Hydrogen sulfide and cell signaling

Cascade reaction-based rapid and ratiometric detection of H2S/S2− in the presence of bio-thiols with live cell imaging: demasking of ESIPT approach

For the rapid, ratiometric, fluorogenic and “naked eye” detection of H₂S/S²⁻, a pro-excited state intramolecular proton transfer (ESIPT)-based receptor, 2-formyl-benzoic acid 2-benzothiazol-2-yl-phenyl ester (FBBP), has been designed.

Highly selective naphthalimide-based fluorescent probe for direct hydrogen sulfide detection in the environment

Here, we report a highly selective and sensitive approach for monitoring hydrogen sulfide (H₂S) in the environment through an ingenious naphthalimide-based fluorescent probe.

The ferrocene-pyrylium dyad as a selective colorimetric chemodosimeter for the toxic cyanide and hydrogen sulfide anions in water

A pyrylium derivative showing a remarkable ability to recognize cyanide and hydrogen sulfide anions in aqueous media through two different channels, electrochemical and chromogenic, is described.

Hydrogen sulfide donors in research and drug development

This review summarized most of the H₂S donors such as inorganic compounds, natural products, anethole trithione derivatives and synthetic compounds used in research and drug development. These special bioactivities provided us some effective strategies for antiphlogosis, cancer therapy, cardiovascular protection and so on.

A sensitivity tuneable tetraphenylethene-based fluorescent probe for directly indicating the concentration of hydrogen sulfide

A selective tetraphenylethene-based fluorescent H₂S probe was designed and synthesized, which exhibits tuneable sensitivity and could directly indicate the concentration of H₂S.

TRPA1

The transient receptor potential ankyrin subtype 1 protein (TRPA1) is a nonselective cation channel permeable to Ca(2+), Na(+), and K(+). TRPA1 is a promiscuous chemical nocisensor that is also involved in noxious cold and mechanical sensation. It is present in a subpopulation of Aδ- and C-fiber nociceptive sensory neurons as well as in other sensory cells including epithelial cells. In primary sensory neurons, Ca(2+) and Na(+) flowing through TRPA1 into the cell cause membrane depolarization, action potential discharge, and neurotransmitter release both at peripheral and central neural projections. In addition to being activated by cysteine and lysine reactive electrophiles and oxidants, TRPA1 is indirectly activated by pro-inflammatory agents via the phospholipase C signaling pathway, in which cytosolic Ca(2+) is an important regulator of channel gating. The finding that non-electrophilic compounds, including menthol and cannabinoids, activate TRPA1 may provide templates for the design of non-tissue damaging activators to fine-tune the activity of TRPA1 and raises the possibility that endogenous ligands sharing binding sites with such non-electrophiles exist and regulate TRPA1 channel activity. TRPA1 is promising as a drug target for novel treatments of pain, itch, and sensory hyperreactivity in visceral organs including the airways, bladder, and gastrointestinal tract.

A new fluorescent probe for gasotransmitter H2S: high sensitivity, excellent selectivity, and a significant fluorescence off–on response

A fluorescentoff–onprobe for H₂S was exploited by coupling the azide-based strategy with the excited-state intramolecular proton transfer (ESIPT) sensing mechanism.

Hydrogen sulfide attenuates sFlt1-induced hypertension and renal damage by upregulating vascular endothelial growth factor

Soluble fms-like tyrosine kinase 1 (sFlt1), a circulating antiangiogenic protein, is elevated in kidney diseases and contributes to the development of preeclampsia. Hydrogen sulfide is a vasorelaxant and proangiogenic gas with therapeutic potential in several diseases. Therefore, we evaluated the potential therapeutic effect and mechanisms of action of hydrogen sulfide in an animal model of sFlt1-induced hypertension, proteinuria, and glomerular endotheliosis created by adenovirus-mediated overexpression of sFlt1 in Sprague-Dawley rats. We injected sFlt1-overexpressing animals intraperitoneally with the hydrogen sulfide-donor sodium hydrosulfide (NaHS) (50 µmol/kg, twice daily) or vehicle (n=7 per group). Treatment with NaHS for 8 days significantly reduced sFlt1-induced hypertension, proteinuria, and glomerular endotheliosis. Measurement of plasma protein concentrations with ELISA revealed a reduction of free plasma sFlt1 and an increase of free plasma vascular endothelial growth factor (VEGF) after treatment with NaHS. Renal VEGF-A mRNA expression increased significantly with NaHS treatment. In vitro, NaHS was proangiogenic in an endothelial tube assay and attenuated the antiangiogenic effects of sFlt1. Stimulation of podocytes with NaHS resulted in both short-term VEGF release (120 minutes) and upregulation of VEGF-A mRNA levels (24 hours). Furthermore, pretreatment of mesenteric vessels with a VEGF receptor 2-neutralizing antibody significantly attenuated NaHS-induced vasodilation. These results suggest that hydrogen sulfide ameliorates sFlt1-induced hypertension, proteinuria, and glomerular endotheliosis in rats by increasing VEGF expression. Further studies are warranted to evaluate the role of hydrogen sulfide as a novel therapeutic agent for vascular disorders such as preeclampsia.

