Two's company, three's a crowd: can H2S be the third endogenous gaseous transmitter?

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.

Evidence for a functional genetic polymorphism of the human thiosulfate sulfurtransferase (Rhodanese), a cyanide and H2S detoxification enzyme

Rhodanese or thiosulfate sulfurtransferase (TST) is a mitochondrial matrix enzyme that plays roles in cyanide detoxification, the formation of iron-sulfur proteins and the modification of sulfur-containing enzymes. Transsulfuration reaction catalyzed by TST is also involved in H(2)S detoxification. To date, no polymorphism of the human TST gene had been reported. We developed a screening strategy based on a PCR-SSCP method to search for mutations in the 3 exons of TST and their proximal flanking regions. This strategy has been applied to DNA samples from 50 unrelated French individuals of Caucasian origin. Eleven polymorphisms consisting in seven nucleotide substitutions in non-coding regions, two silent mutations and two missense mutations were characterized. The functional consequences of the identified mutations were assessed in vivo by measurement of erythrocyte TST activity and/or in vitro using heterologous expression in Saccharomyces cerevisiae or transient transfection assay in HT29 and Caco-2 cell lines. The P(285)A variant appears to encode a protein with a 50% decrease of in vitro intrinsic clearance compared to the wild-type enzyme. Additionally, the six polymorphisms located upstream the ATG initiation codon are responsible for a significant decrease (ranging from 40% to 73%) in promoter activity of a reporter gene compared to the corresponding wild-type sequence. This work constitutes the first report of the existence of a functional genetic polymorphism affecting TST activity and should be of great help to investigate certain disorders for which impairment of CN(-) or H(2)S detoxification have been suggested to be involved.

5-Amino-2-hydroxybenzoic acid 4-(5-thioxo-5H-[1,2]dithiol-3yl)-phenyl ester (ATB-429), a hydrogen sulfide-releasing derivative of mesalamine, exerts antinociceptive effects in a model of postinflammatory hypersensitivity

H(2)S functions as a neuromodulator and exerts anti-inflammatory activities. Recent data indicate that irritable bowel syndrome (IBS) is linked to inflammation of the gastrointestinal tract. In this study, we have investigated the role of a novel H(2)S-releasing derivative of mesalamine (5-amino-2-hydroxybenzoic acid 4-(5-thioxo-5H-[1,2]dithiol-3yl)-phenyl ester, ATB-429) in modulating nociception to colorectal distension (CRD), a model that mimics some features of IBS, in healthy and postcolitic rats. Four graded (0.4-1.6 ml of water) CRDs were produced in conscious rats, and colorectal sensitivity and pain were assessed by measuring the abdominal withdrawal response and spinal c-Fos expression. In healthy rats, ATB-429 dose dependently (25, 50, or 100 mg/kg) attenuated CRD-induced hypersensitivity and significantly inhibited CRD-induced overexpression of spinal c-FOS mRNA, whereas mesalamine had no effect. ATB-429-induced antinociception was reversed by glibenclamide, a ATP-sensitive K(+) (K(ATP)) channel inhibitor. The antinociceptive effect of ATB-429 was maintained in a rodent model of postinflammatory hypersensitivity (4 weeks after colitis induction). At a dose of 100 mg/kg, ATB-429 reversed the allodynic response caused by CRD in postcolitic rats. Colonic cyclooxygenase-2 and interkeukin-1beta mRNA and spinal c-FOS mRNA expression were significantly down-regulated by ATB-429, but not by mesalamine. ATB-429, but not mesalamine, increased blood concentrations of H(2)S in both healthy and postcolitic rats. Taken together, these data suggest that ATB-429 inhibits hypersensitivity induced by CRD in both healthy and postcolitic, allodynic rats by a K(ATP) channel-mediated mechanism. This study provides evidence that H(2)S-releasing drugs might have beneficial effects in the treatment of painful intestinal disorders.

Hydrogen sulfide inhibits nitric oxide production and nuclear factor-kappaB via heme oxygenase-1 expression in RAW264.7 macrophages stimulated with lipopolysaccharide

Hydrogen sulfide (H(2)S), a regulatory gaseous molecule that is endogenously synthesized by cystathionine gamma-lyase (CSE) and/or cystathionine beta-synthase (CBS) from L-cysteine (L-Cys) metabolism, is a putative vasodilator, and its role in nitric oxide (NO) production is unexplored. Here, we show that at noncytotoxic concentrations, H(2)S was able to inhibit NO production and inducible NO synthase (iNOS) expression via heme oxygenase (HO-1) expression in RAW264.7 macrophages stimulated with lipopolysaccharide (LPS). Both H(2)S solution prepared by bubbling pure H(2)S gas and NaSH, a H(2)S donor, dose dependently induced HO-1 expression through the activation of the extracellular signal-regulated kinase (ERK). Pretreatment with H(2)S or NaHS significantly inhibited LPS-induced iNOS expression and NO production. Moreover, NO production in LPS-stimulated macrophages that are expressing CSE mRNA was significantly reduced by the addition of L-Cys, a substrate for H(2)S, but enhanced by the selective CSE inhibitor beta-cyano-L-alanine but not by the CBS inhibitor aminooxyacetic acid. While either blockage of HO activity by the HO inhibitor, tin protoporphyrin IX, or down-regulation of HO-1 expression by HO-1 small interfering RNA (siRNA) reversed the inhibitory effects of H(2)S on iNOS expression and NO production, HO-1 overexpression produced the same inhibitory effects of H(2)S. In addition, LPS-induced nuclear factor (NF)-kappaB activation was diminished in RAW264.7 macrophages preincubated with H(2)S. Interestingly, the inhibitory effect of H(2)S on NF-kappaB activation was reversed by the transient transfection with HO-1 siRNA, but was mimicked by either HO-1 gene transfection or treatment with carbon monoxide (CO), an end product of HO-1. CO treatment also inhibited LPS-induced NO production and iNOS expression via its inactivation of NF-kappaB. Collectively, our results suggest that H(2)S can inhibit NO production and NF-kappaB activation in LPS-stimulated macrophages through a mechanism that involves the action of HO-1/CO.

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.

Impact of l-arginine on hydrogen sulfide/cystathionine-γ-lyase pathway in rats with high blood flow-induced pulmonary hypertension

The present study was designed to explore the possible effect of L-arginine on endogenous hydrogen sulfide/cystathionine-gamma-lyase (H(2)S/CSE) pathway in the pathogenesis of pulmonary hypertension and pulmonary vascular structural remodeling induced by high pulmonary blood flow. Thirty-two male Sprague-Dawley rats were randomly divided into control group (n=11), shunt group (n=11) and shunt with L-arginine group (n=10). Rats in the shunt and shunt with L-arginine group underwent an abdominal aorta-inferior cava vein shunt operation. After 11 weeks of shunting, the plasma level of H2S and lung tissue H2S production rate in the shunt with L-arginine group were much higher than those in the shunt group (P<0.01). Meanwhile, the expression of CSE mRNA in the lung tissues of rats in the shunt with L-arginine group was increased significantly (P<0.01), and in situ hybridization showed that CSE mRNA expression was obviously up-regulated in the smooth muscle cells (SMCs) of the pulmonary arteries of shunted rats treated with L-arginine when compared with shunted rats without the treatment of L-arginine (P<0.01). In conclusion, H2S/CSE pathway was up-regulated by L-arginine in pulmonary hypertension induced by high blood flow with the attenuation of pulmonary hypertension and pulmonary vascular structural remodeling.

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.

Methane, a gas produced by enteric bacteria, slows intestinal transit and augments small intestinal contractile activity

The presence of methane on lactulose breath test among irritable bowel syndrome (IBS) subjects is highly associated with the constipation-predominant form. Therefore, we set out to determine whether methane gas can alter small intestinal motor function. In dogs, small intestinal fistulae were created to permit measurement of intestinal transit. Using a radiolabel, we evaluated transit during infusion of room air and subsequently methane. In this model, small intestinal infusion of methane produced a slowing of transit in all dogs by an average of 59%. In a second experiment, guinea pig ileum was pinned into an organ bath for the study of contractile activity in response to brush strokes applied to the mucosa. The force of contraction was measured both orad and aborad to the stimulus. The experiment was repeated while the bath was gassed with methane. Contractile activities orad and aborad to the stimulus were significantly augmented by methane compared with room air (P < 0.05). In a third experiment, humans with IBS who had undergone a small bowel motility study were compared such that subjects who produced methane on lactulose breath test were compared with those producing hydrogen. The motility index was significantly higher in methane-producing IBS patients (1,851 +/- 861) compared with hydrogen producers (1,199 +/- 301) (P < 0.05). Therefore, methane, a gaseous by-product of intestinal bacteria, slows small intestinal transit and appears to do so by augmenting small bowel contractile activity.

