Mechanism of induction of pancreatic acinar cell apoptosis by hydrogen sulfide

Causes of Exocrine Pancreatic Insufficiency Other Than Chronic Pancreatitis

Exocrine pancreatic insufficiency (EPI), an important cause of maldigestion and malnutrition, results from primary pancreatic disease or is secondary to impaired exocrine pancreatic function. Although chronic pancreatitis is the most common cause of EPI, several additional causes exist. These include pancreatic tumors, pancreatic resection procedures, and cystic fibrosis. Other diseases and conditions, such as diabetes mellitus, celiac disease, inflammatory bowel disease, and advanced patient age, have also been shown to be associated with EPI, but the exact etiology of EPI has not been clearly elucidated in these cases. The causes of EPI can be divided into loss of pancreatic parenchyma, inhibition or inactivation of pancreatic secretion, and postcibal pancreatic asynchrony. Pancreatic enzyme replacement therapy (PERT) is indicated for the conditions described above presenting with clinically clear steatorrhea, weight loss, or symptoms related to maldigestion and malabsorption. This review summarizes the current literature concerning those etiologies of EPI less common than chronic pancreatitis, the pathophysiology of the mechanisms of EPI associated with each diagnosis, and treatment recommendations.

Hydrogen sulfide in longevity and pathologies: Inconsistency is malodorous

Hydrogen sulfide (H₂S) is one of the biologically active gases (gasotransmitters), which plays an important role in various physiological processes and aging. Its production in the course of methionine and cysteine catabolism and its degradation are finely balanced, and impairment of H₂S homeostasis is associated with various pathologies. Despite the strong geroprotective action of exogenous H₂S in C. elegans, there are controversial effects of hydrogen sulfide and its donors on longevity in other models, as well as on stress resistance, age-related pathologies and aging processes, including regulation of senescence-associated secretory phenotype (SASP) and senescent cell anti-apoptotic pathways (SCAPs). Here we discuss that the translation potential of H₂S as a geroprotective compound is influenced by a multiplicity of its molecular targets, pleiotropic biological effects, and the overlapping ranges of toxic and beneficial doses. We also consider the challenges of the targeted delivery of H₂S at the required dose. Along with this, the complexity of determining the natural levels of H₂S in animal and human organs and their ambiguous correlations with longevity are reviewed.

Comparison of MS2, synchronous precursor selection MS3, and real-time search MS3 methodologies for lung proteomes of hydrogen sulfide treated swine

Tandem mass tags (TMTs) have increasingly become an attractive technique for global proteomics. However, its effectiveness for multiplexed quantitation by traditional tandem mass spectrometry (MS²) suffers from ratio distortion. Synchronous precursor selection (SPS) MS³ has been widely accepted for improved quantitation accuracy, but concurrently decreased proteome coverage. Recently, a Real-Time Search algorithm has been integrated with the SPS MS³ pipeline (RTS MS³) to provide accurate quantitation and improved depth of coverage. In this mechanistic study of the impact of exposure to hydrogen sulfide (H₂S) on the respiration of swine, we used TMT-based comparative proteomics of lung tissues from control and H₂S-treated subjects as a test case to evaluate traditional MS², SPS MS³, and RTS MS³ acquisition methods on both the Orbitrap Fusion and Orbitrap Eclipse platforms. Comparison of the results obtained by the MS² with those of SPS MS³ and RTS MS³ methods suggests that the MS³-driven quantitative strategies provided a more accurate global-scale quantitation; however, only RTS MS³ provided proteomic coverage that rivaled that of traditional MS² analysis. RTS MS³ not only yields more productive MS³ spectra than SPS MS³ but also appears to focus the analysis more effectively on unique peptides. Furthermore, pathway enrichment analyses of the H₂S-altered proteins demonstrated that an additional apoptosis pathway was discovered exclusively by RTS MS³. This finding was verified by RT-qPCR, western blotting, and TUNEL staining experiments. We conclude that RTS MS³ workflow enables simultaneous improvement of quantitative accuracy and proteome coverage over alternative approaches (MS² and SPS MS³). Graphical abstract.

H2S mediates apoptosis in response to inflammation through PI3K/Akt/NFκB signaling pathway

OBJECTIVES

Hydrogen sulfide (H₂S) is involved in regulating cell apoptosis and proliferation. However, The effects and mechanism of H₂S on the apoptosis of mammary epithelial cells that suffer from an inflammatory response remain unknown.

RESULTS

An inflammatory cell model was used to explore whether exogenous H₂S regulates lipopolysaccharides (LPS)-induced cell proliferation and apoptosis. We found that H₂S affected cell viability, the inflammatory response and apoptosis in LPS-treated cells in a concentration-dependent manner. Moreover, exogenous H₂S rescued LPS-induced cystathionine γ-lyase (CSE) inhibition and cystathionine β-synthase (CBS) synthesis. Interestingly, in cells undergoing inflammation-induced apoptosis, H₂S activated the PI3K/Akt and NFκB signal pathways both tested concentrations. Akt appeared to be a key crosstalk molecule that played a "bridge" role.

CONCLUSIONS

H₂S regulates LPS-induced inflammation and apoptosis by activating the PI3K/Akt/NFκB signaling pathway. Hence, NaHS may be clinically useful for preventing or treating mastitis.

Impaired Exocrine Pancreatic Function Associates With Changes in Intestinal Microbiota Composition and Diversity

BACKGROUND & AIMS

Changes in intestinal microbiome composition are associated with inflammatory, metabolic, and malignant disorders. We studied how exocrine pancreatic function affects intestinal microbiota.

METHODS

We performed 16S ribosomal RNA gene sequencing analysis of stool samples from 1795 volunteers from the population-based Study of Health in Pomerania who had no history of pancreatic disease. We also measured fecal pancreatic elastase by enzyme-linked immunosorbent assay and performed quantitative imaging of secretin-stimulated pancreatic fluid secretion. Associations of exocrine pancreatic function with microbial diversity or individual genera were calculated by permutational analysis of variance or linear regression, respectively.

RESULTS

Differences in pancreatic elastase levels associated with significantly (P < .0001) greater changes in microbiota diversity than with participant age, body mass index, sex, smoking, alcohol consumption, or dietary factors. Significant changes in the abundance of 30 taxa, such as an increase in Prevotella (q < .0001) and a decrease of Bacteroides (q < .0001), indicated a shift from a type-1 to a type-2 enterotype. Changes in pancreatic fluid secretion alone were also associated with changes in microbial diversity (P = .0002), although to a lesser degree.

CONCLUSIONS

In an analysis of fecal samples from 1795 volunteers, pancreatic acinar cell, rather than duct cell, function is presently the single most significant host factor to be associated with changes in intestinal microbiota composition.