Fluorescent probes based on nucleophilic substitution-cyclization for hydrogen sulfide detection and bioimaging

The design, synthesis, properties, and cell imaging applications of a series of 2-pyridyl disulfide based fluorescent probes (WSP1, WSP2, WSP3, WSP4 and WSP5) for hydrogen sulfide detection are reported. The strategy is based on the dual-nucleophilicity of hydrogen sulfide. A hydrogen sulfide mediated tandem nucleophilic substitution-cyclization reaction is used to release the fluorophores and turn on the fluorescence. The probes showed high sensitivity and selectivity for hydrogen sulfide over other reactive sulfur species, including cysteine and glutathione.

High-resolution analytical electron microscopy reveals cell culture media-induced changes to the chemistry of silver nanowires

There is a growing concern about the potential adverse effects on human health upon exposure to engineered silver nanomaterials (particles, wires, and plates). However, the majority of studies testing the toxicity of silver nanomaterials have examined nominally "as-synthesized" materials without considering the fate of the materials in biologically relevant fluids. Here, in-house silver nanowires (AgNWs) were prepared by a modified polyol process and were incubated in three cell culture media (DMEM, RPMI-1640, and DCCM-1) to examine the impact of AgNW-medium interactions on the physicochemical properties of the AgNWs. High-resolution analytical transmission electron microscopy revealed that Ag2S crystals form on the surface of AgNWs within 1 h of incubation in DCCM-1. In contrast, the incubation of AgNWs in RPMI-1640 or DMEM did not lead to sulfidation. When the DCCM-1 cell culture medium was separated into its small molecule solutes and salts and protein components, the AgNWs were found to sulfidize in the fraction containing small molecule solutes and salts but not in the fraction containing the protein component of the media. Further investigation showed the AgNWs did not readily sulfidize in the presence of isolated sulfur containing amino acids or proteins, such as cysteine or bovine serum albumin (BSA). The results demonstrate that the AgNWs can be transformed by the media before and during the incubation with cells, and therefore, the effects of cell culture media must be considered in the analysis of toxicity assays. Appropriate media and material controls must be in place to allow accurate predictions about the toxicity and, ultimately, the health risk of this commercially relevant class of nanomaterial.

Glyphosate, pathways to modern diseases II: Celiac sprue and gluten intolerance

Celiac disease, and, more generally, gluten intolerance, is a growing problem worldwide, but especially in North America and Europe, where an estimated 5% of the population now suffers from it. Symptoms include nausea, diarrhea, skin rashes, macrocytic anemia and depression. It is a multifactorial disease associated with numerous nutritional deficiencies as well as reproductive issues and increased risk to thyroid disease, kidney failure and cancer. Here, we propose that glyphosate, the active ingredient in the herbicide, Roundup(®), is the most important causal factor in this epidemic. Fish exposed to glyphosate develop digestive problems that are reminiscent of celiac disease. Celiac disease is associated with imbalances in gut bacteria that can be fully explained by the known effects of glyphosate on gut bacteria. Characteristics of celiac disease point to impairment in many cytochrome P450 enzymes, which are involved with detoxifying environmental toxins, activating vitamin D3, catabolizing vitamin A, and maintaining bile acid production and sulfate supplies to the gut. Glyphosate is known to inhibit cytochrome P450 enzymes. Deficiencies in iron, cobalt, molybdenum, copper and other rare metals associated with celiac disease can be attributed to glyphosate's strong ability to chelate these elements. Deficiencies in tryptophan, tyrosine, methionine and selenomethionine associated with celiac disease match glyphosate's known depletion of these amino acids. Celiac disease patients have an increased risk to non-Hodgkin's lymphoma, which has also been implicated in glyphosate exposure. Reproductive issues associated with celiac disease, such as infertility, miscarriages, and birth defects, can also be explained by glyphosate. Glyphosate residues in wheat and other crops are likely increasing recently due to the growing practice of crop desiccation just prior to the harvest. We argue that the practice of "ripening" sugar cane with glyphosate may explain the recent surge in kidney failure among agricultural workers in Central America. We conclude with a plea to governments to reconsider policies regarding the safety of glyphosate residues in foods.

