Production and physiological effects of hydrogen sulfide

Hydrogen sulfide accumulates LDL receptor precursor via downregulating PCSK9 in HepG2 cells

Endogenous hydrogen sulfide (H2S) affects cholesterol homeostasis and liver X receptor α (LXRα) expression. However, whether low-density lipoprotein (LDL) receptor (LDLR), a key player in cholesterol homeostasis, is regulated by exogenous H2S through LXRα signaling has not been determined. We investigated the effects of sodium hydrosulfide (NaHS, H2S donor) on LDLR expression in the presence or absence of LXR agonists, T0901317 or GW3965 in HepG2 cells. We found that H2S strongly accumulated LDLR precursor in the presence of T0901317. Hence, LDLR transcription and the genes involved in LDLR precursor maturation and degradation were studied. T0901317 increased the LDLR mRNA level, whereas H2S did not affect LDLR transcription. H2S had no significant effect on the expression of LXRα and inducible degrader of LDLR (IDOL). H2S and T0901317 altered mRNA levels of several enzymes for N- and O-glycosylation and endoplasmic reticulum (ER) chaperones assisting LDLR maturation, but did not affect their protein levels. H2S decreased proprotein convertase subtilisin/kexin type 9 (PCSK9) protein levels and its mRNA level elevated by T0901317. T0901317 with PCSK9 siRNA also accumulated LDLR precursor as did T0901317 with H2S. High glucose increased PCSK9 protein levels and attenuated LDLR precursor accumulation induced by T0901317 with H2S. Taken together, H2S accumulates LDLR precursor by downregulating PCSK9 expression but not through the LXRα-IDOL pathway, LDLR transcriptional activation, or dysfunction of glycosylation enzymes and ER chaperones. These results also indicate that PCSK9 plays an important role in LDLR maturation in addition to its well-known effect on the degradation of LDLR mature form.

GASOMEDIATOR H2S IN THROMBOSIS AND HEMOSTASIS

This review was aimed to briefly summarize current knowledge of the biological roles of gasomediator H2S in hemostasis and cardiovascular diseases. Since the discovery that mammalian cells are enzymatically producing H2S, this molecule underwent a dramatic metamorphosis from dangerous pollutant to a biologically relevant mediator. As a gasomediator, hydrogen sulfide plays a role of signaling molecule, which is involved in a number of processes in health and disease, including pathogenesis of cardiovascular abnormalities, mainly through modulating different patterns of vasculature functions and thrombotic events. Recently, several studies have provided unequivocal evidence that H2S reduces blood platelet reactivity by inhibiting different stages of platelet activation (platelet adhesion, secretion and aggregation) and thrombus formation. Moreover, H2S changes the structure and function of fibrinogen and proteins associated with fibrinolysis. Hydrogen sulfide regulates proliferation and apoptosis of vascular smooth muscle cells, thus modulating angiogenesis and vessel function. Undoubtedly, H2S is also involved in a multitude of other physiological functions. For example, it exhibits anti-inflammatory effects by inhibiting ROS production and increasing expression of antioxidant enzymes. Some studies have demonstrated the role of hydrogen sulfide as a therapeutic agent in various diseases, including cardiovascular pathologies. Further studies are required to evaluate its importance as a regulator of cell physiology and associated cardiovascular pathological conditions such as myocardial infarction and stroke.

Crescent-Shaped Supramolecular Tetrapeptide Nanostructures

Self-assembly of amphiphilic peptide-based building blocks gives rise to a plethora of interesting nanostructures such as ribbons, fibers, and tubes. However, it remains a great challenge to employ peptide self-assembly to directly produce nanostructures with lower symmetry than these highly symmetric motifs. We report here our discovery that persistent and regular crescent nanostructures with a diameter of 28 ± 3 nm formed from a series of tetrapeptides with the general structure AdKSKSEX (Ad = adamantyl group, KS = lysine residue functionalized with an S-aroylthiooxime (SATO) group, E = glutamic acid residue, and X = variable amino acid residue). In the presence of cysteine, the biological signaling gas hydrogen sulfide (H2S) was released from the SATO units of the crescent nanostructures, termed peptide-H2S donor conjugates (PHDCs), reducing levels of reactive oxygen species (ROS) in macrophage cells. Additional in vitro studies showed that the crescent nanostructures alleviated cytotoxicity induced by phorbol 12-myristate-13-acetate more effectively than common H2S donors and a PHDC of a similar chemical structure, AdKSKSE, that formed short nanoworms instead of nanocrescents. Cell internalization studies indicated that nanocrescent-forming PHDCs were more effective in reducing ROS levels in macrophages because they entered into and remained in cells better than nanoworms, highlighting how nanostructure morphology can affect bioactivity in drug delivery.

A natural cyanobacterial protein C-phycoerythrin as an HS- selective optical probe in aqueous systems

A naturally fluorescent cyanobacterial protein C-phycoerythrin (CPE) was investigated as a fluorescent probe for biologically and environmentally important hydrosulphide (HS^-) ion. It was selective for HS amongst a large anion screen and the optical response was rapid. Sequential UV-visible titration showed considerable peak shift and attenuation with increasing [HS^-] while fluorescence titration proved that HS^- quenched CPE fluorescence in a concentration dependent manner. The linear response range was 0-2 mM HS^- while the Stern Volmer curve was non-linear and the limit of detection was 185.12 μM. Except bicarbonate and glycine, no anion or biomolecule interfered with the detection even at 10 times the concentration of HS^-. It was also free of influences from other sulphur forms like sulphite, sulphate and thiosulphate. CPE reliably detected HS^- in freshwater and effluent samples, though some under- and over - estimation was evident. The % recovery ranged from ~96 to 105% (RSD ~ 0.035-0.188%). FTIR analysis showed significant changes in the amide I and II regions of CPE, along with minor modifications in the amide III region as well, showing that HS^- was able to influence the protein secondary structure at higher concentrations.

New insights into RhoA/Rho-kinase signaling: a key regulator of vascular contraction

While Rho-signalling controlling vascular contraction is a canonical mechanism, with the modern approaches used in research, we are advancing our understanding and details into this pathway are often uncovered. RhoA-mediated Rho-kinase is the major regulator of vascular smooth muscle cells and a key player manoeuvring other functions in these cells. The discovery of new interactions, such as oxidative stress and hydrogen sulphide with Rho signalling are emerging addition not only in the physiology of the smooth muscle, but especially in the pathophysiology of vascular diseases. Likewise, the interplay between ageing and Rho-kinase in the vasculature has been recently considered. Importantly, in smooth muscle contraction, this pathway may also be affected by sex hormones, and consequently, sex-differences. This review provides an overview of Rho signalling mediating vascular contraction and focuses on recent topics discussed in the literature affecting this pathway such as ageing, sex differences and oxidative stress.

