Interaction between hydrogen sulfide-induced sulfhydration and tyrosine nitration in the KATP channel complex

The Role of Hydrogen Sulfide in the Regulation of the Pulmonary Vasculature in Health and Disease

The gasotransmitter hydrogen sulfide (H2S; also termed sulfide) generally acts as a vasodilator in the systemic vasculature but causes a paradoxical constriction of pulmonary arteries (PAs). In light of evidence that a fall in the partial pressure in oxygen (pO2) increases cellular sulfide levels, it was proposed that a rise in sulfide in pulmonary artery smooth muscle cells (PASMCs) is responsible for hypoxic pulmonary vasoconstriction, the contraction of PAs which develops rapidly in lung regions undergoing alveolar hypoxia. In contrast, pulmonary hypertension (PH), a sustained elevation of pulmonary artery pressure (PAP) which can develop in the presence of a diverse array of pathological stimuli, including chronic hypoxia, is associated with a decrease in the expression of sulfide -producing enzymes in PASMCs and a corresponding fall in sulfide production by the lung. Evidence that PAP in animal models of PH can be lowered by administration of exogenous sulfide has led to an interest in using sulfide-donating agents for treating this condition in humans. Notably, intracellular H2S exists in equilibrium with other sulfur-containing species such as polysulfides and persulfides, and it is these reactive sulfur species which are thought to mediate most of its effects on cells through persulfidation of cysteine thiols on proteins, leading to changes in function in a manner similar to thiol oxidation by reactive oxygen species. This review sets out what is currently known about the mechanisms by which H2S and related sulfur species exert their actions on pulmonary vascular tone, both acutely and chronically, and discusses the potential of sulfide-releasing drugs as treatments for the different types of PH which arise in humans.

Role of hydrogen sulfide in health and disease

In the past, hydrogen sulfide (H2S) was recognized as a toxic and dangerous gas; in recent years, with increased research, we have discovered that H2S can act as an endogenous regulatory transmitter. In mammals, H2S-catalyzing enzymes, such as cystathionine-β-synthase, cystathionine-γ-lyase, and 3-mercaptopyruvate sulfurtransferase, are differentially expressed in a variety of tissues and affect a variety of biological functions, such as transcriptional and posttranslational modification of genes, activation of signaling pathways in the cell, and metabolic processes in tissues, by producing H2S. Various preclinical studies have shown that H2S affects physiological and pathological processes in the body. However, a detailed systematic summary of these roles in health and disease is lacking. Therefore, this review provides a thorough overview of the physiological roles of H2S in different systems and the diseases associated with disorders of H2S metabolism, such as ischemia-reperfusion injury, hypertension, neurodegenerative diseases, inflammatory bowel disease, and cancer. Meanwhile, this paper also introduces H2S donors and novel release modes, as well as the latest preclinical experimental results, aiming to provide researchers with new ideas to discover new diagnostic targets and therapeutic options.

Sulfide and polysulfide as pronociceptive mediators: Focus on Cav3.2 function enhancement and TRPA1 activation

Reactive sulfur species including sulfides, polysulfides and cysteine hydropersulfide play extensive roles in health and disease, which involve modification of protein functions through the interaction with metals bound to the proteins, cleavage of cysteine disulfide (S-S) bonds and S-persulfidation of cysteine residues. Sulfides over a wide micromolar concentration range enhance the activity of Cav3.2 T-type Ca2+ channels by eliminating Zn2+ bound to the channels, thereby promoting somatic and visceral pain. Cav3.2 is under inhibition by Zn2+ in physiological conditions, so that sulfides function to reboot Cav3.2 from Zn2+ inhibition and increase the excitability of nociceptors. On the other hand, polysulfides generated from sulfides activate TRPA1 channels via cysteine S-persulfidation, thereby facilitating somatic, but not visceral, pain. Thus, Cav3.2 function enhancement by sulfides and TRPA1 activation by polysulfides, synergistically accelerate somatic pain signals. The increased activity of the sulfide/Cav3.2 system, in particular, appears to have a great impact on pathological pain, and may thus serve as a therapeutic target for treatment of neuropathic and inflammatory pain including visceral pain.

Sulfur metabolism as a new therapeutic target of heart failure

Sulfur-based redox signaling has long attracted attention as critical mechanisms underlying the development of cardiac diseases and resultant heart failure. Especially, post-translational modifications of cysteine (Cys) thiols in proteins mediate oxidative stress-dependent cardiac remodeling including myocardial hypertrophy, senescence, and interstitial fibrosis. However, we recently revealed the existence of Cys persulfides and Cys polysulfides in cells and tissues, which show higher redox activities than Cys and substantially contribute to redox signaling and energy metabolism. We have established simple evaluation methods that can detect polysulfides in proteins and inorganic polysulfides in cells and revealed that polysulfides abundantly expressed in normal hearts are dramatically catabolized by exposure to ischemic/hypoxic and environmental electrophilic stress, which causes vulnerability of the heart to mechanical load. Accumulation of hydrogen sulfide, a nucleophilic catabolite of persulfides/polysulfides, may lead to reductive stress in ischemic hearts, and perturbation of polysulfide catabolism can improve chronic heart failure after myocardial infarction in mice. This review focuses on the (patho)physiological role of sulfur metabolism in hearts, and proposes that sulfur catabolism during ischemic/hypoxic stress has great potential as a new therapeutic strategy for the treatment of ischemic heart failure.

Hydrogen sulfide and its role in female reproduction

Hydrogen sulfide (H2S) is a gaseous signaling molecule produced in the body by three enzymes: cystathionine-β-synthase (CBS), cystathionine-γ-lyase (CSE) and 3-mercaptopyruvate sulfurtransferase (3-MST). H2S is crucial in various physiological processes associated with female mammalian reproduction. These include estrus cycle, oocyte maturation, oocyte aging, ovulation, embryo transport and early embryo development, the development of the placenta and fetal membranes, pregnancy, and the initiation of labor. Despite the confirmed presence of H2S-producing enzymes in all female reproductive tissues, as described in this review, the exact mechanisms of H2S action in these tissues remain in most cases unclear. Therefore, this review aims to summarize the knowledge about the presence and effects of H2S in these tissues and outline possible signaling pathways that mediate these effects. Understanding these pathways may lead to the development of new therapeutic strategies in the field of women's health and perinatal medicine.

