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

Inhibition of endogenous hydrogen sulfide production reduces activation of hepatic stellate cells via the induction of cellular senescence

In chronic liver injury, quiescent hepatic stellate cells (HSCs) transdifferentiate into activated myofibroblast-like cells and produce large amounts of extracellular matrix components, e.g. collagen type 1. Cellular senescence is characterized by irreversible cell-cycle arrest, arrested cell proliferation and the acquisition of the senescence-associated secretory phenotype (SASP) and reversal of HSCs activation. Previous studies reported that H2S prevents induction of senescence via its antioxidant activity. We hypothesized that inhibition of endogenous H2S production induces cellular senescence and reduces activation of HSCs. Rat HSCs were isolated and culture-activated for 7 days. After activation, HSCs treated with H2S slow-releasing donor GYY4137 and/or DL-propargylglycine (DL-PAG), an inhibitor of the H2S-producing enzyme cystathionine γ-lyase (CTH), as well as the PI3K inhibitor LY294002. In our result, CTH expression was significantly increased in fully activated HSCs compared to quiescent HSCs and was also observed in activated stellate cells in a in vivo model of cirrhosis. Inhibition of CTH reduced proliferation and expression of fibrotic markers Col1a1 and Acta2 in HSCs. Concomitantly, DL-PAG increased the cell-cycle arrest markers Cdkn1a (p21), p53 and the SASP marker Il6. Additionally, the number of β-galactosidase positive senescent HSCs was increased. GYY4137 partially restored the proliferation of senescent HSCs and attenuated the DL-PAG-induced senescent phenotype. Inhibition of PI3K partially reversed the senescence phenotype of HSCs induced by DL-PAG. Inhibition of endogenous H2S production reduces HSCs activation via induction of cellular senescence in a PI3K-Akt dependent manner. Our results show that cell-specific inhibition of H2S could be a novel target for anti-fibrotic therapy via induced cell senescence.

Observation and comparison of gas formation during holmium:YAG laser lithotripsy of cystine, uric acid, and calcium oxalate stones: a chromatographic and electron microscopic analysis

The primary aim of the present in vitro study is to analyze the chemical content of the bubbles occurring during the fragmentation of cystine stones with both the high-power and low-power holmium:YAG (Ho:YAG) lasers. The secondary aim is to discuss their clinical importance. Three types of human renal calculi calcium oxalate monohydrate (COM), cystine, and uric acid were fragmented with both low-power and high-power Ho:YAG lasers in separate experimental setups at room temperature, during which time it was observed whether gas was produced. After laser lithotripsy, a cloudy white gas was obtained, after the fragmentation of cystine stones only. A qualitative gas content analysis was performed with a gas chromatography-mass spectrometry (GC-MS) device. The fragments in the aqueous cystine calculi setup were dried and taken to the laboratory to be examined by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) and X-ray diffraction analysis. No gas production was observed after fragmentation in the COM and uric acid stones. Free cystine, sulfur, thiophene, and hydrogen sulfide gas were produced by both low-power and high-power Ho:YAG laser lithotripsy of the cystine stones. In the SEM-EDX mapping analysis, a free cystine molecule containing 42.8% sulfur (S), 21% oxygen (O), 14.9% carbon (C), and 21% nitrogen (N) atoms was detected in the cystine stone experimental setup. The evidence obtained, which shows that hydrogen sulfide emerges in the gaseous environment during Ho:YAG laser fragmentation of cystine stones, indicates that caution is required to prevent the risk of in vivo production and toxicity.

Hydrogen Sulfide: Physiological Roles and Therapeutic Implications against COVID-19

The COVID-19 pandemic due to severe acute respiratory syndrome coronavirus 2 (SARS-COV-2) poses a major menace to economic and public health worldwide. Angiotensin-converting enzyme 2 (ACE2) and transmembrane protease serine 2 (TMPRSS2) are two host proteins that play an essential function in the entry of SARS-- COV-2 into host cells. Hydrogen sulfide (H2S), a new gasotransmitter, has been shown to protect the lungs from potential damage through its anti-inflammatory, antioxidant, antiviral, and anti-aging effects. It is well known that H2S is crucial in controlling the inflammatory reaction and the pro-inflammatory cytokine storm. Therefore, it has been suggested that some H2S donors may help treat acute lung inflammation. Furthermore, recent research illuminates a number of mechanisms of action that may explain the antiviral properties of H2S. Some early clinical findings indicate a negative correlation between endogenous H2S concentrations and COVID-19 intensity. Therefore, reusing H2S-releasing drugs could represent a curative option for COVID-19 therapy.

