Hydrogen sulphide is a mediator of carrageenan-induced hindpaw oedema in the rat

Inhibition of hydrogen sulfide synthesis attenuates chemokine production and protects mice against acute pancreatitis and associated lung injury

OBJECTIVES

The present study investigated whether chemokines are involved in hydrogen sulfide (H2S)-associated pathogenesis of acute pancreatitis and associated lung injury.

METHODS

We have examined the effect of DL-propargylglycine, a cystathionine gamma-lyase inhibitor, on the synthesis of CC chemokine monocyte chemotactic protein 1, Regulated upon Activation, Normal T-cell Expressed, and Secreted, and macrophage inflammatory protein-1alpha (MIP-1alpha), and CXC chemokine MIP-2 in an in vitro and in vivo model of cerulein-induced acute pancreatitis and associated lung injury. In addition, the pancreatic acinar cells were treated with H2S donor drug, sodium hydrosulfide. The expression of these chemokines in the pancreatic acini, pancreas, and lungs was determined by quantitative real-time reverse transcriptase polymerase chain reaction, enzyme-linked immunosorbent assay, and immunohistochemistry.

RESULTS

After treatment with DL-propargylglycine, reverse transcriptase polymerase chain reaction, and enzyme-linked immunosorbent assay demonstrated down-regulation of cerulein-induced increase in monocyte chemotactic protein 1, MIP-1alpha, and MIP-2 expression but had no apparent effect on Regulated upon Activation, Normal T-cell Expressed, and Secreted expression.

CONCLUSIONS

These results suggest that the proinflammatory effect of H2S may be mediated by chemokines.

Treatment with H2S-releasing diclofenac protects mice against acute pancreatitis-associated lung injury

Impaired lung function in severe acute pancreatitis is the primary cause of morbidity and mortality in this condition. Hydrogen sulfide (H(2)S) is a naturally occurring gas that has been shown to be a potent vasodilator. Diclofenac is a nonsteroidal anti-inflammatory drug and has been shown to have anti-inflammatory, analgesic, and antipyretic activity. ACS15 is an H(2)S-releasing derivative of diclofenac. Little is known about its effectiveness as an anti-inflammatory drug. In this report, we describe the effect of diclofenac and its H(2)S-releasing derivative on acute pancreatitis and associated lung injury in the mouse. Acute pancreatitis was induced in mice by hourly i.p. injections of cerulein. Diclofenac and ACS15 were administered either 1 hour before or 1 hour after starting cerulein injections, and the severity of acute pancreatitis and associated lung injury was assessed. The severity of acute pancreatitis was determined by hyperamylasemia, neutrophil sequestration in the pancreas (pancreatic myeloperoxidase activity), and pancreatic acinar cell injury/necrosis on histological examination of pancreas sections. The severity of acute pancreatitis-associated lung injury was assessed by neutrophil sequestration in the lungs (lung myeloperoxidase activity) and by histological examination of lung sections. ACS15, given prophylactically and therapeutically, significantly reduced lung inflammation without having any significant effect on pancreatic injury. These results suggest the usefulness of H(2)S-releasing nonsteroidal anti-inflammatory drugs as potential treatments for pancreatitis-associated lung injury.

Hydrogen sulfide up-regulates substance P in polymicrobial sepsis-associated lung injury

Hydrogen sulfide (H2S) has been shown to induce the activation of neurogenic inflammation especially in normal airways and urinary bladder. However, whether endogenous H2S would regulate sepsis-associated lung inflammation via substance P (SP) and its receptors remains unknown. Therefore, the aim of the study was to investigate the effect of H2S on the pulmonary level of SP in cecal ligation and puncture (CLP)-induced sepsis and its relevance to lung injury. Male Swiss mice or male preprotachykinin-A gene knockout (PPT-A-/-) mice and their wild-type (PPT-A+/+) mice were subjected to CLP-induced sepsis. DL-propargylglycine (50 mg/kg i.p.), an inhibitor of H2S formation was administered either 1 h before or 1 h after the induction of sepsis, while NaHS, an H2S donor, was given at the same time as CLP. L703606, an inhibitor of the neurokinin-1 receptor was given 30 min before CLP. DL-propargylglycine pretreatment or posttreatment significantly decreased the PPT-A gene expression and the production of SP in lung whereas administration of NaHS resulted in a further rise in the pulmonary level of SP in sepsis. PPT-A gene deletion and pretreatment with L703606 prevented H2S from aggravating lung inflammation. In addition, septic mice genetically deficient in PPT-A gene or pretreated with L703606 did not exhibit further increase in lung permeability after injection of NaHS. The present findings show for the first time that in sepsis, H2S up-regulates the generation of SP, which contributes to lung inflammation and lung injury mainly via activation of the neurokinin-1 receptor.