Redox Regulation of Mitochondrial Potassium Channels Activity

Redox reactions exert a profound influence on numerous cellular functions with mitochondria playing a central role in orchestrating these processes. This pivotal involvement arises from three primary factors: (1) the synthesis of reactive oxygen species (ROS) by mitochondria, (2) the presence of a substantial array of redox enzymes such as respiratory chain, and (3) the responsiveness of mitochondria to the cellular redox state. Within the inner mitochondrial membrane, a group of potassium channels, including ATP-regulated, large conductance calcium-activated, and voltage-regulated channels, is present. These channels play a crucial role in conditions such as cytoprotection, ischemia/reperfusion injury, and inflammation. Notably, the activity of mitochondrial potassium channels is intricately governed by redox reactions. Furthermore, the regulatory influence extends to other proteins, such as kinases, which undergo redox modifications. This review aims to offer a comprehensive exploration of the modulation of mitochondrial potassium channels through diverse redox reactions with a specific focus on the involvement of ROS.

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.

Cardioprotective Effects of Hydrogen Sulfide and Its Potential Therapeutic Implications in the Amelioration of Duchenne Muscular Dystrophy Cardiomyopathy

Hydrogen sulfide (H2S) belongs to the family of gasotransmitters and can modulate a myriad of biological signaling pathways. Among others, its cardioprotective effects, through antioxidant, anti-inflammatory, anti-fibrotic, and proangiogenic activities, are well-documented in experimental studies. Cardiorespiratory failure, predominantly cardiomyopathy, is a life-threatening complication that is the number one cause of death in patients with Duchenne muscular dystrophy (DMD). Although recent data suggest the role of H2S in ameliorating muscle wasting in murine and Caenorhabditis elegans models of DMD, possible cardioprotective effects have not yet been addressed. In this review, we summarize the current understanding of the role of H2S in animal models of cardiac dysfunctions and cardiac cells. We highlight that DMD may be amenable to H2S supplementation, and we suggest H2S as a possible factor regulating DMD-associated cardiomyopathy.

Sulfur signaling pathway in cardiovascular disease

Hydrogen sulfide (H2S) and sulfur dioxide (SO2), recognized as endogenous sulfur-containing gas signaling molecules, were the third and fourth molecules to be identified subsequent to nitric oxide and carbon monoxide (CO), and exerted diverse biological effects on the cardiovascular system. However, the exact mechanisms underlying the actions of H2S and SO2 have remained elusive until now. Recently, novel post-translational modifications known as S-sulfhydration and S-sulfenylation, induced by H2S and SO2 respectively, have been proposed. These modifications involve the chemical alteration of specific cysteine residues in target proteins through S-sulfhydration and S-sulfenylation, respectively. H2S induced S-sulfhydrylation can have a significant impact on various cellular processes such as cell survival, apoptosis, cell proliferation, metabolism, mitochondrial function, endoplasmic reticulum stress, vasodilation, anti-inflammatory response and oxidative stress in the cardiovascular system. Alternatively, S-sulfenylation caused by SO2 serves primarily to maintain vascular homeostasis. Additional research is warranted to explore the physiological function of proteins with specific cysteine sites, despite the considerable advancements in comprehending the role of H2S-induced S-sulfhydration and SO2-induced S-sulfenylation in the cardiovascular system. The primary objective of this review is to present a comprehensive examination of the function and potential mechanism of S-sulfhydration and S-sulfenylation in the cardiovascular system. Proteins that undergo S-sulfhydration and S-sulfenylation may serve as promising targets for therapeutic intervention and drug development in the cardiovascular system. This could potentially expedite the future development and utilization of drugs related to H2S and SO2.

Chemistry of Hydrogen Sulfide-Pathological and Physiological Functions in Mammalian Cells

Hydrogen sulfide (H2S) was recognized as a gaseous signaling molecule, similar to nitric oxide (-NO) and carbon monoxide (CO). The aim of this review is to provide an overview of the formation of hydrogen sulfide (H2S) in the human body. H2S is synthesized by enzymatic processes involving cysteine and several enzymes, including cystathionine-β-synthase (CBS), cystathionine-γ-lyase (CSE), cysteine aminotransferase (CAT), 3-mercaptopyruvate sulfurtransferase (3MST) and D-amino acid oxidase (DAO). The physiological and pathological effects of hydrogen sulfide (H2S) on various systems in the human body have led to extensive research efforts to develop appropriate methods to deliver H2S under conditions that mimic physiological settings and respond to various stimuli. These functions span a wide spectrum, ranging from effects on the endocrine system and cellular lifespan to protection of liver and kidney function. The exact physiological and hazardous thresholds of hydrogen sulfide (H2S) in the human body are currently not well understood and need to be researched in depth. This article provides an overview of the physiological significance of H2S in the human body. It highlights the various sources of H2S production in different situations and examines existing techniques for detecting this gas.

Mapping Pregnancy-dependent Sulfhydrome Unfolds Diverse Functions of Protein Sulfhydration in Human Uterine Artery

Uterine artery (UA) hydrogen sulfide (H2S) production is augmented in pregnancy and, on stimulation by systemic/local vasodilators, contributes to pregnancy-dependent uterine vasodilation; however, how H2S exploits this role is largely unknown. S-sulfhydration converts free thiols to persulfides at reactive cysteine(s) on targeted proteins to affect the entire proteome posttranslationally, representing the main route for H2S to elicit its function. Here, we used Tag-Switch to quantify changes in sulfhydrated (SSH-) proteins (ie, sulfhydrome) in H2S-treated nonpregnant and pregnant human UA. We further used the low-pH quantitative thiol reactivity profiling platform by which paired sulfhydromes were subjected to liquid chromatography tandem mass spectrometry-based peptide sequencing to generate site (cysteine)-specific pregnancy-dependent H2S-responsive human UA sulfhydrome. Total levels of sulfhydrated proteins were significantly greater in pregnant vs nonpregnant human UA and further stimulated by treatment with sodium hydrosulfide. We identified a total of 360 and 1671 SSH-peptides from 480 and 1186 SSH-proteins in untreated and sodium hydrosulfide-treated human UA, respectively. Bioinformatics analyses identified pregnancy-dependent H2S-responsive human UA SSH peptides/proteins, which were categorized to various molecular functions, pathways, and biological processes, especially vascular smooth muscle contraction/relaxation. Pregnancy-dependent changes in these proteins were rectified by immunoblotting of the Tag-Switch labeled SSH proteins. Low-pH quantitative thiol reactivity profiling failed to identify low abundance SSH proteins such as KATP channels in human UA; however, immunoblotting of Tag-Switch-labeled SSH proteins identified pregnancy-dependent upregulation of SSH-KATP channels without altering their total proteins. Thus, comprehensive analyses of human UA sulfhydromes influenced by endogenous and exogenous H2S inform novel roles of protein sulfhydration in uterine hemodynamics regulation.

