The emerging roles of hydrogen sulfide in the gastrointestinal tract and liver

Novel H2S Releasing Nanofibrous Coating for In Vivo Dermal Wound Regeneration

Hydrogen sulfide (H₂S), together with nitric oxide and carbon monoxide, has been recognized as an important gasotransmitter. It plays an essential physiological role in regulating cyto-protective signal process, and H₂S-based therapy is considered as the next generation of promising therapeutic strategies for many biomedical applications, such as the treatment of cardiovascular disease. Through electrospinning of polycaprolactone (PCL) containing JK1, a novel pH-controllable H₂S donor, nanofibers with H₂S releasing function, PCL-JK1, are fabricated. This fibrous scaffold showed a pH-dependent H₂S releasing behavior, i.e., lower pH induced greater and faster H₂S release. In addition, the H₂S release of JK1 was prolonged by the fibrous matrix as shown by decreased releasing rates compared to JK1 in solutions. In addition, in vitro studies indicated that PCL-JK1 exhibited excellent cyto-compatibility, similar to PCL fibers. Finally, we investigated PCL-JK1 as a wound dressing toward a cutaneous wound model in vivo and found that PCL-JK1 could significantly enhance the wound repair and regeneration compared with the control PCL scaffold, likely due to the release of H₂S, which results in a broad range of physiologically protective functions toward the wound.

Effect of endotoxemia in mice genetically deficient in cystathionine-γ-lyase, cystathionine-β-synthase or 3-mercaptopyruvate sulfurtransferase

Hydrogen sulfide (H₂S) has been proposed to exert pro- as well as anti-inflammatory effects in various models of critical illness. In this study, we compared bacterial lipopolysaccharide (LPS)-induced changes in inflammatory mediator production, indices of multiple organ injury and survival in wild-type (WT) mice and in mice with reduced expression of one of the three H₂S-producing enzymes, cystathionine-γ-lyase (CSE), cystathionine-β-synthase (CBS) or 3-mercaptopyruvate sulfurtransferase (3MST). Mice were injected intraperitoneally (i.p.) with LPS (10 mg/kg). After 6 h, the animals were sacrificed, blood and organs were collected and the following parameters were evaluated: blood urea nitrogen (BUN) levels in blood, myeloperoxidase (MPO) and malondialdehyde (MDA) in the lung, cytokine levels in plasma and the expression of the three H₂S-producing enzymes (CBS, CSE and 3MST) in the spleen, lung, liver and kidney. LPS induced a tissue-dependent upregulation of some of the H₂S-producing enzymes in WT mice (upregulation of CBS in the spleen, upregulation of 3MST in the liver and upregulation of CBS, CSE and 3MST in the lung). Moreover, LPS impaired glomerular function, as evidenced by increased BUN levels. Renal impairment was comparable in the CSE^−/− and Δ3MST mice after LPS challenge; however, it was attenuated in the CBS^+/− mice. MPO levels (an index of neutrophil infiltration) and MDA levels (an index of oxidative stress) in lung homogenates were significantly increased in response to LPS; these effects were similar in the WT, CBS^+/−, CSE^−/− and Δ3MST mice; however, the MDA levels tended to be lower in the CBS^+/− and CSE^−/− mice. LPS induced significant increases in the plasma levels of multiple cytokines [tumor necrosis factor (TNF)α, interleukin (IL)-1β, IL-6, IL-10, IL-12 and interferon (IFN)γ] in plasma; TNFα, IL-10 and IL-12 levels tended to be lower in all three groups of animals expressing lower levels of H₂S-producing enzymes. The survival rates after the LPS challenge did not show any significant differences between the four animal groups tested. Thus, the findings of this study indicate that a deficiency in 3MST does not significantly affect endotoxemia, while a deficiency in CBS or CSE slightly ameliorates the outcome of LPS-induced endotoxemia in vivo.

Decoding the vasoregulatory activities of bile acid-activated receptors in systemic and portal circulation: role of gaseous mediators

Bile acids are end products of cholesterol metabolism generated in the liver and released in the intestine. Primary and secondary bile acids are the result of the symbiotic relation between the host and intestinal microbiota. In addition to their role in nutrient absorption, bile acids are increasingly recognized as regulatory signals that exert their function beyond the intestine by activating a network of membrane and nuclear receptors. The best characterized of these bile acid-activated receptors, GPBAR1 (also known as TGR5) and the farnesosid-X-receptor (FXR), have also been detected in the vascular system and their activation mediates the vasodilatory effects of bile acids in the systemic and splanchnic circulation. GPBAR1, is a G protein-coupled receptor, that is preferentially activated by lithocholic acid (LCA) a secondary bile acid. GPBAR1 is expressed in endothelial cells and liver sinusoidal cells (LSECs) and responds to LCA by regulating the expression of both endothelial nitric oxide synthase (eNOS) and cystathionine-γ-lyase (CSE), an enzyme involved in generation of hydrogen sulfide (H₂S). Activation of CSE by GPBAR1 ligands in LSECs is due to genomic and nongenomic effects, involves protein phosphorylation, and leads to release of H₂S. Despite that species-specific effects have been described, vasodilation caused by GPBAR1 ligands in the liver microcirculation and aortic rings is abrogated by inhibition of CSE but not by eNOS inhibitor. Vasodilation caused by GPBAR1 (and FXR) ligands also involves large conductance calcium-activated potassium channels likely acting downstream to H₂S. The identification of GPBAR1 as a vasodilatory receptor is of relevance in the treatment of complex disorders including metabolic syndrome-associated diseases, liver steatohepatitis, and portal hypertension.

The novel H2 S donor 4-carboxy-phenyl isothiocyanate inhibits mast cell degranulation and renin release by decreasing intracellular calcium

BACKGROUND AND PURPOSE

Hydrogen sulfide (H₂ S) modulates many pathophysiological processes, including inflammation and allergic reactions, in which mast cells act as major effector cells. IgE receptor (FcεRI) cross linking leads to an increase in intracellular calcium ([Ca⁺² ]_i ), a critical step in mast cell degranulation. The aim of this study was to investigate the role of H₂ S in [Ca⁺² ]_i -dependent mast cell activation.

EXPERIMENTAL APPROACH

We investigated the effects of H₂ S, either endogenously produced or released by the slow H₂ S donor 4-carboxy-phenyl isothiocyanate (PhNCS-COOH), on antigenic- and non-antigenic degranulation of native murine mast cells, and human and rat (RBL-2H3) mast cell lines. We measured the release of specific mast cell degranulation markers (β-hexosaminidase and renin), as well as changes in [Ca⁺² ]_i and phosphorylation of proteins downstream of FcεRI activation.

KEY RESULTS

Endogenously produced H₂ S inhibited antigen-induced degranulation in RBL-2H3. Similarly, H₂ S released by PhNCS-COOH (10-300 μM) reduced, in a concentration-dependent manner, antigenic and non-antigenic degranulation and renin release in all mast cell types. Notably, PhNCS-COOH also prevented in a concentration-dependent mode the increase in [Ca⁺² ]_i elicited by Ca⁺² ionophore, thapsigargin and FcεRI activation. Moreover, PhNCS-COOH attenuated the phosphorylation of Syk, cPLA-2 and PLCγ1 in antigen-stimulated RBL-2H3 cells.

CONCLUSION AND IMPLICATIONS

Collectively, our results demonstrate that, by attenuating the phosphorylation of proteins downstream of FcεRI cross-linking on mast cells, H₂ S diminishes [Ca⁺² ]_i availability and thus mast cell degranulation and renin release. These findings suggest that PhNCS-COOH could be a strategic therapeutic tool in mast cell-mediated allergic conditions.

