Actions and interactions of nitric oxide, carbon monoxide and hydrogen sulphide in the cardiovascular system and in inflammation--a tale of three gases!

Sulfurous gases as biological messengers and toxins: comparative genetics of their metabolism in model organisms

Gasotransmitters are biologically produced gaseous signalling molecules. As gases with potent biological activities, they are toxic as air pollutants, and the sulfurous compounds are used as fumigants. Most investigations focus on medical aspects of gasotransmitter biology rather than toxicity toward invertebrate pests of agriculture. In fact, the pathways for the metabolism of sulfur containing gases in lower organisms have not yet been described. To address this deficit, we use protein sequences from Homo sapiens to query Genbank for homologous proteins in Caenorhabditis elegans, Drosophila melanogaster, and Saccharomyces cerevisiae. In C. elegans, we find genes for all mammalian pathways for synthesis and catabolism of the three sulfur containing gasotransmitters, H₂S, SO₂ and COS. The genes for H₂S synthesis have actually increased in number in C. elegans. Interestingly, D. melanogaster and Arthropoda in general, lack a gene for 3-mercaptopyruvate sulfurtransferase, an enzym for H₂S synthesis under reducing conditions.

Hydrogen sulfide promotes calcium signals and migration in tumor-derived endothelial cells

Hydrogen sulfide (H(2)S) is a gasotransmitter that plays several roles in various tissues, including the cardiovascular system. Because it has been recently proposed to act as a mediator of angiogenesis progression, here we investigate the effects of H(2)S in a well-established model of tumor angiogenesis: endothelial cells obtained from human breast carcinoma (B-TECs). Ca(2+) imaging and patch-clamp experiments reveal that acute perfusion with NaHS, a widely employed H(2)S donor, activates cytosolic calcium (Ca(c)) increase, as well as potassium and nonselective cationic currents, in B-TECs. Stimulation with NaHS in the same concentration range (1 nM-200 μM) evoked Ca(c) signals also in "normal" human microvascular endothelial cells (HMVECs), but the amplitude was significantly lower. Moreover, although NaHS failed to promote either migration or proliferation on HMVECs, B-TEC migration was enhanced at low-micromolar NaHS concentrations (1-10 μM). Remarkably H(2)S mediates tumor proangiogenic signaling triggered by vascular endothelial growth factor (VEGF). B-TECs pretreated with dl-propargylglycine (5mM, 30 min), an inhibitor of the H(2)S-producing enzyme cystathionine γ-lyase, showed drastically reduced migration and Ca(c) signals induced by VEGF (20 ng/ml). We conclude that H(2)S plays a role in proangiogenic signaling of tumor-derived but not normal human ECs. Furthermore the ability of this gasotransmitter to interfere with B-TEC responsiveness to VEGF suggests that it could be an interesting target for antiangiogenic strategies in tumor treatment.

Interplay of hydrogen sulfide and nitric oxide on the pacemaker activity of interstitial cells of cajal from mouse small intestine

We studied whether nitric oxide (NO) and hydrogen sulfide (H(2)S) have an interaction on the pacemaker activities of interstitial cells of Cajal (ICC) from the mouse small intestine. The actions of NO and H(2)S on pacemaker activities were investigated by using the whole-cell patch-clamp technique and intracellular Ca(2+) analysis at 30℃ in cultured mouse ICC. Exogenously applied (±)-S-nitroso-N-acetylpenicillamine (SNAP), an NO donor, or sodium hydrogen sulfide (NaHS), a donor of H(2)S, showed no influence on pacemaker activity (potentials and currents) in ICC at low concentrations (10 µM SNAP and 100 µM NaHS), but SNAP or NaHS completely inhibited pacemaker amplitude and pacemaker frequency with increases in the resting currents in the outward direction at high concentrations (SNAP 100 µM and NaHS 1 mM). Co-treatment with 10 µM SNAP plus 100 µM NaHS also inhibited pacemaker amplitude and pacemaker frequency with increases in the resting currents in the outward direction. ODQ, a guanylate cyclase inhibitor, or glibenclamide, an ATP-sensitive K(+) channel inhibitor, blocked the SNAP+NaHS-induced inhibition of pacemaker currents in ICC. Also, we found that SNAP+NaHS inhibited the spontaneous intracellular Ca(2+) ([Ca(2+)](i)) oscillations in cultured ICC. In conclusion, this study describes the enhanced inhibitory effects of NO plus H(2)S on ICC in the mouse small intestine. NO+H(2)S inhibited the pacemaker activity of ICC by modulating intracellular Ca(2+). These results may be evidence of a physiological interaction of NO and H(2)S in ICC for modulating gastrointestinal motility.

Application of medical gases in the field of neurobiology

Medical gases are pharmaceutical molecules which offer solutions to a wide array of medical needs. This can range from use in burn and stroke victims to hypoxia therapy in children. More specifically however, gases such as oxygen, helium, xenon, and hydrogen have recently come under increased exploration for their potential theraputic use with various brain disease states including hypoxia-ischemia, cerebral hemorrhages, and traumatic brain injuries. As a result, this article will review the various advances in medical gas research and discuss the potential therapeutic applications and mechanisms with regards to the field of neurobiology.

Carbon monoxide affects electrical and contractile activity of rat myocardium

BACKGROUND

Carbon monoxide (CO) is a toxic gas, which also acts in the organism as a neurotransmitter. It is generated as a by-product of heme breakdown catalyzed by heme oxygenase. We have investigated changes in electrical and contractile activity of isolated rat atrial and ventricular myocardium preparations under the influence of CO.