Circulating Levels of Hydrogen Sulfide (H2S) in Patients with Age-Related Diseases: A Systematic Review and Meta-Analysis

Hydrogen sulfide (H₂S) is an endogenous gasotransmitter that promotes multiple biological effects in many organs and tissues. An imbalanced biosynthesis of H₂S has been observed in animal models of age-related pathological conditions. However, the results from human studies are inconsistent. We performed a systematic review with meta-analysis of studies searched in Medline, Embase, Scopus, and CENTRAL databases. We included observational studies on patients with age-related diseases showing levels of H₂S in blood, plasma, or serum. All the analyses were carried out with R software. 31 studies were included in the systematic review and 21 in the meta-analysis. The circulating levels of H₂S were significantly reduced in patients with progressive, chronic, and degenerative diseases compared with healthy people (standardized mean difference, SMD: -1.25; 95% confidence interval, CI: -1.98; -0.52). When we stratified results by type of disorder, we observed a significant reduction in circulating levels of H₂S in patients with vascular disease (e.g., hypertension) (SMD: -1.32; 95% CI: -2.43; -0.22) or kidney disease (SMD: -2.24; 95% CI: -4.40; -0.08) compared with the control group. These results could support the potential use of compounds targeting the "H₂S system" to slow down the progression of many diseases in the elderly.

Sulfur-Containing Amino Acids, Hydrogen Sulfide, and Sulfur Compounds on Kidney Health and Disease

Hydrogen sulfide (H₂S) plays a decisive role in kidney health and disease. H₂S can ben synthesized via enzymatic and non-enzymatic pathways, as well as gut microbial origins. Kidney disease can originate in early life induced by various maternal insults throughout the process, namely renal programming. Sulfur-containing amino acids and sulfate are essential in normal pregnancy and fetal development. Dysregulated H₂S signaling behind renal programming is linked to deficient nitric oxide, oxidative stress, the aberrant renin-angiotensin-aldosterone system, and gut microbiota dysbiosis. In animal models of renal programming, treatment with sulfur-containing amino acids, N-acetylcysteine, H₂S donors, and organosulfur compounds during gestation and lactation could improve offspring's renal outcomes. In this review, we summarize current knowledge regarding sulfide/sulfate implicated in pregnancy and kidney development, current evidence supporting the interactions between H₂S signaling and underlying mechanisms of renal programming, and recent advances in the beneficial actions of sulfide-related interventions on the prevention of kidney disease. Modifying H₂S signaling is the novel therapeutic and preventive approach to reduce the global burden of kidney disease; however, more work is required to translate this into clinical practice.

Comparative Study of Different H2S Donors as Vasodilators and Attenuators of Superoxide-Induced Endothelial Damage

In the last years, research proofs have confirmed that hydrogen sulfide (H₂S) plays an important role in various physio-pathological processes, such as oxidation, inflammation, neurophysiology, and cardiovascular protection; in particular, the protective effects of H₂S in cardiovascular diseases were demonstrated. The interest in H₂S-donating molecules as tools for biological and pharmacological studies has grown, together with the understanding of H₂S importance. Here we performed a comparative study of a series of H₂S donor molecules with different chemical scaffolds and H₂S release mechanisms. The compounds were tested in human serum for their stability and ability to generate H₂S. Their vasorelaxant properties were studied on rat aorta strips, and the capacity of the selected compounds to protect NO-dependent endothelium reactivity in an acute oxidative stress model was tested. H₂S donors showed different H₂S-releasing kinetic and produced amounts and vasodilating profiles; in particular, compound 6 was able to attenuate the dysfunction of relaxation induced by pyrogallol exposure, showing endothelial protective effects. These results may represent a useful basis for the rational development of promising H₂S-releasing agents also conjugated with other pharmacophores.

Sulfide regulation of cardiovascular function in health and disease

Hydrogen sulfide (H2S) has emerged as a gaseous signalling molecule with crucial implications for cardiovascular health. H2S is involved in many biological functions, including interactions with nitric oxide, activation of molecular signalling cascades, post-translational modifications and redox regulation. Various preclinical and clinical studies have shown that H2S and its synthesizing enzymes - cystathionine γ-lyase, cystathionine β-synthase and 3-mercaptosulfotransferase - can protect against cardiovascular pathologies, including arrhythmias, atherosclerosis, heart failure, myocardial infarction and ischaemia-reperfusion injury. The bioavailability of H2S and its metabolites, such as hydropersulfides and polysulfides, is substantially reduced in cardiovascular disease and has been associated with single-nucleotide polymorphisms in H2S synthesis enzymes. In this Review, we highlight the role of H2S, its synthesizing enzymes and metabolites, their roles in the cardiovascular system, and their involvement in cardiovascular disease and associated pathologies. We also discuss the latest clinical findings from the field and outline areas for future study.

Hydrogen sulfide in the experimental models of arterial hypertension

Hydrogen sulfide (H2S) is the third member of gasotransmitter family together with nitric oxide and carbon monoxide. H2S is involved in the regulation of blood pressure by controlling vascular tone, sympathetic nervous system activity and renal sodium excretion. Moderate age-dependent hypertension and endothelial dysfunction develop in mice with knockout of cystathionine γ-lyase (CSE), the enzyme involved in H2S production in the cardiovascular system. Decreased H2S concentration as well as the expression and activities of H2S-producing enzymes have been observed in most commonly used animal models of hypertension such as spontaneously hypertensive rats, Dahl salt-sensitive rats, chronic administration of NO synthase inhibitors, angiotensin II infusion and two-kidney-one-clip hypertension, the model of renovascular hypertension. Administration of H2S donors decreases blood pressure in these models but has no major effects on blood pressure in normotensive animals. H2S donors not only reduce blood pressure but also end-organ injury such as vascular and myocardial hypertrophy and remodeling, hypertension-associated kidney injury or erectile dysfunction. H2S level and signaling are modulated by some antihypertensive medications as well as natural products with antihypertensive activity such as garlic polysulfides or plant-derived isothiocyanates as well as non-pharmacological interventions. Modifying H2S signaling is the potential novel therapeutic approach for the management of hypertension, however, more experimental clinical studies about the role of H2S in hypertension are required.

