Hydrogen sulfide contributes to cardioprotection during ischemia-reperfusion injury by opening K ATP channels

Therapeutic Potential of Hydrogen Sulfide in Ischemia and Reperfusion Injury

Ischemia-reperfusion (I/R) injury, a prevalent pathological condition in medical practice, presents significant treatment challenges. Hydrogen sulfide (H2S), acknowledged as the third gas signaling molecule, profoundly impacts various physiological and pathophysiological processes. Extensive research has demonstrated that H2S can mitigate I/R damage across multiple organs and tissues. This review investigates the protective effects of H2S in preventing I/R damage in the heart, brain, liver, kidney, intestines, lungs, stomach, spinal cord, testes, eyes, and other tissues. H2S provides protection against I/R damage by alleviating inflammation and endoplasmic reticulum stress; inhibiting apoptosis, oxidative stress, and mitochondrial autophagy and dysfunction; and regulating microRNAs. Significant advancements in understanding the mechanisms by which H2S reduces I/R damage have led to the development and synthesis of H2S-releasing agents such as diallyl trisulfide-loaded mesoporous silica nanoparticles (DATS-MSN), AP39, zofenopril, and ATB-344, offering a new therapeutic avenue for I/R injury.

Recent Developments On Activatable Turn-On Fluorogenic Donors of Hydrogen Sulfide (H2S)

Hydrogen sulfide (H2S) is considered the third member of the gasotransmitter family, along with nitric oxide (NO) and carbon monoxide (CO). Besides its role in physiological and pathophysiological conditions, the promising therapeutic potential of this small-molecule makes it advantageous for various pharmaceutical applications. The endogenous production of H2S at a lower concentration is crucial in maintaining redox balance and cellular homeostasis, and the dysregulation leads to various disease states. In the event of H2S deficiency, the exogenous donation of H2S could help maintain the optimal cellular concentration of H2S and cellular homeostasis. Over the last several years, researchers have developed numerous small-molecule non-fluorogenic organosulfur compounds as H2S donors and investigated their pharmacological potentials. However, reports on stimuli-responsive turn-on fluorogenic donors of H2S have appeared recently. Interestingly, the fluorogenic H2S donors offer additional advantages with the non-invasive real-time monitoring of the H2S release utilizing the simultaneous turn-on fluorogenic processes. The review summarizes the recent developments in turn-on fluorogenic donors of H2S and the potential biological applications that have developed over the years.

Hydrogen Sulfide and Irisin, Potential Allies in Ensuring Cardiovascular Health

Irisin is a myokine secreted under the influence of physical activity and exposure to low temperatures and through different exogenous stimuli by the cleavage of its precursor, fibronectin type III domain-containing protein 5 (FNDC5). It is mainly known for maintaining of metabolic homeostasis, promoting the browning of white adipose tissue, the thermogenesis process, and glucose homeostasis. Growing experimental evidence suggests the possible central role of irisin in the regulation of cardiometabolic pathophysiological processes. On the other side, hydrogen sulfide (H2S) is well recognized as a pleiotropic gasotransmitter that regulates several homeostatic balances and physiological functions and takes part in the pathogenesis of cardiometabolic diseases. Through the S-persulfidation of cysteine protein residues, H2S is capable of interacting with crucial signaling pathways, exerting beneficial effects in regulating glucose and lipid homeostasis as well. H2S and irisin seem to be intertwined; indeed, recently, H2S was found to regulate irisin secretion by activating the peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α)/FNDC5/irisin signaling pathway, and they share several mechanisms of action. Their involvement in metabolic diseases is confirmed by the detection of their lower circulating levels in obese and diabetic subjects. Along with the importance of metabolic disorders, these modulators exert favorable effects against cardiovascular diseases, preventing incidents of hypertension, atherosclerosis, heart failure, myocardial infarction, and ischemia-reperfusion injury. This review, for the first time, aims to explore the role of H2S and irisin and their possible crosstalk in cardiovascular diseases, pointing out the main effects exerted through the common molecular pathways involved.

Using mechanism-based combinations of H2S-donors to maximize the cardioprotective action of H2S

H2S-donors are cardioprotective in ischemia/reperfusion (I/R) injury. Some H2S-donors exert their beneficial effects in a nitric oxide (NO)-dependent manner, while others act using NO-independent pathways. The aims of the present study were to (i) evaluate whether H2S-donors with distinct pharmacodynamic properties act synergistically in I/R injury and (ii) determine if H2S-donors remain cardioprotective in obese mice. C57BL/6 mice were subjected to 30 min of ischemia followed by 120 min of reperfusion. Donors were administered intravenously at the end of ischemia (Na2S: 1 μmol/kg, GYY4137: 25 μmol/kg, AP39: 0,25 μmol/kg), while the 3-mercaptopyruvate sulfurtransferase (10 mg/kg) inhibitor was given intraperitonially 1 h prior to ischemia. Infarct size was estimated by 2,3,5-triphenyltetrazolium staining, while the area at risk was calculated using Evans blue. All three donors reduced infarct size when administered as a sole treatment. Co-administration of Na2S/GYY4137, as well as Na2S/AP39 reduced further the I/R injury, beyond what was observed with each individual donor. Since inhibition of the H2S-producing enzyme 3-mercaptopyruvate sulfurtransferase is known to reduce infarct size, we co-administered C3 with Na2S to determine possible additive effects between the two agents. In this case, combination of C3 with Na2S did not yield superior results compared to the individual treatments. Similarly, to what was observed in healthy mice, administration of a H2S-donor (Na2S or AP39) reduced I/R injury in mice rendered obese by consumption of a high fat diet. We conclude that combining a NO-dependent with a NO-independent H2S-donor leads to enhanced cardioprotection and that H2S-donors remain effective in obese animals.

Synthesis of 2-(2-(4-thioxo-3H-1,2-dithiole-5-yl) phenoxy)ethyl)isoindole-1,3-thione, a novel hydrogen sulfide-releasing phthalimide hybrid, and evaluation of its activity in models of inflammatory pain

Hydrogen sulfide (H₂S) is a gaseous mediator that modulates several physiological and pathological processes. Phthalimide analogues, substances that have the phthalimide ring in the structure, belong to the group of thalidomide analogues. Both H₂S donors and phthalimide analogues exhibit activities in models of inflammation and pain. As molecular hybridization is an important strategy aiming to develop drugs with a better pharmacological profile, in the present study we synthesized a novel H₂S-releasing phthalimide hybrid, 2-(2-(4-thioxo-3H-1,2-dithiole-5-yl) phenoxy)ethyl)isoindole-1,3-thione (PTD-H₂S), and evaluated its activity in models of inflammatory pain in mice. Per os (p.o.) administration of PTD-H₂S (125 or 250 mg/kg) reduced mechanical allodynia induced by carrageenan and lipopolysaccharide. Intraperitoneal (i.p.) administration of PTD-H₂S (25 mg/kg), but not equimolar doses of its precursors 5-(4-hydroxyphenyl)-3H-1,2-dithiole-3-thione (14.2 mg/kg) and 2-phthalimidethanol (12 mg/kg), reduced mechanical allodynia induced by lipopolysaccharide. The antiallodynic effect induced by PTD-H₂S (25 mg/kg, i.p.) was more sustained than that induced by the H₂S donor NaHS (8 mg/kg, i.p.). Previous administration of hydroxocobalamin (300 mg/kg, i.p.) or glibenclamide (40 mg/kg, p.o.) attenuated PTD-H₂S antiallodynic activity. In conclusion, we synthesized a novel H₂S-releasing phthalimide hybrid and demonstrated its activity in models of inflammatory pain. PTD-H₂S activity may be due to H₂S release and activation of ATP-sensitive potassium channels. The demonstration of PTD-H₂S activity in models of pain stimulates further studies aiming to evaluate H₂S-releasing phthalimide hybrids as candidates for analgesic drugs.