Hydrogen sulfide potentiates interleukin-1beta-induced nitric oxide production via enhancement of extracellular signal-regulated kinase activation in rat vascular smooth muscle cells

Hydrogen sulfide (H(2)S) and nitric oxide (NO) are endogenously synthesized from l-cysteine and l-arginine, respectively. They might constitute a cooperative network to regulate their effects. In this study, we investigated whether H(2)S could affect NO production in rat vascular smooth muscle cells (VSMCs) stimulated with interleukin-1beta (IL-1beta). Although H(2)S by itself showed no effect on NO production, it augmented IL-beta-induced NO production and this effect was associated with increased expression of inducible NO synthase (iNOS) and activation of nuclear factor (NF)-kappaB. IL-1Beta activated the extracellular signal-regulated kinase 1/2 (ERK1/2), and this activation was also enhanced by H(2)S. Inhibition of ERK1/2 activation by the selective inhibitor U0126 inhibited IL-1beta-induced NF-kappaB activation, iNOS expression, and NO production either in the absence or presence of H(2)S. Our findings suggest that H(2)S enhances NO production and iNOS expression by potentiating IL-1beta-induced NF-kappaB activation through a mechanism involving ERK1/2 signaling cascade in rat VSMCs.

L-cysteine inhibits insulin release from the pancreatic beta-cell: possible involvement of metabolic production of hydrogen sulfide, a novel gasotransmitter

Hydrogen sulfide (H(2)S) was historically recognized as a toxic gas generated by natural resources. However, its enzymatic production from L-cysteine has recently been demonstrated in mammals. Cystathionine beta-synthase and cystathionine gamma-lyase, both of which can produce H(2)S, were expressed in mouse pancreatic islet cells and the beta-cell line, MIN6. L-cysteine and the H(2)S donor NaHS inhibited glucose-induced insulin release from islets and MIN6 cells. These inhibitory effects were reproduced when insulin release was stimulated by alpha-ketoisocaproate, tolbutamide, or high K+. L-cysteine and NaHS inhibited glucose-potentiated insulin release in the copresence of diazoxide and high K+. Real-time imaging of intracellular Ca2+ concentration ([Ca2+](i)) demonstrated that both L-cysteine and NaHS reversibly suppressed glucose-induced [Ca2+](i) oscillation in a single beta-cell without obvious changes in the mean value. These substances inhibited Ca2+ - or guanosine 5'-0-3-thiotriphosphate-induced insulin release from islets permeabilized with streptolysin-O. L-cysteine and NaHS reduced ATP production and attenuated glucose-induced hyperpolarization of the mitochondrial membrane potential. Finally, L-cysteine increased H(2)S content in MIN6 cells. We suggest here that L-cysteine inhibits insulin release via multiple actions on the insulin secretory process through H(2)S production. Because the activities of H(2)S-producing enzymes and the tissue H(2)S contents are known to increase under diabetic conditions, the inhibition may participate in the deterioration of insulin release in this disease.

Free radical biology and medicine: it's a gas, man!

We review gases that can affect oxidative stress and that themselves may be radicals. We discuss O(2) toxicity, invoking superoxide, hydrogen peroxide, and the hydroxyl radical. We also discuss superoxide dismutase (SOD) and both ground-state, triplet oxygen ((3)O(2)), and the more energetic, reactive singlet oxygen ((1)O(2)). Nitric oxide ((*)NO) is a free radical with cell signaling functions. Besides its role as a vasorelaxant, (*)NO and related species have other functions. Other endogenously produced gases include carbon monoxide (CO), carbon dioxide (CO(2)), and hydrogen sulfide (H(2)S). Like (*)NO, these species impact free radical biochemistry. The coordinated regulation of these species suggests that they all are used in cell signaling. Nitric oxide, nitrogen dioxide, and the carbonate radical (CO(3)(*-)) react selectively at moderate rates with nonradicals, but react fast with a second radical. These reactions establish "cross talk" between reactive oxygen (ROS) and reactive nitrogen species (RNS). Some of these species can react to produce nitrated proteins and nitrolipids. It has been suggested that ozone is formed in vivo. However, the biomarkers that were used to probe for ozone reactions may be formed by non-ozone-dependent reactions. We discuss this fascinating problem in the section on ozone. Very low levels of ROS or RNS may be mitogenic, but very high levels cause an oxidative stress that can result in growth arrest (transient or permanent), apoptosis, or necrosis. Between these extremes, many of the gasses discussed in this review will induce transient adaptive responses in gene expression that enable cells and tissues to survive. Such adaptive mechanisms are thought to be of evolutionary importance.

Hydrogen sulfide prevents apoptosis of human PMN via inhibition of p38 and caspase 3

Hydrogen sulfide, together with carbon monoxide and nitric oxide, is now considered a gasotransmitter able to induce specific cellular responses. As hydrogen sulfide is a component of several natural compounds known to be effective in many inflammatory pathologies, particularly of the respiratory tract, we studied its effects in vitro on the survival and bactericidal activity of purified human neutrophils. We found that (1) HS(-) ions promote the survival of granulocytes, but not that of lymphocytes or eosinophils, cultured in serum-free medium; (2) the pro-survival effect of HS(-) is due to inhibition of caspase-3 cleavage and p38 MAP kinase phosphorylation; (3) the bactericidal activity of neutrophils is not impaired by hydrogen sulfide. We conclude that HS(-) promotes the short-term survival of neutrophils potentially accelerating the resolution of inflammatory processes and preventing the occurrence of new ones.

Down-regulation of endogenous hydrogen sulfide pathway in pulmonary hypertension and pulmonary vascular structural remodeling induced by high pulmonary blood flow in rats

BACKGROUND

The mechanisms responsible for the development of pulmonary hypertension (PH) and pulmonary vascular structural remodeling induced by high pulmonary blood flow are not fully understood. The present study was designed to explore the possible changes in endogenous hydrogen sulfide (H2S), a novel gasotransmitter, on the pathogenesis of PH and pulmonary vascular structural remodeling induced by high pulmonary blood flow.

METHODS AND RESULTS

Twenty-two male Sprague-Dawley rats were randomly divided into a shunting group (n=11) and control group (n=11). Rats in the shunting group underwent an abdominal aorta-inferior cava vein shunting operation. After 11 weeks of shunting, the plasma level of H2S and lung tissue H2S producing rate were much lower than those of the control group (p<0.01). In situ hybridization analysis showed that the expression of cystathionine gamma-lyase (CSE) mRNA was down-regulated in the pulmonary arteries of the shunting rats compared with the control group (p<0.01), and competitive quantitative reverse transcription-polymerase chain reaction showed that the relative amount of CSEmRNA in lung tissue was decreased significantly (p<0.01).

CONCLUSIONS

The endogenous H2S pathway is down-regulated in PH and pulmonary vascular structural remodeling is induced by high pulmonary blood flow.

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 ameliorates vascular calcification induced by vitamin D3 plus nicotine in rats

AIM

To investigate the role of the endogenous cystathionine gamma-synthase (CSE)/hydrogen sulfide (H2S) pathway in vascular calcification in vivo.

METHODS

A rat vascular calcification model was established by administration of vitamin D3 plus nicotine (VDN). The amount of CSE and osteopontin (OPN) mRNA was determined by using semi-quantitative reverse-transcription polymerase chain reaction. The calcium content, 45Ca2+ accumulation and alkaline phosphatase (ALP) activity were measured. H2S production and CSE activity were measured.

RESULTS

von Kossa staining produced strong positive black/brown staining in areas among the elastic fibers of the medial layer in the calcified aorta. The calcium content, 45Ca2+ accumulation and ALP activity in calcified arteries increased by 6.77-, 1.42-, and 1.87-fold, respectively, compared with controls. The expression of the OPN gene was upregulated (P<0.01). Expression of the CSE gene was downregulated. However, calcium content, 45Ca2+ uptake and ALP activity in the VDN plus NaHS group was lower than that in the VDN group. The content of calcium and 45Ca2+ accumulation and activity of ALP in the aorta were 34.8%, 40.75% and 63.5% lower in the low-dosage NaHS group than in the VDN group, respectively (P<0.01), and the calcium content and deposition of 45Ca2+ and activity of ALP was 83.9%, 37.8 % and 46.2% lower in the aorta in the high-dosage NaHS group than in the VDN group, respectively (P<0.01). The expression of the OPN gene was downregulated.