Detection of protein S-sulfhydration by a tag-switch technique

Protein S-sulfhydration (forming -S-SH adducts from cysteine residues) is a newly defined oxidative posttranslational modification and plays an important role in H2 S-mediated signaling pathways. In this study we report the first selective, "tag-switch" method which can directly label protein S-sulfhydrated residues by forming stable thioether conjugates. Furthermore we demonstrate that H2 S alone cannot lead to S-sulfhydration and that the two possible physiological mechanisms include reaction with protein sulfenic acids (P-SOH) or the involvement of metal centers which would facilitate the oxidation of H2 S to HS(.) .

Synthesis of a photocontrollable hydrogen sulfide donor using ketoprofenate photocages

We report the design, synthesis and application of a directly photocontrollable hydrogen sulfide (H2S) donor, which releases H2S proportionally to the intensity and duration of photoirradiation. Photocontrolled H2S release from this donor was also demonstrated in bovine serum. This H2S donor should be suitable for use in various biological systems.

NBD-based colorimetric and fluorescent turn-on probes for hydrogen sulfide

Hydrogen sulfide (H2S) is an important endogenous signalling molecule and also an important environmental target for detection. New reaction-based colorimetric and fluorescent turn-on probes based on selective thiolyling of NBD (7-nitro-1,2,3-benzoxadiazole) ether were explored for sensing of H2S in aqueous buffer. The syntheses of both probes are simple and quite straightforward. The probes are highly sensitive and selective toward H2S over other biologically relevant species. Probe 1 can be used to directly visualize H2S by the naked eye and shows more than 1000-fold fluorescence increase upon reaction with H2S. Probe 2 is a near-infrared fluorescent sensor for H2S at physiological pH.

Genetically encoded fluorescent redox probes

Redox processes are involved in almost every cell of the body as a consequence of aerobic life. In the past decades, redox biology has been increasingly recognized as one of the key themes in cell signaling. The progress has been accelerated by development of fluorescent probes that can monitor redox conditions and dynamics in cells and cell compartments. This short paper focuses on fluorescent redox probes that are genetically encoded, and discusses their properties, molecular mechanism, advantages and pitfalls. Our recent work on reaction-based encoded probes that are responsive to particular redox signaling molecules is also reviewed. Future challenges and directions are also commented.

Sulfhydration mediates neuroprotective actions of parkin

Increases in S-nitrosylation and inactivation of the neuroprotective ubiquitin E3 ligase, parkin, in the brains of patients with Parkinson’s Disease (PD) are thought to be pathogenic and suggest a possible mechanism linking parkin to sporadic PD. Here we demonstrate that physiologic modification of parkin by hydrogen sulfide (H₂S), termed sulfhydration, enhances its catalytic activity. Sulfhydration sites are identified by mass spectrometry analysis and investigated by site directed mutagenesis. Parkin sulfhydration is markedly depleted in the brains of patients with PD, suggesting that this loss may be pathologic. This implies that H₂S donors may be therapeutic.

Hydrogen sulphide inhibits Ca2+ release through InsP3 receptors and relaxes airway smooth muscle

Hydrogen sulphide (H2S) is a signalling molecule that appears to regulate diverse cell physiological process in several organs and systems including vascular and airway smooth muscle cell (SMC) contraction. Decreases in endogenous H2S synthesis have been associated with the development of cardiovascular diseases and asthma. Here we investigated the mechanism of airway SMC relaxation induced by H2S in small intrapulmonary airways using mouse lung slices and confocal and phase-contrast video microscopy. Exogenous H2S donor Na2S (100 μm) reversibly inhibited Ca(2+) release and airway contraction evoked by inositol-1,4,5-trisphosphate (InsP3) uncaging in airway SMCs. Similarly, InsP3-evoked Ca(2+) release and contraction was inhibited by endogenous H2S precursor l-cysteine (10 mm) but not by l-serine (10 mm) or either amino acid in the presence of dl-propargylglycine (PPG). Consistent with the inhibition of Ca(2+) release through InsP3 receptors (InsP3Rs), Na2S reversibly inhibited acetylcholine (ACh)-induced Ca(2+) oscillations in airway SMCs. In addition, Na2S, the H2S donor GYY-4137, and l-cysteine caused relaxation of airways pre-contracted with either ACh or 5-hydroxytryptamine (5-HT). Na2S-induced airway relaxation was resistant to a guanylyl cyclase inhibitor (ODQ) and a protein kinase G inhibitor (Rp-8-pCPT-cGMPS). The effects of H2S on InsP3-evoked Ca(2+) release and contraction as well as on the relaxation of agonist-contracted airways were mimicked by the thiol-reducing agent dithiothreitol (DTT, 10 mm) and inhibited by the oxidizing agent diamide (30 μm). These studies indicate that H2S causes airway SMC relaxation by inhibiting Ca(2+) release through InsP3Rs and consequent reduction of agonist-induced Ca(2+) oscillations in SMCs. The results suggest a novel role for endogenously produced H2S that involves the modulation of InsP3-evoked Ca(2+) release - a cell-signalling system of critical importance for many physiological and pathophysiological processes.