Hydrogen sulfide inhalation-induced immune damage is involved in oxidative stress, inflammation, apoptosis and the Th1/Th2 imbalance in broiler bursa of Fabricius

Hydrogen sulfide (H₂S) is widely accepted to be a signaling molecule that exhibits some potentially beneficial therapeutic effects at physiological concentrations. At elevated levels, H₂S is highly toxic and has a negative effect on human health and animal welfare. Studies have shown that H₂S exposure induces an immune function in mice, but there are few studies of the effect of continuous H₂S exposure on immune organs in poultry. In this study, one-day-old broilers were selected and exposed to 4 or 20 ppm of H₂S gas for 14, 28 and 42 days of age. After exposure, the bursa of Fabricius (BF) was harvested. The results showed that continuous H₂S exposure reduced the body weight, abdominal fat percentage, and antibody titer in broilers. H₂S exposure also decreased mRNA expression of IgA, IgM and IgG in the broiler BF. A histological study revealed obvious nuclear debris, and a few vacuoles in the BF, and an ultrastructural study revealed mitochondrial and nuclear damage to BF cells after H₂S exposure for 42 d. Terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assay suggested H₂S exposure remarkably increased the number of TUNEL positive nuclei and significantly increased apoptotic index. The expression of apoptotic genes also confirmed that H₂S inhalation damaged the broiler BF. Increased cytokines and reduced antioxidant responses were detected in the BF after exposure to H₂S. Cytokines promoted inflammation and caused a Th1/Th2 imbalance. We suggest that continuous H₂S intoxication triggers oxidative stress, inflammation, apoptosis and a Th1/Th2 imbalance in the BF, leading to immune injury in broilers.

Role of the cystathionine β-synthase/H2S system in liver cancer cells and the inhibitory effect of quinolone-indolone conjugate QIC2 on the system

Hydrogen sulfide (H2S), the third gasotransmitter, plays important roles in cancer biological processes. As endogenous H2S exerts pro-cancer functions, inhibition of its production in cancer cells may provide a new cancer treatment strategy and be achieved via regulation of the function of cystathionine β-synthase (CBS), one of the main metabolic enzymes synthesizing H2S. This enzyme plays important roles in the development and progression of colon and ovarian cancer, primarily regulating mitochondrial bioenergetics and accelerating cell cycle progression. In the present study, we firstly investigated the role of the CBS/H2S system in human hepatoma cells, and then the inhibitory effect of a quinolone-indolone conjugate QIC2 on this system. When CBS was overexpressed in human hepatoma HepG2 and SMMC-7721 cells, inhibition of endogenous CBS/H2S significantly reduced their viability and growth rate, as well as the proliferation of SMMC-7721 cells. Meanwhile, CBS knockdown caused multiple effects, including apoptosis of SMMC-7721 cells, an increase in the Bcl-2-associated X protein (Bax)/B cell lymphoma/leukemia (Bcl-2) ratio, activation of caspase-3 and polyADP-ribose polymerase (PARP), when compared with the scramble siRNA (Sc siRNA)-transfected groups. Heme oxygenase-1 (HO-1; a microsomal enzyme) expression was significantly decreased while the reactive oxygen species (ROS) level was increased in the CBS siRNA-transfected SMMC-7721 cells. QIC2 significantly reduced SMMC-7721 cell viability in a dose-dependent manner and showed a lower toxicity in human normal liver HL-7702 cells relative to the positive controls sunitinib and doxorubicin (DOX). The compound also inhibited cell proliferation and induced cell apoptosis in SMMC-7721 cells. Further analysis indicated that QIC2 downregulated the CBS/H2S system, decreased both HO-1 protein and glutathione (GSH) levels while increased the ROS level and activated the caspase-3 cascade. Collectively, our results demonstrated that the CBS/H2S system plays important roles in human hepatoma cells and QIC2 significantly inhibited cell growth via downregulation of the system.

The NF-κB pathway participates in the response to sulfide stress in Urechis unicinctus

The NF-κB pathway is known to be involved in regulating apoptosis, inflammation and immunity in organisms. In this study, we first identified full-length cDNA sequences of two key molecules in the NF-κB pathway, namely, NEMO and p65, and characterized their responses in the hindgut of Urechis unicinctus (Echiura, Urechidae) exposed to sulfide. The full-length of cDNA was 2491 bp for U. unicinctus NEMO (UuNEMO) and 1971 bp for U. unicinctus p65 (Uup65), and both polyclonal antibodies were prepared using UuNEMO or Uup65 expressed prokaryotically with the sequence of their whole open reading frame. Immunoprecipitation and Western blotting showed that the NF-κB pathway was activated in U. unicinctus exposed to sulfide, in which the content of UuNEMO ubiquitination and nuclear Uup65 increased significantly (p < 0.05) in hindgut tissue of U. unicinctus exposed to sulfide. Furthermore, the mRNA level of UuBcl-xL, a downstream anti-apoptosis gene of the NF-κB pathway, increased significantly (p < 0.05) from 48 h to 72 h and the mRNA level of UuBax, a Bcl-xL antagonist gene, decreased significantly (p < 0.05) at 48 h in the hindgut of U. unicinctus exposed to 50 μM sulfide. During the 150 μM sulfide exposure, the level of UuBcl-xL showed no obvious change, whereas the UuBax mRNA level increased significantly (p < 0.05) at 72 h post-exposure to 150 μM sulfide. We suggested that the activated NF-κB pathway up-regulates UuBcl-xL expression, and evokes an anti-apoptotic response to resist sulfide damage at 50 μM in U. unicinctus. Meanwhile, a Bax-mediated pro-apoptotic response occurs when U. unicinctus is exposed to 150 μM sulfide.

Basolateral Kir4.1 activity in the distal convoluted tubule regulates K secretion by determining NaCl cotransporter activity

PURPOSE OF REVIEW

Renal potassium (K) secretion plays a key role in maintaining K homeostasis. The classic mechanism of renal K secretion is focused on the connecting tubule and cortical collecting duct, in which K is uptaken by basolateral Na-K-ATPase and is secreted into the lumen by apical ROMK (Kir1.1) and Ca-activated big conductance K channel. Recently, genetic studies and animal models have indicated that inwardly rectifying K channel 4.1 (Kir4.1 or Kcnj10) in the distal convoluted tubule (DCT) may play a role in the regulation of K secretion in the aldosterone-sensitive distal nephron by targeting the NaCl cotransporter (NCC). This review summarizes recent progresses regarding the role of Kir4.1 in the regulation of NCC and K secretion.

