Hydrogen sulfide and cell signaling

Toward Hydrogen Sulfide Based Therapeutics: Critical Drug Delivery and Developability Issues

Hydrogen sulfide (H₂ S), together with nitric oxide (NO) and carbon monoxide (CO), belongs to the gasotransmitter family and plays important roles in mammals as a signaling molecule. Many studies have also shown the various therapeutic effects of H₂ S, which include protection against myocardial ischemia injury, cytoprotection against oxidative stress, mediation of neurotransmission, inhibition of insulin signaling, regulation of inflammation, inhibition of the hypoxia-inducible pathway, and dilation of blood vessels. One major challenge in the development of H₂ S-based therapeutics is its delivery. In this manuscript, we assess the various drug delivery strategies in the context of being used research tools and eventual developability as therapeutic agents.

Heat shock protein 90/Akt pathway participates in the cardioprotective effect of exogenous hydrogen sulfide against high glucose-induced injury to H9c2 cells

It has been reported that exogenous hydrogen sulfide (H2S) protects against high glucose (HG)-induced cardiac injury and has a modulatory effect on heat shock protein (HSP) and Akt, which play a cardioprotective role. In this study, we examined whether the HSP90/Akt pathway contributes to the protective effects of exogenous H2S against HG-induced injury to H9c2 cardiac cells. Our results revealed that the exposure of H9c2 cardiac cells to 35 mM glucose (HG) for 1 to 24 h decreased the expression of HSP90 and markedly reduced the expression level of phosphorylated (p)-Akt in a time-dependent manner. Co-exposure of the cells to HG and geldanamycin (GA; an inhibitor of HSP90) aggravated the inhibition of the p-Akt expression level by HG. Of note, treatment of the cells with 400 µM NaHS (a donor of H2S) for 30 min prior to exposure to HG significantly attenuated the HG-induced decrease in the expression levels of both HSP90 and p-Akt, along with inhibition of HG-induced cell injury, as indicated by the increase in cell viability and superoxide dismutase (SOD) activity, and by a decrease in the number of apoptotic cells, reactive oxygen species (ROS) generation, as well as by the decreased dissipation of mitochondrial membrance potential (MMP). Importantly, treatment of the cells with GA or LY294002 (an inhibitor of Akt) prior to exposure to NaHS and HG considerably blocked the cardioprotective effects of NaHS against the HG-induced injury mentioned above. On the whole, the findings of this study demonstrate that the inhibition of the HSP90/Akt pathway may be an important mechanism responsible for HG-induced cardiomyocyte injury. We also provide novel evidence that exogenous H2S protects H9c2 cells against HG-induced injury by activating the HSP90/Akt pathway.

Broad-Range Antiviral Activity of Hydrogen Sulfide Against Highly Pathogenic RNA Viruses

Hydrogen sulfide is an important endogenous mediator that has been the focus of intense investigation in the past few years, leading to the discovery of its role in vasoactive, cytoprotective and anti-inflammatory responses. Recently, we made a critical observation that H₂S also has a protective role in paramyxovirus infection by modulating inflammatory responses and viral replication. In this study we tested the antiviral and anti-inflammatory activity of the H₂S slow-releasing donor GYY4137 on enveloped RNA viruses from Ortho-, Filo-, Flavi- and Bunyavirus families, for which there is no FDA-approved vaccine or therapeutic available, with the exception of influenza. We found that GYY4137 significantly reduced replication of all tested viruses. In a model of influenza infection, GYY4137 treatment was associated with decreased expression of viral proteins and mRNA, suggesting inhibition of an early step of replication. The antiviral activity coincided with the decrease of viral-induced pro-inflammatory mediators and viral-induced nuclear translocation of transcription factors from Nuclear Factor (NF)-kB and Interferon Regulatory Factor families. In conclusion, increasing cellular H₂S is associated with significant antiviral activity against a broad range of emerging enveloped RNA viruses, and should be further explored as potential therapeutic approach in relevant preclinical models of viral infections.

Effects of Hydrogen Sulfide-Releasing Compounds on Aqueous Humor Outflow Facility in Porcine Ocular Anterior Segments, Ex Vivo

PURPOSE

To investigate the pharmacological actions of hydrogen sulfide (H₂S)-releasing compounds l-cysteine and sodium hydrosulfide (NaHS) on aqueous humor (AH) outflow facility in porcine ocular anterior segment.

METHODS

Porcine ocular anterior segments were perfused with Dulbecco's modified Eagle's medium at a constant pressure of 7.35 mmHg. After stable outflow baseline, explants were exposed to NaHS or l-cysteine. The increase in outflow generated by the H₂S-releasing compounds was measured in the absence and presence of inhibitor of H₂S biosynthesis (aminooxyacetic acid; AOAA), blocker of K_ATP channels (glibenclamide), and inhibitor of adenylyl cyclase (SQ 22536). Hematoxylin and eosin (H&E) staining was used to assess trabecular meshwork (TM) morphology.

