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

Hydrogen sulphide pathway contributes to the enhanced human platelet aggregation in hyperhomocysteinemia

Homocysteine is metabolized to methionine by the action of 5,10 methylenetetrahydrofolate reductase (MTHFR). Alternatively, by the transulfuration pathway, homocysteine is transformed to hydrogen sulphide (H2S), through multiple steps involving cystathionine β-synthase and cystathionine γ-lyase. Here we have evaluated the involvement of H2S in the thrombotic events associated with hyperhomocysteinemia. To this purpose we have used platelets harvested from healthy volunteers or patients newly diagnosed with hyperhomocysteinemia with a C677T polymorphism of the MTHFR gene (MTHFR++). NaHS (0.1-100 µM) or l-cysteine (0.1-100 µM) significantly increased platelet aggregation harvested from healthy volunteers induced by thrombin receptor activator peptide-6 amide (2 µM) in a concentration-dependent manner. This increase was significantly potentiated in platelets harvested from MTHFR++ carriers, and it was reversed by the inhibition of either cystathionine β-synthase or cystathionine γ-lyase. Similarly, in MTHFR++ carriers, the content of H2S was significantly higher in either platelets or plasma compared with healthy volunteers. Interestingly, thromboxane A2 production was markedly increased in response to both NaHS or l-cysteine in platelets of healthy volunteers. The inhibition of phospholipase A2, cyclooxygenase, or blockade of the thromboxane receptor markedly reduced the effects of H2S. Finally, phosphorylated-phospholipase A2 expression was significantly higher in MTHFR++ carriers compared with healthy volunteers. In conclusion, the H2S pathway is involved in the prothrombotic events occurring in hyperhomocysteinemic patients.

Thrombospondin-1 is a CD47-dependent endogenous inhibitor of hydrogen sulfide signaling in T cell activation

Thrombospondin-1 is a potent suppressor of T cell activation via its receptor CD47. However, the precise mechanism for this inhibition remains unclear. Because H2S is an endogenous potentiator of T cell activation and is necessary for full T cell activation, we hypothesized that thrombospondin-1 signaling through CD47 inhibits T cell activation by antagonizing H2S signaling. Primary T cells from thrombospondin-1 null mice were more sensitive to H2S-dependent activation assessed by proliferation and induction of interleukin-2 and CD69 mRNAs. Exogenous thrombospondin-1 inhibited H2S responses in wild type and thrombospondin-1 null T cells but enhanced the same responses in CD47 null T cells. Fibronectin, which shares integrin and glycosaminoglycan binding properties with thrombospondin-1 but not CD47 binding, did not inhibit H2S signaling. A CD47-binding peptide derived from thrombospondin-1 inhibited H2S-induced activation, whereas two other functional sequences from thrombospondin-1 enhanced H2S signaling. Therefore, engaging CD47 is necessary and sufficient for thrombospondin-1 to inhibit H2S-dependent T cell activation. H2S stimulated T cell activation by potentiating MEK-dependent ERK phosphorylation, and thrombospondin-1 inhibited this signaling in a CD47-dependent manner. Thrombospondin-1 also limited activation-dependent T cell expression of the H2S biosynthetic enzymes cystathionine β-synthase and cystathionine γ-lyase, thereby limiting the autocrine role of H2S in T cell activation. Thus, thrombospondin-1 signaling through CD47 is the first identified endogenous inhibitor of H2S signaling and constitutes a novel mechanism that negatively regulates T cell activation.

Oxygen-sensitive mitochondrial accumulation of cystathionine β-synthase mediated by Lon protease

Oxygen-sensitive accumulation and degradation, two opposite but intrinsically linked events, of heme proteins in mitochondria affect mitochondrial functions, including bioenergetics and oxygen-sensing processes. Cystathionine β-synthase (CBS) contains a prosthetic heme group and catalyzes the production of hydrogen sulfide in mammalian cells. Here we show that CBS proteins were present in liver mitochondria at a low level under normoxia conditions. Ischemia/hypoxia increased the accumulation of CBS proteins in mitochondria. The normalization of oxygen partial pressure accelerated the degradation of CBS proteins. Lon protease, a major degradation enzyme in mitochondrial matrix, recognized and degraded mitochondrial CBS by specifically targeting at the oxygenated heme group of CBS proteins. The accumulation of CBS in mitochondria increased hydrogen sulfide production, which prevented Ca(2+)-mediated cytochrome c release from mitochondria and decreased reactive oxygen species generation. Mitochondrial accumulation of heme oxygenase-1, another heme protein, was also regulated by oxygen level and Lon protease in the same mechanism as for CBS. Our findings provide a fundamental and general mechanism for oxygen-sensitive regulation of mitochondrial functions by linking oxygenation level to the accumulation/degradation of mitochondrial heme proteins.

Chemical foundations of hydrogen sulfide biology

Following nitric oxide (nitrogen monoxide) and carbon monoxide, hydrogen sulfide (or its newer systematic name sulfane, H2S) became the third small molecule that can be both toxic and beneficial depending on the concentration. In spite of its impressive therapeutic potential, the underlying mechanisms for its beneficial effects remain unclear. Any novel mechanism has to obey fundamental chemical principles. H2S chemistry was studied long before its biological relevance was discovered, however, with a few exceptions, these past works have received relatively little attention in the path of exploring the mechanistic conundrum of H2S biological functions. This review calls attention to the basic physical and chemical properties of H2S, focuses on the chemistry between H2S and its three potential biological targets: oxidants, metals and thiol derivatives, discusses the applications of these basics into H2S biology and methodology, and introduces the standard terminology to this youthful field.

Hydrogen sulfide chemical biology: pathophysiological roles and detection

Hydrogen sulfide (H2S) is the most recent endogenous gasotransmitter that has been reported to serve many physiological and pathological functions in different tissues. Studies over the past decade have revealed that H2S can be synthesized through numerous pathways and its bioavailability regulated through its conversion into different biochemical forms. H2S exerts its biological effects in various manners including redox regulation of protein and small molecular weight thiols, polysulfides, thiosulfate/sulfite, iron-sulfur cluster proteins, and anti-oxidant properties that affect multiple cellular and molecular responses. However, precise measurement of H2S bioavailability and its associated biochemical and pathophysiological roles remains less well understood. In this review, we discuss recent understanding of H2S chemical biology, its relationship to tissue pathophysiological responses and possible therapeutic uses.

Effect of sodium hydrosulphide after acute compression injury of spinal cord

BACKGROUND

Early treatment of spinal cord white matter injury has been found beneficial. H2S, a neurotransmitter is neuroprotective at lower doses.

PURPOSE

In the present study the effect of NaHS after clip compression injury of spinal cord white matter in vivo was studied.

METHODS

The injury was induced in 8-10 weeks old Wistar rats by exposing the spinal cord at T8-T10 level by laminectomy and applying 35 g clip for 1 min. A dose of 50 µM NaHS was given intraperitoneally after 1h of injury. 0.5mm Spinal cord tissues were collected 8h after injury from both sides including epicenter and dorsal column was microdissected and used for further study.

RESULTS

NaHS treatment decreases nitric oxide (NO) by 27% and lipid peroxide (LPO) by 18% as compared to injury, which are hallmark of attenuation in oxidative stress. Western blots shows significant changes in Myeloperoxidase (MPO) level went down by 10%. GSH contents increased 44% in treated group as compared to the injury group. NaHS treatment increased Nrf-2 expression 1.8 times. We found NaHS treatment reduced the GFAP expression 8%, there was no significant changes in NF-200 after treatment and no evident morphological changes with H and E staining.

CONCLUSIONS

With the above data we conclude that NaHS at 50 µM dose at 1h after injury reduces the NO, LPO, GFAP and MPO level at injury site by increasing the expression of Nrf-2. We expect that a decrease in these parameters during acute phase of spinal cord injury would be helpful in neuroprotection and regeneration.

Chemical aspects of hydrogen sulfide measurements in physiological samples

BACKGROUND

Owing to recent discoveries of many hydrogen sulfide-mediated physiological processes, sulfide biology is in the focus of scientific research. However, the promiscuous chemical properties of sulfide pose complications for biological studies, which led to accumulation of controversial observations in the literature.

