Modulating effect of hydrogen sulfide on gamma-aminobutyric acid B receptor in recurrent febrile seizures in rats

Hydrogen sulfide mitigates memory impairments via the restoration of glutamatergic neurons in a mouse model of hemorrhage shock and resuscitation

Impaired long-term memory, a complication of traumatic stress including hemorrhage shock and resuscitation (HSR), has been reported to be associated with multiple neurodegenerations. The ventral tegmental area (VTA) participates in both learned appetitive and aversive behaviors. In addition to being prospective targets for the therapy of addiction, depression, and other stress-related diseases, VTA glutamatergic neurons are becoming more widely acknowledged as powerful regulators of reward and aversion. This study revealed that HSR exposure induces memory impairments and decreases the activation in glutamatergic neurons, and decreased β power in the VTA. We also found that optogenetic activation of glutamatergic neurons in the VTA mitigated HSR-induced memory impairments, and restored β power. Moreover, hydrogen sulfide (H2S), a gasotransmitter with pleiotropic roles, has neuroprotective functions at physiological concentrations. In vivo, H2S administration improved HSR-induced memory deficits, elevated c-fos-positive vesicular glutamate transporters (Vglut2) neurons, increased β power, and restored the balance of γ-aminobutyric acid (GABA) and glutamate in the VTA. This work suggests that glutamatergic neuron stimulation via optogenetic assay and exogenous H2S may be useful therapeutic approaches for improving memory deficits following HSR.

Benzylic Trifluoromethyl Accelerates 1,6-Elimination Toward Rapid Probe Activation

Activity-based detection of hydrogen sulfide in live cells can expand our understanding of its reactivity and complex physiological effects. We have discovered a highly efficient method for fluorescent probe activation, which is driven by H2S-triggered 1,6-elimination of an α-CF3-benzyl to release resorufin. In detecting intracellular H2S, 4-azido-(α-CF3)-benzyl resorufin offers significantly faster signal generation and improved sensitivity compared to 4-azidobenzyl resorufin. Computed free energy profiles for the 1,6-elimination process support the hypothesis that a benzylic CF3 group can reduce the activation energy barrier toward probe activation. This novel probe design allows for near-real-time detection of H2S in HeLa cells under stimulation conditions.

Biomimetic Vesicles with Designer Phospholipids Can Sense Environmental Redox Cues

Cell-like materials that sense environmental cues can serve as next-generation biosensors and help advance the understanding of intercellular communication. Currently, bottom-up engineering of protocell models from molecular building blocks remains a grand challenge chemists face. Herein, we describe giant unilamellar vesicles (GUVs) with biomimetic lipid membranes capable of sensing environmental redox cues. The GUVs employ activity-based sensing through designer phospholipids that are fluorescently activated in response to specific reductive (hydrogen sulfide) or oxidative (hydrogen peroxide) conditions. These synthetic phospholipids are derived from 1,2-dipalmitoyl-rac-glycero-3-phosphocholine and they possess a headgroup with heterocyclic aromatic motifs. Despite their structural deviation from the phosphocholine headgroup, the designer phospholipids (0.5-1.0 mol %) mixed with natural lipids can vesiculate, and the resulting GUVs (7-20 μm in diameter) remain intact over the course of redox sensing. All-atom molecular dynamics simulations gave insight into how these lipids are positioned within the hydrophobic core of the membrane bilayer and at the membrane-water interface. This work provides a purely chemical method to investigate potential redox signaling and opens up new design opportunities for soft materials that mimic protocells.

Advancements in Brain Research: The In Vivo/In Vitro Electrochemical Detection of Neurochemicals

Neurochemicals, crucial for nervous system function, influence vital bodily processes and their fluctuations are linked to neurodegenerative diseases and mental health conditions. Monitoring these compounds is pivotal, yet the intricate nature of the central nervous system poses challenges. Researchers have devised methods, notably electrochemical sensing with micro-nanoscale electrodes, offering high-resolution monitoring despite low concentrations and rapid changes. Implantable sensors enable precise detection in brain tissues with minimal damage, while microdialysis-coupled platforms allow in vivo sampling and subsequent in vitro analysis, addressing the selectivity issues seen in other methods. While lacking temporal resolution, techniques like HPLC and CE complement electrochemical sensing's selectivity, particularly for structurally similar neurochemicals. This review covers essential neurochemicals and explores miniaturized electrochemical sensors for brain analysis, emphasizing microdialysis integration. It discusses the pros and cons of these techniques, forecasting electrochemical sensing's future in neuroscience research. Overall, this comprehensive review outlines the evolution, strengths, and potential applications of electrochemical sensing in the study of neurochemicals, offering insights into future advancements in the field.

A novel hydrogen sulfide donor reduces neuroinflammation and seizures by activating ATP-sensitive potassium channels

Epilepsy is a common neurological disorder worldwide. Hydrogen sulfide (H2S) has been found to have anti-seizure effects. However, its mechanism remains to be explored. In the present study, we showed that a novel H2S donor attenuated neuroinflammation by up-regulating ATP-sensitive potassium channel (KATP) expression to reduce seizures. The novel H2S donor significantly reduced the expression of TNF-α and increased the expression of IL-10 in LPS-treated BV2 cells and the hippocampus of pilocarpine-induced epileptic mice. The modulatory effects of the H2S donor on inflammatory cytokines were prevented by glibenclamide, a common KATP channels blocker. The H2S donor promoted the expression of KATP channel subunits SUR2 and Kir6.1 in LPS-treated BV2 cells and the hippocampus of pilocarpine-induced epileptic mice. In addition, the H2S donor reduced the electroencephalography amplitude of hippocampal epileptic waves and reduced seizures in pilocarpine-induced epileptic mice, which were also attenuated by glibenclamide. These results indicated that the novel H2S donor reduced seizures and regulated microglial inflammatory cytokines by activating KATP channels, which may provide a prospective therapeutic strategy for the anti-seizure effects of H2S donor.