RECENT FINDINGS

Kir4.1 is expressed in the basolateral membrane of the DCT, and plays a predominant role in contributing to the basolateral K conductance and in participating in the generation of negative membrane potential. Kir4.1 is also the substrate of src-family tyrosine kinase and the stimulation of src-family tyrosine kinase activates Kir4.1 activity in the DCT. The genetic deletion or functional inhibition of Kir4.1 depolarizes the membrane of the DCT, inhibits ste20-proline-alanine rich kinase, and suppresses NCC activity. Moreover, the downregulation of Kir4.1 increases epithelial Na channel expression in the collecting duct and urinary K excretion. Finally, mice with low Kir4.1 activity in the DCT are hypomagnesemia and hypokalemia.

SUMMARY

Recent progress in exploring the regulation and the function of Kir4.1 in the DCT strongly indicates that Kir4.1plays an important role in initiating the regulation of renal K secretion by targeting NCC and it may serves as a K sensor in the kidney.

Transcriptional response to sulfide in the Echiuran Worm Urechis unicinctus by digital gene expression analysis

Background

Urechis unicinctus, an echiuran worm inhabiting the U-shaped burrows in the coastal mud flats, is an important commercial and ecological invertebrate in Northeast Asian countries, which has potential applications in the study of animal evolution, coastal sediment improvement and marine drug development. Furthermore, the worm can tolerate and utilize well-known toxicant-sulfide. However, knowledge is limited on the molecular mechanism of U. unicinctus responding to sulfide due to deficiency of its genetic information.

Methods

In this study, we performed Illumina sequencing to obtain the first Urechis unicinctus transcriptome data. Sequenced reads were assembled and then annotated using blast searches against Nr, Nt, Swiss-Prot, KEGG and COG. The clean tags from four digital gene expression (DGE) libraries were mapped to the U. unicinctus transcriptome. DGE analysis and functional annotation were then performed to reveal its response to sulfide. The expressions of 12 candidate genes were validated using quantitative real-time PCR. The results of qRT-PCR were regressed against the DGE analysis, with a correlation coefficient and p-value reported for each of them.

Results

Here we first present a draft of U. unicinctus transcriptome using the Illumina HiSeq^TM 2000 platform and 52,093 unique sequences were assembled with the average length of 738 bp and N50 of 1131 bp. About 51.6 % of the transcriptome were functionally annotated based on the databases of Nr, Nt, Swiss-Prot, KEGG and COG. Then based on the transcriptome, the digital gene expression analysis was conducted to examine the transcriptional response to sulfide during 6, 24 and 48 h exposure, and finally 1705, 1181 and 1494 tag-mapped genes were identified as differentially expressed genes in the 6-h, 24-h and 48-h libraries, then were further subjected to pathway analyses.

Conclusions

In the DGE database of U. unicinctus, the alterations in certain known sulfide-related pathways indicate similar changes in response to sulfide. For more than 80 % of the identified pathway members, this is the first report on their association with sulfide stress, among which glycolysis pathway and PIDD involving pathways were unique and discussed in details, and were thought to play important roles in the sulfide tolerance of U. unicinctus. All the results are helpful to explain the mechanism of sulfide tolerance and detoxification.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-2094-z) contains supplementary material, which is available to authorized users.

A H2S-Nampt dependent energetic circuit is critical to survival and cytoprotection from damage in cancer cells

We recently demonstrated that cancer cells that recover from damage exhibit increased aerobic glycolysis, however, the molecular mechanism by which cancer cells survive the damage and show increased aerobic glycolysis remains unknown. Here, we demonstrate that diverse cancer cells that survive hypoxic or oxidative damage show rapid cell proliferation, and develop tolerance to damage associated with increased production of hydrogen sulfide (H₂S) which drives up-regulation of nicotinamide phosphoribosyltransferase (Nampt). Consistent with existence of a H₂S-Nampt energetic circuit, in damage recovered cancer cells, H₂S, Nampt and ATP production exhibit a significant correlation. Moreover, the treatment of cancer cells with H₂S donor, NaHS, coordinately increases Nampt and ATP levels, and protects cells from drug induced damage. Inhibition of cystathionine beta synthase (CBS) or cystathionase (CTH), enzymes which drive generation of H₂S, decreases Nampt production while suppression of Nampt pathway by FK866, decreases H₂S and ATP levels. Damage recovered cells isolated from tumors grown subcutaneously in athymic mice also show increased production of H₂S, Nampt and ATP levels, associated with increased glycolysis and rapid proliferation. Together, these data show that upon recovery from potential lethal damage, H₂S-Nampt directs energy expenditure and aerobic glycolysis in cancer cells, leads to their exponential growth, and causes a high degree of tolerance to damage. Identification of H₂S-Nampt as a pathway responsible for induction of damage tolerance in cancer cells may underlie resistance to therapy and offers the opportunity to target this pathway as a means in treatment of cancer.

Inhibition of hydrogen sulfide synthesis provides protection for severe acute pancreatitis rats via apoptosis pathway

We aimed to investigate the relationship between the synthesis of hydrogen sulfide (H(2)S) and the pancreatic acinar cell apoptosis in severe acute pancreatitis (SAP) rats, as well as analyse the potential apoptotic pathway involved in this process. Sixty rats had been equally divided into four groups: sham, SAP, SAP + sodium hydrosulfide (NaHS) and SAP + DL-propargylglycine (PAG). 24 h after SAP induction, all surviving animals of each group were sacrificed to collect blood and tissue samples for the following measurements: the level of serum H(2)S as well as the levels of tumor necrosis factor-alpha (TNF-α), interleukin-10 (IL-10), H(2)S synthesizing activity, CSE mRNA and protein expression, maleic dialdehyde (MDA) and myeloperoxidase (MPO) activity, the expression of Bax, Bcl-2, caspase-3, -8 and -9, the release of cytochrome c and the activation of nuclear factor-kappa B (NF-κB), ERK1/2, JNK1/2 and p38 in pancreas. Furthermore, in situ detection of cell apoptosis was examined and the severity of pancreatic damage was analyzed by pathological grading and scoring. Results Significant differences in every index except IL-10 had been found between the SAP, NaHS and PAG groups (P < 0.05). Treatment with PAG obviously induced the pancreatic acinar cell apoptosis as well as improved all the pathological changes and inflammatory parameters. In contrast, administration of NaHS significantly attenuated apoptosis in the pancreas and aggravated the severity of pancreatic damage. Moreover, the expressions of caspase-3, -8, -9 and the release of cytochrome c were all increased in the apoptotic cells, and the activity of NF-κB as well as the phosphorylation of ERK1/2, JNK1/2 and p38 decreased accompanying with the reduction of the serum H(2)S level. H(2)S plays a pivotal role in the regulation of pancreatic acinar cell apoptosis in SAP rats. The present results showed that inhibition of H(2)S synthesis provided protection for SAP rats via inducing acinar cell apoptosis. This process acted through both extrinsic and intrinsic apoptotic pathways, and may be regulated by reducing the activity of NF-κB.