CONCLUSION

The production of H2S, and CSE activity were decreased and CSE gene expression was downregulated in rats with vascular calcification. H2S can ameliorate vascular calcification, suggesting that the H2S/CSE pathway plays a regulatory role in the pathogenesis of vascular calcification.

Carbon monoxide and hydrogen sulfide: gaseous messengers in cerebrovascular circulation

This review focuses on two gaseous cellular messenger molecules, CO and H2S, that are involved in cerebrovascular flow regulation. CO is a dilatory mediator in active hyperemia, autoregulation, hypoxic dilation, and counteracting vasoconstriction. It is produced from heme by a constitutively expressed enzyme [heme oxygenase (HO)-2] expressed highly in the brain and by an inducible enzyme (HO-1). CO production is regulated by controlling substrate availability, HO-2 catalytic activity, and HO-1 expression. CO dilates arterioles by binding to heme that is bound to large-conductance Ca2+-activated K+ channels. This binding elevates channel Ca2+ sensitivity, that increases coupling of Ca2+ sparks to large-conductance Ca2+-activated K+ channel openings and, thereby, hyperpolarizes the vascular smooth muscle. In addition to dilating blood vessels, CO can either inhibit or accentuate vascular cell proliferation and apoptosis, depending on conditions. H2S may also function as a cerebrovascular dilator. It is produced in vascular smooth muscle cells by hydrolysis of l-cysteine catalyzed by cystathione gamma-lyase (CSE). H2S dilates arterioles at physiologically relevant concentrations via activation of ATP-sensitive K+ channels. In addition to dilating blood vessels, H2S promotes apoptosis of vascular smooth muscle cells and inhibits proliferation-associated vascular remodeling. Thus both CO and H2S modulate the function and the structure of circulatory system. Both the HO-CO and CSE-H2S systems have potential to interact with NO and prostanoids in the cerebral circulation. Much of the physiology and biochemistry of HO-CO and CSE-H2S in the cerebral circulation remains open for exploration.

Hydrogen sulfide facilitates carotid sinus baroreflex in anesthetized rats

AIM

To study effects of hydrogen sulfide (H2S) on the carotid sinus baroreflex (CSB).

METHODS

The functional curve of the carotid sinus baroreflex was measured by recording changes in arterial pressure in anesthetized male rats with perfused carotid sinus.

RESULTS

H2S (derived from sodium hydrosulfide) at concentrations of 25, 50, and 100 micromol/L facilitated the CSB, shifting the functional curve of the baroreflex downward and to the left. There was a marked increase in peak slope (PS) and reflex decrease in blood pressure (RD). Effects were concentration-dependent. Pretreatment with glibenclamide (20 micromol/L), a K(ATP) channel blocker, abolished the above effects of H2S on CSB. Pretreatment with Bay K8644 (an agonist of calcium channels; 500 nmol/L) eliminated the effect of H2S on CSB. An inhibitor of cystathionine gamma-lyase (CSE), DL-propargylglycine (PPG; 200 micromol/L), inhibited CSB in male rats and shifted the functional curve of the baroreflex upward and to the right.

CONCLUSION

These data suggest that exogenous H2S exerts a facilitatory role on isolated CSB through opening K(ATP) channels and further closing the calcium channels in vascular smooth muscle. Endogenous H2S may activate the activity of the CSB in vivo.

Hydrogen Sulfide and Carbon Monoxide Are in Synergy with Each Other in the Pathogenesis of Recurrent Febrile Seizures

1. The purpose of the present study was to investigate the interaction between hydrogen sulfide (H(2)S) and carbon monoxide (CO) during recurrent febrile seizures (FS) 2.H(2)S and CO are important intra- and intercellular messengers, regulating various brain functions. Our recent studies showed that both of them alleviate the hippocampal damage induced by recurrent FS. In the present study, on a rat model of recurrent FS, we found that hydroxylamine (an inhibitor of cystathionine b-synthase, CBS) reduced CO level and down regulated heme oxygenase (HO-1) expression, while NaHS (a donor of H(2)S) elevated CO level and upregulated HO-1 expression. ZnPP-IX (an inhibitor of HO-1) decreased H(2)S formation and down regulated CBS expression, while hemin (which increases the production of endogenous CO) enhanced H(2)S formation and elevated CBS expression. 3. Our data demonstrate that endogenous H(2)S and CO are in synergy with each other in recurrent FS.

Pro‐apoptotic effect of endogenous H2S on human aorta smooth muscle cells

Cystathionine gamma-lyase (CSE) is a key enzyme in the trans-sulfuration pathway, which uses L-cysteine to produce hydrogen sulfide (H2S). The CSE/H2S system has been shown to play an important role in regulating cellular functions in different systems. In the present study, we overexpressed CSE in human aorta smooth muscle cells (HASMCs) using a recombinant defective adenovirus containing CSE gene (Ad-CSE). Infection of HASMCs with Ad-CSE resulted in a significant increase in the expression of CSE protein and H2S production. Ad-CSE transfection inhibited cell growth and stimulated apoptosis, as evidenced by cell viability assay, Hoechst 33258 staining, TUNEL, and caspase 3 activation. CSE-mediated apoptosis was associated with an increased ERK and p38 MAPK activation, up-regulation of p21(Cip/WAK-1), and down-regulation of cyclin D1 expression. After inhibiting endogenous background CSE gene expression, direct administration of H2S at 100 microM induced apoptosis of HASMCs. The other two endproducts of CSE-catalyzed enzymatic reaction, ammonium and pyruvate, failed to do so. These results demonstrate that overexpression of CSE stimulates SMC apoptosis due to an increased endogenous production of H2S. Adenovirus-mediated transfer of CSE gene may provide a novel therapeutic approach in treating vascular diseases linked to abnormal cellular proliferation and vascular remodeling.

Long-term modifications of blood pressure in normotensive and spontaneously hypertensive rats by gene delivery of rAAV-mediated cytochrome P450 arachidonic acid hydroxylase

Arachidonic acid cytochrome P-450 (CYP) hydroxylase 4A isoforms, including 4A1, 4A2, 4A3 and 4A8 in the rat kidney, catalyze arachidonic acid to produce 19/20-Hydroxyeicosatetraenoic acids (20-HETE), a biologically active metabolite, which plays an important role in the regulation of blood pressure. However, controversial results have been reported regarding the exact role of 20-HETE on blood pressure. In the present study, we used recombinant adeno-associated viral vector (rAAV) to deliver CYP 4A1 cDNA and antisense 4A1 cDNA into Sprague-Dawley (SD) rats and spontaneously hypertensive rats (SHR), respectively, to investigate the effects of long-term modifications of blood pressure and the potential for gene therapy of hypertension. The mean systolic pressure increased by 14.2+/-2.5 mm Hg in rAAV.4A1-treated SD rats and decreased by 13.7+/-2.2 mm Hg in rAAV.anti4A1-treated SHR rats 5 weeks after the injection compared with controls and these changes in blood pressure were maintained until the experiments ended at 24 weeks. In 4A1 treated animals CYP4A was overexpressed in various tissues, but preferentially in the kidney at both mRNA and protein levels. In anti-4A1-treated SHR, CYP4A mRNA in various tissues was probed, especially in kidneys, but 4A1 protein expression was almost completely inhibited. These results suggest that arachidonic acid CYP hydroxylases contribute not only to the maintenance of normal blood pressure but also to the development of hypertension. rAAV-mediated anti4A administration strategy has the potential to be used as targeted gene therapy in human hypertension by blocking expression of CYP 4A in kidneys.