SCOPE OF REVIEW

We intend to provide an overview of fundamental thermodynamic and kinetic features of sulfide redox- and coordination-chemical reactions and protonation equilibria in relation to its biological functions. In light of these chemical properties we review the strengths and limitations of the most commonly used sulfide detection methods and recently developed fluorescent probes. We also give a personal perspective on blood and tissue sulfide measurements based on proposed biomolecule-sulfide interactions and point out important chemical aspects of handling sulfide reagent solutions.

MAJOR CONCLUSIONS

The diverse chemistries of sulfide detection methods resulted in orders of magnitude differences in measured physiological sulfide levels. Investigations that were aimed to dissect the underlying molecular reasons responsible for these controversies made the important recognition that there are large sulfide reserves in biological systems. These sulfide pools are tightly regulated in a dynamic manner and they are likely to play a major role in regulation of endogenous-sulfide-mediated biological functions and avoiding toxic side effects.

GENERAL SIGNIFICANCE

Working with sulfide is challenging, because it requires considerable amounts of chemical knowledge to adequately handle reagent sulfide solutions and interpret biological observations. Therefore, we propose that a rigorous chemical approach could aid the reconciliation of the increasing number of controversies in sulfide biology. This article is part of a Special Issue entitled Current methods to study reactive oxygen species - pros and cons and biophysics of membrane proteins. Guest Editor: Christine Winterbourn.

High-fat diet stimulates hepatic cystathionine β-synthase and cystathionine γ-lyase expression

Cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE) catalyze homocysteine (Hcy) metabolism via the trans-sulfuration pathway. They are also responsible for hydrogen sulfide (H2S) production via desulfuration reactions. The liver contributes significantly to the regulation of Hcy and H2S homeostasis, which might participate in many physiological and pathological processes. The aim of this study was to investigate the effect of a high-fat diet (HFD) on hepatic CBS and CSE expression and its impact on Hcy and H2S metabolism. Mice (C57BL/6) fed a HFD (60% kcal fat) for 5 weeks developed fatty liver. The mRNA and protein levels of CBS and CSE in the liver were significantly elevated in mice fed a HFD. Subsequently the metabolism of Hcy by CBS and CSE was increased in the liver, and its level decreased in the circulation. Increased CBS and CSE expression also caused a significant elevation in H2S production in the liver. The level of lipid peroxides was elevated, indicating oxidative stress, while the level of total glutathione remained unchanged in the liver of HFD-fed mice. Upregulation of the trans-sulfuration pathway might play an adaptive role against oxidative stress by maintaining total glutathione levels in the liver.

Exogenous hydrogen sulfide prevents cardiomyocyte apoptosis from cardiac hypertrophy induced by isoproterenol

Oxidative stress is a crucial factor inducing cardiomyocyte apoptosis due to cardiac hypertrophy. Additional evidence has revealed that H2S plays an antioxidant role and is cytoprotective. Hence, we aimed to elucidate whether H2S prevents cardiomyocyte apoptosis due to cardiac hypertrophy via its antioxidant function. The cardiac hypertrophy model was obtained by injecting a high dose of isoproterenol (ISO) subcutaneously, and the hemodynamic parameters were measured in groups that received either ISO or ISO with the treatment of NaHS. TUNEL (terminal deoxynucleotidyl transferase mediated dUTP nick-end labeling) and EM (electron microscopy) experiments were performed to determine the occurrence of apoptosis in heart tissues. The expression of caspase-3 protein in the cytoplasm and NADPH oxidase 4 (NOX4), and cytochrome c (cyt c) proteins in the mitochondria were analyzed using Western blotting. In contrast, to determine whether ISO-induced apoptosis in the cultured cardiomyocytes may be related to oxidative stress, JC-1 and MitoSOX assays were performed to detect the mitochondrial membrane potential and reactive oxygen species (ROS) production in the mitochondria. Exogenous H2S was found to ameliorate cardiac function. The histological observations obtained from TUNEL and EM demonstrated that treatment with NaHS inhibited the occurrence of cardiac apoptosis and improved cardiac structure. Moreover, H2S reduced the expression of the cleaved caspase-3, NOX4 and the leakage of cyt c from the mitochondria to the cytoplasm. We also observed that exogenous H2S could maintain the mitochondrial membrane potential and reduce ROS production in the mitochondria. Therefore, H2S reduces oxidative stress due to cardiac hypertrophy through the cardiac mitochondrial pathway.

Gaseous hydrogen sulfide protects against myocardial ischemia-reperfusion injury in mice partially independent from hypometabolism

Background

Ischemia-reperfusion injury (IRI) is a major cause of cardiac damage following various pathological processes. Gaseous hydrogen sulfide (H₂S) is protective during IRI by inducing a hypometabolic state in mice which is associated with anti-apoptotic, anti-inflammatory and antioxidant properties. We investigated whether gaseous H₂S administration is protective in cardiac IRI and whether non-hypometabolic concentrations of H₂S have similar protective properties.

Methods

Male C57BL/6 mice received a 0, 10, or 100 ppm H₂S-N₂ mixture starting 30 minutes prior to ischemia until 5 minutes pre-reperfusion. IRI was inflicted by temporary ligation of the left coronary artery for 30 minutes. High-resolution respirometry equipment was used to assess CO₂-production and blood pressure was measured using internal transmitters. The effects of H₂S were assessed by histological and molecular analysis.

Results

Treatment with 100 ppm H₂S decreased CO₂-production by 72%, blood pressure by 14% and heart rate by 25%, while treatment with 10 ppm H₂S had no effects. At day 1 of reperfusion 10 ppm H₂S showed no effect on necrosis, while treatment with 100 ppm H₂S reduced necrosis by 62% (p<0.05). Seven days post-reperfusion, both 10 ppm (p<0.01) and 100 ppm (p<0.05) H₂S showed a reduction in fibrosis compared to IRI animals. Both 10 ppm and 100 ppm H₂S reduced granulocyte-influx by 43% (p<0.05) and 60% (p<0.001), respectively. At 7 days post-reperfusion both 10 and 100 ppm H₂S reduced expression of fibronectin by 63% (p<0.05) and 67% (p<0.01) and ANP by 84% and 63% (p<0.05), respectively.

Conclusions

Gaseous administration of H₂S is protective when administered during a cardiac ischemic insult. Although hypometabolism is restricted to small animals, we now showed that low non-hypometabolic concentrations of H₂S also have protective properties in IRI. Since IRI is a frequent cause of myocardial damage during percutaneous coronary intervention and cardiac transplantation, H₂S treatment might lead to novel therapeutical modalities.

Cystathionine γ-lyase protects against renal ischemia/reperfusion by modulating oxidative stress

Hydrogen sulfide (H2S) is an endogenous gasotransmitter with physiologic functions similar to nitric oxide and carbon monoxide. Exogenous treatment with H2S can induce a reversible hypometabolic state, which can protect organs from ischemia/reperfusion injury, but whether cystathionine γ-lyase (CSE), which produces endogenous H2S, has similar protective effects is unknown. Here, human renal tissue revealed abundant expression of CSE, localized to glomeruli and the tubulointerstitium. Compared with wild-type mice, CSE knockout mice had markedly reduced renal production of H2S, and CSE deficiency associated with increased damage and mortality after renal ischemia/reperfusion injury. Treatment with exogenous H2S rescued CSE knockout mice from the injury and mortality associated with renal ischemia. In addition, overexpression of CSE in vitro reduced the amount of reactive oxygen species produced during stress. Last, the level of renal CSE mRNA at the time of organ procurement positively associated with GFR 14 days after transplantation. In summary, these results suggest that CSE protects against renal ischemia/reperfusion injury, likely by modulating oxidative stress through the production of H2S.

