Polysulfide promotes neuroblastoma cell differentiation by accelerating calcium influx

A mitochondrial targeted near-infrared ratio fluorescent probe for ferroptosis related hydrogen polysulfides imaging in arthritis

Hydrogen polysulfide (H2Sn, n > 1), as an active sulfur substance derived from hydrogen sulfide, is considered a new potential signaling molecule that occupies an irreplaceable position in physiological regulation and signal transduction processes. Ferroptosis, an iron-dependent form of programmed cell death, is caused by the iron dependent accumulation of lipid peroxides associated with reactive oxygen species. The process of ferroptosis generates abundant reactive oxygen species, indirectly promoting the elevation of intracellular hydrogen polysulfide levels. There is evidence to suggest a close relationship between ferroptosis and arthritis. This work developed a near-infrared ratiometric fluorescent probe (Mito-S4) with a large Stokes shift (∼240 nm) based on nucleophilic addition mechanism, which can quickly (18 s) and sensitively (Detection Limit = 0.165 μM) detect H2Sn in cells. The mechanism of action was verified through theoretical calculations and nuclear magnetic analysis, and the probe Mito-S4 was successfully applied to visualize H2Sn in cellular mitochondria. The cell imaging results showed that the probe successfully achieved tracking of H2Sn in mitochondria during inflammation and ferroptosis processes. In addition, pathological section experiments have confirmed that the probe has good in vivo imaging ability. It is worth mentioning that further in vivo imaging experiments have for the first time delved into the mechanism of H2Sn in the process of ferroptosis in arthritis, which can provide new research methods and therapeutic targets for the treatment of arthritis.

Polysulfide and persulfide-mediated activation of the PERK-eIF2α-ATF4 pathway increases Sestrin2 expression and reduces methylglyoxal toxicity

Unfolded protein response (UPR) is activated in cells under endoplasmic reticulum (ER) stress. One sensor protein involved in this response is PERK, which is activated through its redox-dependent oligomerization. Prolonged UPR activation is associated with the development and progression of various diseases, making it essential to understanding the redox regulation of PERK. Sulfane sulfur, such as polysulfides and persulfides, can modify the cysteine residues and regulate the function of various proteins. However, the regulatory mechanism and physiological effects of sulfane sulfur on the PERK-eIF2α-ATF4 pathway remain poorly understood. This study focuses on the persulfidation of PERK to elucidate the effects of polysulfides on the PERK-eIF2α-ATF4 pathway and investigate its cytoprotective mechanism. Here, we demonstrated that polysulfide treatment promoted the oligomerization of PERK and PTP1B in neuronal cells using western blotting under nonreducing conditions. We also observed that l-cysteine, a biological source of sulfane sulfur, promoted the oligomerization of PERK and the knockdown of CBS and 3-MST, two sulfane sulfur-producing enzymes, and reduced PERK oligomerization induced by l-cysteine treatment. Furthermore, the band shift assay and LC-MS/MS studies revealed that polysulfides and persulfides induce PTP1B and PERK persulfidation. Additionally, polysulfides promoted eIF2α phosphorylation and ATF4 accumulation in the nucleus, suggesting that polysulfides activate the PERK-eIF2α-ATF4 pathway in neuronal cells. Moreover, polysulfides protected neuronal cells from methylglyoxal-induced toxicity, and this protective effect was reduced when the expression of Sestrin2, regulated by ATF4 activity, was suppressed. This study identified a novel mechanism for the activation of the PERK-eIF2α-ATF4 pathway through persulfidation by polysulfides and persulfides. Interestingly, activation of this pathway overcame the toxicity of methylglyoxal in dependence on Sestrin2 expression. These findings deepen our understanding of neuronal diseases involving ER stress and UPR disturbance and may inspire new therapeutic strategies.

