Methods in sulfide and persulfide research

Supersulfide formation in the sinus mucosa of chronic rhinosinusitis

Objectives

Disruption of the oxidative stress defense system is involved in developing various diseases. Sulfur compounds such as glutathione (GSH) and cysteine (CysSH) are representative antioxidants in the body. Recently, supersulfides, including reactive persulfide and polysulfide species, have gained attention as potent antioxidants regulating oxidative stress and redox signaling. However, their involvement in the pathogenesis of chronic rhinosinusitis (CRS) remains unclear.

Methods

To clarify the changes in sulfur compounds within the sinus mucosa of each CRS subtype, we measured sulfur compound levels in the sinus mucosa of control individuals (n = 9), patients with eosinophilic CRS (ECRS) (n = 13), and those with non-ECRS (nECRS) (n = 11) who underwent sinus surgery using mass spectrometry.

Results

GSH and CysSH levels were significantly reduced, and the glutathione disulfide (GSSG)/GSH ratio, an oxidative stress indicator, was increased in patients with ECRS. Despite the absence of notable variations in supersulfides, patients with ECRS and nECRS exhibited a significant reduction in glutathione trisulfide (GSSSG), which serves as the precursor for supersulfides.

Conclusions

This study is the first quantitative assessment of supersulfides in normal and inflamed sinus mucosa, suggesting that sulfur compounds contribute to the pathogenesis of CRS.

Level of Evidence

N/A.

Next-Generation Green Hydrogen: Progress and Perspective from Electricity, Catalyst to Electrolyte in Electrocatalytic Water Splitting

Green hydrogen from electrolysis of water has attracted widespread attention as a renewable power source. Among several hydrogen production methods, it has become the most promising technology. However, there is no large-scale renewable hydrogen production system currently that can compete with conventional fossil fuel hydrogen production. Renewable energy electrocatalytic water splitting is an ideal production technology with environmental cleanliness protection and good hydrogen purity, which meet the requirements of future development. This review summarizes and introduces the current status of hydrogen production by water splitting from three aspects: electricity, catalyst and electrolyte. In particular, the present situation and the latest progress of the key sources of power, catalytic materials and electrolyzers for electrocatalytic water splitting are introduced. Finally, the problems of hydrogen generation from electrolytic water splitting and directions of next-generation green hydrogen in the future are discussed and outlooked. It is expected that this review will have an important impact on the field of hydrogen production from water.

Deciphering pathophysiological mechanisms underlying cystathionine beta-synthase-deficient homocystinuria using targeted metabolomics, liver proteomics, sphingolipidomics and analysis of mitochondrial function

BACKGROUND

Cystathionine β-synthase (CBS)-deficient homocystinuria (HCU) is an inherited disorder of sulfur amino acid metabolism with varying severity and organ complications, and a limited knowledge about underlying pathophysiological processes. Here we aimed at getting an in-depth insight into disease mechanisms using a transgenic mouse model of HCU (I278T).

METHODS

We assessed metabolic, proteomic and sphingolipidomic changes, and mitochondrial function in tissues and body fluids of I278T mice and WT controls. Furthermore, we evaluated the efficacy of methionine-restricted diet (MRD) in I278T mice.

RESULTS

In WT mice, we observed a distinct tissue/body fluid compartmentalization of metabolites with up to six-orders of magnitude differences in concentrations among various organs. The I278T mice exhibited the anticipated metabolic imbalance with signs of an increased production of hydrogen sulfide and disturbed persulfidation of free aminothiols. HCU resulted in a significant dysregulation of liver proteome affecting biological oxidations, conjugation of compounds, and metabolism of amino acids, vitamins, cofactors and lipids. Liver sphingolipidomics indicated upregulation of the pro-proliferative sphingosine-1-phosphate signaling pathway. Liver mitochondrial function of HCU mice did not seem to be impaired compared to controls. MRD in I278T mice improved metabolic balance in all tissues and substantially reduced dysregulation of liver proteome.

CONCLUSION

The study highlights distinct tissue compartmentalization of sulfur-related metabolites in normal mice, extensive metabolome, proteome and sphingolipidome disruptions in I278T mice, and the efficacy of MRD to alleviate some of the HCU-related biochemical abnormalities.

