AP39, a novel mitochondria-targeted hydrogen sulfide donor, stimulates cellular bioenergetics, exerts cytoprotective effects and protects against the loss of mitochondrial DNA integrity in oxidatively stressed endothelial cells in vitro

Cardiovascular effects of gasotransmitter donors

Gasotransmitters represent a subfamily of the endogenous gaseous signaling molecules that include nitric oxide (NO), carbon monoxide (CO), and hydrogen sulphide (H(2)S). These particular gases share many common features in their production and function, but they fulfill their physiological tasks in unique ways that differ from those of classical signaling molecules found in tissues and organs. These gasotransmitters may antagonize or potentiate each other's cellular effects at the level of their production, their downstream molecular targets and their direct interactions. All three gasotransmitters induce vasodilatation, inhibit apoptosis directly or by increasing the expression of anti-apoptotic genes, and activate antioxidants while inhibiting inflammatory actions. NO and CO may concomitantly participate in vasorelaxation, anti-inflammation and angiogenesis. NO and H(2)S collaborate in the regulation of vascular tone. Finally, H(2)S may upregulate the heme oxygenase/carbon monoxide (HO/CO) pathway during hypoxic conditions. All three gasotransmitters are produced by specific enzymes in different cell types that include cardiomyocytes, endothelial cells and smooth muscle cells. As translational research on gasotransmitters has exploded over the past years, drugs that alter the production/levels of the gasotransmitters themselves or modulate their signaling pathways are now being developed. This review is focused on the cardiovascular effects of NO, CO, and H(2)S. Moreover, their donors as drug targeting the cardiovascular system are briefly described.

H2S-Releasing Polymer Micelles for Studying Selective Cell Toxicity

We report the preparation of S-aroylthiooxime (SATO) functionalized amphiphilic block copolymer micelles that release hydrogen sulfide (H₂S), a gaseous signaling molecule of relevance to various physiological and pathological conditions. The micelles release H₂S in response to cysteine with a half-life of 3.3 h, which is substantially slower than a related small molecule SATO. Exogenous administration of H₂S impacts growth and proliferation of cancer cells; however, the limited control over H₂S generation from inorganic sulfide sources results in conflicting reports. Therefore, we compare the cellular cytotoxicity of SATO-functionalized micelles, which release H₂S in a sustained manner, to Na₂S, which releases H₂S in a single dose. Our results show that H₂S-releasing micelles significantly reduce the survival of HCT116 colon cancer cells relative to Na₂S, GYY4137, and a small molecule SATO, indicating that release kinetics may play an important role in determining toxicity of H₂S toward cancer cells. Furthermore, H₂S-releasing micelles are well tolerated by immortalized fibroblasts (NIH/3T3 cells), suggesting a selective toxicity of H₂S toward cancer cells.

Toward Hydrogen Sulfide Based Therapeutics: Critical Drug Delivery and Developability Issues

Hydrogen sulfide (H₂ S), together with nitric oxide (NO) and carbon monoxide (CO), belongs to the gasotransmitter family and plays important roles in mammals as a signaling molecule. Many studies have also shown the various therapeutic effects of H₂ S, which include protection against myocardial ischemia injury, cytoprotection against oxidative stress, mediation of neurotransmission, inhibition of insulin signaling, regulation of inflammation, inhibition of the hypoxia-inducible pathway, and dilation of blood vessels. One major challenge in the development of H₂ S-based therapeutics is its delivery. In this manuscript, we assess the various drug delivery strategies in the context of being used research tools and eventual developability as therapeutic agents.

Hydrogen Sulfide Protects Renal Grafts Against Prolonged Cold Ischemia-Reperfusion Injury via Specific Mitochondrial Actions

Ischemia-reperfusion injury is unavoidably caused by loss and subsequent restoration of blood flow during organ procurement, and prolonged ischemia-reperfusion injury IRI results in increased rates of delayed graft function and early graft loss. The endogenously produced gasotransmitter, hydrogen sulfide (H₂ S), is a novel molecule that mitigates hypoxic tissue injury. The current study investigates the protective mitochondrial effects of H₂ S during in vivo cold storage and subsequent renal transplantation (RTx) and in vitro cold hypoxic renal injury. Donor allografts from Brown Norway rats treated with University of Wisconsin (UW) solution + H₂ S (150 μM NaSH) during prolonged (24-h) cold (4°C) storage exhibited significantly (p < 0.05) decreased acute necrotic/apoptotic injury and significantly (p < 0.05) improved function and recipient Lewis rat survival compared to UW solution alone. Treatment of rat kidney epithelial cells (NRK-52E) with the mitochondrial-targeted H₂ S donor, AP39, during in vitro cold hypoxic injury improved the protective capacity of H₂ S >1000-fold compared to similar levels of the nonspecific H₂ S donor, GYY4137 and also improved syngraft function and survival following prolonged cold storage compared to UW solution. H₂ S treatment mitigates cold IRI-associated renal injury via mitochondrial actions and could represent a novel therapeutic strategy to minimize the detrimental clinical outcomes of prolonged cold IRI during RTx.

AP39, a mitochondria-targeting hydrogen sulfide (H2 S) donor, protects against myocardial reperfusion injury independently of salvage kinase signalling

BACKGROUND AND PURPOSE

H₂ S protects myocardium against ischaemia/reperfusion injury. This protection may involve the cytosolic reperfusion injury salvage kinase (RISK) pathway, but direct effects on mitochondrial function are possible. Here, we investigated the potential cardioprotective effect of a mitochondria-specific H₂ S donor, AP39, at reperfusion against ischaemia/reperfusion injury.

EXPERIMENTAL APPROACH

Anaesthetized rats underwent myocardial ischaemia (30 min)/reperfusion (120 min) with randomization to receive interventions before reperfusion: vehicle, AP39 (0.01, 0.1, 1 μmol·kg^-1 ), or control compounds AP219 and ADT-OH (1 μmol·kg^-1 ). LY294002, L-NAME or ODQ were used to investigate the involvement of the RISK pathway. Myocardial samples harvested 5 min after reperfusion were analysed for RISK protein phosphorylation and isolated cardiac mitochondria were used to examine the direct mitochondrial effects of AP39.

KEY RESULTS

AP39, dose-dependently, reduced infarct size. Inhibition of either PI3K/Akt, eNOS or sGC did not affect this effect of AP39. Western blot analysis confirmed that AP39 did not induce phosphorylation of Akt, eNOS, GSK-3β or ERK1/2. In isolated subsarcolemmal and interfibrillar mitochondria, AP39 significantly attenuated mitochondrial ROS generation without affecting respiratory complexes I or II. Furthermore, AP39 inhibited mitochondrial permeability transition pore (PTP) opening and co-incubation of mitochondria with AP39 and cyclosporine A induced an additive inhibitory effect on the PTP.

CONCLUSION AND IMPLICATIONS

AP39 protects against reperfusion injury independently of the cytosolic RISK pathway. This cardioprotective effect could be mediated by inhibiting PTP via a cyclophilin D-independent mechanism. Thus, selective delivery of H₂ S to mitochondria may be therapeutically applicable for employing the cardioprotective utility of H₂ S.

H2S as a possible therapeutic alternative for the treatment of hypertensive kidney injury

Hypertension is the most common cause of cardiovascular morbidities and mortalities, and a major risk factor for renal dysfunction. It is considered one of the causes of chronic kidney disease, which progresses into end-stage renal disease and eventually loss of renal function. Yet, the mechanism underlying the pathogenesis of hypertension and its associated kidney injury is still poorly understood. Moreover, despite existing antihypertensive therapies, achievement of blood pressure control and preservation of renal function still remain a worldwide public health challenge in a subset of hypertensive patients. Therefore, novel modes of intervention are in demand. Hydrogen sulfide (H₂S), a gaseous signaling molecule, has been established to possess antihypertensive and renoprotective properties, which may represent an important therapeutic alternative for the treatment of hypertension and kidney injury. This review discusses recent findings about H₂S in hypertension and kidney injury from both experimental and clinical studies. It also addresses future direction regarding therapeutic use of H₂S.