RESULTS

l-cysteine elicited a concentration-dependent increase in AH outflow facility, reaching maximal effect at 100 nM (150.6% ± 17.2% of basal level). This increase in outflow induced by l-cysteine was significantly (P < 0.001) antagonized by AOAA (30 μM) and glibenclamide (100 μM). AOAA and glibenclamide had no significant action on baseline outflow, whereas SQ 22536 (100 μM) increased outflow for only an hour. In addition, NaHS produced a concentration-dependent increase in AH outflow, with a maximal effect at 10 μM (151.4% ± 22.9% of basal level). Likewise, the increase in outflow caused by NaHS was significantly (P < 0.04) blocked by glibenclamide and SQ 22536. H&E staining revealed that l-cysteine or NaHS did not alter TM conformation.

CONCLUSION

H₂S-releasing compounds can increase outflow facility in porcine ocular anterior segment. The stimulatory action of these compounds on outflow is mediated, in part by endogenously produced H₂S, K_ATP channels, and adenylyl cyclase.

Cu2+-Mediated turn-on fluorescence assay for sulfide ions using glutathione-protected gold nanoclusters: enhanced sensitivity, good reusability, and cell imaging

Cu²⁺-Mediation enables turn-on fluorescence detection of S²⁻using GSH-Au NCs with good sensitivity, reusability, and applicability in cell imaging.

A two-photon fluorescent probe for specific detection of hydrogen sulfide based on a familiar ESIPT fluorophore bearing AIE characteristics

A two-photon fluorescent probe based on an ESIPT fluorophore bearing AIE characteristics was utilized to detect H₂S.

A near-infrared fluorescence off–on probe for sensitive imaging of hydrogen polysulfides in living cells and mice in vivo

A new near-infrared fluorescence off–on probe with phenyl 2-(benzoylthio)benzoate as the recognition moiety is developed and applied in imaging H₂S_n in living cells and mice in vivo.

Thiolysis of NBD-based dyes for colorimetric and fluorescence detection of H2S and biothiols: design and biological applications

H₂S-specific fluorescent/colorimetric probes based on the thiolysis of NBD dyes are summarized.

A nitroolefin functionalized DPP fluorescent probe for the selective detection of hydrogen sulfide

A novel reduction-based fluorescent probe for the sensitive detection of hydrogen sulfide has been reasonably designed and developed.

o,o-Difluorination of aromatic azide yields a fast-response fluorescent probe for H2S detection and for improved bioorthogonal reactions

Based on the o,o′-difluorinated aromatic azide, a new fluorescent probe was developed for the fast detection of H₂S and for improved copper-free click and Staudinger reactions.

A new ESIPT-based fluorescent probe for highly selective and sensitive detection of hydrogen sulfide and its application in live-cell imaging

A new ESIPT-based fluorescent probe for the sensitive detection of hydrogen sulfide has been reasonably designed and developed.

Garlic-inspired trisulfide linkers for thiol-stimulated H2S release

Garlic-inspired cholesterol-mPEG conjugates incorporating a trisulfide linkage have the ability to cleave upon exposure to thiols with a concomitant release of H₂S.

Cinnamaldehyde Ameliorates Cadmium-Inhibited Root Elongation in Tobacco Seedlings via Decreasing Endogenous Hydrogen Sulfide Production

Cinnamaldehyde (CA) is natural plant-derived compound that has been highly appreciated for its medicinal properties. However, little information is known about the regulation of plant intrinsic physiology by CA. To address these gaps, physiological, histochemical, and biochemical approaches were applied to investigate CA-facilitated cadmium (Cd) tolerance in the roots of tobacco (Nicotiana tabacum) seedlings. Treatment with CdCl₂ at 20 μM for 72 h resulted in the significant decrease in root elongation by 40.39% as compared to control. CA alleviated Cd-inhibited root elongation in dose- and time-dependent manners. The addition of CA at 20 μM induced significant increase in root elongation by 42.58% as compared to Cd treatment alone. CA abolished Cd-induced ROS (reactive oxygen species) accumulation, lipid peroxidation, loss of membrane integrity, cell death, and free Cd2+ accumulation in roots. CA blocked the Cd-induced increase in the endogenous H₂S level through the down-regulation of d-cysteine desulfhydrase (DCD) expression. H₂S scavenger hypotaurine (HT) or potent H₂S-biosynthetic inhibitor dl-propargylglicine (PAG) were able mimic the action of CA on the blockade of Cd-induced H₂S accumulation, cell death, and growth inhibition. Enhancement of the endogenous H₂S level with NaHS (H₂S donor) abrogated all the beneficial capabilities of CA, HT, and PAG. Collectively, these results suggest that CA has great potential to confer plant tolerance against Cd stress, which is closely associated with its capability to inhibit Cd-induced H₂S production. This study not only provides evidences for the regulation of plant physiology by CA but also sheds new light on the cross-talk between CA and H₂S in physiological modulations.

Functional and Molecular Insights of Hydrogen Sulfide Signaling and Protein Sulfhydration

Hydrogen sulfide (H2S), a novel gasotransmitter, is endogenously synthesized by multiple enzymes that are differentially expressed in the peripheral tissues and central nervous systems. H2S regulates a wide range of physiological processes, namely cardiovascular, neuronal, immune, respiratory, gastrointestinal, liver, and endocrine systems, by influencing cellular signaling pathways and sulfhydration of target proteins. This review focuses on the recent progress made in H2S signaling that affects mechanistic and functional aspects of several biological processes such as autophagy, inflammation, proliferation and differentiation of stem cell, cell survival/death, and cellular metabolism under both physiological and pathological conditions. Moreover, we highlighted the cross-talk between nitric oxide and H2S in several bilogical contexts.

