Proresolution effects of hydrogen sulfide during colitis are mediated through hypoxia-inducible factor-1α

Microbial assimilatory sulfate reduction-mediated H2S: an overlooked role in Crohn's disease development

BACKGROUND

H2S imbalances in the intestinal tract trigger Crohn's disease (CD), a chronic inflammatory gastrointestinal disorder characterized by microbiota dysbiosis and barrier dysfunction. However, a comprehensive understanding of H2S generation in the gut, and the contributions of both microbiota and host to systemic H2S levels in CD, remain to be elucidated. This investigation aimed to enhance comprehension regarding the sulfidogenic potential of both the human host and the gut microbiota.

RESULTS

Our analysis of a treatment-naive CD cohorts' fecal metagenomic and biopsy metatranscriptomic data revealed reduced expression of host endogenous H2S generation genes alongside increased abundance of microbial exogenous H2S production genes in correlation with CD. While prior studies focused on microbial H2S production via dissimilatory sulfite reductases, our metagenomic analysis suggests the assimilatory sulfate reduction (ASR) pathway is a more significant contributor in the human gut, given its high prevalence and abundance. Subsequently, we validated our hypothesis experimentally by generating ASR-deficient E. coli mutants ∆cysJ and ∆cysM through the deletion of sulfite reductase and L-cysteine synthase genes. This alteration significantly affected bacterial sulfidogenic capacity, colon epithelial cell viability, and colonic mucin sulfation, ultimately leading to colitis in murine model. Further study revealed that gut microbiota degrade sulfopolysaccharides and assimilate sulfate to produce H2S via the ASR pathway, highlighting the role of sulfopolysaccharides in colitis and cautioning against their use as food additives.

CONCLUSIONS

Our study significantly advances understanding of microbial sulfur metabolism in the human gut, elucidating the complex interplay between diet, gut microbiota, and host sulfur metabolism. We highlight the microbial ASR pathway as an overlooked endogenous H2S producer and a potential therapeutic target for managing CD. Video Abstract.

Allyl isothiocyanate, a TRPA1 agonist, protects against olanzapine-induced hypothalamic and hepatic metabolic aberrations in female mice

Olanzapine, a widely prescribed atypical antipsychotic, poses a great risk to the patient's health by fabricating a plethora of severe metabolic and cardiovascular adverse effects eventually reducing life expectancy and patient compliance. Its heterogenous receptor binding profile has made it difficult to point out a specific cause or treatment for the related side effects. Growing body of evidence suggest that transient receptor potential (TRP) channel subfamily Ankyrin 1 (TRPA1) has pivotal role in pathogenesis of type 2 diabetes and obesity. With this background, we aimed to investigate the role of pharmacological manipulations of TRPA1 channels in antipsychotic (olanzapine)-induced metabolic alterations in female mice using allyl isothiocyanate (AITC) and HC-030031 (TRPA1 agonist and antagonist, respectively). It was found that after 6 weeks of treatment, AITC prevented olanzapine-induced alterations in body weight and adiposity; serum, and liver inflammatory markers; glucose and lipid metabolism; and hypothalamic appetite regulation, nutrient sensing, inflammatory and TRPA1 channel signaling regulating genes. Furthermore, several of these effects were absent in the presence of HC-030031 (TRPA1 antagonist) indicating protective role of TRPA1 agonism in attenuating olanzapine-induced metabolic alterations. Supplementary in-depth studies are required to study TRPA1 channel effect on other aspects of olanzapine-induced metabolic alterations.

Mitochondrial dysfunctions in T cells: focus on inflammatory bowel disease

Mitochondria has emerged as a critical ruler of metabolic reprogramming in immune responses and inflammation. In the context of colitogenic T cells and IBD, there has been increasing research interest in the metabolic pathways of glycolysis, pyruvate oxidation, and glutaminolysis. These pathways have been shown to play a crucial role in the metabolic reprogramming of colitogenic T cells, leading to increased inflammatory cytokine production and tissue damage. In addition to metabolic reprogramming, mitochondrial dysfunction has also been implicated in the pathogenesis of IBD. Studies have shown that colitogenic T cells exhibit impaired mitochondrial respiration, elevated levels of mROS, alterations in calcium homeostasis, impaired mitochondrial biogenesis, and aberrant mitochondria-associated membrane formation. Here, we discuss our current knowledge of the metabolic reprogramming and mitochondrial dysfunctions in colitogenic T cells, as well as the potential therapeutic applications for treating IBD with evidence from animal experiments.

Hydrogen Sulfide-Releasing Indomethacin-Derivative (ATB-344) Prevents the Development of Oxidative Gastric Mucosal Injuries

Hydrogen sulfide (H2S) emerged recently as an anti-oxidative signaling molecule that contributes to gastrointestinal (GI) mucosal defense and repair. Indomethacin belongs to the class of non-steroidal anti-inflammatory drugs (NSAIDs) and is used as an effective intervention in the treatment of gout- or osteoarthritis-related inflammation. However, its clinical use is strongly limited since indomethacin inhibits gastric mucosal prostaglandin (PG) biosynthesis, predisposing to or even inducing ulcerogenesis. The H2S moiety was shown to decrease the GI toxicity of some NSAIDs. However, the GI safety and anti-oxidative effect of a novel H2S-releasing indomethacin derivative (ATB-344) remain unexplored. Thus, we aimed here to compare the impact of ATB-344 and classic indomethacin on gastric mucosal integrity and their ability to counteract the development of oxidative gastric mucosal injuries. Wistar rats were pretreated intragastrically (i.g.) with vehicle, ATB-344 (7-28 mg/kg i.g.), or indomethacin (5-20 mg/kg i.g.). Next, animals were exposed to microsurgical gastric ischemia-reperfusion (I/R). Gastric damage was assessed micro- and macroscopically. The volatile H2S level was assessed in the gastric mucosa using the modified methylene blue method. Serum and gastric mucosal PGE2 and 8-hydroxyguanozine (8-OHG) concentrations were evaluated by ELISA. Molecular alterations for gastric mucosal barrier-specific targets such as cyclooxygenase-1 (COX)-1, COX-2, heme oxygenase-1 (HMOX)-1, HMOX-2, superoxide dismutase-1 (SOD)-1, SOD-2, hypoxia inducible factor (HIF)-1α, xanthine oxidase (XDH), suppressor of cytokine signaling 3 (SOCS3), CCAAT enhancer binding protein (C/EBP), annexin A1 (ANXA1), interleukin 1 beta (IL-1β), interleukin 1 receptor type I (IL-1R1), interleukin 1 receptor type II (IL-1R2), inducible nitric oxide synthase (iNOS), tumor necrosis factor receptor 2 (TNFR2), or H2S-producing enzymes, cystathionine γ-lyase (CTH), cystathionine β-synthase (CBS), or 3-mercaptopyruvate sulfur transferase (MPST), were assessed at the mRNA level by real-time PCR. ATB-344 (7 mg/kg i.g.) reduced the area of gastric I/R injuries in contrast to an equimolar dose of indomethacin. ATB-344 increased gastric H2S production, did not affect gastric mucosal PGE2 content, prevented RNA oxidation, and maintained or enhanced the expression of oxidation-sensitive HMOX-1 and SOD-2 in line with decreased IL-1β and XDH. We conclude that due to the H2S-releasing ability, i.g., treatment with ATB-344 not only exerts dose-dependent GI safety but even enhances gastric mucosal barrier capacity to counteract acute oxidative injury development when applied at a low dose of 7 mg/kg, in contrast to classic indomethacin. ATB-344 (7 mg/kg) inhibited COX activity on a systemic level but did not affect cytoprotective PGE2 content in the gastric mucosa and, as a result, evoked gastroprotection against oxidative damage.

