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

Exploring the impact of hydrogen sulfide on hematologic malignancies: A review

Hydrogen sulfide (H2S) is one of the three most crucial gaseous messengers in the body. The discovery of H2S donors, coupled with its endogenous synthesis capability, has sparked hope for the treatment of hematologic malignancies. In the last decade, the investigation into the impact of H2S has expanded, particularly within the fields of cardiovascular function, inflammation, infection, and neuromodulation. Hematologic malignancies refer to a diverse group of cancers originating from abnormal proliferation and differentiation of blood-forming cells, including leukemia, lymphoma, and myeloma. In this review, we delve deeply into the complex interrelation between H2S and hematologic malignancies. In addition, we comprehensively elucidate the intricate molecular mechanisms by which both H2S and its donors intricately modulate the progression of tumor growth. Furthermore, we systematically examine their impact on pivotal aspects, encompassing the proliferation, invasion, and migration capacities of hematologic malignancies. Therefore, this review may contribute novel insights to our understanding of the prospective therapeutic significance of H2S and its donors within the realm of hematologic malignancies.

Cystine rather than cysteine is the preferred substrate for β-elimination by cystathionine γ-lyase: implications for dietary methionine restriction

Dietary methionine restriction (MR) increases longevity by improving health. In experimental models, MR is accompanied by decreased cystathionine β-synthase activity and increased cystathionine γ-lyase activity. These enzymes are parts of the transsulfuration pathway which produces cysteine and 2-oxobutanoate. Thus, the decrease in cystathionine β-synthase activity is likely to account for the loss of tissue cysteine observed in MR animals. Despite this decrease in cysteine levels, these tissues exhibit increased H2S production which is thought to be generated by β-elimination of the thiol moiety of cysteine, as catalyzed by cystathionine β-synthase or cystathionine γ-lyase. Another possibility for this H2S production is the cystathionine γ-lyase-catalyzed β-elimination of cysteine persulfide from cystine, which upon reduction yields H2S and cysteine. Here, we demonstrate that MR increases cystathionine γ-lyase production and activities in the liver and kidneys, and that cystine is a superior substrate for cystathionine γ-lyase catalyzed β-elimination as compared to cysteine. Moreover, cystine and cystathionine exhibit comparable Kcat/Km values (6000 M-1 s-1) as substrates for cystathionine γ-lyase-catalyzed β-elimination. By contrast, cysteine inhibits cystathionine γ-lyase in a non-competitive manner (Ki ~ 0.5 mM), which limits its ability to function as a substrate for β-elimination by this enzyme. Cysteine inhibits the enzyme by reacting with its pyridoxal 5'-phosphate cofactor to form a thiazolidine and in so doing prevents further catalysis. These enzymological observations are consistent with the notion that during MR cystathionine γ-lyase is repurposed to catabolize cystine and thereby form cysteine persulfide, which upon reduction produces cysteine.

S-Allyl-L-Cysteine Affects Cell Proliferation and Expression of H2S-Synthetizing Enzymes in MCF-7 and MDA-MB-231 Adenocarcinoma Cell Lines

S-allyl-L-cysteine (SAC) is a sulfur compound present in fresh garlic. The reference literature describes its anticancer, antioxidant and neuroprotective effects. Breast cancer is infamously known as one of the most commonly diagnosed malignancies among women worldwide. Its morbidity and mortality make it reasonable to complete and expand knowledge on this cancer's characteristics. Hydrogen sulfide (H2S) and its naturally occurring donors are well-known investigation subjects for diverse therapeutic purposes. This study was conducted to investigate the SAC antiproliferative potential and effect on three enzymes involved in H2S metabolism: 3-mercaptopyruvate sulfurtransferase (MPST), cystathionine γ-lyase (CTH), and cystathionine β-synthase (CBS). We chose the in vitro cellular model of human breast adenocarcinomas: MCF-7 and MDA-MB-231. The expression of enzymes after 2, 4, 6, 8, and 24 h incubation with 2.24 mM, 3.37 mM, and 4.50 mM SAC concentrations was examined. The number of living cells was determined by the MTS assay. Changes in cellular plasma membrane integrity were measured by the LDH test. Expression changes at the protein level were analyzed using Western blot. A significant decrease in viable cells was registered for MCF-7 cells after all incubation times upon 4.50 mM SAC exposure, and after 6 and 24 h only in MDA-MB-231 upon 4.50 mM SAC. In both cell lines, the MPST gene expression significantly increased after the 24 h incubation with 4.50 mM SAC. S-allyl-L-cysteine had opposite effects on changes in CTH and CBS expression in both cell lines. In our research model, we confirmed the antiproliferative potential of SAC and concluded that our studies provided current information about the increase in MPST gene expression mediated by S-allyl-L-cysteine in the adenocarcinoma in vitro cellular model for the MCF-7 and MDA-MB-231 cell lines. Further investigation of this in vitro model can bring useful information regarding sulfur enzyme metabolism of breast adenocarcinoma and regulating its activity and expression (gene silencing) in anticancer therapy.

Hydrogen Sulfide and Liver Health: Insights into Liver Diseases

Significance: Hydrogen sulfide (H2S) is a recently recognized gasotransmitter involved in physiological and pathological conditions in mammals. It protects organs from oxidative stress, inflammation, hypertension, and cell death. With abundant expression of H2S-production enzymes, the liver is closely linked to H2S signaling. Recent Advances: Hepatic H2S comes from various sources, including gut microbiota, exogenous sulfur salts, and endogenous production. Recent studies highlight the importance of hepatic H2S in liver diseases such as nonalcoholic fatty liver disease (NAFLD), liver injury, and cancer, particularly at advanced stages. Endogenous H2S production deficiency is associated with severe liver disease, while exogenous H2S donors protect against liver dysfunction. Critical Issues: However, the roles of H2S in NAFLD, liver injury, and liver cancer are still debated, and its effects depend on donor type, dosage, treatment duration, and cell type, suggesting a multifaceted role. This review aimed to critically evaluate H2S production, metabolism, mode of action, and roles in liver function and disease. Future Direction: Understanding H2S's precise roles and mechanisms in liver health will advance potential therapeutic applications in preclinical and clinical research. Targeting H2S-producing enzymes and exogenous H2S sources, alone or in combination with other drugs, could be explored. Quantifying endogenous H2S levels may aid in diagnosing and managing liver diseases. Antioxid. Redox Signal. 40, 122-144.

