Hydrogen sulfide: neurochemistry and neurobiology

Neuromodulator hydrogen sulfide attenuates sickness behavior induced by lipopolysaccharide

Sickness behavior reflects a state of altered physiology and central nervous system function that occurs during systemic infection or inflammation, serving as an adaptive response to illness. This study aims to elucidate the role of hydrogen sulfide (H2S) in regulating sickness behavior and neuroinflammatory responses in a rat model of systemic inflammation. Adult male Wistar rats were treated with lipopolysaccharide (LPS) to induce sickness behavior. Intracerebroventricular (i.c.v.) pretreatments included aminooxyacetic acid (AOAA), an inhibitor of H2S synthesis, and sodium sulfide (NaHS), an H2S donor. Behavioral assays were conducted, along with the assessment of astrocyte activation, as indicated by GFAP expression in the hypothalamus. Pretreatment with NaHS mitigated LPS-induced behavioral changes, including hypophagia, social and exploratory deficits, without affecting peripheral cytokine levels, indicating a central modulatory effect. AOAA, conversely, accentuated certain behavioral responses, suggesting a complex role of endogenous H2S in sickness behavior. These findings were reinforced by a lack of effect on plasma interleukin levels but significant reduction in GFAP expression. Our findings support the central role of H2S in modulating neuroinflammation and sickness behavior, highlighting the therapeutic potential of targeting H2S signaling in neuroinflammatory conditions.

Recent advances in sulfur dioxide releasing nanoplatforms for cancer therapy

Sulfur dioxide (SO2), long considered to be a harmful atmospheric pollutant, has recently been posited as the fourth gasotransmitter, as it is produced endogenously in mammals and has important pathophysiological effects. The field of tumor therapy has witnessed a paradigm shift with the emergence of SO2-based gas therapy. This has been possible because SO2 is a potent glutathione consumer that can promote the production of reactive oxygen species, eventually leading to oxidative-stress-induced cancer cell death. Nevertheless, this therapeutic gas cannot be directly administrated in gaseous form. Thus, various nano formulations incorporating SO2 donors or prodrugs capable of storing and releasing SO2 have been developed in an attempt to achieve active/passive intratumoral accumulation and SO2 release in the tumor microenvironment. In this review article, the advances over the past decade in nanoplatforms incorporating sulfur SO2 prodrugs to provide controlled release of SO2 for cancer therapy are summarized. We first describe the synthesis of polypeptide SO2 prodrugs to overcome multiple drug resistance that was pioneered by our group, followed by other macromolecular SO2 prodrug structures that self-assemble into nanoparticles for tumor therapy. Second, we describe nanoplatforms composed of various small-molecule SO2 donors with endogenous or exogenous stimuli responsiveness, including thiol activated, acid-sensitive, and ultraviolet or near-infrared light-responsive SO2 donors, which have been used for tumor inhibition. Combinations of SO2 gas therapy with photodynamic therapy, chemotherapy, photothermal therapy, sonodynamic therapy, and nanocatalytic tumor therapy are also presented. Finally, we discuss the current limitations and challenges and the future outlook for SO2-based gas therapy. STATEMENT OF SIGNIFICANCE: Gas therapy is attracting increasing attention in the scientific community because it is a highly promising strategy against cancer owing to its inherent biosafety and avoidance of drug resistance. Sulfur dioxide (SO2) is recently found to be produced endogenously in mammals with important pathophysiological effects. This review summarizes recent advances in SO2 releasing nanosystems for cancer therapy, including polymeric prodrugs, endogenous or exogenous stimulus-activated SO2 donors delivered by nanoplatform and combination therapy strategies.

H2S-RhoA/ROCK Pathway and Glial Cells in Axonal Remyelination After Ischemic Stroke

Ischemic stroke is one of the main reasons of disability and death. Stroke-induced functional deficits are mainly due to the secondary degeneration of the white matter characterized by axonal demyelination and injury of axon-glial integrity. Enhancement of the axonal regeneration and remyelination could promote the neural functional recovery. However, cerebral ischemia-induced activation of RhoA/Rho kinase (ROCK) pathway plays a crucial and harmful role in the process of axonal recovery and regeneration. Inhibition of this pathway could promote the axonal regeneration and remyelination. In addition, hydrogen sulfide (H2S) has the significant neuroprotective role during the recovery of ischemic stroke via inhibiting the inflammatory response and oxidative stress, regulating astrocyte function, promoting the differentiation of endogenous oligodendrocyte precursor cells (OPCs) to mature oligodendrocyte. Among all of these effects, promoting the formation of mature oligodendrocyte is a crucial part of axonal regeneration and remyelination. Furthermore, numerous studies have uncovered the crosstalk between astrocytes and oligodendrocyte, microglial cells and oligodendrocyte in the axonal remyelination following ischemic stroke. The purpose of this review was to discuss the relationship among H2S, RhoA/ROCK pathway, astrocytes, and microglial cells in the axonal remyelination following ischemic stroke to reveal new strategies for preventing and treating this devastating disease.

Low level exposure to hydrogen sulfide: a review of emissions, community exposure, health effects, and exposure guidelines

Hydrogen sulfide (H2S) is a toxic gas that is well-known for its acute health risks in occupational settings, but less is known about effects of chronic and low-level exposures. This critical review investigates toxicological and experimental studies, exposure sources, standards, and epidemiological studies pertaining to chronic exposure to H2S from both natural and anthropogenic sources. H2S releases, while poorly documented, appear to have increased in recent years from oil and gas and possibly other facilities. Chronic exposures below 10 ppm have long been associated with odor aversion, ocular, nasal, respiratory and neurological effects. However, exposure to much lower levels, below 0.03 ppm (30 ppb), has been associated with increased prevalence of neurological effects, and increments below 0.001 ppm (1 ppb) in H2S concentrations have been associated with ocular, nasal, and respiratory effects. Many of the studies in the epidemiological literature are limited by exposure measurement error, co-pollutant exposures and potential confounding, small sample size, and concerns of representativeness, and studies have yet to consider vulnerable populations. Long-term community-based studies are needed to confirm the low concentration findings and to refine exposure guidelines. Revised guidelines that incorporate both short- and long-term limits are needed to protect communities, especially sensitive populations living near H2S sources.

