Whole tissue hydrogen sulfide concentrations are orders of magnitude lower than presently accepted values

Sodium thiosulfate: A donor or carrier signaling molecule for hydrogen sulfide?

Sodium thiosulfate has been used for decades in the treatment of calciphylaxis and cyanide detoxification, and has recently shown initial therapeutic promise in critical diseases such as neuronal ischemia, diabetes mellitus, heart failure and acute lung injury. However, the precise mechanism of sodium thiosulfate remains incompletely defined and sometimes contradictory. Although sodium thiosulfate has been widely accepted as a donor of hydrogen sulfide (H2S), emerging findings suggest that it is the executive signaling molecule for H2S and that its effects may not be dependent on H2S. This article presents an overview of the current understanding of sodium thiosulfate, including its synthesis, biological characteristics, and clinical applications of sodium thiosulfate, as well as the underlying mechanisms in vivo. We also discussed the interplay of sodium thiosulfate and H2S. Our review highlights sodium thiosulfate as a key player in sulfide signaling with the broad clinical potential for the future.

Bodipy-Based highly sensitive hydrogen sulfide fluorescent probe and its fluorescence imaging in cells and zebrafish

Hydrogen sulfide (H2S) is a crucial endogenous gasotransmitter that plays a role in various physiological and pathological processes. Therefore, accurate and rapid monitoring of H2S in organisms is highly significant for understanding the underlying pathological mechanisms and facilitating early diagnosis of related diseases. In this study, we developed a novel fluorescent probe, B-CHO-NO2, based on a bodipy fluorophore, which exhibits excellent sensitivity and selectivity towards H2S. The design of the probe exploits the nucleophilicity of H2S by introducing a formyl group as the ortho-participating moiety, significantly enhancing the reaction rate with H2S. In cellular and zebrafish models, the probe B-CHO-NO2 successfully achieved fluorescence imaging of endogenous and exogenous H2S. The development of probe B-CHO-NO2 provides a powerful tool for biological studies of H2S and diagnosis of related diseases.

Responsive β-Diketonate-europium(III) Complex-Based Probe for Time-Gated Luminescence Detection and Imaging of Hydrogen Sulfide In Vitro and In Vivo

As a crucial biological gasotransmitter, hydrogen sulfide (H2S) plays important roles in many pathological and physiological processes. Highly selective and sensitive detection of H2S is significant for the precise diagnosis and evaluation of diverse diseases. Nevertheless, challenges remain in view of the interference of autofluorescence in organisms and the stronger reactivity of H2S itself. Herein, we report the design and synthesis of a novel H2S-responsive β-diketonate-europium(III) complex-based probe, [Eu(DNB-Npketo)3(terpy)], for background-free time-gated luminescence (TGL) detection and imaging of H2S in autofluorescence-rich biological samples. The probe, consisting of a 2,4-dinitrobenzenesulfonyl (DNB) group coupled to a β-diketonate-europium(III) complex, shows almost no luminescence owing to the existence of intramolecular photoinduced electron transfer. The cleavage of the DNB group by a H2S-triggered reaction results in the recovery of the long-lived luminescence of the Eu3+ complex, allowing the detection of H2S in complicated biological samples to be performed in TGL mode. The probe showed a fast response, high specificity, and high sensitivity toward H2S, which enabled it to be successfully used for the quantitative TGL detection of H2S in tissue homogenates of mouse organs. Additionally, the low cytotoxicity of the probe allowed it to be further used for the TGL imaging of H2S in living cells and mice under different stimuli. All of the results suggested the potential of the probe for the investigation and diagnosis of H2S-related diseases.

The role of N-acetylcysteine in osteogenic microenvironment for bone tissue engineering

Bone defect is a common clinical symptom which can arise from various causes. Currently, bone tissue engineering has demonstrated positive therapeutic effects for bone defect repair by using seeding cells such as mesenchymal stem cells and precursor cells. N-acetylcysteine (NAC) is a stable, safe and highly bioavailable antioxidant that shows promising prospects in bone tissue engineering due to the ability to attenuate oxidative stress and enhance the osteogenic potential and immune regulatory function of cells. This review systematically introduces the antioxidant mechanism of NAC, analyzes the advancements in NAC-related research involving mesenchymal stem cells, precursor cells, innate immune cells and animal models, discusses its function using the classic oral microenvironment as an example, and places particular emphasis on the innovative applications of NAC-modified tissue engineering biomaterials. Finally, current limitations and future prospects are proposed, with the aim of providing inspiration for targeted readers in the field.

H2S Increases Blood Pressure via Activation of L-Type Calcium Channels with Mediation by HS• Generated from Reactions with Oxyhemoglobin

Although the gasotransmitter hydrogen sulfide (H2S) is well known for its vasodilatory effects, H2S also exhibits vasoconstricting properties. Herein, it is demonstrated that administration of H2S as intravenous sodium sulfide (Na2S) increased blood pressure in sheep and rats, and this effect persisted after H2S has disappeared from the blood. Inhibition of the L-type calcium channel (LTCC) diminished the hypertensive effects. Incubation of Na2S with whole blood, red blood cells, methemoglobin, or oxyhemoglobin produced a hypertensive product of H2S, which is not hydrogen thioperoxide, metHb-SH- complexes, per-/poly- sulfides, or thiolsulfate, but rather a labile intermediate. One-electron oxidation of H2S by oxyhemoglobin generated its redox cousin, sulfhydryl radical (HS•). Consistent with the role of HS• as the hypertensive intermediate, scavenging HS• inhibited Na2S-induced vasoconstriction and activation of LTCCs. In conclusion, H2S causes vasoconstriction that is dependent on the activation of LTCCs and generation of HS• by oxyhemoglobin.

A water quality assessment model involving novel fluorescence technology

The reasonable utilization of water resources and real-time monitoring of water pollution are the core tasks of current world hydrological and water conservancy work. Novel technologies and methods for monitoring water pollution are important means to ensure water health. However, the absence of intuitive and simple analysis methods for the assessment of regional pollution in large-scale water bodies has prevented scientists from quickly grasping the overall situation of water pollution. In this study, we propose a strategy based on the unique combination of fluorescence technology and simple kriging (SK) interpolation (FL-SK) for the first time. This strategy could present the relative magnitude and distribution of the physicochemical indicators of a whole natural lake intuitively and accurately. The unique FL-SK model firstly offers a simple and effective water quality method that provides the pollution index of different sampling points in lakes. The macroscopic evaluation of large-scale water bodies by the FL-SK model primarily relies on the fluorescence response of the RDM-TPE to the comprehensive indicators of the water body, as experimental results have revealed a good correlation between fluorescent responses and six normalized physicochemical indicators. Multiple linear regression and fluorescence response experiments on RDM-TPE indicate that to some extent, the fluorescence signals of the FL-SK model may originate from a certain type of sulfide in the water body. Pattern discovery could enable the analysis of pollution levels in other ecosystems and promote early pollution assessment in the future.