A Small-Molecule Approach to Bypass In Vitro Selection of New Aptamers: Designer Pre-Ligands Turn Baby Spinach into Sensors for Reactive Inorganic Targets

Fluorescent light-up aptamer (FLAP) systems are promising biosensing platforms that can be genetically encoded. Here, we describe how a single FLAP that works with specific organic ligands can detect multiple, structurally unique, non-fluorogenic, and reactive inorganic targets. We developed 4-O-functionalized benzylidene imidazolinones as pre-ligands with suppressed fluorescent binding interactions with the RNA aptamer Baby Spinach. Inorganic targets, hydrogen sulfide (H2S) or hydrogen peroxide (H2O2), can specifically convert these pre-ligands into the native benzylidene imidazolinones, and thus be detected with Baby Spinach. Adaptation of this approach to live cells opened a new opportunity for top-down construction of whole-cell sensors: Escherichia coli transformed with a Baby Spinach-encoding plasmid and incubated with pre-ligands generated fluorescence in response to exogenous H2S or H2O2. Our approach eliminates the requirement of in vitro selection of a new aptamer sequence for molecular target detection, allows for the detection of short-lived targets, thereby advancing FLAP systems beyond their current capabilities. Leveraging the functional group reactivity of small molecules can lead to cell-based sensors for inorganic molecular targets, exploiting a new synergism between synthetic organic chemistry and synthetic biology.

The Role of Hydrogen Sulfide in Regulation of Cell Death following Neurotrauma and Related Neurodegenerative and Psychiatric Diseases

Injuries of the central (CNS) and peripheral nervous system (PNS) are a serious problem of the modern healthcare system. The situation is complicated by the lack of clinically effective neuroprotective drugs that can protect damaged neurons and glial cells from death. In addition, people who have undergone neurotrauma often develop mental disorders and neurodegenerative diseases that worsen the quality of life up to severe disability and death. Hydrogen sulfide (H₂S) is a gaseous signaling molecule that performs various cellular functions in normal and pathological conditions. However, the role of H₂S in neurotrauma and mental disorders remains unexplored and sometimes controversial. In this large-scale review study, we examined the various biological effects of H₂S associated with survival and cell death in trauma to the brain, spinal cord, and PNS, and the signaling mechanisms underlying the pathogenesis of mental illnesses, such as cognitive impairment, encephalopathy, depression and anxiety disorders, epilepsy and chronic pain. We also studied the role of H₂S in the pathogenesis of neurodegenerative diseases: Alzheimer's disease (AD) and Parkinson's disease (PD). In addition, we reviewed the current state of the art study of H₂S donors as neuroprotectors and the possibility of their therapeutic uses in medicine. Our study showed that H₂S has great neuroprotective potential. H₂S reduces oxidative stress, lipid peroxidation, and neuroinflammation; inhibits processes associated with apoptosis, autophagy, ferroptosis and pyroptosis; prevents the destruction of the blood-brain barrier; increases the expression of neurotrophic factors; and models the activity of Ca²⁺ channels in neurotrauma. In addition, H₂S activates neuroprotective signaling pathways in psychiatric and neurodegenerative diseases. However, high levels of H₂S can cause cytotoxic effects. Thus, the development of H₂S-associated neuroprotectors seems to be especially relevant. However, so far, all H₂S modulators are at the stage of preclinical trials. Nevertheless, many of them show a high neuroprotective effect in various animal models of neurotrauma and related disorders. Despite the fact that our review is very extensive and detailed, it is well structured right down to the conclusions, which will allow researchers to quickly find the proper information they are interested in.

Possible involvement of brain hydrogen sulphide in the inhibition of the rat micturition reflex induced by activation of brain alpha7 nicotinic acetylcholine receptors

We previously reported that brain α7 nicotinic acetylcholine receptors inhibited the rat micturition reflex. To elucidate the mechanisms underlying this inhibition, we focused on the relationship between α7 nicotinic acetylcholine receptors and hydrogen sulphide (H₂S) because we found that H₂S also inhibits the rat micturition reflex in the brain. Therefore, we investigated whether H₂S is involved in the inhibition of the micturition reflex induced by the activation of α7 nicotinic acetylcholine receptors in the brain. Cystometry was performed in male Wistar rats under urethane anesthesia (0.8 g/kg, ip) to examine the effects of icv pre-treated GYY4137 (H₂S donor, 1 or 3 nmol/rat) or aminooxyacetic acid (AOAA; non-selective H₂S synthesis inhibitor, 3 or 10 μg/rat) on PHA568487 (α7 nicotinic acetylcholine receptor agonist, icv)-induced prolongation of intercontraction intervals. PHA568487 administration at a lower dose (0.3 nmol/rat, icv) had no significant effect on intercontraction intervals, while under pre-treatment with GYY4137 (3 nmol/rat icv), PHA568487 (0.3 nmol/rat, icv) significantly prolonged intercontraction intervals. PHA568487 at a higher dose (1 nmol/rat, icv) induced intercontraction interval prolongation, and the PHA568487-induced prolongation was significantly suppressed by AOAA (10 μg/rat, icv). The AOAA-induced suppression of the PHA568487-induced intercontraction interval prolongation was negated by supplementing H₂S via GYY4137 at a lower dose (1 nmol/rat, icv) in the brain. GYY4137 or AOAA alone showed no significant effect on intercontraction intervals at each dose used in this study. These findings suggest a possible involvement of brain H₂S in inhibiting the rat micturition reflex induced by activation of brain alpha7 nicotinic acetylcholine receptors.