Perivascular adipose tissue as a regulator of vascular disease pathogenesis: identifying novel therapeutic targets

Adipose tissue (AT) is an active endocrine organ with the ability to dynamically secrete a wide range of adipocytokines. Importantly, its secretory profile is altered in various cardiovascular disease states. AT surrounding vessels, or perivascular AT (PVAT), is recognized in particular as an important local regulator of vascular function and dysfunction. Specifically, PVAT has the ability to sense vascular paracrine signals and respond by secreting a variety of vasoactive adipocytokines. Due to the crucial role of PVAT in regulating many aspects of vascular biology, it may constitute a novel therapeutic target for the prevention and treatment of vascular disease pathogenesis. Signalling pathways in PVAT, such as those using adiponectin, H₂ S, glucagon-like peptide 1 or pro-inflammatory cytokines, are among the potential novel pharmacological therapeutic targets of PVAT.

LINKED ARTICLES

This article is part of a themed section on Molecular Mechanisms Regulating Perivascular Adipose Tissue - Potential Pharmacological Targets? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.20/issuetoc.

Slow generation of hydrogen sulfide from sulfane sulfurs and NADH models

Here we report the model studies of the reactions between NADH models (using HEH and BNAH) and sulfane sulfurs (using polysulfides). Such reactions could lead to the oxidation of NADH models and the production of hydrogen sulfide (H₂S). Kinetics of the reaction between BNAH and elemental sulfur S₈ were determined in ethanol and the second-order rate constant was found to be 0.074M^-1min^-1 (at 37°C) suggesting this is a slow process.

Hydrogen Sulfide Regulates Homeostasis of Mesenchymal Stem Cells and Regulatory T Cells

Hydrogen sulfide (H2S) has long been known as a toxic gas. However, recently accumulated evidence suggests that H2S contributes to a variety of physiologic and pathologic processes. Endogenous H2S production is regulated by multiple enzymes that are differentially expressed in the cardiovascular, neuronal, immune, renal, respiratory, gastrointestinal, reproductive, liver, and endocrine systems. Alteration of H2S metabolism may affect multiple signaling pathways and tissue homeostasis. The growing number of diverse targets for which H2S serves as a gasotransmitter has been extensively reviewed elsewhere. In this review, the authors discuss current emerging evidence that H2S regulates mesenchymal stem cell and T-cell functions.

H2S biosynthesis and catabolism: new insights from molecular studies

Hydrogen sulfide (H₂S) has profound biological effects within living organisms and is now increasingly being considered alongside other gaseous signalling molecules, such as nitric oxide (NO) and carbon monoxide (CO). Conventional use of pharmacological and molecular approaches has spawned a rapidly growing research field that has identified H₂S as playing a functional role in cell-signalling and post-translational modifications. Recently, a number of laboratories have reported the use of siRNA methodologies and genetic mouse models to mimic the loss of function of genes involved in the biosynthesis and degradation of H₂S within tissues. Studies utilising these systems are revealing new insights into the biology of H₂S within the cardiovascular system, inflammatory disease, and in cell signalling. In light of this work, the current review will describe recent advances in H₂S research made possible by the use of molecular approaches and genetic mouse models with perturbed capacities to generate or detoxify physiological levels of H₂S gas within tissues.

Novel Fluorescein-Based Fluorescent Probe for Detecting H2S and Its Real Applications in Blood Plasma and Biological Imaging

A broad-spectrum fluorescent probe, which can be applied to monitoring H₂S in various biological systems, has been rationally designed and synthesized. This specific probe was applied to localize the endogenous H₂S in living Raw264.7 macrophage cells, HepG2 cells, and H9C2 cells. At the same time, the probe has successfully visualized CBS- and CSE-induced endogenous H₂S production and monitored CBS and CSE activity in H9C2 cells. This probe could serve as a powerful molecular imaging tool to further explore the physiological function and the molecular mechanisms of endogenous H₂S in living animal systems.

Hydrogen sulfide enhances nitric oxide-induced tolerance of hypoxia in maize (Zea mays L.)

Our data present H ₂ S in a new role, serving as a multi-faceted transducer to different response mechanisms during NO-induced acquisition of tolerance to flooding-induced hypoxia in maize seedling roots. Nitric oxide (NO), serving as a secondary messenger, modulates physiological processes in plants. Recently, hydrogen sulfide (H₂S) has been demonstrated to have similar signaling functions. This study focused on the effects of treatment with H₂S on NO-induced hypoxia tolerance in maize seedlings. The results showed that treatment with the NO donor sodium nitroprusside (SNP) enhanced survival rate of submerged maize roots through induced accumulation of endogenous H₂S. The induced H₂S then enhanced endogenous Ca²⁺ levels as well as the Ca²⁺-dependent activity of alcohol dehydrogenase (ADH), improving the capacity for antioxidant defense and, ultimately, the hypoxia tolerance in maize seedlings. In addition, NO induced the activities of key enzymes in H₂S biosynthesis, such as L-cysteine desulfhydrases (L-CDs), O-acetyl-L-serine (thiol)lyase (OAS-TL), and β-Cyanoalanine Synthase (CAS). SNP-induced hypoxia tolerance was enhanced by the application of NaHS, but was eliminated by the H₂S-synthesis inhibitor hydroxylamine (HA) and the H₂S-scavenger hypotaurine (HT). H₂S concurrently enhanced the transcriptional levels of relative hypoxia-induced genes. Together, our findings indicated that H₂S serves as a multi-faceted transducer that enhances the nitric oxide-induced hypoxia tolerance in maize (Zea mays L.).