Non-steroidal Anti-inflammatory Drug Induced Injury to the Small Intestine

Non-steroidal anti-inflammatory drug (NSAIDs) induced enteropathy represents an important complication of one of the most commonly used drugs worldwide. Due to previous diagnostics difficulties the real prevalence of this disease was underestimated for a long time. The pathogenesis of NSAID-enteropathy is more multifactorial and complex than formerly assumed but has still not been fully uncovered. A combination of the local and systemic effect plays an important role in pathogenesis. Thanks to novel enteroscopy methods (wireless capsule endoscopy, double balloon enteroscopy), small bowel lesions are described in a substantial section of NSAID users although most are clinically asymptomatic. The other non-invasive tests (small bowel permeability, faecal calprotectin, scintigraphy using faecal excretion of 111-indium-labelled leukocytes etc.) proposed for diagnostics are not generally used in clinical practice, mainly because of their non-specificity. Despite intensive research into possible treatment, the main measure for patients with NSAID-enteropathy is still withdrawal of NSAIDs. Double balloon enteroscopy plays an important role in the treatment of complications (bleeding, strictures).

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.

Screening of a composite library of clinically used drugs and well-characterized pharmacological compounds for cystathionine β-synthase inhibition identifies benserazide as a drug potentially suitable for repurposing for the experimental therapy of colon cancer

Cystathionine-β-synthase (CBS) has been recently identified as a drug target for several forms of cancer. Currently no potent and selective CBS inhibitors are available. Using a composite collection of 8871 clinically used drugs and well-annotated pharmacological compounds (including the LOPAC library, the FDA Approved Drug Library, the NIH Clinical Collection, the New Prestwick Chemical Library, the US Drug Collection, the International Drug Collection, the ‘Killer Plates’ collection and a small custom collection of PLP-dependent enzyme inhibitors), we conducted an in vitro screen in order to identify inhibitors for CBS using a primary 7-azido-4-methylcoumarin (AzMc) screen to detect CBS-derived hydrogen sulfide (H₂S) production. Initial hits were subjected to counterscreens using the methylene blue assay (a secondary assay to measure H₂S production) and were assessed for their ability to quench the H₂S signal produced by the H₂S donor compound GYY4137. Four compounds, hexachlorophene, tannic acid, aurintricarboxylic acid and benserazide showed concentration-dependent CBS inhibitory actions without scavenging H₂S released from GYY4137, identifying them as direct CBS inhibitors. Hexachlorophene (IC₅₀: ∼60 μM), tannic acid (IC₅₀: ∼40 μM) and benserazide (IC₅₀: ∼30 μM) were less potent CBS inhibitors than the two reference compounds AOAA (IC₅₀: ∼3 μM) and NSC67078 (IC₅₀: ∼1 μM), while aurintricarboxylic acid (IC₅₀: ∼3 μM) was equipotent with AOAA. The second reference compound NSC67078 not only inhibited the CBS-induced AzMC fluorescence signal (IC₅₀: ∼1 μM), but also inhibited with the GYY4137-induced AzMC fluorescence signal with (IC₅₀ of ∼6 μM) indicative of scavenging/non-specific effects. Hexachlorophene (IC₅₀: ∼6 μM), tannic acid (IC₅₀: ∼20 μM), benserazide (IC₅₀: ∼20 μM), and NSC67078 (IC₅₀: ∼0.3 μM) inhibited HCT116 colon cancer cells proliferation with greater potency than AOAA (IC₅₀: ∼300 μM). In contrast, although a CBS inhibitor in the cell-free assay, aurintricarboxylic acid failed to inhibit HCT116 proliferation at lower concentrations, and stimulated cell proliferation at 300 μM. Copper-containing compounds present in the libraries, were also found to be potent inhibitors of recombinant CBS; however this activity was due to the CBS inhibitory effect of copper ions themselves. However, copper ions, up to 300 μM, did not inhibit HCT116 cell proliferation. Benserazide was only a weak inhibitor of the activity of the other H₂S-generating enzymes CSE and 3-MST activity (16% and 35% inhibition at 100 μM, respectively) in vitro. Benserazide suppressed HCT116 mitochondrial function and inhibited proliferation of the high CBS-expressing colon cancer cell line HT29, but not the low CBS-expressing line, LoVo. The major benserazide metabolite 2,3,4-trihydroxybenzylhydrazine also inhibited CBS activity and suppressed HCT116 cell proliferation in vitro. In an in vivo study of nude mice bearing human colon cancer cell xenografts, benserazide (50 mg/kg/day s.q.) prevented tumor growth. In silico docking simulations showed that benserazide binds in the active site of the enzyme and reacts with the PLP cofactor by forming reversible but kinetically stable Schiff base-like adducts with the formyl moiety of pyridoxal. We conclude that benserazide inhibits CBS activity and suppresses colon cancer cell proliferation and bioenergetics in vitro, and tumor growth in vivo. Further pharmacokinetic, pharmacodynamic and preclinical animal studies are necessary to evaluate the potential of repurposing benserazide for the treatment of colorectal cancers.

Targeting the transsulfuration-H2S pathway by FXR and GPBAR1 ligands in the treatment of portal hypertension

Cirrhosis is a end-stage disease of the liver in which fibrogenesis, angiogenesis and distortion of intrahepatic microcirculation lead to increased intrahepatic resistance to portal blood flow, a condition known as portal hypertension. Portal hypertension is maintained by a variety of molecular mechanisms including sinusoidal endothelial cells (LSECs) hyporeactivity, activation of hepatic stellate cells (HSCs), reduction in hepatic endothelial nitric oxide synthase (eNOS) activity along with increased eNOS-derived NO generation in the splanchnic and systemic circulations. A reduction of the expression/function of the two major hydrogen sulfide (H2S)-producing enzymes, cystathionine γ-lyase (CSE) and cystathionine β-synthase (CBS), has also been demonstrated. A deficit in the transsulfuration pathway leading to the accumulation of homocysteine might contribute to defective generation of H2S and endothelial hyporeactivity. Bile acids are ligands for nuclear receptors, such as farnesoid X receptor (FXR), and G-protein-coupled receptors (GPCRs), such as the G-protein bile acid receptor 1 (GPBAR1). FXR and GPBAR1 ligands regulate the expression/activity of CSE by both genomic and non-genomic effects and have been proved effective in protecting against endothelial dysfunction observed in rodent models of cirrhosis. GPBAR1, a receptor for secondary bile acids, is selectively expressed by LSECs and its activation increases the expression of CSE and attenuates the production of endotelin-1, a potent vasoconstrictor agent. In vivo GPBAR1 ligand attenuates the imbalance between vasodilatory and vaso-constricting agents, making GPBAR1 a promising target in the treatment of portal hypertension.

Perfusion of Isolated Carotid Sinus With Hydrogen Sulfide Attenuated the Renal Sympathetic Nerve Activity in Anesthetized Male Rats

The purpose of the present study was to define the indirect central effect of hydrogen sulfide (H2S) on baroreflex control of sympathetic outflow. Perfusing the isolated carotid sinus with sodium hydrosulfide (NaHS), a H2S donor, the effect of H2S was measured by recording changes of renal sympathetic nerve activity (RSNA) in anesthetized male rats. Perfusion of isolated carotid sinus with NaHS (25, 50, 100 μmol/l) dose and time-dependently inhibited sympathetic outflow. Preconditioning of glibenclamide (20 µmol/l), a ATP-sensitive K+ channels (KATP) blocker, the above effect of NaHS was removed. With 1, 4-dihydro-2, 6-dimethyl-5-nitro-4-(2-[trifluoromethyl] phenyl) pyridine-3-carboxylic acid methyl ester (Bay K8644, 500 nmol/l) pretreatment, which is an agonist of L-calcium channels, the effect of NaHS was eliminated. Perfusion of cystathionine γ-lyase (CSE) inhibitor, DL-propargylglycine (PPG, 200 μmol/l), increased sympathetic outflow. The results show that exogenous H2S in the carotid sinus inhibits sympathetic outflow. The effect of H2S is attributed to opening KATP channels and closing the L-calcium channels.

