The liver as a central regulator of hydrogen sulfide

Structure and gene expression changes of the gill and liver in juvenile black porgy (Acanthopagrus schlegelii) under different salinities

Black porgy (Acanthopagrus schlegelii) is an important marine aquaculture species in China. It is an ideal object for the cultivation of low-salinity aquaculture strains in marine fish and the study of salinity tolerance mechanisms in fish because of its strong low-salinity tolerance ability. Gill is the main osmoregulatory organ in fish, and the liver plays an important role in the adaptation of the organism to stressful environments. In order to understand the coping mechanisms of the gills and livers of black porgy in different salinity environments, this study explored these organs after 30 days of culture in hypoosmotic (0.5 ppt), isosmotic (12 ppt), and normal seawater (28 ppt) at histologic, physiologic, and transcriptomic levels. The findings indicated that gill exhibited a higher number of differentially expressed genes than the liver, emphasizing the gill's heightened sensitivity to salinity changes. Protein interaction networks and enrichment analyses highlighted energy metabolism as a key regulatory focus at both 0.5 ppt and 12 ppt salinity in gills. Additionally, gills showed enrichment in ions, substance transport, and other metabolic pathways, suggesting a more direct regulatory response to salinity stress. The liver's regulatory patterns at different salinities exhibited significant distinctions, with pathways and genes related to metabolism, immunity, and antioxidants predominantly activated at 0.5 ppt, and molecular processes linked to cell proliferation taking precedence at 12 ppt salinity. Furthermore, the study revealed a reduction in the volume of the interlamellar cell mass (ILCM) of the gills, enhancing the contact area of the gill lamellae with water. At 0.5 ppt salinity, hepatic antioxidant enzyme activity increased, accompanied by oxidative stress damage. Conversely, at 12 ppt salinity, gill NKA activity significantly decreased without notable changes in liver structure. These results underscore the profound impact of salinity on gill structure and function, highlighting the crucial role of the liver in adapting to salinity environments.

Digestive dynamics: Unveiling interplay between the gut microbiota and the liver in macronutrient metabolism and hepatic metabolic health

Although the liver is the largest metabolic organ in the body, it is not alone in functionality and is assisted by "an organ inside an organ," the gut microbiota. This review attempts to shed light on the partnership between the liver and the gut microbiota in the metabolism of macronutrients (i.e., proteins, carbohydrates, and lipids). All nutrients absorbed by the small intestines are delivered to the liver for further metabolism. Undigested food that enters the colon is metabolized further by the gut microbiota that produces secondary metabolites, which are absorbed into portal circulation and reach the liver. These microbiota-derived metabolites and co-metabolites include ammonia, hydrogen sulfide, short-chain fatty acids, secondary bile acids, and trimethylamine N-oxide. Further, the liver produces several compounds, such as bile acids that can alter the gut microbial composition, which can in turn influence liver health. This review focuses on the metabolism of these microbiota metabolites and their influence on host physiology. Furthermore, the review briefly delineates the effect of the portosystemic shunt on the gut microbiota-liver axis, and current understanding of the treatments to target the gut microbiota-liver axis.

The role and mechanism of hydrogen sulfide in liver fibrosis

Hydrogen sulfide (H2S) is the third new gas signaling molecule in the human body after the discovery of NO and CO. Similar to NO, it has the functions of vasodilation, anti-inflammatory, antioxidant, and regulation of cell formation. Enzymes that can produce endogenous H2S, such as CSE, CSB, and 3-MST, are common in liver tissues and are important regulatory molecules in the liver. In the development of liver fibrosis, H2S concentration and expression of related enzymes change significantly, which makes it possible to use exogenous gases to treat liver diseases. This review summarizes the role of H2S in liver fibrosis and its complications induced by NAFLD and CCl4, and elaborates on the anti-liver fibrosis effect of H2S through the mechanism of reducing oxidative stress, inhibiting inflammation, regulating autophagy, regulating glucose and lipid metabolism, providing theoretical reference for further research on the treatment of liver fibrosis with H2S.

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.

Exogenous hydrogen sulfide alleviates hepatic endoplasmic reticulum stress via SIRT1/FoxO1/PCSK9 pathway in NAFLD

High-fat-induced endoplasmic reticulum (ER) stress has been the main reason for the occurrence and development of nonalcoholic fatty liver disease (NAFLD). Hydrogen sulfide (H2 S) produces a marked effect on regulating lipid metabolism and antioxidation, whose effects on ER stress of NAFLD are still unclear. Here, we studied the influence of exogenous H2 S on NAFLD and its potential mechanism. In vivo, NAFLD model was induced by high-fat diet (HFD) for 12 weeks, followed by intraperitoneal injection of exogenous H2 S intervention for 4 weeks. HepG2 cells exposure to lipid mixture (LM) were used as vitro model to explore the potential mechanism. We found exogenous H2 S significantly inhibited the hepatic ER stress and improved the liver fat deposition of HFD-fed mice. These similar results were also observed in HepG2 cells dealt with LM after exogenous H2 S treatment. Further mechanism studies showed exogenous H2 S strengthened the combination of FoxO1 with the PCSK9 promoter gene through SIRT1-mediated deacetylation, thereby inhibiting the PCSK9 expression to relieve the hepatic ER stress. However, SIRT1 knockout eliminated the effects of exogenous H2 S on FoxO1 deacetylation, PCSK9 inhibition, and remission of hepatic ER stress and steatosis. In conclusion, exogenous H2 S improved NAFLD by inhibiting hepatic ER stress through SIRT1/FoxO1/PCSK9 pathway. Exogenous H2 S and ER stress may be potential drug and target for the treatment of NAFLD, respectively.