S-Sulfhydration of ATP synthase by hydrogen sulfide stimulates mitochondrial bioenergetics

Mammalian cells can utilize hydrogen sulfide (H2S) to support mitochondrial respiration. The aim of our study was to explore the potential role of S-sulfhydration (a H2S-induced posttranslational modification, also known as S-persulfidation) of the mitochondrial inner membrane protein ATP synthase (F1F0 ATP synthase/Complex V) in the regulation of mitochondrial bioenergetics. Using a biotin switch assay, we have detected S-sulfhydration of the α subunit (ATP5A1) of ATP synthase in response to exposure to H2S in vitro. The H2S generator compound NaHS induced S-sulfhydration of ATP5A1 in HepG2 and HEK293 cell lysates in a concentration-dependent manner (50-300μM). The activity of immunocaptured mitochondrial ATP synthase enzyme isolated from HepG2 and HEK293 cells was stimulated by NaHS at low concentrations (10-100nM). Site-directed mutagenesis of ATP5A1 in HEK293 cells demonstrated that cysteine residues at positions 244 and 294 are subject to S-sulfhydration. The double mutant ATP synthase protein (C244S/C294S) showed a significantly reduced enzyme activity compared to control and the single-cysteine-mutated recombinant proteins (C244S or C294S). To determine whether endogenous H2S plays a role in the basal S-sulfhydration of ATP synthase in vivo, we compared liver tissues harvested from wild-type mice and mice deficient in cystathionine-gamma-lyase (CSE, one of the three principal mammalian H2S-producing enzymes). Significantly reduced S-sulfhydration of ATP5A1 was observed in liver homogenates of CSE-/- mice, compared to wild-type mice, suggesting a physiological role for CSE-derived endogenous H2S production in the S-sulfhydration of ATP synthase. Various forms of critical illness (including burn injury) upregulate H2S-producing enzymes and stimulate H2S biosynthesis. In liver tissues collected from mice subjected to burn injury, we detected an increased S-sulfhydration of ATP5A1 at the early time points post-burn. At later time points (when systemic H2S levels decrease) S-sulfhydration of ATP5A1 decreased as well. In conclusion, H2S induces S-sulfhydration of ATP5A1 at C244 and C294. This post-translational modification may be a physiological mechanism to maintain ATP synthase in a physiologically activated state, thereby supporting mitochondrial bioenergetics. The sulfhydration of ATP synthase may be a dynamic process, which may be regulated by endogenous H2S levels under various pathophysiological conditions.

The Evolutionary Ecology of Animals Inhabiting Hydrogen Sulfide–Rich Environments

Hydrogen sulfide (H2S) is a respiratory toxicant that creates extreme environments tolerated by few organisms. H2S is also produced endogenously by metazoans and plays a role in cell signaling. The mechanisms of H2S toxicity and its physiological functions serve as a basis to discuss the multifarious strategies that allow animals to survive in H2S-rich environments. Despite their toxicity, H2S-rich environments also provide ecological opportunities, and complex selective regimes of covarying abiotic and biotic factors drive trait evolution in organisms inhabiting H2S-rich environments. Furthermore, adaptation to H2S-rich environments can drive speciation, giving rise to biodiversity hot spots with high levels of endemism in deep-sea hydrothermal vents, cold seeps, and freshwater sulfide springs. The diversity of H2S-rich environments and their inhabitants provides ideal systems for comparative studies of the effects of a clear-cut source of selection across vast geographic and phylogenetic scales, ultimately informing our understanding of how environmental stressors affect ecological and evolutionary processes.

The Control of Calcium Metabolism in Zebrafish (Danio rerio)

Zebrafish is an emerging model for the research of body fluid ionic homeostasis. In this review, we focus on current progress on the regulation of Ca²⁺ uptake in the context of Ca²⁺ sensing and hormonal regulation in zebrafish. Na⁺-K⁺-ATPase-rich cells (NaRCs), the specialized ionocytes in the embryonic skin and adult gills, play a dominant role in Ca²⁺ uptake in zebrafish. Transepithelial Ca²⁺ transport in NaRC, through apical epithelial Ca²⁺ channels (ECaC), basolateral plasma membrane Ca²⁺-ATPase (PMCA), and Na⁺/Ca²⁺ exchanger (NCX), is analogous to mammalian renal and intestinal Ca²⁺-absorption cells. Several hormones were demonstrated to differentially regulate Ca²⁺ uptake through modulating the expression of Ca²⁺ transporters and/or the proliferation/differentiation of NaRC in zebrafish. In addition, the counterbalance among these hormones is associated with the maintenance of body fluid Ca²⁺ homeostasis. Calcium-sensing receptor (CaSR) is expressed in several hormone-secreting tissues in zebrafish, and activated CaSR differentially controls calciotropic hormones. The major principles of Ca²⁺ transport and the hormonal control appear to be conserved from zebrafish to other vertebrates including mammals. The new knowledge gained from zebrafish studies provides new insights into the related issues in vertebrates.