Carbon Monoxide: Endogenous Production, Physiological Functions, and Pharmacological Applications

Over the last decade, studies have unraveled many aspects of endogenous production and physiological functions of carbon monoxide (CO). The majority of endogenous CO is produced in a reaction catalyzed by the enzyme heme oxygenase (HO). Inducible HO (HO-1) and constitutive HO (HO-2) are mostly recognized for their roles in the oxidation of heme and production of CO and biliverdin, whereas the biological function of the third HO isoform, HO-3, is still unclear. The tissue type-specific distribution of these HO isoforms is largely linked to the specific biological actions of CO on different systems. CO functions as a signaling molecule in the neuronal system, involving the regulation of neurotransmitters and neuropeptide release, learning and memory, and odor response adaptation and many other neuronal activities. The vasorelaxant property and cardiac protection effect of CO have been documented. A plethora of studies have also shown the importance of the roles of CO in the immune, respiratory, reproductive, gastrointestinal, kidney, and liver systems. Our understanding of the cellular and molecular mechanisms that regulate the production and mediate the physiological actions of CO has greatly advanced. Many diseases, including neurodegenerations, hypertension, heart failure, and inflammation, have been linked to the abnormality in CO metabolism and function. Enhancement of endogenous CO production and direct delivery of exogenous CO have found their applications in many health research fields and clinical settings. Future studies will further clarify the gasotransmitter role of CO, provide insight into the pathogenic mechanisms of many CO abnormality-related diseases, and pave the way for innovative preventive and therapeutic strategies based on the physiologic effects of CO.

Endogenous hydrogen sulfide in patients with COPD

OBJECTIVES

COPD is characterized by progressive airway obstruction. Recent studies showed that besides nitric oxide (NO) and carbon monoxide (CO), endogenous hydrogen sulfide (H(2)S) might be the third signaling gasotransmitter. To clarify the role of endogenous H(2)S in the pathogenesis of COPD, we investigated the relation of serum H(2)S level to severity of COPD as defined by lung function and airway inflammation.

METHODS

Levels of serum H(2)S and NO, lung function, and cell differential counts in induced sputum were studied in 27 patients with acute exacerbation of COPD (AECOPD), 37 patients with stable COPD, and 13 healthy subjects. Patients with AECOPD had arterial blood gas levels measured and underwent Doppler echocardiography. In addition, in order to clarify the effects of age and smoking status on serum H(2)S level, we recruited three groups who were age matched to the study group but had no airflow limitation (59 subjects).

RESULTS

Serum H(2)S level (34.0 +/- 0.9 to 36.4 +/- 1.1 micromol/L [+/- SEM]) did not differ among healthy control subjects with different ages (56.6 to 75.0 years, respectively). Serum H(2)S level was significantly higher in patients with stable COPD than in patients with AECOPD and age-matched control subjects (p < 0.01) and correlated positively with NO level in all healthy control subjects and all patients with COPD (r = 0.352, p = 0.000). Serum H(2)S level was significantly lower in smokers than nonsmokers, both with AECOPD (p < 0.05) and healthy control subjects (p < 0.01). It was significantly lower in smokers with AECOPD than healthy smokers and smokers with stable COPD (p < 0.01). Serum H(2)S level differed and was decreased (p < 0.05) among stable COPD patients by stage of airway obstruction (p < 0.05), and it was lower in patients with stage III than stage I obstruction (p < 0.05). Serum H(2)S level in all patients with COPD and healthy control subjects correlated positively with the percentage of predicted FEV(1) value (r = 0.300, p = 0.009). It was lower in patients with AECOPD and systolic pulmonary artery pressure (PASP) > or = 35 mm Hg than those with PASP within the normal range (< 35 mm Hg) [p < 0.05] and was negatively correlated with PASP (r = - 0.561, p = 0.011). Serum H(2)S level was negatively correlated with proportion of neutrophils in sputum (r = - 0.422, p = 0.001) and positively correlated with proportion of lymphocytes (r = 0.286, p = 0.028) and macrophages (r = 0.334, p = 0.01) in all patients with COPD.

CONCLUSIONS

Endogenous H(2)S is involved in the pathogenesis of airway obstruction in COPD, and its alteration in level may be connected with disease activity and severity.

Exogenous hydrogen sulfide (H2S) protects against regional myocardial ischemia-reperfusion injury--Evidence for a role of K ATP channels

Hydrogen sulfide (H2S) is a gaseous mediator, produced by the metabolic pathways that regulate tissue concentrations of sulfur-containing amino acids. Recent studies indicate that endogenous or exogenous H2S exerts physiological effects in the cardiovascular system of vertebrates, possibly through modulation of K ATP channel opening. The present study was undertaken to examine the hypothesis that H2S is cytoprotective against myocardial ischemia-reperfusion injury and that this protective action is mediated by K ATP opening. Rat isolated hearts were Langendorff-perfused and underwent 30 min left main coronary artery occlusion and 120 min reperfusion. The resulting injury was assessed as infarct size, determined by tetrazolium staining. Treatment of hearts with the H2S-donor, NaHS, commencing 10 min prior to the onset of coronary occlusion and maintained until 10 min reperfusion, resulted in a concentration-dependent limitation of infarct size (control, 41.0 +/- 2.6% of risk zone; NaHS 0.1 microM, 33.9 +/- 2.1%, [0.05 > P < 0.1]; NaHS 1 microM, 20.2 +/- 2.1% [P < 0.01]). Pretreatment with the K ATP channel blockers glibenclamide 10 microM or sodium 5-hydroxydecanoate (5HD) 100 microM led to abrogation of the infarct-limiting effect of NaHS 1 microM (glibenclamide + NaHS 42.5 +/- 3.6%; 5HD + NaHS 44.7 +/- 2.2%). No statistically significant effects of NaHS treatment on coronary flow, heart rate or left ventricular developed pressure were observed in this experimental preparation. These data provide the first evidence that exogenous H2S protects against irreversible ischemia-reperfusion injury in myocardium and support the involvement of K ATP opening in the mechanism of action. Further work is required to elucidate the potential role of endogenous H2S as a cytoprotective mediator against myocardial ischemia-reperfusion injury, the mechanisms regulating its generation, and the nature of its interaction with protein targets such as the K ATP channel.

Role of Hydrogen Sulfide in the Cardioprotection Caused by Ischemic Preconditioning in the Rat Heart and Cardiac Myocytes

Endogenous H(2)S is synthesized mainly by cystathionine gamma-lyase in the heart. The present study investigated the role of H(2)S in cardioprotection induced by ischemic preconditioning. We have examined the effect of endogenous H(2)S and exogenous application of NaHS (H(2)S donor) on cardiac rhythm in the isolated rat heart subjected to low-flow ischemia insults as well as cell viability and function in isolated myocytes exposed to simulated ischemia solution. Preconditioning with NaHS (SP) or ischemia (IP) for three cycles (3 min each cycle separated by 5 min of recovery) significantly decreased the duration and severity of ischemia/reperfusion-induced arrhythmias in the isolated heart while increasing cell viability and the amplitude of electrically induced calcium transients after ischemia/reperfusion in cardiac myocytes. Both IP and SP also significantly attenuated the decreased H(2)S production during ischemia. Moreover, decreasing endogenous H(2)S production significantly attenuated the protective effect of IP in both the isolated heart and isolated cardiac myocytes. Blockade of protein kinase C with chelerythrine or bisindolylmaleimide I as well as ATP-sensitive K(+) (K(ATP)) channel with glibenclamide (a nonselective K(ATP) blocker) and HMR-1098 (1-[[5-[2-(5-Chloro-o-anisamido)ethyl]-2-methoxyphenyl]sulfonyl]-3-methylthiourea) (a sarcolemmal K(ATP) channel blocker) reversed the cardioprotection induced by SP or IP. However, blockade of mitochondrial K(ATP) channels with 5-hydroxydecanoic acid had no effect on the cardioprotection of SP, suggesting that, unlike the mechanism involved in IP, mitochondrial K(ATP) channels most probably do not play a major role in the cardioprotection of SP. Our findings suggest that endogenous H(2)S contributes to cardioprotection induced by IP, which effect may involve protein kinase C and sarcolemmal K(ATP) channels.

Inhibition of hydrogen sulfide generation contributes to gastric injury caused by anti-inflammatory nonsteroidal drugs

BACKGROUND & AIMS

Hydrogen sulfide (H(2)S), an endogenous gaseous mediator that causes vasodilation, is generated in mammalian tissues by cystathionine beta-synthase (CBS) and cystathionine-gamma-lyase (CSE). Here, we have investigated the role of H(2)S in a rodent model of nonsteroidal anti-inflammatory drug (NSAID) gastropathy.

