A critical life-supporting role for cystathionine γ-lyase in the absence of dietary cysteine supply

Kidney ischemia/reperfusion injury causes cholangiocytes primary cilia disruption and abnormal bile secretion

BACKGROUND

Acute kidney injury (AKI) causes distant liver injury, to date, which causes poor outcomes of patients with AKI. Many studies have been performed to overcome AKI-associated liver injury. However, those studies have mainly focused on hepatocytes, and AKI-induced liver injury still remains a clinical problem. Here, we investigated the implication of cholangiocytes and their primary cilia which are critical in final bile secretion. Cholangiocyte, a lining cell of bile ducts, are the only liver epithelial cell containing primary cilium (a microtubule-based cell surface signal-sensing organelle).

METHODS

Cystathione γ-lyase (CSE, a transsulfuration enzyme) deficient and wild-type mice were subjected to kidney ischemia followed by reperfusion (KIR). Some mice were administered with N-acetyl-cysteine (NAC).

RESULTS

KIR damaged hepatocytes and cholagiocytes, disrupted cholangiocytes primary cilia, released the disrupted ciliary fragments into the bile, and caused abnormal bile secretion. Glutathione (GSH) and H2S levels in the livers were significantly reduced by KIR, resulting in increased the ratio oxidized GSH to total GSH, and oxidation of tissue and bile. CSE and cystathione β-synthase (CBS) expression were lowered in the liver after KIR. NAC administration increased total GSH and H2S levels in the liver and attenuated KIR-induced liver injuries. In contrast, Cse deletion caused the reduction of total GSH levels and worsened KIR-induced liver injuries, including primary cilia damage and abnormal bile secretion.

CONCLUSIONS

These results indicate that KIR causes cholangiocyte damage, cholangiocytes primary cilia disruption, and abnormal bile secretion through reduced antioxidative ability of the liver.

Thiol starvation triggers melanoma state switching in an ATF4 and NRF2-dependent manner

The cystine/glutamate antiporter xCT is an important source of cysteine for cancer cells. Once taken up, cystine is reduced to cysteine and serves as a building block for the synthesis of glutathione, which efficiently protects cells from oxidative damage and prevents ferroptosis. As melanomas are particularly exposed to several sources of oxidative stress, we investigated the biological role of cysteine and glutathione supply by xCT in melanoma. xCT activity was abolished by genetic depletion in the Tyr::CreER; BrafCA; Ptenlox/+ melanoma model and by acute cystine withdrawal in melanoma cell lines. Both interventions profoundly impacted melanoma glutathione levels, but they were surprisingly well tolerated by murine melanomas in vivo and by most human melanoma cell lines in vitro. RNA sequencing of human melanoma cells revealed a strong adaptive upregulation of NRF2 and ATF4 pathways, which orchestrated the compensatory upregulation of genes involved in antioxidant defence and de novo cysteine biosynthesis. In addition, the joint activation of ATF4 and NRF2 triggered a phenotypic switch characterized by a reduction of differentiation genes and induction of pro-invasive features, which was also observed after erastin treatment or the inhibition of glutathione synthesis. NRF2 alone was capable of inducing the phenotypic switch in a transient manner. Together, our data show that cystine or glutathione levels regulate the phenotypic plasticity of melanoma cells by elevating ATF4 and NRF2.

H2S regulation of iron homeostasis by IRP1 improves vascular smooth muscle cell functions

Either H2S or iron is essential for cellular processes. Abnormal metabolism of H2S and iron has increased risk for cardiovascular diseases. The aim of the present study is to examine the mutual interplay of iron and H2S signals in regulation of vascular smooth muscle cell (SMC) functions. Here we found that deficiency of cystathionine gamma-lyase (CSE, a major H2S-producing enzyme in vascular system) induced but NaHS (a H2S donor) administration attenuated iron accumulation in aortic tissues from angiotensin II-infused mice. In vitro, iron overload induced labile iron levels, promoted cell proliferation, disrupted F-actin filaments, and inhibited protein expressions of SMC-specific markers (αSMA and calponin) more significantly in SMCs from CSE knockout mice (KO-SMCs) than the cells from wild-type mice (WT-SMCs), which could be reversed by exogenously applied NaHS. In contrast, KO-SMCs were more vulnerable to iron starvation-induced cell death. Either iron overload or NaHS did not affect elastin level and gelatinolytic activity. We further found that H2S induced more aconitase activity of iron regulatory protein 1 (IRP1) but inhibited its RNA binding activity accompanied with increased protein levels of ferritin and ferriportin, which would contribute to the lower level of labile iron level inside the cells. In addition, iron was able to suppress CSE-derived H2S generation, while iron also non-enzymatically induced H2S release from cysteine. This study reveals the mutual interaction between iron and H2S signals in regulating SMC phenotypes and functions; CSE/H2S system would be a target for preventing iron metabolic disorder-related vascular diseases.

Hydrogen sulfide signalling in neurodegenerative diseases

The gaseous neurotransmitter hydrogen sulfide (H2 S) exerts neuroprotective efficacy in the brain via post-translational modification of cysteine residues by sulfhydration, also known as persulfidation. This process is comparable in biological impact to phosphorylation and mediates a variety of signalling events. Unlike conventional neurotransmitters, H2 S cannot be stored in vesicles due to its gaseous nature. Instead, it is either locally synthesized or released from endogenous stores. Sulfhydration affords both specific and general neuroprotective effects and is critically diminished in several neurodegenerative disorders. Conversely, some forms of neurodegenerative disease are linked to excessive cellular H2 S. Here, we review the signalling roles of H2 S across the spectrum of neurodegenerative diseases, including Huntington's disease, Parkinson's disease, Alzheimer's disease, Down syndrome, traumatic brain injury, the ataxias, and amyotrophic lateral sclerosis, as well as neurodegeneration generally associated with ageing.

Recent Progress in the Rational Design of Biothiol-Responsive Fluorescent Probes

Biothiols such as cysteine, homocysteine, and glutathione play significant roles in important biological activities, and their abnormal concentrations have been found to be closely associated with certain diseases, making their detection a critical task. To this end, fluorescent probes have become increasingly popular due to their numerous advantages, including easy handling, desirable spatiotemporal resolution, high sensitivity, fast response, and favorable biocompatibility. As a result, intensive research has been conducted to create fluorescent probes for the detection and imaging of biothiols. This brief review summarizes recent advances in the field of biothiol-responsive fluorescent probes, with an emphasis on rational probe design, including the reaction mechanism, discriminating detection, reversible detection, and specific detection. Furthermore, the challenges and prospects of fluorescence probes for biothiols are also outlined.

Hydrogen sulfide and its donors: Novel antitumor and antimetastatic agents for liver cancer

Hepatocellular carcinoma (HCC) is the sixth most frequent human cancer and the world's third most significant cause of cancer mortality. HCC treatment has recently improved, but its mortality continues to increase worldwide due to its extremely complicated and heterogeneous genetic abnormalities. After nitric oxide (NO) and carbon monoxide (CO), the third gas signaling molecule discovered is hydrogen sulfide (H₂S), which has long been thought to be a toxic gas. However, numerous studies have proven that H₂S plays many pathophysiological roles in mammals. Endogenous or exogenous H₂S can decrease cell proliferation, promote apoptosis, block cell cycle, invasion and migration through various cellular signaling pathways. This review analyzes and discusses the recent literature on the function and molecular mechanism of H₂S and H₂S donors in HCC, so as to provide convenience for the scientific research and clinical application of H₂S in the treatment of liver cancer.