Advances of H2S in Regulating Neurodegenerative Diseases by Preserving Mitochondria Function

Neurotoxicity is induced by different toxic substances, including environmental chemicals, drugs, and pathogenic toxins, resulting in oxidative damage and neurodegeneration in mammals. The nervous system is extremely vulnerable to oxidative stress because of its high oxygen demand. Mitochondria are the main source of ATP production in the brain neuron, and oxidative stress-caused mitochondrial dysfunction is implicated in neurodegenerative diseases. H2S was initially identified as a toxic gas; however, more recently, it has been recognized as a neuromodulator as well as a neuroprotectant. Specifically, it modulates mitochondrial activity, and H2S oxidation in mitochondria produces various reactive sulfur species, thus modifying proteins through sulfhydration. This review focused on highlighting the neuron modulation role of H2S in regulating neurodegenerative diseases through anti-oxidative, anti-inflammatory, anti-apoptotic and S-sulfhydration, and emphasized the importance of H2S as a therapeutic molecule for neurological diseases.

A near infrared two-channel fluorescent probe for the detection of hydrogen sulfide and viscosity with a negligible crosstalk influence

Both imbalance of H₂S production and the change of viscosity in cells are associated with many diseases such as inflammation, Alzheimer's disease, and Parkinson's disease. Thus, the development of two-channel fluorescent probes for the detection of H₂S and viscosity is of great significance for the study of pathogenic mechanisms. Herein, we design a two-channel NIR fluorescent probe RHO-DCO-DNP, which was able to selectively respond to H₂S in one channel (λex = 580 nm, λem = 760 nm) and to viscosity in another channel (λex = 400 nm, λem = 585 nm). It should be emphasized that there is a negligible impact from the crosstalk between the two optical channels and the two targets. In addition, with the low cytotoxicity and unique dual lysosome/mitochondria targeting capability, the probe was successfully applied to the sensing of H₂S and viscosity in normal cells and inflammation cells through fluorescent imaging. The probe could be a promising molecular tool for exploring the pathological role of H₂S, viscosity, and both of them.

Unmet needs in glaucoma therapy: The potential role of hydrogen sulfide and its delivery strategies

Glaucoma is an optic neuropathy disorder marked by progressive degeneration of the retinal ganglion cells (RGC). It is a leading cause of blindness worldwide, prevailing in around 2.2% of the global population. The hallmark of glaucoma, intraocular pressure (IOP), is governed by the aqueous humor dynamics which plays a crucial role in the pathophysiology of the diesease. Glaucomatous eye has an IOP of more than 22 mmHg as compared to normotensive pressure of 10-21 mmHg. Currently used treatments focus on reducing the elevated IOP through use of classes of drugs that either increase aqueous humor outflow and/or decrease its production. However, effective treatments should not only reduce IOP, but also offer neuroprotection and regeneration of RGCs. Hydrogen Sulfide (H₂S), a gasotransmitter with several endogenous functions in mammalian tissues, is being investigated for its potential application in glaucoma. In addition to decreasing IOP by increasing aqueous humor outflow, it scavenges reactive oxygen species, upregulates the cellular antioxidant glutathione and protects RGCs from excitotoxicity. Despite the potential of H₂S in glaucoma, its delivery to anterior and posterior regions of the eye is a challenge due to its unique physicochemical properties. Firstly, development of any delivery system should not require an aqueous environment since many H₂S donors are susceptible to burst release of the gas in contact with water, causing potential toxicity and adverse effects owing to its inherent toxicity at higher concentrations. Secondly, the release of the gas from the donor needs to be sustained for a prolonged period of time to reduce dosing frequency as per the requirements of regulatory bodies. Lastly, the delivery system should provide adequate bioavailability throughout its period of application. Hence, an ideal delivery system should aim to tackle all the above challenges related to barriers of ocular delivery and physicochemical properties of H₂S itself. This review discusses the therapeutic potential of H₂S, its delivery challenges and strategies to overcome the associated chalenges.

Near-Infrared Fluorescent Probe with Large Stokes Shift for Imaging of Hydrogen Sulfide in Tumor-Bearing Mice

Hydrogen sulfide (H₂S) is an important endogenous gas signal molecule in living system, which participates in a variety of physiological processes. Very recent evidence has accumulated to show that endogenous H₂S is closely associated with various cancers and can be regarded as a biomarker of cancer. Herein, we have constructed a new near-infrared fluorescent probe (DCP-H₂S) based on isophorone-xanthene dye for sensing hydrogen sulfide (H₂S). The probe shows remarkable NIR turn-on signal at 770 nm with a large Stokes shift of 200 nm, together with high sensitivity (15-fold) and rapid detection ability for H₂S (4 min). The probe also possesses excellent selectivity for H₂S over various other analytes including biothiols containing sulfhydryl (-SH). Moreover, DCP-H₂S has been successfully applied to visualize endogenous and exogenous H₂S in living cells (293T, Caco-2 and CT-26 cells). In particular, the excellent ability of DCP-H₂S to distinguish normal mice and tumor mice is shown, and it is expected to be a powerful tool for detection of H₂S in cancer diagnosis.

Methods for Suppressing Hydrogen Sulfide in Biological Systems

Significance: Hydrogen sulfide (H₂S) plays critical roles in redox biology, and its regulatory effects are tightly controlled by its cellular location and concentration. The imbalance of H₂S is believed to contribute to some pathological processes. Recent Advances: Downregulation of H₂S requires chemical tools such as inhibitors of H₂S-producing enzymes and H₂S scavengers. Recent efforts have discovered some promising inhibitors and scavengers. These advances pave the road toward better understanding of the functions of H₂S. Critical Issues: Precise H₂S downregulation is challenging. The potency and specificity of current inhibitors are still far from ideal. H₂S-producing enzymes are involved in complex sulfur metabolic pathways and ubiquitously present in biological matrices. The inhibition of these enzymes can cause unwanted side effects. H₂S scavengers allow targeted H₂S clearance, but their options are still limited. In addition, the scavenging process often results in biologically active by-products. Future Directions: Further development of potent and specific inhibitors for H₂S-producing enzymes is needed. Scavengers that can rapidly and selectively remove H₂S while generating biocompatible by-products are needed. Potential therapeutic applications of scavengers and inhibitors are worth exploring. Antioxid. Redox Signal. 36, 294-308.

