Hydrogen sulfide and cell signaling

A Novel Mechanism To Prevent H2S Toxicity in Caenorhabditis elegans

Hydrogen sulfide (H2S) is an endogenously produced signaling molecule that can be cytoprotective, especially in conditions of ischemia/reperfusion injury. However, H2S is also toxic, and unregulated accumulation or exposure to environmental H2S can be lethal. In Caenorhabditis elegans, the hypoxia inducible factor (hif-1) coordinates the initial transcriptional response to H2S, and is essential to survive exposure to low concentrations of H2S. We performed a forward genetic screen to identify mutations that suppress the lethality of hif-1 mutant animals in H2S. The mutations we recovered are specific for H2S, as they do not suppress embryonic lethality or reproductive arrest of hif-1 mutant animals in hypoxia, nor can they prevent the death of hif-1 mutant animals exposed to hydrogen cyanide. The majority of hif-1 suppressor mutations we recovered activate the skn-1/Nrf2 transcription factor. Activation of SKN-1 by hif-1 suppressor mutations increased the expression of a subset of H2S-responsive genes, consistent with previous findings that skn-1 plays a role in the transcriptional response to H2S. Using transgenic rescue, we show that overexpression of a single gene, rhy-1, is sufficient to protect hif-1 mutant animals in H2S. The rhy-1 gene encodes a predicated O-acyltransferase enzyme that has previously been shown to negatively regulate HIF-1 activity. Our data indicate that RHY-1 has novel, hif-1 independent, function that promotes survival in H2S.

Potential for therapeutic use of hydrogen sulfide in oxidative stress-induced neurodegenerative diseases

Oxidative phosphorylation is a source of energy production by which many cells satisfy their energy requirements. Endogenous reactive oxygen species (ROS) are by-products of oxidative phosphorylation. ROS are formed due to the inefficiency of oxidative phosphorylation, and lead to oxidative stress that affects mitochondrial metabolism. Chronic oxidative stress contributes to the onset of neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS). The immediate consequences of oxidative stress include lipid peroxidation, protein oxidation, and mitochondrial deoxyribonucleic acid (mtDNA) mutation, which induce neuronal cell death. Mitochondrial binding of amyloid-β (Aβ) protein has been identified as a contributing factor in AD. In PD and HD, respectively, α-synuclein (α-syn) and huntingtin (Htt) gene mutations have been reported to exacerbate the effects of oxidative stress. Similarly, abnormalities in mitochondrial dynamics and the respiratory chain occur in ALS due to dysregulation of mitochondrial complexes II and IV. However, oxidative stress-induced dysfunctions in neurodegenerative diseases can be mitigated by the antioxidant function of hydrogen sulfide (H2S), which also acts through the potassium (KATP/K+) ion channel and calcium (Ca2+) ion channels to increase glutathione (GSH) levels. The pharmacological activity of H2S is exerted by both inorganic and organic compounds. GSH, glutathione peroxidase (Gpx), and superoxide dismutase (SOD) neutralize H2O2-induced oxidative damage in mitochondria. The main purpose of this review is to discuss specific causes and effects of mitochondrial oxidative stress in neurodegenerative diseases, and how these are impacted by the antioxidant functions of H2S to support the development of advancements in neurodegenerative disease treatment.

Endoplasmic reticulum targeted fluorescent probe for the detection of hydrogen sulfide based on a twist-blockage strategy

Hydrogen sulfide (H₂S) is very important for humans and is involved in many physiological processes. Here, we designed and reported a new naked-eye colorimetric fluorescent probe Z1 for detecting H₂S in absolute HEPES solution. The fluorescence intensity, after the reaction of the probe and H₂S, is about 32 times that of the probe alone. When the concentration of H₂S is 0-100 μM, the detection limit (DL) is rather low at about 0.15 μM (3σ/slope). The response mechanism is based on the leaving of the 2,4-dinitrobenzene moiety, followed by intramolecular cyclization to give a fluorescent iminocoumarin-benzothiazole group. Moreover, Z1 was applied to endogenous and exogenous H₂S imaging in living cells. The high overlap coefficient proved that probe Z1 has good ER-tracker localization in living cells.

d-Cysteine-Induced Rapid Root Abscission in the Water Fern Azolla Pinnata: Implications for the Linkage between d-Amino Acid and Reactive Sulfur Species (RSS) in Plant Environmental Responses

Reactive Oxygen Species (ROS) and Reactive Nitrogen Species (RNS) have been proposed as universal signaling molecules in plant stress responses. There are a growing number of studies suggesting that hydrogen sulfide (H₂S) or Reactive Sulfur Species (RSS) are also involved in plant abiotic as well as biotic stress responses. However, it is still a matter of debate as to how plants utilize those RSS in their signaling cascades. Here, we demonstrate that d-cysteine is a novel candidate for bridging our gap in understanding. In the genus of the tiny water-floating fern Azolla, a rapid root abscission occurs in response to a wide variety of environmental stimuli as well as chemical inducers. We tested five H₂S chemical donors, Na₂S, GYY4137, 5a, 8l, and 8o, and found that 5a showed a significant abscission activity. Root abscission also occurred with the polysulfides Na₂S₂, Na₂S₃, and Na₂S₄. Rapid root abscission comparable to other known chemical inducers was observed in the presence of d-cysteine, whereas l-cysteine showed no effect. We suggest that d-cysteine is a physiologically relevant substrate to induce root abscission in the water fern Azolla.