Glutathione restores the mitochondrial redox status and improves the function of the cardiovascular system in old rats

Introduction: Aging is accompanied by cardiovascular disorders which is associated with an imbalance of pro- and antioxidant systems, the mitochondrial dysfunction, etc. Glutathione (GSH) plays a critical role in protecting cells from oxidative damage. The aim of the work was to study the effect of exogenous glutathione on the redox status of mitochondria, the content of H₂S and the function of the cardiovascular system in old rats. Methods: Experiments were performed on adult (6 months) and old (24 months) Wistar rats divided into three groups: adult, old and glutathionetreated old rats. Glutathione was injected intraperitoneally at a dose of 52 mg/kg. We investigated glutathione redox balance, H₂S levels, oxidative stress, the opening of the mitochondrial permeability transition pore (mPTP), the resistance of isolated heart to ischemia/reperfusion in Langendorff model, endothelium-dependent vasorelaxation of isolated aortic rings, and cardiac levels of 3-MST, CSE, and UCP3 mRNA were determined using real-time PCR analysis. Results: Our data shows that in old rats treated with glutathione, the balance of its oxidized and reduced form changes in the direction of a significant increase (by 53.6%) of the reduced form. Glutathione pretreatment significantly increased the H₂S levels, mtNOS activity, and UCP3 expression which considered as protective protein, and conversely, significantly decreased oxidative stress markers (the rate of O₂•^- generation, the levels of H₂O₂, diene conjugates and malone dialdehyde, in 2.5, 2.3, 2, and 1.6 times, respectively) in heart mitochondria. This was associated with the inhibition mitochondrial permeability transition pore opening and increased resistance of the isolated heart to ischemia/reperfusion in these animals. At the same time, in glutathione-treated old rats, we also observed restoration of endothelium-dependent vasorelaxation responses to acetylcholine, which were almost completely abolished by the NO-synthase inhibitor L-NAME. Conclusion: Thus, the pretreatment of old rats with glutathione restores the mitochondrial redox status and improves the function of the cardiovascular system.

Hepatocellular cystathionine γ lyase/hydrogen sulfide attenuates nonalcoholic fatty liver disease by activating farnesoid X receptor

BACKGROUND AND AIMS

Hydrogen sulfide (H₂ S) plays a protective role in NAFLD. However, whether cystathionine γ lyase (CSE), a dominant H₂ S generating enzyme in hepatocytes, has a role in the pathogenesis of NAFLD is currently unclear.

APPROACH AND RESULTS

We showed that CSE protein expression is dramatically downregulated, especially in fibrotic areas, in livers from patients with NAFLD. In high-fat diet (HFD)-induced NAFLD mice or an oleic acid-induced hepatocyte model, the CSE/H₂ S pathway is also downregulated. To illustrate a regulatory role for CSE in NAFLD, we generated a hepatocyte-specific CSE knockout mouse (CSE^LKO ). Feeding an HFD to CSE^LKO mice, they showed more hepatic lipid deposition with increased activity of the fatty acid de novo synthesis pathway, increased hepatic insulin resistance, and higher hepatic gluconeogenic ability compared to CSE^Loxp control mice. By contrast, H₂ S donor treatment attenuated these phenotypes. Furthermore, the protection conferred by H₂ S was blocked by farnesoid X receptor (FXR) knockdown. Consistently, serum deoxycholic acid and lithocholic acid (FXR antagonists) were increased, and tauro-β-muricholic acid (FXR activation elevated) was reduced in CSE^LKO . CSE/H₂ S promoted a post-translation modification (sulfhydration) of FXR at Cys138/141 sites, thereby enhancing its activity to modulate expression of target genes related to lipid and glucose metabolism, inflammation, and fibrosis. Sulfhydration proteomics in patients' livers supported the CSE/H₂ S modulation noted in the CSE^LKO mice.

CONCLUSIONS

FXR sulfhydration is a post-translational modification affected by hepatic endogenous CSE/H₂ S that may promote FXR activity and attenuate NAFLD. Hepatic CSE deficiency promotes development of nonalcoholic steatohepatitis. The interaction between H₂ S and FXR may be amenable to therapeutic drug treatment in NAFLD.

Transsulfuration, minor player or crucial for cysteine homeostasis in cancer

Cysteine, a thiol-containing amino acid, is crucial for the synthesis of sulfur-containing biomolecules that control multiple essential cellular activities. Altered cysteine metabolism has been linked to numerous driver oncoproteins and tumor suppressors, as well as to malignant traits in cancer. Cysteine can be acquired from extracellular sources or synthesized de novo via the transsulfuration (TSS) pathway. Limited availability of cystine in tumor interstitial fluids raises the possible dependency on de novo cysteine synthesis via TSS. However, the contribution of TSS to cancer metabolism remains highly contentious. Based on recent findings, we provide new perspectives on this crucial but understudied metabolic pathway in cancer.

Mutant Huntingtin Derails Cysteine Metabolism in Huntington's Disease at Both Transcriptional and Post-Translational Levels

Cysteine is a semi-essential amino acid that not only plays an essential role as a component of protein synthesis, but also in the generation of numerous sulfur-containing molecules such as the antioxidant glutathione and coenzyme A. We previously showed that the metabolism of cysteine is dysregulated in Huntington's disease (HD), a neurodegenerative disorder triggered by the expansion of polyglutamine repeats in the protein huntingtin. In this study, we showed that cysteine metabolism is compromised at multiple levels in HD, both transcriptional and post-translational. Accordingly, restoring cysteine homeostasis may be beneficial in HD.

Cysteine metabolism and hydrogen sulfide signaling in Huntington's disease

The semi-essential amino acid, cysteine, plays important roles in both essential cellular processes as well as in modulation of signaling cascades. Cysteine is obtained both from the diet as well as generated endogenously via the transsulfuration pathway. Cysteine is further utilized in protein synthesis and biosynthesis of various sulfur containing molecules. One of the products of cysteine catabolism, hydrogen sulfide (H₂S), is a gaseous signaling molecule, which regulates a multitude of cellular processes. Cysteine metabolism is dysregulated in several neurodegenerative diseases and during aging. This minireview focuses on aberrant cysteine and H₂S metabolism in Huntington's disease, a neurodegenerative disease caused by expansion of polyglutamine encoding repeats in the gene huntingtin, which leads to motor and cognitive deficits.

TLRs-JNK/ NF-κB Pathway Underlies the Protective Effect of the Sulfide Salt Against Liver Toxicity

Hydrogen sulfide (H₂S) is an endogenously gas transmitter signaling molecule with known antioxidant, anti-inflammatory, and cytoprotective properties. Although accumulating evidence shows the therapeutic potential of H₂S in various hepatic diseases, its role in cyclophosphamide (CP)-induced hepatotoxicity remains elusive. The present study was undertaken to investigate the impact of endogenous and exogenous H₂S on toll-like receptors (TLRs)-mediated inflammatory response and apoptosis in CP-induced hepatotoxicity. Either an H₂S donor (NaHS (100 μM/kg) or an H2S blocker [dl-propargylglycine (PAG) (30 mg/kg, i. p.)], was administered for 10 days before a single ip injection of CP (200 mg/kg). NaHS attenuated conferred hepatoprotection against CP-induced toxicity, significantly decreasing serum hepatic function tests and improving hepatic histopathology. Additionally, NaHS-treated rats exhibited antioxidant activity in liver tissues compared with the CP group. The upregulated hepatic levels of TLR2/4 and their downstream signaling molecules including c-Jun N-terminal kinase (JNK) and nuclear factor-kappa B (NF-κB) were also suppressed by NaHS protective treatment. NaHS showed anti-inflammatory and antiapoptotic effects; reducing hepatic level tumor necrosis factor-alpha (TNF-α) and caspase-3 expression. Interestingly, the cytotoxic events induced in CP-treated rats were not significantly altered upon the blocking of endogenous H₂S. Taken together, the present study suggested that exogenously applied H₂S rather than the endogenously generated H₂S, displayed a hepatoprotective effect against CP-induced hepatotoxicity that might be mediated by TLRs-JNK/NF-κB pathways.