Mechanism-based and computational modeling of hydrogen sulfide biogenesis inhibition: interfacial inhibition

Hydrogen sulfide (H₂S) is a gaseous signaling molecule that participates in various signaling functions in health and diseases. The tetrameric cystathionine γ-lyase (CSE) contributes to H₂S biogenesis and several investigations provide evidence on the pharmacological modulation of CSE as a potential target for the treatment of a multitude of conditions. D-penicillamine (D-pen) has recently been reported to selectively impede CSE-catalyzed H₂S production but the molecular bases for such inhibitory effect have not been investigated. In this study, we report that D-pen follows a mixed-inhibition mechanism to inhibit both cystathionine (CST) cleavage and H₂S biogenesis by human CSE. To decipher the molecular mechanisms underlying such a mixed inhibition, we performed docking and molecular dynamics (MD) simulations. Interestingly, MD analysis of CST binding reveals a likely active site configuration prior to gem-diamine intermediate formation, particularly H-bond formation between the amino group of the substrate and the O3' of PLP. Similar analyses realized with both CST and D-pen identified three potent interfacial ligand-binding sites for D-pen and offered a rational for D-pen effect. Thus, inhibitor binding not only induces the creation of an entirely new interacting network at the vicinity of the interface between enzyme subunits, but it also exerts long range effects by propagating to the active site. Overall, our study paves the way for the design of new allosteric interfacial inhibitory compounds that will specifically modulate H₂S biogenesis by cystathionine γ-lyase.

Cystathionine γ-lyase and hydrogen sulfide modulates glucose transporter Glut1 expression via NF-κB and PI3k/Akt in macrophages during inflammation

Macrophages play a crucial role in inflammation, a defense mechanism of the innate immune system. Metabolic function powered by glucose transporter isoform 1 (Glut1) is necessary for macrophage activity during inflammation. The present study investigated the roles of cystathionine-γ-lyase (CSE) and its byproduct, hydrogen sulfide (H2S), in macrophage glucose metabolism to explore the mechanism by which H2S acts as an inflammatory regulator in lipopolysaccharide- (LPS) induced macrophages. Our results demonstrated that LPS-treated macrophages increased Glut1 expression. LPS-induced Glut1 expression is regulated via nuclear factor (NF)-κB activation and is associated with phosphatidylinositol-3-kinase PI3k activation. Small interfering (si) RNA-mediated silencing of CSE decreased the LPS-induced NF-κB activation and Glut1 expression, suggesting a role for H2S in metabolic function in macrophages during pro-inflammatory response. Confoundingly, treatment with GYY4137, an H2S-donor molecule, also displayed inhibitory effects upon LPS-induced NF-κB activation and Glut1 expression. Moreover, GYY4137 treatment increased Akt activation, suggesting a role in promoting resolution of inflammation. Our study provides evidence that the source of H2S, either endogenous (via CSE) or exogenous (via GYY4137), supports or inhibits the LPS-induced NF-κB activity and Glut1 expression, respectively. Therefore, H2S may influence metabolic programming in immune cells to alter glucose substrate availability that impacts the immune response.

Regulating the Expression of HIF-1α or lncRNA: Potential Directions for Cancer Therapy

Previous studies have shown that tumors under a hypoxic environment can induce an important hypoxia-responsive element, hypoxia-induced factor-1α (HIF-1α), which can increase tumor migration, invasion, and metastatic ability by promoting epithelial-to-mesenchymal transition (EMT) in tumor cells. Currently, with the deeper knowledge of long noncoding RNAs (lncRNAs), more and more functions of lncRNAs have been discovered. HIF-1α can regulate hypoxia-responsive lncRNAs under hypoxic conditions, and changes in the expression level of lncRNAs can regulate the production of EMT transcription factors and signaling pathway transduction, thus promoting EMT progress. In conclusion, this review summarizes the regulation of the EMT process by HIF-1α and lncRNAs and discusses their relationship with tumorigenesis. Since HIF-1α plays an important role in tumor progression, we also summarize the current drugs that inhibit tumor progression by modulating HIF-1α.

The effect of HIF on metabolism and immunity

Cellular hypoxia occurs when the demand for sufficient molecular oxygen needed to produce the levels of ATP required to perform physiological functions exceeds the vascular supply, thereby leading to a state of oxygen depletion with the associated risk of bioenergetic crisis. To protect against the threat of hypoxia, eukaryotic cells have evolved the capacity to elicit oxygen-sensitive adaptive transcriptional responses driven primarily (although not exclusively) by the hypoxia-inducible factor (HIF) pathway. In addition to the canonical regulation of HIF by oxygen-dependent hydroxylases, multiple other input signals, including gasotransmitters, non-coding RNAs, histone modifiers and post-translational modifications, modulate the nature of the HIF response in discreet cell types and contexts. Activation of HIF induces various effector pathways that mitigate the effects of hypoxia, including metabolic reprogramming and the production of erythropoietin. Drugs that target the HIF pathway to induce erythropoietin production are now approved for the treatment of chronic kidney disease-related anaemia. However, HIF-dependent changes in cell metabolism also have profound implications for functional responses in innate and adaptive immune cells, and thereby heavily influence immunity and the inflammatory response. Preclinical studies indicate a potential use of HIF therapeutics to treat inflammatory diseases, such as inflammatory bowel disease. Understanding the links between HIF, cellular metabolism and immunity is key to unlocking the full therapeutic potential of drugs that target the HIF pathway.

Hypoxia-dependent changes in cellular metabolism have important implications for the effective functioning of multiple immune cell subtypes. This Review describes the inputs that shape the hypoxic response in individual cell types and contexts, and the implications of this response for cellular metabolism and associated alterations in immune cell function.

Hypoxia is a common feature of particular microenvironments and at sites of immunity and inflammation, resulting in increased activity of the hypoxia-inducible factor (HIF).

In addition to hypoxia, multiple inputs modulate the activity of the HIF pathway, allowing nuanced downstream responses in discreet cell types and contexts.

HIF-dependent changes in cellular metabolism mitigate the effects of hypoxia and ensure that energy needs are met under conditions in which oxidative phosphorylation is reduced.

HIF-dependent changes in metabolism also profoundly affect the phenotype and function of immune cells.

The immunometabolic effects of HIF have important implications for targeting the HIF pathway in inflammatory disease.

The Role of Exhaled Hydrogen Sulfide in the Diagnosis of Colorectal Adenoma

Purpose

Exhaled determination can detect metabolite hydrogen sulfide in the intestine. We aim to analyze the predictive value of hydrogen sulfide in the diagnosis of colorectal adenoma.

Methods

We recruited seventy patients diagnosed with colorectal adenoma as the observation group and sixty-six healthy subjects as the control group. The colorectal adenoma was diagnosed by colonoscopy at the Endoscopy Center of Huashan Hospital affiliated to Fudan University from June 2018 to November 2019. Exhaled gas was collected through the nose and mouth, respectively, and hydrogen sulfide in exhaled gas was determined according to the manufacturer's instructions.

Results

Receiver operating characteristic (ROC) curve was analyzed based on the exhaled data of the observation group and the control group. The ROC curve showed an area under ROC curve (AUC) 0.724 for nasal exhaled H₂S, which had a diagnostic value. When nasal exhaled H₂S was >13.3 part per billion (ppb), the sensitivity and the specificity of predicting colorectal adenoma were 57% and 78%, respectively. The exhaled H₂S of the observation group was significantly different from that of the control group. The AUC value was 0.716 as a prognostic factor of colorectal adenoma. As exhaled H₂S was >28.8 ppb, the sensitivity and the specificity of predicting colorectal adenoma were 63% and 77%, respectively.

Conclusion

Exhaled and nasal H₂S determination has a predictive value for colorectal adenoma as a novel and noninvasive method. Therefore, it is worth conducting more research to analyze exhaled and nasal H₂S.

Biological Functions of Diallyl Disulfide, a Garlic-Derived Natural Organic Sulfur Compound

Garlic is widely accepted as a functional food and an excellent source of pharmacologically active ingredients. Diallyl disulfide (DADS), a major bioactive component of garlic, has several beneficial biological functions, including anti-inflammatory, antioxidant, antimicrobial, cardiovascular protective, neuroprotective, and anticancer activities. This review systematically evaluated the biological functions of DADS and discussed the underlying molecular mechanisms of these functions. We hope that this review provides guidance and insight into the current literature and enables future research and the development of DADS for intervention and treatment of multiple diseases.