Hydrogen sulphide inhibits Ca2+ release through InsP3 receptors and relaxes airway smooth muscle

Hydrogen sulphide (H2S) is a signalling molecule that appears to regulate diverse cell physiological process in several organs and systems including vascular and airway smooth muscle cell (SMC) contraction. Decreases in endogenous H2S synthesis have been associated with the development of cardiovascular diseases and asthma. Here we investigated the mechanism of airway SMC relaxation induced by H2S in small intrapulmonary airways using mouse lung slices and confocal and phase-contrast video microscopy. Exogenous H2S donor Na2S (100 μm) reversibly inhibited Ca(2+) release and airway contraction evoked by inositol-1,4,5-trisphosphate (InsP3) uncaging in airway SMCs. Similarly, InsP3-evoked Ca(2+) release and contraction was inhibited by endogenous H2S precursor l-cysteine (10 mm) but not by l-serine (10 mm) or either amino acid in the presence of dl-propargylglycine (PPG). Consistent with the inhibition of Ca(2+) release through InsP3 receptors (InsP3Rs), Na2S reversibly inhibited acetylcholine (ACh)-induced Ca(2+) oscillations in airway SMCs. In addition, Na2S, the H2S donor GYY-4137, and l-cysteine caused relaxation of airways pre-contracted with either ACh or 5-hydroxytryptamine (5-HT). Na2S-induced airway relaxation was resistant to a guanylyl cyclase inhibitor (ODQ) and a protein kinase G inhibitor (Rp-8-pCPT-cGMPS). The effects of H2S on InsP3-evoked Ca(2+) release and contraction as well as on the relaxation of agonist-contracted airways were mimicked by the thiol-reducing agent dithiothreitol (DTT, 10 mm) and inhibited by the oxidizing agent diamide (30 μm). These studies indicate that H2S causes airway SMC relaxation by inhibiting Ca(2+) release through InsP3Rs and consequent reduction of agonist-induced Ca(2+) oscillations in SMCs. The results suggest a novel role for endogenously produced H2S that involves the modulation of InsP3-evoked Ca(2+) release - a cell-signalling system of critical importance for many physiological and pathophysiological processes.

Sulfidation of silver nanowires inside human alveolar epithelial cells: a potential detoxification mechanism

Silver nanowires (AgNWs) are being developed for use in optoelectronics. However before widespread usage, it is crucial to determine their potential effects on human health. It is accepted that Ag nanoparticles (AgNPs) exert toxic effects by releasing Ag(+) ions, but much less is known about whether Ag(+) reacts with compounds, or any downstream bioactive effects of transformed AgNPs. Analytical high-resolution transmission electron microscopy has been employed to elucidate cellular uptake and reactivity of AgNWs inside human alveolar epithelial type 1-like cells. AgNWs were observed in the cytoplasm and membrane-bound vesicles, and precipitation of Ag2S within the cell occurred after 1 h exposure. Cell viability studies showed no evidence of cytotoxicity and reactive oxygen species were not observed on exposure of cells to AgNWs. We suggest that Ag2S formation acts as a 'trap' for free Ag(+), significantly limiting short-term toxicological effects - with important consequences for the safety of Ag-nanomaterials to human health.

Mechanistic implications of persulfenate and persulfide binding in the active site of cysteine dioxygenase

Describing the organization of substrates and substrate analogues in the active site of cysteine dioxygenase identifies potential intermediates in this critical yet poorly understood reaction, the oxidation of cysteine to cysteine sulfinic acid. The fortuitous formation of persulfides under crystallization conditions has allowed their binding in the active site of cysteine dioxygenase to be studied. The crystal structures of cysteine persulfide and 3-mercaptopropionic acid persulfide bound to iron(II) in the active site show that binding of the persulfide occurs via the distal sulfide and, in the case of the cysteine persulfide, the amine also binds. Persulfide was detected by mass spectrometry in both the crystal and the drop, suggesting its origin is chemical rather than enzymatic. A mechanism involving the formation of the relevant disulfide from sulfide produced by hydrolysis of dithionite is proposed. In comparison, persulfenate {observed bound to cysteine dioxygenase [Simmons, C. R., et al. (2008) Biochemistry 47, 11390]} is shown through mass spectrometry to occur only in the crystal and not in the surrounding drop, suggesting that in the crystalline state the persulfenate does not lie on the reaction pathway. Stabilization of both the persulfenate and the persulfides does, however, suggest the position in which dioxygen binds during catalysis.