METHODS

Rats were given acetyl salycilic acid (ASA) or an NSAID alone or in combination with NaHS, an H(2)S donor, and killed 3 hours later. Gastric blood flow was measured by laser-Doppler flowmetry, whereas intravital microscopy was used to quantify adhesion of leukocytes to mesenteric postcapillary endothelium.

RESULTS

At a dose of 100 micromol/kg, NaHS attenuated by 60%-70% the gastric mucosal injury, and tumor necrosis factor (TNF)-alpha, intercellular adhesion molecule (ICAM)-1, and lymphocyte function-associated antigen (LFA)-1 mRNA up-regulation induced by NSAIDs (P < .05) NaHS administration prevented the associated reduction of gastric mucosal blood flow (P < .05) and reduced ASA-induced leukocyte adherence in mesenteric venules. NaHS did not affect suppression of prostaglandin E(2) (PGE(2)) synthesis by NSAIDs. Glibenclamide, a K(ATP) channel inhibitor, and DL-propargylglycine, a CSE inhibitor, exacerbated, whereas pinacidil, a K(ATP) opener, attenuated gastric injury caused by ASA. Exposure to NSAIDs reduced H(2)S formation and CSE expression (mRNA and protein) and activity by 60%-70%. By promoter deletion and mutation analysis, an Sp1 consensus site was identified in the CSE promoter. Exposure to NSAIDs inhibits Sp1 binding to its promoter and abrogates CSE expression in HEK-293 cells transfected with a vector containing the core CSE promoter. Exposure to NSAIDs inhibits Sp1 and ERK phosphorylation.

CONCLUSIONS

These data establish a physiologic role for H(2)S in regulating the gastric microcirculation and identify CSE as a novel target for ASA/NSAIDs.

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.

Activation of KATP channels by H2S in rat insulin-secreting cells and the underlying mechanisms

H2S is an important gasotransmitter, generated in mammalian cells from L-cysteine metabolism. As it stimulates K(ATP) channels in vascular smooth muscle cells, H2S may also function as an endogenous opener of K(ATP) channels in INS-1E cells, an insulin-secreting cell line. In the present study, K(ATP) channel currents in INS-1E cells were recorded using the whole-cell and single-channel recording configurations of the patch-clamp technique. K(ATP) channels in INS-1E cells have a single-channel conductance of 78 pS. These channels were activated by diazoxide and inhibited by gliclazide. ATP (3 mm) in the pipette solution inhibited K(ATP) channels in INS-1E cells. Significant amount of H2S was produced from INS-1E cells in which the expression of cystathinonie gamma-lyase (CSE) was confirmed. After INS-1E cells were transfected with CSE-targeted short interfering RNA (CSE-siRNA) or treated with DL-propargylglycine (PPG; 1-5 mm) to inhibit CSE, endogenous production of H2S was abolished. Increase in extracellular glucose concentration significantly decreased endogenous production of H2S in INS-1E cells, and increased insulin secretion. After transfection of INS-1E cells with adenovirus containing the CSE gene (Ad-CSE) to overexpress CSE, high glucose-stimulated insulin secretion was virtually abolished. Basal K(ATP) channel currents were significantly reduced after incubating INS-1E cells with a high glucose concentration (16 mm) or lowering endogenous H2S level by CSE-siRNA transfection. Under these conditions, exogenously applied H2S significantly increased whole-cell K(ATP) channel currents at concentrations equal to or lower than 100 microm. H2S (100 microm) markedly increased open probability by more than 2-fold of single K(ATP) channels (inside-out recording) in native INS-1E cells (n = 4, P < 0.05). Single-channel conductance and ATP sensitivity of K(ATP) channels were not changed by H2S. In conclusion, endogenous H2S production from INS-1E cells varies with in vivo conditions, which significantly affects insulin secretion from INS-1E cells. H2S stimulates K(ATP) channels in INS-1E cells, independent of activation of cytosolic second messengers, which may underlie H2S-inhibited insulin secretion from these cells. Interaction among H2S, glucose and the K(ATP) channel may constitute an important and novel mechanism for the fine control of insulin secretion from pancreatic beta-cells.

Direct stimulation of K(ATP) channels by exogenous and endogenous hydrogen sulfide in vascular smooth muscle cells

ATP-sensitive K+ (K(ATP)) channels in vascular smooth muscle cells (VSMC) are important targets for endogenous metabolic regulation and exogenous drug therapy. H2S, as a novel gasotransmitter, has been shown to relax rat aortic tissues via opening of K(ATP) channels. However, interaction of H2S, exogenous-applied or endogenous-produced, with K(ATP) channels in resistance artery VSMC has not been delineated. In the present study, using the whole-cell and single-channel patch-clamp technique, we demonstrated that exogenous H2S activated K(ATP) channels and hyperpolarized cell membrane in rat mesenteric artery VSMC. H2S enhanced the amplitude of whole-cell K(ATP) currents with an EC50 value of 116 +/- 8.3 microM and increased the open probability of single K(ATP) channels. H2S hyperpolarized membrane potentials by -12 mV in nystatin-perforated VSMC. Furthermore, inhibition of endogenous H2S production with D,L-propargylglycine (PPG) reduced whole-cell K(ATP) currents. PPG alone had no effect on unitary K(ATP) channel currents in cell-free membrane patches. In addition, effects of H2S on K(ATP) channels and membrane potentials were independent of cGMP-mediated phosphorylation. This study demonstrated modulation of K(ATP) channel activity by exogenous and endogenous H2S in resistance artery VSMC, thus helping elucidate cardiovascular functions of this endogenous gas.

The third gas: H2S regulates perfusion pressure in both the isolated and perfused normal rat liver and in cirrhosis

The regulation of sinusoidal resistance is dependent on the contraction of hepatic stellate cells (HSC) around sinusoidal endothelial cell (SEC) through paracrine cross-talk of vasoconstrictor and vasodilator agents. Hydrogen sulfide (H2S), a recently discovered gas neurotransmitter, is a putative vasodilator whose role in hepatic vascular regulation and portal hypertension is unexplored. Four-week bile duct-ligated (BDL) rats with cirrhosis and control rats were treated daily with NaHS (56 micromol/kg) for 5 days. Isolated livers were perfused first with NaHS for 20 minutes and then with norepinephrine (NE) and the intrahepatic resistance studied. In normal rats and animals with cirrhosis, administration of NE resulted in a dose-dependent increase of portal pressure. This effect was attenuated by H2S treatment (P < .05). The H2S-induced relaxation of hepatic microcirculation was attenuated by glibenclamide, an adenosine triphosphate (ATP)-sensitive K+ channel inhibitor. L-Cysteine, a substrate of cystathionine-gamma-lyase (CSE), decreased vasoconstriction in normal rat livers (P < .05) but failed to do so in livers with cirrhosis. BDL resulted in a downregulation of CSE mRNA/protein levels and activity (P < .05). Our in vitro data demonstrate that CSE is expressed in hepatocytes, HSCs, but not in sinusoidal endothelial cells (SEC). HSC activation downregulates CSE mRNA expression, resulting in a defective production of H2S and abrogation of relaxation induced by L-cysteine. In conclusion, CSE-derived H2S is involved in the maintenance of portal venous pressure. The reduction of CSE expression in the liver with cirrhosis contributes to the development of increased intrahepatic resistance and portal hypertension.

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.

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

Hydrogen sulphide (H(2)S) is a naturally occurring gas, with potent vasodilator activity. In this report, we identify a role for H(2)S in carrageenan-induced hindpaw oedema in the rat. Intraplantar injection of carrageenan (150 microl, 2% (w v(-1))) resulted in an increase in hindpaw H(2)S synthesising enzyme activity and increased myeloperoxidase (MPO) activity. Pretreatment (i.p. 60 min before carrageenan) with DL-propargylglycine (PAG, 25-75 mg kg(-1)), an inhibitor of the H(2)S synthesising enzyme cystathionine-gamma-lyase (CSE), significantly reduced carrageenan-induced hindpaw oedema in a dose-dependent manner (e.g. increase in hindpaw weight at 3 h, saline: 0.12+/-0.017 g; carrageenan, 1.39+/-0.037 g; PAG, 50 mg kg(-1), 1.11+/-0.06 g, n=10) and MPO activity (fold increase) in the hindpaw (saline: 1.0+/-0.12; carrageenan, 2.92+/-0.45 g; PAG, 50 mg kg(-1), 1.1+/-0.22, n=10); PAG (50 mg kg(-1)) also inhibited H(2)S synthesising enzyme activity (nmol microg DNA(-1)) in the hindpaw in a dose-dependent manner (saline, 0.46+/-0.05; carrageenan, 0.71+/-0.08 g; PAG, 50 mg kg(-1), 0.17+/-0.05, n=10).