Sulfur metabolism as a new therapeutic target of heart failure

Sulfur-based redox signaling has long attracted attention as critical mechanisms underlying the development of cardiac diseases and resultant heart failure. Especially, post-translational modifications of cysteine (Cys) thiols in proteins mediate oxidative stress-dependent cardiac remodeling including myocardial hypertrophy, senescence, and interstitial fibrosis. However, we recently revealed the existence of Cys persulfides and Cys polysulfides in cells and tissues, which show higher redox activities than Cys and substantially contribute to redox signaling and energy metabolism. We have established simple evaluation methods that can detect polysulfides in proteins and inorganic polysulfides in cells and revealed that polysulfides abundantly expressed in normal hearts are dramatically catabolized by exposure to ischemic/hypoxic and environmental electrophilic stress, which causes vulnerability of the heart to mechanical load. Accumulation of hydrogen sulfide, a nucleophilic catabolite of persulfides/polysulfides, may lead to reductive stress in ischemic hearts, and perturbation of polysulfide catabolism can improve chronic heart failure after myocardial infarction in mice. This review focuses on the (patho)physiological role of sulfur metabolism in hearts, and proposes that sulfur catabolism during ischemic/hypoxic stress has great potential as a new therapeutic strategy for the treatment of ischemic heart failure.

In pursuit of feedback activation: New insights into redox-responsive hydropersulfide prodrug combating oxidative stress

Redox-responsive hydropersulfide prodrugs are designed to enable a more controllable and efficient hydropersulfide (RSSH) supply and to thoroughly explore their biological and therapeutic applications in oxidative damage. To obtain novel activation patterns triggered by redox signaling, we focused on NAD(P)H: quinone acceptor oxidoreductase 1 (NQO1), a canonical antioxidant enzyme, and designed NQO1-activated RSSH prodrugs. We also performed a head-to-head comparison of two mainstream structural scaffolds with solid quantitative analysis of prodrugs, RSSH, and metabolic by-products by LC-MS/MS, confirming that the perthiocarbamate scaffold was more effective in intracellular prodrug uptake and RSSH production. The prodrug was highly potent in oxidative stress management against cisplatin-induced nephrotoxicity. Strikingly, this prodrug possessed potential feedback activation properties by which the delivered RSSH can further escalate the prodrug activation via NQO1 upregulation. Our strategy pushed RSSH prodrugs one step further in the pursuit of efficient release in biological matrices and improved druggability against oxidative stress.

Redox Regulation of Xenobiotics by Reactive Sulfur and Supersulfide Species

Significance: Routine exposure to xenobiotics is unavoidable during our lifetimes. Certain xenobiotics are hazardous to human health, and are metabolized in the body to render them less toxic. During this process, several detoxification enzymes cooperatively metabolize xenobiotics. Glutathione (GSH) conjugation plays an important role in the metabolism of electrophilic xenobiotics. Recent Advances: Recent advances in reactive sulfur and supersulfide (RSS) analyses showed that persulfides and polysulfides bound to low-molecular-weight thiols, such as GSH, and to protein thiols are abundant in both eukaryotes and prokaryotes. The highly nucleophilic nature of hydropersulfides and hydropolysulfides contributes to cell protection against oxidative stress and electrophilic stress. Critical Issues: In contrast to GSH conjugation to electrophiles that is aided by glutathione S-transferase (GST), persulfides and polysulfides can directly form conjugates with electrophiles without the catalytic actions of GST. The polysulfur bonds in the conjugates are further reduced by perthioanions and polythioanions derived from RSS to form sulfhydrated metabolites that are no longer electrophilic but rather nucleophilic, and differ from metabolites that are formed via GSH conjugation. Future Directions: In view of the abundance of RSS in cells and tissues, metabolism of xenobiotics that is mediated by RSS warrants additional investigations, such as studies of the impact of microbiota-derived RSS on xenobiotic metabolism. Metabolites formed from reactions between electrophiles and RSS may be potential biomarkers for monitoring exposure to electrophiles and for studying their metabolism by RSS. Antioxid. Redox Signal. 40, 679-690.