The cysteine dioxgenase knockout mouse: altered cysteine metabolism in nonhepatic tissues leads to excess H2S/HS(-) production and evidence of pancreatic and lung toxicity

AIMS

To define the consequences of loss of cysteine dioxygenase (CDO) on cysteine metabolism at the tissue level, we determined levels of relevant metabolites and enzymes and evidence of H2S/HS(-) (gaseous hydrogen sulfide and its conjugate base) toxicity in liver, pancreas, kidney, and lung of CDO(-/-) mice that were fed either a taurine-free or taurine-supplemented diet.

RESULTS

CDO(-/-) mice had low tissue and serum taurine and hypotaurine levels and high tissue levels of cysteine, consistent with the loss of CDO. CDO(-/-) mice had elevated urinary excretion of thiosulfate, high tissue and serum cystathionine and lanthionine levels, and evidence of inhibition and destabilization of cytochrome c oxidase, which is consistent with excess production of H2S/HS(-). Accumulation of cystathionine and lanthionine appeared to result from cystathionine β-synthase (CBS)-mediated cysteine desulfhydration. Very high levels of hypotaurine in pancreas of wild-type mice and very high levels of cystathionine and lanthionine in pancreas of CDO(-/-) mice were observed, suggesting a unique cysteine metabolism in the pancreas.

INNOVATION

The CDO(-/-) mouse model provides new insights into tissue-specific cysteine metabolism, particularly the role of pancreas in metabolism of excess cysteine by CBS-catalyzed reactions, and will be a useful model for studying the effects of excess endogenous production of H2S/HS(-).

CONCLUSION

The CDO(-/-) mouse clearly demonstrates that H2S/HS(-) production in tissues can exceed the capacity of the animal to oxidize sulfide to sulfate and demonstrates that pancreas and lung are more susceptible to toxicity from endogenous H2S/HS(-)production than are liver and kidney.

Studies of iron(III) porphyrinates containing silanethiolate ligands

The chemistry of several iron(III) porphyrinates containing silanethiolate ligands is described. The complexes are prepared by protonolysis reactions of silanethiols with the iron(III) precursors, [Fe(OMe)(TPP)] and [Fe(OH)(H2O)(TMP)] (TPP = dianion of meso-tetraphenylporphine; TMP = dianion of meso-tetramesitylporphine). Each of the compounds has been fully characterized in solution and the solid state. The stability of the silanethiolate complexes versus other iron(III) porphyrinate complexes containing sulfur-based ligands allows for an examination of their reactivity with several biologically relevant small molecules including H2S, NO, and 1-methylimidazole. Electrochemically, the silanethiolate complexes display a quasi-reversible one-electron oxidation event at potentials higher than that observed for an analogous arenethiolate complex. The behavior of these complexes versus other sulfur-ligated iron(III) porphyrinates is discussed.

Molecular biology of atherosclerosis

At least 468 individual genes have been manipulated by molecular methods to study their effects on the initiation, promotion, and progression of atherosclerosis. Most clinicians and many investigators, even in related disciplines, find many of these genes and the related pathways entirely foreign. Medical schools generally do not attempt to incorporate the relevant molecular biology into their curriculum. A number of key signaling pathways are highly relevant to atherogenesis and are presented to provide a context for the gene manipulations summarized herein. The pathways include the following: the insulin receptor (and other receptor tyrosine kinases); Ras and MAPK activation; TNF-α and related family members leading to activation of NF-κB; effects of reactive oxygen species (ROS) on signaling; endothelial adaptations to flow including G protein-coupled receptor (GPCR) and integrin-related signaling; activation of endothelial and other cells by modified lipoproteins; purinergic signaling; control of leukocyte adhesion to endothelium, migration, and further activation; foam cell formation; and macrophage and vascular smooth muscle cell signaling related to proliferation, efferocytosis, and apoptosis. This review is intended primarily as an introduction to these key signaling pathways. They have become the focus of modern atherosclerosis research and will undoubtedly provide a rich resource for future innovation toward intervention and prevention of the number one cause of death in the modern world.

redox Signaling by 8-nitro-cyclic guanosine monophosphate: nitric oxide- and reactive oxygen species-derived electrophilic messenger

SIGNIFICANCE

Emerging evidence has revealed that nitric oxide (NO)- and reactive oxygen species (ROS)-derived electrophiles formed in cells mediate signal transduction for responses to oxidative stress.

