsted relation.

In vitro Conversion of Model Sulfenamide Prodrugs in the Presence of Small Molecule Thiols

“…24 Following three prodrug models were used in all experiments: N-(phenylthio) linezolid (1), N-(ethylthio) linezolid (2), and N-(phenylthio) phthalimide (3) (Fig. 1).…”

A nanoparticle delivery vehicle for S-nitroso-N-acetyl cysteine: Sustained vascular response

“…RSNO half-lives are measured in the minutes to hours [40; 41; 42], whereas free NO has been shown to have a half-life measured in the seconds or less depending on site of production [1]. RSNO-based therapeutics appear to have many very similar physiologic effects as other NO-related therapeutics [34; 43; 44; 45].…”

How widespread is stable protein S-nitrosylation as an end-effector of protein regulation?

“…The bond energy of an S-N bond has been found to vary from 22 to 32 kcal/mol, meaning the lifetime of the bond could theoretically span from seconds to years [8]. However, the stability of S-nitrosothiols is unclear as published half-lives vary dramatically and are clearly condition-dependent [65][66][67][68]. Non-protein Snitrosothiols studied in vitro in the presence of metal chelators are relatively stable with a half-life of S-nitrosocysteine reported at 11 hours [69], although this is decreased to less than 2 minutes when metal ions are present [70], or to less than 20 seconds in the case of cysteine ethyl ester cysteine [16].…”

“…Non-protein Snitrosothiols studied in vitro in the presence of metal chelators are relatively stable with a half-life of S-nitrosocysteine reported at 11 hours [69], although this is decreased to less than 2 minutes when metal ions are present [70], or to less than 20 seconds in the case of cysteine ethyl ester cysteine [16]. The rate of S-nitrosothiols decomposition via transnitrosation is second-order, although rates vary depending on the chemical properties of the thiols involved [66]. Transnitrosation between Snitroso-N-acetylpenicillamine and GSH was observed to be 5.4 M −1 .s −1 whereas transfer of NO from GSNO to cysteine was 675.8 M −1 .s −1 [71].…”