Regulation of blood pressure by natural sulfur compounds: Focus on their mechanisms of action

Natural sulfur compounds are emerging as therapeutic options for the management of hypertension and prehypertension. They are mainly represented by polysulfides from Alliaceae (i.e., garlic) and isothiocyanates from Brassicaceae (or crucifers). The beneficial cardiovascular effects of these compounds, especially garlic polysulfides, are well known and widely reported both in preclinical and clinical studies. However, only a few authors have linked the ability of natural sulfur compounds to induce vasorelaxation and subsequent antihypertensive effects with their ability to release hydrogen sulfide (H2S) in biological tissue. H2S is an endogenous gasotransmitter involved in vascular tone regulation. Some cardiovascular diseases, such as hypertension, are associated with lower plasma H2S levels. Consequently, exogenous sources of H2S (H2S donors) have been designed and synthesized or identified among secondary plant metabolites as potential therapeutic options. In addition to antioxidant effects due to its chemical properties as a reducing agent, H2S induces vasorelaxation by interacting with a range of molecular targets. The mechanisms of action accounting for H2S-induced vasodilation include opening of vascular potassium channels (such as ATP-sensitive (KATP) and voltage-operated (Kv7) channels), inhibition of 5-phosphodiesterase (5-PDE), and activation of vascular endothelial growth factor receptor-2 (VEGFR-2). These effects may be attributed to H2S-induced S-persulfidation (or S-sulfhydration), which is a posttranslational modification of cysteine residues of many types of proteins resulting in structural and functional alterations (activation/inhibition). Thus, H2S donors, such as natural sulfur compounds, are promising antihypertensive agents with novel mechanisms of action.

Functional Regulation of KATP Channels and Mutant Insight Into Clinical Therapeutic Strategies in Cardiovascular Diseases

ATP-sensitive potassium channels (KATP channels) play pivotal roles in excitable cells and link cellular metabolism with membrane excitability. The action potential converts electricity into dynamics by ion channel-mediated ion exchange to generate systole, involved in every heartbeat. Activation of the KATP channel repolarizes the membrane potential and decreases early afterdepolarization (EAD)-mediated arrhythmias. KATP channels in cardiomyocytes have less function under physiological conditions but they open during severe and prolonged anoxia due to a reduced ATP/ADP ratio, lessening cellular excitability and thus preventing action potential generation and cell contraction. Small active molecules activate and enhance the opening of the KATP channel, which induces the repolarization of the membrane and decreases the occurrence of malignant arrhythmia. Accumulated evidence indicates that mutation of KATP channels deteriorates the regulatory roles in mutation-related diseases. However, patients with mutations in KATP channels still have no efficient treatment. Hence, in this study, we describe the role of KATP channels and subunits in angiocardiopathy, summarize the mutations of the KATP channels and the functional regulation of small active molecules in KATP channels, elucidate the potential mechanisms of mutant KATP channels and provide insight into clinical therapeutic strategies.

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.

Effect of visfatin on KATP channel upregulation in colonic smooth muscle cells in diabetic colon dysmotility

The mechanisms of diabetes-related gastrointestinal dysmotility remains unclear. This study aimed to investigate the effect and mechanisms of proinflammatory adipokine visfatin (VF) in the contractile dysfunction of diabetic rat colonic smooth muscle. Twenty Sprague-Dawley rats were randomly divided into control and type 2 diabetes mellitus groups. VF levels in the serum and colonic muscle tissues were tested, the time of the bead ejection and contractility of colonic smooth muscle strips were measured, and the expression of ATP-sensitive potassium (K_ATP) channels in the colonic muscle tissues was analyzed. In vitro, we tested VF's effects on intracellular reactive oxygen species (ROS) levels, NF-κB's nuclear transcription, K_ATP channel expression, intracellular Ca²⁺ concentrations, and myosin light chain (MLC) phosphorylation in colonic smooth muscle cells (CSMCs). The effects of NAC (ROS inhibitor) and BAY 11-7082 (NF-κB inhibitor) on K_ATP expression were also tested. Diabetic rats showed elevated VF levels in serum and colonic muscle tissues, a delayed distal colon ejection response time, weakened contractility of colonic smooth muscle strips, and increased K_ATP channel expression in colonic muscle tissues. VF significantly inhibited the contractility of colonic smooth muscle strips from normal rats. In cultured CSMCs, VF caused ROS overload, increased NF-κB nuclear transcription activity and increased expression of Kir6.1, eventually reducing intracellular Ca²⁺ levels and MLC phosphorylation. NAC and BAY 11-7082 inhibited the VF-induced Kir6.1 upregulation. In conclusion, VF may cause contractile dysfunction of CSMCs by upregulating the expression of the Kir6.1 subunit of K_ATP channels via the ROS/NF-κB pathway and interfering with Ca²⁺ signaling.

Mycoplasma pneumoniae Infections: Pathogenesis and Vaccine Development

Mycoplasma pneumoniae is a major causative agent of community-acquired pneumonia which can lead to both acute upper and lower respiratory tract inflammation, and extrapulmonary syndromes. Refractory pneumonia caused by M. pneumonia can be life-threatening, especially in infants and the elderly. Here, based on a comprehensive review of the scientific literature related to the respective area, we summarize the virulence factors of M. pneumoniae and the major pathogenic mechanisms mediated by the pathogen: adhesion to host cells, direct cytotoxicity against host cells, inflammatory response-induced immune injury, and immune evasion. The increasing rate of macrolide-resistant strains and the harmful side effects of other sensitive antibiotics (e.g., respiratory quinolones and tetracyclines) in young children make it difficult to treat, and increase the health risk or re-infections. Hence, there is an urgent need for development of an effective vaccine to prevent M. pneumoniae infections in children. Various types of M. pneumoniae vaccines have been reported, including whole-cell vaccines (inactivated and live-attenuated vaccines), subunit vaccines (involving M. pneumoniae protein P1, protein P30, protein P116 and CARDS toxin) and DNA vaccines. This narrative review summarizes the key pathogenic mechanisms underlying M. pneumoniae infection and highlights the relevant vaccines that have been developed and their reported effectiveness.