H2S biosynthesis and catabolism: new insights from molecular studies

Hydrogen sulfide (H₂S) has profound biological effects within living organisms and is now increasingly being considered alongside other gaseous signalling molecules, such as nitric oxide (NO) and carbon monoxide (CO). Conventional use of pharmacological and molecular approaches has spawned a rapidly growing research field that has identified H₂S as playing a functional role in cell-signalling and post-translational modifications. Recently, a number of laboratories have reported the use of siRNA methodologies and genetic mouse models to mimic the loss of function of genes involved in the biosynthesis and degradation of H₂S within tissues. Studies utilising these systems are revealing new insights into the biology of H₂S within the cardiovascular system, inflammatory disease, and in cell signalling. In light of this work, the current review will describe recent advances in H₂S research made possible by the use of molecular approaches and genetic mouse models with perturbed capacities to generate or detoxify physiological levels of H₂S gas within tissues.

Diabetic nephropathy: A potential savior with 'rotten-egg' smell

Diabetic nephropathy (DN) is currently the leading cause of end-stage renal disease. Despite optimal management, DN is still a major contributor to morbidity and mortality of diabetic patients worldwide. The major pathological alterations in DN include excessive accumulation and deposition of extracellular matrix, leading to expansion of mesangial matrix, thickening of glomerular basement membrane and tubulointerstitial fibrosis. At the molecular level, accumulating evidence suggests that hyperglycemia or high glucose mediates renal injury in DN via multiple molecular mechanisms such as induction of oxidative stress, upregulation of renal transforming growth factor beta-1 expression, production of proinflammatory cytokines, activation of fibroblasts and renin angiotensin system, and depletion of adenosine triphosphate. Also worrying is the fact that existing therapies only retard the disease progression but do not prevent it. Therefore, there is urgent need to identify novel therapies to target additional disease mechanisms. Hydrogen sulfide (H₂S), the third member of the gasotransmitter family, has recently been identified and demonstrated to possess important therapeutic characteristics that prevent the development and progression of DN in experimental animals by targeting several important molecular pathways, and therefore may represent an alternative or additional therapeutic approach for DN. This review discusses recent experimental findings on the molecular mechanisms underlying the therapeutic effects of H₂S against the development and progression of DN and its clinical application in the future.

The mitochondria-targeted imidazole substituted oleic acid 'TPP-IOA' affects mitochondrial bioenergetics and its protective efficacy in cells is influenced by cellular dependence on aerobic metabolism

A variety of mitochondria-targeted small molecules have been invented to manipulate mitochondrial redox activities and improve function in certain disease states. 3-Hydroxypropyl-triphenylphosphonium-conjugated imidazole-substituted oleic acid (TPP-IOA) was developed as a specific inhibitor of cytochrome c peroxidase activity that inhibits apoptosis by preventing cardiolipin oxidation and cytochrome c release to the cytosol. Here we evaluate the effects of TPP-IOA on oxidative phosphorylation in isolated mitochondria and on mitochondrial function in live cells. We demonstrate that, at concentrations similar to those required to achieve inhibition of cytochrome c peroxidase activity, TPP-IOA perturbs oxidative phosphorylation in isolated mitochondria. In live SH-SY5Y cells, TPP-IOA partially collapsed mitochondrial membrane potential, caused extensive fragmentation of the mitochondrial network, and decreased apparent mitochondrial abundance within 3h of exposure. Many cultured cell lines rely primarily on aerobic glycolysis, potentially making them less sensitive to small molecules disrupting oxidative phosphorylation. We therefore determined the anti-apoptotic efficacy of TPP-IOA in SH-SY5Y cells growing in glucose or in galactose, the latter of which increases reliance on oxidative phosphorylation for ATP supply. The anti-apoptotic activity of TPP-IOA that was observed in glucose media was not seen in galactose media. It therefore appears that, at concentrations required to inhibit cytochrome c peroxidase activity, TPP-IOA perturbs oxidative phosphorylation. In light of these data it is predicted that potential future therapeutic applications of TPP-IOA will be restricted to highly glycolytic cell types with limited reliance on oxidative phosphorylation.

Inhibition of hydrogen sulfide biosynthesis sensitizes lung adenocarcinoma to chemotherapeutic drugs by inhibiting mitochondrial DNA repair and suppressing cellular bioenergetics

Therapeutic manipulation of the gasotransmitter hydrogen sulfide (H₂S) has recently been proposed as a novel targeted anticancer approach. Here we show that human lung adenocarcinoma tissue expresses high levels of hydrogen sulfide (H₂S) producing enzymes, namely, cystathionine beta-synthase (CBS), cystathionine gamma lyase (CSE) and 3-mercaptopyruvate sulfurtransferase (3-MST), in comparison to adjacent lung tissue. In cultured lung adenocarcinoma but not in normal lung epithelial cells elevated H₂S stimulates mitochondrial DNA repair through sulfhydration of EXOG, which, in turn, promotes mitochondrial DNA repair complex assembly, thereby enhancing mitochondrial DNA repair capacity. In addition, inhibition of H₂S-producing enzymes suppresses critical bioenergetics parameters in lung adenocarcinoma cells. Together, inhibition of H₂S-producing enzymes sensitize lung adenocarcinoma cells to chemotherapeutic agents via induction of mitochondrial dysfunction as shown in in vitro and in vivo models, suggesting a novel mechanism to overcome tumor chemoresistance.

S-Sulfhydration of ATP synthase by hydrogen sulfide stimulates mitochondrial bioenergetics

Mammalian cells can utilize hydrogen sulfide (H2S) to support mitochondrial respiration. The aim of our study was to explore the potential role of S-sulfhydration (a H2S-induced posttranslational modification, also known as S-persulfidation) of the mitochondrial inner membrane protein ATP synthase (F1F0 ATP synthase/Complex V) in the regulation of mitochondrial bioenergetics. Using a biotin switch assay, we have detected S-sulfhydration of the α subunit (ATP5A1) of ATP synthase in response to exposure to H2S in vitro. The H2S generator compound NaHS induced S-sulfhydration of ATP5A1 in HepG2 and HEK293 cell lysates in a concentration-dependent manner (50-300μM). The activity of immunocaptured mitochondrial ATP synthase enzyme isolated from HepG2 and HEK293 cells was stimulated by NaHS at low concentrations (10-100nM). Site-directed mutagenesis of ATP5A1 in HEK293 cells demonstrated that cysteine residues at positions 244 and 294 are subject to S-sulfhydration. The double mutant ATP synthase protein (C244S/C294S) showed a significantly reduced enzyme activity compared to control and the single-cysteine-mutated recombinant proteins (C244S or C294S). To determine whether endogenous H2S plays a role in the basal S-sulfhydration of ATP synthase in vivo, we compared liver tissues harvested from wild-type mice and mice deficient in cystathionine-gamma-lyase (CSE, one of the three principal mammalian H2S-producing enzymes). Significantly reduced S-sulfhydration of ATP5A1 was observed in liver homogenates of CSE-/- mice, compared to wild-type mice, suggesting a physiological role for CSE-derived endogenous H2S production in the S-sulfhydration of ATP synthase. Various forms of critical illness (including burn injury) upregulate H2S-producing enzymes and stimulate H2S biosynthesis. In liver tissues collected from mice subjected to burn injury, we detected an increased S-sulfhydration of ATP5A1 at the early time points post-burn. At later time points (when systemic H2S levels decrease) S-sulfhydration of ATP5A1 decreased as well. In conclusion, H2S induces S-sulfhydration of ATP5A1 at C244 and C294. This post-translational modification may be a physiological mechanism to maintain ATP synthase in a physiologically activated state, thereby supporting mitochondrial bioenergetics. The sulfhydration of ATP synthase may be a dynamic process, which may be regulated by endogenous H2S levels under various pathophysiological conditions.

