RSNOs

RSNOs, or S-nitrosothiols, are a class of organic compounds in which a nitroso group is bonded to a sulfur atom of a thiol, giving the general structure R–S–NO. They are formed when a thiol (R–SH) is nitrosated or when nitroso groups are transferred between thiol-containing partners (transnitrosation). RSNOs exist widely in biological systems and can act as reservoirs or carriers of nitric oxide (NO) for signaling purposes.

In biology, RSNOs can form endogenously through reactions involving NO-derived nitrosating species and thiols, or via enzymatic and non-enzymatic pathways that generate N2O3 or related nitrosating agents. They can also be generated in vitro for research by nitrosating thiols or by transferring NO groups from other nitrosothiols. Their stability and reactivity depend on the R group, the redox environment, metal ions, and light exposure.

Chemically, RSNOs are relatively labile and can release NO under various conditions. They decompose by thermal or photolytic pathways, and can undergo denitrosation catalyzed by metal ions or redox-active species. They also participate in transnitrosation reactions, transferring the nitroso group to other thiols to form new RSNOs, thereby propagating redox signaling. As NO donors, RSNOs have been implicated in vascular regulation, neurotransmission, and cellular signaling, and are studied as biomarkers of NO bioavailability and in various disease contexts.

Notable examples include glutathione nitrosothiol (GSNO) and cysteine nitrosothiol (CysNO).