A Case for Hydrogen Sulfide Metabolism as an Oxygen Sensing Mechanism

The ability to detect oxygen availability is a ubiquitous attribute of aerobic organisms. However, the mechanism(s) that transduce oxygen concentration or availability into appropriate physiological responses is less clear and often controversial. This review will make the case for oxygen-dependent metabolism of hydrogen sulfide (H₂S) and polysulfides, collectively referred to as reactive sulfur species (RSS) as a physiologically relevant O₂ sensing mechanism. This hypothesis is based on observations that H₂S and RSS metabolism is inversely correlated with O₂ tension, exogenous H₂S elicits physiological responses identical to those produced by hypoxia, factors that affect H₂S production or catabolism also affect tissue responses to hypoxia, and that RSS efficiently regulate downstream effectors of the hypoxic response in a manner consistent with a decrease in O₂. H₂S-mediated O₂ sensing is then compared to the more generally accepted reactive oxygen species (ROS) mediated O₂ sensing mechanism and a number of reasons are offered to resolve some of the confusion between the two.

Diet and Hydrogen Sulfide Production in Mammals

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

Fighting Oxidative Stress with Sulfur: Hydrogen Sulfide in the Renal and Cardiovascular Systems

Hydrogen sulfide (H2S) is an essential gaseous signaling molecule. Research on its role in physiological and pathophysiological processes has greatly expanded. Endogenous enzymatic production through the transsulfuration and cysteine catabolism pathways can occur in the kidneys and blood vessels. Furthermore, non-enzymatic pathways are present throughout the body. In the renal and cardiovascular system, H2S plays an important role in maintaining the redox status at safe levels by promoting scavenging of reactive oxygen species (ROS). H2S also modifies cysteine residues on key signaling molecules such as keap1/Nrf2, NFκB, and HIF-1α, thereby promoting anti-oxidant mechanisms. Depletion of H2S is implicated in many age-related and cardiorenal diseases, all having oxidative stress as a major contributor. Current research suggests potential for H2S-based therapies, however, therapeutic interventions have been limited to studies in animal models. Beyond H2S use as direct treatment, it could improve procedures such as transplantation, stem cell therapy, and the safety and efficacy of drugs including NSAIDs and ACE inhibitors. All in all, H2S is a prime subject for further research with potential for clinical use.

Production of hydrogen sulfide by the intestinal microbiota and epithelial cells and consequences for the colonic and rectal mucosa

Among bacterial metabolites, hydrogen sulfide (H₂S) has received increasing attention. The epithelial cells of the large intestine are exposed to two sources of H₂S. The main one is the luminal source that results from specific bacteria metabolic activity toward sulfur-containing substrates. The other source in colonocytes is from the intracellular production mainly through cystathionine β-synthase (CBS) activity. H₂S is oxidized by the mitochondrial sulfide oxidation unit, resulting in ATP synthesis, and, thus, establishing this compound as the first mineral energy substrate in colonocytes. However, when the intracellular H₂S concentration exceeds the colonocyte capacity for its oxidation, it inhibits the mitochondrial respiratory chain, thus affecting energy metabolism. Higher luminal H₂S concentration affects the integrity of the mucus layer and displays proinflammatory effects. However, a low/minimal amount of endogenous H₂S exerts an anti-inflammatory effect on the colon mucosa, pointing out the ambivalent effect of H₂S depending on its intracellular concentration. Regarding colorectal carcinogenesis, forced CBS expression in late adenoma-like colonocytes increased their proliferative activity, bioenergetics capacity, and tumorigenicity; whereas, genetic ablation of CBS in mice resulted in a reduced number of mutagen-induced aberrant crypt foci. Activation of endogenous H₂S production and low H₂S extracellular concentration enhance cancerous colorectal cell proliferation. Higher exogenous H₂S concentrations markedly reduce mitochondrial ATP synthesis and proliferative capacity in cancerous cells and enhance glycolysis but do not affect their ATP cell content or viability. Thus, it appears that, notably through an effect on colonocyte energy metabolism, endogenous and microbiota-derived H₂S are involved in the host intestinal physiology and physiopathology.

Exploring the role and mechanisms of diallyl trisulfide and diallyl disulfide in chronic constriction-induced neuropathic pain in rats

Background

Garlic oil is a rich source of organosulfur compounds including diallyl disulfide and diallyl trisulfide. There have been studies showing the neuroprotective actions of these organosulfur compounds. However, the potential of these organosulfur compounds in neuropathic pain has not been explored. The present study was aimed at investigating the pain attenuating potential of diallyl disulfide and diallyl trisulfide in chronic constriction injury (CCI)-induced neuropathic pain in rats. The study also explored their pain-attenuating mechanisms through modulation of H₂S, brain-derived neurotrophin factor (BDNF) and nuclear factor erythroid 2-related factor 2 (Nrf2).

Methods

The rats were subjected to CCI injury by ligating the sciatic nerve in four places. The development of neuropathic pain was measured by assessing mechanical hyperalgesia (Randall–Selittotest), mechanical allodynia (Von Frey test), and cold allodynia (acetone drop test) on 14th day after surgery.

Results

Administration of diallyl disulfide (25 and 50 mg/kg) and diallyl trisulfide (20 and 40 mg/kg) for 14 days led to a significant reduction in pain in CCI-subjected rats. Moreover, treatment with these organosulfur compounds led to the restoration of H₂S, BDNF and Nrf2 levels in the sciatic nerve and dorsal root ganglia. Co-administration of ANA-12 (BDNF blocker) abolished pain attenuating actions as well as BDNF and the Nrf2 restorative actions of diallyl disulfide and diallyl trisulfide, without modulating H₂S levels.

Conclusions

Diallyl disulfide and diallyl trisulfide have the potential to attenuate neuropathic pain in CCI-subjected rats possibly through activation of H₂S-BDNF-Nrf2 signaling pathway.

Microbiota Metabolites in Health and Disease

Metabolism is one of the strongest drivers of interkingdom interactions—including those between microorganisms and their multicellular hosts. Traditionally thought to fuel energy requirements and provide building blocks for biosynthetic pathways, metabolism is now appreciated for its role in providing metabolites, small-molecule intermediates generated from metabolic processes, to perform various regulatory functions to mediate symbiotic relationships between microbes and their hosts. Here, we review recent advances in our mechanistic understanding of how microbiota-derived metabolites orchestrate and support physiological responses in the host, including immunity, inflammation, defense against infections, and metabolism. Understanding how microbes metabolically communicate with their hosts will provide us an opportunity to better describe how a host interacts with all microbes—beneficial, pathogenic, and commensal—and an opportunity to discover new ways to treat microbial-driven diseases.

Synergisms, Discrepancies and Interactions between Hydrogen Sulfide and Carbon Monoxide in the Gastrointestinal and Digestive System Physiology, Pathophysiology and Pharmacology

Endogenous gas transmitters, hydrogen sulfide (H₂S), carbon monoxide (CO) and nitric oxide (NO) are important signaling molecules known to exert multiple biological functions. In recent years, the role of H₂S, CO and NO in regulation of cardiovascular, neuronal and digestive systems physiology and pathophysiology has been emphasized. Possible link between these gaseous mediators and multiple diseases as well as potential therapeutic applications has attracted great attention from biomedical scientists working in many fields of biomedicine. Thus, various pharmacological tools with ability to release CO or H₂S were developed and implemented in experimental animal in vivo and in vitro models of many disorders and preliminary human studies. This review was designed to review signaling functions, similarities, dissimilarities and a possible cross-talk between H₂S and CO produced endogenously or released from chemical donors, with special emphasis on gastrointestinal digestive system pathologies prevention and treatment.

Health risk of Licorice-Yuanhua combination through induction of colonic H2S metabolism

ETHNOPHARMACOLOGICAL RELEVANCE

Licorice and Yuanhua are both famous herbs in Traditional Chinese Medicine (TCM), and their combination is used by some TCM doctors to treat renal and gastrointestinal diseases as well as tumors. On the other hand, the compatibility theory of TCM warns that toxic effects might be triggered by Licorice-Yuanhua combination. The usability of Licorice-Yuanhua combination has long been controversial due to lack of evidence and mechanism illustration. Colonic hydrogen sulfide (H₂S) metabolism imbalance is closely related with colonic inflammation, tumor promotion and many other diseases.

AIM OF THE STUDY

This study was carried out to investigate if licorice-Yuanhua combination could induce potential toxic effects in the aspect of colonic H₂S metabolism.

MATERIALS AND METHODS

Normal mice were treated with high or low doses of Licorice, Yuanhua and Licorice-Yuanhua combination. Fecal H₂S concentration was measured by colorimetric method, colon sulfomucin production was compared through tissue staining, fecal microbiota and microbial metagenomes were analyzed by 16S rDNA sequencing and data mining.

