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

Hydrogen sulfide impairs keratinocyte cell growth and adhesion inhibiting mitogen-activated protein kinase signaling

The effects of exogenous hydrogen sulfide (H2S) on normal skin-derived immortalized human keratinocytes have been investigated in detail. We show in vitro that exogenous hydrogen sulfide reduces clonal growth, cell proliferation and cell adhesion of human keratinocytes. H(2)S, in fact, decreases the frequency of the putative keratinocyte stem cell subpopulation in culture, consequently affecting clonal growth, and impairs cell proliferation and adhesion of mature cells. As a mechanistic explanation of these effects, we show at the molecular level that (i) H2S reduces the Raf/MAPK kinase/ERK signaling pathway; (ii) the reduced adhesion of sulfur-treated cells is associated to the downregulation of the expression of beta4, alpha2 and alpha6 integrins that are necessary to promote cell adhesion as well as anti-apoptotic and proliferative signaling in normal keratinocytes. One specific interest of the effects of sulfurs on keratinocytes derives from the potential applications of the results, as sulfur is able to penetrate the skin and a sulfur-rich balneotherapy has been known for long to be effective in the treatment of psoriasis. Thus, the relevance of our findings to the pathophysiology of psoriasis was tested in vivo by treating psoriatic lesions with sulfurs at a concentration comparable to that most commonly found in sulfurous natural springs. In agreement with the in vitro observations, the immunohistochemical analysis of patient biopsies showed a specific downregulation of ERK activation levels, the key molecular event in the sulfur-induced effects on keratinocytes.

Hydrogen sulfide scavenges the cytotoxic lipid oxidation product 4-HNE

Highly reactive alpha,beta-unsaturated aldehydes like 4-hydroxy-2-nonenal (4-HNE), generated from oxidation of polyunsaturated fatty acids, can bind to proteins, polynucleotides and exert cytotoxicity. 4-HNE is known to react readily with thiol and amino groups on free or bound amino acids. Recently, hydrogen sulfide (H(2)S) has been identified as an endogenous vascular gasotransmitter and neuromodulator which can reach up to 160 micromol/l in the brain. Markedly higher 4-HNE concentrations were reported in the brain of patients suffering from Alzheimer's disease. Assuming that the low molecular thiol H(2)S may react with 4-HNE, we have tested the ability of H(2)S to counteract the cytotoxic and protein-modifying activity of 4-HNE. The results show that H(2)S at physiologically relevant concentrations could effectively protect neuronal cells (SH-SY5Y) from the cytotoxic action of 4-HNE. The HNE-modification of cellular proteins was also inhibited in presence of H(2)S. These data suggest that H(2)S may be an important protective factor against carbonyl stress by inactivating/modulating the action of highly reactive alpha,beta-unsaturated aldehydes like 4-HNE in the brain.

Structural and functional insights into sulfide:quinone oxidoreductase

A sulfide:quinone oxidoreductase (SQR) was isolated from the membranes of the hyperthermoacidophilic archaeon Acidianus ambivalens, and its X-ray structure, the first reported for an SQR, was determined to 2.6 A resolution. This enzyme was functionally and structurally characterized and was shown to have two redox active sites: a covalently bound FAD and an adjacent pair of cysteine residues. Most interestingly, the X-ray structure revealed the presence of a chain of three sulfur atoms bridging those two cysteine residues. The possible implications of this observation in the catalytic mechanism for sulfide oxidation are discussed, and the role of SQR in the sulfur dependent bioenergetics of A. ambivalens, linked to oxygen reduction, is addressed.

The endogenous hydrogen sulfide producing enzyme cystathionine-beta synthase contributes to visceral hypersensitivity in a rat model of irritable bowel syndrome

Background

The pathogenesis of visceral hypersensitivity, a characteristic pathophysiological feature of irritable bowel syndrome (IBS), remains elusive. Recent studies suggest a role for hydrogen sulfide (H₂S) in pain signaling but this has not been well studied in visceral models of hyperalgesia. We therefore determined the role for the endogenous H₂S producing enzyme cystathionine-β-synthetase (CBS) in a validated rat model of IBS-like chronic visceral hyperalgesia (CVH). CVH was induced by colonic injection of 0.5% acetic acid (AA) in 10-day-old rats and experiments were performed at 8–10 weeks of age. Dorsal root ganglion (DRG) neurons innervating the colon were labeled by injection of DiI (1,1'-dioleyl-3,3,3',3-tetramethylindocarbocyanine methanesulfonate) into the colon wall.

Results

In rat DRG, CBS-immunoreactivity was observed in approximately 85% of predominantly small- and medium-sized neurons. Colon specific DRG neurons revealed by retrograde labeling DiI were all CBS-positive. CBS-positive colon neurons co-expressed TRPV1 or P2X3 receptors. Western blotting analysis showed that CBS expression was significantly increased in colon DRGs 8 weeks after neonatal AA-treatment. Furthermore, the CBS inhibitor hydroxylamine markedly attenuated the abdominal withdrawal reflex scores in response to colorectal distention in rats with CVH. By contrast, the H₂S donor NaHS significantly enhanced the frequency of action potentials of colon specific DRG neurons evoked by 2 times rheobase electrical stimulation.

Conclusion

Our results suggest that upregulation of CBS expression in colonic DRG neurons and H₂S signaling may play an important role in developing CVH, thus identifying a specific neurobiological target for the treatment of CVH in functional bowel syndromes.

Hydrogen sulfide suppresses migration, proliferation and myofibroblast transdifferentiation of human lung fibroblasts

We previously reported that hydrogen sulfide (H(2)S) was implicated in the pathogenesis of bleomycin-induced pulmonary fibrosis in rat, but the cellular mechanisms underlying the role it played were not well characterized. The present study was undertaken to investigate the role of the exogenous H(2)S in human lung fibroblast (MRC5) migration, proliferation and myofibroblast transdifferentiation induced by fetal bovine serum (FBS) and growth factors in vitro, to elucidate the mechanisms by which H(2)S inhibits pathogenesis of pulmonary fibrosis. We found that H(2)S incubation significantly decreased the MRC5 cell migration distance stimulated by FBS and basic fibroblast growth factor (bFGF), inhibited MRC5 cell proliferation induced by FBS and platelet-derived growth factor-BB (PDGF-BB), and also inhibited transforming growth factor-beta1 (TGF-beta1) induced MRC5 cell transdifferentiation into myofibroblasts. Moreover, preincubation with H(2)S decreased extracellular signal-regulated kinase (ERK1/2) phosphorylation in MRC5 cells induced by FBS, PDGF-BB, TGF-beta1, and bFGF. However, the inhibition effects of H(2)S on MRC5 cell migration, proliferation and myofibroblast transdifferentiation were not attenuated by glibenclamide, an ATP-sensitive K(+) channel (K(ATP)) blocker. Thus, H(2)S directly suppressed fibroblast migration, proliferation and phenotype transform stimulated by FBS and growth factors in vitro, which suggests that it could be an important mechanism of H(2)S-suppressed pulmonary fibrosis. These effects of H(2)S on pulmonary fibroblasts were, at least in part, mediated by decreased ERK phosphorylation and were not dependent on K(ATP) channel opening.

