Hydrogen sulfide attenuates hyperhomocysteinemia-induced cardiomyocytic endoplasmic reticulum stress in rats

Homocysteine in renovascular complications: hydrogen sulfide is a modulator and plausible anaerobic ATP generator

Homocysteine (Hcy) is a non-protein amino acid derived from dietary methionine. High levels of Hcy, known as hyperhomocysteinemia (HHcy) is known to cause vascular complications. In the mammalian tissue, Hcy is metabolized by transsulfuration enzymes to produce hydrogen sulfide (H2S). H2S, a pungent smelling gas was previously known for its toxic effects in the central nervous system, recent studies however has revealed protective effects in a variety of diseases including hypertension, diabetes, inflammation, atherosclerosis, and renal disease progression and failure. Interestingly, under stress conditions including hypoxia, H2S can reduce metabolic demand and also act as a substrate for ATP production. This review highlights some of the recent advances in H2S research as a potential therapeutic agent targeting renovascular diseases associated with HHcy.

Hydrogen sulfide inhibits homocysteine-induced endoplasmic reticulum stress and neuronal apoptosis in rat hippocampus via upregulation of the BDNF-TrkB pathway

AIM

Homocysteine (Hcy) can elicit neuronal cell death, and hyperhomocysteinemia is a strong independent risk factor for Alzheimer's disease. The aim of this study was to examine the effects of hydrogen sulfide (H2S) on Hcy-induced endoplasmic reticulum (ER) stress and neuronal apoptosis in rat hippocampus.

METHODS

Adult male SD rats were intracerebroventricularly (icv) injected with Hcy (0.6 μmol/d) for 7 d. Before Hcy injection, the rats were treated with NaHS (30 or 100 μmol·kg(-1)·d(-1), ip) and/or k252a (1 μg/d, icv) for 2 d. The apoptotic neurons were detected in hippocampal coronal slices with TUNEL staining. The expression of glucose regulated protein 78 (GRP78), C/EBP homologous protein (CHOP), cleaved caspase-12, and BDNF in the hippocampus were examined using Western blotting assays. The generation of H2S in the hippocampus was measured with the NNDPD method.

RESULTS

Hcy markedly inhibited the production of endogenous H2S and increased apoptotic neurons in the hippocampus. Furthermore, Hcy induced ER stress responses in the hippocampus, as indicated by the upregulation of GRP78, CHOP, and cleaved caspase-12. Treatment with the H2S donor NaHS increased the endogenous H2S production and BDNF expression in a dose-dependent manner, and significantly reduced Hcy-induced neuronal apoptosis and ER stress responses in the hippocampus. Treatment with k252a, a specific inhibitor of TrkB (the receptor of BDNF), abolished the protective effects of NaHS against Hcy-induced ER stress in the hippocampus.

CONCLUSION

H2S attenuates ER stress and neuronal apoptosis in the hippocampus of Hcy-treated rats via upregulating the BDNF-TrkB pathway.

Exogenous hydrogen sulfide alleviates high glucose-induced cardiotoxicity via inhibition of leptin signaling in H9c2 cells

Hydrogen sulfide (H₂S) protects cardiomyoblasts against high glucose (HG)-induced injury by inhibiting the activation of p38 mitogen-activated protein kinase (MAPK). This study aims to determine whether the leptin-p38 MAPK pathway is involved in HG-induced injury and whether exogenous H2S prevents the HG-induced insult through inhibition of the leptin-p38 MAPK pathway in H9c2 cells. H9c2 cells were treated with 35 mM glucose (HG) for 24 h to establish a HG-induced cardiomyocyte injury model. Cell viability; mitochondrial membrane potential (ΔΨ m); apoptosis; reactive oxygen species (ROS) level; and leptin, leptin receptor, and p38 MAPK expression level were measured by the methods indicated. The results showed pretreatment of H9c2 cells with NaHS before exposure to HG led to an increase in cell viability, decrease in apoptotic cells, ROS generation, and a loss of ΔΨ m. Exposure of H9c2 cells to 35 mM glucose for 24 h significantly upregulated the expression levels of leptin and leptin receptors. The increased expression levels of leptin and leptin receptors were markedly attenuated by pretreatment with 400 μM NaHS. In addition, the HG-induced increase in phosphorylated (p) p38 MAPK expression was ameliorated by pretreatment with 50 ng/ml leptin antagonist. In conclusion, the present study has demonstrated for the first time that the leptin-p38 MAPK pathway contributes to the HG-induced injury in H9c2 cells and that exogenous H₂S protects H9c2 cells against HG-induced injury at least in part by inhibiting the activation of leptin-p38 MAPK pathway.