H2S Attenuates Sleep Deprivation-Induced Cognitive Impairment by Reducing Excessive Autophagy via Hippocampal Sirt-1 in WISTAR RATS

Sleep deprivation (SD) is widespread in society causing serious damage to cognitive function. Hydrogen sulfide (H2S), the third gas signal molecule, plays important regulatory role in learning and memory functions. Inhibition of excessive autophagy and upregulation of silent information regulator 1 (Sirt-1) have been reported to prevent cognitive dysfunction. Therefore, this present work was to address whether H2S attenuates the cognitive impairment induced by SD in Wistar rats and whether the underlying mechanisms involve in inhibition of excessive autophagy and upregulation of Sirt-1. After treatment with SD for 72 h, the cognitive function of Wistar rats was evaluated by Y-maze, new object recognition, object location, and Morris water maze tests. The results shown that SD-caused cognitive impairment was reversed by treatment with NaHS (a donor of H2S). NaHS also prevented SD-induced hippocampal excessive autophagy, as evidenced by the decrease in autophagosomes, the down-regulation of Beclin1, and the up-regulation of p62 in the hippocampus of SD-exposed Wistar rats. Furthermore, Sirtinol, an inhibitor of Sirt-1, reversed the inhibitory roles of NaHS in SD-induced cognitive impairment and excessive hippocampal autophagy in Wistar rats. Taken together, our results suggested that H2S improves the cognitive function of SD-exposed rats by inhibiting excessive hippocampal autophagy in a hippocampal Sirt-1-dependent way.

NBD-based synthetic probes for sensing small molecules and proteins: design, sensing mechanisms and biological applications

Compounds with a nitrobenzoxadiazole (NBD) skeleton exhibit prominent useful properties including environmental sensitivity, high reactivity toward amines and biothiols (including H2S) accompanied by distinct colorimetric and fluorescent changes, fluorescence-quenching ability, and small size, all of which facilitate biomolecular sensing and self-assembly. Amines are important biological nucleophiles, and the unique activity of NBD ethers with amines has allowed for site-specific protein labelling and for the detection of enzyme activities. Both H2S and biothiols are involved in a wide range of physiological processes in mammals, and misregulation of these small molecules is associated with numerous diseases including cancers. In this review, we focus on NBD-based synthetic probes as advanced chemical tools for biomolecular sensing. Specifically, we discuss the sensing mechanisms and selectivity of the probes, the design strategies for multi-reactable multi-quenching probes, and the associated biological applications of these important constructs. We also highlight self-assembled NBD-based probes and outline future directions for NBD-based chemosensors. We hope that this comprehensive review will facilitate the development of future probes for investigating and understanding different biological processes and aid the development of potential theranostic agents.

S-Adenosylmethionine Alleviates Amyloid-β-Induced Neural Injury by Enhancing Trans-Sulfuration Pathway Activity in Astrocytes

BACKGROUND

Glutathione (GSH) is an important endogenous antioxidant protecting cells from oxidative injury. Cysteine (Cys), the substrate limiting the production of GSH, is mainly generated from the trans-sulfuration pathway. S-adenosylmethionine (SAM) is a critical molecule produced in the methionine cycle and can be utilized by the trans-sulfuration pathway. Reductions in GSH and SAM as well as dysfunction in the trans-sulfuration pathway have been documented in the brains of Alzheimer's disease (AD) patients. Our previous in vivo study revealed that SAM administration attenuated oxidative stress induced by amyloid-β (Aβ) through the enhancement of GSH.

OBJECTIVE

To investigate the effect of Aβ-induced oxidative stress on the trans-sulfuration pathway in astrocytes and neurons, respectively, and the protective effect of SAM on neurons.

METHODS

APP/PS1 transgenic mice and the primary cultured astrocytes, neurons, and HT22 cells were used in the current study.

RESULTS

SAM could rescue the low trans-sulfuration pathway activity induced by Aβ only in astrocytes, accompanying with increasing levels of Cys and GSH. The decrease of cellular viability of neurons caused by Aβ was greatly reversed when co-cultured with astrocytes with SAM intervention. Meanwhile, SAM improved cognitive performance in APP/PS1 mice.

CONCLUSION

In terms of astrocyte protection from oxidative stress, SAM might be a potent antioxidant in the therapy of AD patients.

Biocompatible metal-organic frameworks for the storage and therapeutic delivery of hydrogen sulfide

Hydrogen sulfide (H2S) is an endogenous gasotransmitter with potential therapeutic value for treating a range of disorders, such as ischemia-reperfusion injury resulting from a myocardial infarction or stroke. However, the medicinal delivery of H2S is hindered by its corrosive and toxic nature. In addition, small molecule H2S donors often generate other reactive and sulfur-containing species upon H2S release, leading to unwanted side effects. Here, we demonstrate that H2S release from biocompatible porous solids, namely metal-organic frameworks (MOFs), is a promising alternative strategy for H2S delivery under physiologically relevant conditions. In particular, through gas adsorption measurements and density functional theory calculations we establish that H2S binds strongly and reversibly within the tetrahedral pockets of the fumaric acid-derived framework MOF-801 and the mesaconic acid-derived framework Zr-mes, as well as the new itaconic acid-derived framework CORN-MOF-2. These features make all three frameworks among the best materials identified to date for the capture, storage, and delivery of H2S. In addition, these frameworks are non-toxic to HeLa cells and capable of releasing H2S under aqueous conditions, as confirmed by fluorescence assays. Last, a cellular ischemia-reperfusion injury model using H9c2 rat cardiomyoblast cells corroborates that H2S-loaded MOF-801 is capable of mitigating hypoxia-reoxygenation injury, likely due to the release of H2S. Overall, our findings suggest that H2S-loaded MOFs represent a new family of easily-handled solid sources of H2S that merit further investigation as therapeutic agents. In addition, our findings add Zr-mes and CORN-MOF-2 to the growing lexicon of biocompatible MOFs suitable for drug delivery.

Adsorptive-Oxidative Removal of Sulfides from Water by MnO2-Loaded Carboxylic Cation Exchangers

Hybrid ion exchangers (HIX) containing manganese(IV) oxide (MnO₂) based on macroporous and gel-type carboxylic cation exchangers as supporting materials were obtained. The hybrid materials were characterized using scanning electron microscopy with energy dispersive spectrometry (SEM/EDS), Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD) and nitrogen adsorption isotherms at 77 K and mercury porosimetry. HIX with introduced MnO₂ (20.0–32.8 wt% Mn) were tested for removal of dissolved sulfides from anoxic aqueous solutions with 100–500 mg S²⁻/dm³ concentrations. The process proceeded effortlessly at pH 10–13 despite unfavorable electrostatic interactions of the reactants. The highest exhibited sorption capacity was 144.3 ± 7.1 mg S²⁻/g. Approximately 65% of dissolved sulfides were oxidized to S₂O₃²⁻ ions and repelled from HIX structure. On average, 13% of sulfide removal products were adsorbed by the MnO₂ surface. The impact of MnO₂ load and the ionic form of HIX functional groups on removal of sulfides and resulting products was examined. The mechanism of the process is suggested.