Endogenous and exogenous hydrogen sulfide promotes resolution of colitis in rats

BACKGROUND & AIMS

Hydrogen sulfide (H(2)S) is an endogenous gaseous mediator of mucosal defense with antiinflammatory effects that promote ulcer healing. The effects of H(2)S during the pathogenesis of colitis have not been established. We analyzed the contribution of H(2)S to inflammation and ulceration of the colon in a rat model of colitis.

METHODS

Colitis was induced by intracolonic administration of trinitrobenzene sulfonic acid. The ability of the colon to synthesize H(2)S was studied over the course of the resolution of the colitis. Expression of 2 enzymes involved in the synthesis of H(2)S and the effects of inhibitors of these enzymes were examined. We also examined the effects of H(2)S donors on the resolution of colitis.

RESULTS

The capacity for the colon to produce H(2)S increased markedly over the first days after induction of colitis and then declined toward control levels as the colitis was resolved. Inhibition of colonic H(2)S synthesis markedly exacerbated the colitis, resulting in significant mortality. Inhibition of H(2)S synthesis in healthy rats resulted in inflammation and mucosal injury in the small intestine and colon along with down-regulation of cyclooxygenase-2 messenger RNA expression and prostaglandin synthesis. Intracolonic administration of H(2)S donors significantly reduced the severity of colitis and reduced colonic expression of messenger RNA for the proinflammatory cytokine tumor necrosis factor alpha.

CONCLUSIONS

In rats, H(2)S modulates physiological inflammation and contributes to the resolution of colitis.

Anti-apoptotic action of hydrogen sulfide is associated with early JNK inhibition

The mechanism of action of Hydrogen sulfide (H(2)S) as a novel endogenous gaseous messenger and potential cardioprotectant is not fully understood. We therefore investigated the prevention of cardiomyocyte apoptosis by exogenous H(2)S and the signaling pathways leading to cardioprotection. Using a simulated ischemia-reperfusion (I/Re) model with primary cultured rat neonatal cardiomyocytes, I/Re induced a rapid, time-dependent phosphorylation of c-Jun N-terminal kinase (JNK), with significant elevation at 0.25 h and a peak at 0.5h during reperfusion. NaHS (H(2)S donor) significantly inhibited the early phosphorylation of JNK, especially at 0.5h. Both NaHS and SP600125 (specific JNK inhibitor) decreased the number of apoptotic cells, lowered cytochrome C release and enhanced Bcl-2 expression. When NaHS application was delayed 1h after reperfusion, the inhibition of apoptosis by H(2)S was negated. In conclusion, this is novel evidence that early JNK inhibition during reperfusion is associated with H(2)S-mediated protection against cardiomyocyte apoptosis.

EDHF: an update

The endothelium controls vascular tone not only by releasing NO and prostacyclin, but also by other pathways causing hyperpolarization of the underlying smooth muscle cells. This characteristic was at the origin of the term 'endothelium-derived hyperpolarizing factor' (EDHF). However, this acronym includes different mechanisms. Arachidonic acid metabolites derived from the cyclo-oxygenases, lipoxygenases and cytochrome P450 pathways, H(2)O(2), CO, H(2)S and various peptides can be released by endothelial cells. These factors activate different families of K(+) channels and hyperpolarization of the vascular smooth muscle cells contribute to the mechanisms leading to their relaxation. Additionally, another pathway associated with the hyperpolarization of both endothelial and vascular smooth muscle cells contributes also to endothelium-dependent relaxations (EDHF-mediated responses). These responses involve an increase in the intracellular Ca(2+) concentration of the endothelial cells, followed by the opening of SK(Ca) and IK(Ca) channels (small and intermediate conductance Ca(2+)-activated K(+) channels respectively). These channels have a distinct subcellular distribution: SK(Ca) are widely distributed over the plasma membrane, whereas IK(Ca) are preferentially expressed in the endothelial projections toward the smooth muscle cells. Following SK(Ca) activation, smooth muscle hyperpolarization is preferentially evoked by electrical coupling through myoendothelial gap junctions, whereas, following IK(Ca) activation, K(+) efflux can activate smooth muscle Kir2.1 and/or Na(+)/K(+)-ATPase. EDHF-mediated responses are altered by aging and various pathologies. Therapeutic interventions can restore these responses, suggesting that the improvement in the EDHF pathway contributes to their beneficial effect. A better characterization of EDHF-mediated responses should allow the determination of whether or not new drugable targets can be identified for the treatment of cardiovascular diseases.

Hydrogen sulphide: A novel physiological inhibitor of LDL atherogenic modification by HOCl

Hypochlorite (HOCl), the product of the activated myeloperoxidase/H(2)O(2)/chloride (MPO/H(2)O(2)/Cl(- )) system is favored as a trigger of LDL modifications, which may play a pivotal role in early atherogenesis. As HOCl has been shown to react with thiol-containing compounds like glutathione and N-acetylcysteine protecting LDL from HOCl modification, we have tested the ability of hydrogen sulfide (H(2)S) - which has recently been identified as an endogenous vasorelaxant - to counteract the action of HOCl on LDL. The results show that H(2)S could inhibit the atherogenic modification of LDL induced by HOCl, as measured by apolipoprotein alterations. Beside its HOCl scavenging potential, H(2)S was found to inhibit MPO (one may speculate that this occurs via H(2)S/heme interaction) and destroy H(2)O(2). Thus, H(2)S may interfere with the reactants and reaction products of the activated MPO/H(2)O(2)/Cl(- ) system. Our data add to the evidence of an anti-atherosclerotic action of this gasotransmitter taking the role of HOCl in the atherogenic modification of LDL into account.

Serum hydrogen sulfide as a novel marker predicting bacterial involvement in patients with community-acquired lower respiratory tract infections

BACKGROUND AND OBJECTIVE

Endogenous hydrogen sulfide (H2S) may be involved in the pathogenesis of systemic inflammation. It was investigated whether serum H2S levels differed among patients with community-acquired pneumonia, those with exacerbations of COPD or control subjects, and whether H2S may be used as a surrogate marker of the need for antibiotic treatment.

METHODS

Serum H2S levels were measured in 129 patients with pneumonia or COPD exacerbations and in 72 healthy control subjects.