Physiological roles of hydrogen sulfide in mammalian cells, tissues and organs

H2S belongs to the class of molecules known as gasotransmitters, which also includes nitric oxide (NO) and carbon monoxide (CO). Three enzymes are recognized as endogenous sources of H2S in various cells and tissues: cystathionine g-lyase (CSE), cystathionine β-synthase (CBS) and 3-mercaptopyruvate sulfurtransferase (3-MST). The current article reviews the regulation of these enzymes as well as the pathways of their enzymatic and non-enzymatic degradation and elimination. The multiple interactions of H2S with other labile endogenous molecules (e.g. NO) and reactive oxygen species are also outlined. The various biological targets and signaling pathways are discussed, with special reference to H2S and oxidative posttranscriptional modification of proteins, the effect of H2S on channels and intracellular second messenger pathways, the regulation of gene transcription and translation and the regulation of cellular bioenergetics and metabolism. The pharmacological and molecular tools currently available to study H2S physiology are also reviewed, including their utility and limitations. In subsequent sections, the role of H2S in the regulation of various physiological and cellular functions is reviewed. The physiological role of H2S in various cell types and organ systems are overviewed. Finally, the role of H2S in the regulation of various organ functions is discussed as well as the characteristic bell-shaped biphasic effects of H2S. In addition, key pathophysiological aspects, debated areas, and future research and translational areas are identified A wide array of significant roles of H2S in the physiological regulation of all organ functions emerges from this review.

Activation of Endogenous H2S Biosynthesis or Supplementation with Exogenous H2S Enhances Adipose Tissue Adipogenesis and Preserves Adipocyte Physiology in Humans

Aims: To investigate the impact of exogenous hydrogen sulfide (H₂S) and its endogenous biosynthesis on human adipocytes and adipose tissue in the context of obesity and insulin resistance. Results: Experiments in human adipose tissue explants and in isolated preadipocytes demonstrated that exogenous H₂S or the activation of endogenous H₂S biosynthesis resulted in increased adipogenesis, insulin action, sirtuin deacetylase, and PPARγ transcriptional activity, whereas chemical inhibition and gene knockdown of each enzyme generating H₂S (CTH, CBS, MPST) led to altered adipocyte differentiation, cellular senescence, and increased inflammation. In agreement with these experimental data, visceral and subcutaneous adipose tissue expression of H₂S-synthesising enzymes was significantly reduced in morbidly obese subjects in association with attenuated adipogenesis and increased markers of adipose tissue inflammation and senescence. Interestingly, weight-loss interventions (including bariatric surgery or diet/exercise) improved the expression of H₂S biosynthesis-related genes. In human preadipocytes, the expression of CTH, CBS, and MPST genes and H₂S production were dramatically increased during adipocyte differentiation. More importantly, the adipocyte proteome exhibiting persulfidation was characterized, disclosing that different proteins involved in fatty acid and lipid metabolism, the citrate cycle, insulin signaling, several adipokines, and PPAR, experienced the most dramatic persulfidation (85-98%). Innovation: No previous studies investigated the impact of H₂S on human adipose tissue. This study suggests that the potentiation of adipose tissue H₂S biosynthesis is a possible therapeutic approach to improve adipose tissue dysfunction in patients with obesity and insulin resistance. Conclusion: Altogether, these data supported the relevance of H₂S biosynthesis in the modulation of human adipocyte physiology. Antioxid. Redox Signal. 35, 319-340.

Hydrogen sulfide stimulates lipid biogenesis from glutamine that is dependent on the mitochondrial NAD(P)H pool

Mammalian cells synthesize H2S from sulfur-containing amino acids and are also exposed to exogenous sources of this signaling molecule, notably from gut microbes. As an inhibitor of complex IV in the electron transport chain, H2S can have a profound impact on metabolism, suggesting the hypothesis that metabolic reprogramming is a primary mechanism by which H2S signals. In this study, we report that H2S increases lipogenesis in many cell types, using carbon derived from glutamine rather than from glucose. H2S-stimulated lipid synthesis is sensitive to the mitochondrial NAD(P)H pools and is enabled by reductive carboxylation of α-ketoglutarate. Lipidomics analysis revealed that H2S elicits time-dependent changes across several lipid classes, e.g., upregulating triglycerides while downregulating phosphatidylcholine. Direct analysis of triglyceride concentration revealed that H2S induces a net increase in the size of this lipid pool. These results provide a mechanistic framework for understanding the effects of H2S on increasing lipid droplets in adipocytes and population studies that have pointed to a positive correlation between cysteine (a substrate for H2S synthesis) and fat mass.

Cystathionine gamma-lyase/H2 S signaling facilitates myogenesis under aging and injury condition

Hydrogen sulfide (H₂ S) can be endogenously produced and belongs to the class of signaling molecules known as gasotransmitters. Cystathionine gamma-lyase (CSE)-derived H₂ S is implicated in the regulation of cell differentiation and the aging process, but the involvements of the CSE/H₂ S system in myogenesis upon aging and injury have not been explored. In this study, we demonstrated that CSE acts as a major H₂ S-generating enzyme in skeletal muscles and is significantly down-regulated in aged skeletal muscles in mice. CSE deficiency exacerbated the age-dependent sarcopenia and cardiotoxin-induced injury/regeneration in mouse skeletal muscle, possibly attributed to inefficient myogenesis. In contrast, supplement of NaHS (an H₂ S donor) induced the expressions of myogenic genes and promoted muscle regeneration in mice. In vitro, incubation of myoblast cells (C2C12) with H₂ S promoted myogenesis, as evidenced by the inhibition of cell cycle progression and migration, altered expressions of myogenic markers, elongation of myoblasts, and formation of multinucleated myotubes. Myogenesis was also found to upregulate CSE expression, while blockage of CSE/H₂ S signaling resulted in a suppression of myogenesis. Mechanically, H₂ S significantly induced the heterodimer formation between MEF2c and MRF4 and promoted the binding of MEF2c/MRF4 to myogenin promoter. MEF2c was S-sulfhydrated at both cysteine 361 and 420 in the C-terminal transactivation domain, and blockage of MEF2c S-sulfhydration abolished the stimulatory role of H₂ S on MEF2c/MRF4 heterodimer formation. These findings support an essential role for H₂ S in maintaining myogenesis, presenting it as a potential candidate for the prevention of age-related sarcopenia and treatment of muscle injury.

The mechanism of action of N-acetylcysteine (NAC): The emerging role of H2S and sulfane sulfur species

Initially adopted as a mucolytic about 60 years ago, the cysteine prodrug N-acetylcysteine (NAC) is the standard of care to treat paracetamol intoxication, and is included on the World Health Organization's list of essential medicines. Additionally, NAC increasingly became the epitome of an "antioxidant". Arguably, it is the most widely used "antioxidant" in experimental cell and animal biology, as well as clinical studies. Most investigators use and test NAC with the idea that it prevents or attenuates oxidative stress. Conventionally, it is assumed that NAC acts as (i) a reductant of disulfide bonds, (ii) a scavenger of reactive oxygen species and/or (iii) a precursor for glutathione biosynthesis. While these mechanisms may apply under specific circumstances, they cannot be generalized to explain the effects of NAC in a majority of settings and situations. In most cases the mechanism of action has remained unclear and untested. In this review, we discuss the validity of conventional assumptions and the scope of a newly discovered mechanism of action, namely the conversion of NAC into hydrogen sulfide and sulfane sulfur species. The antioxidative and cytoprotective activities of per- and polysulfides may explain many of the effects that have previously been ascribed to NAC or NAC-derived glutathione.