A new insight into the hepatoprotective effect of sildenafil: The role of H2S

High-calorie diet, alcohol, and multiple drug use increase reactive oxygen species (ROS) and cause liver damage. ROS are crucial in the initiation/progression of liver diseases. Antioxidants have beneficial effects but produce clinically complex results. The hydrogen sulfide (H2S) pathway is considered a promising therapeutic target since it plays role in the pathogenesis/treatment of liver diseases. Sildenafil exerts antioxidant and hepatoprotective effects by increasing specific antioxidants such as superoxide dismutase, glutathione peroxidase, and regulating the Keap1/Nrf2 pathway which are common mechanisms underlying the effects of H2S. We aimed to determine if H2S has a role in the hepatoprotective and antioxidant effects of sildenafil. The effect of sildenafil on endogenous H2S production was elucidated with an H2S microsensor in the presence/absence of pyrogallol-induced oxidative stress and H2S synthesis inhibitor aminoxyacetic acid (AOAA) in the liver. The relation between the antioxidant effect of sildenafil and H2S was determined by luminol and lucigenin chemiluminescence. Sildenafil increased L-cysteine-induced H2S synthesis in the healthy liver and prevented the pyrogallol-induced reduction in H2S production. Sildenafil decreased the ROS production induced by pyrogallol and its protective effect was inhibited by AOAA. These results reveal that H2S is a new pharmacological mechanism of action of sildenafil on the liver. Therefore, sildenafil can be a potential therapeutic agent in treating many liver diseases in which H2S bioavailability is impaired. Additionally, the hepatoprotective effect of sildenafil by increasing endogenous H2S synthesis advances our knowledge in terms of developing H2S-targeting molecules.

Dose-Dependent Effect of Hydrogen Sulfide in Cyclophosphamide-Induced Hepatotoxicity in Rats

BACKGROUND

Cyclophosphamide is a commonly used anticancer and immunosuppressive agent; however, hepatotoxicity is one of its severe toxicities. Hydrogen sulfide is a gaseous signaling molecule that plays crucial regulatory roles in various physiological functions. This study aimed to evaluate the hepatoprotective effect of hydrogen sulfide against cyclo phosp hamid e-ind uced hepatic damage in rats.

METHODS

Hepatotoxicity was induced by the single intraperitoneal administration of cyclophosphamide (200 mg/kg). Sprague-Dawley rats were treated by hydrogen sulfide donor, sodium hydrosulfide (25, 50, and 100 μmol/kg, intraperitoneal) 7 days before and 7 days after the administration of a single intraperitoneal injection of cyclophosphamide (200 mg/kg). Cyclo phosp hamide-ind uced hepatotoxicity was evaluated by serum and tissue biochemical and histopathological assessments. The levels of hydrogen sulfide, nitric oxide, cyclic guanosine monophosphate, interleukin 6, and interleukin 10 in liver homogenates were also determined by ELISA. One-way analysis of variance and Kruskal-Wallis tests were used as statistical analyses.

RESULTS

Cyclophosphamide increased liver function enzymes (alanine aminotransferase and aspartate aminotransferase), immunoreactivity to caspase-3 and Apaf-1, and proinflammatory cytokines. Cyclophosphamide also induced histopathological alterations including pycnotic nucleus with eosinophilic cytoplasm, increased sinusoidal dilatation, congestion, and edema. Hydrogen sulfide cotreatment significantly reduced cyclo phosp hamid e-ind uced inflammation, histological alterations, and apoptosis in the liver. 50 mg/kg sodium hydrosulfide was more effective against cyclo phosp hamid e-ind uced hepatotoxicity.

CONCLUSION

In conclusion, hydrogen sulfide with its anti-inflammatory and anti-apoptotic effects seems to be beneficial as an adjunct to cyclophosphamide treatment to reduce cyclo phosp hamid e-ind uced hepatotoxicity and thereby can be suggested as a promising agent to increase the therapeutic efficacy of cyclophosphamide.

Blueberry and cranberry extracts mitigate CCL4-induced liver damage, suppressing liver fibrosis, inflammation and oxidative stress

The current study aims to evaluate potential hepatoprotective effect of lingonberry, cranberry and blueberry polyphenols on carbon tetrachloride (CCL-4)-induced acute and subacute liver injury in rats. A total of 55 male Wistar rats, divided into six experimental and control groups. With the exception of the negative control group, all groups received an intraperitoneal injection of CCl-4, twice a week for 14 days. An extract of lingonberry, cranberry, blueberry polyphenols and the positive control, silymarin were administered daily via intragastric route, for 14 consecutive days. The untreated control group showed characteristic of classical oxidative stress-mediated liver damage with vacuolization of the hepatocyte cytoplasm, infiltration by immune cells and proliferation of collagen fibers, decrease in body weight and increase in liver weight; increased levels of AST and ALT in serum, an increased lipid peroxidation in the liver. However, the use of cranberry and blueberry polyphenols significantly suppressed liver damage, exerting an effect comparable to the hepatoprotective effect of the positive control. The extracts prevented and reduced inflammatory liver damage by reducing IL-6, TNF-α and IFN-γ levels. In conclusion, blueberry and cranberry extracts have a protective effect against acute and subacute CCl4-induced hepatotoxicity in rats.

Hydrogen sulfide alleviates ischemia induced liver injury by repressing the SPHK1/S1P pathway

Background

Ischemia/reperfusion (I/R) induced liver injury is a severe pathological process which frequently occurs during clinical hepatic operations. The current study investigated the protective function and underlying mechanisms of hydrogen sulfide (H₂S) in I/R induced liver injury.