Sulfide oxidation promotes hypoxic angiogenesis and neovascularization

Angiogenic programming in the vascular endothelium is a tightly regulated process for maintaining tissue homeostasis and is activated in tissue injury and the tumor microenvironment. The metabolic basis of how gas signaling molecules regulate angiogenesis is elusive. Here, we report that hypoxic upregulation of ·NO in endothelial cells reprograms the transsulfuration pathway to increase biogenesis of hydrogen sulfide (H2S), a proangiogenic metabolite. However, decreased H2S oxidation due to sulfide quinone oxidoreductase (SQOR) deficiency synergizes with hypoxia, inducing a reductive shift and limiting endothelial proliferation that is attenuated by dissipation of the mitochondrial NADH pool. Tumor xenografts in whole-body (WBCreSqorfl/fl) and endothelial-specific (VE-cadherinCre-ERT2Sqorfl/fl) Sqor-knockout mice exhibit lower mass and angiogenesis than control mice. WBCreSqorfl/fl mice also exhibit decreased muscle angiogenesis following femoral artery ligation compared to control mice. Collectively, our data reveal the molecular intersections between H2S, O2 and ·NO metabolism and identify SQOR inhibition as a metabolic vulnerability for endothelial cell proliferation and neovascularization.

H2S preconditioning induces long-lived perturbations in O2 metabolism

Hydrogen sulfide exposure in moderate doses can induce profound but reversible hypometabolism in mammals. At a cellular level, H2S inhibits the electron transport chain (ETC), augments aerobic glycolysis, and glutamine-dependent carbon utilization via reductive carboxylation; however, the durability of these changes is unknown. We report that despite its volatility, H2S preconditioning increases P50(O2), the O2 pressure for half-maximal cellular respiration, and has pleiotropic effects on oxidative metabolism that persist up to 24 to 48 h later. Notably, cyanide, another complex IV inhibitor, does not induce this type of metabolic memory. Sulfide-mediated prolonged fractional inhibition of complex IV by H2S is modulated by sulfide quinone oxidoreductase, which commits sulfide to oxidative catabolism. Since induced hypometabolism can be beneficial in disease settings that involve insufficient or interrupted blood flow, our study has important implications for attenuating reperfusion-induced ischemic injury and/or prolonging the shelf life of biologics like platelets.

Listeria monocytogenes utilizes glutathione and limited inorganic sulfur compounds as sources of essential cysteine

Listeria monocytogenes (Lm) is a Gram-positive facultative intracellular pathogen that leads a biphasic lifecycle, transitioning its metabolism and selectively inducing virulence genes when it encounters mammalian hosts. Virulence gene expression is controlled by the master virulence regulator PrfA, which is allosterically activated by the host- and bacterially derived glutathione (GSH). The amino acid cysteine is the rate-limiting substrate for GSH synthesis in bacteria and is essential for bacterial growth. Unlike many bacteria, Lm is auxotrophic for cysteine and must import exogenous cysteine for growth and virulence. GSH is enriched in the host cytoplasm, and previous work suggests that Lm utilizes exogenous GSH for PrfA activation. Despite these observations, the import mechanism(s) for GSH remains elusive. Analysis of known GSH importers predicted a homologous importer in Lm comprised of the Ctp ABC transporter and the OppDF ATPases of the Opp oligopeptide importer. Here, we demonstrated that the Ctp complex is a high-affinity GSH/GSSG importer that is required for Lm growth at physiologically relevant concentrations. Furthermore, we demonstrated that OppDF is required for GSH/GSSG import in an Opp-independent manner. These data support a model where Ctp and OppDF form a unique complex for GSH/GSSG import that supports growth and pathogenesis. In addition, we show that Lm utilizes the inorganic sulfur sources thiosulfate and H2S for growth in a CysK-dependent manner in the absence of other cysteine sources. These findings suggest a pathoadaptive role for partial cysteine auxotrophy in Lm, where locally high GSH/GSSG or inorganic sulfur concentrations may signal arrival to distinct host niches.

Miniaturized Capsule System Toward Real-Time Electrochemical Detection of H2 S in the Gastrointestinal Tract

Hydrogen sulfide (H2 S) is a gaseous inflammatory mediator and important signaling molecule for maintaining gastrointestinal (GI) homeostasis. Excess intraluminal H2 S in the GI tract has been implicated in inflammatory bowel disease and neurodegenerative disorders; however, the role of H2 S in disease pathogenesis and progression is unclear. Herein, an electrochemical gas-sensing ingestible capsule is developed to enable real-time, wireless amperometric measurement of H2 S in GI conditions. A gold (Au) three-electrode sensor is modified with a Nafion solid-polymer electrolyte (Nafion-Au) to enhance selectivity toward H2 S in humid environments. The Nafion-Au sensor-integrated capsule shows a linear current response in H2 S concentration ranging from 0.21 to 4.5 ppm (R2 = 0.954) with a normalized sensitivity of 12.4% ppm-1 when evaluated in a benchtop setting. The sensor proves highly selective toward H2 S in the presence of known interferent gases, such as hydrogen (H2 ), with a selectivity ratio of H2 S:H2 = 1340, as well as toward methane (CH4 ) and carbon dioxide (CO2 ). The packaged capsule demonstrates reliable wireless communication through abdominal tissue analogues, comparable to GI dielectric properties. Also, an assessment of sensor drift and threshold-based notification is investigated, showing potential for in vivo application. Thus, the developed H2 S capsule platform provides an analytical tool to uncover the complex biology-modulating effects of intraluminal H2 S.

Hydrogen Sulfide (H2S)/Polysulfides (H2Sn) Signalling and TRPA1 Channels Modification on Sulfur Metabolism

Hydrogen sulfide (H2S) and polysulfides (H2Sn, n ≥ 2) produced by enzymes play a role as signalling molecules regulating neurotransmission, vascular tone, cytoprotection, inflammation, oxygen sensing, and energy formation. H2Sn, which have additional sulfur atoms to H2S, and other S-sulfurated molecules such as cysteine persulfide and S-sulfurated cysteine residues of proteins, are produced by enzymes including 3-mercaptopyruvate sulfurtransferase (3MST). H2Sn are also generated by the chemical interaction of H2S with NO, or to a lesser extent with H2O2. S-sulfuration (S-sulfhydration) has been proposed as a mode of action of H2S and H2Sn to regulate the activity of target molecules. Recently, we found that H2S/H2S2 regulate the release of neurotransmitters, such as GABA, glutamate, and D-serine, a co-agonist of N-methyl-D-aspartate (NMDA) receptors. H2S facilitates the induction of hippocampal long-term potentiation, a synaptic model of memory formation, by enhancing the activity of NMDA receptors, while H2S2 achieves this by activating transient receptor potential ankyrin 1 (TRPA1) channels in astrocytes, potentially leading to the activation of nearby neurons. The recent findings show the other aspects of TRPA1 channels-that is, the regulation of the levels of sulfur-containing molecules and their metabolizing enzymes. Disturbance of the signalling by H2S/H2Sn has been demonstrated to be involved in various diseases, including cognitive and psychiatric diseases. The physiological and pathophysiological roles of these molecules will be discussed.

