Hydrogen sulfide attenuates hepatic ischemia-reperfusion injury: role of antioxidant and antiapoptotic signaling

Inhalative preconditioning with hydrogen sulfide attenuated apoptosis after retinal ischemia/reperfusion injury

PURPOSE

Retinal ischemia/reperfusion (I/R) injury plays an important role in the pathophysiology of various ocular diseases. Retinal ganglion cells (RGCs) are particularly vulnerable to ischemia. Hydrogen sulfide (H(2)S) was recently shown to be neuroprotective in the brain and retina due to its antiapoptotic effects. Rapid preconditioning of retinal neurons by inhaled H(2)S before I/R injury may reduce apoptosis in the rat retina.

METHODS

I/R injury was created on the left eye of rats (n=8) with or without inhaled H(2)S preconditioning (80 ppm) for one hour before ischemia. Densities of fluorogold prelabeled RGCs were analyzed 7 days after injury in retinal whole mounts. Retinal tissue was harvested to analyze protein expression of heat shock protein (HSP)-90 and the mitogen-activated protein kinases (MAPKs) c-jun N-terminal kinase (JNK), extracellular signal-regulated kinase (ERK)1/2 and p38 to elucidate a possible pathway of neuroprotection. DNA binding activity of the transcription factors nuclear factor-kappa-light-chain-enhancer of activated B-cells (NF-κB), cyclic adenosine monophosphate response element binding protein (CREB), and heat shock element (HSE), as well as caspase-3 cleavage and activity, were determined. Retinal sections were further assessed using anti-glial fibrillary acidic protein staining.

RESULTS

RGC death after I/R injury decreased by 41.5% after H(2)S preconditioning compared to room air (p<0.001). H(2)S inhalation before ischemia reduced caspase-3 cleavage (p<0.001) and attenuated caspase-3 activity (p<0.001). Furthermore, HSP-90 expression was significantly elevated in the retina after H(2)S preconditioning. NF-κB but not CREB or HSE showed specific, H2S-dependent regulation, as well as the MAPKs ERK1/2 and JNK but not p38.

CONCLUSIONS

H(2)S preconditioning mediates antiapoptotic effects in retinal I/R injury, thus exhibiting neuroprotection. Based on these observations, H(2)S could represent a novel and promising therapeutic agent to counteract neuronal injuries in the eye. Further studies are needed to prove H(2)S's neuroprotective propensity using a postconditioning approach.

Hydrogen sulphide protects mouse pancreatic β-cells from cell death induced by oxidative stress, but not by endoplasmic reticulum stress

BACKGROUND AND PURPOSE

Hydrogen sulphide (H₂S), a potentially toxic gas, is also involved in the neuroprotection, neuromodulation, cardioprotection, vasodilatation and the regulation of inflammatory response and insulin secretion. We have recently reported that H₂S suppresses pancreatic β-cell apoptosis induced by long-term exposure to high glucose. Here we examined the protective effects of sodium hydrosulphide (NaHS), an H₂S donor, on various types of β-cell damage.

EXPERIMENTAL APPROACH

Isolated islets from mice or the mouse insulinoma MIN6 cells were cultured with palmitate, cytokines (a mixture of tumour necrosis factor-α, interferon-γ and interleukin-1β), hydrogen peroxide, thapsigargin or tunicamycin with or without NaHS. We examined DNA fragmentation, caspase-3 and -7 activities and reactive oxygen species (ROS) production in the treated cells thereafter. Apoptotic cell death in isolated islets was also assessed by the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labelling (TUNEL) method.

KEY RESULTS

NaHS suppressed DNA fragmentation and the activities of caspase-3 and -7 induced by palmitate, the cytokines or hydrogen peroxide. In contrast, NaHS failed to protect islets and MIN6 cells from apoptosis induced by thapsigargin and tunicamycin, both of which cause endoplasmic reticulum stress. NaHS suppressed ROS production induced by cytokines or hydrogen peroxide but it had no effect on ROS production in thapsigargin-treated cells. NaHS increased Akt phosphorylation in MIN6 cells treated with cytokines but not in cells treated with thapsigargin. Treatment with NaHS decreased TUNEL-positive cells in cytokine-exposed islets.

CONCLUSIONS AND IMPLICATIONS

H₂S may prevent pancreatic β-cells from cell apoptosis via an anti-oxidative mechanism and the activation of Akt signalling.

Emergent role of gasotransmitters in ischemia-reperfusion injury

Nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H2S) are lipid-soluble, endogenously produced gaseous messenger molecules collectively known as gasotransmitters. Over the last several decades, gasotransmitters have emerged as potent cytoprotective mediators in various models of tissue and cellular injury. Specifically, when used at physiological levels, the exogenous and endogenous manipulation of these three gases has been shown to modulate ischemia/reperfusion injury by inducing a number of cytoprotective mechanisms including: induction of vasodilatation, inhibition of apoptosis, modulation of mitochondrial respiration, induction of antioxidants, and inhibition of inflammation. However, while the actions are similar, there are some differences in the mechanisms by which these gasotransmitters induce these effects and the regulatory actions of the enzyme systems can vary depending upon the gas being investigated. Furthermore, there does appear to be some crosstalk between the gases, which can provide synergistic effects and additional regulatory effects. This review article will discuss several models and mechanisms of gas-mediated cytoprotection, as well as provide a brief discussion on the complex interactions between the gasotransmitter systems.

Effects of intravenous sulfide during porcine aortic occlusion-induced kidney ischemia/reperfusion injury

In rodents, inhaled H2S and injection of H2S donors protected against kidney ischemia/reperfusion (I/R) injury. During porcine aortic occlusion, the H2S donor Na2S (sulfide) reduced energy expenditure and decreased the noradrenaline requirements needed to maintain hemodynamic targets during early reperfusion. Therefore, we tested the hypothesis whether sulfide pretreatment may also ameliorate organ function in porcine aortic occlusion-induced kidney I/R injury. Anesthetized, ventilated, and instrumented pigs randomly received either sulfide or vehicle and underwent 90 min of kidney ischemia using intraaortic balloon-occlusion, and 8 h of reperfusion. During reperfusion, noradrenaline was titrated to maintain blood pressure at baseline levels. Sulfide attenuated the fall in creatinine clearance and the rise in creatinine blood levels, whereas renal blood flow and fractional Na+ excretion were comparable. Sulfide also lowered the blood IL-6, IL-1β, and nitrite + nitrate concentrations, which coincided with reduced kidney oxidative DNA base damage and iNOS expression, and attenuated glomerular histological injury as assessed by the incidence of glomerular tubularization. While expression of heme oxygenase 1 and cleaved caspase 3 did not differ, sulfide reduced the expression Bcl-xL and increased the activation of nuclear transcription factor κB. During porcine aortic occlusion-induced kidney I/R injury, sulfide pretreatment attenuated tissue injury and organ dysfunction as a result of reduced inflammation and oxidative and nitrosative stress. The higher nuclear transcription factor κB activation was probably due to the drop in temperature.