Sodium thiosulfate refuels the hepatic antioxidant pool reducing ischemia-reperfusion-induced liver injury

Ischemia-reperfusion injury is a critical liver condition during hepatic transplantation, trauma, or shock. An ischemic deprivation of antioxidants and energy characterizes liver injury in such cases. In the face of increased reactive oxygen production, hepatocytes are vulnerable to the reperfusion driving ROS generation and multiple cell-death mechanisms. In this study, we investigate the importance of hydrogen sulfide as part of the liver's antioxidant pool and the therapeutic potency of the hydrogen sulfide donors sodium sulfide (Na₂S, fast releasing) and sodium thiosulfate (STS, Na₂S₂O₃, slow releasing). The mitoprotection and toxicity of STS and Na₂S were investigated on isolated mitochondria and a liver perfusion oxidative stress model by adding text-butyl hydroperoxide and hydrogen sulfide donors. The respiratory capacity of mitochondria, hepatocellular released LDH, glutathione, and lipid-peroxide levels were quantified. In addition, wild-type and cystathionine-γ-lyase knockout mice were subjected to warm selective ischemia-reperfusion injury by clamping the main inflow for 1 h followed by reperfusion of 1 or 24 h. A subset of animals was treated with STS shortly before reperfusion. Glutathione, plasma ALT, and lipid-peroxide levels were investigated alongside mitochondrial changes in structure (electron microscopy) and function (intravital microscopy). Liver tissue necrosis quantified 24 h after reperfusion indicates the net effects of the treatment on the organ. STS refuels and protects the endogenous antioxidant pool during liver ischemia-reperfusion injury. In addition, STS-mediated ROS scavenging significantly reduced lipid peroxidation and mitochondrial damage, resulting in better molecular and histopathological preservation of the liver tissue architecture. STS prevents tissue damage in liver ischemia-reperfusion injury by increasing the liver's antioxidant pool, thereby protecting mitochondrial integrity.

Oxygen-binding properties of blood in insulin resistance with different asprosin content

The oxygen-binding properties of blood were studied in male patients with insulin resistance (IR) with different levels of asprosin. The content of asprosin, parameters of blood oxygen transport function, as well as gas transmitters, nitrogen monoxide and hydrogen sulfide, were determined in the venous blood plasma. In the studied IR patients with increased blood asprosin content, impaired blood oxygenation was noted; IR patients with normal body weight had increased hemoglobin affinity for oxygen, while in IR patients with overweight and the 1st degree obesity, this parameter decreased. The detected increase in the concentration of nitrogen monoxide and the decrease in hydrogen sulfide may be important for the oxygen-binding properties of the blood and the development of metabolic imbalance.

1,25-Dihydroxycholecalciferol down-regulates 3-mercaptopyruvate sulfur transferase and caspase-3 in rat model of non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is the commonest cause of liver morbidity and mortality and has multiple unclear pathogenic mechanisms. Vitamin D deficiency was associated with increased incidence and severity of NAFLD. Increased hepatic expression of 3-mercaptopyruvate sulfur transferase (MPST) and dysregulated hepatocyte apoptosis were involved in NAFLD pathogenesis. We aimed to explore the protective effect of 1,25-Dihydroxycholecalciferol (1,25-(OH)₂ D3) against development of NAFLD and the possible underlying mechanisms, regarding hepatic MPST and caspase-3 expression. 60 male adult rats were divided into 4 and 12 week fed groups; each was subdivided into control, high-fat diet (HFD), and HFD + VD. Serum levels of lipid profile parameters, liver enzymes, insulin, glucose, C-reactive protein (CRP), tumor necrosis factor alpha (TNF-α), and hepatic levels of malondialdehyde (MDA), total antioxidant capacity (TAC), and reactive oxygen species (ROS) were measured. BMI and HOMA-IR were calculated, and liver tissues were processed for histopathological and immunohistochemical studies. The present study found that 1,25-(OH)₂ D3 significantly decreased BMI, HOMA-IR, serum levels of glucose, insulin, liver enzymes, lipid profile parameters, CRP, TNF-α, hepatic levels of MDA, ROS, hepatic expression of MPST, TNF-α, 8-hydroxy-2'-deoxyguanosine (8-OHdG), and caspase-3; and significantly increased hepatic TAC in both HFD-fed groups. In conclusion: Administration of 1,25-(OH)₂ D3 with HFD abolished the NAFLD changes associated with HFD in 4-week group, and markedly attenuated the changes in 12-week group. The anti-apoptotic effect via decrement of caspase-3 and MPST expression are novel mechanisms suggested to be implicated in the protective effect of 1,25-(OH)₂ D3.

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.

The double-edged role of hydrogen sulfide in the pathomechanism of multiple liver diseases

In mammalian systems, hydrogen sulfide (H₂S)-one of the three known gaseous signaling molecules in mammals-has been found to have a variety of physiological functions. Existing studies have demonstrated that endogenous H₂S is produced through enzymatic and non-enzymatic pathways. The liver is the body's largest solid organ and is essential for H₂S synthesis and elimination. Mounting evidence suggests H₂S has essential roles in various aspects of liver physiological processes and pathological conditions, such as hepatic lipid metabolism, liver fibrosis, liver ischemia‒reperfusion injury, hepatocellular carcinoma, hepatotoxicity, and acute liver failure. In this review, we discuss the functions and underlying molecular mechanisms of H₂S in multiple liver pathophysiological conditions.

Hydrogen Availability Is Dependent on the Actions of Both Hydrogen-Producing and Hydrogen-Consuming Microbes