A novel hydrogen sulfide prodrug, SG1002, promotes hydrogen sulfide and nitric oxide bioavailability in heart failure patients

Recent studies demonstrate robust molecular cross talk and signaling between hydrogen sulfide (H2 S) and nitric oxide (NO). Heart failure (HF) patients are deficient in both H2 S and NO, two molecules that are critical for cardiovascular homeostasis. A phase I clinical trial of a novel H2 S prodrug (SG1002) was designed to assess safety and changes in H2 S and NO bioavailability in healthy and HF subjects. Healthy subjects (n = 7) and heart failure patients (n = 8) received oral SG1002 treatment in escalating dosages of 200, 400, and 800 mg twice daily for 7 days for each dose. Safety and tolerability were assessed by physical examination, vital signs, and ECG analysis. Plasma samples were collected during a 24-h period each week for H2 S and NO analysis. BNP and glutathione levels were analyzed as markers of cardiac health and redox status. Administration of SG1002 resulted in increased H2 S levels in healthy subjects. We also observed increased H2 S levels in HF subjects following 400 mg SG1002. Nitrite, a metabolite of NO, was increased in both healthy and HF patients receiving 400 mg and 800 mg SG1002. HF subjects treated with SG1002 displayed stable drug levels over the course of the trial. SG1002 was safe and well tolerated at all doses in both healthy and HF subjects. These data suggest that SG1002 increases blood H2 S levels and circulating NO bioavailability. The finding that SG1002 attenuates increases in BNP in HF patients suggests that this novel agent warrants further study in a larger clinical study.

Korean red ginseng ameliorated experimental pancreatitis through the inhibition of hydrogen sulfide in mice

AIM

Effective therapy to treat acute pancreatitis (AP) or to prevent its recurrence/complication is still not available. Based on previous results that suggest that: i) hydrogen sulfide (H2S) levels were significantly increased in pancreatitis and gastritis and ii) Korean red ginseng (KRG) efficiently attenuated Helicobacter pylori-associated gastritis through the suppressive actions of H2S, we hypothesized that KRG can ameliorate experimental pancreatitis through suppression of H2S generation.

METHODS

C57BL/6 mice were pre-administered KRG and then subjected to cerulein injection or pancreatic duct ligation (PDL) to induce pancreatitis. Blood and pancreas tissues were collected and processed to measure serum levels of amylase, lipase and myeloperoxidase and the concentration of H2S and the levels of various inflammatory cytokine in pancreatic tissues of mice with induced AP.

RESULTS

KRG significantly inhibited NaHS-induced COX-2 and TNF-α mRNA in pancreatic cells, but dl-propargylglycine did not. KRG ameliorated cerulein-induced edematous pancreatitis accompanied with significant inactivation of NF-κB and JNK in pancreatic tissues of C57BL/6 mice (p < 0.001) and also significantly ameliorated PDL-induced necrotizing pancreatitis (p<0.01); in both conditions, the significant suppression of H2S resulting from KRG pretreatment afforded rescuing outcomes. Along with suppressed levels of H2S consequent to depressed expressions of CBS and CSE mRNA, KRG administration efficiently decreased the serum level of amylase, lipase, and myeloperoxidase and the expression of inflammatory cytokines in animal models of mild or severe AP.

CONCLUSIONS

These results provide evidence for the preventive and therapeutic roles of KRG against AP mediated by H2S suppression.

The CBS/CSE system: a potential therapeutic target in NAFLD?

Non-alcoholic fatty liver disease (NAFLD) is a broad spectrum liver disorder diagnosed in patients without a history of alcohol abuse. NAFLD is growing at alarming rates worldwide. Its pathogenesis is complex and incompletely understood. The cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE) system regulates homocysteine and cysteine metabolism and contributes to endogenous hydrogen sulfide (H2S) biosynthesis. This review summarizes our current understanding of the hepatic CBS/CSE system, and for the first time, positions this system as a potential therapeutic target in NAFLD. As will be discussed, the CBS/CSE system is highly expressed and active in the liver. Its dysregulation, presenting as alterations in circulating homocysteine and (or) H2S levels, has been reported in NAFLD patients and in NAFLD-associated co-morbidities such as obesity and type 2 diabetes. Intricate links between the CBS/CSE system and a number of metabolic and stress related molecular mediators have also emerged. Various dysfunctions in the hepatic CBS/CSE system have been reported in animal models representative of each NAFLD spectrum. It is anticipated that a newfound appreciation for the hepatic CBS/CSE system will emerge that will improve our understanding of NAFLD pathogenesis, and give rise to new prospective targets for management of this disorder.

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.

Gastroprotective effects of thymol on acute and chronic ulcers in rats: The role of prostaglandins, ATP-sensitive K(+) channels, and gastric mucus secretion

Thymol, a monoterpene phenol derivative of cymene, is found in abundance in the essential oils of Thymus, Origanum, and Lippia species. The present study investigated the gastroprotective actions of thymol (10, 30, and 100 mg/kg, p.o.) in the acute (ethanol- and nonsteroidal anti-inflammatory drug-induced ulcers) and chronic (acetic acid-induced ulcers) ulcer models in rats. Some of the mechanisms underlying to the gastroprotective effect of thymol were investigated in the ethanol-induced ulcer model. Gastric secretion parameters (volume, pH, and total acidity) were also evaluated by the pylorus ligature model, and the mucus in the gastric content was determined. The anti-Helicobacter pylori activity of thymol was performed using the agar-well diffusion method. Thymol (10, 30, and 100 mg/kg) produced dose dependent reduction (P < 0.01) on the total lesion area in the ethanol-induced ulcer model. The gastroprotective response caused by thymol (30 mg/kg) was significantly attenuated (P < 0.001) by intraperitoneal treatment of rats with indomethacin (a non-selective inhibitor of cyclo-oxygenase, 10 mg/kg) and glibenclamide (ATP-sensitive K(+) channel blocker, 10 mg/kg), but not by DL-Propargylglycine (PAG, a cystathionine-γ-lyase inhibitor, 25 mg/kg) and Nw-nitro-L-arginine methyl ester hydrochloride (L-NAME, a non-selective inhibitor of nitric oxide synthase, 70 mg/kg). Thymol (30 and 100 mg/kg) also reduced the ulcer index (P < 0.05) and the total lesion area (P < 0.001) in the indomethacin- and acetic-acid-induced ulcer models, respectively. In the model pylorus ligature, the treatment with thymol failed to significantly change the gastric secretion parameters. However, after treatment with thymol (30 and 100 mg/kg), there was a significant increase (P < 0.01) in mucus production. Thymol no showed anti-H. pylori activity in vitro. Collectively, the present results provide convincing evidence that thymol displays gastroprotective actions on the acute and chronic ulcer models through mechanisms that involve increased in the amount of mucus, prostaglandins, and ATP-sensitive K(+) channels.

Reversal of Endothelial Dysfunction by GPBAR1 Agonism in Portal Hypertension Involves a AKT/FOXOA1 Dependent Regulation of H2S Generation and Endothelin-1

Background

GPBAR1 is a bile acids activated receptor expressed in entero-hepatic tissues. In the liver expression of GPBAR1 is restricted to sinusoidal and Kuppfer cells. In the systemic circulation vasodilation caused by GPBAR1 agonists is abrogated by inhibition of cystathione-γ-liase (CSE), an enzyme essential to the generation of hydrogen sulfide (H₂S), a vasodilatory agent. Portal BAR501 is a semisynthetic bile acid derivative endowed with a potent and selective agonistic activity toward GPBAR1.