METHODS

Standard microelectrode technique was used for intracellular registration of electrical activity in isolated preparations of atrial and ventricular myocardium. Contractions of atrial myocardial stripes were registered via force transducer.

RESULTS

CO (10(-4)-10(-3) M) caused prominent decrease of action potential duration (APD) in working atrial myocardium as well as significant acceleration of sinus rhythm. In addition CO reduced force of contractions and other parameters of contractile activity. Inhibitor of heme oxygenase zinc protoporphyrin IX exerts opposite effects: prolongation of action potential, reduction of sinus rhythm rate and enhancement of contractile function. Therefore, endogenous CO, which may be generated in the heart due to the presence of active heme oxygenase, is likely to exert the same effects as exogenous CO applied to the perfusing medium. In ventricular myocardium preparations exogenous CO also induced shortening of action potential, while zinc protoporphyrin IX produced the opposite effect.

CONCLUSIONS

Thus, endogenous or exogenous carbon monoxide may act as an important regulator of electrical and contractile cardiac activity.

Regulation of heart function by endogenous gaseous mediators-crosstalk between nitric oxide and hydrogen sulfide

Both nitric oxide (NO) and hydrogen sulfide (H(2)S) are two important gaseous mediators regulating heart function. The present study examined the interaction between these two biological gases and its role in the heart. We found that l-arginine, a substrate of NO synthase, decreased the amplitudes of myocyte contraction and electrically induced calcium transients. Sodium hydrogen sulfide (an H(2)S donor), which alone had minor effect, reversed the negative inotropic effects of l-arginine. The effect of l-arginine + sodium hydrogen sulfide was abolished by three thiols (l-cysteine, N-acetyl-cysteine, and glutathione), suggesting that the effect of H(2)S + NO is thiol sensitive. The stimulatory effect on heart contractility was also induced by GYY4137, a slow-releasing H(2)S donor, when used together with sodium nitroprusside, an NO-releasing donor. More importantly, enzymatic generation of H(2)S from recombinant cystathionine-γ-lyase protein also interacted with endogenous NO generated from l-arginine to stimulate heart contraction. In summary, our data suggest that endogenous NO may interact with H(2)S to produce a new biological mediator that produces positive inotropic effect. The crosstalk between H(2)S and NO also suggests an intriguing potential for the endogenous formation of a thiol-sensitive molecule, which may be of physiological significance in the heart.

The therapeutic potential of hydrogen sulfide: separating hype from hope

Hydrogen sulfide (H(2)S) has become the hot new signaling molecule that seemingly affects all organ systems and biological processes in which it has been investigated. It has also been shown to have both proinflammatory and anti-inflammatory actions and proapoptotic and anti-apoptotic effects and has even been reported to induce a hypometabolic state (suspended animation) in a few vertebrates. The exuberance over potential clinical applications of natural and synthetic H(2)S-"donating" compounds is understandable and a number of these function-targeted drugs have been developed and show clinical promise. However, the concentration of H(2)S in tissues and blood, as well as the intrinsic factors that affect these levels, has not been resolved, and it is imperative to address these points to distinguish between the physiological, pharmacological, and toxicological effects of this molecule. This review will provide an overview of H(2)S metabolism, a summary of many of its reported "physiological" actions, and it will discuss the recent development of a number of H(2)S-donating drugs that show clinical potential. It will also examine some of the misconceptions of H(2)S chemistry that have appeared in the literature and attempt to realign the definition of "physiological" H(2)S concentrations upon which much of this exuberance has been established.

Role of carbon monoxide in impaired endothelial function mediated by acute second-hand tobacco, incense, and candle smoke exposures

The aim of this study was to determine if carbon monoxide (CO) is responsible for acute adverse cardiovascular effects of different sources of smoke: second-hand tobacco smoke (SHS), incense and candle smoke. Endothelial function was tested using flow-mediated dilation (FMD) in pigs and was shown to be sensitive to nitric oxide synthase blockade. Subsequent experiments showed that FMD was significantly impaired compared to sham-exposed pigs at 30 min after a 30-min exposure to all three sources of smoke. In contrast, SHS significantly increased systolic, diastolic and pulse pressures compared to sham-exposure, while both incense and candle smoke exposure had no effect. The FMD impairment correlated well with CO levels in the exposure chamber, but not total particulates or venous CO-hemoglobin. Therefore, this study suggests a gas phase component of smoke that accompanies CO, but not CO itself, is responsible for acute endothelial dysfunction after SHS, incense or candle smoke exposure.

Oxygen/ozone as a medical gas mixture. A critical evaluation of the various methods clarifies positive and negative aspects

Besides oxygen, several other gases such as NO, CO, H₂, H₂S, Xe and O₃ have come to age over the past few years. With regards to O₃, its mechanisms of action in medicine have been clarified during the last two decades so that now a comprehensive framework for understanding and recommending ozone therapy in various pathologies is available. O₃ used within the determined therapeutic window is absolutely safe and more effective than golden standard medications in numerous pathologies, like vascular diseases. However, ozone therapy is mostly in practitioners' hands and some recent developments for increasing cost effectiveness and speed of treatment are neither standardized, nor evaluated toxicologically. Hence, the aim of this article is to emphasize the need to objectively assess the pros and cons of oxygen/ozone as a medical gas mixture in the hope that ozone therapy will be accepted by orthodox medicine in the near future.