Methods

The effects of H₂S were examined using the fibroblast-like rat liver cell line BRL-3A (the name of normal hepatocytes in rats) cultured under hypoxic conditions and an I/R rat model. The viability of BRL-3A cells was assessed using the methylthiazolyldiphenyl-tetrazolium (MTT) assay and Hoechst analysis. The expression of C/EBP homologous protein (CHOP), sphingosine kinase 1 (SPHK1), and sphingosine 1-phosphate (S1P) were determined in hypoxic BRL-3A cells with or without H₂S treatment. CHOP was overexpressed in hypoxic BRL-3A cells to further evaluate whether H₂S protected the liver against I/R injury by decreasing endoplasmic reticulum (ER) stress. Finally, the inflammation levels in the serum and the histopathological changes of liver were examined in the I/R rat model to evaluate the therapeutic function of H₂S on I/R induced liver injury in vivo.

Results

H₂S alleviated hypoxic damage in BRL-3A cells. In addition, hypoxia increased the expression of CHOP, SPHK1, and S1P in BRL-3A cells, and this was abolished by H₂S pretreatment. Notably, overexpression of CHOP significantly inhibited the effect of H₂S on the viability of BRL-3A cells during hypoxia. Overall, H₂S effectively protected against I/R induced liver injury, decreased the inflammatory responses, and attenuated apoptosis of hepatocyte via inhibiting the ER stress response.

Conclusions

These findings demonstrated that pre-treatment of H₂S protected against I/R induced liver injury by repressing the SPHK1/S1P pathway via inhibition of ER stress, suggesting an effective therapeutic method for the treatment of I/R induced liver injury.

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.

Cystathionine γ-lyase mediates cell proliferation, migration, and invasion of nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is an epithelia-derived malignancy with a distinctive geographic distribution. Cystathionine γ-lyase (CSE) is involved in cancer development and progression. Nevertheless, the role of CSE in the growth of NPC is unknown. In this study, we found that CSE levels in human NPC cells were higher than those in normal nasopharyngeal cells. CSE overexpression enhanced the proliferative, migrative, and invasive abilities of NPC cells and CSE downregulation exerted reverse effects. Overexpression of CSE decreased the expressions of cytochrome C, cleaved caspase (cas)-3, cleaved cas-9, and cleaved poly-ADP-ribose polymerase, whereas CSE knockdown exhibited reverse effects. CSE overexpression decreased reactive oxygen species (ROS) levels and the expressions of phospho (p)-extracellular signal-regulated protein kinase 1/2, p-c-Jun N-terminal kinase, and p-p38, but promoted the expressions of p-phosphatidylinositol 3-kinase (PI3K), p-AKT, and p-mammalian target of rapamycin (mTOR), whereas CSE knockdown showed oppose effects. In addition, CSE overexpression promoted NPC xenograft tumor growth and CSE knockdown decreased tumor growth by modulating proliferation, angiogenesis, cell cycle, and apoptosis. Furthermore, DL-propargylglycine (an inhibitor of CSE) dose-dependently inhibited NPC cell growth via ROS-mediated mitogen-activated protein kinase (MAPK) and PI3K/AKT/mTOR pathways without significant toxicity. In conclusion, CSE could regulate the growth of NPC cells through ROS-mediated MAPK and PI3K/AKT/mTOR cascades. CSE might be a novel tumor marker for the diagnosis and prognosis of NPC. Novel donors/drugs that inhibit the expression/activity of CSE can be developed in the treatment of NPC.

Hydrogen Sulfide and Its Donors: Keys to Unlock the Chains of Nonalcoholic Fatty Liver Disease

Hydrogen sulfide (H2S) has emerged as the third “gasotransmitters” and has a crucial function in the diversity of physiological functions in mammals. In particular, H2S is considered indispensable in preventing the development of liver inflammation in the case of excessive caloric ingestion. Note that the concentration of endogenous H2S was usually low, making it difficult to discern the precise biological functions. Therefore, exogenous delivery of H2S is conducive to probe the physiological and pathological roles of this gas in cellular and animal studies. In this review, the production and metabolic pathways of H2S in vivo, the types of donors currently used for H2S release, and study evidence of H2S improvement effects on nonalcoholic fatty liver disease are systematically introduced.

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.

Hydrogen Sulfide Biology and Its Role in Cancer

Hydrogen sulfide (H₂S) is an endogenous biologically active gas produced in mammalian tissues. It plays a very critical role in many pathophysiological processes in the body. It can be endogenously produced through many enzymes analogous to the cysteine family, while the exogenous source may involve inorganic sulfide salts. H₂S has recently been well investigated with regard to the onset of various carcinogenic diseases such as lung, breast, ovaries, colon cancer, and neurodegenerative disorders. H₂S is considered an oncogenic gas, and a potential therapeutic target for treating and diagnosing cancers, due to its role in mediating the development of tumorigenesis. Here in this review, an in-detail up-to-date explanation of the potential role of H₂S in different malignancies has been reported. The study summarizes the synthesis of H₂S, its roles, signaling routes, expressions, and H₂S release in various malignancies. Considering the critical importance of this active biological molecule, we believe this review in this esteemed journal will highlight the oncogenic role of H₂S in the scientific community.