RESULTS

Data shows that although licorice cannot change colonic H₂S concentration, it can exacerbate Yuanhua induced H₂S rising. Licorice or Yuanhua increases colon sulfomucin production, and their combination further enhances this effect. 16S rDNA sequencing analysis revealed that licorice or Yuanhua has little influence on gut microbiota, however, licorice-Yuanhua combination can impact gut microbiota structural balance and increase the abundance of Desulfovibrio genus and other related genera. Moreover, the combination extensively changes microbial metagenomes, influencing 1172 genes that cannot be changed by individual licorice or Yuanhua. By searching in KEGG database, ten genes are annotated with H₂S producing gene, and these genes are remarkably increased by licorice-Yuanhua combination, more significantly than licorice or Yuanhua.

CONCLUSIONS

This study provides evidences and mechanisms for licorice induced risks, which is related with colonic H₂S metabolism disturbance, gut microbiota and microbial metagenomes. More risk assessment should be evaluated when licorice was used in combination with foods, herbs or drugs. The study provides an example where healthy risks can be induced by combination of food additive, herbs or drugs, through regulating gut microbiota and its metagenomes.

Effects of sulfide and polysulfides transmitted by direct or signal transduction-mediated activation of TRPA1 channels

Hydrogen sulfide (H₂S) is a gaseous mediator in various physiological and pathological processes, including neuroimmune modulation, metabolic pathways, cardiovascular system, tumour growth, inflammation and pain. Now the hydrogen polysulfides (H₂S_n) have been recognised as signalling molecules modulating ion channels, transcription factors and protein kinases. Transient receptor potential (TRP) cation channels can be activated by mechanical, thermal or chemical triggers. Here, we review the current literature regarding the biological actions of sulfide and polysulfide compounds mediated by TRP channels with special emphasis on the role of TRPA1, best known as ion channels in nociceptors. However, the non‐neuronal TRPA1 channels should also be considered to play regulatory roles. Although sulfide and polysulfide effects in different pathological circumstances and TRPA1‐mediated processes have been investigated intensively, our review attempts to present the first comprehensive overview of the potential crosstalk between TRPA1 channels and sulfide‐activated signalling pathways.

Linked Articles

This article is part of a themed section on Chemical Biology of Reactive Sulfur Species. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.4/issuetoc

Endogenous H2S production deficiencies lead to impaired renal erythropoietin production

INTRODUCTION

Patients suffering from chronic kidney disease (CKD) experience a number of associated comorbidities, including anemia. Relative deficiency in renal erythropoietin (EPO) production is thought to be a primary cause of anemia. Interestingly, CKD patients display low levels of hydrogen sulfide (H₂S), an endogenously derived renal oxygen sensor. Previous in vitro experiments have revealed that H₂S-deficient renal cell lines produce less EPO than wild-type renal cell lines during hypoxia.

METHODS

We postulated that H₂S might be a primary mediator of EPO synthesis during hypoxia, which was tested using an in vivo murine model of whole-body hypoxia and in clinical samples obtained from CKD patients.

RESULTS

Following a 72-hour period of hypoxia (11% O₂), partial H₂S knockout mice (lacking the H₂S biosynthetic enzyme cystathionine γ-lyase [CSE]) displayed lower levels of hemoglobin, EPO and cystathionine-β-synthase (CBS) (another H₂S biosynthetic enzyme) compared to wild-type mice, all of which was rescued by exogenous H2S supplementation. We also found that anemic CKD patients requiring exogenous EPO exhibited lower urinary thiosulfate levels compared to non-anemic CKD patients of similar CKD classification.

CONCLUSIONS

Together, our results confirm an interplay between the actions of H₂S during hypoxia and EPO production.

Hepatic PHD2/HIF-1α axis is involved in postexercise systemic energy homeostasis

Exercise plays an important role in the prevention and treatment of chronic liver disease and associated metabolic disorders. A single bout of exercise induces tissue blood flow redistribution, which decreases splanchnic circulation and leads to physiologic hypoxia in the gastrointestinal system and liver. The transcription factor, hypoxia inducible factor-1α (HIF-1α), and its regulator, prolylhydroxylase 2 (PHD2), play pivotal roles in the response to oxygen flux by regulating downstream gene expression levels in the liver. We hypothesized that exercise increases the HIF-1α levels in the liver, and that the hepatic PHD2/HIF-1α axis is involved in postexercise restoration of systemic energy homeostasis. Through constant O₂ consumption, CO₂ production, food and water intake, and physical activity detection with metabolic chambers, we observed that one 30-min session of swimming exercise enhances systemic energy metabolism in mice. By using the noninvasive bioluminescence imaging ROSA26 oxygen-dependent domain Luc mouse model, we reveal that exercise increases in vivo HIFα levels in the liver. Intraperitoneal injections of the PHD inhibitor, dimethyloxalylglycine, mimicked exercise-induced HIFα increase, whereas the HIF-1α inhibitor, PX-478, blocked this effect. We next constructed liver-specific knockout (LKO) mouse models with albumin- Cre-mediated, hepatocyte-specific Hif1a and Phd2 deletion. Compared with their controls, Hif1a-LKO and Phd2-LKO mice exhibited distinct patterns of hepatic metabolism-related gene expression profiles. Moreover, Hif1a-LKO mice failed to restore systemic energy homeostasis after exercise. In conclusion, the current study demonstrates that a single bout of exercise disrupts systemic energy homeostasis, increasing the HIF-1α levels in the liver. These findings also provide evidence that the hepatic PHD2/HIF-1α axis is involved in postexercise systemic metabolic homeostasis.-Luo, B., Xiang, D., Wu, D., Liu, C., Fang, Y., Chen, P., Hu, Y.-P. Hepatic PHD2/HIF-1α axis is involved in postexercise systemic energy homeostasis.

Gancao-Gansui combination impacts gut microbiota diversity and related metabolic functions

ETHNOPHARMACOLOGICAL RELEVANCE

The theory of "eighteen incompatible medicaments" (EIM) in traditional Chinese medicine (TCM) is the most representative case of herbal-herbal interactions. Gancao and Gansui are one of the incompatible herbal pairs in EIM. Gancao, also known as "licorice", is the most frequently used Chinese herb or food additive. Gansui, the root of Euphorbia kansui T.P. Wang, is another famous Chinese herb usually used to treat edema, ascites and asthma but could induce gastrointestinal (GI) tract irritation. Although Gancao and Gansui are incompatible herbal pairs, they are still used in combination in the famous "Gansui-Banxia" decoction.

AIM OF THE STUDY

This study was conducted to investigate if Gancao-Gansui combination could exacerbate Gansui induced GI tract injury. Moreover, the impact of Gancao-Gansui combination to gut microbiota and related metabolism pathways were evaluated.

MATERIALS AND METHODS

Normal mice were divided into different groups and treated with Gancao extracts, Gansui extracts, and Gancao-Gansui combination extracts for 7 days. Serum biomarkers (diamine oxidase activity, lipopolysaccharide, motilin, IL-1β, IL-6, TNF-α) were determined to reflect GI tract damage. Gut microbiota diversity was studied by 16S rDNA sequencing and metagenomes analysis were also conducted to reflect functional genes expression alteration. Fecal hydrogen sulfide concentrations were measured by spectrophotometry to confirm the alteration of Desulfovibrio genus. Fecal lipid metabolomics study was conducted by GC-MS analysis to confirm the change of metagenomes and Mycoplasma abundance.

RESULTS

Gancao-Gansui combination did not exacerbate GI tract tissue or functional damage but caused gut microbiota dysbiosis and increased some rare genus's abundance including Desulfovibrio and Mycoplasma. Desulfovibrio genus proliferation was confirmed by the disturbance of fecal hydrogen sulfide homeostasis. Gancao-Gansui combination also dys-regulated the metabolic genes in metagenomes. Mycoplasma genus proliferation and the metagenomes changes were both confirmed by metabolic profile analysis of fecal lipids, especially cholesterol.

CONCLUSIONS

Gancao-Gansui combination can impact the gut microbiota diversity and related metabolic functions. Further studies should be carried out when the combination of Gancao-Gansui is used in herbal formulations as this may alter the diversity of the microbiota.