Hydrogen sulfide and cell signaling

Hydrogen sulfide (H₂S) is a gaseous mediator synthesized from cysteine by cystathionine γ lyase (CSE) and other naturally occurring enzymes. Pharmacological experiments using H₂S donors and genetic experiments using CSE knockout mice suggest important roles for this vasodilator gas in the regulation of blood vessel caliber, cardiac response to ischemia/reperfusion injury, and inflammation. That H₂S inhibits cytochrome c oxidase and reduces cell energy production has been known for many decades, but more recently, a number of additional pharmacological targets for this gas have been identified. H₂S activates K(ATP) and transient receptor potential (TRP) channels but usually inhibits big conductance Ca²(+)-sensitive K(+) (BK(Ca)) channels, T-type calcium channels, and M-type calcium channels. H₂S may inhibit or activate NF-κB nuclear translocation while affecting the activity of numerous kinases including p38 mitogen-activated protein kinase (p38 MAPK), extracellular signal-regulated kinase (ERK), and Akt. These disparate effects may be secondary to the well-known reducing activity of H₂S and/or its ability to promote sulfhydration of protein cysteine moieties within the cell.

Designed iron carbonyls as carbon monoxide (CO) releasing molecules: rapid CO release and delivery to myoglobin in aqueous buffer, and vasorelaxation of mouse aorta

The physiological roles of CO in neurotransmission, vasorelaxation, and cytoprotective activities have raised interest in the design and syntheses of CO-releasing materials (CORMs) that could be employed to modulate such biological pathways. Three iron-based CORMs, namely, [(PaPy(3))Fe(CO)](ClO(4)) (1), [(SBPy(3))Fe(CO)](BF(4))(2) (2), and [(Tpmen)Fe(CO)](ClO(4))(2) (3), derived from designed polypyridyl ligands have been synthesized and characterized by spectroscopy and X-ray crystallography. In these three Fe(II) carbonyls, the CO is trans to a carboxamido-N (in 1), an imine-N (in 2), and a tertiary amine-N (in 3), respectively. This structural feature has been correlated to the strength of the Fe-CO bond. The CO-releasing properties of all three carbonyls have been studied in various solvents under different experimental conditions. Rapid release of CO is observed with 2 and 3 upon dissolution in both aqueous and nonaqueous media in the presence and absence of dioxygen. With 1, CO release is observed only under aerobic conditions, and the final product is an oxo-bridged diiron species while with 2 and 3, the solvent bound [(L)Fe(CO)](2+) (where L = SBPy(3) or Tpmen) results upon loss of CO under both aerobic and anaerobic conditions. The apparent rates of CO loss by these CORMs are comparable to other CORMs such as [Ru(glycine)(CO)(3)Cl] reported recently. Facile delivery of CO to reduced myoglobin has been observed with both 2 and 3. In tissue bath experiments, 2 and 3 exhibit rapid vasorelaxation of mouse aorta muscle rings. Although the relaxation effect is not inhibited by the soluble guanylate cyclase inhibitor ODQ, significant inhibition is observed with the BK(Ca) channel blocker iberiotoxin.

The vasorelaxing effect of hydrogen sulfide on isolated rat aortic rings versus pulmonary artery rings

AIM

To compare the vasorelaxing effects of hydrogen sulfide (H(2)S) on isolated aortic and pulmonary artery rings and to determine their action mechanisms.

METHODS

H(2)S-induced vasorelaxation of isolated rat aortic versus pulmonary artery rings under 95% O(2) and 5% CO(2) was analyzed. The expression of cystathinonine gamma-lyase (CSE), cystathionine beta synthase (CBS), 3-mercaptopyruvate sulfurtransferase (3MST), SUR2B and Kir6.1 was examined.

RESULTS

NaHS caused vasorelaxation of rat aortic and pulmonary artery rings in a dose-dependent manner. NaHS dilated aortic rings to a greater extent (16.4%, 38.4%, 64.1%, 84.3%, and 95.9% at concentrations of 50, 100, 200, 500, and 1000 μmol/L, respectively) than pulmonary artery rings (10.1%, 22.2%, 50.6%, 73.6%, and 84.6% at concentrations of 50, 100, 200, 500 and 1000 μmol/L, respectively). The EC(50) of the vasorelaxant effect for aortic rings was 152.17 μmol/L, whereas the EC(50) for pulmonary artery rings was 233.65 μmol/L. The vasorelaxing effect of H(2)S was markedly blocked b y cellular and mitochondrial membrane K(ATP) channel blockers in aortic rings (P<0.01). In contrast, only the cellular membrane K(ATP) channel blocker inhibited H(2)S-induced vasorelaxation in pulmonary artery rings. SUR2B mRNA and protein expression was higher in aortic rings than in pulmonary artery rings. Cystathinonine gamma-lyase (CSE) but not cystathionine beta synthase (CBS) expression in aortic rings was higher than in pulmonary artery rings. 3-Mercapto pyruvate sulfurtransferase (3MST) mRNA was lower in aortic rings than in pulmonary artery rings.

CONCLUSION

The vasorelaxing effect of H(2)S on isolated aortic rings was more pronounced than the effect on pulmonary artery rings at specific concentrations, which might be associated with increased expression of the K(ATP) channel subunit SUR2B.