The Evolutionary Ecology of Animals Inhabiting Hydrogen Sulfide–Rich Environments

Hydrogen sulfide (H2S) is a respiratory toxicant that creates extreme environments tolerated by few organisms. H2S is also produced endogenously by metazoans and plays a role in cell signaling. The mechanisms of H2S toxicity and its physiological functions serve as a basis to discuss the multifarious strategies that allow animals to survive in H2S-rich environments. Despite their toxicity, H2S-rich environments also provide ecological opportunities, and complex selective regimes of covarying abiotic and biotic factors drive trait evolution in organisms inhabiting H2S-rich environments. Furthermore, adaptation to H2S-rich environments can drive speciation, giving rise to biodiversity hot spots with high levels of endemism in deep-sea hydrothermal vents, cold seeps, and freshwater sulfide springs. The diversity of H2S-rich environments and their inhabitants provides ideal systems for comparative studies of the effects of a clear-cut source of selection across vast geographic and phylogenetic scales, ultimately informing our understanding of how environmental stressors affect ecological and evolutionary processes.

Hydrogen sulfide, an enhancer of vascular nitric oxide signaling: mechanisms and implications

Nitric oxide (NO) vascular signaling has long been considered an independent, self-sufficient pathway. However, recent data indicate that the novel gaseous mediator, hydrogen sulfide (H₂S), serves as an essential enhancer of vascular NO signaling. The current article overviews the multiple levels at which this enhancement takes place. The first level of interaction relates to the formation of biologically active hybrid S/N species and the H₂S-induced stimulation of NO release from its various stable "pools" (e.g., nitrite). The next interactions occur on the level of endothelial calcium mobilization and PI3K/Akt signaling, increasing the specific activity of endothelial NO synthase (eNOS). The next level of interaction occurs on eNOS itself; H₂S directly interacts with the enzyme: sulfhydration of critical cysteines stabilizes it in its physiological, dimeric state, thereby optimizing eNOS-derived NO production and minimizing superoxide formation. Yet another level of interaction, further downstream, occurs at the level of soluble guanylate cyclase (sGC): H₂S stabilizes sGC in its NO-responsive, physiological, reduced form. Further downstream, H₂S inhibits the vascular cGMP phosphodiesterase (PDE5), thereby prolonging the biological half-life of cGMP. Finally, H₂S-derived polysulfides directly activate cGMP-dependent protein kinase (PKG). Taken together, H₂S emerges an essential endogenous enhancer of vascular NO signaling, contributing to vasorelaxation and angiogenesis. The functional importance of the H₂S/NO cooperative interactions is highlighted by the fact that H₂S loses many of its beneficial cardiovascular effects when eNOS is inactive.

Both the H2S biosynthesis inhibitor aminooxyacetic acid and the mitochondrially targeted H2S donor AP39 exert protective effects in a mouse model of burn injury

Hydrogen sulfide (H₂S) exerts beneficial as well as deleterious effects in various models of critical illness. Here we tested the effect of two different pharmacological interventions: (a) inhibition of H₂S biosynthesis using the cystathionine-beta-synthase (CBS)/cystathionine-gamma-lyase (CSE) inhibitor aminooxyacetic acid (AOAA) and the mitochondrially targeted H₂S donor [10-oxo-10-[4-(3-thioxo-3H-1,2-dithiol-5-yl)phenoxy]decyl]triphenyl-phosphonium (AP39). A 30% body surface area burn injury was induced in anesthetized mice; animals were treated with vehicle, AOAA (10mg/kg i.p. once or once a day for 6days), or AP39 (0.3mg/kg/day once or once a day for 6days). In two separate groups, animals were sacrificed, at 24h post-burn or on Day 7 post-burn, blood and lungs were collected and the following parameters were evaluated: myeloperoxidase (MPO) and malondialdehyde (MDA) in lung homogenates, plasma cytokines (Luminex analysis) and circulating indicators of organ dysfunction (Vetscan analysis). Lung MPO levels (an index of neutrophil infiltration) and MDA levels (an index of oxidative stress) were significantly increased in response to burn injury both at 24h and at 7days; both AOAA and AP39 attenuated these increases. From a panel of inflammatory cytokines (TNFα, IL-1β, IL-6, IL-10, MCP-1, MIP-2, VEGF and IFNγ) in the plasma, IL-6 and IL-10 levels were markedly elevated at 24h and VEGF was slightly elevated. IL-6 remained highly elevated at 7days post-burn while IL-10 levels decreased, but remained slightly elevated over baseline 7days post-burn. The changes in cytokine levels were attenuated both by AP39 and AOAA at both time points studied. The burn-induced increases in the organ injury markers ALP and ALT, amylase and creatinine were reduced by both AOAA and AP39. We conclude that both H₂S biosynthesis inhibition (using AOAA) and H₂S donation (using AP39) suppresses inflammatory mediator production and reduces multi-organ injury in a murine model of burn injury, both at an early time point (when systemic H₂S levels are elevated) and at a later time point (at which time systemic H₂S levels have returned to baseline). These findings point to the complex pathogenetic role of H₂S in burns.

The novel mitochondria-targeted hydrogen sulfide (H2S) donors AP123 and AP39 protect against hyperglycemic injury in microvascular endothelial cells in vitro

The development of diabetic vascular complications is initiated, at least in part, by mitochondrial reactive oxygen species (ROS) production in endothelial cells. Hyperglycemia induces superoxide production in the mitochondria and initiates changes in the mitochondrial membrane potential that leads to mitochondrial dysfunction. Hydrogen sulfide (H₂S) supplementation has been shown to reduce the mitochondrial oxidant production and shows efficacy against diabetic vascular damage in vivo. However, the half-life of H₂S is very short and it is not specific for the mitochondria. We have therefore evaluated two novel mitochondria-targeted anethole dithiolethione and hydroxythiobenzamide H₂S donors (AP39 and AP123 respectively) at preventing hyperglycemia-induced oxidative stress and metabolic changes in microvascular endothelial cells in vitro. Hyperglycemia (HG) induced significant increase in the activity of the citric acid cycle and led to elevated mitochondrial membrane potential. Mitochondrial oxidant production was increased and the mitochondrial electron transport decreased in hyperglycemic cells. AP39 and AP123 (30–300 nM) decreased HG-induced hyperpolarisation of the mitochondrial membrane and inhibited the mitochondrial oxidant production. Both H₂S donors (30–300 nM) increased the electron transport at respiratory complex III and improved the cellular metabolism. Targeting H₂S to mitochondria retained the cytoprotective effect of H₂S against glucose-induced damage in endothelial cells suggesting that the molecular target of H₂S action is within the mitochondria. Mitochondrial targeting of H₂S also induced >1000-fold increase in the potency of H₂S against hyperglycemia-induced injury. The high potency and long-lasting effect elicited by these H₂S donors strongly suggests that these compounds could be useful against diabetic vascular complications.