Yohimbine Alleviates Oxidative Stress and Suppresses Aerobic Cysteine Metabolism Elevated in the Rat Liver of High-Fat Diet-Fed Rats

Yohimbine is a small indole alkaloid derived from the bark of the yohimbe tree with documented biological activity, including anti-inflammatory, erectile dysfunction relieving, and fat-burning properties. Hydrogen sulfide (H₂S) and sulfane sulfur-containing compounds are regarded as important molecules in redox regulation and are involved in many physiological processes. Recently, their role in the pathophysiology of obesity and obesity-induced liver injury was also reported. The aim of the present study was to verify whether the mechanism of biological activity of yohimbine is related to reactive sulfur species formed during cysteine catabolism. We tested the effect of yohimbine at doses of 2 and 5 mg/kg/day administered for 30 days on aerobic and anaerobic catabolism of cysteine and oxidative processes in the liver of high-fat diet (HFD)-induced obese rats. Our study revealed that HFD resulted in a decrease in cysteine and sulfane sulfur levels in the liver, while sulfates were elevated. In the liver of obese rats, rhodanese expression was diminished while lipid peroxidation increased. Yohimbine did not influence sulfane sulfur and thiol levels in the liver of obese rats, however, this alkaloid at a dose of 5 mg decreased sulfates to the control level and induced expression of rhodanese. Moreover, it diminished hepatic lipid peroxidation. It can be concluded that HFD attenuates anaerobic and enhances aerobic cysteine catabolism and induces lipid peroxidation in the rat liver. Yohimbine at a dose of 5 mg/kg can alleviate oxidative stress and reduce elevated concentrations of sulfate probably by the induction of TST expression.

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.

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.

Hydrogen sulphide in liver glucose/lipid metabolism and non-alcoholic fatty liver disease

BACKGROUND

For a long time, hydrogen sulphide (H₂ S) was considered only as a toxic gas, inhibiting mitochondrial respiration at the level of cytochrome c oxidase, and an environmental pollutant. Nowadays, H₂ S is recognized as the third mammalian gasotransmitter, playing an important role in inflammation, septic shock, ischaemia reperfusion events, cardiovascular disease and more recently in liver physiology and chronic liver diseases such as non-alcoholic fatty liver disease (NAFLD).

METHODS

This narrative review is based on literature search using PubMed.

RESULTS

From a bioenergetic perspective, H₂ S is a very unique molecule, serving as a mitochondrial poison at high concentrations or as an inorganic mitochondrial substrate at low concentrations. By using transgenic animal models to specifically modulate liver H₂ S biosynthesis or exogenous compounds that release H₂ S, several studies demonstrated that H₂ S is a key player in liver glucose and lipid metabolism. Liver H₂ S content and biosynthesis were also altered in NAFLD animal models with the in vivo administration of H₂ S-releasing molecules preventing the further escalation into non-alcoholic-steatohepatitis. Liver steady-state levels of H₂ S, and hence its cell signalling properties, are controlled by a tight balance between its biosynthesis, mainly through the transsulphuration pathway, and its mitochondrial oxidation via the sulphide oxidizing unit. However, studies investigating mitochondrial H₂ S oxidation in liver dysfunction still remain scarce.

CONCLUSIONS

Since H₂ S emerges as a key regulator of liver metabolism and metabolic flexibility, further understanding the physiological relevance of mitochondrial H₂ S oxidation in liver energy homeostasis and its potential implication in chronic liver diseases are of great interest.

Highly Selective Fluorescent Probe Design for Visualizing Hepatic Hydrogen Sulfide in the Pathological Progression of Nonalcoholic Fatty Liver

Hydrogen sulfide (H₂S), emerging as an important gaseous signal, has attracted more and more attention for its key role in chronic fatty liver diseases. However, lacking tools for H₂S-specific in situ detection, the changes of endogenous hepatic H₂S levels in the pathological progression of chronic liver diseases are still unclear. To this end, we adopted a strategy of combining molecular probe design and nanofunctionalization to develop a highly selective near-infrared (NIR) fluorescent probe, which allows in vivo real-time monitoring of hepatic H₂S levels in the process of nonalcoholic fatty liver disease (NAFLD). As a proof of strategy demonstration, we first designed NIR molecular probes for H₂S sensing through chemical design and probe screening and then loaded molecular probes into mesoporous silicon nanomaterials (MSNs) with surface encapsulation using poly(ethylene glycol) to construct a highly selective probe MSN@CSN@PEG, with significantly improved selectivity and photostability. Moreover, MSN@CSN@PEG exhibited high selectivity and sensitivity for endogenous H₂S in cells and tumors in vivo, eliminating the interference of a high concentration of biothiols and sulfhydryl proteins. Furthermore, the probe was applied to in situ intravital imaging and systematic assessment of hepatic H₂S levels in different stages of NAFLD for the first time, which may offer a promising tool for the future study of fatty liver diseases and other chronic liver diseases.

Diet and Hydrogen Sulfide Production in Mammals

Significance: In recent times, it has emerged that some dietary sulfur compounds can act on mammalian cell signaling systems via their propensity to release hydrogen sulfide (H₂S). H₂S plays important biochemical and physiological roles in the heart, gastrointestinal tract, brain, kidney, and immune systems of mammals. Reduced levels of H₂S in cells and tissues correlate with a spectrum of pathophysiological conditions, including heart disease, diabetes, obesity, and altered immune function. Recent Advances: In the last decade, researchers have now begun to explore the mechanisms by which dietary-derived sulfur compounds, in addition to cysteine, can act as sources of H₂S. This research has led to the identified several compounds, organic sulfides, isothiocyanates, and inorganic sulfur species including sulfate that can act as potential sources of H₂S in mammalian cells and tissues. Critical Issues: We have summarised progress made in the identification of dietary factors that can impact on endogenous H₂S levels in mammals. We also describe current research focused on how some sulfur molecules present in dietary plants, and associated chemical analogues, act as sources of H₂S, and discuss the biological properties of these molecules as studied in a range of in vitro and in vivo systems. Future Directions: The identification of sulfur compounds in edible plants that can act as novel H₂S releasing molecules is intriguing. Research in this area could inform future studies exploring the impact of diet on H₂S levels in mammalian systems. Despite recent progress, additional work is needed to determine the mechanisms by which H₂S is released from these molecules following ingestions of dietary plants in humans, whether the amounts of H₂S produced is of physiological significance following the metabolism of these compounds in vivo, and if diet could be used to manipulated H₂S levels in humans. Importantly, this will lead to a better understanding of the biological significance of H₂S generated from dietary sources, and this information could be used in the development of plant breeding initiatives to increase the levels of H₂S releasing sulfur compounds in crops, or inform dietary intervention strategies that could be used to alter the levels of H₂S in humans.