Nitric oxide reduces sickle hemoglobin polymerization: potential role of nitric oxide-induced charge alteration in depolymerization

We previously demonstrated that inhaling nitric oxide (NO) increases the oxygen affinity of sickle red blood cells (RBCs) in patients with sickle cell disease (SCD). Our recent studies found that NO lowered the P(50) values of sickle hemoglobin (HbS) hemolysates but did not increase methemoglobin (metHb) levels, supporting the role of NO, but not metHb, in the oxygen affinity of HbS. Here we examine the mechanism by which NO increases HbS oxygen affinity. Because anti-sickling agents increase sickle RBC oxygen affinity, we first determined whether NO exhibits anti-sickling properties. The viscosity of HbS hemolysates, measured by falling ball assays, increased upon deoxygenation; NO treatment reduced the increment. Multiphoton microscopic analyses showed smaller HbS polymers in deoxygenated sickle RBCs and HbS hemolysates exposed to NO. These results suggest that NO inhibits HbS polymer formation and has anti-sickling properties. Furthermore, we found that HbS treated with NO exhibits an isoelectric point similar to that of HbA, suggesting that NO alters the electric charge of HbS. NO-HbS adducts had the same elution time as HbA upon high performance liquid chromatography analysis. This study demonstrates that NO may disrupt HbS polymers by abolishing the excess positive charge of HbS, resulting in increased oxygen affinity.

Hydrogen sulfide dilates cerebral arterioles by activating smooth muscle cell plasma membrane KATP channels

Hydrogen sulfide (H(2)S) is a gaseous signaling molecule that appears to contribute to the regulation of vascular tone and blood pressure. Multiple potential mechanisms of vascular regulation by H(2)S exist. Here, we tested the hypothesis that piglet cerebral arteriole smooth muscle cells generate ATP-sensitive K(+) (K(ATP)) currents and that H(2)S induces vasodilation by activating K(ATP) currents. Gas chromatography/mass spectrometry data demonstrated that after placing Na(2)S, an H(2)S donor, in solution, it rapidly (1 min) converts to H(2)S. Patch-clamp electrophysiology indicated that pinacidil (a K(ATP) channel activator), Na(2)S, and NaHS (another H(2)S donor) activated K(+) currents at physiological steady-state voltage (-50 mV) in isolated cerebral arteriole smooth muscle cells. Glibenclamide, a selective K(ATP) channel inhibitor, fully reversed pinacidil-induced K(+) currents and partially reversed (∼58%) H(2)S-induced K(+) currents. Western blot analysis indicated that piglet arterioles expressed inwardly rectifying K(+) 6.1 (K(ir)6.1) channel and sulfonylurea receptor 2B (SUR2B) K(ATP) channel subunits. Pinacidil dilated pressurized (40 mmHg) piglet arterioles, and glibenclamide fully reversed this effect. Na(2)S also induced reversible and repeatable vasodilation with an EC(50) of ∼30 μM, and this effect was partially reversed (∼55%) by glibenclamide. Vasoregulation by H(2)S was also studied in pressurized resistance-size cerebral arteries of mice with a genetic deletion in the gene encoding SUR2 (SUR2 null). Pinacidil- and H(2)S-induced vasodilations were smaller in arterioles of SUR2 null mice than in wild-type controls. These data indicate that smooth muscle cell K(ATP) currents control newborn cerebral arteriole contractility and that H(2)S dilates cerebral arterioles by activating smooth muscle cell K(ATP) channels containing SUR2 subunits.

The transsulfuration pathway: a source of cysteine for glutathione in astrocytes

Astrocyte cells require cysteine as a substrate for glutamate cysteine ligase (γ-glutamylcysteine synthase; EC 6.3.2.2) catalyst of the rate-limiting step of the γ-glutamylcycle leading to formation of glutathione (L: -γ-glutamyl-L: -cysteinyl-glycine; GSH). In both astrocytes and glioblastoma/astrocytoma cells, the majority of cysteine originates from reduction of cystine imported by the x (c) (-) cystine-glutamate exchanger. However, the transsulfuration pathway, which supplies cysteine from the indispensable amino acid, methionine, has recently been identified as a significant contributor to GSH synthesis in astrocytes. The purpose of this review is to evaluate the importance of the transsulfuration pathway in these cells, particularly in the context of a reserve pathway that channels methionine towards cysteine when the demand for glutathione is high, or under conditions in which the supply of cystine by the x (c) (-) exchanger may be compromised.

Mechanism of vasorelaxation and role of endogenous hydrogen sulfide production in mouse aorta