Sensitive Method for Reliable Quantification of Sulfane Sulfur in Biological Samples

Sulfane sulfur has been recognized as a common cellular component, participating in regulating enzyme activities and signaling pathways. However, the quantification of total sulfane sulfur in biological samples is still a challenge. Here, we developed a method to address the need. All tested sulfane sulfur reacted with sulfite and quantitatively converted to thiosulfate when heated at 95 °C in a solution of pH 9.5 for 10 min. The assay condition was also sufficient to convert total sulfane sulfur in biological samples to thiosulfate for further derivatization and quantification. We applied the method to detect sulfane sulfur contents at different growth phases of bacteria, yeast, mammalian cells, and zebrafish. Total sulfane sulfur contents in all of them increased in the early stage, kept at a steady state for a period, and declined sharply in the late stage of the growth. Sulfane sulfur contents varied in different species. For Escherichia coli, growth media also affected the sulfane sulfur contents. Total sulfane sulfur contents from different organs of mouse and shrimp were also detected, varying from 1 to 10 nmol/(mg of protein). Thus, the new method is suitable for the quantification of total sulfane sulfur in biological samples.

Hydrogen sulfide is a novel regulator implicated in glucocorticoids-inhibited bone formation

Glucocorticoids contribute to the increased incidence of secondary osteoporosis. Hydrogen sulfide (H₂S) is a gasotransmitter and plays an essential role in bone metabolism. In this study, we investigated the therapeutic effects of H₂S on glucocorticoid-induced osteoporosis (GIO). We found that dexamethasone (Dex) decreased serum H₂S and two key H₂S-generating enzymes in the bone marrow in vivo, cystathione b-synthase and cystathione g-lyase. Treatment of H₂S-donor GYY4137 in rat significantly relieved the inhibitory effect of Dex on bone formation. Dex inhibited osteoblasts proliferation and osteogenic differentiation and decreased the expressions of the two H₂S-generating enzymes. Further investigation showed that H₂S was involved in Dex-mediated osteoblasts proliferation, differentiation, and apoptosis. Mechanistically, GYY4137 promoted osteoblastogenesis by activating Wnt signaling through increased production of the Wnt ligands. In comparison, the blockage of Wnt/β-catenin signaling pathway significantly alleviated the effect of H₂S on osteoblasts. In conclusion, the restoration of H₂S levels is a potential novel therapeutic approach for GIO.

Hydrogen Sulfide Mediated Tandem Reaction of Selenenyl Sulfides and Its Application in Fluorescent Probe Development

A unique reaction between H₂S and a selenenyl sulfide containing benzoate ester template was discovered. This reaction could be specifically triggered by H₂S and lead to ester bond cleavage. The reaction was not affected by the presence of thiols such as glutathione and cysteine. With this reaction, a series of fluorescent probes were synthesized and evaluated. The probes exhibited high sensitivity/selectivity for H₂S in both buffers and cells.

Hydrogen sulfide donor GYY4137 suppresses proliferation of human colorectal cancer Caco-2 cells by inducing both cell cycle arrest and cell death

Conflicting data regarding the ability of hydrogen sulfide (H₂S), which reaches high levels in the large intestine owing to biosynthesis in the intestinal cells and intestinal bacteria, to promote or inhibit colorectal cancer cell proliferation have been reported recently. In the present study, the effect of H₂S on the proliferation of the human colorectal cancer cell line Caco-2 was examined by using the H₂S donor GYY4137. At concentrations of 0.5 mM and 1.0 mM, GYY4137 significantly inhibited Caco-2 cell viability. Cell cycle analysis, and apoptosis and necrosis detection revealed that the anti-proliferative effect of GYY4137 was partially attributable to the induction of S-G₂/M cell cycle arrest, apoptosis and necrosis. These results suggest that H₂S has the potential to suppress human colorectal cancer cell proliferation by influencing both cell cycle and cell death.

Hydrogen sulfide stimulates activation of hepatic stellate cells through increased cellular bio-energetics

Hepatic fibrosis is caused by chronic inflammation and characterized as the excessive accumulation of extracellular matrix (ECM) by activated hepatic stellate cells (HSCs). Gasotransmitters like NO and CO are known to modulate inflammation and fibrosis, however, little is known about the role of the gasotransmitter hydrogen sulfide (H₂S) in liver fibrogenesis and stellate cell activation. Endogenous H₂S is produced by the enzymes cystathionine β-synthase (CBS), cystathionine γ-lyase (CTH) and 3-mercaptopyruvate sulfur transferase (MPST) [1]. The aim of this study was to elucidate the role of endogenously produced and/or exogenously administered H₂S on rat hepatic stellate cell activation and fibrogenesis. Primary rat HSCs were culture-activated for 7 days and treated with different H₂S releasing donors (slow releasing donor GYY4137, fast releasing donor NaHS) or inhibitors of the H₂S producing enzymes CTH and CBS (DL-PAG, AOAA). The main message of our study is that mRNA and protein expression level of H₂S synthesizing enzymes are low in HSCs compared to hepatocytes and Kupffer cells. However, H₂S promotes hepatic stellate cell activation. This conclusion is based on the fact that production of H₂S and mRNA and protein expression of its producing enzyme CTH are increased during hepatic stellate cell activation. Furthermore, exogenous H₂S increased HSC proliferation while inhibitors of endogenous H₂S production reduce proliferation and fibrotic makers of HSCs. The effect of H₂S on stellate cell activation correlated with increased cellular bioenergetics. Our results indicate that the H₂S generation in hepatic stellate cells is a target for anti-fibrotic intervention and that systemic interventions with H₂S should take into account cell-specific effects of H₂S.