Methods

Cirrhosis was induced in mice by carbon tetrachloride (CCL₄) administration for 9 weeks. Liver endothelial dysfunction was induced by feeding wild type and Gpbar1^-/- mice with methionine for 4 weeks. In both models, mice were administered BAR501, 15 mg/kg/day.

Results

By transactivation assay we demonstrate that BAR501 is a selective GPBAR1 agonist devoid of any FXR agonistic activity. In naïve rats, BAR501 effectively reduced hepatic perfusion pressure and counteracted the vasoconstriction activity of norepinephrine. In the CCl₄ model, 9 weeks treatment with BAR501 effectively protected against development of endothelial dysfunction by increasing liver CSE expression and activity and by reducing endothelin (ET)-1 gene expression. In mice feed methionine, treatment with BAR501 attenuated endothelial dysfunction and caused a GPBAR1-dependent regulation of CSE. Using human liver sinusoidal cells, we found that modulation of CSE expression/activity is mediated by both genomic (recruitment of CREB to CRE in the CSE promoter) and non-genomic effects, involving a Akt-dependent phosporylation of CSE and endothelial nitric oxide (NO) synthase (eNOS). BAR501, phosphorylates FOXO1 and inhibits ET-1 transcription in liver sinusoidal cells.

Conclusions

BAR501, a UDCA-like GPBAR1 agonist, rescues from endothelial dysfunction in rodent models of portal hypertension by exerting genomic and non-genomic effects on CSE, eNOS and ET-1 in liver sinusoidal cells.

Gastroprotective effect of diligustilide isolated from roots of Ligusticum porteri coulter & rose (Apiaceae) on ethanol-induced lesions in rats

ETHNOPHARMACOLOGICAL RELEVANCE

The rhizome of Ligusticum porteri Coulter& Rose (LP) has been traditionally used by the ethnic group Raramuri in the North of México for treatment of diabetes, tuberculosis, stomachaches, diarrhea and ritual healing ceremonies. It is use as antiulcer remedy has been extended to all Mexico.

AIM OF THE STUDY

To evaluate the gastroprotective activity of LP organic extracts and the major natural product diligustilide (DLG),using as experimental model the inhibition of the ethanol-induced lesions in rats.

MATERIALS AND METHODS

Gastric ulcers were induced by intragastric instillation of absolute ethanol (1 mL). We tested the gastroprotective activity of the organic extracts of LP and the pure compound DLG. The ulcer index (UI) was determined to measure the activity. In order to elucidate the action mechanism of DLG the animals were treated with L-NAME, N-ethylmalemide, Forskolin, 2',5'-dideoxyadenosine, Indomethacin, Glibenclameide, Diazoxide, NaHS and DL-Propargylglycine. The pylorus-ligated rat model was used to measure gastric secretion.

RESULTS

The oral administration of organic extracts of Ligusticum porteri showed gastroprotective effect at 30 mg/Kg on ethanol induced gastric lesions; hexane and dichloromethane extracts were the most active. DLG was the major compound in the hexane extract. This compound at 10 mg/kg prevented significantly the gastric injuries induced by ethanol. The alkylation of endogenous non-protein-SH groups with N-ethylmaleimide abolished the gastroprotective effect of DLG and blocking the formation of endogenous prostaglandins by the pretreatment with indomethacin attenuated the gastroprotective effect of DLG.

CONCLUSION

The gastroprotective activity demonstrated in this study tends to support the ethnomedical use of Ligusticum porteri roots. DLG, isolated as major compound of this medicinal plant has a clear gastroprotective effect on the ethanol-induced gastric lesions. The results suggest that the antiulcer activity of DLG depends on the participation of the endogenous non-protein -SH groups and prostaglandins.

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

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

H2S-induced S-sulfhydration of pyruvate carboxylase contributes to gluconeogenesis in liver cells

BACKGROUND

Cystathionine gamma-lyase (CSE)-derived hydrogen sulfide (H(2)S) possesses diverse roles in the liver, affecting lipoprotein synthesis, insulin sensitivity, and mitochondrial biogenesis. H(2)S S-sulfhydration is now proposed as a major mechanism for H(2)S-mediated signaling. Pyruvate carboxylase (PC) is an important enzyme for gluconeogenesis. S-sulfhydration regulation of PC by H(2)S and its implication in gluconeogenesis in the liver have been unknown.

METHODS

Gene expressions were analyzed by real-time PCR and western blotting, and protein S-sulfhydration was assessed by both modified biotin switch assay and tag switch assay. Glucose production and PC activity was measured with coupled enzyme assays, respectively.

RESULTS

Exogenously applied H(2)S stimulates PC activity and gluconeogenesis in both HepG2 cells and mouse primary liver cells. CSE overexpression enhanced but CSE knockout reduced PC activity and gluconeogenesis in liver cells, and blockage of PC activity abolished H(2)S-induced gluconeogenesis. H(2)S had no effect on the expressions of PC mRNA and protein, while H(2)S S-sulfhydrated PC in a dithiothreitol-sensitive way. PC S-sulfhydration was significantly strengthened by CSE overexpression but attenuated by CSE knockout, suggesting that H(2)S enhances glucose production through S-sulfhydrating PC. Mutation of cysteine 265 in human PC diminished H(2)S-induced PC S-sulfhydration and activity. In addition, high-fat diet feeding of mice decreased both CSE expression and PC S-sulfhydration in the liver, while glucose deprivation of HepG2 cells stimulated CSE expression.

CONCLUSIONS

CSE/H(2)S pathway plays an important role in the regulation of glucose production through S-sulfhydrating PC in the liver.

GENERAL SIGNIFICANCE

Tissue-specific regulation of CSE/H(2)S pathway might be a promising therapeutic target of diabetes and other metabolic syndromes.

Protective effect of hydrogen sulfide on TNF-α and IFN-γ-induced injury of intestinal epithelial barrier function in Caco-2 monolayers

BACKGROUND AND AIM

Studies have verified the protective effect of Hydrogen Sulfide (H2S) on gastric ulcer and ulcerative colitis, but the mechanisms are not fully illustrated. In this study, the possible protective effect of H2S on TNF-α/IFN-γ induced barrier dysfunction was investigated in Caco-2 cell monolayers.

METHOD

The barrier function of Caco-2 monolayers was evaluated by measuring trans-epithelial electrical resistance (TEER) and FITC-Dextran 4 kDa (FD-4) trans-membrane flux. ZO-1 and Occludin were chosen as markers of the localization of tight junction (TJ) proteins for immunofluorescence. The expression of MLCK and phosphorylation level of myosin light chain (MLC) were measured by immunoblotting. The activation of NF-kB p65 was analyzed by EMSA and immunofluorescence.

RESULTS

NaHS at 500 uM significantly attenuated TNF-α/IFN-γ-indueced Caco-2 monolayer barrier injury. The increased expression of MLCK and increased phosphorylation level of MLC induced by TNF-α/IFN-γ was also inhibited significantly by NaHS. Additionally, NaHS inhibited TNF-α/IFN-γ induced activation and nuclear translocation of NF-kB p65.

CONCLUSION

The present study reveals the protective effect of H2S on TNF-α and IFN-γ-induced injury of intestinal epithelial barrier function in Caco-2 monolayers and suggests that the suppression of MLCK-P-MLC signaling mediated by NF-kB P65 might be one of the mechanisms underlying the protective effect of H2S.