This study aimed to elucidate the molecular mechanism of H(2)S-induced vasorelaxation. Vasorelaxation responses to the H(2)S donor NaHS and the H(2)S precursor L: -cysteine were examined by measuring isometric tone of mouse aortic rings in a small vessel myograph. H(2)S concentrations in Krebs' solution were determined with a polarographic sensor. H(2)S expression was examined by Western blot, and H(2)S production from CSE was assayed using a spectroscopic method. In pre-constricted mouse aorta, NaHS (1 μM-3 mM) elicited vasorelaxation of 95 ± 7%, EC(50) 189 ± 69 μM. This response was unaffected by removal of the endothelium. Maximum vasorelaxation was significantly attenuated by global blockade of K(+) channels (50 mM K(+)) and the K(ATP) channel blocker glibenclamide (10 μM) alone (P < 0.01, ANOVA). Specific inhibition of K(Ca), K(IR), or K(V) channels elicited a significant shift to the right in the concentration-response curve to NaHS (P < 0.01, ANOVA) without affecting maximum relaxation. NaHS-mediated vasorelaxation was inhibited by the Cl(-) channel inhibitor DIDS (1 mM, P < 0.05, t test), and NaHS caused a significant concentration-dependent inhibition of voltage-gated Ca(2+) channels (P < 0.001, two-way ANOVA). The H(2)S-producing enzyme cystathionine-γ-lyase (CSE) was expressed in mouse aorta and had activity of 7 ± 3 μmol H(2)S/g/min. L: -cysteine (1 μM-3 mM) elicited a CSE-dependent vasorelaxation of mouse aorta with intact endothelium (20 ± 7%), but not when the endothelium was removed. CSE inhibitors DL: -propargylglycine (20 mM) and β-cyanoalanine (1 mM) caused concentration-dependent contraction of mouse aorta. In mouse aorta, H(2)S elicits endothelium-independent vasorelaxation involving several different ion channels and seems to converge at the vascular smooth muscle cell voltage-gated Ca(2+) channel. The L: -cysteine-CSE-H(2)S pathway contributes to vasorelaxation and appears to modulate basal vessel tone.

Nitric oxide and redox mechanisms in the immune response

The role of redox molecules, such as NO and ROS, as key mediators of immunity has recently garnered renewed interest and appreciation. To regulate immune responses, these species trigger the eradication of pathogens on the one hand and modulate immunosuppression during tissue-restoration and wound-healing processes on the other. In the acidic environment of the phagosome, a variety of RNS and ROS is produced, thereby providing a cauldron of redox chemistry, which is the first line in fighting infection. Interestingly, fluctuations in the levels of these same reactive intermediates orchestrate other phases of the immune response. NO activates specific signal transduction pathways in tumor cells, endothelial cells, and monocytes in a concentration-dependent manner. As ROS can react directly with NO-forming RNS, NO bioavailability and therefore, NO response(s) are changed. The NO/ROS balance is also important during Th1 to Th2 transition. In this review, we discuss the chemistry of NO and ROS in the context of antipathogen activity and immune regulation and also discuss similarities and differences between murine and human production of these intermediates.

Hydrogen sulphide: novel opportunity for drug discovery

Hydrogen sulphide (H(2)S) is emerging as an important endogenous modulator, which exhibits the beneficial effects of nitric oxide (NO) on the cardiovascular (CV) system, without producing toxic metabolites. H(2)S is biosynthesized in mammalian tissues by cystathionine-β-synthase and cystathionine-γ-lyase. H(2)S exhibits the antioxidant properties of inorganic and organic sulphites, behaving as a scavenger of reactive oxygen species. There is also clear evidence that H(2)S triggers other important effects, mainly mediated by the activation of ATP-sensitive potassium channels (K(ATP)). This mechanism accounts for the vasorelaxing and cardioprotective effects of H(2)S. Furthermore, H(2)S inhibits smooth muscle proliferation and platelet aggregation. In non-CV systems, H(2)S regulates the functions of the central nervous system, as well as respiratory, gastroenteric, and endocrine systems. Conversely, H(2)S deficiency contributes to the pathogenesis of hypertension. Likewise, impairment of H(2)S biosynthesis is involved in CV complications associated with diabetes mellitus. There is also evidence of a cross-talk between the H(2)S and the endothelial NO pathways. In particular, recent observations indicate a possible pathogenic link between deficiencies of H(2 S activity and the progress of endothelial dysfunction. These biological aspects of endogenous H(2)S have led several authors to look at this mediator as "the new NO" that has given attractive opportunities to develop innovative classes of drugs. In this review, the main biological actions of H(2)S are discussed. Moreover, some examples of H(2)S-donors are shown, as well as some hybrids, in which H(2)S-releasing moieties are added to well-known drugs, for improving their pharmacodynamic profile or reducing the potential for adverse effects, are reported.

Hydrogen sulfide-mediated cardioprotection: mechanisms and therapeutic potential

H2S (hydrogen sulfide), viewed with dread for more than 300 years, is rapidly becoming a ubiquitously present and physiologically relevant signalling molecule. Knowledge of the production and metabolism of H2S has spurred interest in delineating its functions both in physiology and pathophysiology of disease. Although its role in blood pressure regulation and interaction with NO is controversial, H2S, through its anti-apoptotic, anti-inflammatory and antioxidant effects, has demonstrated significant cardioprotection. As a result, a number of sulfide-donor drugs, including garlic-derived polysulfides, are currently being designed and investigated for the treatment of cardiovascular conditions, specifically myocardial ischaemic disease. However, huge gaps remain in our knowledge about this gasotransmitter. Only by additional studies will we understand more about the role of this intriguing molecule in the treatment of cardiovascular disease.

Signaling mechanisms involved in the intestinal pro-secretory actions of hydrogen sulfide

BACKGROUND

H(2) S actions in the gut involve neural activation. This study aimed to reveal the signaling mechanisms responsible for the pro-secretory effect of H(2) S by using TRPV1 and unselective TRP blockers and inhibitors of other signaling cascades hitherto described to be targeted by H(2) S elsewhere.

METHODS

Ussing chamber voltage clamp technique was used to study actions of the H(2) S donor NaHS on secretion in guinea-pig and human colon. NaHS effects on guinea-pig primary afferents were also evaluated.