Analysis and characterization of sulfane sulfur

In the late 1970s, sulfane sulfur was defined as sulfur atoms covalently bound only to sulfur atoms. However, this definition was not generally accepted, as it was slightly vague and difficult to comprehend. Thus, in the early 1990s, it was defined as "bound sulfur," which easily converts to hydrogen sulfide upon reduction with a thiol-reducing agent. H2S-related bound sulfur species include persulfides (R-SSH), polysulfides (H2Sn, n ≥ 2 or R-S(S)nS-R, n ≥ 1), and protein-bound elemental sulfur (S0). Many of the biological effects currently associated with H2S may be attributed to persulfides and polysulfides. In the 20th century, quantitative determination of "sulfane sulfur" was conventionally performed using a reaction called cyanolysis. Several methods have been developed over the past 30 years. Current methods used for the detection of H2S and polysulfides include colorimetric assays for methylene blue formation, sulfide ion-selective or polarographic electrodes, gas chromatography with flame photometric or sulfur chemiluminescence detection, high-performance liquid chromatography analysis with fluorescent derivatization of sulfides, liquid chromatography with tandem mass spectrometry, the biotin switch technique, and the use of sulfide or polysulfide-sensitive fluorescent probes. In this review, we discuss the methods reported to date for measuring sulfane sulfur and the results obtained using these methods.

Physiological roles of hydrogen sulfide in mammalian cells, tissues and organs

H2S belongs to the class of molecules known as gasotransmitters, which also includes nitric oxide (NO) and carbon monoxide (CO). Three enzymes are recognized as endogenous sources of H2S in various cells and tissues: cystathionine g-lyase (CSE), cystathionine β-synthase (CBS) and 3-mercaptopyruvate sulfurtransferase (3-MST). The current article reviews the regulation of these enzymes as well as the pathways of their enzymatic and non-enzymatic degradation and elimination. The multiple interactions of H2S with other labile endogenous molecules (e.g. NO) and reactive oxygen species are also outlined. The various biological targets and signaling pathways are discussed, with special reference to H2S and oxidative posttranscriptional modification of proteins, the effect of H2S on channels and intracellular second messenger pathways, the regulation of gene transcription and translation and the regulation of cellular bioenergetics and metabolism. The pharmacological and molecular tools currently available to study H2S physiology are also reviewed, including their utility and limitations. In subsequent sections, the role of H2S in the regulation of various physiological and cellular functions is reviewed. The physiological role of H2S in various cell types and organ systems are overviewed. Finally, the role of H2S in the regulation of various organ functions is discussed as well as the characteristic bell-shaped biphasic effects of H2S. In addition, key pathophysiological aspects, debated areas, and future research and translational areas are identified A wide array of significant roles of H2S in the physiological regulation of all organ functions emerges from this review.

Synthesis of Reactive Sulfur Species in Cultured Vascular Endothelial Cells after Exposure to TGF-β1: Induction of Cystathionine γ-Lyase and Cystathionine β-Synthase Expression Mediated by the ALK5-Smad2/3/4 and ALK5-Smad2/3-ATF4 Pathways

Transforming growth factor-β₁ (TGF-β₁) occurs at high levels at damage sites of vascular endothelial cell layers and regulates the functions of vascular endothelial cells. Reactive sulfur species (RSS), such as cysteine persulfide, glutathione persulfide, and hydrogen persulfide, are cytoprotective factors against electrophiles such as reactive oxygen species and heavy metals. Previously, we reported that sodium trisulfide, a sulfane sulfur donor, promotes vascular endothelial cell proliferation. The objective of the present study was to clarify the regulation and significance of RSS synthesis in vascular endothelial cells after exposure to TGF-β₁. Bovine aortic endothelial cells in a culture system were treated with TGF-β₁ to assess the expression of intracellular RSS, the effect of RSS on cell proliferation in the presence of TGF-β₁, induction of RSS-producing enzymes by TGF-β₁, and intracellular signal pathways that mediate this induction. The results suggest that TGF-β₁ increased intracellular RSS levels to modulate its inhibitory effect on proliferation. The increased production of RSS, probably high-molecular-mass RSS, was due to the induction of cystathionine γ-lyase and cystathionine β-synthase, which are RSS-producing enzymes, and the induction was mediated by the ALK5-Smad2/3/4 and ALK5-Smad2/3-ATF4 pathways in vascular endothelial cells. TGF-β₁ regulates vascular endothelial cell functions such as proliferation and fibrinolytic activity; intracellular high-molecular-mass RSS, which are increased by TGF-β₁, may modulate the regulation activity in vascular endothelial cells.

