Low molecular thiols, pH and O2 modulate H2S-induced S-nitrosoglutathione decomposition – •NO release

Abstract

Abstract.We studied the involvement of O 2 , pH and low molecular thiols in H 2 S-induced decomposition of S-nitrosoglutathione (GSNO). The GSNO decomposition -• NO release was evaluated by UV-VIS spectroscopy and Griess assay. The H 2 S donor Na 2 S was used. O 2 slightly increased, but was not necessary for the H 2 S-induced GSNO decomposition. The rate of GSNO decomposition depended on pH; the maximum rate was observed at pH 7.4-8.0, and this decreased with lowering pH (6.4-4.5) as well as with increasing pH at 9.0-12.0. H 2 S-induced GSNO decomposition was slowed by the presence of other thiols, such as L-cysteine (Cys), N-acetyl-L-cysteine (NAC) and Lglutathione (GSH), but not in the presence of L-methionine (Met) or oxidized glutathione (GSSG). In sharp contrast, at pH 6.0, H 2 S-induced GSNO decomposition was negligible, yet the presence of Cys, NAC and GSH induced the H 2 S-driven GSNO decomposition (whilst Met and GSSG were inactive). In conclusion we postulate an involvement of low molecular thiols and pH in• NO signaling, by modulating the interactions of H 2 S with nitroso compounds, and hence in part they also appear to control H 2 S-triggered• NO release. The interaction of H 2 S and/or its derivatives with the thiol group may be responsible for the observed effects.

The reaction products of sulfide and S-nitrosoglutathione are potent vasorelaxants

“…A broad absorption band at~260-360 nm was assigned to belong to Sn, also known to be formed in the reaction [12]. After addition of HCl to the product mixture, which decreased pH from 7.4 to 2-4, the peak at λmax 412 nm disappeared within less than 1 min [11,12]. The spectra are similar to those in our previous reports using Sulfide/GSNO at different molar ratios and using S-nitrosopenicillamine as NO-donor [11,12].…”

“…After addition of HCl to the product mixture, which decreased pH from 7.4 to 2-4, the peak at λmax 412 nm disappeared within less than 1 min [11,12]. The spectra are similar to those in our previous reports using Sulfide/GSNO at different molar ratios and using S-nitrosopenicillamine as NO-donor [11,12]. The same UV-VIS absorbance features were used to study precursor and product stabilities.…”

“…Similarly, H2S can be stored in the form of sulfane sulfur and transported and released in response to a physiological stimulus [3]. A number of publications reported on the molecular interaction between H2S and NO or NO-donors [4][5][6][7][8][9][10][11][12][13][14], and H2S and NO were found to cooperatively regulate vascular tone by activating a neuroendocrine signaling pathway in which formation of nitroxyl (HNO) appears to play an important role [13]. Products of this H2S/NO interaction appear to have pronounced biological effects; however the nature of the reaction intermediates is currently unclear and many inconsistencies remain; for example, H2S donors were found to either potentiate or attenuate relaxation effect of NO donors in isolated aortic rings in vitro [15,16], or result in complete loss of vasodepressor activity in anesthetized rats [16].…”

Inorganic Reactive Sulfur-Nitrogen Species: Intricate Release Mechanisms or Cacophony in Yellow, Blue and Red?

“…There have been various reports on a potential • NO release from RSNO triggered by such sulfur species [8,9,10,11,12,13]. Yet from a chemical perspective, such a release would require a nucleophilic attack, and it seems highly unlikely that a mono-, di- or polysulfanes can perform such an attack independently.…”

“…This effect is in accordance with the p K a value of thiol groups (p K a (GSH) > p K a (Cys)). For instance, the presence of 5 mM of GSH in the mixture of 200 µM GSNO and 200 µM Na 2 S almost completely abolishes the formation of SSNO − [12]. The mechanism by which the presence of reduced and low molecular thiols influences the rate of GSNO decomposition and SSNO − formation is therefore still somewhat controversial.…”