A Biochemical Corrosion Monitoring Sensor with a Silver/Carbon Comb Structure for the Detection of Living Escherichia coli

For the detection and monitoring of live bacteria, we propose a biochemical corrosion monitoring (BCM) sensor that measures galvanic current by using a Ag/C sensor comprising silver and carbon comb electrodes. The deposition of an Escherichia coli suspension containing an LB liquid medium on the Ag/C sensor increased the galvanic current. The time required for the current to reach 20 nA is defined as T20. T20 tends to decrease as the initial number of E. coli in the E. coli solution increases. A linear relationship was obtained between the logarithm of the E. coli count and T20 in a bacterial count range of 1-108 cfu/mL under culture conditions in which the growth rate of the bacteria was constant. Hence, the number of live E. coli could be determined from T20. Ag2S precipitation was observed on the surface of the Ag electrode of the Ag/C sensor, where an increase in the current was observed. This generation of galvanic current was attributed to the reaction between a small amount of free H2S metabolized by E. coli in the bacterial solution during its growth process and Ag-the sensor anode. The Ag/C sensor can detect a free H2S concentration of 0.041 μM in the E. coli solution. This novel biochemical sensor can monitor the growth behavior of living organisms without damaging them.

Sulfur metabolic response in macrophage limits excessive inflammatory response by creating a negative feedback loop

The excessive inflammatory response of macrophages plays a vital role in the pathogenesis of various diseases. The dynamic metabolic alterations in macrophages, including amino acid metabolism, are known to orchestrate their inflammatory phenotype. To explore a new metabolic pathway that regulates the inflammatory response, we examined metabolome changes in mouse peritoneal macrophages (PMs) in response to lipopolysaccharide (LPS) and found a coordinated increase of cysteine and its related metabolites, suggesting an enhanced demand for cysteine during the inflammatory response. Because Slc7a11, which encodes a cystine transporter xCT, was remarkably upregulated upon the pro-inflammatory challenge and found to serve as a major channel of cysteine supply, we examined the inflammatory behavior of Slc7a11 knockout PMs (xCT-KO PMs) to clarify an impact of the increased cysteine demand on inflammation. The xCT-KO PMs exhibited a prolonged upregulation of pro-inflammatory genes, which was recapitulated by cystine depletion in the culture media of wild-type PMs, suggesting that cysteine facilitates the resolution of inflammation. Detailed analysis of the sulfur metabolome revealed that supersulfides, such as cysteine persulfide, were increased in PMs in response to LPS, which was abolished in xCT-KO PMs. Supplementation of N-acetylcysteine tetrasulfide (NAC-S2), a supersulfide donor, attenuated the pro-inflammatory gene expression in xCT-KO PMs. Thus, activated macrophages increase cystine uptake via xCT and produce supersulfides, creating a negative feedback loop to limit excessive inflammation. Our study highlights the finely tuned regulation of macrophage inflammatory response by sulfur metabolism.

Synthesis of Sulfides and Persulfides Is Not Impeded by Disruption of Three Canonical Enzymes in Sulfur Metabolism

Reactive sulfur species, or persulfides and polysulfides, such as cysteine hydropersulfide and glutathione persulfide, are endogenously produced in abundance in both prokaryotes and eukaryotes, including mammals. Various forms of reactive persulfides occur in both low-molecular-weight and protein-bound thiols. The chemical properties and great supply of these molecular species suggest a pivotal role for reactive persulfides/polysulfides in different cellular regulatory processes (e.g., energy metabolism and redox signaling). We demonstrated earlier that cysteinyl-tRNA synthetase (CARS) is a new cysteine persulfide synthase (CPERS) and is responsible for the in vivo production of most reactive persulfides (polysulfides). Some researchers continue to suggest that 3-mercaptopyruvate sulfurtransferase (3-MST), cystathionine β-synthase (CBS), and cystathionine γ-lyase (CSE) may also produce hydrogen sulfide and persulfides that may be generated during the transfer of sulfur from 3-mercaptopyruvate to the cysteine residues of 3-MST or direct synthesis from cysteine by CBS/CSE, respectively. We thus used integrated sulfur metabolome analysis, which we recently developed, with 3-MST knockout (KO) mice and CBS/CSE/3-MST triple-KO mice, to elucidate the possible contribution of 3-MST, CBS, and CSE to the production of reactive persulfides in vivo. We therefore quantified various sulfide metabolites in organs derived from these mutant mice and their wild-type littermates via this sulfur metabolome, which clearly revealed no significant difference between mutant mice and wild-type mice in terms of reactive persulfide production. This result indicates that 3-MST, CBS, and CSE are not major sources of endogenous reactive persulfide production; rather, CARS/CPERS is the principal enzyme that is actually involved in and even primarily responsible for the biosynthesis of reactive persulfides and polysulfides in vivo in mammals.