Diet and Hydrogen Sulfide Production in Mammals

Significance: In recent times, it has emerged that some dietary sulfur compounds can act on mammalian cell signaling systems via their propensity to release hydrogen sulfide (H₂S). H₂S plays important biochemical and physiological roles in the heart, gastrointestinal tract, brain, kidney, and immune systems of mammals. Reduced levels of H₂S in cells and tissues correlate with a spectrum of pathophysiological conditions, including heart disease, diabetes, obesity, and altered immune function. Recent Advances: In the last decade, researchers have now begun to explore the mechanisms by which dietary-derived sulfur compounds, in addition to cysteine, can act as sources of H₂S. This research has led to the identified several compounds, organic sulfides, isothiocyanates, and inorganic sulfur species including sulfate that can act as potential sources of H₂S in mammalian cells and tissues. Critical Issues: We have summarised progress made in the identification of dietary factors that can impact on endogenous H₂S levels in mammals. We also describe current research focused on how some sulfur molecules present in dietary plants, and associated chemical analogues, act as sources of H₂S, and discuss the biological properties of these molecules as studied in a range of in vitro and in vivo systems. Future Directions: The identification of sulfur compounds in edible plants that can act as novel H₂S releasing molecules is intriguing. Research in this area could inform future studies exploring the impact of diet on H₂S levels in mammalian systems. Despite recent progress, additional work is needed to determine the mechanisms by which H₂S is released from these molecules following ingestions of dietary plants in humans, whether the amounts of H₂S produced is of physiological significance following the metabolism of these compounds in vivo, and if diet could be used to manipulated H₂S levels in humans. Importantly, this will lead to a better understanding of the biological significance of H₂S generated from dietary sources, and this information could be used in the development of plant breeding initiatives to increase the levels of H₂S releasing sulfur compounds in crops, or inform dietary intervention strategies that could be used to alter the levels of H₂S in humans.

Persulfide Signaling in Stress-Initiated Calmodulin Kinase Response

Significance: Calcium ion (Ca²⁺)/calmodulin (CaM)-dependent protein kinases (CaMKs) are activated by phosphorylation of a crucial threonine residue either by itself (CaMKII) or by upstream kinases, CaMK kinases (CaMKKs) (CaMKI and CaMKIV). CaMKs, present in most mammalian tissues, can phosphorylate many downstream targets, thereby regulating numerous cellular functions. Recent Advances: Aside from canonical post-translational modifications, cysteine-based redox switches in CaMKs affect their enzyme activities. In addition to reactive oxygen species (ROS) and reactive nitrogen species (RNS), reactive sulfur species (RSS) are also recognized as key signaling molecules, regulating protein function through polysulfidation, formation of polysulfides [-S-(S)_n-H] on their reactive cysteine residues. To comprehend the biological significance of RSS signaling-related CaMK regulation, here we introduce a novel concept defining CaMKs as RSS targets in stress responses. The stress responses include an irreversible electrophile attack for CaMKI, inflammation for CaMKII, and endoplasmic reticulum stress for CaMKIV. Critical Issues: Development of various human diseases is associated with increased ROS, RNS, and RSS generation. Therefore, depending on specific pathophysiology, RSS could have very particular effects on CaMK functions. Future Directions: How multiple sources and mutual reactions of ROS, RNS, and RSS are coordinated is obscure. Elucidating the mechanisms through applications of enzymology, chemical biology, and mass spectrometry enables to uncover the complexities of redox regulation of CaMK cascades.