S-Propargyl-Cysteine, a Novel Hydrogen Sulfide Donor, Inhibits Inflammatory Hepcidin and Relieves Anemia of Inflammation by Inhibiting IL-6/STAT3 Pathway

Anemia of inflammation (AI) is clinically prevalent and greatly threatens public health. Traditional remedies have raised controversy during clinical practice, calling for alternative therapies. We have recently found that hydrogen sulfide (H₂S) inhibits inflammatory hepcidin, the critical mediator of AI. However, due to the chemical property of H₂S, there remains an urgent need for a stable H₂S donor in AI treatment. Here we reported that S-propargyl-cysteine (SPRC), a novel water-soluble H₂S donor, suppressed hepatic hepcidin and corrected hypoferremia induced by lipopolysaccharide. The effects of SPRC were reversed by inhibition of cystathionine γ-lyase, one of the major endogenous H₂S synthases. Moreover, SPRC reduced serum hepcidin, improved transferrin saturation, and maintained erythrocyte membrane integrity in a chronic mouse AI model. Consistently, splenomegaly was ameliorated and splenic iron accumulation relieved. Mechanism study indicated that serum IL-6 content and hepatic Il-6 mRNA were decreased by SPRC, in parallel with reduced hepatic JAK2/STAT3 activation. On the whole, our data reveal the inhibition of inflammatory hepcidin by SPRC, and suggest SPRC as a potential remedy against AI.

Cardioprotection by H2S Donors: Nitric Oxide-Dependent and ‑Independent Mechanisms

Hydrogen sulfide (H2S) is a signaling molecule with protective effects in the cardiovascular system. To harness the therapeutic potential of H2S, a number of donors have been developed. The present study compares the cardioprotective actions of representative H2S donors from different classes and studies their mechanisms of action in myocardial injury in vitro and in vivo. Exposure of cardiomyocytes to H2O2 led to significant cytotoxicity, which was inhibited by sodium sulfide (Na2S), thiovaline (TV), GYY4137 [morpholin-4-ium 4 methoxyphenyl(morpholino) phosphinodithioate], and AP39 [(10-oxo-10-(4-(3-thioxo-3H-1,2-dithiol5yl)phenoxy)decyl) triphenylphospho-nium bromide]. Inhibition of nitric oxide (NO) synthesis prevented the cytoprotective effects of Na2S and TV, but not GYY4137 and AP39, against H2O2-induced cardiomyocyte injury. Mice subjected to left anterior descending coronary ligation were protected from ischemia-reperfusion injury by the H2S donors tested. Inhibition of nitric oxide synthase (NOS) in vivo blocked only the beneficial effect of Na2S. Moreover, Na2S, but not AP39, administration enhanced the phosphorylation of endothelial NOS and vasodilator-associated phosphoprotein. Both Na2S and AP39 reduced infarct size in mice lacking cyclophilin-D (CypD), a modulator of the mitochondrial permeability transition pore (PTP). Nevertheless, only AP39 displayed a direct effect on mitochondria by increasing the mitochondrial Ca(2+) retention capacity, which is evidence of decreased propensity to undergo permeability transition. We conclude that although all the H2S donors we tested limited infarct size, the pathways involved were not conserved. Na2S had no direct effects on PTP opening, and its action was nitric oxide dependent. In contrast, the cardioprotection exhibited by AP39 could result from a direct inhibitory effect on PTP acting at a site different than CypD.

Capsaicin-Sensitive Sensory Nerves Mediate the Cellular and Microvascular Effects of H2S via TRPA1 Receptor Activation and Neuropeptide Release

It is supposed that TRPA1 receptor can be activated by hydrogen sulphide (H2S). Here, we have investigated the role of TRPA1 receptor in H2S-induced [Ca(2+)]i increase in trigeminal ganglia (TRG) neurons, and the involvement of capsaicin-sensitive sensory nerves in H2S-evoked cutaneous vasodilatation. [Ca(2+)]i was measured with ratiometric technique on TRG neurons of TRPA1(+/+) and TRPA1(-/-) mice after NaHS, Na2S, allylisothiocyanate (AITC) or KCl treatment. Microcirculatory changes in the ear were detected by laser Doppler imaging in response to topical NaHS, AITC, NaOH, NaSO3 or NaCl. Mice were either treated with resiniferatoxin (RTX), or CGRP antagonist BIBN4096, or NK1 receptor antagonist CP99994, or K(+) ATP channel blocker glibenclamide. Alpha-CGRP(-/-) and NK1 (-/-) mice were also investigated. NaHS and Na2S increased [Ca(2+)]i in TRG neurons derived from TRPA(+/+) but not from TRPA1(-/-) mice. NaHS increased cutaneous blood flow, while NaOH, NaSO3 and NaCl did not cause significant changes. NaHS-induced vasodilatation was reduced in RTX-treated animals, as well as by pre-treatment with BIBN4096 or CP99994 alone or in combination. NaHS-induced vasodilatation was significantly smaller in alpha-CGRP(-/-) or NK1 (-/-) mice compared to wild-types. H2S activates capsaicin-sensitive sensory nerves through TRPA1 receptors and the resultant vasodilatation is mediated by the release of vasoactive sensory neuropeptides CGRP and substance P.