Investigating the debrominations of a subset of brominated flame retardants by biogenic reactive sulfur species

Brominated flame retardants (BFRs) are persistent organic pollutants. Many bacteria are able to debrominate BFRs, but the underlying mechanism is unclear. Herein, we discovered that reactive sulfur species (RSS), which have strong reductive activity and are commonly present in bacteria, might be one of the reasons leading to such ability. Experiments performed with RSS (H₂S and HSSH) and BFRs indicated that RSS can debrominate BFRs via two different mechanisms simultaneously: the substitutive debromination that generates thiol-BFRs and the reductive debromination that generates hydrogenated BFRs. Debromination reactions rapidly happened under neutral pH and ambient temperature, and the debromination degree was around 30% - 55% in one hour. Two Pseudomonas strains, Pseudomonas sp. C27 and Pseudomonas putida B6-2 both produced extracellular RSS and showed debromination activity. C27 debrominated HBCD, TBECH, and TBP by 5.4%, 17.7%, and 15.9% in two days. Whereas, B6-2 debrominated the three BFRs by 0.4%, 0.6%, and 0.3% in two days. The two bacteria produced different amounts and species of RSS, which were likely responsible for the contrasted degrees of the debromination. Our finding unveiled a novel, non-enzymatic debromination mechanism that many bacteria may possess. RSS producing bacteria have potentials to contribute to bioremediation of BFRs-polluted environments.

Intranasal administration of polysulfide prevents neurodegeneration in spinal cord and rescues mice from delayed paraplegia after spinal cord ischemia

BACKGROUND

Delayed paraplegia is a devastating complication of thoracoabdominal aortic surgery. Hydrogen sulfide (H₂S) was reported to be protective in a mouse model of spinal cord ischemia and the beneficial effect of H₂S has been attributed to polysulfides. The objective of this study was to investigate the effects of polysulfides on delayed paraplegia after spinal cord ischemia.

METHODS AND RESULTS

Spinal cord ischemia was induced in male and female C57BL/6J mice by clamping the aortic arch and the left subclavian artery. Glutathione trisulfide (GSSSG), glutathione (GSH), glutathione disulfide (GSSG), or vehicle alone was administered intranasally at 0, 8, 23, and 32 h after surgery. All mice treated with vehicle alone developed paraplegia within 48 h after surgery. GSSSG, but not GSH or GSSG, prevented paraplegia in 8 of 11 male mice (73%) and 6 of 8 female mice (75%). Intranasal administration of ³⁴S-labeled GSSSG rapidly increased ³⁴S-labeled sulfane sulfur species in the lumbar spinal cord. In mice treated with intranasal GSSSG, there were increased sulfane sulfur levels, and decreased neurodegeneration, microglia activation, and caspase-3 activation in the lumbar spinal cord. In vitro studies using murine primary cortical neurons showed that GSSSG increased intracellular levels of sulfane sulfur. GSSSG, but not GSH or GSSG, dose-dependently improved cell viability after oxygen and glucose deprivation/reoxygenation (OGD/R). Pantethine trisulfide (PTN-SSS) also increased intracellular sulfane sulfur and improved cell viability after OGD/R. Intranasal administration of PTN-SSS, but not pantethine, prevented paraplegia in 6 of 9 male mice (66%).

CONCLUSIONS

Intranasal administration of polysulfides rescued mice from delayed paraplegia after transient spinal cord ischemia. The neuroprotective effects of GSSSG were associated with increased levels of polysulfides and sulfane sulfur in the lumbar spinal cord. Targeted delivery of sulfane sulfur by polysulfides may prove to be a novel approach to the treatment of neurodegenerative diseases.