Polysulfide-mediated sulfhydration of SIRT1 prevents diabetic nephropathy by suppressing phosphorylation and acetylation of p65 NF-κB and STAT3

Diabetic kidney disease is known as a major cause of chronic kidney disease and end stage renal disease. Polysulfides, a class of chemical agents with a chain of sulfur atoms, are found to confer renal protective effects in acute kidney injury. However, whether a polysulfide donor, sodium tetrasulfide (Na₂S₄), confers protective effects against diabetic nephropathy remains unclear. Our results showed that Na₂S₄ treatment ameliorated renal dysfunctional and histological damage in diabetic kidneys through inhibiting the overproduction of inflammation cytokine and reactive oxygen species (ROS), as well as attenuating renal fibrosis and renal cell apoptosis. Additionally, the upregulated phosphorylation and acetylation levels of p65 nuclear factor κB (p65 NF-κB) and signal transducer and activator of transcription 3 (STAT3) in diabetic nephropathy were abrogated by Na₂S₄ in a sirtuin-1 (SIRT1)-dependent manner. In renal tubular epithelial cells, Na₂S₄ directly sulfhydrated SIRT1 at two conserved CXXC domains (Cys371/374; Cys395/398), then induced dephosphorylation and deacetylation of its targeted proteins including p65 NF-κB and STAT3, thereby reducing high glucose (HG)-caused oxidative stress, cell apoptosis, inflammation response and epithelial-to-mesenchymal transition (EMT) progression. Most importantly, inactivation of SIRT1 by a specific inhibitor EX-527, small interfering RNA (siRNA), a de-sulfhydration reagent dithiothreitol (DTT), or mutation of Cys371/374 and Cys395/398 sites at SIRT1 abolished the protective effects of Na₂S₄ on diabetic kidney insulting. These results reveal that polysulfides may attenuate diabetic renal lesions via inactivation of p65 NF-κB and STAT3 phosphorylation/acetylation through sulfhydrating SIRT1.

Activation of 3-Mercaptopyruvate Sulfurtransferase by Glutaredoxin Reducing System

Glutaredoxin (EC 1.15-1.21) is known as an oxidoreductase that protects cysteine residues within proteins against oxidative stress. Glutaredoxin catalyzes an electron transfer reaction that donates an electron to substrate proteins in the reducing system composed of glutaredoxin, glutathione, glutathione reductase, and nicotinamide-adenine dinucleotide phosphate (reduced form). 3-mercaptopyruvate sulfurtransferase (EC 2.8.1.2) is a cysteine enzyme that catalyzes transsulfuration, and glutaredoxin activates 3-mercaptopyruvate sulfurtransferase in the reducing system. Interestingly, even when glutathione or glutathione reductase was absent, 3-mercaptopyruvate sulfurtransferase activity increased, probably because reduced glutaredoxin was partly present and able to activate 3-mercaptopyruvate sulfurtransferase until depletion. A study using mutant Escherichia coli glutaredoxin1 (Cys¹⁴ is the binding site of glutathione and was replaced with a Ser residue) confirmed these results. Some inconsistency was noted, and glutaredoxin with higher redox potential than either 3-mercaptopyruvate sulfurtransferase or glutathione reduced 3-mercaptopyruvate sulfurtransferase. However, electron-transfer enzymatically proceeded from glutaredoxin to 3-mercaptopyruvate sulfurtransferase.

Duloxetine-Induced Neural Cell Death and Promoted Neurite Outgrowth in N2a Cells

Duloxetine is a clinical drug that is primarily used for treatment of depression and pain, but it has side effects of addiction and tolerance. Cytochrome P450 (CYP) is its metabolic enzyme, and the drug's biofunction results from its neuro-protective effect in animal and cell models. We aimed to investigate the duloxetine-induced neural cytotoxicity effect and its performance in an N2a cell neurite outgrowth model. Cell death was assessed as cell viability using a Cell Count Kit-8 and further evaluated using bright-field images, propidium iodide (PI) and annexin V staining, colony-formation analysis, TUNEL staining of the cells, and biochemical testing. N2a cells were committed to differentiation by serum withdrawal and RA induction, and the neurite outgrowth was evaluated as the number of differentiated cells, longest neurite length, and average neurite length. Cell cycle analysis, PI and annexin V staining, mRNA expression, and biochemical testing were used to evaluate the drug effects on differentiation. The induction of neural cell death by duloxetine was not affected by classic cell death inhibitors but was promoted by the CYP inducer rifampicin. N2a cell neurite outgrowth was promoted by duloxetine via reduction of the CYP2D6 and MDA levels and induction of Bdnf protein levels. Duloxetine induces neural cell death through effects on CYP and promotes N2a cell neurite outgrowth by regulating CYP, Bdnf protein, and the intracellular lipid peroxidation level.