The summer of hydrogen sulfide: highlights from two international conferences

A great deal of interest has been paid recently to the hydrogen sulfide, the newest member of the gasotransmitter family. With the growing interest in the biology of H2S, the need for meetings and conferences dedicated solely to the field of H2S has also grown. In 2009, scientist from around the world met in Shanghai, China for the first time to discuss the physiological relevance of H2S. In 2012, two conferences were organized to bring scientists, clinicians, and industry representatives together to discuss the latest breakthroughs concerning the emergent field of H2S. The following is a summary report of The First European Conference on the Biology of Hydrogen Sulfide and the Second International Conference on Hydrogen Sulfide Biology and Medicine.

H2S signaling in redox regulation of cellular functions

Hydrogen sulfide (H2S) is traditionally recognized as a toxic gas with a rotten-egg smell. In just the last few decades, H2S has been found to be one of a family of gasotransmitters, together with nitric oxide and carbon monoxide, and various physiologic effects of H2S have been reported. Among the most acknowledged molecular mechanisms for the cellular effects of H2S is the regulation of intracellular redox homeostasis and post-translational modification of proteins through S-sulfhydration. On the one side, H2S can promote an antioxidant effect and is cytoprotective; on the other side, H2S stimulates oxidative stress and is cytotoxic. This review summarizes our current knowledge of the antioxidant versus pro-oxidant effects of H2S in mammalian cells and describes the Janus-faced properties of this novel gasotransmitter. The redox regulation for the cellular effects of H2S through S-sulfhydration and the role of H2S in glutathione generation is also recapitulated. A better understanding of H2S-regualted redox homeostasis will pave the way for future design of novel pharmacological and therapeutic interventions for various diseases.

Hydrogen sulfide as an endogenous modulator in mitochondria and mitochondria dysfunction

Hydrogen sulfide (H₂S) has historically been considered to be a toxic gas, an environmental and occupational hazard. However, with the discovery of its presence and enzymatic production through precursors of L-cysteine and homocysteine in mammalian tissues, H₂S has recently received much interest as a physiological signaling molecule. H₂S is a gaseous messenger molecule that has been implicated in various physiological and pathological processes in mammals, including vascular relaxation, angiogenesis, and the function of ion channels, ischemia/reperfusion (I/R), and heart injury. H₂S is an endogenous neuromodulator and present studies show that physiological concentrations of H₂S enhance NMDA receptor-mediated responses and aid in the induction of hippocampal long-term potentiation. Moreover, in the field of neuronal protection, physiological concentrations of H₂S in mitochondria have many favorable effects on cytoprotection.

Hydrogen sulfide stimulates ischemic vascular remodeling through nitric oxide synthase and nitrite reduction activity regulating hypoxia-inducible factor-1α and vascular endothelial growth factor-dependent angiogenesis

Background

Hydrogen sulfide (H₂S) therapy is recognized as a modulator of vascular function during tissue ischemia with the notion of potential interactions of nitric oxide (NO) metabolism. However, little is known about specific biochemical mechanisms or the importance of H₂S activation of NO metabolism during ischemic tissue vascular remodeling. The goal of this study was to determine the effect of H₂S on NO metabolism during chronic tissue ischemia and subsequent effects on ischemic vascular remodeling responses.

Methods and Results

The unilateral, permanent femoral artery ligation model of hind‐limb ischemia was performed in C57BL/6J wild‐type and endothelial NO synthase–knockout mice to evaluate exogenous H₂S effects on NO bioavailability and ischemic revascularization. We found that H₂S selectively restored chronic ischemic tissue function and viability by enhancing NO production involving both endothelial NO synthase and nitrite reduction mechanisms. Importantly, H₂S increased ischemic tissue xanthine oxidase activity, hind‐limb blood flow, and angiogenesis, which were blunted by the xanthine oxidase inhibitor febuxostat. H₂S treatment increased ischemic tissue and endothelial cell hypoxia‐inducible factor‐1α expression and activity and vascular endothelial growth factor protein expression and function in a NO‐dependent manner that was required for ischemic vascular remodeling.

Conclusions

These data demonstrate that H₂S differentially regulates NO metabolism during chronic tissue ischemia, highlighting novel biochemical pathways to increase NO bioavailability for ischemic vascular remodeling.

Inhibition of hydrogen sulfide generation contributes to lung injury after experimental orthotopic lung transplantation

BACKGROUND

Lung injury induced by ischemia or reperfusion significantly accounts for the risk of early mortality of lung transplantation (LT). Recent studies have demonstrated that hydrogen sulfide (H2S) and its endogenous synthase cystathionine-γ-lyase (CSE) confer protection against injury induced by ischemia or reperfusion in various organs. This prompted us to define the role of CSE/H2S pathway in transplantation-induced lung injury.

METHODS

We performed single left LT in male Sprague-Dawley rats after 3 h of cold ischemia time. H2S donor NaHS (14 μmol/kg, intraperitoneally) or CSE inhibitor propargylglycine (37.5 mg/kg, intraperitoneally) was administered 15 min before the start of the LT. CSE protein expression, H2S generation, and the severity of pulmonary graft injuries were estimated at 24 h after reperfusion.

RESULTS

Both CSE protein expression and H2S generation were markedly decreased in transplanted rat lungs compared with those in sham-operated lungs. In the lung-transplanted rats, NaHS administration significantly improved pulmonary function and decreased lipid peroxidation and myeloperoxidase activity. In addition, NaHS inhibited the production of interleukin 1β but increased interleukin 10 levels in graft lung tissues. In contrast, propargylglycine further exacerbated pulmonary function and lung injuries after experimental orthotopic LT.

CONCLUSIONS

To our knowledge, this study for the first time has demonstrated that the suppression of CSE expression and H2S production is associated with transplantation-induced lung injury. Both exogenous and endogenous H2S seem to have protective effects against acute LT injury by their multiple functions including antioxidation and anti-inflammation, suggesting that modulation of H2S levels may be considered a potential therapeutic approach in LT.

Hydrogen sulfide and inflammation: the good, the bad, the ugly and the promising

Hydrogen sulfide is rapidly gaining ground as a physiological mediator of inflammation, but there is no clear consensus as to its precise role in inflammatory signaling. This article discusses the disparate anti-inflammatory ('the good') and proinflammatory ('the bad') effects of endogenous and pharmacological H(2)S in disparate animal model and cell culture systems. We also discuss 'the ugly', such as problems of using wholly specific inhibitors of enzymatic H(2)S synthesis, and the use of pharmacological donor compounds, which release H(2)S too quickly to be physiologically representative of endogenous H(2)S synthesis. Furthermore, recently developed slow-release H(2)S donors, which offer a more physiological approach to understanding the complex role of H(2)S in acute and chronic inflammation ('the promising') are discussed.

Cystathionine β-synthase-derived hydrogen sulfide regulates lipopolysaccharide-induced apoptosis of the BRL rat hepatic cell line in vitro

Hydrogen sulfide (H₂S), is a member of the novel family of endogenous gaseous transmitters, termed “gasotransmitters exhibiting diverse physiological activities, and is generated in mammalian tissues mainly by cystathionine β-synthase (CBS), cystathionine γ-lyase (CSE) and 3-mercaptopyruvate sulfurtransferase (3MST) in conjunction with cysteine (aspartate) aminotranferase (CAT). The distributions of these enzymes are species- and tissue-specific. The liver, as the main organ that generates H₂S in vivo, functions in biotransformation and metabolism. However, the liver is vulnerable to damage from internal and external factors, including inflammatory mediators, drugs and poisons. The present study evaluated the endogenous CBS-H₂S synthesis regulating lipopolysaccharide (LPS)-induced apoptosis of hepatic cells. The rat hepatic cell line, BRL, was incubated with LPS for various time periods to establish a cell-damage model. Incubation with LPS resulted in a significant increase in CBS expression and H₂S production. It also stimulated apoptosis and decreased the mitochondrial membrane potential. Pretreatment with the CBS inhibitor aminooxyacetic acid (AOAA) or CBS small interfering RNA (siRNA) decreased LPS-enhanced H₂S production. Notably, apoptosis increased for a short period and then decreased gradually, while the mitochondrial membrane potential demonstrated the opposite trend. These results showed that endogenous CBS-H₂S synthesis demonstrated early anti-apoptotic activity and subsequent pro-apoptotic activity in LPS-induced apoptosis. These results suggest a new approach for developing novel drugs for this condition.