A biotin-guided hydrogen sulfide fluorescent probe and its application in living cell imaging

Hydrogen sulfide (H2S), a well-known signaling molecule, exerts significant regulatory effects on the cardiovascular and nervous systems. Therefore, monitoring the metabolism of H2S offers a potential mechanism to detect various diseases. In addition, biotin is significantly used as a targeting group to detect cancer cells exclusively. In this work, a biotin-guided benzoxadizole-based fluorescent probe, NP-biotin, was developed for H2S detection and evaluated in normal liver cell (LO2) and liver cancer cell (HepG2) lines. Results reveal that NP-biotin can detect cellular H2S with high sensitivity and selectivity. Moreover, NP-biotin has been confirmed to possess the ability to target cancer cells under the guidance of the biotin group.

The Role of Amino Acids in Neurotransmission and Fluorescent Tools for Their Detection

Neurotransmission between neurons, which can occur over the span of a few milliseconds, relies on the controlled release of small molecule neurotransmitters, many of which are amino acids. Fluorescence imaging provides the necessary speed to follow these events and has emerged as a powerful technique for investigating neurotransmission. In this review, we highlight some of the roles of the 20 canonical amino acids, GABA and β-alanine in neurotransmission. We also discuss available fluorescence-based probes for amino acids that have been shown to be compatible for live cell imaging, namely those based on synthetic dyes, nanostructures (quantum dots and nanotubes), and genetically encoded components. We aim to provide tool developers with information that may guide future engineering efforts and tool users with information regarding existing indicators to facilitate studies of amino acid dynamics.

The role of medical gas in stroke: an updated review

Medical gas is a large class of bioactive gases used in clinical medicine and basic scientific research. At present, the role of medical gas in neuroprotection has received growing attention. Stroke is a leading cause of death and disability in adults worldwide, but current treatment is still very limited. The common pathological changes of these two types of stroke may include excitotoxicity, free radical release, inflammation, cell death, mitochondrial disorder, and blood-brain barrier disruption. In this review, we will discuss the pathological mechanisms of stroke and the role of two medical gases (hydrogen and hydrogen sulfide) in stroke, which may potentially provide a new insight into the treatment of stroke.

Hydrogen Sulfide and Endoplasmic Reticulum Stress: A Potential Therapeutic Target for Central Nervous System Degeneration Diseases

There are three members of the endogenous gas transmitter family. The first two are nitric oxide and carbon monoxide, and the third newly added member is hydrogen sulfide (H₂S). They all have similar functions: relaxing blood vessels, smoothing muscles, and getting involved in the regulation of neuronal excitation, learning, and memory. The cystathionine β-synthase (CBS), 3-mercaptopyruvate sulfur transferase acts together with cysteine aminotransferase (3-MST/CAT), cystathionine γ-lyase (CSE), and 3-mercaptopyruvate sulfur transferase with D-amino acid oxidase (3-MST/DAO) pathways are involved in the enzymatic production of H₂S. More and more researches focus on the role of H₂S in the central nervous system (CNS), and H₂S plays a significant function in neuroprotection processes, regulating the function of the nervous system as a signaling molecule in the CNS. Endoplasmic reticulum stress (ERS) and protein misfolding in its mechanism are related to neurodegenerative diseases. H₂S exhibits a wide variety of cytoprotective and physiological functions in the CNS degenerative diseases by regulating ERS. This review summarized on the neuroprotective effect of H₂S for ERS played in several CNS diseases including Alzheimer’s disease, Parkinson’s disease, and depression disorder, and discussed the corresponding possible signaling pathways or mechanisms as well.

H2S-Donating trisulfide linkers confer unexpected biological behaviour to poly(ethylene glycol)-cholesteryl conjugates

Inspired by the properties of the naturally occurring H₂S donor, diallyl trisulfide (DATS, extracted from garlic), the biological behaviour of trisulfide-bearing PEG-conjugates was explored. Specifically, three conjugates comprising an mPEG tail and a cholesteryl head were investigated: conjugates bridged by a trisulfide linker (T), a disulfide linker (D) or a carbamate linker (C), and a fourth comprising two mPEG tails bridged by a trisulfide linker (P). H₂S testing using both a fluorescent chemical probe in HEK293 cells and an amperometric sensor to monitor release in suspended cells, demonstrated the ability of the trisulfide conjugates, T and P, to release H₂S in the presence of cellular thiols. Cytotoxicity and cyto-protective capacity on HEK293 cells showed that T was the best tolerated of the conjugates studied, and remarkably more so than D or C. Moreover, it was noted that application of T conferred a protective effect to the cells, effectively abolishing the toxicity associated with co-administered C. The interaction of conjugates and combinations thereof with the cell membrane of HEK cells, as well as ROS generation were also investigated. It was found that C caused significant membrane perturbation, correlating with high losses in cell viability and pronounced generation of ROS, especially in the mitochondria. T, however, did not disturb the membrane and was able to mitigate the generation of ROS, especially in the mitochondria. The interplay of the cholesteryl group and H₂S donation for conferring cytoprotective effects was clearly demonstrated as P did not display the same beneficial characteristics as T.