Sodium nitroprusside potentiates hydrogen-sulfide-induced contractions in body wall muscle from a marine worm

Hydrogen sulfide (H2S) at concentrations of about 0.05 to 1 mmol.l(-1) appears to function as a gasotransmitter in vertebrates, analogous to nitric oxide (NO) and carbon monoxide, but the actions of H2S in invertebrate tissue have not been well studied. In this study, we investigated the role of H2S in modulating body wall muscle tone in the marine echiuran worm Urechis caupo (Echiuridae). We first determined that U. caupo body wall homogenates produce H2S upon addition of L-cysteine and pyridoxal-5'-phosphate (PLP), and that the rate is increased by addition of 2-mercaptoethanol, suggesting the presence of an activated L-serine sulfhydrase pathway. We then measured the contractile response of U. caupo body wall circular muscle strips to sodium hydrosulfide (NaHS)--which produces H2S in solution--and the NO donor sodium nitroprusside (SNP), both with and without subsequent application of acetylcholine (ACh). We found that NaHS alone stimulated contraction in muscle strips equivalent to about one-third the force of ACh alone, whereas SNP alone had no effect on muscle tone. However, simultaneous addition of NaHS with SNP elicited a much stronger contraction, reaching more than twice that of ACh alone, which could be increased further by subsequent application of ACh.

Streptozotocin-induced diabetes in the rat is associated with enhanced tissue hydrogen sulfide biosynthesis

This investigation is aimed to determine whether the biosynthesis of H(2)S, an endogenous vasodilator gas, is altered in the streptozotocin-diabetic rat. Plasma H(2)S concentration as well as the activity, and expression, of H(2)S synthesizing enzymes (namely cystathionine-gamma-lyase (CSE) and cystathionine-beta-synthetase (CBS)) were measured in various tissues of non-diabetic, streptozotocin-diabetic and insulin-treated diabetic rats. H(2)S formation in pancreas and liver was increased in diabetic rats. Both CSE and CBS mRNAs were increased in liver of diabetic animals. Similarly, CBS mRNA was increased in pancreas. Insulin treatment restored the changes in H(2)S metabolism seen. The findings of this study suggest that the metabolism of H(2)S in pancreas and liver is altered in the streptozotocin-diabetic rat. This is the first study in which a derangement in H(2)S biosynthesis in diabetes has been demonstrated. H(2)S may play a part in the aetiology or development of diabetes in this animal model.

Hydrogen sulfide is synthesized in the gills of the clam Mercenaria mercenaria and acts seasonally to modulate branchial muscle contraction

Previously we showed that when the gill muscles of the venerid clam Mercenaria mercenaria are stimulated to contract by 5-hydroxytryptamine (5HT), the contraction is about doubled when another identical dose of 5HT is applied after washout. Furthermore, this "endogenous potentiation" is mimicked by nitric oxide (NO), which is synthesized in the gill. We now report that the isolated gills also synthesize H2S; the basal rate of synthesis was 0.70 micromol.g(-1).h(-1) (se = 0.14; n = 24), but in the presence of 5HT (10(-2) M), the rate increased markedly to 35.82 micromol.g(-1).h(-1) (se = 4.93; n = 4). In addition, dithiothreitol (DTT; 2.2 mM) increased the rate of synthesis significantly to 4.9 micromol.g(-1).h(-1) (se = 0.8; n = 8). Stimulation of H2S synthesis by 5HT (5 x 10(-3) M) was seasonal; that is, the rates measured monthly from December through June are significantly lower than those measured from July through November. We also found that if isolated gills were pretreated with the H2S donor, sodium hydrosulfide (NaHS), their contractions in response to 5HT were potentiated. The threshold of the potentiation was 10(-8) M NaHS, and the largest effect was at 10(-6) M. During August, however, when endogenous and NO-induced potentiations are both absent, 10(-6) M NaHS was also ineffective. Like the effect of NO, that of NaHS (10(-6) M) was blocked by oxadiasoloquinoxalin (ODQ; 5 x 10(-5) M), an inhibitor of soluble guanylate cyclase (sGC). Moreover, Rp-8-CPT-cGMPS (10(-5) M), which inhibits protein kinase-G, also blocked the effect of NaHS (10(-6) M). When isolated gills were treated with 2.2 mM DTT, the endogenous potentiation of a second 5HT-induced contraction more than doubled in comparison to untreated controls. In conclusion, H2S is synthesized in the gill and, along with NO, is a seasonal, endogenous modulator of branchial muscle contraction; its action may be mediated through a sGC/cGMP signaling cascade.

Vascular actions of hydrogen sulfide in nonmammalian vertebrates

Hydrogen sulfide (H(2)S) vasoactivity has been observed in isolated vessels from all vertebrate classes, and its effects, which include constriction, dilation, and multiphasic responses, are both species- and vessel-specific. H(2)S is synthesized by mammalian and fish vessels, and because plasma H(2)S titers are also vasoactive in vitro, it is likely that H(2)S is a tonic effector of cardiovascular homeostasis in many vertebrates. Mechanisms of H(2)S vasoactivity in nonmammalian vertebrates have been limited to the trout where the triphasic relaxation-contraction-relaxation includes endothelium-dependent and -independent components, ATP-dependent K(+) channels, and extracellular and intracellular Ca(2+), all independent of cyclic GMP production. The observation that at least some H(2)S constrictory activity has been observed in all vertebrates except sharks suggests that H(2)S may have been an ancestral pressor gasotransmitter. However, the ability of H(2)S to serve as either (or both) an endothelium-independent constrictor or dilator, which is relatively unique among vasoregulatory molecules, is a feature that seems to have been exploited, for unknown reasons, by nearly all vertebrates. Aquatic vertebrates appear particularly vulnerable to H(2)S because of their intrinsically low blood pressure and the potential for increased H(2)S exposure from the environment.

Role of hydrogen sulfide in acute pancreatitis and associated lung injury

Hydrogen sulfide (H2S) is a naturally occurring gas with potent vasodilator activity. Cystathionine-gamma-lyase (CSE) and cystathionine-beta-synthase (CBS) utilize L-cysteine as substrate to form H2S. Of these two enzymes, cystathionine-gamma-lyase (CSE) is believed to be the key enzyme that forms H2S in the cardiovascular system. Whilst H2S has been reported to relax precontracted rat arteries in vitro and to lower blood pressure in the rat, its effect in an inflammatory condition such as acute pancreatitis has not previously been reported. In this paper, we report the presence of H2S synthesizing enzyme activity and CSE (as determined by mRNA signal) in the pancreas. Also, prophylactic, as well as therapeutic, treatment with the CSE inhibitor, DL-propargylglycine (PAG), significantly reduced the severity of caerulein-induced pancreatitis and associated lung injury, as determined by 1) hyperamylasemia [plasma amylase (U/L) (control, 1204+/-59); prophylactic treatment: placebo, 10635+/-305; PAG, 7904+/-495; therapeutic treatment: placebo, 10427+/-470; PAG, 7811+/-428; P<0.05 PAG c.f. placebo; n=24 animals in each group]; 2) neutrophil sequestration in the pancreas [pancreatic myeloperoxidase oxidase (MPO) activity (fold increase over control) (prophylactic treatment: placebo, 5.78+/-0.63; PAG, 2.97+/-0.39; therapeutic treatment: placebo, 5.48+/-0.52; PAG, 3.03+/-0.47; P<0.05 PAG c.f. placebo; n=24 animals in each group)]; 3) pancreatic acinar cell injury/necrosis; 4) lung MPO activity (fold increase over control) [prophylactic treatment: placebo, 1.99+/-0.16; PAG, 1.34+/-0.14; therapeutic treatment: placebo, 2.03+/-0.12; PAG, 1.41+/-0.97; P<0.05 PAG c.f. placebo; n=24 animals in each group]; and 5) histological evidence of lung injury. These effects of CSE blockade suggest an important proinflammatory role of H2S in regulating the severity of pancreatitis and associated lung injury and raise the possibility that H2S may exert similar activity in other forms of inflammation.