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.

Hypoxia and anoxia tolerance of vertebrate hearts: an evolutionary perspective

Extreme changes in environmental oxygen (O(2)) is a constant issue that ectotherm vertebrates have to deal with, whereas for endotherms severe hypoxia and reoxygenation are usually related to a pathological state. The physiological mechanisms of hypoxia tolerance in ectotherms are based on biochemical evolutionary adaptations and may serve in understanding endogenous phenomena of protection against diminished O(2) availability in the heart. In this review, we will, therefore, describe different species of fish, amphibian, and reptile that are well-known examples of cardiac tolerance to O(2) deficiency. We will then focus on a subset of Antarctic fishes which have lost physiological transporters of O(2) such as hemoglobin and myoglobin (Mb) and that have reached a surprising adaptation to this extreme environment. Moreover, we will concentrate on the cardio-protective effects of the interaction between Mb and nitric oxide with particular emphasis on the nitrite-reductase function of Mb. Finally, the role of a recently described gasotransmitter, the free diffusible hydrogen sulfide, will be briefly discussed in relation to hypoxia. This evolutionary and comparative perspective may provide a useful and heuristic stimulus for medically oriented research aimed at elucidating the environmental and genetic risk factors underlying the vulnerability of the human heart.

Therapeutic delivery of hydrogen sulfide for salvage of ischemic skeletal muscle after the onset of critical ischemia

BACKGROUND

Recent evidence suggests that hydrogen sulfide is capable of mitigating the degree of cellular damage associated with ischemia-reperfusion injury (IRI).

METHODS

This study evaluated the potential utility of hydrogen sulfide in preventing IRI in skeletal muscle by using in vitro (cultured myotubes subjected to sequential hypoxia and normoxia) and in vivo (mouse hind limb ischemia, followed by reperfusion) models to determine whether intravenous hydrogen sulfide delivered after the ischemic event had occurred (pharmacologic postconditioning) conferred protection against IRI. Injury score and apoptotic index were determined by analysis of specimens stained with hematoxylin and eosin and terminal deoxynucleotide transferase-mediated deoxy-uridine triphosphate nick-end labeling, respectively.

RESULTS

In vitro, hydrogen sulfide reduced the apoptotic index after 1, 3, or 5 hours of hypoxia by as much as 75% (P = .002), 80% (P = .006), and 83% (P < .001), respectively. In vivo, hydrogen sulfide delivered after the onset of hind limb ischemia and before reperfusion resulted in protection against IRI-induced cellular changes, which was validated by significant decreases in the injury score and apoptotic index. The timing of hydrogen sulfide delivery was crucial: when delivered 20 minutes before reperfusion, hydrogen sulfide conferred significant cytoprotection (P < .001), but treatment 1 minute before reperfusion did not provide protection (P = NS).

CONCLUSIONS

These findings confirm that hydrogen sulfide limits IRI-induced cellular damage in myotubes and skeletal muscle, even when delivered after the onset of ischemia in this murine model. These data suggest that when given in the appropriate dose and within the proper time frame, hydrogen sulfide may have significant therapeutic applications in multiple clinical scenarios.

Reactivity of hydrogen sulfide with peroxynitrite and other oxidants of biological interest

Hydrogen sulfide (H(2)S) is an endogenously generated gas that can also be administered exogenously. It modulates physiological functions and has reported cytoprotective effects. To evaluate a possible antioxidant role, we investigated the reactivity of hydrogen sulfide with several one- and two-electron oxidants. The rate constant of the direct reaction with peroxynitrite was (4.8±1.4)×10(3)M(-1) s(-1) (pH 7.4, 37°C). At low hydrogen sulfide concentrations, oxidation by peroxynitrite led to oxygen consumption, consistent with a one-electron oxidation that initiated a radical chain reaction. Accordingly, pulse radiolysis studies indicated that hydrogen sulfide reacted with nitrogen dioxide at (3.0±0.3)×10(6)M(-1) s(-1) at pH 6 and (1.2±0.1)×10(7)M(-1) s(-1) at pH 7.5 (25°C). The reactions of hydrogen sulfide with hydrogen peroxide, hypochlorite, and taurine chloramine had rate constants of 0.73±0.03, (8±3)×10(7), and 303±27M(-1) s(-1), respectively (pH 7.4, 37°C). The reactivity of hydrogen sulfide was compared to that of low-molecular-weight thiols such as cysteine and glutathione. Considering the low tissue concentrations of endogenous hydrogen sulfide, direct reactions with oxidants probably cannot completely account for its protective effects.

Divergent roles of superoxide and nitric oxide in liver ischemia and reperfusion injury

Liver ischemia and reperfusion-induced injury is a major clinical complication associated with hemorrhagic or endotoxin shock and thermal injury as well as liver transplantation and resectional surgery. Data obtained from several different studies suggest that an important initiating event in the pathophysiology of ischemia and reperfusion-induced tissue injury is enhanced production of superoxide concomitant with a decrease in the bioavailability of endothelial cell-derived nitric oxide. This review will summarize the evidence supporting the hypothesis that the redox imbalance induced by alterations in superoxide and nitric oxide generation creates a more oxidative environment within the different cells of the liver that enhances the nuclear transcription factor-κB-dependent expression of a variety of different cytokines and mediators that may promote as well as limit ischemia and reperfusion-induced hepatocellular injury. In addition, the evidence implicating endothelial cell nitric oxide synthase-dependent and -independent generation of nitric oxide as important regulatory pathways that act to limit ischemia and reperfusion-induced liver injury and inflammation is also presented.