Deodorized Garlic Decreases Oxidative Stress Caused by Lipopolysaccharide in Rat Heart through Hydrogen Sulfide: Preliminary Findings

Deodorized garlic (DG) may favor the activity of the antioxidant enzymes and promote the synthesis of hydrogen sulfide (H₂S). The objective was to test if DG favors an increase in H₂S and if it decreases the oxidative stress caused by lipopolysaccharide (LPS) in rat hearts. A total of 24 rats were divided into 4 groups: Group 1 control (C), Group 2 LPS, Group 3 DG, and Group 4 LPS plus DG. The cardiac mechanical performance (CMP), coronary vascular resistance (CVR), and oxidative stress markers, such as total antioxidant capacity (TAC), glutathione (GSH), selenium (Se), lipid peroxidation (LPO), thiols, hydrogen sulfide (H₂S), and the activities and expressions of thioredoxin reductase (TrxR), glutathione peroxidase (GPx), and glutathione-S-transferase (GST), cystathionine synthetase (CBS), cystathionine γ-lyase (CTH), iNOS, and eNOS-p, were analyzed in the heart. Infarct zones in the cardiac tissue were present (p = 0.01). The CMP and CVR decreased and increased (p ≤ 0.05), TAC, GSH, H₂S, NO, thiols, and GST activity (p ≤ 0.01) decreased, and LPO and iNOS increased (p ≤ 0.05). The activities and expressions of TrxR, GPx, eNOS-p, CTH, and CBS (p ≤ 0.05) decreased with the LPS treatment; however, DG normalized this effect. DG treatment decreases heart damage caused by LPS through the cross-talk between the H₂S and NO systems.

Hydrogen Sulfide: An Emerging Precision Strategy for Gas Therapy

Advances in nanotechnology have enabled the rapid development of stimuli-responsive therapeutic nanomaterials for precision gas therapy. Hydrogen sulfide (H₂ S) is a significant gaseous signaling molecule with intrinsic biochemical properties, which exerts its various physiological effects under both normal and pathological conditions. Various nanomaterials with H₂ S-responsive properties, as new-generation therapeutic agents, are explored to guide therapeutic behaviors in biological milieu. The cross disciplinary of H₂ S is an emerging scientific hotspot that studies the chemical properties, biological mechanisms, and therapeutic effects of H₂ S. This review summarizes the state-of-art research on H₂ S-related nanomedicines. In particular, recent advances in H₂ S therapeutics for cancer, such as H₂ S-mediated gas therapy and H₂ S-related synergistic therapies (combined with chemotherapy, photodynamic therapy, photothermal therapy, and chemodynamic therapy) are highlighted. Versatile imaging techniques for real-time monitoring H₂ S during biological diagnosis are reviewed. Finally, the biosafety issues, current challenges, and potential possibilities in the evolution of H₂ S-based therapy that facilitate clinical translation to patients are discussed.

An evolutionary perspective on the interplays between hydrogen sulfide and oxygen in cellular functions

The physiological effects of the endogenously generated hydrogen sulfide (H2S) have been extensively studied in recent years. This review summarized the role of H2S in the origin of life and H2S metabolism in organisms from bacteria to vertebrates, examined the relationship between H2S and oxygen from an evolutionary perspective and emphasized the oxygen-dependent manner of H2S signaling in various physiological and pathological processes. H2S and oxygen are inextricably linked in various cellular functions. H2S is involved in aerobic respiration and stimulates oxidative phosphorylation and ATP production within the cell. Besides, H2S has protective effects on ischemia and reperfusion injury in several organs by acting as an oxygen sensor. Also, emerging evidence suggests the role of H2S is in an oxygen-dependent manner. All these findings indicate the subtle relationship between H2S and oxygen and further explain why H2S, a toxic molecule thriving in an anoxia environment several billion years ago, still affects homeostasis today despite the very low content in the body.

Donor Heart Preservation with Hydrogen Sulfide: A Systematic Review and Meta-Analysis

Preclinical studies have shown that postconditioning with hydrogen sulfide (H2S) exerts cardioprotective effects against myocardial ischemia-reperfusion injury (IRI). The aim of this study was to appraise the current evidence of the cardioprotective effects of H2S against IRI in order to explore the future implementation of H2S in clinical cardiac transplantation. The current literature on H2S postconditioning in the setting of global myocardial ischemia was systematically reviewed and analyzed, performing meta-analyses. A literature search of the electronic databases Medline, Embase and Cinahl identified 1835 studies that were subjected to our pre-defined inclusion criteria. Sixteen studies were considered eligible for inclusion. Postconditioning with H2S showed significant robust effects with regard to limiting infarct size (standardized mean difference (SMD) = -4.12, 95% CI [-5.53--2.71], p < 0.00001). Furthermore, H2S postconditioning consistently resulted in a significantly lower release of cardiac injury markers, lower levels of oxidative stress and improved cardiac function. Postconditioning with slow-releasing H2S donors offers a valuable opportunity for novel therapies within cardiac preservation for transplantation. Before clinical implication, studies evaluating the long-term effects of H2S treatment and effects of H2S treatment in large animal studies are warranted.

Hydrogen Sulfide Upregulates Acid-sensing Ion Channels via the MAPK-Erk1/2 Signaling Pathway

Hydrogen sulfide (H₂S) emerged recently as a new gasotransmitter and was shown to exert cellular effects by interacting with proteins, among them many ion channels. Acid-sensing ion channels (ASICs) are neuronal voltage-insensitive Na⁺ channels activated by extracellular protons. ASICs are involved in many physiological and pathological processes, such as fear conditioning, pain sensation, and seizures. We characterize here the regulation of ASICs by H₂S. In transfected mammalian cells, the H₂S donor NaHS increased the acid-induced ASIC1a peak currents in a time- and concentration-dependent manner. Similarly, NaHS potentiated also the acid-induced currents of ASIC1b, ASIC2a, and ASIC3. An upregulation induced by the H₂S donors NaHS and GYY4137 was also observed with the endogenous ASIC currents of cultured hypothalamus neurons. In parallel with the effect on function, the total and plasma membrane expression of ASIC1a was increased by GYY4137, as determined in cultured cortical neurons. H₂S also enhanced the phosphorylation of the extracellular signal-regulated kinase (pErk1/2), which belongs to the family of mitogen-activated protein kinases (MAPKs). Pharmacological blockade of the MAPK signaling pathway prevented the GYY4137-induced increase of ASIC function and expression, indicating that this pathway is required for ASIC regulation by H₂S. Our study demonstrates that H₂S regulates ASIC expression and function, and identifies the involved signaling mechanism. Since H₂S shares several roles with ASICs, as for example facilitation of learning and memory, protection during seizure activity, and modulation of nociception, it may be possible that H₂S exerts some of these effects via a regulation of ASIC function.