Sulfide regulation of cardiovascular function in health and disease

Hydrogen sulfide (H2S) has emerged as a gaseous signalling molecule with crucial implications for cardiovascular health. H2S is involved in many biological functions, including interactions with nitric oxide, activation of molecular signalling cascades, post-translational modifications and redox regulation. Various preclinical and clinical studies have shown that H2S and its synthesizing enzymes - cystathionine γ-lyase, cystathionine β-synthase and 3-mercaptosulfotransferase - can protect against cardiovascular pathologies, including arrhythmias, atherosclerosis, heart failure, myocardial infarction and ischaemia-reperfusion injury. The bioavailability of H2S and its metabolites, such as hydropersulfides and polysulfides, is substantially reduced in cardiovascular disease and has been associated with single-nucleotide polymorphisms in H2S synthesis enzymes. In this Review, we highlight the role of H2S, its synthesizing enzymes and metabolites, their roles in the cardiovascular system, and their involvement in cardiovascular disease and associated pathologies. We also discuss the latest clinical findings from the field and outline areas for future study.

Cysteine hydropersulfide reduces lipid peroxidation and protects against myocardial ischaemia-reperfusion injury - Are endogenous persulfides mediators of ischaemic preconditioning?

Earlier studies revealed the presence of cysteine persulfide (CysSSH) and related polysulfide species in various mammalian tissues. CysSSH has both antioxidant and oxidant properties, modulates redox-dependent signal transduction and has been shown to mitigate oxidative stress. However, its functional relevance in the setting of myocardial ischaemia-reperfusion injury (IRI) remains unknown. The present study was undertaken to (1) study the dynamics of production and consumption of persulfides under normoxic and hypoxic conditions in the heart, and (2) determine whether exogenous administration of the CysSSH donor, cysteine trisulfide (Cys-SSS-Cys) at the onset of reperfusion rescues functional impairment and myocardial damage by interfering with lipid peroxidation. Utilising a well-established ex vivo Langendorff murine model, we here demonstrate that endogenous tissue concentrations of CysSSH are upregulated when oxygen supply is compromised (global myocardial ischaemia) and rapidly restored to baseline levels upon reperfusion, suggestive of active regulation. In a separate set of experiments, exogenous administration of Cys-SSS-Cys for 10 min at the onset of reperfusion was found to decrease malondialdehyde (MDA) concentrations, formation of 4-hydroxynonenal (4-HNE) protein adducts and rescue the heart from injury. Cys-SSS-Cys also restored post-ischaemic cardiac function, improving both coronary flow and left ventricular developed pressure (LVDP). Taken together, these results support the notion that endogenous CysSSH plays an important role as a "redox preconditioning" agent to combat the oxidative insult in myocardial IRI.

Oral Administration of Glutathione Trisulfide Increases Reactive Sulfur Levels in Dorsal Root Ganglion and Ameliorates Paclitaxel-Induced Peripheral Neuropathy in Mice

Peripheral neuropathy is a dose-limiting side effect of chemotherapy with paclitaxel. Paclitaxel-induced peripheral neuropathy (PIPN) is typically characterized by a predominantly sensory neuropathy presenting with allodynia, hyperalgesia and spontaneous pain. Oxidative mitochondrial damage in peripheral sensory neurons is implicated in the pathogenesis of PIPN. Reactive sulfur species, including persulfides (RSSH) and polysulfides (RSnH), are strong nucleophilic and electrophilic compounds that exert antioxidant effects and protect mitochondria. Here, we examined the potential neuroprotective effects of glutathione trisulfide (GSSSG) in a mouse model of PIPN. Intraperitoneal administration of paclitaxel at 4 mg/kg/day for 4 days induced mechanical allodynia and thermal hyperalgesia in mice. Oral administration of GSSSG at 50 mg/kg/day for 28 days ameliorated mechanical allodynia, but not thermal hyperalgesia. Two hours after oral administration, 34S-labeled GSSSG was detected in lumber dorsal root ganglia (DRG) and in the lumber spinal cord. In mice treated with paclitaxel, GSSSG upregulated expression of genes encoding antioxidant proteins in lumber DRG, prevented loss of unmyelinated axons and inhibited degeneration of mitochondria in the sciatic nerve. In cultured primary neurons from cortex and DRG, GSSSG mitigated paclitaxel-induced superoxide production, loss of axonal mitochondria, and axonal degeneration. These results indicate that oral administration of GSSSG mitigates PIPN by preventing axonal degeneration and mitochondria damage in peripheral sensory nerves. The findings suggest that administration of GSSSG may be an approach to the treatment or prevention of PIPN and other peripheral neuropathies.