The Impact of H2S on Obesity-Associated Metabolic Disturbances

Over the last several decades, hydrogen sulfide (H₂S) has gained attention as a new signaling molecule, with extensive physiological and pathophysiological roles in human disorders affecting vascular biology, immune functions, cellular survival, metabolism, longevity, development, and stress resistance. Apart from its known functions in oxidative stress and inflammation, new evidence has emerged revealing that H₂S carries out physiological functions by targeting proteins, enzymes, and transcription factors through a post-translational modification known as persulfidation. This review article provides a critical overview of the current state of the literature addressing the role of H₂S in obesity-associated metabolic disturbances, with particular emphasis on its mechanisms of action in obesity, diabetes, non-alcoholic fatty liver disease (NAFLD), and cardiovascular diseases.

Involvement of amylin B-H2S-connexin 43 signaling pathway in vascular dysfunction and enhanced ischemia-reperfusion-induced myocardial injury in diabetic rats

The present study was designed to investigate the role of amylin, H₂S, and connexin 43 in vascular dysfunction and enhanced ischemia–reperfusion (I/R)-induced myocardial injury in diabetic rats. A single dose of streptozotocin (65 mg/kg) was employed to induce diabetes mellitus. After 8 weeks, there was a significant decrease in the plasma levels of amylin, an increase in I/R injury to isolated hearts (increase in CK-MB and cardiac troponin release) on the Langendorff apparatus. Moreover, there was a significant impairment in vascular endothelium function as assessed by quantifying acetylcholine-induced relaxation in norepinephrine-precontracted mesenteric arteries. There was also a marked decrease in the expression of H₂S and connexin 43 in the hearts following I/R injury in diabetic rats. Treatment with amylin agonist, pramlintide (100 and 200 µg/kg), and H₂S donor, NaHS (10 and 20 μmol/kg) for 2 weeks improved the vascular endothelium function, abolished enhanced myocardial injury and restored the levels of H₂S along with connexin 43 in diabetic animals. However, pramlintide and NaHS failed to produce these effects the presence of gap junction blocker, carbenoxolone (20 and 40 mg/kg). Carbenoxolone also abolished the myocardial levels of connexin 43 without affecting the plasma levels of amylin and myocardial levels of H₂S. The decrease in the amylin levels with a consequent reduction in H₂S and connexin 43 may contribute to inducing vascular dysfunction and enhancing I/R-induced myocardial injury in diabetic rats.

The Role of the Transsulfuration Pathway in Non-Alcoholic Fatty Liver Disease

The prevalence of non-alcoholic fatty liver disease (NAFLD) is increasing and approximately 25% of the global population may have NAFLD. NAFLD is associated with obesity and metabolic syndrome, but its pathophysiology is complex and only partly understood. The transsulfuration pathway (TSP) is a metabolic pathway regulating homocysteine and cysteine metabolism and is vital in controlling sulfur balance in the organism. Precise control of this pathway is critical for maintenance of optimal cellular function. The TSP is closely linked to other pathways such as the folate and methionine cycles, hydrogen sulfide (H₂S) and glutathione (GSH) production. Impaired activity of the TSP will cause an increase in homocysteine and a decrease in cysteine levels. Homocysteine will also be increased due to impairment of the folate and methionine cycles. The key enzymes of the TSP, cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE), are highly expressed in the liver and deficient CBS and CSE expression causes hepatic steatosis, inflammation, and fibrosis in animal models. A causative link between the TSP and NAFLD has not been established. However, dysfunctions in the TSP and related pathways, in terms of enzyme expression and the plasma levels of the metabolites (e.g., homocysteine, cystathionine, and cysteine), have been reported in NAFLD and liver cirrhosis in both animal models and humans. Further investigation of the TSP in relation to NAFLD may reveal mechanisms involved in the development and progression of NAFLD.

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.

Randomized nutrient bar supplementation improves exercise-associated changes in plasma metabolome in adolescents and adult family members at cardiometabolic risk

BACKGROUND

Poor diets contribute to metabolic complications of obesity, insulin resistance and dyslipidemia. Metabolomic biomarkers may serve as early nutrition-sensitive health indicators. This family-based lifestyle change program compared metabolic outcomes in an intervention group (INT) that consumed 2 nutrient bars daily for 2-months and a control group (CONT).

METHODS

Overweight, predominantly minority and female adolescent (Teen)/parent adult caretaker (PAC) family units were recruited from a pediatric obesity clinic. CONT (8 Teen, 8 PAC) and INT (10 Teen, 10 PAC) groups randomized to nutrient bar supplementation attended weekly classes that included group nutrition counseling and supervised exercise. Pre-post physical and behavioral parameters, fasting traditional biomarkers, plasma sphingolipids and amino acid metabolites were measured.

RESULTS

In the full cohort, a baseline sphingolipid ceramide principal component composite score correlated with adiponectin, triglycerides, triglyceride-rich very low density lipoproteins, and atherogenic small low density lipoprotein (LDL) sublasses. Inverse associations were seen between a sphingomyelin composite score and C-reactive protein, a dihydroceramide composite score and diastolic blood pressure, and the final principal component that included glutathionone with fasting insulin and the homeostatic model of insulin resistance. In CONT, plasma ceramides, sphinganine, sphingosine and amino acid metabolites increased, presumably due to increased physical activity. Nutrient bar supplementation (INT) blunted this rise and significantly decreased ureagenic, aromatic and gluconeogenic amino acid metabolites. Metabolomic changes were positively correlated with improvements in clinical biomarkers of dyslipidemia.

CONCLUSION

Nutrient bar supplementation with increased physical activity in obese Teens and PAC elicits favorable metabolomic changes that correlate with improved dyslipidemia. The trial from which the analyses reported upon herein was part of a series of nutrient bar clinical trials registered at clinicaltrials.gov as NCT02239198.

Maternal Fructose Intake Increases Liver H2 S Synthesis but Exarcebates its Fructose-Induced Decrease in Female Progeny

SCOPE

Fructose intake from added sugars correlates with the epidemic rise in metabolic syndrome and cardiovascular diseases (CVD). However, consumption of beverages containing fructose is allowed during gestation. Homocysteine (Hcy) is a well-known risk factor for CVD while hydrogen sulfide (H₂ S), a product of its metabolism, has been proved to exert opposite effects to Hcy.

METHODS AND RESULTS

First, it is investigated whether maternal fructose intake produces subsequent changes in Hcy metabolism and H₂ S synthesis of the progeny. Carbohydrates are supplied to pregnant rats in drinking water (10% wt/vol) throughout gestation. Adult female descendants from fructose-fed, control or glucose-fed mothers are studied. Females from fructose-fed mothers have elevated homocysteinemia, hepatic H₂ S production, cystathionine γ-lyase (CSE) (the key enzyme in H₂ S synthesis) expression and plasma H₂ S, versus the other two groups. Second, it is studied how adult female progeny from control (C/F), fructose- (F/F), and glucose-fed (G/F) mothers responded to liquid fructose and compared them to the control group (C/C). Interestingly, hepatic CSE expression and H₂ S synthesis are diminished by fructose intake, this effect being more pronounced in F/F females.