Hydrogen sulfide-releasing anti-inflammatory drugs

Non-steroidal anti-inflammatory drugs are among the most commonly used drugs. Despite efforts to produce non-steroidal anti-inflammatory drugs that do not cause gastrointestinal ulceration and bleeding, these adverse effects remain major limitations to their use. In recent years, physiological roles of hydrogen sulfide (H2S) have been recognized, and there is emerging evidence that this endogenous gaseous substance can modulate inflammatory processes. Indeed, H2S donors have been shown to reduce edema formation and leukocyte adherence to the vascular endothelium, and to inhibit pro-inflammatory cytokine synthesis. Moreover, H2S donors can increase the resistance of the gastric mucosa to injury and accelerate repair. Taken together, these observations and others suggest that anti-inflammatory drugs that are modified to release H2S will exhibit improved efficacy and reduced toxicity. Such compounds have now been synthesized and shown to be markedly improved in many respects over the parent anti-inflammatory drugs.

Haemostatic imbalance following carrageenan-induced rat paw oedema

Carrageenan-induced rat paw oedema is a widely used model to investigate the physiopathology of an acute local inflammation. Recently, much attention has been focused on the link between haemostasis and inflammation, and on the impact that inflammation might have on thrombotic events. It is known that the systemic response to inflammation is the "acute phase reaction" that represents a highly complex reaction of the organism to a variety of injuries, aimed to restore homeostasis; one important feature of the acute phase reaction is the hepatic synthesis of proteins involved in the coagulation cascade. Much attention has been focused on the role that systemic inflammation might have on thrombotic events, while there is not much information on the role played by an acute local inflammation on haemostasis, that can lead toward a pro-thrombotic state. The present study was conducted to evaluate the haemostatic balance in the early and the late phase of carrageenan-induced rat paw oedema; i.e. at 3 h, when paw inflammation is maximally expressed, and 24 h following carrageenan injection, when there is an almost complete absence of local inflammatory symptoms. We found that in inflamed animals, 24 h following oedema induction, there was an increase in plasma fibrinogen levels, antithrombin III activity and serum interleukin-6 levels, concomitant to a shortened prothrombin time and to an increased platelet responsiveness to ADP. Furthermore, in inflamed tissues at 3 h there was an increase in antithrombin III proteic expression. Our results demonstrate that a haemostatic imbalance occurs following carrageenan-induced rat paw oedema.

Hydrogen sulfide acts as a mediator of inflammation in acute pancreatitis: in vitro studies using isolated mouse pancreatic acinar cells

Hydrogen sulphide (H₂S) is synthesized from L-cysteine via the action of cystathionine-γ-lyase (CSE) and cystathionine-β-synthase (CBS). We have earlier shown that H₂S acts as a mediator of inflammation. However the mechanism remains unclear. In this study, we investigated the presence of H₂S and the expression of H₂S synthesizing enzymes, CSE and CBS, in isolated mouse pancreatic acini. Pancreatic acinar cells from mice were incubated with or without caerulein (10⁻⁷ M for 30 and 60 min). Caerulein increased the levels of H₂S and CSE mRNA expression while CBS mRNA expression was decreased. In addition, cells pre-treated with DL-propargylglycine (PAG, 3 mM), a CSE inhibitor, reduced the formation of H₂S in caerulein treated cells, suggesting that CSE may be the main enzyme involved in H₂S formation in mouse acinar cells. Furthermore, substance P (SP) concentration in the acini and expression of SP gene (preprotachykinin-A, PPT-A) and neurokinin-1 receptor (NK-1R), the primary receptor for SP, are increased in secretagogue caerulein-treated acinar cells. Inhibition of endogenous production of H₂S by PAG significantly suppressed SP concentration, PPT-A expression and NK1-R expression in the acini. To determine whether H₂S itself provoked inflammation in acinar cells, the cells were treated with H₂S donor drug, sodium hydrosulphide (NaHS), (10, 50 and 100 μM), that resulted in a significant increase in SP concentration and expression of PPT-A and NK1-R in acinar cells. These results suggest that the pro-inflammatory effect of H₂S may be mediated by SP-NK-1R related pathway in mouse pancreatic acinar cells.

Endogenous hydrogen sulfide regulates leukocyte trafficking in cecal ligation and puncture-induced sepsis

