SG1002 and Catenated Divalent Organic Sulfur Compounds as Promising Hydrogen Sulfide Prodrugs

Investigating the impact of protein S-sulfhydration modification on vascular diseases: A comprehensive review

The post-translational modification of cysteine through redox reactions, especially S-sulfhydration, plays a critical role in regulating protein activity, interactions, and spatial arrangement. This review focuses on the impact of protein S-sulfhydration on vascular function and its implications in vascular diseases. Dysregulated S-sulfhydration has been linked to the development of vascular pathologies, including aortic aneurysms and dissections, atherosclerosis, and thrombotic diseases. The H2S signaling pathway and the enzyme cystathionine γ-lyase (CSE), which is responsible for H2S generation, are identified as key regulators of vascular function. Additionally, potential therapeutic targets for the treatment of vascular diseases, such as the H2S donor GYY4137 and the HDAC inhibitor entinostat, are discussed. The review also emphasizes the antithrombotic effects of H2S in regulating platelet aggregation and thrombosis. The aim of this review is to enhance our understanding of the function and mechanism of protein S-sulfhydration modification in vascular diseases, and to provide new insights into the clinical application of this modification.

Hydrogen sulfide and sulfaceutic or sulfanutraceutic agents: Classification, differences and relevance in preclinical and clinical studies

Hydrogen sulfide (H2S) has been extensively studied as a signal molecule in the body for the past 30 years. Researchers have conducted studies using both natural and synthetic sources of H2S, known as H2S donors, which have different characteristics in terms of how they release H2S. These donors can be inorganic salts or have various organic structures. In recent years, certain types of sulfur compounds found naturally in foods have been characterized as H2S donors and explored for their potential health benefits. These compounds are referred to as "sulfanutraceuticals," a term that combines "nutrition" and "pharmaceutical". It is used to describe products derived from food sources that offer additional health advantages. By introducing the terms "sulfaceuticals" and "sulfanutraceuticals," we categorize sulfur-containing substances based on their origin and their use in both preclinical and clinical research, as well as in dietary supplements.

Diallyl trisulfide ameliorates bone loss and alters specific gut microbiota and serum metabolites in natural aging mice

Aging is a major cause of bone loss and osteoporosis. Diallyl trisulfide (DATS), one of the main organic sulfides in garlic oil, has been shown to alleviate arthritis in mice. However, further research is still needed to determine how DATS affects bone formation and bone loss in aging mice. Here, we established a mouse model of natural aging for dietary DATS intervention. DATS treatment improved the bone microstructure, including the disorganized arrangement of bone trabeculae and promoted collagen synthesis, as confirmed by micro-CT and histological analyses. The abundance of beneficial bacteria for bone formation, such as Clostridiaceae and Erysipelotrichaceae, and the microbial diversity and community richness were all altered by DATS, according to 16S rRNA sequencing data. 14 potential biomarkers and 9 important metabolic pathways were examined using serum metabolomics analysis. Additionally, there has been a significant reduction in sphingosine, which is directly associated with bone metabolism. The level of sphingosine and relative abundance of Clostridium were found to be negatively correlated by correlation analysis, indicating that bacteria may regulate bone reconstruction via influencing metabolites. Furthermore, Runx2 and β-catenin gene expression levels increased in bones, which may be related to the ameliorative mechanism of DATS. Our results suggested that DATS may prevent age-related bone loss by upregulating osteogenic gene expression through altering gut microbes and serum metabolism.

Protein persulfidation: Rewiring the hydrogen sulfide signaling in cell stress response

The past few decades have witnessed significant progress in the discovery of hydrogen sulfide (H₂S) as a ubiquitous gaseous signaling molecule in mammalian physiology, akin to nitric oxide and carbon monoxide. As the third gasotransmitter, H₂S is now known to exert a wide range of physiological and cytoprotective functions in the biological systems. However, endogenous H₂S concentrations are usually low, and its potential biologic mechanisms responsible have not yet been fully clarified. Recently, a growing body of evidence has demonstrated that protein persulfidation, a posttranslational modification of cysteine residues (RSH) to persulfides (RSSH) elicited by H₂S, is a fundamental mechanism of H₂S-mediated signaling pathways. Persulfidation, as a biological switch for protein function, plays an important role in the maintenance of cell homeostasis in response to various internal and external stress stimuli and is also implicated in numerous diseases, such as cardiovascular and neurodegenerative diseases and cancer. In this review, the biological significance of protein persulfidation by H₂S in cell stress response is reviewed providing a framework for understanding the multifaceted roles of H₂S. A mechanism-guided perspective can help open novel avenues for the exploitation of therapeutics based on H₂S-induced persulfidation in the context of diseases.