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

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

The Protective Effects of Hydrogen Sulfide New Donor Methyl S-(4-Fluorobenzyl)-N-(3,4,5-Trimethoxybenzoyl)-l-Cysteinate on the Ischemic Stroke

In this paper, we report the design, synthesis and biological evaluation of a novel S-allyl-l-cysteine (SAC) and gallic acid conjugate S-(4-fluorobenzyl)-N-(3,4,5-trimethoxybenzoyl)-l-cysteinate (MTC). We evaluate the effects on ischemia-reperfusion-induced PC12 cells, primary neurons in neonatal rats, and cerebral ischemic neuronal damage in rats, and the results showed that MTC increased SOD, CAT, GPx activity and decreased LDH release. PI3K and p-AKT protein levels were significantly increased by activating PI3K/AKT pathway. Mitochondrial pro-apoptotic proteins Bax and Bim levels were reduced while anti-apoptotic protein Bcl-2 levels were increased. The levels of cleaved caspase-9 and cleaved caspase-3 were also reduced in the plasma. The endoplasmic reticulum stress (ERS) was decreased, which in turns the survival rate of nerve cells was increased, so that the ischemic injury of neurons was protected accordingly. MTC activated the MEK-ERK signaling pathway and promoted axonal regeneration in primary neurons of the neonatal rat. The pretreatment of MEK-ERK pathway inhibitor PD98059 and PI3K/AKT pathway inhibitor LY294002 partially attenuated the protective effect of MTC. Using a MCAO rat model indicated that MTC could reduce cerebral ischemia-reperfusion injury and decrease the expression of proinflammatory factors. The neuroprotective effect of MTC may be due to inhibition of the over-activation of the TREK-1 channel and reduction of the current density of the TREK1 channel. These results suggested that MTC has a protective effect on neuronal injury induced by ischemia reperfusion, so it may have the potential to become a new type of neuro-ischemic drug candidate.

A pilot study for the prediction of liver function related scores using breath biomarkers and machine learning

Volatile organic compounds (VOCs) present in exhaled breath can help in analysing biochemical processes in the human body. Liver diseases can be traced using VOCs as biomarkers for physiological and pathophysiological conditions. In this work, we propose non-invasive and quick breath monitoring approach for early detection and progress monitoring of liver diseases using Isoprene, Limonene, and Dimethyl sulphide (DMS) as potential biomarkers. A pilot study is performed to design a dataset that includes the biomarkers concentration analysed from the breath sample before and after study subjects performed an exercise. A machine learning approach is applied for the prediction of scores for liver function diagnosis. Four regression methods are performed to predict the clinical scores using breath biomarkers data as features set by the machine learning techniques. A significant difference was observed for isoprene concentration (p < 0.01) and for DMS concentration (p < 0.0001) between liver patients and healthy subject's breath sample. The R-square value between actual clinical score and predicted clinical score is found to be 0.78, 0.82, and 0.85 for CTP score, APRI score, and MELD score, respectively. Our results have shown a promising result with significant different breath profiles between liver patients and healthy volunteers. The use of machine learning for the prediction of scores is found very promising for use of breath biomarkers for liver function diagnosis.

Physical Exercise Repairs Obstructive Jaundice-Induced Damage to Intestinal Mucosal Barrier Function via H2S-Mediated Regulation of the HMGB1/Toll Like Receptors 4/Nuclear Factor Kappa B Pathway

The present study aimed to determine the effect of aerobic exercise on improving damage to intestinal mucosal barrier function caused by obstructive jaundice (OJ) and explore the mechanism. Fifty male KM mice were divided into five groups: sham operation group (S), model group (M), exercise group (TM), DL-propargylglycine + exercise (PT) group, and sodium hydrosulfide + exercise (NT) group. Additionally, mice in S group underwent common bile duct ligation for 48 h to establish a murine obstructive jaundice model. In PT group, propargylglycine (40 mg/kg) was intraperitoneally injected 7 days after surgery. NaHS (50 μmol/kg) was intraperitoneally injected into mice in the NT group 7 days after surgery. The TM group, NT group and PT group exercised on a slope of 0% at a speed of 10 m/min without weight training (30 min/day). HE staining showed that the intestinal mucosa of group M was atrophied and that the villi were broken. The intestinal mucosal structure of mice in the TM group was improved. Serum assays showed that H2S levels were higher in the TM group than in the M group; compared with the levels in the TM group, the PT group levels were decreased and the NT group levels were increased. In addition, aerobic exercise inhibits the HMGB1/TLR4/NF-κB signaling pathway by promoting endogenous H2S production, thereby exerting a protective effect on the intestinal mucosal barrier.

Effect of microbiota metabolites on the progression of chronic hepatitis B virus infection

Accumulating evidence shows that the intestinal microbiota is closely related to the pathophysiology and the disease progression of chronic hepatitis B virus (HBV) infection. The intestinal microbiota acts on the host through its metabolites. This review aimed to discuss the effects of gut microbiota metabolites on the disease progression of chronic HBV infection. A literature search on PubMed database and Wiley Online Library with pre-specified criteria yielded 96 unique results. After consensus by all authors, the contents from 86 original publications were extracted and included in this review. In liver disease with HBV infection, the intestinal microbiota changed in different stages and affected the production of bacterial metabolites. The abundance of bacteria producing short-chain fatty acids such as butyrate reduced, which was associated with bacterial translocation and the progression of liver disease. The intestinal microbiota-bile acid-host axis was destroyed, affecting the progression of the disease. Under the control of intestinal microbiota, tryptophan affected the gut-liver axis through three main metabolic pathways, among which the kynurenine pathway was closely related to the immune response of hepatitis B. The level of trimethylamine-N-oxide decreased in liver cancer with HBV infection and were used as a potential biomarker of liver cancer. Vitamin deficiencies, including those of vitamin D and vitamin A related to microbiota, were common and associated with survival. Hydrogen sulfide regulated by the intestinal microbiota was also closely related to the gut-liver axis. In liver disease with hepatitis B infection, the intestinal microbiota is imbalanced, and a variety of intestinal microbiota metabolites participate in the occurrence and development of the disease.