Prolonged gaseous hypothermia prevents the upregulation of phagocytosis-specific protein annexin 1 and causes low-amplitude EEG activity in the aged rat brain after cerebral ischemia

In aged humans, stroke is a major cause of disability for which no neuroprotective measures are available. In animal studies of focal ischemia, short-term hypothermia often reduces infarct size. Nevertheless, efficient neuroprotection requires long-term, regulated lowering of whole-body temperature. Previously, we reported that post-stroke exposure to hydrogen sulfide (H(2)S) effectively lowers whole-body temperature and confers neuroprotection in aged animals. In the present study using magnetic resonance imaging, electroencephalogram recording, DNA arrays, reverse transcriptase polymerase chain reaction, western blotting and immunofluorescence, we characterized the central nervous system response to H(2)S-induced hypothermia and report, for the first time, that annexin A1, a major pro-inflammatory protein that is upregulated after stroke, was consistently downregulated in polymorphonuclear cells in the peri-lesional cortex of post-ischemic, aged rat brain after 48 hours of hypothermia induced by exposure to H(2)S. Our data suggest that long-term hypothermia may be a viable clinical approach to protecting the aged brain from cerebral injury. Our findings further suggest that, in contrast to monotherapies that have thus far uniformly failed in clinical practice, hypothermia has pleiotropic effects on brain physiology that may be necessary for effective protection of the brain after stroke.

L-cysteine supplementation as an adjuvant therapy for type-2 diabetes

Diabetes remains a major public health issue. According to the American Diabetes Association, 23.5 million, or 10.7% of people in the USA aged 20 years and older, have diabetes. Type-2 diabetes is treated both by controlling the diet and with oral hypoglycemic drugs. However, for many patients, achieving a tight control of glucose is difficult with current regimens. This chapter discusses a relatively low-cost dietary supplement that could be used as an adjuvant therapy for type-2 diabetes. A review of the literature indicates that cysteine-rich whey protein improves glucose metabolism in diabetic animals and type-2 diabetic patients. Similarly, in animal studies, improvement in glucose metabolism is observed after supplementation with L-cysteine, or molecules containing a cysteine moiety. This chapter discusses the biochemical mechanisms by which L-cysteine can upregulate the insulin-dependent signaling cascades of glucose metabolism. Further studies are needed to examine whether clinical interventions using L-cysteine as an adjuvant therapy indeed help to control glycemia and vascular inflammation in the diabetic patient population.

Physiological implications of hydrogen sulfide: a whiff exploration that blossomed

The important life-supporting role of hydrogen sulfide (H(2)S) has evolved from bacteria to plants, invertebrates, vertebrates, and finally to mammals. Over the centuries, however, H(2)S had only been known for its toxicity and environmental hazard. Physiological importance of H(2)S has been appreciated for about a decade. It started by the discovery of endogenous H(2)S production in mammalian cells and gained momentum by typifying this gasotransmitter with a variety of physiological functions. The H(2)S-catalyzing enzymes are differentially expressed in cardiovascular, neuronal, immune, renal, respiratory, gastrointestinal, reproductive, liver, and endocrine systems and affect the functions of these systems through the production of H(2)S. The physiological functions of H(2)S are mediated by different molecular targets, such as different ion channels and signaling proteins. Alternations of H(2)S metabolism lead to an array of pathological disturbances in the form of hypertension, atherosclerosis, heart failure, diabetes, cirrhosis, inflammation, sepsis, neurodegenerative disease, erectile dysfunction, and asthma, to name a few. Many new technologies have been developed to detect endogenous H(2)S production, and novel H(2)S-delivery compounds have been invented to aid therapeutic intervention of diseases related to abnormal H(2)S metabolism. While acknowledging the challenges ahead, research on H(2)S physiology and medicine is entering an exponential exploration era.

Roles of hydrogen sulfide in the pathogenesis of diabetes mellitus and its complications

SIGNIFICANCE

Diabetes and its complications represent a major socioeconomic problem.

RECENT ADVANCES

Changes in the balance of hydrogen sulfide (H(2)S) play an important role in the pathogenesis of β-cell dysfunction that occurs in response to type 1 and type 2 diabetes. In addition, changes in H(2)S homeostasis also play a role in the pathogenesis of endothelial injury, which develop on the basis of chronically or intermittently elevated circulating glucose levels in diabetes.

CRITICAL ISSUES

In the first part of this review, experimental evidence is summarized implicating H(2)S overproduction as a causative factor in the pathogenesis of β-cell death in diabetes. In the second part of our review, experimental evidence is presented supporting the role of H(2)S deficiency (as a result of increased H(2)S consumption by hyperglycemic cells) in the pathogenesis of diabetic endothelial dysfunction, diabetic nephropathy, and cardiomyopathy.

FUTURE DIRECTIONS

In the final section of the review, future research directions and potential experimental therapeutic approaches around the pharmacological modulation of H(2)S homeostasis in diabetes are discussed.

Hydrogen sulfide in biochemistry and medicine

SIGNIFICANCE

An abundance of experimental evidence suggests that hydrogen sulfide (H(2)S) plays a prominent role in physiology and pathophysiology. Many targets exist for H(2)S therapy. The molecular targets of H(2)S include proteins, enzymes, transcription factors, and membrane ion channels.

RECENT ADVANCES

Novel H(2)S precursors are being synthesized and discovered that are capable of releasing H(2)S in a slow and sustained manner. This presents a novel and advantageous approach to H(2)S therapy for treatment of chronic conditions associated with a decline in endogenous H(2)S, such as diabetes and cardiovascular disease.

CRITICAL ISSUES

While H(2)S is cytoprotective at physiological concentrations, it is not universally cytoprotective, as it appears to have pro-apoptotic actions in cancer cells and is well known to be toxic at supraphysiological concentrations. Many of the pleiotropic effects of H(2)S on health are associated with the inhibition of inflammation and upregulation of prosurvival pathways. The powerful anti-inflammatory, cytoprotective, immunomodulating, and trophic effects of H(2)S on the vast majority of normal cells seem to be mediated mainly by its actions as an extremely versatile direct and indirect antioxidant and free radical scavenger. While the overall effects of H(2)S on transformed (i.e., malignant) cells can be characterized as pro-oxidant and pro-apoptotic, they contrast sharply with the cytoprotective effects on most normal cells.

FUTURE DIRECTIONS

H(2)S has become a molecule of great interest, and several slow-releasing H(2)S prodrugs are currently under development. We believe that additional agents regulating H(2)S bioavailability will be developed during the next 10 years.

Beneficial effects of gaseous hydrogen sulfide in hepatic ischemia/reperfusion injury

Hydrogen sulfide (H2 S) can induce a reversible hypometabolic state, which could protect against hypoxia. In this study we investigated whether H2 S could protect livers from ischemia/reperfusion injury (IRI). Male C57BL/6 mice were subjected to partial hepatic IRI for 60 min. Animals received 0 (IRI) or 100 ppm H2 S (IRI + H2 S) from 30 min prior to ischemia until 5 min before reperfusion. Core body temperature was maintained at 37° C. Animals were sacrificed after 1, 6 or 24 h. Hepatic ischemia caused extensive hepatic necrosis in the IRI animals which coincided with an increase in ALT and AST serum levels. Animals treated with H2 S showed attenuated serum ALT and AST levels and reduced necrotic lesions after 24 h. IRI animals had increased Bcl-2 mRNA expression and increased active Caspase 3 protein, which were both significantly lower in H2 S treated animals. Increased TNFα and IL-6 mRNA in the IRI livers was significantly attenuated by H2 S treatment, as was hepatic influx of Ly-6G positive granulocytes. Hepatic superoxide production after ischemia was attenuated by H2 S treatment. In hepatic ischemia/reperfusion injury, gaseous H2 S treatment is highly protective, substantially reducing necrosis, apoptosis and inflammation. Gaseous H2 S is therefore a very promising treatment for reducing IRI during hepatic transplantation.