H2S Prodrug, SG-1002, Protects against Myocardial Oxidative Damage and Hypertrophy In Vitro via Induction of Cystathionine β-Synthase and Antioxidant Proteins

Endogenously produced hydrogen sulfide (H₂S) is critical for cardiovascular homeostasis. Therapeutic strategies aimed at increasing H₂S levels have proven cardioprotective in models of acute myocardial infarction (MI) and heart failure (HF). The present study was undertaken to investigate the effects of a novel H₂S prodrug, SG-1002, on stress induced hypertrophic signaling in murine HL-1 cardiac muscle cells. Treatment of HL-1 cells with SG-1002 under serum starvation without or with H₂O₂ increased the levels of H₂S, H₂S producing enzyme, and cystathionine β-synthase (CBS), as well as antioxidant protein levels, such as super oxide dismutase1 (SOD1) and catalase, and additionally decreased oxidative stress. SG-1002 also decreased the expression of hypertrophic/HF protein markers such as atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), galectin-3, TIMP1, collagen type III, and TGF-β1 in stressed HL-1 cells. Treatment with SG-1002 caused a significant induction of cell viability and a marked reduction of cellular cytotoxicity in HL-1 cells under serum starvation incubated without or with H₂O₂. Experimental results of this study suggest that SG-1002 attenuates myocardial cellular oxidative damage and/or hypertrophic signaling via increasing H₂S levels or H₂S producing enzymes, CBS, and antioxidant proteins.

Development of novel hydrogen sulfide depletion aided platform for photodynamic therapy with enhanced anticancer performance

Hydrogen sulfide (H₂S) as a key fundamental gasotransmitter regulates various biological processes, and the incontrollable H₂S is essentially associated with the occurrence and development of multiple diseases, including cancers. Photodynamic therapy (PDT), as an invasive tumor treatment technology, has also attracted great attentions. Due to the key role of elevated H₂S in cancers, integrating H₂S depletion/recognition and PDT should be an effective strategy to enhance anticancer performance. In this work, we report a H₂S depletion aided PDT platform (3RAX-NBD) by the chemical ligation of 3RAX and NBD. 3RAX-NBD can react rapidly with H₂S and generate a novel 3RAX derivative compound 3 with increased fluorescence in vitro and in vivo. More notably, 3RAX-NBD can effectively kill multiple cancer cells through in situ irradiation, and 3RAX-NBD also has prominent anticancer effects on 4 T1 tumor-bearing BALB/c female mice with no notably toxic side effects. We believe that our H₂S depletion aided PDT platform may provide a powerful tool for studying the key roles of H₂S in diseases, and also give another promising candidate for cancer treatment.

Implications of hydrogen sulfide in colorectal cancer: Mechanistic insights and diagnostic and therapeutic strategies

Hydrogen sulfide (H₂S) is an important signaling molecule in colorectal cancer (CRC). It is produced in the colon by the catalytic synthesis of the colonocytes' enzymatic systems and the release of intestinal microbes, and is oxidatively metabolized in the colonocytes' mitochondria. Both endogenous H₂S in colonic epithelial cells and exogenous H₂S in intestinal lumen contribute to the onset and progression of CRC. The up-regulation of endogenous synthetases is thought to be the cause of the elevated H₂S levels in CRC cells. Different diagnostic probes and combination therapies, as well as tumor treatment approaches through H₂S modulation, have been developed in recent years and have become active area of investigation for the diagnosis and treatment of CRC. In this review, we focus on the specific mechanisms of H₂S production and oxidative metabolism as well as the function of H₂S in the occurrence, progression, diagnosis, and treatment of CRC. We also discuss the present challenges and provide insights into the future research of this burgeoning field.