Hydrogen gas (H₂) is produced by H₂-producing microbes in the gut during polysaccharide fermentation. Gut microbiome also includes H₂-consuming microbes utilizing H₂ for metabolism: methanogens producing methane, CH₄, and sulfate-reducing bacteria producing hydrogen sulfide, H₂S. H₂S is not measured in the evaluation of gaseous byproducts of microbial fermentation. We hypothesize that the availability of measured H₂ depends on both hydrogen producers and hydrogen consumers by measuring H₂ in vitro and in vivo. In the in vitro study, groups were Bacteroides thetaiotaomicron (B. theta, H₂ producers), Desulfovibrio vulgaris (D. vulgaris, H₂ consumers), and D. vulgaris + B. theta combined. Gas samples were collected at 2 h and 24 h after incubation and assayed for H₂, CH₄, and H₂S. In the in vivo study Sprague-Dawley rats were gavaged with suspended bacteria in four groups: B. theta, D. vulgaris, combined, and control. Gas was analyzed for H₂ at 60 min. In the in vitro experiment, H₂ concentration was higher in the combined group (188 ± 93.3 ppm) compared with D. vulgaris (27.17 ± 9.6 ppm) and B. theta groups (34.2 ± 29.8 ppm; P < 0.05); H₂S concentration was statistically higher in the combined group (10.32 ± 1.5 ppm) compared with B. theta (0.19 ± 0.03 ppm) and D. vulgaris group (3.46 ± 0.28 ppm; P < 0.05). In the in vivo study, H₂ concentrations were significantly higher in the B. theta group (44.3 ± 6.0 ppm) compared with control (31.8 ± 4.3) and the combined group (34.2 ± 8.7, P < 0.05). This study shows that sulfate-reducing bacteria could convert available H₂ to H₂S, leading to measured hydrogen levels that are dependent on the actions of both H₂ producers and H₂ consumers.

Function of gaseous hydrogen sulfide in liver fibrosis

Over the past few years, hydrogen sulfide (H₂S) has been shown to exert several biological functions in mammalian. The endogenous production of H₂S is mainly mediated by cystathione β-synthase, cystathione γ-lyase and 3-mercaptopyruvate sulfur transferase. These enzymes are broadly expressed in liver tissue and regulates liver function by working on a variety of molecular targets. As an important regulator of liver function, H₂S is critically involved in the pathogenesis of various liver diseases, such as non-alcoholic steatohepatitis and liver cancer. Targeting H₂S-generating enzymes may be a therapeutic strategy for controlling liver diseases. This review described the function of H₂S in liver disease and summarized recent characterized role of H₂S in several cellular process of the liver.

Ratiometric Detection of H2S in Liver Injury by Activated Two-Wavelength Photoacoustic Imaging

Metformin is commonly used for clinical treatment of type-2 diabetes, but long-term or overdose intake of metformin usually causes selective upregulation of H₂S level in the liver, resulting in liver injury. Therefore, tracking the changes of H₂S content in the liver would contribute to the prevention and diagnosis of liver injury. However, in the literature, there are few reports on ratiometric PA molecular probes for H₂S detection in drug-induced liver injury (DILI). Accordingly, here we developed a H₂S-activated ratiometric PA probe, namely BDP-H₂S, based Aza-BODIPY dye for detecting the H₂S upregulation of metformin-induced liver injury. Due to the intramolecular charge transfer (ICT) effect, BDP-H₂S exhibited a strong PA signal at 770 nm. Following the response to H₂S, its ICT effect was recovered which showed a decrement of PA₇₇₀ and an enhancement of PA₈₄₀. The ratiometric PA signal (PA₈₄₀/PA₇₇₀) showed excellent H₂S selectivity response with a low limit of detection (0.59 μM). Bioimaging experiments demonstrated that the probe has been successfully used for ratiometric PA imaging of H₂S in cells and metformin-induced liver injury in mice. Overall, the designed probe emerges as a powerful tool for noninvasive and accurate imaging of H₂S level and tracking its distribution and variation in liver in-real time.

[Features of ozone effect on the oxygen-dependent blood processes under hypercapnia conditions]

The aim of this work is to study of ozone effect on blood oxygen-dependent processes under hypercapnia conditions. The studied blood samples are pretreated with a hypercapnic gas mixture followed by the addition of ozonized isotonic sodium chloride solution (with an ozone concentration of 6 mg/l), as well as gaseous transmitters donors, nitroglycerin and sodium hydrosulfide. It has been established that hypercapnia enhanced the ozone effect on the blood oxygen transport function and was characterized by the oxyhemoglobin dissociation curve shift to the right, also increased hydrogen sulfide synthesis and absence of changes in the nitrates/nitrites concentration. Under these conditions nitroglycerin and sodium hydrosulfide did not change the parameters of the blood gas transport function, but increased the level of nitrate/nitrite and hydrogen sulfide. Preliminary hypercapnia does not eliminate the activating effect of ozone on the free radical oxidation processes, and the addition of the applied gaseous transmitter donors does not contribute to the regulation of the studied parameters.

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.

Desulfovibrio vulgaris, a potent acetic acid-producing bacterium, attenuates nonalcoholic fatty liver disease in mice

The emerging evidence supports the use of prebiotics like herb-derived polysaccharides for treating nonalcoholic fatty liver disease (NAFLD) by modulating gut microbiome. The present study was initiated on the microbiota-dependent anti-NAFLD effect of Astragalus polysaccharides (APS) extracted from Astragalus mongholicus Bunge in high-fat diet (HFD)-fed mice. However, the exact mechanisms underlying the beneficial effects of APS on NAFLD formation remain poorly understood.Co-housing experiment was used to assess the microbiota dependent anti-NAFLD effect of APS. Then, targeted metabolomics and metagenomics were adopted for determining short-chain fatty acids (SCFAs) and bacteria that were specifically enriched by APS. Further in vitro experiment was carried out to test the capacity of SCFAs-producing of identified bacterium. Finally, the anti-NAFLD efficacy of identified bacterium was tested in HFD-fed mice.Our results first demonstrated the anti-NAFLD effect of APS in HFD-fed mice and the contribution of gut microbiota. Moreover, our results indicated that SCFAs, predominantly acetic acid were elevated in APS-supplemented mice and ex vivo experiment. Metagenomics revealed that D. vulgaris from Desulfovibrio genus was not only enriched by APS, but also a potent generator of acetic acid, which showed significant anti-NAFLD effects in HFD-fed mice. In addition, D. vulgaris modulated the hepatic gene expression pattern of lipids metabolism, particularly suppressed hepatic fatty acid synthase (FASN) and CD36 protein expression.Our results demonstrate that APS enriched D. vulgaris is effective on attenuating hepatic steatosis possibly through producing acetic acid, and modulation on hepatic lipids metabolism in mice. Further studies are warranted to explore the long-term impacts of D. vulgaris on host metabolism and the underlying mechanism.