Detection of exhaled hydrogen sulphide gas in healthy human volunteers during intravenous administration of sodium sulphide

INTRODUCTION

Hydrogen sulphide (H(2)S) is an endogenous gaseous signaling molecule and potential therapeutic agent. Emerging studies indicate its therapeutic potential in a variety of cardiovascular diseases and in critical illness. Augmentation of endogenous sulphide concentrations by intravenous administration of sodium sulphide can be used for the delivery of H(2)S to the tissues. In the current study, we have measured H(2)S concentrations in the exhaled breath of healthy human volunteers subjected to increasing doses sodium sulphide in a human phase I safety and tolerability study.

METHODS

We have measured reactive sulphide in the blood via ex vivo derivatization of sulphide with monobromobimane to form sulphide-dibimane and blood concentrations of thiosulfate (major oxidative metabolite of sulphide) via ion chromatography. We have measured exhaled H(2)S concentrations using a custom-made device based on a sulphide gas detector (Interscan).

RESULTS

Administration of IK-1001, a parenteral formulation of Na(2)S (0.005-0.20 mg kg(-1), i.v., infused over 1 min) induced an elevation of blood sulphide and thiosulfate concentrations over baseline, which was observed within the first 1-5 min following administration of IK-1001 at 0.10 mg kg(-1) dose and higher. In all subjects, basal exhaled H(2)S was observed to be higher than the ambient concentration of H(2)S gas in room air, indicative of on-going endogenous H(2)S production in human subjects. Upon intravenous administration of Na(2)S, a rapid elevation of exhaled H(2)S concentrations was observed. The amount of exhaled H(2)S rapidly decreased after discontinuation of the infusion of Na(2)S.

CONCLUSION

Exhaled H(2)S represents a detectable route of elimination after parenteral administration of Na(2)S.

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.

Attenuation of warm ischemia-reperfusion injury in the liver by bucillamine through decreased neutrophil activation and Bax/Bcl-2 modulation

BACKGROUND AND AIM

Liver transplantation and resection surgery involve a period of ischemia and reperfusion to the liver, which initiates an inflammatory cascade resulting in liver and remote organ injury. Bucillamine is a low molecular weight thiol antioxidant that is capable of rapidly entering cells. We hypothesized that bucillamine acts by replenishing glutathione levels, thus reducing neutrophil activation, modulating Bax/Bcl-2 expression, and subsequently, attenuating the effects of warm ischemia-reperfusion injury (IRI) in the liver.

METHODS

The effect of bucillamine was studied in a rat model of liver IRI with 45 min of partial (70%) liver ischemia and 3 h of reperfusion. Liver injury was assessed by measuring serum transaminases (aspartate aminotransferase [AST] and alanine aminotransferase [ALT]) and liver histology. Oxidative stress was quantified by measuring F(2) isoprostane and glutathione levels. Leukocyte adhesion was assessed by intravital microscopy, and inflammatory cytokine response was assessed by measuring serum cytokine-induced neutrophil chemoattractant-1 (CINC-1) levels. Bax and Bcl-2 expression was measured by reverse transcription-polymerase chain reaction.

RESULTS

The model produced significant liver injury with elevated transaminases and an acute inflammatory response. Bucillamine reduced the liver injury, as indicated by reduced AST (932 ± 200.8 vs 2072.5 ± 511.79, P < 0.05). Bucillamine reduced Bax expression, serum CINC-1 levels, and neutrophil adhesion, and upregulated Bcl-2. However, bucillamine did not affect tissue glutathione levels nor the levels of oxidative stress, as measured by plasma and hepatic F(2) isoprostane levels.

CONCLUSIONS

Bucillamine reduces warm ischemia-reperfusion in the liver by inhibiting neutrophil activation and modulating Bax/Bcl-2 expression.

A monobromobimane-based assay to measure the pharmacokinetic profile of reactive sulphide species in blood

BACKGROUND AND PURPOSE

Hydrogen sulphide (H(2)S) is a labile, endogenous metabolite of cysteine, with multiple biological roles. The development of sulphide-based therapies for human diseases will benefit from a reliable method of quantifying H(2)S in blood and tissues.

EXPERIMENTAL APPROACH

Concentrations of reactive sulphide in saline and freshly drawn whole blood were quantified by reaction with the thio-specific derivatization agent monobromobimane, followed by reversed-phase fluorescence HPLC and/or mass spectrometry. In pharmacokinetic studies, male rats were exposed either to intravenous infusions of sodium sulphide or to H(2)S gas inhalation, and levels of available blood sulphide were measured. Levels of dissolved H(2)S/HS(-) were concomitantly measured using an amperometric sensor.

KEY RESULTS

Monobromobimane was found to rapidly and quantitatively derivatize sulphide in saline or whole blood to yield the stable small molecule sulphide dibimane. Extraction and quantification of this bis-bimane derivative were validated via reversed-phase HPLC separation coupled to fluorescence detection, and also by mass spectrometry. Baseline levels of sulphide in blood were in the range of 0.4-0.9 microM. Intravenous administration of sodium sulphide solution (2-20 mg x kg(-1) x h(-1)) or inhalation of H(2)S gas (50-400 ppm) elevated reactive sulphide in blood in a dose-dependent manner. Each 1 mg x kg(-1) x h(-1) of sodium sulphide infusion into rats was found to be pharmacokinetically equivalent to approximately 30 ppm of H(2)S gas inhalation.

CONCLUSIONS AND IMPLICATIONS

The monobromobimane derivatization method is a sensitive and reliable means to measure reactive sulphide species in whole blood. Using this method, we have established a bioequivalence between infused sodium sulphide and inhaled H(2)S gas.

Curative effects of hydrogen sulfide against acetaminophen-induced hepatotoxicity in mice

AIMS

Hydrogen sulfide (H(2)S), an endogenous gaseous mediator, plays an important role in regulation of many physiological and pathological processes. On the other hand, acetaminophen overdose is a major cause of drug-induced liver failure. The aim of this study therefore is to evaluate the possible curative effects of H(2)S against acetaminophen-induced hepatotoxicity.

MAIN METHODS

Male Swiss mice were treated with sodium hydrogen sulfide, a H(2)S donor, 30 min after acetaminophen administration. N-acetylcysteine, a therapeutic antidote, was used as a reference drug.