Hydrogen sulfide (H(2)S) is recognized increasingly as a proinflammatory mediator in various inflammatory conditions. Here, we have investigated the role of H(2)S in regulating expression of some endothelial adhesion molecules and recruitment of leukocytes to inflamed sites in sepsis. Male Swiss mice were subjected to cecal ligation and puncture (CLP)-induced sepsis and treated with saline (i.p.), DL-propargylglycine (PAG; 50 mg/kg, i.p.), an inhibitor of H(2)S formation or NaHS (10 mg/kg, i.p.), an H(2)S donor. PAG was administered 1 h before or after the induction of sepsis, and NaHS was given at the same time of CLP. Using intravital microcopy, we found that in sepsis, prophylactic and therapeutic administration of PAG reduced leukocyte rolling and adherence significantly in mesenteric venules coupled with decreased mRNA and protein levels of adhesion molecules (ICAM-1, P-selectin, and E-selectin) in lung and liver. In contrast, injection of NaHS up-regulated leukocyte rolling and attachment significantly, as well as tissue levels of adhesion molecules in sepsis. Conversely, normal mice were given NaHS (10 mg/kg, i.p.) to induce lung inflammation, with or without NF-kappaB inhibitor BAY 11-7082 pretreatment. NaHS treatment enhanced the level of adhesion molecules and neutrophil infiltration in lung. These alterations were reversed by pretreatment with BAY 11-7082. Moreover, expression of CXCR2 in neutrophils obtained from H(2)S-treated mice was up-regulated significantly, leading to an obvious elevation in MIP-2-directed migration of neutrophils. Therefore, H(2)S acts as an important endogenous regulator of leukocyte activation and trafficking during an inflammatory response.

Effect of S-diclofenac, a novel hydrogen sulfide releasing derivative, on carrageenan-induced hindpaw oedema formation in the rat

S-diclofenac (2-[(2,6-dichlorophenyl)amino]benzeneacetic acid 4-(3H-1,2-dithiole-3-thione-5-yl)-phenyl ester) is a novel derivative of diclofenac which, in vivo, undergoes enzymatic cleavage of its ester linkage to release hydrogen sulfide (H(2)S) along with the parent moiety, diclofenac. In this study the anti-inflammatory activity of S-diclofenac and diclofenac was studied in a carrageenan-evoked hindpaw oedema model in the rat. Drugs or vehicle were administered 3 h before carrageenan. Both drugs produced a dose-dependent anti-inflammatory effect in this model. However, S-diclofenac (ED(30), 14.2+/-0.6 micromol/kg) was more potent (P<0.05) than diclofenac (ED(30), 39.3+/-1.4 micromol/kg) as an inhibitor both of hindpaw swelling and in reducing the carrageenan-evoked rise in hindpaw myeloperoxidase activity reflecting tissue neutrophil infiltration (ED(50)s of 12.0+/-2.1 micromol/kg and 21.9+/-2.0 micromol/kg). Intraplantar carrageenan injection also significantly (P<0.05) increased hindpaw concentrations of prostaglandin E(2) (PGE(2)), nitrite/nitrate and H(2)S synthesizing activity measured at 6 h. Both S-diclofenac and diclofenac pretreatment reduced the carrageenan-induced rise in hindpaw PGE(2), nitrite/nitrate and H(2)S synthesizing activity. Whilst treatment with either drug produced similar inhibition of hindpaw PGE(2) and H(2)S synthesizing activity--S-diclofenac more effectively reduced hindpaw nitrite/nitrate concentration than did diclofenac. It is proposed that the enhanced anti-inflammatory effect of S-diclofenac relates to its ability to release H(2)S at the inflamed site. These data provide evidence for an anti-inflammatory effect of H(2)S.

Hydrogen sulfide acts as an inflammatory mediator in cecal ligation and puncture-induced sepsis in mice by upregulating the production of cytokines and chemokines via NF-κB

Recent studies have implied that hydrogen sulfide (H2S) plays a crucial role in several inflammatory conditions. However, so far little is known about the mechanism by which H2S provokes the inflammatory response in sepsis. Thus the aim of this study was to investigate if H2S regulates sepsis-associated systemic inflammation and production of proinflammatory mediators via the activation of NF-κB. Male Swiss mice were subjected to cecal ligation and puncture (CLP)-induced sepsis and treated with dl-propargylglycine (PAG; 50 mg/kg ip), NaHS (10 mg/kg ip), or saline. PAG, an inhibitor of H2S formation, was administered either 1 h before or 1 h after CLP, whereas NaHS, an H2S donor, was given at the time of CLP. Some normal mice were given NaHS (10 mg/kg ip) to induce lung inflammation with or without pretreatment with the NF-κB inhibitor BAY 11-7082. Eight hours after CLP, both prophylactic and therapeutic administration of PAG significantly reduced the mRNA and protein levels of IL-1β, IL-6, TNF-α, monocyte chemotactic protein-1, and macrophage inflammatory protein-2 in lung and liver coupled with decreased activation and translocation of NF-κB in lung and liver. Inhibition of H2S formation also significantly reduced lung permeability and plasma alanine aminotransferase activity. In contrast, injection of NaHS significantly aggravated sepsis-associated systemic inflammation and increased NF-κB activation. In addition, H2S-induced lung inflammation was blocked by BAY 11-7082. Therefore, H2S upregulates the production of proinflammatory mediators and exacerbates the systemic inflammation in sepsis through a mechanism involving NF-κB activation.