A Dinuclear Persulfide-Bridged Ruthenium Compound is a Hypoxia-Selective Hydrogen Sulfide (H2 S) Donor

Hydrogen sulfide (H2 S) is a gaseous molecule that has received attention for its role in biological processes and therapeutic potential in diseases, such as ischemic reperfusion injury. Despite its clinical relevance, delivery of H2 S to biological systems is hampered by its toxicity at high concentrations. Herein, we report the first metal-based H2 S donor that delivers this gas selectively to hypoxic cells. We further show that H2 S release from this compound protects H9c2 rat cardiomyoblasts from an in vitro model of ischemic reperfusion injury. These results validate the utility of redox-activated metal complexes as hypoxia-selective H2 S-releasing agents for use as tools to study the role of this gaseous molecule in complex biological systems.

Interaction among Hydrogen Sulfide and Other Gasotransmitters in Mammalian Physiology and Pathophysiology

Hydrogen sulfide (H₂S), nitric oxide (NO), carbon monoxide (CO), and sulfur dioxide (SO₂) were previously considered as toxic gases, but now they are found to be members of mammalian gasotransmitters family. Both H₂S and SO₂ are endogenously produced in sulfur-containing amino acid metabolic pathway in vivo. The enzymes catalyzing the formation of H₂S are mainly CBS, CSE, and 3-MST, and the key enzymes for SO₂ production are AAT1 and AAT2. Endogenous NO is produced from L-arginine under catalysis of three isoforms of NOS (eNOS, iNOS, and nNOS). HO-mediated heme catabolism is the main source of endogenous CO. These four gasotransmitters play important physiological and pathophysiological roles in mammalian cardiovascular, nervous, gastrointestinal, respiratory, and immune systems. The similarity among these four gasotransmitters can be seen from the same and/or shared signals. With many studies on the biological effects of gasotransmitters on multiple systems, the interaction among H₂S and other gasotransmitters has been gradually explored. H₂S not only interacts with NO to form nitroxyl (HNO), but also regulates the HO/CO and AAT/SO₂ pathways. Here, we review the biosynthesis and metabolism of the gasotransmitters in mammals, as well as the known complicated interactions among H₂S and other gasotransmitters (NO, CO, and SO₂) and their effects on various aspects of cardiovascular physiology and pathophysiology, such as vascular tension, angiogenesis, heart contractility, and cardiac protection.

Organic Isothiocyanates as Hydrogen Sulfide Donors

Significance: Hydrogen sulfide (H₂S), the "new entry" in the series of endogenous gasotransmitters, plays a fundamental role in regulating the biological functions of various organs and systems. Consequently, the lack of adequate levels of H₂S may represent the etiopathogenetic factor of multiple pathological alterations. In these diseases, the use of H₂S donors represents a precious and innovative opportunity. Recent Advances: Natural isothiocyanates (ITCs), sulfur compounds typical of some botanical species, have long been investigated because of their intriguing pharmacological profile. Recently, the ITC moiety has been proposed as a new H₂S-donor chemotype (with a l-cysteine-mediated reaction). Based on this recent discovery, we can clearly observe that almost all the effects of natural ITCs can be explained by the H₂S release. Consistently, the ITC function was also used as an original H₂S-releasing moiety for the design of synthetic H₂S donors and original "pharmacological hybrids." Very recently, the chemical mechanism of H₂S release, resulting from the reaction between l-cysteine and some ITCs, has been elucidated. Critical Issues: Available literature gives convincing demonstration that H₂S is the real player in ITC pharmacology. Further, countless studies have been carried out on natural ITCs, but this versatile moiety has been used only rarely for the design of synthetic H₂S donors with optimal drug-like properties. Future Directions: The development of more ITC-based synthetic H₂S donors with optimal drug-like properties and selectivity toward specific tissues/pathologies seem to represent a stimulating and indispensable prospect of future experimental activities.

Pro-arrhythmic Effects of Hydrogen Sulfide in Healthy and Ischemic Cardiac Tissues: Insight From a Simulation Study

Hydrogen sulfide (H₂S), an ambient air pollutant, has been reported to increase cardiac events in patients with cardiovascular diseases, but the underlying mechanisms remain not elucidated. This study investigated the pro-arrhythmic effects of H₂S in healthy and ischemic conditions. Experimental data of H₂S effects on ionic channels (including the L-type Ca²⁺ channel and ATP-sensitive K⁺ channel) were incorporated into a virtual heart model to evaluate their integral action on cardiac arrhythmogenesis. It was shown that H₂S depressed cellular excitability, abbreviated action potential duration, and augmented tissue’s transmural dispersion of repolarization, resulting in an increase in tissue susceptibility to initiation and maintenance of reentry. The observed effects of H₂S on cardiac excitation are more remarkable in the ischemic condition than in the healthy condition. This study provides mechanistic insights into the pro-arrhythmic effects of air pollution (H₂S), especially in the case with extant ischemic conditions.

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

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

Immunomodulatory Effects of Glutathione, Garlic Derivatives, and Hydrogen Sulfide

Glutathione and aged garlic extract are sulfur-containing products that play important protective and regulatory roles within the immune system and in oxidative processes. Hydrogen sulfide (H₂S), an endogenous, gaseous, signaling transmitter, has also been shown to be involved in the regulation of inflammation. Recent studies have shown that sulfur-containing compounds from garlic have beneficial effects in attenuating outcomes associated with cardiovascular disease and inflammation by a mechanism that may be related to the H₂S signaling pathway. In this review, we summarize the main functions of glutathione (GSH), garlic derivatives and H₂S and their role in the immune response and impact on health and disease.

In Vivo Measurement of H2S, Polysulfides, and "SSNO- Mix"-Mediated Vasoactive Responses and Evaluation of Ten Hemodynamic Parameters from Rat Arterial Pulse Waveform

The chapter describes protocols and pitfalls in in vivo studies of drug effects on anesthetized rats. It focuses on the preparation of Na₂S, Na₂S₄, and "SSNO^- mix" solutions for rat intravenous administration, surgical preparation of jugular vein for drug administration, and preparation of carotid and tail arteries for recording of arterial pulse waveform (APW) at high resolution. It describes evaluation of ten hemodynamic parameters from APW and measurement of apparent pulse wave velocity.

Expanding reversible chalcogenide binding: supramolecular receptors for the hydroselenide (HSe-) anion

Synthetic supramolecular receptors have been widely used to study reversible solution binding of anions; however, few systems target highly-reactive species. In particular, the hydrochalcogenide anions hydrosulfide (HS^-) and hydroselenide (HSe^-) have been largely overlooked despite their critical roles in biological systems. Herein we present the first example of reversible HSe^- binding in two distinct synthetic supramolecular receptors, using hydrogen bonds from N-H and aromatic C-H moieties. The arylethynyl bisurea scaffold 1 ^{t Bu} achieved a binding affinity of 460 ± 50 M^-1 for HSe^- in 10% DMSO-d ₆/CD₃CN, whereas the tripodal-based receptor 2^CF₃ achieved a binding affinity of 290 ± 50 M^-1 in CD₃CN. Association constants were also measured for HS^-, Cl^-, and Br^-, and both receptors favored binding of smaller, more basic anions. These studies contribute to a better understanding of chalcogenide hydrogen bonding and provide insights into further development of probes for the reversible binding, and potential quantification, of HSe^- and HS^-.