CONCLUSION

Maternal fructose intake produces a fetal programming that increases hepatic H₂ S production and, in contrast, exacerbates its fructose-induced drop in female progeny.

Kidney Ischemia-Reperfusion Elicits Acute Liver Injury and Inflammatory Response

Ischemia-reperfusion (IR) is a common risk factor that causes acute kidney injury (AKI). AKI is associated with dysfunction of other organs also known as distant organ injury. The liver function is often compromised in patients with AKI and in animal models. However, the underlying mechanisms are not fully understood. Inflammatory response plays an important role in IR-induced tissue injury. Although increased proinflammatory cytokines have been detected in the kidney and the distant organs after renal IR, their original sources remain uncertain. In the present study, we investigated the acute effect of renal IR on hepatic inflammatory cytokine expression and the mechanism involved. Sprague-Dawley rats that were subjected to renal IR (ischemia for 45 min followed by reperfusion for 1 h or 6 h) had increased plasma levels of creatinine, urea, and transaminases, indicating kidney and liver injuries. There was a significant increase in the expression of proinflammatory cytokine mRNA (MCP-1, TNF-α, IL-6) in the kidney and liver in rats with renal IR. This was accompanied by a significant increase in proinflammatory cytokine protein levels in the plasma, kidney, and liver. Activation of a nuclear transcription factor kappa B (NF-κB) was detected in the liver after renal IR. The inflammatory foci and an increased myeloperoxidase (MPO) activity were detected in the liver after renal IR, indicating hepatic inflammatory response and leukocyte infiltration. These results suggest that renal IR can directly activate NF-κB and induce acute production of proinflammatory cytokines in the liver. Renal IR-induced hepatic inflammatory response may contribute to impaired liver function and systemic inflammation.

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.

Vagus Nerve Stimulation Alleviates Hepatic Ischemia and Reperfusion Injury by Regulating Glutathione Production and Transformation

Inflammation and oxidative stress are pivotal mechanisms for the pathogenesis of ischemia and reperfusion injury (IRI). Vagus nerve stimulation (VNS) may participate in maintaining oxidative homeostasis and response to external stimulus or injury. We investigated whether the in vivo VNS can protect the liver from IRI. In this study, hepatic IRI were induced by ligating the vessels supplying the left and middle lobes of the liver, which underwent 1 h occlusion followed with 24 h reperfusion. VNS was initiated 15 min after ischemia and continued 30 min. Hepatic function, histology, and apoptosis rates were evaluated after 24 h reperfusion. Compared with the IRI group, VNS significantly improved hepatic function. The protective effect was accompanied by a reduction in histological damage in the ischemic area, and the apoptosis rate of hepatocytes has considerable reduction. To find the underlying mechanism, proteomic analysis was performed and differential expression of glutathione synthetase (GSS) and glutathione S-transferase (GST) was observed. Subsequently, test results indicated that VNS upregulated the expression of mRNA and protein of GSS and GST. Meanwhile, VNS increased the plasma levels of glutathione and glutathione peroxidases. We found that VNS alleviated hepatic IRI by upregulating the antioxidant glutathione via the GSS/glutathione/GST signaling pathway.

Increased susceptibility of mice obtained from in vitro fertilization to global cerebral ischemia-reperfusion injury: possible role of hydrogen sulphide and its biosynthetic enzymes

Aim of the Study: This study was designed to explore the relative susceptibility of in vitro fertilization (IVF)-conceived mice to global cerebral ischemic injury with the possible role of hydrogen sulphide and enzymes responsible for its production.Materials and Methods: IVF was carried to obtain pups, which were allowed to grow to the age of eight weeks. Thereafter, male mice were subjected to 20 min of global ischemia and 24 h of reperfusion. The mice obtained from other groups including normal mating, superovulation but normal mating and normal mating but embryo implantation were also subjected to global ischemia-reperfusion (I/R) injury.Results: IVF-derived mice exhibited significant more injury in response to I/R injury in comparison to other groups assessed in terms of impairment in locomotor activity, development of motor in coordination, neurological severity score, cerebral infarction and apoptosis markers (caspase-3 activity and Bcl-2 expression). Moreover, there was a relative decrease in the brain levels of hydrogen sulphide (H₂S) and its biosynthetic enzymes viz. cystathionine-β-synthase and cystathionine-γ-lyase. Interestingly, the levels of H₂S and cystathionine-γ-lyase were significantly low in IVF-derived mice in basal conditions also, i.e. before subjecting to I/R injury and these biochemical alterations were associated with the behavioural deficits in mice, even before subjecting to I/R injury.Conclusion: It is concluded that in vitro fertilization-derived mice are more susceptible to global cerebral I/R injury, which may be possibly due to decreased levels of hydrogen sulphide and its biosynthetic enzymes viz., cystathionine-β-synthase and cystathionine-γ-lyase.

Involvement of Endothelin-1, H2S and Nrf2 in Beneficial Effects of Remote Ischemic Preconditioning in Global Cerebral Ischemia-Induced Vascular Dementia in Mice

The present study explored the role of endothelin-1, H₂S, and Nrf2 in remote preconditioning (RIPC)-induced beneficial effects in ischemia-reperfusion (I/R)-induced vascular dementia. Mice were subjected to 20 min of global ischemia by occluding both carotid arteries to develop vascular dementia, which was assessed using Morris water maze test on 7th day. RIPC was given by subjecting hind limb to four cycles of ischemia (5 min) and reperfusion (5 min) and it significantly restored I/R-induced locomotor impairment, neurological severity score, cerebral infarction, apoptosis markers along with deficits in learning and memory. Biochemically, there was increase in the plasma levels of endothelin-1 along with increase in the brain levels of H₂S and its biosynthetic enzymes viz., cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CLS). There was also an increase in the expression of Nrf2 and glutathione reductase in the brain in response to RIPC. Pretreatment with bosentan (dual blocker of ET_A and ET_B receptors), amino-oxyacetic acid (CBS synthase inhibitor), and DL-propargylglycine (CLS inhibitor) significantly attenuated RIPC-mediated beneficial effects and biochemical alterations. The effects of bosentan on behavioral and biochemical parameters were more significant than individual treatments with CBS or CLS inhibitors. Moreover, CBS and CLS inhibitors did not alter the endothelin-1 levels possibly suggesting that endothelin-1 may act as upstream mediator of H₂S. It is concluded that RIPC may stimulate the release endothelin-1, which may activate CBS and CLS to increase the levels of H₂S and latter may increase the expression of Nrf2 to decrease oxidative stress and prevent vascular dementia.