Hydrogen sulfide inhibits formaldehyde-induced endoplasmic reticulum stress in PC12 cells by upregulation of SIRT-1

Background

Formaldehyde (FA), a well-known environmental pollutant, has been classified as a neurotoxic molecule. Our recent data demonstrate that hydrogen sulfide (H₂S), the third gaseous transmitter, has a protective effect on the neurotoxicity of FA. However, the exact mechanisms underlying this protection remain largely unknown. Endoplasmic reticulum (ER) stress has been implicated in the neurotoxicity of FA. Silent mating type information regulator 2 homolog 1 (SIRT-1), a histone deacetylases, has various biological activities, including the extension of lifespan, the modulation of ER stress, and the neuroprotective action.

Objective

We hypothesize that the protection of H₂S against FA-induced neurotoxicity involves in inhibiting ER stress by upregulation of SIRT-1. The present study attempted to investigate the protective effect of H₂S on FA-induced ER stress in PC12 cells and the contribution of SIRT-1 to the protection of H₂S against FA-induced injuries, including ER stress, cytotoxicity and apoptosis.

Principal Findings

We found that exogenous application of sodium hydrosulfide (NaHS; an H₂S donor) significantly attenuated FA-induced ER stress responses, including the upregulated levels of glucose-regulated protein 78, C/EBP homologous protein, and cleaved caspase-12 expression. We showed that NaHS upregulates the expression of SIRT-1 in PC12 cells. Moreover, the protective effects of H₂S on FA-elicited ER stress, cytotoxicity and apoptosis were reversed by Sirtinol, a specific inhibitor of SIRT-1.

Conclusion/Significance

These data indicate that H₂S exerts its protection against the neurotoxicity of FA through overcoming ER stress via upregulation of SIRT-1. Our findings provide novel insights into the protective mechanisms of H₂S against FA-induced neurotoxicity.

Hydrogen sulfide [corrected] increases survival during sepsis: protective effect of CHOP inhibition

Sepsis is a major cause of mortality, and dysregulation of the immune response plays a central role in this syndrome. H2S, a recently discovered gaso-transmitter, is endogenously generated by many cell types, regulating a number of physiologic processes and pathophysiologic conditions. We report that H2S increased survival after experimental sepsis induced by cecal ligation and puncture (CLP) in mice. Exogenous H2S decreased the systemic inflammatory response, reduced apoptosis in the spleen, and accelerated bacterial eradication. We found that C/EBP homologous protein 10 (CHOP), a mediator of the endoplasmic reticulum stress response, was elevated in several organs after CLP, and its expression was inhibited by H2S treatment. Using CHOP-knockout (KO) mice, we demonstrated for the first time, to our knowledge, that genetic deletion of Chop increased survival after LPS injection or CLP. CHOP-KO mice displayed diminished splenic caspase-3 activation and apoptosis, decreased cytokine production, and augmented bacterial clearance. Furthermore, septic CHOP-KO mice treated with H2S showed no additive survival benefit compared with septic CHOP-KO mice. Finally, we showed that H2S inhibited CHOP expression in macrophages by a mechanism involving Nrf2 activation. In conclusion, our findings show a protective effect of H2S treatment afforded, at least partially, by inhibition of CHOP expression. The data reveal a major negative role for the transcription factor CHOP in overall survival during sepsis and suggest a new target for clinical intervention, as well potential strategies for treatment.

Disturbance of endogenous hydrogen sulfide generation and endoplasmic reticulum stress in hippocampus are involved in homocysteine-induced defect in learning and memory of rats

Homocysteine (Hcy) is a risk factor for Alzheimer's disease (AD). Hydrogen sulfide (H2S) acts as an endogenous neuromodulator and neuroprotectant. It has been shown that endoplasmic reticulum (ER) stress is involved in the pathological mechanisms of the learning and memory dysfunctions and that H2S exerts its neuroprotective role via suppressing ER stress. In the present work, we explored the effects of intracerebroventricular injection of Hcy on the formation of learning and memory, the generation of endogenous H2S, and the expression of ER stress in the hippocampus of rats. We found that intracerebroventricular injection of Hcy in rats leads to learning and memory dysfunctions in the Morris water maze and novel of object recognition test and decreases in the expression of cystathionine-β-synthase, the major enzyme responsible for endogenous H2S generation, and the generation of endogenous H2S in the hippocampus of rats. We also showed that exposure of Hcy could up-regulate the expressions of glucose-regulated protein 78 (GRP78), CHOP, and cleaved caspase-12, which are the major mark proteins of ER stress, in the hippocampus of rats. Taken together, these results suggest that the disturbance of hippocampal endogenous H2S generation and the increase in ER stress in the hippocampus are related to Hcy-induced defect in learning and memory.

Sodium hydrosulfide alleviates lung inflammation and cell apoptosis following resuscitated hemorrhagic shock in rats

AIM

To investigate the protective effects of hydrogen sulfide (H2S) against inflammation, oxidative stress and apoptosis in a rat model of resuscitated hemorrhagic shock.