A highly selective fluorescent probe for hydrogen polysulfides in living cells based on a naphthalene derivative

Hydrogen polysulfides (H₂S_n, n > 1) are members of reactive sulfur species (RSS) and signaling molecules derived from hydrogen sulfide (H₂S). Recently, the functions of H₂S_n in physiological and pathological processes have been increasingly recognized. However, their biological effects and detailed mechanisms of action are still little known. Therefore, there is an urgent need to develop highly selective and sensitive techniques for monitoring hydrogen polysulfides (H₂S_n) in living cells. In this study, we designed and synthesized a fluorescent probe based on a naphthalene derivative for the detection of hydrogen polysulfides. A naphthalene derivative was applied as the fluorescent main structure and the 2-fluoro-5-nitrobenzoate group was chosen as the recognition unit. In the absence of hydrogen polysulfides, the fluorescent probe displayed almost no fluorescence. In the presence of hydrogen polysulfides, the fluorescent probe exhibited strong fluorescence. The sensing mechanism was based on H₂S_n-mediated aromatic substitution-cyclization reactions. The linear range of the response concentration of the probe to hydrogen polysulfide was acquired in a concentration range of H₂S_n from 7.5 × 10^-7 to 2.5 × 10^-5 mol L^-1. The detection limit was evaluated to be 5.0 × 10^-7 mol L^-1 for H₂S_n. The fluorescent probe can applied in a wide pH range including physiological condition pH. The fluorescent probe showed high specificity for H₂S_n over other reactive sulfur species (RSS). Moreover, the fluorescent probe has been successfully applied to confocal imaging of hydrogen polysulfides in HepG2 cells without cell cytotoxicity. All of such good qualities indicated that it could be used to detect H₂S_n in living cells.

Hydrogen Sulfide Impairs Meiosis Resumption in Xenopus laevis Oocytes

The role of hydrogen sulfide (H₂S) is addressed in Xenopus laevis oocytes. Three enzymes involved in H₂S metabolism, cystathionine β-synthase, cystathionine γ-lyase, and 3-mercaptopyruvate sulfurtransferase, were detected in prophase I and metaphase II-arrested oocytes and drove an acceleration of oocyte meiosis resumption when inhibited. Moreover, meiosis resumption is associated with a significant decrease in endogenous H₂S. On another hand, a dose-dependent inhibition was obtained using the H₂S donor, NaHS (1 and 5 mM). NaHS impaired translation. NaHS did not induce the dissociation of the components of the M-phase promoting factor (MPF), cyclin B and Cdk1, nor directly impacted the MPF activity. However, the M-phase entry induced by microinjection of metaphase II MPF-containing cytoplasm was diminished, suggesting upstream components of the MPF auto-amplification loop were sensitive to H₂S. Superoxide dismutase and catalase hindered the effects of NaHS, and this sensitivity was partially dependent on the production of reactive oxygen species (ROS). In contrast to other species, no apoptosis was promoted. These results suggest a contribution of H₂S signaling in the timing of amphibian oocytes meiosis resumption.

A dual-ratiometric fluorescent probe for individual and continuous detection of H2S and HClO in living cells

A dual-ratiometric fluorescent probe, Han-HClO-H2S, was developed for the individual and continuous detection of H₂S and HClO with high sensitivity and good selectivity, and had been applied to detect intracellular H₂S and/or HClO in living cells.

Protective effect of hydrogen sulfide on oxidative stress-induced neurodegenerative diseases

Hydrogen sulfide is an antioxidant molecule that has a wide range of biological effects against oxidative stress. Balanced oxidative stress is also vital for maintaining cellular function in biological system, where reactive oxygen species are the main source of oxidative stress. When the normal redox balance is disturbed, deoxyribonucleic acid, lipid, and protein molecules are oxidized under pathological conditions, like diabetes mellitus that leads to diabetic peripheral neuropathy. In diabetes mellitus-induced diabetic peripheral neuropathy, due to hyperglycemia, pancreatic beta cell (β cell) shows resistance to insulin secretion. As a consequence, glucose metabolism is disturbed in neuronal cells which are distracted from providing proper cell signaling pathway. Not only diabetic peripheral neuropathy but also other central damages occur in brain neuropathy. Neurological studies regarding type 1 diabetes mellitus patients with Alzheimer’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis have shown changes in the central nervous system because high blood glucose levels (HbA1c) appeared with poor cognitive function. Oxidative stress plays a role in inhibiting insulin signaling that is necessary for brain function. Hydrogen sulfide exhibits antioxidant effects against oxidative stress, where cystathionine β synthase, cystathionine γ lyase, and 3-mercaptopyruvate sulfurtransferase are the endogenous sources of hydrogen sulfide. This review is to explore the pathogenesis of diabetes mellitus-induced diabetic peripheral neuropathy and other neurological comorbid disorders under the oxidative stress condition and the anti-oxidative effects of hydrogen sulfide.

Hydrogen sulfide protects against cell damage through modulation of PI3K/Akt/Nrf2 signaling

Hydrogen sulfide as the third endogenous gaseous mediator had protective effects against traumatic brain injury-induced neuronal damage in mice. However, the exact pathophysiological mechanism underlying traumatic brain injury is complicated and the protective role of H₂S is not yet fully known. Therefore, we combined the mechanical injury (scratch) with secondary injury including metabolic impairment (no glucose) together to investigate the underlying cellular mechanism of hydrogen sulfide in vitro models of traumatic brain injury. In the present study, we found that H₂S could prevent the scratch-induced decrease in the expression of cystathionine-β-synthetase, a key enzyme involved in the source of hydrogen sulfide, and endogenous hydrogen sulfide generation in PC12 cells. We also found that hydrogen sulfide could prevent scratch-induced cellular injury, alteration of mitochondrial membrane potential, intracellular accumulation of reactive oxygen species and cell death (autophagic cell death and apoptosis) in PC12 cells. It was also found that blocking PI3K/AKT pathway by LY294002, abolished the protection of H₂S against scratch-induced cellular reactive oxygen species level and NRF2 accumulation and function in the nucleus. These results suggest that hydrogen sulfide protects against cell damage induced by scratch injury through modulation of the PI3K/Akt/Nrf2 pathway. This study raises the possibility that hydrogen sulfide may have therapeutic efficacy in traumatic brain injury.

Formation or Cleavage of Rings via Sulfide-Mediated Reduction Offers Background-Free Detection of Sulfide

A set of three highly selective probes for sulfide detection has been developed. Two novel mechanistic strategies for the detection, including (a) transformation of a pro-fluorophore into an active fluorophore and (b) destruction of a fused ring to activate a fluorophore, have been explored. The structural features of the probes including azido groups ("active" and "latent") and leaving groups (with or without being attached to the fluorophore) have been investigated. During the course of the mechanistic studies, the single-crystal structures of all the probes and the products were obtained. One of the probes proved to be superior in terms of its ability to detect sulfide in pure water via an in situ formation of a fluorophore from a nonfluorescent precursor. These cheap and easy-to-prepare probes offer practical applications of sulfide recognition in environmental water samples and in the ovaries of fruit flies. A detection and quantification method using one of these probes and analysis with a smartphone enabled nonspecialists to detect sulfide reliably.