Sodium/calcium exchanger is upregulated by sulfide signaling, forms complex with the β1 and β3 but not β2 adrenergic receptors, and induces apoptosis

Hydrogen sulfide (H2S) as a novel gasotransmitter regulates variety of processes, including calcium transport systems. Sodium calcium exchanger (NCX) is one of the key players in a regulation calcium homeostasis. Thus, the aims of our work were to determine effect of sulfide signaling on the NCX type 1 (NCX1) expression and function in HeLa cells, to investigate the relationship of β-adrenergic receptors with the NCX1 in the presence and/or absence of H2S, and to determine physiological importance of this potential communication. As a H2S donor, we used morpholin-4-ium-4-methoxyphenyl(morpholino) phosphinodithioate-GYY4137. We observed increased levels of the NCX1 mRNA, protein, and activity after 24 h of GYY4137 treatment. This increase was accompanied by elevated cAMP due to the GYY4137 treatment, which was completely abolished, when NCX1 was silenced. Increased cAMP levels would point to upregulation of β-adrenergic receptors. Indeed, GYY4137 increased expression of β1 and β3 (but not β2) adrenergic receptors. These receptors co-precipitated, co-localized with the NCX1, and induced apoptosis in the presence of H2S. Our results suggest that sulfide signaling plays a role in regulation of the NCX1, β1 and β3 adrenergic receptors, their co-localization, and stimulation of apoptosis, which might be of a potential importance in cancer treatment.

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.

Calpain mediates caspase-dependent apoptosis initiated by hydrogen peroxide in pancreatic acinar AR42J cells

Several studies have shown that oxidative stress induces apoptosis in many cellular systems including pancreatic acinar cells. However, the exact molecular mechanisms leading to apoptosis remain partially understood. This study aimed to investigate the role of the cytosolic cysteine protease calpain in H2O2-induced apoptosis in pancreatic AR42J cells. Apoptosis was evaluated using flow cytometric analysis of sub-G1 DNA populations, electron-microscopic analysis, caspase-3-specific αII-spectrin breakdown, and measuring the proteolytic activities of the initiator caspase-12 and caspase-8, and the executioner caspase-3. H2O2 induced an increase in the calpain proteolytic activity immediately after starting the experiments that tended to return to a nearly normal level after 8 h and could be attributed to m-calpain. Whereas no caspase-12, caspase-8 and caspase-3 activations could be detected within the first 0.5 h, significantly increased proteolytic activities were observed after 8 h compared with the control. At the same time, the cells showed first ultrastructural hallmarks of apoptosis and a decreased viability. In addition, αII-spectrin fragmentation was identified using immunoblotting that could be attributed to both calpain and caspase-3. Calpain inhibition reduced the activities of caspase-12, caspase-8, and caspase-3 leading to a decrease in the number of apoptotic cells. Immunoblotting analyses of caspase-12 and caspase-8 indicate that calpain may be involved in the activation process of both proteases. The results suggest that H2O2-induced apoptosis of AR42J cells requires activation of m-calpain initiating the endoplasmic reticulum stress-induced caspase-12 pathway and a caspase-8-dependent pathway. The findings also suggest that calpain may be involved in the execution phase of apoptosis.

Sulfide induces apoptosis and Rho kinase-dependent cell blebbing in Jurkat cells

Hydrogen sulfide (H₂S) is a toxic gaseous substance, and accidental exposure to high concentrations of H₂S has been reported to be lethal to humans. Inhaled and absorbed H₂S is partially dissolved within the circulation and causes toxic effects on lymphocytes. However, the mechanisms involved in H₂S toxicity have not been well documented. In this study, we examined the cellular uptake and injury of sulfide-exposed human T lymphocytes (Jurkat). Cells were exposed to a H₂S donor, sodium hydroxysulfide (NaHS), at pH 6.0, 7.0, or 8.0 for 1 h at 37 °C in a sealed conical tube to avoid the loss of dissolved H₂S gas. Cytotoxicity and cellular sulfide concentrations increased dramatically as the pH of the NaHS solution decreased. Sulfide enhanced the cleavage of caspase-3 and poly (ADP-ribose) polymerase and induced early cellular apoptosis. A pan-caspase inhibitor reduced sulfide-induced apoptosis. These results indicate that sulfide induces pH-dependent and caspase-dependent apoptosis. We also found that blebbing of the plasma membrane occurred in sulfide-exposed cells. Both ROCK-1 and ROCK-2 (Rho kinases) were activated by sulfide, and sulfide-induced cell blebbing was suppressed by a ROCK inhibitor, suggesting that a Rho pathway is involved in sulfide-induced blebbing in lymphocytes.

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.

Hydrogen sulfide in cell survival: a double-edged sword

Hydrogen sulfide (H(2)S) has been found to play an important role as a signal molecule in regulating cell survival. It appears paradoxical that, on one side, H(2)S acts as a physiological intercellular messenger to stimulate cell growth, and on the other side, it may display cytotoxic activity. This article summarizes the current body of evidence demonstrating the cytoprotective versus cytotoxic effects of H(2)S in mammalian cells and describes the janus-faced properties of this important gasotransmitter. This article will also provide a brief description of the current signaling mechanisms that have been demonstrated to be responsible for these different actions. The pharmacologic regulation of H(2)S production and the potential clinical significance of H(2)S are highlighted.

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.

Preclinical assessment of the distribution, metabolism, and excretion of S-propargyl-cysteine, a novel H2S donor, in Sprague-Dawley rats

AIM

To study the distribution, metabolism and excretion of S-propargyl-cysteine (SPRC), a novel hydrogen sulfide (H2S) donor, after oral administration in rats.

METHODS

Adult Sprague-Dawley rats were used. The tissue distribution of [(35)S] SPRC-derived radioactivity was measured using a liquid scintillation counter. The plasma protein binding of SPRC was examined using 96-well equilibrium dialysis. The excretion of SPRC in urine, bile and feces was analyzed using the LC-MS/MS method. The major metabolites in rat biomatrices were identified using MRM information-dependent, acquisition-enhanced product ion (MRM-IDA-EPI) scans on API 4000QTrap system.

RESULTS

After oral administration of [(35)S]-SPRC at a dose of 75 mg/kg, [(35)S] SPRC-derived radioactivity displayed broad biological distribution in various tissues of rats, including its target organs (heart and brain) with the highest in kidney. On the other hand, the binding of SPRC to human, rat and dog plasma protein was low. Only 2.18% ± 0.61% and 0.77% ± 0.61% of the total SPRC administered was excreted unchanged in the bile and urine. However, neither intact SPRC nor its metabolites were detected in rat feces. The major metabolic pathway in vivo (rat bile, urine, and plasma) was N-acetylation.

CONCLUSION

The preliminary results suggest that SPRC possesses acceptable pharmacokinetic properties in rats.

