An outlook on vascular hydrogen sulphide effects, signalling, and therapeutic potential

Hydrogen Sulfide and Endoplasmic Reticulum Stress: A Potential Therapeutic Target for Central Nervous System Degeneration Diseases

There are three members of the endogenous gas transmitter family. The first two are nitric oxide and carbon monoxide, and the third newly added member is hydrogen sulfide (H₂S). They all have similar functions: relaxing blood vessels, smoothing muscles, and getting involved in the regulation of neuronal excitation, learning, and memory. The cystathionine β-synthase (CBS), 3-mercaptopyruvate sulfur transferase acts together with cysteine aminotransferase (3-MST/CAT), cystathionine γ-lyase (CSE), and 3-mercaptopyruvate sulfur transferase with D-amino acid oxidase (3-MST/DAO) pathways are involved in the enzymatic production of H₂S. More and more researches focus on the role of H₂S in the central nervous system (CNS), and H₂S plays a significant function in neuroprotection processes, regulating the function of the nervous system as a signaling molecule in the CNS. Endoplasmic reticulum stress (ERS) and protein misfolding in its mechanism are related to neurodegenerative diseases. H₂S exhibits a wide variety of cytoprotective and physiological functions in the CNS degenerative diseases by regulating ERS. This review summarized on the neuroprotective effect of H₂S for ERS played in several CNS diseases including Alzheimer’s disease, Parkinson’s disease, and depression disorder, and discussed the corresponding possible signaling pathways or mechanisms as well.

Exogenous H2S Promoted USP8 Sulfhydration to Regulate Mitophagy in the Hearts of db/db Mice

Hydrogen sulfide (H₂S), an important gasotransmitter, regulates cardiovascular functions. Mitochondrial damage induced by the overproduction of reactive oxygen species (ROS) results in myocardial injury with a diabetic state. The purpose of this study was to investigate the effects of exogenous H₂S on mitophagy formation in diabetic cardiomyopathy. In this study, we found that exogenous H₂S could improve cardiac functions, reduce mitochondrial fragments and ROS levels, enhance mitochondrial respiration chain activities and inhibit mitochondrial apoptosis in the hearts of db/db mice. Our results showed that exogenous H₂S facilitated parkin translocation into mitochondria and promoted mitophagy formation in the hearts of db/db mice. Our studies further revealed that the ubiquitination level of cytosolic parkin was increased and the expression of USP8, a deubiquitinating enzyme, was decreased in db/db cardiac tissues. S-sulfhydration is a novel posttranslational modification of specific cysteine residues on target proteins by H₂S. Our results showed that the S-sulfhydration level of USP8 was obviously decreased in vivo and in vitro under hyperglycemia and hyperlipidemia, however, exogenous H₂S could reverse this effect and promote USP8/parkin interaction. Dithiothreitol, a reducing agent that reverses sulfhydration-mediated covalent modification, increased the ubiquitylation level of parkin, abolished the effects of exogenous H₂S on USP8 deubiquitylation and suppressed the interaction of USP8 with parkin in neonatal rat cardiomyocytes treated with high glucose, oleate and palmitate. Our findings suggested that H₂S promoted mitophagy formation by increasing S-sulfhydration of USP8, which enhanced deubiquitination of parkin through the recruitment of parkin in mitochondria.

Cystathionine‑γ‑lyase promotes the metastasis of breast cancer via the VEGF signaling pathway

The present study aimed to provide data to support the association between cystathionine‑γ‑lyase (CSE) and breast cancer metastasis. Reverse transcription‑quantitative polymerase chain reaction, immunohistochemistry and western blot analysis were used to detect the mRNA and protein expression levels of CSE in human breast cancer tissues and cells. MTS and 5‑ethynyl‑2'‑deoxyuridine assays were used to assess cell viability and proliferation. Scratch wound and Transwell assays were conducted to determine cell migration and invasion. In addition, hydrogen sulfide determination was performed using the methylene blue method. The expression of CSE was upregulated in samples from patients with breast cancer that also exhibit lymph node metastasis, and in grade III and readily metastatic breast cancer cell lines. The proliferation, migration and invasion of breast cancer cells were examined in the present study, and tumor metastasis was observed in nude mice. The function of CSE in breast cancer metastasis depends on the vascular endothelial growth factor (VEGF) signaling pathway, a key mediator of angiogenesis that is crucial for the development and metastasis of tumors. CSE positively regulated the expression of VEGF and increased the levels of certain key proteins in the VEGF pathway, including the phosphoinositide (PI3K)/protein kinase B (AKT) pathway [PI3K, Akt and phosphorylated (p)Akt], focal adhesion kinase (FAK)‑paxillin pathway (FAK and paxillin) and rat sarcoma (Ras)‑mitogen‑activated protein kinase pathway [Ras, rapidly accelerated fibrosarcoma, extracellular signal‑regulated kinase (ERK)1/2 and pERK1/2]. Furthermore, the novel CSE inhibitor I157172 possessed antiproliferative and anti‑metastatic activities in early MDA‑MB‑231 metastatic breast cancer cells via inhibition of the VEGF signaling pathway, which further confirmed the role of CSE in breast cancer metastasis. Overall, these data demonstrate for the first time, to the best of our knowledge, that the functions of CSE in breast cancer metastasis are associated with the VEGF signaling pathway.