Effects of initiating time and dosage of Panax notoginseng on mucosal microvascular injury in experimental colitis

AIM

To investigate the effects of Panax notoginseng (PN) on microvascular injury in colitis, its mechanisms, initial administration time and dosage.

METHODS

Dextran sodium sulfate (DSS)- or iodoacetamide (IA)-induced rat colitis models were used to evaluate and investigate the effects of ethanol extract of PN on microvascular injuries and their related mechanisms. PN administration was initiated at 3 and 7 d after the model was established at doses of 0.5, 1.0 and 2.0 g/kg for 7 d. The severity of colitis was evaluated by disease activity index (DAI). The pathological lesions were observed under a microscope. Microvessel density (MVD) was evaluated by immunohistochemistry. Vascular permeability was evaluated using the Evans blue method. The serum concentrations of cytokines, including vascular endothelial growth factor (VEGF)A121, VEGFA165, interleukin (IL)-4, IL-6, IL-10 and tumor necrosis factor (TNF)-α, were detected by enzyme-linked immunosorbent assay. Myeloperoxidase (MPO) and superoxide dismutase (SOD) were measured to evaluate the level of oxidative stress. Expression of hypoxia-inducible factor (HIF)-1α protein was detected by western blotting.

RESULTS

Obvious colonic inflammation and injuries of mucosa and microvessels were observed in DSS- and IA-induced colitis groups. DAI scores, serum concentrations of VEGFA121, VEGFA165, VEGFA165/VEGFA121, IL-6 and TNF-α, and concentrations of MPO and HIF-1α in the colon were significantly higher while serum concentrations of IL-4 and IL-10 and MVD in colon were significantly lower in the colitis model groups than in the normal control group. PN promoted repair of injuries of colonic mucosa and microvessels, attenuated inflammation, and decreased DAI scores in rats with colitis. PN also decreased the serum concentrations of VEGFA121, VEGFA165, VEGFA165/VEGFA121, IL-6 and TNF-α, and concentrations of MPO and HIF-1α in the colon, and increased the serum concentrations of IL-4 and IL-10 as well as the concentration of SOD in the colon. The efficacy of PN was dosage dependent. In addition, DAI scores in the group administered PN on day 3 were significantly lower than in the group administered PN on day 7.

CONCLUSION

PN repairs vascular injury in experimental colitis via attenuating inflammation and oxidative stress in the colonic mucosa. Efficacy is related to initial administration time and dose.

Regulation of immunity and inflammation by hypoxia in immunological niches

Immunological niches are focal sites of immune activity that can have varying microenvironmental features. Hypoxia is a feature of physiological and pathological immunological niches. The impact of hypoxia on immunity and inflammation can vary depending on the microenvironment and immune processes occurring in a given niche. In physiological immunological niches, such as the bone marrow, lymphoid tissue, placenta and intestinal mucosa, physiological hypoxia controls innate and adaptive immunity by modulating immune cell proliferation, development and effector function, largely via transcriptional changes driven by hypoxia-inducible factor (HIF). By contrast, in pathological immunological niches, such as tumours and chronically inflamed, infected or ischaemic tissues, pathological hypoxia can drive tissue dysfunction and disease development through immune cell dysregulation. Here, we differentiate between the effects of physiological and pathological hypoxia on immune cells and the consequences for immunity and inflammation in different immunological niches. Furthermore, we discuss the possibility of targeting hypoxia-sensitive pathways in immune cells for the treatment of inflammatory disease.

Structural elucidation and physiologic functions of specialized pro-resolving mediators and their receptors

The acute inflammatory response is host-protective to contain foreign invaders. Many of today's pharmacopeia that block pro-inflammatory chemical mediators can cause serious unwanted side effects such as immune suppression. Uncontrolled inflammation is now considered a pathophysiologic basis associated with many widely occurring diseases such as cardiovascular disease, neurodegenerative diseases, diabetes, obesity and asthma, as well as the classic inflammatory diseases, e.g. arthritis, periodontal diseases. The inflammatory response is designated to be a self-limited process that produces a superfamily of chemical mediators that stimulate resolution of inflammatory responses. Specialized proresolving mediators (SPM) uncovered in recent years are endogenous mediators that include omega-3-derived families resolvins, protectins and maresins, as well as arachidonic acid-derived (n-6) lipoxins that stimulate and promote resolution of inflammation, clearance of microbes, reduce pain and promote tissue regeneration via novel mechanisms. Here, we review recent evidence from human and preclinical animal studies, together with the structural and functional elucidation of SPM indicating the SPM as physiologic mediators and pharmacologic agonists that stimulate resolution of inflammation and infection. These results suggest that it is time to develop immunoresolvents as agonists for testing resolution pharmacology in nutrition and health as well as in human diseases and during surgery.

The smell of renal protection against chronic kidney disease: Hydrogen sulfide offers a potential stinky remedy

Chronic kidney disease (CKD) is a common global health challenge characterized by irreversible pathological processes that reduce kidney function and culminates in development of end-stage renal disease. It is associated with increased morbidity and mortality in addition to increased caregiver burden and higher financial cost. A central player in CKD pathogenesis and progression is renal hypoxia. Renal hypoxia stimulates induction of oxidative and endoplasmic reticulum stress, inflammation and tubulointerstitial fibrosis, which in turn, promote cellular susceptibility and further aggravate hypoxia, thus forming a pathological vicious cycle in CKD progression. Although the importance of CKD is widely appreciated, including improvements in the quality of existing therapies such as dialysis and transplantation, new therapeutic options are limited, as there is still increased morbidity, mortality and poor quality of life among CKD patients. Growing evidence indicates that hydrogen sulfide (H₂S), a small gaseous signaling molecule with an obnoxious smell, accumulates in the renal medulla under hypoxic conditions, and functions as an oxygen sensor that restores oxygen balance and increases medullary flow. Moreover, plasma H₂S level has been recently reported to be markedly reduced in CKD patients and animal models. Also, H₂S has been established to possess potent antioxidant, anti-inflammatory, and anti-fibrotic properties in several experimental models of kidney diseases, suggesting that its supplementation could protect against CKD and retard its progression. The purpose of this review is to discuss current clinical and experimental developments regarding CKD, its pathophysiology, and potential cellular and molecular mechanisms of protection by H₂S in experimental models of CKD.

Redox regulation of gasotransmission in the vascular system: A focus on angiogenesis

Reactive oxygen species have emerged as key participants in a broad range of physiological and pathophysiological processes, not least within the vascular system. Diverse cellular functions which have been attributed to some of these pro-oxidants within the vasculature include the regulation of blood pressure, neovascularisation and vascular inflammation. We here highlight the emerging roles of the enzymatically-generated reaction oxygen species, O₂^- and H₂O₂, in the regulation of the functions of the gaseous signalling molecules: nitric oxide (NO), carbon monoxide (CO), and hydrogen sulphide (H₂S). These gasotransmitters are produced on demand from distinct enzymatic sources and in recent years it has become apparent that they are capable of mediating a number of homeostatic processes within the cardiovascular system including enhanced vasodilation, angiogenesis, wound healing and improved cardiac function following myocardial infarction. In common with O₂^- and/or H₂O₂ they signal by altering the functions of target proteins, either by the covalent modification of thiol groups or by direct binding to metal centres within metalloproteins, most notably haem proteins. The regulation of the enzymes which generate NO, CO and H₂S have been shown to be influenced at both the transcriptional and post-translational levels by redox-dependent mechanisms, while the activity and bioavailability of the gasotransmitters themselves are also subject to oxidative modification. Within vascular cells, the family of nicotinamide adenine dinucleotide phosphate oxidases (NAPDH oxidases/Noxs) have emerged as functionally significant sources of regulated O₂^- and H₂O₂ production and accordingly, direct associations between Nox-generated oxidants and the functions of specific gasotransmitters are beginning to be identified. This review focuses on the current knowledge of the redox-dependent mechanisms which regulate the generation and activity of these gases, with particular reference to their roles in angiogenesis.