METHODS

Hemorrhagic shock was induced in adult male SD rats by drawing blood from the femoral artery for 10 min. The mean arterial pressure was maintained at 35-40 mmHg for 1.5 h. After resuscitation the animals were observed for 200 min, and then killed. The lungs were harvested and bronchoalveolar lavage fluid was prepared. The levels of relevant proteins were examined using Western blotting and immunohistochemical analyses. NaHS (28 μmol/kg, ip) was injected before the resuscitation.

RESULTS

Resuscitated hemorrhagic shock induced lung inflammatory responses and significantly increased the levels of inflammatory cytokines IL-6, TNF-α, and HMGB1 in bronchoalveolar lavage fluid. Furthermore, resuscitated hemorrhagic shock caused marked oxidative stress in lung tissue as shown by significant increases in the production of reactive oxygen species H2O2 and ·OH, the translocation of Nrf2, an important regulator of antioxidant expression, into nucleus, and the decrease of thioredoxin 1 expression. Moreover, resuscitated hemorrhagic shock markedly increased the expression of death receptor Fas and Fas-ligand and the number apoptotic cells in lung tissue, as well as the expression of pro-apoptotic proteins FADD, active-caspase 3, active-caspase 8, Bax, and decreased the expression of Bcl-2. Injection with NaHS significantly attenuated these pathophysiological abnormalities induced by the resuscitated hemorrhagic shock.

CONCLUSION

NaHS administration protects rat lungs against inflammatory responses induced by resuscitated hemorrhagic shock via suppressing oxidative stress and the Fas/FasL apoptotic signaling pathway.

Sulfur dioxide preconditioning increases antioxidative capacity in rat with myocardial ischemia reperfusion (I/R) injury

BACKGROUND

The study was designed to explore if sulfur dioxide (SO2) preconditioning increased antioxidative capacity in rat with myocardial ischemia reperfusion (I/R) injury.

METHODS

The myocardial I/R model was made by left coronary artery ligation for 30min and reperfusion for 120min in rats. Myocardial infarct size and plasma lactate dehydrogenase (LDH) and creatine kinase (CK) activities, plasma superoxide dismutase (SOD), malondialdehyde (MDA), glutathione peroxidase (GSH-Px) and glutathione (GSH) changes were detected for the rats. The contents of myocardial hydrogen sulfide (H2S) and nitric oxide (NO) were measured. Myocardial protein expressions of SOD1, SOD2, cystathionine γ-lyase (CSE) and iNOS were tested using Western blot.

RESULTS

Myocardial infarction developed and plasma CK and LDH activities were significantly increased in I/R group compared with those in control group, but SO2 preconditioning significantly reduced myocardial infarct size, and plasma CK and LDH activities. SO2 preconditioning successfully increased plasma SOD, GSH and GSH-Px levels and myocardial SOD1 protein expression, but decreased MDA level in rats of I/R group. Compared with controls, the myocardial H2S level and CSE expression were decreased after I/R, but myocardial NO level and iNOS expression were increased. With the treatment of SO2, myocardial H2S level and CSE expression were increased, but myocardial NO level and iNOS expression were decreased compared with those in I/R group.

CONCLUSIONS

SO2 preconditioning could significantly reduce I/R-induced myocardial injury in vivo in association with increased myocardial antioxidative capacity, upregulated myocardial H2S/CSE pathway but downregulated NO/iNOS pathway.

The PI3K/Akt pathway mediates the protection of SO(2) preconditioning against myocardial ischemia/reperfusion injury in rats

AIM

To explore the mechanisms underlying the protection by SO2 preconditioning against rat myocardial ischemia/reperfusion (I/R) injury.

METHODS

Male Wistar rats underwent 30-min left coronary artery ligation followed by 120-min reperfusion. An SO2 donor (1 μmol/kg) was intravenously injected 10 min before the ischemia, while LY294002 (0.3 mg/kg) was intravenously injected 30 min before the ischemia. Plasma activities of LDH and CK were measured with an automatic enzyme analyzer. Myocardial infarct size was detected using Evans-TTC method. The activities of caspase-3 and -9 in myocardium were assayed using a commercial kit, and the levels of p-Akt, Akt, PI3K and p-PI3K were examined with Western blotting.

RESULTS

Pretreatment with SO2 significantly reduced the myocardial infarct size and plasma LDH and CK activities, as well as myocardial caspase-3 and -9 activities in the rats. Furthermore, the pretreatment significantly increased the expression levels of myocardial p-Akt and p-PI3K p85. Administration of the PI3K inhibitor LY294002 blocked all the effects induced by SO2 pretreatment.

CONCLUSION

The results suggest that the PI3K/Akt pathway mediates the protective effects of SO2 preconditioning against myocardial I/R injury in rats.