KEY RESULTS

NaHS evoked secretion was significantly reduced in guinea-pig and human tissue by the selective TRPV1 blockers capsazepine, AMG9801, SB705498, BCTC; LY294002 (Phosphatidylinositol-3 kinase (PI3K) inhibitor), SKF96365 (store operated calcium channel blocker), 2-APB (inositol triphosphate blocker), and atropine but not by HC030031 (TRPA1 blocker) or L- and T-type calcium channel antagonists. Actions of TRPV1 antagonists suggested non-competitive inhibition at multiple sites. In guinea-pig colon, Gd(3+) and La(3+) (unselective TRP blockers) had no effects while ruthenium red reduced NaHS effects; in human colon Gd(3+) attenuated NaHS response. NaHS response was inhibited by neurokinin-1 and -3 receptor blockers in guinea-pig and neurokinin-1 and -2 receptor blockade in human tissue. There was cross-desensitization between NaHS and capsaicin responses. NaHS induced capsazepine and LY294002 sensitive afferent discharge.

CONCLUSIONS & INFERENCES

H(2) S evokes mucosal secretion by targeting TRPV1 expressing afferent nerves which activate cholinergic secretomotor neurons via release of substance P acting in a species dependent manner on neurokinin-1, -2 or -3 receptors. Besides TRPV1 signaling H(2) S may target intracellular calcium dependent pathways and PI3K.

Bicarbonate-dependent effect of hydrogen sulfide on vascular contractility in rat aortic rings

Hydrogen sulfide (H2S), an endogenous gaseous mediator, produces both vasorelaxation and vasoconstriction at different concentrations. We found in the present study that NaHS, an H2S donor, produced stronger vasorelaxant and weaker vasoconstrictive effects in HEPES solution compared with those achieved in Krebs solution. We further screened the buffer components and found that bicarbonate (HCO3−) was the ion to influence the effect of H2S. After examining the vasorelaxant effects of acetylcholine, a vasodilator by releasing nitric oxide, and isoprenaline, a β-adrenoceptor agonist, in HEPES and Krebs buffers, we found the HCO3−-dependent effect was specific to H2S. Blockade of anion exchanger-2 activity with 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS) or with HCO3−-free solution abolished the vasoconstrictive effect of NaHS. Moreover, NaHS decreased nitric oxide level in the rat aorta in HCO3−-containing buffer, but this effect was abolished by HCO3−-free buffer or DIDS. In summary, we found for the first time that H2S stimulates anion exchanger to transport extracellular HCO3− in exchange for intracellular superoxide anions, which may further inactivate nitric oxide and induces vasoconstriction.

Whole body periodic acceleration (pGz) improves survival and allows for resuscitation in a model of severe hemorrhagic shock in pigs

BACKGROUND

Whole body periodic acceleration (pGz), the repetitive, head-foot sinusoidal motion of the body, increases pulsatile shear stress on the vascular endothelium producing increased release of endothelial derived nitric oxide (eNO) into circulation. Based upon prior CPR investigations, we hypothesized that pGz instituted prior to and during hemorrhagic shock (HS) should improve survival.

MATERIALS AND METHODS

Sixteen anesthetized male pigs, 23 ± 5 kg, were randomized to receive 1 h pGz or no pGz (CONT) prior to and during severe controlled graded HS up to 2-1/2 h. HS was induced by removing blood at 10 mL/kg increments from the circulation at 30-min intervals up to a maximum blood loss of 50 mL/kg. Thirty minutes after maximum blood loss, shed blood and lactated Ringers solution was infused intravenously.

RESULTS

All animals survived up to 30 mL/kg blood loss. Survival and return to normal blood pressure to 120 min was achieved in 50% of animals receiving pGz compared with none in CONT. Cardiac output, blood pressure, and oxygen delivery decreased equally in both groups but oxygen consumption was significantly lower with pGz than CONT during all hemorrhage time points. Regional blood flow (RBF) was preserved in brain, heart, kidneys, ileum, and stomach in both groups up to 40 mL/kg of blood loss. After 40 mL/kg blood loss, RBF was much better preserved in pGz than CONT.

CONCLUSIONS

pGz applied 1 h prior to and during severe graded hemorrhagic shock delays onset of irreversible shock, enabling potential restoration of blood loss and survival.

Adiposity is a major determinant of plasma levels of the novel vasodilator hydrogen sulphide

AIMS/HYPOTHESIS

Hydrogen sulphide is a recently identified endogenous endothelium-dependent vasodilator. Animal models of diabetes have shown that low plasma H(2)S levels are associated with marked endothelial dysfunction and insulin resistance. However, human studies on H(2)S and vascular function in health and disease are lacking.

METHODS

Plasma was obtained from male patients with type 2 diabetes (n = 11), overweight (n = 16) and lean (n = 11) volunteers. H(2)S levels were determined by zinc trap spectrophotometry. Anthropometric measurements (BMI/waist:hip ratio), lipid profile, systemic blood pressure, biochemical indices of diabetes (fasting glucose, insulin sensitivity, Hb(1Ac)) and microvascular function (minimum vascular resistance) were determined.