Chemical probes for molecular imaging and detection of hydrogen sulfide and reactive sulfur species in biological systems

Hydrogen sulfide (H2S), a gaseous species produced by both bacteria and higher eukaryotic organisms, including mammalian vertebrates, has attracted attention in recent years for its contributions to human health and disease. H2S has been proposed as a cytoprotectant and gasotransmitter in many tissue types, including mediating vascular tone in blood vessels as well as neuromodulation in the brain. The molecular mechanisms dictating how H2S affects cellular signaling and other physiological events remain insufficiently understood. Furthermore, the involvement of H2S in metal-binding interactions and formation of related RSS such as sulfane sulfur may contribute to other distinct signaling pathways. Owing to its widespread biological roles and unique chemical properties, H2S is an appealing target for chemical biology approaches to elucidate its production, trafficking, and downstream function. In this context, reaction-based fluorescent probes offer a versatile set of screening tools to visualize H2S pools in living systems. Three main strategies used in molecular probe development for H2S detection include azide and nitro group reduction, nucleophilic attack, and CuS precipitation. Each of these approaches exploits the strong nucleophilicity and reducing potency of H2S to achieve selectivity over other biothiols. In addition, a variety of methods have been developed for the detection of other reactive sulfur species (RSS), including sulfite and bisulfite, as well as sulfane sulfur species and related modifications such as S-nitrosothiols. Access to this growing chemical toolbox of new molecular probes for H2S and related RSS sets the stage for applying these developing technologies to probe reactive sulfur biology in living systems.

Possible mechanisms of action of Caesalpinia pyramidalis against ethanol-induced gastric damage

ETHNOPHARMACOLOGICAL RELEVANCE

Caesalpinia pyramidalis Tul. (Fabaceae), known as "catingueira", is an endemic tree of the Northeast region of Brazil. This plant, mainly inner bark and flowers, has been used in traditional medicine to treat gastritis, heartburn, indigestion, stomachache, dysenteries, and diarrheas.

MATERIALS AND METHODS

The ethanol extract of C. pyramidalis inner bark was used in rats via oral route, at the doses of 30, 100, and 300 mg/kg, in the ethanol-induced ulcer model and some of the mechanisms underlying to the gastroprotective effect of this plant investigated.

RESULTS

The ethanol extract of C. pyramidalis inner bark (100 mg/kg) produced reduction (P < 0.001) on the total lesion area in the ethanol-induced gastric damage. The gastroprotective response caused by the ethanol extract (100 mg/kg) was significantly attenuated (P < 0.05) by intraperitoneal treatment of rats with DL-Propargylglycine (PAG, a cystathionine-γ-lyase inhibitor; 25 mg/kg), but not by Nw-nitro-L-arginine methyl ester hydrochloride (L-NAME, an inhibitor of nitric oxide synthase; 70 mg/kg), and confirmed by microscopic evidence. The ethanol extract significantly decreased the number of mucosal mast cells compared to vehicle-treated group. The inflammatory cells of the ethanol extract (100 mg/kg)-treated ulcerated rats exhibited an upregulation of interleukin (IL)-4 protein expression and downregulation of inducible nitric oxide synthase (iNOS) expression, observed by immunohistochemistry and flow cytometer.

CONCLUSIONS

The present results suggest that the ethanol extract of C. pyramidalis produced dose-related gastroprotective response on ethanol-induce ulcer in rats through mechanisms that involved an interaction with endogenous hydrogen sulfide and reduction of inflammatory process with imbalance between pro-inflammatory and anti-inflammatory mediators, supporting the popular usage of this plant.

Protective Factors of the Gastric and Duodenal Mucosa: An Overview

The structural and functional integrity of the gastric and duodenal mucosa represents equilibrium between aggressive factors and protective mechanisms. Mucus-buffers-phospholipid layer as pre-epithelial barrier, enhanced by prostaglandins and epidermal growth factor, remains a vanguard of mucosal protection. It maintains a neutral pH at the surface epithelial luminal interface, facing luminal pH dropping to 1.0, i.e., hydrogen ion concentration gradient equal 1,000,000. The surface epithelial cells, elaborating mucins, buffers, phospholipids, prostaglandins, trefoil peptides, peptide growth factor and their receptors, heat shock proteins, cathelicidins, and β-defensins form the second line of defense. Endothelium exerts mucosal protection through production of potent vasodilators like nitric oxide and prostacyclins and through release of angiogenic growth factors, securing adequate blood flow and representing the third and an ultimate line of mucosal protection. This microcirculation is instrumental for supply of oxygen, nitric oxide, hydrogen sulfide and removal of ad hoc generated toxic substances as well as for continuous mucosal cell renewal from progenitor cells, secured by growth factors accompanied by survivin preventing early apoptosis.

[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.

Hydrogen Sulfide Levels and Nuclear Factor-Erythroid 2-Related Factor 2 (NRF2) Activity Are Attenuated in the Setting of Critical Limb Ischemia (CLI)

Background

Cystathionine γ-lyase, cystathionine β-synthase, and 3-mercaptopyruvate sulfurtransferase are endogenous enzymatic sources of hydrogen sulfide (H₂S). Functions of H₂S are mediated by several targets including ion channels and signaling proteins. Nuclear factor-erythroid 2-related factor 2 is responsible for the expression of antioxidant response element–regulated genes and is known to be upregulated by H₂S. We examined the levels of H₂S, H₂S-producing enzymes, and nuclear factor-erythroid 2-related factor 2 activation status in skeletal muscle obtained from critical limb ischemia (CLI) patients.

Methods and Results

Gastrocnemius tissues were attained postamputation from human CLI and healthy control patients. We found mRNA and protein levels of cystathionine γ-lyase, cystathionine β-synthase, and 3-mercaptopyruvate sulfurtransferase were significantly decreased in skeletal muscle of CLI patients as compared to control. H₂S and sulfane sulfur levels were significantly decreased in skeletal muscle of CLI patients. We also observed significant reductions in nuclear factor-erythroid 2-related factor 2 activation as well as antioxidant proteins, such as Cu, Zn-superoxide dismutase, catalase, and glutathione peroxidase in skeletal muscle of CLI patients. Biomarkers of oxidative stress, such as malondialdehyde and protein carbonyl formation, were significantly increased in skeletal muscle of CLI patients as compared to healthy controls.

Conclusions

The data demonstrate that H₂S bioavailability and nuclear factor-erythroid 2-related factor 2 activation are both attenuated in CLI tissues concomitant with significantly increased oxidative stress. Reductions in the activity of H₂S-producing enzymes may contribute to the pathogenesis of CLI.

Hydrogen Sulfide as a Potential Therapeutic Target in Fibrosis

Hydrogen sulfide (H2S), produced endogenously by the activation of two major H2S-generating enzymes (cystathionine β-synthase and cystathionine γ-lyase), plays important regulatory roles in different physiologic and pathologic conditions. The abnormal metabolism of H2S is associated with fibrosis pathogenesis, causing damage in structure and function of different organs. A number of in vivo and in vitro studies have shown that both endogenous H2S level and the expressions of H2S-generating enzymes in plasma and tissues are significantly downregulated during fibrosis. Supplement with exogenous H2S mitigates the severity of fibrosis in various experimental animal models. The protective role of H2S in the development of fibrosis is primarily attributed to its antioxidation, antiapoptosis, anti-inflammation, proangiogenesis, and inhibition of fibroblasts activities. Future studies might focus on the potential to intervene fibrosis by targeting the pathway of endogenous H2S-producing enzymes and H2S itself.