Hyperhomocysteinemia promotes insulin resistance by inducing endoplasmic reticulum stress in adipose tissue

Type 2 diabetes is a chronic inflammatory metabolic disease, the key point being insulin resistance. Endoplasmic reticulum (ER) stress plays a critical role in the pathogenesis of type 2 diabetes. Previously, we found that hyperhomocysteinemia (HHcy) induced insulin resistance in adipose tissue. Here, we hypothesized that HHcy induces ER stress, which in turn promotes insulin resistance. In the present study, the direct effect of Hcy on adipose ER stress was investigated by the use of primary rat adipocytes in vitro and mice with HHcy in vivo. The mechanism and the effect of G protein-coupled receptor 120 (GPR120) were also investigated. We found that phosphorylation or expression of variant ER stress markers was elevated in adipose tissue of HHcy mice. HHcy activated c-Jun N-terminal kinase (JNK), the downstream signal of ER stress in adipose tissue, and activated JNK participated in insulin resistance by inhibiting Akt activation. Furthermore, JNK activated c-Jun and p65, which in turn triggered the transcription of proinflammatory cytokines. Both in vivo and in vitro assays revealed that Hcy-promoted macrophage infiltration aggravated ER stress in adipose tissue. Chemical chaperones PBA and TUDCA could reverse Hcy-induced inflammation and restore insulin-stimulated glucose uptake and Akt activation. Activation of GPR120 reversed Hcy-induced JNK activation and prevented inflammation but not ER stress. Therefore, HHcy inhibited insulin sensitivity in adipose tissue by inducing ER stress, activating JNK to promote proinflammatory cytokine production and facilitating macrophage infiltration. These findings reveal a new mechanism of HHcy in the pathogenesis of insulin resistance.

Hydrogen sulfide attenuates doxorubicin-induced cardiotoxicity by inhibition of the p38 MAPK pathway in H9c2 cells

We previously demonstrated the protective effect of hydrogen sulfide (H2S) against doxorubicin (DOX)-induced cardiotoxicity through inhibition of endoplasmic reticulum stress. The aim of the present study was to explore the role of p38 mitogen-activated protein kinase (MAPK) in DOX-induced cardiotoxicity and ascertain whether exogenous H2S protects DOX-induced injury by inhibiting p38 MAPK in cardiomyoblasts (H9c2). We observed that exposure of H9c2 cells to 5 µM DOX not only markedly induced injuries, including cytotoxicity, apoptosis, overproduction of reactive oxygen species (ROS) and dissipation of mitochondrial membrane potential (MMP), but also enhanced the expression level of phosphorylated (p)-p38 MAPK. The DOX-induced increase in expression of p-p38 MAPK was significantly attenuated by pretreatment of H9c2 cells with either 400 µM sodium hydrogen sulfide (NaHS) (a donor of H2S) or 1,000 µM N-acetyl-L-cysteine (NAC, an ROS scavenger) prior to exposure to DOX. Pretreatment with either 400 µM NaHS or 3 µM SB203580, a selective inhibitor of p38 MAPK, ameliorated DOX-induced cardiomyocyte injuries, as evidenced by an increase in cell viability, and decreases in the number of apoptotic cells, ROS generation as well as dissipation of MMP. In conclusion, the findings of the present study demonstrated that the activation of p38 MAPK contributes to DOX-induced injuries, including cytotoxicity, apoptosis, mitochondrial damage and oxidative stress in H9c2 cells. We also provide novel evidence that exogenous H2S protects H9c2 cells against DOX-induced cardiotoxicity by inhibition of the p38 MAPK pathway.

An exogenous hydrogen sulphide donor, NaHS, inhibits the nuclear factor κB inhibitor kinase/nuclear factor κb inhibitor/nuclear factor-κB signaling pathway and exerts cardioprotective effects in a rat hemorrhagic shock model

Hemorrhagic shock (HS) is a common condition and leading cause of death in trauma patients universally. Severe inflammatory responses during HS finally lead to multiple-organ failure. Hydrogen sulphide (H₂S) is increasingly recognized as an important signaling molecule with various protective effects. In the present study, we investigated the antiinflammatory and cardioprotective effects of an exogenous H₂S donor, sodium hydrosulfide (NaHS), in an HS rat model. Male Sprague-Dawley rats were randomly divided into the sham-operated, sham-operated treated with NaHS (28 µmol/kg, intraperitoneally (i.p.)), HS, and HS treated with NaHS (28 µmol/kg, i.p.) groups. The HS groups were subjected to mimicked HS for 1 h and then treated with NaHS or left untreated. The rats were then resuscitated with Ringer lactate solution for 1 h. Myocardial enzymes and inflammatory cytokines were evaluated. Morphologic changes in cardiac tissue and ultrastructural injury were also analyzed. HS resulted in significant hemodynamic deterioration and increased myocardial enzyme and inflammatory cytokine levels. Intraperitoneal administration of NaHS significantly prevented hemodynamic deterioration and decreased the elevation of myocardial enzymes. NaHS also inhibited the nuclear factor κB inhibitor kinase (IKK)/nuclear factor κB inhibitor (IκB)/nuclear factor κB (NF-κB) signaling pathway. The results suggest that NaHS exerts cardioprotective effects against HS. The protective effects of NaHS may occur via down-regulation of the IKK/IκB/NF-κB signaling pathway.