KEY FINDINGS

H(2)S treatment resulted in hepatocurative effects as evident by a significant decrease in serum alanine aminotransferase and hepatic malondialdehyde and nitric oxide levels, with a concurrent increase in hepatic glutathione content compared to acetaminophen-treated group. H(2)S did not alter catalase activity. Additionally, immunohistochemical analysis demonstrated that H(2)S treatment markedly reduced tumor necrosis factor-α expression, while expression of cyclooxygenase-2 was markedly enhanced with nuclear localization into hepatocytes. The curative effects of H(2)S were confirmed by liver histopathological examination and were maintained in the presence of glibenclamide, an antagonist of ATP-sensitive potassium (K(ATP)) channels.

SIGNIFICANCE

H(2)S treatment markedly alleviates acetaminophen hepatotoxicity in mice possibly, in part, through anti-oxidative and anti-inflammatory effects but not likely to be coupled with activation of K(ATP) channels. The hepatocurative effects of H(2)S are comparable to N-acetylcysteine. Hence, H(2)S has a potential therapeutic value for treatment of acetaminophen hepatotoxicity.

Hydrogen sulfide attenuates intestinal ischemia-reperfusion injury when delivered in the post-ischemic period

BACKGROUND AND AIM

To investigate whether pharmacologic post-conditioning of intestinal tissue with hydrogen sulfide (HS) protects against ischemia reperfusion injury (IRI).

METHODS

In vitro, enterocytes were made hypoxic for 1, 2, or 3 h, treated with media containing between 0 and 100 µM HS 20 min prior to the end of the hypoxic period, then returned to normoxia for 3 h. An apoptotic index (AI) was determined for each time point and (HS). In vivo, jejunal ischemia was induced in male Sprague-Dawley rats for 1, 2, or 3 h; 20 min prior to the end of the ischemic period animals were given an intravenous injection of NaHS sufficient to raise the bloodstream concentration to 0, 10 µM, or 100 µM HS. This was followed by jejunal reperfusion for 3 h, histologic processing, and measurement of villus height.

RESULTS

In vitro, there was a significant decrease in AI compared with non-HS-treated control at all time points after treatment with 10 µM HS, and at the 2 h time point with 100 µM HS (P < 0.017). In vivo, after 1 h ischemia, qualitative reduction of injury was noted with 10 µM and 100 µM; after 2 h ischemia, reduction was noted with 10 µM but not 100 µM; and after 3 h ischemia, there was no injury reduction. HS treatment resulted in significant quantitative preservation (P < 0.05) of villus height at all time points and doses, except for 3 h ischemia and delivery of 100 µM (P = 0.129).

CONCLUSIONS

Hydrogen sulfide provides significant protection to intestinal tissues in vitro and in vivo when delivered after the onset of ischemia.

Effects of hydrogen sulfide on hemodynamics, inflammatory response and oxidative stress during resuscitated hemorrhagic shock in rats

Introduction

Hydrogen sulfide (H₂S) has been shown to improve survival in rodent models of lethal hemorrhage. Conversely, other authors have reported that inhibition of endogenous H₂S production improves hemodynamics and reduces organ injury after hemorrhagic shock. Since all of these data originate from unresuscitated models and/or the use of a pre-treatment design, we therefore tested the hypothesis that the H₂S donor, sodium hydrosulfide (NaHS), may improve hemodynamics in resuscitated hemorrhagic shock and attenuate oxidative and nitrosative stresses.

Methods

Thirty-two rats were mechanically ventilated and instrumented to measure mean arterial pressure (MAP) and carotid blood flow (CBF). Animals were bled during 60 minutes in order to maintain MAP at 40 ± 2 mm Hg. Ten minutes prior to retransfusion of shed blood, rats randomly received either an intravenous bolus of NaHS (0.2 mg/kg) or vehicle (0.9% NaCl). At the end of the experiment (T = 300 minutes), blood, aorta and heart were harvested for Western blot (inductible Nitric Oxyde Synthase (iNOS), Nuclear factor-κB (NF-κB), phosphorylated Inhibitor κB (P-IκB), Inter-Cellular Adhesion Molecule (I-CAM), Heme oxygenase 1(HO-1), Heme oxygenase 2(HO-2), as well as nuclear respiratory factor 2 (Nrf2)). Nitric oxide (NO) and superoxide anion (O₂^-) were also measured by electron paramagnetic resonance.

Results

At the end of the experiment, control rats exhibited a decrease in MAP which was attenuated by NaHS (65 ± 32 versus 101 ± 17 mmHg, P < 0.05). CBF was better maintained in NaHS-treated rats (1.9 ± 1.6 versus 4.4 ± 1.9 ml/minute P < 0.05). NaHS significantly limited shock-induced metabolic acidosis. NaHS also prevented iNOS expression and NO production in the heart and aorta while significantly reducing NF-kB, P-IκB and I-CAM in the aorta. Compared to the control group, NaHS significantly increased Nrf2, HO-1 and HO-2 and limited O₂^- release in both aorta and heart (P < 0.05).

Conclusions

NaHS is protective against the effects of ischemia reperfusion induced by controlled hemorrhage in rats. NaHS also improves hemodynamics in the early resuscitation phase after hemorrhagic shock, most likely as a result of attenuated oxidative stress. The use of NaHS hence appears promising in limiting the consequences of ischemia reperfusion (IR).

Development of hydrogen sulfide-based therapeutics for cardiovascular disease

The physiological role of the gaseous signaling molecule hydrogen sulfide (H(2)S) was first realized in the mid-1990s with the work of Abe and Kimura. Since then, it has become evident that this endogenous gas is extremely important in the homeostasis of the cardiovascular system and the pathogenesis of cardiovascular disease. Several biotechnology companies have developed and are developing H(2)S-based therapeutic compounds, and there are ongoing clinical trials investigating the therapeutic potential of H(2)S. Several organic and chemical compounds that are known H(2)S donors have the potential to be developed into effective H(2)S-based therapeutic agents. This review will provide a historical and current perspective on the role(s) of H(2)S in the cardiovascular system and the current state of development and future outlook of H(2)S-based therapies for cardiovascular disease.

Hydrogen sulfide attenuates ischemia-reperfusion injury in in vitro and in vivo models of intestine free tissue transfer

BACKGROUND

Ischemia-reperfusion injury is the propagation of injury following reintroduction of oxygen to previously ischemic tissue. The purpose of this study was to evaluate whether hydrogen sulfide provides protection against ischemia-reperfusion injury in enteric tissue.