Enhanced activity of a hydrogen sulphide-releasing derivative of mesalamine (ATB-429) in a mouse model of colitis

BACKGROUND AND PURPOSE

Mesalamine is the first-line therapy for colitis, but it lacks potency and is only effective for mild-to-moderate forms of this disease. Hydrogen sulphide has been shown to be a potent, endogenous anti-inflammatory substance, modulating leukocyte-endothelial adhesion and leukocyte migration. The purpose of this study was to determine if an H(2)S-releasing derivative of mesalamine (ATB-429) would exhibit increased potency and effectiveness in a mouse model of colitis.

EXPERIMENTAL APPROACH

Colitis was induced in mice with trinitrobenzene sulphonic acid and the effects of ATB-429 and mesalamine were compared in several treatment regimens. The severity of colitis was determined using several indices, including a disease activity score (comprised of scores for diarrhea, weight loss and fecal blood), colonic myeloperoxidase activity and macroscopic/microscopic scoring of tissue injury.

KEY RESULTS

Irrespective of the treatment regiment, ATB-429 was more effective than mesalamine in reducing the severity of colitis. ATB-429 was particularly effective in reducing granulocyte infiltration into the colonic tissue (by approximately 70%), as well as reducing the expression of mRNA for several key proinflammatory cytokines/chemokines (e.g., TNFalpha, IFNgamma). Treatment with ADT-OH, the H(2)S-releasing moiety of ATB-429, did not affect severity of colitis.

CONCLUSIONS AND IMPLICATIONS

ATB-429 exhibits a marked increase in anti-inflammatory activity and potency in a murine model of colitis, as compared to mesalamine. These results are consistent with recently described anti-inflammatory effects of H(2)S. ATB-429 may represent an attractive alternative to mesalamine for the treatment of inflammatory bowel disease.

Anti-inflammatory and gastrointestinal effects of a novel diclofenac derivative

S-diclofenac (2-[(2,6-dichlorophenyl)amino]benzeneacetic acid 4-(3H-1,2,dithiol-3-thione-5-yl)phenyl ester; ACS 15) is a novel molecule comprising a hydrogen sulfide (H2S)-releasing dithiol-thione moiety attached by an ester linkage to diclofenac. S-diclofenac administration inhibited lipopolysaccharide-induced inflammation (as evidenced by reduced lung and liver myeloperoxidase activity) and caused significantly less gastric toxicity than diclofenac. S-diclofenac did not affect blood pressure or heart rate of the anesthetized rat. S-diclofenac administration downregulated expression of genes encoding enzymes which synthesize nitric oxide, prostanoids, and H2S; reduced plasma IL-1beta/TNF-alpha; and elevated plasma IL-10. Reduced liver NF-kappaB p65 and AP-1/c-fos DNA-binding activity was also observed. These effects were mimicked in large part by a combination of diclofenac plus an H2S-releasing moiety (ADT-OH). Incubation of S-diclofenac (100 microM) with rat plasma or liver homogenate caused a time-dependent release of H2S, which was inhibited by sodium fluoride (10 mM). Administration of S-diclofenac (47.2 micromol/kg, i.p.) to conscious rats significantly increased plasma H2S concentration (at 45 min and 6 h). We propose that H2S release from S-diclofenac in vivo contributes to the observed effects.

Hydrogen sulfide induces the synthesis of proinflammatory cytokines in human monocyte cell line U937 via the ERK-NF-κB pathway

Hydrogen sulfide (H2S) is now considered an endogenous, gaseous mediator, which has been demonstrated to be involved in many inflammatory states. However, the mechanism of its proinflammatory function remains unknown. In the present study, we used IFN-gamma-primed human monocytic cell line U937 to investigate the effects of H2S in vitro on monocytes. We found that treatment with the H2S donor, sodium hydrosulfide, led to significant increases in the mRNA expression and protein production of TNF-alpha, IL-1beta, and IL-6 in U937 cells. H2S-triggered monocyte activation was confirmed further by the up-regulation of CD11b expression on the cell surface. We also observed that H2S could induce a rapid degradation of IkappaBalpha and subsequent activation of NF-kappaB p65, and this effect was attenuated by Bay 11-7082, a specific inhibitor of NF-kappaB. Furthermore, pretreatment of cells with Bay 11-7082 substantially inhibited the secretion of TNF-alpha, IL-1beta, and IL-6 induced by H2S. We also found that H2S stimulated the phosphorylation and activation of ERK1/2, but not of p38 MAPK and JNK, and pretreatment with PD98059, a selective MEK1 antagonist, could inhibit H2S-induced NF-kappaB activation markedly. Together, our findings suggest for the first time that H2S stimulates the activation of human monocytes with the generation of proinflammatory cytokines, and this response is, at least partially, through the ERK-NF-kappaB signaling pathway.