The hepatic compensatory response to elevated systemic sulfide promotes diabetes

Impaired hepatic glucose and lipid metabolism are hallmarks of type 2 diabetes. Increased sulfide production or sulfide donor compounds may beneficially regulate hepatic metabolism. Disposal of sulfide through the sulfide oxidation pathway (SOP) is critical for maintaining sulfide within a safe physiological range. We show that mice lacking the liver- enriched mitochondrial SOP enzyme thiosulfate sulfurtransferase (Tst-/- mice) exhibit high circulating sulfide, increased gluconeogenesis, hypertriglyceridemia, and fatty liver. Unexpectedly, hepatic sulfide levels are normal in Tst-/- mice because of exaggerated induction of sulfide disposal, with associated suppression of global protein persulfidation and nuclear respiratory factor 2 target protein levels. Hepatic proteomic and persulfidomic profiles converge on gluconeogenesis and lipid metabolism, revealing a selective deficit in medium-chain fatty acid oxidation in Tst-/- mice. We reveal a critical role of TST in hepatic metabolism that has implications for sulfide donor strategies in the context of metabolic disease.

Portal Venous Flow Is Increased by Jejunal but Not Colonic Hydrogen Sulfide in a Nitric Oxide-Dependent Fashion in Rats

Hydrogen sulfide (H2S) is a recently discerned endogenous signaling molecule that modulates the vascular system. Endogenous hydrogen sulfide has been shown to dilate both the mesenteric and portal vasculature. Gut microbiome, via sulfur reducing bacteria, is another source of H2S production within the gut lumen; this source of H2S is primarily produced and detoxified in the colon under physiologic conditions. Nitric oxide (NO), a major endogenous vasodilator in the portal circulation, participates in H2S-induced vasodilation in some vascular beds. We hypothesize that jejunal but not colonic H2S increases portal vein flow in a NO-dependent fashion. To evaluate the effects of luminal H2S, venous blood flow, portal venous pressure, and systemic venous pressure were measured in rats after administration of either vehicle or an H2S donor (NaHS) into the jejunum or the colon. We found that portal venous pressure and systemic pressure did not change and were similar between the three study groups. However, portal venous blood flow significantly increased following jejunal administration of NaHS but not in response to colonic NaHS or vehicle administration. To test the contribution of NO production to this response, another group of animals was treated with either an NO synthase inhibitor (N-Ω-nitro-L-arginine, L-NNA) or saline prior to jejunal NaHS infusion. After L-NNA pretreatment, NaHS caused a significant fall rather than increase in portal venous flow compared to saline pretreatment. These data demonstrate that H2S within the small intestine significantly increases portal venous blood flow in a NO-dependent fashion.

Characterization of hyperglycemia due to sub-chronic administration of red ginseng extract via comparative global proteomic analysis

Ginseng (Panax ginseng Meyer) is commonly used as an herbal remedy worldwide. Few studies have explored the possible physiological changes in the liver although patients often self-medicate with ginseng preparations, which may lead to exceeding the recommended dose for long-term administration. Here, we analyzed changes in the hepatic proteins of mouse livers using quantitative proteomics after sub-chronic administration of Korean red ginseng (KRG) extract (control group and 0.5, 1.0, and 2.0 g/kg KRG) using tandem mass tag (TMT) 6-plex technology. The 1.0 and 2.0 g/kg KRG groups exhibited signs of liver injury, including increased levels of aspartate transaminase (AST) and alanine aminotransferase (ALT) in the serum. Furthermore, serum glucose levels were significantly higher following KRG administration compared with the control group. Based on the upregulated proteins found in the proteomic analysis, we found that increased cystathionine beta-synthase (CBS) and cystathionine gamma-lyase (CSE) levels promoted greater hydrogen sulfide (H₂S) synthesis in the liver. This investigation provides novel evidence that sub-chronic administration of KRG can elevate H₂S production by increasing protein expression of CBS and CSE in the liver.

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.

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.

Liquid carbohydrate intake modifies transsulfuration pathway both in pregnant rats and in their male descendants

INTRODUCTION

Fructose, alone or in combination with glucose, has been used as a source of added sugars to manufacture sugary drinks and processed foods. High consumption of simple sugars, mainly fructose, has been demonstrated to be one of the causes of developing metabolic diseases. Maternal nutrition is a key factor in the health of the progeny when adult. However, ingestion of fructose-containing foods is still permitted during gestation. Hydrogen sulphide (H₂S) is a gasotransmitter produced in the transsulfuration pathway with proved beneficial effects to combat metabolic diseases.

METHODS

Carbohydrates were supplied to pregnant rats in drinking water (10% wt/vol) throughout gestation, and the pregnant rats, their foetuses, and adult male descendants were studied. Later, adult male progeny from control, fructose- and glucose-fed mothers were subjected to liquid fructose, and were compared to the control group. Liver H₂S production was determined.

RESULTS

This study shows that, in pregnancy, either a fructose-rich diet per se or situations that produce an impaired insulin sensitivity such as an excessive intake of glucose, decrease hepatic and placental production of H₂S. Furthermore, this effect was also observed in the liver of male offspring (both in foetal and adult stages). Interestingly, when these adult descendants were subjected to a high fructose intake, decreases in H₂S synthesis in liver and adipose tissue due to this fructose intake were maternal consumption dependent.

CONCLUSIONS

Given H₂S is a protective agent against diseases such as diabetes, obesity, cardiovascular diseases, and metabolic syndrome, the fact that carbohydrate consumption reduces H₂S synthesis both in pregnancy and in their progeny could have clear and relevant clinical implications.

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.

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.

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.

Reevaluating our understanding of lactulose breath tests by incorporating hydrogen sulfide measurements

Background and Aim

Breath testing has become a commonly used tool in gastroenterology to evaluate changes in the fermentation pattern of the gut microbiome. Currently, hydrogen and methane gas concentrations are measured in breath testing and evaluated against specific cut‐off values for interpretation as normal or abnormal. However, microbial gas kinetics is a complex process that is not currently fully considered when interpreting breath gas results. Gas exchange between hydrogen producers and hydrogen consumers (methanogens and sulfate‐reducing bacteria) is a process whereby hydrogen availability is determined by both its production and removal. Hydrogen sulfide is a crucial gas involved in this process as it is a major hydrogen‐consumptive pathway involved in energy exchange.

