Cysteine persulfides and polysulfides produced by exchange reactions with H2S protect SH-SY5Y cells from methylglyoxal-induced toxicity through Nrf2 activation

Many physiological functions of hydrogen sulfide (H 2 S) have been reported in mammalian cells over the last 20 years. These physiological effects have been ascertained through in vitro treatment of cells with Na 2 S or NaHS, both of which are precursors of H 2 S. Since H 2 S exists as HS − in a neutral solution, a disulfide compound such as cystine could react with HS − in culture medium as well as in the cell. This study demonstrated that after the addition of Na 2 S solution into culture medium, HS − was transiently generated and disappeared immediately through the reaction between HS − and cystine to form cysteine persulfides and polysulfides in the culture medium (bound sulfur mixture: BS-Mix). Furthermore, we found that the addition of Na 2 S solution resulted in an increase of intracellular cysteine persulfide levels in SH-SY5Y cells. This alteration in intracellular persulfide was also observed in cystine-free medium. Considering this reaction of HS − as a precursor of BS-Mix, we highlighted the cytoprotective effect of Na 2 S on human neuroblastoma SH-SY5Y cells against methylglyoxal (MG)-induced toxicity. BS-Mix produced with Na 2 S in cystine-containing medium provided SH-SY5Y cells significant protective effect against MG-induced toxicity. However, the protective effect was attenuated in cystine-free medium. Moreover, we observed that Na 2 S or BS-Mix activated the Keap1/Nrf2 system and increased glutathione (GSH) levels in the cell. In addition, the activation of Nrf2 is significantly attenuated in cystine-free medium. These results suggested that Na 2 S protects SH-SY5Y cells from MG cytotoxicity through the activation of Nrf2, mediated by cysteine persulfides and polysulfides that were generated by Na 2 S addition. • Neuronal cells were protected from methylglyoxal-induced toxicity by cysteine persulfides. • H 2 S immediately reacts with cystine to form persulfides and polysulfides in culture medium. • Cysteine persulfides protect neuronal cells from carbonyl stress through the activation of Nrf2. fx1