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

Many physiological functions of hydrogen sulfide (HS) have been reported in mammalian cells over the last 20 years. These physiological effects have been ascertained through in vitro treatment of cells with NaS or NaHS, both of which are precursors of HS. Since HS 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 NaS 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 NaS 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 NaS on human neuroblastoma SH-SY5Y cells against methylglyoxal (MG)-induced toxicity. BS-Mix produced with NaS 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 NaS 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 NaS protects SH-SY5Y cells from MG cytotoxicity through the activation of Nrf2, mediated by cysteine persulfides and polysulfides that were generated by NaS addition.