Hydrogen sulfide, oxygen, and calcium regulation in developing human airway smooth muscle

Preterm infants can develop airway hyperreactivity and impaired bronchodilation following supplemental O2 (hyperoxia) in early life, making it important to understand mechanisms of hyperoxia effects. Endogenous hydrogen sulfide (H2 S) has anti-inflammatory and vasodilatory effects with oxidative stress. There is little understanding of H2 S signaling in developing airways. We hypothesized that the endogenous H2 S system is detrimentally influenced by O2 and conversely H2 S signaling pathways can be leveraged to attenuate deleterious effects of O2 . Using human fetal airway smooth muscle (fASM) cells, we investigated baseline expression of endogenous H2 S machinery, and effects of exogenous H2 S donors NaHS and GYY4137 in the context of moderate hyperoxia, with intracellular calcium regulation as a readout of contractility. Biochemical pathways for endogenous H2 S generation and catabolism are present in fASM, and are differentially sensitive to O2 toward overall reduction in H2 S levels. H2 S donors have downstream effects of reducing [Ca2+ ]i responses to bronchoconstrictor agonist via blunted plasma membrane Ca2+ influx: effects blocked by O2 . However, such detrimental O2 effects are targetable by exogenous H2 S donors such as NaHS and GYY4137. These data provide novel information regarding the potential for H2 S to act as a bronchodilator in developing airways in the context of oxygen exposure.

HNF4α regulates sulfur amino acid metabolism and confers sensitivity to methionine restriction in liver cancer

Methionine restriction, a dietary regimen that protects against metabolic diseases and aging, represses cancer growth and improves cancer therapy. However, the response of different cancer cells to this nutritional manipulation is highly variable, and the molecular determinants of this heterogeneity remain poorly understood. Here we report that hepatocyte nuclear factor 4α (HNF4α) dictates the sensitivity of liver cancer to methionine restriction. We show that hepatic sulfur amino acid (SAA) metabolism is under transcriptional control of HNF4α. Knocking down HNF4α or SAA enzymes in HNF4α-positive epithelial liver cancer lines impairs SAA metabolism, increases resistance to methionine restriction or sorafenib, promotes epithelial-mesenchymal transition, and induces cell migration. Conversely, genetic or metabolic restoration of the transsulfuration pathway in SAA metabolism significantly alleviates the outcomes induced by HNF4α deficiency in liver cancer cells. Our study identifies HNF4α as a regulator of hepatic SAA metabolism that regulates the sensitivity of liver cancer to methionine restriction.

The molecular determinants of differential responses of different cancer cells to methionine restriction are poorly understood. Here the authors show that hepatocyte nuclear factor 4α regulates sulfur amino acid metabolism and dictates the sensitivity of liver cancer to this dietary manipulation.

Curcumin analogs (B2BrBC and C66) supplementation attenuates airway hyperreactivity and promote airway relaxation in neonatal rats exposed to hyperoxia

BACKGROUND

This study was undertaken to test the hypothesis that the newly synthesized curcuminoids B2BrBC and C66 supplementation will overcome hyperoxia-induced tracheal hyperreactivity and impairment of relaxation of tracheal smooth muscle (TSM).

MATERIALS AND METHODS

Rat pups (P5) were exposed to hyperoxia (>95% O2 ) or normoxia for 7 days. At P12, tracheal cylinders were used to study in vitro contractile responses induced by methacholine (10-8 -10-4 M) or relaxation induced by electrical field stimulation (5-60 V) in the presence/absence of B2BrBC or C66, or to study the direct relaxant effects elicited by both analogs.

RESULTS

Hyperoxia significantly increased contraction and decreased relaxation of TSM compared to normoxia controls. Presence of B2BrBC or C66 normalized both contractile and relaxant responses altered by hyperoxia. Both, curcuminoids directly induced dose-dependent relaxation of preconstricted TSM. Supplementation of hyperoxic animals with B2BrBC or C66, significantly increased catalase activity. Lung TNF-α was significantly increased in hyperoxia-exposed animals. Both curcumin analogs attenuated increases in TNF-α in hyperoxic animals.

CONCLUSION

We show that B2BrBC and C66 provide protection against adverse contractility and relaxant effect of hyperoxia on TSM, and whole lung inflammation. Both analogs induced direct relaxation of TSM. Through restoration of catalase activity in hyperoxia, we speculate that analogs are protective against hyperoxia-induced tracheal hyperreactivity by augmenting H2 O2 catabolism. Neonatal hyperoxia induces increased tracheal contractility, attenuates tracheal relaxation, diminishes lung antioxidant capacity, and increases lung inflammation, while monocarbonyl CUR analogs were protective of these adverse effects of hyperoxia. Analogs may be promising new therapies for neonatal hyperoxic airway and lung disease.

Gestational Exposure to Cigarette Smoke Suppresses the Gasotransmitter H2S Biogenesis and the Effects Are Transmitted Transgenerationally

Rationale: Gestational cigarette smoke (CS) impairs lung angiogenesis and alveolarization, promoting transgenerational development of asthma and bronchopulmonary dysplasia (BPD). Hydrogen sulfide (H₂S), a proangiogenic, pro-alveolarization, and anti-asthmatic gasotransmitter is synthesized by cystathionine-γ-lyase (CSE), cystathionine-β-synthase (CBS), and 3-mercaptopyruvate sulfur transferase (3MST). Objective: Determine if gestational CS exposure affected the expression of H₂S synthesizing enzymes in the mouse lung and human placenta. Methods: Mice were exposed throughout gestational period to secondhand CS (SS) at approximating the dose of CS received by a pregnant woman sitting in a smoking bar for 3 h/days during pregnancy. Lungs from 7-days old control and SS-exposed pups and human placenta from mothers who were either non-smokers or smokers during pregnancy were analyzed for expression of the enzymes. Measurements: Mouse lungs and human placentas were examined for the expression of CSE, CBS, and 3MST by immunohistochemical staining, qRT-PCR and/or Western blot (WB) analyses. Results: Compared to controls, mouse lung exposed gestationally to SS had significantly lower levels of CSE, CBS, and 3MST. Moreover, the SS-induced suppression of CSE and CBS in F1 lungs was transmitted to the F2 generation without significant change in the magnitude of the suppression. These changes were associated with impaired epithelial-mesenchymal transition (EMT)-a process required for normal lung angiogenesis and alveolarization. Additionally, the placentas from mothers who smoked during pregnancy, expressed significantly lower levels of CSE, CBS, and 3MST, and the effects were partially moderated by quitting smoking during the first trimester. Conclusions: Lung H₂S synthesizing enzymes are downregulated by gestational CS and the effects are transmitted to F2 progeny. Smoking during pregnancy decreases H₂S synthesizing enzymes is human placentas, which may correlate with the increased risk of asthma/BPD in children.

Nanotoxicity of ZrS3 Probed in a Bioluminescence Test on E. coli Bacteria: The Effect of Evolving H2S

Materials from a large family of transition metal trichalcogenides (TMTCs) attract considerable attention because of their potential applications in electronics, optoelectronics and energy storage, but information on their toxicity is lacking. In this study, we investigated the toxicity of ZrS₃, a prominent TMTC material, toward photoluminescent E. coli bacteria in a bioluminescence test. We found that freshly prepared ZrS₃ suspensions in physiological saline solution with concentrations as high as 1 g/L did not exhibit any toxic effects on the bacteria. However, ZrS₃ suspensions that were stored for 24 h prior to the bioluminescence tests were very toxic to the bacteria and inhibited their emission, even at concentrations down to 0.001 g/L. We explain these observations by the aqueous hydrolysis of ZrS₃, which resulted in the formation of ZrO_x on the surface of ZrS₃ particles and the release of toxic H₂S. The formation of ZrO_x was confirmed by the XPS analysis, while the characteristic H₂S smell was noticeable for the 24 h suspensions. This study demonstrates that while ZrS₃ appears to be intrinsically nontoxic to photoluminescent E. coli bacteria, it may exhibit high toxicity in aqueous media. The results of this study can likely be extended to other transition metal chalcogenides, as their toxicity in aqueous solutions may also increase over time due to hydrolysis and the formation of H₂S. The results of this study also demonstrate that since many systems involving nanomaterials are unstable and evolve over time in various ways, their toxicity may evolve as well, which should be considered for relevant toxicity tests.