Hydrogen sulfide in the pathogenesis of atherosclerosis and its therapeutic potential

Hydrogen sulfide (H(2)S) was the third gaseous transmitter to be discovered, along with nitric oxide and carbon monoxide, and has been proposed to be involved in numerous physiological processes and pathology of various diseases. Hyperhomocysteinemia is an independent risk factor for cardiovascular disease, including atherosclerosis. Atherosclerosis is characterized by multiple key events including endothelial dysfunction, monocyte infiltration and their differentiation into macrophages, conversion of lesion-resident macrophages into foam cells, and smooth muscle cell proliferation. Increasing evidence has indicated that H(2)S plays a potentially significant role in all of these biological processes and that malfunction of H(2)S homeostasis may contribute to the pathogenesis of atherosclerosis. Experiments have demonstrated that H(2)S supplementation ameliorated many of these atherogenic processes and hence, such supplementation potentially may prove to be of therapeutic benefit in the prevention or treatment of atherosclerosis. H(2)S levels may be induced by the administration of H(2)S or H(2)S donors, or alternatively be reduced by the administration of specific cystathionine β-synthase or cystathionine γ-lyase inhibitors. However, issues remain with the potential use of currently available H(2)S-modulating agents in a clinical setting. This review will provide a description of the current literature on the involvement of H(2)S in these key aspects of vascular biology that contribute to the development of atherosclerosis, as well as the therapeutic potential of currently available H(2)S-modulating agents.

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.

Hydrogen sulfide in the mammalian cardiovascular system

For more than a century, hydrogen sulfide (H(2)S) has been regarded as a toxic gas. This review surveys the growing recognition of the role of H(2)S as an endogenous signaling molecule in mammals, with emphasis on its physiological and pathological pathways in the cardiovascular system. In biological fluids, H(2)S gas is a weak acid that exists as about 15% H(2)S, 85% HS(-), and a trace of S(2-). Here, we use "H(2)S" to refer to this mixture. H(2)S has been found to influence heart contractile functions and may serve as a cardioprotectant for treating ischemic heart diseases and heart failure. Alterations of the endogenous H(2)S level have been found in animal models with various pathological conditions such as myocardial ischemia, spontaneous hypertension, and hypoxic pulmonary hypertension. In the vascular system, H(2)S exerts biphasic regulation of a vascular tone with varying effects based on its concentration and in the presence of nitric oxide. Over the past decade, several H(2)S-releasing compounds (NaHS, Na(2)S, GYY4137, etc.) have been utilized to test the effect of exogenous H(2)S under different physiological and pathological situations in vivo and in vitro. H(2)S has been found to promote angiogenesis and to protect against atherosclerosis and hypertension, while excess H(2)S may promote inflammation in septic or hemorrhagic shock. H(2)S-releasing compounds and inhibitors of H(2)S synthesis hold promise in alleviating specific disease conditions. This comprehensive review covers in detail the effects of H(2)S on the cardiovascular system, especially in disease situations, and also the various underlying mechanisms.

Hydrogen sulfide protects SH-SY5Y cells against 6-hydroxydopamine-induced endoplasmic reticulum stress

Endoplasmic reticulum (ER) stress has been implicated in several neurodegenerative diseases, including Parkinson's disease. The present study attempted to investigate the effect of hydrogen sulfide (H(2)S) on 6-hydroxydopamine (6-OHDA)-induced ER stress in SH-SY5Y cells. We found in the present study that exogenous application of sodium hydrosulfide (NaHS; an H(2)S donor, 100 μM) significantly attenuated 6-OHDA (50 μM)-induced cell death. NaHS also reversed the upregulation of cleaved poly(ADP-ribose) polymerase and caspase 9 in 6-OHDA-treated cells. Consistent with its cytoprotective effects, NaHS markedly reduced 6-OHDA induced-ER stress responses, including the upregulated levels of eukaryotic initiation factor-2α phosphorylation, glucose-regulated protein 78, and C/EBP homologous protein expression. The protective effect of H(2)S on ER stress was attenuated by blockade of Akt activity with an Akt inhibitor or inhibition of heat shock protein (Hsp)90 with geldanamycin but not by suppression of ERK1/2 with PD-98059. Blockade of Akt also significantly decreased the protein abundance of Hsp90 in SH-SY5Y cells. Moreover, overexpression of cystathionine β-synthase (a main H(2)S-synthesizing enzyme in the brain) elevated the Hsp90 protein level and suppressed 6-OHDA-induced ER stress. In conclusion, the protective effect of H(2)S against 6-OHDA-induced ER stress injury in SH-SY5Y cells involves the Akt-Hsp90 pathway.