Accurate Fluorescence Diagnosis of Cancer Based on Sequential Detection of Hydrogen Sulfide and pH

Cancer ranks as a leading cause of death in every country of the world. However, if they are discovered early, a lot of cancers can be prevented or cured. Discovering and monitoring cancer markers are the main methods for early diagnosis of cancer. To date, many fluorescent probes designed and used for early cancer diagnosis can only react with a single marker, which always causes insufficient accuracy in complex systems. Herein, a novel near-infrared (NIR) fluorescent probe (CyO-DNP) for the sequential detection of H₂S and H⁺ is synthesized. In this probe, a heptamethine dye is selected as the fluorophore and a 2,4-dinitrophenyl (DNP) ether is chosen as recognition group. In the presence of H₂S, CyO-DNP is transformed into CyO, which exhibits an intense fluorescence at 663 nm. Then, H⁺ induces the protonation of CyO to obtain CyOH, and the final fluorescence emission at 793 nm significantly enhances. Owing to the low cytotoxicity and the NIR fluorescence emission, CyO-DNP can sequentially monitor endogenous H₂S and H⁺ in cancer cells and image exogenous and endogenous H₂S and H⁺ in mice. It is worth mentioning that CyO-DNP can effectively avoid the false positive signal caused by the liver and kidney and discriminate normal mice and tumor mice accurately. For all we know, CyO-DNP is the first fluorescent probe for early accurate diagnosis of cancer by sequentially detecting H₂S and H⁺.

Hypertension and Aging Affect Liver Sulfur Metabolism in Rats

Hypertension and age are key risk factors for cardiovascular morbidity and mortality. Hydrogen sulfide (H2S), a gaseous transmitter, contributes significantly to regulating arterial blood pressure and aging processes. This study evaluated the effects of hypertension and aging on the hepatic metabolism of sulfur-containing compounds, the activity of the enzymes involved in sulfur homeostasis, and the liver's ability to generate H2S. Livers isolated from 16- and 60-week-old normotensive Wistar Kyoto rats (WKY) and Spontaneously Hypertensive Rats (SHR) were used to evaluate gene expression using RT-PCR, and the activity of enzymes participating in H2S metabolism, including thiosulfate sulfurtransferase (rhodanese; TST), cystathionine gamma-lyase (CTH), and 3-mercaptopyruvate sulfurtransferase (MPST). The levels of cysteine, cystine, reduced and oxidized glutathione were measured using RP-HPLC. SHR livers from both age groups showed a higher capacity to generate H2S than livers from WKY. The gene expression and activity of enzymes involved in sulfur metabolism differed between WKY and SHR, and between the age groups. For example, 16-week-old SHR had significantly higher activity of TST than 16-week-old WKY. Furthermore, differences between younger and older WKY rats in the expression and/or activity of TST and MPST were present. In conclusion, our study shows that arterial hypertension and aging affect hepatic sulfur metabolism and H2S production in rats. These findings pave the way for interventional studies evaluating a potential causal relation between liver sulfur metabolism, hypertension and aging.

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.

Role of Hydrogen Sulfide and 3-Mercaptopyruvate Sulfurtransferase in the Regulation of the Endoplasmic Reticulum Stress Response in Hepatocytes

It is estimated that over 1.5 billion people suffer from various forms of chronic liver disease worldwide. The emerging prevalence of metabolic syndromes and alcohol misuse, along with the lack of disease-modifying agents for the therapy of many severe liver conditions predicts that chronic liver disease will continue to be a major problem in the future. Better understanding of the underlying pathogenetic mechanisms and identification of potential therapeutic targets remains a priority. Herein, we explored the potential role of the 3-mercaptopyruvate sulfurtransferase/hydrogen sulfide (H₂S) system in the regulation of the endoplasmic reticulum (ER) stress and of its downstream processes in the immortalized hepatic cell line HepG2 in vitro. ER stress suppressed endogenous H₂S levels and pharmacological supplementation of H₂S with sodium hydrogen sulfide (NaHS) mitigated many aspects of ER stress, culminating in improved cellular bioenergetics and prevention of autophagic arrest, thereby switching cells’ fate towards survival. Genetic silencing of 3-MST or pharmacological inhibition of the key enzymes involved in hepatocyte H₂S biosynthesis exacerbated many readouts related to ER-stress or its downstream functional responses. Our findings implicate the 3-MST/H₂S system in the intracellular network that governs proteostasis and ER-stress adaptability in hepatocytes and reinforce the therapeutic potential of pharmacological H₂S supplementation.