Recent advances in the neuroprotective effects of medical gases

Central nervous system injuries are a leading cause of death and disability worldwide. Although the exact pathophysiological mechanisms of various brain injuries vary, central nervous system injuries often result in an inflammatory response, and subsequently lead to brain damage. This suggests that neuroprotection may be necessany in the treatment of multiple disease models. The use of medical gases as neuroprotective agents has gained great attention in the medical field. Medical gases include common gases, such as oxygen, hydrogen and carbon dioxide; hydrogen sulphide and nitric oxide that have been considered toxic; volatile anesthetic gases, such as isoflurane and sevoflurane; and inert gases like helium, argon, and xenon. The neuroprotection from these medical gases has been investigated in experimental animal models of various types of brain injuries, such as traumatic brain injury, stroke, subarachnoid hemorrhage, cerebral ischemic/reperfusion injury, and neurodegenerative diseases. Nevertheless, the transition into the clinical practice is still lagging. This delay could be attributed to the contradictory paradigms and the conflicting results that have been obtained from experimental models, as well as the presence of inconsistent reports regarding their safety. In this review, we summarize the potential mechanisms underlying the neuroprotective effects of medical gases and discuss possible candidates that could improve the outcomes of brain injury.

Implications of hydrogen sulfide in liver pathophysiology: Mechanistic insights and therapeutic potential

Background

Over the last several decades, hydrogen sulfide (H₂S) has been found to exert multiple physiological functions in mammal systems. The endogenous production of H₂S is primarily mediated by cystathione β-synthase (CBS), cystathione γ-lyase (CSE), and 3-mercaptopyruvate sulfurtransferase (3-MST). These enzymes are widely expressed in the liver tissues and regulate hepatic functions by acting on various molecular targets.

Aim of Review

In the present review, we will highlight the recent advancements in the cellular events triggered by H₂S under liver diseases. The therapeutic effects of H₂S donors on hepatic diseases will also be discussed.

Key Scientific Concepts of Review

As a critical regulator of liver functions, H₂S is critically involved in the etiology of various liver disorders, such as nonalcoholic steatohepatitis (NASH), hepatic fibrosis, hepatic ischemia/reperfusion (IR) injury, and liver cancer. Targeting H₂S-producing enzymes may be a promising strategy for managing hepatic disorders.

The role of mitochondrial reactive oxygen species, NO and H2 S in ischaemia/reperfusion injury and cardioprotection

Redox signalling in mitochondria plays an important role in myocardial ischaemia/reperfusion (I/R) injury and in cardioprotection. Reactive oxygen and nitrogen species (ROS/RNS) modify cellular structures and functions by means of covalent changes in proteins including among others S‐nitros(yl)ation by nitric oxide (NO) and its derivatives, and S‐sulphydration by hydrogen sulphide (H₂S). Many enzymes are involved in the mitochondrial formation and handling of ROS, NO and H₂S under physiological and pathological conditions. In particular, the balance between formation and removal of reactive species is impaired during I/R favouring their accumulation. Therefore, various interventions aimed at decreasing mitochondrial ROS accumulation have been developed and have shown cardioprotective effects in experimental settings. However, ROS, NO and H₂S play also a role in endogenous cardioprotection, as in the case of ischaemic pre‐conditioning, so that preventing their increase might hamper self‐defence mechanisms. The aim of the present review was to provide a critical analysis of formation and role of reactive species, NO and H₂S in mitochondria, with a special emphasis on mechanisms of injury and protection that determine the fate of hearts subjected to I/R. The elucidation of the signalling pathways of ROS, NO and H₂S is likely to reveal novel molecular targets for cardioprotection that could be modulated by pharmacological agents to prevent I/R injury.

Strain-specificity in the hydrogen sulphide signalling network following dietary restriction in recombinant inbred mice

Modulation of the ageing process by dietary restriction (DR) across multiple taxa is well established. While the exact mechanism through which DR acts remains elusive, the gasotransmitter hydrogen sulphide (H2S) may play an important role. We employed a comparative-type approach using females from three ILSXISS recombinant inbred mouse strains previously reported to show differential lifespan responses following 40% DR. Following long-term (10 months) 40% DR, strain TejJ89-reported to show lifespan extension under DR-exhibited elevated hepatic H2S production relative to its strain-specific ad libitum (AL) control. Strain TejJ48 (no reported lifespan effect following 40% DR) exhibited significantly reduced hepatic H2S production, while H2S production was unaffected by DR in strain TejJ114 (shortened lifespan reported following 40% DR). These differences in H2S production were reflected in highly divergent gene and protein expression profiles of the major H2S production and disposal enzymes across strains. Increased hepatic H2S production in TejJ89 mice was associated with elevation of the mitochondrial H2S-producing enzyme 3-mercaptopyruvate sulfurtransferase (MPST). Our findings further support the potential role of H2S in DR-induced longevity and indicate the presence of genotypic-specificity in the production and disposal of hepatic H2S in response to 40% DR in mice.

Synergisms, Discrepancies and Interactions between Hydrogen Sulfide and Carbon Monoxide in the Gastrointestinal and Digestive System Physiology, Pathophysiology and Pharmacology

Endogenous gas transmitters, hydrogen sulfide (H₂S), carbon monoxide (CO) and nitric oxide (NO) are important signaling molecules known to exert multiple biological functions. In recent years, the role of H₂S, CO and NO in regulation of cardiovascular, neuronal and digestive systems physiology and pathophysiology has been emphasized. Possible link between these gaseous mediators and multiple diseases as well as potential therapeutic applications has attracted great attention from biomedical scientists working in many fields of biomedicine. Thus, various pharmacological tools with ability to release CO or H₂S were developed and implemented in experimental animal in vivo and in vitro models of many disorders and preliminary human studies. This review was designed to review signaling functions, similarities, dissimilarities and a possible cross-talk between H₂S and CO produced endogenously or released from chemical donors, with special emphasis on gastrointestinal digestive system pathologies prevention and treatment.

Reactive oxygen, nitrogen, and sulfur species in human male fertility. A crossroad of cellular signaling and pathology

Infertility is a significant global health problem that currently affects one of six couples in reproductive age. The quality of male reproductive cells dramatically decreased over the last years and almost every aspect of modern life additionally worsen sperm functional parameters that consequently markedly increase male infertility. This clearly points out the importance of finding a new approach to treat male infertility. Redox signaling mediated by reactive oxygen, nitrogen and sulfur species (ROS, RNS, and RSS respectively), has appeared important for sperm reproductive function. Present review summarizes the current knowledge of ROS, RNS, and RSS in male reproductive biology and identifies potential targets for development of novel pharmacological and therapeutic approaches for male infertility by targeted therapeutic modulation of redox signaling.