Hydrogen Sulfide as a Novel Regulatory Factor in Liver Health and Disease

Hydrogen sulfide (H₂S), a colorless gas smelling of rotten egg, has long been recognized as a toxic gas and environment pollutant. However, increasing evidence suggests that H₂S acts as a novel gasotransmitter and plays important roles in a variety of physiological and pathological processes in mammals. H₂S is involved in many hepatic functions, including the regulation of oxidative stress, glucose and lipid metabolism, vasculature, mitochondrial function, differentiation, and circadian rhythm. In addition, H₂S contributes to the pathogenesis and treatment of a number of liver diseases, such as hepatic fibrosis, liver cirrhosis, liver cancer, hepatic ischemia/reperfusion injury, nonalcoholic fatty liver disease/nonalcoholic steatohepatitis, hepatotoxicity, and acute liver failure. In this review, the biosynthesis and metabolism of H₂S in the liver are summarized and the role and mechanism of H₂S in liver health and disease are further discussed.

Endogenous Hydrogen Sulfide Promotes Apoptosis via Mitochondrial Pathways in the Livers of Broilers with Selenium Deficiency Exudative Diathesis Disease

Hydrogen sulfide (H₂S), an endogenous gasotransmitter, plays an important role in apoptosis. Exudative diathesis (ED) disease is associated with dietary selenium (Se) deficiency in broilers. The liver is one of the target organs of Se deficiency; however, little is known about the effect of H₂S on apoptosis via mitochondrial pathways in the livers of broilers with ED disease. In the present study, we aimed to investigate the correlation between endogenous H₂S and mitochondrial-mediated apoptosis in the livers of broilers with ED disease, as induced by Se deficiency. One hundred twenty healthy, 1-day-old broilers were randomly assigned to one of two groups (60 each) based on diet: Basal diet (control group, 0.2 mg/kg Se) or a low-Se diet (-Se group, 0.033 mg/kg Se). At day 20, 15 broilers of a similar weight were sacrificed from the control group, while the same number of broilers were euthanatized from the -Se group when displaying typical symptoms of ED between days 18 and 25. The livers were collected, and apoptosis was measured using a TUNEL assay. Additionally, H₂S concentration, the expression of H₂S synthases of cystathionine γ-lyase (CSE), cystathionine β-synthase (CBS), and 3-mercaptopyruvate sulfurtransferase (3-MST), as well as mitochondrial apoptosis-related genes of Bcl-2, Bax, Bak, Cyt-C, Caspase-9, Caspase-3, and p53, were examined in livers. The results indicated that Se deficiency could induce apoptosis in the livers of broilers. Swelling, fractures, and vacuolization were visible in the mitochondrial cristae in the livers of the -Se group. The expression of H₂S synthase-related genes and H₂S concentration was significantly enhanced (P < 0.05) in the livers of the -Se group compared to controls. Moreover, a low-Se diet downregulated (P < 0.05) the level of Bcl-2 and upregulated (P < 0.05) the levels of Bax, Bak, Cyt-C, Caspase-9, Caspase-3, and p53. These results suggest that an H₂S increase in the livers of ED broilers, which was induced by Se deficiency, is related to apoptosis mediated by mitochondrial pathways.

Metabolite and gene expression profiles suggest a putative mechanism through which high dietary carbohydrates reduce the content of hepatic betaine in Megalobrama amblycephala

BACKGROUND

High-carbohydrate diets (HCD) are favoured by the aquaculture industry for economic reasons, but they can produce negative impacts on growth and induce hepatic steatosis. We hypothesised that the mechanism behind this is the reduction of hepatic betaine content.

OBJECTIVE

We further explored this mechanism by supplementing betaine (1%) to the diet of a farmed fish Megalobrama amblycephala.

METHODS

Four diet groups were designed: control (CD, 27.11% carbohydrates), high-carbohydrate (HCD, 36.75% carbohydrates), long-term betaine (LBD, 35.64% carbohydrates) and short-term betaine diet (SBD; 12 weeks HCD + 4 weeks LBD). We analysed growth performance, body composition, liver condition, and expression of genes and profiles of metabolites associated with betaine metabolism.

RESULTS

HCD resulted in poorer growth and liver health (compared to CD), whereas LBD improved these parameters (compared to HCD). HCD induced the expression of genes associated with glucose, serine and cystathionine metabolisms, and (non-significantly, p = .20) a betaine-catabolizing enzyme betaine-homocysteine-methyltransferase; and decreased the content of betaine, methionine, S-adenosylhomocysteine and carnitine. Betaine supplementation (LBD) reversed these patterns, and elevated betaine-homocysteine-methyltransferase, S-adenosylmethionine and S-adenosylhomocysteine (all p ≤ .05).

CONCLUSION

We hypothesise that HCD reduced the content of hepatic betaine by enhancing the activity of metabolic pathways from glucose to homocysteine, reflected in increased glycolysis, serine metabolism, cystathionine metabolism and homocysteine remethylation. Long-term dietary betaine supplementation improved the negative impacts of HCD, inculding growth parameters, body composition, liver condition, and betaine metabolism. However, betaine supplementation may have caused a temporary disruption in the metabolic homeostasis.

Specific downregulation of cystathionine β-synthase expression in the kidney during obesity

Hydrogen sulfide (H2 S) is recognized as a novel gasotransmitter involved in the regulation of nervous system, cardiovascular functions, inflammatory response, gastrointestinal system, and renal function. Cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE) are the major enzymes responsible for H2 S production through desulfuration reactions. H2 S is reported to play a protective role in both high-fat diet (HFD)-induced obese and diabetic mice. However, the synthesizing enzyme involved is not clearly elucidated. The current study was aimed to investigate the regulation of CBS and CSE in different tissues including the kidney, liver, and epididymal fat in C57BL/6 mice after a HFD (60% kcal fat) for 24 weeks. The protein and mRNA expression of CBS was specifically decreased in the kidney while CSE remained unchanged, which was further confirmed in db/db mice. In the liver, CSE expression was downregulated after HFD accompanied with unchanged CBS. Moreover, CSE expression was even upregulated in epididymal fat. The specific downregulation of renal CBS may contribute to decreased H2 S production, which could be a pathogenic mechanism of obesity. Increased CSE/H2 S pathway in epididymal fat possibly resulted in impaired glucose uptake and aggravated insulin resistance. In conclusion, our results revealed that CBS was selectively downregulated in both diet and gene-induced obesity models.

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.

Chemical Biology of H2S Signaling through Persulfidation

Signaling by H2S is proposed to occur via persulfidation, a posttranslational modification of cysteine residues (RSH) to persulfides (RSSH). Persulfidation provides a framework for understanding the physiological and pharmacological effects of H2S. Due to the inherent instability of persulfides, their chemistry is understudied. In this review, we discuss the biologically relevant chemistry of H2S and the enzymatic routes for its production and oxidation. We cover the chemical biology of persulfides and the chemical probes for detecting them. We conclude by discussing the roles ascribed to protein persulfidation in cell signaling pathways.