Nitric oxide-releasing flurbiprofen reduces formation of proinflammatory hydrogen sulfide in lipopolysaccharide-treated rat

The biosynthesis of both nitric oxide (NO) and hydrogen sulfide (H2S) is increased in lipopolysaccharide (LPS)-injected mice and rats but their interaction in these models is not known. In this study we examined the effect of the NO donor, nitroflurbiprofen (and the parent molecule flurbiprofen) on NO and H2S metabolism in tissues from LPS-pretreated rats. Administration of LPS (10 mg kg(-1), i.p.; 6 h) resulted in an increase (P<0.05) in plasma TNF-alpha, IL-1beta and nitrate/nitrite (NO(x)) concentrations, liver H2S synthesis (from added cysteine), CSE mRNA, inducible nitric oxide synthase (iNOS), myeloperoxidase (MPO) activity (marker for neutrophil infiltration) and nuclear factor-kappa B (NF-kappaB) activation. Nitroflurbiprofen (3-30 mg kg(-1), i.p.) administration resulted in a dose-dependent inhibition of the LPS-mediated increase in plasma TNF-alpha, IL-1beta and NO(x) concentration, liver H2S synthesis (55.00+/-0.95 nmole mg protein(-1), c.f. 62.38+/-0.47 nmole mg protein(-1), n = 5, P<0.05), CSE mRNA, iNOS, MPO activity and NF-kappaB activation. Flurbiprofen (21 mg kg(-1), i.p.) was without effect. These results show for the first time that nitroflurbiprofen downregulates the biosynthesis of proinflammatory H2S and suggest that such an effect may contribute to the augmented anti-inflammatory activity of this compound. These data also highlight the existence of 'crosstalk' between NO and H2S in this model of endotoxic shock.

Inhibition of endogenous hydrogen sulfide formation reduces the organ injury caused by endotoxemia

Hydrogen sulfide (H2S) is a naturally occurring gaseous transmitter, which may play important roles in normal physiology and disease. Here, we investigated the role of H2S in the organ injury caused by severe endotoxemia in the rat. Male Wistar rats were subjected to acute endotoxemia (Escherichia coli lipopolysaccharide (LPS) 6 mg kg(-1) intravenously (i.v.) for 6 h) and treated with vehicle (saline, 1 ml kg(-1) i.v.) or DL-propargylglycine (PAG, 10-100 mg kg(-1) i.v.), an inhibitor of the H2S-synthesizing enzyme cystathionine-gamma-lyase (CSE). PAG was administered either 30 min prior to or 60 min after the induction of endotoxemia. Endotoxemia resulted in circulatory failure (hypotension and tachycardia) and an increase in serum levels of alanine aminotransferase and aspartate aminotransferase (markers for hepatic injury), lipase (indicator of pancreatic injury) and creatine kinase (indicator of neuromuscular injury). In the liver, endotoxemia induced a significant increase in the myeloperoxidase (MPO) activity, and in the expression and activity of the H2S-synthesizing enzymes CSE and cystathionine-beta-synthase. Administration of PAG either prior to or after the injection of LPS dose-dependently reduced the hepatocellular, pancreatic and neuromuscular injury caused by endotoxemia, but not the circulatory failure. Pretreatment of rats with PAG abolished the LPS-induced increase in the MPO activity and in the formation of H2S and in the liver. These findings support the view that an enhanced formation of H2S contributes to the pathophysiology of the organ injury in endotoxemia. We propose that inhibition of H2S synthesis may be a useful therapeutic strategy against the organ injury associated with sepsis and shock.

Regulation of vascular nitric oxide in vitro and in vivo; a new role for endogenous hydrogen sulphide?

BACKGROUND AND PURPOSE

The aim of these experiments was to evaluate the significance of the chemical reaction between hydrogen sulphide (H2S) and nitric oxide (NO) for the control of vascular tone.

EXPERIMENTAL APPROACH

The effect of sodium hydrosulphide (NaHS; H2S donor) and a range of NO donors, such as sodium nitroprusside (SNP), either alone or together, was determined using phenylephrine (PE)-precontracted rat aortic rings and on the blood pressure of anaesthetised rats.

KEY RESULTS

Mixing NaHS with NO donors inhibited the vasorelaxant effect of NO both in vitro and in vivo. Low concentrations of NaHS or H2S gas in solution reversed the relaxant effect of acetylcholine (ACh, 400 nM) and histamine (100 microM) but not isoprenaline (400 nM). The effect of NaHS on the ACh response was antagonized by CuSO(4) (200 nM) but was unaffected by glibenclamide (10 microM). In contrast, high concentrations of NaHS (200-1600 microM) relaxed aortic rings directly, an effect reduced by glibenclamide but unaffected by CuSO4. Intravenous infusion of a low concentration of NaHS (10 micromol kg(-1) min(-1)) into the anaesthetized rat significantly increased mean arterial blood pressure. L-NAME (25 mg kg(-1), i.v.) pretreatment reduced this effect.

CONCLUSIONS AND IMPLICATIONS

These results suggest that H2S and NO react together to form a molecule (possibly a nitrosothiol) which exhibits little or no vasorelaxant activity either in vitro or in vivo. We propose that a crucial, and hitherto unappreciated, role of H2S in the vascular system is the regulation of the availability of NO.