A Novel Hydrogen Sulfide Donor Reduces Pilocarpine-Induced Status Epilepticus and Regulates Microglial Inflammatory Profile

Although epilepsy is one of the most common neurologic disorders, there is still a lack of effective therapeutic drugs for it. Recently, we synthesized a novel hydrogen sulfide (H₂S) donor, which is found to reduce seizures in animal models effectively. But it remains to be determined for its mechanism. In the present study, we found that the novel H₂S donor could reduce pilocarpine-induced seizures in mice. It alleviated the epileptic behavior, the hippocampal electroencephalography (EEG) activity of seizures, and the damage of hippocampal neurons in status epilepticus mice. In addition, the novel H₂S donor could reduce microglial inflammatory response. It not only reduced the upregulation of pro-inflammatory markers [inducible nitric oxide synthase (iNOS) and cyclooxygenase 2 (COX2)] in status epilepticus mice, but also increased the levels of microglial anti-inflammatory marker arginase-1 (Arg-1). In lipopolysaccharide-treated microglia BV2 cells, administration of the H₂S donor also significantly reduced the lipopolysaccharide-induced upregulation of the expression of the pro-inflammatory markers and increased the expression of the anti-inflammatory markers. Thus, the novel H₂S donor regulates microglial inflammatory profile in status epilepticus mice and in vitro. These results suggested that the novel H₂S donor can reduce seizures and regulate microglial inflammatory profile, which may be a novel mechanism and potential therapeutic strategy of the H₂S donor anti-seizures.

Central Administration of Hydrogen Sulfide Donor NaHS Reduces Iba1-Positive Cells in the PVN and Attenuates Rodent Angiotensin II Hypertension

Hydrogen sulfide (H2S) is a gaseous signaling molecule with neuromodulatory, anti-inflammatory, and anti-hypertensive effects. Here, we investigate whether chronic intracerebroventricular (ICV) infusion of sodium hydrosulfide (NaHS), an H2S donor, can alleviate angiotensin II (Ang II)-induced hypertension (HTN), improve autonomic function, and impact microglia in the paraventricular nucleus (PVN) of the hypothalamus, a brain region associated with autonomic control of blood pressure (BP) and neuroinflammation in HTN. Chronic delivery of Ang II (200 ng/kg/min, subcutaneous) for 4 weeks produced a typical increase in BP and sympathetic drive and elevated the number of ionized calcium binding adaptor molecule 1-positive (Iba1+) cells in the PVN of male, Sprague-Dawley rats. ICV co-infusion of NaHS (at 30 and/or 60 nmol/h) significantly attenuated these effects of Ang II. Ang II also increased the abundance of cecal Deltaproteobacteria and Desulfovibrionales, among others, which was prevented by ICV NaHS co-infusion at 30 and 60 nmol/h. We observed no differences in circulating H2S between the groups. Our results suggest that central H2S may alleviate rodent HTN independently from circulating H2S via effects on autonomic nervous system and PVN microglia.

Psychological/mental stress-induced effects on urinary function: Possible brain molecules related to psychological/mental stress-induced effects on urinary function

Exposure to psychological/mental stress can affect urinary function, and lead to and exacerbate lower urinary tract dysfunctions. There is increasing evidence showing stress-induced changes not only at phenomenological levels in micturition, but also at multiple levels, lower urinary tract tissues, and peripheral and central nervous systems. The brain plays crucial roles in the regulation of the body's responses to stress; however, it is still unclear how the brain integrates stress-related information to induce changes at these multiple levels, thereby affecting urinary function and lower urinary tract dysfunctions. In this review, we introduce recent urological studies investigating the effects of stress exposure on urinary function and lower urinary tract dysfunctions, and our recent studies exploring "pro-micturition" and "anti-micturition" brain molecules related to stress responses. Based on evidence from these studies, we discuss the future directions of central neurourological research investigating how stress exposure-induced changes at peripheral and central levels affect urinary function and lower urinary tract dysfunctions. Brain molecules that we explored might be entry points into dissecting the stress-mediated process for modulating micturition.

The Slow-Releasing and Mitochondria-Targeted Hydrogen Sulfide (H2S) Delivery Molecule AP39 Induces Brain Tolerance to Ischemia

Ischemic stroke is the third leading cause of death in the world, which accounts for almost 12% of the total deaths worldwide. Despite decades of research, the available and effective pharmacotherapy is limited. Some evidence underlines the beneficial properties of hydrogen sulfide (H₂S) donors, such as NaSH, in an animal model of brain ischemia and in in vitro research; however, these data are ambiguous. This study was undertaken to verify the neuroprotective activity of AP39, a slow-releasing mitochondria-targeted H₂S delivery molecule. We administered AP39 for 7 days prior to ischemia onset, and the potential to induce brain tolerance to ischemia was verified. To do this, we used the rat model of 90-min middle cerebral artery occlusion (MCAO) and used LC-MS/MS, RT-PCR, Luminex^TM assays, Western blot and immunofluorescent double-staining to determine the absolute H₂S levels, inflammatory markers, neurotrophic factor signaling pathways and apoptosis marker in the ipsilateral frontal cortex, hippocampus and in the dorsal striatum 24 h after ischemia onset. AP39 (50 nmol/kg) reduced the infarct volume, neurological deficit and reduced the microglia marker (Iba1) expression. AP39 also exerted prominent anti-inflammatory activity in reducing the release of Il-1β, Il-6 and TNFα in brain areas particularly affected by ischemia. Furthermore, AP39 enhanced the pro-survival pathways of neurotrophic factors BDNF-TrkB and NGF-TrkA and reduced the proapoptotic proNGF-p75^NTR-sortilin pathway activity. These changes corresponded with reduced levels of cleaved caspase 3. Altogether, AP39 treatment induced adaptative changes within the brain and, by that, developed brain tolerance to ischemia.