RESULTS

The mean serum H2S concentration was 36% lower in patients with pneumonia (22.7 +/- 14.6 micromol/L) than in control subjects (35.4 +/- 5.3 micromol/L) (P < 0.01). Serum H2S concentration did not differ between patients with acute exacerbations of COPD (33.8 +/- 18.6 micromol/L) and control subjects. Within the COPD group, patients with Anthonisen type 1 exacerbations had a lower serum H(2)S concentration (22.5 +/- 11.6 micromol/L) than control subjects, and those with type 3 exacerbations had a higher serum H2S concentration (54.2 +/- 21.3 micromol/L) than control subjects. There was no difference between patients with type 2 exacerbations (41.7 +/- 8.4 micromol/L) and control subjects. In patients requiring antibiotics, serum H2S concentration was 41% lower than in those not requiring antibiotics. The area under the receiver operating characteristic curve for H(2)S as a surrogate marker of the need for antibiotics was 0.862 (95% confidence interval: 0.805-0.919, P < 0.01). Serum H2S levels were inversely correlated with serum CRP levels (r = -0.337, P < 0.01).

CONCLUSIONS

Serum H2S levels may be used as a marker in lower respiratory tract infections. Further studies are required to validate the role of serum H2S levels in guiding antibiotic selection.

Physiological and pharmacological features of the novel gasotransmitter: hydrogen sulfide

Hydrogen sulfide (H(2)S) has been known for hundreds of years because of its poisoning effect. Once the basal bio-production became evident its pathophysiological role started to be investigated in depth. H(2)S is a gas that can be formed by the action of two enzymes, cystathionine gamma-lyase and cystathionine beta-synthase, both involved in the metabolism of cysteine. It has several features in common with the other two well known "gasotransmitters" (nitric oxide and carbon monoxide) in the biological systems. These three gasses share some biological targets; however, they also have dissimilarities. For instance, the three gases target heme-proteins and open K(ATP) channels; H(2)S as NO is an antioxidant, but in contrast to the latter molecule, H(2)S does not directly form radicals. In the last years H(2)S has been implicated in several physiological and pathophysiological processes such as long term synaptic potentiation, vasorelaxation, pro- and anti-inflammatory conditions, cardiac inotropism regulation, cardioprotection, and several other physiological mechanisms. We will focus on the biological role of H(2)S as a molecule able to trigger cell signaling. Our attention will be particularly devoted on the effects in cardiovascular system and in cardioprotection. We will also provide available information on H(2)S-donating drugs which have so far been tested in order to conjugate the beneficial effect of H(2)S with other pharmaceutical properties.

Hydrogen sulfide inhibits MPP(+)-induced apoptosis in PC12 cells

AIMS

Hydrogen sulfide (H2S) is a well-known cytotoxic gas. Recently it has been shown to protect neurons against oxidative stress caused by glutamate, hypochlorous acid (HOCl), and beta-amyloid. The aim of the present study is to explore the cytoprotection of H2S against 1-methyl-4-phenylpyridinium ion (MPP(+))-induced apoptosis and the molecular mechanisms underlying in PC12 cells, a rat cell line derived from pheochromocytoma cells.

MAIN METHODS

Cell viability was determined by the conventional 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction assay. Apoptosis was assessed by Hoechst 33258 nuclear staining and flow cytometric (FCM) analysis after propidium iodide staining. The mitochondrial membrane potential (MMP) was measured by rhodamine 123 (Rh123) probe and reactive oxygen species (ROS) were measured by dihydrorhodamine probe using FCM analysis.

KEY FINDINGS

MPP(+) reduced the cell viability and induced apoptosis of PC12 cells along with dissipation of MMP as well as overproduction of ROS. Sodium hydrosulfide (NaHS), a H2S donor, protected PC12 cells against MPP(+)-induced cytotoxicity and apoptosis not only by reducing the loss of MMP, but also by attenuating an increase in intracellular ROS.

SIGNIFICANCE

H2S significantly protected PC12 cells against cytotoxicity and apoptosis induced by MPP(+), which was associated with the inhibition by H(2)S of MPP(+)-induced dissipation of MMP and overproduction of ROS. These findings can significantly advance therapeutic approaches to the neurodegenerative diseases which are associated with oxidative stress, such as Parkinson's disease.

The structure of Aquifex aeolicus sulfide:quinone oxidoreductase, a basis to understand sulfide detoxification and respiration

Sulfide:quinone oxidoreductase (SQR) is a flavoprotein with homologues in all domains of life except plants. It plays a physiological role both in sulfide detoxification and in energy transduction. We isolated the protein from native membranes of the hyperthermophilic bacterium Aquifex aeolicus, and we determined its X-ray structure in the "as-purified," substrate-bound, and inhibitor-bound forms at resolutions of 2.3, 2.0, and 2.9 A, respectively. The structure is composed of 2 Rossmann domains and 1 attachment domain, with an overall monomeric architecture typical of disulfide oxidoreductase flavoproteins. A. aeolicus SQR is a surprisingly trimeric, periplasmic integral monotopic membrane protein that inserts about 12 A into the lipidic bilayer through an amphipathic helix-turn-helix tripodal motif. The quinone is located in a channel that extends from the si side of the FAD to the membrane. The quinone ring is sandwiched between the conserved amino acids Phe-385 and Ile-346, and it is possibly protonated upon reduction via Glu-318 and/or neighboring water molecules. Sulfide polymerization occurs on the re side of FAD, where the invariant Cys-156 and Cys-347 appear to be covalently bound to polysulfur fragments. The structure suggests that FAD is covalently linked to the polypeptide in an unusual way, via a disulfide bridge between the 8-methyl group and Cys-124. The applicability of this disulfide bridge for transferring electrons from sulfide to FAD, 2 mechanisms for sulfide polymerization and channeling of the substrate, S(2-), and of the product, S(n), in and out of the active site are discussed.

Prevention of nonsteroidal anti-inflammatory drug-induced ulcer: looking to the future

The great challenge for those attempting to develop safer NSAIDs is shifting from a focus on GI toxicity to the increasingly more appreciated cardiovascular toxicity. At present, coxib shows an unmatched GI safety and appears to be a rational choice for patients at a low cardiovascular risk who have had serious GI events. In these patients, however, a cost-effective alternative is the use of tNSAIDs associated with comedication with a low-cost PPI or PN400. Because it seems prudent to avoid coxibs in patients who have cardiovascular disease or who are at risk for it, naproxcinod will be an appealing alternative to coxibs and tNSAIDs. However, because naproxcinod carries a significant risk of GI bleeding, a comedication therapy with a PPI inhibitor will be required if these patients also present risk factors for GI events. Although the development of H2S-releasing anti-inflammatory drugs is in its infancy, the preclinical data available thus far provide cause for optimism. The quest for the development of NSAIDs devoid of cardiovascular toxicity and that spare the gastric mucosa to the same extent as that of a coxib, however, is still open.