An efficient dual-function fluorescent probe for sulfites and sulfides and its imaging application in cells

As gas signaling molecules in organisms, SO2 derivatives and H2S play crucial regulating roles in a series of physiological processes. Therefore, developing an assay that can accurately monitor the concentration of SO2 derivatives and H2S in cells is extremely important for the research and treatment of related illnesses. A bifunctional probe SN-F based on FRET mechanism for SO2 derivatives and H2S was designed. SN-F had a short response time to SO2 (2 min), excellent anti-interference capability and selectivity in the non-organic solvent system (pH = 7.4), which was suitable for the determination of SO2 derivatives in cells. SN-F had a wide linear range for H2S. Moreover, SN-F was applied in cell imaging successfully with high targeting ability to endoplasmic reticulum (ER) and could monitor endogenous and exogenous H2S in cells.

Hydrogen Sulfide Promotes Postnatal Cardiomyocyte Proliferation by Upregulating SIRT1 Signaling Pathway

Hydrogen sulfide (H2S) has been identified as a novel gasotransmitter and a substantial antioxidant that can activate various cellular targets to regulate physiological and pathological processes in mammals. However, under physiological conditions, it remains unclear whether it is involved in regulating cardiomyocyte (CM) proliferation during postnatal development in mice. This study mainly aimed to evaluate the role of H2S in postnatal CM proliferation and its regulating molecular mechanisms. We found that sodium hydrosulfide (NaHS, the most widely used H2S donor, 50-200 μM) increased neonatal mouse primary CM proliferation in a dose-dependent manner in vitro. Consistently, exogenous administration of H2S also promoted CM proliferation and increased the total number of CMs at postnatal 7 and 14 days in vivo. Moreover, we observed that the protein expression of SIRT1 was significantly upregulated after NaHS treatment. Inhibition of SIRT1 with EX-527 or si-SIRT1 decreased CM proliferation, while enhancement of the activation of SIRT1 with SRT1720 promoted CM proliferation. Meanwhile, pharmacological and genetic blocking of SIRT1 repressed the effect of NaHS on CM proliferation. Taken together, these results reveal that H2S plays a promotional role in proliferation of CMs in vivo and in vitro and SIRT1 is required for H2S-mediated CM proliferation, which indicates that H2S may be a potential modulator for heart development in postnatal time window.

Metabolic control analysis of the transsulfuration pathway and the compensatory role of the cysteine transport in Trypanosoma cruzi

Trypanosoma cruzi is the causal agent of American Trypanosomiasis or Chagas Disease in humans. The current drugs for its treatment benznidazole and nifurtimox have inconveniences of toxicity and efficacy; therefore, the search for new therapies continues. Validation through genetic strategies of new drug targets against the parasite metabolism have identified numerous essential genes. Target validation can be further narrowed by applying Metabolic Control Analysis (MCA) to determine the flux control coefficients of the pathway enzymes. That coefficient is a quantitative value that represents the degree in which an enzyme/transporter determines the flux of a metabolic pathway; those with the highest coefficients can be promising drug targets. Previous studies have demonstrated that cysteine (Cys) is a key precursor for the synthesis of trypanothione, the main antioxidant metabolite in the parasite. In this research, MCA was applied in an ex vivo system to the enzymes of the reverse transsulfuration pathway (RTP) for Cys synthesis composed by cystathionine beta synthase (CBS) and cystathionine gamma lyase (CGL). The results indicated that CGL has 90% of the control of the pathway flux. Inhibition of CGL with propargylglycine (PAG) decreased the levels of Cys and trypanothione and depleted those of glutathione in epimastigotes (proliferative stage in the insect vector); these metabolite changes were prevented by supplementing with Cys, suggesting a compensatory role of the Cys transport (CysT). Indeed, Cys supplementation (but not PAG treatment) increased the activity of the CysT in epimastigotes whereas in trypomastigotes (infective stage in mammals) CysT was increased when they were incubated with PAG. Our results suggested that CGL could be a potential drug target given its high control on the RTP flux and its effects on the parasite antioxidant defense. However, the redundant Cys supply pathways in the parasite may require inhibition of the CysT as well. Our findings also suggest differential responses of the Cys supply pathways in different parasite stages.

Chemistry of Hydrogen Sulfide-Pathological and Physiological Functions in Mammalian Cells

Hydrogen sulfide (H2S) was recognized as a gaseous signaling molecule, similar to nitric oxide (-NO) and carbon monoxide (CO). The aim of this review is to provide an overview of the formation of hydrogen sulfide (H2S) in the human body. H2S is synthesized by enzymatic processes involving cysteine and several enzymes, including cystathionine-β-synthase (CBS), cystathionine-γ-lyase (CSE), cysteine aminotransferase (CAT), 3-mercaptopyruvate sulfurtransferase (3MST) and D-amino acid oxidase (DAO). The physiological and pathological effects of hydrogen sulfide (H2S) on various systems in the human body have led to extensive research efforts to develop appropriate methods to deliver H2S under conditions that mimic physiological settings and respond to various stimuli. These functions span a wide spectrum, ranging from effects on the endocrine system and cellular lifespan to protection of liver and kidney function. The exact physiological and hazardous thresholds of hydrogen sulfide (H2S) in the human body are currently not well understood and need to be researched in depth. This article provides an overview of the physiological significance of H2S in the human body. It highlights the various sources of H2S production in different situations and examines existing techniques for detecting this gas.

How super is supersulfide?: Reconsidering persulfide reactivity in cellular biology

In an attempt to understand the cellular mechanisms of H2S signalling, recent research has focused on supersulfide (i.e., alkyl and inorganic hydropersulfide) formation and subsequent reactivity. While our understanding of supersulfides in biology has rapidly advanced, there are some chemical features of this unique functional group that require re-evaluation. Persulfides, such as glutathione hydropersulfide, have been called "supersulfide" as it is assumed that the alkyl hydropersulfide (RSSH) functional group is a superior nucleophile compared to the corresponding thiol (RSH) due to the alpha effect. However, recent quantum mechanical calculations and experimental data show that persulfides are not "super" nucleophiles, but rather potent electrophiles in cellular biology. It is proposed here that persulfides, via their electrophilic signalling effects, induces a cellular hormesis effect, which may explain the observed effects of altered RSSH production. Therefore, the electrophilic and thiol oxidant properties of persulfides should considered in cellular biology.