Hydrogen sulfide‐induced apoptosis of human aorta smooth muscle cells via the activation of mitogen‐activated protein kinases and caspase‐3

The endogenous production of hydrogen sulfide (H2S) and its physiological functions, including membrane hyperpolarization and smooth muscle cell relaxation, position this gas well in the family of gasotransmitters together with nitric oxide (NO) and carbon monoxide (CO). In this study, we demonstrate that H2S at physiologically relevant concentrations induced apoptosis of human aorta smooth muscle cells (HASMCs). Exposure of HASMCs to H2S did not induce necrosis as verified with Trypan blue exclusion and LDH release analysis. After inhibiting endogenous H2S production, exogenous H2S induced much more significant apoptosis, which was not altered by the presence of albumin or glutathione. H2S treatment increased the activities of ERK and p38 mitogen-activated protein kinase (MAPK), but not c-Jun N-terminal kinase activity. Suppression of extracellular signal-regulated kinase (ERK) activity, but not of p38 activity, inhibited the H2S-induced apoptosis of HASMCs. The activation of ERK by H2S in HASMCs was accompanied by increased caspase-3 activity. Inhibition of caspase-3 by AC-DEVD-CHO attenuated the H2S-induced cell apoptosis. Inhibition of ERK by U0126 decreased caspase-3 activity, whereas AC-DEVD-CHO did not alter ERK activity. In conclusion, exogenous H2S induces apoptosis of HASMCs, which is significantly affected by the endogenous H2S level. Of the three investigated MAPKs, only ERK played an active role in mediating H2S-induced apoptosis of HASMCs by activating caspase-3. These findings may help reveal novel mechanisms for many diseases linked to H2S-related abnormal cellular proliferation and apoptosis.

Cystathionine gamma-lyase overexpression inhibits cell proliferation via a H2S-dependent modulation of ERK1/2 phosphorylation and p21Cip/WAK-1

Cystathionine gamma-lyase (CSE) is a key enzyme in the trans-sulfuration pathway. CSE uses L-cysteine as a substrate to produce hydrogen sulfide (H2S). The CSE/H2S system has been shown to play an important role in regulating cellular functions in different systems. In the present study, we used CSE stably overexpressed HEK-293 cells to explore the effect of the CSE/H2S system on cell growth and proliferation. The overexpression of CSE resulted in increases in CSE mRNA levels, CSE proteins, and intracellular H2S production rates, as well as the inhibition of cell proliferation and DNA synthesis. These effects were accompanied by a sustained ERK activation and up-regulation of the cyclin-dependent kinase inhibitor p21Cip/WAK-1. Blocking the action of ERK with U0126 inhibited the induction of p21Cip/WAK-1, suggesting that ERK activation functions upstream of p21Cip/WAK-1 activation to initiate the CSE overexpression-induced cell growth inhibition. The antiproliferative effect of CSE is likely mediated by endogenously produced H2S because the H2S scavenger methemoglobin (10 microm) significantly decreased the H2S production rate and reversed the antiproliferative effect afforded by CSE. Exogenous H2S (100 microm) also inhibited cell proliferation. However, the other CSE-catalyzed products, ammonium and pyruvate, failed to inhibit cell proliferation. Methemoglobin also abolished the inhibitory effect of exogenous H2S on cell proliferation. Moreover, exogenous H2S induced a sustained ERK and p21Cip/WAK-1 activation. These findings support the hypothesis that endogenously produced H2S may play a fundamental role in cell proliferation and survival.

Vertebrate phylogeny of hydrogen sulfide vasoactivity

Hydrogen sulfide (H(2)S) is a recently identified endogenous vasodilator in mammals. In steelhead/rainbow trout (Oncorhynchus mykiss, Osteichthyes), H(2)S produces both dose-dependent dilation and a unique dose-dependent constriction. In this study, we examined H(2)S vasoactivity in all vertebrate classes to determine whether H(2)S is universally vasoactive and to identify phylogenetic and/or environmental trends. H(2)S was generated from NaHS and examined in unstimulated and precontracted systemic and, when applicable, pulmonary arteries (PA) from Pacific hagfish (Eptatretus stouti, Agnatha), sea lamprey (Petromyzon marinus, Agnatha), sandbar shark (Carcharhinus milberti, Chondrichthyes), marine toad (Bufo marinus, Amphibia), American alligator (Alligator mississippiensis, Reptilia), Pekin duck (Anas platyrhynchos domesticus, Aves), and white rat (Rattus rattus, Mammalia). In otherwise unstimulated vessels, NaHS produced 1) a dose-dependent relaxation in Pacific hagfish dorsal aorta; 2) a dose-dependent contraction in sea lamprey dorsal aorta, marine toad aorta, alligator aorta and PA, duck aorta, and rat thoracic aorta; 3) a threshold relaxation in shark ventral aorta, dorsal aorta, and afferent branchial artery; and 4) a multiphasic contraction-relaxation-contraction in the marine toad PA, duck PA, and rat PA. Precontraction of these vessels with another agonist did not affect the general pattern of NaHS vasoactivity with the exception of the rat aorta, where relaxation was now dominant. These results show that H(2)S is a phylogenetically ancient and versatile vasoregulatory molecule that appears to have been opportunistically engaged to suit both organ-specific and species-specific homeostatic requirements.

Modulation of endogenous production of H2S in rat tissues

H2S is an important gasotransmitter with a vasorelaxant property. The modulation of endogenous H2S generation from different tissues and the functional consequence of this modulation are not clear. In the present study, the production of H2S from vascular tissues as well as the liver and ileum of rats was measured. The H2S production rate was significantly greater in rat liver than rat vascular tissues. H2S production in rat aortae, ileum, and liver tissues was upregulated by sodium nitroprusside in a cGMP-dependent fashion. Amino-oxyacetate (AOA) (1 mM) abolished H2S production in liver tissues and partially inhibited H2S production in the ileum, while D,L-propargylglycine (PPG) at a similar concentration only slightly inhibited H2S production in liver. Intraperitoneal injection PPG, but not AOA, significantly suppressed H2S production in liver, aorta, and ileum tissues. The systolic blood pressure of rats was significantly increased 2-3 weeks after i.p. injection of PPG. It is concluded that the endogenous production of H2S could be modulated by NO. AOA and PPG have different capacities in regulating the endogenous production of H2S in different types of tissues.

Endogenous hydrogen sulfide regulation of myocardial injury induced by isoproterenol

Previous work has shown that the endogenous cystathionine gamma-synthase (CSE)/hydrogen sulfide (H(2)S) pathway participates in the regulation of cardiac contraction. We hypothesized that the pathway might participate in the pathophysiological regulation of ischemic heart disease. Isoproterenol injection of rat hearts induced a myocardial ischemic injury model, with reduced myocardial and plasma H(2)S levels, decreased CSE activity, and upregulated CSE gene expression. Exogenous administration of the H(2)S donor NaHS reduced the mortality rate; increased left-ventricular pressure development and left-ventricular-end systolic pressure; and decreased left-ventricular-end diastolic pressure (LVEDP) and subendocardial necrosis, capillary dilatation, leukocytic infiltration, fibroblast swelling, and fibroblastic hyperplasia. As well, production of lipid peroxidation, including myocardial malondialdehyde (MDA), and plasma MDA and conjugated diene, was reduced. Oxidative stress injury is an important mechanism of isoproterenol-induced myocardial injury. In vitro experiments revealed that NaHS might antagonize myocyte MDA production by oxygen-free radicals and that NaHS directly scavenged hydrogen peroxide and superoxide anions. Our results suggest that the endogenous CSE/H(2)S pathway contributes to the pathogenesis of isoproterenol-induced myocardial injury. Administration of exogenous H(2)S effectively protects myocytes and contractile activity, at least by its direct scavenging of oxygen-free radicals and reducing the accumulation of lipid peroxidations.

H2S, un nouveau neuromodulateur

The formation of H2S from cyst(e)ine is catalyzed by three enzymes, cystathionine beta synthase, cystathionase, and 3-mercaptopyruvate sulfurtransferase. In the liver, kidney, enterocytes and vascular smooth muscle cells, H2S is principally synthesized by cystathionase. In contrast, it is synthesized by cystathionine beta synthase in the brain and partially by 3-mercaptopyruvate sulfurtransferase in cardiac tissue. H2S is catabolized, essentially in mitochondria by thiosulfate reductase. The sulfite generated is then oxidized to sulfate by sulfite oxidase. The amount of thiosulfate excreted in the urine is the best indicator of H2S biosynthesis, together with sulfhemoglobin determination in erythrocytes. H2S acts as a neuromodulator in the brain, increasing responses mediated by NMDA receptors, facilitating the induction of long-term potentialization in the hippocampus. H2S also acts as a vasodilator, acting directly on ATP-dependent potassium channels in vascular smooth muscle cells. The concentration of H2S is abnormally low in the brains of subjects with Alzheimer's disease, due to changes in the concentration of the physiological activator of cystathionine beta synthase. The overproduction of H2S described in subjects with Down's syndrome probably results from the overproduction of cystathionine beta synthase, as the gene encoding this protein is located on chromosome 21.