Controlled release hydrogen sulfide delivery system based on mesoporous silica nanoparticles protects graft endothelium from ischemia-reperfusion injury

Hydrogen sulfide (H₂S) functions as a protective gas transmitter in various physiological and pathological processes, but the lack of ideal donors severely hampers the clinical application of H₂S. This study aims to construct a controlled release H₂S donor and evaluate its protective effect on graft endothelium. Mesoporous silica nanoparticles (MSNs) were synthesized using the sol–gel method and loaded with diallyl trisulfide (DATS), an H₂S-releasing agent named DATS-MSN. In vitro experiments showed that DATS-MSN could alleviate endothelial cell inflammation and enhance endothelial cell proliferation and migration. In vivo experiments demonstrated that the apoptosis of graft endothelium was mitigated in the presence of DATS-MSN. Our results indicated that DATS-MSN, releasing H₂S in a controlled release fashion, could serve as an ideal H₂S donor.

Cardioprotection by H2S Donors: Nitric Oxide-Dependent and ‑Independent Mechanisms

Hydrogen sulfide (H2S) is a signaling molecule with protective effects in the cardiovascular system. To harness the therapeutic potential of H2S, a number of donors have been developed. The present study compares the cardioprotective actions of representative H2S donors from different classes and studies their mechanisms of action in myocardial injury in vitro and in vivo. Exposure of cardiomyocytes to H2O2 led to significant cytotoxicity, which was inhibited by sodium sulfide (Na2S), thiovaline (TV), GYY4137 [morpholin-4-ium 4 methoxyphenyl(morpholino) phosphinodithioate], and AP39 [(10-oxo-10-(4-(3-thioxo-3H-1,2-dithiol5yl)phenoxy)decyl) triphenylphospho-nium bromide]. Inhibition of nitric oxide (NO) synthesis prevented the cytoprotective effects of Na2S and TV, but not GYY4137 and AP39, against H2O2-induced cardiomyocyte injury. Mice subjected to left anterior descending coronary ligation were protected from ischemia-reperfusion injury by the H2S donors tested. Inhibition of nitric oxide synthase (NOS) in vivo blocked only the beneficial effect of Na2S. Moreover, Na2S, but not AP39, administration enhanced the phosphorylation of endothelial NOS and vasodilator-associated phosphoprotein. Both Na2S and AP39 reduced infarct size in mice lacking cyclophilin-D (CypD), a modulator of the mitochondrial permeability transition pore (PTP). Nevertheless, only AP39 displayed a direct effect on mitochondria by increasing the mitochondrial Ca(2+) retention capacity, which is evidence of decreased propensity to undergo permeability transition. We conclude that although all the H2S donors we tested limited infarct size, the pathways involved were not conserved. Na2S had no direct effects on PTP opening, and its action was nitric oxide dependent. In contrast, the cardioprotection exhibited by AP39 could result from a direct inhibitory effect on PTP acting at a site different than CypD.

Cystathionine: A novel oncometabolite in human breast cancer

In this study, we have identified cystathionine (CTH), a sulfur containing metabolite, to be selectively enriched in human breast cancer (HBC) tissues (∼50-100 pmoles/mg protein) compared with undetectable levels in normal breast tissues. The accumulation of CTH, specifically in HBC, was attributed to the overexpression of cystathionine beta synthase (CBS), its synthesizing enzyme, and the undetectable levels of its downstream metabolizing enzyme, cystathionine gamma lyase (CGL). Interestingly both CBS and CGL could not be detected in normal breast tissues. We further observed that CTH protected HBC cells against excess reactive oxygen species (ROS) and chemotherapeutic drug-induced apoptosis. Moreover, CTH promoted both mitochondrial and endoplasmic reticulum homeostasis in HBC cells. As both the mitochondria and the endoplasmic reticulum are key organelles regulating the onset of apoptosis, we reasoned that endogenous CTH could be contributing towards increasing the apoptotic threshold in HBC cells. An increased apoptotic threshold is a hallmark of all cancer types, including HBC, and is primarily responsible for drug resistance. Hence this study unravels one of the possible pathways that may contribute towards drug resistance in HBC.

Improved tag-switch method reveals that thioredoxin acts as depersulfidase and controls the intracellular levels of protein persulfidation

Hydrogen sulfide (H2S) has emerged as a signalling molecule capable of regulating several important physiological functions such as blood pressure, neurotransmission and inflammation. The mechanisms behind these effects are still largely elusive and oxidative posttranslational modification of cysteine residues (protein persulfidation or S-sulfhydration) has been proposed as the main pathway for H2S-induced biological and pharmacological effects. As a signalling mechanism, persulfidation has to be controlled. Using an improved tag-switch assay for persulfide detection we show here that protein persulfide levels are controlled by the thioredoxin system. Recombinant thioredoxin showed an almost 10-fold higher reactivity towards cysteine persulfide than towards cystine and readily cleaved protein persulfides as well. This reaction resulted in H2S release suggesting that thioredoxin could be an important regulator of H2S levels from persulfide pools. Inhibition of the thioredoxin system caused an increase in intracellular persulfides, highlighting thioredoxin as a major protein depersulfidase that controls H2S signalling. Finally, using plasma from HIV-1 patients that have higher circulatory levels of thioredoxin, we could prove depersulfidase role in vivo.

Cystathionine-beta-synthase inhibition for colon cancer: Enhancement of the efficacy of aminooxyacetic acid via the prodrug approach

Colon cancer cells contain high levels of cystathionine-beta-synthase (CBS). Its product, hydrogen sulfide (H₂S) promotes the growth and proliferation of colorectal tumor cells. In order to improve the antitumor efficacy of the prototypical CBS inhibitor aminooxyacetic acid (AOAA), we have designed and synthesized YD0171, a methyl ester derivative of AOAA. The antiproliferative effect of YD0171 exceeded the antiproliferative potency of AOAA in HCT116 human colon cancer cells. The esterase inhibitor paraoxon prevented the cellular inhibition of CBS activity by YD0171. YD0171 suppressed mitochondrial respiration and glycolytic function and induced G0/G1 arrest, but did not induce tumor cell apoptosis or necrosis. Metabolomic analysis in HCT116 cells showed that YD0171 affects multiple pathways of cell metabolism. The efficacy of YD0171 as an inhibitor of tumor growth was also tested in nude mice bearing subcutaneous HCT116 cancer cell xenografts. Animals were treated via subcutaneous injection of vehicle, AOAA (1, 3 or 9 mg/kg/day) or YD0171 (0.1, 0.5 or 1 mg/kg/day) for 3 weeks. Tumor growth was significantly reduced by 9 mg/kg/day AOAA, but not at the lower doses. YD0171 was more potent: tumor volume was significantly inhibited at 0.5 and 1 mg/kg/day. Thus, the in vivo efficacy of YD0171 is 9-times higher than that of AOAA. YD0171 (1 mg/kg/day) attenuated tumor growth and metastasis formation in the intracecal HCT116 tumor model. YD0171 (3 mg/kg/day) also reduced tumor growth in patient-derived tumor xenograft (PDTX) bearing athymic mice. YD0171 (3 mg/kg/day) induced the regression of established HCT116 tumors in vivo. A 5-day safety study in mice demonstrated that YD0171 at 20 mg/kg/day (given in two divided doses) does not increase plasma markers of organ injury, nor does it induce histological alterations in the liver or kidney. YD0171 caused a slight elevation in plasma homocysteine levels. In conclusion, the prodrug approach improves the pharmacological profile of AOAA; YD0171 represents a prototype for CBS inhibitory anticancer prodrugs. By targeting colorectal cancer bioenergetics, an emerging important hallmark of cancer, the approach exemplified herein may offer direct translational opportunities.