Hydrogen sulfide protects against high-glucose-induced apoptosis in endothelial cells

Hydrogen sulfide (H2S) is the third endogenous gaseous mediator identified after nitric oxide and carbon monoxide. It has been demonstrated that H2S has protective effects on myocardial ischemia/reperfusion-induced cell apoptosis. To date, little is known about the role of H2S in the pathophysiology of diabetic vascular complications. In this study, we investigated the effects of sodium hydrosulfide on high-glucose-induced apoptosis of primary human umbilical vein endothelium cells. Exposure to high glucose (25 mmole/L) for 48 hours resulted in the induction of apoptosis by 41.6% ± 1.01%, which was attenuated by pretreatment with sodium hydrosulfide (50 μmole/L) for 30 minutes. Further investigation of the apoptotic mechanisms in the cells demonstrated that high glucose upregulated the ratio of Bax/Bcl-2 and activated caspase-3 and also increased the levels of reactive oxygen species and malondialdehyde while reducing superoxide dismutase activity. All the above responses could be prevented by pretreatment with 50 μmole/L of sodium hydrosulfide. These results indicated that the protective effects of H2S on endothelial cells in the condition of high glucose might involve an antioxidative stress mechanism.

The role of AKT1 and autophagy in the protective effect of hydrogen sulphide against hepatic ischemia/reperfusion injury in mice

Hydrogen sulphide (H 2S) exerts a protective effect in hepatic ischemia-reperfusion (I/R) injury. However, the exact mechanism of H 2S action remains largely unknown. This study was designed to investigate the role of the PtdIns3K-AKT1 pathways and autophagy in the protective effect of H 2S against hepatic I/R injury. Primary cultured mouse hepatocytes and livers with or without NaHS (a donor of H 2S) preconditioning were exposed to anoxia/reoxygenation (A/R) and I/R, respectively. In certain groups, they were also pretreated with LY294002 (AKT1-specific inhibitor), 3-methyladenine (3MA, autophagy inhibitor) or rapamycin (autophagy enhancer), alone or simultaneously. Cell viability, expression of P-AKT1, T-AKT1, LC3 and BECN1 were examined. The severity of liver injury was measured by the levels of serum aminotransferase and inflammatory cytokine, apoptosis and histological examination. GFP-LC3 redistribution and transmission electron microscopy were used to test the activity of autophagy. H 2S preconditioning activated PtdIns3K-AKT1 signaling in hepatocytes. LY294002 could abolish the AKT1 activation and attenuate the protective effect of H 2S on hepatocytes A/R and hepatic I/R injuries. H 2S suppressed hepatic autophagy in vitro and in vivo. Further reducing autophagy by 3MA also diminished the protective effect of H 2S, while rapamycin could reverse the autophagy inhibitory effect and enhance the protective effect of H 2S against hepatocytes A/R and hepatic I/R injuries, consequently. Taken together, H 2S protects against hepatocytic A/R and hepatic I/R injuries, at least in part, through AKT1 activation but not autophagy. An autophagy agonist could be applied to potentiate this hepatoprotective effect by reversing the autophagy inhibition of H 2S.

Methionine excess in diet induces acute lethal hepatitis in mice lacking cystathionine γ-lyase, an animal model of cystathioninuria

Physiological roles of the transsulfuration pathway have been recognized by its contribution to the synthesis of cytoprotective cysteine metabolites, such as glutathione, taurine/hypotaurine, and hydrogen sulfide (H(2)S), whereas its roles in protecting against methionine toxicity remained to be clarified. This study aimed at revealing these roles by analyzing high-methionine diet-fed transsulfuration-defective cystathionine γ-lyase-deficient (Cth(-/-)) mice. Wild-type and Cth(-/-) mice were fed a standard diet (1 × Met: 0.44%) or a high-methionine diet (3 × Met or 6 × Met), and hepatic conditions were monitored by serum biochemistry and histology. Metabolome analysis was performed for methionine derivatives using capillary electrophoresis- or liquid chromatography-mass spectrometry and sulfur-detecting gas chromatography. The 6 × Met-fed Cth(-/-) (not 1 × Met-fed Cth(-/-) or 6 × Met-fed wild type) mice displayed acute hepatitis, which was characterized by markedly elevated levels of serum alanine/aspartate aminotransferases and serum/hepatic lipid peroxidation, inflammatory cell infiltration, and hepatocyte ballooning; thereafter, they died of gastrointestinal bleeding due to coagulation factor deficiency. After 1 week on 6 × Met, blood levels of ammonia/homocysteine and hepatic levels of methanethiol/3-methylthiopropionate (a methionine transamination product/methanethiol precursor) became significantly higher in Cth(-/-) mice than in wild-type mice. Although hepatic levels of methionine sulfoxide became higher in 6 × Met-fed wild-type mice and Cth(-/-) mice, those of glutathione, taurine/hypotaurine, and H(2)S became lower and serum levels of homocysteine became much higher in 6 × Met-fed Cth(-/-) mice than in wild-type mice. Thus, transsulfuration plays a critical role in the detoxification of excessive methionine by circumventing aberrant accumulation of its toxic transamination metabolites, including ammonia, methanethiol, and 3-methylthiopropionate, in addition to synthesizing cysteine-derived antioxidants to counteract accumulated pro-oxidants such as methionine sulfoxide and homocysteine.

Total plasma sulfide as a marker of shock severity in nonsurgical adult patients

Previous animal and human studies have suggested that total plasma sulfide plays a role in the pathophysiology of shock. This study's aim was to determine the value of total plasma sulfide as a marker of shock severity in nonsurgical adult patients admitted to the ICU. Forty-one patients, with various types of shock (septic, cardiogenic, obstructive, and hypovolemic), were included in the study, with an average total plasma sulfide concentration of 23.2 ± 26.3 µM. Survivors (of shock) had lower total plasma sulfide concentrations than nonsurvivors (13.0 ± 26.3 vs. 31.9 ± 31.5 µM; P = 0.02). Total plasma sulfide correlated with dose of administered norepinephrine (R linear = 0.829; P = 0.001) and with Acute Physiology and Chronic Health Evaluation II (APACHE II) score (R cubic = 0.767; P = 0.001). Area under the receiver operating characteristic for total plasma sulfide as a predictor of ICU mortality was 0.739 (confidence interval, 0.587-0.892; P = 0.009). Even after correcting for APACHE II score and lactate values, total plasma sulfide correlated with mortality (odds ratio, 1.058; 95% confidence interval, 1.001-1.118; P = 0.045). The study provides evidence that, in nonsurgical adult ICU patients admitted because of any type of shock, total plasma sulfide correlates with administered norepinephrine dose at admission, severity of disease (APACHE II score ≥30 points), and survival outcome.

Hydrogen sulfide decreases reactive oxygen in a model of lung transplantation

BACKGROUND

Ischemia-reperfusion injury is a common complication after lung transplantation. Ischemia-reperfusion injury is thought to be mediated by reactive oxygen species (ROS). Hydrogen sulfide (H(2)S) is a novel agent that has been previously shown to scavenge ROS and slow metabolism. We evaluated the effect of infused H(2)S on the presence of ROS after reperfusion in an ex vivo model of lung transplantation.

METHODS

Heart-Lung blocks were recovered from New Zealand white rabbits (n = 12) and cold stored in Perfadex solution for 18 h. After storage, the heart-lung blocks were reperfused ex vivo with donor rabbit blood. In the treatment group (n = 7), a bolus of sodium H(2)S was added at the beginning of reperfusion (100 μg/kg) and continuously infused throughout the 2-h experiment (1 mg/kg/h). The vehicle group (n = 5) received an equivalent volume of saline. Serial airway and pulmonary artery pressures and arterial and venous blood gases were measured.

RESULTS

Oxygenation and pulmonary artery pressures were similar between the 2 groups. However, treatment with H(2)S resulted in a dramatic reduction in the presence of ROS after 2 h of reperfusion (4,851 ± 2,139 versus 235 ± 462 related fluorescence units/mg protein; P = 0.003). A trend was seen toward increased levels of cyclic guanosine monophosphate in the H(2)S-treated group (3.08 ± 1.69 versus 1.73 ± 1.41 fmol/mg tissue; P = .23).