Hydrogen sulfide induces Ca2+ release from the endoplasmic reticulum and suppresses ATP-induced Ca2+ signaling in rat spinal cord astrocytes

Hydrogen sulfide (H2S) has a variety of physiological functions. H2S reportedly increases intracellular Ca2+ concentration ([Ca2+]i) in astrocytes. However, the precise mechanism and functional role of this increase are not known. Here, we examined the effects of H2S on [Ca2+]i in astrocytes from the rat spinal cord and whether H2S affects ATP-induced Ca2+ signaling, which is known to be involved in synaptic function. Na2S (150 μM), an H2S donor, produced a nontoxic increase in [Ca2+]i. The [Ca2+]i increase by Na2S was inhibited by Ca2+ depletion in the endoplasmic reticulum (ER) but not by removal of extracellular Ca2+, indicating that H2S releases Ca2+ from the ER. On the other hand, Na2S inhibited ATP-induced [Ca2+]i increase when Na2S clearly increased [Ca2+]i in the astrocytes, which was not suppressed by a reducing agent. In addition, Na2S had no effect on intracellular cyclic AMP (cAMP) level. These results indicate that oxidative post-translational modification of proteins and cAMP are not involved in the inhibitory effect of H2S on ATP-induced Ca2+ signaling. We conclude that H2S indirectly inhibits ATP-induced Ca2+ signaling by decreasing Ca2+ content in the ER in astrocytes. In this way, H2S may influence intercellular communication between astrocytes and neurons, thereby contributing to neuronal signaling in the nervous system.

S-Persulfidation: Chemistry, Chemical Biology, and Significance in Health and Disease

Significance: S-Persulfidation generates persulfide adducts (RSSH) on both small molecules and proteins. This process is believed to be critical in the regulation of biological functions of reactive sulfur species such as H₂S, as well as in signal transduction. S-Persulfidation also plays regulatory roles in human health and diseases. Recent Advances: Some mechanisms underlying the generation of low-molecular-weight persulfides and protein S-persulfidation in living organisms have been uncovered. Some methods for the specific delivery of persulfides and the detection of persulfides in biological systems have been developed. These advances help to pave the road to better understand the functions of S-persulfidation. Critical Issues: Persulfides are highly reactive and unstable. Currently, their identification relies on trapping them by S-alkylation, but this is not always reliable due to rapid sulfur exchange reactions. Therefore, the presence, identity, and fates of persulfides in biological environments are sometimes difficult to track. Future Directions: Further understanding the fundamental chemistry/biochemistry of persulfides and development of more reliable detection methods are needed. S-Persulfidation in specific protein targets is essential in organismal physiological health and human disease states. Besides cardiovascular and neuronal systems, the roles of persulfidation in other systems need to be further explored. Contradictory results of persulfidation in biology, especially in cancer, need to be clarified.

Gasotransmitters in pregnancy: from conception to uterine involution

Gasotransmitters are endogenous small gaseous messengers exemplified by nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S or sulfide). Gasotransmitters are implicated in myriad physiologic functions including many aspects of reproduction. Our objective was to comprehensively review basic mechanisms and functions of gasotransmitters during pregnancy from conception to uterine involution and highlight future research opportunities. We searched PubMed and Web of Science databases using combinations of keywords nitric oxide, carbon monoxide, sulfide, placenta, uterus, labor, and pregnancy. We included English language publications on human and animal studies from any date through August 2018 and retained basic and translational articles with relevant original findings. All gasotransmitters activate cGMP signaling. NO and sulfide also covalently modify target protein cysteines. Protein kinases and ion channels transduce gasotransmitter signals, and co-expressed gasotransmitters can be synergistic or antagonistic depending on cell type. Gasotransmitters influence tubal transit, placentation, cervical remodeling, and myometrial contractility. NO, CO, and sulfide dilate resistance vessels, suppress inflammation, and relax myometrium to promote uterine quiescence and normal placentation. Cervical remodeling and rupture of fetal membranes coincide with enhanced oxidation and altered gasotransmitter metabolism. Mechanisms mediating cellular and organismal changes in pregnancy due to gasotransmitters are largely unknown. Altered gasotransmitter signaling has been reported for preeclampsia, intrauterine growth restriction, premature rupture of membranes, and preterm labor. However, in most cases specific molecular changes are not yet characterized. Nonclassical signaling pathways and the crosstalk among gasotransmitters are emerging investigation topics.

Estrogen Receptors and Estrogen-Induced Uterine Vasodilation in Pregnancy

Normal pregnancy is associated with dramatic increases in uterine blood flow to facilitate the bidirectional maternal–fetal exchanges of respiratory gases and to provide sole nutrient support for fetal growth and survival. The mechanism(s) underlying pregnancy-associated uterine vasodilation remain incompletely understood, but this is associated with elevated estrogens, which stimulate specific estrogen receptor (ER)-dependent vasodilator production in the uterine artery (UA). The classical ERs (ERα and ERβ) and the plasma-bound G protein-coupled ER (GPR30/GPER) are expressed in UA endothelial cells and smooth muscle cells, mediating the vasodilatory effects of estrogens through genomic and/or nongenomic pathways that are likely epigenetically modified. The activation of these three ERs by estrogens enhances the endothelial production of nitric oxide (NO), which has been shown to play a key role in uterine vasodilation during pregnancy. However, the local blockade of NO biosynthesis only partially attenuates estrogen-induced and pregnancy-associated uterine vasodilation, suggesting that mechanisms other than NO exist to mediate uterine vasodilation. In this review, we summarize the literature on the role of NO in ER-mediated mechanisms controlling estrogen-induced and pregnancy-associated uterine vasodilation and our recent work on a “new” UA vasodilator hydrogen sulfide (H₂S) that has dramatically changed our view of how estrogens regulate uterine vasodilation in pregnancy.

Organic Isothiocyanates as Hydrogen Sulfide Donors

Significance: Hydrogen sulfide (H₂S), the "new entry" in the series of endogenous gasotransmitters, plays a fundamental role in regulating the biological functions of various organs and systems. Consequently, the lack of adequate levels of H₂S may represent the etiopathogenetic factor of multiple pathological alterations. In these diseases, the use of H₂S donors represents a precious and innovative opportunity. Recent Advances: Natural isothiocyanates (ITCs), sulfur compounds typical of some botanical species, have long been investigated because of their intriguing pharmacological profile. Recently, the ITC moiety has been proposed as a new H₂S-donor chemotype (with a l-cysteine-mediated reaction). Based on this recent discovery, we can clearly observe that almost all the effects of natural ITCs can be explained by the H₂S release. Consistently, the ITC function was also used as an original H₂S-releasing moiety for the design of synthetic H₂S donors and original "pharmacological hybrids." Very recently, the chemical mechanism of H₂S release, resulting from the reaction between l-cysteine and some ITCs, has been elucidated. Critical Issues: Available literature gives convincing demonstration that H₂S is the real player in ITC pharmacology. Further, countless studies have been carried out on natural ITCs, but this versatile moiety has been used only rarely for the design of synthetic H₂S donors with optimal drug-like properties. Future Directions: The development of more ITC-based synthetic H₂S donors with optimal drug-like properties and selectivity toward specific tissues/pathologies seem to represent a stimulating and indispensable prospect of future experimental activities.

