Nitrosopersulfide (SSNO^-) targets the Keap-1/Nrf2 redox system

Nitric oxide (NO), hydrogen sulfide and polysulfides have been proposed to contribute to redox signaling by activating the Keap-1/Nrf2 stress response system. Nitrosopersulfide (SSNO^-) recently emerged as a bioactive product of the chemical interaction of NO or nitrosothiols with sulfide; upon decomposition it generates polysulfides and free NO, triggering the activation of soluble guanylate cyclase, inducing blood vessel relaxation in vitro and lowering blood pressure in vivo. Whether SSNO^- itself interacts with the Keap-1/Nrf2 system is unknown. We therefore sought to investigate the ability of SSNO^- to activate Nrf2-dependent processes in human vascular endothelial cells, and to compare the pharmacological effects of SSNO^- with those of its precursors NO and sulfide at multiple levels of target engagement. We here demonstrate that SSNO^- strongly increases nuclear levels, binding activity and transactivation activity of Nrf2, thereby increasing mRNA expression of Hmox-1, the gene encoding for heme oxygenase 1, without adversely affecting cell viability. Under all conditions, SSNO^- appeared to be more potent than its parent compounds, NO and sulfide. SSNO^--induced Nrf2 transactivation activity was abrogated by either NO scavenging with cPTIO or inhibition of thiol sulfuration by high concentrations of cysteine, implying a role for both persulfides/polysulfides and NO in SSNO^- mediated Nrf2 activation. Taken together, our studies demonstrate that the Keap-1/Nrf2 redox system is a biological target of SSNO^-, enriching the portfolio of bioactivity of this vasoactive molecule to also engage in the regulation of redox signaling processes. The latter suggests a possible role as messenger and/or mediator in cellular sensing and adaptations processes.