Hydrogen sulfide regulates muscle RING finger-1 protein S-sulfhydration at Cys44 to prevent cardiac structural damage in diabetic cardiomyopathy

BACKGROUND AND PURPOSE

Hydrogen sulfide (H₂ S) plays important roles as a gasotransmitter in pathologies. Increased expression of the E3 ubiquitin ligase, muscle RING finger-1 (MuRF1), may be involved in diabetic cardiomyopathy. Here we have investigated whether and how exogenous H₂ S alleviates cardiac muscle degradation through modifications of MuRF1 S-sulfhydration in db/db mice.

EXPERIMENTAL APPROACH

Neonatal rat cardiomyocytes were treated with high glucose (40 mM), oleate (100 μM), palmitate (400 μM), and NaHS (100 μM) for 72 hr. MuRF1 was silenced with siRNA technology and mutation at Cys⁴⁴ . Endoplasmic reticulum stress markers, MuRF1 expression, and ubiquitination level were measured. db/db mice were injected with NaHS (39 μmol·kg^-1 ) for 20 weeks. Echocardiography, cardiac ultrastructure, cystathionine-γ-lyase, cardiac structure proteins expression, and S-sulfhydration production were measured.

KEY RESULTS

H₂ S levels and cystathionine-γ-lyase protein expression in myocardium were decreased in db/db mice. Exogenous H₂ S reversed endoplasmic reticulum stress, including impairment of the function of cardiomyocytes and structural damage in db/db mice. Exogenous H₂ S could suppress the levels of myosin heavy chain 6 and myosin light chain 2 ubiquitination in cardiac tissues of db/db mice, and MuRF1 was modified by S-sulfhydration, following treatment with exogenous H₂ S, to reduce the interaction between MuRF1 and myosin heavy chain 6 and myosin light chain 2.

CONCLUSIONS AND IMPLICATIONS

Our findings suggest that H₂ S regulates MuRF1 S-sulfhydration at Cys⁴⁴ to prevent myocardial degradation in the cardiac tissues of db/db mice.

LINKED ARTICLES

This article is part of a themed section on Hydrogen Sulfide in Biology & Medicine. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.4/issuetoc.

Exogenous H2S facilitating ubiquitin aggregates clearance via autophagy attenuates type 2 diabetes-induced cardiomyopathy

Diabetic cardiomyopathy (DCM) is a serious complication of diabetes. Hydrogen sulphide (H₂S), a newly found gaseous signalling molecule, has an important role in many regulatory functions. The purpose of this study is to investigate the effects of exogenous H₂S on autophagy and its possible mechanism in DCM induced by type II diabetes (T2DCM). In this study, we found that sodium hydrosulphide (NaHS) attenuated the augment in left ventricular (LV) mass and increased LV volume, decreased reactive oxygen species (ROS) production and ameliorated H₂S production in the hearts of db/db mice. NaHS facilitated autophagosome content degradation, reduced the expression of P62 (a known substrate of autophagy) and increased the expression of microtubule-associated protein 1 light chain 3 II. It also increased the expression of autophagy-related protein 7 (ATG7) and Beclin1 in db/db mouse hearts. NaHS increased the expression of Kelch-like ECH-associated protein 1 (Keap-1) and reduced the ubiquitylation level in the hearts of db/db mice. 1,4-Dithiothreitol, an inhibitor of disulphide bonds, increased the ubiquitylation level of Keap-1, suppressed the expression of Keap-1 and abolished the effects of NaHS on ubiquitin aggregate clearance and ROS production in H9C2 cells treated with high glucose and palmitate. Overall, we concluded that exogenous H₂S promoted ubiquitin aggregate clearance via autophagy, which might exert its antioxidative effect in db/db mouse myocardia. Moreover, exogenous H₂S increased Keap-1 expression by suppressing its ubiquitylation, which might have an important role in ubiquitin aggregate clearance via autophagy. Our findings provide new insight into the mechanisms responsible for the antioxidative effects of H₂S in the context of T2DCM.