Toxic effects of hydrogen sulfide donor NaHS induced liver apoptosis is regulated by complex IV subunits and reactive oxygen species generation in rats

In recent years, the protective effect of hydrogensulfide donor sodium hydrosulfide(NaHS) on multiple organs has been widely reported. The study aimed to explorethe effect of commonly used concentration of NaHS on theliver and its potential damage mechanism. Rats divided into 4 groups: control, NaHS I (1 mg/kg), II (3 mg/kg) and III(5 mg/kg) groups, and each group is divided into four-timepoints (2, 6, 12, and 24 hours). Results showed that H2S concentration increased, mitochondrial complex IV activity inhibited, the COX I and IV subunits and mitochondrial apoptosis pathway-related proteins expression increased in atime- and dose-dependent manner. We confirmed that 1 mg/kg NaHS had no injuryeffect on the liver, 3 and 5 mg/kg NaHS inhibitsthe activity of mitochondrial complex IV by promoting COX I and IV subunits expression, leading to the increase in ROS and ultimately inducing apoptosis and liver injury.

The re-emerging pathophysiological role of the cystathionine-β-synthase - hydrogen sulfide system in Down syndrome

Down syndrome (DS) is associated with significant perturbances in many morphological and biochemical features. Cystathionine-β-synthase (CBS) is one of the key mammalian enzymes that is responsible for the biological production of the gaseous transmitter hydrogen sulfide (H₂ S). When H₂ S is overproduced, it can exert detrimental cellular effects, in part due to inhibition of mitochondrial Complex IV activity. An increased expression of CBS and the consequent overproduction of H₂ S are well documented in individuals with DS. Two decades ago, it has been proposed that a toxic overproduction of H₂ S importantly contributes to the metabolic and neurological deficits associated with DS. However, until recently, this hypothesis has not yet been tested experimentally. Recent data generated in human dermal fibroblasts show that DS cells overproduce H₂ S, which, in turn, suppresses mitochondrial Complex IV activity and impairs mitochondrial oxygen consumption and ATP generation. Therapeutic CBS inhibition lifts the tonic (and reversible) suppression of Complex IV: This results in the normalization of mitochondrial function in DS cells. H₂ S may also contribute to the cellular dysfunction via several other molecular mechanisms through interactions with various mitochondrial and extramitochondrial molecular targets. The current article provides a historical background of the field, summarizes the recently published data and their potential implications, and outlines potential translational approaches (such as CBS inhibition and H₂ S neutralization) and future experimental studies in this re-emerging field of pathobiochemistry.

Anomalous Kv 7 channel activity in human malignant hyperthermia syndrome unmasks a key role for H2 S and persulfidation in skeletal muscle

BACKGROUND AND PURPOSE

Human malignant hyperthermia (MH) syndrome is induced by volatile anaesthetics and involves increased levels of cystathionine β-synthase (CBS)-derived H2 S within skeletal muscle. This increase contributes to skeletal muscle hypercontractility. Kv 7 channels, expressed in skeletal muscle, may be a molecular target for H2 S. Here, we have investigated the role of Kv 7 channels in MH.

EXPERIMENTAL APPROACH

Skeletal muscle biopsies were obtained from MH-susceptible (MHS) and MH-negative (MHN) patients. Immunohistochemistry, RT-PCR, Western blot, and in vitro contracture test (IVCT) were carried out. Development and characterization of primary human skeletal muscle cells (PHSKMC) and evaluation of cell membrane potential were also performed. The persulfidation state of Kv 7 channels and polysulfide levels were measured.

KEY RESULTS

Kv 7 channels were similarly expressed in MHN and MHS biopsies. The IVCT revealed an anomalous contractility of MHS biopsies following exposure to the Kv 7 channel opener retigabine. Incubation of negative biopsies with NaHS, prior to retigabine addition, led to an MHS-like positive response. MHS-derived PHSKMC challenged with retigabine showed a paradoxical depolarizing effect, compared with the canonical hyperpolarizing effect. CBS expression and activity were increased in MHS biopsies, resulting in a major polysulfide bioavailability. Persulfidation of Kv 7.4 channels was significantly higher in MHS than in MHN biopsies.

CONCLUSIONS AND IMPLICATIONS

In skeletal muscle of MHS patients, CBS-derived H2 S induced persulfidation of Kv 7 channels. This post-translational modification switches the hyperpolarizing activity into depolarizing. This mechanism can contribute to the pathological skeletal muscle hypercontractility typical of MH syndrome.

LINKED ARTICLES

This article is part of a themed section on Hydrogen Sulfide in Biology & Medicine. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.4/issuetoc.

Nitric oxide and hydrogen sulfide crosstalk during heavy metal stress in plants

Gases such as ethylene, hydrogen peroxide (H₂ O₂ ), nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H₂ S) have been recognized as vital signaling molecules in plants and animals. Of these gasotransmitters, NO and H₂ S have recently gained momentum mainly because of their involvement in numerous cellular processes. It is therefore important to study their various attributes including their biosynthetic and signaling pathways. The present review provides an insight into various routes for the biosynthesis of NO and H₂ S as well as their signaling role in plant cells under different conditions, more particularly under heavy metal stress. Their beneficial roles in the plant's protection against abiotic and biotic stresses as well as their adverse effects have been addressed. This review describes how H₂ S and NO, being very small-sized molecules, can quickly pass through the cell membranes and trigger a multitude of responses to various factors, notably to various stress conditions such as drought, heat, osmotic, heavy metal and multiple biotic stresses. The versatile interactions between H₂ S and NO involved in the different molecular pathways have been discussed. In addition to the signaling role of H₂ S and NO, their direct role in posttranslational modifications is also considered. The information provided here will be helpful to better understand the multifaceted roles of H₂ S and NO in plants, particularly under stress conditions.

Extracellular Signal-Regulated Kinase 1/2 Pathway Is Insufficiently Involved in the Neuroprotective Effect by Hydrogen Sulfide Supplement in Experimental Glaucoma

Purpose

Glaucoma is a neurodegenerative eye disease characterized by gradually impaired visual field and irreversible blindness due to retinal ganglion cell (RGC) loss. Our previous studies have confirmed that hydrogen sulfide (H2S) takes part in the glaucomatous process and contributes to RGC protection. The present study aimed to further investigate the role of extracellular signal-regulated kinase 1/2 (ERK 1/2) pathway underlying the impact of H2S, to better understand the mechanism through which H2S exerts neuroprotection in glaucoma.

Methods

An established rat glaucoma model was used and 168 rats were qualified to undergo sodium hydrosulfide (NaHS, a H2S donor)/PD98059 (an ERK inhibitor) treatment. Then the survival and apoptosis of RGC were evaluated through retrograde labeling and TUNEL staining, along with activity evaluations of ERK 1/2 pathway, intrinsic apoptotic pathway, glial activation, nuclear factor kappa B (NF-κB) pathway, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, autophagy, and TNF-α production through immunohistochemistry, Western blotting, and ELISA.

Results

The study demonstrated that NaHS suppressed ERK 1/2 pathway activity similarly to PD98059 in retinas of experimental glaucoma rats, while PD98059 also similarly suppressed glial activation, NF-κB pathway, NADPH oxidase, and TNF-α production. However, PD98059 did not affect RGC survival, apoptotic regulation, or autophagy as NaHS did.

Conclusions

Our study indicated that inhibition of ERK 1/2 pathway might partly contribute to the neuroprotection by H2S in experimental glaucoma; however, it was insufficient to initiate the therapeutic effect on its own.