A complete series of uranium(iv) complexes with terminal hydrochalcogenido (EH) and chalcogenido (E) ligands E = O, S, Se, Te

We here report the synthesis and characterization of a complete series of terminal hydrochalcogenido, U-EH, and chalcogenido uranium(iv) complexes, U≡E (with E = O, S, Se, Te), supported by the (^Ad,MeArOH)₃tacn (1,4,7-tris(3-(1-adamantyl)-5-methyl-2-hydroxybenzyl)-1,4,7-triazacyclononane) ligand system. Reaction of H₂E with the trivalent precursor [((^Ad,MeArO)₃tacn)U] (1) yields the corresponding uranium(iv) hydrochalcogenido complexes [((^Ad,MeArO)₃tacn)U(EH)] (2). Subsequent deprotonation of the terminal hydrochalcogenido species with KN(SiMe₃)₂, in the presence of 2.2.2-cryptand, gives access to the uranium(iv) complexes with terminal chalcogenido ligands [K(2.2.2-crypt)][((^Ad,MeArO)₃tacn)U≡E] (3). In order to study the influence of the varying terminal chalogenido ligands on the overall molecular and electronic structure, all complexes were studied by single-crystal X-ray diffractometry, UV/vis/NIR, electronic absorption, and IR vibrational spectroscopy as well as SQUID magnetometry and computational analyses (DFT, MO, NBO).

Exogenous Hydrogen Sulfide Offers Neuroprotection on Intracerebral Hemorrhage Injury Through Modulating Endogenous H2S Metabolism in Mice

Hydrogen sulfide (H₂S), an important endogenous signaling molecule, has a significant neuroprotective role in the central nervous system. In this study, we examined the protective effects of exogenous H₂S against intracerebral hemorrhage (ICH), as well as its underlying mechanisms. We investigated the effects of exogenous H₂S on ICH using Western blotting, injury volume, measurement of brain edema, propidium iodide (PI) staining, and behavior assessment, respectively. We found that endogenous H₂S production was downregulated in the brain after ICH, which is caused by the decrease in cystathionine β-synthase (CBS) as the predominant cerebral H₂S-generating enzyme in the brain. Treatment with sodium hydrosulfide (NaHS; an H₂S producer) could restore the H₂S production and the expression of CBS. NaHS could also attenuate brain edema, injury volume, and neurological deficits in the Morris water maze test after ICH. Western blotting results indicated that H₂S pretreatment reversed the increase in caspase 3 cleavage and the decrease in Bcl-2, suppressed the activation of autophagy marker (LC3II and Beclin-1), and maintained the p62 level in injured striatum post-ICH. However, H₂S could not restore brain CBS expression and H₂S content, reduce brain edema, and improve motor performance and memory function after ICH through modulating autophagy and apoptosis when pretreated with the CBS inhibitor aminooxyacetic acid (AOAA). We also found that AOAA reduced the endogenous H₂S production through inhibiting the enzyme activity of CBS rather than modulating the expression of CBS protein level. These present results indicate that H₂S may possess potential therapeutic value in the treatment of brain injury after ICH, and the protective effect of exogenous H₂S against ICH may be not a direct action but an indirect effect through inducing endogenous H₂S metabolism responses.

Hydrogen Sulfide Promotes Nodulation and Nitrogen Fixation in Soybean-Rhizobia Symbiotic System

The rhizobium-legume symbiotic system is crucial for nitrogen cycle balance in agriculture. Hydrogen sulfide (H2S), a gaseous signaling molecule, may regulate various physiological processes in plants. However, whether H2S has regulatory effect in this symbiotic system remains unknown. Herein, we investigated the possible role of H2S in the symbiosis between soybean (Glycine max) and rhizobium (Sinorhizobium fredii). Our results demonstrated that an exogenous H2S donor (sodium hydrosulfide [NaHS]) treatment promoted soybean growth, nodulation, and nitrogenase (Nase) activity. Western blotting analysis revealed that the abundance of Nase component nifH was increased by NaHS treatment in nodules. Quantitative real-time polymerase chain reaction data showed that NaHS treatment upregulated the expressions of symbiosis-related genes nodA, nodC, and nodD of S. fredii. In addition, expression of soybean nodulation marker genes, including early nodulin 40 (GmENOD40), ERF required for nodulation (GmERN), nodulation signaling pathway 2b (GmNSP2b), and nodulation inception genes (GmNIN1a, GmNIN2a, and GmNIN2b), were upregulated. Moreover, the expressions of glutamate synthase (GmGOGAT), asparagine synthase (GmAS), nitrite reductase (GmNiR), ammonia transporter (GmSAT1), leghemoglobin (GmLb), and nifH involved in nitrogen metabolism were upregulated in NaHS-treated soybean roots and nodules. Together, our results suggested that H2S may act as a positive signaling molecule in the soybean-rhizobia symbiotic system and enhance the system's nitrogen fixation ability.

Recent Progress in Metal-Organic Framework (MOF) Based Luminescent Chemodosimeters

Metal-organic frameworks (MOFs), as a class of crystalline hybrid architectures, consist of metal ions and organic ligands and have displayed great potential in luminescent sensing applications due to their tunable structures and unique photophysical properties. Until now, many studies have been reported on the development of MOF-based luminescent sensors, which can be classified into two major categories: MOF chemosensors based on reversible host-guest interactions and MOF chemodosimeters based on the irreversible reactions between targets with a probe. In this review, we summarize the recently developed luminescent MOF-based chemodosimeters for various analytes, including H2S, HClO, biothiols, fluoride ions, redox-active biomolecules, Hg2+, and CN-. In addition, some remaining challenges and future perspectives in this area are also discussed.

Role of hydrogen sulfide in the musculoskeletal system

Hydrogen sulfide (H₂S) has been known as a gasotransmitter, and it contributes to various physiological and pathological processes. Multiple enzymes such as cystathionine-β-synthase (CBS), cystathionine-γ-lyase (CSE) and 3-Mercaptopyruvate sulfurtransferase (MST) produce endogenous H₂S, and these are differentially expressed in the various tissue systems including the skeletal system. However, abnormal H₂S production is associated with deregulation of the signaling cascade and imbalanced tissue homeostasis. Several studies have previously provided evidence showing the essential regulatory action of H₂S in skeletal homeostasis. In this review, we have emphasized the novel function of H₂S in both bone and skeletal muscle anabolism, in particular. Additionally, we also reviewed the molecular and epigenetic basis of H₂S signaling in bone development and skeletal muscle function.