Hydrogen sulfide ameliorates hyperhomocysteinemia-associated chronic renal failure

Elevated level of homocysteine (Hcy), known as hyperhomocysteinemia (HHcy), is associated with end-stage renal diseases. Hcy metabolizes in the body to produce hydrogen sulfide (H(2)S), and studies have demonstrated a protective role of H(2)S in end-stage organ failure. However, the role of H(2)S in HHcy-associated renal diseases is unclear. The present study was aimed to determine the role of H(2)S in HHcy-associated renal damage. Cystathionine-beta-synthase heterozygous (CBS+/-) and wild-type (WT, C57BL/6J) mice with two kidney (2-K) were used in this study and supplemented with or without NaHS (30 micromol/l, H(2)S donor) in the drinking water. To expedite the HHcy-associated glomerular damage, uninephrectomized (1-K) CBS(+/-) and 1-K WT mice were also used with or without NaHS supplementation. Plasma Hcy levels were elevated in CBS(+/-) 2-K and 1-K and WT 1-K mice along with increased proteinuria, whereas, plasma levels of H(2)S were attenuated in these groups compared with WT 2-K mice. Interestingly, H(2)S supplementation increased plasma H(2)S level and normalized the urinary protein secretion in the similar groups of animals as above. Increased activity of matrix metalloproteinase (MMP)-2 and -9 and apoptotic cells were observed in the renal cortical tissues of CBS(+/-) 2-K and 1-K and WT 1-K mice; however, H(2)S prevented apoptotic cell death and normalized increased MMP activities. Increased expression of desmin and downregulation of nephrin in the cortical tissue of CBS(+/-) 2-K and 1-K and WT 1-K mice were ameliorated with H(2)S supplementation. Additionally, in the kidney tissues of CBS(+/-) 2-K and 1-K and WT 1-K mice, increased superoxide (O(2)(*-)) production and reduced glutathione (GSH)-to-oxidized glutathione (GSSG) ratio were normalized with exogenous H(2)S supplementation. These results demonstrate that HHcy-associated renal damage is related to decreased endogenous H(2)S generation in the body. Additionally, here we demonstrate with evidence that H(2)S supplementation prevents HHcy-associated renal damage, in part, through its antioxidant properties.

Dual effect of exogenous hydrogen sulfide on the spontaneous contraction of gastric smooth muscle in guinea-pig

Hydrogen sulfide (H(2)S) is produced endogenously in mammalian tissues and is important in both physiological and pathological processes. Despite its importance, little is known regarding the effect of H(2)S on gastrointestinal motility. We evaluated the effect of H(2)S on the spontaneous contraction of gastric antrum smooth muscle in the guinea pig (Cavia porcellus) using a physiograph. In addition, we investigated whether the effect of H(2)S was mediated by ionic channels by recording membrane currents in freshly dispersed gastric antrum myocytes using a whole-cell patch clamp. Sodium hydrogen sulfide (NaHS), an H(2)S donor, had a dual effect on the spontaneous contraction of gastric antrum muscle strips. At high concentrations (0.3-1.0 mM), NaHS suppressed the amplitude of spontaneous contraction. At low concentrations (0.1-0.3 mM), NaHS enhanced the resting tension of muscle strips while slightly reducing the contractile amplitude. The excitatory effect on spontaneous contraction, caused by low concentrations of NaHS, was abolished when the muscle strips were pretreated with 10 mM tetraethylammonium (TEA), a nonselective potassium channel blocker, or 0.5 mM 4-Aminopyridine (4-AP), a voltage-gated K(+) channel blocker. However, the excitatory effect of NaHS was not completely blocked by low concentrations of TEA (1 mM). Pretreatment with both TEA (1 mM) and 4-AP (0.5 mM) completely abolished the excitatory effect. The dose-response curve for the inhibitory effect of NaHS on the spontaneous contraction of gastric smooth muscle was shifted significantly to the left by TEA and 4-AP. Both Pinacidil, a K(ATP) channel opener, and NaHS significantly inhibited TEA-potentiated spontaneous contraction. Glibenclamide, a K(ATP) channel blocker, partially, but significantly, reversed the reduction in amplitude. NaHS enhanced the amplitude of the K(ATP) current, but inhibited the voltage-gated K(+) channel current (IK(V)) in a dose-dependent manner. NaHS had no effect on STOC at low concentrations (0.1-1.0 mM) but significantly inhibited STOC at high concentrations (4-10 mM). Our results suggest that H(2)S has multiple actions during the regulation of gastric motility in the guinea-pig. An excitatory effect is mediated via inhibition of the voltage-gated K(+) channel and an inhibitory effect is mediated via activation of the K(ATP) channel.

Ischemia-reperfusion reduces cystathionine-beta-synthase-mediated hydrogen sulfide generation in the kidney

Cystathionine-beta-synthase (CBS) catalyzes the rate-limiting step in the transsulfuration pathway for the metabolism of homocysteine (Hcy) in the kidney. Our recent study demonstrates that ischemia-reperfusion reduces the activity of CBS leading to Hcy accumulation in the kidney, which in turn contributes to renal injury. CBS is also capable of catalyzing the reaction of cysteine with Hcy to produce hydrogen sulfide (H(2)S), a gaseous molecule that plays an important role in many physiological and pathological processes. The aim of the present study was to examine the effect of ischemia-reperfusion on CBS-mediated H(2)S production in the kidney and to determine whether changes in the endogenous H(2)S generation had any impact on renal ischemia-reperfusion injury. The left kidney of Sprague-Dawley rat was subjected to 45-min ischemia followed by 6-h reperfusion. The ischemia-reperfusion caused lipid peroxidation and cell death in the kidney. The CBS-mediated H(2)S production was decreased, leading to a significant reduction in the renal H(2)S level. The activity of cystathionine-gamma-lyase, another enzyme responsible for endogenous H(2)S generation, was not significantly altered in the kidney upon ischemia-reperfusion. Partial restoration of CBS activity by intraperitoneal injection of the nitric oxide scavenger, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide not only increased renal H(2)S levels but also alleviated ischemia-reperfusion-induced lipid peroxidation and reduced cell damage in the kidney tissue. Furthermore, administration of an exogenous H(2)S donor, NaHS (100 microg/kg), improved renal function. Taken together, these results suggest that maintenance of tissue H(2)S level may offer a renal protective effect against ischemia-reperfusion injury.