Gasotransmitter Heterocellular Signaling

SIGNIFICANCE

The family of gasotransmitter molecules, nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H₂S), has emerged as an important mediator of numerous cellular signal transduction and pathophysiological responses. As such, these molecules have been reported to influence a diverse array of biochemical, molecular, and cell biology events often impacting one another. Recent Advances: Discrete regulation of gasotransmitter molecule formation, movement, and reaction is critical to their biological function. Due to the chemical nature of these molecules, they can move rapidly throughout cells and tissues acting on targets through reactions with metal groups, reactive chemical species, and protein amino acids.

CRITICAL ISSUES

Given the breadth and complexity of gasotransmitter reactions, this field of research is expanding into exciting, yet sometimes confusing, areas of study with significant promise for understanding health and disease. The precise amounts of tissue and cellular gasotransmitter levels and where they are formed, as well as how they react with molecular targets or themselves, all remain poorly understood.

FUTURE DIRECTIONS

Elucidation of specific molecular targets, characteristics of gasotransmitter molecule heterotypic interactions, and spatiotemporal formation and metabolism are all important to better understand their true pathophysiological importance in various organ systems. Antioxid. Redox Signal. 26, 936-960.

Characterizing the anti-inflammatory and tissue protective actions of a novel Annexin A1 peptide

Inflammation in now appreciated to be at the centre of may diseases that affect Western civilization. Current therapeutics for managing these conditions may interfere with the host response leading to immune suppression. We recently developed an annexin (Anx) A1-derived peptide, coined CR-AnxA12-50, which displays potent pro-resolving and tissue protective actions. Herein, we designed a novel peptide using CR-AnxA12-50 as a template that was significantly more resistant to neutrophil-mediated degradation. This peptide, termed CR-AnxA12-48, retained high affinity and specificity to the pro-resolving Lipoxin A4 receptor (ALX) with an IC50 of ~20nM. CR-AnxA12-48 dose dependently (100fM-10nM) promoted the efferocytosis of apoptotic neutrophils, an action that was mediated by the murine orthologue of human ALX. The neutrophil-directed actions were also retained with human primary cells were CR-AnxA12-48 reduced human neutrophil recruitment to activated endothelial cells at concentrations as low as 100 pM. This protective action was mediated by human ALX, since incubation of neutrophils with an anti-ALX antibody reversed this anti-inflammatory actions of CR-AnxA12-48. Administration of this peptide to mice during dermal inflammation led to a significant and dose dependent decrease in neutrophil recruitment. This reduction in neutrophil numbers was more pronounced than that displayed by the parent peptide CR-AnxA12-50. CR-AnxA12-48 was also cardioprotecitve reducing infarct size and systemic chemokine (C-C motif) ligand 5 concentration following ischemia reperfusion injury. These findings identify CR-AnxA12-48 as a new ALX agonist that regulates phagocyte responses and displays tissue-protective actions.

Treating inflammation and infection in the 21st century: new hints from decoding resolution mediators and mechanisms

Practitioners of ancient societies from the time of Hippocrates and earlier recognized and treated the signs of inflammation, heat, redness, swelling, and pain with agents that block or inhibit proinflammatory chemical mediators. More selective drugs are available today, but this therapeutic concept has not changed. Because the acute inflammatory response is host protective to contain foreign invaders, much of today's pharmacopeia can cause serious unwanted side effects, such as immune suppression. Uncontrolled inflammation is now considered pathophysiologic and is associated with many widely occurring diseases such as cardiovascular disease, neurodegenerative diseases, diabetes, obesity, and asthma, as well as classic inflammatory diseases (e.g., arthritis and periodontal diseases). The inflammatory response, when self-limited, produces a superfamily of chemical mediators that stimulate resolution of the response. Specialized proresolving mediators (SPMs), identified in recent years, are endogenous mediators that include the n-3-derived families resolvins, protectins, and maresins, as well as arachidonic acid-derived (n-6) lipoxins, which promote resolution of inflammation, clearance of microbes, reduction of pain, and promotion of tissue regeneration via novel mechanisms. Aspirin and statins have a positive impact on these resolution pathways, producing epimeric forms of specific SPMs, whereas other drugs can disrupt timely resolution. In this article, evidence from recent human and preclinical animal studies is reviewed, indicating that SPMs are physiologic mediators and pharmacologic agonists that stimulate resolution of inflammation and infection. The findings suggest that it is time to challenge current treatment practices-namely, using inhibitors and antagonists alone-and to develop immunoresolvents as agonists to test resolution pharmacology and their role in catabasis for their therapeutic potential.-Serhan, C. N. Treating inflammation and infection in the 21st century: new hints from decoding resolution mediators and mechanisms.

Roles of Dietary Amino Acids and Their Metabolites in Pathogenesis of Inflammatory Bowel Disease

Inflammatory Bowel Disease (IBD) is a kind of chronic inflammation, which has increasing incidence and prevalence in recent years. IBD mainly divides into Crohn's disease (CD) and ulcerative colitis (UC). It is hard to cure IBD completely, and novel therapies are urgently needed. Amino acids (AAs) and their metabolites are regarded as important nutrients for humans and animals and also play an important role in IBD amelioration. In the present study, the potential protective effects of AAs and their metabolites on IBD had been summarized with the objective to provide insights into IBD moderating using dietary AAs and their metabolites as a potential adjuvant therapy.

Interaction between endogenous carbon monoxide and hydrogen sulfide in the mechanism of gastroprotection against acute aspirin-induced gastric damage

Acetylsalicylic acid (ASA) is mainly recognized as painkiller or anti-inflammatory drug. However, ASA causes serious side effects towards gastrointestinal (GI) tract which limits its usefulness. Carbon monoxide (CO) and hydrogen sulfide (H₂S) have been described to act as important endogenous messengers and mediators of gastroprotection but whether they can interact in gastroprotection against acute ASA-induced gastric damage remains unknown. In this study male Wistar rats were pretreated with 1) vehicle (saline, i.g.), 2) tricarbonyldichlororuthenium (II) dimer (CORM-2, 5mg/kg i.g.), 3) sodium hydrosulfide (NaHS, 5mg/kg i.g.), 4) zinc protoporphyrin (ZnPP, 10mg/kg i.p.), 5) D,L-propargylglycine (PAG, 30mg/kg i.g.), 6) ZnPP combined with NaHS, 7) PAG combined with CORM-2 or 8) 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 10mg/kg i.p.) combined with CORM-2 or NaHS and 30min later ASA was administered i.g. in a single dose of 125mg/kg. After 1h, gastric blood flow (GBF) was determined by H₂ gas clearance technique and gastric lesions were assessed by planimetry and histology. CO content in gastric mucosa and COHb concentration in blood were determined by gas chromatography and H₂S production was assessed in gastric mucosa using methylene blue method. Protein and/or mRNA expression for cystathionine-γ-lyase (CSE), cystathionine-β-synthase (CBS), 3-mercaptopyruvate sulfurtransferase (3-MST), heme oxygenase (HO)-1, HO-2, hypoxia inducible factor-alpha (HIF)-1α, nuclear factor (erythroid-derived 2)-like 2 (Nrf-2), cyclooxygenase (COX)-1 and COX-2, inducible nitric oxide synthase (iNOS) and interleukin (IL)-1β were determined by Western blot or real-time PCR, respectively. ASA caused hemorrhagic gastric mucosal damage and significantly decreased GBF, H₂S production, CO content, mRNA or protein expression for CSE, 3-MST, HO-2 and increased mRNA and/or protein expression for CBS, HO-1, Nrf-2, HIF-1α, iNOS, IL-1β, COX-2 in gastric mucosa and COHb concentration in blood. Pretreatment with CORM-2 or NaHS but not with PAG decreased ASA-damage and increased GBF. ZnPP reversed protective and hyperemic effect of NaHS but PAG failed to affect CORM-2-induced gastroprotection. CORM-2 elevated CO content, mRNA or protein expression for HO-1, Nrf-2, and decreased expression of CBS, HIF-1α, COX-2, IL-1β, iNOS, the H₂S production in gastric mucosa and COHb concentration in blood. NaHS raised mRNA or protein expression for CSE, COX-1 and decreased mRNA expression for IL-1β and COHb level in blood. We conclude that CO is involved in gastroprotection induced by H₂S while beneficial protective action of CO released from CORM-2 in gastric mucosa seems to be H₂S-independent. In contrast to H₂S, CO ameliorates hypoxia, regulates Nrf-2 expression but similarly to H₂S acts on sGC-dependent manner to restore gastric microcirculation and exhibit anti-inflammatory activity in gastric mucosa compromised by ASA.