Efficacy of Covexir® (Ferula foetida oleo-gum) treatment in symptomatic improvement of patients with mild to moderate COVID-19: A randomized, double-blind, placebo-controlled trial

The SARS-CoV-2 COVID-19 pandemic has emerged as an unprecedented emergency state in healthcare system and global challenge. In recent decade, the function of exogenous H₂ S in the treatment of respiratory diseases has been investigated using H₂ S-donor agents. Ferula foetida is a medicinal plant that is traditionally used in respiratory diseases including asthma and viral respiratory diseases. The oleo-gum of this plant is a rich source of several organic sulfides including thiophenes, disulfides and polysulfide derivatives, which can act as H₂ S-donor agents. The purpose of this study was to investigate the efficacy of Covexir® (F. foetida oleo-gum) treatment as a rich source of H₂ S-donor compounds in clinical presentations of patients with COVID-19. The efficacy of Covexir® was evaluated in a randomized, double-blind, placebo-controlled trial in outpatients with COVID-19. Covexir® could significantly inhibit cough when compared to the placebo group (p < .01 and p < 001, respectively). Moreover, there was a significant difference (p < 001) between the two groups in dyspnea symptom at follow-up interval of 7 day after receiving Covexir®. Furthermore, on days 3 and 7, statistically significant differences were observed in myalgia, anorexia, anosmia, and sense of taste severity between two groups. Our findings revealed that Covexir® was very safe in the treatment of COVID-19 patients with mild to moderate symptoms and it can be recommended to improve clinical presentations of patients with COVID-19 such as cough, shortness of breath, myalgia, anorexia, anosmia, and sense of taste.

Dibenzyl trisulfide induces caspase-independent death and lysosomal membrane permeabilization of triple-negative breast cancer cells

The Petiveria alliacea L. (P. alliacea) plant is traditionally used in folklore medicine throughout tropical regions of the world to treat arthritis, asthma, and cancer. Dibenzyl trisulfide (DTS) is one of the active ingredients within the P. alliacea plant. Triple-negative breast cancer (TNBC) is associated with a poor prognosis, particularly among women of West African ancestry, due in part to limited effective therapy. Though potent anticancer actions of DTS have been reported in a TNBC cell line, the mechanism of DTS-mediated cytotoxicity and cell death remains ill-defined. In the current study, we show that DTS exhibits cytotoxicity in a panel of triple-negative breast cancer (TNBC) cells derived from patients of European and West African ancestry. We found that DTS inhibits proliferation and migration of CRL-2335 cells derived from a patient of West African ancestry. DTS induces the expression of pro-apoptotic genes BAK1, GADD45a, and LTA in CRL2335 cells though it primarily promotes caspase-independent CRL-2335 cell death. DTS also promotes destabilization of the lysosomal membrane resulting in cathepsin B release in CRL-2335 cells. Finally, Kaplan-Meier survival curves reveal that higher expression of BAK1 and LTA in tumors from patients with TNBC is associated with longer relapse-free survival. Collectively, our data suggest that DTS confers promising antitumor efficacy in TNBC, in part, via lysosomal-mediated, caspase-independent cell death to warrant furthering its development as an anticancer agent.

Inhibition of the 3-mercaptopyruvate sulfurtransferase-hydrogen sulfide system promotes cellular lipid accumulation