Hydrogen Sulfide as a "Double-Faced" Compound: One with Pro- and Antioxidant Effect

Hydrogen sulfide (H₂S), like other gasotransmitters such as nitric oxide (NO^•) and carbon monoxide (CO), acts as a signaling molecule in various biological systems. It may also regulate the oxidative stress observed in several diseases sometimes associated with changes of H₂S concentration. This chapter describes the "double face" of hydrogen sulfide as both an antioxidant and a prooxidant in biological systems. One proposed mechanism by which H₂S exerts its antioxidative effects is its ability to modulate the concentration of glutathione, which is a very important physiological antioxidant. This chapter discusses the interactions of H₂S with various reactive oxygen species and reactive nitrogen species, including the superoxide radical anion [Formula: see text] , hydrogen peroxide (H₂O₂), and peroxynitrite anion (ONOO^-), which is produced in a rapid reaction between [Formula: see text] and NO^•.

Urothelium muscarinic activation phosphorylates CBS(Ser227) via cGMP/PKG pathway causing human bladder relaxation through H2S production

The urothelium modulates detrusor activity through releasing factors whose nature has not been clearly defined. Here we have investigated the involvement of H2S as possible mediator released downstream following muscarinic (M) activation, by using human bladder and urothelial T24 cell line. Carbachol stimulation enhances H2S production and in turn cGMP in human urothelium or in T24 cells. This effect is reversed by cysthationine-β-synthase (CBS) inhibition. The blockade of M1 and M3 receptors reverses the increase in H2S production in human urothelium. In T24 cells, the blockade of M1 receptor significantly reduces carbachol-induced H2S production. In the functional studies, the urothelium removal from human bladder strips leads to an increase in carbachol-induced contraction that is mimicked by CBS inhibition. Instead, the CSE blockade does not significantly affect carbachol-induced contraction. The increase in H2S production and in turn of cGMP is driven by CBS-cGMP/PKG-dependent phosphorylation at Ser(227) following carbachol stimulation. The finding of the presence of this crosstalk between the cGMP/PKG and H2S pathway downstream to the M1/M3 receptor in the human urothelium further implies a key role for H2S in bladder physiopathology. Thus, the modulation of the H2S pathway can represent a feasible therapeutic target to develop drugs for bladder disorders.

Screening of a composite library of clinically used drugs and well-characterized pharmacological compounds for cystathionine β-synthase inhibition identifies benserazide as a drug potentially suitable for repurposing for the experimental therapy of colon cancer

Cystathionine-β-synthase (CBS) has been recently identified as a drug target for several forms of cancer. Currently no potent and selective CBS inhibitors are available. Using a composite collection of 8871 clinically used drugs and well-annotated pharmacological compounds (including the LOPAC library, the FDA Approved Drug Library, the NIH Clinical Collection, the New Prestwick Chemical Library, the US Drug Collection, the International Drug Collection, the ‘Killer Plates’ collection and a small custom collection of PLP-dependent enzyme inhibitors), we conducted an in vitro screen in order to identify inhibitors for CBS using a primary 7-azido-4-methylcoumarin (AzMc) screen to detect CBS-derived hydrogen sulfide (H₂S) production. Initial hits were subjected to counterscreens using the methylene blue assay (a secondary assay to measure H₂S production) and were assessed for their ability to quench the H₂S signal produced by the H₂S donor compound GYY4137. Four compounds, hexachlorophene, tannic acid, aurintricarboxylic acid and benserazide showed concentration-dependent CBS inhibitory actions without scavenging H₂S released from GYY4137, identifying them as direct CBS inhibitors. Hexachlorophene (IC₅₀: ∼60 μM), tannic acid (IC₅₀: ∼40 μM) and benserazide (IC₅₀: ∼30 μM) were less potent CBS inhibitors than the two reference compounds AOAA (IC₅₀: ∼3 μM) and NSC67078 (IC₅₀: ∼1 μM), while aurintricarboxylic acid (IC₅₀: ∼3 μM) was equipotent with AOAA. The second reference compound NSC67078 not only inhibited the CBS-induced AzMC fluorescence signal (IC₅₀: ∼1 μM), but also inhibited with the GYY4137-induced AzMC fluorescence signal with (IC₅₀ of ∼6 μM) indicative of scavenging/non-specific effects. Hexachlorophene (IC₅₀: ∼6 μM), tannic acid (IC₅₀: ∼20 μM), benserazide (IC₅₀: ∼20 μM), and NSC67078 (IC₅₀: ∼0.3 μM) inhibited HCT116 colon cancer cells proliferation with greater potency than AOAA (IC₅₀: ∼300 μM). In contrast, although a CBS inhibitor in the cell-free assay, aurintricarboxylic acid failed to inhibit HCT116 proliferation at lower concentrations, and stimulated cell proliferation at 300 μM. Copper-containing compounds present in the libraries, were also found to be potent inhibitors of recombinant CBS; however this activity was due to the CBS inhibitory effect of copper ions themselves. However, copper ions, up to 300 μM, did not inhibit HCT116 cell proliferation. Benserazide was only a weak inhibitor of the activity of the other H₂S-generating enzymes CSE and 3-MST activity (16% and 35% inhibition at 100 μM, respectively) in vitro. Benserazide suppressed HCT116 mitochondrial function and inhibited proliferation of the high CBS-expressing colon cancer cell line HT29, but not the low CBS-expressing line, LoVo. The major benserazide metabolite 2,3,4-trihydroxybenzylhydrazine also inhibited CBS activity and suppressed HCT116 cell proliferation in vitro. In an in vivo study of nude mice bearing human colon cancer cell xenografts, benserazide (50 mg/kg/day s.q.) prevented tumor growth. In silico docking simulations showed that benserazide binds in the active site of the enzyme and reacts with the PLP cofactor by forming reversible but kinetically stable Schiff base-like adducts with the formyl moiety of pyridoxal. We conclude that benserazide inhibits CBS activity and suppresses colon cancer cell proliferation and bioenergetics in vitro, and tumor growth in vivo. Further pharmacokinetic, pharmacodynamic and preclinical animal studies are necessary to evaluate the potential of repurposing benserazide for the treatment of colorectal cancers.