Hydrogen sulfide modulates chromatin remodeling and inflammatory mediator production in response to endotoxin, but does not play a role in the development of endotoxin tolerance

Background

Pretreatment with low doses of LPS (lipopolysaccharide, bacterial endotoxin) reduces the pro-inflammatory response to a subsequent higher LPS dose, a phenomenon known as endotoxin tolerance. Moreover, hydrogen sulfide (H₂S), an endogenous gaseous mediator (gasotransmitter) can exert anti-inflammatory effects. Here we investigated the potential role of H₂S in the development of LPS tolerance. THP1 differentiated macrophages were pretreated with the H₂S donor NaHS (1 mM) or the H₂S biosynthesis inhibitor aminooxyacetic acid (AOAA, 1 mM).

Methods

To induce tolerance, cells were treated with a low concentration of LPS (0.5 μg/ml) for 4 or 24 h, and then treated with a high concentration of LPS (1 μg/ml) for 4 h or 24 h. In in vivo studies, male wild-type and CSE^-/- mice were randomized to the following groups: Control (vehicle); Endotoxemic saline for 3 days before the induction of endotoxemia with 10 mg/kg LPS) mg/kg; Tolerant (LPS at 1 mg/kg for 3 days, followed LPS at 10 mg/kg). Animals were sacrificed after 4 or 12 h; plasma IL-6 and TNF-α levels were measured. Changes in histone H3 and H4 acetylation were analyzed by Western blotting.

Results

LPS tolerance decreased pro-inflammatory cytokine production. AOAA did not affect the effect of tolerance on reducing cytokine production. Treatment of the cells with the H₂S donor reduced cytokine production. Induction of the tolerance increased the acetylation of H3; AOAA reduced histone acetylation. H₂S donation increased histone acetylation. Tolerance did not affect the responses to H₂S with respect to histone acetylation.

Conclusions

In conclusion, both LPS tolerance and H₂S donation decrease LPS-induced cytokine production in vitro and modulate histone acetylation. However, endogenous, CSE-derived H₂S does not appear to play a significant role in the development of LPS tolerance.

Emerging role of hydrogen sulfide-microRNA crosstalk in cardiovascular diseases

Despite an obnoxious smell and toxicity at a high dose, hydrogen sulfide (H2S) is emerging as a cardioprotective gasotransmitter. H2S mitigates pathological cardiac remodeling by regulating several cellular processes including fibrosis, hypertrophy, apoptosis, and inflammation. These encouraging findings in rodents led to initiation of a clinical trial using a H2S donor in heart failure patients. However, the underlying molecular mechanisms by which H2S mitigates cardiac remodeling are not completely understood. Empirical evidence suggest that H2S may regulate signaling pathways either by directly influencing a gene in the cascade or interacting with nitric oxide (another cardioprotective gasotransmitter) or both. Recent studies revealed that H2S may ameliorate cardiac dysfunction by up- or downregulating specific microRNAs. MicroRNAs are noncoding, conserved, regulatory RNAs that modulate gene expression mostly by translational inhibition and are emerging as a therapeutic target for cardiovascular disease (CVD). Few microRNAs also regulate H2S biosynthesis. The inter-regulation of microRNAs and H2S opens a new avenue for exploring the H2S-microRNA crosstalk in CVD. This review embodies regulatory mechanisms that maintain the physiological level of H2S, exogenous H2S donors used for increasing the tissue levels of H2S, H2S-mediated regulation of CVD, H2S-microRNAs crosstalk in relation to the pathophysiology of heart disease, clinical trials on H2S, and future perspectives for H2S as a therapeutic agent for heart failure.

Puerarin Attenuates Anoxia/Reoxygenation Injury Through Enhancing Bcl-2 Associated Athanogene 3 Expression, a Modulator of Apoptosis and Autophagy

Background

Puerarin has protective effects on ischemia-reperfusion injury, but the underlying mechanisms are not fully revealed. This study explored the effect of puerarin on the expression of Bcl-2 associated athanogene 3 (BAG3) in an in vitro model of anoxia/reoxygenation injury (A/RI) in neonate rat primary cardiomyocytes and the functions of BAG3 in A/RI.

Material/Methods

BAG3 expression in cardiomyocytes with or without puerarin pre-treatment was quantified using qRT-PCR and Western blot analysis. The effects of BAG3 on A/RI were studied by measuring the activity of lactate dehydrogenase (LDH) and creatine phosphate kinase (CPK), the concentration of malondialdehyde (MDA), superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px). The effects of BAG3 on autophagy and apoptosis of the cardiomyocytes after A/RI were further studied.

Results

Puerarin significantly promoted BAG3 expression in the rat primary cardiomyocytes after A/RI. Enforced BAG3 expression presented similar effects as puerarin pre-treatment in attenuating A/RI in terms of CPK, LDH, MDA, SOD, GSH-Px, ROS generation, and cell viability. BAG3 overexpression significantly stimulated autophagy in cardiomyocytes after A/RI, which presented protective effects on A/RI in terms of cell viability and apoptosis. Autophagy inhibition partly abrogated the protective effects of BAG3.

Conclusions

Puerarin can directly increase BAG3 transcription and translation in cardiomyocytes after A/RI. The elevated BAG3 expression presents protective effects on A/RI at least through enhancing autophagy and reducing apoptosis, which is a novel protective mechanism of puerarin in ARI.

Hydrogen Sulfide--Mechanisms of Toxicity and Development of an Antidote

Hydrogen sulfide is a highly toxic gas—second only to carbon monoxide as a cause of inhalational deaths. Its mechanism of toxicity is only partially known, and no specific therapy exists for sulfide poisoning. We show in several cell types, including human inducible pluripotent stem cell (hiPSC)-derived neurons, that sulfide inhibited complex IV of the mitochondrial respiratory chain and induced apoptosis. Sulfide increased hydroxyl radical production in isolated mouse heart mitochondria and F₂-isoprostanes in brains and hearts of mice. The vitamin B₁₂ analog cobinamide reversed the cellular toxicity of sulfide, and rescued Drosophila melanogaster and mice from lethal exposures of hydrogen sulfide gas. Cobinamide worked through two distinct mechanisms: direct reversal of complex IV inhibition and neutralization of sulfide-generated reactive oxygen species. We conclude that sulfide produces a high degree of oxidative stress in cells and tissues, and that cobinamide has promise as a first specific treatment for sulfide poisoning.

Effects of hydrogen sulphide in smooth muscle

In recent years, it has become apparent that the gaseous pollutant, hydrogen sulphide (H2S) can be synthesised in the body and has a multitude of biological actions. This review summarizes some of the actions of this 'gasotransmitter' in influencing the smooth muscle that is responsible for controlling muscular activity of hollow organs. In the vasculature, while H2S can cause vasoconstriction by complex interactions with other biologically important gases, such as nitric oxide, the prevailing response is vasorelaxation. While most vasorelaxation responses occur by a direct action of H2S on smooth muscle cells, it has recently been proposed to be an endothelium-derived hyperpolarizing factor. H2S also promotes relaxation in other smooth muscle preparations including bronchioles, the bladder, gastrointestinal tract and myometrium, opening up the opportunity of exploiting the pharmacology of H2S in the treatment of conditions where smooth muscle tone is excessive. The original concept, that H2S caused smooth muscle relaxation by activating ATP-sensitive K(+) channels, has been supplemented with observations that H2S can also modify the activity of other potassium channels, intracellular pH, phosphodiesterase activity and transient receptor potential channels on sensory nerves. While the enzymes responsible for generating endogenous H2S are widely expressed in smooth muscle preparations, it is much less clear what the physiological role of H2S is in determining smooth muscle contractility. Clarification of this requires the development of potent and selective inhibitors of H2S-generating enzymes.