Regulation of vascular nitric oxide in vitro and in vivo; a new role for endogenous hydrogen sulphide?

BACKGROUND AND PURPOSE

The aim of these experiments was to evaluate the significance of the chemical reaction between hydrogen sulphide (H2S) and nitric oxide (NO) for the control of vascular tone.

EXPERIMENTAL APPROACH

The effect of sodium hydrosulphide (NaHS; H2S donor) and a range of NO donors, such as sodium nitroprusside (SNP), either alone or together, was determined using phenylephrine (PE)-precontracted rat aortic rings and on the blood pressure of anaesthetised rats.

KEY RESULTS

Mixing NaHS with NO donors inhibited the vasorelaxant effect of NO both in vitro and in vivo. Low concentrations of NaHS or H2S gas in solution reversed the relaxant effect of acetylcholine (ACh, 400 nM) and histamine (100 microM) but not isoprenaline (400 nM). The effect of NaHS on the ACh response was antagonized by CuSO(4) (200 nM) but was unaffected by glibenclamide (10 microM). In contrast, high concentrations of NaHS (200-1600 microM) relaxed aortic rings directly, an effect reduced by glibenclamide but unaffected by CuSO4. Intravenous infusion of a low concentration of NaHS (10 micromol kg(-1) min(-1)) into the anaesthetized rat significantly increased mean arterial blood pressure. L-NAME (25 mg kg(-1), i.v.) pretreatment reduced this effect.

CONCLUSIONS AND IMPLICATIONS

These results suggest that H2S and NO react together to form a molecule (possibly a nitrosothiol) which exhibits little or no vasorelaxant activity either in vitro or in vivo. We propose that a crucial, and hitherto unappreciated, role of H2S in the vascular system is the regulation of the availability of NO.

Mechanism of induction of pancreatic acinar cell apoptosis by hydrogen sulfide

The present study investigated the mechanism of mouse pancreatic acinar cell apoptosis induced by H2S in an in vitro system, using isolated pancreatic acini. Treatment of pancreatic acini with 10 μM NaHS (a donor of H2S) for 3 h caused phosphatidylserine externalization as shown by annexin V binding, an indicator of early stages of apoptosis. This treatment also resulted in the activation of the caspase cascade and major changes at the mitochondrial level. Caspase-3, -8, and -9 activities were stimulated by H2S treatment. Treatment with inhibitors of caspase-3, -8, and -9 significantly inhibited H2S-induced phosphatidylserine externalization as shown by reduced annexin V staining. The mitochondrial membrane potential was collapsed in H2S-treated acini as evidenced by fluorescence microscopy and quantitative analysis. Furthermore, the treatment of acini with H2S caused the release of cytochrome c by the mitochondria. To investigate the mechanism underlying pancreatic acinar cell apoptosis, we also characterized the protein expression of a range of molecules that are each known to influence the apoptotic pathway. Among proapoptotic proteins, Bax expression was activated in H2S-treated cells but not Bid, and the antiapoptotic proteins Bcl-XL and Bcl-2 did not show any activation in pancreatic acinar cell apoptosis. The death effector domain-containing protein Flip is downregulated in H2S-treated acini. These results demonstrate the induction of pancreatic acinar cell apoptosis in vitro by H2S and the involvement of both mitochondrial and death receptor pathways in the process of apoptosis.

Hydrogen sulfide is an endogenous modulator of leukocyte-mediated inflammation

Hydrogen sulfide (H2S) is increasingly recognized as an important signaling molecule in the cardiovascular and nervous systems. Recently, H2S donors were reported to induce neutrophil apoptosis and to suppress expression of some leukocyte and endothelial adhesion molecules. Using rats, we examined the possibility that H2S is an endogenous regulator of key inflammatory events at the leukocyte-endothelial interface. Via intravital microscopy, we observed that H2S donors (NaHS and Na2S) inhibited aspirin-induced leukocyte adherence in mesenteric venules (ED50 of 5.0 micromol/kg for Na2S), likely via activation of ATP-sensitive K+ (K(ATP)) channels. Inhibition of endogenous H2S synthesis elicited leukocyte adherence. Leukocyte infiltration in an air pouch model was also suppressed by H2S donors (NaHS, Lawesson's reagent, and N-acetylcysteine; ED50 of 42.7, 1.3, and 29.9 micromol/kg, respectively) and exacerbated by inhibition of endogenous H2S synthesis. Carrageenan-induced paw edema was suppressed by H2S donors (NaHS and Na2S; ED50s of 35 and 28 micromol/kg, respectively) to the same extent as by diclofenac and enhanced by an inhibitor of H2S synthesis. Suppression of edema formation by H2S donors was mimicked by a K(ATP) channel agonist and reversed by an antagonist of this channel. These results suggest that endogenous H2S is an important mediator of acute inflammation, acting at the leukocyte-endothelium interface. These findings have important implications for anti-inflammatory drug development.