A hydrogen sulfide donor suppresses pentylenetetrazol-induced seizures in rats via PKC signaling

Epilepsy is a serious neurological disorder. Available antiepileptic drugs are still lacking. Hydrogen sulfide (H2S), a neuron-protective endogenous gasotransmitter, is reported to have effect on epilepsy. But it remains to be determined for its mechanism. In the present study, we found that a novel carbazole-based H2S donor could effectively suppress pentylenetetrazol-induced seizures in rats. The H2S donor could alleviate not only the epileptic behavior of animals but also the hippocampal EEG activity of seizures. The H2S donor down-regulated the expression of aquaporin 4 in the hippocampus of epilepsy rats. The H2S donor also decreased the seizure-induced release of inflammatory cytokines including IL-1β, IL-6 and TNF-α. In addition, the H2S donor increased protein kinase C (PKC) expression in the hippocampus of epilepsy rats. These effects of the H2S donor on epilepsy rats were attenuated after blockade of PKC signaling by Go6983, suggesting that PKC signaling participated in the antiepileptic process of H2S donor. Taken together, the H2S donor has a beneficial effect on epilepsy control in a PKC-dependent manner.

The role of brain gaseous neurotransmitters in anxiety

Although anxiety is perhaps one of the most significant current medical and social problems, the neurochemical mechanistic background of this common condition remains to be fully understood. Multifunctional regulatory gasotransmitters are novel, atypical inorganic factors of the brain that are involved in the mechanisms of anxiety responses. Nitric oxide (NO) signaling shows ambiguous action in animal models of anxiety, while NO donors exert anxiogenic or anxiolytic effect depending on their chemical structure, dose, treatment schedule and gas release rapidity. The majority of NO synthase inhibitors act as a relatively potent axiolytic agents, while hydrogen sulfide (H₂S) and carbon monoxide (CO) delivered experimentally in the form of "slow" or "fast" releasing donors have recently been considered as anxiolytic neurotransmitters. In this comprehensive review we critically summarize the literature regarding the intriguing roles of NO, H₂S and CO in the neuromolecular mechanisms of anxiety in the context of their putative, yet promising therapeutic application. A possible mechanism of gasotransmitter action at the level of anxiety-related synaptic transmission is also presented. Brain gasesous neuromediators urgently require further wide ranging studies to clarify their potential value for the current neuropharmacology of anxiety disorders.

H2S-producing enzymes in anoxia-tolerant vertebrates: Effects of cold acclimation, anoxia exposure and reoxygenation on gene and protein expression

To lend insight into the potential role of the gasotransmitter hydrogen sulfide (H₂S) in facilitating anoxia survival of anoxia-tolerant vertebrates, we quantified the gene expression of the primary H₂S-synthesizing enzymes, 3-mercaptopyruvate sulfurtransferase (3MST), cystathionine γ-lyase (CSE) and cystathionine β-synthase (CBS), in ventricle and brain of normoxic, anoxic and reoxygenated 21 °C- and 5 °C-acclimated freshwater turtles (Trachemys scripta) and 10 °C-acclimated crucian carp (Carassius carassius). Semi-quantitative Western blotting analysis was also conducted to assess 3MST and CBS protein abundance in ventricle and brain of 5 °C turtles and 10 °C crucian carp subjected to normoxia, anoxia and reoxygenation. We hypothesized that if H₂S was advantageous for anoxia survival, expression levels would remain unchanged or be upregulated with anoxia and/or reoxygenation. Indeed, for both species, gene and protein expression were largely maintained with anoxia exposure (24 h, 21 °C; 5 d, 10 °C; 14 d, 5 °C). With reoxygenation, 3MST expression was increased in turtle and crucian carp brain at the protein and gene level, respectively. Additionally, the effect of cold acclimation on gene expression was assessed in several tissues of the turtle. Expression levels were maintained in most tissues, but decreased in others. The maintenance of gene and protein expression of the H₂S-producing enzymes with anoxia exposure and the up-regulation of 3MST with reoxygenation suggests that H₂S may facilitate anoxic survival of the two champions of vertebrate anoxia survival. The differential effects of cold acclimation on H₂S enzyme expression may influence blood flow to different tissues during winter anoxia.

Hydrogen sulfide intoxication induced brain injury and methylene blue

Hydrogen sulfide (H₂S) remains a chemical hazard in the gas and farming industry. It is easy to manufacture from common chemicals and thus represents a potential threat for the civilian population. It is also employed as a method of suicide, for which incidence has recently increased in the US. H₂S is a mitochondrial poison and exerts its toxicity through mechanisms that are thought to result from its high affinity to various metallo-proteins (such as - but not exclusively- the mitochondrial cytochrome c oxidase) and interactions with cysteine residues of proteins. Ion channels with critical implications for the cardiac and the brain functions appear to be affected very early during and following H₂S exposure, an effect which is rapidly reversible during a light intoxication. However, during severe H₂S intoxication, a coma, associated with a reduction in cardiac contractility, develops within minutes or even seconds leading to death by complete electro-mechanical dissociation of the heart. If the level of intoxication is milder, a rapid and spontaneous recovery of the coma occurs as soon as the exposure stops. The risk, although probably very small, of developing long-term debilitating motor or cognitive deficits is present. One of the major challenges impeding our effort to offer an effective treatment against H₂S intoxication after exposure is that the pool of free/soluble H₂S almost immediately disappears from the body preventing agents trapping free H₂S (cobalt or ferric compounds) to play their protective role. This paper (1) presents and discusses the neurological symptoms and lesions observed in various animals models and in humans following an acute exposure to sub-lethal or lethal levels of H₂S, (2) reviews the potential interest of methylene blue (MB), a potent cyclic redox dye - currently used for the treatment of methemoglobinemia - which has potential rescuing effects on the mitochondrial activity, as an antidote against sulfide intoxication.