METHODS

In vitro (enterocyte anoxia-normoxia) and in vivo (rat intestinal ischemia-reperfusion) models of ischemia-reperfusion injury were tested with or without the addition of hydrogen sulfide. Apoptotic index was determined in vitro, and gross appearance, histology, and villus height (a measure of mucosal integrity) were assessed in vivo. Statistical analysis was performed, and significance was defined as p < 0.05.

RESULTS

In vitro, cells treated with 10 microM hydrogen sulfide after 1-hour anoxia experienced a significant decrease in apoptotic index compared with untreated control (0.5 +/- 0.3 percent versus 2.8 +/- 0.7 percent); after 3 hours of anoxia, cells treated with 1 microM, 10 microM, and 100 microM hydrogen sulfide experienced significant decreases in apoptotic index versus untreated control (1.6 +/- 0.8 percent, 1.8 +/- 0.9 percent, and 2.8 +/- 0.7 percent versus 8.6 +/- 1.7 percent). In vivo, intestine treated with [10 microM] or [100 microM] hydrogen sulfide retained normal coloration and villus architecture after 1-hour ischemia; after 2 hours of ischemia, only intestine treated with [10 microM] hydrogen sulfide appeared uninjured. After 1, 2, or 3 hours of ischemia, villus heights of intestine treated with [10 microM] or [100 microM] hydrogen sulfide were significantly higher than heights of non-hydrogen sulfide-treated villi.

CONCLUSIONS

Hydrogen sulfide significantly attenuates ischemia-reperfusion injury in intestinal tissue in vitro and in vivo. These results have significant implications for enteric free tissue transfers and other gastrointestinal procedures in which ischemic intervals may be anticipated.

Hydrogen sulfide and ischemia-reperfusion injury

Gasotransmitters are lipid soluble, endogenously produced gaseous signaling molecules that freely permeate the plasma membrane of a cell to directly activate intracellular targets, thus alleviating the need for membrane-bound receptors. The gasotransmitter family consists of three members: nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H(2)S). H(2)S is the latest gasotransmitter to be identified and characterized and like the other members of the gasotransmitter family, H(2)S was historically considered to be a toxic gas and an environmental/occupational hazard. However with the discovery of its presence and enzymatic production in mammalian tissues, H(2)S has gained much attention as a physiological signaling molecule. Also, much like NO and CO, H(2)S's role in ischemia/reperfusion (I/R) injury has recently begun to be elucidated. As such, modulation of endogenous H(2)S and administration of exogenous H(2)S has now been demonstrated to be cytoprotective in various organ systems through diverse signaling mechanisms. This review will provide a detailed description of the role H(2)S plays in different model systems of I/R injury and will also detail some of the mechanisms involved with its cytoprotection.

Low levels of hydrogen sulfide in the blood of diabetes patients and streptozotocin-treated rats causes vascular inflammation?

Hydrogen sulfide (H(2)S) is emerging as a physiological neuromodulator as well as a smooth muscle relaxant. We submit the first evidence that blood H(2)S levels are significantly lower in fasting blood obtained from type 2 diabetes patients compared with age-matched healthy subjects, and in streptozotocin-treated diabetic rats compared with control Sprague-Dawley rats. We further observed that supplementation with H(2)S or an endogenous precursor of H(2)S (l-cysteine) in culture medium prevents IL-8 and MCP-1 secretion in high-glucose-treated human U937 monocytes. These first observations led to the hypothesis that lower blood H(2)S levels may contribute to the vascular inflammation seen in diabetes.

Novel insights into hydrogen sulfide--mediated cytoprotection

Hydrogen sulfide (H(2)S) is a colorless, water soluble, flammable gas that has the characteristic smell of rotten eggs. Like other members of the gasotransmitter family (nitric oxide and carbon monoxide), H(2)S has traditionally been considered to be a highly toxic gas and environmental hazard. However, much like for nitric oxide and carbon monoxide, the initial negative perception of H(2)S has evolved with the discovery that H(2)S is produced enzymatically in mammals under normal conditions. As a result of this discovery, there has been a great deal of work to elucidate the physiological role of H(2)S. H(2)S is now recognized to be cytoprotective in various models of cellular injury. Specifically, it has been demonstrated that the acute administration of H(2)S, either prior to ischemia or at reperfusion, significantly ameliorates in vitro or in vivo myocardial and hepatic ischemia-reperfusion injury. These studies have also demonstrated a cardioprotective role for endogenous H(2)S. This review article summarizes the current body of evidence demonstrating the cytoprotective effects of H(2)S with an emphasis on the cardioprotective effects. This review also provides a detailed description of the current signaling mechanisms shown to be responsible for these cardioprotective actions.

Cardiac and metabolic effects of hypothermia and inhaled hydrogen sulfide in anesthetized and ventilated mice

OBJECTIVE

To test the hypothesis whether inhaled hydrogen sulfide amplifies the effects of deliberate hypothermia during anesthesia and mechanical ventilation as hypothermia is used to provide organ protection after brain trauma or circulatory arrest. Awake mice inhaling hydrogen sulfide exhibit reduced energy expenditure, hypothermia, and bradycardia despite unchanged systolic heart function. In rodents, anesthesia alone causes decreased metabolic rate and thus hypothermia and bradycardia.

DESIGN

Prospective, controlled, randomized study.

SETTING

University animal research laboratory.

SUBJECTS

Male C57/B6 mice.

INTERVENTIONS

After surgical instrumentation (central venous, left ventricular pressure-conductance catheters, ultrasound flow probes on the portal vein and superior mesenteric artery), normo- or hypothermic animals (core temperature = 38 degrees C and 27 degrees C) received either 100 ppm hydrogen sulfide or vehicle over 5 hrs (3 hrs hydrogen sulfide during normothermia).

MEASUREMENTS AND MAIN RESULTS

During normothermia, hydrogen sulfide had no hemodynamic or metabolic effect. With or without hydrogen sulfide, hypothermia decreased blood pressure, heart rate, and cardiac output, whereas stroke volume, ejection fraction, and end-diastolic pressure remained unaffected. Myocardial and hepatic oxidative deoxyribonucleic acid damage (comet assay) and endogenous glucose production (rate of appearance of 1,2,3,4,5,6-13C6-glucose) were similar in all groups. Hypothermia comparably decreased CO2 production with or without inhaled hydrogen sulfide. During hypothermia, inhaled hydrogen sulfide increased the glucose oxidation rate (derived from the expiratory 13CO2/12CO2 ratio). This shift toward preferential carbohydrate utilization coincided with a significantly attenuated responsiveness of hepatic mitochondrial respiration to stimulation with exogenous cytochrome-c-oxidase (high-resolution respirometry).