NOSH-aspirin (NBS-1120), a dual nitric oxide and hydrogen sulfide-releasing hybrid, reduces inflammatory pain

The development of nitric oxide (NO)- and hydrogen sulfide (H₂S)-releasing nonsteroidal anti-inflammatory drugs (NSAIDs) has generated more potent anti-inflammatory drugs with increased safety profiles. A new hybrid molecule incorporating both NO and H₂S donors into aspirin (NOSH-aspirin) was recently developed. In the present study, the antinociceptive activity of this novel molecule was compared with aspirin in different models of inflammatory pain. It was found that NOSH-aspirin inhibits acetic acid-induced writhing response and carrageenan (Cg)-induced inflammatory hyperalgesia in a dose-dependent (5–150 μmol/kg, v.o.) manner, which was superior to the effect of the same doses of aspirin. NOSH-aspirin’s antinociceptive effect was also greater and longer compared to aspirin upon complete Freund’s adjuvant (CFA)-induced inflammatory hyperalgesia. Mechanistically, NOSH-aspirin, but not aspirin, was able to reduce the production/release of interleukin-1 beta (IL-1β) during Cg-induced paw inflammation. Furthermore, NOSH-aspirin, but not aspirin, reduced prostaglandin E₂-induced hyperalgesia, which was prevented by treatment with a ATP-sensitive potassium channel (K_ATP) blocker (glibenclamide; glib.). Noteworthy, the antinociceptive effect of NOSH-aspirin was not associated with motor impairment. The present results indicate that NOSH-aspirin seems to present greater potency than aspirin to reduce inflammatory pain in several models. The enhanced effects of NOSH-aspirin seems to be due to its ability to reduce the production of pronociceptive cytokines such as IL-1 β and directly block hyperalgesia caused by a directly acting hyperalgesic mediator in a mechanism dependent on modulation of K_ATP channels. In conclusion, we would like to suggest that NOSH-aspirin represents a prototype of a new class of analgesic drugs with more potent effects than the traditional NSAID, aspirin.

Hydrogen sulfide improves resuscitation via non-hibernatory mechanisms in a porcine shock model

BACKGROUND

Hydrogen sulfide (H2S) has been demonstrated to induce a "suspended animation-like" state in rodent models by reversible inhibition of cellular respiration and marked metabolic suppression and has been proposed as a potential pharmacologic adjunct to resuscitation from shock states. There are few data currently available about the mechanisms and efficacy of H2S in larger animals or humans. We examined H2S as a pharmacologic adjunct to resuscitation in a porcine model of severe traumatic shock.

METHODS

Twenty-one adult swine were assigned to three study arms: sham, H2S, and saline vehicle controls (SC). All pigs underwent laparotomy and instrumentation, and the two study arms then underwent a 35% controlled hemorrhage followed by 50 min of truncal ischemia via aortic cross-clamp. H2S (5 mg/kg) or saline was administered immediately before reperfusion, followed by 6 h of resuscitation. Resuscitation requirements, laboratory parameters, end-organ histology, and inflammatory product gene expression (by reverse transcription-polymerase chain reaction) were measured and compared between groups.

RESULTS

All animals survived to the 6-h postresuscitation time point. Both treatment arms demonstrated severe shock characterized by fluid and vasopressor requirements, metabolic acidosis, and hypotension compared with sham animals. Animals treated with H2S demonstrated significantly lower resuscitative requirements (total epinephrine 727 versus 3052 μg; P < 0.05), decreased fluid requirements, and lower serum lactate levels (7 versus 10 mmol/L) versus SC. Cardiac output was slightly decreased with H2S treatment but all other hemodynamic and metabolic parameters were equivalent between H2S and C groups. Serum liver and kidney biomarkers were unchanged, but administration of H2S was associated with a significant improvement in histopathologic liver and kidney injury scores compared with SC (both P < 0.05). Both study groups demonstrated significantly increased gene expression of hypoxia-inducible factor 1α and nitric oxide synthase (endogenous nitric oxide synthase, inducible nitric oxide synthase [iNOS]2, iNOS3) relative to sham animals. However, H2S was associated with increased expression of hypoxia-inducible factor 1α and decreased iNOS2 levels compared with SC.

CONCLUSIONS

Administration of H2S in a large-animal model of severe traumatic shock resulted in a significant decrease in resuscitative requirements, decreased metabolic acidosis, and less end-organ histologic injury compared with standard resuscitation. H2S did not induce profound metabolic suppression as seen in rodents, and appears to have alternative mechanisms of action in large animals.

Hydrogen sulfide attenuates cytokine production through the modulation of chromatin remodeling

Hydrogen sulfide (H2S) is an endogenous gaseous biological mediator, which regulates, among others, the oxidative balance of cells under normal physiological conditions, as well as in various diseases. Several previous studies have reported that H2S attenuates inflammatory mediator production. In this study, we investigated the role of H2S in chromatin modulation in an in vitro model of lipopolysaccharide (LPS)-induced inflammation and evaluated its effects on inflammatory cytokine production. Tamm-Horsfall protein 1 (THP-1) differentiated macrophages were pre-treated with sodium hydrosulfide (NaHS) (an H2S donor) at 0.01, 0.1, 0.5 or 1 mM for 30 min. To stimulate cytokine production, the cells were challenged with bacterial LPS (1 µg/ml) for 1, 4, 8 or 24 h. Histone H3 acetylation was analyzed by chromatin immunoprecipitation (ChIP), cytokine production was measured by ELISA and histone deacetylase (HDAC) activity was analyzed using a standard biochemical assay. H2S inhibited the production of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) in a concentration-dependent manner; it was most effective at the two highest concentrations used. This effect was associated with a decrease in histone H3 acetylation at the IL-6 and TNF-α promoters in the cells exposed to H2S or H2S + LPS. The findings of the present study suggest that H2S suppresses histone acetylation, which, in turn, inhibits chromatin openness, leading to a decrease in the gene transcription of various pro-inflammatory cytokines. Therefore, this mechanism may contribute to the previously demonstrated anti-inflammatory effects of H2S and various H2S donors.

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.

Hydrogen sulfide regulates the colonic motility by inhibiting both L-type calcium channels and BKCa channels in smooth muscle cells of rat colon

Objective

To examine the hypothesis that hydrogen sulfide (H₂S) regulates the colonic motility by modulating both L-type voltage-dependent calcium channels and large conductance Ca²⁺-activated K⁺ (BK_Ca) channels.

Methods

Immunohistochemistry was performed on rat colonic samples to investigate the localization of the H₂S-producing enzymes cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE). The contractions of proximal colonic smooth muscle were studied in an organ bath system. The whole-cell patch-clamp technique was used to record both L-type calcium currents (I_Ca,L) and BK_Ca currents in colonic smooth muscle cells (SMCs) isolated from male Wistar rats.

Results

Immunohistochemistry revealed the presence of CBS and CSE in mucosa, smooth muscle cells and myenteric neurons. The H₂S donor NaHS inhibited spontaneous contractions of the longitudinal muscle and circular muscle strips in a dose-dependent manner, and the inhibitory effects were not blocked by tetrodotoxin. NaHS inhibited the peak I_Ca,L in colonic SMCs at a membrane potential of 0 mV. The current-voltage (I-V) relationship of L-type calcium channels was modified by NaHS, and the peak of the I-V curve was shifted to the right. NaHS (200μΜ) evoked a significant rightward shift of the steady-state activation curve and inhibited the inactivation of L-type calcium channels. Furthermore, NaHS reversibly decreased the peak I_Ca,L in a dose-dependent manner. Likewise, BK_Ca channels were significantly inhibited by NaHS, and the addition of NaHS caused a time- and dose-dependent reduction in the BK_Ca current.

Conclusion

The relaxant effect of H₂S on colonic muscle strips may be associated with the direct inhibition of H₂S on L-type calcium channels. H₂S may be involved in the regulation of calcium homeostasis in colonic SMCs of rat colon.