Hydrogen sulfide destroys lipid hydroperoxides in oxidized LDL

LOOHs (lipid hydroperoxides) in oxLDL [oxidized LDL (low-density lipoprotein)] are potentially atherogenic compounds. Recently, H2S was identified as the third endogenous gasotransmitter in the vasculature. H2O2 is known to be destroyed by H2S. Assuming that H2S may also react with LOOHs, the results show that H2S can destroy LOOHs in oxLDL. The ability of LOOH-enriched LDL to induce HO-1 (haem oxygenase 1) in endothelial cells was abolished by H2S pretreatment. HPLC analysis showed that 9-HPODE [(9S)-hydroperoxy-(10E,12Z)-octadecadienoic acid], a compound found in oxLDL, was reduced to 9-HODE [(9S)-hydroxy-(10E,12Z)-octadecadienoic acid] in the presence of H2S. Thus H2S may act as an antiatherogenic agent by reducing LOOHs to the less reactive LOHs and could abrogate the pathobiological activity of oxLDL.

Nervous control of circulation--the role of gasotransmitters, NO, CO, and H2S

The origins and actions of gaseous signaling molecules, nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H(2)S) in the mammalian cardiovascular system have received considerable attention and it is evident that these three "gasotransmitters" perform a variety of homeostatic functions. The origins, actions and disposition of these gasotransmitters in the piscine vasculature are far from resolved. In most fish examined to date, NO or NO donors are generally in vitro and in vivo vasodilators acting via soluble guanylyl cyclase, although there is evidence for NO-mediated vasoconstriction. Injection of sodium nitroprusside into trout causes hypotension that is attributed to a reduction in systemic resistance. Unlike mammals, NO does not appear to have an endothelial origin in fish blood vessels as an endothelial NO synthase has not identified. However, neural NO synthase is prevalent in perivascular nerves and is the most likely source of NO for cardiovascular control in fish. CO is a vasodilator in lamprey and trout vessels, and it, like NO, appears to exert its action, at least in part, via guanylyl cyclase and potassium channel activation. Inhibition of CO production increases resting tone in trout vessels suggestive of tonic CO activity, but little else is known about the origin or control of CO in the fish vasculature. H(2)S is synthesized by fish vessels and its constrictory, dilatory, or even multi-phasic actions, are both species- and vessel-specific. A small component of H(2)S-mediated basal activity may be endothelial in origin, but to a large extent H(2)S affects vascular smooth muscle directly and the mechanisms are unclear. H(2)S injected into the dorsal aorta of unanesthetized trout often produces oscillations in arterial blood pressure suggestive of H(2)S activity in the central nervous system as well as peripheral vasculature. Collectively, these studies hint at significant involvement of the gasotransmitters in piscine cardiovascular function and hopefully provide a variety of avenues for future research.

Calcium sulfide (CaS), a donor of hydrogen sulfide (H(2)S): a new antihypertensive drug?

Hypertension is the leading cause of cardiovascular diseases, and an estimated 972 million people in the world are suffering from this problem. Indubitably, hypertension is an important worldwide public-health challenge. In recent years many efforts have been made to devise novel therapies involving new targets implicated in cardiovascular diseases. Hydrogen sulfide (H(2)S) is a member of a growing family of "gasotransmitters". It is clear that H(2)S plays a pivotal role in the basal regulation of vessels tone. Also studies demonstrate that intravenous sodium hydrosulfide (NaHS), a donor of H(2)S, dose-dependently decreases systolic blood pressure. However, because of its active chemical property, NaHS can be easily oxidized, even spontaneously ignited in the open air. Moreover, its solution is not stable. So the pharmacal use of NaHS is limited by its properties. Calcium sulfide (CaS), one of the effective components in a traditional herb, is another donor of H(2)S. It has more stable chemical properties than NaHS. We hypotheses that CaS might be given by mouth as a new antihypertensive drug through certain dosage form designing. To test this hypothesis, we should establish animal models for studies including drug efficacy, drug safety, drug toxicology, drug metabolism and drug kinetics.

Signaling by gasotransmitters

Nitric oxide is well established as a major signaling molecule. Evidence is accumulating that carbon monoxide and hydrogen sulfide also are physiologic mediators in the cardiovascular, immune, and nervous systems. This Review focuses on mechanisms whereby they signal by binding to metal centers in metalloproteins, such as in guanylyl cyclase, or modifying sulfhydryl groups in protein targets.

Is hydrogen sulfide a circulating "gasotransmitter" in vertebrate blood?

Hydrogen sulfide (H(2)S) is gaining acceptance as a signaling molecule and has been shown to elicit a variety of biological effects at concentrations between 10 and 1000 micromol/l. Dissolved H(2)S is a weak acid in equilibrium with HS(-) and S(2-) and under physiological conditions these species, collectively referred to as sulfide, exist in the approximate ratio of 20% H(2)S, 80% HS(-) and 0% S(2-). Numerous analyses over the past 8 years have reported plasma or blood sulfide concentrations also in this range, typically between 30 and 300 micromol/l, thus supporting the biological studies. However, there is some question whether or not these concentrations are physiological. First, many of these values have been obtained from indirect methods using relatively harsh chemical conditions. Second, most studies conducted prior to 2000 failed to find blood sulfide in micromolar concentrations while others showed that radiolabeled (35)S-sulfide is rapidly removed from blood and that mammals have a relatively high capacity to metabolize exogenously administered sulfide. Very recent studies using H(2)S gas-sensing electrodes to directly measure sulfide in plasma or blood, or HPLC analysis of head-space gas, have also indicated that sulfide does not circulate at micromolar levels and is rapidly consumed by blood or tissues. Third, micromolar concentrations of sulfide in blood or exhaled air should be, but are not, malodorous. Fourth, estimates of dietary sulfur necessary to sustain micromolar levels of plasma sulfide greatly exceed the daily intake. Collectively, these studies imply that many of the biological effects of sulfide are only achieved at supra-physiological concentrations and they question whether circulating sulfide is a physiologically relevant signaling molecule. This review examines the blood/plasma sulfide measurements that have been reported over the past 30 years from the perspective of the analytical methods used and the potential sources of error.

Novel dithiolethione-modified nonsteroidal anti-inflammatory drugs in human hepatoma HepG2 and colon LS180 cells

PURPOSE

Nonsteroidal anti-inflammatory drugs (NSAID) are promising chemopreventive agents against colon and other cancers. However, the molecular basis mediated by NSAIDs for chemoprevention has not been fully elucidated. Environmental carcinogens induce DNA mutation and cellular transformation; therefore, we examined the effect of NSAIDs on carcinogenesis mediated by the aryl hydrocarbon receptor signaling pathway. In this study, we investigated the activities of a new class of NSAIDs containing dithiolethione moieties (S-NSAID) on both arms of carcinogenesis.

EXPERIMENTAL DESIGN

We investigated the effects of the S-NSAIDs, S-diclofenac and S-sulindac, on carcinogen activation and detoxification mechanisms in human hepatoma HepG2 and human colonic adenocarcinoma LS180 cells.