CONCLUSIONS

In anesthetized and mechanically ventilated mice, inhaled hydrogen sulfide did not amplify the systemic hemodynamic and cardiac effects of hypothermia alone. The increased aerobic glucose oxidation together with the reduced responsiveness of cellular respiration to exogenous cytochrome-c stimulation suggest that, during hypothermia, inhaled hydrogen sulfide improved the yield of mitochondrial respiration, possibly via the maintenance of mitochondrial integrity. Hence, inhaled hydrogen sulfide may offer metabolic benefit during therapeutic hypothermia.

Small interfering RNA targeting heme oxygenase-1 (HO-1) reinforces liver apoptosis induced by ischemia-reperfusion injury in mice: HO-1 is necessary for cytoprotection

We have shown that overexpression of heme oxygenase-1 (HO-1) prevents the liver inflammation response leading to ischemia and reperfusion injury (IRI). This study was designed to explore the precise function and mechanism of HO-1 cytoprotection in liver IRI by employing a small interfering RNA (siRNA) that effectively suppresses HO-1 expression both in vitro and in vivo. Using a partial lobar liver warm ischemia model, mice were injected with HO-1 siRNA/nonspecific control siRNA or Ad-HO-1/Ad-beta-gal. Those treated with HO-1 siRNA showed increased serum glutamic-oxaloacetic transaminase levels, significant liver edema, sinusoidal congestion/cytoplasmic vacuolization, and severe hepatocellular necrosis. In contrast, Ad-HO-1-pretreated animals revealed only minimal sinusoidal congestion without edema/vacuolization or necrosis. Administration of HO-1 siRNA significantly increased local neutrophil accumulation and the frequency of apoptotic cells. Mice treated with HO-1 siRNA were characterized by increased caspase-3 activity and reduced HO-1 expression, whereas those given Ad-HO-1 showed decreased caspase-3 activity and increased HO-1/Bcl-2/Bcl-x(L), data confirmed by use of an in vitro cell culture system. Thus, by using an siRNA approach this study confirms that HO-1 provides potent cytoprotection against hepatic IRI and regulates liver apoptosis. Indeed, siRNA provides a powerful tool with which to study gene function in a wide range of liver diseases.

Applying gases for microcirculatory and cellular oxygenation in sepsis: effects of nitric oxide, carbon monoxide, and hydrogen sulfide

PURPOSE OF REVIEW

Nitric oxide, carbon monoxide, and hydrogen sulfide (H2S) are gases that have received attention as signaling molecules regulating many biological processes. All of them were reported to have beneficial effects in inflammatory states, in particular for microcirculatory perfusion and tissue energy balance. Thus, this review will highlight the most important results with a focus on resuscitated, clinically relevant experimental models and, if available, human studies.

RECENT FINDINGS

There is ample evidence that nitric oxide, carbon monoxide, and H2S may exert cytoprotective effects in shock states due to their vasomotor, antioxidant, and anti-inflammatory properties as well as their potential to induce a hibernation-like metabolic state called 'suspended animation' resulting from inhibition of cytochrome-c-oxidase. It must be emphasized, however, that the three molecules may also be cytotoxic, not only because of their inhibition of cellular respiration but also because of their marked pro-inflammatory effects.

SUMMARY

It is still a matter of debate whether manipulating nitric oxide, carbon monoxide, or H2S tissue concentrations, either by using the inhaled gas itself or by administering donor molecules or inhibitors of their endogenous production, is a useful therapeutic approach to improve microcirculatory blood flow, tissue oxygenation, and cellular respiration. This is mainly due to their 'friend and foe character' documented in various experimental models, but also to the paucity of data from long-term, resuscitated large animal experiments that fulfil the criteria of clinically relevant models.

Lipids modulate H(2)S/HS(-) induced NO release from S-nitrosoglutathione

Recently we observed that a gas messenger H(2)S/HS(-) released NO from S-nitrosoglutathione (Ondrias et al., Pflugers Arch. 457 (2008) 271-279). However, the effect of biological compounds on the release is not known. Measuring the NO oxidation product, which is nitrite, by the Griess reaction, we report that unsaturated fatty acid-linoleic acid and lipids having unsaturated fatty acids: asolectin, dioleoylphosphocholine and dioleoylphosphoserine depressed the H(2)S/HS(-) induced NO release from S-nitrosoglutathione. On the other hand, a depression effect of the saturated fatty acid-myristic acid and lipids having saturated fatty acids, dilauroylphosphatidylcholine, dimyristoylphosphatidylcholine, dipalmitoylphosphatidylcholine and distearoylphosphatidylcholine was less pronounced. The inhibition effect increased with the decreasing gel-to-liquid phase transitions temperature of the fatty acids and lipids. We suggest that lipid composition of biological membranes modulates NO release from nitrosoglutathione induced by H(2)S/HS(-), assuming that a reaction of H(2)S/HS(-) with unsaturated bonds of fatty acids may be partially responsible for the effect.

Beneficial effect of a hydrogen sulphide donor (sodium sulphide) in an ovine model of burn- and smoke-induced acute lung injury

BACKGROUND AND PURPOSE

The present study investigated whether the pathophysiological changes induced by burn and smoke inhalation are modulated by parenteral administration of Na(2)S, a H(2)S donor.

EXPERIMENTAL APPROACH

The study used a total of 16 chronically instrumented, adult female sheep. Na(2)S was administered 1 h post injury, as a bolus injection at a dose of 0.5 mg.kg(-1) and subsequently, as a continuous infusion at a rate of 0.2 mg.kg(-1).h(-1) for 24 h. Cardiopulmonary variables (mean arterial and pulmonary arterial blood pressure, cardiac output, ventricular stroke work index, vascular resistance) and arterial and mixed venous blood gases were measured. Lung wet-to-dry ratio and myeloperoxidase content and protein oxidation and nitration were also measured. In addition, lung inducible nitric oxide synthase expression and cytochrome c were measured in lung homogenates via Western blotting and enzyme-linked immunosorbent assay (elisa) respectively.