A novel S-sulfhydrated human serum albumin preparation suppresses melanin synthesis

Products of ultraviolet (UV) irradiation such as reactive oxygen species (ROS) and nitric oxide (NO) stimulate melanin synthesis. Reactive sulfur species (RSS) have been shown to have strong ROS and NO scavenging effects. However, the instability and low retention of RSS limit their use as inhibitors of melanin synthesis. The free thiol at Cys34 on human serum albumin (HSA) is highly stable, has a long retention and possess a high reactivity for RSS. We report herein on the development of an HSA based RSS delivery system. Sulfane sulfur derivatives released from sodium polysulfides (Na₂S_n) react readily with HSA. An assay for estimating the elimination of sulfide from polysulfide showed that almost all of the sulfur released from Na₂S_n bound to HSA. The Na₂S_n-treated HSA was found to efficiently scavenge ROS and NO produced from chemical reagents. The Na₂S_n-treated HSA was also found to inhibit melanin synthesis in B16 melanoma cells and this inhibition was independent of the number of added sulfur atoms. In B16 melanoma cells, the Na₂S_n-treated HSA also inhibited the levels of ROS and NO induced by UV radiation. Finally, the Na₂S_n-treated HSA inhibited melanin synthesis from L-DOPA and mushroom tyrosinase and suppressed the extent of aggregation of melanin pigments. These data suggest that Na₂S_n-treated HSA inhibits tyrosinase activity for melanin synthesis via two pathways; by directly inhibiting ROS signaling and by scavenging NO. These findings indicate that Na₂S_n-treated HSA has potential to be an attractive and effective candidate for use as a skin whitening agent.

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We developed of an Reactive sulfur species delivery system based on human serum albumin.

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The novel polysulfides-added albumin could inhibit melanin synthesis in melanocyte.

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The polysulfides-added albumin also inhibited the levels of ROS and NO induced by UV radiation.

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The polysulfides-added albumin has the potential to be an attractive candidate for a whitening agent.

Reduced adipose tissue H2S in obesity

Hydrogen sulfide (H₂S) is an endogenously produced signaling molecule synthesized by cystathionine γ-lyase (CSE), cystathionine β-synthase (CBS) and 3-mercaptopyruvate sulfurtransferase (3-MST). Given that H₂S exerts significant effects on bioenergetics and metabolism, the goal of the current study was to determine the expression of H₂S-producing enzymes in adipose tissues in models of obesity and metabolic disruption. Mice fed a western diet expressed lower mRNA levels of all three enzymes in epididymal fat (EWAT), while only CSE and 3-MST were reduced in brown adipose tissue (BAT). At the protein level 3-MST was reduced in all fat depots studied. Using db/db mice, a genetic model of obesity, we found that CSE, CBS and 3-MST mRNA were reduced in white fat, while only CSE was reduced in BAT. CBS and CSE protein levels were suppressed in all three fat depots. In a model of age-related weight gain, no reduction in the mRNA of any of the enzymes was noted. Smaller amounts of 3-MST protein were found in EWAT, while both CSE and 3-MST were reduced in BAT. Tissue levels of H₂S were lower in WAT in HFD mice; both WAT and BAT contained lower H₂S amounts in db/db animals. Taken together, our data suggest that obesity is associated with a decreased expression of H₂S-synthesizing enzymes and reduced H₂S levels in adipose tissues of mice. We propose that the reduction in H₂S may contribute to the metabolic response associated with obesity. Further work is needed to determine whether restoring H₂S levels may have a beneficial effect on obesity-associated metabolic alterations.

Downregulation of Glutathione Biosynthesis Contributes to Oxidative Stress and Liver Dysfunction in Acute Kidney Injury

Ischemia-reperfusion is a common cause for acute kidney injury and can lead to distant organ dysfunction. Glutathione is a major endogenous antioxidant and its depletion directly correlates to ischemia-reperfusion injury. The liver has high capacity for producing glutathione and is a key organ in modulating local and systemic redox balance. In the present study, we investigated the mechanism by which kidney ischemia-reperfusion led to glutathione depletion and oxidative stress. The left kidney of Sprague-Dawley rats was subjected to 45 min ischemia followed by 6 h reperfusion. Ischemia-reperfusion impaired kidney and liver function. This was accompanied by a decrease in glutathione levels in the liver and plasma and increased hepatic lipid peroxidation and plasma homocysteine levels. Ischemia-reperfusion caused a significant decrease in mRNA and protein levels of hepatic glutamate-cysteine ligase mediated through the inhibition of transcription factor Nrf2. Ischemia-reperfusion inhibited hepatic expression of cystathionine γ-lyase, an enzyme responsible for producing cysteine (an essential precursor for glutathione synthesis) through the transsulfuration pathway. These results suggest that inhibition of glutamate-cysteine ligase expression and downregulation of the transsulfuration pathway lead to reduced hepatic glutathione biosynthesis and elevation of plasma homocysteine levels, which, in turn, may contribute to oxidative stress and distant organ injury during renal ischemia-reperfusion.

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.

Maternal N-acetylcysteine therapy regulates hydrogen sulfide-generating pathway and prevents programmed hypertension in male offspring exposed to prenatal dexamethasone and postnatal high-fat diet

Nitric oxide (NO) and hydrogen sulfide (H2S) pathways are involved in the development of hypertension, a condition that can originate from early life. We examined whether asymmetric dimethylarginine (ADMA, a nitric oxide synthase inhibitor)/NO and H2S generating pathway contributed to programmed hypertension in offspring exposed to prenatal dexamethasone (DEX) and postnatal high-fat (HF) and whether N-acetylcysteine (NAC) therapy prevented this process. We examined 16-week-old male rat offspring from five groups: control, DEX (0.1 mg/kg i.p. from gestational day 16-22), HF (58% high-fat diet from weaning to 4 months of age), DEX+HF, and NAC (1% in drinking water during lactation). Prenatal DEX and postnatal HF diet synergistically induced programmed hypertension in adult offspring, which was prevented by maternal NAC therapy. We attributed the protective effects of NAC on two-hit induced programmed hypertension to the reduction of plasma ADMA, restoration of plasma l-arginine-to-ADMA ratio, upregulation of gene expression of H2S-generating enzymes, restoration of renal 3-mercaptopyruvate sulphurtransferase (3MST) protein levels and activity, induction of plasma glutathione level, and reduction of oxidative stress. Manipulation of the ADMA-NO and H2S-generating pathways by maternal NAC therapy may be a potential approach to prevent programmed hypertension induced by two-hit insults.