H₂S is generated in the adipose tissue by cystathionine γ-lyase, cystathionine β-synthase, and 3-mercaptopyruvate sulfurtransferase (3-MST). H₂S plays multiple roles in the regulation of various metabolic processes, including insulin resistance. H₂S biosynthesis also occurs in adipocytes. Aging is known to be associated with a decline in H₂S. Therefore, the question arises whether endogenous H₂S deficiency may affect the process of adipocyte maturation and lipid accumulation. Among the three H₂S-generating enzymes, the role of 3-MST is the least understood in adipocytes. Here we tested the effect of the 3-MST inhibitor 2-[(4-hydroxy-6-methylpyrimidin-2-yl)sulfanyl]-1-(naphthalen-1-yl)ethan-1-one (HMPSNE) and the H₂S donor (GYY4137) on the differentiation and adipogenesis of the adipocyte-like cells 3T3-L1 in vitro. 3T3-L1 cells were differentiated into mature adipocytes in the presence of GYY4137 or HMPSNE. HMPSNE significantly enhanced lipid accumulation into the maturing adipocytes. On the other hand, suppressed lipid accumulation was observed in cells treated with the H₂S donor. 3-MST inhibition increased, while H₂S donation suppressed the expression of various H₂S-producing enzymes during adipocyte differentiation. 3-MST knockdown also facilitated adipocytic differentiation and lipid uptake. The underlying mechanisms may involve impairment of oxidative phosphorylation and fatty acid oxidation as well as the activation of various differentiation-associated transcription factors. Thus, the 3-MST/H₂S system plays a tonic role in suppressing lipid accumulation and limiting the differentiation of adipocytes. Stimulation of 3-MST activity or supplementation of H₂S—which has been recently linked to various experimental therapeutic approaches during aging—may be a potential experimental approach to counteract adipogenesis.

Efficient inhibition of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) by sulfuration with solubilized elemental sulfur

Hydrogen sulfide (H₂S), carbon monoxide (CO), and nitric oxide (NO) have garnered increasing scientific interest in recent decades due to their classifications as members of the gasotransmitter family of signaling molecules. Due to the versatility of sulfur redox chemistry in biological systems, H₂S specifically is being studied for its ability to modulate cellular redox environments, particularly through the downstream production of oxidized sulfur species. A major mechanism of this regulation is through a posttranslational modification known as persulfidation, where oxidized sulfur atoms are appended to free cysteine in proteins. Currently, it is difficult to discern the activity of H₂S itself versus these oxidized sulfur species, particularly sulfane sulfur (S⁰). We have previously developed a method of solvating S₈, a source of pure S⁰, to more accurately study persulfidation and sulfuration in general. Here, we apply this pure S⁰ to glyceraldehyde-3-phosphate dehydrogenase (GAPDH), which has previously been shown to be inhibited by S⁰-containing polysulfides via persulfidation. Using solvated S⁰, we demonstrate that native, reduced GAPDH can be completely inhibited by sulfuration with S⁰. Further, oxidized GAPDH activity cannot be rescued using S⁰, demonstrating that it is the oxidation of reduced GAPDH by S⁰ that curtails its activity. We also compare inhibition of GAPDH by pure S⁰ to different polysulfides and demonstrate the modulating effects that pendant alkyl groups have on GAPDH inhibition. These results highlight the promise of this novel, simplified system for the study of S⁰.

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

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

Protein S-sulfhydration: Unraveling the prospective of hydrogen sulfide in the brain, vasculature and neurological manifestations

Hydrogen sulfide (H₂S) and hydrogen polysulfides (H₂S_n) are essential regulatory signaling molecules generated by the entire body, including the central nervous system. Researchers have focused on the classical H₂S signaling from the past several decades, whereas the last decade has shown the emergence of H₂S-induced protein S-sulfhydration signaling as a potential therapeutic approach. Cysteine S-persulfidation is a critical paradigm of post-translational modification in the process of H₂S signaling. Additionally, studies have shown the cross-relationship between S-sulfhydration and other cysteine-induced post-translational modifications, namely nitrosylation and carbonylation. In the central nervous system, S-sulfhydration is involved in the cytoprotection through various signaling pathways, viz. inflammatory response, oxidative stress, endoplasmic reticulum stress, atherosclerosis, thrombosis, and angiogenesis. Further, studies have demonstrated H₂S-induced S-sulfhydration in regulating different biological processes, such as mitochondrial integrity, calcium homeostasis, blood-brain permeability, cerebral blood flow, and long-term potentiation. Thus, protein S-sulfhydration becomes a crucial regulatory molecule in cerebrovascular and neurodegenerative diseases. Herein, we first described the generation of intracellular H₂S followed by the application of H₂S in the regulation of cerebral blood flow and blood-brain permeability. Further, we described the involvement of S-sulfhydration in different biological and cellular functions, such as inflammatory response, mitochondrial integrity, calcium imbalance, and oxidative stress. Moreover, we highlighted the importance of S-sulfhydration in cerebrovascular and neurodegenerative diseases.