Biological Effects of Morpholin-4-Ium 4 Methoxyphenyl (Morpholino) Phosphinodithioate and Other Phosphorothioate-Based Hydrogen Sulfide Donors

Significance: Hydrogen sulfide (H₂S) is regarded as the third gasotransmitter along with nitric oxide and carbon monoxide. Extensive studies have demonstrated a variety of biological roles for H₂S in neurophysiology, cardiovascular disease, endocrine regulation, and other physiological and pathological processes. Recent Advances: Novel H₂S donors have proved useful in understanding the biological functions of H₂S, with morpholin-4-ium 4 methoxyphenyl (morpholino) phosphinodithioate (GYY4137) being one of the most common pharmacological tools used. One advantage of GYY4137 over sulfide salts is its ability to release H₂S in a slow and sustained manner akin to endogenous H₂S production, rather than the delivery of H₂S as a single concentrated burst. Critical Issues: Here, we summarize recent progress made in the characterization of the biological activities and pharmacological effects of GYY4137 in a range of in vitro and in vivo systems. Recent developments in the structural modification of GYY4137 to generate new compounds and their biological effects are also discussed. Future Directions: Slow-releasing H₂S donor, GYY4137, and other phosphorothioate-based H₂S donors are potent tools to study the biological functions of H₂S. Despite recent progress, more work needs to be performed on these new compounds to unravel the mechanisms behind H₂S release and pace of its discharge, as well as to define the effects of by-products of donors after H₂S liberation. This will not only lead to better in-depth understanding of the biological effects of H₂S but will also shed light on the future development of a new class of therapeutic agents with potential to treat a wide range of human diseases.

Neuroprotective mechanism of L-cysteine after subarachnoid hemorrhage

Hydrogen sulfide, which can be generated in the central nervous system from the sulfhydryl-containing amino acid, L-cysteine, by cystathionine-β-synthase, may exert protective effects in experimental subarachnoid hemorrhage; however, the mechanism underlying this effect is unknown. This study explored the mechanism using a subarachnoid hemorrhage rat model induced by an endovascular perforation technique. Rats were treated with an intraperitoneal injection of 100 mM L-cysteine (30 μL) 30 minutes after subarachnoid hemorrhage. At 48 hours after subarachnoid hemorrhage, hematoxylin-eosin staining was used to detect changes in prefrontal cortex cells. L-cysteine significantly reduced cell edema. Neurological function was assessed using a modified Garcia score. Brain water content was measured by the wet-dry method. L-cysteine significantly reduced neurological deficits and cerebral edema after subarachnoid hemorrhage. Immunofluorescence was used to detect the number of activated microglia. Reverse transcription-polymerase chain reaction (RT-PCR) was used to detect the levels of interleukin 1β and CD86 mRNA in the prefrontal cortex. L-cysteine inhibited microglial activation in the prefrontal cortex and reduced the mRNA levels of interleukin 1β and CD86. RT-PCR and western blot analysis of the complement system showed that L-cysteine reduced expression of the complement factors, C1q, C3α and its receptor C3aR1, and the deposition of C1q in the prefrontal cortex. Dihydroethidium staining was applied to detect changes in reactive oxygen species, and immunohistochemistry was used to detect the number of NRF2- and HO-1-positive cells. L-cysteine reduced the level of reactive oxygen species in the prefrontal cortex and the number of NRF2- and HO-1-positive cells. Western blot assays and immunohistochemistry were used to detect the protein levels of CHOP and GRP78 in the prefrontal cortex and the number of CHOP- and GRP78-positive cells. L-cysteine reduced CHOP and GRP78 levels and the number of CHOP- and GRP78-positive cells. The cystathionine-β-synthase inhibitor, aminooxyacetic acid, significantly reversed the above neuroprotective effects of L-cysteine. Taken together, L-cysteine can play a neuroprotective role by regulating neuroinflammation, complement deposition, oxidative stress and endoplasmic reticulum stress. The study was approved by the Animals Ethics Committee of Shandong University, China on February 22, 2016 (approval No. LL-201602022).

A homogeneous photoelectrochemical hydrogen sulfide sensor based on the electronic transfer mediated by tetrasulfophthalocyanine

A homogeneous photoelectrochemical sensor for H₂S detection based on the electronic transfer mediated by [Fe(iii)PcS₄]⁺was developed with an un-modified photoelectrode.

A BODIPY-based ratiometric probe for sensing and imaging hydrogen polysulfides in living cells

Hydrogen polysulfides (H₂S_n, n > 1) have attracted increasing attention in biological systems due to its redox signaling effect. To illustrate the process of the physiological and pathological roles played by H₂S_n, accurate detection is highly desired. In this work, we report a BODIPY-based fluorescent probe (BDP-PHS) for ratiometric H₂S_n sensing. BDP-PHS shows higher sensitivity and selectivity ratiometric response toward H₂S_n than various biological related species. Moreover, BDP-PHS has been successfully applied in imaging of H₂S_n in living cells.

Hydrogen Sulfide Effects on the Survival of Lactobacilli with Emphasis on the Development of Inflammatory Bowel Diseases

The gut microbiota is a complex component of humans that depends on diet, host genome, and lifestyle. The background: The study purpose is to find relations between nutrition, intestinal lactic acid bacteria (LAB) from various environments (human, animal intestine, and yogurt) and sulfate-reducing microbial communities in the large intestine; to compare kinetic growth parameters of LAB; and to determine their sensitivity to different concentration of hydrogen sulfide produced by intestinal sulfate-reducing bacteria.

METHODS

Microbiological (isolation and identification), biochemical (electrophoresis), molecular biology methods (DNA isolation and PCR analysis), and statistical processing (average and standard error calculations) of the results were used.

THE RESULTS

The toxicity of hydrogen sulfide produced by sulfate-reducing bacteria, the survival of lactic acid bacteria, and minimal inhibitory concentrations (MIC) were determined. The measured hydrogen sulfide sensitivity values were the same for L. paracasei and L. reuteri (MIC > 1.1 mM). In addition, L. plantarum and L.fermentum showed also a similar sensitivity (MIC > 0.45 mM) but significantly (p < 0.05) lower than L.reuteri and L. paracasei (1.1 > 0.45 mM). L. paracasei and L. reuteri are more sensitive to hydrogen sulfide than L. fermentum and L. plantarum. L. pentosus was sensitive to the extremely low concentration of H2S (MIC > 0.15 mM).

CONCLUSIONS

The Lactobacillus species were significantly sensitive to hydrogen sulfide, which is a final metabolite of intestinal sulfate-reducing bacteria. The results are definitely helpful for a better understanding of complicated interaction among intestinal microbiota and nutrition.

Hydrogen sulfide-mediated resistance against water avoidance stress-induced gastritis by maintenance of gastric microbial homeostasis

Chronic persistent stress is an important cause of gastritis, but the underlying mechanism remains to be further researched, especially the role of the gastric microbiota in this process. Here, we used the water avoidance stress (WAS) test in mouse models for chronic stress‐induced gastritis to investigate the underlying mechanisms of this disease. The effect of stress on the gastric microbiota was analyzed based on 16S rRNA sequencing; the changes in hydrogen sulfide (H₂S) and inflammatory cytokine levels in gastric tissues were detected by Western blotting, ELISA, immunofluorescence, and qRT‐PCR. Hematoxylin and eosin staining was used as an indicator of the gastritis histological score. This finding is consistent with previous studies showing that gastric H₂S is negatively associated with the inflammatory index and might protect the gastrointestinal tract from inflammation. WAS‐induced gastritis was associated with a reduction in H₂S release, which appeared to affect the homeostasis of the gastric microbiota of mice. Inflammation and microbial dysbiosis were partially reversed by sodium hydrosulfide (NaHS) and vitamin B6 (VB6) supplementation, suggesting the therapeutic potential of VB6 supplementation for the treatment of stress‐induced gastritis. Gastritis has a serious impact on health and quality of life. An increasing number of people are suffering from chronic gastritis linked to a high‐stress lifestyle, and our research provides clues for the prevention and treatment of stress‐induced gastritis.