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

Hydrogen sulfide, like nitric oxide, was best known as a toxic pollutant before becoming recognized as a key regulator of several physiologic processes. In recent years, evidence has accumulated to suggest important roles for hydrogen sulfide as a mediator of several aspects of gastrointestinal and liver function. Moreover, alterations in hydrogen sulfide production could contribute to disorders of the gastrointestinal tract and liver. For example, nonsteroidal anti-inflammatory drugs can reduce production of hydrogen sulfide in the stomach, and this has been shown to contribute to the generation of mucosal injury. Hydrogen sulfide has also been shown to play a key role in modulation of visceral hyperalgesia. Inhibitors of hydrogen sulfide synthesis and drugs that can generate safe levels of hydrogen sulfide in vivo have been developed and are permitting interventional studies in experimental models and, in the near future, humans.

Role of substance P in hydrogen sulfide-induced pulmonary inflammation in mice

We have shown earlier that H(2)S acts as a mediator of inflammation. In this study, we have investigated the involvement of substance P and neurogenic inflammation in H(2)S-induced lung inflammation. Intraperitoneal administration of NaHS (1-10 mg/kg), an H(2)S donor, to mice caused a significant increase in circulating levels of substance P in a dose-dependent manner. H(2)S alone could also cause lung inflammation, as evidenced by a significant increase in lung myeloperoxidase activity and histological evidence of lung injury. The maximum effect of H(2)S on substance P levels and on lung inflammation was observed 1 h after NaHS administration. At this time, a significant increase in lung levels of TNF-alpha and IL-1beta was also observed. In substance P-deficient mice, the preprotachykinin-A knockout mice, H(2)S did not cause any lung inflammation. Furthermore, pretreatment of mice with CP-96345 (2.5 mg/kg ip), an antagonist of the neurokinin-1 (NK(1)) receptor, protected mice against lung inflammation caused by H(2)S. However, treatment with antagonists of NK(2), NK(3), and CGRP receptors did not have any effect on H(2)S-induced lung inflammation. Depleting neuropeptide from sensory neurons by capsaicin (50 mg/kg sc) significantly reduced the lung inflammation caused by H(2)S. In addition, pretreatment of mice with capsazepine (15 mg/kg sc), an antagonist of the transient receptor potential vanilloid-1, protected mice against H(2)S-induced lung inflammation. These results demonstrate a key role of substance P and neurogenic inflammation in H(2)S-induced lung injury in mice.

Role of hydrogen sulfide in cecal ligation and puncture-induced sepsis in the mouse

Endogenous hydrogen sulfide (H2S) is naturally synthesized in various types of mammalian cells from l-cysteine in a reaction catalyzed by two enzymes, cystathionine-γ-lyase (CSE) and/or cystathionine-β-synthase. The latest studies have implied that H2S functions as a vasodilator and neurotransmitter. However, so far there is little information about the role played by H2S in systemic inflammation such as sepsis. Thus the aim of this study was to investigate the potential role of endogenous H2S in cecal ligation and puncture (CLP)-induced sepsis. Male Swiss mice were subjected to CLP-induced sepsis and treated with saline (ip), dl-propargylglycine (PAG, 50 mg/kg ip), a CSE inhibitor, or sodium hydrosulfide (NaHS; 10 mg/kg ip). PAG was administered either 1 h before or 1 h after the induction of sepsis, whereas NaHS was given at the same time of CLP. CLP-induced sepsis significantly increased the plasma H2S level and the liver H2S synthesis 8 h after CLP compared with sham operation. Induction of sepsis also resulted in a significant upregulation of CSE mRNA in liver. On the other hand, prophylactic as well as therapeutic administration of PAG significantly reduced sepsis-associated systemic inflammation, as evidenced by myeloperoxidase activity and histological changes in lung and liver, and attenuated the mortality of CLP-induced sepsis. Injection of NaHS significantly aggravated sepsis-associated systemic inflammation. Therefore, the effect of inhibition of H2S formation and administration of NaHS suggests that H2S plays a proinflammatory role in regulating the severity of sepsis and associated organ injury.

Evidence for the formation of a novel nitrosothiol from the gaseous mediators nitric oxide and hydrogen sulphide

The gaseous mediators hydrogen sulphide (H2S) and nitric oxide (*NO) are synthesised in the body from L-cysteine and L-arginine, respectively. In the cardiovascular system, *NO is an important regulator of vascular tone and its over- or under-production has been linked to a variety of diseases. The physiological significance of H2S is not yet clear but, like *NO, it exhibits vasodilator activity and may play a part in septic and haemorrhagic shock, hypertension, regulation of cardiac contractility, and in inflammation. To date, there have been no reports of a chemical interaction between H2S and *NO. Here we show that incubation of the H2S donor, sodium hydrosulphide, with a range of *NO donors and *NO gas in vitro leads to the formation of a nitrosothiol molecule as determined by a combination of techniques; electron paramagnetic resonance, amperometry, and measurement of nitrite. We further show that this nitrosothiol did not induce cGMP accumulation in cultured RAW264.7 cells unless *NO was released with Cu2+. Finally, using liver homogenates from LPS treated rats we present evidence for the endogenous formation of this nitrosothiol. These findings provide the first evidence for the formation of a novel nitrosothiol generated by reaction between H2S and *NO. We propose that generation of this nitrosothiol in the body may regulate the physiological effects of both *NO and H2S.