Cystathionine- γ-lyase promotes process of breast cancer in association with STAT3 signaling pathway

Here we provide evidences to link cystathionine-γ-lyase (CSE) to the development of breast cancer. CSE expression is up-regulated in both breast cancers and breast cancer cell lines and results in proliferation and migration of breast cancer cells. CSE Function in breast cancer depends on the STAT3 signaling pathway, a regulator of critical cell functions including cell growth in a wide variety of human cancer cells via activating the expression of relative genes. STAT3 positively relates to CSE expression. It activates the CSE promoter via a direct binding to the promoter. Moreover, CSE could reversely regulate STAT3 expression and consequently enhance the effect of STAT3 on CSE. Taken together, these data demonstrate for the first time the roles of CSE in breast cancer leading to breast cancer development in association with STAT3 signaling pathway.

Hydrogen sulfide prevents renal ischemia-reperfusion injury in CLAWN miniature swine

BACKGROUND

Hydrogen sulfide (H₂S) has recently been reported to demonstrate both antiinflammatory and cytoprotective effects; however, its efficacy has not been well documented in large animal models. In this study, we examined whether the administration of H₂S offers cytoprotective effects on renal ischemia-reperfusion injury (IRI) in a preclinical miniature swine model.

METHODS

Major histocompatibility complex-inbred, CLAWN miniature swine (n = 9) underwent a right nephrectomy, followed by induction of a 120-min period of warm ischemia via placement of clamps on the left renal artery and vein. Group 1 (n = 3) underwent renal ischemia without H₂S administration. Groups 2 (n = 3) and 3 (n = 3) received Na₂S (prodrug of H₂S) 10 min before reperfusion of the ischemic kidneys followed by a 30-min of Na₂S postreperfusion intravenously (group 2) or selective administration of Na₂S via the left renal artery (group 3). IRI was assessed by kidney biopsies, levels of inflammatory cytokines in sera and kidney tissue.

RESULTS

Animals in group 1 had significantly higher serum creatinine levels compared with animals in groups 2 and 3 (P < 0.01). Histology showed severe tubular damage with TUNEL-positive cells in group 1 on postoperative day 2 compared with mild damage in group 2 and minimal damage in group 3. Furthermore, levels of inflammatory cytokines in both serum (interleukin-6 [IL-6], tumor necrosis factor-α, and high-mobility group box 1) and renal tissue (IL-1 and IL-6) in group 3 were markedly lower than in group 2, suggesting beneficial effects of selective Na₂S administration.

CONCLUSIONS

Na₂S administration, especially via an organ selective approach, appears to potentially offer cytoprotective and antiinflammatory effects following renal IRI.

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.

Hydrogen Sulfide in the Adipose Tissue-Physiology, Pathology and a Target for Pharmacotherapy

Hydrogen sulfide (H₂S) is synthesized in the adipose tissue mainly by cystathionine γ-lyase (CSE). Several studies have demonstrated that H₂S is involved in adipogenesis, that is the differentiation of preadipocytes to adipocytes, most likely by inhibiting phosphodiesterases and increasing cyclic AMP concentration. The effect of H₂S on adipose tissue insulin sensitivity and glucose uptake is controversial. Some studies suggest that H₂S inhibits insulin-induced glucose uptake and that excess of H₂S contributes to adipose tissue insulin resistance in metabolic syndrome. In contrast, other studies have demonstrated that H₂S stimulates glucose uptake and its deficiency contributes to insulin resistance. Similarly, the effect of H₂S on adipose tissue lipolysis is controversial. H₂S produced by perivascular adipose tissue decreases vascular tone by activating ATP-sensitive and/or voltage-gated potassium channels in smooth muscle cells. Experimental obesity induced by high calorie diet has a time dependent effect on H₂S in perivascular adipose tissue; short and long-term obesity increase and decrease H₂S production, respectively. Hyperglycemia has been consistently demonstrated to suppress CSE-H₂S pathway in various adipose tissue depots. Finally, H₂S deficiency may contribute to adipose tissue inflammation associated with obesity/metabolic syndrome.