RECENT ADVANCES

The cyclic nucleotide with a nitrated guanine moiety-8-nitroguanosine 3',5'-cyclic monophosphate (8-nitro-cGMP)-first identified in 2007 as a second messenger for NO and ROS-has certain unique properties that its parental cGMP lacks. For example, it can react with particular protein Cys thiols because of its electrophilicity and can cause unique post-translational modifications of redox-sensor proteins such as Keap1 and H-Ras.

CRITICAL ISSUES

Site-specific S-guanylation of Keap1 at Cys434 induced NO- and ROS-mediated adaptive responses to oxidative stress. H-Ras Cys184 S-guanylation was recently found to be involved in activation of mitogen-activated protein kinase cascades as manifested by cellular senescence and heart failure in mouse cardiac hypertrophy models. The latest finding related to the concept of electrophile-based redox signaling is a potent regulatory function of endogenously produced hydrogen sulfide for redox signaling via 8-nitro-cGMP.

FUTURE DIRECTIONS

Electrophile modification of 8-nitro-cGMP, as a second messenger for NO and ROS, by hydrogen sulfide (i.e., electrophile sulfhydration) can most likely effect physiological regulation of cellular redox signaling. Continued investigation of the precise function of cellular hydrogen sulfide that may control electrophile-dependent redox cellular signaling, most typically via 8-nitro-cGMP formation, may provide novel insights into the molecular mechanisms of oxidative stress responses, oxidative stress-related pathology and disease control, and development of therapeutics for various diseases.

Hydrogen sulfide-based therapeutics and gastrointestinal diseases: translating physiology to treatments

Hydrogen sulfide (H2S) is a gaseous meditator that has various physiological and pathophysiological roles in the body. It has been shown to be an important mediator of gastrointestinal (GI) mucosal defense and contributes significantly to repair of damage and resolution of inflammation. Synthesis of H2S increases markedly after mucosal injury, and inhibition of H2S in such circumstances leads to delayed healing and exacerbated inflammation. The beneficial effects of H2S may be attributable to its ability to elevate mucosal blood flow, prevent leukocyte-endothelial adhesion, reduce oxidative stress, and stimulate angiogenesis. The use of H2S-donating agents and inhibitors of the key enzymes contributing to H2S synthesis have provided strong evidence for the importance of H2S in enhancing mucosal resistance to damage, as well as modulating inflammation and repair. In recent years, significant evidence has been generated to support the notion that these positive aspects of H2S can be exploited in drug design, particularly for arthritis, inflammatory bowel disease, and colon cancer chemoprevention. Thus novel H2S-based therapies have been shown to be effective anti-inflammatories that can promote the resolution of inflammation and accelerate the healing of GI ulcers. Encouraging results have already been seen experimentally with a mesalamine derivative and with H2S-releasing derivatives of nonsteroidal anti-inflammatory drugs.

Hydrogen sulfide alleviates hypoxia-induced root tip death in Pisum sativum

Flooding of soils often results in hypoxic conditions surrounding plant roots, which is a harmful abiotic stress to crops. Hydrogen sulfide (H2S) is a highly diffusible, gaseous molecule that modulates cell signaling and is involved in hypoxia signaling in animal cells. However, there have been no previous studies of H2S in plant cells in response to hypoxia. The effects of H2S on hypoxia-induced root tip death were studied in pea (Pisum sativum) via analysis of endogenous H2S and reactive oxygen species (ROS) levels. The activities of key enzymes involved in antioxidative and H2S metabolic pathways were determined using spectrophotometric assays. Ethylene was measured by gas chromatography. We found that exogenous H2S pretreatment dramatically alleviated hypoxia-induced root tip death by protecting root tip cell membranes from ROS damage induced by hypoxia and by stimulating a quiescence strategy through inhibiting ethylene production. Conversely, root tip death induced by hypoxia was strongly enhanced by inhibition of the key enzymes responsible for endogenous H2S biosynthesis. Our results demonstrated that exogenous H2S pretreatment significantly alleviates hypoxia-induced root tip death in pea seedlings and, therefore, enhances the tolerance of the plant to hypoxic stress.