H2S, Polysulfides, and Enzymes: Physiological and Pathological Aspects

We have been studying the general aspects of the functions of H₂S and polysulfides, and the enzymes involved in their biosynthesis, for more than 20 years. Our aim has been to elucidate novel physiological and pathological functions of H₂S and polysulfides, and unravel the regulation of the enzymes involved in their biosynthesis, including cystathionine β-synthase (EC 4.2.1.22), cystathionine γ-lyase (EC 4.4.1.1), thiosulfate sulfurtransferase (rhodanese, EC 2.8.1.1), and 3-mercaptopyruvate sulfurtransferase (EC 2.8.1.2). Physiological and pathological functions, alternative biosynthetic processes, and additional functions of H₂S and polysulfides have been reported. Further, the structure and reaction mechanisms of related enzymes have also been reported. We expect this issue to advance scientific knowledge regarding the detailed functions of H₂S and polysulfides as well as the general properties and regulation of the enzymes involved in their metabolism. We would like to cover four topics: the physiological and pathological functions of H₂S and polysulfides, the mechanisms of the biosynthesis of H₂S and polysulfides, the properties of the biosynthetic enzymes, and the regulation of enzymatic activity. The knockout mouse technique is a useful tool to determine new physiological functions, especially those of H₂S and polysulfides. In the future, we shall take a closer look at symptoms in the human congenital deficiency of each enzyme. Further studies on the regulation of enzymatic activity by in vivo substances may be the key to finding new functions of H₂S and polysulfides.

A new turn-on fluorescent probe with ultra-large fluorescence enhancement for detection of hydrogen polysulfides based on dual quenching strategy

Based on dual quenching strategy (ESIPT inhibited quenching and PET quenching), we have developed a new turn-on fluorescent probe 1. Combining 3-(benzo[d]thiazol-2-yl)-10-butyl-10H-phenothiazin-2-ol (dye 2) as the fluorophore and 2-fluoro-5-nitro-benzoic as the recognition moiety, probe 1 had feature of notable large Stokes shift, highly sensitivity and selective for monitoring H₂S_n with remarkable fluorescence enhancement (328-fold) response at 534 nm. Probe 1 exhibited excellent performance in the quantitative detection of H₂S_n with a 137 nm Stokes shift and a low detection limit of 26 nM in solution. Finally, probe 1 was successfully utilized to image H₂S_n in living A549 cells and zebrafish.

The active-site cysteine residue of Ca2+/calmodulin-dependent protein kinase I is protected from irreversible modification via generation of polysulfidation

Ca²⁺/calmodulin (CaM)-dependent protein kinase (CaMK) I is activated by the phosphorylation of a crucial activation loop Thr¹⁷⁷ by upstream kinases, CaMK kinase (CaMKK), and regulates axonal or dendritic extension and branching. Reactive sulfur species (RSS) modulate protein functions via polysulfidation of the reactive Cys residues. Here, we report that the activity of CaMKI was reversibly inhibited via its polysulfidation at Cys¹⁷⁹ by RSS. In vitro incubation of CaMKI with the exogenous RSS donor Na₂S₃ resulted in a dose-dependent inhibition of the phosphorylation at Thr¹⁷⁷ by CaMKK and inactivation of the enzymatic activity. Dithiothreitol (DTT), a small molecule reducing reagent, rescued these inhibitions. Conversely, mutated CaMKI (C179V) was resistant to the Na₂S₃-induced inactivation. In transfected cells expressing CaMKI, ionomycin-induced CaMKI activity was decreased upon treatment with Na₂S₄, whereas cells expressing mutant CaMKI (C179V) proved resistant to this treatment. A biotin-polyethylene glycol-conjugated maleimide capture assay revealed that CaMKI was a target for polysulfidation in cells. Furthermore, the polysulfidation of CaMKI protected Cys¹⁷⁹ from its irreversible modification, known as protein succination. Thus, we propose that CaMKI was reversibly inhibited via polysulfidation of Cys¹⁷⁹ by RSS, thereby protecting it from irreversible modification.