Metabolic Reprogramming of Sulfur in Hepatocellular Carcinoma and Sulfane Sulfur-Triggered Anti-Cancer Strategy

Metabolic reprogramming is a cancer hallmark. Although the reprogramming of central carbon has been well documented, the role of sulfur metabolism has been largely overlooked. Additionally, the effects of sulfur are sometimes contradictory in tumorigenesis. In this study, we aimed to investigate the gene expression profile in hepatocellular carcinoma (HCC) and the effects of reactive sulfur species (RSS) on HCC tumor cells. Furthermore, the cell imaging technology was applied to discover some potential anti-cancer compounds. Gene Set Enrichment Analysis (GSEA) of Gene Expression Omnibus (GEO) dataset (GSE102083) revealed that sulfur amino acid-related metabolism and vitamin B₆ binding activity in HCC tissues were downregulated. Calculation of the interaction network identified nine hub genes, among which eight were validated by differential expression and survival analysis in the TCGA_LIHC cohort, and two (CSE and CBS) had the highest enrichment degree. The metabolomics analysis suggested that the hub genes were associated with RSS metabolism including H₂S, H₂S₂, cystine, cysteine, homocysteine, cystathionine, and methionine. The cell viability assay demonstrated that H₂S₂ had significant anti-cancer effects in HCC SNU398 tumor cells. The cell imaging assay showed that treatment with H₂S₂ remarkably increased intracellular sulfane sulfur content. On this basis, the anti-cancer activity of some other sulfane sulfur compounds, such as DATS and DADS, was further verified. Lastly, according to the fact that HCC tumor cells preferentially take in cystine due to high expression of SLC7A11 (a cystine/glutamate transporter), persulfided cysteine precursor (PSCP) was tested for its sulfane sulfur release capability and found to selectively inhibit HCC tumor cell viability. Collectively, this study uncovered sulfur metabolism in HCC was reprogrammed, and provided a potential therapeutic strategy for HCC by donating sulfane sulfur.

Cyanidin-3-O-Glucoside Improves Colonic Motility During Severe Acute Pancreatitis by Inhibiting the H2S-Regulated AMPK/mTOR Pathway

BACKGROUND

Cyanidin-3-O-glucoside (C3G) is an important anthocyanin that can modulate digestive system functioning. Inflammation associated with severe acute pancreatitis (SAP) induces H2S production, which impairs the gastrointestinal (GI) system. We investigated the effects of C3G in attenuating SAP-associated colonic motility loss by examining the H2S level and activity of AMP-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) pathway.

METHODS

A rat model of SAP was induced using sodium taurocholate, and the effect of C3G on colonic mobility, H2S production, and the inflammatory response was investigated. AMPK/mTOR pathway changes were detected to assess the pathways by which H2S influences colonic mobility in SAP-model rats. The mechanism underlying H2S function was further examined by subjecting colonic muscle cells (CMCs) to C3G, SAP plasma and an AMPK activator.

RESULTS

Administering C3G improved colonic motility but suppressed the inflammatory response and H2S production in the SAP-model rats, which was associated with inhibiting the AMPK/mTOR pathway. Furthermore, activating the AMPK/mTOR pathway in CMCs promoted inflammation but suppressed Ca2+ levels, even after administering C3G.

CONCLUSION

Administering C3G may improve SAP-associated colonic mobility by inhibiting the H2S-mediated AMPK/mTOR pathway.

Effect of gaseous hydrogen sulphide on growth performance and cecal microbial diversity of weaning pigs

The purpose of this study was to examine the effect of gaseous hydrogen sulphide on growth performance and cecal microbial diversity in weaning pigs. A total of 24 weaning pigs (Landrace × Yorkshire × Duroc; average body weight = 8.55 ± 0.68 kg；weaning at 28 days) were selected and randomly divided into four groups (six replicates in each group). The piglets were exposed to hydrogen sulphide (0, 5, 10 and 15 mg/m³) during the experiment period, which lasted 28 days in four controlled environmental chambers. The results showed that exposure to hydrogen sulphide reduced the average daily gain (ADG), average daily feed intake (ADFI), and increased the diarrhoea rate of piglets. Hydrogen sulphide could increase the abundance and diversity of intestinal microbiota. The abundance of Firmicutes and Proteobacteria increased and Bacteroides decreased in the treatment groups. Five biomarkers, such as Eubacterium_1coprostanoligenes, Clostridiales, Phascolarctobacterium, Acidaminococcaceae and Ruminococcaceae_UCG_002 were selected by Lefse analysis. Our results reveal that hydrogen sulphide damaged the growth performance and destroyed the microbial bacteria balance of weaning pigs. The concentrations of hydrogen sulphide should fall below 5 mg/m³.

Targeting hydrogen sulphide signaling in breast cancer

Introduction

Hydrogen sulphide (H₂S) has been established as a key member of the gasotransmitters family that recently showed a pivotal role in various pathological conditions including cancer.

Objectives

This study investigated the role of H₂S in breast cancer (BC) pathogenesis, on BC immune recognition capacity and the consequence of targeting H₂S using non-coding RNAs.