AP39, a Mitochondria-Targeted Hydrogen Sulfide Donor, Supports Cellular Bioenergetics and Protects against Alzheimer's Disease by Preserving Mitochondrial Function in APP/PS1 Mice and Neurons

Increasing evidence suggests that mitochondrial functions are altered in AD and play an important role in AD pathogenesis. It has been established that H₂S homeostasis is balanced in AD. The emerging mitochondrial roles of H₂S include antioxidation, antiapoptosis, and the modulation of cellular bioenergetics. Here, using primary neurons from the well-characterized APP/PS1 transgenic mouse model, we studied the effects of AP39 (a newly synthesized mitochondrially targeted H₂S donor) on mitochondrial function. AP39 increased intracellular H₂S levels, mainly in mitochondrial regions. AP39 exerted dose-dependent effects on mitochondrial activity in APP/PS1 neurons, including increased cellular bioenergy metabolism and cell viability at low concentrations (25–100 nM) and decreased energy production and cell viability at a high concentration (250 nM). Furthermore, AP39 (100 nM) increased ATP levels, protected mitochondrial DNA, and decreased ROS generation. AP39 regulated mitochondrial dynamics, shifting from fission toward fusion. After 6 weeks, AP39 administration to APP/PS1 mice significantly ameliorated their spatial memory deficits in the Morris water maze and NORT and reduced Aβ deposition in their brains. Additionally, AP39 inhibited brain atrophy in APP/PS1 mice. Based on these results, AP39 was proposed as a promising drug candidate for AD treatment, and its anti-AD mechanism may involve protection against mitochondrial damage.

Mini-review: diabetic renal complications, a potential stinky remedy

Chronic kidney disease is associated with vasculitis and is also an independent risk factor for peripheral vascular and coronary artery disease in diabetic patients. Despite optimal management, a significant number of patients progress toward end-stage renal disease (ESRD), a suggestion that the disease mechanism is far from clear. A reduction in hydrogen sulfide (H2S) has been suggested to play a vital role in diabetic vascular complications including diabetic nephropathy (DN). This mini-review highlights the recent findings on the role of H2S in mitigating abnormal extracellular matrix metabolism in DN. A discussion on the development of the newer slow-releasing H2S compounds and its therapeutic potential is also included.

AP39, A Mitochondrially Targeted Hydrogen Sulfide Donor, Exerts Protective Effects in Renal Epithelial Cells Subjected to Oxidative Stress in Vitro and in Acute Renal Injury in Vivo

This study evaluated the effects of AP39 [(10-oxo-10-(4-(3-thioxo-3H-1,2-dithiol-5yl) phenoxy)decyl) triphenyl phosphonium bromide], a mitochondrially targeted donor of hydrogen sulfide (H2S) in an in vitro model of hypoxia/oxidative stress injury in NRK-49F rat kidney epithelial cells (NRK cells) and in a rat model of renal ischemia-reperfusion injury. Renal oxidative stress was induced by the addition of glucose oxidase, which generates hydrogen peroxide in the culture medium at a constant rate. Glucose oxidase (GOx)-induced oxidative stress led to mitochondrial dysfunction, decreased intracellular ATP content, and, at higher concentrations, increased intracellular oxidant formation (estimated by the fluorescent probe 2, 7-dichlorofluorescein, DCF) and promoted necrosis (estimated by the measurement of lactate dehydrogenase release into the medium) of the NRK cells in vitro. Pretreatment with AP39 (30-300 nM) exerted a concentration-dependent protective effect against all of the above effects of GOx. Most of the effects of AP39 followed a bell-shaped concentration-response curve; at the highest concentration of GOx tested, AP39 was no longer able to afford cytoprotective effects. Rats subjected to renal ischemia/reperfusion responded with a marked increase (over four-fold over sham control baseline) blood urea nitrogen and creatinine levels in blood, indicative of significant renal damage. This was associated with increased neutrophil infiltration into the kidneys (assessed by the myeloperoxidase assay in kidney homogenates), increased oxidative stress (assessed by the malondialdehyde assay in kidney homogenates), and an increase in plasma levels of IL-12. Pretreatment with AP39 (0.1, 0.2, and 0.3 mg/kg) provided a dose-dependent protection against these pathophysiological alterations; the most pronounced protective effect was observed at the 0.3 mg/kg dose of the H2S donor; nevertheless, AP39 failed to achieve a complete normalization of any of the injury markers measured. The partial protective effects of AP39 correlated with a partial improvement of kidney histological scores and reduced TUNEL staining (an indicator of DNA damage and apoptosis). In summary, the mitochondria-targeted H2S donor AP39 exerted dose-dependent protective effects against renal epithelial cell injury in vitro and renal ischemia-reperfusion injury in vivo. We hypothesize that the beneficial actions of AP39 are related to the reduction of cellular oxidative stress, and subsequent attenuation of various positive feed-forward cycles of inflammatory and oxidative processes.

The Role of Hydrogen Sulfide in Evolution and the Evolution of Hydrogen Sulfide in Metabolism and Signaling

The chemical versatility of sulfur and its abundance in the prebiotic Earth as reduced sulfide (H2S) implicate this molecule in the origin of life 3.8 billion years ago and also as a major source of energy in the first seven-eighths of evolution. The tremendous increase in ambient oxygen ∼600 million years ago brought an end to H2S as an energy source, and H2S-dependent animals either became extinct, retreated to isolated sulfide niches, or adapted. The first 3 billion years of molecular tinkering were not lost, however, and much of this biochemical armamentarium easily adapted to an oxic environment where it contributes to metabolism and signaling even in humans. This review examines the role of H2S in evolution and the evolution of H2S metabolism and signaling.

Using hydrogen sulfide to design and develop drugs

INTRODUCTION

Hydrogen sulfide (H2S) is an endogenous gasotransmitter, involved in the regulation of several biological functions. Conversely, impaired biosynthesis of H2S is associated with important diseases. This paves the way for exciting pharmacological perspectives for drugs acting on the 'H2S system'.

AREAS COVERED

At the beginning of this manuscript, the authors present the biological roles and mechanisms of action of hydrogen sulfide. The authors then discuss the developments in the modulation of the H2S system via heterogeneous molecules, which behave as sources of exogenous H2S, and are promising drugs for a number of diseases.

EXPERT OPINION

The rate of H2S generation, the physicochemical characteristics and the bioavailability greatly affect the overall pharmacological profile of each H2S-releasing compound. Therefore, the development of broad collections of original moieties endowed with heterogeneous rates/mechanisms of H2S release and a variety of physicochemical, biological and pharmacological features is the most timely and compelling issue in the field of H2S-based drug discovery.

Hydrogen sulfide prodrugs-a review

Hydrogen sulfide (H₂S) is recognized as one of three gasotransmitters together with nitric oxide (NO) and carbon monoxide (CO). As a signaling molecule, H₂S plays an important role in physiology and shows great potential in pharmaceutical applications. Along this line, there is a need for the development of H₂S prodrugs for various reasons. In this review, we summarize different H₂S prodrugs, their chemical properties, and some of their potential therapeutic applications.

A Bright Fluorescent Probe for H2S Enables Analyte-Responsive, 3D Imaging in Live Zebrafish Using Light Sheet Fluorescence Microscopy

Hydrogen sulfide (H2S) is a critical gaseous signaling molecule emerging at the center of a rich field of chemical and biological research. As our understanding of the complexity of physiological H2S in signaling pathways evolves, advanced chemical and technological investigative tools are required to make sense of this interconnectivity. Toward this goal, we have developed an azide-functionalized O-methylrhodol fluorophore, MeRho-Az, which exhibits a rapid >1000-fold fluorescence response when treated with H2S, is selective for H2S over other biological analytes, and has a detection limit of 86 nM. Additionally, the MeRho-Az scaffold is less susceptible to photoactivation than other commonly used azide-based systems, increasing its potential application in imaging experiments. To demonstrate the efficacy of this probe for H2S detection, we demonstrate the ability of MeRho-Az to detect differences in H2S levels in C6 cells and those treated with AOAA, a common inhibitor of enzymatic H2S synthesis. Expanding the use of MeRho-Az to complex and heterogeneous biological settings, we used MeRho-Az in combination with light sheet fluorescence microscopy (LSFM) to visualize H2S in the intestinal tract of live zebrafish. This application provides the first demonstration of analyte-responsive 3D imaging with LSFM, highlighting the utility of combining new probes and live imaging methods for investigating chemical signaling in complex multicellular systems.