KEY RESULTS

The H(2)S donor decreased mortality during the 96 h experimental period, improved pulmonary gas exchange and lowered further increase in inspiratory pressure and fluid accumulation associated with burn- and smoke-induced acute lung injury. Further, the H(2)S donor treatment reduced the presence of protein oxidation and 3-nitrotyrosine formation following burn and smoke inhalation injury.

CONCLUSIONS AND IMPLICATIONS

Parenteral administration of the H(2)S donor ameliorated the pulmonary pathophysiological changes associated with burn- and smoke-induced acute lung injury. Based on the effect of H(2)S observed in this clinically relevant model of disease, we propose that treatment with H(2)S or its donors may represent a potential therapeutic strategy in managing patients with acute lung injury.

Hydrogen sulfide improves survival after cardiac arrest and cardiopulmonary resuscitation via a nitric oxide synthase 3-dependent mechanism in mice

BACKGROUND

Sudden cardiac arrest (CA) is one of the leading causes of death worldwide. We sought to evaluate the impact of hydrogen sulfide (H(2)S) on the outcome after CA and cardiopulmonary resuscitation (CPR) in mouse.

METHODS AND RESULTS

Mice were subjected to 8 minutes of normothermic CA and resuscitated with chest compression and mechanical ventilation. Seven minutes after the onset of CA (1 minute before CPR), mice received sodium sulfide (Na(2)S) (0.55 mg/kg IV) or vehicle 1 minute before CPR. There was no difference in the rate of return of spontaneous circulation, CPR time to return of spontaneous circulation, and left ventricular function at return of spontaneous circulation between groups. Administration of Na(2)S 1 minute before CPR markedly improved survival rate at 24 hours after CPR (15/15) compared with vehicle (10/26; P=0.0001 versus Na(2)S). Administration of Na(2)S prevented CA/CPR-induced oxidative stress and ameliorated left ventricular and neurological dysfunction 24 hours after CPR. Delayed administration of Na(2)S at 10 minutes after CPR did not improve outcomes after CA/CPR. Cardioprotective effects of Na(2)S were confirmed in isolated-perfused mouse hearts subjected to global ischemia and reperfusion. Cardiomyocyte-specific overexpression of cystathionine gamma-lyase (an enzyme that produces H(2)S) markedly improved outcomes of CA/CPR. Na(2)S increased phosphorylation of nitric oxide synthase 3 in left ventricle and brain cortex, increased serum nitrite/nitrate levels, and attenuated CA-induced mitochondrial injury and cell death. Nitric oxide synthase 3 deficiency abrogated the protective effects of Na(2)S on the outcome of CA/CPR.

CONCLUSIONS

These results suggest that administration of Na(2)S at the time of CPR improves outcome after CA possibly via a nitric oxide synthase 3-dependent signaling pathway.

Hydrogen sulfide-induced hypometabolism prevents renal ischemia/reperfusion injury

Hydrogen sulfide (H(2)S) can induce a hypometabolic, hibernation-like state in mammals when given in subtoxic concentrations. Pharmacologically reducing the demand for oxygen is a promising strategy to minimize unavoidable hypoxia-induced injury such as ischemia/reperfusion injury during renal transplantation. Here we show that H(2)S reduces metabolism in vivo, ex vivo, and in vitro. Furthermore, we demonstrate the beneficial effects of H(2)S-induced hypometabolism in a model of bilateral renal ischemia/reperfusion injury using three different treatment strategies. The results demonstrate striking protective effects on survival, renal function, apoptosis, and inflammation. A hypometabolic state induced by H(2)S might have therapeutic potential to protect kidneys that suffer from hypoxia.

Hydrogen sulfide mediates cardioprotection through Nrf2 signaling

RATIONALE

The recent emergence of hydrogen sulfide (H(2)S) as a potent cardioprotective signaling molecule necessitates the elucidation of its cytoprotective mechanisms.

OBJECTIVE

The present study evaluated potential mechanisms of H(2)S-mediated cardioprotection using an in vivo model of pharmacological preconditioning.

METHODS AND RESULTS

H(2)S (100 microg/kg) or vehicle was administered to mice via an intravenous injection 24 hours before myocardial ischemia. Treated and untreated mice were then subjected to 45 minutes of myocardial ischemia followed by reperfusion for up to 24 hours, during which time the extent of myocardial infarction was evaluated, circulating troponin I levels were measured, and the degree of oxidative stress was evaluated. In separate studies, myocardial tissue was collected from treated and untreated mice during the early (30 minutes and 2 hours) and late (24 hours) preconditioning periods to evaluate potential cellular targets of H(2)S. Initial studies revealed that H(2)S provided profound protection against ischemic injury as evidenced by significant decreases in infarct size, circulating troponin I levels, and oxidative stress. During the early preconditioning period, H(2)S increased the nuclear localization of Nrf2, a transcription factor that regulates the gene expression of a number of antioxidants and increased the phosphorylation of protein kinase Cepsilon and STAT-3. During the late preconditioning period, H(2)S increased the expression of antioxidants (heme oxygenase-1 and thioredoxin 1), increased the expression of heat shock protein 90, heat shock protein 70, Bcl-2, Bcl-xL, and cyclooxygenase-2 and also inactivated the proapoptogen Bad.

CONCLUSIONS

These results reveal that the cardioprotective effects of H(2)S are mediated in large part by a combination of antioxidant and antiapoptotic signaling.

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.

Bench-to-bedside review: Hydrogen sulfide--the third gaseous transmitter: applications for critical care

Hydrogen sulfide (H2S), a gas with the characteristic odor of rotten eggs, is known for its toxicity and as an environmental hazard, inhibition of mitochondrial respiration resulting from blockade of cytochrome c oxidase being the main toxic mechanism. Recently, however, H2S has been recognized as a signaling molecule of the cardiovascular, inflammatory and nervous systems, and therefore, alongside nitric oxide and carbon monoxide, is referred to as the third endogenous gaseous transmitter. Inhalation of gaseous H2S as well as administration of inhibitors of its endogenous production and compounds that donate H2S have been studied in various models of shock. Based on the concept that multiorgan failure secondary to shock, inflammation and sepsis may represent an adaptive hypometabolic response to preserve ATP homoeostasis, particular interest has focused on the induction of a hibernation-like suspended animation with H2S. It must be underscored that currently only a limited number of data are available from clinically relevant large animal models. Moreover, several crucial issues warrant further investigation before the clinical application of this concept. First, the impact of hypothermia for any H2S-related organ protection remains a matter of debate. Second, similar to the friend and foe character of nitric oxide, no definitive conclusions can be made as to whether H2S exerts proinflammatory or anti-inflammatory properties. Finally, in addition to the question of dosing and timing (for example, bolus administration versus continuous intravenous infusion), the preferred route of H2S administration remains to be settled--that is, inhaling gaseous H2S versus intra-venous administration of injectable H2S preparations or H2S donors. To date, therefore, while H2S-induced suspended animation in humans may still be referred to as science fiction, there is ample promising preclinical data that this approach is a fascinating new therapeutic perspective for the management of shock states that merits further investigation.