Sensitization of P2X3 receptors by cystathionine β-synthetase mediates persistent pain hypersensitivity in a rat model of lumbar disc herniation

Lumbar disc herniation (LDH) is a major cause of discogenic low back pain and sciatica, but the underlying mechanisms remain largely unknown. Hydrogen sulfide (H₂S) is becoming recognized for its involvement in a wide variety of processes including inflammation and nociception. The present study was designed to investigate the roles of the H₂S signaling pathway in the regulation of expression and function of purinergic receptors (P2XRs) in dorsal root ganglion (DRG) neurons from rats with LDH. LDH was induced by implantation of autologous nucleus pulposus (NP), harvested from rat tail, in lumbar 5 and 6 spinal nerve roots. Implantation of autologous NP induced persistent pain hypersensitivity, which was partially reversed by an intrathecal injection of A317491, a potent inhibitor of P2X3Rs and P2X2/3Rs. The NP induced persistent pain hypersensitivity was associated with the increased expression of P2X3Rs, but not P2X1Rs and P2X2Rs, receptors in L5-6 DRGs. NP implantation also produced a 2-fold increase in ATP-induced intracellular calcium signals in DRG neurons when compared to those of controls (P < 0.05). Interestingly, NP implantation significantly enhanced expression of the endogenous hydrogen sulfide producing enzyme, cystathionine-β-synthetase (CBS). Systematic administration of O-(Carboxymethyl) hydroxylamine hemihydrochloride (AOAA), an inhibitor of CBS, suppressed the upregulation of P2X3R expression and the potentiation of ATP-induced intracellular calcium signals in DRG neurons (P < 0.05). Intrathecal injection of AOAA markedly attenuated NP induced- persistent pain hypersensitivity. Our results suggest that sensitization of P2X3Rs, which is likely mediated by CBS-H₂S signaling in primary sensory neurons, contributes to discogenic pain. Targeting CBS/H₂S-P2X3R signaling may represent a potential treatment for neuropathic pain caused by LDH.

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.

The therapeutic potential of cystathionine β-synthetase/hydrogen sulfide inhibition in cancer

SIGNIFICANCE

Cancer represents a major socioeconomic problem; there is a significant need for novel therapeutic approaches targeting tumor-specific pathways.

RECENT ADVANCES

In colorectal and ovarian cancers, an increase in the intratumor production of hydrogen sulfide (H2S) from cystathionine β-synthase (CBS) plays an important role in promoting the cellular bioenergetics, proliferation, and migration of cancer cells. It also stimulates peritumor angiogenesis inhibition or genetic silencing of CBS exerts antitumor effects both in vitro and in vivo, and potentiates the antitumor efficacy of anticancer therapeutics.

CRITICAL ISSUES

Recently published studies are reviewed, implicating CBS overexpression and H2S overproduction in tumor cells as a tumor-growth promoting "bioenergetic fuel" and "survival factor," followed by an overview of the experimental evidence demonstrating the anticancer effect of CBS inhibition. Next, the current state of the art of pharmacological CBS inhibitors is reviewed, with special reference to the complex pharmacological actions of aminooxyacetic acid. Finally, new experimental evidence is presented to reconcile a controversy in the literature regarding the effects of H2S donor on cancer cell proliferation and survival.

FUTURE DIRECTIONS

From a basic science standpoint, future directions in the field include the delineation of the molecular mechanism of CBS up-regulation of cancer cells and the delineation of the interactions of H2S with other intracellular pathways of cancer cell metabolism and proliferation. From the translational science standpoint, future directions include the translation of the recently emerging roles of H2S in cancer into human diagnostic and therapeutic approaches.

Anti-inflammatory and cytoprotective actions of hydrogen sulfide: translation to therapeutics

SIGNIFICANCE

There is a rapidly expanding body of evidence for important roles of hydrogen sulfide in protecting against tissue injury, reducing inflammation, and promoting repair. There is also growing evidence that H2S can be successfully exploited in drug development.

RECENT ADVANCES

H2S synthesis and degradation are regulated in circumstances of inflammation and injury so as to promote repair and re-establish homeostasis. Novel H2S-releasing drugs exhibit enhanced anti-inflammatory and pro-restorative effects, while having reduced adverse effects in many tissues.

CRITICAL ISSUES

H2S is a pleiotropic mediator, having effects on many elements in the inflammatory cascade and promoting the resolution of inflammation and injury. It also contributes significantly to mucosal defence in the gastrointestinal tract, and in host defence against infection. There is strong evidence that novel, H2S-based therapeutics are safe and effective in animal models, and several are progressing through human trials.

FUTURE DIRECTIONS

A better understanding of the physiological and pathophysiological roles of H2S continues to be restrained by the lack of simple, reliable methods for measurement of H2S synthesis, and the paucity of highly selective inhibitors of enzymes that participate in endogenous H2S synthesis. On the other hand, H2S donors show promise as therapeutics for several important indications.

Regulation of mitochondrial bioenergetic function by hydrogen sulfide. Part II. Pathophysiological and therapeutic aspects

Emerging work demonstrates the dual regulation of mitochondrial function by hydrogen sulfide (H2 S), including, at lower concentrations, a stimulatory effect as an electron donor, and, at higher concentrations, an inhibitory effect on cytochrome C oxidase. In the current article, we overview the pathophysiological and therapeutic aspects of these processes. During cellular hypoxia/acidosis, the inhibitory effect of H2 S on complex IV is enhanced, which may shift the balance of H2 S from protective to deleterious. Several pathophysiological conditions are associated with an overproduction of H2 S (e.g. sepsis), while in other disease states H2 S levels and H2 S bioavailability are reduced and its therapeutic replacement is warranted (e.g. diabetic vascular complications). Moreover, recent studies demonstrate that colorectal cancer cells up-regulate the H2 S-producing enzyme cystathionine β-synthase (CBS), and utilize its product, H2 S, as a metabolic fuel and tumour-cell survival factor; pharmacological CBS inhibition or genetic CBS silencing suppresses cancer cell bioenergetics and suppresses cell proliferation and cell chemotaxis. In the last chapter of the current article, we overview the field of H2 S-induced therapeutic 'suspended animation', a concept in which a temporary pharmacological reduction in cell metabolism is achieved, producing a decreased oxygen demand for the experimental therapy of critical illness and/or organ transplantation.

Regulation of mitochondrial bioenergetic function by hydrogen sulfide. Part I. Biochemical and physiological mechanisms

Until recently, hydrogen sulfide (H2 S) was exclusively viewed a toxic gas and an environmental hazard, with its toxicity primarily attributed to the inhibition of mitochondrial Complex IV, resulting in a shutdown of mitochondrial electron transport and cellular ATP generation. Work over the last decade established multiple biological regulatory roles of H2 S, as an endogenous gaseous transmitter. H2 S is produced by cystathionine γ-lyase (CSE), cystathionine β-synthase (CBS) and 3-mercaptopyruvate sulfurtransferase (3-MST). In striking contrast to its inhibitory effect on Complex IV, recent studies showed that at lower concentrations, H2 S serves as a stimulator of electron transport in mammalian cells, by acting as a mitochondrial electron donor. Endogenous H2 S, produced by mitochondrially localized 3-MST, supports basal, physiological cellular bioenergetic functions; the activity of this metabolic support declines with physiological aging. In specialized conditions (calcium overload in vascular smooth muscle, colon cancer cells), CSE and CBS can also associate with the mitochondria; H2 S produced by these enzymes, serves as an endogenous stimulator of cellular bioenergetics. The current article overviews the biochemical mechanisms underlying the stimulatory and inhibitory effects of H2 S on mitochondrial function and cellular bioenergetics and discusses the implication of these processes for normal cellular physiology. The relevance of H2 S biology is also discussed in the context of colonic epithelial cell physiology: colonocytes are exposed to high levels of sulfide produced by enteric bacteria, and serve as a metabolic barrier to limit their entry into the mammalian host, while, at the same time, utilizing it as a metabolic 'fuel'.