A Review of Hydrogen Sulfide Synthesis, Metabolism, and Measurement: Is Modulation of Hydrogen Sulfide a Novel Therapeutic for Cancer?

Significance: Hydrogen sulfide (H2S) has been recognized as the third gaseous transmitter alongside nitric oxide and carbon monoxide. In the past decade, numerous studies have demonstrated an active role of H2S in the context of cancer biology. Recent Advances: The three H2S-producing enzymes, namely cystathionine γ-lyase (CSE), cystathionine β-synthase (CBS), and 3-mercaptopyruvate sulfurtransferase (3MST), have been found to be highly expressed in numerous types of cancer. Moreover, inhibition of CBS has shown anti-tumor activity, particularly in colon cancer, ovarian cancer, and breast cancer, whereas the consequence of CSE or 3MST inhibition remains largely unexplored in cancer cells. Intriguingly, H2S donation at high amounts or a long time duration has also been observed to induce cancer cell apoptosis in vitro and in vivo while sparing noncancerous fibroblast cells. Therefore, a bell-shaped model has been proposed to explain the role of H2S in cancer development. Specifically, endogenous H2S or a relatively low level of exogenous H2S may exhibit a pro-cancer effect, whereas exposure to H2S at a higher amount or for a long period may lead to cancer cell death. This indicates that inhibition of H2S biosynthesis and H2S supplementation serve as two distinct ways for cancer treatment. This paradoxical role of H2S has stimulated the enthusiasm for the development of novel CBS inhibitors, H2S donors, and H2S-releasing hybrids. Critical Issues: A clear relationship between H2S level and cancer progression remains lacking. The possibility that the altered levels of these byproducts have influenced the cell viability of cancer cells has not been excluded in previous studies when modulating H2S producing enzymes. Future Directions: The consequence of CSE or 3MST inhibition in cancer cells need to be examined in the future. Better portrayal of the crosstalk among these gaseous transmitters may not only lead to an in-depth understanding of cancer progression but also shed light on novel strategies for cancer therapy.

A Genetically Encoded, Ratiometric Fluorescent Biosensor for Hydrogen Sulfide

As an important gasotransmitter, hydrogen sulfide (H₂S) plays crucial roles in cell signaling. Incorporation of p-azidophenylalanine ( pAzF) into fluorescent proteins (FPs) via genetic code expansion has been a successful strategy in developing intensity-based, genetically encoded fluorescent biosensors for H₂S. To extend this strategy for ratiometric measurement which eliminates many detection uncertainties via self-calibration at two wavelengths, we modified the chromophore of a circularly permutated, superfolder green fluorescent protein (cpsGFP) with pAzF to derive cpsGFP- pAzF, which subsequently served as a Förster resonance energy transfer (FRET) acceptor to EBFP2, an enhanced blue fluorescent protein. The resultant construct, namely, hsFRET, is the first ratiometric, genetically encoded fluorescent biosensor for H₂S. Both in vitro and in mammalian cells, H₂S reduces the azido functional group of hsFRET to amine, leading to an increase of FRET from EBFP2 to cpsGFP. Our results collectively demonstrated that hsFRET could be used to selectively and ratiometrically monitor H₂S.

Biological Effects of Thermal Water-Associated Hydrogen Sulfide on Human Airways and Associated Immune Cells: Implications for Respiratory Diseases

Natural mineral (thermal) waters have been used for centuries as treatment for various diseases. However, the scientific background of such therapeutic action is mostly empiric and based on knowledge acquired over time. Among the various types of natural mineral waters, sulfurous thermal waters (STWs) are the most common type in the center of Portugal. STWs are characterized by high pH, poor mineralization, and the presence of several ions and salts, such as bicarbonate, sodium, fluoride, silica, and carbonate. Furthermore, these waters are indicated as a good option for the treatment of various illnesses, namely respiratory diseases (e.g., allergic rhinitis, asthma, and chronic obstructive pulmonary disease). From the sulfide species present in these waters, hydrogen sulfide (H₂S) stands out due to its abundance. In healthy conditions, H₂S-related enzymes (e.g., cystathionine β-synthase and cystathionine γ-lyase) are expressed in human lungs, where they have mucolytic, antioxidant, anti-inflammatory, and antibacterial roles, thus contributing to airway epithelium homeostasis. These roles occur mainly through S-sulfhydration, a post-translational modification through which H₂S is able to change the activity of several targets, such as ion channels, second messengers, proteins, among others. However, in respiratory diseases the metabolism of H₂S is altered, which seems to contribute somehow to the respiratory deterioration. Moreover, H₂S has been regarded as a good biomarker of airway dysfunction and severity, and can be measured in serum, sputum, and exhaled air. Hence, in this review we will recapitulate the effects of STWs on lung epithelial-immune crosstalk through the action of its main component, H₂S.

Molecular engineering of a colorimetric two-photon fluorescent probe for visualizing H2S level in lysosome and tumor

As a multifunctional signaling molecule, hydrogen sulfide (H₂S) plays an essential role in diverse physiological and pathological processes. The two-photon fluorescence probes detecting H₂S selectively in vivo could be useful tools to better study the mechanism of diseases. Then, an efficient two-photon lysosome-specific probe 1 has been developed to detect endogenous H₂S in living cells and mice. Probe 1 displays excellent properties with 28-fold fluorescence enhancement, marked color changes in naked-eye and fluorescence, high selectivity and sensitivity, and low detection limit (0.22 μM) to H₂S. These remarkable properties of probe 1 enable its practical applications in detecting H₂S in environment (wastewater) and food (beer). Moreover, as a two-photon probe under near infrared excitation at 790 nm, probe 1 can monitor the level changes of endogenous H₂S of lysosome and tumor in living system with good membrane permeability and high imaging resolution. Specially, the probe detecting H₂S distribution in lysosome could provide more evidences to explain the association of target-organelle and H₂S.