The Protective Effect of Puerarin on Myocardial Infarction Reperfusion Injury (MIRI): A Meta-Analysis of Randomized Studies in Rat Models

Background

Although puerarin is generally considered as a protective agent for cardio-cerebrovascular diseases, the exact effect on reducing myocardial infarction reperfusion injury (MIRI) is not well understood. This study aimed to pool previous randomized controlled studies based on rat models to evaluate the effects of puerarin on MIRI.

Material/Methods

Relevant studies were searched among PubMed, Embase, Medline, and CNKI (China National Knowledge Infrastructure). To assess the therapeutic effects of protective effects of puerarin on myocardial infarction reperfusion injury, the outcome indicators which were reported in at least 3 original studies were extracted and pooled, including size of myocardial ischemia (MIS) and myocardial infarction (MIN), creatine kinase (CK), methylene dioxyamphetamine (MDA), and superoxide dismutase (SOD).

Results

Administration of puerarin could effectively reduce the size of MIN after MIR (mean difference: −29.20, 95%CI: −44.90 to −13.51, p=0.0003). Puerarin directly led to decreased CK (mean difference: −6.89, 95%CI: −9.40 to −4.38, p=0.00001) and MDA (mean difference: −2.41, 95%CI: −3.14 to −1.68, p<0.00001) and increased serum SOD (mean difference: 63.97, 95%CI: 38.19 to 89.75, p<0.00001).

Conclusions

Puerarin might have a protective effect in myocardial tissues during MIRI through increasing SOD and decreasing CK and MDA. However, more animal studies and randomized controlled clinical trials are required to confirm these results.

The role of H2S bioavailability in endothelial dysfunction

Endothelial dysfunction (EDF) reflects pathophysiological changes in the phenotype and functions of endothelial cells that result from and/or contribute to a plethora of cardiovascular diseases. We review the role of hydrogen sulfide (H2S) in the pathogenesis of EDF, one of the fastest advancing research topics. Conventionally treated as an environment pollutant, H2S is also produced in endothelial cells and participates in the fine regulation of endothelial integrity and functions. Disturbed H2S bioavailability has been suggested to be a novel indicator of EDF progress and prognosis. EDF manifests in different forms in multiple pathologies, but therapeutics aimed at remedying altered H2S bioavailability may benefit all.

Role of Hydrogen Sulfide in Ischemia-Reperfusion Injury

Ischemia-reperfusion (I/R) injury is one of the major causes of high morbidity, disability, and mortality in the world. I/R injury remains a complicated and unresolved situation in clinical practice, especially in the field of solid organ transplantation. Hydrogen sulfide (H₂S) is the third gaseous signaling molecule and plays a broad range of physiological and pathophysiological roles in mammals. H₂S could protect against I/R injury in many organs and tissues, such as heart, liver, kidney, brain, intestine, stomach, hind-limb, lung, and retina. The goal of this review is to highlight recent findings regarding the role of H₂S in I/R injury. In this review, we present the production and metabolism of H₂S and further discuss the effect and mechanism of H₂S in I/R injury.

Mitochondria-targeted hydrogen sulfide donor AP39 improves neurological outcomes after cardiac arrest in mice

AIMS

Mitochondria-targeted hydrogen sulfide donor AP39, [(10-oxo-10-(4-(3-thioxo-3H-1,2-dithiol-5yl)phenoxy)decyl) triphenylphosphonium bromide], exhibits cytoprotective effects against oxidative stress in vitro. We examined whether or not AP39 improves the neurological function and long term survival in mice subjected to cardiac arrest (CA) and cardiopulmonary resuscitation (CPR).

METHODS

Adult C57BL/6 male mice were subjected to 8 min of CA and subsequent CPR. We examined the effects of AP39 (10, 100, 1000 nmol kg(-1)) or vehicle administered intravenously at 2 min before CPR (Experiment 1). Systemic oxidative stress levels, mitochondrial permeability transition, and histological brain injury were assessed. We also examined the effects of AP39 (10, 1000 nmol kg(-1)) or vehicle administered intravenously at 1 min after return of spontaneous circulation (ROSC) (Experiment 2). ROSC was defined as the return of sinus rhythm with a mean arterial pressure >40 mm Hg lasting at least 10 seconds.

RESULTS

Vehicle treated mice subjected to CA/CPR had poor neurological function and 10-day survival rate (Experiment 1; 15%, Experiment 2; 23%). Administration of AP39 (100 and 1000 nmol kg(-1)) 2 min before CPR significantly improved the neurological function and 10-day survival rate (54% and 62%, respectively) after CA/CPR. Administration of AP39 before CPR attenuated mitochondrial permeability transition pore opening, reactive oxygen species generation, and neuronal degeneration after CA/CPR. Administration of AP39 1 min after ROSC at 10 nmol kg(-1), but not at 1000 nmol kg(-1), significantly improved the neurological function and 10-day survival rate (69%) after CA/CPR.

CONCLUSION

The current results suggest that administration of mitochondria-targeted sulfide donor AP39 at the time of CPR or after ROSC improves the neurological function and long term survival rates after CA/CPR by maintaining mitochondrial integrity and reducing oxidative stress.

Hydrogen sulfide-based therapeutics: exploiting a unique but ubiquitous gasotransmitter

Hydrogen sulfide (H2S) has become recognized as an important signalling molecule throughout the body, contributing to many physiological and pathological processes. In recent years, improved methods for measuring H2S levels and the availability of a wider range of H2S donors and more selective inhibitors of H2S synthesis have helped to more accurately identify the many biological effects of this highly reactive gaseous mediator. Animal studies of several H2S-releasing drugs have demonstrated considerable promise for the safe treatment of a wide range of disorders. Several such drugs are now in clinical trials.

Regulation of Vascular Tone, Angiogenesis and Cellular Bioenergetics by the 3-Mercaptopyruvate Sulfurtransferase/H2S Pathway: Functional Impairment by Hyperglycemia and Restoration by DL-α-Lipoic Acid