Methods

This is a cross‐sectional study evaluating lactulose breath testing with the inclusion of hydrogen sulfide measurements in patients referred for breath testing for gastrointestinal symptoms of bloating, excessive gas, and/or abdominal pain.

Results

A total of 159 patients were analyzed between October 2016 and June 2017. Mean hydrogen concentrations with a positive trend through a 3‐h period (R² = 0.97), mean methane concentrations with a positive trend (R² = 0.69), and mean hydrogen sulfide concentrations with a negative trend (R² = −0.71) were observed.

Conclusion

By incorporating energy exchange in the interpretation of the lactulose breath test, we reevaluated specific breath gas profiles, including those commonly described as “hydrogen nonproducers” and the “double‐peak” phenomenon.

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.

A Turn-On Optoacoustic Probe for Imaging Metformin-Induced Upregulation of Hepatic Hydrogen Sulfide and Subsequent Liver Injury

Metformin is currently the most prescribed oral agent for diabetes treatment; however the overdose or long-term use may cause some severe side effects such as liver injury. Researches indicate that metformin-induced liver injury is closely related to upregulation of hepatic H2S. Hence, monitoring hepatic H2S generation induced by metformin could be an effective approach for evaluating hepatoxicity of the drug. Methods: We present a novel turn-on and dual-mode probe for detecting and imaging metformin-induced liver injury by specifically tracking the upregulation of hepatic H2S with fluorescent and optoacoustic methods. After reaction with H2S, the strong electron-withdrawing group dinitrophenyl ether (which acts as both the recognition moiety and the fluorescence quencher) was cleaved and replaced by an electron-donating group hydroxyl. This correspondingly leads to the changes of the probe's electronic state and absorption red-shifting as well as the subsequent turn-on fluorescent and optoacoustic signals. Results: The probe was applied to the colon tumor-bearing mice model and the metformin-induced liver injury mice model to achieve tumor imaging and liver injury assessment. The biosafety of the probe was verified by histological analysis (hematoxylin and eosin staining) and serum biochemical assays. Conclusion: The probe responds quickly to H2S in tumors and the liver, and MSOT imaging with the probe offers cross-secitonal and 3D spatial information of liver injury. This study may provide an effective approach for accessing medication side effects by tracking drug-metabolism-related products.

Fatty acids promote fatty liver disease via the dysregulation of 3-mercaptopyruvate sulfurtransferase/hydrogen sulfide pathway

OBJECTIVE

Accumulation of free fatty acids (FFAs) in hepatocytes induces lipotoxicity, leading to non-alcoholic fatty liver disease (NAFLD). This study aimed to investigate the underlying mechanisms by which FFA contributes to the pathogenesis of NAFLD via the regulation of 3-mercaptopyruvate sulfurtransferase (MPST), a key enzyme that regulates endogenous hydrogen sulfide (H₂S) biosynthesis.

DESIGN

Hepatic MPST expression was evaluated in mice and patients with NAFLD. A variety of molecular approaches were used to study the effects of MPST regulation on hepatic steatosis in vivo and in vitro.

RESULTS

In vitro treatment of hepatocytes with FFAs upregulated MPST expression, which was partially dependent on NF-κB/p65. Hepatic MPST expression was markedly increased in high fat diet (HFD)-fed mice and patients with NAFLD. Partial knockdown of MPST via adenovirus delivery of MPST short hairpin RNA or heterozygous deletion of the Mpst gene significantly ameliorated hepatic steatosis in HFD-fed mice. Consistently, inhibition of MPST also reduced FFA-induced fat accumulation in L02 cells. Intriguingly, inhibition of MPST significantly enhanced rather than decreased H₂S production, whereas MPST overexpression markedly inhibited H₂S production. Co-immunoprecipitation experiments showed that MPST directly interacted with and negatively regulated cystathionine γ-lyase (CSE), a major source of H₂S production in the liver. Mechanistically, MPST promoted steatosis via inhibition of CSE/H₂S and subsequent upregulation of the sterol regulatory element-binding protein 1c pathway, C-Jun N-terminal kinase phosphorylation and hepatic oxidative stress.

CONCLUSIONS

FFAs upregulate hepatic expression of MPST and subsequently inhibit the CSE/H₂S pathway, leading to NAFLD. MPST may be a potential therapeutic target for NAFLD.

Hydrogen sulfide alleviates uranium-induced rat hepatocyte cytotoxicity via inhibiting Nox4/ROS/p38 MAPK pathway

As a gasotransmitter, hydrogen sulfide (H₂ S) plays a crucial role in regulating the signaling pathway mediated by oxidative stress. The purpose of this study was to investigate the protective effects of H ₂ S on uranium-induced rat hepatocyte cytotoxicity. Primary hepatocytes were isolated and cultured from Sprague Dawley rat liver tissues. After pretreating with sodium hydrosulfide (an H ₂ S donor) for 1 hour (or GKT-136901 for 30 minutes), hepatocytes were treated by uranyl acetate for 24 hours. Cell viability, reactive oxygen species (ROS), malondialdehyde (MDA), NADPH oxidase 4 (Nox4), and p38 mitogen-activated protein kinase (p38 MAPK) phosphorylation were respectively determined. The effects of direct inhibition of Nox4 expression by GKT-136901 (a Nox4 inhibitor) on ROS and phospho-p38 MAPK levels were examined in uranium-treated hepatocytes. The results implicate that H ₂ S can afford protection of rat hepatocytes against uranium-induced adverse effects through attenuating oxidative stress via prohibiting Nox4/ROS/p38 MAPK signaling.