Hydrogen sulfide protects H9c2 cells against doxorubicin-induced cardiotoxicity through inhibition of endoplasmic reticulum stress

The roles of hydrogen sulfide (H(2)S) and endoplasmic reticulum (ER) stress in doxorubicin (DOX)-induced cardiotoxicity are still unclear. This study aimed to dissect the hypothesis that H(2)S could protect H9c2 cells against DOX-induced cardiotoxicity by inhibiting ER stress. Our results showed that exposure of H9c2 cells to DOX significantly inhibited the expression and activity of cystathionine-γ-lyase (CSE), a synthetase of H(2)S, accompanied by the decreased cell viability and the increased reactive oxygen species (ROS) accumulation. In addition, exposure of cells to H(2)O(2) (an exogenous ROS) mimicked the inhibitory effect of DOX on the expression and activity of CSE. Pretreatment with N-acetyl-L: -cysteine (NAC) (a ROS scavenger) attenuated intracellular ROS accumulation, cytotoxicity, and the inhibition of expression and activity of CSE induced by DOX. Notably, the ER stress-related proteins, including glucose-regulated protein 78 (GRP78) and C/EBP homologous protein (CHOP) were obviously upregulated in DOX-treated H9c2 cells. Pretreatment with sodium hydrosulfide (NaHS, a H(2)S donor) before DOX exposure markedly suppressed DOX-induced overexpressions of GRP78 and CHOP, cytotoxicity and oxidative stress. In conclusion, we have demonstrated that ROS-mediated inhibition of CSE is involved in DOX-induced cytotoxicity in H9c2 cells, and that exogenous H(2)S can confer protection against DOX-induced cardiotoxicity partly through inhibition of ER stress.

RETRACTED: Thapsigargin triggers cardiac contractile dysfunction via NADPH oxidase-mediated mitochondrial dysfunction: Role of Akt dephosphorylation

ER stress triggers myocardial contractile dysfunction although the underlying mechanism is still elusive. Given that NADPH oxidase was recently implicated in ER stress-induced tissue injury, this study was designed to examine the role of NADPH oxidase in ER stress-induced cardiac mechanical defects and the impact of Akt activation on ER stress-induced cardiac anomalies. Wild-type and transgenic mice with cardiac-specific overexpression of an active mutant of Akt (MyAkt) were subjected to the ER stress inducer thapsigargin (1 and 3mg/kg, ip, for 48h). Thapsigargin compromised echocardiographic parameters, including elevating LVESD and reducing fractional shortening; suppressed cardiomyocyte contractile function, intracellular Ca(2+) handling, and cell survival; and enhanced carbonyl formation, apoptosis, superoxide production, NADPH oxidase expression, and mitochondrial damage. Interestingly, these anomalies were attenuated or mitigated by chronic Akt activation. Treatment with thapsigargin also dephosphorylated Akt and its downstream signal GSK3β (leading to activation of GSK3β), the effect of which was abrogated in MyAkt hearts. Knockdown of the cytosolic subunit of NADPH oxidase, p47(phox), using siRNA abrogated thapsigargin-induced apoptosis and cell death in H9C2 myoblasts. In vitro exposure to thapsigargin induced murine cardiomyocyte dysfunction reminiscent of the in vivo setting, the effects of which were ablated by the NADPH oxidase inhibitor apocynin and the mitochondrial Ca(2+) uptake inhibitor Ru360. In addition, apocynin abrogated thapsigargin-induced loss of mitochondrial membrane potential and permeability transition pore opening, similar to chronic Akt activation. In summary, these data suggest that ER stress interrupts cardiac contractile and intracellular Ca(2+) homeostasis, cell survival, and mitochondrial integrity through an Akt dephosphorylation- and NADPH oxidase-dependent mechanism.

H2S-Induced sulfhydration of the phosphatase PTP1B and its role in the endoplasmic reticulum stress response