H2S Synthesizing Enzymes: Biochemistry and Molecular Aspects

Hydrogen sulfide (H2S) is a biologically active gas that is synthesized naturally by three enzymes, cystathionine γ-lyase (CSE), cystathionine β-synthetase (CBS) and 3-mercaptopyruvate sulfurtransferase (3-MST). These enzymes are constitutively present in a wide array of biological cells and tissues and their expression can be induced by a number of disease states. It is becoming increasingly clear that H2S is an important mediator of a wide range of cell functions in health and in disease. This review therefore provides an overview of the biochemical and molecular regulation of H2S synthesizing enzymes both in physiological conditions and their modulation in disease states with particular focus on their regulation in asthma, atherosclerosis and diabetes. The importance of small molecule inhibitors in the study of molecular pathways, the current use of common H2S synthesizing enzyme inhibitors and the relevant characteristics of mice in which these enzymes have been genetically deleted will also be summarized. With a greater understanding of the molecular regulation of these enzymes in disease states, as well as the availability of novel small molecules with high specificity targeted towards H2S producing enzymes, the potential to regulate the biological functions of this intriguing gas H2S for therapeutic effect can perhaps be brought one step closer.

Tyrosol Attenuates High Fat Diet-Induced Hepatic Oxidative Stress: Potential Involvement of Cystathionine β-Synthase and Cystathionine γ-Lyase

The Mediterranean diet is known for its cardioprotective effects. Recently, its protective qualities have also been reported in patients with non-alcoholic fatty liver disease (NAFLD). Oxidative stress is one of the important factors responsible for the development and progression of NAFLD. Hydrogen sulfide (H2S), a multifaceted gasotransmitter, has emerged as a potential therapeutic target in NAFLD. Cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE) are major enzymes responsible for endogenous H2S synthesis. Since oxidative stress contributes to NAFLD pathogenesis, the objective of this study was to investigate the effect of tyrosol, a major compound in olive oil and white wine, on high fat diet-induced hepatic oxidative stress and the mechanisms involved. Mice (C57BL/6) were fed for 5 weeks with a control diet (10 % kcal fat), a high fat diet (60 % kcal fat, HFD) or a HFD supplemented with tyrosol. High fat diet feeding induced hepatic oxidative stress, as indicated by the significant increase in lipid peroxidation and NADPH oxidase activity. Tyrosol supplementation significantly increased hepatic CBS and CSE expression and H2S synthesis in high fat diet-fed mice. Such effects were associated with the attenuation of high fat diet-induced hepatic lipid peroxidation and the restoration of the redox equilibrium of the antioxidant glutathione. Tyrosol also inhibited palmitic acid-induced oxidative stress in hepatocytes (HepG2 cells). These results suggest that the antioxidant properties of tyrosol may be mediated through functional changes in CBS and CSE activity, which might contribute to the hepatoprotective effect of the Mediterranean diet.

Folic acid supplementation during high-fat diet feeding restores AMPK activation via an AMP-LKB1-dependent mechanism

AMPK is an endogenous energy sensor that regulates lipid and carbohydrate metabolism. Nonalcoholic fatty liver disease (NAFLD) is regarded as a hepatic manifestation of metabolic syndrome with impaired lipid and glucose metabolism and increased oxidative stress. Our recent study showed that folic acid supplementation attenuated hepatic oxidative stress and lipid accumulation in high-fat diet-fed mice. The aim of the present study was to investigate the effect of folic acid on hepatic AMPK during high-fat diet feeding and the mechanisms involved. Male C57BL/6J mice were fed a control diet (10% kcal fat), a high-fat diet (60% kcal fat), or a high-fat diet supplemented with folic acid (26 mg/kg diet) for 5 wk. Mice fed a high-fat diet exhibited hyperglycemia, hepatic cholesterol accumulation, and reduced hepatic AMPK phosphorylation. Folic acid supplementation restored AMPK phosphorylation (activation) and reduced blood glucose and hepatic cholesterol levels. Activation of AMPK by folic acid was mediated through an elevation of its allosteric activator AMP and activation of its upstream kinase, namely, liver kinase B1 (LKB1) in the liver. Consistent with in vivo findings, 5-methyltetrahydrofolate (bioactive form of folate) restored phosphorylation (activation) of both AMPK and LKB1 in palmitic acid-treated HepG2 cells. Activation of AMPK by folic acid might be responsible for AMPK-dependent phosphorylation of HMG-CoA reductase, leading to reduced hepatic cholesterol synthesis during high-fat diet feeding. These results suggest that folic acid supplementation may improve cholesterol and glucose metabolism by restoration of AMPK activation in the liver.

H2S-induced S-sulfhydration of pyruvate carboxylase contributes to gluconeogenesis in liver cells

BACKGROUND

Cystathionine gamma-lyase (CSE)-derived hydrogen sulfide (H(2)S) possesses diverse roles in the liver, affecting lipoprotein synthesis, insulin sensitivity, and mitochondrial biogenesis. H(2)S S-sulfhydration is now proposed as a major mechanism for H(2)S-mediated signaling. Pyruvate carboxylase (PC) is an important enzyme for gluconeogenesis. S-sulfhydration regulation of PC by H(2)S and its implication in gluconeogenesis in the liver have been unknown.

METHODS

Gene expressions were analyzed by real-time PCR and western blotting, and protein S-sulfhydration was assessed by both modified biotin switch assay and tag switch assay. Glucose production and PC activity was measured with coupled enzyme assays, respectively.

RESULTS

Exogenously applied H(2)S stimulates PC activity and gluconeogenesis in both HepG2 cells and mouse primary liver cells. CSE overexpression enhanced but CSE knockout reduced PC activity and gluconeogenesis in liver cells, and blockage of PC activity abolished H(2)S-induced gluconeogenesis. H(2)S had no effect on the expressions of PC mRNA and protein, while H(2)S S-sulfhydrated PC in a dithiothreitol-sensitive way. PC S-sulfhydration was significantly strengthened by CSE overexpression but attenuated by CSE knockout, suggesting that H(2)S enhances glucose production through S-sulfhydrating PC. Mutation of cysteine 265 in human PC diminished H(2)S-induced PC S-sulfhydration and activity. In addition, high-fat diet feeding of mice decreased both CSE expression and PC S-sulfhydration in the liver, while glucose deprivation of HepG2 cells stimulated CSE expression.

CONCLUSIONS

CSE/H(2)S pathway plays an important role in the regulation of glucose production through S-sulfhydrating PC in the liver.

GENERAL SIGNIFICANCE

Tissue-specific regulation of CSE/H(2)S pathway might be a promising therapeutic target of diabetes and other metabolic syndromes.