CONCLUSIONS

After prolonged ischemia, infusion of H(2)S during reperfusion was associated with a significant decrease in the presence of ROS, a suspected mediator of ischemia-reperfusion injury. To our knowledge, the present study represents the first reported therapeutic use of H(2)S in an experimental model of lung transplantation.

Hydrogen sulfide is an endogenous potentiator of T cell activation

H(2)S is an endogenous signaling molecule that may act via protein sulfhydrylation to regulate various physiological functions. H(2)S is also a byproduct of dietary sulfate metabolism by gut bacteria. Inflammatory bowel diseases such as ulcerative colitis are associated with an increase in the colonization of the intestine by sulfate reducing bacteria along with an increase in H(2)S production. Consistent with its increased production, H(2)S is implicated as a mediator of ulcerative colitis both in its genesis or maintenance. As T cells are well established mediators of inflammatory bowel disease, we investigated the effect of H(2)S exposure on T cell activation. Using primary mouse T lymphocytes (CD3+), OT-II CD4+ T cells, and the human Jurkat T cell line, we show that physiological levels of H(2)S potentiate TCR-induced activation. Nanomolar levels of H(2)S (50-500 nM) enhance T cell activation assessed by CD69 expression, interleukin-2 expression, and CD25 levels. Exposure of T cells to H(2)S dose-dependently enhances TCR-stimulated proliferation with a maximum at 300 nM (30% increase, p < 0.01). Furthermore, activation increases the capacity of T cells to make H(2)S via increased expression of cystathionine γ-lyase and cystathionine β-synthase. Disrupting this response by silencing these H(2)S producing enzymes impairs T cell activation, and proliferation and can be rescued by the addition of 300 nM H(2)S. Thus, H(2)S represents a novel autocrine immunomodulatory molecule in T cells.

Glutamate oxidative injury to RGC-5 cells in culture is necrostatin sensitive and blunted by a hydrogen sulfide (H2S)-releasing derivative of aspirin (ACS14)

Oxidative stress to RGC-5 cells in culture was delivered by exposure to a combination of glutamate (Glu) and buthionine-S,R-sulfoximine (BSO). The effect of the insult on cell survival was quantified by the resazurin-reduction and a dead/live assays. Moreover, breakdown of DNA, the localisation of phosphatidylserine and reactive radical species (ROS) and its quantification were determined. In addition, various proteins and mRNAs were studied using Western blot, real time PCR and immunocytochemistry. ACS14, its sulfurated moiety ACS1 and aspirin were tested for their ability to blunt the negative effects of Glu/BSO on RGC-5 cells. In addition assays were carried out to see whether any of these substances influenced glutathione (GSH). Glu/BSO dose-dependently kills RGC-5 cells by a mechanism that involves an elevation of ROS accompanied by a breakdown of DNA, expression of phosphatidylserine and the activation of p38 MAPK. The process is unaffected by the pan caspase inhibitor z-VAD-fmk, does not involve the activation of apoptosis inducing factor (AIF) but is sensitive to active necrostatin-1. In cell viability studies (resazurin-reduction assay), ACS1 and ACS14 equally counteracted the negative effects of 5mM Glu/BSO to RGC-5 cells but aspirin was only effective with a milder oxidative stress (1 mM Glu/BSO). In all other assays ACS14 was very much more effective than aspirin at counteracting the influence of 5mM Glu/BSO. Moreover, ACS14 and ACS1 directly stimulated GSH while aspirin was ineffective. In addition the neuroprotecive effect of ACS14 was specifically blunted by the non-specific potassium channel blocker glibenclamide. Also the up-regulation of Bcl-2, HO-1 and XIAP induced by 5mM Glu/BSO were all attenuated to a greater extent by ACS14 (20 μM) than aspirin (20 μM). These data show that ACS14 is a very effective neuroprotectant when compared with aspirin. ACS14 maintains its aspirin characteristics and has the ability to release H(2)S. The combined multiple actions of aspirin and H(2)S in the form of ACS14 is worthy to consider for possible use in the treatment of glaucoma.

Hydrogen sulfide preconditioning or neutrophil depletion attenuates ischemia-reperfusion-induced mitochondrial dysfunction in rat small intestine

The objectives of this study were to determine whether neutrophil depletion with anti-neutrophil serum (ANS) or preconditioning with the hydrogen sulfide (H(2)S) donor NaHS (NaHS-PC) 24 h prior to ischemia-reperfusion (I/R) would prevent postischemic mitochondrial dysfunction in rat intestinal mucosa and, if so, whether calcium-activated, large conductance potassium (BK(Ca)) channels were involved in this protective effect. I/R was induced by 45-min occlusion of the superior mesenteric artery followed by 60-min reperfusion in rats preconditioned with NaHS (NaHS-PC) or a BK(Ca) channel activator (NS-1619-PC) 24 h earlier or treated with ANS. Mitochondrial function was assessed by measuring mitochondrial membrane potential, mitochondrial dehydrogenase function, and cytochrome c release. Mucosal myeloperoxidase (MPO) and TNF-α levels were also determined, as measures of postischemic inflammation. BK(Ca) expression in intestinal mucosa was detected by immunohistochemistry and Western blotting. I/R induced mitochondrial dysfunction and increased tissue MPO and TNF-α levels. Although mitochondrial dysfunction was attenuated by NaHS-PC or NS-1619-PC, the postischemic increases in mucosal MPO and TNF-α levels were not. The protective effect of NaHS-PC or NS-1619-PC on postischemic mitochondrial function was abolished by coincident treatment with BK(Ca) channel inhibitors. ANS prevented the I/R-induced increase in tissue MPO levels and reversed mitochondrial dysfunction. These data indicate that neutrophils play an essential role in I/R-induced mucosal mitochondrial dysfunction. In addition, NaHS-PC prevents postischemic mitochondrial dysfunction (but not inflammation) by a BK(Ca) channel-dependent mechanism.

Protective and Detrimental Effects of Sodium Sulfide and Hydrogen Sulfide in Murine Ventilator-induced Lung Injury

BACKGROUND

The antiinflammatory effects of hydrogen sulfide (H2S) and sodium sulfide (Na2S) treatment may prevent acute lung injury induced by high tidal volume (HVT) ventilation. However, lung protection may be limited by direct pulmonary toxicity associated with H2S inhalation. Therefore, the authors tested whether the inhalation of H2S or intravascular Na2S treatment can protect against ventilator-induced lung injury in mice.

METHODS

Anesthetized mice continuously inhaled 0, 1, 5, or 60 ppm H2S or received a single bolus infusion of Na2S (0.55 mg/kg) or vehicle and were then subjected to HVT (40 ml/kg) ventilation lasting 4 h (n = 4-8 per group).

RESULTS

HVT ventilation increased the concentrations of protein and interleukin-6 in bronchoalveolar lavage fluid, contributing to reduced respiratory compliance and impaired arterial oxygenation, and caused death from lung injury and pulmonary edema. Inhalation of 1 or 5 ppm H2S during HVT ventilation did not alter lung injury, but inhalation of 60 ppm H2S accelerated the development of ventilator-induced lung injury and enhanced the pulmonary expression of the chemoattractant CXCL-2 and the leukocyte adhesion molecules CD11b and L-selectin. In contrast, pretreatment with Na2S attenuated the expression of CXCL-2 and CD11b during HVT ventilation and reduced pulmonary edema. Moreover, Na2S enhanced the pulmonary expression of Nrf2-dependent antioxidant genes (NQO1, GPX2, and GST-A4) and prevented oxidative stress-induced depletion of glutathione in lung tissue.

CONCLUSIONS

The data suggest that systemic intravascular treatment with Na2S represents a novel therapeutic strategy to prevent both ventilator-induced lung injury and pulmonary glutathione depletion by activating Nrf2-dependent antioxidant gene transcription.