Methods

Eighty BC patients have been recruited for the study. BC cell lines were cultured and transfected using validated oligonucleotide delivery system. Gene and protein expression analysis was performed using qRT-PCR, western blot and flow-cytometry. In-vitro analysis for BC hallmarks was performed using MTT, BrdU, Modified Boyden chamber, migration and colony forming assays. H₂S and nitric oxide (NO) levels were measured spectrophotometrically. Primary natural killer cells (NK cells) and T cell isolation and chimeric antigen receptor transduction (CAR T cells) were performed using appropriate kits. NK and T cells cytotoxicity was measured. Finally, computational target prediction analysis and binding confirmation analyses were performed using different software and dual luciferase assay kit, respectively.

Results

The H₂S synthesizing enzymes, cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE), exhibited elevated levels in the clinical samples that correlated with tumor proliferation index. Knock-down of CBS and CSE in the HER2+ BC and triple negative BC (TNBC) cells resulted in significant attenuation of BC malignancy. In addition to increased susceptibility of HER2+ BC and TNBC to the cytotoxic activity of HER2 targeting CAR T cells and NK cells, respectively. Transcriptomic and phosphoprotein analysis revealed that H₂S signaling is mediated through Akt in MCF7, STAT3 in MDA-MB-231 and miR-155/ NOS2/NO signaling in both cell lines. Lastly, miR-4317 was found to function as an upstream regulator of CBS and CSE synergistically abrogates the malignancy of BC cells.

Conclusion

These findings demonstrate the potential role of H₂S signaling in BC pathogenesis and the potential of its targeting for disease mitigation.

Hydrogen: An Endogenous Regulator of Liver Homeostasis

Basic and clinical studies have shown that hydrogen (H₂), the lightest gas in the air, has significant biological effects of anti-oxidation, anti-inflammation, and anti-apoptosis. The mammalian cells have no abilities to produce H₂ due to lack of the expression of hydrogenase. The endogenous H₂ in human body is mainly produced by anaerobic bacteria, such as Firmicutes and Bacteroides, in gut and other organs through the reversible oxidation reaction of 2 H⁺ + 2 e^- ⇌ H₂. Supplement of exogenous H₂ can improve many kinds of liver injuries, modulate glucose and lipids metabolism in animal models or in human beings. Moreover, hepatic glycogen has strong ability to accumulate H₂, thus, among the organs examined, liver has the highest concentration of H₂ after supplement of exogenous H₂ by various strategies in vivo. The inadequate production of endogenous H₂ play essential roles in brain, heart, and liver disorders, while enhanced endogenous H₂ production may improve hepatitis, hepatic ischemia and reperfusion injury, liver regeneration, and hepatic steatosis. Therefore, the endogenous H₂ may play essential roles in maintaining liver homeostasis.

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

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

Hydrogen sulfide alleviates cognitive deficiency and hepatic dysfunction in a mouse model of acute liver failure

Acute liver failure (ALF) is a devastating clinical syndrome with a high mortality rate if not treated promptly. Previous studies have demonstrated the beneficial effects of hydrogen sulfide (H₂S) on the brain and liver. The present study aimed to investigate the potential protective effects of H₂S in ALF. A mouse model of ALF was established following treatment with thioacetamide (TAA). Mice with TAA-induced ALF were intraperitoneally injected with 30 or 100 µmol/kg/day sodium hydrosulfide (NaHS; a H₂S donor drug) for two weeks. According to results from novel object recognition and Y-maze tests, in the present study, NaHS treatment alleviated cognitive deficiency and preserved spatial orientation learning ability in TAA-induced ALF mice compared with those of untreated mice. In addition, NaHS treatment reduced serum levels of aspartate transaminase (AST), alanine transaminase (ALT) and the concentration of ammonia compared with those that received control treatment, resulting in weight loss prevention. These findings suggested a beneficial effect of H₂S on liver function. In conclusion, results from the present study suggested that H₂S treatment may alleviate cognitive deficiency and hepatic dysfunction in mice with ALF, indicating the potential therapeutic benefits of applying H₂S for the treatment of ALF.

Hydrogen Sulfide Protects against Paraquat-Induced Acute Liver Injury in Rats by Regulating Oxidative Stress, Mitochondrial Function, and Inflammation

In addition to the lung, the liver is considered another major target for paraquat (PQ) poisoning. Hydrogen sulfide (H₂S) has been demonstrated to be effective in the inhibition of oxidative stress and inflammation. The aim of this study was to investigate the protective effect of exogenous H₂S against PQ-induced acute liver injury. The acute liver injury model was established by a single intraperitoneal injection of PQ, evidenced by histological alteration and elevated serum aminotransferase levels. Different doses of NaHS were administered intraperitoneally one hour before exposure to PQ. Analysis of the data shows that exogenous H₂S attenuated the PQ-induced liver injury and oxidative stress in a dose-dependent manner. H₂S significantly suppressed reactive oxygen species (ROS) generation and the elevation of malondialdehyde content while it increased the ratio of GSH/GSSG and levels of antioxidant enzymes including SOD, GSH-Px, HO-1, and NQO-1. When hepatocytes were subjected to PQ-induced oxidative stress, H₂S markedly enhanced nuclear translocation of Nrf2 via S-sulfhydration of Keap1 and resulted in the increase in IDH2 activity by regulating S-sulfhydration of SIRT3. In addition, H₂S significantly suppressed NLRP3 inflammasome activation and subsequent IL-1β excretion in PQ-induced acute liver injury. Moreover, H₂S cannot reverse the decrease in SIRT3 and activation of the NLRP3 inflammasome caused by PQ in Nrf2-knockdown hepatocytes. In summary, H₂S attenuated the PQ-induced acute liver injury by enhancing antioxidative capability, regulating mitochondrial function, and suppressing ROS-induced NLRP3 inflammasome activation. The antioxidative effect of H₂S in PQ-induced liver injury can at least partly be attributed to the promotion of Nrf2-driven antioxidant enzymes via Keap1 S-sulfhydration and regulation of SIRT3/IDH2 signaling via Nrf2-dependent SIRT3 gene transcription as well as SIRT3 S-sulfhydration. Thus, H₂S supplementation can form the basis for a promising novel therapeutic strategy for PQ-induced acute liver injury.