Nitric oxide and thiols: Chemical biology, signalling paradigms and vascular therapeutic potential

Nitric oxide (• NO) interactions with biological thiols play crucial, but incompletely determined, roles in vascular signalling and other biological processes. Here, we highlight two recently proposed signalling paradigms: (1) the formation of a vasodilating labile nitrosyl ferrous haem (NO-ferrohaem) facilitated by thiols via thiyl radical generation and (2) polysulfides/persulfides and their interaction with • NO. We also describe the specific (bio)chemical routes in which • NO and thiols react to form S-nitrosothiols, a broad class of small molecules, and protein post-translational modifications that can influence protein function through catalytic site or allosteric structural changes. S-Nitrosothiol formation depends upon cellular conditions, but critically, an appropriate oxidant for either the thiol (yielding a thiyl radical) or • NO (yielding a nitrosonium [NO+ ]-donating species) is required. We examine the roles of these collective • NO/thiol species in vascular signalling and their cardiovascular therapeutic potential.

Surface Functionalised Optical Fibre for Detection of Hydrogen Sulphide

Dysregulated production of hydrogen sulphide in the human body has been associated with various diseases including cancer, underlining the importance of accurate detection of this molecule. Here, we report the detection of hydrogen sulphide using fluorescence-emission enhancement of two 1,8-naphthalimide fluorescent probes with an azide moiety in position 4. One probe, serving as a control, featured a methoxyethyl moiety through the imide to evaluate its effectiveness for hydrogen sulphide detection, while the other probe was modified with (3-aminopropyl)triethoxysilane (APTES) to enable direct covalent attachment to an optical fibre tip. We coated the optical fibre tip relatively homogeneously with the APTES-azide fluorophore, as confirmed via x-ray photoelectron spectroscopy (XPS). The absorption and fluorescence responses of the control fluorophore free in PBS were analysed using UV-Vis and fluorescence spectrophotometry, while the fluorescence emission of the APTES-azide fluorophore-coated optical fibres was examined using a simple, low-cost optical fibre-based setup. Both fluorescent probes exhibited a significant increase (more than double the initial value) in fluorescence emission upon the addition of HS- when excited with 405 nm. However, the fluorescence enhancement of the coated optical fibres demonstrated a much faster response time of 2 min (time for the fluorescence intensity to reach 90% of its maximum value) compared to the control fluorophore in solution (30 min). Additionally, the temporal evolution of fluorescence intensity of the fluorophore coated on the optical fibre was studied at two pH values (7.4 and 6.4), demonstrating a reasonable overlap and confirming the compound pH insensitivity within this range. The promising results from this study indicate the potential for developing an optical fibre-based sensing system for HS- detection using the synthesised fluorophore, which could have significant applications in health monitoring and disease detection.

H 2 S preconditioning induces long-lived perturbations in O 2 metabolism

Hydrogen sulfide exposure in moderate doses can induce profound but reversible hypometabolism in mammals. At a cellular level, H 2 S inhibits the electron transport chain (ETC), augments aerobic glycolysis, and glutamine-dependent carbon utilization via reductive carboxylation; however, the durability of these changes is unknown. We report that despite its volatility, H 2 S preconditioning increases P 50(O2) , the O 2 pressure for half maximal cellular respiration, and has pleiotropic effects on oxidative metabolism that persist up to 24-48 h later. Notably, cyanide, another complex IV inhibitor, does not induce this type of metabolic memory. Sulfide-mediated prolonged fractional inhibition of complex IV by H 2 S is modulated by sulfide quinone oxidoreductase, which commits sulfide to oxidative catabolism. Since induced hypometabolism can be beneficial in disease settings that involve insufficient or interrupted blood flow, our study has important implications for attenuating reperfusion-induced ischemic injury, and/or prolonging shelf life of biologics like platelets.

Listeria monocytogenes utilizes glutathione and limited inorganic sulfur compounds as a source of essential L-cysteine

Listeria monocytogenes ( Lm ) is a Gram-positive facultative intracellular pathogen that leads a biphasic lifecycle, transitioning its metabolism and selectively inducing virulence genes when it encounters mammalian hosts. Virulence gene expression is controlled by the master virulence regulator PrfA, which is allosterically activated by host- and bacterially-derived glutathione (GSH). The amino acid L-cysteine is the rate-limiting substrate for GSH synthesis in bacteria and is essential for bacterial growth. Unlike many bacteria, Lm is auxotrophic for L-cysteine and must import exogenous cysteine for growth and virulence. GSH is enriched in the host cytoplasm, and previous work suggests that Lm utilizes exogenous GSH for PrfA activation. Despite these observations, the import mechanism(s) for GSH remains elusive. Analysis of known GSH importers predicted a homologous importer in Lm comprised of the Ctp ABC transporter and the OppDF ATPases of the Opp oligopeptide importer. Here, we demonstrated that the Ctp complex is a high-affinity GSH/GSSG importer that is required for Lm growth at physiologically relevant concentrations. Further, we demonstrated that OppDF are required for GSH/GSSG import in an Opp-independent manner. These data support a model where Ctp and OppDF form a unique complex for GSH/GSSG import that supports growth and pathogenesis. Additionally, we show that Lm utilizes the inorganic sulfur sources thiosulfate and H 2 S for growth in a CysK-dependent manner in the absence of other L-cysteine sources. These findings suggest a pathoadaptive role for partial cysteine auxotrophy in Lm , where locally high GSH/GSSG or inorganic sulfur concentrations may signal arrival to distinct host niches.

N-Acetylcysteine and Its Immunomodulatory Properties in Humans and Domesticated Animals

N-acetylcysteine (NAC), an acetylated derivative of the amino acid L-cysteine, has been widely used as a mucolytic agent and antidote for acetaminophen overdose since the 1960s and the 1980s, respectively. NAC possesses antioxidant, cytoprotective, anti-inflammatory, antimicrobial, and mucolytic properties, making it a promising therapeutic agent for a wide range of diseases in both humans and domesticated animals. Oxidative stress and inflammation play a major role in the onset and progression of all these diseases. NAC's primary role is to replenish glutathione (GSH) stores, the master antioxidant in all tissues; however, it can also reduce levels of pro-inflammatory tumor necrosis factor-alpha (TNF-∝) and interleukins (IL-6 and IL-1β), inhibit the formation of microbial biofilms and destroy biofilms, and break down disulfide bonds between mucin molecules. Many experimental studies have been conducted on the use of NAC to address a wide range of pathological conditions; however, its effectiveness in clinical trials remains limited and studies often have conflicting results. The purpose of this review is to provide a concise overview of promising NAC usages for the treatment of different human and domestic animal disorders.