Antioxidant action of persulfides and polysulfides against free radical-mediated lipid peroxidation

Hydrogen sulfide, hydropersulfides, and hydropolysulfides have been revealed to play important physiological roles such as cell signaling and protection against oxidative stress, but the underlying mechanisms and dynamics of action remain elusive. It is generally accepted that these species act by two-electron redox mechanisms, while the involvement of one-electron redox chemistry has received less attention. In this study, the radical-scavenging activity of hydrogen persulfide, hydrogen polysulfides (HS_nH n = 2-4), and diallyl- or dialkyl-sulfides (RS_nR, n = 1-4) was measured. Furthermore, their antioxidant effects against free radical-mediated human plasma lipid peroxidation were assessed by measuring lipid hydroperoxides. It was found that disodium disulfide, trisulfide, and tetrasulfide acted as potent peroxyl radical scavengers, the rate constant for scavenging peroxyl radical being 3.5 × 10⁵, 4.0 × 10⁵, and 6.0 × 10⁵ M^-1 s^-1 in PBS pH 7.4 at 37 °C respectively and that they inhibited plasma lipid peroxidation efficiently, the efficacy is increased with the catenation number. Disodium tetrasulfide was 1.5 times as reactive as Trolox toward peroxyl radical and inhibited plasma lipid peroxidation more efficiently than ascorbate and Trolox. On the other hand, diallyl- and dialkyl-sulfides did not exert significant radical-scavenging activity, nor did they inhibit lipid peroxidation efficiently, except for diallyl tetrasulfide, which suppressed plasma lipid peroxidation, despite less significantly than disodium tetrasulfide. Collectively, this study shows that hydrogen persulfide and hydrogen polysulfides act as potent radical-scavenging antioxidants and that, in addition to two-electron redox mechanisms, one electron redox reaction may also play important role in the in vivo defense against deleterious oxidative stress.

Reactive sulfur species and their significance in health and disease

Reactive sulfur species (RSS) have been recognized in the last two decades as very important molecules in redox regulation. They are involved in metabolic processes and, in this way, they are responsible for maintenance of health. This review summarizes current information about the essential biological RSS, including H₂S, low molecular weight persulfides, protein persulfides as well as organic and inorganic polysulfides, their synthesis, catabolism and chemical reactivity. Moreover, the role of RSS disturbances in various pathologies including vascular diseases, chronic kidney diseases, diabetes mellitus Type 2, neurological diseases, obesity, chronic obstructive pulmonary disease and in the most current problem of COVID-19 is presented. The significance of RSS in aging is also mentioned. Finally, the possibilities of using the precursors of various forms of RSS for therapeutic purposes are discussed.

A Caveat When Using Alkyl Halides as Tagging Agents to Detect/Quantify Reactive Sulfur Species

Using alkyl halides to tag reactive sulfur species (RSSs) (H2S, per/polysulfide, and protein-SSH) is an extensively applied approach. The underlying supposition is that, as with thiols, RSS reacts with alkyl halides via a nucleophilic substitution reaction. We found that this supposition is facing a challenge. RSS also initiates a reductive dehalogenation reaction, which generates the reduced unloaded tag and oxidized RSS. Therefore, RSS content in bio-samples might be underestimated, and its species might not be precisely determined when using alkyl halide agents for its analysis. To calculate to the extent of this underestimation, further studies are still required.

Shining a light on SSP4: A comprehensive analysis and biological applications for the detection of sulfane sulfurs

Fluorescent probes are useful tools for the detection of sulfane sulfurs in biological systems. In this work, we report the development of SSP4, a widely used probe generated in our laboratory. We describe its evolution, preparation, and physical/chemical properties. Fluorescence analyses of SSP4 determined its high selectivity and sensitivity to sulfane sulfurs, even with the interfering presence of other species, such as amino acids and metal ions. Protocols for using SSP4 in a relatively quick and simple manner for the detection of persulfidated proteins, including papain, BSA, and GAPDH were developed. The method was then applied to human protein disulfide isomerase (PDI), leading to the discovery that persulfidation can occur at PDI's non-active site cysteines, and that PDI reductase activity is affected by sulfane sulfur treatment. Protocols for using SSP4 for the bioimaging of exogenous and endogenous sulfane sulfurs in different -cell lines were also established. These results should guide further applications of SSP4.