Modulation of K+ channel N-type inactivation by sulfhydration through hydrogen sulfide and polysulfides

Fast N-type inactivation of voltage-gated K⁺ (Kv) channels is important in fine-tuning of cellular excitability. To serve diverse cellular needs, N-type inactivation is regulated by numerous mechanisms. Here, we address how reactive sulfur species-the gaseous messenger H₂S and polysulfides-affect N-type inactivation of the mammalian Kv channels Kv1.4 and Kv3.4. In both channels, the H₂S donor NaHS slowed down inactivation with varying potency depending on the "aging" of NaHS solution. Polysulfides were > 1000 times more effective than NaHS with the potency increasing with the number of sulfur atoms (Na₂S₂ < Na₂S₃ < Na₂S₄). In Kv1.4, C13 in the N-terminal ball domain mediates the slowing of inactivation. In recombinant protein exposed to NaHS or Na₂S₄, a sulfur atom is incorporated at C13 in the protein. In Kv3.4, the N terminus harbors two cysteine residues (C6, C24), and C6 is of primary importance for channel regulation by H₂S and polysulfides, with a minor contribution from C24. To fully eliminate the dependence of N-type inactivation on sulfhydration, both cysteine residues must be removed (C6S:C24S). Sulfhydration of a single cysteine residue in the ball-and-chain domain modulates the speed of inactivation but does not remove it entirely. In both Kv1.4 and Kv3.4, polysulfides affected the N-terminal cysteine residues when assayed in the whole-cell configuration; on-cell recordings confirmed that polysulfides also modulate K⁺ channel inactivation with undisturbed cytosol. These findings have collectively identified reactive sulfur species as potent modulators of N-type inactivation in mammalian Kv channels.

Hydrogen Sulfide (H2S)-Releasing Compounds: Therapeutic Potential in Cardiovascular Diseases

Cardiovascular disease is the main cause of death worldwide, but its pathogenesis is not yet clear. Hydrogen sulfide (H₂S) is considered to be the third most important endogenous gasotransmitter in the organism after carbon monoxide and nitric oxide. It can be synthesized in mammalian tissues and can freely cross the cell membrane and exert many biological effects in various systems including cardiovascular system. More and more recent studies have supported the protective effects of endogenous H₂S and exogenous H₂S-releasing compounds (such as NaHS, Na₂S, and GYY4137) in cardiovascular diseases, such as cardiac hypertrophy, heart failure, ischemia/reperfusion injury, and atherosclerosis. Here, we provided an up-to-date overview of the mechanistic actions of H₂S as well as the therapeutic potential of various classes of H₂S donors in treating cardiovascular diseases.

Vasodilator Activity of Compounds Isolated from Plants Used in Mexican Traditional Medicine

Arterial hypertension is one of the main risk factors in the development of cardiovascular diseases. Therefore, it is important to look for new drugs to treat hypertension. In this study, we carried out the screening of 19 compounds (triterpenes, diterpenes, sesquiterpenes, lignans, and flavonoids) isolated from 10 plants used in Mexican traditional medicine to determine whether they elicited vascular smooth muscle relaxation and, therefore, could represent novel anti-hypertension drug candidates. The vasorelaxant activity of these compounds was evaluated on the isolated rat aorta assay and the results obtained from this evaluation showed that three compounds induced a significant vasodilatory effect: meso-dihydroguaiaretic acid [half maximal effective concentration (EC₅₀), 49.9 ± 11.2 µM; maximum effect (Emax), 99.8 ± 2.7%]; corosolic acid (EC₅₀, 108.9 ± 6.7 µM; Emax, 96.4 ± 4.2%); and 5,8,4′-trihydroxy-3,7-dimethoxyflavone (EC₅₀, 122.3 ± 7.6 µM; Emax, 99.5 ± 5.4%). Subsequently, involvement of the NO/cyclic guanosine monophosphate (cGMP) and H₂S/ATP-sensitive potassium channel (K_ATP) pathways on the vasodilator activity of these compounds was assessed. The results derived from this analysis showed that the activation of both pathways contributes to the vasorelaxant effect of corosolic acid. On the other hand, the vasodilator effect of meso-dihydroguaiaretic acid and 5,8,4′-trihydroxy-3,7-dimethoxyflavone, partly involves stimulation of the NO/cGMP pathway. However, these compounds also showed an important endothelium-independent vasorelaxant effect, whose mechanism of action remains to be clarified. This study indicates that meso-dihydroguaiaretic acid, corosolic acid, and 5,8,4′-trihydroxy-3,7-dimethoxyflavone could be used as lead compounds for the synthesis of new derivatives with a higher potency to be developed as drugs for the prevention and treatment of cardiovascular diseases.

A Hibernation-Like State for Transplantable Organs: Is Hydrogen Sulfide Therapy the Future of Organ Preservation?

SIGNIFICANCE

Renal transplantation is the treatment of choice for end-stage renal disease, during which renal grafts from deceased donors are routinely cold stored to suppress metabolic demand and thereby limit ischemic injury. However, prolonged cold storage, followed by reperfusion, induces extensive tissue damage termed cold ischemia/reperfusion injury (IRI) and puts the graft at risk of both early and late rejection. Recent Advances: Deep hibernators constitute a natural model of coping with cold IRI as they regularly alternate between 4°C and 37°C. Recently, endogenous hydrogen sulfide (H₂S), a gas with a characteristic rotten egg smell, has been implicated in organ protection in hibernation.

CRITICAL ISSUES

In renal transplantation, H₂S also seems to confer cytoprotection by lowering metabolism, thereby creating a hibernation-like environment, and increasing preservation time while allowing cellular processes of preservation of homeostasis and tissue remodeling to take place, thus increasing renal graft survival.

FUTURE DIRECTIONS

Although the underlying cellular and molecular mechanisms of organ protection during hibernation have not been fully explored, mammalian hibernation may offer a great clinical promise to safely cold store and reperfuse donor organs. In this review, we first discuss mammalian hibernation as a natural model of cold organ preservation with reference to the kidney and highlight the involvement of H₂S during hibernation. Next, we present recent developments on the protective effects and mechanisms of exogenous and endogenous H₂S in preclinical models of transplant IRI and evaluate the potential of H₂S therapy in organ preservation as great promise for renal transplant recipients in the future. Antioxid. Redox Signal. 28, 1503-1515.

Effect of Sodium Thiosulfate Postconditioning on Ischemia-Reperfusion Injury Induced Mitochondrial Dysfunction in Rat Heart

The recent research on the therapeutic applications of sodium thiosulfate (STS) has gained importance in the treatment of cardiovascular diseases. Progressively through the present work, we have demonstrated that postconditioning of isolated rat heart subjected to ischemia-reperfusion injury using STS had preserved the mitochondrial structure, function, and number. Heart comprising of two mitochondrial subpopulations interfibrillar (IFM-involved in contractile function) and subsarcolemmal (SSM-involved in metabolic function), STS postconditioning imparted a state of hypometabolism to SSM, thereby reducing the metabolic demand of the reperfused heart. The IFM, on the other hand, provided the energy required to maintain contraction. Moreover, the hypometabolic state induced in SSM can lower the free radical release in addition to STS innate ability to act as an antioxidant and radical scavenger, all of which collectively provided cardioprotection. Therefore, drugs targeting IFM specifically or those reducing the energy demand for SSM can be suitable targets for myocardial ischemia-reperfusion injury.