Multiple role of 3-mercaptopyruvate sulfurtransferase: antioxidative function, H2 S and polysulfide production and possible SOx production

Rat 3-mercaptopyruvate sulfurtransferase (MPST) is a 32 808 Da simple protein. Cys247 is a catalytic site, and Cys154 and Cys263 are on the enzyme surface. MPST is found in all tissues, particularly in the kidneys, although the localization of its activity differs in each tissue. In this review, four functions of MPST are reviewed: (i) antioxidative function: Cys247 is redox-sensitive and serves as a redox-sensing switch. It is oxidized to cysteine sulfenate, which has a low redox potential, upon which the enzyme is inactivated. Then, reduced thioredoxin (Trx) with a reducing system (Trx reductase and NADPH) reduces the sulfenate to restore activity; meanwhile, Cys154 and Cys263 form an intermolecular disulfide bond, which serves as another redox-sensing switch. Consequently, Trx specifically cleaves the intermolecular disulfide bond by converting it from the inactive form (dimer) to the active form (monomer). (ii) Hydrogen sulfide and polysulfide production: hydrogen sulfide is produced via reduction of the persulfurated sulfur-acceptor substrate by reduced Trx or Trx with a reducing system; as an alternative process, stable polysulfurated or persulfurated Cys247 as a reaction intermediate is reduced by Trx with a reducing system to release hydrogen sulfide and polysulfides. (iii) Possible sulfur oxide production: sulfur oxides (SO, SO2 and SO3 ) can be produced in the redox cycle of sulfane sulfur formed at the catalytic site Cys247 (Cys-SO- , Cys-SO2- and Cys-SO3- ) as reaction intermediates and released by reduced Trx or Trx with a reducing system. (iv) Possible anxiolytic-like effects: MPST-knockout mice exhibited anxiolytic-like effects.

[Production of H2S, H2Sn, and persulfide species (CysSSH and GSSH) by 3-mercaptopyruvate sulfurtransferase]

Accumulating evidence shows that hydrogen sulfide (H₂S) has physiological roles in various tissues and organs, including the regulation of neuronal activity, vascular tension, a release of insulin, and protection of the heart, kidney, and brain from ischemic insult. H₂S is produced from l-cysteine by pyridoxal 5'-phosphate (PLP)-dependent enzymes, cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE). 3-Mercaptopyruvate sulfurtransferase (3MST) is the third H₂S-producing enzyme, and its substrate 3-mercaptopyruvate (3MP) is provided from l-cysteine and α-ketoglutarate (α-KG) by a PLP-dependent cysteine aminotransferase (CAT). An additional pathway for the production of H₂S from d-cysteine metabolized by d-amino acid oxidase (DAO) together with 3MST has been identified. Recent studies have shown that hydrogen polysulfides (H₂S_n) have been found to stimulate transient receptor potential ankyrin1 (TRPA1) channel, much more potently than does H₂S. 3MST produces cysteine-persulfide (CysSSH) and its glutathione counterpart (GSSH), potential redox regulators, together with the potential signaling molecules H₂S_n. In addition, the interaction between H₂S and nitric oxide (NO) also generates H₂S_n. These observations provide new insights into the production and physiological roles of these molecules.