Downregulation of the renal and hepatic hydrogen sulfide (H2S)-producing enzymes and capacity in chronic kidney disease

BACKGROUND

Oxidative stress and inflammation are constant features and major mediators of progression and cardiovascular complications of chronic kidney disease (CKD). Hydrogen sulfide (H(2)S) is an endogenous signaling gas, which possesses potent anti-oxidant, anti-inflammatory, anti-hypertensive and other regulatory functions. H(2)S is produced by cystathionine β-synthase (CBS), cystathionine γ-lyase (CSE) and 3-mercaptopyruvate sulphurtransferase (MST). Plasma H(2)S is reduced in humans with hypertension, atherosclerosis and end-stage renal disease (ESRD). Atherosclerosis, hypertension and ischemia/reperfusion-induced acute kidney injury are associated with and, in part, mediated by diminished tissue H(2)S in experimental animals. Expression of the H(2)S-producing enzymes is reduced in the circulating leukocytes of patients with ESRD. However, the effect of CKD on expression of H(2)S-producing enzymes in the diseased kidney and other tissues is unknown and was studied here.

METHODS

Subgroups of rats were subjected to 5/6 nephrectomy or sham operation and observed for 6-12 weeks. Expression of H(2)S-producing enzymes and H(2)S-producing capacity was measured in kidney, liver and brain tissues.

RESULTS

The CKD group exhibited oxidative stress and significant reduction of plasma H(2)S concentration. This was associated with marked reduction of H(2)S-producing capacity of the kidney and liver, marked downregulation of CBS, CSE and MST in the kidney and of CBS and CSE expression in the liver. However, expression of H(2)S-producing enzymes in the brain was not significantly altered in CKD rats.

CONCLUSIONS

CKD is associated with significant reduction in plasma H(2)S concentration, diminished remnant kidney and liver tissue H(2)S-producing capacity and downregulation of the H(2)S-producing enzymes. Given the potent anti-oxidant, anti-inflammatory and cytoprotective properties of H(2)S, its deficiency may contribute to progression of CKD and the associated complications.

Emerging role of hydrogen sulfide in health and disease: critical appraisal of biomarkers and pharmacological tools

H2S (hydrogen sulfide) is a well known and pungent gas recently discovered to be synthesized enzymatically in mammalian and human tissues. In a relatively short period of time, H2S has attracted substantial interest as an endogenous gaseous mediator and potential target for pharmacological manipulation. Studies in animals and humans have shown H2S to be involved in diverse physiological and pathophysiological processes, such as learning and memory, neurodegeneration, regulation of inflammation and blood pressure, and metabolism. However, research is limited by the lack of specific analytical and pharmacological tools which has led to considerable controversy in the literature. Commonly used inhibitors of endogenous H2S synthesis have been well known for decades to interact with other metabolic pathways or even generate NO (nitric oxide). Similarly, commonly used H2S donors release H2S far too quickly to be physiologically relevant, but may have therapeutic applications. In the present review, we discuss the enzymatic synthesis of H2S and its emerging importance as a mediator in physiology and pathology. We also critically discuss the suitability of proposed 'biomarkers' of H2S synthesis and metabolism, and highlight the complexities of the currently used pharmacological H2S 'donor' molecules and 'specific' H2S synthesis inhibitors in their application to studying the role of H2S in human disease.

HIF-1 and SKN-1 coordinate the transcriptional response to hydrogen sulfide in Caenorhabditis elegans

Hydrogen sulfide (H₂S) has dramatic physiological effects on animals that are associated with improved survival. C. elegans grown in H₂S are long-lived and thermotolerant. To identify mechanisms by which adaptation to H₂S effects physiological functions, we have measured transcriptional responses to H₂S exposure. Using microarray analysis we observe rapid changes in the abundance of specific mRNAs. The number and magnitude of transcriptional changes increased with the duration of H₂S exposure. Functional annotation suggests that genes associated with protein homeostasis are upregulated upon prolonged exposure to H₂S. Previous work has shown that the hypoxia-inducible transcription factor, HIF-1, is required for survival in H₂S. In fact, we show that hif-1 is required for most, if not all, early transcriptional changes in H₂S. Moreover, our data demonstrate that SKN-1, the C. elegans homologue of NRF2, also contributes to H₂S-dependent changes in transcription. We show that these results are functionally important, as skn-1 is essential to survive exposure to H₂S. Our results suggest a model in which HIF-1 and SKN-1 coordinate a broad transcriptional response to H₂S that culminates in a global reorganization of protein homeostasis networks.

Hydrogen sulfide and L-cysteine increase phosphatidylinositol 3,4,5-trisphosphate (PIP3) and glucose utilization by inhibiting phosphatase and tensin homolog (PTEN) protein and activating phosphoinositide 3-kinase (PI3K)/serine/threonine protein kinase (AKT)/protein kinase Cζ/λ (PKCζ/λ) in 3T3l1 adipocytes

This work examined the novel hypothesis that reduced levels of H(2)S or L-cysteine (LC) play a role in the impaired glucose metabolism seen in diabetes. 3T3L1 adipocytes were treated with high glucose (HG, 25 mM) in the presence or absence of LC or H(2)S. Both LC and H(2)S treatments caused an increase in phosphatidylinositol-3,4,5 trisphosphate (PIP3), AKT phosphorylation, and glucose utilization in HG-treated cells. The effect of LC on PIP3 and glucose utilization was prevented by propargylglycine, an inhibitor of cystathionine γ-lyase that catalyzes H(2)S formation from LC. This demonstrates that H(2)S mediates the effect of LC on increased PIP3 and glucose utilization. H(2)S and LC caused phosphatidylinositol 3-kinase activation and PTEN inhibition. Treatment with LC, H(2)S, or PIP3 increased the phosphorylation of IRS1, AKT, and PKCζ/λ as well as GLUT4 activation and glucose utilization in HG-treated cells. This provides evidence that PIP3 is involved in the increased glucose utilization observed in cells supplemented with LC or H(2)S. Comparative signal silencing studies with siAKT2 or siPKCζ revealed that PKCζ phosphorylation is more effective for the GLUT4 activation and glucose utilization in LC-, H(2)S-, or PIP3-treated cells exposed to HG. This is the first report to demonstrate that H(2)S or LC can increase cellular levels of PIP3, a positive regulator of glucose metabolism. The PIP3 increase is mediated by PI3K activation and inhibition of PTEN but not of SHIP2. This study provides evidence for a molecular mechanism by which H(2)S or LC can up-regulate the insulin-signaling pathways essential for maintenance of glucose metabolism.

Increased oxidative stress and cytotoxicity by hydrogen sulfide in HepG2 cells overexpressing cytochrome P450 2E1

The main objectives of this work were to evaluate the effects of hydrogen sulfide on oxidative stress and cytotoxicity parameters in HepG2 cells and to assess the extent to which cytochrome P450 2E1 (CYP2E1) activity modulates the effects of hydrogen sulfide on oxidative stress and cytotoxicity. Sodium hydrosulfide (NaHS) caused time- and concentration-dependent cytotoxicity in both non-P450-expressing HepG2 cells (C34 cells) and CYP2E1-overexpressing HepG2 cells (E47 cells); however, NaHS-dependent cytotoxicity was higher in E47 than C34 cells. Cytotoxicity by NaHS in C34 and E47 cells was mainly necrotic in nature and associated with an early decrease in mitochondrial membrane potential. NaHS caused increased oxidation of lipophilic (C11-BODIPY(581/591)) and hydrophilic (DCFH-DA) probes only in E47 cells, at a time point prior to overt cytotoxicity. Trolox, an amphipathic antioxidant, partially inhibited both the cytotoxicity and the increased oxidative stress detected in E47 cells exposed to NaHS. Cell-permeable iron chelators and CYP2E1 inhibitors significantly inhibited the oxidation of C11-BODIPY(581/591) in E47 cells in the presence of NaHS. NaHS produced lipid peroxidation and cytotoxicity in E47 cells supplemented with a representative polyunsaturated fatty acid (docosahexaenoic acid) but not in C34 cells; these effects were inhibited by α-tocopherol, a lipophilic antioxidant. These data suggest that CYP2E1 enhances H(2)S-dependent cytotoxicity in HepG2 cells through the generation of iron-dependent oxidative stress and lipid peroxidation.