Hydrogen sulfide intoxication

Hydrogen sulfide (H2S) is a hazard primarily in the oil and gas industry, agriculture, sewage and animal waste handling, construction (asphalt operations and disturbing marshy terrain), and other settings where organic material decomposes under reducing conditions, and in geothermal operations. It is an insoluble gas, heavier than air, with a very low odor threshold and high toxicity, driven by concentration more than duration of exposure. Toxicity presents in a unique, reliable, and characteristic toxidrome consisting, in ascending order of exposure, of mucosal irritation, especially of the eye ("gas eye"), olfactory paralysis (not to be confused with olfactory fatigue), sudden but reversible loss of consciousness ("knockdown"), pulmonary edema (with an unusually favorable prognosis), and death (probably with apnea contributing). The risk of chronic neurcognitive changes is controversial, with the best evidence at high exposure levels and after knockdowns, which are frequently accompanied by head injury or oxygen deprivation. Treatment cannot be initiated promptly in the prehospital phase, and currently rests primarily on supportive care, hyperbaric oxygen, and nitrite administration. The mechanism of action for sublethal neurotoxicity and knockdown is clearly not inhibition of cytochrome oxidase c, as generally assumed, although this may play a role in overwhelming exposures. High levels of endogenous sulfide are found in the brain, presumably relating to the function of hydrogen sulfide as a gaseous neurotransmitter and immunomodulator. Prevention requires control of exposure and rigorous training to stop doomed rescue attempts attempted without self-contained breathing apparatus, especially in confined spaces, and in sudden release in the oil and gas sector, which result in multiple avoidable deaths.

Hydrogen sulfide and endothelium-dependent vasorelaxation

In addition to nitric oxide and carbon monoxide, hydrogen sulfide (H2S), synthesized enzymatically from l-cysteine or l-homocysteine, is the third gasotransmitter in mammals. Endogenous H2S is involved in the regulation of many physiological processes, including vascular tone. Although initially it was suggested that in the vascular wall H2S is synthesized only by smooth muscle cells and relaxes them by activating ATP-sensitive potassium channels, more recent studies indicate that H2S is synthesized in endothelial cells as well. Endothelial H2S production is stimulated by many factors, including acetylcholine, shear stress, adipose tissue hormone leptin, estrogens and plant flavonoids. In some vascular preparations H2S plays a role of endothelium-derived hyperpolarizing factor by activating small and intermediate-conductance calcium-activated potassium channels. Endothelial H2S signaling is up-regulated in some pathologies, such as obesity and cerebral ischemia-reperfusion. In addition, H2S activates endothelial NO synthase and inhibits cGMP degradation by phosphodiesterase 5 thus potentiating the effect of NO-cGMP pathway. Moreover, H2S-derived polysulfides directly activate protein kinase G. Finally, H2S interacts with NO to form nitroxyl (HNO)-a potent vasorelaxant. H2S appears to play an important and multidimensional role in endothelium-dependent vasorelaxation.

A hypothesis: hydrogen sulfide might be neuroprotective against subarachnoid hemorrhage induced brain injury

Gases such as nitric oxide (NO) and carbon monoxide (CO) play important roles both in normal physiology and in disease. Recent studies have shown that hydrogen sulfide (H₂S) protects neurons against oxidative stress and ischemia-reperfusion injury and attenuates lipopolysaccharides (LPS) induced neuroinflammation in microglia, exhibiting anti-inflammatory and antiapoptotic activities. The gas H₂S is emerging as a novel regulator of important physiologic functions such as arterial diameter, blood flow, and leukocyte adhesion. It has been known that multiple factors, including oxidative stress, free radicals, and neuronal nitric oxide synthesis as well as abnormal inflammatory responses, are involved in the mechanism underlying the brain injury after subarachnoid hemorrhage (SAH). Based on the multiple physiologic functions of H₂S, we speculate that it might be a promising, effective, and specific therapy for brain injury after SAH.

Hydrogen sulfide donors in research and drug development

This review summarized most of the H₂S donors such as inorganic compounds, natural products, anethole trithione derivatives and synthetic compounds used in research and drug development. These special bioactivities provided us some effective strategies for antiphlogosis, cancer therapy, cardiovascular protection and so on.