H2S-based therapies for ischaemic stroke: opportunities and challenges

Stroke is a cerebrovascular disease displaying high mortality and morbidity. Despite extensive efforts, only very few therapies are available for stroke patients as yet. Hydrogen sulfide (H₂S) is thought to be a signalling molecule that is endogenously produced and plays functional roles in the central nervous system. Currently, numerous studies show that H₂S impacts stroke outcomes in animal and cellular models. Here, we review the recent research regarding the effects of endogenously produced H₂S as well as exogenous H₂S donors on stroke pathology, focusing on the potential of H₂S-based therapies in treating ischaemic stroke. We also discuss the several issues that hinder the clinical translation of H₂S-based therapies from the bench. Taken together, we think that H₂S-based therapies are promising strategies for treating cerebral ischaemia if we successfully address these issues.

Memantine prodrug as a new agent for Alzheimer's Disease

Hydrogen sulphide has recently drawn much attention due to its potent anti-inflammatory and neuroprotective roles in brain functions. The purpose of the current study was to exploit these beneficial properties of H₂S to design a new agent for the treatment of Alzheimer's disease (AD). To pursue our aims, we replaced the free amine group of memantine with an isothiocyanate functionality as a putative H₂S-donor moiety. The new chemical entity, named memit, was then tested in vitro to determine whether it retains the pharmacological profile of the "native drug", while also providing a source of H₂S in the CNS. Indeed, Memit showed the ability to release H₂S through a cysteine-mediated mechanism, thus generating memantine. Moreover, the new hybrid molecule exerts protective effects against neuronal inflammation and induces a drastic fall in ROS production. In addition, memit was also able to reduce the Aβ(1-42) self-induced aggregation and exerted cytoprotective effect against Aβ oligomers-induced damage in both human neurons and rat microglia cells. Finally, similarly to memantine, the new compound promotes autophagy, a complex process required for cellular homeostasis in cell survival that results to be altered in neurodegenerative diseases. In conclusion, our study revealed that memit is a prodrug of memantine. Further in vivo studies will be necessary to fully investigate the synergic or cumulative effects due to the H₂S-releasing moiety and the native drug.

Novel Applications of Lead Acetate and Flow Cytometry Methods for Detection of Sulfur-Containing Molecules

Hydrogen sulfide (H₂S) is the most recently established gaseous vasodilator, enzymatically produced from cysteine metabolism, involved in a number of pathophysiological processes. However, its accurate detection in vivo is critical due to its volatility and tendency to form sulfane sulfur derivatives, thus limiting the data interpretation of its biological roles. We developed new applications of the simple and rapid method to measure H₂S release in cell culture systems, based on the lead acetate strip test. This test, previously prevalently used in microbiology, was compared with the agar trap method, applied, in parallel, on both cell cultures and cell-free samples. Sulfane sulfur represents the major species derived from intracellular H₂S. Various fluorescent probes are available for quantitation of H₂S derivatives intracellularly. We present here an alternative to the classic imaging method for sulfane sulfur evaluation, running on a flow cytometer, based on SSP4 probe labeling. Flow cytometry turned out to be more direct, fully quantitative and less time-consuming compared to microscopy and more precise with respect to the fluorescence multi-plate reader assay. The new application methods for H₂S determination appear to be fully suitable for the analysis of H₂S release and sulfane sulfur content in biological samples.

Possible involvement of peripheral TRP channels in the hydrogen sulfide-induced hyperalgesia in diabetic rats

BACKGROUND

Peripheral diabetic neuropathy can be painful and its symptoms include hyperalgesia, allodynia and spontaneous pain. Hydrogen sulfide (H2S) is involved in diabetes-induced hyperalgesia and allodynia. However, the molecular target through which H2S induces hyperalgesia in diabetic animals is unclear. The aim of this study was to determine the possible involvement of transient receptor potential (TRP) channels in H2S-induced hyperalgesia in diabetic rats.

RESULTS

Streptozotocin (STZ) injection produced hyperglycemia in rats. Intraplantar injection of NaHS (an exogenous donor of H2S, 3-100 µg/paw) induced hyperalgesia, in a time-dependent manner, in formalin-treated diabetic rats. NaHS-induced hyperalgesia was partially prevented by local intraplantar injection of capsazepine (0.3-3 µg/paw), HC-030031 (100-316 µg/paw) and SKF-96365 (10-30 µg/paw) blockers, at 21 days post-STZ injection. At the doses used, these blockers did not modify formalin-induced nociception. Moreover, capsazepine (0.3-30 µg/paw), HC-030031 (100-1000 µg/paw) and SKF-96365 (10-100 µg/paw) reduced formalin-induced nociception in diabetic rats. Contralateral injection of the highest doses used did not modify formalin-induced flinching behavior. Hyperglycemia, at 21 days, also increased protein expression of cystathionine-β-synthase enzyme (CBS) and TRPC6, but not TRPA1 nor TRPV1, channels in dorsal root ganglia (DRG). Repeated injection of NaHS enhanced CBS and TRPC6 expression, but hydroxylamine (HA) prevented the STZ-induced increase of CBS protein. In addition, daily administration of SKF-96365 diminished TRPC6 protein expression, whereas NaHS partially prevented the decrease of SKF-96365-induced TRPC6 expression. Concordantly, daily intraplantar injection of NaHS enhanced, and HA prevented STZ-induced intraepidermal fiber loss, respectively. CBS was expressed in small- and medium-sized cells of DRG and co-localized with TRPV1, TRPA1 and TRPC6 in IB4-positive neurons.

CONCLUSIONS

Our data suggest that H2S leads to hyperalgesia in diabetic rats through activation of TRPV1, TRPA1 and TRPC channels and, subsequent intraepidermal fibers loss. CBS enzyme inhibitors or TRP-channel blockers could be useful for treatment of painful diabetic neuropathy.

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 (K_ATP/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.

A reversible and turn-on type fluorescence behaviour of hydrogen sulfide via a redox cycle between selenoxide and selenide

Upon treatment with H₂S in MeCN–PBS, the fluorescence dormant selenoxides of dibenzobarrelene- and benzobarrelene-based 1-seleno-1,3-butadiene derivatives are rapidly converted to strongly fluorescent selenides.