Interaction between the signaling molecules hydrogen sulfide and hydrogen peroxide and their role in vacuolar H+ -ATPase regulation in cadmium-stressed cucumber roots

Vacuolar H⁺ -ATPase (V-ATPase; EC 3.6.3.14) is the main enzyme responsible for generating a proton gradient across the tonoplast. Under cadmium (Cd) stress conditions, V-ATPase activity is inhibited. In the present work, hydrogen sulfide (H₂ S) and hydrogen peroxide (H₂ O₂ ) cross-talk was analyzed in cucumber (Cucumis sativus L.) seedlings exposed to Cd to explain the role of both signaling molecules in the control of V-ATPase. V-ATPase activity and gene expression as well as H₂ S and H₂ O₂ content and endogenous production were determined in roots of plants treated with 100 μM CdCl₂ and different inhibitors or scavengers. It was found that H₂ S donor improved photosynthetic parameters in Cd-stressed cucumber seedlings. Cd-induced stimulation of H₂ S level was correlated with the increased activities of the H₂ S-generating desulfhydrases. Increased H₂ O₂ and lowered H₂ S contents in roots were able to reduce V-ATPase activities similar to Cd. H₂ O₂ and H₂ S-induced modulations in V-ATPase activities were not closely related to the transcript level of encoding genes, suggesting posttranslational modifications of enzyme protein. On the other hand, exogenous H₂ O₂ raised H₂ S content in root tissues independently from the desulfhydrase activity. Although treatment of control plants with H₂ S significantly stimulated NADPH oxidase activity and gene expression, H₂ S did not affect H₂ O₂ accumulation in roots exposed to Cd. The results suggest the existence of two pathways of H₂ S generation in Cd-stressed cucumber roots. One involves desulfhydrase activity, as was previously demonstrated in different plant species. The other, the desulfhydrase-independent pathway induced by H₂ O₂ /NADPH oxidase, may protect V-ATPase from inhibition by Cd.

A fluorescent probe based on tetrahydro[5]helicene derivative with large Stokes shift for rapid and highly selective recognition of hydrogen sulfide

In this work, we have designed and synthesized a dinitrobenzene-sulfonate tetrahydro[5]helicene (H-DNP) as an effective fluorescent probe for detection of hydrogen sulfide (H₂S). Upon the addition of H₂S, a significant fluorescence enhancement (75-fold) at 495 nm can be observed with a distinct color change from colorless to yellow. Additionally, H-DNP shows low background spectroscopic signal, large Stokes Shift up to ~140 nm, good sensitivity, rapid response time less than 2 min, low detection limit (48 nM) and high selectivity toward common bio-thiols (Cysteine, Homocysteine and Glutathione). Compared with the previous dinitrophenoxy tetrahydro[5]helicene, this probe has shorter response time and lower detection limit. Most importantly, this probe H-DNP has low toxicity to cells and excellent cell permeability, which can be applied to visualize H₂S in living cells.

HS- facilitated sulfur pyran realizing hydrogen sulfide detection and imaging in HepG2 cells and chlorella

The new carbazole-based fluorescent probe CA-1 was designed and synthesized for the high selective detection of H₂S based on HS^- facilitated sulfur pyran resulting in UV-Vis and fluorescent spectra changes. At the same time, the probe showed good sensitivity to the detection of H₂S with a low detection limit of 0.16 μM. The detection process can be monitored by naked eye: with the addition of H₂S, the probe system changed from yellow to pink. Importantly, the probe could be applied in monitoring H₂S in HepG2 cells and Chlorella. These results indicate that CA-1 can be used as a promising fluorescent probe for the detection of H₂S in situ.

A novel water-soluble fluorescence probe based on ICT lighten for detecting hydrogen sulfide and its application in bioimaging

Endogenous H₂S, considered to be involved in many physiological processes, has attracted more attention in fluorescence detection and bioimaging. Therefore, it is necessary to design probes with good biocompatibility and high bioavailability. In this study, a novel fluorescent probe, QN-1, based on azide group and quinoline derivatives was developed for detecting H₂S. QN-1 can detect H₂S specifically in aqueous phase, which indicated QN-1 has excellent water solubility. Besides, QN-1 shows excellent properties of higher selectivity and 11-fold fluorescence enhancement at 533 nm. Therefore, QN-1 with excellent properties can be used for cell imaging.

Effect of Ketoprofen and ATB-352 on the Immature Human Intestine: Identification of Responders and Non-responders

BACKGROUND AND OBJECTIVE

The use of nonsteroidal anti-inflammatory drugs (NSAIDs) is associated with a broad spectrum of life-threatening adverse effects on the immature gastrointestinal tract. NSAID derivatives exploiting the beneficial effects of biologically active gases, such as hydrogen sulfide (H2S), have been developed. Herein, we determined the effects of ketoprofen and ATB-352, a H2S-releasing ketoprofen derivative, on selected metabolic pathways previously identified to be significantly altered by indomethacin in the human immature intestine.

METHODS

Ketoprofen and ATB-352 were tested on human mid-gestation small intestinal explants maintained in a serum-free organ culture system for 48 hours. The expression levels of the representative genes involved in selected metabolic pathways were measured by real-time PCR after a treatment of 48 hours.