Transplantation of mesenchymal stem cells preconditioned with hydrogen sulfide enhances repair of myocardial infarction in rats

Stem cell transplantation has become a promising therapeutic approach for the treatment of myocardial infarction (MI). However, the poor survival of the donor cells after transplantation has restricted its therapeutic efficacy. Hydrogen sulfide (H(2)S), one gaseous signaling molecule, has been applied to inhibit cell apoptosis and promote cell survival. In the present study, we therefore examined the effects of H(2)S on the survival of mesenchymal stem cells (MSCs). MSCs were isolated from the femur of male Sprague-Dawley rats (about 4 weeks old, 100 g). Preconditioning MSCs with 200 µmol/L NaHS (as the donor of H(2)S) for 30 min decreased the hypoxia-induced cell apoptosis in vitro. The mechanisms contributing to the beneficial effects of H(2)S on MSCs were associated with increased levels of phosphorylated Akt (pAkt), phosphorylated Erk1/2 (pErk1/2) and phosphorylated glycogen synthase kinase-3β (pGSK-3β) in MSCs. Subsequently, MSCs (1 × 10(6)), MSCs preconditioned with H(2)S (1 × 10(6)), or phosphate buffered saline (PBS) were injected into rat hearts immediately after MI (the ligation of the left anterior descending of coronary artery). Real-time PCR for the Sry gene, located on the Y chromosome, indicated that preconditioning with H(2)S improved the survival rate of the transplanted MSCs in infarcted myocardium 4 days after MI, compared with the untreated MSCs. Furthermore, transplantation of the H(2)S-pretreated MSCs reduced the infarct size and increased left ventricular (LV) function, as judged by transthoracic echocardiography. In conclusion, H(2)S preconditioning effectively promotes MSCs survival under ischemic injury and helps cardiac repair after MI, which has great clinical significance.

Cardiopulmonary, histologic, and inflammatory effects of intravenous Na2S after blunt chest trauma-induced lung contusion in mice

BACKGROUND

When used as a pretreatment, hydrogen sulfide (H2S) either attenuated or aggravated lung injury. Therefore, we tested the hypothesis whether posttreatment intravenous Na2S (sulfide) may attenuate lung injury.

METHODS

After blast wave blunt chest trauma or sham procedure, anesthetized and instrumented mice received continuous intravenous sulfide or vehicle while being kept at 37°C or 32°C core temperature. After 4 hours of pressure-controlled, thoracopulmonary compliance-titrated, lung-protective mechanical ventilation, blood and tissue were harvested for cytokine concentrations, heme oxygenase-1, IκBα, Bcl-Xl, and pBad expression (western blotting), nuclear factor-κB activation (electrophoretic mobility shift assay), and activated caspase-3, cystathionine-β synthase and cystathionine-γ lyase (immunohistochemistry).

RESULTS

Hypothermia caused marked bradycardia and metabolic acidosis unaltered by sulfide. Chest trauma impaired thoracopulmonary compliance and arterial Po2, again without sulfide effect. Cytokine levels showed inconsistent response. Sulfide increased nuclear factor-κB activation during normothermia, but this effect was blunted during hypothermia. While histologic lung injury was variable, both sulfide and hypothermia attenuated the trauma-related increase in heme oxygenase-1 expression and activated caspase-3 staining, which coincided with increased Bad phosphorylation and Bcl-Xl expression. Sulfide and hypothermia also attenuated the trauma-induced cystathionine-β synthase and cystathionine-γ lyase expression.

CONCLUSIONS

Posttreatment sulfide infusion after blunt chest trauma did not affect the impaired lung mechanics and gas exchange but attenuated stress protein expression and apoptotic cell death. This protective effect was amplified by moderate hypothermia. The simultaneous reduction in cystathionine-β synthase and cystathionine-γ lyase expression supports the role of H2S-generating enzymes as an adaptive response during stress states.

H2S donor, S-propargyl-cysteine, increases CSE in SGC-7901 and cancer-induced mice: evidence for a novel anti-cancer effect of endogenous H2S?

Background

S-propargyl-cysteine (SPRC), an H₂S donor, is a structural analogue of S-allycysteine (SAC). It was investigated for its potential anti-cancer effect on SGC-7901 gastric cancer cells and the possible mechanisms that may be involved.

Methods and Findings

SPRC treatment significantly decreased cell viability, suppressed the proliferation and migration of SPRC-7901 gastric cancer cells, was pro-apoptotic as well as caused cell cycle arrest at the G₁/S phase. In an in vivo study, intra-peritoneal injection of 50 mg/kg and 100 mg/kg of SPRC significantly reduced tumor weights and tumor volumes of gastric cancer implants in nude mice, with a tumor growth inhibition rate of 40–75%. SPRC also induced a pro-apoptotic effect in cancer tissues and elevated the expressions of p53 and Bax in tumors and cells. SPRC treatment also increased protein expression of cystathione-γ-lyase (CSE) in cells and tumors, and elevated H₂S levels in cell culture media, plasma and tumoral CSE activity of gastric cancer-induced nude mice by 2, 2.3 and 1.4 fold, respectively. Most of the anti-cancer functions of SPRC on cells and tumors were significantly suppressed by PAG, an inhibitor of CSE activity.

Conclusions

Taken together, the results of our study provide insights into a novel anti-cancer effect of H₂S as well as of SPRC on gastric cancer through inducing the activity of a new target, CSE.

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.

The protective role of hydrogen sulfide in myocardial ischemia-reperfusion-induced injury in diabetic rats

BACKGROUND

Hydrogen sulfide (H(2)S) displays anti-inflammatory and cytoprotective activities to attenuate myocardial ischemia-reperfusion (MIR)-induced injury, but its role in MIR in diabetics is not known. This study was undertaken to investigate whether H(2)S plays a protective role in MIR in diabetic rats.

METHODS

Diabetes was induced by streptozocin in Wistar rats, which were subjected to myocardial ischemia by blocking the left circumflex artery for 30 min, followed by 2h reperfusion. dl-propargylglycine (PAG) and sodium hydrosulfide (NaHS) were administered to the rats to investigate their effects on severity of MIR-induced injury.

RESULTS

Diabetic rats had smaller myocardial infarct sizes and higher serum levels of H(2)S (both P < 0.05) than non-diabetics when they underwent MIR. MIR significantly increased the serum level of H(2)S (49.5 ± 7.1 μM), H(2)S-synthesizing activity (7.4 ± 1.6 nmol/mg) and the myocardial infarct size (44.0 ± 7.2%), compared with sham-operated diabetic rats (21.7 ± 2.1 μM, 0.15 ± 0.4 nmol/mg and 1.2 ± 0.4%, respectively). Administration of NaHS increased the H(2)S level (65.8 ± 6.9 μM) and had little effect on H(2)S production activity (6.5 ± 2.2 nmol/mg), while PAG reduced both the H(2)S level (29.2 ± 5.0 μM) and H(2)S-synthesizing activity (2.2 ± 1.8 nmol/mg). NaHS significantly reduced the myocardial infarct size (31.2 ± 4.7%), inhibited the production of lipid peroxidation, MPO activity, and cell apoptosis, and downregulated expression of caspase-3, Fas, FasL, and TNF-α, which had been elevated by MIR, while PAG further increased the myocardial infarct size (58.3 ± 5.9%), and displayed opposite effects.

