Reactive Sulfur Species and Protein Persulfidation: An Emerging Redox Axis in Human Health and Disease.

Reactive sulfur species (RSS)-hydrogen sulfide (H2S), low-molecular-weight persulfides/polysulfides and protein persulfidation-constitute a third redox axis alongside ROS and RNS. Nanomolar H2S, produced by trans-sulfuration (CBS/CSE) and 3-MST, is oxidized by sulfide-quinone reductase to persulfides that fuel the respiratory chain while curbing superoxide. Reversible persulfidation reprograms cysteine sensors in metabolism (GAPDH), inflammation (NLRP3, p47phox) and transcription (Keap1/NRF2), linking RSS to energy balance, vasodilation, innate immunity and neuroplasticity. Disrupted sulfur signaling-deficit or overload-contributes to heart failure, sarcopenia, neurodegeneration, cancer and post-COVID syndromes. Therapeutically, slow-release donors (SG1002, GYY4137), mitochondria-targeted vectors (AP39), photo- or thiol-activated "smart" scaffolds, diet-derived polysulfides/isothiocyanates and microbiota engineering aim to restore the protective RSS window. Key challenges are a narrow therapeutic margin and real-time quantification of persulfide fluxes. Harnessing RSS therefore offers a route to rebalance redox homeostasis across diverse chronic diseases.