Analysis of endogenous H2S and H2Sn in mouse brain by high-performance liquid chromatography with fluorescence and tandem mass spectrometric detection

Previous studies indicated that bound sulfur species (BSS), including hydrogen polysulfide (H₂S_n), have various physiological functions in mammalian cells. Although H₂S_n molecules have been considered as secondary metabolites derived from hydrogen sulfide (H₂S) based on in vitro studies or predetermined reaction formula, the physiological form of BSS and their endogenous concentration remain unclear. In the present study, we aimed to improve the usual method using monobromobimane (mBB) followed by high performance liquid chromatographic (HPLC) analysis for HS^－ for simultaneous determination of H₂S, H₂S₂, H₂S₃ and cysteine persulfide in biological samples. We demonstrated that mBB derivatization of H₂S and H₂S_n standards under alkaline conditions (pH 9.5) induced significant decreases in H₂S₂ and H₂S₃ levels and a significant increase in the H₂S level in an incubation time-dependent manner. Conversely, the derivatization of mBB adducts of H₂S₂ and H₂S₃ were stable under neutral conditions (pH 7.0), which is physiologically relevant. Therefore, we re-examined the method using mBB and applied an improved method for the evaluation of H₂S, H₂S₂, and H₂S₃ in mouse brain under physiological pH conditions. The concentrations of H₂S and H₂S₂ were 0.030 ± 0.004μmol/g protein and 0.026 ± 0.002μmol/g protein, respectively. Although the level of H₂S₃ was below the quantification limit of this method, H₂S₃ was detected in mouse brain. Using the method established here, we reveal for the first time the existence of endogenous H₂S₂ and H₂S₃ in mammalian brain tissues. H₂S₂ and H₂S₃ exert anti-oxidant activity and anti-carbonyl stress effects through the regulation of redox balance in neuronal cells. Thus, our observations provide novel insights into the physiological functions of BSS in the brain and into neuronal diseases involved in redox imbalance.

A novel S-sulfhydrated human serum albumin preparation suppresses melanin synthesis

Products of ultraviolet (UV) irradiation such as reactive oxygen species (ROS) and nitric oxide (NO) stimulate melanin synthesis. Reactive sulfur species (RSS) have been shown to have strong ROS and NO scavenging effects. However, the instability and low retention of RSS limit their use as inhibitors of melanin synthesis. The free thiol at Cys34 on human serum albumin (HSA) is highly stable, has a long retention and possess a high reactivity for RSS. We report herein on the development of an HSA based RSS delivery system. Sulfane sulfur derivatives released from sodium polysulfides (Na₂S_n) react readily with HSA. An assay for estimating the elimination of sulfide from polysulfide showed that almost all of the sulfur released from Na₂S_n bound to HSA. The Na₂S_n-treated HSA was found to efficiently scavenge ROS and NO produced from chemical reagents. The Na₂S_n-treated HSA was also found to inhibit melanin synthesis in B16 melanoma cells and this inhibition was independent of the number of added sulfur atoms. In B16 melanoma cells, the Na₂S_n-treated HSA also inhibited the levels of ROS and NO induced by UV radiation. Finally, the Na₂S_n-treated HSA inhibited melanin synthesis from L-DOPA and mushroom tyrosinase and suppressed the extent of aggregation of melanin pigments. These data suggest that Na₂S_n-treated HSA inhibits tyrosinase activity for melanin synthesis via two pathways; by directly inhibiting ROS signaling and by scavenging NO. These findings indicate that Na₂S_n-treated HSA has potential to be an attractive and effective candidate for use as a skin whitening agent.

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We developed of an Reactive sulfur species delivery system based on human serum albumin.

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The novel polysulfides-added albumin could inhibit melanin synthesis in melanocyte.

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The polysulfides-added albumin also inhibited the levels of ROS and NO induced by UV radiation.

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The polysulfides-added albumin has the potential to be an attractive candidate for a whitening agent.