RESULTS

We found that S-diclofenac and S-sulindac inhibited the activity and expression of the carcinogen activating enzymes, cytochromes P-450 (CYP) CYP1A1, CYP1B1, and CYP1A2. Inhibition was mediated by transcriptional regulation of the aryl hydrocarbon receptor (AhR) pathway. The S-NSAIDs down-regulated carcinogen-induced expression of CYP1A1 heterogeneous nuclear RNA, a measure of transcription rate. Both compounds blocked carcinogen-activated AhR from binding to the xenobiotic responsive element as shown by chromatin immunoprecipitation. S-diclofenac and S-sulindac inhibited carcinogen-induced CYP enzyme activity through direct inhibition as well as through decreased transcriptional activation of the AhR. S-sulindac induced expression of several carcinogen detoxification enzymes of the glutathione cycle including glutathione S-transferase A2, glutamate cysteine ligase catalytic subunit, glutamate cysteine ligase modifier subunit, and glutathione reductase.

CONCLUSIONS

These results indicate that S-diclofenac and S-sulindac may serve as effective chemoprevention agents by favorably balancing the equation of carcinogen activation and detoxification mechanisms.

Sulphate-reducing bacteria and hydrogen sulphide in the aetiology of ulcerative colitis

BACKGROUND

The aetiology of ulcerative colitis is uncertain but may relate to environmental factors in genetically predisposed individuals. Sulphate-reducing bacteria (SRB) have been implicated through the harmful effects of hydrogen sulphide, a by-product of their respiration. Hydrogen sulphide is freely permeable to cell membranes and inhibits butyrate. This review examines the available evidence relating to SRB as a possible cause of ulcerative colitis.

METHODS

A literature search was conducted using the PubMed database and search terms 'sulphate reducing bacteria', 'hydrogen sulphide', 'ulcerative colitis', 'mucous gel layer' and 'trans-sulphuration'.

RESULTS

Search results were scrutinized and 113 pertinent full-text articles were selected for review. Collected data related to hydrogen sulphide metabolism, SRB respiration, mucous gel layer composition and their association with ulcerative colitis.

CONCLUSION

There is evidence to implicate SRB as an environmental factor in ulcerative colitis. More sophisticated mucosal dissection and molecular techniques using bacteria-directed probes are required to determine an association definitively.

H2S biogenesis by human cystathionine gamma-lyase leads to the novel sulfur metabolites lanthionine and homolanthionine and is responsive to the grade of hyperhomocysteinemia

Although there is a growing recognition of the significance of hydrogen sulfide (H(2)S) as a biological signaling molecule involved in vascular and nervous system functions, its biogenesis and regulation are poorly understood. It is widely assumed that desulfhydration of cysteine is the major source of H(2)S in mammals and is catalyzed by the transsulfuration pathway enzymes, cystathionine beta-synthase and cystathionine gamma-lyase (CSE). In this study, we demonstrate that the profligacy of human CSE results in a variety of reactions that generate H(2)S from cysteine and homocysteine. The gamma-replacement reaction, which condenses two molecules of homocysteine, yields H(2)S and a novel biomarker, homolanthionine, which has been reported in urine of homocystinuric patients, whereas a beta-replacement reaction, which condenses two molecules of cysteine, generates lanthionine. Kinetic simulations at physiologically relevant concentrations of cysteine and homocysteine, reveal that the alpha,beta-elimination of cysteine accounts for approximately 70% of H(2)S generation. However, the relative importance of homocysteine-derived H(2)S increases progressively with the grade of hyperhomocysteinemia, and under conditions of severely elevated homocysteine (200 microm), the alpha,gamma-elimination and gamma-replacement reactions of homocysteine together are predicted to account for approximately 90% of H(2)S generation by CSE. Excessive H(2)S production in hyperhomocysteinemia may contribute to the associated cardiovascular pathology.

Hydrogen sulfide as a mediator of human corpus cavernosum smooth-muscle relaxation

Hydrogen sulfide (H(2)S) is synthesized by 2 enzymes, cystathionine beta-synthase (CBS) and cystathionine gamma-lyase (CSE). L-Cysteine (L-Cys) acts as a natural substrate for the synthesis of H(2)S. Human penile tissue possesses both CBS and CSE, and tissue homogenates efficiently convert L-Cys to H(2)S. CBS and CSE are localized in the muscular trabeculae and the smooth-muscle component of the penile artery, whereas CSE but not CBS is also expressed in peripheral nerves. Exogenous H(2)S [sodium hydrogen sulfide (NaHS)] or L-Cys causes a concentration-dependent relaxation of strips of human corpus cavernosum. L-Cys relaxation is inhibited by the CBS inhibitor, aminoxyacetic acid (AOAA). Electrical field stimulation of human penile tissue, under resting conditions, causes an increase in tension that is significantly potentiated by either propargylglycine (PAG; CSE inhibitor) or AOAA. In rats, NaHS and L-Cys promote penile erection, and the response to L-Cys is blocked by PAG. Our data demonstrate that the L-Cys/H(2)S pathway mediates human corpus cavernosum smooth-muscle relaxation.

Supression of hemin-mediated oxidation of low-density lipoprotein and subsequent endothelial reactions by hydrogen sulfide (H(2)S)

Heme-mediated oxidative modification of low-density lipoprotein (LDL) plays a crucial role in early atherogenesis. It has been shown that hydrogen sulfide (H(2)S) produced by vascular smooth muscle cells is present in plasma at a concentration of about 50 micromol/L. H(2)S is a strong reductant which can react with reactive oxygen species like superoxide anion and hydrogen peroxide. The current study investigated the effect of H(2)S on hemin-mediated oxidation of LDL and oxidized LDL (oxLDL)-induced endothelial reactions. H(2)S dose dependently delayed the accumulation of lipid peroxidation products-conjugated dienes, lipid hydroperoxides (LOOH), and thiobarbituric acid reactive substances-during hemin-mediated oxidation. Moreover, H(2)S decreased the LOOH content of both oxidized LDL and lipid extracts derived from soft atherosclerotic plaque, which was accompanied by reduced cytotoxicity. OxLDL-mediated induction of the oxidative stress responsive gene, heme oxygenase-1, was also abolished by H(2)S. Finally we have shown that H(2)S can directly protect endothelium against hydrogen peroxide and oxLDL-mediated endothelial cytotoxicity. These results demonstrate novel functions of H(2)S in preventing hemin-mediated oxidative modification of LDL, and consequent deleterious effects, suggesting a possible antiatherogenic action of H(2)S.