Detection of exhaled hydrogen sulphide gas in rats exposed to intravenous sodium sulphide

BACKGROUND AND PURPOSE

Sodium sulphide (Na(2)S) disassociates to sodium (Na(+)) hydrosulphide, anion (HS(-)) and hydrogen sulphide (H(2)S) in aqueous solutions. Here we have established and characterized a method to detect H(2)S gas in the exhaled breath of rats.

EXPERIMENTAL APPROACH

Male rats were anaesthetized with ketamine and xylazine, instrumented with intravenous (i.v.) jugular vein catheters, and a tube inserted into the trachea was connected to a pneumotach connected to a H(2)S gas detector. Sodium sulphide, cysteine or the natural polysulphide compound diallyl disulphide were infused intravenously while the airway was monitored for exhaled H(2)S real time.

KEY RESULTS

Exhaled sulphide concentration was calculated to be in the range of 0.4-11 ppm in response to i.v. infusion rates ranging between 0.3 and 1.1 mg x kg(-1) x min(-1). When nitric oxide synthesis was inhibited with N(omega)-nitro-L-arginine methyl ester the amount of H(2)S exhaled during i.v. infusions of sodium sulphide was significantly increased compared with that obtained with the vehicle control. An increase in circulating nitric oxide using DETA NONOate [3,3-bis(aminoethyl)-1-hydroxy-2-oxo-1-triazene] did not alter the levels of exhaled H(2)S during an i.v. infusion of sodium sulphide. An i.v. bolus of L-cysteine, 1 g.kg(-1), and an i.v. infusion of the garlic derived natural compound diallyl disulphide, 1.8 mg x kg(-1) x min(-1), also caused exhalation of H(2)S gas.

CONCLUSIONS AND IMPLICATIONS

This method has shown that significant amounts of H(2)S are exhaled in rats during sodium sulphide infusions, and the amount exhaled can be modulated by various pharmacological interventions.

Hepatocellular protection by nitric oxide or nitrite in ischemia and reperfusion injury

Ischemia and reperfusion (I/R)-induced liver injury occurs in several pathophysiological disorders including hemorrhagic shock and burn as well as resectional and transplantation surgery. One of the earliest events associated with reperfusion of ischemic liver is endothelial dysfunction characterized by the decreased production of endothelial cell-derived nitric oxide (NO). This rapid post-ischemic decrease in NO bioavailability appears to be due to decreased synthesis of NO, enhanced inactivation of NO by the overproduction of superoxide or both. This review presents the most current evidence supporting the concept that decreased bioavailability of NO concomitant with enhanced production of reactive oxygen species initiates hepatocellular injury and that endogenous NO or exogenous NO produced from nitrite play important roles in limiting post-ischemic tissue injury.

Hypotaurine and sulfhydryl-containing antioxidants reduce H2S toxicity in erythrocytes from a marine invertebrate

Hypotaurine (HT) has been proposed to reduce sulfide toxicity in some deep-sea invertebrates by scavenging free radicals produced from sulfide oxidation or by scavenging sulfide via the reaction of HT with sulfide, forming thiotaurine (ThT). We tested whether HT or several antioxidants could reduce the total dissolved sulfide concentration in buffered seawater exposed to H2S, and whether HT, ThT or antioxidants could increase the viability of Glycera dibranchiataerythrocytes exposed to H2S in vitro. We found that 5 and 50 mmol l–1 HT reduced the dissolved sulfide in cell-free buffer exposed to H2S by up to 80% whereas the antioxidants glutathione ethyl ester (GEE), N-acetylcysteine (NAC), l-ascorbic acid (ASC), Tempol and Trolox had no consistent effect. Exposure of erythrocytes to 0.10%–3.2% H2S (producing 0.18–4.8 mmol l–1 sulfide) decreased the fraction of viable cells, as evidenced by loss of plasma membrane integrity, with virtually no cells remaining viable at 1.0% or more H2S. Addition of HT (0.5–50 mmol l–1) significantly increased the fraction of viable cells (e.g. from 0.01 to 0.84 at 0.32% H2S) whereas ThT (0.5 and 5 mmol l–1) decreased cell viability. GEE (0.03–3 mmol l–1) and NAC (0.001–1 mmol l–1), which contain sulfhydryl groups, increased cell viability during H2S exposure but to a lesser extent than HT whereas ASC, Tempol and Trolox, which do not contain sulfhydryl groups, decreased viability or had no effect. These data show that HT can protect cells from sulfide in vitro and suggest that sulfide scavenging, rather than free radical scavenging, is the most important mechanism of protection.

Potential importance of alterations in hydrogen sulphide (H2S) bioavailability in diabetes

Despite its long-standing reputation as a foul smelling and toxic gas that is associated with the decay of biological matter,hydrogen sulphide (H2S) has emerged as an important regulator of cardiovascular homoeostasis. H2S promotes a number of cellular signals that regulate metabolism, cardiac function and cell survival. Endogenous H2S bioavailability is regulated by several enzymes involved in the biosynthesis of cysteine. This study by Brancaleone et al. in the current issue of the British Journal of Pharmacology provides novel insights into the impairment of H2S biosynthesis in the setting of diabetes mellitus. The authors report that enzymic H2S biosynthesis is impaired in a murine model of type 1 diabetes and the attenuation in H2S bioavailability is associated with impaired vascular reactivity. This study has profound implications for the use of pharmacological agents to augment endogenous H2S synthesis or agents that release H2S to augment the levels of this gaseous signalling molecule in cardiovascular disease.