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 (H₂S) have been reported in mammalian cells over the last 20 years. These physiological effects have been ascertained through in vitro treatment of cells with Na₂S or NaHS, both of which are precursors of H₂S. Since H₂S 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 Na₂S 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 Na₂S 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 Na₂S on human neuroblastoma SH-SY5Y cells against methylglyoxal (MG)-induced toxicity. BS-Mix produced with Na₂S 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 Na₂S 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 Na₂S protects SH-SY5Y cells from MG cytotoxicity through the activation of Nrf2, mediated by cysteine persulfides and polysulfides that were generated by Na₂S addition.

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Neuronal cells were protected from methylglyoxal-induced toxicity by cysteine persulfides.

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H₂S immediately reacts with cystine to form persulfides and polysulfides in culture medium.

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Cysteine persulfides protect neuronal cells from carbonyl stress through the activation of Nrf2.

Cross talk between polysulfide and nitric oxide in rat peritoneal mast cells

The aim of this study was to define the effects of polysulfide on intracellular Ca(2+) concentration ([Ca(2+)]i) and the underlying machinery, especially from the hydrogen sulfide (H2S) and nitric oxide (NO) perspectives, in rat peritoneal mast cells. We found that a polysulfide donor, Na2S4, increased [Ca(2+)]i, which is both extracellular and intracellular Ca(2+) dependent. Intracellular Ca(2+) release induced by Na2S4 was attenuated by the addition of a ryanodine receptor blocker. A slow-releasing H2S donor, GYY4137, dose dependently increased [Ca(2+)]i that was independent from extracellular Ca(2+) influx. The GYY4137-induced [Ca(2+)]i release was partially attenuated in the presence of the ryanodine receptor blocker. Both polysulfide and H2S donors increased the intracellular NO levels in DAF-2-loaded mast cells, which were abolished by an NO scavenger, cPTIO. Inhibition of NO synthase (NOS) significantly abolished the polysulfide- or H2S-donor-induced [Ca(2+)]i elevation in the absence of extracellular Ca(2+) An NO donor, diethylamine (DEA) NONOate, increased [Ca(2+)]i in a concentration-dependent manner, in which both extracellular and intracellular Ca(2+) are associated. At higher concentrations, the DEA NONOate-induced [Ca(2+)]i increases were attenuated in the absence of extracellular Ca(2+) and by the addition of the ryanodine receptor blocker. H2S and NO dose dependently induced polysulfide production. Curiously, polysulfide, H2S, and NO donors had no effect on mast cell degranulation. Among synthases, cystathionine-γ-lyase, and neuronal NOS seemed to be the major H2S- and NO-producing synthases, respectively. These results indicate that polysulfide acts as a potential signaling molecule that regulates [Ca(2+)]i homeostasis in rat peritoneal mast cells via a cross talk with NO and H2S.

Slow sulfide donor GYY4137 differentiates NG108-15 neuronal cells through different intracellular transporters than dbcAMP

Cellular differentiation is the process, by which a cell changes from one cell type to another, preferentially to the more specialized one. Calcium fluxes play an important role in this action. Differentiated NG108-15 or PC12 cells serve as models for studying neuronal pathways. NG108-15 cell line is a reliable model of cholinergic neuronal cells. These cells differentiate to a neuronal phenotype due to the dibutyryl cAMP (dbcAMP) treatment. We have shown that a slow sulfide donor - GYY4137 - can also act as a differentiating factor in NG108-15 cell line. Calcium is an unavoidable ion required in NG108-15 cell differentiation by both, dbcAMP and GYY4137, since cultivation in EGTA completely prevented differentiation of these cells. In this work we focused primarily on the role of reticular calcium in the process of NG108-15 cell differentiation. We have found that dbcAMP and also GYY4137 decreased reticular calcium concentration by different mechanisms. GYY4137 caused a rapid decrease in type 2 sarco/endoplasmic calcium ATPase (SERCA2) mRNA and protein, which results in lower calcium levels in the endoplasmic reticulum compared to the control, untreated group. The dbcAMP revealed rapid increase in expression of the type 3 IP3 receptor, which participates in a calcium clearance from the endoplasmic reticulum. These results point to the important role of reticular calcium in a NG108-15 cell differentiation.