Hydrogen sulfide causes vanilloid receptor 1-mediated neurogenic inflammation in the airways

Hydrogen sulfide (H(2)S) is described as a mediator of diverse biological effects, and is known to produce irritation and injury in the lung following inhalation. Recently, H(2)S has been found to cause contraction in the rat urinary bladder via a neurogenic mechanism. Here, we studied whether sodium hydrogen sulfide (NaHS), used as donor of H(2)S, produces responses mediated by sensory nerve activation in the guinea-pig airways. NaHS evoked an increase in neuropeptide release in the airways that was significantly attenuated by capsaicin desensitization and by the transient receptor potential vanilloid 1 (TRPV1) antagonist capsazepine. In addition, NaHS caused an atropine-resistant contraction of isolated airways, which was completely prevented by capsaicin desensitization. Furthermore, NaHS-induced contraction was reduced by TRPV1 antagonism (ruthenium red, capsazepine and SB366791), and was abolished by pretreatment with the combination of tachykinin NK(1) (SR140333) and NK(2) (SR48968) receptor antagonists. In anesthetized guinea-pigs, intratracheal instillation of NaHS increased the total lung resistance and airway plasma protein extravasation. These two effects were reduced by TRPV1 antagonism (capsazepine) and tachykinin receptors (SR140333 and SR48968) blockade. Our results provide the first pharmacological evidence that H(2)S provokes tachykinin-mediated neurogenic inflammatory responses in guinea-pig airways, and that this effect is mediated by stimulation of TRPV1 receptors on sensory nerves endings. This novel mechanism may contribute to the irritative action of H(2)S in the respiratory system.

Evidence that hydrogen sulfide exerts antinociceptive effects in the gastrointestinal tract by activating KATP channels

Hydrogen sulfide (H(2)S) functions as a neuromodulator, but whether it modulates visceral perception and pain is unknown. Cystathionine beta-synthase (CBS) and cystathionine-gamma-lyase (CSE) mediate enzymatic generation of H(2)S in mammalian cells. Here we have investigated the role of H(2)S in modulating nociception to colorectal distension, a model that mimics some features of the irritable bowel syndrome. Four graded (0.4-1.6 ml of water) colorectal distensions (CRDs) were produced in conscious rats (healthy and postcolitic), and rectal nociception was assessed by measuring the behavioral response during CRD. Healthy rats were administered with sodium hydrogen sulfide (NaHS) (as a source of H(2)S), L-cysteine, or vehicle. In a second model, we investigated nociception to CRD in rats recovering from a chemically induced acute colitis. We found that CBS and CSE are expressed in the colon and spinal cord. Treating rats with NaHS resulted in a dose-dependent attenuation of CRD-induced nociception with the maximal effect at 60 micromol/kg (p < 0.05). Administration of L-cysteine, a CSE/CBS substrate, reduced rectal sensitivity to CRD (p < 0.05). NaHS-induced antinociception was reversed by glibenclamide, a ATP-sensitive K(+) (K(ATP)) channel inhibitor, and N(omega)-nitro-L-arginine methyl ester hydrochloride (L-NAME), a nitric-oxide (NO) synthase inhibitor. The antinociceptive effect of NaHS was maintained during the resolution of colon inflammation induced by intrarectal administration of a chemical irritant. In summary, these data show that H(2)S inhibits nociception induced by CRD in both healthy and postcolitic rats. This effect is mediated by K(ATP) channels and NO. H(2)S-releasing drugs might be beneficial in treating painful intestinal disorders.

Hydrogen sulfide as a vasodilator

Gases such as nitric oxide (NO) and carbon monoxide (CO) play important roles both in normal physiology and in disease. The toxic effects of hydrogen sulphide (H2S) on living organisms have been recognized for nearly 300 years. In recent years, however, interest has been directed towards H2S as the third gaseous mediator, which has been shown to exhibit potent vasodilator activity both in vitro and in vivo most probably by opening vascular smooth muscle K(ATP) channels. Of the two enzymes, cystathionine-gamma-lyase (CSE) and cystathionine-beta-synthetase (CBS), which utilize L-cysteine as substrate to form H2S, CSE is believed to be the key enzyme which forms H2S in the cardiovascular system. Recent studies have shown an important role of the vasodilator action of H2S in health and disease.