H2S-induced HCO3- secretion in the rat stomach--involvement of nitric oxide, prostaglandins, and capsaicin-sensitive sensory neurons

Hydrogen sulfide (H2S) is known to be an important gaseous mediator that affects various functions under physiological and pathological conditions. We examined the effects of NaHS, a H2S donor, on HCO3(-) secretion in rat stomachs and investigated the mechanism involved in this response. Under urethane anesthesia, rat stomachs were mounted on an ex vivo chamber and perfused with saline. Acid secretion had been inhibited by omeprazole. The secretion of HCO3(-) was measured at pH 7.0 using a pH-stat method and by the addition of 10 mM HCl. NaHS (0.5-10 mM) was perfused in the stomach for 5 min. Indomethacin or L-NAME was administered s.c. before NaHS treatment, while glibenclamide (a KATP channel blocker), ONO-8711 (an EP1 antagonist), or propargylglycine (a cystathionine γ-lyase inhibitor) was given i.p. before. The mucosal perfusion of NaHS dose-dependently increased the secretion of HCO3(-), and this effect was significantly attenuated by indomethacin, L-NAME, and sensory deafferentation, but not by glibenclamide or ONO-8711. The luminal output of nitric oxide, but not the mucosal production of prostaglandin E2, was increased by the perfusion of NaHS. Mucosal acidification stimulated HCO3(-) secretion, and this response was inhibited by sensory deafferentation, indomethacin, L-NAME, and ONO-8711, but not by propargylglycine. These results suggested that H2S increased HCO3(-) secretion in the stomach, and this effect was mediated by capsaicin-sensitive afferent neurons and dependent on nitric oxide and prostaglandins, but not ATP-sensitive K(+) channels. Further study is needed to define the role of endogenous H2S in the mechanism underlying acid-induced gastric HCO3(-) secretion.

In vitro-controlled release delivery system for hydrogen sulfide donor

Hydrogen sulfide (H2S) is having many potential pharmacological and physiological actions which reported that therapeutically useful concentration is low (100-160 μM) and a higher concentration could be toxic. Most of its donors produce it on coming into contact with water. All of these problems could be solved by a controlled-release delivery system which does not utilize water in any of its development steps. Therefore, 12 sustained release formulations were prepared by dissolving sodium hydrogen sulfide (NaHS)-a model H2S donor-in polymer solutions, prepared by dissolving polymers (consisted of either polylactide (PLA) or polylactide co-glycolide (PLGA), containing free carboxylic acid or capped allyl ester end group) in a mixture of benzyl benzoate (BB) and benzyl alcohol (BA). The formulation was injected in simulated tear fluid (STF) from which samples were withdrawn at specified times and assayed for NaHS content. We found decrease in burst and overall release with increase in polymer concentration from 10 to 20% w/v. The formulations containing free end group showed significant (p < 0.05) reduction of burst release (11% vs 21%). However, the overall release or the average amount released per hour was found to be significantly (p < 0.05) increased for formulations containing polymers with free end group than those with capped end group. A sustained level of H2S was found to be maintained for 72 h which should be further increased to a month to make it a viable H2S donor delivery system in addition to investigating toxicity profile specifically for the purpose of subconjunctival ocular delivery.

Microbiota-host interactions in irritable bowel syndrome: Epithelial barrier, immune regulation and brain-gut interactions

Irritable bowel syndrome (IBS) is a common, sometimes debilitating, gastrointestinal disorder worldwide. While altered gut motility and sensation, as well as aberrant brain perception of visceral events, are thought to contribute to the genesis of symptoms in IBS, a search for an underlying aetiology has, to date, proven unsuccessful. Recently, attention has been focused on the microbiota as a possible factor in the pathogenesis of IBS. Prompted by a number of clinical observations, such as the recognition of the de novo development of IBS following enteric infections, as well as descriptions of changes in colonic bacterial populations in IBS and supported by clinical responses to interventions, such as antibiotics and probiotics, that modify the microbiota, various approaches have been taken to investigating the microbiota-host response in IBS, as well as in animal models thereof. From such studies a considerable body of evidence has accumulated to indicate the activation or upregulation of both factors involved in bacterial engagement with the host as well host defence mechanisms against bacteria. Alterations in gut barrier function, occurring in response, or in parallel, to changes in the microbiota, have also been widely described and can be seen to play a pivotal role in generating and sustaining host immune responses both within and beyond the gut. In this manner a plausible hypothesis, based on an altered microbiota and/or an aberrant host response, for the pathogenesis, of at least some instances of IBS, can be generated.

Hydrogen sulfide-mediated regulation of contractility in the mouse ileum with electrical stimulation: roles of L-cysteine, cystathionine β-synthase, and K+ channels

Hydrogen sulfide (H2S) is considered to be a signaling molecule. The precise mechanisms underlying H2S-related events, including the producing enzymes and target molecules in gastrointestinal tissues, have not been elucidated in detail. We herein examined the involvement of H2S in contractions induced by repeated electrical stimulations (ES). ES-induced contractions were neurotoxin-sensitive and increased by aminooxyacetic acid, an inhibitor of cystathionine β-synthase (CBS) and cystathionine γ-lyase, but not by D,L-propargylglycine, a selective inhibitor of cystathionine γ-lyase, in an ES trial-dependent manner. ES-induced contractions were markedly decreased in the presence of L-cysteine. This response was inhibited by aminooxyacetic acid and an antioxidant, and accelerated by L-methionine, an activator of CBS. The existence of CBS was confirmed. NaHS transiently inhibited ES- and acetylcholine-induced contractions, and sustainably decreased basal tone for at least 20 min after its addition. The treatment with glibenclamide, an ATP-sensitive K+ channel blocker, reduced both the L-cysteine response and NaHS-induced inhibition of contractions. The NaHS-induced decrease in basal tone was inhibited by apamin, a small conductance Ca2+-activated K+ channel blocker. These results suggest that H2S may be endogenously produced via CBS in ES-activated enteric neurons, and regulates contractility via multiple K+ channels in the ileum.

Design and synthesis of polymeric hydrogen sulfide donors

Hydrogen sulfide (H2S) is a gaseous signaling molecule that has several important biological functions in the human body. Because of the difficulties of handling H2S gas, small organic compounds that release H2S under physiological conditions have been developed. The observed bioactivities of these H2S donors have generally been directly correlated with their H2S release properties. However, apart from H2S release, these H2S donors also exert biological effects by direct interaction with intracellular components within the cytoplasm after passive diffusion across cellular membranes. Here we report polymeric H2S donors based on ADT-OH which would alter cellular trafficking of ADT-OH to minimize the unfavorable interactions with intracellular components. We designed and synthesized a poly(ethylene glycol)-ADT (PEG-ADT) conjugate having ADT linked via an ether bond. Whereas ADT-OH significantly reduced cell viability in murine macrophages, the PEG-ADT conjugate did not show obvious cytotoxicity. The PEG-ADT conjugate released H2S in murine macrophages but not in the presence of serum proteins. The PEG-ADT conjugate was taken up by the cell through the endocytic pathway and stayed inside endolysosomes, which is different from the small amphiphilic donor ADT-OH that can directly enter the cytoplasm. Furthermore, PEG-ADT was capable of potentiating LPS-induced inflammation. This polymeric H2S donor approach may help to better understand the H2S bioactivities of the H2S donor ADT-OH.

The cardioprotective actions of hydrogen sulfide in acute myocardial infarction and heart failure

It has now become universally accepted that hydrogen sulfide (H2S), previously considered only as a lethal toxin, has robust cytoprotective actions in multiple organ systems. The diverse signaling profile of H2S impacts multiple pathways to exert cytoprotective actions in a number of pathological states. This paper will review the recently described cardioprotective actions of hydrogen sulfide in both myocardial ischemia/reperfusion injury and congestive heart failure.