Hydrogen sulfide (H2S) has been increasingly recognized as an important signaling molecule that regulates both blood pressure and neuronal activity. Attention has been drawn to its interactions with another gasotransmitter, nitric oxide (NO). Here, we provide evidence that the physiological effects observed upon the application of sodium nitroprusside (SNP) and H2S can be ascribed to the generation of nitroxyl (HNO), which is a direct product of the reaction between SNP and H2S, not a consequence of released NO subsequently reacting with H2S. Intracellular HNO formation has been confirmed, and the subsequent release of calcitonin gene-related peptide from a mouse heart has been demonstrated. Unlike with other thiols, SNP reacts with H2S in the same way as rhodanese, i.e., the cyanide transforms into a thiocyanate. These findings shed new light on how H2S is understood to interact with nitroprusside. Additionally, they offer a new and convenient pharmacological source of HNO for therapeutic purposes.

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.