"Oxygen Sensing" by Na,K-ATPase: These Miraculous Thiols

Control over the Na,K-ATPase function plays a central role in adaptation of the organisms to hypoxic and anoxic conditions. As the enzyme itself does not possess O2 binding sites its "oxygen-sensitivity" is mediated by a variety of redox-sensitive modifications including S-glutathionylation, S-nitrosylation, and redox-sensitive phosphorylation. This is an overview of the current knowledge on the plethora of molecular mechanisms tuning the activity of the ATP-consuming Na,K-ATPase to the cellular metabolic activity. Recent findings suggest that oxygen-derived free radicals and H2O2, NO, and oxidized glutathione are the signaling messengers that make the Na,K-ATPase "oxygen-sensitive." This very ancient signaling pathway targeting thiols of all three subunits of the Na,K-ATPase as well as redox-sensitive kinases sustains the enzyme activity at the "optimal" level avoiding terminal ATP depletion and maintaining the transmembrane ion gradients in cells of anoxia-tolerant species. We acknowledge the complexity of the underlying processes as we characterize the sources of reactive oxygen and nitrogen species production in hypoxic cells, and identify their targets, the reactive thiol groups which, upon modification, impact the enzyme activity. Structured accordingly, this review presents a summary on (i) the sources of free radical production in hypoxic cells, (ii) localization of regulatory thiols within the Na,K-ATPase and the role reversible thiol modifications play in responses of the enzyme to a variety of stimuli (hypoxia, receptors' activation) (iii) redox-sensitive regulatory phosphorylation, and (iv) the role of fine modulation of the Na,K-ATPase function in survival success under hypoxic conditions. The co-authors attempted to cover all the contradictions and standing hypotheses in the field and propose the possible future developments in this dynamic area of research, the importance of which is hard to overestimate. Better understanding of the processes underlying successful adaptation strategies will make it possible to harness them and use for treatment of patients with stroke and myocardial infarction, sleep apnoea and high altitude pulmonary oedema, and those undergoing surgical interventions associated with the interruption of blood perfusion.

Nitrite Therapy Ameliorates Myocardial Dysfunction via H2S and Nuclear Factor-Erythroid 2-Related Factor 2 (Nrf2)-Dependent Signaling in Chronic Heart Failure

BACKGROUND

Bioavailability of nitric oxide (NO) and hydrogen sulfide (H2S) is reduced in heart failure (HF). Recent studies suggest cross-talk between NO and H2S signaling. We previously reported that sodium nitrite (NaNO2) ameliorates myocardial ischemia-reperfusion injury and HF. Nuclear factor-erythroid-2-related factor 2 (Nrf2) regulates the antioxidant proteins expression and is upregulated by H2S. We examined the NaNO2 effects on endogenous H2S bioavailability and Nrf2 activation in mice subjected to ischemia-induced chronic heart failure (CHF).

METHODS AND RESULTS

Mice underwent 60 minutes of left coronary artery occlusion and 4 weeks of reperfusion. NaNO2 (165 μg/kgic) or vehicle was administered at reperfusion and then in drinking water (100 mg/L) for 4 weeks. Left ventricular (LV), ejection fraction (EF), LV end diastolic (LVEDD) and systolic dimensions (LVESD) were determined at baseline and at 4 weeks of reperfusion. Myocardial tissue was analyzed for oxidative stress and respective gene/protein-related assays. We found that NaNO2 therapy preserved LVEF, LVEDD and LVSD at 4 weeks during ischemia-induced HF. Myocardial malondialdehyde and protein carbonyl content were significantly reduced in NaNO2-treated mice as compared to vehicle, suggesting a reduction in oxidative stress. NaNO2 therapy markedly increased expression of Cu,Zn-superoxide dismutase, catalase, and glutathione peroxidase during 4 weeks of reperfusion. Furthermore, NaNO2 upregulated the activity of Nrf2, as well as H2S-producing enzymes, and ultimately increased H2S bioavailability in ischemia-induced CHF in mice as compared with vehicle.

CONCLUSIONS

Our results demonstrate that NaNO2 therapy significantly improves LV function via increasing H2S bioavailability, Nrf2 activation, and antioxidant defenses.