Effects of NaHS and hydroxylamine on the expressions of brain-derived neurotrophic factor and its receptors in rats after cardiac arrest and cardiopulmonary resuscitation

BACKGROUND

H₂S can also protect nerve cells. The objective of the study is to investigate the effects of hydrogen sulfide (H₂S) on the expressions of brain-derived neurotrophic factor (BDNF) and its receptors, tyrosine protein kinase B (TrkB) and p75 neurotrophin receptor (p75NTR), in brain tissues of rats with cardiac arrest and cardiopulmonary resuscitation (CA/CPR) following the restoration of spontaneous circulation (ROSC).

METHODS

Rats (n = 240) with CA/CPR were divided into three groups: Intervention (n = 80) that received sodium hydrosulfide (NaHS, 14 μmoL/kg·d) intervention after ROSC; Inhibition (n = 80) that received hydroxylamine (40 μmoL/kg·d) intervention after ROSC; and Control (n = 80) that received saline after ROSC. Kaplan-Meyer analysis was used to analyze the survival data. Quantitative real-time PCR (q-PCR), Western blot, immunohistochemistry and IODs (integrated optical density) were performed to determine the mRNA and protein expressions of BDNF, TrkB and p75NTR in rat brain tissues.

RESULTS

Survival rate of the three groups had significant difference (χ² = 28.376, p = 0.000). The Intervention group had the highest survival rate (82.5%), while the Inhibition group had the lowest survival rate (62.5%). The mRNA and protein levels of BDNF and TrkB in the Intervention group were significantly higher compared to the Control group (p < 0.05); while the mRNA and protein levels of BDNF and TrkB in the Inhibition group was significantly lower than the Control group (p < 0.05) on days 1, 3, and 7. However, the mRNA and protein levels of p75NTR in the Intervention group were significantly lower than the Control group (p < 0.05); while the mRNA and protein levels of p75NTR in the Inhibition group were significantly higher than the Control group (p < 0.05) on days 1, 3, and 7.

CONCLUSION

NaHS treatment increases the survival rate of rats after CA and ROSC by upregulating the expression and activation of BDNF and its receptor TrkB, and down-regulating p75NTR expression.

SO2 Donors and Prodrugs, and Their Possible Applications: A Review

SO2 is widely recognized as an air pollutant and is a known cause of acid rain. At a sufficiently high level, it also causes respiratory diseases. A much lesser known side of SO2 is its endogenous nature and possible physiological roles. There is mounting evidence that SO2 is produced during normal cellular metabolism and may possibly function as a signaling molecule in normal physiology. The latter aspect is still at the stage of being carefully examined as to the validity of classifying SO2 as a gasotransmitter with endogenous signaling roles. One difficulty in studying the biological and pharmacological roles of SO2 is the lack of adequate tools for its controllable and precise delivery. Traditional methods of using SO2 gas or mixed sulfite salts do not meet research need for several reasons. Therefore, there has been increasing attention on the need of developing SO2 donors or prodrugs that can be used as tools for the elucidation of SO2's physiological roles, pharmacological effects, and possible mechanism(s) of action. In this review, we aim to review basic sulfur chemistry in the context of sulfur signaling and various chemical strategies used for designing SO2 donors. We will also discuss potential pharmacological applications of SO2 donors, lay out desirable features for such donors and possibly prodrugs, analyze existing problems, and give our thoughts on research needs.

The Role of Gaseous Molecules in Traumatic Brain Injury: An Updated Review

Traumatic brain injury (TBI) affects millions of people in China each year. TBI has a high mortality and often times a serious prognosis. The causative mechanisms of TBI during development and recovery from an injury remain vague, leaving challenges for the medical community to provide treatment options that improve prognosis and provide an optimal recovery. Biological gaseous molecules including nitric oxide (NO), carbon monoxide (CO), hydrogen sulfide (H₂S), and molecular hydrogen (H₂) have been found to play critical roles in physiological and pathological conditions in mammals. Accumulating evidence has found that these gaseous molecules can execute neuroprotection in many central nervous system (CNS) conditions due to their highly permeable properties allowing them to enter the brain. Considering the complicated mechanisms and the serious prognosis of TBI, effective and adequate therapeutic approaches are urgently needed. These four gaseous molecules can be potential attractive therapeutic intervention on TBI. In this review, we will present a comprehensive overview on the role of these four biological gasses in the development of TBI and their potential therapeutic applications.

Hydrogen sulfide, nitric oxide, and neurodegenerative disorders

Hydrogen Sulfide (H2S) and Nitric Oxide (NO) have become recognized as important gaseous signaling molecules with enormous pharmacological effects, therapeutic value, and central physiological roles. NO is one of the most important regulators of the pathophysiological condition in central nervous system (CNS). It is critical in the various functioning of the brain; however, beyond certain concentration/level, it is toxic. H2S was regarded as toxic gas with the smell like rotten egg. But, it is now regarded as emerging neuroprotectant and neuromodulator. Recently, the use of donors and inhibitors of these signaling molecules have helped us to identify their accurate and precise biological effects. The most abundant neurotransmitter of CNS (glutamate) is the initiator of the reaction that forms NO, and H2S is highly expressed in brain. These molecules are shedding light on the pathogenesis of various neurological disorders. This review is mainly focused on the importance of H2S and NO for normal functioning of CNS.

Antioxidant and Cell-Signaling Functions of Hydrogen Sulfide in the Central Nervous System

Hydrogen sulfide (H2S), a toxic gaseous molecule, plays a physiological role in regulating homeostasis and cell signaling. H2S is produced from cysteine by enzymes, such as cystathionine β-synthase (CBS), cystathionine γ-lyase (CSE), cysteine aminotransferase (CAT), and 3-mercaptopyruvate sulfurtransferase (3MST). These enzymes regulate the overall production of H2S in the body. H2S has a cell-signaling function in the CNS and plays important roles in combating oxidative species such as reactive oxygen species (ROS) and reactive nitrogen species (RNS) in the body. H2S is crucial for maintaining balanced amounts of antioxidants to protect the body from oxidative stress, and appropriate amounts of H2S are required to protect the CNS in particular. The body regulates CBS, 3MST, and CSE levels in the CNS, and higher or lower levels of these enzymes cause various neurodegenerative diseases. This review discusses how H2S protects the CNS by acting as an antioxidant that reduces excessive amounts of ROS and RNS. Additionally, H2S regulates cell signaling to combat neuroinflammation and protect against central neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS).