RESULTS

Tested at a concentration that allows more than 80% inhibition of PGE2 production, ketoprofen was found to be less damaging than indomethacin at an equivalent dosage. However, based on the inducibility of cyclooxygenase-2 transcript expression, we were able to discriminate between responder individuals in which the deleterious effects observed with indomethacin were attenuated, and non-responder specimens in which the effects were similar to those observed with indomethacin. ATB-352 did not induce significant changes compared to ketoprofen on these metabolic pathways.

CONCLUSIONS

These results show less damaging effects of ketoprofen compared to indomethacin on the immature intestine and indicate that the intestinal response to this NSAID significantly varies between individuals. However, the results did not allow us to demonstrate a specific beneficial effect of H2S release in organ culture.

Hyaluronated liposomes containing H2S-releasing doxorubicin are effective against P-glycoprotein-positive/doxorubicin-resistant osteosarcoma cells and xenografts

Doxorubicin (dox) is one of the first-line drug in osteosarcoma treatment but its effectiveness is limited by the efflux pump P-glycoprotein (Pgp) and by the onset of cardiotoxicity. We previously demonstrated that synthetic doxs conjugated with a H₂S-releasing moiety (Sdox) were less cardiotoxic and more effective than dox against Pgp-overexpressing osteosarcoma cells. In order to increase the active delivery to tumor cells, we produced hyaluronic acid (HA)-conjugated liposomes containing Sdox (HA-Lsdox), exploiting the abundance of the HA receptor CD44 in osteosarcoma. HA-Lsdox showed favorable drug-release profile and higher toxicity in vitro and in vivo than dox or the FDA-approved liposomal dox Caelyx^® against Pgp-overexpressing osteosarcoma, displaying the same cardiotoxicity profile of Caelyx^®. Differently from dox, HA-Lsdox delivered the drug within the endoplasmic reticulum (ER), inducing protein sulfhydration and ubiquitination, and activating a ER stress pro-apoptotic response mediated by CHOP. HA-Lsdox also sulfhydrated the nascent Pgp in the ER, reducing its activity. We propose HA-Lsdox as an innovative tool noteworthy to be tested in Pgp-overexpressing patients, who are frequently less responsive to standard treatments in which dox is one of the most important drugs.

Hydrogen sulfide, a novel small molecule signalling agent, participates in the regulation of ganoderic acids biosynthesis induced by heat stress in Ganoderma lucidum

Hydrogen sulfide (H₂S), an emerging small-molecule signalling agent, was recently shown to play a significant role in many physiological processes, but relatively few studies have been conducted on microorganisms compared with mammals and plants. By studying the pretreatment of H₂S donor sodium hydrosulfide (NaHS) and the scavenger hypotaurine (HT) and Cystathionine β-synthase silenced strains, we found that H₂S could alleviate the HS-induced ganoderic acids (GAs) biosynthesis. Our transcriptome results also showed that many signaling pathways and metabolic pathways, such as the glycolysis, TCA, oxidative phosphorylation and pentose phosphate pathway, are influenced by H₂S. Further experimental results indicated that H₂S could affect the physiological process of Ganoderma lucidum by interacting with multiple signals, including ROS, NO, AMPK, sphingolipid, mTOR, phospholipase D and MAPK, and physiological and pharmacological analyses showed that H₂S might alleviate the biosynthesis of GAs by inhibiting the intracellular calcium in G. lucidum.

Vasodilatory effect of formaldehyde via the NO/cGMP pathway and the regulation of expression of KATP, BKCa and L-type Ca2+ channels

Formaldehyde (FA), a well-known toxic gas molecule similar to nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H₂S), is widely produced endogenously via numerous biochemical pathways, and has a number of physiological roles in the biosystem. We attempted to investigate the vasorelaxant effects of FA and their underlying mechanisms. We found that FA induced vasorelaxant effects on rat aortic rings in a concentration-dependent manner. The NO/cyclic guanosine 5' monophosphate (cGMP) pathway was up-regulated when the rat aortas were treated with FA. The expression of large-conductance Ca²⁺-activated K⁺ (BK_Ca) channel subunits α and β of the rat aortas was increased by FA. Similarly, the levels of ATP-sensitive K⁺ (K_ATP) channel subunits K_ir6.1 and K_ir6.2 were also up-regulated when the rat aortas were incubated with FA. In contrast, levels of the L-type Ca²⁺ channel (LTCC) subunits, Ca_v1.2 and Ca_v1.3, decreased dramatically with increasing concentrations of FA. We demonstrated that the regulation of FA on vascular contractility may be via the up-regulation of the NO/cGMP pathway and the modulation of ion channels, including the upregulated expression of the K_ATP and BK_Ca channels and the inhibited expression of LTCCs. Further study is needed to explore the in-depth mechanisms of FA induced vasorelaxation.

Hydrogen sulfide plays an important protective role by influencing autophagy in diseases

Autophagy can regulate cell growth, proliferation, and stability of cell environment. Its dysfunction can be involved in a variety of diseases. Hydrogen sulfide (H(2)S) is an important signaling molecule that regulates many physiological and pathological processes. Recent studies indicate that H(2)S plays an important protective role in many diseases through influencing autophagy, but its mechanism is not fully understood. This article reviewed the progress about the effect of H(2)S on autophagy in diseases in recent years in order to provide theoretical basis for the further research on the interaction of H(2)S and autophagy and the mechanisms involved.