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).

Physiological Importance of Hydrogen Sulfide: Emerging Potent Neuroprotector and Neuromodulator

Hydrogen sulfide (H2S) is an emerging neuromodulator that is considered to be a gasotransmitter similar to nitrogen oxide (NO) and carbon monoxide (CO). H2S exerts universal cytoprotective effects and acts as a defense mechanism in organisms ranging from bacteria to mammals. It is produced by the enzymes cystathionine β-synthase (CBS), cystathionine ϒ-lyase (CSE), 3-mercaptopyruvate sulfurtransferase (MST), and D-amino acid oxidase (DAO), which are also involved in tissue-specific biochemical pathways for H2S production in the human body. H2S exerts a wide range of pathological and physiological functions in the human body, from endocrine system and cellular longevity to hepatic protection and kidney function. Previous studies have shown that H2S plays important roles in peripheral nerve regeneration and degeneration and has significant value during Schwann cell dedifferentiation and proliferation but it is also associated with axonal degradation and the remyelination of Schwann cells. To date, physiological and toxic levels of H2S in the human body remain unclear and most of the mechanisms of action underlying the effects of H2S have yet to be fully elucidated. The primary purpose of this review was to provide an overview of the role of H2S in the human body and to describe its beneficial effects.

Hydrogen sulfide improves neural function in rats following cardiopulmonary resuscitation

The alleviation of brain injury is a key issue following cardiopulmonary resuscitation (CPR). Hydrogen sulfide (H₂S) is hypothesized to be involved in the pathophysiological process of ischemia-reperfusion injury, and exerts a protective effect on neurons. The aim of the present study was to investigate the effects of H₂S on neural functions following cardiac arrest (CA) in rats. A total of 60 rats were allocated at random into three groups. CA was induced to establish the model and CPR was performed after 6 min. Subsequently, sodium hydrosulfide (NaHS), hydroxylamine or saline was administered to the rats. Serum levels of H₂S, neuron-specific enolase (NSE) and S100β were determined following CPR. In addition, neurological deficit scoring (NDS), the beam walking test (BWT), prehensile traction test and Morris water maze experiment were conducted. Neuronal apoptosis rates were detected in the hippocampal region following sacrifice. After CPR, as the H₂S levels increased or decreased, the serum NSE and S100β concentrations decreased or increased, respectively (P<0.0w. The NDS results of the NaHS group were improved compared with those of the hydroxylamine group at 24 h after CPR (P<0.05). In the Morris water maze experiment, BWT and prehensile traction test the animals in the NaHS group performed best and rats in the hydroxylamine group performed worst. At day 7, the apoptotic index and the expression of caspase-3 were reduced in the hippocampal CA1 region, while the expression of Bcl-2 increased in the NaHS group; and results of the hydroxylamine group were in contrast. Therefore, the results of the present study indicate that H₂S is able to improve neural function in rats following CPR.

[THE ROLE OF HYDROGEN SULFIDE IN REGULATION OF CIRCULATION BLOOD LIVER]

It was shown in acute experiments on laboratory rats that intraportalinjectionof hydrogen sulfide's precursor L-cysteine (15 mg/kg)caused dilatation of the intrahepatic vessels. As a result, systemic blood pressure (SBP) and blood pressure in the portal vein (PVP) significantly decreased on 17,6 and 24,5%, respectively, and the rate of local blood flow in the liver (LF) and its blood filling (BF) increased on 28,2 and 24,4% respectively. Application of hydrogen sulfide donor NaHS (7 mg/kg) resulted in similarly directed changes: SBP and PVP decreased on 20,8% i 26,2% respectively,LF and BF increased on 16,4% and 30,9% respectively. Application of L-cysteine in the conditions of tsystationin-gamma-lyase blockade by LD-proparhilhlitsyn led to an increase in SBP on 20,4 % and PVP on 26,6% and a decrease of BF on 21,5% and LF in the liver on 11,7% comparing with baseline values of these parameters. So, blockade of tsystationin-gamma-lyase not only completely removed the effects of L-cysteine, but also inhibited synthesis of H2S from its endogenous predecessors,which led to vasoconstriction of liver's blood vessels and, consequently, to an increase of blood pressure and a decrease of liver blood flow rat's and volume of blood deposited in liver.

Role of hydrogen sulfide in brain synaptic remodeling

Synapses are the functional connection between neurons which are necessary for the transfer of electric activity or chemical activity from one cell to another. Synapses are formed by the pre- and postsynaptic membrane which communicates between pre- and postneurons while a neurochemical modulator is operated in this process. H2S has been known as a toxic gas with rotten eggs smell. However, increasing number of researches show that it regulate a variety of physiological and pathological processes in mammals. Hence, H2S is a physiologically important molecule and has been referred to as the third gaseous molecule alongside carbon monoxide and nitric oxide. The previous era has made an exponential development in the physiological and pathological significance of H2S. Specifically, in the central nervous system, H2S facilitates long-term potentiation and regulates intracellular calcium concentration in brain cells. We as well as others have also shown that H2S has antioxidant, antiapoptotic, and anti-inflammatory properties against various neurodegenerative disorders such as stroke, Alzheimer's disease, and vascular dementia. In this chapter, we highlight the current knowledge of H2S and its neuroprotective effects with a special emphasis on synaptic remodeling.