[Prooxidant-antioxidant balance depending on endothelial nitric oxide synthase G894T polymorphism]

The aim of the study was to assess the prooxidant-antioxidant balance depending on endothelial nitric oxide synthase G894T polymorphism. The frequency distribution of alleles and genotypes of G894T polymorphism, nitrite concentration, hydrogen sulphide, lipid peroxidation products (diene conjugates, malonic dialdehyde), antioxidants (reduced glutathione, catalase, ceruloplasmin, retinol) were determined in venous blood of healthy males. The incidence of the GG genotype was 49.1%, GT - 44.2%, TT - 6.7%. The level of malonic dialdehyde in erythrocytes with the GG genotype is 16.8% lower than in the genotype GT. The concentration of hydrogen sulphide in the blood with the GG genotype was 27.5 [18,2; 32,5] mM, GT - 28.6 [22.9; 33.8] mM, TT - 36.3 [33.8; 42.5] mM. The content of total nitrites in plasma with the GG genotype was 10.4 [9,0; 12,5] mM, GT - 10.4 [8.9; 11.8] mM, TT - 9.4 [8.8; 9.8] mM. The genotype GG causes a lower level of malonic dialdehyde in comparison with the heterozygous genotype. The G894T polymorphism allele T is associated with a low content of total nitrites in the plasma and a high concentration of hydrogen sulfide. The data obtained suggest that if the oxygen supply of the organism is impaired, the endothelial nitric oxide synthase G894T polymorphism may be important for the oxidative stress development.

Raised plasma levels of H2S and nitrate predict intrapulmonary vascular dilations: A preliminary report in patients with cryptogenic cirrhosis

BACKGROUND AND AIMS

The role of vasoactive chemicals in the pathogenesis of hepatopulmonary syndrome (HPS), a disorder characterized by intrapulmonary vascular dilation (IPVD), is only vaguely elucidated. We aimed to study the association between plasma H₂S, nitrate levels, and presence and severity of IPVD and HPS.

METHODS

Consecutive adult patients with cryptogenic cirrhosis were evaluated for IPVD (by contrast echocardiography) and for hypoxemia (by arterial blood gas analysis). Plasma H₂S and nitrate levels were measured in these patients.

RESULTS

Fifty-eight patients with cryptogenic cirrhosis (male, 45; median age, range, 45, 16-74 years; Child's class; A, 30; B, 18; C, 10) were enrolled in this study. Thirty-four of the 58 (59%) patients had IPVD and 13 (22%) had HPS (mild, 4; moderate, 5; severe, 2; very severe, 2). Plasma H₂S levels were significantly higher in patients with IPVD (19.6, 5.7-83 μmol/L) as compared to patients who had no IPVD (12.3, 0-47 μmol/L; p-value 0.03) with an area under receiver operating characteristic curve of 0.68 (95% CI 0.53-0.84). Plasma H₂S levels were higher in patients with IPVD irrespective of liver disease severity. There was a trend for higher plasma nitrate levels in patients with IPVD (47, 15.8-126.4 nmol/mL) as compared to patients who had no IPVD (32.3, 6.9-51.4 nmol/mL; p-value 0.1). Raised plasma H₂S and nitrate levels had an additive effect on the presence of IPVD. Neither plasma H₂S nor plasma nitrate levels correlated with the degree of hypoxemia.

CONCLUSION

Raised plasma H₂S and nitrate levels predict the presence of IPVD in patients with cryptogenic cirrhosis.

Sulfated polysaccharide from Enteromorpha prolifera increases hydrogen sulfide production and attenuates non-alcoholic fatty liver disease in high-fat diet rats

EP upregulates hepatic CBS expression, thus increasing serum H₂S level, which reduces serum TG level and ameliorates NAFLD induced by a high-fat diet.

[Participation of melatonin in regulation of blood oxygen-transport function in oxidative stress induced by injection of lipopolisaccharide]

The contribution of melatonin to the regulatoin of the blood oxygen transport function was studied during oxidative stress induced by a triple injection of lipopolysaccharide (at a dose of 5 mg/kg) in conditions of erythropoietin and gasetransmitters (nitrogen monoxide, hydrogen sulfide) action. In the experimental groups, intraperitoneal injections of melatonin (5 mg/kg), erythropoietin (1000 U/kg), hydrogen sulfide donor (NaHS 5 mg/kg), and L-arginine (100 mg/kg), were performed. The use of melatonin alone or in combination with erythropoietin, sodium hydrosulfide or L-arginine led to a decrease in lipid peroxidation products and an increase in the antioxidant protection. Melatonin, during lipopolysaccharide administration, caused changes of blood oxygen transport function: blood oxygen saturation increased, hemoglobin oxygen affinity increased. The modifying effect of melatonin on the blood oxygen transport function in combination with erythropoietin and gastransmitters did not exceed the effect of melatonin alone.

Changes in hydrogen sulfide in rats with hepatic cirrhosis in different stages

This study aimed to observe changes in the hydrogen sulfide (H₂S) system in the blood and liver tissue of rats with hepatic cirrhosis at different stages by studying the effect of H₂S on the course of hyperdynamic circulation in rats with hepatic cirrhosis. H₂S concentration in the blood from the portal vein and inferior vena cava of hepatic cirrhosis rat model induced with carbon tetrachloride was detected on the 15th, 30th, and 52nd day. The expression of cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE) protein, and CBS and CSE mRNA in the liver was detected by immunohistochemistry and reverse transcriptase polymerase chain reaction (RT-PCR), respectively. The results indicated that H₂S concentration in the blood from the portal vein and inferior vena cava of rats with hepatic cirrhosis was significantly lower than that in the control group. H₂S was gradually decreased with the development of the disease and significantly lower in the blood from portal vein than in the blood of inferior vena cava at the mid-stage and the late stage groups. The expression levels of CBS and CSE protein, and CBS and CSE mRNA in the livers with hepatic cirrhosis at different stages were all higher than those in the control group, and the expression gradually increased with the development of the disease. The expression of CBS was lower than CSE in the same stages. The results indicated that the CSE mRNA was expressed predominantly in the cirrhosis groups as compared with CBS mRNA. Among experimental rats, the H₂S system has an important effect on the occurrence and development of hyperdynamic circulation in rats with hepatic cirrhosis. This finding adds to the literature by demonstrating that H₂S protects vascular remodelling in the liver, and that CSE is indispensable in this process.