Although originally considered toxic, hydrogen sulfide (H(2)S) has been implicated in mediating various biological processes. Nevertheless, its cellular targets and mode of action are not well understood. Protein tyrosine phosphatases (PTPs), which regulate numerous signal transduction pathways, use an essential cysteine residue at the active site, which is characterized by a low pK(a) and is susceptible to reversible oxidation. Here, we report that PTP1B was reversibly inactivated by H(2)S, in vitro and in cells, through sulfhydration of the active-site cysteine residue. Unlike oxidized PTP1B, the sulfhydrated enzyme was preferentially reduced in vitro by thioredoxin, compared to glutathione or dithiothreitol. Sulfhydration of PTP1B in cells required the presence of cystathionine γ-lyase (CSE), a critical enzyme in H(2)S production, and resulted in inhibition of phosphatase activity. Suppression of CSE decreased H(2)S production and decreased the phosphorylation of tyrosine-619 in PERK [protein kinase-like endoplasmic reticulum (ER) kinase], thus reducing its activation in response to ER stress. PERK, which phosphorylates the eukaryotic translational initiation factor 2, leading to attenuation of protein translation, was a direct substrate of PTP1B. In addition, CSE knockdown led to activation of the nonreceptor tyrosine kinase SRC, previously shown to be mediated by PTP1B. These effects of suppressing H(2)S production on the response to ER stress were abrogated by a small-molecule inhibitor of PTP1B. Together, these data define a signaling function for H(2)S in inhibiting PTP1B activity and thereby promoting PERK activity during the response to ER stress.

Endoplasmic reticulum stress and diabetic cardiomyopathy

The endoplasmic reticulum (ER) is an organelle entrusted with lipid synthesis, calcium homeostasis, protein folding, and maturation. Perturbation of ER-associated functions results in an evolutionarily conserved cell stress response, the unfolded protein response (UPR) that is also called ER stress. ER stress is aimed initially at compensating for damage but can eventually trigger cell death if ER stress is excessive or prolonged. Now the ER stress has been associated with numerous diseases. For instance, our recent studies have demonstrated the important role of ER stress in diabetes-induced cardiac cell death. It is known that apoptosis has been considered to play a critical role in diabetic cardiomyopathy. Therefore, this paper will summarize the information from the literature and our own studies to focus on the pathological role of ER stress in the development of diabetic cardiomyopathy. Improved understanding of the molecular mechanisms underlying UPR activation and ER-initiated apoptosis in diabetic cardiomyopathy will provide us with new targets for drug discovery and therapeutic intervention.

Activation of Akt rescues endoplasmic reticulum stress-impaired murine cardiac contractile function via glycogen synthase kinase-3β-mediated suppression of mitochondrial permeation pore opening

AIMS

The present study was designed to examine the impact of chronic Akt activation on endoplasmic reticulum (ER) stress-induced cardiac mechanical anomalies, if any, and the underlying mechanism involved.

RESULTS

Wild-type and transgenic mice with cardiac-specific overexpression of the active mutant of Akt (Myr-Akt) were subjected to the ER stress inducer tunicamycin (1 or 3 mg/kg). ER stress led to compromised echocardiographic (elevated left ventricular end-systolic diameter and reduced fractional shortening) and cardiomyocyte contractile function, intracellular Ca(2+) mishandling, and cell survival in wild-type mice associated with mitochondrial damage. In vitro ER stress induction in murine cardiomyocytes upregulated the ER stress proteins Gadd153, GRP78, and phospho-eIF2α, and promoted reactive oxygen species production, carbonyl formation, apoptosis, mitochondrial membrane potential loss, and mitochondrial permeation pore (mPTP) opening associated with overtly impaired cardiomyocyte contractile and intracellular Ca(2+) properties. Interestingly, these anomalies were mitigated by chronic Akt activation or the ER chaperon tauroursodeoxycholic acid (TUDCA). Treatment with tunicamycin also dephosphorylated Akt and its downstream signal glycogen synthase kinase 3β (GSK3β) (leading to activation of GSK3β), the effect of which was abrogated by Akt activation and TUDCA. The ER stress-induced cardiomyocyte contractile and mitochondrial anomalies were obliterated by the mPTP inhibitor cyclosporin A, GSK3β inhibitor SB216763, and ER stress inhibitor TUDCA.

INNOVATION

This research reported the direct relationship between ER stress and cardiomyocyte contractile and mitochondrial anomalies for the first time.

CONCLUSION

Taken together, these data suggest that ER stress may compromise cardiac contractile and intracellular Ca(2+) properties, possibly through the Akt/GSK3β-dependent impairment of mitochondrial integrity.

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.

Regulatory effects of sulfur dioxide on the development of atherosclerotic lesions and vascular hydrogen sulfide in atherosclerotic rats

OBJECTIVE

This study was designed to examine the effect of sulfur dioxide (SO(2)) on atherosclerotic progression and endogenous vascular hydrogen sulfide (H(2)S) in rats with atherosclerosis (AS).

METHODS

Twenty-eight male rats were randomly divided into control, AS and AS+SO(2) groups. Rats were given a single dose of vitamin D(3) and fed a high-cholesterol diet for 8 weeks to induce AS. Plasma lipids, aortic ultrastructure, and atherosclerotic lesions were detected at the termination of experiment. Plasma and aortic SO(2) were measured using high-performance liquid chromatography, and aspartate aminotransferase (AAT) 1 and AAT2 mRNAs were detected by real-time PCR. Plasma and aortic H(2)S levels were determined with a sulfide-sensitive electrode. Cystathionine-γ-lyase (CSE) mRNA and protein expression was detected. Plasma glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) activities, malondialdehyde (MDA) and nitric oxide (NO) contents, inducible NO synthase (iNOS) and eNOS activities, and aortic SOD1 and SOD2 expressions were detected.