A novel FRET-based ratiometric fluorescent probe for highly sensitive detection of hydrogen sulfide

A novel ratiometric and colorimetric probeH2S-CRfor the quantitative detection of H₂S was designed and synthesized based on a H₂S induced Michael addition–cyclization cascade reaction and the FRET modulated fluorescence off-on response.

H2S: A New Approach to Lifespan Enhancement and Healthy Ageing?

Ageing, a progressive structural and functional decline, is considered to be a major risk factor for virtually all ageing-associated pathologies and disabilities, including Alzheimer's disease, Parkinson's disease, stroke, diabetes, atherosclerosis and certain cancers. Biogerontology research has now been largely directed towards finding novel drug targets to decelerate the ageing process and attain healthy ageing in order to delay the onset of all ageing-related diseases. H2S has been reported to exert vasodilatory, antioxidant, antiapoptotic and anti-inflammatory actions and has been shown to act as a signalling molecule, neuromodulator and cytoprotectant. Intriguingly, H2S has been reported to regulate cell cycle and survival in healthy cells which suggests that it may regulate cell fate and hence the ageing process. This chapter sets out to provide an overview of the current knowledge regarding the involvement of H2S in ageing, with a specific focus on the invertebrate model nematode C. elegans.

Cocaine exposure alters H2S tissue concentrations in peripheral mouse organs

BACKGROUND

Hydrogen sulfide (H2S) is well-known as a physiological mediator in the mammalian brain and peripheral tissues. Among several factors that change the concentration of H2S, oxidative stress and generation of reactive oxygen species, which accompany neurochemical actions of drugs of abuse, are of recent interest.

OBJECTIVE

Limited data on the connection of cocaine and H2S levels prompted us to investigate the effect of this psychostimulant on the H2S concentration in the mouse brain and peripheral organs.

METHODS

Male BALB/C mice were given several cocaine dosage and treatment regimens, and the free and acid-labile H2S tissue concentrations were determined with a modified spectrophotometric method of Siegel.

RESULTS

We demonstrated the dose- and treatment-dependent decreases in the H2S level in the heart (83% of control level), and in the liver and kidney (17-34% of control levels) homogenates, but no changes were seen in the mouse brain. The strongest effect occurred after repeated administration of cocaine (20mg/kg) in all peripheral tissues.

CONCLUSION

A reduction in the peripheral tissue H2S level in the heart, liver and kidney homogenates after repeated injections of cocaine may be the result of a strong toxic effect of the drug.

Hydrogen sulfide functions as a neuromodulator to regulate striatal neurotransmission in a mouse model of Parkinson's disease

Hydrogen sulfide (H2S), a novel endogenous gasotransmitter, has been considered a neuromodulator to enhance hippocampal long-term potentiation and exerts neuroprotective effects against neurotoxin-induced neurodegeneration in rodent models of Parkinson's disease (PD). However, whether H2S can function as a neuromodulator to regulate the levels of nigrostriatal neurotransmitters and then impact the vulnerability of dopaminergic (DA) neurons in response to neurotoxins remains unknown. For this study, we prepared a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine plus probenecid (MPTP/p)-induced mouse subacute model of PD to explore the modulatory effect of H2S on monoamine and amino acid neurotransmitters in the striatum of MPTP-treated mice. This study shows that NaHS (an H2S donor, 5.6 mg/kg/day, i.p.) administration improves the survival rate and significantly ameliorates the weight loss of MPTP-treated mice. NaHS treatment attenuated MPTP-induced neuronal damage, restored the diminution of DA neurons, and suppressed the overactivation of astrocytes in the mouse striatum. Additionally, NaHS upregulated striatal serotonin levels and modulated the balance of excitatory glutamate and the inhibitory γ-aminobutyric acid system in response to MPTP challenge. The current study indicates that H2S may function as an effective neuromodulator to regulate striatal neurotransmission and provides insight into the potential of H2S for PD therapy.

Selective detection of endogenous H₂S in living cells and the mouse hippocampus using a ratiometric fluorescent probe

As one of three gasotransmitters, the fundamental signalling roles of hydrogen sulphide are receiving increasing attention. New tools for the accurate detection of hydrogen sulphide in cells and tissues are in demand to probe its biological functions. We report the p-nitrobenzyl-based ratiometric fluorescent probe RHP-2, which features a low detection limit, high selectivity and good photostability. The emission intensity ratios had a good linear relationship with the sulphide concentrations in PBS buffer and bovine serum. Our probe was applied to the ratiometric determination and imaging of endogenous H₂S in living cells. Furthermore, RHP-2 was used as an effective tool to measure endogenous H₂S in the mouse hippocampus. We observed a significant reduction in sulphide concentrations and downregulated expression of cystathionine β-synthetase (CBS) mRNA and CBS protein in the mouse hippocampus in a chronic unpredictable mild stress (CUMS)-induced depression model. These data suggested that decreased concentrations of endogenous H₂S may be involved in the pathogenesis of chronic stress depression.

Aggravation of seizure-like events by hydrogen sulfide: involvement of multiple targets that control neuronal excitability

AIMS

Epileptic seizures are well-known neurological complications following stroke, occurring in 3% of patients. However, the intrinsic correlation of seizures with stroke remains largely unknown. Hydrogen sulfide (H2 S) is a gas transmitter that may mediate cerebral ischemic injury. But the role of H2 S in seizures has not been understood yet. We examined the effect of H2 S on seizure-like events (SLEs) and underlying mechanisms.