Diallyl Trisulfide Suppresses Oxidative Stress-Induced Activation of Hepatic Stellate Cells through Production of Hydrogen Sulfide

Accumulating data reveal that garlic has beneficial effects against chronic liver disease. We previously reported that diallyl trisulfide (DATS), the primary organosulfur compound in garlic, reduced fibrosis and attenuated oxidative stress in rat fibrotic liver. The present study was aimed at elucidating the underlying mechanisms. The primary rat hepatic stellate cells (HSCs) were cultured and stimulated with hydrogen peroxide (H₂O₂) for inducing HSC activation under oxidative stress. We examined the effects of DATS on the profibrogenic properties and oxidative stress in H₂O₂-treated HSCs. The results showed that DATS suppressed and reduced fibrotic marker expression in HSCs. DATS arrested cell cycle at G2/M checkpoint associated with downregulating cyclin B1 and cyclin-dependent kinase 1, induced caspase-dependent apoptosis, and reduced migration in HSCs. Moreover, intracellular levels of reactive oxygen species and lipid peroxide were decreased by DATS, but intracellular levels of glutathione were increased in HSCs. Furthermore, DATS significantly elevated hydrogen sulfide (H₂S) levels within HSCs, but iodoacetamide (IAM) reduced H₂S levels and significantly abrogated DATS production of H₂S within HSCs. IAM also abolished all the inhibitory effects of DATS on the profibrogenic properties and oxidative stress in HSCs. Altogether, we demonstrated an H₂S-associated mechanism underlying DATS inhibition of profibrogenic properties and alleviation of oxidative stress in HSCs. Modulation of H₂S production may represent a therapeutic remedy for liver fibrosis.

Blood oxidative stress (BLOS) is a secondary host defense system responding normally to anaerobic wound infection and inadvertently to dietary ultra-exogenous sulfide formation (USF)

Blood oxidative stress (BLOS) is the presence of white blood cells and platelets that are generating high levels of reactive oxygen species (ROS). A mathematical model links the level of BLOS or BLOS# and plasma sulfide concentration. An increase in the BLOS# reduces the plasma sulfide concentration. The reported maximum plasma sulfide concentration for defined health conditions were used to calculate the minimum BLOS#. Elevated BLOS generates high plasma concentration of ROS, which triggers multiple responses in the body that protect the host. First, insulin production by the pancreas is inhibited, which results in elevated blood glucose levels. This results in advanced glycation end products (AGE), which thicken the blood vessel wall. Elevated blood glucose levels also increases urination, which reduces the availability of substrates for infectious bacteria. Second, one or more signaling molecules are stimulated to produce vascular hypertrophy resulting in hypertension. Third, the initial stage of atherosclerosis thickens the blood vessel wall while also protecting the inner surface of the blood vessels from localized infection. The first three mechanisms provide added protection against pathogen migration through the blood vessel wall and reduce the cross-sectional area of blood vessels, which increases the retention time (RT) for improved ROS inactivation of pathogens. Fourth, genes expressed in the liver, which are associated with drug oxidation and uptake transport, are inhibited. This inhibition protects the host from any toxins produced by an anaerobic infection. Elevated BLOS also reduces plasma sulfide concentration, which inhibits wound healing and extends aerobic conditions of the wound. The normal induction of BLOS offers a short-term, cascade of several primary mechanisms for secondary defense against anaerobic infection of a wound. Normal induction of BLOS is due to ultra-exogenous sulfide formation (USF) generated by a local anaerobic infection of a wound in the natural environment. The presence of BLOS without infection is indicative of inadvertent dietary induction. Long-term dietary BLOS results in many severe inflammatory diseases and cancers that are common in an ageing population. Glands were identified as more susceptible to cancers caused by long-term dietary BLOS. Variable BLOS levels in patients of clinical trials may also be reducing effectiveness of experimental drugs and causing drug toxicity. If BLOS is confirmed as a secondary defense against infection that is inadvertently triggered by diet, then a large number of common health problems may be treated and managed by apheresis and dietary changes.

Targeting the transsulfuration-H2S pathway by FXR and GPBAR1 ligands in the treatment of portal hypertension

Cirrhosis is a end-stage disease of the liver in which fibrogenesis, angiogenesis and distortion of intrahepatic microcirculation lead to increased intrahepatic resistance to portal blood flow, a condition known as portal hypertension. Portal hypertension is maintained by a variety of molecular mechanisms including sinusoidal endothelial cells (LSECs) hyporeactivity, activation of hepatic stellate cells (HSCs), reduction in hepatic endothelial nitric oxide synthase (eNOS) activity along with increased eNOS-derived NO generation in the splanchnic and systemic circulations. A reduction of the expression/function of the two major hydrogen sulfide (H2S)-producing enzymes, cystathionine γ-lyase (CSE) and cystathionine β-synthase (CBS), has also been demonstrated. A deficit in the transsulfuration pathway leading to the accumulation of homocysteine might contribute to defective generation of H2S and endothelial hyporeactivity. Bile acids are ligands for nuclear receptors, such as farnesoid X receptor (FXR), and G-protein-coupled receptors (GPCRs), such as the G-protein bile acid receptor 1 (GPBAR1). FXR and GPBAR1 ligands regulate the expression/activity of CSE by both genomic and non-genomic effects and have been proved effective in protecting against endothelial dysfunction observed in rodent models of cirrhosis. GPBAR1, a receptor for secondary bile acids, is selectively expressed by LSECs and its activation increases the expression of CSE and attenuates the production of endotelin-1, a potent vasoconstrictor agent. In vivo GPBAR1 ligand attenuates the imbalance between vasodilatory and vaso-constricting agents, making GPBAR1 a promising target in the treatment of portal hypertension.