X-Ray Structure of Human Sulfide:Quinone Oxidoreductase: Insights into the Mechanism of Mitochondrial Hydrogen Sulfide Oxidation

Hydrogen sulfide (H₂S) is a gasotransmitter exhibiting pivotal functions in diverse biological processes, including activation of multiple cardioprotective pathways. Sulfide:quinone oxidoreductase (SQOR) is an integral membrane flavoprotein that catalyzes the first step in the mitochondrial metabolism of H₂S. As such, it plays a critical role in controlling physiological levels of the gasotransmitter and has attracted keen interest as a potential drug target. We report the crystal structure of human SQOR, unraveling the molecular basis for the enzyme's ability to catalyze sulfane sulfur transfer reactions with structurally diverse acceptors. We demonstrate that human SQOR contains unique features: an electropositive surface depression implicated as a binding site for sulfane sulfur acceptors and postulated to funnel negatively charged substrates to a hydrophilic H₂S-oxidizing active site, which is connected to a hydrophobic internal tunnel that binds coenzyme Q. These findings support a proposed model for catalysis and open the door for structure-based drug design.

Exogenous hydrogen sulfide mitigates LPS + ATP-induced inflammation by inhibiting NLRP3 inflammasome activation and promoting autophagy in L02 cells

The aim of this study is to investigate whether exogenous hydrogen sulfide (H₂S) could mitigate lipopolysaccharide (LPS) + Adenosine Triphosphate (ATP)-induced inflammation by inhibiting nucleotide-binding oligomerization domain-like receptor 3 (NLRP3) inflammasome activation and promoting autophagy in L02 cells. We stimulated L02 cells with different concentrations of LPS, then the cell viability, cell apoptosis, and the protein level of NLRP3 inflammasome were detected by MTT and western blot to determine the appropriate LPS concentration used in this study. The cells were divided into 4 group: the cells in control group were cultured with RPMI-1640 for 23.5 h; the cells in LPS + ATP group were cultured with RPMI-1640 for 0.5 h, then were stimulated with 100 ng/ml LPS for 18 h followed by stimulation with 5 mM ATP for 5 h; the cells in Sodium hydrosulfide (NaHS) + LPS + ATP group were pretreated with NaHS for 0.5 h before exposure to LPS for 18 h and ATP for 5 h; the cells in NaHS group were treated with NaHS for 0.5 h, then were cultured with RPMI-1640 for 23 h. Subsequently, the cells in each group were collected, the protein levels of NLRP3, pro-caspase-1, cleaved caspase-1, P62, toll-like receptor 4 (TLR4), nuclear factor-kappa B (NF-κB), LC3, Beclin-1, and interleukin (IL)-1 beta (β) were detected by western blot and enzyme-linked immunosorbent assay. Our results showed that exogenous H₂S reduced the protein levels of NLRP3, cleaved caspase-1, TLR4, NF-κB, P62, and IL-1β induced by LPS + ATP and increased the ratio of LC3-II/I and the protein levels of Beclin 1 suppressed by LPS + ATP. This study demonstrated that H₂S might suppress LPS + ATP-induced inflammation by inhibiting NLRP3 inflammasome and promoting autophagy. In conclusion, H₂S might have potential applications in the treatment of aseptic hepatitis.

Hydroxycobalamin Reveals the Involvement of Hydrogen Sulfide in the Hypoxic Responses of Rat Carotid Body Chemoreceptor Cells

Carotid body (CB) chemoreceptor cells sense arterial blood PO₂, generating a neurosecretory response proportional to the intensity of hypoxia. Hydrogen sulfide (H₂S) is a physiological gaseous messenger that is proposed to act as an oxygen sensor in CBs, although this concept remains controversial. In the present study we have used the H₂S scavenger and vitamin B₁₂ analog hydroxycobalamin (Cbl) as a new tool to investigate the involvement of endogenous H₂S in CB oxygen sensing. We observed that the slow-release sulfide donor GYY4137 elicited catecholamine release from isolated whole carotid bodies, and that Cbl prevented this response. Cbl also abolished the rise in [Ca²⁺]_i evoked by 50 µM NaHS in enzymatically dispersed CB glomus cells. Moreover, Cbl markedly inhibited the catecholamine release and [Ca²⁺]_i rise caused by hypoxia in isolated CBs and dispersed glomus cells, respectively, whereas it did not alter these responses when they were evoked by high [K⁺]_e. The L-type Ca²⁺ channel blocker nifedipine slightly inhibited the rise in CB chemoreceptor cells [Ca²⁺]_i elicited by sulfide, whilst causing a somewhat larger attenuation of the hypoxia-induced Ca²⁺ signal. We conclude that Cbl is a useful and specific tool for studying the function of H₂S in cells. Based on its effects on the CB chemoreceptor cells we propose that endogenous H₂S is an amplifier of the hypoxic transduction cascade which acts mainly by stimulating non-L-type Ca²⁺ channels.

Rapid measurement of hydrogen sulphide in human blood plasma using a microfluidic method

Hydrogen sulfide (H₂S) is emerging as an important gasotransmitter in both physiological and pathological states. Rapid measurement of H₂S remains a challenge. We report a microfluidic method for rapid measurement of sulphide in blood plasma using Dansyl-Azide, a fluorescence (FL) based probe. We have measured known quantities of externally added (exogenous) H₂S to both buffer and human blood plasma. Surprisingly, a decrease in FL intensity with increase in exogenous sulphide concentration in plasma was observed which is attributed to the interaction between the proteins and sulphide present in plasma underpinning our observation. The effects of mixing and incubation time, pH, and dilution of plasma on the FL intensity is studied which revealed that the FL assay required a mixing time of 2 min, incubation time of 5 min, a pH of 7.1 and performing the test within 10 min of sampling; these together constitute the optimal parameters at room temperature. A linear correlation (with R² ≥ 0.95) and an excellent match was obtained when a comparison was done between the proposed microfluidic and conventional spectrofluorometric methods for known concentrations of H₂S (range 0–100 µM). We have measured the baseline level of endogenous H₂S in healthy volunteers which was found to lie in the range of 70 μM – 125 μM. The proposed microfluidic device with DNS-Az probe enables rapid and accurate estimation of a key gasotransmitter H₂S in plasma in conditions closely mimicking real time clinical setting. The availability of this device as at the point of care, will help in understanding the role of H₂S in health and disease.