RESULTS

Median plasma H(2)S levels (25th, 75th percentiles) in age-matched lean, overweight and type 2 diabetes individuals were 38.9 (29.7, 45.1) micromol/l, 22.0 (18.6, 26.7) micromol/l and 10.5 (4.8, 22.0) micromol/l, respectively. Median plasma H(2)S levels were significantly lower in patients with type 2 diabetes compared with lean (p = 0.001, Mann-Whitney) and overweight participants (p = 0.008). Median plasma H(2)S levels in overweight participants were significantly lower than in lean controls (p = 0.003). Waist circumference was an independent predictor of plasma H(2)S (R (2) = 0.423, standardised beta: -0.650, p < 0.001). This relationship was independent of diabetes, which only contributed a further 5% to the model (R (2) = 0.477). Waist circumference or other measures of adiposity (waist:hip ratio/BMI) remained independent predictors of plasma H(2)S after adjustment for systolic blood pressure, microvascular function, insulin sensitivity, glycaemic control and lipid profile.

CONCLUSIONS/INTERPRETATION

Plasma H(2)S levels are reduced in overweight participants and patients with type 2 diabetes. Increasing adiposity is a major determinant of plasma H(2)S levels.

Hydrogen sulfide interacts with nitric oxide in the heart: possible involvement of nitroxyl

AIMS

The present study aims to investigate the interaction between nitric oxide (NO) and hydrogen sulfide (H(2)S), the two important gaseous mediators in rat hearts.

METHODS AND RESULTS

Intracellular calcium in isolated cardiomyocytes was measured with a spectrofluorometric method using Fura-2. Myocyte contractility was measured with a video edge system. NaHS (50 µM, an H(2)S donor) had no significant effect on the resting calcium level, electrically induced (EI) calcium transients, and cell contractility in ventricular myocytes. Stimulating endogenous NO production with l-arginine or exogenous application of NO donors [sodium nitroprusside (SNP) and 2-(N,N-diethylamino)-diazenolate-2-oxide] decreased myocyte twitch amplitudes accompanied by slower velocities of both cell contraction and relaxation. Surprisingly, NaHS reversed the negative inotropic and lusitropic effects of the above three NO-increasing agents. In addition, the mixture of SNP + NaHS increased, whereas SNP alone decreased, the resting calcium level and the amplitudes of EI calcium transients. Angeli's salt, a nitroxyl anion (HNO) donor, mimicked the effect of SNP + NaHS on calcium handling and myocyte contractility. Three thiols, N-acetyl-cysteine, l-cysteine, and glutathione, abolished the effects of HNO and SNP + NaHS on myocyte contraction. Neither Rp-cAMP [a protein kinase A (PKA) inhibitor] nor Rp-cGMP [a protein kinase G (PKG) inhibitor] affected the effects of SNP + NaHS, suggesting a cAMP/PKA- or cGMP/PKG-independent mechanism.

CONCLUSION

H(2)S may interact with NO to form a thiol sensitive molecule (probably HNO) which produces positive inotropic and lusitropic effects. Our findings may shed light on the interaction of NO and H(2)S and provide new clues to treat cardiovascular diseases.

Hydrogen sulfide is an endogenous inhibitor of phosphodiesterase activity

OBJECTIVE

Recent studies have demonstrated that hydrogen sulfide (H(2)S) is produced within the vessel wall from L-cysteine regulating several aspects of vascular homeostasis. H(2)S generated from cystathione γ-lyase (CSE) contributes to vascular tone; however, the molecular mechanisms underlying the vasorelaxing effects of H(2)S are still under investigation.

METHODS AND RESULTS

Using isolated aortic rings, we observed that addition of L-cysteine led to a concentration-dependent relaxation that was prevented by the CSE inhibitors DL-propargylglyicine (PAG) and β-cyano-l-alanine (BCA). Moreover, incubation with PAG or BCA resulted in a rightward shift in sodium nitroprusside-and isoproterenol-induced relaxation. Aortic tissues exposed to PAG or BCA contained lower levels of cGMP, exposure of cells to exogenous H(2)S or overexpression of CSE raised cGMP concentration. RNA silencing of CSE expression reduced intracellular cGMP levels confirming a positive role for endogenous H(2)S on cGMP accumulation. The ability of H(2)S to enhance cGMP levels was greatly reduced by the nonselective phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine. Finally, addition of H(2)S to a cell-free system inhibited both cGMP and cAMP breakdown.

CONCLUSIONS

These findings provide direct evidence that H(2)S acts as an endogenous inhibitor of phosphodiesterase activity and reinforce the notion that this gasotransmitter could be therapeutically exploited.

Interactions of multiple gas-transducing systems: hallmarks and uncertainties of CO, NO, and H2S gas biology

The diverse physiological actions of the "biologic gases," O2, CO, NO, and H2S, have attracted much interest. Initially viewed as toxic substances, CO, NO, and H2S play important roles as signaling molecules. The multiplicity of gas actions and gas targets and the difficulty in measuring local gas concentrations obscures detailed mechanisms whereby gases exert their actions, and many questions remain unanswered. It is now readily apparent, however, that heme-based proteins play central roles in gas-generation/reception mechanisms and provide a point where multiple gases can interact. In this review, we consider a number of key issues related to "gas biology," including the effective tissue concentrations of these gases and the importance and significance of the physical proximity of gas-producing and gas-receptor/sensors. We also take an integrated approach to the interaction of gases by considering the physiological significance of CO, NO, and H2S on mitochondrial cytochrome c oxidase, a key target and central mediator of mitochondrial respiration. Additionally, we consider the effects of biologic gases on mitochondrial biogenesis and "suspended animation." By evaluating gas-mediated control functions from both in vitro and in vivo perspectives, we hope to elaborate on the complex multiple interactions of O2, NO, CO, and H2S.