Hydrogen-sulfide-mediated vasodilatory effect of nucleoside 5'-monophosphorothioates in perivascular adipose tissue

Hydrogen sulfide (H2S) is synthesized in perivascular adipose tissue (PVAT) and induces vasorelaxation. We examined whether the sulfur-containing AMP and GMP analogs AMPS and GMPS can serve as the H2S donors in PVAT. H2S production by isolated rat periaortic adipose tissue (PAT) was measured with a polarographic sensor. In addition, phenylephrine-induced contractility of aortic rings with (+) or without (-) PAT was examined. Isolated PAT produced H2S from AMPS or GMPS in the presence of the P2X7 receptor agonist BzATP. Phenylephrine-induced contractility of PAT(+) rings was lower than of PAT(-) rings. AMPS or GMPS had no effect on the contractility of PAT(-) rings, but used together with BzATP reduced the contractility of PAT(+) rings when endogenous H2S production was inhibited with propargylglycine. A high-fat diet reduced endogenous H2S production by PAT. Interestingly, AMPS and GMPS were converted to H2S by PAT of obese rats, and reduced contractility of PAT(+) aortic rings isolated from these animals even in the absence of BzATP. We conclude that (i) AMPS and GMPS can be hydrolyzed to H2S by PAT when P2X7 receptors are activated, (ii) a high-fat diet impairs endogenous H2S production by PAT, (iii) AMPS and GMPS restore the anticontractile effects of PAT in obese animals without P2X7 stimulation.

Exogenous hydrogen sulfide mitigates the fatty liver in obese mice through improving lipid metabolism and antioxidant potential

Background

Nonalcoholic fatty liver disease (NAFLD) is the most common liver disease in the world. Hydrogen sulfide (H2S) plays an important role in physiology and pathophysiology of liver. However, whether exogenous H2S could mitigate the hepatic steatosis in mice remains unclear. The aim of this study is to evaluate the effects of H2S on fatty liver.

Methods

C57BL/6 mice were fed with either a high-fat diet (HFD) or a normal fat diet (NFD) for 16 weeks. After 12 weeks of feeding, the HFD-fed mice were injected one time per day with NaHS or saline for the followed 4 weeks.

Results

Compared to NFD, HFD could induce an accumulation of lipids in liver and a damage of hepatic structure. Compared to saline treatment, in the liver of HFD fed mice H2S treatment could significantly (1) recover the structure; (2) decrease the accumulation of lipids including triglyceride (TG) and total cholesterol (TC); (3) decrease the expression of fatty acid synthase (FAS) and increase the expression of carnitine palmitoyltransferase-1 (CPT-1); (4) reduce malondialdehyde (MDA) levels; (5) increase the activities of superoxide dismutase (SOD) and glutathione peroxidase (GPx).

Conclusion

H2S could mitigate the fatty liver by improving lipid metabolism and antioxidant potential in HFD-induced obese mice.

Alternative functions of the brain transsulfuration pathway represent an underappreciated aspect of brain redox biochemistry with significant potential for therapeutic engagement

Scientific appreciation for the subtlety of brain sulfur chemistry has lagged, despite understanding that the brain must maintain high glutathione (GSH) to protect against oxidative stress in tissue that has both a high rate of oxidative respiration and a high content of oxidation-prone polyunsaturated fatty acids. In fact, the brain was long thought to lack a complete transsulfuration pathway (TSP) for cysteine synthesis. It is now clear that not only does the brain possess a functional TSP, but brain TSP enzymes catalyze a rich array of alternative reactions that generate novel species including the gasotransmitter hydrogen sulfide (H2S) and the atypical amino acid lanthionine (Lan). Moreover, TSP intermediates can be converted to unusual cyclic ketimines via transamination. Cell-penetrating derivatives of one such compound, lanthionine ketimine (LK), have potent antioxidant, neuroprotective, neurotrophic, and antineuroinflammatory actions and mitigate diverse neurodegenerative conditions in preclinical rodent models. This review will explore the source and function of alternative TSP products, and lanthionine-derived metabolites in particular. The known biological origins of lanthionine and its ketimine metabolite will be described in detail and placed in context with recent discoveries of a GSH- and LK-binding brain protein called LanCL1 that is proving essential for neuronal antioxidant defense; and a related LanCL2 homolog now implicated in immune sensing and cell fate determinations. The review will explore possible endogenous functions of lanthionine metabolites and will discuss the therapeutic potential of lanthionine ketimine derivatives for mitigating diverse neurological conditions including Alzheimer׳s disease, stroke, motor neuron disease, and glioma.

Downregulation of cystathionine β-synthase and cystathionine γ-lyase expression stimulates inflammation in kidney ischemia-reperfusion injury

Inflammation plays a critical role in kidney ischemia-reperfusion injury but mechanisms of increased proinflammatory cytokine expression are not completely understood. Kidney has a high expression of cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE) that can synthesize hydrogen sulfide. CBE and CSE are also responsible for the synthesis of cysteine, an essential precursor for glutathione, an antioxidant. Reduced hydrogen sulfide and glutathione production is associated with multiple organ injury. Although pro- and anti-inflammatory effects of hydrogen sulfide have been reported, its role in ischemia-reperfusion-induced inflammation in the kidney has not been well addressed. The aim of this study was to investigate the effect of CBS and CSE-mediated hydrogen sulfide and glutathione production on kidney inflammatory response and the mechanism involved. The left kidney of Sprague-Dawley rat was subjected to 45-min ischemia followed by reperfusion for 24 h. Ischemia-reperfusion caused a significant decrease in CBS and CSE mRNA and protein levels with a concomitant reduction of glutathione and hydrogen sulfide production in the kidney while the expression of proinflammatory cytokine expression (MCP-1, IL-6) was elevated. Hypoxia-reoxygenation of proximal tubular cells led to a decrease in CBS and CSE expression and an increase in proinflammatory cytokine expression. Supplementation of glutathione or hydrogen sulfide donor (NaHS) effectively attenuated cytokine expression in tubular cells. These results suggested that ischemia-reperfusion impaired CBS and CSE-mediated glutathione and hydrogen sulfide production in the kidney, which augmented the expression of proinflammatory cytokines. Regulation of CBS and CSE expression may be therapeutically relevant in alleviating ischemia-reperfusion-induced inflammation and improving kidney function.

Hydrogen sulfide and the liver

Hydrogen sulfide (H2S) is a gasotransmitter that regulates numerous physiological and pathophysiological processes in our body. Enzymatic production of H2S is catalyzed by cystathionine γ-lyase (CSE), cystathionine β-synthase (CBS), and 3-mercaptopyruvate sulfurtransferase (MST). All these three enzymes present in the liver and via H2S production regulate liver functions. The liver is the hub for metabolism of glucose and lipids, and maintains the level of circulatory lipids through lipoprotein metabolism. Hepatic H2S metabolism affects glucose metabolism, insulin sensitivity, lipoprotein synthesis, mitochondrial biogenetics and biogenesis. Malfunction of hepatic H2S metabolism may be involved in many liver diseases, such as hepatic fibrosis and hepatic cirrhosis.