The gasotransmitter hydrogen sulfide induces nrf2-target genes by inactivating the keap1 ubiquitin ligase substrate adaptor through formation of a disulfide bond between cys-226 and cys-613

AIMS

The signaling molecule hydrogen sulfide (H2S) protects cells against oxidative stress and activates NF-E2 p45-related factor 2 (Nrf2), a transcription factor that regulates antioxidant genes. We sought to establish whether H2S requires Nrf2 to protect against oxidative stress, and whether activation of Nrf2 by H2S involves antagonism of Kelch-like ECH-associated protein-1 (Keap1), a redox-sensitive ubiquitin ligase substrate adaptor that represses Nrf2 under normal homeostatic conditions.

RESULTS

H2S stabilizes Nrf2 protein and induces Nrf2-target genes via an antioxidant-/electrophile-response element. In mouse embryonic fibroblasts, the ability of H2S to protect against cell death caused by the redox-cycling agent menadione is dependent on Nrf2. Moreover, Nrf2 regulates murine genes involved in the production of H2S (Cystathionine-beta-synthase [Cbs] and Cystathionine-gamma-lyase [Cse]) and the degradation of H2S (Sulfide:quinone reductase-like [yeast] [Sqrdl]). We found that H2S stabilizes Nrf2 through inhibition of Keap1, an event that requires covalent modification of amino acids C226 and C613 in the substrate adaptor. Upregulation of Nrf2 by H2S partially involves the production of H2O2, which inhibits Keap1 by stimulating the formation of an intramolecular disulfide bond between C226 and C613. The Keap1 C226 and C613 residues are also S-sulfhydrated by H2S, and this may entail reduction of the C226-C613 disulfide bridge formed by H2O2.

INNOVATION

Upregulation of Nrf2 by H2S and H2O2 involves inactivation of Keap1 through modification of C226 and C613.

CONCLUSION

Inhibition of Keap1 by H2S leads to Nrf2-mediated induction of cytoprotective genes. Nrf2 controls Cbs, Cse, and Sqrdl, suggesting that a feedback loop exists between Nrf2 and H2S.

Thrombospondin-1 is a CD47-dependent endogenous inhibitor of hydrogen sulfide signaling in T cell activation

Thrombospondin-1 is a potent suppressor of T cell activation via its receptor CD47. However, the precise mechanism for this inhibition remains unclear. Because H2S is an endogenous potentiator of T cell activation and is necessary for full T cell activation, we hypothesized that thrombospondin-1 signaling through CD47 inhibits T cell activation by antagonizing H2S signaling. Primary T cells from thrombospondin-1 null mice were more sensitive to H2S-dependent activation assessed by proliferation and induction of interleukin-2 and CD69 mRNAs. Exogenous thrombospondin-1 inhibited H2S responses in wild type and thrombospondin-1 null T cells but enhanced the same responses in CD47 null T cells. Fibronectin, which shares integrin and glycosaminoglycan binding properties with thrombospondin-1 but not CD47 binding, did not inhibit H2S signaling. A CD47-binding peptide derived from thrombospondin-1 inhibited H2S-induced activation, whereas two other functional sequences from thrombospondin-1 enhanced H2S signaling. Therefore, engaging CD47 is necessary and sufficient for thrombospondin-1 to inhibit H2S-dependent T cell activation. H2S stimulated T cell activation by potentiating MEK-dependent ERK phosphorylation, and thrombospondin-1 inhibited this signaling in a CD47-dependent manner. Thrombospondin-1 also limited activation-dependent T cell expression of the H2S biosynthetic enzymes cystathionine β-synthase and cystathionine γ-lyase, thereby limiting the autocrine role of H2S in T cell activation. Thus, thrombospondin-1 signaling through CD47 is the first identified endogenous inhibitor of H2S signaling and constitutes a novel mechanism that negatively regulates T cell activation.

Hydrogen sulphide may be a novel downstream signal molecule in nitric oxide-induced heat tolerance of maize (Zea mays L.) seedlings