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.

The Role of H2S in the Metabolism of Glucose and Lipids

Glucose and lipids are essential elements for maintaining the body's homeostasis, and their dysfunction may participate in the pathologies of various diseases, particularly diabetes, obesity, metabolic syndrome, cardiovascular ailments, and cancers. Among numerous endogenous mediators, the gasotransmitter hydrogen sulfide (H₂S) plays a central role in the maintenance of glucose and lipid homeostasis. Current evidence from both pharmacological studies and transgenic animal models suggest a complex relationship between H₂S and metabolic dysregulation, especially in diabetes and obesity. This notion is achieved through tissue-specific expressions and actions of H₂S on target metabolic and hormone organs including the pancreas, skeletal muscle, livers, and adipose. In this chapter, we will summarize the roles and mechanisms of H₂S in several metabolic organs/tissues that are necessary for glucose and lipid metabolic homeostasis. In addition, future research directions and valuable therapeutic avenues around the pharmacological regulation of H₂S in glycolipid metabolism disorder will be also discussed.

Gasotransmitter signaling in energy homeostasis and metabolic disorders

Gasotransmitters are small molecules of gases, including nitric oxide (NO), hydrogen sulfide (H₂S), and carbon monoxide (CO). These three gasotransmitters can be endogenously produced and regulate a wide range of pathophysiological processes by interacting with specific targets upon diffusion in the biological media. By redox and epigenetic regulation of various physiological functions, NO, H₂S, and CO are critical for the maintenance of intracellular energy homeostasis. Accumulated evidence has shown that these three gasotransmitters control ATP generation, mitochondrial biogenesis, glucose metabolism, insulin sensitivity, lipid metabolism, and thermogenesis, etc. Abnormal generation and metabolism of NO, H₂S, and/or CO are involved in various abnormal metabolic diseases, including obesity, diabetes, and dyslipidemia. In this review, we summarized the roles of NO, H₂S, and CO in the regulation of energy homeostasis as well as their involvements in the metabolism of dysfunction-related diseases. Understanding the interaction among these gasotransmitters and their specific molecular targets are very important for therapeutic applications.

Cysteine Deprivation Targets Ovarian Clear Cell Carcinoma Via Oxidative Stress and Iron-Sulfur Cluster Biogenesis Deficit

Aims: Current treatment options for ovarian clear cell carcinoma (OCCC) are limited to combination of platinum-based and other cytotoxic agents to which patients respond poorly due to intrinsic chemoresistance. There is therefore an urgent need to develop alternative therapeutic strategies for OCCC. Results: Cysteine deprivation suppresses OCCC growth in vitro and in vivo with no apparent toxicity. Modes of cell death induced by cysteine deprivation in OCCC are determined by their innate metabolic profiles. Cysteine-deprived glycolytic OCCC is abolished primarily by oxidative stress-dependent necrosis and ferroptosis, which can otherwise be prevented by pretreatment with antioxidative agents. Meanwhile, OCCC that relies on mitochondria respiration for its bioenergetics is suppressed through apoptosis, which can otherwise be averted by pretreatment with cysteine precursor alone, but not with antioxidative agents. Cysteine deprivation induces apoptosis in respiring OCCC by limiting iron-sulfur (Fe-S) cluster synthesis in the mitochondria, without which electron transport chain may be disrupted. Respiring OCCC responds to Fe-S cluster deficit by increasing iron influx into the mitochondria, which leads to iron overload, mitochondria damage, and eventual cell death. Innovation/Conclusion: This study demonstrates the importance of cysteine availability in OCCC that is for its antioxidative property and its less appreciated role in mitochondria respiration. Regardless of OCCC metabolic profiles, cysteine deprivation abolishes both glycolytic and respiring OCCC growth in vitro and in vivo. Conclusion: This study highlights the therapeutic potential of cysteine deprivation for OCCC.

Hydrogen sulfide guards myoblasts from ferroptosis by inhibiting ALOX12 acetylation

Recognized as a novel and important gasotransmitter, hydrogen sulfide (H₂S) is widely present in various tissues and organs. Cystathionine gamma-lyase (CSE)-derived H₂S has been shown to regulate oxidative stress and lipid metabolism. The aim of the present study is to examine the role of H₂S in ferroptosis and lipid peroxidation in mouse myoblasts and skeletal muscles. Ferroptosis agonist RSL3 inhibited the expressions of Gpx4 and reduced CSE/H₂S signaling, which lead to increased oxidative stress, lipid peroxidation, and ferroptotic cell death. In addition, ferroptosis antagonist ferrostatin-1 (Fer-1) up-regulated the expression of CSE, scavenged the generation of reactive oxygen species (ROS) and lipid peroxidation, and improved cell viability. Exogenously applied NaHS was also able to block RSL3-induced ferroptotic cell death. Neither RSL3 nor H₂S affected cell apoptosis. Furthermore, H₂S reversed RSL3-induced Drp1 expression and mitochondrial damage, which lead to abnormal lipid metabolism as evidenced by altered expressions of ACSL4, FAS, ACC and CPT1 as well as higher acetyl-CoA contents in both cytoplasm and mitochondria. RSL3 promoted the protein expression and acetylation of ALOX12, a key protein in initiating membrane phospholipid oxidation, while the addition of NaHS attenuated ALOX12 acetylation and protected from membrane lipid peroxidation. Moreover, we observed that CSE deficiency alters the expressions of ferroptosis and lipid peroxidation-related proteins and enhances global protein acetylation in mouse skeletal muscles under aging or injury conditions. These results indicate that downregulation of CSE/H₂S signaling would contribute to mitochondrial damage, abnormal lipid metabolism, membrane lipid peroxidation, and ferroptotic cell death. CSE/H₂S system can be a target for preventing ferroptosis in skeletal muscle.

Chemistry and Biochemistry of Sulfur Natural Compounds: Key Intermediates of Metabolism and Redox Biology

Sulfur contributes significantly to nature chemical diversity and thanks to its particular features allows fundamental biological reactions that no other element allows. Sulfur natural compounds are utilized by all living beings and depending on the function are distributed in the different kingdoms. It is no coincidence that marine organisms are one of the most important sources of sulfur natural products since most of the inorganic sulfur is metabolized in ocean environments where this element is abundant. Terrestrial organisms such as plants and microorganisms are also able to incorporate sulfur in organic molecules to produce primary metabolites (e.g., methionine, cysteine) and more complex unique chemical structures with diverse biological roles. Animals are not able to fix inorganic sulfur into biomolecules and are completely dependent on preformed organic sulfurous compounds to satisfy their sulfur needs. However, some higher species such as humans are able to build new sulfur-containing chemical entities starting especially from plants' organosulfur precursors. Sulfur metabolism in humans is very complicated and plays a central role in redox biochemistry. The chemical properties, the large number of oxidation states, and the versatile reactivity of the oxygen family chalcogens make sulfur ideal for redox biological reactions and electron transfer processes. This review will explore sulfur metabolism related to redox biochemistry and will describe the various classes of sulfur-containing compounds spread all over the natural kingdoms. We will describe the chemistry and the biochemistry of well-known metabolites and also of the unknown and poorly studied sulfur natural products which are still in search for a biological role.