Hydrogen Sulfide and the Kidney: Physiological Roles, Contribution to Pathophysiology, and Therapeutic Potential

Significance: Hydrogen sulfide (H₂S), the third member of the gasotransmitter family, has a broad spectrum of biological activities, including antioxidant and cytoprotective actions, as well as vasodilatory, anti-inflammatory and antifibrotic effects. New, significant aspects of H₂S biology in the kidney continue to emerge, underscoring the importance of this signaling molecule in kidney homeostasis, function, and disease. Recent Advances: H₂S signals via three main mechanisms, by maintaining redox balance through its antioxidant actions, by post-translational modifications of cellular proteins (S-sulfhydration), and by binding to protein metal centers. Important renal functions such as glomerular filtration, renin release, or sodium reabsorption have been shown to be regulated by H₂S, using either exogenous donors or by the endogenous-producing systems. Critical Issues: Lower H₂S levels are observed in many renal pathologies, including renal ischemia-reperfusion injury and obstructive, diabetic, or hypertensive nephropathy. Unraveling the molecular targets through which H₂S exerts its beneficial effects would be of great importance not only for understanding basic renal physiology, but also for identifying new pharmacological interventions for renal disease. Future Directions: Additional studies are needed to better understand the role of H₂S in the kidney. Mapping the expression pattern of H₂S-producing and -degrading enzymes in renal cells and generation of cell-specific knockout mice based on this information will be invaluable in the effort to unravel additional roles for H₂S in kidney (patho)physiology. With this knowledge, novel targeted more effective therapeutic strategies for renal disease can be designed. Antioxid. Redox Signal. 36, 220-243.

H2S Donors and Their Use in Medicinal Chemistry

Hydrogen sulfide (H2S) is a ubiquitous gaseous signaling molecule that has an important role in many physiological and pathological processes in mammalian tissues, with the same importance as two others endogenous gasotransmitters such as NO (nitric oxide) and CO (carbon monoxide). Endogenous H2S is involved in a broad gamut of processes in mammalian tissues including inflammation, vascular tone, hypertension, gastric mucosal integrity, neuromodulation, and defense mechanisms against viral infections as well as SARS-CoV-2 infection. These results suggest that the modulation of H2S levels has a potential therapeutic value. Consequently, synthetic H2S-releasing agents represent not only important research tools, but also potent therapeutic agents. This review has been designed in order to summarize the currently available H2S donors; furthermore, herein we discuss their preparation, the H2S-releasing mechanisms, and their -biological applications.

Ambiguous Effects of Prolonged Dietary Supplementation with a Striatal-Enriched Protein Tyrosine Phosphatase Inhibitor, TC-2153, on a Rat Model of Sporadic Alzheimer’s Disease

Abstract

Alzheimer’s disease (AD) is the most common type of dementia and is currently incurable. After unsuccessful attempts to create drugs targeting the amyloid-β pathway, a search for alternative approaches and treatments targeting nonamyloid AD pathologies is currently underway. One of them is inhibition of striatal-enriched protein tyrosine phosphatase (STEP) activity, which is increased in the prefrontal cortex of AD patients. Here we examined effects of prolonged treatment of OXYS rats which mimic key signs of sporadic AD with a STEP inhibitor, TC-2153, on the progression of signs of AD. TC-2153 had an ambiguous effect on the behavior of the animals: it significantly reduced the already low locomotor and exploratory activities and enhanced anxiety-related behavior in OXYS rats but improved their long-term memory in the Morris water maze. Moreover, TC-2153 had no effect on the accumulation of the amyloid-β protein and on the STEP61 protein level; the latter in the cortex and hippocampus did not differ between OXYS rats and control Wistar rats. These results suggest that the effects of prolonged treatment with TC-2153 may be mediated by mechanisms not related to STEP. In particular, TC-2153 can act as a potential hydrogen sulfide donor and thus substantially affect redox homeostasis.