Contribution of sulfate-reducing bacteria to homeostasis disruption during intestinal inflammation

Alteration in microbial populations and metabolism are key events associated with disruption of intestinal homeostasis and immune tolerance during intestinal inflammation. A substantial imbalance in bacterial populations in the intestine and their relationships with the host have been observed in patients with inflammatory bowel disease (IBD), believed to be part of an intricate mechanism of triggering and progression of intestinal inflammation. Because elevated numbers of sulfate-reducing bacteria (SRB) have been found in the intestines of patients with IBD, the study of their interaction with intestinal cells and their potential involvement in IBD has been the focus of investigation to better understand the intestinal pathology during IBD, as well as to find new ways to treat the disease. SRB not only directly interact with intestinal epithelial cells during intestinal inflammation but may also promote intestinal damage through generation of hydrogen sulfide at high levels. Herein we review the literature to discuss the various aspects of SRB interaction with host intestinal tissue, focusing on their interaction with intestinal epithelial and immune cells during intestinal inflammation.

Dietary and Endocrine Regulation of Endogenous Hydrogen Sulfide Production: Implications for Longevity

SIGNIFICANCE

Hydrogen sulfide (H₂S) at the right concentration is associated with numerous health benefits in experimental organisms, ranging from protection from ischemia/reperfusion injury to life span extension. Given the considerable translation potential, two major strategies have emerged: supplementation of exogenous H₂S and modulation of endogenous H₂S metabolism. Recent Advances: Recently, it was reported that hepatic H₂S production capacity is increased in two of the best-characterized mammalian models of life span extension, dietary restriction, and hypopituitary dwarfism, leading to new insights into dietary and hormonal regulation of endogenous H₂S production together with broader changes in sulfur amino acid (SAA) metabolism with implications for DNA methylation and redox status.

CRITICAL ISSUES

Here, we discuss the role of dietary SAAs and growth hormone (GH)/thyroid hormone (TH) signaling in regulation of endogenous H₂S production largely via repression of H₂S generating enzymes cystathionine γ-lyase (CGL) and cystathionine β-synthase (CBS) on the level of gene transcription, as well as reciprocal regulation of GH and TH signaling by H₂S itself. We also discuss plasticity of CGL and CBS gene expression in response to environmental stimuli and the potential of the microbiome to impact overall H₂S levels.

FUTURE DIRECTIONS

The relative contribution of increased H₂S to health span or lifespan benefits in models of extended longevity remains to be determined, as does the mechanism by which such benefits occur. Nonetheless, our ability to control H₂S levels using exogenous H₂S donors or by modifying the endogenous H₂S production/consumption equilibrium has the potential to improve health and increase "shelf-life" across evolutionary boundaries, including our own. Antioxid. Redox Signal. 28, 1483-1502.

Inhibition of RhoA/Rho kinase pathway and smooth muscle contraction by hydrogen sulfide

Hydrogen sulfide (H₂ S) plays an important role in smooth muscle relaxation. Here, we investigated the expression of enzymes in H₂ S synthesis and the mechanism regulating colonic smooth muscle function by H₂ S. Expression of cystathionine-γ-lyase (CSE), but not cystathionine-β-synthase (CBS), was identified in the colonic smooth muscle of rabbit, mouse, and human. Carbachol (CCh)-induced contraction in rabbit muscle strips and isolated muscle cells was inhibited by l-cysteine (substrate of CSE) and NaHS (an exogenous H₂ S donor) in a concentration-dependent fashion. H₂ S induced S-sulfhydration of RhoA that was associated with inhibition of RhoA activity. CCh-induced Rho kinase activity also was inhibited by l-cysteine and NaHS in a concentration-dependent fashion. Inhibition of CCh-induced contraction by l-cysteine was blocked by the CSE inhibitor, dl-propargylglycine (DL-PPG) in dispersed muscle cells. Inhibition of CCh-induced Rho kinase activity by l-cysteine was blocked by CSE siRNA in cultured cells and DL-PPG in dispersed muscle cells. Stimulation of Rho kinase activity and muscle contraction in response to CCh was also inhibited by l-cysteine or NaHS in colonic muscle cells from mouse and human. Collectively, our studies identified the expression of CSE in colonic smooth muscle and determined that sulfhydration of RhoA by H₂ S leads to inhibition of RhoA and Rho kinase activities and muscle contraction. The mechanism identified may provide novel therapeutic approaches to mitigate gastrointestinal motility disorders.

Protein S-sulfhydration by hydrogen sulfide in cardiovascular system

Hydrogen sulfide (H2 S), independently of any specific transporters, has a number of biological effects on the cardiovascular system. However, until now, the detailed mechanism of H2 S was not clear. Recently, a novel post-translational modification induced by H2 S, named S-sulfhydration, has been proposed. S-sulfhydration is the chemical modification of specific cysteine residues of target proteins by H2 S. There are several methods for detecting S-sulfhydration, such as the modified biotin switch assay, maleimide assay with fluorescent thiol modifying regents, tag-switch method and mass spectrometry. H2 S induces S-sulfhydration on enzymes or receptors (such as p66Shc, phospholamban, protein tyrosine phosphatase 1B, mitogen-activated extracellular signal-regulated kinase 1 and ATP synthase subunit α), transcription factors (such as specific protein-1, kelch-like ECH-associating protein 1, NF-κB and interferon regulatory factor-1), and ion channels (such as voltage-activated Ca2+ channels, transient receptor potential channels and ATP-sensitive K+ channels) in the cardiovascular system. Although significant progress has been achieved in delineating the role of protein S-sulfhydration by H2 S in the cardiovascular system, more proteins with detailed cysteine sites of S-sulfhydration as well as physiological function need to be investigated in further studies. This review mainly summarizes the role and possible mechanism of S-sulfhydration in the cardiovascular system. The S-sulfhydrated proteins may be potential novel targets for therapeutic intervention and drug design in the cardiovascular system, which may accelerate the development and application of H2 S-related drugs in the future.

LINKED ARTICLES

This article is part of a themed section on Spotlight on Small Molecules in Cardiovascular Diseases. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.8/issuetoc.