Hydrogen sulfide supplement attenuates the apoptosis of retinal ganglion cells in experimental glaucoma

Glaucoma is a group of neurodegenerative eye diseases characterized by progressive impairment of visual function due to loss of retinal ganglion cells (RGC). As hydrogen sulfide (H₂S) was reported to play a role in the process of glaucomatous neuropathy and improve RGC survival in experimental glaucoma, the authors aimed to investigate the anti-apoptosis effect of H₂S supplement in a rat glaucoma model, and further tried to explore the involved factors in the neuroprotection. A chronic ocular hypertension (COH) rat model induced by intracameral injection of cross-linking hydrogel was employed to simulate glaucoma and 288 rats were subjected to experimental procedures in the present study. After 4 weeks of sodium hydrosulfide (NaHS) administration following COH induction, the apoptosis of RGC isolated from experimented rats as well as apoptosis of neurons in ganglion cell layer (GCL), intrinsic apoptotic pathway activity, mitochondrial function, glial activation, NF-κB pathway activity, NADPH oxidase activity, autophagy activity and TNF-α level in retina were evaluated. The results showed that H₂S supplement effectively attenuated the apoptosis of RGC in experimental glaucoma, and the neuroprotection by H₂S might correlate with preservation of mitochondrial function, attenuation of oxidative stress, suppression of glial activation, inhibition of inflammatory pathways and downregulation of autophagy. Our study indicated that H₂S supplement resulted in significant neuroprotection through attenuation of RGC apoptosis which might be linked with multiple factors in experimental glaucoma. The new therapeutic strategy might potentially contribute to benefit glaucoma treatment, which is worth further concerns.

Hydrogen Sulfide Antagonizes Chronic Restraint Stress-Induced Depressive-Like Behaviors via Upregulation of Adiponectin

Backgroud: Chronic restraint stress (CRS) induces depressive-like behaviors in rodents, which involves dysregulation of hippocampal synapse formation and excessive autophagy. Adiponectin has antidepressant activity. Hydrogen sulfide (H₂S) is a novel gasotransmitter. The present work was to investigate whether H₂S antagonizes CRS-induced depressive-like behaviors in rats and to explore whether its potential mechanism involves ameliorated synaptic and autophagic dysregulation by upregulation of adiponectin. Methods: Depressive-like behavior was analyzed by the tail suspension test (TST), novelty suppressed feeding test (NSFT), and open field test (OFT). The structure of autophagy was observed under transmission electron microscopy. The expressions of adiponectin, beclin1, and sequestosome 1 (p62/SQSTMI) protein in hippocampus were measured by Western blot. The levels of synapsin1 (SYN1) in the hippocampus were calculated by Western blot and immunofluorescence technique. Results: The behavior experiments, including TST, NSFT, and OFT, showed that NaHS (a donor of H₂S) reduced CRS-induced depressive-like behaviors. NaHS decreased the loss of hippocampal synapse as evidenced by increased the level of SYN1 in the hippocampus of CRS-exposed rats. NaHS rescued CRS-induced excessive hippocampal autophagy as evidenced by declines in the number of autophagosomes and the expression of beclin1 as well as increase in the expression of P62 in the hippocampus of CRS-exposed rats. NaHS upregulated hippocampal adiponectin expression in the CRS-exposed rats. Furthermore, neutralizing adiponectin by Anti-acrp30 reversed the protective response of NaHS to CRS-produced depressive-like behaviors as well as hippocampal synaptic disruption and excessive autophagy. Conclusion: H₂S mitigates CRS-induced depressive behavior via upregulation of adiponectin, which in turn results in amelioration in hippocampal synapse formation dysfunction and excessive autophagy.

Neonatal Colonic Inflammation Increases Spinal Transmission and Cystathionine β-Synthetase Expression in Spinal Dorsal Horn of Rats with Visceral Hypersensitivity

Irritable bowel syndrome (IBS) is a common gastrointestinal disorder characterized by chronic abdominal pain and alteration of bowel movements. The pathogenesis of visceral hypersensitivity in IBS patients remains largely unknown. Hydrogen sulfide (H₂S) is reported to play an important role in development of visceral hyperalgesia. However, the role of H₂S at spinal dorsal horn level remains elusive in visceral hypersensitivity. The aim of this study is designed to investigate how H₂S takes part in visceral hypersensitivity of adult rats with neonatal colonic inflammation (NCI). Visceral hypersensitivity was induced by neonatal colonic injection of diluted acetic acid. Expression of an endogenous H₂S synthesizing enzyme cystathionine β-synthetase (CBS) was determined by Western blot. Excitability and synaptic transmission of neurons in the substantia gelatinosa (SG) of spinal cord was recorded by patch clamping. Here, we showed that expression of CBS in the spinal dorsal horn was significantly upregulated in NCI rats. The frequency of glutamatergic synaptic activities in SG was markedly enhanced in NCI rats when compared with control rats. Application of NaHS increased the frequency of both spontaneous and miniature excitatory post-synaptic currents of SG neurons in control rats through a presynaptic mechanism. In contrast, application of AOAA, an inhibitor of CBS, dramatically suppressed the frequency of glutamatergic synaptic activities of SG neurons of NCI rats. Importantly, intrathecal injection of AOAA remarkably attenuated visceral hypersensitivity of NCI rats. These results suggest that H₂S modulates pain signaling likely through a presynaptic mechanism in SG of spinal dorsal horn, thus providing a potential therapeutic strategy for treatment for chronic visceral pain in patients with IBS.

Hydrogen Sulfide: A Worthwhile Tool in the Design of New Multitarget Drugs

H₂S is a gaseous molecule able to trigger a plethora of central physiological and pharmacological effects as antioxidant, pro- and anti-inflammatory, pro- and anti-nociceptive, neuromodulator, and cytoprotective. The polypharmacology of H₂S depends on the wide variety of targets implicated, but, despite the efforts, the mechanisms of action that should clarify its activity are still not completely unrevealed. Nevertheless, many attempts to exploit the multifaceted profile of this molecule have already been accomplished and many chemical entities containing an H₂S-releasing pharmacophore have been synthetized. Here we discuss recent investigations on multitarget molecules able to release H₂S, with a particular focus on the combinations of "native drug" with moieties structurally able to release H₂S and their applications as therapeutic tools in bone disease, gastrointestinal system and neurodegenerative disorders.