The role of hydrogen sulfide in the retina

The discovery of the hydrogen sulfide (H2S) and the transsulfuration pathway (TSP) responsible for its synthesis in the mammalian retina has highlighted this molecule's wide range of physiological processes that influence cellular signaling, redox homeostasis, and cellular metabolism. The multi-level regulatory program that influences H2S levels in the retina depends on the relative expression and activity of TSP enzymes, which regulate the abundance of competitive substrates that support or abrogate H2S synthesis. In addition, and apart from TSP, intracellular H2S levels are regulated by mitochondrial sulfide oxidizing pathways. Retinal layers natively express differing levels of TSP enzymes, which highlight the differences in the metabolite and substrate requirement. Recent studies indicate that these systems are susceptible to pathophysiologies affecting the retina. Dysregulation at any level can upset the balance of redox and signaling processes and possibly upset oxidative stress, apoptotic signaling, ion channels, and immune response within this sensitive tissue. H2S donors are a potential therapeutic in such cases and have been demonstrated to bridge the gap, positively impacting the damaged retina. Here, we review the recent findings of H2S, how its multi-level regulation impacts the retina, and how its dysregulation is implicated in retinal pathologies.

Sulfur-Element containing metabolic pathways in human health and crosstalk with the microbiome

In humans, methionine derived from dietary proteins is necessary for cellular homeostasis and regeneration of sulfur containing pathways, which produce inorganic sulfur species (ISS) along with essential organic sulfur compounds (OSC). In recent years, inorganic sulfur species have gained attention as key players in the crosstalk of human health and the gut microbiome. Endogenously, ISS includes hydrogen sulfide (H2S), sulfite (SO32-), thiosulfate (S2O32-), and sulfate (SO42-), which are produced by enzymes in the transsulfuration and sulfur oxidation pathways. Additionally, sulfate-reducing bacteria (SRB) in the gut lumen are notable H2S producers which can contribute to the ISS pools of the human host. In this review, we will focus on the systemic effects of sulfur in biological pathways, describe the contrasting mechanisms of sulfurylation versus phosphorylation on the hydroxyl of serine/threonine and tyrosine residues of proteins in post-translational modifications, and the role of the gut microbiome in human sulfur metabolism.

Clinical Applications for Gasotransmitters in the Cardiovascular System: Are We There Yet?

Ischemia is the underlying mechanism in a wide variety of acute and persistent pathologies. As such, understanding the fine intracellular events occurring during (and after) the restriction of blood supply is pivotal to improving the outcomes in clinical settings. Among others, gaseous signaling molecules constitutively produced by mammalian cells (gasotransmitters) have been shown to be of potential interest for clinical treatment of ischemia/reperfusion injury. Nitric oxide (NO and its sibling, HNO), hydrogen sulfide (H2S), and carbon monoxide (CO) have long been proven to be cytoprotective in basic science experiments, and they are now awaiting confirmation with clinical trials. The aim of this work is to review the literature and the clinical trials database to address the state of development of potential therapeutic applications for NO, H2S, and CO and the clinical scenarios where they are more promising.

Synthesis of Sulfur-35-Labeled Trisulfides and GYY-4137 as Donors of Radioactive Hydrogen Sulfide

Hydrogen sulfide has emerged as a key gasotransmitter in humans and in plants, and the addition of exogenous hydrogen sulfide has many beneficial effects in vivo and in vitro. A challenge in investigating the effect of exogenous hydrogen sulfide is tracking the location of exogenous hydrogen sulfide on an organism and cellular level. In this article, we report the synthesis of three key chemicals (cysteine trisulfide, glutathione trisulfide, and GYY-4137) that release radiolabeled 35S as hydrogen sulfide. The synthesis started with the reduction of Na235SO4 mixed with Na2SO4 to generate hydrogen sulfide gas that was trapped with aq NaOH to yield radiolabeled Na2S. The Na2S was converted in one step to GYY-4137 at 65% yield. It was also converted to bis(tributyltin) sulfide that readily reacted with N-bromophthalimide to yield a monosulfur transfer reagent. Trisulfides were synthesized by reaction with the monosulfur transfer reagent and the corresponding thiols. The levels of radioactivity of the final products could be varied on a per gram basis to alter the radioactivity for applications that require different loadings of hydrogen sulfide donors.

A growth chamber for chronic exposure of mammalian cells to H2S

H2S is a redox-active signaling molecule that exerts an array of cellular and physiological effects. While intracellular H2S concentrations are estimated to be in the low nanomolar range, intestinal luminal concentrations can be significantly higher due to microbial metabolism. Studies assessing H2S effects are typically conducted with a bolus treatment with sulfide salts or slow releasing sulfide donors, which are limited by the volatility of H2S, and by potential off-target effects of the donor molecules. To address these limitations, we describe the design and performance of a mammalian cell culture incubator for sustained exposure to 20-500 ppm H2S (corresponding to a dissolved sulfide concentrations of ∼4-120 μM in the cell culture medium). We report that colorectal adenocarcinoma HT29 cells tolerate prolonged exposure to H2S with no effect on cell viability after 24 h although ≥50 ppm H2S (∼10 μM) restricts cell proliferation. Even the lowest concentration of H2S used in this study (i.e. ∼4 μM) significantly enhanced glucose consumption and lactate production, revealing a much lower threshold for impacting cellular energy metabolism and activating aerobic glycolysis than has been previously appreciated from studies with bolus H2S treatment regimens.

Hydrogen sulfide functions as a micro-modulator bound at the copper active site of Cu/Zn-SOD to regulate the catalytic activity of the enzyme

The present study examines whether there is a mechanism beyond the current concept of post-translational modifications to regulate the function of a protein. A small gas molecule, hydrogen sulfide (H₂S), was found to bind at active-site copper of Cu/Zn-SOD using a series of methods including radiolabeled binding assay, X-ray absorption near-edge structure (XANES), and crystallography. Such an H₂S binding enhanced the electrostatic forces to guide the negatively charged substrate superoxide radicals to the catalytic copper ion, changed the geometry and energy of the frontier molecular orbitals of the active site, and subsequently facilitated the transfer of an electron from the superoxide radical to the catalytic copper ion and the breakage of the copper-His61 bridge. The physiological relevance of such an H₂S effect was also examined in both in vitro and in vivo models where the cardioprotective effects of H₂S were dependent on Cu/Zn-SOD.