Supramolecular nanostructures with tunable donor loading for controlled H2S release

Hydrogen sulfide (H₂S), an endogenously generated and regulated signaling gas, plays a vital role in a variety of (patho)physiological processes. In the past few years, different kinds of H₂S-releasing compounds (often referred to as H₂S donors) have been developed for H₂S delivery, but it is still challenging to make H₂S donors with tunable payloads in a simple and efficient manner. Herein, a series of peptide-H₂S donor conjugates (PHDCs) with tunable donor loadings are designed for controlled H₂S release. The PHDCs self-assemble into nanoribbons with different geometries in aqueous solution. Upon addition of cysteine, these nanostructures release H₂S, delivering their payload into H9C2 cells, as visualized using an H₂S-selective fluorescent probe. Beyond imaging, in vitro studies show that the ability of PHDCs to mitigate doxorubicin-induced cardiotoxicity in H9C2 cardiomyocytes depends on their nanostructures and H₂S release profiles. This strategy may enable the development of sophisticated H₂S-releasing biomaterials for drug delivery and regenerative medicine.

Hydrogen Sulfide From Cysteine Desulfurase, Not 3-Mercaptopyruvate Sulfurtransferase, Contributes to Sustaining Cell Growth and Bioenergetics in E. coli Under Anaerobic Conditions

Endogenous hydrogen sulfide (H₂S), which is primarily generated by 3-mercaptopyruvate sulfurtransferase (3-MST) in Escherichia coli (E. coli) under aerobic conditions, renders bacteria highly resistant to oxidative stress. However, the biosynthetic pathway and physiological role of this gas under anaerobic conditions remains largely unknown. In the present study, we demonstrate that cysteine desulfurase (IscS), not 3-MST, is the primary source of endogenous H₂S in E. coli under anaerobic conditions. A significant decrease in H₂S production under anaerobic conditions was observed in E. coli upon deletion of IscS, but not in 3-MST-deficient bacteria (ΔmstA). Furthermore, the H₂S-producing activity of recombinant IscS using L-cysteine as a substrate exhibited an approximately 2.6-fold increase in the presence of dithiothreitol (DTT), indicating that H₂S production catalyzed by IscS was greatly increased under reducing conditions. The activity of IscS was regulated under the different redox conditions and the midpoint redox potential was determined to be −329 ± 1.6 mV. Moreover, in E. coli cells H₂S production from IscS is regulated under oxidative and reductive stress. A mutant E. coli (ΔiscS) strain lacking a chromosomal copy of the IscS-encoding gene iscS showed significant growth defects and low levels of ATP under both aerobic and anaerobic conditions. The growth defects could be fully restored after addition of 500 μM Na₂S (an H₂S donor) under anaerobic conditions, but not by the addition of cysteine, sodium sulfite or sodium sulfate. We also showed that the addition of 500 μM Na₂S to culture medium stimulates ATP synthesis in the mutant E. coli (ΔiscS) strain in the logarithmic growth phase but suppresses ATP synthesis in wild-type E. coli. Our results reveal a new H₂S-producing pathway in E. coli under anaerobic conditions and show that hydrogen sulfide from IscS contributes to sustaining cell growth and bioenergetics under oxygen-deficient conditions.

Increased susceptibility of mice obtained from in vitro fertilization to global cerebral ischemia-reperfusion injury: possible role of hydrogen sulphide and its biosynthetic enzymes

Aim of the Study: This study was designed to explore the relative susceptibility of in vitro fertilization (IVF)-conceived mice to global cerebral ischemic injury with the possible role of hydrogen sulphide and enzymes responsible for its production.Materials and Methods: IVF was carried to obtain pups, which were allowed to grow to the age of eight weeks. Thereafter, male mice were subjected to 20 min of global ischemia and 24 h of reperfusion. The mice obtained from other groups including normal mating, superovulation but normal mating and normal mating but embryo implantation were also subjected to global ischemia-reperfusion (I/R) injury.Results: IVF-derived mice exhibited significant more injury in response to I/R injury in comparison to other groups assessed in terms of impairment in locomotor activity, development of motor in coordination, neurological severity score, cerebral infarction and apoptosis markers (caspase-3 activity and Bcl-2 expression). Moreover, there was a relative decrease in the brain levels of hydrogen sulphide (H₂S) and its biosynthetic enzymes viz. cystathionine-β-synthase and cystathionine-γ-lyase. Interestingly, the levels of H₂S and cystathionine-γ-lyase were significantly low in IVF-derived mice in basal conditions also, i.e. before subjecting to I/R injury and these biochemical alterations were associated with the behavioural deficits in mice, even before subjecting to I/R injury.Conclusion: It is concluded that in vitro fertilization-derived mice are more susceptible to global cerebral I/R injury, which may be possibly due to decreased levels of hydrogen sulphide and its biosynthetic enzymes viz., cystathionine-β-synthase and cystathionine-γ-lyase.

Visualization of hydrogen polysulfides in living cells and in vivo via a near-infrared fluorescent probe

Hydrogen polysulfides (H₂S_n, n > 1), as the oxidized forms of H₂S, have attracted increasing attention these years due to their involvement in signaling transduction and cytoprotective processes. It is necessary to detect H₂S_n in living systems for the study of their functions. In this work, we report a BODIPY-based near-infrared emitting fluorescence probe NIR-PHS1, with "turn-on" response, rapid response rate (within 10 min), outstanding selectivity and excellent sensitivity (detection limit = 12 nM) response towards H₂S_n. The probe was successfully applied to the visualizing of endogenous H₂S_n in living cells. Moreover, it can be used for near-infrared in vivo imaging of H₂S_n in living mice. Therefore, NIR-PHS1 could be a potential imaging tool to study the biological roles of H₂S_n in living systems.

Chemistry, pharmacology, and cellular uptake mechanisms of thiometallate sulfide donors

BACKGROUND AND PURPOSE

A clinical need exists for targeted, safe, and effective sulfide donors. We recently reported that ammonium tetrathiomolybdate (ATTM) belongs to a new class of sulfide-releasing drugs. Here, we investigated the cellular uptake mechanisms of this drug class compared to sodium hydrosulfide (NaHS) and the effects of a thiometallate tungsten congener of ATTM, ammonium tetrathiotungstate (ATTT).

EXPERIMENTAL APPROACH

In vitro H₂ S release was determined by headspace gas sampling of vials containing dissolved thiometallates. Thiometallate and NaHS bioactivity was assessed by spectrophotometry-derived sulfhaemoglobin formation. Cellular uptake dependence on the anion exchange protein (AE)-1 was investigated in human red blood cells. ATTM/glutathione interactions were assessed by LC-MS/MS. Rodent pharmacokinetic and pharmacodynamic studies focused on haemodynamics and inhibition of aerobic respiration.

KEY RESULTS

ATTM and ATTT both exhibit temperature-, pH-, and thiol-dependence of sulfide release. ATTM/glutathione interactions revealed the generation of inorganic and organic persulfides and polysulfides. ATTM showed greater ex vivo and in vivo bioactivity over ATTT, notwithstanding similar pharmacokinetic profiles. Cellular uptake mechanisms of the two drug classes are distinct; thiometallates show dependence on AE-1, while hydrosulfide itself was unaffected by inhibition of this pathway.