CONCLUSIONS

The study indicates that H(2)S may play a protective role in MIR-induced myocardial injury in diabetics by its anti-apoptotic, anti-oxidative and anti-inflammatory activities.

Hydrogen sulfide gas has cell growth regulatory role

Hydrogen sulfide (H(2)S) has been classified as a third novel gasotransmitter signaling molecule alongside nitric oxide and carbon monoxide. H(2)S rapidly travels through the cell membranes without using any specific receptors/transporters and signaling intracellular proteins. Recently, it has been shown that H(2)S induces DNA damage and alter cell cycle in various mammalian cells. Endogenously produced or exogenously treated H(2)S has a role in the accumulation or proliferation of cells and further may provide for development of a novel therapeutic approach in conditions associated with uncontrolled cell growth. However, the potential biological and clinical significance of H(2)S are subject of intense debate in recent years and despite considerable progress in our understanding about H(2)S, much still needs to be learned about their production at the site of tissue injury and its downstream signaling pathways on cell growth. Here, we provide an overview of the recent findings on its role in DNA damage/repair and cell growth followed by its potential translational implications.

Regulation of acinar cell function in the pancreas

PURPOSE OF REVIEW

This review identifies and puts into context the recent articles which have advanced understanding of the functions of pancreatic acinar cells and the mechanisms by which these functions are regulated.

RECENT FINDINGS

Receptors present on acinar cells, particularly those for cholecystokinin and secretin, have been better characterized as to the molecular nature of the ligand-receptor interaction. Other reports have described the potential regulation of acinar cells by GLP-1 and cannabinoids. Intracellular Ca2+ signaling remains at the center of stimulus secretion coupling and its regulation has been further defined. Recent studies have identified specific channels mediating Ca2+ release from intracellular stores and influx across the plasma membrane. Work downstream of intracellular mediators has focused on molecular mechanisms of exocytosis particularly involving small G proteins, SNARE proteins and chaperone molecules. In addition to secretion, recent studies have further defined the regulation of pancreatic growth both in adaptive regulation to diet and hormones in the regeneration that occurs after pancreatic damage. Lineage tracing has been used to show the contribution of different cell types. The importance of specific amino acids as signaling molecules to activate the mTOR pathway is being elucidated.

SUMMARY

Understanding the mechanisms that regulate pancreatic acinar cell function is contributing to knowledge of normal pancreatic function and alterations in disease.

Hydrogen sulfide protects against vascular remodeling from endothelial damage

Remodeling by its very nature implied synthesis and degradation of extracellular matrix (ECM) proteins. Although oxidative stress, matrix metalloproteinase (MMP) and tissue inhibitor of metalloproteinase (TIMP) have been implicated in vascular remodeling, the differential role of MMPs versus TIMPs and oxidative stress in vascular remodeling was unclear. TIMP-3 induced vascular cell apoptosis, therefore, we hypothesized that during vascular injury TIMP-3, MMP-9 and -12 (elastin-degrading MMP) were increased, whereas MMP-2 (constitutive MMP) and TIMP-4 (cardioprotective TIMP) decreased. Because of the potent anti-oxidant, vasorelaxing, anti-hypertensive agent, hydrogen sulfide (H2S) was used to mitigate the vascular remodeling due to the differential expression of MMP and TIMP. Carotid artery injury was created by inserting a PE-10 catheter and rotating several times before pulling out. The insertion hole was sealed. Mice were grouped: wild type (WT), wild-type damaged artery (WTD), WT+NaHS (sodium hydrogen sulfide, precursor of H2S) treatment (30 µmol/L in drinking water/6 weeks) and WTD+NaHS treatment. Carotid arteries were analyzed for oxidative stress and remodeling, by measuring super oxide dismutase-1 (SOD1), p47 (NADPH oxidase subunit), nitrotyrosine, MMPs and TIMPs by in situ immunolabeling and by Western blot analyses. The results suggested robust increase in p47, nitrotyrosine, MMP-9, MMP-12, TIMP-3 and decrease in SOD1 and MMP-2 levels in the injured arteries. The treatment with H2S ameliorated these effects. We concluded that p47, TIMP-3, MMP-9 and -12 were increased where as SOD-1, MMP-2 and TIMP-4 were decreased in the injured arteries. The treatment with H2S mitigated the vascular remodeling by normalizing the levels of redox stress, MMPs and TIMPs.

Potential role of CXCL10 in the induction of cell injury and mitochondrial dysfunction

Chemokines have been known to play a critical role in pathogenesis of chronic pancreatitis and acinar cell death. However, the role played by one of the CXC chemokines: CXCL10 in regulation of acinar cell death has remained unexplored. Hence, this study was designed to assess the role of CXCL10 promoting apoptosis in ex vivo cultured acinar cells. Primary human pancreatic acinar cell cultures were established and exposed to varying doses of CXCL10 for different time intervals. Apoptotic induction was evaluated by both qualitative as well as quantitative analyses. Various mediators of apoptosis were also studied by Western blotting, membrane potential (Psim) and ATP depletion in acinar cells. Analysis of apoptosis via DNA ladder and cell death detection - ELISA demonstrated that CXCL10 induced 3.9-fold apoptosis when administrated at an optimal dose of 0.1 mug of recombinant CXCL10 for 8 h. Quantitative analysis using FACS and dual staining by PI-annexin showed increased apoptosis (48.98 and 53.78% respectively). The involvement of upstream apoptotic regulators like pJNK, p38 and Bax was established on the basis of their increased expression of CXCL10. The change of Psim by 50% was observed in the presence of CXCL10 in treated acinar cells along with enhanced expression of Cytochrome C, apaf-1 and caspase 9/3 activation. In addition, ATP depletion was also noticed in CXCL10 stimulated acinar cells. CXCL10 induces cell death in human cultured pancreatic cells leading to apoptosis and DNA fragmentation via CXCR3 signalling. These signalling mechanisms may play an important role in parenchymal cell loss and injury in pancreatitis.