Mitochondrial metabolic reprogramming: An important player in liver cancer progression

Mitochondria are known as essential biosynthetic, bioenergetic and signaling organelles, and play a critical role in cell differentiation, proliferation, and death. Nowadays, cancer is emergingly considered as a mitochondrial metabolic disease. Mitochondria also play an essential role in liver carcinogenesis. Liver cells are highly regenerative and require high energy. For that reason, a large number of mitochondria are present and functional in liver cells. Abnormalities in mitochondrial metabolism in human liver are known to be one of the carcinogenic factors. Interestingly, immune checkpoints regulate mitochondrial metabolic energetics of the tumor, the tumor microenvironment, as well as the tumor-specific immune response. This regulation forms a positive loop between the metabolic reprogramming of both cancer cells and immune cells. In this review, we discuss the evidence and mechanisms that mitochondria interplay with immune checkpoints to influence different steps of oncogenesis, as well as the potential of mitochondria as therapeutic targets for liver cancer therapy.

Natural Sulfur-Containing Compounds: An Alternative Therapeutic Strategy against Liver Fibrosis

Liver fibrosis is a pathophysiologic process involving the accumulation of extracellular matrix proteins as collagen deposition. Advanced liver fibrosis can evolve in cirrhosis, portal hypertension and often requires liver transplantation. At the cellular level, hepatic fibrosis involves the activation of hepatic stellate cells and their transdifferentiation into myofibroblasts. Numerous pro-fibrogenic mediators including the transforming growth factor-β1, the platelet-derived growth factor, endothelin-1, toll-like receptor 4, and reactive oxygen species are key players in this process. Knowledge of the cellular and molecular mechanisms underlying hepatic fibrosis development need to be extended to find novel therapeutic strategies. Antifibrotic therapies aim to inhibit the accumulation of fibrogenic cells and/or prevent the deposition of extracellular matrix proteins. Natural products from terrestrial and marine sources, including sulfur-containing compounds, exhibit promising activities for the treatment of fibrotic pathology. Although many therapeutic interventions are effective in experimental models of liver fibrosis, their efficacy and safety in humans are largely unknown. This review aims to provide a reference collection on experimentally tested natural anti-fibrotic compounds, with particular attention on sulfur-containing molecules. Their chemical structure, sources, mode of action, molecular targets, and pharmacological activity in the treatment of liver disease will be discussed.

Hydrogen sulfide modulates IL-6/STAT3 pathway and inhibits oxidative stress, inflammation, and apoptosis in rat model of methotrexate hepatotoxicity

Methotrexate (MTX) is a commonly used anticancer and immunosuppressive agent. However, MTX can induce hepatotoxicity due to oxidative stress, inflammation, and apoptosis. Hydrogen sulfide (H₂S), the endogenous gaseous molecule, has antioxidant, anti-inflammatory, and anti-apoptotic effects. The present work explored the probable protective effect of H₂S against MTX hepatotoxicity in rats and also the possible mechanisms underlying this effect. MTX was given at a single intraperitoneal (i.p.) dose of 20 mg/kg. Sodium H₂S (56 µmol /kg/day, i.p.), as H₂S donor, was given for 10 days, starting 6 days before MTX administration. H₂S significantly reduced serum alanine aminotransferase, hepatic malondialdehyde, interleukin 6, nuclear factor κB p65, cytosolic cytochrome c, phosphorylated signal transducer and activator of transcription 3, and Bax/Bcl-2 ratio and significantly increased hepatic total antioxidant capacity and endothelial nitric oxide synthase (eNOS) in rats received MTX. In addition, H₂S minimized the histopathological injury and significantly decreased the expression of STAT3 in liver tissue of MTX-challenged rats. The effects of H₂S were significantly antagonized by administration of glibenclamide as K_ATP channel blocker, Nω-nitro-l-arginine, as eNOS inhibitor, or ruthenium red, as transient receptor potential vanilloid 1 (TRPV1) antagonist. It was concluded that H₂S provided significant hepatoprotection in MTX-challenged rats through its antioxidant, anti-inflammatory, anti-apoptotic effects. These effects are most probably mediated by the ability of H₂S to act as IL-6/STAT3 pathway modulator, K_ATP channel opener, eNOS activator, and TRPV1 agonist.