[Dibenzyl trisulfide inhibits proliferation and induces apoptosis of HN30 cells via Akt/ p53 signaling pathway]

OBJECTIVE

To explore the effect of dibenzyl trisulfide (DTS) on cell proliferation and apoptosis in human head and neck squamous cell carcinoma (HNSCC) HN30 cells.

OBJECTIVE

The effects of DTS on proliferation of HNSCC cell lines HN30, HN12, and SCC25 were examined by assessing colony formation ability of the treated cells. The effect of different concentrations of DTS on viability of HN30 cells was assessed using MTT assay. HN30 cells were treated with 3, 10, or 30 μmol/L DTS for 24 h, and the cell apoptosis and mitochondrial membrane potential (MMP) were detected using flow cytometry with annexin Ⅴ-FITC/PI double staining and JC-1 fluorescent probe staining. Western blotting was performed to determine the protein expressions of caspase-3, cleaved caspase-3 and Bcl-2 in the treated cells. The phosphorylation levels of Akt and p53 in HN30 cells were detected using Western blotting after treatment with 10 μmol/L DTS for 0.5, 1, 2, 4, 8, or 16 h.

OBJECTIVE

DTS at 1 μmol/L significantly inhibited the proliferation of HN30, HN12 and SCC25 cells as shown by colony formation assay. MTT assay showed that DTS dose-dependently decreased HN30 cell viability as compared with the solvent control group, and 100 μmol/L DTS produced the strongest inhibitory effect (P < 0.0001). Treatment with DTS below 30 μmol/L concentrationdependently promoted apoptosis (P < 0.01) and lowered the MMP (P < 0.01) of HN30 cells, and after treatment for 24 h, the cells showed significantly increased cleaved caspase-3 (P < 0.01) and decreased Bcl-2 expression (P < 0.01). Treatment with 10 μmol/L DTS for 16 h significantly inhibited Akt phosphorylation (P < 0.001) and enhanced p53 phosphorylation (P < 0.01) in HN30 cells.

OBJECTIVE

DTS inhibits proliferation and induces apoptosis of HN30 cells possibly through mechanisms involving the inhibition of Akt and the activation of p53.

Hydrogen Sulfide (H2S) and Polysulfide (H2Sn) Signaling: The First 25 Years

Since the first description of hydrogen sulfide (H₂S) as a toxic gas in 1713 by Bernardino Ramazzini, most studies on H₂S have concentrated on its toxicity. In 1989, Warenycia et al. demonstrated the existence of endogenous H₂S in the brain, suggesting that H₂S may have physiological roles. In 1996, we demonstrated that hydrogen sulfide (H₂S) is a potential signaling molecule, which can be produced by cystathionine β-synthase (CBS) to modify neurotransmission in the brain. Subsequently, we showed that H₂S relaxes vascular smooth muscle in synergy with nitric oxide (NO) and that cystathionine γ-lyase (CSE) is another producing enzyme. This study also opened up a new research area of a crosstalk between H₂S and NO. The cytoprotective effect, anti-inflammatory activity, energy formation, and oxygen sensing by H₂S have been subsequently demonstrated. Two additional pathways for the production of H₂S with 3-mercaptopyruvate sulfurtransferase (3MST) from l- and d-cysteine have been identified. We also discovered that hydrogen polysulfides (H₂S_n, n ≥ 2) are potential signaling molecules produced by 3MST. H₂S_n regulate the activity of ion channels and enzymes, as well as even the growth of tumors. S-Sulfuration (S-sulfhydration) proposed by Snyder is the main mechanism for H₂S/H₂S_n underlying regulation of the activity of target proteins. This mini review focuses on the key findings on H₂S/H₂S_n signaling during the first 25 years.

The Role of Hydrogen Sulfide in Respiratory Diseases

Respiratory diseases are leading causes of death and disability around the globe, with a diverse range of health problems. Treatment of respiratory diseases and infections has been verified to be thought-provoking because of the increasing incidence and mortality rate. Hydrogen sulfide (H₂S) is one of the recognized gaseous transmitters involved in an extensive range of cellular functions, and physiological and pathological processes in a variety of diseases, including respiratory diseases. Recently, the therapeutic potential of H₂S for respiratory diseases has been widely investigated. H₂S plays a vital therapeutic role in obstructive respiratory disease, pulmonary fibrosis, emphysema, pancreatic inflammatory/respiratory lung injury, pulmonary inflammation, bronchial asthma and bronchiectasis. Although the therapeutic role of H₂S has been extensively studied in various respiratory diseases, a concrete literature review will have an extraordinary impact on future therapeutics. This review provides a comprehensive overview of the effective role of H₂S in respiratory diseases. Besides, we also summarized H₂S production in the lung and its metabolism processes in respiratory diseases.