Characterization of Glutathione Dithiophosphates as Long-Acting H2S Donors

Considering the important cytoprotective and signaling roles but relatively narrow therapeutic index of hydrogen sulfide (H₂S), advanced H₂S donors are required to achieve a therapeutic effect. In this study, we proposed glutathione dithiophosphates as new combination donors of H₂S and glutathione. The kinetics of H₂S formation in dithiophosphate solutions suggested a continuous H₂S release by the donors, which was higher for the dithiophosphate of reduced glutathione than oxidized glutathione. The compounds, unlike NaHS, inhibited the proliferation of C2C12 myoblasts at submillimolar concentrations due to an efficient increase in intracellular H₂S. The H₂S donors more profoundly affected reactive oxygen species and reduced glutathione levels in C2C12 myocytes, in which these parameters were elevated compared to myoblasts. Oxidized glutathione dithiophosphate as well as control donors exerted antioxidant action toward myocytes, whereas the effect of reduced glutathione dithiophosphate at (sub-)micromolar concentrations was rather modulating. This dithiophosphate showed an enhanced negative inotropic effect mediated by H₂S upon contraction of the atrial myocardium, furthermore, its activity was prolonged and reluctant for washing. These findings identify glutathione dithiophosphates as redox-modulating H₂S donors with long-acting profile, which are of interest for further pharmacological investigation.

Defining the elusive oncogenic role of the methyltransferase TMT1B

Methyltransferases are enzymes fundamental to a wide range of normal biological activities that can become dysregulated during oncogenesis. For instance, the recent description of the methyltransferase-like (METTL) family of enzymes, has demonstrated the importance of the N⁶-adenosine-methyltransferase (m⁶A) modification in transcripts in the context of malignant transformation. Because of their importance, numerous METTL family members have been biochemically characterized to identify their cellular substrates, however some members such as METTL7B, recently renamed TMT1B and which is the subject of this review, remain enigmatic. First identified in the stacked Golgi, TMT1B is also localized to the endoplasmic reticulum as well as lipid droplets and has been reported as being upregulated in a wide range of cancer types including lung cancer, gliomas, and leukemia. Interestingly, despite evidence that TMT1B might act on protein substrates, it has also been shown to act on small molecule alkyl thiol substrates such as hydrogen sulfide, and its loss has been found to affect cellular proliferation and migration. Here we review the current evidence for TMT1B's activity, localization, and potential biological role in the context of both normal and cancerous cell types.

The Ying and Yang of Hydrogen Sulfide as a Paracrine/Autocrine Agent in Neurodegeneration: Focus on Amyotrophic Lateral Sclerosis

Ever since its presence was reported in the brain, the nature and role of hydrogen sulfide (H2S) in the Central Nervous System (CNS) have changed. Consequently, H2S has been elected as the third gas transmitter, along with carbon monoxide and nitric oxide, and a number of studies have focused on its neuromodulatory and protectant functions in physiological conditions. The research on H2S has highlighted its many facets in the periphery and in the CNS, and its role as a double-faced compound, switching from protective to toxic depending on its concentration. In this review, we will focus on the bell-shaped nature of H2S as an angiogenic factor and as a molecule released by glial cells (mainly astrocytes) and non-neuronal cells acting on the surrounding environment (paracrine) or on the releasing cells themselves (autocrine). Finally, we will discuss its role in Amyotrophic Lateral Sclerosis, a paradigm of a neurodegenerative disease.

A Quencher-Based Blood-Autofluorescence-Suppression Strategy Enables the Quantification of Trace Analytes in Whole Blood

Precise quantification of trace components in whole blood via fluorescence is of great significance. However, the applicability of current fluorescent probes in whole blood is largely hindered by the strong blood autofluorescence. Here, we proposed a blood autofluorescence-suppressed sensing strategy to develop an activable fluorescent probe for quantification of trace analyte in whole blood. Based on inner filter effect, by screening fluorophores whose absorption overlapped with the emission of blood, a redshift BODIPY quencher with an absorption wavelength ranging from 600-700 nm was selected for its superior quenching efficiency and high brightness. Two 7-nitrobenzo[c] [1,2,5] oxadiazole ether groups were introduced onto the BODIPY skeleton for quenching its fluorescence and the response of H2 S, a gas signal molecule that can hardly be quantified because of its low concentration in whole blood. Such detection system shows a pretty low background signal and high signal-to-back ratio, the probe thus achieved the accurate quantification of endogenous H2 S in 20-fold dilution of whole blood samples, which is the first attempt of quantifying endogenous H2 S in whole blood. Moreover, this autofluorescence-suppressed sensing strategy could be expanded to other trace analytes detection in whole blood, which may accelerate the application of fluorescent probes in clinical blood test.

From Gasotransmitter to Immunomodulator: The Emerging Role of Hydrogen Sulfide in Macrophage Biology

Hydrogen sulfide (H₂S) has been increasingly recognized as a crucial inflammatory mediator in immune cells, particularly macrophages, due to its direct and indirect effects on cellular signaling, redox homeostasis, and energy metabolism. The intricate regulation of endogenous H₂S production and metabolism involves the coordination of transsulfuration pathway (TSP) enzymes and sulfide oxidizing enzymes, with TSP's role at the intersection of the methionine pathway and glutathione synthesis reactions. Additionally, H₂S oxidation mediated by sulfide quinone oxidoreductase (SQR) in mammalian cells may partially control cellular concentrations of this gasotransmitter to induce signaling. H₂S is hypothesized to signal through the posttranslational modification known as persulfidation, with recent research highlighting the significance of reactive polysulfides, a derivative of sulfide metabolism. Overall, sulfides have been identified as having promising therapeutic potential to alleviate proinflammatory macrophage phenotypes, which are linked to the exacerbation of disease outcomes in various inflammatory conditions. H₂S is now acknowledged to have a significant influence on cellular energy metabolism by affecting the redox environment, gene expression, and transcription factor activity, resulting in changes to both mitochondrial and cytosolic energy metabolism processes. This review covers recent discoveries pertaining to the involvement of H₂S in macrophage cellular energy metabolism and redox regulation, and the potential implications for the inflammatory response of these cells in the broader framework of inflammatory diseases.

Sulfide oxidation promotes hypoxic angiogenesis and neovascularization

Angiogenic programming in the vascular endothelium is a tightly regulated process to maintain tissue homeostasis and is activated in tissue injury and the tumor microenvironment. The metabolic basis of how gas signaling molecules regulate angiogenesis is elusive. Herein, we report that hypoxic upregulation of NO synthesis in endothelial cells reprograms the transsulfuration pathway and increases H 2 S biogenesis. Furthermore, H 2 S oxidation by mitochondrial sulfide quinone oxidoreductase (SQOR) rather than downstream persulfides, synergizes with hypoxia to induce a reductive shift, limiting endothelial cell proliferation that is attenuated by dissipation of the mitochondrial NADH pool. Tumor xenografts in whole-body WB Cre SQOR fl/fl knockout mice exhibit lower mass and reduced angiogenesis compared to SQOR fl/fl controls. WB Cre SQOR fl/fl mice also exhibit reduced muscle angiogenesis following femoral artery ligation, compared to controls. Collectively, our data reveal the molecular intersections between H 2 S, O 2 and NO metabolism and identify SQOR inhibition as a metabolic vulnerability for endothelial cell proliferation and neovascularization.