Hydrogen sulfide signaling in regulation of cell behaviors

Recent advances in the biomedical importance of H₂S have help us understand various cellular functions and pathophysiological processes from a new aspect. Specially, H₂S has been demonstrated to play multiple roles in regulating cell behaviors, including cell survival, cell differentiation, cell senescence, cell hypertrophy, cell atrophy, cell metaplasia, and cell death, etc. H₂S contributes to cell behavior changes via various mechanisms, such as histone modification, DNA methylation, non-coding RNA changes, DNA damage repair, transcription factor activity, and post-translational modification of proteins by S-sulfhydration, etc. In this review, we summarized the recent research progress on H₂S signaling in control of cell behaviors and discussed the ways of H₂S regulation of gene expressions. Given the key roles of H₂S in both health and diseases, a better understanding of the regulation of H₂S on cell behavior change and the underlying molecular mechanisms will help us to develop novel and more effective strategies for clinical therapy.

Engineering a highly selective probe for ratiometric imaging of H2S n and revealing its signaling pathway in fatty liver disease

Hydrogen polysulfides (H2S n , n > 1) have continuously been proved to act as important signal mediators in many physiological processes. However, the physiological role of H2S n and their signaling pathways in complex diseases, such as the most common liver disease, nonalcoholic fatty liver disease (NAFLD), have not been elucidated due to lack of suitable tools for selective detection of intracellular H2S n . Herein, we adopted a general and practical strategy including recognition site screening, construction of a ratiometric probe and self-assembly of nanoparticles, to significantly improve the probes' selectivity, photostability and biocompatibility. The ratiometric probe PPG-Np-RhPhCO selectively responds to H2S n , avoiding interaction with biothiol and persulfide. Moreover, this probe was applied to image H2S n in NAFLD for the first time and reveal the H2S n generation pathways in the cell model of drug-treated NAFLD. The pathway of H2S n revealed by PPG-Np-RhPhCO provides significant insights into the roles of H2S n in NAFLD and future drug development.

Implications of hydrogen sulfide in liver pathophysiology: Mechanistic insights and therapeutic potential

Background

Over the last several decades, hydrogen sulfide (H₂S) has been found to exert multiple physiological functions in mammal systems. The endogenous production of H₂S is primarily mediated by cystathione β-synthase (CBS), cystathione γ-lyase (CSE), and 3-mercaptopyruvate sulfurtransferase (3-MST). These enzymes are widely expressed in the liver tissues and regulate hepatic functions by acting on various molecular targets.

Aim of Review

In the present review, we will highlight the recent advancements in the cellular events triggered by H₂S under liver diseases. The therapeutic effects of H₂S donors on hepatic diseases will also be discussed.

Key Scientific Concepts of Review

As a critical regulator of liver functions, H₂S is critically involved in the etiology of various liver disorders, such as nonalcoholic steatohepatitis (NASH), hepatic fibrosis, hepatic ischemia/reperfusion (IR) injury, and liver cancer. Targeting H₂S-producing enzymes may be a promising strategy for managing hepatic disorders.

Golgi Stress Response, Hydrogen Sulfide Metabolism, and Intracellular Calcium Homeostasis

Aims: The physiological and pathological importance of hydrogen sulfide (H₂S) as a novel gasotransmitter has been widely recognized. Cystathionine gamma-lyase (CSE) is one of the major H₂S-producing enzymes and it regulates diverse functions in connection with intracellular calcium (Ca²⁺). The aim of this study is to examine the role of H₂S in Golgi stress-related cell injury and skeletal muscle disorders. Results: Golgi stressors (brefeldin A [BFA] and monensin) decreased the expression of GM130 and ATP2C1 (two markers of Golgi stress response), induced Golgi apparatus fragmentation, and caused a higher level of oxidative stress and cell apoptosis in mouse myoblast cells. In addition, Golgi stressors upregulated CSE expression and endogenous H₂S generation, and exogenously applied H₂S was able to protect but inhibition of CSE/H₂S system deteriorated Golgi stress response. Activating transcription factor 4 (ATF4) acted as an upstream molecule to increase CSE expression on Golgi stress response. Mechanically, Golgi stressors induced intracellular level of Ca²⁺, and chelating cellular Ca²⁺ markedly attenuated Golgi stress response, indicating the key role of Ca²⁺ in initiating Golgi stress and cell apoptosis. Further, administration of either angiotensin II or BFA initiated Golgi stress response and induced skeletal muscle atrophy in mice, which was further deteriorated by CSE deficiency but rescued by exogenously applied sodium hydrosulfide (NaHS). Innovation and Conclusion: The activation of the CSE/H₂S pathway and the decrease of intracellular Ca²⁺ are two cellular protective mechanisms against Golgi stress, and the CSE/H₂S system would be a target for preventing skeletal muscle dysfunctions.

Hydrogen Sulfide Mediates Tumor Cell Resistance to Thioredoxin Inhibitor

Thioredoxin (Trx) is a pro-oncogenic molecule that underlies tumor initiation, progression and chemo-resistance. PX-12, a Trx inhibitor, has been used to treat certain tumors. Currently, factors predicting tumor sensitivity to PX-12 are unclear. Given that hydrogen sulfide (H₂S), a gaseous bio-mediator, promotes Trx activity, we speculated that it might affect tumor response to PX-12. Here, we tested this possibility. Exposure of several different types of tumor cells to PX-12 caused cell death, which was reversely correlated with the levels of H₂S-synthesizing enzyme CSE and endogenous H₂S. Inhibition of CSE sensitized tumor cells to PX-12, whereas addition of exogenous H₂S elevated PX-12 resistance. Further experiments showed that H₂S abolished PX-12-mediated inhibition on Trx. Mechanistic analyses revealed that H₂S stimulated Trx activity. It promoted Trx from the oxidized to the reduced state. In addition, H₂S directly cleaved the disulfide bond in PX-12, causing PX-12 deactivation. Additional studies found that, besides Trx, PX-12 also interacted with the thiol residues of other proteins. Intriguingly, H₂S-mediated cell resistance to PX-12 could also be achieved through promotion of the thiol activity of these proteins. Addition of H₂S-modified protein into culture significantly enhanced cell resistance to PX-12, whereas blockade of extracellular sulfhydryl residues sensitized cells to PX-12. Collectively, our study revealed that H₂S mediated tumor cell resistance to PX-12 through multiple mechanisms involving induction of thiol activity in multiple proteins and direct inactivation of PX-12. H₂S could be used to predict tumor response to PX-12 and could be targeted to enhance the therapeutic efficacy of PX-12.

Overexpression of CBS and CSE genes affects lifespan, stress resistance and locomotor activity in Drosophila melanogaster

Recent experimental studies highlighted the role of hydrogen sulfide (H₂S) in aging and longevity. The cystathionine ß-synthase (CBS) and cystathionine γ-lyase (CSE) are the key enzymes responsible for H₂S production. Here we investigated the geroprotective effects of CSE and CBS overexpression in Drosophila. Overexpression of CSE did not affect a lifespan and decrease (mitochondrial form of CSE) or increase (cytoplasmic form of CSE) age dynamics of locomotor activity, while overexpression of CBS increase median (by 12.5%) and maximum (by 6.9%) lifespan and locomotor activity. Increasing of both CSE and CBS expression levels resulted in thermotolerance, but the resistance to combination of arid and food-free conditions decreased. The resistance to oxidative stress (paraquat) was not affected in flies with overexpression of CBS and cytoplasmic CSE, but decreased in flies overexpressing mitochondrial form of CSE. Thus, transgene overexpression of the CSE and CBS in Drosophila induce similar effects on stress-resistance and locomotor activity, however lifespan extending effect was revealed for CBS overexpression only.