METHODS AND RESULTS

Pentylenetetrazole (PTZ)- and pilocarpine-induced rat epileptic seizure models were tested. Low-Mg(2+) /high-K(+) - and 4-aminopyridine (4-AP)-induced epileptic seizure models were examined using patch-clamp recordings in brain slices. It was found that NaHS aggravated both PTZ- and pilocarpine-induced SLEs in rats, while both low-Mg(2+) /high-K(+) - and 4-AP-induced SLEs were also exacerbated by NaHS in brain slices, which may be due to its regulation on the voltage-gated sodium channel, N-methyl-D-aspartic acid receptor (NMDAR), and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) function. Furthermore, these effects were reversed by blocking voltage-gated sodium channel, NMDAR, and AMPAR.

CONCLUSIONS

These results suggest a pathological role of increased H2 S level in SLEs in vivo and in vitro. Enzymes that control H2 S biosynthesis could be interesting targets for antiepileptic strategies in poststroke epilepsy treatment.

Dose-dependent effect of sulfur dioxide on brain damage induced by recurrent febrile seizures in rats

Sulfur dioxide (SO2) regulates many physiological processes. Little is known about its roles in neurological disorders. In this study, we investigated the role of endogenous SO2 in the development of febrile seizures (FS) and related brain damages. In the rat model of recurrent FS, we found that endogenous SO2 in the plasma and hippocampus was increased, accompanied by upregulation of aspartate amino-transferase 1 (AAT1) and AAT2, and neuronal apoptosis and mossy fiber sprouting (MFS) in the hippocampus. Preconditioning with low concentration of SO2 (1-10 μmol/kg) alleviated the neuronal damage, and attenuated neuronal apoptosis and MFS, whereas preconditioning with high concentration of SO2 (100 μmol/kg) or inhibition of AAT aggravated the neuronal damage, and promoted neuronal apoptosis and MFS in hippocampus of rats with recurrent FS. These data indicate that endogenous SO2 is involved in the development of FS and related brain damage. Preconditioning with low concentration of SO2 may protect neurons from toxicity caused by FS.

An ICT-based strategy to a colorimetric and ratiometric fluorescence probe for hydrogen sulfide in living cells

We present a colorimetric and ratiometric fluorescent probe Cy-N(3) that exhibits a selective response to H(2)S. The probe employs a near-infrared cyanine as a fluorophore, and is equipped with an operating azide unit. It is readily employed for assessing intracellular H(2)S levels, and confocal ratiometric imaging is achieved successfully.

Interdependency of cystathione γ-lyase and cystathione β-synthase in hydrogen sulfide-induced blood pressure regulation in rats

Background

Hydrogen sulfide (H₂S), an endogenous vasoactive agent, is produced by cystathionine γ-lyase (CGL) and cystathionine β-synthase (CBS) enzymes. This study was conducted to evaluate the relative contribution of these enzymes in regulating systemic arterial pressure.

Methods

Sprague–Dawley rats were chronically treated with CGL inhibitor, -propargylglycine (PAG, 37.5 mg/kg/day; intraperitoneally, i.p.) or CBS inhibitor, aminooxyacetic acid (AOA, 8.75 mg/kg/day; i.p.) or in combination for 4 weeks and the effects on arterial pressure (tail-cuff plethysmography) and renal excretory function (24 h urine collections using metabolic cages) were assessed once in a week. Changes in renal blood flow (RBF; Ultrasonic flowmetry) and glomerular filtration rate (GFR; Inulin clearance) were assessed in acute experiments in anesthetized rats at the end of treatment period.

Results

Compared to vehicle treated control group, only the rats with combination therapy showed a decrease in urinary sulfate excretion rate (248 ± 47 vs. 591 ± 70 nmol/24 h; marker for endogenous H₂S level) which was associated with an increase in mean arterial pressure (MAP; 130 ± 2 vs. 99 ± 2 mm Hg). Urine flow and sodium excretion were also increased in combination group as consequent to the increase in MAP. GFR did not alter due to these treatments but RBF was lowered (4 ± 0.3 vs. 7 ± 0.4 ml/min/g) only in the combination group compared to the control group.

Conclusion

These findings indicate that a deficiency in one enzyme's activity could be compensated by the activity of the other to maintain the endogenous H₂S level, the deficiency of which modulates systemic and renal vascular resistances leading to the development of hypertension.

The vertebrate homolog of sulfide-quinone reductase is expressed in mitochondria of neuronal tissues

Hydrogen sulfide (H₂S) can be consumed by both invertebrates and vertebrates as an inorganic substrate. The pathway metabolizing H₂S probably involves three mitochondrial enzymes, one of which is sulfide-quinone oxidoreductase (SQR), known as sulfide-quinone reductase-like protein (SQRDL) in vertebrates. Evidence from fission yeast suggests that SQR might have a role in regulating sulfide levels in the cell. Regulation might be essential for H₂S to act as a gaseous transmitter (gasotransmitter). The brain is an organ with high activity of gasotransmitters, like nitric oxide (NO) and H₂S, which are known to affect synaptic transmission. In this study, we provide evidence that SQRDL is expressed in the mammalian brain. Real-time polymerase chain reaction (PCR) showed an increase in the number of Sqrdl transcripts in the brain with increasing age. Cellular fractionation and subsequent analysis by Western blotting indicated that the protein is located in mitochondria, which is the site of sulfide consumption in the cell. With an immunohistochemical approach, we demonstrated that the SQRDL protein is expressed in neurons, oligodendrocytes, and endothelial cells. Taken together, our data suggest that brain tissue harbors the machinery required for local regulation of sulfide levels.