Highlights

Hypoxic induction of •NO in endothelial cells inhibits CBS and switches CTH reaction specificity Hypoxic interruption of the canonical transsulfuration pathway promotes H 2 S synthesis Synergizing with hypoxia, SQOR deficiency induces a reductive shift in the ETC and restricts proliferationSQOR KO mice exhibit lower neovascularization in tumor xenograft and hind limb ischemia models.

Hydrogen sulfide and its donors for the treatment of cerebral ischaemia-reperfusion injury: A comprehensive review

As an endogenous gas signalling molecule, hydrogen sulfide (H₂S) is frequently present in a variety of mammals and plays a significant role in the cardiovascular and nervous systems. Reactive oxygen species (ROS) are produced in large quantities as a result of cerebral ischaemia-reperfusion, which is a very serious class of cerebrovascular diseases. ROS cause oxidative stress and induce specific gene expression that results in apoptosis. H₂S reduces cerebral ischaemia-reperfusion-induced secondary injury via anti-oxidative stress injury, suppression of the inflammatory response, inhibition of apoptosis, attenuation of cerebrovascular endothelial cell injury, modulation of autophagy, and antagonism of P2X7 receptors, and it plays an important biological role in other cerebral ischaemic injury events. Despite the many limitations of the hydrogen sulfide therapy delivery strategy and the difficulty in controlling the ideal concentration, relevant experimental evidence demonstrating that H₂S plays an excellent neuroprotective role in cerebral ischaemia-reperfusion injury (CIRI). This paper examines the synthesis and metabolism of the gas molecule H₂S in the brain as well as the molecular mechanisms of H₂S donors in cerebral ischaemia-reperfusion injury and possibly other unknown biological functions. With the active development in this field, it is expected that this review will assist researchers in their search for the potential value of hydrogen sulfide and provide new ideas for preclinical trials of exogenous H₂S.

Protein persulfidation: Rewiring the hydrogen sulfide signaling in cell stress response

The past few decades have witnessed significant progress in the discovery of hydrogen sulfide (H₂S) as a ubiquitous gaseous signaling molecule in mammalian physiology, akin to nitric oxide and carbon monoxide. As the third gasotransmitter, H₂S is now known to exert a wide range of physiological and cytoprotective functions in the biological systems. However, endogenous H₂S concentrations are usually low, and its potential biologic mechanisms responsible have not yet been fully clarified. Recently, a growing body of evidence has demonstrated that protein persulfidation, a posttranslational modification of cysteine residues (RSH) to persulfides (RSSH) elicited by H₂S, is a fundamental mechanism of H₂S-mediated signaling pathways. Persulfidation, as a biological switch for protein function, plays an important role in the maintenance of cell homeostasis in response to various internal and external stress stimuli and is also implicated in numerous diseases, such as cardiovascular and neurodegenerative diseases and cancer. In this review, the biological significance of protein persulfidation by H₂S in cell stress response is reviewed providing a framework for understanding the multifaceted roles of H₂S. A mechanism-guided perspective can help open novel avenues for the exploitation of therapeutics based on H₂S-induced persulfidation in the context of diseases.

Sol-Gel Dipping Devices for H2S Visualization

In this contribution we report the synthesis and full characterization, via a combination of different spectroscopies (e.g., ¹H NMR, UV-vis, fluorescence, MALDI), of a new family of fluorescent zinc complexes with extended π-conjugated systems, with the final aim of setting up higher performance H₂S sensing devices. Immobilization of the systems into a polymeric matrix for use in a solid-state portable device was also explored. The results provided proof-of-principle that the title complexes could be successfully implemented in a fast, simple and cost-effective H₂S sensing device.

Hydrogen sulfide and its donors: Novel antitumor and antimetastatic agents for liver cancer

Hepatocellular carcinoma (HCC) is the sixth most frequent human cancer and the world's third most significant cause of cancer mortality. HCC treatment has recently improved, but its mortality continues to increase worldwide due to its extremely complicated and heterogeneous genetic abnormalities. After nitric oxide (NO) and carbon monoxide (CO), the third gas signaling molecule discovered is hydrogen sulfide (H₂S), which has long been thought to be a toxic gas. However, numerous studies have proven that H₂S plays many pathophysiological roles in mammals. Endogenous or exogenous H₂S can decrease cell proliferation, promote apoptosis, block cell cycle, invasion and migration through various cellular signaling pathways. This review analyzes and discusses the recent literature on the function and molecular mechanism of H₂S and H₂S donors in HCC, so as to provide convenience for the scientific research and clinical application of H₂S in the treatment of liver cancer.

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.

H2S Sensors: Synthesis, Optical Properties, and Selected Biomedical Applications under Visible and NIR Light

Hydrogen sulfide (H₂S) is an essential signaling gas within the cell, and its endogenous levels are correlated with various health diseases such as Alzheimer's disease, diabetes, Down's syndrome, and cardiovascular disease. Because it plays such diverse biological functions, being able to detect H₂S quickly and accurately in vivo is an area of heightened scientific interest. Using probes that fluoresce in the near-infrared (NIR) region is an effective and convenient method of detecting H₂S. This approach allows for compounds of high sensitivity and selectivity to be developed while minimizing cytotoxicity. Herein, we report a review on the synthesis, mechanisms, optical properties, and selected biomedical applications of H₂S sensors.

Variability in Background Urinary Concentrations of the Hydrogen Sulfide Biomarker Thiosulfate

Hydrogen sulfide is a toxic gas at high concentrations but has recently attracted attention as a naturally produced gaseous signaling molecule in various tissues of the human body, playing key physiological roles at low nanomolar concentrations. This has wide implications for chronic exposure to this gas in air at low levels far below toxicity. Thiosulfate is the currently used biomarker for exposure to hydrogen sulfide via inhalation but has been mainly employed for acute exposure. It is unknown how background thiosulfate concentrations vary on an intraindividual and interindividual basis in humans at normal ambient hydrogen sulfide levels (<1 μg m^-3), which is key for the interpretation of its levels as biomarker for low-level hydrogen sulfide exposure. In the current work, the variability in thiosulfate urinary excretion in a total of 168 urine samples collected from eight volunteers over a period of 8 weeks was investigated. The determination of thiosulfate in urine was carried out by UHPLC-MS/MS. The total average concentration ± SD was 16 ± 6 μM (n = 168). Average urinary thiosulfate concentrations in the studied volunteers were within the range of 10-20 μM, but it was found that urinary thiosulfate can show significant day-to-day and week-to-week variability in some individuals (up to 10-fold), despite adjusting for urine specific gravity. In light of the presented variability data and previous studies about the lack of consistent response of thiosulfate to low levels of hydrogen sulfide inhalation exposure, and based on a review of the biochemistry of the production of thiosulfate and its various biological sources, it can be argued that thiosulfate might not be suitable as a biomarker for chronic environmental exposure to low levels of hydrogen sulfide via inhalation.