Effects of Hydrogen Sulfide on Carbohydrate Metabolism in Obese Type 2 Diabetic Rats

Hydrogen sulfide (H₂S) is involved in the pathophysiology of type 2 diabetes. Inhibition and stimulation of H₂S synthesis has been suggested to be a potential therapeutic approach for type 2 diabetes. The aim of this study was therefore to determine the effects of long-term sodium hydrosulfide (NaSH) administration as a H₂S releasing agent on carbohydrate metabolism in type 2 diabetic rats. Type 2 diabetes was established using high fat-low dose streptozotocin. Rats were treated for 9 weeks with intraperitoneal injections of NaSH (0.28, 0.56, 1.6, 2.8, and 5.6 mg/kg). Serum glucose was measured weekly for one month and then at the end of the study. Serum insulin was measured before and after the treatment. At the end of the study, glucose tolerance, pyruvate tolerance and insulin secretion were determined and blood pressure was measured. In diabetic rats NaSH at 1.6–5.6 mg/kg increased serum glucose (11%, 28%, and 51%, respectively) and decreased serum insulin, glucose tolerance, pyruvate tolerance and in vivo insulin secretion. In controls, NaSH only at 5.6 mg/kg increased serum glucose and decreased glucose tolerance, pyruvate tolerance and insulin secretion. Chronic administration of NaSH in particular at high doses impaired carbohydrate metabolism in type 2 diabetic rats.

Hydrogen sulfide and hepatic lipid metabolism - a critical pairing for liver health

Hydrogen sulfide (H₂ S) is the most recently recognized gasotransmitter, influencing a wide range of physiological processes. As a critical regulator of metabolism, H₂ S has been suggested to be involved in the pathology of many diseases, particularly obesity, diabetes and cardiovascular disorders. Its involvement in liver health has been brought to light more recently, particularly through knockout animal models, which show severe hepatic lipid accumulation upon ablation of H₂ S metabolic pathways. A complex relationship between H₂ S and lipid metabolism in the liver is emerging, which has significant implications for liver disease establishment and/or progression, regardless of the disease-causing agent. In this review, we discuss the critical importance of H₂ S in hepatic lipid metabolism. We then describe the animal models so far related with H₂ S and lipid-associated liver disease, as well as H₂ S-based treatments available. Finally, we highlight important considerations for future studies and identify areas in which much still remains to be determined. 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.

Effects of N-acetyl-L-cysteine on lifespan, locomotor activity and stress-resistance of 3 Drosophila species with different lifespans

N-acetyl-L-cysteine (NAC) is a derivative of the sulphur-containing amino acid L-cysteine with potential anti-aging properties. We studied 3 Drosophila species with contrast longevity differences (D. virilis is longest-lived, D. kikkawai is shortest-lived and D. melanogaster has moderate lifespan) to test the effects of NAC at 8 different concentrations (from 10 nM to 100 mM) on the lifespan, stress-resistance and locomotor activity. Except the adverse effects of highest (10 mM and 100 mM) concentrations NAC demonstrated sexually opposite and male-biased effects on Drosophila lifespan, stress-resistance and locomotor activity and not satisfied the criteria of a geroprotector in terms of the reproducibility of lifespan extending effects in different model organisms. The concentration- and sex-dependent changes in the relative expression levels of the antioxidant genes (Cat/CG6871 and Sod1/CG11793) and genes involved in hydrogen sulfide biosynthesis (Cbs/CG1753, Eip55E/CG5345 and Nfs1/CG12264) suggest the involvement of hormetic mechanisms in the geroprotective effects of NAC.

Regulators of the transsulfuration pathway

The transsulfuration pathway is a metabolic pathway where transfer of sulfur from homocysteine to cysteine occurs. The pathway leads to the generation of several sulfur metabolites, which include cysteine, GSH and the gaseous signalling molecule hydrogen sulfide (H₂ S). Precise control of this pathway is critical for maintenance of optimal cellular function and, therefore, the key enzymes of the pathway, cystathionine β-synthase and cystathionine γ-lyase, are regulated at multiple levels. Disruption of the transsulfuration pathway contributes to the pathology of several conditions such as vascular dysfunction, Huntington's disease and during ageing. Treatment with donors of hydrogen sulfide and/or stimulation of this pathway have proved beneficial in several of these disorders. In this review, we focus on the regulation of the transsulfuration pathway pertaining to cysteine and H₂ S, which could be targeted to develop novel therapeutics. LINKED ARTICLES: This article is part of a themed section on Chemical Biology of Reactive Sulfur Species. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.4/issuetoc.

Hydrogen Sulfide and Glucose Homeostasis: A Tale of Sweet and the Stink

SIGNIFICANCE

Among many endogenous mediators, the gasotransmitter hydrogen sulfide (H₂S) plays an important role in the regulation of glucose homeostasis. In this article we discuss different functional roles of H₂S in several metabolic organs/tissues required in the maintenance of glucose homeostasis. Recent Advances: New evidence has emerged revealing the insulin sensitizing role of H₂S in adipose tissue and skeletal muscle biology. In addition, H₂S was demonstrated to be a potent stimulator of gluconeogenesis via the induction and stimulation of various glucose-producing pathways in the liver.

CRITICAL ISSUES

Similar to its other physiological effects, H₂S exhibits paradoxical characteristics in the regulation of glucose homeostasis: (1) H₂S stimulates glucose production via activation of gluconeogenesis and glycogenolysis in hepatocytes, yet inhibits lipolysis in adipocytes; (2) H₂S stimulates glucose uptake into adipocytes and skeletal muscle but inhibits glucose uptake into hepatocytes; (3) H₂S inhibits insulin secretion from pancreatic β cells, yet sensitizes insulin signaling and insulin-triggered response in adipose tissues and skeletal muscle. It is also unclear the impact H₂S may have on glucose metabolism and utilization by other vital organs, such as the brain.

FUTURE DIRECTIONS

Recent reports and ongoing studies lay the foundation for a general, although highly incomplete, understanding of the effect of H₂S on regulating glucose homeostasis. In this review, we describe the molecular mechanisms and physiological outcomes of the gasotransmitter H₂S on organs and tissues required for homeostatic maintenance of blood glucose. Future directions highlighting the H₂S-mediated homeostatic control of glucose metabolism under physiological and insulin-resistant conditions are also discussed. Antioxid. Redox Signal. 28, 1463-1482.