Hydrogen sulfide (H2S), as a reducing agent and an antioxidant molecule, exerts protective effects against hyperglycemic stress in the vascular endothelium. The mitochondrial enzyme 3-mercaptopyruvate sulfurtransferase (3-MST) is an important biological source of H2S. We have recently demonstrated that 3-MST activity is inhibited by oxidative stress in vitro and speculated that this may have an adverse effect on cellular homeostasis. In the current study, given the importance of H2S as a vasorelaxant, angiogenesis stimulator and cellular bioenergetic mediator, we first determined whether the 3-MST/H2S system plays a physiological regulatory role in endothelial cells. Next, we tested whether a dysfunction of this pathway develops during the development of hyperglycemia and μmol/L to diabetes-associated vascular complications. Intraperitoneal (IP) 3-MP (1 mg/kg) raised plasma H2S levels in rats. 3-MP (10 1 mmol/L) promoted angiogenesis in vitro in bEnd3 microvascular endothelial cells and in vivo in a Matrigel assay in mice (0.3-1 mg/kg). In vitro studies with bEnd3 cell homogenates demonstrated that the 3-MP-induced increases in H2S production depended on enzymatic activity, although at higher concentrations (1-3 mmol/L) there was also evidence for an additional nonenzymatic H2S production by 3-MP. In vivo, 3-MP facilitated wound healing in rats, induced the relaxation of dermal microvessels and increased mitochondrial bioenergetic function. In vitro hyperglycemia or in vivo streptozotocin diabetes impaired angiogenesis, attenuated mitochondrial function and delayed wound healing; all of these responses were associated with an impairment of the proangiogenic and bioenergetic effects of 3-MP. The antioxidants DL-α-lipoic acid (LA) in vivo, or dihydrolipoic acid (DHLA) in vitro restored the ability of 3-MP to stimulate angiogenesis, cellular bioenergetics and wound healing in hyperglycemia and diabetes. We conclude that diabetes leads to an impairment of the 3-MST/H2S pathway, and speculate that this may contribute to the pathogenesis of hyperglycemic endothelial cell dysfunction. We also suggest that therapy with H2S donors, or treatment with the combination of 3-MP and lipoic acid may be beneficial in improving angiogenesis and bioenergetics in hyperglycemia.

Anti-inflammatory and cytoprotective properties of hydrogen sulfide

Hydrogen sulfide is an endogenous gaseous mediator that plays important roles in many physiological processes in microbes, plants, and animals. This chapter focuses on the important roles of hydrogen sulfide in protecting tissues against injury, promoting the repair of damage, and downregulating the inflammatory responses. The chapter focuses largely, but not exclusively, on these roles of hydrogen sulfide in the gastrointestinal tract. Hydrogen sulfide is produced throughout the gastrointestinal tract, and it contributes to maintenance of mucosal integrity. Suppression of hydrogen sulfide synthesis renders the tissue more susceptible to injury and it impairs repair. In contrast, administration of hydrogen sulfide donors can increase resistance to injury and accelerate repair. Hydrogen sulfide synthesis is rapidly and dramatically enhanced in the gastrointestinal tract after injury is induced. These increases occur specifically at the site of tissue injury. Hydrogen sulfide also plays an important role in promoting resolution of inflammation, and restoration of normal tissue function. In recent years, these beneficial actions of hydrogen sulfide have provided the basis for development of novel hydrogen sulfide-releasing drugs. Nonsteroidal anti-inflammatory drugs that release small amounts of hydrogen sulfide are among the most advanced of the hydrogen sulfide-based drugs. Unlike the parent drugs, these modified drugs do not cause injury in the gastrointestinal tract, and do not interfere with healing of preexisting damage. Because of the increased safety profile of these drugs, they can be used in circumstances in which the toxicity of the parent drug would normally limit their use, such as in chemoprevention of cancer.

Medicinal Chemistry: Insights into the Development of Novel H2S Donors

Hydrogen sulfide (H2S) was traditionally considered as a toxic gas. However, recent studies have demonstrated H2S is an endogenously generated gaseous signaling molecule (gasotransmitter) with importance on par with that of two other well-known endogenous gasotransmitters, nitric oxide (NO) and carbon monoxide (CO). Although H2S's exact mechanisms of action are still under investigation, the production of endogenous H2S and the exogenous administration of H2S have been demonstrated to elicit a wide range of physiological responses including modulation of blood pressure and protection of ischemia reperfusion injury, exertion of anti-inflammatory effects, and reduction of metabolic rate. These results strongly suggest that modulation of H2S levels could have potential therapeutic values. In this regard, synthetic H2S-releasing agents (i.e., H2S donors) are not only important research tools, but also potential therapeutic agents. This chapter summarizes the knowledge of currently available H2S donors. Their preparation, H2S releasing mechanisms, and biological applications are discussed.

Investigating the generation of hydrogen sulfide from the phosphonamidodithioate slow-release donor GYY4137

A two-step hydrolytic decomposition pathway has been elucidated for the slow-release hydrogen sulfide donor GYY4137.

Phosphinodithioate and Phosphoramidodithioate Hydrogen Sulfide Donors

Hydrogen sulfide is rapidly emerging as a key physiological mediator and potential therapeutic tool in numerous areas such as acute and chronic inflammation, neurodegenerative and cardiovascular disease, diabetes, obesity and cancer. However, the vast majority of the published studies have employed crude sulfide salts such as sodium hydrosulfide (NaSH) and sodium sulfide (Na2S) as H2S "donors" to generate H2S. Although these salts are cheap, readily available and easy to use, H2S generated from them occurs as an instantaneous and pH-dependent dissociation, whereas endogenous H2S synthesis from the enzymes cystathionine γ-lyase, cystathionine-β-synthase and 3-mercaptopyruvate sulfurtransferase is a slow and sustained process. Furthermore, sulfide salts are frequently used at concentrations (e.g. 100 μM to 10 mM) far in excess of the levels of H2S reported in vivo (nM to low μM). For the therapeutic potential of H2S is to be properly harnessed, pharmacological agents which generate H2S in a physiological manner and deliver physiologically relevant concentrations are needed. The phosphorodithioate GYY4137 has been proposed as "slow-release" H2S donors and has shown promising efficacy in cellular and animal model diseases such as hypertension, sepsis, atherosclerosis, neonatal lung injury and cancer. However, H2S generation from GYY4137 is inefficient necessitating its use at high concentrations/doses. However, structural modification of the phosphorodithioate core has led to compounds (e.g. AP67 and AP105) with accelerated rates of H2S generation and enhanced biological activity. In this review, the therapeutic potential and limitations of GYY4137 and related phosphorodithioate derivatives are discussed.

Persulfidation (S-sulfhydration) and H2S

The past decade has witnessed the discovery of hydrogen sulfide (H2S) as a new signalling molecule. Its ability to act as a neurotransmitter, regulator of blood pressure, immunomodulator or anti-apoptotic agent, together with its great pharmacological potential, is now well established. Notwithstanding the growing body of evidence showing the biological roles of H2S, the gap between the macroscopic descriptions and the actual mechanism(s) behind these processes is getting larger. The reactivity towards reactive oxygen and nitrogen species and/or metal centres cannot explain this plethora of biological effects. Therefore, a mechanism involving modification of protein cysteine residues to form protein persulfides is proposed. It is alternatively called S-sulfhydration. Persulfides are not particularly stable and show increased reactivity when compared to free thiols. Detection of protein persulfides is still facing methodological limitations, and mechanisms by which H2S causes this modification are still largely scarce. Persulfidation of protein such as KATP could contribute to H2S-induced vasodilation, while S-sulfhydration of GAPDH and NF-κB inhibits apoptosis. H2S regulates endoplasmic reticulum stress by causing persulfidation of PTP-1B. Several other proteins have been found to be regulated by this posttranslational modification of cysteine. This review article provides a critical overview of the current state of the literature addressing protein S-sulfhydration, with particular emphasis on the challenges and future research directions in this particular field.

Working with nitric oxide and hydrogen sulfide in biological systems

Nitric oxide (NO) and hydrogen sulfide (H2S) are gasotransmitter molecules important in numerous physiological and pathological processes. Although these molecules were first known as environmental toxicants, it is now evident that that they are intricately involved in diverse cellular functions with impact on numerous physiological and pathogenic processes. NO and H2S share some common characteristics but also have unique chemical properties that suggest potential complementary interactions between the two in affecting cellular biochemistry and metabolism. Central among these is the interactions between NO, H2S, and thiols that constitute new ways to regulate protein function, signaling, and cellular responses. In this review, we discuss fundamental biochemical principals, molecular functions, measurement methods, and the pathophysiological relevance of NO and H2S.