Hydrogen Sulfide Regulates Krüppel-Like Factor 5 Transcription Activity via Specificity Protein 1 S-Sulfhydration at Cys664 to Prevent Myocardial Hypertrophy

Background

Hydrogen sulfide (H₂S) is a gasotransmitter that regulates multiple cardiovascular functions. Krüppel‐like factor 5 (KLF5) exerts diverse functions in the cardiovascular system. Whether and how H₂S regulates KLF5 in myocardial hypertrophy is unknown.

Methods and Results

In our study, hypertrophic myocardial samples in the clinic were collected and underwent histological and molecular biological analysis. Spontaneously hypertensive rats and neonatal rat cardiomyocytes were studied for functional and signaling responses to GYY4137, an H₂S‐releasing compound. Expression of cystathionine γ‐lyase, a principal enzyme for H₂S generation in heart, decreased in human hypertrophic myocardium, whereas KLF5 expression increased. After GYY4137 administration for 4 weeks, myocardial hypertrophy was inhibited in spontaneously hypertensive rats, as demonstrated by improvement in cardiac structural parameters, heart mass, size of cardiac myocytes, and expression of atrial natriuretic peptide. H₂S diminished expression of KLF5 in myocardium of spontaneously hypertensive rats and in hypertrophic cardiomyocytes. H₂S also inhibits platelet‐derived growth factor A promoter activity, decreased recruitment of KLF5 to the platelet‐derived growth factor A promoter, and reduced atrial natriuretic peptide expression in angiotensin II–stimulated cardiomyocytes, and these effects are suppressed by KLF5 knockdown. KLF5 promoter activity and KLF5 expression was also reversed by H₂S. H₂S increased the S‐sulfhydration on specificity protein 1 in cardiomyocytes. Moreover, H₂S decreased KLF5 promoter activity; reduced KLF5 mRNA expression; attenuated specificity protein 1 binding activity with KLF5 promoter; and inhibited hypertrophy after specificity protein 1 mutated at Cys659, Cys689, and Cys692 but not Cys664 overexpression.

Conclusions

These findings suggest that H₂S regulates KLF5 transcription activity via specificity protein 1 S‐sulfhydration at Cys664 to prevent myocardial hypertrophy.

Regulation and role of endogenously produced hydrogen sulfide in angiogenesis

Recent studies have implicated endogenously produced H₂S in the angiogenic process. On one hand, pharmacological inhibition and silencing of the enzymes involved in H₂S synthesis attenuate the angiogenic properties of endothelial cells, including proliferation, migration and tube-like structure network formation. On the other hand, enhanced production of H₂S by substrate supplementation or over-expression of H₂S-producing enzymes leads to enhanced angiogenic responses in cultured endothelial cells. Importantly, H₂S up-regulates expression of the key angiogenic factor vascular endothelial growth factor (VEGF) and contributes to the angiogenic signaling in response to VEGF. The signaling pathways mediating H₂S-induced angiogenesis include mitogen-activated protein kinases, phosphoinositide-3 kinase, nitric oxide/cGMP-regulated cascades and ATP-sensitive potassium channels. Endogenously produced H₂S has also been shown to facilitate neovascularization in prototypical model systems in vivo, and to contribute to wound healing, post-ischemic angiogenesis in the heart and other tissues, as well as in tumor angiogenesis. Targeting of H₂S synthesizing enzymes might offer novel therapeutic opportunities for angiogenesis-related diseases.

Immunologic Consequences of Hypoxia during Critical Illness

Hypoxia and immunity are highly intertwined at clinical, cellular, and molecular levels. The prevention of tissue hypoxia and modulation of systemic inflammation are cornerstones of daily practice in the intensive care unit. Potentially, immunologic effects of hypoxia may contribute to outcome and represent possible therapeutic targets. Hypoxia and activation of downstream signaling pathways result in enhanced innate immune responses, aimed to augment pathogen clearance. On the other hand, hypoxia also exerts antiinflammatory and tissue-protective effects in lymphocytes and other tissues. Although human data on the net immunologic effects of hypoxia and pharmacologic modulation of downstream pathways are limited, preclinical data support the concept of tailoring the immune response through modulation of the oxygen status or pharmacologic modulation of hypoxia-signaling pathways in critically ill patients.

Detrimental effects for colonocytes of an increased exposure to luminal hydrogen sulfide: The adaptive response

Protein fermentation by the gut microbiota releases in the large intestine lumen various amino-acid derived metabolites. Among them, hydrogen sulfide (H2S) in excess has been suspected to be detrimental for colonic epithelium energy metabolism and DNA integrity. The first objective of this study was to evaluate in rats the epithelial response to an increased exposure to H2S. Experiments from colonocyte incubation and intra-colonic instillation indicate that low millimolar concentrations of the sulfide donor NaHS reversibly inhibited colonocyte mitochondrial oxygen consumption and increased gene expression of hypoxia inducible factor 1α (Hif-1α) together with inflammation-related genes namely inducible nitric oxide synthase (iNos) and interleukin-6 (Il-6). Additionally, rat colonocyte H2S detoxification capacity was severely impaired in the presence of nitric oxide. Based on the γH2AX ICW technique, NaHS did not induce DNA damage in colonocytes. Since H2S is notably produced by the gut microbiota from sulfur containing amino acids, the second objective of the study was to investigate the effects of a high protein diet (HPD) on large intestine luminal sulfide content and on the expression of genes involved in H2S detoxification in colonocytes. We found that HPD markedly increased H2S content in the large intestine but the concomitant increase of the content mass maintained the luminal sulfide concentration. HPD also provoked an increase of sulfide quinone reductase (Sqr) gene expression in colonocytes, indicating an adaptive response to increased H2S bacterial production. In conclusion, low millimolar NaHS concentration severely affects colonocyte respiration in association with increased expression of genes associated with intestinal inflammation. Although HPD increases the sulfide content of the large intestine, the colonic adaptive responses to this modification limit the epithelial exposure to this deleterious bacterial metabolite.

Hydrogen Sulfide Signaling Axis as a Target for Prostate Cancer Therapeutics

Hydrogen sulfide (H₂S) was originally considered toxic at elevated levels; however just in the past decade H₂S has been proposed to be an important gasotransmitter with various physiological and pathophysiological roles in the body. H₂S can be generated endogenously from L-cysteine by multiple enzymes, including cystathionine gamma-lyase, cystathionine beta-synthase, and 3-mercaptopyruvate sulfurtransferase in combination with cysteine aminotransferase. Prostate cancer is a major health concern and no effective treatment for prostate cancers is available. H₂S has been shown to inhibit cell survival of androgen-independent, androgen-dependent, and antiandrogen-resistant prostate cancer cells through different mechanisms. Various H₂S-releasing compounds, including sulfide salts, diallyl disulfide, diallyl trisulfide, sulforaphane, and other polysulfides, also have been shown to inhibit prostate cancer growth and metastasis. The expression of H₂S-producing enzyme was reduced in both human prostate cancer tissues and prostate cancer cells. Androgen receptor (AR) signaling is indispensable for the development of castration resistant prostate cancer, and H₂S was shown to inhibit AR transactivation and contributes to antiandrogen-resistant status. In this review, we summarized the current knowledge of H₂S signaling in prostate cancer and described the molecular alterations, which may bring this gasotransmitter into the clinic in the near future for developing novel pharmacological and therapeutic interventions for prostate cancer.

Profound Chemopreventative Effects of a Hydrogen Sulfide-Releasing NSAID in the APCMin/+ Mouse Model of Intestinal Tumorigenesis

Nonsteroidal anti-inflammatory drugs have been shown to reduce the incidence of gastrointestinal cancers, but the propensity of these drugs to cause ulcers and bleeding limits their use. H₂S has been shown to be a powerful cytoprotective and anti-inflammatory substance in the digestive system. This study explored the possibility that a H₂S-releasing nonsteroidal anti-inflammatory drug (ATB-346) would be effective in a murine model of hereditary intestinal cancer (APC^Min+ mouse) and investigated potential mechanisms of action via transcriptomics analysis. Daily treatment with ATB-346 was significantly more effective at preventing intestinal polyp formation than naproxen. Significant beneficial effects were seen with a treatment period of only 3–7 days, and reversal of existing polyps was observed in the colon. ATB-346, but not naproxen, significantly decreased expression of intestinal cancer-associated signaling molecules (cMyc, β-catenin). Transcriptomic analysis identified 20 genes that were up-regulated in APC^Min+ mice, 18 of which were reduced to wild-type levels by one week of treatment with ATB-346. ATB-346 is a novel, gastrointestinal-sparing anti-inflammatory drug that potently and rapidly prevents and reverses the development of pre-cancerous lesions in a mouse model of hereditary intestinal tumorigenesis. These effects may be related to the combined effects of suppression of cyclooxygenase and release of H₂S, and correction of most of the APC^Min+-associated alterations in the transcriptome. ATB-346 may represent a promising agent for chemoprevention of tumorigenesis in the GI tract and elsewhere.