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 Attenuates Inflammatory Hepcidin by Reducing IL-6 Secretion and Promoting SIRT1-Mediated STAT3 Deacetylation

AIMS

Anemia of inflammation is quite prevalent in hospitalized patients with poor prognosis. Concerns about the effectiveness and safety of iron supplementation have arisen, driving the demand for alternative therapies. Induction of hepatic hepcidin, the master hormone of iron homeostasis, causes anemia under inflammatory conditions. Previous studies indicated that hydrogen sulfide (H2S), the third gasotransmitter and a well-known regulator of inflammation, may inhibit the secretion of inflammatory cytokines. We thus investigated the effect of H2S on inflammatory hepcidin induction.

RESULTS

H2S suppressed lipopolysaccharide (LPS)-induced hepcidin production and regulated iron homeostasis in mice by decreasing serum interleukin-6 (IL-6) and Janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) activation; similar results were obtained in Huh7 cells exposed to conditioned medium from LPS-challenged THP-1 macrophages. Intriguingly, we found H2S also attenuated hepcidin levels in Huh7 cells and mouse primary hepatocytes in a sirtuin 1 (SIRT1)-dependent manner. By promoting SIRT1 expression and stabilizing SIRT1-STAT3 interactions, H2S ameliorated IL-6-induced STAT3 acetylation, resulting in reduced hepcidin production. Inhibition and silencing of SIRT1 diminished H2S-mediated suppression of hepcidin, as opposed to SIRT1 activation and overexpression. Consistent results were observed in vivo. Furthermore, knockout of cystathionine γ-lyase (CSE), an endogenous H2S synthase, exaggerated inflammatory hepcidin expression in mice.

INNOVATION

For the first time, we elucidated the effects and possible mechanisms of H2S on inflammatory hepcidin and established a novel regulatory link between SIRT1 and hepcidin.

CONCLUSION

Our work demonstrates that H2S attenuates inflammation-induced hepatic hepcidin via multipathways and suggests new treatment strategies for anemia of inflammation.

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: A Therapeutic Candidate for Fibrotic Disease?

Fibrotic diseases including chronic kidney disease, liver cirrhosis, idiopathic pulmonary fibrosis, and chronic disease account for 45% mortality in the developed countries and pose a great threat to the global health. Many great targets and molecules have been reported to be involved in the initiation and/or progression of fibrosis, among which inflammation and oxidative stress are well-recognized modulation targets. Hydrogen sulfide (H₂S) is the third gasotransmitter with potent properties in inhibiting inflammation and oxidative stress in various organs. Recent evidence suggests that plasma H₂S level is decreased in various animal models of fibrotic diseases and supplement of exogenous H₂S is able to ameliorate fibrosis in the kidney, lung, liver, and heart. This leads us to propose that modulation of H₂S production may represent a promising therapeutic venue for the treatment of a variety of fibrotic diseases. Here, we summarize and discuss the current data on the role and underlying mechanisms of H₂S in fibrosis diseases related to heart, liver, kidney, and other organs.

Regulation of mitochondrial bioenergetic function by hydrogen sulfide. Part I. Biochemical and physiological mechanisms

Until recently, hydrogen sulfide (H2 S) was exclusively viewed a toxic gas and an environmental hazard, with its toxicity primarily attributed to the inhibition of mitochondrial Complex IV, resulting in a shutdown of mitochondrial electron transport and cellular ATP generation. Work over the last decade established multiple biological regulatory roles of H2 S, as an endogenous gaseous transmitter. H2 S is produced by cystathionine γ-lyase (CSE), cystathionine β-synthase (CBS) and 3-mercaptopyruvate sulfurtransferase (3-MST). In striking contrast to its inhibitory effect on Complex IV, recent studies showed that at lower concentrations, H2 S serves as a stimulator of electron transport in mammalian cells, by acting as a mitochondrial electron donor. Endogenous H2 S, produced by mitochondrially localized 3-MST, supports basal, physiological cellular bioenergetic functions; the activity of this metabolic support declines with physiological aging. In specialized conditions (calcium overload in vascular smooth muscle, colon cancer cells), CSE and CBS can also associate with the mitochondria; H2 S produced by these enzymes, serves as an endogenous stimulator of cellular bioenergetics. The current article overviews the biochemical mechanisms underlying the stimulatory and inhibitory effects of H2 S on mitochondrial function and cellular bioenergetics and discusses the implication of these processes for normal cellular physiology. The relevance of H2 S biology is also discussed in the context of colonic epithelial cell physiology: colonocytes are exposed to high levels of sulfide produced by enteric bacteria, and serve as a metabolic barrier to limit their entry into the mammalian host, while, at the same time, utilizing it as a metabolic 'fuel'.

Dedifferentiation of cancer cells following recovery from a potentially lethal damage is mediated by H2S-Nampt

Recently, we reported that cancer cells that recover from a potentially lethal damage gain new phenotypic features comprised of mitochondrial structural remodeling associated with increased glycolytic dependency and drug resistance. Here, we demonstrate that a subset of cancer cells, upon recovery from a potentially lethal damage, undergo dedifferentiation and express genes, which are characteristic of undifferentiated stem cells. While these cells are competent in maintaining differentiated progeny of tumor, they also exhibit transdifferentiation potential. Dedifferentiation is characterized by accumulation of hydrogen sulfide (H2S), which triggers up-regulation of nicotinamide phosphoribosyltransferase (Nampt) accompanied by changes in the redox state. The molecular events triggered by Nampt include elevated production of NAD(+) and up-regulation of H2S producing enzymes, cystathionine beta synthase (CBS) and cystathionase (CTH) with 3-mercaptopyruvate sulfurtransferase (MST) being detectable only in 3D spheroids. Suppression of Nampt, or inactivation of H2S producing enzymes, all reduce H2S production and reverse the ability of cells to dedifferentiate. Moreover, H2S induced stem cell markers in parental cancer cells in a manner similar to that observed in damage recovered cells. These data suggest of existence of a positive feedback loop between H2S and Nampt that controls dedifferentiation in cancer cells that recover from a potentially lethal damage.