Reduction of hydrogen sulfide synthesis enzymes cystathionine-β-synthase and cystathionine-γ-lyase in the colon of patients with Hirschsprungs disease

PURPOSE

Hirschsprung associated enterocolitis (HAEC) is the most common cause of morbidity and mortality in Hirschsprung Disease (HSCR). The pathogenesis of HAEC is poorly understood. In recent years, there is increasing evidence that a compromised intestinal barrier function plays a major role in the pathogenesis of HAEC. Hydrogen sulfide, synthesized from L-cysteine by two key enzymes, cystathionine-β-synthase (CBS) and cystathionine-γ-lysase (CSE) is reported to play a key role in regulating gastrointestinal motility and promoting resolution of inflammation. We designed this study to test the hypothesis that CBS and CSE expression is altered in the colon of patients with HSCR.

METHODS

We investigated CBS and CSE protein expression in both the aganglionic and ganglionic regions of HSCR patients (n=10) versus healthy control colon (n=10). Protein distribution was assessed by using immunofluorescence and confocal microscopy. Gene and protein expression was quantified using quantitative real-time polymerase chain reaction (qPCR), Western blot analysis, and densitometry.

MAIN RESULTS

qPCR and Western blot analysis revealed that CBS and CSE are expressed in the normal human colon. CBS and CSE expression was significantly decreased (p<0.003) in the ganglionic and aganglionic bowel in HSCR compared to controls. Confocal microscopy revealed that CBS and CSE expression in smooth muscles, interstitial cells of Cajal, platelet-derived growth factor-alpha receptor-positive cells, enteric neurons and colonic epithelium was markedly decreased in HSCR specimens compared to controls.

CONCLUSION

We demonstrate for the first time the expression and distribution of CBS/CSE in patients with HSCR. The observed decreased expression of CBS and CSE may affect mucosal integrity and colonic contractility and thus render HSCR patients more susceptible to develop HAEC.

The mechanism of action and role of hydrogen sulfide in the control of vascular tone

Our knowledge about hydrogen sulfide (H₂S) significantly changed over the last two decades. Today it is considered as not only a toxic gas but also as a gasotransmitter with diverse roles in different physiological and pathophysiological processes. H₂S has pleiotropic effects and its possible mechanisms of action involve (1) a reversible protein sulfhydration which can alter the function of the modified proteins similar to nitrosylation or phosphorylation; (2) direct antioxidant effects and (3) interaction with metalloproteins. Its effects on the human cardiovascular system are especially important due to the high prevalence of hypertension and myocardial infarction. The exact molecular targets that affect the vascular tone include the K_ATP channel, the endothelial nitric oxide synthase, the phosphodiesterase of the vascular smooth muscle cell and the cytochrome c oxidase among others and the combination of all these effects lead to the final result on the vascular tone. The relative role of each effect depends immensely on the used concentration and also on the used donor molecules but several other factors and experimental conditions could alter the final effect. The aim of the current review is to give a comprehensive summary of the current understanding on the mechanism of action and role of H₂S in the regulation of vascular tone and to outline the obstacles that hinder the better understanding of its effects.

Augmentation of cGMP/PKG pathway and colonic motility by hydrogen sulfide

Hydrogen sulfide (H2S), like nitric oxide (NO), causes smooth muscle relaxation, but unlike NO, does not stimulate soluble guanylyl cyclase (sGC) activity and generate cyclic guanosine 5'-monophosphate (cGMP). The aim of this study was to investigate the interplay between NO and H2S in colonic smooth muscle. In colonic smooth muscle from rabbit, mouse, and human, l-cysteine, substrate of cystathionine-γ-lyase (CSE), or NaHS, an H2S donor, inhibited phosphodiesterase 5 (PDE5) activity and augmented the increase in cGMP levels, IP3 receptor phosphorylation at Ser1756 (measured as a proxy for PKG activation), and muscle relaxation in response to NO donor S-nitrosoglutathione (GSNO), suggesting augmentation of cGMP/PKG pathway by H2S. The inhibitory effect of l-cysteine, but not NaHS, on PDE5 activity was blocked in cells transfected with CSE siRNA or treated with CSE inhibitor d,l-propargylglycine (dl-PPG), suggesting activation of CSE and generation of H2S in response to l-cysteine. H2S levels were increased in response to l-cysteine, and the effect of l-cysteine was augmented by GSNO in a cGMP-dependent protein kinase-sensitive manner, suggesting augmentation of CSE/H2S by cGMP/PKG pathway. As a result, GSNO-induced relaxation was inhibited by dl-PPG. In flat-sheet preparation of colon, l-cysteine augmented calcitonin gene-related peptide release in response to mucosal stimulation, and in intact segments, l-cysteine increased the velocity of pellet propulsion. These results demonstrate that in colonic smooth muscle, there is a novel interplay between NO and H2S. NO generates H2S via cGMP/PKG pathway, and H2S, in turn, inhibits PDE5 activity and augments NO-induced cGMP levels. In the intact colon, H2S promotes colonic transit.NEW & NOTEWORTHY Hydrogen sulfide (H2S) and nitric oxide (NO) are important regulators of gastrointestinal motility. The studies herein provide the cross talk between NO and H2S signaling to mediate smooth muscle relaxation and colonic transit. H2S inhibits phosphodiesterase 5 activity to augment cGMP levels in response to NO, which, in turn, via cGMP/PKG pathway, generates H2S. These studies suggest that interventions targeted at restoring NO and H2S homeostasis within the smooth muscle may provide novel therapeutic approaches to mitigate motility disorders.

H2S-Induced Sulfhydration: Biological Function and Detection Methodology

At appropriate concentrations, hydrogen sulfide, a well-known gasotransmitter, plays important roles in both physiology and pathophysiology. Increasing evidence suggests that modifying thiol groups of specific cysteines in target proteins via sulfhydration or persulfidation is one of the important mechanisms responsible for the biological functions of hydrogen sulfide. A variety of key proteins of different cellular pathways in mammals have been reported to be sulfhydrated by hydrogen sulfide to participate and regulate the processes of cell survival/death, cell differentiation, cell proliferation/hypertrophy, cellular metabolism, mitochondrial bioenergetics/biogenesis, endoplasmic reticulum stress, vasorelaxtion, inflammation, oxidative stress, etc. Moreover, S-sulfhydration also exerts many biological functions through the cross-talk with other post-translational modifications including phosphorylation, S-nitrosylation and tyrosine nitration. This review summarizes recent studies of hydrogen sulfide-induced sulfhydration as a posttranslational modification, an important biological function of hydrogen sulfide, and sulfhydrated proteins are introduced. Additionally, we discuss the main methods of detecting sulfhydration of proteins.