Hydrogen Sulfide and Carbon Monoxide Protect Gastric Mucosa Compromised by Mild Stress Against Alendronate Injury

BACKGROUND

Alendronate is an inhibitor of osteoclast-mediated bone resorption, but its clinical utility is limited due to gastrointestinal complications including bleeding erosions.

AIMS

We studied whether potent vasodilators hydrogen sulfide (H₂S) and carbon monoxide (CO) can protect against alendronate-induced gastric lesions in rats exposed to mild stress.

METHODS

Three series (A, B, and C) of Wistar rats received alendronate (150-700 mg/kg i.g., series A) with or without NaHS (5 mg/kg), H₂S donor or CORM-2 (5 mg/kg) releasing CO administered i.g. 30 min before alendronate administration (series B) in rats exposed for 3 days before alendronate administration to mild stress (series C). The area of gastric lesions was assessed by planimetry, the gastric blood flow (GBF) was determined by H₂-gas clearance technique, and H₂S production via CSE/CBS/3-MST activity and the gastric expression of HO-1, HO-2, HIF-1α, NF-κB, iNOS, COX-2, IL-1β, TNF-α, GPx-1 and SOD-2 were analyzed by qPCR or Western blot.

RESULTS

Alendronate dose-dependently produced gastric mucosal lesions and significantly decreased GBF, and these effects were exacerbated by mild stress. NaHS and CORM-2 significantly reduced the alendronate-induced gastric lesions in non-stressed and stressed animals, but only NaHS but not CORM-2 raised H₂S production. NaHS and CORM-2 inhibited gastric expression of HIF-1α protein and HO-1, HIF-1α, NF-κB, COX-2, iNOS, IL-1β, TNF-α mRNAs but failed to affect those of HO-2, GPx-1, and SOD-2.

CONCLUSION

Both H₂S and CO released from their donors, NaHS and CORM-2, protect gastric mucosa compromised by stress against alendronate-induced gastric damage via mechanism involving downregulation of HIF-1α, NF-κB and proinflammatory factors COX-2, iNOS, IL-1β, and TNF-α.

Inhibition of Hif1α prevents both trauma-induced and genetic heterotopic ossification

Pathologic extraskeletal bone formation, or heterotopic ossification (HO), occurs following mechanical trauma, burns, orthopedic operations, and in patients with hyperactivating mutations of the type I bone morphogenetic protein receptor ACVR1 (Activin type 1 receptor). Extraskeletal bone forms through an endochondral process with a cartilage intermediary prompting the hypothesis that hypoxic signaling present during cartilage formation drives HO development and that HO precursor cells derive from a mesenchymal lineage as defined by Paired related homeobox 1 (Prx). Here we demonstrate that Hypoxia inducible factor-1α (Hif1α), a key mediator of cellular adaptation to hypoxia, is highly expressed and active in three separate mouse models: trauma-induced, genetic, and a hybrid model of genetic and trauma-induced HO. In each of these models, Hif1α expression coincides with the expression of master transcription factor of cartilage, Sox9 [(sex determining region Y)-box 9]. Pharmacologic inhibition of Hif1α using PX-478 or rapamycin significantly decreased or inhibited extraskeletal bone formation. Importantly, de novo soft-tissue HO was eliminated or significantly diminished in treated mice. Lineage-tracing mice demonstrate that cells forming HO belong to the Prx lineage. Burn/tenotomy performed in lineage-specific Hif1α knockout mice (Prx-Cre/Hif1α(fl:fl)) resulted in substantially decreased HO, and again lack of de novo soft-tissue HO. Genetic loss of Hif1α in mesenchymal cells marked by Prx-cre prevents the formation of the mesenchymal condensations as shown by routine histology and immunostaining for Sox9 and PDGFRα. Pharmacologic inhibition of Hif1α had a similar effect on mesenchymal condensation development. Our findings indicate that Hif1α represents a promising target to prevent and treat pathologic extraskeletal bone.

Hydrogen Sulfide in Physiology and Diseases of the Digestive Tract

Hydrogen sulfide (H₂S) is a Janus-faced molecule. On one hand, several toxic functions have been attributed to H₂S and exposure to high levels of this gas is extremely hazardous to health. On the other hand, H₂S delivery based clinical therapies are being developed to combat inflammation, visceral pain, oxidative stress related tissue injury, thrombosis and cancer. Since its discovery, H₂S has been found to have pleiotropic effects on physiology and health. H₂S is a gasotransmitter that exerts its effect on different systems, such as gastrointestinal, neuronal, cardiovascular, respiratory, renal, and hepatic systems. In the gastrointestinal tract, in addition to H₂S production by mammalian cystathionine-β-synthase (CBS), cystathionine-γ-lyase (CSE), H₂S is also generated by the metabolic activity of resident gut microbes, mainly by colonic Sulfate-Reducing Bacteria (SRB) via a dissimilatory sulfate reduction (DSR) pathway. In the gut, H₂S regulates functions such as inflammation, ischemia/ reperfusion injury and motility. H₂S derived from gut microbes has been found to be associated with gastrointestinal disorders such as ulcerative colitis, Crohn’s disease and irritable bowel syndrome. This underscores the importance of gut microbes and their production of H₂S on host physiology and pathophysiology.

Wound repair: role of immune-epithelial interactions

The epithelium serves as a highly selective barrier at mucosal surfaces. Upon injury, epithelial wound closure is orchestrated by a series of events that emanate from the epithelium itself as well as by the temporal recruitment of immune cells into the wound bed. Epithelial cells adjoining the wound flatten out, migrate, and proliferate to rapidly cover denuded surfaces and re-establish mucosal homeostasis. This process is highly regulated by proteins and lipids, proresolving mediators such as Annexin A1 protein and resolvins released into the epithelial milieu by the epithelium itself and infiltrating innate immune cells including neutrophils and macrophages. Failure to achieve these finely tuned processes is observed in chronic inflammatory diseases that are associated with non-healing wounds. An improved understanding of mechanisms that mediate repair is important in the development of therapeutics aimed to promote mucosal wound repair.

Gaseous mediators nitric oxide and hydrogen sulfide in the mechanism of gastrointestinal integrity, protection and ulcer healing

Nitric oxide (NO) and hydrogen sulfide (H2S) are known as biological messengers; they play an important role in human organism and contribute to many physiological and pathophysiological processes. NO is produced from l-arginine by constitutive NO synthase (NOS) and inducible NOS enzymatic pathways. This gaseous mediator inhibits platelet aggregation, leukocyte adhesion and contributes to the vessel homeostasis. NO is known as a vasodilatory molecule involved in control of the gastric blood flow (GBF) and the maintenance of gastric mucosal barrier integrity in either healthy gastric mucosa or that damaged by strong irritants. Biosynthesis of H2S in mammals depends upon two enzymes cystathionine-β-synthase and cystathionine γ-lyase. This gaseous mediator, similarly to NO and carbon monoxide, is involved in neuromodulation, vascular contractility and anti-inflammatory activities. For decades, H2S has been known to inhibit cytochrome c oxidase and reduce cell energy production. Nowadays it is generally considered to act through vascular smooth muscle ATP-dependent K+ channels, interacting with intracellular transcription factors and promote sulfhydration of protein cysteine moieties within the cell, but the mechanism of potential gastroprotective and ulcer healing properties of H2S has not been fully explained. The aim of this review is to compare current results of the studies concerning the role of H2S and NO in gastric mucosa protection and outline areas that may pose new opportunities for further development of novel therapeutic targets.