Chemical Characterization of the Smallest S-Nitrosothiol, HSNO; Cellular Cross-talk of H₂S and S-Nitrosothiols

Abstract

Dihydrogen sulfide recently emerged as a biological signaling molecule with important physiological roles and significant pharmacological potential. Chemically plausible explanations for its mechanisms of action have remained elusive, however. Here, we report that H2S reacts with S-nitrosothiols to form thionitrous acid (HSNO), the smallest S-nitrosothiol. These results demonstrate that, at the cellular level, HSNO can be metabolized to afford NO+, NO, and NO– species, all of which have distinct physiological consequences of their own. We further show that HSNO can freely diffuse through membranes, facilitating transnitrosation of proteins such as hemoglobin. The data presented in this study explain some of the physiological effects ascribed to H2S, but, more broadly, introduce a new signaling molecule, HSNO, and suggest that it may play a key role in cellular redox regulation.

Hydrogen sulfide as an oxygen sensor

“…A number of in vitro studies in a marine echiuran worm and fish (67), mammalian heart (191,192), and RAW246.7 cells or liver homogenate (185) have shown that addition of H 2 S (as a sulfide salt or slow-releasing donor) to an NO donor (often sodium nitroprusside [SNP]) elicits a response in the tissue that is either greater than or different from the parent compounds. It has been proposed that this new signaling molecule is nitroxyl (HNO/NO -), a oneelectron reduced and protonated form of NO (191,192), and/ or a S-nitrosothiol (thionitrous acid [HSNO]) (40,185). The manner in which H 2 S and NO react has not yet been resolved, and a number of possibilities have been proposed (75).…”

“…Reactions with nitrogenous compounds include an H 2 S reaction with S-nitrosols to produce thionitrous acid (HSNO) (8), an HSNO reaction with excess H 2 S to form HSSNO (SSNO -), which slowly decomposes to nitric oxide (NO), and interaction of H 2 S/HS -and NO as the former is a diamagnetic reductant or nucleophile, whereas NO is a paramagnetic free radical (43,75,86). However, one-electron reduction of H 2 S/HS -to produce the thiyl radical (HS ) or a one-electron oxidized species of NO, such as nitrite (NO 2 -), can react to produce HSNO/SNO - (40). HSNO/SNO -is reported to be further metabolized to NO + , NO, and NO -with a variety of distinct stimulatory functions, and since it can diffuse freely across membranes, it may facilitate transnitrosation of proteins (40).…”

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

“…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].…”

“…H2S was shown to relax uterus from pregnant [17,18] and non-pregnant rats [19], and sodium nitroprusside (SNP) prevented H2S induced relaxation of rat uterus [20]. Thionitrous acid (HSNO) has been proposed to represent an important carrier of bioactivity of the interaction of S-nitrosothiols with H2S [10], but the evidence provided appears to be inconsistent with the known chemical properties of HSNO. Moreover, HSNO would be expected to rapidly react with excess sulfide to form other species; thus its biological effect would be very short-lived.…”

Metal-Based Optical Probes for Live Cell Imaging of Nitroxyl (HNO)

“…Although the direct observation of endogenously produced HNO in mammalian cells has remained elusive, CuBOT1 was also used to investigate the generation of HNO from the S-nitrosothiol GSNO and H 2 S. 17 Human umbilical vein endothelial cells (HUVECs) were incubated with 10 µM CuBOT1 In related work, Ivanović-Burmazović and co-workers showed that sodium nitroprusside (Na 2 [Fe(CN) 5 (NO)]; SNP) reacts in live cells to produce HNO. 18 In this study, the authors employed CuBOT1-loaded HUVECs to show that treatment of these cells with either SNP or H 2 S alone did not elicit a significant fluorescence turn-on.…”