Role of hydrogen sulfide in hepatic ischemia-reperfusion-induced injury in rats

Hydrogen sulfide (H2S) displays anti-inflammatory and cytoprotective activities as evidenced by the inhibition of myocardial ischemia-reperfusion injury and production of lipid peroxidation. H2S also exerts many physiological or pathological effects on livers. Therefore, we designed the present study to investigate the roles of H2S in hepatic ischemia-reperfusion (HIR)-induced injury in rats by measuring H2S levels, H2S synthesizing activity, and cystathionine gamma-lyase (CSE) messenger RNA (mRNA) expression. We also applied DL-propargyl glycine (PAG) and sodium hydrosulfide (NaHS) to investigate their effects on the severity of liver injury induced by HIR. The levels of H2S, H2S production activity, and CSE mRNA expression in livers were increased by HIR. Administration of NaHS significantly attenuated the severity of liver injury and inhibited the production of lipid peroxidation, serum inflammatory factors [including nitric oxide, tumor necrosis factor alpha (TNF-alpha), interleukin 10, and intercellular cell adhesion molecule 1], cell apoptosis, and apoptosis-related proteins (including caspase-3, Fas, Fas ligand, and TNF-alpha), which were caused or elevated by HIR, whereas PAG aggravated them. However, NaHS or PAG did not show significant effects on the activation of caspase-9, which was also increased by HIR. Although further investigation is required, this study may indicate that H2S plays a protective role in HIR-induced injury.

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.

Effect of hydrogen sulfide on the phosphatidylinositol 3-kinase-protein kinase B pathway and on caerulein-induced cytokine production in isolated mouse pancreatic acinar cells

We have shown earlier that mouse pancreatic acinar cells produce hydrogen sulfide (H(2)S) and play a role in the pathogenesis of acute pancreatitis. It is noteworthy that recent evidence indicates that H(2)S has anti-inflammatory effects. To date, the mechanism by which H(2)S directly reduces inflammation has not been elucidated. In the present study, we hypothesized that H(2)S inhibits the production of proinflammatory cytokines by activation of the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) pathway. Pancreatic acinar cells were treated with the H(2)S donor, sodium hydrogen sulfide (NaHS) (5, 10, and 30 microM). To better understand the effect of H(2)S in inflammation, pancreatic acinar cells were stimulated with caerulein after the addition of NaHS (5, 10, and 30 microM). We observed that H(2)S at the 5 microM concentration down-regulates the activation of NF-kappaB and degradation of IkappaB alpha. However, H(2)S (5 microM) activates PI3K as reflected by AKT phosphorylation. We found that H(2)S-mediated activation of PI3K in caerulein-treated acinar cells correlated with the down-regulation of extracellular signal-regulated kinase 1/2 phosphorylation, whereas phosphorylation of p38 and c-Jun NH(2)-terminal kinase and mitogen-activated protein kinases was unchanged. The PI3K inhibitor LY294002 [2-(4-morpholinyl)-8-phenyl-1(4H)-benzopyran-4-one hydrochloride] abolished the H(2)S-mediated activation of AKT and increases tumor necrosis factor alpha and interleukin 1beta levels in caerulein-treated acinar cells. These findings indicate that the phosphatidylinositol 3-kinase plays a negative role in NaHS-treated pancreatic acinar cells and suggest a role for H(2)S in the PI3K/AKT pathway in acute pancreatitis.

H2S-induced pancreatic acinar cell apoptosis is mediated via JNK and p38 MAP kinase

Treatment of pancreatic acinar cells by hydrogen sulphide has been shown to induce apoptosis. However, a potential role of mitogen-activated protein kinases (MAPKs) in this apoptotic pathway remains unknown. The present study examined the role of MAPKs in H₂S-induced apoptosis in mouse pancreatic acinar cells. Pancreatic acinar cells were treated with 10 μM NaHS (a donor of H₂S) for 3 hrs. For the evaluation of the role of MAPKs, PD98059, SP600125 and SB203580 were used as MAPKs inhibitors for ERK1/2, JNK1/2 and p38 MAPK, respectively. We observed activation of ERK1/2, JNK1/2 and p38 when pancreatic acini were exposed to H₂S. Moreover, H₂S-induced ERK1/2, JNK1/2 and p38 activation were blocked by pre-treatment with their corresponding inhibitor in a dose-dependent manner. H₂S-induced apoptosis led to an increase in caspase 3 activity and this activity was attenuated when caspase 3 inhibitor were used. Also, the cleavage of caspase 3 correlated with that of poly-(ADP-ribose)-polymerase (PARP) cleavage. H₂S treatment induced the release of cytochrome c, smac from mitochondria into the cytoplasm, translocation of Bax into mitochondria and decreased the protein level of Bcl-2. Inhibition of ERK1/2 using PD98059 caused further enhancement of apoptosis as evidenced by annexin V staining, while SP600125 and SB203580 abrogated H₂S-induced apoptosis. Taken together, the data suggest that activation of ERKs promotes cell survival, whereas activation of JNKs and p38 MAP kinase leads to H₂S-induced apoptosis.

A protective role of hydrogen sulfide against oxidative stress in rat gastric mucosal epithelium

We investigated effect of hydrogen sulfide (H(2)S) on oxidative stress-caused cell death in gastric mucosal epithelial cells. In rat normal gastric epithelial RGM1 cells, NaHS, a H(2)S donor, at 1.5mM strongly suppressed hydrogen peroxide (H(2)O(2))-caused cell death, while it slightly augmented the H(2)O(2) toxicity at 0.5-1mM. The protective effect of NaHS was abolished by inhibitors of MEK or JNK, but not of p38 MAP kinase. NaHS at 1.5mM actually phosphorylated ERK and JNK in RGM1 cells. Glibenclamide, an ATP-sensitive K(+) (K(ATP)(+)) channel inhibitor, did not affect the protective effect of NaHS, although mRNAs for K(ATP)(+) channel subunits, Kir6.1 and SUR1, were detected in RGM1 cells. In anesthetized rats, oral administration of NaHS protected against gastric mucosal lesion caused by ischemia-reperfusion. These results suggest that NaHS/H(2)S may protect gastric mucosal epithelial cells against oxidative stress through stimulation of MAP kinase pathways, a therapeutic dose range being very narrow.

Hydrogen sulfide attenuates myocardial ischemia-reperfusion injury by preservation of mitochondrial function

The recent discovery that hydrogen sulfide (H(2)S) is an endogenously produced gaseous second messenger capable of modulating many physiological processes, much like nitric oxide, prompted us to investigate the potential of H(2)S as a cardioprotective agent. In the current study, we demonstrate that the delivery of H(2)S at the time of reperfusion limits infarct size and preserves left ventricular (LV) function in an in vivo model of myocardial ischemia-reperfusion (MI-R). This observed cytoprotection is associated with an inhibition of myocardial inflammation and a preservation of both mitochondrial structure and function after I-R injury. Additionally, we show that modulation of endogenously produced H(2)S by cardiac-specific overexpression of cystathionine gamma-lyase (alpha-MHC-CGL-Tg mouse) significantly limits the extent of injury. These findings demonstrate that H(2)S may be of value in cytoprotection during the evolution of myocardial infarction and that either administration of H(2)S or the modulation of endogenous production may be of clinical benefit in ischemic disorders.