Emerging role of hydrogen sulfide in health and disease: critical appraisal of biomarkers and pharmacological tools

H2S (hydrogen sulfide) is a well known and pungent gas recently discovered to be synthesized enzymatically in mammalian and human tissues. In a relatively short period of time, H2S has attracted substantial interest as an endogenous gaseous mediator and potential target for pharmacological manipulation. Studies in animals and humans have shown H2S to be involved in diverse physiological and pathophysiological processes, such as learning and memory, neurodegeneration, regulation of inflammation and blood pressure, and metabolism. However, research is limited by the lack of specific analytical and pharmacological tools which has led to considerable controversy in the literature. Commonly used inhibitors of endogenous H2S synthesis have been well known for decades to interact with other metabolic pathways or even generate NO (nitric oxide). Similarly, commonly used H2S donors release H2S far too quickly to be physiologically relevant, but may have therapeutic applications. In the present review, we discuss the enzymatic synthesis of H2S and its emerging importance as a mediator in physiology and pathology. We also critically discuss the suitability of proposed 'biomarkers' of H2S synthesis and metabolism, and highlight the complexities of the currently used pharmacological H2S 'donor' molecules and 'specific' H2S synthesis inhibitors in their application to studying the role of H2S in human disease.

Hydrogen sulfide: neurophysiology and neuropathology

Hydrogen sulfide (H(2)S) was known to be a toxic gas and an environmental hazard for many decades. However, it is now recognized that H(2)S may serve as a gaseous mediator that is endogenously produced to influence biological functions in mammalian. Together with nitric oxide and carbon monoxide, it forms the group of mediators that has been termed the "gasotransmitters." The past decade has seen an exponential growth of scientific interest in the physiological and pathological significance of H(2)S especially with respect to its role in the central nervous system and the cardiovascular system. In the central nervous system, H(2)S facilitates long-term potentiation and regulates intracellular calcium concentration and pH level in brain cells. Intriguingly, H(2)S produces antioxidant, anti-inflammatory, and antiapoptotic effects that may have relevance to neurodegenerative disorders. Abnormal generation and metabolism of H(2)S have been reported in the pathogenesis of ischemic stroke, Alzheimer's disease, Parkinson's disease, and recurrent febrile seizure. Exogenously applied H(2)S is demonstrated to have value for the treatment of febrile seizure and Parkinson's disease. This article presents an overview of current knowledge of H(2)S in relation to brain functions, with a special emphasis on its neuroprotective effects and the underlying cellular and molecular mechanisms.

Hydrogen sulphide: novel opportunity for drug discovery

Hydrogen sulphide (H(2)S) is emerging as an important endogenous modulator, which exhibits the beneficial effects of nitric oxide (NO) on the cardiovascular (CV) system, without producing toxic metabolites. H(2)S is biosynthesized in mammalian tissues by cystathionine-β-synthase and cystathionine-γ-lyase. H(2)S exhibits the antioxidant properties of inorganic and organic sulphites, behaving as a scavenger of reactive oxygen species. There is also clear evidence that H(2)S triggers other important effects, mainly mediated by the activation of ATP-sensitive potassium channels (K(ATP)). This mechanism accounts for the vasorelaxing and cardioprotective effects of H(2)S. Furthermore, H(2)S inhibits smooth muscle proliferation and platelet aggregation. In non-CV systems, H(2)S regulates the functions of the central nervous system, as well as respiratory, gastroenteric, and endocrine systems. Conversely, H(2)S deficiency contributes to the pathogenesis of hypertension. Likewise, impairment of H(2)S biosynthesis is involved in CV complications associated with diabetes mellitus. There is also evidence of a cross-talk between the H(2)S and the endothelial NO pathways. In particular, recent observations indicate a possible pathogenic link between deficiencies of H(2 S activity and the progress of endothelial dysfunction. These biological aspects of endogenous H(2)S have led several authors to look at this mediator as "the new NO" that has given attractive opportunities to develop innovative classes of drugs. In this review, the main biological actions of H(2)S are discussed. Moreover, some examples of H(2)S-donors are shown, as well as some hybrids, in which H(2)S-releasing moieties are added to well-known drugs, for improving their pharmacodynamic profile or reducing the potential for adverse effects, are reported.

H2S protects hippocampal neurons from anoxia-reoxygenation through cAMP-mediated PI3K/Akt/p70S6K cell-survival signaling pathways

The study aims to investigate the effect of hydrogen sulfide (H(2)S) on the phosphatidylinositol 3-kinase (PI3K)/Akt/p70 ribosomal S6 kinase (p70S6K) signal transduction pathway after oxygen glucose deprivation/reoxygenation (OGD/R) in the rat hippocampus. Newborn Wister rats were decapitated under anesthesia, and hippocampal tissue was dissected. Cells were plated at 1.0 × 10(5) cells/mL on polylysine-treated 96-well and 6-well plates. After 7 days in culture, cells were randomly assigned to six groups: control, OGD/R, sodium hydrosulfide (NaHS) following OGD/R, NaHS/triciribine following OGD/R, NaHS/rapamycin following OGD/R, and NaHS/triciribine/rapamycin following OGD/R. Neuronal purity and cell viability were assessed in each group, as well as apoptosis and expression of cyclic adenosine 3', 5'-monophosphate (cAMP), PI3K, Akt, and p70S6K. NaHS enhanced cAMP concentration and expression of PI3K, Akt, and p70S6K. In addition, neuronal viability was increased and apoptotic neuronal numbers decreased (P<0.01). Triciribine inhibited Akt and p70S6K, as well as decreased cell survival and viability compared with the NaHS group (P<0.05 or P<0.01). Rapamycin resulted in decreased p70S6K expression and neuronal viability, as well as increased number of apoptotic neurons compared with the NaHS group (P<0.05 or P<0.01). H(2)S acted via cAMP-mediated PI3K/Akt/p70S6K signal transduction pathways to inhibit hippocampal neuronal apoptosis and protect neurons from OGD/R-induced injury.