Hydrogen sulphide increases pulmonary veins and atrial arrhythmogenesis with activation of protein kinase C

Hydrogen sulphide (H₂ S), one of the most common toxic air pollutants, is an important aetiology of atrial fibrillation (AF). Pulmonary veins (PVs) and left atrium (LA) are the most important AF trigger and substrate. We investigated whether H₂ S may modulate the arrhythmogenesis of PVs and atria. Conventional microelectrodes and whole-cell patch clamp were performed in rabbit PV, sinoatrial node (SAN) or atrial cardiomyocytes before and after the perfusion of NaHS with or without chelerythrine (a selective PKC inhibitor), rottlerin (a specific PKC δ inhibitor) or KB-R7943 (a NCX inhibitor). NaHS reduced spontaneous beating rates, but increased the occurrences of delayed afterdepolarizations and burst firing in PVs and SANs. NaHS (100 μmol/L) increased I_KATP and I_NCX in PV and LA cardiomyocytes, which were attenuated by chelerythrine (3 μmol/L). Chelerythrine, rottlerin (10 μmol/L) or KB-R7943 (10 μmol/L) attenuated the arrhythmogenic effects of NaHS on PVs or SANs. NaHS shortened the action potential duration in LA, but not in right atrium or in the presence of chelerythrine. NaHS increased PKC activity, but did not translocate PKC isoforms α, ε to membrane in LA. In conclusion, through protein kinase C signalling, H₂ S increases PV and atrial arrhythmogenesis, which may contribute to air pollution-induced AF.

Hydrogen sulfide inhibits Kir2 and Kir3 channels by decreasing sensitivity to the phospholipid phosphatidylinositol 4,5-bisphosphate (PIP2)

Inwardly rectifying potassium (Kir) channels establish and regulate the resting membrane potential of excitable cells in the heart, brain, and other peripheral tissues. Phosphatidylinositol 4,5-bisphosphate (PIP₂) is a key direct activator of ion channels, including Kir channels. The gasotransmitter carbon monoxide has been shown to regulate Kir channel activity by altering channel-PIP₂ interactions. Here, we tested in two cellular models the effects and mechanism of action of another gasotransmitter, hydrogen sulfide (H₂S), thought to play a key role in cellular responses under ischemic conditions. Direct administration of sodium hydrogen sulfide as an exogenous H₂S source and expression of cystathionine γ-lyase, a key enzyme that produces endogenous H₂S in specific brain tissues, resulted in comparable current inhibition of several Kir2 and Kir3 channels. This effect resulted from changes in channel-gating kinetics rather than in conductance or cell-surface localization. The extent of H₂S regulation depended on the strength of the channel-PIP₂ interactions. H₂S regulation was attenuated when channel-PIP₂ interactions were strengthened and was increased when channel-PIP₂ interactions were weakened by depleting PIP₂ levels. These H₂S effects required specific cytoplasmic cysteine residues in Kir3.2 channels. Mutation of these residues abolished H₂S inhibition, and reintroduction of specific cysteine residues back into the background of the cytoplasmic cysteine-lacking mutant rescued H₂S inhibition. Molecular dynamics simulation experiments provided mechanistic insights into how potential sulfhydration of specific cysteine residues could lead to changes in channel-PIP₂ interactions and channel gating.

Analysis of decreases in systemic arterial pressure and heart rate in response to the hydrogen sulfide donor sodium sulfide

The actions of hydrogen sulfide (H2S) on the heart and vasculature have been extensively reported. However, the mechanisms underlying the effects of H2S are unclear in the anesthetized rat. The objective of the present study was to investigate the effect of H2S on the electrocardiogram and examine the relationship between H2S-induced changes in heart rate (HR), mean arterial pressure (MAP), and respiratory function. Intravenous administration of the H2S donor Na2S in the anesthetized Sprague-Dawley rat decreased MAP and HR and produced changes in respiratory function. The administration of Na2S significantly increased the RR interval at some doses but had no effect on PR or corrected QT(n)-B intervals. In experiments where respiration was maintained with a mechanical ventilator, we observed that Na2S-induced decreases in MAP and HR were independent of respiration. In experiments where respiration was maintained by mechanical ventilation and HR was maintained by cardiac pacing, Na2S-induced changes in MAP were not significantly altered, whereas changes in HR were abolished. Coadministration of glybenclamide significantly increased MAP and HR responses at some doses, but methylene blue, diltiazem, and ivabradine had no significant effect compared with control. The decreases in MAP and HR in response to Na2S could be dissociated and were independent of changes in respiratory function, ATP-sensitive K+ channels, methylene blue-sensitive mechanism involving L-type voltage-sensitive Ca2+ channels, or hyperpolarization-activated cyclic nucleotide-gated channels. Cardiovascular responses observed in spontaneously hypertensive rats were more robust than those in Sprague-Dawley rats.NEW & NOTEWORTHY H2S is a gasotransmitter capable of producing a decrease in mean arterial pressure and heart rate. The hypotensive and bradycardic effects of H2S can be dissociated, as shown with cardiac pacing experiments. Responses were not blocked by diltiazem, ivabradine, methylene blue, or glybenclamide.

Rapid Antidepressant Effect of Hydrogen Sulfide: Evidence for Activation of mTORC1-TrkB-AMPA Receptor Pathways

AIMS

We asked whether hydrogen sulfide (H₂S), as the third gaseous mediator, provided fast antidepressant effect on major depressive disorders and underlying mechanisms.

RESULTS

The decreased level of H₂S was detected in the hippocampus of chronic unpredictable mild stress (CUMS)-treated rats. Acute administration of H₂S either by H₂S inhalation or by the donor NaHS produced a rapid antidepressant-like behavioral effect. Further investigation demonstrated that this effect of H₂S was mediated by reversing the CUMS-induced decrease in dendritic spine density and required the activation of mammalian target of rapamycin (mTOR)C1 and neurotrophic TrkB receptors, which proceeded to increase synaptic protein expression, including postsynaptic density protein 95, synaptophysin, and α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptor GluR1/2 subunit.

INNOVATION

This study provides the first direct evidence for detecting the decreased H₂S in hippocampus of CUMS rats and the biological significance of H₂S in treating major depression.

CONCLUSION

Our data demonstrate that H₂S activates mTORC1 signaling cascades and thereby produces fast-onset antidepressant effect. The study provides a profound insight into H₂S or its donors as potent preventive and therapeutic agents for intervention of depression. Antioxid. Redox Signal. 27, 472-488.

Hydrogen sulfide prevents renal ischemia-reperfusion injury in CLAWN miniature swine

BACKGROUND

Hydrogen sulfide (H₂S) has recently been reported to demonstrate both antiinflammatory and cytoprotective effects; however, its efficacy has not been well documented in large animal models. In this study, we examined whether the administration of H₂S offers cytoprotective effects on renal ischemia-reperfusion injury (IRI) in a preclinical miniature swine model.

METHODS

Major histocompatibility complex-inbred, CLAWN miniature swine (n = 9) underwent a right nephrectomy, followed by induction of a 120-min period of warm ischemia via placement of clamps on the left renal artery and vein. Group 1 (n = 3) underwent renal ischemia without H₂S administration. Groups 2 (n = 3) and 3 (n = 3) received Na₂S (prodrug of H₂S) 10 min before reperfusion of the ischemic kidneys followed by a 30-min of Na₂S postreperfusion intravenously (group 2) or selective administration of Na₂S via the left renal artery (group 3). IRI was assessed by kidney biopsies, levels of inflammatory cytokines in sera and kidney tissue.