Production and actions of hydrogen sulfide, a novel gaseous bioactive substance, in the kidneys

Hydrogen sulfide (H(2)S), a novel endogenous gaseous bioactive substance, has recently been implicated in the regulation of cardiovascular and neuronal functions. However, its role in the control of renal function is unknown. In the present study, incubation of renal tissue homogenates with L-cysteine (L-Cys) (as a substrate) produced H(2)S in a concentration-dependent manner. This H(2)S production was completely abolished by inhibition of both cystathionine beta-synthetase (CBS) and cystathionine gamma-lyase (CGL), two major enzymes for the production of H(2)S, using amino-oxyacetic acid (AOAA), an inhibitor of CBS, and propargylglycine (PPG), an inhibitor of CGL. However, inhibition of CBS or CGL alone induced a small decrease in H(2)S production. In anesthetized Sprague-Dawley rats, intrarenal arterial infusion of an H(2)S donor (NaHS) increased renal blood flow, glomerular filtration rate (GFR), urinary sodium (U(Na) x V), and potassium (U(K) x V) excretion. Consistently, infusion of both AOAA and PPG to inhibit the endogenous H(2)S production decreased GFR, U(Na) x V, and U(K) x V, and either one of these inhibitors alone had no significant effect on renal functions. Infusion of L-Cys into renal artery to increase the endogenous H(2)S production also increased GFR, U(Na) x V, and U(K) x V, which was blocked by AOAA plus PPG. It was shown that H(2)S had both vascular and tubular effects and that the tubular effect of H(2)S might be through inhibition of Na(+)/K(+)/2Cl(-) cotransporter and Na(+)/K(+)/ATPase activity. These results suggest that H(2)S participates in the control of renal function and increases urinary sodium excretion via both vascular and tubular actions in the kidney.

The endogenous production of hydrogen sulphide in intrauterine tissues

BACKGROUND

Hydrogen sulphide is a gas signalling molecule which is produced endogenously from L-cysteine via the enzymes cystathionine beta-synthase (CBS) and cystathionine gamma-lyase (CSE). The possible role of hydrogen sulphide in reproduction has not yet been fully investigated. It has been previously demonstrated that hydrogen sulphide relaxes uterine smooth muscle in vitro. The aim of the present study was to investigate the endogenous production of hydrogen sulphide in rat and human intrauterine tissues in vitro.

METHODS

The production of hydrogen sulphide in rat and human intrauterine tissues was measured in vitro using a standard technique. The expression of CBS and CSE was also investigated in rat and human intrauterine tissues via Western blotting. Furthermore, the effects of nitric oxide (NO) and low oxygen conditions on the production rates of hydrogen sulphide were investigated.

RESULTS

The order of hydrogen sulphide production rates (mean +/- SD, n = 4) for rat tissues were: liver (777 +/- 163 nM/min/g) > uterus (168 +/- 100 nM/min/g) > fetal membranes (22.3 +/- 15.0 nM/min/g) > placenta (11.1 +/- 4.7 nM/min/g), compared to human placenta (200 +/- 102 nM/min/g). NO significantly increased hydrogen sulphide production in rat fetal membranes (P < 0.05). Under low oxygen conditions the production of hydrogen sulphide was significantly elevated in human placenta, rat liver, uterus and fetal membranes (P < 0.05). Western blotting (n = 4) detected the expression of CBS and CSE in all rat intrauterine tissues, and in human placenta, myometrium, amnion and chorion.

CONCLUSION

Rat and human intrauterine tissues produce hydrogen sulphide in vitro possibly via CBS and CSE enzymes. NO increased the production of hydrogen sulphide in rat fetal membranes. The augmentation of hydrogen sulphide production in human intrauterine tissues in a low oxygen environment could have a role in pathophysiology of pregnancy.

Hydrogen sulfide triggers late-phase preconditioning in postischemic small intestine by an NO- and p38 MAPK-dependent mechanism

Hydrogen sulfide (H(2)S) is one of three endogenous gases, along with carbon monoxide (CO) and nitric oxide (NO), that exert a variety of important vascular actions in vivo. Although it has been demonstrated that CO or NO can trigger the development of a preconditioned phenotype in postischemic tissues, it is unclear whether H(2)S may also induce protection in organs subsequently exposed to ischemia-reperfusion (I/R). In light of these observations, we postulated that preconditioning with the exogenous H(2)S donor sodium hydrosulfide (NaHS-PC) would inhibit leukocyte rolling (LR) and adhesion (LA) induced by I/R. We used intravital microscopic techniques to demonstrate that NaHS-PC 24 h, but not 1 h, before I/R causes postcapillary venules to shift to an anti-inflammatory phenotype in wild-type (WT) mice such that these vessels fail to support LR and LA during reperfusion. The protective effect of NaHS-PC on LR was largely abolished by coincident pharmacological inhibition of NO synthase (NOS) in WT animals and was absent in endothelial NOS-deficient (eNOS(-/-)) mice. A similar pattern of response was noted in WT mice treated concomitantly with NaHS plus p38 mitogen-activated protein kinase (MAPK) inhibitors (SB 203580 or SK-86002). Whereas the reduction in LA induced by antecedent NaHS was attenuated by pharmacological inhibition of NOS or p38 MAPK in WT mice, the antiadhesive effect of NaHS was still evident in eNOS(-/-) mice. Thus NaHS-PC prevents LR and LA by triggering the activation of an eNOS- and p38 MAPK-dependent mechanism. However, the role of eNOS in the antiadhesive effect of NaHS-PC was less prominent than its effect to reduce LR.

Pancreatic islet overproduction of H2S and suppressed insulin release in Zucker diabetic rats

Hydrogen sulfide (H(2)S) has been traditionally known for its toxic effects on living organisms. The role of H(2)S in the homeostatic regulation of pancreatic insulin metabolism has been unclear. The present study is aimed at elucidating the effect of endogenously produced H(2)S on pancreatic insulin release and its role in diabetes development. Diabetes development in Zucker diabetic fatty (ZDF) rats was evaluated in comparison with Zucker fatty (ZF) and Zucker lean (ZL) rats. Pancreatic H(2)S production and insulin release were also assayed. It was found that H(2)S was generated in rat pancreas islets, catalyzed predominantly by cystathionine gamma-lyase (CSE). Pancreatic CSE expression and H(2)S production were greater in ZDF rats than in ZF or ZL rats. ZDF rats exhibited reduced serum insulin level, hyperglycemia, and insulin resistance. Inhibition of pancreatic H(2)S production in ZDF rats by intraperitoneal injection of DL-propargylglycine (PPG) for 4 weeks increased serum insulin level, lowered hyperglycemia, and reduced hemoglobin A1c level (P<0.05). Although in ZF rats it also reduced pancreatic H(2)S production and serum H(2)S level, PPG treatment did not alter serum insulin and glucose level. Finally, H(2)S significantly increased K(ATP) channel activity in freshly isolated rat pancreatic beta-cells. It appears that insulin release is impaired in ZDF because of abnormally high pancreatic production of H(2)S. New therapeutic approach for diabetes management can be devised based on our observation by inhibiting endogenous H(2)S production from pancreas.