Hydrogen Sulfide as a Potential Therapy for Heart Failure-Past, Present, and Future

Hydrogen sulfide (H₂S) is an endogenous, gaseous signaling molecule that plays a critical role in cardiac and vascular biology. H₂S regulates vascular tone and oxidant defenses and exerts cytoprotective effects in the heart and circulation. Recent studies indicate that H₂S modulates various components of metabolic syndrome, including obesity and glucose metabolism. This review will discuss studies exhibiting H₂S -derived cardioprotective signaling in heart failure with reduced ejection fraction (HFrEF). We will also discuss the role of H₂S in metabolic syndrome and heart failure with preserved ejection fraction (HFpEF).

Recent efforts in drug discovery on vascular inflammation and consequent atherosclerosis

Introduction: Preservation of vascular endothelium integrity and maintenance of its full functionality are fundamental aspects in order to avoid both cardiovascular and non-cardiovascular diseases.Areas covered: Although a massive endothelial disruption is a rare condition, caused by acute and uncontrolled inflammatory responses (e.g. the cytokine storm induced by SARS-CoV-2 infection), more frequently the vascular tree is the first target of slowly progressive inflammatory processes which affect the integrity of endothelium and its 'barrier' function, supporting the onset of atherosclerotic plaque and spreading inflammation. This endothelial dysfunction leads to decrease NO biosynthesis, impaired regulation of vascular tone, and increased platelet aggregation. Such chronic subclinic inflammation leads to macrophage infiltration in atherosclerotic lesions. Therefore, many efforts should be addressed to find useful approaches to preserve vascular endothelium from inflammation. In this review, the authors have evaluated the most recent strategies to counteract this pathological condition.Expert opinion: The therapeutic and nutraceutical approaches represent useful tools to treat or prevent different phases of vascular inflammation. In particular, the pharmacological approach should be used in advanced phases characterized by clinical signs of vascular disease, whilst the nutraceutical approach may represent a promising preventive strategy to preserve the integrity of the endothelial tissue.

Anti-inflammatory and antiviral roles of hydrogen sulfide: Rationale for considering H2 S donors in COVID-19 therapy

The COVID-19 pandemic caused by SARS-Cov-2 demands rapid, safe and effective therapeutic options. In the last decades, the endogenous gasotransmitter hydrogen sulfide (H2 S) has emerged as modulator of several biological functions and its deficiency has been associated with different disorders. Therefore, many H2 S-releasing agents have been developed as potential therapeutic tools for diseases related with impaired H2 S production and/or activity. Some of these compounds are in advanced clinical trials. Presently, the pivotal role of H2 S in modulating the inflammatory response and pro-inflammatory cytokine cascade is well recognized, and the usefulness of some H2 S-donors for the treatment of acute lung inflammation has been reported. Recent data is elucidating several mechanisms of action, which may account for antiviral effects of H2 S. Noteworthy, some preliminary clinical results suggest an inverse relationship between endogenous H2 S levels and severity of COVID-19. Therefore, repurposing of H2 S-releasing drugs may be a potential therapeutic opportunity for treatment of COVID-19. LINKED ARTICLES: This article is part of a themed issue on The Pharmacology of COVID-19. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.21/issuetoc.