RESULTS

Animals in group 1 had significantly higher serum creatinine levels compared with animals in groups 2 and 3 (P < 0.01). Histology showed severe tubular damage with TUNEL-positive cells in group 1 on postoperative day 2 compared with mild damage in group 2 and minimal damage in group 3. Furthermore, levels of inflammatory cytokines in both serum (interleukin-6 [IL-6], tumor necrosis factor-α, and high-mobility group box 1) and renal tissue (IL-1 and IL-6) in group 3 were markedly lower than in group 2, suggesting beneficial effects of selective Na₂S administration.

CONCLUSIONS

Na₂S administration, especially via an organ selective approach, appears to potentially offer cytoprotective and antiinflammatory effects following renal IRI.

Sulfur-containing gaseous signal molecules, ion channels and cardiovascular diseases

Sulfur-containing gaseous signal molecules including hydrogen sulphide and sulfur dioxide were previously recognized as toxic gases. However, extensive studies have revealed that they can be generated in the cardiovascular system via a sulfur-containing amino acid metabolic pathway, and have an important role in cardiovascular physiology and pathophysiology. Ion channels are pore-forming membrane proteins present in the membrane of all biological cells; their functions include the establishment of a resting membrane potential and the control of action potentials and other electrical signals by conducting ions across the cell membrane. Evidence has now accumulated suggesting that the sulfur-containing gaseous signal molecules are important regulators of ion channels and transporters. The aims of this review are (1) to discuss the recent experimental evidences in the cardiovascular system regarding the regulatory effects of sulfur-containing gaseous signal molecules on a variety of ion channels, including ATP-sensitive potassium, calcium-activated potassium, voltage-gated potassium, L- and T-type calcium, transient receptor potential and chloride and sodium channels, and (2) to understand how the gaseous signal molecules affect ion channels and cardiovascular diseases.

LINKED ARTICLES

This article is part of a themed section on Spotlight on Small Molecules in Cardiovascular Diseases. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.8/issuetoc.

Affinin (Spilanthol), Isolated from Heliopsis longipes, Induces Vasodilation via Activation of Gasotransmitters and Prostacyclin Signaling Pathways

Heliopsis longipes roots have been widely used in Mexican traditional medicine to relieve pain, mainly, toothaches. Previous studies have shown that affinin, the major alkamide of these roots, induces potent antinociceptive and anti-inflammatory activities. However, the effect of H. longipes root extracts and affinin on the cardiovascular system have not been investigated so far. In the present study, we demonstrated that the dichloromethane and ethanolic extracts of H. longipes roots, and affinin, isolated from these roots, produce a concentration-dependent vasodilation of rat aorta. Affinin-induced vasorelaxation was partly dependent on the presence of endothelium and was significantly blocked in the presence of inhibitors of NO, H₂S, and CO synthesis (NG-nitro-l-arginine methyl ester (l-NAME), dl-propargylglycine (PAG), and chromium mesoporphyrin (CrMP), respectively); K⁺ channel blockers (glibenclamide (Gli) and tetraethyl ammonium (TEA)), and guanylate cyclase and cyclooxygenase inhibitors (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) and indomethacin (INDO), respectively). Our results demonstrate, for the first time, that affinin induces vasodilation by mechanisms that involve gasotransmitters, and prostacyclin signaling pathways. These findings indicate that this natural alkamide has therapeutic potential in the treatment of cardiovascular diseases.

Garlic oil polysulfides: H2S- and O2-independent prooxidants in buffer and antioxidants in cells

The health benefits of garlic and other organosulfur-containing foods are well recognized and have been attributed to both prooxidant and antioxidant activities. The effects of garlic are surprisingly similar to those of hydrogen sulfide (H2S), which is also known to be released from garlic under certain conditions. However, recent evidence suggests that polysulfides, not H2S, may be the actual mediator of physiological signaling. In this study, we monitored formation of H2S and polysulfides from garlic oil in buffer and in human embryonic kidney (HEK) 293 cells with fluorescent dyes, 7-azido-4-methylcoumarin and SSP4, respectively and redox activity with two redox indicators redox-sensitive green fluorescent protein (roGFP) and DCF. Our results show that H2S release from garlic oil in buffer requires other low-molecular-weight thiols, such as cysteine (Cys) or glutathione (GSH), whereas polysulfides are readily detected in garlic oil alone. Administration of garlic oil to cells rapidly increases intracellular polysulfide but has minimal effects on H2S unless Cys or GSH are also present in the extracellular medium. We also observed that garlic oil and diallyltrisulfide (DATS) potently oxidized roGFP in buffer but did not affect DCF. This appears to be a direct polysulfide-mediated oxidation that does not require a reactive oxygen species intermediate. Conversely, when applied to cells, garlic oil became a significant intracellular reductant independent of extracellular Cys or GSH. This suggests that intracellular metabolism and further processing of the sulfur moieties are necessary to confer antioxidant properties to garlic oil in vivo.

Hydrogen sulphide in cardiovascular system: A cascade from interaction between sulphur atoms and signalling molecules

As a gasotransmitter, hydrogen sulphide exerts its extensive physiological and pathophysiological effects in mammals. The interaction between sulphur atoms and signalling molecules forms a cascade that modulates cellular functions and homeostasis. In this review, we focus on the signalling mechanism underlying the effect of hydrogen sulphide in the cardiovascular system and metabolism as well as the biological relevance to human diseases.

Hydrosulfide attenuates acute myocardial ischemic injury through the glycogen synthase kinase-3β/β-catenin signaling pathway

The endogenous signaling gasotransmitter, hydrosulfide (H2S), has been shown to exert cardioprotective effects against acute myocardial infarction (AMI) due to ischemic injury. However, the mechanisms responsible for these effects are not yet fully understood. In this study, we investigated whether sodium hydrogen sulfide (NaHS), an H2S donor, attenuates acute myocardial ischemic injury through glycogen synthase kinase-3β (GSK-3β)/β-catenin signaling. For this purpose, we utilized an in vivo rat model of AMI by occluding the left anterior descending coronary artery. NaHS (0.39, 0.78 or 1.56 mg/kg, intraperitoneally), the GSK-3β inhibitor, SB216763 (0.6 mg/kg, intravenously), or 1% dimethylsulfoxide (2 ml/kg, intravenously) were administered to the rats. The results demonstrated that the administration of medium- and high-dose NaHS and SB216763 significantly improved rat cardiac function, as evidenced by an increase in the mean arterial pressure, left ventricular developed pressure, contraction and relaxation rates, as well as a decrease in left ventricular end-diastolic pressure. In addition, the administration of NaHS and SB216763 attenuated myocardial injury as reflected by a decrease in apoptotic cell death and in the serum lactate dehydrogenase concentrations, and prevented myocardial structural changes. The administration of NaHS and SB216763 increased the concentrations of phosphorylated (p-)GSK-3β, the p-GSK-3β/t-GSK-3β ratio and downstream protein β-catenin. Moreover, western blot and immunohistochemical analyses of apoptotic signaling pathway proteins further established the cardioprotective potential of NaHS, as reflected by the upregulation of Bcl-2 expression, the downregulation of Bax expression, and a decrease in the number of TUNEL-positive stained cells. These findings suggest that hydrosulfide exerts cardioprotective effects against AMI-induced apoptosis through the GSK-3β/β-catenin signaling pathway.