Caspase-8-mediated apoptosis induced by oxidative stress is independent of the intrinsic pathway and dependent on cathepsins

Cell-death programs executed in the pancreas under pathological conditions remain largely undetermined, although the severity of experimental pancreatitis has been found to depend on the ratio of apoptosis to necrosis. We have defined mechanisms by which apoptosis is induced in pancreatic acinar cells by the oxidant stressor menadione. Real-time monitoring of initiator caspase activity showed that caspase-9 (66% of cells) and caspase-8 (15% of cells) were activated within 30 min of menadione administration, but no activation of caspase-2, -10, or -12 was detected. Interestingly, when caspase-9 activation was inhibited, activation of caspase-8 was increased. Half-maximum activation (t(0.5)) of caspase-9 occurred within approximately 2 min and was identified at or in close proximity to mitochondria, whereas t(0.5) for caspase-8 occurred within approximately 26 min of menadione application and was distributed homogeneously throughout cells. Caspase-9 but not caspase-8 activation was blocked completely by the calcium chelator BAPTA or bongkrekic acid, an inhibitor of the mitochondrial permeability transition pore. In contrast, caspase-8 but not caspase-9 activation was blocked by the destruction of lysosomes (preincubation with Gly-Phe beta-naphthylamide, a cathepsin C substrate), loss of lysosomal acidity (bafilomycin A1), or inhibition of cathepsin L or D. Using pepstatin A-BODIPY FL conjugate, we confirmed translocation of cathepsin D out of lysosomes in response to menadione. We conclude that the oxidative stressor menadione induces two independent apoptotic pathways within pancreatic acinar cells: the classical mitochondrial calcium-dependent pathway that is initiated rapidly in the majority of cells, and a slower, caspase-8-mediated pathway that depends on the lysosomal activities of cathepsins and is used when the caspase-9 pathway is disabled.

H2S, Endoplasmic Reticulum Stress, and Apoptosis of Insulin-secreting Beta Cells

Cystathionine gamma-lyase (CSE) is a key enzyme in the trans-sulfuration pathway, which uses L-cysteine to produce hydrogen sulfide (H2S). Functional changes of pancreatic beta cells induced by endogenous H2S have been reported, but the effect of the CSE/H2S system on pancreatic beta cell survival has not been known. In this study, we demonstrate that H2Sat physiologically relevant concentrations induced apoptosis of INS-1E cells, an insulin-secreting beta cell line. Transfection of INS-1E cells with a recombinant defective adenovirus containing the CSE gene (Ad-CSE) resulted in a significant increase in CSE expression and H2S production. Ad-CSE transfection also stimulated apoptosis. The other two end products of CSE-catalyzed enzymatic reaction, ammonium and pyruvate, had no effects on INS-1E cell apoptosis, indicating that overexpression of CSE may stimulate INS-1E cell apoptosis via increased endogenous production of H2S. Both exogenous H2S (100 microM) and Ad-CSE transfection inhibited ERK1/2 but activated p38 MAPK. Interestingly, BiP and CHOP, two indicators of endoplasmic reticulum (ER) stress, were up-regulated in H2S-and CSE-mediated apoptosis in INS-1E cells. After suppressing CHOP mRNA expression, H2S-induced apoptosis of INS-1E cells was significantly decreased. Inhibition of p38 MAPK, but not of ERK1/2, inhibited the expression of BiP and CHOP and decreased H2S-stimulated apoptosis, suggesting that p38 MAPK activation functions upstream of ER stress to initiate H2S-induced apoptosis. It is concluded that H2S induces apoptosis of insulin-secreting beta cells by enhancing ER stress via p38 MAPK activation. Our findings may help unmask a novel role of CSE/H2S system in regulating pancreatic functions under physiological condition and in diabetes.

Hydrogen sulfide induces the synthesis of proinflammatory cytokines in human monocyte cell line U937 via the ERK-NF-κB pathway

Hydrogen sulfide (H2S) is now considered an endogenous, gaseous mediator, which has been demonstrated to be involved in many inflammatory states. However, the mechanism of its proinflammatory function remains unknown. In the present study, we used IFN-gamma-primed human monocytic cell line U937 to investigate the effects of H2S in vitro on monocytes. We found that treatment with the H2S donor, sodium hydrosulfide, led to significant increases in the mRNA expression and protein production of TNF-alpha, IL-1beta, and IL-6 in U937 cells. H2S-triggered monocyte activation was confirmed further by the up-regulation of CD11b expression on the cell surface. We also observed that H2S could induce a rapid degradation of IkappaBalpha and subsequent activation of NF-kappaB p65, and this effect was attenuated by Bay 11-7082, a specific inhibitor of NF-kappaB. Furthermore, pretreatment of cells with Bay 11-7082 substantially inhibited the secretion of TNF-alpha, IL-1beta, and IL-6 induced by H2S. We also found that H2S stimulated the phosphorylation and activation of ERK1/2, but not of p38 MAPK and JNK, and pretreatment with PD98059, a selective MEK1 antagonist, could inhibit H2S-induced NF-kappaB activation markedly. Together, our findings suggest for the first time that H2S stimulates the activation of human monocytes with the generation of proinflammatory cytokines, and this response is, at least partially, through the ERK-NF-kappaB signaling pathway.

Hydrogen sulfide‐induces DNA damage and changes in apoptotic gene expression in human lung fibroblast cells

Hydrogen sulfide (H2S) has been shown previously to exert proapoptotic activity. However, the mechanism(s) by which H2S affects cell growth and function have not been addressed adequately. In this study, cultured human lung fibroblasts were treated with the H2S donor NaHS (10-75 microM; 12-48 h). NaHS caused a concentration-dependent increase in micronuclei formation (indicating DNA damage) and cell cycle arrest (G1 phase). NaHS increased expression of ku 70 and ku 80 but did not affect the expression of other DNA repair proteins such as proliferating cell nuclear antigen (PCNA) or replication protein A (rNase protection assay). NaHS treatment also resulted in stabilization of p53 coupled with induction of downstream proteins such as p21, Bax, and cytochrome c, as well as translocation of Bax from the cytosol to the mitochondria and release of cytochrome c from mitochondria. NaHS did not up-regulate cell levels of the antiapoptotic protein, Bcl-2. We propose that the genotoxic action of H2S propels the cell toward apoptotic death triggered initially by stabilization of p53 and subsequently involving a cascade of downstream products. These results are of significance as they uncover a hitherto unknown and very fundamental role for H2S in determining cell fate.