The effect of hydrogen sulfide donors on lipopolysaccharide-induced formation of inflammatory mediators in macrophages

The role of hydrogen sulfide (H(2)S) in inflammation is controversial, with both pro- and antiinflammatory effects documented. Many studies have used simple sulfide salts as the source of H(2)S, which give a rapid bolus of H(2)S in aqueous solutions and thus do not accurately reflect the enzymatic generation of H(2)S. We therefore compared the effects of sodium hydrosulfide and a novel slow-releasing H(2)S donor (GYY4137) on the release of pro- and antiinflammatory mediators in lipopolysaccharide (LPS)-treated murine RAW264.7 macrophages. For the first time, we show that GYY4137 significantly and concentration-dependently inhibits LPS-induced release of proinflammatory mediators such as IL-1beta, IL-6, TNF-alpha, nitric oxide (*NO), and PGE(2) but increased the synthesis of the antiinflammatory chemokine IL-10 through NF-kappaB/ATF-2/HSP-27-dependent pathways. In contrast, NaHS elicited a biphasic effect on proinflammatory mediators and, at high concentrations, increased the synthesis of IL-1beta, IL-6, NO, PGE(2) and TNF-alpha. This study clearly shows that the effects of H(2)S on the inflammatory process are complex and dependent not only on H(2)S concentration but also on the rate of H(2)S generation. This study may also explain some of the apparent discrepancies in the literature regarding the pro- versus antiinflammatory role of H(2)S.

The hydrogen sulfide donor NaHS promotes angiogenesis in a rat model of hind limb ischemia

It is not known whether H(2)S can promote angiogenesis with improvement of regional blood flow in ischemic organs. Sodium hydrosulfide (NaHS, a H(2)S donor) was administered once a day for 4 w following femoral artery ligation. Collateral vessel growth, capillary density, regional tissue blood flow, the expression of endothelial growth factor (VEGF), VEGF receptor 2 (VEGFR2) and Akt were examined during or at the end of the treatment period. NaHS treatment significantly increased collateral vessel growth, capillary density, and regional tissue blood flow in ischemic hind limb muscles compared with the controls. These effects were associated with an increase in VEGF expression in the skeletal muscles and VEGFR2 phosphorylation in the neighboring vascular endothelial cells, suggesting a role of VEGF in mediating the NaHS effects in a cell-cell interaction pattern. Moreover, NaHS treatment also resulted in an increase in Akt phosphorylation in ischemic hind limb muscles. In conclusion, our observations with NaHS strongly suggest that H(2)S is a proangiogenic factor in chronic ischemia. The proangiogenic effect of NaHS may be mediated by interaction between the upregulated VEGF in the skeletal muscle cells and the VEGFR2 as well as its downstream signaling element Akt in the vascular endothelial cells.

Mechanisms of angiogenesis: role of hydrogen sulphide

1. Hydrogen sulphide (H(2)S) has recently been recognized as a gasotransmitter that regulates angiogenesis in vitro and in vivo under physiological and ischaemic conditions. 2. In the present review, the mechanisms underlying angiogenesis are summarized briefly and the most recent progress in H(2)S-induced angiogenesis in vivo and in vitro is described. The anti-angiogenic effects of garlic extracts, which may serve as substrates for H(2)S-generating enzymes in vivo, are also discussed. 3. Hydrogen sulphide increases cell growth, migration and the formation of tube-like structures in cultured endothelial cells. These effects are dependent on activation of the phosphatidylinositol 3-kinase-Akt-survivin signalling pathway. Neovascularization in vivo has also been demonstrated to be promoted in the mouse Matrigel plug assay, as well as in chicken chorioallantoic membranes. In a rat unilateral hindlimb ischaemic model, treatment with sodium hydrosulphide (NaHS), an H(2)S donor, promotes significant angiogenesis and improves regional blood flow. These effects may be mediated by interactions between upregulated vascular endothelial growth factor (VEGF) in skeletal muscle cells and VEGF receptor 2 and the downstream signalling element Akt in vascular endothelial cells. However, H(2)S does not exhibit a pro-angiogenic effect at a high concentrations/doses. 4. Based on the studies reviewed in the present article, we assume that, at physiologically relevant doses/concentrations, H(2)S/HS(-) promote angiogenesis at least partly via the VEGF signalling pathway. At high doses, H(2)S/HS(-) may act on additional cellular targets to evoke mechanisms that counteract the pro-angiogenic pathways. More studies need to be performed analysing the general interactions between H(2)S/HS(-) and other molecules, including other gasotransmitters, such as nitric oxide and carbon monoxide (CO).

Gases in the mitochondria

Gasomodulators - nitric oxide, carbon monoxide and hydrogen sulphide - are important physiological mediators that have been implicated in disorders such as neurodegeneration and sepsis. Some of their biological functions involve the mitochondria. In particular, their inhibition of cytochrome c oxidase has received much attention as this can cause energy depletion and cytotoxicity. However, reports that cellular energy production and cell survival are maintained even in the presence of gasomodulators are not uncommon. In both cases, modulation of mitochondrial targets by the gasomodulators appears to be an important event. We provide an overview of the effects of the gasomodulators on the mitochondria.