Postranslational Modification of Ion Channels in Colonic Inflammation

Voltage-gated ion channels are key regulators of cell excitability. There is significant evidence that these channels are subject to modulation by redox status of the cells. Here we review the post-translational modifications of ion channels that occur in colonic inflammation. The redox mechanisms involve tyrosine nitration, covalent modification of cysteine residues and sulfhydration by hydrogen sulfide in experimental colitis. In the setting of colonic inflammation, modifications of cysteine and tyrosine are likely to occur at several sites within the same channel complex. In this review we describe alterations in channel function due to specific modifications of tyrosine and cysteine residues by reactive nitrogen, oxygen and hydrogen-sulfide resulting in altered motility.

Role of epithelial ion transports in inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic inflammatory disorder with a complex pathogenesis. Diarrhea is a highly prevalent and often debilitating symptom of IBD patients that results, at least in part, from an intestinal hydroelectrolytic imbalance. Evidence suggests that reduced electrolyte absorption is more relevant than increased secretion to this disequilibrium. This systematic review analyses and integrates the current evidence on the roles of epithelial Na(+)-K(+)-ATPase (NKA), Na(+)/H(+) exchangers (NHEs), epithelial Na(+) channels (ENaC), and K(+) channels (KC) in IBD-associated diarrhea. NKA is the key driving force of the transepithelial ionic transport and its activity is decreased in IBD. In addition, the downregulation of apical NHE and ENaC and the upregulation of apical large-conductance KC all contribute to the IBD-associated diarrhea by lowering sodium absorption and/or increasing potassium secretion.

The Interplay of Reactive Oxygen Species, Hypoxia, Inflammation, and Sirtuins in Cancer Initiation and Progression

The presence of ROS is a constant feature in living cells metabolizing O2. ROS concentration and compartmentation determine their physiological or pathological effects. ROS overproduction is a feature of cancer cells and plays several roles during the natural history of malignant tumor. ROS continuously contribute to each step of cancerogenesis, from the initiation to the malignant progression, acting directly or indirectly. In this review, we will (a) underline the role of ROS in the pathway leading a normal cell to tumor transformation and progression, (b) define the multiple roles of ROS during the natural history of a tumor, (c) conciliate many conflicting data about harmful or beneficial effects of ROS, (d) rethink the importance of oncogene and tumor suppressor gene mutations in relation to the malignant progression, and (e) collocate all the cancer hallmarks in a mechanistic sequence which could represent a "physiological" response to the initial growth of a transformed stem/pluripotent cell, defining also the role of ROS in each hallmark. We will provide a simplified sketch about the relationships between ROS and cancer. The attention will be focused on the contribution of ROS to the signaling of HIF, NFκB, and Sirtuins as a leitmotif of cancer initiation and progression.

H2S- and NO-Signaling Pathways in Alzheimer's Amyloid Vasculopathy: Synergism or Antagonism?

Alzheimer's type of neurodegeneration dramatically affects H2S and NO synthesis and interactions in the brain, which results in dysregulated vasomotor function, brain tissue hypoperfusion and hypoxia, development of perivascular inflammation, promotion of Aβ deposition, and impairment of neurogenesis/angiogenesis. H2S- and NO-signaling pathways have been described to offer protection against Alzheimer's amyloid vasculopathy and neurodegeneration. This review describes recent developments of the increasing relevance of H2S and NO in Alzheimer's disease (AD). More studies are however needed to fully determine their potential use as therapeutic targets in Alzheimer's and other forms of vascular dementia.

S-sulfhydration as a cellular redox regulation

This review is focused on formation and biological significance of hydropersulfides, i.e. S-sulfhydration process. Biogenesis and properties of reactive sulfur species and their role in redox signaling are presented. The effect of S-sulfhydration on protein function is discussed.

For many years reactive oxygen and nitrogen species (ROS and RNS) have been recognized as key messengers in the process of thiol-based redox regulation. Relatively recently, literature reports began to mention reactive sulfur species (RSS) and their role in thiol regulation. This review is focused on biogenesis and biological properties of RSS, including: hydropersulfides, polysulfides and hydrogen sulfide (H₂S). Based on the most up-to-date literature data, the paper presents biological significance of S-sulfhydration process. In this reaction, sulfane sulfur is transferred to the–SH groups forming hydropersulfides. Protein cysteine residues, called ‘redox switches’ are susceptible to such reversible modifications. In line with the most recent reports, it was emphasized that sulfane sulfur-containing compounds (mainly hydrogen persulfides and polysulfides) are real and better mediators of S-sulfhydration-based signalling than H₂S. We also overviewed proteins participating in the formation and transport of RSS and in mitochondrial H₂S oxidation. In addition, we reviewed many reports about proteins unrelated to sulfur metabolism which are modified by S-sulfhydration that influences their catalytic activity. We also addressed the problem of the regulatory function of S-sulfhydration reaction in the activation of K_ATP channels (vasorelaxant) and transcription factors (e.g. NF_κB) as well as in the mechanism of therapeutic action of garlic-derived sulfur compounds. Some aspects of comparison between RNS and RSS are also discussed in this review.

ABCC9/SUR2 in the brain: Implications for hippocampal sclerosis of aging and a potential therapeutic target

The ABCC9 gene and its polypeptide product, SUR2, are increasingly implicated in human neurologic disease, including prevalent diseases of the aged brain. SUR2 proteins are a component of the ATP-sensitive potassium ("KATP") channel, a metabolic sensor for stress and/or hypoxia that has been shown to change in aging. The KATP channel also helps regulate the neurovascular unit. Most brain cell types express SUR2, including neurons, astrocytes, oligodendrocytes, microglia, vascular smooth muscle, pericytes, and endothelial cells. Thus it is not surprising that ABCC9 gene variants are associated with risk for human brain diseases. For example, Cantu syndrome is a result of ABCC9 mutations; we discuss neurologic manifestations of this genetic syndrome. More common brain disorders linked to ABCC9 gene variants include hippocampal sclerosis of aging (HS-Aging), sleep disorders, and depression. HS-Aging is a prevalent neurological disease with pathologic features of both neurodegenerative (aberrant TDP-43) and cerebrovascular (arteriolosclerosis) disease. As to potential therapeutic intervention, the human pharmacopeia features both SUR2 agonists and antagonists, so ABCC9/SUR2 may provide a "druggable target", relevant perhaps to both HS-Aging and Alzheimer's disease. We conclude that more work is required to better understand the roles of ABCC9/SUR2 in the human brain during health and disease conditions.