Role for Cystathionine γ Lyase (CSE) in an Ethanol (E)-Induced Lesion in Fetal Brain GSH Homeostasis

Earlier, we reported that gestational ethanol (E) can dysregulate neuron glutathione (GSH) homeostasis partially via impairing the EAAC1-mediated inward transport of Cysteine (Cys) and this can affect fetal brain development. In this study, we investigated if there is a role for the transulfuration pathway (TSP), a critical bio-synthetic point to supply Cys in E-induced dysregulation of GSH homeostasis. These studies utilized an in utero E binge model where the pregnant Sprague⁻Dawley (SD) rat dams received five doses of E at 3.5 g/kg by gastric intubation beginning embryonic day (ED) 17 until ED19 separated by 12 h. The postnatal day 7 (PN7) alcohol model employed an oral dosing of 4 g/kg body weight split into 2 feedings at 2 h interval and an iso-caloric and iso-volumic equivalent maltose-dextrin milk solution served as controls. The in vitro model consisted of cerebral cortical neuron cultures from embryonic day (ED) 16⁻17 fetus from SD rats and differentiated neurons from ED18 rat cerebral cortical neuroblasts. E concentrations were 4 mg/mL. E induced an accumulation of cystathionine in primary cortical neurons (PCNs), 2nd trimester equivalent in utero binge, and 3rd trimester equivalent PN7 model suggesting that breakdown of cystathionine, a required process for Cys supply is impaired. This was associated with a significant reduction in cystathionine γ-lyase (CSE) protein expression in PCN (p < 0.05) and in fetal cerebral cortex in utero (53%, p < 0.05) without a change in the expression of cystathionine β-synthase (CBS). Concomitantly, E decreased Cse mRNA expression in PCNs (by 32% within 6 h of exposure, p < 0.05) and in fetal brain (33%, p < 0.05). In parallel, knock down of CSE in differentiated rat cortical neuroblasts exaggerated the E-induced ROS, GSH loss with a pronounced caspase-3 activation and cell death. These studies illustrate the importance of TSP in CSE-related maintenance of GSH and the downstream events via Cys synthesis in neurons and fetal brain.

Cysteine Metabolism in Neuronal Redox Homeostasis

Besides its essential role in protein synthesis, cysteine plays vital roles in redox homeostasis, being a component of the major antioxidant glutathione (GSH) and a potent antioxidant by itself. In addition, cysteine undergoes a variety of post-translational modifications that modulate several physiological processes. It is becoming increasingly clear that redox-modulated events play important roles not only in peripheral tissues but also in the brain where cysteine disposition is central to these pathways. Dysregulated cysteine metabolism is associated with several neurodegenerative disorders. Accordingly, restoration of cysteine balance has therapeutic benefits. This review discusses metabolic signaling pathways pertaining to cysteine disposition in the brain under normal and pathological conditions, highlighting recent findings on cysteine metabolism during aging and in neurodegenerative conditions such as Huntington's disease (HD) and molybdenum cofactor (MoCo) deficiency (MoCD) among others.

Cystathionine gamma-lyase/hydrogen sulfide system is essential for adipogenesis and fat mass accumulation in mice

Hydrogen sulfide (H₂S) has been recognized as an important gasotransmitter analogous to nitric oxide and carbon monoxide. Cystathionine gamma-lyase (CSE)-derived H₂S is implicated in the regulation of insulin resistance and glucose metabolism, but the involvement of CSE/H₂S system in energy homeostasis and fat mass has not been extensively explored. In this study, a potential functional role of the CSE/H₂S system in in vitro adipocyte differentiation and in vivo adipogenesis and the underlying mechanism was investigated. CSE expression and H₂S production were increased during adipocyte differentiation, and that the pattern of CSE mRNA expression was similar to that of CCAAT/enhancer-binding protein (C/EBP) β and δ, two key regulators for adipogenesis. C/EBPβ and γ bind to the CCAAT box in CSE promoter and stimulate CSE gene transcription. H₂S induced PPARγ transactivation activity by S-sulfhydrating all the cysteine residues in the DNA binding domain and stimulated adipogenesis. High fat diet-induced fat mass was lost in CSE deficient mice, and exogenously applied H₂S promoted fat mass accumulation in fruit flies. In conclusion, CSE/H₂S system is essential for adipogenesis and fat mass accumulation through enhancement of PPARγ function in adipocytes. This study suggests that the CSE/H₂S system is involved in the pathogenesis of obesity in mice.

Hydrogen sulfide-producing cystathionine γ-lyase is critical in the progression of kidney fibrosis

Cystathionine γ-lyase (CSE), the last key enzyme of the transsulfuration pathway, is involved in the production of hydrogen sulfide (H₂S) and glutathione (GSH), which regulate redox balance and act as important antioxidant molecules. Impairment of the H₂S- and GSH-mediated antioxidant system is associated with the progression of chronic kidney disease (CKD), characterized by kidney fibrosis and dysfunction. Here, we evaluated the role of CSE in the progression of kidney fibrosis after unilateral ureteral obstruction (UUO) using mice deficient in the Cse gene. UUO of wild-type mice reduced the expression of H₂S-producing enzymes, CSE, cystathionine β-synthase, and 3-mercaptopyruvate sulfurtransferase in the obstructed kidneys, resulting in decreased H₂S and GSH levels. Cse gene deletion lowered H₂S and GSH levels in the kidneys. Deleting the Cse gene exacerbated the decrease in H₂S and GSH levels and increase in superoxide formation and oxidative damage to proteins, lipids, and DNA in the kidneys after UUO, which were accompanied by greater kidney fibrosis, deposition of extracellular matrixes, expression of α-smooth muscle actin, tubular damage, and infiltration of inflammatory cells. Furthermore, Cse gene deletion exacerbated mitochondrial fragmentation and apoptosis of renal tubule cells after UUO. The data provided herein constitute in vivo evidence that Cse deficiency impairs renal the H₂S- and GSH-producing activity and exacerbates UUO-induced kidney fibrosis. These data propose a novel therapeutic approach against CKD by regulating CSE and the transsulfuration pathway.

Leptin concentrations and SCD-1 indices in classical homocystinuria: Evidence for the role of sulfur amino acids in the regulation of lipid metabolism

BACKGROUND

We describe body composition, lipid metabolism and Stearoyl-CoA desaturase-1 (SCD-1) indices in patients with classical homocystinuria (HCU).

METHODS

Eleven treated HCU patients and 16 healthy controls were included. Body composition and bone mineral density were assessed by dual X-ray absorptiometry. Sulfur amino acids (SAA) and their derivatives (total homocysteine, cysteine, methionine, S-adenosylmethionine, S-adenosylhomocysteine, and glutathione), lipids (free fatty acids, acylcarnitines, triglycerides and lipoproteins), glucose, insulin, leptin, adiponectin, and isoprostanes were measured in plasma. Insulin resistance was evaluated by HOMA-IR. To estimate liver SCD-1 activity, SCD-16 [16:1(n-7)/16:0] and SCD-18 [18:1(n-9)/18:0] desaturation indices were determined.

RESULTS

In HCU patients, SCD-16 index was significantly reduced (p=0.03). A trend of an association of SCD-16 index with cysteine was observed (r=0.624, p=0.054). HCU patients displayed lower lean mass (p<0.05), with no differences in fat mass percentage. Leptin and low-density lipoprotein concentrations were lower in HCU patients (p<0.05). Femur bone mineral density Z-scores were correlated with plasma cysteine (r=0.829; p=0.04) and total homocysteine (r=-0.829; p=0.04) in HCU patients.

CONCLUSIONS

We report alterations in leptin and SCD-1 in HCU patients. These results agree with previous findings from epidemiologic and animal studies, and support a role for SAA on lipid homeostasis.

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.

