Unique response of polysulfide in serum albumin to oxidative stress

Supersulfide species have been identified as molecules that have catenated sulfur atoms as persulfides (R-SSH) and polysulfides (R-SS_nH). The physiological activities of intracellular supersulfides have been widely studied, but little is known about the role of supersulfides in extracellular biological fluids. We therefore analyzed the pathological changes and oxidative stress responses of the reduced and oxidized forms of polysulfides in the plasma of patients with diabetic nephropathy. We measured the reduced and oxidized forms of polysulfide with elimination of sulfides using dithiothreitol and ascorbic acid plus alkali conditions, respectively. Oxidation decreased oxidized forms of polysulfide and further polysulfide in human serum albumin, increasing its antioxidative activity. We identified seven cysteine residues that have polysulfides in a reduced form after oxidation in albumin. Further oxidation decreased the levels of the reduced forms of polysulfide and the antioxidative effect of serum albumin. Similar changes were also observed in a mouse model of rhabdomyolysis-induced acute kidney injury; the levels of reduced polysulfide in plasma transiently increased 1 h after glycerol administration, which was accompanied by increased antioxidative activity. In the sera of patients with diabetic nephropathy and chronic renal failure, both forms of polysulfides were decreased compared with those of healthy subjects. Analysis of the stages of renal damage revealed that dithiothreitol-liberated polysulfide increased from stages 1-3 and decreased in stage 5. These results suggest that the antioxidative activity of serum, including that of serum albumin, is regulated by the switch from the oxidized form of polysulfide to its reduced counterparts in response to oxidative stress.