RESULTS

Marked atherosclerotic lesions with elevated levels of TC and LDL-C were observed in AS rats. While, there were decreased plasma SO(2) levels and aortic SO(2) production, with a reduced aortic AAT activity in atherosclerotic rats. Plasma GSH-Px and SOD activities were decreased but MDA level increased. Plasma NO content and iNOS activity were also increased. SO(2) donor, however, significantly decreased the atherosclerotic lesions with an increased aortic H(2)S/CSE pathway. It elevated plasma GSH-Px and SOD activities, reduced plasma MDA level, and increased NO/NOS pathway.

CONCLUSIONS

SO(2) has a marked anti-atherogenic effect with an increase in endogenous H(2)S production in rats with AS.

Cardioprotective effects of hydrogen sulfide

The gaseous mediator hydrogen sulfide (H(2)S) is synthesized mainly by cystathionine γ-lyase in the heart and plays a role in the regulation of cardiovascular homeostasis. Here we first overview the state of the art in the literature on the cardioprotective effects of H(2)S in various models of cardiac injury. Subsequently, we present original data showing the beneficial effects of parenteral administration of a donor of H(2)S on myocardial and endothelial function during reperfusion in a canine experimental model of cardiopulmonary bypass. Overview of the literature demonstrates that various formulations of H(2)S exert cardioprotective effects in cultured cells, isolated hearts and various rodent and large animal models of regional or global myocardial ischemia and heart failure. In addition, the production of H(2)S plays a role in myocardial pre- and post-conditioning responses. The pathways implicated in the cardioprotective action of H(2)S are multiple and involve K(ATP) channels, regulation of mitochondrial respiration, and regulation of cytoprotective genes such as Nrf-2. In the experimental part of the current article, we demonstrate the cardioprotective effects of H(2)S in a canine model of cardiopulmonary bypass surgery. Anesthetized dogs were subjected hypothermic cardiopulmonary bypass with 60 min of hypothermic cardiac arrest in the presence of either saline (control, n=8), or H(2)S infusion (1 mg/kg/h for 2 h). Left ventricular hemodynamic variables (via combined pressure-volume-conductance catheter) as well as coronary blood flow, endothelium-dependent vasodilatation to acetylcholine and endothelium-independent vasodilatation to sodium nitroprusside were measured at baseline and after 60 min of reperfusion. Ex vivo vascular function and high-energy phosphate contents were also measured. H(2)S led to a significantly better recovery of preload recruitable stroke work (p<0.05) after 60 min of reperfusion. Coronary blood flow was also significantly higher in the H(2)S group (p<0.05). While the vasodilatory response to sodium nitroprusside was similar in both groups, acetylcholine resulted in a significantly higher increase in coronary blood flow in the H(2)S-treated group (p<0.05) both in vivo and ex vivo. Furthermore, high-energy phosphate contents were better preserved in the H(2)S group. Additionally, the cytoprotective effects of H(2)S were confirmed also using in vitro cell culture experiments in H9c2 cardiac myocytes exposed to hypoxia and reoxygenation or to the cytotoxic oxidant hydrogen peroxide. Thus, therapeutic administration of H(2)S exerts cardioprotective effects in a variety of experimental models, including a significant improvement of the recovery of myocardial and endothelial function in a canine model of cardiopulmonary bypass with hypothermic cardiac arrest.

Hydrogen sulfide: the third gasotransmitter in biology and medicine

The last two decades have seen one of the greatest excitements and discoveries in science, gasotransmitters in biology and medicine. Leading the trend by nitric oxide and extending the trudge by carbon monoxide, here comes hydrogen sulfide (H(2)S) who builds up the momentum as the third gasotransmitter. Being produced by different cells and tissues in our body, H(2)S, alone or together with the other two gasotransmitters, regulates an array of physiological processes and plays important roles in the pathogenesis of various diseases from neurodegenerative diseases to diabetes or heart failure, to name a few. As a journal dedicated to serve the emergent and challenging field of H(2)S biology and medicine, Antioxidant and Redox Signaling assembles the most recent discoveries and most provoking ideas from leading scientists in H(2)S fields, which were communicated in the First International Conference of H(2)S in Biology and Medicine, and brings them to our readers in two Forum Issues. Through intellectual exchange and intelligent challenge with an open-mind approach, we can reasonably expect that sooner rather than later the exploration of metabolism and function of H(2)S will provide solutions for many of the biological mysteries of life and pave way for the arrival of many more gasotransmitters.