A Redox-Nucleophilic Dual-Reactable Probe for Highly Selective and Sensitive Detection of H2S: Synthesis, Spectra and Bioimaging

Hydrogen sulfide (H2S) is an important signalling molecule with multiple biological functions. The reported H2S fluorescent probes are majorly based on redox or nucleophilic reactions. The combination usage of both redox and nucleophilic reactions could improve the probe's selectivity, sensitivity and stability. Herein we report a new dual-reactable probe with yellow turn-on fluorescence for H2S detection. The sensing mechanism of the dual-reactable probe was based on thiolysis of NBD (7-nitro-1,2,3-benzoxadiazole) amine (a nucleophilic reaction) and reduction of azide to amine (a redox reaction). Compared with its corresponding single-reactable probes, the dual-reactable probe has higher selectivity and fluorescence turn-on fold with magnitude of multiplication from that of each single-reactable probe. The highly selective and sensitive properties enabled the dual-reactable probe as a useful tool for efficiently sensing H2S in aqueous buffer and in living cells.

Hydrogen Sulfide Promotes Surface Insertion of Hippocampal AMPA Receptor GluR1 Subunit via Phosphorylating at Serine-831/Serine-845 Sites Through a Sulfhydration-Dependent Mechanism

AIMS

Hydrogen sulfide (H2 S) has been widely accepted as a gas neuromodulator to regulate synaptic function. Herein, we set out to determine the effect of H2 S on α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor (AMPAR) and its mechanism.

METHODS

BS(3) protein cross-linking, Western blot, patch clamp, and biotin-switch assay.

RESULTS

Bath application of H2 S donor NaHS (50 and 100 μM) rapidly promoted surface insertion of hippocampal AMPAR GluR1 subunit. This effect can be abolished by dithiothreitol (DTT) and mimicked by Na2 S4 , indicating that a sulfhydration-dependent mechanism may be involved. NaHS increased APMAR-mediated EPSC and led to an elevation of GluR2-lacking AMPAR content. Notably, NaHS did not increase the sulfhydration of AMPAR subunits, but it significantly increased the phosphorylation of GluR1 at serine-831 and serine-845 sites. Postsynaptic signal pathways that control GluR1 phosphorylation, such as protein kinase A (PKA), protein kinase C, and calcium/calmodulin-dependent protein kinases II (CaMKII), were sulfhydrated, activated by NaHS, and these effects can be occluded by DTT. H2 S increased S-sulfhydration of protein phosphatase type 2A (PP2A), which may be partially involved in the activation of signal pathways.

CONCLUSION

Our data suggest that H2 S promotes surface insertion of AMPARs via phosphorylation of GluR1, which depends on a sulfhydration-mediated mechanism.

Regulation of soluble guanylyl cyclase redox state by hydrogen sulfide

Soluble guanylate cyclase (sGC) is a receptor for nitric oxide (NO). Binding of NO to ferrous (Fe(2+)) heme increases its catalytic activity, leading to the production of cGMP from GTP. Hydrogen sulfide (H2S) is a signaling molecule that exerts both direct and indirect anti-oxidant effects. In the present, study we aimed to determine whether H2S could regulate sGC redox state and affect its responsiveness to NO-releasing agents and sGC activators. Using cultured rat aortic smooth muscle cells, we observed that treatment with H2S augmented the response to the NO donor DEA/NO, while attenuating the response to the heme-independent activator BAY58-2667 that targets oxidized sGC. Similarly, overexpression of H2S-synthesizing enzyme cystathionine-γ lyase reduced the ability of BAY58-2667 to promote cGMP accumulation. In experiments with phenylephrine-constricted mouse aortic rings, treatment with rotenone (a compound that increases ROS production), caused a rightward shift of the DEA/NO concentration-response curve, an effect partially restored by H2S. When rings were pre-treated with H2S, the concentration-response curve to BAY 58-2667 shifted to the right. Using purified recombinant human sGC, we observed that treatment with H2S converted ferric to ferrous sGC enhancing NO-donor-stimulated sGC activity and reducing BAY 58-2667-triggered cGMP formation. The present study identified an additional mechanism of cross-talk between the NO and H2S pathways at the level of redox regulation of sGC. Our results provide evidence that H2S reduces sGC heme Fe, thus, facilitating NO-mediated cellular signaling events.

Highly Selective and Sensitive One- and Two-Photon Ratiometric Fluorescent Probe for Intracellular Hydrogen Polysulfide Sensing

Hydrogen polysulfide (H2Sn) has attracted increasing attention due to the fact that it is actually the key signaling molecule rather than hydrogen sulfide (H2S). Therefore, developing a sensitive and accurate assay to investigate the biosynthetic pathways of H2Sn is of physiological and pathological significance. In this work, based on the commonly used two-photon fluorophore, 1,8-naphthalimide, a new probe, NRT-HP, has been designed and synthesized that displayed both one- and two-photon ratiometric fluorescence changes toward H2Sn via H2Sn-mediated benzodithiolone formation. NRT-HP exhibits excellent pH stability, high selectivity and low detection limit (0.1 μM) in aqueous media. Furthermore, two-photon fluorescence microscopy experiments have demonstrated that NRT-HP could be used for the H2Sn detection in live cells as well as tissue slices.