The interaction of estrogen and CSE/H2S pathway in the development of atherosclerosis

Both estrogen and hydrogen sulfide (H₂S) have been shown to inhibit the development of atherosclerosis. We previously reported that cystathionine γ-lyase knockout (CSE-KO) male mice develop atherosclerosis earlier than male wild-type (WT) mice. The present study investigated the interaction of CSE/H₂S pathway and estrogen on the development of atherosclerosis in female mice. Plasma estrogen levels were significantly lower in female CSE-KO mice than in female WT mice. NaHS treatment had no effect on plasma estrogen levels in both WT and CSE-KO female mice. After CSE-KO and WT female mice were fed with atherogenic diet for 12 wk, plasma lipid levels were significantly increased and triglyceride levels decreased compared with those of control diet-fed mice. Atherogenic diet induced more atherosclerotic lesion, oxidative stress, intracellular adhesion molecule-1 (ICAM-1), and NF-κB in CSE-KO mice than in WT mice. Estrogen treatment of atherogenic diet-fed WT mice attenuated hypercholesterolemia, oxidative stress, ICAM-1 expression, and NF-κB in WT mice but not in atherogenic diet-fed CSE-KO mice. Furthermore, H₂S production in both the liver and vascular tissues was enhanced by estrogen in WT mice but not in CSE-KO mice. It is concluded that the antiatherosclerotic effect of estrogen is mediated by CSE-generated H₂S. This study provides new insights into the interaction of H₂S and estrogen signaling pathways on the regulation of cardiovascular functions.NEW & NOTEWORTHY Female cystathionine γ-lyase (CSE)-knockout mice have significantly lower plasma estrogen levels and more severe early atherosclerotic lesion than female wild-type mice. H₂S production in liver and vascular tissues is enhanced by estrogen via its stimulatory effect on CSE activity. The antiatherosclerotic effect of estrogen is mediated by CSE-generated H₂S.

Transcriptional control of amino acid homeostasis is disrupted in Huntington's disease

Disturbances in amino acid metabolism, which have been observed in Huntington's disease (HD), may account for the profound inanition of HD patients. HD is triggered by an expansion of polyglutamine repeats in the protein huntingtin (Htt), impacting diverse cellular processes, ranging from transcriptional regulation to cognitive and motor functions. We show here that the master regulator of amino acid homeostasis, activating transcription factor 4 (ATF4), is dysfunctional in HD because of oxidative stress contributed by aberrant cysteine biosynthesis and transport. Consistent with these observations, antioxidant supplementation reverses the disordered ATF4 response to nutrient stress. Our findings establish a molecular link between amino acid disposition and oxidative stress leading to cytotoxicity. This signaling cascade may be relevant to other diseases involving redox imbalance and deficits in amino acid metabolism.

The CBS/CSE system: a potential therapeutic target in NAFLD?

Non-alcoholic fatty liver disease (NAFLD) is a broad spectrum liver disorder diagnosed in patients without a history of alcohol abuse. NAFLD is growing at alarming rates worldwide. Its pathogenesis is complex and incompletely understood. The cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE) system regulates homocysteine and cysteine metabolism and contributes to endogenous hydrogen sulfide (H2S) biosynthesis. This review summarizes our current understanding of the hepatic CBS/CSE system, and for the first time, positions this system as a potential therapeutic target in NAFLD. As will be discussed, the CBS/CSE system is highly expressed and active in the liver. Its dysregulation, presenting as alterations in circulating homocysteine and (or) H2S levels, has been reported in NAFLD patients and in NAFLD-associated co-morbidities such as obesity and type 2 diabetes. Intricate links between the CBS/CSE system and a number of metabolic and stress related molecular mediators have also emerged. Various dysfunctions in the hepatic CBS/CSE system have been reported in animal models representative of each NAFLD spectrum. It is anticipated that a newfound appreciation for the hepatic CBS/CSE system will emerge that will improve our understanding of NAFLD pathogenesis, and give rise to new prospective targets for management of this disorder.

Hydrogen sulfide: physiological properties and therapeutic potential in ischaemia

Hydrogen sulfide (H2 S) has become a molecule of high interest in recent years, and it is now recognized as the third gasotransmitter in addition to nitric oxide and carbon monoxide. In this review, we discuss the recent literature on the physiology of endogenous and exogenous H2 S, focusing upon the protective effects of hydrogen sulfide in models of hypoxia and ischaemia.

Cysteine and hydrogen sulphide in the regulation of metabolism: insights from genetics and pharmacology

Obesity and diabetes represent a significant and escalating worldwide health burden. These conditions are characterized by abnormal nutrient homeostasis. One such perturbation is altered metabolism of the sulphur‐containing amino acid cysteine. Obesity is associated with elevated plasma cysteine, whereas diabetes is associated with reduced cysteine levels. One mechanism by which cysteine may act is through its enzymatic breakdown to produce hydrogen sulphide (H₂S), a gasotransmitter that regulates glucose and lipid homeostasis. Here we review evidence from both pharmacological studies and transgenic models suggesting that cysteine and hydrogen sulphide play a role in the metabolic dysregulation underpinning obesity and diabetes. We then outline the growing evidence that regulation of hydrogen sulphide levels through its catabolism can impact metabolic health. By integrating hydrogen sulphide production and breakdown pathways, we re‐assess current hypothetical models of cysteine and hydrogen sulphide metabolism, offering new insight into their roles in the pathogenesis of obesity and diabetes. © 2015 The Authors. Pathological Society of Great Britain and Ireland.

Biochemical and Pharmacokinetic Properties of PEGylated Cystathionine γ-Lyase from KF723837

Cystathionine &#947;-lyase (CGL) was purified to its electrophoretic homogeneity from<i> Aspergillus carneus</i> by various chromatographic approaches. The purified enzyme has four identical subunits of 52 kDa based on SDS and native PAGE analyses. To improve its structural stability, purified CGL was modified by covalent binding to polyethylene glycol moieties. The specific activity of free-CGL and PEG-CGL was 59.71 and 48.71 U/mg, respectively, with a PEGylation yield of 81.5 and 70.7% modification of surface ε-amino groups. Free- and modified CGL have the same pattern of pH stability (8.0-9.0). At 50°C, the thermal stability [half-life time (T_1/2)] of PEG-CGL was increased by 40% in comparison to free-CGL. The activity of CGL was completely inhibited by hydroxylamine and Hg⁺², with no effect by EDTA. Free-CGL (0.04 m<smlcap>M</smlcap>^-1s^-1) and PEG-CGL (0.03 m<smlcap>M</smlcap>^-1s^-1) have a similar catalytic efficiency to <smlcap>L</smlcap>-cystathionine as a substrate. The inhibition constant values of propargylglycine were 0.31 and 0.52 µ<smlcap>M</smlcap> for the free- and PEG-CGL, respectively. By in vitro proteolysis, PEG-CGL retains >50% of its initial activity compared to <10% of the free-CGL for acid protease for 30 min. From in vivo pharmacokinetics in New Zealand white rabbits, the T_1/2 was 19.1 and 28.9 h for the Holo free-CGL and PEG-CGL, respectively, ensuring the role of PEGylation on shielding the CGL surface from proteolytic attack, reducing its antigenicity, and stabilizing its internal Schiff base. By external infusion of pyridoxal 5′-phosphate (10 µ<smlcap>M</smlcap>), the T_1/2 of free- and PEG-CGL was prolonged to 24 and 33 h, respectively, so dissociation of pyridoxal 5′-phosphate was one of the main causes of loss of enzyme activity. The biochemical and hematological responses of rabbits to free- and PEG-CGL were assessed, with relative similarity to the negative control, confirming the nil toxicity of enzymes. The titer of IgG was duplicated in response to free- versus PEG-CGL after 45 days. To the best of our knowledge, this is the first report concerned with purification and PEGylation of CGL from fungi, with higher affinity for <smlcap>L</smlcap>-cystathionine. With further molecular studies, CGL will be a promising enzyme against various cardiovascular diseases and antioxidant deficiency, as well as for generation of a neurotransmitter (H₂S).