Medical Functions of Hydrogen Sulfide

Hydrogen sulfide (H(2)S) is a gasomediator synthesized from L- and D-cysteine in various tissues. It is involved in a number of physiological and pathological processes. H(2)S exhibits antiatherosclerotic, vasodilator, and proangiogenic properties, and protects the kidney and heart from damage following ischemia/reperfusion injury. H(2)S donors may be natural or synthetic, and may be used for the safe treatment of a wide range of diseases. This review article summarizes the current state of knowledge of the therapeutic function of H(2)S.

A Fast Hydrogen Sulfide-Releasing Donor Increases the Tumor Response to Radiotherapy

Hydrogen sulfide (H2S) is the last gaseous transmitter identified in mammals, and previous studies have reported disparate conclusions regarding the implication of H2S in cancer progression. In the present study, we hypothesized that sodium hydrosulfide (NaHS), a fast H2S-releasing donor, might interfere with the mitochondrial respiratory chain of tumor cells, increase tumor oxygenation, and potentiate the response to irradiation. Using electron paramagnetic resonance (EPR) oximetry, we found a rapid increase in tumor pO2 after NaHS administration (0.1 mmol/kg) in two human tumor models (breast MDA-MB-231 and cervix SiHa), an effect that was due to a decreased oxygen consumption and an increased tumor perfusion. Tumors irradiated 15 minutes after a single NaHS administration were more sensitive to irradiation compared with those that received irradiation alone (increase in growth delay by 50%). This radiosensitization was due to the oxygen effect, as the increased growth delay was abolished when temporarily clamped tumors were irradiated. In contrast, daily NaHS injection (0.1 mmol/kg/day for 14 days) did not provide any effect on tumor growth in vivo. To understand these paradoxical data, we analyzed the impact of external factors on the cellular response to NaHS. We found that extracellular pH had a dramatic effect on the cell response to NaHS, as the proliferation rate (measured in vitro by BrdU incorporation) was increased at pH = 7.4, but decreased at pH = 6.5. Overall, our study highlights the complex role of environmental components in the response of cancer cells to H2S and suggests a new approach for the use of H2S donors in combination with radiotherapy.

Interaction of Hydrogen Sulfide with Nitric Oxide in the Cardiovascular System

Historically acknowledged as toxic gases, hydrogen sulfide (H₂S) and nitric oxide (NO) are now recognized as the predominant members of a new family of signaling molecules, “gasotransmitters” in mammals. While H₂S is biosynthesized by three constitutively expressed enzymes (CBS, CSE, and 3-MST) from L-cysteine and homocysteine, NO is generated endogenously from L-arginine by the action of various isoforms of NOS. Both gases have been transpired as the key and independent regulators of many physiological functions in mammalian cardiovascular, nervous, gastrointestinal, respiratory, and immune systems. The analogy between these two gasotransmitters is evident not only from their paracrine mode of signaling, but also from the identical and/or shared signaling transduction pathways. With the plethora of research in the pathophysiological role of gasotransmitters in various systems, the existence of interplay between these gases is being widely accepted. Chemical interaction between NO and H₂S may generate nitroxyl (HNO), which plays a specific effective role within the cardiovascular system. In this review article, we have attempted to provide current understanding of the individual and interactive roles of H₂S and NO signaling in mammalian cardiovascular system, focusing particularly on heart contractility, cardioprotection, vascular tone, angiogenesis, and oxidative stress.

Contribution of hydrogen sulfide to the control of coronary blood flow

OBJECTIVE

This study examined the mechanisms by which H2 S modulates coronary microvascular resistance and myocardial perfusion at rest and in response to cardiac ischemia.

METHODS

Experiments were conducted in isolated coronary arteries and in open-chest anesthetized dogs.

RESULTS

We found that the H2 S substrate l-cysteine (1-10 mM) did not alter coronary tone of isolated arteries in vitro or coronary blood flow in vivo. In contrast, intracoronary (ic) H2 S (0.1-3 mM) increased coronary flow from 0.49 ± 0.08 to 2.65 ± 0.13 mL/min/g (p < 0.001). This increase in flow was unaffected by inhibition of Kv channels with 4-aminopyridine (p = 0.127) but was attenuated (0.23 ± 0.02-1.13 ± 0.13 mL/min/g) by the KATP channel antagonist glibenclamide (p < 0.001). Inhibition of NO synthesis (l-NAME) did not attenuate coronary responses to H2 S. Immunohistochemistry revealed expression of CSE, an endogenous H2 S enzyme, in myocardium. Inhibition of CSE with β-cyano-l-alanine (10 μM) had no effect on baseline coronary flow or responses to a 15-second coronary occlusion (p = 0.82).

CONCLUSIONS

These findings demonstrate that exogenous H2 S induces potent, endothelial-independent dilation of the coronary microcirculation predominantly through the activation of KATP channels, however, our data do not support a functional role for endogenous H2 S in the regulation of coronary microvascular resistance.

Analysis of erectile responses to H2S donors in the anesthetized rat

Hydrogen sulfide (H2S) is a biologically active endogenous gasotransmitter formed in penile tissue that has been shown to relax isolated cavernosal smooth muscle. In the present study, erectile responses to the H2S donors sodium sulfide (Na2S) and sodium hydrosulfide (NaHS) were investigated in the anesthetized rat. Intracavernosal injections of Na2S in doses of 0.03-1 mg/kg increased intracavernosal pressure and transiently decreased mean arterial pressure in a dose-dependent manner. Blood pressure responses to Na2S were rapid in onset and short in duration. Responses to Na2S and NaHS were similar at doses up to 0.3 mg/kg, after which a plateau in the erectile response to NaHS was reached. Increases in intracavernosal pressure in response to Na2S were attenuated by tetraethylammonium (K(+) channel inhibitor) and iberiotoxin (large-conductance Ca(2+)-activated K(+) channel inhibitor), whereas glybenclamide [ATP-sensitive K(+) (KATP) channel inhibitor] and inhibitors of nitric oxide (NO) synthase, cyclooxygenase, and cytochrome P-450 epoxygenase had no effect. These data indicate that erectile responses to Na2S are mediated by a tetraethylammonium- and iberiotoxin-sensitive mechanism and that KATP channels, NO, or arachidonic acid metabolites are not involved. Na2S did not alter erectile responses to sodium nitroprusside (NO donor) or cavernosal nerve stimulation, indicating that neither NO nor cGMP metabolism are altered. Thus, Na2S has erectile activity mediated by large-conductance Ca(2+)-activated K(+) channels. It is suggested that strategies that increase H2S formation in penile tissue may be useful in the treatment of erectile dysfunction when NO bioavailability, KATP channel function, or poor responses to PGE1 are present.

Analysis of cardiovascular responses to the H2S donors Na2S and NaHS in the rat

Hydrogen sulfide (H2S) is an endogenous gaseous molecule formed from L-cysteine in vascular tissue. In the present study, cardiovascular responses to the H2S donors Na2S and NaHS were investigated in the anesthetized rat. The intravenous injections of Na2S and NaHS 0.03-0.5 mg/kg produced dose-related decreases in systemic arterial pressure and heart rate, and at higher doses decreases in cardiac output, pulmonary arterial pressure, and systemic vascular resistance. H2S infusion studies show that decreases in systemic arterial pressure, heart rate, cardiac output, and systemic vascular resistance are well-maintained, and responses to Na2S are reversible. Decreases in heart rate were not blocked by atropine, suggesting that the bradycardia was independent of parasympathetic activation and was mediated by an effect on the sinus node. The decreases in systemic arterial pressure were not attenuated by hexamethonium, glybenclamide, N(w)-nitro-L-arginine methyl ester hydrochloride, sodium meclofenamate, ODQ, miconazole, 5-hydroxydecanoate, or tetraethylammonium, suggesting that ATP-sensitive potassium channels, nitric oxide, arachidonic acid metabolites, cyclic GMP, p450 epoxygenase metabolites, or large conductance calcium-activated potassium channels are not involved in mediating hypotensive responses to the H2S donors in the rat and that responses are not centrally mediated. The present data indicate that decreases in systemic arterial pressure in response to the H2S donors can be mediated by decreases in vascular resistance and cardiac output and that the donors have an effect on the sinus node independent of the parasympathetic system. The present data indicate that the mechanism of the peripherally mediated hypotensive response to the H2S donors is uncertain in the intact rat.