Thiol-based Oxidative Posttranslational Modifications (OxiPTMs) of Plant Proteins

The thiol group of cysteine (Cys) residues, often present in the active center of the protein, is of particular importance to protein function, which is significantly determined by the redox state of a protein's environment. Our knowledge of different thiol-based oxidative posttranslational modifications (oxiPTMs), which compete for specific protein thiol groups, has increased over the last 10 years. The principal oxiPTMs include S-sulfenylation, S-glutathionylation, S-nitrosation, persulfidation, S-cyanylation and S-acylation. The role of each oxiPTM depends on the redox cellular state, which in turn depends on cellular homeostasis under either optimal or stressful conditions. Under such conditions, the metabolism of molecules such as glutathione, NADPH (reduced nicotinamide adenine dinucleotide phosphate), nitric oxide, hydrogen sulfide and hydrogen peroxide can be altered, exacerbated and, consequently, outside the cell's control. This review provides a broad overview of these oxiPTMs under physiological and unfavorable conditions, which can regulate the function of target proteins.

Hydropersulfides (RSSH) Outperform Post-Conditioning and Other Reactive Sulfur Species in Limiting Ischemia-Reperfusion Injury in the Isolated Mouse Heart

Hydrogen sulfide (H₂S) exhibits protective effects in cardiovascular disease such as myocardial ischemia/reperfusion (I/R) injury, cardiac hypertrophy, and atherosclerosis. Despite these findings, its mechanism of action remains elusive. Recent studies suggest that H₂S can modulate protein activity through redox-based post-translational modifications of protein cysteine residues forming hydropersulfides (RSSH). Furthermore, emerging evidence indicates that reactive sulfur species, including RSSH and polysulfides, exhibit cardioprotective action. However, it is not clear yet whether there are any pharmacological differences in the use of H₂S vs. RSSH and/or polysulfides. This study aims to examine the differing cardioprotective effects of distinct reactive sulfur species (RSS) such as H₂S, RSSH, and dialkyl trisulfides (RSSSR) compared with canonical ischemic post-conditioning in the context of a Langendorff ex-vivo myocardial I/R injury model. For the first time, a side-by-side study has revealed that exogenous RSSH donation is a superior approach to maintain post-ischemic function and limit infarct size when compared with other RSS and mechanical post-conditioning. Our results also suggest that RSSH preserves mitochondrial respiration in H9c2 cardiomyocytes exposed to hypoxia-reoxygenation via inhibition of oxidative phosphorylation while preserving cell viability.

Expanding the Reactive Sulfur Metabolome: Intracellular and Efflux Measurements of Small Oxoacids of Sulfur (SOS) and H2S in Human Primary Vascular Cell Culture

Hydrogen sulfide (H2S) is an endogenous signaling molecule which is important for cardiovascular health, but its mechanism of action remains poorly understood. Here, we report measurements of H2S as well as its oxidized metabolites, termed small oxoacids of sulfur (SOS = HSOH and HOSOH), in four human primary vascular cell lines: smooth muscle and endothelial cells derived from both human arterial and coronary tissues. We use a methodology that targets small molecular weight sulfur species; mass spectrometric analysis allows for species quantification to report cellular concentrations based on an H2S calibration curve. The production of H2S and SOS is orders of magnitude higher in smooth muscle (nanomolar) as compared to endothelial cell lines (picomolar). In all the primary lines measured, the distributions of these three species were HOSOH >H2S > HSOH, with much higher SOS than seen previously in non-vascular cell lines. H2S and SOS were effluxed from smooth muscle cells in higher concentrations than endothelial cells. Aortic smooth muscle cells were used to examine changes under hypoxic growth conditions. Hypoxia caused notable increases in HSOH and ROS, which we attribute to enhanced sulfide quinone oxidase activity that results in reverse electron transport.