Nitric oxide (NO) is a second messenger with multifunction that is involved in plant growth, development and the acquisition of stress tolerance. In recent years, hydrogen sulphide (H(2)S) has been found to have similar functions, but crosstalk between NO and H(2)S in the acquisition of heat tolerance is not clear. In this study, pretreatment with the NO donor sodium nitroprusside (SNP) improved the survival percentage of maize seedlings and alleviated an increase in electrolyte leakage and a decrease in tissue vitality as well as accumulation of malondialdehyde, indicating that pretreatment with SNP improved the heat tolerance of maize seedlings. In addition, pretreatment with SNP enhanced the activity of L-cystine desulfhydrase, which, in turn, induced accumulation of endogenous H(2)S, while application of H(2)S donors, NaHS and GYY4137, increased endogenous H(2)S content, followed by mitigating increase in electrolyte leakage and enhanced survival percentage of seedlings under heat stress. Interestingly, SNP-induced heat tolerance was enhanced by application of NaHS and GYY4137, but was eliminated by inhibitors of H(2)S synthesis DL-propargylglycine, aminooxyacetic acid, potassium pyruvate and hydroxylamine, and the H(2)S scavenger hypotaurine. All of the above-mentioned results suggest that SNP pretreatment could improve heat tolerance, and H(2)S may be a downstream signal molecule in NO-induced heat tolerance of maize seedlings.

Proteome adaptations in Ethe1-deficient mice indicate a role in lipid catabolism and cytoskeleton organization via post-translational protein modifications

Hydrogen sulfide is a physiologically relevant signalling molecule. However, circulating levels of this highly biologically active substance have to be maintained within tightly controlled limits in order to avoid toxic side effects. In patients suffering from EE (ethylmalonic encephalopathy), a block in sulfide oxidation at the level of the SDO (sulfur dioxygenase) ETHE1 leads to severe dysfunctions in microcirculation and cellular energy metabolism. We used an Ethe1-deficient mouse model to investigate the effect of increased sulfide and persulfide concentrations on liver, kidney, muscle and brain proteomes. Major disturbances in post-translational protein modifications indicate that the mitochondrial sulfide oxidation pathway could have a crucial function during sulfide signalling most probably via the regulation of cysteine S-modifications. Our results confirm the involvement of sulfide in redox regulation and cytoskeleton dynamics. In addition, they suggest that sulfide signalling specifically regulates mitochondrial catabolism of FAs (fatty acids) and BCAAs (branched-chain amino acids). These findings are particularly relevant in the context of EE since they may explain major symptoms of the disease.

The redox proteome

The redox proteome consists of reversible and irreversible covalent modifications that link redox metabolism to biologic structure and function. These modifications, especially of Cys, function at the molecular level in protein folding and maturation, catalytic activity, signaling, and macromolecular interactions and at the macroscopic level in control of secretion and cell shape. Interaction of the redox proteome with redox-active chemicals is central to macromolecular structure, regulation, and signaling during the life cycle and has a central role in the tolerance and adaptability to diet and environmental challenges.

K(ATP) channels of parafacial respiratory group (pFRG) neurons are involved in H2S-mediated central inhibition of respiratory rhythm in medullary slices of neonatal rats

We recently found that hydrogen sulfide (H2S) participates in inhibitory regulation of rhythmic respiration by acting on the parafacial respiratory group (pFRG) in medullary slices of neonatal rats. The present study investigated whether ATP-sensitive potassium (KATP) channels are expressed in neurons of the pFRG, and, if so, whether they play a role in central regulation of respiratory activity, in particular the H2S-mediated central inhibition of respiratory rhythm in medullary slices of neonatal rats. Immunohistochemical techniques revealed that KATP channels are expressed in neurons of the pFRG region. Micro-injection of the KATP channel activator, pinacidil, into the pFRG region inhibited the discharge rhythm of hypoglossal rootlets, whereas injection of the KATP channel blocker, glibenclamide (Gl), had no effect. Micro-injection of the H2S donor sodium hydrosulfide (NaHS) into the pFRG region produced identical inhibitory responses to those induced by pinacidil. However, combined micro-injection of Gl and NaHS eliminated inhibitory effects of NaHS and converted to minor excitatory effects on the respiratory rhythm. It can be concluded that KATP channels of pFRG neurons are involved in the central regulation of respiratory rhythm and H2S-mediated inhibitory actions on respiratory rhythm in medullary slices of neonatal rats.

Chemical foundations of hydrogen sulfide biology

Following nitric oxide (nitrogen monoxide) and carbon monoxide, hydrogen sulfide (or its newer systematic name sulfane, H2S) became the third small molecule that can be both toxic and beneficial depending on the concentration. In spite of its impressive therapeutic potential, the underlying mechanisms for its beneficial effects remain unclear. Any novel mechanism has to obey fundamental chemical principles. H2S chemistry was studied long before its biological relevance was discovered, however, with a few exceptions, these past works have received relatively little attention in the path of exploring the mechanistic conundrum of H2S biological functions. This review calls attention to the basic physical and chemical properties of H2S, focuses on the chemistry between H2S and its three potential biological targets: oxidants, metals and thiol derivatives, discusses the applications of these basics into H2S biology and methodology, and introduces the standard terminology to this youthful field.