Hydrogen sulfide stimulates catecholamine secretion in rainbow trout (Oncorhynchus mykiss)

We tested the hypothesis that endogenously produced hydrogen sulfide (H2S) can potentially contribute to the adrenergic stress response in rainbow trout by initiating catecholamine secretion from chromaffin cells. During acute hypoxia (water Po2= 35 mmHg), plasma H2S levels were significantly elevated concurrently with a rise in circulating catecholamine concentrations. Tissues enriched with chromaffin cells (posterior cardinal vein and anterior kidney) produced H2S in vitro when incubated with l-cysteine. In both tissues, the production of H2S was eliminated by adding the cystathionine β-synthase inhibitor, aminooxyacetate. Cystathionine β-synthase and cystathionine γ-lyase were cloned and sequenced and the results of real-time PCR demonstrated that with the exception of white muscle, mRNA for both enzymes was broadly distributed within the tissues that were examined. Electrical field stimulation of an in situ saline-perfused posterior cardinal vein preparation caused the appearance of H2S and catecholamines in the outflowing perfusate. Perfusion with the cholinergic receptor agonist carbachol (1 × 10−6M) or depolarizing levels of KCl (1 × 10−2M) caused secretion of catecholamines without altering H2S output, suggesting that neuronal excitation is required for H2S release. Addition of H2S (at concentrations exceeding 5 × 10−7M) to the perfusion fluid resulted in a marked stimulation of catecholamine secretion that was not observed when Ca2+-free perfusate was used. These data, together with the finding that H2S-induced catecholamine secretion was unaltered by the nicotinic receptor blocker hexamethonium, suggest that H2S is able to directly elicit catecholamine secretion via membrane depolarization followed by Ca2+-mediated exocytosis.

H2S protects against methionine-induced oxidative stress in brain endothelial cells

Homocysteine (Hcy) causes cerebrovascular dysfunction by inducing oxidative stress. However, to date, there are no strategies to prevent Hcy-induced oxidative damage. Hcy is an H2S precursor formed from methionine (Met) metabolism. We aimed to investigate whether H2S ameliorated Met-induced oxidative stress in mouse brain endothelial cells (bEnd3). The bEnd3 cells were exposed to Met treatment in the presence or absence of NaHS (donor of H2S). Met-induced cell toxicity increased the levels of free radicals in a concentration-dependent manner. Met increased NADPH-oxidase-4 (NOX-4) expression and mitigated thioredxion-1(Trx-1) expression. Pretreatment of bEnd3 with NaHS (0.05 mM) attenuated the production of free radicals in the presence of Met and protected the cells from oxidative damage. Furthermore, NaHS enhanced inhibitory effects of apocynin, N-acetyl-l-cysteine (NAC), reduced glutathione (GSH), catalase (CAT), superoxide dismutase (SOD), Nomega-nitro-l-arginine methyl ester (L-NAME) on ROS production and redox enzymes levels induced by Met. In conclusion, the administration of H2S protected the cells from oxidative stress induced by hyperhomocysteinemia (HHcy), which suggested that NaHS/H2S may have therapeutic potential against Met-induced oxidative stress.

Therapeutic antioxidant medical gas

Medical gases are pharmaceutical gaseous molecules which offer solutions to medical needs and include traditional gases, such as oxygen and nitrous oxide, as well as gases with recently discovered roles as biological messenger molecules, such as carbon monoxide, nitric oxide and hydrogen sulphide. Medical gas therapy is a relatively unexplored field of medicine; however, a recent increasing in the number of publications on medical gas therapies clearly indicate that there are significant opportunities for use of gases as therapeutic tools for a variety of disease conditions. In this article, we review the recent advances in research on medical gases with antioxidant properties and discuss their clinical applications and therapeutic properties.

Hydrogen sulfide promotes wheat seed germination and alleviates oxidative damage against copper stress

With the enhancement of copper (Cu) stress, the germination percentage of wheat seeds decreased gradually. Pretreatment with sodium hydrosulfide (NaHS), hydrogen sulfide (H(2)S) donor alleviated the inhibitory effect of Cu stress in a dose-dependent manner; whereas little visible symptom was observed in germinating seeds and radicle tips cultured in NaHS solutions. It was verified that H(2)S or HS(-) rather than other sulfur-containing components derived from NaHS attribute to the potential role in promoting seed germination against Cu stress. Further studies showed that NaHS could promote amylase and esterase activities, reduce Cu-induced disturbance of plasma membrane integrity in the radicle tips, and sustain lower levels of malondialdehyde and H(2)O(2) in germinating seeds. Furthermore, NaHS pretreatment increased activities of superoxide dismutase and catalase and decreased that of lipoxygenase, but showed no significant effect on ascorbate peroxidase. Alternatively, NaHS prevented uptake of Cu and promoted the accumulation of free amino acids in seeds exposed to Cu. In addition, a rapid accumulation of endogenous H(2)S in seeds was observed at the early stage of germination, and higher level of H(2)S in NaHS-pretreated seeds. These data indicated that H(2)S was involved in the mechanism of germinating seeds' responses to Cu stress.

H2S contributes to the hepatic arterial buffer response and mediates vasorelaxation of the hepatic artery via activation of K(ATP) channels

Hepatic blood supply is uniquely regulated by the hepatic arterial buffer response (HABR), counteracting alterations of portal venous blood flow by flow changes of the hepatic artery. Hydrogen sulfide (H(2)S) has been recognized as a novel signaling molecule with vasoactive properties. However, the contribution of H(2)S in mediating the HABR is not yet studied. In pentobarbital-anesthetized and laparotomized rats, flow probes around the portal vein and hepatic artery allowed for assessment of the portal venous (PVBF) and hepatic arterial blood flow (HABF) under baseline conditions and stepwise reduction of PVBF for induction of HABR. Animals received either the H(2)S donor Na(2)S, DL-propargylglycine as inhibitor of the H(2)S synthesizing enzyme cystathionine-gamma-lyase (CSE), or saline alone. Additionally, animals were treated with Na(2)S and the ATP-sensitive potassium channel (K(ATP)) inhibitor glibenclamide or with glibenclamide alone. Na(2)S markedly increased the buffer capacity to 27.4 +/- 3.0% (P < 0.05 vs. controls: 15.5 +/- 1.7%), whereas blockade of H(2)S formation by DL-propargylglycine significantly reduced the buffer capacity (8.5 +/- 1.4%). Glibenclamide completely reversed the H(2)S-induced increase of buffer capacity to the control level. By means of RT-PCR, Western blot analysis, and immunohistochemistry, we observed the expression of both H(2)S synthesizing enzymes (CSE and cystathionine-beta-synthase) in aorta, vena cava, hepatic artery, and portal vein, as well as in hepatic parenchymal tissue. Terminal branches of the hepatic afferent vessels expressed only CSE. We show for the first time that CSE-derived H(2)S contributes to HABR and partly mediates vasorelaxation of the hepatic artery via activation of K(ATP) channels.