CONCLUSIONS AND IMPLICATIONS

The cellular uptake of thiometallates relies upon a plasma membrane ion channel. This advances our pharmacological knowledge of this drug class, and further supports their utility as cell-targeted sulfide donor therapies. Our results indicate that, as a more stable form, ATTT is better suited as a copper chelator. ATTM, a superior sulfide donor, may additionally participate in intracellular redox recycling.

LINKED ARTICLES

This article is part of a themed section on Hydrogen Sulfide in Biology & Medicine. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.4/issuetoc.

Histone deacetylase 6 inhibitor tubastatin A attenuates angiotensin II-induced hypertension by preventing cystathionine γ-lyase protein degradation

Cystathionine γ-lyase (CSEγ) is a hydrogen sulfide (H₂S)-producing enzyme. Endothelial H₂S production can mediate vasodilatory effects, contributing to the alleviation of hypertension (high blood pressure). Recent studies have suggested a role of histone deacetylase 6 (HDAC6) in hypertension, although its underlying mechanisms are poorly understood. Here, we addressed the potential regulation of CSEγ by HDAC6 in angiotensin II (AngII)-induced hypertension and its molecular details focusing on CSEγ posttranslational modification. Treatment of mice with a selective HDAC6 inhibitor tubastatin A (TubA) alleviated high blood pressure and vasoconstriction induced by AngII. Cotreatment of the aorta and human aortic endothelial cells with TubA recovered AngII-mediated decreased H₂S levels. AngII treatment upregulated HDAC6 mRNA and protein expression, but conversely downregulated CSEγ protein. Notably, potent HDAC6 inhibitors and HDAC6 siRNA as well as a proteasomal inhibitor increased CSEγ protein levels and blocked the downregulatory effect of AngII on CSEγ. In contrast, other HDAC isoforms-specific inhibitors and siRNAs did not show such blocking effects. Transfected CSEγ protein levels were also reciprocally regulated by AngII and TubA, and were reduced by wild-type, but not by deacetylase-deficient, HDAC6. Moreover, TubA significantly increased both protein stability and K73 acetylation level of CSEγ. Consistent with these results, AngII induced CSEγ ubiquitination and degradation, which was inhibited by TubA. Our results indicate that AngII promoted HDAC6-dependent deacetylation of CSEγ at K73 residue, leading to its ubiquitin-mediated proteolysis, which underlies AngII-induced hypertension. Overall, this study suggests that upregulation of CSEγ and H₂S through HDAC6 inhibition may be considered as a valid strategy for preventing the progression of hypertension.

Involvement of Endothelin-1, H2S and Nrf2 in Beneficial Effects of Remote Ischemic Preconditioning in Global Cerebral Ischemia-Induced Vascular Dementia in Mice

The present study explored the role of endothelin-1, H₂S, and Nrf2 in remote preconditioning (RIPC)-induced beneficial effects in ischemia-reperfusion (I/R)-induced vascular dementia. Mice were subjected to 20 min of global ischemia by occluding both carotid arteries to develop vascular dementia, which was assessed using Morris water maze test on 7th day. RIPC was given by subjecting hind limb to four cycles of ischemia (5 min) and reperfusion (5 min) and it significantly restored I/R-induced locomotor impairment, neurological severity score, cerebral infarction, apoptosis markers along with deficits in learning and memory. Biochemically, there was increase in the plasma levels of endothelin-1 along with increase in the brain levels of H₂S and its biosynthetic enzymes viz., cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CLS). There was also an increase in the expression of Nrf2 and glutathione reductase in the brain in response to RIPC. Pretreatment with bosentan (dual blocker of ET_A and ET_B receptors), amino-oxyacetic acid (CBS synthase inhibitor), and DL-propargylglycine (CLS inhibitor) significantly attenuated RIPC-mediated beneficial effects and biochemical alterations. The effects of bosentan on behavioral and biochemical parameters were more significant than individual treatments with CBS or CLS inhibitors. Moreover, CBS and CLS inhibitors did not alter the endothelin-1 levels possibly suggesting that endothelin-1 may act as upstream mediator of H₂S. It is concluded that RIPC may stimulate the release endothelin-1, which may activate CBS and CLS to increase the levels of H₂S and latter may increase the expression of Nrf2 to decrease oxidative stress and prevent vascular dementia.

Escherichia coli Uses Separate Enzymes to Produce H2S and Reactive Sulfane Sulfur From L-cysteine

Hydrogen sulfide (H2S) has been proposed to have various physiological functions, and it may function through reactive sulfane sulfur. Since the two sulfur forms often coexist, they are normally considered interchangeable. Here, we characterized the production of H2S and reactive sulfane sulfur in Escherichia coli MG1655 and found that they are not readily interchangeable. They are primarily produced from L-cysteine via different enzymes. L-Cysteine desulfhydrases consumed L-cysteine and directly generated H2S. The produced H2S was mainly lost through evaporation into the gas phase, as E. coli does not have enzymes that easily oxidize H2S to reactive sulfane sulfur. L-Cysteine desulfhydrases were also responsible for the degradation of exogenous L-cysteine, which is toxic at high levels. Conversely, L-cysteine aminotransferase and 3-mercaptopyruvate sulfurtransferase sequentially metabolized endogenous L-cysteine to produce cellular reactive sulfane sulfur; however, it was not a major route of H2S production during normal growth or during the metabolism of exogenous L-cysteine by the resting cells. Noticeably, the 3-mercaptopyruvate sulfurtransferase mutant contained less reactive sulfane sulfur and displayed a greater sensitivity to H2O2 than did the wild type. Thence, reactive sulfane sulfur is likely a common cellular component, involved in protein sulfhydration and protecting cells from oxidative stress.

Hydrogen sulfide downregulates colonic afferent sensitivity by a nitric oxide synthase-dependent mechanism in mice

BACKGROUND

The effect of hydrogen sulfide (H₂ S) on visceral nociception is elusive. The conflicting evidence of its pro- and antinociceptive effects raises a series of questions with respect to the effect of H₂ S on colonic afferent activity and the underlying mechanism, which was further elucidated in this study.

METHODS

Colonic mesenteric afferent nerve spikes of normal male C57BL/6J mice, Cbs^+/- mice, and Wistar rats were recorded in vitro. The abdominal withdrawal reflex (AWR) induced by colorectal distension (CRD) was evaluated in Cbs^+/- mice and WT littermates.

KEY RESULTS

Sodium hydrosulfide (NaHS) significantly decreased colonic afferent spontaneous discharge, chemosensitivity to bradykinin, mechanosensitivity to ramp distention, and intraluminal pressure in mice. Reducing the relaxant action of NaHS on intestinal smooth muscle using the nonspecific K⁺ channel blocker TEA (10 mmol/L) did not block the inhibition of NaHS on afferent nerve activity. The inhibitory effects of NaHS (0.5 mmol/L) on colonic afferent sensitivity were largely eliminated by the pretreatment with nonspecific NOS inhibitor N^G -Methyl-l-arginine acetate salt (1 mmol/L), the specific nNOS inhibitor NPLA (1 μmol/L), or N-type Ca²⁺ channel blocker ω-conotoxin GVIA (1 μmol/L). Compared with WT mice, Cbs^+/- mice showed increased mesenteric afferent sensitivity to colonic distention and enhanced hyperalgesic response to CRD. Intraperitoneal administration of NaHS (60 μmol/kg) alleviated the nociception response to CRD in both Cbs^+/- and WT mice.