Exogenous hydrogen sulfide protects against traumatic hemorrhagic shock via attenuation of oxidative stress

OBJECTIVE

This study was designed to investigate the protective effects of exogenous hydrogen sulfide (H(2)S) on trauma-hemorrhagic shock (T-H).

MATERIALS AND METHODS

Forty-eight male Sprague-Dawley rats were anesthetized, while 32 were subjected to both midline laparotomy and hemorrhagic shock (35-40 mmHg for 90 min) by bleeding them from the femoral artery. One hour later, resuscitation was initiated with Ringer lactate. NaHS (28 μmol/kg) or vehicle alone was administered intraperitoneally at the onset of resuscitation. Two hours later, eight animals from each group were re-anesthetized to determine cardiac function, blood gas concentrations, and hepatic and renal function. Superoxide dismutase activity (SOD), malondialdehyde concentrations (MDA), and the activity of myeloperoxidase (MPO) in the serum were measured and pulmonary wet/dry (W/D) ratio and histopathologic evaluations performed.

RESULTS

NaHS resulted in an increase in mean arterial blood pressure, left ventricular pressure and positive (+dP/dt(max)) and negative (-dP/dt(max)) first derivatives of pressure as compared with the vehicle only group. The pH, PaO(2) and base excess (BE) were increased in the NaHS-treated group compared with the vehicle-treated group. Aspartate aminotransferase, alanine aminotransferase, blood urea nitrogen, and serum creatinine were reduced in the NaHS-treated group. NaHS also significantly reduced the high mortality rate at 24 h otherwise caused by T-H. The NaHS-treated group showed a remarkable decrease in MDA and MPO concentrations in plasma and an increase in SOD as compared with the vehicle-treated group. Histopathologic analysis indicated less edema, congestion, inflammatory cell infiltration and necrosis in heart, lung, liver and kidney tissue in NaHS-treated group.

CONCLUSIONS

The present study demonstrates that exogenous H(2)S administered at an appropriate dose confers protective effects after T-H and resuscitation, by preventing a decrease in the antioxidant defense system.

Hydrogen sulfide protects against chemical hypoxia-induced cytotoxicity and inflammation in HaCaT cells through inhibition of ROS/NF-κB/COX-2 pathway

Hydrogen sulfide (H₂S) has been shown to protect against oxidative stress injury and inflammation in various hypoxia-induced insult models. However, it remains unknown whether H₂S protects human skin keratinocytes (HaCaT cells) against chemical hypoxia-induced damage. In the current study, HaCaT cells were treated with cobalt chloride (CoCl₂), a well known hypoxia mimetic agent, to establish a chemical hypoxia-induced cell injury model. Our findings showed that pretreatment of HaCaT cells with NaHS (a donor of H₂S) for 30 min before exposure to CoCl₂ for 24 h significantly attenuated CoCl₂-induced injuries and inflammatory responses, evidenced by increases in cell viability and GSH level and decreases in ROS generation and secretions of IL-1β, IL-6 and IL-8. In addition, pretreatment with NaHS markedly reduced CoCl₂-induced COX-2 overexpression and PGE₂ secretion as well as intranuclear NF-κB p65 subunit accumulation (the central step of NF-κB activation). Similar to the protective effect of H₂S, both NS-398 (a selective COX-2 inhibitor) and PDTC (a selective NF-κB inhibitor) depressed not only CoCl₂-induced cytotoxicity, but also the secretions of IL-1β, IL-6 and IL-8. Importantly, PDTC obviously attenuated overexpression of COX-2 induced by CoCl₂. Notably, NAC, a ROS scavenger, conferred a similar protective effect of H₂S against CoCl₂-induced insults and inflammatory responses. Taken together, the findings of the present study have demonstrated for the first time that H₂S protects HaCaT cells against CoCl₂-induced injuries and inflammatory responses through inhibition of ROS-activated NF-κB/COX-2 pathway.

Protective action of endogenously generated H₂S on hypoxia-induced respiratory suppression and its relation to antioxidation and down-regulation of c-fos mRNA in medullary slices of neonatal rats

We previously reported that exogenous H(2)S played roles in protection of respiratory centers against hypoxic injury in medullary slices of neonatal rats. The protective action of endogenous H(2)S and its relation to antioxidation and down-regulation of c-fos mRNA were investigated in the present study. Perfusion of the slices with l-cysteine (Cys), substrate of cystathionine β-synthase (CBS, H(2)S synthase), could increase frequency of rhythmic respiratory discharge of the hypoglossal rootlets and prevent respiratory suppression induced by hypoxia, whereas perfusion with hydroxylamine (NH(2)OH, inhibitor of CBS) could postpone recovery of respiration from hypoxic inhibition. NH(2)OH also significantly enhanced hypoxia-induced increase in malondialdehyde (MDA) content of the slices. The hypoxia-induced up-regulation of c-fos mRNA could be markedly antagonized by S-adenosyl-l-methionine (SAM, activator of CBS), but greatly increased by NH(2)OH. Neither NH(2)OH, Cys nor SAM had any effect on expression of bcl-2 mRNA in hypoxic medullary slices. These results indicate that endogenously generated H(2)S was involved in protection of the medullary respiratory centers against hypoxic injury partly via antioxidation and down-regulation of c-fos.

The slow-releasing hydrogen sulfide donor, GYY4137, exhibits novel anti-cancer effects in vitro and in vivo

The slow-releasing hydrogen sulfide (H₂S) donor, GYY4137, caused concentration-dependent killing of seven different human cancer cell lines (HeLa, HCT-116, Hep G2, HL-60, MCF-7, MV4-11 and U2OS) but did not affect survival of normal human lung fibroblasts (IMR90, WI-38) as determined by trypan blue exclusion. Sodium hydrosulfide (NaHS) was less potent and not active in all cell lines. A structural analogue of GYY4137 (ZYJ1122) lacking sulfur and thence not able to release H₂S was inactive. Similar results were obtained using a clonogenic assay. Incubation of GYY4137 (400 µM) in culture medium led to the generation of low (<20 µM) concentrations of H₂S sustained over 7 days. In contrast, incubation of NaHS (400 µM) in the same way led to much higher (up to 400 µM) concentrations of H₂S which persisted for only 1 hour. Mechanistic studies revealed that GYY4137 (400 µM) incubated for 5 days with MCF-7 but not IMR90 cells caused the generation of cleaved PARP and cleaved caspase 9, indicative of a pro-apoptotic effect. GYY4137 (but not ZYJ1122) also caused partial G₂/M arrest of these cells. Mice xenograft studies using HL-60 and MV4-11 cells showed that GYY4137 (100-300 mg/kg/day for 14 days) significantly reduced tumor growth. We conclude that GYY4137 exhibits anti-cancer activity by releasing H₂S over a period of days. We also propose that a combination of apoptosis and cell cycle arrest contributes to this effect and that H₂S donors should be investigated further as potential anti-cancer agents.

Cytoprotective actions of hydrogen sulfide in ischaemia-reperfusion injury

Hydrogen sulfide (H(2)S) has been known as a highly toxic gas for several centuries. There have been considerable advances made in the H(2)S field regarding its physiological role; however, there is much more work that needs to be done. The biosynthesis of H(2)S has been attributed to three endogenous enzymes: cystathionine β-synthase (CBS), cystathionine γ-lyase (CGL or CSE) and 3-mercaptopyruvate sulfurtransferase (3-MST). These enzymes require further investigation to more fully elucidate the cellular expression profile, regulation and precise role of these critical enzymes in the production of H(2)S. In recent years, H(2)S has been demonstrated to have cytoprotective effects in multiple organ systems. In particular, it has been demonstrated that the administration of H(2)S either prior to ischaemia or at reperfusion significantly ameliorates myocardial and hepatic ischaemia-reperfusion injury. Therefore, this review focuses on the cardioprotective and hepatoprotective role of H(2)S. In addition, the review provides a summary of several known molecular targets of H(2)S protection.