Hydrogen sulfide: Therapeutic or injurious in ischemic stroke?

Hydrogen sulfide (H2S) has been identified as a vasodilatory, neuromodulatory, and anti-inflammatory gasotransmitter with antioxidant properties. Studies focused in cardiac tissue suggest H2S functions as a protective agent; however in the central nervous system (CNS) the effects of H2S during states of stress or injury, such as stroke, remain controversial. Currently, the application of H2S donors and modulators in stroke depends on the type of H2S donor and the timing of the therapy.

Dual-biomarker-triggered fluorescence probes for differentiating cancer cells and revealing synergistic antioxidant effects under oxidative stress

Hydrogen sulfide (H2S) and human NAD(P)H:quinine oxidoreductase 1 (hNQO1) are potential cancer biomarkers and also vital participants in cellular redox homeostasis. Simultaneous detection of these two biomarkers would benefit the diagnostic precision of related cancers and could also help to investigate their crosstalk in response to oxidative stress. Despite this importance, fluorescent probes that can be activated by the dual action of H2S detection and hNQO1 activity have not been investigated. To this end, dual-biomarker-triggered fluorescent probes 1 and 2 were rationally constructed by installing two chemoselective triggering groups into one fluorophore. Probe 1 provides a small turn-on fluorescence response toward H2S but a much larger response to both H2S and hNQO1 in tandem. By contrast, fluorescence probe 2 is activated only in the presence of both H2S and hNQO1. Probe 2 exhibits a large fluorescence turn-on (>400 fold), high sensitivity, excellent selectivity as well as good biocompatibility, enabling the detection of both endogenous H2S and hNQO1 activity in living cells. Bioimaging results indicated that probe 2 could differentiate HT29 and HepG2 cancer cells from HCT116, FHC and HeLa cells owing to the existence of relatively high endogenous levels of both biomarkers. Expanded investigations using 2 revealed that cells could generate more endogenous H2S and hNQO1 upon exposure to exogenous hydrogen peroxide (H2O2), implying the synergistic antioxidant effects under conditions of cellular oxidative stress.

The response of sulfur dioxygenase to sulfide in the body wall of Urechis unincinctus

Background

In some sedimentary environments, such as coastal intertidal and subtidal mudflats, sulfide levels can reach millimolar concentrations (2–5 mM) and can be toxic to marine species. Interestingly, some organisms have evolved biochemical strategies to overcome and tolerate high sulfide conditions, such as the echiuran worm, Urechis unicinctus. Mitochondrial sulfide oxidation is important for detoxification, in which sulfur dioxygenase (SDO) plays an indispensable role. Meanwhile, the body wall of the surface of the worm is in direct contact with sulfide. In our study, we chose the body wall to explore the SDO response to sulfide.

Methods

Two sulfide treatment groups (50 µM and 150 µM) and a control group (natural seawater) were used. The worms, U. unicinctus, were collected from the intertidal flat of Yantai, China, and temporarily reared in aerated seawater for three days without feeding. Finally, sixty worms with similar length and mass were evenly assigned to the three groups. The worms were sampled at 0, 6, 24, 48 and 72 h after initiation of sulfide exposure. The body walls were excised, frozen in liquid nitrogen and stored at −80 °C for RNA and protein extraction. Real-time quantitative RT-PCR, enzyme-linked immunosorbent assay and specific activity detection were used to explore the SDO response to sulfide in the body wall.

Results

The body wall of U. unicinctus consists of a rugal epidermis, connective tissue, outer circular muscle and middle longitudinal muscle. SDO protein is mainly located in the epidermis. When exposed to 50 µM sulfide, SDO mRNA and protein contents almost remained stable, but SDO activity increased significantly after 6 h (P < 0.05). However, in the 150 µM sulfide treatment group, SDO mRNA and protein contents and activity all increased with sulfide exposure time; significant increases all began to occur at 48 h (P < 0.05).

Discussion

All the results indicated that SDO activity can be enhanced by sulfide in two regulation mechanisms: allosteric regulation, for low concentrations, and transcription regulation, which is activated with an increase in sulfide concentration.

Visualization of Sulfane Sulfur in Plants with a Near-Infrared Fluorescent Probe

Sulfane sulfur species are an important type of reactive sulfur species. These compounds have unique reactivity to attach reversibly to other sulfur atoms and exhibit regulatory effects in diverse biological systems. Recent studies have suggested that sulfane sulfurs are involved in signal transduction processes of hydrogen sulfide (H₂S). The development of probes for selective, rapid, and sensitive detection of sulfane sulfur is of great significance for studying their physiological and pathological roles in biological systems, especially in plant systems for which physiological research has lagged behind. However, so far there is still a lack of sufficient chemical tools for directly tracking and measuring sulfane sulfur in biological systems, and in particular, the detection of sulfane sulfur in living plant tissues is still challenging. Herein, we report a near-infrared fluorescent probe, SSNIP, for the selective imaging of sulfane sulfur. SSNIP is capable of detecting sulfane sulfur at physiological concentrations in both aqueous buffer and living human cells. Then, with SSNIP, we demonstrate the fluorescent monitoring of endogenous sulfane sulfur in plant tissues such as Arabidopsis thaliana roots for the first time. Furthermore, the application of SSNIP in evaluating the level of sulfane sulfur in Arabidopsis thaliana roots at different growth stages is performed. The results show that the level of sulfane sulfur in Arabidopsis thaliana roots correlates well with their growth stages, which suggests that sulfane sulfurs might act as actual signaling molecules to promote plant growth and root elongation. In addition, it reveals potential applications for the biological and pathological studies of sulfane sulfur, especially in plant physiology.