CONCLUSIONS AND INFERENCES

H₂ S downregulates colonic mesenteric afferent sensitivity by a nNOS-dependent mechanism in mice. Our findings may demonstrate a new mechanism for the antinociceptive effect of H₂ S in colon.

Iterative synthetic strategies and gene deletant experiments enable the first identification of polysulfides in Saccharomyces cerevisiae

Polysulfides, potential signalling molecules, were synthesised and then found and explored for the first time in yeast.

Unexpected reaction patterns enable simultaneous differentiation of H2S, H2Sn and biothiols

A robust fluorescent probe, MCP1, was developed for triple-detection of H₂S, H₂S_n and biothiols for the first time.

Measurements for Sulfide-Mediated Inhibition of Myeloperoxidase Activity

Oxidative stress-alleviating and inflammation-mediatory functions of hydrogen sulfide were reported to be key features of its biological actions. However, the underlying molecular mechanisms of these biological observations are not fully understood. In conditions where sulfide was proposed to be protective against oxidative stress- or inflammation-induced tissue damage (e.g., reperfusion injury, atherosclerosis, vascular inflammation), the reactive oxidant-producing function of a key neutrophil enzyme, myeloperoxidase, was reported to be a protagonist on the detrimental side. We recently described favorable interactions between sulfide and myeloperoxidase and proposed that the potent inhibition of myeloperoxidase activities could contribute to sulfide's beneficial functions in a number of cardiovascular pathologies. Our chapter is dedicated to aid future studies and drug development endeavors in this area by providing methodological guidance on how to assess the inhibitory potential of sulfide on myeloperoxidase enzymatic activities in isolated protein systems, in neutrophil homogenates, and in live neutrophil preparations.

Comparison of sulphide and nitrate removal from synthetic wastewater by pure and mixed cultures of nitrate-reducing, sulphide-oxidizing bacteria

In this study, the activities of hydrogen sulphide (H₂S) oxidation and nitrate (N-NO₃^-) reduction by three pure and mixed strains of nitrate-reducing, sulphide oxidizing bacteria (NR-SOB) were determined. Batch experiments were performed at 35 °C and pH 7.0-8.0 with initial H₂S concentrations of 650-900 ppm_v and N-NO₃^- concentrations of ∼120 mg/L. The strains MAL 1HM19, TPN 1HM1 and TPN 3HM1 were capable of removing 100% gas-phase H₂S. The co-cultures showed better performance for H₂S and N-NO₃^- removal. The mixed NR-SOB strains showed a higher H₂S oxidation rate (143 ± 18 ppm_v/h), while the highest N-NO₃^- removal rate (5.5 ± 0 and 5.1 ± 0.6 N-NO₃^- mg/L·h) was obtained by a mixture of two NR-SOB strains. The 16S rDNA sequence analysis revealed that all strains belonged to the sub-class Alphaproteobacteria and are closely related to Paracoccus sp. (>99%).

Controlled release of hydrogen sulfide significantly reduces ROS stress and increases dopamine levels in transgenic C. elegans

A novel peptide based system has been developed that exhibits slow and sustained H₂S release thereby reducing hydrogen peroxide-induced oxidative stress and increasing dopamine levels in a transgenic C. elegans model.

Hydrogen Sulfide: A Therapeutic Option in Systemic Sclerosis

Systemic sclerosis (SSc) is a lethal disease that is characterized by auto-immunity, vascular injury, and progressive fibrosis of multiple organ systems. Despite the fact that the exact etiology of SSc remains unknown, oxidative stress has been associated with a large range of SSc-related complications. In addition to the well-known detrimental properties of reactive oxygen species (ROS), gasotransmitters (e.g., nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H₂S)) are also thought to play an important role in SSc. Accordingly, the diverse physiologic actions of NO and CO and their role in SSc have been previously studied. Recently, multiple studies have also shown the importance of the third gasotransmitter H₂S in both vascular physiology and pathophysiology. Interestingly, homocysteine (which is converted into H₂S through the transsulfuration pathway) is often found to be elevated in SSc patients; suggesting defects in the transsulfuration pathway. Hydrogen sulfide, which is known to have several effects, including a strong antioxidant and vasodilator effect, could potentially play a prominent role in the initiation and progression of vasculopathy. A better understanding of the actions of gasotransmitters, like H₂S, in the development of SSc-related vasculopathy, could help to create early interventions to attenuate the disease course. This paper will review the role of H₂S in vascular (patho-)physiology and potential disturbances in SSc. Moreover, current data from experimental animal studies will be reviewed. Lastly, we will evaluate potential interventional strategies.

The Ataxia telangiectasia-mutated and Rad3-related protein kinase regulates cellular hydrogen sulfide concentrations

The ataxia telangiectasia-mutated and Rad3-related (ATR) serine/threonine kinase plays a central role in the repair of replication-associated DNA damage, the maintenance of S and G2/M-phase genomic stability, and the promotion of faithful mitotic chromosomal segregation. A number of stimuli activate ATR, including persistent single-stranded DNA at stalled replication folks, R loop formation, hypoxia, ultraviolet light, and oxidative stress, leading to ATR-mediated protein phosphorylation. Recently, hydrogen sulfide (H₂S), an endogenous gasotransmitter, has been found to regulate multiple cellular processes through complex redox reactions under similar cell stress environments. Three enzymes synthesize H₂S: cystathionine-β-synthase, cystathionine γ-lyase, and 3-mercaptopyruvate sulfurtransferase. Since H₂S can under some conditions cause DNA damage, we hypothesized that ATR activity may regulate cellular H₂S concentrations and H₂S-syntheszing enzymes. Here we show that human colorectal cancer cells carrying biallelic knock-in hypomorphic ATR mutations have lower cellular H₂S concentrations than do syngeneic ATR wild-type cells, and all three H₂S-synthesizing enzymes show lower protein expression in the ATR hypomorphic mutant cells. Additionally, ATR serine 428 phosphorylation is altered by H₂S donor and H₂S synthesis enzyme inhibition, while the oxidative-stress induced phosphorylation of the ATR-regulated protein CHK1 on serine 345 is increased by H₂S synthesis enzyme inhibition. Lastly, inhibition of H₂S production potentiated oxidative stress-induced double-stranded DNA breaks in the ATR hypomorphic mutant compared to ATR wild-type cells. Our findings demonstrate that the ATR kinase regulates and is regulated by H₂S.

Self-Assembled Nanostructures Regulate H2S Release from Constitutionally Isomeric Peptides

We report here on three constitutionally isomeric peptides, each of which contains two glutamic acid residues and two lysine residues functionalized with S-aroylthiooximes (SATOs), termed peptide-H2S donor conjugates (PHDCs). SATOs decompose in the presence of cysteine to generate hydrogen sulfide (H2S), a biological signaling gas with therapeutic potential. The PHDCs self-assemble in aqueous solution into different morphologies, two into nanoribbons of different dimensions and one into a rigid nanocoil. The rate of H2S release from the PHDCs depends on the morphology, with the nanocoil-forming PHDC exhibiting a complex release profile driven by morphological changes promoted by SATO decomposition. The nanocoil-forming PHDC mitigated the cardiotoxicity of doxorubicin more effectively than its nanoribbon-forming constitutional isomers as well as common H2S donors. This strategy opens up new avenues to develop H2S-releasing biomaterials and highlights the interplay between structure and function from the molecular level to the nanoscale.