The role of sulfur compounds in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a common respiratory disease that brings about great social and economic burden, with oxidative stress and inflammation affecting the whole disease progress. Sulfur compounds such as hydrogen sulfide (H₂S), thiols, and persulfides/polysulfides have intrinsic antioxidant and anti-inflammatory ability, which is engaged in the pathophysiological process of COPD. Hydrogen sulfide mainly exhibits its function by S-sulfidation of the cysteine residue of the targeted proteins. It also interacts with nitric oxide and acts as a potential biomarker for the COPD phenotype. Thiols’ redox buffer such as the glutathione redox couple is a major non-enzymatic redox buffer reflecting the oxidative stress in the organism. The disturbance of redox buffers was often detected in patients with COPD, and redressing the balance could delay COPD exacerbation. Sulfane sulfur refers to a divalent sulfur atom bonded with another sulfur atom. Among them, persulfides and polysulfides have an evolutionarily conserved modification with antiaging effects. Sulfur compounds and their relative signaling pathways are also associated with the development of comorbidities in COPD. Synthetic compounds which can release H₂S and persulfides in the organism have gradually been developed. Naturally extracted sulfur compounds with pharmacological effects also aroused great interest. This study discussed the biological functions and mechanisms of sulfur compounds in regulating COPD and its comorbidities.

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.

Fluorescent detection of hydrogen sulfide (H2S) through the formation of pyrene excimers enhances H2S quantification in biochemical systems

Hydrogen sulfide (H₂S) is produced endogenously by several enzymatic pathways and modulates physiological functions in mammals. Quantification of H₂S in biochemical systems remains challenging because of the presence of interferents with similar reactivity, particularly thiols. Herein, we present a new quantification method based on the formation of pyrene excimers in solution. We synthesized the probe 2-(maleimido)ethyl 4-pyrenylbutanoate (MEPB) and determined that MEPB reacted with H₂S in a two-step reaction to yield the thioether-linked dimer (MEPB)₂S, which formed excimers upon excitation, with a broad peak of fluorescence emission centered at 480 nm. In contrast, we found that the products formed with thiols showed peaks at 378 and 398 nm. The difference in emission between the products prevented the interference. Furthermore, we showed that the excimer fluorescence signal yielded a linear response to H₂S, with a limit of detection of 54 nM in a fluorometer. Our quantification method with MEPB was successfully applied to follow the reaction of H₂S with glutathione disulfide and to quantify the production of H₂S from cysteine by Escherichia coli. In conclusion, this method represents an addition to the toolkit of biochemists to quantify H₂S specifically and sensitively in biochemical systems.

A Whiff of Sulfur: One Wind a Day Keeps the Doctor Away

Reactive Sulfur Species (RSS), such as allicin from garlic or sulforaphane from broccoli, are fre-quently associated with biological activities and possible health benefits in animals and humans. Among these Organic Sulfur Compounds (OSCs) found in many plants and fungi, the Volatile Sulfur Compounds (VSCs) feature prominently, not only because of their often-pungent smell, but also because they are able to access places which solids and solutions cannot reach that easily. Indeed, inorganic RSS such as hydrogen sulfide (H₂S) and sulfur dioxide (SO₂) can be used to lit-erally fumigate entire rooms and areas. Similarly, metabolites of garlic, such as allyl methyl sulfide (AMS), are formed metabolically in humans in lower concentrations and reach the airways from inside the body as part of one’s breath. Curiously, H₂S is also formed in the gastrointestinal tract by gut bacteria, and the question of if and for which purpose this gas then crosses the barriers and enters the body is indeed a delicate matter for equally delicate studies. In any case, nature is surprisingly rich in such VSCs, as fruits (for instance, the infamous durian) demonstrate, and therefore these VSCs represent a promising group of compounds for further studies.

Hydrogen sulfide disrupts insulin-induced glucose uptake in L6 skeletal muscle cells

Hydrogen sulfide (H2S) has been known for its toxicity. However, recent studies have focused on the mechanisms involved in endogenous production and function. To date, the H2S role in insulin signaling and glucose homeostasis is unclear. This uncertainty is even more evident in skeletal muscle, a physiological niche highly relevant for regulating glycemia in response to insulin. This study aimed to investigate the role of H₂S on insulin signaling and glucose uptake in the L6 skeletal muscle cell line. We evaluated the endogenous synthesis with the fluorescent dye, 7-azido-4-methyl coumarin (7-AzMC). Glucose restriction-induced an increase in the endogenous levels of H2S, likely through stimulation of cystathionine γ-lyase activity, as its specific inhibitor, PAG (5 mM) prevented this increase, and mRNA levels of CSE decreased with glucose and amino acid restriction. Exogenous H₂S reduced insulin-induced glucose uptake at 0.5 up to 24 h, an effect dissociated from the level of Akt phosphorylation. Our results show that glucose restriction induces endogenous production of H2S via CSE. In addition, H2S disrupts insulin-induced glucose uptake independent of the Akt pathway. These results suggest that H2S antagonism over insulin-induced glucose uptake could help maintain the plasmatic glucose levels in conditions that provoke hypoglycemia, which could serve as an H2S-regulated mechanism for maintaining glucose plasmatic levels through the inhibition of the skeletal muscle insulin-depended glucose uptake.

Medical Gas Therapy for Tissue, Organ, and CNS Protection: A Systematic Review of Effects, Mechanisms, and Challenges

Gaseous molecules have been increasingly explored for therapeutic development. Here, following an analytical background introduction, a systematic review of medical gas research is presented, focusing on tissue protections, mechanisms, data tangibility, and translational challenges. The pharmacological efficacies of carbon monoxide (CO) and xenon (Xe) are further examined with emphasis on intracellular messengers associated with cytoprotection and functional improvement for the CNS, heart, retina, liver, kidneys, lungs, etc. Overall, the outcome supports the hypothesis that readily deliverable "biological gas" (CO, H₂ , H₂ S, NO, O₂ , O₃ , and N₂ O) or "noble gas" (He, Ar, and Xe) treatment may preserve cells against common pathologies by regulating oxidative, inflammatory, apoptotic, survival, and/or repair processes. Specifically, CO, in safe dosages, elicits neurorestoration via igniting sGC/cGMP/MAPK signaling and crosstalk between HO-CO, HIF-1α/VEGF, and NOS pathways. Xe rescues neurons through NMDA antagonism and PI3K/Akt/HIF-1α/ERK activation. Primary findings also reveal that the need to utilize cutting-edge molecular and genetic tactics to validate mechanistic targets and optimize outcome consistency remains urgent; the number of neurotherapeutic investigations is limited, without published results from large in vivo models. Lastly, the broad-spectrum, concurrent multimodal homeostatic actions of medical gases may represent a novel pharmaceutical approach to treating critical organ failure and neurotrauma.