[Hydrogen sulfide: A promising therapy in neuroprotection following cardiac arrest?]

Each year, in France, the number of cardiac arrests is evaluated between 30,000 to 50,000. When a patient survives, he undergoes a post-resuscitation syndrome which can aggravate the injuries and for which nowadays, no medication is available. In some kinds of cardiac arrest, a hypothermia protocol can be applied with a need for monitoring because of the appearance of side effects. In this context, hydrogen sulfide, which is a gasotransmitter with numerous physiological and pharmacological properties, may be interesting. Indeed, its use could protect against oxidative, inflammatory and apoptotic troubles induced by the post-resuscitation syndrome. The implied biochemical mechanisms are adenosine triphosphate potassium channels activation and cytochrome c oxidase inhibition. This molecule can also induce a suspended animation state characterized by a metabolism decrease, which could give a delay for physicians to start a therapeutic monitoring. Thus, in spite of a modest and sometimes contradictory literature, this compound could become the first neuroprotective molecule in cardiac arrest.

Flavonoids and mitochondrial pharmacology: A new paradigm for cardioprotection

Acute myocardial ischemia is one of the major causes of illness and of deaths in Western society; therefore the definition of the signaling pathways involved in the cardioprotection represents a challenging goal in order to discover novel pharmacological approaches. In this regard, a number of epidemiologic studies demonstrate a relationship between intake of flavonoid-rich foods and reduction of cardiovascular risk factors and mortality. Moreover, numerous experimental studies have examined flavonoid-induced cardioprotective effects on several animal models of myocardial ischemia/reperfusion. As concerns the mechanisms of action, although the antioxidant effect of flavonoids has been long thought to be a crucial factor accounting for cardioprotection, mitochondrial pathways (ion channels, protein kinases, etc.) are presently emerging as specific pharmacological targets more relevantly involved in the anti-ischemic effects of some flavonoids. Since these pharmacodynamic features seem to be poorly considered, this review examines the mitochondrial role in the cardioprotective mechanisms of some members of this phytochemical class, by describing the biological pathways and reporting an overview of the most important experimental evidence in this field.

The Cardioprotective Effects of Hydrogen Sulfide in Heart Diseases: From Molecular Mechanisms to Therapeutic Potential

Hydrogen sulfide (H₂S) is now recognized as a third gaseous mediator along with nitric oxide (NO) and carbon monoxide (CO), though it was originally considered as a malodorous and toxic gas. H₂S is produced endogenously from cysteine by three enzymes in mammalian tissues. An increasing body of evidence suggests the involvement of H₂S in different physiological and pathological processes. Recent studies have shown that H₂S has the potential to protect the heart against myocardial infarction, arrhythmia, hypertrophy, fibrosis, ischemia-reperfusion injury, and heart failure. Some mechanisms, such as antioxidative action, preservation of mitochondrial function, reduction of apoptosis, anti-inflammatory responses, angiogenic actions, regulation of ion channel, and interaction with NO, could be responsible for the cardioprotective effect of H₂S. Although several mechanisms have been identified, there is a need for further research to identify the specific molecular mechanism of cardioprotection in different cardiac diseases. Therefore, insight into the molecular mechanisms underlying H₂S action in the heart may promote the understanding of pathophysiology of cardiac diseases and lead to new therapeutic targets based on modulation of H₂S production.

Cardioprotection by H2S engages a cGMP-dependent protein kinase G/phospholamban pathway

AIMS

H2S is known to confer cardioprotection; however, the pathways mediating its effects in vivo remain incompletely understood. The purpose of the present study is to evaluate the contribution of cGMP-regulated pathways in the infarct-limiting effect of H2S in vivo.

METHODS AND RESULTS

Anaesthetized rabbits were subjected to myocardial ischaemia (I)/reperfusion (R), and infarct size was determined in control or H2S-exposed groups. The H2S donor sodium hydrosulfide (NaHS, an agent that generates H2S) increased cardiac cGMP and reduced the infarct size. The cGMP-dependent protein kinase (PKG)-I inhibitor DT2 abrogated the protective effect of NaHS, whereas the control peptide TAT or l-nitroarginine methyl ester (l-NAME) did not alter the effect of NaHS. Moreover, the KATP channel inhibitor, glibenclamide, partially reversed the effects of NaHS, whereas inhibition of mitochondrial KATP did not modify the NaHS response. NaHS enhanced phosphorylation of phospholamban (PLN), in a PKG-dependent manner. To further investigate the role of PLN in H2S-mediated cardioprotection, wild-type and PLN KO mice underwent I/R. NaHS did not exert cardioprotection in PLN KO mice. Unlike what was observed in rabbits, genetic or pharmacological inhibition of eNOS abolished the infarct-limiting effect of NaHS in mice.

CONCLUSIONS

Our findings demonstrate (i) that administration of NaHS induces cardioprotection via a cGMP/PKG/PLN pathway and (ii) contribution of nitric oxide to the H2S response is species-specific.

Different patterns of H2S/NO activity and cross-talk in the control of the coronary vascular bed under normotensive or hypertensive conditions

Hydrogen sulfide (H2S) and nitric oxide (NO) play pivotal roles in the cardiovascular system. Conflicting results have been reported about their cross-talk. This study investigated their interplays in coronary bed of normotensive (NTRs) and spontaneously hypertensive rats (SHRs). The effects of H2S- (NaHS) and NO-donors (sodium nitroprusside, SNP) on coronary flow (CF) were measured in Langendorff-perfused hearts of NTRs and SHRs, in the absence or in the presence of propargylglycine (PAG, inhibitor of H2S biosynthesis), L-NAME (inhibitor of NO biosynthesis), ODQ (inhibitor of guanylate cyclase), L-Cysteine (substrate for H2S biosynthesis) or L-Arginine (substrate for NO biosynthesis). In NTRs, NaHS and SNP increased CF; their effects were particularly evident in Angiotensin II (AngII)-contracted coronary arteries. The dilatory effects of NaHS were abolished by L-NAME and ODQ; conversely, PAG abolished the effects of SNP. In SHRs, high levels of myocardial ROS production were observed. NaHS and SNP did not reduce the oxidative stress, but produced clear increases of the basal CF. In contrast, in AngII-contracted coronary arteries of SHRs, significant hyporeactivity to NaHS and SNP was observed. In SHRs, the vasodilatory effects of NaHS were only modestly affected by L-NAME and ODQ; PAG poorly influenced the effects of SNP. Then, in NTRs, the vascular actions of H2S required NO and vice versa. By contrast, in SHRs, the H2S-induced actions scarcely depend on NO release; as well, the NO effects are largely H2S-independent. These results represent the first step for understanding pathophysiological mechanisms of NO/H2S interplays under both normotensive and hypertensive conditions.