Hydrogen sulfide-induced relaxation of resistance mesenteric artery beds of rats

Hydrogen sulfide (H2S) has been shown recently to function as an important gasotransmitter. The present study investigated the vascular effects of H2S, both exogenously applied and endogenously generated, on resistance mesenteric arteries of rats and the underlying mechanisms. Both H2S and NaHS evoked concentration-dependent relaxation of in vitro perfused rat mesenteric artery beds (MAB). The sensitivity of MAB to H2S (EC50, 25.2 +/- 3.6 microM) was about fivefold higher than that of rat aortic tissues. Removal of endothelium or coapplication of charybdotoxin and apamin to endothelium-intact MAB significantly reduced the vasorelaxation effects of H2S. The H2S-induced relaxation of MAB was partially mediated by ATP-sensitive K+ (KATP) channel activity in vascular smooth muscle cells. Pinacidil (EC50, 1.7 +/- 0.1 microM, n=6) mimicked, but glibenclamide (10 microM, n=6) suppressed, the vasorelaxant effect of H2S. KATP channel currents in isolated mesenteric artery smooth muscle cells were significantly augmented by H2S. L-cysteine, a substrate of cystathionine-gamma-lyase (CSE), at 1 mM increased endogenous H2S production by sixfold in rat mesenteric artery tissues and decreased contractility of MAB. DL-propargylglycine (a blocker of CSE) at 10 microM abolished L-cysteine-dependent increase in H2S production and relaxation of MAB. Our results demonstrated a tissue-specific relaxant response of resistance arteries to H2S. The stimulation of KATP channels in vascular smooth muscle cells and charybdotoxin/apamin-sensitive K+ channels in vascular endothelium by H2S represents important cellular mechanisms for H2S effect on MAB. Our study also demonstrated that endogenous CSE can generate sufficient H2S from exogenous L-cysteine to cause vasodilation. Future studies are merited to investigate direct contribution of endogenous H2S to regulation of vascular tone.

Polymorphisms of glutathione S-transferase M1 and T1 modulate blood pressure of individuals chronically exposed to natural sour gas containing sulfur compounds

In order to find the effect of genetic polymorphisms of GSTM1 and GSTT1 on blood pressure of individuals chronically exposed to sulfur compounds, the present study was done. Study subjects (38 males, 38 females) were residents of contaminated areas of Masjid-i-Sulaiman (southwest of Iran). The GSTM1 and GSTT1 genotypes were determined using a polymerase chain reaction (PCR)-based method. The non-parametric Sign test was applied in order to detect differences between the GSTs genotypes of study subjects and the normal mean values according to the sex and age of subjects. From four combination of genotypes, systolic blood pressure significantly decreased in combination of null-GSTM1 and present-GSTT1 (Z=-2.41; P=0.016), and diastolic blood pressure significantly increased in combination of present-GSTM1 and null-GSTT1 (Z=+2.14; P=0.032). It is speculated about polymorphisms of GSTs in individuals chronically exposed to natural sour gas, which contains H2S, fulfilling a physiological role(s) in regulating blood pressure.

Impact of hydrogen sulfide on carbon monoxide/heme oxygenase pathway in the pathogenesis of hypoxic pulmonary hypertension

Hypoxic pulmonary hypertension (HPH) is an important pathophysiological process of a variety of cardiac and pulmonary diseases. But the mechanisms responsible for HPH are still not fully understood. The discoveries of endogenous gas signal molecules, nitric oxide (NO), and carbon monoxide (CO), have been moving the research of HPH to a new phase. Hydrogen sulfide (H2S), which is now being considered as the third new gas transmitter, was found to be possibly involved in the pathogenesis of HPH. But whether there exists an interaction between H2S and CO has not been clear in the pathogenesis of HPH. In this study, we found that H2S was significantly decreased in the pathogenesis of HPH. However, plasma CO level and the expressions of heme oxygenase (HO-1) protein and HO-1 mRNA were significantly increased. Exogenous supply of H2S could alleviate the elevation of pulmonary arterial pressure. At the same time, plasma CO level and the expressions of HO-1 protein and mRNA in pulmonary arteries were significantly increased. Whereas, exogenous supply of propargylglycine (PPG), an inhibitor of cystathionine gamma-lyase (CSE), decreased the plasma H2S content and worsened HPH. At the same time, plasma CO level and the expressions of HO-1 protein and mRNA in pulmonary arteries were decreased. The results showed that H2S could play a regulatory role in the pathogenesis of HPH through up-regulating CO/HO pathway.

Hydrogen sulphide: an endogenous stimulant of capsaicin-sensitive primary afferent neurons?

Hydrogen sulphide (H(2)S) is a gas best known for its rotten egg smell. The toxic effects of high concentrations of H(2)S have been extensively investigated. It is known that H(2)S is generated in mammalian systems, but little is known of its effects in physiological concentrations. In the present issue of this journal, Patacchini et al. present evidence that H(2)S stimulates capsaicin-sensitive primary afferent neurons to release tachykinins in the rat urinary bladder. The possible significance of this finding is discussed in this commentary.

Hydrogen sulfide as an endogenous regulator of vascular smooth muscle tone in trout

Hydrogen sulfide (H(2)S) is an endogenous vasodilator in mammals, but its presence and function in other vertebrates is unknown. We generated H(2)S from NaHS and examined the effects on isolated efferent branchial arteries from steelhead (stEBA) or rainbow (rtEBA) trout. H(2)S concentration was measured colorimetrically (CM) and with ion-selective electrodes (ISE) in rainbow trout plasma. NaHS produced a triphasic response consisting of a relaxation (phase 1), constriction (phase 2), and relaxation (phase 3) in both unstimulated vessels and in stEBA precontracted with carbachol (Carb). Phase 1 and phase 3 in stEBA were decreased and phase 2 increased in unstimulated vessels by K(+)(ATP) channel inhibition (glibenclamide), or a cocktail of inhibitors of cyclooxygenase, lipoxygenase, and cytochrome P-450 (indomethacin, esculetin, and clotrimazole). Inhibition of soluble guanylate cyclase with ODQ o NS-2028 inhibited phase 3 in stEBA, although NaHS decreased cGMP production by tEBA. stEBA phase 2 contractions were partially inhibited by the myosin light chain kinase inhibitor, ML-9, but unaffected by L-type calcium channel inhibition (methoxyverapamil), whereas contraction in tEBA was partially inhibited by nifedipine or removal of extracellular calcium. Phase 3 relaxations were more pronounced in stEBA precontracted with Carb and no epinephrine (NE) than those cont acted by KCl or K(2)SO(4). stEBA phase 2 and phase 3 responses were dose dependent (EC(50) = 1.1 +/- 1.2 x 10(-3) M and 6.7 +/- 0.9 x 10(-5) M, respectively; n = 7). NaHS was also vasoactive in steelhead bulbus arteriosus, celiac mesenteric arteries, and anterior cardinal veins. Rainbow trout plasma sulfide concentration was 4.0 +/- 0.3 x 10(-5) M, n = 4 (CM) and 3.8 +/- 0.4 x 10(-5) M, n = 9 (ISE); similar to phase 3 EC(50). Because NaHS has substantial vasoactive effects at physiological plasma concentrations, we propose that its soluble derivative, H(2)S, is a tonically active endogenous vasoregulator in trout.

Hydrogen sulfide: from the smell of the past to the mediator of the future?

Gases such as nitric oxide and carbon monoxide play important roles both in normal physiology and in disease. In recent years, interest has been directed towards other naturally occurring gases, notably hydrogen sulfide (H(2)S), which is both a potent vasodilator and a mediator of long-term potentiation in the brain. This article focuses on recent work that suggests a role for H(2)S, and perhaps other gases, in the CNS and cardiovascular system.