Role of hydrogen sulfide in cardiovascular ageing

Cardiovascular diseases are the main cause of morbidity and mortality in the Western society and ageing is a relevant non-modifiable risk factor. Morphological and functional alterations at endothelial level represent first events of ageing, inevitably followed by vascular dysfunction and consequent atherosclerosis that deeply influences cardiovascular health. Indeed, myocardial hypertrophy and fibrosis typically occur and contribute to compromise overall cardiac output. As regards the intracellular molecular mechanisms involved in the cardiovascular ageing, an intricate network is emerging, revealing a role for many mediators, including SIRT1/AMPK/PCG1α pathway, anti-oxidants factors (i.e. Nrf-2 and FOXOs) and pro-inflammatory cytokines. Thus, the search for pharmacological and non-pharmacological strategies that can promote a "healthy ageing", in order to slow down age-related machinery, are currently an exciting challenge for the biomedical research. Interestingly, hydrogen sulfide (H₂S) has been recently recognized as a new player capable to influence intracellular machinery involved in ageing and then it is view as a potential target for preventing cardiovascular diseases. Therefore, this review is focused on the role of H₂S in cardiovascular ageing, and on the evidence of the relationship between progressive decline in endogenous H₂S levels and the onset of various cardiovascular age-related diseases.

Hydrogen sulfide: An endogenous regulator of the immune system

Hydrogen sulfide (H₂S) is now recognized as an endogenous signaling gasotransmitter in mammals. It is produced by mammalian cells and tissues by various enzymes - predominantly cystathionine β-synthase (CBS), cystathionine γ-lyase (CSE) and 3-mercaptopyruvate sulfurtransferase (3-MST) - but part of the H₂S is produced by the intestinal microbiota (colonic H₂S-producing bacteria). Here we summarize the available information on the production and functional role of H₂S in the various cell types typically associated with innate immunity (neutrophils, macrophages, dendritic cells, natural killer cells, mast cells, basophils, eosinophils) and adaptive immunity (T and B lymphocytes) under normal conditions and as it relates to the development of various inflammatory and immune diseases. Special attention is paid to the physiological and the pathophysiological aspects of the oral cavity and the colon, where the immune cells and the parenchymal cells are exposed to a special "H₂S environment" due to bacterial H₂S production. H₂S has many cellular and molecular targets. Immune cells are "surrounded" by a "cloud" of H₂S, as a result of endogenous H₂S production and exogenous production from the surrounding parenchymal cells, which, in turn, importantly regulates their viability and function. Downregulation of endogenous H₂S producing enzymes in various diseases, or genetic defects in H₂S biosynthetic enzyme systems either lead to the development of spontaneous autoimmune disease or accelerate the onset and worsen the severity of various immune-mediated diseases (e.g. autoimmune rheumatoid arthritis or asthma). Low, regulated amounts of H₂S, when therapeutically delivered by small molecule donors, improve the function of various immune cells, and protect them against dysfunction induced by various noxious stimuli (e.g. reactive oxygen species or oxidized LDL). These effects of H₂S contribute to the maintenance of immune functions, can stimulate antimicrobial defenses and can exert anti-inflammatory therapeutic effects in various diseases.

Alterations of STEP46 and STEP61 Expression in the Rat Retina with Age and AMD-Like Retinopathy Development

Tyrosine phosphatase STEP (striatal-enriched tyrosine protein phosphatase) is a brain-specific protein phosphatase and is involved in the pathogenesis of many neurodegenerative diseases. Here, we examined the impact of STEP on the development of age-related macular degeneration (AMD)-like pathology in senescence-accelerated OXYS rats. Using OXYS and Wistar rats (control), we for the first time demonstrated age-dependent changes in Ptpn5 mRNA expression, STEP46 and STEP61 protein levels, and their phosphatase activity in the retina. The increases in STEP protein levels and the decrease of total and STEP phosphatase activities in the retina (as compared with Wistar rats) preceded the manifestation of clinical signs of AMD in OXYS rats (age 20 days). There were no differences in these retinal parameters between 13-month-old Wistar rats and OXYS rats with pronounced signs of AMD. Inhibition of STEP with TC-2153 during progressive AMD-like retinopathy (from 9 to 13 months of age) reduced the thickness of the retinal inner nuclear layer, as evidenced by a decreased amount of parvalbumin-positive amacrine neurons. Prolonged treatment with TC-2153 had no effect on Ptpn5 mRNA expression, STEP46 and STEP61 protein levels, and their phosphatase activity in the OXYS retina. Thus, TC-2153 may negatively affect the retina through mechanisms unrelated to STEP.